Method and apparatus for inspecting engine head valve retainer assemblies for missing keys

DETAILED DESCRIPTION With the foregoing in mind, it is an object of the present invention to provide a computer vision method and apparatus for automatically inspecting engine heads for missing valve retainer keys.
A number of problems arise in attempting to automatically inspect valve spring assemblies utilizing computer vision techniques.
During assembly of an engine head, a shuttle conveyor transfers the head between stations along the assembly line in approximately one second.
The engine remains at each station for an eight second dwell time while assembly operations are performed.
Some variations exist in the locations of the valve spring assemblies of different engine heads and in the absolute location of the engine head along the assembly line.
Accordingly, a determination of the location of the center of the assembly is necessary before an inspection for missing keys can be made.
Furthermore, there are significant variations in the reflectances of different valve assemblies and the intensity distribution of typical assemblies is not bi-modal.
For these reasons, thresholding techniques are not very useful in separating regions of the image or in locating the center of the assembly in the image.
In accordance with the present invention, a computer vision system for inspecting valve spring assemblies is provided which is capable of inspecting for missing keys within the nine second cycle time of the existing engine head conveyor.
The inspection for missing keys is based on the observation that the keys are always brighter than the hole which results when a key is missing and from the further observation that typical valve spring assembly images subjected to an edge operation show strong circular patterns which permit a determination of the center of the assembly by a convolution technique.
Thus, by examining the intensity profile of the digitized image along the circumference of a circle of predetermined radius originating at the center of the assembly, a missing key may be detected