JP2021096374A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of leakage between an image carrier and a developer carrier.SOLUTION: An image forming apparatus has: a removable process cartridge that has an image carrier, an electrifying member, a developer carrier that is opposite to the image carrier in a non-contact state and carries a developer, a developing frame body that is provided with an opening part for communicating a developer storage chamber and a developing chamber and supports the developer carrier, a rotating member that is rotated in conjunction with the developer carrier, and a sealing member that seals the opening part and is partially fixed to the rotating member; an application unit that applies a developing bias to the developer carrier; a detection unit that detects the value of current between the image carrier and the developer carrier; and a control unit that detects whether the value of current exceeds a threshold while the developing bias is applied to the developer carrier and controls an AC voltage to be equal to or less than the threshold. The time required for the control unit to control the AC voltage to be equal to or less than the threshold is shorter than the time required from the start of opening the opening part by taking up the sealing member by the rotation of the rotating member until the end of the opening.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus that forms an image on a recording medium using an electrophotographic method.

In an image forming apparatus such as a printer using an electrophotographic method (electrophotographic process), various developing apparatuss are used to develop an electrostatic latent image formed on an image carrier. As an example, in a one-component developing method in which development is performed using a developer that uses only toner without containing carriers, a predetermined gap is formed between the image carrier and the developer carrier facing the image carrier. A one-component non-contact developing method provided and arranged is known.

In the non-contact developing method, a development bias in which a DC voltage and an AC voltage are superimposed is applied to the developer carrier, so that the charged toner flies from the developer carrier to the image carrier and becomes the image carrier. A toner image is developed on the formed electrostatic latent image. The toner image developed on the image carrier is transferred and fixed on a recording medium such as paper.

By the way, in the non-contact developing method, the gap provided between the image carrier and the developer carrier may fluctuate due to the driving of the image carrier and the developer carrier. There is a problem that density unevenness occurs in the formed image because the electric field strength between the image carrier and the developer carrier fluctuates due to the fluctuation of the gap.

To solve this problem, by increasing the inter-peak voltage (peak-to-peak value) of the AC voltage in the development bias, the toner sufficiently flies from the developer carrier to the image carrier, and the occurrence of density unevenness is suppressed. It is possible. However, when the inter-peak voltage of the AC voltage in the development bias becomes large, the potential difference from the surface potential of the image carrier becomes large. Therefore, there is a problem that a discharge occurs between the developer carrier and the image carrier, a current leak (hereinafter referred to as a leak) in which a discharge current flows due to the discharge occurs, and noise is generated in the formed image. It was.

Therefore, in Patent Document 1, by measuring the impedance based on the current value flowing between the image carrier and the developer carrier, the limit value of the peak-to-peak voltage (peak-to-peak value) at which leakage occurs (peak-to-peak value) ( Leak limit) is detected.

Japanese Unexamined Patent Publication No. 2005-78015

However, the technique described in Patent Document 1 has the following problems.

When toner is interposed in the gap between the image carrier and the developer carrier, the resistance between the toner carrier increases the resistance between the image carrier and the developer carrier, and leakage is less likely to occur. Therefore, the state in which the toner is not present on the developer carrier is the state in which leakage is most likely to occur.

Therefore, when the peak voltage is set based on the leak limit detected in the state where the toner is present as in the technique described in Patent Document 1, the developing agent is reduced due to the decrease of the toner in the developing apparatus. Leaks can occur when the amount of toner carried on the carrier is reduced.

An object of the present invention is to suppress a leak generated between an image carrier and a developer carrier regardless of the amount of toner supported on the developer carrier.

In order to achieve the above object, the present invention is provided with a rotatable image carrier, a charging member for charging the image carrier, and a developing agent so as to face the image carrier in a non-contact state. A rotatable developer carrier for carrying the developer, a developer accommodating chamber for accommodating the developer, a developing chamber in which the developer carrier is rotatably provided, a developer accommodating chamber and the developing chamber. A developing frame body that is provided with an opening for communicating with the developer and supports the developing agent carrier, a rotating member that is rotatably provided in the developing frame body and rotates in conjunction with the developing agent carrier, and the above. A process cartridge that seals the opening provided in the developing frame, has a sealing member partially fixed to the rotating member, and is removable from the image forming apparatus, and the developing agent. An application unit that applies a development bias in which a DC voltage and an AC voltage are superimposed on the carrier, a detection unit that detects the current value flowing between the image carrier and the developer carrier, and the current value are used. At the time of detection, with the development bias applied to the developer carrier, it is detected whether or not the current value detected by the detection unit exceeds the threshold value, and the AC voltage is set to be equal to or lower than the threshold value. The time required for the control unit to control the AC voltage so as to be equal to or lower than the threshold value is such that the sealing member is wound up by the rotation of the rotating member and the opening is opened. It is characterized in that it is shorter than the time required from the start of opening the part to the end of opening.

According to the present invention, leakage generated between the image carrier and the developer carrier can be suppressed regardless of the amount of toner supported on the developer carrier.

Schematic diagram of the overall configuration of the image forming apparatus Cross-sectional view of the developing container (A), (b) Explanatory drawing about toner seal winding configuration Explanatory drawing which shows configuration about development bias application and discharge detection Explanatory drawing about leakage current detection by detection part A flowchart showing the flow of the discharge generation detection operation according to the first embodiment. Timing chart showing the drive timing of the discharge detection operation according to the first embodiment Diagram of the relationship between the Vpp set at the time of detecting the discharge operation and the detected current value in Example 1 and Comparative Example 1. A flowchart showing the flow of the discharge generation detection operation according to the second embodiment. Timing chart showing the drive timing of the discharge detection operation according to the second embodiment

Hereinafter, preferred embodiments of the present invention will be described in detail exemplarily with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following examples should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended to limit the scope of the invention to the following examples.

[Example 1]
With reference to FIG. 1, the overall configuration of the image forming apparatus will be described together with the image forming operation. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of the image forming apparatus according to the first embodiment.

<Explanation of image forming apparatus>
The image forming apparatus is a laser printer using an electrophotographic method, and the process cartridge 20 is detachably attached to the apparatus main body M. Here, the apparatus main body M of the image forming apparatus indicates a component of the image forming apparatus excluding the process cartridge 20. Further, the image forming apparatus to which the present invention is applicable is not limited to those shown here. For example, the present invention is also applicable to a color laser printer provided with a plurality of process cartridges 20 and using an intermediate transfer belt (intermediate transfer body) to transfer a plurality of image toner images to a recording medium to form a color image. ..

The photosensitive drum 1 as an image carrier (charged body) has an OPC (organic optical semiconductor) photosensitive layer formed on the outer peripheral surface of the conductive drum. The photosensitive drum 1 receives a driving force from a driving source (not shown) of the main body of the apparatus, and is rotationally driven in the clockwise direction of FIG. 1 at a predetermined process speed (for example, 385 mm / sec).

A charging bias is applied to the charging roller 4 as a charging member at a predetermined timing, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential. The laser beam scanner 6 as an exposure unit forms an electrostatic latent image on the surface of the photosensitive drum 1 by scanning and exposing (irradiating) the charged photosensitive drum 1 with a laser beam corresponding to the image information.

The developing apparatus as a developing unit develops an electrostatic latent image formed on the surface of the photosensitive drum 1 with toner as a developing agent. The developing apparatus includes a developing roller 7, a developing blade 8, a developing container 9, and a stirring member 10. The developing roller 7 is arranged so as to face the photosensitive drum 1, and is a developer carrier for supplying toner to the photosensitive drum 1. The developing blade 8 is a regulating member for regulating the layer thickness of the toner supported on the developing roller 7 and imparting an electric charge to the toner. The stirring member 10 conveys and stirs the toner in the developing container 9. The developing container 9 will be described later.

The developing roller 7 receives a driving force from a driving source (not shown) of the apparatus main body M and is rotationally driven in the counterclockwise direction of FIG. A toner layer (magnetic spike) charged by the developing blade 8 is formed on the surface of the developing roller 7. Then, when a development bias in which an AC voltage and a DC voltage are superimposed is applied to the developing roller 7, the toner carried on the developing roller 7 flies to the photosensitive drum 1 due to the electric field of the developing bias, and the surface of the photosensitive drum 1 is surfaced. The electrostatic latent image formed on the surface is developed as a toner image.

On the other hand, the recording medium P is fed by a feeding roller or the like, and a toner image developed on the surface of the photosensitive drum 1 by the transfer roller 11 to which a transfer bias is applied at the nip portion between the photosensitive drum 1 and the transfer roller 11. (Developer image) is transferred. The recording medium P on which the toner image is transferred is separated from the surface of the photosensitive drum 1 and sent to the fixing device 12, heated and pressurized, and the transferred toner image is fixed on the recording medium P.

The toner that is not transferred to the recording medium P and remains on the surface of the photosensitive drum 1 is removed by the cleaning blade 2 as a cleaning unit that comes into contact with the photosensitive drum 1 and cleans the photosensitive drum 1, and is housed in the cleaning container 5. After that, the surface of the photosensitive drum 1 is charged again by the charging roller 4, and the above steps are repeated to perform a series of image formation cycles.

In this embodiment, the photosensitive drum 1, the charging roller 4, the cleaning blade 2, the cleaning container 5, and the developing roller 7, the developing blade 8, the developing container 9, and the stirring member 10 are integrated as the process cartridge 20. The process cartridge 20 is removable from the device main body M of the image forming apparatus.

<Outline of developing container>
The configuration of the developing container 9 will be described with reference to FIG. FIG. 2 is a cross-sectional view of the developing container.

The developing container 9 is a developing frame that supports the developing roller 7, which is a developing agent carrier. The developing container 9 includes a toner accommodating chamber 9a which is a developing agent accommodating chamber for accommodating toner, a developing chamber 9b provided with a developing roller 7 rotating counterclockwise, and a toner accommodating chamber 9a and a developing chamber 9b. An opening 9c, which is an opening for communicating with the above, is provided.

In the developing chamber 9b, a developing blade 8 which is a regulating member for regulating the layer thickness of the toner supported on the developing roller 7 is arranged.

The toner accommodating chamber 9a is rotatably provided with a stirring member 10 that conveys and stirs the toner. The stirring member 10 is composed of a stirring sheet 10a and a stirring shaft 10b. One end of the stirring sheet 10a is attached to the stirring shaft 10b, and the stirring shaft 10b rotates in the clockwise direction, so that the stirring sheet 10a also rotates. By rotating the stirring sheet 10a, the toner in the toner accommodating chamber 9a is agitated and conveyed from the toner accommodating chamber 9a to the developing chamber 9b through the opening 9c.

The toner conveyed from the toner accommodating chamber 9a to the developing chamber 9b by the stirring member 10 is supplied to the developing roller 7. The toner supplied to the developing roller 7 is supported on the surface of the developing roller 7, and the layer thickness of the toner is regulated by the developing blade 8. The toner regulated by the developing blade 8 is given an appropriate charge by triboelectric charging.

Below, the main parameters of the developing roller 7, the developing blade 8, and the stirring member 10 constituting the developing apparatus are illustrated.

The developing roller 7 has an outer diameter of 14 mm, a material of metal (nickel / aluminum / SUS), a surface roughness of Ra0.2 to 1.0 μm, and a rotation speed of 385 mm / sec (normal printing).

The developing blade 8 is made of urethane and has a thickness of 1.0 mm.

The material of the stirring member 10 is polycarbonate, the thickness is 130 μm, and the rotation speed is 60 rpm (normally at the time of printing).

<Toner seal winding configuration>
The winding configuration of the toner seal will be described with reference to FIGS. 3 (a) and 3 (b). 3A and 3B are explanatory views of a toner seal winding configuration.

When the developing container 9 is shipped in a new state, it is necessary to prevent toner from leaking from the developing container 9 to the outside. Therefore, as shown in FIG. 3A, in the developing container 9, the opening 9c between the toner accommodating chamber 9a accommodating the toner and the developing chamber 9b accommodating the developing roller 7 is a toner as a sealing member. It is sealed by a seal 13. A part of the toner seal 13 is fixed to the toner seal winding shaft 14 which is a rotating member as an opening member of the toner seal 13. As shown in FIG. 3B, the toner seal 13 is wound around the toner seal winding shaft 14 by rotating the toner seal winding shaft 14, and the opening 9c is opened. Further, in this embodiment, the toner seal winding shaft 14 also serves as the stirring shaft 10b, the toner seal winding shaft 14 rotates in conjunction with the rotation of the stirring shaft 10b, and the stirring member 10 rotates once. The toner seal 13 is wound around the toner seal winding shaft 14. The rotational driving force of the stirring shaft 10b is first transmitted by the developing roller 7 from the driving source (not shown) of the apparatus main body M to the rotating driving force of the developing roller 7, and further transmitted to the stirring shaft 10b via the gear. Will be done. That is, the developing roller 7, the stirring shaft 10b, and the toner seal winding shaft 14 rotate in conjunction with each other. Here, the rotation speed of the stirring sheet 10a during the normal printing operation of this embodiment is set to 60 rpm. Therefore, the toner seal 13 is wound up in 1 sec when it operates at the peripheral speed during normal printing operation. Although the structure in which the toner seal winding shaft 14 which is a rotating member also serves as the stirring shaft 10b of the stirring member 10 is illustrated here, the present invention is not limited to this. The toner seal winding shaft 14 which is a rotating member may be rotatably provided in the developing container 9 which is a developing frame body independently of the stirring member 10.

<Explanation of discharge detection configuration between photosensitive drum and developing roller>
Next, with reference to FIG. 4, a configuration relating to application of a development bias to the developing roller 7 and discharge detection between the photosensitive drum 1 and the developing roller 7 will be described. FIG. 4 is an explanatory diagram showing a configuration relating to development bias application and discharge detection.

As shown in FIG. 4, the developing roller 7 has a sleeve 7a that supports toner at the time of image formation, and circular caps 7b are fitted at both ends of the sleeve 7a in the longitudinal direction. The developing roller 7 is rotationally driven around the roller shaft 7c. Here, the outer diameter of the photosensitive drum 1 is 30 mm, and the outer diameter of the developing roller 7 is 14 mm, which is smaller than the outer diameter of the photosensitive drum 1.

Further, the developing roller 7 is provided so as to face the photosensitive drum 1 in a non-contact state with a gap (SD gap). In this embodiment, the cap 7b has a larger outer diameter than the sleeve 7a, and the outer peripheral surface of the cap 7b is in contact with the surface of the photosensitive drum 1. As a result, a predetermined gap (SD gap) is provided between the developing roller 7 and the photosensitive drum 1, and the developing roller 7 and the photosensitive drum 1 face each other in a non-contact state. Here, an SD gap of 200 μm is provided as a predetermined gap.

The configuration in which a predetermined gap (SD gap) is provided between the developing roller 7 and the photosensitive drum 1 is not limited to this. For example, a predetermined gap may be provided between the developing roller 7 and the photosensitive drum 1 by a frame body that rotatably supports the developing roller 7 and the photosensitive drum 1.

Further, a DC voltage application unit 30 and an AC voltage application unit 31 are connected to the roller shaft 7c of the developing roller 7 in order to supply toner to the photosensitive drum 1. The DC voltage application unit 30 and the AC voltage application unit 31 are application units for applying a development bias in which a DC voltage and an AC voltage are superimposed on the developing roller 7.

The DC voltage application unit 30 is a circuit that generates a DC component applied to the developing roller 7, and its output is input to the AC voltage application unit 31. The DC voltage application unit 30 has an output control unit 32. The output control unit 32 controls the value of the bias output by the DC voltage application unit 30 according to the instruction of the CPU 40 as the control unit.

Further, the AC voltage application unit 31 is a circuit that outputs an AC voltage having the DC voltage output by the DC voltage application unit 30 as an average value (area center value). The AC voltage application unit 31 outputs, for example, a rectangular wave-shaped (pulse-shaped) AC voltage having a frequency f = 2.5 kHz and a duty of 50%. The AC voltage application unit 31 has a Vpp control unit 33. The Vpp control unit 33 controls Vpp, which is an inter-peak voltage (peak-to-peak value) of the AC voltage, in response to an instruction from the CPU 40 as a control unit.

The detection unit 35 is a detection unit that detects the current value flowing between the photosensitive drum 1 and the developing roller 7. The detection unit 35 amplifies the detection circuit 36 that converts the current flowing between the development roller 7 and the photosensitive drum 1 into a voltage when a development bias in which a DC voltage and an AC voltage are superimposed is applied, and the converted voltage signal. It is composed of an amplifier 37 that outputs a discharge detection signal to the CPU 40. The A / D converter 38 A / D converts the discharge detection signal from the amplifier 37. The CPU 40 can recognize the magnitude of the current generated between the developing roller 7 and the photosensitive drum 1 from the output of the amplifier 37 that has been A / D converted by the A / D converter 38. As will be described later, the CPU 40 detects whether or not the current value detected by the detection unit 35 exceeds the threshold value in a state where the development bias is applied to the developing roller 7 at the time of detection of detecting the current value, and is equal to or less than the threshold value. It is a control unit that controls the AC voltage so as to be.

<Explanation of leak current detection>
The detection of the leak current by the detection unit 35 will be described with reference to FIG. FIG. 5 is a waveform diagram of an AC voltage and a current value applied with a development bias.

FIG. 5 shows the waveform of the AC voltage applied to the developing roller 7 by the AC voltage applying unit 31 forming a solid white image (dotted line in the figure) and the current value flowing between the developing roller 7 and the photosensitive drum 1. It is a plot of the waveform (solid line in the figure). Since the electric charge on the surface of the developing roller 7 moves due to the potential difference between the photosensitive drum 1 and the developing roller 7, a current flows when the potential of the AC voltage changes. In the configuration of this embodiment, since the AC voltage applied by the AC voltage application unit 31 has a rectangular wave shape, as shown in FIG. 5, at the timing of the time t = 0 when the AC voltage changes from negative to positive, the potential difference is The current value flows with the change. On the other hand, at the timing when a certain time elapses from the timing when the AC voltage changes from negative to positive, the AC voltage becomes constant, and the current value becomes a value near 0 accordingly. Here, the time T is the time of one cycle of the AC voltage, and T = 1 / frequency f. Further, the timing of t = T / 4 is illustrated as a constant time from the timing when the AC voltage changes from negative to positive.

In this embodiment, the timing for detecting the current value flowing between the photosensitive drum 1 and the developing roller 7 is set after T / 4 has elapsed, which is a certain time from the timing when the AC voltage changes from negative to positive. It is not limited to. As shown by the dotted line in FIG. 5, the AC voltage changes from a region where the AC voltage changes from negative to positive (or positive to negative) on the positive side (or negative side) to a region where the AC voltage becomes constant. As long as the timing corresponds to the region where the AC voltage becomes constant as described above, the constant time from the timing when the AC voltage changes from negative to positive is not limited to T / 4. Further, not only when a certain time elapses from the timing when it changes from negative to positive, but also when a certain time elapses from the timing when it changes from positive to negative. If the timing corresponds to the region where the AC voltage becomes constant (the timing when the voltage change becomes approximately 0), the same effect can be obtained even after an arbitrary fixed time from the timing when the AC voltage changes from negative to positive or positive to negative. can get.

In this embodiment, the CPU 40, which is a control unit, uses the current value detected by the detection unit 35 when a certain time elapses from the timing when the AC voltage Vpp applied to the developing roller 7 changes from negative to positive to a threshold value. Make a comparison with. With this configuration, when the AC voltage applied to the developing roller 7 changes, the leak current can be directly detected by the current value flowing between the photosensitive drum 1 and the developing roller 7.

The Vpp at which the leak occurs is determined by the impedance between the photosensitive drum 1 and the developing roller 7. Therefore, the Vpp at which the leak occurs changes due to the fluctuation of the SD gap due to the drive of the photosensitive drum 1 and the developing roller 7, and the timing at which the SD gap is the narrowest is the condition in which the leak is most likely to occur. Therefore, the occurrence of the leak is more accurately determined by rotating the photosensitive drum 1 and the developing roller 7 and continuously detecting the leakage current described above for the time (T2) until the photosensitive drum 1 rotates once. be able to. In this embodiment, since the rotation speed of the photosensitive drum 1 is 385 mm / sec and the outer diameter is 30 mm, the time T2 until the photosensitive drum 1 makes one rotation is 0.25 sec.

<Toner seal winding operation>
Next, the toner seal winding operation in this embodiment will be described. The toner seal winding operation is an operation performed when the process cartridge is new.

First, when the power is turned on to the apparatus main body M, the developing roller 7 is rotationally driven by a drive mechanism (not shown) according to the instruction of the CPU 40. When the driving of the developing roller 7 is started, the rotational driving force is transmitted to the stirring shaft 10b of the stirring member 10 via the gear, and the toner seal winding shaft 14 rotates in conjunction with this. When the toner seal winding shaft 14 makes one rotation, the toner seal 13 is wound around the toner seal winding shaft 14 and the opening 9c is opened. After the opening 9c is opened, the rotational drive to the developing roller 7 by the drive mechanism is stopped by the instruction of the CPU 40.

The time (T3) required for the toner seal winding operation in this embodiment is substantially synonymous with the time required from the start of winding the toner seal 13 by the rotation of the toner seal winding shaft 14 to the opening 9c and the completion of opening. Is. Since the toner seal 13 rotates in conjunction with the stirring member 10, the time T3 required for the toner seal winding operation is 1 sec when the toner seal 13 is operated at the same rotation speed as during the normal printing operation.

<Flowchart of discharge generation detection operation in Example 1>
Next, the flow of control of the discharge generation detection operation of the image forming apparatus according to the first embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a flowchart showing an example of the flow of the discharge generation detection operation of the image forming apparatus according to the first embodiment. Further, FIG. 7 is a timing chart showing the drive timing of the discharge detection operation according to the first embodiment.

In the discharge generation detection operation described below, it is determined whether or not the amount of change in the current value flowing between the photosensitive drum 1 and the developing roller 7 exceeds the threshold value, and the development bias applied to the developing roller 7 is determined from the result. (AC voltage Vpp) is controlled. This discharge generation detection operation is executed by the CPU 40 (see FIG. 2), which is a control unit. This discharge generation detection operation is performed together with the toner seal winding operation performed when the process cartridge 20 is new.

First, when the power of the image forming apparatus is turned on and the discharge generation detection operation is started (start), each rotating body such as the photosensitive drum 1 and the developing roller 7 is driven by a drive mechanism (not shown) according to the instruction of the CPU 40. Is started (step S101). Since the driving of each rotating body is interlocked with the above-mentioned toner seal winding operation, the time until the toner seal winding operation is completed is continued. Next, a charging bias is applied to the charging roller 4, and a DC voltage −300V is applied to the developing roller 7 by the DC voltage application unit 30 (step S102). When the time (T2) for one rotation of the photosensitive drum 1 elapses from step S102 (step S103), the surface of the photosensitive drum 1 becomes the set surface potential −500 V over the entire circumference. Next, the AC voltage Vpp applied to the developing roller 7 is set. The AC voltage Vpp applied to the developing roller 7 is set to an AC voltage Vpp higher by an offset value than the setting at the time of image formation in consideration of changes in temperature and humidity and fluctuations in the SD gap during paper passing (step S104). Here, the AC voltage applied to the developing roller 7 is set to an AC voltage Vpp that is 200 V higher than the AC voltage at the time of image formation. Next, when the set AC voltage Vpp is applied to the developing roller 7, it is determined whether or not the current value flowing between the developing roller 7 and the photosensitive drum 1 exceeds a threshold value which is a predetermined value (step S105). .. Here, as described with reference to FIG. 6, it is determined whether or not the current value exceeds the threshold value when T / 4 elapses for a certain period of time from the timing when the AC voltage changes from negative to positive. In this example, the threshold value is set to 10 μA.

When the current value exceeds the threshold value in step S105, the CPU 40 turns off the AC voltage Vpp of the development bias because a leak has occurred between the photosensitive drum 1 and the developing roller 7 (step S106). .. The reason why Vpp is turned off once in step S106 is that once a development leak occurs, the development leak may continue due to the continuous flow of current, and the continuously generated development leak is cut off once. When such a leak occurs, the AC voltage Vpp applied to the developing roller 7 during image formation at that time is set to a predetermined value (step S107). Here, the predetermined value is set to 1.5 kV, which is an AC voltage that does not cause leakage including the high altitude environment. Subsequently, the charging bias and the developing bias are turned off (step S108), and then the driving of the photosensitive drum 1 and the developing roller 7 is stopped (step S109), and the discharge generation detection operation is terminated (end). In this case, the minimum time required for the operation of controlling the development bias (AC voltage Vpp) so as to be equal to or lower than the threshold value by the CPU 40 is the time (T2) for the photosensitive drum 1 to rotate once and the AC as shown in FIG. The time T2 + T / 4 is obtained by adding a certain time (T / 4) from the timing when the voltage changes from negative to positive. Here, the time required for the operation of controlling the development bias so as to be equal to or less than the threshold value by the CPU 40 is defined as T4.

Here, assuming that the time T for one cycle of the AC voltage, the time T2 for the photosensitive drum 1 to rotate once, and the time T3 required for the toner seal winding operation, the relationship between these times is T << T2 <T3. .. When the current value exceeds the threshold value in step S105, the time required for the CPU 40, which is the control unit, to control the development bias (AC voltage Vpp) so as to be equal to or lower than the threshold value is T4. Therefore, the time T4 is shorter than the time T3 required from when the toner seal 13 is wound by the rotation of the toner seal winding shaft 14 and the opening 9c is started to be opened until the opening is completed (T4 <T3).

On the other hand, when the current value does not exceed the threshold value in step S105, that is, when the current value is equal to or less than the threshold value, step S105 is repeated for a period of time T2 in which the photosensitive drum 1 makes one rotation after applying Vpp (step S105). S110). When the current value is continuously below the threshold value in the above period, the value obtained by lowering the AC voltage Vpp at the time of leak detection at that time by the offset value (200 V) is determined as the AC voltage Vpp at the time of image formation (step S111). Subsequently, the development bias and the charging bias are turned off (step S108), and then the driving of each rotating body such as the photosensitive drum 1 and the developing roller 7 is stopped (step S109), and the discharge generation detection operation is terminated (end). .. In this case, the time required for the operation of controlling the AC voltage so as to be equal to or lower than the threshold value by the CPU 40 is the time obtained by adding the time for one rotation of the photosensitive drum 1 (T2) and the time for one rotation of the photosensitive drum 1 (T2). It is T2 + T2.

From the above, the time required for the operation of controlling the development bias (AC voltage Vpp) so as to be equal to or lower than the threshold value by the CPU 40 is such that the current value sets the threshold value in step S105 rather than the case where the current value exceeds the threshold value in step S105. If it does not exceed, the time until the operation is completed becomes longer (T4 <T2 + T2).

The discharge generation detection operation described above is performed when the process cartridge 20 is new. Therefore, the rotary drive starting from step S101 operates in conjunction with the toner seal winding operation. Therefore, the operation of step S109 is executed after the setting of Vpp at the time of image formation in step S107 or S111 is completed and the toner seal winding operation is completed.

In this embodiment, the time required to complete the operation of S109 is T2 + T2, which is 0.50 sec. On the other hand, the time T3 required for the toner seal winding operation is 1.00 sec. That is, the time T2 + T2 required to control the development bias (AC voltage Vpp) so as to be equal to or less than the threshold value by the CPU 40, which is the control unit, is such that the toner seal 13 is wound by the rotation of the toner seal winding shaft 14 to open the opening 9c. The time required from the start of opening to the end of opening is shorter than T3 (T2 + T2 <T3). Therefore, in this embodiment, the operation of step S109 is executed before the toner seal winding operation is completed.

<Experiment 1>
Here, in order to show the effect of Example 1, an experiment conducted using Comparative Example 1 will be described.

In this experiment, when the discharge detection operation and the toner seal winding operation are executed in an environment of a temperature of 23 ° C. and a humidity of 50%, the value set as Vpp during image formation by the discharge detection operation is compared with Example 1. Compared with 1. In this experiment, Vpp in step S104 of the discharge detection operation shown in FIG. 6 was performed under a plurality of settings.

In Comparative Example 1, the rotation speed of the photosensitive drum 1 is 130 mm / sec, and the rotation speed of the stirring member 10 is 60 rpm. In this configuration, the time T3 required for the toner seal winding operation is 1 sec as in the first embodiment, and the time T2 for one rotation of the photosensitive drum 1 is 0.73 sec, so that the operation of step S109 is completed. The time required for T2 + T2 is 1.46 sec. That is, Comparative Example 1 has a configuration in which the time T3 required for the toner seal winding operation is shorter than the time T2 + T2 required for the operation of controlling the development bias (AC voltage Vpp) so as to be equal to or less than the threshold value by the CPU 40 (T2 + T2>. T3).

On the other hand, in Example 1, as described above, the rotation speed of the photosensitive drum 1 is 385 mm / sec, and the rotation speed of the stirring member 10 is 60 rpm. Therefore, the time T2 until the photosensitive drum 1 makes one rotation is 0.25 sec, and the time T2 + T2 required to complete the operation of step S109 is 0.50 sec. Therefore, in the first embodiment, the time required for the toner seal winding operation T3 is longer than the time required for the operation of controlling the development bias (AC voltage Vpp) so as to be equal to or less than the threshold value by the CPU 40 (T2 + T2 < T3).

The results of this experiment are summarized in FIG. 8 and Table 1. FIG. 8 is a diagram showing the relationship between the Vpp set during the discharge generation detection operation in Example 1 and Comparative Example 1 and the current value detected by the detection unit. In FIG. 8, the horizontal axis is the Vpp set during the discharge generation detection operation, and the horizontal axis is the maximum value of the current value detected by the detection unit.

First, FIG. 8 will be described. As a result of the experiment, the current value detected by the detection unit with respect to the Vpp set in the discharge generation detection operation is different between Example 1 and Comparative Example 1. When Vpp was 3000 V, the current value exceeded the threshold value of 10 μA in the configuration of Example 1, whereas the current value did not exceed the threshold value in the configuration of Comparative Example 1.

As already explained, if toner is present in the SD gap, the resistance between the photosensitive drum 1 and the developing roller 7 increases due to the resistance of the toner, making it difficult for leaks to occur and causing discharge. The current value detected in the detection operation drops.

In this experiment, in Example 1, since the detection of the leak current is completed before the toner seal winding operation is completed, the toner does not intervene in the SD gap when the leak current is detected. On the other hand, in Comparative Example 1, since the toner seal winding operation is completed before the completion of the leakage current detection, the toner is present in the SD gap when the leak current is detected. That is, the result of this experiment is whether or not toner is present in the SD gap when the leak current is detected.

Next, Table 1 will be described. Table 1 shows the presence or absence of a development leak at the Vpp set as the value at the time of image formation with respect to the Vpp set at the time of the discharge generation detection operation in Example 1 and Comparative Example 1. If a development leak does not occur when the image formation operation is executed, it is marked with 〇, and if it does occur, it is marked with x. The presence or absence of a development leak is determined by whether or not toner is printed on the recording material when 500 sheets of so-called all-white images with a printing rate of 0% are printed on the LETTER size recording material after the discharge generation detection operation. ing. If no development leak occurs, toner will not be printed on the recording material, but if a development leak occurs, unintended toner will be printed on the recording material. Therefore, it is possible to determine whether or not a development leak has occurred based on whether or not the toner is printed when the all-white image is printed.

As explained with reference to FIG. 8, attention is paid to the result of Vpp of 3000V. When Vpp was 3000 V, the current value exceeded the threshold value (10 μA) in the configuration of Example 1, whereas the current value did not exceed the threshold value in the configuration of Comparative Example 1. As a result, as shown in Table 1, it was determined that a leak would occur at the Vpp set in the first embodiment, and the value was set to 1500 V, which is a predetermined value at which the leak does not surely occur in this configuration. On the other hand, in Comparative Example 1, the Vpp at the time of image formation was set to 2800 V even though there was a risk of leakage when the change in temperature and humidity during paper passing and the change in SD gap were taken into consideration. Since these Vpps were set, no development leak occurred in Example 1, whereas a development leak occurred in Comparative Example 1.

As shown above, in the case of a configuration in which the time required for the operation of setting the development bias to be equal to or less than the threshold value by the CPU 40 is longer than the time required for the toner seal winding operation as in Comparative Example 1, leakage is unlikely to occur. The presence or absence of a leak is detected. Therefore, in the configuration as in Comparative Example 1, it may be erroneous to determine whether or not a leak occurs with respect to the Vpp set at the time of image formation. On the other hand, in the configuration of the first embodiment, the time required for the operation of setting the development bias to be equal to or less than the threshold value by the CPU 40 is shorter than the time required for the toner seal winding operation. It is possible to correctly judge whether or not a leak occurs. As a result, it is possible to provide an image forming apparatus in which leakage does not occur in long-term use.

The SD gap, charging bias, development bias, current value threshold, etc. described in this embodiment are not intended to limit the scope of the present invention to those unless otherwise specified. Absent.

[Example 2]
Next, the image forming apparatus according to the second embodiment will be described. In this example, the discharge detection control is different from that of the first embodiment, and the other configurations are almost the same as those of the first embodiment. Therefore, in this example, the same reference numerals are given to the same configurations as those in the first embodiment described above, so that detailed description thereof will be omitted.

In the first embodiment described above, when a leak is detected during the discharge generation detection operation, Vpp is set to a predetermined value at which no leak occurs. On the other hand, in the second embodiment, when a leak is detected during the discharge generation detection operation, the Vpp at which the leak does not occur is re-detected and the Vpp at the time of image formation is determined. In this embodiment, the developing roller 7 receives a driving force from a driving source different from that of the photosensitive drum 1, and is rotationally driven independently of the photosensitive drum 1. The details will be described below.

<Flowchart of discharge generation detection operation in Example 2>
A flow of control of the discharge generation detection operation of the image forming apparatus according to the second embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 is a flowchart showing an example of the flow of the discharge generation detection operation of the image forming apparatus according to the second embodiment. Further, FIG. 10 is a timing chart showing the drive timing of the discharge detection operation according to the second embodiment.

First, when the power of the image forming apparatus is turned on and the discharge generation detection operation is started (start), the rotating bodies such as the photosensitive drum 1 and the developing roller 7 are rotated by a drive mechanism (not shown) according to the instruction of the CPU 40. Is started (step S201). Next, a charging bias is applied to the charging roller 4, and a DC voltage −300V is applied to the developing roller 7 by the DC voltage application unit 30 (step S202). When the time (T2) for one rotation of the photosensitive drum 1 elapses from step S202 (step S203), the surface of the photosensitive drum 1 becomes the set surface potential −500 V over the entire circumference. Next, the AC voltage Vpp applied to the developing roller 7 is set. The AC voltage Vpp applied to the developing roller 7 is set to an AC voltage Vpp higher by an offset value than the setting at the time of image formation in consideration of changes in temperature and humidity and fluctuations in the SD gap during paper passing (step S204). Here, the AC voltage applied to the developing roller 7 is set to an AC voltage Vpp that is 200 V higher than the AC voltage at the time of image formation. Next, when the set AC voltage Vpp is applied to the developing roller 7, it is determined whether or not the current value flowing between the developing roller 7 and the photosensitive drum 1 exceeds a threshold value which is a predetermined value (step S205). .. Here, as described with reference to FIG. 6, it is determined whether or not the current value exceeds the threshold value when T / 4 elapses for a certain period of time from the timing when the AC voltage changes from negative to positive. In this example, the threshold value is set to 10 μA.

When the current value exceeds the threshold value in step S205, a leak has occurred between the photosensitive drum 1 and the developing roller 7, so that the CPU 40 turns off the AC voltage Vpp of the developing bias and the developing roller 7 is turned off. (Step S206). At this time, since the stirring shaft 10b and the toner seal winding shaft 14 rotate in conjunction with the developing roller 7, they are stopped at the same time as the developing roller is stopped. Subsequently, while the drive of the developing roller 7 is stopped, the Vpp setting at the time of image formation is lowered to a voltage lower than the current setting (step S207). Here, the Vpp at the time of image formation is reset to a value lowered to a voltage 200 V lower than the development bias (AC voltage Vpp) applied to the developing roller 7 at the time of detecting the current value. Then, when the reset Vpp is applied to the developing roller 7, it is determined whether or not the current value when T / 4 elapses for a certain period of time from the timing when the AC voltage changes from negative to positive exceeds the threshold value (step). S208).

Then, when the current value exceeds the threshold value in step S208, the process returns to step S207, the Vpp applied to the developing roller 7 is gradually lowered, and the above-mentioned operation is repeatedly executed until the current value becomes equal to or less than the threshold value.

On the other hand, when the current value does not exceed the threshold value in step S208, that is, when the current value is equal to or less than the threshold value, step S208 is repeated for a period of time T2 in which the photosensitive drum 1 makes one rotation after applying Vpp (step S209). .. When the current value is continuously below the threshold value in the above period, the value obtained by lowering the AC voltage Vpp at the time of leak detection at that time by the offset value (200 V) is determined as the AC voltage Vpp at the time of image formation (step S210). After that, the rotational drive of the developing roller 7 is restarted (step S211). At this time, since the stirring shaft 10b and the toner seal winding shaft 14 rotate in conjunction with the developing roller 7, the rotation starts at the same time as the driving of the developing roller starts. Then, after the developing roller 7 rotates during the time T3-T2, the developing bias and the charging bias are turned off (step S212), and then the driving of each rotating body such as the photosensitive drum 1 and the developing roller 7 is stopped. (Step S213), the discharge generation detection operation is terminated (end).

The reason why the developing roller 7 is rotationally driven again in step S211 is that the discharge generation detection operation and the toner seal winding operation are linked in the second embodiment as in the first embodiment. At the stage of step S208, as shown in FIG. 10, since the developing roller 7 has only passed the time of T4, the toner seal winding operation is not completed. Therefore, it is necessary to rotationally drive the developing roller 7 during the time T3-T4.

Further, when the current value does not exceed the threshold value in step S205, that is, when the current value is equal to or less than the threshold value, step S205 is performed during the period T2 of the time T2 in which the photosensitive drum 1 makes one rotation after applying the charging bias to the charging roller 4. Repeat (step S214). When the current value is continuously below the threshold value in the above period, 1.8 kV, which is a value obtained by subtracting the offset (200 V) from the AC voltage Vpp at the time of leak detection at that time, is determined as the AC voltage Vpp at the time of image formation ( Step S215). After that, the development bias and the charging bias are turned off (step S212), the driving of each rotating body such as the photosensitive drum 1 and the developing roller 7 is stopped (step S213), and the discharge generation detection operation is terminated (end). In this case, the time required for the operation of controlling the development bias so as to be equal to or less than the threshold value by the CPU 40 is the time obtained by adding the time for one rotation of the photosensitive drum 1 (T2) and the time for one rotation of the photosensitive drum 1 (T2). It is T2 + T2.

In this embodiment, when the current value exceeds the threshold value in step S205, Vpp is set to a value reduced by 200 V, but the amount of reduction is not limited to this. It is possible to increase the reduction width in order to detect Vpp in which leakage does not occur in a shorter time, and it is also possible to decrease the reduction width in order to investigate Vpp in which leak occurs in more detail.

<Experiment 2>
Here, in order to show the effect of Example 2, an experiment was conducted with Example 1 and Comparative Example 1 as comparison targets. This experiment was carried out under the same conditions as in Example 1. Table 2 summarizes the results of this experiment.

Table 2 shows the presence or absence of a development leak at the Vpp set as the value at the time of image formation with respect to the Vpp set at the time of discharge detection in Example 2, Example 1, and Comparative Example 1. In Table 2, when the development leak does not occur when the image forming operation is executed, it is evaluated as ◯, and when it occurs, it is evaluated as ×. The determination of the presence or absence of a development leak is the same as in Table 1. Here, attention is paid to the result that the Vpp set at the time of discharge detection is 3000V. In Example 1, it was determined that a leak would occur at the set Vpp, and it was set to 1500V, which is a predetermined value. In Comparative Example 1, it was set to 2800V, which has a risk of leakage, whereas in Example 2, it was set to 2800V. Vpp is set to 2600V. This is because, when Vpp is 3000 V, it is once determined that a leak occurs in a state where toner does not intervene in the SD gap, as in Example 1, and then the presence or absence of a leak is determined using a value offset by 200 V again. This is because I made a decision. By setting these Vpps, the development leak did not occur in Example 1 and Example 2, whereas the development leak occurred in Comparative Example 1.

As shown above, in the second embodiment, it is possible to detect the presence or absence of leakage while changing the Vpp in a state where the toner does not intervene in the SD gap. Therefore, even when it is determined that a leak occurs at the value set as Vpp at the time of discharge detection, it is possible to select a higher Vpp within the range where the leak does not occur. As a result, it is possible to provide an image forming apparatus in which leakage does not occur in long-term use.

The SD gap, charging bias, development bias, current value threshold, etc. described in this embodiment are not intended to limit the scope of the present invention to those unless otherwise specified. Absent.

[Other Examples]
In the above-described embodiment, the laser beam scanner is used as the exposure unit, but the present invention is not limited to this, and for example, an LED array or the like may be used.

Further, in the above-described embodiment, the photosensitive drum 1 and the charging member, the developing unit, and the cleaning unit as the process means acting on the photosensitive drum 1 are integrated as a process cartridge that can be attached to and detached from the main body of the image forming apparatus. The process cartridge 20 having is illustrated. However, the process cartridge 20 is not limited to this. In addition to the photosensitive drum 1, a process cartridge having any one of a charging member, a developing unit, and a cleaning unit may be used.

Further, in the above-described embodiment, the configuration in which the process cartridge 20 including the photosensitive drum 1 is removable from the device main body of the image forming apparatus is illustrated, but the present invention is not limited to this. For example, an image forming apparatus in which the photosensitive drum 1 and each process means acting on the photosensitive drum 1 are incorporated may be used, or an image forming apparatus in which the photosensitive drum 1 and the process means acting on the photosensitive drum 1 are detachably attached to each other may be used.

Further, in the above-described embodiment, the printer is exemplified as the image forming apparatus, but the present invention is not limited thereto. For example, it may be another image forming apparatus such as a copying machine or a facsimile apparatus, or another image forming apparatus such as a multifunction device combining these functions. Alternatively, it may be an image forming apparatus that uses a recording medium carrier and sequentially superimposes and transfers toner images of each color on the recording medium supported on the recording medium carrier. Alternatively, it is an image forming apparatus that uses an intermediate transfer body, sequentially superimposes and transfers toner images of each color on the intermediate transfer body, and collectively transfers the toner images carried on the intermediate transfer body to a recording medium. May be good. Similar effects can be obtained by applying the present invention to these image forming devices.

M ... Image forming apparatus main body P ... Recording medium 1 ... Photosensitive drum (image carrier)
2 ... Cleaning blade 4 ... Charging roller (charging member)
6 ... Laser beam scanner 7 ... Developing roller (developer carrier)
7a ... Sleeve 7b ... Cap 7b ... Roller shaft 8 ... Development blade 9 ... Development container 9a ... Toner storage chamber 9b ... Development chamber 9c ... Opening 10 ... Stirring member 10a ... Stirring sheet 10b ... Stirring shaft 13 ... Toner seal 14 ... Toner seal Winding shaft 20 ... Process cartridge 30 ... DC voltage application unit 31 ... AC voltage application unit 32 ... Output control unit 33 ... Vpp control unit 35 ... Detection unit 36 ... Detection circuit 37 ... Amplifier 38 ... A / D converter 40 ... CPU (Control unit)

Claims (8)

With a rotatable image carrier,
A charging member that charges the image carrier and
A rotatable developer carrier provided so as to face the image carrier in a non-contact state and carrying a developer, and a rotatable developer carrier.
The developing agent accommodating chamber for accommodating the developing agent, the developing chamber in which the developing agent carrier is rotatably provided, and the opening for communicating the developing agent accommodating chamber and the developing chamber are provided, and the developing is provided. A developing frame that supports the agent carrier and
A rotating member rotatably provided on the developing frame and rotating in conjunction with the developing agent carrier.
A sealing member that seals the opening provided in the developing frame and is partially fixed to the rotating member.
With a process cartridge that has and can be attached to and detached from the image forming apparatus,
An application unit that applies a development bias in which a DC voltage and an AC voltage are superimposed on the developer carrier,
A detection unit that detects the current value flowing between the image carrier and the developer carrier, and
At the time of detection to detect the current value, with the development bias applied to the developer carrier, it is detected whether or not the current value detected by the detection unit exceeds the threshold value, and the value becomes equal to or less than the threshold value. With a control unit that controls the AC voltage
Have,
The time required for the control unit to control the AC voltage so as to be equal to or lower than the threshold value is from the time when the sealing member is wound by the rotation of the rotating member to the time when the opening is started to be opened and the time when the opening is completed. An image forming apparatus characterized in that it is shorter than the required time. The image forming apparatus according to claim 1, wherein the AC voltage applied to the developer carrier has a rectangular wavy shape. The control unit is characterized in that the detection unit detects the current value when a certain time elapses from the timing when the AC voltage applied to the developer carrier changes from negative to positive or positive to negative. The image forming apparatus according to claim 1 or 2. The detection unit is characterized in that it detects a current value flowing between the image carrier and the developer carrier in a region where the AC voltage applied to the developer carrier is constant. The image forming apparatus according to any one of 3 to 3. When a certain time elapses from the timing when the AC voltage applied to the developer carrier changes from negative to positive or positive to negative, the current value detected by the detector exceeds the threshold value. The development bias applied to the developer carrier is lower than the development bias applied to the developer carrier at the time of detecting the current value, according to any one of claims 1 to 4. Image forming device. The control unit changes the development bias applied to the developer carrier when the current value detected by the detector is equal to or less than the threshold value during the time during which the developer carrier or the image carrier rotates at least once. The image forming apparatus according to any one of claims 1 to 5, wherein the image forming apparatus is not provided. The image forming apparatus according to any one of claims 1 to 6, wherein the developer carrier receives a driving force from a driving source different from that of the image carrier. When the control unit detects that the current value exceeds the threshold value, the control unit gradually lowers the AC voltage applied to the developer carrier, and again between the image carrier and the developer carrier. The image forming apparatus according to any one of claims 1 to 7, wherein it detects whether or not the flowing current value exceeds the threshold value and controls the development bias so as to be equal to or less than the threshold value.

Images