JP6225777B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus.

  In Patent Document 1, as a cleaning device for an image forming apparatus, when a friction coefficient between a photosensitive member and a blade increases and the blade is bent and deformed by the friction, a deformation detection unit that detects the bending deformation of the blade. Is provided. The cleaning device attaches toner to a non-image area of the photosensitive member by a developing unit based on the detection signal of the deformation detecting unit, and supplies the toner to the blade. Patent Document 2 describes an image forming apparatus in which a strain gauge is attached to a cleaning blade. In this image forming apparatus, the voltage value output from the strain gauge and amplified to a predetermined level by the amplifier is detected as a value representing the magnitude of the blade distortion that deforms according to the frictional force of the cleaning blade against the photosensitive drum. Then, the presence or absence of the filming layer is determined by comparing this value.

Japanese Patent Application Laid-Open No. 07-230239 Japanese Patent Laid-Open No. 08-129327

  An object of the present invention is to suppress wear of a cleaning member that cleans an image carrier.

According to a first aspect of the present invention, there is provided a developing roll for developing a latent image formed on an image carrier using a developer containing an external additive, and at least a period in which the latent image is formed in the first mode. In the second mode, the amplitude and / or the frequency is larger than that of the first AC component in the period in which the latent image is formed and the period in which the latent image is not formed in the second mode. A developing device having a voltage applying means for applying a voltage containing a second AC component to the developing roll and a cleaning member for cleaning the image holding member is provided.

According to a second aspect of the present invention, there is provided a developing roll for developing a latent image formed on an image carrier using a developer containing an external additive, and a period in which at least the latent image is formed in the first mode. In the second mode, a voltage including a second AC component having an amplitude and / or a frequency greater than that of the first AC component in at least a period in which the latent image is not formed in the second mode. When the detection result of the voltage applying means applied to the developing roll, the cleaning member for cleaning the image carrier, and the detection means for detecting distortion of the cleaning member satisfies a predetermined condition, the first mode is started. A developing device is provided that includes an instruction unit that instructs the voltage application unit to switch to the second mode.
According to a third aspect of the present invention, in the developing device according to the second aspect , the instruction means includes a detection result of the detection means when the cleaning member is cleaning the image carrier, and the cleaning member Instructing the voltage application means to switch from the first mode to the second mode when the difference from the detection result of the detection means when the image carrier is not cleaned satisfies a predetermined condition. It is characterized by doing .

According to a fourth aspect of the present invention, in the developing device according to the third aspect , the instruction unit instructs the switching when the accumulated value of the difference satisfies a predetermined condition.

According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising: the developing device according to any one of the first to fourth aspects; and a transfer unit that transfers an image developed by the developer onto a recording medium. .

According to the first , second, and fifth aspects of the present invention, the cleaning member that cleans the image carrier is not worn with a voltage including the second AC component applied to the developing roll during a period in which the latent image is not formed. It can be suppressed in comparison.
According to the invention which concerns on Claim 3 , compared with the case where it does not determine based on the difference of a detection result, distortion of a cleaning member can be determined more correctly.
According to the invention which concerns on Claim 4 , compared with the case where it does not determine based on the accumulated value of a difference, the distortion of a cleaning member can be determined more correctly.

1 is a diagram illustrating an overall configuration of an image forming apparatus 1. FIG. FIG. 3 is a diagram illustrating a configuration of a developing unit 13. The figure which shows the structure of the drum cleaner. The figure which shows the relationship between the distortion amount of a cleaning blade, and the amount of wear. FIG. 4 is a diagram showing the coverage of external additives on the surface of the photosensitive drum 31. The flowchart which shows the flow of the mode switching process which the control part 11 performs. The figure which shows the detected value of the strain gauge 63. FIG. The figure which shows the relationship between the average value of the distortion amount of a cleaning blade, and the average value of wear amount. The figure which shows the relationship between the distortion amount of a cleaning blade, and the amount of wear. The figure which shows the relationship between the distortion amount of a cleaning blade, and the amount of wear.

1. Embodiment 1-1. Configuration FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is an apparatus that forms an image by electrophotography. The image forming apparatus 1 according to the present embodiment is a so-called tandem type, and forms an image on a sheet P that is an example of a medium based on image data representing an image. In the figure, the control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU stores a computer program (hereinafter simply referred to as “ROM”) stored in the ROM or the storage unit 12. Each unit of the image forming apparatus 1 is controlled by reading out and executing the program. The storage unit 12 is a large-capacity storage unit such as a hard disk drive, and stores a program read by the CPU of the control unit 11. The operation unit 17 includes operation buttons and the like for inputting various instructions. The operation unit 17 receives an operation by the user and supplies a signal corresponding to the operation content to the control unit 11.

  The developing units 13Y, 13M, 13C, and 13K form toner images on the paper P. Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. Although the developing units 13Y, 13M, 13C, and 13K use different toners, there is no significant difference in the configuration. Hereinafter, when it is not necessary to particularly distinguish each of the developing units 13Y, 13M, 13C, and 13K, the alphabet at the end of the code indicating the color of the toner is omitted and referred to as “developing unit 13”. The developing unit 13 is an example of a developing device according to the present invention.

  FIG. 2 is a diagram illustrating a configuration of the developing unit 13. Each developing unit 13 includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a primary transfer roll 35, and a drum cleaner 36. The photosensitive drum 31 is an image carrier having a charge generation layer and a charge transport layer, and is rotated in the direction of an arrow D13 in the drawing by a drive unit (not shown). The photosensitive drum 31 is an example of an image carrier. The charger 32 charges the surface of the photosensitive drum 31. The exposure device 33 includes a laser emission source, a polygon mirror, and the like (both not shown), and a photoconductor after the laser light corresponding to the image data is charged by the charger 32 under the control of the control unit 11. Irradiation toward the drum 31. Thereby, a latent image is held on each photosensitive drum 31. The exposure device 33 is an example of an exposure unit. The image data may be acquired from an external device by the control unit 11 via a communication unit (not shown). The external device is, for example, a reading device that reads an original image or a storage device that stores data indicating an image.

  The developing device 34 accommodates a two-component developer (hereinafter simply referred to as “developer”) including toner of any one of Y, M, C, and K and a magnetic carrier such as ferrite powder. External additives adhere to the surfaces of these toners. The external additive is fine particles having an average particle diameter of several nm to several hundred nm. Examples of the external additive include hydrophobic surface-treated silica, titanium oxide, barium titanate, strontium titanate, hydrotalcite, wax fine particles, metal soap such as potassium stearate, and resin fine particles. The external additive is added for the purpose of improving the fluidity of the toner, stabilizing the charging characteristics of the toner, improving the durability of the toner, and improving the cleaning property. In particular, the external additive is added to stabilize the charging characteristics of the toner. The tip of the magnetic brush formed on the developing unit 34 comes into contact with the surface of the photosensitive drum 31, so that the toner is exposed on the surface of the photosensitive drum 31 by the exposure device 33, that is, the image line portion of the electrostatic latent image. An image is formed (developed) on the photosensitive drum 31. The primary transfer roll 35 generates a predetermined potential difference at a position where the intermediate transfer belt 41 of the transfer unit 14 faces the photosensitive drum 31, and the image is transferred to the intermediate transfer belt 41 by this potential difference.

  The drum cleaner 36 removes untransferred toner remaining on the surface of the photosensitive drum 31 after image transfer, and removes the surface of the photosensitive drum 31. That is, the drum cleaner 36 removes unnecessary toner and charges from the photosensitive drum 31 in preparation for the next image formation.

  The transfer unit 14 (an example of a transfer unit) includes an intermediate transfer belt 41, a secondary transfer roll 42, a belt conveyance roll 43, and a backup roll 44. An image formed by the developing unit 13 is transferred to a user. This is a transfer section for transferring to the paper P of the paper type determined according to the operation. The intermediate transfer belt 41 is an endless belt member, and the belt conveyance roll 43 and the backup roll 44 stretch the intermediate transfer belt 41. At least one of the belt conveyance roll 43 and the backup roll 44 is provided with a drive unit (not shown), and moves the intermediate transfer belt 41 in the direction of arrow D14 in the drawing. Note that the belt conveyance roll 43 or the backup roll 44 that does not have a driving unit rotates following the movement of the intermediate transfer belt 41. As the intermediate transfer belt 41 moves and rotates in the direction of the arrow D14 in the drawing, the image on the intermediate transfer belt 41 is moved to a region sandwiched between the secondary transfer roll 42 and the backup roll 44.

  The secondary transfer roll 42 transfers the image on the intermediate transfer belt 41 onto the paper P conveyed from the conveyance unit 16 by a potential difference with the intermediate transfer belt 41. The belt cleaner 49 removes untransferred toner remaining on the surface of the intermediate transfer belt 41. Then, the transfer unit 14 or the conveyance unit 16 conveys the paper P on which the image is transferred to the fixing unit 15.

  The fixing unit 15 fixes the image transferred onto the paper P by heating. The conveyance part 16 has a container and a conveyance roll. The container accommodates a sheet P as an example of a medium on which an unfixed image that has been cut to a predetermined size and is fixed to the medium by heating is formed. Among the sizes of the paper P, at least two different sizes are defined in the direction perpendicular to the transport direction, that is, in the width direction. Here, two types of paper P are used: a maximum width paper P1 and a narrow paper P2 that is narrower than the maximum width paper P1. The maximum width paper P1 is the paper having the maximum size in the width direction among the papers P handled by the image forming apparatus 1. These two types of paper P are distinguished by the control unit 11 depending on the container in which they are stored. The paper P accommodated in each container is taken out one by one by a transport roll according to an instruction from the control unit 11 and transported to the transfer unit 14 via a paper transport path. The medium is not limited to paper, and may be a resin sheet, for example. In short, the medium may be any medium that can form an image on the surface.

  The developing device 34 includes a storage unit 341, a developing roll 342, and a voltage application unit 343. The storage unit 341 stores a developer including toner and a carrier. The developing roll 342 contains a magnetic roll. The developing roll 342 rotates in the direction of the arrow D15, and the developer accommodated in the accommodating portion 341 is attracted to the surface by magnetic force and conveyed. The voltage application unit 343 applies a voltage to the developing roll 342 under the control of the control unit 11. At this time, the voltage applying unit 343 applies a voltage obtained by superimposing an AC voltage on the DC voltage to the developing roll 342 so that the potential of the developing roll 342 becomes a predetermined potential. Here, the potential of the developing roll 342 refers to the average potential of the voltage applied to the developing roll 342. The voltage application unit 343 causes the surface of the developing roller 342 to have a potential that forms an electric field in a region to be developed (for example, a region where an electrostatic latent image is formed) on the surface of the photosensitive drum 31. A voltage is applied to the developing roll 342. As described above, the developing roller 342 and the voltage applying unit 343 operate, so that the developing device 34 supplies toner to the surface of the photosensitive drum 31 and forms a toner image.

  FIG. 3 is a diagram illustrating the configuration of the drum cleaner 36. The drum cleaner 36 includes a support member 61, a cleaning blade 62, and a strain gauge 63. The support member 61 is a member that supports the cleaning blade 62. The support member 61 is fixed to the housing of the image forming apparatus 1. The cleaning blade 62 is a plate-shaped cleaning member formed of a resin such as rubber. The cleaning blade 62 is in contact with the surface of the photosensitive drum 31 at one side in the longitudinal direction, and is further pressed against the surface of the photosensitive drum 31 to remove deposits attached to the surface of the photosensitive drum 31. This adhering matter is toner or an external additive remaining on the surface of the photosensitive drum 31 without being transferred to the intermediate transfer belt 41. The strain gauge 63 is detection means for detecting the distortion of the cleaning blade 62. The strain gauge 63 is attached to the cleaning blade 62 and outputs a signal indicating the detection result. The greater the distortion of the cleaning blade 62, the greater the amount of wear of the cleaning blade 62.

  FIG. 4 is a diagram showing the relationship between the amount of distortion and the amount of wear of the cleaning blade. In the figure, the vertical axis indicates the amount of distortion of the cleaning blade, and the horizontal axis indicates the amount of wear of the cleaning blade. In the example shown in FIG. 4, the relationship between the wear of the cleaning blade and the amount of distortion when four different types of toner are used is shown. In this example, it can be said that the greater the amount of distortion of the cleaning blade, the greater the amount of wear of the cleaning blade.

  The cleaning blade 62 contacts the surface of the photosensitive drum 31 and cleans the surface of the photosensitive drum 31. Therefore, the wear of the cleaning blade 62 is promoted as the friction coefficient with the photosensitive drum 31 increases. The friction coefficient varies depending on the image density and the type of toner. As the cleaning blade 62 wears, the toner passes through the cleaning blade 62. Due to this slipping, the charging roll (charger 32) is contaminated and the potential of the photosensitive drum 31 becomes non-uniform. As a result, white spots and color streaks occur in the image, which may cause a problem that the image quality deteriorates.

  By the way, when the cleaning blade 62 removes toner and external additives remaining on the surface of the photosensitive drum 31, the residual toner and external additives are interposed between the surface of the photosensitive drum 31 and the cleaning blade 62. It becomes a state. Since the toner and the external additive serve as a lubricant, the friction coefficient between the photosensitive drum 31 and the cleaning blade 62 decreases, and the photosensitive drum 31 advances smoothly with respect to the cleaning blade 62. As described above, the toner and the external additive remaining on the photosensitive drum 31 serve as a lubricant, so that wear of the photosensitive drum 31 and the cleaning blade 62 is suppressed.

1-2. Operation 1-2-1. Image Forming Operation Next, an image forming process performed by the image forming apparatus 1 will be described. The image forming process is triggered by, for example, a user operating the operation unit 17 to instruct the image forming process or receiving image data and instruction data instructing the image forming process from another device. The When the image forming process is instructed, the control unit 11 of the image forming apparatus 1 controls each part of the image forming apparatus 1 to execute the image forming process. In particular, the control unit 11 instructs the voltage application unit 343 to apply a voltage to the developing roll 342. At this time, as a mode in which the voltage application unit 343 applies a voltage to the developing roll 342, in this embodiment, there are a normal mode (first mode) and a wear suppression mode (second mode). The normal mode is a mode for performing a normal image forming process. On the other hand, the wear suppression mode is a mode used for suppressing wear of the cleaning blade 62. These two types of modes are switched by the control unit 11 according to the detection result of the strain gauge 63.

In the normal mode, the voltage application unit 343 applies the voltage V ₁ obtained by superimposing the AC voltage V ₁₁ (first AC component) having a predetermined amplitude and frequency on the DC voltage V ₁₂ to the developing roll 342. The average potential of the voltage V _{1 obtained} by superimposing the AC voltage V ₁₁ on the DC voltage V ₁₂ is a predetermined potential. On the other hand, in the wear suppression mode, the voltage application unit 343 has a voltage V obtained by superimposing an AC voltage V ₂₁ (second AC component) having at least one of amplitude and frequency higher than the AC voltage V ₁₁ on the DC voltage V _{12. 2} is applied to the developing roll 342. That is, in the wear suppression mode, at least one of the amplitude and frequency of the AC voltage V ₁₁ applied to the developing roll 342 is larger than that of the AC voltage V ₂₁ applied in the normal mode.

The voltage V ₁ is applied to the developing roll 342 during a period in which the area where the latent image is formed on the surface of the photosensitive drum 31 (hereinafter referred to as “latent image area”) and the developing roll 342 face each other. Then, the toner adsorbed on the surface of the developing roller 342 adheres to the exposed area on the surface of the photosensitive drum 31, and thereby a toner image is formed (developed) on the photosensitive drum 31. On the other hand, the toner conveyed by the developing roller 342 does not adhere to a region where the latent image is not formed on the surface of the photosensitive drum 31 (hereinafter referred to as “non-latent image region”).

On the other hand, when the voltage V ₂ is applied to the developing roll 342 in the period in which the latent image area of the photosensitive drum 31 and the developing roll 342 face each other, the amplitude and / or frequency of the AC voltage is higher than the voltage V _1. When the voltage V ₁ is large, the amount of the toner and the external additive attached to the photosensitive drum 31 is larger than that when the voltage V ₁ is applied.

Further, when the voltage V ₂ is applied to the developing roll 342 during the period in which the non-latent image area of the photosensitive drum 31 and the developing roll 342 are opposed to each other, the toner and the outside of the photosensitive drum 31 are more affected than the voltage V ₁ applied. The additive is easily peeled off from the developing roll 342. This is because the amplitude and / or frequency of the AC voltage V ₂₁ included in the voltage V ₂ greater than that of the AC voltage V _11. In this example, the AC voltage V ₂₁ is set to an amplitude value or frequency that allows the external additive to peel from the developing roll 342 and adhere to the non-latent image area of the photosensitive drum 31. In this case, the external additive adheres to the non-latent image area of the photosensitive drum 31, but the toner does not adhere to the non-latent image area. As described above, when the voltage V ₂ is applied to the developing roll 342, the external additive conveyed by the developing roll 342 adheres to the non-latent image area of the photosensitive drum 31. When the voltage V ₁ is applied to the developing roll 342, neither the external additive nor the toner adheres to the non-latent image area of the photosensitive drum 31.

  As described above, since the external additive functions as a lubricant, the external additive is interposed between the photosensitive drum 31 and the cleaning blade 62, whereby the friction coefficient between the photosensitive drum 31 and the cleaning blade 62 is obtained. Becomes smaller. As described above, the external additive adheres to the photosensitive drum 31, thereby suppressing wear of the photosensitive drum 31 and the cleaning blade 62.

  FIG. 5 is a diagram showing the coverage of the external additive on the surface of the photosensitive drum 31 in the normal mode and the wear suppression mode. In the figure, the vertical axis represents the coverage of the external additive on the surface of the photosensitive drum 31. In the example shown in FIG. 5, “before development”, “after development”, “after transfer”, and “after cleaning” in the latent image region and the non-latent image region in each of the normal mode and the wear suppression mode. The coverage of the external additive at this timing is shown. The coverage was measured by binarizing the external additive in the optical microscope image and the surface of the photoreceptor, and determining the area ratio of the binarized portion. “Before development” indicates a state before the surface of the photosensitive drum 31 is developed by the developing roll 342. “After development” indicates a state after the surface of the photosensitive drum 31 is developed by the developing roll 342. “After transfer” indicates a state after the toner image on the surface of the photosensitive drum 31 is transferred to the intermediate transfer belt 41. “After cleaning” indicates a state after the surface of the photosensitive drum 31 is cleaned by the cleaning blade 62.

  As shown in FIG. 5, comparing the normal mode and the wear suppression mode, it can be seen that the coverage of the external additive in the wear suppression mode is high in both the latent image region and the non-latent image region. In particular, the coverage of the external additive after transfer is higher in the wear suppression mode in both the latent image region and the non-latent image region. As described above, since the coverage of the external additive serving as a lubricant in the wear suppression mode is high, the friction coefficient between the photosensitive drum 31 and the cleaning blade 62 is smaller than that in the normal mode. As a result, wear of the photosensitive drum 31 and the cleaning blade 62 is suppressed.

1-2-2. Mode Switching Operation FIG. 6 is a flowchart showing the flow of mode switching processing performed by the control unit 11. The control unit 11 switches the mode according to the detection value of the strain gauge 63. In step S1, the control unit 11 detects the value detected by the strain gauge 63 when the developing unit 13 is operating (when the photosensitive drum 31 is rotating) and when the developing unit 13 is stopped (photosensitive). The difference from the detected value of the strain gauge 63 (when the body drum 31 is not rotating) is calculated.

  FIG. 7 is a diagram illustrating the detected value of the strain gauge 63. In the figure, the horizontal axis indicates time, and the vertical axis indicates the detected value of the strain gauge 63. In this example, the developing unit 13 starts operating at time t1, and thereafter the developing unit 13 stops operating at time t2. Thereafter, the developing unit 13 starts operating again at time t3, and stops operating at time t4. The period from the time t1 to the time t2 is a period during which the developing unit 13 is operating. In this period, the detection value is not constant and gradually changes with the passage of time. Further, the period from the time t2 to the time t3 is a period in which the developing unit 13 is not operating, but the detected value is not constant during this period, and gradually changes with time.

  In this example, the control unit 11 acquires the detection value of the strain gauge 63 every predetermined unit time during the period in which the developing unit 13 is operating. Further, the control unit 11 calculates a difference between the acquired detection value and the detection value at a timing immediately before the development unit 13 starts the operation (for example, time t1). The control unit 11 controls the operation of the developing unit 13 and instructs the developing unit 13 to start or stop the operation. The control unit 11 specifies the timing at which the developing unit 13 starts its operation and the timing at which the developing unit 13 stops its operation based on an instruction that the control unit 11 itself issues to the developing unit 13. Note that the method for specifying the timing at which the developing unit 13 starts the operation and the timing at which the operation stops is not limited to this. For example, the control unit 11 monitors the output value of the strain gauge 63, specifies the timing at which the output value is smaller than a predetermined threshold as the operation start timing, and is larger than the predetermined threshold. The timing may be specified as the stop timing. Further, for example, a signal indicating the operation state is output from the developing unit 13 to the control unit 11, and the control unit 11 may specify the start timing and stop timing of the operation based on this signal.

  Returning to the description of FIG. In step S2, the control unit 11 calculates the cumulative value of the difference calculated in step S1 at a predetermined timing. This cumulative value may be a cumulative value of a difference in a predetermined unit period (for example, from one hour ago to the present), or from the time the image forming apparatus 1 is turned on until the present. It may be a cumulative value.

  In step S3, the control unit 11 determines whether the cumulative value calculated in step S2 is greater than or equal to a predetermined threshold value. In this example, when the accumulated value is equal to or greater than a predetermined threshold, it is determined that the wear suppression mode needs to be set, and the process proceeds to step S4. On the other hand, when the accumulated value is less than the predetermined threshold, it is determined that the normal mode is acceptable, and the process proceeds to step S7.

  FIG. 8 is a diagram illustrating the correlation between the average value of the distortion amount of the cleaning blade and the average value of the wear amount. In the figure, the horizontal axis indicates the average value of the distortion amount of the cleaning blade, and the vertical axis indicates the average value of the wear amount. The average value of the distortion amount is obtained by dividing the above-described cumulative value by the number of samples.

  9 and 10 are diagrams illustrating the relationship between the amount of distortion and the amount of wear of the cleaning blade. FIG. 9 shows the relationship between the amount of distortion of the cleaning blade when no image is formed on the paper and the amount of wear when the image is formed on 10,000 sheets (10 kPV). FIG. 10 shows the distortion amount of the cleaning blade in a state where an image is formed on 2500 sheets (2.5 kPV) and the wear amount in a state where an image is formed on 10,000 sheets (10 kPV). The relationship is shown. On the other hand, FIG. 8 shows the relationship between the average value of strain and the average value of wear. As shown in FIGS. 9 and 10, there is little correlation between the strain amount and the wear amount in a plurality of individual measurement results. On the other hand, a correlation is recognized between the average value of the strain amount and the average value of the wear amount as shown in FIG.

In step S4, the control unit 11 determines whether the current mode is the normal mode. If the current mode is not the normal mode, that is, if it is already the wear suppression mode (step S4; NO), there is no need to change the mode, so the control unit 11 skips the processing of step S5 and step S6, and step The process returns to S1. On the other hand, when the current mode is the normal mode, the control unit 11 controls the voltage application unit 343 to change from the normal mode to the wear suppression mode. That is, the control unit 11 increases at least one of the amplitude and the frequency of the AC component included in the voltage applied to the developing roll 342. In step S6, the control unit 11 determines whether the voltage V ₂ is applied to the developing roll 342 regardless of whether the latent image is formed on the photosensitive drum 31 or the latent image is not formed. The voltage application unit 343 is controlled to apply. That is, in the wear suppression mode, the voltage V ₂ is applied to the developing roll 342 even during a period in which no latent image is formed on the photosensitive drum 31.

On the other hand, when it is determined in step S3 that the accumulated value is less than the threshold value (step S3; NO), the control unit 11 performs processing for returning to the normal mode. First, the control unit 11 determines whether the current mode is the wear suppression mode. If the current mode is not the wear suppression mode, that is, the normal mode (step S7; NO), it is not necessary to change the mode, so the control unit 11 skips the processing of step S8 and step S9. The process returns to S1. On the other hand, if it is determined that the current mode is the wear suppression mode, the control unit 11 first controls the voltage application unit 343 to change the voltage applied to the developing roll to the voltage V1 in step S8. To change to normal mode. That is, the control unit 11 returns the amplitude and / or frequency of the AC component included in the voltage applied to the developing roll 342 to the original value. In step S <b> 9, the control unit 11 controls the voltage application unit 343 so that the voltage V ₁ is applied to the developing roll 342 during the period in which the latent image is formed on the photosensitive drum 31.

Incidentally, as described above, in the wear suppression mode, a larger amount of toner is supplied to the latent image area than in the normal mode. Therefore, in the wear suppression mode, the amount of toner remaining on the surface of the photosensitive drum 31 may increase. If the amount of toner remaining on the surface of the photosensitive drum 31 is too large, the charging roll (charger 32) is contaminated, and as a result, the potential of the photosensitive drum 31 becomes non-uniform. This causes a problem that white spots and color streaks occur in the image and the image quality is deteriorated. Therefore, in this embodiment, the control unit 11 does not always operate in the wear suppression mode (that is, always applies the voltage V ₂ to the developing roll 342), but performs a process of switching from the normal mode to the wear suppression mode at a necessary timing. This prevents the residual toner from becoming excessive.

  Further, when the strain of the cleaning blade 62 is measured by the strain gauge 63, as shown in FIG. 7, the detected value is not a constant value but shifts with the passage of time due to factors such as a temperature change in the apparatus. There is a case. In this embodiment, the difference between the detection value at the time of operation of the developing unit 13 and the detection value at the time of stop is calculated, and whether or not it is necessary to change the mode is determined based on the calculated difference. Thereby, the presence or absence of the necessity of a mode change is determined more appropriately.

  Further, in this embodiment, by attaching an external additive to the photosensitive drum 31, the friction coefficient between the cleaning blade 62 and the photosensitive drum 31 is reduced, and wear of the cleaning blade 62 is suppressed. Therefore, it is not necessary to perform a wear suppression process using a so-called toner band. For this reason, in this embodiment, the amount of toner consumed is smaller than when the toner band is used to suppress wear.

2. Modifications Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be implemented in various other forms. An example is shown below. In addition, you may combine each following aspect.

2-1. Modification 1
In the above-described embodiment, the control unit 11 calculates the difference between the detected value of the strain gauge 63 when the developing unit 13 is operating and the detected value of the strain gauge 63 when the developing unit 13 is stopped, and accumulates the difference. It was determined whether to change the mode according to the value. The determination method is not limited to this. For example, the control unit 11 may perform the determination by calculating an average value of the differences and comparing the calculated average value with a predetermined threshold value. As another example, for example, the control unit 11 specifies a maximum value and a minimum value within a predetermined period of the difference, and performs the determination according to the relationship between the specified maximum value and the minimum value. May be. In short, the control unit 11 may determine whether or not the difference satisfies a predetermined condition.

  In the above-described embodiment, the control unit 11 performs control to return the mode to the normal mode when the cumulative value of the difference is less than a predetermined threshold value. The timing for returning the mode to the normal mode is not limited to this. For example, the control unit 11 may perform control to return to the normal mode after a predetermined period has elapsed since the mode was changed to the wear suppression mode. More specifically, for example, after the mode is changed to the wear suppression mode, the photosensitive drum 31 may be controlled to return to the normal mode after being rotated a predetermined number of times. As another example, the control unit 11 may perform control to return to the normal mode after a predetermined time has elapsed after changing to the wear suppression mode.

2-2. Modification 2
In the above-described embodiment, the control unit 11 performs control to change the mode to the wear suppression mode based on the detection value of the strain gauge 63. The timing at which the mode is changed to the wear suppression mode is not limited to this. For example, the control unit 11 may change from the normal mode to the wear suppression mode every time image forming processing is performed on a predetermined number of sheets. As another example, for example, the control unit 11 may change from the normal mode to the wear suppression mode every time the rotational speed of the photosensitive drum 31 exceeds a predetermined threshold. In this case, the control unit 11 may perform a process of returning the mode to the normal mode after a predetermined period has elapsed since the change to the wear suppression mode.

  Further, the user may perform an operation to change the mode using the operation unit 17. In this case, the control unit 11 performs a mode change process based on information output from the operation unit 17.

  As another example, for example, when the developing unit 13 is not operating (the image forming process is not instructed), the control unit 11 performs a predetermined period or until the image forming process is instructed. During the period, the developing unit 13 may be controlled to operate in the wear suppression mode.

2-3. Modification 3
In the above-described embodiment, in the normal mode, during the period in which the latent image is formed on the photosensitive drum 31, the voltage V ₁ is applied to the developing roller 342 and the latent image is not formed on the photosensitive drum 31. No voltage was applied to the developing roll 342. The period in which the voltage is applied to the developing roll 342 in the normal mode is not limited to the period in which the latent image is formed on the photosensitive drum 31, and the voltage V ₁ is applied to the developing roll 342 even in the period in which the latent image is not formed. May be applied. In the normal mode, the voltage V ₁ may be applied to the developing roll 342 at least during the period in which the latent image is formed on the photosensitive drum 31.

In the above-described embodiment, in the wear suppression mode, the voltage V ₂ is applied to the developing roll 342 during the period in which the latent image is formed on the photosensitive drum 31 and the period in which the latent image is not formed. The period during which the voltage is applied to the developing roll 342 in the wear suppression mode is not limited to this. For example, in the wear suppression mode, the voltage V ₂ may be applied to the developing roll 342 during a period in which a latent image is not formed on the photosensitive drum 31. In the wear suppression mode, the voltage V ₂ may be applied to the developing roll 342 at least during a period in which no latent image is formed on the photosensitive drum 31.

2-4. Modification 4
The image forming apparatus provided with the cleaning blade 62 is not limited to the tandem type of the above-described embodiment, and may be another configuration such as a rotary type. The image forming apparatus including the cleaning blade 62 is not limited to an image forming apparatus that forms an image by superimposing a plurality of color toner images, and is an image forming apparatus that forms a single color toner image. May be.

2-5. Modification 5
In the above-described embodiment, the program executed by the control unit 11 of the image forming apparatus 1 may be downloaded via a communication line such as the Internet. The program is provided in a state of being recorded on a computer-readable recording medium such as a magnetic recording medium (magnetic tape, magnetic disk, etc.), an optical recording medium (optical disk, etc.), a magneto-optical recording medium, or a semiconductor memory. May be.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Control part, 12 ... Memory | storage part, 13Y, 13M, 13C, 13K ... Developing part, 14 ... Transfer part, 15 ... Fixing part, 17 ... Operation part, 31 ... Photoconductor drum, 32 ... Charger 33 ... Exposure device 34 ... Developer 35 ... Primary transfer roll 36 ... Drum cleaner 41 ... Intermediate transfer belt 42 ... Secondary transfer roll 43 ... Belt transport roll 44 ... Backup roll 49 ... Belt cleaner, 51... Fixing belt, 63... Cleaning blade, 342.

Claims (5)

A developing roll for developing the latent image formed on the image carrier using a developer containing an external additive;
In the first mode, the voltage including the first AC component is at least during the period in which the latent image is formed, and in the second mode, in the period in which the latent image is formed and the period in which the latent image is not formed. Voltage application means for applying a voltage including a second AC component having an amplitude and / or frequency larger than the first AC component to the developing roll;
A developing device comprising: a cleaning member that cleans the image carrier. A developing roll for developing the latent image formed on the image carrier using a developer containing an external additive;
In the first mode, the voltage including the first AC component is at least during the period in which the latent image is formed, and in the second mode, the amplitude and / or the frequency is at least in the period in which the latent image is not formed. Voltage application means for applying a voltage including a second AC component larger than the AC component to the developing roll;
A cleaning member for cleaning the image carrier;
An instruction unit that instructs the voltage application unit to switch from the first mode to the second mode when a detection result of a detection unit that detects distortion of the cleaning member satisfies a predetermined condition;
A developing device. The instruction means includes a detection result of the detection means when the cleaning member is cleaning the image holding body, and a detection result of the detection means when the cleaning member is not cleaning the image holding body. If the condition is satisfied where the difference is predetermined, that instructs the voltage applying means to switch to the second mode from the first mode
The developing device according to 請 Motomeko 2. The developing device according to claim 3 , wherein the instruction unit instructs the switching when the accumulated value of the difference satisfies a predetermined condition. A developing device according to any one of claims 1 to 4 ,
An image forming apparatus comprising: transfer means for transferring an image developed by the developer onto a recording medium.

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