Abstract:
A vehicle measurement station utilizing at least one displacement sensor systems disposed on each opposite side of a sensor region of a vehicle inspection lane to acquire measurement data, associated with a vehicle passing through the sensor region. Each displacement sensor system is configured to acquire measurement data along at least three discrete and vertically spaced measurement axis in response to a trigger signal indicating the presence of a vehicle moving through the inspection lane. A processing system receives the acquired data for evaluation, identification of outlier data points, and for determining a measurement associated with a characteristic of the moving vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 62/084,396 filed on Nov. 25, 2014, and from U.S. Provisional Patent Application Ser. No. 62/198,860 filed on Jul. 30, 2015, both of which are herein incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present application is related to vehicle measurement or inspection systems, and in particular, to a vehicle inspection or measurement system configured to utilize one or more displacement sensors to acquire measurement data associated with various components of a vehicle as the vehicle moves through a vehicle inspection lane. 
     Systems for measuring or inspecting vehicle properties, such as wheel alignment and associated parameters, are traditionally set up for obtaining measurements to a high degree of accuracy under controlled conditions, such as with the vehicle disposed in a stationary location on a level surface or alignment lift rack. These vehicle measurement or inspection systems may require the temporary placement of various inclinometers or optical targets on the vehicle wheels, from which data is acquired to determine the various measurements. In general, vehicle wheel alignment measurement or inspection procedures require a technician to spend time preparing the vehicle for measurements, acquiring the measurements, and optionally performing adjustments necessary to correct any identified problems. Often, a vehicle brought in to a shop for other services may unknowingly be in need of an alignment service as well. However, unless the service technician and the vehicle owner are willing to spend the time required to prepare the vehicle for measurement and proceed with an alignment measurement process, alignment issues will likely remain undetected and unrepaired. 
     In response to the recognized need for a way to quickly identify vehicles which may require an alignment service, various quick check or dedicated inspection systems have been introduced to the market, such as the Quick Check® System from Hunter Engineering Co. of St. Louis, Mo. These systems provide an operator with the tools and procedures necessary to quickly (in less than three minutes) obtain basic measurements of important vehicle wheel alignment angles, enter vehicle identifying information (such as through a VIN barcode scan), and review vehicle diagnostic information such as battery condition, tire tread depth, and on-board diagnostic messages. If a vehicle quick check or inspection reveals a potential out-of-specification measurement or problem, it can be quickly brought to the attention of the vehicle owner, who may then elect to proceed with a more in-depth vehicle service procedure, such as a full vehicle wheel alignment service using specialized precision equipment. 
     Often, vehicle quick check or inspection systems require a technician to carry out various tasks during the process, including attachment of optical targets or angle sensors to the wheels of the vehicle, manual measurement of tire tread depths, and the coupling of scanner component to vehicle data ports. In order for the technician to complete these tasks, the vehicle must be stationary for part of the time, such as for the attachment (and subsequent removal) of optical targets or angle sensors. This necessitates establishing a routine or procedure which must be followed by a technician each time a vehicle is brought into the shop for service. During busy times, or when multiple customers are waiting, a technician may not have sufficient time to carry out these routines or procedures for every vehicle, potentially failing to identify vehicles in need of additional services. 
     Vehicle wheel alignment systems have utilized a variety of techniques for non-contact measurement of stationary vehicle wheel assembly parameters, from which vehicle wheel alignment angles can be determined. For example, by utilizing multiple displacement measurement sensors, displacement measurements between known sensor locations and multiple locations on a stationary vehicle wheel assembly can be measured. Processing the acquired measurements from sensors observing wheels on opposite sides of an axle can identify planes parallel to the wheel assembly surfaces, from which representations of total toe and camber angles for the vehicle can be determined. In other configurations, two-dimensional images of a stationary vehicle wheel assembly are acquired, and image processing algorithms utilized to identify geometric features such as the wheel rim edge, from which a perspective analysis can be performed to determine estimates of vehicle wheel assembly spatial position and orientation. Alternatively, structured light patterns, such as multiple laser lines, or colored stripes, can be projected onto the stationary wheel assembly surface and observed by an imaging system. Deviations in the projected pattern are analyzed to generate representations of the illuminated surfaces, from which vehicle wheel assembly spatial position and orientation can be estimated. In general, these systems require the vehicle to remain stationary relative to the sensors during the measurement acquisition procedure, but some non-contact measurement systems require either the wheel assembly or the sensors be rotated in place about a stationary axis of rotation during the measurement acquisition procedure. 
     Some non-contact measurement systems can acquire measurements as a vehicle wheel assembly is both rotated and translated past the sensors, i.e., as the vehicle is moved past the sensors. For example, using laser displacement sensors to measure a distance between a fixed sensor and various points on vehicle wheel assemblies on opposite sides of a vehicle as a vehicle is driven at a slow speed between the sensors, enables a system to acquire measurement data along horizontal slices of the wheel assemblies, from which approximations of the wheel spatial orientations can be derived. These types of systems are highly influenced by the speed at which the vehicle travels between the sensors, the angle (straightness) of vehicle travel relative to the sensor observation axis, suspension movement, and changes in steering of the vehicle as it passes between sensors. Measurements acquired from a moving vehicle are useful to provide a vehicle service quick check or audit inspection, capable of identifying vehicles which may be in need of a further, more precise, alignment inspection and/or adjustment. 
     Accordingly, there would be a benefit to the vehicle service quick check or inspection industry if additional vehicle measurements could be acquired as the vehicle is driven, such as by a customer, through a measurement region of a vehicle inspection lane without stopping, and if variations in vehicle speed, steering, suspension movement, or direction of travel could be identified and/or accounted for during the acquisition of measurements associated with the moving vehicle. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, the present application sets forth a vehicle measurement or inspection system which utilizes one or more displacement sensors disposed in sensor units on opposite sides of a sensor region in a vehicle inspection lane to acquire displacement measurement data associated with a moving vehicle passing through the sensor region. Data acquired by the displacement sensors is processed to measure distances between the displacement sensors and surfaces of the vehicle within the observable fields of view associated with the displacement sensors. A processing system is configured to receive and evaluate the measurement data, together with the known parameters of the measurement system, to identify vehicle parameters such as a velocity of a wheel assembly passing through the sensor region, wheel rim or tire dimensions, and wheel assembly spatial orientations. 
     In a further embodiment of the present invention, a series of displacement sensors are laterally spaced along each side of a sensor region in a vehicle inspection lane to acquire a collection of independent displacement measurements from wheel assemblies on opposite side of a moving vehicle passing through the sensor region. An associated processing system is configured to receive the collection of displacement measurements from the displacement sensors for evaluation, identifying outlier displacement measurements, and determining average displacements associated with individual vehicle wheel assemblies of the vehicle, from which approximations of one or more vehicle parameters are computed. These vehicle parameters may include changes in velocity or steering of the vehicle passing through the sensor region, vehicle suspension movement, vehicle axle parameters, and individual wheel assembly spatial orientations. 
     The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments 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 top plan view of a vehicle inspection lane, illustrating exemplary configurations and placement locations for multiple sensor units of the present disclosure; 
         FIG. 2  is a top plan view of a vehicle inspection lane, illustrating an exemplary configuration and placement location for sensor units of the present disclosure in a drive-through configuration; 
         FIG. 3  is a side view of a single displacement sensor system within a sensor unit of  FIG. 2 ; 
         FIG. 4  illustrates an exemplary imaging sensor pixel array of a displacement sensor system, sub-windowed to encompass pixels illuminated by reflected laser light from an associated array of lasers; 
         FIG. 5  is a top plan view of the relationships between a pair of opposed displacement sensors and a pair of wheel assemblies on an axle of a moving vehicle, related to measurements of points on leading tire sidewall surfaces; 
         FIG. 6  is a top plan view similar to  FIG. 5 , related to measurements of points on trailing tire sidewall surfaces; and 
         FIG. 7  is an illustration of the linear and angular relationships between rim edge locations on a moving vehicle wheel assembly. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale. Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure. 
     The term “axle”, as used herein, is intended to refer to a pair of vehicle wheel assemblies, each consisting of a wheel rim and a tire, disposed on opposite lateral sides of the vehicle, and which are generally axially aligned with respect to each other, such as the left and right front wheels or the left and right rear wheels. The pair of vehicle wheel assemblies may be, but is not limited to wheel assemblies coupled by a solid interconnecting axle shaft, by a pair of half-shafts coupled through a differential, those which are partially independent of each other, or those which are fully independent of each other. 
     Since the present application describes features which exist on opposite lateral sides of a vehicle inspection lane, but which are otherwise identical, it will be understood that the use of the reference designations Left and Right, or L and R as in the Figures, identify corresponding components utilized at locations relative the left and right lateral sides of a vehicle or vehicle inspection lane. For example, a sensor unit described generically as  150  will be designated as  150 R and  150 L when specifically shown or described at either the right or left side of the vehicle inspection lane  10 . 
     A vehicle measurement system of the present disclosure is generally intended for use in a vehicle service shop drive-through configuration, where a moving vehicle V is driven through a sensing region  50  within the vehicle service or inspection lane  10 , as seen in  FIGS. 1 and 2 , in a generally straight line (but not necessarily along, or parallel to, a longitudinal midline of the vehicle service or inspection lane  10 ), while being observed by various sensors acquiring measurement data, and optionally, acquiring vehicle-associated still-frame or motion video images. 
     The array of sensors provides an operator with an initial diagnostic overview of the moving vehicle V with minimal operator interaction, and may include displacement sensors for acquiring data related to vehicle wheel alignment, drive-over tire tread depth sensors for measuring tire wear conditions, and tire pressure measurement sensors for measuring tire inflation conditions. Machine vision systems may be included for recording vehicle body panels for damage or misalignment, for observing tire sidewall markings to identify tire parameters, and/or for capturing vehicle identifying information such as license plate data. Depending upon the configuration of the various sensors observing the vehicle V as it moves through the sensing region  50 , an operator may be provided, at an operator console  60 , with a detailed report on the condition of multiple components of the vehicle V, recalled vehicle and customer records, and recommended service and replacement parts without the need to manually identify, record, or retrieve any data. 
     In one embodiment, the present disclosure sets forth a system for capturing data associated with a moving vehicle V, and such as the individual wheel assemblies  104  on each axle  105 . Within the system, one or more sensor assemblies or units  150 , each containing at least one displacement sensor system  200 , are disposed on each lateral side of the sensing region  50  to observe the opposite sides of the vehicle V moving through the sensing region  50 . To facilitate placement within an inspection lane  10 , each sensor unit  150  may be contained within a vertical tower positioned on a floor surface in proximity to the drive-through sensing region  50 , within a wall-mounted housing, within a surface or flush-mount configuration, or within a combination thereof suitable for mounting one or more displacement sensors systems  200  and their associated components to observe the sensing region  50 . 
     Each displacement sensor system  200  is associated with an operational range within which the displacement sensor system  200  is capable of measuring, to within a desired tolerance, a distance to an observed surface. Given the wide variation in configurations of vehicles V, each displacement sensor system  200  is preferably disposed such that the observed surfaces on an intended collection of vehicle configurations will pass through the associated operational ranges. 
     Data from the displacement sensor systems  200  is conveyed to a processing system (local or remote) configured with suitable software instructions to control and/or communicate with the various displacement sensor systems, receive data therefrom, analyze the received data, receive operator input, and convey resulting measurements to an output. The operator input and output is preferably conveyed through a suitably configured operator console  60 . 
     Each sensor unit  150  consists of a support framework configured as necessary to mount at least one displacement sensor system  200 , or preferably, two or more laterally spaced displacement sensor systems  200 , such that an operative field of view for each displacement sensor system  200  encompasses observable lateral side surfaces associated with a range of measurable vehicles V traversing the sensing region  50  of the inspection lane  10 . Displacement sensors systems  200  are preferably laser displacement sensors, as will be described below, but those of ordinary skill in the art will recognize that other types of displacement sensors, including 2D imaging, time-of-flight optical sensors, and ultrasonic sensors capable of obtaining displacement measurements to surfaces within a field of view may be utilized. Provisions may be included within each sensor unit  150  for additional other types of sensors associated with a vehicle inspection system. 
     Within a sensor unit  150  containing multiple displacement sensor systems  200 , a lateral spacing between the displacement sensor systems  200 , as well as an associated vertical position of each, may be either random or determined, as each displacement sensor system  200  functions as an independent measurement sensor to contribute measurement data to a collection of displacement measurements associated with a vehicle V passing through the inspection lane  10 . Displacement measurement data acquired from multiple points or locations on a passing vehicle V, such as from individual wheel assemblies  104 , as the vehicle moves through the sensing region  50  of the inspection lane  10  is utilized by the suitably configured processing system to establish average displacement measurements associated with select features on the vehicle, to discard outlier displacement measurements using tolerance ranges or other statistical analysis techniques, or to detect and identify changes in vehicle velocity (braking or accelerating), oscillations in the vehicle suspension (such as from driving over a raised lip or recessed drain in the inspection lane floor surface), and steering changes as the vehicle V passes through the vehicle inspection lane  10 . 
     An individual laser displacement sensor system  200  generally consists of an imaging sensor  202  having a field of view FOV to receive reflected light from a surface illuminated by at least one associated laser emitter  204  or other associated light source. Preferably, a set of two or more laser emitters  204  are aligned in a vertically spaced arrangement on a support stand  206  together in a fixed relationship with the imaging sensor  202 . In one embodiment, illustrated in  FIG. 3 , a total of four vertically spaced laser emitters  204  are associated with a single imaging sensor  202 . Greater or smaller numbers of laser emitters  204  may be employed without departing from the scope of the present disclosure, depending upon the amount of displacement measurement data to be collected for processing and averaging. The known or determinable vertical spacing between each laser emitter  204  may be uniform, varied, or symmetric. Each laser emitter  204  is configured to project a laser beam  208 , preferably parallel to the ground G or vehicle support surface, onto surfaces of the vehicle V passing through the field of view FOV of the associated imaging sensor  202 , such that reflected laser light  210  from the surfaces is received on a pixel array  205  of the associated imaging sensor  202  after passing through an appropriate focusing lens or optical system. Those of ordinary skill in the art will recognize that additional laser emitters  204  may be utilized to project a plurality of parallel laser beams (for example, defining a grid of illuminated points on the surface of an observed object) which are subsequently reflected onto the pixel array  205  of the associated imaging sensor  202  without departing from the scope of the present disclosure. 
     The distribution and characteristics of the reflected laser light  210  received at the pixel array  205  corresponds at least partially with the characteristics of the surface from which the laser beams  208  are reflected. The spatial location of the pixels  400  (individual light sensing elements) in the pixel array  205  which receive the reflected light are used to determine the precise displacement of the point from which the laser beams  208  were reflected, relative to the light sensing pixel array  205 , preferably to a sub-pixel resolution. As the displacement of the observed surface changes relative to the stationary pixel array  205  due to movement of the vehicle V, corresponding changes occur in the incident location of the reflected laser light  210  on the light sensing pixel array  205 . Through image processing, distribution and characteristics of the observed reflected laser light  210  may be used, together with known parameters of the displacement sensor system  200 , to triangulate at discrete points in time, the relative spatial location of the point of reflection on a surface of the moving vehicle V within the field of view FOV and sensing region  50 . 
     The reflected laser light  210  may be representative of a projected dot, line segment, geometric shape, or other figures, such as an “x” or a “+”, depending upon the particular optical configuration of the associated laser emitter  204  and any intervening focusing lenses or optical elements. As shown in  FIG. 4 , when the laser emitters  204  are arranged in an aligned and vertically stacked configuration, the data acquired from the observing imaging sensor  202  can be limited to pixel data from a sub-window  202   a  of pixels  400  within the pixel array  205  of the imaging sensor  202  which receive the reflected laser light  210  from the vertically spaced array of projected laser beams  208  seen in  FIG. 3 . With suitable hardware, the light sensing pixel array  205  can be virtually segmented into one or more individual sub-windows or regions  202   a , each of which can be “read” individually. For example, a VITA-5000 CMOS image sensor available from ON Semiconductor provides the capability of clocking-out or reading at least two separate sub-windows or regions of interest  202   a  from a single light sensing pixel array  205 . Limiting the region-of-interest to one or more sub-windows  202   a  facilitates data compression, ignores illumination from surfaces outside of a defined region of interest, and increases transfer rates of pixel data from the imaging sensor  202  to an associated processing system. 
     In addition to establishing a displacement measurement, the distribution of the reflected laser light  210  on the pixel array  205 , and any observed changes therein may optionally be analyzed by a processing system to identify characteristics of the reflecting surface, such as material type, reflectivity, or transparency. The established relationship of the laser beams  208  to each other, i.e., parallel, horizontally displaced, vertically displaced, or both horizontally and vertically displaced relative to a reference plane such as the ground G, provides additional information about the illuminated surfaces, such as an angular orientation between the surfaces, or the motion of the surfaces. 
     In an embodiment of the present disclosure illustrated in  FIG. 2 , one sensor unit  150 L,  150 R is disposed on each side of a sensing region  50  of an inspection lane  10  through which a vehicle V passes. Each sensor unit  150 L,  150 R is configured with a set of four laterally spaced displacement sensor systems  200 , each having a set of laser emitters  204  configured to project laser beams  208  in an associated vertical plane containing a corresponding measurement axis. In the embodiment shown, each displacement sensor system  200  is configured to observe reflected light from a set of four vertically spaced laser beams  208 , such that a total of sixteen discrete measurement points are potentially available on each side surface of a vehicle V passing through the sensing region  50 . Those of ordinary skill in the art will recognize that changes in the number of displacement sensor systems  200 , or the number of laser beams  208  associated with each individual displacement sensor system  200 , will provide a corresponding increase (or decrease) in the number of potentially available measurement points from which data can be collected by the associated imaging sensors  202 . At a minimum, a single displacement sensor  200  including a single laser beam  208  may be disposed as the “array” within the sensor units  150 L,  150 R on each side of the sensing region  50  of the inspection lane  10 . 
     To facilitate placement within an inspection lane  10 , the sensor unit  150  support framework for the various displacement sensor systems  200  may be contained within a vertical tower positioned on a floor surface in proximity to the drive-through sensing region  50 , a wall-mounted housing, a surface or flush-mount configuration, or a combination thereof, for mounting a plurality of individual displacement sensors systems  200  and their associated components in a laterally spaced arrangement orientated to view the sensing region  50 . 
     During operation as a vehicle V moves through the sensing region  50 , the laser beams  208  from the individual displacement sensor systems  200  project points of light onto the various surfaces of the vehicle V as the vehicle traverses past the stationary displacement sensor systems  200 . Movement of the vehicle V causes the incident points of the stationary laser beams  208  to traverse across contours of the various vehicle surfaces. Positional changes of the reflected laser light  210  received at the light-sensing pixel arrays  205  of each displacement sensor system  200  are analyzed by a controller or processor to provide displacement measurement values associated with the distance between the individual points of reflection from the vehicle surfaces and the displacement sensor system  200 , generating a set of data points defining contour plots representative of the surfaces of the vehicle V along the measurement axis of each of the laser emitters  204 , defined by the individual laser beams  208 , such as shown in  FIG. 3 . 
     Observed changes in laser spot intensity or laser spot size in the light-sensing pixel array  205  may optionally be analyzed to identify characteristics of the reflecting surface, such as material type, reflectivity, or transparency. The established relationship of the parallel laser beams  208  to each other, i.e., horizontally displaced, vertically displaced, or both horizontally and vertically displaced relative to a reference plane, such as the ground G or vehicle support surface, compared with the observed positions of the reflected laser spots  210  on the light-sensing pixel array  205  provide additional information about the illuminated surfaces. This additional information may include, but is not limited to, an angular orientation between the observed surface and the ground G, or the motion of the observed surface relative to the ground G. 
     Each displacement sensor system  200  within a sensor unit  150  acquires displacement measurements associated with an observed set of spaced illuminated points or locations on the side surfaces of a passing vehicle V. A collection of displacement measurements from multiple points or locations on the side surfaces of a passing vehicle V is evaluated using a variety of techniques to obtain average measurements, to discard outlier measurements which exceed a selected tolerance or which show other statistical deviations, and optionally to detect and identify characteristics of vehicle movement which might influence the measurements. Such characteristics of vehicle movement may include, but are not limited to, changes in vehicle velocity (braking or accelerating), oscillations in the vehicle suspension (such as from driving over elevation changes in an inspection lane floor surface), and steering changes as the vehicle V passes through the sensing region  50  in the vehicle inspection lane  10 . Additional factors which may influence acquired measurements include, but are not limited to, wheel assembly runout, tire sidewall raised letter or features, and tire sidewall non-uniformity. 
     During operation, the displacement measurement of the surfaces on a moving vehicle V passing through an inspection lane  10  or sensing region  50  can be triggered in a variety of ways. For example, as shown in  FIG. 2 , one or more optical triggers  300   a ,  300   b  can be disposed across the path of vehicle travel, such that an optical trigger beam is interrupted by the passage of the vehicle, triggering the acquisition of displacement measurements by each displacement sensor system  200 , as well as measurements or data acquisition by other associated sensors. If the optical triggers  300   a  and/or  300   b  are placed below the level of the vehicle body panels, the trigger beams will be interrupted by the passage of the wheel assemblies  104  on each axle  105  of the vehicle V, providing an indication of specific periods of time during which displacement measurements can be acquired from the wheel assembly surfaces. Alternatively, if the optical triggers  300   a  and/or  300   b  are placed vertically higher, the trigger beams will be interrupted by the vehicle body panels, and provide an indication of the specific period of time during which the vehicle V is passing through the inspection lane  10  or sensing region  50 . If multiple triggers  300   a  and  300   b  are provided, the sequence and frequency of the interruptions may be utilized to identify the presence of a vehicle V (as distinguished from a human operator walking past), the number of axles  105  present on a vehicle V, the velocity of the vehicle V, any change in acceleration of the vehicle V within the sensing region  50  (or between the spaced triggers), and when the vehicle V has exited the sensing region  50  such that measurement acquisition can be terminated. 
     For example, in an inspection lane  10  through which multiple vehicles V will pass in quick succession, utilizing a first optical trigger  300   a ′ at a height suitable for interruption by the vehicle body, together with a second optical trigger  300   a ″, at a height suitable for interruption by the vehicle wheel assemblies, as shown in  FIG. 3 , aids in distinguishing between back-to-back vehicles V and associating displacement measurements acquired from the wheel assemblies  104  on individual axles  105  with specific vehicles. The first optical sensor  300   a ′ is interrupted as the vehicle V enters the sensing regions, identifying the presence of the vehicle V. As the vehicle V moves through the sensing region  50 , the second optical sensor  300   a ″ is alternately blocked and unblocked by the wheel assemblies  104  on each axle  105 . So long as the first optical sensor  300   a ′ remains interrupted by the vehicle V, the blocking and unblocking of the second optical sensor  300   a ″ is associated with axles  105  on the current vehicle V. When the first optical sensor  300   a ′ is unblocked as the vehicle V departs the observation area, the axle association from the second optical sensor  300   a ″ is reset, and the system is ready to receive the next vehicle V in succession. 
     With reference to  FIGS. 5 and 6 , displacement measurement data is acquired by the displacement sensor system  200  from the surfaces of a vehicle V, such as from vehicle wheel assemblies  104 , which are moving generally perpendicular to the optical or measurement axis associated with each laser beam  208  emitted by the laser emitters  204 . As the vehicle V moves through the sensing region  50 , the combination of translational movement and rotational movement about a center point of the wheel assemblies  104  on an axle  105  enables the stationary displacement sensor system  200  to observe displacements as each laser point traverses a horizontal chord across the wheel assembly surfaces. By acquiring a series of displacement measurements over time as the surfaces of the vehicle V or wheel assembly  104  move past, the displacement sensor system  200  generates a time-indexed set of displacement measurement data points, each associated with a discrete point on the surface of the vehicle V or wheel assembly  104 . Preferably, the vertical height of the lasers emitters  204  in each displacement sensor system  200  is set such that each laser beam  208  traverses horizontal chord on each wheel assembly  104  which includes two data points on a tire tread outer circumferential edge, and at least two data points on a wheel rim circumferential edge. However, it will be recognized that due to variations in wheel assembly dimensions, some laser beams  208  may not intersect the wheel assembly at all, or may intersect the tire tread outer circumferential edge, but not the wheel assembly rim circumferential edge. 
     Processing each set of time-indexed displacement measurements is evaluated using a processing system configured with suitable feature recognition software algorithms identifies features of the surfaces of the vehicle V or vehicle wheel assembly  104  such as the wheel well edge, tire edge points, peak tire sidewall bulge points, and wheel rim edge points, from which basic alignment information, such as toe and camber values for the vehicle wheel assembly  104  can be derived. For a vehicle V which is moving in a straight line, with each wheel assembly  104  aligned parallel to the direction of travel (i.e., having zero toe), a horizontal chord of data points acquired as the wheel assembly  104  rolls past the measurement axis of a displacement sensor system  200  will preferably intersect, as shown in  FIG. 7 , at least one circumferential feature of the wheel assembly (such as the tire edge  104   a , rim guard feature (not shown), peak tire bulge  104   b , or wheel rim edge  104   c , at two points, each having the same measured displacement from the sensor. In other words, with reference to  FIGS. 5 and 6 : (LD at time 1 (LD 1 )=LD at time 2 (LD 2 )) or (RD at time 1 (RD 1 )=RD at time 2 (RD 2 )). 
     Vehicle wheels  104  which are not aligned parallel to the straight-line direction of travel for the vehicle (i.e., having non-zero toe such as illustrated in  FIGS. 5 and 6 ) will produce different measured displacements (LD 1 ≠LD 2 ) or (RD 1 ≠RD 2 ) from the displacement sensor system  200  for the two points intersecting the selected circumferential feature. Geometric evaluation (arc-tan) of the difference in the displacement measurements, taking into account an appropriate horizontal spacing D (D 3 , D 4 , or D 5 , respectively as seen in  FIG. 7 ) between the locations of the two points on the vehicle wheel assembly  104  as shown in Equation (1), identifies an associated toe angle measurement. 
     
       
         
           
             
               
                 
                   TOE 
                   = 
                   
                     arctan 
                     ⁢ 
                     
                       
                         ( 
                         
                           
                             LD 
                             1 
                           
                           - 
                           
                             LD 
                             2 
                           
                         
                         ) 
                       
                       D 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eqn 
                     . 
                     
                         
                     
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                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     When combined with a toe angle measurement for a vehicle wheel assembly  104  on the opposite end of the same axle  105 , a measure representative of total toe for that axle can be determined. 
     In an alternate procedure, toe angle measurements for each individual wheel assembly  104  are not calculated, and only a total toe representation for each axle  105  is calculated. The total toe value for an observed axle  105  is computed directly from the set of wheel assembly displacement measurements RD, LD associated with the wheel assemblies  104 L and  104 R on an axle  105 , without reference to the specific sensor unit separation distance W, without reference to the wheel assembly separation distances ST 1  and ST 2 , and without reference the individual toe values for each wheel assembly  104 L and  104 R.
 
Total Toe≈ LD   2   +RD   2   −LD   1   −RD   1   (Eqn. 2)
 
The total toe value can alternatively be expressed in angular form by assuming that the lateral distances MD L  and MD R  between the acquired measurements on the face of each wheel assembly  104 L and  104 R are approximately equal.
 
     
       
         
           
             
               
                 
                   
                     Total 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Toe 
                   
                   ≅ 
                   
                     2 
                     · 
                     
                       arcsin 
                       ⁡ 
                       
                         ( 
                         
                           
                             
                               - 
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                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ST 
                           
                           
                             
                               MD 
                               L 
                             
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                               R 
                             
                           
                         
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                   ( 
                   
                     Eqn 
                     . 
                     
                         
                     
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                     3 
                   
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     Slight differences between MD L  and MD R  resulting from sensor timing, sensor unit  150  placement, or minor steering movement of the vehicle V as it moves through the sensing region  50  can be ignored for purposes of obtaining a Quick Check® type total toe measurement for an axle  105 . 
     In one embodiment, additional information associated with a vehicle wheel assembly  104  and a vehicle V passing through the sensing region  50  is determined using a set of at least six identified points on the vehicle wheel assembly  104  which lie on a common circumferential feature, such as a tire edge  104   a , tire bulge peak  104   b , tire rim guard (not shown), or wheel rim edge  104   c . For example, as shown in  FIG. 7 , a set of measurement points P 1 T 1  and P 1 T 2  corresponding to the two points in time that a laser beam  208  illuminates rim edge  104   c , are identified on an upper horizontal chord of measurement points of a vehicle wheel assembly  104 . Similarly, a pair of measurement points P 2 T 3  and P 2 T 4  corresponding to the two points in time that a second laser beam  208  illuminates the rim edge  104   c , are identified on an lower horizontal chord of measurement points of a vehicle wheel assembly  104 . Finally, a pair of measurement points P 3 T 5  and P 3 T 6  corresponding to the two points in time that a rim edge  104   c  is observed by a third laser beam  208 , are identified on an medial horizontal chord of measurement points of a vehicle wheel assembly  104 . 
     Utilizing these three pairs of data points, together with known characteristics of the displacement sensor system  200 , a processor configured with suitable software instructions can determine the velocity of the vehicle V passing the sensor unit  150 , as well as an estimate of the wheel rim radial dimension R (or the radial dimension for any other circumferential feature on which the measurement points are acquired). Initially unknown parameters include h1, h2, and h3, the respective vertical displacements between the measurement points and the wheel assembly axial center point C xy , and D 3 , D 4 , and D 5 , the respective horizontal displacements between each pair of measurements on the horizontal chords, i.e., (P 1 (T 1 )−P 1 (T 2 )), (P 2 (T 3 )−P 2 (T 4 )), and (P 3 (T 5 )−P 3 (T 6 )). Additional unknown parameters include α 1 , α 2 , and α 3 , the respective angles at which the individual measurements were acquired. It should be noted that the total vertical separations Δh 12 , Δh 13 , and Δh 23  between respective pairs of measurement points are known from the physical configuration of the laser emitters  204  of the displacement sensor system  200 , as is the period of time between each acquired measurement, i.e., T 2 −T 1 =ΔT p1 , T 4 −T 3 =ΔT p2  and T 6 −T 5 =ΔT p3 . 
     Trigonometric relationship establish the following dimensional correspondence:
 
 P   1 ( T   1 )· x=−R ·cos(α 1 );  Eqn. (4)
 
 P   1 ( T   1 )· y=R ·sin(α 1 )= h   1 ;  Eqn. (5)
 
 P   1 ( T   2 )· x=R ·cos(α 1 );  Eqn. (6)
 
 P   1 ( T   2 )· y=R ·sin(α 1 )= h   1 ;  Eqn. (7)
 
 P   2 ( T   3 )· x=−R ·cos(α 2 );  Eqn. (8)
 
 P   2 ( T   3 )· y=−R ·sin(α 2 )=− h   2 ;  Eqn. (9)
 
 P   2 ( T   4 )· x=R ·cos(α 2 );  Eqn. (10)
 
 P   2 ( T   4 )· y=−R ·sin(α 2 )=− h   2 ;  Eqn. (11)
 
     Further simplification yields:
 
 P   1 ( T   1 )· x =−( P   1 ( T   2 )· x );  Eqn. (12)
 
 P   1 ( T   1 )· y=P   1 ( T   2 )· y=h   1 ;  Eqn. (13)
 
 P   2 ( T   3 )· x =−( P   2 ( T   4 )· x );  Eqn. (14)
 
 P   2 ( T   3 )· y=P   2 ( T   4 )· y=h   2 ;  Eqn. (15)
 
     Seeking to solve for D 3 , D 4 , and Δh 12  yields:
 
 D   3   =ΔT   p2   ·V= 2( P   2 ( T   4 )· x )=2 R ·cos(α 2 );  Eqn. (16)
 
 D   4   =ΔT   p1   ·V= 2( P   1 ( T   2 )· x )=2 R ·cos(α 1 );  and Eqn. (17)
 
Δ h   12   =P   1 ( T   2 )· y+P   2 ( T   4 )· y=R [sin(α 1 )+sin(α 2 )].  Eqn. (18)
 
     At this point, the number of known variables is three, while the number of unknown variables is four. Hence, the equations cannot be solved without additional information. Utilizing the displacement measurement data from the third measurement point provides the necessary information:
 
Δ T   p3   ·V= 2 R ·cos(α 3 );  Eqn. (19)
 
Δ h   13   =R [sin(α1)+sin(α 3 )];  and Eqn. (20)
 
Δ h   23   =R [sin(α2)+sin(α 3 )].  Eqn. (21)
 
     At this point, there are now six known variables, and only five unknown variable, which can be mathematically determined. These include the various radial angles α 1 -α 3 , the velocity of the wheel assembly  104 , and the radius R on which the measured points lie. 
     In a further embodiment, a method for identifying the translational velocity of the vehicle V or wheel assembly  104  passing the sensor units  150  is available whenever a single observed location on a surface of the vehicle V or wheel assembly  104  is identified by two or more displacement sensor systems  200  or measurements having a known lateral spacing there between. For example, if a pair of laser beams  208  are projected in horizontal parallel alignment towards the surfaces of the vehicle V or wheel assembly  104 , and have a known spacing there between, each laser beam will trace the same horizontal path across the surfaces as the vehicle V or wheel assembly  104  moves past the sensor unit  150 . Ideally, plots of displacement measurements acquired from the reflected laser light  210  incident at an associated imaging sensor  202 , will be identical, but temporally displaced from each other, i.e., phase shifted. With knowledge of the horizontal spacing between the individual laser beams  208 , and the time at which each laser beam  208  illuminates an identical point on the vehicle V or wheel assembly  104  surface, it becomes possible to mathematically correlate the signals, such that the speed or velocity of the surface of the vehicle V or wheel assembly  104  can be calculated as a ratio of the horizontal spacing and associated time delay or offset between the signals. 
     A cross correlation function y(τ) between signals x 1  and x 2  representative of the measured distances acquired by each displacement sensor system  200  may be defined as:
 
 y (τ)=∫ x   1 ( t +τ) x   2 ( t ) dt   (Eqn. 22)
 
     This reaches a maximum value when τ=τ 0 . The actual time delay τ 0  can be determined by finding the maximum value of the cross correlation function of the signals x 1  and x 2 :
 
τ 0 =Ψ( y   max )  (Eqn. 23)
 
     Where ψ is an inverse function to the cross correlation function of Equation 22. 
     Given the value of τ 0 , the speed of the surface of the vehicle V or wheel assembly  104  surface past the sensor unit  150  can be computed as: 
     
       
         
           
             
               
                 
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     While the present disclosure has described a vehicle measurement or inspection system in which an output is conveyed to an operator through a suitably configured operator console  60 , it will be understood that output may optionally be provided to the operator in the form of a printed report, stored in a machine-readable database, or communicated over a network to a remote vehicle service system or software application. The processing system used with the vehicle measurement or inspection system of the present disclosure may be in the form of a dedicated computer system associated with a specific set of sensors forming a vehicle measurement or inspection system, or may be in the form of a server system configured to communicate with a variety of sensors forming two or more independent vehicle measurement or inspection systems. Communications between the various sensors and the processing system may be via any conventional data transmission means, such as wired networks, wireless networks, or any combination thereof. 
     The present disclosure can be embodied in-part in the form of computer-implemented processes and apparatuses for practicing those processes. The present disclosure can also be embodied in-part in the form of computer program code containing instructions embodied in tangible media, or another computer readable non-transitory storage medium, wherein, when the computer program code is loaded into, and executed by, an electronic device such as a computer, micro-processor or logic circuit, the device becomes an apparatus for practicing the present disclosure. 
     The present disclosure can also be embodied in-part in the form of computer program code, for example, whether stored in a non-transitory storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the present disclosure. When implemented in a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. 
     As various changes could be made in the above constructions without departing from the scope of the disclosure, 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.