Image forming apparatus suppressing occurrence of color shift in images and method of controlling same

Abstract

An image forming apparatus that suppresses occurrence of color shift in images transferred from image bearing members onto an intermediate transfer member. A surface of each of a first photosensitive drum and second photosensitive drums is charged. An exposure device, provided for each photosensitive drum, forms an electrostatic latent image by exposing an associated one of the charged photosensitive drums. A developing device, provided for each photosensitive drum, develops the electrostatic latent image with toner. An intermediate transfer belt friction-drives the photosensitive drums for rotation and has the developed images transferred thereon. Timing for exposing the second photosensitive drums is controlled based on a first surface distance from an exposure light irradiated position to a primary transfer position of the first photosensitive drum, and a second surface distance from an exposure light irradiated position of each second photosensitive drum to a primary transfer position thereof.

Description

technical field [0001] The present invention relates to an electrophotographic image forming apparatus that suppresses occurrence of color shift in an image and a control method thereof. Background technique [0002] In a tandem type electrophotographic image forming apparatus including photosensitive drums, transfer positions at which images are primarily transferred from the respective photosensitive drums to an intermediate transfer member are different among the photosensitive drums. Therefore, if the timing at which the electrostatic latent image starts to be formed on each photosensitive drum is not adjusted so as to be consistent between colors, the transferred image formed on the intermediate transfer member is shifted between colors, resulting in image color shift. shift, which is a positional shift between images of respective colors formed on a recording sheet. To prevent this problem, it is necessary to transfer the image already transferred onto the intermediat...

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Problems solved by technology

[0014] In addition, the technology disclosed in Japanese Patent Laid-Open No. 2002-333752 is also characterized in that even if the speed of the intermediate transfer member varies, for example, due to impact generated when the recording sheet is fed into the secondary transfer portion of the intermediate transfer member At the same time, it is still possible to ensure that the respective images on the photosensitive drum and the image on the intermediate transfer member overlap, so the possibility of image defects caused by the first transfer is reduced

[0015] However, the timing shift in which the electrostatic latent image will start to be formed between the photosensitive drums is used for the period required to transfer the image already transferred on the intermediate transfer member from one photosensitive drum to the next in order to prevent image color from appearing In the method of offset, there is such a problem that the period required for the latent image and the resulting image formed by developing on each photosensitive drum to advance from the exposure light irradiation position to the primary transfer position, and the time required to move the intermediate transfer member onto the intermediate transfer member. There is a difference in the time period required for the transferred image to be transferred from one photosensitive drum to another, the degree of which corresponds to the change in the relative speed of the photosensitive drum and the intermediate transfer member

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