JP7081308B2 - Position detection device, position detection method and image forming device - Google Patents

Description

The present invention relates to an apparatus, method and image forming apparatus for detecting the position of a medium.

In copiers, printers, facsimiles, multifunction devices equipped with these functions, etc. that use the electrophotographic process, if media such as paper is not properly supplied, the printing position will shift and the desired printed matter cannot be obtained. There is.

In view of this, a technique has been proposed in which the position of the paper is detected by using an optical sensor, the transport speed of the paper is adjusted, and the paper is appropriately fed (see, for example, Patent Document 1).

However, in the above-mentioned conventional technique, since it is only possible to detect whether or not there is paper at each sensor position, there is a problem that the position of the paper can be detected only stepwise.

Therefore, an object of the present invention is to provide an apparatus, a method, or the like that can continuously detect the position of a medium such as paper.

In order to solve the above-mentioned problems, in one embodiment of the invention, it is a device for detecting the position of a medium.
A first parallel electrode and a second parallel electrode arranged apart from each other in the transport direction of the medium and each composed of a pair of parallel flat plates.
A measuring means for measuring the capacitance generated by the current supplied between the first parallel electrodes and between the second parallel electrodes, and
Including
The length of the first parallel electrode in the transport direction is shorter than the length of the medium in the transport direction, and the length of the second parallel electrode in the transport direction is longer than the length of the medium in the transport direction. A position detecting device is provided.

According to the present invention, the position of the medium can be continuously detected.

The figure which showed the structural example of the image forming apparatus. The figure explaining the position detection using the conventional capacitance sensor. The figure which showed the 1st configuration example of a capacitance sensor. The figure explaining the position detection using the capacitance sensor of this embodiment. A flowchart showing the flow of position detection. The figure which showed the 2nd configuration example of a capacitance sensor. The figure which showed the 3rd configuration example of a capacitance sensor. The figure explaining the motor control which drives a conventional transfer roller. The figure explaining the motor control using a capacitance sensor. The figure which showed the relationship between the movement distance of a paper and time.

FIG. 1 is a diagram showing a configuration example of an image forming apparatus including a position detecting apparatus. The image forming apparatus shown in FIG. 1 is a multifunction device equipped with the functions of a copier, a printer, a facsimile, and a scanner, but the image forming apparatus is not limited to the multifunction device, and may be a copying machine, a printer, a facsimile, or the like. There may be.

The image forming apparatus is composed of a plurality of apparatus and units. The image forming apparatus includes an automatic document feeder (ADF) 10, an image reading device 11, a printer unit 12, a paper feeding unit 13 for supplying paper as a medium, a manual feeding unit 14, a paper ejection unit 15, an operation panel 16, and the like. .. Further, the image forming apparatus includes a capacitance sensor 17 as a position detecting device for detecting the position of the paper.

Since the device configuration shown in FIG. 1 is an example, the device may be configured without the ADF10, the manual feed unit 14, or the like, or may be configured to include other devices or units. The medium is not limited to paper, but may be a postcard, an envelope, a label, a film, or the like.

Hereinafter, the device for detecting the position of the paper will be described as the capacitance sensor 17, but the position detection device is not limited to the capacitance sensor.

The ADF 10 includes a platen on which a document is placed, a transport mechanism for transporting the originals on the platen, and an ejection tray for ejecting the conveyed documents. The ADF 10 moves the document placed on the platen onto the contact glass of the image reading device 11.

The image reading device 11 includes a light source, a plurality of mirrors, an imaging lens, and an image pickup device. The image reading device 11 irradiates the original on the contact glass with the light from the light source, and causes the reflected light to enter the image pickup element through a plurality of mirrors and an imaging lens. An image sensor is a device that converts incident light into an electrical signal and outputs it as image data. For example, a CCD (Charged Coupled Device) image sensor or CMOS (Complementary)
metal oxide semiconductor) An image sensor or the like can be used.

The printer unit 12 includes a writing unit 20, a photoconductor drum 21, a developing device 22, a transport belt 23, and a fixing device 24. The writing unit 20 irradiates the photoconductor drum 21 with light in response to an instruction from the controller that controls the image forming apparatus, and forms a latent image on the surface of the photoconductor drum 21. The developing device 22 is filled with toner, ejects the toner to the photoconductor drum 21, and visualizes a latent image formed on the surface of the photoconductor drum 21. The transport belt 23 transports the paper and transfers the image developed by visualization onto the paper. The fixing device 24 applies heat and pressure to the paper transferred by the transfer belt 23 after the image is transferred, and fixes the image on the paper.

The paper feed unit 13 includes a paper feed tray 25 for storing paper and a paper feed roller 26 for feeding paper stored in the paper feed tray 25 one by one. The paper feed unit 13 drives the paper feed roller 26 in response to an instruction from the controller, and supplies paper from the paper feed tray 25.

The manual feed unit 14 includes a manual feed tray on which paper is placed and a paper feed roller for feeding paper on the manual feed tray one by one. The manual feed unit 14 receives an instruction from the controller and supplies the paper on the manual feed tray. The paper ejection unit 15 includes a paper ejection tray that ejects the paper on which the image has been fixed by the fixing device 24.

The operation panel 16 accepts the user's operation and instructs the controller to read or print the document. Further, the operation panel 16 displays a button for selecting a function for accepting a user's operation, an execution start button for printing, and the like, and displays an execution status, an error, and the like.

The capacitance sensor 17 is installed in a transport path through which paper is transported, and includes a first parallel electrode and a second parallel electrode each composed of a pair of parallel flat plates. The paper conveyed from the paper feed tray 25 by the paper feed roller 26 passes between the first parallel electrodes and between the second parallel electrodes.

The first parallel electrode and the second parallel electrode have conductivity, and flat plates of the same shape, size, and thickness are arranged in parallel. A metal plate can be used for the flat plate, and for example, a stainless steel plate, a copper plate, an aluminum plate, or the like can be used as the metal plate.

The first parallel electrode and the second parallel electrode are provided apart from each other in the paper transport direction, and their mounting positions are set between the paper feed unit 13 and the manual feed unit 14 and the photoconductor drum 21.

Here, with reference to FIG. 2, a position detection using a conventional capacitance sensor will be briefly described. The conventional capacitance sensor includes a parallel electrode 30 composed of a pair of parallel flat plates. The two flat plates constituting the parallel electrode 30 are arranged apart from each other so that the paper 31 passes between the flat plates, and the size thereof is larger than the paper size.

A current is supplied to the parallel electrode 30. When a current flows between the electrodes, the parallel electrode 30 functions as a capacitor, and electric charges are stored between the electrodes. The amount of electric charge stored is called the capacitance. If the capacitance C (F) is the area S (m2) of the electrodes, the distance d (m) between the electrodes 18, and the permittivity ε, the following equation 1 Can be calculated by.

When a current is passed between the electrodes, the current does not flow due to the insulator such as air existing between the electrodes, but polarization occurs in which one plate is divided into a positive electrode and the other plate is divided into a negative electrode, which causes electric charge to be stored. Can be done. Since the electrode on one side may be ground GND (self-capacity method), it may be a housing sheet metal provided for grounding.

The dielectric constant ε is a value indicating the magnitude of this polarization and changes depending on the insulator existing between the electrodes. Therefore, the dielectric constant ε changes depending on whether the insulator between the electrodes is only air or the paper 31 is present. Further, the dielectric constant ε also changes depending on the ratio of the paper 31 entering between the electrodes.

FIG. 2 shows changes in the position and capacitance of the paper 31 with respect to the parallel electrode 30. As shown in FIG. 2, when the moving distance (X1) until the paper 31 enters between the electrodes is less than the moving distance (X1), the dielectric constant in the case of only air is a low capacitance value. When the moving distance is between X1 and X2 until the paper 31 starts to enter and the entire paper 31 enters between the electrodes, the capacitance increases as the paper 31 enters.

While the entire paper 31 is between the electrodes (between X2 and X3), the capacitance is almost constant, and while the paper 31 is ejected from between the electrodes (between X3 and X4), it is static. The electric capacity decreases.

Therefore, by measuring the capacitance, it is possible to know whether the moving distance of the paper 31 is less than X1, between X1 and X2, between X2 and X3, or between X3 and X4, and at which position the paper 31 is located. Can be detected if is present. Since this is a stepwise position detection, it is not possible to detect a continuous position of how many mm the paper 31 currently penetrates between the electrodes.

Therefore, the capacitance sensor is configured as shown in FIG. The capacitance sensor includes two parallel electrodes (first parallel electrode and second parallel electrode) 40, 41 each composed of a pair of parallel plates. The first parallel electrode 40 and the second parallel electrode 41 are provided apart from each other in the transport direction (secondary scanning direction) of the paper 42.

The sub-scanning direction length of the first parallel electrode 40 is shorter than the sub-scanning direction length of the paper 42, and the sub-scanning direction length of the second parallel electrode 41 is shorter than the sub-scanning direction length of the paper 42. Be lengthened. The reason for making such a length will be described later. Further, in this example, the first parallel electrode 40 and the second parallel electrode 41 are connected by the connecting portion 43 at one edge in the direction perpendicular to the sub-scanning direction (main scanning direction). There is.

The capacitance sensor also has a current generator 44 that generates a current and supplies a current to the first parallel electrode 40 and the second parallel electrode 41, and between the first parallel electrode 40 and the second parallel electrode. A capacitance measuring device 45 for measuring the capacitance generated between 41 is provided.

The current generator 44 generates a current having a predetermined current value, and causes a current to flow between the first parallel electrodes 40 and between the second parallel electrodes 41.

The capacitance measuring device 45 flows an alternating current as the above current, detects the amplitude ratio and phase difference of the voltage and current, calculates the impedance R from the detected amplitude ratio and phase difference, and calculates the impedance R and the frequency of the alternating current. An LCR meter that calculates the impedance L and capacitance C from can be used. Here, the LCR meter is mentioned as an example of the capacitance measuring device 45, but the present invention is not limited to this, and any device that can measure the capacitance C may be used.

The capacitance measuring device 45 measures the capacitance when the paper 42 passes between the first parallel electrodes 40, and subsequently, the static electricity when the paper 42 passes between the second parallel electrodes 41. Measure the capacity.

The capacitance sensor further includes a controller 46 that controls the current generator 44 and the capacitance measuring device 45. The controller 46 detects the position of the paper 42 based on the capacitance measured by the capacitance measuring device 45. The controller 46 is based on the measurement result when the paper 42 passes between the first parallel electrodes 40 and the capacitance measured when the paper 42 passes between the second parallel electrodes 41. Is continuously calculated as to how much the paper has entered between the second parallel electrodes 41.

The controller 46 is a ROM (Read Only Memory) or a flash memory as a storage device for storing a program in order to control a current generator 44 or a capacitance measuring device 45 and execute arithmetic processing such as position detection of a paper 42. Can be provided. Further, the controller 46 can include a CPU (Central Processing Unit) that reads and executes a program from the storage device, a RAM (Random Access Memory) that provides a work area to the CPU, and the like.

A method of detecting the position of the paper 42 using the capacitance sensor will be described with reference to FIG. FIG. 4 shows changes in the position and capacitance of the paper 42 with respect to the first parallel electrode 40 and the second parallel electrode 41. In the example shown in FIG. 4, the sub-scanning direction length of the first parallel electrode 40 is L1 shorter than the sub-scanning direction length of the paper 42, and the sub-scanning direction length of the second parallel electrode 41 is the paper 42. It is said that L0 is longer than the length in the sub-scanning direction of.

Until the paper 42 enters between the first parallel electrodes 40 (in FIG. 4, the paper moving distance is in the range of (1)), the dielectric constant is the case of only air, so that the dielectric constant is measured by the capacitance measuring device 45. The capacitance applied shows a low constant value. When the paper 42 enters between the first parallel electrodes 40 (range (2) in FIG. 4), the capacitance increases as the paper 42 enters.

Since the sub-scanning direction length L1 of the first parallel electrode 40 is shorter than the sub-scanning direction length of the paper 42, before one end (end) of the paper 42 in the sub-scanning direction enters between the first parallel electrodes 40. The other end (tip) of the paper 42 in the sub-scanning direction exits between the first parallel electrodes 40.

The first is from the time when the tip of the paper 42 exits between the first parallel electrodes 40 to the time when the end of the paper 42 enters between the first parallel electrodes 40 (range (3) in FIG. 4). A paper 42 having a length L1 in the sub-scanning direction is always present between the parallel electrodes 40 of the above. Therefore, during this period, the capacitance becomes a substantially constant value. The capacitance at this time is measured by the capacitance measuring device 45 and stored as the capacitance C1.

As the paper 42 is conveyed, the end of the paper 42 enters between the first parallel electrodes 40, and the end enters between the first parallel electrodes 40 (range (4) in FIG. 4). Capacitance decreases.

In this example, the spacing K is the sub-scanning direction length of the paper 42 so that the tip of the paper 42 enters between the second parallel electrodes 41 as soon as the end of the paper 42 exits between the first parallel electrodes 40. Is the same as. Therefore, when the paper 42 starts to enter between the second parallel electrodes 41 (range (5) in FIG. 4), the capacitance increases.

The entry of the paper 42 into the space between the second parallel electrodes 41 was started, and the sub-scanning direction length (entry length) of the paper 42 that had entered between the second parallel electrodes 41 was set to X, and the measurement was performed at that time. Assuming that the capacitance is C2, the relationship shown by the following equation 2 is established.

According to the above equation 2, when the paper 42 enters between the second parallel electrodes 41, the amount of the paper 42 entering between the second parallel electrodes 41 is calculated only by measuring the capacitance. be able to. By continuously measuring the capacitance, it is possible to continuously calculate how much the paper 42 has entered, so that the position of the paper 42 can be continuously detected.

By the way, when the sub-scanning direction length L1 of the first parallel electrode 40 is longer than the sub-scanning direction length of the paper 42, the capacitance becomes a substantially constant value regardless of the length of L1. Therefore, the relationship represented by the above equation 2 does not hold, and the position of the paper 42 cannot be detected. Further, when the sub-scanning direction length L0 of the second parallel electrode 41 is shorter than the sub-scanning direction length of the paper 42, the tip of the paper 42 is before the end of the paper 42 enters between the second parallel electrodes 41. Will come out from between the second parallel electrodes 41, and the position of the paper 42 from the tip coming out from between the second parallel electrodes 41 to the end entering between the second parallel electrodes 41 can be detected. become unable.

The first parallel electrode 40 and the second parallel electrode 41 are partially connected by the connecting portion 43, but the path portion through which the paper 42 is conveyed is separated. The interval K shifts from the range (4) shown in FIG. 4 to the range (5) when the paper 42 is inserted between the first parallel electrodes 40 and between the second parallel electrodes 41. Is set to be longer than the length of the paper 42 in the sub-scanning direction because it becomes difficult to detect.

By providing the connecting portion 43 as in the example shown in FIG. 3, the wiring connected to the current generating device 44 and the capacitance measuring device 45 can be made common wiring, and the number of wirings can be reduced. The connecting portion 43 may be provided by welding an elongated plate or the like, or a notch having the same shape and size may be provided at the same position on each of the two plates, and the first parallel portion 43 may be provided. The electrode 40 and the second parallel electrode 41 may be formed and may be formed.

A process of detecting the position of the paper 42 by the capacitance sensor 17 will be described with reference to FIG. This process starts from step 500 when the print job is executed and the paper 42 is fed from the paper feed tray 25. In step 501, the measurement of the capacitance by the capacitance measuring device 45 is started, and based on the measurement result, it is determined whether or not the paper 42 has entered between the first parallel electrodes 40. After that, the capacitance is continuously measured by the capacitance measuring device 45. If it is determined that the vehicle has entered, the process proceeds to step 502, and if it is determined that the vehicle has not entered, the process of step 501 is repeated until the vehicle enters.

In step 502, it is determined whether the measured capacitance has reached a substantially constant value. That is, it is determined whether the capacitance is within a certain range. By the way, this range can be determined in consideration of the measurement error of the capacitance. If it is determined that the capacitance has reached a substantially constant value, the process proceeds to step 503, and the capacitance C1 at the time when the capacitance reaches a substantially constant value is stored. When multiple values that are almost constant are obtained, the average value can be saved as C1. The capacitance C1 can be stored in the memory included in the controller 46. If it is determined in step 502 that the value is not constant, the determination in step 502 is repeated.

In step 504, it is determined whether or not the paper 42 has entered between the second parallel electrodes 41 based on the measurement result of the capacitance measuring device 45. When it is determined that the electrode has entered, in step 505, the measurement result C2 at that time, the stored capacitance C1, and the predetermined length L1 in the sub-scanning direction of the first parallel electrode 40 are used to obtain the second. The entry length X of the paper 42 between the parallel electrodes 41 of the above is calculated. The position of the paper 42 is detected by the approach length X. If it is determined that the vehicle has not entered, the determination in step 504 is repeated until the vehicle has entered.

In step 506, it is determined whether or not the paper 42 has passed between the second parallel electrodes 41 based on the measurement result of the capacitance measuring device 45. If it is determined that the vehicle has not passed, the process returns to step 505 and the position is continuously detected. If it is determined that the paper has passed, the process proceeds to step 507, and the position detection of the paper 42 is completed. When printing a plurality of sheets continuously in a print job, the processes of steps 500 to 507 are repeated for each sheet.

The capacitance sensor shown in FIG. 3 has a configuration in which the first parallel electrode 40 and the second parallel electrode 41 are connected by a connecting portion 43, but the connecting portion 43 is not provided and is shown in FIG. It may be separated as follows.

When the first parallel electrode 40 and the second parallel electrode 41 are separated, it is necessary to separately provide wiring for connecting to the current generator 44 and the capacitance measuring device 45, but the capacitance is separately provided. Therefore, the distance K between the first parallel electrode 40 and the second parallel electrode 41 can be made shorter than the length in the sub-scanning direction of the paper 42. By shortening the interval K, the size of the device can be reduced.

By measuring the capacitance, the capacitance sensor can detect the position of the paper 42 as well as the distribution of the water content of the paper 42. If there is no water content distribution on the paper 42 and the water content is constant, the capacitance measured each time the paper 42 is transported a certain distance and enters between the electrodes is as shown in FIG. It increases by a fixed amount. On the other hand, when the water content distribution exists, the capacitance increases each time it enters between the electrodes, but the rate of increase changes. From this change, the distribution of water content can be detected. The conversion from capacitance to water content can be performed using a conversion formula or a conversion table.

As for the water content distribution in this case, only the distribution in the sub-scanning direction can be detected. The detected water content distribution can be used for control of changing the heating conditions for reducing the bending phenomenon (curl) of the paper 42 generated at the time of fixing. This control can be executed by the controller 46, and this control can eliminate deterioration of print quality and paper jams.

The first parallel electrode 40 and the second parallel electrode 41 are arranged so that a pair of flat plates of the same shape and size are spaced apart from each other, and the paper 42 passes between them. FIGS. 3 and 6 In the example shown in the above, any point on the tip of the paper 42 is arranged so as to enter between the first parallel electrodes 40 and between the second parallel electrodes 41 at the same time. That is, one side of the tip of the paper 42 and one side of the first parallel electrode 40 and the second parallel electrode 41 facing the tip of the paper 42 to be entered are arranged in parallel.

However, the arrangement is not limited to this, and the arrangement may be such that at least two points on the tip of the paper 42 enter with a time lag. Specifically, as shown in FIG. 7, one side of the first parallel electrode 40 and the second parallel electrode 41 facing the tip of the paper 42 to be entered is oblique to one side of the tip of the paper 42. It can be arranged so as to be. Therefore, for example, points 50a, 50b, and 50c at the tip of the paper 42 enter between the electrodes at different times, not at the same time.

With such an arrangement, in addition to the distribution of the water content in the sub-scanning direction of the paper 42, the distribution of the water content in the main scanning direction perpendicular to the sub-scanning direction can also be detected. In the example shown in FIG. 7, an example in which the first parallel electrode 40 and the second parallel electrode 41 are arranged diagonally with respect to the tip of the paper 42 is shown, but in addition to changing the arrangement, the first parallel electrode 40 and the first parallel electrode 40 and The shape of the flat plate constituting the second parallel electrode 41 may be changed. The shape of the flat plate may be, for example, a stepped shape so that at least two points at the tip of the paper 42 enter with a time lag.

By the way, in the image forming apparatus, paper is conveyed by driving a conveying roller by a motor as a driving means. The conventional motor control is illustrated in FIG. In the conventional motor control, a signal such as an encoder attached to the motor is fed back to the controller of the image forming apparatus, the motor rotation speed is detected by the controller, and the rotation speed becomes the set target motor rotation speed. The motor drive signal is controlled.

Specifically, the detected rotation speed is compared with the target rotation speed, a signal is generated in which the rotation speed is increased or decreased by the difference, and the generated signal is output to the motor.

In such control by the motor rotation speed, if there is a difference between the motor rotation speed and the amount of movement of the paper, the difference cannot be reflected in the control, so that the paper cannot be accurately conveyed.

Therefore, the position of the paper detected by the capacitance sensor 17 is used to control the motor drive signal. This makes it possible to accurately convey the paper by reflecting the difference between the motor rotation speed and the amount of movement of the paper in the control.

The capacitance sensor 17 calculates the entry length X of the paper 42 that has entered between the second parallel electrodes 41, and detects the current position of the paper 42 from the calculated X. As shown in FIG. 9, the controller of the image forming apparatus detects the moving distance of the paper 42 based on the position information output from the capacitance sensor 17, and controls the motor using the detected moving distance.

Specifically, the controller detects the moving distance of the paper 42, calculates the moving distance of the paper corresponding to the target motor rotation speed, and compares them. Then, a signal for increasing or decreasing the motor rotation speed by the difference is generated so that the detected moving distance becomes the target moving distance, and the generated signal is output to the motor.

The detected position of the paper 42 can be used not only for the purpose of accurately transporting the paper 42 by the motor but also for the purpose of detecting an abnormality in the transport of the paper 42. As an example of the transport abnormality, the slip of the paper 42 can be mentioned.

The paper 42 is conveyed by driving the conveying roller by a motor. The rotation speed Vm of the motor is detected from a signal of an encoder or the like.

FIG. 10 is a diagram showing the relationship between the moving distance of the paper 42 and the time. As shown in FIG. 10, the moving distance x (mm) of the paper 42 increases in proportion to the elapsed time t (sec). Therefore, the inclination V1 can be obtained from the moving distance x1 in an arbitrary section and the time t1 required to move by the moving distance x1, and the V1 can be calculated as the transport speed Vp of the paper 42.

If it is operating normally, the rotation speed of the motor and the transfer speed of the paper 42 will be the same, so the detected rotation speed Vm of the motor and the calculated transfer speed Vp of the paper 42 are compared. .. Incidentally, since the motor rotates the transport roller and the transport roller transports the paper 42 by its own rotation, the transport speed of the paper 42 does not exceed the rotation speed of the motor.

As a result of comparison, when Vm> Vp, it indicates that the paper 42 is not properly conveyed (there is a transfer abnormality) even though the motor is rotating, and it can be determined that the paper 42 is slipping. can.

So far, the present invention has been described with the above-described embodiments as a position detection device, a position detection method, and an image forming device. However, the present invention is not limited to the above-described embodiment, and can be modified within the range conceivable by those skilled in the art, such as other embodiments, additions, changes, and deletions. .. Further, any aspect is included in the scope of the present invention as long as the action / effect of the present invention is exhibited.

10 ... ADF
11 ... Image reading device 12 ... Printer unit 13 ... Paper feeding unit 14 ... Manual feeding unit 15 ... Paper ejection unit 16 ... Operation panel 17 ... Capacitive sensor 20 ... Writing unit 21 ... Photoreceptor drum 22 ... Developing device 23 ... Conveying belt 24 ... Fixing device 25 ... Feed tray 26 ... Paper feed roller 30 ... Parallel electrode 31 ... Paper 40 ... First parallel electrode 41 ... Second parallel electrode 42 ... Paper 43 ... Connecting part 44 ... Current generator 45 ... Static Electric capacity measuring device 46 ... Controllers 50a to 50c ... Points

Japanese Unexamined Patent Publication No. 9-328240

Claims (9)

A device that detects the position of a medium
A first parallel electrode and a second parallel electrode arranged apart from each other in the transport direction of the medium and each composed of a pair of parallel flat plates.
A measuring means for measuring the capacitance generated by the current supplied between the first parallel electrodes and between the second parallel electrodes.
Including
The length of the first parallel electrode in the transport direction is shorter than the length of the medium in the transport direction, and the length of the second parallel electrode in the transport direction is longer than the length of the medium in the transport direction. A featured position detector. The first capacitance measured by the measuring means when the medium passes between the first parallel electrodes, and the measuring means when the medium enters between the second parallel electrodes. The position detecting apparatus according to claim 1, further comprising a calculation means for calculating the approach length of the medium entering between the second parallel electrodes based on the second capacitance measured by. In the calculation means, as the first capacitance, the tip in the transport direction of the medium passes between the first parallel electrodes, and then the end in the transport direction of the medium passes between the first parallel electrodes . The position detecting device according to claim 2, wherein the approach length is calculated by using the capacitance measured until the approach . The first parallel electrode and the second parallel electrode are connected by a connecting portion extending in the transport direction.
The position detection device according to any one of claims 1 to 3, wherein the distance between the first parallel electrode and the second parallel electrode is equal to or longer than the length in the transport direction of the medium. The first parallel electrode and the second parallel electrode are flat plates such that at least two points at the tip of the medium are staggered in time and enter between the first parallel electrodes and between the second parallel electrodes. The position detection device according to any one of claims 1 to 4, which has the shape or arrangement of the above. It is a method of detecting the position of the medium.
Of the first parallel electrode and the second parallel electrode, which are arranged apart from each other in the transport direction of the medium and are composed of a pair of flat plates parallel to each other, the length in the transport direction is the length of the transport of the medium. A step of measuring the first capacitance generated by the current supplied between the first parallel electrodes when the medium passes between the first parallel electrodes shorter than the length in the direction.
A step of entering between the second parallel electrodes whose length in the transport direction is longer than the length in the transport direction of the medium, and
A step of measuring the second capacitance generated by the current supplied between the second parallel electrodes when the particles are inserted between the second parallel electrodes.
A position detection method comprising a step of calculating the approach length of the medium entering between the second parallel electrodes based on the first capacitance and the second capacitance. An image forming apparatus comprising the position detecting apparatus according to any one of claims 1 to 5, controlling the transport of a medium based on the position detected by the position detecting apparatus, and forming an image on the medium. A transport means for transporting the medium, a drive means for driving the transport means, and a control means for controlling the drive means are included.
The image forming according to claim 7, wherein the control means calculates a moving amount of the medium from a position detected by the position detecting device, and controls the driving amount of the driving means according to the calculated moving amount. Device. A transport means for transporting the medium, a drive means for driving the transport means, and a control means for controlling the drive means are included.
7. The control means calculates the moving speed of the medium from the position detected by the position detecting device and the elapsed time, and determines the presence or absence of a transport abnormality of the medium according to the calculated moving speed. Or the image forming apparatus according to 8.

Images