JP2002096500A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide a lens that is strongly pressed against a shield electrode provided between a photosensitive drum and a lens of an LED head, causing mechanical distortion of the lens, and accurately forming a lens on the surface of the photosensitive drum. Provided is a mechanism for preventing loss of image formation. A structure for preventing toner from adhering to a lens of an LED head approaching a surface of a photosensitive drum and a cleaning sequence are provided. In an image forming apparatus using an electrophotographic process, a photosensitive drum that rotates around a rotation axis, an LED head arranged to face the photosensitive drum, and a space between the photosensitive drum and the LED head And two electrodes that extend in parallel with the direction of the rotation axis of the photosensitive drum and are arranged with a gap through which writing light from the LED head passes, and the LED head contacts the electrode. In the case of contact, the electrode is biased such that the electrode retreats to the photosensitive drum side in a yielding manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, and more specifically, to a method for controlling the toner on a photosensitive drum when the toner on the photosensitive drum passes under a lens of an LED head. The present invention relates to a configuration for preventing scattered particles from adhering to the lens surface.

[0002]

2. Description of the Related Art FIG. 13 shows a conventional electrophotographic image forming apparatus using an optical system using an LED head 5. As shown in FIG.
Around the photosensitive drum 1, a charging roller 49, a developing roller 71, a transfer roller 73, and a cleaning roller 74 are arranged. An electrostatic latent image is formed on the surface of the photosensitive drum 1 by the LED head 5, developed into a toner image by the developing roller 71, and transferred to a sheet by the transfer roller 73. The surface of the photosensitive drum 1 after the transfer is cleaned by the cleaning roller 74. LED head 5
Lens 8 has a distance L from the lens surface to the focal point,
The focal point is arranged so as to be located on the surface of the photosensitive drum 1.

On the upper frame of the image forming section, shield electrodes 12 and 13 are arranged with a slight gap therebetween, and the LED that exits the lens 83 through the gap between the electrodes 12 and 13. Light from the head impinges on the surface of the photosensitive drum 1. A high voltage having the same polarity as the charged toner is applied to the electrodes 12 and 13. This high voltage is applied to the charging roller 49.
And a high voltage terminal of the developing roller 71 via an elastic conductive member such as a leaf spring (not shown).

[0004]

When the distance from the lens surface to the focal point is shortened for miniaturization, the electrodes 12 and 1
The distance between the lens 3 and the lens 8 is shortened, the mechanical shape and dimensions are required to have higher accuracy than in the past, and the cost of the apparatus is increased. If sufficient dimensional accuracy cannot be obtained, the lens 8
Part strongly presses the electrode, thereby generating a large reaction force. Due to this reaction force, the LED head 5 is pushed back, so that the lens 8 does not accurately form an image on the surface of the photosensitive drum 1.

The electrodes 12 and 13 are connected to the LED head 5
In order not to block the path of the light exiting from the lens 8, a gap must be provided between them. Therefore, it is not possible to completely prevent the charged toner from adhering to the lens 8 through this gap. When an even higher negative voltage is applied to the electrodes 12 and 13 in order to prevent adhesion to the lens 8,
There is a problem that the power supplies 12 and 13 become expensive, and a discharge occurs between the electrodes 12 and 13 and a nearby member or between the electrodes 12 and 13 and the photosensitive drum 1. In addition, the electrode itself easily sucks dust.

Accordingly, the present invention provides a photosensitive drum 1 and an LED.
It is possible to prevent the lens 8 from strongly pressing against the shield electrode provided between the head 5 and the lens 8 to cause mechanical distortion of the lens 8 and prevent an accurate image from being formed on the surface of the photosensitive drum. Is to provide a mechanism. Still another object is to provide a structure and a cleaning sequence for preventing toner from adhering to the lens 8 of the LED head 5 approaching the surface of the photosensitive drum.

[0007]

An image forming apparatus according to the present invention utilizes an electrophotographic process, and comprises a photosensitive drum rotating around a rotation axis, and an optical writing head disposed opposite to the photosensitive drum. And the photosensitive drum and the optical writing head, two extending in parallel with the rotation axis direction of the photosensitive drum and arranged with a gap through which writing light from the optical writing head passes. And the electrode is urged such that when the optical writing head is in contact with the electrode, the electrode retreats to the photosensitive drum side in a yielding manner.

The voltage may be supplied to the electrode via a member for urging the electrode toward the optical writing head.

Another image forming apparatus of the present invention employs a recycling system for reusing the cleaned toner. The toner moved from the cleaning roller to the photosensitive drum is transported to the photosensitive member and travels to the developing device. A writing head irradiates the entire surface of the photoconductor on which the toner is loaded with light.

While the toner transferred from the cleaning roller to the photosensitive drum is carried to the photosensitive member and travels to the developing device, the voltage applied to the charging roller located upstream of the optical writing head with respect to the rotation direction of the photosensitive drum is reduced. .

While the toner moved from the cleaning roller to the photosensitive drum is carried to the photosensitive member and travels to the developing device, the voltage applied to the charging roller located upstream of the optical writing head with respect to the rotating direction of the photosensitive drum is reduced to 0V. To

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. Embodiment 1 FIG. 1 is a schematic configuration diagram showing an entire image forming apparatus according to Embodiment 1 of the present invention. The paper feed cassette 22 is provided at a lower portion of the apparatus main body 21 and can be pulled out from the apparatus main body 21. A plurality of sheets 23 are stored in the sheet cassette 22. Paper 23
The sheet is pressed against the sheet feeding roller 24 with an appropriate force. A separation piece 25 is provided integrally with the sheet feeding cassette 22, and the separation piece 25 is provided.
The paper feed roller 24 is pressed. When the paper feed roller 24 rotates, the separation piece 25 and the paper feed roller 24 cooperate to feed out the paper 23 from the paper feed cassette 22 to the reversing guide 26 one by one. The sheet 23 passes through a reversing guide 26 and is supplied to a registration roller 3 for correcting skew of the sheet.
It is transported to 6. Here, after the skew is corrected, the paper 2
The toner image 3 is transferred through a transfer position between the photosensitive drum 1 and the transfer roller 73 to transfer the toner image. When the sheet carrying the toner image passes through the fixing device 28, the toner image is fixed on the sheet 23. Further, the sheet 23 after fixing is placed on the reversing guide 32.
And is discharged out of the apparatus by discharge rollers 30 and 31.

The lid 35 is rotatably supported on a shaft 34 in the direction of arrow A. The lid 35 is integrally provided with a holder 16 for holding the LED head 5. When the lid 35 is completely closed with respect to the apparatus main body 21, L
The ED head 5 is urged by the spring 6 (7) to move the side plates 17 and 1 together.
8 (FIG. 4). As a result, the LED head 5 is positioned at a predetermined distance from the photosensitive drum 1. The image forming unit 10 includes a photosensitive drum 1, a charging roller 4,
9, the transfer roller 73 and the developing unit. When the image forming unit 10 is attached to or detached from the printer main body or when paper jam is removed, the cover 3 is used.
After rotating 5 in the direction of arrow A, the image forming section 10 is retracted from the apparatus main body.

FIG. 2 is a perspective view showing details of the electrode holders 45 and 46. As shown in FIG. FIG. 3 shows the positional relationship among the photosensitive drum 1, the electrode holders 45 and 46, and the lens 8. In FIG. 2, the rotating shaft of the photosensitive drum 1 is rotatably supported between side plates 17 and 18 arranged in parallel with each other. The side plate 17 is provided with projection shafts 48 and 47, and the side plate 18 is provided with projection shafts 41 and 43. The electrode holder 4 is provided on the protruding shafts 43 and 48.
6 are rotatably supported, and the protruding shafts 41 and 4
7, an electrode holder 45 is rotatably supported.
The electrode holders 45 and 46 extend parallel to the rotation axis of the photosensitive drum 1 and are arranged so as to keep a predetermined distance D between the electrode holders 45 and 46.

The electrode holders 45 and 46 include the photosensitive drum 1
The electrodes 12 and 13 extending in parallel with the rotation axis are fixed respectively. The electrodes 12 and 13 are made of, for example, phosphor bronze. A predetermined interval E is provided between the electrodes 12 and 13, and light exiting the lens 8 of the LED head 5 is
13 and hits the surface of the photosensitive drum 1.
Electrode holders 45 and 46 have conductive torsion spring 4
2 and 44 are provided, and the torsion springs 42 and 44 cause the tips of the opposed electrodes 12 and 13 to be connected to the LED head 5.
It is urged to rotate toward the side. However, as shown in FIG. 3, the opening ends 11a and 11b of the frame 11 contact the electrode holders 45 and 46, and
And 46 are prevented from further rotating. The torsion spring 42 locks one end 42 a of the torsion electrode 42 to the electrode 12 and contacts the other end 42 b of the torsion spring 42 to the electrode of the charging roller 49. The torsion spring 44 has one end 44a locked to the electrode 13 and the other end 44b abutted on an electrode of a developing roller (not shown). Thus, the electrode 12 is supplied with a high negative voltage of -1350 V, and the electrode 13 is supplied with a high negative voltage of -300 V.

FIG. 4 is a sectional view taken along the line IV-IV of FIG. The distance from the lens surface of the lens 8 to the focal point has a slight manufacturing error for each device to be manufactured. Therefore, as shown in FIG.
The adjustment member 50 is provided between the lower plate and the side plate 18 and the LED.
An adjusting member 51 is inserted between the head and the lower part of the head 5 to adjust the distance between the lens 8 and the photosensitive drum 1 so that the light exiting the lens 8 is accurately focused on the surface of the photosensitive drum 1. To As shown in FIG. 3, the lens 8 comprises electrodes 12 and 13
And is in contact with. The lens 8 may come into strong pressure contact with the electrodes 12 and 13 due to dimensional variations during manufacturing. However, since the electrode holders 45 and 46 are rotatably assembled around the projecting shafts 41 and 47 and 43 and 48, respectively, the lens 8 is
Electrodes 12 and 13 are pushed back against the biasing forces of 2 and 44. The force by which the rotational moment by the torsion springs 42 and 44 pushes back the lens 8 is selected to be sufficiently smaller than the sum of the weight of the LED head 5 and the elastic force of the springs 6 and 7.

FIG. 5 shows the relationship between the movement of the toner and the electrodes 12 and 13. As shown in FIG. 5, during the printing operation, the negatively charged toner tends to move from the surface of the photosensitive drum to a location having the highest potential. The voltages for the charging roller (-1350 V) and the voltage for the developing roller (-3
00V) is applied to each of them to shield or capture toner having a different amount of charge that tends to scatter toward the surface of the lens 8 so as not to adhere to the surface of the lens 8. Therefore, the toner adheres to the electrode 13 and hardly adheres to the surface of the lens 8.

Since the lens 8 is made of an insulating material,
Even if the electrodes 12 and 13 are in contact, a large leakage current does not flow. In this embodiment, electrodes 12 and 13 are exposed. However, if an insulating coating is applied to other portions except for a portion connected to the high voltage power supply, it is possible to prevent the electrodes 12 and 13 from discharging to the photosensitive drum 1 when the electrodes approach the photosensitive drum 1. Even when the insulating coating is applied in this way, the effect of preventing the toner from scattering is not changed.

FIG. 6 shows a modification of the electrode holder. Instead of the torsion springs 42 and 44, for example, conductive leaf springs 61 and 62 may be used as shown in FIG.
Due to the resiliency of the leaf springs 61a and 62a, the electrode holders 45 and 46 are urged in the same direction as that of the torsion spring. In the first embodiment, the case where the lens 8 and the electrode are in contact with each other has been described. However, another portion of the LED head 5 may be in contact with the electrodes 12 and 13.

Embodiment 2 Embodiment 2 controls each roller voltage during the cleaning sequence. By this control, residual toner carried on the surface of the photosensitive drum 1 is removed from the lens 8 of the LED head. At the time of passing under, it does not adhere to the lens 8.

FIG. 7 is a control block diagram of the second embodiment. FIG. 8 shows the operation of the electrophotographic process employing the toner recycling method. In FIG. 7, the control unit 60
Controls the drive motor 61 and the LED head 5 during printing and during the cleaning sequence. Further, the switching signals S1 and S2 are changed to switches SW1 and S2 respectively.
W2, and switches the voltage and polarity of the cleaning roller power supply 63 and the developing roller power supply 64 during printing and during the cleaning sequence.

First, the printing sequence will be described.
FIG. 9 shows the relationship between the potential of each roller and the LED head during printing. 8, a charging roller 49, a developing roller 71, a transfer roller 73, and a cleaning roller 74 come into contact with the photosensitive drum 1, and rotate at a predetermined peripheral speed.
The surface of the photosensitive drum 1 is uniformly negatively charged by the charging roller 49. When the toner 80 forming the toner image passes between the transfer roller 73 and the photosensitive drum 1,
Is transferred to a toner image 81. The residual toner 82 remaining on the photosensitive drum without being transferred is carried while being attached to the surface of the photosensitive drum 1 as shown in FIG.
Positively charged toner (oppositely charged toner) moves to the cleaning roller 74, and negatively charged toner moves to the developing roller.

Next, the cleaning sequence will be described. FIG. 10 shows the positional relationship between the potential of each roller and the LED head during the cleaning operation. FIG. 11 is a flowchart showing the operation of the cleaning sequence.
FIG. 12 shows the cleaning roller 7 during the cleaning operation.
4 is a timing chart showing applied voltages to the LED head 5 and the developing roller 71.

The cleaning sequence will be described with reference to FIGS. 8, 10, 11 and 12. When the cleaning sequence is started, the control unit 60 turns on the drive motor 61 (Step S1). Next, at time t1, a negative voltage is applied to the cleaning roller 74 (in this embodiment, the polarity of the charge of the toner is the same) (step S2), so that the toner 83 on the cleaning roller 74 is changed to the surface of the photosensitive drum 1. Move to point A above. The toner returned from the cleaning roller 74 to the photosensitive drum is
The toner 84 is obtained. Since the charging roller 49 has the same negative polarity as the toner 84, the residual toner 84 passes through the charging roller 49 while adhering to the surface of the photosensitive drum 1.

The toner 84 is charged by the charging roller 49 to about-
It is on the photosensitive drum 1 charged to 800V. Since a part of the LED head 5 is grounded, an electric field is formed between the lens 8 and the photosensitive drum 1. When the toner 84 passes through the electric field, the toner 84 easily moves toward the lens 8 due to the electrostatic force of the electric field. To prevent this, the point A on the surface of the photosensitive drum to which the toner 84 has adhered (FIG. 8) at time t2 immediately before passing through the focal point position of the lens 8, L
All the dots of the ED head 5 emit light to irradiate the entire surface of the photosensitive drum 1 with light (step S3). This allows
The potential on the photosensitive drum 1 becomes approximately -100 V (see FIG. 1).
0), the electric field for moving the toner 84 toward the lens 8 is weakened. Time T1 from time t1 to time t2 is
T1 ≒ L1 / V, and time T2 from time t2 to time t3 is T2 ≒ L2 / V, and time t2 to time t
The time T3 up to 3 is T3 ≒ L3 / V. V is the peripheral speed of the photosensitive drum.

Further, since the electrodes 12 and 13 have a shielding effect against the electric field, the toner 84 does not move to the LED side and therefore does not scatter. The toner 84 turns to the developing roller 71 as the toner 86. Photosensitive drum 1
At time t3 immediately before the point A (FIG. 8) on the surface of the developing roller 71 passes the developing roller 71, the developing roller 71 is set to the opposite polarity (positive) (step S4), so that the toner 86 is collected by the developing roller 71. Then, it is reused as the developing toner 80 again. The auxiliary roller 75 rotates while being in contact with the charging roller 49, inverts the polarity of the oppositely charged toner (a polarity opposite to that of the residual toner) 85 attached to the charging roller 49, and makes the polarity the same as that of the residual toner. The toner is returned to the photosensitive drum 1 and collected by the developing roller 71 together with the toner 86.

From the cleaning roller 74 to the photosensitive drum 1
In order to prevent the toner returned to the surface from adhering to the charging roller 49, the surface of the photosensitive drum that has been in contact with the cleaning roller 74 has passed the time required to pass through the charging roller, that is, at time t5. Until then, the voltage of the charging roller 49 is maintained negative. The time length T4 is a time required for the surface of the photosensitive drum that has been in contact with the cleaning roller 74 to pass through the charging roller 49. Charging roller 4
After the toner 84 is collected, the small amount of the oppositely-charged toner 85 remaining at 9 is repelled onto the photosensitive drum 1 by setting the voltage of the charging roller 49 to 0 V at time t5.
It passes under the LED head 5. At time t5, since the voltage of the charging roller 49 is 0V, the surface potential of the photosensitive drum 1 is also charged to around 0V. Therefore, LED
No strong electric field is generated between the head 5 and the photosensitive drum 1, and toner does not scatter toward the LED head 5.

In FIG. 9, in normal printing, most of the residual toner adheres to the cleaning roller 74, and the rest adheres to the charging roller 49.
A small amount of toner passes below the D head 5. In addition, since there is a shielding effect by the negative voltage applied to the electrode, when point A on the surface of the photosensitive drum 1 passes under the LED head 5, there is almost no chance that the toner scatters to the LED head 5 side.

As described above, according to the second embodiment, when a large amount of toner discharged from the cleaning roller 74 passes under the LED head 5 in the cleaning sequence, all the dots of the LED head 5 emit light. Since the surface of the photosensitive drum 1 is irradiated with light to lower the surface potential of the photosensitive drum 1, the toner is
Of the lens 8 can be prevented. Also,
Switching of the voltage supplied to each roller can be realized within the time of the conventional cleaning sequence. For this reason, an improvement in the cleaning sequence can be realized at low cost without requiring a special configuration and reducing the throughput during printing. In the present embodiment, an LED head is described as the optical writing means, but the present invention is not limited to this, and a writing head of a laser type, a liquid crystal type, or the like may be used.

[0030]

According to the present invention, two electrodes are arranged between the photosensitive drum and the LED head, and these two electrodes extend in parallel with the rotation axis direction of the photosensitive drum, and write light from the LED head passes therethrough. It is arranged with a gap. Further, when the LED head comes into contact with the electrode due to a dimensional error or the like, the electrode is configured to be retracted toward the photosensitive drum while being urged against the LED head. This prevents the lens 8 from being strongly pressed against the shield electrode provided between the lens 8 and the lens 8 to prevent mechanical distortion of the lens 8 and prevent an image from being accurately formed on the surface of the photosensitive drum.

While the toner moved from the cleaning roller to the photosensitive drum is conveyed to the photosensitive member and travels to the developing device, the surface of the photosensitive member on which the toner is loaded is irradiated with light or the rotation direction of the photosensitive drum 1 is changed. The voltage applied to the charging roller 49 located upstream with respect to the
The toner is prevented from adhering to the lens 8 by setting the applied voltage of 0 V to 0 V, so that the toner can be prevented from adhering to the surface of the lens 8.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an entire image forming apparatus according to Embodiment 1 of the present invention;

FIG. 2 is a perspective view showing details of electrode holders 45 and 46.

FIG. 3 shows a positional relationship between the photosensitive drum 1, electrode holders 45 and 46, the photosensitive drum 1, and a lens 8.

FIG. 4 is a sectional view taken along the line IV-IV of FIG. 1;

FIG. 5 shows a relationship between toner movement and electrodes 12 and 13;

FIG. 6 shows a modification of the electrode holder.

FIG. 7 is a control block diagram according to a second embodiment.

FIG. 8 illustrates an operation of an electrophotographic process using a toner recycling method.

FIG. 9 shows the relationship between the potential of each roller and the LED head during printing.

FIG. 10 shows the potential and LE of each roller during the cleaning operation.
4 shows the positional relationship between the D head and the cleaning roller 74, the LED head 5, and the developing roller 7 during the cleaning operation.
1 shows an applied voltage.

FIG. 11 is a flowchart illustrating an operation of a cleaning sequence.

FIG. 12 is a timing chart showing the operation of the cleaning sequence.

FIG. 13 shows a conventional electrophotographic image forming apparatus using an optical system with an LED head 5.

[Explanation of symbols]

 Reference Signs List 10 cover, 20 flexible wall, 30 frame, 31 outlet, 40 spring assembly, 41 spring, 42, 44 flexible piece, 43 combination hole, 45 spring, 46, 49 flexible piece, 50 fixed wall

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G03G 21/10 21/00 370 (72) Inventor Ken Nozawa 4-11-11 Shibaura, Minato-ku, Tokyo Offshore Corporation In data (72) Inventor Takuya Goto 4-11-22 Shibaura, Minato-ku, Tokyo F-term in reference to off-shore data of corporation 2C162 AE92 AH22 AJ02 AJ26 FA04 FA17 FA70 2H003 AA12 BB11 CC05 DD03 2H027 DA06 DA07 DA07 EA01 EA07 EA07 EA09 EA18 ED02 ED03 ED07 ED27 2H034 AA06 BC00 CA01 CB01 2H076 AB42 AB60 AB82 EA05

Claims (5)

[Claims] 1. An image forming apparatus using an electrophotographic process, a photosensitive drum rotating around a rotation axis, an optical writing head disposed opposite to the photosensitive drum, the photosensitive drum and the optical writing head And two electrodes extending in parallel to the direction of the rotation axis of the photosensitive drum and arranged with a gap through which writing light from the optical writing head passes. When abut on the electrode, so that the electrode retracts to the photosensitive drum side yielding,
The electrode is energized. 2. The image forming apparatus according to claim 1, wherein a voltage is supplied to the electrode via a member that urges the electrode toward the optical writing head. 3. A recycle type image forming apparatus for reusing a cleaned toner, comprising: a cleaning roller; a photosensitive drum which rotates around a rotation axis, receives the residual toner from the cleaning roller, and carries the toner to a developing device. An optical writing head disposed opposite to the photosensitive drum, wherein the optical writing head is moved from the cleaning roller to the photosensitive drum, while the toner is carried to the photosensitive drum and travels to the developing device, Light is applied to the surface of the photosensitive drum on which the residual toner is loaded. 4. The image forming apparatus further includes a charging roller located upstream of the optical writing head and downstream of the cleaning roller with respect to a rotation direction of the photosensitive drum, and the charging roller is disposed between the cleaning roller and the photosensitive drum. 4. The image forming apparatus according to claim 3, wherein the voltage applied to the charging roller is reduced while the moved toner is conveyed to the photosensitive drum and travels to the developing device. 5. The image forming apparatus further includes a charging roller located upstream of the optical writing head and downstream of the cleaning roller with respect to a rotation direction of the photosensitive drum, and moved from the cleaning roller to the photosensitive drum. 4. The image forming apparatus according to claim 3, wherein the voltage applied to the charging roller is set to 0 V while the toner is carried to the photosensitive drum and travels to the developing device.