JPH04181962A - Image forming device - Google Patents

Abstract

PURPOSE:To always form and output an excellent image by detecting potential on the surface of an image carrier by using a potential sensor and a contact transfer means. CONSTITUTION:The potential sensor 3 is provided on the down stream side of an electrostatic charging roller 2 in the moving direction of the surface of a photosensitive drum 1, and the surface potential of the drum 1 which is electrostatically charged by the roller 2 is fetched as a signal, and feedback is performed to control AC voltage VPP so as to converge the output value Vdc of DC voltage on dark potential VD. Namely, a primary voltage control signal outputted from a CPU in a DC controller 12 passes through a D/A converter 13 and gets in a high voltage power source for primary electrostatic charge 4a so as to impress DC voltage + AC voltage on the roller 2. The surface of the drum 1 which is electrostatically charged passes the potential sensor 3 at a rotating stage, and the voltage detected at such a time is fed back to the CPU through a voltage exchange circuit 10 and an A/D converter 11, then the above operation is executed until the potential on the surface of the photosensitive body is converged on the dark potential VD. Thus, the excellent image is always formed and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides an image forming process for forming an image on the surface of an image carrier such as an electrophotographic photoreceptor or an electrostatic recording dielectric material by an image forming process means including a charging means for charging the surface of the image carrier. The present invention relates to image forming apparatuses such as electrophotographic copying machines, printers, electrostatic recording devices, and printers that perform image formation.

More specifically, the charging means charges the surface of the image carrier by contacting the surface of the image carrier with a charging member to which a bias voltage of DC bias and AC bias (oscillating voltage/pulsating voltage) or superimposed bias voltage is applied (direct contact). ) The present invention relates to an image forming apparatus, which is a charging means.

(Prior Art) FIG. 9 shows a schematic configuration of an example of an image forming apparatus having the above-mentioned system and configuration. This example is a laser beam printer or copier that utilizes a transfer electrophotographic process.

Reference numeral 1 denotes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is rotated clockwise as indicated by arrow a at a predetermined process speed (peripheral speed).

Reference numeral 2 denotes a conductive charging roller (hereinafter referred to as a charging roller) as a charging member of the contact charging means, which is rotatably supported on a bearing substantially parallel to the photosensitive drum 1 and is applied with a predetermined pressing force to charge the photosensitive drum 1. The photosensitive tram 1 rotates as the photosensitive tram 1 rotates. This charging roller 2 has a charge #4a.
A predetermined bias voltage is applied to the rotating photosensitive drum 1.
It is uniformly charged to a predetermined polarity and potential using a surface or contact method.

Since the contact charging means itself is well known, a detailed explanation thereof will be omitted, or ozone charging means, which can reduce the voltage of the power supply compared to the non-contact type corona charger that has been commonly used as a charging means device, is omitted. It has advantages such as very little generation of corona discharge products such as, etc., and has been attracting attention and being used as a charging means for image bearing members.

The surface of the rotating photosensitive drum, which has been uniformly charged, is then exposed to desired image information (laser scanning exposure, slit exposure, etc.) by an exposure means such as a laser scanner or an imaging optical system (not shown). Electrostatic latent images corresponding to target image information are sequentially formed on the surface of the drum.

The formed latent image is subjected to reversal development or regular development by the developing device 5 and is visualized as a transferable toner image.

Reference numeral 7 denotes a transfer means, and in this example, a conductive transfer roller (hereinafter referred to as a transfer roller) is used as a transfer member of the contact transfer means, and is rotatably supported approximately parallel to the photosensitive drum 1, and is supported by a predetermined pressure. It is brought into contact with the surface of the photosensitive drum 1 with pressure, is interposed with the photosensitive tram 1, and is driven to rotate at a peripheral speed in the forward direction of the rotation of the tram 1.

When the leading edge of the toner image area formed and supported on the surface of the photosensitive drum 1 reaches the contact area (transfer area) between the transfer roller 7 and the photosensitive tram 1, the leading edge of the transfer material P just reaches the transfer area and is exposed to light. The transfer material P is timing-fed from a paper feed mtis (not shown) to the transfer site through the registration rollers 6 so as to enter between the tram 1 and the transfer roller 7 .

A predetermined transfer bias having a polarity opposite to that of the toner image is applied from the power source 4b to the transfer roller rough, so that the back surface of the transfer material P is charged to a polarity opposite to that of the toner image, and the transfer material P is exposed to light by the transfer roller rough. By being pressed against the first surface of the drum, the toner image on the first surface of the photosensitive drum is sequentially transferred onto the surface of the introduced transfer material P. The transfer material P that has passed through the transfer site is separated from the surface of the photosensitive drum, introduced into a fixing device (not shown), undergoes image fixation, and is output as an image-formed product.

After the image has been transferred, the surface of the photosensitive drum is cleaned by a cleaning device 8 to remove residual deposits such as untransferred toner, and is then turned over and used for image formation.

The charging member 2 of the contact charging means is not limited to the roller type described above, but may also have a plate type, bat type, rod type, block type, or brush type.

In contact charging means, only applying a DC bias to the charging member 2 is susceptible to the effects of subtle irregularities on the contact surface between the charging member 2 and the image carrier 1, surface dirt, and microscopic variations in surface resistance value. In this case, a small area of charging failure occurs on the charging surface of the image carrier, and this appears as a defect on the output image.

This phenomenon becomes a problem in the reversal development method that prints on the exposed area, which is widely used in laser printers, for example, because it manifests itself as fogging in the background area.

In order to solve the above problem, we propose a technology that improves the convergence of the potential by applying a DC voltage superimposed with an AC voltage to the charging member, eliminates the occurrence of microscopic charging defects, and enables uniform charging. (Japanese Unexamined Patent Publication No. 63-149669)
Publication No.).

However, the resistance of materials used for charging members such as charging rollers and charging plates varies greatly depending on the environment, and the same bias can change the resistance from low temperature and low humidity (L/L) to high temperature and high humidity (H/H).
) It is difficult to cover the environment. Normal temperature and humidity (N
/N) Even if the bias is appropriate in the environment, the resistance of the charging member increases in the L/L environment, resulting in partial charging failure and fog, and conversely in the H/H environment, the resistance of the charging member increases. Since the resistance becomes low, excessive bias occurs, and charging current leaks on the image carrier.

Therefore, a technique has already been proposed in which the alternating current bias superimposed on the direct current voltage is controlled with a constant current, and the amount of charge applied from the charging member to the image carrier is constant, thereby obtaining charging performance that does not change under each environment. (Patent application 1986-0975)
No. 32). In other words, if the DC component of the applied bias is controlled at a constant voltage, and the AC component is controlled at a constant current, it is sufficient to prevent variations in resistance value due to lot differences during the manufacturing of charging members, and changes in resistance value due to environmental changes. It is possible to obtain a desired charging ability by following the above.

(Problem to be solved by the invention) However, constant current control, especially AC bias constant current control, is susceptible to noise, and for example, in an image forming apparatus that applies an AC bias to the developing bias, there is a risk of constant current control malfunctioning. It can be said that it is extremely unstable because it is subject to fluctuations in the capacity of the load it comes in contact with. In addition, if there are pinholes or scratches on the image carrier such as a photoreceptor, current will leak when flowing through the charging member, causing a voltage drop and causing charging defects. ,
In a reversal development system, the charging failure portion becomes a black band and causes fog on the image.

As described above, the alternating current bias applied to the charging member of the contact charging means has its advantages and disadvantages whether it is controlled by constant current or by constant voltage.

Furthermore, a method has been proposed (Japanese Patent Application No. 1-230496) that detects the surface potential on the photoreceptor from changes in load impedance using contact transfer means and changes the DC component of the bias applied to the charging means. Even if the DC bias is changed, the charging ability will not be improved, and the above problem will not be solved.

The present invention relates to a system for applying a superimposed bias of DC bias and AC bias to the charging member of a contact charging means to charge the surface of an image carrier, and the present invention appropriately controls the bias to the charging member using a method different from the conventional method. It is an object of the present invention to provide an image forming apparatus that can always stably output appropriate, high-quality images without the above-mentioned problems.

(Means for Solving the Problems) The present invention includes a contact charging means for charging the surface of an image carrier by bringing a charging member to which a bias voltage in which an AC bias is superimposed on a DC bias into contact with the surface of the image carrier. The image forming apparatus forms an image on the surface of an image carrier using an image forming process means, and includes means for detecting the potential on the image carrier, and adjusts the bias applied to the contact charging means based on the detection means. This is an image forming apparatus characterized by controlling alternating current components.

Further, in the image forming apparatus of the present invention, the present invention includes a transfer means for transferring the transferable image formed on the surface of the image carrier onto a transfer material, and the transfer means transfers the transfer member to which a transfer bias is applied to the surface of the image carrier. contact transfer means for transferring a transferable image from the image carrier surface side to the transfer material surface side by intervening a transfer material between the transfer member and the image carrier;
The image forming apparatus is characterized in that the contact transfer means also serves as means for detecting the potential on the image carrier.

(Function) Experiments conducted by the present inventors have revealed that it is desirable for the material of the charging member of the contact charging means to have a total resistance of around 106 to 107Ω. A very unstable area and a small amount of conductive filler to be dispersed for resistance control! Resistance changes easily due to environmental changes, especially moisture absorption.

Therefore, the present invention detects the surface potential of the surface of the image carrier to detect changes in charging load impedance such as resistance changes due to environmental changes of the charging member, capacitance increases due to wear of the CTL layer of the image carrier caused by long-term paper feeding, etc. By correcting this, it is possible to properly control the AC bias component having a potential convergence function in the contact charging means at a constant voltage. A good image is always formed and output without the interference of high frequency components, charging current leakage due to the presence of holes or scratches on the image carrier surface, and the occurrence of charging failures due to sudden voltage drops accompanying this. It becomes possible to do so.

Furthermore, the charging ability deteriorates due to fluctuations in the load intensity of the contact charging means, abrasion of the surface of the image carrier due to long-term durability, and, in the case of electrophotographic photoreceptors, an increase in capacity due to abrasion of the photosensitive layer, especially the CTL layer. This can be prevented by correcting the AC bias component appropriately, and the life of the system can be extended.

The means for detecting the potential on the image carrier may be provided with a dedicated potential sensor, or may be a device that transfers the transferable image formed on the surface of the image carrier onto a transfer material using contact charging means. In addition, by using the contact charging means as a means for detecting the potential on the image carrier, there is no need to use an expensive dedicated sensor, resulting in cost reduction.

As the waveform of the AC bias, a sine wave, a rectangular wave, a triangular wave, etc. can be used as appropriate. Furthermore, it goes without saying that the alternating current bias includes, for example, a rectangular wave voltage formed by periodically turning on and off a direct current power supply. At this time, the AC bias can be controlled by controlling the peak-to-peak voltage. In this way, an alternating current bias whose voltage value changes periodically can be used.

(Embodiments) <Embodiment 1> (Figs. 1 to 3) Fig. 1 shows a schematic configuration of an image forming apparatus according to an embodiment of the present invention. Basically, it has the same image forming principle and process equipment configuration as the image forming apparatus shown in FIG. 9 described above.
Common equipment will be given the same reference numerals and repeated explanations will be omitted.

(1) Photosensitive drum 1 A photosensitive drum equipped with a photosensitive layer made of organic photoconductor (OPC). A charge generating layer (CGL) in which phthalocyanine pigments are dispersed using styrene resin as a binder;
A charge transport layer (CTL) in which a hydrazone compound is dispersed using a polycarbonate resin as a binder. Tram diameter 30mmφ. Processing speed: 25 mm /
s e c (paper feed speed, A4 size, 4 sheets).

(2) Charging roller 2 A conductive core metal 2a made of SUS with a diameter of 6 mmφ, and a conductive EPDM having a volume resistance of 104 to 105 Ω-cm with carbon dispersed therein as a resistance control, which is formed concentrically with the core metal.
The layer 3b and the volume resistivity 108-1 formed on the surface thereof
Medium resistance surface layer 2C of engineered chlorohydrin of 012Ω・cm
Total diameter 12mmφ, resistance value 106~10
7Ω conductive elastic roller. Rotation driven by photosensitive tram 1. The photosensitive drum 1 is negatively charged.

(3) Exposure: Laser beam scanning exposure.

(4) Developing device 5: Reversal developing device that uses negative toner.

(5) Transfer roller 7 A core metal 7a and carbon formed concentrically with the core metal are dispersed to control the volume resistance to 104 to 105 Ω・Cm.
A conductive elastic roller consisting of an EPDM layer 7b with a hardness of ASKER-C and 30 degrees.

(6) Control 4a is a high voltage power supply for primary charging to charging roller 2;
is a transfer high voltage power supply for the transfer roller rough.

The primary charging bias applied to the charging roller 2 is a DC voltage V.
dc and an alternating current voltage Vl)p, the direct current voltage Vdc is set to a desired charging potential of one surface of the photosensitive tram, that is, a desired dark area potential VD (v), and the alternating current voltage vp
p is the charged potential of one surface of the photosensitive tram and its dark area potential V. It is set to converge to .

In this embodiment, a potential sensor 3 is provided on the downstream side of the charging roller 2 in the moving direction of the photosensitive tram 1 surface, and the surface potential of the photosensitive tram 1 that has been charged by the charging roller 2 is taken out as a signal.
Feedback is applied to the DC voltage output value Vdc or the dark potential V. The AC voltage vpp is controlled so that it converges to .

In FIG. 1, the primary voltage control signal output from the CPU in the DC controller 12 passes through the D/A converter 13 and enters the primary charging high-voltage power source 4a, applying a DC voltage to the charging roller 2. . The charged surface of the photosensitive drum 1 passes through the potential sensor 3 during its rotation. The voltage detected at this time is fed back to the CPU via the voltage exchange circuit 10 and the A/D converter 11, and the process is continued until the potential on the photoreceptor surface converges to VD.

FIG. 2 shows a flowchart of the program used at that time. In this embodiment, VD is set to -600V.

By the way, the principle of charging is to raise the potential of the charging roller repeatedly up to the AC-A voltage or the dielectric breakdown voltage of air. According to Paschen's law, the dielectric breakdown voltage of air depends on the capacitance of the CTL layer of the photoreceptor, and in the photosensitive tram 1 used in this example, it is approximately VT, +
= 550 V. This voltage means that unless an AC voltage of V ppm 1,100 V or more is applied, the voltage will not converge to the set voltage.

Therefore, in the program in this embodiment, the value of the initial (In1tiaJ) of Vl)l) is set to 1,100V. Further, the upper limit value is similarly determined by the pressure resistance of the CTL layer, and in the above-mentioned photosensitive drum, the upper limit value is 2.40
Since it is 0 V, 2,
It was set to count up to 400.

The above program is executed during the pre-multi-rotation period of the image forming apparatus, and the sequence at that time is shown in FIG. The pre-multi-rotation period lasts for 7.5 seconds, which corresponds to two revolutions of the photosensitive drum. The program created based on the flowchart shown in FIG. 2 converges sufficiently within the above-mentioned time.

In this example, when we measured the voltage generated by the primary charged AC component (primary AC) due to environmental changes, we found that L/L (1
2.000 V, H/H under 5℃, 10%RH) environment
(32℃, 85%RH) environment of 1,300 V.
pp was obtained. The voltage generated in each environment was sufficient to converge the potential on the photoreceptor surface to VD.

This eliminates the constant voltage control method using AC voltage as a means of potential convergence in primary charging, which eliminates problems with constant current control methods, such as sudden voltage drops due to scratches on the photoreceptor surface or leaks from holes, and problems during development. This improves the interference of the high frequency component of the developing bias with the primary charging which occurs in a system in which an alternating current bias is applied to the bias.

In addition, this method can compensate for fluctuations in the load impedance of the charging roller 2 and the attenuation of charging ability due to increased capacitance due to abrasion of the photosensitive layer, especially the CTL layer, due to long-term durability, making it possible to extend the life of the system. There are benefits.

<Embodiment 2> (Figures 4 to 6) This embodiment uses a charging method instead of detecting the surface potential of one surface of the photosensitive tram using the dedicated potential sensor 3 in the image forming apparatus of Embodiment 1 (Figure 1). The roller rough also serves as the surface potential detection means. The charging roller 2 and the transfer roller 7 are made of the same material and have the same structure as in the first embodiment.

The charging roller 2 is supplied with a DC voltage Vdc=-600V and an AC voltage V ppm 1. +00 V is applied to temporarily charge the surface of the photoreceptor, and then when it reaches the position of the transfer roller 7,
The transfer roller 7 is controlled with a constant current of 2 μA.

The advantage of constant current control is that there is no risk of excess charge entering the photosensitive layer and forming a positive memory with the opposite polarity to the charge.

In this embodiment, the voltage generated by the current flowing from the transfer roller 7 to the photoreceptor is detected.

Specify the surface potential on the photoconductor and set the potential on the photoconductor to VD=
Measures are taken to select Vl)I) that converges to -600V.

FIG. 4 shows a rough block diagram of a circuit for carrying out the above sequence. As the photosensitive tram 1 rotates, the aforementioned primary charging bias is applied to the charging roller 2. When the charging surface reaches the position of the transfer roller rough, the signal output from the DC controller 12 or the D/A converter 1
5 to a high-voltage transfer power source 4b, which controls the transfer roller 7 with a constant current of 2 μA. The generated voltage v7 is returned from the high-voltage power source 4b for retransfer to the DC controller 12 via the A/D converter 16, and Vpp is determined based on the look-up table shown in FIG. Said vp
A signal for generating p is applied to the charging roller 2 via the D/A converter 13 and the primary charging high-voltage power supply 4a, and uniformly charges the surface of the photoreceptor.

As mentioned in Example 1, the actual resistance of the charging roller 2 is 106
~107Ω, that of the transfer roller rough is 5xlO'~5xf
The resistance value of both rollers depends on the capacity and paper feeding speed of the photoreceptor layer, which is the counter electrode, especially the CTL layer. When a hydrazone-based compound is used and the paper feed speed is 25 mm/sec, the above-mentioned resistance value is most suitable.

The look-up table shown in FIG. 5 is created based on the characteristics of the rollers described above.

The optimal resistance value for the charging roller 2 is 106 to 107Ω.
The resistance range Cm is difficult to control in manufacturing and is also easily affected by moisture, so it can be said to be a very unstable range. Also, the resistance range of the transfer roller 7 is 104
~105 Ω·cm is a stable region that is relatively unaffected by environmental changes. Therefore, using the transfer roller 7, it is possible to detect the potential on the surface of the photoreceptor due to a change in the load intensity of the charging roller 2.

In this example, when the detection means was programmed to be executed during the pre-multi-rotation period of the sequence shown in FIG. 6, good images were obtained in each environment, and the same effect as in Example 1 was obtained. .

Further, when a contact transfer means is used as a means for detecting the surface potential on the photoreceptor, there is no need to use a dedicated expensive sensor, resulting in a high cost.

Further, the same effect can be obtained by controlling the contact transfer means at a constant voltage and using a method of detecting current.

<Embodiment 3> (Figures 7 and 8) This embodiment uses a charging plate 2 instead of the charging roller 2 as the charging member in the printer of the second embodiment (Figure 4).
A is used, and the other configurations are the same as in the second embodiment. FIG. 8 shows an enlarged cross-sectional view of the charging plate 2A portion. The %F electric plate 2A consists of a conductive base plate 2d and a medium resistance layer 2e covering the outer surface thereof.

In this example, the conductive base plate 2d is a 2 mm thick plate made of urethane rubber having a volume resistivity of 10 3 Ω·am by dispersing a conductive filler such as carbon. The medium resistance layer 2e is provided to make charging uniform, and in this example, N-methoxymethylated nylon with a volume resistivity of 109 Ω·cm is used and coated to a thickness of 30 μm to give an actual resistance of 107 Ω. It is controlled so that

This charging blade 2A is brought into contact with the photosensitive drum 1 by bringing its tip side into contact with the photosensitive drum 1.
It is attached to a fixing member (not shown) so that the gap created by the photosensitive tram 1 gradually increases along the surface movement direction of the photosensitive tram 1. Since the charging plate 2A has a simple structure, the cost can be significantly lower than that of the charging roller 2 in terms of low material costs and ease of manufacture.

Since the environmental characteristics of the charging plate 2A used in this example are very similar to those of the charging roller 2 described in Example 2, the look-up table shown in FIG.
The sequence shown here was used as is.

In the case of the device of this example, an environmental test was also conducted under the same conditions as in Example 2, and good images were obtained with the same actions and effects as described in Example 2.

(Effects of the Invention) As described above, the present invention provides an image forming apparatus that performs image formation by charging the surface of an image carrier with a contact charging means. Since it has a means for detecting the potential on the surface of the image carrier using a single potential sensor or contact transfer means, it is possible to control the alternating current voltage, which is the potential convergence means in primary charging, at a constant voltage. This is not affected by the environment in which the device is used, and charging failures may occur due to sudden voltage drops due to scratches on the image carrier surface or leakage from holes, and may occur in machines that apply an AC bias to the developing bias. The interference of the high frequency component of the developing bias with the primary charging is improved, and it becomes possible to always form and output good images.

Furthermore, deterioration in charging performance due to fluctuations in the load impedance of the contact charging means and increase in capacity due to wear of the photoreceptor layer, especially the CTL layer, of the image carrier due to long-term durability is prevented, and the life of the system can be extended.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of a data processing method. Figure 3 is a sequence diagram. FIG. 4 is a schematic diagram of an image forming apparatus according to a second embodiment. Figure 5 is a look up table. FIG. 6 is a sequence diagram. FIG. 7 is a schematic diagram of an image forming apparatus according to a third embodiment. FIG. 8 is an enlarged cross-sectional view of the charging plate portion. FIG. 9 is a schematic diagram of an example of an image forming apparatus using contact charging means. 1 is a photosensitive drum as an image carrier. 2.2A is a charging roller or a charging plate as a charging member of the contact charging means. 3 is a potential sensor. 7 is a transfer roller as a transfer member of the contact transfer means. A/D Voltage converter 2 Figure D/A Converter for primary charging 9 Figure

Claims (2)

[Claims] (1) An image is formed on the image carrier surface by an image forming process means including a contact charging means that charges the image carrier surface by contacting the image carrier surface with a charging member to which a bias voltage in which an AC bias is superimposed on a DC bias is applied. An image forming apparatus that performs the following: comprising a means for detecting a potential on the image carrier, and controlling an alternating current component of a bias applied to the contact charging means based on the detecting means. Forming device. (2) It has a transfer means for transferring the transferable image formed on the surface of the image carrier onto a transfer material, and the transfer means brings a transfer member to which a transfer bias has been applied into contact with the surface of the image carrier, and the transfer member and the image A contact transfer means that transfers a transferable image from the surface of the image carrier to the surface of the transfer material by intervening a transfer material between the contact transfer means and the image carrier, and the contact transfer means detects the potential on the image carrier. 2. The image forming apparatus according to claim 1, further comprising means for performing image forming.