JP4854134B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic printer, and more particularly to an image forming apparatus including a switchback conveying unit that reverses the sheet conveying direction downstream of the fixing unit in the conveying direction.
[0002]
[Prior art]
Some image forming apparatuses such as electrophotographic printers have a sheet conveyance path for performing automatic printing on both sides of a sheet such as paper. In general, such an apparatus is configured to print on the second side by printing on one side of the sheet, then inverting the sheet and transporting it again to the image forming unit.
[0003]
An electrophotographic printer as shown in FIG. 6 has been proposed as an image forming apparatus capable of printing on both sides of a sheet.
[0004]
That is, the image forming unit 101 that forms a toner image on the sheet S, the fixing unit 102 that fixes the toner image formed on the sheet S to the sheet S, and the sheet S provided on the downstream side of the fixing unit 102 in the transport direction. A sheet discharge unit 103 that discharges to the outside of the apparatus; a switchback conveyance unit 104 that is provided downstream of the fixing unit 102 in the conveyance direction and reverses the conveyance direction of the sheet S; and the switchback conveyance unit 104 and the image forming unit 101 On the other hand, a refeed conveyance path 106 that communicates with the sheet conveyance path 105 on the upstream side in the sheet conveyance direction is provided.
[0005]
[Problems to be solved by the invention]
In the apparatus of FIG. 6, as a measure for further downsizing the apparatus, the distance L from the transfer roller 101a of the image forming unit 101 to the fixing device 102 is set to be short. In such an apparatus, since the slack of the sheet S from the transfer roller 101a to the fixing device 102 is small, the tension of the sheet S from the transfer roller 101a to the fixing device 102 is more due to the above-described fluctuation in the sheet conveyance speed between transfer and fixing. It tends to fluctuate and sometimes causes problems such as image expansion and distortion.
[0006]
As means for solving such a problem, a heating device and an image forming apparatus disclosed in Japanese Patent Laid-Open No. 7-261484 have been proposed. In this method, the motor (fixing system motor) that mainly drives the fixing device and the motor that drives other driven parts centering on the image forming unit are separate motors, so the driving speed of the fixing system motor is controlled. By doing so, it is possible to control the sheet tension from the transfer roller 101a to the fixing device 102 so as not to fluctuate, and to solve the above problem.
[0007]
Here, with respect to the apparatus shown in FIG. 6, the motor configuration described above (a motor that mainly drives the fixing device 102 and a motor that drives other driven parts centering on the image forming part 101 are separate motors. ) Is applied, one more motor (three in total) is required to drive the sheet discharging means 103 to be reversed, which increases the cost required for the motor (drive source).
[0008]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of automatic double-sided printing at a low cost.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
An image forming unit for forming a toner image on a sheet;
Across the fixing film between the fixing film in the press nip formed between the heater and the rotating body and the rotating body, while conveying the sheet on which the toner image has been formed, the toner image on the sheet a fixing device for fixing to the seat, has a fixing unit configured to the fixing film by the rotating body is driven to follow the rotation of the rotating body,
In the image forming apparatus for discharging the sheet on which the toner image is fixed by the fixing device to the outside of the apparatus,
A switchback conveying unit that is provided downstream of the fixing unit in the sheet conveying direction from the image forming unit toward the fixing unit, and that switches the sheet conveying direction to the opposite direction and conveys the sheet. A switchback conveying means including a roller that can be rotated forward and backward, and an intermediate paper discharge roller that is disposed between the fixing device and the roller that can rotate forward and backward and that can rotate only in one direction ;
Re-feeding for transporting the sheet transported by the switchback transport means with the transport direction switched to a position upstream of the image forming unit from the image forming unit toward the fixing unit in the sheet transport direction. A transport path;
A drive source that drives the forward and reverse rollers, the intermediate discharge roller, and the rotating body ,
The drive source is capable of forward and reverse rotation so that the forward and reverse reversible roller switches the transport direction,
The intermediate sheet discharge roller conveys a sheet from the fixing device to the forward-reversible roller, and a sheet from the forward-reversible roller whose rotation direction is switched to the reverse direction to the refeed conveyance path. ,
When the drive source rotates forward between the drive source and the rotating body , power is transmitted to the rotating body, and when the drive source reverses, power is not transmitted to the rotating body . Providing transmission means ,
Further, a gear mechanism including a pendulum gear for transmitting the drive from the drive source so that the intermediate sheet discharge roller rotates in one direction regardless of whether the drive source is forward or reverse is provided with the drive source and the intermediate discharge. It is provided between the paper rollers .
[0010]
The forward / reverse roller is preferably a discharge roller for discharging the sheet on which the toner image is fixed to the outside of the apparatus.
[0012]
Further, it is preferable that the driving speed of the driving source is variable.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0014]
An example in which the image forming apparatus according to the embodiment of the present invention is used in a laser printer will be described.
[0015]
FIG. 1 is a cross-sectional view of an image forming apparatus A according to the embodiment. 2 and 3 are side views of the driving unit when the image forming apparatus A is viewed from the back side.
[0016]
The image forming apparatus A includes an image forming unit A1 that forms a toner image on the sheet S, a fixing device 12 that fixes the toner image formed on the sheet S to the sheet, and a sheet provided downstream of the fixing device 12 in the conveyance direction. A discharge roller 14 that forms a sheet discharge unit that discharges S to the outside of the apparatus, and an intermediate discharge roller that forms a switchback conveyance unit that is provided downstream of the fixing unit 12 in the conveyance direction and reverses the conveyance direction of the sheet S 13a, and a re-feed conveyance path B2 that communicates with the intermediate sheet discharge roller 13a and the sheet conveyance path B1 on the upstream side in the sheet conveyance direction with respect to the image forming unit A1.
[0017]
The image forming unit A1 transfers the toner image formed on the photosensitive drum 3 to the sheet S, the process cartridge 2 including the photosensitive drum 3, the laser scanner 1 that writes image information on the photosensitive drum 3 by the laser L, and the like. The transfer roller 4 is provided. The process cartridge 2 forms a toner image on the photosensitive drum 3 by a so-called electrophotographic process, and incorporates a charger, a developer, a cleaner, etc. (not shown).
[0018]
That is, the laser L based on the obtained image information is emitted by the laser scanner 1, and the laser L is irradiated onto the uniformly charged photosensitive drum 3 built in the process cartridge 2. Then, a latent image is formed on the photosensitive drum 3, and the latent image is developed as a toner image by the developing device.
[0019]
On the other hand, the sheets S stacked on the recording paper stacking plate 5 are fed one by one while being separated one by one by the feed roller 6 and the separation pad 7, and the intermediate roller 8 and the transport roller arranged in the sheet transport path B1. 9, the toner image is further conveyed to the downstream side. On the conveyed sheet S, a visible image formed by the toner formed on the photosensitive drum 3 is transferred by the transfer roller 4.
[0020]
Then, the sheet S on which the unfixed toner image is formed is conveyed further downstream, the toner image is fixed by the fixing device 12 having a heat source therein, and then only one side is printed. After passing through the paper roller 13a, the paper is discharged outside by the discharge roller 14.
[0021]
Next, the configuration of the apparatus for printing on both sides of the sheet will be described.
[0022]
The discharge roller 14 is configured to be forward / reverse. Here, when the trailing edge of the sheet S1 passes through the nip formed by the intermediate paper discharge roller 13a and the intermediate paper discharge roller 13b and reaches the position of the solid line in the figure, the discharge roller starts a reverse operation. That is, it rotates in the direction opposite to the direction of the arrow Y that has been rotated so far.
[0023]
The sheet passage detection is performed by the sensor arm 19 and a photo interrupter (not shown) that detects the movement of the sensor arm 19. That is, when the sheet passes through the sensor arm 19, the sensor arm 19 is in the position of the solid line in the figure, and otherwise, it is in the position of the broken line. By detecting this difference in position by a photo interrupter, the trailing edge position of the sheet is detected, and the timing for starting the reverse operation of the discharge roller 14 is determined.
[0024]
By this reverse operation, the sheet is conveyed downward along the guide 16 and guided to a nip formed by the switch roller 15 and the intermediate paper discharge roller 13a. Thereafter, the sheet is conveyed to the intermediate paper discharge roller 13 a and reaches the intermediate roller 8 through the double-sided conveyance roller 17. The image is transferred by the transfer roller 4 in the same manner as the image formation on the first surface, and is discharged out of the apparatus by the discharge roller 14 through the fixing device 12 and the intermediate discharge roller 13a.
[0025]
Here, the configuration of the fixing device 12 will be described in detail.
[0026]
FIG. 5 shows an enlarged view of a cross section of the fixing device 12.
[0027]
The fixing device 12 is a heating device of a pressure member drive type / tensionless type film heating method (Japanese Patent Laid-Open Nos. 4-44075 to 44083, Japanese Patent Laid-Open No. 4-2048080 to 204484, etc.), and is fixed as a heating body. It comprises a film 12b and a fixing pressure roller 12d as a rotating body that rotates while being pressed against the fixing film 12b.
[0028]
Reference numeral 12a denotes a heat-resistant resin stay, which serves as an inner surface guide member of the endless heat-resistant film (fixing film) 12b and has a heater 12c as a heating element. The fixing film 12b is fitted on the stay 12a including the heater 12c. The inner peripheral length of the fixing film 12b and the outer peripheral length of the stay 12a including the heater 12c are larger in the fixing film 12b. Therefore, the fixing film 12b is loose with a sufficient peripheral length with respect to the stay 12a. It touches.
[0029]
The fixing pressure roller 12d sandwiches the fixing film 12b with the heater 12c to form a fixing portion N that is a pressure nip, and drives the fixing film 12b. The fixing pressure roller 12d is composed of a metal shaft and silicon rubber sheathed on the metal shaft.
[0030]
Here, as the heater 12c is heated, the temperature of the fixing pressure roller 12d rises with time, and at this time, the outer diameter increases due to thermal expansion of the rubber portion. Since the fixing pressure roller 12d is normally driven to rotate at a constant rotational speed, when the fixing pressure roller 12d is at a high temperature, the thermal expansion is larger than when it is at a low temperature, the rotational peripheral speed is increased, and the sheet conveying speed is increased. turn into.
[0031]
The first motor 21 as a first drive source capable of rotating forward and backward that drives the switchback transport mechanism A3 and the fixing device 12 and the second as a second drive source that drives the drive portion of the image forming unit A1. A motor 18 is provided.
[0032]
The first motor 21 drives the fixing pressure roller 12 d constituting the fixing device 12 , the intermediate paper discharge roller 13 a and the discharge roller 14, and the double-sided conveyance roller 17 constituting the switchback conveyance unit. The first motor 21 is composed of a step motor, and is capable of speed control and rotation in both forward and reverse directions.
[0033]
The second motor 18 drives the conveying roller 9 and the paper feeding roller 6 together with the photosensitive drum 3, the transfer roller 4, and the intermediate roller 8 that constitute the driving unit of the image forming unit A. The second motor is constituted by a DC motor.
[0034]
Reference numeral 22 denotes a refeed sensor arm that detects the passage of the sheet S, and the passage of the sheet S is detected by the refeed sensor arm 22 and a photo interrupter (not shown) that detects the movement thereof.
[0035]
2 is a side view of the drive mechanism around the first motor 21 of the apparatus A as viewed from the back side of FIG.
[0036]
That is, between the first motor 21 and the fixing pressure roller 12d of the fixing device 12, when the first motor 21 rotates forward, drive transmission to the fixing device 12 is performed, and when the first motor 21 rotates in reverse, the driving force is transmitted to the fixing device 12. A fixing drive transmission mechanism C is provided as power transmission means that does not perform drive transmission.
[0037]
In FIG. 2, 21a is a motor gear attached to the motor shaft of the first motor 21, 39 is a pressure roller gear attached to the fixing pressure roller 12d, and 48 is an intermediate paper discharge roller attached to the intermediate paper discharge roller 13a. Similarly, 49 is an intermediate paper discharge roller pulley attached to the intermediate paper discharge roller 13 a, 35 is a discharge roller gear attached to the discharge roller 14, and 53 is a double-sided conveyance roller pulley attached to the double-sided conveyance roller 17. 31 and 36 are two-stage gears in which two gears are integrally formed. Reference numerals 32, 33, 34, 37, 41, 45, 46 and 47 are idler gears.
[0038]
The fixing drive transmission mechanism C is disposed between the gear transmission mechanism C1 including the motor gear 21a, the two-stage gear 36, the idler gear 37, and the pressure roller gear 39, and between the pressure roller gear 39 and the fixing pressure roller 12d. The one-way clutch 38 is configured. The one-way clutch 38 transmits only the driving force in the direction of arrow V (the forward rotation direction of the fixing pressure roller 12d) from the pressure roller gear 39 to the fixing pressure roller 12d.
[0039]
A pendulum arm 42 is provided so as to be rotatable about the gear shaft 40 of the idler gear 41. The pendulum arm 42 is provided with a pendulum gear 43 that can rotate around a gear shaft 44.
[0040]
51 is an idler pulley. A first drive belt 50 and a second drive belt 52 are hung on the intermediate paper discharge roller pulley 49 and the idler pulley 51, and the idler pulley 51 and the duplex conveying roller pulley 53, respectively. For this reason, the driving force is transmitted to the duplex conveying roller pulley 53 by the first driving belt 48 and the second driving belt 50.
[0041]
FIG. 4 is a developed top view of the drive unit. This figure shows the configuration of gear trains 33 and 34 from the motor gear 21a to the discharge roller gear 35. As shown in FIG. 4, the motor 21 is attached to the frame 54. Each gear shaft is attached to the drive side plate 55, and the driving force of the motor 21 is transmitted to the discharge roller gear 35 and the discharge roller 14 by a gear train that can rotate around the gear shaft. Similarly, drive transmission to other rollers is performed by a gear train sandwiched between the frame 54 and the drive side plate 55.
[0042]
After the sheet S is fed by the feeding roller 6, the motor gear 21a, the pressure roller gear 39 and the fixing pressure roller 12d, and the intermediate discharge roller gear 48 until the trailing edge of the sheet S passes through the fixing pressure roller 12d. The intermediate discharge roller 13a, the discharge roller gear 35, and the discharge roller 14 are rotated in the directions indicated by the arrows in FIG. At this time, the pendulum arm 42 is stationary at the position shown in FIG. 2 due to the transmission of force from the idler gear 41 through the pendulum gear 43, and the pendulum gear 43 rotates in the direction shown in the drawing to transmit the drive to the idler gear 45. ing.
[0043]
Next, a description will be given of a refeed operation when automatic duplex printing is performed on the sheet S1.
[0044]
When the sheet S1 passes through the intermediate paper discharge roller 13a and reaches the position shown in FIG. 1, the first motor 21 starts to rotate in the direction opposite to the arrow shown in FIG.
[0045]
Here, the idler gear 41 tries to start rotating in the direction opposite to the arrow in FIG. 2, so that a force that rotates in the direction of arrow Y is applied to the entire pendulum arm 42. As a result, the pendulum arm 42 starts to rotate in the direction of the arrow Y and rotates to the position shown in FIG. Here, the pendulum gear 43 is connected to the idler gear 46. Accordingly, the intermediate paper discharge roller gear 48 rotates in the same direction as in FIG. 2 by the power transmission of the lower gear. Further, the transmission of the drive by the belts 50 and 52 causes the double-sided conveyance roller pulley 53 to rotate in the same direction.
[0046]
Here, the pressure roller gear 39 rotates in the direction shown in FIG. 3, but the drive is not transmitted to the fixing pressure roller 12 d due to the action of the one-way clutch 38. For this reason, when the first motor 21 reverses, the fixing pressure roller 12d remains stationary.
[0047]
When the leading edge of the sheet reaches the refeed sensor arm 22, the first motor starts to rotate forward again, and the pendulum arm 42 returns to the position shown in FIG. As a result, each roller returns to the original rotation speed and conveys the sheet.
[0048]
Thereafter, the sheet is conveyed to the intermediate paper discharge roller 13 a and reaches the intermediate roller 8 through the double-sided conveyance roller 17. Then, the image is transferred onto the second surface by the transfer roller 4 and discharged to the outside by the discharge roller 14 through the fixing device 12 and the intermediate discharge roller 13a.
[0049]
Here, the advantage that the fixing pressure roller 12d is configured not to rotate in the reverse direction will be described.
[0050]
Normally, in the apparatus of FIG. 1, a sag V as shown in FIG. 5 occurs in the fixing film 12b due to the forward rotation of the fixing pressure roller 12d. For this reason, a space is provided on the downstream side of the fixing film 12b for the slackness of the film.
[0051]
However, if it is assumed that the fixing pressure roller 12d is reversely rotated, the fixing film 12b is also rotated in reverse. In this case, sagging can be made on the upstream side of the fixing film 12b. Here, normally, the fixing inlet guide 18 that guides the sheet to the nip at the inlet of the fixing device 12 is attached with a small clearance d between the sheet S and the nip in order to accurately guide the sheet S to the nip. Accordingly, if a sag is formed on the upstream side of the fixing film 12b, the fixing film 12b and the fixing inlet guide 18 come into contact with each other as a result. Since the fixing film 12b is formed to be extremely thin, it may be broken by this contact.
[0052]
However, in this embodiment, as described above, since the fixing pressure roller 12d is configured to rotate only in one direction, such a problem does not occur.
[0053]
As is apparent from the above description, according to the present embodiment, it is not necessary to add a motor that can rotate forward and reverse in addition to the two motors 21 and 18 in order to reverse the discharge roller 14. . Therefore, according to the present embodiment, it is possible to provide an image forming apparatus capable of automatic duplex printing at low cost.
[0054]
Incidentally, as a switchback conveying means, of the intermediate discharge roller 13a and discharge roller 14, discharge roller 14 also serves as a sheet discharging means.
[0055]
【The invention's effect】
As described above, according to the present invention, the first drive source capable of forward / reverse driving for driving the switchback conveying means and the fixing device, and the second drive source for driving the drive portion of the image forming unit are provided. An image capable of double-sided printing is provided by providing power transmission means that transmits drive to the fixing device when the first drive source rotates forward and does not transmit drive to the fixing device when rotating reversely. A forming apparatus can be provided at low cost.
[0056]
If the switchback conveying means is the same as the sheet discharging means, the apparatus configuration can be further simplified.
[0057]
Since the fixing device includes a heating body and a rotating body that rotates while being in pressure contact with the heating body, the rotating body does not reverse when the rotating body is driven by the first drive source. No slack or the like of the heating body due to forward or reverse rotation occurs.
[0058]
If the drive speed of the first drive source is variable, control can be performed so that the sheet tension between the image forming unit and the fixing device does not fluctuate.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a side view showing a drive mechanism of the apparatus of FIG.
FIG. 3 is an explanatory diagram showing an operation during double-sided image formation of the drive mechanism of FIG. 2;
4 is a top view of the drive mechanism of FIG. 2. FIG.
FIG. 5 is an enlarged view of a cross section of the fixing device of the apparatus of FIG. 1;
FIG. 6 is a cross-sectional view illustrating a configuration of a conventional image forming apparatus.
[Explanation of symbols]
12 Fixing device 12b Fixing film (heating body)
12d fixing pressure roller (rotating body)
13a Intermediate paper discharge roller (switchback transport means)
14 Discharge roller (sheet discharge means)
15 Switch roller 18 Second motor (second drive source)
21 1st motor (1st drive source)
C Fixing drive transmission mechanism (drive transmission means)
C1 gear transmission mechanism 38 one-way clutch B1 sheet conveyance path (upstream side of image forming unit A1)
B2 Refeed conveyance path 42 Pendulum arm

Claims (3)

An image forming unit for forming a toner image on a sheet;
Across the fixing film between the fixing film in the press nip formed between the heater and the rotating body and the rotating body, while conveying the sheet on which the toner image has been formed, the toner image on the sheet a fixing device for fixing to the seat, has a fixing unit configured to the fixing film by the rotating body is driven to follow the rotation of the rotating body,
In the image forming apparatus for discharging the sheet on which the toner image is fixed by the fixing device to the outside of the apparatus,
A switchback conveying unit that is provided downstream of the fixing unit in the sheet conveying direction from the image forming unit toward the fixing unit, and that switches the sheet conveying direction to the opposite direction and conveys the sheet. A switchback conveying means including a roller that can be rotated forward and backward, and an intermediate paper discharge roller that is disposed between the fixing device and the roller that can rotate forward and backward and that can rotate only in one direction ;
Re-feeding for transporting the sheet transported by the switchback transport means with the transport direction switched to a position upstream of the image forming unit from the image forming unit toward the fixing unit in the sheet transport direction. A transport path;
A drive source that drives the forward and reverse rollers, the intermediate discharge roller, and the rotating body ,
The drive source is capable of forward and reverse rotation so that the forward and reverse reversible roller switches the transport direction,
The intermediate sheet discharge roller conveys a sheet from the fixing device to the forward-reversible roller, and a sheet from the forward-reversible roller whose rotation direction is switched to the reverse direction to the refeed conveyance path. ,
When the drive source rotates forward between the drive source and the rotating body , power is transmitted to the rotating body, and when the drive source reverses, power is not transmitted to the rotating body . Providing transmission means ,
Further, a gear mechanism including a pendulum gear for transmitting the drive from the drive source so that the intermediate sheet discharge roller rotates in one direction regardless of whether the drive source is forward or reverse is provided with the drive source and the intermediate discharge. An image forming apparatus provided between a paper roller and a paper roller . Wherein a reversible roller, an image forming apparatus according to claim 1, characterized in that the discharge roller for discharging the sheet on which the toner image is fixed to the outside of the apparatus. The image forming apparatus according to claim 1 or 2, wherein the driving speed of the driving source is variable.

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