Robot programming , accuracy ,repeatability and application

2. ROBOT TECHNOLOGY
by
Dr Vishaldatt
Kohir
Professor
Subject: Computer Integrated Manufacturing
Module 4
Topic : Robot programming , accuracy ,repeatability
and application

3. Part 3 Robot Application
Part 2 Accuracy, Repeatability
Part 1 Robot programming

4. Robot
programming Leadthrough programming
Offline programming
Computer like programming

5. A robot program can be defined as a path in space to be followed by the
manipulator, combined with peripheral actions that support the work cycle.
(1) Lead through programming,
(2) Computer-like robot
(3) Off-line programming.
The robot is physically moved through the various motions needed to perform a
given task, recording the motions into the robot’s computer memory. This can be
done either by physically (manually) moving the manipulator through the motion
sequence or by using a control box (teach pendent) to drive the manipulator
through the sequence.
Robots use two coordinate system to record the motion
(1) world-coordinate system and (2) tool-coordinate system.
Lead through programming

6. In straight line interpolation, the control computer calculates the sequence of
addressable points in space through which the wrist end must move to achieve a
straight line path between two points.
In joint interpolation robot is commanded to move its wrist end between
two points , it actuates each of the joints simultaneously at its own constant speed such
that all of the joints start and stop at the same time.
Advantages
 It can be readily learned by shop personnel.
 The robot programmer to possess knowledge of computer programming.
 The work cycle can be taught no need to write separate program
Disadvantages.
 Regular production must be interrupted during the lead through programming
procedures.
 Limited in terms of the decision-making logic that can be incorporated into the
program.
 It is not readily compatible with modern computer-based technologies such as
CAD/CAM, manufacturing databases, and local communications networks.
Above method is also known as on line programming
Lead through programming

8. Off-line programming permits the robot program to be prepared at a remote
computer terminal and downloaded to the robot controller for execution without
interrupting production.
They use graphical simulation to construct a three-dimensional model of the robot cell
which consist of the robot, machine tools, conveyors, and other hardware.
The simulator displays these cell components on the graphics monitor and shows
the robot performing its work cycle in animated computer graphics.
It is then converted into the textual language corresponding to the particular robot
employed in the cell.
Some adjustment must be performed to account for geometric differences between
the three-dimensional model in the computer and the actual physical cell.
Off-line programming

10. The use of method became an appropriate programming method as digital
computers took over the control function in robotics.
This method of programming is sometimes referred to as on-line/off-line programming.
The textual statements are used to describe the motion, and the lead through methods
are used to define the position and orientation of the robot
To illustrate, the basic motion statement is
MOVE P1
which commands the robot to move from its current position to a position and
orientation defined by the variable name P1.
P1 is defined using either powered leadthrough or manual leadthrough
HERE P1 or LEARN P1
Statements are used in the lead through procedure to indicate the variable name for
the point and is recorded into the robot’s control memory is the set of joint positions or
coordinates used by the controller to define the point.
Computer-like robot

11. Variable Assembly Language (VAL) i
computer-based control system and language designed specifically for use
with Unimation Inc. industrial robots
Machine Control Language (MCL)
developed by McDonnell Douglas corporation
C and C++ , MAT Lab, Python

12. Robot
position
and
orientation
Resolution
Accuracy
Repeatability

13. The capacity of a robot to position and orient the end of its wrist depends on the
1) Resolution
2) Accuracy
3) Repeatability
In robotics, the characteristics are defined at the end of
the wrist and in the absence of any end effector attached to the wrist.
Example:
Assembly The objects be located within 0.05 mm
Spot welding Require accuracies of 0.5–1.0 mm

14. Control Resolution –
This is the smallest change that can be measured by the feedback sensors, or
caused by the actuators, whichever is larger.
It is the distance between adjacent addressable points by the controller
It depends on (1) limitations of the electromechanical components that make
up each joint-link combination
(2) the controller’s bit storage capacity for that joint.
Example:
If a rotary joint has an encoder that measures every 0.01 degree of rotation,
and a direct drive servo motor is used to drive the joint, with a resolution of 0.5
degrees,
worst case resolution is 0.5+0.01 degrees

15. Repeatability and Accuracy

16. Repeatability
It ability to position robot’s end-of-wrist at a previously taught point in the
work volume.
The mechanical errors are principal source for variation in repeatability.
Re = {3s}
where s = standard deviation of the error distribution
Accuracy
It is the robot’s ability to position the end of its wrist at a desired location in
the work volume. For a single axis, using the same reasoning as in NC,
Ac = (CR / 2 )+ 3s
where CR = control resolution

18. Industrial
robot
application Material handling
Processing operations
Assembly

19. The robot must have following features to facilitate material
handling:
1. The manipulator must be able to lift the parts safely.
2. The robot must have the reach needed.
3. The robot must have cylindrical coordinate type.
4. The robot’s controller must have a large enough memory
to store all the programmed points so that the robot can
move from one location to another.
5. The robot must have the speed necessary for meeting the
transfer cycle of the operation.
MATERIAL-HANDLING APPLICATIONS

20. Material-
handling
(1) Part Placement
(2) Palletizing or de-
palletizing
(3) Machine loading or
unloading
(4) Stacking and insertion
operation

21. Part Placement:
• The basic operation in this category is the relatively simple pick-and-place operation.
• This application needs a low-technology robot of the cylindrical coordinate type.
• Only two, three or four joints are required for most of the applications.
• Pneumatically powered robots are often utilized.

22. Palletizing and/or De-palletizing:
Robot has to pick the parts from one location and deposits them onto a pallet or
other container at multiple positions on the pallet. This adds to the degree of
difficulty of the task.
 Robot should able recognize each position on the pallet
 using the powered-lead through method
 Compute location in x, y and z direction with pallet center
Example: Process of taking parts from the assembly line and stacking them on a
pallet or vice versa

23. • Die casting. The robot unloads parts from machine
and include dipping the parts into a water
• Plastic molding. unloads molded parts from the
injection molding machine.
• Forging. loads and holds during the forging strikes, and
removes it from the forge hammer.
• Press work: loads the blank into the press, and the part
falls out of the machine into a after stamping operation
Machine loading and/or unloading:
Three possible cases are
 Robot loads parts into the machine
 Robot unloads the finished parts
 Both loading of the raw work part and
unloading of the finished part by the
robot

24. • In processing operations, the robot performs some
processing actions such as grinding, milling, etc. on the work
part.
• The end effector is equipped with the specialized tool
required for the process.
• The tool is moved relative to the surface of the work part.
• Robot performs a processing procedure on the part.
• Manipulates the tooling relative to the working part during
the cycle.
• Five or six axes are generally required to achieve the
required position and orientation of the endeffector/tool.
• Jointed-arm robots commonly used
PROCESSING OPERATIONS

25. processing operations include:
(1) Spot welding
(2) Continuous arc welding
(3) Spray painting
(4) Metal cutting and deburring operations
(5) Various machining operations like drilling, grinding,
laser and water jet cutting and riveting.
(6) Rotating and spindle operations
(7) Adhesives and sealant dispensing
PROCESSING OPERATIONS

26. Spot welding
The end effector is the spot welding gun used to pinch the car panels together and
perform the resistance welding process.
Robots used for spot welding are usually large, with sufficient payload capacity to
handle the heavy welding gun
It is difficult for humans to manipulate accurately.
As a consequence, there were many instances of missed welds, poorly located
welds, and other defects in the product.
Five or six axes are generally required to achieve the required position and orientation
of the welding gun.

27. Arc Welding
High electrical current is used in the welding process
High temperatures expose to worker
Significant hand–eye coordination is required
Desired path with sufficient accuracy to make a good weld.
Arc-on time is 20–30% worker fatigue.
Fitter set up the job and welder welds
Because of these conditions in manual arc welding, robots are used
it is technically and economically feasible.

28. Spray painting
The use of industrial robots for spray coating offers a number of benefits
 Protect workers from a hazardous environment.
 Greater uniformity in applying the coating
 Reduced waste of paint,
 Lower needs for ventilating the work area
 Greater productivity.

29. Machining processes
The robot must be strong enough to withstand these cutting forces and
maintain the required accuracy of the cut.
Grinding, Drilling, Deburring , water jet machining , laser cutting

30. ASSEMBLY OPERATIONS
 Assembly involves the combining of two or more parts
 Assembly work typically involves diverse tasks
Requires adjustments to be made in parts that don’t quite fit together.
A sense of feel is often required to achieve a close fitting of parts.
Inspection work requires human judgment to check whether a product is within quality
specifications or not.
more precise robots required with repeatabilities of {+or - 0.05 mm }
The most common configurations are jointed arm, SCARA, and Cartesian coordinate.

32. The simplest way to understand how cobots and industrial robots differ, is
that cobots are designed to work alongside human employees, while
industrial robots do work in place of those employees. ... Cobots are also more
easily programmable than industrial robots because they are capable of
“learning” on the job
This allows manufacturing to accommodate short runs with increased
efficiency. The cobot is designed to do the repetitive and precise motions to
help assist workers.

33. The simplest way to understand how cobots and industrial robots differ, is
that cobots are designed to work alongside human employees, while
industrial robots do work in place of those employees. ... Cobots are also more
easily programmable than industrial robots because they are capable of
“learning” on the job
This allows manufacturing to accommodate short runs with increased
efficiency. The cobot is designed to do the repetitive and precise motions to
help assist workers.