JP2017068157A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce the occurrence of an image deletion phenomenon and a difference in density between images, even when a partial difference occurs in the amount of moisture adhered to photosensitive means, such as a photoreceptor drum and the amount of moisture absorbed in a discharge deposit.SOLUTION: An image forming apparatus comprises: a photoreceptor drum 1 that forms an electrostatic latent image; detection means that detects the state of moisture adhered to a plurality of portions on a surface of the photoreceptor drum 1; and a recovery mode that determines the amount of moisture adhered to the photoreceptor drum 1 on the basis of results of a plurality of times of detection performed by the detection means and reduces a variation in the determined amount of moisture.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer (for example, a laser beam printer, an LED printer, etc.), a facsimile machine, and the like, which form an image on a recording medium using, for example, an electrophotographic image forming system.

  In an electrophotographic image forming apparatus, when an image is formed, a photosensitive drum charged by a charging member is selectively irradiated with a laser to perform exposure, and an electrostatic latent image formed by exposure is used. An image is formed by adhering toner to the toner.

  Here, when the photosensitive drum is charged, a discharge product is generated and deposited on the surface of the photosensitive drum due to a discharge phenomenon that occurs during charging. This is not only when using a corona discharge charging member, but also when using a contact charging member that contacts and charges the photosensitive drum. Since there is a very small gap, a discharge phenomenon occurs and a discharge product is generated.

  The discharge products generated and deposited on the surface of the photosensitive drum in this way may adversely affect image formation. For example, when the discharge product deposited on the surface of the photosensitive drum absorbs moisture, the state becomes the same as when a low-resistance film is stretched on the surface of the photosensitive drum. In this case, a low resistance portion and a high resistance portion are mixed on the surface of the photosensitive drum. For this reason, when irradiating the photosensitive drum with laser during exposure, there is a possibility that the boundary between the portion irradiated with the laser and the portion not irradiated with the image becomes ambiguous and an image flow phenomenon in which the electrostatic latent image is blurred may occur. . In addition, there is a possibility that a pseudo injection charging phenomenon in which a charge is retained more in the portion where the discharge product is accumulated at the time of charging than in the normal portion, causing a density difference in the image.

  On the other hand, a method for preventing an image flow phenomenon and an image density difference caused by the influence of such discharge products has been proposed. For example, in Patent Document 1, a voltage lower than the discharge start voltage is applied to the charging roller during charging to detect the current value of the current flowing through the photosensitive drum. Then, the occurrence of injection charging phenomenon is detected based on this current value, and when the injection charging phenomenon is detected, it is determined that a large amount of the absorbed discharge product has accumulated on the surface of the photosensitive drum, and the discharge operation is generated by the recovery operation. Remove moisture from objects.

JP 2010-113103 A

  However, in the configuration of Patent Document 1, a value obtained by averaging the current values for one rotation of the photosensitive drum is used as the current value detected when detecting the injection charging phenomenon. On the other hand, there may be a partial difference in the moisture absorption amount of the discharge product deposited in the circumferential direction of the photosensitive drum and the moisture amount adhering to the photosensitive drum. Therefore, in the configuration of Patent Document 1, even if the recovery operation is performed, the discharge product that has partially absorbed moisture is not completely removed, and even after the recovery operation, a low resistance portion and a high resistance portion are present on the surface of the photosensitive drum. There is a risk that it will remain mixed. For this reason, there is a possibility that an image flow phenomenon or an image density difference occurs.

  Accordingly, an object of the present invention is to generate an image flow phenomenon or a difference in image density even when a partial difference occurs in the amount of moisture adhering to a photosensitive means such as a photosensitive drum or the amount of moisture absorbed by a discharge product. It is an object to provide an image forming apparatus capable of reducing the above.

  In order to achieve this object, an image forming apparatus according to the present invention includes an image carrier that forms an electrostatic latent image, and a detection unit that detects the states of water at a plurality of locations attached to the surface of the image carrier. And recovery means for determining the amount of water adhering to the image carrier based on a plurality of detection results by the detection means and reducing variations in the determined water amount.

  According to the present invention, even if there is a partial difference in the amount of moisture adhering to the photosensitive means such as the photosensitive drum or the amount of moisture absorbed by the discharge product, the occurrence of image flow phenomenon and the difference in image density are reduced. Can be reduced.

1 is a schematic cross-sectional view of an image forming apparatus according to the present invention. 1 is a block diagram showing a system configuration of an image forming apparatus according to the present invention. 3 is a flowchart of a recovery sequence of the image forming apparatus according to the present invention. It is a figure which shows distribution of the feedback current value in the circumferential direction of the photoconductive drum which concerns on this invention. It is a figure which shows distribution of the feedback current value in the circumferential direction of the photoconductive drum which concerns on this invention. It is a figure explaining the determination method of the recovery mode execution time of the recovery sequence which concerns on this invention. FIG. 6 is a diagram illustrating a method for determining a correction value of a charging bias during image formation of the image apparatus according to the present invention. It is a figure which shows the result of the effect confirmation of the recovery sequence of the image forming apparatus which concerns on this invention.

(First embodiment)
<Image forming apparatus>
First, the overall configuration of the image forming apparatus A according to the first embodiment of the present invention will be described with reference to the drawings together with the operation during image formation.

  As shown in FIG. 1, the image forming apparatus A includes an image forming unit that transfers a toner image onto a sheet as a recording material, a sheet feeding unit that supplies the sheet to the image forming unit, and a fixing that fixes the toner image on the sheet. A section.

  The image forming unit includes a photosensitive drum 1 (image carrier), a charging roller 2 (charging member), a developing device 4, a cleaning blade 7, a transfer roller 5, a laser scanner unit 3, and the like.

  During image formation, when the CPU 50 shown in FIG. 2 issues a print signal, the sheets stacked and stored in the sheet stacking unit 10 are sent out to the image forming unit by the feeding roller 9 and the conveying roller 8.

  On the other hand, in the image forming unit, a charging bias is applied to the charging roller 2 to charge the surface of the photosensitive drum 1 in contact with the charging roller 2.

  Thereafter, the laser scanner unit 3 emits laser light from a light source (not shown) provided therein, and irradiates the photosensitive drum 1 with the laser light. As a result, the potential of the photosensitive drum 1 is partially reduced, and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 1.

  Thereafter, a developing bias is applied to the developing sleeve 13 provided in the developing device 4, whereby toner is attached to the electrostatic latent image formed on the surface of the photosensitive drum 1 from the developing sleeve 13 to form a toner image. The toner image formed on the surface of the photosensitive drum 1 is sent to a transfer nip portion formed between the photosensitive drum 1 and the transfer roller 5 that are rotatably provided. When the toner image arrives at the transfer nip portion, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 5, and the toner image is transferred to the sheet.

  Thereafter, the sheet on which the toner image has been transferred is sent to a fixing device 11 (fixing means), and heated and pressed at a fixing nip portion formed between a heating portion and a pressure portion of the fixing device 11, and the toner image Is fixed to the sheet. Thereafter, the sheet is conveyed by the discharge roller 14 and discharged to the discharge unit 15.

<Control unit>
Next, the configuration of the control unit of the image forming apparatus A will be described. As shown in FIG. 2, the control unit first includes a CPU 50 that performs various arithmetic processes and the like, and a ROM 51, a RAM 52, a current value measurement unit 53, a high voltage control unit 54, and the like are connected to the CPU 50.

  The ROM 51 stores an operation program for the CPU 50 and various control programs for image formation. The RAM 52 temporarily stores various data during execution of the program by the CPU 50. The high voltage control unit 54 is connected to a high voltage output unit 55 (bias applying unit), and the CPU 50 controls the high voltage output unit 55 via the high voltage control unit 54 to apply a high voltage charging bias to the charging roller 2. Is done. The current value measuring unit 53 is disposed between the high-voltage output unit 55 and the ground, and measures a current value (hereinafter referred to as a feedback current value) of a current flowing through the photosensitive drum 1 via the charging roller 2.

<Recovery sequence>
Next, an image flow phenomenon or an image that occurs due to a mixture of a low resistance portion and a high resistance portion in the circumferential direction of the photosensitive drum 1 due to the influence of moisture adhering to the surface of the photosensitive drum 1 and the moisture absorption amount of the discharge product. Next, a recovery sequence for reducing the density difference will be described.

  As shown in the flowchart of FIG. 3, when the recovery sequence is started, first, the photosensitive drum 1 starts rotating, and after the pre-exposure member (not shown) performs the pre-exposure processing, the high-voltage output unit 55 causes the charging roller 2 to rotate. A charging bias lower than the discharge start voltage is applied to (S1).

  The discharge start voltage is a voltage value when the surface potential of the photosensitive drum 1 starts to increase when the voltage applied as the charging bias is increased. This discharge start voltage is determined from the gap between the charging roller 2 and the photosensitive drum 1, the thickness of the photosensitive layer, and the relative dielectric constant of the photosensitive layer. In this embodiment, this discharge start voltage is −550 V, and a DC charge bias of −500 V is applied as a charge bias less than the discharge start voltage when the recovery sequence is executed.

  Here, in a normal case, when a voltage equal to or higher than the discharge start voltage is applied to the charging roller 2, discharge development occurs and electric charge starts to be applied to the photosensitive drum 1. On the other hand, when a discharge product or moisture adheres to the surface of the photosensitive drum 1, a pseudo injection phenomenon occurs in the same state as when a low resistance film is stretched on the surface of the photosensitive drum 1. Even when a voltage lower than the discharge start voltage is applied, charge starts to be applied to the photosensitive drum 1. Therefore, by detecting information corresponding to the surface potential of the photosensitive drum 1 when a voltage lower than the discharge start voltage is applied as information on the moisture adhering to the photosensitive drum 1, the photosensitivity is caused by the influence of discharge products and moisture. It can be seen whether the surface resistance of the body drum 1 is low. Further, by detecting information corresponding to the surface potentials at a plurality of locations on the photosensitive drum 1, it is possible to detect the state of moisture at the plurality of locations attached to the surface of the photosensitive drum 1. Further, by detecting the distribution of information corresponding to the surface potential of the photosensitive drum 1 during one cycle of the photosensitive drum 1, the distribution of the surface resistance in the circumferential direction of the photosensitive drum 1 can be obtained.

  Therefore, in this recovery sequence, when a charging bias less than the discharge start voltage is applied to the charging roller 2, a plurality of feedback current values are used as information corresponding to the surface potential of the photosensitive drum 1 during one cycle of the photosensitive drum 1. Detected twice (S2). As a result, the state of moisture at a plurality of locations attached to the surface of the photosensitive drum 1 can be detected, and the distribution of surface resistance and the variation of moisture in the circumferential direction of the photosensitive drum 1 can be known.

  Information corresponding to the surface potential of the photosensitive drum 1 may be detected at least for one cycle along the rotation direction during rotation of the photosensitive drum 1. In addition, the number of detections of the feedback current value in one cycle of the photosensitive drum 1 may be arbitrary as long as it is two times or more, but it is preferable to detect about two to twenty times. In the present embodiment, as shown in FIG. 4, the average value of the feedback current values detected within each detection time obtained by dividing the time in one cycle by eight for three cycles of the photosensitive drum 1 is the feedback current value. Detected 8 times as Idc.

  Here, when the variation of the detected plurality of feedback current values Idc (a plurality of detection results) is large, a difference occurs in the moisture absorption amount and the moisture amount of the discharge product in the circumferential direction of the photosensitive drum 1, and the photosensitive drum 1. It means that a low resistance part and a high resistance part are mixed on the surface. If image formation is performed with a large variation, an image flow phenomenon or a difference in image density may occur.

  Therefore, it is determined whether or not the variation in the feedback current value Idc is greater than or equal to a predetermined value. As a determination method in the present embodiment, as shown in FIG. 5, first, the maximum value (MAX value) and the minimum value (MIN value) of the eight feedback current values Idc detected during one cycle of the photosensitive drum 1 are used. The difference value ΔIdc is calculated (S3).

  Then, it is determined whether or not the difference value ΔIdc is equal to or smaller than a threshold value α stored in advance in the ROM 52 (S4). When the difference value ΔIdc is larger than the threshold value α, it is determined that the variation in the feedback current value Idc is equal to or greater than a predetermined value. In the following cases, it is determined that the variation is less than a predetermined value. The threshold value α is arbitrarily determined for each product from the correlation between the image quality and the detection result. In this embodiment, 2.5 μA is set as the threshold value α.

  Next, when the difference value ΔIdc is larger than the threshold value α, there is a difference in the moisture absorption amount and moisture amount of the discharge product in the circumferential direction of the photosensitive drum 1, and when image formation is performed, an image flow phenomenon and an image density difference occur. May occur. For this reason, a recovery mode (recovery means) for reducing the variation in the feedback current value Idc detected a plurality of times and reducing the difference in the surface resistance caused by the amount of moisture absorbed by the discharge product and moisture in the circumferential direction of the photosensitive drum 1 is provided. Execute (S5).

  Next, the recovery mode will be described. As described above, the cause of the difference in the surface resistance of the photosensitive drum 1 due to the discharge product is that the discharge product that has absorbed moisture and the adhesion of moisture are in the same state as when a low-resistance film is formed. It is. Therefore, if the amount of water contained in the surface of the photosensitive drum 1 and the discharge product is reduced, it is possible to prevent a difference in the surface resistance of the photosensitive drum 1 due to the discharge product.

  For this reason, in this embodiment, as the recovery mode, the amount of water contained in the discharge product attached to the surface of the photosensitive drum 1 is reduced to dry the discharge product. Specifically, for example, air is sent to the photosensitive drum 1 by blowing air, or the photosensitive drum 1 is idly rotated. Alternatively, a heater (heating means) as a drying means is provided to apply heat to the surface of the photosensitive drum 1. As a result, the amount of water contained in the discharge product and the amount of water attached to the photosensitive drum 1 can be reduced, and the low resistance portion and the high resistance in the circumferential direction of the photosensitive drum 1 due to the influence of the discharge product. Mixing of parts can be suppressed. Accordingly, it is possible to reduce the occurrence of image flow phenomenon and the difference in image density.

  Further, a heater (heater member) as a heating unit may be provided inside the photosensitive drum 1 or may be provided outside. Instead of providing a separate heater, a fixing heater (heater member) (not shown) provided as a heat source in the heating unit of the fixing device 11 may be used as a drying unit. For example, the fixing heater is operated to perform fixing idle rotation (fixing temperature control idle rotation, printing operation), thereby increasing the ambient temperature in the image forming apparatus A and drying the discharge product adhering to the photosensitive drum 1. As a result, it is possible to take measures against the discharge product without providing a separate heater, leading to cost reduction. Further, the drying effect can be improved by providing a fan in the image forming apparatus A so that the heated air in the vicinity of the fixing heater is actively sent to the photosensitive drum 1.

  Instead of drying the discharge product, a scraping member that contacts the photoconductive drum 1 and scrapes the discharge product may be provided. For example, the discharge product can be scraped off by using the cleaning blade 7 as a scraping member, rotating the photosensitive drum 1 idle, and polishing the surface of the photosensitive drum 1 with the cleaning blade 7. Thereby, it is possible to prevent the low resistance portion and the high resistance portion from being mixed in the circumferential direction of the photosensitive drum 1 due to the influence of the discharge product. Also, a configuration may be adopted in which a high pressure is applied during idling in order to actively promote the shaving of the photosensitive drum 1. However, in this case, it is necessary to consider the balance of the amount of the discharge product scraped off and the newly generated discharge product. In addition, it is good also as a structure which scrapes off a discharge product with a scraping member, drying a discharge product with the said drying means.

  Next, after executing the recovery mode, the image forming apparatus A returns to step S1 again, applies a charging bias less than the discharge start voltage, and then obtains the difference value ΔIdc again. The same control is repeated until the difference value ΔIdc of the feedback current value becomes equal to or less than the threshold value α.

  Further, the recovery mode execution time is preferably obtained by approximation based on the decrease amount of the difference value ΔIdc detected after the recovery mode is executed and the recovery mode execution time. For example, as shown in FIG. 6A, first, the difference value ΔIdc1 detected after the first execution of the recovery mode, the difference value ΔIdc2 detected after the second execution of the recovery mode, and the execution time of the recovery mode are detected. Then, as shown in FIG. 6B, the recovery amount per unit execution time is calculated from the detection result, and the recovery mode total execution time when the difference value ΔIdc is equal to or less than the threshold value α is calculated. Based on this, the execution time of the third recovery mode is determined. Thereby, the recovery mode can be completed in the shortest time.

  Next, the control after the difference value ΔIdc of the feedback current value becomes equal to or less than the threshold value α in step S4 will be described. First, the image forming apparatus A calculates the average value Iave of the feedback current value Idc during one cycle of the photosensitive drum 1 detected a plurality of times in step S2 (S6).

  Next, as shown in FIG. 7, the calculated average value Iave and the target value Itrg of the feedback current value stored in the ROM 52 in advance are compared, and a correction value for correcting the deviation between Iave and Itrg is calculated and stored in the ROM. Store (S7). This Itrg is a normal value of a feedback current value that flows when a charging bias having a preset discharge start voltage (-500 V in this embodiment) is applied. For this reason, by determining the charging bias value at the time of image formation using the correction value stored in the ROM, the charge amount of the photosensitive drum 1 can be optimized, and high-quality image formation can be performed.

  Thereafter, the image forming apparatus A enters a standby state waiting for an image formation instruction from the CPU 50, and prepares for the image formation instruction (S8).

<Effect confirmation>
Next, the result of the effect confirmation regarding the determination of the recovery mode execution time will be described. The charging roller 2 used in the confirmation of this effect is an elastic solid roller, which has a three-layer structure of a base layer (elastic layer), a dielectric layer, and a protective layer. The outer diameter was φ16 and the Asker C hardness was 48 ± 5 °. Further, the feedback current value Idc was read at intervals of 2 msec by the current value measuring unit 53 during one cycle of the photosensitive drum 1, and a DC voltage of −500 V, which is a voltage lower than the discharge start voltage, was applied as the charging bias.

  As a result of confirming the effect under the above conditions, as shown in FIG. 8A, the transition of the difference value ΔIdc of the feedback current value measured after the execution of the recovery mode is between after the first execution and after the third execution. 10 μA, 9.8 μA, and 9.6 μA were obtained. The recovery mode execution time was about 0.408696 seconds per time. Therefore, as shown in FIG. 8B, the recovery amount per unit execution time in the recovery mode was calculated to be 0.2435 μA. Further, it was found that when the difference value ΔIdc is x and the recovery mode execution time is y, the recovery mode execution time y is calculated from the equation y = −2.0435x + 20.443.

  As a result, it was calculated that the recovery mode had to be executed for a total of 15.73 seconds in order for the difference value ΔIdc to be equal to or less than the threshold value α of 2.5 μA. Then, the recovery mode was executed for a total of 15.73 seconds, and then the difference value ΔIdc value was detected again. As a result, the difference value ΔIdc was 2.5 μA or less, which is the threshold value α. From the above, it was confirmed that the above-described method for determining the recovery mode execution time is appropriate. In the image formation after the completion of the recovery sequence, the image density difference is eliminated.

  The above recovery sequence is performed when image formation has not been performed for a predetermined time or more, for example, when the power of the apparatus main body is switched from OFF to ON, or when returning to the sleep mode that enters when image formation is not performed for a long time. More effective. This is because the longer the time during which the image forming operation is not performed, the higher the possibility that the discharge product is deposited on the surface of the photosensitive drum 1 and absorbs moisture.

  In addition, the necessity of executing a recovery sequence depends on the environment in which the main body of the device is installed. Cheap. Therefore, it is also possible to provide an environmental sensor for detecting the environment such as the temperature and humidity and the absolute water content at the installation location of the apparatus main body, and set the detection result of the environmental sensor as a trigger for starting the recovery sequence. As a result, the recovery sequence can be performed only when necessary, and the power consumption can be reduced.

  In the present embodiment, the feedback current value Idc is used as information regarding the moisture adhering to the photosensitive drum 1, but the present invention is not limited to this. That is, a drum potential measuring device for measuring the surface potential of the photosensitive drum 1 is installed in the vicinity of the photosensitive drum 1. Even if the above-described control is performed based on the charging potential of the photosensitive drum 1 when a DC voltage lower than the discharge start voltage is applied so that the high-voltage output unit 55 has a constant current value, the same effect as described above can be obtained. Can be obtained. Further, the information corresponding to the surface potential of the photosensitive drum 1 may be information corresponding to the surface resistance of the photosensitive drum 1.

  As a means for detecting the density difference of the photosensitive drum 1, a test patch (density detection chart) is placed on the drum, and the amount of toner applied at that time is a value detected by a sensor such as a reflection sensor. It is also possible to use.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 53 ... Current value measurement part A ... Image forming apparatus

Claims (16)

An image carrier for forming an electrostatic latent image;
Detection means for detecting the state of moisture at a plurality of locations attached to the surface of the image carrier;
Recovery means for determining the amount of water adhering to the image carrier based on a plurality of detection results by the detection means, and reducing variations in the determined water amount;
An image forming apparatus comprising: A charging member for charging the image carrier;
Bias applying means for applying a charging bias for generating a discharge between the charging member and the image carrier;
Have
2. The detection unit according to claim 1, wherein the detection unit detects the state of the moisture from information regarding moisture attached to the image carrier obtained when a DC voltage lower than a discharge start voltage is applied to the charging member. The image forming apparatus described.   The image forming apparatus according to claim 2, wherein the detection unit detects the state of the moisture for one rotation along a rotation direction during rotation of the image carrier.   4. The image forming apparatus according to claim 2, wherein the recovery unit executes the recovery unit when variation in the plurality of detection results is equal to or greater than a predetermined value. 5.   5. The method according to claim 2, wherein the recovery unit determines the execution time based on a reduction amount of variation in the plurality of detection results per unit execution time of the recovery unit, and reduces the variation. The image forming apparatus according to claim 1.   The recovery unit corrects a voltage value applied to the charging member during image formation according to the plurality of detection results without executing the recovery unit when variation of the plurality of detection results is less than a predetermined value. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   The information on the moisture adhering to the image carrier is a current value of a current that flows to the image carrier via the charging member when the bias applying unit applies a DC voltage lower than a discharge start voltage. The image forming apparatus according to any one of claims 2 to 6.   The information on the moisture adhering to the image carrier is a charging potential of the image carrier when the bias applying unit applies a DC voltage lower than the discharge start voltage so that a current having a constant current flows. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   9. The image forming apparatus according to claim 1, wherein the recovery unit is a drying unit that dries the surface of the image carrier.   The image forming apparatus according to claim 9, wherein the drying unit is a heating unit that applies heat to the surface of the image carrier to dry the surface of the image carrier. A fixing means for fixing the image by applying heat to the recording material by a heater member for the image transferred to the recording material;
The image forming apparatus according to claim 10, wherein the heating unit applies heat generated from the heater member to a surface of the image carrier.   The image forming apparatus according to claim 10, wherein the heating unit applies heat generated from a heater member provided inside the image carrier to the surface of the image carrier.   13. A scraping member that scrapes off a discharge product that comes into contact with the image carrier and adheres to the surface of the image carrier when the recovery unit is executed. The image forming apparatus described in the item.   14. The detection unit according to claim 1, wherein the detection unit detects the state of moisture at a plurality of locations attached to the surface of the image carrier when the apparatus main body has not performed image formation for a predetermined time or more. The image forming apparatus according to claim 1.   15. The detection unit according to claim 1, wherein when the power supply of the apparatus main body is switched from OFF to ON, the detection unit detects a state of moisture at a plurality of locations attached to the surface of the image carrier. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the variation in the moisture amount is determined based on a difference value between the plurality of detection results.

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