Design and implementation of a cost-effective position control system for an ironless linear motor

Due to attractive features including a high reliability, low maintenance, and a low cost, stepping motors with an open-loop drive have found wide application in motion control systems. However, the performance of a stepping motor that is under open-loop control deteriorates when either the frequency of the input pulse train is increased or an external load is unexpectedly added. A high-performance, cost-effective direct-drive position-control system with an ironless linear permanent-magnet synchronous motor (ILPMSM) is proposed to overcome these difficulties. Instead of using a multi-loop cascaded-feedback control structure, the position is controlled by regulating the orientation and magnitude of the excited space current vector of the moving coil of the ILPMSM. Also, the effect of the dead time on the positioning accuracy is investigated and a cost-effective position-error compensation approach in the d-q plane is introduced. Compared with general hybrid stepping motors several advantages are observed when using the proposed control strategy, including: (i) the resolution of the stepping increment and the holding force are software programmable; and (ii) limited losing steps can be automatically eliminated during the travelling process. A high-performance digital signal processor is used to implement the proposed control algorithm. Experimental results verify that the proposed approach exhibits a satisfactory performance.