An orbital replaceable unit (ORU) is often defined as any orbital unit aboard Space Station with a wearout life of less than 30 years. The capability of successful changeout of these units by remote manipulation is critical to the ORU to telerobot interface design. A human factors evaluation of the selected interface showed certain inadequacies of the alignment target concept that was part of the interface package. Alternative target concepts which addressed these inadequacies were developed and are presented. Recommendations will be incorporated into NASA requirements documents which ORU suppliers and manufacturers must then build to

Fleming, Terence F.

Hwang, Ellen Y.

Legendre, A. Jay

Sampaio, Carlos E.

Stuart, Mark A.

English

NASA Technical Reports Server

N92-22340
A HUMAN FACTORS EVALUATION OF THE ROBOTIC INTERFACE FOR
SPACE STATION FREEDOM ORBITAL REPLACEABLE UNITS
Carlos E. Sampaio 1, Ellen Y. Hwang 1, Terence F. Flemingl,
Mark A. Stuart 1, and A. Jay Legendre 2
1Lockheed Engineering and Sciences Company
Houston, TX 77058
2NASA Johnson Space Center
Houston, TX 77058
ABSTRACT
An orbital replaceable unit (ORU) is often de-
fined as any orbital unit aboard Space Station
with a wearout life of less than 30 years. The
capability of successful changeout of these units
by remote manipulation is critical to the ORU
to telerobot interface design. A human factors
evaluation of the selected interface showed
certain inadequacies of the alignment target
concept that was part of the interface package.
Alternative target concepts which addressed
these inadequacies were developed and are pre-
sented in this paper. Recommendations from
this work will be incorporated into NASA re-
quirements documents which ORU suppliers
and manufactures must then build to.
ACRONYM LIST
IDR Interface Design Review
JSC Johnson Space Center
ORU Orbital Replaceable Unit
ROlL Remote Operator Interaction
Laboratory
RSIS Robotic Systems Integration
Standards
SSF Space Station Freedom
INTRODUCTION
The changeout of orbital replaceable units
(ORU) will be a vital day to day activity for the
crew aboard Space Station Freedom (SSF).
Performing the changeout of these units by
both the extravehicular astronaut as well by the
various robotic devices aboard SSF will be
critical to the success of Freedom's operation.
Therefore it is critical that the interface to
these ORUs assure successful manipulation. In
response to this, an Interface Design Review
(IDR) process has been formed in order to as-
sess SSF robotic interfaces and to establish ap-
propriate interface design standards which will
be published in the Robotic Systems Integration
Standards (RSIS). These will become the stan-
dards which ORU suppliers and manufacturers
must build to.
As a result of the IDR process, the robot to
ORU interface package selected for ORUs of
1200 pounds or less was the Spar Aerospace
Limited design. Once the selection was made, a
design validation process began with the intent
of evaluating the suitability of the selected in-
terface design. This entailed making recom-
mendations intended to refine and improve the
Spar package. Several NASA as well as private
laboratories were chosen to participate in the
design validation process, among them the
Remote Operator Interaction Laboratory
(ROLL) at NASA's Johnson Space Center (JSC)
in Houston. The ROlL was chosen specifically
for its expertise in dealing with human factors
issues relevant to the interface design.
In evaluating the Spar package, personnel at the
ROIL determined that the Spar ORU alignment
target had the greatest impact from a human
factors perspective. Consequently, it was this
part of the interface which ROlL personnel
chose to focus on in an attempt to refine it.
This paper discusses the approach taken by the
ROlL during its evaluation and refinement of
the Spar alignment target.
539
https://ntrs.nasa.gov/search.jsp?R=19920013097 2020-03-17T11:53:55+00:00Z
THE SPAR ALIGNMENT TARGET
Shown graphically in Figure 1, the Spar align-
ment target was 2 inches by 2 inches square.
The front and base plates of the target were
separated by a depth of .5 inch. This .5 inch
separation between the .25 inch diameter white
circle on the face plate and the .284 inch dia-
meter black circle on the base plate provided
the cues necessary to align the pitch and yaw
rotational axes. This was done by making sure
a black ring from the base circle was always
visible around the white circle on the face
plate. An overlay displayed on the end effector
camera view, when aligned properly with the
target, provided the cues necessary to adjust the
additional rotational roll axis as well as the
translational X, Y, and Z axes. Once aligned
properly, the target--mounted 2.5 inches above
the center of the grapple fixture on the ORU--
was designed to assure that the misalignment
tolerances of the grapple fixture were met
before a grapple attempt was made.
Face Plate Base Plate
Figure 1. Face plate and base plate con-
cepts incorporated into the original Spar
target.
Certain aspects of the Spar alignment target
design were very well conceived. The com-
pactness of the target allowed for it to be
mounted appropriately near each grapple point.
Further, because it was an enclosed unit, it
would pose little to no risk of snagging an ex-
travehicular astronaut. The simplicity of the
target was also a good feature. Corrective
alignments were thus logical and easy to inter-
pret. Initial evaluations by the ROLL, however,
pointed out several shortcomings inherent to
the target's design.
First among these limitations was a matter of
geometry. According to the operational sce-
nario provided by Spar, at grapple the camera
to target distance was defined to be 4 inches.
Figure 2 shows that according to the dimen-
sions specified by Spar, the minimum distance
at which the black circle on the base plate
would be visible around the white circle on the
face plate was 3.67 inches. As a result, at the 4
inch grapple distance, the cues provided by the
base circle were so slight that final alignment
corrections were often difficult to determine.
F
Camera|
Target
Formula 1
R1 R2
=
D D + 0.5"
Spar Dimensions
R1 =0.125"
R2 = 0.142"
D = 3.67"
Figure 2. The relevant target and cam-
era dimensions (not to scale) are repre-
sented in Formula 1. Given the specified
Spar dimensions, the minimum distance
necessary to view the base circle around
the face plate circle was 3.67 inches.
Accuracy evaluations were performed by
mounting the target to a rotating base 4 inches
in front of and centered with the camera. An
operator would then call out when they felt that
a zero degree rotational alignment (i.e. perfect
alignment) had been achieved. Due to the ge-
ometry of the Spar target's relevant features,
540
accuracy was typically within 2 ° to 3° to either
side of zero degree rotational alignment.
When examined under controlled lighting
conditions, certain other drawbacks to the Spar
alignment target design became apparent.
When a collimated light source--in this case a
solar simulator--was directed at the target
from an angle displaced 15 ° to 25* from the
camera centerline, certain angular displace-
ments of the target caused the face plate to ob-
scure the black base plate circle by shadows
from either the outside frame of the face plate
or by the white circle on the face plate. The
corrective action needed in these cases would
not be clear and could result in the issuance of
an incorrect command.
Similarly, at certain incident angles, light
would reflect off the highly specular paint
specified by Spar to the point that features of
the target were completely washed out due to
the blooming effect that would appear on the
video monitor. If the iris on the camera's lens
were closed to the point that the blooming ef-
fect was relieved, the contrast would be so
slight that the target's features were still indis-
tinguishable on the monitor view.
PROPOSED TARGET MODIFICATIONS
done specifically with respect to the shadow
and geometric problems encountered in the
Spar design.
Figure 3 depicts an alternative target design,
designated concept A, which both reduced the
likelihood of any potential confusion caused by
shadows as well as assuring that all alignment
cues are clearly discemable at any camera to
target distance. The opening in the face plate
was widened to both allow more light into the
target as well as reduce the likelihood of a
shadow from the edge of the face plate obscur-
ing the center of the base plate. Likewise, the
width of the crosshairs were reduced from the
original Spar dimension of .12 inch to .02 inch.
The narrower crosshair created much less of a
shadow on the target base, eliminating the pos-
sibility of obscuring relevant features on the
base plate. Further, the alternating black and
white colors on the crosshairs, in combination
with the features of the base plate, made them
always distinguishable from the background.
This made corrective movements easier to de-
termine. Consequently, the same accuracy
evaluations as performed with the original Spar
target resulted in accuracy typically within .33*
to either side of zero degree rotational align-
ment with no apparent shadowing problems.
It was clear that the desirable features of the
Spar target concept needed to be preserved in
any new concept to be proposed. Just as clear,
however, was the need to address the limita-
tions of the original Spar target's design. With
this in mind, ROIL personnel began an iterative
process intended to devise target concepts
which preserved the desirable features of the
Spar design, but which also improved upon its
limitations. It should be noted that none of
these proposed target modifications addressed
the reflectivity of the paint due to the long
turnaround time in having a target concept
painted to specification. Paint reflectivity will
be addressed as an issue separate from features
of the target design.
Rather than address each limitation of the Spar
design separately, alternative designs were de-
veloped in order to address the various issues
as a system rather than as independent prob-
lems. This way, solutions which addressed one
potential flaw in the Spar target design would
be less likely to complicate another. This was
Face Plate Base Plate
Figure 3. Face plate and base plate de-
pictions proposed in alternative target
concept A.
Certain concerns were raised regarding target
concept A, however. Chief among them was a
lack of robustness with respect to the
crosshairs. Any contact with the crosshairs by
a robotic end effector or by an extravehicular
astronaut could potentially bend or even break
them. Therefore, further designs were devel-
541
oped with the intent of addressing that concern
in particular.
It was felt that the same level of accuracy could
be maintained if the crosshairs were widened.
Preserving many of the features of target con-
cept A with widened crosshairs could result in
a more robust target that was easy to interpret
and which could provide the cues necessary to
achieve the accuracy of the first alternative de-
sign. At the same time, it was felt that addi-
tional cues could be built into the target which
would provide cues redundant to the primary
alignment cue, in this case the center of the
crosshair.
Figure 4 depicts target concept B. The
crosshairs have been widened to .063 inch,
making them very robust. At the same time,
the level of accuracy exhibited by concept A
was preserved in this concept. Once again, ac-
curacy evaluations resulted in alignment typi-
cally within .33 ° to either side of zero degree
rotational alignment and again, no apparent
shadowing problems appeared. The new fea-
ture incorporated into this target was a redun-
dancy of the alignment cues used prior to
grapple. To achieve proper alignment of the
end effector at the 4 inch camera to target dis-
tance, the center cross on the face plate
crosshairs had to be centered within the white
circle on the base plate. The redundant cues
were provided by the black hashmarks further
out on the crosshairs. When proper alignment
was achieved at the 4 inch distance, the inside
edge of the black hashmarks appeared to touch
the outside edge of the base plate black circle.
Pitch and yaw cues which the target must pro-
vide are then also offered by these redundant
cues as well.
The redundant cues offered by this concept do
two things. First, they provide an extra
measure of certainty that proper alignment has
been achieved prior to attempting grapple. If
both sets of alignment cues tell the operator
that the end effector is positioned properly, the
operator will be that much more sure at the
time of grapple. The second, and perhaps
more important feature offered by the redun-
dant cues is that they can used as primary
alignment cues in the event that the original
cues, i.e. the center of the target, cannot be
used for alignment. This scenario could occur
if certain harsh shadows extended over the tar
.Jr .IL I
----" ,
Face Plate Base Plate
Figure 4. Face plate and base plate de-
pictions proposed in alternative target
concept B.
get, or if the target were partially damaged in
some way. The redundant cues might allow a
successful grapple to be made which might oth-
erwise not be attempted due to the extraneous
circumstances.
FUTURE WORK
The alternative designs presented here are only
two of several iterations on the target concept
conceived by ROlL personnel. While these
represent the most promising of the iterations
attempted so far, other concepts may offer even
greater promise. Consequently, work on im-
proving the design has not terminated and fur-
ther iterations on the concept will proceed.
It is important to note that a clear line of com-
munication has already been established be-
tween ROlL and Spar personnel. Thus, this
work is becoming a collaborative effort
consisting of feedback offered by the ROlL
being strongly considered by personnel at Spar.
Further work is being planned by the ROlL to
address the issues raised in this paper.
Alternative paints will be evaluated at the ROIL
with the intent of determining which have
acceptably low reflectivity characteristics. The
primary effort to be taken on by the ROLL,
however, will be to perform an operational
evaluation of these and other target concepts.
Test subjects will consist of personnel at JSC
with experience in operations, including the
crew. Data will be gathered with respect to ac-
curacy achieved during each alignment run as
well as subjective data regarding how well each
542
subject felt they could interpret the targets
evaluated. Results of these evaluations will be
incorporated into the RSIS documents.
CONCLUSION
It seems clear that these proposed modifications
are improvements upon the original Spar de-
sign. The line of communication opened be-
tween ROlL and Spar personnel as well as the
incorporation of this work into RSIS documen-
tation means that this work will have clear
implications to future space hardware design.
The end product of this work will hopefully
result in an alignment target that is very easily
interpretable and which will work under a wide
variety of situations.
ACKNOWLEDGEMENTS
Support for this work was provided by the
National Aeronautics and Space Administration
through contract NAS9-17900 to Lockheed
Engineering and Sciences Company.
543


A human factors evaluation of the robotic interface for Space Station Freedom orbital replaceable units

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server