JP5427625B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a multi-beam image forming apparatus that performs image formation by scanning light emitted from a plurality of light emitting units on a photoconductor, and more particularly to a technique for correcting a unity magnification shift in the sub-scanning direction.

  In an image forming apparatus that forms an image on a recording paper by a secondary transfer method using an intermediate transfer belt, an image having a size different from the planned size is caused by expansion / contraction of the intermediate transfer belt accompanying a temperature change or the like. In other words, a so-called equal magnification shift may occur. For example, when the temperature of the intermediate transfer belt rises, the intermediate transfer belt expands and the toner image transferred on the surface of the intermediate transfer belt expands, and an image having a size larger than the original size is recorded in the recording medium. Formed on paper.

  Conventionally, in order to correct the equal magnification deviation, for example, an image forming apparatus disclosed in Patent Document 1 detects a sub-scanning magnification error of a transfer conveyance device based on speed information of the transfer conveyance device, and detects the error. The correction amount of the sub-scanning magnification error is calculated, and control is performed to vary the drive speed of the transfer conveyance device so as to reduce the sub-scanning magnification error based on the calculated correction amount.

  In recent years, image forming apparatuses (hereinafter referred to as multi-beam machines) that employ a multi-beam exposure apparatus including a plurality of laser diodes (hereinafter referred to as LDs) as exposure apparatuses in order to speed up image forming processing have been widely used. It's being used. In general, the exposure apparatus scans the surface of the photoreceptor by passing the laser beam emitted from the LD through an optical member including a cylindrical lens, a polygon mirror, an fθ lens, and the like. The laser beam is scanned at a constant speed (main scanning) on the surface of the photosensitive member by the rotation of the polygon mirror, and is scanned at a constant speed in the sub-scanning direction on the surface of the photosensitive member by the rotation of the photosensitive member. In the multi-beam machine, the number of laser beam beams scanned at once in the sub-scanning direction on the surface of the photoconductor increases, so that the number of rotations of the polygon mirror can be reduced as compared with the case of scanning using one laser beam beam. Scanning of the surface of the photoreceptor and formation of an electrostatic latent image can be performed quickly without raising the surface.

JP 2006-259173 A

  In the conventional multi-beam machine, the beam pitch between the laser beams emitted from the respective LDs is normally fixed. Therefore, in the conventional method as disclosed in Patent Document 1, the same magnification in the sub-scanning direction is used. There is a problem that the degree correction cannot be performed.

  A multi-beam machine capable of adjusting the beam pitch in the sub-scanning direction has also been proposed. In such a multi-beam machine, the expansion / contraction of the intermediate transfer belt and the like accompanying changes in the ambient environment such as temperature changes is proposed. The correction of the equal magnification deviation in the sub-scanning direction and the adjustment of the beam pitch were not linked.

  The present invention has been made in order to solve such a conventional problem. In a multi-beam image forming apparatus, the same magnification deviation in the sub-scanning direction due to a change in environmental conditions in the apparatus is reduced. The purpose is to correct.

An image forming apparatus according to the present invention includes a photoreceptor, a charging device that charges the photoreceptor, a light source that includes a plurality of light emitting units that emit light according to image data, and the light source is rotated. An exposure apparatus comprising: a stepping motor configured to vary a sub-scanning direction pitch between the plurality of light emitting units, and forming an electrostatic latent image by scanning the charged photoconductor with light emitted from the plurality of light emitting units. And a developing device that visualizes the electrostatic latent image formed on the photoconductor with toner and forms a toner image on the photoconductor, and is stretched between a plurality of rollers so as to be able to run endlessly in the sub-scanning direction. , and the photosensitive member the toner image formed on the an intermediate transfer belt which is primarily transferred to the outer peripheral surface, a transfer device that secondarily transferred recording paper said intermediate transfer said toner image the is primarily transferred to the belt Detect the temperature of the intermediate transfer belt A temperature detection unit that receives an input from the user, sets a different type of the recording paper according to the paper thickness, and a temperature change detected by the temperature detection unit. In order to increase or decrease the sub-scanning direction pitch, a first storage unit that stores the change amount and the number of drive pulses of the stepping motor in association with each other, and a sheet of the recording sheet with respect to a reference sheet thickness In order to increase or decrease the pitch in the sub-scanning direction according to the amount of change in thickness, a paper thickness difference between the reference paper thickness and a paper thickness according to the type of the recording paper, and the number of drive pulses of the stepping motor A second storage unit that is stored in advance in association with each other, and the number of drive pulses corresponding to the amount of change in temperature detected by the temperature detection unit is read from the first storage unit, and the first paper setting unit The type of recording paper set in The drive pulse number corresponding to the difference in paper thickness between the paper thickness and the reference paper thickness is read from the second storage unit, and the drive pulse number read from the first storage unit is read from the second storage unit. A pitch control unit that outputs a drive pulse number obtained by adding the read drive pulse number to the stepping motor to rotate the light source, and the transfer device includes a secondary transfer counter roller and the secondary transfer counter roller. A secondary transfer roller provided in contact with the surface of the intermediate transfer belt at a position opposed to the intermediate transfer belt, and the secondary transfer roller and the secondary transfer in which the toner image is secondarily transferred to the recording paper. A first portion in which the toner image extends by projecting in the outer peripheral direction of the intermediate transfer belt at the nip portion. Middle And a second portion where the toner image contracts by being convex in the inner circumferential direction of the transfer belt. By being pressed further in the inner circumferential direction of the intermediate transfer belt at the portion, the angle formed between both ends of the second portion and the center of the secondary transfer roller is increased, and the magnification of the secondary transfer is decreased. In the second storage unit, the pitch in the sub-scanning direction is increased in order to cope with the case where the secondary transfer magnification decreases due to an increase in the thickness of the recording sheet. the number of drive pulses that have been stored.
In the above-described configuration, the image forming apparatus has a double-sided printing function, and the image forming apparatus accepts an input from a user and sets the type of the recording paper having a different shrinkage rate during thermal fixing. A third storage unit that stores in advance the correspondence between the contraction rate obtained in advance for each type of recording paper and the number of drive pulses corresponding to the contraction rate. The pitch control unit includes the shrinkage rate of the recording paper type set by the second paper setting unit when the image forming process is performed on the back surface of the recording paper having the heat fixing on the front surface. Is read from the third storage unit, and the drive pulse number read from the third storage unit is output to the stepping motor to rotate the light source.
The present invention includes the following first to fifth inventions.
An image forming apparatus according to a first invention is:
A photoreceptor,
A charging device for charging the photoreceptor;
A plurality of light emitting units that emit light according to image data; and a pitch variable mechanism that varies a pitch in the sub-scanning direction between the plurality of light emitting units, and the plurality of light emitting units are provided on the charged photoreceptor. An exposure device that scans the emitted light to form an electrostatic latent image;
A developing device that visualizes the electrostatic latent image formed on the photoconductor with toner and forms a toner image on the photoconductor;
A transfer device for transferring the toner image on the photoreceptor generated by the developing device to a recording paper;
An environmental condition detector for detecting environmental conditions inside the image forming apparatus;
The sub-scanning direction pitch is determined according to the environmental condition detected by the environmental condition detection unit, and the pitch variable mechanism is configured to set the sub-scanning direction pitch between the plurality of light emitting units at the determined sub-scanning direction pitch. A variable pitch control unit.

According to the first invention, the pitch control unit determines the sub-scanning direction pitch according to the environmental condition detected by the environmental condition detection unit, and the pitch variable mechanism determines the determined sub-scanning direction pitch. Thus, since the sub-scanning direction pitch between the plurality of light emitting units is varied, it is possible to correct a unity magnification shift in the sub-scanning direction in a so-called multi-beam machine.

  This is because the intermediate transfer belt, the secondary transfer roller, etc. expands and contracts according to the environmental conditions in the apparatus such as the temperature and humidity inside the image forming apparatus, and the same magnification deviation in the sub-scanning direction occurs. This is because the sub-scanning direction pitch between the plurality of light emitting units can be varied according to the environmental conditions, and the same-time deviation in the sub-scanning direction can be corrected.

An image forming apparatus according to a second invention is the image forming apparatus according to the first invention , wherein the transfer device is stretched between a plurality of rollers so as to be able to run endlessly in the sub-scanning direction, and is formed on the photoconductor. An intermediate transfer belt on which the toner image is transferred to an outer peripheral surface, the environmental condition detection unit is a temperature detection unit that detects the temperature of the intermediate transfer belt, and the pitch control unit is The sub-scanning direction pitch is determined according to the temperature detected by the detection unit, and the pitch variable mechanism is configured to vary the sub-scanning direction pitch between the plurality of light emitting units at the determined sub-scanning direction pitch.

According to the second invention, the pitch control unit determines the sub-scanning direction pitch according to the temperature of the intermediate transfer belt detected by the temperature detection unit, and the pitch variable mechanism determines the determined sub-scanning. Since the sub-scanning direction pitch between the plurality of light emitting units is varied by the direction pitch, it is possible to correct a unity magnification deviation in the sub-scanning direction in a so-called multi-beam machine.

  This is because the intermediate transfer belt expands and contracts at a coefficient of thermal expansion specific to the constituent material according to the temperature of the intermediate transfer belt, and an equal magnification shift occurs in the sub-scanning direction. This is because the sub-scanning direction pitch between the light emitting units can be varied, and therefore, it is possible to correct the same magnification deviation in the sub-scanning direction.

An image forming apparatus according to a third aspect is the image forming apparatus according to the first aspect , wherein the environmental condition detection unit is a humidity detection unit that detects humidity inside the image forming apparatus, and the pitch control unit. Determines the sub-scanning direction pitch according to the humidity detected by the humidity detection unit, and causes the pitch variable mechanism to set the sub-scanning direction pitch between the plurality of light emitting units at the determined sub-scanning direction pitch. Make it variable.

According to a third invention, the pitch control unit determines the sub-scanning direction pitch according to the humidity detected by the humidity detection unit, and the pitch variable mechanism has the determined sub-scanning direction pitch at the determined sub-scanning direction pitch. Since the pitch in the sub-scanning direction between the plurality of light emitting units is made variable, it is possible to correct an equal magnification shift in the sub-scanning direction in a so-called multi-beam machine.

  This is because the intermediate transfer belt or the like expands and contracts at an expansion coefficient specific to the constituent material according to the humidity inside the image forming apparatus, and an equal magnification shift occurs in the sub-scanning direction. This is because it is possible to vary the pitch in the sub-scanning direction between them, and thus it is possible to correct the same-size shift in the sub-scanning direction.

An image forming apparatus according to a fourth aspect is the image forming apparatus according to the first aspect , wherein the environmental condition detection unit receives an input from a user and sets the type of the recording paper that differs according to the paper thickness. A paper setting unit, wherein the pitch control unit determines the sub-scanning direction pitch according to the paper thickness of the recording paper set by the paper setting unit, and causes the pitch variable mechanism to determine the determined sub-scanning direction. The sub-scanning direction pitch between the plurality of light emitting units is varied by the pitch.

According to the fourth invention, the pitch control unit determines the sub-scanning direction pitch according to the thickness of the recording paper set by the paper setting unit, and the pitch variable mechanism determines the determined sub-scanning direction. Since the pitch in the sub-scanning direction between the plurality of light emitting units is varied by the pitch, it is possible to correct the same magnification deviation in the sub-scanning direction in a so-called multi-beam machine.

  This is because, in the transfer nip portion of the transfer portion where the toner image is transferred to the recording paper, the transfer member (intermediate transfer) on which the toner image is formed according to the increase in the paper thickness of the recording paper conveyed. When the amount of pressing of the recording paper on the belt or the like increases and the transfer member is deformed and the toner image contracts, the sub-scanning direction pitch between the plurality of light emitting units is varied according to the contraction. This is because it is possible to correct an equal magnification shift in the sub-scanning direction.

An image forming apparatus according to a fifth aspect is the image forming apparatus according to the first aspect , wherein the image forming apparatus has a double-sided printing function, and the environmental condition detection unit receives an input from a user and performs heat fixing. A sheet setting unit for setting the type of the recording sheet having different shrinkage rates at the time, and the pitch control unit is configured to perform the image forming process on the back surface of the recording sheet having the heat fixing on the front surface. The sub-scanning direction pitch is determined according to the shrinkage rate of the recording paper set by the setting unit, and the pitch variable mechanism is configured to determine the pitch in the sub-scanning direction between the light emitting units at the determined sub-scanning direction pitch. Is variable.

According to the fifth invention, when the image forming process is performed on the back surface of the recording paper whose front surface is heat-fixed, the pitch control unit is configured to reduce the shrinkage rate of the recording paper set by the paper setting unit. The sub-scanning direction pitch is determined in accordance with the sub-scanning direction pitch, and the pitch variable mechanism varies the sub-scanning direction pitch between the plurality of light emitting units at the determined sub-scanning direction pitch. It is possible to correct a direction equality deviation in a so-called multi-beam machine.

  This is because during double-sided printing, the recording paper is dehumidified and shrunk by heating due to heat fixing after surface printing, and when the image is formed on the back side of the recording paper in a contracted state, the recording paper The image formed on the back side also expands when it absorbs moisture and expands to the original size, and the image on the front and back of the recording paper is shifted by the same magnification. When the image forming process is performed on the back surface of the recording medium, it is possible to vary the pitch in the sub-scanning direction between the plurality of light emitting units according to the shrinkage rate at the time of the thermal fixing, which varies depending on the type of recording paper, and thus double-sided printing. This is because it is possible to correct the same-size shift in the sub-scanning direction that occurs in the images on the front and back of the recording paper.

  According to the present invention, in the multi-beam image forming apparatus, it is possible to correct the same magnification deviation in the sub-scanning direction caused by a change in environmental conditions in the apparatus.

1 is a front sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a cross-sectional structure of an intermediate transfer belt provided in the image forming apparatus illustrated in FIG. 1. It is a figure which shows the laser beam scanning by the exposure apparatus with which the image forming apparatus shown in FIG. 1 is provided. It is an external view of the laser beam light source (light emission part) with which the exposure apparatus shown in FIG. 3 is provided. FIG. 2 is a functional block diagram illustrating an electrical configuration of the image forming apparatus illustrated in FIG. 1. FIG. 6 is a diagram schematically illustrating a state in which an intermediate transfer belt expands and contracts in a portion where secondary transfer is performed. 5 is a flowchart showing control in which a pitch control unit determines the number of drive pulses of a stepping motor and rotates the laser beam light source to vary the beam pitch in the sub-scanning direction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front sectional view for explaining the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a so-called tandem type color copier, and includes an apparatus main body 10 and an original reading unit 16 that reads an original image provided on the upper part of the apparatus main body 10.

  In the apparatus main body 10, an image forming unit 12 that forms an image based on image information of a document read by the document reading unit 16, and heat fixing to an image formed by the image forming unit 12 and transferred to the recording paper P. A fixing device 13 for performing the above and a sheet storage unit 14 for storing a transfer sheet are provided. The paper transport unit 11 transports the paper to each unit in the apparatus main body 10.

  As shown in FIG. 1, the document reading unit 16 is disposed so as to face the document retainer 161 via a contact glass 163 in the upper housing of the apparatus main body 10 and a document retainer 161 provided on the upper surface of the apparatus main body 10 so as to be opened and closed. The optical system unit 162 is provided. The contact glass 163 is dimensioned to a planar shape slightly smaller than the document presser 161 in order to read the document surface of the placed document. The document presser 161 opens and closes by rotating forward and backward about a predetermined axis provided on one side of the upper surface of the housing, which is one component of the document reading unit 16.

  The optical system unit 162 includes a light source (not shown), a plurality of mirrors, a lens unit, a CCD (charge coupled device), and the like. The light from the light source is reflected by the original surface, and the reflected light is input to the CCD as original information through the mirror and the lens unit. Document information as an analog amount input to the CCD is converted into a digital signal and stored in a predetermined storage device.

  The paper transport unit 11 includes a paper transport path 111, a pickup roller 112, a transport roller pair 113, a paper discharge transport path 114, and a paper reverse transport path 116.

  The paper transport path 111 and the paper discharge transport path 114 are paths through which the recording paper P is transported. The paper reverse feeding path 116 is a path through which the recording paper P that has been printed on one side is switched back and turned upside down and conveyed again to the image forming unit 12 when double-sided printing is performed on the recording paper P. The conveyance roller pair 113 is a roller pair provided at an appropriate position of the paper conveyance path 111, the paper discharge conveyance path 114, and the paper reverse conveyance path 116. The recording paper P is transported through the paper transport path 111, the paper discharge transport path 114, and the paper reverse transport path 116 by driving the transport roller pair 113.

  The pickup roller 112 is a roller for feeding the recording paper P one by one from the paper bundle stored in the paper tray 141. The recording paper P fed out from the paper tray 141 is conveyed to the image forming unit 12 by driving the conveyance roller pair 113.

  The image forming unit 12 forms a toner image on the paper fed from the paper storage unit 14, and in this embodiment, the image forming unit 12 is sequentially arranged from the upstream side (left side of the paper surface in FIG. 1) to the downstream side. The magenta unit 12M, the cyan unit 12C, the yellow unit 12Y, the black unit 12K, and the transfer device 125 are provided.

  Each unit 12M, 12C, 12Y, 12K includes a photosensitive drum 121 (photosensitive member), a developing device 122, a charging device 123, and an exposure device 124, respectively. Each photosensitive drum 121 receives supply of toner from a corresponding developing device 122 while rotating counterclockwise in FIG. Each developing device 122 is supplied with toner from a toner container (not shown).

  The charging device 123 is provided at a position directly above each photosensitive drum 121. The exposure device 124 is provided for each unit above the charging device 123 and the developing device 122. Each photosensitive drum 121 is charged uniformly by the charging device 123. Then, each photoconductor is irradiated with laser beam light corresponding to each color based on the image data input from the document reading section 16 from each exposure device 124 to the circumferential surface of each photoconductor drum 121 after charging. An electrostatic latent image is formed on each peripheral surface of the drum 121. Details of the exposure apparatus 124 will be described later.

  By supplying each color toner from the developing device 122 to the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive drum 121.

  A transfer device 125 is provided below the photosensitive drum 121. The transfer device 125 includes a driving roller 125a, a driven roller 125b, a secondary transfer counter roller 125c, a secondary transfer roller 125d, and an intermediate transfer belt 125e.

  The intermediate transfer belt 125e is stretched between the driving roller 125a, the driven roller 125b, the secondary transfer counter roller 125c, and other necessary rollers, and is provided so as to contact the peripheral surface of each photosensitive drum 121. Yes. The intermediate transfer belt 125e is driven by a driving roller 125a while being synchronized with each photosensitive drum 121 while being pressed against the circumferential surface of the photosensitive drum 121 by a primary transfer roller 126 provided corresponding to each photosensitive drum 121. Circulate between the rollers 125b.

  As the intermediate transfer belt 125e circulates, primary transfer of the magenta toner image is performed on the surface of the intermediate transfer belt 125e by the photosensitive drum 121 of the magenta unit 12M. The primary transfer of the cyan toner image by the body drum 121 is performed, then the primary transfer of the yellow toner image by the photosensitive drum 121 of the yellow unit 12Y is performed at the same position on the intermediate transfer belt 125e, and the last black unit. The primary transfer of the black toner image is performed by the 12K photoconductor drum 121, whereby a color toner image is formed on the surface of the intermediate transfer belt 125e.

  FIG. 2 is a diagram showing a cross-sectional structure of the intermediate transfer belt 125e. In FIG. 2, a portion where the intermediate transfer belt 125e is stretched around the secondary transfer counter roller 125c is shown in an enlarged manner. In this embodiment, the intermediate transfer belt 125e includes a base layer 125e1 formed on the inner peripheral side by a resin material such as polyvinylidene fluoride (PVDF), and an elastic layer 125e2 formed on the outer peripheral side by, for example, chloroprene rubber or urethane rubber. And are laminated. By providing the elastic layer 125e2 on the intermediate transfer belt 125e, the followability of the intermediate transfer belt 125e to the recording paper P is improved. Therefore, the transferability of the color image onto the recording paper P is increased, and the secondary transfer onto the recording paper P is performed. The image quality of the transferred color image can be improved.

  Referring to FIG. 1 again, the secondary transfer roller 125d is provided in contact with the surface of the intermediate transfer belt 125e at a position facing the secondary transfer counter roller 125c in the paper transport path 111. The color toner image formed on the surface of the intermediate transfer belt 125e is recorded on the recording paper P conveyed from the paper storage unit 14 at the nip N between the secondary transfer roller 125d and the secondary transfer counter roller 125c. Is transcribed.

  A cleaning device 127 that removes residual toner on the peripheral surface of the photosensitive drum 121 and cleans it is provided at the right side of each photosensitive drum 121 in FIG. The cleaning device 127 cleans the peripheral surface of the photosensitive drum 121, and the peripheral surface after cleaning is directed to the charging device 123 for a new charging process.

  Waste toner removed from the peripheral surface of the photosensitive drum 121 by the cleaning device 127 is collected in a toner collection bottle (not shown) through a predetermined path.

  A paper transport path 111 is formed from the right position of the paper storage unit 14 to the lower part of the image forming unit 12. The recording paper P fed out from the paper storage unit 14 is conveyed toward the lower position of the intermediate transfer belt 125e by driving the conveyance roller pair 113. The recording paper P being conveyed through the paper conveyance path 111 is pressed and sandwiched between the secondary transfer opposing roller 125c and the secondary transfer roller 125d at the nip portion N, whereby the toner image on the intermediate transfer belt 125e is transferred to the recording paper P. Is transcribed.

  The fixing device 13 thermally fixes the toner image on the paper transferred by the image forming unit 12. The fixing device 13 includes a heating roller 131 provided with an energization heating element such as a halogen lamp as a heating source therein, a fixing roller 132 disposed so as to face the heating roller 131, and a tension roller 132 and a heating roller 131. The fixing belt 133 and the pressure roller 134 disposed to face the fixing roller 132 through the fixing belt 133 are provided. The recording paper P after the transfer process is pressed and nipped while being heated at the nip portion between the fixing belt 133 and the pressure roller 134, whereby the toner image on the recording paper P is thermally fixed, A stable color image is formed.

  The recording sheet P with a color image that has been heat-fixed is discharged toward a discharge tray 115 provided on the left side wall of the apparatus main body 10 through a discharge conveyance path 114 extended from the upper part of the fixing device 13. Will be.

  The paper storage unit 14 has a paper tray 141 for storing a bundle of recording papers P that are detachably attached to the lower part of the apparatus main body 10. In the example shown in FIG. 1, the paper tray 141 is provided in two stages. However, the number of stages may be three or more, or may be one.

  The recording paper P is fed out one sheet at a time by driving the pickup roller 112 from the sheet bundle stored in the sheet tray 141. The fed recording paper P is fed toward the nip portion N of the image forming unit 12 through the paper conveyance path 111, and the color toner image formed on the surface of the intermediate transfer belt 125e is transferred. The movement of the recording paper P after the transfer process is as described above.

  FIG. 3 is a diagram showing laser beam scanning by the exposure device 124. FIG. 4 is an external view of the laser beam light source 49 provided in the exposure apparatus 124. The exposure device 124 includes a laser beam light source 49 and a polygon mirror 41. The exposure apparatus 124 further includes optical members such as a collimator lens, a cylindrical lens, and an fθ lens. In order to make the scanning directions of the laser beam beams LB-1 to LB-4 easier to understand, in FIG. The illustration of the optical member is omitted.

  The laser beam light source 49 is formed by unitizing four laser diodes (LD) 49-1 to LD49-4 (light emitting units) arranged in a line at a constant interval on the front end surface F, for example, a monolithic multi-laser diode. It is comprised using. In the present embodiment, a monolithic multi-laser diode having four LDs will be described as an example. However, any monolithic multi-laser diode in which two or more LDs are arranged on the same chip may be used.

  In the laser beam light source 49, the four laser beam lights LB-1 to LB-4 emitted from the LD 49-1 to LD 49-4 are bent and reflected by the polygon mirror 41 to irradiate the surface of the photosensitive drum 121. In addition, the arrangement direction of the irradiation positions (imaging positions) has an inclination angle with respect to each of the main scanning direction (the length direction of the photosensitive drum 121) and the sub-scanning direction (the rotation direction of the photosensitive drum 121). Arranged in a state. With this arrangement, the drawing operation on the plurality of scanning lines SL can be performed by one scan.

  Further, the laser beam light source 49 is configured to be rotatable in the direction of the arrow by using a stepping motor 45 (pitch variable mechanism) with a normal line G passing through the center O of the front end surface F as a rotation axis. ing. As a result, the laser beam light source 49 can adjust the tilt angle, and is configured to be able to adjust the beam pitch in the sub-scanning direction of the LD 49-1 to LD 49-4. That is, the beam pitch control unit 312 described later causes the stepping motor 45 to rotate the laser beam light source 49 in the clockwise direction in FIG. 4 to reduce the beam pitch in the sub-scanning direction. 49 is rotated counterclockwise in FIG. 4 to increase the beam pitch in the sub-scanning direction.

  The polygon mirror 41 is rotated in the rotation direction R about the rotation shaft 53 by the polygon motor 51. The polygon mirror 41 has a reflecting surface 43 made up of, for example, six mirror surfaces 43-1 to 43-6. The four laser beam lights LB-1 to LB-4 emitted from the LD49-1 to LD49-4 are irradiated on the same mirror surface (mirror surface 43-2 in FIG. 2) of the reflection surface 43, and the mirror surface (FIG. 2). Then, the light is refracted and reflected in the direction of the photosensitive drum 121 by the mirror surface 43-2), and is scanned along the four scanning lines SL on the photosensitive drum 121 as the polygon mirror 41 rotates. That is, the four laser beam lights LB-1 to LB-4 are laser beam lights LB-1, LB-2, LB-3 in the sub-scanning direction D1 (corresponding to the rotation direction of the photosensitive drum 121 in FIG. 2). Four scanning lines SL are drawn in the main scanning direction D2 arranged in the order of LB-4. As a result, an electrostatic latent image corresponding to the image data of each color is formed on each photosensitive drum 121.

  FIG. 5 is a functional block diagram showing an electrical configuration of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 31, a paper transport unit 11, an image forming unit 12, a fixing device 13, a document reading unit 16, an input operation unit 32, an image memory 33, an image processing unit 34, a network I / F unit 36, And it is comprised including the temperature sensor 70 (temperature detection part). Since description has been made with reference to FIG. 1, descriptions of the paper transport unit 11, the image forming unit 12, the fixing device 13, and the document reading unit 16 are omitted below.

  The image memory 33 temporarily stores image data output from the document reading unit 16 and image data transmitted from an external device via the network I / F unit 36. The image processing unit 34 performs image processing such as image correction and enlargement / reduction on the image data stored in the image memory 33.

  The input operation unit 32 displays various operation commands such as a display panel on which the user can visually recognize an operation screen and various messages, a power key, a numeric keypad for inputting the number of copies, a start button for instructing reading start of a document, and the like. An operation button for inputting is provided. The input operation unit 32 receives the input of the operation command by the user, so that the type of the recording paper P such as plain paper or thick paper having different paper thickness and shrinkage rate at the time of thermal fixing, the number of prints, execution of double-sided printing, etc. Set. The input operation unit 32 functions as a paper setting unit by setting the type of the recording paper P. When the user sets the type of recording paper P, the number of copies to be printed, execution of double-sided printing, etc. on the computer connected via the network I / F unit 36, the computer functions as the sheet setting unit. Will do.

  The network I / F unit 36 includes a communication module such as a LAN (Local Area Network) board, and transmits / receives various data to / from an external device. The temperature sensor 70 is a contact-type or non-contact-type temperature sensor provided in the vicinity of the nip portion N, for example, and detects the temperature of the intermediate transfer belt 125e.

  The control unit 31 includes a storage unit 313 having a RAM (Random Access Memory) and a ROM (Read Only Memory), a CPU (Central Processing Unit), and the like. Furthermore, the control unit 31 includes an overall control unit 311 and a pitch control unit 312.

  The overall control unit 311 reads and processes the program stored in the storage unit 313 according to an instruction signal or the like input from a computer (not shown) connected via the input operation unit 32 or the network I / F unit 36. Is executed, and the image forming apparatus 1 is comprehensively controlled by outputting instruction signals to each functional unit, transferring data, and the like.

  The pitch control unit 312 performs LD 49-1 to LD 49-1 according to the temperature of the intermediate transfer belt 125e detected by the temperature sensor 70 and the paper thickness corresponding to the type of the recording paper P set by the input operation unit 32 during single-sided printing. The beam pitch in the sub-scanning direction of the LD 49-4 is determined. Further, the pitch control unit 312 determines the beam pitch in the sub-scanning direction of the LDs 49-1 to LD 49-4 according to the type of the recording paper P set by the input operation unit 32 during double-sided printing. The pitch control unit 312 outputs the number of drive pulses corresponding to the determined beam pitch to the stepping motor 45 provided in the exposure apparatus, rotates the laser beam light source 49 around the rotation axis G, and outputs LD49-1 to LD49-4. The beam pitch in the sub-scanning direction of the laser beam lights LB-1 to LB-4 irradiated by is set as the determined beam pitch.

FIG. 6 is a diagram schematically illustrating a state in which the intermediate transfer belt 125e is expanded and contracted in a portion where the secondary transfer is performed on the outer peripheral surface of the intermediate transfer belt 125e. The outer peripheral surface at the portion where the secondary transfer is performed for the intermediate transfer belt 125e of FIG. 5 indicated by M _v1 and M _v2, the toner image is extended in a portion that is convex to the outer peripheral direction shown in M _v1, the M _v2 The toner image contracts at a portion convex in the inner circumferential direction shown. When the boundary between the base layer 125e1 and the elastic layer 125e2 of the intermediate transfer belt 125e is a speed determining surface,
D ₁ : Roller outer diameter (mm) of the drive roller 125a
D ₂ : roller outer diameter (mm) of the secondary transfer roller 126d
L _T1 : thickness of base layer 125e1 (mm)
L _T2 : thickness of elastic layer 125e2 (mm)
θ ₁ : An angle (radian) formed by both ends of M _v1 and the center of the secondary transfer counter roller 125c.
θ ₂ : An angle (radian) formed by both ends of M _v2 and the center of the secondary transfer roller 125d
, The lengths of M _v1 and M _v2 with respect to the rotation direction of the intermediate transfer belt can be expressed by the following equations, respectively.
M _v1 = π × (D ₁ +2 (L _T1 + L _T2 )) × θ ₁ (mm) (1)
M _v2 = π × D ₂ × θ ₂ (mm) (2)

Here, when the secondary transfer magnification is M ₂ and M _v1 : M _v2 = 1: 1 and M ₂ = K, M ₂ : K = M _v1 : M _v2 is obtained, and therefore M ₂ is _expressed by the following equation. Can be represented.
M ₂ = K ₁ × (M _v1 / M _v2 ) (3)
K ₁ : Coefficient calculated in advance by experiment When M ₁ is the primary transfer magnification, M ₂ × M ₁ = 1 when the equality of the toner image transferred to the recording paper P is 1, M ₁ can be expressed by the following equation.
M ₁ = M _v2 / (M _v1 × K ₁ ) (4)

Therefore, the beam pitch P _Sd in the sub-scanning direction of the laser beam beams LB-1 to LB-4 in the scanning line SL can be expressed by the following equation where the distance between one dot in the sub-scanning direction is L _d .
P _Sd = L _d × M ₁ = L _d × (M _v2 / (M _v1 × K ₁ )) (5)

Furthermore, the beam pitch P _SLD in the sub-scanning direction between the laser beams LB-1 to LB-4 from the LD 49-1 to 49-4 to the reflecting surface 43 of the polygon mirror 41 is the sub-scanning direction in the scanning line SL. of the beam pitch P _Sd, since it is multiplied by a predetermined factor K ₁ determined by the optical member in which the exposure apparatus 124 is equipped,
P _SLD = K ₂ × P _Sd = K ₂ × L _d × (M _v2 / (M _v2 × K ₁ )) (6)
It can be expressed as. That is, the beam pitch P _SLD is determined according to L _T1 , L _T2 , θ ₁ , θ determined according to the internal temperature of the image forming apparatus 1 and the type and thickness of the recording paper P from the equations (1), (2), and (6). _The value obtained as a function of ₂ .

By the way, when the temperature of the intermediate transfer belt 125e rises, the intermediate transfer belt 125e expands, so that the toner image formed on the outer peripheral surface of the intermediate transfer belt 125e expands. That is, the secondary transfer magnification M ₂ is increased. Conversely, when the temperature of the intermediate transfer belt 125e decreases, the intermediate transfer belt 125e contracts, so that the toner image contracts. That reduces the secondary transfer magnification M _2.

  For example, rubber such as chloroprene rubber and urethane rubber has a larger thermal expansion coefficient than a resin material such as PVDF. Therefore, when the elastic layer 125e2 is formed on the outer peripheral side of the intermediate transfer belt 125e by using, for example, chloroprene rubber or urethane rubber, as in the present embodiment, for example, compared to the case where the intermediate transfer belt 125e is configured by only a resin material such as PVDF. An equal magnification shift is likely to occur.

  Therefore, in this embodiment, the pitch controller 312 reads the temperature of the intermediate transfer belt 125e detected by the temperature sensor 70 at a predetermined sampling interval, and the amount of change in the temperature T of the intermediate transfer belt 125e detected by the temperature sensor 70. A drive pulse number DP1 corresponding to ΔT is output, the laser beam light source 49 is rotated by a rotation amount proportional to the drive pulse number DP1, and the same magnification in the sub-scanning direction that occurs as the temperature T of the intermediate transfer belt 125e increases or decreases. Correct the deviation.

That is, when the change amount ΔT is a positive value, the pitch control unit 312 increases the secondary transfer magnification M ₂ , so that the change amount ΔT at this time is set to decrease the primary transfer magnification M _1. The corresponding drive pulse number DP1 is output to the stepping motor 45, and the laser beam light source 49 is rotated in the clockwise direction in FIG. 4 to reduce the beam pitch _PSLD . On the contrary, when the change amount ΔT is a negative value, the drive pulse number DP1 corresponding to the change amount ΔT at this time is output to the stepping motor 45, and the laser beam light source 49 is rotated counterclockwise in FIG. Thus, the beam pitch _PSLD is increased. That is, the driving pulse number DP1 takes both positive and negative values, and the stepping motor 45 can output driving force in both the clockwise and counterclockwise directions.

In the present embodiment, a drive pulse number DP1 of the stepping motor 45, the and the beam pitch P _SLD, as the intermediate transfer belt 125e table associated with the variation ΔT of the temperature T of the advance in the storage unit 313 The pitch control unit 312 stores the drive pulse number DP1 corresponding to the change amount ΔT from the table.

Further, when the paper thickness increases according to the recording paper P conveyed to the nip portion N, the intermediate transfer belt 125e is pressed further in the inner circumferential direction at the nip portion N by the recording paper P. That is, θ ₂ increases and the secondary transfer magnification M ₂ decreases.

Therefore, in this embodiment, the pitch control unit 312 sets the paper thickness of the plain paper as the reference paper thickness Th, and the respective paper thicknesses of the reference paper thickness Th and the respective paper thicknesses Th1, Th2,... The drive pulse number DP2 corresponding to the difference d1, d2,... Is determined and output, and the laser beam light source 49 is rotated from the previous position by a rotation angle corresponding to the drive pulse number DP2, and the thickness of the recording paper is determined. The same magnification deviation in the sub-scanning direction that occurs with the increase / decrease is corrected. That is, the pitch controller 312 increases or decreases the value of the beam pitch _PSLD according to the amount of change in the thickness of the recording paper used for image formation with respect to the reference paper thickness Th of the plain paper, and performs secondary transfer. adjusting the magnification _{M 2.} In the present embodiment, a table in which the paper thickness difference d1, d2,... And the drive pulse number DP2 corresponding to the paper thickness difference d1, d2,. The pitch controller 312 reads out the number of drive pulses DP2 corresponding to the paper thickness differences d1, d2,... From the table. When the paper thickness difference d1, d2,... Relative to the reference paper thickness Th is less than 0, a negative drive pulse is set.

  Further, at the time of double-sided printing, the recording paper P is dehumidified and contracted by heating by heat fixing after the front surface printing, and an image is formed on the back surface of the recording paper P in a contracted state. When the image is stretched to the size of the recording paper P, the image formed on the back surface is also stretched, and the images on the front and back sides of the recording paper P are shifted by the same magnification.

Therefore, in the present embodiment, the pitch control unit 312 determines and outputs the drive pulse number DP3 corresponding to the shrinkage rate ΔSh at the time of thermal fixing, which differs depending on the type of the recording paper P set in the input operation unit 32, The laser beam light source 49 is rotated from the previous position by the amount of rotation corresponding to the number of drive pulses DP3, and the same magnification deviation in the sub-scanning direction that occurs with double-sided printing is corrected. That is, the pitch control unit 312, in response to said different shrinkage ΔSh according to the type of the recording paper P, the reduces the value of the beam pitch P _SLD adjusting the secondary transfer magnification M _2. A table in which the shrinkage rate ΔSh obtained in advance for each type of recording paper P and the number of drive pulses DP3 corresponding to the shrinkage rate ΔSh are stored in the storage unit 313 in advance. The pitch control unit 312 reads the number of drive pulses DP3 corresponding to the shrinkage rate ΔSh of the recording paper P set in the input operation unit 32 from the table.

  In this embodiment, the pitch control unit 312 outputs a drive pulse number (DP1 + DP2) obtained by adding the drive pulse number DP2 to the drive pulse number DP1 to the stepping motor 45 at the time of single-sided printing and double-sided printing. The laser beam light source 49 is rotated, and at the time of reverse side printing of double-sided printing, the drive pulse number DP3 is output to the stepping motor 45 to rotate the laser beam light source 49.

FIG. 7 is a flowchart showing control in which the pitch control unit 312 determines the number of drive pulses of the stepping motor 45 and causes the stepping motor 45 to rotate the laser beam light source 49 to vary the beam pitch P _SLD .

  When the image forming operation by the image forming unit 12 is started, the pitch control unit 312 reads the temperature T of the intermediate transfer belt 125e detected by the temperature sensor 70 at a predetermined sampling interval (step S1), and the intermediate in the sampling interval. A change amount ΔT of the temperature T of the transfer belt 125e is calculated (step S2). Subsequently, the pitch control unit 312 reads the number of drive pulses DP1 corresponding to the change amount ΔT from the table stored in the storage unit 313 (step S3).

  When the recording paper P set in the input operation unit 35 is plain paper (YES in step S4), the pitch control unit 312 reads out the change in the paper thickness with respect to the reference paper thickness Th of the plain paper. The drive pulse number DP1 is output to the stepping motor 45 (step S5). On the other hand, when the recording paper P set in the input operation unit 35 is not plain paper (NO in step S4), the pitch control unit 312 stores the drive pulse number DP2 corresponding to the type of the recording paper P in the storage unit 313. Reading from the stored table (step S6), the number of drive pulses obtained by adding DP2 to DP1 (DP1 + DP2) is output to the stepping motor 45 (step S7). As a result, the laser beam light source 49 rotates at a rotation angle proportional to the number of drive pulses (DP1 + DP2), and the thickness of the recording paper P varies depending on the increase / decrease of the temperature T of the intermediate transfer belt 125e and the type of the recording paper P. The accompanying same magnification deviation in the sub-scanning direction is corrected.

  Furthermore, when double-sided printing is set in the input operation unit 32 and printing on the back side is performed (YES in step S8), the pitch control unit 312 determines the number of drive pulses corresponding to the type of the recording paper P. DP3 is read from the table stored in the storage unit 313 (step S9), and the drive pulse number DP3 is output to the stepping motor 45 (step S10). As a result, the laser beam light source 49 rotates at a rotation angle proportional to the number of drive pulses DP3, and the same magnification deviation in the sub-scanning direction that occurs as the recording paper P contracts during thermal fixing is corrected.

  Note that either the amount of change ΔT of the temperature T of the intermediate transfer belt 125e detected by the temperature sensor 70, the type of the recording paper P set in the input operation unit 32, or the type of the recording paper P at the time of reverse side printing in double-sided printing. It is also possible for the pitch control unit 312 to determine the number of drive pulses to be output for only one of them.

  According to the image forming apparatus 1 according to the above-described embodiment described above, it is possible to correct the same magnification deviation in the sub-scanning direction in the multi-beam image forming apparatus.

  The image forming apparatus 1 according to the embodiment of the present invention has been described above. However, the embodiment is merely an example, and the present invention is not limited to the embodiment, and various modifications can be made without departing from the spirit thereof. Modifications, improvements, and the like are possible, and for example, the following modified embodiments can be taken.

  (1) A rubber such as chloroprene rubber or urethane rubber used for the elastic layer 125e2 has less influence than expansion and contraction due to temperature change, but expands due to moisture absorption. Therefore, a humidity sensor is provided inside the image forming apparatus 1, and the humidity sensor Depending on the detected humidity, the pitch controller 312 may change the position of the secondary transfer roller 126d to control the amount of pressure applied to the intermediate transfer belt 125e.

(2) In the above embodiment, the sub-scan by varying the sub-scanning direction of the beam pitch _{P SLD} between the laser beam source 49 LD49-1～49-4 by rotating the to the reflecting surface 43 of the polygon mirror 41 Although the same degree of magnification deviation is corrected, the position of the optical member such as a cylindrical lens provided in the exposure device 124 is changed to change the distance between the LD 49-1 to 49-4 and the reflecting surface 43 of the polygon mirror 41. beam pitch P _SLD in the sub-scanning direction in the left fixed, by varying the sub-scanning direction of the beam pitch P _Sd in the scan line SL, it is also possible to correct the magnification misregistration in the sub-scanning direction.

P recording paper 1 image forming apparatus 12 image forming unit 121 photoconductor drum (photoconductor)
122 Developing Device 123 Charging Device 124 Exposure Device 45 Stepping Motor (Pitch Variable Mechanism)
49 Laser beam light source 49-1 to 49-4 Laser diode (light emitting part)
125 transfer device 125a driving roller 125b driven roller 125c secondary transfer counter roller 125d secondary transfer roller 125e intermediate transfer belt 31 control unit 312 pitch control unit 32 input operation unit (paper setting unit, environmental condition detection unit)
70 Temperature sensor (temperature detector, environmental condition detector)

Claims (2)

A photoreceptor,
A charging device for charging the photoreceptor;
A light source including a plurality of light emitting units that emit light according to image data, and a stepping motor that rotates the light source to vary the pitch in the sub-scanning direction between the plurality of light emitting units, and is charged. An exposure apparatus that forms an electrostatic latent image by scanning light emitted from the plurality of light emitting units on the photoconductor;
A developing device that visualizes the electrostatic latent image formed on the photoconductor with toner and forms a toner image on the photoconductor;
A plurality of endless drivable in tension between the rollers in the sub scanning direction, the photosensitive member the toner image formed on the an intermediate transfer belt which is primarily transferred to the outer peripheral surface, the primary transfer on the intermediate transfer belt a transfer device that secondarily transfers the recording sheet the toner image,
A temperature detector for detecting the temperature of the intermediate transfer belt;
A first paper setting unit that accepts input from a user and sets the type of the recording paper that differs according to the paper thickness;
In order to increase or decrease the pitch in the sub-scanning direction according to the amount of change in temperature detected by the temperature detector, the amount of change and the number of drive pulses of the stepping motor are stored in advance in association with each other. 1 storage unit;
In order to increase or decrease the pitch in the sub-scanning direction according to the amount of change of the recording paper thickness with respect to the reference paper thickness, the paper thickness difference between the reference paper thickness and the paper thickness according to the type of the recording paper, A second storage unit that stores the number of drive pulses of the stepping motor in association with each other;
The number of drive pulses corresponding to the amount of change in temperature detected by the temperature detection unit is read from the first storage unit, and the paper thickness of the type of recording paper set by the first paper setting unit and the reference The number of drive pulses corresponding to the paper thickness difference from the paper thickness is read from the second storage unit, and the drive pulse number read from the second storage unit is added to the drive pulse number read from the first storage unit. A pitch control unit that outputs the added drive pulse number to the stepping motor to rotate the light source , and
The transfer device includes a secondary transfer counter roller, a secondary transfer roller provided in contact with the surface of the intermediate transfer belt at a position facing the secondary transfer counter roller, and the toner image is transferred to the recording paper. A nip portion between the secondary transfer roller and the secondary transfer counter roller, which is secondarily transferred to
The intermediate transfer belt is convex in the outer peripheral direction of the intermediate transfer belt at the nip portion, so that the first portion where the toner image extends and the inner peripheral direction of the intermediate transfer belt are convex. A second portion where the toner image contracts,
When the paper thickness of the recording paper increases, the intermediate transfer belt is pressed by the recording paper at the nip portion in the inner circumferential direction of the intermediate transfer belt, so that both ends of the second portion and the second portion are The angle formed by the center of the next transfer roller is increased, and the secondary transfer magnification is decreased.
The second storage unit is configured to increase the sub-scanning direction pitch in order to cope with a case where the secondary transfer magnification decreases as the paper thickness of the recording paper increases. An image forming apparatus in which the number of pulses is stored . The image forming apparatus has a double-sided printing function,
The image forming apparatus includes:
A second paper setting unit that receives the input from the user and sets the type of the recording paper that has a different shrinkage rate during thermal fixing;
A third storage unit that stores in advance the shrinkage rate obtained in advance for each type of the recording paper and the number of drive pulses corresponding to the shrinkage rate;
The pitch control unit corresponds to the shrinkage rate of the type of the recording paper set by the second paper setting unit when the image forming process is performed on the back surface of the recording paper having the heat fixing on the front surface. The image forming apparatus according to claim 1, wherein the number of drive pulses to be read is read from the third storage unit, the number of drive pulses read from the third storage unit is output to the stepping motor, and the light source is rotated.

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