A new method of temperature control for the uniform heating

Abstract

Uniform temperature control of heating plate which has a wide thermal conduction area is required in many industrial application fields. In this paper, a new method of uniform temperature control is proposed based on an idea of quasi-decoupling. The feature of the proposed method is'easy to &sign a control system without the precise plant dynamics. The controller is designed using the gradient and average of temperature among the arbitrary points. The effectiveness of the proposed control method is confirmed by experiment. I. Int,roductionIn recent years, in equipments for heat treatment, such as developing machines in semiconductor processes, packing machines in foods processes, and a forming and mould machine in plastic processes, the requirement for quality improvement is very strict. Especially, uniformity of the temperature on a heating plate will be an important issue.In general thernial processes, scatter of temperature on the conduction surface is observed in both steady state and transient state. In the steady state, scatter of temperature can be suppressed with simple PID controllers by proper design of the machines considering possible items relating to thermal characteristics. nansient temperature scatter is caused by thermal conduction from the heaters to products. As the heating plate is usually attached to enclosure, the thermal inertia is different in each area. This phenomenon is observed drastically in the case that heating plate is wide and thin. From the view point of production, the thermal process time should be controlled and managed for quality improvement because the thermal energy which causes the chemical reaction depends on the temperature and heating time. So, it is required to make the temperatures uniform in all the points on heating plate as soon as possible, for the quality management of products.For minimizing the scatter of temperature, temperature control using multi-heaters has been used due to increase of heated product size [I]. On the practical applications, the heating surface is divided into many areas, and precise temperature controls are used in each area in order to make the temperature uniform. However, the thermal j 0-7803-7906-3/03/$17.00 02003 IEEE interference among the heaters makes the characteristics of the system quite nonlinear 121. Also, the nonlinearity of the system depends on the application, i.e. the shape of heating surface, heater arrangement, dead time, thermal conduction ratio and convection and so on. Thus, it is difficult to realize the precise temperature control system based on a conventional PID controller. For this difficulty, decoupling control has been investigated in process engineering 131. Main idea of decoupling control is to design the decoupler so as to compensate the thermal interference among heaters. However, the precise identification and modeling of nonlinearity are so difficult, and static or partial decoupling using 'low order information of thermal interference has been studied with the trade off of precision and stability in ge...

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