Dual-axis planar motor providing force constant and thermal stability

Abstract

A motor is provided comprising a magnet assembly having two rows of magnets arranged along a first axis, which are separated by a gap for generating magnetic flux lines between the rows of magnets. The motor further comprises a coil bracket which is located within the gap between the two rows of magnets. The coil bracket includes a first set of coils arranged along the first axis that are operative to drive movement of the coil bracket relative to the magnet assembly along the first axis. A second set of coils arranged along the first axis are operative to drive movement of the coil bracket relative to the magnet assembly along a second axis which is orthogonal to the first axis between a first end position and a second end position along the second axis. The first set of coils is fully located within the flux lines generated by the magnet assembly at both the first and second end positions of the coil bracket and the second set of coils is located at least partially outside the flux lines generated by the magnet assembly at the second end position of the coil bracket.

Description

FIELD OF THE INVENTION[0001]The invention relates to motors for positioning objects, and in particular to a planar motor which provides at least two degrees of freedom.BACKGROUND AND PRIOR ART[0002]Multi-phase linear electromagnetic motors generally comprise a row of permanent magnets to generate magnetic flux. Induction coils or phase coils are arranged facing the magnets and in directions that are transverse to the flux lines generated by the magnets. A typical multi-phase linear motor for driving a motion stage may have two or three coils arranged longitudinally, in such a way as to be arranged in line with the motion directions of the motion stage. Hence, the coils are arranged parallel to the motion direction. In a two-phase motor where there are two sets of phase coils, the two phase currents are mutually offset by 90°. In a three-phase motor, the three phase currents are mutually offset by 120°.[0003]A planar motor which comprises linear drivers may drive motion along two cho...

AI Technical Summary

Benefits of technology

[0006]It is thus an object of the invention to seek to provide a planar motor with thermal stability which is capable of generating motion along two axes simultaneously while minimizing changes to the force constant as well as reducing thermal drift.

Problems solved by technology

This form of planar motor needs two separate sets of coils and magnets, which is therefore not cost-effective in terms of the components required.

When the planar motor runs for a prolonged period, the mechanical components expand and cause thermal drift.

This results in inaccurate positioning operation of the planar motor along the two axes of motion.

This ultimately affects the positioning control performance of the planar motor.

Furthermore, the temperature of the planar motor cannot be kept constant which results in thermal drift and contributes to inaccurate positioning control.

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