Electrostatic recording apparatus for selectively transferring a developing agent conveyed to the surface of a recording electrode to an opposite electrode

An electrostatic recording apparatus includes a magnet roll for conveying a developing agent along a predetermined developing agent convey path. A plurality of recording electrodes are arranged to oppose the magnet roll and along the developing agent convey path. An opposite electrode has a portion opposing the plurality of recording electrodes and is arranged with a predetermined gap from the plurality of recording electrodes. A voltage applying unit applies a recording voltage corresponding to supplied dot recording information to each of the plurality of recording electrodes to generate a transferring electric field for transferring the developing agent to the opposite electrode between the opposite electrode and the plurality of recording electrodes, thereby forming a dot recording image corresponding to the dot recording information on the opposite electrode. The voltage applying unit applies, between the plurality of recording electrodes and the opposite electrode, a recovering electric field for recovering a part of the developing agent transferred on the opposite electrode to the plurality of recording electrodes within one-dot recording period in which one dot of the dot recording information is recorded in the conveying direction of the developing agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a noncontacting electrostatic recording 
apparatus for forming an electrostatic recording image without bringing a 
recording head and a recording medium into contact with each other. 
2. Description of the Related Art 
A multistylus printer is conventionally well known as an electrostatic 
recording apparatus. This multistylus printer has a recording head 
constituted by arranging a large number of needle-like electrodes 
(styluses) in a main scanning direction with equal small intervals 
therebetween and selectively applies a voltage to each needle-like 
electrode in accordance with a recording signal to directly perform 
discharging on paper, thereby forming an electrostatic latent image. In 
this printer, in order to easily and stably hold an electric charge on 
paper, specialty paper coated with a high electrical resistance agent is 
used. Specialty paper of this type, however, is difficult to write 
something on it with a pen or a pencil and has a problem in storage 
stability because it is denatured depending on environmental conditions 
such as a humidity. Therefore, this specialty paper is not preferred as 
office paper. 
In addition, when a gap between the distal end of each needle-like 
electrode and the surface of paper is large, a discharge electric field 
from the needle-like electrodes is widened on the paper surface to 
increase the size of formed dots, thereby making it difficult to obtain a 
high-resolution recording image. Therefore, a gap material is provided on 
the paper surface and brought into slidable contact with the distal ends 
of the needle-like electrodes to ensure a small gap. However, this system 
has a problem in that the distal ends of the needle-like electrodes are 
abraded or wear down. 
Therefore, as an electrostatic recording system capable of using plain 
paper and ensuring a small gap between an image medium and the distal ends 
of recording electrodes, there is a system for forming a toner image on a 
drum-like intermediate recording medium and transferring the toner image 
on paper. According to this system, since the size of an apparatus tends 
to be increased due to the use of an intermediate recording medium, a 
process of simultaneously performing recording and development is adopted 
to avoid the increase in apparatus size. In this case, a large number of 
recording electrodes extending in a conveying direction (sub scanning 
direction) of a developing agent convey path are aligned in its widthwise 
direction (main scanning direction), and a developing agent is selectively 
transferred from the recording electrodes to the surface of an opposite 
electrode also serving as an intermediate recording medium in accordance 
with dot recording information, thereby developing a toner recording image 
consisting of dots. 
In the above system, however, if the length of each recording electrode 
extending in the sub scanning direction is about one dot, an electric 
field capable of transferring toner cannot be obtained to fail to increase 
the image density. Therefore, the recording electrode length must be five 
to ten times the dot pitch in the sub scanning direction. That is, a 
development region becomes five to ten times the dot pitch. Therefore, 
when continuous recording of two or more dots is performed, the toner 
adhesion amount becomes larger as the dot position becomes later. For 
example, since the second dot in two-dot continuous recording is formed by 
repeatedly performing development twice (superposition development), the 
adhesion amount of toner is about twice that of the first dot. In this 
manner, since the toner adhesion amount becomes larger as the dot position 
becomes later, a built-up toner aggregate is broken to enlarge the dot in 
a trailing end portion of a continuously recorded image, thereby degrading 
the reproducibility. That is, the contour of the trailing end portion of 
an image is enlarged to form a low-resolution recording image worse in 
so-called sharpness. 
In addition, in the above system, since the intermediate recording medium 
is repeatedly used, the intermediate recording medium must be cleaned each 
time it is used so as not to produce any residual image. However, if a 
cleaning means is provided around the intermediate recording medium, the 
size of an electrostatic recording apparatus is increased. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an 
electrostatic recording apparatus capable of improving the resolution of a 
recording image and preventing background smudging, thereby improving the 
printing quality. 
In order to achieve the above object, according to the first aspect of the 
present invention, there is provided an electrostatic recording apparatus 
comprising: 
developing agent conveying means for conveying a developing agent along a 
predetermined developing agent convey path; 
a plurality of recording electrodes opposing the developing agent conveying 
means and extending along the developing agent convey path; 
an opposite electrode having a portion opposing the plurality of recording 
electrodes and arranged with a predetermined gap from the plurality of 
recording electrodes, the opposing portion being movable in a conveying 
direction of the developing agent; and 
voltage applying means for applying a recording voltage corresponding to 
supplied dot recording information to each of the plurality of recording 
electrodes to generate a transferring electric field for transferring the 
developing agent to the opposite electrode between the opposite electrode 
and the plurality of recording electrodes, thereby forming a dot recording 
image corresponding to the dot recording information on the opposite 
electrode, 
wherein the voltage applying means applies, between the plurality of 
recording electrodes and the opposite electrode, a recovering electric 
field for recovering a part of the developing agent transferred on said 
opposite electrode to the plurality of recording electrodes within a 
one-dot recording period in which one dot of the dot recording information 
is recorded in the conveying direction of the developing agent. 
According to the second aspect of the present invention, there is provided 
an electrostatic recording apparatus comprising: 
developing agent conveying means for conveying a developing agent along a 
developing agent convey path on a developing agent carrier body; 
a plurality of recording electrodes opposing the developing agent conveying 
means and extending along the developing agent convey path, each of the 
plurality of recording electrodes having a leading end portion; 
an opposite electrode having a portion opposing the plurality of recording 
electrodes and arranged with a predetermined gap from the plurality of 
recording electrodes, the opposing portion being movable in a conveying 
direction of the developing agent; and 
voltage applying means for applying a recording voltage corresponding to 
supplied dot recording information to each of the plurality of recording 
electrodes to generate a transferring electric field for transferring the 
developing agent to the opposite electrode between the opposite electrode 
and the plurality of recording electrodes, thereby forming a dot recording 
image corresponding to the dot recording information on the opposite 
electrode, 
wherein each of the leading end portions of the plurality of recording 
electrodes is arranged at a position shifted from a portion where the 
developing agent carrier body and the opposite electrode are closest to 
each other to the upstream side of a developing agent convey direction 
along the developing agent convey path. 
According to the third aspect of the present invention, there is provided 
an electrostatic recording apparatus comprising: 
developing agent conveying means for conveying a developing agent along a 
developing agent convey path on a developing agent carrier body; 
a plurality of recording electrodes opposing the developing agent conveying 
means and extending along the developing agent convey path, each of the 
plurality of recording electrodes having a leading end portion; 
an opposite electrode having a portion opposing the plurality of recording 
electrodes and arranged with a predetermined gap from the plurality of 
recording electrodes, the opposing portion being movable in a conveying 
direction of the developing agent; 
voltage applying means for applying a recording voltage corresponding to 
supplied dot recording information to each of the plurality of recording 
electrodes to generate a transferring electric field for transferring the 
developing agent to the opposite electrode between the opposite electrode 
and the plurality of recording electrodes, thereby forming a dot recording 
image corresponding to the dot recording information on the opposite 
electrode; 
transferring means for transferring the dot recording image formed on the 
opposite electrode to paper; 
a cleaning electrode arranged at a position on said developing agent 
carrier body where it is shifted from said leading end portions of said 
plurality of recording electrodes and located at the upstream side of a 
developing agent convey direction along said developing agent convey path; 
and 
voltage applying means for applying a voltage having a polarity opposite to 
a charged polarity of the developing agent to the cleaning electrode, 
thereby electrostatically attracting a nontransferred developing agent on 
the opposite electrode to the cleaning electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in detail below with 
reference to the accompanying drawings. 
FIG. 1 is a schematic sectional view showing the overall arrangement of a 
recording apparatus as the first embodiment of the present invention. 
Referring to FIG. 1, reference numeral 1 denotes a paper feed cassette in 
which sheets of plain paper P are stacked and which is detachably mounted 
on a side portion of the apparatus. A paper feed roller 1a is arranged 
above the front end portion of the paper feed cassette 1 inserted in the 
apparatus so as to be rotatable in a direction indicated by an arrow. In 
front of the paper feed roller 1a, upper and lower guide plates 2a and 2b 
each consisting of an insulating member are arranged to form a paper 
convey path. A registration roll pair 3 is arranged in the paper convey 
path to temporarily stop conveyance of the paper P fed by the paper feed 
roller 1a, thereby adjusting the paper posture. Thereafter, the 
registration roll pair 3 feeds the paper again to an image transfer 
section Ot on the downstream side in synchronism with an arrival timing of 
a recording image (to be described later). 
In the image transfer section Ot on the downstream side of the registration 
roll pair 3, a transfer charger 4 is arranged to oppose a cylindrical 
electrode 5 as an opposite electrode also serving as an image carrier. The 
cylindrical electrode 5 is rotated counterclockwise as indicated by an 
arrow .alpha.. A recording image forming unit U (to be described later) is 
arranged to oppose the circumferential surface of the cylindrical 
electrode 5 on the opposite side of the transfer charger 4. A toner 
recording image is formed on the surface of the cylindrical electrode 5 by 
the recording image forming unit U, conveyed to the image transfer section 
Ot by the rotation of the cylindrical electrode 5, and transferred onto 
paper fed again. The arrangement of the recording image forming unit U 
will be described in detail later. 
On the downstream side of the image transfer section Ot, a separating claw 
6 is arranged such that its distal end is urged against the 
circumferential surface of the cylindrical electrode. On the downstream 
side of the separating claw 6, an air-suction type conveyor belt 7 is 
horizontally arranged to convey paper separated from the surface of the 
cylindrical electrode 5 to a fixing unit 8 arranged before the conveyor 
belt 7 while chucking the rear surface of the paper separated from the 
circumferential surface of the cylindrical electrode 5 by the separating 
claw 6 after the image transfer. The fixing unit 8 is constituted by a 
heat roll 8a and a pressure roll 8b and thermally fixes the toner image 
while the paper is conveyed between the two rolls. The paper subjected to 
fixing is exited from an exit port 9 and stacked on a paper exit tray 10 
in a face-down state in that the image surface faces down. 
In the recording apparatus of this embodiment as described above, since the 
entire paper convey path from paper feed to paper exhaust is formed 
substantially straight, a paper conveying operation is generally smooth to 
prevent easy occurrence of an image defect or a paper conveyance defect 
such as jamming. In addition, this recording apparatus has another 
advantage in that a face-down paper exit state not requiring sorting of 
pages is obtained by the above straight paper convey path. 
The arrangement of the recording image forming unit U will be described in 
detail below. 
As shown in FIG. 2, the recording image forming unit U generally comprises 
a development/recording tank 12 having a recording means and a developing 
agent conveying means, and a developing agent storage tank 11 for storing 
a developing agent for replenishment. An agitating blade 11a is pivotally 
arranged in the development agent storage tank 11. In this embodiment, a 
one-component developing agent containing at least an insulating resin, a 
magnetic fine powder, and coloring agent particles is used as a developing 
agent, and an insulating magnetic toner having a negative (-) 
triboelectrification polarity is contained. The developing agent is not 
limited to the one-component developing agent, but a two-component 
developing agent obtained by mixing a magnetic carrier and an insulating 
toner at a predetermined ratio may be used. 
A horizontal circulating path 13 for a developing agent shown in FIG. 3 is 
formed on the bottom portion of the development/recording tank 12. 
Referring to FIG. 3, a pair of auger rolls 14a and 14b are rotatably 
arranged in a pair of parallel longitudinal paths 13a and 13b of the 
horizontal circulating path 13. The auger rolls 14a and 14b are 
constituting by forming a plurality of spiral blades 14a2 and a plurality 
of spiral blades 14b2 on the circumferential surfaces of shafts 14a1 and 
14b1 and forming reverse feed blades 14a3 and 14b3 having opposite spiral 
directions each on one end portion of a corresponding shaft (see the 
perspective view in FIG. 4). The auger rolls 14a and 14b are arranged in 
the longitudinal paths 13a and 13b, respectively, such that the reverse 
feed blades 14a3 and 14b3 are located on opposite sides. The pair of auger 
rolls 14a and 14b are rotated in opposite directions indicated by arrows 
.beta. and .gamma. along which a developing agent is conveyed toward the 
respective reverse feed blades 14a3 and 14b3. As a result, at the corner 
portions having the reverse feed blades 14a3 and 14b3, reverse conveying 
forces in opposite directions collide against each other to push the 
magnetic toner in a perpendicular direction to flow into the other 
longitudinal path. In this manner, the magnetic toner can be 
satisfactorily triboelectrified while being circulated under agitation in 
a direction indicated by a broken arrow .delta.. A necessary charge amount 
of a developing agent can be satisfactorily obtained by 
triboelectrification by changing the shape or material of the auger rolls 
14a and 14b. 
A space S surrounded by a wall Sw to prevent ingress of the circulating 
developing agent is formed in a central portion of the horizontal 
circulating path 13 having the above arrangement. As shown in FIG. 2, 
above the auger roll 14a closer to the developing agent storage tank 11, a 
replenishment port 11b of replenishing magnetic toner d0 is formed along 
the axial direction of the auger roll 14a. 
A development sleeve 15 for vertically conveying the developing agent is 
horizontally arranged above the other auger roll 14b. The developing 
sleeve 15, which incorporates a rotary magnet roll 16, is arranged to 
oppose the cylindrical electrode 5 described above. Opposite magnetic 
poles are alternately formed on the peripheral surface of the magnet roll 
16. When the magnet roll 16 is rotated counterclockwise as indicated by an 
arrow n, the magnetic toner d is conveyed clockwise as indicated by a 
broken arrow .zeta. along the circumferential surface of the developing 
sleeve 15. 
A doctor blade 12a for regulating the layer thickness of the magnetic toner 
d to be a proper value is arranged near the surface of the developing 
sleeve 15 serving as a developing agent convey path and on the upstream 
side in the developing agent conveying direction .zeta.. A toner 
scattering preventing plate 12b is arranged above the doctor blade 12a. 
The toner scattering preventing plate 12b prevents inconvenience in that a 
developing agent conveyed onto the downstream side due to the layer 
thickness regulation by the doctor blade 12a is scattered outside the 
recording/image forming unit U to contaminate an image. In this 
embodiment, the upper end portion of the tank wall of the 
developing/recording tank 12 is branched into two parts, the doctor blade 
12a is formed in one branch, and the toner scattering preventing plate 12b 
is formed in the other. 
A recording section W for forming a toner recording image is arranged as 
follows on the circumferential surface of the cylindrical electrode 5 on 
the downstream side of the toner layer thickness regulating section along 
the toner conveying direction .zeta.. 
A recording electrode sheet 17 having a large number of recording 
electrodes is bonded on the circumferential surface of the development 
sleeve 15 in a region on the upstream side along the toner conveying 
direction from the position closest to the surface of the cylindrical 
electrode 5 (in this embodiment, a region on the circumferential surface 
of the left half shown in FIG. 4). As shown in FIG. 4, in the recording 
electrode sheet 17, a large number of parallel recording electrode lines 
17a are arranged in the longitudinal direction of the sheet along the 
circumferential direction of the surface of the development sleeve 15 with 
a predetermined small pitch in the widthwise direction of the sheet (the 
widthwise direction of the toner convey path: the main scanning 
direction). The number of recording electrode lines 17a is set to 
correspond to the maximum data number of one main scanning line. In the 
recording electrode sheet 17 of this embodiment constituted by a flexible 
printed circuit board (FPC), the recording electrode lines 17a consisting 
of a large number of nonmagnetic conductive materials are patterned at a 
density of 84.6 .mu.m pitch (300 DPI) with intervals of 40 .mu.m 
therebetween on a base film 17b consisting of a flexible insulating 
material. An insulating coat 17c is coated on the surface of the recording 
electrode sheet 17 except for a small region Z at the end of the sheet. 
The insulating coat 17c ensures insulation between the recording electrode 
lines 17a and prevents wear of the recording electrode lines 17a caused by 
friction with the magnetic toner. 
FIG. 5 is a schematic sectional view showing the recording section W in an 
enlarged scale. As shown in FIG. 5, when the end portions of the recording 
electrode lines 17a are not covered with the insulating coat 17c but 
exposed, a necessary recording electric field can be efficiently formed 
between these end portions and the circumferential surface of the opposing 
cylindrical electrode 5. The exposed end portions of the recording 
electrode lines 17a serve as recording electrodes EL which actually 
perform a recording operation. If a length L of the recording electrodes 
EL along the toner conveying direction (sub scanning direction) is too 
small, the strength of a recording electric field is decreased to decrease 
the image density. Therefore, the length L must be larger than the dot 
pitch (in this embodiment, 84.6 .mu.m as described above). If the length L 
of the recording electrodes EL is excessively large, the area influenced 
by the strength of an electric field is widened to decrease the sharpness 
of an image. 
Referring to FIG. 2, on the downstream side of the recording section W 
along the toner conveying direction .zeta., a wall Sw1 on the developing 
agent storage tank 11 side is extended by the wall surrounding the central 
space S of the above-mentioned horizontal circulating path 13 so that the 
distal end of the wall Sw1 abuts against the circumferential surface of 
the development sleeve 15. As a result, a magnetic toner d', which is not 
transferred in the recording section W but remains on the surface of the 
development sleeve 15 and is conveyed upon rotation of the magnet roll 16, 
is scraped on a replenishment tank-side path 13a of the horizontal 
circulating path 13. That is, the magnetic toner d' is prevented from 
entering the central space S or being returned not via the horizontal 
circulating path 13 but directly to the upstream side along the 
circumferential surface of the development sleeve 15. Note that an 
exclusive plate member for scraping the residual magnetic toner d' 
deposited on the development sleeve 15 may be prepared independently of 
the wall of the central space S. In this case, the scraping member is 
vertically supported such that its distal end abuts against the 
circumferential surface of the development sleeve 15 and its proximal end 
extends to the bottom portion of the central space S. When the scraping 
member is formed of a magnetic material, a smoother scraping/returning 
effect can be obtained because the magnetic force of the magnet roll 16 
can be interrupted. 
As described above, the recording electrode sheet 17 arranged on about a 
half of the circumferential surface of the development sleeve 15 is 
extended horizontally and then vertically downward into the central space 
S of the horizontal circulating path described above. A plurality of 
driving circuit elements 18 for applying a recording voltage on the 
respective recording electrodes EL in correspondence with recording data 
are mounted on the vertically extending portion of the recording electrode 
sheet 17. As shown in FIG. 4, N recording electrode lines 17a of the 
recording electrode sheet 17 are connected to each driving circuit element 
18. In this manner, since the end portion of the recording electrode sheet 
17 mounting the driving circuit elements 18 is housed in the central space 
S, the driving circuit elements 18 can be protected from dust such as a 
developing agent, and the structure of the developing/recording tank 12 
can be made significantly compact. 
Referring to FIG. 2, each driving circuit element 18 is connected to the 
recording control section C through a signal line (indicated by a broken 
line) so as to exchange electrical signals therebetween. The driving 
circuit element 18 outputs a recording voltage Vs as shown in FIG. 6 to 
the respective recording electrodes in accordance with dot recording 
information in the form of a bit or a recording voltage control signal 
supplied from the recording control section C. The recording voltage Vs is 
a binary signal voltage which changes between -200 V (ON voltage) and 0 V 
(OFF voltage). If one-bit recording information supplied from the 
recording control section C is "H", the driving circuit element 8 applies 
the ON voltage of -200 V to the corresponding recording electrode EL. As a 
result, since a bias power source 5a is connected to the cylindrical 
electrode opposing the recording electrode and applies a bias voltage of 
-30 V to the cylindrical electrode, a toner transferring electric field 
based on a voltage difference of 170 V is formed from the cylindrical 
electrode 5 to the recording electrodes EL. Since the magnetic toner d 
charged to have a negative polarity moves to a portion where the potential 
is high, only the magnetic toner d on the recording electrode EL applied 
with the voltage of -200 V is selectively transferred to the surface of 
the cylindrical electrode 5 to form one black dot. If the one-bit input 
recording information is "L", the OFF voltage of 0 V is applied to the 
recording electrodes EL. As a result, the potential difference between the 
cylindrical electrode 5 and the recording electrodes EL becomes -30 V from 
the cylindrical electrode 5 side, and a toner recovering electric field is 
formed in the recording section W in a direction opposite to that of the 
above toner transferring electric field. 
In the first embodiment, as is apparent from FIG. 6 for explaining a 
relationship between a recording voltage, an image, and a dot shape, in 
order to form one black dot, the ON voltage is not applied over the entire 
recording period T.sub.W of one dot but the OFF voltage is forcedly 
applied during a predetermined time T.sub.R at the end of the one-dot 
recording period T.sub.W to serve as the developing agent recovering 
electric field. This forced OFF voltage application time T.sub.R is 
periodically assured for every one-dot recording period T.sub.W as shown 
in FIG. 6 not only in recording of only one black dot but also in 
continuous recording of tow or more black dots. In this case, the length 
of the forced OFF voltage application time T.sub.R must be set to be equal 
to or longer than a time (transfer limit) required to actually, reversely 
transfer, i.e., recover toner particles from the cylindrical electrode 5 
to the surfaces of the recording electrodes EL. Since it is experimentally 
confirmed that the shortest toner transfer effective time is about 10 
.mu.sec, the forced OFF voltage application time T.sub.R must be set to be 
10 .mu.sec or more. If the one-dot recording period T.sub.W is a long 
period, exceeding 1 msec, the ratio of the forced OFF voltage application 
time T.sub.R with respect to the one-dot recording period T.sub.W must be 
set to be 1% or more in order to ensure the toner recovering effect. 
Assuming that a recording image formation speed (process speed) is 42.3 
[mm/sec], the one-dot recording period T.sub.W of this embodiment is given 
by: 
EQU T.sub.W =0.0846/42.3=2.0 [msec] 
because the dot diameter corresponding to a dot density of 300 DPI is 
0.0846 mm. In this embodiment, therefore, the forced OFF voltage 
application time T.sub.R is preferably set to be 0.02 msec (as 1% of 2.0 
msec) or more. Note that the process speed is the convenance speed of 
paper conveyed to the transfer position Ot in FIG. 1 and is set to 
coincide with the moving speed of the circum ferential surface of the 
cylindrical electrode 5. 
In order to ensure the forced OFF voltage application time T.sub.R 
described above, a recording control section C outputs a recording voltage 
control signal to the driving circuit elements 18. In this embodiment, AND 
gates are provided in one-to-one correspondence with the recording 
electrodes in the driving circuit elements 18. The recording voltage 
control signal and the dot recording information described above are 
supplied to this AND gate, and the recording voltage is switched between 
the ON and OFF voltages and output to each recording electrode EL on the 
basis of a logical AND signal output from the AND gate. In this case, even 
if the dot recording information supplied to the AND gate is "H", the 
logical AND is switched from "H" to "L" when the recording voltage control 
signal is switched from "H" to "L". As a result, when the recording 
voltage control signal is switched from "H" to "L" during the one-dot 
recording period T.sub.W, the recording voltage is switched from the ON 
voltage to the forced OFF voltage. If the dot recording information is 
"L", the output signal from the AND gate remains "L" over the entire 
one-dot recording period T.sub.W even when the recording voltage control 
signal is switched from "H" to "L". Therefore, the recording voltage 
remains to be the OFF voltage. 
As described above, by ensuring the necessary length of the forced OFF 
voltage application time T.sub.R at the end of each one-black-dot 
recording period T.sub.W, a black dot on which toner uniformly adheres and 
which has an accurate size can be formed, and a dot recording image having 
excellent dot reproducibility can be stably obtained. A recording image 
forming operation will be described below. 
In FIG. 2, when the magnet roll 16 is rotated in the direction indicated by 
the arrow .epsilon., a rotational magnetic field for rotating particles of 
the magnetic toner d is formed on the circumferential surface of the 
development sleeve 15, and the magnetic toner d is conveyed in the 
direction indicated by the arrow .zeta. opposite to the rotating direction 
of the magnet roll 16 while a brush of the toner is formed. The conveyed 
magnetic toner d is regulated to have a predetermined thickness by the 
doctor blade 12a and conveyed to the recording section W. In this 
embodiment, the magnetic toner d is triboelectrified to have a negative 
polarity by friction between the toner particles or the toner and the 
circumferential surface of the development sleeve 15. In the recording 
section W, the recording voltage Vs having the forced OFF voltage 
application time T.sub.R as shown in FIG. 6 is applied to the respective 
recording electrodes EL, and a toner recording image having good dot 
reproducibility is formed as will be described below. 
FIG. 5 is a schematic sectional view showing the state of the recording 
section W at a timing 1 in FIG. 6. At the timing 2 which is immediately 
before execution of two-black-dot continuous recording, the driving 
circuit elements apply the OFF voltage (0 V) to the recording electrodes 
EL, and the bias power source 5a applies the bias voltage of -30 V to the 
cylindrical electrode 5, thereby forming a toner recovering electric field 
in the direction indicated by the arrow in the recording section W. The 
magnetic toner d charged to have a negative (-) polarity and conveyed to 
the recording section W moves in a direction opposite to the direction of 
the electric field. Therefore, the toner d is not transferred to the 
circumferential surface of the cylindrical electrode 5 but held on the 
recording electrodes EL by the toner recovering electric field. 
Referring to FIG. 6, the recording voltage Vs is switched to the ON voltage 
(-200 V) to start recording of one black dot, and the ON voltage is 
applied over a time T.sub.D to form a toner transferring electric field. 
FIG. 7 shows the state of the recording section W at a timing 2 which is 
immediately before switching from ON voltage application to OFF voltage 
application. Since the ON voltage is kept applied to the recording 
electrodes EL by the driving circuit elements and the bias voltage of -30 
V is kept applied to the cylindrical electrode 5, the toner transferring 
electric field in the direction indicated by the arrow is formed in the 
recording section W. Therefore, the magnetic toner d moves to the 
cylindrical electrode 5 and adheres on the circumferential surface of the 
electrode. The toner d is conveyed outside the recording section W as the 
cylindrical electrode 5 rotates in the direction indicated by the arrow 
.alpha., thereby forming a first black dot dB1. 
At a timing 3 at which the recording voltage Vs is switched to the forced 
OFF voltage as shown in FIG. 6, the electric field in the recording 
section W is switched to the toner recovering electric field, and the 
magnetic toner d transferred to the circumferential surface of the 
cylindrical electrode 5 of the recording section W at the timing 2 is 
recovered to the recording electrodes EL, as shown in FIG. 8. In this 
manner, since the toner transferring electric field is switched to the 
toner recovering electric field before the one-dot recording period is 
finished, a super-position phenomenon caused by superposition of the toner 
is suppressed, and a first black dot dB1 in which the magnetic toner d 
uniformly adheres on the entire dot region and which has an accurate 
predetermined size is formed. 
Referring to FIG. 6, a timing 4 is a timing at which the one-dot recording 
period T.sub.W has elapsed from the timing 3 and at which the recording 
voltage is switched from the ON voltage to the forced OFF voltage in order 
to accurately form the second dot in the continuous dot recording. Also at 
this timing 4, as shown in FIG. 9, a toner recovering electric field 
similar to that formed at the timing 3 is formed in the recording section 
W, and a second black dot dB2 is being accurately formed with a uniform 
toner adhesion amount on the circumferential surface of the cylindrical 
electrode 5 subsequently to the first black dot dB1. 
The states of the recording section W at the above timings 3 and 4 will be 
compared with those in a conventional scheme in which no forced OFF 
voltage application time is provided. 
At a timing 3 in FIG. 16 showing a conventional recording voltage Vs', 
since the ON voltage is kept applied to the recording electrodes, the 
toner transferring electric field is kept formed in the recording section 
W as shown in FIG. 17. Therefore, on a first black dot dB1' of continuous 
dot recording, which is being formed on the circumferential surface of the 
cylindrical electrode 5, the adhesion amount of toner is increased as the 
position moves to the trailing end of the dot. In addition the ON voltage 
is kept applied to the recording electrodes EL until a timing 4 after the 
one-dot recording period T.sub.W shown in FIG. 16. Therefore, as is 
apparent from FIG. 18 showing the state obtained at the timing 4, the 
adhesion amount of toner is gradually increased as the position moves to 
the trailing end of the dot by the superposition phenomenon effect, and 
especially the adhesion amount on the second black dot dB2' is increased 
as compared with the state shown in FIG. 9. A large amount of the toner 
deposited on the trailing end portion of the second black dot dB2' tends 
to be broken to enlarge the dot. That is, although T.sub.T shown in FIG. 
16 denotes a period during which no toner is preferably deposited, 
excessive toner adheres for the above reason even after the period T.sub.W 
has elapsed. 
FIG. 19 shows the state of the recording section W at a timing 5 at which 
the two-dot continuous recording is completely finished by applying the 
OFF voltage over the one-dot recording period T.sub.W from the timing 4 
shown in FIG. 16. As is apparent from FIG. 19, even when the recording 
voltage Vs is switched to the OFF voltage to start recovery of the toner 
immediately after a two-dot continuous recording time period 
(2.times.T.sub.W) has elapsed, a large amount of toner deposited on the 
trailing end portion of a dot is broken to enlarge the dot, thereby 
forming an inaccurate toner recording image of two-dot continuous 
recording on the circumferential surface of the cylindrical electrode 5. 
On the contrary, at the timing 5 in FIG. 6 showing the recording voltage Vs 
of this embodiment, a continuous dot recording image consisting of the 
first and second black dots dB1 and dB2, in which the toner uniformly 
adheres and which have accurate sizes, and excellent in dot 
reproducibility and trailing end sharpness is clearly formed on the 
circumferential surface of the cylindrical electrode 5, as shown in FIG. 
10. 
As described above, the dot recording image corresponding to input 
recording information is formed on the circumferential surface of the 
cylindrical electrode 5 with good dot reproducibility. This dot recording 
image is conveyed from the recording section W to the image transfer 
section by the rotation of the cylindrical electrode 5. In this case, 
since a step G corresponding to the thickness of the recording electrode 
sheet 17 is formed on the immediately downstream side of the recording 
section W as shown in FIG. 10, the magnetic toner d' not subjected to 
image formation but remaining on the development sleeve 15 moves away from 
the surface of the cylindrical electrode 5 immediately after passing 
through the recording section W. Therefore, an inconvenience in that the 
toner recording image formed on the circumferential surface of the 
cylindrical electrode 5 in the recording section W is disturbed by mutual 
interference with the residual magnetic toner d' can be reliably avoided. 
Referring to FIG. 1, the toner recording image formed on the surface of the 
cylindrical electrode 5 is conveyed to the image transfer section Ot by 
the rotation of the cylindrical electrode 5 in the counterclockwise 
direction .alpha. and transferred onto paper fed again by the registration 
roll pair 3 in synchronism with it. To adjust the density of the toner 
recording image, the bias voltage of the bias power source 5a need only be 
changed. In this case, a proper adjustment range is about 0 to -50 V, and 
the image density is increased as the value becomes closer to 0 V. 
Referring to FIG. 2, the magnetic toner d' not transferred to the 
cylindrical electrode 5 but remaining in the recording section W moves to 
the downstream side of by the rotation of the magnet roll 16 and is 
scraped from the surface of the development sleeve 15 by the scraping wall 
Sw1. The scraped toner falls into the auger roll 14a and is mixed under 
agitation with magnetic toner d0 replenished from the replenishment port 
11b. 
The fell and returned residual magnetic toner d' is circulated by the 
rotation of the auger roll 14a while being mixed with the replenishing 
magnetic toner d0. Referring to FIG. 3, the magnetic toner circulated in 
the direction indicated by the broken arrow k is vertically conveyed again 
by the rotational magnetic field of the magnet roll 16 extending above the 
longitudinal path 13b on the nonreplenishment side while being conveyed in 
the path 13b. 
In this manner, the residual magnetic toner d' not transferred to the 
cylindrical electrode 5 but conveyed to the downstream side in the 
recording section W is scraped on the horizontal circulating path 13, 
smoothly returned to the upstream side under agitation through the 
horizontal circulating path 13, and subjected to formation of a toner 
recording image again. In this case, since the magnetic toner d before the 
vertical conveyance is conveyed under agitation along the axial direction 
(the widthwise direction of the toner convey path: the main scanning 
direction) of the development sleeve 15, the toner is constantly, 
uniformly supplied on the circumferential surface of the development 
sleeve 15 throughout in its widthwise direction. Therefore, since the 
magnetic toner d is constantly, uniformly carried by the surface of the 
development sleeve 15 throughout in its widthwise direction and conveyed 
to the recording section W, a high-quality recording image having a 
uniform image density can be stably obtained as described above. In 
addition, the magnetic toner is satisfactorily triboelectrified due to the 
friction between the magnetic toner particles caused when the magnetic 
toner d is circulated in the horizontal circulating path 13 under 
agitation. 
Although the forced OFF voltage application time T.sub.R is set once at the 
end of the one-dot recording period T.sub.W, it may be set in the first 
half or the central portion of the one-dot recording period T.sub.W or may 
be set a plurality of times within the one-dot recording period T.sub.W. 
The second embodiment of the present invention obtained by further 
improving the first embodiment will be described below with reference to 
FIGS. 11A and 11B, 12, and 13A to 13D. 
FIGS. 11A and 11B are sectional views each showing a part of FIG. 2 in an 
enlarged scale. 
As described above, a recording electrode sheet 17 is arranged such that 
its longitudinal direction corresponds to the circumferential direction of 
the surface of a development sleeve 15. In the second embodiment, a 
leading end 17d of the recording electrode sheet 17 (recording electrode 
17a) is slightly shifted from a position N where the circumferential 
surfaces of a cylindrical electrode 5 and the development sleeve 15 are 
closest to each other to the upstream side along a 
toner conveying direction .zeta.. The shift amount of the leading end 17d 
is preferably about 1 mm assuming that the outer diameter of the 
cylindrical electrode 5 is 20 mm, the outer diameter of the development 
sleeve 15 is 23 mm, and the thickness of the recording electrode line 17a 
is 23 .mu.m. By setting the leading end 17d of the recording electrode 
line 17a as described above, a high-resolution recording image consisting 
of sharp dots excellent in so-called sharpness can be formed for the 
following reason. 
That is, when the distal end of the recording electrode EL is located at 
the closest distance position N as shown in FIG. 11B, a toner image having 
a pattern as shown in FIG. 13A is formed on the circumferential surface of 
the cylindrical electrode 5 upon application of an ON voltage. 
Subsequently, as shown in FIG. 12, the voltage is switched to an OFF 
voltage after the ON voltage is applied for a time t (one-dot write 
period). The electric field is also switched from a transferring electric 
field to a recovering electric field in correspondence with the switching 
between the voltages, and toner on a trailing end portion of the toner 
image along the conveying direction of the cylindrical electrode is 
recovered to the recording electrode as indicated by a broken line in FIG. 
13B. In this case, as shown in FIG. 11B, a portion Nc of the 
circumferential surface of the cylindrical electrode 5 which is closest to 
the development sleeve 15 is located immediately above the leading end of 
the recording electrode EL. Therefore, the deposited toner immediately 
moves away from the leading end of the recording electrode EL by the 
rotation of the cylindrical electrode 5, and the recovering electric field 
does not sufficiently act on all of the separating toner particles. As a 
result, since toner in the trailing end portion of the formed toner image 
is not sufficiently recovered, a black dot poor in so-called sharpness is 
formed. 
In the second embodiment, however, the leading end of the recording 
electrode EL is slightly shifted from the closest distance position N to 
the upstream side of the toner conveying direction .zeta.. Therefore, 
since the trailing end portion of the recording electrode EL is separated 
from the circumferential surface of the cylindrical electrode 5 by a 
distance larger than that shown in FIG. 11B to weaken the transferring 
electric field in this portion, it becomes difficult to transfer the toner 
from the trailing end portion of the recording electrode EL. That is, the 
trailing end portion of the recording electrode EL falls outside the range 
capable of forming an electric field which can transfer the toner. As a 
result, as shown in FIG. 13C, the adhesion region of the toner image is 
narrowed as compared with that shown in FIG. 13A. When the recovering 
electric field acts on this toner image, recovery of the toner can be 
satisfactorily performed because the adhesion amount on the trailing end 
portion of the toner image to be recovered is smaller than that shown in 
FIG. 13A. In addition, as shown in FIG. 11A, since the closest distance 
position Nc on the circumferential surface of the cylindrical electrode 5 
is located not immediately above the leading end of the recording 
electrode EL but on the downstream side thereof, the toner image does not 
immediately move away from the distal end of the recording electrode EL 
but moves closer thereto and then moves away therefrom, after passing 
through a position immediately above the leading end of the recording 
electrode EL. Therefore, when the transferring electric field is switched 
to the recovering electric field, the recovering electric field 
satisfactorily acts on the portion of the toner image above the leading 
end of the recording electrode EL, thereby improving so-called sharpness 
of the trailing end of the toner image. That is, the contour of the toner 
image is clearly formed throughout the edge of the image. As a result, as 
shown in FIG. 13D, a sharp black dot having better sharpness than that of 
the black dot shown in FIG. 13B is formed. 
When the leading end of the recording electrode is shifted from the closest 
distance position with respect to the circumferential surface of the 
cylindrical electrode to the downstream side along the developing agent 
conveying direction, a speed at which the toner image moves away from the 
distal end of the recording electrode becomes higher than that in the case 
shown in FIG. 11B, and the sharpness of the trailing end of the toner 
image is significantly degraded. As a result, a black dot having a blurred 
contour is formed. 
As shown in FIG. 11A, therefore, the leading end of the recording electrode 
EL is slightly shifted from the position immediately below the position Nc 
where the circumferential surface of the cylindrical electrode 5 is 
closest to the development sleeve 15 to the upstream side along the toner 
conveying direction .zeta.. As a result, a high-resolution recording image 
recording image consisting of sharp black dots excellent in sharpness can 
be stably formed on the circumferential surface of the cylindrical 
electrode 5. In this case, it is confirmed by the present inventors that 
the shift amount of the leading end of the recording electrode EL is 
preferably 1 mm assuming that the outer diameter of the cylindrical 
electrode 5 is 20 mm, the outer diameter of the development sleeve 15 is 
23 mm, and the thickness of the recording electrode is 23 .mu.m. When the 
leading end of the recording electrode was shifted by 0.5 mm to the 
downstream side, an image was blurred significantly, and the image quality 
could not be recovered even by adjusting other image formation conditions. 
As described above, an insulating coat 17c is coated on the surface of the 
recording electrode sheet 17 except for a predetermined small region Z 
from the leading end serving as the recording electrode EL. Therefore, 
insulation between the recording electrode lines 17a can be assured, and 
wear of the recording electrode lines 17a caused by friction with the 
magnetic toner d can be prevented. The insulating coat 17c is not coated 
on the leading end portion of the recording electrode sheet 17 for the 
following reason. 
That is, a toner recording image is formed by applying a recording voltage 
corresponding to recording data to the recording electrode lines 17a to 
form an electric field between the recording electrode lines and the 
cylindrical electrode 5 and selectively transferring the toner charged by 
this electric field force to the cylindrical electrode 5, as will be 
described later. If, however, the insulating coat 17c is coated on the 
surface of the recording electrode lines 17a to be applied with the 
recording voltage, not only a necessary electric field cannot be 
efficiently formed, but also an unnecessary electric charge is stored in 
the insulating coat 17c to lead to image defects such as scumming or image 
contamination. Therefore, as shown in FIG. 4, the insulating coat 17c is 
not coated on the leading end of the recording electrode sheet 17 
contributing to the formation of a toner recording image and the region Z 
close to the leading end so that the recording electrode EL is formed by 
the exposed recording electrode lines 17a. As a result, the necessary 
electric field can be efficiently formed. In addition, since the 
unnecessary electric charge is not stored, occurrence of image defects 
such as scumming caused by the unnecessary electric charge can be reliably 
prevented. 
In the manufacture of the recording electrode sheet 17, a base film 17b 
consisting of a flexible insulating material is etched to form a pattern 
of a large number of recording electrode lines 17a, and the insulating 
coat 17c is coated on the resultant sheet except for the leading end 
region Z. 
The third embodiment of the present invention will be described below with 
reference to FIGS. 14 and 15. 
FIG. 15 is an enlarged sectional view showing a part of FIG. 2, in which a 
recording position W and its peripheral portion are illustrated in detail. 
Referring to FIG. 15, an insulating coat 17c is coated on the surface of a 
recording electrode sheet 17 as in the above embodiments, thereby ensuring 
electrical insulation between recording electrode lines 17a and preventing 
wear of the recording electrode lines 17a caused by friction with magnetic 
toner d. A leading end portion EL located at the recording position W of 
the recording electrode lines 17a is slightly raised to be exposed on the 
surface of the insulating coat 17c. As in the above embodiments, this 
exposed leading end portion EL of the recording electrode lines 17a serves 
as a recording electrode portion for essentially performing a recording 
operation. 
A cleaning electrode 17d consisting of a non-magnetic conductive material 
is arranged at a position on the surface of the recording electrode sheet 
17 separated by a proper distance from the recording electrode portion EL 
to the upstream side of a developing agent convey path. The cleaning 
electrode 17d is extended on the surface of the recording electrode sheet 
17 throughout in its widthwise direction (see FIG. 14) and buried in the 
insulating coat 17c with its upper surface exposed. The insulating coat 
17c ensures electrical insulation between the cleaning electrode 17d and 
the recording electrode lines 17a buried below it. 
A cleaning power source 17e, capable of outputting a DC voltage having a 
polarity opposite to the electrification polarity of a developing agent is 
arranged between the cleaning electrode 17d and a cylindrical electrode 5. 
In this embodiment, the cleaning power source 17e, capable of outputting a 
voltage of +50 V is installed because the magnetic toner d having a 
negative electrification polarity is used. The voltage of +50 V is applied 
from the cylindrical electrode 5 to the cleaning electrode 17d to form a 
cleaning electric field for attracting the negative magnetic toner toward 
the cleaning electrode 17d. By this cleaning electric field, 
nontransferred toner d.sub.U " remaining on the circumferential surface of 
the cylindrical electrode 5 is transferred to the cleaning electrode 17d, 
thereby cleaning the surface of the cylindrical electrode 5, as will be 
described later. Since the cleaning electrode 17d as the cleaning means is 
buried in the recording electrode sheet 17, no exclusive installation 
space for the cleaning means is required to largely contribute to 
miniaturization of the electrostatic recording apparatus. 
In this embodiment, a step G corresponding to the thickness of the 
recording electrode sheet 17 is formed on the immediately downstream side 
of the recording position W. This step G satisfactorily separates magnetic 
toner d" transferred to the circumferential surface of the cylindrical 
electrode 5 to form a recording image from magnetic toner d' remaining on 
the surface of a development sleeve 15 after image formation, thereby 
reliably preventing an inconvenience in that the magnetic toners d' and d" 
interfere with each other to disturb the formed image. 
Referring to FIG. 15, a cleaning electric field is formed on the upstream 
side of the recording position W in a portion where the cleaning electrode 
17d faces the circumferential surface of the cylindrical electrode 5 upon 
application of the voltage of +50 V from the cylindrical electrode 5 to 
the cleaning electrode 17d. By this cleaning electric field, the 
nontransferred toner d.sub.U " remaining on the circumferential surface of 
the cylindrical electrode 5 is transferred to the cleaning electrode 17d. 
In addition, in this cleaning electric field formation region, the 
magnetic toner d conveyed along a toner convey path on the development 
sleeve 15 (recording electrode sheet 17) side and the nontransferred toner 
d.sub.U " recovered from the cylindrical electrode 5 temporarily remain to 
form a toner residue Rt. The nontransferred toner d.sub.U " is removed 
from the circumferential surface of the cylindrical electrode 5 also by 
the scraping effect of a toner chain grown in this toner residue Rt. In 
this manner, since the recording operation is performed again at the 
recording position W after the nontransferred toner d.sub.U " is removed 
from the circumferential surface of the cylindrical electrode 5, an image 
defect such as a residual image caused by poor cleaning does not occur, 
and a high-resolution recording image is stably formed. 
The magnetic toner d' not transferred to the surface of the cylindrical 
electrode 5 but remaining on the recording electrode sheet 17 moves away 
from the surface of the cylindrical electrode 5 immediately after passing 
through the recording position W because the step G is formed on the 
immediately downstream side of the recording position W. Therefore, an 
inconvenience in that a toner recording image consisting of the magnetic 
toner d" transferred to the surface of the cylindrical electrode 5 at the 
recording position W is disturbed by mutual interference with the residual 
magnetic toner d' on the surface of the development sleeve 15 can be 
reliably avoided. 
Note that the present invention is not limited to the above first, second, 
and third embodiments but can be variously modified within the technical 
scope of the present invention. 
For example, although a toner having negative (-) electrification is used 
in the embodiment shown in FIG. 2, a toner having positive (+) 
electrification can be also be used. In this case, a positive (+) polarity 
is imparted to the bias voltage to be applied to a recording electrode and 
a cylindrical electrode. 
As has been described in detail above, according to the first embodiment, a 
recording voltage is so controlled as to periodically form a toner 
recovering electric field each time one black dot is formed over a 
predetermined period, thereby suppressing the super-position phenomenon to 
stably form one black dot having an accurate size with a uniform toner 
adhesion amount. Therefore, since toner can be substantially uniformly 
deposited with good sharpness to the trailing end of an image even in a 
continuous dot recording image, a high-resolution dot recording image with 
good dot reproducibility can be obtained. 
According to the second embodiment, a developing agent is conveyed along 
the surface of the developing agent carrier member by the magnetic field 
conveying means, a plurality of parallel recording electrodes are arranged 
on the surface of the developing agent carrier member with a small gap 
defined with respect to the cylindrical electrode, and the leading end of 
each recording electrode is located on the upstream side along the 
developing agent conveying direction from a position opposite to a 
position on the cylindrical electrode surface closest to the developing 
agent carrier member. Therefore, a high-resolution recording image 
consisting of sharp dots each having a clear contour and good sharpness 
can be stably formed. 
According to the third embodiment of the present invention, a developing 
agent is vertically conveyed upward using a magnetic force from the bottom 
circulating path and then dropped to be returned to the circulating path. 
A plurality of parallel recording electrodes are arranged in the vertical 
convey path, and a cylindrical electrode also serving as an intermediate 
recording medium is arranged with a small gap therebetween. A cleaning 
electrode applied with a voltage having a polarity opposite to the charged 
polarity of the developing agent is arranged on the recording electrode 
side on the upstream side of a portion where the recording electrodes and 
the cylindrical electrode oppose each other. Therefore, the small gap in 
the electrode opposing portion required for formation of a high-resolution 
image can be accurately and stably assured, and a nontransferred 
developing agent can be reliably removed from the surface of the 
cylindrical electrode carrying a toner recording image. As a result, no 
image defect such as a residual image caused by poor cleaning occurs, and 
a high-resolution recording image can be stably formed on plain paper. 
In addition, since the cleaning electrode is arranged in the developing 
agent vertical convey path on the cylindrical member and the signal 
generating means connected to the recording electrodes is arranged in the 
central space of the bottom circulating path, not only no exclusive 
installation spaces for the cleaning means and the signal generating means 
are necessary, but also the recording means packaging a large number of 
recording electrodes at a high density can be incorporated in the 
developing agent conveying means. Therefore, the structure of the 
developing/recording section for simultaneously performing development and 
recording can be largely simplified. As a result, an electrostatic 
recording apparatus capable of stably forming a recording image having 
high resolution on plain paper can be made compact at a low manufacturing 
cost. 
Furthermore, since a developing agent can be uniformly supplied in the 
widthwise direction of the vertical convey path while being conveyed under 
agitation along the bottom circulating path, a variation in image density 
caused by nonuniform supply of the developing agent can be prevented. 
Moreover, since the electrostatic recording apparatus of the present 
invention is of a noncontacting recording type, the recording electrodes 
do not wear to improve the durability of the recording head. Therefore, 
the electrostatic recording apparatus capable of stably forming a 
high-resolution, accurate recording image over a long time period can be 
provided at low cost by miniaturization by the system of simultaneously 
performing development and recording. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, and representative devices shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.