Control strategy for a low-cost Spin Coater

This article discusses the hardware and software modifications that were made to a low-cost Spin Coater prototype in order to improve its stability during operation and reduce the steady state error while maintaining a constant speed. This device uses a brushless DC motor with an Arduino MEGA 2560. The implementation of two additional interfaces based on a frequency to voltage integrated circuit to increase the resolution of the control signal and of the feedback sensor is also discussed. A PI closed-loop controller along with an anti-windup back-calculation algorithm was implemented to allow the user to program the acceleration (and deceleration) time and the desired final speed for up to ten stages. It was possible to reduce the average error from 2% to 0.1% and to produce ramps with an average linearity of 0.9.