JP2007298638A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the deterioration of image quality by hardly causing the change of the diameter of a developing roller. <P>SOLUTION: A color printer 1 forming an image based on image information is equipped with a photoreceptor drum 21, a rotary type developing device 22, a fixing part 4, an image forming operation recognition means 91 and a rotating position control means 92 for a rotary frame. The image forming operation recognition means 91 recognizes that image forming operation is performed. The rotating position control means 92 for the rotary frame controls the rotating position of the rotary frame 222 so that the first developing unit equipped with a developing roller 224 formed of material whose linear expansion coefficient is the smallest out of the plurality of developing units 221 may be located at a position nearest to the fixing part 4 when the image forming operation recognition means 91 does not recognize that the image forming operation is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes an image forming apparatus, in particular, a developing device that is disposed in the vicinity of a fixing device that performs development by supplying a developer to an electrostatic latent image carrier and fixes an image on a sheet. The present invention relates to an image forming apparatus.

An image forming apparatus capable of forming a color image includes a plurality of developing units each having a developer of a different color. In order to reduce the size of an image forming apparatus, there is an image forming apparatus including a rotary developing device in which a plurality of developing devices are arranged around a rotatable rotating frame (see Patent Document 1). In such an image forming apparatus, the developer of each color is supplied from each developing device to the photosensitive drum while the rotating frame rotates, thereby forming a toner image on the photosensitive drum. The toner image on the photosensitive drum is transferred to a sheet. After the toner image on the photosensitive drum is transferred to the sheet, the toner image is fixed on the sheet by being heated and pressurized by the fixing unit. After the toner image is fixed on the paper, it is discharged out of the image forming apparatus.
JP 2005-24575 A

  In the image forming apparatus described in Patent Document 1, since the toner image on the paper is heated by the heated roller in the fixing unit, the temperature of the fixing unit is higher than that of other portions. Therefore, the rotary developing device provided in the vicinity of the fixing unit may be affected by the toner stored in the developing device being dissolved by the heat of the fixing unit. In addition, the diameter of the developing roller provided in the developing device may change (expand) due to the heat of the fixing unit. If the toner inside the developing device is dissolved or if the diameter of the developing roller changes, the image quality may deteriorate.

  An object of the present invention is to make it difficult for the image quality to deteriorate by making the diameter of the developing roller difficult to change.

  An image forming apparatus according to a first aspect of the present invention is an image forming apparatus that forms an image based on image information, the electrostatic latent image carrier, a rotary developing device, a fixing device, and an image forming operation recognition unit. And a rotation position control means of the rotation frame. An electrostatic latent image is formed on the electrostatic latent image carrier based on image information. The rotary developing device includes a plurality of developing devices that store a developer supplied to the electrostatic latent image carrier, and a rotating frame that supports the plurality of developing devices. The fixing device is provided in the vicinity of the rotary developing device, and fixes the image on the paper. The image forming operation recognition unit recognizes that the image forming operation is being performed. The rotation position control means of the rotary frame is developed with a material having the smallest linear expansion coefficient among the plurality of developing devices when the image forming operation recognition means does not recognize that the image forming operation is being performed. The rotational position of the rotary frame is controlled so that the first developing device including the roller is positioned closest to the fixing device.

  In this image forming apparatus, an electrostatic latent image is formed on an electrostatic latent image carrier based on image information. A developer is supplied from the rotary developing device to the electrostatic latent image carrier to form an image. The image formed on the electrostatic latent image carrier is transferred to a sheet. The image transferred to the paper is fixed on the paper by the fixing device. Here, it is recognized whether the image forming operation is being performed by the image forming operation recognizing means. When it is not recognized that the image forming operation is recognized by the image forming operation recognizing unit, a developing roller formed of a material having a small linear expansion coefficient among the plurality of developing units by the rotation position control unit of the rotating frame The first developing device provided is controlled so as to be positioned at a position close to the fixing device.

  Here, since a developing device having a developing roller formed of a material having a small linear expansion coefficient is disposed at a position close to the fixing device, the diameter of the developing roller is hardly changed. For this reason, the image quality is unlikely to deteriorate as the diameter of the developing roller changes.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the developing roller of the first developing device is made of metal. Here, the linear expansion coefficient of aluminum as an example of the metal is 10 ⁻⁶ / ° C.

  Here, since a developing device including a developing roller formed of a metal such as aluminum having a small linear expansion coefficient is disposed at a position closest to the fixing device, the diameter of the developing roller is hardly changed.

  The image forming apparatus according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein the developing roller of the first developing device carries an electrostatic latent image as compared with the developing roller of another developing device. The largest gap with the body.

  Here, since the developing roller of the first developing device is far from the electrostatic latent image carrier, the deterioration of the image quality can be reduced even when the developing roller expands due to the heat of the fixing unit.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the first developer accommodates a magnetic developer therein.

  In the present invention, the image quality can be prevented from being lowered by making the diameter of the developing roller difficult to change.

1. Configuration FIG. 1 shows a color printer 1 which is an image forming apparatus in which an embodiment of the present invention is adopted. FIG. 1 is a schematic diagram for showing the arrangement of each component, and details of each part are omitted.

  The color printer 1 is connected to a computer (not shown) or the like, and is a device that can print a color image on paper based on image information sent from an external computer or the like.

  The color printer 1 includes an image forming unit 2 that forms an image on a sheet based on image information, a sheet conveying unit 3 that conveys the sheet, and a fixing unit 4 that fixes an image formed by the image forming unit 2 on the sheet. A paper storage unit 5 that stores the paper, a discharge unit 6 that discharges the paper to the outside of the color printer 1, and a toner replenishment unit 7.

  The image forming unit 2 includes a photosensitive drum 21, a rotary developing device 22, a charging device 23, a laser unit 24, a cleaning device 25, and a drive mechanism 26.

  The photosensitive drum 21 (electrostatic latent image carrier) is a member on the surface of which an electrostatic latent image is formed, and is disposed almost at the center of the color printer 1. The photosensitive drum 21 is a drum-shaped member, and a rotation shaft is provided in a direction orthogonal to the paper surface of FIG. An intermediate transfer belt 211 for transferring a toner image on the photosensitive drum 21 to a sheet is disposed below the photosensitive drum 21 in the vicinity of the photosensitive drum 21.

  The rotary developing device 22 is a member disposed adjacent to the photosensitive drum 21 and is a cylindrical portion. The rotary developing device 22 has four developing units 221 and a rotary frame 222. The rotation frame 222 is a member in which four plate-like members 226 are arranged at equal intervals on a rotation axis parallel to the rotation axis of the photosensitive drum 21, and four spaces are formed by the four plate-like members 226. Is formed. Developers 221 that store toners of different colors are disposed in the four spaces. The developing device 221 includes a container body 223 and a developing roller 224. The container body 223 has a shape in which a cylinder is divided into four in the circumferential direction, and has an opening extending in the longitudinal direction. In addition, toner to be supplied to the photosensitive drum 21 is stored inside the container body 223. Here, the four container main bodies 223 store therein nonmagnetic yellow toner, nonmagnetic cyan toner, nonmagnetic magenta toner, and magnetic black toner, respectively. The developing roller 224 is a columnar member that extends in the same direction as the direction in which the rotation shaft of the rotary developing device 22 extends, and is a member that is disposed in the opening. The developing roller 224 is a member for supplying toner to the surface of the photosensitive drum 21. As shown in FIG. 2, distance regulating rollers 225 for maintaining the distance between the photosensitive drum 21 and the developing roller 224 are disposed at both ends of the developing roller 224. Here, FIG. 2 is a diagram showing the relationship between the rotary developing device 22 and the photosensitive drum 21. The distance regulating roller 225 is a member on a disk having a larger radius than the developing roller 224.

In the configuration as described above, when the photosensitive drum 21 and the developing roller 224 are opposed to each other, the developing roller 224 of the developing unit 221 storing the nonmagnetic toner (yellow, cyan, magenta toner) and the photosensitive roller are accommodated. The distance between the photosensitive drum 21 and the photosensitive drum 21 is 0.1 mm, and the distance between the developing roller 224 of the developing unit 221 storing the magnetic toner (black toner) and the photosensitive drum 21 is 0.1 mm. Held at 3 mm. Further, the developing roller 224 used in the developing device 221 in which black toner is stored is a cylindrical member formed of a magnet disposed inside and aluminum that can rotate on the outer periphery thereof, and stores toner other than black. The developing roller 224 used in the developing unit 221 is a rubber roller in which a foamed silicon roller is formed on a rotating shaft made of stainless steel or the like, and solid urethane rubber is coated on a columnar foamed silicon on the surface thereof. Here, the linear expansion coefficient of aluminum is 10 ⁻⁶ / ° C., and the linear expansion coefficient of urethane rubber is 10 ⁻⁴ / ° C.

  The rotating frame 222 is a member in which four plate-like members 226 are arranged at equal intervals on a rotating shaft extending in the same direction as the rotating shaft of the photosensitive drum 21, and the four plate-like members 226 are arranged. As a result, four spaces are formed. Developers 221 that store toners of different colors are disposed in the four spaces. In the rotary developing device 22, the rotary frame 222 is arranged so that the developing device 221 storing magnetic toner (black toner) is located closest to the fixing unit 4 except during the image forming operation. The rotational position of is controlled.

  The charging device 23 is a device for charging the surface of the photosensitive drum 21, and is disposed on the upper side of the photosensitive drum 21.

  The laser unit 24 is a member disposed on the upper side of the rotary developing device 22 and is a portion for irradiating a laser beam to form an electrostatic latent image based on image data on the photosensitive drum 21. .

  The cleaning device 25 is a device for removing deposits such as residual toner remaining on the photosensitive drum 21, and in the present color printer 1, cleaning is performed on the entire photosensitive drum 21 in the axial direction above the photosensitive drum 21. A blade is provided.

  As shown in FIG. 2, the drive mechanism 26 is a mechanism for rotating the rotary developing device 22, and includes an input gear 261, a second gear train 262 that rotates the input gear 261, and a second gear train 262. And a motor (drive source) (not shown) connected thereto. The input gear 261 is a member that transmits power from the second gear train 262 and transmits the transmitted power to the rotary frame 222. The input gear 261 includes a pair of disk-shaped members 26a and a pair of disk-shaped members 26a. And a shaft member 26b to be connected. The pair of disk-shaped members 26 a are formed with gear teeth that mesh with the gear teeth of the annular portion 22 b of the rotating frame 222. The shaft member 26 b is provided in parallel with the rotation shaft of the rotary developing device 22. The second gear train 262 is a portion for transmitting power from the motor and transmitting the power transmitted from the motor to the input gear 261, and is configured by a plurality of gears. A motor shaft is fixed to one of the plurality of gears.

  The paper transport unit 3 has a transport path that continues from the paper storage unit 5 through the image forming unit 2 and the fixing unit 4 to the discharge unit 6.

  The fixing unit 4 is disposed below the rotary developing device 22 in proximity to the rotary developing device 22, and includes a heating roller 41 and a pressure roller 42. The heating roller 41 is a member for melting toner that forms an image formed on a sheet by heat, and is disposed on the upper side of the pressure roller 42. During the fixing operation, the temperature of the heating roller 41 is about 150 ° C.

  The paper storage unit 5 is a part disposed at the lower part of the color printer 1 and has a paper feed cassette 51.

  The discharge unit 6 is disposed at the top of the color printer 1.

  The toner replenishing portion 7 is a portion for replenishing toner into the developing device 221 and is disposed on the upper side of the photosensitive drum 21. The toner supply unit 7 includes four toner containers 71 and four toner supply pipes 72 provided corresponding to the toner containers.

  Each of the four toner containers 71 is a box-like member that stores toner to be replenished in the developing device 221, and is arranged in a direction perpendicular to the paper surface of FIG.

  The toner replenishment pipe 72 is a member that replenishes the toner in the toner container 71 into the developing device 221 and is a pipe-shaped member that extends in one direction. The toner supply pipe 72 has an upper retracted position (a position indicated by a solid line in FIG. 1) and a supply position (a two-dot chain line in FIG. 1) where the tip of the toner supply pipe 72 enters the inside of the developing device 16 below. The position indicated by Further, the toner supply pipe 72 has an opening at the tip, and the tip is inserted into the developing device 221 to supply toner into the developing device 221.

  As shown in FIG. 4, the color printer 1 further includes a temperature adjustment device 8 for the fixing unit 4 and a rotation position control device 9 for the rotation frame 222.

  The temperature adjustment device 8 of the fixing unit 4 includes two cooling fans 81 (see FIG. 3; only one cooling fan 81 is shown in FIG. 3), and the CPU (control unit 100) executes the program, thereby FIG. As shown in FIG. 6, the replenishment time detection means 82, the cold air supply amount control means 83, and the temperature adjustment means 84 of the heating roller 41 function. Here, FIG. 3 is a diagram showing a positional relationship between the fixing unit 4 and the cooling fan 81, and FIG. 4 is a block diagram showing the control unit 100.

  As shown in FIG. 3 (only one is shown in FIG. 3), the two cooling fans 81 are provided on both sides of the space above the heating roller 41 of the fixing unit 4, that is, the front side and the back side in FIG. This is an apparatus for supplying cold air between the heating roller 41 and the rotary developing device 22 in order to prevent the heat of the heating roller 41 from being transmitted to the rotary developing device 22. More specifically, one cooling fan is provided to take outside air into the apparatus (the space above the heating roller 41), and the other cooling fan is provided to discharge the air inside the apparatus to the outside. Cold air is supplied and discharged between the rotary developing device 22 and the heating roller 41 by the pair of cooling fans 81. The cooling fan 81 rotates at a predetermined rotational speed during printing and toner replenishment operation. The cooling fan 81 rotates at half the rotational speed during printing and toner replenishment operation except during printing and toner replenishment operation. is doing.

  The replenishment time detection means 82 is a means for detecting the toner replenishment time. Specifically, the amount of consumed toner is detected by counting the number of dots of the image formed from the time of toner replenishment to the present, and development is performed by subtracting from the amount of toner present in the developing device 221 at the time of toner replenishment. The amount of toner present in the container 221 can be detected. When the toner amount inside the developing device 221 is less than a predetermined amount, it is determined that the toner replenishment time is reached.

  The cool air supply amount control means 83 controls the number of revolutions of the cooling fan 81 so that the number of revolutions of the cooling fan 81 at the time of printing operation and toner replenishment is twice that at times other than the time of printing operation and toner replenishment.

  The temperature adjusting means 84 of the heating roller 41 is a means for lowering the temperature of the heating roller 41 from 150 ° C. to 90 ° C. when toner is supplied.

  The rotation position control device 9 of the rotation frame 222 is a device that controls the rotation position of the rotation frame 222 of the rotation developing device 22, and the image forming operation recognition unit 91 is executed by the CPU (control unit 100) executing a program. And functions as a rotation position control means 92 of the rotation frame 222.

  The image forming operation recognition unit 91 is a unit that determines whether an image forming operation is being performed.

  When the image forming operation is not performed, the rotation position control unit 92 of the rotation frame 222 is arranged so that the developing device 221 that stores black toner therein is positioned closest to the fixing unit 4. Control the rotational position of In other words, the rotational position of the rotary frame 222 is controlled so that the developing device 221 that stores the black toner provided with the developing roller 224 formed of aluminum having a small linear expansion coefficient is positioned closest to the fixing unit 4. The image forming operation recognition unit 91, the rotation position control unit 92 of the rotation frame 222, and the rotation developing device 22 constitute a developing device.

2. Operation The image forming operation and the rotational position control operation of the rotary frame 222 will be described. Here, the rotational position control operation of the rotary frame 222 is shown in the flowchart of FIG.

  In this color printer 1, it is determined whether or not an image formation command has been issued (S1). When an image formation command is issued (YES in S1), when image data is transmitted from the computer, laser light is irradiated from the laser unit 24 to the photosensitive drum 21 whose surface is charged by the charging device 23. The When the electrostatic latent image is formed on the surface of the photosensitive drum 21 in this way, the rotating frame 222 of the rotary developing device 22 rotates so that the developing unit 221 storing the first color toner is positioned at the developing position. The rotational position is controlled. That is, the developing device 221 is rotated so that the developing roller 224 of the developing device 221 that stores the first color developer faces the photosensitive drum 21 (S3). Then, the toner inside the developing device 221 is supplied onto the photosensitive drum 21 by the developing roller 224 of the developing device 221. Next, it is determined whether or not development has been completed for all colors (S5). If not completed, the process returns to step S3 to form the next color image. Steps S3 to S5 are repeatedly executed until development of all colors is completed.

  In this way, the toner is sequentially supplied onto the photosensitive drum 21, and the color image formed on the photosensitive drum 21 is transferred onto the sheet conveyed from the paper feed cassette 51 via the intermediate transfer belt 211. Is done. The sheet on which the color image is formed is conveyed to the fixing unit 4 and the color image is fixed on the sheet. Thereafter, the paper is conveyed to the discharge unit 6 and discharged from the discharge unit 6 to the outside of the color printer 1.

  If no image forming command is issued (NO in S1), the developing unit 221 (developing unit 221 including the developing roller 224 formed of aluminum having a small linear expansion coefficient) that stores black toner is connected to the fixing unit 4. The rotational position of the rotary frame 222 is controlled so as to be closest to (S2).

Next, the toner supply operation will be described with reference to FIG. Here, FIG. 6 shows a flowchart of the toner replenishment operation. After the image forming operation as described above is performed (S11), the number of dots of the image formed by the image forming operation is counted (S12), and the image formation is performed. The number of dots of the image that has been operated is added to the previous cumulative dot count (the cumulative number of dots of the image formed so far from the previous toner replenishment), and the cumulative dot count after image formation is calculated. (S13). From this cumulative dot count, the amount of toner consumed up to now is detected. The amount of toner present in the developing device 221 is detected by subtracting the amount of toner consumed from the amount of toner in the developing device 221 present at the time of the previous toner supply (S14).

  Thereafter, it is determined whether or not the amount of toner existing in the developing device 221 is equal to or less than a predetermined amount, that is, whether or not it is a toner replenishment time (S15). If it is not the toner replenishment time (NO in S15), the process waits for the next image forming operation (S19). On the other hand, when it is the toner replenishment time (YES in S15), the developing device whose toner amount is a predetermined amount or less is moved to the toner replenishment position, that is, the position where the toner replenishment pipe 72 can be inserted. Then, the toner supply pipe 72 is moved downward so that the tip of the toner supply pipe 72 is inserted into the developing device 221. The toner is replenished from the toner replenishment pipe 72 into the developing unit 221 with the tip of the toner replenishment pipe 72 being inserted into the developing unit 221. At this time, the temperature of the heating roller 41 of the fixing unit is lowered from 150 ° C. to 90 ° C. (S16). At the same time, the number of rotations of the cooling fan 81 is doubled when the image forming instruction is on standby. For this reason, the amount of cool air supplied to the fixing unit 4 increases (S17).

  When the toner replenishment operation is completed, the rotation amount of the cooling fan 81 is returned to the rotation amount at the time of waiting for the image formation command, and the temperature of the heating roller 41 of the fixing unit 4 is returned to 150 ° C. (S18). Thereafter, it waits for the next image forming operation (S19).

  Here, since the amount of cold air supplied between the fixing roller 41 and the rotary developing device 22 during toner replenishment is increased and the temperature of the heating roller 41 of the fixing unit 4 is lowered, the heat of the fixing unit 4 is reduced. Transmission is interrupted between the fixing unit 4 and the rotary developing device 22. For this reason, the developing unit 221 is affected by heat at the time of toner replenishment, that is, the toner in the developing unit 221 is welded because it is softened by the heat of the fixing unit 4, or between the photosensitive drum 21 and the developing unit 221. It is possible to prevent the distance from changing. For this reason, it is possible to prevent toner deterioration and image quality deterioration.

  Further, when waiting for an image formation command, the rotation position of the rotary frame 222 is controlled, and the developing device 221 having the developing roller 224 formed of aluminum having a small linear expansion coefficient is most at the fixing unit 4. Located close. That is, the developing device 221 having the developing roller 224 that is least affected by the heat of the fixing unit 4 is positioned closest to the fixing unit 4, and the developing roller 224 is less likely to expand due to heat. For this reason, it is possible to prevent deterioration in image quality.

  The developing device 221 including the developing roller 224 having the longest distance between the photosensitive drum 21 and the developing roller 224 in a state where the photosensitive drum 21 and the developing roller 224 face each other is located at a position closest to the fixing unit 4. Therefore, even when the developing roller 224 expands, the distance between the developing roller 224 and the photosensitive drum 21 does not become extremely narrow. For this reason, it is possible to prevent deterioration in image quality.

3. Other Embodiments (a) In the above embodiment, the color printer 1 has been described. However, the present invention is not limited to this and may be a multifunction machine, a copier, or the like.

  (B) In the above embodiment, the toner replenishment time is detected from the dot count of the image, but the present invention is not limited to this, and may be detected by an optical sensor or the like.

  (C) Further, a member (a plate or the like) that changes the air direction may be disposed in the vicinity of the cooling fan 81, and the air that changes the air direction may be operated when supplying toner to supply the cooling air to the fixing unit 4.

  (D) Further, the developing roller disposed in the developing unit for storing the black toner may not be formed of aluminum but may be formed of stainless steel.

  (E) In the above embodiment, the cooling fan 81 forms a cold air layer between the heating roller and the rotary developing device 22 to block heat transfer between the heating roller and the rotary developing device. The invention is not limited to this, and the heat may be blocked by cold water or the heat may be blocked by another substance.

1 is an overall schematic sectional view of a color printer 1. FIG. FIG. 3 is a perspective view illustrating a rotary developing device 22 and a photosensitive drum 21. The figure which shows the position of the fixing | fixed part 4 and the cooling fan 81 (The figure seen from the left side of FIG. 1 (a side wall is abbreviate | omitted)). FIG. 3 is a block diagram of a temperature control device 8 of the developing device 221. 6 is a flowchart of a rotation position control operation of the rotation frame 222. 10 is a flowchart of toner supply operation.

Explanation of symbols

1 Color printer (image forming device)
4 Fixing unit 7 Toner replenishing unit (replenishing device)
8 Fixing Unit Temperature Control Device 21 Photosensitive Drum (Electrostatic Latent Image Carrier)
41 Heating roller 81 Cooling fan (cool air supply means)
82 Supply timing detection means 83 Cold air supply amount control means 84 Heat roller temperature control means 91 Image forming operation recognition means 92 Rotational position control means 221 of the rotating frame 222 Developer 222 Rotating frame 224 Developing roller

Claims (4)

An image forming apparatus that forms an image based on image information,
An electrostatic latent image carrier on which an electrostatic latent image is formed based on image information;
A rotary developing device including a plurality of developing devices that store the developer to be supplied to the electrostatic latent image carrier, and a rotating frame that supports the plurality of developing devices;
A fixing device provided in the vicinity of the rotary developing device and fixing an image on a sheet;
Image forming operation recognition means for recognizing that an image forming operation is being performed;
When the image forming operation recognizing unit does not recognize that the image forming operation is being performed, the first developing includes the developing roller formed of a material having a small linear expansion coefficient among the plurality of developing devices. A rotation position control means for the rotation frame for controlling the rotation position of the rotation frame so as to position the device at a position close to the fixing device;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the developing roller of the first developing device is made of metal.   3. The image forming apparatus according to claim 1, wherein the developing roller of the first developing unit has a largest gap with the electrostatic latent image carrier as compared with a developing roller of another developing unit. The image forming apparatus according to claim 1, wherein the first developing device stores a magnetic developer therein.

Images