Abstract:
A balancer for a wheel rim/tire assembly, including a rotation sensor assembly for measuring rotation, and a motor operatively connected for rotating the wheel rim/tire assembly. A control circuit controls the motor to actively hold the wheel rim/tire assembly at a desired rotational position. A rim measuring apparatus is configured to scan the inner surface of the wheel rim/tire assembly. The optimum plane locations, amounts of correction weights, and the number of correction weights, are calculated by the control circuit to result in a minimized residual static and dynamic imbalance. The control circuit utilizes the motor drive to automatically index and hold the wheel rim/tire assembly at the proper rotational position for placement of an imbalance correction weight, and a laser pointer illuminates the surface of the wheel rim/tire assembly at the axial position of the weight imbalance correction plane at which the imbalance correction weight is to be applied.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to wheel balancers and in particular to an improved wheel balancer including a wheel rim measurement device configured to map the inner surface of a wheel rim, a wheel rim rotational positioning device, and a correction weight placement indicator, each operating in conjunction to facilitate the proper placement of wheel imbalance correction weights on the wheel rim. 
     When balancing a vehicle wheel, several potential sources for operator error exist. First, there is a need to identify the proper correction planes on the wheel rim into which correction weights are to be placed. Second, the wheel rim must be correctly rotated to, and held in, a rotational position such that the operator can place an imbalance correction weight in the identified correction plane, and third, the operator must manually apply the imbalance correction weight to the wheel rim in the identified correction plane and at the proper rotational position. 
     As disclosed in WO Patent No. 97/28431 to Hunter Engineering Company for “Wheel Balancer With Servo Motor”, herein incorporated by reference, 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. 
     It is well known in the art that a variety of types of imbalance correction weights are available for placing on the wheel to correct the measured imbalance. For example, adhesive-backed weights, patch balance weights and hammer-on weights are available from a number of different manufacturers. Most balancers assume that the wheel rim/tire assembly will be rotated to a particular rotational position (for example, disposing the desired weight correction position at the top (twelve o&#39;clock) or bottom (six o&#39;clock) rotational positions) for weight placement. This is generally not a problem, unless it would be more convenient to apply the weight with the wheel/tire assembly in a different orientation, for example, the four-five o&#39;clock rotational position when the operator is standing facing the surface of the wheel mounted on the wheel balancer. 
     As described in the WO 97/28431 patent, drive systems for currently available balancers may be improved to aid in weight placement by automatically rotating and holding the wheel rim to the correct rotational position. Prior art balancers typically require the operator to manually rotate the wheel/tire assembly to the desired position for weight placement. These prior art balancers then use a manual brake or the application of rectified AC current to an AC induction motor to temporarily hold the shaft in the desired position. 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&#39;s time and attention. In conventional systems, 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. 
     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 actual hold the tire in position since the motor would heat up if the “brake” was left on. With conventional equipment, a wheel rim/tire assembly with sufficient static imbalance to overcome its own inertia, therefore, can roll away from the braked dynamic weight attachment position as soon as the braking energy is released. 
     Similarly, currently available balancers require that the wheel rim/tire assembly be manually rotated in practically all circumstances since those balancers have no capability for applying anything other than full power to the balancer motor. That is, the motor in conventional balancers is useful for accelerating the wheel/tire assembly to full speed for determining wheel imbalance, but not for accurately positioning the wheel/tire assembly subsequently for correction of that imbalance. 
     Accordingly, WO Patent No. 97/28431 discloses a wheel balancer including a shaft adapted for receiving a wheel/tire assembly, having a longitudinal axis and which is rotatable about the axis by a direct current motor so as to rotate a wheel/tire assembly removably mounted thereon. A rotation sensor assembly is provided for measuring rotation of the shaft about its longitudinal axis and a vibration sensor assembly is operatively connected to the shaft for measuring vibrations resulting from imbalance in the wheel rim/tire assembly. A control circuit controls the application of direct current to the direct current motor and determines from vibrations measured by the vibration sensor assembly at least one weight placement position on the wheel/tire assembly to correct the vibrations. The control circuit is responsive to determination of a weight placement position to controllably rotate the wheel rim/tire assembly to bring the weight placement position to a predetermined rotational location and to actively hold the wheel/tire assembly in that location. However, it remains up to the operator to correctly position the correction weight on the wheel rim surface. 
     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 or imbalance correction “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, welds, and regions of excessive curvature. 
     With the wheel rim/tire assembly mounted to the balancer, the relative distances from a reference plane (usually the surface of the wheel mounting hub) to the planes are conventionally 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. Conventional wheel balancers employ a computer configured to utilize this input weight plane information, together with variable weight amounts and variable radial placements, to identify the proper locations for the imbalance correction weights on the wheel rim. While utilization of such a system facilitates the placement of an imbalance correction weight by placing the vehicle wheel in a preferred, or optimal rotational position for weight placement, it does not reduce other sources of operator error, such as the placement of an imbalance weight in the incorrect balance plane, a poor selection of imbalance planes by the operator, or failure to compensate for the width of the installed imbalance weights. 
     U.S. Pat. No. 5,915,274 to Douglas for “Method of Correcting Imbalance on a Motor Vehicle Wheel,” herein incorporated by reference, overcomes some of the problems associated with correctly determining the weight location “planes” by providing an apparatus for mapping the surface of the wheel rim. The rim measuring apparatus scans and stores the contour of the surface of the wheel rim, allowing the balancer computer to identify optimal imbalance correction weight planes, and to present the operator with the best imbalance correction weight arrangement. The computer has effectively an infinite number of imbalance correction planes in which to place the correction weights, rather than only the two planes previously selected by the operator. The best plane locations, amount of weight, and even the number of weights, are calculated to result in a minimized residual static and dynamic imbalance while still using incrementally sized weights. A display on the balancer is used to show the actual scanned contour of the wheel, as well as the relative locations of the weights on the display wheel rim, enhancing user understanding and providing confidence that the measuring apparatus is working correctly. However, actual placement of the imbalance correction weights in the identified optimal balance correction planes, and at the ideal rotational positions, must still be done manually by an operator, guided by instructions displayed on the wheel balancer, or by a mechanical or electronic arm. 
     Finally, an improvement to conventional wheel balancers to aid in the actual placement of imbalance correction weights onto the wheel rim is disclosed in WO Patent No. 98/10261 to Snap-on Equipment Europe Limited for “A Wheel Balancer”, herein incorporated by reference. Specifically, the WO 98/10261 patent discloses a conventional wheel balancer having an AC drive motor, which requires the operator to input two imbalance correction planes manually, and which includes a laser light source for illuminating a spot of laser light on the wheel rim, in each of the imbalance correction planes identified by the operator, at the specific angular location for placement of the respective imbalance correction weights. The laser light dot formed on the inner surface of the wheel rim indicates the angular center line of the balance weight position, and an inner edge of the balance weight position, thereby indicating to the operator the precise position at which the imbalance correction weight is to be secured to the wheel rim. The disclosed system assumes that each imbalance correction weight is of a predetermined average width. Furthermore, the laser light dot is only displayed when the operator manually rotates the wheel rim/tire assembly such that the weight application point coincides with a predetermined weight application rotational position, such as the four o&#39;clock position. If the wheel rim/tire assembly is rotated away from the predetermined weight application rotational position, either by the operator or by it&#39;s own weight, the projected laser spot is turned off, preventing misplacement of the weight by the operator. However, since the rotation of the wheel rim/tire assembly to the predetermined weight application position is performed manually, it is difficult for an operator to maintain the wheel in the predetermined rotational position such that the laser light spot remains on while the correction weight is being applied, or the location is being cleaned of debris. Any slight movement of the wheel rim/tire assembly away from the predetermined rotation position results in the laser light spot being turned off, with no indication on the wheel to the operator in which direction the wheel must be rotated to restore the laser projected spot. 
     Accordingly, there is a need in the industry for a vehicle wheel balancer which facilitates the placement of imbalance correction weights to a wheel rim/tire assembly by eliminating or reducing the sources of operator error induced by the selection of correction weight balance planes, rotational positioning of the wheel rim/tire assembly for the application of the imbalance correction weights, and during the actual attachment of the imbalance correction weight to the wheel rim/tire assembly, through automation and improved operator guidance. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, the improved wheel balancer of the present invention includes a shaft adapted for receiving a wheel rim/tire assembly, a rotation sensor assembly for measuring rotation of the shaft about its longitudinal axis, and a motor operatively connected to the shaft for rotating the shaft about its longitudinal axis, thereby rotating the wheel rim/tire assembly. A control circuit controls the application of current to the motor to rotate the wheel rim/tire assembly at desired speeds and to actively hold the wheel rim/tire assembly at desired rotational positions. An automatic measuring apparatus is configured to scan the inner surface of the wheel rim/tire assembly to provide the balancer computer with contour information necessary to identify optimal correction weight plane optimum locations as well to present the operator with the best imbalance correction weight arrangement. The best plane locations, amount of correction weight, the number of correction weights, and the positions of the correction weights in the plane locations, are calculated by the balancer computer to result in a minimized residual static and dynamic imbalance while still using incrementally sized weights. Once the correction planes and rotational positions of the imbalance correction weights is identified, the balancer computer utilizes the motor drive to automatically index and hold the wheel rim/tire assembly at the proper rotational position for placement of the first imbalance correction weight, enhancing weight placement accuracy. To further enhance weight placement accuracy, a laser pointer assembly projects a laser dot onto the inner surface of the wheel rim/tire assembly at the axial position of the weight imbalance correction plane at which the imbalance correction weight is to be applied. The wheel rim/tire assembly is rotated automatically by the drive motor to each determined rotational position for application of successive correction imbalance weights, and the laser dot is correspondingly projected onto each imbalance correction plane in succession. 
     It is a further improvement over the prior art in that the wheel balancer of the present invention that the balancer computer is configured to permit placement of imbalance correction weights adjacent the outer lip of the wheel rim/tire assembly, and that the laser pointer assembly is configured to project a laser spot between spokes of the wheel rim/tire assembly to illuminate the proper spot for placement of such imbalance correction weights. 
     It is a further improvement over the prior art in that the wheel balancer of the present invention is configured to receive as input, the width of a variety of brands of imbalance correction weights, and to utilizes such input widths to adjust the identification of the placement location of individual imbalance correction weights on the wheel rim/tire assembly to provide for optimal imbalance correction, and to indicate the adjusted position using the laser pointer. 
     The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the accompanying drawings which form part of the specification: 
     FIG. 1 is a combination diagrammatic plan view, block function diagram of the present invention system; 
     FIG. 2 is a combination cross section, diagrammatic illustration showing a typical wheel mounted on a wheel balancer and how a rim measuring apparatus is used to scan a wheel surface contour to obtain the entire continuous surface profile available for the placement of imbalance correction weights; 
     FIG. 3 is in the view of FIG. 2, showing the geometric relationships between imbalance and correction weight locations residing on weight correction planes; and 
     FIG. 4 is a combination cross section, diagrammatic illustration similar to FIG. 2, showing how the laser pointer is used to facilitate the placement of imbalance correction weights in the imbalance correction planes and on the front edge of the wheel rim/tire assembly, by projecting a laser beam between spokes of the wheel rim/tire assembly; 
     FIG. 5 is a sectional view of the inner surface of a wheel rim/tire assembly, illustrating an alternate embodiment laser projection illuminating the length and width of an imbalance correction weight; 
     FIG. 6 is a sectional view of the inner surface of a wheel rim/tire assembly, illustrating an alternate embodiment laser projection illuminating the outline of an imbalance correction weight; and 
     FIG. 7 is a sectional view of the inner surface of a wheel rim/tire assembly, illustrating an alternate embodiment laser projection illuminating the outline of an imbalance correction weight and displaying an alphanumerical message. 
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
     Throughout the present invention, the term “spot” as used herein is intended to define the point of intersection between a beam of light, such as a laser, and a surface. For purposes of this description, such a point of intersection is considered to have zero dimensions. The term image, as used herein, is intended to define a projection onto a surface having at least one dimension, such as a line segment, which is distinguished from a spot. 
     Turning to the drawings, FIG. 1 illustrates the mechanical aspects of the automatic measuring and correction weight placement wheel balancing apparatus  10  used for the present invention. An automatic rim measuring component  12  comprises a support tube  14  housing an longitudinally extendible and rotatable shaft  16 . The specific details of construction and operation of the rim measuring component  12  are set forth in U.S. Pat. No. 5,915,274 incorporated herein by reference. The rim measuring component  12  comprises a radius arm  18  fixed to an end of the shaft  16 . The other end of the radius arm  18  has a fixed spacer  20  and a spherical “pointer ball”  22 . Pointer ball  22  is made of nylon or the like, and used by the operator to slide across inner wheel surfaces in a wheel profile scanning mode. The support tube  14  is welded to a bracket which provides the mounting for the apparatus in the wheel balancer  10 , which houses a longitudinal movement transducer  24  which is preferably a rotary linear Hall Effect sensor driven by longitudinal movement of shaft  16 . The bracket also houses a rotational transducer  26 , also preferably a rotary linear Hall Effect sensor, which is similarly directly driven by movement of shaft  16 . It should be noted that with the exception of the pointer ball  22  design and the direct driving of the rotational sensor  26 , this mechanical arrangement is a well-known, durable, and cost effective design already used in balancers manufactured by the assignee, Hunter Engineering Company. 
     The automatic rim measuring component  12  is mounted with its longitudinally extendible shaft  16  parallel with the axis of rotation RA for the vehicle wheel rim/tire assembly  28  undergoing balancing. The automatic rim measuring component  12  is shown in the plan view with the radius arm  18  rotated slightly away from the downward rest position. The longitudinal sensor  24  senses instantaneous distances relative to the balancer as the shaft  16  is extended into the wheel rim/tire assembly  28  while the rotational sensor  26  senses instantaneous radii as the pointer ball  22  is placed in contact with inner surfaces of the wheel rim/tire assembly  28 . Output signals from both sensors  24 ,  26  are fed into an A/D (analog to digital) converter  30  which is preferably an Analog Devices AD7871 fourteen (14) bit converter, and transferred to the wheel balancer central processing unit (CPU)  32  for further processing and utilization. 
     Vehicle wheel rim/tire combinations  28  to be balanced are mounted on a rotatable mounting shaft or spindle  34 , which is driven by a bi-directional, multi-rpm, variable torque motor drive  36  through a belt  38 . Operation of the motor drive  36  is controlled by a motor control unit  40 , in response to signals received from the CPU  32 . For details on the drive motor configuration and operation, refer to WO Patent No. 97/28431, incorporated by reference herein. 
     Mounted on one end of the spindle  34  is a conventional quadrature phase optical shaft encoder  42  which provides rotational position information to the balancer CPU  32 , which is preferably a Texas Instruments TMS34010 graphics processing chip, capable of executing the balancer software and at the same time driving the CRT display  44 . The CPU  32  is connected to EPROM program memory  46 , EEPROM memory  48  for storing and retrieving non-volatile information such as calibration and vehicle specific specifications, and DRAM memory  50  for temporary storage. Manual inputs for the present invention entail keypad entry  52  as well as three digital rotary contacting encoders  54 ,  56 , and  58  of type ECLODC24BD0006 by Bournes Inc. 
     During the operation of wheel balancing, at the other end of spindle  34 , a wheel rim/tire assembly  28  under test is removably mounted for rotation with a spindle hub  60  of conventional design. To determine wheel rim/tire assembly imbalances, the balancer includes at least a pair of force transducers coupled to balance structure  62 . These sensors and their corresponding interface circuitry to the CPU  32  are well known in the art, such as seen in U.S. Pat. No. 5,396,436 to Parker et al., herein incorporated by reference, and thus are not shown. 
     Additionally shown in FIG. 1 is the inclusion of the laser pointer control unit  64  in communication with the balancer CPU  32  for controlling the operation of a laser pointer  66 . The laser pointer  66  is preferably housed in a self-contained laser housing  68 , with a conventional laser emitter  70  positioned on an actuator to project a beam of laser light  72  towards the wheel rim/tire assembly  28  mounted on the spindle  34 . As best seen in FIG. 2, the laser emitter  70  is mounted within the housing  68  on an actuator  74  configured to move the laser emitter  70  such that the laser beam  72  intersects the inner surface of the wheel rim/tire assembly  28  at any point between the inner and outer faces thereof within a predetermined radial sector. Preferably, the laser beam  72  is projected parallel to the axis of rotation of spindle  34 , intersecting the wheel rim/tire assembly  28  radially, however it will be readily apparent that by controlling movement of the laser emitter  70 , the laser beam  72  may be projected onto the surface of the wheel rim/tire assembly  28  at an oblique angle. The point of intersection between the laser beam  72  and the wheel rim/tire assembly  28  is preferably illuminated by a spot of light caused by the scattering and reflecting of the laser beam  72 . 
     Utilizing the wheel balancing apparatus  10  of the present invention to balance a wheel rim/tire assembly  28  involves the following basic steps: 
     Mount the wheel rim/tire assembly  28  on the spindle  34 ; 
     input the wheel rim/tire assembly  28  profile with the rim measuring component  12 ; 
     measure the imbalance in the wheel rim/tire assembly  28 ; 
     identify the imbalance correction planes (axial distances) for placement of imbalance correction weights; 
     identify the angular position for placement of imbalance correction weights within each imbalance correction plane (i.e. at each axial distance); 
     illuminate imbalance correction plane; and 
     attach imbalance correction weights to the wheel rim/tire assembly  28  at a predetermined rotational position of the wheel rim/tire assembly  28 . The first step in balancing the wheel rim/tire assembly  28 , mounting on the spindle  34 , is conventional and well known in the prior art, and is not described herein in detail. The second step, inputting the wheel rim/tire assembly  28  profile utilizing the rim measuring component  12  is described in general with reference to FIG. 2. A detailed description is set forth in the incorporated reference of U.S. Pat. No. 5,915,274. FIG. 2 illustrates the process of inputting the wheel profile or rim contour. A typical wheel rim is shown mounted with conventional mounting hardware  76 , clamped against the face plate  78  of the mounting hub  60 . The rim measuring apparatus  12  is mounted as close to the spindle  34  centerline RA as possible while still allowing the extension shaft  16  to clear the mounting hub face plate  78 . To scan the wheel profile the operator first extends and positions the pointer ball  22  to the farthest distance as physically possible. The CPU  32  recognizes the extension of the pointer ball  22  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  22  is dragged along path  79  against the wheel rim surface, following the contour all the way to the point where the pointer ball  22  contacts the tire or rim edge, at which point the ball  22  is again held steady and the CPU  32  responds with a confirmation beep that the scan is finished, storing sets of distances and diameters, and the apparatus can be returned to the storage position. A right plane measuring apparatus (not shown) capable of reaching the right side of the wheel rim may optionally be provided with the present invention. Like the rim measuring apparatus described above, it could be a variation of an existing proven design such as the “Double Dataset™” apparatus offered on existing wheel balancers manufactured by Hunter Engineering Company. The surfaces suitable for adhesive weights and the right rim location will be scanned in exactly the same manner as the left side of the wheel, providing an even more complete wheel profile. 
     FIG. 3 shows an example weight plane arrangement that could be obtained from any of the distance/diameter 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  80  from the face  78  of the mounting hub  60 , 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 ,  84  and corresponding radii  86 ,  88 , the balancer CPU  32  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 required here. For a full explanation of the math performed during this weight calculation, refer to incorporated U.S. Pat. No. 5,396,436 to Parker et al. 
     By the CPU  32  determining the plane locations instead of the operator, two problems with adhesive weight balancing are solved. First, the imbalance correction planes were located as far apart as possible which in the case of dynamic imbalance can greatly reduce the amount of weight required, and second, the possibility of the operator selecting a balance plane displacement which will result in the need for an imbalance correction weight of an unavailable increment is eliminated. 
     An additional feature provided by the present invention is the ability to automatically index the wheel assembly to the proper angular location for placing a weight. The motor control of FIG. 1 has the ability to controllably rotate the wheel rim/tire assembly  28  to any rotational position desired 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. After a spin, the CPU  32  causes the motor control  40  to position the wheel rim/tire assembly  28  for placement of an imbalance correction weight in the left plane weight. After the imbalance correction weight is applied, the wheel rim/tire assembly  28  is then rotated to the right imbalance correction plane weight placement position by the motor control  40 , initiated by one of three methods: a manual input such as a key press on the keypad  52 , movement of the rim measuring apparatus  12  to where the pointer ball  22  is in closer proximity to the right plane than to the left plane, or if the wheel rim/tire assembly  28  is pushed with enough predetermined force that the CPU  32  understands that the operator must want the wheel rim/tire assembly  28  to move to the next position. For a more complete description of the servo drive and wheel rotational position control, refer to the incorporated reference WO Patent No. 97/28431. 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. 
     A further feature of the wheel balancer of the present invention is the inclusion of a motion-controlled laser emitter  70 , movable along at least one axis parallel to the axis of rotation for the wheel rim/tire assembly, and the laser pointer control  64  to further facilitate the proper placement of the imbalance correction weights by the operator. As seen in FIG. 4, upon identification by the CPU  32  of the wheel balancer of the two imbalance correction planes, the laser emitter  70  is activated by the laser pointer control  64  to project a beam of laser light  72  along one of several paths indicated generally by  72 A- 72 C such that the laser beam  72  intersects the wheel rim/tire assembly  28  at a point on or adjacent one of the imbalance correction planes, thereby illuminating it. Actuation of the laser emitter  70  is independent of the rotational position of the wheel rim/tire assembly  28 , as proper rotational position of the wheel rim/tire assembly  28  is maintained by the motor control  40 , as described above, such that the attachment point for the imbalance correction weight coincides with the laser beam  72  projection point on the wheel rim/tire assembly  28 . Accordingly, the laser emitter  70  emits laser beam  72  continuously until an imbalance correction weight is installed at the indicated imbalance correction plane, and the operator signals the wheel balancer  10  to proceed with the next step in the imbalance correction process, at which point laser beam  72  may be emitted along a second path such as  72 B or  72 C. 
     In FIG. 4, laser beam  72  emitted along path  72 A is seen to pass between the spokes of the wheel rim/tire assembly  28 , and intersect the wheel rim/tire assembly  28  at a point adjacent the front face thereof, identifying a position at which a clip-on style imbalance correction weight is to be attached to the wheel rim/tire assembly  28 . Alternative paths,  72 B and  72 C for the laser  72  indicate possible projection paths for the laser  72  wherein the laser pointer  68  is illuminating the right and left imbalance correction planes for a pair of adhesive imbalance correction weights. Laser paths  72 A,  72 B, and  72 C are considered to be exemplary of the infinite possible paths along which the laser beam  72  may be projected to intersect the surface of the wheel rim/tire assembly, and those of ordinary skill in the art will recognize that the location of the right and left imbalance correction planes may vary from those shown in FIG. 4, and that the angle along which the laser beam  72  is projected may similarly be varied to intersect the wheel rim/tire assembly  28  at a different point about the inner circumference thereof. 
     In contrast, the incorporated prior art reference, WO Patent No. 98/10261 only actuates a laser light source when the wheel rim/tire assembly is exactly positioned manually by the operator to the identified rotational position. If the wheel rim/tire assembly of the WO 98/10261 patent is moved from the identified rotational position, the laser light source is deactivated until such time as the wheel rim/tire assembly is returned to the identified rotational position. 
     In an alternative embodiment, CPU  32  of the present invention is provided with information identifying the type of imbalance correction weight being utilized, or with the width of the imbalance correction weight, either by the operator or from a database, the CPU  32  will direct the laser pointer control  64  to offset the point of intersection between the laser beam  72  and the wheel rim/tire assembly  28  by an amount such that the center of the imbalance correction weight will intersect the imbalance correction plane if an edge of the imbalance correction weight is placed at the intersection point indicated by the laser beam  72 . 
     Turning to FIGS. 5-7, it will be seen that motion of the laser beam  72  may be controlled in multiple axes to provide a visual indication (i.e. an image) of one or more dimensional measurements of, or an outline of, the imbalance correction weight to be applied at the imbalance correction plane. Specifically, as seen in FIG. 5, through rapid motion (i.e. dithering) directed by the laser pointer control  64 , the laser beam  72  may be directed to outline or form a cross-hair pattern  80  on the wheel rim/tire assembly  28 , wherein the center of the cross-hair pattern  80  indicates the computed placement location for the imbalance correction weight relative to the imbalance correction plane, and the length of the arms of the cross-hair  80  correspond to the length and width (i.e. dimensions) of the imbalance correction weight if such information is known to the central processing unit  32 , or to the size of a generic weight if the imbalance correction weight dimensions are not known. Alternatively, the laser beam  72  may be directed by the laser pointer control  64  to project a line (by dithering) on the inner surface of the wheel rim/tire assembly corresponding to either the width or the length of an imbalance correction weight, centered on the imbalance correction plane. 
     Similarly, as is seen in FIG. 6, the laser pointer control  64  may direct the laser beam  72  to outline a perimeter within which the imbalance correction weight is to be secured in the imbalance correction plane. Again, if the dimensions of the imbalance correction weight are known, the perimeter may be controlled to correspond to the known dimensions, or merely to be representative of a generic imbalance correction weight size. Those of ordinary skill in the art will recognize that the laser pointer control  64  may be configured to rapidly move (i.e. dither) the laser beam  72  in a variety of predetermined patterns on the surface of the wheel rim/tire assembly, including the display of alphanumeric messages, as seen in FIG. 7, thereby projecting an image or message to the operator. For example, in FIG. 7, the outline of an imbalance correction weight is projected onto the surface of the wheel rim/tire assembly, together with an alphanumeric message identifying the proper imbalance correction weight amount. As is well understood in the art, movement of the laser beam  72  of sufficient speed will create the optical illusion to a human operator of a continuous projected image on the surface of the wheel rim/tire assembly, in much the same way as a television image is refreshed sufficiently fast for the human eye to incorporate a complete image from a single scanning beam. 
     An additional feature of the present invention is the interaction between the motor control  40  and the laser pointer control  64  through the CPU  32  of the wheel balancer  10 . For example, if the operator desires to place an imbalance correction weight in a different imbalance correction plane than that selected by the CPU  32  and indicated by the laser emitter  70 , the angle of the laser beam  72  may be manually adjusted through the use of the rotary knob inputs  54 - 58  to identify to the CPU  32  the desired imbalance correction plane. The CPU  32  will calculate a new weight magnitude, correspondingly update the rotational position of the wheel rim/tire assembly  28  to which an imbalance correction weight must be applied, and direct the motor control  40  to servo the wheel rim/tire assembly  28  to the new rotational position, corresponding to the operator selected imbalance correction plane. The ability to over-ride the CPU-selected imbalance correction planes is of particular importance when the operator, upon visual inspection of the wheel rim/tire assembly  28 , identifies a surface defect at the CPU-selected weight application point, resulting in the need to adjust at least one weight placement location(s). 
     An alternate embodiment utilizing adjustment of the laser pointer by the operator allows for the calibration of the laser pointer control  64  to the size of a predetermined imbalance correction weight. An imbalance correction weight of a known weight amount is placed on the wheel rim/tire assembly surface, and the position of the laser pointer adjusted by the operator using the rotary knob inputs  54 - 58  until the laser beam outlines the perimeter of the imbalance correction weight, or traces a line corresponding to the length of the imbalance correction weight. Once the laser beam  72  is adjusted to correspond to the imbalance correction weight, the operator signals the central processing unit  32 , preferably through the keypad input  52 , and the dimensions of the imbalance correction weight, as identified from the laser pointer adjustments, are stored for future reference. The operator may further provide the central processing unit  32  with sufficient information to identify a uniform imbalance correction weight dimension increase which is proportional to an increase in the weight of the imbalance correction weight, such that the central processing unit  32  can compute the proper dimensions of any amount of imbalance correction weight to be applied to the inner surface of the wheel rim/tire assembly, and correspondingly direct the laser pointer control  64  to project laser beam  72  in the proper pattern. For example, if the operator identifies the size of a 0.25 oz. weight using the laser pointer, and subsequently identifies the size of a 0.50 oz. weight, wherein only the length of the weight has increased (i.e. doubled), the central processing unit can interpolate that the size of larger weights of the same brand (i.e. a 1.0 oz weight would be 4× as long as the 0.25 oz. weight). 
     A further additional feature of the present invention is the ability of the laser pointer  68  to illuminate weight attachment points adjacent the front face of the wheel rim/tire assembly  28 , as shown by laser beam path  72   a  in FIG. 4, and for the CPU  32  to perform a “reverse split-spoke” calculation to facilitate the placement of weights on the front face of the wheel rim/tire assembly when the laser beam  72  is blocked from illuminating the attachment point by a spoke of the wheel rim/tire assembly  28 . As is known by those of ordinary skill in the art, a technique utilized in balancing is a “split-spoke” calculation, which is performed to distribute the placement of adhesive imbalance correction weights about the inner circumference of a wheel rim, at locations which are hidden from view at the front of the vehicle wheel, by locating the imbalance correction weights behind the spokes of the wheel rim/tire assembly. Such techniques are disclosed in U.S. Pat. No. 5,591,909 to Rothamel et al. and U.S. Pat. No. 4,357,832 to Blackburn et al. In contrast, to perform a “reverse split-spoke” calculation, the operator of the present invention wheel balancer provides an indication to the CPU  32  of the desired spacing required to shift the laser point to points between the spokes of the wheel rim/tire assembly  28 , as is described in connection with the “split-spoke” calculation in U.S. Pat. No. 5,355,729 to Douglas for “Split Weight Balancing”, herein incorporated by reference. The CPU  32  next identifies a combination of incremental imbalance correction weights which may be placed adjacent the front face of the wheel rim/tire assembly  28  between the spokes of the wheel rim/tire assembly  28  at the indicated spacing, and which is the equivalent of a single imbalance correction weight placed in front of a spoke. Alternatively, the operator may enter a “spoke-input” mode in the wheel balancer  10 , and identify to the central processing unit  32  the number, size, and radial placement of the individual spokes of the wheel rim/tire assembly, thereby allowing the central processing unit to automatically determine if the laser beam  72  will be blocked by a spoke and identify an acceptable split-weight substitution which allows the laser beam  72  to reach the outer wheel rim edge. 
     By identifying a combination of incremental imbalance correction weights positioned between the spokes of the wheel rim/tire assembly  28 , the laser pointer  70  is directed by the laser pointer control  64  to illuminate placement points adjacent the front face of the wheel rim/tire assembly  28  along a path such as  72   a  shown in FIG. 4, between the spokes. Such illumination may be as described above, or in an alternative embodiment, the laser beam  72  may be controlled by the laser pointer control  64  to sweep along the surface of the wheel rim/tire assembly in a plane perpendicular to the wheel axis of rotation, and project a line guiding the operator the proper imbalance correction weight placement angular location. 
     In an alternate embodiment, those of ordinary skill in the art will readily recognize the projection of laser beam  72  need not be directed towards the inner surface of the wheel rim/tire assembly, but may be projected directly onto the sidewall of the tire mounted to the wheel rim. Projection of the laser beam  72  onto the sidewall of the tire itself is particularly useful for identifying the location at which the operator is required to install a clip-on weight. Due to the difficulty of viewing the wheel rim/tire assembly  28  mounted to the balancer  10  from directly above, it is difficult for an operator to properly position a clip-on weight for installation. By positioning the laser pointer  68  above the spindle  62 , the laser beam  72  may be directed by the laser pointer control  64  to project an arrow onto the tire inner (or left) sidewall at the 12:00 position, indicating the top dead center of the wheel rim/tire assembly, thereby facilitating the placement of a clip-on imbalance correction weight to the wheel rim/tire assembly edge at the inner imbalance correction plane location, and eliminating a common source of operator error. Those of ordinary skill in the art will recognize that through the use of either a second laser point  68 , or by reflection, the laser beam  72  may be similarly directed to project images onto the outer (or right) sidewall of the wheel rim/tire assembly to facilitate the placement of clip-on weights in the outermost imbalance correction plane. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results are obtained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.