JPH03118582A - Image forming device - Google Patents

Abstract

PURPOSE:To apply a charge quantity required at the time of transfer to a transfer material regardless of the change of a resistance value in a transfer charging means such as a transfer roller or the size of the transfer material by obtaining a 1st specified voltage value by performing constant-current control. CONSTITUTION:When the transfer material S reaches a 1st electrode 9 and a 2nd electrode 31 before it reaches a transfer part A, 2muA of current is applied to a non-image area on a photosensitive drum 2 by the transfer roller 6 while constant-current control is performed by an ATVC 11. At the same time, a high voltage is impressed on the 1st electrode 9 by an HV 32 and the current flowing to the 2nd electrode 31 through the transfer material S is detected by a detection means 10, then the detection information is fed back to the ATVC 11. According to the detection information from the detection means 10 and the 1st specified voltage value E1, the optimum 2nd specified voltage value E2 which is impressed on the transfer material S at the time of transfer is decided, and the image is transferred by the transfer roller 6 while the constant-voltage control is performed so that the voltage impressed on the transfer material S may be kept E2 from the point of time when the transfer material S reaches the transfer part A.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is an electrostatic latent image formed on an image carrier, such as an electrophotographic image forming apparatus such as a copying machine or a laser beam printer. The present invention relates to an image forming apparatus that transfers an image developed with a developer such as toner to a transfer material.

(Prior Art) Conventionally, in this type of image forming apparatus, one
Next, after being charged, an electrostatic latent image is formed, and this electrostatic latent image is developed with toner or the like as a developer.The toner image is brought into contact with the transfer material at the transfer section, and at the same time, the transfer material is transferred by the transfer charging means. Those that transfer a toner image onto a transfer material by charging it to a polarity opposite to that of the toner are widely used. As the transfer charging means, one is used that applies voltage or current through a transfer roller that is brought into contact with the back surface of the transfer material.

In addition, in order to maintain the amount of electric charge applied to the transfer material at the optimum predetermined amount during transfer, constant voltage control is performed to control the voltage applied from the transfer charging means to the transfer material to a predetermined voltage value, or the transfer charging means during transfer Constant current control is performed to control the current flowing from the motor to a predetermined current value.

However, in constant voltage control, low temperature and low humidity environments (hereinafter referred to as L
/L environment), the electrical resistance value (hereinafter referred to as resistance value) of the transfer roller increases, so the amount of charge necessary to transfer the image is not transferred to the transfer material, resulting in transfer defects such as transfer missing. There is a problem in that it causes On the other hand, in constant current control, the envelope.

When using small-sized transfer materials such as postcards, the current flows in a concentrated manner to the surface of the image carrier around the transfer material in the transfer section, which reduces the amount of current flowing on the transfer material and causes transfer defects. There's a problem.

In order to solve this problem, a device as shown in FIG. 11 has been proposed. In this image forming apparatus 100, after primary charging is performed by a primary charging roller 102 on a photosensitive drum 101 as an image carrier rotating in the direction of arrow a, light intensity is emitted from a laser diode 103 according to image information. A modulated laser beam is irradiated to form an electrostatic latent image, and a developer 104 causes toner to adhere to this electrostatic latent image. This toner image is brought into contact with the transfer material 105 at the transfer section A, and after contacting the back surface of the transfer material 105 at the transfer section A, the transfer roller 106, which rotates in direction b, transfers the toner image to the transfer material 105.
The toner image is transferred to the transfer material 105 by applying a voltage to the transfer material 105 to give the transfer material 105 an electric charge of opposite polarity to that of the toner.
Transfer to 5. The toner image transferred to the transfer material 105 is fixed by a fixing device 107. In the figure, 108 is a cleaner for removing residual toner on the photosensitive drum 101;
Reference numeral 9 denotes a lower transfer guide for guiding the transfer material 105 to the transfer section A.

Further, this device is provided with a control means 110,
This control means 110 controls the voltage applied to the transfer material 105 during transfer, as described below. first,
After primary charging is performed on the photosensitive drum 101, the transfer roller 10 is applied to a non-image area where an electrostatic latent image is not formed downstream in the direction of arrow a from the image area where an electrostatic latent image is formed.
6, constant current control is performed to flow a current with a predetermined current value that is optimal for performing transfer, and the applied voltage value necessary to flow the current with this predetermined current value is held as a predetermined voltage value, and the transfer is performed. At times, constant voltage control is performed so that the voltage applied to the transfer material 105 by the transfer roller 106 becomes the predetermined voltage value. Thereby, even if the resistance value of the transfer roller 106 changes depending on the environment or the size of the transfer material is small, it is possible to always apply an optimal predetermined amount of charge to the transfer material 105. Hereinafter, this control means 106 will be referred to as ATV
C (Active Transfer Voltage
Controller).

(Problem to be Solved by the Invention) However, in the above-mentioned conventional technology, when transferring in a high humidity environment, the resistance value of the transfer material 105 becomes small, so that the electric charge applied to the transfer material 105 is transferred. There was a problem in that a large amount of charge flows to the lower guide 109, and the amount of charge necessary for good transfer does not remain on the transfer material 105, resulting in poor transfer. Further, a similar problem occurs when a transfer material having an essentially low resistance value is used.

The present invention was made to solve the problems of the prior art described above, and its purpose is to always optimize the amount of charge present on the transfer material during transfer, regardless of changes in the environment or the state of the transfer material. An object of the present invention is to provide an image forming apparatus that can maintain a predetermined amount and perform good transfer.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, after performing primary charging to uniformly charge the image carrier, an electrostatic latent image is formed on the image carrier. image formation in which an image obtained by developing this electrostatic latent image with a developer is brought into contact with a transfer material in a transfer section, and a charge is applied to the transfer material by a transfer charging means to transfer the image to the transfer material. In the apparatus, an electrode is provided on the transfer material conveyance path, and a current is passed by a transfer charging means to a non-image area where primary charging is performed on the image carrier and no electrostatic latent image is formed, and this current is set to a predetermined value. The voltage applied by the transfer charging means at this time is set as a first predetermined voltage value, the current flowing through the transfer material to the electrode is detected by the detection means, and the detected information and the first predetermined voltage are The present invention is characterized in that it includes a transfer charging voltage control means for controlling the voltage applied by the transfer charging means during transfer to a second predetermined voltage value in accordance with the transfer charging value.

(Function) In the apparatus of the present invention having the above configuration, by obtaining the first predetermined voltage value through constant current control, regardless of the change in the resistance value in the transfer charging means such as the transfer roller or the size of the transfer material. It is now possible to apply the necessary amount of charge to the transfer material during transfer, and by detecting the current flowing through the transfer material, the amount of charge necessary during transfer can be applied to the transfer material regardless of the resistance value of the transfer material. The voltage value applied by the transfer charging means to exist in the second predetermined voltage value can be obtained as the second predetermined voltage value.

Therefore, regardless of changes in the environment or the state of the transfer material, the amount of charge present on the transfer material during transfer can always be maintained at an optimal predetermined amount.

(Example) The present invention will be explained below based on the illustrated example. 1st
The figure is an explanatory diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. In the figure, reference numeral 1 indicates an image forming apparatus which is an electrophotographic printer that performs reversal development. Similar to the conventional example shown, a primary charging roller 3 for performing primary charging, a laser diode 5 for forming an electrostatic latent image on the photosensitive drum 2, and a system for using the electrostatic latent image as a developer. A developing device 4 for developing with toner, a transfer roller 6 as a transfer charging means that comes into contact with the back surface of the transfer material S at the transfer section A, and a fixing device for fixing the toner image transferred to the transfer material S. 7 and a cleaner 8 for removing residual toner on the photosensitive drum 2 in the transfer section.

The transfer roller 6 has a volume resistivity of 1Q7-1oΩ・cm,
It is made of EPDM (ethylene propylene diene rubber) with a hardness of 286, and since EPDM is an elastic material with relatively high resistance, the resistance value of the transfer roller 6 is lowered by dispersing ZnO in order to provide conductivity. Volume resistivity is 107-10
This resistance value was selected as Ω·Cm because it has the least variation in the manufacturing process and is stable.

In this apparatus, a lower transfer guide 9 provided on the document transport path also serves as an electrode, and a detection means 1o for detecting current is connected to the lower transfer guide 9.
This detection means 1o is the ATVC II described in the above conventional example.
It is connected to the.

This ATVC II serves as a transfer charging voltage control means for controlling the voltage applied to the transfer material S during transfer.

In the image forming apparatus 1 of this embodiment, the photosensitive drum 2 is rotated at a process speed of 47 mm/sec, and the surface of the photosensitive drum 2 is negatively charged by the primary charging roller 3 to have a surface potential of -650 V. , a laser diode 5 irradiates laser light to form an electrostatic latent image on the surface of the photosensitive drum 2. As a result, the surface potential of the exposed portion drops to -150V.

This electrostatic latent image is reversely developed by the developing device 4 to form a toner image of negative toner. The transfer material S is guided by the lower transfer guide 9 and conveyed in the direction of arrow d, and is sandwiched between the photosensitive drum 2 and the charging roller 6 rotating in the direction b at the transfer section A. At this time, the charging roller 6 charges the transfer material S. The toner image is transferred onto the transfer material S by applying a voltage and imparting a charge having a polarity opposite to that of the toner to the transfer material S. After this toner image is fixed by the fixing device 7, the transfer material S is discharged outside the machine, the residual toner on the photosensitive drum 2 is removed by the cleaner 8, and the next image is formed by the same operation as above. I do.

Here, in the transfer material S, as shown in FIG. 2, in order to easily separate the transfer material S from the fixing device 7 after the toner image is fixed, toner is applied to the leading edge side of the transfer area B where the image is transferred. A white area 20 with a width of 5 mm (hereinafter referred to as the leading edge margin) to which no adhesion is allowed is provided, and on the photosensitive drum 2 corresponding to this leading edge margin 20, there is a non-image area that is not exposed to light after primary charging. A region is formed.

Next, a method of controlling the voltage applied to the transfer material S during transfer will be explained using FIG. 3.

First, before the transfer material S reaches the transfer section A, the ATVCI
Step (2) in which a current of 2 μA is applied to the non-image area on the photosensitive drum 2 by the transfer roller 6 while controlling the constant current by I, and the voltage E applied by the transfer roller 6 at this time.
1 as the first predetermined voltage value (step ■
). Next, after the transfer material S reaches the nip between the photosensitive drum 2 and the transfer roller 6, that is, the transfer portion A, the transfer material S is conveyed 5 mm by the upper end margin 20 (approximately 0 as the process speed is 47 mm/sec). .11 seconds), the amount of current flowing to the lower transfer guide 9 via the transfer material S is detected by the detection means 10 (step 2), and the amount of current as the detected information is fed back to the ATVC II.

Here, when controlling the voltage applied by the transfer roller 6 by feeding back the amount of current flowing into the electrode (lower transfer guide 9) to the ATVC II, the amount of current flowing into the electrode (lower transfer guide 9) is Since the current flowing from the transfer material S to the lower transfer guide 9 changes every moment depending on the potential of the electrostatic latent image, it is difficult to accurately control the applied voltage.

However, in this embodiment, the current amount is fed back at the upper end margin 20, and the potential on the photosensitive drum 2 is also constant at the upper end margin 20, so it is difficult to accurately control the applied voltage using such feedback. It becomes possible to do so.

By the way, paper left in L/L environment, paper left in N/N environment (standard temperature and humidity environment), paper left in N/N environment (high temperature and high humidity environment), and 0fIP left in N/N environment.
When a solid white image was transferred using paper as a transfer material, the current values flowing from the transfer material to the lower transfer guide 9 during transfer were as shown in the following table.

As can be seen from this table, the value of the current flowing from the transfer material S to the lower transfer guide 9 varies depending on the environment, and depending on this current value, the transfer material It is necessary to determine a second predetermined voltage value E2 to be applied to S. Assuming that the relationship between this second predetermined voltage value E2 and the first predetermined voltage value E1 is E2 = KXF,l, there is a
There is a relationship as shown in the figure. Figure 4 shows the current flowing through the lower transfer guide 9 and the applied voltage necessary for good transfer when transferring a solid black image in an N/N environment, and plotting the results on a graph. The values of the coefficients are determined from the straight line. However, if the value of K is increased without limit, there is a risk of leakage, so a characteristic that saturates at 1.5 is given.

Then, based on the amount of current fed back to the ATVC, the value of the coefficient is determined from FIG. 4, a second predetermined voltage value E2 is calculated, and the voltage applied by the transfer roller 6 is set to It is controlled to the value E2 (step ■). After this, in the transfer area, while performing constant voltage control to keep the voltage applied to the transfer material S by the transfer roller 6 at E2,
Transfer the image (step ■). A time chart of this sequence is shown in FIG.

When I actually transferred a solid black image in an N/N environment,
The first predetermined voltage value E1 was 1.5 kV. When transfer is performed using this applied voltage, transfer gaps occur. In this example, when the applied voltage was El, the current flowing to the lower transfer guide 9 was 25 μA, so from FIG.
．． 4, and the second predetermined voltage value E2 is 1.4 Xl, 5[
kV] = 2.1kV, and the applied voltage was set to 2.1kV.
When the transfer was carried out under constant voltage control at V, a good transferred image could be obtained without any transfer gaps.

In addition, the resistance value of the transfer roller 6 used in the above embodiment is highly dependent on the environment, and when the resistance value was measured by bringing the transfer roller 6 into contact with an aluminum drum, the resistance value was approximately 107Ω under the H/H environment, and the resistance value was approximately 107Ω under the L/H environment. Under the L environment, it is 109Ω, and the resistance value changes by nearly two orders of magnitude depending on the environment. However, in this embodiment, by performing constant voltage control in the non-image area,
Regardless of the environmental dependence of the resistance value of the transfer roller, and even when the size of the transfer material is small, the amount of charge applied to the transfer material S can always be maintained at a predetermined amount, and further, the transfer Even when the resistance value of the material S is low and a large amount of the electric charge applied to the transfer material S flows to the lower transfer guide 9, the optimum second predetermined voltage value E2 is always applied to the transfer material S to prevent the transfer from occurring during transfer. The amount of charge existing on the transfer material S can be maintained at a required predetermined amount.

In the above embodiment, the lower transfer guide 9 also serves as an electrode provided on the transfer material transport path, but an electrode may be provided on the transfer material transport path separately from the lower transfer guide 9.

FIG. 6 is an explanatory diagram showing the configuration of an image forming apparatus according to another embodiment of the present invention. In the figure, the same parts as in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted. In this image forming apparatus 30, the lower transfer guide 9 is also used as the first electrode, and a second electrode 31 is provided on the transfer material conveyance path. is connected to a high voltage power source (hereinafter referred to as 11V) 32, and the second electrode 31 is grounded via the detection means 10.

In this embodiment, the arrangement of the first electrode 9 and the second electrode 31 is as shown in FIG.
Although the second electrode 31 is arranged downstream of the first electrode 9 with respect to the arrow d direction, the arrangement of the two may be reversed as shown in FIG. As shown,
1st regarding the d direction. The second electrode 9.31 may also be arranged in parallel.

Also, 1st. It is preferable that the second electrodes 9, 31 be installed within the area occupied by the smallest size transfer material S, as shown in FIG. This is because the drop in surface potential of the transfer roller 6 that occurs at the paper passing section (the contact area between the transfer material S and the transfer roller 6) due to the escape of charge from the transfer material S at the transfer section A depends on the size of the transfer material S. No, but number one. If the smallest size transfer material S is used when the second electrode 9゜31 is installed outside the area, the voltage drop at the paper passing section will be the same as when the largest size transfer material S is used. Nevertheless, the amount of current detected by the detection means 1o decreases, making it difficult to accurately control the applied voltage.

Next, in this embodiment, a method of controlling the voltage applied to the transfer material S during transfer will be explained using FIG. 9.

First, when the transfer material S reaches the first electrode 9 and the second electrode 31 before the transfer material S reaches the transfer section A, the AT
While performing constant current control by VCII, the transfer roller 6
Step (3) in which a current of 2 μA is applied to the non-image area on the photosensitive drum 2, and the voltage E+ applied by the transfer roller 6 at this time is held as a first predetermined voltage value (Step 0). At the same time, the first electrode 9 is
Step 0)
, feeds back the detection information to ATVCII.

Then, in the same manner as in the above embodiment shown in FIG. Determine the voltage value E2 (Step 2), and from the time the transfer material S reaches the transfer section A, transfer the image while performing constant voltage control to keep the voltage applied to the transfer material S by the transfer roller 6 at E2. Do (step ■). A time chart of this sequence is shown in FIG.

When the above operation was actually performed using the transfer material S left in an H/H environment, the first predetermined voltage value E+ was 1.5k.
It was V. When the transfer was performed using this applied voltage, missing portions of the transfer occurred. On the other hand, in this example, 1lV32
A voltage of 2 kV was applied to the first electrode 9, and the current detected by the detection means 10 was 25 μA, so the coefficient K was determined based on this current value and the first predetermined voltage value E+. As a result, the second predetermined voltage value E2"1.4 xl, 5 [kV] = 2.1 [kV] with K=1.4
It was decided. Then, the voltage applied to the transfer material S is set to 2.1
When the transfer was performed while controlling the voltage at a constant voltage of 'kV, a good transferred image could be obtained without any transfer gaps.

In this embodiment, since the second electrode 31 is provided separately from the first electrode 9, the detection time of the current flowing to the electrode via the transfer material S can be lengthened as necessary.
Another advantage is that the detection by the detection means 10 can be performed simultaneously with the sequence for determining the first predetermined voltage value E1 using ATVC II.

(Effects of the Invention) The present invention has the above-described structure and operation, and the amount of charge present on the transfer material during transfer is always maintained at an optimum predetermined amount regardless of changes in the environment or the size, type, and condition of the transfer material. It is possible to maintain good transfer quality by preventing transfer dropouts and the like. Therefore, a wide variety of transfer materials can be used and high quality images can be formed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a perspective view showing the upper margin of a transfer material in the embodiment, and FIG. FIG. 4 is a flowchart showing the method of controlling the applied voltage. FIG. 4 is a graph showing the relationship between the current flowing to the lower transfer guide and the coefficient in the same embodiment. FIG. A time chart, FIG. 6 is an explanatory diagram showing the configuration of an image forming apparatus according to another embodiment of the present invention,
FIG. 7(a) is a perspective view showing the arrangement positions of the first electrode and the second electrode in the same embodiment, and FIG. 7(b) is a perspective view showing the arrangement positions of the first electrode and the second electrode in the same embodiment. (c) is a perspective view showing another example of the arrangement positions of the first electrode and the second electrode; FIG. 8 is a perspective view for explaining the area occupied by the smallest size transfer material in the same embodiment; FIG. 9 is a flowchart showing a method for controlling the applied voltage during transfer in the same embodiment, FIG. 10 is a time chart of the sequence of controlling the applied voltage during transfer in the same embodiment, and FIG. 11 is a flowchart showing a method of controlling the applied voltage during transfer in the same embodiment. FIG. 2 is an explanatory diagram showing the configuration. Explanation of symbols 1... Image forming device 2... Photosensitive drum (image bearing member) 3... Primary charging roller 4... Developing device 5... Laser diode 6... Transfer roller (transfer charging Means) 9... Lower transfer guide (electrode) 10... Detection means 11... ATVC (transfer charging voltage control means) S...
Transfer material A...transfer part

Claims (1)

[Scope of Claims] After performing primary charging to uniformly charge the image carrier, an electrostatic latent image is formed on the image carrier, and an image obtained by developing this electrostatic latent image with a developer is transferred. In an image forming apparatus, an electrode is provided on a transfer material conveyance path, and an electrode is provided on a transfer material conveyance path, and an electrode is provided on a transfer material conveyance path, and an electrode is provided on a transfer material conveyance path, A current is passed by a transfer charging means to a non-image area where primary charging is applied and no electrostatic latent image is formed, and this current is controlled to a predetermined value, and the voltage value applied by the transfer charging means at this time is set to the first voltage value.
The current flowing to the electrode through the transfer material is detected by a detection means, and the voltage applied by the transfer charging means during transfer is set to a second voltage value according to the detected information and the first predetermined voltage value. An image forming apparatus comprising a transfer charging voltage control means for controlling the voltage to a predetermined voltage value.