JP5440262B2 - Image forming apparatus and sheet length measuring method - Google Patents

Description

  The present invention relates to an image forming apparatus and a sheet length measuring method, and more particularly to an image forming apparatus and a sheet length measuring method for measuring a sheet length as soon as possible.

  In an electrophotographic image forming apparatus, if the specified paper length does not match the length of the paper that is actually fed, a large amount of defective printing such as jams and misalignment, image misalignment, and toner contamination There are problems that occur. To detect the paper length quickly, measure the paper length from the time when the paper is detected by the sensor provided in the separation area where the paper is separated and transported as upstream as possible. A technique for detecting inconsistencies has been proposed.

  For example, in Patent Document 1, when the length of a sheet is calculated from the time when the registration sensor detects the sheet (simply on time) and the actual sheet size is compared with the designated sheet size, A method for informing the user is disclosed.

  However, in the method of measuring the paper size and detecting the mismatch from the time when the paper is detected by the sensor provided in the separation area where the paper is separated and conveyed as described above, the paper is reliably separated. In other words, there is a problem that the detection timing is late because it must be detected by a sensor in a certain area.

  The present invention has been made in view of such a situation, and an object thereof is to measure the sheet length as soon as possible.

  An image forming apparatus according to the present invention includes a sheet stacking plate in which a tilt angle in a sheet feeding direction changes in accordance with a stacking amount of sheets in a sheet feeding cassette, and stacks sheets stacked on the sheet stacking plate at the uppermost position. An image forming apparatus comprising: a sheet feeding unit that sequentially feeds a sheet; and an image forming unit that forms an image by transferring a toner image formed by an image forming unit onto the sheet fed by the sheet feeding unit. An acceleration detection sensor for detecting a change in the inclination angle in the paper feeding direction is provided on the paper stacking plate, and the acceleration detection sensor and a paper presence / absence detection sensor provided downstream of the paper conveyance path are used. After the start of paper feeding, the acceleration sensor detects the vibration of the paper stacking plate that occurs when the trailing edge of the paper passes through the paper feeding roller after the paper presence detection sensor detects the passage of the paper leading edge. Time until it is judged as the rear end Measurement to be characterized by measuring the sheet length.

  The sheet length measuring method according to the present invention includes a sheet stacking plate in which a tilt angle in a sheet feeding direction changes in accordance with a stacking amount of sheets in a sheet feeding cassette, and stacks the sheets stacked on the sheet stacking plate at the uppermost position. The image forming unit includes: a sheet feeding unit that sequentially feeds paper from the first sheet; and an image forming unit that forms an image by transferring the toner image formed by the image forming unit onto the sheet fed by the sheet feeding unit. A method for measuring a sheet length in an apparatus, comprising: an acceleration detection sensor for detecting a change in an inclination angle in the sheet feeding direction provided on the sheet stacking plate; and a sheet presence / absence detection sensor provided on a downstream side of a sheet conveyance path. After the start of paper feeding, the acceleration sensor detects the vibration of the paper stacking plate that occurs when the trailing edge of the paper passes through the paper feeding roller after the paper presence detection sensor detects passage of the paper leading edge. When it is determined that the trailing edge of the paper It was measured, characterized by having a step of measuring the sheet length.

  According to the present invention, the sheet length can be measured as soon as possible.

1 is a block diagram illustrating a functional configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an example in which the image forming apparatus illustrated in FIG. 1 is connected to a PC and a server via a network. FIG. 2 is a side view showing a simplified internal structure when the image forming apparatus shown in FIG. 1 is a tandem full-color printer. 4 is a timing chart showing a timing relationship between image formation and paper feed in the image forming apparatus according to the present invention. FIG. 3 is a side sectional view showing a configuration of an image forming apparatus according to the present invention, a sheet stacking plate provided in a sheet feeding cassette, and a tilt detection sensor mounting portion. FIG. 5 is a side cross-sectional view showing a state in which sheets are similarly stacked on the sheet stacking plate. FIG. 6 is a perspective explanatory view showing three axis directions for measuring an acceleration component when the tilt detection sensor is a MEMS type acceleration sensor. It is a block diagram which similarly shows the structural example of the inclination detection sensor. 6 is an explanatory diagram illustrating a relationship between an inclination angle detected by an inclination detection sensor and a sheet amount in a sheet feeding cassette. FIG. FIG. 6 is a side cross-sectional view schematically showing states in which the amount of paper in a paper feed cassette is near-end, full, and overloaded. 2 is a flowchart showing a flow of processing by the CPU shown in FIG. 1 during image formation in the image forming apparatus according to the present invention. 2 is a flowchart showing a flow of processing by a CPU shown in FIG. 1 when paper is supplied in the image forming apparatus according to the present invention. 6 is a flowchart showing a processing procedure when performing end correction and near-end correction in the image forming apparatus according to the present invention. FIG. 5 is a diagram illustrating timing for measuring a sheet length in the image forming apparatus according to the present invention. 6 is a flowchart showing a processing procedure when paper length measurement and double feed determination are performed in the image forming apparatus according to the present invention. 6 is a flowchart showing a processing procedure when performing paper rear edge determination reference value acceleration correction by tilting a paper stacking plate in the image forming apparatus according to the present invention.

  Embodiments of the present invention will be described below in detail with reference to the drawings. The embodiments described below are preferred embodiments of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

FIG. 1 is a block diagram showing a functional configuration of an embodiment of an image forming apparatus according to the present invention.
The image forming apparatus 100 includes a CPU 101, a plotter control unit 102, an image processing unit 103, a storage unit 104, a network interface (I / F) control unit 105, an I / O control unit 106, an operation / display unit 107, and a plotter. 1 is a printer provided with 108.

  Of these, components other than the plotter 108 are mutually connected by a CPU bus 109 including a data bus, an address bus, and a control bus. The I / O control unit 106 is connected to sensors as various electrical components and drivers as driving means. A PC (personal computer), which is an external device, is connected to the network I / F control unit 105 via a network such as a LAN line.

The CPU 101 controls the entire image forming apparatus 100. The plotter control unit 102 controls the plotter 108 that performs a writing operation on paper (recording paper). The image processing unit 103 performs predetermined image processing on the image data sent from the PC via the network I / F control unit 105. The I / O control unit 106 performs control of sensors and drivers, and selection of a plurality of paper feeding means (not shown). The operation / display unit 107 includes a key for inputting various information to the apparatus by a user operation, a liquid crystal display for displaying various information, and the like. The storage unit 104 includes a ROM, a RAM, a nonvolatile RAM, and the like.

  The ROM stores programs executed by the CPU 101 and fixed data. The RAM stores primary data including print data and is used as a working memory for the CPU 101. The non-volatile RAM stores data that can be updated even if the power including the data of angles α, β, and −γ described later used in the present invention is turned off. The non-volatile RAM may be a RAM backed up by a battery.

  Although this image forming apparatus 100 shows an example of a printer, a scanner unit is provided in addition to the components shown in FIG. 1, and a copy function, a printer function, a scanner function are provided, or a facsimile transmission / reception unit is also provided to provide a facsimile function. It may be a multi-function digital multifunction peripheral. Alternatively, a single function copying machine or facsimile machine may be used.

[Example of network with connected image forming devices]
2 shows that the image forming apparatus 100 is connected to a PC ((personal computer: PC1, PC2 in the illustrated example) or server (in the illustrated example) from the network I / F control unit 105 via the network 200 such as a LAN or a public line. It is a figure which shows the example connected with the server 1 and the server 2).

  In addition to transmitting image data to the image forming apparatus 100 and printing, each PC acquires information on the image forming apparatus 100 and displays it on the display, and gives various instructions and settings to the image forming apparatus 100. be able to. The server 1 is for example a model database, and the server 2 is for example a media database. Any number of PCs and servers can be connected.

[Example of internal structure of image forming apparatus]
FIG. 3 is a side view showing a simplified internal structure (mainly a portion corresponding to the plotter 108) when the image forming apparatus 100 shown in FIG. 1 is a tandem full-color printer.

Here, an example in which an AIO (All In One) cartridge is employed as a process cartridge for performing image forming processing is shown.
As shown in FIG. 3, the image forming apparatus 100, which is a full-color printer, includes four AIO cartridges in which an image forming unit (image forming unit) includes an image forming unit, that is, an AIO cartridge (K) 1 and an AIO cartridge ( C) 2, AIO cartridge (M) 3, AIO cartridge (Y) 4, an intermediate transfer belt 5 positioned below these AIO cartridges 1 to 4, and a secondary transfer bias roller 6 as a secondary transfer member, It has. Y, M, C, and K in parentheses indicate Y for yellow, M for magenta, C for cyan, and K for black.

  The four AIO cartridges 1 to 4 form toner images of different colors. That is, the AIO cartridge 1 uses black toner to produce a black toner image, the AIO cartridge 2 uses cyan toner to produce a cyan toner image, the AIO cartridge 3 uses magenta toner to produce a magenta toner image, The AIO cartridge 4 forms yellow toner images using yellow toner.

  These four AIO cartridges 1 to 4 have the same structure. Cylindrical photoconductors 1a, 2a, 3a, and 4a, which are rotatable image carriers, and an electrophotographic process around each photoconductor. The charging rollers 1b, 2b, 3b, and 4b, the developing rollers 1c, 2c, 3c, and 4c of the developing device, and the cleaning devices 1d, 2d, 3d, and 4d, which are sequentially arranged, are provided. These four photoconductors 1 a, 2 a, 3 a, 4 a are parallel to each other and are arranged at equal intervals so as to be in contact with the upper surface of the intermediate transfer belt 5.

  The photoreceptors 1a, 2a, 3a, 4a are rotationally driven clockwise in FIG. 3 at a peripheral speed of 120 mm / sec, for example, by a motor (not shown) during an image forming operation. Each AIO cartridge 1 to 4 has a built-in memory for storing various information such as manufacturer information, photoconductor driving time, and toner usage. Each AIO cartridge mounting part is provided with mounting detection means. The upper part of the apparatus main body 110 is a cover, and the AIO cartridges 1 to 4 can be attached and detached by opening the cover.

  Each charging roller 1b, 2b, 3b, 4b is in pressure contact with each photoconductor 1a, 2a, 3a, 4a, and is driven to rotate relative to the photoconductor 1a, 2a, 3a, 4a. Each charging roller 1b, 2b, 3b, 4b is applied with AC and DC bias by a high voltage power source (not shown) to uniformly charge the surface of each photoreceptor 1a, 2a, 3a, 4a.

An optical writing unit 9 is disposed above the four AIO cartridges 1 to 4. The optical writing unit 9 emits laser light LK, LC, LM, LY corresponding to image data for each color of black, cyan, magenta, and yellow toward the surface of each photoconductor 1a, 2a, 3a, 4a. Then, an electrostatic latent image is formed on the charged surface of each photoconductor 1a, 2a, 3a, 4a. As the optical writing unit 9, a laser scanning type using a laser light source, a polygon mirror or the like is shown, but a type combining an LED array and an image forming means may be used.

  The developing devices of the AIO cartridges 1 to 4 stir the respective color toners stored in the toner containers 1e, 2e, 3e, and 4e by the rotation of the paddles 1f, 2f, 3f, and 4f, and develop the necessary amount. One-component development is performed by supplying the rollers 1c, 2c, 3c, and 4c. A predetermined developing bias voltage supplied from a high voltage power source (not shown) is applied to each developing roller 1c, 2c, 3c, 4c, and electrostatic latent images formed on the surfaces of the photoreceptors 1a, 2a, 3a, 4a. Each color toner is attached to the toner image to be visualized as a toner image.

  If the developing bias is too low, the electrostatic latent image is not sufficiently developed with toner and becomes a thin toner image. On the other hand, if the developing bias is too high, the toner adheres to the periphery of the electrostatic latent image and the background of the photosensitive member is stained. When the background stains occur, not only can an appropriate image be obtained, but toner consumption can be accelerated unnecessarily, the device can be damaged due to toner scattering, or the cleaning performance can not be caught up with a large amount of toner. is there.

  For this reason, the conventional image forming apparatus is equipped with a means for measuring the toner density and corrects the developing bias in order to prevent image defects due to toner deterioration and photoconductor fatigue. In this apparatus, the setting range of the developing bias is + 30V to + 350V, and the default is + 80V.

The intermediate transfer belt 5 is stretched between a drive roller 5a and a support roller 5b. The intermediate transfer belt 5 is rotated in the direction of the arrow by a motor (not shown).
Inside the upper portion of the intermediate transfer belt 5, four primary transfer bias rollers 5c, which are primary transfer members, are provided. The primary transfer bias rollers 5c are arranged to face the transfer positions of the photoreceptors 1a, 2a, 3a, and 4a via the intermediate transfer belt 5, respectively.

  A primary transfer bias voltage is applied to each primary transfer bias roller 5c by a primary transfer bias application unit (not shown), and the toner images on the surfaces of the photoreceptors 1a, 2a, 3a, 4a are sequentially transferred to the surface of the intermediate transfer belt 5. Transfer it on top of it. The primary transfer bias application unit is a high voltage power source. A cleaning device 7 for cleaning the intermediate transfer belt 5 is provided in the vicinity of the upper portion of the support roller 5b.

  The secondary transfer bias roller 6 is provided at a position facing the support roller 5 b with the intermediate transfer belt 5 interposed therebetween. A secondary transfer bias voltage is applied to the secondary transfer bias roller 6 by a secondary transfer bias applying unit (not shown), and a toner image on the intermediate transfer belt 5 is applied to a sheet 8 that is a recording material sandwiched between the intermediate transfer belt 5. Is secondarily transferred. The secondary transfer bias application unit is a high voltage power source.

  A paper 8 is accommodated and held in a paper feed cassette (sometimes referred to as a paper feed tray) 10, and the paper 8 is separated and fed one by one from the uppermost paper by a paper feed roller 11. The sheets 8 separated and fed one by one are conveyed to the secondary transfer position by registration rollers 12 disposed in the sheet conveyance path 17. The sub-scanning length of the paper 8 is measured by the registration sensor 13 and an acceleration sensor provided on the paper stacking plate of the paper feed tray. The registration sensor 13 is required to be provided in a separation area where the paper is separated and conveyed.

  An inclination detection sensor 16 for detecting the inclination from the gravitational acceleration is provided on a sheet stacking plate (not shown in FIG. 3) in the sheet cassette 10. Along with the amount, a paper near end (remaining paper is a predetermined number or less) and a paper end (no paper) are also detected. Details thereof will be described later.

  The remaining amount of paper may be detected in combination with acceleration or vibration when the paper passes through the paper feed roller 11.

  The fixing device 14 fixes the toner image on the paper 8 by applying heat and pressure by sandwiching the paper 8 onto which the toner image is transferred and transported along the paper transport path 17 between the heating roller 14a and the pressure roller 14b. .

  In the configuration shown in FIG. 3, the secondary transfer bias roller 6 is in contact with the intermediate transfer belt 5, but when a contact / separation mechanism is provided, unnecessary toner on the intermediate transfer belt 5 is 2 In order to prevent transfer to the next transfer bias roller 6, the paper is separated when a paper jam occurs.

[Description of image forming operation]
Next, an image forming operation of the image forming apparatus 100 which is a full color printer will be described. The image forming operation is performed in a state where a photosensitive member having a color corresponding to the image forming mode is in contact with the intermediate transfer belt 5. Laser light LK, LC, LM, LY corresponding to the image data is emitted from the optical writing unit 9, and each laser light is irradiated on the surface of each of the photoconductors 1a, 2a, 3a, 4a to be charged. An electrostatic latent image is formed on the surface of each of the photoreceptors 1a, 2a, 3a, 4a. The toner supplied by the developing rollers 1c, 2c, 3c, and 4c of the developing devices of the AIO cartridges 1 to 4 adheres to the electrostatic latent image, and is visualized as a toner image.

  The toner images are sequentially superposed by the transfer action of each primary transfer bias roller 5c in which a primary transfer bias is applied to the surface of the intermediate transfer belt 5 that moves in synchronization with each of the photoreceptors 1a, 2a, 3a, and 4a. Primary transfer. As described above, the toner images of different colors formed on the surfaces of the respective photoreceptors are sequentially superimposed on the intermediate transfer belt 5 and primarily transferred, whereby a color toner image is formed on the intermediate transfer belt 5. . In the single color mode, there is one color and there is no superposition of toner images.

  The toner image on the intermediate transfer belt 5 is secondarily transferred to the paper 8 fed from the paper feed cassette 10 and sent to the transfer position between the secondary transfer bias roller 6 and the intermediate transfer belt 5. This secondary transfer is executed by the transfer action of the secondary transfer bias roller 6 to which a secondary transfer bias voltage is applied. The sheet 8 on which the color toner image has been transferred is subjected to fixing processing by the fixing device 14, and is discharged from a discharge port 15 provided in the main body 110 of the full-color printer by a discharge roller 18 after the fixing processing. The paper discharge is detected by a paper discharge sensor 19.

  In the duplex mode in which images are formed on both sides of the paper 8, when the paper discharge sensor 19 detects the trailing edge of the paper, the paper discharge roller 18 is reversed and the paper conveyance path is switched to the paper reversal conveyance path 20 side. The conveyance roller 21 is rotated, and the sheet on which the image is formed on one side is reversed and conveyed through the sheet reversal conveyance path 20 and returned to the registration roller 12 to transfer the next image to the other side of the sheet. The double-sided sensor 22 detects a sheet conveyed through the sheet reversal conveyance path 20.

  As described above, the toner image is usually formed prior to paper feeding. Therefore, when “no paper” is detected after the toner image is formed, the toner image formed by the image forming unit is discarded by cleaning. However, if image formation is started after always confirming the presence of paper, the image formation interval will open and productivity will be significantly reduced. Therefore, in general, image formation will be performed before paper supply without confirming the presence of paper. Is started to form a toner image.

  The image forming apparatus according to the present invention solves this problem and prevents the formed toner image from being discarded without being transferred to the paper without reducing the productivity of image formation as much as possible.

  FIG. 4 is a timing chart showing the timing relationship between image formation and paper feed in the image forming apparatus according to the present invention.

  4, (a) is time (seconds), (b) is a period when there is a print request, (c) is an image forming timing and an image forming period, (d) is a paper feeding timing and a paper feeding period, (e ) Indicates a period after detection of a paper near end when the number of remaining sheets is equal to or less than a predetermined number, and (f) indicates a period after detection of a paper end (no sheet) where there is no remaining sheet.

  When there are more than a predetermined number of sheets in the sheet cassette 10, the image formation is preceded without confirming the presence or absence of sheets as in images 1, 2, and 3 in FIG. The sheets 1, 2, and 3 are fed in time for the transfer of each image. After detecting the paper near end where the remaining number of sheets is less than the predetermined number, after the sheet being fed has passed through the sheet feeding roller, it was confirmed that there is a next sheet (indicated by black circles and arrows in FIG. 4). After image formation starts. When there is no remaining paper and a paper end is detected, the print request is stopped and printing is interrupted. By operating in this manner, it is possible to prevent formation of an unnecessary toner image while suppressing a decrease in productivity.

  In the above-described embodiment, an example in which the present invention is applied to a full-color printer has been described. However, the present invention can be similarly applied to a monochrome printer.

[Configuration of paper loading status detection unit]
5 and 6 show the configuration of a sheet stacking state detection unit including a sheet stacking plate and an inclination detection sensor provided in the sheet feeding cassette 10 in the image forming apparatus.

  A paper stacking plate 25 is provided in a paper feed cassette (also referred to as a paper feed tray) 10 such that one end portion 25a thereof is pivotally supported on both side walls of the paper feed cassette 10 by a shaft 26. The inclination angle of the sheet feeding direction with respect to the bottom surface 10a can be freely changed. A compression spring 30 is interposed between the other end portion 25b of the sheet stacking plate 25 and the bottom surface 10a of the sheet feeding cassette 10, and the other end portion 25b is always raised (sheet stacking). The inclination angle with respect to the bottom surface 10a of the plate 25 is increased).

  On the lower surface side of the sheet stacking plate 25, a sensor support plate 27 is pivotally supported at one end portion (left end portion in the drawing), and the other end portion (right end portion in the drawing) of the sensor support plate 27. A tension spring 29 is interposed therebetween. The tilt detection sensor 16 is fixed to the lower surface of the sensor support plate 27, and a projection 28 is fixed to the center of the upper surface perpendicular to the upper surface and is loosely fitted into a through hole 25 c formed in the paper stacking plate 25. doing.

  Since the sensor support plate 27 is urged by the tension spring 29 in the direction indicated by the arrow A with respect to the paper stacking plate 25, when no paper is placed on the paper stacking plate 25, the sensor support plate 27 is shown in FIG. As described above, the upper end portion of the protrusion 28 protrudes from the upper surface of the sheet stacking plate 25.

  When one or more sheets 8 are placed on the sheet stacking plate 25, the projection 28 is pushed down against the urging force of the tension spring 29 in the direction of arrow B in FIG. The paper stacking plate 25 does not protrude from the upper surface. Thus, the relative angle in the paper feeding direction between the paper stacking plate 25 and the sensor support plate 27 varies greatly depending on whether or not the paper 8 is present on the paper stacking plate 25.

  As the tension spring 29, since the protrusion 28 must be pushed down even with one sheet of paper, a weak spring such as that used in a normal filler type sensor is used.

  In the state where the paper 8 is stacked on the paper stacking plate 25, the paper stacking state detection unit keeps a constant relative angle between the paper stacking plate 25 and the sensor support plate 27 as shown in FIG. The paper stacking plate 25 rotates with a weight corresponding to the load amount of the paper 8, and the inclination angle of the paper stacking plate 25 with respect to the bottom surface 10a of the paper feed cassette 10 changes. As a result, the inclination of the inclination detection sensor 16 changes in the same manner, so that the inclination detection angle changes, and the paper stacking amount can be estimated and calculated based on the detection angle.

  The change in inclination per sheet is extremely small, and the amount of change in inclination per sheet varies depending on whether the amount of loaded paper is large or small. However, the outline of the remaining amount of paper can be calculated by performing correction according to the paper stacking amount based on the detection angle by the inclination detection sensor 16. As a result, it is possible to display the decrease of the sheet in a unit of 10%, for example, by a bar graph from the sheet full state.

Further, when the number of printed sheets is designated and the number of printed sheets is larger than the estimated remaining number of sheets by a certain number (corresponding to the maximum error number), it is possible to display a warning of insufficient paper.
Further, when all the sheets 8 in the sheet feeding cassette 10 are fed and the sheets on the sheet stacking plate 25 are exhausted, the sheet stacking state detecting unit detects that the upper end portion of the protrusion 28 is at the sheet stacking plate 25 as shown in FIG. Therefore, the sensor support plate 27 to which the tilt detection sensor 16 is fixed by the urging force of the tension spring 29 approaches the paper stacking plate 25 and rotates greatly in the direction in which the relative angle between the two becomes smaller. . Therefore, the inclination of the inclination detection sensor 16 increases suddenly, and the paper end (no paper) can be detected immediately.

  Although the above-described example of the paper stacking state detection unit has been described in an easy-to-understand manner, the minimum requirement for carrying out the present invention is to detect the inclination angle of the paper feeding direction on the paper stacking plate 25. While the sheet is present on the sheet stacking plate 25, the tilt detection sensor 16 is set so that the relative angle in the sheet feeding direction between the tilt detection sensor 16 and the sheet stacking plate is constant as shown in FIG. When there is no paper on the top, the relative angle is changed so as to decrease as shown in FIG.

  Then, the sheet stacking amount and the paper near end where the number of sheets is equal to or less than a predetermined number are determined based on the tilt angle detected by the tilt detection sensor 16 with the relative angle being constant, and the tilt detection sensor 16 is detected when the relative angle changes. Means for determining the paper end where there is no paper based on the tilt angle detected by the CPU 101 (performed by the CPU 101 in FIG. 1 as will be described later).

  Therefore, the attachment structure of the inclination detection sensor 16 with respect to the paper stacking plate 25 can be changed variously. For example, without providing the sensor support plate 27, the inclination detection sensor 16 is attached to the paper stacking plate 25 so as to be directly rotatable. The convex portion or free end portion of the tilt detection sensor may be allowed to protrude from the upper surface of the paper stacking plate 25, and a notch or the like may be formed in the paper stacking plate 25 in place of the through hole 25c. Instead of the tension spring 29, a weak leaf spring or a torsion spring may be provided on the shaft support, or a resin spring or rubber may be used.

[(Acceleration sensor) Tilt detection sensor configuration example]
FIG. 7 shows a schematic diagram of an (acceleration detection sensor) tilt detection sensor. FIG. 8 shows a block of the (acceleration detection sensor) tilt detection sensor.
(Acceleration detection sensor) As the inclination detection sensor 16, for example, a MEMS (Micro Electro Mechanical System) type acceleration sensor is used, and as shown in FIG. 7, the gravitational acceleration components in the X-axis, Y-axis, and Z-axis directions are displayed. The posture and inclination are detected by measuring the component force.

  Therefore, as shown in the block diagram of FIG. 8, the tilt detection sensor 16 adjusts the amplified signal by detecting a detection element 161 that detects acceleration, a signal amplification circuit 162 that amplifies the signal from the detection element 161, and the like. A signal adjustment circuit 163 for outputting, an A / D conversion circuit 164 for digitizing the output signal, and an inclination calculation circuit 165 for calculating an inclination from the digitized values of the gravitational acceleration components in the three-axis directions.

  The inclination value calculated by the inclination calculation circuit 165 is taken into the CPU 101 shown in FIG. 1 via a 12C interface (not shown). Note that the inclination calculation circuit 165 may be omitted, and the value of the triaxial gravity acceleration component digitized by the A / D conversion circuit 164 may be directly taken into the CPU 101, and the inclination may be calculated by the CPU 101. . In the present invention, acceleration is used to detect vibration of the paper stacking plate.

The detection element 161 includes a capacitance type, a piezoresistive type, a heat detection type, and the like. Here, a piezoresistive type acceleration detection element is used.
The piezoresistive acceleration detecting element has a structure in which a weight provided at the center of the detecting element is supported by a spring portion formed by a beam on which the piezoresistive element is arranged. When the acceleration is received, a change in the resistance value of the piezoresistive element due to the distortion generated in the spring portion due to the fluctuation of the center weight is detected using a bridge circuit.

  Since this tilt detection sensor 16 can simultaneously form peripheral circuits on the substrate by using the MEMS technology, many functions can be integrated and a small and light sensor can be manufactured. In addition, an I2C interface can be used for communication between the tilt detection sensor 16 and the CPU 101, but as a MEMS sensor incorporating a wireless circuit having a transmission / reception circuit as a peripheral device, wireless communication is performed with the CPU 101 side. It may be. In this case, wireless communication eliminates the need for communication wiring and increases the degree of freedom of sensor placement.

  Note that an inclination detection sensor using MEMS technology such as such a three-axis acceleration sensor is known as described in, for example, Japanese Patent Application Laid-Open No. 2007-278759, and a detailed description thereof is omitted. However, the tilt detection sensor 16 used in the present invention only needs to be able to detect the tilt angle in the X-axis direction in FIG. 7 (the paper feed direction when attached to the paper stacking plate 25 as shown in FIGS. 5 and 6).

[Relationship between detected tilt angle and paper amount]
FIG. 9 is an explanatory diagram showing the relationship between the inclination angle in the X-axis direction detected by the inclination detection sensor 16 shown in FIGS. 5 and 6 and the state of the amount of paper in the paper feed cassette.
In this figure, if the inclination angle in the X-axis direction detected by the inclination detection sensor 16 is θ, θ = 0 degrees (horizontal) is the reference position, and then the left rotation direction angle is plus, and the right rotation direction angle is Negative.

  The normal paper amount state is from when the inclination angle θ exceeds 0 degree until it reaches β (paperia end determination threshold), and from 0 degree to −γ (for example, 5 degrees in the negative direction) is full. If θ exceeds −γ in the minus direction, the load is over. If paper is fed in this state, there is a high possibility of non-feed jams, paper skew, folds, tears, etc. There is a need to. -Γ is an angle having a small absolute value, and may be 0 degrees depending on the configuration of the paper stacking state detection unit.

  Thus, the inclination angle when the amount of paper on the paper stacking plate is full is 0 degree or a slight predetermined angle (−γ) at which the inclination detection sensor inclines in the opposite direction to the case where the paper amount decreases. When the detected inclination angle is smaller than that, that is, when the angle becomes 0 degree or larger in the opposite direction than −γ, the overload state is set.

  When the inclination angle θ exceeds β and reaches α (paper end determination threshold), the paper near end state (state where the number of sheets is equal to or less than a predetermined number of sheets) is exceeded. When there is no paper on the paper stacking plate 25, the inclination of the inclination detection sensor 16 suddenly increases as described above, so that the inclination angle θ always exceeds α and can be detected.

Therefore, the relationship between the range of the inclination angle θ shown in FIG. 9 and the state of the amount of paper in the paper feed cassette is as follows.
θ <−γ: Overload
−γ ≦ θ ≦ 0 °: Load capacity full
0 ° <θ ≦ β: Normal paper amount
β <θ ≦ α: Paper near end
α <θ: Paper end

FIG. 5 shows the paper end state, and FIG. 6 shows the paper near end state.
FIG. 10 is a simplified side cross-sectional view of a paper feed cassette that stores paper. FIG. 10A shows a paper near end state, FIG. 10B shows a paper full state, and FIG. 10C shows a paper stacking amount over state. ing.

10, the same parts as those in FIGS. 5 and 6 are denoted by the same reference numerals.
In FIG. 10, reference numeral 11 denotes a paper feed roller, and 30 denotes a compression spring, which pushes and urges the front end of the paper stacking plate 25 so that the top end of the uppermost paper among the papers 8 stacked on the paper stacking plate 25 is moved. The paper can be fed by pressing against the paper feed roller 11. Therefore, the inclination of the paper stacking plate 25 changes depending on the amount of the paper 8 stacked on the paper stacking plate 25, and the inclination of the tilt detection sensor 16 also changes.

[Explanation by flowchart]
Next, processing relating to the present invention by the CPU 101 shown in FIGS. 1 and 8 in the image forming apparatus according to the present invention will be described with reference to FIGS.

FIG. 11 is a flowchart showing the flow of processing by the CPU 101 during image formation.
The CPU 101 regularly inquires of the tilt detection sensor 16 shown in FIG. 8 about the tilt angle via the interface. Then, the remaining amount of paper in the paper cassette is calculated from the tilt angle information, and the remaining amount of paper is displayed on the operation / display unit 107 shown in FIG. Although processing is also performed, the processing is omitted in FIG. Further, the data of the angle β serving as the threshold for paper near end determination and the angle α serving as the threshold for paper end determination are stored in the nonvolatile RAM (angle storage means) of the storage unit 104 shown in FIG.

  When printing is instructed, the processing of FIG. 11 is started. First, in step S11, it is determined whether or not “tilt> β”. If the tilt (tilt angle θ described above) is equal to or less than β (NO), normal paper is used. Since the amount is in the state, the process proceeds to step S14 to start the image forming unit in the image forming preceding process without confirming the presence or absence of paper, and in step S15, the paper is fed at a predetermined timing. The image (toner image) created in step 1 is transferred onto a sheet. In step S16, the presence or absence of the next printing is determined. If there is no next printing, the process ends. If there is, the process returns to step S11 and the above-described processes are repeated.

  If it is determined in step S11 that the slope> β is YES, the paper near end state has been reached, so that the paper for the image that has started image formation in step S12 passes through the paper feed roller to complete the paper feed. In step S13 after completion of paper feeding, it is determined whether or not “tilt> α”. If the result is NO, there is still paper, so image formation is started in the image forming unit in step S14, paper is fed at a predetermined timing in step S15, and an image (toner image) formed in the image forming unit Is transferred to the paper.

In step S16, the presence or absence of the next printing is determined. If there is no next printing, the process ends. If there is, the process returns to step S11 and the above-described processes are repeated.
If inclination> α (YES) in step S13, it is a paper end (no paper), so the process proceeds to step S17, printing is interrupted, and the process is terminated. At this time, for example, a warning such as “There is no paper in the tray. Please replenish.” Is displayed on the operation / display unit 107 of the image forming apparatus 100 shown in FIG. 1 or the console screen of the PC shown in FIG. Good. Thereafter, when paper is supplied to the paper feed cassette, this process can be resumed and the remaining printing can be continued.

  By processing in this way, as described with reference to FIG. 4, in the normal paper amount state, in the image formation preceding process, image formation of the next image is started while paper is fed to the preceding image, and production is performed. Highly continuous printing. In that case, even if an attempt is made to determine the presence or absence of paper at the timing before the start of image formation, paper for the preceding image is being fed at that timing, and it is not possible to confirm the presence or absence of paper for the image to be imaged from now on. Do not check for the presence of paper.

  When the paper near-end state is reached, after the paper supply for the preceding image is completed, after confirming that there is paper (tilt> α), the image forming operation is started, and the paper is fed at a timing that matches the image formed. To start. If it is a paper end, printing is interrupted and image formation is not started. As a result, the wasted toner image can no longer be transferred and discarded.

If there is no response from the tilt detection sensor 16, it is determined that the paper feed cassette 10 has been pulled out from the image forming apparatus main body 110 shown in FIG.
If the image formation is controlled in this way, before the paper near-end state (normal paper amount state), the preceding image formation process is performed without confirming the presence or absence of paper for the image to be imaged. It is possible to start the next image while the paper is being fed for the image to be printed, and to perform continuous printing with high productivity. However, when the paper near-end state is reached, image formation starts after confirming that there is paper for the image to be imaged from now on. It is possible to prevent excessive toner consumption.

FIG. 12 is a flowchart showing the flow of processing by the CPU 101 when paper is supplied.
This process starts when paper is replenished, for example, when the paper feed cassette is pulled out from the image forming apparatus main body 110 and then returned to the normal storage state. In step S21, it is determined whether or not “inclination <−γ” (inclination is less than −γ). If NO, the load amount is not over and the process is terminated. If YES, the load amount is over. Therefore, a warning to that effect is displayed in step S22. For example, a warning such as “Too much paper in tray. Please remove” is displayed on the operation / display unit 107 of the image forming apparatus 100 shown in FIG. 1 or the console screen of the PC shown in FIG.

After that, when the user of the image forming apparatus pulls out the paper cassette to slightly reduce the stacked paper and returns to the normal storage state again, the CPU 101 executes the process of FIG. 12 again with “tilt <−γ”. If it is gone, no warning is displayed.
The data of the angle −γ that is a threshold value for determining the overload amount used in this processing is also stored in the nonvolatile RAM (angle storage means) of the storage unit 104 shown in FIG.

  Next, a processing procedure for performing end correction (correction of angle α) and near-end correction (correction of angle β) in the image forming apparatus according to the present invention will be described with reference to the flowchart of the correction procedure shown in FIG. In this flowchart, the processing performed by the user (worker) of the image forming apparatus and the processing executed by the CPU 101 are shown in time series. It is assumed that the initial values of the angles α and β are stored in the nonvolatile RAM of the storage unit 104 shown in FIG. 1 when the image forming apparatus is manufactured.

  Therefore, the processing described with reference to FIG. 11 can be performed without performing this correction processing, but it is possible to detect the paper near end depending on the use environment of the image forming apparatus, secular change, and the type of paper used. The optimum value of the angle α for detecting the angle β and the paper end changes. For this reason, it is desirable to perform this correction processing when the image forming apparatus is installed or moved, when the paper to be used is changed, and every certain period of use.

  In the correction processing shown in FIG. 13, first, in step S31, the worker puts one sheet on the paper feed tray in the paper feed cassette (on the bottom surface 10a of the paper feed cassette 10 and the paper stacking plate 25 shown in FIG. 10). Set.

  When the worker presses the end correction switch provided on the operation / display unit 107 in step S32, the CPU 101 detects the detected value of the inclination angle (the sheet on the sheet stacking plate 25 from the inclination detection sensor 16 in step S33). 1 is obtained, and an angle α serving as a paper end threshold is calculated from the angle θ1, and the angle α stored in the storage unit 104 of FIG. 1 is updated. .

  In this case, α = θ1 may be used, but when there is no paper in the paper feed tray, the inclination of the inclination detection sensor 16 greatly increases and the detected value of the inclination angle also increases as shown in FIG. If Δmin is Δθ, the value is substantially constant regardless of the type of paper. Therefore, for example, Δθ / 2 may be added to θ1 so that α = θ1 + Δθ / 2. Alternatively, an arbitrary value between 0 degree and Δθ / 2 may be added to θ1.

  Next, in step S34, the worker sets two sheets on the sheet feeding tray in the sheet feeding cassette. In step S35, when the operator depresses the near-end correction switch provided on the operation panel, the CPU 101 detects from the tilt detection sensor 16 in step S36 the detected value of the tilt angle (two sheets of paper on the sheet stacking plate 25). 1 is obtained, an angle β serving as a threshold value for the paper near end is calculated from the angle θ2, and the angle β stored in the storage unit 104 in FIG. 1 is updated.

  In this case, β = θ2−K, and K is a constant. Assuming that the angle corresponding to one sheet is 0.04 degrees, it is preferable to calculate β by calculating β = θ2−K = θ2−0.04 degrees with K = 0.04 degrees.

  The number of sheets set in the paper feed tray in step S34 is the number of sheets fed in the paper near end state, which may be any number, but ideally more than the number of images created before feeding. And it is better to have as few as possible.

  According to the above-described embodiment of the present invention, the paper near end and the paper end can be determined based on the inclination angle detected by a common inclination detection sensor, so that the number of parts and assembly man-hours can be reduced.

  In addition, in an image forming apparatus of an image formation type electrophotographic method, it is possible to perform continuous image formation with a high productivity by always increasing the image forming timing, and a paper near end state in which the number of sheets in the sheet feeding cassette is less than a predetermined number. After that, the image formation starts after confirming that there is paper to which the image is to be transferred, so that an image that is not transferred to the paper is formed, resulting in wasted toner and unnecessary cleaning. No wasteful operations such as performing

By detecting an excess of the paper stacking amount, it is possible to prevent the occurrence of a non-feed jam.
The angle β, which is the threshold value for the paper near-end judgment stored in the angle storage means, and the data of the angle α, which is the threshold value for the paper end judgment, can be corrected or updated, respectively. Even when the type of paper to be used is changed, accurate determination can always be made by correcting or updating the data of the angles β and α.

  Next, sheet length measurement will be described. In the embodiment according to the present invention, an acceleration sensor is provided on the paper stacking plate of the paper feed tray, and even when the paper is not separated, the vibration generated at the timing when the rear edge of the paper passes through the paper feed roller is detected. Since the length can be measured, the paper length can be measured even when the paper is not separated at the timing when the trailing edge of the paper passes through the paper feed roller, so that a mismatch can be detected quickly. In other words, the sensor at the downstream of the paper transport path detects the leading edge of the paper, and the acceleration sensor provided at the paper stacking plate is used to measure the paper length from the vibration that occurs when the trailing edge of the paper leaves the paper feed roller. It is characterized by doing.

FIG. 14 shows the timing of paper length measurement.
When the paper feed roller is turned on / off to feed paper, the acceleration sensor of the paper stacking plate detects the acceleration by the vibration at the start / stop of the roller drive. In addition, the acceleration is always changed by minute vibration during paper feeding. When the trailing edge of the paper passes through the paper feed roller, the paper stacking plate rises by the thickness of the paper, and an upward acceleration is generated. The sheet length is obtained by measuring the time from when the registration sensor is turned on, measuring the time until the trailing edge of the sheet, and multiplying the value by the sheet conveyance speed and the distance from the sheet feeding roller to the registration sensor.

FIG. 15 shows a flowchart of paper length measurement and double feed determination.
As shown in the flow of FIG. 15, the measurement of the paper length starts when the registration sensor is ON (step S42 / Yes), and ends when the acceleration is equal to or greater than the paper rear edge determination reference value K (step S44 / Yes). Note that a determination reference value Km is provided, and when the acceleration is equal to or higher than Km (step S45 / Yes), it may be determined that separation is not possible when a plurality of sheets of paper are fed in blocks (step S46).

FIG. 16 shows a flowchart of the paper rear edge determination reference value acceleration correction based on the inclination of the paper stacking plate.
As the remaining amount of paper decreases, the acceleration that occurs when the trailing edge of the paper passes through the paper feed roller increases, so the reference value is corrected by the inclination of the paper stacking plate. For example, when the inclination of the paper stacking plate is N or more (step S51 / Yes), the reference value K may be corrected to K0 (step S52).

  Note that the program for the CPU to execute the processing shown in the flowcharts of the drawings constitutes a program according to the present invention. As a recording medium for recording the program, a semiconductor storage unit, an optical and / or magnetic storage unit, or the like can be used. By using such a program and recording medium in a system having a configuration different from that of each of the above-described embodiments and causing the CPU to execute the program, substantially the same effects as those of the present invention can be obtained.

  Although the present invention has been specifically described above based on the preferred embodiments, it is needless to say that the present invention is not limited to the above-described ones and can be variously modified without departing from the gist thereof.

1 AIO cartridge (K)
2 AIO cartridge (C)
3 AIO cartridge (M)
4 AIO cartridge (Y)
1a, 2a, 3a, 4a Photoconductor 1b, 2b, 3b, 4b Charging roller 1c, 2c, 3c, 4c Developing roller 1d, 2d, 3d, 4d Cleaning device 1e, 2e, 3e, 4e Toner container 1f, 2f, 3f 4f paddle 5 intermediate transfer belt 5a drive roller 5b support roller 5c primary transfer bias roller 6 secondary transfer bias roller 7 cleaning device 8 paper 9 optical writing unit 10 paper feed cassette 10a bottom surface 11 paper feed roller 12 registration roller 13 resist Sensor 14 Fixing device 15 Discharge port 16 Tilt detection sensor 17 Paper transport path 18 Paper discharge roller 19 Paper discharge sensor 20 Paper reverse transport path 21 Reverse transport roller 22 Double-sided sensor 25 Paper stacking plate 25c Through hole 26 Shaft 27 Sensor support plate 28 Exhaust Paper roller 29 Tension spring 30 Compression spring Ring 100 image forming apparatus (full color printer tandem)
161 detection element 162 signal amplification circuit 163 signal adjustment circuit 164 A / D conversion circuit 165 inclination calculation circuit

JP-A-7-92959

Claims (8)

The paper cassette has a paper stacking plate in which the inclination angle of the paper feeding direction changes according to the amount of paper loaded,
Paper feeding means for sequentially feeding the paper stacked on the paper stacking plate from the topmost paper;
An image forming unit that forms an image by transferring a toner image formed by an image forming unit to a sheet fed by the sheet feeding unit;
An acceleration detection sensor for detecting a change in the inclination angle of the paper feeding direction is provided on the paper stacking plate,
Using the acceleration detection sensor and a paper presence / absence detection sensor provided downstream of the paper conveyance path, after the paper feed starts, the paper presence / absence detection sensor detects the passage of the front end of the paper, and then the paper rear edge is fed. An image forming apparatus characterized by measuring a time required for detecting a vibration of a paper stacking plate generated when the paper roller is pulled out by the acceleration detection sensor to determine a paper rear end, and measuring a paper length.   The image forming apparatus according to claim 1, wherein the acceleration sensor provided on the paper stacking plate also serves to detect the remaining amount of paper from the inclination of the stacking plate.   3. The image forming apparatus according to claim 1, wherein an acceleration reference value for determining that the trailing edge of the sheet has passed through the sheet feeding roller is corrected based on the inclination of the sheet stacking plate.   4. The image forming apparatus according to claim 1, wherein when the acceleration exceeds a predetermined value, it is determined that a double feed incapable of sheet separation has occurred. 5. The paper cassette has a paper stacking plate in which the inclination angle of the paper feeding direction changes according to the amount of paper loaded,
Paper feeding means for sequentially feeding the paper stacked on the paper stacking plate from the topmost paper;
A paper length measuring method in an image forming apparatus, comprising: an image forming unit that forms an image by transferring a toner image formed by an image forming unit to a sheet fed by the sheet feeding unit;
After the start of paper feeding using the acceleration detection sensor provided on the paper stacking plate for detecting a change in the inclination angle of the paper feeding direction and the paper presence / absence detecting sensor provided on the downstream side of the paper transport path, The time from detection of the passage of the leading edge of the paper by the presence sensor to detection of the trailing edge of the paper when the trailing edge of the paper passes through the paper feed roller is detected by the acceleration detection sensor. A paper length measuring method comprising measuring and measuring a paper length.   6. The paper length measuring method according to claim 5, wherein the acceleration sensor provided on the paper stacking plate also serves to detect the remaining amount of paper from the inclination of the stacking plate.   7. The sheet length measuring method according to claim 5, further comprising a step of correcting a reference value of acceleration for determining that the trailing edge of the sheet has passed through the sheet feeding roller based on the inclination of the sheet stacking plate.   8. The sheet length measuring method according to claim 5, further comprising a step of determining that a double feed that cannot be separated is generated when the acceleration exceeds a predetermined value.

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