| 摘要 |
PURPOSE:To obtain an inexpensive developing device with high performance by using magnetic toner to be electrostatically chargeable to both polarity and switching DC biases to be impressed on a toner feeding roller to select regular development or inversional development. CONSTITUTION:At the time of a negative DC power supply 31 is electrically connected to a sleeve 16, a negative DC bias is impressed to the sleeve 16 and an AC bias is impressed to a developing roller 24, so that only the toner 34n negatively charged is fed from a magnetic brush to the developing roller 24. At the time of a positive DC power supply 30 is electrically connected to the sleeve 16, a positive DC bias is impressed to the sleeve 16 and only the positively charged toner 34P is supplied to the developing roller 24. At the time of a bias higher than at the AC bias to be applied to the developing roller 24 is applied to the sleeve 16, regular development is executed if a photosensitive drum 12 is negatively charged. At the time of a bias lower than the AD bias is impressed to the sleeve 16, inversional development is executed. |
