Cogging compensation in embedded brushless motor control for haptics applications

Cogging compensation in embedded brushless motor control for haptics applications

Van, W.

Schiele, A. (mentor)
Babuska, R. (mentor)

Mechanical, Maritime and Materials Engineering

DCSC

Systems & Control

2013-12-16

For the development of a space qualified, 7 degrees of freedom, haptic arm exoskeleton a brushless DC motor with high torque production, power density and efficiency was selected. However, the attraction of the rotor magnets to the stator teeth introduces an additive, position dependent, torque disturbance on the motor shaft called cogging torque. In haptic applications this disturbance impacts the realism of the force reflection and limits control fidelity during master-slave teleoperation. This thesis investigates possible solutions within the constraints of the envisioned application. Due to volume, torque production and efficiency requirements the chosen motor is not to be changed. This rules out the use of motor design based cogging minimization techniques. For this reason only control-based methods are considered. Two methods to identify the cogging waveform were developed. This data was used to do feed-forward compensation using a lookup-table approach and a Fourier series approximation. For comparison, a PID feedback compensation and hybrid approach were also tested. Identification of the cogging torque and testing of compensation methods is done using a custom build measurement setup. A reduction of the RMS cogging of 39% was achieved using the feed-forward approach, while the PID feedback loop resulted in a 46% reduction. A combination of these two methods in the hybrid approach resulted in a reduction of 75%. Thesis done as part of a 'double degree' with Systems & Control at 3mE (DCSC) and Embedded Systems at EWI.

haptics
cogging
brushless

http://resolver.tudelft.nl/uuid:27993f5c-230f-4c48-80d6-3d8bf5cd476e

2013-12-17

Student theses

master thesis

(c) 2013 Van, W.