Gripping device

Claim 2

In a workpiece gripping device including a pair of clamp arms pivotally mounted on a base plate, said clamp arms being connected to a clamp arm opening and closing rod through a pair of links, the improvement wherein one of said pair of clamp arms is shorter than the other clamp arm and an additional clamp arm is pivotally connected to said shorter clamp arm, said additional clamp arm including a pin projecting from the surface thereof, said short clamp arm including a long, narrow hole extending in the swinging direction of said additional clamp arm and formed on the surface thereof facing said additional clamp arm in a position opposite to said pin projecting from said additional clamp arm, whereby the pivotal movement of said additional clamp arm is limited by said pin in said slot.

Claim 3

The workpiece gripping device of claim 1, further including chip means fixed to the end portions of said additional clamp arm and said longer clamp arm for facilitating the gripping efficiency of said device.

Claim 4

The workpiece gripping device of claim 2, further including misgrip detecting means for detecting the misgripping of said workpiece.

Claim 5

The workpiece gripping device as claimed in claim 3, wherein said misgrip detecting means comprises a cylinder tube, a cylindrical free piston having communicating holes at each side face thereof slidably inserted within said cylinder tube, thereby forming first and second pressure chambers at each side of said free piston within said cylinder tube, an inner piston fixedly secured to said clamp arm opening and closing rod and reciprocatingly inserted within said free piston, the diameter of said inner piston being less than the inner diameter of said free piston thereby leaving a circumferential space between the inner periphery of said free piston and the outer periphery of said inner piston said inner piston sealing closing either of said communicating holes to seal said first or second pressure chamber when said inner piston abutts either side end face of said free piston, a first hydraulic fluid conduit connected with said first pressure chamber within said cylinder tube through a first hydraulic fluid port formed in said cylinder tube, a second hydarulic fluid conduit connected with said second pressure chamber within said cylinder tube through a second hydraulic fluid port formed in said cylinder tube, and pressure switches provided in said first and second hydraulic fluid conduits, respectively, wherein said pair of clamp arms including said additional clamp arm contact each other before both said free piston and inner piston are simultaneously carried to their respective stroke ends when said free piston is moved together with said inner piston in a direction to extend said clamp arm opening and closing rod from said cylinder tube such that said communicating hole formed on the side of said first pressure chamber of said free piston is sealed by the side end face of said inner piston.