JPS57166258A - Detecting method of residual quantity of roll paper - Google Patents

Abstract

PURPOSE:To high accurately detect a residual quantity at detection for a residual quantity of roll paper in a printer or the like, by detecting a mark of the roll paper with a sensor, clock measuring an interval of output pulses of said sensor and counting the proportional residual quantity to rotary speed. CONSTITUTION:A disc 5 is rotated together with roll paper 1, and a magnetic mark 6 is detected by a sensor 7 at each turn of revolution, then the paper is fed at a constant speed, if its residual quantity is decreased to a small level, a period T of an output pulse from the sensor 7 is gradually decreased to short length. For a sensor signal S1, shaped in a signal processor circuit 8, at a level L, a counter 11 reads and counts a reference clock signal S2 then measures the period T of the signal S1. If the signal S1 becomes a level H, a latch 12 reads contents of the counter 11 with output of an inverter INV, while the output of the inverter INV resets the counter 11 through a delay circuit 9. Then holding contents of the latch 12 is compared with a reference value B in a comparator 13, at relation of A<B, that is, the residual quantity of the roll paper 1, in proportion to length A of the period T, if becoming smaller than a specified residual quantity, can be alarmed.