JP4622420B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a technique for detecting a defective image generated in a process of changing an image forming condition in an electrophotographic image forming apparatus such as a copying machine or a printer, and controlling the change of the image forming condition based on the detection result.

JP-A-7-253893 JP 2002-108163 A

  At present, the image quality of the output image by the image forming apparatus has improved remarkably, and as a result, the user's demand for image quality fluctuations has become more severe. Therefore, it is necessary to adjust the image quality without affecting the output image.

  When adjusting the image quality, when changing the timing of applying the charging bias to the photosensitive member and the timing of applying the developing bias to the developing unit, or when changing the charging potential and the developing potential, the main scanning direction of the photosensitive member is changed. A parallel belt-like toner image (hereinafter referred to as “toner band”) may be generated. When an image forming apparatus to which two-component development using toner and carrier is applied is changed or changed in the same manner, a developer band in which toner is mixed in the carrier (hereinafter referred to as “carrier band”) is generated. There is.

  Since the toner band and the carrier band are different from regular images, various problems are caused. For example, the periphery of the image carrier such as an intermediate transfer belt or a paper transport belt is soiled, the recording paper is soiled as a result of being transferred to the transfer device, and the fixing device is soiled via the dirty recording paper. Not only the inside of the forming apparatus but also the recording paper is soiled. Further, the toner and carrier from the developing unit are unnecessarily consumed.

  By the way, in the toner band and the carrier band, as a result of changing the timing of applying the charging bias or the developing bias, or as a result of changing the charging potential or the developing potential, the difference between the charging potential of the photosensitive member and the developing potential of the developing device is different. It is caused by exceeding a certain range. For example, a toner charged to a certain polarity is transferred to a portion having a relatively opposite polarity, and a large amount of toner is transferred if the potential difference is large. That is, toner transfer from the developing device to the photosensitive member occurs when the pulling force is larger than the adhesion force between the toner and the carrier. Therefore, in the toner band, if the charging potential of the photosensitive member is equal to the developing potential of the developing device, or if the charging potential is relatively on the toner polarity side from the developing potential, the toner does not transfer from the developing device to the photosensitive member. Even if it is on the opposite polarity side of the toner, if the potential difference is small, no toner band will be generated.

  On the other hand, the carrier band occurs when the carrier transfer from the developing device to the photoconductor is larger than the adhesion force between the carrier and the developing roll as well as the toner transfer. Therefore, the carrier band is not transferred from the developing device to the photosensitive member when the charged potential is equal to the developing potential, or when the charged potential is on the carrier (anti-toner) polarity side relative to the developing potential. Even on the polar side, if the potential difference is small, no carrier band is generated.

Here, FIG. 7 shows a state in which a toner band or a carrier band is formed on the image carrier as a result of changing the timing of applying the charging potential or the developing potential. In the partial diagram (a), the charging potential E (shown by a straight line) rises later than the developing potential D (shown by a dotted line). As a result, a potential difference V ₁ is generated between the developing potential D and the charging potential E in a region where no charging bias is applied even when the developing potential D reaches a predetermined potential. At this time, if the potential difference V ₁ exceeds a certain range, a toner band B is formed on the surface of the image carrier 100.

On the other hand, in the partial diagram (b), the charging potential E (shown by a straight line) rises earlier than the developing potential D (shown by a dotted line). As a result, a potential difference V ₂ occurs between the charging potential E and the developing potential D in a region where the developing bias is not applied even when the charging potential E reaches a predetermined potential. At this time, when the potential difference V ₂ exceeds a certain range, a carrier band C is formed on the surface of the image carrier 100.

  Therefore, as shown in FIG. 7, when changing the timing for applying the charging potential or the developing potential, such as at the start of image formation, or changing the charging potential or the developing potential, Since the difference from the development potential exceeds a certain range for a short time, a toner band and a carrier band are generated.

  As a method for preventing this toner band or carrier band, the relative potential difference between the surface potential of the photosensitive member and the developing bias voltage at the start and stop of the photosensitive member rotation is within the range of the maximum potential difference between the carrier jump generation limit and the minimum potential difference of the toner adhesion amount. A method of controlling in stages (JP-A-7-253893) has been proposed. However, it is complicated to control the potential difference between the surface potential of the photoconductor and the developing bias voltage stepwise within the range of the maximum potential difference of carrier jump generation and the minimum potential difference of toner adhesion amount, which places a load on the control device. There was a problem that. In addition, since the bias is changed stepwise every time the photosensitive member starts and stops rotating, there is a problem that it takes time to form an image.

  Further, when starting image formation, the control means recognizes the time when the surface potential of the photoconductor detected by the surface potential detection means reaches a predetermined potential, and at a time when a certain time has elapsed from this time. A method (Japanese Patent Laid-Open No. 2002-108163) is proposed in which a developing bias is applied to a developer carrying member by a signal from a control means. However, the sensitivity of the surface potential detection means to the surface potential is easily affected by the mounting state. Further, a power source for applying a charging bias to the charger and a power source for applying a developing bias to the developing device have different surface potential rising characteristics and changing characteristics, respectively. For this reason, there is a problem that control is difficult due to the influence of the mounting state of the surface potential detecting means and the variation in the characteristics of the power supply device.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an image forming apparatus capable of preventing toner bands and carrier bands generated under predetermined conditions. .

  In order to achieve the above object, an image forming apparatus according to the present invention includes a rotating photoreceptor, a charging unit that uniformly charges the surface of the photoreceptor, a charging power source that applies a charging bias to the charging unit, A developing unit that forms a toner image on the photoconductor according to the electrostatic latent image, a developing power source that applies a developing bias to the developing unit, an image carrier that transfers the toner image from the photoconductor, and light emission A detecting means for optically reading a toner image formed on the surface of the image carrier, and a charging bias applying signal and a developing bias applying signal to the charging power source and the developing power source, respectively. In the image forming apparatus including the control unit, the detection unit transiently changes the image when changing or changing at least one of the charging bias and the developing bias. A belt-like developer parallel to the main scanning direction formed on the surface of the holder is detected, and the controller is configured to perform the charging based on the width of the belt-like developer in the sub-scanning direction calculated from the detection signal of the detection unit. The transmission timing of at least one of the bias application signal and the development bias application signal is corrected.

  In such an image forming apparatus of the present invention, the charging means must be in contact with the entire width of the photoconductor in the main scanning direction and charge the surface of the photoconductor to a predetermined potential. The charging power source must be capable of applying a charging bias voltage for charging the photosensitive member to a predetermined potential to the charging means. As a result, the surface of the photoreceptor can be charged with a uniform potential.

  The developing means must be in contact with the entire width of the photoconductor in the main scanning direction. The developing power source must be capable of applying a predetermined developing bias voltage required for developing to the developing means. Accordingly, the toner of the developing unit can be transferred to the surface of the photoconductor according to the electrostatic latent image formed on the surface of the photoconductor to form a toner image. The developing means may use a two-component developer composed of toner and carrier. The developing means may be configured to add a special color such as a corporate color in addition to the four colors of cyan, yellow, magenta, and black, and to include each of the developing power sources.

  As the image carrier, an intermediate transfer body belt on which a recording image formed on the surface of each color photoreceptor is transferred in a tandem color image forming apparatus can be applied. Alternatively, a photosensitive belt of each color is disposed at a position opposite to the conveyance belt that electrostatically attracts and conveys the recording sheet, and a conveyance belt that sequentially electrostatically transfers the recording image of each color to the recording sheet is applied along with the conveyance of the recording sheet. It is also possible.

  The detection means may be any means as long as it can detect an image quality adjustment toner image formed on the surface of the image carrier in image quality adjustment. The detection means combines a light emitting element and a light receiving element to obtain the toner image. There is no problem as long as it is arranged at a position where the light reflected from the toner image or the transmitted light transmitted through the toner image can enter the light receiving element when irradiated by the light emitting element. At this time, the light emitting element reflects diffuse reflected light when a yellow, magenta, and cyan toner image is irradiated, and specularly reflected light when a black toner image is irradiated. Therefore, it is preferable to provide a total of two light emitting elements dedicated to diffuse reflected light and regular reflected light, and to arrange each light emitting element at a position where each reflected light can enter. In addition, when the diffuse reflected light is received by the light receiving surface of the light receiving element, the reflected light is imaged on the light receiving surface, that is, in order to focus and project the light, between the image carrier and the light receiving element. It is preferable that a lens is disposed to constitute the imaging optical system. By configuring this imaging optical system, a toner image can be projected onto the light receiving surface in a focused state, and detection with high accuracy is possible. Furthermore, it is preferable to provide a mask for limiting the field of view of the light receiving element on the front surface of the light receiving element. As a result, even when the toner image formed on the surface of the image carrier is small, only light with strong light power reflected from the toner image can be incident on the light receiving element.

  The control unit must be able to transmit a charging bias application signal and a developing bias application signal to the charging power source and the developing power source at a predetermined timing, respectively. As a result, when the belt-like developer is formed on the surface of the image carrier, the belt-like developer can be reduced. The belt-like developer is a toner band formed on the surface of the image carrier with toner, or when a two-component developer is used as the developing means, the toner is mixed into the carrier. Both of the carrier bands formed on the surface of the image carrier are applicable.

  In the image forming apparatus, a charging bias is applied to the charging unit by the charging power source, and the rising characteristics of the potential until the surface of the photoconductor reaches the charging potential are the characteristics of the charging power source itself and the characteristics of the image forming apparatus. Temperature and humidity are affected. Therefore, when the charging bias application signal and the development bias application signal are transmitted from the control unit at the same timing before and after the environment such as temperature and humidity changes, a toner band and a carrier band may be generated.

  When a toner band or a carrier band (hereinafter simply referred to as “band”) occurs, the band may be detected by the detection means. Here, since the detection means is configured to detect a toner image for image quality adjustment, it is possible to detect a band that can occur for each color. Therefore, it is not necessary to newly provide a dedicated detection means for detecting a band, and by configuring the control section so that the width of the band can be calculated from the detection signal of the band detected by the detection means, It is possible to detect a toner image and band for image quality adjustment without increasing the number of detection means.

  In the image forming apparatus, in addition to the characteristics of the charging power source, there are characteristics of the developing power source. In addition, the image forming apparatuses have unique characteristics due to variations in production capacity in the production process. Here, when the generation of the band is caused by the characteristic unique to the image forming apparatus, the band is detected in advance by the detection means at the time of factory shipment or immediately after adjustment of the image forming apparatus, and is calculated from the detection signal. The control unit may be provided with a storage unit that stores the width of the obtained band. As a result, for the band caused by the characteristic unique to the image forming apparatus, the characteristic unique to the image forming apparatus can be ignored by storing the band width in the storage unit, and only under a predetermined condition. In this case, it is possible to perform band detection and adjust the transmission timing of the charging bias application signal or the development bias application signal as necessary. Here, the predetermined condition means that the charged potential is determined when an environmental change in the image forming apparatus is confirmed or when at least one of the charging bias and the developing bias is changed or changed. This corresponds to the case where a change in the rising characteristic of the development potential is expected. This may overlap with the condition for adjusting the image quality, and the interruption of the image forming operation only for band detection can be reduced.

  When band correction is necessary, it is preferable to execute the image forming process by applying a charging bias or a developing bias at a timing at which a toner band can be generated in advance. Accordingly, the generation of the carrier band can be suppressed by generating the toner band with a preset width, and the deviation of the toner band width of the preset width can be detected and calculated. Note that the toner band is generated in advance if the carrier band is generated, the carrier of the developing means is insufficient, or the carrier is included where the toner should normally be developed and transferred. This is because the photoconductor and the image carrier may be damaged.

  According to the image forming apparatus of the present invention configured as described above, it is possible to prevent a toner band or a carrier band generated under a predetermined condition.

  Hereinafter, an image forming apparatus of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a color image forming apparatus using an electrophotographic system to which the present invention is applied. In this configuration diagram, after charging the surface of the photoreceptor with a contact charger, an electrostatic latent image is formed by irradiation with a laser beam, and the xerographic engine that develops the electrostatic latent image with toner is yellow, magenta, cyan, An outline of an IOT (image output terminal: image output unit) of a tandem type color electrophotographic image forming apparatus provided for each color of black is shown. In the drawing, the image reading unit and the image processing unit of the image forming apparatus are omitted.

  The IOT of this image forming apparatus includes four photoconductors 1Y, 1M, 1C, and 1K that rotate in the direction of arrow A in the figure, and contact chargers 2Y, 2M, 2C, and 2K that charge the surface of each photoconductor. ROS (laser output units) 3Y, 3M, 3C, which expose the charged photoreceptor surfaces with exposure light modulated based on the image information of each color and form electrostatic latent images on the photoreceptors. 3K and developing units 4Y, 4M, 4C, and 4K that develop the electrostatic latent image on each photoconductor with each color developer to form a toner image on the photoconductor, and intermediate transfer each color toner image on the photoconductor The primary transfer units 5Y, 5M, 5C, and 5K that transfer to the body belt 6, the secondary transfer unit 7 that transfers the toner image on the intermediate transfer body belt 6 to the paper P, and the toner image transferred to the paper P are fixed. The fixing device 9 for carrying out the paper, the paper tray T for containing the paper P, and the surface of each photoconductor. A cleaner for cleaning (not shown), a static eliminator (not shown) for removing residual charges on the surface of each photoconductor, and a photosensor for detecting a toner image for image quality adjustment transferred to the surface of the intermediate transfer belt 6 10 and a belt cleaner 8 for cleaning the surface of the intermediate transfer belt 6.

  As an image forming operation in the image forming apparatus shown in the configuration diagram, first, an original image signal read from an original by an image reading unit (not shown) or an external computer (not shown) is used. The original image signal is input to an image processing unit (not shown). The input image signal is decomposed into image information of each color and then input to ROS (laser output units) 3Y, 3M, 3C, and 3K, and the laser beam L is modulated. The modulated laser beam L is applied to the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K that are uniformly charged by the contact chargers 2Y, 2M, 2C, and 2K. When the laser beam L is raster-irradiated on the surface of each photoconductor, an electrostatic latent image corresponding to the input image signal is formed on each photoconductor. Subsequently, the electrostatic latent images on the photoconductors are developed with toner by the color developing devices 4Y, 4M, 4C, and 4K, and toner images are formed on the photoconductors. The toner image formed on each photoconductor is transferred to the intermediate transfer belt 6 by the primary transfer units 5Y, 5M, 5C, and 5K. Each photoreceptor after the transfer of the toner image to the intermediate transfer belt 6 is cleaned of adhering matter such as residual toner adhering to the surface by a cleaner, and the residual charge is removed by a static eliminator.

  Next, the toner image on the intermediate transfer belt 6 is transferred onto the paper P sent from the paper tray T by the secondary transfer device 7 and then transferred onto the paper P by the fixing device 9. The image is fixed and a desired image is obtained. The intermediate transfer belt 6 on which the transfer of the toner image onto the paper P has been completed is cleaned of adhering matters such as residual toner adhering to the surface by the belt cleaner 8, and one image forming operation is completed.

  Toner bands when the environmental changes such as temperature and humidity in the color image forming apparatus and the bias to the contact chargers 2Y, 2M, 2C, and 2K and the color developing devices 4Y, 4M, 4C, and 4K are changed or changed And a carrier band occurs. In this case, these bands are detected by the photosensor 10. Then, according to the band width calculated from the output signal when the band is detected, a control unit (not shown) supplies the contact chargers 2Y, 2M, 2C, and 2K and the color developing devices 4Y, 4M, 4C, and 4K. The timing for applying the bias is corrected.

  FIG. 2 is a block diagram showing a flow of band correction in the color image forming apparatus shown in FIG. In the case of forming a recorded image, first, the photosensitive member 1 is charged by the contact charger 2, and the photosensitive member 1 is exposed by the ROS 3 according to the image information, whereby an electrostatic latent image is formed on the surface of the photosensitive member 1. It is formed. Next, after developing by the developing device 4, the recorded image is transferred to the surface of the intermediate transfer belt 6. In order to optimally implement the present invention, when band correction is necessary, an image forming process is executed by applying a bias in advance at a timing such that a toner band is generated with a width of several millimeters in the sub-scanning direction. Good. This is because when the carrier band is generated, the carrier in the developing device 4 is insufficient, or the carrier is included in a place where the toner is normally developed and transferred, so that the photosensitive member 1, the intermediate transfer member belt 6, etc. Because it hurts. That is, by generating the toner band with a preset width, the generation of the carrier band can be suppressed, and the deviation of the toner band width of the preset width can be detected and calculated. In this way, when a toner band is generated, the toner band is read by the photosensor 10.

  The control unit 11 calculates the width of the toner band and the carrier band from the signal output from the photosensor 10. When these bands are generated due to potential rising characteristics of the charging power source 13 and the developing power source 14 or variations in production capacity in the production process of the color image forming apparatus, the bands of the bands are stored in the storage unit 12. Remember the width. Further, the control unit 11 corrects the timing of applying a bias to the charging power source 13 and the developing power source 14 according to the band width.

  FIG. 3 shows a schematic configuration diagram of the photosensor 10 in the color image forming apparatus to which the present invention is applied. The photosensor 10 includes an illumination unit, a light receiving optical system, and a light receiving element. This illumination means consists of two LEDs 10a, 10b. The light receiving optical system includes a lens 10c and a mask 10e. In this figure, the left-right direction is the main scanning direction.

  In order to detect a band with the photo sensor 10, it is necessary to irradiate the band with illumination means and detect reflected light reflected from the band. Bands occur for all colors of cyan, yellow, magenta, and black, and the reflected light from the cyan, yellow, and magenta mark images and the reflected light from the black mark image have different types of reflected light. Different. Therefore, in order to detect these two types of reflected light with one light receiving element (photodiode 10d), it is necessary to irradiate the band from a position where each reflected light can enter the light receiving element. Depending on, two lighting means are used properly. Incidentally, the cyan, yellow, and magenta bands are diffusely reflected, and are therefore irradiated by the LED 10b, and the black band is regularly reflected, so that the bands are symmetrically arranged with respect to the perpendicular of the intermediate transfer body 6. The LED 10a is irradiated.

  The lens 10c of the light receiving optical system is arranged so that diffused reflected light of two types of reflected light can be imaged on the light receiving surface of the photodiode 10d. However, when the reflected light is incident on the photodiode 10d, the reflected light is not limited to whether the reflected light is imaged or not formed on the light receiving surface, and reflected light unnecessary for band detection also enters. Therefore, it is necessary to block this unnecessary reflected light and guide only the reflected light component effective for each detection onto the light receiving surface of the photodiode 10d. Therefore, a mask 10e for restricting the visual field area of the light receiving surface of the photodiode 10d is provided immediately before the photodiode 10d. The mask 10e is black to prevent stray light. The lens 10c and the mask 10e constituting the light receiving optical system can make the viewing area of the light receiving surface of the photodiode 10d substantially equal regardless of which reflected light is incident.

  When reflected light from the toner band or carrier band is projected onto the light receiving surface of the photodiode 10d, the photodiode 10d outputs a current corresponding to the density of these bands. As shown in FIG. 4, the current output from the photodiode 10 d is converted from current to voltage by an AMP 20 provided in the control unit 11 and then converted into a sensor output signal as a comparator 21 and further as a counter. 22 is supplied.

  The comparator 21 outputs a signal to the counter 22 only while the output value of the sensor output signal exceeds a preset threshold value. The counter 22 measures the time when the signal is output from the comparator 21. Furthermore, the sub-scanning direction width of the toner band or carrier band is calculated from the time measured by the counter 22. Note that the threshold value set in the comparator 21 can be set as appropriate.

FIG. 5 shows that the timing for applying the developing bias is corrected based on the result of detecting the toner band by the photo sensor. FIG. 2A shows the positional relationship between the toner band B formed on the intermediate transfer belt 6 and the visual field region R of the photosensor 10 on the intermediate transfer belt 6 with time. The lower graph shows the waveform of the sensor output signal according to the position of the visual field region R of the photosensor 10. A time T exceeding the threshold S in the waveform of the sensor output signal is shown. In part (b), the control unit 11 calculates the width of the toner band B from the time T, and based on the result, the development potentials D ₁ and D ₂ before and after the correction of the timing for applying the development bias, and the charging potential E It is shown.

  The toner band B primarily transferred onto the intermediate transfer belt 6 passes through the front surface of the photosensor 10 as the intermediate transfer belt 6 rotates, and crosses the visual field region R of the photosensor 10. When the toner band B moves together with the intermediate transfer body belt 6 and the visual field area R of the photosensor 10 reaches the point X on the intermediate transfer body belt 6 shown in the partial diagram (a), the toner is contained in the visual field area R. As band B enters, the sensor output signal begins to change. When the toner band B further moves, the area of the toner band B included in the visual field region R, that is, the overlapping area between the visual field region R and the toner band B increases, so that the sensor output signal gradually rises and the visual field region R The sensor output signal becomes maximum at a point Y substantially covered with the toner band B.

  Further, when the toner band B passes the Y point, the area of the toner band B included in the visual field region R, that is, the overlapping area of the visual field region R and the toner band B decreases, so that the sensor output signal gradually increases. When the toner band B is completely removed from the visual field region R of the photosensor 10, the sensor output signal becomes minimum (point Z).

  As shown in the partial diagram (a), when the toner band B passes through the visual field region R of the photosensor 10 (between the X point and the Y point), the visual field region R overlaps with the toner band B. The area continuously changes as the intermediate transfer belt 6 advances, and the sensor output signal having the same intensity is not continuously output from the photosensor 10. That is, since the visual field region R of the photosensor 10 is formed in a circular shape, the sensor output signal is output when the center position (center of gravity) of the width w of the toner band B matches the central position of the visual field region R of the photosensor 10. The maximum value occurs instantaneously. At this time, by measuring the time T exceeding the threshold S, the width w of the toner band B can be calculated.

  The timing for applying the developing bias is corrected based on the width w of the toner band B calculated from the time T when the output signal of the toner band B exceeds the threshold S. The term “timing” as used herein refers to a timing when the developing bias is applied so that the potential difference between the developing bias and the charging bias does not exceed a certain range in which the toner band B can be generated. In addition, the smaller the diameter d of the visual field region R, the larger the signal level, and the skirt spread of the output signal can be reduced. Therefore, the relationship between the timing to be corrected and the time T can be obtained with high accuracy.

As shown in the partial diagram (b), the developing potential D ₁ rises earlier than the charging potential E. Therefore, before correcting the timing of applying the developing bias, the developing potential D ₁ and the charging potential Since the potential difference from the potential E exceeded a certain range, a toner band (not shown) was generated on the intermediate transfer belt 6. Here, by shifting (delaying) the development potential D ₁ to the development potential D ₂ in the direction of the arrow in the drawing for a time corresponding to the width w of the toner band B, the potential difference between the development potential D ₂ and the charging potential E is It is possible to prevent the toner band B from being generated in a range where the toner band B is not generated. Further, in the example of the partial diagram (b), the timing for applying the developing bias is corrected, but the timing for applying the charging bias is shifted in the direction opposite to the arrow in the drawing (accelerated) to develop the developing potential D. It is also possible to prevent the toner band B from being generated by stopping the potential difference between ₁ and the charging potential E within a range where the toner band B is not generated. Further, in addition to correcting the timing of applying the developing bias or the charging bias, the toner band B can adjust the potential difference between the developing potential D ₁ and the charging potential E by adjusting the process speed, that is, the rotation speed of the photosensitive member. It is also possible to prevent the toner band B from being generated by stopping the generation of the toner band B.

  For the carrier band, the carrier band width is calculated from the output signal of the carrier band detected by the photosensor 10, and the timing for applying the developing bias or the charging bias is advanced or delayed based on the width, similarly. It is possible to prevent the generation of a carrier band. Furthermore, the detection of the toner band or the carrier band by the photosensor 10 may be performed at the time of image quality adjustment or at a predetermined time set in advance, and the detection time can be set as appropriate.

  Generally, image forming apparatuses have their own characteristics due to variations in production capacity in the production process. Here, when a toner band or a carrier band is generated due to characteristics unique to the image forming apparatus, an output signal of a band detected in advance by a photosensor at the time of factory shipment or immediately after adjustment of the image forming apparatus The band width calculated from the above may be stored in a storage unit provided in the control unit. As a result, there is a control method for detecting a band only under conditions where the band can be generated, such as when an environmental change in the image forming apparatus is confirmed or when a charging bias or a developing bias is changed or changed for image quality adjustment. In this case, characteristics unique to the image forming apparatus may be ignored.

  Further, at the time of shipment from the factory or immediately after adjustment of the image forming apparatus, a charging bias or a developing bias is applied in advance so that a toner band or a carrier band is generated, and the band of the band calculated from the output signal of the band detected by the photo sensor is used. The width may be stored in a storage unit provided in the control unit. Even in this case, the characteristics unique to the image forming apparatus can be ignored.

The operation when the toner band is generated in advance will be described with reference to the flowchart of FIG. First, in step S1, the timing for applying the charging bias is delayed by t ₀ . At this time, the timing at which the charging bias is applied is such that the potential difference between the developing potential and the charging potential exceeds a certain range, and thus a toner band is generated on the intermediate transfer belt 6 (step S2). Then, the width of the toner band is calculated from the output signal when the photo sensor 10 detects the toner band, and the time t _b corresponding to the width is measured (step S3). Here, the optimum timing for applying the charging bias is the timing for applying the charging bias because the time t ₀ for delaying the timing for applying the charging bias is advanced by the time t _b corresponding to the width of the toner band. Is set to (t ₀ -t _b ) (step S4). Thereby, the timing for applying the charging bias can be set according to the width of the toner band. As for the timing for generating the toner band in advance, it may be performed at the time of image quality adjustment or a predetermined time set in advance when there is an environmental change such as temperature or humidity, and the time for generating the toner band can be set as appropriate. .

1 is a schematic configuration diagram of a color image forming apparatus using an electrophotographic system to which the present invention is applied. FIG. 5 is a diagram illustrating a flow of band correction in the color image forming apparatus. 1 is a diagram illustrating a schematic configuration diagram of a photosensor in a color image forming apparatus to which the present invention is applied. It is a block diagram which shows the flow by which the output signal from a photodiode is processed in a control part. FIG. 6 is a diagram illustrating correction of timing for applying a developing bias based on a result of detecting a toner band by a photosensor. FIG. 6 is a flowchart illustrating an operation when a toner band is generated in advance. FIG. 6 is a diagram illustrating timings at which a charging bias and a developing bias are applied when a toner band and a carrier band are generated.

Explanation of symbols

B: Toner band, R: Field area, w: Toner band width, d: Field area diameter, S: Threshold value, T ... (Over threshold value) time, E ... charge potential, D _1, D ₂ ... development potential, 6 ... intermediate transfer belt

Claims (5)

A rotating photoreceptor, charging means for uniformly charging the surface of the photoreceptor, a charging power source for applying a charging bias to the charging means, and a toner image corresponding to the electrostatic latent image are formed on the photoreceptor. A developing unit, a developing power source for applying a developing bias to the developing unit, an image carrier to which a toner image is transferred from the photoconductor, a light emitting element and a light receiving element, are formed on the surface of the image carrier. An image forming apparatus comprising: a detection unit that optically reads a toner image to be read; and a controller that transmits a charging bias application signal and a developing bias application signal to the charging power source and the developing power source
At a predetermined time set in advance, the control unit changes the transmission timing of at least one of the charging bias and the developing bias to thereby apply a charging bias and a developing bias to a part of the surface of the image carrier. A location where a large potential difference is provided to form a strip-shaped developer parallel to the main scanning direction on the surface of the image carrier, and the detection means detects the strip-shaped developer, and then
The controller controls the charging bias and the development bias so that the belt-like developer is not formed based on a time corresponding to the width of the belt-like developer in the sub-scanning direction calculated from the detection signal of the detection unit . An image forming apparatus , wherein at least one of the transmission times is shifted and corrected by the time .   The detection means includes an imaging optical system that forms an image of the toner image or strip developer on the image carrier, and reflected light that is reflected by the toner image or strip developer and passes through the imaging optical system. The image forming apparatus according to claim 1, further comprising: a light receiving element that receives light.   3. The image forming apparatus according to claim 1, further comprising a mask for limiting a visual field region in front of the light receiving element of the detection unit.   The control unit includes a storage unit that stores a width of the belt-shaped developer detected in advance, and at least one of the charging bias application signal and the development bias application signal based on a detection result stored in the storage unit. The image forming apparatus according to claim 1, wherein one transmission time is corrected.   5. The belt-like developer is subjected to an image forming process by applying a bias in advance at a timing such that the belt-like developer is generated, and the belt-like developer is made of toner. An image forming apparatus according to claim 1.

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