JP2016099430A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress temperature rise inside an apparatus, in the image forming apparatus capable of forming an image on both surfaces.SOLUTION: The image forming apparatus includes an image carrier, a developing member, and a transfer member. The developing member can be switched between a first state where the developing member is in contact with or close to the image carrier and a second state where the developing member is more away from the image carrier than in the first state and develops an electrostatic latent image by a developer in the first state. The image forming apparatus includes a first conveyance path for supplying a recording material to the transfer member, a reversing mechanism for reversing the conveyance direction of the recording material after passing through the transfer member, a second conveyance path for reversing the image forming surface of the recording material whose conveyance direction is reversed and supplying the recording material to the first conveyance path, a separation mechanism for at least switching the developing member into the second state, when the conveyance direction is reversed by the reversing mechanism, and a cooling fan. The developing member takes the second state, to form an air path for guiding air from the cooling fan to the second conveyance path, so that the amount of the air flowing from the cooling fan to the second conveyance path is more increased than that when the developing member takes the first state.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  Some electrophotographic image forming apparatuses such as copying machines, printers, and fax machines can perform double-sided printing by reversing the front and back of a recording material on which an image is fixed by heat and refeeding the image forming unit. . Some image forming apparatuses using an electrophotographic image forming process employ a process cartridge system. In this method, the photosensitive drum and the process means acting on the photosensitive drum are integrated into a cartridge, and the cartridge is detachably mounted on the image forming apparatus. In an image forming apparatus, if the temperature inside the apparatus rises significantly, the toner may deteriorate and good development may not be obtained. When continuous double-sided printing is performed, the recording material that has passed through the high-temperature fixing device during single-sided printing passes through the image forming unit again for printing on the opposite side with high heat. As a result, the temperature around the cartridge rises. As a technique for suppressing the temperature rise, it has been proposed to provide a cooling fan in the image forming apparatus main body to cool the periphery of the cartridge (see Patent Documents 1 and 2).

JP-A-10-133550 JP 2005-283733 A

  However, when the image forming apparatus is downsized, a sufficient clearance between the cartridge and the heat source cannot be ensured, and the temperature rise of the cartridge cannot be sufficiently suppressed. Further, when the operation of the image forming apparatus is speeded up, the periphery of the cartridge is more susceptible to the temperature rise due to the heat of the recording material during double-sided printing. If the temperature of the image forming unit exceeds the allowable temperature, the toner is fixed in the toner container, the image forming stability of the photosensitive drum is lowered, and the toner image formed on the photosensitive drum is recorded on the recording material. Problems such as a decrease in transfer reliability may occur.

  In the present invention, after an image is formed on one side of a recording material by heat fixing, the image forming surface is reversed and fed again to the image forming unit, and an image can be formed on the opposite side by heat fixing. An object of the forming apparatus is to suppress a temperature rise in an image forming unit.

The present invention is an image forming apparatus capable of forming images on both sides of a sheet-like recording material,
An image carrier on which an electrostatic latent image is formed on the surface;
It is possible to switch between a first state that is in contact with or close to the image carrier and a second state that is farther from the image carrier than the first state. A developing member for developing the latent image;
A transfer member for transferring the developer image formed on the developing member to a recording material;
A first conveyance path for supplying a recording material to the transfer member;
A reversing mechanism that reverses the conveying direction of the recording material that has passed through the transfer member;
A second transport path that reverses the image forming surface of the recording material whose transport direction has been reversed and supplies the recording material to the first transport path;
At least when the transport direction is reversed by the reversing mechanism, the developing member is moved to the second position.
A separation mechanism for switching to a state;
A cooling fan,
With
When the developing member takes the second state, an air passage that guides the wind from the cooling fan to the second transport path is formed, and the cooling fan is more than when the developing member takes the first state. The image forming apparatus is characterized in that the amount of air flowing through the second conveyance path increases.

  According to the present invention, after an image is formed on one side of a recording material by heat fixing, the image forming surface is reversed and fed again to the image forming unit to form an image on the opposite side by heat fixing. In the image forming apparatus capable of suppressing the temperature increase of the image forming unit.

Main sectional view in Example 1 Development separation structure of cartridge Development separation timing chart Explanatory drawing of air path Explanatory drawing of double-sided reversing mechanism Parts configuration diagram of planetary gear unit Configuration explanatory diagram during normal rotation of paper ejection gear Configuration explanatory diagram when paper discharge gear reverses Double-sided reversal configuration and development separation configuration explanatory diagram in Example 2 Configuration diagram of development separation in embodiment 2

Example 1
(Image forming apparatus and recording material conveyance path)
FIG. 1 is a cross-sectional view schematically illustrating an image forming apparatus according to the first exemplary embodiment.
Inside the main body of the image forming apparatus 1, a photosensitive drum 3a as an image carrier, a photosensitive drum unit 3 that holds the photosensitive drum 3a, a developing roller 4a for developing toner on the photosensitive drum 3a, and the photosensitive drum 3a are held. A developing unit 4 is provided as a developing member. The apparatus main body further includes a laser scanner unit 5 for exposing the photosensitive drum 3a. Hereinafter, the photosensitive drum unit 3 and the developing unit 4 are collectively referred to as a cartridge 2. The image forming apparatus 1 further includes a paper feed roller 6, a transport roller pair 7, a transfer roller 8 as a transfer member that transfers a developer image to a recording material, a fixing heating device 9, a pressure roller 10, and a paper discharge roller pair 11. A roller for recording material conveyance is installed.

The conveyance path will be described with reference to FIG.
The sheet-like recording materials S stacked and stored in the paper feed tray 12 are fed one by one by the paper feed roller 6 and the separation pad 39. The recording material S is transported by the transport roller pair 7 and sent to the nip portion between the photosensitive drum 3 a and the transfer roller 8.

The photosensitive drum 3a rotates in the direction of the arrow (clockwise direction) in the drawing, and an electrostatic latent image is formed on the peripheral surface by the laser light 5a emitted from the laser scanner unit 5. The formed electrostatic latent image is developed by the developing roller 4a to form a toner image.
The toner image formed on the photosensitive drum 3 a is transferred to the recording material S sent to the nip portion between the photosensitive drum 3 a and the transfer roller 8.
Further, the recording material S onto which the toner image has been transferred is sent to the nip portion between the fixing heating device 9 and the pressure roller 10 where it is heated and pressed to fix the toner image on the recording material S.
The recording material S on which the toner image is fixed is discharged to the paper discharge tray 13 by the paper discharge roller pair 11.

Next, the conveyance path of the recording material S at the time of duplex printing will be described.
At the time of printing the first surface (front surface), the recording material S passes through the transport path (first transport path) as described above. At the time of printing on the second side (back side), after the trailing end of the recording material S passes through the nip portion between the fixing device 9 and the pressure roller 10, the conveyance direction is reversed by the reverse rotation of the paper discharge roller pair 11.
By the reversely rotated paper discharge roller pair 11, the recording material S is conveyed from the rear end of the recording material S to the double-side reversing path 15 (second conveyance path). The second transport path reverses the image forming surface of the recording material S on which the first surface has been imaged and supplies it to the first transport path. Further, the recording material S is transported in the direction of the arrow 15 a and is sent again to the transport roller pair 7 by the duplex transport roller pair 14 disposed in the duplex reversing path 15. Similarly to the first side printing, the image on the second side is transferred by the image forming unit and fixed by the fixing heating device 9. Then, the recording material S on which the second surface is printed is discharged to the paper discharge tray 13 by the paper discharge roller pair 11.

Next, a configuration for separating the developing roller and the photosensitive drum will be described with reference to FIG. In the image forming apparatus according to the first exemplary embodiment, when the main body is stopped or when image formation is not performed, the photosensitive drum 3a and the developing roller 4a are separated from the contacted state (first state) (second state). State).
In a conventional image forming apparatus that does not have a configuration capable of separating the developing roller and the photosensitive drum, the elastic layer of the developing roller is deformed when the cartridge is not used for a long time with the cartridge mounted on the main body of the image forming apparatus. There was a case. In this case, image unevenness may occur during development. In addition, since the photosensitive drum and the developing roller are rotated in contact with each other except during development, deterioration of the photosensitive drum, the developing roller, and the developer is accelerated due to sliding friction between the photosensitive drum and the developing roller. There was a case. On the other hand, since the image forming apparatus according to the first embodiment has a configuration in which the developing roller and the photosensitive drum can be separated from each other, such a phenomenon can be suppressed.

A configuration in which the developing roller and the photosensitive drum in Embodiment 1 can be separated from each other will be described with reference to FIGS. 2 (a) and 2 (b).
The cartridge 2 includes a developing unit 4 configured to be slidable with respect to the photosensitive drum unit 3, and a boss 4 b provided on the developing unit 4.
The image forming apparatus main body is attached to the solenoid, the cam 16 configured to be rotated by half rotation by energization of the solenoid, the slider cam 17 slidably attached to the image forming apparatus main body, and the slider cam 17. And a slit 18. The slit 18 is engaged with the boss 4 b of the developing unit 4. The solenoid is controlled by the controller A.

(Contact state)
In the state where the developing roller and the photosensitive drum are in contact with each other, as shown in FIG. 2A, the slider cam 17 is always urged by the urging spring 40 in the direction of the arrow 40a, and the developing roller 4a. And the photosensitive drum 3a are in contact with each other to determine the position.

(Separated state)
The separated state will be described with reference to FIG.
When a signal is input from the controller A to the solenoid, the cam 16 is rotated halfway.
The slider cam 17 is pushed by the cam 16, and the slider cam moves in the direction of the arrow 17a.
Since the slit 18 and the boss 4 b of the developing unit 4 are fitted, the developing unit 4 also slides in conjunction with the slider cam 17. By this operation, the photosensitive drum 3a and the developing roller 4a are separated from each other.
When the contact is made again, the controller A sends a signal to the solenoid, and the cam 16 can be rotated counterclockwise by half rotation to return to the state shown in FIG.

(Separation timing)
The timing of separation between the developing roller and the photosensitive drum will be described with reference to the timing chart of FIG.
The timing chart shows the contact state and separation state of the developing roller and the photosensitive drum, the rotation direction of the paper discharge roller pair 11, and the image formation timing. The operation shown in this timing chart is realized by the controller A sending a signal to the solenoid.
When the operation of the image forming apparatus main body is stopped, the developing roller and the photosensitive drum are kept apart.
When the operation of the image forming apparatus main body is started (t1), the developing roller and the photosensitive drum come into contact with each other, and the paper discharge roller pair 11 starts normal rotation and image formation on the first surface is performed.
At the timing (t2) when the trailing edge of the recording material S on which image formation has been performed on the first surface passes through the nip portion between the fixing heating device 9 and the pressure roller 10, the toner is fixed to the recording material S (t2). The rotation of the roller pair 11 is reversed, and the recording material S is conveyed to the second conveyance path 15 that is a double-sided reversal path. At the same timing (t2), the developing roller and the photosensitive drum are separated.

  At the timing (t3) when the trailing edge of the recording material S conveyed to the second conveyance path 15 of the double-side reversal path passes through the nip portion of the sheet discharge roller pair 11, the sheet discharge roller pair 11 starts normal rotation again. At that timing (t3), the developing roller and the photosensitive drum are brought into contact with each other. In this configuration, the developing roller and the photosensitive drum are brought into contact with each other when the paper discharge roller pair 11 is removed. However, the timing is not limited to this timing as long as the image formation on the second surface is in time. For example, the timing may be later than the timing t3. That is, within one period from the timing when the image formation (transfer) of the first surface is performed to the timing when the recording material that has passed through the second conveyance path 15 is supplied to the image forming unit, The photosensitive drum is separated. The timing at which the recording material S on which the second surface image is formed, the rear end of the recording material S on which the second surface image is formed has come out of the nip portion of the discharge roller pair 11, and the recording material S is discharged out of the main body. At (t4), the developing roller and the photosensitive drum are separated. After completion of the separation, the discharge roller pair 11 is also stopped at the timing (t5) of the operation stop of the image forming apparatus main body.

(Wind flow)
Next, the flow of air in the image forming apparatus according to the first exemplary embodiment will be described with reference to FIGS. 4 (a) and 4 (b).
In the first embodiment, in order to cool the cartridge 2, a cooling fan 19 is disposed in the main body toward the cartridge 2. The cooling fan may be arranged outside the image forming apparatus main body. In that case, it is set as the structure which provided the air path which leads the wind of an external fan inside.
Further, in the configuration of the first embodiment, the first conveyance path 20 that forms the first and second surface images and the second conveyance path 15 that reverses the recording material S for forming the second surface image are communicated. An air passage 21 that is a communicating passage is formed. The first transport path 20 is positioned upstream of the second transport path 15 in the flow of wind from the cooling fan 19.
The cooling fan 19 rotates while the image forming apparatus main body is operating, and stops rotating together with the operation stop of the image forming apparatus main body.
Next, the difference in wind flow between the image formation on the first side and the image formation on the second side in duplex printing will be described.

(Wind flow when forming the first image)
FIG. 4A shows the first sheet passing path and the flow of wind.
The recording material S is conveyed along the first conveyance path 20.
The wind flows from the cooling fan 19 toward the cartridge 2 in the direction of the arrow 19 a to cool the cartridge 2.

(Wind flow during second-side image formation)
As described with reference to the timing chart of FIG. 3, the developing roller and the photosensitive drum are separated from each other while the discharge roller pair 11 is rotating in the reverse direction. FIG. 4B shows the sheet passing path and the wind flow at that time.
At the time of image formation on the second side of duplex printing, the recording material S passes through the second conveyance path 15 and is conveyed toward the image forming unit (cartridge 2) with the image forming surface reversed.
The wind flows from the cooling fan 19 toward the cartridge 2. Further, as indicated by an arrow 19b, the wind is blocked when the developing roller and the photosensitive drum are in contact with each other, but the wind is formed when the developing roller and the photosensitive drum are retracted by being separated. It is sent to the air passage 21 through the space 22. Then, the wind flows from the air path 21 to the entire second transport path 15.
Thereby, the recording material S being conveyed through the second conveyance path 15 is directly cooled by the wind. Further, the second transport path 15 is cooled by the wind. Therefore, the temperature of the recording material S at the time of image formation on the second side can be lowered.

(effect)
According to the above configuration, the second state in which the developing member and the image carrier are separated from each other flows from the cooling fan to the second transport path than the first state in which the developing member and the image carrier are in contact with each other. The amount of wind increases. Even when image formation is continuously performed in the double-sided printing mode in which the temperature inside the image forming apparatus main body is likely to increase, the recording material being conveyed at the time of image formation on the second surface can be efficiently cooled. For this reason, it is possible to suppress the recording material from passing through the image forming portion while maintaining high heat during the image formation on the second side. Thereby, the temperature rise of the cartridge is suppressed. Therefore, the temperature of the cartridge is suppressed from exceeding the allowable temperature, and stable image formation is possible.
In addition, since the developing roller is separated from the photosensitive drum during conveyance of the recording material for image formation on the second side, the photosensitive drum, the developing roller, and the developer are deteriorated due to the friction between the photosensitive drum and the developing roller. Is suppressed. This allows the cartridge to be used for a longer period.
In the first embodiment, the state in which the developing member and the image carrier are in contact with each other is the first state, the state in which the developing member is in contact is the second state, and the example includes a separation mechanism that can switch between the first state and the second state. However, the developing member and the image carrier are not in contact with each other in the first state, but may be in a close state. In this case, the second state is a state in which the developing member and the image carrier are further separated from each other than the first state, and the separation mechanism is configured to be able to switch between the first state and the second state. According to such a configuration, the present invention is applied to an image forming apparatus of a contact developing type in which a latent image is developed by a developing member (developing roller) approaching an image carrier (photosensitive member) with a minute gap therebetween. Can be applied.

(Example 2)
Next, a second embodiment of the present invention will be described. The description of the same configuration as that of the image forming apparatus of Embodiment 1 is omitted.
In the first exemplary embodiment, the configuration in which the developing roller and the photosensitive drum are separated while the recording material is transporting the second transport path for the image formation on the second surface is shown. The second embodiment is characterized in that the control component of the reversing mechanism of the paper discharge roller pair also serves as a control component for separating the developing roller and the photosensitive drum.
Hereinafter, the reversing mechanism of the discharge roller pair and the separating mechanism between the developing roller and the photosensitive drum will be described in detail.
However, the dimensions, shapes, relative positions, and the like of the components described in Example 2 are appropriately changed depending on the configuration and various conditions to which the present invention is applied. The scope of the invention is not limited thereto.

(Reversing mechanism of paper discharge roller pair)
A reversing mechanism that switches the rotation of the paper discharge roller pair during duplex printing from normal rotation to reverse rotation will be described.
The drive train is shown in FIG.
The drive train includes a drive gear 23 that transmits drive from a drive source, a first planetary gear unit 24, a second planetary gear unit 25, an idler gear 26, and a paper discharge roller gear 27 that drives a paper discharge roller pair. The solenoid 28 controls forward rotation and reverse rotation.
As shown in FIG. 6, the first planetary gear unit 24 includes a sun gear 24a, a planet carrier 24b, a planet gear 24c, and an internal gear 24d. The planetary gear 24c meshes with an internal gear 24d, a sun gear 24a, and a gear (not shown) having a stepped gear configuration. In the first planetary gear unit 24, when the sun gear 24a is locked, the planet carrier 24b and the internal gear 24d are driven integrally, and when the sun gear 24a is in a free state, the internal gear is in relation to the planet carrier 24b. 24d is idling. The detailed mechanism of the planetary gear unit is omitted. The second planetary gear unit 25 has the same configuration.

(During forward rotation)
First, the normal rotation state will be described with reference to FIG.
FIG. 7A shows the rotation direction of each gear.
Here, rotation of the paper discharge roller gear 27 in the clockwise direction is defined as normal rotation, and represents a direction in which the paper discharge roller pair conveys the recording material S from the main body.
The drive gear 23 rotates counterclockwise regardless of whether it is forward or reverse.
Drive is transmitted from the drive gear 23 to the planet carrier 24b of the first planetary gear unit 24, and further transmitted from the coaxial internal gear 24d to the idler gear 26 and the discharge roller gear 27. The discharge roller gear 27 Rotate clockwise.
The above drive transmission path is represented by path 29.
The state of the solenoid at this time is shown in FIG.
A stopper 30 is attached to the tip of the solenoid. The stopper 30 rotates around the shaft 30a by turning on and off the solenoid.
During forward rotation, the solenoid 28 is in an ON state, and the tip of the stopper 30 is engaged with the sun gear 24a of the first planetary gear unit 24, whereby the planet carrier 24b and the internal gear 24d. Rotate as a unit.
On the other hand, the internal gear 25d of the second planetary gear unit 25 idles with respect to the planet carrier 25b.

(When reversed)
Next, the inversion state will be described with reference to FIG.
FIG. 8A shows the rotation direction of each gear.
The drive gear 23 rotates counterclockwise as in the forward rotation.
It is transmitted from the drive gear 23 to the first planet carrier 24 b and from there to the planet carrier 25 b of the second planet gear unit 25. Further, it is transmitted from the coaxial internal gear 25d to the idler gear 26 and the paper discharge roller gear 27, and the paper discharge gear 27 rotates counterclockwise.
The above drive transmission path is represented by path 31.
The state of the solenoid at this time is shown in FIG.
At the time of reversal, the solenoid 28 is in an OFF state, and the tip of the stopper 30 is engaged with the sun gear 25a of the second planetary gear unit 25, whereby the planetary carrier 25b and the internal gear 25d are Rotates as a unit.
On the other hand, the internal gear 24d of the first planetary gear unit 24 is idled with respect to the planet carrier 24b, and thus the forward rotation and reverse rotation of the paper discharge roller gear 27 are controlled.

(Separation mechanism between developing roller and photosensitive drum)
FIG. 9 shows a separation mechanism between the developing roller and the photosensitive drum in the second embodiment.
Drive trains 32, 33, and 34 are connected from an idler gear 26 that performs forward and reverse operations of the paper discharge roller pair, and are transmitted to the developing separation gear 35. A torque limiter 36 is built in the developing separation gear 35. In addition, a stopper 35a is disposed on the gear side and stoppers 37a and 37b are disposed on the image forming apparatus main body side so that the developing separation gear 35 stops in half rotation.

The separation movement will be described with reference to FIG.
FIG. 10A shows a state where the developing roller is in contact with the photosensitive drum.
In order to separate the developing roller from the photosensitive drum, the gear 34 rotates in the direction of the arrow 34a as shown in FIG. The developing separation gear 35 and the coaxial cam 38 rotate in the direction of the arrow 35b.
Then, as shown in FIG. 10C, the stopper 35a of the developing separation gear 35 abuts against the stopper 37a of the main body of the image forming apparatus, so that the subsequent rotation is performed idly by the torque limiter 36 built in the developing separation gear 35. To do. As described above, the slider cam 41 slides in the direction of the arrow 41a by rotating the cam 38 halfway.

As the slider cam 41 slides, the developing roller and the photosensitive drum are separated from each other. The separation mechanism by sliding the slider is the same as in the first embodiment.
When the developing roller and the photosensitive drum are brought into contact again, the cam 34 is rotated in the reverse direction by driving the gear 34 in the direction opposite to that shown in FIG. 10B, and the stopper 35a is abutted against the stopper 37b. When 38 rotates halfway, the state shown in FIG. As a result, the slider cam 41 slides in the direction opposite to that shown in FIG. 10C, and the developing roller and the photosensitive drum come into contact with each other.

(effect)
According to the above configuration, since the control component (solenoid) for the reversing mechanism of the paper discharge roller pair and the control component (solenoid) for separating the developing roller and the photosensitive drum can be shared, the cost can be reduced. Is possible.

S: sheet material, 1: image forming apparatus, 2: cartridge, 3: photosensitive drum unit, 4: developing unit, 8: transfer roller, 11: discharge roller pair, 15: second transport path, 19: cooling fan , 20: first transport path, 21: air path, 22: space

Claims (5)

An image forming apparatus capable of forming images on both sides of a sheet-like recording material,
An image carrier on which an electrostatic latent image is formed on the surface;
It is possible to switch between a first state that is in contact with or close to the image carrier and a second state that is farther from the image carrier than the first state. A developing member for developing the latent image;
A transfer member for transferring the developer image formed on the developing member to a recording material;
A first conveyance path for supplying a recording material to the transfer member;
A reversing mechanism that reverses the conveying direction of the recording material that has passed through the transfer member;
A second transport path that reverses the image forming surface of the recording material whose transport direction has been reversed and supplies the recording material to the first transport path;
A separation mechanism that switches the developing member to the second state when the conveyance direction is reversed at least by the reversing mechanism;
A cooling fan,
With
When the developing member takes the second state, an air passage that guides the wind from the cooling fan to the second transport path is formed, and the cooling fan is more than when the developing member takes the first state. An image forming apparatus, wherein the amount of air flowing from the first to the second conveyance path increases. The first transport path is located upstream of the second transport path in the flow of air from the cooling fan,
A communication path communicating the first conveyance path and the second conveyance path;
2. The air path formed when the developing member takes the second state is an air path from the first transport path to the second transport path through the communication path. Image forming apparatus. When the developing member takes the first state, at least one of the image carrier and the developing member is in the air path and is cooled by the wind from the cooling fan,
3. The image forming apparatus according to claim 1, wherein when the developing member assumes the second state, both the image carrier and the developing member retreat from the air path.   The reversing mechanism and the separation mechanism are configured by common parts, and the developing member is configured to take the second state at a timing at which the transport direction is reversed by the reversing mechanism. 2. The image forming apparatus according to item 1. A control means for controlling the operation of the separation mechanism;
The control means is any period from the timing when the first surface of the recording material is transferred by the transfer member to the timing when the recording material that has passed through the second conveyance path is supplied to the transfer member. The image forming apparatus according to claim 1, wherein the separation mechanism is controlled so that the developing member takes the second state.

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