JP2007271681A - Image forming apparatus with variable nip pressure of fixation part based on width of paper sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that an image forming apparatus with the nip pressure of a fixation part, variable based on the width of a paper sheet, becomes expensive on the whole since a highly accurate thickness sensor is needed to discriminate a difference in paper sheet thickness in a known method of automatically changing fixation conditions by measuring the thickness of the paper sheet to discriminate between regular paper and an envelope, since the nip pressure as one of fixation conditions of the fixation part needs to manually be varied heretofore according to which of the regular paper and envelope is printed, and the operation for that is complicated. <P>SOLUTION: The present invention utilizes the fact that a standard-size envelope for standard-size regular paper has a size larger than the standard-size regulator paper and their difference is much larger than the difference in thickness. The present invention provides the image forming apparatus having a mechanism which discriminates the width of the paper sheet at the position of a paper sheet guide guiding the paper sheet along the width and changes fixation conditions suitably for a paper sheet corresponding to the discriminated width. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of changing a nip pressure of a fixing unit based on a width of a sheet.

  In an electrophotographic image forming apparatus, it is necessary to change the nip pressure of the fixing unit between printing on plain paper and printing on an envelope.

Specifically, when printing on an envelope with a nip pressure suitable for plain paper, the nip pressure is too high and the envelope tends to wrinkle.
Conversely, when printing on plain paper with a nip pressure suitable for envelopes, the nip pressure is too low and problems such as poor fixing tend to occur.

  In order to solve such a problem, conventionally, a nip pressure adjusting lever is attached to the fixing portion, and the user manually adjusts according to “type of paper”. Therefore, a user who uses both envelopes and plain paper needs a complicated operation of switching the nip pressure every time the print target is switched between the envelope and the plain paper.

  In order to solve this problem, a method of automatically adjusting the nip pressure by determining whether the paper is an envelope or plain paper can be considered.

  Envelopes are made by folding paper into a bag shape, and there are also portions that are bonded together to form a bag, so that three or more sheets overlap partially. Moreover, since it is often made of thick paper that is stronger than plain paper, it is often twice as thick as plain paper.

  By utilizing this, it is possible to determine whether the envelope or the plain paper by measuring the paper thickness. However, it is necessary to use a highly accurate sensor in order to measure the sheet thickness, and a complicated mechanism is required to measure the thickness while eliminating the influence of sheet warping and bending. Therefore, the entire image forming apparatus tends to be expensive.

  As one method for solving this problem, the image forming apparatus described in Patent Document 1 discloses a method for estimating the sheet thickness based on the difference in sheet conveyance speed without directly measuring the thickness. .

  In the method disclosed in Patent Document 1, the distance between the rotation roller, the contact point of the sheet, and the contact point between the rollers when the pair of rotation rollers facing the sheet are in contact with each other depends on the sheet thickness. The paper thickness is determined (see FIG. 1 of Patent Document 1).

JP-A-8-87201

  By the way, in the method described in Patent Document 1, when the diameter of the rotating roller is reduced, the difference in distance between the rotating roller, the contact between the sheet and the contact between the rollers due to the thickness of the sheet is reduced, and thus it is difficult to reduce the size.

  In particular, the envelope has a rust shape that narrows toward the tip because the end portion is a fold line formed by folding paper. For this reason, there is a problem that it is difficult to detect the thickness accurately because the leading edge of the actual paper is closer to the contact between the rollers than the contact between the rotating roller and the paper.

  The object of the present invention is to solve the above problems. That is, an object of the present invention is to provide an image forming apparatus that determines the type of print medium to be printed by a small and simple mechanism and automatically adjusts the nip pressure of the fixing unit.

  More specifically, the width of the paper is measured with a paper guide, and if the measured width is the width of the standard envelope, the nip pressure of the fixing unit is changed to a value suitable for printing on the standard envelope.

  In the present invention, attention is paid to the fact that envelopes printed by a laser printer are generally regular envelopes of a size suitable for storing regular plain paper such as A4, B5, and letter size.

  If the envelope is a fixed envelope, the width is known, and instead of measuring the thickness, the width is measured. If the width is the width of the fixed envelope, it can be determined that the paper is a fixed envelope.

  Further, when comparing the regular plain paper and the regular envelope, the regular envelope is designed to have a size that can accommodate the regular plain paper.

That is, the width of the standard envelope is larger than that of the standard plain paper. In order to smoothly insert the paper into the envelope, a gap for human fingers to enter in addition to the paper width is required, so the difference in size between the standard envelope and the standard plain paper is much larger than the difference in thickness. For this reason, if the paper width is measured, it is possible to easily distinguish between the regular plain paper and the regular envelope even by a detection means that is less accurate than when detecting the paper thickness.

<Claim 1>
The image forming apparatus according to claim 1,
A fixing unit including a heating member that contacts a recording medium, a pressure member that faces the heating member, and a nip pressure generation mechanism that generates a nip pressure by pressing the heating member and the pressure member in a direction in contact with each other. When,
A controller that controls the nip pressure generating mechanism to generate a predetermined nip pressure;
An electrophotographic image forming unit for forming an image on the recording medium;
A manual feed tray for manually feeding the recording medium;
A paper guide for guiding a width direction of the recording medium supplied to the manual supply unit;
Paper guide position detecting means for detecting whether or not the paper guide is in a predetermined position;
The control unit controls the nip pressure generating mechanism to generate a first nip pressure when the position of the sheet guide detected by the sheet guide position detecting unit is the predetermined position;
The nip pressure generating mechanism is controlled to generate a second nip pressure when the paper guide position detected by the paper guide position detecting means is not the predetermined position.

<Claim 2>
An image shape forming apparatus according to claim 2 is provided.
The image forming apparatus according to claim 1.
At least one paper feed cassette holding the recording medium;
A paper feed switching unit capable of selectively selecting whether to feed from the manual feed tray or the paper feed cassette;
The control unit controls the nip pressure generating mechanism so that the nip pressure becomes the second nip pressure when the paper feed switching unit is selected to supply a recording medium from the paper feed cassette. It is the structure which carries out.

<Claim 3>
The image forming apparatus according to claim 3 is the image forming apparatus according to claim 1 or 2,
The first nip pressure is smaller than the second nip pressure.

<Claim 4>
The image forming apparatus according to claim 4,
The image forming apparatus according to any one of claims 1 to 3,
The predetermined position of the paper guide is a position suitable for guiding the width direction of the fixed envelope,
The first nip pressure is a value suitable for printing on the fixed envelope.

<Claim 5>
The image forming apparatus according to claim 5,
The image forming apparatus according to any one of claims 1 to 4,
The predetermined position of the paper guide is a position suitable for guiding the width direction of the fixed envelope,
The second nip pressure is a value suitable for printing on plain paper.

<Claim 6>
The image forming apparatus according to claim 6,
The image forming apparatus according to any one of claims 1 to 5,
The heating member is a cylindrical heating roller supported rotatably,
The pressure member is a cylindrical pressure roller supported rotatably.

<Claim 7>
The image forming apparatus according to claim 7,
The image forming apparatus according to claim 1, wherein:
The nip pressure generating mechanism includes a crimping mechanism and an eccentric cam mechanism,
The pressure-bonding mechanism pressure-bonds the pressure member in a direction in contact with the heating member by the elastic force of the elastic member, and the eccentric cam mechanism can change the nip pressure by changing the deformation amount of the elastic member. Features.

  According to the image forming apparatus of the first aspect, the nip pressure of the image forming apparatus is automatically set by simply setting the recording medium on the manual feed tray and moving the paper guide to a position matching the width of the recording medium. Since the nip pressure is set to a predetermined value, it is possible to save the user from setting both the paper width and the nip pressure.

  According to the image forming apparatus of claim 2, the nip pressure is set to the first nip pressure only by the user selecting whether to form an image on the recording medium in the cassette or on the recording medium of the manual feed tray. And the second nip pressure can be automatically switched to each other, so that it is possible to save the trouble of resetting the nip pressure every time the paper feeding position is changed.

  According to the image forming apparatus of the third aspect, when the paper is fed from the manual feed tray, two kinds of nip pressures can be set depending on the position of the paper guide.

  According to the image forming apparatus of claim 4, when feeding the standard envelope from the manual feed tray, the user only needs to adjust the position of the paper guide to the width of the standard envelope and is optimal for printing on the standard envelope. The nip pressure can be set.

  According to the image forming apparatus of the fifth aspect, when the plain paper other than the standard envelope is fed from the manual feed tray, the user simply adjusts the position of the paper guide to the width of the plain paper. The optimal nip pressure for printing can be set.

  In the image forming apparatus according to the sixth aspect, the fixing operation can be continuously performed by rotating the fixing roller and the pressure roller while the recording medium is sandwiched between the heating roller and the pressure roller.

In the image forming apparatus according to the seventh aspect, the nip pressure can be easily switched by an eccentric cam mechanism having a simple structure and easy control.

1. Overall Structure of the Present Embodiment One embodiment of the present invention will be described with reference to FIGS.

  In the following description, the depth direction of the laser printer is the X direction (the front side is + X), the width direction (the right front side in FIG. 4 is + Z) is the Z direction, and the height direction is the Y direction (in FIG. 4). The upper side is assumed to be + Y).

  As shown in FIG. 1, the laser printer 1 includes a housing 2, a feeder unit 4 for feeding a sheet 3 as a recording medium, and an image forming unit for forming an image on the fed sheet 3. 5 etc.

(1) Housing An attachment / detachment opening 6 for attaching / detaching a process cartridge 20 to be described later is formed on one side wall of the enclosure 2. As shown in FIG. 1 and FIG. A front cover 7 for opening and closing is provided. The front cover 7 is rotatably supported by a cover shaft (not shown) inserted through the lower end portion thereof.

  As a result, when the front cover 7 is closed around the cover shaft, as shown in FIG. 1, the attachment / detachment opening 6 is closed by the front cover 7 and when the front cover 7 is opened with the cover shaft as a fulcrum (when tilted), The attachment / detachment opening 6 is opened, and the process cartridge 20 can be attached / detached to / from the housing 2 via the attachment / detachment opening 6.

  Further, a cassette housing portion 2A that opens forward is provided at the bottom of the housing 2, and a paper feeding cassette 9 described below can be housed therein by an operation from the front (right side in FIG. 1), or The housed paper cassette 9 can be removed.

(2) Paper Feed Unit The paper feed unit feeds the paper stored in the paper feed cassette 9 one by one to the image forming unit and the paper placed on the manual feed tray 93 one by one to the image forming unit. A manual feed unit is provided.

(2-A) Feeder Unit As shown in FIG. 1, the feeder unit 4 is mainly composed of a paper feed cassette 9 and each roller for feeding the paper 3 to the paper transport path 56 one by one. As shown in FIG. 3, the paper feed cassette 9 has a tray shape with a shallow bottom, and includes a cassette body 71 on which the paper 3 is placed in a stacked state, and a wall portion 75 provided at the front thereof. A sheet pressing plate 15 is attached to the front portion of the bottom wall 71 </ b> A of the cassette body 71. The sheet pressing plate 15 is fixed at the left end in FIG. 3 to the bottom wall 71A, but is not fixed at the opposite end, and has a structure that can be bent up and down.

  A lever 17 is provided between the leading end of the sheet pressing plate 15 and the bottom wall 71A of the sheet feeding cassette 9 (see FIG. 1). The lever 17 rotates about the lever shaft 18. When a counterclockwise rotational driving force in the figure is input to the lever shaft 18, the lever 17 rotates about the lever shaft 18 as a fulcrum. Thus, the front end portion of the lever 17 lifts the front end of the paper pressing plate 15, and eventually the paper 3 stacked in the paper feed cassette 9, thereby bringing the paper 3 into contact with a paper feed roller 12 described later.

  The wall portion 75 includes a plate-like front plate 76 and an inclined surface 77 that is opposite to the front plate 76 and is inclined downward toward the cassette body 71 side. At the center of the inclined surface 77 in the width direction, a paper dust removing roller 8 and a separation pad 11 are arranged vertically. Further, a guide piece 115 is provided on the inclined surface 77 so as to protrude inward of the cassette (left side in FIG. 3).

  The paper dust removing roller 8 is held by a pair of holding walls 75 </ b> A formed at the wall 75 at both ends of the rotating shaft with the axis line oriented in the width direction of the paper feeding cassette 9.

  On the other hand, as shown in FIG. 1, the paper feed roller 12, the separation roller 10, and the counter roller 13 are sequentially arranged at the front side of the ceiling wall in the cassette housing portion 2 </ b> A, that is, at a position facing the wall portion 75 of the paper feed cassette 9. Has been placed.

  Here, the roller support structure will be briefly described. As shown in FIG. 3, the central axis C1 of the separation roller 10 and the central axis C2 of the counter roller 13 extend in the width direction of the paper feed cassette 9, respectively. Both ends of the central axes C1 and C2 are supported by the housing 2 in a state in which is oriented in a direction orthogonal to the paper transport direction. On the other hand, the paper feed roller 12 does not have a central shaft connected to the housing 2 such as the separation roller 10 or the counter roller 13, and can rotate around the central shaft C <b> 1 by a substantially U-shaped holder 12 </ b> A. Is retained.

  3 is a perspective view of the paper feed cassette, whereas the separation roller 10, the opposing roller 13, and the paper feed roller 12 are components attached to the housing 2. FIG. For this reason, the separation roller 10 and the counter roller 13 are components that do not originally appear in the drawing, but are shown on the drawing in order to show the relationship with the paper feed cassette 9 or the roller 8 provided in the cassette. is there.

  When the paper feed cassette 9 is accommodated in the cassette housing portion 2A, the front plate 76 of the paper feed cassette 9 is flush with the front wall of the housing 2 to block the entrance of the cassette housing portion 2A, as shown in FIG. At the same time, the separation roller 10 and the separation pad 11 face each other, and the paper dust removing roller 8 and the facing roller 13 face each other.

  As a result, the paper transport path 56 is formed by the rollers 8, 10, 12, 13 and the guide piece 115 of the wall 75. Further, the separation pad 11 is pressed by the separation roller 10. Accordingly, an appropriate frictional force is applied to the conveyed sheet, and the sheet 3 is prevented from being supplied into the sheet conveying path 56 in a state where a plurality of sheets are overlapped.

  Further, M shown in FIG. 1 is a driving motor. When the motor M is driven, the driving torque of the motor M is transmitted by a power transmission gear (not shown), whereby each of the central axes C1, C2 and thus each roller. 10, 12 and 13 rotate. As shown in FIG. 1, the paper conveyance path 56 is folded back to the rear side (left side in the figure) in the U shape from the vicinity of the arrangement of the paper dust removing roller 8, and a pair of the paper conveyance path 56 is disposed below the process cartridge 20. A registration roller 14 composed of a roller is provided. As a result, as the motor M is driven, the sheet 3 follows the sheet conveyance path 56 and is sent to the image forming unit 5 described below.

(2-B) Manual Paper Feed Unit The manual paper feed unit will be described below with reference to FIGS. 1, 2, and 5 to 9.

  As shown in FIGS. 1 and 2, a manual feed tray 93 for manually supplying the paper 3 is disposed on the front cover 7.

  The manual feed tray 93 is supported by a tray shaft (not shown) at the lower end thereof so that the entire manual feed tray 93 can be opened and closed. FIG. 1 shows a state in which the manual feed tray 93 is closed, and FIG. 2 shows an open state.

  When the manual feed tray 93 is opened as shown in FIG. 2, the manual feed port 94 on the side surface close to the tray axis of the housing 2 is opened. Inside the manual paper feed port 94, there are a holder 91A having a paper feed roller 90 and a separation roller 91, and a separation pad 92. The holder 91 </ b> A is pressed in a direction to press the separation roller 91 against the separation pad 92 by a spring (not shown).

As shown in FIG. 2, when the paper 3 is stored in the manual feed tray 93 and the leading end of the paper 3 is inserted into the manual paper feed port 94, the paper feed roller 90 contacts the upper surface of the paper 3, and the separation pad 92 is a separation roller. It will be in the state pressed by 91. Accordingly, an appropriate frictional force is applied between the sheet 3 and the separation roller 91 to prevent the sheet 3 from being supplied into the sheet conveyance path 56 in a state where a plurality of sheets are overlapped.

  FIG. 5 is a perspective view showing the structure of the paper guide.

  FIG. 6 is a partial view of the paper guide as seen from the side opposite to the surface on which the paper is placed in the manual feed tray.

  FIG. 7 shows a state in which the sensor arm does not press the actuator of the switch when the paper guide is viewed from the side of the manual tray where the paper is placed, and FIG. 8 shows a state in which the sensor arm also presses the actuator of the switch. FIG.

  As shown in FIGS. 2, 5, and 6, the manual feed tray 93 is provided with a pair of paper guides 95 </ b> A and 95 </ b> B that regulate the position of the paper 3 in the width direction. The manual feed tray 93 is provided with a sensor arm 80 and a switch 81, which will be described later.

  As shown in FIG. 6, a rib 89 is provided at the other end of the sensor arm 80 and faces the actuator of the switch 81. The switch 81 is OFF when the actuator is not pressed, and is ON when the actuator is pressed.

  As shown in FIGS. 2 and 5, the sheet guides 95 </ b> A and 95 </ b> B include wall-shaped guide parts 82 </ b> A and 82 </ b> B that are substantially perpendicular to the sheet 3 stacked on the sheet tray 93 and a slide part 83 </ b> A that is parallel to the sheet 3. , 83B.

  Racks 84A and 84B are carved in the slide portions 83A and 83B, and the racks 84A and 84B of the left and right paper guides 95A and 95B are engaged with a common pinion 97. Therefore, when either one of the sheet guides 95A or 95B is moved, the pinion 97 is rotated accordingly, and the other is interlocked so that the two approach or separate from each other. With the above structure, the paper guides 95A and 95B open and close symmetrically with respect to the pinion 97.

  Further, as shown in FIGS. 7 and 8, notches 85A, 85B, 85C, and 85D are carved at predetermined positions on the side surface 89 of the slide portion 83B opposite to the side on which the rack 84B is carved.

  A pin 86 is disposed at one end of the sensor arm 80.

  The sensor arm 80 is rotatably attached around a shaft 87, and a rotational moment is applied in a direction in which the pin 86 is pressed against the side surface 89 of the slide portion 83 by a spring 88.

  Here, the operation of the sensor arm 80 and the switch 81 will be described with reference to FIGS.

  As shown in FIG. 7, when none of the notches 85 </ b> A, 85 </ b> B, 85 </ b> C, 85 </ b> D of the slide portion 83 </ b> B is in a position facing the pin 86 of the sensor arm 80, the pin 86 is on the side surface 89. Therefore, the rib 89 is held at a position where the actuator of the switch 81 is not pressed.

  As shown in FIG. 8, when the notch 85 </ b> B of the slide portion 83 comes to a position facing the pin 86 of the sensor arm 80, the pin 86 enters the notch 85 </ b> B facing from the side 89 by the rotational moment of the spring 88. Depressed. Therefore, the sensor arm 80 rotates counterclockwise in FIG. As a result, the rib 89 depresses the actuator of the switch 81.

  Here, the notch 85B has been described as an example, but the same applies to the notches 85A, 85C, and 85D.

  Here, the notches 85A, 85B, 85C, and 85D are formed at positions facing the pins 86 when the paper guides 95A and 95B are respectively positioned to guide the width direction of the corresponding fixed envelope. Yes. In other words, this embodiment corresponds to four types of fixed envelopes.

  With the above structure, whether or not the notch 85 is at a position facing the pin 86 of the sensor arm 80, whether or not the actuator of the switch 81 is depressed, that is, whether the switch 81 is in an ON / OFF state. Can be determined by examining.

  Here, the notches 85A, 85B, 85C, and 85D face the pin 86 when the paper guides 95A and 95B are set to positions suitable for guiding the width direction of the fixed envelope, so that the switch 81 is turned on. When this happens, it can be determined that the paper guide has been set to a position suitable for guiding the standard envelope.

(3) Image Forming Unit The image forming unit 5 includes a scanner unit 19, a process cartridge 20, a fixing unit 21, and the like. Hereinafter, the image forming unit will be described with reference to FIG.

(3-A) Scanner Unit The scanner unit 19 is provided in the upper part of the housing 2, and includes a laser light source (not shown), a polygon mirror 22 that is rotationally driven, an FΘ lens 23, a reflecting mirror 24, a lens 25, and a reflecting mirror 26. It has. The laser beam based on the image data emitted from the laser light source is deflected by the polygon mirror 22 as shown by a chain line, passes through the FΘ lens 23, the optical path is turned back by the reflecting mirror 24, and further passes through the lens 25. After that, the optical path is further bent downward by the reflecting mirror 26, so that the surface of a photosensitive drum 29 (to be described later) of the process cartridge 20 is irradiated.

(3-B) Process Cartridge The process cartridge 20 is detachably attached to the housing 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 as a casing. The process cartridge 20 includes a photosensitive drum 29 as an image carrier, a scorotron charger 30 as a charging unit, a developing cartridge 31, a transfer roller 32 as a transfer unit, and a cleaning brush 33 in a housing. .

  The photosensitive drum 29 includes a cylindrical drum main body 34 and a metal drum shaft 35 extending along the longitudinal direction of the drum main body 34 at the axial center of the drum main body 34. The outermost layer of the drum body 34 is formed of a positively chargeable photosensitive layer made of polycarbonate or the like. 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 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, and is disposed between the discharge wire 37 and the photosensitive drum 29 so as to face the photosensitive drum 29 at a predetermined interval. And a grid 38 for controlling the 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 developing cartridge 31 includes a box-shaped storage case 60 whose rear side is opened, and is detachably attached to the lower frame 28. In the developing cartridge 31, a toner storage chamber 39, a toner supply roller 40, a developing roller 41, and a layer thickness regulating blade 42 are provided.

  The toner storage chamber 39 is formed as an internal space on the front side of the storage case 60 partitioned by the partition plate 43. The toner storage chamber 39 is filled with a positively chargeable nonmagnetic one-component toner T as a developer.

  In the toner storage chamber 39, an agitator 44 supported by a rotation shaft 55 provided in the center is provided. The agitator 44 is rotationally driven by the input of power from a motor (not shown). When the agitator 44 is driven to rotate, the toner T in the toner storage chamber 39 is agitated and discharged toward the toner supply roller 40 from the opening 45 communicating in the front-rear direction below the partition plate 43.

  The toner supply roller 40 is disposed on the rear side of the opening 45 and is rotatably supported by the developing cartridge 31. The toner supply roller 40 is structured by covering a metal roller shaft with a roller made of a conductive foam material.

  The developing roller 41 is rotatably supported by the developing cartridge 31 in a state in which the developing roller 41 is in contact with the toner supplying roller 40 so as to be compressed on the rear side of the toner 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 roller shaft 41 </ b> A has both ends projecting outward from the side surface of the developing cartridge 31 in the width direction (Z-axis direction) of the apparatus main body at the front end portion of the developing cartridge 31. 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 toner supply roller 40 by the input of power from a motor (not shown).

  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 T discharged from the opening 45 is supplied to the developing roller 41 by the rotation of the toner supply roller 40. At this time, the toner T is positively frictionally charged between the toner supply roller 40 and the developing roller 41. The toner T 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 as a thin layer with a constant thickness. 41 is carried.

  The transfer roller 32 is rotatably supported by the lower frame 28. When the upper frame 27 and the lower frame 28 are combined, the transfer roller 32 is opposed to and contacts the photosensitive drum 29 in the vertical direction. They are arranged to form a nip therebetween. The transfer roller 32 is structured by covering a metal roller shaft 32A with a roller made of a conductive rubber material. A transfer bias is applied to the transfer roller 32 during transfer.

  The cleaning brush 33 is attached to the lower frame 28, and is arranged to face and contact the photosensitive drum 29 on the rear side of the photosensitive drum 29 in a state where the upper frame 27 and the lower frame 28 are combined. ing.

  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, as shown in FIG. 1, the toner image carried on the surface of the photosensitive drum 29 is passed through the transfer position between the photosensitive drum 29 and the transfer roller 32 by the sheet 3 conveyed by the registration roller 14. In the meantime, the image is transferred to the paper 3 by a transfer bias applied to the transfer roller 32. 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, paper dust from the paper 3 adhering to the photosensitive drum 29 after the transfer is collected by the cleaning brush 33.

(3-C) Fixing Unit The structure and operation of the fixing unit will be described below with reference to FIGS.

  FIG. 9 is an external view of the fixing unit 21.

  10 and 11 are cross-sectional views of the fixing unit 21 taken along the line AA.

  As shown in FIG. 1, the fixing unit 21 is provided on the rear side of the process cartridge 20.

  As shown in FIGS. 10 and 11, the fixing unit includes a heating roller 49 as a heating member and a pressure roller 50 as a pressure member in a fixing frame 48.

  The heating roller 49 is a metal tube whose surface is coated with a fluororesin. In the metal tube, a halogen lamp is provided as a heat source for heating the heating roller.

  The rotating shaft of the heating roller 49 is rotatably held by the heating frame 48 and is driven to rotate by the input of power from a motor (not shown).

  On the other hand, the pressure roller 50 is disposed opposite the heating roller 49 so as to press the heating roller 49. The pressure roller 50 has a structure in which a metal roller shaft is covered with a roller made of a rubber material. The heating roller 49 rotates following the rotational drive.

  The rotation shaft of the pressure roller 50 is rotatably held by the pressure frame 54.

  The pressure frame 54 is rotatably held by the pressure frame shaft 57, and a rotation moment is applied in a direction in which the pressure roller 50 is pressed against the heating roller 49 around the pressure frame shaft 57 by a pressure spring 55 (not shown). It has been.

  Due to this rotational moment, the heating roller 49 is deformed and indented by a roller made of a rubber material of the pressure roller 50. Hereinafter, the indented portion is referred to as nip 61, and the force required to deform the rubber material in the nip 61 is referred to as nip pressure.

  The nip pressure becomes larger as the amount of the heating roller 49 that is embedded in the pressure roller 50 is larger.

  The distance between the rotation centers of the heating roller 49 and the pressure roller 50 is a distance that balances the nip pressure and the elastic repulsion force that restores the deformed portion of the rubber of the pressure roller to the original shape.

  The pressure frame 54 further includes a cam follower 58. When the cam follower 58 is pushed as the eccentric cam 59 rotates, the pressure roller 50 moves in a direction away from the heating roller 49.

  In this embodiment, the eccentric cam 59 is driven by the motor M2, the short diameter side of the eccentric cam 59 faces the cam follower 58, the eccentric cam 59 and the cam follower 58 are not in contact, and the long diameter side of the eccentric cam 59 is the cam follower 58. It is configured so that the two states of pressing and touching can be realized alternatively.

  10 shows a state in which the eccentric cam 59 does not push the cam follower 58, and FIG. 11 shows a state in which the eccentric cam 59 has rotated half a turn from the position shown in FIG.

  The origin switch 109 is switched ON / OFF every time the eccentric cam 59 makes a half rotation by the action of a semicircular cam integrally formed with the eccentric cam 59. An origin switch 109 is connected to a control unit 100, which will be described later, and operates as a sensor that detects the setting state of the nip pressure.

  As shown in FIG. 10, when the cam follower 58 is not pushed, the nip force of the pressure spring 55 is supported only by the pressure roller 49.

  On the other hand, as shown in FIG. 11, when the cam follower 58 is pushed, a part of the rotational moment by the pressure spring 55 is also supported by the eccentric cam 59 via the cam follower 58, so that the force applied to the pressure roller 50 is the nip pressure. Becomes smaller. Therefore, the nip 61 is also reduced.

  With the above structure, the nip pressure applied to the pressure roller 50 is reduced when the eccentric cam 59 is rotated and the cam follower 58 is driven as compared with the case where the eccentric cam 59 is not rotated and the cam follower 58 is not pushed. . Thus, the nip pressure can be changed by switching the stop position of the eccentric cam 59.

  Generally, when fixing an image formed on an envelope using an envelope as the paper 3, it is necessary to lower the nip pressure compared to fixing an image formed on the plain paper using plain paper as the paper 3. . The reason is as follows.

  The envelope has a bag-like structure in which two sheets of paper are overlapped. The envelope is sent while being bent along the surface of the heating roller. At that time, the amount of feed accompanying the rotation of the heating roller 50 is different between the paper on the side of the envelope touching the fixing roller and the paper on the side of the pressure roller 50. . This is because the paper on the side touching the pressure roller 50 is bent at a radius larger than the paper on the side touching the heating roller 49 by the thickness of the paper.

  However, since the paper on the side touching the pressure roller 50 and the paper touching the heating roller 49 are connected at the edge of the envelope, the difference in feed amount is collected at the edge of the envelope.

  When the difference in feed amount is small, wrinkles do not occur because they are absorbed by the elongation of the paper. However, if the difference in feed amount becomes so large that it cannot be absorbed by the elongation of the paper, wrinkles occur at the edge of the envelope after passing through the fixing portion.

  In order to reduce the difference in the feeding amount, the length of the envelope that is fed while being bent along the heating roller 49 may be shortened.

  The length of the envelope that is sent while being bent along the heating roller 49 is the length of the nip portion 61. If the nip portion 61 is shortened, the difference in feed amount can be reduced. Therefore, in order to shorten the nip portion, the nip pressure is lowered and the deformation amount of rubber of the pressure roller 50 is reduced.

  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.

  As shown in FIG. 1, 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 housing 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 housing 2 by a sheet discharge roller 52 provided on the upper side.

2. Mechanism of setting the nip pressure A mechanism for setting the nip pressure will be described below.

  FIG. 12 is a block diagram of the laser printer.

  FIG. 13 is a flowchart showing the flow of control.

  As shown in FIG. 12, the control unit 100 of the laser printer 1 includes a CPU 101 that controls each unit of the laser printer 1, a ROM 102 that stores a control program, font data, and the like, data necessary for control and image formation, And a RAM 103 that is a storage area for use as a work area.

  A motor M, a motor M2, a scanner unit 19, a fixing unit 21 and the like are connected to the control unit 100 via a drive circuit 105. Further, the display panel 106 for displaying a message such as the status of the laser printer 1 and a paper out condition, a switch 81 for determining whether or not the paper guide 95B is in a predetermined position, and detecting whether or not there is paper in the manual feed tray. A line-of-sight difference 108, an origin switch 109 for detecting the rotation angle of the eccentric cam 59, and the like are connected.

  The control unit 100 also includes a host I / F 104 for communicating with a host that supplies data that is the basis of an image to be formed on the paper 3 and a command that supports where the paper is fed from.

  Next, the nip pressure setting process will be described with reference to FIG.

  FIG. 13 is a flowchart showing the flow of nip pressure setting processing.

  When a signal for starting image formation is input from the host I / F 104 to the control unit 100, a nip pressure setting process is started (S001).

  If the laser printer 1 receives a command for feeding paper from the manual paper feeding unit together with data necessary for image formation from the host I / F 104 (S002: Yes), the control unit 100 first switches It is checked whether 81 is ON or OFF, that is, whether the paper guides 95A and 95B of the manual feed tray 93 are at positions corresponding to the standard envelopes.

  When the switch 81 is ON, that is, when the paper guides 95A and 95B are at a position corresponding to the width of the standard envelope (S004: Yes), the control unit 100 pushes the eccentric cam 59 and the cam 59 longer diameter side pushes down the cam follower 58. Rotate to (Fig. 11). Thereby, the nip pressure is set to a low value suitable for the fixed envelope (S005). Thereafter, the image forming process is subsequently started.

  When the paper guides 95A and 95B are not at positions corresponding to the width of the standard envelope, that is, when the switch 81 is OFF (S004: No), the control unit 100 sets the eccentric cam 59 to the cam 59 short axis side facing the cam follower 58 (Fig. 10). Thereby, the nip pressure is set to a high value suitable for plain paper other than the standard envelope (S006). Thereafter, the image forming process is subsequently started.

  When the laser printer 1 receives from the host I / F 104 a command to feed paper from the feeder unit together with data necessary for image formation, that is, has not received a command to feed paper from the manual paper feed unit. In this case (S002: No), the nip pressure is set to a value suitable for plain paper, the nip pressure setting process is terminated, and the image forming process is subsequently started.

  As described above, when the paper is fed from the manual paper feeder and printed, and the paper 3 is either a standard envelope or other plain paper, the user sets the positions of the paper guides 95A and 95B. Simply changing it will automatically change the nip pressure.

3. Other Embodiments The present invention is not limited to the embodiment described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and the gist is not limited to the following. Various modifications can be made without departing from the scope.

  (1) In the above embodiment, only the regular envelope and other plain paper are distinguished. However, if the paper has a certain correlation between the width and the thickness, it is determined by providing the position of the notch 85. The nip pressure can be switched.

  (2) In the above embodiment, only two types of nip pressure are switched, but three or more types of switching may be possible.

  In the above embodiment, since the paper is discriminated by turning on / off the switch 81, it is only possible to distinguish whether it is a fixed envelope or not.

  However, for example, if the position of the paper guide 95 is measured with a potentiometer, the width of the paper can be directly measured.

Furthermore, if the shape of the eccentric cam 59 is changed so that the amount of pushing the cam follower 58 is variable in three steps or more, three or more types of nip pressures can be generated.
With the above combination, it is possible to determine the type of paper based on the width, and it is possible to realize processing for selecting and setting the optimum nip pressure for the paper from two or more types of nip pressure.

(3) In the above embodiment, the paper guide for measuring the paper width and the surrounding mechanism are installed in the manual feed tray. However, these are installed in the paper feed cassette, and the paper in the paper feed cassette is enveloped. It is also possible to discriminate between paper and plain paper.

FIG. 1 is a side sectional view showing a main part of a laser printer as an image forming apparatus of the present invention. FIG. 2 is a cross-sectional view (partial view) of the laser printer with the manual feed tray opened. FIG. 3 is a perspective view of the paper feed cassette. FIG. 4 is a perspective view of the laser printer. FIG. 5 is a perspective view showing the structure of the paper guide. FIG. 6 is a partial view of the paper guide as seen from the side opposite to the surface on which the paper is placed in the manual feed tray. FIG. 7 is a partial view showing a state where the sensor arm does not press the actuator of the switch when the paper guide is viewed from the side of the manual feed tray where the paper is placed. FIG. 8 is a partial view of a state in which the sensor arm is pressing the actuator of the switch, as viewed from the side of the manual feed tray on which the paper guide is placed. FIG. 9 is an external view of the fixing unit. FIG. 10 is a cross-sectional view of the fixing unit taken along the line AA with a high nip pressure. FIG. 11 is a cross-sectional view of the fixing unit taken along the line AA with a low nip pressure. FIG. 12 is a block diagram of the laser printer. FIG. 13 is a flowchart of nip pressure setting control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser printer 2 ... Case 2A ... Cassette accommodating part 3 ... Paper 4 ... Feeder part 5 ... Image formation part 6 ... Removable port 7 ... Front cover 8・ ・ ・ Paper dust removal roller 9 ・ ・ ・ Paper feed cassette 10 ・ ・ ・ Separation roller C1 ・ ・ ・ Center axis M of the separation roller 10 ・ ・ ・ Motor M2 ・ ・ ・ Motor 11 ・ ・ ・ Separation pad 12 ・ ・ ・Paper feed roller 12A ... Holder 13 ... Counter roller C2 ... Center shaft 14 of counter roller 13 ... Registration roller 15 ... Paper pressing plate 17 ... Lever 18 ... Lever shaft 19・ ・ Scanner unit 20 ・ ・ ・ Process cartridge 21 ・ ・ ・ Fixing unit 22 ・ ・ ・ Polygon mirror 23 ・ ・ ・ FΘ lens 24 ・ ・ ・ Reflective mirror 25 ・ ・ ・ Lens 26 ・ ・ ・ Reflective mirror 27 ・ ・ ・ Top Rame 28 ... Lower frame 29 ... Photosensitive drum 30 ... Scorotron charger 31 ... Development cartridge 32 ... Transfer roller 32A ... Roller shaft 33 ... Cleaning brush 34 ... Drum Main body 35 ... Drum shaft 37 ... Discharge wire 38 ... Grid 39 ... Toner storage chamber 40 ... Toner supply roller T ... Toner 41 ... Development roller 41A ... Roller shaft 42 ... Layer thickness regulating blade 43 ... Partition plate 44 ... Agitator 45 ... Opening 46 ... Blade body 47 ... Pressing part 48 ... Fixing frame 49 ... Heating roller 50・ ・ Pressure roller 51 ・ ・ ・ Discharge path 52 ・ ・ ・ Discharge roller 53 ・ ・ ・ Discharge tray 54 ・ ・ ・ Pressure frame 55 ・ ・ ・ Pressure spring 6 ... paper conveying path 57 ... pressing frame shaft 58 ... eccentric cam follower 59 ... eccentric cam 60 ... housing case 61 ... nip (nip pressure roller)
71 ... Cassette body 71A ... Bottom wall 75 ... Wall 75A ... Holding wall 76 ... Front plate 77 ... Inclined surface 80 ... Sensor arm 81 ... Switch 82A・ Guide part 82B ... Guide part (side with notch 85)
83A ... Slide part 83B ... Slide part (the side with the notch 85)
84A ・ ・ ・ Rack 84B ・ ・ ・ Rack 85A ・ ・ ・ Notch 85B ・ ・ ・ Notch 85C ・ ・ ・ Notch 85D ・ ・ ・ Notch 86 ・ ・ ・ Pin 87 ・ ・ ・ Shaft 88 ・ ・ ・ Spring 89 ・ ・ ・ Side 90 ... Paper feed roller 91 ... Separation roller 91A ... Holder 92 ... Separation pad 93 ... Manual feed tray 94 ... Manual feed port 95A ... Paper guide 95B ... Paper guide (Side with cutout 85)
97 ・ ・ ・ Pinion 100 ・ ・ ・ Control unit 101 ・ ・ ・ CPU
102 ... ROM
103 ... RAM
104 ・ ・ ・ Host I / F
105 ... Drive circuit 106 ... Display panel 108 ... Paper sensor 109 ... Origin switch 115 ... Guide piece

Claims (7)

A fixing unit including a heating member that contacts a recording medium, a pressure member that faces the heating member, and a nip pressure generation mechanism that generates a nip pressure by pressing the heating member and the pressure member in a direction in contact with each other. When,
A controller that controls the nip pressure generating mechanism to generate a predetermined nip pressure;
An electrophotographic image forming unit for forming an image on the recording medium;
A manual feed tray for manually feeding the recording medium;
A paper guide for guiding a width direction of the recording medium supplied to the manual supply unit;
Paper guide position detecting means for detecting whether or not the paper guide is in a predetermined position;
The control unit controls the nip pressure generating mechanism to generate a first nip pressure when the position of the sheet guide detected by the sheet guide position detecting unit is the predetermined position;
The image is characterized in that the nip pressure generating mechanism is controlled so as to generate a second nip pressure when the paper guide position detected by the paper guide position detecting means is not the predetermined position. Forming equipment. The image forming apparatus according to claim 1.
At least one paper feed cassette for holding the recording medium;
A paper feed switching unit capable of selectively selecting whether to feed from the manual feed tray or the paper feed cassette;
The control unit controls the nip pressure generating mechanism so that the nip pressure becomes the second nip pressure when the paper feed switching unit is selected to supply a recording medium from the paper feed cassette. An image forming apparatus having the configuration described above. The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the first nip pressure is smaller than the second nip pressure. The image forming apparatus according to any one of claims 1 to 3,
The predetermined position of the paper guide is a position suitable for guiding the width direction of the fixed envelope,
The image forming apparatus according to claim 1, wherein the first nip pressure is a value suitable for printing on the fixed envelope. 5. The image forming apparatus according to claim 1, wherein:
The predetermined position of the paper guide is a position suitable for guiding the width direction of the fixed envelope,
The image forming apparatus, wherein the second nip pressure is a value suitable for printing on plain paper. The image forming apparatus according to any one of claims 1 to 5,
The heating member is a cylindrical heating roller supported rotatably,
The image forming apparatus, wherein the pressure member is a cylindrical pressure roller supported rotatably. The image forming apparatus according to claim 1,
The nip pressure generating mechanism includes a crimping mechanism and an eccentric cam mechanism,
The crimping mechanism is configured to crimp the pressure member in a direction in contact with the heating member by an elastic force of an elastic member,
The image forming apparatus, wherein the eccentric cam mechanism can change a nip pressure by changing a deformation amount of the elastic member.

Images