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UBC Theses and Dissertations

Multi-degree of freedom position sensor for planar motors Maguire, Keir


This thesis presents the development and verification of a multi-degree of freedom (DOF), non-contact position sensor for a magnetically levitated planar motor. Planar motors are intended to replace X-Y stages in various manufacturing processes resulting in higher accuracy, higher speed, and no friction. To obtain position feedback, previous planar motors have used laser interferometers, planar encoders, stereo vision, capacitive sensors, and Hall sensor arrays. For applications requiring micrometre-level precision, Hall sensor arrays are cost-effective, absolute, high bandwidth, can be integrated into the stator, and are capable of sensing multiple movers in 6-DOF over large stroke and rotation. However, previous Hall sensor arrays suffered from excessive error, low bandwidth, absolute position only within one pitch of the magnet array, modifications to the mover, lack of 6-DOF or multi-mover capability, or limited range. A 2-D Hall sensor array was developed. There are three sensors per wavelength of the magnetic field, which decouples sensor outputs for orthogonal 1-D Halbach magnet arrays. The position in 2-DOF, X and Z, is calculated for a 1-D Halbach array. The position in 6-DOF can be calculated for a planar motor mover composed of four orthogonal Halbach arrays. This sensor solution measures absolute position and is high bandwidth, multi-mover capable, and scalable with stroke. A prototype was designed, consisting of a Hall sensor array, summing amplifiers, and signal processing electronics. The prototype was tested in 2-DOF using a CNC to move a Halbach array to discrete points. Position error is approximately 200 µm peak to peak; however, the error is periodic and can be compensated. Resolution is 5 µm. Due to redundancy and averaging, improved accuracy and resolution is expected for 6-DOF sensing of the planar motor. Variation in sensor gain is a common cause of error in previous Hall sensor arrays. Previous Hall sensor arrays have only achieved good accuracy by using laser interferometers for error mapping or individual differential amplifiers to control each sensor’s gain. A sensor sorting setup was designed, built, and used to sort more than 12,000 sensors based on gain. The sorted sensors can be used for a sensor array with micrometre-level accuracy.

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Attribution-NonCommercial-NoDerivs 2.5 Canada