JP2022049530A - Image formation apparatus - Google Patents

Abstract

To enable smoothly performing both-sided printing on media.SOLUTION: An image formation apparatus comprises: a printing processing part Pr1 which generates image data; an image formation part which forms an image on a medium; a fist medium conveyance path for feeding the medium to the image formation part; a second medium conveyance path for making a medium having an image formed on one surface retreat; a third medium conveyance path for returning the medium, made to retreat into the second medium conveyance path, to the first medium conveyance path; first and second medium detection parts which detect the medium; a medium inversion processing part which conveys the medium just by a retreat conveyance distance and makes it retreat into the second medium conveyance path, and turns over and feeds the medium, made to retreat, to a third medium conveyance path; and a conveyance correction processing part Pr3 which corrects the retreat conveyance distance based upon a detection result of the medium by the second medium detection part. The medium can be not only conveyed by the accurate retreat conveyance distance, but also stopped at a predetermined stop position on the second medium conveyance path.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a compound machine, for example, in a printer, the surface of a photoconductor drum uniformly charged by a charging roller is exposed by an LED head to perform an electrostatic latent image. Is formed, the electrostatic latent image is developed by the developer to form a toner image on the photoconductor drum, and then the toner image is transferred to the paper as a medium by the transfer roller and fixed on the paper in the fuser. It is designed to be made to.

By the way, in order to perform double-sided printing in which an image is formed on both sides of a paper, a printer is provided in which the paper is inverted and conveyed.

In the printer, when the paper ejected from the fuser and having an image formed on one surface is sent to the paper transport path for evacuation after changing the position of the separator against the urging force of the spring. The separator is designed to return to its original position by the urging force of the spring. Subsequently, when the position of the paper is detected by the sensor, the paper is fed from the paper transport path for evacuation to the paper transport path for return, returned to the main paper transport path, and an image is formed on the other side. (See, for example, Patent Document 1.).

Japanese Unexamined Patent Publication No. 2012-181387

However, in the conventional printer, when a weak paper such as thin paper is used as a medium, it may not be possible to change the position of the separator against the urging force of the spring. In that case, the paper is not sent to the paper transport path for saving, and not only is it impossible to perform double-sided printing, but also paper jam occurs.

Therefore, it is conceivable to dispose a sensor in the main paper transport path, and when the sensor detects the paper, the position of the separator is switched so that the paper is fed to the paper transport path for retracting.

However, if the outer diameter of the transport member arranged on the downstream side of the sensor changes due to aging, or if the paper dimensions change due to the environment such as temperature and humidity, even if the transport motor is driven, It is not possible to transport the paper by an accurate distance, and it is not possible to stop the paper at a predetermined position in the paper transport path for evacuation.

As a result, paper jam occurs and the tamming of sending the paper to the return paper transport path is slowed down, which reduces the printing throughput and enables smooth double-sided printing on the paper. It will disappear.

An object of the present invention is to solve a problem of a conventional printer and to provide an image forming apparatus capable of smoothly performing double-sided printing on a medium.

Therefore, in the image forming apparatus of the present invention, a print processing unit that receives a print job for double-sided printing from a higher-level device and performs printing processing to generate image data, and an image data sent from the printing processing unit are used. An image forming unit that forms an image on a medium, a first medium transport path for sending a medium to the image forming section, and a branch from the first medium transport path are formed, and an image is printed on one surface. A second medium transport path for retracting the formed medium and a medium formed by branching from the second medium transport path and retracted to the second medium transport path are transferred to the first medium transport path. A third medium transport path for returning to the path, a first medium transport section arranged in the first medium transport path to detect the medium, and a medium arranged in the third medium transport path. Based on the detection of the medium by the second medium detection unit that detects It has a medium inversion processing unit that is inverted and sent to a third medium transfer path, and a transfer correction processing unit that corrects the retracted transfer distance based on the result of detection of the medium by the second medium detection unit.

According to the present invention, in the image forming apparatus, the image forming apparatus is based on a print processing unit that receives a print job for double-sided printing from a higher-level apparatus and performs printing processing to generate image data, and an image data sent from the printing processing unit. An image forming unit that forms an image on a medium, a first medium transport path for sending a medium to the image forming section, and a branch from the first medium transport path are formed, and an image is printed on one surface. A second medium transport path for retracting the formed medium and a medium formed by branching from the second medium transport path and retracted to the second medium transport path are transferred to the first medium transport path. A third medium transport path for returning to the path, a first medium transport section arranged in the first medium transport path to detect the medium, and a medium arranged in the third medium transport path. Based on the detection of the medium by the second medium detection unit that detects It has a medium inversion processing unit that is inverted and sent to a third medium transfer path, and a transfer correction processing unit that corrects the retracted transfer distance based on the result of detection of the medium by the second medium detection unit.

In this case, based on the detection of the medium by the first medium detection unit, the medium is conveyed by the evacuation transfer distance and is retracted to the second medium transfer path, and the retracted medium is inverted and the third. The evacuation transport distance is corrected based on the result of detection of the medium by the second medium detection unit, so that the transport member is arranged on the downstream side of the first medium detection unit. Even if the outer diameter of the medium changes due to deterioration over time or the dimensions of the medium change due to the environment such as temperature and humidity, not only can the medium be transported by an accurate evacuation transport distance, but also the medium can be transported by a second. It can be stopped at a predetermined stop position in the medium transport path.

Therefore, the print throughput can be improved because jamming of the medium does not occur and the tamming of sending the medium to the third medium transport path is not delayed. As a result, double-sided printing can be smoothly performed on the medium.

Further, since it is not necessary to dispose a separator whose position changes against the urging force of the spring in the medium transport path, the structure of the image forming apparatus can be simplified and the image forming apparatus can be miniaturized. .. Further, even when a medium having a weak stiffness such as thin paper is used, the medium can be smoothly sent to the second medium transport path.

It is a control block diagram of the control device of the printer in embodiment of this invention. It is a conceptual diagram of the main part of the printer in embodiment of this invention. It is the first figure for demonstrating operation of a printer at the time of correcting a stop position in embodiment of this invention. It is a 2nd figure for demonstrating operation of a printer at the time of correcting a stop position in embodiment of this invention. It is a 3rd figure for demonstrating operation of a printer at the time of correcting a stop position in embodiment of this invention. It is a figure which shows the state of the paper in the case where the rear end in the embodiment of this invention is located in the center of the rear end stop area. It is a figure which shows the state of the paper in the case where the rear end in the embodiment of this invention is within the error range of the rear end stop region. It is a figure which shows the state of the paper in the case where the back end is not within the error range of the rear end stop region because the paper is carried excessively in the embodiment of this invention. It is a figure which shows the state of the paper in the case where the transport of the paper in the embodiment of this invention is insufficient and the rear end does not fall within the error range of the rear end stop region.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

FIG. 2 is a conceptual diagram of a main part of a printer according to an embodiment of the present invention.

In the figure, 10 is a printer, Bd is the main body of the printer 10, that is, the main body of the apparatus, and a paper cassette (not shown) as a medium accommodating portion is arranged under the main body Bd of the apparatus, and is adjacent to the front end of the paper cassette. A paper feeding mechanism for separating the paper P (FIG. 3) as a medium one by one and feeding the paper into the paper transport path Rt1 as the first medium transport path and as the main paper transport path. Is arranged.

The paper P fed by the paper feed mechanism is conveyed along the paper transport path Rt1 by a paper feed roller pair (not shown) as a first transport member, and subsequently arranged on the downstream side of the paper feed roller pair. After the skew is corrected by the resist roller pair m1 as the second transport member, the paper is sent to the image forming unit Q1 arranged on the downstream side of the resist roller pair m1 for forming an image.

The image forming unit Q1 includes an image forming unit 20, an LED head 22 as an exposure device, a transfer roller 25 as a transfer member, a fixing device 31 as a fixing device arranged on the downstream side of the image forming unit 20, and the like. , An image is formed on the paper P based on the image data sent from the print processing unit Pr1 (FIG. 1) described later.

The image forming unit 20 is arranged in contact with a photoconductor drum 21 as an image carrier, a charging roller 27 as a charging device arranged in contact with the photoconductor drum 21, and the photoconductor drum 21. A developing roller 28 as a developer carrier provided, a toner supply roller 29 as a supply member arranged in contact with the developing roller 28, and the like are provided, and the photoconductor drum 21 is provided in the apparatus main body Bd. The LED head 22 is arranged above the photoconductor drum 21 so as to face the photoconductor drum 21, and the transfer roller 25 is arranged below the photoconductor drum 21 so as to be in contact with the photoconductor drum 21 via the paper transport path Rt1. Will be set up.

After the surface of the photoconductor drum 21 is uniformly charged by the charging roller 27, it is exposed by the LED head 22 based on the image data, and an electrostatic latent image as a latent image is exposed on the surface of the photoconductor drum 21. Is formed. Subsequently, the toner as a developer supplied to the developing roller 28 by the toner supply roller 29 is adhered to the electrostatic latent image to develop the electrostatic latent image, and the surface of the photoconductor drum 21 is used as a developer image. A toner image is formed.

The paper P conveyed from the paper cassette through the paper transport path Rt1 and supplied to the image forming section Q1 passes through the transfer section between the photoconductor drum 21 and the transfer roller 25, and at this time, the transfer roller 25. The toner image formed on the photoconductor drum 21 is transferred to the paper P.

Subsequently, the paper P is sent to a fuser 31 arranged on the downstream side of the transfer unit, in which the toner image is fixed on the paper P and an image is formed on the paper P.

Therefore, the fuser 31 includes a heating roller 33 as a first fixing member and a pressure roller 34 as a second fixing member pressed against the heating roller 33, and a toner image on the paper P. Is heated and pressurized in the nip portion between the heating roller 33 and the pressurizing roller 34 to be fixed on the paper P, and an image is formed.

The paper P on which the image is formed is discharged from the fixing device 31, is conveyed by the discharging roller pair m2 as a third transport member arranged on the downstream side of the fixing device 31, and then downstream from the discharge roller pair m2. It is discharged to the outside of the apparatus main body Bd by the discharge roller pair m3 as the fourth transport member arranged on the side, and is loaded on the first stacker (not shown) formed on the top of the printer 10.

By the way, in the printer 10, images can be formed on both sides of paper P and double-sided printing can be performed. Further, in the printer 10, the paper P can be ejected face-down from the apparatus main body Bd with the printing surface facing down and loaded on the first stacker, and the printing surface can be turned up. It can be ejected face-up and loaded onto a second stacker (not shown).

Therefore, a branch portion pt1 is formed on the downstream side of the discharge roller pair m2 in the paper transport path Rt1 and adjacent to the discharge roller pair m2, and the paper is branched from the branch portion pt1 toward the downstream side. A paper transport path Rt2 is formed as a second medium transport path for retracting P and as a paper transport path for retracting. Then, a separator 36 as a first switching member for switching between the paper transport path Rt1 and the paper transport path Rt2 is swingably arranged in the branch portion pt1. The separator 36 is placed in the first and second positions by driving the driver dr1 (FIG. 1) described later, and blocks the paper transport path Rt1 and the paper transport path Rt2 at the first position. At the second position, the paper transport path Rt1 and the paper transport path Rt2 are communicated with each other.

The paper transport path Rt2 has a retract roller pair m4 as a fifth transport member at a predetermined distance downstream from the branch portion pt1 and a sixth transport member downstream from the retract roller pair m4. The evacuation roller pair m5 is arranged as.

Further, a branch portion pt2 is formed on the upstream side of the evacuation roller pair m4 in the paper transport path Rt2 and adjacent to the evacuation roller pair m4, and the paper is branched from the branch portion pt2 toward the downstream side. A paper discharge path Rt3 is formed as a medium discharge path for discharging P from the device main body Bd face-up. Then, a separator 37 (FIG. 1) as a second switching member, which will be described later, for switching between the paper transport path Rt2 and the paper discharge path Rt3 is swingably arranged in the branch portion pt2. The separator 37 is placed in the first and second positions by driving the driver dr2 described later, and at the first position, the paper transport path Rt2 and the paper discharge path Rt3 are blocked, and the second position. The paper transport path Rt2 and the paper discharge path Rt3 are communicated with each other.

In the paper discharge path Rt3, a discharge roller pair m6 as a seventh transport member is arranged on the downstream side of the branch portion pt2 and adjacent to the branch portion pt2.

In the present embodiment, the retract roller pair m4 and the discharge roller pair m6 share the pinch roller ra that receives the rotation of the reversing motor M3 as the third drive unit described later, and the reversing motor M3 is positive. When rotated, the retract roller pair m4 conveys the paper P toward the downstream side in the paper transport path Rt2, and when the reversing motor M3 is rotated in the reverse direction, the retract roller pair m4 transports the paper P toward the upstream side in the paper transport path Rt2. The discharge roller pair m6 discharges the paper P from the device main body Bd in the paper discharge path Rt3.

Further, a branch portion pt3 is formed at a predetermined position on the upstream side of the branch portion pt2 in the paper transport path Rt2 at a predetermined distance from the branch portion pt2, and is branched from the branch portion pt3 toward the upstream side. Therefore, a paper transport path Rt4 is formed as a third medium transport path for returning the retracted paper P to the paper transport path Rt1 and as a return paper transport path.

By the way, since the branch portion pt3 is formed in a curved portion connecting a portion extending in the horizontal direction and a portion extending in the vertical direction in the paper transport path Rt2 with a predetermined curvature, the inclination angle of the paper transport path Rt4 in the branch portion pt3 is formed. Is larger than the inclination angle of the paper transport path Rt2.

Therefore, when the paper P retracted to the downstream side from the branch portion pt3 in the paper transport path Rt2 is conveyed in the opposite direction, the paper P is fed to the paper transfer path Rt4 by its own weight, so that the paper transfer path Rt2 and the paper transfer path Rt4 Can be switched without using a separator such as the separator 37 disposed in the branch portion pt2. As a result, the structure of the printer 10 can be simplified and the printer 10 can be miniaturized.

In the paper transport path Rt4, the transport roller pair m7 as the eighth transport member is located downstream of the branch portion pt3 and at a predetermined distance from the branch portion pt3. A predetermined distance is set from the transfer roller pair m7, and the transfer roller pair m8 as the ninth transfer member is placed downstream from the transfer roller pair m8 at a predetermined distance from the transfer roller pair m8. A transport roller pair m9 as a transport member of the above is arranged.

Then, between the resist roller pair m1 and the transfer unit in the paper transport path Rt1, the writing sensor s1 as the first sensor is located between the fuser 31 and the discharge roller pair m2 in the paper transport path Rt1. , The discharge sensor s2 as the first medium detection unit and the second sensor detects the inverted paper P between the branch portion pt3 and the transport roller pair m7 in the paper transport path Rt4. The reversing sensor s3 as the second medium detection unit and the third sensor for the purpose of the paper transport path Rt4 has the reversing sensor s4 as the fourth sensor between the transport rollers m8 and m9 in the paper transport path Rt4. Disposed, each sensor detects the position of the paper P when the front edge of the paper P is reached.

The resist roller pair m1, the photoconductor drum 21, the transfer roller 25, the transport roller pair m7 to m9, and the like are rotated by driving the ID motor M1 as the first drive unit, and the heating roller 33 and the pressurization are performed. The rollers 34, the discharge rollers vs. m2, m3, etc. are rotated by driving the fixing motor M2 as the second drive unit, and the retracting rollers vs. m4, m5, the discharge rollers vs. m6, etc. drive the reversing motor M3. It can be rotated by.

Next, the operation of the printer 10 will be described.

When an image is formed on one side of the paper P and the paper P is ejected face-down from the apparatus main body Bd, the paper P contained in the paper cassette is fed to the paper transport path Rt1 by the paper feed mechanism. The paper transport path Rt1 is conveyed by the paper feed roller pair, the skew is corrected by the resist roller pair m1, and the paper is sent to the image forming unit Q1.

In the image forming unit Q1, the toner image on the photoconductor drum 21 is transferred when the paper P passes through the transfer unit between the photoconductor drum 21 and the transfer roller 25, and the toner image is transferred to the fuser 31. It is heated, pressurized and fixed, and an image is formed on one side of the paper P.

Subsequently, the paper P is conveyed along the paper transport path Rt1 in the direction of arrow A by the discharge rollers pairs m2 and m3, is discharged from the apparatus main body Bd, and is loaded on the first stacker.
On the other hand, when an image is formed on both sides of the paper P, the paper P fed from the paper cassette is conveyed along the paper transport path Rt1 by the paper feed roller pair, and the skew is corrected by the resist roller pair m1 to form an image. It is sent to the part Q1.

Then, on the paper P, the toner image is transferred at the image forming unit Q1, the toner image is fixed at the fixing device 31, and the image is formed on one surface of the paper P.

Subsequently, the paper P is sent to the paper transport path Rt2 and conveyed in the arrow B direction, then further conveyed in the arrow C direction by the retract roller pairs m4 and m5, and at the retracted position set in the sheet transport path Rt2. After being stopped, it is inverted and sent to the paper transport path Rt4. The paper P is conveyed along the paper transport path Rt4 in the direction of arrow D by the transport roller pairs m7 to m9, and is returned to the paper transport path Rt1.

Then, the paper P is conveyed again through the paper transport path Rt1, the toner image is transferred in the image forming unit Q1, the toner image is fixed in the fixing device 31, and the image is formed on the other surface of the paper P. In this way, the paper P on which the images are formed on both sides is conveyed along the paper transport path Rt1 in the direction of the arrow A, discharged from the apparatus main body Bd, and loaded on the first stacker.

Further, when an image is formed on one side of the paper P and the paper P is ejected face-up from the apparatus main body Bd, the paper P fed from the paper cassette has an image on one side in the image forming unit Q1. Once formed, it is sent to the paper transport path Rt2 and transported in the direction of arrow B, then sent to the paper discharge path Rt3, transported by the discharge roller pair m6 to the paper discharge path Rt3, and discharged from the apparatus main body Bd. It is loaded on the second stacker.

By the way, in the case of double-sided printing, as described above, after an image is formed on one side of the paper P, the paper P is sent to the paper transport path Rt2 and conveyed in the direction of the arrow B, and the evacuation roller pair. By m4 and m5, the paper is further conveyed in the direction of arrow C, retracted, inverted, and sent to the paper transport path Rt4.

At this time, if the rear end of the retracted paper P is positioned between the branch portions pt2 and pt3, the paper P can be smoothly sent to the paper transport path Rt4, and jam of the paper P occurs. Not only is there no problem, but the tamming of feeding the paper P to the paper transport path Rt4 is not delayed.

However, the outer diameter of the discharge roller to m2 arranged in the paper transport path Rt1 changes due to aged deterioration, or the dimensions of the paper P change depending on the environment such as temperature and humidity, so that the paper P is accurately retracted. If the paper P cannot be smoothly fed to the paper transport path Rt4, the paper P may be jammed or the tamming to feed the paper P to the paper transport path Rt4 may be delayed, resulting in printing. The throughput will drop. As a result, double-sided printing cannot be smoothly performed on the paper P.

Therefore, in the present embodiment, two sheets are based on the position of the rear end when the first sheet P when double-sided printing is performed is retracted to the sheet transport path Rt2, that is, the stop position of the sheet P. The stop position of the paper P after the stitch is corrected.

Subsequently, the operation of the printer 10 when correcting the stop position of the paper P will be described.

FIG. 1 is a control block diagram of a control device for a printer according to an embodiment of the present invention, and FIG. 3 is a first diagram and a diagram for explaining the operation of the printer when correcting a stop position according to the embodiment of the present invention. 4 is a second figure for explaining the operation of the printer when correcting the stop position in the embodiment of the present invention, and FIG. 5 shows the operation of the printer when correcting the stop position in the embodiment of the present invention. A third figure for illustration, FIG. 6 is a diagram showing the state of the paper when the rear end in the embodiment of the present invention is located at the center of the rear end stop region, and FIG. 7 is a diagram showing the state of the paper in the embodiment of the present invention. The figure which shows the state of the paper when the rear end is within the error range of the rear end stop region, FIG. The figure showing the state of the paper when it does not fit in, FIG. 9 shows the state of the paper when the transport of the paper in the embodiment of the present invention is insufficient and the rear end does not fit within the error range of the rear end stop region. It is a figure which shows.

In the figure, 10 is a printer, 51 is a control unit, 53 is a ROM as a first storage unit, and 54 is a RAM as a second storage unit.

The control unit 51 includes a CPU (not shown) as an arithmetic unit, performs various operations, executes a program recorded in the ROM 53, performs various processes, and controls the entire printer 10.

Therefore, the control unit 51 includes a print processing unit Pr1, a paper reversing processing unit Pr2 as a medium reversing processing unit, a transport correction processing unit Pr3, and the like.

The ROM 53 is a non-volatile recording medium, and programs for performing various processes are recorded.

The RAM 54 is a volatile recording medium and includes a work area used by the CPU to execute the program.

The print processing unit Pr1 performs printing processing, receives a print job consisting of print data of a plurality of pages for forming an image on paper P from a host computer (not shown) as a higher-level device, and prints print data for each page. It is edited, image data is generated, and the image data is sent to the LED head 22.

The paper reversing processing unit Pr2 performs a paper reversing process as a medium reversing process, transports the paper P by the retracting transport distance Ls described later based on the detection of the paper P by the ejection sensor s2, and retracts the paper P to the paper transport path Rt2. Then, based on the detection of the paper P by the reversing sensor s3, the paper P retracted to the paper transport path Rt2 is inverted and sent to the paper transport path Rt4.

The transport correction processing unit Pr3 performs transport correction processing, calculates the reverse transport distance Le described later based on the detection result of the paper P on the previous page by the reverse sensor s3, and describes the reverse transport distance Le as the reverse transport distance Le. The retracted transport distance Ls of the paper P on the next page is corrected based on the difference ΔL from the theoretical reverse transport distance Lx.

Bd is the main body of the device, M1 is the ID motor, M2 is the fixing motor, M3 is the reversing motor, s1 is the writing sensor, s2 is the discharge sensor, s3 and s4 are the reversing sensors, pt2 and pt3 are the branching parts, and Ar1 is the branching part. The rear end stop area Cn set between the portions pt2 and pt3 is the design stop position of the paper P retracted to the paper transfer path Rt2 set in the center of the rear end stop area Ar1, 36, 37 is a separator, and dr1 and dr2 are drivers that swing the separators 36 and 37 to the first and second positions, respectively. The write sensor s1, the discharge sensor s2, the inversion sensor s3, and s4 turn on the sensor output when the front end tf of the paper P is detected, and turn off the sensor output when the rear end tr of the paper P is detected. Further, each of the drivers dr1 and dr2 includes actuators such as a motor and a solenoid.

The paper reversing processing unit Pr2 drives the drivers dr1 and dr2 to place the separator 36 in the second position and the separator 37 in the first position, and drives the fixing motor M2 and the reversing motor M3, as shown in FIG. The paper P is sent from the paper transport path Rt1 to the paper transport path Rt2. At this time, when the ejection sensor s2 detects the rear end tr of the paper P, the paper reversing processing unit Pr2 is preset so that the rear end tr of the paper P is located at the stop position Cn of the rear end stop region Ar1. After transporting the paper P by the transport distance for retracting the paper P, that is, the retractable transport distance Ls, the reversing motor M3 is stopped.

The retracted transport distance Ls is a reference value of the distance between the discharge sensor s2 and the stop position Cn calculated by the mechanical dimensions of the printer 10, and the reversing motor M3 has a retracted transport distance Ls and a discharge roller vs. m2. It is rotated by the number of rotations calculated based on the outer diameter and the like.

When the paper P is transported by the retracted transport distance Ls, as shown in FIG. 6, the rear end tr is positioned at the stop position Cn in the paper transport path Rt2 and stopped, or as shown in FIG. , The rear end tr can be stopped by positioning it within the error range ε of the stop position Cn, but as described above, the outer diameter of the discharge roller vs. m2 changes due to aging, or the size of the paper P. However, even if the reversing motor M3 is driven, the paper P cannot be accurately transported by the retracted transport distance Ls, and the paper P is transported excessively at the rear end. tr is not within the error range ε of the stop position Cn, is positioned at the branch portion pt2 as shown in FIG. 8, or the paper P is insufficiently conveyed, and is not within the error range ε of the stop position Cn. , It may be located at the branch portion pt3 as shown in FIG.

Therefore, the paper reversing processing unit Pr2 drives the reversing motor M3 in the opposite direction, feeds the paper P to the paper transport path Rt4, and stops the reversing motor M3 when the rear end tr of the paper P is detected by the reversing sensor s3. Then, as shown in FIG. 5, the paper P is stopped at the paper transport path Rt4.

Subsequently, the paper reversing processing unit Pr2 was retracted to the paper transport path Rt2 based on the number of rotations from when the reversing motor M3 was driven in the reverse direction until it was stopped and the diameters of the retract roller pairs m4 and m5. The paper P is inverted and fed to the paper transport path Rt4, and the transport distance actually transported until it is detected by the flip sensor s3, that is, the reverse transport distance Le is calculated. In the present embodiment, since the retract roller pairs m4 and m5 that convey the paper P are rotated only when double-sided printing is performed, the outer diameters of the retract roller pairs m4 and m5 hardly change due to aged deterioration. .. Therefore, the reverse transfer distance Le can be calculated accurately.

When the paper P is transported by the retracted transport distance Ls and the rear end tr is stopped at the stop position Cn, the reverse transport distance Le is the stop position Cn and the reverse sensor s3 calculated by the mechanical dimensions of the printer 10. The distance between, that is, equal to the theoretical reversal transport distance Lx, but as shown in FIGS. 8 and 9, when the rear end tr of the paper P is not stopped at the stop position Cn, the reversal transport distance Le. And the theoretical reversal transport distance Lx are different.

Therefore, the transport correction processing unit Pr3 calculates the difference ΔL between the reverse transport distance Le and the theoretical reverse transport distance Lx, and the adjustment value α which is 1/2 of the error range ε from the difference ΔL.
α = ε / 2
Is subtracted, and the correction value Lμ
Lμ = ΔL-α
Is calculated, and the evacuation transport distance Ls is corrected by the correction value Lμ. Then, the transport correction processing unit Pr3 corrects the time for driving the reversing motor M3 by the amount of the correction of the retracted transport distance Ls.

As shown in FIG. 8, the correction value Lμ is set to a negative value when the paper P is excessively conveyed by the evacuation transfer distance Ls, and is set to a negative value by the evacuation transfer distance Ls as shown in FIG. If the paper P is not sufficiently conveyed, it is set to a positive value.

In the present embodiment, when double-sided printing is performed, after an image is formed on one side of the paper P on the first page, each time the paper P on the second and subsequent pages is sent to the paper transport path Rt2, The paper transport processing unit Pr2 transports the paper P by the retracted transport distance Ls, and subsequently transports the paper P by the reverse transport distance Ls, and the transport correction processing unit Pr3 calculates the difference ΔL.

The value of the adjustment value α is set within the range of ± 30 [%] of the initial addition value ρ described later.

Further, the transport correction processing unit Pr3 calculates the average value of the accumulated difference ΔL, that is, the difference average value ΔLav until the print job of double-sided printing is completed, and 1 / of the error range ε from the difference average value ΔLav. Subtract 2 and correct the value Lμ
Lμ = ΔLav-ε / 2
Is updated, and the difference average value ΔLav is recorded in the RAM 54.

When a new print job for double-sided printing is started, the transport correction processing unit Pr3 erases the difference average value ΔLab recorded in the RAM 54.

Immediately after the start of double-sided printing, the paper P is conveyed by the retracted transfer distance Ls calculated in advance, and the difference ΔL is not corrected. Therefore, the transfer of the paper P is insufficient, and the paper P is not conveyed. It is conceivable that the paper P is stopped without the rear end tr reaching the rear end stop region Ar1, and in that case, when the reversing motor M3 is driven, the paper P is not fed to the paper transport path Rt4 and the paper is conveyed. The road Rt2 is sent as it is toward the branch portion pt1.

Therefore, in the present embodiment, when double-sided printing is performed, when the paper transport processing unit Pr2 retracts the paper P on the first page to the paper transport path Rt2, a predetermined addition value is added to the retracted transport distance Ls. In the present embodiment, the initial addition value ρ
ρ = 15 [mm]
Is added so that the paper P is not stopped before the rear end tr of the paper P reaches the rear end stop area Ar1.

As described above, in the present embodiment, based on the detection of the paper P by the discharge sensor s2, the paper P is conveyed by the evacuation transfer distance Ls and is retracted to the sheet transfer path Rt2, and the retracted paper P is produced. It is inverted and sent to the paper transport path Rt4, and the retracted transport distance Ls is corrected based on the detection result of the paper P by the reversing sensor s3, so that the outer diameter of the discharge roller vs. m2 changes due to aged deterioration. Or, even if the dimensions of the paper P change depending on the environment such as temperature and humidity, the paper P can be transported by an accurate retracting transport distance Ls, and the paper P can be stopped at the stop position Cn in the paper transport path Rt2. can.

Therefore, the printing throughput can be improved because the jam of the paper P does not occur and the tamming of feeding the paper P to the paper transport path Rt4 is not delayed. As a result, double-sided printing can be smoothly performed on the paper P.

Further, since it is not necessary to dispose a separator for switching between the paper transport path Rt2 and the paper transport path Rt4 against the urging force of the spring at the branch portion pt3, the structure of the printer 10 can be further simplified. The printer 10 can be further miniaturized. Further, even when a weak paper P such as thin paper is used as the medium, the paper P can be sent to the paper transport paths Rt2 and Rt4.

Although the printer 10 has been described in the present embodiment, the present invention can be applied to an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction device.

The present invention is not limited to the above-described embodiment, and various modifications can be made based on the gist of the present invention, and these are not excluded from the scope of the present invention.

10 Printer Ls Ejection transport distance P Paper Pr1 Print processing unit Pr2 Paper reversing processing unit Pr3 Conveying correction processing unit Q1 Image forming unit Rt1, Rt2, Rt4 Paper transport path s2 Ejection sensor s3 Reversing sensor

Claims (5)

(A) A print processing unit that receives a print job for double-sided printing from a host device, performs printing processing, and generates image data.
(B) An image forming unit that forms an image on a medium based on the image data sent from the printing processing unit, and an image forming unit.
(C) A first medium transport path for sending a medium to the image forming unit, and
(D) A second medium transport path for retracting a medium formed by branching from the first medium transport path and having an image formed on one surface thereof.
(E) A third medium transfer path for returning the medium formed by branching from the second medium transfer path and retracted to the second medium transfer path to the first medium transfer path.
(F) A first medium detection unit arranged in the first medium transport path to detect a medium, and a first medium detection unit.
(G) A second medium detection unit arranged in the third medium transport path to detect the medium, and a second medium detection unit.
(H) Based on the detection of the medium by the first medium detection unit, the medium is conveyed by the evacuation transfer distance and retracted to the second medium transfer path, and based on the detection of the medium by the second medium detection unit. Then, the medium reversing processing unit that inverts the medium retracted in the second medium transport path and sends it to the third medium transport path,
(I) An image forming apparatus including a transport correction processing unit that corrects the evacuation transport distance based on the detection result of the medium by the second medium detection unit. (A) The print job consists of print data for forming an image on a medium of a plurality of pages.
(B) The image according to claim 1, wherein the transport correction processing unit corrects the evacuation transport distance for retracting the medium on the next page based on the detection result of the medium on the previous page by the second medium detection unit. Forming device. The image forming apparatus according to claim 2, wherein the medium inversion processing unit conveys the medium by adding an initial addition value to the evacuation transfer distance when the medium on the first page is retracted to the second medium transfer path. .. The evacuation transfer distance is an image between the first medium detection unit arranged in the first medium transfer path and the stop position of the retractable medium set in the second medium transfer path. The image forming apparatus according to any one of claims 1 to 3, which is a distance calculated by the mechanical dimensions of the forming apparatus. The transport correction processing unit actually transports the medium retracted to the second medium transport path until it is inverted and sent to the third medium transport path and detected by the second medium transport path. A claim for correcting the retracted transport distance based on the difference between the inverted transport distance to be performed and the theoretical inverted transport distance calculated by the mechanical dimensions of the image forming apparatus between the stop position and the second medium detection unit. Item 4. The image forming apparatus according to Item 4.

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