Method of correcting imbalance on a motor vehicle wheel

An apparatus and method of correcting imbalance on a motor vehicle wheel/tire assembly. A sensing device coupled to an electronic measuring apparatus is used to scan the wheel in a continuous motion, obtaining the profile of the surface intended for the placement of at least one imbalance correction weight. The balancer computer analyzes the scanned profile and determines the best arrangement of correction weight locations and magnitudes. This system reduces the amount of weight, number of weights, and/or residual imbalance caused by systems where the operator determines the correction planes. The display shows the scanned profile and the weights exactly as the physical wheel and placed weights appear, improving intuitiveness and providing confidence in the measuring apparatus. The correction weight magnitudes and locations can be manually adjusted via the user interface and a real-time display update of required weights and the corresponding residual imbalance. Another improvement minimizes operator weight placement error by using the measuring apparatus and display as a guide to place a weight at the proper angular location on a correction plane.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to motor vehicle wheel balancing systems, 
and more particularly to electronic measurement devices used on such 
systems for the purpose of entering wheel dimensions needed for 
determining sizes and locations of imbalance correction weights. 
2. Description of the Related Art 
It is well known in the automotive wheel balancing art that to compensate 
for a combination of static imbalance (where the heaviest part of the 
assembly will seek a position directly below the mounting shaft) and 
couple imbalance (where the assembly upon rotation causes torsional 
vibrations on the mounting shaft), at least two correction weights are 
required which are separated axially along the wheel surface, coincident 
with weight location "planes". For using clip-on weights the "left plane" 
comprises the left (innermost) rim lip circumference while the "right 
plane" comprises the right rim lip. If adhesive weights are used, the 
planes can reside anywhere between the rim lips, barring physical 
obstruction such as wheel spokes and welds. With the wheel assembly 
mounted to the balancer, the relative distances from a reference plane 
(usually the surface of the wheel mounting hub) to the planes are made 
known either by manually measuring with pull-out gauges and calipers and 
then entering the observed values through a keypad, potentiometer, or 
digital encoder, or by using an automatic electronic measuring apparatus. 
The radius at which the weights will be placed must also be entered, again 
either manually or by use of the electronic measuring apparatus. The 
balancer then determines what angular position the weights must be placed 
in the left and right weight planes and guides the operator through the 
display, typically a bar graph pertaining to each weight plane, to rotate 
the wheel assembly to a rotational position for each plane at which the 
correction weight is to be placed at the "12:00" position (straight up 
from the centerline of the wheel). 
A problem sometimes arises with such systems when using adhesive weights 
when the operator enters the weight planes at less than optimum locations. 
The operator is usually unfamiliar with the importance of maximizing the 
distance between the two planes and is tempted to locate both near the 
inside of the wheel, much closer together than possible, for easier reach 
for weight placement. The closer the planes are together, the more weight 
is required to correct for the same couple imbalance, and the harder it is 
to balance below the "blind" (display for a weight plane shows zero if the 
residual imbalance is below the blind amount). The situation is further 
aggravated by the fact that adhesive weights are easily mis-applied since 
there is no physical means forcing the weights to reside on the correction 
planes as with rim-lip mounted weights. U.S. Pat. No. 4,891,981 discloses 
a system where an automatic measuring apparatus is used to input the 
weight planes and is later used again as a placement aid to insure the 
distances to the applied weights agree with the previously inputted 
planes. This is an improvement over the prior art as long as the planes 
are inputted at reasonable locations, but this often is not the case. It 
also has been observed that the operator is tempted to input the planes at 
grooves or score lines within wheels to use these features as a reference 
later to place weights. In the case of a groove, the adhesion of the 
weight to the wheel is hampered because of the depressed shape of the 
groove and because the groove allows road water to enter the underside of 
the weight. In the case of a score line, it is possible that the surface 
may have a taper which the operator did not notice. If a long strip of 
adhesive weights is required, a substantial portion of the weight will 
tilt away from the weight plane as it is pressed to conform to the conical 
surface formed by the taper, resulting in balancing error. Adhesive weight 
balancing is even avoided by many operators because of the aforementioned 
effects from expecting the operator to locate the weight planes. Quite 
simply, what is needed is to make adhesive weight balancing as easy as 
clip-on weight balancing. 
A second problem with such systems exists because incremental weights are 
used. Using the most widely used increment of 0.25 oz., the required 
weight amount, no matter how accurately calculated and no matter to how 
fine a resolution, must be rounded to this increment. Residual imbalance 
as high as half the blind per weight plane will certainly occur. U.S. Pat. 
No. 4,891,981 to Scholdfield discloses a system which provides automatic 
iteration and comparison of different weight amount increments and angular 
positions for the two weight planes to minimize residual static imbalance, 
but it does so at the expense of residual dynamic imbalance. The rounding 
and blind problem can be overcome by shrewd users by disabling the blind 
and rounding and repeatedly re-entering the plane locations either 
manually or with an automatic input device (almost all balancers allow 
weight recalculation without having to re-spin the wheel assembly) until 
the displayed weights are very close to available incremental amounts. 
This process is still very time consuming and requires the operator to 
interpret the meaning of weights displayed to fine resolution. 
Furthermore, adjusting one plane location can affect the required amount 
and location of the weight required for the other plane, potentially 
confusing the unskilled operator. What is needed is to release the 
operator from the task of determining where the planes need to be, as well 
as a fast way to adjust plane locations and to know what the result of the 
balance job will be because of the adjustment. 
A third problem with such systems is angular weight placement error by the 
operator. Present balancers precisely guide the operator to rotate the 
wheel to weight placement position to within as little as 0.35 degrees, 
corresponding to less than 1/16" movement at the lip of a 15" wheel. 
Unfortunately, the operator must judge for himself where the 12:00 
position is for placing the weight. Placement errors of more than 1/2" are 
commonplace. The larger the weight, the harder it is to judge the 12:00 
position, and the more residual imbalance a misplacement will cause. 
Working with the inside surface of a wheel to place adhesive weights is 
the most error prone situation of all since the operator must crouch down 
and look upside-down into the mounted wheel to see the 12:00 position. 
Light spotters of various types have been offered which project a line 
onto the wheel/tire assembly but these devices add cost, can only spot one 
side of the tire at a time, and/or cannot spot the inside of the wheel for 
adhesive weight placement. U.S. Pat. No. 5,447,064 to Drechsler discloses 
a novel electronic measuring apparatus geometry where a pivoting 
telescoping arm insures that the contact point of the device on the wheel 
is always at the 12:00 position. This design, however, makes cleaning of 
the wheel surface for adhesive weights difficult since the contact point 
is not visible to the operator. Also the design forces the apparatus to 
reside on top of the weight tray at the front of the balancer even when 
not in use, exposed to carelessly tossed mounting cones and taking up 
valuable space in the tray that could have been used for weight storage 
pockets. 
A fourth problem with such systems is that even when the wheel assembly is 
angularly positioned for a weight placement, it can rotate away when the 
operator lets go if the static imbalance component overcomes the friction 
of the mounting shaft bearings and drive system. It is also difficult for 
the operator to keep from bumping into the assembly while leaning over the 
tire to judge the 12:00 position. Foot brake devices are offered by some 
manufacturers to address this problem but their use can make it difficult 
to reach for weights, instruction manuals, etc., while standing on the 
foot brake. 
A fifth problem exists regarding the display of the data obtained by 
electronic measuring devices with such systems. Firstly, the operator 
cannot easily tell if the device is working correctly. The distance and 
diameter dimensions electronically measured for each weight plane are 
typically displayed with LED's or as values on a CRT display. Operators 
tend to trust the electronic measuring device, however, and ignore these 
displayed values. A measurement in error goes unnoticed and the resulting 
displayed balance weight amounts and placement angles are incorrect as 
well. For example: The distance entered for the left plane is usually 
expressed in mm. If the electronic measuring device is out of calibration 
and results in a left plane input display of 125 instead of a correct 
value of 135, the operator is unlikely to notice and will "chase weights", 
where each spin calls for more weight because the weights are not being 
placed where the balancer thinks they are. Verifying the accuracy of a 
display of digits for each wheel balance job would defeat the purpose of 
electronic dimension entry because some kind of mechanical distance and/or 
internal diameter gauge would have to be applied at each weight plane and 
compared to the display digits. Secondly, it is often confusing on such 
systems when switching between adhesive weight modes and clip-on modes. 
Because adhesive weight locations are measured at the inside surface of 
the wheel while clip-on weight locations are measured at the rim lips 
(nominal rim data), the measurement procedure is different for each type 
of weight (discounting methods where the adhesive weight locations are 
estimated based on nominal wheel data). Most systems allow taking data for 
one type without changing the other. If the user forgets this fact and 
switches to the other type of weight to balance the wheel, the weight 
values shown are calculated from data taken from the last wheel assembly 
which was used in that mode. One manufacturer requires entering adhesive 
locations as well as rim lip locations before calculating weights; however 
this requires double the effort and confuses the operator as to why both 
input procedures must be used when only one type of weight will be used. 
Some balancers have the capability of switching context between multiple 
operators where operator B, for example, can interrupt operator A by 
recalling his last wheel data without retaking of data and without 
destroying operator A's data. The prior art where the only item that 
changes is the wheel data is especially dangerous in this case as the 
operators probably do not remember the dimensions of their particular 
wheel assemblies. It has been observed that even though some kind of 
display prompt is given as a reminder as to which operator is currently 
enabled, operators can accidentally balance their wheels with the wrong 
operator mode, especially if they did not notice that another operator 
changed the mode. 
SUMMARY OF THE INVENTION 
The invention described herein is usable with vehicle wheel balancers and 
includes an automatic measuring apparatus which is used in a novel method 
to balance a wheel assembly. In the prior art the user fixed the 
correction plane locations with the measuring apparatus and the computer 
then used variable amount and angular location to determine the required 
weight residing in each weight plane. The present invention uses the 
apparatus to scan the surface of the wheel and then the balancer computer 
uses variable weight plane locations as well to present the operator with 
the best weight arrangement. The computer has effectively an infinite 
number of planes to place the weights rather than two planes fixed by the 
operator. The best plane locations, amounts of the weights, and even the 
number of weights, are calculated to result in a minimized residual static 
and dynamic imbalance while still using incrementally sized weights. One 
variation of the invention used a CRT display to show the actual scanned 
profile of the wheel as well as the relative locations of the weights on 
the display wheel, enhancing user understanding and providing confidence 
that the measuring apparatus is working correctly because display wheel 
looks like the actual wheel. Another novel feature is the ability to move 
the weight planes, change weight amounts, and/or change the number of 
weights while observing a real-time residual imbalance display. Also the 
present invention uses the same measuring apparatus as an angular weight 
location placement aid by using the contact point between the measuring 
apparatus and the wheel as the placement spot for a weight, eliminating 
weight placement errors when the operator must judge the "12:00" placement 
position. Finally, a new motor drive design for the balancing art 
automatically indexes and holds the wheel at the proper angular position 
for weight placement, further enhancing weight placement accuracy. 
A first object of the present invention is to provide improved correction 
weight placement plane locations. 
A second object of the present invention is to provide improved balancing 
using incrementally sized weights. 
A third object of the present invention is to reduce the amount of added 
weight per correction plane. 
A fourth object of the present invention is to reduce the required number 
of planes to one when possible. 
A fifth object of the present invention is to provide an improved display 
of wheel dimensional data to convey to the operator that the measured data 
agrees with the physical wheel/tire assembly. 
A sixth object of the present invention is to provide a method of adjusting 
the weight arrangements prior to applying weights, guided by a real-time 
display of resulting residual imbalance condition. 
A seventh object of the present invention is to improve operator weight 
placement accuracy. 
An eighth object of the present invention is to provide improved angular 
wheel positioning accuracy during weight placement. 
Other objects and features will be in part apparent and in part pointed out 
hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning to the drawings, FIG. 1 illustrates the mechanical aspects of the 
automatic measuring apparatus 1 used for the present invention. A support 
tube 3 houses a longitudinally extendible and rotatable shaft 2. A radius 
arm 9 is fixed to the right end of shaft 2. The other end of the radius 
arm 9 has a fixed spacer 6 and a spherical "pointer ball" 7. Pointer ball 
7 is made of nylon or the like since it is used by the operator to slide 
across wheel surfaces in a wheel profile scanning mode. For use in a 
weight locating mode the pointer ball 7 has a line feature 8 through the 
center of the ball to aid in viewing the contact point between the ball 
and the wheel surface. The support tube 3 is welded to a bracket 4 which 
provides the mounting for the apparatus in the wheel balancer WB (FIG. 2). 
A "C" shaped bracket 5 houses a longitudinal movement transducer 10 which 
is preferably a rotary potentiometer driven by a gear 12 traveling on a 
geared rack 13 mounted to bracket 4. Bracket 5 also has holes through 
which the shaft 2 passes. Bracket 5 is fixed longitudinally to shaft 2 by 
snap rings 15 and 16, and slides with shaft 2 while being held vertical by 
slots straddling a bend 14 at the base of bracket 4. Bracket 5 also houses 
a rotational transducer 11, also a rotary potentiometer, which is directly 
driven by shaft 2. A return spring 17 pushes the shaft back to the storage 
position when the apparatus is not in use. A scale 18 is provided on 
opposing sides of shaft 2 for manual reading by the operator in the event 
of a problem with the apparatus electronics. It should be noted that with 
the exception of the pointer ball 7 design and the direct driving of the 
rotational sensor 11, this mechanical arrangement is a well-known, durable 
and cost effective design already used in balancers manufactured by the 
assignee. This design has one disadvantage for being used as a weight 
placement aid in that radial location of the device (ball) contact point 
with the wheel varies with wheel diameter (see FIG. 3B), requiring more 
accurate rotational sensor data than the prior art. This can easily be 
overcome, however, by eliminating the backlash inherent with gear-driving 
the rotational sensor and by incorporating compensation software for the 
device geometry. It will become clear that these improvements plus a novel 
wheel profile scanning method allow a relatively inexpensive yet durable 
apparatus to be used in a novel and useful way. The improvements herein 
could be accomplished with other device geometries that vary the wheel 
contact point as a function of wheel diameter by using the appropriate 
compensation software. Likewise, components of the apparatus could be 
changed. The sensors, for example, instead of potentiometers could be Hall 
effect sensors, magneto-resistive sensors, or among a myriad of well-known 
optical sensing technologies. 
FIG. 2 illustrates the overall wheel balancer system of the present 
invention. A rotatable mounting shaft or spindle 45 is driven by motor M 
via a bi-directional, multi-rpm, variable torque motor drive 40 by a belt 
41. For details on the drive see co-pending and co-assigned application 
Ser. No. 08/594,756 filed Jan. 31, 1996, the disclosure of which is hereby 
incorporated herein by reference. Mounted on one end of the spindle 45 is 
a conventional quadrature phase optical shaft encoder 46 which provides 
rotational position information to the balancer CPU (central processing 
unit) 30, preferably a Texas Instruments TMS34010 graphics processing 
chip, capable of executing the balancer software and at the same time 
driving the CRT display 35. The CPU is connected to EPROM program memory 
32, EEPROM memory 33 for storing and retrieving non-volatile information 
such as calibration and vehicle specific specifications, and DRAM memory 
34 for temporary storage. Manual inputs for the present invention entail 
keypad entry 36 as well as three digital rotary contacting encoders 37, 
38, and 39 are of type sold under the trade designation ECLODC24BD0006 by 
Bournes Inc. During the operation of wheel balancing, at the other end of 
spindle 45, a wheel/tire assembly 43 under test is removably mounted for 
rotation with a spindle hub 44 of conventional design. To determine 
wheel/tire assembly imbalance, the balancer includes at least a pair of 
force transducers coupled to balance structure 42. These sensors and their 
corresponding interface circuitry to the CPU 30 are well known in the art, 
thus are not shown. The automatic measuring apparatus 1 of FIG. 1 is 
mounted with its longitudinally extendible shaft 2 parallel with the 
spindle 45 centerline. The apparatus 1 is shown in the plan view with the 
radius arm 9 rotated slightly away from the downward rest position. The 
longitudinal sensor 10 senses, instantaneous distances relative to the 
balancer as the shaft 2 is extended into the wheel while the rotational 
sensor 11 senses instantaneous radii as the pointer ball 7 is placed in 
contact with surfaces of the wheel. Both sensors are fed into an A/D 
(analog to digital converter) which is preferably an Analog Devices AD7871 
fourteen (14) bit converter. 
FIG. 3A illustrates the process of inputting the wheel profile. A typical 
wheel is shown (in cross section with the tire removed for clarity) 
mounted with conventional mounting hardware 86, clamped against the face 
plate 47 of the mounting hub 44. The measuring apparatus 1 is mounted as 
close to the spindle 45 centerline as possible while still allowing the 
extension shaft 2 to clear the mounting hub face plate. To scan the wheel 
the operator first extends and positions the pointer ball 7 to the 
farthest distance and smallest radius as physically possible. The computer 
recognizes this action as a desire to initiate a scan, transmits a 
confirmation beep, and waits for the apparatus to be held steady. After 
the apparatus is held steady for approximately 1 second, a beep is 
transmitted to signal the operator to begin the scan. The pointer ball is 
dragged against the wheel surface, following the contour all the way to 
the point where the ball contacts the tire, at which point the ball is 
again held steady and the CPU responds with a confirmation beep that the 
scan is finished and the apparatus can be returned to the storage 
position. The path 85 traveled by the ball and three ball positions during 
the scan are shown. FIG. 3B shows a view into the wheel of the same three 
ball positions. Notice that the radial angle from the 12:00 position to 
the ball contact point with the wheel varies with internal wheel diameter. 
During the scan the CPU takes pairs of data at predetermined extension 
distance intervals of 2 mm so that the speed at which the operator moves 
the arm has no affect on the accuracy or the amount of paired samples 
acquired. The pairs consist of distance sensor 10 and angle sensor 11 data 
which after the scan are compensated for the radius of the pointer ball, 
providing a discrete array of diameters and radii that define the wheel 
profile. The CPU then uses conventional interpolation and curve fitting 
methods on the array to produce a second wheel profile array with a radius 
and distance pair for every 0.5 mm of shaft 2 extension, essentially a 
continuous array for the purposes of the invention. Finally, the CPU 
searches the data for tapered surfaces such as the steps 87 and 88 in FIG. 
3A. FIG. 3C shows that because the pointer ball does not contact the wheel 
through its vertical center line the actual radius to the wheel requires 
an additional distance to be added to radii values corresponding to the 
tapered surface. This correction distance CD is calculated by: 
##EQU1## 
where RP is the radius of the pointer ball 7 and .theta.P is the angle 
formed by the taper, determined from the change in radius divided by the 
change in distance between the data pairs acquired at the endpoints of the 
tapered surface. 
Notice that with the present method the rim lip shape is simultaneously 
acquired along with the internal profile. This is a sharp contrast to the 
prior art where rim-lip dimensions (nominal tire bead seating dimensions) 
are acquired as a separate distinct procedure from adhesive weight plane 
inputting. There is no confusion as in the prior art as to whether the 
data shown after changing weight modes pertains to the presently mounted 
wheel or one which was previously mounted the last time that mode was 
used. Note further that the present invention could also use a right plane 
measuring apparatus capable of reaching the right side of the wheel. Like 
the apparatus of FIG. 1, it could be a variation of an existing proven 
design (such as that sold under the trade designation Double Dataset by 
the present assignee on existing wheel balancers). With such a right plane 
measuring device, the surfaces suitable for adhesive weights and the right 
rim location can be scanned in exactly the same manner as the left side of 
the wheel, providing an even more complete wheel profile. 
FIG. 3D shows an example weight plane arrangement that could be obtained 
from any of the data sets from the wheel scanning step. The plane 
locations are simply distances from some fixed reference plane known to 
the balancer. In this case the reference plane is an imaginary fixed 
offset 84 from the face 47 of the mounting hub 44, which yields positive 
values in mm units along any measurable point reachable by the measuring 
apparatus. With a particular measured static and couple imbalance obtained 
from a measurement spin and with a particular set weight plane locations 
82, 83 and corresponding radii 80,81, the balancer CPU determines the 
required weight amount and radial placement angle for a weight in each 
plane. Because this step by itself is not novel to the art, the actual 
math involved is not shown herein. For a full explanation of the math 
performed during this weight calculation, refer to U.S. Pat. No. 5,396,436 
to Parker and Douglas. 
The balancer CPU then performs the novel step of determining the plane 
locations, described here by example: 
1. Using the wheel profile data, the areas at which adhesive weights should 
not be placed are determined. This includes the bend at the left rim lip, 
vertical steps, tapers more than 10 degrees, deep grooves, etc. 
2. From the static imbalance, couple imbalance, and available weight plane 
locations, the CPU determines if it is possible to balance with only one 
weight (see below for an explanation of this feature). In the present 
example it is not possible so the CPU proceeds to the next step. 
3. The left and right planes are located as far apart as possible, avoiding 
the areas derived from step 1 by half the known width of the adhesive 
weight. In this case the left plane is set to 152 mm and the right plane 
is set to 284 mm. 
4. The weight amounts are calculated for these two planes without any blind 
or rounding applied. In this case the left plane requires 2.39 oz. and the 
right plane requires 2.04 oz. 
5. The left plane distance is adjusted away from the rim lip bend by adding 
1 mm and the weights are recalculated. It is important to realize that by 
relocating only one of the planes the amounts and placement angles for 
both weights are affected. The process is repeated until one of the 
weights changes by more than half the weight increment being used. 
6. The right weight plane is adjusted in the same manner for each of the 
trial locations and weight results obtained from step 4, yielding a matrix 
of adjusted left and right plane locations and the corresponding required 
weight amounts and placement angles. 
7. The best placement is chosen which yields weights closest to the 
increment being used. For this example the left plane is located at 157 mm 
and the right plane stays at 284 mm, yielding required weights of 2.49 oz. 
and 2.00 oz. 
8. The weights are rounded to 0.25 oz. and displayed as 2.5 oz., 2.00 oz. 
along with the required placement angles and the new plane locations. 
By the CPU determining the plane locations instead of the operator, two 
problems with adhesive weight balancing are solved. First, the planes are 
located as far apart as possible which in the case of dynamic imbalance 
can greatly reduce the amount of weight required. In the prior art the 
operator could have placed the planes at say, 202 mm and 152 mm, and the 
required weights would have been 3.75 oz. and 5.5 oz. to cause the exact 
same correction force as 2.5 oz. and 2.00 oz. weights at the more 
separated plane locations. Second, even if the operator would place the 
planes as far apart as possible (152 mm, 284 mm) the residual imbalance 
for the left plane in this example would have been 2.50 oz.-2.39 oz.=0.11 
oz., or nearly half a weight increment| Obviously, a slight placement 
error could add up to even more residual imbalance error, possibly enough 
to cause more weight to be displayed after the check spin. 
Step 2 of the plane location calculation above saves the operator time in 
cases where the assembly can be balanced with only one weight. As a second 
example, consider a wheel which is balanced both statically and 
dynamically and the planes are set at 100 mm and 200 mm. Now add a 0.25 
oz. adhesive weight at a distance of 150 mm into the wheel. The wheel now 
has pure static imbalance which is certainly possible with new tires and 
wheels. The prior art would call for zero weight at each plane in dynamic 
mode since to correct for pure static imbalance at the two fixed planes 
requires half of the 0.25 oz. at each plane (the required amounts of 0.12 
oz. fall below the blind amount of 0.25 oz.). The operator would think 
he's finished when in fact the wheel has 0.25 oz. of static imbalance at 
that particular diameter. Even if the blind and round amounts are reduced 
in a "precision" balancing mode, it is completely unnecessary and time 
consuming to place 0.12 oz. (which still is not an incremental size) at 
each plane. The present invention recognizes the fact that there is no 
dynamic imbalance and switches the display to show one 0.25 oz. weight 
with the plane located in-line with the imbalance. In fact, the present 
invention easily demonstrates the unique ability to find static weight. If 
the adhesive weight is moved axially, the plane displayed moves with it 
after the imbalance measurement spin. 
The ability for the CPU to find and set a static plane has a great 
advantage over static balancing in the prior art as well. It is a fact 
that if a correction weight is not added at a point directly opposing the 
centroid of a static heavy spot, a force couple will be induced. For this 
reason manufacturers recommend placing weights near the center of the rim 
to reduce residual dynamic imbalance. Unfortunately, most operators are 
unaware of this fact and place the weight near the left side so they can 
more easily place the weight. The present invention introduces a new 
concept for static balancing, then, in that a weight plane distance is 
used. Before, no "plane" was required to be inputted and the operator 
could place the static correction weight anywhere he wished at the 
possible risk of causing dynamic imbalance. Now, a static plane is found 
and set by the CPU so that the dynamic imbalance is minimized and for 
cases where the wheel has only static imbalance, no dynamic imbalance is 
induced at all. Another provision is made to signal the operator in cases 
where an unacceptable amount of dynamic imbalance will result by using the 
static balancing mode. This simply automates the past method of constantly 
switching back to dynamic mode to view the weights, plus the user is made 
aware of dynamic problems before weights are applied. 
The data obtained from the measurement arm 1 is also used in a novel way 
for the display. FIG. 4A shows three typical wheel profiles that might be 
used in a balance mode which places two adhesive weights on the left 
inside surface of the wheel. It is obvious that these surfaces have very 
different shapes. The stamped steel wheel 100, although usually used with 
two clip-on weights, can certainly be mounted and balanced with adhesive 
weights in cases where the customer wants to hide weights. This is a 
relatively narrow wheel which offers only two narrow surfaces 103 and 104 
for placing adhesive weights. Wheel 110 is a typical aluminum type which 
has two wide surfaces 113 and 114 available for weights. Wheel 120 is a 
popular high performance aluminum wheel which has two very narrow surfaces 
for weights 123 and 124 as well as a slight taper 125 for most of the left 
interior surface. FIG. 4B shows typical CRT display results 101, 111, and 
121 corresponding to each of the wheels in FIG. 4A after inputting the two 
weight planes with automatic measuring methods of the prior art. Note that 
because only one diameter and one distance is inputted for each of the two 
weight plane locations the balancer cannot know what the wheel shape 
really is; therefore only the dimensions are accurately represented while 
the wheel and relative weight location display graphics remain identical 
for any wheel being balanced. Also notable is the fact that no matter 
where the weight planes are entered the weights are shown in the same 
place on the display. FIG. 4C shows the present invention display results 
for the same three wheels. The essentially continuous data array 
describing the wheel surface is transformed from the physical size to the 
CRT display coordinate system by simple x-y scaling and the resulting 
profile is plotted on the display. Surfaces scanned by the pointer ball 7 
are represented as solid black while unknown areas are "constructed" by 
software and shown as the dot pattern for the purposes of the figure in 
lieu of the color that is actually used. In this way the user understands 
that the important surface that was actually scanned should be accurately 
represented but the reconstructed portion may be in error as those 
surfaces were not scanned. The display wheel 102 does not look quite right 
for the reconstructed portion; however this could easily be resolved by 
incorporating a measuring apparatus capable of scanning the rightmost 
inside surface as well. Another possibility would involve comparing the 
scanned portion to profiles in a database and finding a recognizable wheel 
shape to draw on the CRT for the unscanned portion. Alternatively an 
entire wheel profile array could be recalled from a database after finding 
the closest match to the scanned wheel area. Note that the right rim lip 
106, although not actually scanned, is shown in solid black since it must 
be a mirror image of the scanned left lip 105 and the physical separation 
from lip 105 is known in this case from the well known method of manually 
entering a value measured with a rim width caliper. Display wheel 112 
shows how accurately a wheel can be drawn when using the aforementioned 
measuring apparatus capable of reaching the right side of the wheel. 
Display wheel 122 shows an example of using a database to determine the 
unscanned portion of a wheel. The width and slight taper in this case 
easily identifies the wheel. The pattern for the unscanned shape is 
retrieved from permanent memory 32 and drawn with the required scaling to 
match up to the scanned data as shown. 
Drawing the actual wheel shape has many advantages over the prior art: 
First, because the wheel shapes are drawn on the CRT with the same shape, 
weight, and width as the actual mounted wheel, the user has great 
confidence that the automatic measuring system worked perfectly. Second, 
the display weights can now be shown in the actual longitudinal positions 
(weight plane locations) required, guaranteeing that the user understands 
where the balancer thinks the weights must be placed. Notice that for 
display wheel 112 it might seem reasonable that the user would wish to 
place the left weight 115 a bit closer to left, using the lip bend 116 as 
a visual guide. The explanation is that the balancer adjusted the left 
plane location to allow minimal residual imbalance, also adjusting the 
drawn location of the weight to the exact relative location the real 
weight will be on the actual wheel. The user has no doubt that the weight 
must really be placed slightly away from the edge. Display wheel 122 shows 
that the left weight 126 was calculated to be away from the ridge 127. 
Display wheel 121 of the prior art, although not at all obvious, shows by 
the distance digits that the groove is exactly where the user inputted the 
left plane, in which case the weight will have a hard time staying on 
because of road water entering the groove under the weight. Also display 
wheel 122 is showing the operator that the wheel has a substantial taper 
where otherwise this fact is difficult to realize without cutting the 
wheel in half. The right plane was wisely calculated to avoid this taper 
since otherwise the curvature of long weight strips would tilt the bulk of 
the weight mass away from the weight plane. The displayed wheels of FIG. 
4C graphically remind the operator that the correct data is in use for the 
mounted wheel. These three wheels could be in use at the same time by 
three different users interrupting each other. As each user recalls his 
wheel assembly, the present invention presents a graphical verification 
for the mounted wheel, a definite improvement to being presented one of 
the displays of FIG. 4B. 
It is, of course, possible to further expand the advantages of this display 
method to display an accurate representation of the tire. Co-pending 
application Ser. No. 08/594,756 filed Jan. 31, 1996 discloses a radial 
loaded roller arm which can be used to obtain the diameter of the mounted 
tire. In addition, a measuring apparatus capable of reaching the right 
side of the wheel, as mentioned above, could be adapted to also scan the 
surface of the right half of the tire. The resulting display could then 
show the tire mounted to the scanned wheel, further confirming user 
confidence that the data is correct. Patch weight balancing, where 
adhesive patches are placed inside the tire, also benefits for two 
reasons: Firstly, the step of measuring the outside diameter of the tire 
is eliminated. Secondly, patch weights are clearly shown on the display as 
residing inside the tire, a sharp contrast to the prior art of still 
showing the weight against the wheel surface. 
With the surface scanning and database comparing method of the present 
invention, it is possible to retrieve other parameters about the mounted 
assembly that would be useful for other aspects of wheel balancing. These 
parameters could be the entire wheel profile, wheel mass, spoke 
arrangement, lug hole arrangement, or any parameter that could be known 
for a particular wheel once it is identified. Parameters for the most 
likely mounted tire could also be retrieved, or in the case of using a 
measuring device capable of scanning the tire surface, parameters for any 
style tire could be retrieved. 
The display of correction weight locations and magnitudes on display screen 
35 is illustrated in FIG. 5. Display screen 35 has associated therewith 
selector knobs 37, 38 and 39, mentioned above, and a set of four soft keys 
K1, K2, K3 and K4. The soft keys are used, in conventional manner, to 
select from choices displayed on the screen. For example, the primary 
choices "Change Brand", "Adjust Left Weight", "Adjust Right Weight", and 
"oz/gm" are shown in FIG. 5. An alternative set of choices "Improve 
Dynamic", "Improve Static", "Print Screen" and "Help" are also 
displayable. A key 211 is used to select between the sets of displayed 
choices. 
Note that screen 35 also displays the identity of the vehicle wheel under 
test (in this case a 15" aluminum wheel for a 92-93 Mercury Sable LE), the 
location of the wheel on the vehicle, and provides the cross-sectional 
view (here labeled 213) of the scanned profile of the wheel under test. 
The weight planes (labeled 215, 217) for the correction weights 221, 223 
are displayed, along with plane dimensional information ("154 mm" and "284 
mm"), and the correction weight amounts ("2.00 oz" and "1.00 oz"). To the 
left of the cross-sectional profile 213 on screen 35 is shown a residual 
error display 219 which identifies the particular wheel under test, the 
residual dynamic imbalance which would remain after the displayed weights 
are mounted at the required locations, and the static imbalance which 
would remain in the same situation. Below the residual error display the 
type of correction weight to be used is displayed. 
In most instances, the CPU can determine precise correction weight amounts 
and placements to eliminate residual imbalance. These amounts, however, 
usually differ from the incremental weight amounts available. The balancer 
has the incremental weight amount stored therein, and it knows to only 
display the proper, incremental amounts. When incremental weights are 
used, there will be some residual static and dynamic imbalance, in general 
(although these are minimized by the CPU), and these are displayed in 
display 219. 
In some instances, however, the user will not want to apply the correct 
weights at the displayed positions. The user may desire to move one of the 
weight planes to avoid a brake caliper, for example. Or the displayed 
weight size may be temporarily unavailable. To adjust the left plane 
position, the user operates knob 37 to move the left plane in and out. 
Simultaneously, the residual error indications all change to correspond to 
the new proposed weight plane position, as does the correction weight 
amount when the new position requires a new incremental weight. Similarly, 
knob 39 is used to adjust the left plane correction weight amount to the 
desired value. An adjustment of the weight amount also causes all the 
residual imbalance displays to be changed, and the weight plane to move as 
determined by the CPU to minimize the resulting imbalance. 
FIG. 3E shows an additional feature provided by the balancer where the 
wheel has a tapered surface. If a plane is adjusted to coincide with a 
tapered surface 125 such as that of the wheel in FIG. 4A, the weight plane 
error due to the adhesive weight strip 225 center of gravity shift CG 
caused by the taper is taken into account by the balancer. The 
compensation factor TCF depends on the length of the adhesive strip, the 
diameter of the wheel at the plane location, and the angle .theta.T of the 
tapered surface where: 
##EQU2## 
This compensation is also provided in cases where the balancer 
automatically determines the plane locations and only tapered surfaces are 
available for adhesive weight placement. 
Although operator control of the left plane and weight amount have been 
described, it should be understood that the right plane values can be 
changed similarly by the simple expedient of pressing K3, the "Adjust 
Right Weight" key, and then using knobs 37 and 39 to adjust the right 
plane position and correction weight value. 
Also shown in residual imbalance display 219 is a slider bar 241 which 
visually indicates to the user the relative weighting the CPU affords to 
dynamic versus static imbalance. The user may manually adjust this 
allocation by pressing the "Improve Dynamic" or "Improve Static" keys (K1 
and K2, using the alternative choices) as desired. As the "Improve Static" 
key is depressed, the indicator on slider bar 241 moves down. Conversely, 
as the "Improve Dynamic" key is depressed, the indicator moves up. In this 
way, the user can, instruct the CPU to favor dynamic balance or static 
balance as desired by adjusting the planes or weights automatically to 
correspond to the desired allocation. 
The present invention also provides a means to overcome operator error when 
judging the 12:00 position to place an adhesive weight. FIG. 6 shows that 
with the pointer ball 7 of the measuring device contacting the inside 
surface of a wheel 110, an angle .theta.2 is known via the angle 
transducer 11 (see FIG. 1). The angle displacement .theta.4 from the 12:00 
position to this contact point is calculated as: 
##EQU3## 
where D1 is the known distance from the measuring apparatus sliding shaft 
2 from the mounting spindle 45, .theta.1 is the known angular location of 
the sliding shaft from the 12:00 position, and R is the known radius of 
the radius arm 9. As can be seen from FIG. 6 and the above equation, 
.theta.4 is a diameter dependent contact angle, since it varies with the 
diameter of the wheel rim at the contact point. During the operation of 
placing a weight, the display guides the operator to rotate the wheel to 
position .theta.4 rather than the prior art 12:00 position. The contact 
point is easily viewed compared to looking upside down into the wheel for 
the 12:00 position. Moreover, the area can be cleaned without rotating the 
wheel since the weight placement spot is already at a natural position for 
this action. Notice that from the geometry of FIG. 6, if the thickness of 
an adhesive weight is inserted between the pointer ball wheel surface, the 
equation will automatically adjust .theta.4 for the slight change in the 
radius arm 9 position. This eliminates the need to pull the arm device 
away from the weight placement spot before attaching the weight, and also 
allows the arm disc to be used to initially press on an adhesive weight. 
It is also possible to include a weight holding device for clip-on or 
adhesive weight types (not illustrated) in place of or in addition to the 
pointer disc to eliminate the need to handle the weight while manipulating 
the input device. FIG. 7A and FIG. 7B show the contrast between the prior 
art "12:00" method and the present invention. In both cases the weight is 
placed at the same spot on the wheel (coincident with the "5" in the tire 
size label), but in the case of the present invention it takes advantage 
of the existing measuring device to place the weight more easily and 
accurately. 
The measuring apparatus is also used to end 12:00 position judgment errors 
when placing a clip-on weight. The geometry of FIG. 6 shows that if the 
radius arm 9 is rotated to contact the rim in the up position the measured 
angle .theta.2 will be negative, resulting in .theta.3 being negative and 
thus still providing the proper calculation of .theta.4. FIG. 8A and FIG. 
8B show the contrast between the prior art "12:00" method and the present 
invention for placing a clip-on weight. The angular placement spot is 
quickly and accurately determined, then, without the cost and problems 
aforementioned with optical weight placement spotters. The present 
invention could also be used with a holder for clip-on weights as well as 
using the aforementioned measuring apparatus to place weights on the right 
(visible) side of the wheel. 
The final feature provided by the present invention is the ability to 
automatically index the wheel assembly to the proper angular location for 
placing a weight at the pointer ball contact spot (non-12:00 weight 
placement). The motor control 40 of FIG. 2 has the ability to controllably 
rotate the wheel assembly to any position desirable and actively hold that 
position, overcoming all the aforementioned problems associated with 
mechanical and electrical braking schemes as well as eliminating the step 
of manually positioning the wheel in the first place. After a spin the CPU 
causes the motor control to position the wheel for the left plane weight. 
After the weight is applied the wheel then servos to the right plane 
position, initiated by one of three methods: A manual input such as a key 
press, a measuring apparatus that is moved to where the pointer ball is in 
closer proximity to the right plane than to the left plane, or the tire is 
pushed with enough predetermined force that the CPU understands that the 
operator must want the wheel to move to the next position. For a more 
complete description of the servo drive, refer to co-pending application 
Ser. No. 08/594,756 filed Jan. 31, 1996 to the assignee. For the method 
where a measurement device initiates the servo change, the operator is 
presented with the unique ability of not having to look at the display at 
all except for noting and selecting the required weights after a spin. The 
equivalent to this feature in the prior art would be a second operator 
positioning the wheel and applying a brake as needed so that the first 
operator can concentrate on placing the weight. 
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.