Precision Grasp Control with a Pneumatic Gripper and a Novel Fingertip Force Sensor

Grippers equipped with tactile sensors are very important in high performance robotic manipulation tasks, where the robot must adapt to shape and characteristics of unknown objects. Such adaptability reduces cycle time and cost, eliminates the need for customization and tool changers, and enhances the automation process. In addition, while handling fragile objects, it may be necessary to regulate the grip force to avoid slipping, dropping, or breaking the object being manipulated. In this study, a pneumatic gripper was augmented with a novel custom-fabricated compliant skin sensor packaged in the gripper fingertip. The sensor is a strain gauge printed onto a Kapton substrate, patterned with a polymer piezo-resistive material, and encased in an elastic Silicone encapsulant. Using feedback from this sensor, a model-free explicit force control scheme was implemented and compared to the native pressure regulation scheme to control gripping force. Experiments were performed to investigate the performance of this gripper compared against similar data obtained from a commercial load cell. Results indicate that the augmented gripper can maintain a more precise control of the force applied and can better accommodate grasp transitions.