JPH03138678A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a paper jam and to form a sharp image without narrowing transfer width by detecting the stiffness of paper by a stiffness detecting means, sending the result to a control means controlling the drive of the shield case of a transfer part, controlling the driving means by the control means and driving the shield case. CONSTITUTION:The stiffness detecting means 33 detects the stiffness of the paper 13 and if it is not stiff, a shielding member 31 is controlled not to shield the downstream of the contact point of the paper 13 with an image carrier 7. If the paper 13 is stiff, the opening part of the shield case 32 is moved or its direction is changed, so that the transfer width of a transfer wire 24 is prevented from narrowing. Consequently, transfer performance providing excellent image density and image quality is obtained. Moreover, since a paper guide plate 30 is movable, the paper 13 closely adheres to the image carrier 7, thereby preventing a paper jam.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an image forming apparatus such as a copying machine.

[Prior Art] Conventionally, image forming apparatuses such as copying machines use a method of transferring a toner image developed on an image bearing member in a developing process onto a sheet of paper by corona transfer.

FIG. 6 is a sectional view showing a main part of a transfer process of a conventional image forming apparatus.

In the figure, the latent image formed on the image carrier 7 is
The toner image is visualized. The paper fed by the paper supply means is -H at the registration roller 20.
The sheet is stopped, the timing of copying is adjusted, the sheet is sent to the transfer section 10 via the sheet guide plate 30, and the sheet is transferred by the transfer wire 24 which generates corona discharge. The transferred paper then advances to the separating section 11. In the separating section 11, the image carrier 7 and the paper are separated, the paper passes through a conveyor belt, is thermally fixed by a heat fixing device, and is discharged from the apparatus.

In such a copying process, the paper guide plate 30 that guides the paper to the transfer section 10 is generally fixed, and the shield case 32 that regulates the corona discharge of the transfer section 10 is also fixed. Further, a shielding member 31 is fixed to the paper guide plate 30. That is, if the transfer corona discharge reaches an area where the image bearing member 7 and the paper are not in close contact, there will be an inconvenience that the toner will scatter.
This shielding member 31 can prevent such inconvenient corona discharge.

[Problems to be Solved by the Invention] However, although there is a paper guide plate, the point at which the paper comes into close contact with the image carrier is different between paper with high rigidity and paper with low rigidity. ! 1) A sheet of paper with low rigidity will come into close contact with the image carrier on the −L side of the photoreceptor, and a sheet of paper with high rigidity will come into close contact with the image carrier on the downstream side. Then,
11. In the case of paper with low resistance, the contact point is on the upstream side, so the above-mentioned shielding member that attempts to shield excess corona discharge may not be able to cover the necessary corona discharge! ! cover That is, there is a problem in that a part of the required transfer width (transfer charged area) is also blocked, resulting in a narrow transfer width.

On the other hand, since the temporary paper guide is fixed, there is also the problem that paper jams are likely to occur. In this regard, in order to prevent paper jams, etc., if the paper is rigid, a structure in which the paper guide plate moves downward may be adopted; move downwards,
The corona discharge reaches areas where the paper is not in close contact with the image carrier, causing toner to be released and resulting in deterioration of image quality. Therefore, if a shielding member were to be provided, the problem would arise that the transfer width would be narrowed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that can prevent paper jams and form clear images without narrowing the transfer width.

[Means for Solving the Problems] The present invention includes a transfer section for transferring a toner image developed on an image bearing member in a developing process onto a sheet of paper, and a shielding section for guiding the paper to the transfer section and providing a shield near the leading end thereof. In an image forming apparatus including a paper guide plate having a member, a rigidity detecting means for detecting the rigidity of the paper, and an opening that is connected to a transfer wire A.
- a shield case of the transfer section that can move or face toward the downstream side in the paper conveyance direction in order to change the transfer width that is the discharge width of the corona from the head; a drive means that can move the shield case; and the rigidity detection means. and a control means for controlling the driving means based on a detection result obtained by the image forming apparatus.

[Function] According to the above configuration, the present invention detects the rigidity of the paper by the rigidity detection means, sends the result to the control means for controlling the drive of the shield case of the transfer section, and controls the drive means by the control means. Drive the shield case. As a result, when the paper is highly rigid, the shield case moves toward the downstream side of the paper or changes its direction, thereby avoiding reduction in the transfer width.

[Embodiment] FIG. 1 is a schematic cross-sectional view showing an embodiment of an image forming apparatus according to the present invention.

Incidentally, the same members as in FIG. 6 of the conventional example are given the same reference numerals.

An original is placed on the original placing plate 2, and the original cover l is adapted to hold down the original. Further, an optical system 100 including a lamp 3, a reflecting mirror 4, etc. is configured to move along the document placement plate 2 so as to scan the document. Further, a photosensor 5 is arranged below the leading edge of the document for detecting that the optical system 100 has reached that position.

Around the image carrier 70, there are a main charger 8 that charges the image carrier 7, a developer 9 that develops toner on a latent image formed by exposure with image light incident from the optical system 100; A transfer unit 1O1 transfers the developed toner image onto the paper 13, a separation unit 11 charges the transferred paper 13 to separate it from the image carrier 7, and a cleaning device 12 cleans the remaining toner after transfer. It is located.

On the other hand, a conveyance path 14 for paper 13 is arranged upstream of transfer section 10 . The paper 13 is fed into this conveyance path 14 from each paper feed roller 15 (an example of a paper storage means) and a manual feed tray 16 by a paper feed roller 17 (an example of a paper supply means), and then by a conveyance roller 18. A portion of the registration roller 200 is stopped, the conveyance deviation is (1) corrected, and the timing is adjusted. Reference numeral 19 denotes a registration switch that detects the presence of the paper 13 at the location of the registration roller 20. The paper 13 is then guided by the paper guide Vi3O and fed to the transfer unit 10. A shielding member 31 is provided at the tip of this paper guide plate 30. Further, this paper guide plate is attached so as to be rotatable about a lower fulcrum 50. Further, a rigidity detection means 33 for detecting the rigidity of the paper 13 is provided near the paper guide plate 30. A driving means 34 for moving the shield case 32 in order to change the transfer width is located below the shield case 32 of the transfer section 10. A control means 35 for controlling the drive means 34 based on the detection result of the stiffness detection means 33 is provided in the main body of the apparatus.

Further, a conveyor belt 21 is provided downstream of the separating section 11 and conveys the separated paper 13 to a heat fixing device 22 . The toner image on the paper 13-1 is thermally melted and fixed by the thermal fixing device 22. This heat-fixed paper 13 is
It is designed to be discharged onto a discharge tray 23.

Next, the present invention will be explained in detail with reference to the block diagram shown in FIG. 2 showing the configuration of the present invention, the perspective view of the main part of the invention in FIG. 3, and the simplified diagram of the main part in FIG.

The paper guide plate 30 is for feeding the paper 13 that has been fed to the registration rollers 20 to the transfer section 10, and has a shielding member 31 at its tip. As shown in FIG. 3, this paper guide plate 30 has a mounting piece 42 and an L-shaped bracket 4 provided on the paper guide plate 30.
0 or the like, and is rotatable about a fulcrum 50. Also rotated paper guide plate 3
0 is restored by the spring 41 when the paper 13 passes. That is, when the paper 13 is highly rigid, the paper guide plate 30 rotates downward and feeds the paper 13 into the transfer section 10 without causing a paper jam. The shielding member 31 provided on the paper guide plate 30 is provided to prevent transfer corona discharge in areas where the image carrier 7 and the paper 13 are not in close contact with each other, and to obtain a clear image without toner scattering. This shielding member 31 may be formed by forming the paper guide plate 30 as a single plate and bending its tip member, or may be formed by forming the paper guide plate 30 as a single plate on a straight line and forming the lower part of the tip. You can also attach it to Further, this shielding member 31 is designed so as not to shield the downstream side of the contact point between the image carrier 7 and the paper 13 when the rigidity of the paper 13 is weak.

The rigidity detection means 33 detects the rigidity of the paper 13. In this embodiment, the paper guide plate 30 rotates around a point 50 at its lower end as shown in FIG. If the paper guide plate 30 is highly rigid,
rotates downward.

The photosensor 33 optically detects this rotational displacement. That is, the photosensor 33 discharges light to a part of the paper guide plate 30 and receives the reflected light. However, as the paper guide plate 30 rotates, the amount of the reflected light received changes. By detecting the change, the rigidity of the paper 13 is detected. In addition, the paper guide plate 30
may be fixed, and a thickness detection sensor that detects the thickness of the sheet 13 may be used as the sensor.

The control means 35 controls the driving of the shield case 32, and is, for example, a microcomputer installed in the main body of the apparatus. When the paper 13 is highly rigid, the paper guide plate 30 rotates, and its displacement is detected by the photosensor 33, and the presence or absence of displacement is detected by the control means 35.
That is why it is sent to. Note that, without using a microcomputer, a dedicated electric circuit having the above-mentioned functions may be incorporated as a control means. Such control may be simple on/off control or continuous control depending on the degree of rigidity. For example, in addition to checking the presence or absence of displacement of the paper guide plate 30, control may be performed by checking the displacement of the paper guide plate 30 in several stages, such as three or four stages, depending on the rigidity of the paper 13. Specifically, for example, a first stage flag, a second stage flag,
If a flag for the third stage is provided and the stiffness of the paper is at the level of the third stage, this can be handled by setting the flag for the third stage to 1 and setting the other flags to O. Control is performed based on the flag information.

The driving means 34 moves the shield case 32, and corresponds to the motor 34. When the paper 13 is highly rigid, the motor 34 rotates, and the elliptical camco 36 provided on the extension of the motor 34 rotates the opening X of the shield case downward as shown by the dotted line in FIG. 4. . Further, after the paper 13 has passed, the motor 34 is rotated in reverse, and the opening X of the shield case 32 is returned to its original state. Control means 35
When controlling in several stages depending on the rigidity of the paper 13 and applying the control signal to the driving means 34, this can be done by changing the shape of the elliptical cam 36 and changing the rotation speed of the motor 34.

Note that, for example, a stepping motor can be used as the motor.

FIG. 5 shows a modification in which the method of moving the shield case 32 is changed.The method is the same as that of the motor 34, but the opening of the shield case 32 is moved in parallel. That is, the motor 34 and the gear 37 are interlocked, and the gear 37 and the rack 38 are meshed to open the opening X of the shield case 32.
It attempts to move the transfer width downstream in parallel by moving downstream. In Figure 5, the dotted line indicates the state of discharge from the transfer wire 24 when the shield case 32 is moved in parallel.The transfer width is wider than the state of discharge drawn by the solid line before the shield case 32 is moved in parallel. I can see that it is happening.

Next, the operation of this embodiment of the present invention will be explained.

The paper 13 is fed from the paper feed cassette 15 or the manual tray 16 by the paper feed roller 17, from the transport roller 18 to the registration rollers 20, the timing is adjusted, and the paper is sent to the paper guide plate 30.

When the paper 13 has high rigidity, the paper kite plate 30 rotates. The photosensor (rigidity detection means) 33 detects the rigidity of the paper 13 by discharging light onto a part of the paper guide plate 30 and detecting a change in the amount of received reflected light.

The detected results of the stiffness of the paper 13 are sent to the computer (control means) 35, and the computer 3
5 sends a control signal to a motor (driving means) 34 that drives the movement of the shield case 32. The motor 34 that has received the control signal is driven (rotated) by this control signal indicating the rigidity of the paper 13, the elliptical cam 36 rotates, and the shield case 32 moves.

For example, if the paper 13 is highly rigid, the shield case 3
2 tilts toward the downstream side to avoid a reduction in the transfer width, which is the width of corona discharge from the transfer wire 24.

In the embodiment shown in FIG. 5, the motor 34, which similarly receives a control signal, moves the opening X of the shield case 32 in parallel via a gear 37 and a rack 38. This avoids a reduction in the transfer width, which is the width of corona discharge from the transfer wire 24.

Note that the present invention is also applicable to image forming apparatuses other than copying machines.

[Effects of the Invention] As explained above, the image forming apparatus according to the present invention has the following features.
If the rigidity of the paper is weak, prevent the shielding member from blocking the downstream side of the contact point between the image carrier and the paper, and if the rigidity of the paper is strong, move or change the direction of the opening of the shield case to prevent transfer. Since the wire transfer width is prevented from becoming narrow, it is possible to obtain good transfer performance in terms of image density and image quality. Further, since the paper guide plate is movable, the paper can be brought into close contact with the image carrier smoothly, and paper jams can be prevented from occurring.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a block diagram showing the configuration of the present invention, and FIG. 3 is a main part of the embodiment. FIG. 4 is a simplified diagram showing the main parts of the embodiment, FIG. 5 is a simplified diagram of the main parts of the embodiment of the pond of the present invention, and FIG. 6 is a simplified diagram of the conventional image forming apparatus. FIG. l...Document cover 7...Image carrier 10...Transfer section 13...Paper 24...Transfer wire 30
...paper guide plate 31...shielding member 32...
Shield case 33... Rigidity detection means (photo sensor) 34... Drive means (motor) 35... Control means (microcomputer)

Claims (1)

[Claims] a transfer section that transfers the toner image developed on the image carrier in the development step onto a sheet of paper; and a transfer section that guides the sheet of paper to the transfer section;
In an image forming apparatus including a paper guide plate having a shielding member near its leading end, a rigidity detection means detects the rigidity of the paper, and an opening detects a transfer width, which is a discharge width of corona from a transfer wire. a shield case of the transfer unit that can move or face toward the downstream side in the paper conveyance direction in order to change the rigidity; a drive unit that can move the shield case; and a control unit that controls the drive unit based on a detection result by the rigidity detection unit. An image forming apparatus comprising: