Patent ID: 8867934

Claim:
A method for determining a toner shortage for use in an image forming apparatus, said image forming apparatus comprising a developing device in which toner is supplied into a circulation carrying path through a toner supply inlet which is located in a part of the circulation carrying path in which developer, containing toner and magnetic carrier, is circulated and carried, said method determining that toner to be supplied has run short, by use of a sensor output of a magnetic permeability sensor which detects a magnetic permeability of the developer which is circulated and carried through the circulation carrying path, said method comprising the steps of: carrying out a monitoring operation, in which (i) sensor outputs of the magnetic permeability sensor are periodically sampled, (ii) a time period, corresponding to one (1) circulation period which is required for the developer to be circulated once in the circulation carrying path, is evenly divided into a plurality of blocks, and (iii) an average of the sensor outputs in one (1) block time period corresponding to one (1) block is calculated for each of the plurality of blocks; and determining that the toner has run short, in a case where the number of times that the averages of the sensor outputs consecutively exceed a threshold becomes not less than the number of the plurality of blocks which correspond to the time period corresponding to one (1) circulation period, the threshold being set to be higher than a reference value of the sensor outputs of the magnetic permeability sensor.