Sensors, Identification, and Low Level Control of a Flexible Anthropomorphic Robot Hand

The successful control of a robot hand with multiple degrees of freedom not only requires sensors to determine the state of the hand but also a thorough understanding of the actuator system and its properties. This article presents a set of sensors and analyzes the actuator properties of an anthropomorphic robot hand driven by flexible fluidic actuators. These flexible and compact actuators are integrated directly into the finger joints, they can be driven either pneumatically or hydraulically. The sensors for the measurement of joint angles, contact forces, and fluid pressure are described; the designs utilize mostly commodity components. Hall sensors and customized half-ring rare-earth magnets are used to integrate the joint angle sensors directly into the actuated joints. A force sensor setup allowing soft finger surfaces is evaluated. Fluid pressure sensors are needed for the model-based computation of joint torques and to limit the actuator pressure. Static and dynamic actuator characteristics are determined in a theoretical process analysis, and suitable parameters are identified in several experiments. The resulting actuator model incorporates the viscoelastic material behavior and describes the relations of joint angle, actuator pressure, and actuator torque. It is used in simulations and for the design of a joint position controller.