| 摘要 |
An image forming apparatus includes an image bearing member (1) movable through a first developing position and a second developing position in the order named; a bias voltage applying device (33,34) for applying a first developing bias voltage to a first developer carrying member (13) and a second developing bias voltage to a second developer carrying member, wherein the first bias voltage has a phase of a first electric field for applying to the toner force in a direction from the developer carrying member to the image bearing member (1) for a time period t11 in the first developing position and a phase of a second electric field in a direction opposite to the first electric field for a time period t21 in the first developing position, and wherein the second bias voltage has a phase of a third electric field for applying to the toner force in a direction from the developer carrying member (14) to the image bearing member (1) for a period t12 in the second developing position and a phase of a fourth electric field in the opposite direction to the third electric field for a time period t22 in the second developing zone; wherein a ratio of the period t21 to the period t11 is larger than a ratio of the period t22 to the period t12; a peak level of the second bias voltage in the period t12 is larger than a peak level of the first bias voltage in the time period t11; and a peak level of the second bias voltage in the period t22 is smaller than a peak level of the first voltage in the period t21.
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