A gripper and sensor system for controlled slip and force

The paper describes the development of a robot gripper, sensors and associated electronics suitable for controlling slippage and contact force. A typical application is the handling of glass test tubes in an automated medical analysis laboratory. Through force control, the gripper first holds an object, then repeatedly releases and regrasps it for controlled slip. The basic mechanical principle consists of a rolling cylinder in direct contact with the (cylindrical) object, forming a cylinder-cylinder pivot with 5 degrees of freedom. A stable grasp is achieved by a finger/counter-finger arrangement with 3 contact points. In the left finger, contact force is reflected in the pivots of the roll and measured by piezoresistive force sensors. In the right finger, motion is measured by optical encoders. Analog electronics deal with gripper motor control and signal processing for the force sensors. Digital circuits handle the motion measurement from the optical encoders, A/D conversion of force sensor outputs and force feedback for motor control and communications with an external computer. The proposed design has been built and tested using an industrial SCARA robot