JPH05313516A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory transfer image by achieving optimum transfer and separation. CONSTITUTION:Power is supplied from a power source part 17 to one of a pair of detection rollers 13, composed of conductive rubber rollers, in a transfer sheet carrying path 19, and a current corresponding to the electric resistance of a transfer sheet sandwiched between the detection rollers is detected by a current detection circuit 18. One of the detection rollers is movably disposed, and a sheet thickness detection sensor 15 for measuring the displacement of one of the detection rollers, which floats when the transfer sheet is sandwiched between them, is provided. An arithmetic control circuit 22 selects optimum transfer current values from data on the detection of the thickness of the transfer sheet and the data on the detection of the electric resistance of the transfer sheet, determines one of the selected transfer current values based on certain conditions, and gives an instruction to a transfer unit high voltage power source 23 by means of a control signal corresponding to the transfer current, thereby controlling the transfer current flowing to a transfer charger 6.

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 for transferring a toner image formed on an image carrier onto a transfer paper and fixing it to form an image.

[0002]

2. Description of the Related Art In an electrostatographic image forming apparatus such as an electrophotographic copying machine, a laser printer, a facsimile, etc., as shown in FIG. A container 4, a transfer charger 6, a separation charger 7 and a cleaner 8 are arranged. Photoreceptor 2 uniformly charged by charger 3 by electrostatic photography process
An image of the original is exposed by the writing beam 9 to form an electrostatic latent image thereon. Subsequently, the electrostatic latent image on the photoconductor 2 is developed by the developing device 4 to form a toner image. This toner image is transferred by the action of the transfer charger 6 from the transfer paper cassette 10 to the transfer paper fed from the paper feed unit 11 through the registration roller pair 26 to the transfer unit along the photoconductor. The transfer paper after the transfer is separated from the photoconductor by the separation charger 7, is conveyed by the conveyance belt 14, is fixed by the fixing device 12 to complete the image formation, and is discharged to the outside of the machine. On the other hand, the toner remaining on the photoconductor 2 is removed by the cleaner 8.

[0003]

The optimum values (levels) of the transfer current and the separation current applied to the transfer charger and the separation charger differ depending on the paper thickness of the transfer paper.
However, in the past, it was general that the transfer paper was constant regardless of the paper thickness. Further, since the action of the transfer / separation charger reaches the toner through the transfer paper, recently, a technique has been proposed in which the applied current level is changed according to the paper thickness. However, for thick paper that absorbs a large amount of moisture, paper that does not easily absorb moisture even if it is thin, or paper that easily absorbs moisture, the optimum transfer current value cannot be discussed simply by the paper thickness.

As a paper thickness detection sensor for a transfer paper, for example, in Japanese Patent Laid-Open No. 2-190885, a laser light emitting element and a photo diode are provided in a positional relationship of sandwiching the transfer paper in a transfer paper conveyance path to transmit light of the transfer paper. A method of knowing the paper thickness from the rate change has been proposed. However, even if the paper thickness is thin, it has low transmittance, for example, colored transfer paper, or if the paper thickness is thick, the transmittance is high relative to the thickness, OHP, etc. are used. It is not possible to accurately determine the thickness of the paper only by itself. Conversely, if an imbalanced transfer current is judged from the judgment error, the image quality will deteriorate.

Further, when the transfer current value is set to the optimum value, the transfer paper having a large thickness such as drawing paper, postcard paper, certificate paper, etc. must maintain a constant pressing force of the transfer paper to the photosensitive drum. There has been a problem that image rubbing or the like occurs and a good transferred image cannot always be obtained. In view of the above problems, an object of the present invention is to automatically detect a change in a physical quantity according to a paper thickness of a transfer paper and a moisture absorption condition, and always perform an optimum transfer / separation. Is provided. Another object of the present invention is to provide an image forming apparatus capable of automatically controlling a transfer current and a paper plunge angle in accordance with a thickness of a transfer paper and a moisture absorption condition to obtain a good transferred image. is there.

[0006]

In order to achieve the above object, an image forming apparatus of the present invention includes an image carrier and a transfer paper provided on a transport path for transporting the transfer paper to the image carrier. A paper thickness detecting means for detecting the thickness and an electric resistance detecting means for detecting the electric resistance of the transfer paper are compared with a paper thickness detecting signal output from each of the detecting means and a transfer current value selected by the electric resistance detecting signal. When the transfer current value selected by the electric resistance is larger than the transfer current value selected by the paper thickness and smaller than a predetermined reference value, the transfer current value selected by the electric resistance is When the above conditions are not satisfied, an arithmetic control unit that determines the transfer current value selected by the paper thickness is provided, and the arithmetic control unit outputs the control signal of the determined transfer current value, and the transfer charger. Control the transfer current of Is shall. Further, in the above invention, a photosensitive drum as an image carrier, a rotatable paper thrusting guide provided at a position closest to the photosensitive drum on a transfer paper conveying path to the photosensitive drum, and the paper thrusting. Drive means for operating the guide based on the rotation control signal, the arithmetic control means determines the sheet plunge angle of the sheet plunge guide from the sheet thickness detection signal, and outputs a control signal according to this value to output the sheet. The plunge guide is rotated to adjust the sheet plunge angle.

[0007]

In the one in which an appropriate transfer current is controlled by the paper thickness and electric resistance of the transfer paper, the arithmetic control means selects an appropriate transfer current value depending on the paper thickness from the paper thickness detection signal detected by the paper thickness detection means. In addition, an appropriate transfer current value due to the electric resistance is selected from the electric resistance detection signal detected by the electric resistance detecting means. When the transfer current value selected by the electric resistance satisfies the condition that it is larger than the transfer current value selected by the paper thickness and smaller than the predetermined reference value, the transfer current value selected by the electric resistance is If the above conditions are not satisfied, the transfer current value selected by the paper thickness is determined and the transfer current of the transfer charger is controlled to change the electric resistance of the transfer paper in the moisture absorption state. A normal transfer image can be obtained even if it is lost. Further, in addition to the control of the transfer current described above, in the case of adjusting the sheet plunge angle according to the sheet thickness, the arithmetic control means selects the angle of the sheet plunge guide from the sheet thickness detection signal, and the rotation control signal corresponding to this value selects the sheet By rotating the plunge guide a predetermined angle to adjust the plunge angle according to the paper thickness, the pressure contact force to the photosensitive drum can be made constant even if the paper thickness changes, and a better transferred image can be obtained. Be done.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure of a main body of an image forming apparatus having a photosensitive drum as an image carrier, and FIG. 2 shows a structure of a feed roller section. In this embodiment, FIG.
The components having the same functions as the components shown in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. The transfer paper transport unit 11 on the upstream side of the transfer unit feeds the transfer paper supplied from the transfer paper cassette 10 by the paper transport rollers 24 and 25 through the paper transport path 19 to the timing for transporting the paper to the transfer unit. To the department. A volume resistivity of 10 ³ to 10 ⁵ Ω · cm is provided at the end of the registration roller pair 26 (hereinafter referred to as “feed roller 26”) that constitutes the feed roller unit, as a structural member separate from the feed roller 26. A paper thickness / electrical resistance detection roller pair (hereinafter referred to as “detection roller”) 13 formed of the conductive rubber is provided rotatably on the feed roller shaft. When the transfer sheet is conveyed to the feed roller unit and sandwiched by the registration roller pair 26, the transfer sheet is also sandwiched by the detection roller 13.

As shown in FIG. 3, the detecting roller 13 is supported so as to roll around the feed roller shafts 26a and 26b. One of the feed roller shafts is supported by a fixed bearing, and the other of the feed roller shafts is movably supported in the vertical direction with respect to the transfer paper transport surface. In the case of this example, the side of the feed roller shaft 26b disposed below the transfer sheet transport path is the fixed bearing 26c, while the side of the feed roller shaft 26a disposed above the transfer sheet transport path is movable. It is constituted by the bearing 26d. A ring-shaped coil spring 26e is mounted between the feed roller shafts to keep the contact pressure of the feed roller 26 and the contact pressure of the detection roller 13 constant.

By arranging the detection rollers in this manner, it is possible to accurately detect the paper thickness and the electric resistance without being affected by any size of the paper from small to large. The paper thickness detection means is one detection roller of a detection roller pair, for example, the detection roller 13a, a paper thickness detection sensor 15 having a laser displacement meter function in which a laser light emitting element and a photodiode are integrally incorporated, and a drive power source for the sensor. It is composed of 20. The paper thickness detection sensor 15 is arranged close to the outer peripheral surface of the detection roller 13a in a positional relationship capable of irradiating a laser beam. When the paper thickness of the transfer paper changes, the detection roller 13a moves up and down according to the paper thickness (several tens to several hundreds of microns), and the displacement amount at this time is detected as an output change of the paper thickness detection sensor 15 to The paper thickness can be known from the output.

According to this paper thickness detecting means, even if the paper thickness is thin, the transmittance is low, for example, if the paper is colored, or if the paper thickness is large, the transmittance is high relative to the thickness, or light such as OHP. It can also be applied to transfer paper for which it is difficult to accurately determine the paper thickness based on the transmittance alone. The electric resistance detection means includes a detection roller 13 formed of a conductive rubber roller, an electrode roller 16 arranged in contact with one detection roller 13a, and the detection roller 13a.
A power supply unit 17 for supplying power via the electrode roller 16 and a current detection circuit 18 for detecting a current flowing through the transfer paper sandwiched by the detection rollers. The current detection circuit 18 is inserted between the other detection roller 13b and the ground, and is configured to detect a current according to the electric resistance of the transfer paper. The electric resistance of the transfer paper is detected by the transfer paper 1
It is possible to detect the current value before being sandwiched by 3 and the current value at the time of being sandwiched, and obtain the difference from these.

In the above embodiment of the detecting means, a common mechanism portion, that is, a common detection roller, is used for detecting the paper thickness of the transfer paper and the electric resistance detection, but it is also possible to configure them by independent mechanism portions. .. Further, the detection roller 13 is
Although it is arranged coaxially at the end of the feed roller pair 26, it may be provided separately from the feed roller pair 26 at a position different from that of the feed roller pair. FIG. 4 shows a basic block diagram for controlling the optimum transfer current depending on the paper thickness and the electric resistance of the transfer paper. The paper thickness detecting means and the transfer paper electric resistance detecting means used in the present embodiment are constituted by a mechanism section in which one roller of the conductive rubber roller pair 13a or 13b arranged at the end of the feed roller 26 is common. Therefore, the paper thickness and the electric resistance change of the transfer paper are respectively detected from the physical change amount of the roller.

The arithmetic control circuit 22 is composed of a CPU system, for example, and processes the paper thickness detection signal output from the paper thickness detection sensor 15 and the electric resistance detection signal of the transfer paper output from the electric resistance detection circuit 18. Then, the paper thickness and the electric resistance of the transfer paper are obtained, an appropriate transfer current value is determined from the result, and the high voltage power supply 23 for the transfer device is instructed by a control signal according to the transfer current value. High voltage power supply 23 for transfer device
Supplies a transfer current to the transfer charger 6 based on the control signal. Next, the relationship between the paper thickness and the electrical resistance of the transfer paper and the transfer current will be conceptually described. FIG. 5 is a graph qualitatively showing the relationship between the photo diode detection output and the paper thickness of the transfer paper. In FIG. 5, as a typical value of standard paper,
The paper thickness when the detection output of the photodiode is Y (mW) is X (μm). Photodiode detection output Y (m
By comparing W) with the reference value, the transfer current of the transfer charger 6 is increased / decreased with respect to the initial value and controlled to be an appropriate value. Here, the reference value is an optimum transfer current value for general high-quality paper, so-called standard paper.

Actually, as shown in FIG. 6, the level of the detection output of the photodiode, that is, the transfer current value Z corresponding to the paper thickness X is determined as the representative value of the standard paper. Then, the transfer current value with respect to the paper thickness is divided into groups in multiple stages, and one group is controlled to have the same transfer current. Therefore, from the paper thickness X (μm) by the detection output Y (mW) of the photodiode, the transfer current value Z (μ
A) is determined, and the transfer device high-voltage power supply 23 is controlled so that the transfer current value Z is obtained. FIG. 7 is a graph qualitatively showing the relationship between the electric resistance value and the optimum transfer current value when the electric resistance of the transfer paper is taken into consideration. In FIG. 7, it can be seen that when the detected value by the current detection circuit 18 is A × 10 ⁻⁸ (A), the optimum transfer current value is B × 10 ⁻⁶ (A). By the way, since the transfer current value with respect to the electric resistance value is not necessarily required to be controlled with a linear relationship, it is sufficient to divide the transfer current value into groups in multiple stages as in the control based on the paper thickness described above. is there. In practice, for example, the transfer current values shown in FIG. 8 have no problem in practical use.

Next, the optimum control of the transfer current, which is performed based on the two physical changes of the paper thickness and the electric resistance of the transfer paper, will be described. FIG. 9 shows a flow chart of the transfer current control by the paper thickness of the transfer paper and the electric resistance. First, when the print button is pressed, the transfer paper is supplied from the paper cassette, reaches the feed roller 26 through the conveying system, and is pinched. At the same time, since the transfer paper is also sandwiched by the detection roller 13a, the detection roller is pushed upward by the paper thickness, and the displacement at this time is detected by the paper thickness detection sensor 15,
In addition to outputting paper thickness detection data as a photodiode output (S1), a DC voltage is applied to the detection roller from the DC power supply 17 through the rubber roller 16 for power feeding, and the current detection circuit 18 detects the current flowing through the transfer paper and transfers it. Outputs electric resistance detection data according to the electric resistance of the paper (S
3).

The arithmetic control circuit 22 takes in the above data and determines the optimum transfer current value. First, the thickness of the transfer paper is obtained based on the voltage data output from the paper thickness detection sensor 15 using the data table regarding the photodiode output vs. paper thickness shown in FIG. Then, the transfer current value Z depending on the paper thickness is selected using the data table relating to the output transfer current vs. paper thickness shown in FIG. 6 (S2). On the other hand, the transfer current value C due to the electric resistance is selected using the data table relating to the output transfer current shown in FIG. 8 and the detected current corresponding to the electric resistance of the paper (S4). In the steps up to this point, the transfer current value is temporarily selected as an appropriate value for each of the detection data.

Comparison operation of transfer current value Z selected by paper thickness and transfer current value C selected by electric resistance (R = Z-C)
Is performed (S5). Based on the calculation result R and the determination result of the magnitude of the transfer current C with respect to the reference value, it is determined whether the transfer current value Z or C is selected (S6). When C ≦ reference value and C> Z are not satisfied, the transfer current value Z is determined (S7). When the above conditions are satisfied, the transfer current value C is determined (S8).

For example, assuming that the transfer paper is set in the cassette when the humidity is high in summer, in the case of plain paper, the transfer current Z is about 25 .mu.m toward the drum.
As A, at this time, the paper is fresh paper (4 to 5% by weight)
Since the transfer current Z is larger than that, the transfer current Z is determined. When the paper is left in the cassette and absorbs moisture, the result of the transfer current C is about 20% up to 30 μA. Therefore, in this case, the transfer current C is determined. Next, the adjustment of the angle of the sheet entry guide according to the sheet thickness will be described. FIG. 10 is a schematic diagram showing the relationship of the plunge angle of the sheet plunge guide with respect to the sheet thickness. FIG. 11 is a basic block diagram for controlling the optimum transfer current by the paper thickness and the electric resistance of the transfer paper and at the same time adjusting the angle of the paper entry guide. Since the optimum transfer current control system based on the paper thickness and electric resistance of the transfer paper has the same configuration as that in FIG. 4, these constituent elements are given the same reference numerals and the description thereof is omitted.

The photosensitive drum 2 is provided on the transfer paper conveying path 19.
Stepping motor (not shown) closest to
A sheet entry guide 27 that is rotated by is provided. The sheet plunge guide 27 adjusts the sheet plunge angle so that the difference in pressure contact force with the photosensitive drum 2 caused by the sheet thickness of the transfer sheet is constant. As shown in FIG. 10, when the paper thickness is large, the stiffness is generally strong and the pressure contact force to the photosensitive drum is also large. Therefore, the contact point p at which the leading end of the transfer paper contacts the photosensitive drum 2 is set to the transfer charger 6. Close them to reduce the paper entry angle θ. That is, the paper entry guide 27 is rotated by a predetermined angle in the direction a shown in the drawing. On the other hand, when the paper thickness is thin, the stiffness is weak and the contact point p to the photosensitive drum is moved away from the transfer charger 6 to increase the paper entry angle θ. That is, the paper entry guide 27 is rotated by a predetermined angle in the b direction shown in the figure.

As shown in FIG. 12, the arithmetic control circuit 22 selects the angle of the sheet entry guide 27 from the sheet thickness detection data of the transfer sheet detected in step S1 (S10),
A rotation control signal corresponding to this value is output (S11). The drive circuit 28 drives the stepping motor based on the rotation control signal to rotate the sheet plunge guide 27 by a predetermined angle to adjust the sheet plunge angle according to the sheet thickness (S12). According to the present embodiment, the transfer current value is corrected to the optimum value according to the type of the transfer paper and the state change of the transfer paper, and the optimum transfer plunge angle is automatically set depending on the paper thickness of the transfer paper. Even thick paper, which could not be dealt with only by controlling the transfer current, has an appropriate pressure contact force with respect to the photosensitive drum, and a better transferred image can be obtained. In the above example,
Although no measures have been taken to prevent overcurrent in the current detection circuit 18, a current limiting resistor may be connected in series to the current detection circuit 18 if necessary.

[0021]

As described above, according to the present invention, the paper thickness of the transfer paper detected by the displacement amount of the detection roller that floats up by the paper thickness, and the electricity of the transfer paper detected by the energization of the detection roller. Since the transfer current is controlled based on the resistance, it is possible to accurately respond to the optimum transfer current shift, etc., in response to changes in the properties of the transfer paper, where the moisture absorption level changes in various ways. It is possible to obtain good transfer image quality that is not affected by the quality of thick transfer paper or colored paper. In addition to the control of the optimum transfer current value based on the paper thickness and electrical resistance, by automatically controlling the angle of the paper entry guide depending on the paper thickness, the transfer paper is particularly thick, and it is possible to respond well only by controlling the transfer current value. A good transfer image can always be obtained even if it is not present.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus body of an image forming apparatus of the present invention.

FIG. 2 is a plan view showing a configuration of a feed roller unit.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a control block diagram of a transfer current depending on the paper thickness and the electric resistance of the transfer paper.

FIG. 5 is a graph diagram qualitatively showing the relationship between the photo diode detection output and the paper thickness of the transfer paper.

FIG. 6 is a graph showing a relationship between a transfer current to be controlled and a paper thickness of a transfer paper.

FIG. 7 is a graph diagram qualitatively showing a relationship between an electric resistance value and a transfer current value when the transfer paper is captured only from the viewpoint of the electric resistance.

FIG. 8 is a graph showing a relationship between a transfer current to be controlled and an electric resistance of a transfer sheet.

FIG. 9 is a flowchart of transfer current control based on the paper thickness of transfer paper and electric resistance.

FIG. 10 is a schematic diagram for explaining adjustment of the plunge angle of the sheet plunge guide with respect to the sheet thickness.

FIG. 11 is a block diagram for controlling the optimum transfer current and adjusting the angle of the paper entry guide according to the paper thickness and the electrical resistance of the transfer paper.

FIG. 12 is a flow chart of a transfer current control by a paper thickness of a transfer paper and an electric resistance, and an angle adjustment control of a paper entry guide.

FIG. 13 is a schematic configuration diagram of an apparatus main body of a conventional image forming apparatus.

[Explanation of symbols]

1 device body, 2 photoconductor (image carrier), 3 charger,
4 developing device, 6 transfer charger, 7 separation charger, 8 cleaner, 9 writing beam, 10 transfer paper cassette, 11 paper feed unit, 12 fixing device, 13 detection roller pair, 15 paper thickness detection sensor, 17 DC power supply, 1
8 current detection circuit, 22 arithmetic control circuit, 23 high-voltage power supply for transfer device, 26 registration roller pair, 27 paper entry guide, 28 paper entry guide drive circuit

Claims (2)

[Claims] 1. An image carrier, a paper thickness detecting means for detecting the thickness of the transfer paper and an electric resistance of the transfer paper, which are arranged on a conveyance path for conveying the transfer paper to a transfer portion of the image carrier. The electric resistance detecting means for detecting is compared with the transfer current value selected by the electric resistance detecting signal and the paper thickness detecting signal output from each detecting means, and the transfer current value selected by the electric resistance is selected by the paper thickness. The transfer current value selected by the electric resistance is determined when the condition that is larger than the transfer current value and smaller than the predetermined reference value is satisfied, and when the condition is not satisfied, the transfer current value selected by the paper thickness is selected. An image forming apparatus comprising: an arithmetic control unit that determines a transfer current value, wherein the arithmetic control unit outputs a control signal of the determined transfer current value to control the transfer current of the transfer charger. 2. A photosensitive drum, a rotatable paper entry guide provided at a position closest to the photosensitive drum on a transfer paper transport path leading to the photosensitive drum, and a rotation control signal for the paper entrance guide. The arithmetic control means determines the sheet plunge angle of the sheet plunge guide from the sheet thickness detection signal, outputs a control signal according to this value, and rotates the sheet plunge guide. The image forming apparatus according to claim 1, wherein the sheet plunge angle is adjusted.