Improvement on Heating Head Performance

Abstract

We have been improving the heating head structure for thermal printing processes. The major structural change is that the heating element is on the back side of ceramic substrate in a conventional sense. There are several advantages in this configuration such as the increased thermal capacity of the heating head, much higher mechanical anti-abrasion and scratch resistance ability, simplified substrate manufacturing process.We will discuss how the new heating head functionality can be improved from an application point of view. There are two areas we are addressing in this report: Heating head driving method and heating surface coating.The first area is maintaining the heating temperature constant. The heating head has the temperature sensing element alongside of the heating element which is made of resistive material having a large positive temperature coefficient of resistance. The temperature change is reflected in the resistance change of sensing element which is fed into the heating element control circuit. The heating element energy can be controlled by varying the driving voltage with continuous on-time or varying the on time with constant supply voltage. We employed the later control method for this paper with the pulse width modulation circuit for a simplified way of maintaining the desired process heating head temperature.The second area is the ability to overcoat the heating surface with a material suitable for the heating process. Unlike the existing heating heads where the heating surfaces are overcoated by an insulative material such as glass which gives a limited freedom for the coating process on top, the new heating surface is ceramic and various coating materials which can be conductive and/or lower coefficient of friction can be used for overcoating. This capability enhances the width of heating process application range as the wider variety of media can be heated as well as the applications beyond printing field.