A twin-grip control yoke was designed as an ergonomic case study that allows dual axis control inputs, both axes being rotational. Inputs are effected by rotating the grips. How the handles were designed with respect to their shape and size and how the angular range of the control yoke in both rotational axes was evaluated. The control yoke which requires two-hand operation was tested to determine its operating range. The intention of this investigation was to find out the optimal form of the control yoke and the maximum permissible range in both rotating axes. In these experiments controls had no spring resistance

Gaertner, K. P.

English

NASA Technical Reports Server

_ mmmh..._
|, N79- 15609
THE DETERMINATION OF THE OPERATING RANGE OF A TWIN-GRIP
CONTROL YOKE THROUGH BIOMECHANICAL MEANS
by Klaus-PeterG_irtner
Forschungslmtitutfur Anthropotechnik(FAT)
(Researchinstitute for HumanEngineering) ....
Meckenhelm, F.R. Germany
Summary
A twln-grlp control yoke was designedas an ergonomiccasestudy that allows
dual axis control inputs, both axes being rotational. Inputsare effected by rotating i
the grips. It will be reportedhow the handleswere designedwith respectto their I
shapeand size and how the angular range of the control yoke in both rotational
axes was evaluated. 1
The hand grip design is basedon the anthropometrlcdata of the hand. Themain i
parametersfor the layout are the breadth of the hand, the grip circumference,and 1
_ the thumb length. The steeringtask for which the control yoke is designedrequires
that the grip shapetakes into account task relevant grip characteristics,suchas a
!: rest for hand and thumbas well as a thumboperatedswitch button. One of the design
requirementsis the full use of the available motionrange for steering inputs in the "_, A
two rotational axes which is limited by the humanarm-hand-system. !_
Using EMG activities, which were measuredat the forearm, the permissible
pitch and roll anglesof the control yoke were evaluated to be + 30°. The llmlta- !i
_ tlon stemsexclusively from the combinedlimits of the radial and"ulnar rangesof
_ abductionof the humanwrist joint. It shouldbe pointed out that in this studythe
I control range was not limited by musclefatigue which is also measurablewith EMG
but rather by EMG levels which avoid painful loadson tendon and ligament struc-
i tures. The experimentalseriesis basedon an isotonic rotation in both axes. EMG
_ activities were only measurableunderextreme angles of deflection. If the operator
i has to deflect the control element from its neutral position againsta springresistance
a further reductionof the operational rangewill be expected.
[ Introduction
i In this study, a control yoke which requirestwo-hand operationwas tested to
_: determine its operating ranges. The intention of this investigationwas to find out
the optimal form of the control yoke and the maximumpermissibleoperating range in
both rotating axes. In theseexperimentscontrolshad no springresistance.Future
studieswill involve controlswlth springresistance.
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The control yoke has two rotating axes. Vehicle direction changes to the left
or right are accomplished bY turning the yoke as with a steering wheel of an auto-
mobile, called here roll motion. Vertical vehicle direction changes are accomplished
by rotating the yoke handles towards or away from the operator which will be called
pitch motion•
• pitchaxis
neutralposition radialabduction ulnarabduction _,
-
Figure 1 : Influence of roll axis rotation of a twin grip control yoke
on radial and ulnar abduction angles of both hands
In the left of the upper row of figure I is to be seen the neutral position and
in the middle and right pictures of this row the extreme excursion during the pitch
movement. These two pictures illustrate the biomechanical position limits of the hand
when rotating the yoke towards and away from the operator. The pitch motion of the
hand towards the operator is accomplished by radial abduction ; pitch motion away
!ram the operator is accomplished by ulnar abduction• Similar hand positions are shown
0 • • min the lower row of pictures with a 45 roll angle position coupled with neutral, ra
dlal and ulnar pitch abduction.
With 0° pitch angle and roll motion to the right, radial pre-abduction will
have ocoured in the right hand and some ulnar pre-abduction in the left hand, there-
by restricting the available amount of further abduction for pitch command purposes.
It can be shown that with increases in roll motion to the right pre-abduction will
increase until blomechanical limitations make pitch commandsimpossible or very
difficult. Similar pre-abduction occurs with left roll motions.
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1979007417-290
ORIGINAL PAGE IS
OF POOR QUALITy
Biomechanicalcomlderatlon of the arm-hand-system
Figure 2 illustrates the abductionrange of the hand. In the left part of the
picture there is showna hand in two positionsholding a stick. The hand rotates by
an assumedaxis of rotation throughthe wrist joint, as indicated by a small circle.
Thishand, turned 8 to 12°, correspondsto the normalrestingposition of the human
hand.
If the prolongedcenter llne of the forearm is consideredas the reference llne
a natural pre-abducfion of the hand can be noticed. The values given in the
literature [e.g. 11 for the ulnar and radial abductionof the hand are basedon this
resting position. There is obviouslyno relationshipbetween the angle at which the 1
hand is in the natural restingpositionand the maximumrange of abduction of the l
5th to 95th percentile. On the right part of the figure the angle3range_is shownfor
_ the radial abductionwith 35° and for the ulnar abduction with measuredfrom i
_: the restingpositionof the hand. This abductionangle of 88° is equivalent to the
!: 90th percentile.
ulnar abduction radial abduction
i
I I \wrist joint as/ I J
I I c.tero, I Irotation _
naturalhandposition total rangeof hand °
: movement
i (90th percentile)
i Figure 2 • Abduction range of the hand
i If 9° is subtracted, which correspondsto the natural pre-abduction from
_: the range of the ulnar abduction, a value of 44° both for the ulnar and for the
_,
_ radial angular rangewill be obtained. This considerationis importantfor practical
i applicationsin so far as there shouldbe the sameangular range in radial as in ulnardirection for the pitch movement, i.e. the up and downmaneuverof the vehicle.If the total abductionability of the hand is usedfor turning a control yoke, two
299 :"_
1979007417-291
? :
t
!I
! rotational axes can be selected. Thesetwo rotational axes of the control yoke cross
i in the steeringcolumn. In figure 3 the case is shownwhere the rotational axis of
! the wrist joint is equal to the axis of the control element. Consequently,there is
t hardly any motionof the forearm. The total range of abduction is usedas pitch angle
I range, that is for radial abductionof 35° and for ulnar abduction of 53°, measured
from the restingposition. There is a light disadvantageof forearmmovementwhen
i the rotational axis of the wrist joint doesnot correspondwith the rotational axis *''_
i of the hand grip for small and large hands. This effect doesnot occur if the rotational
shoulder joint
/ '
\ radial abduction _ f/ _)
center of rotGtion far the wrist C..
joint and control yoke iul _arabduction
a) rotational axis through the wrist joint
total abduction range
shoulder joint is 88 ° (90 th percentile)
T"---¢/,
ulnar abduction_. /
rial abduction
b) rotational axis through the volar hand
i Figure 3 : The range of forearmmotionfor different
i rotational axes of the control yoke O_GI__/_b I)/_G_ _
: 300
,w
1979007417-292
axis of the hand grip correspondswith the center of the hand volar or palm as shown
in the picture below. A pronounced up and down movement of the forearm which re-
sults during ulnar and radial abduction i_ ;ollustrated in figure 3. Though, radial andulnar abductio come to their limits at 8 for th maximal abduction of the 90th
percentile, the maneuvering pitch angle range only reaches 68° , e.g. 27° for radial
and 41 for ulnar abductions from the resting position.
A nthropometrlcal Design of the control grip
Figure 4 shows the c_)erator sitting in front of the control console. The angle
of inclination with respect to the body will be selected in a way so that the arm-
hand-system of a 50th percentile operator measured from the shoulder reference point
is in a position to turn the control yoke with* the same angular values in ulnar and
radial direction. A control yoke is shown, the rotational axis of which goes through
the volar hand.
Figure 4 : Suggested anthropometric parameters for seated q_erator console
301
_ ,,_
1979007417-293
The control task for which the control yoke was designedrequires a specially
J shapedgrip which takes into account task relevant grip characteristics, suchas a
hand and a thumbrest and a switch button that is thumboperated (figure 5). The
designof the grip was basedon the 95th percentile hand. The dlmemion A of the
palm was basedon hand width. The hand fits between the hand rest and the top
sectionof the grip. The fingersspan the grip slantwiseto the longitudinalaxis of
the grip and not in parallel fashionas they would with a cone.
gripdiameter switchbutton
hand
handrest
Figure 5 : Anthropometricparametersfor d_s;gn|nga handgrip
So long as the switch button is not used, the operator can smoothlymove his
handswith the control yoke and follows its motions.Under these working conditions
the hand of the 95th percentile man is restingon the hand supportand the thumbis
on its thumbrest. Smallerhandssuchas the 50th or 5th percentile handscan use
either the hand rest or the thumbrest as a basicworking positionduring the control
task.
top section concave thumb
/of the grip deepening "-_
i thumb resty i
i"
,,_ grip diameter i
_r rest
Figure 6 : Anthropometric parameters for designinga hondgrip
302
1979007417-294
The basic dlmemlomof the grip are the dimemiom of an ideal conical bar
which was first usedby Hennlng. Hennlngsuggestsan increasein radius by 5 mm
for each 80 mm in length. The grip is finger parallel and the forearmaxis is ver-
t|col to the cone axis.The circumference is about 150 mm for o 95th percentile hand.
As can be seen from the left picture of figure 6 the finger tips touch lightly the
opposite part of the hand and the thumb rests on partsof the pointing finger. If the
cone is clmed the fingersare inclined to the longitudinal axis of the cone. A grip ......
was designedusing finger indentation and an appropriatedeviation of the coneshape
m may be seen in figure 5.
With this grip the finger tips oft he 95th percentile hand are at small but
constantdistancefrom the opposite port of the hand. For the smallerhands like
or 5th percentile handsthis distance becomeslarger but still guarantiesa good
form clasum. With this designa larger thumbrest was used which results in a sepa-
rationof the possibletouch between the thumband the fingers. The location of a
switch button in the grip head was basedon the thumb length of the 50th percentile
hand. Thumbswhich are longer and shorterthan 50th percentile are still in position
to operate the switch button by use of lower or upperportsof the thumbrespec=
tively.A concavedepressionin the top section of the grip allows sufficient motion
for larger thumbswhen pressingthe switch.
Biomechanicaldeterminationof the operatingrange of the twln-grip contro! yoke
t
For the layout of a control yoke both enthropometricand biomechenic ClUol-
itles of the humanhand-arm systemmust be comidered. A method is prclx_ed In this
paper which permitsa determination of a biomechanical range on the basisof sur-
face electromyogrophyactivities which are involved in movementand force exertion.
At the limits of movement,rather high EMG activity occurstogether with suchcon-
sequencmas muscle, tendon, or ligament strain and/or pal'n.
For EMG measurements,ubjectswere lmtructed to grip the yoke lightly with
both handsso that no foremm muscleswere contracted. For each selected roll angle
positionof the yoke, the control was then slowly moved through both pitch direc-
tions. Raw EMG signalswere processedwith a double wave rectifier end o special
averaging filter [ 2, 3, 4_ .
EMG activity for the right hand in o numberof different roll angle positions
are illustrated in figure 7 r_ a tunction of pitch angles far roll angles in the right
direction. The curves Illustratedore only far EMG values recordedduring increasing
pitch angles as these representthe wcnt case for control evaluation.
The upperEMG value of "1" unit was arbitrarily given to the EMG level oh..
to!ned when wrist joint pain was experiencedafter repeatedly holding an angle po-
sition far a few seconds.The maximumvalue of the curves (approx..75 units) is
obtainedat the maximumpitch angle which wasmeasured. The maximumpitch angle
303
1979007417-295
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,Will_I _I('d'_n_l_)' i °lli_°a
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Figure 7 : F.J_Goctivlt!es of.rodiol and .ulnarobductarsof o right hond with
90th percenhle wmr movementronge os o function of pitch angle
far variousroll angles. Roll movementis in right
l
,1('_'-_1 _1r L_
I"" "t "'-/,t_/ / _
_ .so ao 40 ,at ._o
"Idle" "_"
Figure 8 z EMG actI,,l_iesof rodlotondulnarobductarsof o right handwith i
90111percentile wrist movementrangeas o function of pitch angle
for variousroll angles.Rollmovementis in left
304
k..... _ ......................... ....._ ._,ti
1979007417-296
i Jl L __ I iii i
............ I,iII,
measuredwas selected after experimentally determiningthe maximumpitch angle at
which no wrist pain build-up occuredduring fairly long measuringsessions.For any
given pitch angle there is a tendencyfor Ere-abductlon to be larger with larger con..
stont roll angles, it can Le seen that at 0v roll angle the full range of possiblewlrst
movementof the subject con be usedfor pitch commandsin both directions because
there is no pre-abdeotion. At60 ° roll angle to the right, radial pre-abduotion is so
lar§e that no pitch angle movementin this "pull up*' direction is possible. In the
rlghs side of the figure the EMG curv_ofor ulnar abduction i.e. in the "pushdown"
direction ;s illustrated. The 45° and 60 roll angle permit relatively large "pull up"
commandsalthoughthe curvesdo not rise as high as thosefor radial abduction on
h' ithe left side of the figure. The reasonfor t ,s is that ulnar abduction of the left
h_r_cl,which is not illustrated, reachesa limit at thesepitch anglesbefore the right
hand, thereby preventing further ulnar abduction of the right herod.Of course, re-
leaseof the control by the left handwould have permitted further movement.
EMG values for ulnar and radial abduction of ._e right hand is shownin fig-
ure 8 for left roll at variousroll angles. As con be seen on the left side of the
figure for left roll, right hand "pule-up" pitch commandsor radial abductionmove..
ment is so severel_ limited by radial pre-abduction of the left hand in oil roll angle
pmitlom except 0 that further movementsore not pmslble. The range of ulnar ab-
duotion or "push=down"commandsillustrated on the right side of the figure is slightly
reducedby ulnar pre-abduction thereby allowing comiderable movementbefore the
ulnar abduction limits are reached, i
Discussionof the EMG-measumments i
In designing a range far this control device the following points are the mast
impc_rtontto consider. !. It shouldpermit the largest passiblepitch angle in both
directiom far each of the largest passibleroll angles f_ subjectswith 5th p_rcentile •
wrist movementranges. 2. Only lower levels of EMG activity should occur mostof
the time during control eperotiom. Moderate EMG activity levels shouldoccur very
briefly and no high EMG activity at all. ,
As con be noticed in the figure 7 and 8 these requirementscar_be sotlsfied
for the subject tested with roll and pitch angle rangesof approx. + 30° each (at
which no mare than 0,5 units of F.MG activity are reached). It sh'ouldbe pointed
out that in this study the control range was not determinedby musclefatigue limits
which are also measurablewith EMG but rather by EMG levels which ovoid pain-.
ful loads on tendon and ligamentstructures.The F.MG measuringmethodpresented
proved to be a valuable objective aid for determiningan advantageouscontrolrange.
305
1979007417-297
o" _eferences
!
[ 1] Damon, A., H.W. Stoudt, R.A. McFarland. 1966. The HumanBody in
EquipmentDesign• Havard UniversltyPress, Cambridge.
[2] Kreifeldt, J.G. 1971. Signal versusnoisecharacteristicsOf filtered EMG
used as a control source. IEEETram. Blamed. Eng. 18.. 16- 22. _ f_
[ 3] Rau, G. 1973. Ein verbessertesMe_ystem zur quantltatlven Oberfl_dchen-
_ myographle(An improved.measuringsystemfor quantification of surface i: electromyography).AnthropotechnlscheMitteilung No. 2/73. Forschungs-
_ instltut fur Anthropotechmk,BuschstraSe,5309 Meckenhelm, Germany.
_r_.} + _ [ 4] Rau, G. 1974. ImprovedEMG quantification throughsuppressionof skin _
i
_ impedanceinfluences. In : RichardC. Nelson and ChaunceyA. Morehouse !
r
(eds.) Biomechanlcs IV, pp. 322- 327. University Park Press,Baltimore.
J
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The determination of the operating range of a twin-grip control yoke through biomechanical means

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