U.S. patent application number 09/750433 was filed with the patent office on 2002-07-04 for versatile robot control system.
Invention is credited to Lapham, John R..
Application Number | 20020087232 09/750433 |
Document ID | / |
Family ID | 25017852 |
Filed Date | 2002-07-04 |
United States Patent
Application |
20020087232 |
Kind Code |
A1 |
Lapham, John R. |
July 4, 2002 |
VERSATILE ROBOT CONTROL SYSTEM
Abstract
An improved, versatile robot control system comprises a general
purpose computer with a general purpose operating system in
electronic communication with a real-time computer subsystem. The
general purpose computer includes a program execution module to
selectively start and stop processing of a program of robot
instructions and to generate a plurality of robot move commands.
The real-time computer subsystem includes a move command data
buffer for storing the plurality of move commands, a robot move
module linked to the data buffer for sequentially processing the
moves and calculating a required position for a robot mechanical
joint. The real-time computer subsystem also includes a dynamic
control algorithm in software communication with the move module to
repeatedly calculate a required actuator activation signal from a
robot joint position feedback signal.
Inventors: |
Lapham, John R.; (Fort
Myers, FL) |
Correspondence
Address: |
OLSON & HIERL, LTD.
36th Floor
20 North Wacker Drive
Chicago
IL
60606
US
|
Family ID: |
25017852 |
Appl. No.: |
09/750433 |
Filed: |
December 28, 2000 |
Current U.S.
Class: |
700/245 |
Current CPC
Class: |
B25J 9/1697 20130101;
Y10S 901/48 20130101; Y10S 901/42 20130101; G05B 2219/34047
20130101; A61B 1/00158 20130101; A61B 1/0055 20130101; Y10S 901/47
20130101; G05B 2219/34261 20130101; A61B 1/31 20130101; A61B 1/041
20130101; G05B 2219/33242 20130101; G05B 2219/39001 20130101; B25J
9/1656 20130101; G06F 30/00 20200101; Y10S 901/41 20130101; B25J
9/161 20130101; Y10S 901/46 20130101 |
Class at
Publication: |
700/245 |
International
Class: |
G06F 007/00 |
Claims
We claim:
1. A control system for processing a program of robot instructions
for robots having a mechanical joint, a mechanical actuator to move
the joint and a position feedback sensor, the mechanical actuator
being adapted to receive an activation signal and the feedback
sensor providing a position signal, the control system comprising:
a general purpose computer with a general purpose operating system,
said general purpose computer including a program execution module
to selectively start and stop processing of the program of robot
instructions and to generate a plurality of robot move commands;
and a real-time computer subsystem in electronic communication with
said general purpose computer and operably linked to the mechanical
actuator and the position feedback sensor, a move command data
buffer for storing said plurality of move commands, a robot move
module linked to said data buffer to sequentially process said
plurality of move commands and calculate a required position for
the mechanical joint, and a control algorithm in software
communication with said robot move module to repeatedly calculate a
required activation signal from the feedback signal and said
required position for the mechanical joint.
2. The control system according to claim 1 further comprising a
watchdog intercommunication between said real-time computer
subsystem and said general purpose computer for detecting faults in
operation of said general purpose computer.
3. The control system according to claim 2 wherein said watchdog
intercommunication includes: a timer variable for storing an
elapsed time indication; a timer code segment for adjusting said
timer variable according to passing time; an activity software
switch having an active position and an unset position; a status
code segment installed in said general purpose computer for
repeatedly setting said activity software switch to said active
position; a timer reset code segment installed in said real-time
computer subsystem for repeatedly resetting said timer variable to
a predetermined amount of time when said activity software switch
is in said active position and repeatedly setting said activity
software switch to said unset position; and a fail safe code
segment installed in said real-time computer subsystem for
repeatedly inspecting said timer variable and setting said
activation signal to shut down the robot if said timer variable
reaches a predetermined value.
4. The control system according to claim 3 wherein said activity
software switch is implemented as an integer software variable with
said unset position being represented by zero and said active
position being represented by one.
5. The control system according to claim 1 further comprising a
data bus for receiving bus cards and wherein said real-time
computer subsystem includes a bus card with a central processing
unit, said bus card being installed in said data bus.
6. The control system according to claim 1 wherein said
general-purpose computer and said real-time computer subsystem are
electronically linked via a standard data bus.
7. The control system according to claim 1 wherein said
general-purpose computer and said real-time computer subsystem are
electronically linked via an ISA data bus.
8. The control system according to claim 1 further comprising a
data bus for receiving bus cards and wherein said real-time
computer subsystem includes a first bus card with a central
processing unit and said general purpose computer includes a second
bus card with a central processing unit, both said first and said
second bus cards being installed in said data bus.
9. The control system according to claim 1 wherein said real-time
computer subsystem includes a digital signal processor (DSP) based
computer.
10. The control system according to claim 1 wherein said general
purpose computer is an Intel Pentium.RTM. processor based
computer.
11. The control system according to claim 1 wherein said general
purpose computer is a DEC/Compaq Alpha.RTM. processor based
computer.
12. The control system according to claim 1 wherein said general
purpose operating system is a not tied to real-time.
13. The control system according to claim 1 wherein said general
purpose operating system is a member of the group consisting of a
Windows-NT.RTM., a Windows 2000.RTM., a Windows 95.RTM., a Windows
98.RTM., an Open VMS.RTM., a PC/MS DOS, and a Unix.
14. The control system according to claim 1 wherein said general
purpose computer is an Intel Pentium.RTM. processor based computer
and said general purpose operating system is a Microsoft Windows
NT.RTM..
15. The control system according to claim 1 wherein the mechanical
actuator is a servo motor and said control algorithm is a servo
control algorithm.
16. The control system according to claim 1 wherein said robot move
module includes a kinematics model for calculating a required joint
position in response to a move command.
17. A versatile robot control system suitable for controlling
robots of different electromechanical configurations, the control
system comprising: a robot-independent computer unit including a
video display and a first digital processor running an operator
interface module for creating a sequence of robot move commands;
and a robot-specific controller unit operably linked to the robot
and including a second digital processor running a real-time tied
operating system and a robot move module for executing said robot
move commands, said robot specific controller unit being in
electronic communication with said robot independent computer
unit.
18. The control system according to claim 17 wherein said
general-purpose computer and said real-time computer subsystem are
electronically linked via a standard data bus.
19. The control system according to claim 17 wherein said first
digital processors runs an operator interface module including: a
configuration variable for storing data specifying the
electromechanical configuration of the robot; a first code segment
for generating a first operator display according to a first
electromechanical configuration; a second code segment for
generating a second operator display according to a second
electromechanical configuration; and a third code segment for
selecting said first or second code segment according to said
electromechanical configuration.
20. The control system according to claim 19 wherein said first
code segment generates an operator display requesting operating
limits for a revolute joint.
21. The control system according to claim 19 wherein said second
code segment generates an operator display requesting operating
limits for a linear joint.
22. The control system of claim 19 wherein said configuration
variable is defined to store data specifying a robot joint
type.
23. The control system of claim 19 wherein said configuration
variable is defined to store data specifying a linear joint
type.
24. The control system of claim 19 wherein said configuration
variable is defined to store data specifying a revolute joint
type.
25. The control system of claim 19 wherein said configuration
variable is defined to store data specifying whether a robot joint
is windable.
26. An operator interface module for controlling robots of
different electromechanical configurations, the operator interface
module comprising: a first code segment for generating a first
operator display according to a first electromechanical
configuration; a second code segment for generating a second
operator display according to a second electromechanical
configuration; and a third segment for selecting said first or
second code segment according to said electromechanical
configuration.
27. The operator interface according to claim 26 wherein said first
code segment generates an operator display requesting operating
limits for a revolute joint.
28. The operator interface according to claim 26 wherein said
second code segment generates an operator display requesting
operating limits for a linear joint.
29. The operator interface module of claim 26 wherein said
configuration variable is defined to store data specifying a robot
joint type.
30. The operator interface module of claim 26 wherein said
configuration variable is defined to store data specifying a linear
joint type.
31. The operator interface module of claim 26 wherein said
configuration variable is configured to store data specifying a
revolute joint type.
32. The operator interface module of claim 26 wherein said
configuration variable is defined to store data specifying whether
a robot joint is windable.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an apparatus and method for
controlling a robot, and more particularly, to a versatile control
system suitable for controlling robots of various electromechanical
configurations.
COPYRIGHT NOTIFICATION
[0002] Portions of this patent application contain materials that
are subject to copyright protection. The copyright owner has no
objection to the facsimile reproduction by anyone of the patent
document, or the patent disclosure, as it appears in the Patent and
Trademark Office.
BACKGROUND OF THE INVENTION
[0003] Industrial robots and similar highly flexible machine tools
gained commercial acceptance during the late 1970s. Since then, the
use of industrial robots has only increased, particularly for
automobile manufacturing.
[0004] The guiding purpose for industrial robots is manufacturing
flexibility. Robots allow assembly lines and work cells to make
different articles with no or minimal manual equipment changes. The
list of robot applications in manufacturing is long and ever
increasing. Examples include computer vision inspection, spot and
arc welding, spray painting, drilling, part placement, and adhesive
application.
[0005] The boundary between robots and machine tools is not
strictly defined. Compared with conventional machine tools, robots
generally have more joints (or axes) of motion thereby offering
more degrees of freedom for positioning an end effector. In the
robotics field, the term "end effector" has been adopted to cover
the variety of active equipment carried by robots. Such equipment
varies according to the manufacturing application, e.g. spot
welding.
[0006] Robots generally include positioning arms with mechanical
joints, actuators such as motors for causing movement about the
joints, and sensors which aid in determining the position (or pose)
of the robot. Although most include these core components,
industrial robots new and old otherwise vary greatly in their
electromechanical configurations.
[0007] For example, some robots rely only on revolute, (i.e.
rotary) joints, while some are equipped with combinations of linear
and revolute axes. Robots with a series of extending arms and
revolute joints have been labeled articulating robots.
[0008] Even among a given class of robots there is mechanical
variation. The revolute joints of articulating robots may be, for
example, offset from their supporting arm--a shoulder joint,
centered to the supporting arm--an elbow joint or axially aligned
with the supporting arm--a wrist joint. Likewise, linear joints may
be co-linear or orthogonal. Actuators and feedback sensors are
another source of the varying configurations. For example, some
robots are equipped with stepper motors, others servo motors.
[0009] Electronic control systems are employed to control and
program the actions of robots. For the necessary coordinated action
between the end effector and the robot positioning, robot control
systems preferably provide some level of software programming and
an interface to field I/O and end effector subsystems. Conventional
robot control systems are collections of customized electronics
that vary according to robot configuration and robot
manufacturer.
[0010] In manufacturing processes, robots are directed by a list of
control instruction to move their end effector through a series of
points in the robot workspace. The sequence (or program) of robot
instructions are preferably maintained in a non-volatile storage
system (e.g. a computer file on magnetic-disk).
[0011] Manufacturing companies, the robot users, through their
engineers and technicians, have come to demand two important
features from manufacturing control systems. First, robot users
seek control systems implemented using commercially standard
computers and operating systems rather than customized proprietary
systems. This trend toward the use of commercially standard
computer hardware and software has been labeled the "open systems
movement."
[0012] Control systems based on standard computers are preferred
because they offer robot users simplified access to manufacturing
data via standard networks and I/O devices (e.g. standard floppy
drives), the ability to run other software, and a competitive
marketplace for replacement and expansion parts. Underlying the
open systems movement is the goal of reducing robot users'
long-term reliance on machine tool and robot manufacturers for
system changes and maintenance.
[0013] A second feature sought by robot users is a common operator
and programmer interface for all robots, facility (if not company)
wide. A common user interface for all robots reduces the need for
specialized operator training on how to use the customized
proprietary systems.
[0014] With respect to the open-systems feature, efforts at
delivering a robot control system based on standard, general
purpose computer systems have not been fully successful because of
the limitations of general purpose operating systems. Robot safety
and accuracy requirements dictate that robot control systems be
highly reliable, i.e. crash resistant, and tied to real-time. The
multi-feature design objectives for general purpose operating
systems such as Microsoft Windows NT.RTM. have yielded very
complex, somewhat unreliable software platforms. Moreover, such
systems cannot guarantee execution of control loops in
real-time.
[0015] With respect to the common operator interface features,
attempts to offer even limited standards to operator interfaces
have not extended beyond a specific robot manufacturer.
Notwithstanding the difficulty in getting different robot
manufacturers to cooperate, the wide variety of electromechanical
configurations has heretofore substantially blocked the development
of robot control systems with a common operator interface.
[0016] Accordingly, it would be desirable to provide an improved
robot control system that both employs commercially standard
computer systems and accommodates robots of different
configurations. Specifically, it would be desirable to provide the
advantages of open systems and a common operator interface to robot
control.
SUMMARY OF THE INVENTION
[0017] Robot control systems of the present invention provide robot
control via commercially standard, general purpose computer
hardware and software. The control systems and methods according to
the present invention are usable with robots of varying
electromechanical configurations thereby allowing a common operator
interface for robots from different robot manufacturers.
[0018] The present invention provides a control system for running
or processing a program of robot instructions for robots equipped
with a mechanical joint, a mechanical actuator to move the joint
and a position feedback sensor. The robot mechanical actuators
receive an activation signal and the feedback sensor provides a
position signal.
[0019] A control system according to the present invention includes
a general purpose computer with a general purpose operating system
and a real-time computer subsystem in electronic communication with
the general purpose computer and operably linked to the mechanical
actuator and the position feedback sensor. The general purpose
computer includes a program execution module to selectively start
and stop processing of the program of robot instructions and to
generate a plurality of robot move commands.
[0020] Within the real-time computer system is a move command data
buffer for storing a plurality of move commands. The real-time
computer subsystem also includes a robot move module and a control
algorithm. The move module is linked to the data buffer to
sequentially process the plurality of move commands and calculate a
required position for the mechanical joint. The control algorithm
is in software communication with the robot move module to
repeatedly calculate a required activation signal from the feedback
signal and the required position for the mechanical joint.
[0021] Another aspect of the present invention provides a robot
control system suitable for controlling robots of different
electromechanical configurations. The control system includes a
robot-independent computer unit in electronic and software
communications with a robot-specific controller unit.
[0022] The robot-independent computer unit is operably linked to
the robot by an I/O interface and includes a video display and a
first digital processor running an operator interface module for
creating a sequence of robot move commands. The robot-specific
controller unit includes a second digital processor running a
real-time tied operating system and a robot move module for
executing the robot move commands.
[0023] The operator interface module preferably includes a
configuration variable for storing data defining the
electromechanical configuration of the robot, a first code segment
for generating a first operator display according to a first
electromechanical configuration, a second code segment for
generating a second operator display according to a second
electromechanical configuration, and a third code segment for
selecting the first or second code segment according to the
electromechanical configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In the accompanying drawings that form part of the
specification, and in which like numerals are employed to designate
like parts throughout the same,
[0025] FIG. 1 is schematic block diagram illustrating the software
programs, computer hardware and robot connections of a robot
control system according to the present invention;
[0026] FIG. 2 is simplified flowchart of a preferred embodiment of
software and method steps for providing the watchdog
intercommunication between the general purpose computer and the
real-time computer subsystem;
[0027] FIG. 3 is a side elevation view of an articulating
industrial robot illustrating another type of robot configuration
controllable by embodiments of the present invention;
[0028] FIG. 4 is a side elevation view of an industrial robot
equipped with linear joints and illustrating one of the many types
of robot configurations controllable by embodiments of the present
invention;
[0029] FIG. 5 is a simplified flow chart of preferred software and
method steps for accommodating robots of different
electromechanical configurations and demonstrating the role of the
configuration variable in control systems according to the present
invention;
[0030] FIG. 6 is likewise an exemplary operator interface display
screen generated in response to data stored in the configuration
variable specifying a rotational joint configuration; and
[0031] FIG. 7 is an exemplary operator interface display screen
generated in response to data stored in the configuration variable
specifying a linear joint.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The invention disclosed herein is, of course, susceptible of
embodiment in may different forms. Shown in the drawings and
described herein below in detail are preferred embodiments of the
invention. It is to be understood, however, that the present
disclosure is an exemplification of the principles of the invention
and do not limit the invention to the illustrated embodiments.
[0033] In the FIGURES, a single block or cell may indicate several
individual software and/or hardware components that collectively
perform the identified single function. Likewise, a single line may
represent several individual signals or several instances of
software data sharing or interconnection.
[0034] Robots as well as other manufacturing machines include
positioning arms with mechanical joints, positioning actuators such
as motors for causing movement about the joints, and position
feedback sensors which provide an indication the position of some
part of the robot. As used herein, the term "mechanical actuator"
is a reference to the variety of devices used for robot motion.
Exemplary robot actuators are hydraulic pistons, pneumatic pistons,
servo motors, stepper motors and linear motors.
[0035] Referring to FIG. 1, the elements of a control system 10 are
shown with an industrial robot 4, a Cincinnati Milacron 776 robot.
Robot 4 includes a series of revolute joints 5, 6, 7 and 8,
corresponding servo motors and an end effector 9. Control system 10
includes a general purpose computer 14 and a real-time computer
subsystem 16.
[0036] The phrase "general purpose computer," as used herein, is a
reference to commercially standard computers which are designed for
multiple applications as opposed to CPU-based electronics
customized for a specific application such as device control.
Examples include the well-known group of computers conventionally
labeled IBM-compatible personal computers, or more simply PCs. PCs
are based on complex instruction set (CISC) CPUs from Intel
Corporation (INTEL), Advanced Micro Devices, Inc. (AMD) and VIA
Technologies, Inc. The related, evolving CPU product line from
INTEL includes CPU chipsets available under the designations
"80486.RTM.," "Pentium.RTM.," "Pentium.RTM. II," "Pentium.RTM.
III." An exemplary CPU product line for general purpose computers
by AMD is available under the designation "AMD-K6.RTM.." VIA
Technologies, Inc. CPUs for general purpose computers are sold
under the designation "Cyrix.RTM.."
[0037] General purpose computers based on reduced instruction set
(RISC) CPUs are also well known. Examples include computers based
on the Alpha.RTM. chipset available from the Compaq Computer
Corporation.
[0038] As indicated in FIG. 1, general purpose computer 14 operates
with a general purpose operating system. The phrase "general
purpose operating system" is a reference to commercially standard
operating systems such as those available from the Microsoft Corp.
under the designations MS-DOS.RTM., Windows 95.RTM., Windows
98.RTM., Windows.RTM. NT and Windows 2000.RTM.. Other examples of
general purpose operating systems include Macintosh.RTM. (Apple
Computers, Inc.), UNIX (various resellers), Open VMS.RTM. (Compaq
Computer Corporation).
[0039] Installed for running on the general purpose computer are a
program execution module 18, an operator interface module 20, and
watchdog communication code segments 22. The term "module," as used
herein is a reference to a software element such as a program,
subprogram, software process, subroutine, or grouping of code
segments and the like. The software modules of control system 10
are preferably discrete executable programs which run as discrete
processes. Unless otherwise indicated, the software modules and
code segments are configured to share access to a variety of
software variables and constants as needed through subroutine
calls, common shared memory space, and the like.
[0040] Program execution module 18 processes programs of robot
instructions 24, which can be stored as data files as represented
in FIG. 1. From robot instruction programs 24, program execution
module 18 generates robot move commands 26 for delivery to
real-time computer subsystem 16. Via execution module 18, the
relatively more human readable robot instructions 24 generated by a
robot operator are interpreted and translated into move commands 26
for real-time computer subsystem 16.
[0041] As well, program execution module 18 allows operator control
of the running of robot programs 24 by selectively starting and
stopping the transfer of move commands 26 to real-time computer
subsystem 16 in response to prompts from the operator via operator
interface module 20.
[0042] Operator interface module 20 is operably linked to an
operator display screen 28, a keyboard and/or mouse 30, and other
standard peripherals as desired. In a preferred embodiment, display
screen 28 is a touch screen which allows a robot operator to input
prompts and data through both displays and keyboard/mouse 30.
[0043] With robot operator prompts and selections, operator
interface module 20 allows robot instruction files 24 to be loaded
from disk and processed (or executed) by program execution module
18 for controllably moving robot 4. Operator interface module 20
generates operator screens and accepts from the operator numeric
data and prompts. Numeric data entries are communicated to other
program modules as necessary. Prompts by the robot operator to
start and stop the running of a robot program are received by
operator interface module 20 and forwarded to execution module
18.
[0044] In addition to accepting operator inputs for loading,
starting and stopping programs 24, operator interface 20 preferably
includes an editor for use by an operator to generate new programs
of robot instructions 25. Because the present invention provides a
control system which relies upon general purpose computers such as
a Windows NT PC, it is equally possible to generate robot programs
on another PC such as an office PC and then transfer the file to
general purpose computer 14 through standard peripherals such as
disk drives or computer network connections.
[0045] General purpose computer 14 is electronically linked for
data exchange (i.e. communication) with real-time computer
subsystem 16. Real-time computer subsystem 16 preferably includes a
hardware, firmware and software combination designed for process
control applications. As opposed to general purpose computers with
general purpose operating systems, real-time computers provide for
substantially uninterruptible execution of calculations required
for a plurality of control loops with relatively fast cycle times
(e.g. 0.5-2 msec).
[0046] Because of the extensive signal processing requirements, the
CPU computer of real-time computer subsystem 16 is preferably a
DSP-based computer. In this category of DSP-based control
computers, the systems commercially available from Delta Tau Data
Systems, Inc. (Chatsworth, Calif.) under the designations "PMAC",
"PMAC2," "Turbo PMAC" and "UMAC" are presently preferred.
[0047] Real-time computer subsystem 16 includes a robot move module
32, a move command data buffer 34, kinematic models 36, servo
control algorithms 38, and watchdog intercommunication code
segments 40. Real-time subsystem 16 also includes I/O hardware and
software drivers to provide an operable link to the positioning
related electronics of robot 4. Represented by block 42 are the
hardware and software components necessary for receiving and
translating robot feedback signals 44 into computer data feedback
signals 46. Likewise, block 48 represents the components necessary
for converting computer data setpoints 50 into actuator-appropriate
activation signals 52.
[0048] Activation signals 52 and feedback signals 44 may be analog
signals, digital signals or combinations of both depending upon the
configuration of robot 4. For example, the typical
motor-with-amplifier actuator calls for an analog activation
signal. Newer, so-called "smart" devices can be directly activated
by digital signals, however. Thus, the type of signal conversion
performed by I/O systems 42 and 48 varies by robot
configuration.
[0049] Robot move module 32 is resident in real-time computer
subsystem 16 to accept move commands 26 and feedback signals 44/46
to generate the necessary activation signals 50/52. Robot move
module 32 relies upon kinematic models 36 and servo control
algorithms 38 to translate move commands 26 required joint
positions and then appropriate activation signal setpoints 50. In a
preferred embodiment of the present invention, move commands 26 are
expressed as changes in joint position or as changes in
end-effector position.
[0050] Move commands based on joint position rely upon a predefined
range on a one-dimensional joint axis model, for example, +90
degrees to -90 degrees for a revolute axis and 0 to 1200
millimeters (mm) for a linear joint. An example of a move command
based on joint position is "set joint one at 60 degrees." In a
preferred embodiment of the present invention, robot move module 32
is programmed to accept joint move commands as a function call
specifying the position of all robot mechanical joints 5, 6, 7 and
8, thereby allowing only one or all joints to be moved.
[0051] Move commands expressed as end-effector positions rely upon
a predefined, but customary, three-dimensional coordinate system
for locating the end-effector. A move command based on end-effector
position is a call to move the end effector to a point in the
end-effector's workspace.
[0052] For joint position move commands, robot move module 32
includes software models for translating data from feedback signals
46 into joint position. The required calculation varies according
to joint type and the type feedback signal available. For example,
a feedback sensor directly measuring an indication of joint
position require limited translation, while a feedback sensor
measuring the number of rotations of a positioning motor may
require a more complex translation.
[0053] To process move commands based on end-effector position,
robot move module 32 additionally includes a kinematic model for
calculating the required position of joints 5, 6, 7 and 8, given a
desired position for end effector 9.
[0054] More specifically, real-time computer subsystem 16 uses
kinematic model algorithms for computation of the forward and
inverse kinematics of the robot. Forward kinematics computation
refers to the determination of end-effector position and
orientation given known joint positions or actuator positions of
the robot. Inverse kinematics is the determination of the joint
angle or actuator positions given an end-effector position.
[0055] The required combination of individual joint axes models and
overall kinematics models is represented in FIG. 1 by block 36.
Kinematic algorithms are described in other patents and the
technical literature. See, for example, Chapters 3 and 4 of Craig,
John J. Introduction to Robotics: Mechanics and Control, 2nd Ed.,
Addison-Wesley, 1989. The specific models employed vary according
to the electromechanical configuration of the robot to be
controlled.
[0056] Because the positioning actuator and feedback sensor
combination make up a dynamic system, real-time computer subsystem
16 also includes control algorithms 38 to provide the required
dynamic calculations. Preferred among available closed loop servo
motor control schemes is a proportional-integral-derivative (PID)
with feedforward algorithm.
[0057] Data buffer 34 is a software variable available to programs
in both general purpose computer 14 and real-time computer
subsystem 16 for storing multiple move commands 26 received from
program execution module 18. Although the desired storage capacity
for data buffer 34 can vary, in a preferred embodiment of the
present invention data buffer 34 and connected modules are
preferably configured such that from 2 to 10, and more preferably
from 3 to 4, move commands are stored.
[0058] With move command data buffer 34, control system 10 provides
for substantially continuous, uninterrupted control of robot 4 even
in response to program execution delays in general purpose computer
14.
[0059] As noted above, general purpose computers running general
purpose operating systems are relatively unreliable, exhibiting
unpredictable control program interruption. Specific motion control
of robot 4 by real-time computer subsystem 16 is not affected by
unpredictable delays in operations of general purpose computer 14
because robot move module 32 can continue to draw move commands 26
from data buffer 34.
[0060] Although a variety of data transfer mechanisms are available
to provide electronic and software-level communication between
general purpose computer 14 and real-time computer subsystem 16, a
commercially standard data bus backplane is preferred. The data bus
connection is symbolically represented in FIG. 1 by reference
numeral 54. The ISA bus, the PCI bus, and the VME bus are exemplary
standard data buses, with the ISA bus being presently
preferred.
[0061] For convenient space-saving connection to data bus 54, the
computer mother board portions of general purpose computer 14 and
real-time computer subsystem 16 are data bus cards. As used herein,
the term "bus card" is a reference to printed circuit boards with
electronic components and a tab with a plurality of contacts that
is received in the card slots of a data bus chassis. The DSP
real-time computers available from Delta Tau Data Systems, Inc.
noted above are available as ISA data bus cards.
[0062] In a preferred embodiment, control system 10 includes a
security (or "watchdog") communication (blocks 22 and 40) between
general purpose computer 14 and real-time computer subsystem 16.
Flowchart FIG. 2 shows the preferred code segments for maintaining
the watchdog management. As illustrated, a preferred watchdog
scheme includes code segments operating in both general purpose
computer 14 and real-time computer subsystem 16. Resident in
general purpose computer 14 is a status code segment 56 and
resident in the real-time computer subsystem are a timer code
segment 58, a timer reset code segment 60, and a fail safe code
segment 62.
[0063] The code segments interact with two software variables: an
activity software switch (ASW) 64 for indicating whether programs
in general purpose computer 14 are active and/or error free, and a
timer variable (TV) 66 for storing an elapsed time indication.
Timer variable 66 is resident in real-time computer subsystem 16
while activity software switch 64 is shared via data bus 54 or
other means. Activity software switch 64 is implemented as an
integer software variable with an unset position being represented
by zero and a set, or active position, being represented by
one.
[0064] Status code segment 56 optionally, but preferably, runs
sequentially with program execution module 18 (box 68) and
repeatedly sets activity software switch 64 to the active position
(box 74). After the completion of a run cycle of program execution
module 18, status code segment 56 examines other software variables
which indicate special errors (box 70) or delays in the processing
of other programs (box 72) in the general purpose computer 14.
Accordingly, if program execution module 18 is interrupted or if
errors or other delays are detected, activity switch 64 is not
set.
[0065] Timer code segment 58 counts down timer variable 66
according to elapsing time. Timer code segment 58 is preferably a
system service function of real-time computer subsystem 16 and
expressed in execution cycles.
[0066] When the activity software switch is in the active position
(box 76), timer reset code segment 60 repeatedly resets the timer
variable to a predetermined amount of time (box 78; preferably two
seconds) and repeatedly sets the activity software switch back to
the unset position (box 80). Fail safe code segment 62 responds to
an overrun of timer variable 66 (box 82) by shutting down robot 4
via activation signals 50/52 and other robot I/O.
[0067] Acting together, code segments 56, 58, 60 and 62, provide a
watchdog service which will shut down robot 4 if the operation of
general purpose computer 14 is stopped or delayed for more than two
seconds.
[0068] Referring back to FIG. 1, another feature of the present
invention is that the software provided for general purpose
computer 14 is suitable for controlling robots of various
electromechanical configurations. According to this aspect of the
invention, general purpose computer 14 serves as a
robot-independent computer unit while real-time computer subsystem
16 serves as a somewhat robot-specific controller unit, or
customized interface or adapter to the robot.
[0069] Important to the multi-configuration aspect of the present
invention is the enhanced versatility of operator interface module
20. Viewed together, FIGS. 3 and 4 demonstrate the challenge of
working with robots of different electromechanical configurations.
FIG. 3 is side view of articulating robot 4 from FIG. 1 in slightly
larger scale to reveal greater detail. The arms of robot 4 are
connected by a series of revolute (or rotary) joints 5, 6, 7 and 8.
In contrast, FIG. 4 is side view of a robot 86 which is equipped
with a revolute, torso joint 87 and two linear joints 88 and
89.
[0070] Assigning joint numbers from the base up, the second and
third joints of robot 4 are of a different type than the second and
third joints of robot 86. To overcome this difference in
configuration, the operator interface of the present invention
includes a configuration variable for storing data specifying the
electromechanical configuration of the robot and display generating
code segments for each type of configuration.
[0071] In a preferred embodiment, the configuration variable is
defined and/or sized to store data defining the type of robot
joint, linear or revolute, and whether a specified revolute joint
is windable, i.e. capable of turning more than 360 degrees.
[0072] FIGS. 5 through 7 provide an example of how operator
interface module 20 uses the configuration variable to accommodate
different types of robots. As illustrated in FIG. 5, a display
selecting code segment 90 responds to an operator request to set
limits for joint/axis 3 (box 92). Code segment 90 checks in
configuration variable 94 for data specifying whether joint 3 is
linear or revolute (box 96).
[0073] Depending upon whether the third joint of the robot to be
controlled is revolute as with robot 4 or linear as with robot 86,
code segment 90 selects one of two available displays for setting
joint limits. For a revolute joint type, box 98 is selected and the
revolute joint/axis display of FIG. 6 is generated at screen 28.
For a linear joint type, box 100 is selected and the linear
joint/axis display of FIG. 7 is generated.
[0074] The foregoing specification and drawings are to be taken as
illustrative but not limiting of the present invention. Still other
configurations and embodiments utilizing the spirit and scope of
the present invention are possible, and will readily present
themselves to those skilled in the art.
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