Method and apparatus for vehicle service system optical target assembly

A method and apparatus for determining the alignment of a vehicle wheel using an optical target assembly secured to the vehicle wheel in a non-determined position, the optical target assembly having a dimensionally stable shape and a plurality of optical target elements disposed on a plurality of target surfaces. Images of the optical target elements are acquired by an imaging system, together with target identifying indicia, and utilized together with previously stored target characterization data to determine a spatial orientation of the optical target assembly and an alignment of the vehicle wheel onto which it is secured.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates to machine vision vehicle service systems, and in particular to an optical target assembly configured for mounting to a surface of a vehicle, such as a vehicle wheel, during a machine-vision vehicle wheel alignment procedure.

A machine-vision vehicle service system, such as a vehicle wheel alignment system like the Series 811 Wheel Alignment System utilizing the DSP 600 Series sensors, manufactured and sold by Hunter Engineering Company of Bridgeton, Mo., consists generally of a console having a computer or processing unit, one or more display devices such as a monitor, and one or more input devices such as a keyboard. In a machine-vision vehicle wheel alignment system, one or more imaging sensor arrays are mounted away from a vehicle undergoing an alignment inspection, and are configured to obtain images of alignment targets or other identifiable features associated with the vehicle for communication to the processing unit. Correspondingly, the processing unit is configured with one or more software applications, at least one of which is adapted to facilitate the alignment of vehicle wheels which generally consist of a rim and an associated tire, using input received from the imaging sensors.

The machine-vision imaging sensors are traditionally part of a camera system or imaging system configured to view optical targets within associated fields of view to obtain images thereof for processing by the software applications in the console. Commonly, the observed optical targets incorporate highly accurate patterns that have known control features. The three-dimensional positions and relationships of the features in the images are determined, and the orientation of the wheels or other vehicle components to which the optical targets are attached are calculated by well known algorithms. Exemplary configurations for the high-accuracy optical targets are described in U.S. Pat. No. 6,064,750 to January, and in U.S. Pat. No. 6,134,792 to January. Each exemplary optical target consists of a target face, on which are disposed identifiable optical elements, a precision flat base, and a mounting shaft adapted for attachment to a separate clamping assembly secured to the vehicle or vehicle wheel assembly.

The conventional configuration for an optical target is precisely engineered with high-contrast optical elements such as circles, squares, or triangles. The accuracy of such conventionally configured optical targets is dependant upon how well the high contrast edges of the optical target elements can be located in an image produced by the imaging components of the wheel alignment system. For the best accuracy, the individual optical elements must be large enough to have relatively long straight or curved boundaries, and they must be separated far enough to prevent the individual optical target elements from appearing to fuse into a single object when reduced edge sharpness causes two or more optical target elements to bleed into the same pixel in the imaging system. These factors combine to limit the number of individual image pixels generated by the imaging system whose values are utilized to calculate a position and orientation of a conventionally configured optical target.

Each image of a conventional high-contrast optical target acquired by the optical imaging vehicle wheel alignment system is processed to identify a number of reference points in the image. Either the computer or the imaging system is configured to mathematically manipulate the positional relationships of the observed reference points, as identified in an image, to match them with a set of predetermined positional relationships based on the known parameters of the conventional high-contrast optical target. Once the relationship between the observed positional relationships and the predetermined positional relationships is identified for the reference points, the position and orientation in three-dimensional space of the target (and an associated vehicle wheel) relative to the position and orientation of the imaging system is identified, from which one or more vehicle wheel alignment angles can be identified. Accordingly, for an optical imaging vehicle wheel alignment system to function, it is necessary for the system to be capable of extracting a set of control or reference points from acquired images.

To further facilitate the operation of a machine vision vehicle wheel alignment system, the separate optical targets are secured to the vehicle wheels with precision wheel adaptors configured to clamp onto the vehicle wheel edges and to position a mounting point for the optical target substantially coaxial with the wheel rim's axis of rotation. The traditional precision wheel adaptors typically include a set of claws or feet adapted to secure the wheel adaptor to the vehicle wheel assembly by engaging the lip or rim of the wheel rim at the tire junction. A centering mechanism on the wheel adaptor ensures that the claws or feet of the wheel adaptor are adjusted in a symmetrical manner to maintain the mounting point for the optical target in a determined centered configuration in relation to the axial center of the wheel rim.

Some variations of traditional wheel adaptors, such as the Tire Clamp Adaptor Model No. 20-1789-1 from Hunter Engineering Co., and those shown in U.S. Pat. No. 5,987,761 to Ohnesorge and U.S. Pat. No. 6,131,293 to Maioli et al. further utilize a set of gripping arms adapted to engage tire surfaces in conjunction with a set of contact supports and centering mechanisms for symmetrically engaging the circumferential lip of the wheel rim and securing the wheel adaptors in an axially centered position on the vehicle wheel assembly.

Other vehicle-specific wheel adaptors, such as those for use with Mercedes Benz and BMW automobiles, are configured with a set of pins which are designed to pass through the wheel assembly, and to contact predetermined surfaces on the vehicle wheel hubs, positioning the vehicle-specific wheel adaptor in a predetermined axially centered location about the wheel assembly. These vehicle specific wheel adaptors are then held in place by means of tire clamps or spring mechanisms which grip to the tire tread surfaces.

Traditional wheel adaptors that will universally adapt to the wide range of wheel sizes on the market today are difficult to design and costly to build. Many times additional parts are required, such as extenders, in order to allow the adaptor to work with wheels that are very small or very large which also adds additional cost and complication to the adaptor system. Additionally, traditional adaptors have to provide a substantial amount of clamping force in order to hold the weight of the target or sensor on the wheel assembly. This clamping force can scratch or dent the wheel assembly where it is attached. This is very undesirable especially when the wheel assembly is a very costly aftermarket wheel.

Accordingly, it would be advantageous to provide a machine vision vehicle service system, such as a wheel alignment system, with an optical target assembly which incorporates both an optical target and a simplified adaptor for attachment the optical target assembly to a vehicle wheel, and which does not require a determined precision mounting on the vehicle wheel assembly in relation to the wheel axis of rotation.

It would be further advantageous to provide a machine vision vehicle wheel alignment system with a mechanically simplified optical target assembly which is light weight, dimensionally stable, less abrasive to the wheel rim surfaces, and which does not require precision construction.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present disclosure provides a machine vision vehicle wheel alignment system optical target assembly which incorporates an adaptor for attachment of an optical target to a vehicle wheel assembly. The adaptor includes at least one contact surface for seating in a non-determined position against surfaces of a vehicle wheel assembly, and a pair of clamping arms configured to grip the tread surfaces of a tire mounted to the wheel rim, to hold the optical target assembly in contact with the wheel assembly surfaces. The optical target is secured to the adaptor, and maintained in a stationary relationship to the wheel assembly thereby during a vehicle wheel alignment procedure.

In an alternate embodiment, the present disclosure provides a machine vision vehicle wheel alignment system optical target assembly consisting of a rigid body supporting a target identification marking and at least two non-determined optical targets on associated discrete surfaces for temporary attachment to a vehicle wheel assembly. The optical target assembly includes at least one contact surface for seating in a non-determined position against a surface of a vehicle wheel assembly, and a pair of clamping arms configured to grip the tread surfaces of a tire mounted to the wheel rim, to hold the optical target assembly in contact with the wheel assembly surface. The optical targets are adjustably secured to the rigid body in a selected rotational orientation, and maintained in a stationary relationship to the wheel assembly onto which the rigid body is mounted during a vehicle wheel alignment procedure.

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.

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.

In order to fully describe the apparatus and methods of the present disclosure, the following terms and definitions will be utilized in reference to a vehicle wheel assembly. The term “inboard surface” refers to the surface of an object, disposed on the axis of rotation of a vehicle wheel, which is facing the point of intersection between the axis of rotation and the centerline of the vehicle on which the wheel is mounted. The term “inboard direction” refers to movement along a wheels axis of rotation towards a point of intersection between the axis of rotation and the centerline of the vehicle. The terms “outboard surface” and “outboard direction” refer to the opposite surfaces and movement in the opposite direction from the inboard surface and direction. Based on these definitions, it will be readily understood that an object can be described as being “inboard” or “outboard” from another object relative to a defined axis.

Turning toFIGS. 1 through 5, an embodiment of the optical target assembly100of the present invention is shown in front left and right perspective views. The optical target assembly100consists of a generally cylindrical base assembly102, a pair of opposed wheel clamp arms104A and104B coupled to a tension and locking mechanism106mounted to the base assembly102, and a target support assembly108coupled to an outboard end of the base assembly102. The opposite (inboard) end of the base assembly102defines an annular contact surface110adapted for abutting contact with the generally vertical outer surfaces of a vehicle wheel rim10, in a non-determined placement between the outer circumferential lip of the wheel rim and the wheel assembly axis of rotation. The contact surface110is preferably in the form of a ring, and may optionally be covered with a removable or replaceable protective covering110A of a pliable or conforming material, such as a rubber or other soft compound, as seen inFIG. 4, which aids in preventing damage to the wheel rim surfaces during use, as well as to provide increased friction there between.

As best seen inFIG. 4, the base assembly102consists generally of a annular base112defining the contact surface110, and a target pivot mount114coupled to the annular base112opposite from the contact surface110by a connecting web of support struts116. The tension and locking mechanism106is pivotally mounted on a pair of double-pivoting supports118at pivot points119A, which in turn are secured to diametrically opposite pivot points119B on a mounting ring120fitted within the inner diameter of the annular base112. Preferably, each of the opposed wheel clamp arms104A and104B are detachable from the tension and locking mechanism106, such as by the removal of a quick-release pin122from pivot couplings117, allowing for replacement and/or exchange of the wheel clamp arms104A,104B as required. The wheel clamp arms104A and104B as shown inFIGS. 1 and 3have an adjustable configuration, and may be adjusted longitudinally by extension or retracting. In alternate configurations300, such as shown inFIG. 6, the wheel clamp arms are non-adjustable, and cannot be either extended or retracted.

Since the base assembly102of the present invention is intended for a non-determined placement against the wheel assembly surface, the base assembly102does not require or include any adjustment mechanisms for centering the contact surfaces110relative to either the wheel rim circumferential lip or axis of rotation, such as those commonly found in self-centering or adjustable wheel adaptors.

Those of ordinary skill in the art will recognize that the specific configuration of the tension and locking mechanism106, as well as the wheel clamp arms104A and104B may be varied from that which is shown in the accompanying figures. Any suitable mechanism capable of mechanical adjustment to engage the surfaces of a tire mounted to a vehicle wheel rim upon which the optical target assembly100is to be mounted, and which is further capable of providing a releasable clamping and/or tensioning force, such as by means of a combination of springs, levers, such as shown in the parent application U.S. Patent Application Publication No. 2008-0209744 A1 to Stieff et al, may be utilized without departing from the scope of the present disclosure.

The target pivot mount114at the axial end of the base assembly102provides a mounting surface for the target support assembly108, shown inFIG. 5, or for an optional conventional sensor assembly having a suite of conventional wheel alignment sensors capable of measuring spatial orientation and/or rotation. For embodiments utilizing optical targets, the target support assembly108is axially coupled to the target pivot mount114by a retainer124having a shaft126which passes through an axial bore128in the target support assembly108, through an aligned axial bore130in the target pivot mount114, and is engaged with a retention plate132secured axially to the rear of the target pivot mount114by a plurality of bolts132A. Various rotational positions of the target support assembly108relative to the target pivot mount114may be selected by loosening the retainer124, rotating the target support assembly108to a desired rotational position, and then re-tightening the retainer124to secured the target support assembly. Optionally, a plurality of predetermined rotational positions may be provided with positive stops or detents134on the upper surface of the target pivot mount114, as seen inFIG. 4, for engaging one or more suitable tabs (not shown) on the underside of the target support assembly108.

For some embodiments, it will be recognized by those of ordinary skill in the art that the target pivot mount114and the target support assembly108may be replaced by a target support assembly directly integrated into the axial end of the base assembly102in a rigid configuration, without the ability to rotate between various rotational positions.

As is best shown inFIG. 5, the target support assembly108consists generally of an outer annular member136coupled to an inner annular member138by a plurality of raised connecting webs or struts140and planar base surfaces142disposed in the recessed regions between the inner and outer annular members. At least one of the planar base surfaces142is provided with one or more windows or openings144, through which markings146on the upper surface of the target pivot mount114are visible when the target support assembly108is disposed in one or more selected rotational positions relative to the target pivot mount114(See:FIGS. 1,6, and9). Suitable label graphics148or other graphics may be provided on the planar base surfaces142adjacent the windows or openings144to provide a visual indication of the selected rotational position of the target support assembly108relative to the target pivot mount114.

The primary function of the target support assembly108is to provide two or more discrete surfaces200A,200B on the outer annular member136, having optical target elements202which can be observed by a machine vision measurement system. The optical target elements202may be printed elements on appliqué204of retro-reflective or high-contrast material, which is suitably affixed or bonded to the surfaces200A,200B, or may be applied directly to the discrete surfaces200.

Those of ordinary skill in the art will readily recognize that the optical target elements202may have any of a variety of shapes, configurations, and/or colors as may be suitable for use with the intended observing machine vision measurement system. The optical target elements202provide visible features which are identifiable in images acquired by the imaging system associated with a vehicle service device, and provide a sufficient number of data points to enable a determination as to the position and orientation of the optical target surfaces200in three-dimensional space from acquired images. For example, the optical target elements202may include a set of geometric figures arranged in a predetermined configuration as shown in U.S. Pat. No. 6,134,792 to January, herein incorporated by reference, or simply a set of identifiable fixed features, such as shown in U.S. Pat. No. 6,894,771 to Dorrance et al., herein incorporated by reference.

As is best seen inFIGS. 1 and 6, surfaces200A and200B are separate from each other, and aligned to present the associated optical target elements202in substantially the same field of view, generally orthogonal to the axis of rotation of the target support assembly. Preferably, one of the target surfaces200A,200B is offset from the other in an axial direction, such that one target surface is positioned further away from the contact surface110. While shown in a generally parallel planar configuration in the Figures, those of ordinary skill in the art will recognize that the surfaces200A and200B need not be planar, may be inclined relative to each other, may be curved, or may be defined as separate regions of a smoothly continuous surface.

In order to minimize the weight of the optical target assembly100, it is preferable that the target surfaces200and optical target elements202are positioned on the target support assembly108at positions which do not extend axially from the contact surface110substantially more than is necessary for the optical target elements202to remain visible when viewed from an imaging system having a line of sight parallel to the wheel rim surface (FIG. 7A), and when the wheel assembly is steered outward through an arc of at least 10 degrees, such as over a range from 0 to 20 degrees, as seen inFIGS. 7B and 7C. As the wheel assembly is steered, a line of sight from the imaging system to the target surfaces200and optical target elements202may become partially or fully blocked by the leading edges of the tire. (FIG. 7C), however, it has been found that at least 10 degrees of steering arc visibility is generally sufficient to enable the imaging system to acquire most necessary wheel alignment angle measurements. Those of ordinary skill in the art will recognize that the optical target assembly100may be modified or configured to position the target surfaces200and optical target elements202at locations which are visible to an imaging system disposed as indicated, through a steering arc which is smaller than, or greater than, the 10 degrees of steering described above without departing from the scope of the present disclosure.

Under some circumstances it may be necessary to enable viewing of optical target elements202at a steering angle which is greater than 20 degrees, or to displace the optical target elements202axially further outward from the contact surfaces110to enable viewing around obstructions in the imaging system line of sight. Accordingly, the target support assembly108is provided with an extended target mounting212, onto which a removable target structure400, shown inFIGS. 8 and 9, may be temporarily secured in a position which is axially outward from the target surfaces200incorporated into the target support assembly108. The extended target mounting212is preferably a magnetic plate, as seen inFIG. 5, configured to magnetically secure a corresponding magnetic base of the removable target structure400, but those of ordinary skill in the art will recognize that any of a variety of suitable mounting means408may be employed, including mechanical engagements, threaded connectors, clips, etc., provided that the removable target structure400is removably secured in a substantially stable relationship to the target support assembly108. Preferably, the removable target structure consists of a rigid body402, and includes two separate target surfaces404A and404B, on which are disposed associated target elements406A and406B. The target elements406A and406B on the removable target structure400function identically to the optical target elements202on the target support assembly108, but are axially displaced further outward from the vehicle wheel assembly, and therefore remain visible to an imaging system over a wider range of steering angles for the vehicle wheel assembly.

When employing non-planar optical targets having identifiable optical target elements202that are not precisely known or predetermined, methods such as described by U.S. Pat. No. 6,894,771 to Dorrance et al. may be utilized by an observing measurement system to compute the three-dimensional location of the optical target elements202in relation to each other, in order to use the target with a vehicle wheel alignment system. Using these methods, the locations of the optical target elements202can be determined each time the vehicle wheels are compensated. However, if the target support assembly108is dimensionally stable, and the optical target elements202or406are fixed to the target, it is not necessary and computationally expensive to repeatedly determine the locations of the optical target elements202relative to each other. It is much more efficient to compute, or characterize, the relationships of the optical target elements202,406once when the system is installed, and then use those computed relationships whenever the same optical target assembly100is used by the system.

A machine vision vehicle wheel alignment system employs a single optical target assembly100at each wheel assembly or rim10, and there can be a number of different alignment systems in use at one vehicle service location. Hence, there can be a large number of optical target assemblies100in use at a single vehicle service location. A target identification method for use by the vehicle wheel alignment measurement system is required in order to be able to identify each observed optical target assembly100to permit the correct stored target characterization data to be employed by a suitably configured processing system when evaluating acquired images of the optical targets. Preferably, the target support assembly108incorporates visible identifying markings or indicia, such as a row of retro-reflective squares210A in a known relationship to at least one of the optical target features202, which can be identified in images of the target support assembly acquired by an observing imaging system. A unique identification pattern for each target support assembly108can be provided by covering one or more of the reflective squares210A with something such as a black adhesive square2108or another suitable indicia210C.

Those of ordinary skill in the art will recognize that there are many possible schemes for providing for a target identification pattern. For example, one scheme would be to treat the identification pattern like binary digits, where a visible square210A would be a binary “1” and a covered square210B would be a binary “0”. In this scheme each target assembly108would have a unique binary coded number that would be used by the associated processing system to access target characterization data. Another scheme would be to assign four of the squares to represent a wheel position where target will be used. The square that's covered will indicate which wheel position (left front, right front, left rear or right rear) the target assembly108is assigned to, ensuring the same target assembly108is utilized at the same location for each vehicle wheel alignment measurement procedure. Other visible or occluded squares can similarly be used to indicate which service bay the target assembly108is being used. In this way the target assembly108would be identified to an observing processing system by both vehicle wheel position and vehicle service bay.

During use, an optical target assembly100of the present disclosure is placed with the contact surface110(110A) in a non-determined position against an outboard surface of a vehicle wheel assembly, generally between the center hub and wheel rim lip, such that the optical target elements202associated with the target assembly108are orientated generally for viewing by one or more imaging sensors. To hold the contact surface110in engagement with a generally vertical surface of a vehicle wheel rim10, as shown inFIG. 11A, the opposed wheel clamp arms104A and104B,300, coupled to the tension and locking mechanism106mounted to the base assembly102, are positioned to engage the treads of the associated tire. Each wheel clamp arm104includes a tire hook104TH configured to grip a tire tread surface of a vehicle wheel12, which may be pivotally coupled to the wheel clamp arms as seen inFIG. 1, or which may be fixed relative to the wheel clamp arms as seen inFIG. 6. Each opposed wheel clamp arm104is adjustable in multiple dimensions to accommodate wheel assemblies of different dimensions, while wheel clamp arms300are of a fixed configuration, and instead rely upon the adjustments to the locking and clamping mechanism to accommodate wheel assemblies of different dimensions.

For extremely deep wheel rims, a base extender ring216shown inFIG. 2, having an axial thickness may be fitted to the contact surface110prior to placement against the outboard surface of the vehicle wheel assembly, providing increased axial length to the optical target assembly sufficient to ensure the optical target elements202are visible to an associated imaging system. The base extender ring216essentially provides a second contact surface110A, which is identical to contact surface110, and may be secured to the base assembly102by any suitable means, such as rubber catches217configured to engage corresponding tabs217A on the base assembly102.

Those of ordinary skill in the art will recognize that any of a variety of mechanical components may be utilized to achieve the desired range of movement for the wheel clamp arms104, including, but not limited to, sliding assemblies, threaded assemblies, pivoting assemblies, and expanding assemblies. It is not required that the wheel clamp arms104be adjusted synchronously, or that they be disposed in mirror-image configurations, provided the wheel clamp arms104are sufficiently positioned to engage the tire tread surfaces of a vehicle wheel to secure the contact surface110of the base assembly102against the surfaces of the wheel rim10between the circumferential lip and the axial center point, in a stationary and stable manner during wheel alignment angle measurements and procedures.

The optical target assembly100is held against the vehicle wheel assembly by forces exerted between the wheel clamp arms104,300from the tension and locking mechanism106. These forces pull the optical target assembly100against the vehicle wheel assembly surface using the tire hooks104TH. The geometry of the entire assembly transfers the load from the tension and locking mechanism106to the tire hooks104TH and in turn creates a force pulling the optical target adapter100firmly against the surface of the wheel assembly.

Those of ordinary skill in the art will recognize that the tension and locking mechanism106may have a variety of different configurations suitable for exerting forces on the wheel clamp arms104,300and other components of the optical target assembly100to achieve the effect of providing a clamping force to hold the optical target assembly100to a vehicle wheel rim surface. For example, threaded screw components, or resilient elastic components may be utilized in place of spring-biased mechanisms, and/or the geometric configuration of the various components may be varied to produce different forces and moments which achieve the desired effect of clamping the optical target assembly100securely in place.

Once the optical target assembly100is secured, the target support assembly108is rotationally adjusted to align the target surfaces200for optimal viewing from the location of the imaging sensors associated with the machine vision measurement system when the vehicle is disposed at an alignment service position. During a vehicle wheel alignment service procedure, it is necessary to observe the relationship between the mounted targets and the wheel assemblies upon which they are secured. This is typically done by mounting the target assemblies to the vehicle wheels, and rolling the vehicle a short distance to acquire images of the mounted targets at different rotational positions of the wheel vehicle wheels. Some rolling procedures require that the vehicle be rolled forward only, while others require that the vehicle be rolled forward and returned to the initial position. Accordingly, to ensure optimal viewing, the target support assemblies are rotationally adjusted at the time of mounting for optimal viewing at either the subsequent roll-forward position of the vehicle wheels or at the initial position of the vehicle wheels, depending upon the particular procedure to be utilized.

The rotational adjustments may be accomplished by loosening the retainer124, rotating the target support assembly108to a desired rotational position, and then re-tightening the retainer124to secured the target support assembly. Predetermined rotational positions, such as may be associated with placement on a front vehicle wheel or a rear vehicle wheel, may be identified by aligning markings on the labels148with marking visible through the windows144in the target support assembly108. Generally, with an imaging system disposed at an elevated position adjacent the front of the vehicle, the target support assemblies108mounted to the front wheels of the vehicle will be required to have a greater degree of rotation relative to those mounted to the rear wheels of the vehicle.