A precision linear positioning system is proposed. The system can move with high speed, smooth motion, high resolution and over long stroke. Those are the requirements of precision machining and inspection system of next generation. To meet the requirements, a conceptual design and configuration of the positioning system is proposed. The system consists of air bearing as a guide mechanism, linear motor as an actuator, laser interferometer as a position sensor and several electronics to control and drive the system. The system can move over long stoke motion with fast speed and high resolution by one servo. The linear motor is coreless type. In order to overcome the problem of the coreless motor, low actuating force, multi-segmented trapezoidal (MST) magnet array is used.
Magnetic field due to the MST magnet array, coil winding and yoke is modeled analytically. The MST array has magnets with isosceles trapezoidal shape and variable width whereas conventional multi-segmented magnet arrays rectangular shape and identical dimension. This model can consider the more complex shape and dimension of the magnets. Because magnetic field by each magnet and coil block is calculated and superposed, inherent finiteness of the linear motor`s mover can be modeled. Using the magnetic filed, characteristic of the motor such as actuating force, inductance and back electro-motive force can be calculated. So the model is the more flexible and precise than conventional. The model is also applicable to many computer added analysis such as optimal design, dynamic simulation and etc.
Design optimization is performed for the linear motors with several types of MST magnet array. Objective of the optimal design is maximize the actuating force per volume under constraints such as heat generation, input current and voltage limit, force ripple and so on. From the results of the optimization, a linear motor type and design is selected under consideration of the performance and manufacturing cost. 2-segmented trapezoidal magnet array is selected for it enables the actuating force larger with small increase of the manufacturing cost.
A linear positioning system is constructed using the linear motor with the optimally designed design parameters and the suitably selected type of MST magnet array. The positioning system has also guide mechanism, position sensor, controller and amplifier for the linear motor. Using the system, the model is verified. Also performance and problems of the system investigated. The force ripple is measured and compensated by input current shaping. Using the input current, the system controlled to meet the requirements of the positioning system of next generation such as high speed, high precision and long stoke. As a results it comes to a conclusion that the system can meet the requirements of positioning system of next generation.
