Three Function Switch for Point of Sale Printers
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-20
This invention applies to printers and specifically thermal, point-of-sale printers. These printers require that both the absence of paper and an open paper cover be detected so that printing can be stopped when either condition exists. Most of these printers have a paper cutter which also typically has a switch that detects when the cutter blades are open. The result is that most point of sale printers have three separate switches. This invention combines all three of these switching functions into a single sensor. This combination is possible because all three conditions; paper out, cover open or cutter blades closed require in the same result which is to stop printing and signal the operator that the printer has a problem. Rectification of the problem will be obvious to the operator as soon as the paper cover is opened. The only real functional concern is that if the cutter is manually moved to the closed position when cover was open, the printer will not detect that the problem has been rectified. A simple operator procedure corrects this problem. The operator is instructed to feed paper after closing the cover. Depressing the paper feed button ensures that the cutter is in its open position and that paper is loaded correctly. Figure 1 shows an embodiment of this invention. A Switch Lever is pivotally mounted in a slot (fixed to the printer frame) that is open on the side of the pivot opposite the paper. One end of the Switch Lever has a protrusion that presses lightly against the paper which is supported by part of the paper cover. The light force is the result of a spring force near the pivot that applies a moment on the Switch Lever. The other end of the Switch Lever is a Sensor Surface that faces an optical sensor (not shown) which is mounted on the printer's logic card. Between the pivot and the Sensor Face is another protrusion that engages that cutter mechanism as the cutter closes. Printer logic checks the status of the three function switch prior to printing. Figure 2 shows how this embodiment works. In the Normal Position, the Sensor Face is held opposite the Sensor (Status On) by the Paper and Paper Cover. The cutter is open thus the Cutter Cam does not engage the Switch Lever.