JP2018054653A - Image formation device - Google Patents

Abstract

In a tandem type image forming apparatus, when performing monochrome printing with a color image bearing member in contact, the amount of color toner in a developing unit does not reach the amount necessary for cleaning blade protection operation. In this case, the image formation was stopped. Therefore, the image formation that can be executed if the image carrier is separated is stopped, and the usability is impaired. When a color toner whose remaining amount is insufficient is detected by a toner remaining amount detecting unit, the separation mechanism performs separation so that only a single image carrier is brought into contact with the belt member and the transfer member. Therefore, when the monochrome mode is realized and the image is formed in the monochrome mode, whether or not printing is possible is determined according to the basis weight of the printing paper detected by the paper type detection unit, and it is determined that printing is not possible during monochrome mode printing. If the user presses, the user selects whether to continue printing in the forced printing mode or to cancel printing. [Selection] Figure 4

Description

  The present invention relates to an image forming apparatus.

  Image forming apparatuses that form color images are becoming mainstream in response to demands from the market. A color image is obtained by sequentially superimposing a plurality of photosensitive drums corresponding to each color and each color toner image obtained by developing an electrostatic latent image formed on each photosensitive drum on a transfer material. Hereinafter, this color image forming apparatus is a tandem type image forming apparatus.

  In the tandem type image forming apparatus described above, from the viewpoint of the life of the photosensitive drum, in the monochrome mode for forming a monochrome image, only the black photosensitive drum is brought into contact with the intermediate transfer belt, and the color photosensitive member for color image formation is used. The drum (magenta, cyan, yellow) is separated from the intermediate transfer belt and stopped to increase the life of the color photosensitive drum.

  As described above, while color image formation has become the mainstream in recent years, the market demand for paper thickness has further increased. This means that there is a demand for an image forming apparatus that can provide a certain quality of image quality on any kind of paper. However, when an image is formed on a paper of a predetermined thickness or more, usually a paper called “thick paper”, a streak-like line called so-called banding appears on the image and the image quality deteriorates. is there. The following describes the process of banting.

  As described above, in the tandem image forming apparatus, from the viewpoint of the life of the photosensitive drum, in the monochrome mode, the color photosensitive drum is separated from the intermediate transfer belt, and only the black photosensitive drum is brought into contact with the intermediate transfer belt. Since the intermediate transfer belt rotates in a state in which no load is applied, the intermediate transfer belt is very weak against an external load. When thick paper enters the secondary transfer section in this state, the load fluctuation of the intermediate transfer belt due to the entry of the paper becomes noticeable. This appears as a fluctuation in the speed of the intermediate transfer belt, and ultimately causes a reduction in image quality called banding.

  In order to reduce banding, a photosensitive drum for black and a photosensitive drum for color, an intermediate transfer belt in contact with these photosensitive drums, and a toner image formed on each photosensitive drum are provided for each photosensitive drum. An intermediate transfer belt in an image forming apparatus in which a primary transfer means for primary transfer to an intermediate transfer belt and all photosensitive drums including a black photosensitive drum are brought into contact with the intermediate transfer belt when forming an intermediate transfer image. A load applying means for selectively applying a load to the intermediate transfer belt is provided upstream of the contact portion between the black photosensitive drum and the intermediate transfer belt in the rotation direction of the intermediate transfer belt. An image forming apparatus characterized by applying a load to an intermediate transfer belt has been proposed (Patent Document 1).

  The load applying means is a color photosensitive drum that exists upstream of the black photosensitive drum in the rotation direction of the intermediate transfer belt. Here, when three color photosensitive drums (yellow, magenta, cyan) are used as load applying means, banding can be sufficiently reduced to print thick paper. When a color photosensitive drum is used as a load applying unit, a cleaning blade as a cleaning unit continues to touch the rotating photosensitive drum without a lubricant. If the cleaning blade continues to touch the rotating photosensitive drum in the absence of lubricant for a certain number of sheets or more, the cleaning blade will turn over and be damaged.

  For the purpose of preventing damage to the cleaning blade, the toner in the developing device that serves to replenish the latent image on the photosensitive drum is discharged to the photosensitive drum as a specific image pattern. Cleaning blade protection is realized by the cleaning blade collecting the discharged toner.

  When the color photosensitive drum is in contact with the intermediate transfer belt to apply a load, the cleaning blade protection operation cannot be performed if the amount of color toner in the developing unit does not reach the amount required for the cleaning blade protection operation. Therefore, in the case of thick paper, the image formation is stopped, and in the case of plain paper, a color photosensitive drum is separated to form a monochrome image.

Japanese Patent No. 5223468

  However, in a tandem type image forming apparatus, when printing thick paper in monochrome mode with a color photosensitive drum in contact, the amount of color toner in the developing device is the amount necessary for the cleaning blade protection operation. If not, the image formation was stopped. Even if there was paper other than cardboard, printing was stopped, and usability was impaired.

In order to solve the above problems, an image forming apparatus according to claim 1 of the present invention provides:
An image carrier for black (209K);
A plurality of color image carriers (209Y, 209M, 209C);
An intermediate transfer member (230) in contact with these image carriers,
A primary transfer means (211) provided for each image carrier and primary-transferring the toner image formed on the image carrier to the intermediate transfer member;
A toner remaining amount detecting means (403) for detecting the remaining amount of toner for each color;
A paper type detection means (40) for determining the type of paper on which image formation is performed;
A print control unit (302) for forming an image based on the print data;
Operation display means (40) for performing input from the user and output to the user;
Contact and separation means (501) for operating a primary transfer means for color to contact and separate the image carrier for color from the intermediate transfer body;
A first monochrome mode in which only the black image carrier is brought into contact with the intermediate transfer member when forming a monochrome image;
When forming a color image, a color mode in which the entire image carrier including the image carrier for black is brought into contact with the intermediate transfer member by the contact / separation unit;
The black image carrier is provided on the upstream side in the rotation direction of the intermediate transfer member with respect to the contact portion between the black image carrier and the intermediate transfer member, and the black image carrier is formed by the contact / separation means when forming a monochrome image. A second monochrome mode in which the entire image carrier including the body is brought into contact with the intermediate transfer member;
With
In the first monochrome mode,
When color toner whose remaining amount is insufficient is detected by the toner remaining amount detecting means,
Determining whether the contact / separation means can be executed according to the paper type of the printing paper detected by the paper type detection means;
When it is determined that the contact / separation unit needs to be executed when forming a monochrome image, the operation display unit selects whether to switch to the forced printing mode or to stop printing.

An image forming apparatus according to claim 2 of the present invention is the image forming apparatus according to claim 1,
In the forced printing mode, it is possible to selectively switch whether to print on a paper type different from the designated paper type or to give priority to the designated paper type through an operation display unit.

  According to the image forming apparatus of the present invention, one of the color toners has a remaining amount equal to or less than the amount necessary for the cleaning blade protection operation, and the paper type causes banding in the monochrome mode in which all the color primary transfer portions are separated. Even in this case, when the user determines to continue printing, a monochrome image can be formed. As a result, usability is improved.

1 is a main cross-sectional view of an image forming apparatus according to an embodiment. 1 is a system block diagram that governs overall control of an image forming apparatus according to an exemplary embodiment. 3 is a block diagram of a print control unit 302 according to the present embodiment. FIG. 3 is a flowchart illustrating an entire image forming process according to the present exemplary embodiment. It is a figure which shows the operation display apparatus 40 of the image forming apparatus which is this embodiment. FIG. 2 is a schematic diagram of the image forming unit according to the present embodiment in a color mode. FIG. 2 is a schematic diagram of an image forming unit according to the present embodiment in a monochrome mode. It is a selection screen when selecting whether or not to continue printing in the operation display device according to the present embodiment. It is a selection screen when selecting the paper type change in the operation display apparatus which is this embodiment.

  Below, the form for implementing this invention is demonstrated. The configuration and means of the apparatus described in the present embodiment are examples for explaining the present invention, and are not limited to the described contents.

[Example]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a configuration diagram showing a longitudinal sectional structure of a main part of an image forming system according to an embodiment of the present invention.

  This image forming apparatus 10 is an image forming apparatus capable of forming a full color image of an intermediate transfer system in which four photosensitive drums 209 are arranged in tandem. The image forming apparatus 10 in FIG. 1 includes an image reader 20 that reads an image from a document and a printing unit 30 that forms the read image on a sheet. The document feeder 200 feeds the documents set upward on the document tray 201 one by one from the top page in order to the left in FIG. 2, passes through a curved path, and moves from the left on the platen glass 219 to the home. The paper is conveyed to the right through the scanner unit 202 at the position, and then discharged toward the paper discharge tray 220.

  When this original passes through the home position of the scanner unit 202 on the platen glass 219 from the left to the right, the original image is read by the scanner unit 202 stored in the home position. When the document passes through the home position of the scanner unit 202, the reading surface of the document is irradiated with light from the scanner unit 202, and reflected light from the document is guided to the lens 206 via the mirrors 203, 204, and 205. The light that has passed through the lens 206 forms an image on the imaging surface of the image sensor 207.

  In this way, by transporting the document so that it passes through the home position of the scanner unit 202 from left to right, the direction perpendicular to the document transport direction is set as the main scanning direction, and the transport direction is set as the sub-scanning direction. An original reading operation is being performed. That is, when the original passes the home position of the scanner unit 202, the original image is read by conveying the original in the sub-scanning direction while reading the original image by the image sensor 207 line by line in the main scanning direction. Do.

  The optically read image is converted into image data by the image sensor 207 and output. Image data output from the image sensor 207 is input to the exposure unit 208 of the printing unit 30 as a video signal. It is also possible to read the document by transporting the document onto the platen glass 219 by the document feeder 200 and stopping at a predetermined position, and scanning the scanner unit 202 from left to right in this state. This reading method is a so-called fixed original reading method.

  When reading a document without using the document feeder 200, first, the user lifts the document feeder 200 to place the document on the platen glass 219, and then scans the scanner unit 202 from left to right. The original is read by. That is, when reading a document without using the document feeder 200, a fixed document reading is performed.

  Hereinafter, in the color mode, all YMCKs are to be operated, and in the monochrome mode, only K operates. The exposure unit 208 of the printing unit 30 modulates and outputs a laser beam based on the video signal input from the image reader 20. The laser light is irradiated onto the photosensitive drum 209 charged by the charger 233. An electrostatic latent image corresponding to the scanned laser beam is formed on the photosensitive drum 209.

  Here, the exposure unit 208 outputs a laser beam so that an erect image (an image that is not a mirror image) is formed during document fixed reading. The electrostatic latent image on the photosensitive drum 209 is visualized as a toner image by toner supplied by the developing sleeve of the developing device 212.

  The intermediate transfer belt 230 as an intermediate transfer member is formed of an endless belt-like film, and is stretched around a driving roller 228, a tension roller 229, and a secondary transfer counter roller 231 as a plurality of stretching members. Intermediate transfer belt 230 is driven to rotate clockwise by drive roller 228. A primary transfer roller 211 is disposed on the inner peripheral surface side of the intermediate transfer belt 230 at a position facing each photosensitive drum 209. The primary transfer roller 211 is pressed against the photosensitive drum 209 via the intermediate transfer belt 230 to form a primary transfer portion (primary transfer nip) where the intermediate transfer belt 230 and the photosensitive drum 209 come into contact with each other.

  The toner image formed by the photosensitive drum 209 is primarily transferred to the intermediate transfer belt 230 by the primary transfer unit. Further, on the outer peripheral surface side of the intermediate transfer belt 230, a secondary transfer roller 232 serving as a roller-type transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 231. The secondary transfer roller 232 is pressed against the secondary transfer counter roller 232 via the intermediate transfer belt 230 to form a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 230 and the secondary transfer roller 231 come into contact with each other. Has been. The toner image on the intermediate transfer member is transferred onto the sheet by the secondary transfer portion.

  In this embodiment, the exposure unit 208, the photosensitive drum 209, the cleaning device 210, the primary transfer roller 211, and the charger 233 are collectively referred to as an image forming unit 234.

  On the other hand, the sheet fed from the upper cassette 215 or the lower cassette 216 provided in the printing unit 30 by the pickup rollers 213 and 214 is conveyed to the registration roller 222 by the vertical pass roller 221. The leading edge of the sheet is detected by the pre-registration sensor 223, and the sheet is temporarily stopped when the registration roller 222 is reached.

  Similarly, the sheet fed from the manual feed tray 224 by the manual pickup roller 217 is also conveyed to the registration roller 222. The manual feed tray 224 includes a manual feed tray paper detection sensor (not shown) for detecting the presence or absence of paper on the manual feed tray, and a length detection sensor (not shown) for detecting the size of the paper feed direction on the manual feed tray. A width detection sensor (not shown) for detecting the size in the width direction orthogonal to the paper transport direction is provided.

  Then, a skew is corrected by creating a loop at the leading edge of the paper that has been transported to the registration roller 222 and once stopped. Thereafter, the registration roller 222 is driven at an arbitrary timing, and the sheet is conveyed to the secondary transfer unit at a timing synchronized with the start of laser beam irradiation. Then, the toner image on the intermediate transfer belt 230 is secondarily transferred to the paper in the secondary transfer portion. The sheet on which the toner image is transferred is conveyed to the fixing unit 226, and the fixing unit 226 fixes the toner image on the sheet by heating and pressing the sheet. The sheet that has passed through the fixing unit 226 is discharged from the printing unit 30 toward the outside of the image forming apparatus via the flapper 218 and the discharge roller 227.

  FIG. 5 is a diagram showing the operation display device 40 in the image forming apparatus of FIG. The operation display device 40 includes a start key 602 for starting an image forming operation, a stop key 603 for interrupting the image forming operation, ten keys 604 to 612 and 614 for setting the number of copies, an ID key 613, and a clear key 615. A reset key 616 and the like are arranged. In addition, a display unit 620 having a touch panel formed thereon is arranged, and a soft key can be created on the screen.

  6 and 7 are schematic views of a tandem type image forming apparatus adopting an indirect transfer system having a plurality of photosensitive drums. FIG. 6 illustrates a state during color printing in which all the photosensitive drums 209 are in contact with the intermediate transfer belt 230, and FIG. 7 illustrates a monochrome mode in which only the black photosensitive drum 209K is in contact with the intermediate transfer belt 230. The same members as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The primary transfer roller separation operation (first transfer separation operation) will be described with reference to FIG. When the eccentric cam 501 is rotated in the direction in which the primary transfer roller holding frame 502 is separated from FIG. 6, the primary transfer roller holding frame 502 is separated from the color photosensitive drums 209Y, 209M, and 209C by the biasing force of the spring 500, and the black primary Only the transfer roller 211K comes into contact with the black photosensitive drum 209K (FIG. 7). As a result, the intermediate transfer belt 230 is in contact with only the black photosensitive drum. This series of operations is called a one-time separation operation.

  The primary transfer roller contact operation (first transfer contact operation) will be described with reference to FIG. When the eccentric cam 501 is rotated in the direction in which the primary transfer roller holding frame 502 is separated from FIG. The primary transfer roller 211 comes into contact with the photosensitive drum 209 (FIG. 6). As a result, the intermediate transfer belt 230 is in contact with all the photosensitive drums 209. This series of operations is called a one-turn contact operation.

  However, as described above, in the monochrome mode as shown in FIG. 7, since only the black photosensitive drum 209K is in contact with the intermediate transfer belt 230, the intermediate transfer belt rotates with a little load. It is in a very weak state against external loads. Therefore, when a sheet having a predetermined thickness or more such as thick paper enters the secondary transfer units 231 and 232 (FIG. 1), or when the sheet enters at a conveyance speed higher than a predetermined speed, the speed is applied to the intermediate transfer belt 230. Since fluctuations are likely to occur, banding is likely to occur. In order to reduce banding, the image forming apparatus of this embodiment has a mode in which a primary transfer roller for color is brought into contact with a paper type to form a monochrome image.

2. Control Mode FIG. 2 is a block diagram showing a control mode of the main part of the image forming apparatus 10 of this embodiment. The image forming apparatus 10 includes a CPU circuit unit 305 that performs overall control of the operation of each unit of the image forming apparatus 10. The CPU circuit unit 305 includes a CPU 306 as a control unit that performs control processing of the image forming apparatus 10. The CPU circuit unit 305 includes a ROM 307 that stores a program for the CPU 306 to operate. The CPU 306 comprehensively controls each of the control units 302, 303, and 304 with a program stored in the ROM 307.

  The CPU circuit unit 305 includes a RAM 308 that is a storage unit used for the CPU 306 to temporarily store data. The CPU circuit unit 305 includes the CPU 306, the ROM 307, and the RAM 308. The external I / F 301 sends a print job input from the computer 300 or the operation display unit 309 to the image processing unit 303. The image reader control unit 304 performs drive control on the scanner unit 202 and the like.

  The image processing unit 303 converts a print job sent from the external I / F 301 or the image reader control unit 304 into image data in one unit or image data in one page in accordance with a control signal from the CPU 306 and prints it. Image data is sent to the control unit. Further, the received print job is stored in the RAM 308 together with the order of reception until the end of the job. The print control unit 302 controls various loads for printing in accordance with a control signal from the CPU 306.

  FIG. 3 shows details of the print control unit 302. A conveyance control unit 401 drives a motor, a roller, a clutch, a solenoid, a flapper, and the like for supplying and conveying paper. The fixing control unit 402 controls the fixing unit 226 to fix the toner on the paper. A sensor detection unit 403 reads the value of a sensor provided in the image forming apparatus. The image formation control unit 409 transfers the toner image to the intermediate transfer belt 230 by the development control unit 405, the photosensitive drum control unit 406, the exposure control unit 407, the charging control unit 408, and the primary transfer control unit 410.

  The secondary transfer control unit 411 transfers the toner image on the intermediate transfer belt 230 to a sheet. The one-time separation / separation operation and the one-time contact operation are performed for each photosensitive drum 209 by the one-time attachment / detachment control unit 412. The operation unit 309 controls the operation display device 40. The operation display unit 309 performs control to pass various inputs from the user made by the operation display device 40 to the external I / F 301. Further, the operation display unit 309 is controlled to receive data from the external I / F 301 that is displayed on the operation display device 40 as a processing result of the CPU circuit unit 305 and notify the user and output the data to the operation display device 40. I do.

  FIG. 4 shows an entire execution flowchart in the image forming apparatus having a configuration in which the transfer / removal is switched depending on the paper type when printing in the monochrome mode. In S001, the CPU 306 obtains a response from the sensor for detecting the remaining amount of toner attached to the black image forming unit 234K from the sensor detection unit 403. Thereafter, based on the program stored in the ROM 307, the CPU 306 determines whether printing with black toner is possible.

  If the black toner is insufficient, that is, if the black toner remaining amount has not reached the printable amount, the CPU 306 determines in S002 whether or not the toner bottle replacement has been completed based on the result of the sensor detection unit 403. to decide. If it is determined that toner bottle replacement has not been completed, the CPU 306 repeats S002 until the toner bottle replacement is completed. If it is determined that the toner bottle replacement has been completed, the CPU 306 determines again in S001 whether or not the remaining amount of black toner has reached the printable amount.

  On the other hand, if it is determined that the black toner has reached the printable amount, the CPU 306 determines in S003 whether or not a job has been received through the external I / F 301. The accepted job is converted into print data and stored in the RAM 308. The CPU 306 determines whether there is print data stored in the RAM 308.

  If it is determined that there is no job, the CPU 306 continues the determination until a job arrives in S003. If it is determined that the job has arrived, in step S004, the CPU 306 determines whether there is a color whose remaining toner amount has not reached the printable amount. When it is determined that the remaining amount of all color toners has reached the printable amount, in step S005, the CPU 306 determines whether the print data of the job stored in the RAM 308 is monochrome or color in order to perform normal printing. .

  When it is determined that the print data is color, the CPU 306 performs a one-way contact control in S006. When printing in the color mode, it is necessary to bring all the photosensitive drums 209 into contact with the intermediate transfer belt 230. Therefore, the contact control described above is performed. Thereafter, in S007, the CPU 306 performs printing in the color mode. The basic operation described in section 1 is the operation for printing one page. In S007, one page printing is repeated until the job is completed based on the print data. When the job is finished, S007 is finished, and the CPU 306 executes S001.

  If it is determined in S005 that the job is monochrome, the CPU 306 performs paper type determination in S008. The user inputs the paper type set in the upper cassette 215 or the lower cassette 216 through the operation display device 40. The CPU 306 determines whether or not the input paper type is a paper type that causes banding at the time of separation. Judgment criteria include paper basis weight. When the paper type is cardboard, that is, when the basis weight set for each paper type is 106 gsm or more, the CPU 306 determines that banding occurs. If it is determined that banding does not occur, the CPU 306 performs the above-described one-off separation control in S009.

  Thereafter, in S010, the CPU 306 executes printing in the monochrome mode. If it is determined that banding occurs, in S011, the CPU 306 performs the one-time contact control described above. Thereafter, in S012, the CPU 306 executes monochrome printing.

  If it is determined in S004 that there is at least one color whose remaining toner amount does not reach the printable amount, the CPU 306 determines from the print data whether the job stored in S013 is monochrome or color. If it is determined that the job is color, the CPU 306 issues an error notification in S014. In the error notification method, the error warning character stored in the ROM 307 is sent to the operation display unit 309 through the external I / F unit 301 and displayed on the operation display device 40.

  The operation display device 40 displays a message “Replace toner bottle because toner is insufficient”. In S015, the CPU 306 determines whether the toner bottle has been replaced. If the replacement has not been completed, S015 is repeated until the toner bottle is replaced. If the exchange has been completed, the CPU 306 resumes the job from S004.

  If the job is monochrome in S013, the CPU 306 makes the same determination in S016 as in S008. When it is determined that the basis weight is 106 gsm or less, the CPU 306 performs the same one-off separation control as S009 in S023. In step S024, the CPU 306 executes the same monochrome printing as in step S010.

  If it is determined in S016 that the basis weight is 106 gsm or more, the CPU 306 issues a warning to ask the user whether or not to continue printing in S017. As shown in FIG. 8, the character string “Color toner is insufficient. Do you want to continue printing?” Stored in the ROM 307 is output to the operation display device 40 as a pop window. When the user touches the NO button 622, that is, when printing is stopped, the process of S014 is performed. If the user touches the YES button 623, that is, if printing is to be continued, in S018, the CPU 306 performs the same one-off separation control as in S009.

  In S019, the CPU 306 outputs a warning “Do you want to change the paper type to print?” Stored in the ROM 307 to the operation display device 40 as a pop-up window 624 as shown in FIG. Wait for. When the user touches NO626, that is, when paper type priority is selected, the CPU 306 executes printing in the monochrome mode in S020 as in S010.

  If the response from the user in S019 indicates that the paper type has not been changed, the CPU 306 automatically prints the print data of the job with the paper set to the upper cassette 215 or the lower cassette 216 having a paper type of less than 106 gsm automatically in S021. To change. In S022, the CPU 306 executes monochrome printing in the same manner as in S010.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 40 Operation display apparatus, 209 Photosensitive drum, 211 Primary transfer roller, 230 Intermediate transfer belt, 302 Print control part, 403 Sensor detection part, 501 Eccentric cam

Claims (2)

An image carrier for black (209K);
A plurality of color image carriers (209Y, 209M, 209C);
An intermediate transfer member (230) in contact with these image carriers,
A primary transfer means (211) provided for each image carrier and primary-transferring the toner image formed on the image carrier to the intermediate transfer member;
A toner remaining amount detecting means (403) for detecting the remaining amount of toner for each color;
A paper type detection means (40) for determining the type of paper on which image formation is performed;
A print control unit (302) for forming an image based on the print data;
Operation display means (40) for performing input from the user and output to the user;
Contact and separation means (501) for operating a primary transfer means for color to contact and separate the image carrier for color from the intermediate transfer body;
A first monochrome mode in which only the black image carrier is brought into contact with the intermediate transfer member when forming a monochrome image;
When forming a color image, a color mode in which the entire image carrier including the image carrier for black is brought into contact with the intermediate transfer member by the contact / separation unit;
The black image carrier is provided on the upstream side in the rotation direction of the intermediate transfer member with respect to the contact portion between the black image carrier and the intermediate transfer member, and the black image carrier is formed by the contact / separation means when forming a monochrome image. A second monochrome mode in which the entire image carrier including the body is brought into contact with the intermediate transfer member;
With
In the first monochrome mode,
When color toner whose remaining amount is insufficient is detected by the toner remaining amount detecting means,
Determining whether the contact / separation means can be executed according to the paper type of the printing paper detected by the paper type detection means;
In the case of forming a monochrome image, if it is determined that the contact / separation unit needs to be executed, the operation display unit selects whether to switch to the forced printing mode or to cancel printing. apparatus. 2. The forced print mode is configured to selectively switch between printing with a paper type different from the designated paper type or giving priority to the designated paper type through an operation display unit. The image forming apparatus described in 1.