Ficure 2. Control panel with front cover removed.

the rotatory part of the stabilization unit. To
prevent damage to the system, limit switches
are secured to each end of the integrator ball
carriage. The switches de-energize the mag-
netic clutch in the control system when the
ball carriage approaches the limit of its vertical
displacement. A zero switch is also located on
the integrator. The arm of this microswitch
is activated by a cam fastened to the end of
the drive shaft connecting the turntable and
the control unit.

Control System

The control unit is shown in Figure 2. The
unit is activated by a toggle switch on the
control panel which starts two 1/70 hp shaded
pole motors,* one for CW and the other for
CCW rotation of the drive shaft.

5 Dayton 50 rpm gear motors, 4 in. Ib. torque full-load
iytor & rq!
amps 0.63,

Each motor is coupled to the output shaft
of a small ball-and-disc integrator,’ thereby
driving the shafts at constant rates. The shafts,
in turn, drive the ball and the position of each
ball carriage is adjusted and set so that the
integrator discs are rotated at a particular rate
(in this case, approximately 13 rpm) deter-
mined during calibration procedures. These
small mechanical integrators were used in lieu
of a variable speed motor to. provide a readily
adjustable means of calibrating output from
the control unit to the acceleration dials on
the control panel.

The disc of each of the two small integrators
noted above is coupled directly to the disc
of a companion large integrator.’ Thus, the
discs of the latter two (large) integrators turn

© Tracking computer assembly no. R5257677.
"Tracking computer assembly no, 824118,

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TURNTABLE VELOCITY IN RPM

. s 0 s 2 2

ACCELERATION DIAL SETTINGS

ors

TURNTABLE VELOCITY IN RPM

70 40 o 20 0 1

TIME IN SECONDS

Ficune 7, Performance data from the turntable. Each point is based on a mean of 3 readings, Upper graph: time
of stimulus (37-24) was held constant for each rate of angular acceleration tested. Thus, after every 3
readings, the acceleration dial. setting was changed. Lower graph: table performance at low (0.50,
0.75, and 1.00°/sec*) rates of angular accele-ation.

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LOCK
ccw ACCEL.

APPROX,
& 13 RPM

50 RPM

APPROX.
fm 13 RPM

MAGNETIC
CLUTCH

OUTPUT SHAFT

VARIABLE O TO 30 RPM
cw OR CCW

MAGNETIC
CLUTCH

MECHANICAL FLOW DIAGRAM

Ficuae 3. Mechanical flow diagram.

at constant rates (approximately 13 rpm) as
determined by the disc speed of the small
integrators.

A shaft couples each of the two large in-
tegrator ball carriages to its respective accelera-
tion dial on the control panel (see Figure 3).
Changes in the dials, then, vary the position of
the ball carrriages and, thereby, the output
speed of the integrators. This output is cou-
pled, through gears, to a magnetic clutch (one
for each integrator) which is energized and
controlled by a Libel-Flarsheim Nuclear Timer
(Model III). When de-energized, the output
shafts of the clutches are held against a brake
(although the input shafts continue to turn).
The clutch outputs (from both the CW and
CCW drives) are coupled through a single
planetary gear differential to the turntable
drive shaft. A schematic diagram of the cir-
cuitry involved in control of the turntable ap-
pears in Figure 4.

Control Panel

The control panel is depicted in Figure 5.
At the extreme left of the figure are located
the acceleration timer and the toggle switch,
which in the “on” position starts the two shaded
pole motors of the control unit, the two timer
motors, and the drive motor in the turntable
room. The acceleration timer controls the
duration of the acceleration only. The decel-
eration time is determined directly by the rate
of deceleration.

At the extreme right of the figure, the auto-
matic start button and the run timer are evi-
dent. The latter determines the period of con-
stant velocity before deceleration begins. The
start button initiates a complete cycle of activ-
ity, ie. from acceleration through constant ve-
locity through deceleration to the stop position.

A milliameter, connected to the output of
the tachgenerator, is located in the center of
the control unit and is calibrated to provide the


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Ficunn 6. Tach-generator (upper tracing of each set) and accelerometer (lower tracing of each set) recordings for

4 rates of angular acceleration.

manual button allows the operator to have
complete control over the accel-decel cycle
but also requires changes on the acceleration
toggle switch when it is desired to decelerate
the turntable. The rates of acceleration and
deceleration are still determined by settings of
the CW and the CCW dials.

Calibration

Three types of data were obtained relevant
to the performance characteristics of the turn-
table: (a) accelerometer recordings, (b) tach-
generator recordings, and (c) measurements
made by an electronic counter of the time re-
quired for a complete revolution of the turn-
table following a given acceleration.

The tachgenerator recordings indicate linear-
ity of acceleration and deceleration responses
in both the CW and CCW directions (see Fig-
ure 6). Recordings from the accelerometer

indicate that little variation in the acceleration
rate and in the rate of turning at terminal
velocity occurred. The maximum noise range
recorded from the accelerometer during motion
of the turntable (including vibration) was less
than 1.5°/sec’ at any given instant. These
statements hold for all acceleration rates up
through 25°/sec’ and for all terminal velocities
less than 25 rpm.

Other data were obtained with a Hewlett-
Packard Electronic Counter (Model 5215).
Under these conditions, the acceleration counter
dial was set at a given value (e.g., at 5 to give
a nominal acceleration rate of 5°/sec’). Accel-
eration time was then varied and the number
of seconds required for a complete revolution
of the turntable was obtained from the elec-
tronic counter during the period of constant
velocity following the acceleration. Three
readings for each acceleration rate-duration
combination were averaged for the data points

_7T-—



AM-64-15

DESIGN AND PERFORMANCE CHARACTERISTICS
OF A MECHANICALLY DRIVEN
VESTIBULAR STIMULATOR

William E, Collins, Ph.D
Psychology Laboratories

and

Harlie W. Huffman
Research Engineering Service

Approved by Released by
Stamtey Romehir vA uf While
Srantey R, Monten, M.D. M. S. Warre, M.D.

Dinscton, CARI Fevenat, Ain SURGEON

FEDERAL AVIATION AGENCY
Office of Aviation Medicine
Civil Aeromedical Research Institute
Oklahoma City, Oklahoma





in Figure 7. These data indicate that: (a) up
to 25 rpm there is a linear relationship between
turntable velocity and settings of the accelera-
tion dial. Above this level, velocity tends to
fall below expected values. (b) the dial set-
tings are very closely calibrated to acceleration
rates. That is, for both CW and CCW direc-
tions, the rate of acceleration is almost exactly
that indicated by the numbers on the corre-
sponding counter dial setting. Differences are
less than 0.1°/sec*.

TABLE 1

Maximum variability in angular acceleration
rates as a result of re-setting acceleration dials.
Several durations of the acceleration stimulus
were examined for each rate. Each rate-
duration test consisted of 10 independent set-
tings of the acceleration dials.

Maximum % + Maximum

Acceleration No. of rate- Variability Variability is
Rate (°/sec*) durations tested (+ °/sec*) of rate
0.25 10 02 8.0
0.50 10 OL 10
1.00 10 01 1.0
5.00 9 05, 10
10.00 4 07 0.7
15.00 2 Boa 0.7
20.00 2 13 0.7
25.00 2 60 2.4

Data were also obtained to provide an indi-
cation of the reliability of accelerations ‘with
re-settings of the counter dial. Two to 10

durations for each of 8 rates of acceleration
were examined. For each rate-duration com-
bination, 10 re-settings were made and read-
ings were obtained from the counter at ter-
minal velocity. These values were translated
into rates of angular acceleration and the maxi-
mum range (°/sec*) for each rate appears in
Table 1. At 0.25°/sec*, maximum variability is
only + 0.02°/sec’. From 0.50°/sec* through
20°/sec’ variability ranges from + 0.01 to
+ 0.13°/sec*, but does not exceed + 1.0% of
the rate of acceleration. Above 20°/sec’ vari-
ability increases markedly and reaches levels
which preclude the use of those higher accel-
eration rates if precise control of the stimulus
is required from trial-to-trial. For all rates of
acceleration, stimulus durations of 3 sec or less
resulted in somewhat wider divergences than
those depicted in Table 1.

CONCLUSION

A mechanical-drive angular accelaration de-
vice was designed and constructed for use as
a vestibular stimulator, Calibration data ob-
tained with a tachgenerator, an angular accel-
erometer, and an electronic counter indicate
that: (a) accelerations at all rates below
25°/sec’ and to all terminal velocities less than
25 rpm are linear; (b) maximum trial-to-trial
variability between 0.25°/sec’ and 20°/sec*
does not exceed + 0.02°/sec* or + 1.0% of the
acceleration rate, whichever is larger. Thus,
the stimulator may be used for a large number
of vestibular experiments where rates of accel-
eration and terminal velocities are not required
to exceed 20°/sec’ and 25 rpm, respectively.



Ficure 5. View of control panel.

operator with a constant indication of the
rotatory velocity of the turntable. A small
toggle switch beneath the meter permits con-
version from a full-scale deflection equal to
10 rpm to a full-scale deflection equal to 30
rpm. A Cramer stop-clock’ is mounted below
the toggle switch and permits a ready means
of monitoring the terminal velocity reached by
the turntable. The clock reads in hundredths-
of-a-second and is started and stopped by a
magnetic switch on the turntable.

Multi-turn counter dials’ are positioned on
each side of the ammeter, one for setting CW,
and the other for CCW, acceleration rates.
Lock screws below the panel dials secure the
dials to their adjusted positions. Between the
CCW dial and the ammeter are located a toggle
switch for determining direction of acceleration

® Model no. 691 H - 60S.
* E, F, Johnson part no, 116-208-X.

and a jack for plugging in an electronic counter.
A “reset” button for the counter is set just
below the jack. With the acceleration toggle
switch in the CW position, a CW acceleration
is initiated by depressing the “start” button.
The rate of acceleration is determined by the
position of the CW acceleration dial, and its
duration by the setting on the acceleration
timer (activated by closing of the zero switch
on the turntable). A: period of constant ve-
locity (or none, if so desired) follows and is
of a duration determined by settings on the
run timer. The latter then, by means of relays,
actuates the deceleration. The rate of decelera-
tion, in this case, is determined by the CCW
dial settings and its duration by the time re-
quired to bring the turntable to a complete
stop.

Between the ammeter and the CW dial are
located a manual button and an auxiliary jack
for tachometer recordings when desired. The


Ficure 1. Front view of the rotatory device with side panels removed. A portion of the drive shaft leading back
into the control room is evident behind the motor.

-~2-


DESIGN AND PERFORMANCE CHARACTERISTICS OF A
MECHANICALLY DRIVEN VESTIBULAR STIMULATOR

William E. Collins, Ph.D, and Harlie W. Huffman

In order to determine basic response char-
acteristics of mammalian vestibular systems, the
systems so important for spatial orientation, a
device to provide programs of controlled angu-
lar accelerations about the vertical axis was
required. The small rotation device described
in the present report was designed to meet this
need.

Rotatory Structure

The basic structure of the turntable is a
modified section of a surplus K-4 navigational
computer previously used in a B-47 aircraft.
The case holding the stabilization unit’ from
the computer was inverted and legs added to
form the turntable base. Thus, the slip ring
system of the unit is at the bottom of the struc-
ture, and the outer gimbal and its ball bearings
at the top. To the latter, the formica-covered,
wooden table-top, 4 feet in diameter, was
added. The table-top actually rests on two
additional circular wooden bases, 1 and 2 feet
in diameter, respectively, to provide additional
support. A Statham unbonded strain gage
angular accelerometer* with (a) a liquid rotor,
(b) a range of + 1.5 rad/sec’, (c) infinite
resolution, and (d) a 4 cps natural frequency,
is mounted within the stabilization unit (see
Figure 1).

The size and other characteristics of the
rotator super-structure are such that its most
efficent use is limited to relatively light weights
(less than 50 Ib.) if the subjects are to be
positioned away from the center of rotation.
Considerably more weight (up to 150 Ib.) can
be tolerated without affecting characteristics

1 National Cash Register Company, part no. 667126.
? Model no. AA 17-1.5-350.

of the acceleratory stimulus for a wide range
of values, if the weight is positioned directly
over the center of rotation.

Drive System

The drive system consists of 2 major com-
ponents:

1) Bodine Type NC1-34RH constant speed
motor’; 1/15 hp with 86.0 rpm output; 29 in. Ib.
torque rating.

2) Ball-and-disc integrator* with overall di-
mensions of 8” X 6 3/4” X 6”. The disc-to-
cylinder ratio can be varied from 1:4 clockwise,
(CW), through 1:0, to 1:4 counterclockwise
(CCW) by turning the ball-positioning control
wheel approximately 4.1 times.

The Bodine motor drives the integrator disc
at 86.0 rpm while the control system, to be
described below, displaces the ball carriage of
the integrator from its center position by
values determined at the control panel. The
output shaft of the integrator is activated by
the rotary motion of the ball. The lacter is
immobile when positioned at the center of the
disc. As the ball is displaced from center, it
revolves at rates determined by the speed of
the disc and the radial position of the ball on
the disc. Displacement of the ball is accom-
plished by means of a gear-driven shaft extend-
ing from the control unit to the integrator.

Output from the integrator is translated into
motion of the turntable by means of a short,
linking shaft. The latter is attached, at one
end, to the integrator. At the other end, a
precision-ground, rubber-coated, steel disc, 1”
in diameter, is in spring-loaded contact with

* Bodine catalog no. B 3810-20 H.
*C & H Co, (Pasadena, California) stock no. BDI -107.

-1-