JP5943772B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  A contact developing method in which a developing roller having an elastic layer is brought into contact with a photosensitive drum is widely known as a developing method using a one-component toner in an image forming apparatus such as a copying machine, a printer, a facsimile, or the like that forms an image by electrophotography. Yes. More specifically, a non-magnetic developer is carried on a developing roller, which is an elastic roller having a dielectric layer, and development is performed by bringing it into contact with the surface of the photosensitive drum. Various control techniques have been proposed to maintain and control the process state such as development. For example, a technique for obtaining a desired process condition by controlling a moving speed of a desired driven body by detecting a driving motor current and comparing it with a moving speed of a driving body corresponding to a driving motor current stored in advance. Has been proposed (Patent Document 1). Furthermore, in order to detect the property of the toner layer on the developing roller and control the developing conditions, a technique for detecting the current flowing between the photosensitive drum and the developing roller that occurs when the toner is transferred from the developing roller to the photosensitive drum has been proposed. (Patent Document 2).

JP 2007-164093 A JP 2005-208147 A

  In the contact development method, the moving speed ratio of the developing roller with respect to the photosensitive drum (hereinafter referred to as the peripheral speed ratio) is adjusted to a desired value to form an image. However, when a lot shake or the like of the developing roller or the photosensitive drum occurs, a desired peripheral speed ratio value changes, and an image defect due to the peripheral speed ratio fluctuation occurs. Specifically, since the peripheral speed ratio changes, an image defect such as fluctuation from a desired density occurs. For example, the rubber part, which is an elastic part used in the developing roller, changes in diameter due to expansion, contraction, aging, etc. depending on the environment, and an image defect occurs with a change in peripheral speed ratio. The technique described in Patent Document 1 controls the drive motor rotation speed based on a drive motor current value stored in advance, and controls fluctuations in the peripheral speed ratio caused by changes in the diameter and circumference of the driven body. It is not reflected in. Therefore, there is a possibility that an image defect due to a change in the peripheral speed ratio may occur. The technique described in Patent Document 2 can detect a change in the property of the toner layer on the developing roller by detecting a current flowing between the photosensitive drum and the developing roller, but cannot detect a change in peripheral speed ratio. . Therefore, an image defect due to the peripheral speed ratio fluctuation occurs.

  An object of the present invention is to provide an image forming apparatus capable of suppressing image defects caused by fluctuations in the peripheral speed ratio.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
An image carrier on which an electrostatic latent image is formed and rotated;
A developer for forming the developer image by developing the electrostatic latent image is carried, abutting on the image carrier and rotating in the forward direction with respect to the image carrier, the developer carried by the image carrier A developer carrier to be supplied to the body;
Voltage application means for applying a DC voltage between the image carrier and the developer carrier;
Current detection means for detecting a direct current flowing in the developer carrying member by applying a direct current voltage to the voltage application means; and
Drive means for variably rotating the image carrier and the developer carrier according to the current value of the applied drive current;
Drive current application means for variably applying the drive current to the drive means; and
Control means for controlling a current value of the drive current applied by the drive current application means to the drive means;
An image forming apparatus comprising:
In the state where the image carrier is in contact with the developer non-carrying region of the developer carrier during non-image formation, the control unit applies the drive current while the voltage application unit applies a DC voltage. The control means based on the current value of the direct current detected by the current detection means when the rotational speed of either the image carrier or the developer carrier is changed by changing the current value. Corrects the current value of the drive current for rotating the one during image formation.

  As described above, according to the present invention, it is possible to suppress image defects caused by the peripheral speed ratio fluctuation.

Schematic showing the configuration of a developing device according to an embodiment of the present invention 1 is a schematic cross-sectional view illustrating an image forming apparatus according to an embodiment of the present invention. Schematic sectional view showing a process cartridge according to an embodiment of the present invention Schematic of current detection means in the present invention Schematic showing the relationship between the development current Id and the peripheral speed ratio Vs in the present invention. Flowchart schematic diagram in the first embodiment of the present invention Flow chart explanation schematic diagram in Example 2 of the present invention Flow chart explanation schematic diagram in Example 3 of the present invention Schematic explaining the peripheral speed ratio correction method in Embodiment 1 of the present invention Schematic explaining the peripheral speed ratio correction method in Embodiment 2 of the present invention Schematic showing the relationship between developing roller drive motor applied current and peripheral speed

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

(Schematic configuration of image forming apparatus)
FIG. 2 is a schematic configuration diagram of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus A shown in FIG. 2 is a full color laser printer using an electrophotographic process. In this image forming apparatus A, four process cartridges B corresponding to yellow, magenta, cyan, and black are arranged in series, and a toner image formed by each process cartridge B is transferred onto the intermediate transfer belt 20 of the transfer device. As a result, a full-color image is formed. The process cartridge B has a configuration in which the charging device E, the developing device F, the cleaning device C, and the photosensitive drum 1 shown in FIG. The image forming process in the process cartridge B will be described later.

Primary transfer rollers 22 y, 22 m, 22 c, and 22 k are provided at opposite positions of the photosensitive drum (image carrier) 1 of each process cartridge B with the intermediate transfer belt 20 interposed therebetween. The toner images of the respective colors formed on the photosensitive drum 1 which is the development target in each process cartridge B are transferred onto the intermediate transfer belt 20 by the primary transfer rollers 22y, 22m, 22c and 22k, respectively. The toner images superimposed and transferred on the intermediate transfer belt 20 are collectively transferred onto the recording paper P by the secondary transfer roller 23 provided on the downstream side in the moving direction of the intermediate transfer belt 20. Untransferred toner on the intermediate transfer belt 20 is collected by the intermediate transfer belt cleaner 21.

  The recording paper P is stacked in a cassette 24 below the image forming apparatus A, and is conveyed by a paper feeding roller 25 together with a request for a printing operation, and is formed on the intermediate transfer belt 20 at the position of the secondary transfer roller 23. The transferred toner image is transferred. Thereafter, the toner image of the recording paper P is heated and fixed by the fixing unit 26, and is discharged to the outside of the image forming apparatus A through the paper discharge unit 27.

  In the image forming apparatus A, an upper unit that accommodates detachable process cartridges B of four colors and a lower unit that accommodates a transfer unit, recording paper, and the like are separable. When jam processing such as a paper jam occurs or when the process cartridge B is replaced, the upper and lower units are opened to perform such processing.

(Image formation process)
FIG. 3 shows a cross section in the vicinity of one of the four process cartridges B placed in parallel. In this embodiment, as the photosensitive drum 1 that is the center of the image forming process, an organic photosensitive drum 1 in which an undercoat layer that is a functional film, a carrier generation layer, and a carrier transfer layer are sequentially coated on the outer peripheral surface of an aluminum cylinder is used. Used. In the image forming process, the photosensitive drum 1 is rotationally driven by the image forming apparatus A at a speed of 180 mm / sec.

  The charging roller 2 which is a charging device presses and contacts the roller portion of the conductive rubber against the photosensitive drum 1 and rotates following the rotational direction of the arrow b with respect to the photosensitive drum 1. Here, as a charging process, a DC voltage of −1100 V is applied to the core of the charging roller 2 with respect to the photosensitive drum 1, and the surface potential of the photosensitive drum 1 is −550 V due to the electric charge induced thereby. A uniform dark portion potential (Vd) is formed.

  A spot pattern of laser light emitted by the scanner unit 10 corresponding to the image data on the uniform surface charge distribution surface exposes the surface of the photosensitive drum 1 as indicated by an arrow L in FIG. . The exposed portion of the surface of the photosensitive drum 1 loses its surface charge due to carriers from the carrier generation layer, and the potential decreases. As a result, an electrostatic latent image is formed on the photosensitive drum 1 with the light portion potential Vl = −100 V at the exposed portion and the dark portion potential Vd = −550 V at the unexposed portion.

  The electrostatic latent image is developed by a developing device F in which a toner coat layer having a predetermined coating amount and charge amount is formed on the developing roller 3. A method for forming the toner coat layer will be described later. The developing roller 3 rotates in the forward direction with respect to the photosensitive drum 1 as shown by an arrow c while contacting the photosensitive drum 1. In the present embodiment, the toner charged negatively by frictional charging with respect to the DC bias applied to the developing roller 3 is −300 V. In the developing portion where the photosensitive drum 1 comes into contact with the photosensitive drum 1, the bright portion potential is determined. Fly to only the part to make the electrostatic latent image a real image.

The intermediate transfer belt 20 is pressed against the photosensitive drum 1 of each process cartridge B by primary transfer rollers 22y, 22m, 22c, and 22k, and a DC voltage is applied to each primary transfer roller. An electric field is formed between the drum 1 and the drum 1. As a result, the toner image (developer image) that is actualized on the photosensitive drum 1 receives the force of an electric field from the photosensitive drum 1 on the intermediate transfer belt 20 in a transfer region that is in pressure contact with the intermediate transfer belt 20. Transcribed above. On the other hand, the untransferred toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 20 is scraped off from the drum surface by the urethane rubber cleaning blade 6 installed in the cleaning device C, and the inside of the cleaning device C It is stored in.

(Developer)
FIG. 1 is a schematic diagram illustrating a configuration of a developing device F according to an embodiment of the present invention. FIG. 1A is a schematic diagram illustrating a developing device F and a part of an image forming apparatus related to the developing device F. FIG. 1B is a schematic view showing a configuration of a mechanism for controlling the rotation of the developing roller. The developing device F includes a developing container T, a developing roller 3, a supply roller 5, a toner regulating member 4, and a stirring member 11. The developing container T contains a nonmagnetic one-component toner. The developing roller 3 which is a developer carrying member rotates in a direction c which is a forward direction with respect to the rotation direction of the photosensitive drum 1 while contacting the photosensitive drum 1 (the rotation direction is opposite to that of the photosensitive drum 1). The supply roller 5 rotates in a direction d opposite to the rotation direction of the developing roller 3 while being in contact with the developing roller 3 (the rotation direction is the same as the developing roller 3). The toner regulating member 4 that is a developer regulating means is in contact with the developing roller 3 on the downstream side of the supply roller 5. The stirring member 11 stirs the one-component nonmagnetic toner that is a developer.

  The one-component nonmagnetic toner was prepared by a suspension polymerization method including a binder resin and a charge control agent, and was prepared to have a negative polarity by adding a fluidizing agent or the like as an external additive. A polymerization method is preferable from the viewpoint of high image quality, but may be adjusted by a pulverization method.

In this embodiment, the developing roller 3 is a φ16 mm elastic roller in which a conductive elastic layer 5 mm is formed on a core metal having an outer diameter φ6 mm, and a silicone rubber having a volume resistance of 10 ⁶ Ωm is used for the elastic layer. Using. A coat layer having a function of imparting charge to the developer may be provided on the surface of the elastic roller. In the present embodiment, in order to stably and elastically contact the photosensitive drum 1, the hardness of the elastic layer is 45 ° according to JIS-A, and the surface roughness of the developing roller 3 depends on the particle size of the toner used. However, the arithmetic average roughness Ra was set to 0.05 to 3.0 μm. The surface roughness Ra in the present embodiment was measured using a surface roughness tester SE-30 manufactured by Kosaka Laboratory Co., Ltd. based on JIS B0601. In order to improve the image quality, the arithmetic average roughness is preferably 0.3 to 1.0 μm.

  In the present embodiment, an elastic sponge roller having an outer diameter of φ16 mm in which a polyurethane foam having a foamed skeleton structure and a relatively low hardness is formed on a core metal having an outer diameter of φ5 mm is used as the supply roller 5. The supply roller 5 is made of a foam having a continuous foaming property, so that the supply roller 5 contacts the developing roller 3 without applying excessive pressure, and at the time of supplying toner to the developing roller 3 and developing with moderate irregularities on the surface of the foam. The residual toner is removed without being consumed. The scraping property of the cell structure is not limited to urethane foam, and rubber or the like obtained by foaming silicone rubber or ethylene propylene diene rubber (EPDM rubber) can be used.

  A toner regulating member 4 that is a toner regulating means (developer regulating means) that contacts the developing roller 3 is provided on the downstream side of the contact surface between the supply roller 5 and the developing roller 3 with respect to the rotation direction c of the developing roller 3. ing. The toner regulating member 4 is a member for controlling the toner on the developing roller 3 to a predetermined coating amount suitable for development on the photosensitive drum 1 and a predetermined charge amount. The toner regulating member 4 supports a thin plate-like elastic member 42 such as a phosphor bronze plate or a stainless steel plate in a cantilever manner on a support metal plate 41 fixed to the developing container T, and the abdominal surface of the opposite portion is opposed to the developing roller 3. It is in contact. In the present embodiment, an iron plate having a thickness of 1.2 mm is used as the support metal plate 41, and a phosphor bronze plate having a thickness of 120 μm is fixedly supported on the support metal plate 41 as a thin plate-like elastic member 42. The distance from the cantilever support portion of the thin plate-like elastic member 42 to the contact portion with the developing roller 3, the so-called free length, is 14 mm, and the pushing amount of the developing roller 3 into the thin plate-like elastic member 42 is 1.5 mm. .

(Circumferential speed ratio control means)
The peripheral speed ratio control means of the developing roller 3 with respect to the photosensitive drum 1 will be described. In the present embodiment, peripheral speed ratio control is performed by controlling the rotation speed of the developing roller 3. As shown in FIG. 1B, the rotation shaft of the developing roller 3 is connected to the developing roller drive control motor 3b via the attachment 3a, and the developing roller drive control motor 3b as a drive means receives the applied current. Driving is performed by applying a current from a variable power source S2. The moving speed of the developing roller 3 is set by adjusting the variable power source S2. As the peripheral speed ratio control means, the number of rotations of the photosensitive drum 1 can be made variable. The voltage application to the developing roller 3 is performed by the power source S1. Here, the peripheral speed means the moving speed of the peripheral surface (surface) of the roller-shaped rotating body. The peripheral speed ratio is the speed ratio of the peripheral surface of the roller-shaped rotating body. For example, when the peripheral speeds of the developing roller 3 and the photosensitive drum 1 are the same, the peripheral speed ratio is 100%, and the developing roller 3 When the peripheral speed is half that of the photosensitive drum 1, the peripheral speed ratio is 50%.

(Development roller speed control)
Control of the moving speed (rotational speed) of the developing roller 3 by the current applied to the developing roller drive control motor will be described. A data table of the moving speed of the developing roller 3 with respect to the current flowing through the developing roller drive control motor, which is measured in advance, is stored in the ROM. In the present embodiment, as shown in FIG. 11, a drive motor having a relationship in which the developing roller peripheral speed linearly changes with respect to the current applied to the drive motor is used. FIG. 11 is a schematic diagram showing the relationship between the current applied to the drive motor that drives the developing roller 3 and the moving speed (circumferential speed) of the surface of the developing roller 3. When a desired peripheral speed ratio is set, a predetermined motor current is applied based on the data table, and the moving speed and the peripheral speed ratio Vs are set.

  The developing device and the process cartridge in the present embodiment use a product whose lifetime including the toner capacity is set to be equivalent to 15,000 sheets in terms of 5% A4 paper printing rate.

Example 1
The configuration of the developing device and the image forming apparatus main body related to the developing device in Embodiment 1 of the present invention is as shown in FIG. A voltage-variable power source S1 as a voltage application unit and a power source S2 as a drive current application unit that supplies a motor drive current to the drive motor are connected to an arithmetic processing unit J provided in the image forming apparatus main body. In addition, an ammeter I is provided as a current detecting means for measuring the value of the developing current Id flowing through the developing roller 3, the regulating blade 4, and the supply roller 5 as a whole. The positive direction i of the current value was the direction shown in the figure. The ammeter I is also connected to the arithmetic processing means J so that the detection data can be transferred.

  As shown in FIG. 4, the ammeter I in the present embodiment is configured such that when the current value is detected, the switch SW is connected to the terminal p3 and the voltage between the terminal p2 and the terminal p3 is detected by the voltmeter V. Is detected. At this time, the resistor R was 10 kΩ, and the switch SW was set to be connected to the terminal p1 when the current value was not detected. Therefore, the voltage value and the switch are also connected to the arithmetic processing means J. Further, the arithmetic processing means J is constituted by a CPU of an arithmetic processing unit that performs arithmetic processing, a rewritable storage device RAM that stores detection data, and a storage device ROM that stores data prepared in advance. Set to be readable.

With reference to FIG. 6, the process of setting the peripheral speed ratio of the developing roller 3 to the photosensitive drum 1 to a desired peripheral speed ratio Vs_d (new control speed ratio) in the first embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing a step of setting a desired peripheral speed ratio Vs_d. In step sa01, the peripheral speed ratio Vs_100 as the reference speed ratio stored in the RAM in the previous peripheral speed ratio setting step, and Vs_d as the control speed ratio that becomes a predetermined speed ratio difference α with respect to the peripheral speed ratio Vs_100. =
Vs_100 + α is read out. Here, the peripheral speed ratios Vs_100 and Vs_d indicate the set value Vs_100 of the peripheral speed ratio 100% set previously and the set value Vs_d of the desired peripheral speed ratio (100 + α)%. An initial image forming apparatus that has not performed the peripheral speed ratio setting step sets the predetermined initial value Vso_100 to Vs_100. Next, at step sa02, the peripheral speed ratio set value Vs is controlled by the variable developing roller drive control power source S2, and the developing current Id corresponding to the set value Vs is detected by the ammeter I and stored in the RAM. In this embodiment, the circumferential speed of the developing roller 3 was changed by 1 mm / sec and the current measurement process was repeated.

  Next, in step sa03, a relational expression Id = f (Vs) of the developing current Id with respect to the peripheral speed ratio set value Vs is calculated by the CPU from the peripheral speed ratio set value Vs and the developing current Id stored in the RAM and stored in the RAM. Store. Here, a schematic diagram of the relational expression f0 (Vs) before detection and the relational expression f (Vs) after detection is shown in FIG.

  The extreme value detection process at step sa04 will be described with reference to FIG. The peripheral speed ratio Vmin at the minimum value of Id = f (Vs) calculated in step sa03 is detected by the CPU and stored in the RAM as Vs_100_ex. At this time, it is known that the peripheral speed ratio Vs_100_ex taking the minimum value is 100%. Details of this reason will be described later.

  Next, the step of calculating the peripheral speed ratio set value Vs_d, which is step sa05, will be described. The peripheral speed ratio Vs_100 of the data called in step sa01 is replaced with the set value Vs_100_ex calculated in the previous step sa04 as the peripheral speed ratio of 100%, and set as a new reference speed ratio. Then, the CPU added the α of the desired peripheral speed ratio (100 + α) to Vs_100_ex to calculate the set value Vs_d_ex. In step sa06, the power source S2 is activated, and the setting value Vs_d, which is the old control speed ratio, is set by replacing it with the above-described new control speed ratio, Vs_d_ex, and the control ends.

  Here, a desired setting method of the motor current Im in this example will be described with reference to FIG. FIG. 9B shows the relationship between the previously stored developing roller peripheral speed and the motor current. First, the difference between the calculated peripheral speed Vm_100_ex corresponding to the detected peripheral speed ratio Vs_100_ex and the peripheral speed Vm_100 corresponding to the pre-detected peripheral speed ratio Vs_100_ex changes by one correction. If the predetermined peripheral speed ratio is β (for example, 150%), it can be calculated by a desired peripheral speed Vm_d_ex = β × Vm_100_ex. That is, the value of the driving motor current Im that drives the developing roller 3 at the peripheral speed Vm_d_ex at which the peripheral speed difference (speed difference) corresponding to the predetermined peripheral speed ratio difference α is 50% with respect to the detected peripheral speed Vm_100_ex. Becomes a current value for forming a desired control peripheral speed ratio. The drive motor current Im_ex corresponding to Vm_d_ex can be calculated as shown in the table. Formally, the process of correction 1 → correction 2 → correction 3 in FIG. 9B was obtained to correct the motor drive current.

  Here, it will be described that the above-mentioned minimum value becomes a peripheral speed ratio of 100%. As a result of intensive studies, the inventors of the present application have revealed the following. The diagram shown in FIG. 5 is a measurement result of the development current with respect to the peripheral speed ratio in the initial state in Example 1. As can be seen from the figure, the value of the developing current Id becomes an extreme value at a peripheral speed ratio of 100 [%], and the absolute value of the developing current increases as the peripheral speed ratio increases or decreases. It has also been found that similar similar curves can be obtained when the developing roller not coated with toner is brought into contact with the photosensitive drum. Therefore, the phenomenon that has an extreme value when the peripheral speed ratio is 100% is a phenomenon that occurs when the photosensitive drum and the developing roller are in direct contact with each other and perform electrical exchange.

Next, the reason why the actual peripheral speed ratio becomes V = 100 [%] in the peripheral speed ratio set value Vs_100_ex which is an extreme value of Id = f (Vs) will be described. When a point on the surface of the photosensitive drum or developing roller comes into contact with the surface of the developing roller or photosensitive drum, it is assumed that charge is injected at the certain point. Assume a set of such contact points. It is considered that the peripheral speed ratio between the photosensitive drum and the developing roller affects the number of times of contact per unit time (number of contact points) on each surface. When the peripheral speed ratio is 100%, that is, when there is almost no difference between the moving speed of the photosensitive drum surface and the moving speed of the developing roller surface, the number of contact times per unit time between the photosensitive drum surface and the developing roller surface is minimized. Conceivable. At this time, the chance of friction between the surface of the photosensitive drum and the surface of the developing roller and the opportunity to inject charges are minimized, and as a result, the absolute value of the developing current Id flowing through the developing roller is minimized. That is, it is considered that the extreme value is taken. When the peripheral speed ratio is other than 100%, the larger the peripheral speed difference between the photosensitive drum surface and the developing roller surface, the greater the number of contacts per unit time and the larger the absolute value of the developing current Id.

  The control according to the present invention is performed when a non-toner-coated area (developer non-carrying area) on the developing roller is in contact with the photosensitive drum and when non-image formation is performed. During the control operation of the present invention, the control method can perform the operation without affecting the state of the toner layer coated on the developing roller. Therefore, the peripheral speed ratio control can be performed with a simple configuration and low cost.

  In this embodiment, a DC voltage of −1100 V is applied to the core of the charging roller so that the dark potential portion is uniformly −600 V as the surface potential of the photosensitive drum. As for the voltage application to the developing roller, the regulating member, and the supply roller, −300 V was applied from the power source S1. At this time, the potential difference Vback = 300V between the dark potential and the developing bias is set. Furthermore, in this embodiment, the peripheral speed ratio of the developing roller to the photosensitive drum is set to 150% (α = 50).

  In this embodiment, there are a toner coat portion and a toner non-coat portion on the surface of the developing roller, and the toner non-coat portion is provided at both end portions in the longitudinal direction of the developing roller by 15 mm each. The toner non-coated portion is preferably provided at 10 mm or more. The peripheral speed control operation is set so as to operate at the time of power-on at the time of image formation, replacement of the toner cartridge, and output of 500 sheets. Furthermore, when an environment sensor or the like is provided, the peripheral speed ratio fluctuation can be remarkably suppressed by performing the peripheral speed ratio control when the environment changes.

(Example 2)
With reference to FIGS. 7 and 10, an image forming apparatus according to Embodiment 2 of the present invention will be described. FIG. 7 is a flowchart of the peripheral speed ratio control in the second embodiment of the present invention. FIG. 10 is a schematic diagram for explaining a peripheral speed ratio correction method according to the second embodiment of the present invention. FIG. 10A is a diagram showing the relationship between the peripheral speed ratio and the development current value, and FIG. These are figures which show the relationship between a circumferential speed and a drive motor electric current. The present embodiment basically conforms to the first embodiment, but differs in the following points. In addition, about the structure which is not demonstrated here, since it is common in Example 1, description is abbreviate | omitted.

  In the second embodiment, unlike the first embodiment, the peripheral speed ratio control is performed without calculating the peripheral speed ratio 100%, which is the minimum value of the developing current with respect to the peripheral speed ratio. Specifically, a relational expression representing the relationship between the change in the current value of the development current and the change in the peripheral speed ratio is calculated, and the same current value between the previously calculated relational expression and the newly calculated relational expression is calculated. The shift amount of each speed ratio when the development current is detected is calculated. Then, the current value of the drive current is corrected according to the shift amount.

As shown in FIG. 7, in step sb01, a relational expression Ido = fo (Vs) of the developing current Id with respect to the peripheral speed ratio Vs before detection is read out. Next, similarly to steps sa02 and sa03 in the first embodiment, after detecting the developing current Id with respect to the peripheral speed ratio Vs in steps sb02 and sb03, a relational expression Id = f (Vs) is calculated. In step sb04, as shown in FIG. 10A, a shift amount Δ in the direction of the peripheral speed ratio Vs between Ido and Id before detection is calculated, and a desired peripheral speed ratio Vs_ex is calculated.

  In this embodiment, the shift amount Δ is calculated by the least square method so that [fdo (Vs−Δ) −fd (Vs)] is minimized. Thereafter, the desired peripheral speed ratio Vs_d is replaced with Vs_d_ex in step sb05, the peripheral speed ratio is corrected in step sb06, and the peripheral speed ratio control is terminated. Further, in step sb05, the motor current is calculated by calculating the peripheral speeds Vm and Vm_ex corresponding to the peripheral speed ratios Vs_d and Vs_d_ex based on the data table as shown in FIG. Was calculated.

(Example 3)
With reference to FIG. 8, an image forming apparatus according to Embodiment 3 of the present invention will be described. FIG. 8 is a flowchart of the peripheral speed ratio control in the third embodiment of the present invention. The present embodiment basically conforms to the first embodiment, but differs in the following points. In addition, about the structure which is not demonstrated here, since it is in common with the said Example, description is abbreviate | omitted.

  The difference is that the predetermined peripheral speed ratio (control speed ratio) in Example 1 is set to 100%. Specifically, this will be described with reference to the flowchart shown in FIG. In this example, step sa01 performed in Example 1 is not included, and data relating to the peripheral speed ratio before detection is not read. First, steps sc01 to sc03 correspond to steps sa02 to sa04 in the first embodiment, and calculate a peripheral speed ratio Vs_100_ex when the peripheral speed ratio is 100% (at the minimum value). Next, in step sc04, the desired peripheral speed ratio is replaced with Vs_d by the peripheral speed ratio Vs_100_ex, and in step sc05, the corrected peripheral speed ratio Vs_d is set, and the control is terminated.

Example 4
Example 4 of the present invention basically conforms to Example 3, but differs in the following points. In addition, about the structure which is not demonstrated here, since it is in common with the said Example, description is abbreviate | omitted.

  In the step of detecting the developing current Id with respect to the peripheral speed ratio setting value Vs, the difference Vback between the dark potential on the photosensitive drum surface and the developing bias is Vback = 500 [V], which is larger than that during image formation. .

  As described above, in the vicinity of the peripheral speed ratio V = 100 [%], the influence of the image density fluctuation on the peripheral speed ratio fluctuation is larger than that when the peripheral speed ratio V> 100 [%]. In order to obtain this, it is necessary to correct the peripheral speed ratio to V = 100 [%] with high accuracy.

  As described above, when the absolute value of the potential difference Vback [V] is large, the gradient of the relational expression Id = f (Vs) is large at the same peripheral speed ratio setting value. In this embodiment, by setting the absolute value of the potential difference Vback [V] to a value larger than that at the time of image formation, the minimum value Vs_100_ex of the relational expression Id = f (Vs) can be detected with high accuracy in the minimum value calculation process. it can. However, the absolute value of the potential difference Vback in this embodiment is a value that does not exceed the discharge threshold voltage.

(Comparative Example 1)
The first comparative example is basically the same as the first embodiment except that the peripheral speed ratio control is not performed. That is, the comparative example 1 has a configuration in which the arithmetic processing means J and the ammeter I are not provided in the configuration of the first embodiment shown in FIG.

(Comparative Example 2)
Comparative Example 2 is basically the same as Example 1, but differs in the following points. In this example, the peripheral speed ratio control method is different. First, the drive motor current was detected, and control was performed so that the drive motor current was stored in advance.

(Comparative Example 3)
Comparative Example 3 is basically the same as Comparative Example 1, but differs in that the peripheral speed ratio V is set to 100 [%].

≪Evaluation method of each experimental example and comparative example≫
In the following, image evaluation for examining the difference between the present embodiment and the comparative example will be described.

a) Initial density fluctuation (difference in initial development unit differences)
The image density of the front black image portion developed on the paper was measured, and each example and comparative example were evaluated. A method for evaluating density fluctuation in the initial state will be described below.

  The image density measurement is carried out with the images of 10 cartridges each having the same developer configuration, and the difference between the density value and the target density value 1.4 is 0.1 or less. evaluated.

○: 8 or more △: 5-7
×: 4 or less

  In this image density evaluation, a process for setting a desired peripheral speed ratio was performed in each Example and each Comparative Example in the initial stage, and then density measurement was performed.

b) Image density fluctuation evaluation (initial to endurance fluctuation)
The image density of the front black image portion developed on the paper was measured, and each example and comparative example were evaluated. A method for evaluating density fluctuation in the initial state will be described below.

  The image density measurement was performed on images created by each of the ten developing units having the same developing unit configuration. The absolute value of the difference between the initial and endurance density values in each developing unit was calculated, and the average value of 10 developing units was evaluated according to the following criteria.

○: Less than 0.2 Δ: 0.2 or more and less than 0.3 ×: 0.3 or more

  In this image density evaluation, in each example and each comparative example, a process of setting a desired peripheral speed ratio was performed after the initial stage and endurance, and then the density measurement was performed. Here, the density measurement after the endurance was performed after printing 15,000 sheets in terms of 5% A4 paper printing rate.

c) Sweeping fluctuation evaluation (initial to endurance fluctuation)
An image (patch image) in which a white image is followed by an all-black image of 30 mm x 20 mm in length and width is output, and the sweeping portion is digitized by the following method to evaluate each example and each comparative example. did. Image density unevenness is visually evaluated and evaluated as “+” when density unevenness can be recognized at the leading edge of the patch image, “−” when density unevenness can be recognized at the trailing edge of the patch density, and “0” when not recognized. did. The fluctuation of the sweeping value of the developing machine used for the evaluation from the initial stage to after the endurance was calculated with 10 cartridges, and the sweeping fluctuation evaluation was performed according to the following criteria.

A: "+" or "-" evaluation result is 1 or less.
○: “+” or “−” evaluation results are 2 to 3 pieces.
Δ: “+” or “−” evaluation result is 4-6.
×: “+” or “−” evaluation result is 7 or more.

  In this evaluation, in each example and each comparative example, a step of setting a desired peripheral speed ratio was performed after the initial stage and endurance, and then the concentration was measured. Here, the density measurement after the endurance was performed after printing the initial 100 sheets and after the endurance printing 15,000 sheets in terms of 5% A4 paper printing rate.

<Mechanism of sweeping image defects>
The reason why the tip density of the patch image is high will be described. When the developing roller peripheral speed is greater than the peripheral speed of the photosensitive drum, development is performed so that the developing roller passes the photosensitive drum at the leading edge of the patch image. The transfer of the toner to the photosensitive drum starts upstream of the portion where the photosensitive drum and the developing roller abut. Thereafter, it is presumed that a step of leveling the toner layer occurs in the abutting nip where the developing roller and the photosensitive drum abut. At that time, when the developing roller is set to pass the photosensitive drum, the toner layer is leveled so as to sweep the toner in the direction of rotation. However, since there is a non-exposed area at the tip of the patch image, movement in the traveling direction is restricted. As a result, it is considered that the density at the tip of the patch image is increased. On the other hand, if the developing roller is set to be overtaken by the photosensitive drum (peripheral speed ratio is less than 1.0), the patch density rear end is considered to be dark.

  The image evaluation results of Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 below.

≪Advantages over conventional examples≫
First, the superiority of Example 1 will be described by comparing with Comparative Example 1. Comparative Example 1 is an example in which the desired peripheral speed ratio V is set to 150% and the peripheral speed ratio is not controlled. In Comparative Example 1, the initial density fluctuation is larger than that in Example 1. The reason is considered as follows. It is presumed that there are some cartridges in which the diameters of the photosensitive drum and the developing roller are deviated from desired values. In Comparative Example 1, since the peripheral speed ratio control is not performed, it is considered that the peripheral speed ratio fluctuation of the cartridge having the above-mentioned deviation cannot be corrected, and the initial density fluctuation accompanying it is generated. On the other hand, in the first embodiment, in the cartridge having the above-described deviation, the peripheral speed ratio fluctuation is corrected as appropriate, so that a good image density can be obtained.

  Next, the superiority of Examples 1 to 4 will be described by comparing Examples 1 to 4 and Comparative Examples 1 to 3.

≪Advantages over other comparative examples≫
(A) Initial density fluctuation evaluation (initial cartridge variation)
Examples 1 to 4 and Comparative Examples 1 to 3 are compared for initial density fluctuation evaluation (initial cartridge variation).

  As described above, Comparative Example 1 and Comparative Example 3 are examples in which control is not performed with respect to the peripheral speed ratio fluctuation. For this reason, variations in the peripheral speed ratio due to cartridge differences cannot be corrected, and initial image density fluctuations occur.

  On the other hand, in the first, third, and fourth embodiments, even if the peripheral speed ratio varies due to the difference in the cartridges, the peripheral speed ratio fluctuation can be corrected as appropriate. Therefore, initial density fluctuation is suppressed. On the other hand, in Example 2, the effect of suppressing the initial density fluctuation as in Examples 1, 3, and 4 cannot be obtained. In Examples 1, 3, and 4, the peripheral speed ratio is set based on the value of Vs_min (peripheral speed ratio 100%) when the direct current I (Vs) is minimal with respect to the peripheral speed Vs. On the other hand, in the second embodiment, the peripheral speed ratio is set without detecting the value of Vs_min (peripheral speed ratio 100%) when the direct current I (Vs) is a minimum value with respect to the peripheral speed Vs. For this reason, for example, if the deviation of the developing roller resistance causes a large deviation from the relational expression of the measured direct current before detection, the correction accuracy is considered to be lowered. As a result, the second embodiment cannot obtain the effects of the first, third, and fourth embodiments with respect to the accuracy of correction for the peripheral speed ratio fluctuation. As a result, slight initial density fluctuation occurs.

  In Comparative Example 2, the peripheral speed ratio is set so as to obtain a predetermined developing roller driving current value stored in advance, but the evaluation result of the initial density fluctuation is the same as in Comparative Examples 1 and 3 in which the control is not performed. It ’s bad. The reason is that it is impossible to detect and control the peripheral speed ratio fluctuation according to the fluctuation of the photosensitive drum and developing roller diameter of each cartridge. As a result, similar to Comparative Examples 1 and 3, the initial density fluctuation deteriorates.

(B) Image density fluctuation evaluation (initial to endurance fluctuation)
Next, Examples 1-4 and Comparative Examples 1-3 are compared for image density fluctuation evaluation (initial to endurance fluctuation).

  As described above, Comparative Example 1 and Comparative Example 3 do not perform the peripheral speed ratio control. For this reason, fluctuations in image density due to changes in the peripheral speed ratio due to changes in the diameter of the photosensitive drum and the developing roller due to deterioration over time cannot be suppressed.

  In Examples 1, 3, and 4, the peripheral speed ratio 100% is detected from the minimum value of the relational expression Id = f (Vs), and the desired peripheral speed ratio is set from the detected value. For this reason, appropriate peripheral speed ratio control can be accurately adjusted through durability with respect to Comparative Example 1 and Comparative Example 3.

  In the second embodiment, the peripheral speed ratio is set without detecting the value of Vs_min (peripheral speed ratio 100%) when the direct current I (Vs) is a minimum value with respect to the peripheral speed Vs. For this reason, for example, if the deviation of the developing roller resistance causes a large deviation from the relational expression of the measured direct current before detection, the correction accuracy is considered to be lowered. Therefore, a slight image defect occurs.

  In Comparative Example 2, although the initial peripheral speed ratio fluctuation cannot be controlled, a slight change in the image density occurs because the change in the drive motor current during endurance is controlled.

  As described above, in the present invention, the peripheral speed ratio 100% is detected as appropriate, and the peripheral speed ratio control is performed based on the detected value, so that it is stable even during time-dependent changes such as endurance fluctuations and environmental fluctuations. As a result, a good image can be obtained.

(C) Sweeping evaluation (initial to endurance fluctuation)
Next, Examples 1 to 4 and Comparative Examples 1 to 3 are compared for sweeping evaluation (initial to endurance fluctuation).

  In Examples 1 and 2 and Comparative Examples 1 and 2, the effects as in Example 3 cannot be obtained through durability from the beginning. As for the image defect of sweeping, it is predicted that the sweeping amount increases as the peripheral speed ratio of the developing roller differs with respect to the photosensitive drum. Examples 1 and 2 and Comparative Examples 1 and 2 are set to a peripheral speed ratio of 150%, whereas sweeping image defects are remarkable, whereas Example 3 is set to a peripheral speed ratio of 100%. Therefore, the sweeping amount is considered to be good.

  On the other hand, although the comparative example 3 is set to the peripheral speed ratio of 100%, the sweeping amount is slightly bad. Since the comparative example 3 does not perform the peripheral speed ratio control, it is considered that when the peripheral speed ratio fluctuation occurs, the sweeping fluctuation increases. The reason is considered as follows. When the peripheral speed ratio of the developing roller to the photosensitive drum is large, the sweeping image defect causes density unevenness at the front end of the patch image, and when the peripheral speed ratio is low, density unevenness occurs at the rear end of the patch image. For this reason, when the peripheral speed ratio variation occurs when the peripheral speed ratio is 100%, density unevenness occurs at the leading edge or the trailing edge of the patch image, and the patch image varies greatly. As a result, it is considered that Comparative Example 3 has a large sweeping fluctuation.

  Further, when the peripheral speed ratio is 100%, the influence of the image defect due to the peripheral speed ratio fluctuation is large, and in Comparative Example 3 in which control is not performed through the endurance, after the endurance, the sweeping image defect occurs more. On the other hand, when the peripheral speed ratio is 100%, the peripheral speed ratio control is appropriately performed even in a state where the influence of the image defect due to the peripheral speed ratio fluctuation is large, so that sweeping can be remarkably suppressed.

  Further, the fourth embodiment can significantly reduce the sweeping image defect as compared with the third embodiment. The fourth embodiment is an example in which the absolute value of the bias applied between the photosensitive drum and the developing roller is increased when the peripheral speed ratio is detected as compared with the third embodiment.

  When the bias applied between the photosensitive drum and the developing roller is large, the amount of current flowing between the photosensitive drum and the developing roller in an area not coated with toner increases. When the amount of current increases, the detection accuracy of the minimum value of the direct current I (Vs) with respect to the peripheral speed ratio Vs, that is, the peripheral speed ratio 100% is improved, and more accurate peripheral speed ratio control can be performed. As a result, it is considered that Example 4 can remarkably suppress image defects due to sweeping.

  From the above, in the embodiment of the present invention, when the peripheral speed fluctuation such as the peripheral speed ratio of 100% is set such that an image defect is likely to occur due to sweeping, the peripheral speed ratio of 100% is accurately detected and controlled. Therefore, a good image can be obtained. In addition, since the peripheral speed ratio control is appropriately performed, a good image can be stably obtained even with respect to a change with time such as a durability change and an environmental change. Further, by increasing the bias applied between the photosensitive drum and the developing roller at the time of detecting the peripheral speed ratio, it is possible to perform peripheral speed ratio control with higher accuracy, and to obtain a more stable and good image. it can.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Charging roller, 3 ... Developing roller, A ... Image forming apparatus main body, B ... Process cartridge, C ... Cleaning device, F ... Developing apparatus, S1, S2 ... Power supply, I ... Ammeter, J ... Arithmetic processing means

Claims (7)

An image carrier on which an electrostatic latent image is formed and rotated;
A developer for forming the developer image by developing the electrostatic latent image is carried, abutting on the image carrier and rotating in the forward direction with respect to the image carrier, the developer carried by the image carrier A developer carrier to be supplied to the body;
Voltage application means for applying a DC voltage between the image carrier and the developer carrier;
Current detection means for detecting a direct current flowing in the developer carrying member by applying a direct current voltage to the voltage application means; and
Drive means for variably rotating the image carrier and the developer carrier according to the current value of the applied drive current;
Drive current application means for variably applying the drive current to the drive means; and
Control means for controlling a current value of the drive current applied by the drive current application means to the drive means;
An image forming apparatus comprising:
In the state where the image carrier is in contact with the developer non-carrying region of the developer carrier during non-image formation, the control unit applies the drive current while the voltage application unit applies a DC voltage. The control means based on the current value of the direct current detected by the current detection means when the rotational speed of either the image carrier or the developer carrier is changed by changing the current value. Corrects a current value of the drive current for rotating the one during image formation. The speed ratio between the moving speed of the surface of the image carrier and the moving speed of the surface of the developer carrier during image formation is a predetermined speed ratio difference with respect to a predetermined reference speed ratio. An image forming apparatus that sets a current value of the drive current for rotating the one so as to obtain a control speed ratio,
The control means includes
Calculate the moving speed of the one surface when the current value of the direct current detected by the current detection means becomes an extreme value,
The current value of the driving current for rotating the one at the moving speed of the one surface that is a speed difference corresponding to the predetermined speed ratio difference with respect to the calculated moving speed of the one surface is the control. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to a current amount for forming a speed ratio.   3. The image forming apparatus according to claim 2, wherein the reference speed ratio is a speed ratio in which there is no substantial difference between a moving speed of the surface of the image carrier and a moving speed of the surface of the developer carrier. The control means includes
Calculate the current value of the drive current at which the current value of the direct current detected by the current detection means becomes an extreme value,
The image forming apparatus according to claim 1, wherein the calculated current value is set to a current value of the driving current for rotating the one during image formation.   The calculated current value is a current value for forming a speed ratio in which there is substantially no difference between the moving speed of the surface of the image carrier and the moving speed of the surface of the developer carrier. 5. The image forming apparatus according to 4. The control means includes
Relational expression representing the relationship between the change in the current value of the direct current detected by the current detection means and the change in the speed ratio between the moving speed of the surface of the image carrier and the moving speed of the surface of the developer carrier To calculate
Calculating a shift amount of each speed ratio when a direct current of the same current value is detected between the previously calculated relational expression and the newly calculated relational expression;
The image forming apparatus according to claim 1, wherein a current value of the drive current that rotates the one is corrected during image formation according to the shift amount.   The absolute value of the potential difference between the image carrier and the developer carrier when the current detector detects a direct current is larger than that during image formation and smaller than a discharge threshold. The image forming apparatus according to any one of claims 1 to 6.

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