JP2014178548A - Image forming unit, process unit, image forming apparatus, and operation method of developing clutch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of abnormal images such as toner drop due to a toner accumulated on a periphery of a developing sleeve, in a simple and reliable way at a low cost without requiring an additional mechanical mechanism.SOLUTION: An image forming unit 1 includes a motor 17 driving a photoreceptor 3 that is connected to a developing sleeve 15 with a clutch 19, and a control unit 18 that controls the motor 17 and the clutch 19. The control unit 18 controls a plurality of times of connection and separation of the clutch 19 before the start of a print job.

Description

  The present invention relates to an image forming unit, a process unit, an image forming apparatus, and a method for operating a developing clutch, in which a developing clutch connecting method is improved to prevent toner dropping.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine of these, as a driving method of a developing sleeve of the image forming apparatus, the developing sleeve is connected to a photosensitive drum (hereinafter simply referred to as a photosensitive member) via a clutch. And a developing motor is connected by connecting the clutch. Hereinafter, the drive motor for the photosensitive member is referred to as an OPC motor (OPC: Organic Photoconductor). Such a designation is for the sake of simplicity, and is not intended to limit the image forming apparatus of the present invention to one having an OPC photoreceptor. The clutch is referred to as “developing clutch” or simply “clutch”.

  The following reason has been pointed out as a reason for driving the developing sleeve via the clutch. That is, in general, it is desirable to drive the photosensitive member and the developing sleeve by separate motors, but this greatly increases the cost. On the other hand, when the photosensitive member and the developing sleeve are always driven synchronously by one OPC motor without a clutch, for example, toner or carrier is transferred from the developing sleeve onto the photosensitive member when the predetermined bias is not applied to the photosensitive member and the developing sleeve. May be exhaled. It has also been pointed out that when the developing sleeve is driven unnecessarily, its travel distance is unnecessarily increased, leading to deterioration of the developer.

  Therefore, as an actual driving method, a method in which the developing sleeve is connected to the OPC motor via the clutch, and the developing clutch is connected only while the OPC motor is being driven and at the time of the print job. It is. In this driving method, the developing clutch is connected to the place where the OPC motor is driven, so that vibration is applied to the developing sleeve due to an impact when the clutch is connected.

  Conventionally, when a toner pool is formed with toner scattered around the developing sleeve, the toner sleeve is pumped up to the photosensitive member by the vibration of the developing sleeve when the developing clutch is connected, and an abnormal image such as toner dropping is generated. There was a problem to become.

  When the toner pool around the developing sleeve becomes depleted, conventionally, there is almost no method other than cleaning the periphery of the developing sleeve or replacing the developing unit. Further, even after the cleaning, once a predetermined number of sheets are passed, the toner drop occurred again.

  Japanese Patent Application Laid-Open No. 2012-118359 describes that an inlet seal is disposed between a photosensitive member and a developing sleeve so as to be able to reciprocate for the purpose of preventing toner dropping. Then, during normal image formation, the entrance seal is kept in contact with the photosensitive member, and the cam is rotated in conjunction with the developing sleeve at an appropriate timing such as at the end of image formation (after completion of the print job). The inlet seal is brought into contact with the developing sleeve from the photosensitive member. As a result, the toner deposited on the inlet seal is pumped up to the developing sleeve and collected in the developing device.

  However, when the photosensitive member is driven at a slow linear speed, such as through thick paper, for example, the method of Patent Document 1 cannot effectively collect the toner reservoir in the developing device. That is, when the photosensitive member is driven at a slow linear speed, the toner reservoir that causes toner drop is surely increased even if the growth speed is reduced.

  When the linear velocity of the photosensitive member is low, the contact speed when the developing clutch is connected and the inlet seal contacts the developing sleeve from the photosensitive member also becomes slow, and the toner accumulated on the inlet seal is effectively pumped to the developing sleeve. I can't. For this reason, there has been a problem that toner drop cannot be sufficiently prevented. In order to reliably prevent the toner drop even at a slow linear speed using the method of Patent Document 1, the rotation of the developing sleeve is once lowered and returned to the full speed (normal linear speed) before the clutch is connected. A device for control is necessary.

  Further, the method of Cited Document 1 requires a separate drive mechanism such as a cam for driving the inlet seal of the developing unit, and has problems such as an increase in the number of parts, a complicated structure, and an increase in cost.

  The object of the present invention is to collect the toner reservoir accumulated around the developing sleeve easily and reliably on the developing device side without an additional mechanical mechanism for swinging the inlet seal, and to perform normal output. The purpose is to prevent toner from dropping in the image.

  In order to solve the above-described problems, the present invention provides a photosensitive member driven by a driving unit, and is connected to the driving unit through a clutch unit, and is driven together with the photosensitive unit by connecting the clutch unit. In an image forming unit comprising a developer carrier for supplying a developer to a body and a control means for controlling operation of the drive means and connection / separation of the clutch means, the control means activates the drive means The image forming unit is characterized in that the clutch means is set to repeat connection / separation a plurality of times before the start of a print job.

  The present invention also relates to a method for operating a developing clutch in which driving means for driving a photosensitive member is detachably connected to a developer carrying member, and the print job after the driving of the photosensitive member by the driving means is started. The developing clutch operating method is characterized in that the clutch means is repeatedly connected and disconnected a plurality of times before starting.

  According to the present invention, it is possible to give an impact to the toner pool collected around the image carrier by repeating connection / separation of the clutch means for driving the image carrier a plurality of times before the start of the print job. Due to this impact, the toner reservoir is discharged in advance to the photosensitive member side, collected in the developer container, or recharged by rotating on the developing sleeve to cause toner drop in a normal output image. It can be prevented from being generated. Since the present invention does not require addition of a mechanical mechanism only by controlling the clutch means, it can be implemented at a low cost.

  The conditions for toner drop are that a certain amount or more of toner is accumulated around the developing sleeve and that the developing clutch is connected after the toner is accumulated. In general, when an image is passed, toner accumulates around the developing sleeve, and when the clutch is connected, toner accumulated by the impact is discharged and reduced.

  A method is also conceivable in which the toner is discharged and reduced by controlling the developing sleeve to rotate forward or reverse for a predetermined time or repeat forward or reverse for a predetermined time before or after image formation. However, when these operations are performed, it takes a long time to start up and shut down the image formation, and the downtime increases. On the other hand, in the present invention, since the connection time per one time of the developing clutch can be shortened to about 50 msec, for example, even if the clutch is connected / separated a plurality of times continuously, the toner can be obtained in a short time. Drop can be eliminated.

  The present invention calculates the condition for toner drop, that is, the amount of toner accumulated from the usage of the image forming unit or the development unit, and determines whether the development clutch is connected or separated before the toner runs out. It is also possible to prevent the occurrence of toner drop by repeating a plurality of times corresponding to the number of times.

1 is a schematic diagram illustrating an overall configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram illustrating a configuration example of a yellow image forming unit in FIG. 1. It is a figure which shows the operation | movement timing chart of a developing clutch. It is a figure which shows the clutch connection frequency | count of the developing sleeve of less than the total number of printed sheets 50k. It is a figure which shows the clutch connection frequency | count of the developing sleeve of 50k or more of total printed sheets. It is a figure which shows the frequency | count of idling of the developing sleeve of less than the total number of printed sheets 50k. It is a figure which shows the frequency | count of idling of the developing sleeve of 50k or more of total printed sheets. It is a figure which shows clutch connection control of a developing sleeve. FIG. 6 is a diagram illustrating a relationship between the number of clutch engagements of a developing sleeve and the occurrence rate of toner drop.

  Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration of an embodiment of an electrophotographic image forming apparatus according to the present invention, and FIG. 2 is a schematic configuration diagram showing a configuration example of a yellow image forming unit 1Y in the image forming unit. The image forming apparatus of FIG. 1 is a tandem type intermediate transfer type color printer that forms a full-color image. This printer has four image forming units 1Y, 1C, 1M, and 1K for forming yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) toner images. These four image forming units 1Y, 1C, 1M, and 1K are arranged at predetermined intervals along the longitudinal direction on the lower surface side of the transfer unit 40. Each of these image forming units 1Y, 1C, 1M, and 1K uses Y toner, C toner, M toner, and K toner of different colors as image forming materials for forming an image, but the other configurations are the same. Yes.

  Therefore, the configuration of the image forming unit 1Y for generating a Y toner image will be briefly described with reference to FIG. As shown in FIG. 2, the image forming unit 1Y includes a photosensitive unit 2Y having a drum-shaped photosensitive member 3Y as a latent image carrier, and a developing unit 7Y that is a developing device for developing a latent image on the photosensitive member 3Y. And have.

  The photoreceptor unit 2Y and the developing unit 7Y are integrally configured as an image forming unit 1Y, and are detachable from the image forming apparatus main body. That is, the image forming unit 1Y can be configured as a process unit that can be attached to and detached from the image forming apparatus main body. In a state where it is detached from the image forming apparatus main body, the developing unit 7Y can be attached to and detached from the photoreceptor unit 2Y. Details of the photosensitive unit 2Y and the developing unit 7Y will be described later.

  In FIG. 1, an optical writing unit 20 as image writing means is disposed below the image forming units 1Y, 1C, 1M, and 1K. The optical writing unit 20 irradiates the uniformly charged surfaces of the photoreceptors 3Y, 3C, 3M, and 3K of the image forming units 1Y, 1C, 1M, and 1K based on the image information. Thereby, electrostatic latent images corresponding to the image information of Y, C, M, and K are formed on the surfaces of the photoreceptors 3Y, 3C, 3M, and 3K.

  The optical writing unit 20 deflects and scans the laser light L emitted from the laser light source by the polygon mirror 21 that is rotationally driven by a motor, and the photoreceptors 3Y, 3C, and 3M through a plurality of optical lenses and mirrors. , 3K. Instead of such a configuration, an optical writing unit that performs optical scanning with an LED array may be employed.

  Below the optical writing unit 20, a first paper feed cassette 31 and a second paper feed cassette 32 for supplying a recording paper P as a recording medium are disposed so as to overlap in the vertical direction. Each of these paper feed cassettes stores a plurality of recording papers P in a stack of recording papers. The uppermost recording paper P includes a first paper feeding roller 31a and a second paper feeding roller 31a. The paper feed rollers 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is sent out to the right, Paper is fed toward a paper feed path 33 extending in the vertical direction.

  When the second paper feed roller 32 a is driven to rotate counterclockwise by a driving unit (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Paper is fed. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P sent to the paper feed path 33 is fed between the rollers of the transport roller pairs 34 while being fed. It is conveyed in the path 33 from the lower side to the upper side in FIG.

  A timing roller pair 35 is disposed at the end of the paper feed path 33. The timing roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P transported by the transport roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out to a secondary transfer nip described later at an appropriate timing.

  A transfer unit 40 is disposed above each of the image forming units 1Y, 1C, 1M, and 1K. The transfer unit 40 stretches the intermediate transfer belt 41, which is an intermediate transfer member, by a driving roller 47, a secondary transfer backup roller 46, an auxiliary roller 48, and a tension roller 49, and rotates it counterclockwise.

  The transfer unit 40 further includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. The first bracket 43 includes three primary transfer rollers 45Y, 45C, and 45M, and the second bracket 44 includes a primary transfer roller 45K.

  The primary transfer rollers 45Y, 45C, 45M, and 45K sandwich the intermediate transfer belt 41 that moves around the photosensitive members 3Y, 3C, 3M, and 3K to form primary transfer nips. Then, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41.

  As the intermediate transfer belt 41 moves, the intermediate transfer belt 41 sequentially passes through the primary transfer nips for the colors Y, C, M, and K. In this process, primary transfer is performed so that the Y toner images, C toner images, M toner images, and K toner images on the photoreceptors 3Y, 3C, 3M, and 3K are superimposed on the front surface. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 41. When performing monochrome printing, the first bracket 43 is moved backward to separate the primary transfer rollers 45Y, 45C, 45M from the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. Then, the recording paper P sandwiched between the rollers by the timing roller pair 35 is sent out toward the secondary transfer nip at a timing synchronized with the formation of the four-color toner image on the intermediate transfer belt 41.

  The four-color toner image on the intermediate transfer belt 41 is subjected to a secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, or a nip pressure. Secondary transfer is performed collectively on the recording paper P in the next transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  The residual transfer toner remaining on the intermediate transfer belt 41 without being transferred to the recording paper P even after passing through the secondary transfer nip is cleaned by the belt cleaning unit 42. The belt cleaning unit 42 brings the cleaning blade 42a into contact with the front surface of the intermediate transfer belt 41 and scrapes off and removes the transfer residual toner on the belt.

  A fixing unit 60 as fixing means for fixing the toner image on the recording paper P is disposed above the secondary transfer nip in the drawing. The fixing unit 60 includes a pressure heating roller 61 incorporating a heat source such as a halogen heater, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64, a heating roller 63 incorporating a heat source 63a such as a halogen heater, a tension roller 65, a driving roller 66, and the like.

  Then, the fixing belt 64 is stretched by the heating roller 63, the tension roller 65, and the driving roller 66, and is rotated in the counterclockwise direction in the drawing. In the course of this movement, the fixing belt 64 is heated from the back side by the heating roller 63.

  A pressure heating roller 61 that is driven to rotate in the clockwise direction in the drawing is in contact with the surface of the fixing belt 64 that has been heated in this manner. As a result, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  A temperature sensor (not shown) is disposed outside the loop of the fixing belt 64 so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt immediately before entering the fixing nip. 64 surface temperature is detected. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source 63a in the heating roller 63 and the heat generation source (not shown) in the pressure heating roller 61 based on the detection result by the temperature sensor. Thereby, the surface temperature of the fixing belt 64 is maintained at about 140 ° C., for example.

  The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then fed into the fixing unit 60. A full color toner image is heated and pressed by the fixing belt 64 and the pressure heating roller 61 in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched by the fixing nip in the fixing unit 60. Is fixed to the recording paper P.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the image forming apparatus main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Note that four toner cartridges 100Y, 100C, 100M, and 100K containing Y toner, C toner, M toner, and K toner are disposed above the transfer unit 40 in the image forming apparatus main body. The toner of each color in the toner cartridges 100Y, 100C, 100M, and 100K is appropriately supplied to the developing units 7Y, 7C, 7M, and 7K of the image forming units 1Y, 1C, 1M, and 1K, respectively. These toner cartridges 100Y, 100C, 100M, and 100K are detachable from the image forming apparatus main body independently of the image forming units 1Y, 1C, 1M, and 1K.

(Image forming unit)
The image forming units 1Y, 1C, 1M, and 1K have the same structure except for the color of the toner used. The details of the structure will be described with reference to FIG. 2 by taking the image forming unit 1Y as an example. As shown in FIG. 2, the image forming unit 1Y includes a photoconductor unit 2Y and a developing unit 7Y.

  The photoreceptor unit 2Y includes a photoreceptor 3Y, a drum cleaning device 4Y, a static eliminator (not shown), and a charging device 5Y that charges the surface of the photoreceptor 3Y. The photoreceptor 3Y is rotationally driven in the clockwise direction in the drawing by an OPC motor 17 as a driving means (not shown). The OPC motor 17 is controlled by a control unit 18 as control means. The photoconductor 3Y can use amorphous metal having photoconductivity, amorphous metal such as amorphous selenium, or organic compound such as bisazo pigment and phthalocyanine pigment. In consideration of environmental problems and post-treatment after use, an OPC photoreceptor using an organic compound is preferable.

  The charging device 5Y includes a charging roller 6Y to which a charging bias is applied close to the surface of the photoconductor 3Y, and the surface of the photoconductor 3Y is made uniform by rotating the charging roller 6Y counterclockwise. Charge. In addition, as the charging device, a device in which a charging brush is brought into contact with the photosensitive member instead of the charging roller may be used. Alternatively, a charger that charges the photosensitive member by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by the laser light L emitted from the optical writing unit 20 to carry an electrostatic latent image for Y.

  The developing unit 7Y includes a first developer accommodating portion 9Y in which a first conveying screw 8Y is disposed, and a second developer accommodating portion 14Y in which a second conveying screw 11Y is disposed. In the second developer container 14Y, a toner concentration sensor 10Y including a magnetic permeability sensor, a developer carrier 12Y, a doctor blade 13Y as a developer regulating member, and the like are disposed. In these first and second developer accommodating portions 9Y and 14Y, a Y developer (not shown) having a magnetic carrier and negatively chargeable Y toner is accommodated.

  The first conveying screw 8Y is rotationally driven by a driving unit (not shown), and conveys the Y developer in the first developer accommodating portion 9Y from the near side to the far side in the direction perpendicular to the paper surface. Then, Y developer enters the second developer accommodating portion 14Y through a communication port (not shown) provided in the partition wall between the first developer accommodating portion 9Y and the second developer accommodating portion 14Y. Let

  The second conveying screw 11Y in the second developer accommodating portion 14Y is rotationally driven to convey the Y developer from the back side to the near side in the drawing. The toner density of the Y developer being conveyed is detected by the toner density sensor 10Y fixed to the bottom of the second developer container 14Y.

  Above the second conveying screw 11Y, a developer carrier 12Y is disposed in parallel with the second conveying screw 11Y. The developer carrier 12Y is connected to a rotating shaft of the OPC motor 17 via a developing clutch 19 as a clutch means so as to be able to contact and separate. The connecting / separating of the developing clutch 19 is controlled by the control unit 18. The contents of the control will be described later. The developer carrier 12Y includes a magnet roller 16Y built in a developing sleeve 15Y made of a non-magnetic pipe.

  Part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force of the magnet roller 16Y. Then, after the layer thickness is regulated by the doctor blade 13Y disposed so as to maintain a predetermined gap from the developing sleeve 15Y, the layer thickness is regulated and conveyed to the developing area facing the photosensitive member 3Y, and the Y for the photosensitive member 3Y is used. Y toner is adhered to the electrostatic latent image. This adhesion forms a Y toner image on the photoreceptor 3Y.

  The Y developer that has consumed Y toner by the development is returned onto the second conveying screw 11Y as the developing sleeve 15Y rotates. Then, when the paper is transported to the front end in the figure, it returns to the first developer accommodating portion 9Y through a communication port not shown.

  The result of detecting the magnetic permeability of the Y developer by the toner concentration sensor 10Y is sent to the control unit 18 as a voltage signal. Since the magnetic permeability of the Y developer shows a correlation with the Y toner density of the Y developer, the toner density sensor 10Y outputs a voltage having a value corresponding to the Y toner density.

The control unit 18 includes a memory such as a RAM as storage means. In this memory, Y V _tref which is a target value of the output voltage from the toner density sensor 10Y, and C V _tref which is a target value of the output voltage from each toner density sensor mounted in another developing unit, M use V _tref, that contains the V _tref of data for K.

For the Y developing unit 7Y, the value of the output voltage from the toner density sensor 10Y is compared with the Y V _tref , and the Y toner supply device described later is driven for a time corresponding to the comparison result. Due to this driving, an appropriate amount of Y toner is supplied to the Y developer whose Y toner density has been reduced in the first developer accommodating portion 9Y. Accordingly, the Y toner density in the second developer accommodating portion 14Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the image forming units (1C, 1M, 1K) for other colors.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to the intermediate transfer belt 41. The drum cleaning device 4Y removes the toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. The surface of the photoreceptor 3Y subjected to the cleaning process is neutralized by a neutralization device (not shown). By the charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation.

  In the image forming units 1C, 1M, and 1K for other colors in FIG. 1, C toner images, M toner images, and K toner images are similarly formed on the photoreceptors 3C, 3M, and 3K, and the intermediate transfer belt 41 is formed. Intermediate transfer. Further, the image forming unit 1Y is provided with a temperature sensor (not shown) which is a sensor unit of the temperature detecting means. The temperature sensor is installed at a position in the developing unit 7Y or in the vicinity of the developing unit 7Y in the image forming apparatus body, that is, at a position where the detected temperature has a high correlation with the temperature in the developing unit 7Y.

  The temperature sensor detects the temperature inside or around the developing device that changes corresponding to the temperature of the developing sleeve 15Y. Similarly, temperature sensors are installed in the developing units of the image forming units 1C, 1M, and 1K for other colors. However, it is not essential to provide temperature sensors in all the developing devices, and one or more temperature sensors may be provided at appropriate positions for detecting the temperature in the main body of the image forming apparatus.

  The configuration of the image forming unit 1Y described above is common to the other image forming units 1C, 1M, and 1K. Therefore, in the following description, the reference numerals of the components constituting the image forming units 1Y, 1C, 1M, and 1K are shown in FIG. 2 except for the photoreceptors 3Y, 3C, 3M, and 3K also shown in FIG. In addition, only a numeral code in which “Y” is deleted from the codes of the respective parts is used.

(Development clutch control)
FIG. 3 shows a clutch operation timing chart of the developing sleeve 15 according to the embodiment of the present invention in a clutch operation timing chart. When a print command is received from the control unit 18, the OPC motor 17 starts to be driven. Thereafter, although not shown, a bias is applied to the photosensitive member 3 and the developing sleeve 15, the developing clutch 19 is connected, and the developing sleeve 15 is driven. When the image output is completed, the development is normally stopped, and then the OPC motor 17 is also stopped.

  In the embodiment of the present invention, at the start of image formation, the connection and separation of the clutch 19 are continuously repeated a plurality of times, and the developing sleeve 15 is driven in small increments. By continuously connecting and separating the clutch 19 when the photosensitive member 3 is driven at a target speed, it is possible to give an impact to the developing sleeve 15 in the same manner as in normal printing.

  In FIG. 3, as an example, the clutch 19 is connected / separated (ON / OFF) five times before printing of an image portion, which is a print job, is started. The number of times that the clutch 19 is continuously connected / separated can be changed depending on how the image forming apparatus or the developing unit 7 is used, such as an image area ratio (%). Since the purpose is to apply the connection impact of the clutch 19 to the developing sleeve 15, the connection time for one time may be any time. Short times can minimize downtime.

  In this embodiment, the connection time per time is 100 msec, and the separation time is also 100 msec. This time of 100 msec is the time required for the developing sleeve 15 to reach the target linear speed after the clutch 19 is connected in the image forming apparatus according to the present invention. In this case, even if the connection and separation are repeated five times, the result is only within one second, so there is almost no influence of downtime.

  Further, the developing sleeve 15 is continuously driven (idly rotated) for a predetermined time after the fifth clutch 19 is connected. The purpose of the continuous driving operation for a certain period of time is to process the toner pumped up on the developing sleeve 15 by the impact of the clutch connection so that the toner does not fall out. That is, the toner pumped up on the developing sleeve 15 is discharged to the photosensitive member 3 side, collected in the second developer container 14, or recharged by rotating on the developing sleeve 15. Prevents toner deficiency. For this reason, it is desirable to drive the developing sleeve 15 continuously for at least one round. However, the idling is not necessarily executed every time after the connection and separation of the developing clutch 19 are repeated. Depending on the number of repetitions of connection / separation and the use state of the developing unit 7, it is possible to effectively eliminate the toner drop only by repeatedly connecting / separating the clutch 19 without idling the developing sleeve 15. .

(Conditions for clutch connection / separation times)
Next, FIG. 4 and FIG. 5 show the conditions for changing the number of times the clutch 19 is continuously connected / separated according to the image area ratio (%) and the number of continuously passing sheets in the embodiment of the present invention. The reason why the clutch connection / separation frequency is changed depending on how the image forming apparatus or the developing unit 7 is used is as follows.

  The toner drop that is a problem to be avoided by the present invention is caused by the presence of a weakly charged toner that causes toner drop around the developing sleeve 15 or a toner pool of reversely charged toner. Examples of the location of the toner reservoir include the upper portion of the second developer accommodating portion 14Y in FIG. 2 and the vicinity of the doctor blade 13Y around the developing sleeve 15.

  When the toner reservoir is sufficiently grown and the developing clutch 19 is connected when the OPC motor 17 is rotating at the target speed, a connection impact occurs, and this impact acts on the toner reservoir. Then, the weakly charged toner and the reversely charged toner that have accumulated in the vicinity of the developing sleeve 15 are pumped onto the developing sleeve 15 without toner dropping. Therefore, if the growth rate of the toner reservoir and the discharge speed (amount) are known, the appropriate number of times of connection of the developing clutch 19 can be obtained, and the downtime can be minimized.

  4 and 5 show the number of engagements of the clutch 19 in a table, and the control value is changed in accordance with the number of continuous sheets passing through the developing unit 7 as an object. As a precondition, in a high temperature / humidity environment, the toner charge amount is low, and the toner pool tends to grow. As an example, a log of usage conditions at a temperature of 23 degrees and a humidity of 50% or more is stored in the image forming apparatus main body. It is good to record it.

  At this time, the number of clutch engagement / separation times in the job is determined in correspondence with the image area ratio (%) for each print job and the number of continuous sheets. The higher the image area ratio (%), the larger the amount of toner replenished, and the weakly charged toner in the developing unit 7 increases. In the opposite case, the weakly charged toner in the developing unit 7 decreases. On the other hand, the smaller the number of continuous sheets to be passed, the more frequently the start-up operation is performed, and the number of connection times of the developing clutch 19 is increased accordingly, and the amount of toner discharged is also increased. In the opposite case, the amount of toner discharged is reduced.

  Further, it is known that the growth rate of the toner reservoir is remarkably increased by developer deterioration. Therefore, in the embodiment of the present invention, the number of clutch engagements is controlled so that the total number of printed sheets is 50k. More precisely, the developer deterioration progresses with an increase in the actual travel distance of the developing unit, which varies depending on the paper size, not the total number of printed sheets. Therefore, the total number of printed sheets 50k may be replaced with the cumulative running distance of the developing unit (for example, 17 km in standard use).

  The total number of printed sheets 50k may be changed to the total average image area ratio of the image forming apparatus. The total number of printed sheets 50k may be changed to the total environmental conditions such as the temperature and humidity of the image forming apparatus. Further, the number of repetitions of connection / separation of the clutch 19 and the number of idle rotations after the connection / separation of the clutch 19 a plurality of times may be set corresponding to each color of the plurality of developing units 7. As described above, in the embodiment of the present invention, when a high image is continuously output over time, the clutch 19 is continuously connected up to 15 times after the print job.

  6 and 7 show how much idling operation is performed after the clutch 19 is continuously connected and separated. Each number in the table indicates the number of rotations of how many rotations the developing sleeve 15 is idling (idling). Normally, the toner that has fallen off the toner pumped up to the developing sleeve 15 is pumped up to the photoreceptor 3 side or collected in the second developer container 14Y by rotating the developing sleeve 15 by one turn. be able to. However, depending on the degree and size of the toner pool, the rotation of the developing sleeve 15 cannot rotate the aggregate that causes the toner to fall, and the developing sleeve 15 must be rotated more than one turn. The toner drop may not disappear completely.

  For this reason, the control value is changed in accordance with the total number of printed sheets (less than 50k sheets or 50k sheets or more), the image area ratio (%), and the continuous sheet passing number, respectively. The reason why the control value is changed in this way and the reason why the control value is changed at the boundary of the total number of printed sheets of 50k are the same as those explained for the reason why the control value is changed as shown in FIGS.

  During the idling operation of the developing sleeve 15, it is preferable to apply a charging bias to the photosensitive member. That is, if the same bias voltage is applied to the photosensitive member as when printing with the charger during the idling operation of the developing sleeve 15, the development of the photosensitive member can be prevented, and wasteful toner consumption can be suppressed.

  Further, the rotation speed of the developing sleeve 15 in the idling operation may be higher than the rotation speed of the developing sleeve during printing.

  Finally, the linear velocity of the photosensitive member 3 when the connection and separation of the clutch 19 are repeated a plurality of times will be described with reference to FIG. In FIG. 3, the linear velocity of the photosensitive member 3 when the connection and separation of the clutch 19 are repeated a plurality of times is the same as the linear velocity during the normal printing operation. On the other hand, in FIG. 8, the linear velocity of the photosensitive member 3 when the connection and separation of the clutch 19 are repeated a plurality of times is set to a higher linear velocity than the linear velocity during the normal printing operation.

  Assuming that the speed (linear speed) during normal printing is A, the image is started up at a speed (linear speed) B (A <B) that is faster than the speed A before image formation. After the clutch 19 is continuously connected and separated, the developing sleeve 15 is rotated idly by one turn. After that, after various motors are stopped, the motor is normally started at the normal linear speed A. By increasing the speed B, it is possible to increase the impact at the time of clutch engagement, and it is possible to increase the effect of toner loss disappearance. In addition, by increasing the speed B, it is possible to shorten the time until the start of the print job by reducing the number of times the clutch 19 is connected / separated and reducing the idling speed of the developing sleeve 15. . That is, it is possible to set the number of times the clutch 19 is connected / separated repeatedly and the idling speed of the developing sleeve 15 according to the linear velocity of the photosensitive member 3.

  FIG. 9 shows the effect of toner drop reduction by the clutch connection according to the present invention. After 500 sheets of an image area ratio of 20% have been continuously passed, the OPC motor 17 is driven at the linear speed at the time of image formation, and in this state, the connection and separation of the developing clutch 19 are repeated 5 times at 100 msec each (1 second in total) . Thereafter, 10 images having a low image area with an image area ratio lower than 20% are printed again. This is a summary of the toner drop occurrence rate (%) (average value of 10 times) when the above operation is repeated 10 times. Even when the clutch connection / separation time (each 100 msec) and the number of repetitions (5 times) were increased or decreased, the same results as in FIG. 9 were obtained.

  “One time” in the table means that the developing clutch is connected by a normal start-up operation. The “one-time” polygonal line indicates that an image with an image area ratio of 20% is continuously passed through 500 sheets, the OPC motor 17 is stopped once, and an image with an image area ratio lower than 20% is again displayed. This represents the toner drop occurrence rate (%) (average value of 10 times) when printing 10 sheets is repeated 10 times.

  From FIG. 9, it can be seen that from the point where the total number of printed sheets exceeds 60k, toner drop starts to occur in the conventional normal startup operation, and the generation rate increases as the total number of printed sheets increases. On the other hand, when the number of clutch engagements is increased from one to two, toner drop starts to occur when the total number of printed sheets exceeds 80k. However, it can be seen that the occurrence rate is half of the occurrence rate of the normal start-up operation at any time point of the number of printed sheets 100k, 150k, and 200k.

  As mentioned above, although embodiment of this invention was described, this invention can be variously deformed without being limited to the said embodiment. For example, the image forming apparatus exemplifies a tandem type intermediate transfer type color printer. However, the present invention is not limited to the tandem type, and various types of copiers, printers, facsimiles, or a combination of these electrophotographic type images. It can be applied to a forming apparatus. As the developer used in these image forming apparatuses, either a two-component developer composed of a carrier and a toner or a one-component developer (magnetic toner, non-magnetic toner) that does not use a carrier can be used. .

1Y, 1C, 1M, 1K: image forming units 2Y, 2C, 2M, 2K: photoconductor units 3Y, 3C, 3M, 3K: photoconductor 4Y: drum cleaning device 5Y: charging device 6Y: charging rollers 7Y, 7C, 7M , 7K: Development unit 8Y: Conveying screw 9Y: First developer accommodating portion 10Y: Toner density sensor 11Y: Conveying screw 12Y: Developer carrier 13Y: Doctor blade 14Y: Second developer accommodating portion 15Y: Developing sleeve 16Y: Magnet roller 17: Motor 18: Control unit 19: Development clutch 20: Optical writing unit 21: Polygon mirror 31: Paper feed cassette 31a: Paper feed roller 32: Paper feed cassette 32a: Paper feed roller 33: Paper feed path 34: Conveying roller pair 35: Timing roller pair 40: Transfer unit 41: Intermediate transfer belt 42: Belt Cleaning unit 42a: Cleaning blade 43: Bracket 44: Bracket 45K: Primary transfer roller 45Y, 45C, 45M, 45K: Primary transfer roller 46: Secondary transfer backup roller 47: Drive roller 48: Auxiliary roller 49: Tension roller 50: Secondary transfer roller 60: fixing unit 61: pressure heating roller 62: fixing belt unit 63: heating roller 63a: heat source 64: fixing belt 65: tension roller 66: driving roller 67: paper discharge roller pair 68: stack unit 100Y , 100C, 100M, 100K: toner cartridge L: laser beam P: recording paper

JP 2012-118359 A

Claims (17)

  A photosensitive member driven by a driving unit, and a developer carrier connected to the driving unit via a clutch unit, and driven with the photosensitive unit by connecting the clutch unit to supply the developer to the photosensitive unit And an image forming unit that controls the operation of the driving unit and the connection / separation of the clutch unit before the print job starts after the driving unit operates the clutch. An image forming unit characterized in that the means is set to repeat connection / separation a plurality of times.   The control means is set such that after the connection / separation of the clutch means is repeated a plurality of times, the developer carrier is continuously idled for at least one round before the start of a print job. The image forming unit according to claim 1.   The number of repetitions of connection / separation of the clutch unit or the number of idle rotations after the connection / separation of the clutch unit a plurality of times is set corresponding to the number of continuous sheets of the previous print job. The image forming unit according to claim 2.   The number of repetitions of connection / separation of the clutch unit or the number of idle rotations after the connection / separation of the clutch unit a plurality of times is set corresponding to the image area ratio of the immediately preceding print job. The image forming unit according to claim 2.   The control means is set so that the linear speed of the photosensitive member is higher than the linear speed during normal printing when the clutch means is connected / separated a plurality of times. One image forming unit.   The number of repetitions of connection / separation of the clutch unit, or the number of idling speeds after the clutch unit is connected / separated a plurality of times is set in accordance with a linear velocity of the photoconductor. 2 image forming units.   The number of repetitions of connection / separation of the clutch unit or the number of idling speeds after the clutch unit is connected / separated a plurality of times is set corresponding to the cumulative travel distance of the image forming unit. 2 image forming units.   The number of repetitions of connection / separation of the clutch unit, or the number of idle rotations after the clutch unit is connected / separated a plurality of times is set corresponding to the total average image area ratio of the image forming unit. The image forming unit according to claim 2.   2. The image forming unit according to claim 1, wherein the control unit is set so that the connection / separation of the clutch unit is repeated within one second.   The number of repetitions of connection / separation of the clutch means, or the number of idle rotations after the connection / separation of the clutch means a plurality of times is set according to the total environmental conditions such as the temperature and humidity of the image forming unit. The image forming unit according to claim 2.   2. The image forming unit according to claim 1, comprising a plurality of color developing units for forming a full-color image, and the number of repetitions of connection / separation of the clutch means or the number of idling speeds after the connection / separation of the clutch means multiple times The image forming unit according to claim 2, wherein the image forming unit is set corresponding to each color.   A process unit comprising the image forming unit according to claim 1, wherein the process unit is detachable from a main body of the image forming apparatus.   An image forming apparatus comprising the image forming unit according to claim 1 or the process unit according to claim 12.   A developing clutch operating method in which driving means for driving a photosensitive member is detachably connected to a developer carrying member, wherein the clutch before the start of a print job after driving of the photosensitive member by the driving means is started. A developing clutch operating method characterized in that connection / separation of the means is repeated a plurality of times.   13. The developing clutch operating method according to claim 12, wherein after the connection / separation of the clutch means is repeated a plurality of times, the developer carrying member is continuously idled for at least one round before the start of a print job.   14. The number of repetitions of connection / separation of the clutch unit or the number of idle rotations after the connection / separation of the clutch unit a plurality of times is made to correspond to the number of continuous sheets of the previous print job. How to operate the development clutch.   14. The development according to claim 13, wherein the number of repetitions of connection / separation of the clutch means or the number of idle rotations after the connection / separation of the clutch means is made to correspond to the image area ratio of the immediately preceding print job. How to operate the clutch.