JP2006162855A - Image printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image printer capable of more simply cleaning a carrying route. <P>SOLUTION: The printer 10 is provided with a printing part 12 for printing out an image on a transported sheet and an image reader 17 for reading out the sheet passed through the printing part 12 and acquiring inspection image data. When removing dirt on the transport route, an image printing control part instructs the printing part 12 to execute blank printing for allowing a sheet to pass the printing part 12, without performing image printing. Then the control part decides on the presence of dirt stuck to the sheet in transport process, on the basis of the inspected image data of the sheet after blank printing, which is acquired by the image reader 17 to detect dirt on the carrying route. Until there is no dirt existing on the transport route is decided, blank printing is repeated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image printing apparatus such as a printer, and more particularly to an image printing apparatus including an image reading unit that reads a paper surface of a sheet that has passed through a printing unit.

  When an image is printed by the image printing apparatus, the paper is transported along a predetermined transport path, and is printed after the image is printed by the printing unit. At this time, if the conveyance path is dirty, the paper passing through the transfer path is also dirty, which causes a defective printing result.

  For example, in the case of an electrophotographic image printing apparatus that performs image printing with toner, a transfer roller, a fixing roller, and the like exist in a paper conveyance path. The transfer roller is a roller for transferring the toner image developed on the photoconductor to the paper, and the fixing roller is a roller for fixing the transferred toner image on the paper. The toner that cannot be transferred or fixed by the transfer roller or the fixing roller remains on the transfer roller or the fixing roller and becomes unnecessary toner. This unnecessary toner is usually removed each time printing is performed by a blade or the like provided downstream of the roller. However, unnecessary toner on the roller surface may not be completely removed due to aging of the blade itself or an increase in unnecessary toner staying on the blade. Further, when a paper trouble such as a paper jam occurs in the fixing roller, a repair operation called JAM is performed. This JAM includes an operation of pulling out a sheet in the middle of printing sandwiched between fixing rollers. At this time, a large amount of unfixed toner on the paper may adhere to the fixing roller and generate a large amount of unnecessary toner.

  Such unnecessary toner on the conveyance path adheres to the paper and causes paper stains. Therefore, conventionally, after a JAM operation, a predetermined number of blank sheets are automatically conveyed, and stains such as fixing rollers are removed with the sheets. At this time, the transported blank paper is discarded as waste paper. Japanese Patent Application Laid-Open No. 2004-228561 provides a reading head that optically reads the toner image forming surface of the photoconductor near the photoconductor, and the presence or absence of unnecessary toner on the toner image forming surface based on a reading signal acquired by the reading head. An image forming apparatus is disclosed that detects an error and issues a warning when there is unnecessary toner.

JP-A-6-236091

  However, with the conventional method, it is difficult to reliably remove dirt on the transport path. For example, according to the method of transporting a blank sheet after the JAM operation, it is possible to surely remove stains such as the fixing roller. However, this method always conveys a predetermined number of sheets regardless of the amount of dirt on the conveyance path. Therefore, there are cases where the conveyance of the paper is terminated without completely removing the dirt on the conveyance path. On the contrary, there are cases where the paper is transported after the stain on the transport path is removed, and the paper is consumed more than necessary. That is, the method of automatically transporting a predetermined number of blank paper sheets cannot properly remove the stain on the transport path. Further, with the technology of Patent Document 1, although the presence or absence of unnecessary toner on the toner image forming surface can be detected, the stain cannot be removed. That is, in the conventional method, the stain on the conveyance path cannot be appropriately removed, and as a result, the printing accuracy may be lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides an image printing apparatus capable of improving printing accuracy more easily.

  An image printing apparatus according to the present invention includes a printing unit that prints an image on a conveyed sheet, and an image reading unit that is provided downstream of the printing unit and that reads the paper surface of the sheet that has passed through the printing unit to obtain inspection image data. An image printing apparatus comprising: a control unit that instructs the printing unit to execute blank printing that passes the printing unit without printing an image on a sheet; and a sheet after blank printing acquired by the image reading unit And detecting means for detecting the presence or absence of dirt attached to the sheet in the course of conveyance based on the inspection image data and detecting the dirt on the conveyance path.

  In a preferred aspect, the control means instructs blank paper printing until the detection means determines that there is no dirt on the conveyance path. In another preferred aspect, the control unit sets the printing parameter when executing blank paper printing to a value at which dirt on the transport path is likely to adhere to the transported paper. When the image printing apparatus is an electrophotographic image printing apparatus that forms an image with toner, it is preferable that the control unit sets at least the temperature of the fixing roller to be high when performing blank paper printing. It is also desirable to set at least a high nip pressure for bringing the paper into close contact with the fixing roller when performing blank paper printing.

  In another preferred aspect, the control unit instructs blank printing after a predetermined process for paper trouble in the printing unit is performed. In another preferred aspect, when normal printing for printing an image on a sheet is performed by the printing unit, the detection unit includes original image data that is original data of an image to be printed and an inspection acquired by the image reading unit. The image data is compared and checked to determine whether the print result is good or bad. It is desirable that the detection means set the detection threshold to a value that makes it easier to detect the stain attached to the paper when the stain on the conveyance path is detected than when the print result is judged as good or bad. In another preferred aspect, the control unit reverses the paper once printed with a blank sheet and causes the sheet to be printed again with the sheet.

  Here, the image printing apparatus refers to all types of models that print an image on paper, such as a printer, a copying machine, a facsimile, and a digital multifunction machine that combines these. In addition, an electrophotographic image printing apparatus that performs image printing with toner is preferable, but an image printing apparatus that prints an image by another method such as an ink jet method may be used. In addition to normal printing paper, paper refers to all sheet-like printing media such as postcards, cardboard, cloth, and OHP sheets.

  According to the present invention, the stain on the conveyance path can be removed by the paper, and the removal result can be determined based on the inspection image data. Accordingly, it is possible to appropriately remove dirt on the conveyance path, and as a result, it is possible to improve printing accuracy.

  Hereinafter, a printer 10 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration diagram of the printer 10. The printer 10 described below is assumed to be a relatively large high-speed printer. However, it may be applied to other image forming apparatuses such as a copying machine and a small printer by appropriately changing a part of the configuration.

  The printer 10 is controlled by an image printing control unit (not shown), and prints the same image as the original image data stored in the image printing control unit on paper. The paper stored in the storage unit 22 is transported along the main transport path 14 and an image is printed in the printing unit 12. The print result is inspected by an inspection device 16 provided downstream of the printing unit 12. When the inspection result is normal, the sheet is conveyed to the normal paper discharge tray 34 or the duplex conveyance path 18. On the other hand, when the inspection result is abnormal, the sheet is conveyed to the abnormal paper discharge tray 36. In addition, the image printing control unit instructs the printing unit 12 to print a blank sheet without outputting an image, if necessary. The inspection device 16 reads the paper surface of the blank printed paper and detects dirt on the conveyance path. Hereinafter, the printer 10 will be described in detail.

  The conveyance path 13 through which the sheet is conveyed is roughly divided into a main conveyance path 14, a duplex conveyance path 18, and a discharge conveyance path 21. The main conveyance path 14 is a conveyance path that guides paper from the storage unit 22 to the printing unit 12 and the inspection device 16. The main conveyance path 14 is branched downstream into a duplex conveyance path 18 and a discharge conveyance path 21. The double-sided conveyance path 18 is a conveyance path that turns the paper over and guides it to the main conveyance path 14 again. The paper discharge conveyance path 21 guides the printed paper to the paper discharge unit 24. Each of the transport paths 14, 18, and 21 is formed by a transport guide plate 38 that guides the movement of the paper. The transport guide plate 38 is provided with a plurality of transport means 40 for sequentially feeding the sheets downstream.

  Each transport unit 40 includes a transport roller 42 and a transport idler 44. The transport roller 42 is rotated by a driving unit (not shown), and applies a transport force to the paper by contacting the paper. The conveyance idler 44 is provided at a position facing the conveyance roller 42 and sandwiches the paper in cooperation with the conveyance roller 42. And it rotates with conveyance of the said paper by the frictional force which arises between the paper currently pinched | interposed.

  The storage unit 22 includes two first paper supply trays 30 having a relatively small capacity and two second paper supply trays 32 having a relatively large capacity as paper supply trays for storing paper. Each of the trays 30 and 32 is connected to the main transport path 14 so that paper can be appropriately supplied to the main transport path 14. The size of the paper stored in each of the paper feed trays 30 and 32 is stored in the image printing control unit.

  The printing unit 12 prints an image on a sheet in response to an instruction from the image printing control unit. The printing unit 12 is roughly divided into a developing unit 26 that forms and transfers a toner image based on document image data, and a fixing unit 28 that fixes the toner image on a sheet. The developing unit 26 forms an electrostatic latent image on the photoconductor by a charging unit and an exposure unit (not shown), and forms a toner image by attaching toner to the surface of the photoconductor by electrostatic force. The toner image formed here is formed based on the document image data transmitted from the image printing control unit. The transfer roller 27 to which the toner image is transferred from the photosensitive member is provided on the main conveyance path 14, and the toner is transferred onto the sheet by conveying the sheet here.

  The fixing unit 28 is provided downstream of the developing unit 26 and includes a fixing roller 29. The fixing roller 29 includes a heat roll 31 that melts toner with heat, and a pressure roll 33 that presses the paper against the heat roll 31. The heat roll 31 and the pressure roll 33 are provided to face each other, and the two rolls 31 and 33 sandwich and convey the paper. The heat roll 31 is provided on the paper printing surface side, and the pressure roll 33 is provided on the paper back side. The toner image transferred onto the sheet is melted by heat from the heat roll 31 and the toner is fixed.

  Here, the toner that cannot be transferred and fixed onto the paper may adhere to and remain on the transfer roller 27, the fixing roller 29, and the like. Normally, such residual toner is removed by a blade (not shown) provided downstream of the rollers 27 and 29. However, with the aging of the blade and the increase in the volume of toner in the blade, the toner removal capability decreases, and unnecessary toner may remain on the rollers 27 and 29. Further, when a paper jam occurs in the fixing unit 28, a JAM operation for extracting a toner non-fixed paper from the fixing roller 29 is required. At this time, a large amount of unfixed toner may adhere to the fixing roller 29. Such toner adheres to a sheet conveyed thereafter and stains the sheet, resulting in a decrease in printing accuracy. Further, not only the toner but also dirt on the paper transport path adheres to the paper and causes a decrease in printing accuracy.

  Therefore, in this embodiment, in order to remove such stains, in particular, residual toner, blank paper printing that outputs paper without image printing is performed as necessary. This blank printing is performed in accordance with an instruction from the image printing control unit, and the printing unit 12 that has received this instruction does not print on the conveyed paper, but outputs it to the downstream side as it is. . Therefore, in the case of blank paper printing, the developing unit 26 does not form the electrostatic latent image or the toner image described above, and only carries the paper in the downstream direction. The fixing roller 29 of the fixing unit 28 sandwiches and conveys the sheet and conveys the sheet in the downstream direction. At this time, when the sheet comes into contact with the transfer roller 27 and the fixing roller 29, residual toner and dust attached to the rollers 27 and 29 are transferred to the sheet and removed. The paper used for blank paper printing is output to the abnormal paper discharge tray 36 after being inspected by the inspection device 16 described later.

  Next, the inspection device 16 will be described with reference to FIGS. FIG. 2 is a schematic side view around the inspection apparatus 16, and FIG. 3 is a schematic top view around the inspection apparatus. The inspection device 16 includes an image reading device 17 and an inspection control unit (not shown). The image reading device 17 reads the paper surface (printing surface) of the paper that has passed through the printing unit 12 and acquires inspection image data. The image reading device 17 is fixedly installed on the conveyance guide plate 38 and incorporates a lamp 45, an imaging lens 46, and a CCD line sensor 48. The CCD line sensor 48 reads an image at the image reading position R as a line image. When the front end of the sheet reaches the image reading position R, the CCD line sensor 48 performs image reading at a predetermined interval until the rear end of the sheet passes the image reading position R. The image reading device 17 combines a plurality of line-shaped images obtained at this time, and obtains them as inspection image data. The acquired inspection image data is output to the inspection control unit. The inspection image data is acquired in both normal printing and blank paper printing. That is, the image reading apparatus 17 according to the present embodiment acquires not only the paper surface of the paper on which image printing has been performed but also the paper surface of the paper output without image printing as inspection image data.

  The image reading device 17 may be provided anywhere as long as it is downstream of the fixing roller 29. However, it is desirable that the image reading device 17 be close to the fixing roller 29 in order to shorten the entire processing time and downsize the apparatus. In this embodiment, a CCD line sensor is used as a reading device. However, as long as it reads an image printed on a sheet, other devices such as a CCD sensor and a CMOS sensor that read a small area may be used. Good.

  The inspection control unit controls the scanning timing of the image reading device 17 and performs various inspections based on the inspection image data acquired by the image reading device. Specifically, the inspection control unit instructs the image reading device 17 to start and end image reading based on the output from the paper detection sensor 56 provided immediately before the image reading position R. Further, the image reading device 17 is instructed to set an image reading interval based on the paper conveyance speed detected by the speed detecting means (not shown).

  The inspection control unit performs a printing result inspection or a conveyance path contamination inspection in accordance with an instruction from the image printing control unit. When the print result inspection is performed, the inspection control unit determines whether the print result is good or not by comparing and comparing the inspection image data output from the image reading device 17 with the document image data stored in advance. The document image data is input from the image printing control unit. As a result of the comparison and collation, when the difference amount between the two image data is small, it is determined that the printing is normally performed, and when the difference amount is large, it is determined that the printing result is defective. The obtained inspection result is output to the image printing control unit.

  When performing the inspection for the presence or absence of contamination on the conveyance path, the inspection control unit detects the presence or absence of contamination attached to the sheet based on the inspection image data output from the image reading device 17. As will be described later, this presence / absence inspection is executed only in the case of blank paper printing in which paper is output without image printing. In other words, when the presence / absence inspection of the dirt is performed, the output paper is supposed to be a blank sheet. However, if there is unnecessary residual toner or dirt on the conveyance path, for example, the fixing roller 29, the transfer roller 27, or the conveyance guide plate 38, this is transferred to a blank sheet. The inspection control unit determines the presence or absence of residual toner or the like (dirt) transferred to the sheet based on the inspection image data. If it is determined that the sheet is dirty, it is determined that the conveyance path is dirty, and the result is output to the image printing control unit.

  The paper discharge unit 24 includes a normal paper discharge tray 34 and an abnormal paper discharge tray 36. The paper for which image printing has been completed normally is discharged to the normal paper discharge tray. In addition, paper on which the printing result is determined to be defective and paper on which blank printing has been performed are discharged to the abnormal paper discharge tray. A switch provided at the branch point of each transport path determines whether the paper transported along the main transport path 14 is led to the normal paper discharge tray 34, the abnormal paper discharge tray 36, or the double-side transport path 18. (Not shown). This switch is controlled by the image printing control unit.

  An image printing control unit (not shown) outputs various instructions to the above-described printing unit 12, inspection device 16, etc., and controls the entire printer 10. The image printing control unit according to the present embodiment is configured so that at least two types of printing can be executed, that is, normal printing that prints and outputs an image on paper and blank printing that outputs without printing an image on paper. Outputs instructions. That is, when executing normal printing, the image printing control unit transmits document image data input from another computer via a network or input using a scanner function of the printer to the printing unit 12. And instructing the original image data to be printed on paper. At the same time, the conveyance unit 40 is instructed to convey the sheet. Further, the original image data is transmitted to the inspection device 16 to instruct whether or not the print result is acceptable. Then, if a pass / fail judgment result from the inspection device 16 is received, the output destination of the paper is controlled according to the pass / fail result.

  On the other hand, blank paper printing is executed for the purpose of removing dirt when the dirt on the transport path increases, or for the purpose of inspecting the presence or absence of dirt on the transport path. The image printing control unit instructs execution of blank page printing when a predetermined repair operation is performed for a paper jam in the fixing unit. Specifically, the conveyance unit 40 is instructed to convey the sheet, and the printing unit 12 is instructed to output the sheet without image printing. Further, the inspection device 16 is instructed to inspect the presence or absence of paper stains. In response to the instruction, the inspection device 16 performs an inspection for the presence of paper stains and outputs the result to the image printing control unit. If it is determined that there is no paper contamination, the image printing control unit determines that the contamination on the transport path has been removed, and ends blank paper printing. On the other hand, if it is determined that there is paper contamination, it is determined that there is contamination on the transport path, and the execution of blank paper printing is instructed again.

  Next, the flow of blank paper printing in the printer 10 will be described in detail. As described above, the blank page printing is automatically executed after a predetermined repair operation is performed on a paper jam generated in the fixing unit 28. That is, the repairing operation for the paper jam is usually completed by opening the casing that covers the printer 10, removing the jammed paper in the vicinity of the fixing unit 28, and closing the casing. The removal of the paper and the opening / closing of the housing can be detected by sensors provided in each part of the printer 10. The image printing control unit detects the completion of the repair work based on the output from each sensor. When it is determined that the repair work has been completed, a blank paper printing instruction is automatically output to the printing unit 12 or the like. Here, blank paper printing is performed after occurrence of a paper jam in the fixing unit 28 because a large amount of unnecessary toner adheres to the fixing roller 29 and the like due to a paper jam in the fixing unit 28 and its repairing operation.

  Of course, blank paper printing may be executed at another timing. For example, an operator for instructing blank page printing may be provided on the operation panel of the printer 10, and blank page printing may be executed at the timing when the operator is operated. This makes it possible to print blank paper at the timing desired by the user, in other words, to clean the transport path.

  Further, blank paper printing may be executed at the timing when it is determined that the contamination on the transport path has increased in the printing result inspection performed after normal printing. That is, in the print result inspection, the quality of the print result is determined by comparing and comparing the inspection image data and the document image data. At this time, if the inspection image data includes an image due to contamination on the conveyance path equal to or greater than a predetermined threshold value, it is naturally determined that the printing result is defective. If printing result defects continuously occur due to such contamination on the conveyance path, blank paper printing may be automatically executed to remove the contamination on the conveyance path.

  Furthermore, you may make it perform blank paper printing regularly. For example, the normal printing of a predetermined number or more from the previous blank printing or the blank printing may be automatically executed when a predetermined time has elapsed since the previous blank printing. By periodically performing blank paper printing in this manner, it is possible to always reduce the contamination on the transport path.

  When performing blank paper printing, the image printing control unit instructs the transport unit 40 to transport the paper. At this time, the transported paper is an unprinted paper stored in the storage unit 22, and is the same as the paper transported during normal printing. However, in order to remove dirt in a wider range, it is desirable to transport a relatively large size sheet. In some cases, paper that easily adheres to the conveyance path, such as thick paper or paper that is compatible with unnecessary toner, is placed in a specific paper tray to wait for printing on blank paper. Alternatively, the paper may be conveyed.

  Along with this sheet conveyance instruction, the image printing control unit instructs the printing unit 12 to pass the sheet without printing the image on the sheet. In other words, the printing unit 12 is instructed to execute printing without transmitting the document image data. Accordingly, the paper that has reached the printing unit 12 is conveyed downstream by the transfer roller 27 and the fixing roller 29 without transferring the toner image. At this time, the sheet is conveyed while being in contact with the transfer roller 27 and the fixing roller 29, so that dirt such as residual toner adhering to these rollers 29 and 27 is transferred to the sheet. By this transfer, dirt on the transfer roller 27 and the fixing roller 29 is removed.

  Here, the image printing control unit also sets values of various printing parameters such as the conveyance speed and the temperature of the heat roll 31. In the case of blank page printing, the image printing control unit sets these print parameters to values at which dirt on the conveyance path is likely to adhere to the sheet. Specifically, the temperature of the heat roll 31 of the fixing roller 29 is set higher than usual. By increasing the temperature of the heat roll 31, the residual toner adhering to the heat roll 31 and the pressure roll 33 is melted and easily adheres to the paper. It is also effective to set a high nip pressure for bringing the paper into close contact with the heat roll 31 and the pressure roll 33. The nip pressure can be adjusted by changing the position of the pressure roll 33, and the nip pressure can be increased by bringing the pressure roll 33 closer to the heat roll 31. By increasing the nip pressure, the sheet is brought into close contact with the heat roll 31 and the pressure roll 33, and dirt such as unnecessary toner is more easily transferred.

  The paper that has passed through the printing unit 12 is inspected for contamination by the inspection device 16. That is, the paper surface is read by the image reading device 17 and inspection image data is acquired. The inspection control unit reads the inspection image data and detects the presence or absence of dirt. First, the inspection image data is binarized with a predetermined threshold. Subsequently, the presence / absence of a black portion having a predetermined area or more is detected in the inspection image data after binarization. If there is a black portion having a predetermined area or more, it is determined that there is a paper stain.

  Here, it is desirable that the threshold for detecting paper contamination is set to be lower than that during normal print result inspection. Specifically, it is desirable that the threshold value for binarization is set lower than that at the time of print result inspection so that it is converted to black even if it is low density (low luminance) stains. It is also desirable to set the area of the black part that is judged as dirty to be lower than that at the time of printing result inspection. By setting such parameters, even a low density and small area stain can be easily detected as “paper stain”, and the presence or absence of stain on the transport path can be detected with high accuracy.

  The result of the paper smear inspection in the inspection device 16 is output to the image printing control unit. When it is determined that there is no paper contamination, the image printing control unit outputs the paper to the abnormal paper discharge tray 36 and ends the blank printing. On the other hand, if it is determined that the paper is dirty, the paper is output to the abnormal paper discharge tray 36, and a new blank paper conveyance and blank printing are instructed again. Then, the blank printing is repeated until the inspection device 16 determines that there is no paper contamination.

  As described above, the printing on the conveyance path can be reliably performed by repeating the blank printing until it is determined that the sheet is not soiled. During this time, the user does not have to give any instruction or determination, and thus the transport path can be cleaned very easily. Conventionally, printing of a predetermined number of blank pages is always executed after a paper jam occurs in the fixing unit 28 regardless of the degree of contamination. Therefore, blank paper printing may continue even after the removal of dirt on the transport path. However, as in this embodiment, it is possible to prevent unnecessary blank printing by determining whether or not to continue blank printing according to the result of the paper smudge presence / absence check, thereby minimizing the number of discarded paper. Can do.

  That is, according to the present embodiment, it is possible to more easily clean the conveying path more easily, and as a result, it is possible to improve printing accuracy. Although the present embodiment has been described with a printer that is an electrophotographic image printing apparatus, it is naturally applicable to other types of image printing apparatuses such as an inkjet system. Further, the timing of executing blank paper printing, the value of the printing parameter at that time, and the like are not limited to the above description.

  Alternatively, the front and back of the paper that has once passed through the printing unit 12 may be reversed by blank paper printing, and the blank paper printing may be executed again. This will be described with reference to FIGS. FIG. 4 is a schematic cross-sectional view when the sheet passes through the fixing unit, and FIG. 5 is a diagram illustrating an example of inspection image data obtained after executing blank paper printing. In FIG. 4, the back side of the paper is hatched for easy understanding.

  Usually, in the first blank paper printing, as shown in FIG. 4A, the front surface 50 a of the paper 50 is in contact with the heat roll 31 and the back surface 50 b is in contact with the pressure roll 33. That is, the stain 60a on the heat roll 31 is transferred to the paper surface 50a, and the stain 60b on the pressure roll 33 is transferred to the paper back surface 50b. Thereafter, the paper 50 is conveyed to the inspection device 16, and the printing surface (front surface 50 a) is read by the image reading device 17. The inspection image data obtained by this reading is shown in FIG. As shown in FIG. 5A, the inspection image data includes only an image caused by the dirt 60a of the heat roll 31 and does not include an image caused by the dirt 60b of the pressure roll 33. Accordingly, the paper stain on the back surface 50b cannot be inspected in the first blank printing.

  Therefore, it is desirable that the paper 50 once printed with blank paper is sent to the double-sided conveyance path 18 and turned upside down, and then printed again with blank paper. The paper 50 that has been turned upside down is conveyed again to the fixing roller 29. The state at this time is shown in FIG. When the blank paper is printed again, the paper is turned upside down, so that the back surface 50 b of the paper 50 is in contact with the heat roll 31 and the front surface 50 a is in contact with the pressure roll 33. Therefore, when the second blank page printing is completed, the back surface 50b of the pressure roll 33 adhered by the first blank sheet printing 60b and the dirt 60a of the heat roll 31 adhered by the second blank sheet printing are displayed. Both exist. FIG. 5B shows inspection image data obtained by reading the sheet back surface 50b. As apparent from FIG. 5B, the inspection image data includes both an image resulting from the dirt 60 a of the heat roll 31 and an image resulting from the dirt 60 b of the pressure roll 33. Based on this inspection image data, the presence / absence of contamination can be inspected not only for the heat roll 31 but also for the pressure roll 33.

  As described above, once both the front and back sides of the sheet on which the blank page is printed are reversed and the blank page is printed again, it is possible to detect both the heat roll 31 and the pressure roll 33. Further, by executing blank printing twice with a single sheet, it is possible to clean the transport path with a smaller number of sheets.

1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. It is a schematic side view around an inspection apparatus. It is a schematic top view around an inspection device. FIG. 3 is a schematic cross-sectional view when a sheet passes through a fixing unit. It is a figure which shows an example of the test | inspection image data obtained after blank paper printing execution.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Printer, 12 Printing part, 13 Conveyance path, 16 Inspection apparatus, 17 Image reading apparatus, 22 Storage part, 24 Paper discharge part, 26 Developing part, 28 Fixing part, 27 Transfer roller, 29 Fixing roller, 31 Heat roll, 33 Pressure roll, 38 transport guide plate, 40 transport means, 50 sheets.

Claims (9)

A printing section for printing an image on the conveyed paper;
An image reading unit that is provided downstream of the printing unit, reads the paper surface of the paper that has passed through the printing unit, and acquires inspection image data;
An image printing apparatus comprising:
Control means for instructing the printing unit to execute blank printing that passes the printing unit without printing an image on paper;
Detection means for determining the presence or absence of dirt attached to the paper in the course of conveyance based on the inspection image data of the paper after blank printing acquired by the image reading means, and detecting dirt on the conveyance path;
An image printing apparatus comprising: The image printing apparatus according to claim 1,
An image printing apparatus, wherein the control means instructs printing of a blank sheet until it is determined by the detection means that there is no stain on the conveyance path. The image printing apparatus according to claim 1, wherein:
The control means sets the printing parameter for executing blank paper printing to a value at which dirt on the transport path is likely to adhere to the transported paper. The image printing apparatus according to claim 3, wherein
When the image printing apparatus is an electrophotographic image printing apparatus that forms an image with toner,
An image printing apparatus characterized in that the control means sets at least the temperature of the fixing roller to be high when executing blank paper printing. The image printing apparatus according to claim 3 or 4,
When the image printing apparatus is an electrophotographic image printing apparatus that forms an image with toner,
The control means sets at least a high nip pressure for bringing the paper into close contact with the fixing roller when performing blank paper printing. The image printing apparatus according to any one of claims 1 to 5,
An image printing apparatus characterized in that the control means instructs printing of a blank sheet after a predetermined process for paper trouble in the printing unit is performed. The image printing apparatus according to any one of claims 1 to 6,
When normal printing that prints images on paper is performed by the printing unit,
An image printing method characterized in that the detection means compares the original image data, which is the original data of the image to be printed, with the inspection image data acquired by the image reading means, and judges whether the print result is good or bad apparatus. The image printing apparatus according to claim 7, wherein
An image printing apparatus characterized in that the detection means sets a detection threshold value at a value that makes it easier to detect dirt adhering to a sheet when detecting dirt on the transport path than when judging whether the printing result is good or bad. . The image printing apparatus according to any one of claims 1 to 8,
An image printing apparatus characterized in that the control means reverses the paper once printed with a blank sheet and reverses the blank sheet with the sheet again.

Images