Patent ID: 7045803

Claim:
A method for determining the presence or absence of a target object at a holding site on a collet assembly, the collet assembly including collet which is operable to pickup the target object at a first location and to hold the target object at the holding site, and which is adapted to be moved from the first location to a second location to which the target object is to be transported, and to deposit the target object at the second location, the method comprising the steps of: illuminating at least a portion of the holding site; arranging a light detector to receive illuminating light reflected from the target object if it is present at the holding site and to provide an output representative of the reflected light; and determining the presence or absence of the target object at the holding site on the basis of the detector output, wherein at least one of the illuminating light and the light received by the detector moves with the collet when the collet is moved from the first to the second location.