Work clamping method and apparatus using multi-positional finger members

An apparatus for confirming clamping of a workpiece, comprising:

• a pair of finger members for clamping the workpiece;
• memory means for storing data peculiar to the workpiece to be clamped;
• first position setting means for setting, in accordance with data derived from said memory means, a first position of said finger members at a location where said finger members contact the workpiece with a first force;
• second position setting means for setting, in accordance with the data derived from said memory means, a second position of said finger members at a location where said finger members engage the workpiece with a second and greater force;
• and
• detecting means for detecting whether movement of said finger members from the first position to the second position has occurred, and for determining responsive thereto whether the workpiece is present in a clamping position.

A workpiece clamping method comprising the steps of:

• setting parameters relating to a workpiece to be clamped, said setting step including the substeps of:
• inputting information regarding the dimensions and elasticity of the workpiece and workpiece reference value information into storage means;
• setting, in accordance with a dimensional information of the workpiece, a first target position to which fingers for clamping the workpiece are moved, the fingers when at the first target position being located around a perimeter of the workpiece;
• setting, in accordance with the elasticity information of the workpiece, a second target position to which the fingers are moved, the fingers when at the second target position being located inside of the perimeter of the workpiece;
• and
• setting a first clamping force of the fingers;
• moving the fingers to the first target position;
• determining whether or not the workpiece is positioned between the fingers, said determining step including the substeps of:
• (i) moving the fingers from the first target position toward the second target position using the first clamping force;
• (ii) determining a distance between the first target position and the position of the fingers as they are moved toward the second target position;
• (iii) determining that the workpiece is positioned between the fingers if the first clamping force is offset by the rigidity of the workpiece corresponding to the elasticity information thereof whereby the fingers have stopped, and if the determined distance has not exceeded a value in the workpiece reference value information;
• and
• (iv) determining that the workpiece is not positioned between the fingers if the fingers have not stopped, and if the determined distance has exceeded said value in the workpiece reference value information;
• and
• executing a clamping operation with the fingers if the workpiece is determined to be positioned between the fingers in the determining step, said executing step including the substeps of:
• (i) moving the fingers to the first target position;
• (ii) setting a second clamping force of the fingers large enough to reliably clamp the workpiece;
• and
• (iii) moving the fingers from the first target position toward the second target position using the second clamping force.