Workpiece identification apparatus

Apparatus for use in identifying to which of a number of predetermined types a workpiece belongs, the apparatus being operable in a learning mode in which it is presented with a workpiece of each of the predetermined types in order to learn those workpieces or in an identifying mode in which it identifies workpieces presented thereto by comparison with the learnt workpiece, the apparatus comprising a light source, an array of light detectors each operable to detect whether a workpiece is present on the optical path between the light source and the detector, moving means operable to cause relative movement such that a workpiece moves across the optical paths between the light source and the detectors, recording means operable to record after each unit distance of movement caused by the moving means which of the detectors detects a workpiece, calculating means operable, when the apparatus is in the learning mode, to calculate, from the data recorded by the recording means, a predetermined set of parameters of the workpiece, selecting means operable, when the apparatus is in the learning mode and after the calculating means has calculated a set of parameters for all the workpieces to be learnt, to select a sub-set of the parameters such that the sub-set formed by those parameters for each learnt workpiece differs from every other such learned sub-set in at least a number of respects equal to twice a preselected acceptable error plus one, where the preselected acceptable error is a number selected as the number of the parameters which it is acceptable to erroneously determine, the calculating means being operable in the identifying mode to calculate the parameters of the workpiece which form an equivalent sub-set to the learnt sub-sets, and comparing means operable in the identifying mode to compare the equivalent sub-set with the learnt sub-sets and in the event of finding identity with the sub-set of a workpiece of a particular type except for a number of differences not greater than the acceptable error to identify the workpiece as being of that particular type.