Patent ID: 8993955
Filing Date: 2015-03-31
Classification: G01D

Abstract:
1. An encoder comprising: a scale provided with a first periodic pattern and a second periodic pattern having a period larger than that of the first periodic pattern; a detector relatively movable with respect to the scale and whose detection state is switchable between (a) a first detection state to read the first periodic pattern and output a first signal having a changing period corresponding to the first periodic pattern and (b) a second detection state to read the second periodic pattern and output a second signal having a changing period corresponding to the second periodic pattern; and a processor configured (a) to perform a first process to detect a first absolute position by using both the first and second signals respectively obtained from the detector set in the first and second detection states and (b) to perform, after performing the first process, a second process to calculate a relative movement amount by using a specific signal that is one of the first and second signals obtained from the detector set in one of the first and second detection states and detect a second absolute position by using the relative movement amount and the first absolute position, wherein the processor is configured to obtain in the second process the specific signal from the detector set in a same detection state of the first and second detection states as that set last in the first process.