JP4050083B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device disposed in various copying machines, electrophotographic image forming apparatuses such as printers and facsimiles.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, an electrostatic latent image formed on a photoconductor is visualized by applying toner with a developing device, and this is transferred onto a recording material such as transfer paper / OHP sheet, The transferred image (unfixed toner image) is fixed on the recording material by a fixing device.
[0003]
A fixing device equipped in such an image forming apparatus generally includes a fixing roller pair including a fixing roller having a built-in heating device and a pressure roller in pressure contact with the fixing roller. A guide member for guiding the recording material to be fixed to the roller pair is disposed at the immediately preceding position.
[0004]
In the example shown in FIG. 5, the fixing device 31 includes a fixing roller pair 34 including a fixing roller 32 that incorporates a heating device and rotates in the direction of an arrow, and a pressure roller 33 that rotates in contact with the fixing roller 32. In addition, a guide member 35 for guiding the transfer paper P to the fixing nip portion of the fixing roller pair 34 is disposed between the photosensitive member 26 and the fixing roller pair 34.
[0005]
Although not shown, an upper guide member is often provided to face the guide member 35, and an upper guide plate and a lower guide plate are also arranged behind (on the downstream side) the fixing roller pair 34. Often installed. In FIG. 5, 21 is a paper feed cassette, 22 is a manual feed tray, 23 and 24 are paper feed rollers, 25 is a transport roller, 27 is a charger, 28 is a transfer roller, 29 is a cleaning device, and 36 is a transport roller. , 37 are discharge rollers.
[0006]
Among image forming apparatuses, in a printer apparatus, it is desirable that recording sheets discharged during continuous printing are stacked in page order except for some models such as personal use. Accordingly, in order to clear the constraints such as operability, cost, apparatus size, apparatus installation space and the like while satisfying this requirement, the upper surface (upper part) of the printer main body (apparatus main body) is placed on the paper discharge unit as in the example of FIG. In many cases, the transfer position of the toner image from the photosensitive member to the recording paper is set at the lower part or the side part of the photosensitive member.
[0007]
When the transfer position is set to the upper part of the photoconductor, the toner image is transferred to the lower surface of the recording paper. Therefore, when the upper surface of the apparatus body is used as the paper discharge unit, the recording paper is conveyed from the transfer position to the paper discharge unit. In the meantime, it is necessary to switch back the recording paper or form the transport path in an S-shape (or reverse S-shape) to discharge the recording paper downward, which makes the transport path complicated and disadvantageous.
[0008]
As described above, when the upper surface of the apparatus main body is used as the paper discharge unit (when the lower or side surface of the photosensitive member is used as the transfer position, the fixing device is in the path from the transfer position to the paper discharge unit on the upper surface of the apparatus. The fixing device is provided above the transfer position. However, since the toner image transferred on the recording paper is not fixed between the transfer position and the fixing device, the peripheral member is provided. Therefore, it is necessary to prevent the image from being disturbed due to a mechanical external cause such as paper contact with the paper, and therefore, a guide member for lifting the recording paper P (for preventing drooping) is provided immediately after the exit of the transfer position. It was. Alternatively, as shown in FIG. 5, a fixed guide member 35 is provided between the photosensitive member 26 and the fixing device 31.
[0009]
By the way, when the supplied recording paper P is carried into a transfer position where the photosensitive member 26 and the transfer roller 28 face each other, the recording paper P is superimposed on the toner image on the surface of the photosensitive member at the transfer position. A charge opposite in polarity to the normal charge polarity of the toner is applied to the recording paper P from the opposite surface of the surface on the photoreceptor side via the transfer roller 28, and the toner is transferred to the recording paper P by electrostatic force.
[0010]
At this time, the toner adhesion surface of the recording paper P has the same polarity as the toner, and the opposite side surface has the opposite polarity to the toner. The toner adhering surface of the recording paper P is an electrostatic force due to the charge applied by the transfer roller 28 when passing through the transfer position, and the charge in the background area on the photosensitive member is transferred to the recording paper P as well as the toner.
[0011]
Further, at this time, the recording paper P causes frictional charging with the photosensitive member 26, and the charge on the photosensitive member is transferred to the recording paper P by friction. This is a cause of excessive charge having the same polarity as the toner on the toner adhesion surface of the recording paper P after passing through the transfer position.
[0012]
Therefore, the heating roller 32 is grounded by grounding the sheet guide member 35 to release the charge having the opposite polarity to the toner from the surface opposite to the toner adhesion surface of the recording sheet P or increasing the conductivity of the release layer of the heating roller 32. In order to prevent the offset phenomenon caused by the toner being electrostatically adsorbed on the surface of the heating roller 32 by releasing the electric charge due to the friction between the release layer and the toner.
[0013]
[Problems to be solved by the invention]
As described above, conventionally, two factors that lower the print quality, that is, mechanical factors and electrostatic factors, have been individually dealt with.
[0014]
(Mechanical factors)
When the fixing device 31 is disposed above the transfer position, the recording paper P is transported upward from the transfer position. Therefore, if the trailing edge of the recording paper passes the transfer position, the paper rear edge is free. Therefore, the recording paper hangs down due to its own weight. The degree of sag of the recording paper varies depending on the type of recording paper and environmental conditions, but when the recording paper hangs down, if there is an unfixed toner image on the recording paper, the toner may come into contact with peripheral members. The image is rubbed, the print quality is liable to deteriorate, and the surroundings are contaminated (→ therefore, for example, the paper guide member 35 is provided).
[0015]
(Electrostatic factor)
When the paper guide member arranged immediately before the fixing device entrance side is in a grounded state or when the conductivity of the release layer of the heating roller is improved, the surface opposite to the toner adhesion surface of the recording paper , The charge having the opposite polarity to that of the toner formed before the fixing device escapes from the surface opposite to the toner adhesion surface of the recording paper.
[0016]
Therefore, the charge having the opposite polarity to the toner on the side opposite to the toner adhesion surface of the recording paper is reduced. That is, the electrostatic force for attracting the toner to the recording paper is reduced, and the toner has an electric charge of the same polarity as the toner on the recording paper in the region where the heating roller and the pressure roller are in contact with each other. Thus, an electrostatic force that promotes the separation of the toner from the recording paper acts between the toner adhering surface of the recording paper and the toner.
[0017]
For this reason, when the recording paper passes through the fixing device, a phenomenon of toner adhesion to the heating roller occurs, and when the heating roller makes one turn, the toner reattaches to the recording paper and causes image smearing. An offset phenomenon occurs and print quality is lowered (→ therefore, the conductivity of the heating roller is increased).
[0018]
As described above, in order to eliminate the print quality degradation due to (mechanical factors) and the print quality degradation due to (electrostatic factors), there is a separate correspondence immediately after the transfer position and on the fixing device side.
[0019]
Therefore, with respect to the paper guide member provided immediately after the transfer position, it is necessary to set the edge height to a detent in order to prevent the occurrence of paper jam, which is high although the effect of lifting the paper is insufficient. Parts accuracy and assembly accuracy were required.
[0020]
Further, regarding the fixing device, since the heating roller surface layer is made conductive, the toner is pulled to the surface layer of the heating roller by the mirror image charge having the opposite polarity to the toner with respect to the charge held by the toner. Since it becomes easy to stick to the heating roller, it is difficult to say that it has an effect of suppressing the offset phenomenon.
[0021]
Thus, in the past, it was individually dealt with (mechanical factor) and (electrostatic factor) that reduce the print quality, but still there are structural difficulties and ambiguity of the effect, More appropriate measures were required.
[0022]
The present invention has been made in view of such circumstances, and does not require strict component accuracy or assembly accuracy, has excellent paper guide properties to the fixing roller pair, is less likely to cause jamming, and reliably eliminates edge stains and offset phenomena. An object of the present invention is to provide a fixing device that is simple and has a configuration capable of obtaining sufficient stiffness.
[0023]
[Means for Solving the Problems]
In the present invention, means for solving the above-described problems are configured as follows.
[0024]
  (1)In the fixing device, in which the paper guide means is provided in the paper conveyance path from the transfer position of the toner image to the paper to the fixing nip portion of the fixing roller pair consisting of a heating roller and a pressure roller that are pressed against each other, the paper guide means The sheet is disposed below the sheet conveyed from the transfer position, lifts the front end of the sheet, guides the front end of the sheet toward the fixing nip, and the pair of fixing rollers conveys the guided sheet in a substantially vertical direction. The paper guide means is divided into a plurality of paper guide members, and at least one of the divided paper guide members is a movable paper guide whose posture changes. And detecting the sheet immediately before the front end of the sheet passes through the fixing nip portion and the rear end of the sheet passes through the transfer position, and the movable end of the movable sheet guide member is moved to the fixed position. Providing attitude control means for displacing beyond the line connecting the transfer position and the nip.
[0025]
When the paper discharge unit is disposed at the top of the image forming apparatus main body, the fixing device is often disposed above the transfer position. In such a case, the recording paper is located above the transfer position. When the recording paper trailing edge passes through the transfer position, the leading edge of the paper is held by the fixing device, but the trailing edge of the paper is free and hangs down due to its own weight and moves in the direction toward the back of the paper. Try to (try to shake).
[0026]
In this configuration, since the paper guide means is divided into a plurality of paper guide members, the degree of freedom of layout of the paper guide means is remarkably improved. For example, the paper discharge unit is located above the apparatus main body of the image forming apparatus. Even when it is provided, each paper guide member can be arranged in an appropriate position at an appropriate position on the paper conveyance path formed in a vertical path shape without requiring strict component accuracy and assembly accuracy. it can.
[0027]
Therefore, it is possible to improve the guide property and the effect of applying the recording paper to the fixing device, and it is possible to more effectively prevent the recording paper from dripping as described above. This makes it possible to eliminate contamination of the surroundings and effectively prevent jamming.
[0030]
In this configuration, since the paper guide member is movable, the corresponding angle (posture) with respect to the paper can be set more appropriately, and the guide property of the recording paper to the fixing device can be further improved. . Further, the effect of applying the stiffness to the recording paper can be made remarkable.
[0031]
  (2)The movable sheet guide member is disposed at a position closest to the upstream side of the fixing device.
[0032]
In this configuration, the movable paper guide member is disposed at the closest position on the upstream side of the fixing device, so that the guide property of the recording paper to the fixing device can be further improved, and the fixing roller pair Since the recording paper can be stiffened in a state of being sandwiched between the two, the stiffening action becomes even more remarkable.
[0033]
  In addition,The movable paper guide member is disposed on the back side of the paper along a line connecting the fixing nip portion and the transfer position, and is provided with a posture control means for controlling the posture of the paper guide member,
  The posture control means displaces the movable end of the sheet guide member toward the heating roller immediately before the trailing end of the sheet passes the transfer position.May be allowed.
[0034]
In this configuration, the recording paper can be guided to the fixing device by reliably guiding the back surface of the recording paper by the movable paper guide member disposed on the back side of the paper. Even if the trailing edge of the recording sheet becomes free, the trailing edge of the recording sheet does not move (shake) in the direction of the surface of the sheet. The toner image on the recording paper is not disturbed by a mechanical external cause without contacting a member or the like.
[0035]
When the paper is transported, the paper guide member is displaced toward the heating roller, so that the recording paper is always transported in contact with the paper guide member, and the charge accumulated on the paper edge is transferred via the paper guide member. It can escape to the outside, and the occurrence of the electrostatic offset phenomenon can be prevented.
[0036]
  (3)The posture control means is configured to return the sheet guide member to an initial position when the sheet trailing edge has passed through the fixing nip portion.
[0037]
In this configuration, when the trailing edge of the sheet passes between the fixing nip portion, the sheet guiding member is returned to the initial position so that the sheet guiding member is returned in a timely manner until the next recording sheet is fed. Can be made.
[0038]
  In addition,When the paper enters the fixing roller pair, the movable paper guide member is at a lower position retracted from the back side of the paper along the line connecting the fixing nip and the transfer position, and when the paper guide member is displaced, The movable end is displaced to the inner side of the line connecting the fixing nip and the transfer position.May.
[0039]
In this configuration, when the recording paper enters the roller pair of the fixing device, the paper guide member is in a lower position retracted from the back side of the paper along the line connecting the fixing nip and the transfer position. The transfer paper can smoothly enter the paper guide member by reducing the amount of paper.
[0040]
Then, after the trailing edge of the recording paper passes through the transfer position, the paper guiding member is displaced upward, and the paper rigidity is improved by performing a caulking action on the trailing edge side of the transfer paper. Can be prevented.
[0041]
  (4)A cross-sectional shape of the movable paper guide member is a crown shape that is convex toward the side in contact with the paper, and the thickness is reduced as it moves to both side ends.
[0042]
In this configuration, since the center portion in the recording paper width direction is deformed upward, the action of applying a stiffness to the recording paper is promoted, so that the rigidity of the paper is improved, so that drooping due to the weight of the paper is prevented. be able to.
[0043]
  (5)The movable paper guide member has a cross-sectional shape in a circular arc shape on the side in contact with the paper.
[0044]
In this configuration, since the center portion in the recording paper width direction is deformed upward, the action of applying a stiffness to the recording paper is promoted, so that the rigidity of the paper is improved, so that drooping due to the weight of the paper is prevented. be able to.
[0045]
  (6)A cross-sectional shape of the movable paper guide member is a mountain shape on the side in contact with the paper.
[0046]
In this configuration, the center portion in the recording sheet width direction is deformed upward, thereby promoting the effect of applying stiffness to the recording sheet.
[0047]
  (7)A cross-sectional shape of the movable paper guide member is a trapezoidal shape with a side contacting the paper as an upper base.
[0048]
In this configuration, the center portion in the recording sheet width direction is deformed upward, thereby promoting the effect of applying stiffness to the recording sheet.
[0049]
  (8)The movable end of the movable sheet guide member on the sheet conveyance surface side has a chamfered shape or a rounded shape.
[0050]
When chamfering or rounding is not given to the movable end of the sheet guide member, it is inevitable that it becomes a load when entering the transfer sheet, and it is difficult for the transfer sheet tip to smoothly enter the roller-nip. Become.
[0051]
Therefore, the leading edge of the transfer paper hits the movable end side corner of the paper guide member or receives a large resistance, so paper jam occurs at the fixing part or shock occurs when the transfer paper hits the corner. Received and transferred.
[0052]
In this configuration, the movable guide side corner of the paper guide member is chamfered or rounded, so that the transfer paper can smoothly enter the fixing unit and the shock received when hitting the corner is distributed. Alternatively, it can be reduced.
[0053]
(9) At least one paper guide member among the divided paper guide members is configured such that the back surface of the paper after image transfer conveyed on the paper conveyance path contacts and is grounded / discharged. It is characterized by.
One of the paper guide members is formed of a conductive member, or a simple configuration in which a conductive member is attached to a contact surface with the paper, and the back surface of the paper after image transfer is brought into contact with the paper, Since the charge accumulated at the edge can be grounded / discharged, the occurrence of the electrostatic offset phenomenon can be effectively prevented, and the image quality can be improved stably.
When the paper is transported, the paper guide member is displaced toward the heating roller, so that the recording paper is always transported in contact with the paper guide member, and the charge accumulated on the paper edge is transferred via the paper guide member. It can escape to the outside, and the occurrence of the electrostatic offset phenomenon can be prevented.
  (10)The movable paper guide member is made of a conductive member.
[0054]
In this configuration, the electric charge accumulated at the paper edge can be efficiently released to the outside through the paper guide member, and the occurrence of the electrostatic offset phenomenon can be prevented.
[0055]
  (11) Paper discharge position after image formationIs arranged in the upper part of the apparatus main body.
[0056]
In this configuration, since the paper discharge unit is disposed in the upper part of the apparatus main body, the sheet conveyance path to the fixing device is easily formed in a vertical path shape. Accordingly, although the sheet after the transfer is likely to sag, the sheet guiding means is divided into a plurality of sheet guiding members, so that the degree of freedom in layout of the sheet guiding means is remarkably improved. Even if the path is formed in a vertical path shape, each sheet guide member can be disposed at an appropriate position in an appropriate posture without requiring strict component accuracy and assembly accuracy, and the recording sheet guide to the fixing device This makes it possible to improve the stability and firmness of the image, thereby enabling stable fixation of the transferred image, eliminating contamination to the surroundings, and effectively preventing jamming, and electrostatic offset. Occurrence of the phenomenon can be effectively prevented, and the image quality can be stably improved.
[0057]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a fixing device according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0058]
(Schematic configuration of image forming apparatus)
FIG. 2 shows a schematic configuration of the image forming apparatus. This image forming apparatus applies a light image based on image information from an optical system to the photosensitive drum 2 in the image forming unit 1 formed as a process cartridge. An image of a developer (hereinafter referred to as “toner”) is formed.
[0059]
The process cartridge constituting the image forming unit 1 includes a charging unit 3, an exposing unit 4, a developing unit 5, a cleaning unit 6, and the like around the photosensitive drum 2 as process units that act on the photosensitive drum 2. And these are integrated.
[0060]
In synchronism with the formation of the toner image in the image forming unit 1, a recording sheet (paper) P is supplied from a paper cassette (not shown) or a manual paper feeding unit, and includes a pickup roller, a pinch roller pair, a registration roller pair, etc. (not shown). The toner image conveyed by the paper conveyance system and formed on the photosensitive drum 2 in the image forming unit 1 is transferred onto the recording paper P by the transfer roller 7.
[0061]
The recording paper P is conveyed through the paper guiding means 9 to the fixing means 8 having a fixing roller pair including a heating roller 81 incorporating a heater and a pressure roller 82, and the transferred toner image is heated on the recording paper P. To settle. The recording paper P is conveyed by a pair of intermediate rollers (not shown) and discharged to a discharge portion (not shown) provided at the top of the apparatus main body. A guide member for guiding the recording paper P is disposed between the rollers of the paper transport system, although not shown.
[0062]
(Arrangement of paper guide means)
The sheet guiding means 9 for guiding the recording sheet P to the fixing device 8 is divided into a plurality of sheet guiding members. In the example shown in FIG. 1, the sheet guiding means 9 is divided into a fixed guiding member 91 and a movable guiding member 92. . The fixed guide member 91 is disposed at a lower position slightly offset downward from a tangent line (transfer / fixing tangent line) connecting the transfer position and the fixing position (fixing nip position). The load on the recording sheet P after transfer conveyed in the sheet conveying direction is reduced so that the recording sheet P can be smoothly entered.
[0063]
On the other hand, the movable guide member 92 is disposed at a position closest to the upstream side of the fixing unit 8, and a support shaft 92 a disposed in a direction orthogonal to the sheet conveyance direction is used as a rotation center axis, and the upstream side in the sheet conveyance direction is disposed. The free end (movable end) side is configured to freely rotate (swing), and is rotated at a predetermined timing by a control signal output from the control device 100 (see FIG. 4), as will be described later. It has become.
[0064]
Until the recording paper P arrives, as shown by a solid line, the recording paper P is in a standby position with the free end side directed downward, and the recording paper P guided along the fixed guide member 91 is surely entered and fixed. Jam generation is reduced by making the guide to the apparatus 8 good. After the leading end is guided to the fixing nip position, as shown by a two-dot chain line, the free end side is rotated upward (rotating position, movable position), and the recording paper P is pushed up from below. Apply stiffness to the paper. Thereby, it is possible to prevent the image quality from being deteriorated due to the stain (edge stain) of the unfixed image caused by the trailing edge of the paper (removal of mechanical factors).
[0065]
Since the recording paper P is offset downward from the transfer / fixing tangent line and is conveyed along the fixed guide member 91 (there is a space that allows deformation of the paper), the movable guide member 92 is provided immediately before the fixing device 8. The transfer paper is deformed in a curved shape toward the upper side of the transfer / fixing tangent line, as shown by a two-dot chain line, so that the portion at the transfer position is not pulled. The occurrence of paper blur at the position is prevented. Note that the movable guide member 92 returns to the initial position when the trailing edge of the sheet passes through the fixing nip portion (until the next sheet arrives).
[0066]
The movable guide member 92 is formed of a conductive member. As described above, the movable guide member 92 is brought into contact with the back surface of the recording paper P (in a half-biased state) immediately before the fixing device 8 to push it up. In addition to performing the stiffening, it is possible to reliably ground and discharge the reverse polarity charge remaining on the back surface of the recording paper P. As a result, the recording paper P in a state where the electric charge has been removed is carried into the fixing roller pair, and an offset phenomenon occurs (without making the fixing roller conductive in the fixing process as in the prior art). Can be effectively prevented (removal of electrostatic factors).
[0067]
As described above, in the present embodiment, the sheet guide unit 9 is divided into the single fixed sheet guide member 91 and the movable guide member 92, and the movable guide member 92 is formed of the conductive member, thereby fixing the fixing device. By disposing it immediately upstream of 8, it is possible to eliminate both (mechanical factor) and (electrostatic factor) that lower the print quality in the paper transporting process up to the fixing process.
[0068]
(Cross-sectional shape of the movable guide member)
As shown in FIGS. 3A to 3C, the movable guide member 92 has a cross-sectional shape in a direction orthogonal to the paper conveying direction as a substantially crown shape that protrudes upward, and moves to both side ends. It is preferable to form it in such a shape that the thickness is reduced as it goes on. By adopting such a shape, the effect of applying the stiffness to the paper when the movable guide member 92 is moved to the movable position and the paper is pushed up becomes remarkable.
[0069]
That is, when the cross-sectional shape of the movable guide member 92 is an arc shape as shown in FIG. 3A, it is easy to form with a conductive material (sheet metal), and it moves to both ends in the paper width direction. Accordingly, it is preferable that the thickness is smoothly reduced, the paper conveyance surface is formed in an arc shape, and the radius of curvature of the arc portion is set to about 300 to 400 mm.
[0070]
In the case of a mountain shape as shown in FIG. 3B, it is easy to form with a conductive material (sheet metal), and it is gently inclined as it moves to both ends in the paper width direction, and the center of the paper transport surface is Inclined toward the sides as a ridgeline.
[0071]
In the case of a trapezoidal shape as shown in FIG. 3C, it is easy to form with a conductive material (sheet metal), and the vicinity of the central portion in the paper width direction is flat, and as it moves to both ends in the paper width direction. Gently tilt.
[0072]
Any of the shapes can promote the effect of applying the stiffness to the paper when it acts on the trailing edge of the paper. In addition, the movable end portion of the movable guide member 92 on the sheet conveyance surface side is chamfered or rounded so that the sheet can smoothly enter the fixing device 8, and the corner portion It is preferable to disperse or reduce the shock received by the paper when it hits the head.
[0073]
When the trailing edge of the sheet has not reached the movable guide member 92 and does not act on the recording sheet P, the free end side of the movable guide member 92 connects the fixing nip portion and the transfer position as described above. It is offset to a lower position retracted from the back side of the sheet along the line, and the load when the transfer sheet enters the roller pair of the fixing device 8 is reduced to ensure the smooth entry of the transfer sheet.
[0074]
On the other hand, when the movable guide member 92 is rotated (when the trailing edge of the recording sheet passes through the transfer position and then acts on the trailing edge of the sheet), the free end is moved between the fixing nip portion and the transfer position. Rotate upward to the inner side (image transfer side) of the connecting line, lift the rear end side of the transfer paper P, and use the crown shape convex upward to the rear end side of the transfer paper P Thus, the stiffness of the paper can be improved, and the occurrence of harmful effects caused by sagging due to the weight of the paper can be prevented.
[0075]
(Position control of movable guide member)
A control system for controlling the attitude of the movable guide member 92 is shown in FIG. The control device (attitude control means) 100 includes a CPU (central processing unit) that performs various calculations, a ROM (storage means), a RAM (temporary storage means), an input unit, and an output unit. A sensor and a set button are connected, and an input button is connected to the RAM. On the other hand, a motor driver for driving a drive motor (not shown) connected to the rotation shaft 92a of the movable guide member 92 is connected to the output section.
[0076]
In this configuration, the input unit receives humidity information from a humidity sensor, image information from an image forming unit (not shown), and paper size information from a set button provided on the control panel. Is done. A correction input button provided on the control panel is used to correct data stored in the control device 100, and can input a data correction signal to the memory.
[0077]
In this control device 100, various information for performing posture control of the movable guide member 92 is transmitted to a motor driver as a drive unit via the output unit based on information from the input unit. Here, in the control device 100, a suitable timing for performing the posture control of the movable guide member 92 is set according to the humidity, the paper size, the image information, and the like.
[0078]
As for the timing of the posture control of the movable guide member 92, since the paper size to be fed and transported is known in advance, for example, the timer is started based on the timing when the leading edge of the fed paper passes through the registration roller section. Or by counting the number of pulses, the paper trailing edge is rotated in the forward direction to the upper rotation position immediately before passing the transfer position, and in the opposite direction when the paper trailing edge passes through the fixing nip. It can be set to rotate and return to the initial position. The rotating operation of the movable guide member 92 in the forward and reverse directions can be performed by sending a control signal from the drive unit to the motor driver to drive the drive motor in the forward and reverse directions.
[0079]
Incidentally, conventionally, as a measure for preventing the offset phenomenon, as described above, it is performed separately from the removal of the (mechanical factor). For example, when the fixing roller is made conductive, the fixing roller for the paper is fixed. The charge does not escape only by rotating one turn, and an offset occurs in the next sheet. Further, if the transfer current is turned off just before the trailing edge of the paper, no fixing offset occurs, but in this case, streaks stored as a memory on the photosensitive drum appear in the image. Therefore, any method was insufficient in effect.
[0080]
In the present embodiment, the paper guide means 8 is divided into a plurality of paper guide members, and in particular, as a simple configuration in which one of them is disposed as a movable guide member 92 made of a conductive member at a position immediately before the fixing device 8. By rotating the movable guide member 92 at a predetermined timing according to the use conditions such as in the paper transporting process up to the fixing process, (mechanical factor) and (electrostatic factor) are combined. Thus, the recording paper P can be sufficiently stiffened and the occurrence of the offset phenomenon can be effectively prevented.
[0081]
In order to remove the reverse polarity charge staying on the recording paper P, the movable guide member 92 is preferably formed of a conductive member (for example, a sheet metal material) as described above. The main body of the member 92 may be formed of a resin material or the like, and a conductive member may be attached to a portion of the main body that contacts the recording paper P. Or although illustration is abbreviate | omitted, you may form a fixed guide member with an electroconductive member.
[0082]
Further, the dividing method of the sheet guiding means 8 is not limited to the configuration as shown in FIG. 1 and may be appropriately divided according to the model. Although illustration is omitted, a plurality of movable guiding members are provided. It may be arranged on both sides of the fixed guide member, may be divided only into a plurality of fixed guide members, or may be divided into only a plurality of movable guide members.
[0083]
Furthermore, the image forming apparatus includes not only an image forming apparatus having a vertical path-shaped paper conveyance path as shown in FIG. 2 but also an image forming apparatus in which the paper conveyance path is formed in an oblique path shape or a horizontal path shape. Needless to say, the present invention can be applied.
[0084]
【The invention's effect】
As apparent from the above description, the present invention has the following effects.
[0085]
(1) Since the paper guide means is divided into a plurality of paper guide members, the degree of freedom of layout of the paper guide means is remarkably improved. For example, the paper discharge unit is provided in the upper part of the image forming apparatus main body. Even in such a case, each sheet guide member can be disposed at an appropriate position and in an appropriate position on the sheet conveyance path formed in a vertical path shape without requiring strict component accuracy and assembly accuracy.
[0086]
Therefore, it is possible to improve the guideability and stiffness of the recording paper to the fixing device, to effectively prevent the paper from drooping, to enable stable fixation of the transferred image, and to prevent contamination to the surroundings. In addition, the occurrence of jam can be effectively prevented.
[0088]
PaperSince the guide member is movable, the corresponding angle (posture) with respect to the paper can be set more appropriately, and the guide property of the recording paper to the fixing device can be further improved. Further, the effect of applying the stiffness to the recording paper can be made even more remarkable.
[0089]
  (2)Since the movable paper guide member is disposed at the closest position upstream of the fixing device, the guide property of the recording paper to the fixing device can be further improved, and it is sandwiched between the fixing roller pair. Since it is possible to apply a stiffening to the recording paper, the stiffening action becomes even more remarkable.
[0090]
  In addition,By operating the movable paper guide member disposed on the back side of the paper by the attitude control means, the back of the recording paper can be reliably guided to guide the recording paper to the fixing device. Even if the trailing edge of the recording sheet becomes free, the trailing edge of the recording sheet does not move (shake) in the direction of the surface of the sheet. The toner image on the recording paper is not disturbed by a mechanical external cause without contacting a member or the like.
[0092]
  (3)The posture control means returns the sheet guide member to the initial position when the trailing edge of the sheet passes through the fixing nip portion, so that the sheet guide member is returned in a timely manner until the next recording sheet is fed. be able to.
[0093]
  In addition,When the recording paper enters the roller pair of the fixing device, the paper guide member is at a lower position retracted from the back side of the paper along a line connecting the fixing nip and the transfer position, so that the load is reduced to transfer paper. Can smoothly enter the paper guide member.
[0094]
Then, after the trailing edge of the recording paper passes through the transfer position, the paper guiding member is displaced upward, and the paper rigidity is improved by performing a caulking action on the trailing edge side of the transfer paper. Can be prevented.
[0095]
  (4)The cross-sectional shape of the movable paper guide member has a crown shape that is convex toward the side in contact with the paper, and the thickness decreases as it moves to the ends of both sides. Since the portion is deformed upward and the effect of applying the stiffness to the recording sheet is promoted, the rigidity of the sheet is improved, so that the drooping due to the weight of the sheet can be prevented.
[0096]
  (5)Since the cross-sectional shape of the movable paper guide member has an arc shape on the side in contact with the paper, the central portion in the recording paper width direction is deformed upward, and the action of applying stiffness to the recording paper is promoted. Since the rigidity of the paper is improved, it is possible to prevent sagging due to the weight of the paper.
[0097]
  (6)Since the cross-sectional shape of the movable paper guide member is a mountain shape on the side in contact with the paper, the central portion in the width direction of the recording paper is deformed upward, and the action of applying a stiffness to the recording paper is promoted.
[0098]
  (7)The cross section of the movable paper guide member has a trapezoidal shape with the side that contacts the paper as the upper base, so the central part in the width direction of the recording paper is deformed upwards, and the action of applying stiffness to the recording paper is promoted Is done.
[0099]
  (8)Since the movable end of the movable paper guide member on the paper conveyance surface side is chamfered or rounded, the transfer paper smoothly enters the fixing section and is received when it strikes the corner section. Shock can be dispersed or reduced.
[0100]
(9) By bringing the back surface of the paper after image transfer into contact with one of the paper guide members, the charge accumulated on the paper edge can be grounded / discharged, so the occurrence of electrostatic offset phenomenon is effective. Therefore, it is possible to improve the stability of image quality.
When the paper is transported, the paper guide member is displaced toward the heating roller, so that the recording paper is always transported in contact with the paper guide member, and the charge accumulated on the paper edge is transferred via the paper guide member. It can escape to the outside, and the occurrence of the electrostatic offset phenomenon can be prevented.
  (10)Since the movable paper guide member is formed of a conductive member, the charge accumulated on the paper edge can be efficiently released to the outside through the paper guide member, and the occurrence of an electrostatic offset phenomenon can be prevented. .
[0101]
  (11) Paper discharge position after image formationHowever, since the sheet conveyance path to the fixing device is easily formed in a vertical path shape, the sheet guide means is divided into a plurality of sheet guide members, so that the sheet guide The degree of freedom of the layout of the means is remarkably improved, so even if the paper transport path is formed in a vertical path shape, each paper guide member can be placed in an appropriate position without requiring strict component accuracy or assembly accuracy. It can be placed in an appropriate posture and can improve the guideability and stiffness of the recording paper to the fixing device. This enables stable fixing of the transferred image and eliminates contamination to the surroundings. Further, the occurrence of jam can be effectively prevented, and the occurrence of the electrostatic offset phenomenon can also be effectively prevented, so that the image quality can be stably improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a main part configuration according to an embodiment of a fixing device of the present invention.
FIG. 2 is a schematic configuration diagram of the image forming apparatus.
FIG. 3 is a sectional view of the movable guide member.
FIG. 4 is a control system block diagram of the attitude control means.
FIG. 5 is an explanatory diagram illustrating an example of a configuration of a conventional image forming apparatus.
[Explanation of symbols]
9-Paper guide means
81-Heating roller
82-Pressure roller
91, 92-paper guide members
100-Attitude control means

Claims (11)

In a fixing device provided with a sheet guide means in a sheet conveyance path from a transfer position of a toner image to a sheet to a fixing nip portion of a fixing roller pair composed of a heating roller and a pressure roller that are in pressure contact with each other,
The sheet guide means is disposed below the sheet conveyed from the transfer position, lifts the front end of the sheet, guides the front end of the sheet toward the fixing nip portion, and the pair of fixing rollers guides the guided sheet. It is transported in a substantially vertical direction,
Further, the sheet guiding means is divided into a plurality of sheet guide members, among the divided sheet guide member, the at least one sheet guide member, a sheet guide member movable to its posture is changed,
A line connecting the movable end of the movable paper guide member with the fixing nip portion and the transfer position at the timing immediately before the front end of the paper passes the fixing nip portion and the rear end of the paper passes the transfer position. Fixing device provided with posture control means for displacing beyond . The fixing device according to claim 1, wherein the movable sheet guide member is disposed at a position closest to the upstream side of the fixing device. The fixing device according to claim 1, wherein the posture control unit returns the sheet guide member to an initial position when the sheet trailing edge passes between the fixing nip portions. The cross-sectional shape of the movable paper guide member is a crown shape convex toward the side in contact with the paper, and the thickness is reduced as it moves to both side ends. The fixing device according to any one of 1 to 3. The fixing device according to claim 1, wherein a cross-sectional shape of the movable paper guide member is an arc shape on a side in contact with the paper. The fixing device according to claim 1, wherein a cross-sectional shape of the movable paper guide member is a mountain shape on a side in contact with the paper. The fixing device according to claim 1, wherein a cross-sectional shape of the movable paper guide member is a trapezoidal shape with a side contacting the paper as an upper base. The fixing device according to claim 1, wherein a movable end of the movable sheet guide member on a sheet conveyance surface side is formed into a chamfered shape or a rounded shape. The at least one paper guide member among the divided paper guide members is configured such that the back surface of the paper after image transfer conveyed on the paper conveyance path contacts and is grounded / discharged. The fixing device according to claim 1. The fixing device according to claim 9, wherein the movable sheet guide member is made of a conductive member. The fixing device according to claim 1, wherein a paper discharge position after the image formation is disposed at an upper portion of the apparatus main body .

Images