JPH0457083A - Liquid developing device - Google Patents

Abstract

PURPOSE:To stabilize the startup of the circulation of developer and to perform excellent development where a void image is not generated by making the force of attracting a recording medium to the aperture part of a developer supply groove stronger at the time from starting the driving of a negative pressure generating means till starting development than while the development is being performed. CONSTITUTION:When a recording action is started after a standby state, both electromagnetic valves 11 and 14 are turned on and the driving of a pump motor 12 is started. Since air does not flow from a valve 15 for adjusting negative pressure by making a supply pipe 9 in a shutoff state and turning on the electromagnetic valve 14, the attracting action of the motor 12 is all allotted for attracting the air from the aperture part of the developer supply grooves 31 and 32 through a gap between the surface of a developing head 3 and the surface of a recording paper. Then, the recording paper is surely attracted to the aperture part and contacts to the surface of the head 3, so that the aperture part is nearly tightly closed and the negative pressure in the grooves 31 and 32 rapidly becomes high. By turning off the electromagnetic valve 11, the developer is pumped to the grooves 31 and 32, the air flows from the valve 15, and the negative pressure in the grooves 31 and 32 is kept at a negative pressure adjusting level after it is lowered to the negative pressure adjusting level.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a liquid developing device employed in image forming apparatuses such as electrophotographic or electrostatic recording type copying machines, facsimile machines, printers, etc. relates to a liquid developing device that performs development using a developing head disposed facing a conveyance path of a recording medium on which an electrostatic latent image or the like is formed.

[Conventional technology]

A liquid developing device that develops an image to be developed on a recording medium by filling a developer supply groove extending in the width direction of the recording medium provided on the developing head surface facing the recording medium transport path with a developer is disclosed in, for example, Japanese Patent Laid-Open No. Publication No. 1794.77/1986, Japanese Patent Application Publication No. 1-18/1983
It is known from Publication No. 5569 and the like.

In this type of liquid developing device, negative pressure is generated in the developer supply groove by driving a negative pressure generating means such as a pump motor with the developer supply groove blocked by a recording medium such as electrostatic recording paper. By using this negative pressure, the recording medium is sucked to the developing head surface, and the developer supply groove is almost sealed, until the negative pressure reaches such a level that the developer in the developer tank can be sucked into the developer supply groove. The developer in the developer tank is supplied to the developer supply groove through a developer supply path forming means such as a supply pipe, and the developer in the developer supply groove is removed by forming a developer recovery path such as a recovery pipe. By circulating the developer between the developer tank and the developer supply groove while collecting the developer into the developer tank through the means, the developer supply groove is filled with the developer and the electrostatic latent image etc. on the recording medium is removed. The image to be developed is developed, and after the development is completed, the developer in the developer supply groove is collected into the developer tank.

[Problem to be solved by the invention]

However, if the suction force of the negative pressure generating means is set too large, the latent image on the recording medium will be damaged by the airflow flowing into the developer supply groove through the gap between the developing head surface and the recording paper during development. The adhered toner image is scraped off and a blank image appears. As a countermeasure for this, it is possible to set the suction force by the negative pressure generating means to a relatively small suction force that does not generate an image (the white area in the box below is indicated by "-"); Immediately after the drive of the device is started, the suction of the recording medium to the developing head surface becomes insufficient, and the start-up of the developer circulation becomes unstable, and as a result, the developer circulation does not start until some time. , even if the developer circulation has started, the period of instability will be longer, and if you wait for the developer circulation to stabilize before starting development, the speed of image formation will decrease, or conversely, the unstable period of the developer circulation will become unstable. It has been confirmed that there is a problem in that if development is started from a certain point, development defects may occur.

The present invention has been made in view of the problems of the prior art, and its purpose is to provide a stable start-up of developer circulation and to achieve good development without white areas forming an image. An object of the present invention is to provide a liquid developing device capable of performing the following steps.

[Means to solve the problem]

In order to achieve the above object, the liquid developing device of the present invention includes:
A developing head having an opening in the developing head surface facing the recording medium transport path and having a developer supply groove extending in the width direction of the recording medium, a developer tank containing the developer, and a developer tank containing the developer. A means for forming a developer supply path to the developer supply groove; a means for forming a developer recovery path from the developer supply groove to the developer tank; and a means for forming a developer recovery path from the developer supply groove to the developer tank; Negative pressure generating means generates negative pressure in the developer supply groove when the developer supply groove is blocked by the medium, and generates negative pressure in the developer supply groove to open the developer supply groove. In a liquid developing device that develops an image to be developed on a recording medium by filling the developer supply groove with the developer by circulating the developer between the developer tank and the developer supply groove while sucking the recording medium into the liquid developing device. During a predetermined period from the start of driving the negative pressure generating means until the start of the development, the force for attracting the recording medium to the opening of the developer supply groove is applied to a force greater than that during the development. It is characterized by:

[Effect]

In the present invention configured as described above, during a predetermined period from the start of driving the negative pressure generating means until the start of development,
By making the force that attracts the recording medium to the opening of the developer supply groove larger than that during development, the recording medium is reliably attracted to the opening of the developer supply groove and the negative pressure in the developer supply groove is reduced. The developer in the developer tank is reliably supplied into the developer supply groove through the developer supply path forming means, and during development, the suction force for white areas is switched to a relatively small level to the extent that no image is generated. It is something that works.

〔Example〕

A first embodiment in which the present invention is applied to a developing device of an electrostatic recording type recording device used in connection with an information processing device such as a computer will be described with reference to FIGS. 1 to 5.

FIG. 1 is a schematic configuration diagram of a recording apparatus.

First, to explain the outline of the operation of this image forming apparatus, in FIG. The part extends over the electrostatic recording head 2 and the developing head 3, and the tip thereof is held between the drive roller 4 and the pinch roller 5, and waits for the start of the recording operation and enters a standby state. . When the recording operation is started after the data processing of recorded information received from an information processing device (not shown) is completed, the developer supply groove 3 provided in the developing head 3
At 1.32, a developer is supplied from the per-develop tank 6 located below the developing head 3, and circulation of the developer begins between the two, and at the same time, the drive roller 4 and the feeding shaft 1 begin to rotate. An electrostatic latent image is recorded on the recording paper on the electrostatic recording head 2, and this electrostatic latent image is developed on the developing head 3 while the recording paper continues to be conveyed. Immediately before the developed image passes through the cutter 7, the cutter 7 is rotated to cut off the leading edge of the recording paper, and immediately after the trailing edge of the developed image passes through the cutter 7, the cutter 7 is rotated to cut the recording paper. , the rotation of the feeding shaft 1 and the drive roller 4 is stopped, while only the paper ejection roller 8 is rotated to eject the sheet-shaped recording paper onto a paper ejection tray (not shown).

Next, the liquid developing device of this embodiment will be described in detail. Second
As shown in the perspective view of the figure, two developer supply grooves 31 extending in the width direction of the recording paper are provided on the surface of the development head 3 facing the recording paper conveyance path of the square rod-shaped development head 3 elongated in the width direction of the recording paper.
．． 32 are provided. These two developer supply grooves 31
．． The upper front end of No. 32 in the figure is a developing device that accommodates the developer through a hole penetrating through the back side of the developing head surface as shown by the broken line in the central cross-section seen from the top rear side of FIG. 2 in FIG. 3. It is connected to a supply pipe 9 which is a means for forming a developer supply path from the liquid tank 6 to the developer supply grooves 31 and 32, and the other end is connected to a supply pipe 9 which is a means for forming a developer supply path from the liquid tank 6 to the developer supply grooves 31 and 32. It is connected to a recovery pipe 10 which is a means for forming a developer recovery path from the supply grooves 31 and 32 to the developer tank 6. The supply pipe 9 is provided with an electromagnetic valve 11 that switches the supply pipe 9 between a communication state and a cutoff state, and the recovery pipe 10 is provided with an opening of a developer supply groove 31 and 32 that is blocked with recording paper. A pump motor 12 is provided as a negative pressure generating means for generating negative pressure in the developer supply grooves 31 and 32 when the developer is in a state where the developer is in the developer supply groove 31 and 32. Further, on the side of the developing head 3 from the part of the recovery pipe 10 where the pump motor 12 is provided,
A negative pressure regulating valve 15 is also provided via a pressure sensor I3 and a solenoid valve 14 that outputs an ON signal when the negative pressure exceeds a set level which will be described later. Switching of both electromagnetic valves 11 and 14 and driving of the pump motor 12 are controlled by electromagnetic valve means and negative pressure control means provided in a control section 16 that controls the operation of the entire apparatus.

Here, both solenoid valves 1. The valves i and 14 are used to shut off the pipe section where they are installed when activated (ON), and to communicate when they are inactivated (OFF). It's okay.

In the above configuration, in the standby state, the pump motor 12
When the solenoid valve 11 is OFF and the supply pipe 9 is in communication, and the solenoid valve 14 is also OFF and the negative pressure adjustment valve is stopped, the development head 3 is in communication with the recovery pipe 10. The openings of the developer supply grooves 3], 32 on the surface are as follows:
Although it is blocked by the recording paper, there are minute irregularities on the surface of the recording paper, so the 3 sides of the developing head and the surface of the recording paper (
There is a small gap between the developing head (3 side),
The developer supply grooves 31, 32 communicate with the atmosphere through this gap. After this standby state, when the recording operation is started, both the solenoid valves 11 and 14 are turned on, and the pump motor 12 is turned on.
Start driving. By turning on the solenoid valve 11,
Supply pipe 9 is in a cutoff state, and solenoid valve 1 is closed.
4 is turned on, there is no inflow of air from the negative pressure adjustment valve 15, so that all the suction action of the pump motor 12 is directed to the developer through the gap between the surface of the developing head 3 and the surface of the recording paper. Directed to the suction of air from the openings of the supply grooves 31,32. As a result, the recording paper is reliably attracted to the opening and comes into close contact with the surface of the developing head 3, so that the opening is substantially sealed, and the negative pressure within the developer supply grooves 31 and 32 increases rapidly. Negative pressure in the developer supply grooves 31 and 32 flows into the developer tank 6.
When the pressure reaches a level large enough to pump up the developer in the developer into the developer supply grooves 31 and 32 (hereinafter referred to as the developer circulation level), the pressure sensor 13 that maintains this negative pressure at the set level outputs an output. Occur. The output of this pressure sensor 13 is used to control an IF to prevent development defects, which will be described later. Developer supply groove 31. When the negative pressure inside the pump motor 12 reaches a peak determined by the capacity of the pump motor 12, both the electromagnetic valves 11 and 14 are turned off in preparation for starting development. The peak point of this negative pressure may be detected by a pressure sensor, but in this embodiment, the time from the start of driving the pump motor 12 until the negative pressure reaches its peak is also determined in advance from the negative pressure characteristic curve. A timer is used which has been determined through experiments, starts counting when the pump motor 12 starts driving, and generates an output after this time t1, and both electromagnetic valves 11, 1.4 are turned on based on the output of this timer. Turn off solenoid valve 11
By F, the supply pipe 9 becomes in communication state,
The negative pressure in the developer supply grooves 31 and 32 causes the developer in the developer tank 6 to flow through the supply pipe 9 to the developer supply groove 31.
The developer is pumped up to 31°32, and then the developer is pumped up to
The developing solution flows through the developer supply grooves 31 and 32 so as to be filled with the recording paper that closes the opening, and the recovery pipe 10
The developer is circulated between the developer supply groove 31 , 32 and the developer tank 6 by returning to the developer tank 6 via the developer tank 6 . During this time, the solenoid valve 14 is also OFF, so air flows in from the negative pressure adjustment valve 15 and the negative pressure in the developer supply groove 31, 32 decreases to the negative pressure adjustment level. will be maintained. This negative pressure adjustment level is set at a level (hereinafter referred to as the development level) that allows stable circulation of the developer in a state in which development is performed by conveying the recording paper. When the negative pressure in the developer supply grooves 31 and 32 reaches this development level, the feeding shaft 1 and the drive roller 4 start rotating, and the recording head 2 starts recording the electrostatic latent image. As a result, the development period begins (hereinafter, the period from the start of driving the pump motor to the start of the development period is referred to as the start-up period). The point in time when this development level is reached may also be detected by a pressure sensor, but in this embodiment, after the negative pressure reaches its peak from the start of driving the pump motor 12, both electromagnetic valves 1.1, 1.4 OF
The period t2 during which the negative pressure decreases and reaches the development level due to F is experimentally determined in advance from the negative pressure characteristic curve.
A timer is used which starts counting when the pump motor 12 starts to drive, and generates an output after t2, and the feeding shaft 1, drive roller 4, and recording head 2 are started to be driven by the output of this timer. As a result, the electrostatic latent image recorded on the recording paper by the recording head 2 is conveyed onto the developing head 3, and developed by being supplied with developer from the openings of the developer supply grooves 31 and 32. At this time, the developer supply groove 32 on the downstream side in the recording paper transport direction not only performs a developing function, but also performs an excess developer removal function to remove excess developer attached to the recording paper. Even during development, the developer supply groove 32 is leaked from the gap between the developing head 3 and the surface of the recording paper due to minute irregularities on the surface of the recording paper.
This is thought to be due to the fact that air flows into the recording paper, and this air flow blows away excess developer that has adhered to the recording paper.

When the rear end of the electrostatic latent image on the paper passes through the developing head 3UIJJ and development is completed, both the electromagnetic valves 11 and 14 are turned on while the pump motor 12 is driven. By turning on the solenoid valve 11, the supply pipe 9 is cut off, and the pumping of the developer ρ from the developer tank 6 is interrupted, and by turning on the solenoid valve 14, the negative pressure adjustment valve 15 is shut off. Since the pump motor 12 continues to drive without air flowing in, the developer supply groove 31.3
Quickly remove most of the developer in the developer tank 6.
After this recovery, the entire suction action of the pump motor 12 is directed to sucking air from the openings of the developer supply grooves 31 and 32. Thereby, the meniscus developer and the like adhering to the corner formed by the upper part of the inner surface of the developer supply groove 31, 32 and the recording paper can be reliably sucked and collected.

Such suction and collection of the residual developer is performed for a set time t3 as a squeeze period, and when the trailing edge of the developed image passes the cutter 7, the cutter 7 is rotationally driven to cut the recording paper, and at the same time, the feed shaft is rotated. When the rotation of the pump motor 1 and the drive roller 4 is stopped, the drive of the pump motor 12 is stopped,
Moreover, both electromagnetic valves 11 and 14 are turned off. Figure 4(a)
is a timing chart for the above operation,
FIG. 5 is a flow chart thereof. Furthermore, Figure 4 (c
) shows the change over time in the negative pressure within the developer supply grooves 31 and 32. As shown in FIG.
Both electromagnetic valves 11.1 detect that the negative pressure in 1.32 reaches the developer circulation level and the pressure sensor 13 turns ON (YES in step 4) to start the developer circulation.
4, 0FF (step 7.8) and the start of conveyance of the recording paper to start development (step 6.9), so there is no possibility that the negative pressure in the developer supply grooves 31 and 32 will increase due to some abnormality. It is possible to prevent the development from occurring due to the developer not being circulated or due to unstable developer circulation due to the developer starting the development without any adjustment.

Next, a second embodiment of the liquid developing device according to the present invention will be described based on FIG. 4(b) and FIG. 6. The difference between this embodiment and the first embodiment is that in the first embodiment,
While the driving state of the pump motor 12 is kept the same throughout the start-up period, development period, and squeeze period, in this embodiment, a frequency converter 17 (a third During the start-up period and the squeeze period, the frequency 1-, which is higher than the frequency 1 during development, is provided.
The two points are that the driving state is changed so that the pump function is improved by supplying an alternating current of 1, and that the solenoid valve 11 is not provided in the supply pipe 9. FIG. 6 shows the flowchart 1 of the control, and FIG. 4(b) shows the timing chart.

During the start-up period, unlike the first embodiment, the supply pipe 9 is always in communication, but the developer supply groove 31
, 32 reaches the developer circulation level, all of the suction action of the pump motor 12 is directed to suction of air from the opening of the developer supply groove 31, 32, and the pump motor 12 ] 2, an alternating current with a higher frequency than during the development period is supplied, and a larger suction action than during development works, so the negative pressure in the developer supply grooves 31 and 32 is reliably raised to the developer circulation level. I can do it.

Thereafter, during the development period, an alternating current with a relatively low frequency is supplied to the pump motor 12 so as to produce a suction effect to the extent that no white image is generated. During the squeeze period, the pump motor 12/\By again supplying the alternating current of frequency 1-1, the developer supply groove 3], 32
It is also possible to reliably suction and collect the meniscus developer and the like adhering to the corner formed by the upper inner surface of the recording paper and the recording paper.

In each of the above-mentioned embodiments, the end time of the suction period for the residual developer after the end of development coincides with the end time of conveyance of the recording paper, but the present invention is not limited to this, and the developer supply groove 31.3
2. From the viewpoint of preventing staining of the recording paper due to suction of the developer remaining on the recording paper, etc., it is possible to set it independently of the end time of conveyance of the recording paper.

Further, in order to better remove the surplus developer on the recording paper, a separate head dedicated to sucking the surplus developer may be provided on the downstream side of the L image head 3 in the recording paper transport direction. Further, the number of developer supply grooves on the surface of the developing head 3 is not limited to two (or may be three or more).

Furthermore, in each of the above embodiments, the developer is supplied to the developing head 3 from one developer tank 6, but it is possible to supply different colors of developer to each other through appropriate liquid path switching means such as valves. It is also possible to make a developing device for color development by selectively connecting to any one of the plurality of developer tanks accommodated therein and a tank containing a cleaning solution for cleaning the developer supply groove etc. when changing colors. can. Further, a set of the developing head 3 and developer tank 6 as in each of the above embodiments is provided for each color, and the developing head 3 is mounted on a suitable elevating means, and any one of the developing heads 3 is selectively moved to the recording paper conveyance path. By facing the camera, it can also be used as a developing device for color development.

Further, in the above embodiment, a liquid developing device employed in an electrostatic recording type image forming apparatus has been described, but it can also be employed in an electrophotographic type image forming apparatus.

〔Effect of the invention〕

As described above, according to the present invention, during the predetermined period from the start of driving the negative pressure generating means until the start of development,
By making the force that attracts the recording medium to the opening of the developer supply groove larger than that during development, the recording medium is reliably attracted to the opening of the developer supply groove and the negative pressure in the developer supply groove is reduced. Since the developer in the developer tank is reliably supplied into the developer supply groove through the developer supply path forming means, the start-up of the developer circulation can be stabilized, and during development, no white areas are formed. Since the suction force is switched to a relatively small level that does not generate an image, it is possible to perform good development without forming an image in white areas.

[Brief explanation of the drawing]

1 to 4 and 6 are drawings for explaining a liquid developing device according to an embodiment of the present invention, and FIG. 1 is an electrostatic recording method using the liquid developing device according to an embodiment. A schematic configuration diagram of the image forming apparatus, FIG. 2 is a perspective view of the developing head,
FIG. 3 is a central cross-sectional view of the developing head seen from the top back side of FIG. 2, FIG. Timing chart of the device, (b) is a timing chart of the liquid developing device according to the second embodiment, (C) is a diagram showing the change in negative pressure in the developer supply groove over time, and FIG. 5 is the first embodiment FIG. 6 is a flowchart explaining the operation of the liquid developing device according to the second embodiment. 3...Development head, 31.32.Developer supply groove, 6.
...Developer tank, 9.. Supply pipe, 10.. Recovery pipe, 11.14.. Solenoid valve, 12.. Pump motor.

Claims (1)

[Claims] A developing head having an opening in the developing head surface facing the recording medium transport path and having a developer supply groove extending in the width direction of the recording medium, a developer tank containing the developer, and a developer tank containing the developer. A means for forming a developer supply path to the developer supply groove; a means for forming a developer recovery path from the developer supply groove to the developer tank; and a means for forming a developer recovery path from the developer supply groove to the developer tank; Negative pressure generating means generates negative pressure in the developer supply groove when the developer supply groove is blocked by the medium, and generates negative pressure in the developer supply groove to open the developer supply groove. In a liquid developing device that develops an image to be developed on a recording medium by filling the developer supply groove with the developer by circulating the developer between the developer tank and the developer supply groove while sucking the recording medium into the liquid developing device. During a predetermined period from the start of driving the negative pressure generating means until the start of the development, the force for attracting the recording medium to the opening of the developer supply groove is applied to a force greater than that during the development. A liquid developing device characterized by: