Position estimation and control of compact BLDC motors based on analog linear Hall effect sensors

Abstract

Bio-mimetic robotic systems, among many other engineered systems, require motors which possess high torque, little or no torque ripple, compact size, and precise position control. It is frequently challenging to include a motor with a design which fits all of these requirements. Several companies have recently released compact pancake brushless DC motors which possess excellent characteristics. However, ripple-free precision control of brushless motors requires precision position measurement. It can be difficult to mount encoders directly to the shafts of these motors, and for precision position control, a sensorless configuration may be inappropriate. We propose a novel method of measuring rotor position using analog Hall effect sensors to measure the magnetic field of the rotor magnets to create an absolute position measurement of the electrical cycle, which can be used efficiently to create a computationally simple motor control scheme. These Hall effect sensors are mounted directly to the motor and are highly compact, have high bandwidth, are extremely low cost, and have high precision, providing position measurements with insignificant increases to motor size.