JP2013057926A - Development device, process cartridge and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of an agitating roller which improves agitation force by rotating an agitation fin and minimizes stress on developer by stopping the agitation fin, according to a printing state.SOLUTION: The two-component development device includes, in a device housing, a developer circulation and conveyance passage extending parallel to a longitudinal direction of a developing roller to be arranged so as to face a latent image carrier. Along the developer circulation and conveyance passage, there are provided a developer conveyance screw for conveying developer in the longitudinal direction, and a developer agitation fin for agitating the developer in a direction orthogonal to the longitudinal direction, so that their rotation axes are on the same straight line, but arranged individually. Rotation/stop of the developer conveyance screw and the developer agitation fin can be switched independently to each other.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developing device using a two-component developer, a process cartridge provided with the developing device, and an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having both functions. is there.

  In an electrophotographic copying machine or printer, a developing device attaches toner to an electrostatic latent image written using a laser beam on a photosensitive member, which is a latent image carrier, and visualizes the image. In the case of the dry two-component development system, a developer that is frictionally charged by mixing toner (colored resin powder) and carrier (magnetic material) is used. The developer is pumped up magnetically onto the surface of the developing roller charged with a magnet, and forms a magnetic spike on the developing roller. A developing bias is applied to the developing nip portion where the developing roller and the photosensitive member are close to each other, and the toner on the magnetic brush is electrostatically attracted to the photosensitive member, and the toner adheres on the photosensitive member. The developer that has consumed the toner is conveyed to a range of a toner replenishing port that communicates with the outside and is replenished with toner. Then, the developer is again conveyed to the range of a developing roller and pumped up.

  In order to circulate the developer between the developing roller and the toner replenishing port in this manner, a developer circulation conveyance path is provided, and the developer is stirred and conveyed by stirring with a spiral conveyance screw in the conveyance path. A developing device having a configuration of performing is generally known.

  When an image forming apparatus equipped with such a developing device is used for continuous printing for a long time, the temperature of the developing device rises due to heat generated by the drive unit, and the developer melts in the conveyance path. It was. For the temperature rise during continuous printing, a configuration in which air cooling is performed using a cooling fan or a duct is generally known. However, in recent years, there is a strong demand for energy saving of OA equipment, and the heater consumption of the fixing unit is high. In order to reduce power consumption, development of toner that can be fixed on transfer paper at low temperatures is progressing, the amount of heat generated in the drive section increases with the trend of increasing the printing speed from the past, and the developer can be developed by using low-temperature fixing toner. Since it has become easy to melt even at low temperatures, conventional air cooling with cooling fans and ducts has become insufficient. Furthermore, when left in a room where air conditioning is not effective in summer or a room where direct sunlight enters, the temperature rises similarly, and the developer melts in the developing device.

  When the developer melts, aggregates (so-called lumps) are formed, which adhere to the transfer paper, thereby forming speckled or meteor-like abnormal images. Further, when the aggregate is clogged in the gap between the developing roller and the doctor blade (the blade that regulates the amount of developer drawn up to the developing roller), a white streak-like abnormal image is formed. In the worst case, the developer is solidified, clogging the circulation conveyance path, and destroying the conveyance screw.

  The following problems are also recognized. The developer in the developing device is agitated by a conveying screw during printing, and has a low bulk density (bubbles enter the developer and are fluffy). On the other hand, when printing is started with a developing device that has been stopped for a long time, the bulk density of the developer has temporarily increased immediately after the start (the air bubbles between the developers have escaped and clogged tightly) ). As described above, there is a problem that the image density is not stable because the volume of the developer varies and the amount of the developer drawn up to the developing roller changes.

  In general, a T sensor that measures the toner concentration of the developer by the magnetic permeability of the carrier is mounted, and the detected value is fed back to the toner replenishing device to keep the toner concentration of the developer constant. In the configuration in which such a T sensor is mounted, a change in the bulk density of the developer leads to a detection deviation of the toner density. When the bulk density rises after stopping for a long time, the T sensor detects the toner density of the developer with a low deviation (for T sensor, the state where the bulk density is high is the same as the state where the toner density is lowered). ), There is a problem that toner is excessively replenished. Excess toner replenishment leads to abnormalities such as fluctuations in image density, background contamination, and toner scattering.

  There is yet another problem. That is, when a new toner is replenished from the toner replenishment port in a state where the toner density of the developer in the developing device is high, the replenished toner is conveyed while being floated on the developer, and enters the developer. It is a problem that it is difficult to mix. Such replenished toner is insufficiently charged, and when pumped up to the developing roller, abnormalities such as local fluctuations in image density, background contamination, and toner scattering occur.

  In order to deal with these problems, a screw blade (conveying screw) forming a spiral around the rotation shaft is formed directly below the toner supply port, and stirring is performed radially extending with respect to the rotation shaft. Patent Document 1 discloses a configuration in which a stirring roller provided with blade (stirring fin) formation regions alternately in the axial direction is provided. While the spirally arranged conveying screw has a conveying force, it has the disadvantage that the stirring force is small, so the stirring force of the developer can be improved by adding stirring fins that extend radially. ing. In other words, break up aggregates, prevent solidification of the developer, bring the developer to a steady state with a low bulk density immediately after standing for a long time, or mix replenishment toner into the developer. A certain effect can be expected.

  However, since the stirring fins extending radially apply a force in a direction perpendicular to the transport direction of the developer, there is a side effect that stress on the developer is strong. Specifically, toner external additives in the developer (fine particles such as silica applied to the toner surface to improve fluidity and chargeability) are buried or released, and the coat layer on the carrier surface is damaged. To do. Then, abnormalities such as background contamination due to a decrease in the charge amount of the developer, toner scattering, and a blurred image due to deterioration in transferability occur. In particular, when printing a large amount of images with a low image area ratio, since the toner consumption is small, the same toner continues to be stirred in the developing device for a long time, which is caused by embedding / releasing toner external additives. Background stains, toner scattering, and blurred images tend to deteriorate significantly. When performing such printing, it is better to reduce the stress on the developer by lowering the stirring force.

  An object of the present invention is to propose a stirring roller configuration that improves the stirring force by rotating the stirring fin according to the printing situation or stops the stirring fin to minimize stress on the developer. This prevents abnormal images in any situation and enables high-quality printing.

  The above-described problem is a two-component developing device in which a developer circulation transport path extending in parallel with the longitudinal direction of the developing roller to be disposed opposite to the latent image carrier is formed in the device housing. A developer conveying screw that conveys the developer in the longitudinal direction along the conveyance path and a developer agitation fin that agitates the developer in the direction orthogonal to the longitudinal direction, while their rotational axes are positioned on the same straight line The problem is solved by providing the developer conveying screws and the developer agitating fins so that they can be switched between driving (rotating) and stopping independently of each other.

  According to the present invention, the developer agitation fin can be switched between driving and stopping independently of the developer conveying screw, so that it is necessary to enhance the agitation action of the developer according to the printing situation, and to the developer. Both when you want to reduce the stress of printing and avoid spots, meteors, white streaks, clogging of the transport path and background stains, toner scattering, and blurring due to low image area ratio due to temperature rise during continuous printing Therefore, it is possible to realize high-quality image formation without any abnormality.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic view of a developing device according to an embodiment of the present invention. FIG. 2 is a conceptual plan view of a developing device showing a characteristic configuration of the present invention. It is a graph which shows the relationship between the detection temperature of an image formation temperature sensor, the rotation / stop timing of a developer stirring fin, and the change of the aggregate amount in a developer. 6 is a graph showing the relationship between the driving / stopping of the developing device and the rotation / stopping of the developer stirring fin, and the detection deviation of the toner density sensor when the stopping time of the developing device becomes long. 6 is a graph showing a relationship between a detected value by a toner density sensor and rotation / stop of a developer stirring fin, and a difference in image density deviation depending on presence / absence of a developer stirring fin when the detected value is high. It is a schematic perspective view of a developing device provided with a thermo color sensor. It is a schematic perspective view which shows a mode that the thermo color sensor developed color. It is a schematic perspective view which shows a mode that a thermo color sensor is replaced | exchanged. It is a schematic perspective view of a developing device provided with a bimetal thermostat. It is a schematic perspective view which shows a mode that a bimetal thermostat is returned. It is a figure which shows the structure which detects the temperature history at the time of power-off by a storage battery, FIG. 12a is a mode during energization, and FIG.

  FIG. 1 is a schematic diagram showing the overall configuration of a printer that is an example of an image forming apparatus according to an embodiment of the present invention. The printer generates four toner images of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K: these abbreviations may be omitted below for simplification of display). Two image forming units 1Y, 1C, 1M, and 1K are provided. These image forming units 1 use different colors of Y toner, C toner, M toner, and K toner as image forming substances for forming an image, but the other configurations are the same. The Y toner image forming unit 1Y will be described as an example. 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 photosensitive member 3Y. And a developing unit 7Y as a developing device that develops the latent image, and is detachable integrally with the printer main body. When detached from the printer main body, the developing unit 7Y is attached to the photosensitive unit 2Y. On the other hand, it can be attached and detached. That is, in the printer shown in FIG. 1, the image forming unit is configured as a process cartridge.

  In FIG. 2, the photoconductor unit 2Y includes a photoconductor 3Y, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y as a charging unit for charging the surface of the photoconductor 3Y, and the like. The charging device 5Y uniformly charges the surface of the photoreceptor 3Y that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown) (for example, −690 V). In the example of FIG. 2, a charging device 5 </ b> Y is shown that uniformly charges the surface of the photoreceptor 3 </ b> Y by applying a charging bias to the charging roller 6 </ b> Y close to the photoreceptor 3 </ b> Y. Instead of the charging roller 6Y, a charging system such as a charging brush or a scorotron charger may be used.

  In FIG. 1, an optical writing unit 20 as a latent image forming unit is provided below the image forming unit 1 in the drawing. The optical writing unit 20 irradiates the photoconductor 3 after uniform charging of the image forming unit 1 with laser light L based on the image information. In the example of FIG. 1, the optical writing unit 20 irradiates the photoreceptor 3 through a plurality of optical lenses and mirrors while deflecting the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor. It has become. However, instead of such a polygon scanning method, light scanning with an LED array can also be performed.

  Returning to FIG. 2, the surface potential of the photoreceptor 3 </ b> Y decreases only in the area exposed by the laser beam L (for example, −50 V), and an electrostatic latent image is formed. The electrostatic latent image is conveyed to the developing area facing the developing roller 12Y of the developing unit 7Y as the photoconductor 3Y rotates. The developing unit 7Y includes a first transport agitating unit 8Y having a transport screw and a stirring fin, a first developer circulation transport path 9Y provided with a toner replenishing port (not shown), a first developer having a transport screw and a stirring fin. It has a second conveying stirring means 11Y, a toner concentration sensor 10Y comprising a magnetic permeability sensor, a developing roller 12Y, and a second developer circulation conveying path 14Y provided with a doctor blade 13Y and the like. The developer circulation transport passages 9Y and 14Y are connected by connecting ports at both ends (the front side and the back side in FIG. 2), and contain Y developer having negatively chargeable Y toner and a magnetic carrier. Details of the first and second transport agitating units 8Y and 11Y will be described later.

  The first transport agitating means 8Y is rotated by a driving means (not shown) to transport the Y developer in the first transport path 9Y from the back side to the front side in FIG. The Y developer conveyed to the front side moves to the second conveyance path 14Y through a communication port (not shown) on the front side of the sheet. The second transport agitating unit 11Y rotates in the same manner, and transports the Y developer that has entered the second transport path 14Y from the front side to the back side in FIG. The Y developer in the middle of conveyance is detected by the toner concentration sensor 10Y fixed to the bottom of the second conveyance path 14Y. Above the second conveyance path 14Y, the developing roller 12Y is arranged in parallel with the second conveyance agitating means 11Y. The developing roller 12Y includes a non-magnetic developing sleeve 15Y that rotates counterclockwise in FIG. 2 and a non-rotating magnet roller 16Y that is included in the developing sleeve 15Y. A part of the Y developer conveyed in the second conveyance path 14Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force of the magnet roller 16Y. The developing sleeve 15Y is provided with a doctor blade 13Y that is opposed to each other while holding a minute gap, and the layer thickness (pumping amount) of the pumped Y developer is regulated when passing through the doctor blade 13Y. . The Y developer that has passed through the doctor blade 13Y is transported to a developing area facing the photoreceptor 3Y. Due to the potential difference between the developing potential (for example, −550 V) applied to the developing sleeve 15Y and the surface potential (for example, −50 V) of the exposed portion of the photoreceptor 3Y, only the Y toner in the Y developer conveyed to the developing area is the photoreceptor. It adheres to the exposed portion of 3Y. As a result, a Y toner image is formed on the photoreceptor 3Y. The Y developer that has consumed Y toner by the development is returned to the second transport path 14Y, transported to the back side of the sheet of FIG. 2 by the second transport agitating means 11Y, and at the back side communication port (not shown). It moves to the first transport path 9Y. The Y developer that has returned to the first conveyance path 9Y is newly replenished with toner at a toner replenishing port (not shown), and is again conveyed to the front side of the sheet of FIG. 2 by the first conveyance agitating means 8Y.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to the intermediate transfer belt 41 in FIG. Waste toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer is removed by the drum cleaning device 4Y. The surface of the photoreceptor 3Y from which the waste toner has been removed is neutralized by a neutralizing device (not shown), and is directed to the charging device 5Y to perform the next image formation.

  Although an image forming temperature sensor to be provided in the vicinity of the developer conveyance path is not shown, the developer in the conveyance paths 9Y and 14Y, such as in the development unit 7Y or in the vicinity of the development unit 7Y on the main body side of the image forming apparatus, is not shown. It is installed at a position where temperature detection is highly correlated with the temperature.

  Returning to FIG. 1, a first paper feed cassette 31 and a second paper feed cassette 32 are provided below the optical writing unit 20. A plurality of recording papers P are stored in these paper feeding cassettes, and the first paper feeding roller 31a and the second paper feeding roller 32a are applied to the uppermost recording paper P, respectively. It comes to touch. By driving these paper feed rollers 31 a and 32 a counterclockwise, the uppermost recording paper P in the paper feed cassettes 31 and 32 is discharged to the paper feed path 33. The recording paper P is conveyed upward by the conveying roller pair 34, temporarily stopped at the position of the skew correction / timing adjusting roller pair (so-called registration roller) 35, and then subjected to the secondary transfer at a timing according to the image on the intermediate transfer belt 41. It is conveyed to the nip (the contact position between the secondary transfer roller 50 and the secondary transfer counter roller 46).

  An intermediate transfer unit 40 is disposed above the image forming unit 1. The intermediate transfer unit 40 includes an intermediate transfer belt 41, a belt cleaning unit 42, primary transfer rollers 45Y, 45C, 45M, 45, a secondary transfer counter roller 46, a drive roller 47, and the like. The intermediate transfer belt 41 is rotated counterclockwise by the driving roller 47. The four primary transfer rollers 45 form primary transfer nips between the corresponding color photoreceptors 3 with the intermediate transfer belt 41 interposed therebetween. The primary transfer roller 45 applies a primary transfer bias to the inner peripheral side of the intermediate transfer belt 41. Due to the potential difference between the primary transfer roller 45 and the photoreceptor 3, the toner image on the photoreceptor 3 is transferred to the intermediate transfer belt 41 at the primary transfer nip. At the primary transfer nip of each color, a Y toner image, a C toner image, an M toner image, and a K toner image are sequentially transferred to the intermediate transfer belt 41, and the four-color toner in which the four color toner images are superimposed on the intermediate transfer belt 41. An image is formed.

  The secondary transfer counter roller 46 is provided at a position facing the secondary transfer roller 50, and both form a secondary transfer nip with the intermediate transfer belt 41 interposed therebetween. In accordance with the timing of the four-color toner image formed on the intermediate transfer belt 41, the skew correction / timing adjusting roller pair 35 conveys the recording paper P to the secondary transfer nip. A secondary transfer bias is applied between the secondary transfer counter roller 46 and the secondary transfer roller 50, and the four-color toner image on the intermediate transfer belt 41 is secondarily transferred onto the transfer paper P by that force. Then, combined with the background color of the recording paper P, a full color toner image is obtained. Waste toner remaining on the intermediate transfer belt 41 after passing through the secondary transfer nip is removed by the belt cleaning unit 42.

  A fixing unit 60 is provided above the secondary transfer nip. The fixing unit 60 includes a pressure roller 61 containing a heat source such as a halogen lamp, and a fixing belt unit 62. Further, the fixing belt unit 62 includes a fixing belt 64, a heating roller 63 containing a heat source such as a halogen lamp, and a driving roller 66. The fixing belt 64 is rotated counterclockwise in the drawing by the driving roller 66 and is heated by the heating roller 63 to be maintained at a constant temperature (for example, 140 ° C.). The pressure roller 61 also rotates clockwise and is heated by an internal heat source and maintained at a constant temperature (for example, 120 ° C.). The fixing belt 64 and the pressure roller 61 are in contact with each other to form a fixing nip. The recording paper P that passes through the secondary transfer nip and has a toner image thereon is conveyed to the fixing nip in the fixing unit 60. The toner image is fixed on the recording paper P by being heated and pressurized at the fixing nip. The recording paper P on which the toner image is fixed passes through a pair of paper discharge rollers 67 and is discharged to a paper discharge stack unit 68 outside the apparatus.

  Above the intermediate transfer unit 40, four toner cartridges 100Y, 100C, 100M, and 100K that respectively store Y toner, C toner, M toner, and K toner are provided. Each color toner in the toner cartridge 100 is supplied to the developing unit 7 from a toner supply port (not shown) through a supply path (not shown). These toner cartridges 100 are detachable from the image forming apparatus main body independently of the image forming unit 1.

  The developing device 7 according to the embodiment of the present invention will be described again with reference to FIG. As described above, the developing device 7 is provided with the first developer circulation conveyance path 9 and the second developer circulation conveyance path 14 in which the developer circulates. The developer is circulated by the first conveyance agitation means 8 and the second conveyance agitation means 11 provided in the respective conveyance paths 9 and 14. A developing roller 12 is provided above the second conveyance path 14. The first transport path 9 has a toner supply port 107 (not shown in FIG. 2), and the developer that has consumed toner by the developing roller 12 is supplied with the toner.

  Since the 1st conveyance stirring means 8 and the 2nd conveyance stirring means 11 are fundamentally the same structures, only the 1st conveyance stirring means 8 is explained in full detail. The conveyance agitation means includes an area of the conveyance screw 101 that is a blade spirally provided around the rotation axis, and an area of the agitation fin 102 that is at least one plate blade extending radially with respect to the rotation axis. I know. The transport screw 101 and the stirring fin 102 rotate around the same rotational axis, and the rotational shaft has a double structure of the transport screw shaft 103 and the stirring fin shaft 104. That is, the conveying screw 101 is attached to the conveying screw shaft 103 and the agitating fin 102 is attached to the agitating fin shaft 104, and the agitating fin shaft 104, which is a small-diameter cylindrical body, passes through the conveying screw shaft 103, which is a large-diameter cylindrical body. ing. The conveying screw shaft 103 does not exist in the region where the stirring fins 102 are formed and is in a state of being interrupted. In this region, there is a hollow screw piece 108 having the same diameter as the conveying screw 101, and the adjacent conveying screw shaft 103. It is connected to. The stirring fin 102 rotates in the inner region of the coiled hollow screw piece 108. A conveying screw gear 105 and an agitation fin gear 106 are provided at one end of the conveying agitation means 8. The conveying screw gear 105 is connected to the conveying screw shaft 103, and the agitation fin gear 106 is connected to the agitation fin shaft 104. That is, if the conveying screw gear 105 is rotated, only the conveying screw shaft 103, the conveying screw 101 attached thereto, and the hollow screw piece 108 are rotationally driven, and if the agitating fin gear 106 is rotated, the agitating fin shaft 104 is attached thereto. Only the agitated fin 102 is driven to rotate. These may be rotated by separate motors, but may be rotated by a common motor by interposing a clutch configuration.

  An example of stirring fin control based on the image forming temperature sensor will be described with reference to FIG. When an image is formed (printed) for a long time using an image forming apparatus such as a printer, the temperature of the developing device rises due to heat generated by the drive unit. The temperature at which the temperature of the developing device rises depends on the printing frequency (number of prints per job, interval between jobs), full color / monochrome, and the like. Incidentally, full-color continuous printing has the highest temperature rise. The top graph in FIG. 4 shows the temperature transition of the image forming temperature sensor in the vicinity of the developing device when printing is performed under conditions such that the printing frequency and the printing mode vary with time. In the lowermost graph, the solid line represents the transition of the amount of aggregates observed in the developer when the above printing is performed by a conventional developing device having no stirring fin. Here, the aggregate amount is defined by the relative amount of developer remaining on the sieve when the developer is sieved with a sieve having a mesh of 100 μm, and the aggregate amount data measured at regular intervals is smooth. Connected to the graph.

  On the other hand, in this example, Temp1 = 40 ° C. and Temp2 = 38 ° C., when the detected value of the image forming temperature sensor exceeds 40 ° C., the rotation of the stirring fin is started, and when it falls below 38 ° C., the rotation of the stirring fin is stopped. Control was performed (see the middle graph in FIG. 4). When printing is performed with this developing device under the above conditions, the stirring fins rotate and stop as shown in the middle graph. At this time, the amount of agglomerates in the developer changes in the direction of the broken line in the bottom graph, and even if the agglomerates are once formed by melting the developer due to the high temperature of the developing device, the stirring fins are broken. It was confirmed that the state of a small amount of aggregates could be maintained by the effect of force. In addition, it was confirmed that there were far fewer white streaks, black spots, and meteors, which were abnormal images that would be generated by aggregates at this time, as compared with the conventional developing device. The problem of clogging the conveyance path due to solidification of the developer can also be prevented by breaking the solidified developer with a stirring fin. On the other hand, by stopping the rotation of the stirring fins when the detected temperature falls below Temp2, the stress on the developer can be minimized, and background stains, toner scattering, and blurred images are generated due to the deterioration of the developer. Can be suppressed.

  In addition, the amount of aggregate corresponding to a certain temperature because the aggregate is generated while the developer is heated and the aggregate amount corresponding to a certain temperature is reached. Each has a time lag. That is, when the amount of aggregate formed in the developer is plotted against the temperature of the developer, the amount of aggregate present at that moment is larger during cooling for the same temperature. It is important to rotate the stirring fin only while the amount of aggregate exceeds a certain value. Setting the threshold Temp2 during cooling to the threshold Temp1 during temperature rise is the most effective. Stir fins can be used.

  Next, stirring fin control based on the stop time of the developing device will be described with reference to FIG. If the developing device is stopped for a long time and the developer is not moved by the conveying and stirring means, the bubbles contained in the developer are removed and the bulk density becomes high. For a toner density sensor that measures magnetic permeability, a state where the bulk density is high is the same as a state where the toner density is lowered, and therefore the toner density is detected with a deviation from a lower level than the correct state (see “SENSOR” in the lower part of FIG. 5). Detection deviation "). Actually, since the developing device is stopped and neither toner is consumed nor replenished, the toner density of the developer does not change at all.

  For this reason, when the developing device is stopped for a long time and the driving is resumed and the conveying stirring means is moved, the bulk density of the developer is highest immediately after the driving is resumed, and returns to the original bulk density (low bulk density) as the driving time increases. As a result, the detection deviation of the toner density sensor is reduced accordingly. However, in the case of a conventional developing device that does not have a stirring fin, it takes a long time until the detection deviation of the toner density sensor is settled, and unnecessary toner replenishment is executed during that time, resulting in an oversupply state.

  In this example, when time1 = 180 min and time2 = 10 min are set and the stop time of the developing device / conveying screw exceeds 3 hours (time1), the stirring fin is rotated for 10 minutes (time2) when printing is resumed. Take control. Since the time management device capable of measuring the drive start / stop timing of the conveying screw and the elapsed time from these timings for such control is known per se, description thereof will be omitted (this device does not require development). The driving start timing of the agent stirring fin and its elapsed time can also be measured). When the driving (= printing) / stop of the developing device / conveying screw is repeated as shown in the uppermost graph in FIG. 5, the stirring fin rotates / stops as shown in the middle graph. At this time, the transition of the detected value of the toner density sensor is as shown by the broken line in the bottom graph, and it was confirmed that the detection deviation of the toner density sensor was quickly settled compared to the conventional developing device without the stirring fin. . In addition, by installing this control, the number of replenishments after resuming printing has been reduced (= oversupply can be prevented, toner scattering can be suppressed, and image density can be stabilized), and after printing has finished It was confirmed that the background dirt was improved. By limiting the driving time of the stirring fin, it was possible to suppress the stress on the developer after the bulk density of the developer returned to its original shape.

  The stirring fin control based on the toner density of the developer will be described with reference to FIG. If the toner is replenished in a state where the developer has a high toner concentration, there is a problem that the replenished toner is pumped up to the developing roller without being mixed into the developer. In the developing device shown in FIG. 3, a large amount of insufficiently charged replenishment toner is pumped to the right side of the developing roller 12 close to the toner replenishing port 107 (as the developer transport direction). The image density is higher than the left side (local image density fluctuation, background stain). The solid line in the bottom graph shows how the image density deviation changes in a conventional developing device without a stirring fin when the toner density changes as in the top graph in FIG. While the toner density is high, the image density deviation tends to be large.

  On the other hand, in this example, TC0 = 8.5%, and when the developer toner concentration exceeds 8.5%, the stirring fin is controlled to rotate. When the toner concentration changes as shown in the uppermost graph, the stirring fin rotates and stops as shown in the middle graph. At this time, the transition of the image density deviation changes as shown by the broken line in the bottom graph, and it can be confirmed that the image density deviation at the high toner density is improved (reduced) as compared with the conventional developing device. It was.

  The image forming temperature sensor detects and records the temperature only when the printer as the image forming apparatus is energized, and does not grasp the temperature history while the main power is off or the outlet is disconnected. For this reason, for example, when an image forming apparatus placed in an extremely hot environment in the daytime in summer is used after cooling in the evening, the developer state change in the developing apparatus at a high temperature when left standing, that is, It does not address situations where developer melting is suspected. Therefore, an improved example for grasping the temperature history of the developing device when not energized will be described below.

  That is, a temperature sensor for grasping the temperature history when the main power is off is added. First, temperature history detection using a thermo color sensor that develops color when a certain temperature threshold is exceeded will be described with reference to FIG. A thermo color sensor 121 is mounted on the lid portion of the developing unit 7, and a color detection unit 122 that detects the color of the color developing portion of the thermo color sensor 121 is provided on the main body side of the printer. The color detection unit 122 includes a pair of light emitting / receiving elements, and the light 123 emitted from the light emitting unit is reflected by the coloring unit of the thermo color sensor 121 and reaches the light receiving unit. The light receiving unit can determine whether the thermo color sensor 121 is colored by detecting the reflected light intensity. In this example, as the thermo color sensor 121, an object in which the color developing portion changes from white to black when the temperature threshold value exceeds 40 ° C. is used.

  FIG. 7 shows the developing unit in a normal state, that is, in a state where there is no history of high temperature, and the coloring portion of the thermo color sensor 121 is white. Therefore, the light 123 emitted from the color detection unit 122 is reflected by the coloring unit, and the reflected light intensity detected by the light receiving unit is high. On the other hand, FIG. 8 shows the developing unit at a high temperature, that is, in a state where there is a history of the high temperature, and the coloring portion of the thermo color sensor 121 ′ is black. Therefore, the light 123 emitted from the color detection unit 122 is absorbed and not reflected by the coloring unit, and the reflected light intensity detected by the light receiving unit is small.

  An example of stirring fin control using such a thermo color sensor will be described. While the user turns off the power switch and the printer is shut down, the color detection unit 122 emits light 123 to detect the color of the coloring unit of the thermo color sensor 121. If the reflected light intensity detected by the light receiving unit is larger than a certain threshold (intensity corresponding to 40 ° C.), the color developing unit is white, and it can be determined that there is no history of high temperature when the power is turned off. At this time, “0” is recorded in the first memory area (hereinafter referred to as “previous OFF memory”). On the contrary, if the reflected light intensity is smaller than the threshold value, the color-developing portion is black, and it can be determined that there is a history of high temperature already (eg during printing) when the power is turned off. In this case, “1” is recorded in the memory when previously turned off. After the recording to the memory at the time of the previous off is completed, the printer is turned off.

  Next, while the user turns on the power switch and the printer is activated, the color detection unit 122 emits light 123 to detect the color of the coloring unit of the thermo color sensor 121. If the reflected light intensity detected by the light receiving unit is larger than the threshold value and the color developing unit is white, it can be determined that there is no history of high temperatures at the time of power-on. At this time, “0” is recorded in a second memory area (hereinafter referred to as “currently on-time memory”). On the contrary, if the reflected light intensity is small and the coloring portion is black, it can be determined that there is a history of high temperature when the power is turned on. In this case, “1” is recorded in the on-time memory this time.

  Then, the operation content of the stirring fin is determined based on the combination of the previously-off memory value and the current-on memory value. Table 1 summarizes the correspondence between the combinations of memory values and the operation contents of the stirring fins.

  First, when both the previous off time / current on time are “0”, it can be determined that there is no history of high temperatures during power off. Therefore, since it is not necessary to stir the developer strongly, it is only necessary to rotate only the normal conveying screw 101 while the stirring fin 102 is stopped at the time of startup. Next, when the previous off time is “0” and the current on time is “1”, it can be determined that there is a history of high temperatures during power off. Therefore, since it is necessary to break up the developer aggregate generated at a high temperature while the power is off, the stirring fin 102 is also rotated for a long time at the start-up, and the printing is started after the developer is vigorously stirred. Note that the thermo color sensor 121 'once colored black does not return to the original white color, so it is necessary to replace the thermo color sensor 121' with an uncolored new one. Therefore, it is necessary to display “Please replace the sensor” on the operation screen to prompt the user to replace the sensor or to record that the sensor needs to be replaced so that the service person can replace it at the regular visit.

  Next, when the previous off time is “1” and the current on time is “0”, it is considered that the thermo color sensor 121 has been replaced while the power is off. In this case, both a case where there is a history of high temperature before replacing the thermo color sensor 121 during power-off and a case where the temperature does not become high during power-off are considered. Considering the necessity of preventing abnormal images in the former case and the necessity of minimizing the user's (unnecessary) waiting time in the latter case, the stirring fin 102 is rotated only for a short time. Start printing. Finally, if the previous off time is “1” and the current on time is “1”, there is already a history of high temperature before turning off the power, and whether there is a history of high temperature during power off. It cannot be determined. Therefore, in order to achieve both the prevention of abnormal images and the reduction of waiting time, the stirring fin 102 is rotated only for a short time. Further, since the thermo color sensor 121 ′ has been colored and needs to be replaced with a new one, “Please replace the sensor” is displayed on the operation screen.

  As described above, the thermo color sensor 121 cannot perform the next detection unless the sensor is replaced every time the color exceeds the temperature threshold value. Therefore, in this example, as shown in FIG. 9, a thermo color sensor mounting portion 124 is provided so that the thermo color sensor 121 can be easily attached and detached. Thus, the used thermo color sensor 121 ′ can be easily replaced with a new thermo color sensor 121. Since the thermo color sensor is in the form of a small sheet, the addition of such a sensor has little effect on the size of the developing device, and has the advantage of space saving.

  Next, temperature history detection using a bimetal thermostat that deforms when a certain temperature threshold is exceeded will be described with reference to FIG. A bimetal thermostat 131 is attached to the lid portion of the developing unit 7. The bimetal thermostat 131 is configured such that when a certain temperature threshold is exceeded, the bimetal is deformed to cut the internal electronic circuit. In this example, a bimetal thermostat set so that the electronic circuit is disconnected at a temperature threshold of 40 ° C. is used. A lead wire (not shown) extends from the bimetal thermostat 131 and is connected to the printer main body through a connector (not shown) on the back side of the image forming unit 1. The printer has a continuity detection unit (not shown) that detects whether or not the electronic circuit is energized, and the continuity detection unit can determine whether or not the bimetal is deformed. Further, the bimetal thermostat 131 is an irreversible type with respect to temperature, and a manual return switch 132 is provided for return. A switch pressing member 133 is provided at a position facing the manual return switch 132 on the printer main body side.

  An example of stirring fin control using such a bimetal thermostat will be described. While the user turns off the power switch and the printer is shut down, the continuity detection unit confirms the continuity of the bimetal thermostat. If the bimetal is not deformed, turn off the printer without doing anything. If the bimetal is deformed and the circuit is disconnected, as shown in FIG. 11, the switch pressing member 133 is operated and the manual return switch 132 is pressed to return the bimetal thermostat 131. After the recovery is completed, turn off the printer.

  Next, when the user turns on the power switch and the printer is activated, the continuity detection unit confirms the continuity of the bimetal thermostat. If the bimetal is not deformed, it can be determined that there is no history of high temperatures during power-off. Therefore, since it is not necessary to stir the developer strongly, it is only necessary to rotate only the normal conveying screw 101 while the stirring fin 102 is stopped at the time of startup. Conversely, if the bimetal is deformed and the circuit is disconnected, it can be determined that there is a history of high temperatures during power-off. Therefore, since it is necessary to break up the developer aggregate generated at a high temperature while the power is off, the stirring fin 102 is also rotated for a long time at the start-up, and the printing is started after the developer is vigorously stirred. Since the bimetal thermostat can be manually reset, it can be used repeatedly, which is advantageous in terms of cost.

  Finally, an example in which temperature is detected at regular intervals using a storage battery will be described with reference to FIG. A storage battery is installed in the printer, and is charged using surplus power from the AC outlet during printing or power-on standby (FIG. 12a). When the user turns off the power switch, the printer resets all of the temperature history recording memory during shutdown and then turns off the power. When the power is turned off, the storage battery supplies power to a temperature sensor (thermistor) and a memory for recording temperature history in the vicinity of the developing device. The thermistor detects the current temperature every 15 minutes and records the temperature information in the temperature history memory. The temperature history memory has 10 areas of a 35 ° C. counter to a 44 ° C. counter, and each area can take a value of 0 to 255 in 1 byte. When the thermistor detects the temperature, the corresponding temperature region counter is incremented by one.

  Next, the user turns on the power switch and reads the temperature history memory while the printer is activated. When the 44 ° C counter is 1 or more, the total of 42 ° C to 44 ° C counter is 4 or more, the 40 ° C counter to 44 ° C counter is 12 or more, and the total of 35 ° C to 44 ° C counter is 24 or more The developing device determines that there is a history of high temperature for a long time while the power is off. In this case, since it is necessary to break up the developer aggregate generated while the power is off, the stirring fin 102 is rotated for a long time when starting up, and the developer is strongly stirred, and then printing is started. On the other hand, if none of the above conditions is satisfied, it is determined that there is no history of high temperature for a long time during power-off. In this case, it is only necessary to stop the stirring fin 102 at the time of activation and rotate only the normal conveying screw 101. With such a configuration, it is possible to accurately predict the melting of the developer and rotate the stirring fin when the power is turned on without excess or deficiency.

DESCRIPTION OF SYMBOLS 2 Photoconductor unit 3 Photoconductor 4 Drum cleaning apparatus 5 Charging apparatus 6 Charging roller 7 Developing unit 8 First conveyance agitation means 9 First developer circulation conveyance path 10 Toner density sensor 11 Second conveyance agitation means 12 Developing roller 13 Doctor blade 14 Second developer circulation conveyance path 15 Non-magnetic development sleeve 16 Magnet roller

Japanese Patent No. 3636217

Claims (11)

  A two-component developing device in which a developer circulation conveyance path extending in parallel with the longitudinal direction of a developing roller to be arranged opposite to a latent image carrier is formed in the apparatus housing, and is along the developer circulation conveyance path Thus, the developer conveying screw that conveys the developer in the longitudinal direction and the developer agitation fin that agitates the developer in the direction orthogonal to the longitudinal direction are separated from each other while their rotational axes are located on the same straight line. And a developer conveying screw and a developer agitating fin that are capable of switching rotation / stop independently of each other.   A temperature detection unit for the developer existing in the developer circulation conveyance path is provided, and when the detection value by the temperature detection unit exceeds a first threshold value, rotation of the developer stirring fin is started to detect the temperature. 2. The developing device according to claim 1, wherein the developer stirring fin is stopped when a value detected by the means falls below a second threshold value equal to or lower than a first threshold value.   Provided with a time management device capable of measuring the drive start timing and drive stop timing of the developer transport screw, the drive start timing of the developer stirring fin, and the elapsed time from these timings, and the drive start of the developer transport screw 3. The developer agitating fin is driven for a predetermined time when the elapsed time from the last time when the developer conveying screw is stopped exceeds a predetermined time. Development device.   4. The toner stirring sensor is provided, and the developer stirring fin is driven while a density value detected by the toner density sensor exceeds a predetermined value. Development device.   A second temperature detection unit capable of grasping the temperature history without requiring energization is provided, and the developer agitation at the next energization is performed according to the temperature history during non-energization grasped by the second temperature detection unit. The developing device according to claim 1, wherein rotation and stop of the fin is determined and executed.   The second temperature detecting means includes an irreversible thermo color sensor that changes color when a predetermined temperature threshold is exceeded, and a pair of light emitting and receiving portions that detect the color of the thermo color sensor. 5. The developing device according to 5.   6. The developing device according to claim 5, wherein the second temperature detecting means includes a bimetal thermostat that deforms when a predetermined temperature threshold is exceeded, and an electronic circuit that can recognize the deformation of the bimetal thermostat.   The second temperature detecting means stores a storage battery that stores surplus power while the apparatus is being driven, a memory that stores a temperature history during non-energization, and stores an actual temperature at regular intervals using the power of the storage battery during non-energization. The developing device according to claim 5, further comprising a temperature detection unit that performs the operation.   The rotation / stop of the developer agitating fin at the next energization is determined and executed according to a time when a predetermined temperature threshold is exceeded in the temperature history stored in the memory at the time of non-energization. The developing device according to 8.   A process cartridge comprising the developing device according to claim 1.   An image forming apparatus comprising the developing device according to claim 1.

Images