Patent ID: 8726802

Claim:
A controller for an electric servo press for linearly driving a slide through a rotary-to-linear motion converting mechanism for rotating a decentering shaft by a rotational output of a servo motor to convert a rotation of the decentering shaft into a linear motion, to perform press working, the controller comprising: a press load sensor for detecting a pressure-force of the slide; a pressure-force determination device for determining whether the pressure-force of the slide reaches one or a plurality of different pressure-force setting values based on the one or the plurality of different pressure-force setting values and an output signal of the press load sensor, and for generating a pressure-force achievement signal each time the pressure-force of the slide reaches each of the one or the plurality of different pressure-force setting values; a servo motor drive controller for controlling the servo motor; and a motion command device configured to provide the servo motor drive controller with a motion command, wherein when a stroke of the electric servo press starts at one of a standby position and a top dead center (PS) of the slide, the motion command device is configured to provide a motion command to the servo motor drive controller to control the servo motor by a positional control, the motion command device is configured to provide a motion command to the servo motor drive controller to switch a drive control mode for the servo motor from the positional control to a speed control, in response to a first pressure-force achievement signal to be generated at an actual processing start point at which predetermined pressure-force is generated between an upper die and a lower die, the motion command device is configured to provide a motion command to the servo motor drive controller to lower a rotating speed of the servo motor, in response to a second pressure-force achievement signal to be generated when a pressure-force greater than the predetermined pressure-force is generated between the upper die and the lower die, while the servo motor drive controller is performing the speed control on the servo motor, and the motion command device is configured to provide a motion command to the servo motor drive controller to switch the drive control mode for the servo motor from the speed control to a torque control, in response to a third pressure-force achievement signal to be generated when a maximum pressure-force is generated between the upper die and the lower die.