Patent ID: 8626016
Filing Date: 2014-01-07
Classification: G03G

Abstract:
1. An image forming apparatus comprising: a main body; a rotatable image bearing member configured to bear an electrostatic latent image; a charge unit configured to charge the image bearing member; a plurality of developing units each including a developer bearing member that bears developer used for developing the electrostatic latent image; a rotatable developing unit support configured to support the plurality of developing units, the developing unit support being rotated to move each developing unit to a developing position where the developing unit opposes the image bearing member for developing, the developing unit support including support side electrical contacts at which a bias is applied to the developer bearing members provided in the corresponding developing units; a stop position detecting unit configured to detect a stop position of the developing unit support; a main-body side electrical contact configured to apply a bias to each of the support side electrical contacts in a state in which the main-body side electrical contact is in contact with the support side electrical contact, the main-body side electrical contact being provided in the main body; and a control unit configured to control a bias to be applied to the main-body side electrical contact and a bias to be applied to the charge unit, wherein the voltage of the main-body side electrical contact when each developing unit performs the image formation at the developing position is referred to as a first developing voltage, the voltage of a non-image portion of the image bearing member when the developing unit performs the image formation at the developing position is referred to as a first image bearing member voltage, and the image forming apparatus is capable of performing a position detection sequence in which the developing unit support is rotated to move the developing unit support to a normal stop position by the stop position detecting unit, and wherein the voltage of the main-body side electrical contact when each developing unit passes along the developing position in the position detection sequence is referred to as a second developing voltage, the voltage of the image bearing member when the developing unit passes along the developing position in the position detection sequence is referred to as a second image bearing member voltage, and the control unit controls the bias to be applied to the main-body side electrical contact and the bias to be applied to the charge unit so that the second developing voltage has the same polarity as that of the first developing voltage and has an absolute value smaller than that of the first developing voltage, the second image bearing member voltage has the same polarity as that of the first image bearing member voltage and has an absolute value smaller than that of the first image bearing member voltage, and the difference between the second developing voltage and the second image bearing member voltage is larger than that between the first developing voltage and the first image bearing member voltage.