| Gripper mechanism is commonly found in industrial applications. An ideal gripper should have a simple and low-cost structure, fast and robust response. Various types of grippers have been designed but none of them is capable of fulfilling the requirements of an ideal gripper. Variable Reluctance (VR) actuator has a simple and robust structure, therefore it has been used in low-cost industrial applications. Together with its high-torque density in compared with classical DC motors, VR actuator can be a very attractive solution in gripping mechanism. However, due to its nonlinear characteristics, high-precision gripping applications tend to avoid it by employing other actuators which require less control effort. As a result, VR actuator is not popular in both industrial application and academic research. Due to the recent advancement of semiconductor components and micro-processors, more complex simulation model and advanced controller can be realized. In the past few years, VR actuators have regained much research attention.; The project aims to investigate the feasibility of employing VR technology in precision two-finger gripping application. Under this overall goal, initial research efforts have been devoted to the analysis of VR actuator operating principles and the actual gripper design. Results have shown that torque density can be raised by 3--4% for less than 2A and more than 30% with the use of mutual flux coupling effect when the pole-faces are saturated with 4A. This is achieved by connecting the flux return paths of two single VR fingers together.; In order to fully understand the behaviour of the two-finger VR gripper prototype, detailed characterization experiments have been carried out. Flux-linkage and torque profiles are measured with Alternate Current (AC) current excitation method and direct torque measurement respectively. Measurement results confirm that the VR gripper prototype behaves like a VR actuator and enjoys an increase in efficiency once it operates within the saturation region. Other magnetic characteristics including leakage flux, hysteresis loss and eddy current loss, and spring stiffness have also been measured.; After reviewing various modeling techniques commonly used in VR actuators, the nonlinear characteristics of the VR finger gripper, flux-linkage and torque profiles, are modeled with an exponential description function. Then, a concise dynamic nonlinear model of the VR finger gripper basing on state equations is established. This model is further verified by step responses and confirmed to be an accurate mathematical description for the VR finger gripper. (Abstract shortened by UMI.)... |
