Get a Grip : Dynamic force adjustment in robotic gripper

Abstract: Autonomous mobile robots are on the rise and are to be expected on the market in about 5-10 years. Several challenges need to be solved for this to happen, and the most crucial ones are to develop versatile and safe robots. The Get a Grip robot is a dynamic force adjustment gripper using inputs from two different sensory systems. The construction of the robot consists of two parallel gripper plates moved by a rack and pinion gear attached to a direct current (DC) motor. Embedded into one of the plates is a Force Sensitive Resistor (FSR) for input of the gripper’s exerted force. Mounted to the other plate is a self constructed Slip sensor used for measuring the occurrence of slip and slip rate. A surrounding crane for mounting of the gripper and lifting was also constructed. The idea of this bachelor’s thesis project is to enable lifting of objects with unknown weight without the gripper exerting more force than necessary. This is something that will be useful in both industrial applications and in household robots in the future. In order to realize the concept two different methods for calculating the gripper’s applied force were tested, one using motor current and the other using a FSR sensor. Through testing it was concluded that the FSR sensor was the method giving better accuracy and consistency. Proportional–Integral–Derivative (PID) controllers were then tested for both setting force references for the gripper using the Slip sensor as input, and controlling the exerted force in the gripper using the FSR as input. The results led to two PID controllers thought to be sufficient as starting points for further testing of the complete system.