When it comes to the control of a linear motors, the position sensor system moves into focus. Commercially available sensor systems are more than sufficient for many applications and meet their requirements without difficulty. This changes when the focus is for example on canned tubular (oscillatory) linear motors. The critical requirements are here the rather large quasi air-gap resulting from the encapsulated mover, the encapsulation itself and the restricted construction space. When the system demands bush bearings, the radial position of the mover is required for condition monitoring in addition to the obviously required axial position information of the mover. With a low-cost requirement put on top, a new eddy current position sensory system is proposed and investigated in this paper. The sensor system consists of four sensor coils equally distributed around the circumference and arranged opposite conical surfaces at both ends of the mover. All eight coils together form a low-cost eddy current position measurement system capable of determining the position of the mover in five axes. The paper analyzes the relevant systematic errors and shows how the sensors must be positioned and evaluated to eliminate these errors. Moreover the proposed evaluation strategy rejects common mode errors, decouples and linearizes the sensor output of the axes. A manufactured prototype of the system validates the simulated results, demonstrates the performance and shows the accuracy limits of the system.

Eddy current sensor， absolute linear sensor， low-cost eddy current sensor， five axes sensor， cone shaped target， multi axis sensor