Automatic balancing device for use on frictionless supported attitude-controlled test platform

Hatcher, N. M.

Young, R. N.

English

NASA Technical Reports Server

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Copy of Patent uited abwe 
https://ntrs.nasa.gov/search.jsp?R=19710004070 2020-03-17T02:32:36+00:00Z
N, M. HATCHER ETAL 
AUTOMATIC BALANCING DEVICE 
Ff led Peb. 27, 1969 
United States Patent 86 3,534,584 ce Patented 0.L 2% 1970 
- . --. compatibilitv with all vehicular torauing svstems. ability 
3,534,354 
AUTOMATIC BALANClNG DEVICE 
Norman M. Hatcher, Houston, Tex., and Richard N. 
Young, Hampton, Va., assignors to the United States 
of America as represented by the Administrator of the 
National Aeronautics and Space Administration 
Riled Feb. 27. 1969. Ser. No. 802,820 
to operate within a wide range of ;mbil;nces, and low 
weight, volume and power consumption. 
Further objects and advantages of the invention will be- 
come apparent hereinafter and in the drawings in which: 
FIG. 1 is a block diagram of the invention; and 
FIG. 2 is a schematic diagram of the electronic cir- 
Int. CI. ~ 0 1 ~  21/00 ' - cuitry used in the invention. 
U.S. CI. 73-1 6 Claims Turning now to the embodiment of the invention 
selected for illustration in the drawings, the number 11 in 
ABSTRACT OF THE DISCLOSURE FIG. 1 designates a test platform which is mounted for rotation about an axis 12. The attitude of platform 11 
An automatic balancing device for a frictionlessly sup- 
ported, attitude-controlled test platform about an axis 
that is orthogonal to the gravity vector. The device deter- 
mines imbalance during limit cycle operation by measur- 
ing the differences in total impulse exerted by opposing 
torquers that are used for attitude control during a time 
interval. The device then moves a small weight an appro- 
priate distance to compensate for the measured im- 
balance. 
The invention described herein was made by employees 
of the United States Government and may be manu- 
factu~ed and used by or for the Government for gov- 
ernmental purposes without the payment of any royalties 
thereon or therefor. 
The invention relates generally to automatic balancing 
system and more particularly concerns an automatic 
balancing device for use on frictionlessly supported at- 
titude-controlled test platforms. 
In developing and preflight testing spacecraft attitude 
sensors, attitude-control (torquing) systems, and other 
spacecraft components, it is often necessary to test these 
components on air-bearing or other supported, attitude- 
control-led platforms. For these applications the platforms 
must be balanced to the best possible extent; that is, to 
within a few thousand dyne-cm. Any imbalance can in- 
crease control-fuel usage or power consumption, decrease 
orientation accuracy, and inc~ease the time initially re- 
quired for the system to orient the platform. 
Currently, most air-bearing supported platforms are 
balanced manually. However, balancing a platform manu- 
ally is undesirable because the balancing plocess is time 
consuming and limited to accuracy. Another balancing 
system that the inventors have knowledge of derives im- 
balance information prior to a test by sensing the angular 
acceleration of the platform about its control axes. Neith- 
er this system nor the manual-balancing techniques can 
maintain the balance of a platform while a test is in 
progress. For tests of more than a few minutes, the plat- 
form may have to be rebalanced periodically to compen- 
sate for center-of-gravity shifts. These shifts can be caused 
by anisoelasticity (deflections of platform components 
due to gravity); unequal expansion of components due to 
temperature changes: component shifts due to necessary 
clearances between gears, bearings, and other devices, 
movements of such items as leads, which ale not securely 
tied down; and unsyn~metrical fuel usage with respect to 
the center of support. Compensation may also be made 
for the torquing effects of wire Ieads to the platform, ail- 
bearing torques, and room air culrents, for they may not 
vary appreciably with time. Thus, the need for a com- 
pletely automatic balancing system is apparent. 
It is therefore the primary object of this invention to 
provide an automatic balancing device for use on f ~ i c -  
tionlessly supported attitude-control test platforms. 
Other objects of this invention are that this automatic 
balancing device have accuracy, reliability, fast response, 
about axis 12 is controlled by forces applied-to the plat- 
form by opposing torquers 13 and 14. Torquers 13 and 
15 14 are controlled by electrical signals from sensors (not 
shown) through wires 15 and 16, respectively. Torquer 13 
is operative while a signal is applied across wires 15, and 
torquer 13 is operative while a signal is applied across 
wires 16. The coil of a relay 17 is connected across wires 
20 15 so that while torquer 13 is operative relay 17 is closed 
and a +E voltage is applied to an electronic circuit 18. 
The coil of a relay 19 is connected across wires 16 so that 
while torquer 14 is operative relay 19 is closed and a -E 
voltage is applied to electronic ci~cuit 18. Inasmuch as 
torquers 13 and 14 are never both operative at the same 
time, the +E and -E voltages can be applied directly 
to electronic circuit 18. 
A small weight 20 is located on platform 11 such that 
when there is any imbalance of platform 11, the weight 
can be moved to compensate for the imbalance. The shaft 
21 of a motor 22 is attached to weight 20 to move it on 
platform 11. This can be done by having shaft 21 
threaded. Electronic circuit 18 includes an integrator 
which periodically integrates the voltages applied to it for 
a predetermined period of time and then drives motor 22 
at a constant speed for a time proportional to the ampli- 
tude of the voltage at the output of the integrator at the 
end of each predetermined period of time. If the output 
of the integrator is positive the motor is driven in one 
direction and if the output of the integrator is negative 
the motor is driven in the other direction. Hence, weight 
20 is moved in either of two directions to compensate for 
any imbalance of platform 11 about axis 12. 
In FIG. 2 there is shown a schematic drawing of the 
electronic circuit 18 in FIG. 1.  The input to this circuit 
is an input terminal 25 which is connected through a 
relay 26 and a potentiometer 27 to ground. The pulpose 
of potentiometer 27 is to  provide an adjustment for the 
input-signal amplitude to make it compatible with the gain 
of the following circuitry. The slider of potentiometer 27 
is connected through a resistor 28 to the input of an in- 
leglator consisting of an amplifier 29 with a feedback 
capacitor 30. The output of the integrator is connected 
through a ~ e l a y  31 and a resistor 32 to an amplifier 33 
having a feedback resistor 34. The coils of lelays 26 and 
31 ale coqnected to a timer 35. The function of timer 35 
is to periodically apply no voltage to the coils of relays 26 
and 31, during a f i ~ s t  predetermined tnteival of time and 
apply a voltage to the two coils during a second peck 
termined interval of time Hence, during the first prede 
termined interval of time the contacts of relays 26 and 
31 are as shorn and the input is applied to the integrator 
and du~ing the foliu\ving second predete~rnineci interwal 
of time the input is disconnected flom the integiator and 
the output of the integrator is applied to amplifier 34. 
After a second predetermined interval of time the iqput is 
again applied to the integrator for the filst pledeteinlined 
interval of time. Timers that will pel form the function of 
timer 35 are well known, hence the details of timer 35 are 
not disclosed. 
3,534, 
a 
*a 
The orrtput of anlplifiel 33 is connected to a telay d~ibe  
circuit including tran';istorr 36 and 37, and to an inte- 
gtatoi discharge c~lcutt rncluding transistois 38, 39, 49 
a ~ d  41. Ii, the relay d ~ i v e  c11ctllt a resistance netwolk 
~onsrsting of iesistors 42, 43, 44 and 45 is connected to 
the bases of tlansistors 36 and 37, and to the output of ' 
amplifie~ 33 th~ough diodes 46 and 47. The emitters of 
transistois 36 and 37 aie connected to ground. The col- 
lector of tlansistor 36 is connected thlough the coil of a 
relay 48 to a 28-volt supply, and the collector of tlansistor 
37 is connected through the coil of a relay 49 to a -28 
volt supply. While the coils of relays 48 and 49 have no 
culrent passing thiough them the contacts of the relays 
are as shown and terminals 50 and 51 are connected to 
ground. While the coil of lelay 48 has curlent passing 15 
thiough it, terminal 50 is connected to a 20-volt supply 
and while the coil of relay $9 has current passing through 
it terminal 51 is connected to the 20-volt supply. Ter- 
minals 50 and 51 are connected to motor 22 in FIG. 1. 
In the integrator discharge circuit the bases of tran- 20 
sistors 39 and 41  are connected to ground and their emit- 
teis ale connected through resistois 52 and 53, respec- 
tively, to the output of amplifier 33. The collector of tran- 
sistor 39 is connected through resistors 54 and 55 to a 
15-volt supply, and the collector of tlansistor 41 is con- 25 
nected through resistois 56 and 57 to a -15 volt supply. 
The base of transistor 38 is connected to the junction of 
lesistois 54 and 55, and the base of t~ansistor 40 is con- 
nected to the junction of resistors 56 and 57. The emitter 
of t~ansistoi 38 is connected to the 15-volt supply and 30 
the emitter of tlansistor 40 is connected to the -15 volt 
supply. The collectors of transistors 38 and 40 are con- 
nected together and to a potentiometer 58. The slidel of 
potention~eter 58 is connected through a resistor 59 to the 
input of amplifier 29. If the output of amplifier 33 is posi- 3 j 
tive, tlansistor 41 becomes conductive causing transi~tor 
40 to become conductive. Hence, the -15 volt supply 
is applied to the input of amplifier 20 to discharge capac- 
itor 30. If the output of amplifier 33 is negative, tlansis- 
tois 38 and 39 become conductive and the 15-volt supply JO 
is applied to the input of amplifier 29 to discharge capac- 
itor 30. The purpose of potentiometer 58 is to control the 
discharge late of capacitor 30. 
In describing the operation of this invention it will be 
assumed that there is an imbalance in platfo~m PI. Hence, 4j 
there is an input applied to either torquer 13 or torquer 
14. Consequently the contacts of either relay 17 or relay 
19 are closed and a voltage is applied to the electronic 
circuit 18. Assunle that the state of timer 35 is such that 
no current is flowing through the coils of relays 26 and 50 
31. Then the voltage applied to the electronic circuit is 
applied through potentiometer 27 and resistor 28 to the 
integrator thus charging integrating capacitor 30. When 
timer 35 changes state current flows through the coils of 
relays 26 and 31 causing their contacts to close. In this 55 
state the input to the integiator is disconnected flcm the 
input terminal 25 and the output of the integrator is con- 
nected to the input of amplifier 33. Assume that the 
charge on capacito~ 30 is such that the output of amplifier 
33 is positive. Then the emitter of transistor 41 is positive 
with respect to its base causing it to conduct. The result- 
ing flow of cu~rent  hrough resistors 56 and 57 causes the 
base of transistor 40 lo  become positive wit11 respect lo 
~ t s  emitter. Hence, iranslstor 40 conducts arid the - I S  
volt suppiy is applied to kmtentiorileter 58. The negative i,S 
vo1:age at the sltder of potentrometer is applied through 
iesistor 59 to ~apaciior 30 to discharge it. The poskive 
voltage at the output of amplifier 33 is also applied 
thtough diode 46 and resist01 4% to the base of transistor 
36, causing it to conduct. The ~esulting flow of curlent 
thlough the coil of relay 48 actuates the ielay and con- 
nects the 10-volt supply to motor 22. This causes the 
motor to i~love weight 20 to compensate for the imbalance 
of plaifuim P I .  
If the chalge on capacitor 30 is such Lhat the output of 15 
584 
4 
amplifier 33 is negative, trans is to^.^ 38 and 39 become con- 
ductive and the 15-volt supply is applied through poten- 
tiometer 58 and resistor 59 to capacitor 30 to discharge 
it. The negative voltage at the output of amplifier 33 is 
also applied through diodc 47 and resistor 45 to the base 
of transistor 37, causing it to conduct. The resulting flow 
of current through the coil of relay 49 actuates the relay 
and connects the 20-volt supply to motor 22 which moves 
weight 20 to compensate for the imbalance of platform 
11. The purpose of diodes 46 and 47 is to hold the sen- 
sitivity of the relay-drive circuit below that of the inte- 
grator-discharged circuit so that motor 22 will turn off 
before capacitor 30 ceases to discharge. 
This invention has several advantages over the prior 
art. It  can balance a platform more quickly with a higher 
degree of balance accuracy. It  can operate automatically 
for any desired period of time, and it eliminates the re- 
quirement of interrupting tests in progress in order to 
rebalance the platform. 
What is claimed is: 
1. A device for automatically balancing an attitude- 
controlled test platform of the type that utilizes two 
torque-producing devices for controlling the rotational 
attitude of the platform about an axis comprising: 
means for producing an electrical signal indicative of 
the direction of the torque produced by said two 
torque-producing devices; 
means for periodically integrating said electrical signal 
for a predetermined length of time; 
a weight on the surface of said platform; 
a motor connected to said weight for moving it in 
either of two directions on said surface; and 
means connected to the output of said integrating means 
for driving said motor at a constant speed for a 
time proportional to the amplitude of the output of 
said integrating means at the end of said predeter- 
mined time and in a direction indicative of the polar- 
ity of the output of the integrating means whereby 
said weight is moved on the surface of said plat- 
form to compensate for any imbalance of said plat- 
form. 
2. A device according to claim 1 wherein said means 
for periodically integrating said electrical signal for a 
predetermined length of time includes an integrator, 
switching means connected between said means for pro- 
ducing an electrical signal and the input of said integrator, 
and timer means for controlling said switching means so 
that said electrical signal is connected to the input of 
said integrator for said predetermined length of time and 
then disconnected therefrom for a second predetermined 
length of time. 
3. ?'he device according to claim 2 including an in- 
tegrator discharge circuit and a second switching means 
connected between the output of said integrator and the 
integrator discharge circuit under the control of said timer 
means for disconnecting said integrator from said in- 
tegrator discharge circuit during said predetermined time 
and for connecting said integrator to said integrator dis- 
charge circuit during said second predetermined time. 
4. A device according to claim P wherein said means 
for driving said motor includes an integrator discharge 
circuit for discharging said integrating meens at a con- 
stant rate until the integrating means is fully discharged 
and means connected to the output of said integrating 
means for applying a constant voltage to said motor in 
a direction indicative of the polarity of the charge on 
the integrating means and for a period beginning at 
the time that the integrating means begins to discharge 
and ending when the integrating means becomes fully 
discharged. 
5.  A device according to claim 4 wherein said integrator 
discharge circuit includes means responsive to the output 
of said integrating means for applying an opposite polar- 
ity constant voltage to the input of the integrating means 
to discharge the integrating means. 
3,534,584 
5 
6.  A device accordillg to clairn 4 wherein said irleans 
6 
References Cited 
for applying a tonstanl voltage io said motor incirrdes 
switching means responsive to the output of said in- UNITED STATES PAT'ENTS 
tegrating means for applying said constant voltage to 3,203j224. /lske. 
said motor in one direction while the polarity of the 3,210,989 10/1965 Samborsky et al. ------ 73-65 
3~ltput Of Said inlegrating means is positi.de for 5 3,427,896 2/1969 Ha.rtman ------------ 74----573 
applying said constant voltage to said motor in the 
other direction while the polarity of the output of said S. CLEMENT SWISHER, Primary Examiner 
integrating means is negative. 


Automatic balancing device Patent

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