Image forming device having sheet conveyance device

An image forming device for forming an image on a sheet. A pair of transport rollers are provided for transporting the sheet by their rotation so that the sheet exits from between the pair of rollers while substantially aligned with a tangent plane of both of the pair of rollers. An elongated chute is provided for guiding the sheet after the sheet exits from between the pair of transport rollers. The chute is supported so as to intersect the tangent plane to cross from one side of the tangent plane to another in the direction followed by the sheet. A toner control electrode is supported adjacent to the chute at its end opposite the transport rollers. A back electrode with an electrode tip is supported so that the electrode tip confronts the toner control electrode as separated by a space. The sheet is transported through the space as guided by the chute.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a image forming device and more 
particularly to the image forming device having a sheet transportation 
unit for transporting a sheet to be printed on past a print head. 
2. Description of the Related Art 
There has been known an image forming device having an elongated flat plate 
(hereinafter referred to as chute) for guiding a sheet to be recorded on. 
The chute is supported so as to run between a toner fixing device and a 
pair of rotatable transport rollers. An aperture electrode body and a back 
electrode with an electrode tip are supported near the center of the chute 
on opposite sides thereof. The back electrode and aperture electrode are 
positioned so that the aperture electrode and the electrode tip of the 
back electrode are separated by a space. 
A sheet to be recorded on is transported between the pair of transport 
rollers by the rotation thereof. The thus transported sheet follows the 
chute toward the toner fixing device, thereby passing through the space 
separating the aperture electrode and the tip of the back electrode. 
The space separating the aperture electrode and the tip of the back 
electrode is extremely narrow. Although actual values vary with the 
voltage applied to the back electrode, the space can be as narrow as 0.5 
mm to 1 mm. To accurately feed the sheet through this space, the pair of 
transport rollers need to be as close to the aperture electrode and the 
back electrode as possible. 
However, other components, such as those required for development 
processes, also must be positioned near the aperture electrode. This 
limits how close the pair of transport rollers can be positioned adjacent 
to the aperture electrode and the back electrode. Conventionally the chute 
is supported between the thermal fixing device and the pair of transport 
rollers so as to be substantially parallel to a direction tangential to 
both transport rollers. Because of this the sheet is unstably transported 
between the aperture electrode and the back electrode during printing. 
Because the toner charged by and discharged from the aperture electrode 
body does not become fixed when it impinges to the sheet surface, the 
characters formed from toner on the surface of the sheet might be smudged 
if scraped against the aperture electrode body. The quality of printed 
characters can therefore suffer greatly. Additional components such as 
plate springs can be provided to support and stabilize the posture of the 
sheet, but adding new components increases costs. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to overcome the 
above-described drawbacks, and to provide an inexpensive image forming 
device that effectively uses the stiffness of the sheet to be printed on 
so that the sheet can be passed stably through the space separating a 
conductor electrode, of, for example, an aperture electrode, and a back 
electrode without contacting the conductor electrode thereby producing 
good quality printed images without smudges. 
An image forming device according to the present invention includes a pair 
of transport rollers, an elongated chute, a toner control electrode, and a 
back electrode. 
The pair of transport rollers are rotatably supported so as to be rotatable 
in opposite directions. The pair of transport rollers are for transporting 
the sheet therebetween by the rotation thereof so that the sheet exits 
from between the pair of rollers in a tangential direction while 
substantially aligned with a tangent plane of both of the pair of rollers. 
The elongated chute is for guiding the sheet after the sheet exits from 
between the pair of transport rollers. The chute has at opposite ends 
thereof a roller end and a back electrode end. The chute is supported so 
as to intersect the tangent plane so that the roller end is on one side of 
the tangent plane in confrontation with a roller of the pair of transport 
rollers and so that the back electrode end is on another side of the 
tangent plane. 
The toner control electrode is supported on the another side of the tangent 
plane adjacent to the back electrode end of the chute. 
The back electrode has an electrode tip. The back electrode is supported 
adjacent to the back electrode end of the chute so that the electrode tip 
is on the another side of the tangent plane and is closer to the tangent 
plane than the toner control electrode and so that the electrode tip 
confronts the toner control electrode as separated by a space. The sheet 
is transported through the space as guided by the chute. 
The chute preferably defines a chute plane which divides space into a toner 
control electrode side and another side. The toner control electrode is 
supported in the toner control electrode side. The back electrode is 
supported so that the tip electrode cuts across the chute plane and 
protrudes into the toner control electrode side. 
It is preferable that the toner control electrode be formed with a 
plurality of apertures having axes. The apertures are aligned in the toner 
control so that their axes define an axis plane that is perpendicular to 
the chute plane. An angle formed between the axis plane and the tangent 
plane is preferably less than 90o and preferably corresponds to a space 
that encompasses the back electrode end of the chute section. 
It is preferable that a toner supply roller is supported adjacent to the 
toner control electrode for supplying toner thereto. The toner supply 
roller is supported at a side of the toner control electrode opposite a 
side at which the back electrode is supported. The toner supply roller has 
an axis through which an axis plane passes. The axis plane is 
perpendicular to the chute plane. An angle formed between the axis plane 
and the tangent plane is preferably less than 90.degree. and preferably 
corresponds to a space that encompasses the back electrode end of the 
chute section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An image forming device according to a preferred embodiment of the present 
invention will be described while referring to the accompanying drawings 
wherein like parts and components are designated by the same reference 
numerals to avoid duplicating description. 
FIG. 1 is a cross-sectional view of a facsimile machine according to the 
present invention. The facsimile machine includes a document supply system 
30, a document reading system 40, and a document discharge system (36, 51) 
disposed along a document transport path. 
The document supply system 30 includes a document tray 31, a paper supply 
roller 33, a separator 34, and a document transport roller 35. The 
document tray 31 is provided at the top of the facsimile machine at a 
downward slant. Several sheets of documents 32 to be transmitted can be 
stacked on the document tray 31 with the image surface (surface recorded 
with an image to be transmitted) facing downward. The document supply 
roller 33, the separator 34, and the document transport rollers 35 are 
disposed in order along the document transport path between the lower end 
of the document tray 31 and the document reading system 40. 
The document reading system 40 includes a light emission diode (LED) 41, 
reflection mirrors 43 and 42, a focus lens 44, and a charge coupled device 
(CCD) 45. The reflection mirrors 43 and 42, the focus lens 44, and the 
charge coupled device (CCD) 45 are disposed along a path followed by light 
produced by the LED 41 and reflected off the document 32 in the document 
reading system 40. 
The document discharge system includes a discharge roller 36 and a 
discharged document tray 51. The discharge roller 36 is provided adjacent 
to the document reading system 34 for picking up a read document 32 and 
discharging it from the facsimile machine. The discharged document tray 
51, which is for receiving document sheets 32 discharged by the discharge 
roller 36, is provided to the top surface of a sheet supply cassette 50 
provided at the base of the facsimile machine. 
When a document is to be transmitted, the supply roller 33 and the 
separator 34 separate one document sheet 32 at a time from the stack and 
transport it toward the document transport roller 35. The document 
transport roller 35 picks up the separated document sheet 32 and 
transports it toward the document reading system 40. The image surface of 
the document sheet 32 is illuminated by the LED 41. The illumination light 
reflects off the image surface of the document sheet 32 toward the 
reflection mirrors 43 and 42. The reflection mirrors 43 and 42 reflect the 
light so it is incident on the CCD 45 after being focused by the focus 
lens 44. After being read, the document sheet 32 is discharged by the 
discharge roller 36 onto the discharge document tray 51. 
The facsimile machine further includes a sheet supply system, a sheet 
transport system 70, a development process unit 60, a thermal fixing 
device 80, and a sheet discharge system all disposed along a sheet 
transport path followed by a sheet to be recorded on from the sheet supply 
cassette 50 of the sheet supply system to a discharged sheet tray 85 of 
the sheet discharge system. 
The sheet supply system includes the sheet supply cassette 50, a supply 
roller 53, and a pair of claws 54 (only one of the pair of claws is shown 
in FIG. 1), all disposed in order along the sheet transport path. The 
sheet supply cassette 50 stores a stack of sheets of a predetermined size 
for receiving incoming images. The supply roller 53 is semicircular in 
cross section. 
The facsimile machine is provided with a housing 10. A panel cover 20 is 
swingably attached to the housing 10 and so can be opened and closed. The 
housing 10 includes a curved partition 11 with a tip portion 11a. A charge 
removing brush 12 for removing charges from sheets 52 supplied from the 
sheet supply cassette 50 is fixed to the tip portion 11a of the partition 
11. 
The transport system 70 includes a pair of transport relay rollers 71 and 
72 and a chute 73 (to be described later). The pair of relay rollers 71 
and 72 are disposed adjacent to the development process unit 60 at 
opposite sides of the sheet transport path between the charge removing 
brush 12 and the development process unit 60. The pair of relay rollers 71 
and 72 are rotatably supported about their axes, in the directions 
indicated by the arrows in FIG. 2, so that a sheet 52 with charge removed 
by the charge removing brush 12 is serially transported between the supply 
rollers 71 and 72 following a line L1 that is tangential to both relay 
rollers 71 and 72. Line L1 described while referring to the 
cross-sectional view shown in FIG. 2 would, in three-dimensional space, be 
a tangent plane of both relay rollers 71 and 72. 
The development process unit 60 is similar to the image recording 
apparatuses described in detail in U.S. Pat. Nos. 5,229,794 and 5,231,427, 
the disclosures of which are herein incorporated by reference. As shown in 
FIGS. 1 and 2, the development process unit 60 includes a toner casing 61 
positioned directly upstream (in regards to the direction a sheet moves in 
the sheet transport path) of the transport system 70 and the tip portion 
11a of curved partition 11. Toner 62 fills the toner casing 61. An 
agitator 63 for preventing the toner from clumping is provided in the 
toner casing 61. A toner supply port 61a is formed in the lower left hand 
side (as viewed in FIG. 2) of the toner casing 61. A supply roller 64 is 
supported on its axis in the toner supply port 61a so as to be rotatable 
about its axis in the direction indicated by the arrow in the drawing. 
A supplementary chamber 61b is provided adjacent to the toner supply port 
61a. A toner bearing roller 65 is rotatably supported on its axis in the 
supplementary chamber 61b so as to contact the toner supply roller 64 
while the toner bearing roller 65 and the toner supply roller 64 rotate. A 
toner layer regulating plate 66 is fixed to the inner wall of the 
supplementary chamber 61 for regulating the thickness of the toner layer 
on the surface of the toner bearing roller 65. 
An elongated aperture electrode 67 is provided to the supplementary chamber 
61b adjacent to the toner bearing roller 65 at one side of the sheet 
transport path. A plurality of apertures 67a are formed in the aperture 
electrode 67 so that the axes of the plurality of apertures 67a are 
parallel with each other. The aperture electrode 67 is positioned so that 
the axis of an aperture 67a is aligned with a line L2 that is 
perpendicular with the axis of the toner bearing roller 65. Although line 
L2 was described while referring to cross-sectional FIG. 2, in 
three-dimensional space the line L2 would be a plane substantially aligned 
with the axes of all the apertures 67a and passing through the axis of the 
toner bearing roller 65. The aperture electrode 67 is electrically 
connected to a control unit (not shown) for controlling the aperture 
electrode 67 according to a control voltage so as to draw toner from the 
toner bearing roller 65 toward and through desired apertures 67a. 
The chute 73 of the transport system 70 is formed from three elongated 
sections: a first section 73a, a second section 73b, and a third section 
73c. The first section 73a is a substantially planer plate supported 
between the relay rollers 71 and 72 and one side of line L2 so that if 
extended so as to intersect line L2 it would be perpendicular to line L2. 
The first section 73a is positioned so as to intersect line L1 at an 
intersection point P upstream from the aperture electrode 67, the first 
section 73a crossing in the downstream direction from one side of line L1 
to the side of L1 on which the aperture electrode 67 is provided. 
The second section 73b is supported between the other side of line L2 and 
the thermal fixing device 80. The third section 73b of the chute 73 is 
supported between the thermal fixing device 80 and the discharge sheet 
system. The first through third sections 73a through 73b can be, for 
example, three separate sections separately supported, three sections 
connected together, or one continuous piece with openings formed therein 
at the back electrode 74 and the thermal fixing unit 80. A tip sensor 75 
for optically detecting the sheet and determining the timing for start of 
recording on the sheet is provided confronting the first section 73a. 
A back electrode 74 is mounted between the first section 73a and the second 
section 73b so that its length runs parallel to the lengthwise direction 
of the aperture electrode 67. It should be noted that the lengthwise 
direction of the aperture electrode 67 and the back electrode 74 is the 
direction cut through to form the cross-sectional views shown in the 
diagrams. The back electrode 74 is supported on the side of the sheet 
transport path opposite the side on which the aperture electrode 67 is 
provided. The back electrode 74 is supported so that its electrode tip 74a 
confronts the apertures 67a of the aperture electrode 67 and cuts across 
the sheet transport path (as guided by the first section 73a) so as to 
protrude in the direction of the apertures 67a a distance A as shown in 
FIG. 3. In the present embodiment distance A is between 1.5 to 2.0 mm but 
other values are possible. The electrode tip 74a of the back electrode 74 
and the aperture electrode 67 are separated by a space B shown in FIG. 3. 
In the present embodiment space B is about 0.5 mm wide although other 
values are possible. The back electrode 74 is positioned so that a line 
dividing its cross-sectional surface (see FIG. 3) is aligned with line L2. 
The thermal fixing device 80 is positioned downstream from the development 
process unit 60. The thermal fixing device 80 includes a pressure spring 
(not shown), a pressure roller 82, and a heat roller 81 with an internal 
heater 81a. The heat roller 81 and the pressure roller 82 are rotatably 
provided so as to contact each other while rotating. The pressure spring 
is provided to as to press the pressure roller 82 against the heat roller 
81. 
The sheet discharge system includes a discharge sensor 84 and, as shown in 
FIG. 1, a discharge roller 83 and the discharged sheet tray 85. 
The following is an explanation of an image recording operation of the 
facsimile machine according to the present embodiment. Rotation of the 
supply roller 53 draws the top sheet from the stack of sheets 52 stored in 
the cassette. One sheet at a time is separated from the stack by the pair 
of claws 54 and fed toward the pair of relay rollers 71 and 72. The relay 
rollers 71 and 72 transport the sheet 52 downstream in alignment with line 
L1. 
The agitator 63 supplies toner 62 to the toner supply port 61a. Rotation of 
the toner supply roller 64 transports toner from the toner supply port 61a 
toward the toner bearing roller 65. Rotation of the toner bearing roller 
65 scrapes toner off the surface of the toner supply roller 64 where the 
surface of the toner supply roller 64 and the surface of the toner bearing 
roller 65 contact. Rotation of the toner bearing roller 65 supplies toner 
to the apertures 67a. 
The sheet 52 transported from the relay rollers 71 and 72 abuts the first 
section 73a of the chute 73 at point P. The resiliency or stiffness of the 
sheet 52 urges the sheet 52 in the direction of the first section 73a, 
that is, urges the sheet 52 to return to a path parallel with line L1, 
thereby forming the portion of the sheet 52 between the relay rollers 71 
and 72 and point P on the first section 73a into an arc shape. The charge 
removing brush 12 removes any charge from the surface of the sheet 52 to 
be recorded on. The sheet 52 is guided by following the chute 73 until it 
reaches the position of the tip sensor 75. The tip sensor 75 detects the 
front edge of the sheet 52. 
The first section 73a guides the sheet 52 to the back electrode 74. The 
sheet 52 first hits the back electrode 74. The sheet then passes over the 
back electrode 74 so as to pass between the back electrode 74 and the 
aperture electrode 67 while in firm contact with the back electrode 74. 
When the front edge of the sheet 52 as determined by the tip sensor 75 has 
passed a predetermined distance past the tip electrode surface 74a of the 
back electrode 74 and the apertures 67a of the aperture electrodes 67, the 
aperture electrodes 67 are selectively energized by application of voltage 
according to an image signal from the control unit (not shown). The image 
signal can be generated according to, for example, an incoming signal from 
a remote facsimile machine or image information read from the document 32 
by the document reading system 40. The toner is controllingly passed 
through the apertures 67a of the aperture electrode 67. Toner that passes 
through the apertures 67a is attracted by the electric field produced by 
the back electrode 74. The toner impinges on the sheet 52 to form an image 
thereon. 
In this way an unfixed toner image is serially formed on the sheet 52 while 
it follows the chute 73 toward the thermal fixing unit 80. As mentioned 
above the angle a formed by lines L1 and L2 is less than 90.degree.. 
Therefore the first section 73a intersects line L1 at point P so that the 
portion of the first section 73a upstream from the intersection point P is 
on one side of line L1 and the portion of the first section 73a downstream 
from intersection point P is on the other side of line L1. Because the 
sheet 52 is urged to return to a path parallel with line L1, the sheet 52 
is urged against the second section 73b. The sheet 52 will therefore not 
come into contact with the aperture electrode 67 even if only a narrow 
space separates the opposing surfaces of the aperture electrode 67 and the 
electrode tip 74a of the back electrode 74. The unfixed toner image will 
therefore not be smudged. The resiliency from the arc does not allow the 
sheet 52 to touch the surface of the aperture electrode 67 and the sheet 
52 is normally pressed on the electrode tip of the back electrode 74 as 
guided by following the chute 73. 
The sheet 52 with a toner image formed thereon is guided by the second 
section 73b of the chute 73 toward the thermal fixing device 80. The toner 
image is thermally fixed by the heat roller 81 and the pressure roller 82. 
The sheet 52 with the fixed toner image is guided by the third section 73c 
of the chute 73 toward the discharge roller 83 and is discharged thereby 
onto the discharged sheet tray 85. 
As described above, in the present invention the first section 73a of the 
chute 73 is provided so as to intersect line L1 at intersection point P. 
Therefore the first section 73a intersects line L1 at point P so that the 
portion of the first section 73a upstream from the intersection point P is 
on one side of line L1 and the portion of the first section 73a downstream 
from intersection point P is on the other side of line L1. Therefore even 
if only a narrow space separates the opposing surfaces of the aperture 
electrode 67 and the electrode tip 74a of the back electrode 74, the 
resiliency from the arc does not allow the sheet 52 to touch the surface 
of the aperture electrode 67. Because of this, and because the back 
electrode 74 is positioned in the path of a sheet guided by the first 
section 73a, the sheet 52 is pressed in good contact with the electrode 
tip 74a of the back electrode 74 when guided by the first section 73a. The 
surface of the sheet 52 with the unfixed toner will not touch the aperture 
electrode 67 and so will not smudge. As a result, quality of recorded 
images is stable without adding extra components and raising the cost of 
production. 
Although the present invention has been described in detail with reference 
to a specific embodiment thereof, it would be apparent to those skilled in 
the art that various changes and modifications may be made therein without 
departing from the spirit of the invention. 
For example, the preferred embodiment described the present invention used 
in a facsimile machine. However, the present invention can be used in 
other image forming devices as well, such as printers and plotters. Also 
the toner 62 was described as being a one component non-magnetic toner 
used in electrophotographic copy machines. However, other types of toner 
can be used, such as a single component magnetic toner or a toner with 
more than one component. Also a mesh type electrode can be used instead of 
the aperture electrode 67.