JP2006259551A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining high transfer efficiency while preventing image-fogging, particularly, under an environment at high or low humidity, and capable of forming a good image free from color slippage in an color image by preventing the distortion of a transfer medium. <P>SOLUTION: The humidity in the image forming apparatus 1 is detected by a humidity detecting means 7, and a plurality of rotational driving means for separately rotating photoreceptors 14y, 14m, 14c and 14k and a driving roller 25 for driving a conveying belt 23 are controlled in accordance with the detected humidity, then, the rotating velocity of the photoreceptors 14y, 14m, 14c and 14k and the velocity of the conveying belt 23 are adjusted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus using an electrophotographic method generally includes a rotating image carrier and a charging unit, an exposing unit, a developing unit, a transferring unit, a fixing unit, a cleaning unit, and a discharging unit arranged around the rotating image carrier. The The charging unit uniformly charges the surface of the image carrier. The exposure means exposes light according to image information to the charged image carrier surface to form an electrostatic latent image. The developing means stirs the toner and frictionally charges it, and forms the toner image by attaching the frictionally charged toner to the electrostatic latent image formed on the surface of the image carrier. The transfer unit transfers the toner image to the recording medium by applying a charge having a polarity opposite to that of the toner to the recording medium. The fixing unit fixes the toner image transferred by means such as heating and pressing on the recording medium. The cleaning unit collects toner remaining on the surface of the image carrier without being transferred to the recording medium. The neutralizing unit neutralizes the image carrier after the toner image is transferred. A desired image is formed on a recording medium by the image forming apparatus using the electrophotographic system configured as described above.

  In recent years, color image forming apparatuses have been developed along with the colorization of originals and the colorization of display devices such as computers. As a color image formation method, color image information is separated into yellow, magenta, cyan, and black hues, developed using a color image forming developer corresponding to the color-separated image information, and subtractive color mixing. There is a method of forming a full-color image using the action.

  When such a full-color image is formed, a toner image formed on a plurality of image carriers provided for each color is transferred to a recording medium, and is directly applied to a recording medium such as paper carried and conveyed by a conveying belt. Direct transfer method for transferring, and transferring a toner image of each color to an intermediate transfer medium such as an intermediate transfer belt that moves in the same direction at a plurality of image carriers and their contact positions. An intermediate transfer method is used in which a plurality of color toner images formed on the intermediate transfer medium are collectively transferred onto a recording medium.

  The image quality of an image formed by an image forming apparatus using a transfer method is greatly affected by the use environment. For example, in a high-temperature and high-humidity environment, the charging characteristics of the toner are deteriorated and a sufficient amount of charge cannot be imparted to the toner, so that the image density is lowered and fogging on the photoreceptor is likely to occur. In a high-temperature and high-humidity environment, the amount of moisture in a recording medium such as paper increases and the resistivity becomes low, so that toner scattering is likely to occur, fogging occurs on the recording medium, and transfer efficiency decreases. . On the other hand, in a low-temperature and low-humidity environment, the toner charge amount is extremely increased, and image fogging and density unevenness tend to occur. In a low-temperature and low-humidity environment, the moisture content of the recording medium such as paper decreases, the resistance value of the recording medium increases, the toner image on the image carrier is not efficiently transferred to the recording medium, and the image is lost. Therefore, high transfer efficiency cannot be obtained.

  In order to solve such a problem, the rotational speed of the image carrier and the speed of the recording medium or intermediate transfer medium (hereinafter sometimes referred to as a transfer medium) are suitably controlled according to the usage environment and the like. An image forming apparatus capable of obtaining transfer efficiency has been proposed (see, for example, Patent Document 1). The image forming apparatus disclosed in Patent Document 1 detects the temperature and humidity of the environment with a temperature and humidity sensor, and the speed of the transfer medium and the rotation of the image carrier according to the temperature and humidity detected by the temperature and humidity sensor. The speed is controlled to change. In the image forming apparatus disclosed in Patent Document 1, the plurality of image carriers provided for each color all rotate at the same rotational speed.

  In the image forming apparatus disclosed in Patent Document 1, the rotation speed of the image carrier and the speed of the transfer medium are controlled according to the detection result of the temperature and humidity sensor. If there is a difference between the rotational speed of the image carrier and the speed of the transfer medium, a frictional force is generated at the nip where the transfer medium and the image carrier abut due to the speed difference, and the frictional force causes the toner image to be imaged. Since it contributes to transfer from the carrier to the transfer medium, transfer efficiency can be improved. Further, in the image forming apparatus disclosed in Patent Document 1, since the image fog occurs when the difference between the rotation speed of the image carrier and the speed of the transfer medium becomes too large, the transfer efficiency is prevented while preventing the occurrence of image fog. Preferred speed difference values are described that can be increased.

  However, in the image forming apparatus of Patent Document 1, it is assumed that a plurality of image carriers provided for each color rotate all at the same rotational speed. However, in an image forming method using an actual direct transfer method or an intermediate transfer method. Due to factors such as manufacturing errors of the photoconductor as the image carrier, all of the plurality of photoconductors may not be driven at the same rotational speed with respect to the transfer medium.

  When the plurality of image carriers do not rotate at the same rotational speed, the frictional force received by the transfer medium at the nip portion where the plurality of image carriers and the transfer medium abut is different at the nip portion where the image carrier abuts. For example, when the speed of the transfer medium is higher than the rotation speed of the image carrier, the frictional force that the transfer medium receives is opposite to the direction in which the transfer medium moves, and the magnitude of the frictional force is that of the image carrier. The larger the difference between the rotational speed and the transfer medium speed, the larger the difference.

  Here, the difference between the rotational speed of the image carrier provided on the downstream side in the moving direction of the transfer medium and the speed of the transfer medium is the difference between the rotational speed of the image carrier provided on the upstream side and the speed of the transfer medium. The frictional force received at the nip portion with the image carrier provided on the downstream side is larger than the frictional force received at the nip portion with the image carrier provided on the upstream side. In such a case, a large frictional force acts on the downstream side in the moving direction of the transfer medium, and as a result, the transfer medium becomes slack.

  Such looseness of the transfer medium is different from that in a normal environment where the moisture content of the transfer medium in a low or high humidity environment is different from that in a normal environment, such as the dynamic friction coefficient of the transfer medium, the timing at which the transfer medium and the image carrier contact each other This problem is particularly likely to occur in different environments. When such looseness of the transfer medium occurs, the image transfer position from the image carrier on the transfer medium is shifted, and there is a problem that color shift occurs in the color image.

JP 2004-219489 A

  An object of the present invention is to obtain a good image which can obtain a high transfer efficiency while preventing image fogging, and prevents a color medium from being color-shifted by preventing a transfer medium from loosening, particularly in an environment of high or low humidity. Is to provide an image forming apparatus capable of forming the image.

The present invention is provided with a plurality of image carriers that respectively carry toner images of different colors and a plurality of image carriers, and the toner images formed on the plurality of image carriers are superimposed and transferred. An image forming apparatus including a recording medium carrier that carries and conveys a recording medium.
A plurality of rotation driving means for respectively rotating a plurality of image carriers;
A recording medium carrier driving means for driving the recording medium carrier;
Humidity detecting means for detecting humidity in the image forming apparatus;
Control means for controlling the operation of the rotation driving means and the recording medium carrier driving means in accordance with the humidity detected by the humidity detection means, and adjusting the rotational speed of the image carrier and the speed of the recording medium carrier. An image forming apparatus.

In the present invention, the plurality of image carriers are:
A yellow toner image carrier for carrying a yellow toner image and a magenta toner image carrier for carrying a magenta toner image, which are provided in order from the upstream side to the downstream side in the carrying direction of the recording medium carried by the recording medium carrier. A cyan toner image carrier that carries a cyan toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the speed of the recording medium carrier is Va. and when,
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Va / Vk) which is a ratio between the speed Va of the recording medium carrier and the rotational speed Vk of the black toner image carrier. When the operation of the rotation driving means and the recording medium carrier driving means is controlled so as to be larger than 1.0 and the humidity detected by the humidity detecting means is lower than a predetermined reference value, the speed ratio (Va / Vk) Is a value closer to 1.0 than the speed ratio (Va / Vk) when the humidity is within the predetermined reference value range and larger than 1.0, and satisfies the following formula: Thus, the operation of the plurality of rotation driving means and the recording medium carrier driving means is controlled.
Vk>Vc>Vm> Vy

In the present invention, the control means includes
When the humidity detected by the humidity detection means is within a predetermined reference value range, the rotational drive means and the recording medium carrier drive means so that the speed ratio (Va / Vk) is 1.008 or more and 1.012 or less. When the humidity detected by the humidity detecting means is lower than a predetermined reference value, a plurality of rotational driving means and recording are performed so that the speed ratio (Va / Vk) is 1.005 or more and 1.007 or less. The operation of the medium carrier driving means is controlled.

In the present invention, the plurality of image carriers are:
A yellow toner image carrier for carrying a yellow toner image and a magenta toner image carrier for carrying a magenta toner image, which are provided in order from the upstream side to the downstream side in the carrying direction of the recording medium carried by the recording medium carrier. A cyan toner image carrier that carries a cyan toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the speed of the recording medium carrier is Va. and when,
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Va / Vk) which is a ratio between the speed Va of the recording medium carrier and the rotational speed Vk of the black toner image carrier. When the operation of the rotation driving means and the recording medium carrier driving means is controlled so that the value is larger than 1.0, and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the speed ratio (Va / Vk) Is a value closer to 1.0 than the speed ratio (Va / Vk) when the humidity is within the predetermined reference value range and larger than 1.0, and satisfies the following formula: Thus, the operation of the plurality of rotation driving means and the recording medium carrier driving means is controlled.
Vk>Vc>Vm> Vy

In the present invention, the control means includes
When the humidity detected by the humidity detection means is within a predetermined reference value range, the rotational drive means and the recording medium carrier drive means so that the speed ratio (Va / Vk) is 1.008 or more and 1.012 or less. When the humidity detected by the humidity detecting means is higher than a predetermined reference value, a plurality of rotational driving means and recording are performed so that the speed ratio (Va / Vk) is 1.005 or more and 1.007 or less. The operation of the medium carrier driving means is controlled.

In addition, the present invention provides a plurality of image carriers that respectively carry toner images of different colors and a plurality of image carriers, and the toner images formed on the plurality of image carriers are superimposed and transferred. In an image forming apparatus including an intermediate transfer medium
A plurality of rotation driving means for respectively rotating a plurality of image carriers;
Intermediate transfer medium driving means for driving the intermediate transfer medium;
Humidity detecting means for detecting humidity in the image forming apparatus;
Control means for controlling the operation of the rotation driving means and the intermediate transfer medium driving means in accordance with the humidity detected by the humidity detection means, and adjusting the rotation speed of the image carrier and the speed of the intermediate transfer medium. An image forming apparatus.

In the present invention, the plurality of image carriers are:
A yellow toner image carrier that carries a yellow toner image, a magenta toner image carrier that carries a magenta toner image, and a cyan toner image that are provided in order from the upstream side to the downstream side in the moving direction of the intermediate transfer medium. A cyan toner image carrier that carries a black toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the intermediate transfer medium speed is Vb. When
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Vb / Vk) which is a ratio between the speed Vb of the intermediate transfer medium and the rotational speed Vk of the black toner image carrier is obtained. When the rotation driving means and the intermediate transfer medium driving means are controlled to be larger than 1.0 and the humidity detected by the humidity detecting means is lower than a predetermined reference value, the speed ratio (Vb / Vk) is The value is closer to 1.0 than the speed ratio (Vb / Vk) when the humidity is within the range of the predetermined reference value, and is larger than 1.0, and the following equation is satisfied. And a plurality of rotation driving means and intermediate transfer medium driving means.
Vk>Vc>Vm> Vy

In the present invention, the control means includes
When the humidity detected by the humidity detecting means is within a predetermined reference value range, the rotation driving means and the intermediate transfer medium driving means are set so that the speed ratio (Vb / Vk) is 1.008 or more and 1.012 or less. When the operation is controlled and the humidity detected by the humidity detecting unit is lower than a predetermined reference value, the plurality of rotation driving units and the intermediate transfer unit are set so that the speed ratio (Vb / Vk) is 1.005 or more and 1.007 or less. The operation of the medium driving means is controlled.

In the present invention, the plurality of image carriers are:
A yellow toner image carrier that carries a yellow toner image, a magenta toner image carrier that carries a magenta toner image, and a cyan toner image that are provided in order from the upstream side to the downstream side in the moving direction of the intermediate transfer medium. A cyan toner image carrier that carries a black toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the intermediate transfer medium speed is Vb. When
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Vb / Vk) which is a ratio between the speed Vb of the intermediate transfer medium and the rotational speed Vk of the black toner image carrier is obtained. When the rotation driving means and the intermediate transfer medium driving means are controlled to be larger than 1.0 and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the speed ratio (Vb / Vk) is The value is closer to 1.0 than the speed ratio (Vb / Vk) when the humidity is within the range of the predetermined reference value, and is larger than 1.0, and the following equation is satisfied. And a plurality of rotation driving means and intermediate transfer medium driving means.
Vk>Vc>Vm> Vy

In the present invention, the control means includes
When the humidity detected by the humidity detecting means is within a predetermined reference value range, the rotation driving means and the intermediate transfer medium driving means are set so that the speed ratio (Vb / Vk) is 1.008 or more and 1.012 or less. When the operation is controlled and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the plurality of rotational driving means and intermediate transfer means so that the speed ratio (Vb / Vk) is 1.005 or more and 1.007 or less. The operation of the medium driving means is controlled.

  According to the present invention, a plurality of image carriers that respectively carry toner images of different colors and a plurality of image carriers that are provided so as to be in contact with each other, the toner images formed on the plurality of image carriers are superimposed. A plurality of rotation driving means for rotating each of the plurality of image carriers, and a recording medium carrier driving means for driving the recording medium carrier. And a humidity detecting means for detecting the humidity in the image forming apparatus, and controlling the rotation driving means and the recording medium carrier driving means in accordance with the humidity detected by the humidity detecting means to control the rotation speed and recording of the image carrier. An image forming apparatus including a control unit that adjusts the speed of the medium carrier is provided. As described above, since the rotation speed of the image carrier and the speed of the recording medium carrier can be adjusted according to the detected humidity, the image fogging can be performed even in an environment where the humidity is different from the predetermined reference value range. As a result, high transfer efficiency can be obtained, and the transfer medium can be prevented from slacking to form a good image without causing color misregistration of the color image. In addition, by controlling the rotation speed of each image carrier in this way, it is possible to reduce a speed shift due to an error in manufacturing a photoconductor as an image carrier.

  According to the invention, the plurality of image carriers are yellow toner images that carry yellow toner images sequentially provided from the upstream side to the downstream side in the conveyance direction of the recording medium conveyed by the recording medium carrier. A carrier, a magenta toner image carrier that carries a magenta toner image, a cyan toner image carrier that carries a cyan toner image, and a black toner image carrier that carries a black toner image. When the humidity detected by the humidity detection means is in a low humidity environment lower than a predetermined reference value, the speed of the recording medium carrier and the black are lower than in an ordinary humidity environment where the humidity is within the predetermined reference value range. The speed ratio, which is the ratio to the rotational speed of the color toner image carrier, is a value close to 1.0 and larger than 1.0, and is set on the downstream side in the conveyance direction of the recording medium. Rotational speed of the image bearing member to be is controlled to be greater than the rotational speed of the image bearing member provided on the upstream side. In a low-humidity environment, by increasing the ratio of the speed of the recording medium carrier to the rotational speed of the image carrier, a frictional force is generated at the contact portion between the recording medium and the image carrier, and the friction Since the toner image formed on the image carrier by force can be more efficiently transferred to the transfer medium, the transfer efficiency can be improved. Further, by making the speed ratio closer to 1.0 in a low humidity environment than in a normal humidity environment, a difference in image quality, particularly image fogging, occurs between a formed image in a low humidity environment and a formed image in a normal humidity environment. The amount difference can be reduced. Further, in a low humidity environment, the rotational speed of the downstream image carrier is made larger than the rotational speed of the upstream image carrier so as to be close to the speed of the recording medium carrier. The friction force generated at the contact portion with the medium is smaller than the friction force generated at the contact portion between the upstream image carrier and the recording medium. For this reason, the frictional force decreases from the upstream side to the downstream side in the direction in which the recording medium is transported, and the tension generated at the contact portion between the downstream image carrier and the recording medium causes the upstream image carrier to move. Since the tension is greater than the tension generated at the contact portion between the body and the recording medium, the recording medium can be prevented from slacking, and a good image without color misregistration can be formed.

  According to the present invention, the control means controls the operation of the rotation driving means and the recording medium carrier driving means so that the speed ratio becomes 1.008 or more and 1.012 or less under the normal humidity environment. Under the environment, the operation of the plurality of rotation driving means and the recording medium carrier driving means is controlled so that the speed ratio becomes 1.005 or more and 1.007 or less. By setting the speed ratio to such a value in each of the normal humidity environment and low humidity environment, high transfer efficiency can be obtained for the formed image, and constant image quality can be maintained even in environments with different humidity. can do.

  Further, according to the present invention, when the humidity detected by the humidity detecting means is in a high humidity environment where the humidity is higher than a predetermined reference value, the control means performs the speed of the recording medium carrier and the image carrier in the same manner as described above. Since the rotation speed is adjusted, the transfer efficiency is high even in a high humidity environment, and a good image that does not cause image fogging and color misregistration can be formed.

  Further, according to the present invention, since a suitable speed ratio is set for each of the normal humidity environment and the high humidity environment, stable transfer efficiency and image fog generation amount can be obtained regardless of the humidity environment.

  Further, according to the present invention, a plurality of image carriers that respectively carry toner images of different colors and a plurality of image carriers that are provided so as to be in contact with the plurality of image carriers and the toner images formed on the plurality of image carriers are superimposed. A plurality of rotation driving means for rotating a plurality of image carriers, an intermediate transfer medium driving means for driving the intermediate transfer medium, and humidity in the image forming apparatus. Humidity control means for controlling the operation of the rotation drive means and the intermediate transfer medium drive means in accordance with the humidity detected by the humidity detection means, and a control means for adjusting the rotation speed of the image carrier and the speed of the intermediate transfer medium. An image forming apparatus is provided. As described above, since the rotation speed of the image carrier and the speed of the intermediate transfer medium are adjusted according to the detected humidity, even if the humidity is different from a predetermined reference value range, An image with high transfer efficiency can be formed while preventing color misregistration.

  Further, according to the present invention, in a low humidity environment, the control means has a speed ratio, which is a ratio between the speed of the intermediate transfer medium and the rotation speed of the black color toner image carrier, than the speed ratio in the normal humidity environment. Is also a value close to 1.0 and larger than 1.0, and the rotational speed of the image carrier provided on the downstream side in the moving direction of the intermediate transfer medium is the image provided on the upstream side. Control is performed so as to be larger than the rotational speed of the carrier. By increasing the speed ratio from 1.0 in a low humidity environment, the transfer efficiency is improved, and by making the speed ratio closer to 1.0 than in a normal humidity environment, the formed image and the normal humidity in the low humidity environment. The difference in the amount of image fog generation under the environment can be reduced. Further, the rotational speed of the image carrier is preferably controlled in a low humidity environment, so that the recording medium can be prevented from slacking and a good image without color misregistration can be formed.

  Further, according to the present invention, since a suitable speed ratio is set for each of the normal humidity environment and the low humidity environment, stable transfer efficiency and image fog generation amount can be obtained regardless of the humidity environment.

  According to the present invention, when the humidity detected by the humidity detecting means is in a high humidity environment where the humidity is higher than a predetermined reference value, the control means performs the speed of the intermediate transfer medium and the rotation of the image carrier in the same manner as described above. Since the speed is adjusted, the transfer efficiency is high even in a high humidity environment, and it is possible to form a good image that does not cause image fogging and color misregistration.

  Further, according to the present invention, since a suitable speed ratio is set for each of the normal humidity environment and the high humidity environment, a stable image can always be formed even under an environment with different humidity. .

  The image forming apparatus of the present invention includes a plurality of image bearing members that respectively carry toner images of different colors, and a toner image that is provided so as to contact the plurality of photosensitive members and is formed on the plurality of photosensitive members. Conveying belt, which is a recording medium carrying member that carries and conveys a recording medium to which images are superimposed and transferred, a plurality of rotation driving means that respectively rotate a plurality of photosensitive members, and a recording medium carrying member drive that drives the conveying belt A drive roller that is a means, a humidity detection means that detects humidity in the image forming apparatus, and a drive roller that is a rotation drive means and a recording medium carrier drive means according to the humidity detected by the humidity detection means. And a control means for adjusting the rotational speed of the photosensitive member and the speed of the conveyor belt.

  FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 generally includes an image forming unit 2 that forms an image on a recording medium 5, a paper feeding unit 3 that supplies the recording medium 5 to the image forming unit 2, and a document placed on a document table 6. And an image reading unit 4 for reading the images and / or characters. In addition, the image forming apparatus 1 of the present embodiment is provided with a humidity detection sensor 7 that is a humidity detection means for detecting the humidity in the image forming apparatus 1, and is not shown depending on the humidity detected by the humidity detection sensor 7. The control means provided in the CPU (Central Processing Unit) controls the operation of the image forming apparatus 1. The operation control of the image forming apparatus 1 by the control unit will be described later.

  The image forming unit 2 includes image forming units 10y, 10m, 10c, and 10k, a transfer unit 11, a fixing unit 12, and a paper discharge unit 13.

  The image forming units 10y, 10m, 10c, and 10k form electrostatic latent images corresponding to the image information of the respective hues on the surfaces of the photoreceptors 14y, 14m, 14c, and 14k that are image carriers, and the electrostatic latent images are formed. Development is performed to form toner images of each color. That is, the image forming unit 10y forms a toner image corresponding to yellow image information, the image forming unit 10m forms a toner image corresponding to magenta image information, and the image forming unit 10c uses cyan image information. The image forming unit 10k forms a toner image corresponding to black image information.

  The image forming units 10m, 10c, and 10k have the same structure as the image forming unit 10y except that they use a magenta developer, a cyan developer, or a black developer, respectively. Further, “m” indicating magenta, “c” indicating cyan, or “k” indicating black is added to the end of each reference numeral, and the description is omitted. The image forming units 10y, 10m, 10c, and 10k are arranged in a line in this order from the upstream side in the sub-operation direction, that is, the direction of the arrow 23a, which is the moving (rotating) direction of the conveyance belt 23 that is a recording medium carrier. Arranged.

  The image forming unit 10y includes a photoreceptor 14y that is a yellow toner image carrier that carries a yellow toner image, a charging unit 15y that uniformly charges the surface of the photoreceptor 14y, and a surface of the charged photoreceptor 14y. An exposure unit 16y that exposes light according to image information to form an electrostatic latent image; and a developing unit 17y that forms a toner image by attaching toner to the electrostatic latent image formed on the surface of the photoreceptor 14y; The cleaning unit 18y removes and collects toner remaining on the surface of the photoreceptor 14y without being transferred to the recording medium 5 by the transfer unit 11 described later.

  The photoreceptor 14y is an image carrier on which an electrostatic latent image is formed by exposure with light according to image information, and is provided rotatably. The photoconductor 14y is supported by a rotation driving means (not shown) so as to be rotatable around an axis, and includes a cylindrical or columnar conductive substrate and a photosensitive layer formed on the surface of the conductive substrate. The The rotation driving unit of the photoconductor 14y is controlled by a control unit provided in the CPU, and the rotation speed Vy of the photoconductor 14y is determined.

  The surface of the photoconductor 14y is provided with a rotation speed detection means (not shown) that detects the actual rotation speed of the photoconductor 14y. The rotational speed detection means can detect the rotational speed when the photosensitive member 14y actually rotates by detecting a mark previously added to the photosensitive member 14y, for example, and can detect the detected rotational speed of the photosensitive member 14y. Output to the control means. The control means controls the operation of the rotation driving means according to the humidity detected by the humidity detection means and the actual rotation speed of the photoconductor 14y detected by the rotation speed detection means, and the rotation speed Vy of the photoconductor 14y. Adjust. Details of the control of the rotational speed Vy of the photoreceptor 14y by this control means will be described later.

  For example, an aluminum base tube can be used as the conductive substrate of the photoreceptor 14y. The photosensitive layer may be formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material, and includes the charge generation material and the charge transport material in one layer. There may be. An underlayer may be provided between the photosensitive layer and the conductive substrate. Furthermore, a protective layer may be provided on the surface of the photosensitive layer. The photoconductor 21y is driven to rotate in the clockwise direction toward the paper surface of FIG.

  The charging unit 15y charges the surface of the photoreceptor 14y to a potential having a predetermined polarity. The charging unit 15y of this embodiment charges the photoreceptor 14y by a non-contact corona charging method. The charging unit is not limited to the corona charging method, and may be a contact charging unit such as a charging roller or a charging brush.

  The exposure unit 16y receives a pixel signal corresponding to the yellow color of the image data of the document placed on the document table 6 from the image reading unit 4 to be described later, and is a laser that is dot light modulated according to the pixel signal. A semiconductor laser element (not shown) that emits light, a polygon mirror 19y for deflecting laser light from the semiconductor laser element in the main scanning direction, and a laser beam deflected by the polygon mirror 19y are imaged on the surface of the photoreceptor 14y. Fθ lens 20y and a plurality of mirrors 21y and 22y. The exposure unit 16y irradiates the surface of the photoreceptor 14y with a laser beam, and forms an electrostatic latent image corresponding to yellow image information on the surface of the photoreceptor 14y.

  The developing means 17y is provided facing the photoreceptor 14y, supplies toner to the photoreceptor 14y, and uses the electrostatic latent image on the photoreceptor 14y formed by the exposure unit 16y as a toner image. The developing unit 17y is provided so as to be in contact with the surface of the photoreceptor 14y and to be rotatable about an axis, and accommodates a developing roller for supplying yellow toner to the electrostatic latent image on the surface of the photoreceptor 14y, and the yellow toner. The toner container includes a toner container, and a stirring roller that is rotatably provided around the axis inside the toner container and supplies yellow toner to the surface of the developing roller.

  The yellow toner accommodated in the toner container of the present embodiment is frictionally charged by the agitation of the agitation roller, becomes negatively charged, and is supplied to the developing roller. The developing roller includes a fixed magnetic pole and is supported by the toner container so as to be driven to rotate counterclockwise toward the paper surface of FIG. 1. A developing bias (not shown) is applied to the developing roller. A developing bias having the same polarity as the toner, that is, a negative polarity is applied by the means.

  The yellow toner supplied to the surface of the developing roller is supplied to the electrostatic latent image on the surface of the photoconductor 14y using a potential difference between the photoconductor 14y and the developing roller, and a toner image corresponding to the yellow image information is generated. Form.

  The cleaning unit 18y removes and collects the yellow toner remaining on the surface of the photoreceptor 14y after the yellow toner image on the surface of the photoreceptor 14y is transferred to the recording medium 5 carried on the transport belt 23 described later. .

  Hereinafter, the operation of the image forming unit 10y will be described. First, the surface of the photoconductor 14y is charged to, for example, -600 V by the charging unit 15y while the photoconductor 14y is rotated around its axis. Next, the surface of the charged photoreceptor 14y is irradiated with laser light corresponding to yellow image information from the exposure unit 16y, and an electrostatic latent image having an exposure potential of −70 V corresponding to yellow image information is obtained. Form. Next, yellow toner supplied to the surface of the developing roller of the developing unit 17y is brought into contact with the surface of the photoreceptor 14y. A DC voltage of −240 V is applied as a developing bias to the developing roller, and yellow toner in a negatively charged state adheres to the electrostatic latent image due to a potential difference between the developing roller and the photosensitive member 14y, and the surface of the photosensitive member 14y. A yellow toner image is formed. As will be described later, the yellow toner image formed on the surface of the photoreceptor 14y is transferred to the recording medium 5 that is carried and conveyed by the conveyance belt 23 that is pressed against the surface of the photoreceptor 14y and driven in the direction of the arrow 23a. The When the toner image is transferred to the recording medium 5, the yellow toner remaining on the surface of the photoreceptor 14y is removed and collected by the cleaning unit 18y.

  The transfer unit 11 includes a conveyance belt 23 that is a recording medium carrier, transfer means 24y, 24m, 24c, and 24k, a driving roller 25 that is a recording medium carrier driving means, and a driven roller 26. .

  The conveyor belt 23 is provided so as to abut on the photoreceptors 14y, 14m, 14c, and 14k that are a plurality of image carriers, and the toner images formed on the photoreceptors 14y, 14m, 14c, and 14k are superimposed and transferred. This is a recording medium carrier that carries and conveys the recording medium 5. The conveyance belt 23 is stretched between a driving roller 25 which is a recording medium carrier driving means for driving the conveyance belt 23 which is a recording medium carrier and a driven roller 26 to form a loop-shaped movement path. And is driven in the sub-operation direction, that is, in the direction of the arrow 23a.

  The conveyor belt 23 is in pressure contact with the photoreceptors 14y, 14m, 14c, and 14k in this order. The positions where the conveyor belt 23 is pressed against the photoreceptors 14y, 14m, 14c, and 14k are the transfer positions of the toner images of the respective hues. Transfer means 24y, 24m, 24c, and 24k are disposed at positions facing the photoconductors 14y, 14m, 14c, and 14k via a recording medium 5 and a conveying belt 23 that are supplied by a sheet feeding unit 3 to be described later.

  The transfer units 24y, 24m, 24c, and 24k are respectively a transfer drive roller that is in pressure contact with the transport belt 23 and can be driven to rotate about its axis by a drive unit (not shown), and a transfer driven roller that is driven by the rotation of the transfer drive roller. And a transfer belt stretched between the transfer driving roller and the transfer driven roller. Further, the transfer means 24y, 24m, 24c, and 24k have toners for transferring the toner images formed on the surfaces of the photoreceptors 14y, 14m, 14c, and 14k onto the recording medium 5 carried and conveyed by the conveyance belt 23. A transfer bias having a polarity opposite to the charging polarity is applied.

  A high voltage is uniformly applied to the conveyance belt 23 and the recording medium 5 carried on the conveyance belt 23 by the transfer bias applied to the transfer units 24y, 24m, 24c, and 24k. Thus, the yellow, magenta, cyan, and black toner images formed on the photoreceptors 14y, 14m, 14c, and 14k are sequentially superimposed on the recording medium 5 and transferred to the recording medium 5. A multicolor toner image is formed. However, when image information of only a part of the hues of yellow, magenta, cyan, and black is input, the hue of the input image information among the image forming units 10y, 10m, 10c, and 10k. A toner image is formed only in the image forming unit corresponding to.

  The driving roller 25 is a recording medium carrier driving unit that drives the conveyance belt 23 that is a recording medium carrier. The driving roller 25 is controlled by a control unit provided in the CPU, and the speed Va of the conveying belt 23 that moves (rotates) is determined by the rotation of the driving roller 25. The speed Va of the transport belt 23 is the speed at which the recording medium 5 is transported. Details of the control of the speed Va of the conveyor belt 23 will be described later. The driven roller 26 rotates following the rotation of the driving roller 25 while applying a constant tension to the conveyor belt 23 so that the conveyor belt 23 does not sag.

  A neutralization unit 27 is provided between the image forming unit 10k and a fixing unit 12 described later. An AC voltage is applied to the charge removal unit 27 by an AC voltage application unit (not shown), and the recording medium 5 electrostatically attracted to the conveyance belt 23 is separated from the conveyance belt 23.

  The transfer unit 11 superimposes and transfers the toner images of the respective colors formed on the photoreceptors 14y, 14m, 14c, and 14k to a predetermined position of the recording medium 5 carried and transported by the transport belt 23, and multi-color toner images. Form. This toner image is fixed on the recording medium 5 by the fixing unit 12.

  The fixing unit 12 includes a heating roller 28 and a pressure roller 29. The heating roller 28 is provided so as to be rotatable around an axis by a driving means (not shown). Inside the heating roller 28, a heater such as a halogen lamp is provided. The pressure roller 29 is provided in pressure contact with the heating roller 28 via the recording medium 5.

  In the fixing unit 12, the recording medium 5 onto which the toner image has been transferred by the transfer unit 11 is conveyed to the pressure contact portion between the heating roller 28 and the pressure roller 29, and is heated and pressed by the heating roller 28 and the pressure roller 29. Is done. In this way, the toner image transferred to the recording medium 5 is fixed to the recording medium 5. The recording medium 5 on which the toner image is fixed by the fixing unit 12 is conveyed to the paper discharge unit 13 of the image forming apparatus 1.

  The paper discharge unit 13 includes a paper discharge tray 30 provided outside the housing of the image forming apparatus 1 and paper discharge rollers 31 a and 31 b provided near the paper discharge tray 30. The recording medium 5 on which the toner image is fixed by the fixing unit 12 is fed by the paper discharge rollers 31 a and 31 b, discharged to the outside of the image forming apparatus 1, and placed on the paper discharge tray 30.

  The image forming apparatus 1 including the image forming unit 2 as described above includes a paper feeding unit 3. The paper feeding unit 3 includes a recording medium cassette 32 that accommodates the recording medium 5, a pickup roller 33 that feeds the recording medium 5 one by one to the conveyance path P, and a toner image on the photosensitive member 14y that is in contact with the transfer unit 24y. A plurality of sets of registration rollers for feeding the recording medium 5 to the transfer position in synchronism with the transfer to the transfer position, which is a pressure contact portion with the body 14y.

  In the paper feeding section 3, the recording medium 5 accommodated in the recording medium cassette 32 is fed one by one to the transport path P by the pickup roller 33, and the transfer means 24y and the photoreceptor 14y are transferred by a plurality of sets of registration rollers. It is fed to the transfer position which is the press contact part.

  Further, the image reading unit 4 provided in the image forming apparatus 1 reads an image and / or characters of a document placed on the document table 6. The document table 6 is supported such that the upper surface thereof can be opened and closed with respect to the document table 6, and a document placement surface on which the document is placed is provided. The placement of the document on the document table 6 may be performed manually by the user or may be performed by an automatic document feeder (not shown).

  The image reading unit 4 is disposed below the document table 6 in order to read an image of the document placed on the document table 6. The image reading unit 4 includes a first document scanning unit 35 and a second document scanning unit 36 that reciprocate in parallel along the lower surface of the document table 6, an optical lens 37, and a CCD (Charge Coupled Device) that is a photoelectric conversion element. And a line sensor 38.

  The first document scanning unit 35 includes an exposure lamp that exposes the surface of the document image, and a first mirror that deflects the reflected light image from the document toward the second document scanning unit 36. , While reciprocating in parallel at a constant scanning speed while maintaining a constant distance. The second document scanning unit 36 includes second and third mirrors that deflect the reflected light image from the document deflected by the first mirror of the first document scanning unit 35 further toward the optical lens 37. The first document scanning unit 35 reciprocates in parallel with the first document scanning unit 35 while maintaining a constant speed relationship.

  The optical lens 37 reduces the reflected light image from the original deflected by the third mirror of the second original scanning unit 36 and forms the reduced optical image at a predetermined position on the CCD line sensor 38. The CCD line sensor 38 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 38 reads a black and white image or a color image, converts the image information of the image into an electrical signal of each color, and outputs it to the exposure units 16y, 16m, 16c, and 16k.

  Hereinafter, operation control of the image forming apparatus 1 by the control unit provided in the above-described CPU, which is the most characteristic feature of the image forming apparatus 1 of the present embodiment, will be described. As described above, the control means depends on the humidity detected by the humidity detection sensor 7 and the actual rotation speed detected by the rotation speed detection means provided in each of the plurality of photoconductors 14y, 14m, 14c, and 14k. The operation of the image forming apparatus 1, more specifically, a rotation driving means (not shown) for rotating the photoreceptors 14y, 14m, 14c, and 14k, and a driving roller that is a recording medium carrier driving means for driving the conveying belt 23, respectively. 25 operations are controlled. With this control, the rotational speeds Vy, Vm, Vc, Vk of the photoreceptors 14y, 14m, 14c, 14k and the speed Va of the conveyor belt 23 can be adjusted according to the humidity detected by the humidity detection sensor 7, respectively.

In a normal temperature and humidity environment (N / N environment), for example, a temperature of 23 ° C. and a humidity of 60% RH (Relative
In the environment of Humidity), the rotational speeds Vy, Vm, Vc, Vk of the photoconductors 14y, 14m, 14c, 14k and the speed Va of the conveyor belt 23 are the same, that is, the photoconductors 14y, 14m, The rotational speeds Vy, Vm, Vc, Vk of 14c and 14k and the speed Va of the conveyor belt 23 are controlled as represented by the following formula (1). Further, the ratio of the speed Va of the conveyor belt 23 to the rotational speed Vk of the photosensitive member 14k carrying the black toner image (Va / Vk; hereinafter simply referred to as a speed ratio) is greater than 1.0. It is controlled to be large.
Vk = Vc = Vm = Vy (1)

  On the other hand, in a low-temperature and low-humidity environment (L / L environment), for example, in an environment at a temperature of 15 ° C. and humidity of 10% RH, or in a high-temperature and high-humidity environment (H / H environment), for example, in an environment of a temperature of 32 ° C. and humidity of 85% RH In this case, image fog is likely to occur. Also, in a low or high humidity environment, the moisture content of the recording medium 5 such as paper is different from that in the normal humidity environment, and the transfer efficiency is lowered and the recording medium 5 is slack that causes color shift of the formed image. Is likely to occur.

The control means provided in the image forming apparatus 1 of the present embodiment is a low humidity environment where the humidity is lower than a predetermined reference value that may cause the above-described problem, or a high humidity that is higher than the predetermined reference value. In a humid environment, the rotational speeds Vy, Vm, Vc, Vk of the photoreceptors 14y, 14m, 14c, and 14k and the speed Va of the conveyor belt 23 satisfy the following formula (2), and in a low-humidity environment or high Control is performed so that the speed ratio (Va / Vk) in a wet environment is a value closer to 1.0 than the speed ratio (Va / Vk) in a normal temperature and normal humidity environment and is larger than 1.0. Is done.
Vk>Vc>Vm> Vy (2)

  When the above formula (2) is satisfied, a difference can be provided between the rotational speed of the photoconductors 14y, 14m, 14c, and 14k and the speed of the conveyor belt 23. Furthermore, since the speed ratio (Va / Vk) in a low or high humidity environment is a value larger than 1.0, Va> Vk is satisfied, whereby the rotational speed of the photoreceptors 14y, 14m, 14c, and 14k and the conveyance belt are satisfied. A difference can be made to the speed of 23. Due to such a speed difference, a frictional force acting in the direction in which the recording medium 5 is conveyed is generated in the contact portion between the photosensitive members 14y, 14m, 14c, and 14k and the recording medium 5 carried and conveyed by the conveying belt 23. This can contribute to efficiently transferring the toner images carried on the photoreceptors 14y, 14m, 14c, and 14k to the recording medium 5.

  Further, the magnitude of the frictional force generated at the contact portion between the photoconductors 14y, 14m, 14c, and 14k and the recording medium 5 carried and transported by the transport belt 23 is determined by the photoconductors 14y, 14m, and 14c at the respective contact portions. , 14k and the speed Va of the conveyor belt 23 are determined by the magnitude of the difference between the rotational speeds Vy, Vm, Vc, and Vk. That is, by setting the speed ratio (Va / Vk) to a value larger than 1.0 and satisfying the above formula (2), the speed is provided in order from the upstream side to the downstream side in the movement (rotation) direction of the conveyor belt 23. The photoconductors 14y, 14m, 14c, and 14k have a frictional force that decreases in this order at each contact portion with the recording medium 5. As a result, the tension generated at the contact portion between the photoconductors 14y, 14m, 14c, 14k and the recording medium 5 provided in order from the upstream side to the downstream side is in the order provided from the downstream side, that is, the photoconductor 14k. , 14c, 14m, and 14y, the slackness of the recording medium 5 can be prevented, and a good image without color misregistration can be formed.

  In the present invention, the humidity is within a predetermined reference value range (normal humidity environment) is an environment where the humidity is higher than 20% RH and lower than 80% RH, and the humidity is lower than the predetermined reference value. A low environment (low humidity environment) is an environment where the humidity is 20% RH or less, and an environment where the humidity is higher than a predetermined reference value (high humidity environment) is an environment where the humidity is 80% RH or more. .

  Further, the rotational speed of the photoconductors 14y, 14m, 14c, and 14k and the speed of the transport belt 23 in the normal humidity environment, and the rotational speed and the transport belt 23 of the photoconductors 14y, 14m, 14c, and 14k in the low-humidity or high-humidity environment. The speed of the toner can also be determined by individually adjusting in each environment. The rotational speed of any one of the photoconductors or the speed of the conveyor belt 23 is fixed, and the remaining speed is adjusted so as to satisfy the above. May be.

  FIG. 2 is a graph showing the relationship between the speed ratio (Va / Vk) and the transfer efficiency. According to the results shown in FIG. 2, the transfer efficiency deteriorates as the speed ratio (Va / Vk) approaches 1.0, and when the speed ratio (Va / Vy) moves away from 1.0 to some extent, high transfer efficiency is obtained. Obtainable. Here, assuming that the transfer efficiency when no image omission occurs in the formed image is a reference level, the speed ratio (Va / Vk) in any of a normal temperature and normal humidity environment, a low temperature and low humidity environment, and a high temperature and high humidity environment. It can be seen that a transfer efficiency of a reference level can be obtained when is 1.005 or more.

  FIG. 3 is a diagram showing the relationship between the speed ratio (Va / Vk) and the amount of image fogging. According to the results shown in FIG. 3, when the speed ratio (Va / Vk) is farther from 1.0, the amount of image fog increases, and when the same speed ratio (Va / Vk) is compared, The amount of image fog generation increases in a low-temperature, low-humidity environment and a high-temperature, high-humidity environment as compared with a wet environment. Here, as the reference level of image fogging, when an image fog generation amount in which image fogging is slightly recognized but is not practically problematic, the speed ratio (Va / Vk) is obtained in a low temperature and low humidity environment and a high temperature and high humidity environment. ) Is 1.007 or less, it was found that the image fog generation amount is smaller than the reference level.

  From the above, in order to obtain high transfer efficiency and to form an image with a small amount of image fog, the speed Va of the conveyor belt 23 in a low and high humidity environment and a black toner image are supported. It is preferable that the ratio (Va / Vk) to the rotational speed Vk of the photosensitive member 14k is 1.005 or more and 1.007 or less.

  Further, in the normal humidity environment, since the image fog is within the range of the reference level, the speed ratio (Va / Vk) is preferably 1.012 or less. Further, in order to obtain a high transfer efficiency, the speed ratio (Va / Vk) is preferably 1.005 or more. However, in order to reduce the difference in image quality between the formed image in a low and high humidity environment, The speed ratio (Va / Vk) is preferably 1.008 or more. That is, it is preferable that the speed ratio (Va / Vk) in the normal humidity environment is 1.008 or more and 1.012 or less.

  Note that in the image forming apparatus 1 of the present embodiment, the actual rotation speed is detected by the rotation speed detection means provided in each of the plurality of photoconductors 14y, 14m, 14c, and 14k, and based on the actual rotation speed, respectively. The rotational speeds Vy, Vm, Vc and Vk of the photoconductors 14y, 14m, 14c and 14k can be controlled. Therefore, even if there are manufacturing errors of the photoconductors 14y, 14m, 14c, and 14k, the occurrence of a speed difference between the controlled rotational speed and the actual rotational speed can be reduced.

  Hereinafter, the operation of the image forming apparatus 1 will be described. The image forming apparatus 1 forms each color toner image on the surface of the photoreceptors 14y, 14m, 14c, and 14k by the image forming units 10y, 10m, 10c, and 10k included in the image forming unit 2. The transfer unit 11 transfers the toner images on the photoconductors 14y, 14m, 14c, and 14k onto the recording medium 5 that is supplied by the paper feeding unit 3 and carried on the conveyance belt 23 to form a multicolor toner image. To do. At this time, the control means provided in the CPU controls the rotational speed of the photoreceptors 14y, 14m, 14c, and 14k and the speed of the transport belt 23 according to the humidity detected by the humidity detection sensor 7, and the transport belt. The ratio (Va / Vk) of the speed Va of 23 to the rotational speed Vk of the photoconductor 14k is, for example, 1.010 in the normal humidity environment, and is, for example, 1.005 in the low or high humidity environment. The fixing unit 12 fixes the multicolor toner image transferred to the recording medium 5 onto the recording medium 5 by heating and pressing with the heating roller 28 and the pressure roller 29 to form an image.

  According to the image forming apparatus 1 of the present embodiment, the rotational speeds Vy, Vm, Vc, and the like of the photoreceptors 14y, 14m, 14c, and 14k provided for each of the plurality of colors according to the humidity detected by the humidity detection sensor 7. Since Vk and the speed Va of the conveying belt 23 can be controlled, high transfer efficiency can be obtained while preventing image fogging even in a low or high humidity environment, and the transfer medium can be prevented from slackening. Thus, it is possible to form a good image that does not cause a color shift of the color image.

  Such an image forming apparatus 1 is not limited to the above-described configuration, and various modifications can be made.

  The image forming apparatus 1 according to the present embodiment uses a direct transfer method in which the toner images on the photoconductors 14y, 14m, 14c, and 14k are directly transferred to the recording medium 5 that is carried and conveyed by the conveyance belt 23. Regardless of the method used, intermediate transfer method image formation in which a toner image on a photoreceptor is transferred to an intermediate transfer medium such as an intermediate transfer belt, and then the toner image transferred to the intermediate transfer medium is transferred to a recording medium. It may be a device.

  FIG. 4 is a diagram schematically showing a configuration of an image forming apparatus 41 according to the second embodiment of the present invention. The image forming apparatus 41 of the present embodiment is similar to the image forming apparatus 1 of the first embodiment described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

  The image forming apparatus 41 is an image forming apparatus that uses an intermediate transfer method. Similar to the image forming apparatus 1, the image forming apparatus 41 includes an image forming unit 42 that forms an image on the recording medium 5, a paper feeding unit 43 that supplies the recording medium 5 to the image forming unit 42, and an image reading unit 4. It is comprised including.

  The image forming unit 42 includes image forming units 10y, 10m, 10c, and 10k, an intermediate transfer unit 44, a secondary transfer roller 45, a fixing unit 17, and a paper discharge unit 18.

  The intermediate transfer unit 44 includes an intermediate transfer belt 46, intermediate transfer rollers 47y, 47m, 47c, and 47k, a driving roller 48, a driven roller 49, and a belt cleaner 50.

  The intermediate transfer belt 46 is provided so as to abut on the photoreceptors 14y, 14m, 14c, and 14k that are a plurality of image carriers, and the toner images formed on the photoreceptors 14y, 14m, 14c, and 14k are superimposed and transferred. Intermediate transfer medium. The intermediate transfer belt 46 is an endless belt that is stretched between a driving roller 48 that is an intermediate transfer medium driving means for driving the intermediate transfer belt 46 and a driven roller 49 to form a loop-shaped movement path. Driven in the direction, that is, in the direction of the arrow 46b. The surface of the intermediate transfer belt 46 on which the toner image is transferred becomes a toner image carrying surface 46a.

  The toner image carrying surface 46a of the intermediate transfer belt 46 is in pressure contact with the photoreceptors 14y, 14m, 14c, and 14k in this order. The positions where the intermediate transfer belt 46 is in pressure contact with the photoreceptors 14y, 14m, 14c, and 14k are the intermediate transfer positions of the toner images of the respective hues. Intermediate transfer rollers 47y, 47m, 47c, and 47k are disposed at positions facing the photoconductors 14y, 14m, 14c, and 14k through the intermediate transfer belt 46.

  The intermediate transfer rollers 47y, 47m, 47c, and 47k are provided so as to be in pressure contact with the surface opposite to the toner image carrying surface 46a of the intermediate transfer belt 46 and to be rotationally driven around its axis by a driving unit (not shown). The intermediate transfer rollers 47y, 47m, 47c and 47k are opposite to the charging polarity of the toner in order to transfer the toner images formed on the surfaces of the photoreceptors 14y, 14m, 14c and 14k onto the intermediate transfer belt 46. A polar intermediate transfer bias is applied.

  A high voltage is uniformly applied to the intermediate transfer belt 46 by the intermediate transfer bias applied to the intermediate transfer rollers 47y, 47m, 47c, and 47k. As a result, the yellow, magenta, cyan and black toner images formed on the photoreceptors 14y, 14m, 14c and 14k are sequentially superimposed on the toner image carrying surface 46a of the intermediate transfer belt 46. The toner image is transferred and a multicolor toner image is formed on the toner carrying surface 46 a of the intermediate transfer belt 46.

  The driving roller 48 is an intermediate transfer medium driving unit that drives the intermediate transfer belt 46 that is an intermediate transfer medium. The driving roller 48 is controlled by a control unit provided in the CPU, and the speed Vb of the conveying belt 46 that moves (rotates) is determined by the rotation of the driving roller 48. The driven roller 49 is rotated by the rotation of the driving roller 48 while applying a constant tension to the intermediate transfer belt 46 so that the intermediate transfer belt 46 does not sag.

  The belt cleaner 50 is a member that removes toner remaining on the toner image carrying surface 46a after the toner image on the toner image carrying surface 46a of the intermediate transfer belt 46 is transferred to the recording medium 5 by a secondary transfer roller 45 described later. And is provided so as to face the driven roller 49 via the intermediate transfer belt 46, and is pressed against the toner image carrying surface 46a of the intermediate transfer belt 46 by a pressing means (not shown), and the residual toner on the toner image carrying surface 46a. And a toner storage container that stores toner scraped off by the cleaning blade.

  The intermediate transfer unit 44 superimposes and transfers the toner images of the respective colors formed on the photoreceptors 14y, 14m, 14c, and 14k on a predetermined position of the toner image carrying surface 46a of the intermediate transfer belt 46, and thereby multicolor toner images. Form. After this toner image is transferred to the recording medium 5 by a secondary transfer roller 45 described later, residual toner, offset toner, paper dust and the like on the toner image carrying surface 46a are removed by the belt cleaner 50, and the toner image carrying surface. The toner image is transferred again to 46a.

  The secondary transfer roller 45 is provided so as to be in pressure contact with the drive roller 48 via the intermediate transfer belt 46 and to be rotatable in the axial direction. When the toner image on the intermediate transfer belt 46 is transferred to the recording medium 5, a voltage having a polarity opposite to that of the toner is applied to the core of the secondary transfer roller 45.

  In synchronization with the transfer of the intermediate transfer belt 46 carrying the multicolor toner image to the pressure contact portion between the secondary transfer roller 45 and the drive roller 48, the recording medium 5 is fed from a paper feed portion 43 described later, The multicolor toner image on the intermediate transfer belt 46 is transferred to the surface of the recording medium 5 by pressing. The recording medium 5 onto which the multicolor toner image has been transferred is conveyed to the fixing unit 17.

  The paper feed unit 43 includes a recording medium cassette 51 that stores the recording medium 5, a pickup roller 52 that feeds the recording medium 5 to the conveyance path P one by one, and a multicolor toner image on the intermediate transfer belt 46 that is secondary. A plurality of sets of registration rollers for feeding the recording medium 5 to the pressure contact portion between the secondary transfer roller 45 and the drive roller 48 in synchronization with the conveyance to the pressure contact portion between the transfer roller 45 and the drive roller 48. Consists of.

  In the paper feeding unit 43, the recording medium 5 accommodated in the recording medium cassette 51 is fed one by one to the conveyance path P by the pickup roller 52, and the secondary transfer roller 45 and the driving roller 48 are set by a plurality of registration rollers. To the pressure contact part.

  Further, in the image forming apparatus 41 of the present embodiment, the actual rotation speeds of the humidity detection sensor 7 and the photoconductors 14y, 14m, 14c, and 14k are detected as in the image forming apparatus 1 of the first embodiment. Rotational speed detecting means is provided for the CPU according to the humidity detected by the humidity detecting sensor 7 and the actual rotational speeds of the photoconductors 14y, 14m, 14c, 14k detected by the rotating means detecting means. The control means controls the operation of a drive roller 48 which is a rotation drive means (not shown) for rotating the photoreceptors 14y, 14m, 14c and 14k and an intermediate transfer medium drive means for driving the intermediate transfer belt 46. By this control, the rotational speeds Vy, Vm, Vc, Vk of the photoreceptors 14y, 14m, 14c, 14k and the speed Vb of the intermediate transfer belt 46 can be adjusted.

In a normal temperature and humidity environment, the rotational speeds Vy, Vm, Vc, Vk of the photoreceptors 14y, 14m, 14c, 14k and the speed Vb of the intermediate transfer belt 46 are the same, that is, the photoreceptors 14y, 14m. , 14c and 14k, and the speed Vb of the intermediate transfer belt 46 are controlled as represented by the following equation (3). Further, the ratio of the speed Vb of the intermediate transfer belt 46 to the rotational speed Vk of the photoconductor 14k carrying the black toner image (Vb / Vk; hereinafter, sometimes simply referred to as speed ratio) is 1.0 or more. Is controlled to be larger.
Vk = Vc = Vm = Vy (3)

On the other hand, the rotational speeds Vy, Vm, Vc, Vk of the photoreceptors 14y, 14m, 14c, 14k and the speed Vb of the intermediate transfer belt 46 satisfy the following formula (4) in a low or high humidity environment. In addition, the speed ratio (Vb / Vk) in a low or high humidity environment is closer to 1.0 than the speed ratio (Vb / Vk) in a normal temperature and normal humidity environment, and is larger than 1.0. Each is controlled to be a value.
Vk>Vc>Vm> Vy (4)

  Note that the ratio (Vb / Vk) between the speed Vb of the intermediate transfer belt 46 in a low or high humidity environment and the rotational speed Vk of the photosensitive member 14k carrying the black toner image is the same as that in the above-described embodiment. Similarly to the ratio (Va / Vk) between the speed Va of the conveyor belt 23 and the rotational speed Vk of the photosensitive member 14k in the image forming apparatus 1 of one embodiment, it is preferably 1.005 or more and 1.007 or less. Similarly, the speed ratio (Vb / Vk) under the normal humidity environment is preferably 1.008 or more and 1.012 or less.

  Hereinafter, the operation of the image forming apparatus 41 will be described. The image forming apparatus 41 forms each color toner image on the surface of the photoreceptors 14y, 14m, 14c, and 14k by the image forming units 10y, 10m, 10c, and 10k included in the image forming unit 42. The intermediate transfer unit 44 transfers the toner images on the photoreceptors 14y, 14m, 14c, and 14k onto the intermediate transfer belt 46 to form a multicolor toner image. The multicolor toner image formed on the intermediate transfer belt 46 is transferred to the recording medium 5 conveyed from the paper supply unit 43 at the press contact portion between the secondary transfer roller 45 and the driving roller 48. At this time, the control means provided in the CPU controls the rotational speed of the photoreceptors 14y, 14m, 14c, and 14k and the speed of the intermediate transfer belt 46 in accordance with the humidity detected by the humidity detection sensor 7, and the intermediate The ratio (Vb / Vk) between the speed Vb of the transfer belt 46 and the rotational speed Vk of the photoconductor 14k is, for example, 1.010 in the normal humidity environment, and is, for example, 1.005 in the low or high humidity environment. To do. The fixing unit 17 fixes the multicolor toner image transferred to the recording medium 5 on the recording medium 5 by heating and pressing with the heating roller 28 and the pressure roller 29 to form an image.

  According to such an image forming apparatus 41, the speed ratio (Vb / Vk) is a speed ratio (Vb / Vk) in a normal humidity environment so that the above formula (4) is satisfied in a low humidity environment and a high humidity environment. Vb / Vk) is close to 1.0, and the speed of the photoreceptors 14y, 14m, 14c, 14k and the intermediate transfer belt 46 is controlled so as to be a value greater than 1.0. In addition to preventing a decrease in transfer efficiency that tends to occur in an environment or in a high-temperature and high-humidity environment, image fogging can also be prevented.

  Further, in a low or high humidity environment, the moisture content of the recording medium 5 such as paper is not only different from that in the normal humidity environment, but also the moisture content of the intermediate transfer belt 46 is different. The intermediate transfer belt 46 becomes slack. According to the image forming apparatus 41 of the present embodiment, when the above formula (4) is satisfied, the tension generated at the contact portion between the photoreceptors 14y, 14m, 14c, and 14k and the intermediate transfer belt 46 is intermediate transfer. Since it acts greatly at the contact portion with the photoreceptor on the downstream side in the movement (rotation) direction of the belt 46, the intermediate transfer belt 46 does not become slack and forms a good image without color misregistration. Can do.

1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention. It is a figure which shows the relationship between speed ratio (Va / Vk) and transfer efficiency. It is a figure which shows the relationship between speed ratio (Va / Vk) and the generation amount of image fog. It is a figure which shows schematically the structure of the image forming apparatus 41 which is the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41 Image forming apparatus 2,42 Image forming part 3,43 Paper feeding part 4 Image reading part 5 Recording medium 6 Document base 7 Humidity detection sensor 10y, 10m, 10c, 10k Image forming unit 11 Transfer unit 12 Fixing unit 13 Ejection Paper unit 14y, 14m, 14c, 14k Photoconductor 15y, 15m, 15c, 15k Charging means 16y, 16m, 16c, 16k Exposure unit 17y, 17m, 17c, 17k Developing means 18y, 18m, 18c, 18k Cleaning means 19y, 19m , 19c, 19k Polygon mirror 20y, 20m, 20c, 20k fθ lens 21y, 21m, 21c, 21k, 22y, 22m, 22c, 22k Mirror 23 Conveying belt 24y, 24m, 24c, 24k Transfer means 25, 48 Drive roller 26, 49 Followed roller 7 Static elimination means 28 Heating roller 29 Pressure roller 30 Paper discharge tray 31a, 31b Paper discharge roller 32, 51 Recording medium cassette 33, 52 Pickup roller 35 First original scanning unit 36 Second original scanning unit 37 Optical lens 38 CCD line sensor 44 Intermediate transfer unit 45 Secondary transfer roller 46 Intermediate transfer belt 47y, 47m, 47c, 47k Intermediate transfer roller 50 Belt cleaner

Claims (10)

A plurality of image carriers that respectively carry toner images of different colors, and a recording medium that is provided in contact with the plurality of image carriers and onto which the toner images formed on the plurality of image carriers are superimposed and transferred. In an image forming apparatus including a recording medium carrier carried and conveyed,
A plurality of rotation driving means for respectively rotating a plurality of image carriers;
A recording medium carrier driving means for driving the recording medium carrier;
Humidity detecting means for detecting humidity in the image forming apparatus;
Control means for controlling the operation of the rotation driving means and the recording medium carrier driving means in accordance with the humidity detected by the humidity detection means, and adjusting the rotational speed of the image carrier and the speed of the recording medium carrier. An image forming apparatus. The plurality of image carriers are:
A yellow toner image carrier for carrying a yellow toner image and a magenta toner image carrier for carrying a magenta toner image, which are provided in order from the upstream side to the downstream side in the carrying direction of the recording medium carried by the recording medium carrier. A cyan toner image carrier carrying a cyan toner image and a black toner image carrier carrying a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the speed of the recording medium carrier is Va. and when,
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Va / Vk) which is a ratio between the speed Va of the recording medium carrier and the rotational speed Vk of the black toner image carrier. When the operation of the rotation driving means and the recording medium carrier driving means is controlled so as to be larger than 1.0 and the humidity detected by the humidity detecting means is lower than a predetermined reference value, the speed ratio (Va / Vk) Is a value closer to 1.0 than the speed ratio (Va / Vk) when the humidity is within the predetermined reference value range and larger than 1.0, and satisfies the following formula: 2. The image forming apparatus according to claim 1, wherein the operation of the plurality of rotation driving means and the recording medium carrier driving means is controlled.
Vk>Vc>Vm> Vy The control means
When the humidity detected by the humidity detection means is within a predetermined reference value range, the rotational drive means and the recording medium carrier drive means so that the speed ratio (Va / Vk) is 1.008 or more and 1.012 or less. When the humidity detected by the humidity detecting means is lower than a predetermined reference value, a plurality of rotational driving means and recording are performed so that the speed ratio (Va / Vk) is 1.005 or more and 1.007 or less. 3. The image forming apparatus according to claim 2, wherein the operation of the medium carrier driving means is controlled. The plurality of image carriers are:
A yellow toner image carrier for carrying a yellow toner image and a magenta toner image carrier for carrying a magenta toner image, which are provided in order from the upstream side to the downstream side in the carrying direction of the recording medium carried by the recording medium carrier. A cyan toner image carrier that carries a cyan toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the speed of the recording medium carrier is Va. and when,
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Va / Vk) which is a ratio between the speed Va of the recording medium carrier and the rotational speed Vk of the black toner image carrier. When the operation of the rotation driving means and the recording medium carrier driving means is controlled so that the value is larger than 1.0, and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the speed ratio (Va / Vk) Is a value closer to 1.0 than the speed ratio (Va / Vk) when the humidity is within the predetermined reference value range and larger than 1.0, and satisfies the following formula: The image forming apparatus according to claim 1, wherein the operation of the plurality of rotation driving units and the recording medium carrier driving unit is controlled.
Vk>Vc>Vm> Vy The control means
When the humidity detected by the humidity detection means is within a predetermined reference value range, the rotational drive means and the recording medium carrier drive means so that the speed ratio (Va / Vk) is 1.008 or more and 1.012 or less. When the humidity detected by the humidity detecting means is higher than a predetermined reference value, a plurality of rotational driving means and recording are performed so that the speed ratio (Va / Vk) is 1.005 or more and 1.007 or less. 5. The image forming apparatus according to claim 4, wherein the operation of the medium carrier driving means is controlled. A plurality of image carriers that respectively carry toner images of different colors, and an intermediate transfer medium that is provided so as to be in contact with the plurality of image carriers and to which toner images formed on the plurality of image carriers are superimposed and transferred In an image forming apparatus including
A plurality of rotation driving means for respectively rotating a plurality of image carriers;
Intermediate transfer medium driving means for driving the intermediate transfer medium;
Humidity detecting means for detecting humidity in the image forming apparatus;
Control means for controlling the operation of the rotation driving means and the intermediate transfer medium driving means in accordance with the humidity detected by the humidity detection means, and adjusting the rotation speed of the image carrier and the speed of the intermediate transfer medium. Image forming apparatus. The plurality of image carriers are:
A yellow toner image carrier that carries a yellow toner image, a magenta toner image carrier that carries a magenta toner image, and a cyan toner image that are provided in order from the upstream side to the downstream side in the moving direction of the intermediate transfer medium. A cyan toner image carrier that carries a black toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the intermediate transfer medium speed is Vb. When
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Vb / Vk) which is a ratio between the speed Vb of the intermediate transfer medium and the rotational speed Vk of the black toner image carrier is obtained. When the rotation driving means and the intermediate transfer medium driving means are controlled to be larger than 1.0 and the humidity detected by the humidity detecting means is lower than a predetermined reference value, the speed ratio (Vb / Vk) is The value is closer to 1.0 than the speed ratio (Vb / Vk) when the humidity is within the range of the predetermined reference value, and is larger than 1.0, and the following equation is satisfied. 7. The image forming apparatus according to claim 6, wherein the plurality of rotation driving means and the intermediate transfer medium driving means are controlled to operate.
Vk>Vc>Vm> Vy The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, the rotation driving means and the intermediate transfer medium driving means are set so that the speed ratio (Vb / Vk) is 1.008 or more and 1.012 or less. When the operation is controlled and the humidity detected by the humidity detecting unit is lower than a predetermined reference value, the plurality of rotation driving units and the intermediate transfer unit are set so that the speed ratio (Vb / Vk) is 1.005 or more and 1.007 or less. 8. The image forming apparatus according to claim 7, wherein the operation of the medium driving unit is controlled. The plurality of image carriers are:
A yellow toner image carrier that carries a yellow toner image, a magenta toner image carrier that carries a magenta toner image, and a cyan toner image that are provided in order from the upstream side to the downstream side in the moving direction of the intermediate transfer medium. A cyan toner image carrier that carries a black toner image and a black toner image carrier that carries a black toner image,
The rotational speeds of the yellow toner image carrier, magenta toner image carrier, cyan toner image carrier and black toner image carrier are Vy, Vm, Vc and Vk, respectively, and the intermediate transfer medium speed is Vb. When
The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, a speed ratio (Vb / Vk) which is a ratio between the speed Vb of the intermediate transfer medium and the rotational speed Vk of the black toner image carrier is obtained. When the rotation driving means and the intermediate transfer medium driving means are controlled to be larger than 1.0 and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the speed ratio (Vb / Vk) is The value is closer to 1.0 than the speed ratio (Vb / Vk) when the humidity is within the range of the predetermined reference value, and is larger than 1.0, and the following equation is satisfied. The image forming apparatus according to claim 6, wherein the plurality of rotation driving units and the intermediate transfer medium driving unit are controlled to operate.
Vk>Vc>Vm> Vy The control means
When the humidity detected by the humidity detecting means is within a predetermined reference value range, the rotation driving means and the intermediate transfer medium driving means are set so that the speed ratio (Vb / Vk) is 1.008 or more and 1.012 or less. When the operation is controlled and the humidity detected by the humidity detecting means is higher than a predetermined reference value, the plurality of rotational driving means and intermediate transfer means so that the speed ratio (Vb / Vk) is 1.005 or more and 1.007 or less. The image forming apparatus according to claim 9, wherein the operation of the medium driving unit is controlled.

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