The present invention relates to a clamp apparatus that clamps a workpiece or the like that is to be supplied for machining processing, and in particular relates to such a clamp apparatus in which it is arranged to perform clamp driving while multiplying the clamping force that acts on a piston member by fluid pressure.
In a clamp apparatus that employs fluid pressure, it is possible to strengthen the clamping force by increasing the pressure reception area of the piston member. However, in this case, the clamp apparatus is increased in size, and this is disadvantageous because it reduces the freedom in designing the system. Thus, various types of clamp apparatus have been implemented in which the clamping force is strengthened by the provision of a force multiplication mechanism (servomechanism). In particular, there are a number of examples of provision of a force multiplication mechanism when pressurized air is used as the pressurized fluid.
In the clamp apparatus described in FIG. 4 of JP Patent 5,129,378: a cylinder bore is formed within the clamp main body; a first piston fitted in the cylinder bore, and an axial second piston fitted into the first piston, are installed so as to slide freely; an output rod is formed integrally with the second piston; a tubular portion that projects from above into the interior of the upper end portion of the first piston is formed integrally with the clamp main body; and there is provided a force multiplication mechanism which multiplies force generated by fluid pressure acting on the first piston and transfers the result to the second piston. There is also provided a compression spring for maintaining clamping force to bias the first piston in the direction for clamping operation.
The force multiplication mechanism includes: a plurality of support holes in the tubular portion; a plurality of spheres installed in these support holes so as to be movable in radial directions; a part conical surface that is formed on the inner surface of the upper end portion of the first piston; and a plurality of cam grooves that are formed on the second piston so as to be capable of contacting against the plurality of spheres. A first fluid pressure operation chamber is defined below the first and second pistons in the cylinder bore, and a second fluid pressure operation chamber is defined above the first and second pistons.