U.S. patent application number 09/797348 was filed with the patent office on 2001-08-16 for wheel balancer with speed setting.
Invention is credited to Colarelli, Nicholas J. III, Douglas, Michael W., Parker, Paul Daniel.
Application Number | 20010013250 09/797348 |
Document ID | / |
Family ID | 27405508 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013250 |
Kind Code |
A1 |
Colarelli, Nicholas J. III ;
et al. |
August 16, 2001 |
Wheel balancer with speed setting
Abstract
A wheel balancer is provided that includes a shaft adapted for
receiving a wheel/tire assembly, the shaft having a longitudinal
axis and being rotatable about the axis so as to rotate a
wheel/tire assembly removably mounted thereon, a rotation sensor
for measuring rotation of the shaft about its longitudinal axis and
a vibration sensor operatively connected to the shaft for measuring
vibrations resulting from imbalance in the wheel/tire assembly. A
motor operatively connected to the shaft for rotating the shaft
about its longitudinal axis to rotate the wheel/tire assembly is
also included. The wheel balancer further includes a control
circuit for controlling the application of current to the motor to
rotate the wheel/tire assembly at a plurality of sustainable
speeds. The control circuit may also be adapted for determining
from vibrations measured by the vibration sensor at least one
weight placement position on the wheel/tire assembly to correct the
vibrations. In that embodiment, a manually operable input device is
included to set a desired speed of rotation of the wheel/tire
assembly, the control circuit being responsive to the input device
to cause the motor to rotate the wheel/tire assembly at the desired
speed, whereby a user can input a desired speed and balancer tests
the wheel/tire assembly at that speed.
Inventors: |
Colarelli, Nicholas J. III;
(Creve Coeur, MO) ; Douglas, Michael W.; (St.
Peters, MO) ; Parker, Paul Daniel; (Kirkwood,
MO) |
Correspondence
Address: |
Thompson Coburn LLP
One Firstar Plaza
St. Louis
MO
63101
US
|
Family ID: |
27405508 |
Appl. No.: |
09/797348 |
Filed: |
March 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09797348 |
Mar 1, 2001 |
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09311472 |
May 13, 1999 |
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09311472 |
May 13, 1999 |
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08706742 |
Sep 9, 1996 |
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08706742 |
Sep 9, 1996 |
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08594756 |
Jan 31, 1996 |
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Current U.S.
Class: |
73/462 ;
73/460 |
Current CPC
Class: |
G01M 17/022 20130101;
G01M 1/225 20130101 |
Class at
Publication: |
73/462 ;
73/460 |
International
Class: |
G01M 001/16 |
Claims
We claim:
1. A wheel balancer comprising: a shaft adapted for receiving a
wheel/tire assembly, said shaft having a longitudinal axis and
being rotatable about said axis so as to rotate a wheel/tire
assembly removably mounted thereon; a rotation sensor for measuring
rotation of the shaft about its longitudinal axis; a vibration
sensor operatively connected to the shaft for measuring vibrations
resulting from imbalance in the wheel/tire assembly; a motor
operatively connected to the shaft for rotating said shaft about
its longitudinal axis, thereby to rotate the wheel/tire assembly;
and a control circuit for controlling the application of current to
the motor to rotate the wheel/tire assembly at a plurality of
sustainable speeds.
2. The wheel balancer as set forth in claim 1 wherein the control
circuit is responsive to a wheel/tire assembly having a parameter
greater than a predetermined threshold, to cause the wheel/tire
assembly to rotate at a first sustained speed and causing
wheel/tire assemblies which do not exceed the predetermined
threshold to rotate at a second speed, the first speed being slower
than the second speed.
3. The wheel balancer as set forth in claim 2 wherein the parameter
is wheel size, said wheel size being manually inputted.
4. The wheel balancer as set forth in claim 2 wherein the parameter
is wheel inertia.
5. The wheel balancer as set forth in claim 1 wherein the control
circuit is responsive to the vibration detecting sensor assembly to
determine the imbalance of the wheel/tire assembly, said control
circuit being further responsive to vibration greater than a
predetermined vibration to cause the wheel/tire assembly to rotate
at a speed slower than a preset, standard speed of rotation.
6. The wheel balancer as set forth in claim 1 wherein the speed
selection signal is a manual input signal representing a desired
speed of rotation, said control circuit being responsive thereto to
cause the wheel/tire assembly to rotate at said desired speed.
7. The wheel balancer as set forth in claim 6 wherein the balancer
includes a measuring device for measuring the outer diameter of the
wheel/tire assembly and the desired speed of rotation is expressed
in units of linear velocity, the control circuit being responsive
to the measured diameter of the wheel/tire assembly to convert the
selected linear velocity to the corresponding speed of rotation for
the wheel/tire assembly.
8. The wheel balancer as set forth in claim 1 wherein said control
circuit has a calibration mode in which it controls the motor to
rotate the shaft at a variety of sustained speeds without a
wheel/tire assembly mounted thereon to detect resonances of the
balancer.
9. The wheel balancer as set forth in claim 1 wherein said control
circuit is responsive to signals from the vibration sensor assembly
indicative of a possible resonance condition to select a sustained
speed of rotation of the wheel/tire assembly which differs from the
speed of rotation at which the resonance indicative signals were
obtained.
10. The wheel balancer as set forth in claim 9 wherein the possible
resonance condition indicating signals are obtained with a
wheel/tire assembly mounted on the balancer.
11. The wheel balancer as set forth in claim 1 further including at
least one input device for providing speed selection signals to the
control circuit, the control circuit being responsive to at least
one speed selection signal to cause the wheel/tire assembly to
rotate at a sustained speed lower than the maximum speed of the
motor.
12. The wheel balancer as set forth in claim 11 further including a
hood having an operational position covering a portion of the
wheel/tire assembly during rotation and having a second position in
which it does not cover the wheel/tire assembly, wherein said input
device includes a sensor for sensing the position of the hood, said
control circuit being responsive to the hood being in the second
position to cause the wheel/tire assembly to rotate at a relatively
low speed and at relatively low torque.
13. A wheel balancer comprising: a shaft adapted for receiving a
wheel/tire assembly, said shaft having a longitudinal axis and
being rotatable about said axis so as to rotate a wheel/tire
assembly removably mounted thereon; a rotation sensor for measuring
rotation of the shaft about its longitudinal axis; a vibration
sensor operatively connected to the shaft for measuring vibrations
resulting from imbalance in the wheel/tire assembly; a motor
operatively connected to the shaft for rotating said shaft about
its longitudinal axis, thereby to rotate the wheel/tire assembly; a
control circuit for controlling the application of current to the
motor and for determining from vibrations measured by the vibration
sensor at least one weight placement position on the wheel/tire
assembly to correct said vibrations; a manually operable input
device to set desired speed of rotation of the wheel/tire assembly,
said control circuit being responsive to the input device to cause
the motor to rotate the wheel/tire assembly at the desired speed,
whereby a user can input a desired speed and balancer tests the
wheel/tire assembly at that speed.
14. The wheel balancer as set forth in claim 13 wherein the desired
speed is in revolutions per unit time.
15. The wheel balancer as set forth in claim 13 wherein the desired
speed is a linear velocity and the control circuit is responsive to
the desired linear velocity to rotate the wheel/tire assembly at a
rotational rate which corresponds to that linear velocity on the
vehicle for the wheel/tire assembly under test.
16. The wheel balancer as set forth in claim 13 further including a
display of the desired speed which includes a simulation of a
dashboard of a vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. application Ser. No.
09/311,472, filed May 13, 1999, which is a continuation-in-part of
U.S. application Ser. No. 08/706,742, filed Sep. 9, 1996, which is
a continuation-in-part of U.S. application Ser. No. 08/594,756,
filed Jan. 31, 1996, now abandoned.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
REFERENCE TO MICROFICHE APPENDIX
[0003] Not Applicable.
BACKGROUND OF THE INVENTION
[0004] This invention relates to wheel balancers and in particular
to wheel balancers with speed settings.
[0005] The determination of unbalance in vehicle wheels is carried
out by an analysis with reference to phase and amplitude of the
mechanical vibrations caused by rotating unbalanced masses in the
wheel. The mechanical vibrations are measured as motions, forces,
or pressures by means of transducers, which convert the mechanical
vibrations to electrical signals. Each signal is the combination of
fundamental oscillations caused by imbalance and noise.
[0006] It is believed that the drive systems for currently
available balancers could be improved to aid in operation. For
example, prior art balancers typically require the operator to
manually rotate the wheel/tire assembly to the desired position for
weight placement and/or runout correction. These balancers then use
a manual brake or the motor itself to temporarily hold the shaft in
the desired position. However, such a system could be improved.
Manual rotation to the desired position is less than satisfactory
since it requires the operator to interpret the balancer display
correctly. Moreover, manual rotation itself is not desirable, since
it ties up the operator's time and attention. In conventional
systems, however, the balancer motor cannot be used to rotate the
wheel/tire assembly to the correct position since available motor
controllers used in balancers are incapable of performing this
function.
[0007] Using the motor itself to provide a braking action is not
completely satisfactory either. Such braking is normally
accomplished by applying rectified alternating current to an AC
motor. This method is inherently subject to error. The actual
stopping position may be incorrect if the tire is larger than
average or turning too fast for the "brake" to respond. Moreover,
although currently available motor braking systems stop the wheel
in approximately the correct position, they do not actually hold
the tire in position since the motor would heat up if the "brake"
was left on. With conventional equipment, a wheel/tire assembly
with sufficient static imbalance to overcome its own inertia,
therefore, can roll away from the braked dynamic weight position as
soon as the braking energy is released. In addition, electrical
braking systems are usually of little use when power is removed
from the circuit, as could occur should a power failure take
place.
[0008] Currently available balancers could also be improved in
another way. Presently, the balancer shaft position is sensed and
the resulting signal is supplied to the control circuit. The
control circuit typically analyzes the signal using software to
determine if certain conditions (excessive rpm, excessive
acceleration, etc.) exist. These systems are not foolproof, and
could be improved.
[0009] Even when a wheel/tire assembly is balanced, non-uniformity
in the construction of the tire as well as runout in the rim can
cause significant vibration forces as the wheel rolls under vehicle
load. Most tire manufacturers inspect their tires on tire
uniformity machines and grind rubber off the tires as required to
improve rolling characteristics of the tires. Even after this
procedure, tires will often produce vibration forces (not related
to imbalance) of 20 pounds as they roll on a smooth road. To put
this in perspective of balancing, a 0.8 ounce balance weight is
required to produce a 20 pound vibration force on a typical wheel
traveling at 70 mph.
[0010] Prior art balancers are also not well equipped to take into
account and correct for variations in uniformity of the wheel rim
and the tire. It would be desirable, for example, to place a
measured amount of imbalance in a wheel to counter tire
non-uniformity forces or to detect and mark the position on a tire
which should be matched to a corresponding position on the rim to
reduce vibration due to non-uniformity of either or both. To the
extent that presently available balancers do measure rim and tire
runout, it is believed that the information they acquire is not
particularly useful to the operator. In particular, presently
available balancers which do measure runout generally display that
runout to the user in the form of sine waves referenced to some
arbitrary point. For a conventional system, which typically
measures radial runout of both rims, this results in two (basically
incomprehensible) sine waves. Such a system could be improved.
SUMMARY OF THE INVENTION
[0011] Among the various objects and features of the present
invention is a wheel balancer with improved performance.
[0012] Another object is the provision of such a wheel balancer
with an improved drive circuit.
[0013] A third object is the provision of such a wheel balancer
with an improved display.
[0014] Other objects and features will be in part apparent and in
part pointed out hereinafter.
[0015] Briefly, in a first aspect of the present invention, a wheel
balancer includes a shaft adapted for receiving a wheel/tire
assembly, the shaft having a longitudinal axis and being rotatable
about the axis so as to rotate a wheel/tire assembly removably
mounted thereon, a rotation sensor for measuring rotation of the
shaft about its longitudinal axis, a vibration sensor operatively
connected to the shaft for measuring vibrations resulting from
imbalance in the wheel/tire assembly, a motor operatively connected
to the shaft for rotating the shaft about its longitudinal axis,
thereby rotating the wheel/tire assembly, and a control circuit for
controlling the application of current to the motor to rotate the
wheel/tire assembly at a plurality of sustainable speeds.
[0016] In a second aspect of the present invention, a wheel
balancer includes a shaft adapted for receiving a wheel/tire
assembly, the shaft having a longitudinal axis and being rotatable
about the axis so as to rotate a wheel/tire assembly removably
mounted thereon, a rotation sensor for measuring rotation of the
shaft about its longitudinal axis, a vibration sensor operatively
connected to the shaft for measuring vibrations resulting from
imbalance in the wheel/tire assembly, a motor operatively connected
to the shaft for rotating the shaft about its longitudinal axis,
thereby rotating the wheel/tire assembly and a control circuit. The
control circuit controls the application of current to the motor
and determines, from vibrations measured by the vibration sensor,
at least one weight placement position on the wheel/tire assembly
to correct the vibrations. A manually operated input devices is
also included to set a desired speed of rotation of the wheel/tire
assembly, the control circuit being responsive to the input device
to cause the motor to rotate the wheel/tire assembly at the desired
speed, whereby a user can input a desired speed and balancer tests
the wheel/tire assembly at that speed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a diagrammatic view illustrating a generic wheel
balancer suitable for use with the present invention;
[0018] FIG. 2 is a simplified top plan view illustrating the
preferred embodiment of the wheel balancer of the present
invention;
[0019] FIG. 3 is a block diagram illustrating electrical circuitry
of the wheel balancer of FIG. 1 or FIG. 2;
[0020] FIG. 4 is a simplified schematic of the electronic control
circuitry of the balancer of the present invention;
[0021] FIG. 5 is a block diagram of motor control circuitry of the
balancer of the present invention;
[0022] FIG. 6 is a simplified block plan view illustrating the use
of the balancer of the present invention with a load roller and
various measuring devices;
[0023] FIG. 7 is a schematic circuit diagram of the drive circuitry
used in the present invention;
[0024] FIG. 7A is a schematic circuit diagram of control signal
circuitry used in the present invention;
[0025] FIG. 8 is a schematic circuit diagram of electrical braking
circuitry used in the present invention;
[0026] FIG. 9 is a schematic circuit diagram of a hardware safety
interlock circuit used in the present invention;
[0027] FIGS. 10 and 10A illustrate various displays used in the
present invention; and
[0028] FIG. 11 illustrates an additional speed setting display used
in the present invention.
[0029] Similar reference characters indicate similar parts
throughout the several views of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0030] Turning to the drawings, FIG. I illustrates (in simplified
form) the mechanical aspects of a wheel balancer 11 suitable for
the present invention. Balancer 11 includes a rotatable shaft or
spindle 13 driven by a suitable drive mechanism such as a direct
current 0.5 horsepower electric motor M and drive belt 53 (FIG. 2).
Mounted on spindle 13 is a conventional quadrature phase optical
shaft encoder 15 which provides speed and rotational position
information to the circuitry of FIG. 3.
[0031] During the operation of wheel balancing, at the end of
spindle 13, a wheel/tire assembly 17 under test is removably
mounted for rotation with spindle hub 13A (FIG. 2). To determine
wheel/tire assembly imbalance, the balancer includes at least a
pair of piezoelectric type imbalance force sensors 19 and 21 (or
other suitable sensors such as strain gauges) coupled to spindle 13
and mounted on the balancer base 12. For ease of reference herein,
sensor 19 is referred to as the "L" (Left) sensor and sensor 21 is
referred to as the "R" (Right) sensor.
[0032] Turning to FIG. 2, it can be seen that the actual
construction of the mechanical aspects of balancer 11 can take a
variety of forms. For example, spindle 13 can include a hub 13A
against which wheel/tire assembly 17 abuts during the balancing
procedure. Moreover, sensor "L," sensor "R," and sensor 22 need not
directly abut spindle 13. For example, various arms or rods as
shown in FIG. 2 can be used to mechanically couple the sensors to
the spindle so that they are exposed to the vibrations and/or
forces of the spindle.
[0033] When wheel/tire assembly 17 is unbalanced, it vibrates in a
periodic manner as it is rotated, and these vibrations are
transmitted to spindle 13. The "L" and "R" sensors are responsive
to these vibrations of the spindle. Specifically, they generate a
pair of analog electrical signals corresponding in phase and
magnitude to the vibrations of the spindle at the particular
transducer locations. These analog signals are input to the
circuitry of FIG. 3, described below, which determines the required
magnitudes and positions of correction weights to correct the
imbalance.
[0034] Turning to FIG. 3, wheel balancer 11 includes not only the
"L" and "R" sensors, and spindle encoder 15, but also a graphic
signal processing (GSP) chip 23. Preferably GSP chip 23 is a Texas
Instruments model TMS34010 chip. GSP chip 23 performs signal
processing on the output signals from the "L" and "R" sensors to
determine wheel imbalance. In addition it is connected to and
controls a display 25 which provides information to the user,
controls motor M through motor control circuitry 27 described in
more detail below, and keeps track of the spindle position from
encoder 15. More specifically, encoder 15 is a 128 count, two
channel quadrature encoder, which is fully decoded to 512 counts
per wheel revolution by GSP chip 23. Although GSP chip 23 is
preferred, it should be understood that other controller circuitry
could be used as well.
[0035] Balancer 11 also includes manual inputs 29 (such as a
keyboard and parameter input data dials) which are also connected
to GSP chip 23. Chip 23 has sufficient capacity to control via
software all the operations of the balancer in addition to
controlling the display. The GSP chip is connected to EEPROM memory
31, EPROM program memory 32, and dynamic RAM (DRAM) memory 33. The
EEPROM memory is used to store non-volatile information, such as
calibration data, while the GSP chip uses DRAM 33 (as discussed
below) for storing temporary data.
[0036] GSP chip 23 is also connected to an ADC 35, which is
preferably an Analog Devices AD7871 type device or any other
appropriate chip. ADC 35 is a fourteen (14) bit A/D converter with
an on-board voltage reference.
[0037] The signals from the "L" and "R" sensors 19 and 21 are
supplied through anti-aliasing circuitry 37, 39 to ADC 35. More
specifically, the signals are each fed through unity gain buffers
(not shown but well known in the art) to anti-aliasing filters
making up part of circuitry 37, 39. Sallen/Key type low pass
Butterworth filters function well for this purpose.
[0038] The operation of the various components described above is
fully described in U.S. Pat. No. 5,365,786 and 5,396,436, the
disclosures of which are incorporated herein by reference. It
should be understood that the above description is included for
completeness only, and that various other circuits could be used
instead. The GSP chip could be replaced by a general purpose
microcontroller, for example, with no loss of efficiency in
carrying out the present invention. The motor drive aspects of the
present invention may be better understood by reference to the
simplified diagram of FIG. 4 in which the GSP chip is replaced with
a generic CPU 51 and motor M drives the wheel/tire assembly through
a 5.37:1 belt drive 53. Also indicated in FIG. 4 is a 30 Hz
watchdog pulse supplied on a set of control lines 55 to motor
control drive 27. In addition, control line set 55 includes a
digital signal of software settable duty cycle which is interpreted
by the motor drive as a linear function of desired "torque." In
other implementations of this invention, it is also possible to
achieve this function using a varying analog level, a frequency
modulated digital signal, and other such approaches, depending on
the drive input requirements. The third control line to the motor
drive is a drive enable line.
[0039] The motor control drive 27 is illustrated in FIG. 5. Drive
circuit 27 has four drive transistors Q1, Q2, Q3 and Q4 connected
as shown to provide direct current to the windings of direct
current motor M selectively with each polarity. Specifically,
transistor Q1 is connected to supply current from a dc rectified
source to one side of the windings of the motor. When current is
supplied through transistor Q1 to the windings, the circuit is
completed through the windings and transistor Q4 (and a current
sensing resistor RS) to ground. This causes the windings of motor M
to be energized so as to cause rotation of the balancer shaft in a
first rotational direction. Similarly, when transistors Q1 and Q4
are rendered non-conductive and transistors Q2 and Q3 conduct, the
windings are energized in the opposite polarity. It is preferred
that the direction of rotation of motor M be controlled by pulse
width modulating (PWM) current to the transistors. A duty cycle of
50% causes the current to flow through motor M in both directions
in equal amounts. By the use of a suitably high pulse rate, the
motor has insufficient time to respond to the rapidly reversing
currents, with the result that the motor velocity is zero. As
explained below, the de motor actively holds the shaft at its
present location. This provides, in effect, a "detent" function for
the drive circuit 27.
[0040] A duty cycle of less than 50%, on the other hand, causes
counterclockwise rotation of the motor shaft. As the duty cycle
decreases from 50%, the counterclockwise torque becomes stronger
and stronger. Similarly, a duty cycle of more than 50% causes
clockwise rotation of the motor shaft. As the duty cycle increases
above 50%, the clockwise torque in turn becomes stronger and
stronger. A 0% duty cycle results in maximum torque
counterclockwise, while a 100% duty cycle results in maximum torque
clockwise.
[0041] It is preferred that transistors Q1-Q4 be insulated gate
bipolar transistors (IGBTs) such as those sold by International
Rectifier under the trade designation IRGPC40KD2. Other similar
transistors, or transistors having similar characteristics such as
MOSFETS, could also be used.
[0042] If it is desired to use an AC motor, the drive system would
preferably be some type of AC vector drive, although such drives
are at present significantly more expensive.
[0043] Whatever drive system is used, it preferably has interface
circuits 34, 36, and 38 for the drive enable, "torque" input, and
watchdog inputs respectively from the CPU. These signals are
supplied to a control logic circuit 40 which performs necessary
logic functions, as well as conventional deadband, and current
limit functions. Circuits to perform the functions of circuit 40
are well known. The current limit function of circuit 40 depends
upon the current measured by current sense resistor RS, the voltage
across which is detected by a current limit detection and reference
circuit 41.
[0044] Circuit 40 has four outputs. The first, a drive fault line
DF, is used to signal the CPU chip that a drive fault has occurred.
The second and third, labeled GD1 and GD2, supply PWM control
signals to the actual gate drive circuits 43 and 45, circuit 43
being connected to the gates of transistors Q1 and Q3, and circuit
45 being connected to the gates of transistors Q2 and Q4. The
fourth output of circuit 40, labeled SD, allows circuit 40 to
provide a shutdown signal to gate drive circuits 43 and 45. In
addition, the shutdown signal is supplied to a transistor Q5 (FIG.
7A) whose drain is connected to braking resistor RB. When the
shutdown signal occurs, the drive transistors Q1-Q4 turn off and
the braking resistor gets shorted between the 390 VDC bus and
ground. This provides braking for the motor during a shutdown
condition.
[0045] To understand the improvements of the present invention, it
is helpful to examine some terms. FIG. 6 shows a tire 17 with a
load roller 91 pressing against it, along with the three contact
forces which are defined as radial, lateral and tractive. Tire
uniformity is a term which refers to a condition in which some
property of a tire is not symmetric about its rotational axis.
There are many uniformity parameters which can be quantified.
[0046] The root-mean-square value of radial force variation is a
good uniformity parameter to use, as shown in U.S. Pat. No.
4,702,103, because it is representative of the power produced by
the tire rotating on the vehicle as a result of force variations in
the vertical direction.
[0047] A value for the tire stiffness is required to convert rim
runout into radial force variation due to rim runout: (rim
runout)(tire stiffness)=radial force variation due to rim runout.
Loaded radial runout of the wheel tire assembly can also be
converted to a force variation value by using the tire stiffness or
it can be measured directly as will be shown later. By subtracting
the rim force variation from the wheel/rim assembly force
variation, the tire force variation can be obtained. By shifting
the angle of the tire force variation relative to the rim force
variation, the root-mean-square value of wheel/tire assembly force
variation can be computed at many remount angles of tire to rim.
Selecting the remount angle with the lowest wheel/tire assembly
radial force variation is then possible.
[0048] The first harmonic of radial force variation is believed to
be the best uniformity parameter to use to minimize wheel vibration
because it also helps minimize the first harmonic tractive force
variation. U.S. Pat. No. 4,815,004 shows how tractive force
variation can be determined based on wheel properties and
rotational speed squared. Taking equation (17) in U.S. Pat. No.
4,815,004 and applying it to a vehicle moving on a flat road at
constant speed, one finds: 1 F = I 2 r i = l .infin. iU i cos ( i t
+ i )
[0049] where F.sub.t is the tractive force on the tire, I is the
polar moment of inertia of the wheel/tire assembly and vehicle hub,
.omega. is the angular velocity of the wheel, r is the outer radius
of the tire, U.sub.i is the ith Fourier coefficient of the change
in effective radius per revolution of the tire, t is elapsed time,
and .phi. is the phase shift of the ith harmonic. This equation may
be used to calculate the radial and tractive force variations on a
wheel with typical properties as illustrated by the following
example:
[0050] Wheel/tire assembly is perfectly uniform except for 0.005"
radial mounting offset on the vehicle hub
[0051] Wheel assembly weight=35 lb.
[0052] O.D. of wheel=24 inches
[0053] Polar moment of inertia of the wheel/tire assembly and
vehicle hub=0.7 slug ft.sup.2
[0054] Vehicle speed=75 mph, which means the wheel rotational speed
is 110 radians/second
[0055] Tire stiffness is 1200 lb/inch
[0056] Peak to Peak Radial force variation=(0.005")(1200
lb/in)(2)=12.0 lb
[0057] Peak to Peak Tractive force variation=((0.7 slug
ft.sup.2)(110.sup.2)(radian/sec).sup.2/1 ft)* (0.005/12 ft)(2)=7.1
lb
[0058] Note: 90 degrees of wheel rotation occurs between peak
radial and tractive forces. The combination of radial and tractive
forces, therefore, is equivalent to a force vector which rotates
with the tire. It is believed that the relationship between
wheel/tire assembly radial and tractive force variations caused by
factors other than mounting offset used in this example is
similar.
[0059] Turning to FIG. 6, there is shown a load roller 91 suitably
disposed adjacent wheel/tire assembly 17 so that it may be forced
into engagement with the tire so as to measure loaded runout of the
assembly. More specifically, load roller 91 is carried on a shaft
92 suitably journaled on an L-shaped arm 93 (only the lower limb of
which is clearly visible in FIG. 7) designed to pivot about the
axis of a shaft 94. CPU 51 causes the arm to pivot to place load
roller into engagement with the tire by actuating an air cylinder
95 or an air bag actuator. Air pressure to cylinder 95 can be
variably adjusted by CPU control. Air pressure feedback is provided
by a sensor 102 such as those sold under the trade designation MPX
5700D by Motorola Inc. The feedback enables precise load roller
forces to be generated and provides a unique safety feature in that
the CPU can detect pressure problems and remove air pressure if
needed. Rotation of shaft 94 (specifically rotation of a magnet 94A
mounted on shaft 94) is sensed by a sensor 96 such as a Hall-effect
sensor such as those sold under the trade designation 3506, 3507 or
3508 by Allegro Microsystems Inc. and the amount of rotation is
signaled to the CPU.
[0060] By applying a known force to the tire with the load roller
and watching the output of sensor 96, the CPU can determine the
loaded runout of the wheel/tire assembly. Specifically, CPU 51 uses
the output of sensor 96 to measure the runout of wheel/tire
assembly 17 under the predetermined load. To determine imbalance
weight amounts which are required to counteract the forces due to
runout of the wheel, the CPU also needs tire stiffness information.
Stiffness information can be downloaded directly from another
measuring device such as a shock tester (not shown), or can be
manually input using the manual input device 29, or can be recalled
from a stored database. Alternatively, the CPU can determine tire
stiffness directly by sequentially applying at least two different
loads to load roller 91 and measuring the change in deflection. The
amount of additional correction weight needed to counteract the
forces due to the loaded runout is found by the following formula:
2 correction mass = loaded runout first harmonic * tire stiffness *
% radial force for counteract ( radius to place correction weight )
* ( rotational speed ) 2
[0061] With the additional mechanisms of FIG. 6, it is possible to
further improve the balancing of the wheel/tire assembly. For
example, by manually inputting the load range of the tire under
test, the operator can cause CPU 51 to adjust the force on load
roller 91 to a value which will make the loaded runout measurement
most closely agree with the vibration of the wheel when it is
mounted on the vehicle. Moreover, the speed at which the vibration
is to be minimized may also be inputted to CPU 51 so that imbalance
correction may be optimized for this parameter as well. Generally,
that speed would be selected to be at or slightly above the wheel
hop resonant frequency. This speed also should be close enough to
the maximum operating speed to prevent excessive correction at the
maximum speed. The amount of this correction also should have a
maximum limit of 0.5 oz.
[0062] In addition, CPU 51 is preferably connected to suitable
sensors 88 and 97 for measuring the axial and radial runout of the
inside and outside rims of assembly 17 at the bead seats. Various
sensors suitable for the task are known. These outputs are radial
and axial rim runout signals. The first harmonic of radial rim
runout (both angle and magnitude) is determined by CPU 51 using a
suitable procedure such as digital filtering or discrete Fourier
transform (DFT). The same process can be performed to determine
axial runout for each rim. With both tire and rim roundness
measurements, CPU 51 is able to compare the measured values with
stored rim and tire runout specifications. When those
specifications are not met, it is a simple calculation to determine
a remounted orientation of the tire on the rim, which minimizes the
total loaded runout. CPU 51 causes the display of such an
orientation on display 25, along with the residual loaded runout
which would remain after remounting. Alternatively, this
information may be used to calculate the positions and amounts of
required tire grinding to correct the loaded runout.
[0063] Since the present motor control circuitry is capable of
rotating the balancer shaft at any speed, it may, if desired,
slowly rotate the wheel/tire assembly while the various runout
measurements are being taken. If desired, such measurements may be
taken over two or more revolutions of the wheel/tire assembly, and
the results averaged. If measurements over different revolutions
differ by more than a preset amount, CPU 51 is preferably
programmed to take additional measurements.
[0064] Since the angular position of the wheel/tire assembly is
directly controllable with the motor control circuitry of the
present invention, after the minimized loaded runout position is
calculated, CPU 51 may cause the assembly to slowly rotate to that
position (putting that position on the tire at a predetermined
position such as twelve o'clock, for example) and then hold that
position. If a tire bead breaker is integrated with the balancer,
motor M can index the rim while the tire is held stationary by the
bead breaker, eliminating many steps of current matching procedures
involving a separate tire changer.
[0065] Instead of measuring deflection of the load roller 91 as
described above, alternatively CPU 51 can use the balancer force
transducers 19 and 21 to measure the load applied by a rigidly
mounted roller. Roller 91 can be rigidly mounted, for example, by
loading it with a desired force from an air cylinder and then
locking it into place with a pawl or using an electric motor with
lead screw and nut. This measurement (known as radial force
variation) can be used to determine what correction weights are
needed to cancel out the vibrations due to this wheel assembly
non-uniformity. Note that tire stiffness is not required to find
the correction weights needed to counteract the wheel's radial
force variation. Using this system, the 3 correction mass = first
harmonic of radial force variation ( radius to place correction
weight ) * ( rotational speed ) 2
[0066] If there is a difference in effective diameters in two
wheels mounted on the front of a front wheel drive vehicle, there
will be a tendency for the vehicle to steer away from a straight
line when driven on a flat road. The effective diameter of a
wheel/tire assembly is the distance a vehicle will advance in a
straight line on a flat road when the wheel/tire assembly rotates
exactly one revolution, divided by the value of .pi.. Differences
in effective diameter as small as 0.013 inches have caused
noticeable steering problems. The output of sensor 96 show in FIG.
7, which measures the rotational position of the load roller arm,
can be used to determine a value related to the effective diameter
of the wheel/tire assembly. An alternate method to determine the
effective diameter is by measuring the ratio of the angular
rotation of the load roller and the angular rotation of the
wheel/tire assembly and then multiplying this ratio times the
diameter of the load roller. Displaying a message to the operator
pertaining to effective diameters (or differences in diameters) of
the wheel/tire assemblies and to stored specifications is
useful.
[0067] Different vehicles are sensitive to non-uniformity in
wheel/tire assemblies at different levels. For example, a medium
duty truck with a first harmonic radial force variation of 50 lb.
will not be likely to receive ride quality complaints while the
same value of first harmonic radial force variation on a small
automobile is very likely to produce an objectionable ride. By
providing means for the operator to input the vehicle model or the
class of vehicle on which the wheel/tire assembly is to be mounted,
and by having stored uniformity specifications contained in the
balancer's control circuit, it is possible for the balancer to
compare the measured wheel/tire assembly's uniformity parameters to
the specifications and send a message to the operator when the
wheel/tire assembly is outside of specification. A very complete
listing of hundreds of vehicle models and optional equipment
packages could be used, or a very simple class system with as few
as two classes (such as car vs. truck) could be used to apply
stored specifications. The use of these specifications can help the
operator spend time where it is useful and avoid wasting time and
effort when the specifications show that a large value of a
uniformity parameter is acceptable.
[0068] After measurements and computations have been made to
determine the values of various uniformity parameters, this
information can be displayed to the operator.
[0069] Immediately after a tire is mounted to a rim, the tire bead
is not always firmly located against the rim bead seat. This can
result in errors in imbalance measurements. An important benefit of
the load roller is that it strains the tire and causes the tire
bead to seat firmly before balancing. Additionally, the load roller
provides a break-in of the tire carcass (reducing or eliminating
non-uniformities due to initial construction of the tire or from
the tire being deformed during shipping and storage).
[0070] Although automatic movement to a calculated rotational
position is described above in connection with loaded runout, it
should be understood that the present balancer is capable of such
automatic movement to any calculated position, such as correction
weight application points other than the standard 12:00 o'clock
position. For example, to mount an adhesive backed weight, the CPU
causes the motor to rotate the wheel/tire assembly so that the
correction weight position matches the 6:00 position so that the
operator can more easily apply the weight. The particular type of
weight(s) being used are manually input using device 29 so that the
CPU can perform the proper calculation of correction weight
position. In addition, a desired wheel/tire assembly rotational
position may be manually requested by manual input device 29.
Alternatively, an operator may manually move the wheel/tire
assembly from one position at which the motor is holding the
assembly to another. CPU 51 is programmed to cease holding at any
given position once an angular force greater than a predetermined
threshold force is applied to the assembly, such as by the operator
pushing the tire. The magnitude of such a force is sensed
indirectly by the CPU 51 by examining the amount of current
required to overcome the applied force and hold the wheel/tire
assembly in place. Once the manual movement of the assembly stops,
CPU 51 controls motor M to rotate the wheel to the other balance
plane weight location and hold the assembly in the new
position.
[0071] CPU 51 also controls the torque applied by the motor
indirectly. The EEPROM has stored the current vs. torque
characteristics of the motor M and uses those characteristics to
determine the actual torque applied. This actual torque is compared
to the desired torque for any particular application, several of
which are described below. A simple example is the application of
relatively low torque at the start of the spin, which prevents
jerking of the wheel by the balancer, followed by relatively higher
torque to accelerate the tire to measurement speed as quickly as
possible.
[0072] Slow rotation of the wheel/tire assembly is useful in
several situations. For example, in measuring rim runout (whether
loaded or unloaded) CPU 51 can rotate the assembly 17 at a
controlled slow speed (1 Hz or so). This frees both of the
operator's hands so that left and right rim runout may be measured
simultaneously. Slow rotation is also useful in tightening wing nut
101 (FIG. 2) onto shaft 13. In this mode of operation CPU 51 causes
the shaft to rotate at about 2 Hz while the operator holds wing nut
101 in place. This provides a quick spin-on of the wing nut.
Rotation continues until the current draw indicates resistance
against further movement. Alternatively, the CPU may examine the
current vs. torque characteristics of the motor to allow the
operator to continue tightening the wing nut until a desired preset
torque is reached. In yet another mode, the shaft rotates at an
even slower speed (1/2 Hz or so) while the operator tightens the
wing nut. This allows the wheel to "roll" up the cone taper,
instead of being shoved sideways up the taper, resulting in better
wheel centering on the cone.
[0073] Although the present motor control is capable of very slow
rotation and fast rotation for measurement, intermediate speeds for
imbalance measurement are also achievable and useful. For example,
a large tire (as measured by sensor 96 or as indicated by a manual
input from device 29) may be rotated at a speed which is somewhat
slower than that used for smaller tires. This shortens total cycle
time and also allows the rotary inertia of big tires to be kept
below predefined safety limits (which feature is especially useful
with low speed balancing with no wheel cover). Similarly, a tire
with a large imbalance may be tested at a slower speed than usual
to keep the outputs of sensors 19 and 21 within measurable range.
This prevents analog clipping of the sensor signals and permits
accurate imbalance measurements to be taken under extreme imbalance
conditions. In addition, large tires may be rotated at a slower
rotary speed than smaller tires to achieve the same linear speed
(MPH) for those operators who desire to test wheel imbalance at
speeds corresponding as much as possible to highway speeds or a
"problem" speed.
[0074] Since the speed of rotation can be accurately controlled
with the present invention, it is desirable to perform a
calibration run on the balancer in which the balancer is
automatically sequenced through a multitude of speeds. If balancer
resonant vibrations are detected by CPU 51 at any of those speeds,
CPU 51 stores those resonant speeds in memory and avoids those
resonant speeds in subsequent measurement operations on a
wheel/tire assembly. The magnitude of signal from an imbalance
force sensor normally increases nearly proportionally to the square
of the rotational speed. The angular relationship of the signal to
the balancer spindle normally does not change significantly with
rotational speed. Any deviation from this signal/frequency
relationship can be detected as a resonance.
[0075] In a similar manner, the balancer can detect that an
imbalance measurement of a wheel is invalid by comparing each
revolution's sensor reading and if the magnitude or angle changes
beyond preset limits then the measurement is considered "bad" and
the CPU changes the speed of rotation until a good reading can be
obtained.
[0076] Inasmuch as the present invention permits the wheel/tire
assembly to be rotated in either direction, the present balancer
may be used to rotate in either direction, as selected by the
operator. In addition, if desired, the assembly may be rotated in a
first direction for measurement of imbalance and in the opposite
direction during the check spin after correction weight(s) are
applied.
[0077] The motor control drive is illustrated in more detail in
FIG. 7. The drive circuit has four drive transistors Q1, Q2, Q3 and
Q4 connected as shown to provide direct current to the windings W
of motor M selectively with each polarity. Specifically, transistor
Q1 is connected to supply current from a 390VDC source to one side
of the windings of the motor. When current is supplied through
transistor Q1 to the windings, the circuit is completed through the
windings and transistor Q4 to ground. This causes motor M to drive
the balancer shaft in a first rotational direction. When rotation
in the opposite direction is required, transistors Q1 and Q4 are
rendered non-conductive and transistors Q2 and Q3 conduct. This
causes current from the 390VDC source to flow through Q3 and
through windings W in the opposite direction. The circuit is
completed through transistor Q2 to ground. This causes rotation of
the balancer shaft in the opposite direction.
[0078] It is preferred that transistors Q1-Q4 be insulated gate
bipolar transistors (IGBTs) such as those sold by International
Rectifier under the trade designation IRGPC40KD2. Other similar
transistors, or transistors having similar characteristics such as
MOSFETS, could also be used.
[0079] The control signals for transistors Q1-Q4 comes from the
gate and emitter outputs of corresponding gate and emitter outputs
of driver chips U1-U4, which are preferably Fuji EXB-840 type
hybrid circuits. The outputs of chips U1 and U2 are always
complementary, as are those of U3 and U4, so as to energize the
drive transistors Q1-Q4 as described above. This is accomplished
through common drive signals PHASE1 and PHASE2 applied to the
driver chips. These drive signals are generated by a PWM generator
U5 under the control of the CPU 23, which thereby controls the
direction of current through motor M (and hence the direction of
rotation of the shaft), as described above. Each driver has its own
power source derived from square wave signals DRV1 and DRV2 applied
to corresponding transformers T1-T4 associated with each driver
chip.
[0080] Referring to the bottom portion of FIG. 7, it can be seen
that the motor winding current in every case flows through a
sensing resistor R1 or a sensing resistor R3. This current is
supplied to a comparator and filtering circuit 65 composed of four
op amps U11 configured with passive devices to provide warning
signals when the current through resistor R1 exceeds a preset
amount (such as 8 amps). When a warning signal occurs, the drive
signals (labeled Phase1 and Phase2) all go low, thereby shutting
off the flow of current through the motor windings. The PWM
generator also receives a TORQUE-A signal and a SHUT DOWN signal,
both of which are described below. More specifically, the TORQUE-A
signal and a signal representing motor current are supplied to an
op-amp network 66 whose output is supplied to the PWM generator.
During normal operation, the output of network 66 controls the duty
cycle of PWM generator U5 as commanded by the CPU 23 to control
operation of the motor as described above. The SHUT DOWN signal is
used to shut down the motor during an abnormal situation.
[0081] The SHUT DOWN signal is generated in the circuitry of FIG.
7A. FIG. 7A shows a plug J2 attached to the CPU 23 (the CPU is not
shown in FIG. 7A) which supplies the desired torque information,
and the watchdog and enable pulses, from the CPU to the circuitry
of FIG. 7A. The plug also passes back to the CPU a fault signal.
The desired torque watchdog and enable signals are passed through
optical isolators OP1-OP3 to the remaining circuitry. In similar
fashion, the fault signal is optically isolated by unit OP4.
[0082] The desired torque signal is converted by a circuit 78 to
analog form, with the corresponding analog signal being labeled
TORQUE. The desired torque signal is also supplied to a
multivibrator circuit 80, whose output is an indication of whether
or not the desired torque signal is being received from the CPU.
This is ORed with other signals, and supplied through an inverter
82 to a flip-flop 84, whose output is the SHUT DOWN output. The
enable signal is supplied directly from isolator OP2 to the enable
pin of flip-flop 84, so that when the enable signal from the CPU is
missing, the SHUT DOWN signal is active.
[0083] The watchdog signal is supplied to a multivibrator circuit
86, whose output is also supplied through the inverter 82 to
flip-flop 84. The final ORed input to the flip-flop is an OVERSPEED
signal, described below. As can be seen, when any of the control
signals indicate a problem, the SHUT DOWN signal represents that
fact. This signal is supplied directly to the PWM generator U5
(FIG. 7) to shut down the motor.
[0084] Turning to FIG. 8, there is shown an alternative circuit for
providing a dynamic braking function. Specifically, if power is
removed from balancer 11 during operation, the dc motor M functions
as a generator so long as the wheel/tire assembly continues
rotating. This keeps the dc bus alive during the dynamic braking
process. The braking circuit includes a 33 ohm, 50 watt resistor
R15 connected between the 390-volt source and a transistor Q9. When
the transistor conducts, resistor R15 serves to dissipate the
energy in the rotating motor, bringing it to a halt. Transistor Q9
conducts when the back emf of the motor rises above a threshold.
This can occur during two situations: normal motor deceleration and
power loss. The motor is normally decelerated by applying a reverse
torque to the motor using the H-bridge described above. This causes
the back emf to rise. During deceleration, the transistor Q9 is
pulsed to keep the bus at a nominal level during reverse torque
braking. During power loss, the transistor is held full-on, thereby
providing electric braking.
[0085] FIG. 9 illustrates a hardware safety interlock circuit of
the present invention. In this circuit, various signals (such as
hood open signals, and rotation rate signals (labeled CHA and CHB))
are supplied to an independent 8051-type processor U21. When the
encoder signal represent a rotational speed above a preset limit
(such as 20 to 30 rpm) and the hood is open, chip U21 provides an
overspeed signal through an opto-coupler OPT11 and a transistor Q21
to the connection labeled OVERSPEED on FIG. 9. This, as described
above, is used to shut down the motor by controlling the operation
of PVM generator U5.
[0086] Similarly, when the inputs indicate an excessive torque
situation (e.g., over 2-3 ft-lbs.) when the hood is open, chip U21
signals this condition through an opto-coupler OPT13 which controls
the output of a 4053-type 1-of-2 switch U23. Switch U23 also
provides the regular "Torque" signal (described above in connection
with FIG. 7A) to the rest of the control circuitry when the hood is
down. When the hood is up, switch U23 connects the TORQUE input to
a 1/3 voltage divider, which thereupon supplies a signal through a
voltage follower to the TORQUE-A output, which is supplied (FIG. 7)
to the drive circuit to limit the torque to a preset amount (2-3
ft-lbs.). When the hood is down, the TORQUE input is supplied
directly through the voltage follower.
[0087] Turning to FIG. 10, there is shown an improved display 25B
of the present invention. As described above, the present balancer
can acquire the loaded runout, axial runouts and radial runouts of
the wheel/tire assembly. These are displayed in connection a
three-dimensional representation of the wheel/tire assembly.
Specifically, the display of FIG. 10 represents an example of the
runout display after the spin has determined loaded runout and
after the runout arms 88 and 97 have been used and retracted. The
CPU translates the runouts and force variations obtained at the
devices' particular contact points to 12:00 position runouts, and
displays the acquired runouts with respect to the instantaneous
position of the main shaft encoder as if the user had taken the
time and expense to place runout gauges on the physical wheel.
[0088] The display of FIG. 10 shows the total indicated readings of
runout (by means of the numerals on the displayed needle gauges
111, 113, 115, 117), any bad total readings (by highlighting the
corresponding numerals in a contrasting color), and the graphical
range of the runout readings (by providing a lighter colored pie
section in each needle gauge representation corresponding to the
measured variation in runout). This latter feature allows the user
to tell at a glance the total travel the needle of each gauge would
have without rotating the wheel at all. It is preferred that the
gauge representations have green, yellow and red color bands, which
are automatically scaled per the sensitivity of that particular
reading for that particular type of vehicle.
[0089] Note that the display includes bumps on the rim and tire.
These represent the relative magnitudes and locations of the
measured runouts. These features move around the axis of the
displayed wheel as the actual wheel is moved. The display also
includes a representation 121 of the position of the valve stem on
the display. This position is acquired by the system via encoder
15. For example, the user can be instructed to start the
measurements with the rotational position of the valve stem at the
12:00 o'clock position.
[0090] In the display of FIG. 10, the loaded runout "high spot" is
nearly opposite the rim high spots, as can be seen readily from the
display. This means that matching of the tire to the rim by
removing the tire and repositioning it could greatly reduce or even
eliminate total runout. The system is programmed to respond to the
"Show after Optimized" switch 125 to illustrate the various runouts
that would result if this matching were performed, thereby
informing the user if the procedure would be worthwhile.
[0091] The various key displays on FIG. 10 (Show After Optimized
key 125, Exit key 127, Measure Rim Runouts 129, and Show Before
Optimized key 131) can be replaced by the key displays shown in
FIG. 10A to allow the user to request additional functions as
indicated by those displays. The show T.I.R. Readings (total
indicated readings) is the default. Alternatively, live readings as
obtained from the data acquisition system may be displayed, as may
be the tolerance values for the total indicated readings for the
measurement for the selected vehicle. The Rotate to Next Position
key can be used to signal the motor to position and hold the
wheel/tire assembly at the various high spots for the purpose of
applying indicator marks to the assembly.
[0092] If sensor 88 or 97 is pulled away from its home position
while the runout screen of FIG. 10 is displayed, the balancer turns
that sensor into a virtual dial indicator. By placing the sensor
against the rim, a key (not shown) can be pressed to zero the
corresponding gauge display, just like a real dial indicator. Then,
as the wheel/tire assembly is turned, the gauge display shows the
runout as it is measured, just like a real dial indicator.
[0093] Turning to FIG. 11, there is shown a display of the present
balancer which allows the user/operator to manually set the desired
speed at which the balancing is to occur. This feature is useful,
for example, when the vehicle owner complains of a vibration at a
particular speed, such as 30 mph. To test the balance of the
wheel/tire assembly at 30 mph, the operator presses soft key 141,
labeled "Velocity Mode", which causes the display of the simulation
of a vehicle dashboard 143 as shown in FIG. 11. The operator can
use a soft key 145 to select either the linear speed (e.g., the
complained of 30 mph) or the actual rotational speed in revolutions
per minute by toggling key 145. Soft keys 147, 149 can then be used
to set the linear speed or rpm as desired. As the selected speed is
changed, the dashboard display changes accordingly. Once the
desired speed is reached on the display, the operator uses another
soft key (not shown) to initiate the actual balancing procedure. As
the balancer starts accelerating the wheel/tire assembly,
preferably the dashboard display shows the corresponding vehicle
speed, so that the operator (and customer) can verify that the
balance is tested at the desired speed.
[0094] In the event the operator selects a linear speed, the CPU 23
converts the selected linear speed to the corresponding revolutions
per minute for that particular wheel/tire assembly. Whether linear
speed or rpm is selected, CPU 23 is responsive thereto to cause the
motor to rotate the wheel/tire assembly at the desired speed. In
this way, the operator can input a desired speed and balancer tests
the wheel/tire assembly at that speed.
[0095] A knob 159 is disposed adjacent display 25. Knob 159 is used
to enter a desired force to be applied to the wheel/tire assembly
by load roller 91 during the balancing procedure. For example, the
operator may wish to test the wheel/tire assembly under normal
operating conditions, which would involve applying a force which
corresponds to the weight normally applied to that particular wheel
for that particular vehicle. To do this the knob is turned as
needed to change the numerals 161 displayed adjacent knob 159 until
they reach the desired value. Alternatively, if the vehicle type
has already been entered into the system, the CPU 23 can preset the
load to be applied once the axle on which the wheel/tire assembly
is to be mounted is identified.
[0096] In view of the above, it will be seen that all the objects
and features of the present invention are achieved, and other
advantageous results obtained. The description of the invention
contained herein is illustrative only, and is not intended in a
limiting sense.
* * * * *