Die cushion control device

Abstract

Die cushion control device that implements die cushion control while making a switch between position control and pressure control by using servomotors, and reduces the impact caused by a collision between a press axis and a die cushion axis during position control. Die cushion members are controlled by servomotors Md. The changeover switch is connected to the “a”-side, to thereby control the position (velocity) of the servomotors Md by commands from a numerical controller and control the position of the die cushion members. During position control, the output torque of the servomotors Md is limited by torque limit means. During position control, even if the press axis hits the die cushion members due to erroneous setting, wrong operation or the like, the servomotors Md merely output only a limited torque or less, so that impact force is reduced, which prevents damage to the die cushion members and the press axis. During press operation, when a position detector detects that the press axis moves downward to reach a predetermined position, the changeover switch is connected to the “b”-side, to thereby implement pressure control.

1 . A die cushion control device for a press machine that presses sheet metal between a set of dies relatively movable along a press axis while controlling a pressure exerted on the sheet metal, comprising: 
 a die cushion member for cushioning the pressure exerted on the sheet metal by the relative motion of the set of dies;    a servomotor for moving said die cushion member in a direction of the press axis; and    a controller for controlling said servomotor by selectively performing one of a position control and a pressure control of said die cushion member, and having torque limit means for effecting a torque limit on the servomotor during the position control of said die cushion member.    
   
   
       2 . A die cushion control device according to  claim 1 , wherein said torque limit means applies a torque limit to a torque command for said servomotor to move said die cushion member in a direction that the set of dies press the sheet metal, and does not apply the torque limit to a torque command for said servomotor to move said die cushion member in a direction opposite to the direction that the set of dies press the sheet metal.  
   
   
       3 . A die cushion control device according to  claim 1 , wherein said toque limit means applies a first torque limit to a torque command for said servomotor to move said die cushion member in a direction that the set of dies press the sheet metal, and applies a second torque limit of a value different from a value of the first torque limit to a torque command for said servomotor to move said die cushion member in a direction opposite to the direction that the set of dies press the sheet metal.