Development of spin coater with close loop control system using ATMega8535 microcontroller

Abstract

Abstract. 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 closeloop 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.

Design and implementation of a feedback programmable spin coating system

“…Hence, the driver controls the rotation speed by changing the PWM duty cycle (D). For example, if the voltage reference of the driver is 10 V then the supplied voltage (V=(10/100)×D) [14]. For the maximum value of designed spinning speed (8000 rpm), the obtained spinning speed (ω=(8000/10)×V).…”

“…There are many commercial spin coating systems available, however, many researchers have been and still proposed to build spin coater for research purposes [10,[12][13][14]. Most of the spin coater based research purposes work utilized brushless DC motor (BLDC motor), that usually employed as a computer hard drive using pulse width modulation (PWM) to control DC motor speed.…”

“…Changing the working cycle is employed through the built-in Module in the controller circuit [16]. In addition, the feedback control system is essential to be deployed to get accurate spinning speed [14]. To solve the degradation of spinning speed over longterm utilization.…”

“…Also, to confirm the accurate spinning speed, regardless of the shape, size and mass substrates, within the limit of the system capabilities. However, most of the previously reported works are quite simple without the feedback circuit and using a single stage voltage [10,[12][13][14].…”