Image forming device

Abstract

To provide means that detects leakage between an image carrier and a developer carrier with an inexpensive and simple configuration.SOLUTION: An image forming apparatus can execute an image forming operation, and has: an image carrier 1; a developer carrier 10 that is opposite to the image carrier 1 with a predetermined gap provided therebetween and develops a latent image formed on the image carrier 1 with developer; a frame body that supports at least the developer carrier 10; application means 19, 20 that apply, to the developer carrier 10, a developing bias in which a DC voltage and an AC voltage are superimposed on each other; a conductive member 18 that is provided on the frame body; detection means 24 that detects an AC current induced by the conductive member 18 through the application of the developing bias to the developer carrier 10; and a control unit 23 that controls the application means 19, 20. The control unit 23 controls the developing bias in the image forming operation based on the AC current detected by the detection means 24 when the application means 19, 20 apply the bias.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material by using an electrophotographic method. [Background technology]

[0002] In image forming devices such as printers using an electrophotographic image forming method (electrophotographic process), a non-contact development method is used to develop an electrostatic image into a toner image using a developer (also called toner), in which development is performed with a gap between the image carrier and the developer carrier. This method can reduce the load on the toner, so stable images can be obtained throughout the life of the device. In the case of a developing device using such a non-contact development method, the gap may fluctuate due to the driving of the developer carrier and the image carrier, and the electric field strength between the developer carrier and the image carrier may fluctuate, causing problems such as uneven density in the formed image. To address the above issue, the peak-to-peak value of the AC voltage in the developing bias voltage applied between the developer carrier and the image carrier is increased, and the developer is sufficiently scattered between the developer carrier and the image carrier, thereby suppressing the occurrence of uneven density. However, when the peak-to-peak value is increased, the potential difference between the surface potential of the image carrier and the peak value of the developing bias increases, causing a high-voltage leak between the developer carrier and the image carrier, resulting in noise in the formed image.

[0003] The peak-to-peak value of the AC voltage at which a high-voltage leak occurs varies depending on the gap value of the development area, air pressure, etc., and therefore varies depending on the individual image forming apparatus and the usage environment. Therefore, in a conventional example, the peak-to-peak value of the AC voltage between the developer carrier and the image carrier is changed to cause a leak between the image carrier and the developer carrier, and the toner that has adhered to the image carrier due to the leak is detected by a concentration sensor to determine whether a leak has occurred (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-098707 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned conventional example has a problem that the concentration sensor is expensive and if a leak occurs in a portion where there is no concentration sensor, the leak cannot be detected.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a means for detecting leakage between an image carrier and a developer carrier, which is inexpensive and has a simple structure. [Means for solving the problem]

[0007] In order to solve the above problems, an image forming apparatus according to the present invention comprises: An image forming apparatus capable of performing an image forming operation, Image carrier A first cartridge that is detachably mounted to a main body of an image forming apparatus. and, a developer carrier that faces the image carrier with a predetermined gap therebetween and develops the latent image formed on the image carrier with a developer; ,before a frame for supporting the developer carrier; a second cartridge that is detachably attached to a main body of an image forming apparatus; an application means for applying a developing bias, which is a superimposed DC voltage and AC voltage, to the developer carrier; A conductive member provided on the frame; a detection unit that detects an AC current induced in the conductive member by application of the developing bias to the developer carrier by the application unit; A control unit that controls the application means, The control unit controls the developing bias in the image forming operation based on the AC current detected by the detection unit when the developing bias is applied by the application unit. and detecting whether the first cartridge is attached to or detached from the main body of the apparatus and whether the second cartridge is attached to or detached from the main body of the apparatus based on the AC current detected by the detection means. The present invention is characterized by the above. Effect of the Invention

[0008] As described above, according to the present invention, leakage between the image carrier and the developer carrier can be detected at low cost and with a simple configuration. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a developing device and a process cartridge according to an embodiment of the present invention; [Diagram 2] FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention; [Diagram 3] Relationship between Vpp of AC voltage applied to the developing sleeve and the current value induced in the electrode [Figure 4] Flowchart of the first embodiment [Diagram 5] FIG. 11 is a diagram showing the connection between the process cartridge and the main body in the second embodiment. [Figure 6] FIG. 11 is a relationship diagram between Vpp of AC voltage applied to the developing sleeve and the current value induced in the electrode in the second embodiment. [Figure 7] Flowchart of Example 2 [Figure 8] Relationship between Vpp of AC voltage applied to the developing sleeve and the current value induced in the electrode with and without a drum cartridge [Figure 9] Flowchart of Example 3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration and various conditions of the device to which the invention is applied. In other words, the scope of the present invention is not limited to the following embodiment.

[0011] Example 1 A first embodiment of the present invention will be described with reference to FIGS.

[0012] <Description of Image Forming Apparatus> 2 shows an example of an image forming apparatus capable of performing an image forming operation equipped with the developing device 4 of this embodiment. The figure is a vertical cross-sectional view showing a schematic configuration of the image forming apparatus. The image forming apparatus shown in the figure is equipped with an image forming apparatus main body (hereinafter simply referred to as "apparatus main body") serving as a printer engine.

[0013] Inside the main body of the apparatus, a drum-shaped electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 is provided as an image carrier. The photosensitive drum 1 is driven to rotate around its axis in the direction of arrow R1 in FIG. 2 at a predetermined process speed (circumferential speed) by the transmission of a driving force. In this embodiment, the photosensitive drum 1, which is the center of the image forming process, is an organic photosensitive drum 1 in which an undercoat layer, a carrier generating layer, and a carrier transport layer, which are functional films, are coated in this order on the outer peripheral surface of an aluminum cylinder with a diameter of 30 mm. The surface of the photosensitive drum 1 is charged by a charging roller 2 serving as a charging device (charging means, charging member). The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1, and is rotated in accordance with the rotation of the photosensitive drum 1 in the direction of arrow R1. The charging roller 2 is charged with, for example, a DC voltage by a charging bias application power source (not shown). As a result, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential with a predetermined polarity.

[0014] After charging, an electrostatic latent image is formed on the surface of the photosensitive drum 1 by an exposure device. The exposure device has a laser scanner 14a, a polygon mirror (not shown), a reflecting lens 14b, etc., and irradiates the surface of the photosensitive drum 1 with laser light based on image information, removes the charge of the irradiated portion, and forms an electrostatic latent image. Toner is attached to the electrostatic latent image thus formed on the surface of the photosensitive drum 1 by the developing device 4, and the electrostatic latent image is developed into a toner image. The developing device 4 will be described in detail later.

[0015] The toner image formed on the surface of the photosensitive drum 1 is transferred onto a transfer material 13 by a transfer roller 5 serving as a transfer device. This transfer material 13 is stored in a paper feed cassette 14 and is supplied to the transfer nip portion in the direction of arrow P by a paper feed roller 12, a registration roller 15, etc. in synchronization with the toner image on the photosensitive drum 1. The toner image on the photosensitive drum 1 is transferred onto the transfer material 13 by the transfer roller 5 via a transfer bias application power source (not shown). After the toner image has been transferred onto the transfer material 13, any toner remaining on the surface is removed by a cleaning blade 7 of a cleaning device 6, and the photosensitive drum 1 is then used for the next image formation.

[0016] Meanwhile, the transfer material 13 after the toner image transfer is transported to the fixing device 8, where it is heated and pressed by the fixing roller 8a and the pressure roller 8b, and the toner image on the surface is fixed. The transfer material 13 after the toner image is fixed is discharged outside the main body of the apparatus, and image formation is completed. As shown in Fig. 1, among the above-mentioned members that perform the image formation process, the photosensitive drum 1, the cleaning device 6 having the charging roller 2, and the developing device 4 are integrated as a process cartridge, and are configured to be detachably attached to the main body of the image forming apparatus as an integral part.

[0017] Next, the developing device 4 of this embodiment will be described in detail with reference to Fig. 1. This figure is a vertical cross-sectional view showing the schematic configuration of the developing device. The developing device 4 is a developing device that uses magnetic one-component toner, and has a toner container as a frame, which is divided by an opening into a toner storage chamber T1 that stores toner 11 and a developing chamber T2 that has a developing sleeve 10 and a developing blade. Mainly, the toner storage chamber T1 has a stirring member 16 for loosening and transporting the toner 11, and the developing chamber T2 has a developing sleeve 10 that carries and transports the transported toner 11, and a developing blade 9 that regulates the layer thickness of the toner carried on the developing sleeve 10.

[0018] The developing sleeve 10 is a non-magnetic sleeve formed of an aluminum or stainless steel pipe, and is supported by a toner container so as to be rotatable in the direction of the arrow R2. In this embodiment, a hollow cylindrical tube made of aluminum with a diameter of 14 mm is used. Rollers (not shown) are fixed to both ends of the developing sleeve 10 in the longitudinal direction (axial direction). The developing sleeve 10 is designed to ensure a predetermined gap (space) between the developing sleeve 10 and the surface of the photosensitive drum 1 by abutting the outer circumferential surface of the roller against the opposing photosensitive drum 1. In this embodiment, the thickness of the roller is adjusted so that the developing sleeve 10 and the surface of the photosensitive drum 1 face each other with a gap of 300 μm.

[0019] The surface of the developing sleeve 10 is coated with a solvent in which carbon, a charge control agent, and fine particles for roughening the surface are dispersed in phenolic resin, so that the appropriate charge can be applied when the desired amount of toner is carried. The surface of the developing sleeve 10 is roughened by the paint coating, and in this embodiment, a surface with an arithmetic mean roughness Ra=1.2 μm is used. A magnet 17 is disposed inside the developing sleeve 10. The magnet 17 is formed in a cylindrical shape, with multiple N poles and S poles formed alternately in the circumferential direction. Unlike the developing sleeve 10 which rotates in the direction of arrow R2, the magnet 17 is fixedly disposed inside the developing sleeve 10.

[0020] The developing blade 9 is configured with a support member 9a and an elastic blade 9b, and the elastic blade 9b is provided so as to abut against the surface of the developing sleeve 10. The elastic blade 9b is, for example, a plate-shaped urethane rubber, and its base end is fixed to the supporting metal plate 9a, and its tip end is elastically deformed by abutting against the surface of the developing sleeve 10 with a predetermined pressure. The elastic blade 9b regulates the layer thickness of the toner 11 attracted to the surface of the developing sleeve 10 by the magnetic force of the magnet 17. The toner carried on the surface of the developing sleeve 10 is subjected to frictional charging between the toners as it is transported by the rotation of the developing sleeve 10 in the direction of the arrow R2, and frictional charging by the friction between the developing sleeve 10 and the elastic blade 9b when the layer thickness is regulated by the developing blade 9. As a result, the toner carried on the surface of the developing sleeve 10 is transported from the surface of the developing sleeve 10 to a development area facing the surface of the photosensitive drum 1 while being given an appropriate charge. 1, a DC voltage power supply 19 and an AC voltage power supply 20 are connected to the developing sleeve 10, and a developing bias in which DC and AC are superimposed is applied via a sliding contact. As a result, the toner on the developing sleeve 10 flies to the photosensitive drum 1 in the developing area and electrostatically adheres to the electrostatic latent image, developing the electrostatic latent image into a toner image.

[0021] The DC voltage power supply 19, as an application means, is a circuit that generates a DC component to be applied to the developing sleeve 10, and the output of the DC voltage power supply 19 is input to the AC voltage power supply 20. The DC voltage power supply 19 has an output control section 21, which controls the value of the bias output by the DC voltage power supply 19 in response to an instruction from the CPU 23. The AC voltage power supply 20, as an application means, is a circuit that outputs an AC voltage, for example, in a rectangular wave (pulse shape) with a frequency f=2.5 kHz and a duty of 50%, with the DC voltage output by the DC voltage power supply 19 as the average value (area center value). The AC voltage power supply 20 has a peak-to-peak value (hereinafter, Vpp) control section 22. The Vpp control section 22 controls the peak-to-peak voltage of the AC voltage in response to an instruction from the CPU 23.

[0022] In this embodiment, the CPU 23 serves as a control unit that controls the overall operation of the image forming apparatus, and also serves as an acquisition unit and a detection unit of the present invention.

[0023] <Detection of leaks from photosensitive drums and developing sleeves> Next, a mechanism for detecting leakage between the photosensitive drum 1 and the developing sleeve 10 will be described. In this embodiment, a metal plate 18, which is a conductive detection member (conductive member), is disposed in a toner chamber T1 as shown in FIG. 1. A contact structure for electrically connecting the image forming apparatus main body and the process cartridge is provided between the image forming apparatus main body and the process cartridge. That is, the process cartridge has a cartridge-side first contact and a cartridge-side second contact, and the image forming apparatus main body has a main body-side first contact and a main body-side second contact. The developing sleeve 10 is electrically connected to the cartridge-side first contact, and the metal plate 18 is electrically connected to the cartridge-side second contact via a conductor or the like. When the process cartridge is mounted in the image forming apparatus main body, the cartridge-side first contact and the cartridge-side second contact are electrically connected to the main body-side first contact and the main body-side second contact of the printer main body, respectively. A bias voltage including an AC component is applied to the main body-side first contact from a power source in the printer main body. When a bias voltage containing an AC component is applied from a power source to the developing sleeve 10, a current corresponding to the applied bias is induced in the metal plate 18. By detecting this current, a leak state between the photosensitive drum 1 and the developing sleeve 10 can be detected.

[0024] The current detection circuit as the detection means will be described in detail below with reference to Fig. 1. The current detection circuit includes a rectifier circuit 24 that rectifies the current induced in the metal plate electrodes, and a current-voltage conversion circuit 25 that converts the current signal generated by the rectifier circuit 24 into a voltage Vdc. The rectifier circuit 24 is electrically connected to the second contact on the main body side. The current-voltage conversion circuit 25 is also , and is connected to the CPU 23 to compare the relationship with the peak-to-peak voltage of the AC voltage. Note that, in this embodiment, the current signal generated by the rectifier circuit 24 is converted into a voltage, but the present invention is not limited to this.

[0025] 3 shows the relationship between the AC voltage Vpp applied to the developing sleeve 10 from the power supply in this embodiment and the current value detected by the rectifier circuit 24 at that time. It was found that as the AC voltage Vpp is increased, the detected current increases proportionally, but once a certain value is exceeded, the detected current barely changes. Furthermore, when an image printed at the same time was checked, image defects caused by developer leaks began to occur from the timing when the change in the detected current became small.

[0026] This is believed to be because the AC voltage Vpp becomes large, causing leakage between the photosensitive drum and the developing sleeve, and the AC voltage is no longer able to maintain a normal bias waveform. In other words, when the AC voltage is no longer able to maintain a normal bias waveform, the developing waveform does not change even if Vpp is increased further, and the current induced in the metal plate in the toner chamber does not change. In other words, when a developing leak occurs, at the point of Vpp (Vpp=1500V in the case of FIG. 3) applied when the developing leak occurs, no further voltage is effectively applied to the developing roller. Then, since the potential difference itself generated between the developing roller and the metal plate in the toner chamber does not change even if Vpp is continued to be increased after the developing leak, the current induced in the metal plate in the toner chamber is saturated at the point of Vpp at the time when the developing leak occurs. In other words, the current that should not flow flows to the photosensitive drum side as a leakage current, and the current induced in the metal plate in the toner chamber does not increase. By utilizing this phenomenon, the developing leak can be detected using the metal plate in the toner chamber at Vpp where the developing leak occurs.

[0027] At this time, if the circuit has a large internal impedance relative to the output of the AC voltage power supply 20, the detection accuracy is improved. A high-voltage power supply having a high voltage output has the advantage of being able to suppress development leakage, but because it can suppress development leakage, the upper limit of the applicable voltage is high, and there is a risk that a large current will flow once leakage occurs. Furthermore, a high-voltage power supply capable of high voltage output is expensive and has a large board area. Therefore, in Example 1, a configuration was adopted in which the high-voltage output is limited to the voltage required for image formation to reduce costs and achieve a small size, and is sensitive to resistance fluctuations when development leakage occurs.

[0028] Fig. 4 is an example of a flow chart showing the flow of detecting leakage between the photosensitive drum and the developing sleeve. This discharge occurrence detection operation is performed when the installation environment of the printer, such as atmospheric pressure, temperature, and humidity, changes, or when the developing device is replaced or paper is passed through the developing device, which may change the SD gap (the closest distance between the developing sleeve and the photosensitive drum). The execution timing is not limited to the above example, and can be set appropriately. The detection process of this embodiment will be described below with reference to Fig. 1.

[0029] First, when the power supply of the printer body is turned on and the discharge occurrence detection operation is started (S1), the rotation of the photosensitive drum is started by a drive mechanism (not shown) in response to an instruction from the CPU (S2). This driving of the photosensitive drum continues until the discharge occurrence detection operation is completed. Next, a DC bias of -300V is applied to the developing sleeve, and a charging bias is applied so that the surface potential of the photosensitive drum becomes -500V (S3). When the photosensitive drum rotates one revolution from S3, the surface potential becomes the target value (S4). Next, Vpp to be applied to the developing sleeve is set. First, it is set to Vpp(0) which ensures that no leakage occurs (S5), and the current I(0) induced in the metal plate in the toner chamber at that time is detected (S6). Next, it is set to Vpp(n+1) which is 100V higher than Vpp(n) (S7), and the current I(n+1) induced at that time is detected (S8). For example, when n=0, Vpp(1) is set to 100 V higher than Vpp(0). The current I(1) is detected by repeating this step (S9, S10, S15) until the induced current Vpp(n+1) is found, for example, such that {I(n+2)-I(n+1)} / {I(n+1)-I(n)}<1 / 2 (S11). When Vpp(n+1) is found, a value obtained by lowering Vpp(n+1) by 200 V is adopted as Vpp during image formation, taking into consideration changes in temperature, humidity, and air pressure during paper feed (S12). Next, the developing bias and charging bias are turned OFF (S13), and then the rotational drive of the photosensitive drum is stopped (S14). In this embodiment, only the photosensitive drum is rotated and the detection is performed with the rotation of the developing sleeve stopped, but this is to suppress the transfer of toner from the developing sleeve to the photosensitive drum as much as possible, and there is no functional problem even if the developing sleeve is rotated.

[0030] In this way, by detecting the current induced in the metal plate in the toner chamber when the AC voltage Vpp is changed, it is possible to determine with a simple configuration whether or not a leak has occurred between the photosensitive drum and the developing sleeve.

[0031] In this embodiment, the slope, which is the ratio of the change in the magnitude of the AC current detected by the detection means to the change in the magnitude of the bias applied by the application means, is acquired multiple times, and when a predetermined change is observed in the slope, it is detected that the magnitude of the bias has reached a value at which leakage occurs. In acquiring the slope, the application means applies the bias with different magnitudes multiple times, and acquires multiple AC currents induced in the conductive member by the bias application. Note that in this embodiment, the detection means detects the AC current multiple times, and judges whether or not leakage has occurred by checking whether or not there is a predetermined change in the slope, which is the ratio of the change in the magnitude of the AC current, but this is not limited to this. In other words, if a current value that is a threshold value for judging whether or not leakage has occurred is stored in advance in a storage means such as a memory, and whether or not there is a change in the slope is checked by comparing it with the threshold value, it is not necessary to detect the AC current multiple times.

[0032] Here, in the above embodiment, the bias applied is changed so that its absolute value gradually increases, but the method is not limited to this. For example, the bias may be changed roughly at first to roughly estimate the boundary between a non-leakage bias that does not cause leakage and a leakage bias that causes leakage, and then the bias may be changed finely. That is, the bias applied by the application means belongs to either a non-leakage region in which the AC current changes approximately according to a predetermined reference slope (1 / 2 in this embodiment) with respect to the change in bias, or a leakage region in which the AC current does not increase even if the bias is increased. Therefore, for example, a first bias of a magnitude that would approximately belong to the non-leakage region (first region) is applied at first, and then a second bias of a magnitude that would approximately belong to the leakage region (second region) is applied this time. Next, a third bias larger than the first bias but smaller than the second bias is applied, and if the third bias is a bias belonging to the first region, a fourth bias larger than the third bias but smaller than the second bias is applied. In this manner, a method of applying biases that gradually narrows the difference in absolute value may be adopted. This makes it possible to set the development bias during image formation based on a bias closer to the leak occurrence boundary bias.

[0033] The leak referred to here is a phenomenon in which the AC voltage cannot maintain a predetermined normal rectangular bias waveform, causing uneven density, as described above. This invention does not take into consideration minute leaks that do not adversely affect image formation operations.

[0034] In addition, the magnitude of the bias is the magnitude of the absolute value. For example, in an image forming apparatus using toner whose normal charging polarity is negative, a negative bias is applied as a developing bias, etc. The configuration described above is adopted.

[0035] Example 2 In Example 1, the AC voltage applied to the developing sleeve was gradually changed, and the current induced in the metal plate was detected at that time to detect leakage between the photosensitive drum and the developing sleeve. In Example 2 of the present invention, the detection time is shortened by performing detection before pulling the toner seal when the process cartridge is new. The basic configuration is the same as in Example 1, but this example is characterized in that the metal plate is placed in the developing chamber, and detection is performed in a state where the developing chamber and the toner storage chamber are separated by the toner seal.

[0036] <Method of Detecting Leakage from Photosensitive Drum and Developing Sleeve in the Present Embodiment> 5 is a diagram showing the connection between the process cartridge and the main body in this embodiment. This embodiment is different from the first embodiment in that a metal plate is disposed in the developing chamber, and an opening communicating between the developing chamber and the toner storage chamber is separated by a toner seal 26 as a sealing member.

[0037] In this configuration, when the process cartridge is new, leakage can be detected without the toner existing between the developing sleeve and the metal plate, so there is no need to consider the change in the dielectric constant between the developing sleeve and the metal plate due to the change in the amount of toner. That is, the current induced in the metal plate by applying the developing Vpp depends on the diameter of the developing sleeve, the size of the metal plate, the distance between the developing sleeve and the metal plate, and the dielectric constant of the air between the developing sleeve and the metal plate. In addition, since the dielectric constant of the air changes little depending on the environment and the atmospheric pressure, the gradient a of the current induced in the metal plate with respect to the developing Vpp can be determined almost by the configuration of the cartridge. Therefore, the gradient a of the current induced in the metal plate with respect to the developing Vpp is saved and stored in a memory tag or the like as a storage means attached to the cartridge in advance. Then, by applying two different developing Vpp and detecting the current value induced in the metal plate at that time, it is possible to determine the developing Vpp at which the developing leak has occurred from the result.

[0038] FIG. 6 shows the relationship between the development Vpp and the detection current. The open plots show the relationship between the development Vpp and the detection current under conditions where no development leak occurs (for example, when the SD gap is sufficiently wide), and the relationship is proportional even if the development Vpp increases. The slope a depends on the diameter of the development sleeve and the size of the sheet metal, the distance between the development sleeve and the sheet metal, and the dielectric constant of the air between the development sleeve and the sheet metal. On the other hand, the solid plots show the same change in the development Vpp at the SD gap of 200 μm shown in Example 1, and the detection current becomes constant from the timing when the development leak occurs. This is because, as explained in Example 1, the AC voltage cannot maintain a normal bias waveform, and the development waveform does not change even if Vpp is increased any further.

[0039] The detection process of this embodiment will be described with reference to the flowchart of FIG. 7. First, the power supply of the printer body is turned on (S21), and it is determined whether the process cartridge is new or not using data of the memory tag, etc. (S22). If the process cartridge is not new, the operation is terminated. If it is determined that the process cartridge is new, the driving of the photosensitive drum is started (S23). This driving of the photosensitive drum continues until the discharge occurrence detection operation is completed. Next, a DC bias of -300V is applied to the developing sleeve, and a charging bias is applied so that the surface potential of the photosensitive drum is -500V (S24). When the photosensitive drum rotates one revolution from S4, the surface potential reaches a target value (S25). Next, Vpp(1) that reliably does not cause leakage is applied (S26), and the current I(1) induced in the metal plate in the toner chamber at that time is detected (S27). Next, the maximum outputtable Vpp(2) is applied (S28), and the current I(2) induced at that time is detected (S29). Based on the detection result, the leakage voltage Vpp(leak) = {I(2)-I(1)+aVpp(1)} / a is calculated (S30). After Vpp(leak) is calculated, Vpp(l A value obtained by subtracting 200 V from the initial voltage (Vpp) is adopted as Vpp during image formation (S31). Next, the developing bias and charging bias are turned OFF (S32), and thereafter the rotation of the photosensitive drum is stopped (S33).

[0040] In this way, when the developing chamber and the toner storage chamber are separated by a toner seal and there is no toner between the developing sleeve and the metal plate, the developing Vpp at which leakage occurs can be found by simply changing the developing Vpp in two steps and measuring the current induced in the metal plate. This makes it possible to set an appropriate Vpp in a shorter time.

[0041] In this embodiment, (i) a slope, which is a ratio of a change in the magnitude of the AC current to a change in the magnitude of the bias, is set in advance, so that a reference for plotting a graph of the change in the bias / AC current according to the slope (reference slope) is obtained. That is, (ii) a bias of a first magnitude belonging to the non-leak region and an AC current of the first magnitude obtained thereby, and (iii) a bias of a second magnitude belonging to the leak region and an AC current of the second magnitude obtained thereby are obtained. By using the applied bias of (ii) and the AC current obtained thereby, a straight line of the change in the bias / AC current according to the reference slope of (i) can be drawn as shown in FIG. 6. Then, by using the AC current obtained by the applied bias of (iii), a leak occurrence boundary bias, which is a bias at the boundary between the non-leak region and the leak region, can be obtained.

[0042] Example 3 In the first embodiment, leakage between the photosensitive drum and the developing sleeve is detected by detecting the current induced in the metal plate according to the AC voltage applied to the developing sleeve. In the third embodiment of the present invention, a means is provided for detecting whether a drum cartridge having a photosensitive drum and a developing cartridge having a developing sleeve are attached to an image forming apparatus by detecting the current induced in the metal plate.

[0043] The basic configuration is the same as in the first embodiment, but in this embodiment, the process cartridge is separated into a drum cartridge (first cartridge) having a photosensitive drum and a developing cartridge (second cartridge) having a developing sleeve. In a conventional process cartridge in which the photosensitive drum and developing sleeve are integrated, there are some that judge whether the process cartridge is attached to the main body by the presence or absence of a current induced in the metal plate when a specific developing bias is applied.

[0044] However, when this method is used in this embodiment, it is possible to determine whether a developer cartridge is installed, but it is not possible to determine whether a drum cartridge is installed. Therefore, in this embodiment, a developer Vpp that reliably generates a leak is applied, and the current induced in the metal plate at that time is detected to determine whether a drum cartridge is installed.

[0045] <How to determine if a drum cartridge is installed> In this embodiment, the presence or absence of the drum cartridge is determined by detecting the current induced in the metal plate when two different development Vpp are applied. Specifically, a development Vpp that reliably does not cause development leak and a development Vpp that reliably causes development leak are applied, and the current induced in the metal plate is detected.

[0046] Figure 8 shows the results of measuring the current induced in the metal plate when the development Vpp is changed when the drum cartridge is installed (solid line) and when it is not (dotted line). The absolute value of the current induced by the drum cartridge shifts depending on whether or not it is installed because it changes depending on the stray capacitance adjacent to the development sleeve and the amount of toner in the development device. As shown above, when a drum cartridge is installed (solid line), once the development Vpp exceeds a certain value, the current stops changing due to the effects of development leak. On the other hand, when a drum cartridge is not installed, the current value increases in proportion to the development Vpp. This is because, since there is no photosensitive drum facing the development sleeve, no leakage occurs even if the development Vpp is increased.

[0047] That is, when detection is performed with no drum cartridge installed, since there is no photosensitive drum, no leakage occurs even if a high development Vpp is applied, and an induced current proportional to the development Vpp flows. On the other hand, when the same detection is performed with a drum cartridge installed, since there is a photosensitive drum, if a development Vpp that definitely causes leakage is applied, the value of the induced current will be smaller than when no leakage occurs. By utilizing this difference, it is possible to determine the presence or absence of a drum cartridge.

[0048] <Explanation of how to determine whether a cartridge is present or not> FIG. 9 is an example of a flowchart for determining the presence or absence of a cartridge in this embodiment. The detection process of this embodiment will be described below with reference to FIG. 9. First, the printer body is turned on, or the front door of the printer body is closed with the printer body turned on (S41). Next, a development Vpp(1) that will definitely not cause leakage is applied (S42). The current value I(1) that flows at that time is detected (S43). It is determined whether or not a current is detected (S44), and if no current flows (No), it is reported that a development cartridge is not installed (S49). If a current flows, a development Vpp(2) that will definitely cause leakage is applied (S45), and the detected current value I(2) is measured (S46). At that time, it is determined whether or not {I(2)-I(1)} / {Vpp(2)-Vpp(1)} is smaller than a threshold value c (S47). If it is larger (No), no leakage occurs, and it is reported that a drum cartridge is not installed (S50). If the detected value is equal to or less than the threshold value c, it is determined that a leak has occurred and the developing cartridge and drum cartridge are correctly installed, and a predetermined print preparation operation is carried out (S48).

[0049] In this way, by applying the development Vpp to the development sleeve and detecting the current induced in the metal plate placed inside the development device, it is possible to simultaneously determine whether or not a development device is present and whether or not a cleaning device is present.

[0050] The configurations of the above-mentioned embodiments 1 to 3 can be combined with each other to the extent that no technical contradiction occurs. [Explanation of symbols]

[0051] 1...photosensitive drum, 4...developing device, 6...cleaning device, 10...developing sleeve, 18...metal plate, 19...DC voltage power supply, 20...AC voltage power supply, 21...output control section, 22...Vpp control section, 23...CPU, 24...rectifier circuit, 25...current-voltage conversion circuit, 26...toner seal

Claims

1. An image forming apparatus capable of performing an image forming operation, a first cartridge including an image carrier and detachably mountable to a main body of an image forming apparatus; a second cartridge which is detachably attached to a main body of an image forming apparatus and which faces the image carrier with a predetermined gap therebetween and which develops a latent image formed on the image carrier with a developer, and which includes a frame for supporting the developer carrier; an application means for applying a developing bias, which is a superimposed DC voltage and AC voltage, to the developer carrier; A conductive member provided on the frame; a detection unit that detects an AC current induced in the conductive member by application of the developing bias to the developer carrier by the application unit; A control unit that controls the application means, The control unit controls the developing bias in the image forming operation based on the AC current detected by the detection means when the developing bias is applied by the application means, and detects whether the first cartridge has been attached or detached to the device main body and whether the second cartridge has been attached or detached to the device main body based on the AC current detected by the detection means.

2. 2. The image forming apparatus according to claim 1, wherein the detection means detects the AC current when the application means applies the developing bias a plurality of times with the magnitude of the developing bias being varied.

3. An image forming apparatus capable of performing an image forming operation, An image carrier; a developer carrier that faces the image carrier with a predetermined gap therebetween and develops the latent image formed on the image carrier with a developer; a frame for supporting the developer carrier; an application means for applying a developing bias, which is a superimposed DC voltage and AC voltage, to the developer carrier; A conductive member provided on the frame; a detection unit that detects an AC current induced in the conductive member by application of the developing bias to the developer carrier by the application unit; A control unit for controlling the application means; acquiring the developing bias applied to the developer carrier during the image forming operation, the control unit controls the developing bias in the image forming operation based on the AC current detected by the detection unit when the developing bias is applied by the application unit, The image forming apparatus is characterized in that the acquisition means acquires a slope of the change in the magnitude of the AC current detected by the detection means relative to the change in the magnitude of the developing bias multiple times by applying the developing bias with different magnitudes by the application means multiple times, acquires a leak occurrence bias, which is the developing bias when the magnitude of the slope becomes smaller than a predetermined magnitude, and acquires the developing bias that is smaller than the leak occurrence bias by a predetermined magnitude as the developing bias.

4. The developing bias is applied to the developer carrier during the image forming operation. The acquisition means includes: applying the developing bias a plurality of times with different magnitudes by the application means, thereby obtaining a gradient of a change in the magnitude of the AC current detected by the detection means with respect to a change in the magnitude of the developing bias a plurality of times; A leak occurrence bias, which is the developing bias when the magnitude of the gradient is smaller than a predetermined magnitude, is obtained; 2. The image forming apparatus according to claim 1, wherein the developing bias is smaller than the leak occurrence bias by a predetermined magnitude.

5. 5. The image forming apparatus according to claim 3, wherein the leakage generating bias is a bias that does not increase the AC current detected by the detecting means even if the developing bias applied by the applying means is increased.

6. the frame has a storage chamber for storing a developer, 6. The image forming apparatus according to claim 1, wherein the conductive member is provided in the storage chamber.

7. The acquisition means includes: (i) a reference gradient that is determined in advance as a gradient of a change in the magnitude of the AC current relative to a change in the magnitude of the developing bias; (ii) the AC current of a first magnitude detected by the detection means when the application means applies the developing bias of a first magnitude; and (iii) the AC current of a second magnitude detected by the detection means when the application means applies the developing bias of a second magnitude having an absolute value larger than that of the first magnitude; and Based on the above, a leak occurrence boundary bias is obtained, which is a boundary at which the magnitude of the slope changes to a slope smaller than the magnitude of the reference slope by a predetermined magnitude, 4. The image forming apparatus according to claim 3, wherein the developing bias is smaller than the leak occurrence boundary bias by a predetermined magnitude.

8. The leak occurrence boundary bias has a first region in which the magnitude of the AC current detected by the detection means changes substantially in accordance with the reference gradient with respect to the change in the magnitude of the developing bias applied by the application means, and a second region in which the magnitude of the AC current detected by the detection means does not increase even if the magnitude of the developing bias applied by the application means is increased.

8. The image forming apparatus according to claim 7, wherein the bias is at the boundary.

9. 9. The image forming apparatus according to claim 8, wherein the second magnitude of the developing bias is a magnitude included in the second region.

10. Further comprising a storage means for storing at least the reference slope, The image forming apparatus according to any one of claims 7 to 9, wherein the developer carrier, the frame, and the memory means are integrated as a cartridge that is detachably attached to the main body of the image forming apparatus.

11. 11. The image forming apparatus according to claim 10, wherein said storage means also stores information as to whether said cartridge is a new one or not.

Images