The present invention is related generally to machine vision vehicle service systems, and in particular, to a multi-element optical target which may be temporarily positioned in a non-determined placement on a surface within a field of view of an imaging sensor associated with a machine vision vehicle service system during a vehicle service procedure, to facilitate the acquisition of measurements associated with the surface.
Machine vision vehicle service systems typically utilize one or more imaging sensors to acquire images of objects disposed within a field of view. The acquired images are processed by suitably configured processing systems to extract data associated with the observed objects. The extracted data may identify the position and orientation of the observed object within the field of view, or may provide measurements of movement of the object.
Some machine vision vehicle service systems are configured to process images of objects directly observed, i.e. the surfaces of wheel assemblies or wheel rims, vehicle body panels, or suspension components. These machine vision vehicle service systems require significant image processing capabilities, as the objects being observed are generally of an unknown configuration, which renders it difficult to obtain meaningful measurements without the use of complex imaging sensor configurations or advanced image processing techniques.
Traditionally, most machine vision vehicle service systems require the operator to dispose one or more optical target structures within the field of view of the imaging sensors prior to the acquisition of the images. The optical target structures have known or predetermined features which are highly visible to the imaging sensors, such as retro-reflective geometric patterns, and are disposed in the field of view in such a manner as to be associated with the objects being observed. For example, it is well known to secure rigid optical target structures, such as shown in U.S. Pat. No. 6,710,866 B1 to Adolph having a plurality of optical target elements onto a vehicle body panel or onto vehicle wheel assemblies using a mounting or other attachment structure which can be removably secured to the wheel assembly in a fixed relationship. The use of optical target structures provides the imaging sensors with highly visible elements in the acquired images, which have known features for subsequent image processing. Since the optical target structures are mounted in association with the observed objects, position and measurement data acquired from the observation of the optical targets may be related to the observed object.
While the use of optical target structures offers distinct advantages to a machine vision vehicle service system in terms of processing the images acquired by the imaging sensors, it introduces a new set of problems. In particular, the construction of the optical target structures is time consuming and expensive, as they are manufactured to precise specifications, and they require specialized mounting components for attachment to the object surfaces, such as wheel assemblies, which limit the possible placement locations within a field of view.
Accordingly, it would be advantageous to provide a low-cost optical target which may be temporarily placed in a non-determined position on a wide range of object surfaces within the field of view of a machine vision vehicle service system to provide a set of identifiable features or target elements within an acquired image for subsequent measurement processing. It would be further advantageous to provide such a low-cost optical target with a means for attachment to the object surfaces which does not require specialized mounting structures, and which is readily removable and is optionally reusable or consumable.