Image forming apparatus

Abstract

An image forming apparatus includes an image holding unit; a charging unit; an exposure unit that exposes a surface of the image holding unit charged by the charging unit to form an electrostatic latent image; a developing unit that develops the electrostatic latent image; a transfer unit that transfers a visible image formed on the image holding unit; an exposure static elimination unit that, when image formation on the image holding unit is stopped, electrostatically eliminates residual charge of the image holding unit using the exposure unit; a transfer static elimination unit that, when image formation on the image holding unit is stopped, electrostatically eliminates the residual charge of the image holding unit using at least the transfer unit; and a switching unit that, when the residual charge does not exceed a threshold value of an allowable static elimination level that the exposure static elimination unit can electrostatically eliminate, electrostatically eliminates by the exposure static elimination unit, and when the residual charge exceeds the threshold value, electrostatically eliminates by the transfer static elimination unit from the exposure static elimination unit.

Description

Technical Field

[0001] This invention relates to an image forming apparatus. Background Technology

[0002] As existing image forming apparatuses, for example, the image forming apparatuses described in Patent Documents 1 and 2 are known.

[0003] In Patent Document 1, a first mode that minimizes toner adhesion to the developing sleeve and a second mode that suppresses toner consumption waste caused by blurring are switched based on information about the effect of toner charge on the toner. The potential of the image carrier is forcibly reduced by electrostatic elimination of the image carrier surface. Thus, a technique is disclosed that simultaneously suppresses toner adhesion to the developing sleeve and suppresses wasteful toner consumption, even under DC charging conditions.

[0004] Patent Document 2 discloses the following technology: when image formation is stopped, while the potential applied to the developing unit is brought close to the ground potential, the potential of the image holder is brought close to the ground potential by exposing the surface of the image holder by the electrostatic latent image forming unit, and the potential of the image holder, which is determined by the potential of the image holder in sequence based on the amount of light when the electrostatic latent image forming unit exposes the surface of the image holder, is brought close to the ground potential.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-206597 (Detailed Embodiments) Figure 5 )

[0006] Patent Document 2: Japanese Patent Application Publication No. 2013-228491 (Detailed Embodiments) Figure 2 ) Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide an image forming apparatus that, when performing electrostatic elimination on an image holding unit composed of a photoreceptor having a surface protective layer, suppresses the impact on the lifespan of the image holding unit while stabilizing the electrostatic elimination performance of the charge on the surface of the image holding unit.

[0008] The invention involved in Scheme 1 is an image forming apparatus, characterized by comprising: an image holding unit composed of a photoreceptor having a surface protective layer; a charging unit that charges the surface of the image holding unit by a DC potential; an exposure unit that exposes the surface of the image holding unit charged by the charging unit to form an electrostatic latent image; a developing unit that develops the electrostatic latent image formed on the image holding unit; a transfer unit that transfers the visible image formed on the image holding unit to a transfer medium; an exposure electrostatic elimination unit that, when image forming on the image holding unit is stopped, uses the exposure unit to electrostatically eliminate the residual charge of the image holding unit; a transfer electrostatic elimination unit that, when image forming on the image holding unit is stopped, at least uses the transfer unit to electrostatically eliminate the residual charge of the image holding unit; and a switching unit that, when the residual charge of the image holding unit does not exceed a threshold of an allowable electrostatic elimination level that can be electrostatically eliminated by the exposure electrostatic elimination unit, performs electrostatic elimination by the exposure electrostatic elimination unit, and when the threshold is exceeded, performs electrostatic elimination by the transfer electrostatic elimination unit instead of the exposure electrostatic elimination unit.

[0009] The invention involved in Scheme 2, in the image forming apparatus involved in Scheme 1, is characterized in that the developing unit uses a two-component developing agent containing a toner and a carrier as the imaging material to develop the electrostatic latent image.

[0010] The invention involved in Scheme 3, in the image forming apparatus involved in Scheme 1 or 2, is characterized in that the exposure electrostatic elimination unit reduces the developing voltage applied to the developing unit to the ground potential, and the electrostatic elimination is performed by the exposure unit.

[0011] The invention involved in Scheme 4, in the image forming apparatus involved in Scheme 3, is characterized in that the exposure electrostatic elimination unit outputs the light amount of the exposure unit in stages, so that the developing voltage applied to the developing unit approaches the ground voltage, while the residual potential of the image holding unit approaches the ground potential in stages.

[0012] The invention involved in Scheme 5, in the image forming apparatus involved in Scheme 1, is characterized in that the electrostatic discharge removal unit applies an electrostatic discharge removal voltage to the transfer unit so that the surface potential of the image holding unit becomes the target potential after electrostatic discharge removal, thereby performing electrostatic discharge removal on the image holding unit.

[0013] The invention involved in Scheme 6, in the image forming apparatus involved in Scheme 5, is characterized in that the electrostatic discharge removal unit applies an electrostatic discharge removal voltage to the transfer unit to perform electrostatic discharge removal on the image holding unit, so that the surface potential of the image holding unit exceeds the target potential after electrostatic discharge removal, and then the image holding unit is charged by the charging unit to become the target potential after electrostatic discharge removal.

[0014] The invention involved in Scheme 7, in the image forming apparatus involved in any one of Schemes 1 to 6, is characterized in that the switching unit has a usage condition recognition unit that can recognize the usage conditions of the image holding unit, and the exposure electrostatic elimination unit or the transfer electrostatic elimination unit performs electrostatic elimination based on the recognition result of the usage condition recognition unit.

[0015] The invention involved in Scheme 8, in the image forming apparatus involved in Scheme 7, is characterized in that the switching unit includes an environment detection unit that can detect environmental information including the temperature and humidity around the image holding unit as the usage condition identification unit, and when the detection result of the environment detection unit belongs to a predetermined low temperature and low humidity environment, the electrostatic discharge unit performs electrostatic discharge.

[0016] The invention involved in Scheme 9, in the image forming apparatus involved in Scheme 7, is characterized in that the switching unit includes a concentration detection unit that can detect the concentration of the visible image formed on the image holding unit as the usage condition identification unit, and when the concentration information detected by the concentration detection unit is lighter than a predetermined reference concentration, the electrostatic discharge unit performs electrostatic discharge.

[0017] The invention involved in Scheme 10, in the image forming apparatus involved in Scheme 7, is characterized in that the switching unit includes an image discrimination unit that can determine the average image density of a visible image formed on the image holding unit as the usage condition recognition unit, and when the average image density determined by the image discrimination unit is lower than the reference image density in a predetermined number of consecutive images formed, electrostatic elimination is performed by the transfer electrostatic elimination unit.

[0018] The invention involved in Scheme 11, in the image forming apparatus involved in Scheme 7, is characterized in that the switching unit includes a counting unit that can count the rotational speed of the image holding unit as the usage condition identification unit, and when the rotational speed of the image holding unit counted by the counting unit reaches or exceeds a predetermined reference rotational speed, the electrostatic discharge unit performs electrostatic discharge.

[0019] Invention Effects

[0020] According to the first aspect of the present invention, when electrostatic elimination is performed on an image holding unit composed of a photoreceptor having a surface protective layer, compared to the case where the electrostatic elimination method is determined independently of the residual charge value of the image holding unit, the effect on the lifespan of the image holding unit is suppressed while the electrostatic elimination performance of the charge on the surface of the image holding unit is stabilized.

[0021] According to the second aspect of the present invention, compared with the case of only performing exposure electrostatic elimination, it is possible to suppress carrier discharge from the developing unit caused by residual charge in the image holding unit.

[0022] According to the third aspect of the present invention, the influence of the developing unit is suppressed, and exposure electrostatic discharge can be eliminated on the image holding unit.

[0023] According to the fourth aspect of the present invention, compared with the case where the amount of light output by the exposure unit is not phased, exposure electrostatic elimination can be effectively performed on the image holding unit.

[0024] According to the fifth aspect of the present invention, electrostatic discharge of the image holding unit can be performed using only the transfer unit.

[0025] According to the sixth aspect of the present invention, compared with the case where electrostatic discharge is eliminated by only using the transfer unit, electrostatic discharge can be eliminated by effectively using the image holding unit.

[0026] According to the seventh aspect of the present invention, by identifying the usage conditions of the image holding unit, the electrostatic discharge method of the image holding unit can be appropriately switched.

[0027] According to the eighth aspect of the present invention, environmental information is considered as the usage conditions of the image holding unit, and the electrostatic discharge mode of the image holding unit can be switched appropriately.

[0028] According to the ninth aspect of the present invention, the density information of the visible image is considered as a condition for the use of the image holding unit, and the electrostatic discharge mode of the image holding unit can be switched appropriately.

[0029] According to the tenth aspect of the present invention, the average image density information of the visible image is considered as a condition for the use of the image holding unit, and the electrostatic discharge mode of the image holding unit can be switched appropriately.

[0030] According to the eleventh aspect of the present invention, the use of historical information is considered as a condition for the use of the image holding unit, and the electrostatic discharge method of the image holding unit can be switched appropriately. Attached Figure Description

[0031] The embodiments of the present invention will be described in detail with reference to the following figures.

[0032] Figure 1 These are explanatory diagrams illustrating a summary of an embodiment of the image forming apparatus to which the present invention is applied;

[0033] Figure 2 This is an explanatory diagram showing the overall structure of the image forming apparatus according to Embodiment 1;

[0034] Figure 3 This is an explanatory diagram showing the detailed contents of the image forming unit used in Embodiment 1 and its drive control system;

[0035] Figure 4 (a) is an explanatory diagram showing the characteristics of exposure electrostatic elimination for photosensitive materials with and without a protective surface layer. Figure 4 (b) is an explanatory diagram showing an example of the surface structure of a photoreceptor with a protective surface layer;

[0036] Figure 5 This is an explanatory diagram showing the flowchart of the start of the cyclic descent of the image forming apparatus according to this embodiment;

[0037] Figure 6 This is an explanatory diagram of other flowcharts illustrating the start of the cyclic descent of the image forming apparatus according to this embodiment;

[0038] Figure 7 This is an explanatory diagram showing the flowchart for implementing the electrostatic discharge (ESD) process.

[0039] Figure 8 (a) is a timing diagram showing the operation of each device during the electrostatic discharge process. Figure 8 (b) is an explanatory diagram schematically illustrating the developing action during imaging processing;

[0040] Figure 9 (a) is an explanatory diagram showing the device group used to perform the electrostatic discharge (ESD) elimination process for transfer printing. Figure 9 (b) is an illustration showing the principle of electrostatic discharge treatment in transfer printing;

[0041] Figure 10 This is an explanatory diagram showing the flowchart for implementing electrostatic discharge (ESD) elimination in transfer printing. Detailed Implementation

[0042] ◎Summary of Implementation Methods

[0043] Figure 1 This section outlines an embodiment of the image forming apparatus to which the present invention is applied.

[0044] In 1, the image forming apparatus includes: an image holding unit 1, comprising a photoreceptor having a surface protective layer 1a; a charging unit 2, which charges the surface of the image holding unit 1 with a DC potential; an exposure unit 3, which exposes the surface of the image holding unit 1 charged by the charging unit 2 to form an electrostatic latent image; a developing unit 4, which develops the electrostatic latent image formed on the image holding unit 1; a transfer unit 5, which electrostatically transfers the visible image formed on the image holding unit 1 to a transfer medium 6; and an exposure electrostatic elimination unit 11, which, when image formation on the image holding unit 1 is stopped, uses an exposure electrostatic elimination unit 11 to eliminate the electrostatic latent image formed on the image holding unit 1. The light unit 3 performs electrostatic discharge removal on the residual charge of the image holding unit 1; the transfer electrostatic discharge removal unit 12 performs electrostatic discharge removal on the residual charge of the image holding unit 1 using at least the transfer unit 5 when image formation on the image holding unit 1 is stopped; and the switching unit 13 performs electrostatic discharge removal by the exposure electrostatic discharge removal unit 11 when the residual charge of the image holding unit 1 does not exceed the threshold of the permissible electrostatic discharge removal level that can be electrostatically discharged by the exposure electrostatic discharge removal unit 11, and performs electrostatic discharge removal by the transfer electrostatic discharge removal unit 12 from the exposure electrostatic discharge removal unit 11 when the residual charge exceeds the threshold.

[0045] In addition, Figure 1 In the diagram, symbol 7 is the cleaning unit for cleaning residues left on the image holding unit 1, symbol 2a is the power supply for the charged unit 2, and symbol 5a is the power supply for the transfer unit 5.

[0046] In this technical means, the image holding unit 1 uses a photoreceptor with a surface protective layer 1a as the applicable object. As the surface protective layer 1a, it can be any protective layer with a higher hardness than the photoreceptor. Of course, it can also be a protective layer that is separate from the photoreceptor, or it can be a protective layer whose surface of the photoreceptor has been cured.

[0047] Here, compared with an organic photoreceptor without a surface protective layer 1a, a photoreceptor with a surface protective layer 1a accumulates charge within the surface protective layer 1a or at the interface with the electrical transport layer, and tends to have residual charge on the surface of the photoreceptor that is difficult to remove by electrostatic elimination through exposure alone.

[0048] Furthermore, the charging unit 2 is designed for components energized by DC potential. In AC charging, the high charging performance easily leads to the formation of discharge products on the photoreceptor surface. The photoreceptor with the surface protective layer 1a exhibits high wear resistance, making it difficult to remove these discharge products. Therefore, discharge products readily form a film on the photoreceptor surface. In contrast, in DC charging, the applied electrical stress to the photoreceptor surface is low, which suppresses the formation of discharge products.

[0049] Furthermore, regarding the exposure electrostatic elimination unit 11, as shown in Patent Document 1, it is effective for staged exposure electrostatic elimination that causes the exposure level to change in stages, but it also includes uniform exposure electrostatic elimination that causes the exposure level to change in stages.

[0050] Furthermore, the electrostatic discharge unit 12 can be a method of electrostatic discharge performed solely by the transfer unit 5, or it can be a combination of the transfer unit 5 and the charged unit 2.

[0051] Next, a representative or preferred embodiment of the image forming apparatus according to this embodiment will be described.

[0052] First, as a preferred embodiment of the developing unit 4, a method in which a two-component developing agent containing a toner and a carrier is used as the imaging material G to develop the electrostatic latent image can be described. For example, in the case where the image holding unit 1 has a photoreceptor with a surface protective layer 1a, the dielectric constant becomes high, and it is easy for residual charge to remain on the photoreceptor by electrostatic elimination based solely on the exposure electrostatic elimination unit 11. However, in addition to excessive blurring of the toner, carrier discharge becomes significant, and poor image quality is likely to occur. Therefore, it is preferable to switch to an electrostatic elimination method based on this application for more effective operation.

[0053] Furthermore, as a representative method of the exposure electrostatic elimination unit 11, the following method can be used: the developing voltage applied to the developing unit 4 is reduced to the ground potential, and electrostatic elimination is performed by the exposure unit 3.

[0054] In this case, for example, in terms of improving the efficiency of electrostatic elimination, the exposure electrostatic elimination unit 11 is preferably configured to output the amount of light from the exposure unit 3 in stages, so that the developing voltage applied to the developing unit 4 approaches the ground potential, and the residual potential of the image holding unit 1 approaches the ground potential in stages.

[0055] Furthermore, as a representative method of the transfer electrostatic elimination unit 12, the following method can be cited: applying an electrostatic elimination voltage from the power supply 5a to the transfer unit 5 to perform electrostatic elimination on the image holding unit 1, so that the surface potential of the image holding unit 1 becomes the target potential after electrostatic elimination.

[0056] In particular, from the viewpoint of improving the efficiency of static electricity elimination, for example, as the transfer static electricity elimination unit 12, it is preferable to apply a static electricity elimination voltage from the power supply 5a to the transfer unit 5 to perform static electricity elimination on the image holding unit 1, so that the surface potential of the image holding unit 1 exceeds the target potential after static electricity elimination, and then charge the image holding unit 1 through the power supply 2a of the charging unit 2 to reach the target potential after static electricity elimination.

[0057] Furthermore, as a representative embodiment of the switching unit 13, the following embodiment can be provided: a usage condition recognition unit 14 is provided that can recognize the usage conditions of the image holding unit 1, and electrostatic elimination is performed by the exposure electrostatic elimination unit 11 or the transfer electrostatic elimination unit 12 based on the recognition result of the usage condition recognition unit 14.

[0058] Here, the usage conditions of the image holding unit 1 include environmental conditions, imaging conditions (density, image density), and usage history conditions (rotation speed).

[0059] Hereinafter, the specific way of using the condition identification unit 14 is as follows.

[0060] (1) The use of condition recognition unit 14 is a way of environmental detection unit

[0061] In this example, the switching unit 13 has an environment detection unit that can detect environmental information including the temperature and humidity around the image holding unit 1 as a usage condition recognition unit 14. When the detection result of the environment detection unit belongs to a predetermined low temperature and low humidity environment, the electrostatic discharge unit 12 performs electrostatic discharge.

[0062] (2) The condition recognition unit 14 is used as a concentration detection unit.

[0063] In this example, the switching unit 13 has a concentration detection unit that can detect the concentration of the visible image formed on the image holding unit 1 as a usage condition recognition unit 14. When the concentration information detected by the concentration detection unit is lighter than a predetermined reference concentration, electrostatic elimination is performed by the transfer electrostatic elimination unit 12.

[0064] (3) Using the condition recognition unit 14 as an image discrimination unit

[0065] In this example, the switching unit 13 has an image discrimination unit that can determine the average image density of the visible image formed on the image holding unit 1 as a usage condition recognition unit 14. When the average image density determined by the image discrimination unit is lower than the reference image density in the predetermined number of consecutive images formed, electrostatic elimination is performed by the transfer electrostatic elimination unit 12.

[0066] (4) The condition recognition unit 14 is used as a counting unit.

[0067] In this example, the switching unit 13 has a counting unit that can count the rotation speed of the image holding unit 1 as a usage condition recognition unit 14. When the rotation speed of the image holding unit 1 counted by the counting unit reaches or exceeds a predetermined reference rotation speed, static electricity elimination is performed by the transfer static electricity elimination unit 12.

[0068] ◎Implementation Method 1

[0069] The present invention will now be described in more detail with reference to the embodiments shown in the accompanying drawings.

[0070] -Overall structure of the image forming apparatus-

[0071] Figure 2 This is an explanatory diagram showing the overall structure of the image forming apparatus according to Embodiment 1.

[0072] exist Figure 2 In this embodiment, the image forming apparatus 20 has an imaging engine 30 mounted in the apparatus housing 21, which forms images of multiple colors (in this embodiment, yellow, magenta, blue-green and black). Below the imaging engine 30, a recording material supply device 50 is provided to hold recording materials such as paper, and the recording material transport path 55 from the recording material supply device 50 is arranged in a generally vertical direction.

[0073] In this example, the imaging engine 30 arranges the image forming units 31 (specifically, 31a to 31d) that form images of various colors in a generally horizontal direction, and arranges a transfer module 40 above them, which includes, for example, a strip-shaped intermediate transfer body 45 that moves cyclically along the arrangement direction of the image forming units 31. The images of various colors formed in each image forming unit 31 are transferred to the recording material via the transfer module 40.

[0074] In this embodiment, such as Figure 2 and Figure 3 As shown, each image forming unit 31 (31a-31d) sequentially forms toner images for, for example, yellow, magenta, blue-green, and black (the arrangement is not necessarily limited to this order) from the upstream side of the circulation direction of the intermediate transfer body 45, and includes a photoreceptor 32, a charger (in this example, a charged roller) 33 for pre-charging the photoreceptor 32, an exposure unit (in this example, an LED writing head) 34 for writing electrostatic latent images onto each photoreceptor 32 charged by the charger 33, a developer 35 for developing the electrostatic latent images formed on the photoreceptor 32 with corresponding color component toners (in this embodiment, for example, negative polarity), and a cleaner 36 for cleaning residues on the photoreceptor 32.

[0075] In this example, such as Figure 3 As shown, the developer 35 has a developing container 35a that contains a developer including a toner and a carrier and has an opening opposite to the photoreceptor 32. A developing roller 35b is provided at the opening of the developing container 35a. The developer is held in the developing roller 35b to supply the developer to the part opposite to the photoreceptor 32. A stirring and conveying component 35c and 35d are provided in the developing container 35a to charge the developer and to stir and convey it.

[0076] Furthermore, in this example, the cleaner 36 has a cleaning container 36a that holds the residue on the photoreceptor 32 and has an opening opposite to the photoreceptor 32. A plate-shaped cleaning member 36b for scraping off the residue on the photoreceptor 32 is installed on the edge of the opening of the cleaning container 36a, and a conveying member 36c for conveying the residue in a homogenized manner is disposed inside the cleaning container 36a.

[0077] Additionally, symbol 37 (specifically, 37a to 37d) is a toner cartridge used to replenish the toners of each color component in each developer 35.

[0078] Furthermore, in this embodiment, the transfer module 40 mounts a strip-shaped intermediate transfer body 45 on a plurality of tension rollers 41 to 44. For example, the tension rollers 41 are used as drive rollers to make the intermediate transfer body 45 move cyclically. Then, a transfer device (in this example, a transfer roller) 46 for primary transfer is provided on the back side of the intermediate transfer body 45, which is opposite to the photoreceptor 32 of each image forming unit 31. By applying a transfer voltage with a polarity opposite to that of the toner to the transfer device 46, the toner image on the photoreceptor 32 is electrostatically transferred to the intermediate transfer body 45 side.

[0079] In addition, a cleaner 47 is provided on the upstream side of the upstream image forming section 31a of the intermediate transfer body 45 to remove residual toner on the intermediate transfer body 45.

[0080] Furthermore, in this embodiment, a secondary transfer device 60 is provided at the downstream side of the image forming section 31d of the intermediate transfer body 45, opposite to the tension roller 42, so as to transfer the primary transfer image on the intermediate transfer body 45 to the recording material in a secondary transfer (together).

[0081] In this example, the secondary transfer unit 60 includes: a secondary transfer roller 61, which is pressed against the toner image holding surface of the intermediate transfer body 45; and a support roller (which also serves as a tension roller 42 in this example), which is disposed on the back side of the intermediate transfer body 45 and constitutes the opposing electrode of the secondary transfer roller 61. Moreover, for example, the secondary transfer roller 61 is grounded, and a secondary transfer voltage with the same polarity as the polarity of the toner is applied to the support roller (tension roller 42).

[0082] Furthermore, the recording material supply device 50 is provided with a supply roller 51 for supplying recording material, a conveying roller (not shown) is provided on the recording material conveying path 55, and an alignment roller (positioning roller) 56 is provided on the recording material conveying path 55 located directly in front of the secondary transfer section to supply the recording material to the secondary transfer section at a predetermined time.

[0083] Furthermore, a fuser 70 is provided on the recording material transport path 55 located downstream of the secondary transfer section. This fuser 70 includes, for example, a heated fuser roller 71 with a built-in heater (not shown) and a pressure fuser roller 72 that is pressed against and rotates with the heated fuser roller. Downstream of the fuser 70, a recording material discharge roller 57 is provided within the discharge device frame 21, which clamps and transports the recording material for discharge, allowing the recording material receiving receiver 58 formed on the upper part of the device frame 21 to receive the recording material.

[0084] In addition, although the illustration is omitted in this example, it is of course possible to separately attach a manual feeding device for recording materials or a double-sided recording module that can record materials on both sides.

[0085] -Control system of the image forming section-

[0086] In this embodiment, the control system of the image forming unit 31 (31a-31d) includes a control device 100 comprising a processor and memory. On this control device 100, a start button 101 for starting the imaging process of the image forming apparatus 20 is connected as the input destination for collecting various information; an environment sensor 102 for detecting environmental conditions around the image forming unit 31, such as temperature and humidity; a density sensor 103 for detecting the density of the evaluation image formed on the intermediate transfer body 45; and a counting sensor 104 for counting the rotational speed (number of cycles) of the photoreceptor 32. Furthermore, a drive motor 110 for the photoreceptor 32 is connected as the output destination for outputting control signals, and a voltage V is applied to the charge carrier 33. C The power supply 111, the light intensity adjuster 112 that adjusts the exposure of the exposure unit 34, the drive motor 113 that drives the developing roller 35b of the developing unit 35, and the developing voltage V applied to the developing roller 35b. D The developing power supply 114 applies a transfer voltage V to the transfer unit 46. T The transfer power supply 115, etc. Furthermore, the term "processor" here refers to a processor in a broad sense, including general-purpose processors (e.g., CPU: Central Processing Unit, etc.) and special-purpose processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

[0087] In this example, the control device 100 accepts input signals from various input destinations, executes various control programs pre-installed in memory (including the loop descent start program described later), and outputs specified control signals to each output destination.

[0088] -Characteristics of photosensitive elements with a protective surface layer-

[0089] In this embodiment, such as Figure 4 As shown in (b), the photoreceptor 32 has an organic photosensitive layer 32b stacked on a metal (aluminum in this example) substrate 32a, and a surface protective layer 32c with excellent wear resistance stacked on the organic photosensitive layer 32b.

[0090] Here, the organic photosensitive layer 32b is formed by sequentially stacking a base layer 321, a charge generation layer 322, and a charge transport layer 323 on the substrate 32a. The base layer 321 prevents the injection of reverse charges (+) generated by charging. The charge generation layer 322 generates charges (+-) through photoelectric conversion. Furthermore, the charge transport layer 323 transports the charges (+) generated in the charge generation layer 322 to the surface protective layer 32c. The surface protective layer 32c only needs to be formed of a high-hardness material to prevent wear of the organic photosensitive layer 32b.

[0091] In a photoreceptor 32 having such a surface protective layer 32c (equivalent to a so-called outer coating photoreceptor), compared to an organic photoreceptor without a surface protective layer 32c, residual charges on the photoreceptor 32 may not be removed in an exposure electrostatic elimination method (details will be described later) that utilizes exposure based on an exposure unit 34, by storing charge within the surface protective layer 32c or at the interface with the charge transport layer 323.

[0092] Regarding this point, such as Figure 4 As shown in (a), regarding the photoreceptor with surface protective layer 32c ( Figure 4 (a) marked as photosensitive material with outer coating) and photosensitive material without surface protective layer ( Figure 4 (a) shows the results of an experiment on the organic photoreceptor, in which the exposure amount for electrostatic elimination was changed and the residual potential was plotted. For the organic photoreceptor, by increasing the exposure amount, the residual potential on the photoreceptor 32 after electrostatic elimination can be lower than the predetermined permissible electrostatic elimination level VHs. In contrast, for the outer coating photoreceptor, under a predetermined high temperature and high humidity environment, by increasing the exposure amount of the electrostatic elimination method, the current potential on the photoreceptor 32 can be lower than the permissible electrostatic elimination level VHs. However, under a predetermined low temperature and low humidity environment, even if the exposure amount is increased by the electrostatic elimination method, it is difficult to reduce the residual potential on the photoreceptor 32 to a level lower than the permissible electrostatic elimination level.

[0093] In this embodiment, since a negative photosensitive element 32 is used, it is charged in the - direction and de-electrostatically neutralized in the + direction. In this case, the term "reduction" refers to a change in potential from the charged polarity towards a direction closer to 0V.

[0094] exist Figure 4 In (a), it can be understood that sometimes the electrostatic discharge method of exposure cannot work effectively depending on environmental conditions.

[0095] Furthermore, in the outer coating photoreceptor, regardless of environmental conditions, even when the charge of the toner increases due to continuous low-density image processing or when the amount of charge generated in the photoreceptor 32 changes over time, it may be possible to insufficiently reduce the residual potential on the photoreceptor 32.

[0096] Therefore, in this embodiment, when the cyclic descent process for removing residual charge from the photoreceptor 32 is started after the image forming process is completed, if the residual charge on the photoreceptor 32 can be removed in the exposure electrostatic elimination method, the exposure electrostatic elimination method is implemented; if the residual charge on the photoreceptor 32 cannot be removed in the exposure electrostatic elimination method, the transfer electrostatic elimination method using the transferr 46, which is different from the exposure electrostatic elimination method, is implemented (details will be described later).

[0097] The term "cycle descent" here refers to a cycle that stops the operation of the image forming apparatus in a normal imaging cycle.

[0098] -Processing begins with the cyclic descent--

[0099] In this example, the control device 100 implements, for example... Figure 5 or Figure 6 The cyclic descent shown is now being processed.

[0100] <Initial Processing of Cyclic Descent I>

[0101] exist Figure 5 During the cycle descent process shown, environmental conditions, average image density conditions, and photoreceptor cycle count conditions are determined as the methods for electrostatic elimination of the residual potential of the photoreceptor 32. The exposure electrostatic elimination method ("stage exposure electrostatic elimination" in this example) or the transfer electrostatic elimination method is switched.

[0102] First, as an environmental condition judgment process, the detection information of the environmental sensor 102 is used to determine whether the environmental conditions are low temperature and low humidity conditions. In the case of a low temperature and low humidity environment, the "transfer static electricity elimination method" is implemented.

[0103] Here, regarding low temperature and low humidity environments, in this example, the conditions are set as a predetermined temperature below Tm (e.g., 15°C) and a predetermined humidity below Hm (e.g., 30%).

[0104] Furthermore, as a discrimination process for the average image density condition, the image discrimination unit (a functional unit that performs calculation processing on the average image density from the image data to be formed) within the control device 100 determines whether the average image density after the predetermined k images (e.g., 100 images) are below the threshold Gm (e.g., 1%). If it is below Gm, the "transfer electrostatic elimination mode" is implemented.

[0105] In this case, because the charge of the toner increases with the continuous movement of the low-density image, the required image potential (development voltage V) needs to be increased compared to the case where the charge of the toner does not increase. D With the potential V of the image part L The difference; reference Figure 8 (b) However, if the residual potential is high, the required image potential and non-image part potential VH will become higher, so electrostatic elimination cannot be achieved by exposure electrostatic elimination alone.

[0106] In addition, as a process for determining the number of photoreceptor cycles, the counting sensor 104, which counts the number of photoreceptor cycles 32, determines whether the number of photoreceptor cycles is above a predetermined threshold Xm. If it is above Xm, the amount of charge generated by the photoreceptor changes due to the repeated stress of exposure over time, and it is speculated that the residual potential of the photoreceptor increases and a "transfer electrostatic elimination mode" is implemented.

[0107] <Circular Descent Start Processing II>

[0108] exist Figure 6 During the cyclic descent start process shown, as a way to determine environmental conditions and image density conditions and to perform electrostatic elimination on the residual potential of the photoreceptor 32, the exposure electrostatic elimination mode (in this example, "staged exposure electrostatic elimination") or the transfer electrostatic elimination mode is switched.

[0109] In this example, as a discrimination process for environmental conditions, and Figure 5 The cyclic descent shown begins with the same process as I.

[0110] Furthermore, as a discrimination process based on image density conditions, it is determined according to... Figure 3 The concentration sensor 103 shown uses the concentration information in the image to determine whether the concentration is lighter than the reference concentration. When it is determined to be lighter, the "transfer electrostatic elimination method" is implemented.

[0111] In this case, if the image density does not reach the predetermined reference density, it is necessary to increase the required image potential (development voltage V).D With the potential V of the image part L The difference; reference Figure 8 (b) However, if the residual potential is high, the required image potential and non-image part potential VH will become higher, so electrostatic elimination cannot be achieved by exposure electrostatic elimination alone.

[0112] -Exposure Static Electricity Elimination Method-

[0113] Figure 7 This is a flowchart of the electrostatic discharge (ESD) elimination process implemented in this embodiment. Figure 8 (a) is a timing diagram showing the action times of each part during the exposure electrostatic elimination process.

[0114] exist Figure 3 , Figure 7 and Figure 8 In (a), if the electrostatic discharge process for exposure begins, the control device 100 first shuts off the developing voltage V of the developer 35. D (AC), Transfer voltage V of transferor 46 T and the voltage V of the electrical appliance 33 C .

[0115] Then, the control device 100 obtains the potential of the photoreceptor 32 from the potential sensor not shown, and obtains temperature and humidity information from the environmental sensor 102.

[0116] Then, the control device 100 raises the potential of the developing power supply 114 and lowers the developing voltage V. D (DC). Additionally, the developing roller 35b is charged with a negative potential, so the potential is actually rising towards 0, but in... Figure 8 In (a), the negative potential side is set at the top of the diagram, therefore the developing voltage V D (DC) decreases linearly downwards in the graph. At this point, the time when the decrease will begin is... Figure 8 (a) is shown as E. Moreover, this E is the time from when the part of the photoreceptor 32 that begins to be electrostatically eliminated by the exposure unit 34 reaches the position of the developing roller 35b. That is, the photoreceptor 32 is rotated by the drive motor 110, so the part moves to the position of the developing roller 35b within the time ED. Then, starting from this part, the potential applied to the developing roller 35b begins to decrease.

[0117] Furthermore, in this embodiment, the potential on the surface of the photoreceptor 32 is compared with the potential applied to the developing roller 35b (developing voltage V). D The difference between (DC) and (V) cln Assume it is within a predetermined range.

[0118] Here, as Figure 8(b) schematically illustrates the surface potential distribution of the photoreceptor 32 during image formation. If the potential of the non-image portion is VH (e.g., -600V), and the potential of the image portion is V... L (e.g., -50V), developing voltage V D (DC) is V DEVE VH and V DEVE The difference is V cln V DEVE With V L The difference is V cont If V cont If the concentration is too low, V will become insufficient. cln Control the blurring of the toning agent or the discharge of the carrier to the non-image part potential VH.

[0119] Therefore, the potential difference between the surface of the photoreceptor 32 and the potential of the developing roller 35b is within a predetermined range. cln The range varies depending on environmental conditions, for example, 100±30V. Then, if V cln Deviation from this range can easily lead to the excretion of colorants or carriers. That is, if V cln If the value is too small, the toner will easily migrate to the photoreceptor 32 side. Furthermore, if V... cln If the value is too large, the carrier can easily move to the photoreceptor 32 side. In this embodiment, the discharge of the toner or carrier is suppressed by setting Vcln within a predetermined range.

[0120] Furthermore, in this example, such as Figure 7 and Figure 8 As shown in (a), the amount of light in the exposure unit (in this example, the LED writing head) 34 is increased in stages. This causes the potential on the surface of the photoreceptor 32 to change relative to the developing voltage V. D (DC) is reduced. Then, the potential on the surface of the photoreceptor 32 is compared with the developing voltage V. D (DC) difference (V) cln Assume it is within a predetermined range. Figure 8 In (a), a step diagram is used to illustrate the situation in which the amount of light in the exposure unit 34 is increased in stages, thereby progressively reducing the potential of the surface of the photoreceptor 32 to approach the ground potential.

[0121] Then, as Figure 7 As shown, at the developing voltage V D When the DC voltage is almost zero, the control device 100 stops the exposure of the photoreceptor 32 by the exposure unit 34 and changes the control signals to the drive motors 110 and 113 from on to off. This shuts down the exposure unit 34 and stops the drive motors 110 and 113, thereby stopping both the photoreceptor 32 and the developing roller 35b. Figure 8In (a), this time is illustrated as F. At time F, the stopping action during image formation ends.

[0122] -Static Eradication Method in Transfer Printing-

[0123] Figure 9 (a) A schematic representation of the device group performing the electrostatic discharge process for transfer, wherein the charged position of the charger 33 is represented by PC, the developing position of the developer 35 is represented by PD, and the transfer position of the transferor 46 is represented by PT.

[0124] and, Figure 9 (b) is an illustration of the principle of static electricity elimination process in transfer printing.

[0125] Figure 9 (b) shows the change in the charge potential of the photoreceptor 32 caused by electrostatic discharge. Here, an electrostatic discharge voltage is applied to the transferor 46 to allow an electrostatic discharge current to flow, which is greater than the current applied when transferring a toner image by the transfer voltage V. T The transfer current is large. Figure 3 The transfer power supply 115 shown is a high-current capacity power supply, through which an electrostatic elimination current flows to reduce the photoreceptor 32 from its pre-electrostatic elimination potential to a level exceeding the target potential. Then, by allowing this electrostatic elimination current to flow, the photoreceptor 32 is reduced to an electrostatic elimination potential exceeding the target potential. After being reduced to the electrostatic elimination potential, an electrostatic elimination voltage is applied to the charging device 33 to restore the surface that has become the electrostatic elimination potential to the target potential during electrostatic elimination, thereby restoring the surface that has become the electrostatic elimination potential to the target electrostatic elimination potential during electrostatic elimination.

[0126] During the stage where the charged potential of the photoreceptor 32 is transformed into an electrostatic discharge charged potential due to the action of the transferor 46, there is a potential distribution along the axial direction of the photoreceptor 32, but it becomes an almost uniform target potential after being charged based on the charger 33.

[0127] Figure 9 (b) assumes that the potential of the photoreceptor 32 immediately changes to the charging potential at the final target static elimination during one rotation of the photoreceptor 32. When the charging capability (static elimination capability) of the transferor 46 to the photoreceptor 32 is sufficiently high, this can be achieved. Figure 9 The timing of the immediate transition is shown in (b). However, there are limitations in the charging capability (static discharge capability) of the transferor 46, i.e., in Figure 3If the transfer power supply 115 shown does not have sufficient current to immediately change the transferor 46 from the charged potential at the time of imaging to an electrostatic discharge potential that is significantly different from that charged potential, a timing sequence in which the photoreceptor 32 is rotated multiple times and electrostatic discharge is gradually eliminated with each rotation can be adopted.

[0128] Figure 10 It is a flowchart showing the process of rotating the photoreceptor 32 multiple times while performing electrostatic discharge removal treatment in stages. Additionally, in Figure 10 In this context, n represents the rotational speed of the photoreceptor 32, for example, assuming n = 2. Furthermore, during the electrostatic discharge process, a negative voltage [-V] is applied to the charge carrier 33 and the developer 35, and a positive voltage [+V] is applied to the transfer unit 46 to allow current to flow in the direction that cancels out the negative charge of the photoreceptor 32.

[0129] exist Figure 10 If the cyclic descent begins, the rotation of the developer 35 is first stopped, and then the first rotation of the photoreceptor 32 is performed.

[0130] At this time, the control device 100 changes the output of the transfer unit 46 to V for the first cycle of static elimination. T (1). The output of the transfer printer 46 here is 20A.

[0131] Next, the output of transfer unit 46 was changed to static elimination in the first week using V. T (1) At the moment when the transfer position PT of the photosensitive element 32 facing the transferor 46 reaches the belt charger 33, then as Figure 9 As shown in (a), if the photoreceptor 32 rotates by a specified angle, the output of the charger 33 changes to V for the first cycle of static elimination. C (1). In this example, the output of the livery 33 is -900V.

[0132] In addition, the output of the electrical appliance 33 was changed to static elimination in the first week using V. C (1) At the moment when the charged position PC of the photoreceptor 32 facing the charged capacitor 33 reaches the developer 35, then as Figure 9 As shown in (a), the output of developer 35 is changed to use V for electrostatic elimination in the first cycle. D (1). In this example, the output of the developer 35 is -170V.

[0133] Next, the output of the developer 35 was changed to electrostatic elimination in the first cycle using V. D (1) At the moment when the developing position PD of the photoreceptor 32 facing the developer 35 reaches the transfer unit 46, that is, if the photoreceptor 32 rotates one revolution after the start of the cyclic descent, the output of the transfer unit 46 changes to electrostatic elimination in the second revolution using V. T(2). However, in this example, the output of the transferor 46, as the second cycle of static elimination, is the same as that used in the first cycle of static elimination. T (1) Same current value.

[0134] Then, the output of the transfer unit 46 is changed to static elimination in the second week using V. T (2) If the transfer position PT of the photosensitive element 32 facing the transferor 46 reaches the belt charger 33, then the output of the belt charger 33 changes to static elimination in the second week using V. C (2). In this example, the output of the charger 33 is -600V. Through the output of this -600V charger 33, the photosensitive element 32 is charged to a voltage of 0V.

[0135] Next, in the second week, the output of the livery 33 was changed to electrostatic elimination using V. C (2) If the charged position PC of the photoreceptor 32 facing the charged capacitor 33 reaches the developer 35, then the output of the developer 35 changes to electrostatic elimination in the second cycle using V. D (2). In this example, the output of the developer 35 is 0V.

[0136] Next, the output of the developer 35 was changed to electrostatic elimination in the second cycle using V. D (2) If the developing position PD of the photoreceptor 32 facing the developer 35 reaches the transfer unit 46, that is, if the photoreceptor 32 rotates 2 times after the cyclic descent begins, then the electrostatic discharge process of the transfer is set to end, and the output of the transfer unit 46 is changed to disconnect (0μA).

[0137] Next, when the output of the transferor 46 is switched off, if the transfer position PT of the photosensitive element 32 facing the transferor 46 reaches the belt charger 33, then the output of the belt charger 33 is switched off.

[0138] Furthermore, when the output of the capacitor 33 is switched off, if the charged position PC of the photoreceptor 32 facing the capacitor 33 reaches the developer 35, then the output of the developer 35 is switched off. In this example, the output of the developer 35 is already 0V during the second cycle of electrostatic discharge, but considering the fine adjustment of the output of the developer 35 during the second cycle of electrostatic discharge, a step is provided to switch the output of the developer 35 off.

[0139] Therefore, after the outputs of the transfer unit 46, the belt charger 33, and the developer 35 are switched off, the rotation of the photoreceptor 32 stops.

[0140] Furthermore, in the aforementioned cyclic descent sequence, the rotation of the developer 35 is stopped immediately after the cyclic descent begins. Stopping the rotation of the developer 35 is done because it suppresses toner blurring or carrier transfer compared to performing the cyclic descent sequence while the developer 35 is rotating. However, for the purpose of suppressing toner blurring or carrier transfer, it is not necessary to stop the rotation of the developer 35 immediately after the cyclic descent begins; it is sufficient as long as the developing position PD of the photoreceptor 32 facing the developer 35 is at the electrical potential during imaging.

[0141] If a cyclical descent with the timing described above is employed, the photoreceptor 32 can be destaticated to the target potential while suppressing toner blurring or carrier transfer. Furthermore, if multiple stages of destatic elimination are employed (two stages in this example), compared to immediately destaticating the photoreceptor 32 to the target potential in one stage, the current flowing through the transferor 46 can be suppressed, and a transfer power supply 115 with a smaller current capacity can be used.

[0142] However, when there is a margin in the current capacity of the transfer power supply 115, the photoreceptor 32 can be electrostatically eliminated to the target potential in one step. In this case, for example, it can be omitted. Figure 10 The voltage for the first week of electrostatic elimination shown can be changed to that of the second week of electrostatic elimination immediately from the time of imaging.

[0143] Alternatively, when the current capacity of the transfer power supply 115 is smaller, it can be dispersed into more than three stages to gradually eliminate static electricity.

[0144] Furthermore, although an image forming apparatus employing an intermediate transfer body 45 has been described here as an example, the present invention can also be applied to monochrome image forming apparatuses that do not employ an intermediate transfer body 45 but have only one image forming section.

[0145] ◎Comparison Method 1

[0146] In this embodiment, a structure is provided that can implement either the exposure electrostatic elimination method or the transfer electrostatic elimination method, and can be switched to implement either method. However, in the case of the comparison method that is always implemented simultaneously, since transfer electrostatic elimination is always present, even the photoreceptor 32 with a surface protective layer cannot effectively extend its lifespan.

[0147] The embodiments of the present invention described above are provided for illustrative purposes. Furthermore, these embodiments do not encompass the entirety of the invention, nor do they limit the invention to the disclosed methods. It will be apparent to those skilled in the art that various modifications and variations will be readily understood. These embodiments were chosen and described to most readily explain the principles and applications of the invention. Thus, those skilled in the art can understand the invention through various modifications that are assumed to be optimized for specific uses of various embodiments. The scope of the invention is defined by the foregoing claims and their equivalents.

[0148] Symbol Explanation

[0149] 1-Image holding unit, 1a-Surface protective layer, 2-Charging unit, 2a-Power supply, 3-Exposure unit, 4-Developing unit, 5-Transfer unit, 5a-Power supply, 6-Transfer medium, 7-Cleaning unit, 11-Exposure electrostatic elimination unit, 12-Transfer electrostatic elimination unit, 13-Switching unit, 14-Usage condition recognition unit, G-Imaging material.

Claims

1. An image forming apparatus, characterized in that, have: The image holding unit is composed of a photoreceptor with a surface protective layer; The charged unit charges the surface of the image holding unit using a DC potential; An exposure unit exposes the surface of the image holding unit, which is charged by the charged unit, to form an electrostatic latent image; The developing unit develops the electrostatic latent image formed on the image holding unit. The transfer unit transfers the visible image formed on the image holding unit to the transfer medium; An exposure electrostatic elimination unit is used to eliminate residual charge in the image holding unit when image formation on the image holding unit is stopped. The electrostatic discharge unit is used to discharge residual charge on the image holding unit at least when image formation on the image holding unit is stopped. and The switching unit performs electrostatic elimination by the exposure electrostatic elimination unit when the residual charge in the image holding unit does not exceed a threshold of the permissible electrostatic elimination level that can be electrostatically eliminated by the exposure electrostatic elimination unit; and switches from the exposure electrostatic elimination unit to the transfer electrostatic elimination unit when the residual charge in the image holding unit exceeds the threshold.

2. The image forming apparatus according to claim 1, characterized in that, The developing unit uses a two-component developing agent containing a toner and a carrier as the imaging material to develop electrostatic latent images.

3. The image forming apparatus according to claim 2, characterized in that, The exposure electrostatic elimination unit reduces the developing voltage applied to the developing unit to ground potential, and the exposure unit performs electrostatic elimination.

4. The image forming apparatus according to claim 3, characterized in that, The exposure electrostatic elimination unit outputs the light amount of the exposure unit in stages, so that the developing voltage applied to the developing unit approaches the ground voltage, while the residual potential of the image holding unit approaches the ground potential in stages.

5. The image forming apparatus according to claim 1, characterized in that, The electrostatic discharge removal unit applies an electrostatic discharge removal voltage to the transfer unit so that the surface potential of the image holding unit becomes the target potential after electrostatic discharge removal, thereby performing electrostatic discharge removal on the image holding unit.

6. The image forming apparatus according to claim 5, characterized in that, The electrostatic discharge unit applies an electrostatic discharge voltage to the transfer unit to discharge electrostatic discharge onto the image holding unit, so that the surface potential of the image holding unit exceeds the target potential after electrostatic discharge. Then, the charging unit charges the image holding unit to reach the target potential after electrostatic discharge.

7. The image forming apparatus according to any one of claims 1 to 6, characterized in that, The switching unit has a usage condition recognition unit that can identify the usage conditions of the image holding unit, and switches to electrostatic elimination performed by the exposure electrostatic elimination unit or the transfer electrostatic elimination unit based on the recognition result of the usage condition recognition unit.

8. The image forming apparatus according to claim 7, characterized in that, The switching unit includes an environment detection unit that can detect environmental information including the temperature and humidity around the image holding unit as the usage condition identification unit. When the detection result of the environment detection unit belongs to a predetermined low temperature and low humidity environment, the system switches to electrostatic elimination performed by the transfer electrostatic elimination unit.

9. The image forming apparatus according to claim 7, characterized in that, The switching unit includes a concentration detection unit that can detect the concentration of the visible image formed on the image holding unit as the usage condition recognition unit. When the concentration information detected by the concentration detection unit is lighter than the predetermined reference concentration, the electrostatic elimination is switched to be performed by the transfer electrostatic elimination unit.

10. The image forming apparatus according to claim 7, characterized in that, The switching unit includes an image discrimination unit that can determine the average image density of the visible image formed on the image holding unit as the usage condition recognition unit. When the average image density determined by the image discrimination unit is lower than the reference image density in the predetermined number of consecutive images formed, the electrostatic elimination is switched to be performed by the transfer electrostatic elimination unit.

11. The image forming apparatus according to claim 7, characterized in that, The switching unit includes a counting unit that can count the rotation speed of the image holding unit as the usage condition recognition unit. When the rotation speed of the image holding unit counted by the counting unit reaches or exceeds a predetermined reference rotation speed, the system switches to electrostatic elimination performed by the transfer electrostatic elimination unit.

Images