JP2020189738A - Image formation device, printing medium conveyance device, and image formation method - Google Patents

Abstract

To accurately and easily detect a bending state of a printing medium.SOLUTION: An image formation device includes: first electrostatic capacity sensors 11 and 12 which are installed in a conveyance path of a printing medium and allow at least a specific side of a printing medium to pass therethrough; second electrostatic capacity sensors 21 and 22 which are installed at a position farther from the first electrostatic capacity sensors on the conveyance path of the printing medium and allow a side same as the specific side to pass therethrough; and a detection part 102 which detects a bending amount of the printing medium from a difference between the electrostatic capacity value obtained from the first electrostatic capacity sensors and the electrostatic capacity value obtained from the second electrostatic capacity sensors. The detection part 102 detects the bending amount of the printing medium to enable correction of the beading amount and correction of the image formation state for the printing medium.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus, a printing medium conveying apparatus, and an image forming method, and more particularly to a technique for detecting an attitude of a printing medium.

Conventionally, in an image forming apparatus such as a printing machine, it is necessary to detect the posture of the paper for forming an image and control so that the image is formed at a correct position on the paper. That is, the image forming apparatus detects the bending or deviation of the paper conveyed from the built-in (or connected) paper conveying device by the optical sensor, and is conveyed to the image forming unit according to the detected posture. The posture of the paper is corrected. An optical sensor that detects the posture of paper is such that a sensor in which a light emitting part and a light receiving part are paired is placed at a place where the paper passes, and the paper blocks between the light emitting part and the light receiving part to pass the paper. It detects the state.

However, the paper posture detection mechanism using the optical sensor may not be able to detect the paper depending on the type of paper (printing medium). That is, in the case of a special print medium such as a transparent film or colored paper, the detection state by the optical sensor is different from that of general white paper, and a situation occurs in which the posture cannot be detected.

Patent Document 1 describes a technique for determining the offset of paper from the capacitance detected by using an electrode facing the paper. That is, in Patent Document 1, when two triangular electrode plates are arranged close to the front surface and the back surface of the paper so as to sandwich the paper to be conveyed, and the paper passes between the two electrode plates. Describes a technique for determining the offset of paper from the change in the capacitance value between the two electrode plates.

Japanese Unexamined Patent Publication No. 2018-11566

As described in Patent Document 1, it has been conventionally known to detect a deviation of a print medium from a capacitance value.
However, the technique described in Patent Document 1 can only detect the offset of the print medium, and cannot detect the bent state in which the print medium is bent at an angle and transported. For this reason, it has been desired to make it easier to detect the posture of a more advanced print medium.

An object of the present invention is to provide an image forming apparatus, a printing medium conveying apparatus, and an image forming method capable of satisfactorily detecting a biased or bent posture of a print medium.

The image forming apparatus of the present invention is installed in a transport path of a print medium, and includes a first capacitance sensor through which at least a specific side of the print medium passes and a first capacitance sensor in the transport path of the print medium. Is installed at a distant position, and the capacitance value obtained from the second capacitance sensor, the capacitance value obtained from the first capacitance sensor, and the second capacitance sensor through which the same side as a specific side passes. Based on the difference between the obtained capacitance value and the bending amount of the printing medium detected by the detection unit and the detecting unit, the position of the image formed on the printing medium is corrected or printed. It is provided with a control unit that corrects the bending state of the medium.

Further, the print medium transfer device of the present invention is installed in the transfer path of the print medium, and has a first capacitance sensor through which at least a specific side of the print medium passes and a first capacitance in the transfer path of the print medium. A second capacitance sensor that is installed at a position away from the capacitance sensor and that the same side as a specific side passes through, a capacitance value obtained from the first capacitance sensor, and a second capacitance. It is provided with a detection unit that detects the amount of bending of the print medium from the difference from the capacitance value obtained from the capacitance sensor.

Further, in the image forming method of the present invention, the first capacitance sensor installed in the transport path of the print medium detects the capacitance when a specific side of the print medium passes through. The capacitance detection process, the second capacitance detection process that detects the capacitance when a specific side of the print medium passes at a position different from that of the first capacitance sensor, and the first capacitance. From the difference between the capacitance value detected by the capacitance detection process and the capacitance value detected by the second capacitance detection process, the bend amount detection process that detects the bend amount of the print medium and the detection process detect it. The control process includes correction of the position of the image formed on the print medium or correction of the bending state of the print medium based on the bending amount of the print medium.

According to the present invention, the bending condition of the print medium can be detected from the capacitance values detected by the plurality of capacitance sensors, and the processing according to the detected bending condition becomes possible.

It is a block diagram which shows the example of the image forming apparatus by one Embodiment of this invention. It is a block diagram which shows the arrangement example of the electrode plate by one Embodiment of this invention. It is a flowchart which shows the example of the paper detection processing by the example of one Embodiment of this invention. It is a flowchart which shows the correction processing example by one Embodiment of this invention. It is a figure which shows the positional relationship between the electrode plate and a paper at the time of capacitance detection and the equivalent circuit at the time of capacitance detection by one Embodiment of this invention. It is explanatory drawing which shows the change example of the positional relationship between two sets of sensors and a paper by one Embodiment of this invention. It is a figure explaining the change characteristic by the change of the paper position by one Embodiment of this invention. It is explanatory drawing of the detection state of the bending of the paper by one Embodiment of this invention. It is explanatory drawing of the detection state of the offset of the paper by one Embodiment of this invention. It is a block diagram which shows the arrangement example of the electrode plate by the example of another Embodiment of this invention.

Hereinafter, an example of an embodiment of the present invention (hereinafter, referred to as “this example”) will be described with reference to FIGS. 1 to 9.

[Overall configuration of image forming apparatus]
FIG. 1 shows an example of the image forming apparatus 100 of the present embodiment.
The image forming apparatus 100 of the embodiment is a digital multifunction device called an MFP (Multi-Function Peripheral). However, the image forming apparatus 100 is an example of a digital multifunction device, and other image forming apparatus such as a color printer, a monochrome printer, and a fax machine may be used.

The image forming apparatus 100 includes a tray 50, storage units 60A to 60D for paper (printing medium) P, and an image forming unit 110. Then, the image forming unit 110 of the image forming apparatus 100 performs an image forming process for printing a toner image on the paper P conveyed from the storage units 60A to 60D and the like to the image forming unit 110, and the image is formed on the paper P. Is discharged to the tray 50.

The image forming apparatus 100 includes a paper feed roller 61, a paper transport roller 62, 73, a paper sensor 63, 64, a capacitance sensor 65, a transport path 66, and a timing roller 67, as components for transporting the paper. It includes a timing sensor 68, a switching claw 69, and a reversing roller 70.
The paper feed roller 61, the transfer rollers 62, 73, and the reversing roller 70 are rotationally driven by a motor (not shown). Further, the switching position of the switching claw 69 is changed by a drive mechanism (not shown) in conjunction with the switching of the paper transport path.
Further, the image forming apparatus 100 detects the posture of the paper based on the image forming processing in the image forming unit 110, the control unit 101 that controls the transport of the paper, and the detection by the capacitance sensor 65. A detection unit 102 is provided.
The positions of the rollers and sensors shown in FIG. 1 are shown as an example, and are not limited to the positions shown in FIG.

The storage units 60A to 60D are cassettes in which a printing medium such as paper is set. Hereinafter, the storage units 60A to 60D are collectively referred to as the storage unit 60. In the following description, the print medium set in the storage unit 60 is referred to as paper, and the paper here includes various print media such as a film in addition to the so-called paper print medium.
The storage unit 60 is configured to be removable from the image forming apparatus 100. The user can set the paper P in the storage unit 60 by removing the storage unit 60 from the image forming apparatus 100. The size of the paper P to be stored may be different or the same between the storage units 60A to 60D.

The control unit 101 rotates and drives the rollers 61 based on the printing instruction from the user, and sends out the paper P from the storage unit 60 to the transport path 66 one by one.
The paper P sent out to the transport path 66 passes through the paper sensor 63 and the capacitance sensor 65 in the process of being transported to the image forming unit 110.
The paper sensor 63 is arranged so that its detection area includes the transport path 66, and the paper sensor 63 detects that the paper P has been transported to the transport path 66.
The capacitance sensor 65 is arranged in the middle of the transport path 66, and the paper detection unit 102 is in the posture of the paper P (biased or bent state) based on the capacitance value detected by the capacitance sensor 65. Is detected. Details of the capacitance sensor 65 will be described later.

The paper P sent out from the storage unit 60 is sent to the image forming unit 110 after passing through the paper sensor 63 and the capacitance sensor 65. The image forming unit 110 forms a toner image according to an image pattern to be printed, and prints the formed toner image on the paper P. The timing at which the paper P is sent to the image forming unit 110 is adjusted by the timing roller 67. More specifically, the timing roller 67 adjusts the transport of the paper P according to the position of the toner image to be transported in the image forming unit 110 based on the detection result of the paper by the timing sensor 68. As a result, the toner image formed by the image forming unit 110 is printed at an appropriate position on the paper P.

When the image forming apparatus 100 receives the instruction for single-sided printing, the control unit 101 drives the switching claw 69 to eject the paper P to the tray 50. When the image forming apparatus 100 receives the instruction for double-sided printing, the control unit 101 drives the switching claw 69 to send the paper P to the reversing roller 70. After that, the paper P is sent to the transport roller 73 and passes through the image forming unit 110 again. A toner image is printed on the back surface of the paper P that has been conveyed to the image forming unit 110 again, and the paper P is discharged to the tray 50.

In the case of the image forming apparatus 100 shown in FIG. 1, the capacitance sensors 65 are arranged at two locations, one in the middle of the path for directly conveying from the storage unit 60 and the other in the middle of the path for conveying the inverted paper. It is an example that the capacitance sensors 65 are arranged at two places in this way. For example, the capacitance sensors 65 may be provided at only one place in the transport path 66 near the image forming unit 110. Alternatively, conversely, similarly to the paper sensor 63, the capacitance sensor 65 may be arranged for each of the storage portions 60A to 60D.
Further, in the example shown in FIG. 1, the image forming apparatus 100 is integrated with the paper accommodating portions 60A to 60D, which are the printing medium conveying devices. On the other hand, even if the print medium transport device separate from the image forming apparatus 100 is provided with the capacitance sensor 65 in the middle of the transport path, the posture is corrected during the transport. Good. Alternatively, the print medium transport device may only detect the posture, and the posture correction process may be performed by the image forming device that forms an image on the paper transported by the transport device.

[Capacitance sensor configuration]
FIG. 2 shows the configuration of the capacitance sensor 65 of this example.
As shown in FIG. 2, the capacitance sensor 65 is arranged in the middle of the paper P passing over the transport path 66. The paper P is conveyed in the direction indicated by the arrow M.
The capacitance sensor 65 includes two electrode plates 11 and 12 constituting the first capacitance sensor and two electrode plates 21 and 22 constituting the second capacitance sensor. The capacitance sensor with each pair of electrode plates is arranged at a position where the right side Pr (or the left side), which is a side substantially parallel to the direction M in which the paper P is conveyed, passes.

That is, the two electrode plates 11 and 12 are arranged in a state of being close to the front surface and the back surface of the paper P so as to sandwich the right side Pr (or the left side) of the paper P passing through the transport path 66. The capacitance value generated between the two electrode plates 11 and 12 is detected by the first capacitance detecting unit 13.
Further, the two electrode plates 21 and 22 sandwich the right side Pr (or left side) of the paper P at a position slightly advanced in the transport direction (for example, a position shifted by about several cm) from the two electrode plates 11 and 12. Arranged like this. The capacitance value generated between the two electrode plates 21 and 22 is detected by the second capacitance detection unit 23.
Each of the electrode plates 11, 12, 21, and 22 is, for example, a quadrangle having a side of several mm to several cm. The distance between the pair of electrode plates 11 and 12 and the pair of electrode plates 21 and 22 may be any distance as long as one sheet of paper P passes through the pair of two electrode plates at the same time.

The capacitance value detected by the first capacitance detection unit 13 and the capacitance value detected by the second capacitance detection unit 23 are supplied to the paper detection unit 102. The paper detection unit 102 detects the posture of the paper P from a change state such as a difference between the two capacitance values. Specifically, the bending state of the paper P and the offsetting state of the paper P are detected. The details of the bending state of the paper P and the principle of detecting the biased state of the paper P will be described later, but briefly, the bending state of the paper P is detected by the capacitance detection units 13 and 23. Detect from the difference in capacitance value. Further, the offset state of the paper P is detected from the value of the capacitance value itself detected by the capacitance detection units 13 and 23.

Information on the posture of the paper P detected by the paper detection unit 102 is supplied to the control unit 101 (FIG. 1). When the control unit 101 detects a bend or bias of the paper P during transportation, the control unit 101 performs a process of correcting the bend or bias. There are two types of processing for correcting bending and deviation performed by the control unit 101: correction of the transport position of the paper P by driving each roller and correction of the image to be printed on the paper P performed by the image forming unit 110. ..

That is, in the correction of the transport position of the paper P by driving each roller, for example, a part of the rollers for transporting the paper (conveying rollers 62, 73, etc.) is divided and driven, so that the paper P is bent or biased. It is a correction to return to the correct posture from the situation.
Further, in the correction of the image printed on the paper P by the image forming unit 110, for example, when the bending of the paper P is detected, the image to be printed on the corresponding paper P by the image forming unit 110 corresponds to the detected bending condition. This is a correction that makes a bent image. Further, even when the offset of the paper P is detected, the image to be printed on the corresponding paper P by the image forming unit 110 is corrected as a shifted (biased) image according to the detected offset situation.

[Flow of paper orientation correction processing]
3 and 4 are flowcharts showing a flow of paper posture correction processing executed under the control of the control unit 101.
First, the control unit 101 starts printing (printing) on the paper P, and starts conveying the paper P from any of the storage units 60A to 60D designated by the user (step S11). After that, the control unit 101 determines whether or not the paper P that has started to be conveyed has reached the arrangement location of the capacitance sensor 65 (step S12).

If it is determined in step S12 that the paper P that has started to be conveyed has not reached the location where the capacitance sensor 65 is arranged (No in step S12), the control unit 101 determines that the location where the capacitance sensor 65 is arranged. Wait until you reach. Then, when it is determined in step S12 that the paper P that has started to be conveyed has reached the location where the capacitance sensor 65 is arranged (Yes in step S12), the paper detection unit 102 detects the capacitance value (step). S13). In this step S13, the detection by the first capacitance detection unit 13 (first capacitance detection process) when the paper P passes and the detection by the second capacitance detection unit 23 (second static electricity). Both of the capacitance detection processes) are performed, and the respective capacitance values are acquired.

When each capacitance value is acquired, the paper detection unit 102 performs a bending amount detection process for calculating the bending amount of the paper P from the difference between the respective capacitance values (step S14), and the calculated bending amount is calculated. The quantity information is supplied to the control unit 101. Then, the control unit 101 determines whether or not the paper P has a bend from the acquired information on the bending amount (step S15).

When it is determined in step S15 that the paper P is bent (Yes in step S15), the control unit 101 executes the bending correction process (step S16). The correction processing here includes an image correction in which the image forming unit 110 tilts the image to be printed on the paper P by the amount of bending, and a correction by alignment adjustment for correcting the bending by using one of the rollers driving the paper P. , Any one of the corrections in which one of the rollers for driving the paper P is divided and driven independently is performed. Here, dividing the rollers and driving them independently means driving by changing the left and right driving states of one roller.
Alternatively, the control unit 101 executes the correction by combining any two or three of the three corrections. When performing the bending correction using the rollers here, the paper P may be temporarily retracted in the direction opposite to the defined transfer direction in the transfer path 66 to correct the bending.

Then, when it is determined in step S15 that the paper P is not bent (No in step S14), and after the bending is corrected in step S16, the paper detection unit 102 further performs the first static electricity when the paper P passes through. The detection value of the electric capacity detection unit 13 and the detection value of the second capacitance detection unit 23 are acquired (step S17). The capacitance detection value acquired in step S17 is a new capacitance detection value that is performed when the paper P passes through the arrangement portion of the capacitance sensor 65 again after the bending correction. It is also possible to use the detected value of the capacitance acquired in step S13 as it is without detecting the capacitance value in step S17.

When the capacitance value is acquired by the first capacitance detection unit 13 and the second capacitance detection unit 23, the paper detection unit 102 calculates the offset amount of the paper P from the difference between the respective capacitance values. Then, the calculated offset amount information is supplied to the control unit 101 (step S18). Then, the control unit 101 determines whether or not the paper P has a bias from the acquired information on the bias amount (step S19).

When it is determined in step S19 that the paper P is offset (Yes in step S19), the control unit 101 executes the offset correction process (step S20). The correction processing here includes image correction in which the image forming unit 110 shifts the image to be printed on the paper P by the amount of deviation, and correction of deviation by swinging one of the rollers driving the paper P. Do any one of the above.
Then, when it is determined in step S19 that the paper P is not biased (No in step S19), and when the correction is performed in step S20, the posture correction process of the paper P is completed.

In the correction in step S16 and the correction in step S20, especially when the image forming unit 110 forms an image and the correction is performed when printing on the corresponding paper P, the image forming unit is based on the instruction of the control unit 101. 110 collectively executes these corrections.
The flowchart of FIG. 4 shows an example of the flow of image correction processing performed by the control unit 101 on the image forming unit 110.

First, the control unit 101 determines whether or not to perform the bending correction of the paper P by the image correction (step S21). When it is determined in step S21 that the bending correction of the paper P by the image correction is necessary (Yes in step S21), the control unit 101 prints the image printed on the paper P by the image forming unit 110 in accordance with the bending amount. An instruction is given to tilt the image (step S22).

Then, when it is determined in step S21 that the paper P is not bent (No in step S21), and after the correction for tilting in step S22 is performed, the control unit 101 further corrects the offset of the paper P by image correction. It is determined whether or not to perform (step S23). When it is determined in step S23 that the offset correction of the paper P by image correction is necessary (Yes in step S23), the control unit 101 corresponds to the offset amount of the image printed on the paper P by the image forming unit 110. Then, an instruction to shift the image is given (step S24). The shift in step S24 is executed at the same time for the same image when the tilt is instructed in step S22.

Then, when it is determined in step S23 that the paper P is not biased (No in step S23), and after the correction for shifting is performed in step S24, the image correction for the paper P is completed.

[Details of processing to detect attitude with two capacitance sensors]
Next, with reference to FIGS. 5 to 9, the details of the process of detecting the posture of the paper P by the image forming apparatus 100 of this example will be described.
5 (a) to 5 (c) show the arrangement relationship between the electrode plates 11 and 12 and the electrode plates 21 and 22 shown in FIG. 2 and the paper P, and the mechanism of mutual capacitance detected by the arrangement relationship. It is a figure.
As shown in FIG. 5A, the electrode plates 11 and 12 and the electrode plates 21 and 22 of each set are arranged so as to cover a specific side (for example, the right side Pr shown in FIG. 2) of the paper P. At this time, the width (size of the transport direction M) of each of the electrode plates 11, 12, 21, and 22 is X, and the length (size in the direction orthogonal to the transport direction M) is Y. Further, the length at which the electrode plates 11, 12, 21, 22 and the paper P overlap is defined as Y'.

Further, as shown in FIG. 5 (b), the area of the electrode plates 11 and 12 (or the electrode plates 21 and 22) of each set is S [mm ² ], and the two opposing electrode plates 11 and 12 (or Let the distance between the electrode plates 21, 22) be d [mm]. Further, the thickness of the paper P passing between the electrode plates 11 and 12 (or the electrode plates 21 and 22) is set to A [mm], and the electrode plates 11 and 12 (or the electrode plates 21 and 22) and the paper P are separated from each other. Let the overlapping area be S'[mm ² ].

At this time, the mutual capacitance value detected by the electrode plates 11 and 12 (or the electrode plates 21 and 22) can be shown by the circuit of FIG. 5 (c).
The left side of the circuit of FIG. 5 (c) shows the capacitance at the portion where the electrode plates 11 and 12 (or the electrode plates 21 and 22) and the paper P overlap, and the right side of the circuit of FIG. 5 (c) shows the paper. The capacitance of the electrode plates 11 and 12 (or the electrode plates 21 and 22) not overlapping with P is shown. As shown in FIG. 5C, the connected capacitance is generated between the two electrode plates 11 and 12 (or the electrode plates 21 and 22).

That is, at the place where the electrode plates 11 and 12 (or the electrode plates 21 and 22) and the paper P overlap, the relative dielectric constant εp [F / m] peculiar to the paper P and the thickness A [mm] of the paper P , The capacitance of the paper P determined by the overlapping area S'[mm ² ] and the distance d of the opposing electrode plates 11, 12 (or the electrode plates 21 and 22) minus the thickness A of the paper P d- The capacitance obtained by adding the capacitance of A [mm] in the air is detected.

Further, in the portion where the sheet P is not overlapped, the area obtained by subtracting the area S '[mm ^2] from the area S [mm ^2] of the opposing electrode plates 11, 12 (or the electrode plates 21 and 22), electrode plates The capacitance determined by the distance d [mm] of 11 and 12 (or the electrode plates 21 and 22) and the relative permittivity εp [F / m] in the air is detected.
The combination of these capacitances is the capacitance between the electrode plates 11 and 12 (or the electrode plates 21 and 22), which is the first capacitance detection unit 13 (or the second capacitance detection unit 23). ) Is detected.

FIG. 6 shows an example of a change in the positional relationship between the paper P and each of the electrode plates 11, 12, 21, 22 when the paper P passes through the arrangement locations of the electrode plates 11, 12, and the electrode plates 21, 22. Shown. In FIG. 6, the paper P is conveyed in the direction M in a bent state, and the right side Pr of the paper passes through the paired portion of the electrode plates 11 and 12 and the paired portion of the electrode plates 21 and 22.
As shown in FIG. 6A, by transporting the paper P in the direction M, the paper upper side Pf first passes through the portion sandwiched between the electrode plates 11 and 12, and then the paper upper side Pf becomes the electrode. It reaches the part sandwiched between the plates 21 and 22. In the state shown in FIG. 6A, the capacitance can be detected on the electrode plates 11 and 12.

As the paper P is further conveyed from the state shown in FIG. 6 (a), as shown in FIG. 6 (b), the upper side Pf of the paper advances at the portion sandwiched between the electrode plates 21 and 22, and then FIG. As shown in (c), the upper side Pf of the paper passes through the electrode plates 21 and 22. In the state shown in FIG. 6B, the capacitance can be detected on the electrode plates 11 and 12, but the capacitance on the electrode plates 21 and 22 is not completely detected. Only in the state shown in FIG. 6C, the capacitance can be detected by the electrode plates 11 and 12, and the capacitance can be detected by the electrode plates 21 and 22.

Further, as the paper P is conveyed, the lower side Pe of the paper passes the edges of the electrode plates 11 and 12, as shown in FIG. 6D. In the state shown in FIG. 6D, the capacitance can be detected on the electrode plates 21 and 22.
In this way, the paper P passes through the positions where the electrode plates 11 and 12 and the electrode plates 21 and 22 are arranged, and the detection of the capacitance on the electrode plates 11 and 12 and the electrode plates 21 and 22 is shown in FIG. 6 (c). ), The paper upper side Pf has passed through the electrode plates 21 and 22, and the paper lower side Pe has not reached the electrode plates 11 and 12.

As shown in FIG. 6, when the paper P passes through the electrode plates 11 and 12 and the electrode plates 21 and 22, and the paper P is bent, when the paper P passes through the respective electrode plate pairs. The area of the portion overlapping the paper P of the paper P changes, and the detected coupling capacity changes.
In FIG. 7, the capacitance detected by the electrode plate pair changes from the change in the area of the portion overlapping the paper P when passing through the pair of the electrode plates 11 and 12 (or the pair of the electrode plates 21 and 22). Shows gradient characteristics.

The positional relationship between the electrode plates 11 and 12 shown in FIG. 7 and the paper P is the position of the paper right side Pr2 (in the figure) after a predetermined time from the position of the paper right side Pr1 (the position indicated by the broken line in the figure) at a certain time. The case where the position is changed to the solid line) is shown. Here, ΔS [mm ² ] is the difference in paper area at both positions.
The gradient characteristic ΔC [F] of the capacitance when the position of the paper right side Pr1 is changed to the position of the paper right side Pr2 is expressed by the following equation.

In this example, the paper detection unit 102 detects the bending state of the paper P from the gradient characteristic of the capacity value due to the change in the paper position.

FIG. 8 shows an example of a process for detecting the bending amount of the paper P in conjunction with the change in the paper position.
As shown in FIG. 8, it is assumed that a range D11 in which the electrode plates 11 and 12 overlap the paper P is generated, and a range D12 in which the electrode plates 21 and 22 overlap the paper is generated.
At this time, the area difference value ΔS of the two ranges D11 and D12 is proportional to the capacitance difference value ΔC. Here, the paper detection unit 102 holds in advance the relationship between the difference value ΔC of the capacitance at the specific area difference value ΔS and the bending angle θ in that state as a reference value.
Then, the paper detection unit 102 calculates the bending angle θ'in that situation from the difference value ΔC'of the capacitance obtained in the detection result by the following formula.

For example, when the area difference value ΔS = 10, the difference value ΔC = 10 of the capacitance value and the bending angle 1 °, the paper detection unit 102 bends the angle when the detected capacitance difference value ΔC = 1. = 0.1 ° is detected.
In order to correctly calculate the bending angle, information on the relative permittivity determined by the type of paper P (printing medium) and the thickness of paper P (printing medium) is required, and the paper detection unit 102 uses the reference. Hold values for each paper type and thickness. Then, the type and thickness of the paper P used by the image forming apparatus 100 are selected in advance by user operation or the like, and the bending angle is calculated using the reference value for the selected paper type and thickness. It can be performed.

Next, a process of detecting the offset of the paper by the paper detection unit 102 based on the capacitance value detected by the electrode plates 11 and 12 and the capacitance value detected by the electrode plates 21 and 22 will be described.
FIG. 9 shows a range D21 in which the electrode plates 11 and 12 overlap the paper P and a range in which the electrode plates 21 and 22 overlap the paper in a state where the paper P is not bent (the above-mentioned bending angle θ ′ = 0 °). From D22, the state of detecting the offset amount is shown.
When the paper P is not bent, the area D21 where the electrode plates 11 and 12 overlap the paper P and the area D22 where the electrode plates 21 and 22 overlap the paper have the same area.

Here, the paper detection unit 102 sets the capacitance value C1 of each electrode plate pair corresponding to the areas of the ranges D21 and D22 when the paper P is not bent and the paper P is not offset. Hold as a reference value. At this time, in addition to the reference capacitance value C1, the paper detection unit 102 has a distance Y ′ [mm] (FIG.) that overlaps with the paper P of the electrode plates 11 and 12 (or the electrode plates 21 and 22) at that time. 5 (a)), the distance D between the centers of the paper P, and the reference passing position d of the paper edge according to the size of the paper P are also held.
Then, the paper detection unit 102 calculates the offset amount in that situation from the capacitance value C2 obtained from the detection result by the following formula.

The capacitance value C1 as a reference for offset detection is also prepared for each type and thickness of the paper P.

As described above, according to the image forming apparatus 100 of this example, the paper detection unit 102 is detected by two sets of capacitance sensors (sensors by electrode plates 11 and 12 and sensors by electrode plates 21 and 22). Based on the capacitance value, it is possible to accurately detect the bending angle and the amount of offset of the paper. When both the bending situation is detected and the biasing situation is detected, as described in the flowchart of FIG. 3, the bending situation is detected and corrected, and then the biased situation is detected. It is preferable to correct it.
Further, in the case of this example, if a reference value is prepared in advance, it becomes possible to correspond to various types of paper (printing medium). For example, even when a film is used as a print medium, the bending angle and the amount of offset can be accurately detected.

In the case of the sensor arrangement shown in FIG. 2, in order to detect the bending amount of the paper P, the electrode plates 11, 12, 21, and 22 are lengthened according to the type of paper size used at the time of printing. It is necessary to set the length Y) in FIG. 5 (a) to be long.
Alternatively, a plurality of electrode plate pairs may be arranged for each size of the paper. For example, two sets of electrode plate pairs are arranged corresponding to the position where the right side or the left side of A4 size paper passes, and are separated from the position corresponding to the position where the right side or left side of A3 size paper passes. Two pairs of electrode plates may be arranged.

[Another example of sensor placement]
In the example shown in FIG. 2, the electrode plates 11 and 12 and the electrode plates 21 and 22 are arranged at positions in contact with Pr on the right side of the paper P. On the other hand, two sets of electrode plate pairs may be arranged so as to be in contact with the sides of the paper P at other positions. For example, although not shown, two sets of electrode plate pairs may be arranged at positions in contact with the left side of the paper P. The detection process in this case is exactly the same as the case where the paper P is arranged at a position in contact with the right side of the paper P.

Alternatively, as shown in FIG. 10, two sets of electrode plate pairs may be arranged at positions in contact with the upper side Pf of the paper P.
That is, one set of electrode plates 31 and 32 is arranged so as to be sandwiched at a position in contact with the upper side Pf of the paper P, and another set is arranged at a position slightly separated from the electrode plates 31 and 32 and in contact with the same upper side Pf. The electrode plates 41 and 42 of the above are arranged.

Then, the capacitance value generated by one set of electrode plates 31 and 32 is detected by the first capacitance detection unit 13, and the capacitance value generated by the other set of electrode plates 41 and 42 is set to the second static electricity. The capacitance detection unit 23 detects it. The capacitance value detected by the first capacitance detection unit 13 and the capacitance value detected by the second capacitance detection unit 23 are supplied to the paper detection unit 102. The paper detection unit 102 detects the bending state of the paper P from the difference between the two capacitance values.
Since the paper P is transported as shown in FIG. 10 as the transport direction M, the capacitance value is detected from each electrode plate pair at the timing when the upper side Pf of the paper P passes through each electrode plate pair. There is a need. Alternatively, although not shown, the capacitance value may be detected from each pair of electrode plates at the timing when the lower side of the paper P passes through each pair of electrode plates.

In this way, even when the electrode plates 31, 32, 41, and 42 are arranged on the upper side (or lower side) of the paper P, the bending state of the paper can be detected. In the case of the configuration shown in FIG. 10, regardless of the size of the paper, the same electrode plate pair can detect the capacitance value according to the bending condition of the paper. However, in the case of the sensor arrangement shown in FIG. 10, it is not possible to detect the offset of the paper.

11,12,21,22,31,32,41,42 ... Electrode plate, 13 ... 1st capacitance detection unit, 23 ... 2nd capacitance detection unit, 50 ... Tray, 60 ... Paper transfer device, 60A ~ 60D ... Storage unit, 61 ... Paper feed roller, 62, 73 ... Transfer roller, 63, 64 ... Paper sensor, 65 ... Capacitive sensor, 66 ... Transfer path, 67 ... Timing roller, 68 ... Timing sensor, 69 ... Switching claw, 70 ... reversing roller, 100 ... image forming device, 101 control unit, 102 paper detecting unit, 110 image forming unit, P ... paper (printing medium), Pf ... paper upper side, Pe ... paper lower side, Pr ... paper right side

Claims (9)

A first capacitance sensor installed in the transport path of the print medium and through which at least a specific side of the print medium passes.
A second capacitance sensor that is installed at a position away from the first capacitance sensor in the transport path of the print medium and that the same side as the specific side passes through.
A detection unit that detects the amount of bending of the print medium from the difference between the capacitance value obtained from the first capacitance sensor and the capacitance value obtained from the second capacitance sensor.
An image forming apparatus including a control unit that corrects the position of an image formed on the print medium or the bending state of the print medium based on the amount of bending of the print medium detected by the detection unit. A specific side of the print medium is a side substantially parallel to the direction in which the print medium is conveyed.
The image forming apparatus according to claim 1, wherein the first capacitance sensor and the second capacitance sensor are arranged so as to shift in a direction in which the print medium is conveyed. Further, the detection unit shifts the print medium based on the capacitance value obtained from the first capacitance sensor and the capacitance value obtained from the second capacitance sensor. Detect the amount,
According to claim 2, the control unit corrects the position of an image formed on the print medium or corrects the offset state of the print medium based on the amount of deviation of the print medium detected by the detection unit. The image forming apparatus described. The control unit corrects the bending state of the print medium and the biased state by the drive system installed in the transport path of the printing medium, and after correcting the bending state of the print medium, the above-mentioned The image forming apparatus according to claim 3, wherein the offset state of the print medium is corrected. In the detection of the bending amount of the print medium by the detection unit, the difference between the capacitance value of the first capacitance sensor and the capacitance value of the second capacitance sensor is held in advance. The image forming apparatus according to claim 1, wherein the retained difference is compared with the detected difference. A specific side of the print medium is a side substantially orthogonal to the direction in which the print medium is conveyed.
The image forming apparatus according to claim 1, wherein the first capacitance sensor and the second capacitance sensor are arranged side by side in a direction substantially orthogonal to a direction in which the print medium is conveyed. The first capacitance sensor and the second capacitance sensor are according to any one of claims 1 to 6, which are composed of two electrode plates close to the front surface and the back surface of the print medium, respectively. The image forming apparatus described. A first capacitance sensor installed in the transport path of the print medium and through which at least a specific side of the print medium passes.
A second capacitance sensor that is installed at a position away from the first capacitance sensor in the transport path of the print medium and that the same side as the specific side passes through.
A detection unit that detects the amount of bending of the print medium from the difference between the capacitance value obtained from the first capacitance sensor and the capacitance value obtained from the second capacitance sensor. A print medium transfer device comprising. A first capacitance detection process that detects the capacitance when a specific side of the print medium passes by a first capacitance sensor installed in the transport path of the print medium, and a first capacitance detection process.
A second capacitance detection process that detects the capacitance when a specific side of the print medium passes at a position different from that of the first capacitance sensor.
The amount of bending that detects the amount of bending of the print medium from the difference between the capacitance value detected by the first capacitance detection process and the capacitance value detected by the second capacitance detection process. Detection processing and
An image forming method including a control process for correcting the position of an image formed on the print medium or a bending state of the print medium based on the amount of bending of the print medium detected by the detection process.

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