JPH0536788B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] Regarding a conductive brush charging device using a conductive brush charger, the purpose is to perform stable and uniform charging. The current power supply includes a high voltage power supply circuit that applies high voltage to the conductive brush charger, a current detection circuit that detects the current supplied to the conductive brush charger, a comparison circuit that compares the detected current value with a reference value, and a comparison circuit that compares the detected current value with a reference value. a control circuit that controls the high voltage power supply circuit so that the output is zero;
and a pulse removal circuit that removes pulse components included in the detected current value or the comparison output value.

[Industrial application field]

The present invention relates to a conductive brush charging device using a conductive brush charger.

In image forming devices such as electrophotographic copying machines and electrophotographic printers, a non-contact corona charging method has been adopted to charge electrostatic recording media such as photosensitive drums, but because it causes corona discharge. several kV to
In addition to requiring a higher voltage, there was also the problem of ozone generation. Therefore, a conductive brush charging method was proposed in which conductive fibers of a conductive brush charger are brought into contact with an electrostatic recording medium. In this direct contact conductive brush charging system, it is necessary to stabilize the operation.

[Conventional technology]

FIG. 9 is a schematic configuration explanatory diagram of a printer using a conductive brush charger, in which 10 is a photosensitive drum, 20
30 is a conductive brush charger, 30 is a laser optical system, 40 is a conductive brush charger;
1 is a developing device, 50 is a paper cassette, 60 is a belt transfer device, 70 is a fixing device, 80 is a static eliminator, 90 is a cleaner, and 11 is an apparatus housing.

The photosensitive drum 10 is rotated at a constant speed in the direction of arrow A by a motor (not shown) or the like.
For example, as shown in FIG. 10, a charge generation layer (CGL) 102 and a charge transport layer (CTL) 103 are sequentially laminated on an aluminum drum 101 using a copper phthalocyanine-based organic photoconductor. , and is charged by a power source 300 so that its surface has negative polarity.

Further, the conductive brush charger 20 includes, for example, a conductive substrate 21 made of aluminum or the like, as shown in FIG.
In addition, a conductive brush 22 made by weaving conductive fibers 221 into a pile shape is fixed with a conductive adhesive 23.

Further, the laser optical system uses, for example, a semiconductor laser as a light source, uses a rotating polygon mirror and a lens, and irradiates recording information light onto the photosensitive drum 10 by uniform speed scanning as shown by arrow B. The recording information light turns on the drive current of the semiconductor laser according to the recording information.
It can be obtained by controlling off.

The developing device 40 stores a two-component developer consisting of toner and carrier in a container 40a, and attaches the developer to the electrostatic latent image on the photosensitive drum 10 using a magnetic brush formed by a sleeve and a magnet roller 40b. The electrostatic latent image on the photosensitive drum 10 is visualized.

Further, the paper cassette 50 has a receiving plate 51 for the paper 53.
When a large number of sheets are stacked and stored on top of each other and installed in the device housing 11, the pick roller 52 inside the device
It has a configuration in which the sheets 53 are fed out one by one.

The belt transfer device 60 is composed of pulleys 61 and 62 and a belt 63, and conveys the paper 53 fed out from the paper cassette 50 by the pick roller 52, and transfers the toner image (visible image) on the photosensitive drum 10 by electrostatic force. The image is transferred onto the paper 53 and conveyed to the fixing device 70.

Further, the fixing device 70 is composed of a heat roller 71, a back-up roller 72, discharge rollers 75a, 75b, and a stacker 76, and transfers the paper 53 onto which the toner image has been transferred between the heat roller 71 and the back-up roller 72.
The toner image is fixed on the paper 53 by heating and pressure contact between the paper 53 and the paper 53, and the toner image is discharged to the stacker 76 by discharge rollers 75a and 75b.

Further, the static eliminator 80 is constituted by, for example, a red light emitting diode that generates light with a wavelength of 660 nm, and irradiates the light onto the photosensitive drum 10 to remove residual charges.

The cleaner 90 is composed of a container 91 and a fur brush 92, and removes toner remaining on the photosensitive drum 10 with the fur brush 92.
It is to be collected within the same period.

The power supply 300 in FIG. 10 is a constant current power supply that supplies a constant charge onto the photosensitive drum 10 to keep the charging potential of the photosensitive drum 10 constant. For example, the output current is 0 to 100. −
20μA, and the output voltage can be set in the range of 0 to -2kV.

FIG. 11 is an explanatory diagram of a conventional power supply.
32 is a current detection circuit, 32 is a reference value generation circuit, 33 is a comparison circuit, 34 is a control circuit, 35 is a high-voltage power supply circuit, and 10 and 20 are the aforementioned photosensitive drum and conductive brush charger.

From the high voltage power supply circuit 35 to the conductive brush charger 20
By applying a voltage of 0 to -2kV to
A current of ~-20 μA flows, and the photosensitive drum 10 is negatively charged. The current flowing at that time is detected by the current detection circuit 31, the detected current value and the reference value from the reference value generation circuit 32 are compared by the comparison circuit 33, the comparison output is added to the control circuit 34, and the control circuit 34 outputs the comparison output. The output current of the high voltage power supply circuit 35 is controlled so that the voltage becomes zero.

By charging the photosensitive drum 10 with the conductive brush charger 20 using the power supply 300 with such constant current characteristics, even if environmental conditions such as temperature and humidity change, fluctuations in the charging potential can be ignored. becomes.

[Problem that the invention seeks to solve]

When the conductive brush charger 20 is used to charge the photosensitive drum 10 rotating in the direction of the arrow, if a pinhole exists in the photosensitive layer (charge generation layer 102, charge transport layer 103) of the photosensitive drum 10, the aluminum drum 101 and the conductive fibers 221 of the conductive brush 22 come into direct contact at the pinhole, resulting in a short circuit. Therefore, the current supplied to the conductive brush charger 20 flows in a concentrated manner through this pinhole portion. At this time, if the power supply 300 is configured with only a normal high voltage power supply circuit, an excessive current will flow.
Problems such as burnout of the conductive fibers 221 and enlargement of pinholes occurred.

Therefore, as described above, the power supply 300 is configured to have constant current characteristics to prevent the pinhole from expanding. However, when an excessive current flows through the pinhole, the control circuit 34 is configured to have a constant current characteristic. In order to limit the supplied current to a set value, the output voltage of the high voltage power supply circuit 35 is reduced.
Therefore, since no current is supplied to areas other than the pinholes, the photosensitive drum 10 cannot be charged. That is, there was a drawback that the charging potential became non-uniform due to the presence of pinholes.

An object of the present invention is to perform stable and uniform charging.

[Means for solving problems]

The present invention will be described with reference to FIG. 1. The present invention includes a conductive brush charger 2 having conductive fibers 2a formed in a brush shape for charging an electrostatic recording medium such as a photosensitive drum 1, and this conductive brush. In a conductive brush charger including at least a power source 3 connected to the charger 2, the power source 3 connected to the conductive brush charger 2 is used as a constant current power source, and a high voltage power supply circuit supplies current to the conductive brush charger 2. 305, a current detection circuit 301 that detects the current supplied from the high voltage power supply circuit 305 to the conductive brush charger 2, a current value detected by the current detection circuit 301, and a reference value from the reference value generation circuit 302. A comparison circuit 303 that compares and outputs a difference signal, a control circuit 304 that controls the high-voltage power supply circuit 305 so that the difference signal becomes zero, and a pulse remover that removes pulse components included in the detected current value or difference signal. A circuit 306 is provided.

[Effect]

By setting and applying a voltage in the range of 0 to -2 kV from the high voltage power supply circuit 305 to the conductive brush charger 2, a set current in the range of about 0 to -20 μA is supplied. This current is detected by a current detection circuit 301, a reference value from a reference value generation circuit 302 and the detected current value are compared by a comparison circuit 303, and a difference signal between the reference value and the detected current value is applied to a control circuit 304. .
The control circuit 304 controls the high voltage power supply circuit 305 to supply a constant current to the conductive brush charger 2 so that the difference signal becomes zero.

When a pinhole exists in an electrostatic recording medium such as the photosensitive drum 1, the electrostatic recording medium such as the photosensitive drum 1 and the conductive brush charger 2 are moving relative to each other, so a large current flowing through the pinhole is The time is about several hundred milliseconds or less. That is, the current value detected by the current detection circuit 301 changes in a pulsed manner.

The pulse removal circuit 306 removes the pulse-like changing portion of the detected current value and applies it to the comparison circuit 303. Therefore, the difference signal from the comparison circuit 303 is a difference between the detected current value in the steady state and the reference value. Even if an excessive current due to a pinhole is detected, the output voltage of the high voltage power supply circuit 305 remains in a steady state. Therefore, it is possible to charge parts other than pinholes.

In addition, a pulse removal circuit 306 is connected between the comparison circuit 303 and the control circuit 304 to remove a pulse-like change part contained in the difference signal from the comparison circuit 303 due to a pinhole and add it to the control circuit 304. In this case, the output voltage of the high-voltage power supply circuit 305 remains in a steady state, making it possible to charge parts other than the pinhole.

〔Example〕

FIG. 2 is an explanatory diagram of an embodiment of the present invention, in which 1 is a photosensitive drum, 2 is a conductive brush charger, 2a is a conductive fiber, 3 is a constant current power source as a power source, and 301 is a current detection device consisting of a resistor _R3. circuit, 302 is a resistor R ₇ ,
303 is a comparison circuit consisting of resistors _{R 5 and} R ₆ and an operational amplifier OP ₂ ; 304 is an amplifier.
Control circuit 30 consisting of AMP ₂ and transmitter circuit Q ₁
5 is a high-voltage power supply circuit consisting of a transformer _T1 , a diode _D1 , a resistor _R4 , and a capacitor _C3 . Also 3
06 is amplifier AMP ₁ , resistor R ₁ , R ₂ and capacitor
This is a pulse removal circuit consisting of _C2 and operational amplifier _OP1 .

The high-voltage power supply circuit 305 rectifies a voltage of approximately several 100 V to 2 kV induced in the secondary winding of the transformer T ₁ with a diode D ₁ , smoothes it with a capacitor C ₃ and a resistor R ₄ , and supplies it to the conductive brush charger 2. Add as negative polarity voltage. The current flows from the high voltage power supply circuit 305→
Resistance R ₃ of current detection circuit 301 → earth → photosensitive drum 1 → conductive brush charger 2 → high voltage power supply circuit 30
5, the current flows through the resistance R ₃ of the current detection circuit 301.
The current can be detected by the voltage across the .

Further, the reference value set by adjusting the resistor R ₇ of the reference value generation circuit 302 is applied to the non-inverting input terminal (+) of the operational amplifier OP ₂ of the comparison circuit 303 .
In addition, the detected current value via the pulse removal circuit 306 is
It is applied to the inverting input terminal (-) of the operational amplifier OP ₂ via the resistor R ₅ , and a difference signal between the reference value and the detected current value is output and applied to the control circuit 304 .

The control circuit 304 amplifies the difference signal using an amplifier AMP ₂ and inputs it to the oscillation circuit Q ₁ .
The output signal of Q ₁ is applied to the primary winding of transformer T ₁ of high voltage power supply circuit 305. Transmission circuit
Q ₁ can be configured by a switching circuit whose on period is controlled depending on the magnitude of the difference signal, and the current supplied from the high voltage power supply circuit 305 to the conductive brush charger 2 is set to the reference value. If the difference signal from the comparator circuit 303 becomes larger, the on-period is shortened to reduce the induced voltage in the secondary winding of the transformer _T1 . Conversely, when the current becomes smaller than the reference value, the polarity of the difference signal from the comparator circuit 303 is reversed, so the on period is lengthened and the induced voltage in the secondary winding of the transformer _T1 is increased. It can be controlled as follows.

The pulse removal circuit 306 shows a case in which a low-pass filter is configured by resistors R ₁ , R ₂ , capacitors C ₁ , C _{2 ,} and operational amplifier OP ₁ , where R ₁ =R ₂ =R,
When C ₂ =C ₁ /2, the cutoff frequency is expressed as =1/2πC ₁ R.

When the photosensitive drum 10 is rotated at a constant speed in the direction of the arrow and a large pulse-like current flows through the conductive brush charger 2 that is in contact with the pinhole of the photosensitive drum 10, the current value detected by the current detection circuit 301 is also pulse-like. Becomes the property of The pulse included in this detected current value is removed by a pulse removal circuit 306. Therefore, the detected current value in the steady state is applied to the comparator circuit 303, and the high voltage power supply circuit 3
05 will maintain steady state output voltage.

Therefore, under normal conditions, the constant current characteristic of the power source 3 allows the charged potential of the photosensitive drum 1 to be stabilized regardless of changes in environmental conditions. Even if there is a pinhole in the photosensitive drum 1, the high voltage power supply circuit 305 maintains the output voltage immediately before the pinhole, so the photosensitive drum 1 can be charged.

The pulse removal circuit 306 is shown to have a configuration of a low-pass filter using the operational amplifier _OP1 , but it is of course possible to adopt other configurations that can remove pulses.

FIG. 3 is an explanatory diagram of the operating principle of the conductive brush charging device, in which a shows a charging model and b shows an equivalent circuit.
The photosensitive drum 1 has a photosensitive layer having a thickness Ld and a dielectric constant ε _r , the conductive fibers 2a of the conductive brush charger 2 are in contact with this photosensitive layer, and the voltage Va of the power source 3 is applied to the conductive brush charger 2. The voltage is applied to the photosensitive layer of the photosensitive drum 1.

Rb in the equivalent circuit of b in Figure 3 is the conductive fiber 2a
, Rc is the contact resistance between the conductive fiber 2a and the photosensitive layer of the photosensitive drum 1, Cc is the capacitance of the adjacent conductive fiber 2a at the contact portion, and Cd is the capacitance of the photosensitive layer. This capacitance is determined by the thickness Ld of the photosensitive layer and its dielectric constant _εr , and since the photosensitive layer of the photosensitive drum 1 at the start of charging has been previously neutralized by a static eliminator, that portion of the photosensitive layer is No charge is accumulated in the capacitance Cd of the photosensitive layer.

Therefore, when a negative voltage Va is applied from the power source 3 to the photosensitive layer of the photosensitive drum 1 via the conductive brush charger 2, a current I flows in the direction of the arrow, and the photosensitive layer of the photosensitive drum 1 is charged.

When this current I comes into contact with the pinhole in the photosensitive layer of the photosensitive drum 1 and the conductive fiber 2a of the conductive brush charger 2, the photosensitive layer becomes short-circuited, the current I increases, and is concentrated in the pinhole area. do. Therefore, conductive fiber 2 that contacts the pinhole part
There is a risk that a may be burned down. In relation to the limiting current at which such burnout occurs, the resistance of the conductive fiber 2a
We investigated Rb and applied voltage Va.

Figure 4 is a relationship curve diagram between the applied voltage Va and the limiting current Ib. For conductive fibers with various resistance values, the length of the conductive fibers is set to 5 mm, the voltage is gradually increased as shown in the arrow, and the conductive fibers are burnt out. current (limiting current)
Ib) was measured and normalized to a length of 1 mm and a thickness of 1 denier and shown as a circle. Due to normalization, the limiting current Ib on the vertical axis is expressed in μA/denier. Note that 1 denier is a unit that indicates the thickness of a fiber that is 9000 m long and weighs 1 g.

As is clear from this curve diagram, the conditions under which the conductive fibers are burnt out are the product of the applied voltage Va and the limiting current Ib, Va・Ib=
This is the case when the power is 4mW or more. Therefore, it is practically preferable to set the condition of Va·Ib≦2mW, taking into account the variation in the resistance value of the conductive fibers and providing some margin. The curve under this condition is shown as a dotted line.

By configuring the conductive brush charger 2 using conductive fibers having a resistance value under such conditions, even if a short circuit due to a pinhole or the like occurs, the power supply 3 equipped with the above-mentioned pulse removal circuit 306 can It becomes possible to uniformly charge the photosensitive drum 1, and it is also possible to prevent the conductive fibers from being burned out. Therefore, the operation of an electrophotographic copying machine, an electrophotographic printer, etc. using a conductive brush charging device can be further stabilized.

Further, in order to obtain a desired charging potential in an electrophotographic printer, the upper limit of the voltage applied to the conductive brush charger is usually about 1500V. At this upper limit, the resistance value of the conductive fiber under the condition of Va・Ia≦2mW is 4.5× per 1 denier thickness and 1 mm length.
10 ⁷ Ω or more. In addition, in the above-mentioned Fig. 4, the measured value for a conductive fiber with a hair length of 5 mm is normalized to 1 mm, so assuming that the resistance value of the conductive fiber is uniform, the applied voltage on the horizontal axis The voltage Va indicates 1/5 of the value at the time of actual measurement.

Furthermore, when the resistance value of the conductive fibers is increased, the voltage applied to the photosensitive drum 1 is reduced, resulting in a reduction in the charging potential. FIG. 5 is a relationship curve diagram between the resistance value and charging potential of conductive fibers, and the third
In the equivalent circuit of b in the figure, the resistance Rb of the conductive fiber per 1 denier and 1 mm is 0Ω, 10 ¹³ Ω, and 10 ¹⁴ Ω.
and shows the change in charging potential over time. In addition, as other values of the equivalent circuit, Cd=
1.0 μF/m ² , Cc=0.2 μF/m ² , and Rc=300 kΩ.

As can be seen from Figure 5, when the resistance value is 10 ¹³ Ω, there is almost no difference in the charging potential from when the resistance value is 0 Ω, but when the resistance value is 10 ¹⁴ Ω, the charging potential changes due to the charging time ( It can be seen that the change in charging potential due to the passage of time (s) becomes slower, and when the charging time (s) is kept the same, the charging potential decreases.

From this point of view, we fabricated a conductive brush using conductive rayon fibers with a thickness of 6 denier and a length of 5 mm, with a resistance value of 4.5 × 10 ⁷ to 10 ¹³ Ω per 1 denier thickness and 1 mm length, and used it for electronic purposes. When applied to a photographic printer for recording, stable recording operation was possible for a long time even if there were pinholes on the photosensitive drum.

Conductive fibers are made by uniformly dispersing carbon particles within rayon fibers to impart conductivity, such as "Retsku" (trade name) manufactured by Unitika, or
"Beltron" (trade name) manufactured by Kanebo can be used.

FIG. 6 is an explanatory diagram of main parts of another embodiment of the present invention, in which 1 is a photosensitive drum, 111 is an aluminum drum, 112 is a charge generation layer, 113 is a charge transport layer, 2 is a conductive brush charger, 2a is conductive fiber,
3 is a power source consisting of a constant current power source, 201 is a conductive substrate such as aluminum, 202 is a conductive brush, 20
3 is a conductive adhesive, 204 is a support member, and 205 is a device housing.

The conductive fibers 2a have a thickness of 10 to 15 μm in diameter, a resistance value of 10 ⁹ Ω per fiber, and a density of 155 when the length is 5 mm.
A conductive brush 202 with a width of 15 mm is constructed by implanting the fibers at a rate of 1/mm ² , and is fixed to the conductive substrate 201 with a conductive adhesive 203 .
was fixed to the device housing 205 via the support member 204.

This support member 204 is made of a synthetic resin that has good moisture absorption characteristics and does not reduce its resistance value even in high humidity. As the synthetic resin, fluororesin (typically, tetrafluoroethylene), epoxy resin, silicone resin, etc. can be used.

The conductive brush charger 2 was attached to the device housing 205 via the support member 204, and the conductive fiber 2a was brought into contact with the photosensitive drum 1 at a depth of about 0.5 mm. A power source 3 connected to this conductive brush charger 2 is connected to a second
This is a constant current power supply equipped with the pulse removal circuit 306 shown in the figure.

Regarding the conductive brush charging device having such a configuration, the relationship between humidity and charging potential was measured.
The results are shown in FIG. 7, with the vertical axis representing the charging potential (V) and the horizontal axis representing the current (μA). Curve a shows the charging potential at a temperature of 25° C. and humidity of 50% RH as standard conditions, and curve b shows the charging potential at a temperature of 35° C. and humidity of 80% RH.

As can be seen from curves a and b, the difference in charging potential with respect to changes in humidity is about 10V, and by attaching the conductive brush charger 2 to the device housing 205 via the support member 204 with good moisture absorption characteristics, Since the surface resistance of the support member 204 does not decrease even under high humidity, leakage current does not increase, thereby enabling stable charging.

FIG. 8 is an explanatory diagram of a main part of still another embodiment of the present invention, and the same reference numerals as in FIG. 6 indicate the same parts. This embodiment uses a conductive substrate 201 such as aluminum.
For example, a resin layer 206 of epoxy resin is placed on the surface of
was formed. The thickness of this resin layer 206 can be, for example, 50 μm. This resin layer 206, like the support member 204 in FIG. 6, can prevent an increase in surface leakage current even in high humidity.

Therefore, when a negative voltage is applied to the photosensitive drum 1 from the power source 3, which is a constant current power source, through the conductive brush charger 2, stable charging is possible without being affected by humidity.

The present invention is not limited to the above-mentioned embodiments, and for example, the photosensitive layer may not only be an organic photoreceptor, but also a selenium-based photoreceptor, an amorphous silicon-based photoreceptor, or the like. In addition to the drum shape, it is also possible to use a photoreceptor on a belt. The conductive brush charger 2 can also be in the form of a brush roller in which a brush made of conductive fibers is attached to a rotating shaft.

〔Effect of the invention〕

As explained above, the present invention includes a high voltage power supply circuit 305 connected to the conductive brush charger 2, a current detection circuit 301 that detects the current supplied to the conductive brush charger 2, and a detection current value and a reference value. A comparison circuit 303 that compares the difference signal of the comparison output, a control circuit that controls the high voltage power supply circuit 305 so that the difference signal of the comparison output becomes zero, and a pulse removal circuit 306 that removes the pulse component included in the detected current value or the difference signal. This device is equipped with a constant current power source, and can always stably charge an electrostatic recording medium without being affected by environmental conditions such as humidity. Furthermore, even if the conductive fibers 2a of the conductive brush charger 2 come into contact with the pinholes of the electrostatic recording medium such as the photosensitive drum 1 and an excessive pulsed current flows, this pulsed detected current value or difference signal Since this method performs constant current control by removing , it has the advantage that desired charging can be performed even if a pinhole exists.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of an embodiment of the present invention, Fig. 3 a and b is an explanatory diagram of the operating principle of the conductive brush charging device, and Fig. 4 is an applied voltage and limit current. Figure 5 is a diagram showing the relationship between the resistance value of conductive fibers and charging potential, Figure 6 is an explanatory diagram of main parts of another embodiment of the present invention, and Figure 7 is a measurement of charging potential. 8 is an explanatory diagram of main parts of still another embodiment of the present invention, FIG. 9 is an explanatory diagram of a schematic configuration of a printer using a conductive brush charger, and FIG. 10 is an explanatory diagram of a conventional example. FIG. 11 is an explanatory diagram of a conventional power supply. 1 is a photosensitive drum as an electrostatic recording medium, 2 is a conductive brush charger, 2a is a conductive fiber, 3 is a power source,
301 is a current detection circuit, 302 is a reference value generation circuit, 303 is a comparison circuit, 304 is a control circuit, 30
5 is a high voltage power supply circuit.

Claims (1)

[Claims] 1. A conductive brush charger 2 having conductive fibers 2a formed in a brush shape, and the conductive brush charger 2
A conductive brush charging device includes at least a power source 3 connected to a conductive brush charging device, wherein the power source 3 is a constant current power source, a high voltage power source circuit 305 that supplies current to the conductive brush charger 2, and the high voltage power source circuit 305. a current detection circuit 30 for detecting the current supplied from the conductive brush charger 2 to the conductive brush charger 2;
1, a comparison circuit 303 that compares the current value detected by the current detection circuit 301 with a reference value and outputs a difference signal, and a control that controls the high voltage power supply circuit 305 so that the difference signal becomes zero. a circuit 304; and a pulse removal circuit 306 that removes pulse components included in the current value detected by the current detection circuit 301 or the difference signal from the comparison circuit 303.
A conductive brush charging device comprising: