JP2011154087A - Method for adjusting developing roller position and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for adjusting the width of a development nip area to a predetermined value. <P>SOLUTION: In the image forming apparatus provided with a developing roller by which a developer containing toner and carrier is brought into contact with an image carrier, the developing roller is rotated in a state that relative movement of the image carrier relative to the developing roller is stopped. Thus, two toner adhesion patterns are formed on the image carrier along each other across a belt area, the belt area extending in the direction of the rotary shaft of the developing roller. The width of the belt area sandwiched between the toner attached patterns is measured. According to the measurement result of the width, the dimension of the gap between the developing roller and image carrier is adjusted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a developing roller position adjusting method for an electrophotographic image forming apparatus. The image forming apparatus includes a printer, a copier, a facsimile machine, and a multifunction peripheral (also referred to as MFP: Multifunction Peripherals).

  In image formation by electrophotography, magnetic brush development using a developer mainly composed of toner and a magnetic carrier is performed. A developing roller is arranged in the vicinity of a photosensitive drum as an image carrier that carries a latent image, and a magnetic brush that covers the peripheral surface of the developing roller is brought into contact with the toner to adhere the toner to the surface of the photosensitive drum. The magnetic brush is composed of a carrier that is attracted to the peripheral surface of the developing roller by magnetic action and toner that is electrostatically attracted to the carrier. The photosensitive drum is rotated so that a portion (referred to as a developing nip region) in contact with the magnetic brush is changed, and the developing roller is rotated to bring a toner-rich portion of the magnetic brush into contact with the surface of the photosensitive drum. As a result, the latent image on the surface of the photosensitive drum is developed into a toner image. After development, the image formation is completed through transfer of the toner image onto a recording sheet and fixing by heating and pressing.

  In such development, the width of the development nip region (the dimension in the circumferential direction of the photosensitive drum) affects the density of the toner image. Generally, the toner image is dark when the width of the development nip region is large, and the toner image is light when the width is small. Since the width of the developing nip region depends on the distance between the developing roller and the photosensitive drum (hereinafter referred to as a developing gap), it is necessary to set the developing gap appropriately in order to obtain an image with a desired image quality.

  Technology that measures the humidity near the image carrier that affects the attractive force between the toner and the carrier in relation to the setting of the development gap, and automatically adjusts the development gap so that the toner adheres well according to the measurement results (Patent Document 1). Further, an image forming apparatus having a gap measuring device that optically measures a development gap is known (Patent Document 2).

Japanese Patent Laid-Open No. 10-333435 JP-A-8-286508

  The width of the developing nip region is affected not only by the developing gap but also by the size of the magnetic brush in the radial direction of the developing roller. Therefore, even if the size of the development gap is measured and adjusted, or the development gap is adjusted according to the operating environment such as humidity and temperature, the width of the development nip region is not always appropriate.

  The present invention aims to provide a method and apparatus for adjusting the width of the development nip region to a desired value.

  A method for achieving the above object is a method for adjusting the position of a developing roller in an image forming apparatus having a developing roller for bringing a developer containing toner and a carrier into contact with the image bearing member. The developing roller is rotated in a state where the relative movement is stopped, thereby forming two toner adhering patterns along each other across a belt-like region extending in the rotation axis direction of the developing roller on the image carrier, The width of the band-like region sandwiched between the toner adhesion patterns is measured, and the gap dimension between the developing roller and the image carrier is adjusted according to the measurement result of the width.

  An apparatus that achieves the above object is an image forming apparatus that forms an image on a recording medium using a developer containing toner and a carrier, the image carrier carrying a toner image, and the development on the image carrier. A developing roller that contacts the developer, and rotating the developing roller in a state in which the relative movement of the image bearing member with respect to the developing roller is stopped, thereby rotating the developing roller on the image bearing member in the rotation axis direction of the developing roller. Two toner adhesion patterns are formed along each other across an extending belt-like region.

  According to the present invention, it is possible to measure the width of the development nip region itself depending on the state of the developer on the developing roller and adjust the width of the development nip region to a desired value.

1 is a diagram illustrating an outline of a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a main part including a developing roller in the image forming apparatus. It is a figure which shows typically the formation state of a toner adhesion pattern. It is a figure which shows the procedure of formation of a toner adhesion pattern. It is a figure which shows the output signal of the sensor which detects a toner adhesion pattern. It is a figure which shows the image development nip width. It is a figure which shows an example of development gap adjustment. It is a figure which shows the other example of development gap adjustment. It is a figure which shows an example of the positioning mechanism of a developing roller. It is a graph which shows an example of the relationship between a development gap and a development nip width.

  An image forming apparatus 1 illustrated in FIG. 1 is a tandem color printer that forms a color image or a monochrome image by electrophotography. Since four color toner images of black (K), cyan (C), magenta (M), and yellow (Y) are formed in parallel during color image formation, the image forming apparatus 1 includes four process units UK, UC. , UM, UY. The process unit UK for forming a black (K) image includes a photosensitive drum 11, a charging device 12, a print head 13, a developing device 14, a primary transfer device 15, and a cleaning device 16. The four process units UK, UC, UM, UY are basically similar components except that the process unit UK, which is relatively frequently used, is larger than the other process units UC, UM, UY. It has.

  It should be noted that not all of the components need to be integrated in each process unit UK, UC, UM, UY. For example, in the process unit UK, the charging device 12 and the primary transfer device 15 may be assembled to the image forming apparatus 1 separately from other elements. In order to operate the four process units UK, UC, UM, UY, the image forming apparatus 1 is provided with a drive mechanism (not shown) that combines a single or a plurality of motors and clutches.

  The image forming apparatus 1 operates as follows in forming a black monochrome image, for example.

  The charging device 12 uniformly charges the surface of the photosensitive drum 11 as an image carrier. The print head 13 performs pattern exposure by light beam scanning on the photosensitive drum 11 to form a latent image corresponding to the image to be formed on the photosensitive drum 11. The developing device 14 develops the latent image into a toner image by attaching toner to a portion where the charge has disappeared due to pattern exposure on the surface of the photosensitive drum 11. The primary transfer device 15 presses the intermediate transfer belt 20 against the photosensitive drum 11. As a result, the toner image is primarily transferred from the photosensitive drum 11 to the intermediate transfer belt 20. As the intermediate transfer belt 20 moves, the toner image moves to the secondary transfer position where the secondary transfer roller 23 is disposed. On the other hand, in parallel with the formation of the toner image, the recording paper P having a predetermined size is taken out from the multistage paper storage unit and conveyed. When the recording paper P passes the secondary transfer position, the secondary transfer roller 23 presses the recording paper P being conveyed against the intermediate transfer belt 20. As a result, the toner image is secondarily transferred from the intermediate transfer belt 20 to the recording paper P. Thereafter, the fixing device 24 fixes the toner image on the recording paper P by heating and pressing. When the recording paper P that has undergone the fixing process is sent out by the paper discharge roller pair 26 to the paper discharge tray, the image formation on one recording paper P is completed. At an appropriate timing during image formation, the cleaning device 16 removes the developer remaining on the surface of the photosensitive drum 11, and the cleaning device 28 removes the developer remaining on the surface of the intermediate transfer belt 20.

  The operation of the image forming apparatus 1 is controlled by the control unit 100. The control unit 100 built in the image forming apparatus 1 includes a computer that executes a control program. The control unit 100 is responsible for driving control of the process units UK, UC, UM, UY at the time of image formation, and driving control of the process units UK, UC, UM, UY when measuring the development nip width described later.

  Hereinafter, a method for adjusting the development gap in the process unit UK will be described. However, the following method can also be applied to the adjustment of the development gap in the other process units UC, UM, UY.

  As shown in FIG. 2A, the developing device 14 is disposed in the vicinity of the photosensitive drum 11. The developing device 14 contacts the surface of the photosensitive drum 11 with a circulating mixing unit 14A that mixes toner supplied from a toner container (not shown) with the developer circulating in the device, and a magnetic brush (not shown) made of the developer. And a developing head portion 14B. The developing head unit 14B has a developing roller 40 as a developer carrying member, and rotates the developing roller 40 during development to continuously supply toner to the surface of the photosensitive drum 11. The developing roller 40 is provided with a rotational force transmission mechanism 46 (see FIG. 6B) that can be rotated even when the movable part for stirring and circulating the developer in the circulating and mixing unit 14A is stopped. . A gap between the peripheral surface of the developing roller 40 and the peripheral surface of the photosensitive drum 11 is a development gap Dg. Generally, the value of the development gap Dg is about 0.5 mm.

  A density measuring device 43 related to the adjustment of the development gap Dg is disposed in the vicinity of the photosensitive drum 11. The arrangement position of the density measuring device 43 is a position downstream of the developing device 14 and upstream of the primary transfer position in the rotation direction of the photosensitive drum 11 (clockwise in the drawing). As shown in FIG. 2B, the density measuring device 43 is disposed at one end and the other end in the rotation axis direction (longitudinal direction) of the photosensitive drum 11, and corresponds to the reflection density on the surface of the photosensitive drum 11. The detected signal is output. The detection signal of each density measuring device 43 is input to the above-described control unit 100 and used for measuring the development nip width. In the illustration, there are two reflection density detection points, but the present invention is not limited to this. For example, only one central point in the longitudinal direction may be used as the detection point, or three or more detection points may be provided to measure the variation in the longitudinal direction of the development nip width in detail.

  The adjustment of the development gap Dg is performed based on the measurement result of the development nip width. The development nip width is a circumferential dimension of a development nip region that is substantially supplied with toner from the development roller 40 on the surface of the photosensitive drum 11. The development nip region is a region that is substantially in contact with the magnetic brush 90 having a height of less than 1 mm schematically shown in FIG. 3, and is a strip-like region that does not appear in FIG. 3 but extends in the longitudinal direction. In order to measure the development nip width, the image forming apparatus 1 forms two toner adhesion patterns 91 and 92 on the surface of the photosensitive drum 11. The procedure for measuring the development nip width is shown in FIGS.

  As shown in FIG. 4A, the developing roller 40 is rotated while the rotation of the photosensitive drum 11 is stopped. At this time, the photosensitive drum 11 is grounded and the surface potential is set to approximately 0 volts. The number of rotations of the developing roller 40 may be equal to or greater than the number at which a toner image having a sufficient density for detection is formed, but it is desirable to select the minimum number so that the toner is not scattered more than necessary. For example, about 2 to 10 rotations. An appropriate bias voltage is applied to the developing roller 40. The bias voltage needs to be set so that the toner adheres to the photosensitive drum 11 and the carrier does not adhere. For example, the surface potential of the developing roller 40 is about 300 to 1200 volts with respect to the surface potential of the photosensitive drum 11. A low potential (−300 to −1200 volts) is set.

  As the developing roller 40 rotates, the toner adheres so as to accumulate on both sides of the developing nip region in the photosensitive drum 11 in the circumferential direction as shown in FIG. Of the toner adhering to and near the developing nip region due to contact with the magnetic brush 90, the toner adhering to the developing nip region moves in the magnetic brush 90 as the magnetic brush 90 moves following the rotation of the developing roller 40. It is scraped off by the carrier. The toner scraped off returns to the magnetic brush 90 or is swept out in the vicinity of the developing nip region. As a result, almost no toner is attached to the development nip region, and a state where the toner is attached in the vicinity of the development nip region is obtained.

  After the toner adhesion pattern is formed on both sides of the development nip area, the rotation of the development roller 40 is stopped. Then, as shown in FIGS. 4C and 4D, the photosensitive drum 11 is rotated at a constant speed so that the toner adhesion pattern passes the detection point of the density measuring device 43. Since the reflection density of the toner-attached portion on the surface of the photosensitive drum 11 is higher than the reflection density of the other portions, the toner measurement pattern can be detected by the density measuring device 43.

  In the output signal of the density measuring device 43 as shown in FIG. 5, the time Td from when the toner adhesion pattern at one end of the development nip region passes until the toner adhesion pattern at the other end arrives at the detection point is the development time. Corresponds to the nip width. The longer the time Td, the larger the development nip width. The product of the time Td and the rotational peripheral speed of the photosensitive drum 11 is the value of the development nip width.

  In the determination of the time Td based on the output signal of the density measuring device 43, the reflection density in the development nip region may be larger than the background density depending on the state of scraping of the toner. Detect concentration. As shown in FIG. 5, when the time from peak to peak is measured in the time-dependent change in density that exhibits two peaks, it is affected by indefinite factors such as the toner adhesion state and the scattering state. For this reason, after the first peak time, the time from when the detected concentration drops to the cutoff level to the time before the next peak time and when the detected concentration starts to increase from the cutoff level, that is, the detected concentration is cut. A period that is a level is measured as time Td.

  As shown in FIGS. 6A and 6B, the toner adhesion patterns 91 and 92 formed for the measurement of the development nip width Dn are belt-like developments extending in the longitudinal direction of the photosensitive drum 11 and the development roller 40. The nip regions 93 are separated from each other. The shapes of the toner adhesion patterns 91 and 92 are macroscopically band-like. What is important is the edge on the development nip region 93 side in each toner adhesion pattern 91, 92, and the position and shape of the edge on the side far from the development nip region 93 in each toner adhesion pattern 91, 92 is not important.

  In the example of FIG. 6B, the edges on the developing nip region 93 side in the toner adhesion patterns 91 and 92 are substantially parallel to each other. That is, the development nip width Dn is uniform over the entire length of the development nip region 93. Accordingly, the outputs of the two concentration measuring devices 43 are substantially the same. In this case, if processes other than development are normal in actual image formation, an image having no longitudinal unevenness is formed. However, if the development nip width Dn is not within a predetermined appropriate range, it is necessary to optimize the development nip width Dn.

  The image forming apparatus 1 automatically adjusts the above-described development gap Dg in order to optimize the development nip width Dn. When the value of the developing nip width Dn measured based on the output of the density measuring device 43 is smaller than the appropriate value, the photosensitive drum 11 and the developing roller 40 are brought relatively close to each other. For example, by similarly driving the positioning mechanisms 48 arranged on both sides of the developing roller 40, the developing roller 40 is brought close to the photosensitive drum 11 uniformly over the entire length in the longitudinal direction. Conversely, when the measured value of the development nip width Dn is larger than the appropriate value, the developing roller 40 is evenly moved away from the photosensitive drum 11 over the entire length in the longitudinal direction. In either case, it is desirable that the entire developing device 14 is moved integrally with the developing roller 40 and the operating conditions inside the developing device 14 are not changed.

  7 and 8 illustrate the development gap adjustment when the development nip width is not uniform.

  In the example of FIG. 7A, the development nip region 93b between the two belt-like toner adhesion patterns 91b and 92b becomes narrower from the left side to the right side in the drawing. That is, the value of the right development nip width Dn2 is smaller than the value of the left development nip width Dn1. A typical situation in which the values of the left and right development nip widths Dn 1 and Dn 2 are different is a situation in which the developing roller 40 is inclined with respect to the photosensitive drum 11. The cause of this is assembly error and secular change.

  In order to form a uniform image, it is necessary to make the left and right development nip widths Dn1 and Dn2 uniform. In order to make the developing nip widths Dn1 and Dn2 uniform, one end side (left side in this example) of the developing roller 40 corresponding to the wider one of the two measured developing nip widths Dn1 and Dn2 is separated from the photosensitive drum 11. It is only necessary to adjust the position of the developer roller 40, or move the other end side (right side in this example) of the developing roller 40 closer to the photosensitive drum 11, or move one end side away and bring the other end side closer. In FIG. 7B, the developing roller 40 after the position adjustment is drawn by a solid line, and the position of the developing roller 40 before the position adjustment is shown by a one-dot chain line.

  In the example of FIG. 8A, the developing nip region 93c between the two belt-like toner adhesion patterns 91c and 92c is seen from the left side in the drawing even though the developing roller 40 is not inclined with respect to the photosensitive drum 11. It gets thicker as you go to the right. That is, the value of the right development nip width Dn4 is larger than the value of the left development nip width Dn3. In this case, a situation is considered in which the height of the magnetic brush 90c (the radial dimension of the developing roller 40) is not uniform. This situation occurs due to variations in blades provided in the developing device 14 and mounting errors in order to regulate the height of the magnetic brush 90c.

  Also in the case of FIG. 8A, the development nip widths Dn3 and Dn4 can be made uniform by adjusting the position of the developing roller 40. One end side (right side in this example) of the developing roller 40 corresponding to the wider one of the measured two development nip widths Dn3 and Dn4 is moved away from the photosensitive drum 11 or the other end side of the developing roller 40 (this example). The left side) may be moved closer to the photosensitive drum 11 or one end side may be moved away and the other end side moved closer. In FIG. 8B, the developing roller 40 after the position adjustment is drawn by a solid line, and the position of the developing roller 40 before the position adjustment is shown by a one-dot chain line.

  FIG. 9 shows the configuration of the positioning mechanism 48. The positioning mechanism 48 includes an urging member 482 and an adjustment screw 484 that are supported by the support of the developing device 14. The urging member 482 urges the rotating shaft 401 of the developing roller 40 to move away from the photosensitive drum 11. The adjustment screw 484 is disposed so as to be movable along the urging direction of the urging member 482. When a driving source (not shown) advances the adjustment screw 484 whose tip is in contact with the rotating shaft 401, the developing roller 40 approaches the photosensitive drum 11 by overcoming the urging force of the urging member 482. When the adjustment screw 484 moves backward, the developing roller 40 is moved away from the photosensitive drum 112 by the biasing force of the biasing member 482.

  As shown in the graph of FIG. 10, the development nip width depends on the amount of developer carried by the developing roller 40 (the amount of developer conveyed to the developing roller 40 in the developing device). When the developer amount is small, the development nip region is relatively narrow and the development nip width is small. When the amount of developer is large, the development nip region is relatively wide and the development nip width is large. The developer amount is related to a change in the bulk density depending on the mixing ratio of the carrier and the toner, a change in the charge amount of the developer due to the environment, the deterioration of the developer, the deterioration of the developing roller, and the like.

  Although the development nip width depends on the developer amount, it is possible to adjust the development gap based on the detection information of the toner adhesion pattern so that the development nip width becomes uniform along the longitudinal direction. For example, it is assumed that the rotational peripheral speed of the photosensitive drum 11 is 50 mm / sec, and the time Td, which is a cutoff level period at the output to one of the two density measuring devices 43, is 0.11 sec. In this case, the development nip width is calculated to be 5.5 mm. If the amount of developer is small, the graph shows that the development gap is about 0.35 mm. When the time Td based on the output of the remaining one of the density measuring devices 43 is different from 0.11 sec, the developing nip width is not uniform in the longitudinal direction, so the times Td based on the outputs of the two density measuring devices 43 are the same. Thus, the image forming apparatus 1 adjusts the development gap. After the adjustment, the operation of measuring and adjusting the time Td again can be repeated to adjust more precisely.

  The timing of developing gap adjustment is arbitrary except during image formation. For example, the development gap can be adjusted as an adjustment before shipment at a factory that manufactures the image forming apparatus 1 or as a timely maintenance adjustment after shipment. An operation switch that causes the control unit 100 to execute drive control for adjustment may be provided by hardware or software.

  According to the above embodiment, the width of the development nip region is measured at two locations to adjust the development gap, so that the rotation shaft of the developing roller 40 is inclined with respect to the rotation shaft of the photosensitive drum 11, or the magnetic brush Even if there is an inclination distribution whose height changes monotonically at 90 and 90c, an image with reduced density unevenness in the direction of the rotation axis can be formed.

  The image forming apparatus 1 of the above-described embodiment has a function of automatically adjusting the development gap, but is not limited thereto. A configuration in which the adjustment screw 484 of the positioning mechanism 48 is manually moved can be employed. In that case, the measurement result of the time Td based on the output of the concentration measuring device 43 or information indicating the adjustment amount corresponding to the measurement result is displayed on the display of the operation panel or output in the form of a data signal to an external display device. Then, the manual adjustment operator can reflect the measurement result in the work.

  Further, it is not always necessary for the image forming apparatus 1 to measure the development nip width. After the toner adhesion patterns 91, 92, 91b, 92b, 91c, and 92c are formed, the toner adhesion patterns 91, 92, 91b, 92b, 91c, and 92c are transferred to the recording paper P and discharged in the same manner as normal image formation. The operation may be set so as to. If the operator or measuring device measures the dimension between the two toner adhesion patterns fixed on the discharged recording paper P, the developing nip width can be determined.

  As another modification of the above-described embodiment, the positioning mechanism 48 is disposed only on one side of the developing roller 40, and the end of one side of the developing roller 40 is moved forward or backward to equalize the developing gap Dg in the longitudinal direction. May be performed.

  As an image carrier for carrying a latent image to be developed, a structure such as a photoreceptor roller other than the photoreceptor drum or a photoreceptor belt, which is opposed to the developing roller 40 in a macroscopic line contact manner, can be used.

  The image forming apparatus 1 is not limited to a color printer, and may be any apparatus that forms an image by an electrophotographic process, such as a monochrome printer, a copying machine, or a multifunction machine.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photosensitive drum (image carrier)
40 Developing roller 90, 90c Magnetic brush (developer)
91, 92, 91b, 92b, 91c, 92c Toner adhesion pattern 93, 93b, 93c Development nip area (band-like area)
Dn, Dn1, Dn2, Dn3, Dn4 Development nip width Dg Development gap (gap between development roller and image carrier)
48 Positioning mechanism 43 Concentration measuring device (sensor)

Claims (6)

A method for adjusting a developing roller position in an image forming apparatus including a developing roller for bringing a developer including toner and a carrier into contact with an image carrier,
The developing roller is rotated in a state in which the relative movement of the image carrier with respect to the developing roller is stopped, and thereby, two belts are formed along each other across a belt-like region extending in the direction of the rotation axis of the developing roller on the image carrier. Forming two toner adhesion patterns,
Measure the width of the band-like region sandwiched between the toner adhesion patterns,
A developing roller position adjusting method, wherein a gap dimension between the developing roller and the image carrier is adjusted according to the measurement result of the width. Measure the width of both ends in the direction of the rotation axis in the band-shaped region,
The one end side of the developing roller corresponding to the wider one of the two measured widths is moved away from the image carrier, the other end side of the developing roller is brought closer to the image carrier, or the one end side is moved The developing roller position adjusting method according to claim 1, wherein the developing roller position is moved away from the image carrier and the other end side is brought closer to the image carrier. An image forming apparatus for forming an image on a recording medium using a developer containing toner and a carrier,
An image carrier that carries a toner image; and a developing roller that brings the developer into contact with the image carrier;
By rotating the developing roller in a state where the relative movement of the image carrier with respect to the developing roller is stopped, two belts that extend along the rotation axis of the developing roller are separated from each other with a belt-like region extending on the developing roller. An image forming apparatus that forms two toner adhesion patterns. A mechanism for positioning the developing roller so that the position can be adjusted;
A sensor for detecting the density of the toner image on the image carrier,
Moving the image carrier on which the toner adhesion pattern is formed relative to the sensor;
The image forming apparatus according to claim 3, wherein a gap dimension between the developing roller and the image carrier is automatically adjusted by the mechanism according to a difference in detection timing of the two toner adhesion patterns by the sensor. A sensor for detecting the density of the toner image on the image carrier;
Moving the image carrier on which the two toner adhesion patterns are formed relative to the sensor;
The image forming apparatus according to claim 3, wherein measurement information indicating a difference between detection times of the two toner adhesion patterns by the sensor is output. The image forming apparatus according to claim 3, wherein the two toner adhesion patterns are transferred to a recording sheet and discharged.

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