Design of a robot gripper with force feedback control

Abstract

The design of a two-jaw robot gripper using a D.C. servomotor with optical encoder is described. Force control of the gripper is achieved using armature current sensing as a means of detecting motor torque and hence the force applied between the gripper jaws. The motor was modelled mathematically to obtain the second order equation relating armature current to the applied motor voltage. This relationship was used to develop a proportional plus integral digital control algorithm enabling force feedback to be achieved. Two-way communication between the ASEA robot controller and the IBM-XT gripper controller enables a range of gripping forces to be accessed throughout the robot programme cycle, any one of which may be selected at a particular time. Anticipated problems associated with the thermal drift and transient responses have largely been overcome by repeatedly recalibrating the gripper throughout a work shift.