JP7200563B2 - Curl detection device and image forming device - Google Patents

Description

The present invention relates to a curl detection device and an image forming apparatus for detecting a curled state of a recording medium.

In the fixing device of Patent Document 1, the guide has one end connected to the first gear, and the first gear meshes with the rotating gear of the stepping motor. One end of the pressure spring is provided on the pressure lever, one end of the pressure lever is connected to the second gear, and the second gear meshes with the rotating gear via the idle gear. Then, the stepping motor is driven based on the thickness of the paper, the rotating gear is rotated to move the guide guide and the pressure lever, and the height of the guide guide and the pressing force of the pressure roller are adjusted.

The image forming apparatus of Japanese Patent Laid-Open No. 2002-200000 has curl detection means having a plurality of spur rollers for detecting the curl amount and the curl direction of the curled paper. Further, the image forming apparatus has a plurality of curl correcting means arranged downstream of the curl detecting means in the paper conveying direction, and correcting the curl by curving and deforming the curled paper in a direction opposite to the direction in which the curl occurs. . Based on the curl amount and the curl direction detected by the curl detection means, the curl correction means for reducing the curl is selected from among the plurality of curl correction means, and the curl of the paper is corrected.

The curl correction system of Patent Document 3 includes a curl correction device and a curl amount measuring device that measures the curl amount of the paper after the curl has been corrected by the curl correction device. In addition, the curl correction system adjusts the curl correction amount set based on the curl generation factor conditions by the correction amount setting means of the curl correction device as needed, based on the curl amount after the curl correction measured by the curl amount measuring device. correction amount correction means for correcting by

JP-A-11-265128 Japanese Patent Application Laid-Open No. 2007-320668 Japanese Patent Application Laid-Open No. 2002-080158

SUMMARY OF THE INVENTION It is an object of the present invention to provide a curl detection apparatus and an image forming apparatus that improve the detection accuracy compared to the case where the curl state of a recording medium is detected during conveyance.

Aspect 1 includes a pressing portion that presses the recording medium at a pressing position on one side in the transport direction in a state in which the recording medium is stopped while being transported along a reference surface, and a pressing portion that presses the recording medium at another position different from the pressing position in the transport direction. and a detector that detects the degree of separation of the recording medium from the surface.

In aspect 2, the detection unit includes a first detection unit that performs detection at a first detection position on the other side of the conveying direction of the recording medium, and a second detection position that is between the pressing position and the first detection position. The curl detection device according to aspect 1, further comprising a second detection unit that performs

Aspect 3 is the curl detection device according to Aspect 2, further comprising determination means for determining a curl state based on the degree of separation detected by the first detection section and the degree of separation detected by the second detection section.

Aspect 4 is the curl detection device according to aspect 1, wherein the reference surface protrudes between the pressing position and the other position.

Aspect 5 is the curl detection device according to aspect 4, further comprising a determination means for determining a curl state based on the degree of separation detected by the detection unit.

Aspect 6 is the curl detection device according to any one of Aspects 1 to 5, wherein the detection unit is a contact type detector that measures a retraction amount of a contact extending from the detector main body toward the reference surface. .

Aspect 7 is the curl detection device according to any one of Aspects 1 to 5, wherein the detection unit is a non-contact detector that measures the amount of reflection of light irradiated to the detection location.

Aspect 8 is from Aspect 1, further comprising a roll that rotates with the recording medium held therebetween on the other side in the conveying direction from the pressing position in a state where the recording medium is pressed by the pressing portion, and pulls the recording medium to the other side in the conveying direction. A curl detection device according to any one of aspects 7.

Aspect 9 is the curl detection device according to any one of Aspects 1 to 8; a fixing device provided downstream of the curl detection device in the conveying direction and fixing the toner image formed on the recording medium; image forming apparatus.

In mode 1, detection accuracy is improved as compared with the case where the curled state of the recording medium is detected during conveyance.

In aspect 2, the type of curl to be judged can be known.

In mode 3, the curl direction is determined by the determining means.

In mode 4, the type of curl determined by a single detection unit can be known.

In aspect 5, the curl direction is determined by the determining means.

In mode 6, it is possible to detect the curled state of even a transparent recording medium.

In mode 7, it is possible to detect the curled state while suppressing the influence of the curl on the recording medium.

In aspect 8, the curl of the recording medium can be corrected as compared with the case where no roll for pulling the recording medium is provided.

In aspect 9, detection accuracy is improved compared to the case where the curled state of the recording medium is detected during conveyance.

1 is a schematic diagram showing an image forming apparatus according to a first embodiment; FIG. It is a top view which shows the reference surface of 1st embodiment. FIG. 3 is a cross-sectional view taken along line AA of FIG. 2; FIG. 10 is a diagram showing how the curl of the recording medium is corrected in the first embodiment; It is a flow chart which shows operation of a first embodiment. FIG. 10 is a side view showing how a print medium with an upper curl is detected in the first embodiment; FIG. 10 is a side view showing how a down-curled print medium is detected in the first embodiment; FIG. 4 is a side view showing how a print medium without curl is detected in the first embodiment; FIG. 7 is an explanatory diagram showing how smear occurs when the recording medium enters the fixing device; FIG. 10 is an explanatory diagram showing how a recording medium with an upper curl is thrust into a fixing device; FIG. 10 is an explanatory diagram showing how a down-curled recording medium enters the fixing device; It is a flowchart which shows the operation|movement of 2nd embodiment. FIG. 10 is a side view showing how a print medium with upper curl is detected in the second embodiment. FIG. 10 is a side view showing how a down-curled recording medium is detected in the second embodiment. FIG. 11 is a side view showing how a print medium without curl is detected in the second embodiment; It is a flowchart which shows the operation|movement of 3rd embodiment. FIG. 11 is a side view showing how a recording medium with an upper curl is detected in the third embodiment; FIG. 11 is a side view showing how a down-curled recording medium is detected in the third embodiment; FIG. 11 is a side view showing how a print medium without curl is detected in the third embodiment; It is a schematic diagram which shows 4th embodiment.

<First Embodiment>
<Overview>
An example of the first embodiment will be described based on the drawings. In the drawing, the direction indicated by arrow Y is the height direction of the apparatus, and the direction indicated by arrow X is the width direction of the apparatus. Also, the direction indicated by an arrow Z in the drawing is defined as the device depth direction orthogonal to the device height direction and the device width direction.

<Configuration of Image Forming Apparatus>
As shown in FIG. 1, the image forming apparatus 10 is an apparatus that forms an image on a recording medium P by electrophotography.

As the recording medium P, different types of OHP, film sheet, coated paper, and the like can be used. As for the types, strength of stiffness, difference in thickness dimension, and the like can be mentioned.

To explain the difference in the thickness dimension of the recording medium P, thick paper, plain paper, and thin paper can be mentioned. In this embodiment, cardboard refers to paper having a basis weight of 106 g/m ² or more. Specific examples of cardboard include those with a basis weight of 157 g/m ² and a thickness of 180 μm or 184 μm, and those with a basis weight of 209 g/m ² and a thickness of 236 μm or 247 μm.

The image forming apparatus 10 includes an image forming unit 14 that forms an image on a recording medium P, and a fixing device 16 that is an example of fixing means that fixes a toner image, which is an example of an image transferred onto the recording medium P, onto the recording medium P. and The image forming apparatus 10 also includes a medium conveying section 18 that conveys the recording medium P, and a post-processing section 20 that performs post-processing and the like on the recording medium P on which an image has been formed.

The image forming apparatus 10 includes a control section 22 that controls each section, and the control section 22 is mainly composed of a microcomputer containing a CPU (CPU core), ROM, RAM, and the like.

[Image forming section]
The image forming section 14 includes a toner image forming section 24 that forms a toner image, and a transfer device 26 that transfers the image formed by the toner image forming section 24 onto the recording medium P. FIG.

<Toner image forming unit>
A plurality of toner image forming units 24 are provided so as to form a toner image for each color, and the toner image forming units 24 are arranged linearly along the width direction X of the apparatus.

In this embodiment, toner image forming units 24Y, 24M, 24C, and 24K are provided for a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K). Note that Y, M, C, and K attached to the symbols indicate the respective colors described above. In the following description, the toner image forming units 24Y, 24M, 24C, and 24K and the respective members constituting them will be described by omitting the suffixes Y, M, C, and K when it is not necessary to distinguish between toner colors. .

The toner image forming section 24 includes a photosensitive drum 28 , a charging device 30 , an exposure device 32 and a developing device 34 .

(photosensitive drum)
A photosensitive layer is formed on the outer peripheral surface of the photoreceptor drum 28 , and an electrostatic latent image is formed by the exposure device 32 on the outer peripheral surface of the photoreceptor drum 28 charged by the charging device 30 . The electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 28 is developed into a toner image by the developing device 34 .

(Exposure device)
The exposure device 32 irradiates the outer peripheral surface of the photosensitive drum 28 with exposure light modulated according to the image data received from the controller 22 to form an electrostatic latent image.

(developing device)
The developing device 34 develops the electrostatic latent image on the outer circumferential surface of the photoreceptor drum 28 as a toner image with developer containing toner and carrier.

<Transfer device>
The transfer device 26 includes an endless belt-like intermediate transfer body 36, and the intermediate transfer body 36 is wound around a plurality of rolls 38, 38B, and 38D. The roll 38D is rotated by a motor and moves around the intermediate transfer member 36 in the direction A of rotation.

The transfer device 26 includes a primary transfer section 40 that primarily transfers the toner image formed on the photosensitive drum 28 onto the intermediate transfer body 36, and a secondary transfer of the toner image that has been primarily transferred onto the intermediate transfer body 36 onto the recording medium P. A secondary transfer unit 42, which is an example of a transfer unit, is provided.

(Primary transfer section)
The primary transfer unit 40 primarily transfers the toner images formed on the photoreceptor drums 28 of the respective colors onto the intermediate transfer member 36 at the primary transfer positions 44 in contact with the respective photoreceptor drums 28 so as to overlap each other. The toner image held by each photoreceptor drum 28 is primarily transferred onto the intermediate transfer member 36 by the electric field between the primary transfer roll 46 to which the primary transfer bias voltage is applied and the outer peripheral surface of the photoreceptor drum 28 .

The photoreceptor drums 28 are spaced apart in the rotation direction A of the rotating intermediate transfer member 36 .

(Secondary transfer unit)
The secondary transfer unit 42 secondarily transfers the superimposed toner images onto the intermediate transfer member 36 by the primary transfer by each photosensitive drum 28 onto the recording medium P at the secondary transfer position 54 . The secondary transfer unit 42 includes a roll 38B arranged on the inner peripheral surface side of the intermediate transfer body 36 and a secondary transfer roll 56 arranged on the outer peripheral surface side of the intermediate transfer body 36. A transfer nip NT is formed between it and the next transfer roll 56 .

The toner image, which is primarily transferred onto the intermediate transfer member 36 and superimposed with each color, is transferred onto the recording medium P passing through the transfer nip NT by the electric field between the roll 38B to which the secondary transfer bias voltage is applied and the secondary transfer roll 56. be done.

[Fixing device]
The fixing device 16 includes a pair of fixing rolls 16A, and a fixing nip NF is formed between both fixing rolls 16A. The fixing device 16 nips the toner image transferred onto the recording medium P by the secondary transfer portion 42 of the transfer device 26 between the fixing nip NF, pressurizes the toner image, heats the toner image, and fixes the toner image onto the recording medium P. FIG.

[Medium Conveying Unit]
The medium conveying section 18 includes a medium supply section 62 that supplies the recording medium P to the image forming section 14, and a medium discharge section 64 that discharges the recording medium P on which an image has been formed. Further, the medium conveying section 18 includes a medium returning section 66 that is used when images are formed on both sides of the recording medium P, and an intermediate conveying section 68 that conveys the recording medium P from the secondary transfer position 54 to the fixing device 16 . is composed of

The medium supply unit 62 supplies the recording medium P sheet by sheet to the transfer nip NT of the image forming unit 14 in synchronization with the transfer timing of the secondary transfer. The medium ejection section 64 ejects the recording medium P on which the toner image is fixed by the fixing device 16 and the image is formed to the outside of the apparatus. When forming an image on the other side of the recording medium P having an image formed on one side thereof, the medium returning section 66 turns over the recording medium P and conveys it again to the secondary transfer section 42 .

[Post-processing section]
The post-processing section 20 includes a medium cooling section 70, a correcting device 72, and reading means 74, which is an example of an image inspection section. The medium cooling unit 70 cools the recording medium P on which the image is formed.

The correction device 72 is configured by a decurler, for example, and corrects the curvature of the recording medium P cooled by the medium cooling section 70 .

The correction device 72 bends the recording medium P in the out-of-plane direction between the leading edge on the front side in the transport direction H and the rear edge on the rear side in the transport direction H, thereby curling the recording medium P. As shown in FIG.

The reading unit 74 is configured by a device that reads and inspects an image formed on the recording medium P, and an in-line sensor can be given as an example.

A curl detection device 100 is provided on the upstream side of the secondary transfer section 42 in the conveyance path of the recording medium P formed by the medium conveyance section 18 .

(curl detector)
As shown in FIGS. 2 and 3, the curl detection device 100 includes a rectangular support plate 102 that supports the passing recording medium P. The upper surface of the support plate 102 forms a flat reference surface 104. do.

Rectangular upstream openings 106 are formed in the support plate 102 on both sides of the transport direction one side HI, which is the upstream side in the transport direction H. As shown in FIG. Rectangular downstream openings 108 are formed on both side portions of the support plate 102 on the downstream side in the transport direction H on the other transport direction side HT.

An upstream driving roll 110 is arranged in each upstream opening 106 , and the circumferential surface of the upstream driving roll 110 is exposed to the reference surface 104 . Specifically, the top of the upstream drive roll 110 is aligned with the reference surface 104 or slightly protrudes.
A downstream drive roll 112 is arranged at each downstream opening 108 , and the peripheral surface of the downstream drive roll 112 is exposed to the reference surface 104 . Specifically, the top of the downstream drive roll 112 is aligned with the reference surface 104 or slightly protrudes.

A pressing roll 114 is arranged above the upstream driving roll 110 , and the pressing roll 114 sandwiches the recording medium P sent from upstream between itself and the upstream driving roll 110 .

The upstream drive roll 110 is rotationally controlled by the controller 22 . As the upstream drive roll 110 rotates forward and the pressure roll 114 follows, the recording medium P sandwiched between the rolls 110 and 114 is sent downstream. Further, by stopping the rotation of the upstream drive roll 110, the conveyance of the recording medium P sandwiched between the two rolls 110 and 114 is stopped.

As a result, while the recording medium P being transported along the reference surface 104 is stopped on the reference surface 104, the pressing portion 118 presses the recording medium P at the pressing position 116 on the one side HI in the transport direction. It is composed of a pressing roll 114 .

An elevating roll 120 is arranged above the downstream drive roll 112, and the elevating roll 120 is elevated by an elevation mechanism (not shown). When the elevating roll 120 is lifted, the recording medium P on the reference surface 104 is released from the pressing force of the elevating roll 120 . On the other hand, when the elevating roll 120 descends, the recording medium P on the reference surface 104 is sandwiched between the elevating roll 120 and the downstream drive roll 112, as shown in FIG.

The downstream drive roll 112 is rotationally controlled by the controller 22 . With the lifting roll 120 lowered, the downstream drive roll 112 rotates forward and the lifting roll 120 follows, so that the portion of the recording medium P sandwiched between the rolls 112 and 120 is moved to the other side of the conveying direction, which is the downstream side. Gives power towards HT.

At this time, if the upstream drive roll 110 rotates forward at the same speed as the downstream drive roll 112, the recording medium P on the reference surface 104 is transported downstream in the other transport direction HT.
On the other hand, if the upstream drive roll 110 is stopped, the recording medium P, whose rear end portion of the upstream one side HI in the transport direction is pressed by the pressing portion 118, is moved to the other downstream side HT in the transport direction. The leading end portion is pulled toward the other side HT in the conveying direction, which is the downstream side. Thereby, tension in the transport direction H is applied to the recording medium P, and the downstream drive roll 112 constitutes a roll that pulls the recording medium P to the other transport direction side TG.
Note that even when the upstream drive roll 110 rotates forward at a slower speed than the downstream drive roll 112, the leading edge of the recording medium P on the other transport direction side HT on the downstream side is the other transport direction side HT on the downstream side. pulled to.

2 and 3, the curl detection device 100 detects the curl from the reference surface 104 at the first detection position 132, which is an example of another position different in the conveying direction H from the pressing position 116 by the pressing portion 118. A detection unit 122 for detecting the degree of separation of the recording medium P is provided.

The detection unit 122 is arranged between the upstream drive roll 110 and the downstream drive roll 112 and closer to the downstream drive roll 112, and is located at the center of the support plate 102 in the width direction (the direction intersecting the conveying direction H). placed in the department.

The detection unit 122 includes a detector body 124 and a contactor 126 extending from the detector body 124 toward the reference surface 104. The contactor 126 extends into the detector body 124 so as to be retractable. . In other words, the detector 122 is a contact detector that measures the amount of retraction of the contactor 126, and the detector 122 outputs the amount of retraction of the contactor 126 to the control section 22 as an electrical signal as a measured value.

A detector body 124 of the detection unit 122 is fixed at a position separated from the reference plane 104 by a predetermined distance, and the distance from the tip of the contact 126 to the reference plane 104 is determined based on the retraction amount of the contact 126. grasped. Accordingly, the control unit 22 can calculate the separation distance 128 from the reference surface 104 to the surface of the recording medium P based on the measurement value from the detection unit 122, and the distance of the recording medium P from the reference surface 104 can be calculated. The degree is grasped by the control unit 22 .
In other words, the separation degree can be rephrased as the separation distance 128 along the apparatus height direction Y from the reference surface 104 at the first detection position 132 to the surface of the recording medium P.

(flowchart)
FIG. 5 is a flow chart showing determination processing, and the operation of the curl detection device 100 will be described according to the flow chart.

That is, when the CPU of the microcomputer constituting the control unit 22 starts operating according to the program stored in the ROM and the determination process is called from the main routine, the determination process is executed.

In the determination process, when the conveyed recording medium P passes over the reference surface 104, the upstream drive roll 110 is moved so that the recording medium P is positioned on the reference surface 104 based on, for example, an input from a sensor (not shown). Stop (S1). As a result, the recording medium P is stopped on the reference surface 104, and the rear end of the recording medium P is kept pressed by the pressing portion 118 at the pressing position 116 on the one side HI in the transport direction.

Then, after the lifting roll 120 is lifted by the lifting mechanism to release the pressure on the front end of the recording medium P (S2), a measurement value is input from the detection unit 122 (S3).

Next, the separation distance 128 from the reference surface 104 to the surface of the recording medium P is calculated from the measured value input from the detection unit 122, and the separation degree of the recording medium P from the reference surface 104 is obtained. It is determined whether or not it is equal to or greater than the first threshold value stored in the ROM (S4: determination means). Here, the first threshold is a threshold used for determining upper curl.

At this time, as shown in FIG. 6, if an upper curl occurs in which the front end of the recording medium P bends toward the surface side, the contactor 126 of the detection unit 122 is pushed up by the recording medium P and retreats. Then, the degree of separation of the recording medium P from the reference surface 104 increases, and it is determined that the degree of separation is greater than or equal to the first threshold. In this case, the upper curl flag secured in the RAM is set to "1" (S5) and the process returns to the main routine.

On the other hand, as shown in FIG. 7, when the front end of the recording medium P bends toward the back side and curls down, the contactor 126 of the detection unit 122 is not pushed up and does not retreat. Further, as shown in FIG. 8, even when the recording medium P is not curled and is flat, the contactor 126 of the detection unit 122 is not pushed up and does not retreat. In these cases, it is determined in step S4 that the degree of separation is less than the first threshold, so nothing is done and the process returns to the main routine.

Here, the upper curl flag is a flag for determining whether or not the recording medium P being conveyed has an upper curl.

When this upper curl flag is set to "1", the recording medium P on the support plate 102 is supplied as it is to the secondary transfer section 42 in the printing process called from the main routine.

On the other hand, when the upper curl flag is cleared to "0", in the printing process, the front end portion of the recording medium P being conveyed is flexed toward the surface side to impart an upper curl to the recording medium P, and then the upper curl is applied. It is supplied to the next transfer section 42 .

Specifically, as shown in FIG. 1, the recording medium P on the support plate 102 is passed through the correcting device 72 to give an upper curl once without being transferred, and then supplied to the secondary transfer position 54 . As a result, even when a recording medium P such as thick paper having a high elasticity or stickiness is used, the recording medium P is bent downward when the leading edge of the recording medium P is sandwiched between the fixing rolls 16A of the fixing device 16. be able to. Therefore, it is possible to suppress the change in the moving speed of the recording medium P that may occur when the fixing device 16 enters the fixing device 16, suppress the occurrence of smear at the time of entering the fixing device due to the speed change, and suppress the deterioration of the toner image formed on the recording medium P. .

(Smear when entering fixing)
FIG. 9 is an explanatory diagram showing how smear occurs at the time of entry into fixing.

When using a recording medium P such as thick paper having high elasticity and stickiness, when the leading edge PF of the recording medium P is sandwiched between the fixing nips NF between the fixing rollers 16A of the fixing device 16, the recording medium P is conveyed downstream. The movement of the recording medium P in the conveying direction H may be hindered and the speed change may occur. At this time, the toner image of each color that is secondarily transferred from the intermediate transfer member 36 to the recording medium P at the secondary transfer position 54 is affected (occurrence of color misregistration).

Then, the toner image of each color affected by the secondary transfer is fixed on the recording medium P. FIG. For this reason, in the image formed on the recording medium P, a smear consisting of streaks extending in the direction intersecting the conveying direction H is formed in the toner image of all colors primarily transferred from the photosensitive drum 28 of each color. .

At this time, as shown in FIG. 10, if the path direction 130 of the recording medium P at the secondary transfer position 54 and the curling direction of the recording medium P are the same, then a The recording medium P bends at . That is, in the present embodiment, if the recording medium P is an upper curl, the recording medium P bends between the secondary transfer position 54 and the fixing position 58 to absorb the speed change. Therefore, smear is less likely to occur at the time of entry into fixing.

However, as shown in FIG. 11, when the recording medium P is flat, or when the curling direction is opposite to the path direction 130, the recording medium P draws an S-shape, and the behavior of the recording medium P is stretched. occur. In this case, smear is likely to occur at the time of entering fixing.

Therefore, when the upper curl flag is cleared to "0", the toner is formed on the recording medium P by performing the secondary transfer after giving the upper curl to the recording medium P as described above. Suppress image deterioration.

In addition to the methods described above, the method of suppressing deterioration of the toner image includes a method of controlling the driving torque of the secondary transfer roll 56 to be constant, a method of lowering the nip pressure of the fixing device 16, and a method of lowering the process speed to prevent transfer. One way is to slow it down.

Further, depending on the arrangement conditions of the mechanism, as shown in FIG. 4, by applying a pulling force in the conveying direction H to the recording medium P to correct the curl and then performing the secondary transfer, deterioration of the toner image can be suppressed. be done.

(action/effect)
The operation of this embodiment according to the above configuration will be described.

In this embodiment, the recording medium P conveyed along the reference surface 104 is stopped at the pressing position 116 and pressed by the pressing portion 118 . In this pressed state, the detection unit 122 detects the degree of separation of the recording medium P from the reference surface 104 at a first detection position 132 that is an example of another position different from the pressing position 116 in the transport direction H. Therefore, detection accuracy is improved compared to the case where the curled state of the recording medium P is detected during conveyance.

Further, the detection unit 122 is a contact-type detector that measures the retraction amount of the contactor 126 extending from the detector main body 124 toward the reference surface 104 . Therefore, even if the recording medium P is transparent, the curled state can be detected.

A downstream drive roll 112 is provided that rotates across the recording medium P on the other side HT in the transport direction from the pressing position 116 in a state where the recording medium P is pressed by the pressing portion 118 and pulls the recording medium P to the other side HT in the transport direction. ing. As a result, compared to the case where the downstream drive roll 112 that pulls the recording medium P is not provided, it is possible to correct curling of the recording medium P such as plain paper or thin paper.

Further, the image forming apparatus 10 of this embodiment includes the curl detection device 100 and the fixing device 16 that fixes the toner image formed on the recording medium P. As shown in FIG. Therefore, compared to the case where the curled state of the recording medium P is detected during transportation, the detection accuracy is improved, and countermeasures can be taken to suppress the occurrence of smear at the time of entry into fixing.

<Second embodiment>
12 to 15 are diagrams showing the second embodiment, the same or equivalent parts as those of the first embodiment are denoted by the same reference numerals and explanations thereof are omitted, and only different parts will be explained.

The image forming apparatus 10 according to the present embodiment differs from the first embodiment in the detection unit 122 for detecting curling of the recording medium P. FIG.

That is, the detection unit 122 includes a first detection unit 134 that performs detection at a first detection position 132 on the other side HT in the conveying direction of the recording medium P, and a second detection position 136 between the holding position 116 and the first detection position 132. and a second detection unit 138 that performs detection at .

The pressing unit 118 presses the rear end of the recording medium P placed on the reference surface 104 , and the first detection unit 134 moves the front end of the recording medium P placed on the reference surface 104 from the reference surface 104 . to detect the degree of separation. The second detection unit 138 detects the degree of separation from the reference surface 104 at the central portion in the length direction of the recording medium P placed on the reference surface 104 .

The first detection unit 134 includes a first detector body 140 and a first contactor 142 extending from the first detector body 140 toward the reference surface 104. The first contactor 142 serves as the first detector. It is configured to be retractable into the device body 140 . The first detection unit 134 can be rephrased as a contact-type detector that measures the amount of retreat of the first contactor 142, and the first detection unit 134 uses the amount of retreat of the first contactor 142 as a measured value to generate an electric signal. Output to the control unit 22 .

The first detection unit 134 is fixed at a position separated by a predetermined distance from the reference surface 104, and based on the retraction amount of the first contactor 142, the distance from the tip of the first contactor 142 to the reference surface 104 is determined. is grasped. As a result, the control unit 22 calculates the separation distance 128 from the reference surface 104 to the surface of the recording medium P based on the measurement value from the first detection unit 134, thereby determining the separation of the recording medium P from the reference surface. degree is understood.
In other words, the separation degree can be rephrased as the separation distance 128 from the reference surface 104 to the surface of the recording medium P.

The second detection unit 138 includes a second detector body 144 and a second contactor 146 extending from the second detector body 144 toward the reference surface 104. The second contactor 146 serves as a second detector. It is configured to be retractable into the container body 144 . In other words, the second detection unit 138 is a contact-type detector that measures the amount of retraction of the second contactor 146. The second detection unit 138 measures the amount of retraction of the second contactor 146 as a measured value. A signal is output to the control unit 22 .

The second detection unit 138 is fixed at a position separated from the reference surface 104 by a predetermined distance, and based on the retreat amount of the second contact 146, the distance from the tip of the second contact 146 to the reference surface 104 is determined. is grasped. As a result, the control unit 22 calculates the separation distance 128 from the reference surface 104 to the surface of the recording medium P based on the measurement value from the second detection unit 138, so that the recording medium P from the reference surface 104 is grasped.
In other words, the separation degree can be rephrased as the separation distance 128 from the reference surface 104 to the surface of the recording medium P.

(flowchart)
FIG. 12 is a flow chart showing determination processing, and the operation of the curl detection device will be described according to the flow chart.

That is, when the CPU of the microcomputer constituting the control unit 22 starts operating according to the program stored in the ROM and the determination process is called from the main routine, the determination process is executed.

In the determination process, when the conveyed recording medium P passes over the reference surface 104, the upstream drive roll 110 is stopped (SB1). As a result, the recording medium P is stopped on the reference surface 104, and the rear end of the recording medium P is kept pressed by the pressing portion 118 at the pressing position 116 on the one side HI in the transport direction.

After the lifting mechanism lifts the lifting roll 120 to release the front end of the recording medium P (SB2), measurement values are input from the first detection unit 134 and the second detection unit 138 (SB3).

Next, the separation distance 128 from the reference surface 104 to the surface of the recording medium P is calculated from the measured value input from the first detection unit 134, and the degree of separation of the recording medium P from the reference surface 104 at the first detection position 132 is calculated. demand. Then, it is determined whether or not this degree of separation is equal to or greater than a second threshold stored in advance in the ROM (SB4: determination means). Here, the second threshold is a threshold used for determining upper curl.

At this time, as shown in FIG. 13, if an upper curl occurs in which the front end portion of the recording medium P bends toward the surface side, the first contactor 142 of the first detection unit 134 is pushed up by the recording medium P. to retreat. Then, the degree of separation of the recording medium P increases, and it is determined that the degree of separation is greater than or equal to the second threshold. In this case, the upper flag secured in the RAM is set to "1" (SB5: judgment means) and the process returns to the main routine.

If it is determined in step SB4 that the degree of separation at the front end of the recording medium P is less than the second threshold value, the separation distance 128 from the reference surface 104 to the surface of the recording medium P is calculated from the measured value input from the second detection unit 138. calculate. Based on this calculation result, the degree of separation of the recording medium P from the reference surface 104 at the second detection position 136 is obtained, and it is determined whether or not the degree of separation is equal to or greater than a third threshold stored in advance in the ROM (SB6). Here, the third threshold is a threshold used for determining down curl.

At this time, as shown in FIG. 14, when the front end portion of the recording medium P bends toward the back side and the downward curling occurs, the downward bending of the leading end portion of the recording medium P is prevented by the reference surface 104 . be done. In this state, the recording medium P such as thick paper having high elasticity and stickiness is curved so that the central portion in the transport direction H protrudes toward the surface side. As a result, the second contactor 146 is pushed up by the curved portion of the recording medium P, and the second detector 138 retreats.

Then, at the second detection position 136, the degree of separation of the recording medium P increases, and it is determined that the degree of separation is greater than or equal to the third threshold. In this case, the down curl flag secured in the RAM is set to "1" (SB7) and the process returns to the main routine.

This down-curl flag is a flag for determining whether or not down-curl occurs in the recording medium P being conveyed.

When this down-curl flag is set to "1", in the printing process, the front end of the recording medium P being conveyed is warped toward the front side as described above to impart an upper curl. Then secondary transfer is performed. As a result, the occurrence of smear at the time of entering fixing is suppressed, and the deterioration of the toner image formed on the recording medium P is suppressed.

FIG. 15 is a diagram showing a case where the recording medium P is flat with no curl or slightly curled. Therefore, the first contactor 142 of the first detection unit 134 does not retreat, and the degree of separation at the first detection position 132 is determined to be less than the second threshold (SB4). Also, the second contactor 146 of the second detection unit 138 does not retreat, and the degree of separation at the second detection position 136 is determined to be less than the third threshold value (SB6), so the process returns to the main routine without doing anything. .

In this case, in the print processing called from the main routine, processing is performed according to the path direction of the recording medium P at the secondary transfer position 54 in the image forming apparatus 10, and the occurrence of smear at the time of entering fixing is suppressed, and recording is performed. To prevent deterioration of a toner image formed on a medium P.

(action/effect)
Also in this embodiment according to the above configuration, it is possible to achieve the same effects as those of the first embodiment.

Further, the detection unit 122 includes a first detection unit 134 that performs detection at a first detection position 132 on the other side HT of the transport direction of the recording medium P, and a second detection position 136 between the holding position 116 and the first detection position 132 . and a second detection unit 138 that performs detection at . Therefore, the type of curl to be determined can be known.

Then, the curl state is determined based on the separation degree detected by the first detection unit 134 and the separation degree detected by the second detection unit 138 . Therefore, the curl direction is determined based on the determination result.

As compared with the first embodiment, not only the upper curl generated in the recording medium P, but also the down curl can be determined, so it is possible to take detailed measures according to the curl direction.
Note that the type of curl may be determined from the relationship between the distance 128 detected by the first detection unit 134 and the distance 128 detected by the second detection unit 138 .
That is, when the separation distance 128G detected by the first detection unit 134 is greater than the separation distance 128 detected by the second detection unit 138, it is determined that the curl is an upper curl. Further, when the separation distance 128 detected by the second detection section 138 is larger than the separation distance 128 detected by the first detection section 134, it is determined that the curl is down. If the separation distance 128 detected by the first detection unit 134 and the separation distance 128 detected by the second detection unit 138 are substantially the same, it is determined that there is no curl.

<Third Embodiment>
16 to 19 are diagrams showing the third embodiment, the same or equivalent parts as those of the first embodiment are denoted by the same reference numerals and the explanation thereof is omitted, and only the different parts are explained.

The image forming apparatus 10 according to this embodiment differs from the first embodiment in the support plate 102 that supports the recording medium P. FIG.

That is, the support plate 102 is curved so that the central portion in the transport direction H protrudes toward the reference surface 104 on which the recording medium P is transported. A portion to a certain first detection position 132 protrudes upward. That is, protruding between the pressing position 116 and the first detection position 132, which is another position, is a concept including a configuration in which the reference surface 104 is curved so as to protrude upward.

(flowchart)
FIG. 16 is a flow chart showing determination processing, and the operation of the curl detection device will be described according to the flow chart.

That is, when the CPU of the microcomputer constituting the control unit 22 starts operating according to the program stored in the ROM and the determination process is called from the main routine, the determination process is executed.

In the determination process, when the conveyed recording medium P passes over the reference surface 104, the upstream drive roll 110 is stopped (SC1). As a result, the recording medium P is stopped on the reference surface 104, and the rear end of the recording medium P is kept pressed by the pressing portion 118 at the pressing position 116 on the one side HI in the transport direction.

Then, after the lifting roll 120 is lifted by the lifting mechanism to release the pressure on the front end of the recording medium P (SC2), a measurement value is input from the detection unit 122 (SC3).

Next, the separation distance 128 from the reference plane 104 to the surface of the recording medium P is calculated from the measured value input from the detection unit 122, and the separation degree of the recording medium P from the reference plane 104 is obtained. (SC4: judging means). Here, the fourth threshold is a threshold used to determine upper curl.

At this time, as shown in FIG. 17, if an upper curl occurs in which the front end of the recording medium P bends toward the surface side, the contactor 126 of the detection unit 122 is pushed up by the recording medium P and retreats greatly. . Then, the degree of separation increases, and it is determined that the degree of separation is equal to or greater than the fourth threshold, that is, the degree of separation is not less than the fourth threshold. In this case, the upper flag reserved in the RAM is set to "1" (SC5) and the process returns to the main routine.

In step SC4, when it is determined that the degree of separation of the recording medium P from the reference surface 104 is less than the fourth threshold, the degree of separation is stored in advance in the ROM and whether or not it is equal to or greater than a fifth threshold smaller than the fourth threshold. is determined (SC6: determination means).

At this time, as shown in FIG. 18, when the front end portion of the recording medium P bends toward the back surface side, and the down curl occurs, the recording medium P is curved such that the central portion in the transport direction H protrudes. Arranged along the surface 104, the contactor 120 of the detection section 122 is not pushed up and does not retract.

In this case, in step SC6, it is determined that the degree of separation is equal to or greater than the fifth threshold, so the process returns to the main routine without doing anything. Here, the fifth threshold is a threshold used for determining down curl.

On the other hand, as shown in FIG. 19, when the recording medium P is not curled, the leading edge of the recording medium P is curved downward toward the other transport direction side HT, which is the downstream side of the transport direction. Leaves upward from the reference plane 104 . As a result, the contactor 126 of the detection unit 122 is pushed up by the recording medium P and retreats.

At this time, the leading edge of the recording medium P positioned at the first detection position 132 is less distant from the reference plane 104 than in the case of the recording medium P with upper curl (see FIG. 17). Therefore, in step SC6, it is determined that the degree of separation is less than the fifth threshold, so the down curl flag secured in the RAM is set to "1" (SC7) and the process returns to the main routine.

(action/effect)
Also in this embodiment according to the above configuration, it is possible to achieve the same effects as those of the first embodiment.

Also, the reference surface 104 formed by the support plate 102 protrudes at the center in the transport direction H between the holding position 116 and the first detection position 132, which is an example of another position. Therefore, it is easier to determine the curl direction than when the reference surface 104 is flat.

Further, the curl direction is determined by determining the curl state based on the separation degree detected by the detection unit 122 .

As a result, it is possible to determine whether the recording medium P has an upper curl, the recording medium P has a down curl, or the recording medium P has no curl, using a single detection unit 122 .

Note that in each embodiment, as the detection unit 122 that detects the degree of separation of the recording medium P from the reference surface 104, a contact that measures the retraction amount of the contactor 126 that extends from the detector main body 124 toward the reference surface 104 is used. Although a formula detector was used, it is not limited to this.

<Fourth embodiment>
For example, as shown in FIG. 20, the detection unit 122 may be configured with a non-contact detector that measures the amount of reflected light RL of the light L irradiated to the detection point.

In this case, the separation distance 128 to the recording medium P is measured from the amount of reflected light RL reflected from the recording medium P, and the amount of curl is measured based on this.

Further, when the detection section 122 of the non-contact type detector is used, the detection section 122 can be arranged below the support plate 102 by providing the support plate 102 with an opening 102B through which the light L is transmitted.

10 Image forming apparatus 22 Control unit 28 Photoreceptor drum 100 Curl detection device 104 Reference surface 120 Contact 122 Detection unit 124 Detector body 126 Contact 128 Spacing distance 132 First detection position 134 First detection unit 136 Second detection position 138 Second detector 140 First detector main body 142 First contactor 144 Second detector main body 146 Second contactor H Conveyance direction HI Conveyance direction one side HT Conveyance direction other side P Recording medium

Claims (8)

a pressing portion that presses the recording medium at a pressing position on one side in the transport direction while the recording medium is stopped while being transported along the reference surface;
a detection unit that detects the degree of separation of the recording medium from the reference surface at another position different from the pressing position in the conveying direction;
with
The curl detecting device , wherein the reference surface protrudes between the pressing position and the other position . 2. A curl detecting device according to claim 1, further comprising judging means for judging a curled state based on the degree of separation detected by said detector . 3. A curl detector according to claim 1, wherein said detector is a contact detector that measures the retraction amount of a contact extending from a detector body toward said reference surface . a pressing portion that presses the recording medium at a pressing position on one side in the transport direction while the recording medium is stopped while being transported along the reference surface;
a detection unit that detects the degree of separation of the recording medium from the reference surface at another position different from the pressing position in the conveying direction;
with
The curl detection device , wherein the detection unit is a contact type detector that measures the amount of retraction of the contact extending from the detector main body toward the reference surface . 5. A roller for pulling the recording medium to the other side in the conveying direction by rotating the recording medium on the other side in the conveying direction from the pressing position while the recording medium is pressed by the pressing portion. The curl detection device according to any one of . a pressing portion that presses the recording medium at a pressing position on one side in the transport direction while the recording medium is stopped while being transported along the reference surface;
a detection unit that detects the degree of separation of the recording medium from the reference surface at another position different from the pressing position in the conveying direction;
with
A curl detection device comprising a roll that rotates while sandwiching the recording medium on the other side in the conveying direction from the pressing position and pulls the recording medium to the other side in the conveying direction while the recording medium is pressed by the pressing portion. A curl detection device according to any one of claims 1 to 6;
a fixing device provided downstream of the curl detection device in the conveying direction for fixing the toner image formed on the recording medium;
image forming apparatus. a pressing portion that presses the recording medium at a pressing position on one side in the transport direction while the recording medium is stopped while being transported along the reference surface;
a curl detection device comprising: a detector that detects the degree of separation of the recording medium from the reference surface at a position different from the pressing position in the conveying direction;
a fixing device provided downstream of the curl detection device in the conveying direction for fixing the toner image formed on the recording medium;
image forming apparatus.

Images