Patent ID: 9103699
Filing Date: 2015-08-11
Classification: G01D

Abstract:
1. An encoder comprising: a scale provided with a first periodic pattern and a second periodic pattern whose period is different from that of the first periodic pattern; a sensor relatively movable with the scale and switchable to a first detection state to read the first periodic pattern and a second detection state to read the second periodic pattern, the sensor being configured to output in the first detection state a first periodic signal that changes with a change period corresponding to the first periodic pattern and to output in the second detection state a second periodic signal that changes with a longer change period corresponding to the second periodic pattern than that of the first periodic signal; and a processor configured to calculate a position in a relative movement direction of the scale and sensor by using both the first and second periodic signals taken in from the sensor, wherein the processor is configured (a) to take in the second periodic signal, the first periodic signal and the second periodic signal in this order at mutually different times, (b) to calculate phases of the second, first and second periodic signals and (c) to calculate the position at a specific time by using the calculated phases.