JP2003302846A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cope with the high speed of transference by providing a transfer control method for obtaining a satisfactory image without depending on the resistance value of a transfer material while applying proper transfer voltages to transfer materials having different resistance values in accordance with transfer materials having a wide range of resistance values in a transferring type image forming device in which a contact type transferring means is used. <P>SOLUTION: In a system in which a transfer voltage is decided by a PTVC (programmable transfer voltage control) control and to which a constant voltage is applied, when an impression voltage is decided by detecting a transfer current at the top end of a transfer material and by comparing it with a threshold, the threshold is changed by referring to information of a paper feeding port. Moreover, the threshold is decided by referring to at least one side of the resistance value of the transfer material and size information of the transfer material. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus.

More specifically, a transfer member is provided which contacts the back side of the transfer material in order to transfer the toner image formed and carried on an image carrier such as an electrophotographic photoreceptor or an electrostatic recording dielectric to the transfer material. The present invention relates to an image forming apparatus such as a copying machine / printer.

[0003]

2. Description of the Related Art In a transfer type image forming apparatus, a transfer means for transferring a toner image formed and carried on an image carrier to a transfer material is compared with a transfer means using a non-contact type corona charger. Since no ozone is generated in the image forming apparatus, a contact-type transfer unit having a transfer member that forms a pressure contact nip portion with the image carrier and transfers the toner image on the image carrier to the transfer material inserted in the pressure contact nip portion. In particular, the roller transfer method using a roller body (transfer roller) as a contact transfer member has the advantage that it is further excellent in transfer material conveyance stability and is in the mainstream.

The roller transfer method is used as a contact transfer member.
A conductive elastic roller (hereinafter referred to as a transfer roller) having a medium resistance elastic layer whose resistance is adjusted to 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω is used, and this is placed on an image carrier (hereinafter referred to as a photosensitive drum). A transfer nip portion formed by the photosensitive drum and the transfer roller (hereinafter referred to as a transfer nip portion) while nipping and conveying the transfer material, and applying a transfer bias to the transfer roller The toner image on the photosensitive drum is transferred onto the transfer material by applying an electric charge having a polarity opposite to that of the toner image.

The resistance value of the transfer roller is appropriately adjusted by dispersing inorganic conductive particles such as carbon in rubber or sponge or using ion conductive rubber in which a surfactant or the like is kneaded. It is a roller having an elastic layer, and it is well known that the resistance value of this transfer roller changes by one digit or more due to variations in manufacturing, temperature / humidity, and resistance value changes due to long-term use (durability).

In order to always supply an optimum current to the transfer roller whose resistance changes in this way, the "constant current application method" is used.
It is conceivable to apply a transfer voltage to the transfer roller in this case, but in this case, a small-sized transfer material having a width narrower than the maximum paper passing width of the apparatus is used, and the length of the photosensitive drum is long in the transfer nip. When a non-sheet passing area where the transfer roller comes into direct contact with the transfer roller is formed, a current flows intensively there, resulting in insufficient current supply to the transfer material, which causes a problem of transfer failure.

Therefore, in many image forming apparatuses, the "constant voltage application method" is used in order to flow an appropriate current regardless of the transfer material size. In the constant voltage application method, in order to flow an appropriate current to the resistance value of the transfer roller that changes depending on the manufacturing conditions and environment, a constant current value to be passed to the transfer roller at the time of paper passing before the transfer operation is passed to the transfer roller. Bias control method (ATCV control method: Active Transfer Voltage Control)
l) or a constant current value before passing the paper is passed through the transfer roller,
A bias control method (PTVC control method: Programmable Transfer Voltage Coat) in which a voltage calculated at that time is put in a predetermined control expression and a calculated voltage is applied at the time of transfer
It detects the impedance of the transfer system before passing the paper, and applies the transfer voltage so that the current in the proper range flows.

In particular, the PTVC control system is composed of a circuit having a hardware configuration and can perform more precise bias control as compared with the ATVC system in which only a few bias values can be applied, and a hardware circuit for voltage control. This is a voltage control method that is advantageous in terms of cost because it does not require.

This PTVC control system will be described in a little more detail. The PWM signal (Pulse Width Modulation) is stepped with a constant current value as a target in a state where the surface of the photosensitive drum is charged before the paper is passed through before printing. A voltage is applied to the transfer roller in a targeted manner, and the voltage value reaching the target current value is held as Vt0. Based on the Vt0 value and the transfer output table stored in advance in the CPU of the control circuit, the transfer voltage Vt during printing suitable for the Vt0 value.
The PW corresponding to the transfer voltage Vt during printing.
This is a control method in which an M signal is output and Vt is applied to the transfer roller.

Thus, by determining the transfer voltage Vt at the time of printing by referring to the generated voltage Vt0 of each transfer roller with respect to the constant current value, the optimum voltage can be applied at the time of printing according to the resistance value of the transfer roller. Therefore, a good image can be obtained with a transfer roller having a wide range of resistance values.

[0011]

However, the above-mentioned conventional transfer voltage control method has the following problems.

That is, in the conventional transfer voltage control methods such as the ATVC method and the PTVC method, a constant current value is applied to the transfer roller in a state where there is no transfer material in the transfer nip portion, and the transfer voltage applied at the time of transfer is determined from the voltage generated at that time. I have decided.
In this way, by detecting the impedance of the entire transfer system when the paper is not passed, even if the resistance value of the transfer roller changes, an appropriate transfer bias can be applied.

However, when a transfer material whose resistance value is largely deviated from a transfer material resistance value assumed in advance such as when the transfer material has a high resistance value or a low resistance value, a transfer current to be flown during printing is generated. It may deviate from the range of the proper transfer current value.

When the impedance of the transfer material changes greatly as described above, there is a problem in that the transfer current becomes excessive and deficient, resulting in an image defect. In particular, as the number of types of transfer materials used for printing has increased due to the recent worldwide spread of image forming apparatuses, the resistance of the transfer materials has also diversified, and good images can be obtained regardless of the environment or transfer material type. Getting harder is getting harder.

Further, as the speed is increased, there is a problem that the optimum transfer current value is completely different depending on the resistance of the transfer material. Therefore, it is required to develop a transfer control system which can cope with various transfer materials.

On the other hand, it is possible to optimize the transfer voltage control by providing a special paper mode and letting the user specify the transfer material type, but this is troublesome for the user and is not so preferable. Absent.

Further, a transfer voltage is applied while the transfer material is present in the transfer nip portion, and the transfer current at that time is measured to estimate the transfer material resistance, so that the transfer current reaches the target current value. Although a method of correcting the voltage has been proposed, this method cannot give different current values to transfer materials with different optimum transfer currents, and is especially suitable for high-speed machines that require different currents for each transfer material type. There was a limit to what I could do.

Therefore, the present invention is applicable to a transfer material having a wide resistance range in a transfer type image forming apparatus using a contact type transfer means without providing a special paper mode specified by the user as described above. An object of the present invention is to provide a transfer control method for applying a proper transfer voltage to transfer materials having corresponding different resistance values and obtaining a good image regardless of the resistance values of the transfer materials. Moreover, it aims at responding to speeding up.

[0019]

The present invention is an image forming apparatus having the following configuration.

(1) An image carrier, a transfer member for forming a pressure contact nip portion with the image carrier and transferring a toner image on the image carrier to a transfer material inserted in the pressure contact nip portion, and the transfer member. Voltage applying means for applying a voltage to the voltage detecting means, a current detecting circuit for detecting a current value output from the voltage applying means, and a current of the current detecting circuit after a predetermined time has elapsed since the transfer material was inserted in the pressure contact nip portion. The output voltage of the voltage application unit is determined from a plurality of transfer voltage values prepared in advance with reference to the detection result and the paper feed port information, and the determined voltage is applied from the voltage application unit to the transfer member during printing. An image forming apparatus comprising: a control unit.

(2) An image carrier, a transfer member for forming a pressure contact nip portion with the image carrier and transferring the toner image on the image carrier to a transfer material inserted in the pressure contact nip portion, and the transfer member. Voltage applying means for applying a voltage to the voltage detecting means, a current detecting circuit for detecting a current value output from the voltage applying means, and a resistance detecting means for detecting the resistance of the transfer member in the absence of the transfer material in the pressure contact nip portion. And the output of the voltage applying means from a plurality of transfer voltage values prepared in advance with reference to the current detection result of the current detection circuit and the sheet feed port information after a predetermined time has elapsed since the transfer material was inserted into the pressure contact nip portion. Control means for determining a voltage and for applying the determined voltage from the voltage applying means to the transfer member during printing, and transferring a threshold value for determining the applied voltage to the resistance detection means. Member resistance detection result When an image forming apparatus and changes with reference to at least one of the information of the transfer material size information.

<Operation> To solve the above problems, the present invention applies a transfer voltage according to the PTVC detection result from the transfer material tip to the transfer material in addition to the transfer control method in which the transfer voltage is determined by the PTVC control. The transfer current value at a certain time after the transfer material front end is inserted into the transfer nip portion, which is the pressure contact nip portion between the image carrier and the transfer member, is monitored, and the transfer current monitoring result at the transfer material front end is supplied. From the paper edge information, the transfer voltage of any resistance value can be determined by determining the optimum applied voltage from a plurality of transfer voltage values optimized for transfer materials with different resistance values and applying a constant voltage during printing. However, a good image is obtained.

Further, by referring to the transfer member resistance detection result, paper size information, etc., a more optimal transfer voltage setting is performed.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> (FIGS. 1 to 8) (1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus. The image forming apparatus of this example is a reversal development type laser printer having a double-sided printing function (double-sided printing function) using a transfer type electrophotographic process.

Reference numeral 1 denotes a photosensitive drum which is an image carrier, and OP
A photosensitive material such as C or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel, and is rotated in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving unit (not shown).

Reference numeral 2 is a primary charging means for uniformly charging the periphery of the rotating photosensitive drum 1 to a predetermined polarity and potential.
In this example, the contact charging device uses a charging roller. In this example, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2 to a negative polarity having the same polarity as the negative toner, and becomes the dark portion potential Vd.

Reference numeral 3 is a laser beam scanner as an image information exposing means. The scanner 3 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and is ON / OFF controlled according to a time series electric digital pixel signal of image information sent from a host device (not shown). The laser beam L is emitted and the uniformly charged surface of the photosensitive drum 1 is scanned and exposed through the reflection mirror 3a to form an electrostatic latent image. That is, the absolute value of the electric potential of the exposed portion of the surface of the photosensitive drum 1 image-exposed by the scanner 3 becomes small, and the potential becomes the bright portion potential Vl and the potential of the dark portion potential Vd of the unexposed portion of the photosensitive drum surface. An electrostatic latent image is formed by the contrast.

Reference numeral 4 denotes a reversal developing device using negative toner, which reversely develops the electrostatic latent image on the photosensitive drum 1 as a toner image. A rotary developing sleeve 4a is coated with a thin layer of toner, and the toner is negatively charged. A bias voltage Vb (| Vd |> | V between the dark potential Vd and the light potential Vl of the photosensitive drum 1 is applied to the developing sleeve 4a.
b |> | Vl |) is given by an external power source (not shown), the toner on the developing sleeve 4a is transferred only to the bright potential Vl portion of the photosensitive drum 1 and the electrostatic latent image is visualized. (Reversal development).

As a developing method, a jumping developing method,
A two-component developing method or the like is used, and it is often used in combination with image exposure and reversal development.

Reference numeral 5 denotes a transfer roller as a contact transfer member in the form of a rotary body having an elastic layer. A transfer nip portion N is formed by being brought into pressure contact with the photosensitive drum 1, and the peripheral speed of rotation of the photosensitive drum 1 is counterclockwise as indicated by an arrow in the forward direction of the rotation of the photosensitive drum 1 by a driving unit (not shown). Is driven to rotate at a predetermined peripheral speed substantially corresponding to.

Reference numeral 22 denotes a paper feeding cassette portion as a first paper feeding port, and the transfer materials P are stacked and stored in the cassette.

Reference numeral 24 denotes a manual paper feed tray section (multi-purpose tray) as a second paper feed port.

When the cassette sheet feeding mode is selected and designated by the selection designation means (not shown), the sheet feeding cassette unit 22
The transfer materials P stacked and accommodated in the sheet are separated and fed by the sheet feeding roller 21 at a predetermined sheet feeding control timing.

When the manual paper feed mode is selected and designated, the transfer material P of the stack set is fed to the manual paper feed tray section 24 by the paper feed roller 23 at a predetermined paper feed control timing.

The transfer material P fed from the paper feed cassette unit 22 or the manual paper feed tray unit 24 waits at the pre-feed sensor 21a, and then is transferred to the transfer nip via the registration roller 11, the registration sensor 11a, and the pre-transfer guide 10. The sheet is fed to the section N (image forming section) at a predetermined control timing. That is, the transfer material P is supplied to the transfer nip portion N in synchronization with the toner image formed on the surface of the photosensitive drum 1 by the registration sensor 11a.

The transfer material P supplied to the transfer nip portion N is nipped between the photosensitive drum 1 and the transfer roller 5 and conveyed by the rotation of the photosensitive drum 1 and the transfer roller 5. Transfer material P
While the paper is being nipped and conveyed through the transfer nip portion N, the transfer high voltage power supply (transfer high voltage transformer, transfer high voltage circuit) 34 sets a predetermined control timing for the transfer roller 5 contacting the back side of the transfer material P. And a predetermined control transfer bias is applied. As a result, charges having the opposite polarity to the toner image are applied to the transfer material P, and the toner images on the photosensitive drum 1 are sequentially transferred onto the transfer material P.

The transfer material P which has received the transfer of the toner image at the transfer nip portion N and has passed through the transfer nip portion N is separated from the surface of the photosensitive drum 1, and the sheet path (guide member) 12
And is conveyed to the fixing device 13. 8 is a charge elimination needle. The fixing device 13 in this example is a so-called film heating type fixing device which comprises a heating film unit 13a and a pressure roller 13b in pressure contact with each other, and the transfer material P holding a toner image is a heating film unit 13a and a pressure roller 13b. The toner image is fixed on the transfer material P and becomes a permanent image by being nipped and conveyed at the fixing nip portion n which is a pressure contact portion of the sheet and subjected to heat and pressure.

When the one-sided printing mode is selected and designated, the transfer material P exiting the fixing device 13 is guided to the conveyance path B1 side and discharged outside the machine as a one-sided printed matter.

When the double-sided printing mode (automatic double-sided printing) is selected and designated, the transfer material P that has been printed on the first side (image-formed) exiting the fixing device 13 is automatically double-sided as a third paper feed port. The paper is conveyed into the paper feed unit 50, is inverted by passing through the switchback conveyance path B2, and is circulated.
3, the sheet is re-fed to the transfer nip portion N via the re-feeding roller 25 and the re-feeding sensor 25a, and enters the printing process for the second surface of the inverted transfer material P.

The transfer material P, which has received the toner image transferred to the second surface at the transfer nip portion N, is separated from the surface of the photosensitive drum 1, passes through the sheet path 12, and is again fixed to the fixing device 1.
3, the toner image is fixed on the second side, the route is guided to the side of the conveying path B1, and the sheet is discharged outside the apparatus as a double-sided print.

On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is cleaned by the cleaning device 6 to remove the residual transfer toner, and is repeatedly used for image formation. The cleaning device 6 of this example is a blade cleaning device, and 6a is its cleaning blade.

(2) Transfer Roller 5 The transfer roller 5 as a contact transfer member is a solid (filled meat) using a core metal 5a of iron, SUS or the like and EPDM, silicone, NBR, urethane or other rubber on the core metal 5a, or A rubber roller with a foamed sponge-like medium resistance elastic layer 5b formed, with a roller hardness of 25 to 70 degrees (Asker C / total load 9.8N (1k
g) Under load, the same shall apply hereinafter), and the resistance value is in the range of 10 ⁶ to 10 ¹⁰ Ω. The elastic layer 5b of the transfer roller 5 is
After the primary vulcanization, the secondary vulcanization is performed, and then the surface is polished to obtain the outer diameter shape having a desired size.

The transfer roller 5 used in this example has a diameter of 6 mm.
An elastic layer (medium resistance elastic layer) 5b made of 8 × 10 ⁷ [Ω] NBR type ion conductive solid rubber is formed on the Fe core metal 5a, and the roller hardness is 60 degrees and the outer diameter is φ16 m.
m is a solid conductive / elastic roller having a rubber part longitudinal dimension of 218 mm.

As shown in FIG. 2, the transfer roller 5 is rotatably supported by bearing members 5c and 5c at both ends of the core metal 5a. The bearing members 5c, 5c are movable members that are slidably held in the approaching direction and the leaving direction with respect to the photosensitive drum 1 by guide members (not shown), and the movable bearing members 5c, 5c are respectively pressed springs. The transfer roller 5 is pressed against the photosensitive drum 1 against the elasticity of the elastic layer 5b by forming a transfer nip portion N having a predetermined width by urging the transfer roller 5 toward and away from the photosensitive drum 1 by 5d and 5d. I am allowed. G is the core 5 of the transfer roller 5.
The drive gear is fixed to one end of a, and the rotational force is transmitted to the drive gear G from a drive unit (not shown) so that the transfer roller 5 rotates in the forward direction of the rotation of the photosensitive drum 1 and the rotation of the photosensitive drum 1. It is rotationally driven at a peripheral speed almost the same as the peripheral speed.

FIG. 3 is a diagram showing a method for measuring the resistance of the transfer roller 5. That is, the total pressure to the aluminum cylinder 71 is 9.8 N (1
The transfer roller 5 is brought into contact with and rotated at 000 g (500 g on one side), and when an arbitrary voltage (for example, +2.0 kV) is applied to the core metal 5a of the transfer roller 5 from the DC high voltage power source 72, it is applied to both ends of the resistor 74. The voltmeter 73 reads the maximum value and the minimum value of the generated voltage value. The resistance value of the transfer roller is calculated by obtaining the average value of the voltage values flowing in the circuit from the read voltage value. Measurement environment is normal environment N / N: 2
It is 3 ° C and 60%.

(3) Transfer Bias Control In this embodiment, a plurality of transfer bias control systems are set in advance in the transfer bias control system that determines the transfer voltage during printing based on the impedance detection result of the transfer roller 5 by the PTVC and the transfer current detection result via the transfer material. 2 or more control formulas corresponding to the transfer material types are prepared, and the feed port information, that is, the transfer material P is fed to the transfer nip portion N in the case of the present embodiment. Controllable depending on whether it is made from the paper feed cassette unit 22, is made from the manual paper feed tray unit 24 as the second paper feed port, or is made from the automatic double-sided paper feed unit 50 as the third paper feed port Determine the threshold of separation, compare the result of transfer current detection through the transfer material with the threshold,
An example of switching the plurality of control expressions to determine the transfer voltage will be described.

A) PTVC control method The PTVC control method of this embodiment will be described in detail with reference to FIG. 9 is a CPU for controlling the transfer bias, which has a pulse width P corresponding to a desired transfer output voltage from the OUT terminal.
Output WM signal. Actually, a transfer output table (not shown) corresponding to the pulse width is stored in the CPU 9. This PWM signal is a low pass filter (Low Pass Filter).
er) 14 to DC and amplified by the amplifier 15 to become the transfer output voltage Vt. Current value It flowing at this time
The signal corresponding to is input to the IN terminal of the CPU 9, and CP
The flow is such that detection is performed within U9.

In this embodiment, the current value flowing in the transfer high-voltage power supply 34 is detected by the current detection circuit 34a, and the value digitally converted by the A / D converter 31 (hereinafter referred to as "transfer AD value") is sent to the CPU 9. It is input and the value of the current flowing through the transfer roller 5 is determined.

When "constant voltage control" is desired, it is judged from the PWM and transfer output correspondence table set in the CPU 9 in advance, and the pulse width P corresponding to the desired voltage value is determined.
Output WM signal.

When "constant current control" is desired, CP
Gradually increase the pulse width of the PWM signal from U9,
The signal input to the IN terminal of the CPU is continued until it reaches a value corresponding to the desired current value (constant current value), and then the voltage (pulse width) is made to follow along with the change in the current value for constant current control. To do.

B) Transcription control algorithm FIG. 5 shows the transfer control algorithm of this embodiment.

When the print signal is received from the host computer and the charging of the photosensitive drum 1 is completed, first, the PTVC detection is performed once with the photosensitive drum 1 and the transfer roller 5 being in direct contact with each other (Step 1).

In the PTVC detection, the output voltage from the high voltage power supply 34 for transfer is gradually increased and the voltage value when the transfer current reaches a preset constant current value is held as Vt0.

Based on the detection result here, C
The first target value Vt1 of the transfer voltage applied during transfer is determined by the transfer control formula 1 stored in the PU 9 (Step
2).

Vt1 = αVt0 + β (Equation 1) Vt0: Generated voltage α and β generated when a predetermined detection current is applied to the transfer roller during PTVC detection. After determining the constants Vt1 preset by the transfer system, the image When the preparation for formation is completed, the printing operation is started, and the transfer material P is fed to the transfer nip portion N in synchronization with the toner image on the photosensitive drum 1. At the same time when the front end of the transfer material P enters the transfer nip portion N, a constant voltage is applied to the above-mentioned initial transfer target value Vt1 (Step 3), and the transfer current is monitored once after a fixed time from the start of the application of the initial transfer target value Vt1. The transfer AD value detected at that time is recorded in the CPU 9 (Step 4).

The detection timing of the transfer AD value is a point at which the transfer current settles down to some extent after the transfer voltage Vt1 is applied, and it is desirable to detect the transfer AD value within the tip margin in order to eliminate the influence of the presence or absence of toner. In this embodiment, an image forming apparatus that prints at a process speed of 120 mm / sec was used, and the transfer AD value was monitored 40 msec after the front end of the transfer material. In this case, the monitor point of the transfer AD value is a point of about 4.8 mm from the front end of the transfer material, and if the front end margin is about 5 mm, the change in transfer current due to the difference in impedance of the transfer material can be stably monitored. .

Next, the threshold value of the transfer AD value for dividing the control expression is determined based on the transfer material feed port information for the transfer nip portion N (Step 5), and the transfer AD value is set here. The transfer voltage Vt is determined by comparison with the value (Step 5), the transfer voltage Vt determined here is applied to the transfer roller at a constant voltage (Step 6), and transfer is performed to the rear end of the transfer material at a constant voltage.

As shown in the equation 1, the initial transfer target voltage Vt1 is applied according to the detection result of the transfer roller resistance value. This is because when the voltage applied when the transfer material current is detected at the front end of the transfer material has a constant value, a defect on the image due to a difference in the current value flowing at the front end of the transfer material due to the resistance of the transfer roller is prevented. For example, when the transfer roller resistance value is low, if Vt1 is a constant value, an excessive current flows to the photosensitive drum 1 at the leading end of the transfer material to cause density unevenness. Conversely, if the transfer roller resistance value is high, Vt1 changes from Vt1. Since the voltage difference when raising the high voltage to the voltage required for transfer becomes large, it takes time for the necessary current to flow,
This is because an electric current becomes insufficient at the tip of the transfer material and an explosion or transfer failure occurs.

By changing Vt1 according to Vt0 as in the present example, the above-mentioned problems can be prevented, and the impedance of the transfer material can be detected stably with almost the same transfer current.

As the initial transfer target voltage Vt1, it is desirable to apply the minimum transfer voltage required for transferring plain paper in order to raise the transfer voltage to the voltage required for the transfer process in a short time.

FIG. 6 is a diagram showing changes in the transfer current value (AD value) at the leading end of the transfer material when the transfer materials having different resistance values are passed. In this embodiment, the transfer voltage initial target value Vt1 at the time of sheet passing determined based on the PTVC detection result is
Since the optimum current value is set for plain paper, when printing on plain paper, a transfer current (AD value) substantially the same as the target current value is obtained as shown in line A.

On the other hand, when high resistance paper is printed,
As the resistance of the transfer material is high, the current value flowing through the transfer roller is decreased by ΔIdown as shown in the line B.

Therefore, by monitoring the transfer current value (AD value) after an arbitrary time T1 after the transfer material front end reaches the transfer nip portion N, the difference in the transfer current drop due to the transfer material resistance value is known. It is possible to detect whether the transfer material resistance value is high or low.

FIG. 7 shows the relationship between the optimum transfer voltage ranges for plain paper, high-resistance paper on one side, and automatic double-sided printing. The horizontal axis represents the resistance detection result of the transfer roller by PTVC, and the vertical axis represents the applied voltage during transfer.

The thin solid line indicated by (1) in FIG. 7 is a line representing the image margin when printing the first side of plain paper.
When printing on one side of plain paper, if the transfer voltage is too low, the transfer material cannot be supplied with a sufficient transfer current necessary for transfer.
Transfer failure occurs. On the contrary, if the transfer voltage is too high, an excessive current flows to the photosensitive drum, and at that time, a drop in the potential on the photosensitive drum appears in the image, causing punch-through. When the transfer voltage control is set in the range surrounded by the line of defective transfer and the line of punch-through, a good image can be obtained when the first surface of plain paper is printed.

Similarly, the dotted line shown in (1) of FIG. 7 indicates the image margin when printing the first surface of the high-resistance paper, and the required control voltage becomes higher as the transfer material resistance is higher than that when the first surface is printed.
Also, it can be seen that the margin is narrowed because the current required for explosion prevention is increased due to the higher transfer material resistance.

A portion (shaded portion) where the margins of both .. and .. overlap is a control area where good images can be obtained on both plain paper and high resistance paper. In this case, if transfer control as shown by line A is performed, Good images can be obtained on both the first side of the plain paper and the first side of the high-resistance paper.

In the case of printing on the second side, the margin is determined by the phenomenon of explosion on the low voltage side of transfer and white stripes on the high voltage side. White streaks occur when high voltage is applied to the transfer roller.
Discharge occurs before and after the transfer nip, and the polarity of the toner on the photosensitive drum (or transfer material) is reversed due to the discharge, resulting in a transfer failure (or retransfer) phenomenon. The higher the voltage, the more likely it is to occur. Explosion is caused by the nonuniformity of the transfer charge caused by the transfer current flowing more in the dark portion potential Vd with respect to the potential difference between the light portion potential Vl and the dark portion potential Vd on the photosensitive drum. This is a phenomenon in which toner scatters with respect to the Vd portion, and the higher the resistance of the paper, the more difficult the horizontal movement of electric charges on the transfer material in the transfer nip occurs, and the more remarkable the occurrence thereof.

The thin dotted line shown in (2) of FIG. 7 is a line showing the image margin on the second side of the plain paper. In the case of printing on the second side, once passing through the fixing device 13 when printing on the first side,
Since the moisture in the transfer material evaporates and the resistance of the paper becomes high, the current required for explosion prevention rises, and the optimum transfer margin area is entirely shifted to the high voltage side as compared with the first surface of the plain paper. When printing on the second side of plain paper, a high voltage is applied when the transfer roller is on the high resistance side, so the white stripe determines the upper limit of the transfer margin, and when the transfer roller is on the low resistance side, excess current easily flows. The penetration limit determines the soil limit of the transfer margin.

Similarly, the thin solid line shown in (2) of FIG.
Is a line indicating the image margin on the second side of high-resistance paper. Since the transfer material resistance is higher than that on the second side of plain paper, the control voltage is high because it is necessary to prevent explosion, and the white stripes are generated due to discharge. It can be seen that the optimum transfer margin itself has become narrower because it is easier to perform, and the overlap area (the area surrounded by the diagonal lines in the figure) with the optimum transfer margin area on the second side of plain paper has almost disappeared. I understand.

As described above, it is difficult for the transfer material resistances having extremely different resistances to satisfy the image quality by the same transfer control method. In this case, it is necessary to set separate control formulas for plain paper and high-resistance paper, such as line B and line C shown in (2) of FIG.

FIG. 8 uses the image forming apparatus of this embodiment,
Single-sided printing and automatic double-sided printing on plain paper (volume resistivity: 1 × 10 ¹¹ Ω · cm) and high-resistance paper (volume resistivity: 1 × 10 ¹³ Ω · cm) at a process speed of 120 mm / sec. The detection result of the transfer AD value at the front end of the transfer material is shown.

The environment is a high humidity environment (humidity 85% R
H), normal humidity environment (humidity 60% RH), low humidity environment (humidity 1
Each environment of 5% RH) was used, the AD value was monitored once 40 msec from the tip of the transfer material, and the results are plotted for each environment. The AD value shown here is a value proportionally converted to 256 steps from 0 to 255 so that the AD value becomes 160 when the transfer current is 6 A.

The transfer voltage is the voltage generated when PTVC detection is performed at a constant current value of 6 μA and the CPU beforehand.
The value calculated based on the following control equation 2 stored in 9 is applied.

Vt1 = 0.7 × Vt0 + 700 Equation 2
(All units are [V]) As shown in FIG. 8, it can be seen that the transfer AD value of the high resistance paper is smaller than that of the plain paper. Regarding the environmental humidity, the higher the humidity, the higher the humidity in which the transfer material immediately absorbs, and the higher the transfer AD value becomes.
There is a tendency that the D value is large. When the resistance of the transfer material is low in this way, an appropriate amount of charge transfer occurs on the transfer material, so that an explosion is less likely to occur, and conversely, current easily flows through the transfer material to the photosensitive drum, resulting in punch-through, etc. Image problems are likely to occur. For the transfer material in such a state, it is preferable to set the transfer voltage control in a direction to prevent punch-through (to weaken the transfer current).

On the contrary, it can be seen that the AD value becomes low in a low humidity environment or high resistance paper. This decrease in the AD value is particularly noticeable in high-resistance paper having a high transfer material resistance, and in the transfer material in such a state, it is difficult for charges to move in the transfer nip, and an explosion is likely to occur. On the contrary, in the transfer material in such a state, since the current flowing through the transfer material to the photosensitive drum is small, the punch-through hardly occurs. Contrary to the state in which the AD value is large, a large amount of current is supplied to prevent the explosion. Transfer voltage control should be set.

In the present invention, the threshold value for dividing the transfer control is determined with reference to the paper feed port through which the transfer material is fed.

This is the AD at the tip of the transfer material in a low humidity environment.
When the transfer material type is cut based on the value detection result, since the transfer material does not absorb moisture from the beginning, the impedance change of the transfer material of the first side printing and the second side printing is small, and the cut of the printing surface and the transfer material resistance value This is because it is difficult to separate them. Even in the same second-side printing, there is a difference in time between automatic double-sided printing and manual double-sided printing until the second-side printing starts after the first-side printing. Although different, the difference in the transfer AD value at this time is small, and it is difficult to separate them.

Table 1 shows the transfer AD value and the transfer margin current when the image forming apparatus shown in this example is used to print single-sided and double-sided plain paper and high-resistance paper in a normal humidity environment.

[0080]

[Table 1]

As shown in Table 1, both plain paper and high resistance paper are 1
The second surface printing in which the water content of the transfer material once evaporates after passing through the fixing device 13 is lower than that of the first surface printing, and the transfer AD value is generally low, and the second surface becomes high resistance. Has less transfer current and is more likely to explode. For this reason,
It is necessary to apply a higher voltage to the second surface than to the first surface. Further, it can be seen that the high resistance paper requires higher voltage on both sides.

Further, as shown in Table 1, automatic double-sided 2
With double-sided printing and double-sided printing, the time for printing on the second side after printing on the first side is faster in automatic double-sided printing, and the transfer material after printing on the first side passes through the machine and is printed on the second side without being exposed to the outside air. Due to the fact that it is provided for
It can be seen that the transfer current required to prevent explosion is higher than when printing on the surface. On the other hand, the difference between the transfer AD values at the tip of the transfer material is small, and it is difficult to distinguish the two. Further, it can be seen that in a low humidity environment, the difference in the transfer AD value due to the resistance of the transfer material is small, and it is difficult to distinguish the printed surface.

In the present invention, the transfer AD value is detected in the margin of the transfer material in order to eliminate the change in the transfer current depending on the presence or absence of an image. However, at this detection timing, the transfer AD value is detected in a state where the transfer current does not completely relieve the candy. Therefore, the deviation due to the variation in the transfer speed of the transfer material tip on the software and the actual transfer material tip causes a deviation in the CPU. The transfer AD value is detected with a certain degree of variation due to a deviation in the timing of the detection time due to an error in the timer count.

Therefore, there is a possibility that an erroneous detection may occur.

Therefore, in order to determine the optimum transfer control method under any condition, the present invention estimates the printing surface from the paper feed port information, and sets the threshold value of the transfer control separation according to the printing surface. The accuracy of the transfer material resistance is improved by making the determination.

In this embodiment, three control expressions are prepared as shown in Expression 3, Expression 4, and Expression 5 below. The relationship between the transfer voltages calculated from Expression 3, Expression 4, and Expression 5 is Vt1l <Vt1m <Vt1.
h.

Vt1l = 0.7 × Vt0 + 800 ... Equation 3 (control equation for the first surface of plain paper and the first surface of high-resistance paper, all units are [V]) Vt1m = 0.8 × Vt0 + 900 ... Equation 4 ( Control formula for the second surface of plain paper, all units are [V]) Vt1h = 0.8 × Vt0 + 1100 ... Equation 5 (Control formula for second surface of high resistance paper, all units are [V]) In this embodiment, Assuming that there are three paper feed openings, that is, cassette feed, manual feed, and automatic double-sided feed, the threshold of the AD value is set as shown in Table 2. When feeding from the automatic double-sided paper feed port, the printing side is specified as the second side only, and the threshold value is set mainly for separating the transfer material type. On the contrary, cassette feeding is only one side printing. Therefore, it is also set to separate the transfer material type.
The threshold value is set on the assumption that both single-sided printing and manual double-sided printing are performed from the manual feed port.

Table 2 shows the transfer AD threshold value of each sheet feeding port,
The corresponding transcription control formula is shown. In the image forming apparatus used in this embodiment, AD = 120 corresponds to a transfer current of 4.5 μA.

[0089]

[Table 2]

The transfer voltage Vt determined here is applied to the transfer roller immediately after the detection of the transfer AD value, but the high voltage rises to the target value in about 10 msec, and an image defect due to the switching of the transfer bias occurs. There wasn't.

Printing was performed on plain paper and high-resistance paper in each environment with the image forming apparatus to which this embodiment was applied. In each case, good images were obtained without explosion or penetration.

In this example, three transfer control formulas are prepared,
One transfer AD value threshold value for each paper feed port,
Alternatively, two control equations are selected, but any number of control equations may be set in advance as long as two or more control equations are set. In that case, transfer A according to the set number of control formulas
The threshold value of D value is set.

As described above, in the system that uses the PTVC control method and determines the transfer voltage during printing based on the result of detection of the transfer material resistance at the transfer material front end, the threshold value for performing the control type separation is supplied. By determining with reference to the paper edge information, the transfer material resistance value and the accuracy of separating the printing surface are improved, and it becomes possible to obtain a good image on each of the transfer material and the printing surface.

<Embodiment 2> (FIGS. 9 and 10) In this embodiment, in the image forming apparatus which determines the transfer voltage by monitoring the transfer current when the front end of the transfer material enters the transfer nip portion N, transfer is performed. An example is shown in which the transfer AD value, which serves as a threshold for selecting the transfer voltage applied inside, is changed with reference to the feed port information and the transfer roller resistance detection result.

As described in the above embodiment, the transfer AD value changes depending on the resistance value state of the transfer material P, but the transfer AD value of the transfer roller 5 as the transfer member is as shown in FIG. It also changes depending on the resistance value.

FIG. 9 shows the resistance detection result by PTVC on the abscissa, showing that the transfer roller resistance value is higher toward the right, and the transfer A of the plain paper 2 surface and the high resistance paper 2 surface against that is shown.
The D value is plotted.

The difference in the transfer current caused by the difference in the resistance value of the transfer material P is caused when the increase rate of the impedance of the entire transfer system when the transfer material P is contained is high with respect to the impedance of the transfer system during non-transfer. Grows to. When the impedance of the entire transfer system at the time of non-transfer is low, the difference in the transfer current due to the difference in the resistance value of the transfer material P is large, and the drop amount of the transfer AD value when using high-resistance paper is also large. Conversely, when the impedance of the entire transfer system is high, the current difference due to the resistance value difference of the transfer material P is also small, and as a result, the drop amount of the transfer AD value when using high-resistance paper is smaller than that of plain paper.

As described above, the change amount of the transfer AD value also changes according to the resistance value of the transfer roller 5. In particular, in an image forming apparatus in which the resistance value of the transfer roller 5 used is greatly changed due to environmental changes, it becomes difficult to set the threshold value of the transfer AD value while ignoring the change in the resistance value of the transfer roller 5.

In the case of the image forming apparatus having such a transfer structure, in order to take this difference into consideration, the threshold value for determining the transfer voltage is referred to the paper feed port information as described in the first embodiment. In addition to this, it may be changed according to the detection result of PTVC.

As a result, the resistance value of the transfer material can be divided regardless of the resistance value of the transfer roller 5, and a good image can be obtained.

In this embodiment, as shown in FIG. 10, the transfer AD threshold value is set as a function of the transfer roller resistance detection result and the transfer AD value.

As a result of the transfer roller resistance detection by PTVC, Vt0, using the image forming apparatus having the same structure as in the first embodiment.
And the relationship between the transfer AD value at the front end of the transfer material at the time of printing the first and second surfaces of plain paper and high-resistance paper.
℃), normal temperature environment (temperature 23 ℃), low temperature environment (temperature 15
C.), and determined the transcription control by the transcription AD threshold method shown in Table 3.

The image forming apparatus used here uses a transformer having a maximum transfer voltage output of 5 kV.
t0 is detected in the range of 0.5 kV to 4 kV, and in the formula shown in Table 3, Vt0 is represented as a PWM value (expressed as PWM0) obtained by dividing the maximum voltage of the transformer of 5 kV into 256.

[0104]

[Table 3]

In the image forming apparatus to which this embodiment is applied, plain paper, high-resistance paper on one side, automatically in high temperature environment (temperature 32.5 ° C.), room temperature environment (temperature 23 ° C.), and low temperature environment (temperature 15 ° C.) Double-sided printing was performed, but good images were obtained in any environment and on the printed surface.

As described above, in the system in which the transfer control is determined by detecting the transfer current at the front end of the transfer material, the threshold value for determining the transfer control by the transfer AD value is determined by referring to the transfer roller resistance detection result. As a result, the accuracy of the transfer material resistance value division can be improved, and a good image can be obtained regardless of the transfer roller resistance and the environment.

<Embodiment 3> (FIG. 11) In this embodiment, in the image forming apparatus for monitoring the transfer current when the leading end of the transfer material enters the transfer nip portion N to determine the transfer voltage, the voltage is applied during transfer. An example is shown in which the transfer AD value, which serves as a threshold for selecting the transfer voltage to be set, is changed with reference to the paper feed port information and the size information of the transfer material that is passed through the apparatus.

In this embodiment, the transfer AD threshold is set to three paper feed ports of manual paper feed, cassette paper feed, and automatic double-sided paper feed.
A4 / Letter / Large size system and B5 /
It was set for each combination of two small size paper sizes such as executives.

FIG. 11 shows the difference between the transfer AD values when the transfer materials having the same resistance value and different sizes are printed.
As shown in FIG. 11, in the A4 size paper having a width of 210 mm and the letter size paper having a width of about 216 mm, the transfer AD values flowing at the leading end of the transfer material are almost the same.
The B5 size paper of mm and the executive size paper of about 184 mm width each have a transfer AD value larger than that of the A4 size paper and the letter size paper. This is A4 size,
During the passage of the letter size transfer material, almost the entire length of the medium resistance elastic layer portion 5b of the transfer roller 5 is the transfer material paper passage area, whereas in the case of B5 size or executive size, a part of the paper passage area is provided. This is because there is a region where the transfer roller elastic layer portion 5b directly contacts the photosensitive drum 1 because there is only a transfer material, and a transfer current flows directly from the transfer roller 5 to the photosensitive drum 1 in that region. Therefore, when the transfer material resistance value is the same, the smaller the transfer material width, the larger the transfer AD value.

Therefore, when the transfer material P having a narrow width is used, it is necessary to set the threshold of the transfer AD in consideration of the paper size in order to determine the optimum transfer voltage.

In this embodiment, when the transfer material size is designated, the transfer voltage is determined by referring to the transfer material size information and setting the threshold values as shown in Table 3 below.

As shown in Table 4, in this embodiment, the transfer AD threshold value is uniformly shifted by 20 depending on the transfer material size.

In order to deal with irregular sizes, a sensor for detecting the transfer material width is provided in the transfer material conveying path, and the transfer AD threshold value is changed according to the detection result of the transfer material width detection sensor. You may.

Further, the transfer A is performed by referring to both the transfer roller resistance value detection result and the transfer material size information described in the above embodiment.
You may set a D threshold value.

[0115]

[Table 4]

As in this example, by referring to the transfer material size information, the accuracy of separating the transfer material resistance value is improved,
In any case, a good image can be obtained regardless of the transfer material size.

<Others> 1) Formation of a toner image on an image bearing member is not limited to an electrophotographic process using an electrophotographic photosensitive member as an image bearing member. An image forming method for forming and carrying a toner image on the image carrier may be used, such as an electrostatic recording process using a magnetic recording process using a magnetic recording magnetic substance as an image carrier.

2) The contact transfer member is not limited to the form of a roller body, but may be a form of a rotary belt body.

3) In the present invention, the transfer material includes an intermediate transfer material such as an intermediate transfer belt or an intermediate transfer drum.

[0120]

As described above, according to the present invention, P
In addition to the transfer control method in which the transfer voltage is determined by TVC control, a transfer voltage according to the PTVC detection result is applied to the transfer material from the transfer material front end, and transfer is performed after a certain time has elapsed since the transfer material front end was inserted into the transfer nip portion. The current value is monitored, and the optimum applied voltage is determined from a plurality of transfer voltage values optimized in advance for transfer materials having different resistance values from the transfer current monitoring result at the transfer material tip and the feed port information. By applying a constant voltage during printing, a good image can be obtained with a transfer material having any resistance value.

Furthermore, by referring to the transfer roller resistance detection result, paper size information, etc., it is possible to set the transfer voltage more optimally.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an example of an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is an explanatory diagram of the structure of a transfer roller.

FIG. 3 is an explanatory diagram of a transfer roller resistance measuring method.

FIG. 4 is an explanatory diagram of PVTC control.

FIG. 5 is a flowchart of a transfer control algorithm according to the first embodiment.

FIG. 6 is a diagram illustrating changes in the transfer current at the tip of the transfer material.

FIG. 7 is a diagram showing a relationship between each transfer material type and an image margin of a printing surface.

FIG. 8 is a schematic diagram showing the relationship between the transfer AD value depending on the environment and the transfer material type.

FIG. 9 is a transfer roller resistance value and transfer A in the second embodiment.
The figure which shows the relationship of D value

FIG. 10 is a diagram showing transfer AD value setting.

FIG. 11: Transfer material size and transfer AD in Example 3
Diagram showing value relationships

[Explanation of symbols]

1 ... Photosensitive drum, 5 ... Transfer roller, 11a ... Registration sensor, 21a ... Paper feed sensor, 21a ... Paper feed sensor, 32 ... DC controller, 34 ... High voltage power supply for transfer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akito Kanamori             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA39 DC04 DC19 DC20 DE04                       DE07 DE10 EA03 EC06 EC20                       ED17 ED18 ED24 EE07 EF10                       FA05 FA13 FA15                 2H200 FA18 GA14 GA16 GA18 GA23                       GA34 GA45 GA54 GA59 GB12                       GB26 GB50 HA03 HA28 HB12                       HB22 HB45 HB46 HB47 HB48                       JA02 JA25 JA26 JA27 JA28                       JA29 MA03 MA08 MA20 MB06                       MC02 NA02 NA08 NA09 NA15                       PA05 PA10 PA20 PA23 PA29                       PB05 PB08 PB12 PB38

Claims (2)

[Claims] 1. An image carrier, a transfer member which forms a pressure contact nip portion with the image carrier, and transfers a toner image on the image carrier to a transfer material inserted in the pressure contact nip portion, and the transfer member. A voltage applying unit for applying a voltage, a current detecting circuit for detecting a current value output from the voltage applying unit, and a current detecting circuit for detecting a current after a fixed time has elapsed since the transfer material was inserted in the pressure contact nip portion. Control for determining the output voltage of the voltage applying unit from a plurality of transfer voltage values prepared in advance with reference to the result and the paper feed port information, and applying the determined voltage from the voltage applying unit to the transfer member during printing. An image forming apparatus comprising: 2. An image carrier, a transfer member which forms a pressure contact nip portion with the image carrier, and transfers a toner image on the image carrier to a transfer material inserted in the pressure contact nip portion, and the transfer member. Voltage applying means for applying a voltage, a current detecting circuit for detecting a current value output from the voltage applying means, and resistance detecting means for detecting the resistance of the transfer member in the absence of the transfer material in the pressure contact nip portion. The output voltage of the voltage applying unit is determined from a plurality of transfer voltage values prepared in advance by referring to the current detection result of the current detection circuit and the paper feed port information after a predetermined time has elapsed since the transfer material was inserted into the pressure contact nip portion. And a control means for applying the determined voltage from the voltage application means to the transfer member during printing, and a threshold value for determining the applied voltage is set to the transfer member of the resistance detection means. Resistance detection result , An image forming apparatus and changes with reference to at least one of the information of the transfer material size information.