JP4497901B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment having a process cartridge using an electrophotographic method.

  An electrophotographic image forming apparatus (laser beam printer) has a photosensitive drum that forms an electrostatic latent image corresponding to each color of Y, M, C, and Bk, and is developed on each photosensitive drum. Images are sequentially transferred onto an intermediate transfer belt to form a color image, and the color image is transferred onto a recording sheet by a transfer roller to record the color image.

  In the laser beam printer having such a configuration, in the color printing mode, the photosensitive drums corresponding to all colors are in contact with the intermediate transfer belt. The intermediate transfer belt is pressed to the government transfer drum side by a primary transfer roller disposed through the intermediate transfer belt at a position facing each photoconductor drum. On the other hand, at the time of printing in the monochrome mode, the photosensitive drum and the belt are separated from each other by separating the primary transfer roller corresponding to the photosensitive drum corresponding to each color of Y, M, and C from the intermediate belt.

Here, the rotational drive system of the photosensitive drum is, for example, a drive system as disclosed in Patent Document 1. Here, in order to transmit the driving from the main body to the developing container (toner cartridge) put into the main body of the apparatus, the driving main body and the photosensitive drum 1 are engaged with each other (FIGS. 2A and 2B). B)). This is because it is necessary to release the engagement when the cartridge is taken out from the apparatus main body when the cartridge is exchanged or when the jam processing is performed. In order to release the meshing, it is necessary to rotate the rotation driving means of the photosensitive drum 1 in the direction opposite to the rotation direction during the image forming operation. The engagement release mechanism as shown in Document 1 is used.
JP 2002-91249 A Japanese Patent Laid-Open No. 06-003891

  However, in the laser beam printer described above, although the engagement (fitting) of the drive transmission portion is normally performed between the apparatus main body and the photosensitive drum 1 described above, due to an unforeseen situation, for example, the fitting may occur. There may be a case where the convex gear 101 of the photosensitive drum 1 and the concave gear 102 on the main body side are not coupled, such as dust adhering to the joint. In this case, although the developing roller in contact with the photosensitive drum 1 is rotating, the photosensitive drum 1 is not rotating, so that the toner layer of the developing roller is stopped by the photosensitive drum 1. It is scraped off. The toner thus scraped off scatters into the main body, stains the inside of the main body, or damages the developing roller if printing is continued in this state.

  Further, when the intermediate transfer belt comes into contact with the photosensitive drum 1 that is not rotating, the intermediate transfer belt is rotating, so that the photosensitive drum and the intermediate transfer belt are damaged. As a result, problems such as the need to replace the cartridge and the intermediate transfer belt and the need to clean the inside of the main body have arisen.

  In addition, in the conventional apparatus, as shown in Patent Document 2, although a proposal regarding the mounting failure of the process cartridge has been made, the mounting failure refers to the contact state between the photosensitive drum and the charging member, for example, not contacting. It does not mention even the rotation failure of the photosensitive drum. In the method of Patent Document 2, when the photosensitive drum is not rotating even though the intermediate transfer belt and the photosensitive drum are in a correct contact state, the charging current is generated at the moment when the voltage is applied to the transfer unit. Since it flows, there is a possibility that it is erroneously recognized as being in a normal wearing state.

The present invention has been made in view of the above problems, and the feature of the present invention is whether or not there is an abnormality in the transmission of driving force for rotating the photosensitive member from the apparatus main body in the electrophotographic image forming apparatus. Is to provide an image forming apparatus capable of detecting the above.

A feature of the present invention is to prevent damage to the image forming apparatus and dirt in the apparatus main body that occur when the gears of the photosensitive member are not properly fitted.

The image forming apparatus of the present invention has the following configuration. That is,
A photoconductor that carries a toner image ; a rotation driving unit that is fitted to the photoconductor and transmits a driving force from the apparatus main body to the photoconductor to rotate the photoconductor; and a charging unit that charges the photoconductor An exposure means for exposing the photoconductor, a transfer belt for transferring a toner image on the photoconductor to a transfer material, a transfer roller facing the photoconductor via the transfer belt, and a transfer roller An image forming apparatus comprising: a transfer bias power source for applying a voltage; and a current detection unit for detecting a current flowing through the transfer roller,
After charging the surface of the photoconductor to a predetermined potential by the charging unit, a voltage is applied from the transfer bias power source to the transfer roller so that a current flowing through the transfer roller has a predetermined target current value, An average value of the current values detected by the current detection means during a predetermined period while the voltage is applied from the transfer bias power supply to the transfer roller so as to be the target current value is defined as an average current value, and the target current When the difference between the value and the average current value is larger than a predetermined amount, it is determined that there is an abnormality in the transmission of the driving force to the photoconductor via the rotation driving means .

According to the present invention, it is possible to detect a rotation failure of the photosensitive member due to a poor fitting of the gear of the photosensitive member. As a result, it is possible to prevent contamination in the apparatus caused by the rotation failure of the photoconductor.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic sectional view of a recording and transfer unit of a color laser beam printer using an electrophotographic process according to an embodiment of the present invention, particularly a laser beam printer having a process cartridge using an electrophotographic system. The process cartridge is a cartridge in which a charging unit, a developing unit, or a cleaning unit and an electrophotographic photosensitive drum are integrally formed, and the cartridge can be attached to and detached from the image forming apparatus main body. Alternatively, at least one of a charging unit, a developing unit, and a cleaning unit and an electrophotographic photosensitive drum are integrally formed into a cartridge that can be attached to and detached from the main body of the image forming apparatus. Alternatively, it means that at least the developing means and the electrophotographic photosensitive drum are integrated into a cartridge so that the image forming apparatus (laser beam printer) can be attached to and detached from the body.

  The color laser beam printer has a plurality of photosensitive drums 1 (four in total for Y, M, C, and Bk) that are a plurality of first image carriers, and in turn an intermediate that is a second image carrier. This is a four-drum type (in-line type) printer that continuously transfers multiple images onto the transfer belt 6 and obtains a full-color print image.

  The photoconductor drum 1 is, for example, a negatively charged organic photoconductor, and has a photoconductor layer (not shown) on an aluminum drum base (not shown), and in the arrow direction (counterclockwise) at a predetermined peripheral speed. The charging roller 2 that is driven to rotate in the direction of the rotation and contacts in the rotation process is uniformly charged with negative polarity. A charging roller 2 as a charging unit is rotatably contacted to the surface of the photosensitive drum 1 and uniformly charges the photosensitive drum 1 to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). To do. The developing device is a contact one-component developing device that performs development with a non-magnetic toner as a one-component developer, and is arranged in a clockwise direction disposed opposite to the photosensitive drum 1 at an opening of a developing container (toner cartridge) 8. A developing roller 9 as a rotatable developer carrying member, a rotatable elastic roller 10 in pressure contact with the developing roller 9, a regulating blade (not shown) having elasticity in contact with the developing roller 9, and the toner in the developing container 8 are stirred. A stirring member (not shown) is provided. The regulating blade is in contact with the developing roller 9 on the downstream side in the rotation direction of the developing roller 9 with respect to the pressure contact portion between the developing roller 9 and the elastic roller.

  The toner stirred by the stirring member in the developing container 8 is supplied to the surface of the developing roller 9. The toner supplied to the surface of the developing roller 9 is conveyed along with the rotation of the developing roller 9, and a charge is applied by friction at the contact portion between the regulating blade and the developing roller 9, so that the surface of the developing roller 9 is thin. Layered. The thinned toner is conveyed by the rotation of the developing roller 9 and adheres to the electrostatic latent image formed on the photosensitive drum 1 at a contact portion (developing portion) with the photosensitive drum 1 and appears. Imaged. The toner that has not contributed to the development of the developing roller 9 is peeled off by the elastic roller 10.

  Next, the transfer part will be described.

  An endless intermediate transfer belt 6 is suspended from a drive roller 6a, a tension roller 6b, and a secondary transfer counter roller 6c, and rotates in the direction of the arrow in the figure. The tension roller 6b is loaded from both sides by a 2.0 kgf spring on one side. Four photosensitive drums 1 are arranged in series in the moving direction of the intermediate transfer belt 6 corresponding to each color. A photosensitive drum 1 in a process unit (yellow) having a yellow developing device is uniformly charged to a predetermined polarity and potential by a primary charging roller 2 in a rotating process, and then an image exposure means (color original image) (not shown). Color separation, imaging exposure optical system, scanning exposure system by laser scanning that outputs a laser beam modulated in response to time-series electric digital pixel signals of image information, etc.) An electrostatic latent image corresponding to the first color component image (yellow component image) of the image is formed. Next, the electrostatic latent image is developed by the first developer 4 (yellow developer) with yellow toner as the first color.

  The yellow image formed on the photosensitive drum 1 enters the primary transfer nip portion with the intermediate transfer belt 6. In the transfer nip portion, the primary transfer roller 7 is brought into contact with and contacted with the back side of the intermediate transfer belt 6. The voltage application member has a primary transfer bias source (not shown) so that a bias can be applied independently at each port. The intermediate transfer belt 6 first transfers yellow at the port of the first color, and then, through the above-described steps, sequentially transfers magenta, cyan, and black colors from the photosensitive drum 1 corresponding to each color at each port. The toner remaining on each photoconductor drum 1 is cleaned by a cleaning blade in contact with each photoconductor drum 1, and the cleaned toner is collected in a waste toner container (not shown).

  The four-color full-color image thus formed on the intermediate transfer belt 6 is then collectively transferred to the transfer material P by the secondary transfer roller 13 and melted and fixed by the fixing device 80 to obtain a color print image.

  On the other hand, in the monochrome mode, the primary transfer rollers 7 (yellow, magenta, cyan) described above are separated as indicated by dotted line portions 7a to 7c in FIG. As a result, the intermediate transfer belt 6 is separated from the photosensitive drums 1 for yellow, magenta, and cyan. In such a separation mechanism, the yellow, magenta, and cyan primary transfer portions and the black primary transfer portion are each divided within the ITB unit, and the color unit 11 has a cam 12 with 14 as the rotation center. Thus, the structure can be contacted and separated. In the full color mode, the cam 12 rotates in the direction of the arrow 12 a to lift the color unit 11, and the primary transfer portions of yellow, magenta, and cyan are in contact with the photosensitive drum 1. In the monochrome mode, the cam 12 rotates in the direction opposite to the arrow 12a, and the color unit 11 is separated from the drum 1. For this reason, the intermediate transfer belt 6 is separated from the photosensitive drum 1 for color image formation.

  With this configuration, in the normal full color mode, as shown in FIG. 1, the primary transfer roller 7 presses the intermediate transfer belt 6 toward the photosensitive drum 1, and the intermediate transfer belt 6 and the photosensitive drum 1 are exposed. The body drum 1 is in pressure contact. On the other hand, in the monochrome mode, the photosensitive drum 1, the developing sleeve, and the charging roller 2 in the yellow, magenta, and cyan process units that are disconnected from the intermediate transfer belt 6 stop rotating, and only the black image is displayed. Formation is performed to obtain a monochrome image.

  FIG. 3 is a view for explaining the structure of the process cartridge according to the present embodiment, in which the elastic roller 10 is omitted.

A charging roller 2, a developing container 8, and a cleaning blade 15 are installed around the photosensitive drum 1, and exposure with the laser beam 3 is performed between the charging roller 2 and the developing container 8. The photoconductor drum 1 is, for example, a negatively charged organic photoconductor, and has a photoconductor layer (not shown) on an aluminum drum base (not shown), and in the arrow direction (counterclockwise) at a predetermined peripheral speed. The charging roller 2 that is driven to rotate in the direction of the rotation and contacts in the rotation process is uniformly charged with negative polarity. The diameter of the photosensitive drum 1 is φ25, and is an organic photoconductor in which a charge generation layer and a charge transport layer are sequentially laminated on a conductive substrate such as an aluminum drum. Further, the electrostatic capacity per 1 cm ^{2 of} this charge transport layer is 1.5 pF or more and 6.0 pF or less. From the viewpoint of preventing current leakage and the potential stability of the photosensitive drum, in the generally used potential setting, the thickness of the photosensitive drum 1, that is, the thickness of the charge transport layer is preferably 5 to 20 μm. In this embodiment, the thickness of the charge transport layer of the photosensitive drum 1 is 15 μm.

  Further, as shown in FIG. 2, the rotational drive system has a convex gear 101 on the photosensitive drum 1 side and a concave gear 102 on the main body side, and the concave gear 102 on the main body side is the longitudinal length of the photosensitive drum 1. By projecting in the direction, it is coupled with the gear 101 on the photosensitive drum 1 side. With such a configuration, it is possible to take out the cartridge from the apparatus main body at the time of cartridge replacement or jam processing, thereby improving usability.

  The charging roller 2 is a conductive elastic roller having a diameter of φ12 and a surface length of 230 mm, in which at least an elastic body layer is coated around a φ6 cored bar (conductive shaft) 80c. The charging roller 2 is a multilayer roller in which an elastic layer, a dielectric layer, and a surface layer are laminated on the outer periphery of the conductive shaft 80c. The charging roller 2 is configured such that both ends of the cored bar 80c are rotatably supported by a bearing member (not shown) and are arranged in parallel to the shaft of the photosensitive drum 1, and are placed on the surface of the photosensitive drum 1 by a pressing means (not shown). On the other hand, it is brought into pressure contact with a predetermined uniform pressing force in the longitudinal direction (the load on one side of the roller is 4.9 N (500 gf)), and rotates following the rotation of the photosensitive drum 1. A contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) N.

  By applying a predetermined charging bias to the charging roller 2 from a charging bias applying power source 801, the surface of the photosensitive drum 1 is contact-charged to a predetermined polarity and potential. In the present embodiment, a DC charging method is applied, and a DC voltage of −800 V is applied to the charging roller 2 from the charging bias application power source 801, and the surface of the photosensitive drum 1 is contact charged to a charging potential (dark portion potential) of −450V. I am letting.

  The developing container 8 reversely develops the electrostatic latent image on the surface of the photosensitive drum 1 with the negative toner in the developing unit D. A developing roller 9 is in proximity to or in contact with the photosensitive drum 1 and functions as a developer carrying member. The developing roller 9 is rotationally driven at a predetermined peripheral speed in the clockwise direction of the arrow. The developing roller 9 is in contact with the photosensitive drum 1 with a contact width and has a faster peripheral speed (170 mm / second) than the peripheral speed (process speed 94.2 mm / second) of the photosensitive drum 1. Driven by rotation. Further, the developing roller 9 has a mechanism that contacts only when printing is performed, because if the toner is kept in contact with the photosensitive drum 1 for a long time, the portion deforms and an image defect occurs.

  The surface of the developing roller 9 has an appropriate unevenness for increasing the probability of rubbing with the toner (t) and carrying the toner satisfactorily. In this embodiment, the surface is 16 mm in diameter and long. A silicon rubber layer having a thickness of 240 mm and a thickness of 4 mm is coated with an acrylic / urethane thin layer. A negative development bias of −450 V is applied to the development roller 9 from a development bias power source 201. The developing roller 9 had a resistance of 1.0e + 4 to 1.0e + 6 [Ω], a surface roughness of 0.5 to 0.9 μm, and an Asker C hardness of 45 ° (load 1 kgf). The resistance value of the developing roller 9 is measured by bringing an aluminum roller (not shown) having a diameter of 30 mm and the developing roller 9 into contact with each other in the entire longitudinal direction with a contact load of 500 gf, and rotating the aluminum roller at 0.5 rps. Then, a DC voltage of −400 V is applied to the developing roller 9 and a 10 kΩ resistor is disposed on the ground side. Then, the voltage at both ends of the resistor is measured, the current value is calculated from the measured voltage value, and the resistance of the developing roller 9 is calculated.

A doctor blade 300 made of urethane rubber or the like having a base end attached to the developing container 8 is in elastic contact with the developing roller 9, and the layer thickness of the toner on the surface of the developing roller 9 is made uniform by the doctor blade 300. The predetermined value is 0.4 mg / cm ² . The developing roller 9 rotates at a speed 1.6 times that of the photosensitive drum 1, and the amount of toner developed on the photosensitive drum 1 is approximately 0.6 mg / cm ² for a solid color. . The developer (toner) t stored in the developing container 8 is stirred by the stirring member 70, and a part of the developer (toner) is supplied to the developing roller 9 and applied to the developing roller 9 by the doctor blade 300.

  Reference numeral 3 denotes an exposure unit (not shown) as a latent image forming unit, for example, a laser beam output from a semiconductor laser 505 (FIG. 5). The laser beam 3 scans and exposes the charged surface of the photosensitive drum 1. As a result, the charged potential (bright portion potential) of the exposed portion of the photosensitive drum 1 is attenuated to −150V. Thus, an electrostatic latent image of image information corresponding to the scanning exposure pattern is formed on the peripheral surface of the rotating photosensitive drum 1 by the potential contrast with the dark portion potential portion.

  A photosensitive drum 1 having a yellow developing device is uniformly charged to a predetermined polarity and potential by a primary charging roller 2 in the course of rotation, and then image exposure means (not shown) (color separation and concatenation of a color original image). The image exposure optical system, the image exposure 3 by a laser scanning scanning exposure system that outputs a laser beam modulated in accordance with the time series electric digital pixel signal of the image information, etc. An electrostatic latent image corresponding to the color component image (yellow component image) is formed.

  Next, the electrostatic latent image is developed by the first developing device 8 (yellow developing device) with yellow toner as the first color. The yellow image thus formed on the photosensitive drum 1 enters the primary transfer nip portion with the intermediate transfer belt 6. In the transfer nip portion, the primary transfer roller 7 is brought into contact with and contacted with the back side of the intermediate transfer belt 6. The primary transfer roller 7 has a primary transfer bias source so that a bias can be applied independently at each port. The bias power source 501 (FIG. 5) has a constant voltage power source 502 (FIG. 5) having a D / A conversion port, and can output a voltage in the range of 0 to 3 KV. Thus, the CPU 510 (FIG. 5) can adjust the output in 256 steps. Further, the bias power source 501 has a current detection circuit 503 (FIG. 5), and supplies current (discharge current between the transfer roller 7 and the photosensitive drum 1) with accuracy in 256 steps within a range of 0 to 15 μA. The detected current value is A / D converted and input to the CPU 510.

  As the bias to the primary transfer roller 7 during image formation, several levels of voltage values are applied before the printing operation so as to obtain a predetermined current value, and a current detection circuit corresponding to the voltage value. At 503, the current is detected to determine the optimum applied voltage. In the present embodiment, the current setting value is 7 μA. When the control is executed, the charging potential of the photosensitive drum 1 is set to a dark potential VD = -450 V which is substantially equal to that during printing. Based on this, the optimum voltage is determined so that the current flowing to the dark potential portion is 7 μA.

  In the present embodiment, the reason why the dark potential portion current is set to 7 μA is that if the current flows too much in the dark potential portion, the retransfer amount increases (the image that is primarily transferred upstream in the downstream primary transfer portion is exposed to light. This is because if the dark potential portion current is too small, the primary transfer property itself deteriorates. A neutralizing needle (not shown) is disposed downstream of each primary transfer roller 7.

  The primary transfer roller 7 is a conductive roller, and is a roller having an outer diameter of 14 mm covered with foamed rubber obtained by mixing NBR and epichlorohydrin on a stainless steel shaft having an outer diameter of 6 mm.

  FIG. 4 is a diagram for explaining a state in which the resistance value of the conductive roller is measured.

  The roller 39 to be measured is brought into contact with an aluminum cylinder 40 of φ30 at 4.9 N (500 gf) on one side and rotated at 30 rpm. A voltage of 50 V to 1000 V is applied to the roller 39 from the power supply 43. 50V is applied to a roller having a resistance value of about 1.0e + 6 [Ω], and 1000 V is applied to a roller having a resistance value of 1.0e + 7 [Ω] or more. The current flowing at this time is obtained by measuring the voltage between the terminals of the resistor 42 with the voltmeter 41.

  A roller having a resistance value of 1.0e + 8 [Ω] was used as a result of such measurement. The roller hardness was 30 degrees in Asker C. Regarding the pressing of the roller, 4.9 N (500 gf) springs were arranged at both ends of the roller and pressed against the photosensitive drum 1 via the intermediate transfer belt 6.

  Under such conditions, at the first color station (Y), first, a yellow image is primarily transferred onto the intermediate transfer belt 6, and then, through the above-described steps, sequentially from the photosensitive drum 1 corresponding to each color, magenta, Cyan and black colors are multiple transferred at each color station. The four full-color images thus formed on the intermediate transfer belt 6 are then collectively transferred to the transfer material P by the secondary transfer roller 13, and the toner is melted and fixed by the fixing device 80 to obtain a color print image. Here, the intermediate transfer belt 6 has a circumferential length of 670 mm and a length in the longitudinal direction of 220 mm. The intermediate transfer belt 6 is a polyimide single-layer belt. The physical properties of the intermediate transfer belt 6 are a thickness of 60 μm and a resistance value (volume resistance value) of 1.0e + 9 [Ωcm].

  The resistance value is based on JIS-K6911. In order to obtain good contact between the electrode and the surface of the belt 6, conductive rubber is used as an electrode, and the volume resistivity ρv of the belt 6 is 50 V for 30 seconds. It is the result of having measured using the R8340 super high resistance meter (trademark) made from Advantest under the voltage application conditions.

  In the present embodiment, the intermediate transfer belt 6 is not limited to this. For example, polystyrene, styrene resin (chloropolystyrene, styrene-butadiene copolymer, etc.), methyl methacrylate resin, ethyl acrylate Resin, modified acrylic resin (silicone-modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, polyurethane resin, silicone resin , Fluororesin, modified polyphenylene oxide resin, polyimide resin, PES and the like. One or more of these can be used. The coating layer can be formed by any method such as spray coating, dip coating, electrostatic coating, and extrusion molding.

  In order to adjust the resistance value of the intermediate transfer belt 6 to a desired value, a conductive agent can be added to the elastic layer or the coating layer as necessary. The conductive agent is not particularly limited to the embodiment. For example, carbon, metal powder such as aluminum and nickel, metal oxide such as titanium oxide, quaternary ammonium salt-containing polymethyl methacrylate, polyvinyl Examples thereof include conductive polymer compounds such as aniline, polyvinyl pyrrole, polydiacetylene, polyethyleneimine, boron-containing polymer compound, and polypyrrole. These 1 type (s) or 2 or more types can be used.

  FIG. 5 is a block diagram illustrating a main functional configuration for detecting a coupling failure of the photosensitive drum 1 in the laser beam printer according to the present embodiment, and parts common to the previous drawings are denoted by the same symbols. Those explanations are omitted. For the sake of simplicity, the following description will be made with respect to a single photosensitive drum 1 corresponding to each of Y, M, C, and Bk. However, it is possible to detect a coupling failure in all the photosensitive drums 1. Of course, it is configured.

  A control unit 500 controls the operation of the laser beam printer to perform printing based on print data input from, for example, a host computer (not shown) or the like, and a photosensitivity characteristic of the present embodiment. A process for detecting a coupling failure of the body drum 1 is executed. As described above, the bias power source unit 501 includes the bias power source 502 for applying a bias voltage to the primary transfer roller 7 and the current detection circuit 503 for detecting a current value when the bias power source 502 applies a voltage. Reference numeral 504 denotes a switch for detecting opening / closing of the door of the laser beam printer. A semiconductor laser 505 emits laser light in accordance with an image signal or a control signal from the control unit 500. Reference numeral 506 denotes a display unit which displays a message to the operator and an error display. In particular, when a rotation failure of the photosensitive drum 1 is detected as described later, a warning is displayed to the operator to confirm the fitting of the photosensitive drum 1 by opening and closing the door of the apparatus main body. In addition, a warning buzzer or LED may be provided.

  Next, the control unit 500 will be described. Reference numeral 510 denotes a CPU that executes control processing by the control unit 500 in accordance with programs and data stored in the ROM 511. A RAM 512 is used as a work area during the control operation of the CPU 510 and temporarily stores various data. The ROM 511 stores programs executed by the CPU 510 and fixed data such as various setting data.

  Next, characteristic control processing executed by the laser beam according to the embodiment of the present invention will be described.

  This control is performed at the time of switching from the monochrome mode to the color printing mode at the time of power off / on, the front multi-rotation control at the time of opening / closing the door, and the monochrome printing mode. This is because the coupling failure of the photosensitive drum 1 is caused when the user opens or closes the door when the power is turned off, or even when the power is turned on, the user opens or closes the door for the purpose of jam processing or cartridge replacement. This is because it may occur in some cases. Further, since the photosensitive drum for color image formation is not rotated in the monochrome printing mode, coupling failure occurs when coupling the photosensitive drum 1 for color again when shifting from the monochrome mode to the color printing mode. This is because it may occur.

  Next, a process for detecting a coupling failure of the photosensitive drum 1 will be described.

  A bias voltage is applied to the charging roller 2 from the charging bias 801, and the surface of the photosensitive drum 1 is brought to a predetermined potential by contact with the charging roller 2. In the present embodiment, a bias is applied so that the charged potential is −450V. After the surface of the photosensitive drum 1 passes through the transfer portion, a voltage is applied to the transfer roller 7. At this time, the applied voltage value is controlled by the CPU 510, and constant current control is executed so that a target current value can be obtained during a time corresponding to one rotation of the transfer roller 7.

  6A shows a change in the voltage applied to the transfer roller 7, and FIG. 6B shows a current change corresponding to FIG. 6A.

  In the control according to the present embodiment, 500 V is first applied, and when the current value does not reach the target current, the voltage is increased stepwise by 50 V every 10 msec. At this time, when the current value falls within (target current value ± 0.5) μA, the width for increasing the voltage stepwise or the width for decreasing the voltage stepwise is switched to 20V.

  Therefore, when a coupling failure occurs, the voltage continues to rise because no current flows as shown in FIG. 7B. Therefore, as shown in FIG. 7A, the power supply output value reaches 3 KV which is the maximum value. The target current value is a preset value, and is 8 μA here. The target current value is a current value that causes a memory-like history to remain in the photosensitive layer of the photosensitive drum 1 when a current higher than this is passed, causing image formation failure. The generated voltage and current values are sampled 50 times at 10 msec intervals for 500 msec corresponding to one rotation of the transfer roller 7, and the average voltage value Vavg and average current value Iavg (FIGS. 6 and 7) are obtained. Store in the RAM 512.

  FIG. 8 is a flowchart for explaining a detection process of a coupling failure of the photosensitive drum 1 in the laser beam printer according to the present embodiment. A program for executing this process is stored in the ROM 511, and is controlled under the control of the CPU 510. Executed.

  When this processing is started, the process proceeds to step S1, and as described above, 500 V is first applied to the primary transfer roller 7, and the current value flowing through the photosensitive drum 1 at that time is output from the current detection circuit 503 as A /. Obtained by D conversion. If the obtained current value does not reach the target current value, the voltage is increased stepwise by 50 V every 10 msec. Then, the current value flowing at this time is obtained in the same manner, and the average current Iavg and the average voltage Vavg are calculated as shown in FIGS. 6 and 7, and the average voltage and current value are stored in the RAM 512 (this) (Corresponding to a section indicated by 901 in FIG. 9B). Then, the difference between the target current value (here 8 μA) and the average current value Iavg is obtained. Then, depending on whether the difference is equal to or less than a predetermined amount (here, 2 μA), it is determined whether or not the photosensitive drum 1 has caused a coupling failure, that is, whether or not a coupling failure has occurred. In this case, according to the study by the inventors of the present application, it is known that if the difference between the target current value and the average current value Iavg is within 2 μA, it can be determined that no coupling failure has occurred. The reason will be described below.

  The current that flows from the primary transfer roller 7 to the photosensitive drum 1 is a discharge current. If the photosensitive drum 1 is rotating, a current constantly flows according to the voltage value applied to the transfer roller 7. However, when the rotation of the photosensitive drum 1 is stopped, the discharge current flows only about 2 to 3 μA. Originally, almost no current flows through the dielectric layer of the photosensitive drum 1 steadily as is known from a phenomenon called a transient phenomenon. In this transient phenomenon, the instantaneous charging current changes with time, such as absorption current and leakage current, and the amount of leakage current is almost zero. However, due to the characteristic that the photosensitive layer of the photosensitive drum 1 in electrophotography is a photo-organic semiconductor, the negatively charged photosensitive layer functions to move positive charges. For this reason, a current of about 2 to 3 μA is observed. Therefore, increasing the difference from the target current value increases the possibility of erroneous detection. For this reason, the above set values are used.

  On the other hand, if the difference between the target current value and the average current value Iavg is 2 μA or more in step S1, the process proceeds to step S6, where it is determined that the coupling is abnormal, and an alarm is generated in step S7 to open / close the door. To instruct.

  In step S1, if the difference from the target current value is 2 μA or less, the process proceeds to step S2, and it is determined whether the average voltage value Vavg is 3 KV (maximum pressure value) or more. If it is less than 3.0 KV, it is determined that no coupling failure has occurred, and the process proceeds to step S5.

  On the other hand, if it is 3.0 KV or more, the process proceeds to step S3, and check control is executed. Hereinafter, this check control will be described with reference to FIGS.

As shown in FIGS. 9A and 9B, in this check control, first, as shown by 902, the laser 505 is driven for about 500 msec corresponding to one turn of the primary transfer roller 7. A laser beam is scanned and exposed on the photosensitive drum 1 to lower the potential of the photosensitive drum 1. In this embodiment, the voltage is lowered to about −100V. The potential at this time is referred to as a bright potential. At this time, the voltage held in step S1 (the voltage value applied in 901) is applied to the primary transfer roller 7, and the current value flowing during this time (90 2 ) is averaged. The average current value thus obtained is defined as current B (Bright current value). Next, the driving of the laser 505 is stopped, the laser exposure is turned off, and the current value is detected and averaged for about 500 msec (903) corresponding to one rotation of the primary transfer roller 7 as in the previous time. The average current value at this time is defined as a current D (Dark current value).

  Here, the reason why the current in the bright potential portion is detected first is to increase the detection accuracy. When the current of the light potential portion is detected after the detection of the current of the dark potential portion, the amount of current becomes (dark potential portion)> (light potential portion). Shows the same change as the transient current, and the detection accuracy falls. Therefore, the inventors of the present application set the control to detect the current of the light potential portion first and detect the dark potential portion later.

  Next, in step S4, it is determined whether or not the coupling is performed based on whether or not the current B and the current D obtained previously satisfy the following relational expression (1), that is, whether or not the photosensitive drum 1 is rotating normally. To do.

(Current B−Current D) <0.5 Formula (1)
If the above equation is satisfied, it is determined that the coupling is normal. In principle, the threshold value in this case may be “0”. Actually, however, the measured current has a ripple, and an error of about 0.4 μA occurs after the averaging process. Therefore, such a value (0.5) is set as the threshold value.

  The above control is executed, and 50 times corresponding to a value obtained by multiplying the lifetime of 100 Kp of the laser beam printer by the lifetime of 4 KP of the process cartridge including the photosensitive drum 1 and the safety factor of 2 times, is obtained. The coupling failure was intentionally generated, and it was confirmed whether it could be detected when the power was turned off / on and the door was opened / closed. As a result, all the coupling failures could be detected. When this coupling failure is detected, a message prompting the user to open / close the door is displayed.

  Further, even when the photosensitive drum 1 was reliably coupled, no erroneous detection occurred in 50 tests.

From the above results, it was possible to detect the coupling failure of the photosensitive drum 1 using the detection of the transfer current, and to prevent toner scattering from the developing roller 9 that occurred when the coupling was defective.
[ Reference example ]
Next, a reference example that is a modification of the above-described first embodiment will be described. Note that the configuration of the laser beam printer according to this reference example is the same as that of the first embodiment described above, and a description thereof will be omitted.

FIG. 10 is a flowchart for explaining the process according to the reference example . A program for executing this process is stored in the ROM 511 and is executed under the control of the CPU 510. In FIG. 10, the steps common to those in FIG. 8 are given the same numbers, and the description thereof is omitted.

If it is determined in step S2 that the applied voltage is 3.0 KV or higher, the process proceeds to step S11 and check control is executed. Hereinafter, the check control according to this reference example will be described with reference to FIGS. FIG. 11A is a diagram showing the operation of the laser beam printer. Regarding the rotation of the photosensitive member and the intermediate transfer belt, the operation is stopped when the signal is low and the operation is performed when the signal is high. Indicates that there is. As for the charging roller bias, the value of the bias voltage of the charging roller 2 having a negative signal level is shown, and the upward direction of the vertical axis is the negative direction. The bias applied to the charging roller 2 is 0 V until the predetermined time has elapsed since the photosensitive drum 1 and the intermediate transfer belt 6 started to rotate from the stopped state, and then the bias voltage of −800 used for normal printing is used. Further, the absolute value in the negative direction is set to −400 V, which is lower than the normal bias voltage (−800 V), and subsequently, the absolute value in the negative direction is set to −900 V, which is higher than the normal bias voltage (−800 V).

  As shown in FIG. 11, in this check control, first, the bias voltage of the charging roller 2 is lowered to −400 V for about 500 msec corresponding to one rotation of the primary transfer roller 7, and the charged potential is first transferred after the primary transfer. A low potential is formed at about −200 V, which is substantially equal to the lowered potential (1100). At this time, the voltage held in step S1 (corresponding to a section indicated by 901) is applied to the primary transfer roller 7, and the flowing current value is averaged. This averaging processing method is the same as that in the first embodiment. The average current value in this case is defined as current L.

  Next, the bias voltage of the charging roller 2 is switched to -900V, and the charging potential of the photosensitive drum 1 is switched to the high potential -550V. At this time, the current value is detected and averaged for about 500 msec corresponding to one rotation of the primary transfer roller 7 in the same manner as described above (1101). The current value at this time is defined as current H. Thereafter, the charging bias (−800 V) used for normal printing is switched.

  Next, it progresses to step S12 and it is determined whether the electric current L and the electric current H which were calculated | required satisfy | fill the following relational expression (2).

(Current L−current H) <0.5 (2)
If this equation is satisfied, the photosensitive drum 1 is rotating normally. That is, it is determined that the coupling is normal.

  By carrying out the above control, the laser beam printer life of 100 Kp is divided by the life of the process cartridge including the photosensitive drum 1 4 Kp, and multiplied by a safety factor of 50 times, which is equivalent to 50 times. A coupling failure of the body drum 1 was intentionally generated, and it was confirmed whether it could be detected when the power was turned off / on and the door was opened / closed. As a result, all the coupling failures could be detected. When this coupling failure is detected, a message prompting the user to open / close the door is displayed.

  Further, even when the photosensitive drum 1 was reliably coupled, no erroneous detection occurred in 50 tests.

  From the above results, it was possible to detect the coupling failure of the photosensitive drum 1 using the detection of the transfer current, and to prevent the toner from being scattered from the developing roller 9 when the coupling failure occurred.

(Other examples)
Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) composed of a single device even if it is applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer, etc.). May be.

  Another object of the present invention is to provide a storage medium (or recording medium) in which a program code of software for realizing the functions of the above-described embodiments (processing performed on the camera side and various printing processes performed on the printer side) is recorded. Is also supplied to the apparatus, and the system or the computer (or CPU or MPU) of the apparatus reads and executes the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. This includes a case where part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. The case where the CPU of the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is also included. For example, it goes without saying that this processing is performed by a driver on a PC.

It is a figure explaining the structure of the recording part of the laser beam printer which concerns on embodiment of this invention, and a transfer part. It is a figure explaining the coupling of the photoconductive drum which concerns on this Embodiment. It is a figure explaining the structure of the process cartridge which concerns on this Embodiment. It is a figure explaining the state which measures the resistance value of a conductive roller. FIG. 5 is a block diagram illustrating a main functional configuration for detecting a coupling failure of a photosensitive drum in the laser beam printer according to the present embodiment. It is a figure explaining the change of the applied voltage to the transfer roller which concerns on embodiment of this invention, and the change of the electric current corresponding to it. It is a figure explaining the change of the applied voltage to a transfer roller at the time of coupling failure generation, and the change of the electric current corresponding to it. 6 is a flowchart for explaining detection processing for a coupling failure of a photosensitive drum in the laser beam printer according to the first embodiment. It is a figure explaining the change of the voltage applied to the transfer roller which concerns on Embodiment 1 of this invention, and the change of the electric current corresponding to it. It is a flowchart explaining the detection process of the coupling defect of the photosensitive drum in the laser beam printer of a reference example . It is a figure explaining the change of the applied voltage to the transfer roller which concerns on a reference example , and the change of the electric current corresponding to it.

Claims (4)

A photoconductor that carries a toner image ; a rotation driving unit that is fitted to the photoconductor and transmits a driving force from the apparatus main body to the photoconductor to rotate the photoconductor; and a charging unit that charges the photoconductor An exposure means for exposing the photoconductor, a transfer belt for transferring a toner image on the photoconductor to a transfer material, a transfer roller facing the photoconductor via the transfer belt, and a transfer roller An image forming apparatus comprising: a transfer bias power source for applying a voltage; and a current detection unit for detecting a current flowing through the transfer roller,
After charging the surface of the photoconductor to a predetermined potential by the charging unit, a voltage is applied from the transfer bias power source to the transfer roller so that a current flowing through the transfer roller has a predetermined target current value, An average value of the current values detected by the current detection means during a predetermined period while the voltage is applied from the transfer bias power supply to the transfer roller so as to be the target current value is defined as an average current value, and the target current When the difference between the value and the average current value is larger than a predetermined amount, it is determined that there is an abnormality in the transmission of the driving force to the photosensitive member via the rotation driving unit . A photoconductor that carries a toner image; a rotation driving unit that is fitted to the photoconductor and transmits a driving force from the apparatus main body to the photoconductor to rotate the photoconductor; and a charging unit that charges the photoconductor An exposure means for exposing the photoconductor, a transfer belt for transferring a toner image on the photoconductor to a transfer material, a transfer roller facing the photoconductor via the transfer belt, and a transfer roller An image forming apparatus comprising: a transfer bias power source that applies a voltage; and a current detection unit that detects a current value flowing through the transfer roller,
The average value of the current values detected by the current detection means during a predetermined period while the photosensitive member surface is exposed by the exposure means and the photosensitive member surface is exposed by the exposure means is a first average current value. Then, the exposure of the exposure means is stopped, and the average value of the current values detected by the current detection means during a predetermined period while the surface of the photoconductor is not exposed by the exposure means is set as the second average current value. When the difference between the first average current value and the second average current value is larger than a predetermined amount, it is determined that there is an abnormality in the transmission of the driving force to the photoconductor via the rotation driving unit. An image forming apparatus. When the difference between the target current value and the average current value is a predetermined amount or less and the voltage applied by the transfer bias power supply is the maximum voltage that can be applied by the transfer bias power supply, An average value of current values detected by the current detection means during a predetermined period during exposure by the exposure means and exposure of the photoreceptor surface by the exposure means is set as a first average current value, and then Exposure of the exposure means is stopped, and an average value of the current values detected by the current detection means during a predetermined period during which the surface of the photoconductor is not exposed by the exposure means is defined as a second average current value. When the difference between the average current value and the second average current value is larger than a predetermined amount, it is determined that there is an abnormality in transmission of the driving force to the photoconductor via the rotation driving unit. Item 1 Image forming apparatus.   4. The current detection means detects an average value of a current value flowing between the photosensitive member and the transfer roller, which is detected during one rotation of the transfer roller. The image forming apparatus according to claim 1.

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