JP2006349764A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing image quality from being deteriorated even when residual toner amount left after transfer becomes large because of the change of environment or the like. <P>SOLUTION: A color printer 1 has: a photoreceptor drum 20 carrying a toner image; and a transfer device 60 transferring the toner image on the photoreceptor drum 20 to a body to be transferred, and has: a brush roller 71 which temporarily recovers the toner on the photoreceptor drum 20 which has passed through the transfer device 60 and also discharges the recovered toner to the photoreceptor drum 20, and to which bias voltage for the photoreceptor drum 20 is applied; a toner concentration sensor 72 detecting the residual toner amount on the photoreceptor drum 20 at a position between the transfer device 60 and the brush roller 71; and a controller 80 changing the bias voltage to the brush roller 71 to a recovery side further than the bias voltage at the normal time if the residual toner amount is larger than predetermined amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a so-called cleanerless type image forming apparatus that returns untransferred toner to a developing unit without discarding. More specifically, the present invention relates to an image forming apparatus that appropriately collects and discharges untransferred toner in response to fluctuations in toner transfer efficiency and fluctuations in toner accumulation status in a temporary collection member.

  Conventionally, in an electrophotographic image forming apparatus, a toner image is generally formed on an image carrier such as a photosensitive drum, and the toner image is transferred onto a sheet or the like to obtain an image. There is also an image forming apparatus called cleanerless in which residual toner remaining on the photoconductor after transfer is recovered by a developing device and reused instead of being removed and discarded by a cleaning device such as a blade.

  As a conventional cleanerless image forming apparatus, for example, Patent Document 1 has a rotating brush that contacts a photosensitive member between a transfer device and a charging device, and an AC bias voltage is applied to the brush. An image forming apparatus is disclosed. In the image forming apparatus described in this document, it is supposed that toner can be prevented from sticking to the charging brush by causing the rotating brush to disturb the toner and collect the toner that is easily released.

Patent Document 2 discloses an image forming apparatus having a memory removal brush. In the technique of this document, the transfer residual toner remaining on the photosensitive drum is diffused by the memory removal brush. Further, when excessive toner is accumulated in the memory removal brush, a cleaning sequence is performed and the toner is collected by the developing device.
JP 2001-272860 A JP 2002-156881 A

  However, in an electrophotographic image forming apparatus, the transfer efficiency of the transfer apparatus varies depending on the environment. For this reason, even if the toner is collected or diffused as in the conventional image forming apparatus described above, if the amount of transfer residual toner originally remaining on the photosensitive drum increases, the collected toner in the charging button, the exposure tool, and the developing device. There was a risk of image quality degradation due to defects or the like.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that does not cause deterioration in image quality even when the amount of untransferred toner increases due to environmental changes.

  An image forming apparatus of the present invention, which has been made for the purpose of solving this problem, is an image forming apparatus having an image carrier that carries a toner image and a transfer unit that transfers the toner image on the image carrier to a transfer target. A temporary recovery member that temporarily collects toner on the image carrier after passing through the transfer unit, discharges the collected toner onto the image carrier, and applies a bias voltage to the image carrier; and a transfer unit A residual toner amount detection unit for detecting a residual toner amount on the image carrier at a position between the temporary recovery member and a temporary recovery member bias voltage when the residual toner amount exceeds a predetermined amount. And a bias control unit for changing to the collection side.

  According to the image forming apparatus of the present invention, the toner image carried on the image carrier is transferred to the transfer target. Thereafter, the toner remaining on the image carrier is temporarily collected by the temporary collection member and discharged again onto the image carrier. At this time, the residual toner amount detection unit detects the residual toner amount on the image carrier, and when the residual toner amount is larger than a predetermined amount, the bias control unit causes the bias voltage of the temporary recovery member to be higher than the normal side. Changed to Therefore, control is performed so as to collect more when the amount of residual toner increases. As a result, even if the amount of toner remaining after transfer increases due to changes in the environment or the like, image quality does not deteriorate.

Furthermore, in the present invention, it is desirable that the bias controller changes the bias voltage when the amount of residual toner after transfer of the standard pattern is larger than a predetermined amount.
In such a case, when the residual toner amount after transfer is too large due to a change in the environment or the like, the bias voltage is changed to increase the recovery amount compared to the discharge amount. If it is not too much, it will be controlled as usual, so the amount recovered will not be too high.

The image forming apparatus of the present invention is an image forming apparatus having an image carrier that carries a toner image and a transfer unit that transfers the toner image on the image carrier to a transfer target, and passes through the transfer unit. The toner on the image carrier is temporarily collected and the collected toner is discharged onto the image carrier, and the temporary collection member to which a bias voltage is applied to the image carrier and the toner accumulation amount of the temporary collection member are detected. And a bias control unit that changes the bias voltage of the temporary recovery member from the normal bias voltage to the recovery side when the toner storage amount is larger than a predetermined amount.
In general, as the amount of accumulated toner in the temporary collection member increases, the toner collection efficiency decreases. That is, the recovery amount is insufficient with a normal bias voltage. According to the present invention, when the toner accumulation amount is larger than the predetermined amount, the bias control unit changes the bias voltage of the temporary recovery member from the normal bias voltage to the recovery side, so that an appropriate recovery amount is maintained. Can do.

Further, in the present invention, the temporary collection member is a temporary collection rotation member that contacts the image carrier while rotating, and the toner accumulation amount detection unit is a torque detection unit that detects the torque of the temporary collection rotation member. It is preferable that the unit changes the bias voltage when the torque of the temporary collection rotating member is smaller than a predetermined value.
The rotational torque of the temporary collection rotating member is changed by the friction between the temporary collection rotating member and the image carrier in contact therewith. In general, toner has a lubricating action, and if a large amount of toner is present between contact surfaces, friction is reduced. That is, by detecting the torque of the temporary collection rotating member, the amount of toner accumulated in the temporary collection rotating member can be grasped.

Further, in the present invention, the toner accumulation amount detection unit is a current detection unit that detects the current of the temporary recovery member, and the bias control unit changes the bias voltage when the current of the temporary recovery member is smaller than a predetermined value. Is desirable.
When toner accumulates, the resistance value of the temporary recovery member increases. Since the temporary recovery member is controlled on a voltage basis, the degree of increase in resistance can be determined by detecting the current. That is, the amount of toner accumulated in the temporary recovery member can be grasped by detecting the current of the temporary recovery member.

Further, in the present invention, it is desirable that the bias controller controls the bias voltage so that the amount of toner discharged to the image carrier is 0.3 g / m ² or less when the bias voltage is changed to the collection side.
When the toner discharge amount is 0.3 g / m ² or less, the image quality is not deteriorated by the residual toner.

Further, in the present invention, it is desirable that the bias control unit changes the bias voltage to the collection side only for a portion that becomes an in-image region for the next image formation on the image carrier.
Even if a large amount of toner remains in the area outside the image, the image quality is not affected. In other words, it is sufficient to control only the part that becomes the image area.

The present invention further includes a cleaning control unit for performing a cleaning sequence for discharging toner from the temporary recovery member to a non-image area for the next image formation of the image carrier, and the cleaning control unit includes bias control. When the unit changes the bias voltage to the recovery side, it is desirable to lengthen the execution time of the cleaning sequence or increase the execution frequency as compared with the normal time.
When the bias voltage is changed to the collection side by the bias control unit, toner tends to accumulate in the temporary collection member. Therefore, by increasing the execution time of the cleaning sequence or increasing the execution frequency, the toner accumulated in the temporary collection member can be released without affecting the image quality.

  According to the present invention, even when the amount of residual toner increases due to a change in environment or the like, image quality does not deteriorate.

"First form"
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a cleanerless color printer.

  The color printer 1 of this embodiment has image forming units 10Y, 10M, 10C, and 10Bk for each color, an intermediate transfer belt 11, a secondary transfer device 12, and a belt cleaner 13, as schematically shown in FIG. Yes. The image forming units 10Y, 10M, 10C, and 10Bk for each color are arranged along the intermediate transfer belt 11 and form the toner images of the respective colors on the intermediate transfer belt 11. The superimposed toner images are transferred to the recording paper 14 by the secondary transfer device 12. Further, the toner remaining on the intermediate transfer belt 11 is scraped off by the belt cleaner 13. In this embodiment, the color printer 1 uses negatively charged toner. In the following description, the subscript YMCBk for each color is omitted when there is no need for distinction.

  Each color image forming unit 10 has the same configuration. As shown in FIG. 1, each image forming unit 10 has a charging device 30, an exposure device 40, a developing device 50, and a transfer device 60 around the photosensitive drum 20. Each device uses a general one. In the color printer 1 of this embodiment, a residual toner control unit 70 is provided between the transfer device 60 and the charging device 30. The residual toner control unit 70 for each color is controlled by a controller 80.

  As shown in FIG. 2, the residual toner control unit 70 includes a brush roller 71 and a toner density sensor 72. The brush roller 71 is provided such that the hair tip contacts the surface of the photosensitive drum 20. The toner density sensor 72 is arranged on the upstream side of the brush roller 71 with respect to the rotation of the photosensitive drum 20 and detects the amount of toner remaining on the surface of the photosensitive drum 20. Further, a power source 73 is connected to the brush roller 71 and a superimposed bias voltage of direct current and alternating current is applied. Further, the power source 73 and the toner density sensor 72 are controlled by a controller 80 connected thereto. Note that both the brush roller 71 and the photosensitive drum 20 are rotated clockwise as indicated by arrows in the drawing.

  Next, the operation of the residual toner control unit 70 in the color printer 1 of this embodiment will be described. At the time of image formation, the photosensitive drum 20 is uniformly charged by the charging device 30, and an electrostatic latent image is formed by the exposure device 40 based on the image data. The formed electrostatic latent image is developed with toner by the developing device 50 and transferred to the intermediate transfer belt 11 by the transfer device 60. The toner remaining on the photosensitive drum 20 after this transfer step is residual toner. A bias is applied to the brush roller 71 by a power source 73. As a result, the residual toner on the photosensitive drum 20 is temporarily collected by the brush roller 71 and discharged again onto the photosensitive drum 20. By this process, the residual toner is dispersed to some extent.

Here, the transfer efficiency generally varies depending on factors such as the environment. For this reason, in an environment where the transfer efficiency is very low, there is a risk that the image quality such as exposure dust will be reduced even if the residual toner is dispersed as described above. Therefore, the inventors first determined the range of the residual toner concentration that would not cause a decrease in image quality by experiments. In the experiments by the inventors, the relationship between the remaining toner amount and the image density unevenness is as shown in FIG. In other words, it was found that when the residual toner density is 0.3 g / m ² or less, the image quality such as the exposure dust does not deteriorate. Therefore, in the color printer 1 of this embodiment, the controller 80 controls the residual toner density so as to be 0.3 g / m ² or less.

  Next, a control method will be described. As described above, since the bias voltage is applied to the brush roller 71, the controller 80 changes the DC component of the bias voltage or the duty of the AC component. As a result, the ratio between the collection and discharge of the residual toner by the brush roller 71 is changed. When the DC component Vdc of the bias voltage is changed, as shown in FIG. 4, the discharge rate decreases as Vdc increases.

  As the duty of the AC component is increased, the discharge rate increases as shown in FIG. Here, a rectangular wave is used as an AC component, and its Vpp is 300V. Further, Duty is the ratio of the time during which a negative voltage corresponding to the voltage on the discharge side is output among the AC components.

In the color printer 1 of this embodiment, in order to control the residual toner density, the residual toner density is first detected at a predetermined timing. For example, a predetermined density detection pattern is formed and transferred to the intermediate transfer belt 11 when the power is turned on or before image formation. Thereafter, the toner density sensor 72 detects the density of the toner remaining on the surface of the photosensitive drum 20. If the residual toner concentration is 0.3 g / m ² or less, there is no need to change the control, and therefore a normal bias voltage is applied.

On the other hand, when the residual toner concentration exceeds 0.3 g / m ² , the discharge rate is lowered by changing the bias voltage. That is, the DC component of the bias voltage is increased or the duty of the AC component is decreased. For example, the DC component of the bias voltage may be adjusted in multiple steps within a range of about −200 V to 150 V, and switched according to the detected residual toner density. Alternatively, two levels of bias voltages of about −200 V and +100 V may be prepared and switched. The same applies when the duty is changed.

  By the way, the control by the controller 80 includes a cleaning control for performing a cleaning sequence. In the cleaning sequence, the bias voltage is changed to the discharge side, and the toner accumulated in the brush roller 71 is discharged to the photosensitive drum 20. Then, the discharged toner is collected by the developing device 50. Even in normal control, this processing is performed when toner accumulates on the brush roller 71 to some extent. Note that image formation is not performed during this control.

  When the bias voltage is controlled as described above to lower the toner discharge rate, naturally, a lot of toner gradually accumulates on the brush roller 71. Therefore, in this embodiment, after decreasing the discharge rate, the cleaning sequence interval of the brush roller 71 is shortened or the execution time of the cleaning sequence is lengthened. As a result, the toner accumulated on the brush roller 71 is discharged, and the influence on the subsequent image formation is prevented.

  That is, according to the color printer 1 of the present embodiment, the residual toner of the standard pattern is detected at a predetermined timing, and when it is determined that the transfer efficiency is lowered, the DC component of the bias voltage is increased, or the AC voltage is increased. Reduces the duty of the component. As a result, the discharge rate of the toner from the brush roller 71 is lowered, so that the toner density on the photosensitive drum 20 can be reduced. Therefore, even if the amount of residual toner after transfer increases due to changes in the environment or the like, the color printer 1 does not cause deterioration in image quality.

"Second form"
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, only the residual toner control unit is slightly different from the first embodiment, and the other parts are the same. Therefore, the same reference numerals are given and description thereof is omitted.

  The residual toner control unit 75 of this embodiment includes a torque detection unit 76 in the brush roller 71 instead of the toner density sensor 72. The torque detector 76 detects the power consumption of the motor for rotating the brush roller 71 at a constant speed, and detects whether the torque applied to the rotation of the brush roller 71 is within a predetermined range based on the result. The detection result by the torque detector 76 is input to the controller 80. The controller 80 receives the detection result of the torque detector 76 and controls the power source 73.

  Generally, toner has lubricity. Therefore, if a certain amount or more of toner is accumulated on the brush roller 71, the friction between the brush roller 71 and the photosensitive drum 20 is reduced, and the torque for rotating the brush roller 71 is reduced. That is, when the detection result of the torque detector 76 is smaller than the predetermined range, it can be determined that the amount of toner accumulated in the brush roller 71 has increased.

When a large amount of toner is accumulated on the brush roller 71, the toner collection efficiency is lower than normal. For this reason, there is a possibility that the residual toner after passing through the residual toner control unit 75 increases from the normal time. Therefore, at this time, as in the first embodiment, the power source 73 is controlled to increase the DC component of the bias voltage or reduce the duty of the AC component. Thus, the controller 80 controls the toner discharge rate from the brush roller 71 to be lowered and the residual toner concentration to be 0.3 g / m ² or less.

  In this embodiment as well, when the toner discharge rate is lowered, naturally, a lot of toner gradually accumulates on the brush roller 71. Therefore, in that case, the cleaning sequence interval of the brush roller 71 may be shortened, or the cleaning sequence execution time may be lengthened.

  As a result, as in the first embodiment, even if the amount of untransferred toner increases due to a change in the environment or the like, the color printer does not deteriorate image quality.

"Third form"
Hereinafter, a third embodiment of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, only the residual toner control unit is slightly different from the first embodiment, and the other parts are the same. Therefore, the same reference numerals are given and description thereof is omitted.

  The residual toner control unit 77 of this embodiment includes a current detection unit 78 in the brush roller 71 instead of the toner density sensor 72. The current detector 78 detects the magnitude of the current flowing through the brush roller 71. Since the bias applied to the brush roller 71 is voltage controlled, the current value changes when the resistance value of the brush roller 71 changes. Since the toner accumulated in the brush roller 71 works as a resistance, the current value is large in the brush roller 71 with little toner accumulation, and the current value becomes small as the toner accumulates. Therefore, the degree of toner accumulation in the brush roller 71 can be determined from the detection result of the current detection unit 78. The controller 80 controls the power supply 73 in response to the detection result of the current detection unit 78.

Therefore, in the residual toner control unit 77 of this embodiment, the current detection unit 78 detects the current value at a predetermined timing. If the current value is equal to or less than the predetermined value, it can be determined that the amount of toner accumulated in the brush roller 71 has increased. At this time, similarly to the first and second embodiments, the power source 73 is controlled to increase the DC component of the bias voltage or decrease the duty of the AC component. Thus, the controller 80 controls the toner discharge rate from the brush roller 71 to be lowered and the residual toner concentration to be 0.3 g / m ² or less.

  In this embodiment as well, when the toner discharge rate is lowered, naturally, a lot of toner gradually accumulates on the brush roller 71. Therefore, in that case, the cleaning sequence interval of the brush roller 71 may be shortened, or the cleaning sequence execution time may be lengthened.

  As a result, as in the first embodiment, even if the amount of untransferred toner increases due to a change in the environment or the like, the color printer does not deteriorate image quality.

Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the above embodiment, a brush roller is used as a residual toner temporary collection member. However, the present invention is not limited to this, and a fixed brush or a vibrating brush may be used.
For example, the present invention can be applied not only to color printers but also to image forming apparatuses such as monochrome printers, copiers, and fax machines.

1 is a schematic configuration diagram illustrating a color printer according to an embodiment. FIG. 3 is an explanatory diagram illustrating a residual toner control unit according to a first embodiment. FIG. 6 is an explanatory diagram illustrating a relationship between a toner remaining amount and image density unevenness. It is explanatory drawing which shows the relationship between the direct current | flow component of a bias voltage, and a discharge rate. It is explanatory drawing which shows the relationship between Duty of bias voltage, and a discharge rate. FIG. 10 is an explanatory diagram illustrating a residual toner control unit according to a second embodiment. It is explanatory drawing which shows the residual toner control part which concerns on a 3rd form.

Explanation of symbols

1 Color printer (image forming device)
20 Photosensitive drum (image carrier)
60 Transfer device (transfer section)
71 Brush roller (temporary recovery member, temporary recovery rotating member)
72 Toner density sensor (residual toner amount detection unit)
76 Torque detector (torque detector, toner accumulation amount detector)
78 Current detection unit (current detection unit, toner accumulation amount detection unit)
80 controller (bias controller, cleaning controller)

Claims (8)

In an image forming apparatus comprising: an image carrier that carries a toner image; and a transfer unit that transfers the toner image on the image carrier to a transfer member.
A temporary collection member that temporarily collects the toner on the image carrier after passing through the transfer section and discharges the collected toner onto the image carrier, and a bias voltage is applied to the image carrier;
A residual toner amount detection unit for detecting a residual toner amount on the image carrier at a position between the transfer unit and the temporary recovery member;
An image forming apparatus comprising: a bias control unit configured to change a bias voltage of the temporary recovery member from a normal bias voltage to a recovery side when a residual toner amount is larger than a predetermined amount. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the bias controller changes the bias voltage when the amount of residual toner after transfer of the standard pattern is greater than a predetermined amount. In an image forming apparatus comprising: an image carrier that carries a toner image; and a transfer unit that transfers the toner image on the image carrier to a transfer member.
A temporary collection member that temporarily collects the toner on the image carrier after passing through the transfer section and discharges the collected toner onto the image carrier, and a bias voltage is applied to the image carrier;
A toner accumulation amount detection unit for detecting a toner accumulation amount of the temporary recovery member;
An image forming apparatus comprising: a bias control unit configured to change the bias voltage of the temporary recovery member from the normal bias voltage to the recovery side when the toner accumulation amount is larger than a predetermined amount. The image forming apparatus according to claim 3,
The temporary collection member is a temporary collection rotation member that contacts the image carrier while rotating,
The toner accumulation amount detection unit is a torque detection unit that detects torque of the temporary collection rotating member,
The image forming apparatus according to claim 1, wherein the bias controller changes the bias voltage when the torque of the temporary collection rotating member is smaller than a predetermined value. The image forming apparatus according to claim 3,
The toner accumulation amount detection unit is a current detection unit that detects a current of the temporary recovery member,
The image forming apparatus according to claim 1, wherein the bias controller changes the bias voltage when the current of the temporary recovery member is smaller than a predetermined value. In the image forming apparatus according to any one of claims 1 to 5,
The bias controller controls the bias voltage so that the amount of toner discharged to the image carrier is 0.3 g / m ² or less when the bias voltage is changed to the collection side. apparatus. In the image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus according to claim 1, wherein the bias control unit changes the bias voltage to the collection side only for a portion that becomes an image area for the next image formation on the image carrier. In the image forming apparatus according to any one of claims 1 to 7,
A cleaning control unit for performing a cleaning sequence for discharging toner from the temporary recovery member to a portion to be a non-image area for the next image formation of the image carrier;
When the bias control unit changes the bias voltage to the recovery side, the cleaning control unit increases the execution time of the cleaning sequence or increases the execution frequency as compared with the normal time. An image forming apparatus.

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