Patent ID: 11892791
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 9:
10. An image forming apparatus comprising:
first and second image forming portions each including a rotatable photosensitive member, a charging portion configured to electrically charge a surface of the photosensitive member, and a developing member configured to develop an electrostatic latent image on the photosensitive member with toner into a toner image in contact with a surface of the photosensitive member;
an exposure portion configured to expose the charged surface of the photosensitive member of each of the first and second image forming portions to light to form the electrostatic latent image on the photosensitive member of each of the first and second image forming portions;
an intermediary transfer member which is configured to form a transfer portion in contact with the surface of the photosensitive member of each of the first and second image forming portions and to convey the toner image transferred from the photosensitive member in the transfer portion of each of the first and second image forming portions, for being secondary-transferred onto a recording material in a secondary transfer portion and which is rotatable in a predetermined rotational direction;
a contact and separation portion configured to move the developing member of each of the first and second image forming portions to a contact position in which the developing member contacts the surface of the photosensitive member of each of the first and second image forming portions and a separated position where the developing member is separated from the surface of the photosensitive member of each of the first and second image forming portions;
a charging voltage applying portion configured to apply, to the charging portion of each of the first and second image forming portions, a charging voltage for charging the photosensitive member;
a transfer voltage applying portion configured to apply, to the transfer portion of each of the first and second image forming portions, a transfer voltage for transferring the toner image from the photosensitive member;
a detecting portion configured to detect the toner image, formed on the photosensitive member, on the photosensitive member or the intermediary transfer member; and
a controller capable of controlling the contact and separation portion, the charging voltage applying portion, the transfer voltage applying portion, and the exposure portion,
wherein toner remaining on the photosensitive member without being transferred onto the intermediary transfer member is collected by the developing member, and with respect to the rotational direction, the photosensitive member of the second image forming portion is positioned downstream of the first image forming portion and upstream of the secondary transfer portion,
wherein the controller is capable of executing:
an operation in an image forming mode in which the controller carries out control so that the toner image to be formed on the recording material in each of the first and second image forming portions is formed, and
an operation in a detecting mode in which the controller carries out control so that a predetermined instruction to position the developing member in the separated position is sent to the contact and separation portion in each of the first and second image forming portions and an electrostatic latent image for a test pattern is formed on the photosensitive member in each of the first and second image forming portions and then so that in a case that the developing member in at least one of the first and second image forming portions is positioned in the contact position in accordance with the predetermined instruction without being positioned in the separated position under application of the transfer voltage to the transfer portion when a region of the test pattern on the surface of the photosensitive member contacts the intermediary transfer member in each of the first and second image forming portions, a toner image for the test pattern formed by developing the electrostatic latent image for the test pattern with toner is detected by the detecting portion,
wherein in the operation in the detecting mode, the region of the test pattern on the surface of the photosensitive member of the first image forming portion is defined as a first region, the region of the test pattern on the surface of the photosensitive member of the second image forming portion is defined as a second region, a region on a surface of the intermediary transfer member contacting the first region is defined as a third region, and a region on the surface of the intermediary transfer member contacting the second region is defined as a fourth region,
wherein the controller carries out control so that the third region and the fourth region do not overlap with each other, and
wherein the controller carries out control so that in the second image forming portion, an absolute value of a difference between a potential of a non-image portion on the photosensitive member and a potential of the transfer voltage in the operation in the detecting mode is lower than a value of a difference between a potential of the non-image portion on the photosensitive member and a potential of the transfer voltage in the operation in the image forming mode.