JP4737308B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a laser printer.

  An image forming apparatus such as a printer is usually provided with a paper feed tray for feeding paper. The sheet feed tray is provided with a sheet pressing plate on which sheets are stacked and a pickup roller for picking up the uppermost sheet on the sheet pressing plate. The end of the sheet pressing plate that is far from the pickup roller is swingably supported, and the end that is closer to the sheet pressing plate is biased toward the sheet feeding roller by a spring. Therefore, the uppermost sheet on the sheet pressing plate is pressed toward the pickup roller and is fed by the rotation of the pickup roller.

  However, in such a configuration, the weight applied to the paper pressing plate varies depending on the number and size of the papers placed on the paper pressing plate, so the paper on the paper pressing plate is pressed against the pickup roller. The pressing force changes. Such a change in the pressing force causes double feeding or idle feeding. That is, if the pressing force is too large, a multiple feed is generated in which a plurality of sheets are overlapped and fed, and if the pressing force is too small, the sheet is not fed even when the pickup roller is rotated.

  In addition, every time a sheet is picked up by the pickup roller, the sheet pressing plate swings slightly, and the sheet on the sheet pressing plate is pressed against the pickup roller. There is also.

Therefore, the sheet placing means for placing the sheet is moved by the driving force of the drive source from the position where the sheet on the sheet placing means is separated from the pickup roller to the position where the uppermost sheet contacts the pickup roller. Thus, a configuration has been proposed in which the uppermost sheet is held at a certain height with respect to the pickup roller (see, for example, Patent Document 1).
Japanese Patent No. 2698535

  However, in Patent Document 1, if a drive source is newly provided, the device cost becomes high.

  An object of the present invention is to provide an image forming apparatus capable of improving recording medium feeding accuracy and reducing noise during continuous feeding while suppressing an increase in apparatus cost.

  In order to achieve the above object, the invention described in claim 1 includes a first drive source, a photoconductor to which a drive force from the first drive source is input, and a recording medium conveyed toward the photoconductor. Is mounted, a mounting member that is movable to a mounting position for mounting the recording medium and a transport position for transporting the recording medium, and a driving force from the first drive source are input, A driving mechanism for moving the mounting member from the mounting position to the transport position; and a driving force input path from the first driving source to the photosensitive member; Switching means for switching between transmission and interruption of the driving force transmitted to the photosensitive member, determination means for determining whether or not the mounting member is located at the transport position, and the mounting member by the determining means Is determined not to be located at the transfer position In the period in which the switching member is moved from the mounting position to the transport position by the drive mechanism by controlling the switching unit, the switching mechanism is transmitted from the first driving source to the photoconductor for at least a predetermined period. And a control means for cutting off the driving force.

  According to such a configuration, the mounting member on which the recording medium is mounted is moved from the mounting position to the transport position by the driving force from the first driving source, and the recording medium is moved from the mounting member to the photosensitive member. The recording medium on the mounting member can be pressed against the feeding means for sending out with a constant pressing force. Therefore, it is possible to improve the feeding accuracy of the recording medium and reduce noise during continuous feeding.

  In addition, in this configuration, the driving force of the first driving source is input to both the photosensitive member and the mounting member, and the first driving source is also used as a driving source for the photosensitive member and the mounting member. Increase in cost can be suppressed.

  Further, in this configuration, since the photosensitive member is not driven at least for a predetermined period within the moving period of the mounting member, it is possible to suppress deterioration due to driving of the photosensitive member accordingly. Therefore, the life of the photoreceptor can be extended.

  According to a second aspect of the present invention, in the first aspect of the present invention, the determination unit is configured to place the mounting member within a predetermined time after the end of the image forming operation for forming an image on a recording medium. It is characterized that it is located at the transport position.

  According to such a configuration, it is determined that the placing member is located at the transport position within a predetermined time after the end of the image forming operation. Since the mounting member is not moved from the transport position to the mounting position in a short time after the end of the image forming operation, the mounting member is positioned at the transport position within a predetermined time after the end of the image forming operation. By determining that the mounting member is present, it is possible to correctly determine whether or not the placement member is located at the transport position.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a tray that is detachably attached to the image forming apparatus and accommodates the mounting member, and the tray Detecting means for detecting attachment and detachment to the image forming apparatus, and the determination means detects the attachment of the tray to the image forming apparatus by the detection means while the placement member is in the transport position. It is characterized by determining that it is located in.

  According to such a configuration, while the tray is continuously mounted on the image forming apparatus, it is determined that the placing member is located at the transport position. When the mounting member is housed in a tray that is detachable from the image forming apparatus, when the recording medium is mounted on the mounting member, the tray is detached from the image forming apparatus, so that the tray is continuously mounted. By determining that the mounting member is located at the transport position while the user is in the vehicle, it is possible to correctly determine whether or not the mounting member is positioned at the transport position.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the position detecting means for detecting that the mounting member is located at the transport position is provided, and the determination is made. The means determines that the placement member is located at the transport position when the position detection means detects that the placement member is located at the transport position. Yes.

  According to such a configuration, since the position detection means for detecting that the placement member is positioned at the transport position is provided, the placement member is positioned at the transport position based on the detection of the position detection means. It can be correctly determined whether or not. According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the second drive source and the second drive source are used to scan the photosensitive member with laser light. And an optical member for forming an electrostatic latent image, wherein the photosensitive member carries a developer image formed by developing the electrostatic latent image, and the control means starts driving the second drive source. To transfer timing for transferring the developer image from the photosensitive member to the recording medium based on the scanning preparation period until the driving speed reaches the scanning start speed at which the optical member can scan the laser beam. Then, the recording medium conveyance start timing is set so that the recording medium placed on the mounting member is conveyed to the photosensitive member by the transfer timing, and the conveyance start is performed within the scanning preparation period. Before the timing, And controlling means is characterized by transmitting the driving force to the photosensitive member from the first drive source.

  According to such a configuration, the driving force of the first driving source is transmitted to the photosensitive member before the conveyance of the recording medium is started, and from the mounting member by the transfer timing set based on the scanning preparation period. The recording medium conveyed can reach the photosensitive member driven by the driving force from the first driving source. Therefore, even if the transmission of the driving force to the photosensitive member is interrupted during the movement period of the mounting member, the transfer of the developer image to the recording medium can be completed without delaying the transfer timing.

  According to a sixth aspect of the invention, in the fifth aspect of the invention, the control means sets the drive start timing of the first drive source at a timing different from the drive start timing of the second drive source. It is characterized by doing.

  According to such a configuration, since the drive start timing of the first drive source and the drive start timing of the second drive source are shifted, a large load is applied to the power supply unit for supplying power to the first drive source and the second drive source. Can be avoided. Therefore, power can be stably supplied from the power supply unit to the first drive source and the second drive source. As a result, the first drive source and the second drive source can be driven stably.

  According to a seventh aspect of the present invention, there is provided a transfer means for transferring a developer image formed on the photoconductor to a recording medium according to any of the first to sixth aspects, and the transfer means. A transfer bias applying means capable of selectively applying a transfer bias and a transfer cleaning bias having a reverse polarity to the transfer bias, and the control means is within the scanning preparation period and before the conveyance start timing. The transfer bias is applied to the transfer means by the transfer bias applying means, and the cleaning process for cleaning the transfer means is completed.

  According to such a configuration, the cleaning of the transfer unit can be completed by the start of conveyance of the recording medium. Therefore, it is possible to apply a transfer bias during conveyance of the recording medium to achieve stable transfer of the developer image to the recording medium.

  The invention according to an eighth aspect is the invention according to the seventh aspect, wherein the control means is configured such that the transfer bias is applied to the transfer means by the transfer bias applying means at the same time as or after the conveyance start timing. Is started.

  According to such a configuration, since the transfer bias is not applied to the transfer unit before the start of conveyance of the recording medium, it is possible to prevent the transfer bias from being applied to the transfer unit for a long time and to improve the durability of the transfer unit. it can.

  According to a ninth aspect of the invention, there is provided the cleaning device according to any of the fifth to eighth aspects, further comprising a cleaning unit for cleaning the photoconductor by applying a photoconductor cleaning bias, and the control unit includes: The application of the photosensitive member cleaning bias to the cleaning unit is started within the scanning preparation period and before the conveyance start timing.

  According to such a configuration, application of the photosensitive member cleaning bias to the cleaning unit is started before the start of conveyance of the recording medium. Therefore, the cleaning of the photoconductor can be completed before the scanning of the laser beam with respect to the photoconductor is started, and a reliable formation of an electrostatic latent image can be achieved.

  According to the first aspect of the present invention, it is possible to improve the feeding accuracy of the recording medium and reduce noise during continuous feeding while suppressing an increase in apparatus cost. In addition, the life of the photoreceptor can be extended.

  According to the second aspect of the present invention, it is possible to correctly determine whether or not the placement member is located at the transport position.

  According to invention of Claim 3, it can be judged correctly whether the mounting member is located in a conveyance position.

  According to invention of Claim 4, it can be judged correctly whether the mounting member is located in a conveyance position.

  According to the fifth aspect of the present invention, the developer image can be transferred to the recording medium without delaying the transfer timing even if the transmission of the driving force to the photosensitive member is interrupted during the movement period of the mounting member. Can be completed.

  According to the sixth aspect of the invention, the first drive source and the second drive source can be driven stably.

  According to the seventh aspect of the present invention, the cleaning of the transfer means can be completed before the start of conveyance of the recording medium. Therefore, it is possible to apply a transfer bias during conveyance of the recording medium to achieve stable transfer of the developer image to the recording medium.

  According to the eighth aspect of the invention, the durability of the transfer means can be improved.

  According to the ninth aspect of the present invention, it is possible to complete the cleaning of the photoconductor before the start of the scanning of the laser beam on the photoconductor, thereby achieving a reliable formation of an electrostatic latent image.

  FIG. 1 is a side sectional view of an essential part showing a reference example of a laser printer as an image forming apparatus. The laser printer 1 includes a main body casing 2, a feeder unit 4 for feeding paper 3 serving as a recording medium housed in the main body casing 2, and an image formed on the fed paper 3. The image forming unit 5 is provided.

  An attachment / detachment opening 6 for attaching / detaching a process cartridge 20 described later is formed on one side wall of the main casing 2, and a front cover 7 for opening / closing the attachment / detachment opening 6 is provided. The front cover 7 is rotatably supported by a cover shaft (not shown) inserted through the lower end portion thereof. Thus, when the front cover 7 is closed around the cover axis, the attachment / detachment opening 6 is closed by the front cover 7, and when the front cover 7 is opened with the cover axis as a fulcrum (tilted), the attachment / detachment opening 6 is opened, The process cartridge 20 can be attached to and detached from the main casing 2 through the attachment / detachment opening 6.

  In the following description, in the laser printer 1 and the process cartridge 20 described later, when the process cartridge 20 is mounted on the main casing 2, the side on which the front cover 7 is provided is referred to as “front side”, and the opposite side is defined as the front side. “Back side”.

  The feeder unit 4 includes a sheet feeding tray 9 as a tray that is detachably attached to the bottom of the main casing 2, and a sheet feeding roller 10 and a sheet feeding pad 11 provided above the front end of the sheet feeding tray 9. The pickup roller 12 serving as a feeding unit provided on the rear side of the paper feed roller 10, the pinch roller 13 disposed opposite to the front lower side of the paper feed roller 10, and the front upper side of the paper feed roller 10 are opposed to each other. A paper dust removing roller 8 and a registration roller 14 provided on the upper rear side of the paper feeding roller 10 are provided.

  The paper feed tray 9 is detachably attached to the main body casing 2 by sliding in the front-rear direction (substantially horizontal direction).

  Inside the paper feed tray 9, a paper pressing plate 15 is provided as a placement member on which the paper 3 can be placed in a stack. The paper pressing plate 15 is supported at the rear end portion so as to be swingable, so that the paper pressing plate 15 extends along the bottom plate 16 of the paper feed tray 9, and the front end portion thereof is indicated by a solid line spaced downward from the pickup roller 12. The position is inclined so that the front end portion is lifted upward with the rear end portion as a fulcrum, and the front end portion is swingable to a conveyance position indicated by a two-dot chain line close to the pickup roller 12.

  A lever 17 is provided at the front end portion of the paper feed tray 9 as a drive mechanism for lifting the front end portion of the paper pressing plate 15 upward. The lever 17 is formed in a substantially L-shaped cross section so as to go from the front side to the lower side of the paper pressing plate 15, and its upper end is attached to a lever shaft 18 provided at the front end of the paper feed tray 9. The rear end portion is in contact with the front end portion of the lower surface of the paper pressing plate 15. Accordingly, when a rotational driving force from a main motor 95 described later is input to the lever shaft 18, the lever 17 rotates around the lever shaft 18, and the rear end portion of the lever 17 moves the front end portion of the paper pressing plate 15. lift.

  The paper pressing plate 15 is lifted when its front end is lifted, is positioned at the transport position, and presses the uppermost paper 3 on the paper pressing plate 15 against the pickup roller 12. In a state where the paper pressing plate 15 is located at the transport position, when a rotational driving force from a main motor 95 described later is input to the pickup roller 12 and the pickup roller 12 is rotated, A certain sheet 3 is picked up by the pickup roller 12 and fed toward the space between the sheet feed roller 10 and the sheet feed pad 11.

  On the other hand, when the paper feed tray 9 is detached from the main casing 2, the front end of the paper pressing plate 15 is lowered by its own weight and is separated downward from the pickup roller 12, and the paper pressing plate 15 is moved to the paper feeding tray 9. It is located in the mounting position extended along the bottom plate 16 of the. In a state where the paper pressing plate 15 is located at the placement position, the paper 3 can be placed on the paper pressing plate 15 in a stacked manner.

  The sheet 3 sent out between the sheet feeding roller 10 and the sheet feeding pad 11 by the pickup roller 12 is separated from the sheet feeding roller 10 by the rotation of the sheet feeding roller 10 by a rotational driving force from a main motor 95 described later. When the sheet is sandwiched between the sheet feeding pads 11, the sheets are reliably separated and fed. The fed paper 3 passes between the paper feed roller 10 and the pinch roller 13, and after the paper dust is removed by the paper dust removing roller 8 driven by the paper feed roller 10, it is conveyed to the registration roller 14. The The registration roller 14 is composed of a pair of rollers. After the registration of the sheet 3, the transfer between the photosensitive drum 29 and the transfer roller 32, which will be described later, is performed to transfer the toner image on the photosensitive drum 29 to the sheet 3. Transport to position.

  A registration sensor 106 for detecting the passage of the paper 3 is provided on the downstream side of the paper feed roller 10 in the conveyance direction of the paper 3 and on the upstream side of the registration roller 14. The registration sensor 106 is provided in the main casing 2 so as to be swingable. By swinging as the paper 3 passes, the registration sensor 106 detects the passage of the paper 3 and is turned on while the paper 3 is passing. Otherwise it is turned off.

  The image forming unit 5 includes a scanner unit 19, a process cartridge 20, a fixing unit 21, and the like.

  The scanner unit 19 is provided in an upper portion of the main casing 2 and includes a laser light source (not shown), a scanner motor 108 as a second drive source, a polygon mirror 22 as an optical member, an f exciting tower Y23, a reflecting mirror 24, and a lens 25. And a reflecting mirror 26 and the like. The laser beam based on the image data emitted from the laser light source is deflected by the polygon mirror 22 that is rotationally driven by the scanner motor 108 as shown by the chain line, passes through the f exciting tower Y23, and then reflected by the reflecting mirror 24. After the optical path is turned back and further passes through the lens 25, the optical path is further bent downward by the reflecting mirror 26, so that the surface of the photosensitive drum 29 described later of the process cartridge 20 is irradiated.

  The process cartridge 20 is detachably attached to the main body casing 2 below the scanner unit 19. The process cartridge 20 includes an upper frame 27 and a lower frame 28 formed separately from the upper frame 27 and combined with the upper frame 27. The process cartridge 20 includes a photosensitive drum 29 as a photosensitive member, a scorotron charger 30, a developing cartridge 31, and a transfer roller 32 as transfer means in a housing formed by combining an upper frame 27 and a lower frame 28. And a cleaning brush 33 as a cleaning means.

  The photosensitive drum 29 has a cylindrical shape, the outermost layer is formed of a positively chargeable photosensitive layer made of polycarbonate or the like, and an axial center of the drum main body 34 along the longitudinal direction of the drum main body 34. An extending metal drum shaft 35 is provided. The drum shaft 35 is supported by the upper frame 27, and the drum main body 34 is rotatably supported by the drum shaft 35, so that the photosensitive drum 29 is rotatable about the drum shaft 35 in the upper frame 27. Is provided. The photosensitive drum 29 is rotationally driven by the input of power from the main motor 95 (see FIG. 7).

  The scorotron charger 30 is supported by the upper frame 27, and is disposed opposite to the photosensitive drum 29 at a predetermined interval so as not to contact the photosensitive drum 29 at an obliquely upper rear side of the photosensitive drum 29. The scorotron charger 30 is provided between the discharge wire 37 and the photosensitive drum 29, which are disposed to face each other at a predetermined interval in the axial direction of the photosensitive drum 29, and from the discharge wire 37 to the photosensitive drum 29. And a grid 38 for controlling the discharge amount. In the scorotron charger 30, a bias voltage is applied to the grid 38 and at the same time, a high voltage is applied to the discharge wire 37 to cause corona discharge of the discharge wire 37, so that the surface of the photosensitive drum 29 is uniformly positive. Can be charged.

  The scorotron charger 30 is provided with a cleaning member 36 for cleaning the discharge wire 37 so as to sandwich the discharge wire 37.

  The developing cartridge 31 is detachably attached to the lower frame 28. In the developing cartridge 31, a toner accommodating chamber 39, a supply roller 40, a developing roller 41, and a layer thickness regulating blade 42 as an accommodating portion are provided.

  The toner storage chamber 39 is formed as an internal space on the front side of the developing cartridge 31 partitioned by the partition plate 43. The toner storage chamber 39 is filled with positively charged non-magnetic one-component toner as a developer. Examples of the toner include polymerizable monomers such as styrene monomers such as styrene, and acrylic monomers such as acrylic acid, alkyl (C1 to C4) acrylate, and alkyl (C1 to C4) methacrylate. Polymerized toner obtained by copolymerization by suspension polymerization or the like is used. Such a polymerized toner has a substantially spherical shape, has extremely good fluidity, and can achieve high-quality image formation.

  Such a toner is blended with a colorant such as carbon black, wax, and the like, and an external additive such as silica is added to improve fluidity. The average particle diameter of the toner is about 6 to 10 μm.

  Further, an agitator 44 as stirring means is provided in the toner storage chamber 39. The toner in the toner storage chamber 39 is agitated by the agitator 44 and discharged toward the supply roller 40 from the opening 45 communicating in the front-rear direction below the partition plate 43.

  The supply roller 40 is disposed behind the opening 45 and is rotatably supported by the developing cartridge 31. The supply roller 40 is configured by covering a metal roller shaft with a roller made of a conductive foam material. The supply roller 40 is rotationally driven by power input from a main motor 95 (see FIG. 7).

  The developing roller 41 is rotatably supported by the developing cartridge 31 in a state where the developing roller 41 is in contact with the supplying roller 40 so as to be compressed with respect to the rear side of the supplying roller 40. The developing roller 41 is opposed to and contacts the photosensitive drum 29 in a state where the developing cartridge 31 is mounted on the lower frame 28. The developing roller 41 is configured by covering a metal roller shaft with a roller made of a conductive rubber material. In the roller of the developing roller 41, the surface of a roller body made of conductive urethane rubber or silicone rubber containing carbon fine particles or the like is coated with a coating layer of urethane rubber or silicone rubber containing fluorine. A developing bias is applied to the developing roller 41 during development. The developing roller 41 is rotationally driven in the same direction as the supply roller 40 by the input of power from the main motor 95 (see FIG. 7).

  The layer thickness regulating blade 42 includes a pressing portion 47 having a semicircular cross section made of insulating silicone rubber at the tip of a blade body 46 made of a metal leaf spring material. The layer thickness regulating blade 42 is supported by the developing cartridge 31 above the developing roller 41, and the pressing portion 47 is pressed onto the developing roller 41 by the elastic force of the blade body 46.

  The toner discharged from the opening 45 is supplied to the developing roller 41 by the rotation of the supply roller 40, and at this time, the toner is positively frictionally charged between the supply roller 40 and the developing roller 41. The toner supplied onto the developing roller 41 enters between the pressing portion 47 of the layer thickness regulating blade 42 and the developing roller 41 as the developing roller 41 rotates, and forms the developing roller 41 as a thin layer having a constant thickness. Supported on.

  The transfer roller 32 is rotatably supported by the lower frame 28, is opposed to and contacts the photosensitive drum 29 in the vertical direction, and is disposed so as to form a nip with the photosensitive drum 29. The transfer roller 32 is configured by covering a metal roller shaft with a roller made of a conductive rubber material. A transfer forward bias is applied to the transfer roller 32 at the time of transfer under the control of the CPU 103 described later, and a transfer reverse bias having a polarity opposite to the transfer forward bias is applied during a transfer cleaning process described later. The transfer roller 32 is rotationally driven in the opposite direction to the photosensitive drum 29 by the input of power from the main motor 95 (see FIG. 7).

  The cleaning brush 33 is attached to the lower frame 28 and is disposed on the rear side of the photosensitive drum 29 so as to face and contact the photosensitive drum 29. A cleaning bias is applied to the cleaning brush 33 during the drum cleaning process under the control of the CPU 103 described later.

  The surface of the photosensitive drum 29 is first uniformly charged positively by the scorotron charger 30 as the photosensitive drum 29 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 19. An electrostatic latent image corresponding to the image to be formed is formed.

  Next, the electrostatic charge formed on the surface of the photosensitive drum 29 when the positively charged toner carried on the developing roller 41 comes into contact with the photosensitive drum 29 by the rotation of the developing roller 41. The latent image is supplied to an exposed portion of the surface of the photosensitive drum 29 that is uniformly positively charged and exposed to a laser beam and having a lowered potential. As a result, the electrostatic latent image on the photosensitive drum 29 is visualized, and a toner image by reversal development is carried on the surface of the photosensitive drum 29.

  Thereafter, the toner image carried on the surface of the photosensitive drum 29 is transferred to the transfer roller 32 while the sheet 3 conveyed by the registration roller 14 passes through the transfer position between the photosensitive drum 29 and the transfer roller 32. The image is transferred to the paper 3 by the applied transfer forward bias. The sheet 3 on which the toner image is transferred is conveyed to the fixing unit 21.

  The transfer residual toner remaining on the photosensitive drum 29 after the transfer is collected by the developing roller 41. Further, the paper dust from the paper 3 adhering to the photosensitive drum 29 after the transfer is collected by a cleaning brush 33 to which a cleaning bias is applied.

  The fixing unit 21 is provided on the rear side of the process cartridge 20, and includes a fixing frame 48, and a heating roller 49 and a pressure roller 50 in the fixing frame 48.

  The heating roller 49 includes a metal base tube and a halogen lamp for heating in the metal base tube, and is rotationally driven by input of power from a main motor (see FIG. 7).

  The pressure roller 50 is disposed below the heating roller 49 so as to press the heating roller 49. The pressure roller 50 is configured by covering a metal roller shaft with a roller made of a rubber material, and is driven in accordance with the rotational drive of the heating roller 49.

  In the fixing unit 21, the toner transferred onto the paper 3 at the transfer position is thermally fixed while the paper 3 passes between the heating roller 49 and the pressure roller 50. The sheet 3 on which the toner is fixed is conveyed to a sheet discharge path 51 that extends in the vertical direction toward the upper surface of the main casing 2. The sheet 3 conveyed to the sheet discharge path 51 is discharged onto a sheet discharge tray 53 formed on the upper surface of the main body casing 2 by a sheet discharge roller 52 provided on the upper side.

  FIG. 2 is a plan view of the paper feed tray 9. The sheet feed tray 9 is erected from a front wall 54 erected from the front edge of the bottom plate 16, a rear wall 55 erected from the rear edge of the bottom plate 16, and both edges of the bottom plate 16 in a direction perpendicular to the front-rear direction. A pair of side walls 56 and 57 are integrally provided. A grip portion (not shown) is formed on the front wall 54, and the paper feed tray 9 is attached to and detached from the main body casing 2 from the front side of the main body casing 2 by gripping the grip portion when attaching and detaching.

  In the following description, a direction orthogonal to the front-rear direction is referred to as a “width direction”. In addition, one side in the width direction is “right side” and the other side in the width direction is “left side”.

  The front wall 54, the rear wall 55, the left side wall 56, and the right side wall 57 each extend perpendicularly to the bottom plate 16, and surround the space on the bottom plate 16 in a rectangular shape in plan view. In the space surrounded by the front wall 54, the rear wall 55, the left side wall 56, and the right side wall 57, the lever 17, the lever shaft 18, and the lever are disposed on the right side of the paper pressing plate 15 and the paper pressing plate 15. A drive gear 61 is provided.

  The lever shaft 18 is rotatably supported by a bearing portion (not shown) provided on the right side wall 57, and on the front side of the paper pressing plate 15, the left end portion thereof corresponds to the right front end portion of the paper pressing plate 15 along the width direction. It extends to the opposite position. And the lever 17 is attached to the left end part of the lever shaft 18 so that relative rotation is impossible.

  The lever drive gear 61 is attached to the right end portion of the lever shaft 18 so as not to be relatively rotatable, with the lever shaft 18 inserted through the center thereof. When the paper feed tray 9 is mounted on the main body casing 2, the lever drive gear 61 is disposed below the transmission gear 79 of the paper feed drive unit 58 described below and meshes with the transmission gear 79.

  The paper feed drive unit 58 is provided in the main casing 2 and, as shown in FIG. 3, an input gear to which a rotational drive force from a main motor 95 (see FIG. 7) described later is input via an output gear 100 described later. 59, a roller driving mechanism 60 for rotating the paper feed roller 10 and the pickup roller 12, and a rotational driving force input to the input gear 59 are transmitted to the roller driving mechanism 60 and the lever driving gear 61, as necessary. And a drive transmission mechanism 62 as drive shut-off means.

  The input gear 59 is rotatably supported by the main body casing 2, and an input gear shaft 63 extending in the width direction is inserted through the center and attached to the input gear shaft 63 so as not to rotate relative to the input gear shaft 63. When the output gear 100 is rotated by the rotational driving force from the main motor 95, the input gear 59 receives the rotational driving force from the output gear 100 and rotates in the opposite direction to the output gear 100.

  The roller drive mechanism 60 includes a paper feed roller shaft 64, a paper feed roller drive gear 65, a drive output gear 66, a swing box 67, a pickup roller shaft 68, a pickup roller drive gear 69, and an intermediate gear 70. It has.

  The paper feed roller shaft 64 is rotatably supported by the main body casing 2 and extends in the width direction above the right front end of the paper feed tray 9 with the paper feed tray 9 mounted on the main body casing 2. The paper feed roller 10 is attached to the left end portion of the paper feed roller shaft 64 so as not to be relatively rotatable.

  The paper feed roller drive gear 65 is inserted through the right end of the paper feed roller shaft 64 at the center, and is attached so as not to rotate relative to the paper feed roller shaft 64. The paper feed roller drive gear 65 meshes with a paper feed drive transmission gear 76 described later, and rotates in the opposite direction to the paper feed drive transmission gear 76 when the paper feed drive transmission gear 76 is rotated. Further, the paper feed roller drive gear 65 includes a paper feed clutch 111 (see FIG. 7) that is an electromagnetic clutch for switching between transmission and interruption of the rotational driving force received from the paper feed drive transmission gear 76 to the paper feed roller shaft 64. Is built-in.

  The drive output gear 66 is provided adjacent to the right side of the paper feed roller 10, the paper feed roller shaft 64 is inserted through the center, and is attached so as not to rotate relative to the paper feed roller shaft 64.

  The swing box 67 is provided between the paper feed roller drive gear 65 and the drive output gear 66, and is opposed to the left plate portion 71 and the right plate portion 72 facing each other at a predetermined interval in the width direction. The upper plate part 73 which connects between the upper end edge of the board part 71 and the right side board part 72 is provided. The swing box 67 is supported by the paper feed roller shaft 64 so that the paper feed roller shaft 64 is inserted through the front lower end portions of the left side plate portion 71 and the right side plate portion 72. Further, an operating arm 74 for operating a stopper arm 80 described later is supported on the right side plate portion 72 of the swing box 67 so as to extend from the right side plate portion 72 toward the right side.

  The pickup roller shaft 68 is rotatably supported at the rear lower end portion of the left plate portion 71 of the swing box 67 and extends from the left plate portion 71 toward the left side so as to be parallel to the paper feed roller shaft 64. Yes. The pickup roller 12 is attached to the pickup roller shaft 68 at the left end thereof so as not to be relatively rotatable.

  The pickup roller drive gear 69 is inserted between the pickup roller 12 and the left side plate portion 71 of the swinging box 67 with the pickup roller shaft 68 passing through the center, and is attached to the pickup roller shaft 68 so as not to be relatively rotatable. ing. The pickup roller drive gear 69 is formed to have the same diameter as the drive output gear 66, and has the same number of gear teeth as the drive output gear 66 on the outer peripheral surface thereof.

  The intermediate gear 70 is rotatably supported by the left side plate portion 71 of the swing box 67 and a gear shaft 75 extending in the width direction is inserted through the center, and is attached to the gear shaft 75 so as not to be relatively rotatable. The intermediate gear 70 meshes with the drive output gear 66 and the pickup roller drive gear 69.

  Accordingly, when the paper feed roller drive gear 65 rotates in a state where the paper feed clutch 111 is on (a transmission state in which the rotational driving force is transmitted to the paper feed roller shaft 64), the paper feed roller shaft 64 rotates. As the paper roller shaft 64 rotates, the paper feed roller 10 and the drive output gear 66 rotate in the same direction as the paper feed roller drive gear 65. Further, the rotational driving force of the drive output gear 66 is transmitted to the intermediate gear 70 and rotates the intermediate gear 70 in the opposite direction to the drive output gear 66. Further, the rotational driving force of the intermediate gear 70 is transmitted to the pickup roller driving gear 69 to rotate the pickup roller driving gear 69 in the opposite direction to the intermediate gear 70. As a result, the pickup roller 12 rotates in the same direction as the pickup roller drive gear 69, that is, in the same direction as the paper feed roller 10 via the pickup roller shaft 68.

  As shown in FIGS. 3 and 4, the drive transmission mechanism 62 includes a paper feed drive transmission gear 76, a swing gear 77, an internal gear 78, a transmission gear 79, and a stopper arm 80.

  The paper feed drive transmission gear 76 is attached to a rotation shaft 81 extending in the width direction so as not to be relatively rotatable, and is disposed between the input gear 59 and the paper feed roller drive gear 65 and meshes therewith. As shown in FIG. 4, the paper feed drive transmission gear 76 includes a cylindrical portion 82 that externally fits the rotary shaft 81, and an eccentric cam portion that is provided on the left side of the cylindrical portion 82 and is eccentric with respect to the rotary shaft 81. 83 is integrally provided. A large number of external teeth that mesh with the input gear 59 and the paper feed roller drive gear 65 are formed at the right end of the cylindrical portion 82. The rotating shaft 81 is rotatably supported in the main body casing 2 by a bearing portion (not shown).

  The swing gear 77 is externally fitted to the eccentric cam portion 83 of the paper feed drive transmission gear 76 so as not to be relatively rotatable. The swing gear 77 is integrally provided with a cylindrical gear portion 84 formed so as to surround the cylindrical portion 82 of the paper feed drive transmission gear 76. External teeth 85 are formed.

  The internal gear 78 includes a cylindrical insertion portion 86 through which the cylindrical portion 82 of the paper feed drive transmission gear 76 is inserted so as to be relatively rotatable, and a cylindrical gear portion provided so as to surround the insertion portion 86. 87 and an annular plate-like connecting portion 88 that connects the right end portion of the insertion portion 86 and the right end portion of the gear portion 87 are integrally provided. The insertion portion 86 and the gear portion 87 are spaced apart from each other in the radial direction of the rotating shaft 81, and the gear portion 84 of the swing gear 77 enters between the insertion portion 86 and the gear portion 87. Yes. An inner tooth 89 that meshes with the outer tooth 85 of the gear portion 84 of the swing gear 77 is formed on the inner peripheral portion of the gear portion 87. Note that the number of teeth of the inner teeth 89 is set slightly larger than the number of teeth of the outer teeth 85. In addition, a large number of locked portions 90 to which the stopper arm 80 is engaged and disengaged are formed in a sawtooth shape on the outer peripheral portion of the gear portion 87.

  The transmission gear 79 is externally fitted to the rotary shaft 81 via the one-way clutch 91 and is engaged with the lever drive gear 61 at a position spaced apart from the swinging gear 77 by a predetermined distance. The transmission gear 79 is connected to the swing gear 77 via a substantially conical elastic piece 92 provided around the rotation shaft 81.

  As shown in FIG. 3, the stopper arm 80 is supported by a support shaft 93 extending in the width direction on the rear side of the operation arm 74 so that its rear end portion is rotatable, and above the operation arm 74 and the internal gear 78. It arrange | positions so that it may extend in the front-back direction. A locking claw 94 that can be locked to the locked portion 90 of the internal gear 78 is formed at the tip of the stopper arm 80. The stopper arm 80 is elastically biased by a torsion spring (not shown) in a direction in which the locking claw 94 is locked to the locked portion 90 of the internal gear 78.

  In a state where the paper pressing plate 15 is in the loading position, the swing box 67 is inclined so that the rear side sinks downward with the paper feed roller shaft 64 as a fulcrum, and the operation arm 74 is separated downward from the stopper arm 80. is doing. As shown in FIG. 5, the locking claw 94 of the stopper arm 80 is locked to the locked portion 90 of the internal gear 78 to restrict the rotation of the internal gear 78.

  In this state, when a rotational driving force is input to the input gear 59, the rotational driving force is transmitted to the paper feed drive transmission gear 76, and the paper feed drive transmission gear 76 rotates in the opposite direction to the input gear 59.

  When the paper feed drive transmission gear 76 rotates, the swing gear 77 rotates integrally with the paper feed drive transmission gear 76. At this time, since the rotation of the internal gear 78 is restricted by the locking claw 94 of the stopper arm 80, the swinging gear 77 engages the internal teeth while engaging the external teeth 85 with the internal teeth 89 of the internal gear 78. Rolls on the inner circumference of the gear 78. As the internal gear 78 rolls, the transmission gear 79 connected to the swing gear 77 via the elastic piece 92 causes the internal teeth 89 of the internal gear 78 and the external teeth of the swing gear 77 to move. It rotates around the rotation shaft 81 at a speed reduced according to the difference in the number of teeth from 85. When the transmission gear 79 rotates, the lever drive gear 61 meshing with the transmission gear 79 rotates in the opposite direction to the transmission gear 79, and the lever shaft 18 rotates together with the lever drive gear 61. As a result, the lever 17 attached to the lever shaft 18 rotates so as to lift the rear end portion thereof, and the front end portion of the paper pressing plate 15 is lifted so as to be close to the pickup roller 12.

  In this way, the front end of the paper pressing plate 15 is lifted, and after the paper 3 placed on the paper pressing plate 15 comes into contact with the pickup roller 12, the front end of the paper pressing plate 15 is further lifted by the lever 17. Then, the pickup roller 12 is pushed up by the paper 3. Then, the swing box 67 is rotated so that the rear side is lifted with the paper feed roller shaft 64 as a fulcrum. As the swing box 67 is rotated, the operation arm 74 is lifted and the stopper arm 80 is moved. Abuts the lower end surface.

  Thereafter, when the front end portion of the sheet pressing plate 15 is further lifted, the operation arm 74 rotates the stopper arm 80 in the direction in which the locking claw 94 is lifted upward with the support shaft 93 as a fulcrum. Then, the locking claw 94 is detached from the locked portion 90 of the internal gear 78, and the internal gear 78 becomes rotatable.

  When the internal gear 78 becomes rotatable, the rotational driving force of the swing gear 77 is transmitted from the external teeth 85 to the internal teeth 89 of the internal gear 78, and the internal gear 78 is transferred to the cylinder of the paper feed drive transmission gear 76. Rotate around the part 82. Therefore, rolling of the swing gear 77 on the inner periphery of the internal gear 78 stops. When the rotation of the rocking gear 77 stops, the transmission gear 79 stops rotating along with this, and the rotation of the lever driving gear 61 and the lever shaft 18 also stops. As a result, the lever 17 stops, the lifting operation of the paper pressing plate 15 by the lever 17 is stopped, and the paper pressing plate 15 stops at the transport position. Accordingly, it is possible to prevent the driving force from being input to the lever 17 subsequently after the movement of the paper pressing plate 15 to the placement position is completed. Therefore, the paper pressing plate 15 can be reliably stopped at the transport position.

  The rotational driving force input to the input gear 59 is transmitted to the paper feed roller shaft 64 via the paper feed drive transmission gear 76 and the paper feed roller drive gear 65 when the paper feed clutch 111 is on. The As a result, the paper feed roller 10 and the pickup roller 12 rotate, and the uppermost paper 3 on the paper pressing plate 15 is picked up by the pickup roller 12 and sent out.

  As the number of sheets 3 placed on the sheet pressing plate 15 decreases, the sheet pressing plate 15 is lowered from the transport position, and the swing box 67 is moved downward with the sheet feeding roller shaft 64 as a fulcrum. Rotate to sink. When the operation arm 74 is lowered to a predetermined position along with the rotation of the swing box 67, the locking claw 94 of the stopper arm 80 is locked to the locked portion 90 of the internal gear 78, and the internal gear The rotation of 78 is again restricted. Then, as described above, the rotational driving force input to the input gear 59 is transmitted to the lever driving gear 61 via the swing gear 77 and the like, and the paper pressing plate 15 is lifted to the transport position by the lever 17. It is done. Thereby, regardless of the weight of the paper 3 placed on the paper pressing plate 15, the position of the paper pressing plate 15 can be kept at the transport position, and the paper 3 on the paper pressing plate 15 is moved to the pickup roller 12. It can be pressed with a substantially constant pressing force.

  FIG. 6 is a diagram schematically showing a gear transmission mechanism for transmitting the rotational driving force to the photosensitive drum 29 and the paper feed driving unit 58. This gear transmission mechanism is provided in the main body casing 2, and is relative to the motor gear 97 externally fitted to the output shaft 96 of the main motor 95 as the first drive source so as not to rotate relative to the drum shaft 35 of the photosensitive drum 29. A drum gear 98 that is rotatably supported and is provided so as not to rotate relative to the drum main body 34, an intermediate gear group 99 having one end meshed with the motor gear 97 and the other end meshed with the drum gear 98, and an input of the paper feed drive unit 58. An output gear 100 that meshes with the gear 59 and a transmission gear train 102 that is connected in a line by meshing a plurality of transmission gears 101 are provided.

  In the transmission gear train 102, the transmission gear 101 at one end meshes with the motor gear 97, and the transmission gear 101 at the other end meshes with the output gear 100. As a result, when the main motor 95 is driven and the motor gear 97 rotates together with the output shaft 96, the rotational driving force of the motor gear 97 is transmitted to the output gear 100 via the transmission gear train 102, and output. The gear 100 is rotated. When the output gear 100 is rotated, a rotational driving force is input from the output gear 100 to the input gear 59.

  On the other hand, the rotational driving force of the motor gear 97 is transmitted to the drum gear 98 via the intermediate gear group 99, and the drum gear 98 is rotated about the drum shaft 35 as a fulcrum. When the drum gear 98 rotates, the drum main body 34 rotates integrally with the drum gear 98 around the drum shaft 35.

  FIG. 7 is a block diagram showing an electrical configuration of the laser printer 1. The laser printer 1 includes a CPU 103 as control means and determination means.

  The CPU 103 includes a ROM 104 and a RAM 105. The ROM 104 stores an operation program for the laser printer 1. The RAM 105 functions as a work area when the CPU 103 executes the operation program stored in the ROM 104 and stores temporary numerical values.

  A registration sensor 106 is connected to the CPU 103, and a detection signal of the registration sensor 106 is input. The CPU 103 receives a print activation instruction signal for instructing the start of a printing operation for forming an image on the paper 3 from an external device (for example, a personal computer PC) connected to the laser printer 1.

  On the other hand, the CPU 103 has a main drive circuit 107 for driving the main motor 95, a scanner drive circuit 109 for driving the scanner motor 108, and a high voltage for generating a high voltage for applying a transfer bias and a cleaning bias. A power supply circuit 110 and a paper feed clutch 111 are connected as control targets.

  Connected to the high-voltage power supply circuit 110 are a transfer bias circuit 112 as a transfer bias applying means for applying a bias to the transfer roller 32 and a cleaning bias circuit 113 for applying a cleaning bias to the cleaning brush 33. .

  The CPU 103 controls the bias applied from the transfer bias circuit 112 to the transfer roller 32 by controlling the high voltage power supply circuit 110 and the transfer bias circuit 112. Specifically, the transfer roller 32 is selectively provided with a transfer forward bias for transferring the toner image onto the paper 3 and a transfer reverse bias for transferring the toner attached to the transfer roller 32 to the photosensitive drum 29. Applied.

  Further, the CPU 103 controls the cleaning bias applied from the cleaning bias circuit 113 to the cleaning brush 33 by controlling the high-voltage power supply circuit 110 and the cleaning bias circuit 113.

  Further, the CPU 103 controls the drive of the main motor 95 via the main drive circuit 107. The rotational driving force generated by the main motor 95 by this control rotates the photosensitive drum 29 as described above. Further, the rotational driving force generated by the main motor 95 is input to the paper feed drive unit 58 to drive the paper pressing plate 15 (lever 17), and through the paper feed clutch 111, the paper feed roller 10 and the pickup roller. 12 is driven. Further, as described above, the rotational driving force generated by the main motor 95 is also transmitted to the supply roller 40, the developing roller 41, the transfer roller 32, and the heating roller 49 to rotate them.

  Further, the CPU 103 controls driving of the scanner motor 108 via the scanner driving circuit 109.

  FIG. 8 is a flowchart showing the flow of control from the input of the print activation instruction signal to the CPU 103 until the feeding of the paper 3 is started. FIG. 9 is a time chart showing the operation timing of each part during the control.

  When a print activation instruction signal is input to the CPU 103, the processing shown in FIG. 8 is started. First, the driving of the scanner motor 108 is started under the control of the CPU 103 (S1). If the scanner motor 108 is not driven at a stable speed when the electrostatic latent image is formed on the photosensitive drum 29, the polygon mirror 22 is unevenly rotated, and the electrostatic latent image formed on the photosensitive drum 29 is distorted. And so on. Therefore, the electrostatic latent image is formed on the photosensitive drum 29 from the start of the drive of the scanner motor 108 until the scanner motor 108 is driven at a stable speed to reach a scan start speed at which the laser beam can be stably scanned. This is performed after the necessary and sufficient scanning preparation time t1 has elapsed (see FIG. 9).

  Next, the CPU 103 determines whether or not to execute the low speed control for moving the paper pressing plate 15 from the placement position to the transport position at a low speed (S2). Specifically, as shown in FIG. 10, if it is immediately after cancellation of the paper-free state in which the paper 3 is not placed on the paper pressing plate 15 (S21: YES), it is determined that the low speed control is executed (S21: YES). S25). Also, when it is immediately after the jam state of the sheet 3 is released (S22: YES), it is determined that the low speed control is executed (S25). On the other hand, if it is immediately after the stirring operation (warming) for warming up by the agitator 44 (within a predetermined time after swirling) (S23: YES), it is determined that the low speed control is not performed (S26). Also, when it is immediately after the end of the previous printing operation (for example, within 3 seconds from the end of the previous printing operation) (S24: YES), it is determined that the low speed control is not executed (S26).

  Since the paper out state is canceled by placing the paper 3 on the paper pressing plate 15, it is determined that the paper pressing plate 15 is located at the mounting position immediately after the paper out state is released. can do. When the paper 3 is jammed, the paper feed tray 9 is detached from the main casing 2 and the jammed paper 3 is removed, so that the jammed state of the paper 3 is released. Immediately after the release of the jam state 3, it can be determined that the sheet pressing plate 15 is located at the placement position.

  On the other hand, since the stirring operation for warming up by the agitator 44 is performed immediately before the conveyance of the sheet 3 is started, it is determined that the sheet pressing plate 15 is located at the conveyance position within a predetermined time after the stirring operation. can do. Further, since the paper pressing plate 15 is not moved from the transport position to the placement position in a short time after the printing operation is finished, the placement member is positioned at the transportation position within a predetermined time after the printing operation is finished. Can be determined. If the paper pressing plate 15 is located at the transport position, there is no need to move the paper pressing plate 15 from the placement position to the transport position, so the paper press plate 15 is moved from the placement position to the transport position at a low speed. It is determined not to execute the low speed control for the purpose. As a result, it is possible to avoid the low speed control from being executed until it is not necessary to move the paper pressing plate 15.

  Further, when it is not within the predetermined time (immediately after) after the stirring operation for warming up by the agitator 44 (S23: NO), and when it is not within the predetermined time after the end of the previous printing operation (S24: YES), the speed is low It is determined to execute control (S25).

  When the low speed control is not executed (S2: NO), after waiting for a predetermined time t2 (see FIG. 9, for example, t2 = 2.7 seconds) from the start of driving of the scanner motor 108 (S3), the CPU 103 controls The main motor 95 is rotationally driven at a first motor speed (normal motor speed) as a first drive speed that is a rotational speed at the time of transporting the paper 3 (S4). The standby time t2, that is, the drive start time of the main motor 95 that is rotationally driven at the first motor speed is set based on a sheet feed timing t10 described later. Then, the count-up speed in the timer counter using the RAM 105 is set to a predetermined first count speed (normal count speed) (S5), and the elapsed time from the start of driving of the main motor 95 is measured by this timer counter. The

  On the other hand, when executing the low speed control (S2: YES), after waiting for a predetermined time t3 (see FIG. 9, 0 ≦ t3 <t2) from the start of the driving of the scanner motor 108 (S6), The main motor 95 is rotationally driven at a second motor speed as a second drive speed that is slower than the first motor speed (S7). The standby time t3, that is, the drive start time of the main motor 95 that is rotationally driven at the second motor speed is set based on a sheet feed timing t10 described later. Then, the count-up speed in the timer counter using the RAM 105 is set to a second count speed that is slower than the first count speed (S8), and the elapsed time from the start of driving of the main motor 95 is measured by this timer counter. .

  At this time, the paper feed clutch 111 is turned off, and even if the main motor 95 is rotationally driven at the first motor speed or the second motor speed, the rotational driving force from the main motor 95 is The paper is not transmitted to the pickup roller 12, and the paper feed roller 10 and the pickup roller 12 are not rotated.

  The second count speed is set to a speed that is decelerated from the first count speed in accordance with the deceleration rate of the second motor speed with respect to the first motor speed. For example, when the second motor speed is set to ½ of the first motor speed, the second count speed is set to ½ of the first count speed. As a result, during the period in which the timer counter counts up to a predetermined number of counts at the first count speed, the amount of rotation (drive amount) of the main motor 95 driven at the first motor speed, and the timer counter at the second count speed. During the period of counting up to the same count, the amount of rotation of the main motor 95 driven at the second motor speed is the same.

  When the main motor 95 is driven to rotate at the second motor speed, the input gear 59 of the paper feed drive unit 58 rotates at a lower speed than when the main motor 95 is driven to rotate at the first motor speed. As the input gear 59 rotates at a low speed, the lever drive gear 61 and the lever shaft 18 rotate at a low speed. For this reason, the lever 17 can slowly lift the front end of the paper pressing plate 15 and move the paper pressing plate 15 from the loading position to the transport position at a low speed. As a result, the sheet 3 on the sheet pressing plate 15 is slowly pressed by the pickup roller 12, so that the sheet pressing plate 15 is accurately stopped at the transport position where the sheet 3 can be favorably picked up by the pickup roller 12. Can be made.

  After starting the driving of the main motor 95, pre-process processing such as transfer cleaning processing and drum cleaning processing is performed at each timing according to the count-up speed of the timer counter (driving speed of the main motor 95) (S9).

  That is, when the count-up speed of the timer counter is the first count speed, as indicated by a two-dot chain line in FIG. 9, when a predetermined time t4 has elapsed from the start of driving of the scanner motor 108, the CPU 103 controls the cleaning brush 33. Application of the cleaning bias is started. On the other hand, when the count-up speed of the timer counter is the second count speed, as shown by the solid line in FIG. 9, the cleaning is performed when a time t5 shorter than the predetermined time t4 has elapsed from the start of driving of the scanner motor 108. Application of a cleaning bias to the brush 33 is started.

  When the count-up speed of the timer counter is the second count speed, the main motor 95 is driven to rotate at the second motor speed, and the photosensitive drum 29 is rotated as compared with the case where the main motor 95 is driven to rotate at the first motor speed. Since the rotation is slow, if the cleaning bias is applied at the same timing as when the main motor 95 is driven to rotate at the first motor speed, the cleaning of the photosensitive drum 29 can be completed by the paper feed timing t10 described later. Can not. Therefore, when the count-up speed of the timer counter is the second count speed, the timing for starting the application of the cleaning bias to the cleaning brush 33 is earlier than when the count-up speed is the first count speed. As a result, the cleaning of the photosensitive drum 29 can be completed by the paper feed timing t10 described later regardless of whether the driving speed of the main motor 95 is the first motor speed or the second motor speed. Therefore, reliable formation of an electrostatic latent image on the photosensitive drum 29 can be achieved.

  Further, when the count-up speed of the timer counter is the first count speed, as shown by a two-dot chain line in FIG. 9, when a predetermined time t6 has elapsed from the start of driving of the scanner motor 108, the CPU 103 controls the transfer roller 32 to On the other hand, a reverse transfer bias is applied for a predetermined time t8. On the other hand, when the count-up speed of the timer counter is the second count speed, the driving of the scanner motor 108 is started as shown by the solid line in FIG. 9 for the same reason as in the case of applying the cleaning bias to the cleaning brush 33. When a time t7 shorter than the predetermined time t6 has elapsed, a reverse transfer bias is applied to the transfer roller 32 for a predetermined time t9 longer than the predetermined time t8. As a result, regardless of whether the driving speed of the main motor 95 is the first motor speed or the second motor speed, the toner adhering to the transfer roller 32 is transferred to the photosensitive drum 29 by the paper feed timing t10 described later. The transfer roller 32 can be cleaned by applying a reverse transfer bias. Therefore, stable transfer of the toner image onto the paper 3 can be achieved.

  In addition, when a transfer reverse bias is applied to the transfer roller 32, it is not possible to transfer the toner charged with the reverse polarity to that of the transfer of the toner image onto the paper 3 from the transfer roller 32 to the photosensitive drum 29. The charged toner is transferred from the transfer roller 32 to the photosensitive drum 29 and removed from the surface of the transfer roller 32 at an initial stage when a transfer forward bias is applied to the transfer roller 32. The transfer forward bias is applied to the transfer roller 32 after a paper feed timing t10 described later. As a result, it is possible to prevent the transfer forward bias from being applied to the transfer roller 32 for a long time and to improve the durability of the transfer roller 32.

  Even if the main motor 95 is driven to rotate at the second motor speed after the driving of the main motor 95 is started, a time sufficient for the sheet pressing plate 15 to move from the loading position to the transport position (for example, 1.2 seconds) ) Elapses, the count-up speed of the timer counter is set to the first count speed (S10), and at the same time, the driving speed of the main motor 95 is set to the first motor speed (S11). Thereby, after the paper feed timing t10, the main motor 95 is driven at the first motor speed. If the low speed control is not executed, the drive at the first motor speed of the main motor 95 is already started in the above step (S4), and the timer counter count is started in the above step (S5). Since the up speed is set to the first count speed, no particular changes are made to the drive speed of the main motor 95 and the count up speed of the timer counter in the steps (S10, S11) at this time.

  Thereafter, the CPU 103 obtains the transfer timing of the toner image from the photosensitive drum 29 to the paper 3 based on the scanning preparation period t1, and the transfer of the paper 3 between the photosensitive drum 29 and the transfer roller 32 by this transfer timing. Based on a time t11 (see FIG. 9) until the sheet 3 reaches the registration roller 14 from the sheet pressing plate 15 so as to reach the position, a sheet feeding timing t10 for starting feeding of the sheet 3 is set. . When the paper feed timing t10 comes (S12: YES), the paper feed clutch 111 is switched from OFF to ON (S13). As a result, the rotational driving force from the main motor 95 is transmitted to the pickup roller 12, and the uppermost sheet 3 on the sheet pressing plate 15 is picked up by the pickup roller 12 and sent out by the rotation of the pickup roller 12.

  At this time, since the sheet 3 on the sheet pressing plate 15 is pressed against the pickup roller 12 with a substantially constant pressing force, the uppermost sheet 3 on the sheet pressing plate 15 is removed without causing double feeding or idle feeding. Can be sent out. In the configuration in which the paper 3 on the paper pressing plate 15 is pressed against the pickup roller 12 with a substantially constant pressing force, the paper pressing plate 15 slightly swings every time the paper 3 is picked up by the pickup roller 12. Therefore, it is possible to reduce noise during continuous feeding of the paper 3.

  In this laser printer 1, the rotational driving force of the main motor 95 is input to both the photosensitive drum 29 and the paper pressing plate 15 (lever 17), and the main motor 95 drives the photosensitive drum 29 and the paper pressing plate 15. Therefore, an increase in apparatus cost can be suppressed.

  Further, since the sheet pressing plate 15 is moved at a low speed from the placement position to the conveying position by the low speed control, the sheet pressing plate 15 can be accurately stopped at the conveying position without shortening the life of the photosensitive drum 29.

  That is, if the gear ratio of the lever drive gear 61 to the motor gear 97 is increased in order to move the paper pressing plate 15 at a low speed, the main motor 95 required to move the paper pressing plate 15 from the loading position to the transport position. As the driving amount increases, the driving amount of the photosensitive drum 29 driven by the driving force of the main motor 95 increases accordingly. Since the photosensitive drum 29 deteriorates as the driving amount increases, increasing the gear ratio causes a problem that the life of the photosensitive drum 29 is shortened. On the other hand, the driving amount of the photosensitive drum 29 during the movement period of the paper pressing plate 15 remains unchanged even if the moving speed of the paper pressing plate 15 is lowered by reducing the driving speed of the main motor 95. Therefore, the moving speed of the paper pressing plate 15 can be reduced without shortening the life of the photosensitive drum 29, and the paper pressing plate 15 can be stopped at the transport position with high accuracy.

  Further, as described above, regardless of whether or not the low speed control is executed, the transfer timing is set based on the scanning preparation period t1, the paper feed timing t10 is set based on the transfer timing, and this The drive start times t2 and t3 of the main motor 95 are set based on the paper feed timing t10, and the drive start timings t2 and t3 of the main motor 95 are set after the drive of the scanner motor 108 is started. Even in the case of execution, without delaying the transfer timing, the image formation time from the start of driving the scanner motor 108 to the transfer of the toner image onto the paper 3 can be made the same as when the low speed control is not performed. Therefore, it is possible to avoid an increase in the image forming time due to the low speed control.

  Further, after waiting for a predetermined time t2 or a predetermined time t3 from the start of driving of the scanner motor 108, the main motor 95 is started to drive, whereby the drive start timing of the main motor 95 and the drive start timing of the scanner motor 108 are shifted. Therefore, it is possible to avoid applying a large load to a power supply unit (not shown) for supplying power to the main motor 95 and the scanner motor 108. Therefore, power can be stably supplied from the power supply unit to the main motor 95 and the scanner motor 108. As a result, the main motor 95 and the scanner motor 108 can be driven stably.

  FIG. 11 is a block diagram showing an embodiment of the present invention of the laser printer 1. 11, portions corresponding to the respective portions shown in FIG. 7 described above are denoted by the same reference numerals as those in FIG. 7, and detailed description thereof will be omitted below.

  In the laser printer 1, a drum clutch 115 serving as a switching unit including an electromagnetic clutch is interposed in the intermediate gear group 99 (see FIG. 6), and this drum clutch 115 is connected to the CPU 103 as a control target. . The CPU 103 controls on / off of the drum clutch 115 according to the operation program stored in the ROM 104, and thereby controls transmission and disconnection of the rotational driving force of the motor gear 97 to the drum gear 98.

  In this laser printer 1, the gear ratio of the lever drive gear 61 to the motor gear 97 is set higher than the gear ratio of the lever drive gear 61 to the motor gear 97 in the laser printer 1 of the above-described reference example. As a result, even when the main motor 95 is driven to rotate at the first motor speed, the sheet pressing plate 15 is moved at a low speed from the placement position to the transport position, similarly to the case where it is driven at the second motor speed.

  FIG. 12 is a flowchart showing the flow of control from the input of a print start instruction signal to the CPU 103 to the start of conveyance of the paper 3 in the laser printer 1 of this embodiment. FIG. 13 is a time chart showing the operation timing of each part during the control.

  When a print activation instruction signal is input to the CPU 103, the processing shown in FIG. 12 is started. First, the driving of the scanner motor 108 is started under the control of the CPU 103 (S31).

  Next, the CPU 103 determines whether or not it is necessary to move the paper pressing plate 15 from the placement position to the transport position (S32). This determination process is the same as the low speed control determination process (see FIG. 10) for determining whether or not to perform the low speed control in the reference example.

  That is, immediately after the release of the paper-out state, it is determined that the paper pressing plate 15 needs to be moved to the transport position, assuming that the paper pressing plate 15 is located at the placement position. Further, even immediately after the jammed state of the sheet 3 is released, it is determined that the sheet pressing plate 15 needs to be moved to the transport position, assuming that the sheet pressing plate 15 is positioned at the loading position. On the other hand, if it is immediately after the stirring operation for warming up by the agitator 44, it is determined that it is not necessary to move the paper pressing plate 15 because the paper pressing plate 15 is already in the transport position. Even immediately after the end of the previous printing operation, it is determined that it is not necessary to move the paper pressing plate 15 because the paper pressing plate 15 is already positioned at the transport position.

  When it is not necessary to move the paper pressing plate 15 (S32: NO), that is, when the paper pressing plate 15 is already positioned at the transport position, a predetermined time t2 from the start of driving of the scanner motor 108 (see FIG. 13). For example, after waiting for t2 = 2.7 seconds (S33), the main motor 95 is rotationally driven at the first motor speed under the control of the CPU 103 (S34). Simultaneously with the start of driving of the main motor 95, the drum clutch 115 is turned on (S39), so that the rotational driving force of the main motor 95 can be transmitted to the drum gear 98.

  On the other hand, when it is necessary to move the paper pressing plate 15 (S32: YES), after waiting for a predetermined time t3 (see FIG. 13, 0 ≦ t3 <t2) from the start of the driving of the scanner motor 108 (S35), Under the control of the CPU 103, the drum clutch 115 is not turned on and is turned off (S36), that is, the state in which the rotation driving force from the main motor 95 is not transmitted to the drum gear 98 is maintained, and the main motor 95 is in the first state. It is rotationally driven at the motor speed (S37).

  When the main motor 95 is driven to rotate, the rotational driving force of the main motor 95 is transmitted to the paper feed drive unit 58, and the front end of the paper pressing plate 15 is slowly lifted by the lever 17, so that the paper pressing plate 15 Is moved from the placement position to the transport position at a low speed. As a result, the sheet 3 on the sheet pressing plate 15 is slowly pressed against the pickup roller 12.

  At this time, the paper feed clutch 111 is turned off, and even if the main motor 95 is rotationally driven at the first motor speed or the second motor speed, the rotational driving force from the main motor 95 is The paper is not transmitted to the pickup roller 12, and the paper feed roller 10 and the pickup roller 12 are not rotated.

  When a predetermined time t2 has elapsed from the start of driving of the scanner motor 108 (S38: YES), at the same time, the drum clutch 115 is turned on (S39), and the rotational driving force of the main motor 95 is transmitted to the drum gear 98. .

  After the drum clutch 115 is switched on, pre-process processes such as a transfer cleaning process and a drum cleaning process are performed at each timing (S40).

  That is, when a predetermined time t4 (see FIG. 13) elapses from the start of driving of the scanner motor 108, application of the cleaning bias to the cleaning brush 33 is started under the control of the CPU 103. When a predetermined time t6 has elapsed since the start of driving of the scanner motor 108, a transfer reverse bias is applied to the transfer roller 32 over a predetermined time t8 (see FIG. 13) under the control of the CPU 103.

  At predetermined times t4 and t6, the CPU 103 determines the transfer timing of the toner image from the photosensitive drum 29 to the sheet 3 based on the scanning preparation period t1, and the sheet 3 is transferred to the photosensitive drum 29 by this transfer timing. Based on the time t11 until the sheet 3 reaches the registration roller 14 from the sheet pressing plate 15 so as to reach the transfer position with the roller 32, the sheet feeding timing t10 at which the feeding of the sheet 3 is started is set. Further, the transfer cleaning process and the drum cleaning process are set to be completed by the paper feed timing t10. Accordingly, the cleaning of the photosensitive drum 29 can be completed by the paper feeding timing t10. Therefore, reliable formation of an electrostatic latent image on the photosensitive drum 29 can be achieved. Also, the toner adhering to the transfer roller 32 can be transferred to the photosensitive drum 29 by the paper feed timing t10, and the cleaning of the transfer roller 32 by applying a reverse transfer bias can be achieved. Therefore, stable transfer of the toner image onto the paper 3 can be achieved.

  Thereafter, when the paper feed timing t10 comes (S41: YES), the CPU 103 switches on the paper feed clutch 111 (S42). As a result, the rotational driving force from the main motor 95 is transmitted to the pickup roller 12, and the uppermost sheet 3 on the sheet pressing plate 15 is picked up by the pickup roller 12 and sent out by the rotation of the pickup roller 12.

  The transfer forward bias is applied to the transfer roller 32 after the paper feed timing t10. As a result, it is possible to prevent the transfer forward bias from being applied to the transfer roller 32 for a long time and to improve the durability of the transfer roller 32.

  As described above, in the laser printer 1 of this embodiment, when the paper pressing plate 15 is moved from the placement position to the transport position, the drum clutch 115 is turned off for a predetermined period after the driving of the main motor 95 is started. Continued, the photosensitive drum 29 is not driven. Thereby, deterioration due to driving of the photosensitive drum 29 can be suppressed, and the life of the photosensitive drum 29 can be extended.

  In this process, the transfer timing is set based on the scanning preparation period t1, the paper feed timing t10 is set based on the transfer timing, and the drum clutch 115 is turned on based on the paper feed timing t10. By setting the timing and setting the driving start timing of the main motor 95 after starting the driving of the scanner motor 108, the driving of the scanner motor 108 is started without delaying the transfer timing even when the paper pressing plate 15 is moved. The image formation time from the transfer of the toner image to the paper 3 can be made the same as when the paper thick plate 15 is not moved. Therefore, it is possible to avoid an increase in image formation time.

  Further, in this laser printer 1 as well, when the main motor 95 is started after waiting for the predetermined time t2 or the predetermined time t3 from the start of driving of the scanner motor 108, the drive start timing of the main motor 95 and the scanner motor 108 are started. Therefore, it can be avoided that a large load is applied to a power supply unit (not shown) for supplying power to the main motor 95 and the scanner motor 108. Therefore, power can be stably supplied from the power supply unit to the main motor 95 and the scanner motor 108. As a result, the main motor 95 and the scanner motor 108 can be driven stably.

  As indicated by phantom lines in FIG. 1, a tray presence / absence sensor 114 as a detecting means for detecting whether or not the paper feed tray 9 is mounted on the main body casing 2 is disposed in the main body casing 2, and FIG. As indicated by a virtual line, the detection signal of the tray presence / absence sensor 114 is input to the CPU 103 so that the low speed control determination process shown in FIG. 14 is performed instead of the low speed control determination process shown in FIG. Also good. The tray presence / absence sensor 114 detects attachment of the paper feed tray 9 to the main body casing 2 by contacting the rear end portion of the main body casing 2 when the paper feed tray 9 is attached to the main body casing 2, for example. The contact type sensor can be configured.

  In the low-speed control determination process shown in FIG. 14, the paper feed tray 9 is not detached from the main body casing 2 after the previous printing operation, and the tray presence sensor 114 continues to detect the attachment of the paper feed tray 9 to the main body casing 2. (S51: NO), it is determined not to execute the low speed control (S52).

  When the paper 3 is placed on the paper pressing plate 15, the paper feeding tray 9 is detached from the main body casing 2, so that the paper pressing plate 15 is kept in place while the paper feeding tray 9 continues to be attached to the main body casing 2. It can be determined that it is located at the transfer position. If the paper pressing plate 15 is located at the transport position, it is not necessary to move the paper pressing plate 15 from the placement position to the transport position, so it can be determined that the low speed control is not performed.

  On the other hand, when the separation of the paper feed tray 9 with respect to the main body casing 2 is detected by the tray presence / absence sensor 114 after the previous printing operation (S51: YES), the paper pressing plate 15 is moved by the separation of the paper feed tray 9. Since it has been moved to the mounting position, it is determined that the low speed control is to be executed (S53).

  Further, as indicated by phantom lines in FIG. 2, as a position detection means for detecting that the paper pressing plate 15 is located at the transport position in a state where the paper feed tray 9 is mounted on the main casing 2. 10 is arranged in the main casing 2 so that the detection signal of the pressure plate position sensor 116 is input to the CPU 103 as indicated by a virtual line in FIG. Instead of this, the low speed control determination process shown in FIG. 15 may be performed. Note that the pressure plate position sensor 116 can be constituted by, for example, a light projecting element and a light receiving element that are arranged so that the optical path is blocked when the paper pressing plate 15 is located at the placement position.

  In the low speed control determination process shown in FIG. 15, when the pressure plate position sensor 116 detects that the paper pressing plate 15 is located at the transport position (S61: YES), the paper pressing plate 15 is placed at the loading position. Therefore, it is determined that the low speed control is not executed (S62). On the other hand, when the pressure plate position sensor 116 does not detect that the paper pressing plate 15 is positioned at the transport position, that is, when the paper pressing plate 15 is not positioned at the transport position (S61: NO), It is determined that the low speed control is to be executed (S63).

  As described above, it is more accurately determined whether or not it is necessary to execute the low speed control by accurately detecting whether or not the sheet pressing plate 15 is located at the transport position by the dedicated pressure plate position sensor 116. be able to.

  Further, as indicated by a virtual line in FIG. 11, the detection signal of the tray presence sensor 114 or the pressure plate position sensor 116 is input to the CPU 103, and in the determination step (S32) shown in FIG. A process similar to the low speed determination process shown in FIG.

It is a principal part side sectional view showing a reference example of a laser printer as an image forming device. FIG. 2 is a plan view of the paper feed tray shown in FIG. 1. FIG. 2 is a perspective view of a paper feed drive unit provided in the main body casing shown in FIG. 1 and its periphery. It is sectional drawing of the drive transmission mechanism shown in FIG. It is sectional drawing which shows the state in which rotation of the internal gear shown in FIG. 3 is controlled by the latching claw of a stopper arm. FIG. 4 is a diagram schematically showing a gear transmission mechanism for transmitting a rotational driving force to the photosensitive drum shown in FIG. 1 and the paper feed driving unit shown in FIG. 3. FIG. 2 is a block diagram showing an electrical configuration of the laser printer shown in FIG. 1. FIG. 8 is a flowchart showing a control flow from the input of a print activation instruction signal to the CPU shown in FIG. 7 to the start of paper feeding. It is a time chart which shows the operation timing of each part at the time of control shown in FIG. It is a flowchart which shows the low speed control judgment process which judges whether CPU shown in FIG. 7 performs low speed control. 1 is a block diagram showing an embodiment (a mode in which a drum clutch is provided) of a laser printer of the present invention. FIG. 12 is a flowchart showing a control flow from the input of a print activation instruction signal to a CPU to the start of paper conveyance in the laser printer shown in FIG. 11. 13 is a time chart showing the operation timing of each part during the control shown in FIG. It is a flowchart which shows the other aspect (Aspect judged based on the detection signal of a tray presence sensor) of the low speed control judgment process shown in FIG. It is a flowchart which shows the other aspect (Aspect judged based on the detection signal of a pressure plate position sensor) of the low speed control judgment process shown in FIG.

DESCRIPTION OF SYMBOLS 1 Laser printer 3 Paper 9 Paper feed tray 12 Pickup roller 15 Paper press plate 17 Lever 22 Polygon mirror 32 Transfer roller 33 Cleaning brush 39 Toner storage chamber 44 Agitator 62 Drive transmission mechanism 95 Main motor 103 CPU
108 Scanner motor 112 Transfer bias circuit 114 Tray presence sensor 115 Drum clutch 116 Pressure plate position sensor

Claims (9)

A first drive source;
A photoreceptor to which a driving force from the first driving source is input;
A recording medium that is transported toward the photosensitive member, and a mounting member that is movable to a mounting position for mounting the recording medium and a transport position for transporting the recording medium;
A driving mechanism that receives a driving force from the first driving source and moves the mounting member from the mounting position to the transport position;
A switching means provided in the middle of an input path of driving force from the first driving source to the photoconductor, for switching between transmission and interruption of the driving force transmitted from the first driving source to the photoconductor;
Determining means for determining whether or not the mounting member is located at the transport position;
When the determination unit determines that the placement member is not located at the transport position, the switching unit is controlled so that the drive member moves the placement member from the placement position to the transport position. An image forming apparatus comprising: a control unit that cuts off a driving force transmitted from the first driving source to the photosensitive member for at least a predetermined period of time during which the driving force is moved.   The determination unit determines that the placement member is located at the transport position within a predetermined time after the end of an image forming operation for forming an image on a recording medium. The image forming apparatus described in 1. A tray that is detachably attached to the image forming apparatus and that accommodates the mounting member;
Detecting means for detecting attachment and detachment of the tray with respect to the image forming apparatus,
The determination unit determines that the placement member is located at the transport position while the detection unit detects that the tray is mounted on the image forming apparatus. The image forming apparatus according to 1 or 2. Comprising a position detecting means for detecting that the placing member is located at the transport position;
The determination means determines that the placement member is located at the transport position when the position detection means detects that the placement member is located at the transport position. The image forming apparatus according to claim 1, wherein the image forming apparatus is characterized in that: A second drive source;
An optical member that is driven by the second drive source and scans the photosensitive member with a laser beam to form an electrostatic latent image;
The photoreceptor carries a developer image formed by developing an electrostatic latent image,
The control means is configured to start from the photosensitive member based on a scanning preparation period from the start of driving of the second drive source until the drive speed reaches a scan start speed at which the optical member can scan laser light. Set the transfer timing to transfer the developer image to the recording medium,
By setting the conveyance start timing of the recording medium so that the recording medium placed on the mounting member is conveyed to the photoconductor by the transfer timing,
5. The driving force is transmitted from the first driving source to the photosensitive member by controlling the switching unit within the scanning preparation period and before the conveyance start timing. 6. An image forming apparatus according to claim 1.   The image forming apparatus according to claim 5, wherein the control unit sets the drive start timing of the first drive source at a timing different from the drive start timing of the second drive source. Transfer means for transferring the developer image formed on the photoreceptor to a recording medium;
A transfer bias applying means capable of selectively applying a transfer bias and a transfer cleaning bias having a reverse polarity to the transfer bias to the transfer means;
The control unit applies the transfer cleaning bias to the transfer unit by the transfer bias applying unit and completes a cleaning process for cleaning the transfer unit within the scanning preparation period and before the conveyance start timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   8. The image forming apparatus according to claim 7, wherein the control unit starts application of the transfer bias to the transfer unit by the transfer bias application unit at the same time as or after the conveyance start timing. . A cleaning means for cleaning the photoconductor by applying a photoconductor cleaning bias;
9. The control unit according to claim 5, wherein the control unit starts applying the photosensitive member cleaning bias to the cleaning unit before the conveyance start timing within the scanning preparation period. 10. Image forming apparatus.