Device for clamping a workpiece

A clamping device in a machine tool, said clamping device holding a workpiece at a predetermined position during a machining operation of the workpiece by the machine tool and comprising:

• a housing;
• a clamper carried by said housing to be movable for clamping said workpiece;
• a feed device for moving said clamper toward said workpiece;
• a load sensor means for detecting a clamping force generated by said clamper;
• a position detecting means for detecting an axial position of said clamper;
• a memory means in which a target clamping force is stored;
• a first control means for actuating said feed device until the clamping force detected by said load sensor means reaches the target clamping force stored in said memory means in preparation for a machining operation;
• a second control means for inputting a signal output from said position detecting means when said clamper is stopped after the movement by said first control means so as to detect an initial stop position;
• and
• a third control means for actuating said feed device when the position detected by said position detecting means deviates from the initial stop position during the machining operation, whereby said clamper is prevented from moving from the initial stop position after clamping.

A clamping device in a machine tool, said clamping device holding a workpiece at a predetermined position during a machining operation of the workpiece by the machine tool and comprising:

• a housing;
• a clamper carried by said housing to be movable for clamping said workpiece;
• a feed device for moving said clamper toward said workpiece;
• a load sensor means for detecting a clamping force generated by said clamper;
• a position detecting means for detecting an axial position of said clamper;
• a memory means in which a target clamping force is stored;
• a first control means for actuating said feed device until the clamping force detected by said load sensor means reaches the target clamping force stored in said memory means in preparation for a machining operation;
• a second control means for inputting a signal output from said position detecting means when said clamper is stopped after the movement by said first control means so as to detect an initial stop position;
• a third control means for increasing a clamping force applied by said feed device when a position detected by said position detecting means is in a backward side of said stop position during the machining operation;
• and
• a fourth control means for comparing the clamping force detected by said load sensor means during the machining operation with the target clamping force, and for controlling said feed device in response to a deviation between the detected clamping force and the target clamping force so that the workpiece is held with the target clamping force during the machining operation and when the position detected by said position detecting means is not in a backward side of said stop position.

A clamping device in a machine tool, said clamping device holding a workpiece at a predetermined position during a machining operation of the workpiece by the machine tool and comprising:

• a housing;
• a clamper carried by said housing to be movable for clamping said workpiece;
• a feed device for moving said clamper toward said workpiece;
• a load sensor means for detecting a clamping force generated by said clamper;
• a position detecting means for detecting an axial position of said clamper;
• a memory means in which a target clamping force is stored;
• a first control means for actuating said feed device until the clamping force detected by said load sensor means reaches the target clamping force stored in said memory means in preparation for a machining operation;
• a second control means for inputting a signal output from said position detecting means when said clamper is stopped after the movement by said first control means so as to detect an initial stop position;
• a third control means for activating said feed device to return said clamper to the stop position when a position detected by said position detecting means is in a backward side of said stop position during the machining operation;
• and
• a fourth control means for comparing the clamping force detected by said load sensor means during the machining operation with the target clamping force, and for controlling said feed device so that the workpiece is held with the target clamping force during the machining operation and when the position detected by said position detecting means is not in a backward side of said stop position during the machining operation.

A clamping device in a machine tool, said clamping device holding a workpiece at a predetermined position during a machining operation of the workpiece by the machine tool and comprising:

• a housing;
• a clamper carried by said housing to be movable for clamping said workpiece;
• a feed device for moving said clamper toward said workpiece;
• a position detecting means for detecting an axial position of said clamper;
• a first control means for moving said clamper until said workpiece is held with a predetermined clamping force, before the machining operation;
• a second control means for inputting a stop position where said clamper is stopped after the movement by said first control means;
• a third control means operable when the position detected by said position detecting means deviates from said stop position during the machining operation, for actuating said feed device depending on such deviation.