JP2013097146A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that quickly performs accurate resistance detection for every recording medium, and provides excellent transferability without causing a reduction in productivity.SOLUTION: Resistance detection means 70 has a detection unit 72 including a plurality of electrode members. The detection unit 72 contacts a top face of a sheet S stored in a paper cassette at an appropriate pressure. A current flowing in the resistance detection means 70 by an application of voltage is detected by an ammeter 76, and the sheet resistance is determined from the voltage and the current. A primary transfer current and voltage, and a secondary transfer current and voltage are controlled according to the determined sheet resistance.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or a multifunction machine provided with at least one of them.

  In this type of image forming apparatus, a latent image is formed on an image carrier such as a photoconductor by an exposure unit based on image data, the latent image is visualized as a toner image by a developing device, and the toner image is directly converted. Alternatively, the image is transferred to a recording medium indirectly via an intermediate transfer member, and the recording medium is fixed by passing it through a fixing device.

In recent years, image forming apparatuses such as color copying machines and laser printers are required to obtain high-quality images on various recording media (hereinafter also referred to as “paper” or “paper”). The image quality obtained by the transfer is susceptible to paper characteristics, particularly resistance.
The resistance of the paper varies greatly depending on how it is handled, and the moisture content changes depending on the outside air environment when left untreated (hereinafter referred to as “humidity control”), and the resistance increases or decreases.
The surface paper of the stacked sheets is most susceptible to humidity adjustment, and the humidity adjustment speed becomes slower as the lower layer is reached. In other words, when printing is performed continuously using the left paper, an image is formed on the paper whose resistance is changed for each sheet.
It is known that the change in the resistance of the paper affects the transferability of the toner image onto the paper. A change in transferability leads to a change in image density, and consequently to a reduction in image quality.

Japanese Patent Application Laid-Open No. H10-228561 proposes controlling the transfer current by passing paper before image formation and measuring the resistance between the transfer roller and the photoreceptor.
However, since the sheet passing without image formation is performed for resistance measurement, an extra time for measuring the resistance is required, and the copying speed becomes slow. Furthermore, for paper whose resistance has been changed for each sheet when left for a long time, measurement is performed for each sheet, which is not practical. Another problem is the need for a tray for storing the passed paper for resistance measurement.

Patent Document 2 proposes correcting the secondary transfer bias by measuring the combined resistance of a plurality of sheets with a sheet interposed between the intermediate transfer member and the secondary transfer unit.
In order to reduce the influence on the image, it is necessary to measure the resistance in a very short time. However, in recent years, the process speed has increased, and the detection accuracy is inferior due to the rapid rise time of the resistance measurement system.
Based on the method of Patent Document 2, it is conceivable to measure the combined resistance at the leading edge of the paper and control the secondary transfer voltage and current. However, in the resistance measurement in a very short time, the detection accuracy is inferior. The image is deteriorated while the secondary transfer current or voltage correction is completed. When measuring the combined resistance at the secondary transfer portion, the primary transfer current and voltage cannot be controlled because the primary transfer is almost completed.
Although it is possible to provide a roller electrode pair for measuring the paper resistance between the paper feed cassette and the registration roller pair, there is a problem in that it is likely to have an effect on the conveyance and the cost is increased due to layout restrictions. ing.

  Patent Document 3 proposes measuring the moisture content of the paper and controlling the transfer bias. Although the moisture content and resistance correlate for the same paper, even with the same moisture content, the resistance is different for different papers with different material properties. Correct resistance measurement is difficult.

  The present invention has been made in view of such a current situation, and can quickly detect resistance with high accuracy for each recording medium, and can obtain good transferability without causing a decrease in productivity. An object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, the present invention provides an image carrier, a charging unit for charging the image carrier, an exposure unit for exposing the image carrier in accordance with image information, and an image on the image carrier. Resistance detection for detecting the resistance of the surface of the recording medium in a developing unit that visualizes the formed latent image as a toner image and an image forming apparatus that finally transfers the toner image to a recording medium by a transfer unit And the resistance detecting means includes at least two electrode members that can be brought into contact with and separated from the surface of the recording medium before the toner image is formed, and voltage is applied to at least one of the electrode members. Applying and detecting a current flowing between the other electrode members to which the voltage is not applied, and controlling at least one of a transfer current and a voltage based on a detection result of the resistance detection unit. Characterize

According to the present invention, even when the resistance variation between recording media increases due to long-term storage or when the resistance near the top surface of the loaded recording media changes due to a sudden environmental change, the recording media are changed for each recording medium. The resistance can be measured with high accuracy.
Thereby, it is possible to maintain a uniform transfer property regardless of the resistance variation between the recording media, and to obtain a good image quality.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the paper resistance measuring method by a resistance detection means. It is a figure which shows the shape and arrangement configuration of the electrode member of a resistance detection means, (a) is a top view of only an electrode member, (b) is a side view. FIG. 6 is a characteristic diagram illustrating a relationship between humidity control time and resistance change when a sheet is left in the environment. 2A and 2B are perspective views illustrating a configuration of a paper feed cassette, in which FIG. 1A is a view of a conventionally used paper feed cassette, and FIG. 2B is a view of a paper feed cassette according to the present embodiment. It is a control block diagram.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. In the figure, reference numeral 100 denotes an apparatus main body, 200 denotes a paper feed table on which the apparatus main body is placed, 300 denotes a scanner attached to the apparatus main body 100, and 400 denotes an automatic document feeder (ADF) attached thereon. . Subscripts Y, M, C, and K indicate yellow, cyan, magenta, and black (black) colors, respectively.
The apparatus main body 100 is provided with an endless belt-like intermediate transfer belt 10 as an intermediate transfer member near the center. The intermediate transfer belt 10 is wound around three support rollers 14, 15, and 16 so as to be able to rotate and convey in the clockwise direction in the drawing.

A cleaning device 17 for the intermediate transfer belt is provided on the left of the second support roller 15. The cleaning device 17 removes residual toner remaining on the intermediate transfer belt 10 after image transfer.
On the intermediate transfer belt 10 stretched between the first support roller 14 and the second support roller 15, four image forming units 18Y, 18M, yellow, cyan, magenta, and black are arranged along the conveyance direction. 18C and 18K are arranged side by side to form a tandem-type image forming unit 20.
An exposure device 21 is provided on the image forming unit 20.
Each image forming unit 18 of the image forming unit 20 includes photosensitive drums 40Y, 40M, 40C, and 40K as image carriers that support toner images of yellow, cyan, magenta, and black.
At the primary transfer position where the toner image is transferred from the photoconductor drums 40Y, 40M, 40C, and 40K to the intermediate transfer belt 10, the photoconductor drums 40Y, 40M, 40C, and 40K face each other with the intermediate transfer belt 10 interposed therebetween. As described above, primary transfer rollers 62Y, 62M, 62C, and 62K as constituent elements of the primary transfer unit are provided at positions downstream of the transfer nip.

The first support roller 14 is a drive roller that rotationally drives the intermediate transfer belt. When a black single color image is formed on the intermediate transfer belt, the support rollers 15 and 16 other than the driving roller are moved to separate the yellow, cyan, and magenta photoreceptors 40Y, 40M, and 40C from the intermediate transfer belt. Is also possible.
The present invention can be implemented even in an apparatus having only one photoconductor, instead of the tandem type as in this embodiment.

A secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 10 from the image forming unit 20. The secondary transfer device 22 has a configuration in which the secondary transfer roller 16 ′ is pressed against the secondary transfer counter roller 16 to apply a transfer electric field, whereby the image on the intermediate transfer body 10 is illustrated as a recording medium. Not transferred to the sheet.
A fixing device 25 for fixing the transfer image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 that is an endless belt.
The sheet after image transfer is conveyed to the fixing device 25 by the conveyance belt 24. The sheet conveyance after the image transfer may be performed by a fixed guide member instead of the conveyance belt 24.
Under the secondary transfer device 22 and the fixing device 25, a sheet reversing device 28 for reversing the sheet so as to record images on both sides of the sheet is provided in parallel with the image forming unit 20.

When making a copy using the image forming apparatus, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it.
When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then set on the other contact glass 32. The scanner 300 is immediately driven and the first traveling body 33 and the second traveling body 34 travel.
The first traveling body 33 emits light from the light source, reflects reflected light from the document surface toward the second traveling body 34, reflects off the mirror of the second traveling body 34, and passes through the imaging lens 35 to read the sensor. 36 to read the contents of the document.

When a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 (here, the support roller 14) is rotationally driven by a drive motor (not shown), and the other two support rollers are driven to rotate to perform intermediate transfer. The belt 10 is rotated and conveyed. At the same time, the photoconductors 40 are rotated by the individual image forming means 18 so that yellow, cyan, magenta, and black single-color images are formed on the photoconductors 40, respectively. Along with the conveyance of the intermediate transfer belt 10, these single color images are sequentially transferred by the primary transfer roller 62 in the primary transfer portion, and a composite color image is formed on the intermediate transfer body 10.
When a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated, and paper is fed out from one of paper feed cassettes 44 provided in multiple stages in the paper bank 43 for separation. The sheets are separated one by one by the rollers 45 and put into the sheet feeding path 46.
The paper is transported by the transport roller pair 47 and guided to the paper feed path 48 in the apparatus main body 100, and is abutted against the resist roller pair 49 and stopped.

Alternatively, the paper feed roller 50 rotates to feed the paper on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual paper feed path 53, and abutted against the registration roller pair 49 and stopped. .
The registration roller pair 49 rotates in synchronization with the composite color image on the intermediate transfer belt 10, and a sheet is fed between the intermediate transfer belt 10 and the secondary transfer device 22 and transferred by the secondary transfer device 22. A color image is recorded on the paper.
The sheet after the image transfer is transported by the transport belt 24 and sent to the fixing device 25, and heat and pressure are applied by the fixing device 25 to fix the transferred image. Thereafter, the sheet is switched by the switching claw 55, discharged by the discharge roller pair 56, and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and is put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and after the image is recorded also on the back surface, the discharge roller pair 56 puts it on the discharge tray 57. Discharged.

After the image transfer, the intermediate transfer belt 10 is cleaned by the intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after the image transfer, and prepares for image formation by the image forming unit 20 again.
In general, the registration roller pair 49 is often used while being grounded, but it is also possible to apply a bias for removing paper dust from the paper.
The intermediate transfer member can be used regardless of a single layer structure or a laminated structure. The production method of the intermediate transfer member is not limited, and can be produced by all production methods such as dipping method, centrifugal molding method, extrusion molding method, inflation method, and coating method.
Materials include polyimide resin, polyamideimide resin, polycarbonate resin, polyphenylene sulfide resin, polyurethane resin, polybutylene terephthalate resin, polyvinylidene fluoride resin, polysulfone resin, polyethersulfone resin, polymethylpentene resin, etc. . Polyimide resin and polyamideimide resin are preferable from the viewpoint of strength, and resistance is controlled by adding conductive carbon black or the like.

  Transfer rollers include epichlorohydrin rubber, urethane rubber, nitrile butadiene rubber, acrylic rubber, chloroprene rubber, fluorine rubber, nitrile rubber, norbornene rubber, and other rubbers having ionic conductivity, natural rubber (NR), and butadiene rubber. Various materials such as isoprene rubber, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer rubber (EPDM), butyl rubber, and silicon rubber can be used.

Table 1 shows the measured voltage and surface resistance in each environment of the paper. In the table, “2.44E + 13” means “2.44 × 10 ¹³ ”. The same applies to other measured values.

As is apparent from Table 1, the sheet resistance is extremely large in the measurement environment.
Measurement is possible at 100 to 1000 V at 23 ° C. and 50% RH, which is the standard environment, but at 10 ° C. and 15% RH, the resistance exceeds the upper limit (indicated as “over” in the table), and current measurement becomes insufficient when 500 V is applied. Some papers cannot be used. Conversely, at 27 ° C. and 80% RH, the resistance exceeds the lower limit (indicated as “under” in the table), and there are some papers that cannot be measured due to excessive current when 500 V is applied. If only the paper used for this experiment is judged, the measurement is 1000 V in the low humidity environment and 100 V measurement in the high humidity environment.
The measurement voltage is determined from the detected environmental conditions, but it is also possible to measure the determined voltage and further change the measurement voltage from the detected voltage and current.

Recognition of humidity control time and resistance fluctuation is important for the development of technology that detects paper resistance and controls feedback to transfer conditions.
FIG. 4 shows the result of measuring the resistance according to the elapsed time by placing a single sheet flat on a desk, assuming resistance change due to humidity adjustment of the topmost sheet of the stacked sheets.
The horizontal axis indicates the elapsed time since the paper left in the room temperature environment is removed from the moisture-proof bag, and the minutes (min) are logarithmically displayed. Further, the humidity adjustment time of 0.1 min is a resistance measured in a normal temperature environment, and is the start of the resistance.
The resistance is almost saturated at a humidity control time of 10 to 100 minutes. As can be seen, the resistance change due to humidity adjustment occurs in the outermost sheet of the stacked sheets in a very short time.

The resistance was measured by placing the paper on the insulating member and using the method shown in FIG. 10 ° C. and 15% RH are 1000 V, and room temperature and 27 ° C. and 80% RH are value resistances 10 seconds after 100 V is applied.
As shown in FIG. 2, the surface resistance of the paper S was measured by placing the detection unit of the resistance detection means 70 on the surface of the stacked paper (the surface of the paper located at the uppermost surface).
The resistance detection unit 70 includes a detection unit 72, a high voltage power source 86 (see FIG. 6) as a voltage application unit, a voltmeter 74, and an ammeter 76. In this configuration, the resistance is obtained from the value of the current flowing by applying a constant voltage.

Based on FIG. 3, the structure of the detection part 72 is demonstrated in detail.
The detection unit 72 includes a base 78 and electrodes 80 a, 80 b, and 80 c as three electrode members fixed to the lower surface of the base 78.
A voltage is applied from the high voltage power source 86 to the electrode 80b as the center electrode, and the current flowing through the electrodes 80a and 80c as the grounded counter electrodes provided at both ends of the center electrode is measured.
By providing the counter electrode at both ends of the center electrode, the current is doubled, and the resistance can be stably measured even when the paper resistance is increased. Of course, it is also possible to measure with two electrodes, a central electrode and one counter electrode.

The electrode member used in this embodiment was 2 mm × 20 mm, and the inter-electrode distance d was 5 mm. The base 78 is movable in the vertical direction by a spring-like member (not shown), and improves the close contact property with the paper.
More specifically, the contact width W of the electrode member in the paper width direction orthogonal to the paper transport direction is 2 mm. Therefore, the contact width of the three electrode members with respect to the paper surface is 3 × W, which is 6 mm in total, the long side length L of the electrode member is smaller than 20 mm, and the resistance to sliding with the paper is also reduced.

When the electrode member is brought into contact with the paper, there is a possibility that the paper is transported due to friction between the electrode member and the paper.
In order to reduce the frictional resistance, it is conceivable to make the contact area of the electrode member as small as possible.
However, if the area of the electrode member is simply reduced, the detected current value is also reduced, and measurement is likely to be impossible due to a relatively low sheet resistance.
As the electrode member shape for measuring the surface resistance of the paper, a disk shape or a cylindrical shape is also conceivable. By rotating the electrode member having such a shape, there is a merit that the frictional resistance is reduced. However, in order to measure a small current, the durability quality of the conductivity with the bearing becomes a problem.
In order to increase the current value, it is necessary to increase the electrode length of the electrode member to which the voltage is applied and the counter electrode through which the current flows. When the electrode shape is a rectangle and the long side is arranged at right angles to the sheet conveyance direction, the frictional resistance increases.
With the shape and arrangement of the electrode members as shown in FIG. 3, the sheet feeding operation is not hindered by the presence of the resistance detection means 70, and the sheet can be stably conveyed and fed. Occurrence of paper defects can be prevented.

FIG. 5 shows the structure of the paper feed cassette 44 in this embodiment.
The apparatus main body is on the left side in the figure, and the paper feed cassette 44 is attached to and detached from the apparatus main body in the direction indicated by the arrow.
Normally, the side fence height on the apparatus main body side is substantially equal to the left and right as shown in FIG. 5A, but the sheet feeding cassette 44 of the present embodiment is as shown in FIG. 5B. In addition, at least a part of the side fence on the apparatus main body side has recesses 44a and 44b lower than the others so as not to interfere with the resistance detecting means 70.
As shown in FIG. 1, resistance detecting means 70 is provided corresponding to each paper feed cassette 44.
The resistance detection means 70 is separated from the surface of the paper according to the pulling-out operation of the paper feed cassette 44 by an attachment member and contact / separation means (not shown), and contacts the paper surface with an appropriate pressure according to insertion of the paper feed cassette 44. It is like that. As a result, it is possible to prevent damage to the electrodes and paper due to sliding between the electrodes and the paper.
The paper height in the paper feed cassette 44 varies depending on the number of paper sheets, but the detection unit 72 of the resistance detection means 70 is provided so that the contact pressure becomes constant following the change in the paper height.
The concave portions 44a and 44b are provided so that the operation between the resistance detection means 70 and the paper feed cassette 44 can be performed smoothly without further interference.

Since the height of the paper feed cassette or paper feed tray is optimized for the number of paper sets, the distance between the paper feed cassettes or paper feed trays is shortened. Therefore, a sufficient space for contacting and separating the resistance detection means cannot be provided. When the paper feed cassette or paper feed tray is attached and detached with a small separation, the resistance detection means easily interferes with the main body side side fence of the paper feed cassette or paper feed tray, and the resistance detection means tends to be damaged.
By adopting the configuration as shown in FIG. 5B, it is possible to prevent interference between the resistance detection means and the side fence without increasing the distance between the paper feed tray and the paper feed cassette.

As shown in FIG. 6, the image forming apparatus according to the present embodiment includes an environmental condition detection unit 82 that detects at least humidity. The control unit 84 acquires environmental information (temperature / humidity) from the environment detection unit 82, determines a sheet resistance measurement voltage based on the detected environmental information based on the print start signal, and supplies the determined voltage to the resistance detection unit 70. Apply.
The current flowing through the resistance detection means 70 by applying a voltage is detected by an ammeter 76 as a current detection means, and the sheet resistance is obtained from the voltage and current. The primary transfer current / voltage and the secondary transfer current / voltage are controlled from the obtained sheet resistance and environmental information. The relationship between these data is obtained in advance and stored as a control table.

The resistance of the paper varies greatly depending on the environment. In general, the resistance is measured at a constant voltage. However, when the resistance is measured at the same voltage in all environments, there are the following problems.
That is, when resistance increases in a low-humidity environment, the measured current value decreases and detection is impossible. On the other hand, when the resistance is lowered in a high humidity environment, the current increases and the voltage of the power source cannot be maintained, and measurement may be impossible.
On the other hand, there is a method of measuring with a constant current value. However, when the resistance increases, the voltage for passing the specified current increases, and the voltage output upper limit of the power supply is exceeded and measurement is impossible.
According to the configuration of the present exemplary embodiment, even when the use environment of the image forming apparatus greatly changes, it is possible to detect the sheet resistance under the optimum measurement conditions.

  By shortening the side fence height of the portion of the paper feed cassette 44 where the resistance detection means 70 interferes when pulled out, interference with the resistance detection means can be completely prevented, and the separation distance between the resistance detection means 70 and the paper surface Can be further reduced. Further, by reducing the distance between the resistance detection unit 70 and the paper feed cassette, it is possible to measure the paper resistance without reducing the paper feed capacity.

16 'Secondary transfer roller as secondary transfer means 21 Exposure means 40 Photosensitive drum as image carrier 44 Paper feed cassette 62 Primary transfer roller as primary transfer means 70 Resistance detection means 80 Electrode as electrode member S Paper as a recording medium

JP-A-6-161295 JP 2002-72717 A JP 2009-258473 A

Claims (6)

An image carrier, a charging unit for charging the image carrier, an exposure unit for exposing the image carrier in accordance with image information, and a latent image formed on the image carrier as a toner image. An image forming apparatus for finally transferring the toner image to a recording medium by a transfer unit;
Having resistance detection means for detecting the resistance of the surface of the recording medium;
The resistance detecting unit includes at least two electrode members that can contact and separate from the surface of the recording medium before forming a toner image, and applies a voltage to at least one of the electrode members. Having a configuration for detecting a current flowing between other electrode members not applying
An image forming apparatus that controls at least one of a transfer current and a voltage based on a detection result of the resistance detection unit. The image forming apparatus according to claim 1.
The toner image is transferred to the intermediate transfer member by the primary transfer unit, and the toner image on the intermediate transfer member is transferred to the recording medium by the secondary transfer unit. Based on the detection result, the primary transfer current is transferred. Alternatively, the image forming apparatus controls at least one of a voltage, a secondary transfer current, and a voltage. The image forming apparatus according to claim 1, wherein
The image forming apparatus according to claim 1, wherein the electrode member contacts and separates in conjunction with an attachment / detachment operation of a paper feed tray or a paper feed cassette containing the recording medium. The image forming apparatus according to claim 3.
The image is characterized in that the side fence height of the paper feed tray or paper feed cassette on the side crossing the resistance detection means in the attaching / detaching direction is low at a portion where the resistance detection means moves relatively. Forming equipment. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising: an environmental condition detection unit that detects at least humidity; and controls a voltage applied to the electrode member in accordance with a detection result of the environmental condition detection unit. The image forming apparatus according to any one of claims 1 to 5,
The image forming apparatus according to claim 1, wherein a length of the electrode member in a width direction of the recording medium perpendicular to the conveyance direction of the recording medium is shorter than a length in the conveyance direction of the recording medium.

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