.. .a. 

TELXROBOTIC ASSEMBLY OF 

By Grahme Fischer 

- 

SPACE STATION TRUSS STRUCTURE -_ 

A09-25, GRMN SPACE SYSTEMS DIVISION, BETHPAGE, NEW YORK 

11714-3588 

Yi 

1. ABSTRACT 

.. This paper discusses methods of assembling the Space Station's 

structure which only utilize telerobotic devices 

0 an approximately anthropormorpic telerobot 

0 the Shuttle Remote Manipulator System (SRMS) 

0 various material handling machines. 

Timelines and task recommendations for autonomous operations are 

also included. The paper also describes some experimental results 

comparing two manipulator control devices. 

with two dextrous arms 

2. INTRODUCTION: 

Recent studies at Grumman have shown the feasibility of 

assembling the Space Station truss structure in space using only 

telerobotic systems. The studies investigated the use of a pair 

of cooperating dextrous manipulators in an anthropomorphic 

telerobotic system. Two types of investigations were conducted: 

o Computer Aided Design (CAD) studies of the assembly 

of the Space Station truss structure 

0 Experimental tests of several subjects and control 

devices performing some truss assembly tasks using a 

pair of dextrous manipulators. 

These studies were based upon the capabilities of current 

state-of-the art electro-mechanical devices. Although human 

directed telepresence control was the baseline of these 

investigations, the truss assembly activities described here lend 

themselves very nicely to autonomous (or supervised) robotic 

operations. This paper will present some of the results from both 

the CAD studies and the experimental investigations. 

The CAD studies addressed the problem of assembling the entire 

Space Station truss structure from the Cargo Bay of the STS 

Orbiter, without using Extra Vehicular Activity (EVA). The 

studies only addressed structural connections and did not consider 

the installation of utility lines (fluid and electrical). Two 

different methods of assembly were explored. Both utilized an 

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(NASA-CB- 180239) IELEECBCIIC A55EdELY CP N87- 1 ES 64 

ZFACE SIASICL TfiLES STiiUC'fUEE (Grumman 

BcrosFace COE~.) 10 F CSCL 05H 

Unclas 

G3/54 4373b 
anthropomgrphic 

to perform all 

assemble the 

characteristics 

machine known as SAM (Surrogate Astronaut Machine) , 

the dextrous manipulation tasks needed in vacuum to 

. The "third arm", which normally functions as a 

structure. Figure 1 displays some of SAM's 1 

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means of attaching SAM to a worksite to allow the-SAM mobility aid 

(SRMS or MSC) to depart and perform other functions, was not 

utilized in this study. This paper reports the features and 

significant differences (including task timelines) of the two 

assembly methobs. 

A number of experimental results were obtained from a series 

of test subjects operating a pair of six degree-of-freedom 

(6 DOF) manipulator arms in a telepresence mode. Through the use 

of voice controlled cameras, the operators relied on video and 

force feedback to retrieve a "strut" and connect it to a truss 

node (see Figure 2). Two different control devices were used by 

each operator: 

0 A pair of 6 DOF ball type hand controllers utilized 

a resolved rate control law (see Figure 3). Some 

force feedback was provided by auditory signals. No 

force feedback was provided through the ball 

controller. 

0 A pair of bilateral force reflecting (BFR) replica 

master controllers utilized position-position error 

signals to produce forces in both master and slave 

arms (see Figure 4). 

This paper reports the significant differences found in 

operating with both of these control systems. 

3. STRUCTU RE ASS EMBLY TESTS 

Three struts were assembled into a node which contained strut 

termination fittings (see Fig. 2). The strut connections, known 

as the "Wendel-Wendel" joints, require that one manipulator hand 

hold a strut in position while the other manipulator hand 

translates a collar over the joint and then locks the joint by 

rotating the collar about half a revolution. The struts were 

positioned in the nodes in three orientations: vertical, diagonal 

and horizontal. In a gravity field, task difficulty was strongly 

influenced by strut orientation. The vertical strut installation 

was very easy to do. The horizontal strut installation was quite 

difficult. Task times were recorded from the start of strut 

removal from the vertical storage (the left zone of Fig. 2) until 

the visual indicator on the strut locking collar indicated a 

locked condition. 

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Figure 3 shows the two types of control devices which were 

utilized for these tests. The Master Controllers are 6 DOF BFR I 

arms which have an additional DOF squeeze grip for operating 

parallel jaw motion end effectors on the slave arm. The master 

and slave arms have identical structures and kinematics (i.e., a 

geometry ratio of 1:l). The control laws used by this BFR replica 

system develop torques, at both the master and slave joints, which 

are proportional to the position error signal between the 

corresponding master and slave joints. That is, when the master 

elbow is displaced 30° with respect to the slave elbow, the 

operator feels- a force at the control handle (which was generated 

at the master elbow) which tends to drive the master arm to the 

same position as the slave arm. Simultaneously, the slave arm 

experiences a torque at its elbow which tends to drive the slave 

arm to the same position as the master. Thus, high forces at the 

slave arm are experienced by the operator as high forces on the 

master arm. This type of control system is known as bilateral 

force reflection (BFR). 

The second type of manipulator controller shown in Fig. 3 is a 

6 DOF ball gripper type which is under development by 

CAE Electronics, Ltd. This compact device, and its supporting 

electronics, translate operator displacement commands (+ - X, y, 

z,tk+, p 1 at. th? btll grip.into slave end effector rate 

commands (+ - XI y0 z,&, in one of two (selectable) 

coordinate axis systems. For these tests, the selected system 

fixed the slave hand x, y and z axes to the slave hand, and, when 

the hand grabbled a strut or collar, to the work object. Thus, 

ball grip input commands were in a work object coordinate system. 

Operator forces at the ball grip were very light (with no felt 

feedback from the slave arm). An auditory system supplied some 

indication of high forces on the slave arm. This auditory system 

was not very helpful for manipulator operators of this test series. 

I 

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Figure 4 shows the laboratory in which these tests were 

conducted. The worksite region is on the right side. The 

operator region is on the left side. An opaque curtain was placed 

between these regions for these tests. The operator received all 

visual information from three TV monitors (see Fig. 3). These 

monitors received images from three fixed location comeras in the 

worksite region. The cameras had 3 DOF (scan, tilt, and zoom) and 

were controlled by manipulator operator voice commands. 

One of the major objectives of this test program was to 

evaluate the effects of the two manipulator control systems 

(master vs ball controller) on task timelines and to identify 

benefits and problems associated with them. The results we found 

were: 

o 230% faster strut installation with the master 

controllers 

-least time difference for the vertical strut, which 

required the lowest cognitive workload of the ball 

controller tasks. 

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o.::benefits & D roblems 

-speed of movement 

-mobility (zone of wk) 

-single axis motion: 

o in coordinates of 

control system 

o inclined to control 

soordinates 

-coordinated b constrained 2 arm motions 

-operator ability with 

little practice 

-ability to join objects 

without understanding 

-operator fatigue 

-control over fine 

(small) motions 

These, and other, experimental 

detail in Reference [l.]. 

BFR-Maste r 

good 

good 

difficult 

difficult 

good 

excel lent 

very tiring 

poor 

rate-Ba 11 

too slow 

too restricted 

excellent 

very difficult 

dangerous b 

very difficult 

fair 

almost impossible 

very comfortable 

excellent 

results are reported in greater 

5. SPACE S TATION ASSEMBLY STU DY 

Two different methods of using telerobotic devices (SAM) for 

assembling the Fall 1986 Langley Task Force Space Station Design 

were explored. Both methods used SAM in an operator controlled 

telepresence mode. The major differences between the two methods 

were in how SAM moved around the worksite and the amount of 

automation used to enable SAM to obtain supplies for the 

construction activity. 

0 Method 1 

-2 Telepresence controlled SAMs 

-Rotating/Translating Fixture Tool for SAM 

-Automatic strut b node dispensers 

0 Method 2 

-1 telepresence controlled SAM on SRMS 

-Rotating assy fixture 

Figure 5 depiects a partially completed Space Station truss 

structure emerging from an assembly fixture at the back of the 

Orbiter's Cargo Bay. The truss is formed of cubical "bays" which 

are 5 meters long. Each face of a cube has a diagonal strut in 

addition to "horizontal" and "vertical" struts. Figure 6 shows more 

details of the support of the Truss Assembly Fixture within the 

Orbiter's Cargo Bay. The truss is assembled in the lower bay region 

by a SAM attached to a "horizontal" beam. The beam is attached to a 

turntable which provides 2 DOF: translation in the "vertical" 

(Orbiter z axis) direction and 360° rotation about this "vertical" 

axis. These 2 DOF, and the 10 DOF within SAM, allow SAM to reach 

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I 

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all corners of the lower bay and the storage regions for struts and 

nodes (which are located outside the truss at the midpoints of the 

lower horizontal face of the cube). When the truss element feed 

system canisters become empty, they are replaced with full canisters 

by a second SAM which is mounted on a Shuttle Remote Manipulator 

System (SRMS). The canisters contain mechanisms which deliver all 

truss elements (i.e.8 struts and nodes) to the same location within 

a canister to expedite assembly operations. 

All Space Station structural assembly sub-tasks have been 

considered for telerobotic assembly. Reference 12.1 contains a 

listing of these sub-tasks and our estimates for the time required 

for their completion. These sub-task times were grouped into major 

task activities and summed for the entire operation of assembling 

the structure of the Space Station's Transverse Boom, which required 

70 hours of on-orbit time. These data are displayed on Figure 7. 

We examined a second method of assembling the Space Station's 

Transverse Boom structure. This method only used a single SAM which 

remained attached to the SRMS. The partially constructed ss 

structure was rotated about the centerline of the assembly fixture 

(Orbiter z axis) to locate all teleoperations in the same region of 

the Orbiter. This region allowed easy access to strut and node 

storage areas within the Cargo Bay and allowed SRMS motion from top 

to bottom of the assembly fixture. Figure 8 shows part of the 

fixture assembly operation: the upper portion of one of the four 

truss supports is about to be inserted by SAM into the previously 

installed lower two pieces. Figure 9 depicts a node receptacle 

(which contains 6 nodes) installation into the assembly fixture. 

Figure 10 shows an assembled truss bay above four previously 

assembled "horizontal" truss faces within the assembly fixture. SAM 

is positioned to raise the completed bay to the top of the fixture 

where it will be held by the fixture. The second bay is completed 

by SAM attaching vertical and diagonal struts between the completed 

bay and the next "horizontal" truss face, which has to be raised up 

to the bottom position. During vertical face assembly, the 

partially completed structure is rotated 900 to present SAM with a 

new corner of the truss. During this 900 rotation, angular 

accelerations have been limited to 1 "g". This limits bending 

moments on the cantilevered diagonal struts (since they are attached 

at only one end during rotation) to values which are substantially 

below their strength. The six timelines associated with assembly 

Method 2 are contained in Reference 121. The last of these is 

reproduced here as Figure 11. Method 2 required 72 hours of 

on-orbit time to assemble the Space Station's Transverse Boom 

structure (work began after 8 hours on orbit). 

I 

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6. TASKS FOR AUTONOMOUS TEJiEROBOTI~ 

. 

Both of the assembly methods which are discussed in this paper 

have assumed that all motions of the telerobot (SAM) and the SRMS 

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have been commanded by astronauts at control stations within the 

Orbiter. Since telerobot operations are planned f.or 16 hours per 

day, astronauts controlling these devices may experience fatigue, 

even with frequent shift changes. Consequently, the reduction of 

astronaut workload is desireable to reduce fatigue and the 

concomitant probability of errors. 

-. 

Selective autonomous telerobot actions can reduce astronaut 

fatigue by occasionally eliminating the need for an astronaut * s 

physical effort and mental attention to details. At the completion 

of an autonomous robotic task, the astronaut acts like a supervisor 

and verifies that the autonomous task was performed properly. 

Selective autonomy is stressed because of the prohibitive costs 

of providing a telerobot which is capable of performing all Space 

Station assembly tasks in an autonomous mode. Also, to perform 

autonomous tasks in a manner which does not impose a significant 

“weight burden on the Space Station, a high level of machine 

intelligence is required. At this time, one can not predict that 

this machine intelligence technology will be available in time to 

perform the complete assembly of the Space Station. 

Figures 12 and 13 list the major tasks which make up the Method 

2 assembly activities. Note that some tasks are conducted only once 

while other tasks are conducted hundreds of times. The three 

highest repetition tasks use up 20 hours (which is 30%) of dextrous 

manipulation time. All the tasks selected as candidates for 

autonomy in Figure 12 represent 1/2 of the dextrous manipulation 

time for the assembly of Space Station structure. A similar 

analysis of SRMS tasks (Fig. 13) yields 13 hours (90%) of SRMS 

operations which lend themselves to autonomous operations. 

7. CONC LWSIO NS 

Our work has persuaded us that the Space Station structure can 

be reliably assembled by telerobotic systems. We believe 

0 that the majority of tasks should be under astronaut 

0 that selective tasks should be performed autonomously 

control using telepresence technology, 

by the telerobot 

0 that the primary telepresence control device should be 

a bilateral force reflecting replica master 

0 that the initial Space Station structure can be 

assembled during 1 STS mission without EVA. 

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KNO~EDGEMENTS , 

8. AC 

I 

The work described in this paper was performed under contract to 

the National Aeronautics and Space Administration, Johnson Space 

Center. Testing was conducted at Grumman's Manipulator Development 

Laboratory . I would like to thank Mr. Erik Eriksen and Dr. John O'Hara for 

their contributions to our test programs, and, Mr. Dan Guinan and 

Mr. Kirk Sneddon for their Space Station assembly studies. 

. 9. PEFERE NCES 

[l] O'Hara, John M., "Telerobotic Work System: Space-Station 

Truss-Structure Assembly Using A Two-Arm Dextrous 

Manipulator", Grumman Space Systems Division, Bethpage, NY, 

November 1986. 

121 Fischer, Grahme, "Telerobotic Work System, System 

Definition Study, Phase 2, Final Presentation", Grumman 

Space Systems Division, Bethpage, NY, January 1987. 

,/ / 

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0373B 
ASTRONAUT CAPABILITIES WITH SAM 

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