JP2007219090A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus which reduces or eliminates a noise by appropriately setting a bias voltage related to a member for recovering residual toner left after transfer. <P>SOLUTION: The electrophotographic image forming apparatus is configured to form an image through respective processes of electrifying, exposing, developing on a photoreceptor drum 21 and transferring. The image forming apparatus includes a cleanerless system for recovering the residual toner left after transfer from the surface of the photoreceptor drum 21, then, returning the recovered toner to a developing device 23 that emits the recovered toner onto the photoreceptor drum 21 by applying the bias voltage to a toner recovery brush 25 that comes in contact with the photoreceptor drum 21. The amplitude and frequency of the bias voltage to be applied to the recovery brush 25 are changed based on at least either of a temperature/humidity condition, the number of printed sheets, a driving time, a toner electrification amount and an operating condition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus such as a copying machine or a printer that forms an image on an image carrier through various processes of charging, exposure, development, and transfer.

  Conventionally, a cleanerless system has been adopted in an image forming apparatus using electrophotography. In the cleanerless system, a toner collecting member that contacts the photoconductor is provided on the downstream side of the transfer unit and on the upstream side of the charging unit, and the transfer residual toner on the photoconductor is once collected on the collecting member, and the collected toner is supplied to a predetermined unit. This is a system that releases the toner onto the photosensitive member at a timing and returns it to the developing unit. The transfer residual toner once recovered by the recovery member is discharged to the photosensitive member and returned to the developing unit. To prevent toner spillage due to excessive recovery of the toner by the recovery member and to reuse the transfer residual toner for development. It is aimed.

  A bias voltage is applied to the collecting member so that the transfer residual toner is collected from the photoconductor during image formation, and a potential bias that releases toner from the collecting member to the photoconductor when an image passes through the collecting member. A voltage is applied. In order to improve the performance of the recovery member, an AC voltage having a constant amplitude and frequency is usually applied to the bias voltage.

  However, if the amplitude and frequency of the AC bias voltage applied to the recovery member are set high, there is a problem that relatively unpleasant noise is generated due to the brush of the recovery member sliding on the photoreceptor. As shown in FIG. 6, the sound pressure is increased by increasing the amplitude of the AC bias voltage applied to the recovery member. Moreover, regarding the frequency, it becomes annoying when the frequency becomes 500 Hz or higher.

  Patent Documents 1 and 2 describe that the frequency of an oscillating voltage applied to a contact charging member can be varied to suppress charging noise and image defects. Patent Document 3 describes that the peak-to-peak voltage or current value of the oscillating voltage applied to the contact charging member is changed to reduce charging noise and prevent the photoconductor from being scraped. However, there is no prior literature regarding the bias voltage applied to the transfer residual toner collecting member.

JP-A-5-11571 JP-A-5-11572 JP-A-9-120197

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of reducing and eliminating noise by appropriately setting a bias voltage for a transfer residual toner collecting member.

In order to achieve the above object, the present invention provides:
In an image forming apparatus by electrophotography that forms an image on an image carrier through processes of charging, exposure, development, and transfer,
A cleanerless system that collects transfer residual toner from the image carrier by applying a bias voltage to the toner collecting member that contacts the image carrier, and discharges the collected toner onto the image carrier and returns it to the developing unit. With
Changing the amplitude and frequency of the bias voltage applied to the recovery member based on at least one of environmental conditions, number of printed sheets, driving time, toner charge amount, and operating conditions;
It is characterized by.

  In the image forming apparatus according to the present invention, the amplitude and frequency of the bias voltage applied to the recovery member are changed based on at least one of environmental conditions, the number of printed sheets, driving time, toner charge amount, and operating conditions. Further, it is possible to reduce and eliminate the noise at the time of collecting the transfer residual toner without significantly reducing the collecting performance.

  For example, when the environmental condition is a high humidity environment, an AC voltage having a frequency of 600 Hz or more and an amplitude of 800 V or more is applied to the recovery member. In an environment other than high humidity, the DC voltage or frequency is less than 600 Hz to the recovery member. Then, an AC voltage having an amplitude of less than 800 V may be applied. In a situation where the number of printed sheets or driving time is short, a DC voltage or an AC voltage having a frequency of less than 600 Hz and an amplitude of less than 800 V is applied to the collecting member, and in a situation where the number of printed sheets or driving time is large, the collecting member. Further, an AC voltage having a frequency of 600 Hz or more and an amplitude of 800 V or more may be applied.

  Alternatively, the bias voltage applied to the recovery member for recovering the black toner may be set to be 200 Hz or higher in frequency or 200 V or higher in amplitude than the bias voltage applied to the color toner recovery member. Further, the recovery member may be controlled so that an AC voltage is applied during image formation and a DC voltage is applied or a bias voltage is not applied during operations other than image formation.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
FIG. 1 shows a main part of an electrophotographic color printer 10 which is an embodiment of an image forming apparatus according to the present invention. In this color printer 10, a charging roller 22, a developing device 23, a primary transfer roller 24, and a transfer brush 25 for collecting residual toner are arranged around a photosensitive drum 21 to constitute a photosensitive unit 20. A laser scanning device 31 and an intermediate transfer belt 32 are installed.

  The photoconductor units 20 are arranged in parallel to form three primary colors (yellow, magenta, cyan) and a black image, and the toner images formed on the photoconductor drums 21 are transferred to the intermediate transfer belt. The image is primarily transferred onto the image 32 and combined with a color toner image, and the combined toner image is secondarily transferred onto a sheet (not shown). A temperature / humidity sensor 33 is disposed in the printer 10.

  In the color printer 10, the photosensitive drum 21 is rotationally driven in the direction of arrow A, and a voltage is applied to the charging roller 22 so that the photosensitive drum 21 has a predetermined surface potential (−500V). Next, an image is exposed by the laser scanning device 31 to form an electrostatic latent image on the photosensitive drum 21, and the electrostatic latent image is so-called reversely developed by the developing device 23 using negatively charged toner. This toner image is primarily transferred onto the intermediate transfer belt 32 that moves in the direction of arrow B by the electric field applied from the primary transfer roller 24.

  On the other hand, the toner remaining on the photosensitive drum 21 is once electrostatically taken into the collection brush 25, and then discharged onto the photosensitive drum 21 when the portion between the images passes, and passes through the transfer roller 22. Then, it is collected by the developing device 23. It should be noted that such a transfer residual toner recovery method is referred to as a cleanerless system as described above.

  The collection brush 25 is provided with conductive fibers in the form of a brush around a cylindrical conductive base material, and is arranged so as to rub while rotating the surface of the photosensitive drum 21. As described below, a bias is applied. A voltage is applied.

(Application of bias voltage to the collecting roller, see FIGS. 2 to 5)
FIG. 2 shows toner recoverability according to environmental conditions when a DC voltage is applied to the recovery brush 25. In an environment with a temperature of 15 ° C. and a humidity of 10% (hereinafter referred to as an LL environment), the recoverability is high, and in an environment with a temperature of 30 ° C. and a humidity of 80% (hereinafter referred to as an HH environment), the recoverability is low. In an environment having a temperature of 23 ° C. and a humidity of 65% (hereinafter referred to as NN environment), the recoverability is high at a relatively low voltage, and the recoverability is low at a high voltage.

  The decrease in the recoverability is due to the high humidity in the environment, and the charge amount of the toner is reduced, and the charge amount distribution approaches the positive side, but a positive bias voltage is applied to the recovery brush 25 with a direct current. This is because the electrostatic response of the toner is lowered. The toner that is not collected adheres to the charging roller 22 and causes charging failure. Further, the image may be transferred to the intermediate transfer belt 32 to cause image loss.

  In this embodiment, by applying an AC voltage to the recovery brush 25, both positive and negative charged toners can be recovered. 3 and 4 show toner recoverability when an AC bias voltage is applied to the recovery brush 25. FIG. Recoverability is improved by increasing the amplitude and frequency of the AC voltage. Even in an HH environment where the toner charge amount is low, sufficient recoverability can be obtained by setting the amplitude to 800 V or higher and the frequency to 600 Hz or higher. Can do.

  However, when the amplitude and frequency of the AC voltage applied to the recovery brush 25 are increased, noise is generated due to friction between the brush fibers or between the brush and the photosensitive drum 21. Therefore, in this embodiment, the AC voltage is controlled to the lowest possible amplitude and frequency that satisfies the toner recoverability according to various conditions.

(Control example 1)
That is, the bias control unit 50 (see FIG. 5) sets the AC bias voltage amplitude to 800 V or higher and the frequency to 600 Hz or higher under the environmental condition of 70% or higher humidity by the input from the temperature / humidity sensor 33 and 70% humidity. Control is performed so that the amplitude is set to less than 800 V and the frequency is set to less than 600 Hz, or a DC voltage of about 100 to 300 V is applied in an environmental condition below.

  In this control example 1, the noise of the collection brush 25 can be reduced as much as possible by setting the amplitude and frequency of the AC voltage as low as possible in a low-humidity environment where the toner collection performance is originally good.

  In the control example 1, the boundary condition for changing the AC voltage is set to 70% or higher humidity, but this boundary condition is not necessarily required. In addition, temperature conditions may be taken into account, and control may be performed so that the AC voltage is changed in three or more steps according to temperature and humidity.

(Control example 2)
Further, as the number of printed sheets increases, in this cleanerless system, the transfer residual toner may be collected in the developing device 23, the toner in the developing device 23 deteriorates, the charge amount decreases, and the collecting by the collecting brush 25 occurs. Tend to decrease. Therefore, in the present control example 2, the bias control unit 50 performs the collection brush 25 based on the number of printed sheets from the memory 52 that stores the count value of the number of printed sheets 51 or based on the driving time information of the developing device 23. The AC bias voltage applied to is controlled.

  That is, if the driving time is 80% or more of the durability life of the developer, the amplitude of the AC bias voltage is set to 800 V or more and the frequency is set to 600 Hz or more. If the driving time is less than 80% of the durability life, the amplitude is less than 800 V. The frequency is set to less than 600 Hz, or control is performed so that a DC voltage of about 100 to 300 V is applied.

  Alternatively, if the number of printed sheets counted by the number counter 51 is 80% or more of the sheet life, the amplitude of the AC bias voltage is set to 800 V or more and the frequency is set to 600 Hz or more. Is set to less than 800 V and the frequency is set to less than 600 Hz, or a DC voltage of about 100 to 300 V is applied.

  In this control example 2, the AC voltage amplitude and frequency are set as low as possible under conditions that do not reach the end of the endurance life where the toner recoverability is originally good, or under conditions where the number of printed sheets is not large. The noise of the brush 25 can be reduced as much as possible.

  In Control Example 2, the boundary condition for changing the AC voltage is set to 80% or more of the durability life of the developer or 80% or more of the number life of the developer. However, this boundary condition is not necessarily required. Further, it may be controlled so as to be changed according to the type of the photoconductor unit 20 using the boundary condition, the type of toner, and the like.

(Control example 3)
The color printer 10 uses various toners of yellow, magenta, cyan, and black. Among these, the black toner may be obtained by adding carbon to the pigment, and the electrical resistance and charge amount are lower than those of other color toners, so that the recoverability with the recovery brush is relatively low. Therefore, in the present control example 3, the AC bias voltage applied to the collection brush 25 by the bias controller 50 is controlled based on the toner type information from the developing device 23.

  That is, with respect to the recovery brush 25 of the photoconductor unit 20 using black toner, the applied AC bias voltage has an amplitude of 200 V or a frequency higher than that of the recovery brush 25 of the photoconductor unit 20 using other color toner. Set to be 200 Hz higher.

  In this control example 3, the noise of the collecting brush 25 when collecting color toners other than black toner is reduced as much as possible, while the amplitude and frequency of the AC bias voltage are slightly increased for black toner with low recoverability. Thus, it is possible to improve black toner recovery.

(Experimental result)
Here, actually, the printing experiment result before the running durability operation in the NN environment and the printing experiment result in the running durability operation for 60 hours in the HH environment are shown in Table 1 below. In Table 1, as a result of evaluating the actual image, a case where no image noise is generated is indicated by a circle, and a case where image noise (toner spillage, image memory, etc.) due to the recoverability of the recovery brush 25 occurs is indicated by ×. This is indicated by a mark.

  As can be seen from Table 1, after the endurance operation experiment in the HH environment, when the collection brush 25 is controlled to apply an AC voltage having an amplitude of 800 V and a frequency of 600 Hz, sufficient recoverability is maintained. There was no noise. However, when only the DC voltage was applied, the low-charged toner could not be sufficiently collected, and streaks and image memory were seen in the image. Even with black toner having a low charge amount, sufficient image quality could be maintained by applying an AC voltage.

  Before the endurance operation in the NN environment, even when only the DC voltage is applied to the recovery brush 25, sufficient image quality can be maintained. When the AC voltage amplitude and frequency are set low under the condition of less than 80%, the generation of noise by the recovery brush 25 can be minimized.

(Release of toner from the collection brush)
The toner taken into the collection brush 25 is discharged onto the photosensitive drum 21 at a timing at which the image portion does not pass through the collection brush 25 by applying a bias voltage having a polarity opposite to that at the time of collection to the collection brush 25, and developed. It is recovered by the apparatus 23 and reused or transferred to the intermediate transfer belt 32 and then recovered and discarded by a blade (not shown). The toner can be discharged from the recovery brush 25 even if the potential difference is lower than that of the recovery. Therefore, an AC voltage may be applied, but a DC voltage is preferably applied for the purpose of reducing noise. .

  When a DC voltage is applied at the time of discharge, it is preferable to set a positive voltage and a negative voltage in order to efficiently discharge positively charged toner and negatively charged toner. Further, during the operation other than image formation, a DC voltage for discharge is applied to the collection brush 25 or no bias voltage is applied.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the present invention can be applied not only to the tandem type color printer shown in the above embodiment but also to various image forming apparatuses such as a monochrome printer, a color / monochrome copying machine, and a facsimile.

1 is a schematic configuration diagram illustrating a color printer which is an embodiment of an image forming apparatus according to the present invention. It is a graph which shows the relationship between DC bias voltage applied to a collection | recovery brush, and collection | recovery. It is a graph which shows the relationship between the amplitude of AC bias voltage applied to a recovery brush, and recoverability. It is a graph which shows the relationship between the frequency of AC bias voltage applied to a recovery brush, and recoverability. It is a block diagram which shows the control part of a color printer. It is a graph which shows the relationship between the AC bias voltage applied to a collection | recovery brush, and a sound pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Color printer 20 ... Photoconductor unit 21 ... Photoconductor drum 23 ... Developing device 25 ... Collection | recovery brush 33 ... Temperature / humidity sensor 50 ... Bias control part 51 ... Number counter 52 ... Memory

Claims (5)

In an image forming apparatus by electrophotography that forms an image on an image carrier through processes of charging, exposure, development, and transfer,
A cleanerless system that collects transfer residual toner from the image carrier by applying a bias voltage to the toner collecting member that contacts the image carrier, and discharges the collected toner onto the image carrier and returns it to the developing unit. With
Changing the amplitude and frequency of the bias voltage applied to the recovery member based on at least one of environmental conditions, number of printed sheets, driving time, toner charge amount, and operating conditions;
An image forming apparatus. When the environmental condition is a high humidity environment, an AC voltage having a frequency of 600 Hz or more and an amplitude of 800 V or more is applied to the recovery member,
In an environment other than high humidity, applying a DC voltage or an AC voltage with a frequency of less than 600 Hz and an amplitude of less than 800 V to the recovery member;
The image forming apparatus according to claim 1. Under a situation where the number of printed sheets or the driving time is short, a DC voltage or an AC voltage having a frequency of less than 600 Hz and an amplitude of less than 800 V is applied to the recovery member,
Under a situation where the number of printed sheets or the driving time is large, an AC voltage having a frequency of 600 Hz or more and an amplitude of 800 V or more is applied to the recovery member;
The image forming apparatus according to claim 1.   The bias voltage applied to the collecting member for collecting the black toner is set to be 200 Hz or higher in frequency or 200 V or higher in amplitude than the bias voltage applied to the collecting member for color toner. Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein an AC voltage is applied to the recovery member during image formation, and a DC voltage is applied or a bias voltage is not applied during operations other than image formation. .

Images