Patent ID: 7864075

Claim:
A rotary electrostatic encoder comprising: a disk-shaped fixed element having a first transmission electrode disposed in an external peripheral part; a second transmission electrode disposed in a center part; and four reception electrodes disposed at intervals at 90-degree angles in the circumferential direction between the first transmission electrode and the second transmission electrode; a disk-shaped rotating element provided parallel and rotatable with respect to the fixed element, the rotating element having a first induction electrode superposed on and facing the first transmission electrode, a portion of the first induction electrode being a protruding eccentric perforated external peripheral part; and a second induction electrode positioned on the inside of the first induction electrode and superposed on and facing the second transmission electrode, a portion of the second induction electrode being a protruding eccentric circular part; transmission means for applying a transmission signal to the first transmission electrode and the second transmission electrode of the fixed element; and signal processing means for generating an output signal relating to the absolute rotational displacement of the rotating element on the basis of two signal components outputted from the four reception electrodes of the fixed element.