The control of a positioning system using bi-axial variable reluctance actuator

This article presents a study about a new positioning system using variable reluctance electro-magnetic actuators. The positioning system can produce movements in a plan. The system is composed of two moving tables series connected and guided using leaf springs, with a pair of opposite actuators acting on each table. In the paper is presented the design, control and testing of this system. The controlling signals applied to the coils are pulse width modulation type. The control algorithm has two parts: the predictive positioning algorithm and the stability algorithm. To achieve a desired position the system use tabular data (starting and ending position) to extract command parameters (fill factors). This tabular data is obtained through several simulations using a FEM analysis. Because the position control is realized in PWM and not in DC current the transitory behavior was evaluated when is applied a PWM signal up to stabilization of the mobile armature at a position. This second step is performed using a finite difference model. The finite difference model implied at each iteration, data from FEM simulation. Because the FEM software (FEMM) can´t solve finite difference equation, a software routine was build in LUA scripting program which call the FEM simulation software at each step. Due to the low mechanically stiffness another algorithm was proposed to stabilize the structure around the target point, using a linearised model. The results of the experimental test confirmed the functioning of the system and allowed to optimize the coefficients of the command algorithm.