1. Field of the Invention
The invention relates to a method and apparatus for non-contact determination of run-out of a rotating body, and more particularly to an optical method and apparatus for determining the run-out of a rotating body, especially an automobile tire.
2. Description of Related Art
Heretofore known methods and apparatus to determine run-out, in particular radial run-out, of rotating bodies, e.g., automobile tires, has been accomplished by means of rollers applied against the tire and displacement transducers connected to the rollers. The mechanical radial run-out detected is transformed, e.g., by means of inductive displacement transducers, into a proportional electrical signal. That approach to run-out determination and measurement requires mechanical contact of the roller with the tire.
On the other hand, it is known to determine run-out of rubber-coated paper rolls via a reflection measuring technique. For that purpose the rubber-coated surface of the paper roll is exposed to radiation that emanates from a suitable radiation source and the radiation that is reflected by the rubber-coated surface is received and measured in a receiver. With rotating bodies that have circumferential surfaces that are grooved, or otherwise have an intentional surface roughness, such as, for example, automobile tires, it is possible to ascertain the quality of the sidewalls by using the reflection technique, but similar determination of radial run-out of such rotating bodies is difficult, particularly if the groove depth is larger than the radial run-out. With automobile tires the tread groove depth is about 8 mm and radial run-out is generally about 0.2 mm. Consequently the interfering signal obtained as a result of the grooves, or the surface roughness, would mask the run-out signal.