JP4725222B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to a transfer technique for transferring a toner image onto a recording material.

  In recent electrophotographic image forming apparatuses, contact-type transfer means using conductive rollers or conductive brushes tend to be used instead of widely used corona dischargers (for example, Patent Document 1).

However, in the contact type transfer device, a phenomenon referred to as “missing” is a problem, and in Patent Document 1, in order to prevent this missing, the transfer means is controlled according to the thickness of the recording material. It has been proposed to control the pressing force.
JP-A-6-258967

  According to the inventor's study, it has been found that if the pressing force of the transfer means is controlled according to the thickness of the recording material as in Patent Document 1, it is not possible to sufficiently prevent voids and image unevenness.

  The voids that occur in the transfer process occur when the recording material is hard, but the hardness of the recording material does not depend only on the thickness of the recording material, but varies depending on the type of recording material. For example, a coated paper has a higher hardness than a thick non-coated paper, and is likely to be hollow out. Among the coated papers, the light coated paper, the coated paper, and the art paper have different paper hardness and different conditions that do not cause a transfer defect such as a void. Therefore, if the pressing force is changed according to the thickness of the recording material as in Patent Document 1, it is not possible to sufficiently prevent the hollowing out and the unevenness of the image.

  The present invention solves the above-described problems in the prior art, prevents voids and image irregularities that are likely to occur in the transfer process, and can form a high-quality image over a long period of time. The purpose is to provide.

The object is achieved by the following invention.
1. In an image forming apparatus having an image carrier, an image forming unit for forming a toner image on the image carrier, and a contact type transfer unit for transferring the toner image on the image carrier to a recording material.
A measuring means for measuring the hardness of the recording material;
Depending on the measurement result of the measuring means, the pressing force of the transfer means, the speed difference between the linear velocity of the image carrier and the linear velocity of the recording material, and the image carrier when the toner image is formed by the image forming means Control means for controlling at least one image forming condition of the toner adhesion amount ;
An image forming apparatus comprising:
2. 2. The image forming apparatus according to 1, wherein the control unit sets the pressing force to be lower as the hardness is higher .
3. 3. The image forming apparatus according to 1 or 2 , wherein the control unit sets the speed difference to be larger as the hardness is higher .
4). 4. The image forming apparatus according to any one of 1 to 3, wherein the control unit decreases the toner adhesion amount as the hardness is higher .
5. 5. The image forming apparatus according to any one of claims 1 to 4, further comprising a storage unit that stores a correspondence table of the hardness versus the image forming conditions .
6). In an image forming apparatus having an image carrier, an image forming unit for forming a toner image on the image carrier, and a contact type transfer unit for transferring the toner image on the image carrier to a recording material.
An image having control means for controlling the toner adhesion amount to the image carrier when the toner image is formed by the image forming means so that the toner adhesion amount decreases as the hardness of the recording material increases. Forming equipment.
7). 7. The image forming apparatus as described in 6 above, further comprising an input unit for inputting the hardness of the recording material .
8). 8. The image forming apparatus according to 6 or 7, further comprising storage means for storing a correspondence table of the hardness versus the image forming conditions.

  According to the present invention, it is possible to realize an image forming apparatus that can sufficiently prevent a void or image unevenness due to a transfer defect and stably form a high-quality image.

The present invention will be described below with reference to embodiments, but the present invention is not limited to these embodiments.
(1) Embodiment 1
(1) -1 Apparatus Configuration FIG. 1 is an overall configuration diagram of an electrophotographic color image forming apparatus capable of forming images on both sides, which is an example of an image forming apparatus according to an embodiment of the present invention. The forming apparatus 3 has a single-side mode for forming an image on one side of a sheet and a double-side mode for forming an image on both sides of the sheet.

  In FIG. 1, an image forming apparatus 3 is called a tandem color image forming apparatus, and includes an automatic document feeder 10, a document reading device 20 having a scanner function, an image forming means 31, an image processing unit 32, and a fixing device. 36, a paper feeding / conveying section 35, a paper discharging section 37, a paper discharging tray 37C, and a re-conveying means (ADU) 38 for automatic duplex copying. An image forming unit 31 that forms a toner image on the intermediate transfer member 6 as an image carrier includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K.

  The image forming unit 10Y that forms a yellow image includes a charging device 2Y, an exposure device 3Y, a developing device 4Y, a primary transfer device 7Y, and a cleaning device 8Y disposed around the photoreceptor 1Y. The image forming unit 10M that forms a magenta image includes a photoreceptor 1M, a charging device 2M, an exposure device 3M, a developing device 4M, a primary transfer device 7M, and a cleaning device 8M. The image forming unit 10C that forms a cyan image includes a photoreceptor 1C, a charging device 2C, an exposure device 3C, a developing device 4C, a primary transfer device 7C, and a cleaning device 8C. The image forming unit 10K that forms a black image includes a photoreceptor 1K, a charging device 2K, an exposure device 3K, a developing device 4K, a primary transfer device 7K, and a cleaning device 8K. The charging device 2Y and the exposure device 3Y, the charging device 2M and the exposure device 3M, the charging device 2C and the exposure device 3C, and the charging device 2K and the exposure device 3K constitute a latent image forming unit.

  The intermediate transfer member 6 as an image carrier is an endless belt, is stretched by a plurality of rollers 6A to 6E, and is rotatably supported.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred to the rotating intermediate transfer body 6 by the primary transfer devices 7Y, 7M, 7C, and 7K (primary transfer). A synthesized color image is formed. The paper P stored in the paper feed cassette 35A is fed by the paper feed means 21, and is conveyed to the secondary transfer device 7A as a transfer means via the paper feed rollers 22A, 22B, 22C, the registration rollers 23, and the like. Then, a color image is transferred onto the paper P (secondary transfer). The sheet P on which the color image has been transferred is subjected to fixing processing by heat and pressure fixing by the fixing device 36, is sandwiched between the discharge rollers 25, and is discharged and stacked on a discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred onto the paper P by the secondary transfer device 7A, the residual toner is removed from the intermediate transfer body 6 from which the paper P has been separated by the cleaning device 8A.

  Reference numerals 5Y, 5M, 5C, and 5K denote toner replenishing units that replenish new toner to the developing devices 4Y, 4M, 4C, and 4K, respectively.

  An image reading device YS including an automatic document feeder 10 and a document reading device 20 is installed on the upper part of the image forming apparatus 3. The document d placed on the document table of the automatic document feeder 10 is conveyed by a conveying unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document reader 20, and is read by the line image sensor CCD. .

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in the image processing unit, and then image writing units (exposure devices) 3Y, 3M, 3C. Send a signal to 3K.

  The automatic document feeder 10 is provided with automatic double-sided document conveying means. The automatic document feeder 10 can continuously read the contents of a large number of documents d fed from the document table and store them in the storage means (electronic RDH function). This is convenient when copying the contents of a large number of originals by the function or when transmitting a large number of originals d by the facsimile function.

  In the duplex mode, the paper P that has finished forming the image on the first surface and passed through the fixing device 36 is sent to the re-conveying means 38 by the paper discharge path switching plate 37A, and the image forming means 31 again forms an image on the second surface. After that, the paper is discharged and stacked on the paper discharge tray 37C by the paper discharge roller 37B of the paper discharge unit 37.

  FIG. 3 is a block diagram of the control system in the first embodiment of the present invention.

  In FIG. 3, reference numeral 100 denotes a control means for performing overall control, 101 denotes a paper type setting button provided in the operation unit 39 in FIG. 1, and as shown in FIG. 2, art paper, coated paper, non-coated paper , OHP, and postcards can be specified. 102 is a motor that rotationally drives the registration roller 23 and the transfer roller 7R in FIG. 1, and 103 is a motor that controls the pressing force of the transfer roller 7R. Reference numeral 104 denotes a developing bias power source for the developing devices 4Y, 4M, 4C, and 4K in FIG. 1 and is collectively shown in FIG. 104, but actually, 4YE (bias power source for the developing device 4Y) 4YE (developing device 4Y Bias power source 4YE (bias power source of developing device 4Y), 4ME (bias power source of developing device 4M), 4CE (bias power source of developing device 4C), 4KE (bias power source of developing device 4K), and developing bias power source 4YE, 4ME, 4CE, and 4KE are individually controlled.

FIG. 4 shows a mechanism for controlling the pressing force of the transfer roller 7A. The transfer roller 7R presses the recording material P against the intermediate transfer member 6 supported by the backup roller 6C, and the pressing force is applied by a compression spring SP. The pressing force by the spring SP is adjusted by rotating the cam CM by the motor 103. The secondary transfer device 7A as a transfer means is composed of a transfer roller 7R and a transfer power source 7E. In image formation, the transfer power source 7E applies a transfer roller 7R that presses the recording material P to an intermediate transfer body 6 as an image carrier. A transfer voltage is applied, and the toner image is transferred from the intermediate transfer member 6 to the recording material P.
(1) -2 Control of image forming conditions In the present invention, depending on the hardness of the recording material, the pressing force of the transfer means, the speed difference between the linear velocity of the image carrier and the linear velocity of the recording material, and the image forming means By controlling at least one image forming condition of the amount of toner adhering to the image carrier at the time of toner image formation, voids and image unevenness that are problematic in transfer are prevented.

  The void is a phenomenon in which the toner image is not locally transferred and the image is partially lost, and the image unevenness is a phenomenon in which the density of the solid image becomes non-uniform as a result of non-uniform transfer. .

  In Embodiment 1, the hardness of the recording material is measured in advance for various types of paper, the hardness of the recording material is specified by the operator specifying the paper type, and the image formation corresponding to the specified hardness is performed. A condition is set. In the first embodiment, the transfer roller 7A is used as a contact-type transfer unit, and an intermediate transfer body is used as an image carrier. However, as the contact-type transfer unit, in addition to the transfer roller, A transfer brush, transfer pad, or transfer belt can also be used.

  The present invention can also be used in an image forming apparatus that does not use an intermediate transfer member, that is, an image forming apparatus that directly transfers a toner image from a photosensitive member to a recording material. In such an image forming apparatus, A photoreceptor is used as an image carrier.

  In the first embodiment, the image forming conditions are controlled by pressing the transfer roller 7A, the linear velocity of the intermediate transfer body 6, and the linear velocity of the recording material P according to the paper type set by the operator using the paper type setting button 101. And controlling at least one of the toner adhesion amount on the image carrier when the toner image is formed by the image forming means.

  The pressing force of the transfer roller 7 </ b> R is controlled by rotating the cam CM by driving the motor 103. The difference between the linear velocity of the intermediate transfer member 6 and the linear velocity of the recording material P is that the linear velocity of the intermediate transfer member 6 is made constant, the rotational speed of the transfer roller 7R is controlled, and the linear velocity of the recording material is changed. Be controlled. The toner adhesion amount is controlled by controlling the developing bias voltage applied to the developing sleeve of the developing device 4Y, the developing sleeve of the developing device 4M, the developing sleeve of the developing device 4C, and the developing sleeve of the developing device 4K. .

  The control of the toner adhesion amount will be described by taking the developing device 4Y as an example in FIG.

  A developing bias is applied to the developing sleeve 4YS of the developing device 4Y by a developing bias power source 4YE. In the present embodiment in which reversal development using negatively charged toner is performed, a negative voltage is applied to the developing sleeve 4YS, and the output of the developing bias power supply 4YE is controlled.

  The control based on the difference in the paper type is performed using a correspondence table in which the difference in the hardness of the recording material due to the difference in the paper type is measured in advance and the image forming conditions are associated with the hardness of the recording material. The correspondence table is stored in the storage means 105 composed of a nonvolatile memory.

  This correspondence table will be described with reference to FIG. 6 and Table 1.

  The hardness of the recording material was measured using a micro rubber hardness meter MD-1 manufactured by Kobunshi Keiki Co., Ltd.

As shown by L in FIG. 6 , the micro rubber hardness tester MD-1 shows an output that varies linearly with respect to the hardness, but the output level is 1R (low hardness), 2R (low hardness), Rank to 3R (high hardness).

  Corresponding to the hardness rank levels 1R, 2R, and 3R, optimum conditions that do not cause white spots or unevenness, that is, the pressing force, speed difference, and toner adhesion amount shown in Table 1 are set.

  As shown in Table 1, the higher the hardness, the smaller the pressing force of the transfer means, the greater the speed difference, and the smaller the toner adhesion.

  For paper types such as art paper, coated paper, uncoated paper, OHP, postcard, etc., the hardness is measured using a micro rubber hardness meter MD-1, and the rank of these papers is set, The data is stored in the storage means 105.

  As is clear from the above description, the operator selects the paper type by operating the operation unit 101, whereby the hardness of the recording material is designated, and the control means CR controls the motors 102 and 103 and the developing bias power source 104. Then, image formation is performed by setting the optimum image formation conditions for the hardness of the selected recording material.

  Setting of image forming conditions will be described with reference to Table 2.

The recording materials used are classified into the following five types A to E.
A / B: Non-coated paper (plain paper is classified as non-coated paper)
C: Coated paper D: Postcard E: Art paper In Table 2, ◯ indicates a good example with almost no voids and image unevenness, Δ indicates an example in which some voids or unevenness occurs, and × indicates a void Alternatively, an example in which unevenness has occurred is shown, and xx indicates an example in which significant hollowing has occurred.

  As is apparent from Table 2, when the recording material has a low hardness, the results are good under the image forming conditions set for rank 1R, and when the recording material has a high hardness, it is set for rank 3R. The results were good under image forming conditions.

  That is, the higher the hardness of the recording material, the better the image is formed by increasing the pressing force of the transfer means, increasing the speed difference, and decreasing the toner adhesion amount.

  In Table 2, a good image is formed with the paper types A and B under the image forming conditions set for the hardness rank 1R, and with the paper type C, the image forming conditions set for the hardness ranks 2R and 3R. A good image was formed on the paper types D and E, and a good image was formed on the image forming conditions set for the hardness rank 3R.

  The relationship between the thickness or basis weight of the recording material and the image forming conditions has almost no regularity, and it is inevitable that transfer defects occur when control based on the thickness or basis weight is performed. Table 2 shows that there is regularity between the hardness of the recording material and the image forming conditions, and a good image can be formed by setting the image forming conditions corresponding to the hardness. ing.

When the control unit 100 sets the image forming condition based on the information input from the paper type setting button 101, the image forming condition for forming a good image is set.
<Embodiment 2>
The mechanical configuration of the image forming apparatus is the same as in the first and third embodiments. FIG. 7 is a block diagram of a control system according to the second embodiment of the present invention, and FIG. 8 is a diagram showing a hardness meter.

  7, 106 is a hardness meter having a performance equivalent to that of the micro rubber hardness meter MD-1, and has the structure shown in FIG.

  The hardness meter 50 includes a sensor support frame 51, a facing member 52, a probe 53, a compression spring 54, and a pressure detection sensor 55.

  A paper path through which the recording material P passes is formed between the sensor support frame 51 and the opposing member 52, and the recording material P travels through the paper path when transporting the recording material.

  When measuring the hardness of the recording material P, the recording material P is stopped, and the sensor support frame 51 is lowered as shown by an arrow to contact the recording material P. In this state, the probe 53 is moved by the force of the spring 54. As shown, the recording material P is deformed. The repulsive force of the recording material P measured by the pressure detection sensor 55 is the hardness of the recording material P.

  The output characteristic of the hardness meter 50 is adjusted to be equal to the micro hardness meter MD-1.

  The control unit 100 controls the image forming conditions by controlling the motors 102 and 103 and the developing bias power source 104 based on the output of the hardness meter 50. In the control, as in the first embodiment, an image forming condition that does not cause voids and unevenness is selected according to the hardness of the recording material.

1 is a diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows a paper type setting button. It is a block diagram of the control system in Embodiment 1 of this invention. It is a figure which shows the control mechanism of the pressing force of a transfer roller. It is a figure which shows a developing bias power supply. It is a figure which shows a hardness rank. It is a block diagram of the control system of Embodiment 2 of this invention. It is a figure which shows a hardness meter.

Explanation of symbols

3 Image forming apparatus 7A Secondary transfer apparatus 100 Control means 101 Paper type setting button 102, 103 Motor 104 Development bias power supply 105 Storage means 106 Hardness formation P Recording material

Claims (8)

In an image forming apparatus having an image carrier, an image forming unit for forming a toner image on the image carrier, and a contact type transfer unit for transferring the toner image on the image carrier to a recording material.
A measuring means for measuring the hardness of the recording material;
Depending on the measurement result of the measuring means, the pressing force of the transfer means, the speed difference between the linear velocity of the image carrier and the linear velocity of the recording material, and the image carrier when the toner image is formed by the image forming means Control means for controlling at least one image forming condition of the toner adhesion amount ;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the control unit sets the pressing force to be lower as the hardness is higher . Wherein, the higher the hardness is high, the image forming apparatus according to claim 1 or 2, characterized in that larger the speed difference. The image forming apparatus according to claim 1, wherein the control unit decreases the toner adhesion amount as the hardness increases . The image forming apparatus according to claim 1, further comprising a storage unit that stores a correspondence table of the hardness versus the image forming conditions . In an image forming apparatus having an image carrier, an image forming unit for forming a toner image on the image carrier, and a contact type transfer unit for transferring the toner image on the image carrier to a recording material.
An image having control means for controlling the toner adhesion amount to the image carrier when the toner image is formed by the image forming means so that the toner adhesion amount decreases as the hardness of the recording material increases. Forming equipment. The image forming apparatus according to claim 6 , further comprising an input unit configured to input the hardness of the recording material . The image forming apparatus according to claim 6, further comprising a storage unit that stores a correspondence table of the hardness versus the image forming conditions.

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