Designing space-based telerobotic systems presents many problems unique to telerobotics and the space environment, but it also shares many common hardware and software design problems with Earth-based industrial robot applications. Such problems include manipulator design and placement, grapple-fixture design, and of course the development of effective and reliable control algorithms. Since first being applied to industrial robotics just a few years ago, interactive graphic simulation has proven to be a powerful tool for anticipating and solving problems in the design of Earth-based robotic systems and processes. Where similar problems are encountered in the design of space-based robotic mechanisms, the same graphic simulation tools may also be of assistance. The capabilities of PLACE, a commercially available interactive graphic system for the design and simulation of robotic systems and processes is described. A space-telerobotics application of the system is presented and discussed. Potential future enhancements are described

Baumann, E. W.

English

NASA Technical Reports Server

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Real-Time Graphic Simulation for Space Telerobotics Applications
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Designing space-based telerobotic systems present_ many probleme unique to
te--_robotics and the space environment, but it also shares many common hardware and
software design problems with Earth-based industrial robot applications. Such problems
include manipulator desiqn and placement, grapple-fixture design, and of course the
development of effective and reliable control algorithms.
Since first being applied to industrial robotics _ust a few years ago, interactive
graphic simulation has proven to be a powerful tool for anticipating and solving problems
in the design of Earth-based robotic systems and processes. Where similar problems are
encountered _n the design of space-based robotic mechanisms, the same graphic simulation
tools may also De of assistance.
• - - - " : the capabilities of PLACE, a commercially available interactive
graphic system for the de_'ign and simulation of robotic systems and processes, A
space-telerobotlcs application of the system Is presented and discussed. Pote_tlal future
enhancements are described.
J. Introductlon
As the number and complexity of robot applicati:ons increase, the importance of being
able to effeztively evaluate design and programm!,_g alternatives will also increase. While
such evaluation can, in most cases, be performe_/on a trlal-and-error basis in the "real
world", there are idvantages to be gained by f2fst testing those ideas in a simulated
environment uslng computer graphics. The major advantages are:
• The time and materials spent physlcall_/prototyping alternative robotic systems is
r_iucod or ellmlnlted. I
• _he posslpillty of inflictlng p_}.slca/ _arm to personnel or equipment in the event of a
proqrammln_ error _s reduced. /
• Characteristics of the space envlrotment that cannot be physically reproduced on Earth
may be amenable to computer simul_io_.
I
The ma3or disadvantage of using _omputer simulations to develop robotic systems and
processes [s that simulations are n_er perfect representations of what will happen in the
reai wor!J. The user must theretor_be careful to understand which aspects Of the real
_o_Ja_e_yIor are _mportant to hl_ application and how well they are reproduced by the/
The following portions of t_s aper discuss some areas of robotics in which graphic
simulation tools can be of val_ and describe several products produced by McDonnell
Doug1._s :or thls DurFose. _
2. Conceptual Design Using_raphic Simulation
!
Before detailed des'ign _ork can begin on a new robot application, it is first necessary
to develop a general conce_ of t_e system and processes that will be required to achieve
the s_ecifled goal within _ partlcuiar environment. This conceptual design is useful not
.only _s _he initial step _n the top-down design of a new robotic system, but also as a
means to effectively desc_Ibe )'our concepts to Others. [t :s generally easier to get an
idea acrols "by viewing th_ simulated system in action than by reading pages of text and
static drawings.
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https://ntrs.nasa.gov/search.jsp?R=19890017145 2020-03-20T02:08:26+00:00Z
PLACE (Positloner Layout and Cell Evaluator) was the first in a series of NcDonnell
Douglas Robotics Software Products. It executes on DEC VAX II/TS0, II/750. and Nicro-V/_
couputers using an Evens & Sutherland PS)O0 Computer Graphics System. The pLACE software
is dealqned to qraphically create, analyze, and _xllfy robotic -tmrk-cell" descriptions. A
"work-cell" description is a collection of CAD-generated qemsetry representinq the
components of a robot-baaed nanufacturinq eystms or "york-cell". These components include
robots, and-effectors, fixtures, NC smchines, raw natertal, completed parts, and
elscellaneoua tooling. The deaiqner has the option of creating an oriqinal cell
description or ueinq HcDonnell Douglas supplied robots or work-cells found in the library
of cell description files. These files contain models of mmny commercially available
robots, as well as cells for a variety of robot applications.
PLACE includes the following features:
* Kinematic equations to sinulate the motion of over 100 industrial robots.
. Continuous readout of Joint angle data during robot motion.
* 3-D graphics for manipulation, notion specification, and visual collision detection
(automatic collision detection is also available}.
* Intaractively controlled dynamic ]-D scaling, translating, and rotatinq of parts,
devices, and the entire cell.
* Recording of robot motion sequences for playback and analysis.
. The ability to define attachment/detachment of parts.
* Simulation and programming of device 1/O.
• Sensor support.
* Conditional execution based upon internal conputatlon or device I/O.
* Parallel, coordinated device motion.
• A user-expandable library of robots and other work-cell components.
The addition of new robots to the library referred to above has been greatly simplified
by a software package called "BUILD". BUILD automatically determines the kinematic
equations of a robot manipulator from its geometric model, thereby allnlnating the need to
perform a custom kinematic analysis for each new robot. This makes it easy for the user to
test many different manipulators or many variations of the same eanlpulator in order to
approach an optimal design for the task to be performed. Since BUILD is limited to devices
having six degrees of freedom or less, the PLACE system includes the ability to define
"Compound Devices" comprised of suitably coordinated sub-devices. In this way mechanisms
having greater than six coordinated degrees of freedom can be simulated.
3. Off-Line Proqramminq
Off-line programming of robotic systems may eventually prove to be the most important
application of graphic simulation tools. As robots are required to perform increasinqly
complex tasks in less structured environments, greater emphasis will be placed on the
senslnq and logical control aspects of robot pro<jraes, one way to gonerata such programs
is to comblne motion sequences produced by a system like PLACE with r,he remainder of a
program written in the robot's native language. In this way an off-line program can be
created that will already have the robot motion portions largely debugged.
McDonnell Douglas has produced a system called ,COMMAND" that provides a set of
translators for generating off-line programs from motion sequences created usinq PLACE.
The transl_tors also process instructions entered in the robot's native language. These
instructions can include references to the motion sequences defined previously in PLACE.
Translator output consists of a robot source program and an object code data file. This
data file can be automatically written to tape or diskette as required for loading into the
robot controller.
4. Space Telerobotics Example
Specific questions in the realm of space talerobotics that could be resolved, at least
in part, by someone using PLACE and BUILD include:
* Can an "off-the-shelf" industrial robot be used for a space-based application? If not,
then can a slightly modified version be used?
* Can a modular, reconfigurable manipulator capable Of supporting a wide range of
assembly and repair tasks be designed?
* Can a general-purpose gripper for space-based assembly and repair tasks be designed?
* Where Should the base of a manipulator o_'the space station be located in order to
perform a .cooperative task with the shuttle manipulator?
* Where should themanipulator(s) be located 6n a teleoperated maneuvering vehic[e(T_q)?
* _ How should the tool-bay of a TMV be o[ganized? Can the tools be reached by the
manipulator(s}?
* Where should the cameras be located? Where. should they be looking during a particular
stage of the process?
* If a manipulator needs to move a payload between two points, what paths are collision
free and do not cause joint limit errors?
208
To illustrate and assess the capabilities of PLACE and BUILD as applied to the
space-telerobotics domain, an example telsrobotics scenario was developed and used as the
basis for I PLACE demonstration. The basic scenario is shown in flq_res I through 7,
plotted directly from the PLACE display. Here are descriptions of eaCh figure and a few
comments regarding the simulation at that point:
Figure I - Shuttle Arriving at the Space Station
All ma_or movable components of the station are modelled as devices. This includes the
solar panels, the large radio dish antenna, and the waste-heat radiator panels (below
theradio dish). The large box-like structure located between the solar panels on the
center truss is a hangar in which astronauts can perform satellite repair work. The
primary goal at this point is to move the shuttle safely into a good position for
transferring the laboratory module from the shuttle to the station manipulator, it is
important that the position chosen not cause Joint errors in either manipulator or
require repositioning of the shuttle during the module transfer. Locations satisfying
these constraints can be readily found by having the station end shuttle manipulators
"track" the module as you use the simulator's control dials to change the shuttle
vehicle's position while monitoring the manipulator joint displays.
Figure 2 - Laboratory Module Being Transferred From the Shuttle Manipulator
to the Station Manipulator.
The main problem encountered here was in determining the locations for the two grapple
fixtures on the module. The center grapple location worked well for the shuttle
manipulator. Having the station manipulator grab the module on top and then moving the
station manlpulator's platform vertically to insert the module required minimal motion
of the station manipulator.
Figure ] - Teleoperated Maneuvering Vehicle (TMV) Preparing to Capture a
Satellite.
Each of the TMV's main arms has six degrees Of freedom. Each finger has five degrees
of freedom. The arms and fingers can be controlled independently or as a single
"Coordinated Motion Compound Device". The vehicle has two cameras, one located on the
left boom and one on the right. Two disk shaped communication antennas are located
behind and slightly uelow the camera booms. The fingers on the TMV's right hand are
brought to a point fo: insertion into the recessed nozzle of the satellite. The
flrgers of the left hax,J are opened to form a flat surface to push against the opposite
end of the satellite.
F:gure 4 - TMV Transferring Satellite to Space Station Hangar.
Here the TM_ is getting into position to deposit the satellite into the hangar. It's
approach from "below" (between the hangar and the radiators) requires that the
station's antenna De moved out of the way to avoid a possible collision. It may have
been better tm enter the hangar from above (where the two trusses meet) but in that
case there mlght still be a need to reposition the solar panels to reduce the chance of
collision.
Figure 5 - Station Climbing, Observing, and RePair (SCORP) Vehicle
Attached to Station Manipulator.
By replacing the three-fingered hands with cylindrical grippers suitable for grasping
space station struts, replacing the fixed cameras on booms with movable cameras on
"eyestalks", and by adding a "tail" capable of securely latching onto any portion of
the station's truss structure, the TMV can be converted into a vehicle capable of
climbing on, inspecting, and repairing the Space station. It is shown here attached to
the station manipulator prior to being placed on the truss structure. The SCORP has no
engines and therefore must always be attached to the station in some way. A parts bay
is located inside the SCORP's "chest" below its left arm. A tool bay is located below
Its right arm.
Figure 6 - SCORP Climbing on Station While Performing Visual Inspection
Climbing is'accomplished by declaring the arms and body of the vehicle to be a
"Coordinated Motlon Device", thereby forcing them to begin and end their motion
simultaneously. The requirement that one hand continue to grasp the station while the
body_and ar_s are being repositioned is indicated to the PLACE system by temporarily
declaring _he corresponding arm to be a "Dependent Motion Device". The sy'stem then
asks:the user to specify the spatial relationship (in this case between hand and strut)
that must be maintained during the execution of this climbing step. Once all of the
goal positions and dependencies are defined, the simulation can proceed. The same
approach can be used to simulate walking.
209
Figure 7 - SCORP Anchored to Station Wh..le Welding Reinforcement Strut to
Space Station Box-Truss Structure.
When a repair Job requires the use of both arms, the SCORP'a "tail u can be used to grab
the station structure, thereby freeing the sras while still providing substantial local
uobiltty for the vehicle. The grapple position shown in this figure actually causes
the tall-arJ to exceed two Joint limits in its wrist and should be changed. Exceeding
joint limits in this way is a common error that would be difficult and time consuming
to identify without the use of a simulation system like PLACE.
5. Future Directions
The primary emphasis of these "first generation" graphic simulation systems has been on
providing user-friendly methods for specifying robot motion, end then accurately portraying
the programmed motion. There Is no doubt that additional improvements can, and will, be
made in th_se areas.
As more complex robot applications appear, greater attention will be paid to simulating
sensor-based robot behavior and in keeping track of accusulated position and force errors
that may lead to failure. Automatic generation of "sensory expectations" for the robot's
sensory systems will also be necessary if a complete off-line programming environment is to
be realized.
So far these systems have only acted as providers of relatively raw information to a
human decision maker. In the not-too-distant future we may see systems having the ability
to analyze their own simulation results and give advice to the human user during a cell
design or programming session. Perhaps planning some parts of the process, such as finding
collision-free manipulator trajectories, will gradually be turned over to the system, with
the human user acting increasingly as -supervisor" rather than programer. Ultimately there
will cease to be a need for graphic output from the robot simulation and planning system,
except to serve as a window into the machine's planning process as it determines how to
accomplish to goals we have set before it.
6. Acknowledgments
I would like to thank Nicholas Denissen for his assistance in creating several of the
Unigraphics CAD models used in the space telerobotics example.
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Real-time graphic simulation for space telerobotics applications

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