Abstract:
An improved position determination system that is resistant to interference caused by glint, such as from the Sun. The position determination system for determining positional parameters of an object has a target device comprising a base configured for attaching to the object, first and second target surfaces connected to the base; wherein the planes on which the first target surface and the second target surface are located are non-parallel to each other. The position determination system further comprises an image sensing device configured for forming a viewing path intersecting the target device and generating image information indicative of the geometric characteristics of the target device, and a data processing device configured to couple to the image sensing device for determining the orientation of the object based on the image information. If one of the target surfaces becomes obscured as a result of glint, the image of the other target surface alone is sufficient to determine object orientation.

Description:
RELATED APPLICATION 
     The present application claims the benefit of priority from U.S. Provisional Patent Application Serial No. 60/214,390 filed Jun. 28, 2000, entitled “METHOD AND APPARATUS FOR PERFORMING UNDERCAR DIAGNOSTICS.” 
    
    
     FIELD OF INVENTION 
     The present invention relates to an improved position determination system, and more particularly, to a position determination system that is resistant to interference caused by glint. 
     BACKGROUND OF THE INVENTION 
     Certain types of position determination system, such as wheel alignment systems, use a vision imaging system that employs optical sensing devices to determine the positions of various target devices. A wheel alignment system of this type is capable of obtaining positional information about a vehicle, such as ride height, toe curve, tilt angle, and the angular relationship of the vehicle&#39;s body relative to the vehicle&#39;s wheels. 
     The wheels of a motor vehicle may be aligned in a number of ways. For example, an operator or an alignment technician can use a vision imaging system, such as a computer-aided, three-dimensional (3D) machine vision that employs image sensing devices, such as cameras, to determine the positions of various target devices. Although such vision imaging systems are typically used for alignment purposes, these systems can also be used to obtain other positional and angular orientation information about a motor vehicle. Examples of such apparatus and methods are disclosed in U.S. Pat. No. 5,724,743, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Mar. 10, 1998 and in U.S. Pat. No. 5,535,522, entitled “Method and Apparatus for Determining the Alignment of Motor Vehicle Wheels,” issued to Jackson, et al. on Jul. 16, 1996, each incorporated herein by reference. 
     A computer is often used in conjunction with such vision imaging systems to calculate the orientation of the target device by identifying certain geometric characteristics on the target device. The computer takes perspective measurements and compares these measurements with the true image previously pre-programmed into the memory of the computer. 
     An example of a typical target device that can be used in a wheel alignment system is illustrated in FIG.  1 . Target device  54  consists of a flat plate with a pattern of two or more differently sized circles  62 ,  63  marked in a pre-determined format thereon. Although a specific pattern is shown, a large number of different patterns can be used on the target device  54 . In practice, a mathematical representation, or data corresponding to a true image (i.e. an image taken by viewing the target device perpendicularly to its primary plane) and the dimensions of the target device are preprogrammed into the memory of a computer so that, during the alignment process, the computer has a reference image to which the viewed perspective images of the target devices can be compared. 
     The computer calculates the orientation of the target device  54  by identifying certain geometric characteristics on the target device. The computer takes perspective measurements and compares these measurements with the true image previously pre-programmed into the memory of the computer. 
     The computer could, for example, calculate the center of each of the circles  62   a,    62   b  by means of centroiding. This is a method commonly used by image analysis computers to determine the positioning of the center point or centerline of an object. Once the center points of the two circles  62   a,    62   b  have been determined, the distance between the two can be measured. This process is then repeated for other circles in the pattern on the target device  54 . These distances can then be compared to the true distances (i.e. non-perspective distances) between the respective centers. Similarly, the angle to the horizontal (or vertical) of the line joining the two centers can be determined. A calculation can then be made as to what the orientation of the target device  54  is. 
     Other methods of calculation can be used to determine the orientation of the target device  54 . For example, the camera could sight onto only one of the circles, for example the circle  63 , and by using the perspective image thereof (the distorted ellipse), calculate the orientation of that circle and, therefore, the orientation of the target device  54  as more fully described in U.S. Pat. Nos. 5,535,522 and 5,724,743. 
     Position determination systems using target devices and image sensing devices sometimes encounter problems when operated under strong light sources, such as the Sun. With the existence of strong light, the surface of the target devices may reflect the light in a direction entering the lens of the camera. The reflection of strong light into the camera produces a large white spot, called blooming. Blooming will interfere the receipt of images from the target devices. Although some of the target devices are made from materials that are 99% nonreflective of light, the 1% reflection of light from a strong light source, such as the sun, can still cause problem to the measurements until the sun moves off-target. Moving the target or optics as the Sun moves across the sky is impractical. 
     SUMMARY OF THE INVENTION 
     Accordingly, there exists a need for reducing the effects caused by glint to a position determination system. There is also a need to allow position determination in the presence of strong light sources. There is another need to provide a position determination system that is resistant to interference caused by glint and does not require movement or adjustment of equipment. 
     These and other needs are addressed by the present invention. The present invention provides an improved position determination system using target devices that prevent interference from strong light sources. This invention increases accuracy of measurements by eliminating interference from glint. 
     One aspect of the present invention relates to a target device for attaching to an object. The target device comprises a base configured for attaching on the object, a first target surface connected to the base, and a second target surface connected to the base, wherein the first target surface and the second target surface are on different planes. The planes on which the target surfaces locate are not parallel to each other. Since the target surfaces are on non-parallel planes, any light source producing glint on the first target surface will not cause glint on the second target surface. If light reflected by the first target surface causes interference, the image of the second target surface is still available for processing. Therefore, the interference caused by glint is eliminated. 
     According to one embodiment, a position determination system for measuring positional parameters of an object comprises: a target device which includes a base configured for attaching to the object, a first target surface connected to the base; and a second target surface connected to the base; wherein the planes on which the first target surface and the second target surface locate are not parallel. The position determination system has an image sensing device configured for forming a viewing path intersecting the target device and generating image information indicative of the geometric characteristics of the target device, and a data processing device configured to couple to the image sensing device for determining the orientation of the target device or the object on which the target device is attached based on the image information. 
     During measurement, the target device is attached to the object, such as a wheel of a vehicle, for marking each measurement. The images of the target surfaces are captured by the image sensing device, such as a camera, and analyzed by a data processing device, such as a controller or a computer coupled to the image sensing device. 
     According to one aspect of the present invention, the data processing device is configured for executing position determination software, such as alignment, and receiving image information representative of images captured by the image sensing device. The orientation of the target device used during the position determination process is determined based on the image information. The image information may be compared with reference information representative of images of the target device captured at a reference position. Alternatively, the reference position may be viewed from an angle perpendicular to the surface of the base. The reference information may be obtained from a hard drive memory. 
     As an example, the images of both target surfaces are captured by the image sensing device and transformed into image information to be processed by the data processing device. Whenever one of the target surfaces produces glint that interferes with the images received by the image sensing device, the other target surface, as discussed above, still provides reliable image information indicative of the geometric characteristics of that target surface. Therefore, interference from glint is eliminated. 
     Still other advantages of the present invention will become readily apparent from the following detailed description, simply by way of illustration of the invention and not limitation. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which: 
     FIG. 1 illustrates an example of a typical target device that can be used on the wheels of a vehicle for position determination. 
     FIG. 2 shows an example of a position determination system on which the present invention may be implemented. 
     FIGS. 3 a  and  3   b  is an perspective view of examples of target device implemented according to the present invention. 
     FIGS. 4 a  and  4   b  illustrate of an example of a target device implemented according to the present invention operated under a strong light source. 
     FIG. 5 shows an example of a wheel alignment system implemented according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Techniques for providing a position determination system that is resistant to glint interference are presented for better explanation of the present invention. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
     A position determination system implemented according to the present invention is capable of obtaining positional information about an object. For example, the position determination system can be used to measure ride height, toe curve, tilt angle, and the angular relationship of a vehicle&#39;s body relative to the vehicle&#39;s wheels. 
     An example of a position determination system on which the present invention may be implemented is illustrated in FIG.  2 . The position determination system  100  includes a vision imaging system  102  having a pair of fixed, spacedapart cameras  110 ,  112  mounted on a beam  114 . The beam  114  has a length sufficient to position the cameras  110 ,  112  respectively outboard of the sides of the vehicle to be imaged by the position determination system  100 . Also, the beam  114  positions the cameras  110 ,  112  high enough above the shop floor  116  to ensure that the two target devices  118 ,  120  on the left side of the vehicle are both within the field of view of the left side camera  110 , and two target devices  122 ,  124  on the right side of the vehicle are both within the field of view of the right side camera  112 . 
     Target devices  118 ,  120 ,  122 ,  124  are mounted on each of the wheels  126 ,  128 ,  130 ,  132  of the motor vehicle, with each target device  118 ,  120 ,  120 ,  124  including a target body  134 , and an attachment apparatus  138 . The attachment apparatus  138  attaches the target device  118 ,  120 ,  120 ,  124  to wheel  126 ,  128 ,  130 ,  132 . An example of an attachment apparatus is described in U.S. Pat. No. 5,024,001, entitled “Wheel Alignment Rim Clamp Claw” issued to Borner et al. on Jun. 18, 1991, incorporated herein by reference. 
     In operation, once the position determination system  100  has been calibrated using a calibration target (not shown), as described in U.S. Pat. No. 5,535,522 and 5,724,743, a vehicle can be driven onto the rack  133 , and, if desired, the vehicle lifted to an appropriate repair elevation. The target devices  118 ,  120 ,  122 ,  124 , once attached to the wheel rims, are then oriented so that the target devices face the respective camera  110 ,  112 . 
     A computer-implemented database may be used to assist determination of the target position. As an example, the vehicle model and year can be entered into the vision imaging system  102  along with other identifying parameters, such as vehicle VIN number, license number, owner name, etc. A database associated with the vision imaging system  102  preferably includes specifications for each model of vehicle that might be inspected. Upon identification of the vehicle being inspected, the information associated with the specific vehicle model is extracted from the database to assist determination of the position of the target devices  118 ,  120 ,  122 ,  124 . Alternatively, a previous inspection history of the particular vehicle can be used to indicate the likely position of the target devices  118 ,  120 ,  122 ,  124 . 
     The location of the target devices  118 ,  120 ,  122 ,  124  relative to the rim of the wheels  126 ,  128 ,  130 ,  132  to which the target devices are attached are typically known to an accuracy of about 0.01′ and about 0.010. Once the target devices  118 ,  120 ,  122 ,  124  have been imaged in one position, the wheels  126 ,  128 ,  130 ,  132  are rolled to another position and a new image can be taken. Using the imaged location of the target devices  118 ,  120 ,  122 ,  124  in the two positions, the actual position and orientation of the wheels  126 ,  128 ,  130 ,  132  and wheel axis can be calculated by the vision imaging system  102 . Although the distance between the two positions varies, the distance is often approximately 8 inches both forward and back. 
     FIGS. 3 a  and  3   b  illustrate examples of target devices implemented according to the present invention. Target device  20  in FIG. 3 a  has a base  21 , a first target surface  22  and a second target surface  23  extending from the base. Patterns, such as the circles described in FIG. 1, are provided on the target surfaces. Base  21  is configured to attach to an object where measurement will be conducted, such as the target body  134  or the attachment apparatus  138  as illustrated in FIG.  2 . In one example, the target body  134  works as the base  21 , and the target surfaces are attached to the target body  134 . As another example, the attachment apparatus  138  works as the base of the target device and the target surfaces are connected to the attachment apparatus. The angle between target surface  22  and target surface  23  is Θ. The proper angle θ between the target surfaces may be measured empirically in the environment in which the system will be used. The angle θ is typically 170° or less, depending on the environment and optics employed. 
     Another embodiment of target devices, illustrated in FIG. 3 b,  is designated as  26  and has a first target surface  27  connected to a second target surface  28 . Unlike the target device illustrated in FIG. 3 a,  the plane on which target surface  27  is located is not parallel to the base  21 . The angle between target surfaces  27  and  28  is θ, and, like θ in FIG. 3 a,  is easily determined empirically. 
     FIGS. 4 a  and  4   b  illustrate an example of a target device implemented according to the present invention operated under a strong light source. In FIG. 4 a,  a target device  20  similar to that illustrated in FIG. 3 a  is attached to the surface of an object  31 . Target surfaces  22  and  23  have patterns similar to those illustrated in FIG. 1. A camera  33  is used to capture images from the target device  20 . Images of patterns on target surfaces  22  and  23  are captured by the camera  33  via paths  32  and  34  respectively. 
     FIG. 4 b  shows the effects of a strong light source to the target device implemented according to the present invention. When the sun  30  moves to a specific position where the angle a between the sunlight  35  and a line  39  normal to target surface  22  equals the angle between path  32  and the line  39 , sunlight  35  will be reflected by the target surface  22  and enters the camera  33  along the path  32  by which the camera  33  used to capture images from patterns on target surface  22 . In this case, the reflection of the sunlight  35  will interfere with the pattern images captured from target surface  22 . 
     However, since target surfaces  22  and  23  locate on non-parallel planes, sunlight  35  will not be reflected by the target surface  23  and thus will not interfere with the pattern images captured from target surface  23  along path  34 . Accordingly, calculation of positional parameters can be made based on the unaffected images. Therefore, interference from glint is eliminated. 
     As another example, FIG. 5 shows a wheel alignment system implemented according to the present invention. A motor vehicle  200 , on which wheel alignment is to be performed, is represented by a schematic illustration of its chassis and is shown to include two front wheels  22 L and  22 R and two rear wheels  24 L and  24 R. The vehicle  200  is shown positioned on a conventional wheel alignment test bed  260 , indicated in dotted lines. The system uses target devices  54  similar to those shown in FIGS. 3 a  or  3   b  having target surfaces  22  and  23  attached thereto. 
     Camera  30  forms viewing paths intersecting the target devices  54  by using combinations of lens and mirrors. Camera  30  sights simultaneously both onto one of the target surfaces of each target device  54  attached on wheels  22 L,  22 R,  24 L and  24 R along a view path  38  which passes through lens  40  and onto a beam splitter  42  and mirrors  46 L and  46 R. Mirrors  46 L and  46 R may comprise a plurality of mirrors aiming at different wheels, respectively, so that the image of each wheel is captured by a separate mirror. 
     A computer  32  is coupled to the camera  30 . Images captured by camera  30  are transformed into image information accessible by the computer  32 . The calculation of positional parameters will be made based on image information that is not affected by the glint. According to one embodiment, image information produced by glint can be removed by a low-pass filter circuit. 
     The computer  32  stores information about the patterns on the target surfaces viewed from a certain angle. The information can be used to calculate the orientations of the target surfaces and the surfaces of the wheels. In one embodiment, patterns viewed from an angle perpendicular to the base of the target device are stored in the computer  32 . Information with regard to configurations of the target device, such as the angle between the two target surfaces, the dimensions of the target devices, and the angles between the target surfaces and the base, may be pre-stored in the computer  32  as in the previously described embodiment, details on the calculations made to determine object orientation based on target images are given in the patents cited. 
     While this invention has been described in connection with an exemplary embodiment, it is to be understood that the invention is not limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.