JP2964601B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric, such as an electrophotographic or electrostatic recording type image forming apparatus. The present invention relates to an image forming apparatus that forms an image by an image forming process unit including a charging unit that charges a surface of the image forming apparatus.

More specifically, the present invention relates to an image forming apparatus adopting a contact charging type charging unit for charging a surface of an image carrier by bringing a charging member to which a bias voltage is applied into contact with the surface of the image carrier as the charging unit.

(Prior Art) In an image forming apparatus, a non-contact type corona charging device is generally used as a device for uniformly charging a surface of an image carrier to a predetermined polarity and potential.

The corona charging device is effective as a device for uniformly charging a surface of an image carrier such as a photosensitive member to a predetermined polarity and potential. However, using a high voltage (for example, 6 to 8 KV) requires an expensive high-voltage transformer. There are problems such as the necessity of a large-scale configuration such as insulation against the high voltage, poor power efficiency, generation of a relatively large amount of undesired corona discharge generated gas such as ozone, and necessity of a configuration for removing and eliminating the problem. Have.

For such a corona charging device, there is a contact charging type charging device that performs charging processing on the image carrier surface by bringing the charging member to which the bias voltage is applied into contact with the surface of the image carrier as an object to be charged as described above. This has the advantages that the power supply can be reduced in pressure, the amount of generated ozone is remarkably small, the structure of the apparatus is simple and the cost can be reduced, and the image carrier is used instead of the corona charging apparatus in an image forming apparatus or the like. Attention has been paid to means for performing charging treatment of such materials, and practical use thereof has been attempted.

In a contact charging device, when only a DC bias is applied to the charging member, fine irregularities on the surface of the contact portion between the charging member and the image carrier, dirt on the surface, and microscopic measurement of the resistance value of the surface. Variations and the like cause poor charging of a minute area on the image carrier, which appears as a defect on an output image. This phenomenon appears as a so-called fog on the image background portion in the reversal developing method widely used in laser printers and the like.

In order to solve such a problem, by applying a DC bias in which an AC bias is superimposed on the charging member, it is possible to eliminate the occurrence of microscopic charging failure which is likely to occur when only the DC bias is applied, and to achieve uniform charging. There has been proposed a technique which enables a proper charging (JP-A-63-149669).

However, in the contact charging device, the material used for the charging member to be brought into contact with the surface of the image carrier as the object to be charged has a large change in resistance depending on the environment. Executing the image formation by applying the voltage causes the following problems.

That is, even if the bias voltage is an appropriate value in a normal temperature and normal humidity environment, in a low temperature and low humidity environment, the resistance of the charging member increases and the partial pressure of the charging member increases, and As a result, the bias partial pressure applied to the image carrier is reduced, and partial charging failure occurs. Conversely, in a high-temperature and high-humidity environment, the charging member has a low resistance, so that a high bias is directly applied to the image carrier, and a charging current leak occurs.

Therefore, in order to solve such a problem, the alternating current bias superimposed on the direct current bias is set to constant current control, and the amount of charge applied from the charging member to the image carrier is always constant, so that it can be used in any environment. Techniques have been proposed that enable good charging. That is, by changing the DC bias applied to the charging member to constant voltage control and the AC bias to constant current control, the resistance value of the charging member changes due to environmental fluctuations as described above and the resistance value at the time of manufacturing the charging member. This makes it possible to obtain a good charging ability by sufficiently following the variation of the above.

(Problems to be Solved by the Invention) However, the constant current control of the charging member, particularly the constant current control of the AC bias, is vulnerable to noise from the surroundings. For example, an image using the AC bias as the developing bias applied to the developing means is used. In the forming apparatus, there is a danger that the constant current control may malfunction due to interference between them, and the capacity of the image carrier or the like with which the charging member is in contact is easily affected. It can be said that the situation is unstable.

Furthermore, when a pinhole is formed on the image carrier,
In the case where there is a flaw, when the charging member to which the bias voltage is applied comes into contact with the pinhole, the charging current flows intensively from the charging member into the pinhole, etc. Due to the current control, the voltage applied to the charging member may be reduced at a stretch, and charging failure may occur.

The present invention is an image forming apparatus employing a contact charging device as a charging means for charging the surface of the image carrier, but does not have the above-mentioned problems, that is, a change in the resistance value of the charging member due to environmental fluctuations, and noise from surroundings. Regardless of presence / absence, presence / absence of pinholes or scratches on the image carrier, etc., an image capable of outputting a high-quality image free of image defects due to poor charging by maintaining a stable and good charging ability at all times. It is an object to provide a forming device.

(Means for Solving the Problems) According to the present invention, an image is formed by an image forming process unit including a contact charging unit for charging a surface of an image bearing member by applying a bias voltage to the surface of the image bearing member to charge the surface of the image bearing member. A predetermined DC bias is applied to the charging member when the charging member is in contact with the non-image area surface of the image carrier on which no image is to be formed. A value or a voltage value, and when the charging member is in contact with the area surface of the image carrier on which image formation is to be performed, a predetermined DC bias of a constant voltage control is applied to the charging member, A charging process is performed on a surface of an image carrier on which an image is to be formed by applying a superimposed bias with an AC bias that is set based on the detected current value or voltage value and that is controlled at a constant voltage. Make up An image forming apparatus characterized in that:

(Operation) That is, a voltage value Vc or a current value Ic generated when a constant current control or a constant voltage controlled DC bias is applied to the charging member brought into contact with the image bearing member varies depending on the environment. The resistance differs depending on the current resistance value.In a low-temperature and low-humidity environment, the charging member has a high resistance, and the generated voltage Vc increases or the generated current Ic decreases. Has a low resistance and the generated voltage Vc decreases or the generated current Ic increases.

Therefore, the current environmental condition can be detected by detecting the voltage value Vc or the current value Ic, and an appropriate bias to be applied to the charging member is set based on the detection information to execute good charging in the current environmental condition. can do.

Therefore, the present invention provides the above-described voltage value Vc when the charging member is in contact with the non-image area surface of the image carrier on which no image is formed.
Alternatively, the current value Ic is detected, and when the charging member is in contact with the area surface of the image carrier on which image formation is to be performed, a predetermined DC bias of constant voltage control is applied to the charging member, Applying a superimposed bias with an AC bias controlled based on a constant voltage controlled based on the detected voltage value Vc or current value Ic to perform a charging process on an area of the image carrier on which image formation is to be performed. This prevents charging failure phenomena and charging current leak development that are likely to occur under low-temperature, low-humidity environments or high-temperature, high-humidity environments. Since an appropriate bias to be applied to the charging member is set and applied so that good charging can be performed, good charging is always maintained in all environments, and a high-quality image can be output.

Also, since the AC bias to the charging member is controlled by a constant voltage, there is no possibility that the control may malfunction due to the influence of noise from the surroundings, and even if the charging member comes into contact with a pinhole or the like existing on the surface of the image carrier. The voltage applied to the charging member does not drop at a stroke, and it is possible to prevent poor charging due to the presence of pinholes and the like.

(Embodiment) <First Embodiment> (FIGS. 1 to 3) FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus configured according to the present invention. The apparatus of this embodiment is a laser printer using a transfer type electrophotographic process.

(1) Process Equipment / Imaging Process 1 is a photosensitive drum as an image carrier. This example has an outer diameter of 30 mm formed by forming an organic semiconductor (OPC) layer 1b on the surface of a drum base 1a made of aluminum.
Is rotated clockwise at a peripheral speed (process speed) of 70 mm / sec.

Reference numeral 2 denotes a charging roller as a charging member of the contact charging device. This charging roller is made by mixing and dispersing a conductive core material 2a and a conductive material (conductive filler) such as carbon in an elastic material such as EPDM which is formed concentrically and integrally on the outer periphery of the core metal and has a volume specific resistance. and the low-resistance layer 2b was adjusted to about 10 ³ [Omega] cm and a high resistance layer 23c made of volume resistivity 10 ⁸ [Omega] cm approximately epichlorohydrin rubber formed on an outer surface thereof, made of.

The charging roller 2 is rotatably supported substantially parallel to the photosensitive drum 1 and is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force by a pressing spring 10. The charging roller 2 rotates following the rotation of the photosensitive drum 1.

Then, a predetermined bias voltage is applied to the charging roller 2 from the high voltage power supply 3 as described later, and the surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a contact charging method. In this embodiment, the surface of the photosensitive drum 1 is negatively charged.

A scanning exposure 5 is performed on the charged photosensitive drum 1 surface with a laser beam (not shown) and a laser beam output from a scanner and modulated according to a time-series electric digital pixel signal of target image information. As a result, an electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 1. The laser beam scanning exposure 5 is so-called image exposure for irradiating an image area, and a negative electrostatic latent image is formed on the surface of the photosensitive drum 1.

Numeral 6 denotes a reversal developing device. The surface of the photosensitive drum 1 on which the electrostatic latent image is formed as described above is reversal-developed (toner is adhered to the exposed light portion) by the negatively charged toner of the developing device. Is visualized as

The toner image on the surface of the photosensitive drum 1 is transferred to a contact nip (transfer section) between the photosensitive drum 1 and a transfer roller 7 serving as a transfer unit from a paper supply unit (not shown) at a predetermined timing in synchronization with the transfer material P. It is sequentially transferred to the surface.

The transfer material P that has passed through the transfer unit is sequentially separated from the surface of the photosensitive drum 1, is introduced into a fixing device (not shown), undergoes permanent fixing of the toner image, and is output as an image formed product.

After the transfer material is separated, the surface of the photosensitive drum 1 is cleaned by a cleaning device 8 to remove adhered contaminants such as untransferred toner and the like. It is repeatedly provided for image formation.

(2) Driving Sequence of Apparatus FIG. 2 shows a driving sequence of the image forming apparatus of the present embodiment.

. When the main power switch of the apparatus is turned on, a pre-multiple rotation period of the photosensitive drum 1 is started, and the photosensitive drum 1 is driven to rotate a plurality of predetermined times. During this time, the temperature of the heat fixing unit is raised to a predetermined fixing temperature, and a warming operation of other necessary process equipment is performed.

This period is a print prohibition period. Even if a print start signal is input to the control system, a print (image forming) process is not performed, and the surface of the rotating photosensitive drum 1 is a non-image area surface on which no image is formed.

. When the previous multi-rotation period ends, the rotation drive of the photosensitive drum 1 is stopped, and the image forming apparatus enters a standby (waiting) period for waiting for input of a print start signal.

. When a print start signal is input to the control system, a pre-rotation period of the photosensitive drum 1 is started, and the photosensitive drum 1 is driven by a predetermined rotation of at least one rotation. Image formation and output for one sheet or a series of a plurality of predetermined sheets are sequentially performed.

When the image formation / output of one or a plurality of predetermined sheets is completed in the print execution period, the photosensitive drum 1 enters a post-rotation period, and after the rotation of at least one predetermined rotation is performed, the rotation drive is stopped, and the image formation is performed. The apparatus enters a standby period waiting for the input of the next print start signal.

Although not shown in the drawing, a photosensitive drum corresponding to a so-called paper interval between image forming cycles when a series of predetermined plural sheets are sequentially formed in a print execution period. The drum surface portion is a non-image area surface on which no image is formed.

(3) Application and Control of Bias Voltage to Charging Roller 2 In the present embodiment, the environment is detected during the previous multiple rotation period, which is the non-image area surface of the rotating photosensitive drum 1. At this time, the photosensitive drum 1 has been discharged to OV by the discharge lamp 9. Then, a constant current controlled DC bias is applied to the charging roller 2. The voltage value generated at this time differs depending on the resistance value of the charging roller 2 changed according to the environment. Therefore, by detecting this voltage value, the environment at that time can be detected. In other words, in a low-temperature and low-humidity environment, the charging roller 2 has a high resistance and the generated voltage increases. Conversely, in a high-temperature and high-humidity environment, the charging roller 2 has a low resistance and the generated voltage decreases. . For example, when a constant current control of −20 μA is performed, in a low-temperature and low-humidity environment, the resistance value of the charging roller 2 is about 10 ⁷ Ω, and the generated voltage Vc is as high as about −1.5 KV. Under the environment, the resistance value of the charging roller 2 is about 10 ⁵ Ω, and the generated voltage Vc is as low as −1.2 KV.

The environment information obtained in this way is fed back to the setting of an appropriate value of the AC bias applied to the charging roller 2 which is in contact with the surface of the photosensitive drum 1 where the image formation is to be performed during the print execution period.

That is, when the charging roller 2 has a high resistance as in a low-temperature and low-humidity environment, a charging failure is prevented by increasing the peak-to-peak voltage of the AC bias, and conversely, as in a high-temperature and high-humidity environment. In the case where the charging roller 2 has resistance, it is necessary to prevent a leak or the like by lowering the peak-to-peak voltage of the AC bias. Therefore, for example, in a low-temperature and low-humidity environment, the peak-to-peak voltage Vpp is 2.3 KV
And in a high temperature and high humidity environment, the peak-to-peak voltage Vp
By setting p as low as 1.2 KV, it is possible to avoid the above-mentioned problems and to perform sufficient charging.
At this time, since the AC bias is controlled at a constant voltage, the control is not affected by noise from the surroundings, and the charging roller 2 comes into contact with a pinhole or the like existing on the photosensitive drum 1. In addition, the voltage applied to the charging roller 2 does not drop at a stretch, and poor charging can be prevented.

FIG. 3 shows the relationship between the voltage Vc generated when a DC bias of −20 μA constant current control is applied to the charging roller 2 when the photosensitive drum is OV, and the photosensitive drum surface area where image formation is to be performed. An example of the relationship with the peak-to-peak voltage Vpp of the AC bias to be applied to the contacting charging roller 2 and controlled by the constant voltage has been shown.

First, during the previous multi-rotation period, a charging control signal is output from the CPU 4 (FIG. 1), which passes through the constant current circuit 11 to the DC power supply 3a in the high voltage power supply 3, and the charging roller 2
DC constant current control of μA is performed. DC voltage Vc generated at this time
Is detected by the voltage detection circuit 12, and then sent to the CPU 4 again. In the CPU 4, a peak-to-peak voltage Vpp of an AC bias to be applied to the charging roller 2 is set based on a previously input look-up table as shown in FIG. Then, a charging control signal is output from the CPU 4 again, which passes through the constant voltage circuit 13 to the DC power supply 3a and the AC power supply 3b in the high voltage power supply 3, and a predetermined bias is applied to the charging roller 2 during a printing execution period. Is done.

The image forming apparatus having the above-described configuration does not cause a problem such as charging failure or leakage in each environment of normal temperature and normal humidity, low temperature and low humidity, and high temperature and high humidity. Was done.

<Embodiment 2> (FIG. 4) In the present embodiment, the static elimination lamp 9 is omitted from the apparatus of the above-described Embodiment 1 (FIG. 1), and instead, the photosensitive drum 1 is used in the front multiple rotation period and the post rotation period. The static elimination process is performed by applying only an AC bias to the charging roller 2 as in the drive sequence of FIG.

In the preceding multi-rotation period, in the period of one or more rotations of the photosensitive drum at the beginning of the period, only the AC bias is applied to the charging roller 2 as described above, so that the photosensitive drum 2 is subjected to the charge elimination process, and the photosensitive drum surface is removed. OV is discharged, thereafter, the application of the AC bias is cut off, and a constant current controlled DC bias is applied to the charging roller 2 to detect the voltage Vc generated at that time during at least one rotation of the photosensitive drum 1, This is to feed back to CPU4.

By configuring such a drive sequence, it is possible to omit the static elimination lamp 9, thereby simplifying the apparatus,
This will greatly contribute to reducing costs.

In the image forming apparatus according to the present embodiment, as in the first embodiment, the DC bias applied to the charging roller 2 for detecting the environment is a constant current control of −20 μA. The peak-to-peak voltage Vp of the AC bias to be applied to the charging roller 2 under constant voltage control based on the voltage Vc
The same lookup table as that shown in FIG. 3 was used for setting p.

An image forming apparatus having such a configuration is provided at normal temperature and normal humidity,
When the device was operated under low-temperature, low-humidity, and high-temperature, high-humidity environments, problems such as poor charging and leakage did not occur, and good output images were obtained in each case.

<Embodiment 3> (FIG. 5.6) In this embodiment, a blade type (charging blade) 2A is used as a charging member of a contact charging device.

The charging blade 2A has a thickness of 2 mm, a low-resistance layer 2d in which carbon is dispersed in an elastic material such as urethane rubber and the volume resistivity is adjusted to about 10 ² Ωcm, and the surface thereof is coated. And a high resistance layer 2e made of N-methoxymethylated nylon having a specific resistance of about 10 ⁹ Ωcm. The charging blade 2A is pressed against the photosensitive drum 1 in a so-called counter direction with a predetermined pressure while being supported by the blade holder 2f.

A bias voltage is applied to the low resistance layer 2d of the charging blade 2A by the same voltage application circuit as in FIG. 1 of the first embodiment, and the charging process of the photosensitive drum 1 is executed.

The image forming apparatus of the present embodiment also omits the discharge lamp 9 as in the second embodiment, and the discharge process of the photosensitive drum 1 is performed by a discharge blade.
This is performed by applying an AC bias to 2A.

The driving sequence of the image forming apparatus shown in the present embodiment is the same as that shown in the second embodiment, except that in this embodiment, the driving sequence is applied to the charging blade 2A during the multi-rotation before detecting the environment. The DC bias is a constant voltage control of -1.2 KV, and a lookup table for setting a peak-to-peak voltage Vpp of the AC bias to be applied to the charging blade 2A at a constant voltage to be applied to the charging blade 2A based on the DC current Ic generated at this time. The one shown in FIG. 6 was used.

An image forming apparatus having such a configuration is provided at normal temperature and normal humidity,
When the device was operated in low-temperature, low-humidity, and high-temperature, high-humidity environments, problems such as poor charging and leakage did not occur, and good images were obtained in each case.

In the first to third embodiments, the detection of the voltage Vc or the current Ic is not limited to the pre-multiple rotation period of the photosensitive drum 1, but may be performed in a non-image forming period such as a pre-rotation period or a post-rotation period.
Alternatively, the AC bias may be turned off, and the DC bias may be applied under constant current control or constant voltage control to detect Vc or Ic and feed back to the CPU 4.

(Effect of the Invention) As described above, the environment in which the image forming apparatus is used is detected by utilizing the bias control for the charging member of the contact charging device, and the AC to be applied to the charging member is detected based on this information. A bias is set, and a constant voltage controlled AC bias is superimposed on a constant voltage controlled DC bias, and a bias is applied to the charging member. Regardless of the presence or absence of pinholes on the image carrier, it is necessary to constitute an image forming layer immersion using a contact charging device that can maintain stable and good charging ability at all times and can output high-quality images. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of the first embodiment apparatus. FIG. 2 is a drive sequence diagram of the device. FIG. 3 is a diagram showing a relationship between a generated voltage Vc and an AC voltage Vpp. FIG. 4 is a drive sequence diagram of the device of the second embodiment. FIG. 5 is a main part view of the device of the third embodiment. FIG. 6 is a diagram showing a relationship between a generated current Ic of the device and an AC voltage Vpp. 1 is a photosensitive drum as an image carrier, and 2 and 2A are a charging roller or a charging blade as a charging member of a contact charging device.

Claims (1)

(57) [Claims] An image forming apparatus for forming an image by image forming process means including a contact charging means for charging a surface of the image bearing member by applying a bias voltage to the surface of the image bearing member to charge the surface of the image bearing member; When the charging member is in contact with the non-image area surface of the image carrier on which no image is formed, a predetermined DC bias is applied to the charging member to detect a generated current value or a voltage value at this time, When the charging member is in contact with the surface of the image carrier on which the image formation is to be performed, a predetermined DC bias controlled by a constant voltage and the detected current value or voltage value are applied to the charging member. Image forming of an image carrier on an area on which image formation is to be performed by applying a superimposed bias to an AC bias which is set based on the constant voltage control. Dress .