JPH082680Y2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a two-component development type image forming apparatus having a toner recovery mechanism.

[Prior art and its problems]

Conventionally, one type of image forming apparatus using a dry developer,
There is a recycling system that enhances the usage efficiency of the developer. In this method, the developer collected by the cleaner is returned to the developing device and used again for development. In this case, normally, a communication pipe is installed from the cleaner to the developing device, and the recovered developer is returned through this communication pipe.

On the other hand, a unit-type image forming apparatus, which has improved maintenance operability, is often used. This is a detachable unit of a member such as a developing device, a cleaner, or a photosensitive drum that requires regular maintenance.

Therefore, the recycling-type unit-structured image forming apparatus is excellent in both developer utilization efficiency and maintenance operability, but has the following problems.

The process unit in which the developing device, the cleaner and the photoconductor drum are integrated may be inadvertently inverted during transportation. When the process unit is reversed, the developer charged in the developing device flows back into the communication tube. Even if the once inverted process unit is set in the image forming apparatus as it is, most of the developer flowing back into the communication tube has not returned to the original developing device. So in this case,
At the time of initial setting, the amount of the developer in the developing device has already decreased to a much smaller amount than the regular amount.

When a two-component developer composed of toner and carrier is used as the developer, the toner density is controlled. In this case, the toner concentration sensor detects the toner concentration in the developer, and the toner is replenished according to the detected value. This toner concentration sensor normally has a proper range of the amount of developer that can normally detect the toner concentration. Therefore, as described above, when the developer flows back into the communication tube and falls below the appropriate range, the toner density control is hindered. As a result, various image defects such as image blurring and blurring when the toner concentration is excessively lowered, and background stains when the toner concentration is excessively increased are caused.

Therefore, in order to prevent the backflow of the developer, a method has been proposed in which the developer discharge port of the communication pipe is provided with a shutter that opens and closes the discharge port in association with the operation of the developing device and the cleaner. However, such an interlocking shutter has a complicated structure, is prone to failure, and is expensive.

[Purpose of device]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive image forming apparatus capable of preventing abnormalities in toner concentration control due to backflow of a developer with a simple structure and stably obtaining a good image.

[Key points of device]

In order to achieve the above-mentioned object, the present invention is detachably mountable to the main body of an image forming apparatus, and contains a developing section for individually accommodating a developer consisting of a toner and a carrier and a reinforcing toner,
A cleaning unit for removing residual toner on the image carrier,
A toner collecting mechanism for collecting the residual toner from the cleaning unit to the developing unit, a toner concentration detecting unit for detecting the toner concentration in the developer, and a toner replenishment output according to the detection value of the toner concentration detecting unit. In an image forming apparatus including an image forming process unit having a toner replenishing unit that replenishes toner based on a signal, the toner replenishment from the toner concentration detecting unit is performed for a predetermined period during initial operation of the image forming process unit. The point is to provide a toner replenishment control means for prohibiting the operation of the toner replenishment means regardless of the signal output, and to discharge the developer flowing back to the toner recovery mechanism to the developing section during the toner replenishment prohibition period. It is what

[Example of device]

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 8.

FIG. 7 is a sectional view showing a process unit U and its peripheral members in an electrophotographic printer as an embodiment of the present invention. In the figure, the photosensitive drum 1 is rotatably supported by the frame 2 of the process unit U. The photosensitive drum 1 is driven and rotated at a predetermined speed in the arrow A direction by a driving device (not shown). A charger 3 for uniformly charging the peripheral surface of the photosensitive drum 1 to a predetermined polarity is provided near the upper peripheral surface of the photosensitive drum 1. An image exposure unit 4 is formed on the downstream side of the charger 3 with respect to the rotation direction of the photosensitive drum 1. Here, the recording light R is projected onto the surface of the photosensitive drum 1 from an opening (not shown) provided in the frame 2 to form an electrostatic latent image.

A developing unit 5 is arranged downstream of the image exposure unit 4.
The developing device 5 adopts a two-component developing method, and in this example, a two-component magnetic phenomenon agent formed by mixing magnetic particles as a carrier and toner is used. The developing device 5 is generally composed of a toner hopper portion 5a that stores a replenishment toner t and a developer hopper portion 5b that agitates the developer d and supplies the developer d to the photosensitive drum 1. An input port 5c for inputting the toner t is provided above the toner hopper portion 5a, and a lid 5d is attached to the input port 5c. A stirring roll 5e is provided inside the toner hopper section 5a, and stirs the toner t charged from the charging port 5c. A replenishment port 5f is formed at the boundary between the toner hopper unit 5a and the developer hopper unit 5b, and a toner replenishment roll 5g is arranged in the replenishment port 5f. By rotating the toner replenishing roll 5g, an appropriate amount of toner t is replenished to the developer hopper section 5b side.

A stirring roll 5h is also provided at the bottom of the developer hopper portion 5b. A toner concentration sensor 5i is provided on the side wall of the hopper near the stirring roll 5h. Toner density sensor 5i in this example
Is a differential transformer system, detects a change in inductance according to a change in toner concentration, and outputs a voltage signal based on the change to a control unit (not shown). The control unit rotates the toner replenishing roll 5g by an appropriate amount according to the output signal, and the toner t
To replenish. On the photosensitive drum 1 side of the stirring roll 5h,
The developing sleeves 5j are rotatably arranged side by side. The developing sleeve 5j is rotated in the direction of arrow B by a driving device (not shown),
With the rotation, the developer d is conveyed in the same direction.
A doctor blade 5k is arranged above the developing sleeve 5j. The developer d that is conveyed following is the doctor blade 5k.
Is regulated to a predetermined layer thickness. The developer d whose layer thickness is regulated is conveyed to the closest position (developing position) Dp to the photosensitive drum 1 with the rotation of the developing sleeve 5j, and electrostatically transfers to the surface of the photosensitive drum 1 here. . As a result, the electrostatic latent image is developed into a toner image.

A transfer device 6 is disposed downstream of the developing device 5. The toner image is now electrostatically transferred onto the transfer paper p. A cleaner 7 is provided on the downstream side of the transfer device 6. The cleaner 7 of the present example is a blade type cleaner, and the tip of the cleaning blade 7a is brought into pressure contact with substantially the entire area in the circumferential surface width direction (axial direction) of the photosensitive drum 1, and the untransferred toner t ′ remaining on the surface of the photosensitive drum 1 is left. Scrape off. The surface of the photoconductor drum 1 from which the untransferred toner t ′ has been scraped off is returned to the position where the charger 3 is provided, and is used for new image formation.

A toner recovery device is provided between the cleaner 7 and the developing device 5 to return the untransferred toner t ′ scraped and removed into the developing device 5. The toner collecting device of this example is a cleaner 7
A coil spring 9 as a toner conveying means is inserted in a communication pipe 8 that communicates the internal spaces of the developing device 5 and the developing device 5. The communication pipe 8 projects from the bottom side wall of the cleaner 7, extends obliquely upward to the upper part of the developer hopper portion 5b of the developing device 5, and extends from the side wall of the developer hopper portion 5b to the inside thereof. In the developer hopper portion 5b, as shown in FIG. 8, the end portion of the communicating pipe 8 is extended to above the central portion of the stirring roll 5h, and the toner discharge port 8a is cut out on the pipe wall below the tip portion thereof. There is.

The coil spring 9 is laid in a U-shape over the entire length of the bottom of the cleaner 7 (direction along the axial direction of the photosensitive drum 1) and the entire distribution pipe 8. The end of the coil spring 9 extending to the bottom of the cleaner 7 is fixed to a drive terminal (not shown) provided on the inner surface of the cleaner side wall (the side wall opposite to the side wall on which the communication pipe 8 is provided). The drive terminal is driven and rotated by an external drive means.

The drive terminal (not shown) rotates the drive terminal, and the coil spring 9 rotates together with the drive terminal. By the rotation of the coil spring 9, the collected toner scraped off by the cleaning blade 7a and falling to the bottom of the cleaner is conveyed along the extending direction of the coil spring 9. The collected toner is conveyed in the direction of the arrow C in the communication tube 8 with the rotation of the coil spring 9, and eventually reaches the end of the communication tube 8 extended into the developer hopper portion 5b, and then from the discharge port 8a to the arrow D. As shown by, the toner is dropped and discharged to the developer hopper portion 5b.

In this example, as the image forming process unit U, the photosensitive drum 1, the charger 3, the developing device 5, and the cleaner 7 are integrally detachably unitized. Generally, the image forming process unit is set to have a fixed life depending on the durability of the photoconductor and the developer. In the process unit U of this example, the number of printed sheets is counted by the counter of the printer control unit, and the printing operation is prohibited when the set limit number of sheets is reached. In this case, it is necessary to reset the counter for the number of printed sheets to the initial value (0) every time the process unit U is replaced, and therefore the reset mechanism Cr shown in FIGS. 5 and 6 is provided. Process unit U
On the outer surface of the frame side wall 2a of the developing device 5 portion, there is rotatably provided a truncated circle gear 10 with a tooth portion cut off over a certain range of the circumference. The missing circle gear 10 is arranged so as to be capable of meshing with a drive gear 11 fixed to a rotary shaft 5h1 of a stirring roll 5h (see FIG. 7). A stopper cam 12 and a switch cam 13 are fixed to the rotary shaft 10a of the truncated gear 10. Stopper cam 12
Has a pair of flat portions 12a and 12b on the circumferential surface. A stopper 14 is brought into contact with the peripheral surface of the stopper cam 12. The stopper 14 is made of an elastic material and is provided upright along the side wall 2a on the convex portion 2b on the outer surface of the frame side wall 2a. The switch cam 13 has an oval shape, and a micro switch is provided on its peripheral surface.
Fifteen actuators 15a are in contact. The micro switch 15 is connected to a CPU 16 provided in a control unit on the printer body side via a connector (not shown). CPU16
Has a counter for counting the number of printed sheets, manages the life of the process unit U described above, and controls the toner density according to the number of printed sheets according to a program described later.

In the process unit U before use, as shown in FIG. 5, the switch cam 13 is in a state of pushing down the actuator 15a of the micro switch 15. In this case, the stopper 14 abuts on one flat surface portion 12b on the peripheral surface of the stopper cam 12, and the above-mentioned switch-down state is reliably held. When such a process unit U is attached to the printer main body, the micro switch 15 and the CPU 16 of the control unit are electrically connected.

When the power of the printer is turned on, the warm-up operation is started before printing is started. In this warm-up operation, the stirring roll 5h of the developing device 5 is rotated. With the rotation of the stirring roll 5h, the truncated circle gear 10, the stopper cam 12 and the switch cam 13 connected to the stirring roll 5h via the drive gear 11 rotate integrally in the counterclockwise direction. On this occasion,
As shown by the chain double-dashed line in FIG. 6, the stopper cam 12 rotates while pushing and bending the abutting stopper 14. The missing gear 10
The meshing with the drive gear 11 is released at the time of rotating about 130 degrees. After this, due to the elastic force of the stopper 14, the missing circle gear
10, the stopper cam 12 and the switch cam 13 are integrally rotated in the same direction, and as shown in FIG. 6, the stopper 14 comes into contact with the other flat surface portion 12a of the peripheral surface of the stopper cam 12 to stop the rotation. In this state, the switch cam 13 is at the position where the pressing of the micro switch 15 is released, and the micro switch 15 is turned off. By turning off the micro switch 15, CP
The number of printed sheets counter in U16 is reset to the initial value (0 sheets).

The counter reset operation described above is performed only when the unused process unit U is used for the first time. Therefore, the counter is not inadvertently reset during use of the process unit U, and normal life management of the process unit U can be stably performed.

FIG. 1 is a block diagram showing a circuit configuration for the printer controller to control the toner density. Near the process unit installation part of the printer body,
A drive unit Du is provided, and a toner replenishing solenoid 17 is installed here. The toner supply solenoid 17 and the toner supply roll 5g in the process unit U are connected by a drive transmission mechanism. Toner supply solenoid 17
Is electrically connected to the CPU 16 of the control unit via the driver 18. Therefore, the CPU 16 drives and controls the driver 18 according to the output signal of the toner sensor 5i, and the toner replenishment solenoid 17
Operate. As a result, the rotation of the toner supply roll 5g is controlled, and the toner t is appropriately supplied into the developer hopper 5b. As a result, the toner concentration in the developer d is kept within the proper range.

Here, the toner density control operation according to the number of printed sheets in this example will be described with reference to the flowchart of FIG.

The operator presses the print key to start printing (ST
1) First, it is determined whether the number of printed sheets counted by the counter is 100 sheets or less (ST2). Here, the number of prints is 100
If there are less than one sheet, unconditionally turn off the toner supply solenoid (ST3) to prohibit toner supply.

When the number of printed sheets is more than 100 in the above-described step of determining the number of printed sheets (ST2), the normal feedback type toner density control is performed. That is, first, the toner concentration is judged (ST4), and the toner concentration is 9 wt%.
If it is more than%, the toner is sufficiently present, so the toner replenishment solenoid is turned off (ST3) and the toner is not replenished. If the toner concentration is less than 9 wt%, the toner in the developer is insufficient, so turn on the toner replenishment solenoid (ST5) and rotate the toner replenishment roll for a predetermined time.
A certain amount of toner is replenished in the developer.

By repeating the above operation flow at regular intervals, the toner concentration in the developer can be stably maintained within an appropriate range for obtaining a good image. Incidentally, the proper range of the toner concentration in this example is 7 to 11 wt%.

Further, as described above, by prohibiting the toner replenishment when the number of printed sheets is 100 or less, it is possible to reliably prevent the occurrence of the toner density control failure due to the backflow developer in the initial use of the process unit. The reason is as follows.

In FIG. 3, the process unit U is reversed and the communication pipe 8 is shown.
The developer hopper 5b when the developer is caused to flow back inside and the process unit U is attached to the printer for printing.
FIG. 6 is a graph showing the relationship between the amount of developer inside and the number of printed sheets.
According to this, it can be seen that when the number of printed sheets is about 60, the amount of developer in the developer hopper 5b has recovered to the prescribed amount of developer, 250 g. Therefore, it is possible to determine that most of the backflow developer can be returned during the printing of 100 sheets, even in consideration of variations such as the backflow rate of the developer.

FIG. 4 shows the developer hopper 5b when the toner density control according to the number of printed sheets shown in FIG. 2 is executed.
6 is a graph showing the relationship between the toner concentration in the developer inside and the number of printed sheets. FIG. Unused process unit U for printer
Mount and start printing. The initial toner concentration in the developing device 5 of this process unit U is set to 11 wt%. In FIG. 4, since the toner is not replenished until 100 sheets are printed, the toner density gradually decreases with the printing. When the number of printed sheets reaches 100,
The toner concentration has dropped to about 9 wt%. However, in the developing device 5 of this example, the proper toner concentration for obtaining a good image is set to 7 to 11 wt%. Therefore, the number of printed sheets is 0
It can be seen that a good image can be stably obtained without replenishing the toner for 100 sheets.

After the number of printed sheets exceeds 100, the prohibition of toner replenishment is lifted, but since the developer amount has reached the normal amount, the normal toner concentration control is normally performed and the toner concentration is 7 to 11 wt. It is held securely within the range of%.

From the experimental results shown in FIGS. 3 and 4, at the time when the total number of printed sheets (counter count value) is 100, if the prohibition of the toner replenishment is released and the normal toner density control is performed, the process unit U It can be seen that a good image can be stably formed over the entire life period of the service life from the beginning of use.

It should be noted that the present invention should not be limited to the above specific embodiment, and various modifications can be made within the technical scope of the present invention.

For example, the toner supply prohibition period is 0-10
Not only between 0 sheets, but depending on image forming conditions such as developing characteristics,
An appropriate period may be set from the initial use of the image forming process unit.

[Effect of device]

As described above in detail, according to the present invention, the toner is prevented from being replenished for a predetermined period from the initial use of the image forming process unit, and the image is formed by the toner supply. It is possible to prevent the occurrence of toner concentration control failure by returning the developed developer to the developing device and then controlling the toner concentration. Therefore, even if the image forming process unit, which has been turned over before use, is mounted on the image forming apparatus as it is to form an image, a good image can be stably obtained over the entire life of the image forming process unit. . Further, the adverse effect of the backflow of the developer can be eliminated only by changing the operation control program set in the control section of the image forming apparatus main body, so that the image forming apparatus having the above-mentioned advantages can be provided at low cost. Become.

[Brief description of drawings]

FIG. 1 is a block diagram showing a toner density control system in an electrophotographic printer as one embodiment of the present invention, FIG. 2 is a flow chart showing the operation of the toner density control, and FIG. 3 is the electrophotographic printer. Graph showing the relationship between the amount of developer and the number of printed sheets in
FIG. 4 is a graph showing the relationship between toner density and the number of printed sheets in the electrophotographic printer, and FIGS. 5 and 6 are explanatory views showing the configuration and operation of the reset mechanism in the electrophotographic printer, respectively. FIG. 7 is a sectional view showing an image forming process unit of the electrophotographic printer, and FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7 showing a collected toner discharging portion of the image forming process unit. 1 ... Photosensitive drum 5 ... Developing device 5a ... Toner hopper section 5b ... Developer hopper section 5g ... Toner supply roll 5h ... Agitation roll 5i ... Toner sensor 5j ... Development sleeve 7 ... Cleaner 7a ... Cleaning blade 8 ... Communication tube 8a ... Exhaust Exit 9 ... Coil spring 16 ... CPU (central processing unit) Cr ... Reset mechanism (counter)

Claims (1)

[Scope of utility model registration request] 1. A developing unit detachably mountable on the main body of the image forming apparatus, the developing unit accommodating a developer composed of toner and carrier and the replenishing toner individually, and the cleaning unit removing residual toner on the image carrier. And a toner recovery mechanism for recovering the residual toner from the cleaning unit to the developing unit, a toner concentration detecting unit for detecting the toner concentration in the developer, and an output according to the detection value of the toner concentration detecting unit. In an image forming apparatus provided with an image forming process unit having a toner replenishing means for replenishing toner based on a toner replenishing signal, the toner concentration detecting means is operated for a predetermined period during initial operation of the image forming process unit. Providing a toner replenishment control means for prohibiting the operation of the toner replenishment means regardless of the output of the toner replenishment signal An image forming apparatus, wherein the developer flowing back to the toner collecting mechanism is discharged to the developing section during the period.