Thermal paper is used in thermal printers and particularly in devices such as fax machines, cash registers, and credit card terminals. It is a special fine paper that is coated with one or more chemical substances that change color when exposed to heat. For example, when the thermal paper passes over a thermal print head of the thermal printer, the coating changes its color in the areas where it is heated, thereby producing images.
For correctly installing the thermal paper roll, the thermal paper roll should be placed in a predetermined direction so that the surface of the thermal paper roll coated with the chemical substances can face the thermal print head for producing images. Thus, when the thermal paper roll is installed backward, the thermal print head is not able to produce images on the surface of the thermal paper roll. However, the traditional printers have no any warning system for warning the incorrect installation of the thermal paper roll, so users often install the thermal paper roll incorrectly without notice. When the printer is operated, and the thermal paper roll is installed incorrectly, some of the thermal paper sheet would be wasted, and the user would be confused by that. For example, when a checkout staff uses the cash register to print out a receipt without noticing the incorrect installation of the thermal paper roll, some of the paper roll is wasted, and the checkout staff has to reinstall the thermal paper roll and then to rescan products. Accordingly, developers constantly try to solve the problem that the user often operates the printer while the thermal paper roll is installed incorrectly.