Patent ID: 6842591

Claim:
A method of controlling a charging potential of a charging mechanism including a conductive roller charging an organic photoconductive cell (OPC), a sensing resistor Rs measuring a sensing voltage, which is proportional to a charging potential of the OPC, an analog-to-digital converter (ADC) converting an analog signal corresponding to a voltage variation of the sensing resistor (Rs) to a digital signal, an engine controller unit (ECU) receiving the digital signal from the ADO and outputting a control signal for controlling a charging voltage (Vc) and a duty of a high voltage power supply (HVPS), and the HVPS receiving the control signal from the ECU and applying the charging voltage (Vc) to the conductive roller in a printer, the method comprising performing: a first operation of supplying first and second charging voltages (Vc 1 and Vc 2 ) and first and second duties (D 1 and D 2 ) established in the ECU to the conductive roller via the HVPS to charge the OPC; a second operation of measuring first and second sensing voltages (Vs 1 and Vs 2 ) of the sensing resistor (Rs) so that the ECU establishes a target charging current (It) and calculates a new third charging voltage (Vc 3 ) and a new third duty (D 3 ); a third operation of supplying the new third charging voltage (Vc 3 ) and the new third duty (D 3 ) to the conductive roller via the HVPS to charge the OPC and measuring a charging current (Ic 3 ) of the conductive roller; and a fourth operation of comparing a difference between the charging current (Ic 3 ) of the conductive roller and the target charging current (It) with a tolerance value TOL to control the charging potential by using the target charging current (It) when the difference is smaller than the tolerance value TOL.