Patent ID: 7619185
Filing Date: 2009-11-17
Classification: G03G,H05B

Abstract:
1. An image forming apparatus comprising: an image forming section for forming a toner image on a recording paper; a fixing device for fixing the toner image formed on the recording paper, said fixing device including a cylindrical fixing film, a ceramic heater having heating elements and contacting with an inside surface of said cylindrical fixing film, and a pressure roller forming a fixing nip portion in conjunction with said ceramic heater via said cylindrical fixing film; a temperature detector for detecting a temperature of the ceramic heater; an electric power supply controller for controlling a power duty supplied to the heating elements from a power source so that the temperature detected by the temperature detector is maintained at a target temperature: an electric-current detection circuit for detecting a heater current value supplied to the heating elements; and wherein the electric power supply controller calculates a maximum power duty (D where D1 is a predetermined fixed power duty when starting to supply electric power to the heating elements, I1 is the heater current value detected by the electric-current detection circuit while supplying electric power to the heating elements with the predetermined fixed power duty (D1), and I limit is a predetermined applicable current value after subtracting a current value supplied to the heating elements in the image forming apparatus excluding the ceramic heater from a rated current value of the power source; wherein, (1) when a power duty (Dβ) supplied to the heating elements so as to maintain the ceramic heater at the target temperature equals to or exceeds the predetermined fixed power duty (D1), the electric power supply controller changes the predetermined fixed power duty (D1) of equation 1 the power duty (Dβ), changes the heater current value (I1) to a heater current value (I2) detected by the electric-current detection circuit while supplying electric power to the heating elements with the power duty (Dβ), and calculates and resets new maximum power duty (D wherein (2) when a power duty (Dβ) supplied to the heating elements so as to maintain at the target temperature does not exceed the predetermined fixed power duty (D1), the electric power supply controller does not calculate and reset a new maximum power duty (D