JP5455047B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, an LED printer, and a facsimile.

  Currently, as a color image forming apparatus, multiple color image forming units are arranged side by side with respect to a transfer medium, and a toner image formed by each image forming unit is sequentially transferred onto the transfer medium to obtain an image. Is widely adopted. In addition, as a tandem method, a direct transfer method in which the transfer medium is a final transfer body, for example, a recording medium such as paper, and a paper after the transfer medium is an intermediate transfer body and another color image is formed on the intermediate transfer body. And an indirect transfer method in which an image is obtained by transferring to a recording medium. Compared with the direct transfer method, the indirect transfer method is advantageous for dealing with paper types and the like, and provides a stable image quality.

  However, when an indirect transfer type color image forming apparatus outputs a monochrome image, the intermediate transfer member, the intermediate transfer member cleaning member, and the like need to operate in the same manner as the color image formation. There was a problem that it took about the same time as image formation. Therefore, Patent Document 1 includes a first image forming unit that forms only a single color toner image on a recording material, and a second image forming unit that forms a plurality of color toner images on an intermediate transfer member. There has been proposed a color image forming apparatus in which the first image forming unit is provided separately from the second image forming units of a plurality of colors. Actually, it is assumed that a black image having the highest frequency of use of a single color is formed in the first image forming unit of a single color, and a color image other than black is formed in the second image forming unit of a plurality of colors.

  In the color image forming apparatus of Patent Document 1, when performing color image formation, a plurality of color toners obtained by transferring an image formed by the plurality of second color image forming units onto an intermediate transfer member and superimposing the respective colors. Form an image. The multi-color toner images are transferred at a secondary transfer position onto a recording medium carried and conveyed by a recording medium conveyance belt. On the other hand, the monochromatic toner image formed by the first image forming unit is directly transferred at a transfer position onto the recording medium carried and conveyed by the recording medium conveyance belt. In this way, each image is transferred at different transfer positions, ie, a transfer position on the intermediate transfer member and a transfer position on the recording medium, so that misalignment easily occurs between the images transferred on the recording medium. Problems arise.

  The color image forming apparatus disclosed in Patent Document 2 is a color image forming apparatus that forms a single color image or a plurality of color images by superimposing toner images of respective colors formed by a plurality of color image forming units including a single color on an intermediate transfer member. is there. In Patent Document 2 having such a configuration, as in Patent Document 1, it is necessary to correct misalignment between multiple color images or misalignment between multiple color images and single color images. is there. Therefore, in the correction method proposed in Patent Document 2, a detection pattern for color misregistration adjustment created by each color image forming unit and transferred onto the intermediate transfer member at the time of automatic color misregistration adjustment is optically detected. The amount of deviation detected by this detection means is calculated, and the adjustment amount is reflected in each color creation unit according to the calculated amount of deviation. This correction operation is repeated a plurality of times to correct the positional deviation on the image.

  On the other hand, in a color image forming apparatus, it is necessary to adjust the toner adhesion amount of each color to a target value in order to maintain an appropriate image density, in addition to correcting the misregistration of each color. Japanese Patent Application Laid-Open No. H10-228867 proposes a toner adhesion amount detection. Normally, an optical sensor is used to detect the toner adhesion amount. However, in the black toner layer, the reflected light mainly reflected from the color toner layer is reflected from the reflected light. The reflected light includes regular reflected light, diffuse reflected light generated in a color toner layer composed of a plurality of layers, and diffuse reflected light (noise component) from the belt background. Therefore, in order to obtain specularly reflected light from the color toner layer, it is necessary to detect and remove each diffusely reflected light from the reflected light. Therefore, in Patent Document 3, a reflected light sensor that detects reflected light from the color toner layer, diffuse reflected light that is reflected through the toner layer from the belt background, and diffused that is reflected from the color toner layer itself. A detecting means including a diffuse reflected light sensor for detecting reflected light is disposed to face the intermediate transfer member or the recording medium conveying belt.

  Of the detection means proposed in Patent Document 3, it is conceivable that the reflected light sensor that detects reflected light from the toner is also used as the pixel position shift optical sensor described in Patent Document 2 described above. When the detection means is installed opposite to the intermediate transfer member, color toner adhesion amount control and alignment control can be performed. However, when black toner adhesion amount control and alignment control are performed, the detection means includes Since it is disposed opposite to the intermediate transfer member, first, a black control pattern is transferred to the intermediate transfer member from the recording medium conveying belt in the reverse direction to that during normal image formation in the secondary transfer unit. Then, by detecting the black control pattern on the intermediate transfer member by the detection means, the black toner adhesion amount control and the alignment control are performed.

  However, in the case of black, as described above, the transfer is performed in the reverse direction at the time of image formation at the secondary transfer portion, and charging of the intermediate transfer member by the transfer electric field for this transfer is different from that at the time of normal transfer. For this reason, when the black image is secondarily transferred, abnormal discharge occurs in the intermediate transfer member. As countermeasures against the abnormal discharge, for example, adjustment of the intrusion angle of the recording paper can be considered. However, the adjustment is very difficult in terms of design, and thus cannot be performed. As a result, black toner on the intermediate transfer member is caused by abnormal discharge. The amount of adhesion decreases. Therefore, although alignment control is possible, there arises a problem that it is difficult to perform toner adhesion amount control correctly.

  In the case where the detection unit is installed opposite to the recording medium conveyance belt, the color control pattern is transferred from the intermediate transfer member to the recording medium conveyance belt and then detected by the detection unit. Therefore, even when it is desired to perform the adhesion amount control and the alignment control only for the color, it is necessary to drive the black image forming unit and the recording medium conveyance belt, which is inefficient. In addition, since the distance from the color image forming unit to the detection unit is long, the time required for the toner adhesion amount control and the alignment control becomes long and the standby time becomes long, so that the speed cannot be increased.

  Further, in order to solve these problems, there is also a method in which the detection means having a detection function for performing toner adhesion amount control and alignment control is simply installed on both the intermediate transfer member and the recording medium conveyance belt. is there. However, the detection means itself has an optical sensor that detects reflected light and an optical sensor that detects diffusely reflected light, and becomes an expensive detection means. If the detection means is installed on both the intermediate transfer member and the recording medium conveyance belt, there arises a problem that the cost in view of the entire apparatus is further increased.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of controlling the toner adhesion amount and the alignment control with high accuracy in a short time while reducing the cost. .

According to the first aspect of the present invention, there is provided an intermediate transfer member that is rotatably stretched on a plurality of roller members, and a plurality of first image carriers that are disposed to face the front surface of the intermediate transfer member. First image forming means for forming each image on each first image carrier, and primary for primary transfer of each image formed on each first image carrier on the intermediate transfer member A transfer means, a secondary transfer means for secondary transfer of the image transferred onto the intermediate transfer body onto the recording medium, and a secondary transfer position at which the image is secondarily transferred from the intermediate transfer body onto the recording medium. A second image carrier provided upstream or downstream in the recording medium conveyance direction, a second image forming unit for forming an image on the second image carrier, and the second image. A direct transfer means for directly transferring an image formed on the carrier onto the recording medium, and an image on the recording medium from the second image carrier. A recording medium conveying belt that is rotatably stretched by a plurality of roller members and carries the recording medium so as to pass through the direct transfer position where the image is directly transferred and the secondary transfer position. In the image forming apparatus, at least one specular reflection light detection type optical sensor and at least one specular reflection light / scattered light simultaneous detection type optical sensor are disposed to face the intermediate transfer member, and at least one Two or more specular reflection light detection type optical sensors are installed facing the recording medium conveyance belt or the second image carrier, and the black toner adhesion amount control is performed by the recording medium conveyance belt or the second image carrier. At least one of the specular reflection light detection type optical sensors installed opposite to the toner, and the toner adhesion amount control other than black is controlled to face the intermediate transfer member. At least one specularly reflected / scattered light simultaneous detection type optical sensor that performs the alignment control of each color and faces the intermediate transfer member is performed using the above specularly reflected / scattered light simultaneous detection type optical sensor. An image forming apparatus comprising: a sensor and at least one specular reflection light detection type optical sensor.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the regular reflection light detection type optical sensor and the regular reflection light / scattered light simultaneous detection type optical sensor are arranged in the image forming region of the intermediate transfer member. It arrange | positions so that the center line of this may be pinched | interposed.
Further, the invention according to claim 3 is the image forming apparatus according to claim 1, wherein the arrangement position of the specular reflection / scattered light simultaneous detection type optical sensor in the longitudinal direction and the center line of the image forming area of the intermediate transfer member are provided. Is equal to or shorter than the distance between the longitudinal position of the specular reflection light detection optical sensor and the center line of the image forming area of the intermediate transfer member, and the specular reflection light detection optical sensor and the A specular reflection / scattered light simultaneous detection type optical sensor is arranged.

  As described above, according to the present invention, it is possible to provide an image forming apparatus capable of performing toner adhesion amount control and alignment control with reduced cost.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus of the present invention. It is the schematic which shows the structure of a regular reflection light detection type optical sensor. It is the schematic which shows the structure of a regular reflection light / diffuse light simultaneous detection type optical sensor. FIG. 6 is a schematic diagram illustrating positions of optical sensors installed on an intermediate transfer body and a recording medium conveyance belt. It is the figure which showed the relationship between a sensor position and adhesion amount dispersion | variation when there exists an adhesion amount deviation in a longitudinal direction. It is a figure which shows the positional relationship of the optical sensor in an image formation area. It is a figure which shows another positional relationship of the optical sensor in an image formation area. It is the schematic which shows the position of the example which installed the regular reflection light detection type photosensor facing the black image carrier.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. In the image forming apparatus shown in FIG. 1, three image forming units 30Y, 30C, and 30M, yellow, cyan, and magenta (hereinafter abbreviated as Y, C, and M) are arranged in series along the intermediate transfer belt 6. The black (hereinafter abbreviated as “B”) image forming unit 30B is a color image forming apparatus (color digital multifunction peripheral) provided independently upstream of the tandem arrangement in the recording sheet moving direction. However, in the present embodiment, the black image formed by the image forming unit 30B is arranged to be directly transferred onto the recording paper.

  Around each of the photoreceptors 1Y, 1C, 1M, and 1B, which are latent image carriers for each color shown in FIG. 1, charging devices 2Y, 2C, 2M, and 2B for charging the surfaces of the photoreceptors 1Y, 1C, 1M, 1B, A toner image is formed by supplying toner to the latent image on the photoreceptors 1Y, 1C, 1M, 1B, the exposure device 5 that forms a latent image on the surface of the charged photoreceptors 1Y, 1C, 1M, and 1B with a laser. Developing devices 3Y, C, M, and B, and photoreceptors 1Y, C, M, and B are provided with cleaning devices 4Y, M, C, and B that remove deposits such as toner that adhere to the surface of the photoreceptors. Although the cleaning devices 4Y, 4C, 4M, and 4B used in the present embodiment are of a blade type, the present invention is not limited to this, and a fur brush roller or a magnetic brush cleaning system is used. May be. Further, the exposure apparatus 5 is not limited to the laser system, but may be a system such as an LED system. Further, the photosensitive members 1Y, 1C, 1M, 1B, the charging devices 2Y, 2C, 2M, 3B, the developing devices 3Y, 3C, 3M, 3B, and the cleaning devices 4Y, 4C, 4M, 4B M and B are integrally formed.

  Document data read by a scanner, received data such as a facsimile, or color image information transmitted from a computer is color-separated into each color, plate data for each color is formed, and sent to the exposure device 5. The uniformly charged photoreceptors 1Y, 1C, 1M, and 1B are exposed on the image portion by the exposure device 5, and toner images are formed by the developing devices 3Y, 3C, M, and B.

  The color toner images formed on the photoreceptors 1Y, 1C, and 1M are transferred to the intermediate transfer belt 6 that is an intermediate transfer body at the same timing, and a color-superposed toner image is formed.

  The black toner image formed on the photoreceptor 1B is directly transferred onto the recording paper conveyed by the recording medium conveying belt 8, and then the YCM toner image superimposed on the intermediate transfer belt 6 is transferred onto the recording paper. The

  In addition, recording paper, which is a recording medium on which an output image is formed, is set in the paper feed tray 40. The recording paper is fed from the paper feed tray 40 to the recording medium transport belt 8 by a paper feed roller or the like (not shown). And is carried on the front surface which is the outer surface of the loop of the recording medium conveyance belt 8.

  A direct transfer roller 15 is provided at a position facing the photoconductor 1B via the recording medium conveyance belt 8, and a direct transfer nip is formed by the photoconductor 1B and the direct transfer roller 15 via the recording medium conveyance belt 8. Has been.

  A voltage having a polarity opposite to that of the toner is applied to the direct transfer roller 15, and the voltage is formed on the photoreceptor 1 </ b> B on the recording paper sandwiched between the photoreceptor 1 </ b> B and the recording medium transport belt 8 at the direct transfer nip. A black toner image is transferred.

  In FIG. 1, three image forming units 30Y, 30C, and 30M are arranged in series along the intermediate transfer belt 6. The primary transfer rollers 14Y, 14C, and 14M are respectively opposed to the photoreceptors 1Y, 1C, and 1M provided in the image forming units 30Y, 30C, and 30M via the intermediate transfer belt 6 and slightly downstream in the rotation direction of the intermediate transfer belt. It is provided corresponding to the photoreceptors 1Y, 1C, 1M.

  A high voltage having a polarity opposite to that of the toner is applied to the primary transfer rollers 14Y, 14C, and 14M, and each color toner image on the photoreceptors 1Y, 1C, and 1M is transferred onto the intermediate transfer belt 6 by the electric field generated by this voltage. Are sequentially transferred so as to overlap each other, and a color image composed of three colors Y, M, and C is formed on the intermediate transfer belt 6.

  The color image on the intermediate transfer belt 6 is applied between the secondary transfer roller 16 and the counter roller 17 at a secondary transfer nip formed by the secondary transfer roller 16 and the counter roller 17 via the intermediate transfer belt 6. Is transferred to the recording paper conveyed to the secondary transfer nip by the recording medium conveying belt 8. At this time, a high voltage having a polarity opposite to the charging polarity of the toner may be applied to the secondary transfer roller 16, or a voltage having the same polarity as the charging polarity of the toner may be applied to the counter roller 17.

  When a high voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 16, it is possible to use a high voltage power source for directly applying a voltage to the transfer roller 15. Since it is not necessary to provide a dedicated power source for applying a voltage, cost reduction and size reduction of the image forming apparatus can be achieved. On the other hand, when a voltage having the same polarity as the charging polarity of the toner is applied to the opposing roller 17, a voltage is applied to the toner through the intermediate transfer belt 6, so that it is satisfactory even if the recording paper absorbs moisture and the resistance decreases. Transcription becomes possible. Further, the secondary transfer roller 16, the counter roller 17, and a power source (not shown) for applying a high voltage thereto constitute a secondary transfer device.

  In this way, the recording paper on which the toner images of Y, C, M, and B are transferred is a roller member that stretches the recording medium conveyance belt 8 downstream of the secondary transfer nip in the rotation direction of the recording medium conveyance belt. At the bent portion where the rotation direction of the recording medium conveyance belt 8 is suddenly changed by the curvature, the curvature of the recording paper is separated from the recording medium conveyance belt 8 by the waist of the recording paper and reaches the fixing device 10, and Y, C, M, The B toner image is finally fixed by the fixing device 10 to form a color image on the recording paper.

  The present invention is not limited to the configuration in which the black image is directly transferred from the photosensitive member 1B onto the recording paper. The intermediate transfer member such as an intermediate transfer belt or an intermediate transfer drum that is different from the photosensitive member 1B to the intermediate transfer belt 6 is used. Alternatively, the black image may be transferred to the recording paper via the recording medium. However, in this case, the laser writing image of the black image exposed from the exposure device 5 becomes a mirror image of the laser writing image of the YCM image, and the writing control becomes complicated.

  The full color mode for creating a full color image composed of Y, C, M, and B toner images on the recording paper has been described so far. However, in the image forming apparatus according to the present embodiment, only the B toner image is formed on the recording paper. There is also a monochrome mode for creating a monochrome image. At the time of monochrome image creation in the monochrome mode, the exposure device 5 uses the data of a black image formed based on received data such as a document read by a scanner, a facsimile, or image information transmitted from a computer. The image portion on the photosensitive member 1B is exposed, a black toner image is formed by the developing device 3B, and the black toner image is directly transferred from the photosensitive member 1B onto the recording paper conveyed by the recording medium conveying belt 8, and then on the recording paper. The black toner image is fixed on the recording paper by the fixing device 10 to form a monochrome image.

  In the monochrome mode, the contact portion (secondary transfer nip) between the intermediate transfer belt 6 and the recording medium transport belt 8 is released and separated by a mechanism (not shown). Thereby, even if the image forming units 30Y, 30C, and 30M and the intermediate transfer belt 6 are not operated, the monochrome image formation is not affected. Therefore, if the image forming units 30Y, 30C, and 30M and the intermediate transfer belt 6 are not operated in the monochrome mode, deterioration of the image forming units 30Y, 30C, and M, the intermediate transfer belt 6 and the like can be suppressed correspondingly, and the image forming unit. 30, YC, M and the advantage that the life of the intermediate transfer belt 6 can be extended.

  In the present embodiment, the recording medium is conveyed downstream in the rotational direction of the recording medium conveyance belt or downstream in the rotational direction of the intermediate transfer belt 6 from the position where the transfer of the four color toner images onto the recording paper is completed. An optical sensor, which will be described later, is arranged facing the front surface that is the loop outer surface of the belt 8 and the front surface that is the loop outer surface of the intermediate transfer belt 6. Then, process control is performed between sheets, and the image of the detection pattern for image density measurement formed on the photoreceptors 1Y, 1C, 1M, and 1B is finally placed on the recording medium conveyance belt 8 or the intermediate transfer belt 6. After the transfer, the toner adhesion amount is detected by reflection with an optical sensor. Then, by adjusting the image forming conditions based on the detection result, the density of the image formed on the recording paper can be maintained at an appropriate density.

  Also, a pattern image for color matching (positional deviation) detection is created on the recording medium conveyance belt 8 and the intermediate transfer belt 6, and the pattern image is detected by an optical sensor described later. Thereby, it is possible to detect the amount of positional deviation of the Y, C, M, and B images. Therefore, the Y, C, M, and B images can be aligned by adjusting the color image forming positions and adjusting the image forming conditions based on the detection result of the optical sensor.

  Further, as shown in FIG. 1, the optical sensor 11a is disposed opposite to the roller that rotatably stretches the recording medium conveyance belt 8 in the separation position, so that the recording medium is detected with respect to the detection result of the optical sensor 11a. Noise due to vibration of the conveyor belt 8 is suppressed, and a more accurate detection result can be obtained.

Here, the configurations of the specular reflection light detection type photosensor and the specular reflection / diffuse light simultaneous detection type photosensor will be described with reference to the drawings. The specular reflection light detection type photosensor 50 has a configuration as shown in FIG. A light-emitting element 51 of the LED, and a regular reflection light-receiving element at an angle at which the light emitted from the light-emitting element 51 is regularly reflected from the toner layer of the detection pattern, the intermediate transfer member, the recording medium transport belt, and the image carrier surface 52 is provided. On the other hand, the specular reflection / diffuse light simultaneous detection type photosensor 60 has a configuration as shown in FIG. 3, and the LED light emitting element 51 and specular reflection light reception provided in the same manner as the specular reflection detection type photosensor 50. In addition to the element 52, a diffuse reflection light receiving element 53 for detecting diffuse reflection light from the color toner layer and the belt background portion is provided. As a matter of course, the specular reflection / diffuse light simultaneous detection type optical sensor 60 is more expensive than the regular reflection light detection type optical sensor 50, and the size of the sensor head portion is easily increased. The black toner can detect the amount of adhesion only with specular reflection light, but the color toner cannot detect the amount of adhesion in the region where the amount of adhesion exceeds about 0.3 [mg / cm ² ]. Therefore, it is necessary to detect diffused light. On the other hand, if it is only necessary to detect the presence or absence of a toner pattern as in the alignment control pattern detection, the specular reflection light detection type optical sensor can also detect the color toner detection pattern. A specular reflection light detection type optical sensor is sufficient as the sensor.

  In the present invention, a black independent layout is adopted instead of using a conventional optical sensor in which a plurality of regular reflection light detection type photosensors and regular reflection / diffuse light simultaneous detection type photosensors are arranged in a line. There are advantages and disadvantages caused by this configuration. As an advantage, since the black image forming unit is independent from the color image forming unit, if the intermediate transfer member and the recording medium conveying member are separated from each other, they can be operated independently. On the other hand, the demerit is that the conventional optical sensor is inferior to the adhesion amount control / positioning control in the quadruple tandem system regardless of which side of the intermediate transfer member or the recording medium conveyance belt is placed.

  In order to take advantage of the above advantages and eliminate the above disadvantages, as shown in FIG. 4, the regular reflection light detection type photosensor 50 of FIG. 2 and the regular reflection light / diffuse light simultaneous detection type photosensor 60 of FIG. Opposed to each other. The color toner adhesion amount control is performed by the specular reflection / diffuse light simultaneous detection type optical sensor 11c disposed to face the intermediate transfer member 6. Further, the black toner adhesion amount control is performed by a specular reflection light detection type photosensor 11a installed facing the recording medium conveyance belt or the black image carrier.

  On the other hand, at least two optical sensors are required for the alignment control. In this embodiment, the specular reflection / diffuse light simultaneous detection type photosensor 11c used for color toner adhesion amount control and the specular reflection detection are used. Type optical sensor 11b. As a result, the adhesion amount control and the alignment control can be performed with the minimum number of optical sensors and the accuracy and standby time equivalent to or better than the 4-tandem tandem system.

  As shown in FIG. 4, the specular reflection light detection type optical sensor 11 a is installed with an upper stretching roller 61 that stretches the recording medium conveyance belt 8 as an opposing member. The position of the specular reflection light detection type optical sensor 11a is downstream of the black image carrier 1B in FIG. 1 in the rotation direction of the recording medium conveying belt 8, and the recording medium conveying belt cleaning member 9 rotates the recording medium conveying belt 8. It may be arranged anywhere as long as it is upstream in the direction. The regular reflection light detection type photosensor 11 b and the regular reflection / diffuse light simultaneous detection type photosensor 11 c are arranged in a row in a direction perpendicular to the rotation direction of the intermediate transfer belt 6, and face the intermediate transfer belt 6. Installed. These two sensors are arranged anywhere downstream of the secondary transfer counter roller 17 in FIG. 1 in the rotation direction of the intermediate transfer belt 6 and upstream of the intermediate transfer belt cleaning member 7 in the rotation direction of the intermediate transfer belt 6. May be. However, the condition that the intermediate transfer belt 6 is arranged in a line in a direction perpendicular to the rotation direction of the intermediate transfer belt 6 is maintained.

When black toner adhesion amount control is performed, an adhesion amount detection pattern is created on the image carrier 1B in the black image forming unit, and then a primary transfer bias having a polarity opposite to that of the toner is applied to the black primary transfer roller 15. Then, the adhesion amount detection pattern is transferred onto the recording medium conveyance belt 8, and the transferred adhesion amount detection pattern is detected by the regular reflection light detection type optical sensor 11a. The detected pattern is collected by the recording medium conveyance belt cleaning member 9. Here, at the start of the control operation, either the secondary transfer roller 16 or the secondary transfer counter roller 17 is retracted and the recording medium transport belt 8 and the intermediate transfer belt 6 are separated from each other. It is possible to control the black toner adhesion amount while the intermediate transfer member is stopped. Further, preferably, when a bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 16 or a bias having the same polarity as that of the toner is applied to the secondary transfer counter roller 17, they are close to each other although they are separated. The toner scattering from the adhesion amount detection pattern on the intermediate transfer belt 6 can be suppressed. The bias to be applied is a constant voltage, preferably about 100V to 1500V for the secondary transfer roller 16, and -100V to -1500V for the secondary transfer counter roller 17. This is because it is difficult to obtain a scattering suppression effect when the voltage is low. This is because when the voltage is high, discharge occurs between the belts and other adjacent members, particularly the grounded member.

  Further, it is desirable that the specular reflection light detection type optical sensor 11a be installed in the vicinity of the center of the image forming area (the center when viewed in the direction perpendicular to the sheet of FIG. 1). This is because when there is a toner adhesion amount deviation in the longitudinal direction from the front side to the back side of the image forming apparatus, if there is a regular reflection light detection type photosensor 11a at the center of the image formation region as shown in plot A of FIG. The maximum deviation width from the image forming area is about half of the difference between the adhesion amounts at both ends of the image forming area. On the other hand, as shown in plot B, if there is the specular reflection light detection type photosensor 11a, the target adhesion amount is obtained. This is because the maximum deviation width from is larger than that in the plot A.

Next, when color toner adhesion amount control is performed, an adhesion amount detection pattern is created by the image forming bodies 1Y, 1C, and 1M in the color image forming unit, and then the color primary transfer rollers 14Y, 14C, and 14M are opposite to the toner. A primary transfer bias of polarity is applied to transfer the adhesion amount detection pattern onto the intermediate transfer belt 6, and the transferred adhesion amount detection pattern is detected by the specular reflection / diffuse light simultaneous detection type optical sensor 11c. The detected pattern is collected by the intermediate transfer belt cleaning member 7. Here, at the start of the control operation, either the secondary transfer roller 16 or the secondary transfer counter roller 17 is withdrawn, and the recording medium conveyance belt 8 and the intermediate transfer belt 6 are separated from each other. It is possible to control the color toner adhesion amount while the recording medium conveyance belt is stopped. Further, desirably, when a secondary transfer bias having the same polarity as the toner is applied to the secondary transfer roller 16 or a bias having a polarity opposite to that of the toner is applied to the secondary transfer counter roller 17, they are close to each other although they are separated. The toner scattering from the adhesion amount detection pattern on the recording medium conveying belt 8 can be suppressed. The bias to be applied is a constant voltage, preferably about -100V to -1500V for the secondary transfer roller 16, and 100V to 1500V for the secondary transfer counter roller 17. This is because if the voltage is low, it is difficult to obtain the toner scattering suppressing effect. This is because when the voltage is high, discharge occurs between the belts and other adjacent members, particularly the grounded member.

  When the black toner and the color toner are controlled at the same time, the black image forming unit / recording medium conveying belt and the color image forming unit / intermediate transfer member may be controlled independently. It is also possible to control the amount of adhesion while the conveyance belt 8 and the intermediate transfer belt 6 are in contact with each other. In this case, the secondary transfer roller 16 and the secondary transfer counter roller 17 are set to have the same potential so that the black toner adhesion amount detection pattern is transferred to the intermediate transfer belt 6 and the color toner adhesion amount detection pattern is recorded. Transfer to the medium transport belt 8 can be suppressed. Desirably, the positions in the longitudinal direction of the specular reflection light detection type photosensor 11a and the specular reflection / diffuse light simultaneous detection type photosensor 11c should be shifted. This is because even if the black / color adhesion amount detection pattern overlaps at the contact portion between the recording medium conveyance belt 8 and the intermediate transfer belt 6 or the detection pattern is shifted in the circumferential direction to avoid overlap, the recording medium conveyance belt is slightly. The regular reflection light detection type optical sensor 11a detects erroneously by the color toner adhesion amount detection pattern transferred to 8, or the regular reflection light / diffuse light simultaneous detection type by the black toner adhesion amount detection pattern slightly transferred to the intermediate transfer belt 6. The problem that the optical sensor 11c erroneously detects can be avoided.

Next, when performing the alignment control, the control is started with the recording medium conveyance belt 8 and the intermediate transfer belt 6 in contact with each other. First, a black alignment control pattern is created on the black image carrier 1B by the black image forming unit, and then a primary transfer bias having a polarity opposite to that of toner is applied to the black primary transfer roller 15 to record the black alignment control pattern. The image is transferred onto the medium conveying belt 8. Further, the black transfer control pattern is applied to the intermediate transfer belt 6 by applying a secondary transfer bias having the same polarity as the toner to the secondary transfer roller 16 or applying a bias having a polarity opposite to that of the toner to the secondary transfer counter roller 17. Transcript. In the transfer to the intermediate transfer belt 6, the toner image is transferred in the direction opposite to that at the time of normal image formation, so that a high transfer rate is difficult to obtain. This is because it is designed to obtain a high transfer rate when performing normal image formation. However, since it is an alignment control pattern, there is no problem in reducing the adhesion amount.

Then, in synchronization with the black alignment pattern, a color alignment control pattern is created on the image carriers 1Y, 1C, and 1M in the color image forming unit, and then the color primary transfer rollers 14Y, 14C, and 14M are opposite to the toner. A polarity primary transfer bias is applied to transfer the adhesion amount detection pattern onto the intermediate transfer belt 6. The transferred color alignment control pattern passes through the contact portion with the recording medium conveyance belt 8, but as described above, whether the secondary transfer bias having the same polarity as the toner is applied to the secondary transfer roller 16 or secondary. Since a bias having a polarity opposite to that of the toner is applied to the transfer counter roller 17, the transfer is not transferred to the recording medium conveyance belt 8. Therefore, the black alignment control pattern and the color alignment control pattern formed on the intermediate transfer belt 6 are detected by the regular reflection light detection type photosensor 11b and the regular reflection light / diffuse light simultaneous detection type photosensor 11c, and are detected for each color. The alignment control is performed. In the case of performing black only alignment control, the black alignment control pattern formed by the black image forming unit is transferred onto the recording medium conveyance belt 8 and further onto the intermediate transfer belt, and the regular reflection light detection type The black alignment control is performed by detection by the optical sensor 11b and the specular reflection / diffuse light simultaneous detection type optical sensor 11c.

  Further, the regular reflection light detection type photosensor 11b and the regular reflection light / diffuse light simultaneous detection type photosensor 11c are arranged so as to be separated at the same distance from the center of the image forming region to both ends as shown in FIG. It is desirable. If they are arranged close to one of them, the alignment accuracy on the arranged side is increased, but the alignment accuracy on the opposite side is remarkably lowered. By arranging the image forming area so as to be separated at the same distance from the center to both ends, the alignment accuracy of the entire image can be ensured.

  Further, among the sensors arranged so as to be separated from the center portion of the image forming region to the both ends, as shown in FIG. 7, the specular reflection / diffuse light simultaneous detection type is provided with the specular reflection detection photosensor 11b closer to the end. By installing the optical sensor 11c closer to the center, a stable target adhesion amount of color toner can be obtained over the entire image area while performing alignment control. That is, the specular reflection / diffuse light simultaneous detection type optical sensor 11c is responsible for color toner adhesion amount control in addition to the alignment control, and is preferably arranged as close to the center as possible. On the other hand, in order to perform alignment control with higher accuracy, it is better to increase the distance between the two sensors. This is because the detection sensitivity with respect to left and right positional shifts such as skew increases. In order to realize this, it is desirable that at least Lb ≧ Lc as shown in FIG.

Further, the regular reflection light detection type optical sensor for controlling the black toner adhesion amount may be disposed to face the black image carrier 1B. In this case, as shown in FIG. 8, the specular reflection light detection type optical sensor 11a ′ is disposed downstream of the contact portion between the image carrier 1B and the recording medium transport belt 8 in the rotational direction of the image carrier 1B and the black image carrier. Arranged upstream of the cleaning member 4B in the rotational direction of the image carrier 1B. When black toner adhesion amount control is performed, an adhesion amount detection pattern is created on the image carrier 1B at the black image forming unit, and then a primary transfer bias having the same polarity as the toner is applied to the black primary transfer roller 15 to generate black. The toner adhesion amount detection pattern is not transferred to the recording medium conveyance belt 8 and is detected by the regular reflection light detection type optical sensor 11a ′. The detected pattern is collected by the black image carrier cleaning member 4B. In addition, when the black toner adhesion amount control is started, if the black primary transfer roller 15 is retracted to separate the image carrier 1B from the recording medium conveyance belt 8, the black toner adhesion amount detection pattern is applied to the recording medium conveyance belt 8. In addition to the effect of preventing the transfer, there is an advantage that it is not necessary to operate the recording medium conveyance belt. More preferably, when a primary transfer bias having the same polarity as the toner is applied to the black primary transfer roller 15, the toner from the black toner adhesion amount detection pattern on the recording medium conveyance belt 8 that is spaced apart but close to the black primary transfer roller 15. Scattering can be suppressed. The bias to be applied is preferably a constant voltage of about -100V to -1500V. This is because if the voltage is low, it is difficult to obtain the toner scattering suppressing effect. This is because when the voltage is high, discharge occurs between the belts and other adjacent members, particularly the grounded member. Further, it is desirable that the specular reflection light detection type optical sensor 11a ′ is installed in the center of the image forming region, and in the vicinity of the center when viewed in the direction perpendicular to the paper surface of FIG.

  As described above, the image forming apparatus according to the present embodiment is disposed so as to face the front surface of the intermediate transfer body 6 and the intermediate transfer body 6 that are rotatably stretched around a plurality of roller members. A plurality of first image carriers 1Y, 1C, 1M, first image forming means for forming each image on each first image carrier, and formed on each first image carrier. Primary transfer means for primary transfer of each of the images transferred onto the intermediate transfer body 6, secondary transfer means for secondary transfer of the image transferred onto the intermediate transfer body 6 onto a recording medium, and the intermediate transfer body A second image carrier 1B provided on the upstream side or downstream side in the recording medium conveyance direction from the secondary transfer position where the image is secondarily transferred from above to the recording medium; and on the second image carrier A second image forming means for forming an image on the recording medium and the image formed on the second image carrier directly transferred onto the recording medium. A direct transfer means, and a rotation that carries and conveys the recording medium so as to pass through a direct transfer position where the image is directly transferred from the second image carrier onto the recording medium and the secondary transfer position. And a recording medium conveying belt 8 stretched by a plurality of roller members.

  Further, as shown in FIG. 4, the specular reflection light detection type photosensor 11 b and the specular reflection / diffuse light simultaneous detection type photosensor 11 c are installed to face the intermediate transfer body 6. Further, a specular reflection light detection type optical sensor 11a is disposed to face the recording medium conveyance belt 8 or the second image carrier.

  When the black toner adhesion amount control is performed, the black toner adhesion amount detection image formed on the second image carrier or the recording medium conveyance belt formed by the second image carrier. The black toner adhesion amount detection image transferred onto 8 is detected by the specular reflection light detection type optical sensor 11a.

  In addition, when controlling the toner adhesion amount other than black, each of the plurality of color toner adhesion amount detection images formed on each of the first image carriers is superposed on the intermediate transfer member and the regular reflection is performed. Detection is performed by the light / diffuse light simultaneous detection type optical sensor 11c.

  Next, when performing the alignment control of each color, the specular reflection light detection type photosensor 11b and the specular reflection / diffuse light simultaneous detection type photosensor 11c are formed on the first image carriers. A plurality of color misregistration detection images obtained by superimposing the plurality of color misregistration detection images on the intermediate transfer member 6 are detected. The specular reflection light detection type photosensor 11b and the specular reflection / diffuse light simultaneous detection type photosensor 11c transfer the black misregistration detection image formed on the second image carrier to the recording medium. The black misregistration detection image after being transferred to the belt 8 or the black misregistration detection image on the intermediate transfer body 6 is detected.

  As described above, in the image forming apparatus according to the present embodiment, detection of the misregistration detection image of the plurality of colors in the first image forming unit and detection of the black misregistration detection image in the second image forming unit are performed. This can be performed using the specular reflection light detection type photosensor 11b and the specular reflection / diffuse light simultaneous detection type photosensor 11c arranged opposite to the intermediate transfer body 6. That is, the regular reflection light detection type photosensor 11b and the regular reflection light / diffuse light simultaneous detection type photosensor 11c also perform detection of a black misregistration detection image in the second image forming means. Therefore, cost can be reduced in view of the entire apparatus.

  Further, the regular reflection light detection type photosensor 11b and the regular reflection / diffuse light simultaneous detection type photosensor 11c sandwich the center line of the image forming region of the intermediate transfer body 6 and each detection unit and the center. Since the distance between the lines is the same, the detection accuracy when detecting the misalignment image is the same, and the alignment accuracy of the entire misalignment detection image can be ensured.

Further, the distance between the arrangement position of the regular reflection light / diffuse light simultaneous detection type photosensor 11c in the longitudinal direction and the center line of the image forming region of the intermediate transfer member is the longitudinal direction of the regular reflection detection type photosensor 11b. The regular reflection light detection type photosensor 11b and the regular reflection light / diffuse light simultaneous detection type photosensor 11c are arranged so as to be shorter than the distance between the arrangement position of the intermediate transfer member and the center line of the image forming area of the intermediate transfer member. . Therefore, it is possible to detect the image near the center of the image forming area when controlling the toner adhesion amount, and to improve the accuracy of toner adhesion amount detection. Sensitivity to the image position shift due to body skew increases.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging member 3 Developing member 4 Cleaning member 5 Exposure device 6 Intermediate transfer belt 7 Intermediate transfer belt cleaning device 8 Recording medium conveyance belt 9 Recording medium conveyance belt cleaning member 10 Fixing device 11 Optical sensor 11a Regular reflection light detection type light Sensor 11b Regular reflection light detection type photo sensor 11c Regular reflection light / diffuse light simultaneous detection type photo sensor 12 Toner container 14 Color primary transfer roller 15 Black primary transfer roller 16 Secondary transfer roller 17 Secondary transfer counter roller

JP 2002-182447 A JP 2007-298858 A JP 2004-354623 A

Claims (3)

An intermediate transfer member stretched around a plurality of roller members in a rotatable manner, a plurality of first image carriers disposed to face the front surface of the intermediate transfer member, and the first images A first image forming means for forming each image on the carrier, a primary transfer means for primarily transferring each image formed on the first image carrier onto the intermediate transfer body, and the intermediate transfer. A secondary transfer means for secondary transfer of the image transferred on the body onto the recording medium, and a secondary transfer position where the image is secondarily transferred from the intermediate transfer body onto the recording medium in the direction of transport of the recording medium. A second image carrier provided on the upstream side or the downstream side, a second image forming unit for forming an image on the second image carrier, and the second image carrier formed on the second image carrier. Direct transfer means for directly transferring the image onto the recording medium, and the image is directly transferred onto the recording medium from the second image carrier. To contact the transfer position and the carrying and conveying the recording medium to pass through and the secondary transfer position, an image forming apparatus and a recording medium conveying belt is stretched by a plurality of roller members rotatably,
At least one specular reflection light detection type optical sensor and at least one specular reflection / scattered light simultaneous detection type optical sensor are disposed to face the intermediate transfer body, and at least one specular reflection is provided. A light detection type optical sensor is disposed opposite to the recording medium conveyance belt or the second image carrier,
Black toner adhesion amount control is performed using at least one specular reflection light detection type optical sensor disposed opposite to the recording medium conveyance belt or the second image carrier to control the toner adhesion amount other than black. Is performed using at least one specularly reflected light / scattered light simultaneous detection type optical sensor disposed opposite to the intermediate transfer member,
The alignment control of each color is performed using at least one specular light / scattered light simultaneous detection optical sensor and at least one specular light detection optical sensor which are disposed to face the intermediate transfer member. An image forming apparatus. The image forming apparatus according to claim 1.
The regular reflection light detection type optical sensor and the regular reflection light / scattered light simultaneous detection type optical sensor are arranged so as to sandwich the center line of the image formation region of the intermediate transfer member. . The image forming apparatus according to claim 1.
The distance between the arrangement position in the longitudinal direction of the specular reflection / scattering light simultaneous detection optical sensor and the center line of the image forming region of the intermediate transfer member is the longitudinal arrangement position of the specular reflection light detection optical sensor and the The regular reflection light detection type optical sensor and the regular reflection light / scattered light simultaneous detection type optical sensor are arranged so as to be equal to or shorter than the distance from the center line of the image forming region of the intermediate transfer member. Image forming apparatus.

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