Imaging equipment

Abstract

An image forming apparatus is provided, which includes: an image bearing member; an exposure unit; a developing member that can rotate at a different rotation speed from the image bearing member; a developer supplying member; a developing voltage applying unit; a supply voltage applying unit; and a control unit. The control unit controls the execution of the following operations: an image forming operation in which a developer image is formed by supplying a developer on the image bearing member; and a cleaning operation in which a substance attached to the image bearing member is removed using the developing member. In the cleaning operation, the control unit controls the developing voltage applying unit or the supply voltage applying unit so that a cleaning force using the developing member becomes greater than a cleaning force in the image forming operation.

Description

Technical Field

[0001] The present invention relates to an imaging device. Background Art

[0002] In an image forming apparatus, an image is formed by developing an electrostatic latent image formed on a surface of an image bearing member with a developer on a developer bearing member. In this image forming, there is known a configuration of a contact developing system in which an image is developed in a state in which a developer bearing member is in contact with an image bearing member. For a developer bearing member having such a configuration, a developing roller having an elastic layer on an outer peripheral surface of a shaft core and being driven to rotate is used.

[0003] On the other hand, in order to reduce the size and cost of an image forming apparatus by minimizing components, an image forming apparatus without an image bearing member cleaner that does not include a cleaning unit for removing and collecting toner remaining on an image bearing member has been proposed.

[0004] In the case of a cleaner-less type imaging apparatus, untransferred toner and toner causing fogging directly enter between the photosensitive drum and the charging roller, so stress may be generated between the photosensitive drum and the charging roller, and melted toner may adhere to the photosensitive drum. If melted toner adheres, exposure may be interrupted and blank spots may be generated in the image. In addition, if the melted portion adheres to the photosensitive drum continuously in the circumferential direction, white streaks may appear in the image.

[0005] In the cleaner-less system, the developing part needs to collect the toner that is not transferred to form an image, but unless a large force is applied in the developing part, the toner that is melted and attached to the photosensitive drum cannot be removed and collected. Usually the developing roller is covered with a toner layer, but if the surface layer of the developing roller is exposed from the toner layer, the photosensitive drum can be scraped more strongly, so that the toner on the photosensitive drum can be removed.

[0006] Japanese Patent No. 4669557 discloses an apparatus including a reset mode in which the applied voltage difference between the developing roller and the toner supply roller is reduced compared to during printing, thereby changing the amount of toner on the developing roller when no image is formed. In the apparatus disclosed in Japanese Patent No. 4669557, the amount of toner on the developing roller is reduced by reducing the applied voltage difference between the developer carrying member and the toner supply roller in the reset mode, so that problems such as fogging do not occur when the amount of toner on the developing roller increases. Therefore, the amount of toner on the developing roller can be maintained at a constant level for a long time. Summary of the invention

[0007] However, Japanese Patent No. 4669557 does not disclose the peripheral speed difference between the developing roller and the photosensitive drum, and its purpose is not to scrape off the molten toner attached to the photosensitive drum. Therefore, if the method disclosed in Japanese Patent No. 4669557 is directly applied, the molten toner attached to the photosensitive drum may not be sufficiently removed, or the photosensitive drum may be excessively rubbed by the developing roller, whereby the developer may accelerate deterioration.

[0008] In view of the above circumstances, an object of the present invention is to prevent fused toner from adhering to a photosensitive drum of an image forming apparatus, thereby obtaining good image quality.

[0009] The present invention provides an imaging device, comprising:

[0010] an image bearing member configured to be rotatable;

[0011] an exposure unit configured to expose the surface of the image bearing member to form an electrostatic latent image on the surface of the image bearing member;

[0012] a developing member configured to be rotatable, to be in contact with the image bearing member to form a developing portion in which a developer is supplied to the surface of the image bearing member, and to rotate at a rotation speed different from that of the image bearing member;

[0013] a developer supplying member configured to supply developer to the surface of the developing member;

[0014] a developing voltage applying unit configured to apply a developing voltage to the developing member;

[0015] a supply voltage applying unit configured to apply a supply voltage to the developer supplying member; and

[0016] a control unit configured to control the developing voltage applying unit and the supply voltage applying unit, wherein

[0017] The control unit performs control to be able to perform: an image forming operation in which a developer image is formed on the surface of the image bearing member by supplying a developer from the developing member to an electrostatic latent image formed on the surface of the image bearing member; a cleaning operation which is an operation other than the image forming operation and removes substances attached to the surface of the image bearing member using the developing member,

[0018] In a case where the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that a cleaning force of cleaning substances attached to the surface of the image bearing member using the developing member is greater than that in a case where the image forming operation is performed, and

[0019] When the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that an amount of developer supplied from the developer supplying member to the developing member is reduced compared with a case where the image forming operation is performed.

[0020] The present invention also provides an imaging device, the imaging device comprising:

[0021] an image bearing member configured to be rotatable;

[0022] an exposure unit configured to expose a surface of the image bearing member to form an electrostatic latent image on the surface of the image bearing member;

[0023] a developing member configured to be rotatable, to be in contact with the image bearing member to form a developing portion in which a developer is supplied to the surface of the image bearing member, and to rotate at a rotation speed different from that of the image bearing member;

[0024] a developer supplying member configured to supply developer to the surface of the developing member;

[0025] a developing voltage applying unit configured to apply a developing voltage to the developing member;

[0026] a supply voltage applying unit configured to apply a supply voltage to the developer supplying member; and

[0027] a control unit configured to control the developing voltage applying unit and the supply voltage applying unit, wherein

[0028] the control unit performs control so as to be able to perform: an image forming operation in which a developer image is formed on the surface of the image bearing member by supplying a developer from the developing member to an electrostatic latent image formed on the surface of the image bearing member; and a cleaning operation which is an operation other than the image forming operation and removes substances attached to the surface of the image bearing member using the developing member,

[0029] In a case where the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that a cleaning force for cleaning substances attached to the surface of the image bearing member using the developing member becomes greater than a cleaning force in a case where the image forming operation is performed, and

[0030] The control unit is capable of varying the cleaning force during the cleaning operation.

[0031] According to the present invention, it is possible to prevent fused toner from adhering to a photosensitive drum of an image forming apparatus, so that good image quality can be obtained.

[0032] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic configuration diagram showing an example of an imaging device of Example 1;

[0034] FIG. 2A to FIG. 2C is a diagram showing an example of a developing roller used in the image forming apparatus of Example 1 and a scraping operation thereof;

[0035] Figure 3 is a diagram showing melt-bonding scraping control for the image forming apparatus of Example 1; and

[0036] Figure 4 is a diagram showing a control block of the imaging device of Example 1. DETAILED DESCRIPTION

[0037] Embodiments of the present invention will be described in detail using examples with reference to the accompanying drawings. The size, material, shape and relative position of the components described in the embodiments may be appropriately changed according to the configuration and various conditions of the equipment to which the present invention is applied. In other words, these details are not intended to limit the scope of the present invention to the following embodiments.

[0038] Example 1

[0039] Imaging Equipment Overview

[0040] Will refer to Figure 1 The overall configuration of an electrophotographic image forming apparatus (hereinafter referred to as "image forming apparatus") according to Example 1 of the present invention and its image forming operation are described. Figure 1 is a schematic cross-sectional view showing the overall configuration of an imaging apparatus 100 according to an embodiment of the present invention.

[0041] In this embodiment, Figure 1In the figure, image forming stations (image forming units) for four colors (yellow, magenta, cyan, and black) are arranged from left to right. Each image forming station has an electrophotographic image forming mechanism of the same configuration, and the only difference is the color of the developer (hereinafter referred to as "toner") 90 contained in each developing device. In the following description, the suffixes Y (yellow), M (magenta), C (cyan), and K (black) attached to each reference numeral to indicate the color of the component will be omitted unless it is particularly necessary to distinguish.

[0042] As the main structure, each imaging station includes a photosensitive drum 1 (image bearing member), a charging roller 2 (charging unit), a developing device 4, a primary transfer device 51, etc. The exposure device 3 can be shared by each imaging station, or can be set in each imaging station. In the present embodiment, the photosensitive drum 1, the charging roller 2 and the developing device 4 are integrated into a processing box 8, and the processing box 8 is constructed to be detachable from the main unit of the imaging device (the part of the imaging device 100 when the processing box 8 is removed). However, the processing box of the present invention may include at least a photosensitive drum 1 and a developing device 4, and the photosensitive drum 1 and the developing device 4 can be detached from the main unit of the device as a whole. The developing device 4 can be constructed to be able to be detached independently from the main unit of the device or from the processing box 8. In addition, the photosensitive drum 1 and the developing device 4 can be fixed on the main unit of the imaging device so that the user does not need to replace them.

[0043] The photosensitive drum 1 is a rotatable cylindrical photosensitive member and moves about its axis in the direction of the arrow ( Figure 1 In this embodiment, the outer peripheral surface is driven to rotate at a speed of 180 mm / sec. Figure 4 As shown, the photosensitive drum 1 is rotated by the rotational driving force of the motor 15 controlled by the control unit 25. The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. In the present embodiment, the charging roller 2 is a conductive roller having a conductive rubber layer formed on a core metal. The charging roller 2 is in parallel contact with the photosensitive drum 1 at a predetermined pressure and rotates as the photosensitive drum 1 rotates. A charging voltage can be applied to the charging roller 2 from the power supply device 67 (power supply unit). In the present embodiment, the photosensitive drum 1 is charged by applying a DC voltage of -1150V to the charging roller 2, in which case the surface potential of the photosensitive drum 1 is approximately -500V.

[0044] The exposure device 3 (exposure unit) acquires an image signal from the control unit 65, and scans the surface of the photosensitive drum 1 with laser light according to the image signal. Thus, an electrostatic latent image is formed on the charged photosensitive drum 1 according to the image signal. The image signal can be acquired from an external information processor (not shown). For the control unit 65, for example, an information processor such as a control circuit including a computing resource (e.g., a processor, a memory) can be used.

[0045] The developing device 4 supplies toner 90 to the electrostatic latent image on the photosensitive drum 1 to make the electrostatic latent image visible as a toner image (developer image). In the present embodiment, the developing device 4 is a contact development type reversal developing device that contains toner 90 as a single-component developer, and the toner 90 has a negative normal charging polarity (charging polarity for developing the electrostatic latent image).

[0046] The developing device 4 includes a rotatable developing roller 42 (developing member), a toner supply roller 43 (developer supply member) and a regulating blade 44 (developer regulating member). The toner supply roller 43 is an elastic sponge roller in which a foam member is arranged on the periphery of a conductive core metal. The toner supply roller 43 is arranged to contact the developing roller 42 with a predetermined degree of pressure. The toner 90 supplied by the toner supply roller 43 and held by the developing roller 42 has a layer thickness regulated by the regulating blade 44 and is provided for a developing process. Here, the regulating blade 44 not only has a function of regulating the layer thickness of the toner 90 on the developing roller 42, but also has a function of a developer charging unit that provides a predetermined charge to the toner 90 on the developing roller 42.

[0047] The power supply device 67 can be used as: a developing voltage applying unit 671, which applies a developing voltage to the developing roller 42 included in the developing device 4; a supply voltage applying unit 672, which applies a supply voltage to the colorant supply roller 43; and a control voltage applying unit, which applies the control voltage to the control scraper 44. Figure 4 An example of a control system of a power supply device 67 related to the control performed by the control unit 25 is shown. For the power supply device 67, a charging power supply for a charging roller and a developing power supply for a developing device can be arranged independently. In this case, the charging power supply and the developing power supply can be regarded as a power supply unit together. In addition, the developing power supply for a developing roller and the power supply for a toner supply roller can be set independently. In this case, the charging power supply, the developing power supply, and the power supply for a toner supply roller can be regarded as a power supply unit together. When performing image transfer, the power supply device 67 can be used to supply power. The transfer power supply can be set independently of the power supply device 67. The power supply device 67 of this embodiment changes the voltage to be applied to each constituent element according to the control of the control unit 65.

[0048] The developing roller 42 is moved in the direction of the arrow ( Figure 1 The developing roller 42 and the surface of the photosensitive drum 1 are driven to rotate clockwise in the same direction. Figure 4As shown, the developing roller 42 and the toner supply roller 43 are rotated by the rotational driving force generated by the motor 16 controlled by the control unit 25. The developing roller 42 can rotate at a rotation speed different from that of the photosensitive drum 1. In this embodiment, in order to obtain a suitable image density, the developing roller 42 is rotationally driven so that the moving speed of the surface of the developing roller 42 is faster than the moving speed of the surface of the photosensitive drum 1. The developing device 4 is pushed toward the photosensitive drum 1 by a pushing device (not shown), and as a result, the developing roller 42 is pressed against the photosensitive drum 1. As a result, the surface of the developing roller 42 is deformed and a developing nip (developing portion) is formed to perform stable development in a stable contact state.

[0049] like Figure 2A As shown, the developing roller 42 is composed of a base layer 422 and a surface layer 423 formed on the outer periphery of the shaft core 421. Figure 2B As shown, the surface layer 423 has a structure in which coarse particles 423b are dispersed in the surface layer binder resin 423a. Therefore, a plurality of concave portions and a plurality of convex portions are formed on the surface of the surface layer 423 for conveying the toner. The ten-point average roughness RzJIS of the convex portion is greater than the volume average particle size of the toner 90, and in the case of the present embodiment, the volume average particle size of the toner is 7μm, and the RzJIS of the surface layer 423 is 10μm. The RzJIS of the surface layer of the developing roller is preferably in the range of about 8μm to 30μm.

[0050] In order to measure the ten-point average roughness RzJIS of the developing roller 42 of the present invention, for example, a contact surface roughness meter SurfCoder SE3500 (manufactured by Kosaka Laboratory) can be used. The measurement conditions used here are: cutoff value 0.8mm; measurement length 2.5mm; feed speed 0.1mm / s. For each developing roller, three arbitrary points arranged at different positions in the longitudinal direction are measured and the average value of the obtained measured values ​​is used as the RzJIS of the developing roller 42.

[0051] For the volume average particle size of toner 90, a measurement value measured by the following method can be used. For the measuring device, Coulter Multi-Sizer IV (manufactured by Beckman Coulter) can be used. For the electrolyte, a high-grade sodium chloride dissolved in deionized water at a mass percentage of about 1%, such as ISOTON II (manufactured by Beckman Coulter) can be used. For the measuring method, 0.5 ml of alkylbenzene sulfonic acid is added to 100 ml of an electrolyte solution as a dispersant, and 10 mg of a measuring sample is added thereto. The electrolyte in which the measuring sample is suspended is then subjected to a dispersion treatment for 1 minute, and the volume particle size distribution is measured using a 30 μm hole of the measuring device, and the median (D50) of the measurement result is regarded as the volume average particle size.

[0052] The toner image formed on the photosensitive drum 1 is electrostatically transferred to the intermediate transfer belt 53 by the primary transfer device 51 as one of the transfer members. Each color of the toner image is sequentially transferred to the intermediate transfer belt 53, overlapping each other to form a full-color toner image. Then, the full-color toner image is transferred to the recording material (transferred member) by the secondary transfer device 52 as another transfer member, and the secondary transfer device 52 is different from the primary transfer device 51. Then, the toner image on the recording material is pressurized and heated by the fixing device 6, whereby the toner image is fixed to the recording material and the recording material is discharged as an image forming product.

[0053] The belt cleaning device 7 is provided on the downstream side of the secondary transfer apparatus 52 in the moving direction of the intermediate transfer belt 53 to remove and collect the untransferred toner 90 remaining on the intermediate transfer belt 53 .

[0054] In the present embodiment, a system without an image bearing member cleaner is used, in which the untransferred colorant 90 remaining on the surface of the photosensitive drum 1 is collected by the developing device 4 without providing a dedicated cleaner device for the photosensitive drum 1. This means that before the surface of the photosensitive drum 1 passing through the position facing the primary transfer device 51 (primary transfer position) reaches the contact position (charging position) with the charging roller 2, no member is in contact with the photosensitive drum 1. Thus, when the developing roller 42 of the developing device 4 contacts the photosensitive drum 1, the untransferred colorant 90 remaining on the photosensitive drum 1 after the image is formed can be collected by the developing device 4. In the case of using such a cleaner-free system, it is preferable to use a non-magnetic single-component developer for the colorant 90. However, the present invention is not limited to the above-mentioned configuration to achieve the effects of the present invention.

[0055] The image forming apparatus 100 includes a detection device (not shown) for detecting a printing state and a printing environment. The control unit 65 can perform an image forming operation or a scraping operation described later, which is an operation other than the image forming operation, according to the detected printing state and printing environment.

[0056] control

[0057] The operation of the image forming apparatus according to the present invention will be described. When forming an image, -300 V is applied to the developing roller 42. On the other hand, -400 V is applied to the regulating blade 44, and -400 V is also applied to the toner supply roller 43. Since the charging polarity of the toner 90 of the present invention is a negative charging polarity, the toner can be easily supplied from the toner supply roller 43 to the developing roller 42.

[0058] Control is performed in the photosensitive drum 1 so that the surface potential of the image printing portion where the toner image is formed is located on the normal charging polarity side of the toner 90 and the absolute value of the surface potential becomes lower than the applied voltage applied to the developing roller 42. On the other hand, in the non-image printing portion where the toner image is not formed, the surface potential is controlled to be a drum potential of -500 V. Thus, in the image printing portion, the toner charged by the potential difference with respect to the developing roller 42 is developed.

[0059] In the primary transfer portion formed by the primary transfer device 51, the toner image developed on the photosensitive drum is transferred onto the intermediate transfer belt 53, but the toner having a low charge level or the toner charged with a polarity opposite to the normal charge polarity is not transferred and enters between the charging roller 2 and the photosensitive drum 1. The toner causing fogging also enters between the charging roller 2 and the photosensitive drum 1.

[0060] As a result, the toner between the charging roller 2 and the photosensitive drum 1 may be stressed, and the toner may be deformed and adhere to the photosensitive drum 1. In the portion of the photosensitive drum to which the toner adheres (indicated by the X symbol), the transferability is low at the next image formation, which means that untransferred toner is more likely to be generated and grow as an adhered substance adhered to the photosensitive drum.

[0061] On the portion of the photosensitive drum to which the melted toner adheres, the laser beam emitted from the exposure device 3 is blocked, so the surface potential of the photosensitive drum 1 does not reach the predetermined potential, and the image density in the solid color printing portion decreases. In particular, if the melted toner is continuously adhered in the rotation direction of the photosensitive drum, white streaks are generated in the image. To prevent this, the toner remaining on the photosensitive drum must be removed.

[0062] Melt-bond scraping operation

[0063] The operation of preventing the growth of the melt-bonded substance on the drum according to the present embodiment will be described. Each voltage in the image forming operation is as follows.

[0064] Voltage V_DEV applied to the developing roller 42: -300 V

[0065] Voltage V_S applied to the toner supply roller 43: -400 V

[0066] In other words, the absolute value of the developing voltage is smaller than the absolute value of the supply voltage in the image forming operation. Therefore, the applied voltage difference between the toner supply roller 43 and the developing roller 42 is -100 V. In this embodiment, the normal charging polarity of the toner is negative, so the potential difference V_DIFF generated as the driving force supplied from the toner supply roller 43 to the developing roller 42 is as follows.

[0067] Potential difference V_DIFF: +100V

[0068] When the image forming operation on the intermediate transfer belt 53 is ended for each print job, the control unit 65 changes the applied voltage V_S applied to the toner supply roller 43 from -400V, which is a value for image forming, to -350V, and allows the toner supply roller 43 to rotate for a predetermined time. As a result, the potential difference V_DIFF changes from 100V to 50V, that is, the pressure acting on the toner from the toner supply roller 43 to the developing roller 42 becomes weaker than the pressure during image forming, and the amount of toner on the developing roller is reduced compared with the amount of toner during image forming. In other words, the potential difference in the scraping operation case is smaller than the potential difference in the image forming operation case. Hereinafter, this control of reducing the potential difference V_DIFF to be smaller than the potential difference in the image forming case so that the developing roller 42 and the photosensitive drum 1 are in contact and rotated in this state is referred to as a "scraping operation". The "scraping operation" mentioned here is given as a preferred example of a "cleaning operation" for cleaning the toner on the photosensitive drum 1.

[0069] As for the potential relationship, the applied voltage applied to the toner supply roller 43 when scraping is performed can be set to -250V, so that the potential difference V_DIFF becomes -50V, and the toner can be returned from the developing roller 42 to the toner supply roller 43 side. When the image forming operation is performed, the absolute value of the developing voltage can be set to be smaller than the absolute value of the supply voltage, and when the scraping operation is performed, the potential difference between the developing voltage and the supply voltage can be set to zero. Alternatively, when the image forming operation is performed, the absolute value of the developing voltage can be set to the absolute value of the supply voltage or less, and when the scraping operation is performed, the absolute value of the developing voltage can be set to be greater than the absolute value of the supply voltage.

[0070] For example, when the normal charging polarity of the colorant is positive, the applied voltage applied to the developing roller 42 can be set to +300V when implementing the imaging operation, and the applied voltage applied to the colorant supply roller 43 can be set to +400V. When implementing the scraping operation, the applied voltage applied to the colorant supply roller 43 can be changed to +350V.

[0071] The end of the image forming operation on the intermediate transfer belt 53 refers to the time when the rear end of the image at each image forming station is transferred to the intermediate transfer belt. In the present embodiment, the scraping operation is started at all the image forming stations Y, M, C, and K at the same time to simplify the control. Therefore, the time that is changed is the time when the rear end of the image at the image forming station K located on the most downstream side is transferred to the intermediate transfer belt 53. However, the scraping operation may be started sequentially from the image forming stations located upstream where the image forming operation ends.

[0072] Figure 3: is a timing chart in the case where the scraping operation of each image forming station is started at the same time. The horizontal axis represents the elapsed time. The vertical axis represents the absolute value of the voltage and represents the applied voltage V_DEV applied to the developing roller 42, the applied voltage V_S1 applied to the toner supply roller 43 during image formation, and the applied voltage V_S2 applied to the toner supply roller 43 during scraping.

[0073] The image forming operation starts at time t1, and the applied voltage applied to the toner supply roller 43 is set to V_S1. Then, at time t2_1 to t2_4, the formation of the Y image, the M image, the C image, and the K image is sequentially completed. At time t2_4, the scraping action is started at the same time at each image forming station, and the applied voltage applied to the toner supply roller 43 is changed to V_S2. At time t3, when a predetermined scraping time has passed, the scraping operation is completed. Then the print end operation starts, and the print end operation is completed at t4.

[0074] Here, the meaning of the scraping operation will be described. In the case where the applied voltage V_S applied to the toner supply roller 43 in the image formation is on the supply side (in the case where the applied voltage difference V_DIFF>0), as in the case of the present embodiment, if the applied voltage V_S applied to the toner supply roller 43 in the scraping operation becomes closer to the applied voltage of the developing roller 42 than the applied voltage V_S in the image formation, it is difficult to supply the toner to the developing roller 42 and the supply amount is reduced. As a result, the amount of toner on the developing roller is reduced, and the concavo-convex parts on the surface of the developing roller 42 are more likely to directly contact the photosensitive drum 1.

[0075] For example, if the applied voltage V_S applied to the toner supply roller 43 changes from −400 V to −350 V, the toner on the developing roller decreases and a portion of the surface layer of the developing roller is exposed from the toner coated on the developing roller 42 after the regulating blade 44 passes. Figure 2B Indicates the portion where the toner is exposed from the convex portion of the coating developing roller surface layer ( Figure 2B and Figure 2C The exposed portion P) in the photosensitive drum and the convex portion are about to scrape off the substance X that has melted and adhered to the photosensitive drum. Figure 2CRepresents the state immediately after the exposed portion P scrapes off most of the substance X that has melted and adhered to the photosensitive drum. Here, when the circumferential speed of the developing roller 42 is V1 and the circumferential speed of the photosensitive drum 1 is V2, V1 and V2 have a circumferential speed difference and in this embodiment, V1>V2. In this way, if the portion exposed from the toner coating on the surface layer of the developing roller contacts the photosensitive drum 1 and rotates at a circumferential speed different from the circumferential speed of the photosensitive drum 1, the substance that has melted and adhered to the photosensitive drum can be scraped off. This operation of the developing roller 42 scraping and removing the toner 90 on the photosensitive drum 1 is referred to as a "scraping operation". In the following, the ability to scrape the toner 90 on the photosensitive drum 1 in the scraping operation is referred to as a "scraping force". The "scraping force" mentioned here is given as a preferred example of the "cleaning force" when cleaning the toner on the photosensitive drum 1. The control unit can increase the scraping force to increase the amount of toner to be scraped or reduce the scraping force to reduce the amount of toner to be scraped, for example, by controlling the voltage to be applied to each constituent element, as described below.

[0076] In the present embodiment, the applied voltage V_S applied to the toner supply roller 43 in the scraping operation becomes -350 V for all the image forming stations, but the applied voltage V_S may be controlled for each image forming station.

[0077] Furthermore, in the present embodiment, the applied voltage V_S applied to the toner supply roller (i.e., -400 V during image formation) is changed to -350 V during scraping. However, the present invention is not limited thereto, as long as the potential difference V_DIFF is reduced by performing control to form the exposed portion P. For example, the applied voltage V_DEV applied to the developing roller 42 may be changed while the applied voltage V_S applied to the toner supply roller 43 is fixed, or both the applied voltage V_S applied to the toner supply roller 43 and the applied voltage V_DEV applied to the developing roller 42 may be changed.

[0078] Then, in a state where the applied voltage V_S applied to the colorant supply roller 43 is lower than that during image formation, the developing roller 42 contacts the photosensitive drum 1 and rotates to perform a scraping operation for a predetermined time, and then the developing roller 42 is separated from the photosensitive drum 1 and a printing end operation is performed.

[0079] Details of Example 1

[0080] As shown in Table 1, Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-3 are the results when the printing operation was carried out for 6000 sheets and then the formed solid black images were evaluated by combining various printing conditions as follows. The peripheral speed difference between the peripheral speed V1 of the developing roller surface and the peripheral speed V2 of the photosensitive drum surface was 70 mm / s.

[0081] Printing environment (room temperature): 15℃ to 30℃

[0082] Number of prints per job: 1 sheet / 2 sheets

[0083] Voltage V_S applied to toner supply roller 43: -400 V / -350 V

[0084] Applied voltage change time (scraping time after each operation): 1.1s to 6s

[0085] For image quality, the results of determining the extent of white streaks caused by melt adhesion are shown in the "melt adhesion white streak results" of Table 1. Here, ○ indicates no problem, Δ indicates slight white streaks that do not cause practical problems, and x indicates white streaks that cause problems. Prolonging the scraping time can increase the scraping force, but extending the scraping time indefinitely accelerates the degradation of the toner in the contact portion between the control blade 44 or the developing roller 42 and the photosensitive drum 1, and produces unevenness of a pure black image in the second half of the durability test. The results are shown in the "development degradation results" of Table 1. Here, ○ indicates no problem, and x indicates that development degradation is observed.

[0086] [Table 1]

[0087]

[0088] Description of Examples 1-1 to 1-3

[0089] In Example 1-1, the number of prints per job is 1, the applied voltage V_S applied to the toner supply roller 43 is -350V, and the scraping time is 1.8 seconds. In Example 1-2, the number of prints per job is 2, and the scraping time is 2.5 seconds. In Example 1-3, the number of prints per job is 2, and the scraping time is 1.8 seconds. The room temperature of the printing environment of Examples 1-1 to 1-3 is 15°C.

[0090] According to the comparison between Example 1-1 and Example 1-3, if the number of prints per job is high, small blank spots are generated even if the scraping time is the same. This is because the interval between scraping operations increases and more molten deposits accumulate. In the case where the number of prints per job is 2, if the scraping time is increased to 2.5 seconds or longer, the growth of molten deposits can be suppressed, as shown in Example 1-2.

[0091] Description of Examples 1-4 and 1-5

[0092] Now, the case where the designated printing environment is a higher temperature will be considered. In Example 1-4, when the designated printing environment room temperature is 23°C, the applied voltage change time is set to 1.6 seconds. In Example 1-5, the designated printing environment room temperature is 30°C. In the case of Example 1-5, when scraping is performed after image formation, constant rotation is maintained while the applied voltage V_S to the toner supply roller 43 does not change compared to the applied voltage V_S during image formation, and the scraping time is set to 1.1 seconds.

[0093] According to the comparison of Examples 1-3 to 1-5, if the temperature in the printing environment becomes lower, the scraping time required to suppress the melt-adhesion becomes longer. This is because in a low temperature environment, the deformation followability of the charging roller is reduced, and a greater stress is applied to the toner, which makes it easier for the toner to deform and melt-adhese. On the other hand, in Example 1-5 where the temperature is particularly high, even if the applied voltage V_S applied to the toner supply roller 43 is not changed, the white streaks can be suppressed with a short scraping time.

[0094] Description of Comparative Example 1-1

[0095] Each comparative example will now be described. In comparative examples 1-1 to 1-3, the specified printing environment room temperature is 15°C. In comparative example 1-1, the scraping time is 1.5 seconds, and the remaining conditions are the same as those of example 1-1. Comparison of example 1-1 and comparative example 1-1 shows that if the scraping time is increased, the generation of melt adhesion can be suppressed. This is because in a state where the applied voltage difference V_DIFF between the developing roller 42 and the toner supply roller 43 is reduced, the distance at which the developing roller 42 and the photosensitive drum 1 rub against each other increases, and the effect of scraping the molten material attached to the photosensitive drum can be increased. In order to scrape each part of the photosensitive drum 1 in the circumferential direction, the scraping time of one scraping operation requires at least the time for the photosensitive drum 1 to rotate one circle.

[0096] Description of Comparative Example 1-2

[0097] In Comparative Example 1-2, the number of prints per job is 2, the applied voltage V_S to the toner supply roller 43 is the same as the applied voltage during image formation, and the scraping time is 2.5 seconds, which is the same as Example 1-2. Comparison of Example 1-2 and Comparative Example 1-2 shows that if the applied voltage V_S to the toner supply roller 43 in scraping is not changed compared to the applied voltage in image formation, white streaks are generated due to melt adhesion.

[0098] Description of Comparative Examples 1-3

[0099] In Comparative Example 1-3, the number of prints per job was 2 and the scraping time was 6 seconds. The scraping force was sufficient, but the development rotation time per job became longer, so the time for the toner to rub inside the development part and at the contact portion between the development roller 42 and the photosensitive drum 1 became longer. As a result, the toner deteriorated and unevenness occurred in the solid black image.

[0100] As described above, in a state where the photosensitive drum 1 and the developing roller 42 have a circumferential speed difference, the voltage to be applied to the developing roller 42 and the colorant supply roller 43, the scraping time (contact rotation time) and other conditions are set according to the printing environment and the printing job conditions, and then the scraping operation is performed, so that the portion exposed from the colorant coating on the surface of the developing roller can remove the molten material attached to the surface of the photosensitive drum.

[0101] Example 2

[0102] Example 2 will be described. Description of the same parts as Example 1 is omitted. In Example 2, when the number of prints per job is high, the applied voltage V_S to the toner supply roller 43 is changed to increase the scraping force. Specifically, when the scraping operation is performed, when the number of prints per job is high, the potential difference V_DIFF of the applied voltage between the developing roller 42 and the toner supply roller 43 in the direction of pressing the toner from the toner supply roller 43 toward the developing roller 42 is reduced. For example, when the potential difference V_DIFF in imaging is +100V, if the number of prints per job is 2, V_DIFF is set to +50V, and if the number of prints per job is 3, V_DIFF is set to 0V. As the potential difference V_DIFF decreases, the amount of toner on the developing roller is reduced, and the concave and convex parts on the surface of the developing roller 42 are exposed more, which means that the scraping force increases.

[0103] The test results of Example 2 are shown in Table 2. In Example 2, the scraping time was a constant value of 1.8 seconds. The peripheral speed difference between the surface of the developing roller and the surface of the photosensitive drum was 70 mm / s. The designated printing environment room temperature was 15°C.

[0104] [Table 2]

[0105]

[0106] Details of Example 2

[0107] In Example 2-1, the number of prints per job is 2, the applied voltage to the toner supply roller 43 during scraping is set to -350 V, and the scraping operation is performed for 1.8 seconds after each job ends (the conditions are the same as those of Example 1-3). In Example 2-2, the applied voltage to the toner supply roller during scraping is set to -300 V. In Example 2-3, the number of prints per job is 3, and the applied voltage during scraping is -300 V.

[0108] Details of Comparative Example 2

[0109] In Comparative Example 2-1, the number of prints per job was 3, and the applied voltage to the toner supply roller 43 during scraping was set to -350 V. Compared with Example 2-1, the number of prints per job was higher.

[0110] Comparison between Example 2 and Comparative Example 2

[0111] As shown in the comparison between Example 2-1 and Example 2-2, the image was slightly fused in the case of V_S = -350 V (potential difference V_DIFF = +50 V), but was not fused in the case of V_S = -300 V (potential difference V_DIFF = 0 V). By reducing the potential difference V_DIFF generated between the developing roller 42 and the toner supply roller 43, the scraping force can be further increased.

[0112] As shown in comparison of Examples 2-1 and 2-3, if the applied voltage V_S to the toner supply roller 43 is changed from -350 V to -300 V to increase the scraping force during scraping, a slight melt-bonding state can be maintained for the image even if the number of prints per job is increased from 2 to 3.

[0113] On the other hand, comparison of Example 2-1 and Comparative Example 2-1 shows that if the applied voltage V_S to the toner supply roller 43 is not changed from -350 V during scraping, white streaks appearing on the image due to melt-bonding worsen when the number of prints per job increases from 2 to 3.

[0114] Example 3

[0115] Example 3 will be described. The description of the same parts as Examples 1 and 2 is omitted. In Example 3, when the number of prints per job is high, the peripheral speed difference between the developing roller 42 and the photosensitive drum surface is increased to be higher than the peripheral speed difference in image formation, and the surface distance is increased to increase the scraping force. Specifically, when the number of prints per job is high, the peripheral speed difference between the developing roller 42 and the photosensitive drum 1 is increased in the scraping operation.

[0116] The test results of Example 3 are shown in Table 3. The scraping time was a constant value of 1.8 seconds, and the applied voltage V_S applied to the toner supply roller 43 during scraping was always -350 V. The designated printing environment room temperature was 15°C.

[0117] [Table 3]

[0118]

[0119] Details of Example 3

[0120] In Example 3-1, white streaks due to melt-bonding are shown when the developing roller 42 and the photosensitive drum 1 rotate with a peripheral speed difference of 70 mm / s during scraping (the developing roller rotates faster). Here, only slight white streaks are generated in the image without causing any practical problems. Example 3-2 shows the results of white streaks due to melt-bonding when the peripheral speed difference is 120 mm / s. In Example 3-2, no white streaks are generated. Example 3-3 shows the results when the peripheral speed difference is 120 mm / s and the number of prints per job is 3. In Example 3-3, the white streaks due to melt-bonding are at a slight level.

[0121] Details of Comparative Example 3

[0122] In Comparative Example 3-1, the peripheral speed difference between the developing roller 42 and the photosensitive drum 1 was 70 mm / s, and the number of prints per job was 3 (same as Comparative Example 2-1). In the case of Comparative Example 3-1, white streaks due to melt adhesion were observed.

[0123] Comparison between Example 3 and Comparative Example 3

[0124] As shown in the comparison between Example 3-1 and Example 3-2, the scraping force can be increased by increasing the peripheral speed difference. In addition, as shown in the comparison between Example 3-1 and Example 3-3 or the comparison between Example 3-1 and Comparative Example 3-1, as the number of prints per job increases, the peripheral speed difference needs to be increased to increase the scraping force.

[0125] Example 4

[0126] The present invention can be appropriately performed by setting appropriate operating conditions according to preconditions such as the printing environment and print job settings and operating the various constituent elements of the image forming apparatus by the control unit 65. For this purpose, it is preferable to pre-store a table or a mathematical formula that associates the preconditions (e.g., printing environment, print job settings) and the operating settings (e.g., applied voltage, scraping time, peripheral speed difference) with each other in a memory or the like. The control unit 65 acquires print job setting information based on the print job instructed by the user, refers to the memory using the print job as a keyword, and sets appropriate operating conditions.

[0127] More preferably, the image forming apparatus includes an environment information acquisition unit 69. The control unit 65 uses the printing environment information detected by the environment information acquisition unit 69 as a key to refer to the memory and sets appropriate operating conditions. The environment information acquisition unit 69 may include a thermometer.

[0128] As described above, according to various examples of the present invention, operating conditions (such as voltages applied to the developing roller 42 and the toner supply roller 43, the scraping time (contact rotation time), and the peripheral speed difference between the photosensitive drum 1 and the developing roller 42, respectively) are set according to preconditions (printing conditions) such as the printing environment (room temperature) and the print job setting (the number of prints per job), and a scraping operation is performed based on the operating conditions. As a result, an exposed portion P is formed on the surface of the developing roller, and the molten material attached to the surface of the photosensitive drum can be removed. In particular, in a cleaner-free imaging device that does not include a cleaning blade for removing the toner 90 remaining on the photosensitive drum 1, performing the scraping operation described in this embodiment is very effective for removing the attached material. As long as the molten material attached to the surface of the photosensitive drum 1 can be removed, the combination of conditions to be set is not limited to the above examples and can be set in any combination.

[0129] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An imaging device, comprising: an image bearing member configured to be rotatable; an exposure unit configured to expose the surface of the image bearing member to form an electrostatic latent image on the surface of the image bearing member; a developing member configured to be rotatable, to be in contact with the image bearing member to form a developing portion in which a developer is supplied to the surface of the image bearing member, and to rotate at a rotation speed different from that of the image bearing member; a developer supplying member configured to supply developer to the surface of the developing member; a developing voltage applying unit configured to apply a developing voltage to the developing member; a supply voltage applying unit configured to apply a supply voltage to the developer supplying member; and a control unit configured to control the developing voltage applying unit and the supply voltage applying unit, wherein The control unit performs control to be able to perform: an image forming operation in which a developer image is formed on the surface of the image bearing member by supplying a developer from the developing member to an electrostatic latent image formed on the surface of the image bearing member; a cleaning operation, the cleaning operation being an operation other than the image forming operation, of removing substances attached to the surface of the image bearing member using the developing member, In a case where the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that a cleaning force of cleaning substances attached to the surface of the image bearing member using the developing member is greater than that in a case where the image forming operation is performed, and When the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that an amount of developer supplied from the developer supplying member to the developing member is reduced compared with a case where the image forming operation is performed.

2. The imaging device according to claim 1, wherein The control unit can increase the amount of the attached matter to be removed when the cleaning force of the developing member for the attached matter on the surface of the image bearing member is greater.

3. The imaging device according to claim 2, wherein: In the case of performing the cleaning operation, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that an exposed portion exposed from the developer is formed and allows the developing member formed with the exposed portion to rub the image bearing member.

4. The imaging device according to claim 1, wherein When the direction in which the normally charged developer is supplied from the developer supply member to the developing member is positive, and the direction in which the developer is collected from the developing member to the developer supply member is negative, in terms of controlling the potential difference between the developer supply member and the developing member, When performing the cleaning operation, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that the potential difference decreases in a positive direction, becomes zero, or decreases in a negative direction compared to the imaging operation.

5. The imaging device according to claim 1, wherein The control unit controls the polarities of the supply voltage and the developing voltage to be the same as the normal charging polarity of the developer, controls the absolute value of the developing voltage to be smaller than the absolute value of the supply voltage when performing the imaging operation, and controls the potential difference between the developing voltage and the supply voltage to be smaller than the potential difference of the imaging operation when performing the cleaning operation.

6. The imaging device according to claim 1, wherein The control unit controls the polarities of the supply voltage and the developing voltage to be the same as the normal charging polarity of the developer, controls the absolute value of the developing voltage to be smaller than the absolute value of the supply voltage when performing the imaging operation, and controls the potential difference between the developing voltage and the supply voltage to be zero when performing the cleaning operation.

7. The imaging device according to claim 1, wherein: The control unit controls the polarities of the supply voltage and the developing voltage to be the same as the normal charging polarity of the developer, controls the absolute value of the developing voltage to be the absolute value of the supply voltage or less when performing the imaging operation, and controls the absolute value of the developing voltage to be greater than the absolute value of the supply voltage when performing the cleaning operation.

8. An imaging device, comprising: an image bearing member configured to be rotatable; an exposure unit configured to expose a surface of the image bearing member to form an electrostatic latent image on the surface of the image bearing member; a developing member configured to be rotatable, to be in contact with the image bearing member to form a developing portion in which a developer is supplied to the surface of the image bearing member, and to rotate at a rotation speed different from that of the image bearing member; a developer supplying member configured to supply developer to the surface of the developing member; a developing voltage applying unit configured to apply a developing voltage to the developing member; a supply voltage applying unit configured to apply a supply voltage to the developer supplying member; and a control unit configured to control the developing voltage applying unit and the supply voltage applying unit, wherein The control unit performs control to enable execution of: an image forming operation in which a developer image is formed on the surface of the image bearing member by supplying a developer from the developing member to an electrostatic latent image formed on the surface of the image bearing member; and a cleaning operation which is an operation other than the image forming operation and removes substances attached to the surface of the image bearing member using the developing member, In a case where the cleaning operation is performed, the control unit controls at least one of the developing voltage applying unit and the supply voltage applying unit so that a cleaning force for cleaning substances attached to the surface of the image bearing member using the developing member becomes greater than a cleaning force in a case where the image forming operation is performed, and The control unit is capable of varying the cleaning force during the cleaning operation.

9. The imaging device according to claim 8, wherein: The control unit increases the cleaning force by increasing the time of the cleaning operation.

10. The imaging device according to claim 8, wherein The control unit increases the cleaning force by increasing a peripheral speed difference between the image bearing member and the developing member.

11. The imaging device according to claim 8, wherein: The control unit is capable of varying the cleaning force during the cleaning operation, and When control is performed so that the potential difference between the supply voltage and the developing voltage is reduced in the cleaning operation compared to the imaging operation, the control unit increases the cleaning force by reducing the potential difference or setting the potential difference to zero, and when control is performed so that the potential difference in a negative direction is set in the cleaning operation, the control unit increases the cleaning force by increasing the potential difference in the negative direction.

12. The imaging device according to claim 8, wherein: The control unit controls to increase the cleaning force when the number of prints per job is high in the image forming operation.

13. The image forming apparatus according to claim 8, further comprising an environment information acquisition unit configured to detect printing environment information of the image forming apparatus, and The control unit controls the cleaning force according to the printing environment information.

14. The imaging device according to claim 13, wherein The environment information acquisition unit acquires temperature as the printing environment information, and When the temperature decreases, the control unit increases the cleaning force.

15. The image forming apparatus according to claim 1, further comprising a transfer member configured to transfer the developer on the image bearing member to a transferred member, wherein The developer remaining on the surface of the image bearing member without being transferred by the transfer member is collected by the developing member.

16. The imaging device according to claim 1, wherein The developer is a non-magnetic single-component developer.

17. The imaging device according to any one of claims 1 to 16, wherein: A plurality of concave portions and convex portions are formed on the surface layer of the developing member to convey the developer, and When the cleaning operation is performed, the control unit performs control so that at least the convex portion of the concave portion and the convex portion is exposed from the developer.

18. The imaging device according to claim 17, wherein: A ten-point average roughness of the convex portions on the surface layer of the developing member is larger than a volume average particle diameter of a developer.

19. The imaging device according to claim 17, wherein: A ten-point average roughness of the convex portion on the surface layer of the developing member is in a range of 8 μm to 30 μm.

Images