Patent ID: 7449678
Filing Date: 2008-11-11
Classification: G01D,H03M

Abstract:
1. An optical encoder having a reference position detecting function, comprising: a light source which irradiates light; a scale on which a periodic optical pattern, and at least one reference position pattern are formed, and which moves relatively with the light source; a photodetector for detecting the periodic pattern, which detects light which is irradiated from the light source via the periodic optical pattern; a photodetector for detecting the reference position, which includes a plurality of photodetector elements arranged one-dimensionally in a direction of movement of the scale, and which detects light irradiated from the light source via the reference position pattern; a differential signal calculating member which calculates a first differential signal of an output signal from at least one photodetector element from among the plurality of photodetector elements, and an output signal from at least one other photodetector element different from the one photodetector element; and a gate signal forming member which generates a gate signal indicating a reference position neighborhood during a period in which the light emitted from the light source is incident on the photodetector via the reference position pattern formed on the scale for detecting the reference position with a movement of the scale, the gate signal forming member calculating a first sum signal which is a sum of output signals from at least two photodetector elements taken from a non-end position among the plurality of photodetector elements arranged one-dimensionally, and a second sum signal which is a sum of output signals from at least two other photodetector elements arranged to sandwich at least the two photodetector elements, the gate signal being output based on the first sum signal and the second sum signal, the optical encoder outputting a reference position signal based on a point of zero crossing of the first differential signal and the gate signal during a period in which the gate signal is generated.