Wheel balancing apparatus

A wheel balancing apparatus for balancing an out-of-balance wheel that is mounted on a rotatable shaft includes force transducers positioned in a horizontal plane against resiliently supported bearings for the shaft to thereby detect horizontal components of the imbalance forces created by the out-of-balance wheel. Photosensitive switches associated with the shaft produce phase-displaced analog signals, which signals are supplied to a pulse producing circuit for generating a train of count pulses on one of two output lines depending upon the direction of rotation of the shaft. A counter, which has a capacity exactly equal to the number of pulses generated by the pulse producing circuit per revolution of the shaft, is set when the horizontal component of the imbalance force for a particular correction plane associated with the counter equals zero. When a command to stop spinning the shaft has been issued, the shaft will slow down until it comes to a stop but the counter will continue to count through each cycle of shaft revolution so that it will stop at a position wherein the relative rotative position of the unbalanced weight can be determined. A digital-to-analog converter responsive to the counter output provides a ramp voltage to drive a null meter and thereby permit the operator to rotate the wheel after it stops until the position of weight imbalance for the particular correction plane is provided in the predetermined location for providing a corrective weight--as is ascertained by bringing the null meter to the null position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to apparatus for balancing 
out-of-balance rotary bodies and more particularly concerns an apparatus 
for measuring the magnitude and angular position of imbalance in at least 
one plane of a rotary body such as a motor vehicle wheel. 
2. Description of the Prior Art 
In the dynamic balancing of a rotary body such as a motor vehicle wheel, 
the wheel is rotated on the vehicle with measurements made directly 
thereto, or the wheel is removed from the vehicle and mounted on a special 
drive shaft and then rotated. When the drive shaft and wheel are spun, the 
out-of-balance forces cause the drive shaft to move slightly off-axis in a 
measuring plane, and force transducers in the measuring plane provide 
signals which are proportional to the magnitude of the unbalanced forces. 
The location of the unbalanced weight is then determined, by means of the 
transducers, with respect to the planes through the inner and outer rims 
of the wheel. To then bring the wheel into dynamic and static balance the 
operator applies weight to the inner and outer rims of the wheel at the 
unbalanced weight locations as determined by the transducers until the 
drive shaft remains on-axis as the wheel is rotated. 
In U.S. Pat. No. 3,835,712 to Muller, an apparatus for dynamically 
balancing a rotary body is disclosed wherein the wheel to be balanced is 
rotated on a balancing shaft. A phase displacement device (i.e., a synchro 
or a resolver) is also provided on the shaft. The shaft is rotated to spin 
the wheel at its normal rotational speed, and a force transducer produces 
a force signal which is indicative of the magnitude of the unbalanced 
wheel weight. The location of the unbalanced weight is provided in an 
output signal by using the force signal to phase shift a reference voltage 
by an angular amount indicative of the position of the unbalanced weight. 
As the wheel is subsequently slowed to a stop, the reference voltage is 
applied to the stator windings of the phase displacement device so that 
the rotor thereof will provide an output signal comprising the reference 
voltage phase shifted by an amount indicative of the position of the 
wheel. When the wheel stops, the two phase shifted signals are compared by 
means including a null meter, and the wheel is rotated until a null is 
obtained at which time the unbalanced weight position will be in a 
predetermined rotative position of the wheel so that the balancing weight 
can be accurately and easily added to the wheel. While the balancing 
apparatus of the Muller patent operates in an entirely satisfactory and 
accurate manner, it will be recognized that it is comprised of complex and 
expensive components which significantly add to the cost of the apparatus. 
In U.S. Pat. No. 3,910,121 to Curchod et al, a two-plane dynamic wheel 
balancing machine is disclosed which includes a force transmission member 
which is supported for movement in one plane. The drive shaft of the 
balancer is mounted on the force transmission member such that the 
imbalance forces tend to move the member in the plane in which it is 
mounted, and force transducers produce signals indicative of the position 
and magnitude of the imbalance forces in the two planes of the wheel to be 
balanced. A photoelectric device produces a reference signal when the 
shaft rotates through a predetermined reference position, and another 
photoelectric device produces position pulse signals indicative of the 
angular position of the shaft with respect to said reference signal. The 
position pulses are counted, and the counter is read when the unbalanced 
weight is in a predetermined rotative position of the wheel. When the 
wheel stops, the operator rotates the wheel until the counter reading is 
again at the number which indicates said predetermined rotative wheel 
position where the balancing weights are applied. 
U.S. Pat. No. 3,732,737 to Forster discloses a two-plane dynamic wheel 
balancing apparatus which operates in a manner similar to that of the 
aforedescribed Curchod et al device in that the positions at which the 
counterbalance weights are to be attached to the wheel rims are determined 
by measuring the phases of analog signals from the force transducers 
relative to some fixed reference point on the balancing shaft. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a dynamic wheel 
balancing apparatus having a position finding system which does not 
require a reference signal associated with a predetermined rotative 
position of the balancing shaft. 
A further object of the present invention is to provide a relatively simple 
but accurate electronic system for indicating the direction in which a 
wheel must be turned to bring it into the rotative position where a 
counterbalance weight should be applied and for further indicating 
directly to the operator when such rotative position is reached. 
The present invention provides an apparatus for measuring the imbalance of 
a rotary body such as an automobile wheel in at least one plane, but 
preferably two planes, which planes are normal to the axis of rotation of 
the wheel. The apparatus includes means for rotating the wheel, means for 
detecting forces generated by the imbalance in the plane of concern and 
for generating a signal representative of the magnitude of the imbalance 
in the plane, means for generating pulses in timed relation to the 
rotation of the wheel, a counter responsive to the generated pulses for 
indicating the angular position of said wheel, means responsive to the 
signal from the detecting means to enable the counter to start counting 
when the angular position of the unbalanced weight is at a preselected 
rotative wheel orientation, means for providing an output signal from the 
counter to visually indicate when the wheel is in said preselected 
rotative position, and means responsive to the signal from the force 
detecting means for determining and displaying the magnitude of the 
imbalance in the plane so that after the wheel has been spun and then 
stopped the operator can readily rotate the wheel to the indicated 
preselected rotative position and apply the correct counterbalancing 
weight as indicated by the imbalance magnitude display means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The wheel balancing apparatus of the present invention, as illustrated in 
FIG. 1, includes a shaft 10 having a clamping assembly 12 at one end 
thereof for detachably securing a wheel W in a plane normal to the axis of 
the shaft 10. An encoder disc and optical switch assembly 14 for producing 
analog signal outputs on lines 20a and 20b is fixed to the end of the 
shaft opposite from that upon which the wheel is mounted. The signals on 
lines 20a and 20b are representative of the angular amount of rotation of 
the shaft 10. The shaft is free to rotate in a pair of spaced bearings 
which are resiliently mounted in axially spaced housings 21 and 22 in a 
manner which allows the shaft and bearing housing assembly to deflect in a 
horizontal plane when subjected to out-of-balance forces produced by an 
unbalanced wheel W. Electrical force measuring elements, or transducers, 
24 and 26, which are mounted between the bearing housings 21 and 22 and 
the fixed frame structure F of the apparatus in the horizontal plane, 
produce signals on output leads 28 and 30, respectively, which represent 
the magnitude of the unbalance forces exerted on the bearing housings 21 
and 22, respectively. Details of the mounting of the bearings and the 
transducers will be discussed hereinafter. The shaft 10 is driven by a 
reversible electric motor M which has a drive pulley on which a belt 34 is 
entrained to transmit drive to a pully 35 keyed to the shaft 10. The motor 
is located directly below and in axial alignment with the balancing shaft 
10. 
Switches, dials and meters for controlling and monitoring the balancing 
operation are located on a console board 36. A weight meter 38 displays 
the magnitude of the counterbalance weight which must be applied to the 
inner rim 11 of the wheel W, and a meter, or display device, 40 indicates 
the position at which such weight should be applied to the rim 11. 
Preferably, the position meter 40 is of the null indicating type having a 
needle and a fixed scale with a zero, or null, mark at the center thereof. 
Meters 39 and 41, which are similar to the meters 38 and 40 respectively, 
indicate the magnitude and position of the counterbalancing weight for the 
outer rim 13 of the wheel. It should be understood that other types of 
position indicating displays can be used with the circuitry of the present 
invention. Also mounted on the console board 36 are a start switch 44 and 
a stop switch 46. Since wheels to be balanced may vary in diameter and in 
width, and since the positions of the inner and outer rims 11 and 13 may 
vary in the offset distance from the bearing housing 22, the console 36 
further includes dials 48, 50 and 52 for providing a force computer 56, to 
be described hereinafter, with the following wheel-related parameters: the 
dial 48 provides an indication of the diameter (or radius) of the rims 11 
and 13; the dial 50 provides an indication of the width of the wheel (the 
distance between the planes P1 and P2 (FIG. 1) through the rims 11 and 
13); and the dial 52 provides an indication of offset distance from the 
transducer 26 to the plane P1. The dials 48, 50 and 52 are manually 
settable by the operator prior to the start of the balancing operation. 
The bearing housings 21 and 22 are resiliently supported by vertical leaf 
springs (not illustrated) which allow the shaft, bearings, and drive 
pulley assembly to deflect generally in a horizontal plane when subjected 
to out-of-balance centrifugal forces produced by an unbalanced wheel. The 
force transmitting elements, or transducers, 24 and 26 comprise 
piezoelectric crystal devices interposed between the respective bearing 
housings 21 and 22 and the frame F for the balancing apparatus. Springs 25 
and 27 are used in a known manner between the transducers and the frame to 
maintain the transducers 24 and 26, respectively, in force-measuring 
contact with their associated bearing housings. The transducers are 
mounted to lie in a horizontal plane containing the centerline of the 
shaft 10 and thus produce sinusoidal signals proportional to the 
horizontal components of the unbalance forces generated by the unbalanced 
wheel W as the wheel is spun. 
As illustrated in FIGS. 2 and 3, the signal outputs of the transducers 24 
and 26 are conveyed on lines 28 and 30 to the force computer 56 which 
provides sinusoidal output signals on lines 58a and 58b therefrom. The 
output signals on lines 58a and 58b are indicative of the magnitudes and 
positions of the weight to be added to the wheel in planes P1 and P2, 
respectively. Thus, the force computer, which is known in the prior art, 
functions to compute from the unbalanced force signals in the planes of 
the transducers the counterbalancing weight signals in the rim planes P1 
and P2. Due to the positioning of the transducers in a horizontal plane 
and the restricted horizontal deflection of the bearing housings 21 and 22 
in the horizontal plane, the heavy (i.e., unbalanced weight) spots for the 
respective planes P1 and P2 will be at bottom-dead-center on the rims 11 
and 13 when the phase angles of the signals on the respective lines 58a 
and 58b are each 180.degree.. Thus, at such a phase angle, the position on 
a rim at which a weight should be placed is at top-dead-center. It will be 
appreciated that any desired rotative wheel position of weight emplacement 
is possible with the present invention; a top-dead-center emplacement 
position has been chosen since such location represents the easiest 
position to apply the counterbalancing weights. 
The computation of the magnitudes of the counterbalance weights to be added 
to the wheel in the planes P1 and P2 to bring the wheel W into dynamic and 
static balance may be made according to the following equations: 
EQU w(2) = aF(1) + b [F(1) - F(2)]/c (Eq. 1) 
EQU w(1) = F(2) - F(1) - w(2) (Eq. 2) 
wherein w(1) and w(2) are the magnitudes of the out-of-balance forces 
acting respectively in planes P1 and P2 effective at the wheel rims 11 and 
13 (such forces thus being proportional, when they are at their maximums, 
to the amount of counterbalance weights to be added to rims to bring the 
wheel W into static and dynamic balance); F(1) and F(2) are the magnitudes 
of the horizontal forces exerted on the transducers 24 and 26, 
respectively, by the rotating and oscillating shaft 10; "a" is the axial 
distance between transducers 24 and 26; "b" is the axial offset distance 
between the plane P1 and the transducer 26; and "c" is the distance 
between the planes P1 and P2, i.e., the width of the wheel W. The values 
of the counterbalance weights, to be applied at positions displaced 
180.degree. from the heavy spots where the maximum values of the unbalance 
forces w(1) and w(2) are applied, equal the magnitudes of the maximum 
out-of-balance forces divided by the radius, r, of the wheel W, that is, 
w(1)/r and w(2)/r for the planes P1 and P2, respectively. 
Inasmuch as the circuitry for force computer 56 for accomplishing the 
computations according to equations 1 and 2 is known in the prior art and 
will be obvious to those skilled in the electronic wheel balancer art, 
only a brief discussion of a preferred embodiment of the force computer 56 
is presented herein. As shown in FIG. 3, the force computer 56 includes a 
first stage including an amplifier AM having its non-inverting terminal 
connected to the line 30 from the force transducer 26. A voltage e2 
representative of the force F(2) exerted on the transducer 26 is provided 
on line 30. The inverting terminal of the amplifier AM has a voltage 
applied thereto which is the sum of a voltage e1, which is proportional to 
the force F(1) exerted on the transducer 24 via line 28, and the output 
voltage e0 of a second stage of the force computer 56, which corresponds 
to the value of force w(2). See equation 2 above. The output signal from 
the amplifier AM will thus be representative of the force magnitude w(1) 
which output is applied to a variable resistor R6 of a settable value 
proportional to the radius r of the wheel, to thereby provide a signal 
proportional to the value of the counterweight to be added to rim 11. The 
value of resistor R6 is set by the console dial 48. 
The second stage of the computer 56 includes a simple adjustable gain 
differential amplifier DAM, the gain of which is controlled by a variable 
resistor R5 of the value K(R2) with the value of K being set by the wheel 
width dial 50. The differential amplifier DAM includes four matched 
resistors R2 and two matched resistors R1. The output voltage e0 of the 
differential amplifier is: 
EQU e0 = 2 (1 + 1/K) (R2/R1) (e1-e3) (Eq. 3) 
The input voltage to the non-inverting terminal of the differential 
amplifier DAM is proportional to the force F(1). The output of the 
differential amplifier DAM is fed back through a first one of a pair of 
matched resistors R3 and summed at point 122 with the output of the 
amplifier AM through the other of the matched resistors R3. The voltage at 
122 is applied to a potentiometer R7 and the output voltage thereof is the 
voltage e3 which is then applied to the inverting terminal of the 
differential amplifier. The value of resistance of the pot R7 is set by 
the offset dial 52 to be proportional to the value of the offset distance 
b (see FIG. 1). 
When the pot R7 is set to indicate an offset distance of zero, the value of 
the resistance will equal zero, thereby grounding the input to the 
inverting terminal of the differential amplifier DAM. This makes e3 in 
equation (3) equal zero; hence, the output voltage e0 which represents 
w(2), will equal 2(1 + 1/K) (R2/R1) e1. Comparing equations 1 and 3, the 
ratio of a/c in equation 1 will be found to equal 2(1 + 1/k) (R2/R1) in 
equation 3. When the pot R7 is set to indicate an offset distance other 
than zero, the input voltage e3 to the inverting terminal will be of a 
value set by the pot R7, and the output voltage e0 will be a function of 
the wheel width parameter K set by the dial 50 through resistor R5. 
Now referring again to FIG. 2, the output signals on lines 58a and 48b are 
applied to filters 60a and 60b tuned to the frequency of wheel rotation 
during the test cycle to provide sine wave signals which are free from 
miscellaneous noise. A standard multi-pole, narrow band pass filter has 
been found to be suitable to perform the filtering operation. As discussed 
hereinafter, when this type of fixed frequency filter is used, it will be 
necessary to assure that measurements are taken when the shaft is being 
driven at a fixed speed. The outputs of the filters 60a and 60b are 
applied through monostable switching circuits 68a and 68b, respectively, 
to weight meter driving circuits 70a and 70b, respectively. The switching 
circuits 68a and 68b each preferably include a field effect transistor 
(not shown) which is in a normally open, non-conductive state and which is 
placed in a closed, conductive state when a high voltage is applied 
thereto during a sampling cycle, as described hereinafter. The switching 
circuits are energized by the outputs of a pair of AND gates 72a and 72b. 
The outputs of the AND gates 72a and 72b will be high to close the 
switches 68a and 68b when the positive half of the force signal from 
filters 60a and 60b is being fed to the respective switching circuit 68a 
and 68b and a spin cycle control circuit 96 is providing a high signal on 
line 97 therefrom indicative of a decision to take weight measurements. 
The enabling signals for gates 72a and 72b are provided by differential 
amplifiers 73 which pass an enabling pulse only on the positive 
half-cycles of the input signals. When the switching circuits 68a and 68b 
are conductive the positive half or the sinusoidal force signal thereby 
passes to the respective weight meter driving circuit 70a and 70b. The 
meter driving circuit 70a and 70b integrate the signals from the 
respective switches 68a and 68b and store the values thereof. As will be 
appreciated by those skilled in the art, a buffering circuit is emloyed in 
each meter driving circuit to retain the last meter reading until the 
operator has had sufficient time to apply the necessary counter-balancing 
weights to the rims 11 and 13. 
The encoder disc and optical switch assembly 14 produces two-phase 
displaced pulse trains at a frequency as determined by the rate of 
rotation of the shaft. The assembly 14 includes a disc 15 which is affixed 
to the shaft 10 and has a plurality of windows 16 (FIG. 2) uniformly 
spaced from each other along the periphery of the disc. the windows have a 
width (measured in the peripheral direction) which is exactly equal to the 
spacing between the adjacent windows. The assembly 14 further includes an 
optical switch portion 17 (FIG. 2) having two optical switches 18a and 18b 
mounted in a housing 19 which is rigidly affixed to the bearing housing 
21. The housing 19 is U-shaped in cross-section (FIG. 1) surrounding the 
apertured edge of the disc 15, and the switches 18a and 18b each include a 
light source (such as a light emitting diode) on one side of the disc and 
a light sensitive transducer (such as phototransistor) on the opposing 
side of the disc. The switches register with the windows in the disc, and 
they are spaced from each other by a distance (measured tangentially to 
the disc) of one and one-half times the width of the windows, whereby the 
signal on lines 20a and 20b will be 90.degree. out of phase with respect 
to each other, the direction of the phase displacement being dependent 
upon the direction of revolution of the shaft 10. 
The leads 20a and 20b from the switches 18a and 18b direct the analog 
signals to a count pulse producing circuit 78 which, dependent upon the 
direction of revolution of balancing shaft 10, provides either a train of 
count-up pulses on a first output lead 80a therefrom or a train of 
count-down pulses on a second output lead 80b therefrom. The leads 80a and 
80b are connected to a first up-down counter 84a and to a second up-down 
counter 84b, with the lead 80a being connected to the up-count inputs and 
the lead 80b being connected to the down-count input. Both counters have a 
counting capacity exactly equal to the total number of count-up or 
count-down pulses generated by the circuit 78 during one complete 
revolution in one direction of the shaft 10. 
The counters 84a and 84b are reset, or reinitialized, in accordance with 
the respective emplacement positions for the counterbalance weights in the 
planes P1 and P2 as indicated by a selected phase angle of the respective 
signals from the filters 60a and 60b, the selected phase angle being 
0.degree. when the unbalanced weight with respect to planes P1 or P2 is 
up. the logic circuitry for reinitializing the counters is discussed 
hereinafter. As a result of the re-initialization of the counters at the 
selected phase angle of zero degrees (when the heavy spot is at 
top-dead-center), the counter outputs will be at mid-count, that is, at a 
count equal to one half of the total counting capacity, when the 
unbalanced weight is at bottom-dead-center. Accordingly, at mid-count the 
emplacement position for a counterbalancing weight will be at 
top-dead-center. 
The digital outputs of the counters 84a and 84b are respectively applied to 
first and second digital-to-analog converters 86a and 86b which provide 
analog ramp voltage outputs to the position meter driving circuits 88a and 
88b. The D/A circuits also shift the voltage level of the ramp voltage 
waveforms so that they are centered on zero volts, i.e., the mid-point of 
the voltage ramps are at 0.degree.. The position meter driving circuits 
essentially comprise differential amplifiers which cause the output 
voltage from the D/A converters to move from maximum negative to maximum 
positive voltage in a narrow range centered on zero volts so that the 
associated meters 40 and 41 are more sensitive to small increments of 
rotation of the shaft 10 and wheel W in the vicinity of the position where 
the respective counterbalance weight is to be placed. To find the position 
at which a counter-balance weight is to be attached to a rim, the operator 
rotates the wheel until the position meter 40 or 41 for such rim indicates 
null, i.e., zero volts. It should be noted that the wheel may be rotated 
in either direction to bring a position meter to a null reading. 
As previously noted, any corrective wheel weight emplacement orientation is 
possible with the apparatus of the present invention. Three ways of 
shifting the corrective weight emplacement position (assuming the force 
transducers to remain in a horizontal plane) are (1) providing a 
controlled phase displacement of the output of the filters 60a and 60b, 
(2) designing the logic circuitry reponsive to the outputs of the filters 
60a and 60b to provide counter reset signals at other selected phase 
angles, and (3) delaying the application of the digital outputs from the 
counters 84a and 84b to the digital-to-analog converters 86a, 86b. Also, 
it will be recognized that rather than resetting the counter to zero, any 
preselected number can be set into the counter to shift the rotative wheel 
position at which the corrective weights are placed. These changes require 
relatively simple and inexpensive modifications of the electronic 
components, without necessitating any change in the construction of the 
mechanical elements of the balancer. 
The logic circuitry for resetting the up-down counters in accordance with 
the phase of an associated unbalance force signal from filters 60a and 60b 
comprises parallel circuits, each circuit including a differential 
amplifier or comparator 73, a NAND gate Gl, and a capacitor C1 for 
coupling the leading (positive-going) edge of the output from the 
comparator to the NAND gate. With reference to that portion of the circuit 
for re-initializing the first up-down counter 84a in dependence on the 
zero-crossing phase of the analog output from the filter 60a, a first 
comparator 73 receives the sinusoidal output signal from the filter 60a, 
which signal has a phase related to the location of the counterbalance 
weight to be added to the first plane P1 of the wheel. A square wave 
signal is emitted from the comparator, with the square wave having a 
negative to positive transition when the sinusoidal unbalance signal from 
the filter 60a has a phase angle of 0.degree. (i.e., positive moving zero 
crossing). The leading edge of the square wave from the comparator is thus 
coincident with the point in time when the heavy spot in the plane P1 of 
the rim 11 is at top-dead-center and the emplacement position for the 
counterbalance weight on rim 11 is at the bottom-dead-center thereof. It 
should be noted at this point that the pulse from the comparator 73 is 
used in conjunction with a pulse issued from the spin cycle control 
circuit 96 on lead 97 to enable the AND gates 72a and 72b and thus close 
the switching circuits 68a and 68b to permit the unbalance force signals 
to be applied to the meter driving circuits 70a and 70b, respectively. The 
leading edge of the square wave output of the comparator 73 is coupled by 
the capacitor C1 to the NAND gate G1. The enabling signal applied via line 
97 is also applied, to the NAND gates G1. Hence, when the output of 
comparator 73 goes high, the output from the NAND gate G1 goes low to 
re-initialize the counter 84a. It will be noted tht when the positive 
signal on line 97 is terminated at the end of a testing cycle, no further 
reset pulses can be emitted, and thus the counters will then only continue 
to cycle in accordance with the wheel speed with the starting point being 
based upon the last reset signal received. Simultaneously, the switches 
68a and 68b will become non-conductive, whereby the readings on the weight 
meters 38 and 39 will be fixed also. 
The logic circuit for re-initializing the second counter 84b for 
determining the corrective weight emplacement position in the second plane 
P2 also includes a comparator 73 responsive to the sinusoidal output of 
the second filter 60b, a capacitor C1, and a NAND gate G1. This circuit, 
of course, functions in the same manner as that just described in 
connection with the first up-down counter 84a. 
As illustrated in FIG. 4, the count pulse producing circuit 78 comprises 
two voltage level detectors, or comparators, 100a and 100b for squaring 
the analog output signals on lines 20a and 20b, respectively. Due to the 
phase displacement of the signals from the switches 18a and 18b, the 
output signal from the first detector 100a will advance or lag the signal 
from the second detector 100b by 90.degree.. With reference to FIGS. 2 and 
3, it is noted that when the shaft 10 is rotated clockwise (which is the 
direction in which the tire is spun), the analog signal from the switch 
18a will lead that from the other switch 18b and accordingly the signal 
produced by the detector 100a will lead that from the other detector 100b 
by 90.degree.. 
The circuit 78 includes a pair of inverters 102a and 102b connected 
respectively to the outputs of the detectors 100a and 100b. The output of 
the inverters 102a and 102b are applied through a logic network, 
consisting of two inverters 104a and 104b and four one-shot circuits 106a, 
106b, 106c, and 106d, to a first AND/OR invert gate 107 (comprising a 
first bank of four AND gates 108a, 108b, 108c, and 108d and a NOR gate 
112) and a second AND/OR invert gate 109 (comprising second bank of four 
AND gates 110a, 110b, 110c, and 110d and a NOR gate 114). The NOR gate 112 
provides count-up pulses if one of the four AND gates 108a-108d produces 
an output signal; likewise, the NOR gate 114 provides count-down pulses if 
one of the four AND gates 110a-110d produces an output signal. The 
illustrated arrangement of logic circuitry acts as a pulse multiplier 
circuit to provide four count-up or four count-down pulses for each pulse 
on the respective input line 20a or 20b. 
It will be recognized from the logic circuitry illustrated in FIG. 4 that 
the AND/OR invert gate 107 will provide a train of output pulses at four 
times the frequency of the input on line 20a whenever the signal on line 
20a leads the signal on line 20b by 90.degree.. When the signal on line 
20b leads the signal on line 20a by 90.degree., the train of output pulses 
is provided on line 80b. 
It will be appreciated that the present invention provides extremely 
accurate angular position finding with a minimum of cost since no complex 
electromechanical or electronic components are required. Specifically, 
with 64 windows being uniformly spaced along the periphery of the disc 15 
and a multiplication factor of 4 being provided by the count pulse 
producing circuit 78, an accuracy of .+-.1.4.degree. is achieved. 
The spin cycle control circuit 96 includes a shaft speed detection means 
driven by the train of count-up pulses on the line 80a, the details of 
such detection means being entirely conventional and not being illustrated 
herein. When the motor M has reached a certain preselected speed, the 
speed detection means senses such condition and generates a signal which, 
after a preset time delay, is transmitted to the motor to reverse the 
power windings thereto and quickly bring the shaft 10 to a stop. When the 
shaft speed detection means subsequently indicates zero speed (by the 
termination of signal on line 80a and the initiation of signal on line 
80b), the reversing signal to the motor is removed and the shaft remains 
stopped. It is preferable to utilize a time delay after the shaft has 
reached a selected percentage of the operating speed of the motor; for 
example, a delay of 5 seconds may be provided after the achievement of a 
speed equal to 90 percent of the fixed operating speed of the motor. This 
sequence assures that the measurements (i.e., loading of the weight meters 
38 and 39 and setting of the counters 84a and 84b) will be made at the 
operating speed of the motor, which is a speed generally the same as the 
wheel W will rotate at when it is being driven on an automotive vehicle. 
It is important that the measurements be made when the shaft is at 
operating speed since the filters 60a and 60b are of a fixed frequency 
type. 
A brief discussion of the operation of the balancer of the present 
invention will now be presented. After mounting the wheel W, the operator 
pushes the start switch 44. The motor is thus activated in the forward 
direction (through control circuit 96), and simultaneously, a high signal 
is transmitted on line 97 to initiate measurement of the counterbalance 
weight magnitudes and positions. After reaching the selected speed plus 
the predetermined time delay, the measurements will have been made while 
the motor is operating at the proper speed; then the control circuit 96 
reverses the windings to the motor to brake rotation of the balancing 
shaft. Immediately at this point, the control circuit 96 removes the 
signal on line 97 whereby the switches 68a and 68b open and whereby reset 
pulses are no longer generated by the NAND gates G1. Thus, the weight 
meters 38 and 39 and the counters 84a and 84b will retain the respective 
magnitude and angular position information that they had on the last 
revolution of the shaft 10 prior to the time when the stop sequence was 
initiated. Upon reaching zero shaft speed, the motor braking mode signal 
is removed to leave the apparatus stopped. The counters 84a and 84b are 
now set to count pulses from starting positions associated with the 
unbalance magnitudes indicated by the respective weight meters 38 and 39, 
such that when the position meters 40 and 41 associated with the counters 
indicate a null, weights of the indicated magnitudes should be placed at 
the top and center of the respective rims. The operator then turns the 
wheel until one of the position meters 40 or 41 is nulled, and then places 
a counterbalance weight of the amount indicated by the associated weight 
meter 38 or 39, respectively, on the corresponding rim 11 or 13 at the top 
and center of the rim. The same wheel turning and weight emplacement 
operation is then carried out to place the corrective balancing weight on 
the other rim. The stop switch 46 is provided so that the operating 
sequence can be interrupted at any point if necessary. 
Although the best mode contemplated for carrying out the present invention 
has been herein shown and described, it will be apparent that modification 
and variation may be made without departing from what is regarded to be 
the subject matter of the invention.