JP7472657B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

Conventionally, in image forming devices, a configuration is known in which an image detection unit is provided at a position facing an image carrier such as an intermediate transfer belt. The image detection unit detects the image formed on the image carrier. For example, Patent Document 1 discloses a configuration having two image detection units facing both ends of the image carrier in the width direction.

JP 2013-41162 A

The image carrier comes into contact with the recording medium at the transfer nip where the image is transferred to the recording medium. However, foreign matter such as dust may adhere to the edge of the recording medium, and such foreign matter is likely to adhere to the position of the image carrier that corresponds to the edge of the transfer area.

Therefore, if the image detection unit is located at a position corresponding to the edge of the transfer area, there is a problem that the image detection unit will erroneously detect the image due to adhesions (the above-mentioned foreign matter) on the image carrier. In particular, when the recording medium is a continuous paper with multiple layers bonded together, such as tack paper, the glue that protrudes from the edge of the recording medium adheres to the image carrier, and the above problem occurs significantly.

The object of the present invention is to provide an image forming apparatus capable of suppressing erroneous detection by the image detection unit caused by adhesion of matter to the image carrier.

The image forming apparatus according to the present invention comprises:
an image carrier that carries an image to be transferred to a recording medium and conveys the image toward a transfer nip;
two or more image detection units disposed opposite to the image carrier at different positions in a width direction of the image carrier and detecting an image on a surface of the image carrier , the two or more image detection units being disposed at positions having different distances from a center line in the width direction of a transfer area corresponding to a contact position of the transfer nip of the image carrier with the recording medium ;
a selection unit that does not select an image detection unit in which a distance in the width direction between an end of the transfer area in the width direction and the image detection unit is within a predetermined distance, and selects an image detection unit in which the distance is greater than the predetermined distance;
Equipped with.

This invention makes it possible to suppress erroneous detection by the image detection unit caused by adhesions on the image carrier.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram showing a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 2 is a diagram showing a portion where two image detection units and an intermediate transfer belt face each other. 5A and 5B are diagrams illustrating an example of a patch image formed on an intermediate transfer belt. 5A and 5B are diagrams illustrating an example of a patch image formed on an intermediate transfer belt. 6A and 6B are diagrams illustrating an example of an inclined patch image formed on an intermediate transfer belt. 10 is a flowchart showing an example of an operation of selection control of an image detection unit in the image forming apparatus. FIG. 2 is a diagram showing a portion where three image detection units face an intermediate transfer belt.

The following describes in detail an embodiment of the present invention with reference to the drawings. FIG. 1 is a diagram showing an outline of the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a diagram showing the main parts of the control system of the image forming apparatus 1 according to this embodiment.

The image forming device 1 is a device that uses tack paper S1, such as continuous paper or long paper shown by the thick line in FIG. 1, or paper S2 (non-tack paper) as the recording medium S, and forms an image on the recording medium S. The tack paper S1 is made up of three layers: a surface layer, an adhesive layer, and a release layer, and is fed into the image forming device 1 from a paper feeder 2 that is configured separately from the image forming device 1, for example.

The image forming apparatus 1 shown in Figures 1 and 2 is an intermediate transfer type color image forming apparatus that utilizes electrophotographic process technology. That is, the image forming apparatus 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 onto the intermediate transfer belt 421, superimposes the four color toner images on the intermediate transfer belt 421, and then secondarily transfers the images onto the recording medium S to form an image.

The image forming device 1 also employs a tandem system in which photoconductor drums 413 corresponding to the four colors YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and each color toner image is transferred sequentially to the intermediate transfer belt 421 in a single step.

As shown in FIG. 2, the image forming device 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, an image detection unit 200, and a control unit 101.

The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, etc. The CPU 102 reads out a program corresponding to the processing contents from the ROM 103, loads it into the RAM 104, and centrally controls the operation of each block of the image forming device 1 in cooperation with the loaded program. At this time, various data stored in the memory unit 72 is referenced. The memory unit 72 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

The control unit 101 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. The control unit 101 receives, for example, image data transmitted from an external device, and forms an image on the recording medium S based on this image data (input image data). The communication unit 71 is composed of, for example, a communication control card such as a LAN card.

As shown in FIG. 1, the image reading unit 10 is configured with an automatic document feeder 11, also known as an ADF (Auto Document Feeder), and a document image scanning device 12 (scanner), etc.

The automatic document feeder 11 transports the document D placed on the document tray using a transport mechanism and sends it to the document image scanning device 12. The automatic document feeder 11 makes it possible to continuously read the images (including both sides) of multiple documents D placed on the document tray all at once.

The document image scanning device 12 optically scans the document transported from the automatic document feeder 11 onto the contact glass or the document placed on the contact glass, and forms an image of the reflected light from the document on the light receiving surface of a CCD (Charge Coupled Device) sensor 12a to read the document image. The image reading unit 10 generates input image data based on the results of the reading by the document image scanning device 12. This input image data is subjected to a predetermined image processing in the image processing unit 30.

As shown in FIG. 2, the operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation statuses of each function, etc. according to a display control signal input from the control unit 101. The operation unit 22 has various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 101.

The image processing unit 30 includes a circuit that performs digital image processing on the input image data according to initial settings or user settings. For example, under the control of the control unit 101, the image processing unit 30 performs gradation correction based on gradation correction data (gradation correction table). In addition to gradation correction, the image processing unit 30 also performs various correction processes such as color correction and shading correction, as well as compression processing, on the input image data. The image forming unit 40 is controlled based on the image data that has been subjected to these processes.

As shown in FIG. 1, the image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K, and an intermediate transfer unit 42 for forming images using color toners of the Y, M, C, and K components based on input image data.

Image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are indicated with the same reference numerals, and when distinguishing between them, the reference numerals are followed by Y, M, C, or K. In FIG. 1, reference numerals are only assigned to the components of image forming unit 41Y for the Y component, and reference numerals are omitted for the components of the other image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, and a drum cleaning device 415.

The photoconductor drum 413 is, for example, an organic photoconductor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal base.

The control unit 101 rotates the photoconductor drum 413 at a constant peripheral speed by controlling the drive current supplied to a drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 is, for example, a charger, and generates a corona discharge to uniformly charge the surface of the photoconductive photoconductor drum 413 to a negative polarity.

The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor drum 413 with laser light corresponding to the image of each color component. As a result, an electrostatic latent image of each color component is formed in the image area on the surface of the photoconductor drum 413 irradiated with the laser light due to the potential difference with the background area.

The developing device 412 is a two-component reversible developing device that visualizes the electrostatic latent image by depositing the developer of each color component onto the surface of the photoconductor drum 413 to form a toner image.

The developing device 412 is applied with, for example, a DC developing bias having the same polarity as the charging polarity of the charging device 414, or a developing bias in which an AC voltage is superimposed with a DC voltage having the same polarity as the charging polarity of the charging device 414. As a result, reversal development is performed in which toner adheres to the electrostatic latent image formed by the exposure device 411.

The drum cleaning device 415 is in contact with the surface of the photosensitive drum 413 and has a flat drum cleaning blade 415A made of an elastic material, and removes toner remaining on the surface of the photosensitive drum 413 that has not been transferred to the intermediate transfer belt 421.

The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, and a belt cleaning device 426. The intermediate transfer belt 421 corresponds to the "image carrier" of the present invention.

The intermediate transfer unit 42 is composed of an endless belt, stretched in a loop around multiple support rollers 423. At least one of the multiple support rollers 423 is a drive roller, and the others are driven rollers. For example, it is preferable that roller 423A, which is arranged downstream in the belt running direction from primary transfer roller 422 for K component, is the drive roller. This makes it easier to maintain a constant running speed of the belt in the primary transfer nip. As drive roller 423A rotates, intermediate transfer belt 421 runs at a constant speed in the direction of arrow A.

The primary transfer roller 422 is disposed on the inner peripheral side of the intermediate transfer belt 421, facing the photoconductor drum 413 of each color component. The primary transfer roller 422 is pressed against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched therebetween, forming a primary transfer nip for transferring the toner image from the photoconductor drum 413 to the intermediate transfer belt 421.

The secondary transfer roller 424 is disposed on the outer circumferential surface side of the intermediate transfer belt 421, facing the backup roller 423B, which is disposed downstream of the drive roller 423A in the belt running direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 sandwiched therebetween, thereby forming a secondary transfer nip for transferring a toner image from the intermediate transfer belt 421 to the recording medium S.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed and primarily transferred onto the intermediate transfer belt 421. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and a charge of the opposite polarity to the toner is applied to the back side of the intermediate transfer belt 421, i.e., the side that contacts the primary transfer roller 422, so that the toner image is electrostatically transferred to the intermediate transfer belt 421.

Then, when the recording medium S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the recording medium S. Specifically, a secondary transfer bias is applied to the backup roller 423B, and a charge of the same polarity as the toner is applied to the surface side of the recording medium S, that is, the side that contacts the intermediate transfer belt 421, so that the toner image is electrostatically transferred to the recording medium S, and the recording medium S is transported toward the fixing unit 60.

The belt cleaning device 426 removes residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Note that instead of the secondary transfer roller 424, a so-called belt-type secondary transfer unit may be used in which the secondary transfer belt is stretched in a loop around multiple support rollers including the secondary transfer roller.

An image detection unit 200 is provided at a position facing the intermediate transfer belt 421 in the intermediate transfer unit 42. By feeding back the detection results of the image detection unit 200 to the image formation conditions (control unit 101), it is possible to improve and stabilize the image quality in the image forming unit 40. Details of the image detection unit 200 will be described later.

The fixing section 60 includes an upper fixing section 60A having a fixing surface side member arranged on the fixing surface of the recording medium S, i.e., the surface on which the toner image is formed, a lower fixing section 60B having a back surface side support member arranged on the back surface of the recording medium S, i.e., the surface opposite the fixing surface, and a heating source 60C. The back surface side support member is pressed against the fixing surface side member to form a fixing nip that clamps and transports the recording medium S.

The fixing unit 60 fixes the toner image to the recording medium S by heating and pressurizing the recording medium S, which has been transported after the toner image has been secondarily transferred, in a fixing nip. The fixing unit 60 is disposed as a unit within the fixing device F. The fixing device F may also be provided with an air separation unit that blows air to separate the recording medium S from the fixing surface side member or the back surface side support member.

The paper transport section 50 includes a paper feed section 51, a paper discharge section 52, and a transport path section 53. The three paper feed tray units 51a to 51c that make up the paper feed section 51 store paper S (standard paper, special paper) identified based on basis weight, size, etc., by preset type. The transport path section 53 has multiple transport rollers, including a pair of registration rollers 53a.

The sheets S2 stored in the paper feed tray units 51a to 51c are sent out one by one from the top and transported to the image forming unit 40 by the transport path unit 53. At this time, the inclination of the fed sheets S2 is corrected and the transport timing is adjusted by the registration roller unit in which the registration roller pair 53a is arranged. Then, in the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred all at once onto one side of the sheets S2, and the fixing process is performed in the fixing unit 60.

The tack paper S1 fed from the paper feeder 2 to the image forming device 1 is transported to the image forming unit 40 by the transport path section 53. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred all at once onto one side of the tack paper S1, and a fixing process is performed in the fixing unit 60. The recording medium S on which the image has been formed is discharged outside the machine by the paper discharge section 52 equipped with a paper discharge roller 52a.

Next, the image detection unit 200 will be described in detail. Figure 3 shows the opposing portions of the two image detection units 200 and the intermediate transfer belt 421.

As shown in FIG. 3, the image detection units 200 are known sensors that detect an image on the surface of the intermediate transfer belt 421, and two of them are provided side by side in the width direction of the intermediate transfer belt 421. The width direction of the intermediate transfer belt 421 is a direction perpendicular to the transport direction of the intermediate transfer belt 421 and parallel to the surface of the intermediate transfer belt 421. In the example shown in FIG. 3, the width direction of the intermediate transfer belt 421 is the left-right direction in FIG. 3.

The two image detection units 200 are disposed facing the intermediate transfer belt 421 at different positions in the width direction of the intermediate transfer belt 421. Specifically, the two image detection units 200 are disposed at positions at different distances from the center line C in the width direction of the transfer area R on the intermediate transfer belt 421.

The transfer area R is the area corresponding to the transfer nip of the intermediate transfer belt 421, i.e., the contact position with the recording medium S. The center line C is at a substantially constant position because the center in the width direction of the recording medium S passing through the transfer nip is substantially constant on the transport path regardless of the size of the recording medium S. The center line C may also be located within a small range that includes a position corresponding to the center position in the width direction of the recording medium S.

The two image detection units 200 are arranged on either side of the center line C. In the example shown in FIG. 3, the first image detection unit 200A on the left side of the center line C is arranged farther from the center line C than the second image detection unit 200B on the right side of the center line C. In other words, the distance L1 between the first image detection unit 200A and the center line C is longer than the distance L2 between the second image detection unit 200B and the center line C.

The control unit 101 selects, from the two image detection units 200, the image detection unit 200 that detects the image on the surface of the intermediate transfer belt 421, based on the widthwise distance between the end of the transfer area R in the widthwise direction and the image detection unit 200. The control unit 101 corresponds to the "selection unit" of the present invention.

Specifically, the control unit 101 does not select an image detection unit 200 in which the widthwise distance between the end of the transfer area R and the image detection unit 200 is within a predetermined distance, but selects an image detection unit 200 in which the distance is greater than the predetermined distance.

The widthwise distance between the end of the transfer area R in the width direction and the image detection unit 200 is the distance between the image detection unit 200 and one of the ends R1, R2 in the width direction of the transfer area R, which is closer to the image detection unit 200. R1 is the left end of the transfer area R in the width direction and corresponds to the end closer to the first image detection unit 200A. R2 is the right end of the transfer area R in the width direction and corresponds to the end closer to the second image detection unit 200B.

Specifically, the distance in the width direction between the end of the transfer area R in the width direction and the first image detection unit 200A is the distance L3 between R1 and the first image detection unit 200A. Also, the distance in the width direction between the end of the transfer area R in the width direction and the second image detection unit 200B is the distance L4 between R2 and the second image detection unit 200B.

The specified distance is the distance within which there is a possibility that adhesion may occur from the edge of the recording medium S to the intermediate transfer belt 421 as the recording medium S passes through the transfer nip, and is a distance that can be set arbitrarily based on experiments, etc. In the example shown in FIG. 3, the specified distance is set to, for example, L5. In addition, the specified distance is set on both the left and right sides of the edges R1 and R2 of the transfer area R.

When the recording medium S is tack paper, the adhering matter is, for example, glue that protrudes from the edge when the tack paper is crushed in the transfer nip, or foreign matter such as dust that has adhered to the edge. When the recording medium S is paper, the adhering matter is foreign matter such as dust or paper powder that has adhered to the edge due to loosening of fibers at the edge of the paper.

For example, assume that the first image detection unit 200A is located within a predetermined distance from the edge of the transfer area R, and the second image detection unit 200B is located at a distance greater than the predetermined distance from the edge of the transfer area R.

In this case, the detection result of the image detected by the first image detection unit 200A may be affected by the attached object, and there is a risk that the image may not be detected accurately.

In this case, the control unit 101 does not select the first image detection unit 200A as the image detection unit 200 that detects an image, and selects the second image detection unit 200B as the image detection unit 200 that detects an image.

As a result, the first image detection unit 200A is not used to detect the image, and therefore image detection in the image detection unit 200 can be prevented from being affected by the attached matter on the intermediate transfer belt 421. Then, the second image detection unit 200B, which is positioned in a position that is unlikely to be affected by the attached matter, is used to detect the image, and therefore image detection can be performed without being affected by the attached matter.

In other words, in this embodiment, it is possible to suppress erroneous detection by the image detection unit 200 caused by adhesions on the intermediate transfer belt 421.

The difference in distance between the two image detection units 200 is greater than twice the above-mentioned predetermined distance. For example, the distance between the image detection unit 200 and the center line C in an image detection unit 200 not selected by the control unit 101 is within the range of (W/2-L5) to (W/2+L5), where W is the width of the recording medium S and L5 is the predetermined distance. Since the minimum value of this distance for image detection units 200 not selected by the control unit 101 is (W/2-L5), in order for at least one image detection unit 200 to be selected by the control unit 101, the condition is that the distance for that image detection unit 200 is shorter than (W/2-L5) or longer than (W/2+L5).

Therefore, by making the distance difference between the two image detection units 200 greater than twice the above-mentioned predetermined distance (L5), it is possible to prevent the control unit 101 from not selecting all of the image detection units 200, and image detection by the image detection units 200 can be performed reliably and accurately.

It is also preferable to position the two image detection units 200 so that the distance difference between the two image detection units 200 is greater than twice the predetermined distance for all types of recording media S that can be used with the image forming device 1.

This makes it possible to prevent the condition that the distance difference between the two image detection units 200 is greater than twice the specified distance from being met, depending on the type of recording medium S.

Also, as shown in FIG. 4, the control unit 101 controls the image forming unit 40 to form a patch image on the intermediate transfer belt 421 to be read by the image detection unit 200. The image forming unit 40 corresponds to the "patch image forming unit" of the present invention.

Specifically, the control unit 101 controls the image forming unit 40 to form patch images at positions corresponding to the two image detection units 200, for example.

The two image detection units 200 are arranged at the same position in the transport direction of the intermediate transfer belt 421.

This allows image detection by the two image detection units 200 to be performed at the same time, so that, for example, two patch images can be detected by each of the two image detection units 200 at the same time. As a result, two patch images of different colors can be detected at the same time, improving image detection efficiency.

Note that the four patch images in Figure 4 and other figures are each a different color (e.g., Y, M, C, or K).

Also, as shown in FIG. 5, the control unit 101 controls the image forming unit 40 to change the position where the patch image is formed on the intermediate transfer belt 421 based on the selection result.

For example, if the control unit 101 selects only the second image detection unit 200B as the image detection unit 200 that detects an image, no image is detected by the first image detection unit 200A, so there is no need to form an image at a position corresponding to the first image detection unit 200A.

Therefore, the control unit 101 controls the image forming unit 40 to form a patch image to be formed at a position corresponding to the first image detection unit 200A at a position corresponding to the second image detection unit 200B.

In other words, the control unit 101 controls the image forming unit 40 to form a patch image on the intermediate transfer belt 421 so that the number of times the patch image is detected in one image detection unit 200 is changed based on the selection result. In the example shown in FIG. 5, the number of times the second image detection unit 200B detects is changed from 2 to 4, and the number of times the first image detection unit 200A detects is changed from 2 to 0.

By doing this, the image detection unit 200 can reliably detect all patch images that need to be detected.

The control unit 101 also controls the detection of the inclination of the image on the intermediate transfer belt 421 using the two image detection units 200. The control unit 101 corresponds to the "inclination detection unit" of the present invention.

Specifically, as shown in FIG. 6, the control unit 101 controls the image forming unit 40 to form tilt patch images for tilt detection at positions corresponding to each of the two image detection units 200. Then, the control unit 101 detects the amount of misalignment of each tilt patch image based on the difference in detection timing of the tilt patch image in each of the two image detection units 200, and detects the tilt of the image on the intermediate transfer belt 421.

In addition, if at least one of the two image detection units 200 is not selected as the image detection unit 200 to be used for image detection, the control unit 101 does not perform control to detect the tilt of the image.

As a result, if there is a risk of the image detection unit 200 making an erroneous detection due to the influence of adhesions on the intermediate transfer belt 421, the image tilt is not detected, thereby preventing inaccurate image tilt detection control.

An example of the operation of the selection control of the image detection unit 200 in the image forming device 1 configured as above will be described. FIG. 7 is a flowchart showing an example of the operation of the selection control of the image detection unit 200 in the image forming device 1. The process in FIG. 7 is executed as appropriate, for example, when the control unit 101 receives a command to form a patch image on the intermediate transfer belt 421.

As shown in FIG. 7, the control unit 101 determines whether the first image detection unit 200A is located within a predetermined distance from the edge of the transfer area R (step S101). If the result of the determination is that the first image detection unit 200A is not located within the predetermined distance (step S101, NO), the control unit 101 selects the second image detection unit 200B (step S102).

On the other hand, if the first image detection unit 200A is located within the predetermined distance (step S101, YES), the control unit 101 determines whether the second image detection unit 200B is located within the predetermined distance from the edge of the transfer area R (step S103).

If the determination result is that the second image detection unit 200B is not located within the predetermined distance (step S103, NO), the control unit 101 selects the first image detection unit 200A (step S104).

On the other hand, if the second image detection unit 200B is located within the predetermined distance (step S103, YES), the control unit 101 selects the first image detection unit 200A and the second image detection unit 200B (two image detection units 200) (step S105). After step S104 or step S105, this control ends.

According to the present embodiment configured as described above, it is possible to suppress erroneous detection by the image detection unit 200 caused by adhesions on the intermediate transfer belt 421.

In addition, since the distance difference between the two image detection units 200 is greater than twice the predetermined distance, it is possible to prevent the control unit 101 from not selecting an image detection unit 200, and image detection can be performed reliably and accurately.

In addition, continuous paper such as tack paper is placed in the paper feeder 2 in a rolled state, but such continuous paper is often stored with the ends of its width facing the ground, making it easy for foreign matter to adhere to the ends.

In this embodiment, even if such continuous paper is used and an image detection unit 200 is provided in a position close to the transfer area R corresponding to the end, the image can be detected by another image detection unit 200. As a result, false detection of the image can be further suppressed, and the image can be detected accurately.

In the above embodiment, two image detection units 200 are provided, but the present invention is not limited to this, and it is sufficient that two or more image detection units are provided. For example, as shown in FIG. 8, the image detection unit 200 may have a third image detection unit 200C in addition to the first image detection unit 200A and the second image detection unit 200B.

The third image detection unit 200C is provided to the left of the center line C (the first image detection unit 200A side), and is positioned such that the distance L6 from the center line C is smaller than the distance L2 between the second image detection unit 200B and the center line C.

Here, when a patch image is formed on the intermediate transfer belt 421 and detected by the image detection unit 200, it is assumed that the setting is such that the patch image is detected using the first image detection unit 200A and the second image detection unit 200B.

For example, let us say that of the three image detection units 200, only the first image detection unit 200A is not selected as the image detection unit 200 to be used for image detection. In this case, the control unit 101 changes the position at which the patch image is formed on the intermediate transfer belt 421 according to the selection result. Specifically, the control unit 101 controls the image forming unit 40 to form the patch image at a position corresponding to the second image detection unit 200B and the third image detection unit 200C.

This allows the available image detection units 200 to be used effectively, and also reduces the overall number of times patch images are detected.

In addition, when a tilt patch image is formed on the intermediate transfer belt 421 and the tilt of the image on the intermediate transfer belt 421 is detected using the image detection unit 200, the control unit 101 selects the image detection unit 200 that detects the tilt of the image based on the selection result.

For example, if, of the three image detection units 200, only the first image detection unit 200A is not selected as the image detection unit 200 to be used for image detection, the control unit 101 selects the second image detection unit 200B and the third image detection unit 200C as the image detection units 200 that detect the inclination of the image.

This allows the image tilt to be detected reliably.

The control unit 101 also selects an image detection unit 200 that detects the tilt of the image based on the distance of each image detection unit 200. Specifically, the control unit 101 selects the two image detection units 200 that are the furthest away from the three image detection units 200. In the example shown in FIG. 8, the first image detection unit 200A and the second image detection unit 200B are selected.

This makes it easier to detect the amount of misalignment of the tilt patch image, improving the accuracy of detecting the tilt of the image.

In addition, in the above embodiment, the control unit 101 constitutes the selection unit and the tilt detection unit, but the present invention is not limited to this, and the selection unit and the tilt detection unit may each be provided separately from the control unit. Furthermore, if tilt detection is not required, it is not necessary to provide a tilt detection unit.

In addition, in the above embodiment, the two image detection units 200 are located on either side of the center line C, but the present invention is not limited to this, and all image detection units may be located on only one side of the center line C.

In addition, in the above embodiment, the image detection unit 200 is provided inside the transfer area R, but the present invention is not limited to this, and the image detection unit may be provided outside the transfer area R.

In addition, in the above embodiment, the two image detection units 200 are arranged at the same position in the transport direction of the intermediate transfer belt 421, but the present invention is not limited to this, and they do not have to be arranged at the same position.

In addition, in the above embodiment, the intermediate transfer belt 421 is exemplified as an image carrier, but the present invention is not limited to this, and an image carrier other than the intermediate transfer belt may be used as long as it is an image carrier that transports an image toward the transfer nip. Also, in addition to the image carrier that contacts the recording medium at the transfer nip, such as the intermediate transfer belt, the image carrier may be an image carrier that indirectly contacts the recording medium at the transfer nip via the intermediate transfer belt, such as the photosensitive drum shown in FIG. 1.

In addition, the above embodiments are merely examples of how the present invention can be implemented, and the technical scope of the present invention should not be interpreted in a limiting manner based on these. In other words, the present invention can be implemented in various forms without departing from its gist or main features.

REFERENCE SIGNS LIST 1 Image forming apparatus 40 Image forming section 101 Control section 200 Image detection section 200A First image detection section 200B Second image detection section 421 Intermediate transfer belt C Center line R Transfer area

Claims (8)

an image carrier that carries an image to be transferred to a recording medium and conveys the image toward a transfer nip;
two or more image detection units disposed opposite to the image carrier at different positions in a width direction of the image carrier and detecting an image on a surface of the image carrier , the two or more image detection units being disposed at positions having different distances from a center line in the width direction of a transfer area corresponding to a contact position of the transfer nip of the image carrier with the recording medium ;
a selection unit that does not select an image detection unit in which a distance in the width direction between an end of the transfer area in the width direction and the image detection unit is within a predetermined distance, and selects an image detection unit in which the distance is greater than the predetermined distance;
Equipped with
Image forming device. a distance difference between two image detection units included in the two or more image detection units is greater than twice the predetermined distance;
The image forming apparatus according to claim 1 . a tilt detection unit that detects a tilt of an image on the image carrier by using two image detection units;
the tilt detection unit does not detect a tilt of the image when at least one of the two image detection units is an image detection unit that is not selected by the selection unit;
3. The image forming apparatus according to claim 1 or 2 . the tilt detection unit selects an image detection unit that detects a tilt of the image from among the two or more image detection units based on a selection result of the selection unit.
The image forming apparatus according to claim 3 . a patch image forming unit that forms a patch image on the image carrier to be read by the image detection unit,
the patch image forming unit changes a position on the image carrier where the patch image is formed in response to a selection result of the selection unit.
The image forming apparatus according to claim 1 . the patch image forming unit forms the patch image on the image carrier such that the number of times the patch image is detected by one image detection unit is changed based on a selection result of the selection unit.
The image forming apparatus according to claim 5 . the two or more image detection units are disposed at the same position in a transport direction of the image carrier;
The image forming apparatus according to any one of claims 1 to 6 . The recording medium is continuous paper.
The image forming apparatus according to any one of claims 1 to 7 .

Images