JP2000218850A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control gray scales while holding an aspect ratio of form dots to be a value close to '1' by flying a powder developer held to a developer carrier by an electric force and adhering the developer to a recording medium. SOLUTION: A back electrode 20 is set in parallel to a developer-holding roller 12 via a predetermined distance to the developer-holding roller 12 below the developer-holding roller 12. The back electrode 20 is connected to a bias power source 24. A predetermined voltage is impressed to the back electrode. A negatively charged developer 18 held to the developer-holding roller 12 is attracted towards the back electrode 20 by an electric field generated between the developer-holding roller 12 and back electrode 20 because of a potential difference therebetween. The developer is adhered to a recording medium 28. Also, the developer 18 is adjusted not to separate from the developer-holding roller 12. The problem of crosstalk which changes a fly amount of the developer 18 is accordingly solved.

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]

By the way, the gradation of dots and images produced by this image forming apparatus can be adjusted by controlling the voltage of the image signal applied to the individual electrodes and the application time. However, although it is technically possible to change the voltage of the image signal corresponding to each dot in accordance with the gradation, a very expensive driver is required for that. When the application time of the image signal is changed, the shape of the dot formed on the recording medium changes. Specifically, as the time for applying the image signal to the individual electrodes becomes longer, the flight time of the developer (the time from the start of the flight of the developer to the end of the flight) becomes longer, and as a result, it is formed on the recording medium. The aspect ratio (aspect ratio) of the dot becomes large, and the dot becomes elliptical. FIG. 11 shows the relationship between the duty ratio of the pulse signal (image signal) applied to the individual electrode and the contour of the developer flying as a lump, and FIG. 12 shows the duty ratio and the state of the developer landing on the recording medium. FIG. 1 shows the relationship between the duty ratio and the dots formed on the recording medium.
3 respectively.

[0005]

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. The developer carrier to be conveyed, and a partition made of an insulating material, which is disposed to face the developer carrier and has a through hole in a region opposed to the developer carrier, and a partition formed of an insulating material, and the A first electrode provided on the upstream side, a second electrode provided in the vicinity of the through hole, and a developer which applies a first signal to the first electrode and is conveyed toward a facing portion of the through hole A first control unit for changing the density of the first signal, and after a predetermined time from the application of the first signal, a second signal is applied to the second electrode to develop the developer passing through the opposing portion of the second electrode. Separated from the developer carrier, fly through the through hole, and on the opposite side of the developer carrier across the partition wall A second control unit to be attached to the recording medium being conveyed, characterized by comprising a.

In the image forming apparatus of the present invention, a plurality of the through holes are arranged in a direction substantially perpendicular to the direction of transport of the developer, and first and second electrodes are provided corresponding to the respective through holes. A third electrode may be arranged between the first electrodes to be formed.

[0007] The first signal may have a polarity different from the charged electrode property of the developer.

Further, the first signal may have the same polarity as the charged electrode property of the developer.

[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 powder developer 18 is carried on the outer periphery of the developer carrying roller 12, and the developer 18 is charged to a predetermined polarity (a negative electrode in the present 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. On one surface of the partition wall 26 facing the developer carrying roller 12, a ring-shaped individual electrode 36 is provided so as to surround each hole 34, and the rotating direction of the developer carrying roller 12 (direction of arrow 14) is provided. On the upstream side of each hole 34, a gradation control electrode 40 is arranged. The width of the gradation control 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. And the individual electrode 36 is
From there, the controller 37 is connected to a controller 38 via a lead 37 extending downstream with respect to the rotational direction of the developer carrying roller 12, and the gradation control electrode 40 is connected to the controller 38 via a lead 41 extending upstream therefrom. Have been. The individual electrodes 36, the gradation control electrodes 40, and the leads 37 and 41 can be formed by a known technique (for example, etching or printing).

As shown in FIG. 3A, the controller 3
Reference numeral 8 denotes an output unit 46 that outputs an image signal corresponding to an image created by the image forming apparatus, a gradation control unit 48 that individually processes the signal output from the output unit 46, and a delay circuit 52
It has. The signal output from the output unit 46 to the gradation control unit 48 includes an on / off signal and gradation information corresponding to each pixel (dot). On the other hand, the signal output from the output unit 46 to the delay circuit 52 includes only ON / OFF signals corresponding to each pixel (dot). Gradation control unit 48
Has a pulse width modulation control circuit 50, generates a pulse in response to the input ON / OFF signal, and adjusts the duty ratio of the pulse in accordance with the input grayscale signal. The adjusted pulse 42 is applied to the gradation control electrode 40. The delay circuit 52 receives the input ON / OFF signal.
The OFF signal is delayed for a predetermined time, and the delayed pulse 44
Is applied to the individual electrode 36. The time Δt delayed by the delay circuit 52 is substantially equal to the time required for any point on the developer carrying roller 12 to move from the opposing portion of the gradation control electrode 40 to the opposing portion of the individual electrode 36 (FIG. 3). (B)).

When the recording medium 28 is conveyed to the printing area 32 during the image producing operation of the image producing section 10 having the above-described configuration, the controller 3 synchronizes with the recording medium 28.
From 8, a pulse 44 is applied to the individual electrode 36. The pulse 44 applied at this time has a positive polarity.

As a result, the negative developer 18 held by the developer carrying roller portion is applied between the individual electrode 36 and the developer carrying roller portion facing the individual electrode 36 toward the back electrode roller 20. A new exciting electric field is formed. This 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,
A group of developer 1 carried on a developer carrying roller portion
8 is separated from the developer carrying roller 12 and is caused to fly.

A group of the developer that has flown passes through the corresponding hole 34 and adheres to a portion of the recording medium facing the hole 34 to form a dot. Then, a target image is created from a set of a large number of dots thus formed. The developer adhering to the recording medium 28 is carried to a fixing step (not shown) together with the recording medium 28, where it is heated and melted and fixed to the recording medium 28.

In the following, the tone control section 48 sends the tone control electrode 4
The pulse 42 applied to 0 will be described. The pulse 42 is applied immediately before the pulse 44 is applied to the individual electrode 36. Now, it is assumed that the pulse 42 has a polarity (positive polarity) different from the charged electrode property of the developer 18. In this case, the pulse 4 is applied from the gradation control unit 48 to the gradation control electrode 40.
2 is applied, an electric field is formed between the gradation control electrode 40 and the developer carrying roller 12 so that the developer 18 on the developer carrying roller 12 is drawn toward the gradation control electrode 40, The developer 18 on the developer carrying roller 12 is attracted to the gradation control electrode 40, so that the bonding force between particles constituting the developer is weakened, and the developer density is reduced. The application time of the pulse 42 and the peak voltage are set so that the developer 18 is not separated from the developer carrying roller 12 by the application of the pulse 42.

After the delay time Δt from the application of the pulse 42 to the gradation control electrode 40, the pulse 44 is applied to the corresponding individual electrode 36. At this time, the developer 18 passing through the opposed portion of the individual electrode 36 applies a pulse 42 to the gradation control electrode 40.
Is applied, a low density is obtained. Therefore, by applying the pulse 44, the toner is easily separated from the developer carrying roller 12, passes through the corresponding hole 34, and then adheres to the recording medium 28 to form a dot.

By changing the duty ratio of the pulse 42 applied to the gradation control electrode 40, the degree of decrease in the developer density varies. In other words, as the duty ratio of the pulse 42 increases, the developer density decreases, and the developer 18 is easily separated from the developer carrying roller 12 by the subsequent application of the pulse 44. As a result, the developer 18 is formed on the recording medium 28. The dot density increases. Therefore, for example, when creating a high-density image, the duty ratio of the pulse 42 is increased (see FIG. 4).
Conversely, when creating a low-density image, the duty ratio of the pulse 42 is reduced (see FIG. 4B). In this case, the pulse 4 applied to the gradation control electrode 40
2 is constant, the duty ratio of the pulse 44 applied to the individual electrode 36 is constant.
The time from the start of flight to the end of flight of No. 8 is constant, and the dot aspect ratio does not change significantly by changing the gradation.

The gradation can be controlled by making the polarity of the pulse 42 the same as the polarity of the charged electrode of the developer 18. In this case, when the pulse 42 is applied from the gradation control unit 48 to the gradation control electrode 40, the developer 18 on the developer carrying roller 12 is placed between the gradation control electrode 40 and the developer carrying roller 12. Is formed on the developer carrying roller 12, whereby the developer 18 on the developer carrying roller 12 is pressed against the developer carrying roller 12, and the bonding force between the particles constituting the developer 18 is formed. And the developer density increases.

Therefore, when the pulse 44 is applied to the corresponding individual electrode 36 after the delay time Δt from the application of the pulse 42 to the gradation control electrode 40, at this time, the development passing through the opposing portion of the individual electrode 36 is performed. The agent 18 is used for the gradation control electrode 4
Since the bonding force between the particles is strengthened by applying the pulse 42 to 0, the amount of the developer separated from the developer carrying roller 12 by the application of the pulse 44 has a polarity different from that of the charged electrode of the developer 18. The number is smaller than when the pulse 42 is applied.

Further, the bonding force between the particles to be enhanced changes by changing the duty ratio of the pulse 42 applied to the gradation control electrode 40. That is, as the duty ratio of the pulse 42 increases, the bonding force between particles (developer density) increases, and the developer 18 is less likely to be separated from the developer carrying roller 12 by the subsequent application of the pulse 44. The density of the dots formed on the recording medium 28 decreases. Therefore, for example, when creating a high-density image, the duty ratio of the pulse 42 is reduced (FIG. 5A).
Conversely, when creating a low-density image, the pulse 42 is used.
(See FIG. 5B). Also in this case, even if the duty ratio of the pulse 42 applied to the gradation control electrode 40 is changed, the pulse 4
Since the duty ratio of No. 4 is constant, the time from the start of the flight of the developer to the end of the flight is constant, and the aspect ratio of the dot does not largely change by changing the gradation.

The above description shows one embodiment of the present invention, and the present invention can be variously improved. For example, as shown in FIG. 6, a shield electrode 54 is provided between the adjacent gradation control electrode 40 and the lead portion 41, so that when a voltage is applied to the gradation control electrode 40, the gradation control electrode adjacent thereto is provided. The crosstalk problem that the flying electric field is affected even by the developer 18 whose flying amount is controlled by 40 and the flying amount is changed can be solved. In order to prevent such crosstalk, it is most effective to dispose a shield electrode between adjacent electrodes for controlling the flying amount. However, as in the present invention, a gradation control electrode having a smaller width than the individual electrode is used. By providing a shield electrode between them, it is possible to effectively prevent crosstalk without lowering the dot density. Although not shown, similarly,
A shield electrode may be provided between the adjacent individual electrodes 36 and the lead portions 37 thereof, thereby preventing crosstalk between the individual electrodes 36.

The image forming apparatus was set under the following conditions. Measurement of density by pulse width modulation control of pulse applied to gradation control electrode, II. Measurement of the effect of shield electrode to prevent crosstalk between gradation control electrodes, III. The actual measurement of the comparison of the aspect ratio between the pulse width modulation control of the pulse applied to the gradation control electrode and the pulse width modulation control of the pulse applied to the individual electrode was performed. In any of the actual measurements, a plurality of holes penetrating the partition wall are formed at predetermined intervals on a line parallel to the central axis of the developer carrying roller. On one surface of the partition wall facing the developer carrying roller, a ring-shaped individual electrode is provided so as to surround each hole, and a gradation control electrode is provided upstream of each hole with respect to the rotation direction of the developer carrying roller. Are arranged (see FIG. 2).

I. Density in gradation control by pulse width modulation (1) Experimental conditions ・ Resolution: 300 dpi ・ Recording medium conveyance speed: 50 mm / sec ・ V _B1 : 0 V ・ V _B2 : +1000 V ・ Inner diameter of through hole: 140 μm ・ Gradation control electrode Width: 160 μm Developer: Epson printer (trade name: LP-920)
0) Toner for (2) Measurement Conditions All of the plurality of individual electrodes have a rectangular wave with a duty ratio of 50% (base value: -50 V, peak value:
200V). One specific gradation control electrode has a duty ratio of 10%, 20%, 30%, 40%, 50% shown in FIGS. 7 (b), (c), (d), (e), and (f).
% Square wave (base value: -100 V, peak value: 300
V) was applied, and the voltage applied to the other plurality of gradation control electrodes was uniformly -100V. The developer was ejected only from the through-hole located downstream of the specific gradation control electrode to which the rectangular wave was applied, and the density of the formed line was measured. (3) Measurement results The measurement results are shown in FIG.

As is clear from FIG. 8 showing the results of the experiment, it can be understood that gradation control is possible by changing the duty ratio of the pulse applied to the gradation control electrode.

II. Effect of shield electrode for preventing crosstalk between gradation control electrodes (1) The experimental conditions are the same as those in the case of the above-mentioned actual measurement of “gradation control by pulse width modulation”. The installation of a shield electrode as shown in FIG. (2) Measurement Conditions As in the case of the above-described actual measurement of “gradation control by pulse width modulation”, a plurality of individual electrodes are all rectangular waves with a duty ratio of 50% (base value: −50 V) shown in FIG. , Peak value: 200 V). The application of the gradation control electrode was classified as follows. All shield electrodes are grounded. In a configuration having a shield electrode, one specific gradation control electrode has a duty ratio of 10%, 20%, 30%,
40%, 50% rectangular waves (base value: -100 V, peak value: 300 V) (FIGS. 7B, 7C, 7D,
(E) and (f)), and the other applied voltages to the gradation control electrode were uniformly -100V. In the configuration without the shield electrode, the duty ratio is 10%, 20%, 30%, 40% for all the gradation control electrodes.
%, 50% square wave (base value: -100 V, peak value: 300 V) (FIGS. 7 (b), (c), (d),
(E) and (f)) were applied. In a configuration having a shield electrode, duty ratios of 10%, 20%, 30%, 40%
%, 50% square wave (base value: -100 V, peak value: 300 V) (FIGS. 7 (b), (c), (d),
(E) and (f)) were applied. In the configuration without the shield electrode, the duty ratio of 10%, 20%, 30%,
40%, 50% rectangular waves (base value: -100 V, peak value: 300 V) (FIGS. 7B, 7C, 7D,
(E) and (f)), and the other applied voltages to the gradation control electrode were uniformly -100V. For the above four cases, the developer was ejected by flying, and the density of the formed lines was measured. (3) Measurement results The measurement results are shown in FIG. The broken line in FIG. 9 in the above case is exactly the same as the broken line in FIG.

In FIG. 9, the density is high at the broken line in the above case. This is the effect of crosstalk. The polygonal line in the above case has a small density difference from the polygonal line in the case of FIG. This can be understood to indicate that crosstalk hardly occurs due to the presence of the shield electrode.

III. Actual measurement of the aspect ratio between the pulse width modulation control of the pulse applied to the gradation control electrode and the pulse width modulation control of the pulse applied to the individual electrode. First, the individual electrode without the gradation control electrode was applied to the individual electrode. Tone control was performed by modulating the pulse width to be formed, dots were formed, and the aspect ratio (that is, major axis / minor axis) was measured (Comparative III). In addition, the aspect ratios of the dots formed when the experiment I was performed were measured and compared (actual measurement).
III). The results are shown in FIG.

In the pulse width modulation control of the pulse applied to the gradation control electrode, the aspect ratio becomes almost constant, but in the pulse width modulation control of the pulse applied to the individual electrode, the aspect ratio increases with the increase of the duty ratio. It is understood that it fluctuates.

[0031]

As is apparent from the above description, according to the image forming apparatus of the present invention, the aspect ratio of the formed dots is maintained at a value close to "1" (that is, the dots are formed in a shape close to a perfect circle). (While maintaining), gradation control can be performed.
Regarding the signal applied to the gradation control electrode, this is possible even if the polarity is different from or the same as the polarity of the charged electrode of the developer.

Further, a plurality of the through-holes are arranged in a direction substantially perpendicular to the direction of transport of the developer, and a gradation control electrode and an individual electrode are provided corresponding to each through-hole. By disposing the shield electrode, when applied to the gradation control electrode, it affects the flying electric field even for the developer whose flying amount is to be controlled by the gradation control electrode adjacent thereto, and changes the flying amount. The problem of crosstalk that would be caused can be solved.

[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. 3A is a circuit diagram of a controller for applying a pulse to a gradation control electrode and an individual electrode, and FIG. 3B is an example of an applied pulse waveform.

4A and 4B are a plan view and a cross-sectional view of a hole and an electrode, showing a state of an action of an electric field on a developer when a pulse of a positive polarity is applied to a gradation control electrode.

5A and 5B are a plan view and a cross-sectional view of a hole and an electrode, showing a state of an action of an electric field on a developer when a pulse of a negative polarity is applied to the gradation control electrode.

FIG. 6 is a plan view of the vicinity of a hole of the image forming apparatus according to the present invention to which a shield electrode is added.

FIG. 7 is a graph of an actual measurement of an aspect ratio between pulse width modulation control of a pulse applied to an individual electrode and a pulse width modulation control of a pulse applied to an individual electrode in actual measurements I and II.

FIG. 8 is a graph of a density change in pulse width modulation control of a pulse applied to a gradation control electrode.

FIG. 9 is an actually measured graph showing the effect of a shield electrode between gradation control electrodes.

FIG. 10 is an actual measurement graph of an aspect ratio comparison between pulse width modulation control of a pulse applied to a gradation control electrode and pulse width modulation control of a pulse applied to an individual electrode.

FIG. 11 is a schematic view of a flying form of the powder developer in an image forming apparatus that forms an image by flying adhesion of the powder developer.

FIG. 12 is a schematic diagram showing the state of adhesion of the powder developer of FIG. 11 onto a recording medium.

FIG. 13 is a schematic diagram of the shape of the powder developer of FIG. 11 attached to a recording medium.

[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: tone control electrode, 41 tone control electrode lead, 42: pulse applied to tone control electrode, 44: applied to individual electrode Pulse 46: image signal output unit, 4
8: gradation control unit, 50: pulse width modulation control circuit, 52:
Delay circuit, 54: shield electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C162 AE04 AE14 AE25 AE31 AE40 AE74 AF13 AF44 AF70 AF72 AH14 AH20 AH40 AH45 AH46 AJ17 CA02 CA12 CA13 CA24 CA32 2H029 AB08 AB10 AB15 AB23 AC02 AD04

Claims (4)

[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, and a first partition provided upstream of the through hole with respect to a developer transport direction.
And a second electrode provided in the vicinity of the through-hole. A first signal is applied to the first electrode to change the density of the developer conveyed toward the facing portion of the through-hole. After a predetermined time from the application of the first signal, a second signal is applied to the second electrode, and the developer passing through the opposing portion of the second electrode is separated from the developer carrier, Fly through the through hole,
An image forming apparatus comprising: a second controller configured to attach the opposite side of the developer holding member to the recording medium being conveyed across the partition. 2. A plurality of said through holes are arranged in a direction substantially perpendicular to the direction of transport of the developer, and first and second electrodes are provided corresponding to each of the through holes, and between the adjacent first electrodes. The image forming apparatus according to claim 1, wherein a third electrode is disposed. 3. The method according to claim 1, wherein the first signal has a polarity different from that of the charged electrode of the developer.
Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the first signal has the same polarity as the charge electrode property of the developer.