Positioning apparatus used for machine tools etc.

A positioning apparatus comprising:

• a hydraulic motor for driving a rotary shaft of a positioned object, the hydraulic motor has an output shaft, the output shaft being disposed in alignment with the rotary shaft of the positioned object,
• a flow control valve connected to the hydraulic motor,
• rotation angle detection means for detecting an angle of rotation of the rotary shaft, the rotation angle detection means being a hollow type rotary encoder disposed around the rotary shaft,
• rotation angle control means for controlling the flow control valve to rotate the hydraulic motor by an angle determined based on a detected result of the rotation angle detection means and a rotation angle instruction, and
• hydraulic locking means for directly or indirectly holding the rotary shaft at a periphery thereof to lock the rotary shaft, the hydraulic locking means being a sleeve disposed between the rotary shaft and an internal surface of a housing, the sleeve having outer circumferential surfaces at both end portions with the outer circumferential surfaces being in a hydraulically tight relation with the internal surface of the housing, and the sleeve expands radially inward by hydraulic fluid supplied from an oil passage formed in the housing for locking of the rotary shaft.