Automatic center holding fixture for an annular workpiece

Apparatus for gripping the interior surface of an annular opening in the center of a generally circular workpiece including in combination:

• a baseplate having a shaft passing therethrough perpendicular to the plane of said plate and means responsive to the application of fluid pressure axially to move said shaft;
• a set of generally arcuate gripping elements circularly positioned about said shaft and coaxial therewith, the elements being circumferentially spaced apart, said elements being slidable upon said baseplate radially of said shaft and each element having an interior radial camming surface and an exterior radial gripping surface, the combined gripping surface generally defining a cylinder, each element has oppositely opening slots on its peripheral ends spaced inwardly of the gripping surfaces,
• spring bias means secured to said baseplate and positioned thereon in relation to said gripping elements normally to exert radially inward pressure on the elements tending to contract the said elements to enable a decrease of the diameter of the cylinder defined by the combined gripping surfaces, the bias means comprise leaf spring means secured to said baseplate and extending between the opposed slots of adjacently positioned elements and bearing against the radially inward surfaces of said slots for exerting said radially inward pressure,
• an actuating member secured to said shaft above the baseplate and movable in response to said shaft movement to cooperate with the camming surfaces on said elements for moving said elements to slide radially outwardly against the inward pressure of said spring bias means whereby to tend to increase the diameter of the cylinder defined by said gripping surfaces to enable said exterior gripping elements frictionally to engage the annular opening of a workpiece disposed on said baseplate.