Positioning mechanism of turret index

A positioning mechanism for use in a turret index comprising:

• an output shaft which includes an output shaft pivot and performs precise positionings by use of a three-piece toothed coupler and first and second oil passages;
• said three-pieced toothed coupler comprises a first piece, a second piece, and a third piece, all of which are annular in shape, wherein said first piece, which is called a moving block, is slidably mounted to an outside surface of said output shaft, said second piece, which is called a datum block, is fixed to a housing for said three-pieced toothed coupler, and said third piece, which is called a rotation block, is fixed to said output shaft;
• further wherein said third piece is exactly located in an inner circle of said second piece of the said three-piece toothed coupler, and said moving block has an inner end surface;
• said output shaft pivot comprises a piston ring which establishes an annularly-shaped concave plane at an outside end plane, said annularly-shaped concave plane has an area is greater than the area of said inner end surface of said moving block of the said toothed coupler;
• wherein said moving block is configured to be driven by a hydraulic device, via said first and second oil passages such that said first oil passage, which is controlled by a first electromagnetic valve, enters at an outer end plane of said moving block of the toothed coupler, and said second oil passage, which is controlled by a second electromagnetic valve, simultaneously enters said inner end surface of said moving block and said annularly-shaped concave plane of said outside end plane of said piston ring.