Development of Spin Coater with Close Loop Control System Using ATMega8535 Microcontroller

摘要

Spin coater usually applied in preparation of a thin layer in industrial coatings and advanced material functionalization in various applications. This paper reports the development of spin coater with a closed loop control system using ATMega8535 microcontroller. The thickness of the thin film layer depend on the rotation of spin coater in which usually controlled by open-loop type. In long-term utilization of the spin coater, the performance of the motor usually degraded and caused the speed of the rotation is no longer accurate. Therefore to resolve the drawback, a close-loop system is applied in currently developed spin coater. The speed range of the spin coater was designed in between 450-6000 rpm, equipped with user interface through push button and LCD display. The rotary encoder transducer was applied to sense the speed of the dc motor. The pulse width modulation (PWM) method is applied to control the speed of the dc motor. The performance of the control system were evaluated based on the applied voltage to the PWM driver (L298) versus speed of the motor and also the rise time, overshoot, and settling time of the control system. The result shows that in the setting of low speed (450 rpm), the settling time is very fast about 12 seconds and very high overshoot about 225 rpm, contrary for the high speed (5550 rpm) the setting time is 71 seconds and very low overshot about 30 rpm. In addition, to evaluate the stability of the mechanical system, the spin coater was tested to prepare a ZnO thin film in various speed of rotations and at various concentrations of the solution, i.e. 10 wt.% and 15 wt.%. It is concluded that the spin coater can be utilized for thin film coating after pass the maximum of the settling time (71 seconds). The currently developed spin coater produce a film with common characteristics of the spin coater where thicker film was obtained when higher concentration was used and thinner the film was obtained when higher speed of the rotation was applied.