MICROCONTROLLER TECHNOLOGY

COURSE OUTLINE:
1. INTRODUCTION TO MICROCONTROLLER TECHNOLOGY
- Elements of microcontroller architecture
- Microcontroller series
- Family members of microcontroller series
2. PROCESS CONTROL SYSTEMS
- Need for process control
- Process control terms
- Block diagram of process control
- Control modes
- Implementation of controllers
- Functions of actuators
- Types of actuators
3. SEQUENTIAL CONTROL SYSTEMS
- Description of sequential control systems
- Time delay units
- Application of decoders/encoders in sequential control
- Practical interlock systems
- Programmable logic controllers (PLC’s)
- Application of flow chart and ladder diagrams
programming methods
- Application of PLC’ s in functional and practical systems
4. DIGITAL CONTROL SYSTEMS
- Basic digital methods
- Computer data logging
- Human Machine Interface (HMI)
- Applications of digital computers
5. ROBOTS FUNDAMENTALS
- Definition of a robot
- Types of robots
- Elements of robotic systems
- Need for robots
- Robotic classification
- Functions of control systems in Robots
- Robot’s performance capabilities specification
- Key features of Robots
- Programming methods
6. ROBOT PROGRAMMING
- Programming methods
- Robot programming functions
- Robot programming environment
- Programming activities
- Basic types of robot programming languages
- On-line and Off-line programming languages
 TOPIC 1: INTRODUCTION TO MICROCONTROLLER
TECHNOLOGY
Microcomputer is a complete computer system comprising at least
three major components, the microprocessor (CPU), Memory and IO
peripheral components.
- A microcomputer could be a general-purpose computer (like a PC) or a
system designed to fulfill a special task (for example a controller system
inside an instrument, microcontroller).

- Microprocessor is a programmable multipurpose-multitasking logic

chip that fabricated by LSI, VLSI or other higher manufacturing
techniques. In a modern computer system, the microprocessor is
usually referred to as CPU (central processing unit).
- Microprocessor by definition means that this is only the central
processing unit, with instruction decoder, registers and Arithmetic Logic
processing Unit. A CPU does not include any memory or I/O
components.

A microprocessor accepts data input in binary form, reads binary

instructions, processes data and provides desired output.
It is classified by its word length i.e.,4-bit, 8-bit, 16 bits
A microcontroller is a compact integrated circuit designed to govern a
specific operation in an embedded system.
Embedded system is a computer system designed to perform one or a few
dedicated functions often with real time computing constraints.

Elements of microcontroller architecture

A microcontroller is a highly integrated chip which includes all or most of
the parts needed for a controller on a single chip
The microcontroller sees the integration of a number of useful functions
into a single IC package. These functions are:
- The ability to execute a stored set of instructions to carry out
user defined tasks
- The ability to be able to access external memory chips and to
both read and write data
The microcontroller typically includes:
- CPU/Microprocessor
- Memory (RAM and ROM)
- Input/output devices (serial, parallel, ADC, DAC)
- Timers
- Interrupt controller
1. CPU
It is responsible for executing stored program and managing the
peripherals. It fetches instruction, decodes it and then executes it.

Registers. These are high speed memory storage areas. These are
useful for interim calculation results (this reduces the number of
read/write operations to external memory which is usually slower)

Arithmetic logic unit is responsible for carrying out arithmetic

operations such as addition and subtraction, and logic operations
such as AND, OR, XOR

Control unit coordinates the CPU’ s functions. It also controls the

data flow between microprocessor and peripheral devices.

System bus is the connection between the several components of

a microprocessor system. It is a collection of wires carrying
information with a common purpose. It is divided into:
- Address bus. It carries the address for a specified memory
location.
- Data bus. It carries information between the CPU and memory
or between the CPU and I/O devices.
- Control bus. It carries control signals supplied by the CPU to
synchronize the movement of information on the address and
data bus
2. Memory
It is used to store data and programs.
RAM- is used for storing values that are liable to change during the
course of the execution of a program. It loses its contents when
power is removed
ROM- is used for storing programs. It does not lose its contents
when power is removed
3. Input/output ports
Microcontrollers receive and output information using ports. There
are two main types of ports:
- Parallel port. It is used to achieve parallel transmission. It is
capable of delivering multiple streams of data hence has a higher
transmission speed.
- Serial port. It is used to achieve serial transmission. It delivers a
single stream of data hence has a relatively low transmission
speed.

4. Timers/counters
A microcontroller has timers and counters that provide all timing
and counting functions. The major operations of this section are to
perform clock functions, modulations, pulse generations, frequency
measuring, making oscillations etc.
Timers are typically constructed using clock source and a counter.
Counters count clock periods that are input to them.

5. Analog to digital converter

Are used for converting the analog signal to digital form. This device
accepts an analogue input and translates this to a digital number
whose size is proportional to the magnitude of the analogue signal.
Each ADC has an associated input voltage range and output
numeric range.

6. Interrupt control
Interrupts are signals that cause the CPU to suspend its current
activity and perform some other tasks. CPU’ s is commonly designed
to handle interrupts from various sources. Each interrupt signal is
associated with a particular memory location which contains the
address of the subroutine that should be executed on receipt of this
interrupt.

7. Special functioning block

Some microcontrollers are only used for special applications, e.g.,
Robotics; hence contain additional ports to perform such special
operations.

Advantages of microcontrollers
The main advantages of microcontrollers are given as:
- Microcontrollers act as a microcomputer without any digital parts.
- As the higher integration inside microcontroller reduce cost and
size
of the system.
- Usage of microcontroller is simple, easy for troubleshoot and
 system maintaining.
- Most of the pins are programmable by the user for performing
different functions.
- Easily interface additional RAM, ROM, I/O ports.
- Low time required for performing operations.
Disadvantages of microcontrollers
- Microcontrollers have got more complex architecture than that of
microprocessors.
- Only perform limited number of executions simultaneously.
- Mostly used in micro-equipment.
- Cannot interface high power devices directly.

Application of microcontrollers
Microcontrollers are widely used in modern electronics equipment. Some
basic applications of microcontroller are given below.
- Used in biomedical instruments.
- Widely used in communication systems.
- Used as peripheral controller in PC.
- Used in robotics.
- Used in automobile fields

Comparison between microprocessor and microcontroller

Microprocessor Microcontroller
- It is only a general purpose
1 - It is a micro computer itself
computer CPU
- Memory, I/O ports, timers,
- All are integrated inside the
2 interrupts are not available
microcontroller chip
inside the chip
- This must have many - Can function as a micro
3 additional digital components to computer without any additional
perform its operation components.
- Systems become bulkier and - Make the system simple,
4
expensive. economic and compact
- Not capable for handling
5 - Handling Boolean functions
Boolean functions
6 - Higher accessing time required - Low accessing time

7 - Very few pins are - Most of the pins are

programmable programmable
 - Very few number of bit
8 handling - Many bit-handling instructions
instructions
- Widely Used in modern PC and
9 - widely in small control systems
laptops
E.g. - INTEL 8086, INTEL Pentium
- INTEL8051,89960, PIC16F877
, series

Classification of microcontrollers
Microcontrollers can be classified on the basis of internal bus width,
architecture, memory and instruction set.
1. Classified on the Basis of Internal Bus Width
a) The 8-Bit Microcontroller
- When the ALU performs arithmetic and logical operations on a byte
(8-bits)
at an instruction, the microcontroller is an 8-bit microcontroller. The
internal
bus width of 8-bit microcontroller is of 8-bit.
- Examples of 8-bit microcontrollers are Intel 8051 family and
Motorola
MC68HC11 family.

b) The 16-Bit Microcontroller

- When the ALU performs arithmetic and logical operations on a
word (16-
bits) at an instruction, the microcontroller is a 16-bit microcontroller.
The
internal bus width of 16-bit microcontroller is of 16-bit.
- Examples of 16-bit microcontrollers are Intel 8096 family and
Motorola
MC68HC12 and MC68332 families. The performance and computing
capability of 16-bit microcontrollers is enhanced with greater
precision as
compared to the 8-bit microcontrollers.

c) The 32-Bit Microcontroller

- When the ALU performs arithmetic and logical operations on a
double word
(32bits) at an instruction, the microcontroller is a 32-bit
microcontroller. The
internal bus width of 32-bit microcontroller is of 32-bit.
- Examples of 32-bit microcontrollers are Intel 80960 family and
Motorola
 M683xx and Intel/Atmel 251 family. The performance and
computing
capability of 32-bit microcontrollers is enhanced with greater
precision as
compared to the 16-bit microcontrollers

2. Classified on the Basis of Memory/ devices

a) Embedded Microcontrollers
- When an embedded system has a microcontroller unit that has all
the
functional blocks (including program as well as data memory)
available on a
chip is called an embedded microcontroller.
- For example, 8051 having Program & Data Memory, I/O Ports,
Serial
Communication, Counters and Timers and Interrupt Control logic on
the
chip is an embedded microcontroller.

b) External Memory Microcontrollers

- When an embedded system has a microcontroller unit that has not
all the functional blocks available on a chip is called an external
memory microcontroller.
- In external memory microcontroller, all or part of the memory units
are externally interfaced using an interfacing circuit called the glue
circuit.
- For example, 8031 has no program memory on the chip is an
external memory microcontroller

3. Classified on the Basis of Architecture

- There are mainly two categories of processors, namely, Von-
Neuman (or Princeton) architecture and Harvard Architecture. These
two architectures differ in the way data and programs are stored
and accessed.

a) Von-Neuman Architecture
- Microcontrollers based on the Von-Neuman architecture have a
single ‘data’ bus that is used to fetch both instructions and data.
Program instructions and data are stored in a common main
memory.
- When such a controller addresses main memory, it first fetches an
instruction, and then it fetches the data to support the instruction.
The two separate fetches slow up the controller’s operation.
- The Von-Neuman architecture’s main advantage is that it simplifies
the microcontroller design because only one memory is accessed.
 - In microcontrollers, the contents of RAM can be used for data
storage and
program instruction storage.

b) Harvard Architecture
- Microcontrollers based on the Harvard Architecture have separate
data bus and an instruction bus. This allows execution to occur in
parallel.
- As an instruction is being “pre-fetched”, the current instruction is
executing on the data bus. Once the current instruction is complete,
the next instruction is ready to go.
- This pre-fetch theoretically allows for much faster execution than
Von-Neuman architecture, on the expense of complexity.
- The Harvard Architecture executes instructions in fewer instruction
cycles than the Von-Neuman architecture

4. Classified on the Basis of Instruction set

a) Complex Instruction Set Computer (CISC) Architecture

Microcontrollers

When a microcontroller has an instruction set that supports many

addressing modes for the arithmetic and logical instructions, data
transfer and memory accesses instructions, the microcontroller is
said to be of CISC architecture.
The advantages of the CISC architecture are that many of the
instructions are macro-like, allowing the programmer to use one
instruction in place of
many simpler instructions.

b) Reduced Instruction Set Computer (RISC) Architecture Microcontrollers

When a microcontroller has an instruction set that supports fewer

addressing modes for the arithmetic and logical instructions and for
data transfer instructions, the microcontroller is said to be of RISC
architecture.
The benefits of RISC design simplicity are a smaller chip, smaller pin
count, and very low power consumption.
Some of the typical features of a RISC processor- Harvard
architecture are:
- Allows simultaneous access of program and data.
- Overlapping of some operations for increased processing
performance.
- Instruction pipelining increases execution speed.
- Allows each instruction to operate on any register or use any
addressing mode
 INTEL 8051 MICROCONTROLLER
- It is an 8-bit microcontroller.
- 8051 is a Harvard architecture, CISC instruction set and is a
single chip microcontroller
- In addition to on-chip clock oscillator, 2 16-bit timers, 4 I/O ports
and a serial port, it has128 bytes of RAM and 4 KB masked ROM.
If necessary, 8051-memory can be expanded up to 128 KB by
adding up to 64 KB of external program and 64KB of data
memory.

A typical 8051 contains:

⇒ CPU with Boolean processor
⇒ 5 or 6 interrupts: 2 are external, 2 priority levels
⇒ 2 or 3 16-bit timer/counters
⇒ Programmable full-duplex serial port (baud rate provided by one of the
timers)
⇒ 32 I/O lines (four 8-bit ports)
⇒ RAM
⇒ ROM/EPROM in some models

- I/O Ports: All 8051 microcontrollers have 4 I/O ports each comprising 8-
bits which can be configured as inputs or outputs. Accordingly, in total of
32 input/output pins enabling the microcontroller to be connected to
peripheral devices are available for use.

- Memory Organization: The 8051 has two types of memory and these
are Program Memory and Data Memory. Program Memory (ROM) is used
to permanently save the program being executed, while Data Memory
(RAM) is used for temporarily storing data and intermediate results
created and used during the operation of the microcontroller.
- All 8051 microcontrollers have a 16-bit addressing bus and are capable
of addressing 64 kb memory.

- Counters and Timers: The 8051 microcontroller has 2 timers/counters

called T0 and T1. As their names suggest, their main purpose is to
measure time and count external events. Besides, they can be used for
generating clock pulses to be used in serial communication, so called
Baud Rate.
Functions of the pins in 8051
EA- External Access input. It is used to enable/disable external memory
interfacing
Pin 1 to Pin 8 (Port 1)- They can be configured as input or output pins depending
on the logic control. If logic 0 is applied it will act as an output pin and if logic 1 is
applied the pin will act as an input.
RESET- it is an active-high, input pin. If the RESETpin is high for a minimum of 2
machine cycles, the microcontroller will reset to its initial values terminating all
activities.
Pin 3.0 to Pin 3.7- They can be used as universal input or output. They are
biderectional.
 P3.0 (RXD)- serial data recieve pin. It is used for serial input
 P3.1 (TXD)- serial data transmit pin. Used for serial data output
 P3.2 and P3.3 (INT0’.INT1’)- are for external hardware interrupt 0 and
interrupt 1 respectively
 P3.4 and P3.5 (T0 and T1)- are for timer 0 and timer 1 external input
 P3.6 (WR’)- is for writing data on external memory
 P3.7 (RO’)- is for reading data from external memory
X1 and X2- are connected to an external oscillator which is generally a quartz
crystal oscillator. They are used to provide an external clock frequency of 4MHz
to 30MHz.
P2.0 to P2.7- When additional external memory is interfaced with the 8051
microcontroller, port 2 acts as higher-order adress bytes.
PSEN (Program Store Enable)- it is used to distinguish between memory chips
when multiple memory chips are used. It is also used to de-multiplex the
multiplexed address and data signals available at port0
EA (external access input)- used to enable/disable external memory interfacing
P0.0 to P0.7- they are bidirectional input/output pins
Physical Addressing
The 8051 architecture supports several physical address spaces
- On-chip program memory
- On-chip data memory
- External program memory
- External data memory
- On-chip special function registers
Addressing Modes
This is the way in which the data sources or destination addresses are
specified in the instruction mnemonic for moving the data.
The various addressing modes include:
1. Register Addressing
The 8051 can access eight working registers (R0-R7). A 3-bit code
within the instruction selects one of the eight registers from the
selected register bank. The programmer can select a register bank
by modifying bits 4 and 3 in the program status word (PSW)

2. Direct Byte Addressing

Direct addressing can access any on chip variable or hardware
register, i.e., on chip RAM and special function register. The most
significant bit of the address decides whether it is a location within
on chip RAM (MSB=0) or in special function register (MSB=1)
3. Register indirect addressing
In this addressing mode R0 and R1 of each register bank can be
used as index or pointer register. R0 and R1 point to the contents in
the RAM. The instruction with indirect addressing uses the @ sign

4. Immediate addressing
In this addressing mode source operand is a constant rather than a
variable. So, the constant can be incorporated in the instruction.
Sign ‘#’ indicates it is an immediate addressing mode

5. Register specific
This refers to a specific register such as accumulator or data pointer
register (DPTR)
6. Index
Only program memory can be accessed in the index addressing.
Either the DPTR or Program Counter (PC) can be used as an index
register
8051 memory mapping

The 8051 address has two separate memory spaces

1. program memory space
2. data memory space

program memory space

- the program memory space is read only memory(ROM)
- it is used for storing programs of variable data
- it is possible to read program instructions from this space but the
processor can not write data into this memory
-all instructions fetches are taken from program memory space
data memory space
- the data memory space is read/write memory space
- the processor can read/write in this memory

8051 REGISTER BANKS

The 8051 micro-controller has a total of 128 bytes of RAM.
The RAM memory space allocation is from 00H to 7FH and it is divided into
3 groups.
• 32 bytes from 00 to 1F which is used for register banks and stack
• 16 bytes from 20H to 2FH which is bit addressable R/W memory
• 80 bytes of read and write storage (scratch pad)
register banks and their address
each bank has 8 registers from R0 to R7. The default register bank is bank
0. one can switch between the register banks using RS0 and RS1 or PSW4
and PSW3
Bank RAM location PSW4 (RS1) PSW3 (RS0)

0 00H-07H 0 0

1 08H-0FH 0 1

2 10H-17H 1 0

3 18H-1FH 1 1

Special function registers (SFR)

In 8051, the SFR are used to perform the following special functions:
to access and control the operation of I/O ports, CPU registers,
interrupt control, timer/counter, serial port and power control
functions
SFR’s are located between memory location 80H and FFH in the RAM.
The list of SFR’s used in 8051 are:
 ACC (accumulator)
 B (register)
 PSW (program status word)
 SP (stack pointer)
 DPTR (data pointer)
 I/O ports (P0, P1, P2, P3)
 IE (interrupt enable register)
 IP (interrupt priority register)
 TMOD (timer mode control)
 TCON (timer control)
 SCON (serial port control)

Accumulator
it is an 8-bit special purpose register used to access the CPU
it’s address is 0E0H in RAM
B-register
it is an 8-bit general purpose register on address 0F0H
PSW (program status word)
it is also called the flag register. It is found in location 0D0H to 0D7H.
It is an 8-bit registers

CY (D7) AC (D6) F0 (D5) RS1 (D4) RS0 (D3) OV (D2) _ (D1) P (D0)

CY- carry flag

AC- auxilliary carrying
F0-flag 0 for user
RS1 and RS0- register bank select signals
OV- overflow flag
P- parity flag
Stack pointer
it is a 16-bit register used to store the address of the last instruction request in a
stack. Its location is 81H
DPTR (data pointer)
it is a 16-bit register used to hold a 16 bit address or data
it is divided into the high byte register (location 83H) and low byte register
(location 82H)
I/O ports:
there are 4 parallel, 8 bit I/O ports:
P0 : address 80H
P1: address 90H
P2: address 0A0H
P3: address 0B0H
 TOPIC 2: PROCESS CONTROL SYSTEM
Process and Control
- Process as used in the terms process control and process
industry, refers to the methods of changing or refining raw materials
to create end products i.e., an operation that uses resources to
transform inputs into outputs. It is the resource that provides the
energy into the process for the transformation to occur.

- Control in process industries refers to the regulation of all aspects

of the process. Precise control of level, temperature, pressure and
flow is important in many process applications.

Process Control
- Process control technology is the tool that enables manufacturers
to keep their operations running within specified limits and to set
more precise limits to maximize profitability, ensure quality and
safety.
- Process control refers to the methods that are used to control
process variables when manufacturing a product.
- It consists of monitoring the state of a critical parameter, detecting
when it varies from desired state, and taking action to restore it. It
involves the process variable, set points and manipulated variable.
- Thus the definition of process control is a controllable process that
must behave in a predictable manner. For a given change in the
manipulated variable the process variable must respond in a
predictable and consistent manner.
- Most basic process control systems consist of a control loop.
Control loops in the process control industry work in the same way,
requiring three tasks to occur: Measurement, Comparison and
Adjustment. This has four main components which are:
A measurement of the state or condition of a process
A controller calculating an action based on this measured value
against
a pre-set or desired value (set point)
An output signal resulting from the controller calculation which is
used
to manipulate the process action through some form of actuator
The process itself reacting to this signal, and changing its state or
condition
Controlling a process requires knowledge of four basic elements, the
process itself, the sensor that measures the process value, the
final control element that changes the manipulated variable, and
the controller.
- In industrial process control, the Process Variable (PV) is
measured by an instrument in the field and acts as an input to an
automatic controller which takes action based on the value of it.
- Devices that measure PV are transducers or sensors. In many
cases, the PV sensor consists of a direct measurement device called
an element and a separate signal processor called a transmitter.
- The controller is the device that processes the error signal,
determines the required control action and provides a control output
Manipulated Variable (MV) to the process. The device that
converts the control output into control action is the actuator

Need for Process Control

- Manufacturers control the production process for the following
reasons:
o Reduce variability
o Increase efficiency
o Ensure safety
o Quality
Process Control Terminologies
i) Process Variable (PV) is a measure of the process output that
changes in response to changes in the manipulated variable.
ii) Set Point (SP) is the value at which the operator wishes to
maintain the process variable at.
iii) Manipulated variables - these input variables are adjusted
dynamically to keep the controlled variables at their set-points.
iv) Controlled variables - these are the variables which quantify the
performance or quality of the final product, which are also called output
variables.
v) Error signal/actuating signals is the deviation of the process
variable from the Set Point and is defined as E = SP - PV.
vi) Offset is a sustained deviation of the process variable from the
setpoint. In the temperature control loop example, if the control system
held the process fluid at 100.5 °C consistently, even though the setpoint is
100 °C, then an offset of 0.5 °C exists.
vii) Load disturbance is an undesired change in one of the factors that
can affect the process variable.
viii) Dead-band is the value that must be traversed before the controller
output will change its direction again. For example, on the heat
exchanger, if the thermostat is configured with a 110°C Set Point and a
20°C dead-band, the steam valve will open at 100°C and close at 120°C. If
such a large fluctuation from the Set Point is acceptable, then the process
is under control.
ix) Process Dead Time is the period of time that passes between a
change in the controller output and a change in the process variable being
measured.
x)Control stability is the ability of a measured variable to return to its
set point after a disturbance.
xi) Process lag is the delay time it takes the controlled variable to
respond to a change in the controller output signal.
xii) Process gain is the response of the process variable to a change in
the controller output
xiii) Linear process is one that has non-varying process characteristics
over the range of the process variable.
xiv) Nonlinear process is one that has varying process characteristics
over the range of the process variable.
Control Modes
- In control, there are control systems which can be discrete or analog,
manual or automated, periodic or continuous.
- Control operations that involve human action to make an adjustment are
called manual control systems. Conversely, control operations in which
no human intervention is required, such as an automatic valve actuator
that responds to a level controller, are called automatic control
systems.
- There are five basic forms of control available in Process Control:
1. On-Off or ‘bang-bang’ control: The oldest strategy for control is to
use a switch giving simple on-off control. This is a discontinuous form of
control action, and is also referred to as two-position control.
- On-Off Control allows only 2 control valve positions; fully opened or fully
closed.
- A perfect on-off controller is 'on' when the measurement is below the
set-point (SP) and the manipulated variable (MV) is at its maximum value.
Above the SP, the controller is 'off' and the MV is at a minimum.
- A thermostat on a heater is an example of control that is on or off. A
temperature sensor turns the heat source on if the temperature falls
below the set point and turns the heat source off when the set point is
reached. There is no measurement of the difference between the set point
and the measured temperature (e.g., no error measurement) and
no adjustment to the rate at which heat is added other than all or none
2. Modulating control: If the output of a controller can move through a
range of values, this is modulating control. Modulation Control takes place
within a defined operating range only. That is, it must have upper and
lower limits. Modulating control is a smoother form
of control than step control. It can be used in both open loop and closed
loop control systems.
3. Open loop control: Open loop control occurs because the control
action (Controller Output Signal) is not a function of the PV (Process
Variable) or load changes. The open loop control does not self-correct,
when these PV’s drift.
4. Feed forward control: Feed forward control is a form of control based
on anticipating the correct manipulated variables required to deliver the
required output variable. It is seen as a form of open loop control as the
PV is not used directly in the control action.
5. Closed loop or feedback control: If the PV, the objective of control,
is used to determine the control action it is called closed loop control
system. In closed loop control the controller output is determined by
difference between the process variable and the Set
Point.
Control Modes in closed loop/feedback control
- Most Closed loop Controllers are capable of controlling with three control
modes which can be used separately or together
1. Proportional Control (P): Determines the speed of response of the loop.
2. Integral or Reset Control (I): Forces the controller to line out at its set
point.
3. Derivative, or Rate Control (D): Enhances stability margin, which
permits the gain to be increased
Mode Characteristics
- The controller output M can be seen as the sum of the outputs of the
individual modes:

Control Error.
- The traditional PID control equation is based entirely on the control error
E, which is the difference between the set point SP and the process
variable PV.
- The sign of the control error depends on the controller action:
E = SP - PV for a reverse acting controller
E = PV - SP for a direct acting controller
- Direct action means that, when the controller sees an increasing signal
from the transmitter, its output will increase (e.g. increased coolant flow
when process fluid is too hot).
- For reverse action, increasing measurement signals cause the
controller output to decrease (decreased steam flow when process fluid is
too hot).
- Many digital systems permit the proportional mode and/or the derivative
mode to be based on the process variable instead of the control error.
Proportional control (P)
- This is the principal means of control. The controller produces action that
is proportional to the error E. That is, the proportional component Mp of
the controller output M is equal to a coefficient-times the current value of
the control error E
- Proportional Control opens and closes a control valve by an amount
which is proportional to the error in the measured variable, i.e., the
magnitude of the deviation from the set point.
- The automatic controller needs to correct the controller output, with an
action proportional to E. The correction starts from an output value at the
beginning of automatic control action.

Integral control (I)

- The integral component M1 is equal to a coefficient times the integral of
the control error E. That is, it produces a control action that is proportional
to the integral of the error E with time.

- When the controller contains only the proportional mode, the controlled
variable is not necessarily equal to the set point when the loop lines out.
- This behaviour, known as droop or offset. When the integral or reset
mode is present, the controlled variable must equal the set point when
the loop lines out.
- This type of behaviour is desirable in most loops, so the integral or reset
mode is usually present.
- Integral action is used to control towards no offset in the output signal.
This means that it controls towards no error (E = 0). Integral control is
normally used to assist proportional control. The combination of both is
called as PI-control.
Derivative control (D)
- The derivative component MD of the controller output M is equal to a
coefficient times the rate of change of the control error E. The control
action is proportional to the rate at which the error is changing dE/dt

- The derivative mode enhances the stability margin for the control loop,
which reduces the overshoot and degree of oscillations.
- When used effectively, the derivative mode permits the controller gain to
be increased, thereby providing a faster response to set – point changes
and disturbances.
- As D-Control on its own has no purpose, it is always used in combination
with P-Control or PI-Control. This results in a PD-Control or PID-Control. PID
Control is mostly used if D-Control is required.

PD Controller
- D mode is used when prediction of the error can improve control or when
it necessary to stabilize the system.
- Often derivative is not taken from the error signal but from the system
output variable. This is done to avoid effects of the sudden change of the
reference input that will cause sudden change in the value of error signal.
- Sudden change in error signal will cause sudden change in control
output. To avoid that, it is suitable to design D mode to be proportional to
the change of the output variable.
- The addition of a derivative mode to a proportional controller modifies its
response to inputs. The PD equation:

- A PD controller provides an element to the response which is largest

when the rate of change of the error is greatest and diminishes as it
becomes smaller.
- Thus with a step input signal, the controller output rises faster when we
apply the step input signal than with just proportional control. With PD
control, the output rises more rapidly toward the steady–state value and
the overshoot is reduced.
- PD controller is often used in control of moving objects such are flying
and underwater vehicles, ships, rockets etc. One of the reasons is in
stabilizing effect of PD controller on sudden changes in heading variable
y(t).
PI Controller:
- The addition of an integral element to a proportional controller modifies
the response removing the offset and giving a steady-state value the
same as the input set value.

- PI controller will eliminate forced oscillations and steady state error

resulting in operation of on-off controller and P controller respectively.
- However, introducing integral mode has a negative effect on speed of
the response and overall stability of the system.
- Thus, PI controller will not increase the speed of response. It can be
expected since PI controller does not have means to predict what will
happen with the error in near future.
- PI controllers are very often used in industry, especially when speed of
the response is not an issue. The PI controllers are used when:
o Fast response of the system is not required
o large disturbances and noise are present during operation of
the process
o There is only one energy storage in process (capacitive or
inductive)
o There are large transport delays in the system
PID Controller
- PID controller has all the necessary dynamics: fast reaction on change of
the controller input (D mode), increase in control signal to lead error
towards zero (I mode) and suitable action inside control error area to
eliminate oscillations (P mode).

- Derivative mode improves stability of the system and enables increase

in gain K and decrease in integral time constant Ti, which increases speed
of the controller response.

Ziegler Nichol’s controller tuning

(determining controller settings)
1. Process reaction method

The procedure with this method is to open the control loop so that no control
action occurs.
Generally, the break is made between the controller and a correction device
(atuator)
A test signal is then applied to the correction unit and the response of the
measured process variable determined i.e. the error signal
The test should be as small as possible
The figure below shows the form of test signal and a typical response
the graph of measured signal plotted against time is called process reaction
curve

The test signal P is expressed as the % change in the correction unit.

The measured variable is expressed as the % of full range
A tangent is drawn to give the maximum gradient of the curve R=m/T
The table below gives the criteria recommended by Ziegler and Nichol’s for
control settings based on the values of P, R and L

Implementation of control loops

- Implementation of the control loops can be achieved using pneumatic, analog
or digital electronics.
- The first process controllers were pneumatic. However, these have largely been
replaced by electronic systems, because of improved reliability, less
maintenance, easier installation, easier adjustment, higher accuracy, lower cost,
can be used with multiple variables, and have higher speed operation.

In this case the furnace temperature sensor moves a flapper that controls the air
flow from a nozzle. When the temperature in the furnace reaches its set point
the sensor moves the flapper toward the nozzle to stop the air flow and allow
pressure to build up in the bellows. The bellows operates an air control relay that
shuts OFF the air flowing to the control valve turning OFF the fuel to the furnace.
When the temperature in the furnace drops below a set level the flapper is
opened by the sensor, reducing the air pressure in the bellows, which in turn
opens the air control valve allowing the air pressure to drop and the control
valve to open, turning ON the fuel to the furnace.
ON/OFF action electrical controller
An example of an ON/OFF action electrical room temperature controller is shown
below. In this case the room temperature is sensed by a bimetallic sensor. The
sensor operates a mercury switch. As the temperature decreases the bimetallic
element tilts the mercury switch down causing the mercury to flow to the end of
the glass envelope and in so doing shorts the two contacts together in the
mercury switch. The contact closure operates a low voltage relay turning ON the
blower motor and the heating element. When the room temperature rises to a
predetermined set point the bimetallic strip tilts the mercury switch back causing
the mercury to flow away from the contacts. The low voltage electrical circuit is
turned OFF, the relay opens, and the power to the heater and the blower motor
is disconnected.
PID action pneumatic controller

The pressure from the sensing device P in is compared to a set or reference

pressure Pref to generate a differential force (error signal) on the flapper to move
the flapper in relation to the nozzle giving an output pressure proportional to the
difference between Pin and Pref.
If the derivative restriction is removed the output pressure is fed back to the
flapper via the proportional bellows to oppose the error signal and to give
proportional action. System gain is adjusted by moving the position of the
bellows along the flapper arm, i.e., the closer the bellows is positioned to the
pivot the greater the movement of the flapper arm. By putting a variable
restriction between the pressure supply and the proportional bellows, a change
in Pin causes a large change in Pout, as the feedback from the proportional bellows
is delayed by the derivative restriction. This gives a pressure transient on P out
before the proportional bellows can react, thus giving derivative action. The
duration of the transient is set by the size of the bellows and the setting of the
restriction. Integral action is achieved by the addition of the integral bellows and
restriction as shown. An increase in P in moves the flapper towards the nozzle
causing an increase in output pressure. The increase in output pressure is fed to
the integral bellows via the restriction until the pressure in the integral bellows is
sufficient to hold the flapper in the position set by the increase in P in , creating
integral action.
PID electronic controller
The measured variable from the sensor is compared to the set point in the first
unity gain comparator; its output is the difference between the two signals or the
error signal. This signal is fed to the integrator via an inverting unity gain buffer
and to the proportional amplifier and differentiator via a second inverting unity
gain comparator, which compares the error signal to the integrator output.
Initially, with no error signal the output of the integrator is zero so that the zero
error signal is also present at the output of the second comparator.When there is
a change in the measured variable, the error signal is passed through the second
comparator to the proportional amplifier and the differentiator where it is
amplified in the proportional amplifier, added to the differential signal in a
summing circuit, and fed to the actuator to change the input variable. Although
the integrator sees the error signal, it is slow to react and so its output does not
change immediately, but starts to integrate the error signal. If the error signal is
present for an extended period of time, the integrator will supply the correction
signal via the summing circuit to the actuator and input the correction signal to
the second comparator. This will reduce the effective error signal to the
proportional amplifier to zero, when the integrator is supplying the full correction
signal to the actuator. Any new change in the error signal will still be passed
through the second comparator as the integrator is only supplying an offset to
correct for the first long-term error signal. The proportional and differential
amplifiers can then correct for any new changes in the error signal.
Process Control Actuators
Actuators converts the command signal from controllers or higher-level
components into physical adjustment in adjustable process variable. Actuators
drive motions in mechanical systems. Most often this is by converting electrical
energy into some form of mechanical motion.
Actuators take fluid, electric or some other source of power and convert it
through a motor, piston or other device to perform work. Basic actuators are
used to move valves to either fully opened or fully closed positions. Actuators for
control or position regulating valves are given a positioning signal to move to
any intermediate position with a high degree of accuracy.
Types of Actuators
1. Electrical actuators
 Solenoids
 Electric motors- - DC servomotors
- AC motors
- Stepper motors
2. Hydraulic actuators
 Use hydraulic fluid to amplify the controller command signal
3. Pneumatic actuators
 Use compressed air as the driving force
1. Manual Actuators
- A manual actuator employs levers, gears, or wheels to facilitate movement
while an automatic actuator has an external power source to provide the force
and motion to operate a valve remotely or automatically.
- Power actuators are a necessity on valves in pipelines located in remote areas;
they are also used on valves that are frequently operated or throttled. Valves
that are particularly large may be impossible or impractical to operate manually
simply because of the sheer horsepower requirements. Some valves may be
located in extremely hostile or toxic environments that preclude manual
operation.
- Additionally, as a safety feature, certain types of power actuators may be
required to operate quickly, shutting down a valve in case of emergency.
2. Electrical Actuators
- The electric actuator has a motor drive that provides torque to operate a valve.
- Electric actuators are frequently used on multi-turn valves such as gate or
globe valves. With the addition of a quarter-turn gearbox, they can be utilized on
ball, plug, or other quarter-turn valves.
Electromagnetic Actuators
This exploits the mutual attraction of soft ferrous materials in a magnetic field.
The device has one coil which provides the field energy and the energy to be
transformed. The attractive force is unidirectional such that the return device of
some type is needed, often a spring.
Relays or solenoids are based on this principle which is widely used in cars to
switch a range of electrical equipment with a current demand of more than
about 10Amps – examples include in fans, head lights, horn, and wipers.
Solenoid Actuators
Solenoids are the most common actuator components. The basic principle of
operation is that, there is a moving ferrous core (a piston) that will move inside
wire coil. Normally the piston is held outside the coil by a spring. When a voltage
is applied to the coil and
current flows, the coil
builds up a magnetic field
that attracts the piston
and pulls it into the center
of the coil. The piston can
be used to supply a linear
force. Well known
applications of these
include in pneumatic
values and car door
openers.
Motors
- Electrical Motors are continuous actuators that convert electrical energy into
mechanical energy.
- There are basically three types of conventional electrical motor available: DC
type Motors, Stepper Motors and AC type Motors.
- The DC motor achieves this by producing a continuous angular rotation that
can be used to rotate pumps, fans, compressors, wheels, etc.
- As well as conventional rotary motors, linear motors are also available which
are capable of producing a continuous liner movement.
- AC Motors are generally used in high power single or multi-phase industrial
applications were a constant rotational torque and speed is required to control
large loads such as fans or pumps.
DC Servo Motor
- DC Servo motors are used in closed loop type applications were the position of
the output motor shaft is fed back to the motor control circuit.
- Typical positional “Feedback” devices include Resolvers, Encoders and
Potentiometers as used in radio control models such as aero-planes and boats
- A servo motor generally includes a built-in gearbox for speed reduction and is
capable of delivering high torques directly.
- The output shaft of a servo motor does not rotate freely as do the shafts of DC
motors because of the gearbox and feedback devices attache
- A servo motor consists of a DC
motor, reduction gearbox, positional
feedback device and some form of
error correction.
The speed or position is controlled in
relation to a positional input signal or
reference signal applied to the
device.
The error detection amplifier looks at
this input signal and compares it with
the feedback signal from the motors output shaft and determines if the motor
output shaft is in an error condition and, if so, the controller makes appropriate
corrections either speeding up the motor or slowing it down.
This response to the positional feedback device means that the servo motor
operates within a “Closed Loop System”.
Hydraulic and Pneumatic Actuators
- Hydraulic and Pneumatic actuators are often simple devices with a minimum of
mechanical parts, used on linear or quarter-turn valves.
- A control valve requires an actuator that is capable of positioning the movable
part to any value between the two extremes of fully open and fully closed.
- Positioning actuators are generally classified as to the source of power:
pneumatic, electric, and occasionally hydraulic.
- Pneumatic actuators their source of power is from compressed air while
hydraulic actuator their source of power is from fluids but principally works the
same way.
- Sufficient air or fluid pressure acts on a piston to provide thrust in a linear
motion for gate or globe valves.
-Alternatively, the thrust may be mechanically converted to rotary motion to
operate a quarter-turn valve.
Hydraulic Actuators
- The most common type of hydraulic actuator is the hydraulic cylinder. A
cylinder uses pressurized fluid to create a linear force/motion.
- Single acting cylinders apply force when extending and typically use a spring to
retract the cylinder. Double acting cylinders apply force in both directions.

-In the figure below, a fluid is pumped into one side of the cylinder under
pressure causing that side of the cylinder to expand, and advancing the piston.

-The fluid on the other side of the piston must be allowed to escape freely - if the
incompressible fluid was trapped the cylinder could not advance. The force the
cylinder can exert is proportional to the cross sectional area of the cylinder
- Under normal operating conditions, both ends of the cylinder are filled with
fluid. If additional fluid enters port A, the piston will move toward the right, but
the fluid must be able to escape through port B
- Some actuators can create rotary motion and are very similar to the pump
designs. The figure below shows a gear motor rotary actuator.

For the motor, fluid is pumped in the left side of the case, putting that area
under pressure. Within the pressurized area, all surfaces receive a force, but only
those three surfaces indicated with arrow will effect rotation.
The pressure on the teeth next to the case will case the gears to rotate. The
pressure on the meshing teeth in the centre would cause the gears to turn in the
opposite direction, but this torque is overpowered because two teeth are pushing
the other way.
Pneumatic Actuators
- They convert air pressure into mechanical motion. There are two basic types:
Linear actuators (cylinder/piston or diaphragm types) and rotary actuators.
- Piston and rotary actuators are functionally similar to their hydraulic
counterparts.
- Pneumatic cylinder consists of a piston in a cylinder in one of two basic internal
configurations.
- The double acting cylinder connects to the valve with two tubes and can be
driven in either direction.
- The single acting cylinder can only be driven in one direction with air pressure
and is returned by a spring.

-
Rotary actuators convert air pressure into rotary mechanical motion. One
common design is the vane motor.

The motor consist of a rotor that is offset in housing. Protruding from the rotor
are spring-loaded vanes that seal against the housing and slide in and out of the
rotor as it turns.
Motion is achieved because the vanes on the top have more exposed surface
area than on the bottom and hence receive more force, causing the rotor to turn
clockwise.
In most cases rotary actuators are not chosen for their efficiencies, but for their
power, speed and torque
Advantages of pneumatic actuators
•They are fast on ON/OFF type tasks.
• Have big forces with elasticity.
• No hydraulic oil leak problems.
Disadvantage:
• Speed control is not possible because the air pressure depends on many
variables that are out of control
Valves
- A valve is a device that starts, stops, or regulates the flow of a fluid/air by
adjusting the position of a movable part.
- Valves may be applied for either ON–OFF service (often called block valves) or
for regulatory service (often called control valves).
- Based on the nature of the moving part, valves are broadly classified into two
categories:
 Rising stem (sliding stem) valves: Examples include globe, angle, and
diaphragm valves.
 Rotary stem valves: Examples include ball and butterfly valves.
- The stem is the movable part that affects the flow through the valve. The term
“ valve position ” refers to the position of the stem. The valve position M is
usually expressed in percent, but expressing M as a fraction is more convenient
in some equations.
- The choice regarding type of valve is based on factors such as cost, pressure
recovery, minimum pressure within the valve, tendency to leak when closed.
- A control valve requires an actuator that is capable of positioning the movable
part to any value between the two extremes of fully open and fully closed.
Positioning actuators are generally classified as to the source of power —
pneumatic, electric, and occasionally hydraulic.
- The figure below shows the means by which valves can be switched between
positions.

Directional control valves

- A directional control valve on the receipt of some external signal, which might
be mechanical, electrical or a pressure signal, change the direction of, or stop, or
start the flow of fluid in some part of the pneumatic/hydraulic circuit.
- Thus, it might be used to control the direction of fluid flow to a cylinder and so
use the movement of its piston to carry out actuation.
Flow-Control Valves
- One common type of actuator used in process control system is the flow-control
valve, which regulates the flow of fluids.
The control valve has a built-in valve-operating mechanism, allowing it to be
controlled remotely by a signal from the controller. Usually, this signal is either
electric or pneumatic.
Figure (a) shows a solenoid–actuated, on-off valve. When the solenoid is
energized, the valve is pulled open, and the fluid flows. When the solenoid is de-
energized, a spring returns the valve to the closed position. On-off valves are
used in batch processes (for example, a washing machine where the tank is filled
to a specified level as quickly as possible, agitated for a while, then emptied).
Many processes require the ability to vary the flow of a fluid in a pipe on a
continuous basis. To do this, the valve stem must be controlled with a linear
actuator of some type.
Figure (b) shows an electrically operated valve. In this case, an electric motor
drives a lead screw-type valve stem, so it can be put in any position.
Pneumatically operated valves use air pressure as the control signal. Shown in
figure(c), you can see that as the air pressure is increased, the diaphragm will
move down (against a spring) and close the valve. This type of valve could be
used in an on-off or a variable-flow application.
 TOPIC 3: Sequential Control System
- A control system in which the individual steps are processed in a
predetermined order, progression from one sequence step to the next being
dependent on defined conditions being satisfied.
- This is where the output is dependent not only on the actual inputs but on the
sequence of the previous inputs and outputs.
- Such a system may be time-dependent, in which the step transition conditions
are functions of time only.
- Every process control facility, even if it is primarily a “continuous” process, has
sequential aspects. Startup and shutdown are two examples.
Internal Relay
- In PLCs there are elements that are used to hold data, i.e. bits, and behave like
relays, being able to be switched on or off and switch other devices on or off.
Hence the term internal relay.
- Such internal relays do not exist as real-world switching devices but are merely
bits in the storage memory that behave in the same way as relays.
- For programming, they can be treated in the same way as an external relay
output and input. Thus inputs to external switches can be used to give an output
from an internal relay.
- This then results in the internal relay contacts being used, in conjunction with
other external input switches to give an output, e.g. activate a motor.
- PLC is a unit of hardware used to control and automate industrial processes. It
is a micro-computer based controller that uses stored instructions in
programmable memory to implement logic, sequencing, timing, counting and
arithmetic functions through digital or analog input/output modules, for
controlling machines and processes.
- A PLC has three main aspects: the inputs and outputs and the control program.
The input is anything that can sense the status of the environment and then
convert that information in to a signal. Often the signal can simply be a voltage
that is either on or off. For example, input devices can be proximity switches,
photoelectric sensors, temperature sensors, push buttons, or pressure sensors.
The outputs are connected to the devices that need to be controlled like motors,
indicator lights, fans, warning sirens or heating elements.
Control processes need devices to monitor events or measure needed values.
These devices are generically called inputs to the PLC. The program uses a set of
logical instructions that drives the outputs based on the inputs.

Practical Interlock System

- An interlock is a device used to prevent undesired states in a state machine,
which in a general sense can include any electrical, electronic, or mechanical
device or system.
- In most applications an interlock is used to help prevent a machine from
harming its operator or damaging itself by stopping the machine when tripped.
 Household microwave ovens are equipped with interlock switches which
disable the magnetron if the door is opened.
 Similarly household washing machines will interrupt the spin cycle when
the lid is open.
- Interlocks also serve as important safety devices in industrial settings, where
they protect employees from devices such as robots, presses, and hammers.
- While interlocks can be something as sophisticated as curtains of infrared
beams and photodetectors, they are often just switches.
Solenoid
- Solenoid is a device that produces mechanical motion from the energization of
an electromagnet coil. The movable portion of a solenoid is called an armature.
- Solenoids can be used to electrically open door latches, open or shut valves,
move robotic limbs, and even actuate electric switch mechanisms. However, if a
solenoid is used to actuate a set of switch contacts, then the term relay
- Solenoid valve is an electromechanically operated valve. The valve is controlled
by an electric current through a solenoid: in the case of a two-port valve the flow
is switched on or off; in the case of a three-port valve, the outflow is switched
between the two outlet ports.
Limit switch
- Some switches are specifically designed to be operated by the motion of a
machine rather than by the hand of a human operator.
- These motion-operated switches are commonly called limit switches, because
they are often used to limit the motion of a machine by turning off the actuating
power to a component if it moves too far.
- They are used for controlling machinery as part of a control system, as a safety
interlocks, or to count objects passing a point.
- A limit switch is an electromechanical device that consists of an actuator
mechanically linked to a set of contacts. When an object comes into contact with
the actuator, the device operates the contacts to make or break an electrical
connection.
Components of limit Switch
Actuator: The portion of the switch that comes in contact with the object being
sensed. When there is no force or torque applied to the actuator it is in the
unactuated, free or rest position. The position to which the actuator must be
moved in order to operate the contacts is called the trip point or operating
position. When the motion of the actuator is reversed, the position at which the
contacts return to their original state is called the reset point or releasing
position.
Head: It houses the mechanism that translates actuator movement into contact
movement. When the actuator is moved as intended, the mechanism operates
the switch contacts.
Contact Block: It houses the electrical contact elements of the switch. It
typically contains either two or four contact pairs.
Terminal Block: The terminal block contains the screw terminations. This is
where the electrical (wire) connection between the switch and the rest of the
control circuit is made.
Switch Body: The switch body houses the contact block in a plug-in switch. It
houses the contact block and terminal block in the nonplug-in switch.
Base: The base houses the terminal block in a plug-in switch. Nonplug-in
switches do not have a separate base
Limit switches come in several varieties:
- Lever actuator limit switch: These limit switches closely resemble rugged
toggle or selector hand switches fitted with a lever pushed by the machine part.
Often, the levers are tipped with a small roller bearing, preventing the lever from
being worn off by repeated contact with the machine part.
- Proximity switches sense the approach of a metallic machine part either by a
magnetic or high-frequency electromagnetic field.
 Another form of proximity switch is the optical switch, comprised of a light
source and photocell. Machine position is detected by either the
interruption or reflection of a light beam. Optical switches are also useful
in safety applications, where beams of light can be used to detect
personnel entry into a dangerous area.
Mechanical Advantages of Limit Switches
- Ease of use
- Simple visible operation
- Durable housing
- Well sealed for reliable operation
- High resistance to different ambient conditions found in industry
- High repeatability

Electrical Advantages of Limit Switches

- Suitable for switching higher power loads than other sensors
- Immunity to electrical noise interference
- Immunity to radio frequency interference (walkie-talkies)
- No leakage current
- Minimal voltage drops
- Simple Normally Open and/or Normally Closed operation

Disadvantages of Limit Switches

- Shorter contact life than solid-state technology
- Moving mechanical parts wear out eventually
- Not all applications can use contact sensing

Typical Applications
- Conveyor systems
- Transfer machines
- Automatic turret lathes
- Milling and boring machines
- Radial drills

Encoder
- The encoder is a device that senses a physical parameter and converts it to a
digital code.
- An encoder is a sensor of mechanical motion that generates digital signals in
response to motion. As an electro-mechanical device, an encoder is able to
provide motion control system users with information concerning position,
velocity and direction.
- There are two different types of encoders: linear and rotary.
- Linear encoder responds to motion along a path, while a rotary encoder
responds to rotational motion. An encoder is generally categorized by the means
of its output.
- Incremental encoder generates a train of pulses which can be used to
determine position and speed.
- Absolute encoder generates unique bit configurations to track positions
directly.
Advantages of an Encoder
- Highly reliable and accurate
- Low-cost feedback
- High resolution
- Integrated electronics
- Can be incorporated into existing applications
- Compact size
Disadvantages of an Encoder
- Subject to magnetic or radio interference (Magnetic Encoders)
- Direct light source interference (Optical Encoders)
- Susceptible to dirt, oil and dust contaminates
a) Linear encoders
- Linear encoder is a sensor or transducer paired with a scale that encodes
position.
- The sensor reads the scale in order to convert the encoded position into an
analog or digital signal, which can then be decoded into position by a digital
readout (DRO) or motion controller.
- Motion can be determined by change in position over time. Linear encoder
technologies include optical, magnetic, inductive, capacitive and eddy current.
b) Rotary encoders
- Rotary Encoders are another type of position sensor which resemble
potentiometers but are non-contact optical devices used for converting the
angular position of a rotating shaft into an analogue or digital data code.
- In other words, they convert mechanical movement into an electrical signal
(preferably digital).
- All optical encoders work on the same basic principle. Light from an LED or
infra-red light source is passed through a rotating high-resolution encoded disk
that contains the required code patterns, either binary, grey code or BCD.
- Photo detectors scan the disk as it rotates and an electronic circuit processes
the information into a digital form as a stream of binary output pulses that are
fed to counters or controllers which determine the actual angular position of the
shaft.
Flowcharts
- Flowchart is a graphical or symbolic representation of an algorithm. It is the
diagrammatic representation of the step-by-step solution to a given problem.
- It is ideal for a process that has sequential process steps. The steps will be
executed in a simple order that may change as the result of some simple
decisions.
- The symbols used for flowcharts are shown below. These blocks are connected
using arrows to indicate the sequence of the steps. The different blocks imply
different types of program actions.
General rules for flowcharts
- All symbols of the flowchart are connected by flow lines (note arrows, not lines)
- Flow lines enter the top of the symbol and exit out the bottom, except for the
Decision symbol, which can have flow lines exiting from the bottom or the sides
- Flowcharts are drawn so flow generally goes from top to bottom
- The beginning and the end of the flowchart is indicated using the terminal
symbol

Example 1
- A flowchart is shown below for a control system for a large water tank.
- When a start button is pushed the tank will start to fill, and the flow out will be
stopped.
- When full, or the stop button is pushed the outlet will open up, and the flow in
will be stopped.
- In the flowchart the general flow of execution starts at the top. The first
operation is to open the outlet valve and close the inlet valve.
- Next, a single decision block is used to wait for a button to be pushed. When
the button is pushed the yes branch is followed and the inlet valve is opened,
and the outlet valve is closed.
- Then the flow chart goes into a loop that uses two decision blocks to wait until
the tank is full, or the stop button is pushed.
- If either case occurs the inlet valve is closed and the outlet valve is opened. The
system then goes back to wait for the start button to be pushed again.
- When the controller is on the program should always be running, so only a start
block is needed.
1. Draw a flow chart for cutting the grass, then develop ladder logic for three of
the actions/decisions.

2. Design a garage door controller using a flowchart. The behavior of the garage
door controller is as follows,
- there is a single button in the garage, and a single button remote control.
- when the button is pushed the door will move up or down.
- if the button is pushed once while moving, the door will stop, a second push will
start motion again in the opposite direction.
- there are top/bottom limit switches to stop the motion of the door.
- there is a light beam across the bottom of the door. If the beam is cut while the
door is closing the door will stop and reverse.
- there is a garage light that will be on for 5 minutes after the door opens or
closes.
 Topic 4: Digital control system
In continuous time control systems, all the system variables are continuous
signals. Whether the system is linear or nonlinear, all variables are continuously
present and therefore known (available) at all times.

However, digital control systems employ a computer as a fundamental

component in the controller.
It can be viewed from different perspectives including control algorithm,
computer program, conversion between analog and digital domains, system
performance etc.
In a digital control system, the control algorithm is implemented in a digital
computer.

Principles of operation
- The computer typically receives a measurement of the controlled variable, also
often receives the reference input, and produces its output using an algorithm.
- This output is usually converted to an analog signal using a D/A converter, and
then amplified by a power amplifier to drive the plant.

The error signal is discretized and fed to the computer by using an A/D
converter. The controller output is again a discrete signal which is applied to the
plant after using a D/A converter. Error signal e(t) is sampled at intervals of T.
Analog to Digital converter (ADC)
ADC is an electronic device that converts an input analog voltage (or current) to
a digital number proportional to the magnitude of the voltage or current.
In order to covert an analogue quantity to a digital number, three processes
takes place; sampling, quantization and binary encoding.

Filtering:
- Before sampling, the analog input must be filtered with an anti-aliasing filter.
- The anti-aliasing filter is a low-pass filter that limits high frequencies in the
input signal to only those that meet the requirements of the sampling theorem.
- The filter eliminates frequencies that exceed a certain limit that is determined
by the sampling rate
Sampling:
- The first step in converting a signal to digital form is to use a sample-and-hold
circuit.
- This circuit samples the input signal at a rate determined by a clock signal and
holds the level on a capacitor until the next clock pulse. The amplitude of an
analog signal is first sampled.
- The purpose of the sample and hold circuit is to take a sample of the input
signal (analog) and hold it essentially constant while the A/D conversion is taking
place.
- This function is usually implemented with a switch and capacitor. The switch
connects the capacitor to the signal conditioning circuit once every sample
period.
- The capacitor then holds the voltage value measured until a new sample is
acquired.
Quantization:
- This is the process of approximating a continuous range of values by relatively
small set discrete symbols or integer values.
- To store or transmit the sampled values via a digital system, the sample values
are represented in numerical form.
- This requires quantizing where each discrete sample value is rounded off to the
closest numerical value in a set of digital words in use.
- Each sampled amplitude must be converted to one of a finite number of
possible values, or levels. For ease in conversion to binary form, the number of
levels is usually a power of 2 depending on the degree of precision required.
- The quantized signal stays at the sample value until the next sampling instants.
In this quantizing process the information in accurate signal values is lost
because of rounds off and the original signal cannot be reproduced exactly any
more.
Binary encoding
- In the next step in the digitization process, the output of the quantizer is
mapped into a binary sequence.
- It is apparent that 8 levels require three binary digits, or bits; 16 levels require
four bits; and 256 levels require eight bits. In general 2 n levels require n bits.
Types of ADC
- There are several types of analog to digital converter.
o Successive approximation (Potentiometric) ADC
o Ramp type ADC
o Integrating Type ADC
o Dual –slope integrating type
Digital to analog conversion
- Today microcomputers are widely used for industrial control. The output of the
microcomputer is a digital quantity.
- In many applications the digital output of the microcomputer has to be
converted into analog quantity which is used for the control of relay, small
motor, actuator etc.
- In communication system digital transmission is faster and convenient but the
digital signals have to be converted back to analog signals at the receiving
terminal.
- DAC converters are also used as a part of the circuitry of several ADC
converters.
- Thus, digital to analog converter is used to convert digital quantity into analog
quantity. DAC converter produces an output current of voltage proportional to
digital quantity (binary word) applied to its input.
- It functions as a zero-order hold, holding its output at a constant value until it
receives the next discrete input.
- There are several ways of making a digital to analog converter. Some of them
are given as under.
1. Binary weighted resistor DAC
2. R-2R Ladder network
3. Serial DAC converter
The Data Acquisition System
- This is electronic instrument, or group of interconnected electronic hardware
items, dedicated to the measurement and quantization of analog signals for
digital analysis or processing.
- Once the parameter to be measure is translated into the analog-electrical
domain, the DAS performs the translation to the digital-electrical domain.
- In some cases the DAS simply records, or stores the digital data. While more
sophisticated systems may be capable of analysis or further processing.
- For instance, a DAS may be as simple as a digital voltmeter (DVM) which
displays its output as a decimal readout, or it may be complex enough to contain
a large-scale computer as part of its hardware.
Elements of DAS
- Analog multiplexer: permits a number of original sources to be automatically
measure by the same data acquisition hardware.
- It consists of a series of switches whose inputs are tied to the various analog
signals and whole outputs are tied to a common measuring point.
- Each input is individually connected to the measuring point in a predetermined
sequence. The number of channels in a multiplexer may vary from two to several
hundred.
Signal conditioning: Very often the signals presented to the inputs of the data
acquisition system are not in a form appropriate for conversion, and so they
must be preconditioned. The required signal conditioning could consist of linear
amplification, logarithmic amplification, filtering, peak detection, or sample-and-
hold.

Analog-to-Digital (A/D) Converter: The analog-to-digital converter actually

translates the analog signal into an encoded digital format.
Digital clock: The digital clock provides the master timing for the data
acquisition system.
Manual Data Entry: Many data acquisition systems provide users with a way to
tag the data they are accumulating, through some sort of manual data entry.
Digital buffer: The ability to record discrete events is often a requirement of a
data acquisition system. Since these events are usually accompanied by the
opening or closing of a switch, they represent a digital input, out-of-tolerance
conditions or some other situations that might invalidate the data collection are
most often designated as “discrete events”.
Output buffer: The output buffer acts as the data collector for the DAS. In an
ordered sequence, it gathers up such data as the multiplexer channel number,
the signal conditioner gain, A/D converter data, manual data, clock information,
and discrete events. The buffer combines the data with the proper format for
entry into the recording or processing system. It also provides the proper
buffering and control to interface with the recording or processing device.
Recording / processing device: A number of different equipment types can fill
the role of the recording or processing device. Some of the equipment types
commonly used are paper tape punches, teleprinters (TTY), magnetic tape units,
line printers, cathode-ray tube displays, floppy disks, general-purpose digital
computers, and special-purpose digital processors.
The data acquisition system potential uses are:-
1. Data logging
2. Signal analysis
3. Automated factory testing, and
4. Process control
Data Logging
- The data logger is a data acquisition system that measures the analog inputs,
translates the results into the digital domain, and stores the data for future
processing or analysis.
- The data logger provides an automated method of making measurements and
recording data.
- It can perform these functions at precise intervals and with a degree of
accuracy beyond any person’s physical capability.
- Because the data is store in digital format, the data analysis is easily performed
by an off-line computer.
Alarm System
- In industrial plants and installations, control systems are used to monitor and
control processes.
- Control Systems, whether a conventional Control Desk or a Computer/PLCs
System with SCADA or a Distributed Control System (DCS), provides a man-
machine-interface to monitor and control the plant equipment and processes.
- Alarm Systems are an integral part of man-machine interface. An alarm system
consists of both hardware and software including; field signal sensors,
transmitters, alarm generators & handlers, alarm processors, alarm displays,
annunciator window panels, alarm recorders and printers.
- Alarm systems indicate the abnormal conditions and problems of the plant and
equipment to the operators, enabling them to take corrective action and bring
the plant/equipment back to normal conditions.
- Alarm systems give signals to the operators in the form of audible sound, visual
indications in different colors and/or continuous blinking, text messages, etc.
An alarm system brings the following to the notice of the operator:
• problems that need operator attention
• process changes that require corrective action
• unsafe operating conditions before Emergency Shut-down of the plant
• hazardous conditions
• deviations from desired/normal conditions
There exist two types of alarms:
- Real Time Alarms are the alarms that show the current alarms in the system.
- Historical alarms are simply the logging of real time alarms. This will give a
historical of the alarms that will allow system engineers to prevent alarms.
Only four alarm priorities should be implemented. These are:
- High priority: Alarms that warn of dangerous conditions that could cause a
shutdown of a major activity.
- Medium priority: Alarms that should be acted on as quickly as possible; but will
not cause a shutdown.
- Low priority: Alarms that should be dealt with when time permits.
- Event only: Statistical or technical information. No enunciator sounds for these.

Human Machine interface (HMI)

- Human–Machine Interface or HMI is the apparatus or device which presents
processed data to a human operator, and through this, the human operator
monitors and controls the process.
- The HMI of a digital control system is where data is processed and presented to
be viewed and monitored by a human operator.
- This interface usually includes control where the individual can interface with
the control system
- It uses the project screens created during project development and animates
them based on real-time data received from field control units and field data
servers.
- Authorized operators can monitor detailed activities for many types of devices
and send commands using standard faceplate command windows and group
displays.
Typical hardware that is provided is:
- One or more operator displays
- Industrial (or Mylar) type keyboards which have audible or tactile feedback
- Operator panels consisting of highlighted keys to bring up predefined graphic
displays
- Printers ( for alarms and for reports)
- Alarm buzzers (or external sirens)
Operator displays and graphics
- The organization of displays should be done in a clear and logical way to allow
the operator to quickly and effectively identify the information of interest.
- The architecture of displays is to have a progressive decrease in scope of the
displays and a progressive increase in detail as the operator looks for some
specific information
Displays should be organized into three layers:
- The primary level which is an overview level and which should be reached
directly from the function keys on the keypad.
- The secondary level, which consists of a number of displays, associated with
that of the primary level. These should be able to be accessed directly from the
primary level displays.
- The tertiary level, which gives more details on certain secondary level, displays.
The various graphic screens that are available are:
- Free form graphic screens: This is where the screen format can be created by
the users, using whatever layout and symbols they can create. These are best
constructed by the operators (with assistance from the engineer). They offer the
designer complete flexibility in the layout of the information.
- Operating group displays: Here a standard set of symbols is used to create
displays as required. These provide the data in a standard presentation format.
- Trend displays: These displays occupy part or the entire screen depending on
the configuration. They provide trends on the data of analog values.
- Alarm displays: These log the current alarms for the system.
 Topic 5: Fundamentals of Robots
Robot is defined as an electromechanical device with multiple degrees-of-
freedom (DOF) that is programmable to accomplish a variety of tasks.
Robotics is the science of robots while humans working in this area are called
roboticists.
Three Laws of Robotics
1. A robot may not injure a human being, or, through inaction, allow a human
being to come to harm.
2. A robot must obey the orders given it by human beings except where such
orders would conflict with the First Law.
3. A robot must protect its own existence as long as such protection does not
conflict with the First or Second Law.
General Characteristics
- Specialized machine tools with a degree of flexibility that distinguishes them
from fixed-purpose automation.
- ability to move mechanical arm to perform work.
- It is essentially a mechanical arm that is bolted to the floor, a machine, the
ceiling, or, in some cases the wall fitted with its mechanical hand, and taught to
do repetitive task in a controlled, ordered environment.
- robot interface with their work environment once a mechanical hand has been
attached to the robot’s toolmounting plate.
- It is a general-purpose, programmable machine possessing certain
anthropomorphic characteristics
• can work in hazardous work environments
• can perform a repetitive work cycle
• has consistency and accuracy
• can perform difficult task that humans can’t
• has multishift operations
• is reprogrammable, flexible
• can be interfaced to other computer systems
Basic Components
- The basic components of an industrial robot are:
• Manipulator
• End effector (which is the part of the manipulator).
• Power supply
• Controller.
• Means for programming.
The manipulator, which is the robot’s arm, consists of segments jointed
together with axes capable of motion in various directions allowing the robot to
perform work.
The end effector which is a gripper tool, a special device, or fixture attached to
the robot’s arm, actually performs the work.
- Power supply provides and regulates the energy that is converted to motion
by the robot actuator, and it may be electric, pneumatic, or hydraulic.
- The controller initiates, terminates, and coordinates the motion of sequences
of a robot. Also it accepts the necessary inputs to the robot and provides the
outputs to interface with the outside world.
- The means for programming is used to record movements into the robot’s
memory. A robot may be programmed using any of several different methods.
The teach pendant, also called a teach box or hand-held programmer, teaches a
robot the movements required to perform a useful task. The operator uses a
teach pendant to move the robot through the series of points that describe its
desired path. The points are recorded by the controller for later use.
Robotics Terminology
1. DOF degrees-of-freedom: the number of independent motions a
device can make. (Also called mobility)

2. Position: The translational (straight-line) location of something.

3. Orientation: The rotational (angle) location of something. A robot’s
orientation is measured by roll, pitch, and yaw angles.
4. Link: A rigid piece of material connecting joints in a robot.
5. Joint: The device which allows relative motion between two links in a robot.
6. Workspace/Work envelop: The volume in space that a robot’s end-effector
can reach, both in position and orientation.
7. Payload: the ability to carry, continuously and satisfactorily, a given
maximum weight at a given speed.
8. Velocity/speed: the maximum speed at which the tip of a robot is capable of
moving at full extension, expressed in inches or millimeters per second. The
speed is usually specified at a specific load or assuming that the robot is carrying
a fixed weight. Actual speed may vary depending upon the weight carried by the
robot.
9. Cycle: time it takes for the robot to complete one cycle of picking up a given
object at a given height, moving it to a given distance, lowering it, releasing it,
and returning to the starting point.
10. Accuracy: a robot’s ability to position the end effector at a specified point in
space upon receiving a control command without previously having attained that
position.
11. Repeatability: the ability of a robot to return consistently to a previously
defined and achieved location.
12. Resolution: the smallest incremental change in position that it make or its
control system can measure.
13. Size: the physical size of a robot, which influences its capacity and its
capabilities.

Controller
- The controller is the part of a robot that coordinates all movements of the
mechanical system.
- It also receives input from the immediate environment through various sensors.
- The heart of the robot’s controller is generally a microprocessor linked to
input/output and monitoring devices.
- The commands issued by the controller activate the motion control mechanism,
consisting of various controllers, amplifiers, and actuators.
- An actuator is a motor or valve that converts power into robot movement.
- This movement is initiated by a series of instructions, called a program, stored
in the controller’s memory.
- The controller has three levels of hierarchical control. Hierarchical control
assigns levels of organization to the controllers within a robotic system.
- Each level sends control signals to the level below and feedback signals to the
level above. The levels become more elemental as they progress toward the
actuator. Each level is dependent on the level above it for instructions.
- The three levels are:
• Level I—Actuator Control. The most elementary level at which separate
movements of the robot along various planes, such as the X, Y, and Z axes
are controlled.
• Level II—Path Control. The path control (intermediate) level coordinates
the separate movements along the planes determined in Level I into the
desired trajectory or path.
 • Level III—Main Control. The primary function of this highest control level is
to interpret the written instructions from the human programmer
regarding the tasks required. The instructions are then combined with
various environmental signals and translated by the controller into the
more elementary instructions that Level II can understand.

Manipulator
- The manipulator consists of segments that may be jointed and that move
about, allowing the robot to do work.
- The manipulator is the arm of the robot which must move materials, parts,
tools, or special devices through various motions to provide useful work.
- A manipulator can be identified by method of control, power source, actuation
of the joints, and other factors. These factors help identify the best type of robot
for the task at hand.
- For example, you would not use an electric robot in an environment where
combustible fumes exist and a spark could cause an explosion.
- The manipulator is made up of a series of segments and joints
- Joints connect two segments together and allow them to move relative to one
another. The joints provide either linear (straight line) or rotary (circular)
movement. A robot uses actuators to move its arm along programmed paths and
then to hold its joints rigid once the correct position is reached.
- Manipulation is carried out using mechanical devices such as linkages, gears,
actuators, and feedback devices. There are two basic types of motion provided
by actuators: linear and rotary.
- Linear actuators provide motion along a straight line; they extend or retract
their attached loads.
- Rotary actuators provide rotation, moving their loads in an arc or circle. Rotary
motion can be converted into linear motion using a lead screw or other
mechanical means of conversion.

- A robot movement can be divided into two general categories: arm and body
(shoulder and elbow) motions and wrist motions.
- The individual joint motions associated with these categories are referred to as
degree of freedom. Each axis is equal to one degree of freedom. typically an
industrial robots are equipped with 4-6 degrees of freedom
- The wrist can reach a point in space with specific orientation by any of three
motions: a pitch (or up-and-down-motion); a yaw (or side-to-side motion); and a
roll (or rotating motion). The joint labeled pitch, yaw, and roll are called
orientation axes.
- The points that manipulator bends, slides, or rotates are called joints or position
axes. Position axes are called as world coordinates, is identified as being fixed
location within the manipulator that serves as absolute frame of reference
• The x-axis travel moves the manipulator in an in-and-out motion.
• The y-axis motion causes the manipulator to move side-to-side.
 • The z axis motion causes the manipulator to move in and up and-down
motion
The mechanical design of a robot manipulator relates directly to its work
envelope and motion characteristics.

End Effector
- The end effector is the robot’s hand, or the end-of-arm tooling on the robot.
- It is a device attached to the wrist of the manipulator for the purpose of
grasping, lifting, transporting, maneuvering, or performing operations on a
workpiece.
- The end effector is one of the most important components of a robot system.
The robot’s performance is a direct result of how well the end effector meets the
task requirements.
- The area within reach of the robot’s end effector is called its work envelope.

Power Supply
- The power supply provides the energy to drive the controller and actuators. It
may convert ac voltage to the dc voltage required by the robot’s internal circuits,
or it may be a pump or compressor providing hydraulic or pneumatic power.
- The three basic types of power supplies are electrical, hydraulic, and
pneumatic. The most common energy source available, where industrial robots
are used, is electricity. The second most common is compressed air, and the
least common is hydraulic power.
- These primary sources of energy must be converted into the form and amount
required by the type of robot being used. The electronic part of the control unit,
and any electric drive actuator, requires electrical power.
- A robot containing hydraulic actuators requires the conversion of electrical
power into hydraulic energy through the use of an electric, motor-driven,
hydraulic pump.
- A robot with pneumatic actuators requires compressed air, which is usually
supplied by a compressor driven by an electric motor.

Degrees of Freedom
- Degrees of freedom (DOF) is a term used to describe a robot’s freedom of
motion in three dimensional space—specifically, the ability to move forward and
backward, up and down, and to the left and to the right.
- For each degree of freedom, a joint is required. A robot requires six degrees of
freedom to be completely versatile.
- The number of degrees of freedom defines the robot’s configuration. For
example, many simple applications require movement along three axes: X, Y,
and Z.

These tasks require three joints, or three degrees of freedom. The three degrees
of freedom in the robot arm are the rotational traverse, the radial traverse, and
the vertical traverse.
• The rotational traverse (x-axis travel) is movement on a vertical axis. This
is the side-to-side swivel of the robot’s arm on its base.
• The radial traverse (y-axis motion)is the extension and retraction of the
arm, creating in-and-out motion relative to the base.
• The vertical traverse (z-axis motion) provides up-and-down motion.
For applications that require more freedom, additional degrees can be obtained
from the wrist, which gives the end effector its flexibility.
The three degrees of freedom in the wrist have aeronautical names: pitch, yaw,
and roll.
o The pitch, or bend, is the
up-and-down movement of
the wrist.
o The yaw is the side-to-side
movement.
o The roll, or swivel,
involves rotation.
A robot requires a total of six degrees of freedom to locate and orient its hand at
any point in its work envelope.
Although six degrees of freedom are required for maximum flexibility, most
applications require only three to five.
When more degrees of freedom are required, the robot’s motions and controller
design become more complex.

Classifying Robots
- Robots can be classified in various ways, depending on their components,
configuration, and use.
- Three common methods of classifying robots are by the types of control
system used, the type of actuator drive used, and the shape of the work
envelope.
Type of Control System
Robots may use one of two control systems—non-servo and servo.

Non-Servo Robots
- Non-servo robots are the simplest robots and are often referred to as “limited
sequence,” “pick-and-place,” or “fixed-stop robots.”
- The non-servo robot is an open-loop system. In an open-loop system, no
feedback mechanism is used to compare programmed positions to actual
positions.
- Non-servo robots are also limited in their movement and these limitations are
usually in the form of a mechanical stop. This form of robot is excellent in
repetitive tasks, such as material transfer.
- The diagram in Figure below represents a pneumatic (air-controlled), non-servo
robot.


- At the beginning of the cycle, the controller sends a signal to the control valve
of the manipulator.
- As the valve opens, air passes into the air cylinder, causing the rod in the
cylinder to move. As long as the valve remains open, this rod continues to move
until it is restrained by the end stop.
- After the rod reaches the limit of its travel, a limit switch tells the controller to
close the control valve.
- The controller sends the control valve a signal to close.
- The controller then moves to the next step in the program and initiates the
necessary signals. If the signals go to the robot’s end effector, for example, they
might cause the gripper to close in order to grasp an object.
The process is repeated until all the steps in the program have been completed.
Characteristics of non-servo robots:
• Relatively inexpensive compared to servo robots.
• Simple to understand and operate.
• Precise and reliable.
• Simple to maintain.
• Capable of fairly high speeds of operation.
• Small in size.
• Limited to relatively simple programs.

Servo Robots
- The servo robot is a closed-loop system because it allows for feedback. In a
closed-loop system, the feedback signal sent to the servo amplifier affects the
output of the system.
- A servo amplifier translates signals from the controller into motor voltage and
current signals. Servo amplifiers are used in motion control systems where
precise control of position or velocity is necessary.
- In a sense, a servomechanism is a type of control system that detects and
corrects for errors.
- Figure below shows a block diagram of a servo robot system.
The diagram in figure above details one of the axes used in a hydraulic robot and
helps to explain its operation.
• When the cycle begins, the controller searches the robot’s programming
for the desired locations along each axis.
• Using the feedback signals, the controller determines the actual locations
on the various axes of the manipulator.
• The desired locations and actual locations are compared.
• When these locations do not match, an error signal is generated and fed
back to the servo amplifier. The greater the error, the higher the intensity
of the signal.
• These error signals are increased by the servo amplifier and applied to the
control valve on the appropriate axis.
• The valve opens in proportion to the intensity of the signal received. The
opened valve admits fluid to the proper actuator to move the various
segments of the manipulator.
• New signals are generated as the manipulator moves.
• The servo control valves close when there are no more error signals,
shutting off the flow of fluid.
• The manipulator comes to rest at the desired position.
 • The controller then addresses the next instruction in the program, which
may be to move to another location or operate some peripheral
equipment.
The process is repeated until all steps of the program are completed.
Characteristics of servo robots are :
- Relatively expensive to purchase, operate, and maintain.
- Use a sophisticated, closed-loop controller.
- Wide range of capabilities.
- Can transfer objects from one point to another, as well as along a controlled,
continuous path.
- Respond to very sophisticated programming.
- Use a manipulator arm that can be programmed to avoid obstructions within
the work envelope.

Type of Actuator Drive

- One common method of classifying robots is the type of drive required by the
actuators.
• Electrical actuators use electric power.
• Pneumatic actuators use pneumatic (air) power.
• Hydraulic actuators, use hydraulic (fluid) power

Electric Drive
- Three types of motors are commonly used for electric actuator drives: ac servo
motors, dc servo motors, and stepper motors.
- Both ac and dc servo motors have built-in methods for controlling exact
position.
- Many newer robots use servo motors rather than hydraulic or pneumatic ones.
- Small and medium-size robots commonly use dc servo motors. Because of their
high torque capabilities, ac servo motors are found in heavy-duty robots.
- A stepper motor is an incrementally controlled dc motor. Stepper motors are
rarely used in commercial industrial robots, but are commonly found in
educational robots.
- Conventional, electric-drive motors are quiet, simple, and can be used in clean-
air environments. Robots that use electric actuator drives require less floor
space, and their energy source is readily available.
- The rotary motion of most electric actuator drives must be geared down
(reduced) to provide the speed or torque required by the manipulator.
- However, the conventionally geared drive causes problems of backlash, friction,
compliance, and wear. These problems cause inaccuracy, poor dynamic
response, need for regular maintenance, poor torque control capability, and
limited maximum speed on longer moves.
- Loads that are heavy enough to stall (stop) the motor can cause damage.
Conventional electric-drive motors also have poor output power compared to
their weight. This means that a larger, heavier motor must be mounted on the
robot arm when a large amount of torque is needed.

Hydraulic Drive
- A hydraulic drive system uses fluid and consists of a pump connected to a
reservoir tank, control valves, and a hydraulic actuator.
- Hydraulic drive systems provide both linear and rotary motion using a much
simpler arrangement than conventional electric-drive systems.
- The storage tank supplies a large amount of instant power, which is not
available from electric-drive systems.
- Hydraulic actuator drives have several advantages.
• They provide precise motion control over a wide range of speeds.
• They can handle heavy loads on the end of the manipulator arm, can be
used around highly explosive materials,
• They are not easily damaged when quickly stopped while carrying a heavy
load.
- However, they are expensive to purchase and maintain and are not energy
efficient.
- Hydraulic actuator drivers are also noisier than electric-drive actuators and are
not recommended for clean-room environments due to the possibility of
hydraulic fluid leaks.

Pneumatic Drive
- Pneumatic drive systems make use of air-driven actuators. Since air is also a
fluid, many of the same principles that apply to hydraulic systems are applicable
to pneumatic systems.
- Pneumatic and hydraulic motors and cylinders are very similar. Since most
industrial plants have a compressed air system running throughout assembly
areas, air is an economical and readily available energy source.
- This makes the installation of robots that use pneumatic actuator drives easier
and less costly than that of hydraulic robots.
- For lightweight pick-and-place applications that require both speed and
accuracy, a pneumatic robot is potentially a good choice.
- Pneumatic actuator drives work at high speeds and are most useful for small-
to-medium loads.
- They are economical to operate and maintain and can be used in explosive
atmospheres.
- However, since air is compressible, precise placement and positioning require
additional components to achieve the smooth control possible with a hydraulic
system.
- It is also difficult to keep the air as clean and dry as the control system
requires.
- Robots that use pneumatic actuator drives are noisy and vibrate as the air
cylinders and motors stop.

Shape of the Work Envelope

- Robots come in many sizes and shapes. The type of coordinate system used by
the manipulator also varies.
- The type of coordinate system, the arrangement of joints, and the length of the
manipulator’s segments all help determine the shape of the work envelope.
- The joints of a robot are designed to enable the robot to move its end-effector
along a path from one position to another as desired.
- To identify the maximum work area, a point on the robot’s wrist is used, rather
than the tip of the gripper or the end of the tool bit.
- Therefore, the work envelope is slightly larger when the tip of the tool is
considered.

Robotic Joints
- A robot joint is a mechanism that permits relative movement between parts of
a robot arm.
- The basic movements required for a desired motion of most industrial robots
are:
• Rotational movement: This enables the robot to place its arm in any
direction on a horizontal plane.
• Radial movement: This enables the robot to move its end-effector radially
to reach distant points.
• Vertical movement: This enables the robot to take its end-effector to
different heights.
These degrees of freedom, independently or in combination with others, define
the complete motion of the end-effector.
These motions are accomplished by movements of individual joints of the robot
arm. The joint movements are basically the same as relative motion of adjoining
links.
Depending on the nature of this relative motion, the joints are classified as
prismatic or revolute.

Rotational joint (R) is identified by its motion, rotation about an axis

perpendicular to the adjoining links. Here, the lengths of adjoining links do not
change but the relative position of the links with respect to one another changes
as the rotation takes place.
Twisting joint (T) is also a rotational joint, where the rotation takes place about
an axis that is parallel to both adjoining links.
Revolving joint (V) is another rotational joint, where the rotation takes place
about an axis that is parallel to one of the adjoining links. Usually, the links are
aligned perpendicular to one another at this kind of joint. The rotation involves
revolution of one link about another.
Physical Configuration
- Four basic configurations are identified with most of the commercially available
industrial robots
1. Cartesian configuration
2. Cylindrical configuration
3. Polar configuration
4. Joint-arm configuration

Disadvantages:
• Requires large operating volume.
• Exposed guiding surfaces require covering in corrosive or dusty environments.
• can only reach front of itself
• axes hard to seal
Disadvantages:
• can't reach above itself
• linear axes is hard to seal
• won’t reach around obstacles
• exposed drives are difficult to cover from dust and liquids

3. Polar configuration:
- This configuration also goes by the name “spherical coordinate” because the
workspace within which it can move its arm is a partial sphere.
- Thus, the polar robots have a work space of spherical shape and the arm is
connected to the base with a twisting (T) joint and rotatory (R) and linear (L)
joints follow.
- Robot with 1 prismatic joint and 2 rotary joints – the axes consistent with a
polar coordinate system.
The designation of the arm for this configuration can be TRL or TRR. Robots with
the designation TRL are also called spherical robots. This robots are commonly
used for:
• handling at die casting or fettling machines
• handling machine tools
• arc/spot welding
Advantages:
• Large working envelope.
• Two rotary drives are easily sealed against liquids/dust.
Disadvantages:
• Complex coordinates more difficult to visualize, control, and program.
• Exposed linear drive.
• low accuracy.

They are commonly used for:

• assembly operations
• welding
• weld sealing
• spray painting
• handling at die casting or fettling machines
Advantages:
• all rotary joints allows for maximum flexibility
• any point in total volume can be reached.
• all joints can be sealed from the environment.
Disadvantages:
• Extremely difficult to visualize, control, and program.
• Restricted volume coverage.
• low accuracy