An instrumented task board was developed at NASA Marshall Space Flight Center (MSFC). An overview of the task board design, and current development status is presented. The task board was originally developed to evaluate operator performance using the Protoflight Manipulator Arm (PFMA) at MSFC. The task board evaluates tasks for Orbital Replacement Unit (ORU), fluid connect and transfers, electrical connect/disconnect, bolt running, and other basic tasks. The instrumented task board measures the 3-D forces and torques placed on the board, determines the robot arm's 3-D position relative to the task board using IR optics, and provides the information in real-time. The PFMA joint input signals can also be measured from a breakout box to evaluate the sensitivity or response of the arm operation to control commands. The data processing system provides the capability for post processing of time-history graphics and plots of the PFMA positions, the operator's actions, and the PFMA servo reactions in addition to real-time force/torque data presentation. The instrumented task board's most promising use is developing benchmarks for NASA centers for comparison and evaluation of telerobotic performance

Bryan, Thomas C.

Carroll, John D.

Gierow, Paul A.

English

NASA Technical Reports Server

Ng -zo6 8
EVALUATION OF TELEROBOTIC SYSTEMS
USING AN
INSTRUMENTED TASK BOARD
Thomas C. Bryan
NASA/Marshall Space Flight Center
Mail Stop: EB24
Huntsville, Alabama 35812
John D. Carroll, Paul A. Gierow
SRS Technologies
990 Explorer Blvd.
Huntsville, Alabama 35806
ABSTRACT
An Instrumented task board has been developed
at NASA Marshall Space Flight Center (MSFC).
An overview of the task board design, and
current development status is presented. The
task board was originally developed to evaluate
operator performance using the Protoflight
Manipulator Arm (PFMA) at MSFC. The task
board evaluates tasks for Orbital Replacement
Unit (ORU), fluid connect and transfers,
electrical connect/disconnect, bolt running and
other basic tasks. The instrumented task board
measures the 3-D forces and torques placed on
the board, determines the robot arm's 3-D
position relative to the task board using IR
optics, and provides the information in real-
time. The PFMA joint input signals can also be
measured from a breakout box to evaluate Ihe
sensitivity or response of the arm operation to
control commands. The data processing system
provides the capability for post processing of
time-history graphics and plots of the PFMA
positions, the operator's actions, and the PFMA
serve reactions in addition to real-time
force/torque data presentation. The
instrumented task board's most promising use is
developing benchmarks for NASA ccnters for
comparison and evaluation of telerobotic
performance.
INTRODUCTION
Telerobotics systems are currently being
developed and evaluated at a number of NASA
centers, Universities and Air Force centers. The
telerobotic systems are being developed to
perform a wide range of on-orbit tasks. Space
operations such as satellite servicing, assembly,
maintainance and payload handling can be
accomplished with telerobotic systems (rcf. 1).
An increased need for telerobotic support will
emerge as the Space Station Freedom evolves. A
baseline for evaluating telerobotic systems and
tasks is needed to establish comparisons of the
performance characteristics among the task
analysis community. An instrumented task
board and data acquisition system can be used to
further quantify parameters used for telerobotic
systems and task evaluations.
TASK BOARD DESCRIPTION
The instrumented task board system consists of
an inner task frame that is instrumented to
measure the forces and torques placed on the
board. The inner frame accepts 19" task panels
which are interchangeable. A variety of tasks
can be performed simply by installing the task
panel desired on the inner frame. An optical
position sensing system determines the position
of the telerobotic end effector relative to the
task panel. A w_ltage breakout box is supplied
to measure thc joint forces on the telerobot. A
user-I'ricndly data acqusition and reduction
system is integrated into the measurement
systems. Figure 1 is a photograph of the task
board system at MSFC with an ORU replacement
task panel. Figure 2 is a photograph of a fluid
transfer demonstration task board used at MSFC.
Instrumented Beam Force/Torque
Sensors
A 4-point suspension system design is used to
fully support the inner frame of the task board.
Cantilever beams instrumented with strain
gauges and signal conditioners are used in order
to determine the forces and torques placed on
the task board. The instrumented beam design
incorporates low friction instrument linear
bearings combined with a spherical bearing. The
instrumented beam design results in no axial
loads or torques placed on the cantilevered
beams. Incorporating the low friction axial and
rotational mounting methods to the task board
results in a perpendicularly applied load to each
instrumented bcam. The unique mounting
method enables the instrumented beam/strain
gauges to measure components of the load on the
beams allowing for force component
measurements.
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Optical Position Sensors
The purpose of the position monitoring system
included in the instrumented task board is to
record quantitative data that can be reviewed
and used as an evaluation and learning tool for
the development and sharpening of the operator's
PFMA skills and task evaluations. The 3-D
position sensing system enables the controller to
know the precise coordinate or location of thc
end effector tool being used, in reference to the
center of the task board. This system is
comprised of two Hamamatus (C2399) two-
dimensional position sensor systems. Each
position sensor system is a compact high-
resolution position sensor using a non-discrete
position-sensitive detector. The non-discrete
position-sensitive detector enables high-speed
measurement of a moving spot with high
accuracy. The position sensor is an opto-
electric unit which measures the position of a
single-point of infrared light focused on the
sensor head. The two dimensional position
sensor systems are comprised of a system
controller, an infrared lens and sensor head, and
a seven infrared LED cluster target.
Each two-dimensional position sensor is
monitored by the Macintosh II through an
analog-to-digital input/output board. The
position of the target, which is mounted near the
PFMA's end effector, is recorded by the sensor
head. The two dimensional coordinates are
transmitted as an analog input to position
controller. The sensor heads are located at 90 °
angles from each other relative to the center of
the instrumentation board, as shown in Figure 3.
By placing the sensors heads 90 ° apart, the thrce
dimensional envelope of coverage resembles an
odd shape cube. The sensors' analog outputs are
read into the computer where they are stored in
a file and plotted, in real-time, on the computer
monitor.
Data Acquisition System
The data acquisition system monitors and
records the interaction of the PFMA operator
with the instrumented task board and each
postion sensor unit. The data acquisition for the
system is achieved through the use of a
Macintosh II, LabVIEW control software, and an
analog-to-digital input/output PC board in
series with an analog multiplexer board. The
system's set up is shown in Figure 4.
The Macintosh 11 consists of a 40 mega byte hard
drive, 5 mega bytes of RAM, 4 bit color video
monitor card, color high-resolution monitor, and
standard keyboard. The analog-to-digital input/
output board (NB-MIO-16L-25) and the analog
multiplexer (AMUX-64), developed by National
Instruments, provides the computer with the
ability to perform data aquisition on a maximum
of 64 channels. The computer system is
controlled with LabVIEW, a data aquisition and
control graphical software developed by National
Instruments. Hard copies of the raw test data and
graphs of the test preformance are obtained from
the Image Writer II, a dot matrix printer. This
computer system provides a user friendly
environment along with efficiency.
Data Acquisition System Software
LabVIEW serves as a software driver and
controller for the NB-MBIO-16 and AMUX-64
hardware data acquisition boards installed in
the Macintosh 11. LabVIEW is a complete
programming environment which allows the user
to construct virtual instruments (VI's) that
control and record operations that are required.
The final instrument design includes integration
of the sub-virtual instruments into a single
virtual instrument for simultaneous data
acquisition and real-time monitoring.
The building block of LabVIEW is the Virtual
Instrument (VI). The Virtual Instruments in
LabVIEW are the software components of the
complete data acquisition and control system
installed in the Macintosh I1. Each VI has a
front panel which specifies the inputs and
outputs of the program. Figure 5 depicts the
controls and indicators of the real-time
measurement system. Behind the front panel in
LabVIEW is a block diagram which represents
the actual executable program. The block
diagram represent graphical programming
functions that are standard in any programming
cnvironmcnt. Any virtual instrument that is
designed can be represented as an icon that can
bc included in other Vl's. The hierarchical
structure of LabVIEW enables the user to
construct complicated control and acquisition
systems from combining the Virtual Instruments
into one complete Virtual Instrument.
Data Acquisition System Capabilities
The data acquisition system on the Macintosh II
for the arm sensor system is driven by the
LabV1EW software. The data acquisition
127
requirements of the arm sensor system include
reading and storing to disk analog signals from
the strain gage conditioning circuits from the
task board, position sensors and current
proportional voltages from the PFMA
servomotors. Information from the PFMA
operator via RS-232 data lines was included in
the data acquisition and storage system on the
Macintosh 1I. A summary of the operations of
the data acquisition and storage system are
shown in Table I.
Force Measurements
Acquisition of the Strain Signals from the Instrumented
Task Board
Conversion of the Strain Data to Force Data
Calculation, Reading and Real Time Graphical Presentation
of the 3-D Forces Applied to the Instrumented Task Board
_osltlon Measurements
Acquisition of the Position Sensors' Outputs
Calculation of the PFMA's 3-D Positive Relative to a
Chosen Origin
Recording and Graphical or Numerical Presenting the 3-D
Location of the PFMA in Reference to a Chosen Origin
_FMA Servomotor Measurements
Acquisition of the Current Proportional Vohagcs frnm the
PFMA's Servomotors
Calculation of Power Used by Each Servomotor, During
Operations (if required)
Resolve Joint Voltages to Task Analysis Primitives
>FMA Control Life Information
Record all PFMA's Control Line Information Which is
Transmitted Over an RS-232/422 Data Rus
Table 1. Current Measurement Capabilities
A double buffer acquisition system is used m
LabVIEW. The system allows the programmer to
store information in a buffer while scanning the
channels of interest on the A/D board. The
buffer is then periodically read and stored to
the desired output file on the computer. The
data is also plotted on the screen while
simultaneous data acquisitions arc occurring.
An external gate is also used for triggering of
data acquisitions. The external gate enables
data acquisitions while the gate is held in a high
position. The external gate enables the board to
perform a scan of the channels at a high rate but
allow for a delay time between each scan. The
delay time is determined by the desired
acquisition rate.
The operator commands via the RS-232 data line
can be read by LabVIEW using an RS-422 port
read virtual instrument. The instrument reads
the contents of the RS-422 buffer. The buffer
size can be configured by the user.
Simultaneous analog data acquisition and RS-422
buffer storage is available if desired. The RS-
422 buffer read VI can be incorporated into the
data acquisition VI.
CONCLUSION
Currenlly there are no standards for laboratory
comparisons of telerobotic systems. The
instrumented task board design developed to
evaluate the PFMA at MSFC could be useful for
establishing a benchmark tool to evaluate
telerobotic systems within the NASA centers.
The data taken from the instrumented task board
could bc used as a departure point for technical
discussions among NASA centers. The task
board will support standardization and further
define lask analysis for telerobotics. Additional
task sets can be added to the task board design
m include a variety of tasks that include
collision avoidance, adjustable inertia crank,
lighting systems and dynamic situations.
ACKNOWLEGEMENTS
This research and development is currently
being supported by the Information &
Electronics Laboratory, NASA Marshall Space
Flight Center (Contract #NAS8-36307). Mr.
Thomas C. Bryan is the technical monitor.
R I_FI:.I_ I':NC ES
I. Drews, Michael, "General Extravehicular and
Tclerobotic Task Primatives for Analysis,
Design, and Integration," JPL Publication
89-XXX, Draft 1.5, Jet Propulsion
Laboratory, Pasadena, CA, January, 1990.
2. Price, Charles, "Status of Benchmark Task/
Task Boards," Telerobotics Intercenter
Working Group, Johnson Space Center, TX,
July 25, 1989.
128
Figure 1 Instrumented Task Board 
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Evaluation of telerobotic systems using an instrumented task board

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