Manual remote space manipulator control: An explorative study

MANUAL REMOTE SPACE MANIPULATOR CONTROL: AN EXPLORATIVE STUDY J . C R u i t e n b e e k L a b . f o r M e a s u r e m e n t a n d C o n t r o l / C y b e r n e t i c E r g o n o m i c s , M a n - M a c h i n e S y s t e m s G r o u p , D e l f t U n i v e r s i t y o f T e c h n o l o g y Mekelweg 2, 2628 CD D E L F T The N e t h e r l a n d s Human o p e r a t o r m a n u a l c o n t r o l o f a r e m o t e s p a c e m a n i p u l a t o r i s c o n s i d e r e d . The e f f e c t s o f t i m e d e l a y s a n d t h e n o n - l i n e a r m a n i p u l a t o r d y n a m i c s a r e d i s c u s s e d . The r e s u l t s o f some e x p l o r a t i v e e x p e r i m e n t s t o a s s e s s human o p e r a t o r c o n t r o l p e r f o r m a n c e i n t h i s p a r t i c u l a r c a s e a r e r e p o r t e d . B a s e d o n t h e s e r e s u l t s , r e c o m m o n d a t i o n s t o i m p r o v e human o p e r a t o r m a n u a l c o n t r o l a r e p r e s e n t e d . INTRODUCTION C u r r e n t s c é n a r i o s o n f u t u r e s p a c e o p é r a t i o n s i n c l u d e t h e a p p l i c a t i o n o f a t e l e -m a n i p u l a t o r , -mounted o n an un-manned s p a c e v e h i c l e , f o r i n - s p a c e i n s p e c t i o n , a s s e m b l y , m a i n t e n a n c e a n d r e p a i r (Lacombe a n d B e r g e r , 1 9 8 2 ) , w h i c h i s c o n t r o l l e d f r o m an e a r t h - b a s e d s t a t i o n .

The r e m o t e c o n t r o l o f t h i s m a n i p u l a t o r b y t h e human o p e r a t o r (HO) c a n be f u n c t i o n -a l l y d i v i d e d i n t o -a number o f h i e r -a r c h i c -a l l y o r d e r e d m o d e s . The h i g h e r modes c -a n be a s s o c i a t e d w i t h m o n i t o r i n g a n d s u p e r v i s o r y c o n t r o l o f t h e o v e r a l l b e h a v i o u r o f t h e m a n i p u l a t o r . The l o w e r modes r e q u i r e m a n u a l c o n t r o l o f t h e m a n i p u l a t o r v a r i a b l e s . D u r i n g n o r m a l o p é r a t i o n o f t h e m a n i p u l a t o r , HO c o n t r o l w i l l be r e s t r i c t e d t o t h e h i g h e r m o d e s . H o w e v e r , a f t e r m a l f u n c t i o n i n g o r a n o m a l i t i e s i n t h e o n - b o a r d c o n t r o l S y s t e m , HO c o n t r o l w i l l e n t e r t h e l o w e r modes t o remedy t h e c a u s e s o r e v e n t o r e c o v e r t h e m a n i p u l a t o r . Whereas t h e h i g h e r c o n t r o l modes may be h i g h l y a u t o m a t e d , t h e l o w e r modes r e q u i r e r e a l - t i m e c o n t r o l o f t h e m a n i p u l a t o r b y t h e HO. I n t h e l o w e s t mode, w h i c h w i l l b e r e f e r r e d t o a s t h e d i r e c t d r i v e mode, t h e HO d i r e c t l y c o n t r o l s t h e i n d i v i d u a l j o i n t s o f t h e m a n i p u l a t o r , b y p a s s i n g a l l o n - b o a r d e l e c t r o n i c c o n t r o l Systems a n d s o f t w a r e . To e n a b l e s u c c e s s f u l HO c o n t r o l b e h a v i o u r i n t h e d i r e c t d r i v e mode i n s p a c e c o n d i t i o n s , HO c o n t r o l b e h a v i o u r i n t h i s mode s h o u l d be a n a l y z e d a n d e s t a b l i s h e d i n a d v a n c e , i n o r d e r t o a s s e s s t h e f e a s i b i l i t y o f t h i s c o n t r o l mode. I n t h i s p a p e r , we c o n s i d e r some a s p e c t s o f HO c o n t r o l i n d i r e c t d r i v e mode o f t h e s p a c e m a n i p u l a t o r . A f t e r a b r i e f d i s c u s s i o n o f some m a i n p r o b l e m s t h a t may hamper a p r o p e r c o n t r o l o f t h e m a n i p u l a t o r b y t h e HO, we r e p o r t t h e r e s u l t s o f some

e x p e r i m e n t s ( R u i t e n b e e k , 1984 b ) . The s c o p e o f t h e s e e x p e r i m e n t s i s an e x p l o r a t i v e o n e . The r e s u l t s a r e l i m i t e d a s o n l y one s u b j e c t was t e s t e d . T h e s e r e s u l t s ,

h o w e v e r , w i l l be u s e d i n f u t u r e r e s e a r c h on t h i s t o p i c ( S t a s s e n a n d V a n L u n t e r e n , 1984) . TIME DELAYS Remote HO c o n t r o l o f t h e s p a c e m a n i p u l a t o r i s s e r i o u s l y i m p e d e d b y s i g n a l t r a n s -m i s s i o n d e l a y s i -m p o s e d b y t h e l i -m i t s o f t h e s p e e d o f l i g h t . F o r s p a c e v e h i c l e s i n low o r b i t , t h e t i m e e l a p s e d b e t w e e n s e n d i n g a s i g n a l u n t i l any r e c e i p t o f f e e d b a c k p e r t a i n i n g t o t h i s s i g n a l i s a b o u t 0 . 5 s e c o n d s . F o r n e a r - m o o n o p é r a t i o n s , t h i s

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:ime d e l a y i s about 3 seconds. Depending on the a v a i l a b i l i t y o f the data r e l a y channels a p p l i e d , queueing and p r o c e s s i n g time d e l a y s , which may vary w i t h i n l i m i t s , w i l l be added.

?o a s s e s s the v a r i o u s s t r a t e g i e s t h a t can be adopted by the HO i n o r d e r t o cope f i t h these time d e l a y s , we c o n s i d e r the c o n t r o l scheme as d e p i c t e d i n F i g . 1.

E(s) H0( s ) C(s) I m H0( s ) H£(s) R(s) F i g u r e 1 HO c o n t r o l loop w i t h time d e l a y s

The p o s i t i o n i n g c o n t r o l o f t h e output R(s) o f t h e manipulator Hc( s ) i s thought t o

be i n i t i a t e d by the step S ( s ) , which s p e c i f i e s t h e t a r g e t t o be reached. The HO, modeled by Ho(s) i s s u e s t h e c o n t r o l commands C ( s ) . The time d e l a y s i n the up- and down-link a r e denoted by exp(-T^S). F o r s i m p l i c i t y , we assume t h a t the HO i s w e l l a b l e t o c o n t r o l the manipulator i n the absence o f time d e l a y s .

In the presence o f time d e l a y s , the HO may adopt the f o l l o w i n g s t r a t e g i e s : <» As time d e l a y s a f f e c t the s t a b i l i t y o f t h e l o o p , adequate s t a b i l i t y margins i n

c l o s e d - l o o p c o n t r o l may be r e - e s t a b l i s h e d by r e d u c t i o n o f the loop g a i n . T h i s can be a c h i e v e d by r e d u c i n g the r a t e o f the commands C(s) as i s s u e d by t h e HO. i» Instead o f reducing the loop g a i n , the HO may c a n c e l the e f f e c t s o f exp(-2Tcjs)

by i n s e r t i n g a f a c t o r exp(2f(js) i . e . adopt a p r e d i c t i v e c o n t r o l s t r a t e g y over

the time span 2 f ^ s e c .

Whereas the f i r s t s t r a t e g y may be hampered by the type o f d e v i c e a p p l i e d t o gener-ate the commands C ( s ) , such as i n the case o f a t o g g l e s w i t c h , which o n l y a l l o w s o n - o f f - r e v e r s e commands, t h e second s t r a t e g y can o n l y be a p p l i e d s u c c e s s f u l l y when the HO has adequate knowledge about the a c t u a l v a l u e o f the time d e l a y s and the dynamics o f the m a n i p u l a t o r . I.e. when the HO has an a c c u r a t e i n t e r n a l r e p r e s e n -t a -t i o n (Veldhuyzen and S -t a s s e n , 1977) .

The i n a b i l i t y t o reduce the l o o p g a i n o r i n a c c u r a c i e s i n the i n t e r n a l model may p r e v e n t t h a t one o f these s t r a t e g i e s o r a s u i t a b l e mixture can be a p p l i e d . Then, the o n l y s t r a t e g y t h a t remains c o n s i s t s o f e f f e c t i v e l y c u t t i n g the c l o s e d - l o o p c o n t r o l i n t o s u c c e s s i v e open-loop c o n t r o l commands: the move-wait-see approach

(e.g. F e r r e l l , 1961; S t a r r , 1978).

Although the c o n t r o l i s segmented i n t o a sequence o f s u c c e s s i v e commands, t h i s s t r a t e g y s t i l l i m p l i e s the p r e d i c t i o n o f the system output f o r the commands t o be i s s u e d . I t a l s o s t r e s s e s the absence o f c o n t r o l commands d u r i n g the wait-phase, i n o r d e r t o p r e v e n t u n d e s i r e d system output t r a n s i t i o n s .

With r e s p e c t t o the v a r i a b l e time d e l a y s , as encountered i n space manipulator c o n t r o l , the HO w i l l almost be f o r c e d t o adopt the move and w a i t s t r a t e g y , as the l a c k o f knowledge about the a c t u a l v a l u e o f the time d e l a y p r e v e n t s the HO t o make adequate p r e d i c t i o n s over the time span o f t h e t o t a l d e l a y i n o r d e r t o m a i n t a i n c l o s e d - l o o p c o n t r o l .

MANIPULATOR DYNAMICS

In t h e d i r e c t d r i v e mode, the HO d i r e c t l y c o n t r o l s t h e i n d i v i d u a l j o i n t s o f t h e m a n i p u l a t o r . As i n t h i s mode a l l onboard c o n t r o l systems and software a r e bypassed, the c o n t r o l commands o n l y c o n s i s t o f o n - o f f - r e v e r s e s w i t c h i n g o f the power t o a s e l e c t e d j o i n t . In t h i s way, the c o n t r o l o f t h e manipulator becomes a "bang-bang"

type o f c o n t r o l .

A major l i m i t a t i o n i n the opération o f t h e space m a n i p u l a t o r i s t h e v a l u e o f the r e a c t i o n torques the manipulator may induce t o the space v e h i c l e i t i s mounted on. I t s low v a l u e , about 3 Nm output torque i n our a p p l i c a t i o n (Kampen and Van Swieten, 1 9 8 4 ) , i s an important f a c t o r i n the o v e r a l l System behaviour. I t causes that the dynamical behaviour h i g h l y dépends on the i n e r t i a o f the o b j e c t s t h a t are a t t a c h e d t o t h e m a n i p u l a t o r .

To i l l u s t r a t e the i n f l u e n c e o f t h e imposed low v a l u e o f the r e a c t i o n t o r q u e s , we c o n s i d e r a bang-bang c o n t r o l o f a s i n g l e - j o i n t m a n i p u l a t o r . F i g . 2 d e p i c t s the r e l a t i o n between the d u r a t i o n and d i r e c t i o n o f the i s s u e d commands v s . the a n g u l a r speed <f> of the manipulator.

F i g u r e 2

Command d u r a t i o n and d i r e c t i o n v s . a n g u l a r speed

As can_be observed, s w i t c h i n g on t h e power Uj_ r e s u l t s i n t o a l i n e a r l y i n c r e a s i n g speed <{>. The a n g u l a r accélération i s c o n s t a n t due t o the l i m i t e d r e a c t i o n t o r q u e s . Depending on the l e n g t h o f the time span t h e power i s switched on, t h e accéléra-t i o n may decrease accéléra-t o zéro, henee accéléra-the speed becomes c o n s accéléra-t a n accéléra-t . R e s e accéléra-t accéléra-t i n g o f accéléra-the power t o zéro causes a l i n e a r decrease o f the a n g u l a r speed. When two s u c c e s s i v e commands a r e i s s u e d , the e f f e c t o f the second command dépends on the s i g n o f the f i r s t command. A r e v e r s e d command i s o n l y e f f e c t i v e a f t e r n e a r - s i g n r e v e r s e o f the a n g u l a r speed; a non-reversed command i s immediately e f f e c t i v e . The a c t u a l v a l u e o f the a n g u l a r accélération i n thèse cases dépends on the c u r r e n t v a l u e o f the i n e r t i a o f t h e l o a d .

To i l l u s t r a t e t h e e f f e c t s o f t h i s l i m i t a t i o n d i f f e r e n t l y , F i g . 3 d e p i c t s the r e l a -t i o n be-tween -the r e q u i r e d d u r a -t i o n o f a s i n g l e command -t o r o -t a -t e -the j o i n -t over 0.02 r a d and the a c t u a l value o f the i n e r t i a o f the o b j e c t , a t t a c h e d t o the manip-u l a t o r . In omanip-ur a p p l i c a t i o n , t h i s r o t a t i o n corresponds t o a 10 cm displacement o f the end e f f e c t o r o f a s i n g l e j o i n t m a n i p u l a t o r o f l e n g t h 5 m. The dashed u n e s i n d i c a t e the o p e r a t i o n a l range o f the i n e r t i a .

T h i s f i g u r e shows t h a t when the m a n i p u l a t o r i s unloaded, the d u r a t i o n o f the com-mand s h o u l d be 2.5 seconds. Then, i t takes 5 seconds t o r o t a t e the arm over 0.02 r a d . F o r a f u l l y loaded manipulator, however, the r e q u i r e d d u r a t i o n o f the command i s 11.5 seconds, so t h a t the r o t a t i o n i s completed a f t e r 23 seconds.

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J.C. Ruitenbeek

4

J , , , ,

Figure 3

Command time vs. i n t e r t i a for Aé=0.02 rad and torque =3Nm

max

s may be clear from these data, the manipulator dynamics are highly non-Linear.

Apart from the sign and r e l a t i v e timing of the commands, these dynamics also

depend on the i n e r t i a of the attached object. Consequently, the HO should be well

aware of the actual v a l u é of the i n e r t i a i n order to g e n é r a t e appropriate commands.

Especially in the unloaded case, the timing of the commands i s c r i t i c a l l y .

In-appropriate timing of the commands may cause that the manipulator i n i t i a l l y

over-shoots the target. Reversed commands to prevent overshooting are ineffective, as

shown in F i g . 2.

EXPERIMENTS

Literature was surveyed (Ruitenbeek, 1984 a) in order to establish theoretically

whether the HO might be able to control the manipulator with the discussed

dynam-ics i n the presence of varying time delays. Although some o v e r a l l properties for

the command strategy, as be would be adopted in controlling this system, could be

deduced, no quantitative assessment of the HO performance could be made in advance.

This was mainly due to the specific non-linear properties of the space manipulator:

no comparable cases in l i t e r a t u r e , which could provide relevant data, were found,

whereas the data of non-comparable cases could not be generalized adequately to

our case.

Therefore, i t was decided to perform some explorative experiments to research HO

positioning control i n this p a r t i c u l a r case.

Within the available time budget, some experimental conditions were designed, in

which a subject had to position the end of a s i n g l e - j o i n t manipulator over a

distance of 10 cm onto a predefined target. The manipulator could be controlled by

means of the discussed bang-bang type of commands. The subject was instructed to

position the manipulator as fast as possible onto the target. The seven conditions

applied are l i s t e d in table 1. The selected v a l ú e s of the i n e r t i a are indicated in

F i g . 3 by means of a cross.

Table 1 : Expérimental c o n d i t i o n s

S y s t e m _{I n e r t i a (kg m )} 2 Time d e l a y (s)

S I 1125 0 1 3

S2 2250

0

-S3 10930 0

-

S21 means System 2 time delay 1 second

The dynamics o f the m a n i p u l a t o r were s i m u l a t e d a c c o r d i n g t o F i g . 4. The a c t u a l v a l u e s o f the s i m u l a t i o n model parameters were s e l e c t e d a c c o r d i n g t o F i g . 2 and 3 . The time d e l a y s were s i m u l a t e d d i g i t a l l y .

u

F i g u r e 4

S i m u l a t i o n model o f t h e s i n g l e - j o i n t m a n i p u l a t o r

The setup a p p l i e d c o n s i s t e d o f a j o y s t i c k and a v i d e o monitor. The j o y s t i c k was c o n f i g u r a t e d as a t o g g l e s w i t c h , a l l o w i n g o n l y on, o f f and r e v e r s e commands. Both the t a r g e t t o be reached and the (delayed) m a n i p u l a t o r p o s i t i o n were d i s p l a y e d as c l e a r l y d i s t i n c t h o r i z o n t a l b a r s . A d e t a i l e d d i s c u s s i o n o f the setup a p p l i e d can be found elsewhere (Ruitenbeek and Janssen, 1984). The s u b j e c t t r a i n e d a i l expéri-mental c o n d i t i o n s p r i o r t o the experiments.

Düring the experiments, each c o n d i t i o n was a p p l i e d between 17 and 53 times i n d i s t i n c t r u n s . The séquence o f t h e runs was s e l e c t e d randomly. P r i o r t o each r u n , the s u b j e c t was informed about t h e a c t u a l v a l u e o f t h e i n e r t i a and the time d e l a y . The (delayed) p o s i t i o n o f the m a n i p u l a t o r , the t a r g e t p o s i t i o n , t h e command s i g n a i s as i s s u e d and the time t o complète each p o s i t i o n i n g movement were r e c o r d e d f o r

o f f - l i n e a n a l y s i s .

RESULTS

As a f i r s t measure on HO c o n t r o l b e h a v i o u r , we c o n s i d e r e d the completion time, d e f i n e d as the time e l a p s e d between the change i n t h e t a r g e t p o s i t i o n and t h e time at which the m a n i p u l a t o r i s p o s i t i o n e d onto t a r g e t . T a b l e 2 l i s t s the mean and s t a n d a r d déviation o f the completion time f o r each c o n d i t i o n .

As can be observed, the c o m p l e t i o n time i n c r e a s e s both when the time d e l a y i n -c r e a s e s as w e l l as when t h e i n e r t i a i n -c r e a s e s . The l a t t e r -can be e x p l a i n e d r e a d i l y when F i g . 3 i s taken i n t o account. The f i r s t i s caused by the adopted move and w a i t s t r a t e g y . When the time d e l a y i n c r e a s e s , t h e wait-phase i n c r e a s e s , which g i v e s r i s e t o l e n g t h e n i n g o f the c o m p l e t i o n time.

As can be shown, when thèse data a r e c o r r e c t e d f o r b o t h e f f e c t s , t a k i n g the number of i s s u e d commands i n t o account, the différences between the completion times i n the v a r i o u s expérimental c o n d i t i o n s v a n i s h .

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Table

2 : Mean and standard déviation of the completion

time for each expérimental condition

I n e r t i a

(kg m

)

Time delay (s)

0 1 3

1125

2250

10930

7.5 (1.3)

9.3 (1.4)

18.9 (4.1)

10.0 (3.0)

13.3 (2.9)

15.9 (4.4)

28.7 (7.0)

As a second measure, the overshooting of the target was considered. A i l recorded

movements were tested whether the Output trajectory of the manipulator exceeded

the actual target p o s i t i o n . F i g . 5 présents the f r a c t i o n of movements i n which

overshoot occurs r e l a t i v e to the t o t a l number of movements i n each condition.

510 511 S13 S 20 S 21 S30 S33 y////////À y///////////A

7/////////A

Figure

5

Relative number of overshooting movements f o r each condition

The figure shows that the f r a c t i o n of overshooting movements increases when the

time delay i n the loop increases. However, overshooting also occurs i n the absence

of time delays (condition

S10, S20 and S30). Hence, thèse data indicate that the

time delay i s not the only cause f o r overshooting. As mentioned before,

inappro-p r i a t e timing of the commands may also cause i n i t i a l l y overshooting movements.

As the subject was instructed to p o s i t i o n the manipulator as f a s t as possible onto

target, a time optimal control strategy would require one single command. Near

optimal control would require some additional commands. To establish the strategy

as adopted by the subject, the d i s t r i b u t i o n of the number of commands as issued

over a i l conditions was calculated. F i g .

6 depicts the cumulative d i s t r i b u t i o n .

As can be observed from t h i s figure, already

76% of a i l positioning movements are

made with or within three commands. I t , therefore, can be concluded that the

subject adopted a (near) optimal control strategy.

100

F i g u r e

6

C u m u l a t i v e d i s t r i b u t i o n o f t h e number o f commands o v e r a l l c o n d i t i o n s

DISCUSSION

W i t h i n t h e l i m i t s o f t h e s e e x p e r i m e n t s , as b r i e f l y r e p o r t e d , we may conclude t h a t

the s u b j e c t i s w e l l a b l e t o c o n t r o l t h e s i n g l e - j o i n t m a n i p u l a t o r i n t h e presence

o f time d e l a y s , a t t h e c o s t , however, o f f r e q u e n t o v e r s h o o t i n g .

W i t h r e s p e c t t o t h e a p p l i c a t i o n o f t h e s e r e s u l t s t o t h e c o n t r o l o f t h e space

m a n i p u l a t o r , t h e f o l l o w i n g remarks can be made.

When t h e space m a n i p u l a t o r has t o be a l i g n e d w i t h a c e r t a i n o b j e c t , i n i t i a l o v e r

-s h o o t i n g o f t h e m a n i p u l a t o r -s h o u l d be a v o i d e d a-s t h i -s may damage t h e o b j e c t t o be

m a n i p u l a t e d . E s p e c i a l l y i n t h e case o f an unloaded m a n i p u l a t o r , t h i s r e s t r i c t i o n

i n t h e c o n t r o l o f t h e m a n i p u l a t o r by t h e HO may be h a r d t o be met, as t h e t i m i n g

o f t h e commands i s r a t h e r c r i t i c a l . D e s p i t e t h e f a c t t h a t t h e s u b j e c t was w e l l

t r a i n e d , o v e r s h o o t i n g o c c u r r e d f r e q u e n t l y . T h i s may i n d i c a t e t h a t t h e HO i n t e r n a l

r e p r e s e n t a t i o n o f t h e system t o be c o n t r o l l e d was i n a c c u r a t e .

As t h e d i r e c t d r i v e mode as c o n s i d e r e d i n t h i s paper i s o n l y e n t e r e d i n t h e case

o f m a l f u n c t i o n i n g o f t h e system, t h e t r a n s i t i o n o f HO c o n t r o l b e h a v i o u r from a

s u p e r v i s o r y c o n t r o l t a s k t o a manual c o n t r o l t a s k may y i e l d an even more worse

i n t e r n a l r e p r e s e n t a t i o n o f t h e a c t u a l system t o be c o n t r o l l e d . C o n s e q u e n t l y , HO

c o n t r o l b e h a v i o u r w i l l be a f f e c t e d n e g a t i v e l y .

I n g e n e r a l , t h e i n c r e a s e i n t h e c o m p l e x i t y o f t h e system t o be c o n t r o l l e d , i n

-c l u d i n g t h e t i m e v a r y i n g a s p e -c t s , i n -c r e a s e s t h e urge f o r an a -c -c u r a t e HO i n t e r n a l

r e p r e s e n t a t i o n o f t h e c o n t r o l l e d system. However, t h e i n c r e a s i n g c o m p l e x i t y

d e c r e a s e s HO a b i l i t y t o o b t a i n an a c c u r a t e i n t e r n a l r e p r e s e n t a t i o n .

To encompass t h e c o n f l i c t i n g n o t i o n s , we, t h e r e f o r e , suggest t o i n c l u d e a human

o p e r a t o r s u p p o r t system i n t h e d i r e c t d r i v e c o n t r o l mode o f t h e space m a n i p u l a t o r

i n o r d e r t o r e l i e f p a r t o f t h e c o n t r o l t a s k o f t h e HO.

The i n t e r f a c e d e s i g n o b j e c t i v e s h o u l d be d i r e c t e d t o a decrease i n t h e c o m p l e x i t y

o f t h e system under c o n t r o l i . e . t h e e f f e c t i v e system, as p e r c e i v e d by t h e HO,

s h o u l d be c o n s i d e r a b l y l e s s complex compared t o t h e r e a l system under c o n t r o l .

T h i s can be a c h i e v e d by t h e a p p l i c a t i o n o f p r e d i c t i v e d i s p l a y s ( S h e r i d a n ,

1984;

P e n n i n g t o n ,

1983; King-Smith, 1968) t o reduce t h e e f f e c t s o f t h e time d e l a y s and

by a s u i t a b l e p r e p r o c e s s i n g o f t h e i s s u e d commands t o s i m p l i f y t h e p e r c e i v e d

dynamics o f t h e m a n i p u l a t o r . The l a t t e r may i n c l u d e t h e a p p l i c a t i o n o f an a d a p t i v e

model o f t h e a c t u a l m a n i p u l a t o r dynamics i n t h e e a r t h - b a s e d s t a t i o n , i n o r d e r t o

reduce p o s i t i o n i n g c o n t r o l t o a low o r d e r c o n t r o l t a s k .

220

J.C. Ruitenbeek

V a r i o u s a l t e r n a t i v e s t o improve HO c o n t r o l performance i n the d i r e c t d r i v e mode, a l o n g the i n d i c a t e d l i n e s , w i l l be i n v e s t i g a t e d i n f u t u r e r e s e a r c h .

ACKNOWLEDGEMENT

P a r t o f t h i s r e s e a r c h was sponsored by the N e t h e r l a n d s O r g a n i z a t i o n f o r t h e Advancement o f Pure Research (ZWO).

The r e p o r t e d r e s e a r c h was performed i n response t o an i n f o r m a l r e q u e s t o f Fokker Space d i v i s i o n , S c h i p h o l , The N e t h e r l a n d s .

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Kampen, S., and A.CM. van Swieten, C o n t r o l l o o p s w i t h human o p e r a t o r s : the r o b o t i c arm case, Fokker, TR-R-84-CHD-131, 1984.

KingSmith, E.A., P r e d i c t i v e compensation o f manual c o n t r o l system.with t r a n s -m i s s i o n d e l a y , P r o c . Ann. Conf. Eng. Med. and B i o l . , V o l . 10, 1968.

Lacombe, J.L., and G. Berger, In-space assembly and maintenance o f unmanned space-c r a f t , IFAC Automatispace-c space-c o n t r o l i n spaspace-ce, 477-488, 1982.

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Ruitenbeek, J.C., and R.J. Janssen, Computer c o n t r o l l e d m a n i p u l a t o r / d i s p l a y system f o r human movement s t u d i e s , Med. and B i o l . Eng. and Comp., 22, 304-308, 1984. S h e r i d a n , T.B., Review o f t e l e o p e r a t o r r e s e a r c h , P r o c . 20th Ann. Conf. Manual C o n t r o l , 361-365, 1984.

S t a r r , G.P., A comparison o f c o n t r o l modes f o r time d e l a y e d m a n i p u l a t i o n , Ph.D. t h e s i s , S t a n f o r d Univ., 1978.

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Veldhuyzen, W., and H.G. S t a s s e n , The i n t e r n a l model concept. An a p p l i c a t i o n t o modeling human c o n t r o l o f l a r g e s h i p s , Hum. F a c t . , V o l . 19, no. 4, 367-380, 1977.