AUTOMATION IN PRODUCTION SYSTEMS

Some elements of the firm’s production system are likely to be automated, whereas others will be
operated manually or clerically. For our purposes here, automation can be defined as a technology
concerned with the application of mechanical, electronic, and computer based systems to operate
and control production.

The automated elements of the production system can be separated into two categories: (1)
automation of the manufacturing systems in the factory and (2) computerization of the manufacturing
support systems. In modern production systems, the two categories overlap to some extent, because
the automated manufacturing systems operating on the factory floor are themselves often
implemented by computer systems and connected to the computerized manufacturing support
systems and management information system operating at the plant and enterprise levels. The term
computer integrated manufacturing is used to indicate this extensive use of computers in production
systems. The two categories of automation are shown in Figure 1.6 as an overlay on Figure 1.1.

1.Automated Manufacturing Systems

Automated manufacturing systems operate in the factory on the physical product. They perform
operations such as processing, assembly, inspection, or material handling, in some cases
accomplishing more than one of these operations in the same system. They are called automated
because they perform their operations with a reduced level of human participation compared with
the corresponding manual process. In some highly automated systems, there is virtually no human
participation. Examples of automated manufacturing systems include:

➢ automated machine tools that process parts

➢ transfer lines that perform a series of machining operations
➢ automated assembly systems
➢ manufacturing systems that use industrial robots to perform processing or assembly
operations
➢ automatic material handling and storage systems to integrate manufacturing operations
➢ automatic inspection systems for quality control.
Automated manufacturing systems can be classified into three basic types (1) fixed automation, (2)
programmable automation, and (3) flexible automation.
 Fixed Automation. Fixed automation is a system in which the sequence of processing (or
assembly) operations is fixed by the equipment configuration. Each of the operations in the sequence
is usually simple, involving perhaps a plain linear or rotational motion or an uncomplicated
combination of the two; for example, the feeding of a rotating spindle. It is the integration and
coordination of many such operations into one piece of equipment that makes the system complex.
Typical features of fixed automation are:

➢ high initial investment for custom-engineered equipment

➢ high production rates
➢ relatively inflexible in accommodating product variety

Examples of fixed automation include machining transfer lines and automated assembly machines.

Programmable Automation. In programmable automation, the production equipment is

designed with the capability to change the sequence of operations to accommodate different product
configurations. The operation sequence is controlled by a program, which is a set of instructions coded
so that they can be read and interpreted by the system. New programs can be prepared and entered
into the equipment to produce new products. Some of the features that characterize programmable
automation include:

➢ high investment in general purpose equipment.

➢ lower production rates than fixed automation.
➢ flexibility to deal with variations and changes in product configuration.
➢ most suitable for batch production.
Programmable automated production systems are used in low and mediumvolume production. The
parts or products are typically made in batches. To produce each new batch of a different product,
the system must be reprogrammed with the set of machine instructions that correspond to the new
product. The physical setup of the machine must also be changed: Tools must be loaded, fixtures must
be attached to the machine table, and the required machine settings must be entered. This
changeover procedure takes time. Consequently, the typical cycle for a given product includes a period
during which the setup and reprogramming takes place, followed by a period in which the batch is
produced. Examples of programmable automation include numerically controlled (NC) machine tools,
industrial robots, and programmable logic controllers.

Flexible Automation. Flexible automation is an extension of programmable automation. A

flexible automated system is capable of producing a variety of parts (or products) with virtually no
time lost for changeovers from one part style to the next. There is no lost production time while
reprogramming the system and altering the physical setup (tooling, fixtures, machine settings).
Consequently, the system can produce various combinations and schedules of parts or products
instead of requiring that they be made in batches. What makes flexible automation possible is that
the differences between parts processed by the system are not significant. It is a case of soft variety,
so that the amount of changeover required between styles is minimal. The features of flexible
automation can be summarized as follows:

➢ high investment for a custom-engineered system

➢ continuous production of variable mixtures of products
➢ medium production rates
 ➢ flexibility to deal with product design variations

Examples of flexible automation are the flexible manufacturing systems for performing machining
operations.

The relative positions of the three types of automation for different production volumes and product
varieties are depicted in Figure 1.7

2. Computerized Manufacturing Support Systems

Automation of the manufacturing support systems is aimed at reducing the amount of manual and
clerical effort in product design, manufacturing planning and control, and the business functions of
the firm. Nearly all modern manufacturing support systems are implemented using computer systems.
Indeed, computer technology is used to implement automation of the manufacturing systems in the
factory as well. The term computer— integrated manufacturing (CIM) denotes the pervasive use of
computer systems to design the products, plan the production, control the operations, and perform
the various business—related functions needed in a manufacturing firm. True CIM involves integrating
all of these functions in one system that operates throughout the enterprise. Other terms are used to
identify specific elements of the CIM system. For example, computer-aided design (CAD) denotes the
use of computer systems to support the product design function. Computer-aided
manufacturing (CAM) denotes the use of computer systems to perform functions related to
manufacturing engineering, such as process planning and numerical control part programming. Some
computer systems perform both CAD and CAM, and so the term CAD/CAM is used to indicate the
integration of the two into one system. Computer—integrated manufacturing includes CAD/CAM, but
it also includes the firm’s business functions that are related to manufacturing.

Let us attempt to define the relationship between automation and CIM by developing a
conceptual model of manufacturing. In a manufacturing firm, the physical production activities that
take place in the factory can be distinguished from the information—processing activities, such as
product design and production planning, that usually occur in an office environment. The physical
activities include all of the processing, assembly, material handling, and inspection operations that are
performed on the product in the factory. These operations come in direct contact with the product
during manufacture. The relationship between the physical activities and the information—processing
activities in our model is depicted in Figure 1.8. Raw materials flow into one end of the factory and
finished products flow out the other end. The physical activities take place inside the factory. In our
model, the information—processing activities form a ring that surrounds the factory, providing the
data and knowledge required to successfully produce the product.

AUTOMATION PRINCIPLES AND STRATEGIES

The preceding discussion leads us to conclude that automation is not always the right answer for a
given production situation. A certain caution and respect must be observed in applying automation
technologies. In this section, we offer three approaches for dealing with automation projects: 2 (1) the
USA Principle, (2) the Ten Strategies for Automation and Production Systems, and (3) an Automation
Migration Strategy.

1.USA Principle

The USA Principle is a common sense approach to automation projects. Similar procedures have been
suggested in the manufacturing and automation trade literature, but none has a more captivating title
than this one. USA stands for:

1. Understand the existing process

2. Simplify the process

3. Automate the process.

Understand the Existing Process. The obvious purpose of the first step in the USA approach is to
comprehend the current process in all of its details. What are the inputs? What are the outputs? What
exactly happens to the work unit between input and output? What is the function of the process?
How does it add value to the product? What are the upstream and downstream operations in the
production sequence, and can they be combined with the process under consideration?

Some of the basic charting tools used in methods analysis are useful in this regard, such as the
operation process chart and the flow process chart . Application of these tools to the existing process
provides a model of the process that can be analyzed and searched for weaknesses (and strengths).
The number of steps in the process, the number and placement of inspections, the number of moves
and delays experienced by the work unit, and the time spent in storage can be ascertained by these
charting techniques.

Mathematical models of the process may also be useful to indicate relationships between input
parameters and output variables. What are the important output variables? How are these output
variables affected by inputs to the process, such as raw material properties, process settings,
operating parameters, and environmental conditions? This information may be valuable in identifying
what output variables need to be measured for feedback purposes and in formulating algorithms for
automatic process control.
Simplify the Process. Once the existing process is understood, then the search can begin for ways to
simplify. This often involves a checklist of questions about the existing process. What is the purpose
of this step or this transport? Is this step necessary? Can this step be eliminated? Is the most
appropriate technology being used in this step? How can this step be simplified? Are there
unnecessary steps in the process that might be eliminated without detracting from function?

Some of the ten strategies of automation and production systems are applicable to try to simplify the
process. Can steps be combined? Can steps be performed simultaneously? Can steps be integrated
into a manually operated production line?.

Automate the Process. Once the process has been reduced to its simplest form, then automation can
be considered. The possible forms of automation include those listed in the ten strategies discussed
in the following section

2 Ten Strategies for Automation and Production Systems.

If automation seems a feasible solution to improving productivity, quality, or other measure of
performance, then the following ten strategies provide a road map to search for these improvements.
We refer to them as strategies for automation and production systems because some of them are
applicable whether the process is a candidate for automation or just for simplification.
i) Specialization of operations. The first strategy involves the use of special—purpose equipment
designed to perform one operation with the greatest possible efficiency. This is analogous to the
concept of labour specialization, which is employed to improve labour productivity.

ii) Combined operations. Production occurs as a sequence of operations. Complex parts may require
dozens, or even hundreds, of processing steps. The strategy of combined operations involves reducing
the number of distinct production machines or workstations through which the part must be routed.
This is accomplished by performing more than one operation at a given machine, thereby reducing
the number of separate machines needed. Since each machine typically involves a setup, setup time
can usually be saved as a consequence of this strategy. Material handling effort and non-operation
time are also reduced. Manufacturing lead time is reduced for better customer service.

iii)Simultaneous operations. A logical extension of the combined operations strategy is to

simultaneously perform the operations that are combined at one workstation. In effect, two or more
processing (or assembly) operations are being performed simultaneously on the same workpart, thus
reducing total processing time.

iv) Integration of operations. Another strategy is to link several workstations together into a single
integrated mechanism, using automated work handling devices to transfer parts between stations. In
effect, this reduces the number of separate machines through which the product must be scheduled.
With more than one workstation, several parts can be processed simultaneously, thereby increasing
the overall output of the system.

v)Increased flexibility. This strategy attempts to achieve maximum utilization of equipment for job
shop and medium volume situations by using the same equipment for a variety of parts or products.
It involves the use of the flexible automation concepts. Prime objectives are to reduce setup time and
programming time for the production machine. This normally translates into lower manufacturing
lead time and less work-in-process.
vi)Improved material handling and storage. A great opportunity for reducing non-productive time
exists in the use of automated material handling and storage systems. Typical benefits include reduced
work-in-process and shorter manufacturing lead times.

vii) Online inspection. Inspection for quality of work is traditionally performed after the process is
completed. This means that any poor quality product has already been produced by the time it is
inspected. Incorporating inspection into the manufacturing process permits corrections to the process
as the product is being made. This reduces scrap and brings the overall quality of product closer to the
nominal specifications intended by the designer.

viii) Process control and optimization. This includes a wide range of control schemes intended to
operate the individual processes and associated equipment more efficiently. By this strategy, the
individual process times can be reduced and product quality improved.

ix) Plant operations control. Whereas the previous strategy was concerned with the control of the
individual manufacturing process, this strategy is concerned with control at the plant level. It attempts
to manage and coordinate the aggregate operations in the plant more efficiently. Its implementation
usually involves a high level of computer networking within the factory.

x) Computer integrated manufacturing (CIM). Taking the previous strategy one level higher, we have
the integration of factory operations with engineering design and the business functions of the firm.
CIM involves extensive use of computer applications, computer data bases, and computer networking
throughout the enterprise.

Elements of an automated system

An automated system consists of three basic elements: (1) power to accomplish the process and
operate the system. (2) a program of instructions to direct the process, and (3) a control system to
actuate the instructions. The relationship amongst these elements is illustrated above Figure. All
systems that qualify as being automated include these three basic elements in one form or another.

Power to Accomplish the Automated Process

An automated system is used to operate some process, and power is required to drive the process as
well as the controls. The principal source of power in automated systems is electricity. the actions
performed by automated systems are generally of two types. (a) Processing (b) Transfer and
positioning. in first case, energy is applied to accomplish some processing operations on some entity.
the process may involve shaping, moulding, loading and unloading. all these actions need power to
transfer the entity from one state or condition into more valuable state.

the second type of actions transfer and positioning. in these cases, the product must generally be
moved from one location to another location during the series of processing steps.

Program of Instructions

The actions performed by an automated process are defined by a set of instructions known as process.
the program instructions determine the set of actions that is to be done automatically by the system.
the program specifies what automated system to do and how its various components must function
in order to accomplish the desired results.

Control System The control element of the automated system executes the Program of Instructions.
the control is in automated system can be (a) open loop (b) closed loop.

A closed loop control system, also known as a feedback control system. is one in which the output
variable is compared with an input parameter, and any difference between the two is used to drive
the output into agreement with the input as shown in Figure . a closed loop control system consists of
six basic elements: (I) input parameter, (2) process, (3) output van. able, (4) feedback sensor. (5)
controller. and (0) actuator. The input parameter. often referred to as the set point, represents the
desired value of the output. In a home temperature can. trot system, the set point is the desired
thermostat setting. The process is the operation or function being controlled. In particular, it is
the output variable that is being controlled in the Loop. in the present discussion, the process of
interest is usually a manufacturing operation, and the output variable is some process variable,
perhaps a critical performance measure in the process, such as temperature or force or flow rate.
A sensor is used to measure the output variable and close the loop between input and output. Sensors
perform the feedback function in a closed loop control system. The controller compares the output
with the input and makes the required adjustment in the process to reduce the difference between
them. The adjustment is accomplished using one or more actuators, which are the hardware devices
that physically carry out the control actions, such as an electric motor or a flow valve. It should be
mentioned that OUT model in Figure 3.3 shows only one loop. Most industrial processes require
multiple loops, one for each process variable that must be controlled.

For the open loop case, the diagram for the positioning system would be similar to the preceding.
except that no feedback loop is present and a stepper motor is used in place of the de servomotor. A
stepper motor is designed to rotate a precise fraction of a tum for each pulse received from the
controller. Since the motor shaft is connected to the leadscrew, and the leadscrew drives the
worktable. each pulse converts into a small constant linear movement of the table. To move the table
a desired distance. the number of pulses corresponding to that distance is setup to the motor. Given
the proper application, whose charactcrisrtcs match the preceding list of operating conditions, an
open loop positioning system works with high reliability.

ADVANCED AUTOMATION FUNCTIONS

1. Safety monitoring

2. Maintenance and repair diagnostics

3. Error detection and recovery.

Safety monitoring Use of sensors to track the systems operation and identify the condition that unsafe
or potentially safe.

Reasons for Safety monitoring. To protect workers and equipments.

Possible responses to hazards;

➢ Complete stoppage of the system.

➢ Sounding an alarm
➢ Reducing operating speed of process
➢ Taking corrective action to recover from the safety violation.

Maintenance and repair diagnostics

Status monitoring .

➢ Monitors and records status of key sensors and parameters during system operation

Failure diagnostics

➢ Invoked when a malfunction occurs.

➢ Purpose : analyze and recorded values so the cause of malfunction can be identified.

Recommendation of repair procedures

➢ provides Recommended procedure for the repair crew to effect repairs

Error detection and recovery
1.Error detection functions

➢ Use the system available sensors to determine when a deviation or malfunctions has occurred.
➢ Correctly interpret the sensor signal
➢ Classify the error.

2. Error recovery-possible strategies

➢ Make adjustment at end of work cycle.

➢ Make adjustment during current work cycle.
➢ Stop the process to invoke corrective action.
➢ Stop the process and call for help.

LEVELS OF AUTOMATION

Device level. This is the lowest level in our automation hierarchy. It includes the actuators, sensors,
and other hardware components that comprise the machine level. The devices are combined into the
individual control loops of the machine; for ex· ample, the feedback control loop for one axis of a CNC
machine or one joint of an industrial robot.

Machine level. Hardware at the device level is assembled into individual machines. Examples include
CNC machine tools and similar production equipment, industrial robots, powered conveyors, and
automated guided vehicles. Control functions at this level include performing the sequence of steps
in the program of instructions in the correct order and making sure that each step is properly
executed.

Cell or system level. This is the manufacturing cell or system level, which operates under instructions
from the plant level. A manufacturing cell or system is a group of machines or workstations connected
and supported by a material handling system, computer. and other equipment appropriate to the
manufacturing process. Production lines are included in this level. functions include part dispatching
and machine loading. coordination among machines and material handling system, and collecting and
evaluating inspection data.

Plant level. This is the factory or production systems level. It receives instructions from the corporate
information system and translates them into operational plans for production. Likely functions
include: order processing, process planning, inventory control, purchasing, material requirements
planning, shop floor control, and quality control.

Enterprise level. This is the highest level. consisting of the corporate information system. It is
concerned with all of the functions necessary to manage the company: marketing and sales,
accounting, design, research, aggregate planning, and master production scheduling.