JP2012155075A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the accurate detection of density unevenness in images without increasing extra detection means.SOLUTION: An image forming apparatus comprises: a photoreceptor 22; light exposing means 20 for forming a latent image on the photoreceptor by irradiating the photoreceptor; charging means 23 for charging the photoreceptor by applying a charging bias to the photoreceptor; developing means 24 for forming a toner image on the photoreceptor by supplying toner to the latent image; and transfer means 26 for transferring the toner image. The image forming apparatus is characterized in having detection means for detecting changes of information of a current flowing the transfer means, and when detecting by the detection means, increasing the value of the charging bias compared to when forming an image.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a FAX, and more particularly to an image forming apparatus having an exposure unit.

  As a general problem of an image forming apparatus, image density unevenness in the rotation direction of an image carrier (for example, a photoreceptor) may occur. In an image forming apparatus that forms a color image, there is a problem that the balance of the toners of the respective colors is lost and a desired color cannot be reproduced. Causes include a decrease in sensitivity of the photoreceptor, a nonuniform charging potential in the width direction, and a decrease in exposure amount.

  When the above problem becomes apparent by using the image forming apparatus for a long time, the image forming process conditions such as the charging potential, the exposure amount, and the developing bias are changed so that the initial image quality can be maintained. However, if it exceeds a certain value, it can no longer be dealt with by improving the process conditions alone, and maintenance such as replacement of the photosensitive member is required.

  Most of the causes of the decrease in exposure amount are floating dust and toner in the machine, dust-proof glass (dust-proof glass) of the optical box, a reflective mirror that guides light to the photoconductor, and a rotating polygon mirror for scanning the polarization. It is attached to the surface of an imaging lens or the like that collects light. In addition, a reduction in the amount of light due to contamination of an optical system such as glass, a reflection mirror, a rotating polygon mirror, and an imaging lens has a greater effect on image quality than a reduction in photoreceptor sensitivity or uneven charging potential.

  Therefore, it is necessary to detect such contamination of the optical system.

  Conventionally, a method for detecting the surface potential of the photoconductor and a detection unit for detecting the usage amount of the photoconductor, and replacing the photoconductor or cleaning the optical system based on the detection result has been proposed. (For example, refer to Patent Document 1).

  Further, Patent Document 2 proposes a method of specifying a location where image density unevenness is generated. Current detection means for detecting current accompanying toner adhesion (movement) to the photosensitive member during development and current detection means for detecting current accompanying toner transfer (movement) from the photosensitive member during transfer are used. Further, current detection means is used to detect a current flowing through the conductive substrate of the photosensitive member upon light irradiation to the photosensitive member at the time of forming a latent image (see, for example, Patent Document 2).

JP-A-8-305226 JP-A-6-130767

  However, the image forming apparatus described in Patent Document 1 has the following problems.

  Providing a detection means for detecting the surface potential of the photoconductor around the photoconductor requires a space for arranging the detection means in the apparatus. Further, if a new detection means is provided, the cost increases.

  Further, the image forming apparatus described in Patent Document 2 has the following problems.

  When providing a current detection means for detecting the current flowing through the conductive substrate of the photosensitive member upon light irradiation to the photosensitive member at the time of forming the latent image, a detection means is newly provided as in Patent Document 1, and space is required. And there are cost issues.

  In addition, since the current generated by toner movement during toner development and transfer and the current flowing through the photosensitive member due to light irradiation during exposure are very weak and difficult to detect, image density unevenness cannot be detected accurately.

  In view of the above problems, an object of the present invention is to make it possible to detect image density unevenness with high accuracy without newly providing detection means.

A typical configuration of the present invention for achieving the above object is as follows.
A photoconductor, an exposure unit that irradiates the photoconductor with light to form a latent image on the photoconductor, a charging unit that applies a charging bias to the photoconductor to charge the photoconductor, and the latent image An image forming apparatus comprising: a developing unit that supplies toner and forms a toner image on the photoreceptor; and a transfer unit that transfers the toner image.
Having detection means for detecting a change in current information flowing in the transfer means;
When detecting by the detecting means, the charging bias value is set larger than that during image formation.

  With the above configuration, it is possible to detect image density unevenness with high accuracy without newly providing a detection unit.

Explanatory drawing of the scanner unit light quantity detection which shows 1st Embodiment. 1 is a configuration diagram of an image forming apparatus showing a first embodiment. FIG. The block diagram of the high voltage bias apparatus which shows 1st Embodiment. 1 is a configuration diagram of a scanner unit showing a first embodiment. FIG. FIG. 3 is a diagram for explaining the surface potential of the photoconductor showing the first embodiment. Explanatory drawing of the result of the light quantity detection which shows 1st Embodiment. The flowchart which shows 1st Embodiment. FIG. 6 is a configuration diagram of an image forming apparatus showing a second embodiment. The block diagram of the scanner unit which shows 2nd Embodiment. Explanatory drawing of the result of the light quantity detection which shows 2nd Embodiment. Explanatory drawing of the latent image pattern which shows 2nd Embodiment. The figure explaining the stain | pollution | contamination of the rotary polygon mirror which shows 2nd Embodiment. Explanatory drawing of the result of the light quantity detection which shows 2nd Embodiment.

[First Embodiment]
A first embodiment of the present invention will be described. In the description, the configuration of the image forming apparatus, the configuration of the high voltage bias device applied to the image forming apparatus, and the configuration of the exposure unit will be described in order. Thereafter, a method for detecting the light amount of the exposure means (scanner unit) will be described. In this embodiment, latent image formation using a scanner unit will be described, but the present invention is not limited to this. For example, an image forming apparatus that forms a latent image using an LED may be used.

(Image forming device)
FIG. 2 is a configuration diagram of the image forming apparatus showing the first embodiment. As shown in FIG. 2, the image forming apparatus 10 to which this embodiment is applied is a four-drum color image forming apparatus. In the description, reference numerals a to d of members corresponding to the respective colors of yellow Y, magenta M, cyan C, and black Bk are appropriately omitted.

  As shown in FIG. 2, the image forming apparatus 10 includes a plurality of photoconductors 22 (22a to 22d) as drum-shaped image carriers. Around the photosensitive member 22, there are process means such as a charging roller 23 (23a to 23d) as a charging means and a scanner unit 20 (20a to 20d) as an exposure means. In addition to the process means, a developing unit 25 (25a to 25d) having a developing sleeve 24 (24a to 24d) as a developing means, a primary transfer roller 26 (26a to 26d) and the like as transfer means.

  The recording medium 12 fed out by the pickup roller 13 is transported to a position where the leading end slightly passes through the transporting roller 14 and the transporting roller 15 after the leading end position is detected by the registration sensor 11. The recording medium 12 stops once at that position.

  On the other hand, the scanner unit 20 disposed below the photoconductor 22 sequentially irradiates the rotationally driven photoconductor 22 with the laser light 21. At this time, the photosensitive member 22 is uniformly charged by the charging roller 23 in advance. For this reason, an electrostatic latent image is formed on the photosensitive member 22 by the irradiation of the laser beam 21.

  The developing device 25 and the developing sleeve 24 supply toner to the electrostatic latent image on the photoreceptor 22 to form a toner image. The developing sleeve 24 arranged in the developing unit 25 is provided with a mechanism for contacting and separating the developing sleeve 24 (not shown) in order to suppress the consumption of the developing sleeve 24. The primary transfer roller 26 primarily transfers the toner image on the photoreceptor 22 to the intermediate transfer belt 30.

  The intermediate transfer belt 30 is driven around by the stretching roller 31, the stretching roller 32, and the stretching roller 33, and conveys the toner image to the position of the secondary transfer roller 27. At this time, the conveyance of the recording medium 12 is resumed so that the timing coincides with the toner image conveyed at the position of the secondary transfer roller 27, and the toner image is transferred from the intermediate transfer belt 30 by the secondary transfer roller 27.

  Thereafter, the toner image on the recording medium 12 is heated and fixed by the fixing roller 16 and the fixing roller 17, and then the recording medium 12 is output to the outside of the apparatus. Here, the toner that has not been transferred from the intermediate transfer belt 30 to the recording medium 12 by the secondary transfer roller 27 is collected in the waste toner container 36 by the cleaning blade 35.

(High voltage bias device)
Next, the configuration of the high-voltage bias device in the image forming apparatus will be described with reference to FIG. FIG. 3 is a configuration diagram of the high-voltage bias device showing the first embodiment.

  As shown in FIG. 3, the high-voltage bias device includes a charging bias device 43, a developing bias device 44 (44a to 44d), a primary transfer bias device 46 (46a to 46d), and a secondary transfer bias device 48.

  The charging bias device 43 forms a background potential on the surface of the photoconductor 22 by applying a voltage to the charging roller 23 and makes it possible to form an electrostatic latent image by irradiation with laser light.

  The developing bias device 44 applies a voltage to the developing sleeve 24 to place toner on the electrostatic latent image on the photoreceptor 22a to form a toner image.

  The primary transfer bias device 46 primarily transfers the toner image on the photosensitive member 22 to the intermediate transfer belt 30 by applying a voltage to the primary transfer roller 26 a.

  The secondary transfer bias device 48 secondarily transfers the toner image on the intermediate transfer belt 30 to the recording medium 12 by applying a voltage to the secondary transfer roller 27.

  Further, the primary transfer bias device 46 includes a current detection circuit 47 (47a to 47d) as a light amount detection unit. This is because the transfer performance of the toner image on the primary transfer roller 26 changes according to the amount of current flowing through the primary transfer roller 26 and is detected. The bias voltage applied to the primary transfer roller 26 is adjusted according to the detection result of the current detection circuit 47, and the transfer performance is kept constant even when the temperature and humidity in the apparatus change. The detection result of the current detection circuit 47 is transmitted to the CPU 40 (control unit) that determines the drive and potential of each process means.

(Scanner unit configuration)
Next, the configuration of the exposure means (scanner unit 20) in the image forming apparatus will be described with reference to FIG. FIG. 4 is a configuration diagram of the scanner unit according to the first embodiment. Since all the scanner units 20a to 20d have the same configuration, the suffixes a to d are removed, and the scanner unit 20 will be described. Further, FIG. 4 will be described in a state in which the cover 57 that is roughly sealed is removed.

  The scanner unit 20 includes a laser light source device 51, a cylindrical lens 52, a rotary polygon mirror 53, an imaging lens 54, and a reflection mirror 55 inside the optical box 50, and is roughly sealed by a cover 57.

  The optical box 50 accommodates various optical members. The laser light source device 51 is a light source. The cylindrical lens 52 condenses the laser light in a linear shape. The rotary polygon mirror 53 has a deflecting reflection surface in the vicinity of a line image of a light beam formed by being condensed by the cylindrical lens 52. The scanner motor 53M is means for rotating the rotary polygon mirror 53. Further, the light beam formed by the imaging lens 54 is reflected by the reflection mirror 55, and the light beam passes through the plate-like glass 56.

  The imaging lens 54 is designed so that the light beam reflected by the rotary polygon mirror 53 is condensed so as to form a spot on the photosensitive member 22, and the scanning speed of the spot is kept constant. By the rotation of the rotary polygon mirror 53, the main scanning (in the direction of the arrow) is performed on the photosensitive member 22 by the light beam. Further, the photoconductor 22 is driven to rotate about the axis of the cylinder, thereby performing sub-scanning. In this way, an electrostatic latent image is formed on the surface of the photoreceptor.

  In this configuration, the light beam deflected and reflected by the rotary polygon mirror 53 irradiates the photoconductor 22 through the imaging lens 54, the reflection mirror 55, and the plate-like glass 56.

(Scanner unit light intensity detection method)
The light amount detection of the scanner unit 20 of the present embodiment using the photosensitive member 22 in the image forming apparatus will be described with reference to FIG. FIG. 1 is an explanatory diagram of scanner unit light quantity detection according to the first embodiment.

  In the present embodiment, the potential setting of the charging roller 23 is different from that during image formation. As a result, the potential of the photosensitive member 22 is set differently from that during image formation. The potential setting will be described later.

  Further, the developing sleeve 24 is separated from the photoconductor 22. The scanner unit 20 irradiates the photosensitive member 22 with laser light to form an electrostatic latent image 70. The electrostatic latent image 70 is drawn as wide as possible in the scanning direction and has a width of about 1 mm in the rotation direction of the photosensitive member 22. This width is desirably set to be equal to or larger than the nip width of the primary transfer roller 26. At this time, the electrostatic latent image 70 is conveyed to the position of the primary transfer roller 26 without placing toner.

  FIG. 5 is a diagram for explaining the surface potential of the photoconductor according to the first embodiment. FIG. 5 shows the dark potential VD and the light potential VL on the surface of the photosensitive member 22 when detecting the light amount of the scanner unit 20. The horizontal axis indicates the surface position of the photosensitive member 22 in the rotational direction, and shows the portion where the area 93 is exposed to the scanner unit to form the electrostatic latent image 70 and the surface potential becomes the bright potential VL. The vertical axis represents the potential, and the dark potential of the photoconductor 22 is described as VD, the bright potential is VL, and the transfer bias potential is VT. The dark potential VD is the potential of the portion of the surface of the photoconductor 22 that is not irradiated with laser light, and the bright potential VL is the potential of the portion of the surface of the photoconductor 22 that is irradiated with laser light. .

  In the region 93 of the electrostatic latent image 70 in FIG. 5, the potential difference 96 between the primary transfer roller 26 and the photosensitive member 22 is set to be smaller than the potential difference 95 in other regions. For this reason, when the electrostatic latent image 70 reaches the primary transfer roller 26, the current value flowing through the primary transfer roller 26 decreases.

  At the time of light amount detection of the scanner unit 20 of the present embodiment, the dark potential VD is set higher than that at the time of image formation, and the dark potential VD = 1000 V, the bright potential VL = 50 V, and the transfer bias potential VT = 30 V are below VL. In addition, it is set near the bright potential VL. Since the dark potential VD is determined by the voltage value of the charging bias applied to the charging roller 23 by the charging bias device 43, the value of the charging bias is also set so that the dark potential VD is larger than that at the time of image formation at the time of detection. It is set larger than the hour.

  Here, if the setting of the dark potential VD at the time of image formation is too high, there is a high possibility that toner is scattered due to discharge between the photosensitive member 22 and the intermediate transfer belt 30 during transfer. The dark potential VD is set to a predetermined potential. For this reason, at the time of detection, the dark potential VD is set higher than that at the time of image formation so that the difference between the potential difference 95 and the potential difference 96 is widened, thereby increasing the influence of the light quantity of the scanner unit and reducing exposure. Sensitivity can be increased.

  It is desirable to raise the dark potential VD to such an extent that the photoconductor 22 does not deteriorate. It is desirable to lower the bright potential VL as close to 0V as possible, and the bright potential VL may be lowered by increasing the amount of light of the scanner unit 20 at the time of detection than at the time of image formation.

  As a result, dirt such as dust, dust, and toner adheres to optical components such as the dust-proof glass 56 disposed in the scanner unit 20 to block the laser beam, and a portion that is not exposed with a sufficient amount of light. It occurs in the electrostatic latent image 70. That is, so-called unevenness or missing occurs in the electrostatic latent image 70, and these cause uneven image density. As described above, when the electrostatic latent image 70 is not exposed with a sufficient amount of light, the bright potential VL is increased, so that a current easily flows to the primary transfer roller 26.

  FIG. 6 is an explanatory diagram of the result of light amount detection according to the first embodiment. In FIG. 6, a change amount ΔI of the current value flowing through the primary transfer roller 26 (difference between the current value of the potential difference 95 and the current value of the potential difference 96) and the latent image are formed without being exposed. The comparison is made with the area of the non-exposed part (area of unexposed light). The current value corresponding to the difference 94 (see FIG. 5) between the potential difference 95 and the potential difference 96 is ΔI.

  The vertical axis indicates the change amount ΔI of the current value flowing through the primary transfer roller 26, and the current change amount 91 indicates the value of the electrostatic latent image 70 in the potential setting at the time of image formation. The current change amount 97 indicates the value of the electrostatic latent image 70 in the potential setting of the present embodiment. This indicates that even with the same laser light, the value of the current flowing through the primary transfer roller 26 varies depending on the potential setting.

  The horizontal axis represents the area of the exposed portion of the electrostatic latent image, which is obtained from the width of the exposed portion of the electrostatic latent image 70 with respect to the width in the scanning direction (the axial direction of the photosensitive member 22).

  The approximate line 92 indicates the amount of change in the current value in the potential setting during image formation, and the approximate line 98 indicates the amount of change in the current value in the potential setting of the present embodiment. From this result, it can be seen that the amount of change in the current value with respect to the width where the latent image is not formed is larger in the potential setting of this embodiment than in the potential setting during image formation. For this reason, it becomes easy to detect whether or not the laser beam is blocked.

  The current value of the potential difference 96 can be obtained by detecting the average value of the current flowing through the primary transfer roller 26 in a predetermined width within the region 93 in FIG. The current value of the potential difference 95 can be obtained by calculation from the dark potential VD and the transfer bias potential VT. The average value of the current flowing through the primary transfer roller 26 in the portion where the electrostatic latent image 70 is not formed is obtained. You may obtain | require by detecting.

  Further, by detecting the developing sleeve 24 away from the photosensitive member 22, the toner held on the developing sleeve 24 comes into contact with the electrostatic latent image 70 of the photosensitive member 22, so that the charge is released and the light potential VL is reduced. It is possible to avoid changing. Further, since the toner adheres to the photosensitive member 22, it is possible to suppress the consumption of the toner other than the image formation, and it is possible to suppress the time when the toner is replenished.

  In this embodiment, an example in which the developing sleeve 24 is separated is shown, but the present invention is not limited to this. For example, even when the developing sleeve 24 is in contact, the same effect as described above can be obtained by setting the bias of the developing sleeve so that the toner does not move from the developing sleeve 24 to the photosensitive member 22.

  Control for detecting the amount of light of the scanner unit of the present embodiment described above will be described with reference to the flowchart of FIG. FIG. 7 is a flowchart showing the first embodiment.

  First, the detection of the light quantity of the scanner unit is executed, for example, together with the processing before printing (S61). Then, the charging roller 23 switches to potential setting for detecting the amount of light of the scanner unit (S62). At this time, the light quantity for detecting the light quantity of the scanner unit may be switched (S62).

  Further, the developing sleeve 24 is separated to prevent the toner from acting on the photosensitive member 22 (S63). Alternatively, it may be confirmed that the developing sleeve 24 is separated. The procedures of S62 and S63 may be performed in parallel, or S62 and S63 may be interchanged.

  Then, the electrostatic latent image 70 is formed by the scanner unit (S64). Thereafter, the electrostatic latent image 70 reaches the primary transfer roller 26 as the photoconductor 22 rotates. At this time, the change amount ΔI of the current value is measured (S65).

  Then, the measured change amount ΔI of the current value is compared with a predetermined threshold value (S66). Here, when an optical component such as the glass 56 of the scanner unit 20 is soiled and the laser beam is blocked and an exposure failure or the like occurs in the electrostatic latent image 70, the bright potential VL increases. For this reason, the amount of change ΔI in the current value becomes small when an exposure failure or the like occurs. For this reason, when the change amount ΔI of the current value is larger than the predetermined threshold value, it is determined as normal and the process proceeds to the printing operation (image forming operation) (S67). If the change amount ΔI of the current value is equal to or less than a predetermined threshold, it is determined that the current value is not normal. In this case, when the image forming apparatus is equipped with a mechanism for cleaning the plate-like glass 56, the cleaning is executed or the user himself / herself is prompted to clean (S68) to return to the normal state.

  As described above, at the time of detection, the developing sleeve 24 is separated from the photosensitive member 22 so that the toner is not attached to the photosensitive member 22 as much as possible, so that toner consumption can be suppressed. Further, by preventing the toner from adhering to the photosensitive member 22 as much as possible, it is possible to prevent the electric charge from escaping when the toner comes into contact with the electrostatic latent image 70, and to detect the change in the current flowing through the primary transfer roller 26 with high accuracy. Density unevenness can be detected with high accuracy.

  In addition, the current generated by toner movement during toner development and transfer, or the current flowing through the photoconductor due to light irradiation during exposure is very weak and difficult to detect, and no toner is attached to the photoconductor 22. In this state, the current flowing through the primary transfer roller 26 is easy to detect. Therefore, the latter method can detect a change in the current value flowing through the primary transfer roller 26 more easily and accurately than the former method, and can detect image density unevenness with high accuracy.

  Further, by increasing the value of the charging bias and raising the dark potential VD higher than that during image formation, the potential difference between the exposed portion and the unexposed portion on the surface of the photosensitive member 22 is increased. As a result, the current flowing through the primary transfer roller 26 can be detected with high accuracy, and image density unevenness can be detected with high accuracy.

  In this embodiment, detection is performed using the change amount ΔI of the current value flowing through the primary transfer roller, but detection is performed using other values corresponding to the change amount ΔI of the current value flowing through the primary transfer roller. Also good.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In general, when the scanner unit is used for a long time in an environment where the atmosphere is polluted, not only the glass 56 outside the scanner unit 80 but also the internal components of the scanner unit 80 such as a rotating polygon mirror are stained. appear. For this reason, even if the glass 56 is cleaned, the image forming apparatus may not return to a normal state.

  Therefore, in the second embodiment of the present invention, an image density unevenness is detected in the same manner as in the first embodiment, and an unclean portion of the scanner unit 80 is specified by using the detection result. The purpose is to enable 80 maintenance.

  A second embodiment of the present invention will be described with reference to FIG. FIG. 8 is a configuration diagram of an image forming apparatus showing the second embodiment. In the description, the same components as those described above are denoted by the same reference numerals and description thereof is omitted.

  The difference from the first embodiment is that, as shown in FIG. 8, the scanner unit 80 irradiates each corresponding photosensitive member with a laser beam by an image signal separated into four colors from one rotary polygon mirror. . In the second embodiment, the scanner unit 80 is used to form a full color image.

  Next, the scanner unit 80 will be described in detail with reference to FIG. FIG. 9 is a configuration diagram of a scanner unit showing the second embodiment. FIG. 9 shows a state in which a cover 82 and a substrate (not shown) for driving the laser light source device are removed for explanation.

  The cover 82 (FIG. 8) substantially seals the inside of the scanner unit 80, and the four glasses 56 (FIG. 8) which are plate-like transmission members for allowing the light beams 21a to 21d to expose the photosensitive members 22a to 22d pass. 8) is provided on the outer surface of the scanner unit 80. The scanner unit 80 includes two laser light source devices 81 (81a to 81d) arranged in two rows on the left and right (in the arrangement direction of the photoconductors 22) and further in two rows on the upper and lower sides (in the axial direction of the rotary polygon mirror 83). Dimensionally arrange.

  The laser light source device 81 has substantially the same configuration as the previous embodiment. Laser light emitted from a plurality of laser light source devices 81 having semiconductor lasers is condensed on a rotating polygonal mirror 83 by a cylindrical lens 90 in which four lens portions corresponding to each laser light source device 81 are integrally formed.

  The scanner unit 80 has lenses 84, 85, and 86 (84L, 84R, 85L, 85R, 86L, and 86R) and mirrors 87, 88, and 89 (87L, 87R, and 88L) that are substantially symmetrical about the rotating polygon mirror 83. , 88R, 89L, 89R).

  First, the laser beam is deflected and scanned by a rotating polygonal mirror 83 as deflection scanning means that rotates at high speed in the CW direction (clockwise). Then, the laser beams emitted from the two laser light source devices 81 arranged on the left side in the drawing are scanned on the photosensitive member 22 in the scanning direction S1 indicated by the arrow.

  On the other hand, the laser beams emitted from the two laser light source devices arranged on the right side are scanned on the photosensitive member 22 in the scanning direction S2 indicated by the arrow. For this reason, an image is formed in the opposite direction on the photosensitive member by the two emitted laser beams.

  Next, a description will be given of a determination when ΔI does not exceed a predetermined threshold q when the same image density unevenness detection as that in the first embodiment is performed on each of the photoconductors 22a to 22d. FIG. 10 is an explanatory diagram of the result of light amount detection showing the second embodiment. In FIG. 10, the amount of change (ΔI) in the current value obtained from each primary transfer roller corresponding to each of the photoreceptors 22a to 22d is shown on the vertical axis as Pa, Pb, Pc, and Pd.

  When all four colors (Pa to Pd) do not satisfy the threshold value q in the same manner as shown in FIG. 10A, the decrease in the exposure amount is caused by the contamination of optical components inside the scanner unit 80 rather than outside. It can be determined that there is a high probability that it has occurred. Specifically, it can be determined that there is a high possibility that the rotating polygonal mirror 83 or the cylindrical lens 90 used in common for the four colors is dirty. In this case, it may be necessary to replace the scanner unit.

  As shown in FIG. 10B, when only one color (Pa) does not satisfy the threshold value q, it is highly possible that the decrease in exposure amount is caused by contamination of optical components used in a single color. I can judge. In this case, it can be determined that there is a high possibility that dust or the like has suddenly adhered to the outside glass 56 from the outside rather than inside the scanner unit 80, and the plate-like glass 56 as shown in the first embodiment is cleaned. It is considered that there is a high possibility of returning at.

  As shown in FIG. 10C, only two colors (Pc, Pd) do not satisfy the threshold value q in the same manner, and two colors (Pc, Pd) that do not satisfy the threshold value q are on the photoconductor. In some cases, the scanning directions (S1, S2) are common. In this case, it can be determined that there is a high possibility that the decrease in the exposure amount is caused by the contamination of the internal optical components, rather than the outside of the scanner unit 80, and there is a possibility that the exposure will be restored even if the glass 56 is cleaned. Can be judged low. In this case, it is considered that the scanner unit 80 needs to be replaced.

  As described above, in the present embodiment, by comparing the current value ΔI for each photoconductor 22, whether the common optical components in the plurality of colors in the scanner unit 80 are contaminated corresponds to each photoconductor 22. It is determined whether the optical component such as the glass 56 provided is dirty.

  That is, in an image forming apparatus in which a plurality of photosensitive members 22 are exposed with common optical components in the scanner unit 80, in the following cases, it is determined that the common optical components are dirty, and the scanner unit is replaced. Prompt display etc. That is, if the change amount ΔI of the current value of the primary transfer roller 26 corresponding to the plurality of photosensitive members 22 exposed by the common optical component does not satisfy the threshold value q, the common optical component is dirty. to decide.

  On the other hand, when the amount of change ΔI in the current value of only the primary transfer roller 26 corresponding to one of the plurality of photosensitive members 22 exposed by the common optical component does not satisfy the threshold value q, The glass 56, which is not an optical component, is cleaned or a display prompting cleaning is displayed. By doing in this way, the maintenance of the scanner unit 80 can be performed appropriately.

  In general, when the scanner unit is used for a long time in an environment where the air is polluted, the rotary polygon mirror 83 becomes dirty and the scanner unit needs to be replaced. In this case, in order to determine the contamination of the rotating polygonal mirror 83, it is necessary to further separate it from the cylindrical lens 90 by the following method.

  FIG. 11 shows an example of a pattern of latent images formed on the photoconductors 22a to 22d. FIG. 11 is an explanatory diagram of a latent image pattern showing the second embodiment.

  As shown in FIG. 11, the electrostatic latent images αa and βa of the photosensitive member 22a are obtained by dividing the electrostatic latent image 70 drawn as wide as possible in the scanning direction into two equal parts in the scanning direction and shifted in the rotational direction. It is. A latent image is formed with the same pattern on all of the photoconductors 22a to 22d.

  Thereafter, the amount of change in the current value is measured from each primary transfer roller by the same means as in the first embodiment. Here, the contamination of the rotary polygon mirror 83 will be described with reference to FIG. FIG. 12 is a view for explaining dirt on the rotary polygon mirror showing the second embodiment.

  As shown in FIG. 12, the reflecting surface 100 of the rotary polygon mirror 83 is gradually soiled from the end. This is because such a stain is caused by the influence of the wind pressure generated at the corners of the rotary polygonal mirror 83. In this way, the dirt is contaminated from the end, so that the amount of light gradually decreases from the writing side in the scanning direction.

  An example in which the amount of change in each current value obtained in FIG. 11 is compared with α / β will be described with reference to FIG. FIG. 13 is an explanatory diagram of the result of light amount detection showing the second embodiment. In FIG. 13, the horizontal axis shows comparisons αa / βa, αb / βb, αc / βc, and αd / βd of the amount of change (ΔI) in the current value obtained from each primary transfer roller. If there is no problem with the electrostatic latent image, α / β is located near 1, and the standard 101 is determined to be normal.

  FIG. 13A shows the amount of change in the current value when contamination of the rotary polygon mirror 83 is affected. In the scanning direction S1, the amount of change in current value is smaller in β than in α, and in the scanning direction S2, the amount of change in current value is smaller in β than in β. Therefore, the values of α / β are different between the scanning directions S1 and S2, and it can be determined that the influence of the rotating polygonal mirror 83 is present.

  FIG. 13B shows the amount of change in the current value when the contamination of the cylindrical lens 90 is affected. The cylindrical lens 90 is disposed closer to the laser light source device than the rotary polygon mirror 83. For this reason, when the amount of light decreases due to the cylindrical lens 90, the entire width in the scanning direction decreases uniformly. For this reason, α / β is positioned in the vicinity of 1.

  In the present embodiment, the electrostatic latent image 70 is divided into two equal parts in the scanning direction, but the number of divisions is not limited thereto.

  As described above, in addition to the contents described in the first embodiment, a dirty portion in the scanner unit 80 can be specified by comparing detection results obtained from the respective colors. For this reason, the maintenance of the scanner unit 80 can be performed appropriately.

[Other Embodiments]
In the above-described image forming apparatus, the primary transfer roller 26 is used as the transfer unit and the intermediate transfer belt 30 is provided. However, the present invention is not limited to this. For example, a transfer roller that directly transfers a toner image to a conveyance belt that conveys a recording medium may be used as a transfer unit that is a source of current information for light amount detection.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 20 ... Scanner unit 21 ... Laser beam 22 ... Photoconductor 23 ... Charge roller 24 ... Development sleeve 26 ... Primary transfer roller 30 ... Intermediate transfer belt 40 ... CPU
46 ... primary transfer bias 47 ... current detection circuit 53 ... rotating polygon mirror 70 ... electrostatic latent image 80 ... scanner unit 81 ... laser light source device 83 ... rotating polygon mirror 91 ... current variation 95 ... potential difference 96 ... potential difference

Claims (6)

A photoconductor, an exposure unit that irradiates the photoconductor with light to form a latent image on the photoconductor, a charging unit that applies a charging bias to the photoconductor to charge the photoconductor, and the latent image An image forming apparatus comprising: a developing unit that supplies toner and forms a toner image on the photoreceptor; and a transfer unit that transfers the toner image.
Having detection means for detecting a change in current information flowing in the transfer means;
An image forming apparatus characterized in that when the detection means performs detection, the value of the charging bias is made larger than that during image formation. A photosensitive member; an exposure unit that irradiates light to the photosensitive member to form a latent image; a charging unit that charges the photosensitive member; and a toner image that is supplied to the latent image by supplying toner to the latent image. In an image forming apparatus comprising: a developing unit that forms a toner image; and a transfer unit that transfers the toner image.
Having detection means for detecting a change in current information flowing in the transfer means;
An image forming apparatus characterized in that, when detecting by the detecting means, a latent image is formed on the photosensitive member and a toner image is not formed.   The image forming apparatus according to claim 2, wherein, when the detection is performed by the detection unit, the developing unit is separated from the photoconductor.   4. The image forming apparatus according to claim 1, wherein when the detection unit detects the light, the light amount of the exposure unit is increased as compared with the time of image formation. A plurality of photoconductors, exposure means for irradiating the plurality of photoconductors with a plurality of light beams corresponding to the plurality of photoconductors emitted from a light source using a common optical component to form a latent image; and the plurality of photoconductors Charging means for charging the toner, developing means for supplying toner to the latent images to form toner images on the plurality of photoconductors, and transfer means for transferring the toner images formed on the plurality of photoconductors. The exposure unit is provided with a plurality of transmission members provided on the outer surface of the exposure unit corresponding to the plurality of photoconductors and transmitting light beams corresponding to the plurality of photoconductors, respectively. In the device
Detecting means for detecting a change in current information flowing through the transfer means for each of the plurality of photoconductors;
The current information obtained from the detection means is compared for each of the plurality of photoconductors to detect a state where the common optical component is dirty and a state where the transmissive member is dirty. Image forming apparatus.   The detection unit detects a change in current information flowing through the transfer unit, thereby responding to a potential difference between a portion irradiated with light by the exposure unit on the surface of the photoconductor and a portion not irradiated with light. The image forming apparatus according to claim 1, wherein information is detected.

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