Optics: measuring and testing – Angle measuring or angular axial alignment – Wheel alignment with photodetection
Reexamination Certificate
2001-06-28
2003-03-11
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Angle measuring or angular axial alignment
Wheel alignment with photodetection
C033S286000, C033S203180
Reexamination Certificate
active
06532062
ABSTRACT:
FIELD OF THE DISCLOSURE
The present disclosure generally relates to motor vehicle maintenance equipment and methods and, more specifically, to apparatus and methods for measuring a scrub radius of a motor vehicle.
BACKGROUND OF THE DISCLOSURE
Motor vehicle alignment systems are important for ensuring that the alignments of wheels on a vehicle are within the specifications provided by motor vehicle manufacturers. If the wheels are out of alignment, there may be excessive or uneven wear. In addition, the performance of the vehicle, particularly handling and stability, may be adversely affected if the wheels are not properly aligned. As used herein, the term “wheel” or “vehicle wheel” refers to the tire and wheel assembly found on a motor vehicle. Such an assembly generally includes a conventional tire that is mounted on a metal wheel or “rim”.
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 alignment system having optical sensing devices, such as cameras, to determine the positions of various objects. Although such machine vision 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 alignment systems using at least one camera to image targets attached to the wheels of a vehicle are shown in U.S. Pat. Nos. 5,724,743 and 5,535,522.
Another type of alignment system uses head units which are attached to various wheels and interconnected by cables or cords. The angles of the head units, and thus the wheels, with respect to the cords are measured by an electromechanical transducer. Examples of this type of measurement device are shown in U.S. Pat. Nos. 4,016,208 and 4,034,479.
An additional type of alignment system uses head units which attach to various wheels and communicate with optical sensing. Examples of optical head unit systems are shown in U.S. Pat. Nos. 3,782,831, 3,892,042, 4,095,902, 4,126,943, 4,138,825, 4,143,970, 4,302,104 and 4,319,838.
The above-described position determination systems provide information, such as the centers of rotation of the vehicle's wheels, which aids in the wheel alignment of a vehicle. However, other information such as wheel scrub radius, can also aid a technician in diagnosing problems with the vehicle's suspension. A scrub radius is the distance between where the wheel's steering axis meets the ground and where the wheel's centerline meets the ground, as viewed from the front of the vehicle.
Being able to measure and confirm the scrub radius of a wheel is important since the scrub radius in combination with rolling friction, such as brake drag, bearing friction and tire rolling friction, can create a moment about the wheel's steering axis during straight ahead driving, causing the wheel to toe-out or toe-in (pivot on the steering axis). Vehicle manufacturers often specify an opposite toe-out or toe-in to compensate for the known vehicle parameters, including scrub radius. Since the scrub radius should remain fixed if the rims and tire of a vehicle are stock, a measured scrub radius that does not match up with a manufacturer's specified scrub radius can be an indication of damage to the vehicle suspension and steering system. In addition, if aftermarket tires of a different diameter, or rims of a different offset are added to the vehicle, the scrub radius will be altered. The toe of the wheels may be compensated for the different scrub radius to minimize tire wear.
Based on the foregoing, there is a clear need in this field for an apparatus and method for measuring the scrub radius of the wheels of a motor vehicle.
There is also a need for an apparatus and method that compares the measured scrub radius of the wheels of a vehicle and the specified scrub radius of the wheels.
There is an additional need for an apparatus and method that displays the results of wheel scrub radius measurements to aid an alignment technician with detecting damaged vehicle suspension or steering parts, and with detecting whether the wheels are of the correct specifications.
There is a further need for an apparatus and method that displays the results of wheel scrub radius measurements to aid an alignment technician with adjusting the toe of the wheel.
SUMMARY OF THE DISCLOSURE
The present disclosure accordingly provides a method of measuring a scrub radius of a wheel that includes using a computer-aided alignment apparatus to determine at least one of a steering axis, a centerline and a ground plane of the wheel. The other of the steering axis, the centerline and the ground plane of the wheel, if not determined using a computer-aided alignment apparatus, are then determined in other conventional manners. The method also includes determining an intersection between the steering axis and the ground plane of the wheel, determining an intersection between the centerline and the ground plane of the wheel, and determining a distance between the intersections, the distance being equal to the scrub radius of the wheel.
According to one aspect, each of the steering axis, the centerline, and the ground plane of the wheel are determined using a computer-aided alignment apparatus.
According to another aspect, the intersection between the steering axis and the ground plane, the intersection between the centerline and the ground plane, and the distance between the intersections are determined using a computer-aided alignment apparatus.
According to an additional aspect, the method includes determining a roll axis and a roll radius of the wheel, and determining the ground plane based on the roll axis and the roll radius.
According to a further aspect, the computer aided alignment apparatus comprises a computer-aided, three-dimensional machine vision apparatus including optical scanning devices and optically scannable targets. The method also includes attaching an optically scannable target to the wheel; optically scanning the target when the wheel is in a first position, and creating and storing values representing the first position; and optically scanning the target when the wheel is in a second position, and creating and storing values representing the second position.
According to an additional aspect, the method includes comparing the determined scrub radius to a specified scrub radius, and generating a warning if the determined scrub radius is not about equal to the specified scrub radius. According to a further aspect, the method includes calculating a new toe for the wheel if the determined scrub radius is not about equal to the specified scrub radius.
The present disclosure also provides an apparatus for measuring a scrub radius of a wheel. The apparatus includes a target fixedly attachable to the wheel, and a vision imager for detecting a first image of the target when the wheel is in a first position and for detecting a second image of the target when the wheel is in a second position. The apparatus also includes a data processor programmed to determine a scrub radius of the wheel based at least in part upon a comparison of the first image and the second image of the target.
The present disclosure further provides a computer-readable medium carrying one or more sequences of instructions which, when executed by at least one processor, cause the processor to detect a first image of a target fixed to a wheel in a first position, detect a second image of the target when the wheel is in a second position, and determine a scrub radius of the wheel based at least in part upon a comparison of the first image and the second image of the target.
Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only an exemplary embodiment of the present disclosure is shown and described, simply by way of illustration of the best mode contemplated for carrying out
Dale, Jr. James L.
Glickman Stephen L.
Healy Donald A.
Jackson David A.
Buczinski Stephen C.
Snap-On Technologies Inc.
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