- Email: [email protected]
Animated simulation of the robot process capability
Computers and Industrial Engineering Vol. 23, Nos 1--4, pp. 237-240, 1992
0360-8352/92 $5.00+0.00 Copyright © 1992 Pergamon Press Ltd
Printed in Great Britain. All fights reserved
of the R o b o t Prooess Capability
Animated S i m u l a t i o n
C h i u - C h i Wai PhoD. C a n d i d a t e & l i Ks R a m r a n i e Ph.D. ~sietant Professor
Hertz7 Wioboe Ph.D. Professor D e p a r t m e n t o f B n g i n e e r i n g IUmagement University of xiseouri-Rolla Roller
Missouri
6s40z
KBeTIULC~J~ This paper describes an interactive computer graphic system developed for simulating robot capability. The system determines the positioning repeatability and accuracy of a robot performing specific operations. Central to the system are three characteristics, information describing the errors of the geometric and kinematic parameters of a robot, a common function to request and display a robot moving from one position to another, and finally a family of charts showing the repeatability of the robot implementing a given task. INTRODUCTION
Quality and price of products have become two strategic weapons in today's severe global market competition, alterations in the market demand and changes in the socio-economic structure force Industriallsts to constantly struggle for improving quality and reducing cost to ensure market share. Of the tactics being used today, factory automation has been given much attention by industry and one of the important factors in meeting this challenge is the use of robots. The authors believe that robots are capable of performing operations with greater reliability and less variation than human workers. It follows, therefore, that given sufficient information, a robotics process can be fine-tuned to operate at optimum conditions to obtain higher productivity and quality. Due to the fact that the robot has the potential to play an important role in the future of manufacturing, the manager responsible for investing in the robot must be able to make rational decisions concerning robot selection and operation. To assist management in making these decisions, an interactive graphic computer simulation model has been developed. This model allows the user to investigate variations in the position of the robot end-effector due to kinematic errors. The user-drlven system enables an investigator to analyze the positioning repeatability and accuracy of a robot performing a variety of tasks. The results can then be determined and displayed using histograms in x, y, and z directions and scattered ellipses on xy, yz, and zx planes. The model allows a variety of robot applications with different structures to be easily analyzed. The system is designed in such a way that only the basic robot structure entity needs to be changed when a new application is required. The software i8 developed using FORTRAN 77 incorporating GMR3D (Graphics Metafile Resource) for the Apollo system. This software allows the user to graphically simulate the robot process capability instead of purchasing, installing and testing an actual robot. This graphical simulation will allow managers to analyze the uncertainties associated with investment decisions by predicating operating results in a tangible fashion. The simulation analysis can then be used to supplement the specifications given by the robot manufacturers and help the users in making a sound decision. B~CKGROD~ND
Industrlal Robots Robots have been extensively used in a large variety of applications such as assembly, inspection, welding and painting. It was pointed out by Robotics Today that material handling and machine loading and unloading appear to be the largest application for robots purchased in 1988, followed by assembly, arc welding, spot welding and coating. In recent years, the demands for having robots with high accuracy and repeatability have become more critical. However, according to the robotic Delphi report in 1987, the major robot performance constraints are repeatability and accuracy followed by uptime, load capacity, velocity, and size of the robot. The specifications of repeatability and accuracy are often stated by robot manufacturers but this information is limited in nature. Not only are
237
238
Proceedings of the 14th Annual Conference on Computers and Industrial Engineering
robot's repeatability and accuracy questions still left unanswered, but also standards for m e a s u r i n g robot performance are nonexistent. Many different approaches have been proposed, however none of them is widely accepted. Computer Simulation The advent of computer technologies allows management to analyze many sophisticated m a n u f a c t u r i n g problems. Computer simulation helps one plan, create, implement, and modify, therefore, simulation can be used as a management tool to efficiently and productively minimize costs and maximize output. This is especially true, when high cost and risk are involved in the process of decision making. With the constant evolution of technology, simulation results can be viewed through graphical means and animations on the computer terminals in a real time fashion. Therefore, the outcome of a m a n u f a c t u r i n g operation can be easily observed without using the actual equipment. Figure 1 illustrate various types of simulation techniques. PROBLEM
8TATEMBNT
Repeatability and accuracy of robots are two major concerns for robot users, and the specifications given by the robot manufacturers are not sufficient to determine the process capability of the robot. As an example, for the Cincinnati Milacron T3 robot, the only specification given by the m a n u f a c t u r e r is the positioning repeatability. This specification is not given as a function of the end effector position in the work envelop and this method of specification is used because no other alternative method has been uniformly adapted. The problem which exist with this method specification is that a robot's performance can be influenced by a number of factors. These factors may include: (i) Environment factors, such as temperature, and humidity. (2) Parametric factors, which includes kinematic parameters like link lengths and dynamic parameters such as friction, and inertia forces. (3) Computational factors, such as computation errors from round-off. (4) Measurement factors, such as instrumental errors. (5) A p p l i c a t i o n factors, such as installation errors. Each category of factors contributes to the robot inaccuracy and poor repeatability. Interaction between different factors may also exist. The Determination of the robot capability is so complicated that some researchers even proposed that an unique kinematic function should be established for each individual robot. ANIMATED
SIMULATION
OF THE ROBOT
PBOCEES
CAPABILITY
The model is written in FORTRAN 77 coupled with GMR3D and runs on the Apollo system. Figure 2 gives the steps in using the model to analyze a robot's capability. A metafile, which is a collection of picture data, made up of structures and entities is created when a hierarchical structure is specified. Figure 3 shows the hierarchical structure of a robot with five degree of freedoms. It is obvious that the gripper is contained by the wrist, the wrist is contained by the upper arm, and so on. Designing the robot structure in such a manner makes it possible to rotate one joint and drive the rotation of all the succeeding joints in the same way an actual robot operates. It is also noted that only one or, at most, a few basic structure entities need to be built. All the other robot structures can be assembled using these initial basic entities. The basic entity is created only once. Each time a new structure is needed, the basic entity is instanced in conjunction with rotation, translation, and scaling. If a new application is required, only the basic entity needs to be changed, all instanced structures are also changed automatically. Consequently, a variety of robot applications with different structures can be easily modeled. In addition, by organizing structures in a top-down manner, the efficiency of search can be greatly increased, since GMR3D performs a top-down traversal every time a metafile is rendered. Figure 4 details the components of the robot, which are stored in the computer and used to create the metafile. A u s e r - d r i v e n menu is designed to assist users to interactively simulate the robot process capability. Figure 5 demonstrates the menu screen. Once a menu is chosen, the robot will perform the required task corresponding to the command. The repeatability and accuracy of the specific operation can be displayed by selecting the "show the result" function from the menu. A set of charts representing the capability of the robot including three histograms and three scattered ellipses can be shown on the screen if the results need to be viewed. Hard copy of the results can also be easily obtained. APPLICATION
OF THE SYSTEM
Several special tasks are chosen for simulating the robot. These tasks include six different test points. The test points are selected so that the robot's capability will be evaluated under a wide range of operating conditions.
WEI et al.: Simulating Robot Capability
239
These points, typically, include the outermost reach and innermost reach at left, right, and middle of the workspace. Figure 6 depicts the robot configurations corresponding to the test points. The joint angles corresponding to the simulated points are s-mmarlzed in Table 1. Results of the simulations are demonstrated on Figure 7, which illustrates the capability elllpses on xy, yz, and zx planes for each task. These ellipses are consistent with the work done by several other researchers. The different pattern of variation of the end-effector in different directions suggest the existence of an optlmal direction for robot travel when undertaking a high precision task such as an assembly operation. Furthermore, the variations of the robot capability at different locatlons inside the workspace imply that the proper working position should also be carefully chosen if better robot capability is to be expected. It is believed b y , h e authors t h a t t h e information stated above will greatly enhance the process of matching robots to specific tasks and thus help to optimize the robot process capability. CONCLUBION
A graphic simulation system useful for determining the repeatability of a robot under a variety of operating conditions has been developed. It is believed that the graphic simulation made possible by the system is a useful management tool that will assist in the decision making associated with matching a robot to a specific task. From this study, the manager will be able to analyze the uncertainties in making investment decisions by visualizing the results in a tangible fashion. RRFBUNCR8
1. Dieter W. Wloka,"Robsim-a Robot Simulation System", IEEE 1986. 2. Dinesh K. Pal, M. C. Leu, "Ineffabelle-An environment for Interactive Computer Graphic Simulation of Robotics Applications", IEEE 1986. 3. Brad Nelson, Kevin Pederson, Max Donath, "Locating Assembly Tasks in a Manipulator's Workspace", IEEE 1987. 4. K. Kitajima, "Robot simulator Based on a General-Purpose Structure Model for Machine",IEEE 1987. 5. Bernard Faverjon, Pierre Tournassond, " A L o c a l Based Approach for Path Planning of Manipulators with a High Number of Degrees of Freedom", IEEE 1987. 6. Arch Naylor et al, "Progress-A Graphical Robot Programming System", IEEE 1987. 7. James F. Cremer, A. James Stewart, "The Architecture of Newton, a General-Purpose Dynamics Simulator", IEEE 1989. 8. Emmanuel Mazer et al, "ACT:~a robot programming environment", IEEE 1991.
(
Mathematical Hodel s
) I
~'~
Quauing Theory
[ initialize graphic s~stem ) !
~set colors, cursor, and input devices)
,~
V !
I
create,tr,ctu~*or robotand ae,u ~init~alizevles
~SStatlc/Archltecturall4od:~ (~ Physical Modeling I) Pilot
~
)
!
process cmmanos (specify loca:ion for simulation) V
Plant )
,
T
show :he results
Reallty /) ( c'-~sesys~e= )
Figure I. Modeling techniques Figure 2. System flowchart
F i g u r e 3. Robot'm h i e r a r c h i c a l
structure
)
240
~per
Proceedings of the 14¢h Annual Conference on Computers and Industrial Engineering
ern
~
,
" "
~-
Hrist
Gripper
Jgtmulete ttl~et l e f t
I Eilmlate JS l l m l | t e
lower l e f t upper r i g h t
gem,late lower r i g h t Figure
4.
Robot
anatomy
~8llmlate upper middle
JSllmlete lower middle ~gttow the r e s u l t ~t~rint the r e ~ l t B l [ alomm t " t t ~
I
FLqure
/.
S.
One OF h~¢ Space b a t
Syeta
menu screen
(a) Upper meddle
(1) Dpper l e f t
/
!:5.. (x) l ~ p e r l e f t
(:t) Opper a i d ~ e
(3) q ~ e r
rq~t
(31 Upper r / 4 ~ t
(4) Lmmr l e f t F
n~ ~i~ (4) ~
left
(S) l x m e r sdddle
(6) Lower r i q ~ t
•
.
.
-
. i..~...
:. Figt~re 6. l ~ b o t c o n f i ~ u r a t i o ~
c~n~npo~ling
to t]~ te#t
.%
*
points
(S} Loumr a t d d l e
(6) ~
i
Figure
Table
1.
I
2
3
4
91
120
120
.tlO
.120
O
0
e2
0
-45
0
.45
0
45
03
30
45
30"
45
30'
45
04
60
60
60
60
60
60
I~
45
45
45
45
45
45
The Joint
anqlea
oorrespondLnq
5
7. 8 1 m u l e t t o n
6
to
the
simulated
poLntm
reaulta
right
0360-8352/92 $5.00+0.00 Copyright © 1992 Pergamon Press Ltd
Printed in Great Britain. All fights reserved
of the R o b o t Prooess Capability
Animated S i m u l a t i o n
C h i u - C h i Wai PhoD. C a n d i d a t e & l i Ks R a m r a n i e Ph.D. ~sietant Professor
Hertz7 Wioboe Ph.D. Professor D e p a r t m e n t o f B n g i n e e r i n g IUmagement University of xiseouri-Rolla Roller
Missouri
6s40z
KBeTIULC~J~ This paper describes an interactive computer graphic system developed for simulating robot capability. The system determines the positioning repeatability and accuracy of a robot performing specific operations. Central to the system are three characteristics, information describing the errors of the geometric and kinematic parameters of a robot, a common function to request and display a robot moving from one position to another, and finally a family of charts showing the repeatability of the robot implementing a given task. INTRODUCTION
Quality and price of products have become two strategic weapons in today's severe global market competition, alterations in the market demand and changes in the socio-economic structure force Industriallsts to constantly struggle for improving quality and reducing cost to ensure market share. Of the tactics being used today, factory automation has been given much attention by industry and one of the important factors in meeting this challenge is the use of robots. The authors believe that robots are capable of performing operations with greater reliability and less variation than human workers. It follows, therefore, that given sufficient information, a robotics process can be fine-tuned to operate at optimum conditions to obtain higher productivity and quality. Due to the fact that the robot has the potential to play an important role in the future of manufacturing, the manager responsible for investing in the robot must be able to make rational decisions concerning robot selection and operation. To assist management in making these decisions, an interactive graphic computer simulation model has been developed. This model allows the user to investigate variations in the position of the robot end-effector due to kinematic errors. The user-drlven system enables an investigator to analyze the positioning repeatability and accuracy of a robot performing a variety of tasks. The results can then be determined and displayed using histograms in x, y, and z directions and scattered ellipses on xy, yz, and zx planes. The model allows a variety of robot applications with different structures to be easily analyzed. The system is designed in such a way that only the basic robot structure entity needs to be changed when a new application is required. The software i8 developed using FORTRAN 77 incorporating GMR3D (Graphics Metafile Resource) for the Apollo system. This software allows the user to graphically simulate the robot process capability instead of purchasing, installing and testing an actual robot. This graphical simulation will allow managers to analyze the uncertainties associated with investment decisions by predicating operating results in a tangible fashion. The simulation analysis can then be used to supplement the specifications given by the robot manufacturers and help the users in making a sound decision. B~CKGROD~ND
Industrlal Robots Robots have been extensively used in a large variety of applications such as assembly, inspection, welding and painting. It was pointed out by Robotics Today that material handling and machine loading and unloading appear to be the largest application for robots purchased in 1988, followed by assembly, arc welding, spot welding and coating. In recent years, the demands for having robots with high accuracy and repeatability have become more critical. However, according to the robotic Delphi report in 1987, the major robot performance constraints are repeatability and accuracy followed by uptime, load capacity, velocity, and size of the robot. The specifications of repeatability and accuracy are often stated by robot manufacturers but this information is limited in nature. Not only are
237
238
Proceedings of the 14th Annual Conference on Computers and Industrial Engineering
robot's repeatability and accuracy questions still left unanswered, but also standards for m e a s u r i n g robot performance are nonexistent. Many different approaches have been proposed, however none of them is widely accepted. Computer Simulation The advent of computer technologies allows management to analyze many sophisticated m a n u f a c t u r i n g problems. Computer simulation helps one plan, create, implement, and modify, therefore, simulation can be used as a management tool to efficiently and productively minimize costs and maximize output. This is especially true, when high cost and risk are involved in the process of decision making. With the constant evolution of technology, simulation results can be viewed through graphical means and animations on the computer terminals in a real time fashion. Therefore, the outcome of a m a n u f a c t u r i n g operation can be easily observed without using the actual equipment. Figure 1 illustrate various types of simulation techniques. PROBLEM
8TATEMBNT
Repeatability and accuracy of robots are two major concerns for robot users, and the specifications given by the robot manufacturers are not sufficient to determine the process capability of the robot. As an example, for the Cincinnati Milacron T3 robot, the only specification given by the m a n u f a c t u r e r is the positioning repeatability. This specification is not given as a function of the end effector position in the work envelop and this method of specification is used because no other alternative method has been uniformly adapted. The problem which exist with this method specification is that a robot's performance can be influenced by a number of factors. These factors may include: (i) Environment factors, such as temperature, and humidity. (2) Parametric factors, which includes kinematic parameters like link lengths and dynamic parameters such as friction, and inertia forces. (3) Computational factors, such as computation errors from round-off. (4) Measurement factors, such as instrumental errors. (5) A p p l i c a t i o n factors, such as installation errors. Each category of factors contributes to the robot inaccuracy and poor repeatability. Interaction between different factors may also exist. The Determination of the robot capability is so complicated that some researchers even proposed that an unique kinematic function should be established for each individual robot. ANIMATED
SIMULATION
OF THE ROBOT
PBOCEES
CAPABILITY
The model is written in FORTRAN 77 coupled with GMR3D and runs on the Apollo system. Figure 2 gives the steps in using the model to analyze a robot's capability. A metafile, which is a collection of picture data, made up of structures and entities is created when a hierarchical structure is specified. Figure 3 shows the hierarchical structure of a robot with five degree of freedoms. It is obvious that the gripper is contained by the wrist, the wrist is contained by the upper arm, and so on. Designing the robot structure in such a manner makes it possible to rotate one joint and drive the rotation of all the succeeding joints in the same way an actual robot operates. It is also noted that only one or, at most, a few basic structure entities need to be built. All the other robot structures can be assembled using these initial basic entities. The basic entity is created only once. Each time a new structure is needed, the basic entity is instanced in conjunction with rotation, translation, and scaling. If a new application is required, only the basic entity needs to be changed, all instanced structures are also changed automatically. Consequently, a variety of robot applications with different structures can be easily modeled. In addition, by organizing structures in a top-down manner, the efficiency of search can be greatly increased, since GMR3D performs a top-down traversal every time a metafile is rendered. Figure 4 details the components of the robot, which are stored in the computer and used to create the metafile. A u s e r - d r i v e n menu is designed to assist users to interactively simulate the robot process capability. Figure 5 demonstrates the menu screen. Once a menu is chosen, the robot will perform the required task corresponding to the command. The repeatability and accuracy of the specific operation can be displayed by selecting the "show the result" function from the menu. A set of charts representing the capability of the robot including three histograms and three scattered ellipses can be shown on the screen if the results need to be viewed. Hard copy of the results can also be easily obtained. APPLICATION
OF THE SYSTEM
Several special tasks are chosen for simulating the robot. These tasks include six different test points. The test points are selected so that the robot's capability will be evaluated under a wide range of operating conditions.
WEI et al.: Simulating Robot Capability
239
These points, typically, include the outermost reach and innermost reach at left, right, and middle of the workspace. Figure 6 depicts the robot configurations corresponding to the test points. The joint angles corresponding to the simulated points are s-mmarlzed in Table 1. Results of the simulations are demonstrated on Figure 7, which illustrates the capability elllpses on xy, yz, and zx planes for each task. These ellipses are consistent with the work done by several other researchers. The different pattern of variation of the end-effector in different directions suggest the existence of an optlmal direction for robot travel when undertaking a high precision task such as an assembly operation. Furthermore, the variations of the robot capability at different locatlons inside the workspace imply that the proper working position should also be carefully chosen if better robot capability is to be expected. It is believed b y , h e authors t h a t t h e information stated above will greatly enhance the process of matching robots to specific tasks and thus help to optimize the robot process capability. CONCLUBION
A graphic simulation system useful for determining the repeatability of a robot under a variety of operating conditions has been developed. It is believed that the graphic simulation made possible by the system is a useful management tool that will assist in the decision making associated with matching a robot to a specific task. From this study, the manager will be able to analyze the uncertainties in making investment decisions by visualizing the results in a tangible fashion. RRFBUNCR8
1. Dieter W. Wloka,"Robsim-a Robot Simulation System", IEEE 1986. 2. Dinesh K. Pal, M. C. Leu, "Ineffabelle-An environment for Interactive Computer Graphic Simulation of Robotics Applications", IEEE 1986. 3. Brad Nelson, Kevin Pederson, Max Donath, "Locating Assembly Tasks in a Manipulator's Workspace", IEEE 1987. 4. K. Kitajima, "Robot simulator Based on a General-Purpose Structure Model for Machine",IEEE 1987. 5. Bernard Faverjon, Pierre Tournassond, " A L o c a l Based Approach for Path Planning of Manipulators with a High Number of Degrees of Freedom", IEEE 1987. 6. Arch Naylor et al, "Progress-A Graphical Robot Programming System", IEEE 1987. 7. James F. Cremer, A. James Stewart, "The Architecture of Newton, a General-Purpose Dynamics Simulator", IEEE 1989. 8. Emmanuel Mazer et al, "ACT:~a robot programming environment", IEEE 1991.
(
Mathematical Hodel s
) I
~'~
Quauing Theory
[ initialize graphic s~stem ) !
~set colors, cursor, and input devices)
,~
V !
I
create,tr,ctu~*or robotand ae,u ~init~alizevles
~SStatlc/Archltecturall4od:~ (~ Physical Modeling I) Pilot
~
)
!
process cmmanos (specify loca:ion for simulation) V
Plant )
,
T
show :he results
Reallty /) ( c'-~sesys~e= )
Figure I. Modeling techniques Figure 2. System flowchart
F i g u r e 3. Robot'm h i e r a r c h i c a l
structure
)
240
~per
Proceedings of the 14¢h Annual Conference on Computers and Industrial Engineering
ern
~
,
" "
~-
Hrist
Gripper
Jgtmulete ttl~et l e f t
I Eilmlate JS l l m l | t e
lower l e f t upper r i g h t
gem,late lower r i g h t Figure
4.
Robot
anatomy
~8llmlate upper middle
JSllmlete lower middle ~gttow the r e s u l t ~t~rint the r e ~ l t B l [ alomm t " t t ~
I
FLqure
/.
S.
One OF h~¢ Space b a t
Syeta
menu screen
(a) Upper meddle
(1) Dpper l e f t
/
!:5.. (x) l ~ p e r l e f t
(:t) Opper a i d ~ e
(3) q ~ e r
rq~t
(31 Upper r / 4 ~ t
(4) Lmmr l e f t F
n~ ~i~ (4) ~
left
(S) l x m e r sdddle
(6) Lower r i q ~ t
•
.
.
-
. i..~...
:. Figt~re 6. l ~ b o t c o n f i ~ u r a t i o ~
c~n~npo~ling
to t]~ te#t
.%
*
points
(S} Loumr a t d d l e
(6) ~
i
Figure
Table
1.
I
2
3
4
91
120
120
.tlO
.120
O
0
e2
0
-45
0
.45
0
45
03
30
45
30"
45
30'
45
04
60
60
60
60
60
60
I~
45
45
45
45
45
45
The Joint
anqlea
oorrespondLnq
5
7. 8 1 m u l e t t o n
6
to
the
simulated
poLntm
reaulta
right