How to use FPGAs for quadrature encoder-based motor control applications

By Glen Young, Actel
September 11, 2007 -- pldesignline.com

Precisely tracking speed, acceleration, and position of a motor's rotor is an essential requirement for many motor control applications found in everyday equipment such as fax machines, elevators, and medical equipment. A closed-loop control scheme is able to bring motor feedback information, such as back electromotive force (BEMF) voltage or supply current to the control system. Rotary encoding is a common mechanism for the delivery of accurate speed, acceleration, and position of the motor rotor.

Rotary encoders are commonly deployed in the closed-loop rotor systems used in a wide variety of applications from robotics and high end photographic lenses to opto-mechanical mice and trackballs to rotating radar platforms. A rotary encoder is an electro-mechanical device for converting the angular position of a shaft or axle to a digital code. For many applications and equipment that need to track object location, velocity and accelerations accurately, a rotary encoder offers a cost-effective solution.

Relative and Absolute are two primary types of rotary encoders. A quadrature encoder is in the relative encoder family and is most commonly used in high-speed motor control systems; it also facilitates the ability to determine motor direction.

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