As known, people usually need to copy paper documents in daily lives or in working places. Generally, the paper document to be printed is placed in a paper input platform. At the time when the paper document is fed into the inner portion of a printer or a copier, the printer or the copier detects the width of the paper document. According to the width of the paper document, the printer or the copier selects the print paper with a suitable size from a paper input tray. Then, the contents of the paper document are printed out and printed on the print paper.
Conventionally, the sensors for measuring the paper width paper are installed within the paper input platform of the printer or the copier. For example, the sensors are infrared sensors, pressure sensors or any other appropriate optical sensors. Since sensors are power-consuming, the printer or the copier has to provide a lot of electric power to the sensors. For allowing the sensors to successfully detect the paper width, the problem of wasting electric power occurs.
Moreover, since the sensors are installed within the paper input platform of the printer or the copier, the paper input platform needs to have the corresponding structures for installing the sensors. Generally, the sensors are only able to detect limited number of paper width sizes. For accurately detecting different paper width sizes, it is necessary to install many sensors within the paper input platform. Under this circumstance, the inner structure of the paper input platform is complicated. Moreover, since the sensors are bulky, the sensors occupy much inner space of the paper input platform. In other words, the conventional paper size detection device is detrimental to miniaturization of the product.