Breadboard models of single and dual motor drives for the shutter, claw and magazine of a space camera system were designed and tested. The single motor technique utilizes a single electronically commutated motor to drive the claw and shutter without resorting to a solenoid actuated clutch for pulse operation. Shutter speed is established by a combination of the cinemode speed and the opening of the conventional DAC two piece shutter. Pulse mode operation is obtained by applying power at a fixed clock rate and removing power at an appropriate point in the mechanical cycle such that the motor comes to rest by system friction. The dual motor approach utilizes a stepper motor to drive the shutter and an electronically commutated dc motor to drive the claw and magazine functions. The motors are synchronized electronically

Sharpsteen, J. T.

Solheim, C. D.

Stoap, L. J.

English

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Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19760018450 2020-03-22T14:19:01+00:00Z
NASA M
Al 7
ADDENDUM
TO
FINAL REPORT
DEVELOPMENT OF A DRIVE SYSTEM
FOR A SEQUENTIAL SPACE CAMERA
tr4ASA-Ck-147759)	 DcEVELOPIENT OF	 A DRIVE N76-25538
SYSTEM FOR A	 SEQUENTIAL SPACE CAMERA
	 FINAL
REPi-;--T	 (PE f".KIN-ELMEk	 CIPP.)	 16	 P	 HC	 $3.50
CSCL	 131 UNCLAS
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PERKIN[-ELMER
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\ ^[ . ADDENDUM
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( FIB REPORT
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</	 a ^ DEVELOPMENT  0 A DRIVE SYSTEM 
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\ Fn A SEQUENTIAL  S AE CAMERA
\ ^
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a Jae T. Sap to n, Curtis  D. Solh i ,^
Louis  J. Sto p
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\ Prepared for / N TO AL AERONAUTICS AND  SP C ADMINISTRATION
\	 \ !^ Johnson  Spce Center 
( Hutn, Texas 	 770B
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TABLE OF CONTENTS
Page
1. GENERAL 1
2. SINGLE MOTOR APPROACH 1
3. TEST PARAMETERS 1
4. TEST CONFIGURATION 1
5. TEST CONDITIONS 4
6. TEST PROCEDURE 4
6.1
	
Shutter Speed - Frame to Frame 4
6.2	 Shutter Speed - Across the Frame (Banding Effect) 4
6.3
	 Maximum Frame Rate - Pulse Mode 4
6.4	 Start-up Time 4
6.5
	
Current 4
7. TEST RESULTS 5
8. DUAL MOTOR APPROACH 8
J. i
st
1.	 GENERAL
At the time the final report was submitted, a short time period remained until
- the scheduled completion of the study. 	 To make the best use of this time,
Perkin-Elmer Aerospace Division (ASD) felt that only one of the two motor drive
techniques should receive a concentrated test effort in the breadboard configu-
ration.	 Based on a study of the test results to date, the since electronically
commutated motor drive scheme had shown the most promise and was therefore
selected for further testing. 	 To provide further backup for this decision, a
synopsis of the test effort to date on the dual motor approach is included in
Paragraph 8 of this Addendum.
2.	 SINGLE MOTOR APPROACH
This technique utilizes a single electronically commutated motor to drive the
claw and shutter without resorting to a solenoid actuated clutch for pulse
operation.	 Shutter speed is established by a combination of the cinemode speed
and the opening of the conventional DAC two piece shutter. 	 Pulse mode opera-
tion is obtained by applying power at a fixed clock rate and removing power at
an appropriate point in the mechanical cycle such that the motor comes to rest
by system friction.	 The following paragraphs describe the additional tests
that were made, and discuss the results.
3. TEST-PARAMETERS
Performance parameters which will most likely be influenced by a commutated
motor drive scheme were selected for measurement. These parameters are listed
below:
a. Shutter Speed - Frame to frame
b. Shutter Speed - Across the frame (banding effect)
C. Maximum Frame Rate - Pulse mode
d. Start-up Time - (Number of frames required)
e. Current - Start-up (peak)
Running (peak and average)
.^.	
4.	 TEST CONFIGURATION
The test circuits for measuring the parameters listed in Paragraph 3 are shown
in Figures 1 and 2. The physical relationship between the shutter, aperture
and LED /Sensor assembly used to measure shutter speed and frame rate are shown
in Figure 3.
1
t
ki
2F
FIGURE 1. Led/Sensor Shutter Speed Test Circuit
+28V DC +28V DC
	
MOTOR	 COMM
POWER	 CONTROL	 MOTOI
SUPPLY	 CIRCUIT
GRD
0.01 S2	
VSIG_r-
SCOPE
GRD
FIGURE 2. Input Current Test Circuit
^I
^ E
u^
t
I
I<	
-_
sa
CENTER LINE OF APERTURE
AND LED/SENSOR ASSEMBLY
-*- SHUTTER BLADES
-4--CIRCUIT BOARD
♦ 	 ♦ 	 A
LEFT	 CENTER	 RIGHT
SENSOR POSITIONS RELATIVE TO APERTURE
FIGURE 3. Optical Configuration for the Shutter Position Detector
3
5. TEST CONDITIONS
All testing was accomplished under room ambient temperature and humidity condi-
tions. Input voltage was maintained at +28 V dc. Since the motor control
circuitry contains a +14 V do regulator, varying the +28 V do does not affect
the parameters being measured.
6. TEST PROCEDURE
6.1 SHUTTER SPEED - FRAME TO FRAME
The LED/Sensor configuration shown in Figure 3 was directed at a point just
inside the right edge of the aperture. During the time the shutter covers this
point, light is reflected to the sensor and a do level of approximately +9 V do
appears at the output. When the shutter opening uncovers this point, the LED
emits into a void and the light is not reflected back to the sensor. This
causes the output signal to return to ground. The time duration of the ground
level thus becomes a measurement of the shutter speed.
6.2 SHUTTER SPEED - ACROSS THE FRAME (BANDING EFFECT)
To ensure that a banding effect (uneven exposure across one frame) does not
exist, the above described procedure was repeated with the LED/Sensor directed
at the center and left edge of the aperture respectively.
6.3 MAXIMUM FRAME RATE - PULSE MODE
The m^.ximum frame rate in pulse mode operation was determined by increasing the
cinemode base speed above 6 fps and then increasing the clock rate at which r
power is applied Above the 2 Hz rate until unreliable operation was observed.
6.4 START-UP TIME
The number of frames required to reach a constant shutter speed at frame rates
of 2, 6, 12, and 24 fps was determined by photography, i.e., the camera was
focused on a known ?:ght source of uniform density and actual photographs taken.
The number of frames that were not exposed at the correct shutter speed were
then counted. This method of testing also provided corroborating data relative
to the possibility of banding effects, as well as a means of correlating expo-
sure densities assocated with the various frame rates.
6.5 CURRENT
Average current for each of the frame rates was obtained by reading the ammeter
on the +28 V de power supply. Peak currents (start-up and running) were deter-
mined by measuring the voltage drop across a precision 0.01 ohm resistor in
series with the power supply.
i
4
t
7. PEST RESULTS
_	 Test results for the breadboard configuration are presented in Table 1. Shut-
ter speeds were measured at the shutter opening extremes of 8.6 and 138°
respectively.
Less than one percent jitter in frame to frame shutter speed variation was
noted at all frame rates with either shutter opening. Shutter speed correla-
tion when compared at various cinemode frame rates was consistent, i.e., 16 ms
at 24 fps, 32 ms at 12 fps and 64 ms at 6 fps, using the 138° opening.
	
This, T
if
Li
same pattern repeated at 8.6% i.e., 1.0 ms at 24 fps, 2 ms at 12 fps and 4 me
at 6 fps.
	
4	 In comparing the 6 fps cinemode and the 2 fps pulse mode, note that the shutter
speed is approximately 10 percent slower in the pulse mode. This indicates
that the shutter has not quite reached speed during one revolution. By increas-
ir.g the base cinemode speed to 6.6 fps, this difference was eliminated without
any apparent shutter speed variation across the frame. In a production model
	
-'	 camera this adjustment in base speed could be easily incorporated in the speed
control electronics, and would be automatic, requiring no attention by the
camera user.
The maximum frame rate achieved utilizing pulse mode operation was 6 fps. To
obtain this speed, the base cinemode speed was increased to 8 fps. Even at
	
U	 this point, pulse mode operation was somewhat marginal as evidenced by shutter
speed readings for the 8.6° opening. The two basic problems in attempting
pulse modes at this frame rate, and at higher frame rates, is apparently the
inability of the system friction to stop the transport mechanism consistently
at the same point, and the inability of the drive system to reach and stabilize
at the higher speed in less than one revolution. This is demonstrated by the
6 fps pulse mode data, which shows that the system is in an overshoot condition
when the shutter opens and the shutter speed is faster than it should be for
a base cinemode speed of 8 fps.
As indicated in paragraph 6, the number of frames lost during start-up was
determined by photography. Reproductions of the results are shown in Figure 4.
These photographs do not show a loss at 2 and 6 fps. One frame is lost at
12 fps and two frames are lost at 24 fps. The developed film also corroborates
the readings obtained utilizing the LED/Sensor technique. Banding is not evi-
dent and verifies the right, left, and center measurements shown in Table 1.
The current measurement data indicates that the maximum average current is 400
mA at 24 fps. Also, note that this is based on a motor and control circuit
designed for a 14 V do input. If the motor were wound for a higher voltage,
this current would be reduced. The peak start-up currents for the cinemode
speeds are similar to the surge current characteristics of a conventional brush
type motor and drop off as the motor reaches speed. In the pulse mode, the
peak start-up and peak running currents are synonymous since the power is con-
tinuously applied and removed at the selected pulse rate.
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FICURE 4. EAposure Density Comparison Fl err rnn i r Commut
-ated Motor 11r 1w
h, 12 and 24 fpti, Unifnrm Light Source of 1300 fl,
8t
B. DUAL MOTOR APPROACH
This technique, as previously described in the final report, utilized a atepp&r
motor to drive the shutter and an electronically commutated do motor to drive
the claw and magazine functions. The two motors are synchronized electroni-
cally.
Exposure control over the 1/30 to 1/500 second range imposed two conflicting
requirements on the stepper motor performaac:e; first, fast step response; and
second, positional accuracy with minimal overshoot at completion ^f the step.
Preliminary calculations indicated that a 90 0 stepper motor driving a shutter
of minimal inertia could cover the exposure range if two fixed openings were
utilized. These calculations were also based on the availability of an off the
shelf motor to meet the following specifications=
a. Stop 90° and come to rest in less than eight milliseconds with
less than 10° overshoot.
b. Stop 180' (two czusecutive 90' steps) and maintain constant
speed during the time the shutter opening was passing the
aperture.
Co Maintain constant speed over two steps with lower voltage
applied such that the shutter speed rate could be varied
(slope change).
To provide a confidence level for the feasibility of this technique, initial
r	 tests were conducted utilizing a 90° stepper motor with an Alnico 5 permanent
magnet rotor. Measurements were made for both the single step and two step
advance utilizing the test circuit shown in Figure S. The results of the single
step test are shown in Figure 6 for three different voltage levels applied to
the motor. The three photographs shown in Figure 6, Sheet 1 represent the
position and rate response with no retrotorque applied. The three photographs
shown in Figure 6, She=t 2 represent a retrotorque applied at approximately
the 45° position. The results of the two step response over 180° with the same
Three voltage levels applied are shown in Figure 7.
The significance of these results were:
a. A 90' step could be achieved in less than eight milliseconds with
minimal overshoot if a retrotorque was applied.
b. The rate of change (slope) could be controlled by varying the
motor voltage.
C. A constant slope could be maintained over two steps if the second
step was applied at the proper point in the rotation.
During the performance of the above tests, the permanent magnet rotor began to
show den.ignetization at the lower voltages. A discussion with the motor manu-
facturer indicated that this was due to the higher voltage application. The
_-	 manufacturer also indicated that a motor utilizing a samarium cobalt magnet
would not demonstrate this degradation. A second motor was therefore ordered
for subsequent testing. This motor, however, wr.s rejected almost immediately
MOTOR
..ONTROL
SINGLE
DUAL STEP
SHUTTER
POWER	
STEPPERSUPPLY	
MOTOR	 a 1 -0-40V DC	 i
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POWER
SUPPLY
0-15V DC
RET
SCOPE
VPOSITION VIN
FTCURE j. Stepper Motor Response Test Circuit
9
L m^
NO REIRO - TORQUE
HORIZ 2 ms/cm	 VERT 30 ( '/cm +20V DC
NOTE
NOISE SUPERIMPOSED
ON THE SIGNAL IS
DUE TO THE POTENTI-
OMETER.
HORIZ 2 ms/cm	 VERT 300/cm +3011 DC
t
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1
Q^ ^^ 1
HORIZ 2 ms/c
FIGURE' #,.	 'ingh
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VERT 30'/cr , +40V DC
I'v-;r I t-111r . ,	 (;lu	 r	 I	 (,f .')
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HORIZ 2 m5/cm	 VERT 30°/cm +20V DC
HORIZ 2 ms/cm
	
VERT 300/cm +30V DC
I
i
NOTE
NOISE SUPERIMPOSED
ON THE SIGNAL IS
DUE TO THE POTENTI-
OMETER.
HORIZ 5 ms/cm
	
VERT 60 0/cm +20V CC
t
s
i
G
n
HORIZ 5 ms/cm	 VERY 600/cm +30V DC
S '
is
ci
HORIZ 5 ris/cm	 VERT 600/cm +40V DC
FTi;tfRF 7.	 TWO Stel) •Petit Rosin is
12
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due to an extremely wide dead band (30°) at the detent points; i.e., with full
voltage applied the motor shaft could be rotated approximately 30° with no
noticeable torque being produced by the motor. A third motor was then ordered
utilizing Almico 8 for the permanent magnet. This motor was, according to the
manufacturer, much less likely to demagnetize if voltage above the rated voltage
of the motor was applied.
This series of events resulted in the present breadboard configuration. The
third motor, along with an optical encoder which could produce the appropriate
retrotorque and advance pulses, was installed in the system. Initial testing
of this configuration achieved operation in time exposure and at the slower
exposures (1130, 1/60 and 1/125 seconds). These exposure times rely on the
ability of the system to take a single 90° step, dwell (for selected exposure
time) with no power applied, and step 90° to close the shutter. An extremely
important requirement of this technique is the ability to remove power between
steps. Otherwise, the average power consumption becomes prohibitive. The
system as presently configured did not allow the removal of power between steps.
The two faster shutter speeds (11250 and 1/500 seconds) rely on the ability of
the system to take two consecutive 90° steps while maintaining constant speed
over the midrange of the positional change. Testing indicated that the motor
was slewing correctly in one direction, but overshooting quite badly in the
other. This resulted in an unstable and therefore inoperable system at these
two speeds.
In attempting to analyze these results, it appears that the inability to remove
power and the stabilization problems at the higher speeds are directly related.
Specific characteristics of the system which, by themselves, or in combination
could contribute to these problems are:
a. Mismatched motor windings, resulting in a different response for
each pair of windings being driven.
b. Optical encoder misalignment, resulting in the retrotorque and
advance pulses being applied at the wrong time in the rotation
cycle.
C. Fixed position application of the retrotorque and advance pulses
at 45 and 90° respectively, i.e., this may not•be the optimum
point for application of these pulses.
As indicated in Paragraph 1, a decision on which way to proceed with the test
was required at this juncture of the program. Since all of the above indi-
cated problems must be resolved before the final results could be determined,
and since this condition required additional time and cost, the direction was
given to complete final testing on the single motor drive technique.


Development of a drive system for a sequential space camera

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