Development of a low cost motion actuator as an artificial joint for the physically handicapped person

Traditionally, actuators for hinge motions are constructed from DC motors and reduction gears. This kind of motion actuator is simple to control, but it has a complex mechanical structure, and it is costly, expensive and requires maintenance. In this paper, a low-cost direct-drive motion hinge actuator based on variable reluctance principle has been developed. The variable reluctance actuator has a simple and robust structure, and it is widely used as a low cost switching actuator in many applications. However, it has not gained widespread acceptance as a proportional actuator due to its inherent nonlinear control characteristics. In this paper, the problem is overcome by using a novel control strategy based on a nonlinear lookup table. The paper first describes the design, construction, fabrication and operating principle of the variable reluctance actuator. After the variable reluctance actuator has been fabricated, essential electrical and mechanical characteristics are measured. Then, a novel nonlinear control algorithm for the trajectory tracking of this actuator has been proposed. The proposed algorithm is implemented on a digital signal processor to control the motion of variable reluctance actuator in trajectory profile following mode. Results from the implementation show that the variable reluctance actuator can be controlled with a high degree of speed and accuracy. This makes the actuator ideal for hinge motions of artificial limbs, and as a motion aid for the physically handicapped person