JP2006184571A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent color misalignment of a color print transferred to paper by a plurality of photoreceptor drums even in case where gears have an error in mesh. <P>SOLUTION: A drum drive mechanism 20 for rotating the photoreceptor drums 121 comprises: drum gears 50 (yellow drum gear 51, magenta drum gear 52, cyan drum gear 53 and black drum gear 54) of the identical shape, which are concentric with the corresponding photoreceptor drums 121 and integrally attached; and relay gears 40 (first and second relay gears 41 and 42) engaged with the adjacent corresponding drum gears 51 to 54 and rotated by the drive of a drive motor 30. The drum gears 51 to 54 are fitted such that specific reference teeth T1 of the identical shape mesh with the corresponding teeth of the first and second relay gears 41 and 42, which have the identical shape, in accordance with the rotation of the first and second relay gears 41 and 42. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and various printers, and relates to an improvement of a drum driving mechanism that transmits a driving force to a plurality of photosensitive drums arranged in parallel. It is.

  Usually, the image forming apparatus irradiates the peripheral surface of the photosensitive drum rotating about the axis from the exposure apparatus based on the input image information, and thereby electrostatic latent images formed on the peripheral surface. The toner is supplied to the image from the developing device to form a toner image, and the toner image is transferred to the paper conveyed from the paper storage unit. The toner image transferred to the sheet is discharged to the outside after being subjected to a fixing process by a heat treatment in a fixing device.

  Among such image forming apparatuses, there is an apparatus for color printing called a so-called tandem system in which a plurality (usually four) photosensitive drums are employed. In this tandem type image forming apparatus, for example, four photosensitive drums are arranged in parallel along the sheet conveyance direction, and each circumferential surface is sequentially arranged from the upstream side with respect to one sheet being conveyed. The yellow, magenta, cyan and black toners formed on the toner are transferred.

  Each photosensitive drum is sequentially rotated from the upstream side in synchronism with the paper conveyance speed, and the rotational phase is shifted, so that the photosensitive drum on the upstream side of the paper being conveyed is at the same position as the transfer position. A transfer process using a downstream photosensitive drum is performed. Therefore, when the paper passes through the last photosensitive drum, the yellow, magenta, cyan and black toners are transferred to the same position on the paper, and color printing is performed on the paper.

  Therefore, in such a tandem type image forming apparatus, synchronous rotation in which the rotation phases of a plurality of photosensitive drums are shifted plays an important role. Conventionally, each of the photosensitive drums is provided with a dedicated drive motor, and each drive motor is controlled to rotate synchronously. However, if four expensive drive motors are used, the cost of parts increases. Alternatively, there is a disadvantage that the space is taken up by the four drive motors, thereby hindering the downsizing of the image forming apparatus.

  In order to eliminate this inconvenience, in recent years, the driving force of one driving motor has been transmitted to a plurality of photosensitive drums via a gear mechanism. Incidentally, when the driving force of the driving motor is transmitted to a plurality of photosensitive drums via a gear mechanism, the meshing error of each gear becomes a problem. That is, the gear is usually manufactured using a precisely machined mold, but the recesses corresponding to all the teeth of the mold itself are not necessarily in exactly the same shape. All of the gears mass-produced using such molds have the same shape as a whole, but when looking at one gear, the shape of each tooth is slight but different. Therefore, when these gears are meshed with each other, a so-called meshing error occurs due to a slight difference in tooth shape.

  Accordingly, when such a gear is combined to form a gear mechanism for transmitting the driving force from one drive motor to a plurality of photosensitive drums, each photosensitive drum rotates synchronously with the others, but the gears The transfer position of the downstream photoconductor drum with respect to the paper cannot be accurately matched with the transfer position of the upstream photoconductor drum due to the meshing error due to the slight difference in the shape of each tooth. There is a problem in that so-called color misregistration occurs in which each color is not accurately positioned on the paper after processing.

  As an example of recognizing such a problem, there is known an eccentricity tolerance determining method and a meshing phase regulating method in a gear drive train described in Patent Document 1 (Note that Patent Document 1 employs a plurality of drive sources. The paragraph [0002] describes the disadvantages caused by the above, and the paragraph [0003] describes the problems in transmitting the driving force from a single drive source to each photosensitive drum by meshing a plurality of gears. .)

In this method, when the gear drive train is composed of three or more gears, the rotation error of the output gear due to the eccentricity of the gears constituting the gear drive train can be approximately calculated. (Paragraph [0005]), and based on this calculation result, the maximum rotation error of the output gear can be made to be a predetermined value or less without setting the eccentricity tolerance in the manufacture of the gear smaller than necessary ( In addition to the paragraph [0062]), by restricting the meshing phase of at least a pair of mutually meshing gears so that the rotation error of the output gear is not more than a predetermined value, even if the eccentricity tolerance of each gear is considerably large, It is described that the rotation error can be set to a predetermined value or less (paragraph [0063]).
JP 2000-18370 A

  However, the one described in Patent Document 1 makes it possible to easily calculate a rotation error (meshing error) of the gear caused by the eccentricity when the gear is eccentric, and based on this unavoidable rotation error, By trying not to manufacture gears more precisely than necessary in the manufacturing process, we will try to contribute to the reduction of gear manufacturing costs. Color printing is caused by meshing errors in the completed gears (gears). It doesn't provide any solution for shifting.

  The present invention has been made in view of such a situation, and even if there is a meshing error in a gear, image formation that can prevent color misregistration in color printing transferred to a sheet by a plurality of photosensitive drums. The object is to provide a device.

  According to the first aspect of the present invention, a toner image is formed by toner supplied to an electrostatic latent image formed on a peripheral surface, and a plurality of photosensitive drums that transfer the toner image to a sheet are provided along a sheet conveying direction. In the image forming apparatus in which the photosensitive drums are configured to be synchronously rotatable around the drum axis by the drum driving mechanism, the drum driving mechanism is concentrically and integrally attached to the photosensitive drums. Each of the drum gears having the same shape, and a relay gear that meshes with each of the adjacent drum gears and that is driven and rotated by the drive means, and each drum gear has a reference tooth position on each drum gear. When defined, each reference tooth is assembled so as to mesh with the same tooth of the relay gear according to the rotation of the relay gear.

  According to such a configuration, the position of the reference teeth is determined for each drum gear, and each drum gear is assembled so that the positions of the reference teeth always mesh with the same pigeon of the relay gear. The teeth of the relay gear (referred to as “second tooth”) meshed with (the second tooth) mesh with the upper teeth of other adjacent drum gears by the rotation of the relay gear, whereby one drum gear and the other drum gear. The teeth that the tooth meshes with both are the same instep. Since the relationship between the upper teeth and the second teeth is established for all the teeth of the drum gear and the relay gear, the teeth of the relay gear engaged with one of the teeth of one drum gear are always the same as those of one drum gear in the other drum gear. It meshes with the same tooth with the same meshing error.

  Therefore, each photoconductor drum rotates while its rotational speed slightly fluctuates according to the meshing error between each drum gear and the relay gear, but the tooth of the relay gear meshes with the instep of one drum gear. In this state, the position of the paper (front position) where the peripheral surface (front surface) of one photoconductor drum is in contact, and then the second tooth of the relay gear meshes with the upper surface of another adjacent drum gear. In this state, if the diameter of the photosensitive drum is set so as to come into contact with the outer circumferential surface of another photosensitive drum, even if the rotational speed of the photosensitive drum varies due to a gear meshing error, The upper circumferential surface of all the photoconductive drums comes into contact with the upper position of the sheet being conveyed, thereby reliably preventing the displacement of the transfer surface with respect to the sheet for each photoconductive drum.

  If necessary, even if there is a manufacturing error due to the mold itself in the drum gear, by setting the reference tooth position to a predetermined position tooth in the mold, each drum gear can be connected to the relay gear. The meshing error becomes the same, which can reliably prevent the displacement of the transfer surface relative to the paper for each photosensitive drum.

  FIG. 8 is an explanatory diagram for specifically explaining the operation of the first aspect of the present invention, and FIG. 8A is a not-illustrated photoconductor related to the yellow drum gear 51 in which the paper P is the drum gear on the upstream side. The state immediately before being fed to the drum, (B) is the state in which the paper P is being transferred by the photosensitive drum of the yellow drum gear 51, and (C) is the magenta drum gear in which the paper P is the downstream drum gear. The state (d) immediately before being fed to the photoconductive drum (not shown) 52 is a state where the paper P is being transferred by the photoconductive drum of the magenta drum gear 52.

  As shown in FIG. 8, one relay gear 40 is interposed between the yellow drum gear 51 and the magenta drum gear 52, and this relay gear 40 meshes with both the yellow drum gear 51 and the magenta drum gear 52. Has been. Therefore, when the relay gear 40 is driven and rotated around the axis by driving of a drive motor (not shown), this drive rotation is transmitted to the drum gears 51 and 52, whereby the yellow drum gear 51 and the magenta drum gear 52 are connected. It is designed to rotate synchronously. In FIG. 8, the drum gears 51 and 52 are set to rotate in the clockwise direction, while the relay gear 40 is set to rotate in the counterclockwise direction.

  In FIG. 8, gears are indicated by circles, and each tooth is indicated by a number in the circle. For the yellow drum gear 51 and the magenta drum gear 52, the teeth with the same numerals have exactly the same shape. Further, in FIG. 8, the number of teeth of each drum gear 51 is assumed to be 8 and the number of teeth of the relay gear 40 is assumed to be 4 so that the description can be made easily. According to the first aspect of the present invention, “when each drum gear has a position of the reference tooth for each drum gear, each reference tooth meshes with the same tooth of the relay gear according to the rotation of the relay gear. When the reference teeth of the yellow drum gear 51 and the magenta drum gear 52 are set to, for example, “1” in order to satisfy the essential requirement of “attached to”, any tooth of the relay gear 40 (for example, the relay gear) 40 "1") and the reference tooth "1" of the yellow drum gear 51 are engaged with each other, the reference tooth "1" of the magenta drum gear 52 is also engaged with the "1" tooth of the relay gear 40. Each gear is assembled as shown.

  In the state shown in FIG. 8A, the sheet P is fed to the photosensitive drum of the yellow drum gear 51, and at the same time, the peripheral surface of the photosensitive drum corresponding to the “6” teeth of the yellow drum gear 51. Is irradiated with light having image information to form an electrostatic latent image “A”. The photosensitive drum of the yellow drum gear 51 on which the electrostatic latent image is formed continues to rotate in the clockwise direction, so that the sheet P in contact with the peripheral surface of the photosensitive drum advances and the magenta drum gear 52 is moved forward. Will head to. In the middle of the process, toner is supplied to the peripheral surface of the photosensitive drum, whereby the electrostatic latent image “A” becomes a toner image “A”.

  Then, when the yellow drum gear 51 rotates by three teeth, the peripheral surface of the photosensitive drum corresponding to the “6” tooth of the yellow drum gear 51 is positioned directly below. As shown in (b) of FIG. 8, the toner image “A” is transferred to the paper P.

  When the teeth of the yellow drum gear 51 continue to rotate by five, the paper P is synchronized so that the paper P reaches the position immediately before being fed to the magenta drum gear 52, as shown in FIG. Being transported. Then, when the paper P reaches the magenta drum gear 52, the positional relationship between the relay gear 40 and each of the drum gears 51 and 52 is the same as in the case of FIG. At this time, the peripheral surface of the photosensitive drum corresponding to the “3” teeth of the magenta drum gear 52 is irradiated with light having image information to form an electrostatic latent image “A”.

  Thereafter, when the magenta drum gear 52 rotates by three teeth, as shown in FIG. 8D, the “3” tooth of the magenta drum gear 52 is positioned directly below and the toner image “A” The toner image “A” on the photosensitive drum corresponding to the “3” tooth of the magenta drum gear 52 is transferred to the paper position where the “” is formed without being displaced. The positional relationship between the relay gear 40 and the drum gears 51 and 52 in this state is the same as in the case of FIG.

  As described above, the positional relationship between the relay gear 40 and each of the drum gears 51 and 52 at the time when the paper P reaches the target photosensitive drum is as follows when the photosensitive drum is that of the yellow drum gear 51 (FIG. 8). (A)) and the case where the photosensitive drum is of the magenta drum gear 52 ((C) in FIG. 8), the transfer process is performed on the paper P by the target photosensitive drum. As for the positional relationship between the relay gear 40 and each of the drum gears 51 and 52 at the time when the photosensitive drum is the yellow drum gear 51 (FIG. 8B), the photosensitive drum is the magenta drum gear 52. (2) in FIG. 8 is exactly the same.

  In the first aspect of the present invention, "when each drum gear 51, 52 determines the position of the reference tooth (for example, the tooth of" 1 ") on each drum gear 51, 52, each reference tooth is connected to the relay gear 40. The drum gears 51 and 52 that mesh with the teeth of the relay gear 40 are the same as each other in the teeth of the relay gear 40. Therefore, the occurrence of meshing errors due to different meshing teeth is avoided. As a result, in the case of color printing, color misregistration caused by misalignment of the transfer position of each photosensitive drum onto the paper P is prevented.

  According to a second aspect of the present invention, in the first aspect of the present invention, each drum gear is provided with a positioning projection that serves as a reference when positioning in the circumferential direction during assembly. is there.

  According to such a configuration, when the drum gear is assembled, the positioning of each drum gear is reliably performed by using the positioning protrusion as a guide.

  According to a third aspect of the present invention, in the second aspect of the present invention, a gear positioning member is provided in a housing in which each of the drum gears is rotatably mounted around the drum shaft, and the gear positioning member is provided on the drum gear. There is an interference part that interferes with each positioning protrusion located at a predetermined reference position when assembled to the housing, and this interference part eliminates interference with each positioning protrusion when the assembly of each drum gear to the housing is completed. It is comprised so that it may be performed.

  According to this configuration, when the drum gear is mounted on the housing, each drum gear is positioned at the respective reference position by causing the positioning protrusions of each drum gear to interfere with the interference portion of the gear positioning member provided on the housing. Therefore, the positioning operation of each drum gear becomes easy. When the assembly of each drum gear to the housing is completed, the interference with the positioning projections of the interference portion is eliminated, so that the subsequent rotation operation of each drum gear is not hindered.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, a lid that is mounted on the housing in a state of covering the drum gears is provided, and the lid is mounted on the housing so that the positioning is performed. It has a pressing part which presses a member and cancels interference to each positioning projection of the above-mentioned interference part.

  According to such a configuration, after each drum gear is mounted on the housing, the lid is mounted on the housing, whereby the pressing portion of the lid presses the positioning member, and interference with the positioning projections of the interference portion is eliminated. In this way, each drum gear in a positioned state can be rotated by a simple operation of mounting the lid, which contributes to improving the workability of the assembly operation of the drum gear.

  The invention according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, two drum gears are meshed with one relay gear.

  According to this configuration, when one relay gear is driven to rotate, the two drum gears meshed with the relay gear are synchronously rotated. For example, in a so-called tandem image forming apparatus having four photoconductor drums for color printing, four photoconductor drums are employed for each color, and four photoconductor drums are provided corresponding to the photoconductor drums. Drum gears are used, but in this case, by making two drum gears mesh with each of the two relay gears, the drum drive mechanism is simplified, and color misregistration is prevented. Realizes clear color printing.

  FIG. 9 is an explanatory diagram for specifically explaining the operation of the inventions according to claims 4 and 5, wherein (a) is a first example of the installation position of the positioning protrusion, and (b) is positioning. A second example of the installation position of the protrusion is shown. FIG. 9 assumes a so-called tandem image forming apparatus in which four photosensitive drums are provided for each of four predetermined colors (yellow, magenta, cyan, and black). In such a tandem type image forming apparatus, four drum gears 50 and two relay gears 40 are employed corresponding to each photosensitive drum, and the two right drum gears 50 (the yellow drum gear 51 and the magenta drum gear in FIG. 9) are employed. The first relay gear 41 is meshed with the drum gear 52), and the second relay gear 42 is meshed with the two left drum gears 50 (the cyan drum gear 53 and the black drum gear 54). Each drum gear 51-54 is manufactured by the same metal mold | die.

  First, in the first example shown in FIG. 9A, the positioning protrusion 60 is provided at an intermediate position between the “1” tooth and the “2” tooth for each of the drum gears 51 to 54. When the drum gears 51 to 54 are assembled, a gear positioning member 70 that is detachable with respect to the positioning protrusion 60 is provided at a predetermined position on the main body side of the image forming apparatus so that the positioning protrusions 60 are arranged in a horizontal row. It has been. The drum gears 51 to 54 are assembled so that the upper surface of each positioning projection 60 is brought into contact with the gear positioning member 70.

  By doing so, the assembly is easily performed in a state where the conditions of the positional relationship of the gear according to the present invention are satisfied. When the assembly is completed, the locking of the gear positioning member 70 with respect to the positioning projection 60 is released, whereby the drum gears 51 to 54 can be rotated.

  By providing the positioning projections 60 on the drum gears 51 to 54 and the gear positioning member 70 on the main body side of the image forming apparatus, the drum gears 51 to 54 can be easily and reliably positioned when the gears are assembled. Then, when the drum gears 51 to 54 are assembled in this manner, “when each drum gear determines the position of the reference tooth on the respective drum gear, each reference tooth corresponds to the relay gear according to the rotation of the relay gear. It is assembled so as to be meshed with the same tooth of “the same tooth”.

  Next, in the second example shown in FIG. 9B, the positioning projection 60 is provided at a position corresponding to the “1” tooth of each of the drum gears 51 to 54. Along with this, as shown in FIG. 9B, the gear positioning member 70 is the one on the right side. “When each drum gear determines the position of the reference tooth on each drum gear, each reference tooth The positioning protrusion 60 of the yellow drum gear 51 and the positioning protrusion of the yellow drum gear 51 are satisfied in a state where the essential requirement of “meshing with the same tooth of the relay gear according to the rotation of the relay gear” is satisfied. The L-shape is laid sideways so as to abut against the positioning projection 60 of the cyan drum gear 53 and the positioning projection 60 of the black drum gear 54 with the left side satisfying the same condition. It is made into the shape made. Other points are the same as in the case of the first example. In the case of the second example, the same effect as the first example can be obtained.

  According to the first aspect of the present invention, each photosensitive drum rotates while its rotational speed slightly varies according to the meshing error between the respective drum gear and the relay gear. The position of the paper (front position) where the peripheral surface (front surface) of one photoconductor drum is in contact with a second tooth meshed with the upper surface of one drum gear. If the diameter of the photosensitive drum is set so that it is in contact with the outer peripheral surface of another photosensitive drum in the state where it is engaged with the upper teeth of another adjacent drum gear, even if the gear meshing error occurs. Even if the rotational speed of the photoconductor drums fluctuates, the back surface of all the photoconductor drums will come into contact with the back position of the paper being conveyed, thereby transferring the photoconductor drum to the paper. It is possible to reliably prevent surface displacement and Can be performed sharp color printing is prevented.

  According to the second aspect of the present invention, each drum gear is provided with positioning projections that serve as a reference for positioning in the circumferential direction during assembly. Therefore, the positioning projection is used as a guide during assembly of the drum gear. As a result, each drum gear can be positioned reliably, which contributes to an improvement in workability.

  According to the third aspect of the present invention, when the drum gear is mounted on the housing, the drum gear is moved to the reference position by causing the positioning protrusion of each drum gear to interfere with the interference portion of the gear positioning member provided on the housing. Since the position is set, the positioning operation of each drum gear can be performed more easily. When the assembly of each drum gear to the housing is completed, interference with the positioning projections of the interference portion is eliminated, so that it is possible to prevent any trouble in the subsequent rotation operation of each drum gear.

  According to the fourth aspect of the present invention, after each drum gear is mounted on the housing, the lid body is mounted on the housing, so that the pressing portion of the lid body presses the positioning member to eliminate interference with the positioning projection of the interference portion. Can be made. Thus, each drum gear in the positioning state can be rotated by a simple operation of mounting the lid, which can contribute to improvement in workability of the assembly work of the drum gear.

  According to the fifth aspect of the present invention, since the two drum gears are meshed with the one relay gear, the two drum gears meshed with the relay gear are synchronized by driving and rotating the one relay gear. Can be rotated. For example, in a so-called tandem image forming apparatus having four photoconductor drums for color printing, four photoconductor drums are employed for each color, and four photoconductor drums are provided corresponding to the photoconductor drums. Drum gears are used, but in this case, by making two drum gears mesh with each of the two relay gears, the drum drive mechanism is simplified, and color misregistration is prevented. And clear color printing.

  First, image forming processing in the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a front sectional view illustrating the internal structure of the image forming apparatus. As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment is used as a copying machine, and includes an apparatus main body 11 having a box shape, and an original image attached to the upper surface of the apparatus main body 11. The image reading device 19 has a basic configuration.

  The apparatus main body 11 includes an image forming unit 12 that forms an image based on image information of a document read by the image reading device 19 and a fixing process performed on the image formed by the image forming unit 12 and transferred to a sheet. A fixing unit 13 to be applied and a paper storage unit 14 for storing a transfer paper are provided.

  The image reading device 19 includes a document holder 191 provided on the upper surface of the apparatus main body 11 so as to be openable and closable, and an optical system unit 192 disposed in the apparatus main body 11 so as to face the document holder 191 through a contact glass 193. ing. The contact glass 193 includes a placed document contact glass 193a having a slightly smaller planar shape than the document presser 191 for reading the document surface of the placed document, and a longitudinal direction for reading the document surface of the automatically fed document. A long and narrow automatic feeding paper contact glass 193b is provided (in a direction orthogonal to the paper surface of FIG. 1).

  On the upper surface of the apparatus main body 11 on the front side (front side of the paper surface in FIG. 1) of the image reading apparatus 19, an operation panel 194 for inputting processing conditions relating to document reading and copying is provided. The operation panel 194 is disposed on the upper surface of the front portion of the processing apparatus main body 11, and is provided with a display panel, a numeric keypad, a start button, a mode switching key, and the like (not shown). The display panel displays various types of input information and output information on a liquid crystal display, or inputs information selected from the displayed processing conditions by a touch-in operation. The numeric keypad is mainly for setting quantity information such as the number of copies. The mode switching key is used to switch the mode of the image forming apparatus 10, and the image forming apparatus 10 can be used as a copying machine, a facsimile machine, or a printer by pressing the mode switching key. You can do that.

  The document presser 191 is attached to the apparatus main body 11 so as to be opened and closed by rotating forward and backward about a predetermined axis provided on one side of the upper surface of the apparatus main body. The document presser 191 has a two-stage structure, and includes a document tray 195 for placing a document provided in the upper stage, and a document discharge tray 196 provided in the lower stage for discharging a document whose image has been read. And have. On the left side of the document retainer 191, a document feeding unit 197 is provided between the document tray 195 and the document discharge tray 196. The document tray 195 is disposed by a document feeding mechanism (not shown) of the document feeding unit 197. The originals are picked up one by one from the original bundle placed thereon and supplied to the automatic paper supply contact glass 193b. The picked-up document is read by the optical system unit 192 through the automatic paper feeding contact glass 193b while being moved. The document after the document image is read is discharged to a document discharge tray 196.

  The optical system unit 192 includes an unillustrated light source, a plurality of mirrors, a lens unit, and a CCD (charge coupled device). 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 image forming unit 12 forms a toner image on a sheet fed from the sheet storage unit 14, and in the present embodiment, the image forming unit 12 sequentially arranges from the upstream side (the right side of the paper surface in FIG. 1) to the downstream side. A yellow unit 12Y, a magenta unit 12M, a cyan unit 12C, and a black unit 12K are provided.

  Each unit 12Y, 12M, 12C, 12K is provided with a photosensitive drum 121 and a developing device 122, respectively. Each photoconductive drum 121 is supplied with toner from a corresponding developing device 122 while rotating clockwise in FIG.

  A charger 123 is provided at a position immediately above each photosensitive drum 121, and an exposure device 124 is provided at a right position. Each photosensitive drum 121 is uniformly charged at its peripheral surface by the charger 123, and a laser beam based on image data input by the image reading device 19 is charged from each exposure device 124 by the photosensitive drum. By irradiating the peripheral surface of 121, an electrostatic latent image is formed on the peripheral surface of each photosensitive drum 121. By supplying 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.

  Further, a cleaning device 125 for removing residual toner on the peripheral surface of the photosensitive drum 121 and cleaning it is provided at the lower left position in FIG. 1 of each photosensitive drum 121. The peripheral surface of the photosensitive drum 121 cleaned by the cleaning device 125 is directed to the charger 123 for a new charging process.

  Below each photoconductor drum 121, a transport belt 126 is provided so that the transport surface faces the photoconductor drum 121. The conveyor belt 126 is wound around a driving roller provided slightly downstream of the black unit 12K and a driven roller provided slightly upstream of the yellow unit 12Y, and circulates by driving rotation of the driving roller. It is supposed to be. The paper supplied from the paper storage unit 14 moves while being in contact with the peripheral surface of the photosensitive drum 121 while being guided by the rotation of the conveyance belt 126, and is subjected to a transfer process.

  The fixing unit 13 performs a fixing process on the toner image on the sheet transferred by the image forming unit 12, and includes a fixing roller 131 having an energized heating element serving as a heating source therein, and a fixing roller 131 below the fixing roller 131. A pressure roller 132 disposed opposite to the roller 131 is provided. Then, the transfer-processed paper led out from the image forming unit 12 by the rotation of the conveyance belt 126 is fixed with the toner image by a heat treatment that is sandwiched between the fixing roller 131 and the pressure roller 132 and heated by the fixing roller 131. Thus, a stable color image that has been subjected to the fixing process is formed on the paper. The paper P with the color image for which the fixing process has been completed passes through the paper discharge conveyance path 102 formed on the downstream side of the curl correction unit 15, and is a paper discharge tray 101 protruding from the left side wall in FIG. It is discharged towards.

  The curl correcting unit 15 determines the type of paper P (whether it is a normal copy paper or a thin paper, etc.) and the status of transfer processing for the paper P (whether it is single-sided printing or double-sided printing). Accordingly, the conveyance direction can be switched between a diagonally upper side and a diagonally lower side toward the downstream side, and the curl formed during the fixing process for the paper P discharged in the set direction is corrected. Thus, the curl formed on the paper P is corrected by the paper P passing through the curl correction unit 15.

  The paper storage unit 14 includes a plurality of paper trays 141 that are detachably attached to the apparatus main body 11. Each sheet tray 141 stores a sheet bundle. Then, the paper P is fed one by one from the paper bundle of the selected paper tray 141 by driving the pickup roller 142, and is introduced into the image forming unit 12 through the paper feed conveyance path 143.

  Further, in the image forming apparatus 10 of the present embodiment, a sheet reversing unit 16 for performing duplex printing on the sheet P is provided in the apparatus main body 11. The sheet reversing unit 16 is interposed between the image forming unit 12 and the sheet storage unit 14 and supports a sheet P having a fixed image on one side, and a position directly below the fixing unit 13. A switching guide 162 that distributes the paper P to one of the paper discharge conveyance path 102 and the return conveyance path 103 with respect to the paper P after fixing processing and the paper P supported by the support plate 161. A reversing roller pair 163 that continues the clamping state is provided.

  The paper P supported by the support plate 161 while being held between the return conveyance path 103 and the reverse roller pair 163 by the switching operation of the switching guide 162 is discharged from the rear end side by the reverse rotation of the reverse roller pair 163. The sheet is directed to the paper feed conveyance path 143 through the reverse conveyance path 104. The paper P that has been turned upside down and supplied to the paper feed conveyance path 143 is supplied to the image forming unit 12 again, whereby the back side is subjected to a transfer process.

  The image forming apparatus 10 configured as described above includes a drum driving mechanism 20 that rotates the respective photosensitive drums 121 provided in the yellow unit 12Y, the magenta unit 12M, the cyan unit 12 and the black unit 12K in synchronization. Is provided. Hereinafter, the drum drive mechanism 20 will be described in detail.

  FIG. 2 is a perspective view showing an embodiment of the drum drive mechanism 20. Incidentally, in the following description, in order to explain the operation of the present invention in the column of “Means for Solving Problems”, an assembling method of each gear different from the method described based on FIGS. 8 and 9 is given as an example. I will explain. As shown in FIG. 2, the drum drive mechanism 20 is transmitted to a drive motor (drive means) 30 installed at a lower position between the cyan unit 12C and the black unit 12K, and the drive of the drive motor 30 is transmitted. And a drum gear 50 that is concentric with and integral with the photosensitive drum 121 that meshes with the relay gear 40 and rotates each photosensitive drum 121 about its axis. .

  The relay gear 40 is cyan, similarly to the first relay gear 41 that meshes with both the drum gear 50 (yellow drum gear 51) of the yellow unit 12Y and the drum gear 50 (magenta drum gear 52) of the magenta unit 12M at the lower part. A pair of the second relay gear 42 meshed with both the drum gear 50 (cyan drum gear 53) of the unit 12C and the drum gear 50 (black drum gear 54) of the black unit 12K is provided.

  The first relay gear 41 is provided with a first small-diameter gear 411 concentrically and integrally projecting in the opposite direction to the photosensitive drum 121, and the second relay gear 42 has the same A second small-diameter gear 421 projecting from the first and second relay gears 411 and 421 is stretched between the first and second relay gears 411 and 421. If one of the first and second relay gears 41, 42 rotates via the timing belt 43, the other also rotates synchronously.

  The drive motor 30 has a drive gear 32 concentrically fixed to the drive shaft 31. In the present embodiment, the drive gear 32 is meshed with the second relay gear 42. Therefore, when the drive motor 30 is driven, this driving force is transmitted to the second relay gear 42 via the drive shaft 31 and the drive gear 32, and the rotation of the second relay gear 42 thereby causes the cyan drum gear 53 and the black drum. While being transmitted to the drum gear 54, the rotation of the second relay gear 42 is transmitted to the yellow drum gear 51 and the magenta drum gear 52 via the second small diameter gear 421, the timing belt 43, the first small diameter gear 411 and the first relay gear 41. As a result, the drum gears 51 to 54 rotate synchronously.

  In the present invention, the drum gears 51 to 54 are assembled such that predetermined reference teeth having the same shape mesh with the same teeth of the relay gear 40 according to the rotation of the relay gear 40. ing. Hereinafter, this will be described in detail with reference to FIG.

  FIG. 3 shows an example of the relationship between one relay gear 40 and two drum gears 50 that mesh with the relay gear 40, and the relationship between the first relay gear 41, the yellow drum gear 51, and the magenta drum gear 52. It is explanatory drawing for demonstrating, (a) is the state which the reference tooth of the 1st relay gear 41 meshed with the reference tooth of the drum gear 51 for yellow, (b) is the drum gear 52 for the magenta for the 1st relay gear 41. Are shown in a meshed state. FIG. 3 shows the meshing relationship between the first relay gear 41 and the yellow drum gear 51 and the magenta drum gear 52 meshed with the first relay gear 41. The same applies to the meshing relationship between the cyan drum gear 53 and the black drum gear 54 meshed with the second relay gear 42.

  First, as a premise, the first relay gear 41 is manufactured by the same mold including the second relay gear 42, and the yellow drum gear 51 and the magenta drum gear 52 are also the cyan drum gear 53 and the black drum gear 54. Are manufactured with the same mold. Accordingly, the mass-produced relay gear 40 has exactly the same shape until it reaches the details, and one of the yellow drum gear 51 and the magenta drum gear 52 is copied from the other. Similarly, the shape is exactly the same until the details are reached.

  By the way, although these molds are precisely designed and manufactured so as to conform to the design, there are few positions that should be the center, but they are eccentric in the micron order or the same, for example. The shape of each tooth, which should have been set to exactly the same pitch, is usually fine, but different in micron order.

  Such eccentricity and minute difference in tooth shape rarely cause a problem in a gear used only for transmitting power, but the image forming apparatus 10 performs precise alignment and accurately synchronizes. For gears used to rotate a plurality of photosensitive drums 121 that would cause color misregistration in color printing results unless they are rotated, minute eccentricity and minute tooth shape differences are fatal. Sometimes it becomes. The present invention is improved so that even if there is a difference in the eccentricity or tooth shape of the gear, color printing can be performed by absorbing them.

  Hereinafter, this improvement will be described in detail with reference to FIG. In FIG. 3, for convenience, the number of teeth of the first relay gear 41 is 24, and the number of teeth of the yellow drum gear 51 and the magenta drum gear 52 is 46. However, in the present invention, the number of teeth is such a number. It is not limited to a certain thing, but is appropriately set according to the situation.

  In the present embodiment, as shown in FIG. 3, reference teeth (reference tooth t1) displayed in a stippled manner on the first relay gear 41 are set in advance, and the yellow drum gear 51 and the magenta drum gear 52 are also set respectively. A reference tooth (reference upper tooth T1) displayed by stippling is set. The prefixes “A” and “B” are used to distinguish whether the “tooth” is a tooth of the drum gear 50 or the tooth of the relay gear 40. Uses “B” for the teeth of the relay gear 40 and “B”. The reason why the reference teeth t1 and T1 are set is that the reference teeth t1 and T1 are used as a reference (guideline) in the gear assembling process. That is, in the yellow drum gear 51 and the magenta drum gear 52, the reference upper teeth T1 and T1 having the same shape correspond to the reference tooth t1 of the first relay gear 41 according to the rotation of the first relay gear 41. It is assembled so as to mesh.

  In the example shown in FIG. 3, when the gear is assembled, as shown in FIG. 3A, the reference tooth t1 of the first relay gear 41 that rotates counterclockwise around the axis is clockwise around the axis. Of the yellow drum gear 51 rotating in the middle and the fifteenth tooth of the magenta drum gear 52 rotating clockwise around the axis of the fifteenth tooth t15 of the first relay gear 41. It meshes with the tooth t37.

  In this way, when the first relay gear 41 rotates counterclockwise around the axis by 10 teeth, the magenta drum gear 52 also rotates around the axis by 10 teeth, and as shown in FIG. As shown, the reference tooth t1 of the first relay gear 41 meshes with the reference upper T1 of the magenta drum gear 52. This is because the teeth of the first relay gear 41 meshed with the arbitrary upper teeth Ti ((b) of FIG. 3) of the yellow drum gear 51 are the teeth i of the magenta drum gear 52 with a time delay corresponding to the number of teeth 10. (That is, the same tooth as that of the yellow drum gear 51).

  Accordingly, the irradiation of the light beam from the exposure device 124 to the circumferential surface of the photosensitive drum 121 related to the magenta drum gear 52 is started 10 times from the start of the light beam irradiation from the exposure device 124 to the circumferential surface of the photosensitive drum 121 related to the yellow drum gear 51. By performing the time delay by the amount of time, an electrostatic latent image of the same condition that absorbs the gear eccentricity and the tooth meshing error is formed on the peripheral surface of each photosensitive drum 121, and the toner image of the same condition is continuously formed. Will be formed.

  Then, the diameter of the photosensitive drum 121 is set so that the toner image at the start of light irradiation on the photosensitive drum 121 of the magenta drum gear 52 overlaps the toner image at the start of light irradiation on the photosensitive drum 121 of the yellow drum gear 51. By doing so, it is possible to reliably eliminate the occurrence of color misregistration in the subsequent transfer process to the paper P due to the rotation of the yellow drum gear 51 and the magenta drum gear 52.

Incidentally, the diameter of the photosensitive drum 121 that does not cause color misregistration is expressed by the following equation:
R ′ = 180LR / πrθ
(Where, R ′: radius (mm) of the photosensitive drum 121, R: effective radius (mm) of the drum gear 50, L: distance between the shaft centers of the yellow drum gear 51 and the magenta drum gear 52 (mm), r : Effective radius (mm) of relay gear 40, θ: 10 teeth of relay gear 40 (in this embodiment, 10 teeth, but can be generalized to n ₀ ) angle (°) )
Can be calculated by:

When the above equation is converted by adopting the number of teeth n ₀ corresponding to the angle θ instead of the angle θ, the following is obtained.

R ′ = 180 LN / πn ₀
(Where N is the number of teeth of the drum gear 51 for yellow).

  The relationship between the relay gear 40 and the drum gear 50 has been described with respect to the first relay gear 41, the yellow drum gear 51, and the magenta drum gear 52, but the second relay gear 42, the cyan drum gear 53, and the black drum gear. The same applies to the area 54.

  In the present invention, in the assembling step of each drum gear 50, a positioning projection 60 is provided as a reference for positioning (phase determination) in the circumferential direction of each drum gear 50. FIG. 4 is an explanatory view showing a state in which the drum gears 51 to 53 are positioned based on positioning protrusions 60 provided on the yellow drum gear 51, the magenta drum gear 52, the cyan drum gear 53, and the black drum gear 54, respectively.

  As shown in FIG. 4, when the drum gear 50 is assembled, the positioning protrusion 60 meshes with the paper P on which the drum gears 51 to 53 are being conveyed under the same conditions as the relay gear 40 (hereinafter referred to as the same condition meshing). Therefore, the drum gears 51 to 54 are for positioning. The positioning protrusions 60 are provided on the back side of the drum gears 51 to 54 (the back side of the paper surface in FIG. 4), and are provided on the first positioning protrusion 61 provided on the yellow drum gear 51 and the magenta drum gear 52. The second positioning projection 62 includes a third positioning projection 63 provided on the cyan drum gear 53 and a fourth positioning projection 64 provided on the black drum gear 54. These positioning projections 60 are formed in a slightly horizontally long rectangular shape so that the upper edge surface is horizontal in a state where the drum gears 51 to 54 are set at the respective reference positions.

  In the yellow drum gear 51, the first positioning protrusion 61 is set so that the upper edge surface of the first positioning protrusion 61 is upward from the center position in a state where the reference upper tooth T1 is engaged with the reference tooth t1 of the first relay gear 41. It is provided at a position separated by a distance (distance d). In the example shown in FIG. 4, it is provided at a position immediately below the 33rd instep T33 in the counterclockwise direction.

  In the example shown in FIG. 4, the second positioning projection 62 is a reference upper tooth at a position facing counterclockwise by 10 teeth from the meshing position of the first relay gear 41 and the magenta drum gear 52 in the magenta drum gear 52. With the T1 positioned, the upper edge surface of the second positioning projection 62 is provided at a position spaced apart from the center position by a distance d. This position is located immediately below the sixth upper tooth T6 from the reference upper tooth T1 in the counterclockwise direction.

  In the example shown in FIG. 4, the third positioning protrusion 63 is a reference upper in the cyan drum gear 53 at a position facing counterclockwise by 20 teeth from the meshing position of the second relay gear 42 and the cyan drum gear 53. With the T1 positioned, the upper edge surface of the third positioning protrusion 63 is provided at a position spaced apart from the center position by a distance d. This position is located immediately below the thirteenth upper tooth T13 from the reference upper tooth T1 in the counterclockwise direction.

  In the example shown in FIG. 4, the fourth positioning protrusion 64 is a reference upper in a position facing the counterclockwise direction by 30 teeth from the meshing position of the second relay gear 42 and the black drum gear 54 in the black drum gear 54. With the T1 positioned, the upper edge surface of the fourth positioning projection 64 is provided at a position spaced apart by a distance d from the center position. This position is located immediately below the 32nd instep T32 from the reference instep T1 in the counterclockwise direction.

  The positioning protrusions 60 (first to fourth positioning protrusions 61 to 64) are used for the yellow drum gear 51, the magenta drum gear 52, and the cyan drum gear after the drum gear 50 is mass-produced with the same mold. 53 and black drum gear 54 are respectively sorted, and fixed to each of the sorted positions by screwing or sticking.

  On the other hand, the first and second relay gears 41 and 42 are previously connected to the first and second relay gears 41 and 42 when the drum gears 51 to 54 are assembled to the first and second relay gears 41 and 42, respectively. A mark 44 for setting the position is provided. The mark 44 includes a first mark 441 for the first relay gear 41 and a second mark 442 for the second relay gear 42.

  The first mark 441 moves upward by a predetermined distance from the axis of the first relay gear 41 in a state where the reference upper T1 of the first relay gear 41 and the reference upper T1 of the yellow drum gear 51 are engaged with each other. It is provided at a spaced position. In the example shown in FIG. 4, it is provided at a position that is directed counterclockwise by five teeth from the reference tooth t1, that is, a position corresponding to the 20th tooth t20.

  Further, in the example shown in FIG. 4, the second mark 442 is located at a position corresponding to the second tooth t2 in the second relay gear 42, which is one counterclockwise direction from the reference tooth t1. Is provided.

  When the drum gears 51 to 54 are assembled to the first and second relay gears 41 and 42, the first and second relay gears 41 and 42 are arranged in advance so that the first and second marks 441 and 442 are positioned at the top. Then, the yellow drum gear 51 and the magenta drum gear 52 are assembled to the first relay gear 41, and the cyan drum gear 53 and the black drum gear 54 are assembled to the second relay gear 42. And when assembling each drum gear 51-54, it adjusts so that the 1st-4th positioning protrusion 61-64 may be located in the highest position.

  In the present embodiment, the gear positioning member 70 is used to efficiently position the drum gears 51 to 54. 5 and 6 are partially cut perspective views showing an embodiment of the gear positioning member 70. FIG. 5 shows a state in which the lid 172 is opened, and FIG. 6 shows that the lid 172 is closed. Each state is shown. First, as shown in FIG. 5, the gear positioning member 70 includes a positioning bar (interference portion) 71 mounted on the outside of the front plate 171 of the housing 17 that houses the photosensitive drum 121, and the front plate 171 of the housing 17. A pressing protrusion (pressing portion) 72 provided on the covering lid 172 and acting on the positioning bar 71 is provided.

  The positioning bar 71 has the first to fourth positioning of the drum gears 51 to 54 when the drum gears 51 to 54 are assembled to the drum shaft 121a of the photosensitive drum 121 that protrudes outwardly through the front plate 171. The outer surfaces in the radial direction of the projections 61 to 64 (upper side in FIG. 5) are brought into contact with each other, and by this contact, the drum gears 51 to 54 are set at predetermined initial positions at the time of assembly (previously based on FIG. 4). The position is set to a position where the same condition engagement described above is realized.

  On the other hand, each of the drum gears 51 to 54 is provided with a fitting insertion hole into which the drum shaft 121a is fitted and inserted at the center position, and a bush 55 is provided concentrically with the fitting insertion hole, and the fitting insertion hole serves as the drum shaft 121a. The drum gears 51 to 54 are fixed to the drum shaft 121a so as to be integrally rotatable by screwing a predetermined screw (not shown) from the bush 55 toward the drum shaft 121a. .

  The positioning bar 71 is provided with a pair of connecting rods 711 projecting from both ends in the longitudinal direction toward the front plate 171. These connecting rods 711 are slidably fitted into connecting holes 171 a formed in the front plate 171. Between the front plate 171 and the positioning bar 71, coil springs 712 in a compressed state fitted on the connecting rods 711 are interposed, and the positioning bar 71 is urged by the urging force of the coil springs 712. It is in the state which protruded toward -54. The first to fourth positioning protrusions 61 to 64 of the respective drum gears 51 to 54 fitted on the drum shaft 121a are brought into contact with the positioning bar 71 in such a state, thereby positioning the respective drum gears 51 to 54. It is.

  A pair of the pressing protrusions 72 are provided on the surface of the lid 172 facing the housing 17 so as to face the positions on both sides of the positioning bar 71 and do not interfere with the drum gear 50. Each of the pressing protrusions 72 has a protruding amount so that the positioning bar 71 can be removed from the first to fourth positioning protrusions 61 to 64 in a state where the lid 172 is attached to the housing 17. Therefore, by attaching the lid 172 to the housing 17, as shown in FIG. 6, the pair of pressing protrusions 72 press the positioning bar 71 toward the front plate 171 against the urging force of the coil spring 712, As a result, the interference state of the positioning bar 71 with respect to the first to fourth positioning protrusions 61 to 64 is eliminated.

  According to the gear positioning member 70, the first to fourth positioning protrusions are fitted while the drum gears 51 to 54 are externally fitted to the target drum shaft 121a and meshed with the relay gear 40 for which initial positioning has been completed in advance. 61 to 64 are brought into contact with the positioning bar 71. By doing so, the drum gears 51 to 54 are set to the initial positioning positions at the time of assembly. In this state, the drum gears 51 to 54 are fixed to the target drum shaft 121a by screws (FIG. 5).

  Next, the lid 172 is put on the front plate 171 of the housing 17. At this time, since the pressing protrusion 72 of the lid 172 presses the positioning bar 71, the positioning bar 71 moves in the direction of the front plate 171 against the urging force of the connecting rod 711, thereby the positioning bar 71. Since the interference with the first to fourth positioning protrusions 61 to 64 is eliminated (FIG. 6), the drum gears 51 to 54 can rotate without any trouble when the lid 172 is attached to the housing 17.

  As described above in detail, the image forming apparatus 10 of the present invention forms a toner image with the toner supplied to the electrostatic latent image formed on the peripheral surface, and transfers the toner image onto the sheet. The photosensitive drums 121 are configured to be synchronously rotatable around the drum shaft 121a by the drum driving mechanism 20, and the drum driving mechanism 20 includes A drum gear 50 (yellow drum gear 51, magenta drum gear 52, cyan drum gear 53, and black drum gear 54) of the same shape, which is concentrically and integrally mounted on the photosensitive drum 121, and the drum gears 51 to 54 adjacent to each other. And a relay gear 40 (first and second relay gears 41 and 42) that is driven and rotated by the drive motor 30. Each of the drum gears 51 to 54 has a predetermined reference upper tooth T1 having the same shape in accordance with the rotation of the first and second relay gears 41 and 42. It is assembled to mesh with the same tooth.

  According to such a configuration, the second tooth engaged with the predetermined upper teeth of one drum gear 50 is different from the upper teeth of the other drum gear 50 adjacently provided by the rotation of the first and second relay gears 41 and 42. In order to mesh, the tooth which meshes with both the one drum gear 50 and the other drum gear 50 becomes the same instep. Since the relationship between the upper teeth and the second teeth is established for all the teeth of the drum gear 50 and the first and second relay gears 41 and 42, the first and second teeth meshed with any one of the teeth of the one drum gear 50. The teeth of the relay gears 41 and 42 always mesh with the same tooth having the same meshing error as that of the one drum gear 50 in the other drum gear 50.

  Accordingly, each photosensitive drum 121 rotates while its rotational speed slightly varies according to the meshing error between the respective drum gear 50 and the relay gear 40, but the second gear of the relay gear 40 has one tooth of the drum gear 50. A predetermined position of the sheet with which the upper surface of one photosensitive drum 121 is in contact with the upper teeth, and then the second teeth of the first and second relay gears 41 and 42 are provided next to each other. If the diameter dimension of the photosensitive drum 121 is set so as to be in contact with the upper circumferential surface of the other photosensitive drum 121 in a state where it is engaged with the upper teeth of the other drum gear 50, even if the gear meshing error occurs, the photosensitive drum is detected. Even if the rotational speed of the body drum 121 fluctuates, the upper circumferential surface of all the photosensitive drums 121 comes into contact with the upper position of the sheet being conveyed. Transfer surface It is possible to reliably prevent the location shift.

  Further, since each drum gear 51 to 54 is provided with positioning projections 60 (first to fourth positioning projections 61 to 64) that serve as a reference for initial positioning in the circumferential direction during assembly, the drum gear 50 is provided. When assembling the drum gears 51, the initial positioning of each of the drum gears 51 to 54 can be ensured by using the positioning projection 60 as a guide.

  A gear positioning member 70 is provided on the housing 17 in which the drum gears 51 to 54 are rotatably mounted around the drum shaft 121a. The gear positioning member 70 is used as a reference when the drum gears 51 to 54 are assembled to the housing 17. The positioning bar 71 interferes with the positioning protrusions 60 located at the positions, and the positioning bar 71 eliminates interference with the positioning protrusions 60 in a state where the assembly of the drum gears 51 to 54 to the housing 17 is completed. Therefore, when the drum gear 50 is mounted on the housing 17, the positioning protrusions 60 of the drum gears 51 to 54 are caused to interfere with the positioning bar 71 of the gear positioning member 70 provided on the housing 17. The drum gears 51 to 54 are set at their respective reference positions, It is possible to easily perform the positioning operation of the drum gear 51 to 54 by Les.

  Since the assembly of the drum gears 51 to 54 to the housing 17 is completed, the interference with the positioning protrusions 60 of the positioning bar 71 is eliminated, so that the subsequent rotation operation of the drum gears 51 to 54 does not hinder. Can be.

  In addition, a cover body 172 that is mounted on the housing 17 in a state of covering the drum gears 51 to 54 is provided. The cover body 172 is mounted on the housing 17 to press the positioning bar 71 and thereby press the positioning bar 71. Since each of the positioning gears 60 has a pressing protrusion 72 that eliminates interference, the drum gears 51 to 54 are mounted on the housing 17, and then the lid body 172 is mounted on the housing 17. 72 can press the positioning bar 71 to eliminate the interference of the positioning bar 71 with the positioning projection 60. Thus, the drum gears 51 to 54 in the positioned state can be rotated by a simple operation of attaching the lid 172, which can contribute to improvement in workability of the assembly work of the drum gear 50.

  In the above-described embodiment, four drum gears 50, that is, a yellow drum gear 51, a magenta drum gear 52, a cyan drum gear 53, and a black drum gear 54 are employed. The first relay gear 41 targets the yellow drum gear 51 and the magenta drum gear 52, and the second relay gear 42 targets the cyan drum gear 53 and the black drum gear 54. A timing belt is stretched between the two relay gears 41 and 42, and one of the relay gears is configured to be driven and rotated by the drive motor 30. Therefore, the four photosensitive drums 121 are provided for color printing. In the so-called tandem image forming apparatus, the photosensitive drum 12 is used. The construction of the drum drive mechanism 20 to on you be simplified, it is possible to realize a clear color printing color shift is prevented.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above embodiment, the positioning bar 71 that interferes all at once is employed as the interference portion of the gear positioning member 70 that interferes with the first to fourth positioning protrusions 61 to 64 provided on the drum gears 51 to 54. However, the present invention is not limited to adopting the positioning bar 71 as the interference portion, and a member that individually interferes with each of the first to fourth positioning protrusions 61 to 64 may be provided. .

  (2) In the above embodiment, in order to eliminate interference with the first to fourth positioning protrusions 61 to 64 of the positioning bar 71, the pressing protrusion 72 that presses the positioning bar 71 is provided on the cover body 172, and the cover body By mounting 172 on the housing 17, interference with the first to fourth positioning protrusions 61 to 64 of the positioning bar 71 is canceled by a pressing operation by the pressing protrusion 72. The present invention is not limited to the adoption, and the interference may be eliminated by operating the operation lever that is separately received regardless of the lid 172.

  (3) In the above embodiment, the initial positioning of the first and second relay gears 41 and 42 is simply the first and second marks 441 provided on the first and second relay gears 41 and 42, respectively. However, instead of this, the first and second relay gears 41 and 42 are also provided with positioning projections similar to the positioning projections 60 of the drum gear 50, and this relay gear is provided only during assembly. An interference portion that interferes with the positioning protrusions 40 may be provided to perform initial positioning with respect to the first and second relay gears 41 and 42 as in the case of the drum gear 50.

  (4) In the above embodiment, the timing belt 43 is stretched between the first and second relay gears 41 and 42, and then the drive rotation of the first relay gear 41 is transferred to the yellow drum gear 51 and the magenta drum gear 52. The transmission rotation of the second relay gear 42 is transmitted to the cyan drum gear 53 and the black drum gear 54, but instead, between the magenta drum gear 52 and the cyan drum gear 53. In addition, the intermediate belt is interposed and the timing belt 43 is not adopted, and the driving rotation of the second relay gear 42 is transmitted to the black drum gear 54 and the cyan drum gear 53, and the driving rotation of the cyan drum gear 53 is also transmitted. It is transmitted to the magenta drum gear 52 via the intermediate relay gear, and the magenta drum gear is transmitted. The rotation of 52 may be transmitted to the yellow drum gear 51 through the first relay gear 41.

  (5) FIG. 7 is an explanatory view for explaining another embodiment of the positioning projection 60 ′ and the gear positioning member 70 ′. In this embodiment, each positioning projection 60 ′ (first to fourth positioning projections 61 ′ to 64 ′) is formed in a cylindrical piece shape, and each drum gear 50 (yellow drum gear 51, magenta drum gear 52, The cyan drum gear 53 and the black drum gear 54) are provided at the same position. In the example shown in FIG. 7, the first to fourth positioning protrusions 61 ′ to 64 ′ are at the same position on a straight line connecting the reference upper tooth T <b> 1 in each drum gear 51 to 54 and the center position of each drum gear 51 to 54. Is provided.

  On the other hand, the gear positioning member 70 ′ includes a positioning bar 71 similar to that of the above-described embodiment, and a protrusion presser rod protruding from the positioning bar 71 toward the first to fourth positioning protrusions 61 ′ to 64 ′. 73 (first to fourth protrusion pressing rods 731 to 734). The protrusion pressing rods 731 to 734 are set to protrude from the positioning bar 71 so as to come into contact with the corresponding protrusion pressing rods 731 to 734 in a state where the drum gears 51 to 54 are respectively set at the reference positions. ing.

  According to such a gear positioning structure, in the manufacture of the drum gear 50 using a mold, it is possible to simultaneously mass-produce the positioning gear 60 including the positioning projection 60 '. As in the previous embodiment, the yellow drum gear 51, magenta Compared with the case where dedicated positioning projections 60 are provided later on each of the drum drum gear 52, the cyan drum gear 53, and the black drum gear 54, the manufacturing cost can be reduced.

It is explanatory drawing of front sectional view for demonstrating the internal structure of an image forming apparatus. It is a perspective view which shows one Embodiment of a drum drive mechanism. It is explanatory drawing for demonstrating the meshing relationship of a relay gear and a pair of drum gear which the said relay gear meshes | engages. FIG. 6 is an explanatory diagram showing a state in which each drum gear is positioned based on positioning protrusions provided on a yellow drum gear, a magenta drum gear, a cyan drum gear, and a black drum gear, respectively. It is a partially cut perspective view which shows one Embodiment of a gear positioning member, and has shown the state by which the cover body was open | released. It is a partially cut perspective view which shows one Embodiment of a gear positioning member, and has shown the state by which the cover body was closed. It is explanatory drawing for demonstrating other embodiment of a positioning protrusion and a gear positioning member. FIG. 6 is an explanatory diagram for specifically explaining the operation of the invention according to claim 1, in which (a) is fed to a photoconductive drum (not shown) related to a yellow drum gear which is a drum gear on the upstream side. The state immediately before, (B) is the state where the paper is being transferred by the photosensitive drum of the yellow drum gear, and (C) is the unillustrated photosensitive drum related to the magenta drum gear where the paper is the downstream drum gear. A state (d) immediately before the sheet is fed shows a state where the sheet is being transferred by the photosensitive drum of the yellow drum gear. It is explanatory drawing for demonstrating the effect | action of invention of Claim 4 and 5 concretely, (A) is the 1st example of the installation position of a positioning protrusion, (B) is the installation position of a positioning protrusion. Each of the second examples is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 12 Image forming part 12Y Yellow unit 12M Magenta unit 12C Cyan unit 12K Black unit 121 Photosensitive drum 121a Drum shaft 122 Developing device 123 Charger 124 Exposure device 125 Cleaning device 126 Conveyor belt 13 Fixing portion 131 Fixing roller 132 Pressure roller 14 Paper storage portion 141 Paper tray 142 Pickup roller 143 Paper feed conveyance path 15 Curl correction portion 16 Paper reversing portion 161 Support plate 17 Housing 171 Front plate 172 Lid 19 Image reading device 191 Document holding 192 Optical system unit 193 Contact glass 194 Operation panel 195 Document tray 196 Document discharge tray 197 Document feed section 20 Drum drive mechanism 30 Drive motor (drive means) 31 Shaft 32 Drive gear 33 Drive gear 40 Relay gear 41 1st relay gear 411 1st small diameter gear 42 2nd relay gear 421 2nd small diameter gear 43 Timing belt 50 Drum gear 51 Yellow drum gear 52 Magenta drum gear 53 Cyan drum gear 54 For black Drum gear 55 Bush 60, 60 'Positioning projection 61-64 First to fourth positioning projection 61'-64' First to fourth positioning projection 70, 70 'Gear positioning member 71 Positioning bar (interference part) 711 Connecting rod 712 Coil Spring 72 Pressing protrusion (Pressing part)
73 Protrusion presser rods 731 to 734 Protrusion presser rods P Paper

Claims (5)

A plurality of photosensitive drums that form toner images with toner supplied to the electrostatic latent image formed on the peripheral surface and transfer the toner images to a sheet are arranged in parallel along the sheet conveying direction. In the image forming apparatus configured such that the drum can be synchronously rotated around the drum axis by the drum driving mechanism.
The drum driving mechanism includes a drum gear having the same shape concentrically and integrally mounted on each photosensitive drum, and a relay gear that meshes with each adjacent drum gear and is driven and rotated by driving of a driving unit. Configured
Each drum gear is assembled so that each reference tooth meshes with the same tooth of the relay gear according to the rotation of the relay gear when the position of the reference tooth is determined for each drum gear. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein each drum gear is provided with a positioning projection serving as a reference when positioning in the circumferential direction during assembly. A gear positioning member is provided in a housing in which each drum gear is rotatably mounted around the drum shaft,
The gear positioning member has an interference portion that interferes with the positioning protrusions located at a predetermined reference position when the drum gear is assembled to the housing, and the interference portion has completed the assembly of the drum gear to the housing. The image forming apparatus according to claim 2, wherein the image forming apparatus is configured to eliminate interference with each positioning protrusion in a state. A lid that is attached to the housing in a state of covering each drum gear is provided;
The image forming apparatus according to claim 3, wherein the lid includes a pressing portion that presses the positioning member and eliminates interference with the positioning protrusions of the interference portion by being attached to the housing. apparatus.   The image forming apparatus according to claim 1, wherein two drum gears are meshed with one relay gear.

Images