JPH09138588A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily maintain transfer efficiency even in the case an amount of toner which is stuck to an image carrier varies, in an electrophotographic image forming device. SOLUTION: The device is a laser printer I in which an electrifying charger 111, a laser scanning optical unit 112, a developing device 113, and a transfer roller 114 are arranged round the photoreceptor drum 100. A test toner image is formed on the photoreceptor drum 100 under the same conditions which are used for the subsequent toner-image formation. Power subjected to constant- current controls is supplied to the transfer roller 114 from a high voltage power source 121, thereby transferring the test toner image to a transfer sheet S. The value of a voltage generated at this time is detected, and feedback on the detected voltage value is provided for constant-voltage control which is exerted in the subsequent toner-image transfer process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus for transferring a toner image formed on an image carrier onto a transfer material.

[0002]

2. Description of the Related Art Generally, in a toner image transfer process of an electrophotographic copying machine or a printer, an electric charge is applied from a transfer roller to the back surface of a transfer sheet conveyed to a transfer position of a photoconductor drum, and the charge is transferred onto the photoconductor drum. The toner image formed on the transfer paper is electrostatically adsorbed on the transfer paper. By the way, in order to cope with the fluctuation of the resistance value of the transfer roller or the transfer material, there is a need for a method disclosed in Japanese Patent Laid-Open No. 5-3238
In Japanese Patent Laid-Open No. 05-2005, before the transfer of a toner image, when the front end of the transfer material is inserted between the photosensitive drum and the transfer roller, constant-current-controlled power is supplied to the transfer roller at that time. It is described that the voltage value to be generated is held, and thereafter, the electric power which is constant-voltage controlled by the held voltage value is supplied to the transfer roller to transfer the toner image to the transfer material.

[0003]

However, it has been difficult for the conventional transfer device to maintain a high transfer efficiency in any case. The reason is that the amount of toner adhered onto the photosensitive drum changes due to environmental changes such as temperature / humidity, the degree of deterioration of the photosensitive member, and density adjustment by the operator.
This is because, in spite of the change in the required transfer voltage, in the conventional transfer device, the voltage value held immediately before the transfer does not include the change in the toner adhesion amount as a measured value. Therefore, image blurring occurs due to transfer failure, or density deficiency occurs even when the density is adjusted to a high density.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to maintain good transfer efficiency even when the amount of toner adhering to the image carrier changes, and to eliminate image blurring and insufficient density. An object of the present invention is to provide an image forming apparatus capable of performing the same.

In order to achieve the above object, the image forming apparatus according to the present invention, the toner image formed on the image carrier,
Means for forming a test toner image on the image carrier under the same conditions as the subsequent toner image formation in an image forming apparatus for transferring an electric charge from a transfer electrode to a transfer material in close contact with the image carrier. A constant current controlled electric power is supplied to the transfer electrode to transfer the test toner image onto a transfer material, and the value of the voltage generated at this time is detected. A transfer control means for supplying a constant voltage controlled electric power to the transfer electrode based on
It has. Here, the transfer material means a transfer paper, an intermediate transfer belt, an intermediate transfer drum, or the like.

In the above arrangement, the test toner image is transferred onto the transfer material under constant current control prior to the transfer of the toner image originally formed as an image, and the value of the voltage generated at the transfer electrode at this time is detected. To do. Next, when transferring the original toner image, constant voltage control is performed based on the detected voltage value to transfer the toner image onto the transfer material. Because the test toner image is formed under the same conditions as the original toner image, environmental changes,
The amount of adhesion is the same as the original toner image, regardless of the degree of deterioration of the photoconductor and the adjustment of image density. In the present invention, since such a test toner image is actually transferred and the transfer voltage is monitored to control the transfer voltage in the original toner image transfer process,
The transfer efficiency is always good, and it is possible to eliminate image blurring and insufficient density.

Further, according to the present invention, when the transfer material is a transfer paper, the test toner image is transferred to the transfer electrode under constant current control, and the voltage value at this time is monitored to perform the original operation. It may be fed back to the constant voltage control at the time of transferring the toner image. In this case, not only good transfer efficiency can be maintained, but also extra consumption of transfer paper can be eliminated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. The embodiments described below apply the present invention to a laser printer.

(First Embodiment, see FIGS. 1 to 3) In the present laser printer, a charging charger 111, a laser scanning optical unit 112, and a developing device 113 are provided around a photosensitive drum 100 that is rotationally driven in the direction of arrow a. , Transfer roller 11
4. A cleaner 115 for residual toner and an eraser 116 for residual charge are provided.

The surface of the photosensitive drum 100 is first uniformly charged to a predetermined potential by the charging charger 111, and an electrostatic latent image is formed by the laser beam emitted from the laser scanning unit 112. This electrostatic latent image is developed by the developing device 11.
3 visualizes as a toner image. On the other hand, the transfer paper S is conveyed between the photoconductor drum 100 and the transfer roller 114 from a paper supply unit (not shown), and the high voltage power supply 121 supplies power to the transfer roller 114, whereby the toner image is transferred to the transfer paper S. Transcribed on. At this time, the transfer roller 1
The transfer voltage supplied to 14 has a polarity opposite to the charging polarity of the toner, and the control of the voltage value will be described in detail below.

After the transfer step, the transfer paper S is sent to the fixing device 118 by the conveyor belt 117 to fix the toner, and is discharged to the outside of the machine.

By the way, in this laser printer, immediately before the original printing operation, under the same conditions as the original toner image, that is, under the same charging voltage / exposure amount / developing bias voltage,
A test toner image is formed on the photosensitive drum 100 using the same toner. This test toner image is, for example, a black solid image having a length of 200 mm and a width of 40 mm in the rotation direction of the photosensitive drum 100, and the transfer paper S of the same type has a constant current controlled electric power controlled to a predetermined current value. Is supplied to the transfer roller 114 from the high-voltage power supply 121 to transfer.

FIG. 2 shows an IV characteristic which is the relationship between the transfer current I and the voltage V of the transfer roller 114 when the test toner image is transferred onto the transfer paper S. Lines B ₁ , B ₂ and B ₃ are
The amount of toner adhered to the photosensitive drum 100 is about 0.
4 mg / cm ² , about 0.7 mg / cm ² , about 1.0 mg /
The characteristics at cm ² are shown. The thick line shows the range where good transfer efficiency is obtained at each adhesion amount. In this laser printer, the toner adhesion amount is 0.4 to 1.0 mg / c due to environmental changes, the degree of deterioration of the photoconductor, and the density adjustment by the operator.
It has been found to change in the range of m ² .

When the current value is set to I ₀ and constant current control is performed, the voltage V ₁ ,
V ₂ and V ₃ are generated. This voltage value is detected, and thereafter, when the original toner image is transferred, the high voltage power supply 121 is controlled to a constant voltage based on this detected voltage value.

Conventionally, the voltage monitoring by the transfer of the test toner image is not executed, and the voltage is about 0.7 mg / cm ^2.
Since the transfer voltage was controlled by using the adhesion amount of (see line B _{2 in} FIG. 2) as a standard, it was not possible to cope with the case where the adhesion amount changed as shown by lines B ₁ and B ₂ . However, in the present embodiment, the transfer voltage can be controlled to an appropriate value corresponding to the change in the toner adhesion amount, and the transfer can always be performed with good efficiency.

If the current value I ₀ is very small during the transfer of the test toner image, it may be difficult to control the high-voltage power supply 121 with a constant current with high accuracy. In this case, the current value may be set to I ₀ ′, the generated voltages V ₁ ′, V ₂ ′ and V ₃ ′ may be detected and converted into voltages V ₁ , V ₂ and V _3. . The IV characteristic for various toner adhesion amounts is used as an arithmetic expression or as a look-up table C
If it is stored in the ROM of the PU, this kind of conversion can be easily performed.

FIG. 3 shows a power supply control circuit 120 for the transfer roller 114. High-voltage power supply (transformer) 121 is a CPU
Switching control section 1 controlled by
A constant current / constant voltage control is performed by 22. The terminal T _C of the CPU outputs a switching signal for constant current control and constant voltage control,
The terminal T _I outputs a constant current value setting signal, and the terminal T _V outputs a constant voltage value setting signal. Further, the transfer output voltage monitor signal is input to the terminal T _M. Electric power is output from the output terminal T _OUT of the high voltage power supply 121 to the transfer roller 114. The output voltage detection point P ₁ is connected to the terminal T _M and the comparator IC ₁ . The output current detection point P ₂ is connected to the comparator IC ₂ .

The CPU first outputs the current value I ₀ or I ₀ ′ from the terminal T _I , outputs the constant current control signal from the terminal T _C , and turns on the high voltage power supply 121. During this constant current control,
The test toner image and the transfer paper S reach the transfer position, and the test toner image is transferred to the transfer paper S. At this time, the voltage value of the output terminal T _OUT is detected at the terminal T _M. Since the detected voltage value at the terminal T _M does not necessarily match the output voltage value at the output terminal T _OUT , the CPU calculates an appropriate voltage value from the data stored in the ROM.

Next, the CPU outputs the calculated voltage value from the terminal T _V and further outputs the print operation start signal or the print ready signal. When the actual printing operation is started, the CPU outputs a constant voltage control signal from the terminal T _C at a predetermined timing to turn on the high voltage power supply 121.
As a result, the high voltage power supply 121 is controlled to a constant voltage, and the original toner image is transferred onto the transfer paper S.

(Second Embodiment, see FIGS. 4 to 6) This second
The embodiment is an application of the present invention to a laser printer having the same configuration as that of the first embodiment shown in FIG. 1, in which a test toner image is transferred to a transfer roller 114 instead of the transfer paper S. The power supply control circuit for the transfer roller 114 is also the same as the control circuit 120 shown in FIG.

Further, the transfer roller 114 is provided with a cleaner 130 for removing the transferred test toner image. The cleaner 130 includes a cleaning blade 131 and a toner storage box 132. In the second embodiment, immediately before the original printing operation, the photosensitive drum 100 is printed under the same conditions as the original toner image.
Form a test toner image on top. This test toner image is transferred to the transfer roller 11 by applying constant-current controlled power to a predetermined current value.
4 is transferred to the surface of the transfer roller 114.

FIG. 5 shows an IV characteristic which is a relationship between the transfer current I and the voltage V of the transfer roller 114 in the transfer step. Lines B ₁ , B ₂ and B ₃ indicate that the toner adhesion amount to the photosensitive drum 100 is about 0.4 mg, respectively, as in FIG.
/ Cm ² , about 0.7 mg / cm ² , about 1.0 mg / cm ²
The characteristics at the time of are shown. When the current value is set to I ₀ and constant current control is performed, voltages V ₁ ″, V ₂ ″, and V ₃ ″ are generated on the transfer roller 114 according to the amount of adhesion, and the values are detected by the CPU. In the second embodiment, since the test toner image is transferred to the transfer roller 114 without the transfer sheet S intervening, the voltages V ₁ ″, V ₂ ″, and V ₃ ″ are the voltages V when the transfer sheet S is intervening. _It is lower than ₁ , V ₂ and V ₃ . So, CP
The lookup table having the characteristics shown in FIG. 6 is stored in the ROM of U, and the detection voltages V ₁ ″, V ₂ ″, and V ₃ ″ are converted into transfer voltages V ₁ , V ₂ , and V ₃ , respectively. During the next printing operation, the high voltage power supply 121 is controlled to a constant voltage based on the converted voltages V ₁ , V ₂ and V ₃ .

(Third Embodiment, See FIGS. 7 to 9) In the third embodiment, the present invention is applied to a full-color laser printer. As shown in FIG. 7, the full-color laser printer generally includes a photoconductor unit 10 having a photoconductor drum 11 that is rotationally driven in the direction of arrow a, a laser scanning optical unit 20, and a full-color developing unit 30.
And an intermediate transfer unit 40 having an endless intermediate transfer belt 41 that is driven to rotate in the direction of arrow b, and a paper feed unit 60.

A charging brush 12 and a cleaner 13 are further installed in the photoconductor unit 10, and a back portion of the cleaner 13 is a waste toner storage chamber 14. Charging brush 1
2 uniformly charges the surface of the photoconductor drum 11 to a predetermined potential. The cleaner 13 scrapes off the toner remaining on the photosensitive drum 11 by the blade 13a.

The laser scanning optical unit 20 is a well-known one having a laser diode, a polygon mirror and an fθ optical element built-in, and its control section has C (cyan), M (magenta), Y (yellow) and Bk (black). The print data for each is transferred from the host computer. The laser scanning optical unit 20 sequentially outputs print data for each color as a laser beam, and scans and exposes the photosensitive drum 11. As a result, an electrostatic latent image for each color is sequentially formed on the photosensitive drum 11.

The full color developing unit 30 includes C, M,
Four color developing devices 31C, 31M, 31Y, 31Bk containing developers containing Y and Bk toners are integrated, and can be rotated clockwise by one step with the support shaft 33 as a fulcrum. . Each developing device includes a photoconductor drum 11
Each time an electrostatic latent image of each color is formed, the developing sleeve 32 of the corresponding developing device is rotated and switched so as to be located at the developing position facing the photoconductor drum 11.

In the intermediate transfer unit 40, the intermediate transfer belt 41 is endlessly stretched over the drive roller 42, the support roller 43, and the tension rollers 44 and 45, and in the direction of arrow b in synchronization with the photosensitive drum 11. It is driven to rotate. A projection (not shown) is provided on a side portion of the intermediate transfer belt 41. The microswitch 49 detects the projection, thereby controlling image forming processes such as exposure, development, and transfer. The intermediate transfer belt 41 is pressed by the rotatable primary transfer roller 46 and comes into contact with the photosensitive drum 11, and this contact portion is the primary transfer portion T ₁ . In addition, the intermediate transfer belt 41
Is exposed to the horizontal conveyance path 65 of the transfer sheet at the portion supported by the support roller 43, and is in contact with the rotatable secondary transfer roller 59. This contact portion is the secondary transfer portion T ₂ .

Further, the intermediate transfer unit 40 is provided with a cleaner 50. The cleaner 50 has a blade 51 for scraping residual toner on the intermediate transfer belt 41. The blade 51 and the secondary transfer roller 59 can be brought into contact with and separated from the intermediate transfer belt 41 at a predetermined timing. The paper feed unit 60 includes a paper feed tray 61, a paper feed roller 62, and a timing roller 63, which can be opened on the front side of the printer body 1 (on which the operator is normally located).
It is composed of The transfer sheets S are stacked on the paper feed tray 61, and are rotated one by one by the rotation of the paper feed roller 62.
The paper is fed to the right in the middle and is sent out to the secondary transfer portion T _{2 in} synchronization with the image formed on the intermediate transfer belt 41 by the timing roller 63. The horizontal conveyance path 65 of the transfer paper is composed of an air suction belt 66, etc., and the transfer paper is fixed by the fixing device 7.
From 0, it is discharged onto the upper surface of the printer main body 1 through the transport rollers 76, 77, 78.

Here, the outline of the full-color printing operation in the third embodiment will be described. At the start of the printing operation, the secondary transfer roller 59 and the cleaning blade 51 are separated from the intermediate transfer belt 41. When the printing operation is started, the photosensitive drum 1
1, the intermediate transfer belt 41 is rotationally driven in the direction of arrow a at the same circumferential speed in the direction of arrow b, and the photosensitive drum 11 is charged to a predetermined potential by the charging brush 12.

Subsequently, the laser scanning optical unit 20 exposes the cyan image, and an electrostatic latent image of the cyan image is formed on the photosensitive drum 11. This electrostatic latent image is immediately developed by the developing device 31C, and the toner image is transferred onto the intermediate transfer belt 41 at the primary transfer portion T ₁ . Immediately after the end of the primary transfer, the developing device 31M is switched to the developing position, and then exposure, development, and primary transfer of the magenta image are performed. Thereafter, similarly, switching to the developing device 31Y, exposure, development, and primary transfer of the yellow image are performed. Further, switching to the developing device 31Bk, exposure of black image, development,
Next transfer is performed, and the toner image is superposed on the intermediate transfer belt 41 for each primary transfer.

When the final primary transfer is completed, the development unit is
Switch 30 to developing device 31C for the next print processing.
The secondary transfer roller 59 and the cleaning are simultaneously changed.
The blade 51 comes into pressure contact with the intermediate transfer belt 41. This and
When the transfer paper S is the secondary transfer portion T _TwoIs sent to and intermediate transfer
The full-color toner image formed on the belt 41 is the transfer paper.
Transcribed on S. When this secondary transfer is completed, the secondary transfer
Image transfer roller 59 and cleaning blade 51 are intermediate transfer
Separated from the belt 41.

In this full-color laser printer, the transfer of the toner image is performed by the primary transfer section T ₁ and the secondary transfer section T ₂ . In the primary transfer, as shown in FIG. 8, power is supplied from the high voltage power supply 121 to the transfer roller 46. Similar to the first embodiment, a test toner image is formed on the photoconductor drum 11 immediately before the printing operation. In this case, the high voltage power supply 121 is controlled on the intermediate transfer belt 41 by constant current control to form the test toner image. Transfer, detect the transfer voltage at that time,
It is fed back to the constant voltage control during the next print operation.

It is also possible to transfer the second color, the third color, the fourth color, and the test toner images on the intermediate transfer belt 41 in an overlapping manner and detect the transfer voltage under the constant current control.

In the secondary transfer, as shown in FIG.
Electric power is supplied to the transfer roller 59 from the high voltage power supply 121.
In this case, the four-color test toner images superposed on the intermediate transfer belt 41 are transferred onto the transfer paper S by controlling the high voltage power supply 121 at a constant current. Detect the transfer voltage at that time,
It is fed back to the constant voltage control during the next print operation. In the case of a mono-color print, the test toner image at the time of secondary transfer has only one color.

A power supply control circuit for the high voltage power supply 121 for supplying power to the transfer rollers 46 and 59 is the same as the control circuit 120 shown in FIG.

(Fourth Embodiment, see FIG. 10) This fourth embodiment is one in which the present invention is applied to a full-color laser printer having the same structure as the third embodiment shown in FIG. In the transfer section, a transfer roller 47 is installed on the downstream side in the traveling direction b, and an insulating guide roller 48a is installed on the upstream side. Electric power is supplied to the transfer roller 47 from the high voltage power supply 121. High voltage power supply 121
The control circuit 120 shown in FIG. 3 controls the constant current when the test toner image is transferred, and controls the constant voltage when the original toner image is transferred based on the detected voltage.

In the fourth embodiment, since the transfer roller 47 is arranged on the downstream side of the transfer portion, even if the transfer roller 47 is made of a metal low resistance material, the overcurrent flowing through the pinhole of the photoconductor is not affected. As a result, the intermediate transfer belt 41 can be prevented from being damaged. Further, the contact portion between the intermediate transfer belt 41 and the photoconductor drum 11 becomes long, and even if a relatively high transfer voltage is applied, discharge before transfer to the toner is prevented.
Therefore, the transfer can be performed with high transfer efficiency.

(Fifth Embodiment, see FIG. 11) In the fifth embodiment, as in the fourth embodiment, a transfer roller 47 is installed on the downstream side of the transfer portion and a conductive guide roller is installed on the upstream side. 48b is installed, and the guide roller 48b is connected to the high voltage power source 12
1 was electrically connected to the return side. When a member having a potential different from that of the transfer roller 47 is arranged near the transfer roller 47, a part of the total current Ia output from the high voltage power supply 121 leaks as a leakage current Is. When the leakage current Is is present, when the total current Ia is controlled by the constant current, the detection sensitivity of the voltage generated according to the toner adhesion amount during the test toner image transfer is lowered. Therefore, the leak current Is, which causes the decrease in the detection sensitivity, is fed back to the high-voltage power supply 121, and the transfer current It is controlled to a constant current, whereby the decrease in the detection sensitivity can be prevented. This makes it possible to obtain the same detection sensitivity as that obtained when there is no leakage current Is.

(Other Embodiments) The image forming apparatus according to the present invention is not limited to the above-mentioned embodiment, but can be variously modified within the scope of the gist thereof. For example,
In a model that uses an intermediate transfer drum instead of the intermediate transfer belt 41 in a full-color printer, the test toner image may be transferred to the intermediate transfer drum and the transfer voltage at that time may be detected. Further, in an image forming apparatus configured to transfer a toner image onto a transfer sheet held on an intermediate transfer belt or an intermediate transfer drum, an embodiment in which a test toner image is transferred onto the transfer sheet held on the belt or the drum, An embodiment in which the test toner image is transferred to the intermediate transfer belt or the intermediate transfer drum that does not hold the paper is also possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a laser printer according to a first embodiment of the present invention.

FIG. 2 is a graph showing IV characteristics in a test toner image transfer step in the first embodiment.

FIG. 3 is a block diagram showing a transfer control circuit according to the first embodiment.

FIG. 4 is a configuration diagram showing a main part of a laser printer according to a second embodiment of the present invention.

FIG. 5 is a graph showing IV characteristics in a test toner image transfer process in the second embodiment.

FIG. 6 is a graph showing conversion characteristics between a detection voltage and a transfer voltage in the second embodiment.

FIG. 7 is an internal configuration diagram showing a full-color laser printer that is a third embodiment of the present invention.

FIG. 8 is a configuration diagram showing a primary transfer portion in a third embodiment.

FIG. 9 is a configuration diagram showing a secondary transfer portion in the third embodiment.

FIG. 10 is a configuration diagram showing a main part of a fourth embodiment of the present invention.

FIG. 11 is a configuration diagram showing a main part of a fifth embodiment of the present invention.

[Explanation of Codes] 11,100 ... Photosensitive drum 12 ... Charging brush 111 ... Charging charger 30 ... Developing unit 113 ... Developing device 41 ... Intermediate transfer belt 46, 47, 59, 114 ... Transfer roller (transfer electrode) 120 ... Control Circuit 121 ... High-voltage power supply 130 ... Toner cleaner CPU ... Microcomputer S ... Transfer paper

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyoshi Hara 2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture Osaka International Building Minolta Co., Ltd. (72) Inventor Akiyo Hayashi Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-chome 3-13 Osaka International Building Minolta Co., Ltd.

Claims (2)

[Claims] 1. An image forming apparatus for transferring a toner image formed on an image carrier by applying an electric charge from a transfer electrode to a transfer material, which is in close contact with the image carrier, and then transferring the toner image on the image carrier. A unit for forming a test toner image under the same conditions as the toner image formation that is performed, and a constant-current-controlled power supply to the transfer electrode to transfer the test toner image onto a transfer material. An image forming apparatus, comprising: a transfer control unit that detects a value and supplies power to the transfer electrode, the electric power being subjected to constant voltage control based on the detected voltage value when the toner image is transferred later. 2. An image forming apparatus for transferring a toner image formed on an image carrier by applying an electric charge from a transfer electrode to a transfer material, which is in close contact with the image carrier, and then transferring the toner image on the image carrier. A unit for forming a test toner image under the same conditions as the toner image formation to be performed, and a constant-current-controlled power is supplied to the transfer electrode to transfer the test toner image to the transfer electrode. Value is detected, and at the time of later-transferred toner image, transfer control means for supplying constant-voltage-controlled power to the transfer electrode based on the detected voltage value, and removing the test toner image transferred to the transfer electrode. An image forming apparatus comprising: a cleaning unit.