JPH10207187A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely prevent both base fog and retransfer and to obtain a satisfactory image by providing an oscillating-voltage application means which applies an oscillating voltage to an electrifying brush, and a voltage waveform adjustment means which adjusts the waveform of the oscillating voltage. SOLUTION: The electrifying brush 24 is in contact with the surface of a photoreceptor 12, and rotates in a normal direction in relation to the direction of the movement of the photoreceptor 12 by means of a motor. To the electrifying brush 24, a power source circuit 26 composing the oscillating-voltage application means is connected. By an output voltage applied from the power source circuit 26 the surface of the photoreceptor 12 is electrified. The power source circuit 26 outputs the output voltage which is proportional to a drive voltage inputted from the voltage waveform adjustment means 46. By switching, according to a paper size, the amplitude of the voltage which is applied to the electrifying brush 24 and then applying the voltage, retransfer does not occur even in a letter size and in a postcard size, and also a satisfactory image flee of base fog can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, to developing an electrostatic latent image formed on the surface of an image bearing member with a developer and simultaneously transferring the latent image from a previous transfer. The present invention also relates to a cleaner-less type image forming apparatus which collects residual developer remaining on the surface of an image carrier.

[0002]

2. Description of the Related Art Heretofore, a cleaner-less image in which a developer (residual developer) remaining on the surface of an image carrier without being transferred to a transfer material is collected without using a dedicated cleaning member. A forming apparatus is provided (Japanese Unexamined Patent Publication No.
20986). As shown in FIG. 19, in this type of image forming apparatus, a charging device 3 including a charging brush 2 along a rotation direction of a cylindrical photoreceptor 1 serving as an image carrier,
A laser device 4, a developing and cleaning device 5, and a transfer charger 6 are arranged in this order.

In order to uniformly charge the surface of the photoreceptor 1, the charging brush 2 has an oscillation voltage of a complete rectangular waveform obtained by switching a DC voltage as shown in FIG. As shown in FIG. 20C, an oscillating voltage of a rectangular waveform having rising and falling edges or a oscillating voltage obtained by superimposing an AC voltage on a DC voltage as shown in FIG.

The surface of the uniformly charged photoreceptor 1 is exposed by a laser beam 7 irradiated by a laser device 4 to form an electrostatic latent image. This electrostatic latent image is visualized by the developing and cleaning device 5, and at the same time, the residual developer is removed by the developing and cleaning device 5.
Will be collected. Specifically, the developer is supplied to the image portion by a potential difference between the potential of the image portion on the surface of the photoconductor 1 attenuated by exposure and the developing bias applied to the developer carrier 7 of the developing cleaning device 5. . Further, the residual developer present in the non-image portion is electrostatically adsorbed to the developer carrier 7 and collected by the potential difference between the potential of the non-exposed non-image portion of the photoconductor 1 and the developing bias voltage. I do.

Thereafter, a transfer current having a polarity opposite to that of the developer is supplied from the transfer charger 6 to the photosensitive member 1, and an image visualized by the developer is transferred onto the sheet P conveyed to the surface of the photosensitive member 1. You.

[0006] As described above, the charging brush 2
In addition to charging the surface, it has a function of collecting the residual developer and a function of injecting charges into the residual developer. That is, the residual developer that reaches the contact portion with the charging brush 2 with the rotation of the photoreceptor 1 is charged not only with the normal charging polarity (the same polarity as the photoreceptor 1) but also with the opposite polarity to the normal charging polarity. Some developer is charged, and the residual developer having the opposite polarity is electrostatically attracted to the charging brush 2 and collected, and then injected with electric charge to be discharged to the photoreceptor 1 with a regular polarity. Also,
Even if the residual developer is charged to the normal polarity, the residual developer having the opposite polarity is electrostatically attracted to the residual developer having the opposite polarity and is collected by the charging brush 2 together with the residual developer having the opposite polarity.
Sometimes it is mechanically scraped off.

[0007]

However, in the above-mentioned conventional image forming apparatus, when a small area of paper P such as a postcard is used, most of the transfer current supplied from the transfer charger 6 has a relative impedance. Since the paper P flows on a portion of the low photoconductor 1 where the paper P is not disposed (non-paper passing portion), the transfer current flowing through the portion where the paper P is disposed (paper passing portion) decreases. Therefore, when the paper P having a small area is used, the efficiency of transferring the developer on the surface of the photoconductor 1 to the paper P (transfer efficiency) decreases, and the residual developer increases. for that reason,
A phenomenon in which the residual developer not recovered by the charging brush 2 or the developing cleaning device 5 reaches the position where the transfer charger 6 is disposed again by the rotation of the photoconductor 1 and is transferred to the newly supplied paper P (re-transfer). ) Occurs.

On the other hand, FIG. 20A, FIG.
If the amplitude W of the oscillation voltage shown in FIG.
The efficiency of collecting the residual developer by the charging brush 2 is improved, and the occurrence of the retransfer can be prevented. However, if the amplitude W is large, the efficiency of injecting charges of the normal polarity into the residual developer charged to the opposite polarity is reduced, and the photosensitive member 1
The amount of the residual developer (fogging toner) charged to the opposite polarity increases. Therefore, if the amplitude W is set to be large, a problem occurs in the case of intermittent printing (a vibration voltage is applied during image formation, a constant voltage having a constant polarity is applied during non-image formation, and the constant voltage application time is set long). There is no printing, but continuous printing (vibration voltage is applied during image formation,
Set the constant voltage application time shorter than that for intermittent printing. In the case of (1), so-called background fogging occurs in the image.

As described above, in the cleaner-less type image forming apparatus, the efficiency of injecting charges into the residual developer of the opposite polarity decreases when the efficiency of recovering the residual developer by the charging brush is increased to prevent retransfer. However, background fog tends to occur during continuous printing. On the other hand, when trying to increase the efficiency of injecting charges into the residual developer of the opposite polarity in order to prevent background fogging during continuous printing, the efficiency of collecting the residual developer by the charging brush is reduced and retransfer is likely to occur. Become.

For example, when the inventor intermittently printed a character chart having a black-and-white ratio of 5% on a letter-size sheet under the conditions shown in Experiment 1 in Table 1, a good image without retransfer and background fogging was obtained. Was obtained, but as shown in Experiment 2,
With the other conditions being the same, the intermittent printing was performed with only the dimensions of the paper as the postcard size (about half the area of the letter size paper), and retransfer occurred. Therefore, as shown in Experiment 3, the amplitude W of the voltage supplied to the charging brush is increased from 1000 V to 1400 V in order to increase the developer collection efficiency.
When intermittent printing was performed with an increase in the number of images, a good image was obtained without retransfer. However, in this case, when continuous printing was performed, background fogging occurred.

[0011]

[Table 1]

In addition to the paper size, the residual developer increases due to conditions such as a transfer voltage, a transfer current, a supplied developer concentration, a black-and-white ratio of an original, a developing sleeve current, and a developing bias. Is generated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the conventional cleaner-less type image forming apparatus, and is capable of reliably preventing both background fogging and retransfer.
It is an object to obtain a good image.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a cleaner which visualizes an electrostatic latent image formed on the surface of an image carrier with a developer and simultaneously recovers the residual developer. A charging brush that rotates in contact with the image carrier, a first potential, and a second potential that is lower than the first potential.
And a voltage waveform adjusting means for adjusting the waveform of the oscillating voltage output by the oscillating voltage applying means.

[0015] More specifically, the image forming apparatus includes detecting means for detecting an image forming parameter correlating with the amount of residual developer present on the surface of the image carrier, and the voltage waveform adjusting means includes a detecting means for detecting the image forming parameter. The waveform of the oscillating voltage is adjusted according to the value.

More specifically, the image forming parameters correlated with the residual developer amount detected by the detecting means include paper size, transfer voltage, transfer current, supplied developer concentration, black and white ratio of the original, sleeve current, and developing current. At least one of the biases.

In accordance with an image forming parameter correlated with the residual developer amount such as the paper size detected by the detecting means,
By adjusting the waveform of the vibration voltage applied to the charging brush, both retransfer and background fog can be prevented, and a good image can be obtained.

The voltage waveform adjusting means adjusts the amplitude of the oscillating voltage. When it is determined from the detection value of the detecting means that the amount of the residual developer is large, the amplitude of the oscillating voltage is increased while the amplitude of the residual developer is increased. When it is determined that the amount is small, it is preferable to reduce the amplitude of the oscillation voltage.

When the amplitude of the oscillating voltage is increased, the efficiency of recovering the residual developer of the charging brush increases, while the efficiency of the charging brush injecting charges into the residual developer charged to the opposite polarity decreases. Conversely, when the amplitude of the oscillating voltage is reduced, the recovery efficiency of the residual developer decreases, but the efficiency of injecting charges into the residual developer charged to the opposite polarity increases. Therefore, if the amplitude of the oscillation voltage is adjusted as described above, when the amount of the residual developer is large, the collecting power of the charging brush is increased to prevent retransfer, while when the amount of the residual developer is small, The efficiency of injecting charges into the residual developer having the opposite polarity is increased, and background fogging can be prevented.

Alternatively, the voltage waveform adjusting means adjusts the duty ratio of the oscillating voltage. When it is determined from the detection value of the detecting means that the amount of the residual developer is large, the application time of the voltage of the first potential is determined. , The application time of the voltage of the second potential is set to be long, and when it is determined that the amount of the residual developer is small, the application time of the voltage of the first potential is lengthened to increase the voltage of the second potential. The application time may be set short.

When the time during which the voltage of the second potential of the oscillating voltage is applied is lengthened, the recovering power of the residual developer is improved.
On the other hand, if the time during which the voltage of the first potential is applied is lengthened, the efficiency of injecting charges into the residual developer charged to the opposite polarity increases. Therefore, if the duty ratio of the oscillating voltage is adjusted as described above, when the amount of the residual developer is large, the collecting power of the charging brush is increased, and re-transfer is prevented. On the other hand, when the amount of the residual developer is large, the efficiency of injecting charges into the residual developer having the opposite polarity increases, and background fogging can be prevented.

Furthermore, it is preferable that the user can manually adjust the voltage waveform adjusting means.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIGS. 1 and 2 show a cleanerless laser beam printer according to an embodiment of the present invention. In this embodiment, the normal charging polarity of the toner is negative.

At a substantially central portion of the main body 11 of the laser beam printer, a photosensitive member 12 constituting an image carrier formed by forming a thin film layer of an organic photoconductive material (OPC) on an outer peripheral surface of a cylindrical body.
Are rotatably arranged. The photoconductor 12 is rotated by a motor (not shown) in a direction indicated by an arrow A in FIG. The photosensitive member 12 has a peripheral speed of 5 mm / sec.
And the light exposure amount is 18 erg / cm ² .

Around the photoreceptor 12, the charging device 13, the laser device 14, the developing cleaning device 1
5 and the transfer charger 16 are arranged in order. A paper feed cassette 17 is provided below the developing and cleaning device 15, and a paper feed roller 18 is in contact with the paper P stored in the paper feed cassette 17. Also, the paper cassette 17
A paper passing path is formed along the guides 19a and 19b and passing through a transfer area sandwiched between the photoconductor 12 and the transfer charger 16. The paper P in the paper feed cassette 17 is fixed to the main body 11 via the fixing roller 20. Is discharged onto a paper discharge tray 21 attached to the printer.

The charging device 13 includes a charging brush 24 disposed in the cover 23 that opens toward the photosensitive member 12 along the axial direction of the photosensitive member 12. The charging brush 24 is formed by densely implanting a contact 24b made of straight-haired fiber on a core metal 24a constituting a rotation shaft. In the present embodiment, the diameter of the core 24a is 6 mm.
And In addition, the contact 24b, the resistance of 10 ^5-1
0 consists ⁷ Omega / cm conductivity rayon, pile length is 5
mm. Furthermore, the pile density of the contact 24b is 5
It is 000 lines / square inch. Furthermore, the outer diameter of the charging brush 24 when the contact 24b is in a beveled state is 14.2 mm.

The charging brush 24 is in contact with the surface of the photoreceptor 12, and is moved by a motor (not shown) as shown by arrow B in FIG. To rotate in the forward direction. In the present embodiment, the rotation speed of the charging brush 24 is
180 rpm.

A power supply circuit 26 constituting an oscillating voltage applying means is connected to the charging brush 24, and the photosensitive member 12 is controlled by an output voltage V _OUT applied from the power supply circuit 26.
The surface is charged. The power supply circuit 26 outputs an output voltage V _OUT proportional to the drive voltage V _d input from the voltage waveform adjusting means 46. As shown in FIG. 3, the constant voltage source 27, the control circuit 28, and the transistor tr1, and a transformer 29, a diode D ₁ and capacitor C _1. The power supply 26 supplies an output voltage V _OUT to the control circuit 28.
, And resistors R ₁ and R ₂ for feeding back the current. In FIG. 3, the capacitor C ₂ and the resistor R ₃ are:
Image forming process section (charging brush 24 and photoconductor 12)
5 is an equivalent circuit showing the resistance and capacitance of the circuit. Figure 4 shows the output characteristics of the power source circuit 26, the output voltage V _OUT from the power supply circuit 26 is proportional to the driving voltage V _d of the voltage waveform adjusting means 46.

The developing / cleaning device 15 includes a casing 34 for containing a triboelectric non-magnetic one-component toner as a developer.
It has. A developing sleeve 3 that conveys toner having the same polarity as that of the photoconductor 12 to the photoconductor 12 is provided in an opening 34 a of the casing 34 that opens toward the photoconductor 12.
5 are provided. The developing sleeve 35 is driven by a motor (not shown) and rotates while being in surface contact with the photoconductor 12. A developing bias (constant at −240 V in the present embodiment) is applied to the developing sleeve 35 from a power supply 36. Further, a blade 38 to which a blade bias is applied from a power supply 37 is in contact with the upstream side in the rotation direction of the developing sleeve 35. Further, a power supply 39 is provided downstream of the developing sleeve 35 in the rotation direction.
The static elimination member 40 to which the static elimination bias is applied is in contact. A stirring blade 42 that rotates in the direction opposite to the developing sleeve 35 is provided in the casing 34.

The transfer charger 16 supplies a current having a polarity opposite to the normal charge polarity of the toner from the back surface to the paper P sent from the paper feed cassette 17 to the transfer area in synchronization with the rotation of the photoconductor 12. The toner is electrostatically attracted, and the toner image on the surface of the photoconductor 12 is transferred to the paper P. In FIG. 2, reference numeral 21 denotes a power supply of the transfer charger 16. In the present embodiment, the current (photoconductor inflow current I _PC ) flowing from the transfer charger 16 to the photoconductor 12 is fixed (9 μA).

A paper width detection sensor 44 is provided on the guide 19a existing between the paper feed cassette 17 and the transfer area. The paper width detection sensor 44 is composed of an optical sensor having a known structure, detects the width of the paper P supplied from the paper feed cassette 17, and outputs the detected width to the voltage waveform adjusting means 46.

The voltage waveform adjusting means 46 is used when forming an image.
And it outputs a driving voltage V _d of the rectangular wave that repeats a high voltage V _hi and low voltage V _low as shown by the solid line in the main switch 27 in FIG. 5 (A). This driving voltage _Vd has a frequency of 30.
Hz. The driving voltage V _d is, 20Mse high voltage V _hi of the application time (see FIG. 5 (A) at time t ₁ ~t ₂₎
c, the application time of the low voltage V _low (time t _{2 to} t ₃ in FIG. 5A) is 13 msec, and the duty ratio is 20:13. The output voltage V _OUT of the power supply circuit 26 applied to the charging brush 24 is proportional to the drive voltage V _d output from the voltage waveform adjusting means 46 as described above. Therefore, the high voltage V _hi of the drive voltage V _d is 4.3 V and the low voltage V _{low is}
If the output voltage V _OUT is 1 V, as shown in FIG. 5 (B), the output voltage V _OUT is a rectangular waveform oscillating voltage having a high voltage of −1300, a low voltage of −300 V, an amplitude of 1000 V, and a rise and fall. Become. On the other hand, the high voltage V of the driving voltage V _{d
If hi} is 5 V and low voltage V _low is 0.33 V, as shown in FIG. 5B, the output voltage V _OUT becomes -15
00, a low-voltage -100 V and amplitude of 1400 V is a vibration waveform having a rising and falling rectangular waveform.

The voltage waveform adjusting means 46 detects the size of the paper P supplied from the paper feed cassette 17 based on the signal input from the paper width detection sensor 44, and according to the detected paper size. switches the driving voltage V _d to be outputted to the power supply circuit 26.

First, when the voltage waveform adjusting means 46 determines that the paper P is a letter size based on a signal supplied from the output of the paper width detection sensor 44, the high voltage V _hi
But 4.3 V, the low voltage V _low outputs a driving voltage V _d of 1V. In this case, the output voltage V _OUT applied to the charging brush 24 is an oscillating voltage having a waveform as shown in FIG. 3B, and its amplitude W is 1000V.

On the other hand, the voltage waveform adjusting means 46 determines that the paper P is a postcard size (the width of the paper is の of the letter size) based on a signal supplied from the output of the paper width detection sensor 44.
, The high voltage V _hi is 5 V and the low voltage V _low
There outputs a driving voltage V _d of 0.33 V. In this case, the output voltage V _OUT applied to the charging brush 24 is as shown in FIG.
It is a vibration voltage having a wave-like waveform as shown in (C), and its amplitude W is 1400V.

Here, the reason why the amplitude W in the case of the letter size and the size of the postcard is set to 1000 V and 1400 V, respectively, is based on the results of Experiments 1 to 3 shown in Table 1 above. That is, according to Experiments 1 to 3, when the paper P has a letter size, the transfer efficiency is high and the residual toner density is low. Therefore, in this case, the amplitude W of the output voltage V _OUT is set as small as 1000 V in order to increase the efficiency of charge injection to the toner of the opposite polarity and prevent the background fog. On the other hand, when the paper P is a postcard size,
The transfer efficiency is low and the residual toner density is high. Therefore, in this case, the amplitude W of the output voltage V _OUT is set to 1400 V and set to be larger than that in the case of the letter size in order to increase the collection efficiency of the toner by the charging brush 24 and prevent retransfer.

As described above, the charging brush 2 according to the paper size
If the voltage is applied while switching the amplitude W of the voltage applied to No. 4, no retransfer occurs in the case of the letter size or the postcard size, and a good image without background fog can be obtained.

(Second Embodiment) Next, a second embodiment of the present invention will be described. Note that the configurations and operations of the second to seventh embodiments are the same as those of the first embodiment unless otherwise specified.
This is the same as the embodiment.

FIG. 4 shows the voltage (transfer) of the transfer charger 16 in the laser printer of the first embodiment when letter-size paper is used, when postcard-size paper is used, and when paper is not supplied. Voltage V
And _T), shows the relationship between the current I _PC flows photoreceptor at that time. As shown in FIG. 4, when the transfer voltage V _T is controlled so that the photoconductor inflow current I _PC is constant at 9 μA, the transfer voltage V _T when the paper is letter size is 4.30 kV, and when the paper is postcard size. Has a transfer voltage V _T of 4.15 kV. Then, as shown in FIG. 5, when the photosensitive member inflow current I _Pc is constant (9 .mu.A) is correlated between the residual toner density and the transfer voltage V _T. That is, when a photosensitive member inflow current I _PC is constant, the residual toner density enough transfer voltage V _T is high becomes low concentrations. In the second embodiment, in response to the transfer voltage V _T, the amplitude W of the output voltage V _OUT to be applied to the charging brush 24
Is adjusted.

As shown in FIG. 6, in the transfer voltage and the voltage meter 48 is interposed for measuring V _T, the output signal of the voltmeter 48 is the voltage waveform adjusting between the power source 21 and the transfer charger 16 It is input to the means 46. The voltage waveform adjusting means 46 controls the transfer voltage V _T measured by the voltmeter 48.
If is 4.15KV, that is, when the transfer voltage V _T is high, the high voltage V _hi is 5V, the low voltage V _low is 0.33
And it outputs a driving voltage V _d of V. And the power supply circuit 26
Has an amplitude W of 1400 V as shown in FIG.
An output voltage V _OUT , which is an oscillating voltage (high voltage is −1500 V, low voltage is −100 V), is applied to the charging brush 24.

On the other hand, the voltage waveform adjusting means 46 comprises a voltmeter 4
When the transfer voltage V _T measured from No. 8 is 4.30 kV,
That transfer voltage V _T is the case of low pressure, the high voltage V _hi is 4.3 V, the low voltage V _low outputs a driving voltage V _d of 1V. Then, the power supply circuit 26 applies the output voltage V _OUT , which is an oscillating voltage having an amplitude W of 1000 V (high voltage −1300 V, low voltage −300 V) as shown in FIG.

As described above, in the second embodiment, when the transfer voltage _VT is high (when the residual toner density is low), the output voltage V applied to the charging brush 24 is emphasized with emphasis on background fog prevention. _When the amplitude W of _OUT is small and the transfer voltage _VT is low (when the residual toner density is high), the amplitude of the output voltage V _OUT applied to the charging brush 24 with emphasis on the recovery efficiency of the residual toner. W is set large. Therefore, it is possible to obtain a good image without retransfer and fogging regardless of the value of the transfer voltage V _T.

(Third Embodiment) In the laser printer of the first embodiment, the transfer voltage _VT is set to a constant voltage (4.3
In the case of 0 kV), as shown in FIG. 7, there is a correlation between the current (transfer current I _T ) supplied from the transfer charger 16 to the sheet P and the photoconductor 12 and the residual toner density. I sand, residual toner density greater the transfer current I _T becomes low concentrations. Therefore, in the third embodiment, in accordance with the transfer current I _T, the output voltage V _OUT to be applied to the charging brush 24
Is adjusted.

As shown in FIG. 8, between the power source 21 and the transfer charger 16, and is interposed ammeter 50 for measuring the transfer current I _T, the output signal of the current meter 50,
It is input to the voltage waveform adjusting means 46. The above ammeter 5
If the transfer current I _T, which is measured by 0 is 25 .mu.A, i.e., when the transfer current I _T is small, the amplitude W is 14
Output voltage V _OUT which is an oscillation voltage of 00V (FIG. 3 (C))
As but applied to the charging brush 24, the voltage waveform adjusting means 46 switches the driving voltage V _d.

On the other hand, if the transfer current I _T, which is measured by the voltmeter 50 is 40 .mu.A, that is, when the transfer current is large, the output voltage V _OUT amplitude W is oscillating voltage of 1000V (Fig 3 (B) ) is to be applied to the charging brush 24, the voltage waveform adjusting means 46 switches the driving voltage V _d.

As described above, in the third embodiment, the transfer current I _T
Is large (when the residual toner density is low),
When the amplitude W of the output voltage V _OUT applied to the charging brush 24 is set small with emphasis on the background fog prevention, and when the transfer current _IT is small (when the residual toner density is high), the recovery efficiency of the residual toner is increased. The amplitude W of the output voltage V _OUT applied to the charging brush 24 is set to be large, with emphasis on. Therefore, regardless of the transfer current I _T, it is possible to obtain a good image without retransfer and background fog.

(Fourth Embodiment) As shown in FIG. 9, there is a correlation between the density of the toner supplied from the developing sleeve 35 (supply toner density) and the residual toner density. That is, the higher the supplied toner density, the higher the residual toner density. Therefore, in the fourth embodiment, the output voltage V applied to the charging brush 24 according to the supplied toner concentration
The amplitude W of _OUT is adjusted. Note that the supplied toner density depends on the image pattern to be printed, and the supplied toner density becomes higher as the number of symbols in the image pattern is larger and the margin is smaller.

As shown in FIG. 10, an optical sensor 52 is disposed around the photosensitive member 12 between the developing cleaning device 15 and the transfer charger 16. The light beam emitted by the optical sensor 52 is reflected by the toner on the surface of the photoconductor 12 and re-enters the optical sensor 52.
The density of the toner on the surface is detected.

When the toner concentration measured by the optical sensor 52 is 1.50 mg / cm ² , that is, when the supplied toner concentration is high, the output voltage V _OUT (the oscillation voltage having an amplitude W of 1400 V) is output. as Figure 3 (C)) is applied to the charging brush 24, the voltage waveform adjusting means 46 switches the driving voltage V _d.

On the other hand, when the developer concentration measured by the optical sensor 52 is 0.30 mg / cm ² , that is, when the supplied toner concentration is low, the output voltage V _OUT having an amplitude W of 1000 V is a vibration voltage. (FIG. 3B) is applied to the charging brush 24 by the voltage waveform adjusting means 46.
The drive voltage _Vd is switched.

As described above, in the fourth embodiment, when the supplied toner density is high (when the residual toner density is high).
The charging brush 24 is designed to emphasize the efficiency of collecting the residual toner.
Set increasing the amplitude W of the output voltage V _OUT to be applied to the supply toner density is in the case of low concentrations (when the residual toner density is low density), is applied to the charging brush 24 with an emphasis on prevention of fogging The amplitude W of the output voltage V _OUT is set small. Therefore, a good image free from retransfer and background fogging can be obtained regardless of the image pattern to be printed.

(Fifth Embodiment) As shown in FIG. 11, between a black-and-white ratio (B / W ratio), which is an area ratio of a portion where a pattern is present in a printed image pattern and a margin portion, and a supply toner density. There is a correlation. That is, the B / W ratio is high (the area of the blank portion is small in the image pattern to be printed)
As the toner density increases, the supplied toner density becomes higher. As described in the fourth embodiment, there is a correlation between the supplied toner density and the residual toner density as shown in FIG. Therefore, the higher the B / W ratio, the higher the residual toner density.
Therefore, in the fifth embodiment, the B of the image pattern to be printed is
Output voltage V applied to the charging brush 24 according to the / W ratio
The amplitude W of _OUT is adjusted.

As shown in FIG. 12, the laser device 14 for exposing the photoreceptor 12 emits laser light polarized by a polygon mirror 55 from a laser light source 54, and the laser light source 54 Driven by the driver 56 based on the input data. In the fifth embodiment,
Between the driver 56 and the laser light source 54, there is provided a counter 57 for counting the number of dots of a portion to be supplied with toner and the number of dots of a portion to be blank in an image pattern defined by input data.

The counter 57 is provided with a voltage waveform adjusting means 46.
And the voltage waveform adjusting means 46 calculates the B / W ratio based on the input number of dots. B / W ratio is 2
In the case of 5%, that is, when the B / W ratio is low, the amplitude W
Is applied to the charging brush 24 so that the output voltage V _OUT (FIG. 3B) of 1000 V is applied to the charging brush 24.
But switches the driving voltage V _d.

On the other hand, when the B / W ratio is 100%, that is, when the B / W ratio is high, an output voltage V _OUT (FIG. 3C) having an amplitude W of 1400 V is applied to the charging brush 24. as such, the voltage waveform adjusting means 46 switches the driving voltage V _d.

As described above, in the fifth embodiment, when the B / W ratio of the image pattern to be printed is high (when the residual toner density is high), the charging brush 24 is placed on the charging brush 24 with emphasis on the recovery efficiency of the residual toner. When the amplitude W of the applied output voltage V _OUT is set large and the B / W ratio of the image pattern to be printed is low (when the residual toner density is low), emphasis is placed on preventing background fogging and the charging brush 24 is used. Output voltage V applied to
_OUT amplitude W is set small. Therefore, regardless of the image pattern to be printed, retransfer and background fogging can be prevented, and a good image can be obtained.

Sixth Embodiment As shown in FIG. 13, there is a correlation between the current supplied to the developing sleeve 35 (developing sleeve current _Is ) and the B / W ratio. That is,
As the developing sleeve current I _s is large, the input data B / W
Low ratio. Further, as described in the fifth embodiment, there is a correlation between the B / W ratio and the residual toner density as shown in FIG. Therefore, there is also a correlation between the developing sleeve current and the residual toner concentration. That is,
The larger the developing sleeve current, the lower the residual toner density, and the smaller the developing sleeve current, the higher the residual toner density. Therefore, in the sixth embodiment, by adjusting the amplitude W of the voltage applied to the charging brush according to the developing sleeve current I _s.

[0058] As shown in FIG. 14, between the power supply 36 the developing sleeve, the ammeter 59 for measuring the developing sleeve current I _s and is interposed, the output signal of the ammeter 59, the voltage waveform adjusting It has been input to means 46.

[0059] When the developing sleeve current I _s, which is measured by the voltmeter 59 is 0.30Myuei, that is, when the developing sleeve current I _s is small, the output voltage of the amplitude W is 1400 V V _OUT (FIG. 3 (C) ) is to be applied to the charging brush 24, the voltage waveform adjusting means 46 switches the driving voltage V _d.

On the other hand, when the developing sleeve current measured by the ammeter 59 is 0.45 μA, that is, when the developing sleeve current is large, the output voltage V _OUT (FIG. 3B) having an amplitude W of 1000 V is charged. as applied to the brush 24, the voltage waveform adjusting means 46 switches the driving voltage V _d.

[0061] In this way, the sixth embodiment, if the developing sleeve current I _s is large (when the residual toner density is low density), the output voltage V _OUT to be applied to the charging brush 24 emphasizes fogging prevention set the amplitude W small, if the developing sleeve current I _s is small (when the residual toner density is high density), the amplitude of the output voltage V _OUT which emphasizes collection efficiency of the residual toner is applied to the charging brush 24 W is set small. Therefore, regardless of the image pattern to be printed, retransfer and background fogging can be prevented, and a good image can be obtained.

(Seventh Embodiment) In the first to sixth embodiments described above, the amplitude W of the output voltage V _OUT applied to the charging brush 24 is adjusted. However, in the seventh embodiment, the output voltage V _OUT is adjusted. The duty ratio of V _OUT is adjusted. In the image forming apparatus of FIG. 1, by changing the duty ratio of the output voltage V _OUT variously, a toner of 1.0 mg / cm ² is supplied to the surface of the photoreceptor 12 and re-transferred when passing through the charging brush 24. When the toner concentration was measured, the results shown in Table 2 below were obtained. From Table 2, it can be seen that the time during which the high potential voltage is applied (t in FIG.
₁ ~t ₂₎ for the more the proportion of time during which a voltage of low potential t ₂ ~t ₃ in (FIG. 3 (A)) is large, the concentration of the toner is re-transferred low concentration, i.e. the residual toner density Becomes low concentration. This is because if the time for applying the low-potential voltage is long, it is easier to collect the toner charged to the regular polarity (-) at the portion (charging nip) of the charging brush 24 that comes into contact with the photoconductor 12.

[0063]

[Table 2]

FIG. 15 shows the relationship between the voltage (developing bias V _s ) applied to the developing sleeve 35 of the developing cleaning device 15 and the duty ratio and the retransfer rank. In FIG. 15, “○”, “Δ”, and “X” indicate the transfer rank again, and the density of the toner to be re-transferred increases in this order.
When the duty ratio is focused on the case of 20:13, there is a correlation between the concentration and thus the residual toner density of the toner is re-transferred and the developing bias V _s, high residual toner density enough developing bias V _s is high Has become. Therefore,
In the seventh embodiment, by adjusting the duty ratio of the output voltage V _OUT to be applied to the charging brush 24 in accordance with the development bias V _s.

[0065] As shown in FIG. 16, between the power source 36 and the developing sleeve 35, a voltmeter 60 for measuring the developing bias V _s and is interposed, the output signal of the voltmeter 60 is the voltage waveform adjusting means 46.

[0066] developing bias V _s which is measured by the voltmeter 60 is the case of -240 V, that is, the development bias V _s
Is low pressure, the voltage waveform adjusting means 46
Switching in (A) as shown by the solid line, the duty ratio of the driving voltage V _d of the 20:13. That is, in this case, the main switch 27 switches the high voltage alternately in the order of 20 msec and the low voltage in the order of 13 msec.

[0067] developing bias V _s which is measured by the voltmeter 60 is the case of -300 V, that is, the development bias V _s
When the voltage is high, the voltage waveform adjusting means 46
As shown by a chain line (A), the switching the duty ratio of the driving voltage V _d to 15:18. That is, in this case, the main switch 27 sets the high voltage to 15 msec.
The low voltage can be switched alternately in the order of 18 msec.

[0068] In this way, the seventh embodiment, when the developing bias V _s is the high pressure (when the residual toner density is high density)
The sets the duty ratio such that the application time becomes longer voltage of the low potential of the output voltage V _OUT to be applied to re-transfer prevention in to charging brush 24 oriented, when the developing bias V _s is the low pressure (residual toner In the case where the density is high, the duty ratio is set so as to shorten the application time of the low potential voltage of the output voltage V _OUT applied with emphasis on background fog prevention. Therefore, regardless of the image pattern to be printed, retransfer and background fogging can be prevented and a good image can be obtained.

The present invention is not limited to the above embodiment, and various modifications are possible. In the first to seventh embodiments, the voltage waveform adjusting means 46 automatically adjusts the amplitude W and the duty ratio according to the output of the sensor or the like. The duty ratio may be finely adjusted. For example, as shown in FIG. 1, a switch 64 for finely adjusting the amplitude W of the output voltage V _OUT may be provided on the operation panel 63 of the laser printer main body 11.

In the above embodiment, the voltage applied to the charging brush is the output voltage V obtained by switching the DC voltage.
_OUT , but a voltage obtained by superimposing an AC voltage on a DC voltage as shown in FIG.
The amplitude W may be changed according to image parameters such as a transfer current, a transfer voltage, a developing sleeve current, a developing bias, a toner adhesion amount sensor value, and a paper size.

Further, in the first to sixth embodiments, the duty ratio may be adjusted instead of the amplitude. Conversely, the amplitude may be adjusted instead of the duty in the seventh embodiment.

[0072]

As is apparent from the above description, in the image forming apparatus according to the present invention, the image forming parameter which is correlated with the amount of the residual developer detected by the detecting means is detected, and the voltage waveform adjusting means detects the residual developer. If it is determined that the amount is large, the amplitude or the duty ratio of the oscillation voltage applied to the charging brush is set to emphasize the prevention of retransfer, that is, to the setting that emphasizes the recovery efficiency of the residual developer. On the other hand, when determining that the residual developer amount is small, the voltage waveform adjusting means sets the amplitude or the duty ratio of the oscillating voltage with emphasis on prevention of background fogging, that is, the charge injection efficiency for the residual developer of the opposite polarity. Is set with emphasis. Therefore, according to the image forming apparatus of the present invention, a good image free from retransfer and background fogging can be obtained regardless of the amount of the residual developer.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a laser printer according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of the laser printer of FIG.

FIG. 3 is a circuit diagram showing a power supply circuit.

FIG. 4 is a diagram showing input / output characteristics of a power supply circuit.

FIG. 5A is a waveform diagram of a driving voltage applied to a power supply,
(B) is a waveform diagram showing a vibration voltage having a small amplitude applied to the charging brush, and (C) is a waveform diagram showing a vibration voltage having a large amplitude applied to the charging brush.

FIG. 6 is a graph showing a relationship between a transfer voltage and a current flowing into a photosensitive member.

FIG. 7 is a graph showing a relationship between a transfer voltage and a residual toner density.

FIG. 8 is a schematic diagram of a main part showing a second embodiment of the present invention.

FIG. 9 is a graph showing a relationship between a transfer current and a residual toner density.

FIG. 10 is a schematic diagram of a main part showing a third embodiment of the present invention.

FIG. 11 is a graph showing a relationship between a supplied toner density and a residual toner density.

FIG. 12 is a schematic diagram of a main part showing a fourth embodiment of the present invention.

FIG. 13 is a graph showing the relationship between the black and white ratio of input data and the residual toner density.

FIG. 14 is a schematic diagram of a main part showing a fifth embodiment of the present invention.

FIG. 15 is a graph showing a relationship between a developing sleeve current and a black-and-white ratio of input data.

FIG. 16 is a schematic diagram of a main part showing a sixth embodiment of the present invention.

FIG. 17 is a graph showing a relationship between a developing bias and a duty ratio and a retransfer rank.

FIG. 18 is a schematic view of a main part showing a seventh embodiment of the present invention.

FIG. 19 is an enlarged view of a main part showing a conventional image forming apparatus.

FIGS. 20A, 20B, and 20C are graphs showing waveforms of an oscillating voltage applied to a charging brush.

[Explanation of symbols]

 Reference Signs List 12 photoconductor 14 laser device 24 charging brush 26 power supply circuit 21, 36, 37, 39 power supply 44 paper width detection sensor 46 voltage waveform adjusting means 48, 60 voltmeter 50, 59 ammeter 52 light sensor 54 laser light source 56 driver 57 counter

Claims (8)

[Claims] 1. A cleaner-less type image forming apparatus which visualizes an electrostatic latent image formed on the surface of an image carrier with a developer and simultaneously recovers a residual developer. And a vibration voltage applying means for applying, to the charging brush, a vibration voltage that oscillates between a first potential and a second potential lower than the first potential. An image forming apparatus comprising: a voltage waveform adjusting unit configured to adjust a waveform of an oscillating voltage output from the oscillating voltage applying unit. 2. The apparatus according to claim 1, further comprising: detecting means for detecting an image forming parameter correlated with an amount of the residual developer present on the surface of the image carrier, wherein said voltage waveform adjusting means includes a waveform of said oscillating voltage according to a detection value of said detecting means. The image forming apparatus according to claim 1, wherein the image forming apparatus is adjusted. 3. An image forming parameter correlated with the residual developer amount detected by the detecting means includes a paper size, a transfer voltage,
3. The image forming apparatus according to claim 2, wherein the current value is at least one of a transfer current, a supplied developer concentration, a black and white ratio of a document, a developing sleeve current, and a developing bias. 4. The image forming apparatus according to claim 2, wherein said voltage waveform adjusting means adjusts the amplitude of said oscillating voltage. 5. The voltage waveform adjusting means increases the amplitude of the oscillating voltage when judging that the amount of the residual developer is large from the detection value of the detecting means, and increases the amplitude of the oscillating voltage when judging that the amount of the residual developer is small. The image forming apparatus according to claim 4, wherein the amplitude of the voltage is reduced. 6. The image forming apparatus according to claim 2, wherein said voltage waveform adjusting means adjusts a duty ratio of said oscillating voltage. 7. The voltage waveform adjusting means, when judging from the detection value of the detection means that the amount of residual developer is large, the first voltage waveform adjusting means.
The application time of the voltage of the second potential is shortened to increase the application time of the voltage of the second potential. On the other hand, if it is determined that the amount of the residual developer is small, the application time of the voltage of the first potential is increased. 7. The image forming apparatus according to claim 6, wherein the application time of the voltage of the second potential is set short. 8. The apparatus according to claim 1, wherein said voltage waveform adjusting means is manually adjustable by a user.
The image forming apparatus according to claim 1.