Due to the complexity of many nonlinear control systems an off-line stability analysis might be extremely difficult. Hence this article presents an on-line fuzzy-based stability supervision system. This system is able to detect and evaluate occurring safety and stability problems. Therefore the supervisor classifies on-line the stability by means of a fuzzy degree of stability between zero and one. The functionality of the supervision system is shown by simulated grasp studies with the elastic robot gripper of the Research Center Karlsruhe.
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.
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