A compact and robust variable reluctance actuator for grasping applications

Variable reluctance actuators have a simple and robust structure, and they are widely used as a low cost switching actuators in many applications. However, they have not gained widespread acceptance as proportional actuators due to their inherent nonlinear control characteristics. In this paper, a robust, compact and easy-to-manufacture grasping actuator based on variable reluctance (VR) technology is presented. Using a novel control strategy, the actuator can be operated in position, velocity and force control modes. This makes the actuator ideal for the high-speed grasping of delicate objects in robotics applications. The paper describes the construction and operating principle of the VR grasping finger. It also describes the fabrication and the measurement of essential electrical and mechanical characteristics of the actuator. A novel nonlinear control algorithm for multi-mode control of position, velocity and force is then proposed. The proposed algorithm is implemented on a DSP system to control the VR grasping finger in various motion control modes. Results from the implementation show that the VR grasping finger can be controlled with a high degree of speed and accuracy, and the application of force on the object in the force control mode is both stable and accurate.