Robotics and Automation in medicine

UNIT- 3

1. Differentiate Forward kinematics and inverse kinematics problems. What are the
solutions of Inverse kinematic problems?
2. Discuss various difficulties associated with the inverse kinematics solution and explain
geometric approach used in inverse kinematic problem.
Inverse kinematics is the mathematical process of calculating the variable joint parameters
needed to place the end of a kinematic chain,
such as a robot manipulator or animation
character's skeleton, in a given position and
orientation relative to the start of the chain.
Given joint parameters, the position and
orientation of the chain's end, e.g. the hand of
the character or robot, can typically be
calculated directly using multiple applications of trigonometric formulas, a process known as
forward kinematics. However, the reverse operation is, in general, much more challenging.
Inverse kinematics is also used to recover the movements of an object in the world from some
other data, such as a film of those movements, or a film of the world as seen by a camera which
is itself making those movements. This occurs, for example, where a human actor's filmed
movements are to be duplicated by an animated character.
In robotics, inverse kinematics makes use of the kinematics equations to determine the joint
parameters that provide a desired configuration (position and rotation) for each of the robot's
end-effectors. This is important because robot tasks are performed with the end effectors, while
control effort applies to the joints. Determining the movement of a robot so that its end-
effectors move from an initial configuration to a desired configuration is known as motion
planning. Inverse kinematics transforms the motion plan into joint actuator trajectories for the
robot. The movement of a kinematic chain, whether it is a robot or an animated character, is
modeled by the kinematics equations of the chain. These equations define the configuration of
the chain in terms of its joint parameters. Forward kinematics uses the joint parameters to
compute the configuration of the chain, and inverse kinematics reverses this calculation to
determine the joint parameters that achieve a desired configuration.
Kinematic analysis: A model of the human skeleton as a kinematic chain allows positioning
using inverse kinematics. Kinematic analysis is one of the first steps in the design of most
industrial robots. Kinematic analysis allows the designer to obtain information on the position
of each component within the mechanical system. This
information is necessary for subsequent dynamic analysis along
with control paths. Inverse kinematics is an example of the
kinematic analysis of a constrained system of rigid bodies, or
kinematic chain. The kinematic equations of a robot can be used
to define the loop equations of a complex articulated system.
These loop equations are non-linear constraints on the
configuration parameters of the system. The independent
parameters in these equations are known as the degrees of
freedom of the system. While analytical solutions to the inverse
kinematics problem exist for a wide range of kinematic chains,
computer modeling and animation tools often use Newton's
method to solve the non-linear kinematics equations. When trying
to find an analytical solution it is often convenient exploit the
geometry of the system and decompose it using subproblems with known solutions.
Inverse kinematics:
Inverse kinematics is important to game programming and 3D animation, where it is used to
connect game characters physically to the world, such as feet landing firmly on top of terrain
An animated figure is modeled with a skeleton of rigid segments connected with joints, called
a kinematic chain. The kinematics equations of the figure define the relationship between the
joint angles of the figure and its pose or configuration. The forward kinematic animation
problem uses the kinematics equations to determine the pose given the joint angles. The inverse
kinematics problem computes the joint angles for a desired pose of the figure. It is often easier
for computer-based designers, artists, and animators to define the spatial configuration of an
assembly or figure by moving parts, or arms and legs, rather than directly manipulating joint
angles. Therefore, inverse kinematics is used in computer-aided design systems to animate
assemblies and by computer-based artists and animators to position figures and characters.
The assembly is modeled as rigid links connected by joints that are defined as mates, or
geometric constraints. Movement of one element requires the computation of the joint angles
for the other elements to maintain the joint constraints. For example, inverse kinematics allows
an artist to move the hand of a 3D human model to a desired position and orientation and have
an algorithm select the proper angles of the wrist, elbow, and shoulder joints. Successful
implementation of computer animation usually also requires that the figure move within
reasonable anthropomorphic limits.
A method of comparing both forward and inverse kinematics for the animation of a character
can be defined by the advantages inherent to each. For instance, blocking animation where
large motion arcs are used is often more advantageous in forward kinematics. However, more
delicate animation and positioning of the target end-effector in relation to other models might
be easier using inverted kinematics. Modern digital creation packages (DCC) offer methods to
apply both forward and inverse kinematics to models.
Analytical solutions to inverse kinematics:
in some, but not all cases, there exist analytical solutions to inverse kinematic problems. One
such example is for a 6-DoF robot (for example, 6 revolute joints) moving in 3D space (with 3
position degrees of freedom, and 3 rotational degrees of freedom). If the degrees of freedom of
the robot exceeds the degrees of freedom of the end-effector, for example with a 7 DoF robot
with 7 revolute joints, then there exist infinitely many solutions to the IK problem, and an
analytical solution does not exist. Further extending this example, it is possible to fix one joint
and analytically solve for the other joints, but perhaps a better solution is offered by numerical
methods (next section), which can instead optimize a solution given additional preferences
(costs in an optimization problem). An analytic solution to an inverse kinematics problem is a
closed-form expression that takes the end-effector pose as input and gives joint positions as
output, {\displaystyle q=f(x)}{\displaystyle q=f(x)}. Analytical inverse kinematics solvers can
be significantly faster than numerical solvers and provide more than one solution, but only a
finite number of solutions, for a given end-effector pose.
Numerical solutions to IK problems: There are many methods of modelling and solving
inverse kinematics problems. The most flexible of these methods typically rely on iterative
optimization to seek out an approximate solution, due to the difficulty of inverting the forward
kinematics equation and the possibility of an empty solution space. The core idea behind
several of these methods is to model the forward kinematics equation using a Taylor series
expansion, which can be simpler to invert and solve than the original system.
3. Differentiate between force control and position control of robotic manipulators. Give
suitable examples.
Position control in robotics: The robot position control using force information finely adjusts
the position of the robot arm to reduce the force applied to the object. Thus, the purpose
of the control is to avoid large force so that the object is not broken. Position Control is a
process by which UCOP Leadership monitors headcount by carefully reviewing all
proposals to temporarily or permanently fill a new or repurposed career, limited or contract
appointment.

Force control in robotics: Force control is used to handle the physical interaction between a
robot and the environment and also to ensure safe and dependable operation in the presence
of humans. Force control is used to handle the physical interaction between a robot and
the environment and also to ensure safe and dependable operation in the presence of
humans. The control goal may be that to keep the interaction forces limited or that to
guarantee a desired force along the directions where interaction occurs while a desired
motion is ensured in the other directions. This entry presents the basic control schemes,
focusing on robot manipulators. The force control algorithms implemented in real-time are
an impedance based control scheme with force tracking capability and a hybrid
force/position control algorithm. A two-degree-of-freedom planar manipulator and a non-
rigid contact surface were constructed for purposes of control evaluation.
4. What are the major components of electronic robotic manipulator? Differentiate
between electronic and pneumatic manipulator.
The main components of an industrial robot are Manipulators, End Effectors,
Feedback devices, Controllers, and Locomotive devices.
Manipulators. ...
End Effectors. ...
Feedback Devices. ...
Controllers. ...
Locomotive Devices.
The biggest difference between electric and pneumatic actuators is the driving force of their
operation. Pneumatic actuators require an air supply of 60 to 125 PSI. The solenoid (pilot)
valve is controlled by either an AC or DC voltage. When no air supply is available, electric
actuators are used. Electric as well as pneumatic actuators are quite well known for their varied
uses. In case you are confused as to which type of actuator out of these two will suit your needs,
then we are there to help you. An electric actuator is the one which makes use of electrical
energy to produce mechanical energy. While, a pneumatic actuator, is an air operated actuator,
which converts air pressure into mechanical force to operate the valve. Read on to find the
basic points of difference between an electric and pneumatic actuator.
Differentiate between electronic and pneumatic manipulator.
High force & speed – When it comes to the force and speed of the pneumatic actuators, then
it is worthwhile to note that they offer more force and speed per unit size than the electric
actuators. One can easily adjust the force and speed on the pneumatic actuators. Thus, for those
of you who need to control and regulate the force and speed in the system, should go for
pneumatic actuators without any doubt.
Component cost – If you are considerate about the component costs of pneumatic actuators,
then you would be glad to know that they are low. The electric actuators come with a hefty
component costs, and are thus often avoided by the users.
Operating cost – Regardless of the low component costs of pneumatic actuators, their
maintenance and operating costs are quite high as compared to the electric actuators. These
costs consist of replacement costs of the cylinders, electricity charges, airline installation and
maintenance, etc.
Heating – Owing to their perfect design that resists overheating, the pneumatic actuators are
favored by many. In contrast, the electric actuators can tend to overheat. So, if you want an
actuator that does not overheat easily, then go for the pneumatic one.
Moisture – Another point of difference between these two types of actuators is their resistance
to moisture. While the pneumatic actuators are insensitive to wet environment or moisture, the
electric actuators need to keep well away from moisture.
Stalling – When it comes to the pneumatic actuators, they can be stalled easily. But, the electric
ones cannot be stalled during their operation or use.
Torque to weight ratio – The pneumatic actuators have a high torque to weight ratio as
compared to the electric actuators.
Thus, keep all these points in mind and go for that actuator that suits your requirements the
best. After all, investing in these tools is not an easy decision to make! So, consider all the
points of differences and opt for the right actuator.