VERFAHREN ZUR MESSUNG DER RESTTONERMENGE IN EINEM TONER-FUELLTRICHTER

摘要

An apparatus for detecting a residual quantity of toner remaining in the supply hopper of a copying machine includes a piezoelectric vibrating element disposed in a wall of the hopper and having a surface normally positioned in contact with toner in the hopper, and an electronic circuit for causing vibration of the element at a predetermined frequency and for detecting changes in operating characteristics of the element as representative of a decrease in the amount of toner in the hopper to operate a warning device.