Patent ID: 9438147
Filing Date: 2016-09-06
CPC Classification: G01D,H02P

Claim Text:
1. A position detecting apparatus comprises: a sensor that outputs two position detection signals with different phases that vary with a same amplitude and a same period in response to a relative movement with respect to a scale; a first amplifier that outputs a first amplified signal obtained by amplifying an amplitude of a first position detection signal with a first phase of the position detection signals and a first inverted signal obtained by inverting the first amplified signal; a second amplifier that outputs a second amplified signal obtained by amplifying an amplitude of a second position detection signal with a second phase of the position detection signals and a second inverted signal obtained by inverting the second amplified signal; a first comparator that compares the first amplified signal and the second amplified signal and outputs a first comparison signal responsive to a result of the comparison; a second comparator that compares the first amplified signal and the second inverted signal and outputs a second comparison signal responsive to a result of the comparison; a phase angle measuring part that measures phase angles of the position detection signals with respect to a reference position, outputs a selection signal that prescribes which one of the first amplified signal, the second amplified signal, the first inverted signal and the second inverted signal should be selected, and outputs a timing signal that prescribes timings at which two of the first amplified signal, the second amplified signal, the first inverted signal and the second inverted signal intersect with each other; an AD converter that receives the first amplified signal, the second amplified signal, the first inverted signal and the second inverted signal, continuously reads a value of a signal selected according to the selection signal from among the first amplified signal, the second amplified signal, the first inverted signal and the second inverted signal, and outputs a digital signal responsive to the read value; a comparing part that compares the value of the digital signal output from the AD converter and a reference value that is based on a preset reference amplitude at the timings and outputs a control signal responsive to a result of the comparison; and an amplitude controlling part that controls amplification factors of the first amplifier and the second amplifier in such a manner that the value of the digital signal output from the AD converter comes closer to the reference value in response to the control signal output from the comparing part.