Patent ID: 7731201

Claim:
A workpiece fixing device for gripping a workpiece having a circular cross section, the workpiece fixing device comprising: a main body having a hole formed therein, the main body being configured such that the workpiece is insertable in the hole; a plurality of guide grooves formed in the main body and extending in a plurality of radial directions, respectively; a plurality of clamps disposed movably along the plurality of guide grooves, respectively, for exerting gripping force on the workpiece, said plurality of clamps including a first set of clamps and a second set of clamps, said first set of clamps being spaced from said second set of clamps in a direction perpendicular to the plurality of radial directions; and a clamp moving mechanism for moving the plurality of clamps in the plurality of radial directions, respectively, wherein said clamp moving mechanism includes a rotary drive mechanism and a plurality of scroll pieces, wherein the rotary drive mechanism includes (i) a first working disc and a second working disc, the hole of the main body extending through each of the first working disc and the second working disc, (ii) a first scroll guide rotatably supported on the main body, the first scroll guide having a spiral shape, (iii) a second scroll guide rotatably supported on the main body, the second scroll guide having a spiral shape, (iv) a first hydraulic cylinder rotatably driving the first working disc in a rotational direction to maintain the gripping force of the first set of clamps on the workpiece, and (v) a second hydraulic cylinder rotatably driving the second working disc in the rotational direction to maintain the gripping force of the second set of clamps on the workpiece, wherein the first hydraulic cylinder and the second hydraulic cylinder are configured to rotatably drive the first and second working discs independently of each other, wherein each scroll piece of the plurality of scroll pieces has a fitting portion engaging one of the first scroll guide and the second scroll guide, and wherein each scroll piece of the plurality of scroll pieces corresponds to a clamp of the plurality of clamps.