| 摘要 |
PURPOSE:To allow two developing device to consume toner equally by generating a signal by a sensor when the toner amount of a developing device which is much in toner consumption decreases to a fixed amount or less, and receiving this signal and then switching high-density development conditions and low- density development conditions of the respective developing devices. CONSTITUTION:A means which switches bias voltages applied to both developing rollers 39 and 39' is provided. This switching means can use, for example, an automatic switching device provided in an electric circuit. Namely, the bias of a high-density developing device 17 is so switched with a signal indicating the remaining amount of toner is small that a bias 400V as the condition of a low-density developing device 17' is applied to the high-density developing device 17 and a bias 200V as the condition of the high-density developing device 17 is applied to the low-density developing device 17'. Consequently, the high- density developing device 17 which is much in toner consumption is switched to a low-density developing device which is small in toner consumption and contains much remaining toner, so toner in both developing devices is consumed equally. |
