NASA Technical Memorandum 4776

Wrist Camera Orientation for Effective

Telerobotic Orbital Replaceable Unit (ORU)

Changeout

Sharon Monica Jones, Hal A. Aldridge, and Sixto L. Vazquez

Langley Research Center • Hampton, Virginia

National Aeronautics and Space Administration

Langley Research Center • Hampton, Virginia 23681-2199

October 1997
Available electronically at the following URL address: http://techreports.larc.nasa.gov/ltrs/ltrs.html

Printed copies available from the following:

NASA Center for AeroSpace Information

800 Elkridge Landing Road

Linthicum Heights, MD 21090-2934

(301) 621-0390

National Technical Information Service (NTIS)

5285 Port Royal Road

Springfield, VA 22161-2171

(703) 487-4650
Contents

Abstract ........................................................................... 1

Introduction ....................................................................... 1

Hydraulic Manipulator Testbed Project Description ........................................ 2

Orbital Replaceable Unit (ORU) Changeout Task .......................................... 3

Problem Definition .................................................................. 3

Experiment ........................................................................ 5

HMTB Laboratory Setup ........................................................... 5

Goal ............................................................................ 7

Subjects ......................................................................... 7

Task Procedure ................................................................... 7

Training ......................................................................... 7

Training Configuration 1 .......................................................... 8

Training Configuration 2 .......................................................... 8

Experiment Design ................................................................ 8

Wrist Camera-Target Configurations .................................................. 8

Experiment Configuration A ....................................................... 8

Experiment Configuration B ...................................................... 10

Experiment Configuration C ...................................................... 10

Experiment Configuration D ...................................................... 10

Experiment Configurations E, F, G, and H ........................................... 10

Results .......................................................................... 20

Data Sets ....................................................................... 21

Subjects ........................................................................ 21

Configurations ................................................................... 22

vrs Design (Configurations B and F) Versus SPDM Design (Configurations A and E) ........ 22

Combining Dexterous Handling Target With View of End-Effector ....................... 22

Modified FTS design (configurations C and G) versus FTS design (configurations B

and F) .................................................................... 22

Modified SPDM design (configurations D and H) versus SPDM design (configurations A

and E) .................................................................... 23

Modified SPDM design (configurations D and H) versus FI'S design (configurations B

and F) ..................................................................... 23

Effects of Lighting Changes ...................................................... 23

Concluding Remarks ............................................................... 23

References ....................................................................... 23

ooo

nl

Abstract

The Hydraulic Manipulator Testbed (HMTB) is the kinematic replica of the

Flight Telerobotic Servicer (FTS). One use of the HMTB is to evaluate advanced control techniques for accomplishing robotic maintenance tasks on board the Space

Station. Most maintenance tasks involve the direct manipulation of the robot by a

human operator when high-quality visual feedback is important for precise control.

An experiment was conducted in the Systems Integration Branch at the Langley

Research Center to compare several configurations of the manipulator wrist camera

for providing visual feedback during an Orbital Replaceable Unit changeout task.

Several variables were considered such as wrist camera angle, camera focal length,

target location, lighting. Each study participant performed the maintenance task by

using eight combinations of the variables based on a Latin square design. The results

of this experiment and conclusions based on data collected are presented.

Introduction

The initial reason that robotics was proposed for

Space Station was to provide support to the assembly,

servicing, and maintenance operations of the Space

Station and its payloads. When NASA discovered, in

1989, that the amount of extravehicular activity (EVA)

time needed on Space Station was four times more than

originally estimated, the agency created the External

Maintenance Task Team (EMTF) to investigate the difference between the estimates. Six months after its formation, the team produced a report (ref. 1) that quantified

the amount of time needed to complete maintenance

tasks both for EVA astronauts and the Space Station

robots. The team concluded that the amount of crew time

needed to perform Orbital Replaceable Unit (ORU)

replacements by using robotics was less than or equal to

that required for an EVA astronaut to perform these same

tasks.

From 1988 to 1991, there were two dexterous

robotic systems for Space Station construction/

maintenance: the Flight Telerobotic Servicer (FTS) from

the United States (fig. 1) and the Special Purpose

Dexterous Manipulator (SPDM) from Canada (fig. 2).

After FTS was canceled by the U.S. Congress in late

1991, SPDM was the only maintenance robot for Space

Station. As a result, all Space Station Robotic Interfaces

were designed for the SPDM wrist camera.

Head-mounted camera---_

I'1

Manipulator arm _

_-- Wrist-mounted '_

camera

Attachment, stabilization, and

positioning system

Figure 1. Flight Telerobotic Servicer. (From ref. 6.)
Hydraulic Manipulator Testbed Project

Description

The Hydraulic Manipulator Testbed (HMTB) (fig. 3)

is a functional laboratory version of one arm of the Flight

Telerobotic Servicer (FTS) flight system (ref. 2). HMTB

shares the same kinematics as the flight system but uses

hydraulic, not electrical, power for operation in a lg

environment.

Figure 2. Special Purpose Dexterous Manipulator.

Canada has not guaranteed that the SPDM will be

available for Space Station and is not scheduled to make

a final decision until July 1997. To provide an alternative, the United States has proposed a lower cost version

of the FTS, the American Fine Arm (AFA). To reduce

costs, no major redesign of the AFA end-effector is

allowed. However, since SPDM is still considered the

primary Space Station robot, AFA must conform to all

existing target designs.

The original purpose of HMTB was to provide a

ground-based training environment for astronauts prior

to flying the FTS. When the U.S. Congress canceled the

FTS program, they appropriated $10 million to capture

technology from the project. As part of this technology

capture, Langley Research Center (LaRC) and Johnson

Space Center (JSC) formed a partnership wherein, upon

completion of the FTS system, LaRC would receive the

HMTB and JSC would receive the flight arm and residual hardware (ref. 3). The purpose of this partnership was

not only to complete the FTS system but also to transfer

robotics control technology to NASA operations (i.e.,

Space Shuttle, Space Station). HMTB was installed at

LaRC and incorporated in a laboratory which included a

mock-up of the Space Shuttle aft flight deck (AFD).

Figure 3. Hydraulic Manipulator Testbed.

L-94--4673
Orbital Replaceable Unit (ORU) Changeout

Task

On Space Station, over 8000 external Orbital

Replaceable Units (ORUs) have been identified, and the

estimation is that there will be 75 Remote Power

Controller Module (RPCM) ORUs (ref. 1). The Space

Station has an expected life of 30 years, but the RPCM

life limit is 20 years; therefore, all the RPCM ORUs will

have to be replaced during the life of Space Station. In a

ranking of ORUs by the number of failures, the RPCM is

number 10 out of 150 types of ORUs. Given such a high

rate of failure, the RPCM will have to be serviced often,

and it is for this reason the RPCM ORU changeout task

was chosen for this study.

A typical RPCM (fig. 4) is equipped with a Micro

Fixture Handle and Dexterous Handling Target. Since

the RPCM ORU exchange is a Space Station task, all

interfaces must adhere to specifications found in the

Robotics Systems Integration Standard (RSIS) (ref. 4).

This RSIS states that the Dexterous Handling Target

must be incorporated into all ORUs with a Micro Fixture

Handle. The version of the Dexterous Handling Target

used in the camera study is the result of design refinement based on tests conducted at Johnson Space Center

(ref. 5). These tests have shown that the Dexterous

L-95-02784

Figure 4. Orbital Replaceable Unit.

Handling Target, when used in combination with an electronic graphic overlay (fig. 5), provides accurate information about the position and orientation of the target

relative to the camera and end-effector.

Problem Definition

The External Maintenance Task Team report states

that "camera positions and orientation coverage are critical to robotics task performance." (See ref. 6.) However,

there is a difference between the wrist camera position in

the FTS specifications and that recommended for use

with the Dexterous Handling Target. In FTS, the camera

is pitched downward, so that the operator can view the

gripper fingers and use the position of the end-effector

relative to the handle to determine orientation. The

Dexterous Handling Target is designed based on the

SPDM wrist camera configuration. At the grasp position,

the wrist camera is bore sighted with the target, but the

operator is no longer able to see the fingers (grippers).

However, if the camera is placed in the FTS position,

pitch and yaw information cannot be obtained from the

Dexterous Handling Target.

The purpose of this study is to answer the following

questions:

1. Is teleoperation better with the FTS wrist camera

design or the SPDM design?

There is one theory in the robotics field that it is

better to pitch the wrist camera downward so that

the operator can see the end-effector while performing a task. Another point of view is that the

operator can rely on targets to perform tasks. If

we are forced to choose between these two

designs, which one is better? "Better" is defined

as a more accurate positioning of the gripper with

respect to the Micro Fixture Handle and a higher

number of successful grasps.

2. Is it possible to combine the FFS and SPDM

designs?

Is it possible to use the Dexterous Handling

Target and also see the end-effector at the same

time? If this is done, can the task be performed

with the same level of accuracy and success? If

the wrist camera designs are combined, will error

increase or decrease?

3. Does lighting have an effect on operator

performance?

Are some designs easier to use under good

lighting conditions but impossible to use in a poor

lighting situation? Do shadows help or hurt?
I

I

Electronic overlay Target

Approach alignment

distance = 9.4 in.

Grapple position

Figure 5. Using the Dexterous Handling Target. (From ref. 4.)

4
Experiment

HMTB Laboratory Setup

The laboratory setup for HMTB was based on specifications for the first scheduled flight of FTS known as

Development Test Flight (DTF-1). The DTF-1 system

was composed of two parts: a Payload Bay Element and

an Aft Flight Deck Element.

The Payload Bay Element contained the sevendegree-of-freedom (shoulder roll, pitch, and yaw; elbow

pitch; and wrist roll, pitch, and yaw) hydraulic manipulator (fig. 6) with a parallel jaw gripper at the end of the

manipulator arm. Two wrist cameras were on the manipulator arm (fig. 7). One wrist camera, which was in

accordance with FTS specifications, was pitched downward 17 ° so that the gripper was in the camera field of

view. The second wrist camera was positioned such that

at the grasp position, it was bore sighted to the Dexterous

Handling Target as specified in the RSIS.

L-95-02088

Figure 7. Wrist cameras and manipulator grippers.

L-95 -02090

Figure 8. Shoulder cameras and shoulder light.

L-95 -02089

Figure 6. Hydraulic manipulator.

The Payload Bay area also contained two shoulder

(head) cameras (fig. 8) with pan, tilt, and zoom capability. The manipulator arm completely blocked the right

shoulder camera view of the task work space; therefore,

this camera was not used in this study. To reduce the

number of variables in the experiment, the left shoulder

camera was placed in a fixed position and subjects were

not allowed to move the camera. Because the left shoulder camera only displayed the task work space, an

additional camera was arbitrarily placed in the payload

area to provide a global view of the manipulator. A global camera view may or may not be available on Space

Station; therefore, its use was restricted to training.

The major components of the Aft Flight Deck

(fig. 9) were the hand controllers, command and display

panel, and video monitors. In Cartesian mode, both hand

controllers (fig. 10) were used to move the manipulator

with respect to a point in space: one hand controller for

translation (X,Y,Z) and the other for rotation (roll, pitch,

and yaw). Operators could manually input commands

into the computer terminal located in the flight deck. The

computer terminal displayed real-time information such

as position, coordinate system, joint angles, operation

mode. This display was disconnected throughout the

experiment to prevent participants from obtaining position and orientation data. The manipulator in the payload

bay work space could be seen either through the windows or the two video monitors. For the study, the windows were covered with a black cloth to force

participants to use the video monitors. During both the

5
i Command and

display panel

Figure 9. Subject in Aft Flight Deck.

L-95-02085

Figure 10. Hand controllers.

L-95-02084

6
training and the data collection phases of the experiment,

one of the wrist camera views was transmitted to the top

video monitor. The bottom monitor displayed either a

global camera view (training) or left shoulder camera

view (experiment).

Goal

The goal of this experiment was to compare wrist

camera-target configurations for providing visual feedback during an ORU changeout task.

Subjects

Eight subjects, seven men and one woman, volunteered to participate in the study. All eight participants

had some previous experience operating a robotic manipulator. One of the eight subjects had actually operated the

system in the HMTB by using hand controllers in the

payload bay area prior to the training. However, this subject was still considered naive because the experiment

was being conducted from the flight deck not the payload

bay area.

Task Procedure

Timing of the task began when subjects were given a

signal to move the end-effector from the start position

(fig. 11) toward the ORU. When the end-effector had

been moved to the grasp position, subjects were not

allowed to actually close the gripper onto the handle.

This constraint was to prevent users from placing the

gripper only within the vicinity of the handle and relying

on force accommodation to compensate for any error.

Instead, the task officially ended when the subject verbally indicated that the end-effector had been placed at

the grasp position (fig. 12). The total time to complete

the task and other data (e.g., joint angles, position in

space) were recorded. Afterwards, the grippers were

closed to determine if the subject actually reached the

grasp position. The run was defined as successful only if

the ORU handle was secure within the closed grippers.

Training

All participants had to become comfortable with

using the hand controllers and performing the task. The

global camera view allowed participants to actually see

the effect of moving the hand controllers on the manipulator. To achieve the second goal, each subject performed

the task with two different wrist camera-target training

configurations. Training under both conditions was completed when the subject could successfully perform the

task within 5 minutes twice in a row. None of the wrist

camera views-target configurations in the training phase

were used in the data collection portion of the

experiment.

Figure 11. Manipulator at start position.

L-95-02087
Figure 12. Manipulator at grasp position.

L-95-02091

Training Configuration 1

Training configuration 1 is the SPDM wrist camera,

bore sighted, with 15-mm lens, target, and electronic

graphic overlay. (See fig. 13.) With a 15-mm lens, the

target fills the entire wrist camera field of view when the

end-effector is near the grasp position. This view forces

the subject to use the graphic overlay and Dexterous

Manipulation Target to align the gripper with the handle

on the ORU.

Training Configuration 2

Training configuration 2 is the FTS wrist camera,

pitched downward 17 ° with 12.5-mm lens, target, and no

overlay. In this configuration, the subject can see the

grippers of the manipulator at the grasp position.

Although the Dexterous Manipulation Target is still

within the camera field of view, it cannot be used properly because a graphic overlay has not been provided and

the camera is pitched downward 17°. As a result, the subject must rely primarily on the position of the gripper relative to the ORU and target to determine the grasp

position.

Experiment Design

To answer the three questions in the section "Problem Definition," four wrist camera setups were examined

under two lighting conditions to produce eight different

experiment configurations. Each subject performed the

task by using a unique sequence of the eight wrist camera, target, and lighting configurations based on the Latin

square design (ref. 7) in figure 14. The Latin square was

used to eliminate the effect of improvements in performance due to learning. A total of 64 runs, 8 runs (1 data

set) for each of the 8 configurations, was completed by

each subject.

Wrist Camera-Target Configurations

Experiment Configuration A (SPDM Design)

Experiment configuration A (fig. 151) is a boresighted camera with 7.5-mm lens, electronic graphic

overlay, and overhead lights. Setup was based on specifications for SPDM. Subjects were unable to see grippers

at grasp position and had to rely on target and overlay for

alignment. All overhead lights (normal laboratory lighting fixtures) were turned on.

1Figures 15-24 are at the end of the section "Wrist CameraTarget Configurations."
(a) Start position.

(b) Grasp position.

Figure 13. Training configuration 1.
Subject

1 2 3 4 5 6 7 8

l A B C D E F G H

2 B E A F C H D G

3 C A D B G E H F

_ 4 D F B H A G C E

5 E C G A H B F D

6 F H E G B D A C

7 G D H C F A E B

8 H G F E D C B A

Figure 14. Latin square design.

Experiment Configuration B (FTS Design)

Experiment configuration B (fig. 16) is a pitched

camera with 12.5-mm lens, no overlay, overhead lights,

and no target; camera was pitched downward 17 °. Camera focal length was still within the range in DTF-1 specifications. A target and overlay were not provided;

therefore, subjects had to rely on gripper with respect to

ORU and handle for alignment.

Experiment Configuration C (Modified FTS

Design)

Experiment configuration C (fig. 17) is a pitched

camera with 12.5-mm lens, electronic graphic overlay,

overhead lights, and target. Configuration C is the same

as configuration B except a target and graphic overlay

were provided. Pitch and other orientation information

were difficult to obtain from the target because it was

designed for a bore-sighted, not pitched, camera. Subjects could see the grippers at the grasp position.

Experiment Configuration D (Modified SPDM

Design)

Experiment configuration D (fig. 18) is a boresighted camera with 4-mm lens, electronic graphic overlay, and overhead lights. Wrist camera was bore sighted

to the target at the grasp position. Configuration D is

similar to configuration A except the focal length was

smaller. This shorter focal length expands the field of

view so that the target and grippers could be seen.

Experiment Configurations E, F, G, and H

Experiment configurations E, F, G, and H (figs. 19

to 22) are the same as configurations A, B, C, and D,

respectively, except the amount of lighting was reduced.

All overhead lights were turned off and the left shoulder

and wrist camera lights were turned on (fig. 23). The left

shoulder light (fig. 8) complied with all DTF-1 shoulder

light specifications except luminance coverage. The

wrist camera lighting unit (fig. 24) installed was actually

designed for the Automated Structural Assembly

Laboratory (ASAL). (See ref. 8.) This unit provided

lighting for close-up positions when the manipulator

either blocked shoulder lights or produced shadows. It

was not based on DTF-1 specifications but was intended

to test the effects of wrist lighting.

10
(a)Startposition.

(b)Graspposition.

Figure15.Experiment configuration A.

11
(a) Startposition.

(b)Graspposition.

Figure16.Experiment configuration B.

12
(a) Start position.

(b) Grasp position.

Figure 17. Experiment configuration C.

13
(a) Start position.

(b) Grasp position.

Figure 18. Experiment configuration D.

14
(a)Startposition.

(b)Graspposition.

Figure19.Experiment configuration E.

15
(a) Start position.

(b) Grasp position.

Figure 20. Experiment configuration F.

16
(a) Start position.

(b) Grasp position.

Figure 21. Experiment configuration G.

17
(a) Start position.

(b) Grasp position.

Figure 22. Experiment configuration H.

18
Figure 23. HMTB under minimum lighting conditions.

L-95-02092

Figure 24. Wrist camera lighting unit.

L-95-02086

19
Results Table 4. ANOVA Table for Y-Axis Translation Error

Eight Latin squares were created by using the following variables for each square: number of successful

gripper closures; total task completion time; X-, Y-, and

Z-axis translation error; and roll, pitch, and yaw error.

Analysis of Variance (ANOVA) tables (tables 1 to 8)

were created for every Latin square (ref. 9). The first column indicates whether the source of variation is due to

rows (data sets), columns (subjects), treatments (wrist

camera-target configurations), or error. The remaining

ANOVA table columns in order are the sum of squares

(SS), degrees of freedom (df), mean square (MS), F-ratio

(F), and probability value (Prob > F).

Table 1. ANOVA Table for Successful Gripper Closures

[Boldface type indicates probability value less than 0.01]

Successful gripper closures

Source SS

Data sets 20.4375

Subjects 33.6875

Configurations 66.9375

Error 89.875

Total 210.9375

df MS

7 2.919643

7 4.8125

7 9.5625

42 2.139881

63

F Prob > F

1.36 0.2455

2.25 0.0489

4.47 0.0009

Table 2. ANOVA Table for Completion Time

[Boldface type indicates probability value less than 0.01]

Completion time, min

Source SS

Data sets 5.412107

Subjects 7.260264

Configurations 0.9648506

Error 6.33103

Total 19.96825

df MS F Prob > F

7 0.7731581 5.13 0.0003

7 1.037181 6.88 0.0000

7 0.137835_ 0.91 0.5050

42 0.150738_

63

Y-axis translation error, in.

Source SS

Data sets 0.829433

Subjects 0.6565122

Configurations 0.9624309

Error 4.671101

Total 7.119477

df MS F Prob > F

7 0.1184904 1.07 0.4022

7 0.09378 0.84 0.5582

7 0.1374901 1.24 0.3051

42 0.1112167

63

Table 5. ANOVA Table for Z-Axis Translation Error

Z-axis translation error, in.

Source

Data sets

Subjects

Configurations

Error

Total 1.52398

SS df MS F Prob > F

0.1705924 7 0.02437 1.21 0.3189

0.3777076 7 0.05395 2.68 0.0219

0.1294663 7 0.01849 0.92 0.5024

0.8462137 42 0.02014

63

Table 6. ANOVA Table for Roll Error

Source

Data sets

Subjects

Configurations

Error

Total

Roll error, rad

SS df MS F Prob > F

0.0006289 7 0.00008984 0.79 0.5989

0.0006007 7 0.00008581 0.76 0.6271

0.001948 7 0.0002783 2.45 0.0335

0.004770 42 0.0001135

0.007948 63

Table 7. ANOVA Table for Pitch Error

[Boldface type indicates probability value less than 0.01]

Source SS

Data sets 0.0007362

Subjects 0.007923

Configurations 0.0007255

Error 0.006745

Total 0.01613

Pitch error, rad

df MS F Prob > F

7 0.0001051 0.65 0.7082

7 0.001131 7.05 0.0000

7 0.0001036 0.65 0.7159

42 0.0001605

63

Table 3. ANOVA Table for X-Axis Translation Error

X-axis translation error, in.

Source SS

Data sets 0.4628669

Subjects 0.4298225

Configurations 0.2879608

Error 2.368396

Total 3.549046

20

df MS F Prob > F

7 .06612 1.17 0.3388

7 .06140 1.09 0.3876

7 .04113 0.73 0.6479

42 .05639

63

Table 8. ANOVA Table for Yaw Error

Source

Data sets

Subjects

Configurations

Error

Total

Yaw error, rad

SS df MS F Prob > F

0.0009836 7 0.0001405 0.68 0.6841

0.002511 7 0.0003588 1.75 0.1238

0.001212 7 0.0001732 0.84 0.5575

0.008619 42 0.0002052

0.01332 63
The F-ratio and probability value were used to evaluate the results of the experiment. The null hypothesis

(Ho), which is that all the means are the same, was tested

against the alternative hypothesis (Hi), which is that

there is at least one mean that is different. Mathematically (refs. 10 and 11), this is written as

Ho: _11 = _2 = .... _k

HI: not all lai are the same

where

i =1,2 ..... k

k order of Latin square, 8

The observed F-ratio is MSt/MSerror, where t is

defined as data set, subject, or configuration. The probability value is the probability that the F-ratio obtained

from an F-distribution table is greater than the observed

F-ratio. The value that we look up in the F-distribution

table is as follows:

where

rl

r2

F(t_;r l,r 2)

significance level

degrees of freedom in numerator (population)

degrees of freedom in denominator (error)

If the probability value is less than or equal to et, we

accept H 1, otherwise we accept H o. For all tests, ct = 0.01

was used. Instances in which the probability value is less

than 0.01 are highlighted in boldface type in the column

Prob > F in the ANOVA tables. If statistically the means

are all determined to be equal, that variable is not used

for comparison purposes.

Data Sets

Average completion time (fig. 25) is the only variable that is statistically significant in comparing data

sets; this was expected because it indicated a learning

curve. The assumption was made that subjects would be

able to perform the tasks more quickly as the number of

trials increased. At the end of the study, subjects were

able to complete the task in almost half the time it took at

the beginning of the study.

Subjects

Two of the eight variables are statistically significant

in comparing subjects: average task completion time and

pitch error. The differences in completion time (fig. 26)

between subjects indicate the various levels of robotics

experience subjects possessed prior to the study.

Figure 27 is the result of several subjects experiencing

trouble distinguishing between pitch error and Z-axis

translation error.

_4

_5

6

' I1_ ' ' '

2.03

' ' ' 1.'_55 _,

- _ 1.599

1.558

_ !.493

1.278

===_=_2-- 1.26

1.097 ,i

I

0 .5 1.0 1.5 2.0

Completion time, min

2.5

Figure 25. Average task completion time for each data set.

1

2

3

4

5

6

7

8 _ 1.7051

0 .5 1.0 1.5 2.0

Completion time, min

__ 2.175

 !447

______7---J_ - 1.366

, t i

_ 1.3.45

i

_ 1.621

:

* g i

2.5

Figure 26. Average task completion time for each subject.

4

_5

6

7

8

0

.025

i , ,

.032

-- .0¢,7

, 1009

t i i i ,

- - -- .048

i , , ,

_.00

___ -- 7.628 !

I I I I I

.01 .02 .03 .04 .05

Pitch error, rad

Figure 27. Average pitch error for each subject.

.06

21
Configurations

The only variable with significant mean differences

between configurations is number of successful gripper

closures (fig. 28 and table 9). Because the goal of this

study is to compare wrist camera and target configurations, this figure and table are used to answer the questions posed in the section "Problem Definition."

Table 9. Average Number of Gripper Closures for Each

Configuration Normalized About Mean

Configuration Description

Gripper closures

Average

number

Normalized

about mean

Difference

from mean,

percent

Maximum lighting

A

B

C

D

SPDM

FTS

Modified

FTS

Modified

SPDM

6.75

6.125

5.875

7.0

1.18

1.07

1.03

1.22

+18

+7

+3

+22

Minimum lighting

E

F

G

H

SPDM

FTS

Modified

FFS

Modified

SPDM

5.875

3.5

5.0

5.625

Mean 5.72

1.03

0.61

0.87

0.98

+3

-39

-13

-2

FTS Design (Configurations B and F) Versus

SPDM Design (Configurations A and E)

First, for successful gripper closures under maximum lighting conditions, the bore-sighted camera-target

configuration (configuration A) is 1 1 percent better than

the pitched camera (configuration B). However, when

the task is performed under minimal lighting conditions,

the bore-sighted camera (configuration E) is 42 percent

better than the pitched camera (configuration F). Therefore, if we had to choose between the FTS or SPDM

wrist camera design, the SPDM design is clearly better.

Combining Dexterous Handling Target With View

of End-Effector

The two approaches to creating this scenario (combining target with end-effector view) are as follows:

Modified FTS (configurations C and G)--Take the

FTS wrist camera setup (configurations B and F) and add

the Dexterous Handling Target and graphic overlay.

Modified SPDM (configurations D and H)--Take

the SPDM wrist camera setup (configurations A and E)

and change the focal length from 7.5 mm to 4 mm. This

change widens the field of view so that the end-effector

can now be seen.

Modified FTS design (configurations C and G)

versus FTS design (configurations B and F). Under

good lighting conditions, the number of gripper closures

for the FTS design (configuration B) is 4 percent better

than the modified FTS (configuration C). However under

poor lighting conditions, for the modified FTS (configuration G), the number of gripper closures is 26 percent

higher than those for the original FTS design (configuration F). As a result, we can conclude that adding the

Dexterous Handling Target and graphic overlay to the

FTS wrist camera design improves performance.

Configuration

A (SPDM)

B (FFS)

i

C (b-TS + target) i

i

D (SPDM + wide lens)!

E (SPDM)

F (FTS)

G (FTS + target)

H (SPDM + wide lens)

0

[7"/_ Maximum lighting

Minimum lighting

"//////_/.////_..//////.////A 6.75

, i i i , i |

i i

_/////)/////,)/////,,)A 6.12

i i J i i m

"/////)/////)_//////)/////)////A ,5.875

"/iilikiliiifil/lli, filllli_/iiiiif'iili//////Z,'_ 7

i i i i i t

_ _ k_:_::_l_[il_:_:._:_::t_ :_i_::_:._!i_ i___7:__ _777_1 _5.875

i i i i

, I

I 2 3 4 5 6 7

Closures

Figure 28. Average number of successful gripper closures for each configuration.

22
Modified SPDM design (configurations D and H)

versus SPDM design (configurations A and E). Under

good lighting conditions, the number of successful gripper closures in the modified SPDM design (configuration D) is 4 percent better than the number for the SPDM

design (configuration A). However under poor lighting,

the number of gripper closures for the modified SPDM

design (configuration H) is 5 percent worse than for the

SPDM design (configuration E). Therefore, changing

the field of view on the SPDM design decreases

performance.

Modified SPDM design (configurations D and H)

versus FTS design (configurations B and F). The number of successful closures is 15 percent (maximum lighting) and 37 percent (minimum lighting) better with the

modified SPDM design than the FTS design. Therefore,

the SPDM design with a wider field of view is still better

than the FTS pitched wrist camera concept.

Effects of Lighting Changes

The number of successful gripper closures for each

configuration decreases under poor lighting conditions.

However, the number of gripper closures for the FTS

design under poor lighting (configuration F) is approximately half the number under maximum lighting (configuration B). This result suggests that good lighting is a

necessity in order to perform the task by using the FFS

design.

Concluding Remarks

The SPDM (Special Purpose Dexterous

Manipulator) wrist camera design (bore-sighted wrist

camera with Dexterous Handling Target and electronic

graphic overlay) is better than the FTS (Flight

Telerobotic Service) design (pitched wrist camera with a

view of the end-effector). If the Dexterous Handling

Target and overlay are added to the FTS design, accuracy

increases. If the field of view for the SPDM design is

changed so that the end-effector can be seen, accuracy

decreases. However, the SPDM design with the wider

field of view is still better than the original FFS design.

Reducing the amount of light in the work space makes

performing the ORU changeout task much more difficult

with the FTS design but only slightly more difficult for

all other configurations.

NASA Langley Research Center

Hampton, VA 23681-2199

May 9, 1997

References

1. Fisher, William E; and Price, Charles R.: Space Station Freedom External Maintenance Task Team--Volume 1, Part 2.

NASA TM-I 11428, 1990.

2. Morris, A. Terry: Comparison of System Identification Techniques for the Hydraulic Manipulator Test Bed (HMTB).

NASA TM-110279, 1996.

3. Shattuck, Paul L.; and Lowrie, James W.: Flight Telerobotic

Servicer Legacy. Cooperative Intelligent Robotics in Space !II,

Jon D. Erickson, ed., SPIE Proceedings, vol. 1829, 1992,

pp. 60-74.

4. Space Station Program Robotic Systems Integration

Standards Volume II: Robotic Interface Standards.

SSP 30550, Vol. II, Rev. A, NASA Johnson Space Center,

1993.

5. Sampaio, Carlos E.; Hwang, Ellen Y.; Fleming, Terence F.;

Stuart, Mark A.; and Legendre, A. Jay: A Human Factors

Evaluation of the Robotic Interface for Space Station Freedom

Orbital Replaceable Units. Fifth Annual Workshop on Space

Operations Applications and Research (SOAR '91), Kumar

Krishen, ed., NASA CP-3127, vol. II, 1992, pp. 539-543.

6. Fisher, William K; and Price, Charles R.: Space Station Freedom External Maintenance Task Team--Volume 1, Part 1.

NASA TM-111430, 1990.

7. Hogg, Robert V.; and Ledolter, Johannes: Engineering Statistics. MacMillian Publ. Co., 1987.

8. Sydow, P. Daniel; and Cooper, Eric G.: Development of a

Machine Vision System for Automated Structural Assembly.

NASA TM-4366, 1992.

9. Hintze, Jerry L.: Number Cruncher Statistical System--

Version 5.0.1. Published by author (Kaysville, Utah), Oct.

1987.

10. Freund, John E.; and Walpole, Ronald E.: Mathematical Statistics. Prentice-Hall Publ. Co., 1987.

11. Anderson, Ian: Combinatorial Designs--Construction Methods. Halsted Press, 1990.

23
REPORT DOCUMENTATION PAGE Fo,m_

OMB No. 0704-0188

Pul_ic reporting burden for this collection of info(mation is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering end maintaining the data needed, and COml_ettng end reviewing the cdilectJon of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Secvicas, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

October 1997 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Wrist Camera Orientation for Effective Telerobotic Orbital Replaceable Unit

(ORU) Changeout WU 233-03-03-02

6. AUTHOR(S)

Sharon Monica Jones, Hal A. Aldridge, and Sixto L. Vazquez

7. PERFORMING ORGANIZATION NAME(S) ANDADORESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

9. SPONSORING/MONITORING AGENCY NAME(S)AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

8. PERFORMING ORGANIZATION

REPORT NUMBER

L-17612

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM-4776

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited

Subject Category 31

Availability: NASA CASI (301) 621-0390

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The Hydraulic Manipulator Testbed (HMTB) is the kinematic replica of the Flight Telerobotic Servicer (FTS). One

use of the HMTB is to evaluate advanced control techniques for accomplishing robotic maintenance tasks on board

the Space Station. Most maintenance tasks involve the direct manipulation of the robot by a human operator when

high-quality visual feedback is important for precise control. An experiment was conducted in the Systems

Integration Branch at the Langley Research Center to compare several configurations of the manipulator wrist camera for providing visual feedback during an Orbital Replaceable Unit changeout task. Several variables were considered such as wrist camera angle, camera focal length, target location, lighting. Each study participant performed

the maintenance task by using eight combinations of the variables based on a Latin square design. The results of

this experiment and conclusions based on data collected are presented.

14. SUBJECT TERMS

Telerobotics; Teleoperators; Cameras; Manipulators; Extravehicular activity; Human

factors engineering; Space Station

17. SECU RITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

NSN 7540-01-280-5500

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

15. NUMBER OF PAGES

28

16. PRICE CODE

A03

20. LIMITATION

OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102