Patent ID: 7584551

Claim:
An absolute position measuring apparatus comprising: a main body; a spindle that is screwed with the main body to be advanceable and retractable while rotating about an axis thereof; a first rotary encoder that detects the rotation of the spindle as a phase signal that varies in a first cycle; a second rotary encoder that detects the rotation of the spindle as another phase signal that varies in a second cycle; and an arithmetic processor that calculates an absolute position of the spindle based on the phase signals output from the first and second rotary encoders; wherein the first rotary encoder includes: a first rotor; a first holder that rotatably holds the first rotor about the axis of the spindle and is rotated by the rotation of the spindle, the first holder being provided with a first gear on an outer circumference thereof; a first stator that is supported by the main body and provided facing the first rotor by a predetermined gap; the second rotary encoder includes: a second rotor; a second holder that rotatably holds the second rotor about the axis of the spindle and is provided with a second gear on an outer circumference thereof; a second stator that is supported by the main body and provided facing the second rotor by a predetermined gap; a relay gear that transmits a rotation of the first gear to the second gear; and the number of cogs for the first gear, the relay gear and the second gear is set to differentiate rotation speeds of the first gear and the second gear.