JP2000211175A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a driving frequency of image signals and eventually increase an image-forming speed by adhering a developer to a recording medium by a first pulse and a third pulse and returning the developer adhering onto a first electrode or in the vicinity of the first electrode to a developer carrier by a second pulse. SOLUTION: A pulse 42 and a pulse 44 are impressed to a return electrode 40 and an independent electrode 36 from a controller 38. A developer 18 is separated from a developer-holding roller 12 and flown. A group of the flown developer adheres to a part of a recording medium 28, thereby forming dots. Some of the developer 18 separated from the developer-holding roller 12 adheres on the return electrode 40 or independent electrode 36. A pulse of an opposite polarity (a negative polarity in this example) is impressed to the return electrode 40 from the controller 38 to return the developer 18 on the return electrode 40 to the developer-holding roller 12. A layer of the developer sufficient for forming next pixels (dots) by an equal hole 34 is formed to the outer periphery of the holding roller 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder developer jet type image forming apparatus in which a powder developer carried on a developer carrier is caused to fly by an electric force and adhere to a recording medium.

[0002]

2. Description of the Related Art As a powder developer injection type image forming apparatus,
Some are disclosed in U.S. Pat. No. 5,477,250. The image forming apparatus includes a developer carrying roller for carrying a charged powder developer, a back electrode facing the developer carrying roller at a predetermined interval, and a back electrode for supplying the developer on the developer carrying roller. A power source for creating an electric field that is energized toward A partition is arranged between the developer carrying roller and the back electrode, and a space through which a recording medium can pass is formed between the partition and the back electrode. The partition has a plurality of through holes formed in a portion located in a region where the developer carrying roller and the back electrode face each other. Also, the partition wall,
Individual electrodes are provided around each through hole, and each individual electrode is connected to a driving device.

According to this image forming apparatus, an image signal corresponding to an image to be created is applied to an individual electrode. At this time, the image signal has a polarity that electrically urges the developer held on the developer carrying roller toward the back electrode. Therefore, the urging force generated by the application of the image signal and the urging force of the electric field formed between the developer carrying roller and the back electrode cooperate with each other to face the individual electrode to which the image signal is applied. A group of the developer is separated from the developer carrying roller, reaches a recording medium between the partition wall and the back electrode through the corresponding through hole, and a dot of the developer is formed on the recording medium. Then, a target image is created on the recording medium by the collection of dots.

[0004]

Incidentally, some of the developer separated from the developer carrying roller adheres to individual electrodes arranged around the through hole without passing through the through hole. . This is because the image signal applied to the individual electrode generates an electric field that urges the developer on the outer periphery of the developer carrying roller in the through hole or a portion slightly larger than the individual electrode to the back electrode, and the image signal is This is because the polarity attracts the developer. If it is attempted to continue the flying of the developer, that is, the formation of dots through the through holes while leaving the attached developer as it is, the following adverse effects occur. In the above-described conventional image forming apparatus, when an image signal is applied to the individual electrode, the developer is discharged from the through-hole, and during and after that, the developer carrying roller rotates by a predetermined amount, and further the same individual electrode is used. If another (next) image signal is applied, the next ejection from the same through hole is performed. Since the carrying roller is rotating in this manner, the positions on the outer periphery of the carrying roller where the developer that flies in these two discharges are provided before flying are different parts.
However, as described above, the developer on the outer periphery of the developer carrying roller at a portion slightly larger than the through-hole or the individual electrode may be separated in one discharge, so that the development which flies in the two discharges is performed. The site on the outer periphery of the carrying roller where the agent was (or would be) before each flight may overlap slightly. Then, the developer is first discharged from the through-hole, and after a predetermined time, when the developer is to be applied again to the same individual electrode so as to fly again, a part of the developer to be fly is already separated and the individual electrode is separated. A situation can occur such as sticking on top. In such a case, it is impossible to obtain a sufficient amount of the developer in the second flight. This adverse effect is remarkable when the rotation speed of the developer carrying roller is low. In order to solve the above-mentioned problems, the rotation speed of the developer carrying roller is increased to increase the moving speed of the developer carried on the outer periphery of the roller. Even if this measure is taken, the application of the image signal as described above to the same individual electrode is usually performed a plurality of times, and many times,
The developer adheres to the individual electrodes each time, and the developer gradually accumulates. As a result, the electric field strength at which the image signal tries to separate the developer held on the developer carrying roller decreases with time, and eventually the developer cannot be sufficiently separated.

As a measure for solving the above-mentioned adverse effects,
After the application of the image signal for flying the developer, a pulse having the same polarity as the developer is applied to the individual electrode to return the developer to the developer carrying roller. In this method, it is assumed that the same polarity pulse is applied at the moment when the developer flying toward the dot formation passes through the through hole. At this time, the developer adhered on the individual electrodes can be returned to the developer carrying roller, but at the same time, the electric field for urging the flying developer toward the back electrode is strengthened, and the flying developer is accelerated. become. Then, the developer collides with the recording medium at a high speed, and furthermore, a repulsive force is applied between the developer particles charged to the same polarity, and the developer spreads greatly on the recording medium. This impairs the resolution of the image. Therefore, it is desirable that a pulse having the same polarity as the developer applied to the individual electrode is applied only after the flying developer arrives on the recording medium. However, in such a case, there is a limit even if an attempt is made to increase the driving frequency of the image signal applied to the individual electrodes for the purpose of flying the developer.

In a powder developer injection type image forming apparatus,
It is an object of the present invention to increase the driving frequency of the above-mentioned image signal and consequently to increase the image forming speed.

[0007]

SUMMARY OF THE INVENTION The image forming apparatus of the present invention has been made to solve the above-mentioned problem, and has a structure in which a charged powder developer is carried and the developer is moved in a predetermined direction. A developer carrier to be conveyed, a partition wall made of an insulating material, disposed opposite to the developer carrier, and having a through hole in a region facing the developer carrier, and a partition made of an insulating material; A first electrode provided on the upstream side of the through-hole with respect to the transport direction of the agent, a second electrode provided near the through-hole and not provided with the first electrode, and a first electrode. First
Is applied at the first timing, and then the first
A first control unit that applies a second pulse having a polarity opposite to that of the first pulse at a second timing, and a first timing that is the same as the start of the application of the first pulse, to the second electrode. A second control unit for applying a third pulse.

Further, in the above three pulses, the first
The third pulse and the third pulse separate the developer passing through the opposing portion between the first electrode and the second electrode from the developer carrier, fly the developer through the through hole, and sandwich the developer with the partition wall interposed therebetween. The opposite side of the carrier is attached to the recording medium being conveyed, and the second pulse returns the developer adhered on or near the first electrode to the developer carrier again.

[0009]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an image forming section 10 in a powder developer injection type image forming apparatus according to the present invention.
The schematic configuration of is shown. The image forming section 10 has a developer carrying roller (developer carrying member) 12 made of a conductive material. The developer carrying roller 12 is rotatably supported in a direction indicated by an arrow 14. Further, the developer carrying roller 12
Is connected to a first bias power supply 16 so that a predetermined voltage (in this embodiment, a negative bias voltage V _B1 ) can be applied. A powdered developer 18 is carried on the outer periphery of the developer carrying roller 12, and the developer 18 is charged to a predetermined polarity (negative in this embodiment).

Below the developer carrying roller 12, a back electrode roller (back electrode) 20 is provided in parallel with the developer carrying roller 12 at a predetermined distance from the developer carrying roller 12. The back electrode roller 20 is rotatably supported in a direction indicated by an arrow 22. Also, the back electrode roller 2
0 is connected to the second bias power supply 24 so that a predetermined voltage (positive bias voltage V _{B2 in} this embodiment) can be applied. The values of the bias voltages V _B1 and V _B2 are
The negatively charged developer 18 carried on the developer carrying roller 12 is attracted toward the rear electrode roller 20 by an electric field formed between the developer carrying roller 12 and the back electrode roller 20 due to a potential difference between the developer carrying roller 12 and the back electrode roller 20. However, the adjustment is performed so that the developer 18 is not separated from the developer carrying roller 12 by only the suction force.

The developer carrying roller 12 and the back electrode roller 2
A partition 26 is arranged between the two. The distance L ₁ between the developer carrying roller 12 and the partition 26 is equal to the developer carrying roller 1.
In order to prevent the developer 18 held in 2 from being scraped off by the contact with the partition 26, a small gap is provided between the two or the contact pressure between the two is set to a minimum. On the other hand, the distance L ₂ between the back electrode roller 20 and the partition 26
The space 30 is formed such that the recording medium 28 (for example, paper or resin film) can pass between them and, as described later, the developer 18 attached to the recording medium 28 does not contact the partition 26. To be set.

The partition 26 is formed of a thin plate made of a non-conductive material. As shown in FIGS. 1 and 2, a part of the partition wall 26, that is, the developer carrying roller 12 and the back electrode roller 2.
A plurality of holes 34 penetrating the partition wall 26 are provided at predetermined intervals on a line parallel to the central axis of the developer carrying roller 12 in a portion included in a region (printing region 32) where 0 faces. Is formed. As shown in FIG. 2, one surface of the partition wall 26 facing the developer carrying roller 12 has
Two electrodes are arranged surrounding 4. First, a return electrode 40 is provided on the upstream side of each hole 34 with respect to the rotation direction of the developer carrying roller 12 (the direction of arrow 14). The width of the return electrode 40 is substantially equal to or slightly larger than the width of the corresponding hole 34 in the direction perpendicular to the rotation direction of the developer carrying roller 12. Next, a ring-shaped individual electrode 36 close to a horseshoe shape is provided in a portion around the hole 34 where the return electrode 40 is not provided. Then, the return electrode 40
Is connected to the controller 38 via a lead portion 41 extending upstream from it, and the individual electrode 36 is connected to the controller 38 via a lead portion 37 extending therefrom downstream with respect to the rotation direction of the developer carrying roller 12. ing. The individual electrode 36 and the return electrode 40 can be formed by a known technique (for example, etching, printing).

In the present embodiment, the individual electrode 36 and the return electrode 40 are provided on the surface of the partition 26 facing the developer carrying roller 12 as shown in FIGS. It may be provided on the opposite surface or inside the partition 26.

As shown in FIG. 3, the controller 38 comprises:
An output unit 46 that outputs an image signal corresponding to an image created by the image forming apparatus, a return waveform control unit 48 that individually processes signals output from the output unit 46, and a flying waveform control unit 50 are provided. Return waveform control unit 4 from output unit 46
8. The signal output to the flight waveform control unit 50 includes only ON / OFF signals corresponding to each pixel (dot).
The return waveform control unit 48 generates a pulse 42 (see FIG. 1) in response to the input ON / OFF signal and, as will be described later, transfers the developer attached to the return electrode 40 to a developer carrying roller. The reverse polarity pulse 52 for returning to the above is again superimposed and applied to the return electrode 40. Flight waveform control unit 50
Is a pulse 44 corresponding to the input on / off signal.
(See FIG. 1) is generated and applied to the individual electrodes 36.

When the recording medium 28 is conveyed to the print area 32 during the image producing operation of the image producing section 10 thus constructed, the recording medium 28 is synchronized with the recording medium 28 and the controller 3
8, the pulse 42 and the pulse 44 are applied to the return electrode 40 and the individual electrode 36. Pulse 42 applied at this time
And pulse 44 have positive polarity.

As a result, the return electrode 40 and the individual electrode 36
And between the developer carrying roller portion facing these,
A new electric field for urging the negative developer 18 held by the developer carrying roller portion toward the back electrode roller 20 is formed. The newly formed electric field is combined with the electric field already formed between the developer carrying roller 12 and the back electrode roller 20 by the first and second bias power supplies 16 and 24, and the developer carrying A group of the developer 18 carried on the roller portion is separated from the developer carrying roller 12 and caused to fly.

The group of the developer that has flown passes through the corresponding hole 34 and adheres to the portion of the recording medium 28 facing the hole 34 to form a dot.

Some of the developer 18 separated from the developer carrying roller 12 adheres to the return electrode 40 or the individual electrode 36. Then, a reverse polarity pulse 52 (here, a negative polarity) is applied to the return electrode 40 from the controller 38, and the developer 18 on the return electrode 40 is returned to the developer carrying roller 12, and the next pixel (dot) 2.) A sufficient developer layer is formed on the outer periphery of the carrying roller 12 for formation. In order to form the next pixel by the same hole 34, it is sufficient to return the developer 18 on the return electrode 40 in consideration of the moving direction (arrow 14) of the outer periphery of the support roller 12.

However, in particular, when a plurality of rows of through holes 34 are provided in the partition wall 26 and the arrangement thereof is arranged in a staggered state with a high density, the discharge from one of the holes 34 is slightly smaller than that of the through holes 34 or the individual electrodes 36. A large portion of the developer 18 on the outer periphery of the developer carrying roller 12 is separated, and at the time of the separation, a part of the developer 18 that should fly in a discharge from a hole in the vicinity thereof is peeled off onto the individual electrode 36. It is easy for it to adhere. With such a situation in mind, the controller 38 applies a reverse polarity pulse (here, a negative polarity) to the individual electrode 36 to apply the developer 18 on the individual electrode 36.
May be returned to the developer carrying roller 12.

A target image is created from a set of a large number of dots formed by repeating these operations. In addition,
The developer 18 attached to the recording medium 28 is transported together with the recording medium 28 to a fixing step (not shown) where it is heated and melted and fixed to the recording medium 28.

The return waveform controller 48 returns the return electrode 4
The first signal 54 applied to 0 will be described with reference to FIG. 4 together with the second signal 56 applied to the individual electrode 36 from the flying waveform control unit 50. The first signal 54 is a series of signals including the pulse 42 and the opposite polarity pulse 52 described above, and the second signal 56 is a series of signals including the pulse 44 described above. Here, FIG. 4 illustrates a portion of the first signal 54 and the second signal 56 in one preferred embodiment of the present invention.

First, at time 0, both the first signal 54 and the second signal 56 have a positive polarity (a polarity opposite to that of the developer). By these applications, the developer carrying roller 1
2 is separated from the roller 12,
To fly.

In this embodiment, the developer 18 separated from the developer carrying roller 12 at time 0
Each electric field strength and each interval are set so as to pass through the through hole 34. In the powder developer ejection type image forming apparatus, the developer 18 that separates and flies usually takes the form of a single spindle, but until the developer 18 passes through the through-hole 34 (FIG. 4).
, The signal 44 of the positive polarity is continuously applied to the individual electrode 34).

On the other hand, after time 2, to the return electrode 40, a signal of a polarity for returning the developer 18 on the return electrode 40 to the support roller 12, that is, a signal 52 of a negative polarity is applied. The application of the negative signal 52 continues until time 5, which is sufficient to return the developer 18 on the return electrode 40 to the support roller 12. Since the application of the negative polarity starts at the same time as the developer 18 separated from the carrying roller 12 passes through the through-hole 34, the same hole 34 is used regardless of whether the rotation speed of the developer carrying roller 12 is slow (FIG. 5) or fast (FIG. 6). The developer 18 sufficient to form the next pixel (dot) can be returned to the outer periphery of the carrying roller 12.

After the time when the developer 18 on the return electrode 40 returns to the outer periphery of the support roller 12, a signal for forming the next pixel (dot) can be applied to the return electrode 40 and the individual electrode 36. . Therefore, as a result, it is possible to increase the drive frequency when the image signal output unit 46 outputs a signal.

A signal having a potential of 0 (zero) is applied to the individual electrode 36 from time 3 to time 6. This is because, when a positive polarity is applied, the developer 18 is separated from the support roller 12 more than necessary, and a part of the developer 18 after passing through the through hole 34 is attracted to the individual electrode 36 and the partition 26
When a negative polarity is applied, an electric field is generated in which the flying speed of the developer 18 after passing through the through hole 34 is accelerated more than necessary, and the developer 18 is scattered on the recording medium 28. That's why.

A negative polarity signal is applied to the individual electrode 36 from time 6 to time 7. This is the individual electrode 3
For the purpose of preventing streak-like noise or the like occurring in the developer layer on the outer periphery of the developer carrying roller 12 due to the accumulation of the developer 18 on the developer carrying roller 6, the developer 18 once adhered to the carrying roller 12 is removed.
It is for moving to the side.

The above description shows one embodiment of the present invention, and the present invention can be variously improved. For example, in the embodiment shown in FIGS. 7A and 7B, the return electrode 40 is expanded in the upstream direction or in the upstream left and right direction with respect to the rotation direction of the developer carrying roller 12 (the direction of arrow 14).
Accordingly, the developer layer control area on the outer periphery of the developer carrying roller 12 expands in the upstream direction in the rotation direction, and it is possible to cope with the case where the developer carrying roller 12 rotates faster.

Further, the developer carrying roller 12 and the back electrode roller
Bias voltage V applied to the _B1, V_B2Polarity and
The size and polarity of the developer are determined by the
Can be changed as long as it does not adversely affect

Further, the developer carrier and the back electrode are not limited to rollers, but may be belts or rigid plates.
In short, the developer carrier may be any member that can carry the developer, and the back electrode cooperates with the developer carrier to attract the developer held on the developer carrier toward the back electrode. Anything that can be done is acceptable.

[0031]

As is apparent from the above description, according to the image forming apparatus of the present invention, whether the rotation speed of the developer carrying roller is low or high, it is enough to form the next pixel (dot) by the same hole. Since the appropriate developer is quickly formed on the outer periphery of the supporting roller, the driving frequency of the image signal can be increased, and as a result, the overall image forming speed can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating an image forming unit of an image forming apparatus according to the present invention.

FIG. 2 is a plan view showing the arrangement of holes and electrodes formed in a partition.

FIG. 3 is a circuit diagram of a controller that applies a pulse to a return electrode and an individual electrode.

FIG. 4 shows an example of a pulse waveform applied to a return electrode (a) and an example of a pulse waveform applied to an individual electrode (b).

FIG. 5 illustrates a case where the rotation speed of the developer carrying roller is low.
FIG. 4 is a time-series view of a cross-sectional view comparing the state of developer flying between a conventional example and the present invention.

FIG. 6 illustrates a case where the rotation speed of the developer carrying roller is high.
FIG. 4 is a time-series view of a cross-sectional view comparing the state of developer flying between a conventional example and the present invention.

FIG. 7 shows two other preferred embodiments of the return electrode according to the invention.

[Explanation of symbols]

10: image forming unit, 12: developer carrying roller (developer carrying body), 16: first bias power supply, 18: developer, 2
0: back electrode roller (back electrode), 24: second bias power supply, 26: partition, 28: recording medium, 34: hole, 3
6: individual electrode, 37: individual electrode lead, 38: controller, 40: return electrode, 41: return electrode lead, 4
2: Positive pulse applied to return electrode, 44: Positive pulse applied to individual electrode, 46: Image signal output unit,
48: return waveform control unit, 50: flight waveform control unit, 52:
Negative pulse applied to the return electrode, 54: signal applied to the return electrode, 56: signal applied to the individual electrode.

Claims (1)

[Claims] 1. A developer carrying member for carrying a charged powder developer and transporting the developer in a predetermined direction, a developer carrying member disposed opposite to the developer carrying member, and facing the developer carrying member. A partition made of an insulating material having a through-hole in a region to be formed, a first electrode provided near the through-hole and upstream of the through-hole with respect to the developer conveying direction, and near the through-hole. And applying a first pulse at a first timing to the second electrode provided at a portion where the first electrode is not provided, and the first electrode, and then having a polarity opposite to that of the first pulse. A first control unit that applies a second pulse at a second timing; and a first control unit that applies a third pulse to the second electrode from a first timing at the same time as the start of the application of the first pulse. And a first controller and a second controller, wherein the first pulse and the third pulse are connected to the first electrode and the second electrode. The developer passing through the opposing portion is separated from the developer carrier, flies through the through-hole, adheres to the recording medium being conveyed on the opposite side of the developer carrier across the partition, and the second pulse Wherein the developer adhered on or near the first electrode is returned to the developer carrier again.