JP2005128043A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the useless ejection of a toner more surely than in a conventional manner, while avoiding abnormal developing caused by the excessively forcible ejection of developer. <P>SOLUTION: An opening/closing shutter 21 for opening/closing an ejection port 19 for ejecting the developer is arranged in a developing apparatus 10. Besides, a shutter solenoid 60 for driving the opening/closing shutter 21 is arranged. A control part (not illustrated) is arranged so that the shutter 21 may be controlled to open only for a prescribed time based on the detection result by a T sensor (not-illustrated) for detecting toner concentration in the developer in the developing apparatus 10 that the toner concentration becomes equal to or below a prescribed threshold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention develops a latent image carried on a latent image carrier such as a photoconductor by a developing means using a developer containing toner and a carrier, and supplies toner to the developing means as necessary. The present invention relates to an image forming apparatus.

  In this type of image forming apparatus, the toner density of the developer is set within a predetermined range by supplying toner from a toner cartridge or the like as necessary to the developer in the developing unit that consumes the toner accompanying development. Keep in. In such a configuration, the carrier in the developer gradually deteriorates as it is repeatedly used without almost consuming the carrier. Therefore, the carrier is renewed at a regular timing such as every predetermined number of printouts. It needs to be replaced. If the user is forced to perform such a regular carrier exchange operation, the maintainability is deteriorated.

  Therefore, conventionally, an image forming apparatus that overflows excess developer from the developing unit while replenishing the toner concentration by supplying a premix agent mixed with carrier and toner to the developer in the developing unit is known. (For example, those described in Patent Document 1). In such a configuration, a new carrier in the premix agent is replenished to the developer while the old carrier is gradually discharged from the developing means due to the overflow of the developer. Then, by replacing the carrier in the developer gradually with a new one by such discharge and replenishment, the user's carrier replacement work can be omitted.

However, in this type of image forming apparatus, due to overflow, not only the old carrier is discharged from the phenomenon means but also the toner is discharged together. Its emissions will be substantial. For example, when the toner concentration of the developer in the developing unit is reduced to 5 [%], the premix agent is supplied to the developing unit having a developer capacity of 100 [cm ³ ] until it reaches 8 [%]. . Further, it is assumed that a premix agent having a toner concentration of 20% (toner specific gravity = 1, carrier specific gravity = 3) is used. Then, the amount of toner overflow per replenishment is about 3.5 [g].

  In view of this, Japanese Patent Application Laid-Open No. 2005-228561 proposes an image forming apparatus provided with an overflow level changing unit that changes an overflow level that is a position in the height direction of the developer discharge port of the developing unit. In this image forming apparatus, when the toner density of the developer is lowered to a predetermined threshold value or lower, in other words, when the toner amount per unit volume in the developer is relatively small, the overflow level is set lower than usual. To do. Then, after a part of the developer is forcibly discharged, the premix agent is supplied after the overflow level is returned to the normal level. In such a configuration, before supplying the premix agent, a part of the developer having a relatively small amount of toner per unit volume is forcibly discharged to ensure a certain amount of empty space for receiving the agent. Thus, wasteful discharge of toner can be suppressed.

Japanese Patent No. 2837309 Japanese Patent No. 3264765

  However, as a result of intensive studies, the present inventors have found that there is a period in which wasteful discharge of toner cannot be sufficiently suppressed in this image forming apparatus. Specifically, if the developer is forcibly discharged by reducing the overflow level, the amount of the developer in the developing unit is remarkably reduced and normal development cannot be performed. For this reason, the forced discharge amount of the developer needs to be limited to a certain amount. Then, the toner density of the developer cannot be sufficiently increased only by replenishing the same amount of the premix agent as the discharge amount. In addition, it is necessary to replenish the premix agent more than the discharge amount, and the developer overflows inevitably. The toner concentration of the developer at the time when the overflow starts is not sufficient, but has recovered to some extent. For this reason, the amount of toner per unit volume of the developer that overflows is larger than when the toner density is equal to or less than the above threshold. Therefore, wasteful discharge of toner cannot be sufficiently suppressed during a period in which the developer overflows when the premix agent is replenished.

  Heretofore, an example in which both the toner and the carrier are supplied to the developing unit using the premix agent has been described, but the same problem may occur in the following cases. That is, there are a case where toner and carrier are replenished separately, or a case where one of them and a premix are replenished.

  The present invention has been made in view of the above background, and an object thereof is to provide the following image forming apparatus. In other words, the image forming apparatus can more reliably suppress wasteful discharge of toner than in the past while avoiding development abnormality due to excessive discharge of developer.

In order to achieve the above object, a first aspect of the present invention provides a developer accommodating portion for accommodating a developer containing toner and a carrier, and a replenishing port provided in the developer accommodating portion for replenishing toner and carrier. And a developing means having a discharge port provided in the developer accommodating portion for discharging the developer, a toner concentration detecting means for detecting the toner concentration of the developer in the developer accommodating portion, and through the replenishing port. Replenishing means for replenishing toner and carrier to the developer accommodating portion; a latent image carrier for carrying a latent image developed by the developing means; and control means for controlling driving of the developing means and the replenishing means. In the image forming apparatus, an opening / closing shutter for opening / closing the discharge port is provided in the developing unit, and a shutter driving unit for driving the opening / closing shutter is provided, and the toner density detected by the toner density detecting unit Based on the detection result is equal to or less than a predetermined threshold value so as to implement a control to open the opening and closing shutter for a predetermined period of time, it is characterized in that constitute the control means.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the toner is replenished to the developer accommodating portion by the replenishing means, the open / close shutter is forcibly set regardless of the detection result. The above-mentioned control means is configured so as to perform the closing control.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, after the replenishing means starts replenishing toner to the developer accommodating portion, the open / close shutter is closed, and the replenishment ends. Up to this point, the control means is configured so as to perform control in which the open / close shutter is forcibly closed regardless of the detection result.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the developing unit is provided with a stirring and conveying unit that circulates and conveys the developer along a predetermined circulation path while stirring the developer in the developer containing portion. The replenishing port is disposed downstream of the discharge port in the direction of circulating and conveying the developer.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a link mechanism for forcibly closing the open / close shutter is linked to the removal of the developing means from the main body of the image forming apparatus. It is characterized by providing.

  In these image forming apparatuses, the developer is discharged from the developing means only when the open / close shutter is opened based on the result of the toner density detection by the toner density detecting means being below a predetermined threshold. Then, as in the image forming apparatus of claim 2, the toner is replenished with the opening / closing shutter being closed, or the toner is replenished after the opening / closing shutter is closed after the toner replenishment is started as in the image forming apparatus of claim 3. Or keep it closed until it is finished. Then, it is possible to avoid the situation where the developer containing the toner immediately after replenishment is discharged from the developing means, and it is possible to discharge only the developer whose toner density is lowered to a threshold value or less. Wasteful discharge of toner can be suppressed more reliably than before. Further, even if a large amount of developer is not forcibly discharged from the developing unit prior to replenishment, a situation in which the developer containing toner immediately after replenishment is discharged from the developing unit is avoided. It is also possible to avoid development abnormalities caused by excessive discharge of the toner.

Hereinafter, an electrophotographic printer (hereinafter simply referred to as “printer”) will be described as an embodiment of an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment. The printer includes a charging unit 2, an optical writing unit 3, a developing device 10 as a developing unit, a transfer unit 5, a drum cleaning unit 6, and a neutralizing unit 7 around a drum-shaped photoconductor 1 as a latent image carrier. ing. Further, a fixing unit 8 disposed on the left side of the transfer unit 5 in the drawing is also provided.

  A photosensitive member 1 that is rotated in the clockwise direction in the drawing by a driving means (not shown) has an organic photosensitive layer formed on the surface of a raw tube made of aluminum or the like. Is uniformly charged. Then, the potential of the exposure unit is attenuated by the scanning of the laser beam L emitted from the optical writing unit 3 that constructs the optical scanning information based on image information sent from a personal computer (not shown) or the like. As a result, an electrostatic latent image having a lower potential than the background portion around the exposed portion is carried. This electrostatic latent image contains toner and a magnetic carrier carried on the developing sleeve 11 of the developing device 10 when passing through the developing position that is opposite to the developing device 10 as the photosensitive member 1 rotates. Is rubbed against the two-component developer. Then, for example, negatively charged toner contained in the two-component developer (hereinafter simply referred to as developer) adheres to the electrostatic latent image on the surface of the photoreceptor 1 and develops it into a toner image.

  A transfer position where the photoconductor 1 and the transfer unit 5 face each other is formed downstream of the developing position in the rotation direction of the photoconductor 1. When the toner image developed on the photosensitive member 1 enters this transfer position as the photosensitive member 1 rotates, it is conveyed by a sheet feeding unit (not shown) in a timely manner to a sheet-like recording material P ( For example, transfer paper). Then, it is electrostatically transferred onto the recording medium P under the influence of a transfer electric field formed between the electrostatic latent image on the photoreceptor 1 and the transfer means 5. The recording material P on which the toner image is electrostatically transferred in this way is sent from the transfer position to the fixing means 8.

  The fixing unit 8 forms a fixing nip by contact between a heating roller 8a having a heat source (not shown) inside and a pressing roller 8b pressed against the heating roller 8a. These rollers are rotationally driven so as to move the respective surfaces in the same direction at the mutual contact portions. The recording material P sent to the fixing means 8 having such a configuration is sandwiched in the fixing nip and conveyed in the roller surface moving direction. At this time, the toner image is fixed by the influence of nip pressure and heating. After fixing, the recording material P is discharged out of the apparatus via a paper discharge means (not shown).

  When the surface of the photoreceptor 1 that has passed through the transfer position passes through a position facing the drum cleaning means 6 as it rotates, the transfer residual toner is cleaned. Then, after the residual charge is removed by the charge eliminating means, the charge is uniformly charged by the charging means and the initial state is restored.

  In FIG. 1, the charging unit 2 is a system in which a bias member such as a charging roller to which a charging bias is applied is brought into contact with the photosensitive member 1, but a non-contact system such as a charging charger is used. Also good. Moreover, although the example which provided the optical writing means 3 which forms an electrostatic latent image by irradiation of a laser beam was shown, what performs optical writing by the LED light from an LED array may be used. Further, an electrostatic latent image may be formed by ion ejection or the like instead of optical writing. Further, as the transfer means 5, a roller contact type in which a transfer roller to which a transfer bias is applied is brought into contact with the photosensitive member 1 is shown. However, a belt contact type in which a belt is contacted, a non-contact type such as a transfer charger May be used. In addition, the drum cleaning unit 6 has a scraping method using a cleaning blade, but an electrostatic recovery method in which a brush or a roller to which a cleaning bias is applied contacts may be used. Further, although an example in which the drum-shaped photoconductor 1 is provided as the latent image carrier has been described, a belt-shaped photoconductor may be used. Further, although an example of a printer in which the photoconductor 1 and its peripheral devices are individually provided has been described, a process cartridge in which the photoconductor 1 and its peripheral devices are housed in a common casing as one unit may be used. . For example, the photosensitive member 1, the charging unit 2, the developing device 10, and the drum cleaning unit 6 are configured as one process unit so as to be detachable from the printer main body.

  FIG. 2 is an enlarged configuration diagram showing the photosensitive member 1, the developing device 10, and a part of the developer recovery device 50 described later. The developing device 10 includes a developing unit and a storage unit in a casing. The developing unit is provided with a developing sleeve 11 that exposes a part of the peripheral surface from the opening of the casing, a magnet roller 12 included in the developing sleeve 11, a doctor blade 13, and the like. The cylindrical developing sleeve 11 is made of a non-magnetic material such as aluminum, brass, stainless steel, or conductive resin, and is driven to rotate counterclockwise in the drawing by a driving means (not shown).

  In the developing sleeve 11, a magnet roller 12 having a plurality of magnetic poles divided in the circumferential direction is fixed so as not to be rotated around the sleeve. A magnetic field is formed around the developing sleeve 11 by the magnetic force generated from the plurality of magnetic poles of the magnet roller 12.

  The accommodating portion as the developer accommodating portion of the developing device 10 is divided into a first accommodating portion and a second accommodating portion by the partition wall 18. In the first storage portion, which is a developer storage portion, a first conveying screw 14 that is driven to rotate counterclockwise in the drawing by a driving unit (not shown), a toner concentration sensor (hereinafter referred to as a T sensor) 16, and the like are disposed. Has been. In addition, a second conveying screw 15 that is driven to rotate counterclockwise in the drawing by a driving means (not shown) is disposed in the second accommodating portion that is a developer accommodating portion.

  The partition wall 48 divides the first housing portion in which the first transport screw 14 is disposed and the second housing portion in which the second transport screw 15 is disposed, A communication port (not shown) is provided at two locations on the front end. For this reason, the 1st accommodating part and the 2nd accommodating part are connected in the area | region of the back end and front end in the figure.

  On the upper wall of the casing of the developing device 10, a replenishing port 17 is provided for receiving toner and magnetic carrier sent from a toner replenishing device and a carrier replenishing device (not shown). The toner or magnetic carrier replenished into the developing device 10 from the replenishing port 17 falls onto the first transport screw 14 of the first storage unit and is taken into the developer. Then, after the first conveying screw 14 is stirred and conveyed in the axial direction (depth direction in the figure) from the front side to the back side in the figure, the second direction passes through the communication port in the rear end region and passes through the second communication port. Enter the containment section.

  In this way, the developer that has entered the second housing portion from the first housing portion is transported from the back side to the near side by the second transport screw 15. In this process, a part of the developing sleeve 11 is attracted to the sleeve surface under the influence of the magnetic field extending from the magnet roller 12. Then, with the rotation of the sleeve, it is pumped up from the agitation section and conveyed toward the development position described above.

  The doctor blade 13 is fixed to the casing so as to maintain a predetermined gap between its tip and the surface of the developing sleeve 11. This gap is called a doctor gap, and is set to about 0.4 to 0.7 [mm], for example. When the developer pumped up from the stirring section passes through the doctor gap along with the sleeve surface, the layer thickness is regulated and the developer becomes a preferable amount. Then, it is sent to a developing position which is a position facing the photoreceptor 1 as the sleeve surface rotates.

  At the developing position, a developing magnetic field that exerts a strong magnetic force in the normal direction of the sleeve is formed by a developing magnetic pole (not shown) of the magnet roller 12. Due to the influence of the developing magnetic field, the developer rises and becomes a magnetic brush. Then, the tip is moved while being rubbed against the photoreceptor 1. At this time, due to a potential difference between the developing sleeve 11 to which a developing bias is applied by a power source (not shown) and the electrostatic latent image on the photosensitive member 1, the toner at the tip of the magnetic brush moves from the sleeve surface side toward the electrostatic latent image side. An electrostatic force is applied. Due to this electrostatic force, the toner in the tip of the magnetic brush is transferred from the surface of the magnetic carrier onto the electrostatic latent image on the photosensitive member 1, and the electrostatic latent image is developed into a toner image. The developer that has consumed toner by development moves along with the sleeve surface and moves into the casing, and is separated from the sleeve surface under the influence of a repulsive magnetic field (not shown) and returns to the agitating portion.

  The developer transported to the front end of the second storage unit in the drawing by the second transport screw 15 passes through the communication port and returns to the second storage unit. In this manner, a circulation path through which the developer repeatedly passes through the first storage portion and the second storage portion is formed in the storage portion of the developing device 10. In other words, in this printer, the first conveying screw 14, the second conveying screw 15, the partition wall 18, and the like disposed in the developing device 10 constitute a stirring and conveying unit that circulates and conveys the developer in the developer accommodating portion. Has been.

  The toner and magnetic carrier are replenished to the first storage unit of the developing device 10 based on the toner density detection result by the T sensor 16. Specifically, the T sensor 16 includes a magnetic permeability sensor, detects the magnetic permeability of the developer conveyed by the first conveying screw 14, and outputs a voltage having a value corresponding to the magnetic permeability. Since the magnetic permeability of the developer shows a good correlation with the toner concentration, the T sensor 16 outputs a voltage having a value corresponding to the toner concentration of the developer. This output voltage value is sent to a control unit (not shown). The control unit includes storage means such as a RAM and a ROM, and stores Vtref which is a target value of the output voltage from the T sensor 16 therein. In addition, a supply start threshold value is also stored. When the output voltage value from the T sensor 16 reaches the replenishment start threshold value, the control unit drives the toner replenishing device to replenish the toner in the agitation unit until it returns to a value equivalent to Vtref. By this replenishment, the toner concentration of the developer in the stirring unit is maintained within a range of about 5 to 8 [%], for example.

  A discharge port 19 for discharging the developer from the first storage portion is provided on the side wall of the first storage portion. The developer discharged from the discharge port 19 falls into a agent receiving hopper 53 of a developer recovery device 50 described later, and is then conveyed toward a recovery agent cartridge (not shown).

Next, a characteristic configuration of the printer will be described.
FIG. 3 is a perspective view showing the developing device 10 and peripheral devices. In FIG. 1, a toner replenishing device 30 for replenishing toner in the developing device 10 and a carrier replenishing device 40 for replenishing magnetic carriers in the developing device 10 are disposed on the side of the developing device 10. A developer collecting device 50 that receives and collects the developer discharged from the developing device 10 is disposed obliquely below the developing device 10.

  The toner replenishing device 30 includes a toner cartridge 31 that stores toner for replenishment, a toner transport tube 32 for transporting toner from there to the developing device 10, and the like. The toner cartridge 31 is configured to be attachable to and detachable from the printer main body and the toner transport tube 32, and is replaced with a new one when the internal toner is almost empty. One end of the toner conveying tube 32 is connected to the bottom of the toner cartridge 31, and the other end is connected to the replenishing port (17 in FIG. 2) of the developing device 10. Then, the supply toner discharged from the toner cartridge 31 is received and guided toward the supply port of the developing device 10.

  Various methods can be adopted as a method of conveying the toner from the toner cartridge 31 to the developing device 10. For example, the toner discharged from the cartridge by the rotation of the rotating member disposed in the toner cartridge 31 is transported in the tube by the rotation of a flexible coiled auger disposed in the toner transport tube 32. It is done. Further, for example, a method may be used in which toner is discharged from the cartridge 31 or transported in the tube by a suction pump using a suction pump disposed in the middle of the toner transport tube 32.

  The toner replenishing device 30 is preferably provided with a characteristic detection sensor that detects some characteristic that allows the toner in the toner cartridge 31 to be known to have decreased to the near-end level. Examples of the characteristic detection sensor include an accommodation toner detection sensor that detects toner in the cartridge inside or outside the toner cartridge 31, and a discharged toner detection sensor that detects toner discharged into the toner transport pipe 32. This is because when the toner is not detected by the stored toner detection sensor or the toner is difficult to be detected by the discharged toner detection sensor, the near-end is reached.

  The carrier replenishing device 40 includes a carrier cartridge 41 that stores a magnetic carrier for replenishment, a carrier transport pipe 42 for transporting the magnetic carrier from there to the developing device 10, and the like. Similar to the toner cartridge 31, the carrier cartridge 41 is configured to be detachable from the printer main body and the carrier transport tube 42, and is replaced with a new one when the internal magnetic carrier becomes almost empty. One end of the carrier transport tube 42 is connected to the bottom of the carrier cartridge 41, and the other end is connected to the supply port (17 in FIG. 2) of the developing device 10. Then, the supply carrier discharged from the carrier cartridge 41 is received and guided toward the supply port of the developing device 10. As a method for conveying the magnetic carrier from the carrier cartridge 41 into the developing device 10, the same method as that for toner can be employed.

  The developer recovery apparatus 50 includes a recovery agent cartridge 51, a recovery agent transport pipe 52, an agent receiving hopper 53, and the like. The agent receiving hopper 53 is configured to be detachable from the side wall of the developing device 10 so as to cover the discharge port (19 in FIG. 2) (not shown). In addition, the recovery agent cartridge 51 is configured to be detachable from the printer main body and the recovery agent transport pipe 52 in the same manner as other cartridges. Then, when the internal recovery agent is almost full, it is replaced with a new one. Further, one end side of the recovery agent transport pipe 52 is connected to the upper portion of the recovery agent cartridge 51, and the other end side is connected to the bottom portion of the agent receiving hopper 53. Then, the recovery agent (developer) received in the agent receiving hopper 53 is guided from the hopper toward the recovery agent cartridge 51. In addition, as a method for conveying the recovery agent from the agent receiving hopper 53 into the recovery agent cartridge 51, a method similar to that for toner or magnetic carrier can be employed. Further, it is desirable that the developer recovery device 50 be provided with a characteristic detection sensor that detects some characteristic that can be known to indicate that the recovery agent in the recovery agent cartridge 51 has increased to the full level.

  On the side wall of the developing device 10, an opening / closing shutter 21 for opening and closing the discharge port (19 in FIG. 2) (not shown) is slidably provided. As shown in FIG. 4, the opening / closing shutter 21 has a long hole formed in a horizontally long shape, and a guide pin 22 protruding from the side wall of the developing device 100 is inserted into the long hole. And it is slidable between a position where the guide pin 22 abuts against the left end of the elongated hole in the figure and a position where it abuts against the right end of the figure.

  On the right side of the opening / closing shutter 21 in the drawing, a shutter solenoid 60 serving as shutter driving means is disposed, and the tip of the driving shaft 62 is hooked on the end of the opening / closing shutter 21. This is a type of solenoid that retracts the drive shaft 62 into the solenoid body 61 in accordance with the excitation, and the open / close shutter 21 is slid from the left side to the right side in the figure by driving. As a result, as shown in the figure, the open / close shutter 21 is retracted from the position facing the discharge port 19 to open the discharge port 19. When the discharge port 19 is opened, among the developer stored in the first storage portion of the developing device 10, the developer present at a level higher than the lower end of the discharge port 10 is spilled from the discharge port 10 and discharged.

  A coil spring 22 is fixed to the open / close shutter 21 so as to urge the shutter from the right side to the left side in the drawing. When the driving of the shutter solenoid 60 is stopped, the opening / closing shutter 21 is slid from the right side to the left side in the drawing by the contraction force of the coil spring 22 as shown in FIG. When the open / close shutter 21 is closed in this manner, the developer is prevented from being discharged from the discharge port 19.

  FIG. 6 is a block diagram showing a part of the electric circuit of the printer. In the figure, the control unit 100 includes a CPU, a ROM, a RAM, and the like (not shown). Then, driving of the toner replenishing device 30, the carrier replenishing device 40, the developer collecting device 50, the developing motor 60, and the shutter solenoid 60 is controlled, and predetermined arithmetic processing is performed based on a signal from the T sensor 16 or the like. .

  FIG. 7 is a graph showing the relationship between the output voltage value from the T sensor (16) and the toner density of the developer present at the detection position of the T sensor. As shown in the figure, the output voltage value from the T sensor decreases as the developer toner concentration increases. This is because the magnetic permeability of the developer decreases as the toner concentration of the developer increases. In the figure, D1, which is a toner density value, indicates a shutter operation threshold value. The control unit (100) is configured to control to drive the shutter solenoid (60) for a predetermined time when the toner density of the developer in the developing device (not shown) becomes equal to or less than the density value D1. With this control, when the toner density of the developer becomes equal to or lower than the density value D1, which is the shutter operation threshold, the open / close shutter (21) is opened for a predetermined time, and the developer is discharged from the developing device (10).

  In this way, the printer opens the open / close shutter (21) for a predetermined time based on the detection result of the toner density by the T sensor (16) as the toner density detecting means being equal to or less than the threshold density value D1. The developer is discharged from the developing device (10) only when the open / close shutter (21) is opened for a predetermined time. In such a configuration, for example, if toner supply is performed with the open / close shutter (21) always closed, or if the open / close shutter (21) is closed after the start of toner supply, it is kept closed until the toner supply is completed. The following becomes possible. That is, it is possible to avoid the situation where the developer containing the toner immediately after replenishment is discharged from the developing device (10), and to discharge only the developer whose toner density is lowered to the density value D1 or less. It becomes possible. Further, wasteful discharge of toner can be suppressed more reliably than before. Further, even if a large amount of developer is not forcibly discharged from the developing device (10) prior to replenishment, the developer containing toner immediately after replenishment is discharged from the developing device (10). To avoid. Therefore, it is possible to avoid development abnormality caused by excessive discharge of the developer.

  In the present invention, the “toner density detection result by the toner density detection means” means not the output signal value itself from the toner density detection means but the toner density value corresponding to the output signal value. In the example shown in the figure, the time when the toner density reaches the density value D1 is the time when the output voltage value from the T sensor (16) becomes the voltage value V1 that is the shutter operation threshold value. The control unit (100) does not perform a calculation process of converting the output voltage value from the T sensor (16) into a toner density value based on the graph of FIG. ) Drive control. Specifically, since it is agreed that the toner density is equal to or lower than the density value D1 and that the output voltage is equal to or higher than the voltage value V1, the control unit (100), when the output voltage becomes equal to or higher than the voltage value V1, The shutter solenoid (60) is driven.

  Further, in this printer, the carrier is also replenished simultaneously with the toner replenishment, and the magnetic carrier is replenished by the amount discharged as the opening / closing shutter (21) is opened. However, replenishment of the magnetic carrier is not necessarily performed during toner replenishment. You may carry out before and after toner replenishment. If the gradually degrading magnetic carrier is replaced with a new one little by little so as to suppress a decrease in toner chargeability over time due to the magnetic carrier, the carrier replenishment timing is not particularly limited.

  In FIG. 3 described above, the developing device 10 is configured to be detachable from the printer main body, the toner replenishing device 30, the carrier replenishing device 40, and the developer collecting device 50. When the printer is removed from the printer body, the engagement between the front end of the drive shaft 62 of the shutter solenoid 60 shown in FIG. 4 and the open / close shutter 21 is automatically released. Then, as shown in FIG. 5, the open / close shutter 21 is forcibly closed by the contraction force of the coil spring 23. As described above, the combination of the shutter solenoid 60 and the coil spring 23 functions as a link mechanism that forcibly closes the open / close shutter 21 by linking to the removal of the developing device 10 from the printer body. In such a configuration, since the opening / closing shutter 21 of the developing device 10 that is not attached to the printer body is forcibly closed, a situation in which the developer flows out from the discharge port (19) of the developing device 10 being transported is avoided. .

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described.
[Example 1]
FIG. 8 is a graph showing the relationship between the output voltage value from the T sensor (16) in the printer according to the first embodiment and the toner density of the developer present at the detection position of the T sensor. In the figure, the toner density value D1 is the above-described shutter operation threshold value and also the replenishment start threshold value. When the toner density becomes equal to or less than the density value D1, the printer opens the opening / closing shutter (21) for a predetermined time or starts toner replenishment based thereon. However, the replenishment of toner is started after the opening / closing shutter (21) is opened and closed for a predetermined time, instead of opening the opening / closing shutter (21) and replenishing toner at the same time. Then, when the toner density is equal to or higher than the density value D2 that is the supply stop threshold, the toner supply ends.

  FIG. 9 is a timing chart showing operation timings related to toner replenishment and shutter operation in the printer. The toner density of the developer in the developing device (not shown) gradually decreases with development as shown. When the toner density is lowered to the density value D1 or less, the opening / closing shutter (21) is immediately opened for a predetermined time. Specifically, the predetermined time is such that almost the entire amount of the developer located above the lower end of the discharge port (19) is opened and closed in the first storage portion and the second storage portion of the developing device (10). It is the length that can be discharged by opening the shutter (21). Therefore, when the opening / closing shutter (21) is opened for a predetermined time, the height level of the developer in the first storage portion and the second storage portion is lowered to the same level as the lower end of the discharge port (19).

  When the open / close shutter (21) opened for a predetermined time is closed, toner replenishment is started. Regarding toner replenishment to the developing means, if it is performed all at once, a significant deviation of the toner density occurs in the developer, and therefore it is generally replenished little by little. And in order to implement | achieve such replenishment, as shown in the figure, the intermittent drive which repeats the drive of a drive means for supply (for example, suction pump etc.) and a stop is often performed. In the present invention, “start toner replenishment” and “end toner replenishment” do not mean individual ON / OFF of the replenishment drive means in the intermittent operation. As indicated by the item “toner replenishment” in the bottom chart of the same figure, it means the start and end of the entire intermittent operation.

  As described above, in the toner replenishment, the toner is replenished little by little. Therefore, the toner density of the developer does not recover to the density value D2 immediately after the toner replenishment starts. It recovers little by little. For this reason, as indicated by the symbol t in the figure, the toner density becomes equal to or less than the density value D1 for a while after the start of toner supply. If the opening / closing control of the opening / closing shutter (21) based on the toner density detection result is performed during this period, the developer containing a large amount of toner just supplied may overflow from the discharge port (19). Therefore, the control unit (100) of the printer forcibly opens the open / close shutter (21) regardless of the toner density detection result when toner is supplied to the first storage unit and the second storage unit. It is comprised so that closing control may be implemented. Therefore, it is possible to reliably avoid wasteful discharge of toner due to overflow of the developer containing a large amount of toner just replenished from the discharge port (19).

Assume that the printing conditions are set as follows in the printer having the above configuration.
-Developer storage capacity in the storage section in a steady state: about 106 [cm ³ ]
-Developer capacity after opening of the shutter (21): 80 [cm ³ ]
Toner specific gravity: 1
・ Specific gravity of magnetic carrier: 3
-Weight mixing ratio of toner and magnetic carrier during toner replenishment: 20 to 80 (corresponding to a premix agent with a toner concentration of 20%)
Density value D1 (see FIG. 8): 5 [%]
Density value D2 (see FIG. 8): 8 [%]

Under such conditions, when the open / close shutter (21) is opened, the toner weight and carrier weight in the 80 [cm ³ ] developer (toner concentration 5%) remaining in the accommodating portion of the developing device (10) are 10 respectively. .9 [g] and 207.3 [g]. Further, the toner volume and the carrier volume are 10.9 [cm ³ ] and 69.1 [cm ³ ], respectively.

From this state, when the open / close shutter (21) is closed and the toner and the magnetic carrier are replenished at the above-mentioned weight mixing ratio until the toner density reaches 8%, the volume of the developer after replenishment is 105. .5 [cm ³ ]. The toner weight and carrier weight in the developer are 21.8 [g] and 221.8 [g], respectively.

Next, when the toner is consumed with the development and the toner concentration is lowered to 5 [%], the volume of the developer is lowered to 96.2 [cm ³ ]. The toner weight and carrier weight at this time are 12.5 [g] and 250.9 [g], respectively.

Further, when the opening / closing shutter (21) is opened from this state and the developer volume is reduced to 80 [cm ³ ], the developer discharge amount at that time becomes 16.2 [cm ³ ]. At this time, the toner weight and the carrier weight are 2.1 [g] and 42.2 [g], respectively. That is, when printing is performed under the above-described conditions, 2.1 [g] of toner is discharged from the developing device (10) corresponding to one toner supply.

On the other hand, it is assumed that the image forming conditions are set as follows in the image forming apparatus described in Patent Document 2 described above.
-Developer storage amount in the developing means at a normal overflow level: 100 [cm ³ ]
-Developer storage amount after lowering the overflow level: 80 [cm ³ ]
Toner specific gravity: 1
・ Specific gravity of magnetic carrier: 3
-Toner concentration of premix agent: 20 [%]
-Overflow level reduction condition: When the toner density is reduced to 5%, it is reduced.
Pre-mix agent replenishment conditions: After the overflow level is returned to the normal level, replenishment is performed until the toner density recovers to 8%.

This condition is almost the same as the above-described condition in the printer according to the first embodiment. When the toner density of the developer with the storage amount of 100 [cm ³ ] is reduced from 8 [%] to 5 [%], the storage amount of the developer is reduced to 91.8 [cm ³ ]. When the overflow level is lowered, 11.8 [cm ³ ] developer is discharged from the developing means. The toner weight in the discharged developer is 1.6 [g].

Next, after replenishment of the premix agent is started after the overflow level is returned to the original level, when the developer storage amount increases to 100 [cm ³ ] immediately before the overflow, the developer toner concentration is 7. It has increased to 5%. Thereafter, when the premix agent is replenished intermittently by 1 [cm ³ ], the replenishment amount of the premix agent required until the developer toner concentration recovers to 8 [%] is about 6 [cm ^3]. ]become. The toner weight that overflows during this time is about 1.2 [g]. Therefore, in the image forming apparatus described in Patent Document 2, when image formation is performed under the same conditions as those of the printer according to the first embodiment, 2.8 [g] of toner is provided for each replenishment. Is discharged from the developing device (10). Compared with this printer, the toner discharge amount corresponding to one replenishment is 0.7 [g] larger. This is because the printer discharges only a developer having a toner concentration of 5% or less, whereas the image forming apparatus discharges a developer having a toner concentration of 7.5% or more during replenishment. is there.

  FIG. 10 is a timing chart illustrating operation timings related to toner replenishment and shutter operation in the modified apparatus of the printer according to the first embodiment. In this modified apparatus, the shutter operation threshold and the replenishment start threshold are different. Specifically, while the shutter operation threshold is the density value D1, the replenishment start threshold is a density value D0 lower than this. Then, after the toner density is lowered to the density value D1 with the development and the opening / closing shutter (21) is opened for a predetermined time, toner replenishment is not started immediately, but the toner density is further lowered to the density value D2. At that time, toner supply is started.

  When the density values D0, D1, and D2 are set to 5 [%], 5.5 [%], and 8 [%], respectively, and printing is performed, when the open / close shutter (21) is opened, the toner density 5.5 [ %] Developer is discharged from the developing device (10). Compared with the case where the timing chart shown in FIG. 9 is realized, the developer whose toner density is higher by 0.5 [%] is discharged. Therefore, the amount of discharged toner corresponding to one replenishment is larger than when the timing chart shown in FIG. 9 is realized, but it is still about 2.5 [g], and the image described in Patent Document 2 is used. The value is smaller than that of the forming apparatus. In order to obtain the same discharge amount as that of the image forming apparatus, the density value D1 is increased to 5.9 [%], that is, the developer having a toner density of 5.9 [%] when the open / close shutter (21) is opened. Need to be set to discharge.

[Example 2]
In FIG. 2 described above, toner replenishment (and carrier replenishment) and toner density detection are performed on the developer accommodated in the first accommodating portion of the developing device (10). Further, the developer is discharged from the first container through the discharge port 19. Further, in FIG. 3 described above, the developer is transported from the front side to the back side in the drawing in the first housing portion where the first transport screw 14 is disposed. Further, the replenishing port (17) is disposed in the vicinity of the back end in the drawing of the first housing portion. After the toner and magnetic carrier replenished in the first storage portion are taken into the developer, the toner and magnetic carrier quickly enter the second storage portion and are transported through the second storage portion from the back side to the front side in the drawing. And it returns to the 1st accommodating part in the area | region of a near end, and is conveyed toward the back | inner side from the near side in the figure this time. At the time of this conveyance, after passing the detection position by the T sensor 16, it passes by the side of the discharge port (19). In such a circulation path, the toner and magnetic carrier immediately after replenishment move away from the discharge port (19), so even if replenishment is performed with the open / close shutter 21 open, the toner or magnetic carrier is immediately discharged. There is no discharge from the outlet (19). It is discharged after making a round of circulation. And it passes the detection position by the T sensor 16 at a slightly earlier stage than this discharge.

  As shown in FIG. 9, the toner concentration of the developer does not rapidly increase immediately after toner replenishment but starts to increase with a slight time lag immediately after replenishment. This is because the replenished toner does not immediately reach the detection position by the T sensor 16 but arrives after passing through the second storage unit.

  FIG. 11 is a timing chart illustrating operation timings related to toner replenishment and shutter operation of the printer according to the second embodiment. As shown in the figure, in this printer, toner supply is started with the open / close shutter (21) being opened by utilizing the fact that it takes a relatively long time for the supplied toner to reach the side of the discharge port. Then, the opening / closing shutter (21) is closed with a time lag of length t2 from the start. At this time, since the replenished toner and carrier have not yet reached the discharge position, even if toner replenishment is started with the open / close shutter opened, a situation where the toner just after replenishment is discharged is avoided. be able to.

  In such a configuration, the toner concentration can be recovered more quickly by starting the toner supply in the stage before the closing, instead of starting the toner supply after closing the open / close shutter. As shown in FIG. 3, in this printer, since the replenishing port 17 is arranged downstream of the discharge port 19 in the developer circulation direction, the toner is supplied from the start of toner replenishment. The time required to reach the discharge position can be secured for a very long time. If the positional relationship between the two ports is reversed, the toner will reach the discharge position soon after the start of replenishment. Therefore, the time lag t2 shown in FIG. 11 is set to a very short value such as less than 1 second. There must be. By disposing the replenishing port 17 on the downstream side of the discharge port, it becomes possible to start toner replenishment from a considerably earlier stage than in the case of disposing it on the upstream side.

  As described above, in the printer according to the first embodiment, when toner is supplied to the first storage unit by the toner supply device (30) which is a part of the supply unit, the detection result by the T sensor (16) is used. First, the control unit (100), which is a control means, is configured to perform control to forcibly close the open / close shutter (21). In this configuration, as described above, it is possible to reliably avoid the discharge of the toner immediately after the supply from the discharge port (19), as compared with the case where the toner supply is started prior to closing the opening / closing shutter (21). Can do.

  In the printer according to the second embodiment, the toner replenishing device (30) starts to replenish toner in the first storage unit, and then closes the open / close shutter (21) until the toner replenishment is completed. The control unit (100) is configured to perform control in which the shutter (21) is forcibly kept closed regardless of the detection result of the T sensor (16). In this configuration, as already described, the toner supply immediately after the replenishment is reliably avoided while the toner replenishment is started more quickly than when the open / close shutter (21) is closed. The toner density can be recovered.

  Further, in the printer according to the second embodiment, the developing device (10) is provided with stirring and conveying means that circulates and conveys the developer along the predetermined circulation path while stirring the developer in the housing portion, and the supply port (17) is provided. The developer is disposed downstream of the discharge port (19) in the direction in which the developer is circulated and conveyed. In this configuration, as already described, toner supply is started from an earlier stage and the toner density is recovered more quickly than in the case where the supply port (17) is disposed upstream of the discharge port (19). Can be made.

  In the printer according to the embodiment and each example, a link mechanism for forcibly closing the open / close shutter (21) is provided in linkage with the removal of the developing device (10) from the printer body. With this configuration, it is possible to avoid a situation in which the developer flows out from the discharge port (19) of the developing device 10 being transported.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a photoconductor, a developing device, and a part of a developer recovery device of the printer. FIG. 2 is a perspective view illustrating a developing device of the printer and peripheral devices. The side view which shows the opening-and-closing shutter of the state which opened the discharge port with the surrounding structure. The side view which shows the opening-and-closing shutter of the state which closed the discharge port with the surrounding structure. FIG. 2 is a block diagram showing a part of an electric circuit of the printer. 6 is a graph showing a relationship between an output voltage value from a T sensor of the developing device and a toner density of a developer present at a detection position of the T sensor. 6 is a graph showing a relationship between an output voltage value from a T sensor in the printer according to the first embodiment and a toner density of a developer present at a detection position of the T sensor. 6 is a timing chart showing operation timings related to toner supply and shutter operation in the printer. 6 is a timing chart showing operation timings related to toner replenishment and shutter operation in a modified apparatus of the printer. 9 is a timing chart illustrating operation timings related to toner replenishment and shutter operation of the printer according to the second embodiment.

Explanation of symbols

1 Photoconductor (latent image carrier)
10 Developing device (Developing means)
14 1st conveyance screw (a part of stirring conveyance means)
15 Second conveying screw (a part of stirring and conveying means)
16 T sensor (toner density detection means)
17 Supply port 18 Partition wall (part of stirring and conveying means)
19 Discharge port 21 Opening / closing shutter 23 Coil spring (part of link mechanism)
30 Toner supply device (part of supply means)
40 Carrier supply device (part of supply means)
60 Shutter solenoid (shutter drive means, part of link mechanism)
100 Control unit (control means)

Claims (5)

Provided in the developer accommodating portion for accommodating a developer containing toner and carrier, a replenishment port provided in the developer accommodating portion for replenishing toner and carrier, and provided in the developer accommodating portion for discharging the developer A developing means having a discharged outlet and a toner concentration detecting means for detecting the toner concentration of the developer in the developer accommodating portion;
Replenishment means for replenishing toner and carrier to the developer accommodating portion through the replenishment port;
A latent image carrier that carries a latent image developed by the developing means;
An image forming apparatus comprising: a control unit that controls driving of the developing unit and the replenishing unit.
An opening / closing shutter for opening and closing the discharge port is provided in the developing means, and a shutter driving means for driving the opening / closing shutter is provided, and the toner density detection result by the toner density detection means is based on a predetermined threshold value or less. An image forming apparatus characterized in that the control means is configured to perform control to open the opening / closing shutter for a predetermined period. The image forming apparatus according to claim 1.
The control means is configured to perform control to forcibly close the open / close shutter regardless of the detection result when toner is supplied to the developer accommodating portion by the supply means. An image forming apparatus. The image forming apparatus according to claim 1.
The opening / closing shutter is closed after the toner supply to the developer container is started by the replenishing means, and the opening / closing shutter is forcibly closed regardless of the detection result until the supply is completed. An image forming apparatus characterized in that the control means is configured to execute the control. The image forming apparatus according to claim 3.
The developing means is provided with stirring and conveying means for circulating and conveying the developer along a predetermined circulation path while stirring the developer in the developer accommodating portion, and the replenishing port is located downstream of the discharge port in the circulating and conveying direction of the developer. An image forming apparatus arranged on the side. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising a link mechanism for forcibly closing the open / close shutter linked to the removal of the developing means from the main body of the image forming apparatus.

Images