Information
-
Patent Grant
-
6275669
-
Patent Number
6,275,669
-
Date Filed
Tuesday, March 7, 200024 years ago
-
Date Issued
Tuesday, August 14, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 399 90
- 432 60
- 219 216
- 439 242
- 439 243
- 439 239
-
International Classifications
-
Abstract
A movable power feeder supports one of terminals of a halogen heater while supplying electric power thereto. The movable power feeder is integrally formed by bending a phosphor bronze thin plate. One of the terminals is secured by use of a screw passing through first and second fastening plates. The first and second fastening plates are supported by a resilient supporting member. Thus, even when the halogen heater generates heat and thermally expands, the terminal shifts while being firmly held by a holding member and stably receiving electric power. Accordingly, the halogen heater is prevented from breaking.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fixing device that heats and melts toner adhering to paper in order to fix the toner thereto and form an image.
2. Description of the Related Art
In a conventional thermal fixing device of a laser beam printer, a hollow cylindrical drum, made of aluminum and covered by heat-resistant rubber, is used as a fixing drum, and a halogen heater is disposed inside the drum to heat the fixing drum.
The halogen heater is provided with a supporting member and a power feeding member, separately. The halogen heater is supported on the frame using the supporting member, while electric power is supplied to the halogen heater using the power feeding member through a flexible lead wire extending from the halogen heater. In the fixing device structured as described above, a power feeding member and a heater supporting member must be provided and assembled. Accordingly, the number of components as well as the number of assembling steps are increased and productivity is reduced. Another problem is that the halogen heater is pressed against the frame and secured directly thereto, which may cause the halogen heater to break.
To address the forgoing problems, Japanese Laid-Open Patent Publication No. 8-44233 discloses a fixing device in which a heater, which has, at its opposite ends, high rigidity pin-shaped terminals, is used to allow support of the heater as well as power supply to the heater. In such a heater, if the terminals at the opposite ends are supported while power is supplied thereto, a heater tube can be supported and supplied with power at the same time.
FIG. 12
shows the heater disclosed in the above publication. As shown in
FIG. 12
, a power feeding member of the heater is a thin metal plate
101
, bent into a U-shape, that holds a terminal
104
of a heater tube
103
disposed along a central axis of a fixing roller
102
. A power feeding terminal
105
is laminated with the thin metal plate
101
, and the power feeding terminal
105
and the thin metal plate
101
are secured to the frame
107
by a screw
106
.
The halogen heater heats up to high temperatures quickly when supplied with electric power. Quartz glass surrounding the periphery of the halogen heater has a lower linear thermal expansion coefficient than usual alkaline line glass, and a high stability against drastic temperature changes. However, quartz glass is low in mechanical strength and susceptible to mechanical shock and strain. Therefore, when the terminal
104
of the halogen heater is directly secured to the power feeding terminal
105
of the frame
107
, as disclosed in the above publication, the heater is apt to be broken due to mechanical strain caused by the difference in thermal expansion coefficient between the heater and the frame.
In another fixing device, a terminal of a heater is held by a power feeding terminal urged by a spring. In this case, the spring urging force is changed due to the difference in thermal expansion coefficient between the heater and the frame, and electric contact becomes unstable.
In still another fixing device, contact surfaces of a terminal of a heater and a terminal supporting member are made smooth, and the terminal is screw-held to the supporting member slidably under a predetermined pressure. However, polishing and smoothing is difficult. In addition, the terminal of the heater is usually made of tungsten, while the terminal supporting member, that is, an electrode, is made of phosphor bronze based upon this material's resilience and conductivity. The difference in hardness of the metals might cause biting and make sliding impossible.
SUMMARY OF THE INVENTION
An object of the invention, therefore, is to solve the forgoing problems and to provide a cost-effective power feeding member capable of stably supporting a heater tube without causing a breakage and stably supplying electric power to the heater tube.
In a fixing device according to the invention, an electrode of the power feeding member is supported by a supporting member such that the electrode can shift. Accordingly, even when the heater thermally expands, the electrode shifts in correspondence with the expansion. Thus, there is substantially no chance that the heater will break. Further, since terminals of the heater are firmly secured to respective electrodes, the heater can be stably supported by the electrodes and, at the same time, electric power can be stably supplied to the heater without causing poor electric contact. Since the supporting member also serves as the power feeding member, the number of components as well as the number of assembling steps can be reduced, resulting in a reduction of manufacturing cost and an increase of productivity.
According to the invention, the supporting member absorbs mechanical strain caused by the difference in thermal expansion coefficient between the heater and a frame, and thus the heater is reliably prevented from being broken.
In order to absorb mechanical strain, the supporting member is made of a resilient material that can resiliently deform and shift. Such resilience allows the heater to be stably supported at a predetermined position.
Further, the supporting member may be made of a resiliently deformable conductive material and integrally formed with the electrode. When the supporting member is integrally formed with the electrode, one member can serve as a heater supporting member and a power feeding member as well as an electrode supporting member. Accordingly, the number of components and the number of assembling steps are reduced, resulting in a reduction of manufacturing cost and an increase of productivity.
In addition, when the supporting member that supports the electrode is formed by a portion of the frame, the number of components and the number of assembling steps are reduced, resulting in a reduction of manufacturing cost and an increase of productivity.
When a halogen heater using a quartz glass tube is used as the heater, the heater can be stably supported without a breakage, even under generation of a great amount of heat or a quick rise in temperature and, as a result, performance of the fixing device is increased. No breakage occurs because quartz glass has a low linear thermal expansion coefficient and high stability against drastic temperature changes.
When pin-shaped terminals having rigidity capable of supporting the heater are used as the terminals, the heater can be supported stably only by the terminals and no other heater supporting members are required, which contributes to a reduction of manufacturing cost of the printer.
Only one of the terminals of the heater may be arranged to be held by a shiftable electrode, while an electrode for the other terminal is simple in structure. Compared with a heater supported at its both ends by shiftable electrodes, the number of components and the number of assembling steps are reduced, resulting in a reduction of manufacturing cost and an increase of productivity.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will be described with reference to the following figures wherein:
FIG. 1
is a sectional view of a printer as viewed from a side perpendicular to a paper feed direction;
FIG. 2
is a sectional view taken along the line II—II of
FIG. 4
;
FIG. 3
is a partially enlarged view of a laser scanner unit, a process unit, and a main frame of the printer of
FIG. 1
;
FIG. 4
is a plan view of the laser scanner as removed from the printer and viewed from the top;
FIG. 5
is a schematic view of a fixing unit;
FIG. 6
is a sectional view taken along the line VI—VI of
FIG. 5
as viewed from a direction opposite to the Z direction;
FIG. 7
is a perspective view of a movable power feeder
57
as viewed from the W direction of
FIG. 5
;
FIG. 8
shows the movable power feeder
57
as viewed from a direction opposite to the Z direction;
FIG. 9
is a fragmentary view of the movable power feeder
57
, with parts omitted, as viewed from the Y direction;
FIG. 10
shows a fixed power feeder
58
as viewed from a direction opposite to the Y direction;
FIG. 11
shows a modified movable power feeder;
FIG. 12
shows a conventional heater; and
FIG. 13
is a perspective view showing the communication of the first conductive member
578
a
, second conductive member
578
b
and connecting member
578
c
with features of the frame
51
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A laser beam printer using a fixing device according to the invention will now be described with reference to the accompanying drawings.
FIG. 1
is a sectional view of a printer
1
as viewed from a side perpendicular to a paper feed direction. The printer
1
is generally shaped to be rectangular parallelepiped by a main frame
11
. The right side of
FIG. 1
shows the front side of the printer
1
while the front side of
FIG. 1
shows the left side of the printer
1
. A paper feed cassette
19
accommodating paper P is provided in the lower part of the main frame
11
. The paper P accommodated in the paper feed cassette
19
is transported from the front side of the printer I by a transport unit
18
. Disposed above the transport unit
18
is a process unit
17
, and disposed above the process unit
17
is a laser scanner
12
.
In the process unit
17
, the laser scanner
12
scans a laser beam LB modulated based on image signals over a photoconductive drum
77
uniformly charged by a scorotron charger
78
, and thereby a latent image is formed. The latent image is developed into a toner image using toner T transported by the developing roller
75
. The toner image is transferred onto paper P by a transfer roller
87
. The paper P with the toner image transferred thereto is transported by the transport unit
18
to a fixing unit
15
disposed on the left of the process unit
17
. The fixing unit
15
heats and presses the paper P with the image to fix the toner T thereto. After that, the paper is discharged to a stacker
69
disposed at the rear or top of the printer by a paper discharge unit
16
that can change the paper discharge direction. The printer
1
is generally structured as described above. Each part of the printer
1
will now be described in detail.
As shown in
FIG. 1
, the paper feed cassette
19
is formed by a generally rectangular parallelepiped box-shaped frame
91
with its upper portion open. The paper feed cassette
19
is similar to a drawer with a handle
97
on its front, and is provided with an accommodating portion
92
where a stack of paper P is accommodated. A swingable paper lifter
93
is pivotally mounted at its base to the central portion of the bottom of the accommodating portion
92
. A coil spring (not shown) is disposed beneath the paper lifter
93
to urge the paper lifter
93
upwardly. Thus, the paper lifter
93
always keeps the uppermost sheet of paper P in contact with the paper feed roller
81
at an appropriate pressure either when paper P is stacked high or when paper P is running short and stacked low.
On the front side (on the right side of
FIG. 1
) of the paper lifter
93
, a separation pad
94
, made of a material having a high friction coefficient, is disposed facing the paper P. The separation pad
94
is urged by a coil spring
95
disposed beneath so as to press the paper P into contact with the paper feed roller
81
. The separation pad
94
feeds only the uppermost sheet to the transport unit
18
while stopping other sheets of paper P by its friction.
The paper feed cassette
19
can be drawn to the front, which facilitates paper supply and removal of jammed paper. When the paper feed cassette
19
is drawn, the separation pad
94
and the driven roller
96
are separated from the paper feed roller
81
to release the paper P pinched therebetween.
The transport unit
18
will now be described. Paper P is fed by the paper feed roller
81
and the driven roller
96
from the paper feed cassette
19
obliquely to the front (to the top right direction in FIG.
1
), and the leading edge of the paper P is guided upwardly by a guide
82
and further guided along the guide
82
to the rear. When the paper P is fed by the paper feed roller
81
and the driven roller
96
, the leading edge of the paper P pushes down a first paper feed sensor
83
to enter into and abut against a contact portion of a resist roller
84
and the driven roller
85
rotated by the resist roller
84
.
The resist roller
84
and the driven roller
85
straighten the paper P. The resist roller
84
is stopped for a predetermined duration after the first paper feed sensor
83
detects the leading edge of the paper P. Since the paper P is continuously fed by the paper feed roller
81
and the driven roller
96
, the leading edge of the paper P will abut against, but not enter into, the contact portion of the stopped resist roller
84
and the driven roller
85
, and thus the paper P cannot be fed further. However, the paper P still continues to be fed by the paper feed roller
81
and the driven roller
96
, the paper P, whose leading edge has been abutting against the resist roller
84
and the driven roller
85
, will slack in its intermediate portion due to lack of the guide
82
. All this while, the paper P is fed by the paper feed roller
81
and the driven roller
96
, and the leading edge of the paper entirely abuts against the contact portion of the resist roller
84
and the driven roller
85
. At this time, the leading edge of the paper P becomes accurately parallel with a rotation axis of the resist roller
84
. In other words, the paper P becomes straightened. In this condition, when the resist roller
84
is rotated by a control unit
20
in the paper feed direction, the paper P is fed in a straitened and proper orientation.
The paper P straitened by the resist roller
84
is further fed, and its leading edge pushes down a second paper feed sensor
86
and enters into a photoconductive drum
77
and a transfer roller
87
. The control unit
20
recognizes the position of the leading edge through the second paper feed sensor
86
. The control unit
20
feeds the paper P to its print starting position while leaving a margin.
The laser scanner
12
will now be described.
FIG. 4
is a plan view of the laser scanner
12
as viewed from the top (from the Y direction in FIG.
1
), with its cover
22
removed. As shown in
FIG. 4
, the laser scanner
12
is surrounded by a side wall
21
d of a supporting member
21
. Provided on the upper side (
FIG. 2
) of the laser scanner
12
are a light emitting unit
47
that includes a laser diode
41
, a laser diode holder
42
for holding the laser diode
41
, and a board
43
to which the laser diode
41
is connected, a collimator lens
45
that collimates a diffused laser beam emitted from the light emitting unit
47
, and a lens cell
44
with a slit regulating the collimated laser beam to a predetermined width. Optical elements that are also provided on the upper side of the laser scanner
12
include a first cylindrical lens
46
that converges the collimated laser beam LB on mirror surfaces of a polygon mirror
23
, the polygon mirror
23
that rotates at high speed and sequentially reflects the converged laser beam by six flat mirrors disposed at the sides of a hexagonal prism to change the direction of the laser beam and, a f( lens
31
that scans at constant speed the laser beam LB changed in direction at constant angular speed by the polygon mirror
23
over the surface of the photoconductive drum
77
(FIG.
3
), and a first fixed mirror
32
that refracts downwardly the laser beam passing the f( lens
31
.
FIG. 2
is a sectional view taken along the line II—II of FIG.
4
. As shown in
FIG. 2
, the laser scanner
12
is separated into the upper and lower sides by a partition
21
e
of the supporting member
21
, and optical elements are disposed on both sides. The laser beam reflected by the polygon mirror
23
passes the f( lens
31
and is diffused vertically (in the Y-axis direction) and refracted downwardly by the first fixed mirror
32
. Then the laser beam is diffused by a second fixed mirror
33
and travels substantially parallel with, and reverse to, the laser beam traveling on the upper side. Optical elements that are disposed on the lower side include a second fixed mirror
33
, a second cylindrical lens
34
that vertically converges the laser beam diffused by the second fixed mirror
33
to form an image on the photoconductive drum
77
, and a third fixed mirror
35
that diffuses and reflects the converged laser beams toward the photoconductive drum
77
.
As shown in
FIG. 3
, the laser scanner
12
scans laser beam LB modulated based on image data over the photoconductive drum
77
to form a latent image.
FIG. 3
is a partially enlarged view of the laser scanner
12
, the process unit
17
, and the main frame
11
.
As shown in
FIG. 3
, the process unit
17
has a frame
70
that accommodates and supports all of the component parts. The frame is roughly divided into a developer chamber
71
and a developing chamber
73
. In the developer chamber
71
, non-magnetic single component toner T is accommodated and a blade-shaped agitator
72
is supported by a rotating shaft driven by a motor (not shown). Thus, the toner T is constantly supplied, by rotation of the agitator
72
, from the developer chamber
71
to the developing chamber
73
.
The developing chamber
73
is provided with the photoconductive drum
77
, a developing roller
75
disposed at the front of the photoconductive drum
77
and rotating in contact with, and in a reverse direction to, the photoconductive drum
77
, and a supply roller
74
disposed at the front of the developing roller
75
and rotating in the same direction as the developing roller
75
. The developing chamber
73
is further provided with a paper dust eliminator
79
disposed at the rear of the photoconductive drum
77
, a charger
78
disposed above the photoconductive drum
77
, and a layer thickness regulating blade
76
in contact with the surface of the developing roller
75
.
The supply roller
74
rotates, and presses its spongy surface into contact with, the developing roller
75
to apply toner particles thereto. The layer thickness regulating blade
76
is urged by a predetermined pressure to be in contact with the developing roller
75
and scrapes excessive toner T off the developing roller
75
to make the amount of toner adhering thereto uniform.
The photoconductive drum
77
is driven to rotate in the paper feed direction (clockwise in
FIG. 3
) and transports the paper P in cooperation with the transfer roller
87
. In advance, the paper dust eliminator
79
eliminates paper dust adhered to the photoconductive drum
77
. The paper dust eliminator
79
is formed by a brush or an nonwoven wiper and traps paper dust while letting pass the toner remaining on the photoconductive drum
77
. The remaining toner, having passed the paper dust eliminator
79
, faces the charger
78
by rotation of the photoconductive drum
77
.
The charger
78
is provided with a tungsten wire
78
a,
50-100 μm in diameter, disposed in parallel with, and away approximately 10 mm from, the photoconductive drum
77
. Although the wire
78
a
is covered by an aluminum shield electrode
78
d
, a groove is defined in a portion facing the photoconductive drum
77
. This groove receives a grid electrode
78
b
made of several wires or a mesh that is electrically insulated from the shield electrode
78
d.
On the opposite side of the shield electrode
78
d
from the side facing the photoconductive drum
77
, a hole
78
c
extends along the longitudinal direction of the photoconductive drum
77
and opens to the scanner support (main frame)
11
. A cleaning member is guided through the hole
78
c
, which pinches and slides along the contaminated wire
78
a.
The wire
78
a
is connected to a positive pole of a power source (not shown) and subjected to high voltages of 5-10 kv. Positive ions generated through the application of high voltages move to the surface of the photoconductive drum
77
, and thereby the surface of the drum
77
is charged. The charging potential can be controlled by biasing the grid electrode
78
b
or by varying the voltage applied to the wire
78
a
. The charger
78
positively charges the surface of the photoconductive drum
77
. The scorotron type charger
78
may be replaced by a corotoron type charger without the grid electrode
78
b
. Any other type of charger, for example a type using a brush, may be used as long as it generates corona discharge.
Of the surface of the photoconductive drum
77
, portions positively charged by the charger
78
are irradiated with the laser beams LB by the laser scanner
12
. The photoconductive drum
77
is formed by an OPC (organic photoconductor), which is relatively low in durability but light and relatively inexpensive. When the surface of the photoconductive drum
77
is irradiated with the laser beam LB, portions irradiated with the laser beam LB become high in conductivity and low in charging potential, and thereby a latent image is formed due to the potential difference. The photoconductive drum
77
may be formed by a photoconductor made of a-Si (amorphous silicon) sensitive to light emitted at high speed and having long-life conductivity, a selenium photoconductor made of Se or Se-alloy, or by a photoconductor made of CdS (cadmium sulphide).
The portions on the photoconductive drum
77
where the latent image is formed make contact with the developing roller
75
to which toner T is applied. The developing roller
75
includes a stainless steel roller shaft and a base material formed around the roller shaft and made of carbon black-dispersed, conductive silicon rubber or urethane rubber. The surface of the roller is coated with fluororesin. The toner T applied to the developing roller
75
is frictionally positively charged by the supply roller
76
and the layer thickness regulating blade.
When the developing roller
75
makes contact with the photoconductive drum
77
, the toner T adheres to the portions irradiated with the laser beam LB and charged to a low potential. As a result, the toner T develops the latent image into a visible image. The toner remaining on the photoconductive drum
77
is collected by the developing roller
75
. The developed image is transported by rotation of the photoconductive drum
77
to the position facing the paper P nipped by the drum
77
and the transfer roller
87
.
The transfer roller
87
is formed by a conductive roller covered by a base material made of carbon black-dispersed, conductive silicon rubber or urethane rubber. The transfer roller
87
is connected to a negative pole of the power source (not shown) and subjected to a voltage. Application of negative voltage to the transfer roller
87
maintains the potential of the paper P negative. The transfer roller
87
is urged toward the photoconductive drum
77
to bring the paper P into contact therewith. The toner image formed on the photoconductive drum
77
is transferred onto the paper P due to the potential difference between the toner and the paper P.
The fixing unit
15
will now be described in detail.
FIG. 5
is a schematic view of the fixing unit
15
, with the parts lower than the paper feed path omitted, as viewed from the bottom of
FIG. 1
(from a direction opposite to the Y direction).
FIG. 6
is a sectional view of the fixing unit
15
taken along the line VI—VI of
FIG. 5
as viewed from the Z direction.
Component parts of the fixing unit
15
are disposed on a frame
51
and integrally mounted to the printer
1
. As shown in
FIG. 6
, in the fixing unit
15
, a heat roller
52
having a halogen heater
53
, a pressure roller
54
urging the paper P to the heat roller
52
, a first discharge roller
55
(
FIG. 6
) disposed downstream in the paper feed direction, first and second driven rollers
56
a
,
56
b
driven by the first discharge roller
55
, and a paper discharge sensor
61
, are integrally disposed on the frame
51
.
The heat roller
52
, as shown in
FIG. 5
with parts omitted, extends substantially along the paper width in a direction (Z direction) perpendicular to the paper feed direction and is rotatably mounted at its opposite ends to frames
51
e
,
51
f
through bearings
52
a
,
52
b
. At this time, the surface of the heat roller
52
makes close contact with paper P. The heat roller
52
is a hollow cylinder made of aluminum-alloy and its outer surface is coated with fluororesin to prevent the toner T from adhering thereto when heated. A drive gear rotatably supported at its opposite ends by the bearings
52
a
,
52
b
, and driven by a motor (not shown) through a gear train, is abutted against a gear portion
52
c
provided at the Z-direction side end (on the left side of
FIG. 5
) of the heat roller
52
, and rotates in the paper feed direction (clockwise in FIG.
6
).
The halogen heater
53
is disposed along a central axis of the heat roller
52
and terminals
53
a
,
53
b
, provided at opposite ends of the halogen heater
53
, are fixedly held by a movable power feeder
57
and a fixed power feeder
58
, respectively. The halogen heater
53
is a halogen lamp formed by a quartz glass tube, as a body, having a tungsten filament (not shown) and filled with halogen gas. The halogen heater
53
can quickly heat its internal temperature to high temperatures when turned on. Due to the so-called halogen cycle, tungsten evaporated from the tungsten filament will return to the tungsten filament without adhering to the inside of the quartz glass tube. Consequently, blackening of the quartz glass is prevented and the amount of heat emitted will not be reduced. The filament will not become thin and thus will have a long service life. The halogen heater
53
, when turned on, heats the heat roller
52
from the inside and raises the surface temperature thereof.
The pressure roller
54
is disposed so as to press the paper P transported to the heat roller
52
into contact with the same. The surface of the pressure roller
54
is made of heat-resistant silicon rubber and coated with fluororesin to prevent the toner T from adhering thereto. The pressure roller
54
is rotated by rotation of the heat roller
52
. The pressure roller
54
is supported at its opposite ends by bearings urged by respective coil springs (not shown) toward the heat roller
52
, and nips the paper P together with the heat roller
54
.
As shown in
FIG. 1
, when the paper P is transported to the fixing unit
15
, the pressure roller
54
urges and presses the paper P with a toner image formed thereon against the surface of the heat roller
52
. At this time, since the surface of the heat roller
52
is at high temperatures, the toner T is melted to penetrate into fibers of the paper P. At this stage, the toner T is kept at relatively high temperatures and is not fully hardened. When the paper T is cooled by the outside air, the toner T is hardened and the toner image formed on the paper P is fully fixed.
Then the paper P is discharged from the fixing unit
15
by the first discharge roller
55
, which is disposed downstream in the paper feed direction from the heat roller
52
and driven by a motor (not shown), and first driven rollers
56
a
and second driven rollers
56
b
, which are driven by the first discharge roller
55
. A discharge direction switching unit
62
is disposed downstream in the paper feed direction from the first driven rollers
56
a
and the second driven rollers
56
b
of the fixing unit
15
.
The discharge direction switching unit
62
has a guide rib
62
a
defining the curved paper feed path where the leading edge of the paper P is guided rearward (leftward in FIG.
1
), upward, and then frontward of the printer I to the stacker
69
. The guide rib
62
a
is journaled at its upper portion by a journal member
62
b
. The journal member
62
b
is restricted by a restricting member
62
d
so as to be movable only vertically and is urged downward by a wire spring
62
e.
A torsion coil spring integrally formed with the wire spring
62
e
is also provided to the journal member
62
b
and urges the guide rib
62
a
to flip it up rearward (to the top left in FIG.
1
). The guide rib
62
a
, when closed, is locked at its lower end by a nearby lock
63
provided on the main frame
11
.
In the discharge direction switching unit
62
structured as described above, since the guild rib
62
a
, when locked by the lock
63
, is urged downward by the wire spring
62
e
, the guide rib
62
a
is not released from its locked state and is not flipped up rearward by the coil spring. Thereby, the leading edge of the paper P discharged from the fixing unit
15
is guided by the guide rib
62
a
to the stacker
69
. At the front of the stacker
69
, an extension tray
68
is pivotally mounted so as to be extendible frontward.
On the other hand, when the guide rib
62
a
is flipped up by raising a finger piece
62
f
, the journal member
62
b
moves upward along the restringing member
62
d
against the urging force of the wire spring
62
e
and releases the guide rib
62
a
from the lock
63
. Then, the guide rib
62
a
is flipped up rearward around the journal member
62
b
by the torsion coil spring. In this state, the paper P, discharged from the fixing unit
15
by the first discharge roller
55
and the driven rollers
56
a
,
56
b
, is discharged to the rear of the printer
1
without being transported to the guide rib
62
a
. At the rear of the printer, a paper discharge tray (not shown) is mounted so as to accommodate a stack of paper P.
As shown in
FIG. 1
, a control unit
20
is provided at the rear portion of the main frame
11
. The control unit
20
comprises a CPU, a ROM, and a RAM. The control unit
20
controls input and processing of image data, emission from the laser diode
41
, the polygon mirror drive motor
24
, the transport unit
18
, the halogen heater
53
, the power source, and the entire system of the printer.
The movable power feeder
57
and the fixed power feeder
58
of the fixing unit
15
according to the invention will now be described in more detail.
As shown in
FIG. 5
, the movable power feeder
57
is disposed in a direction opposite to the Z direction (on the right side of
FIG. 5
) of the heat roller
52
of the fixing unit
15
. As shown in
FIG. 6
, the movable power feeder
57
and the fixed power feeder
58
support the terminals
53
a
,
53
b
of the halogen heater
53
coaxially with the axis of the heat roller
52
. For convenience in illustrating the structure, some parts including the bearings
52
a
,
53
b
and the gear portion
52
c
are omitted from FIG.
6
.
FIG. 7
is a perspective view of the movable power feeder
57
as viewed from the W direction of FIG.
5
.
FIG. 8
shows the movable power feeder
57
as viewed from a direction opposite to the Z direction, and
FIG. 9
is a fragmentary view of the movable power feeder
57
, with parts omitted, as viewed from the Y direction.
The movable power feeder
57
is formed by bending a thin plate having resilience and made of highly conductive metals, such as phosphor bonze or stainless steel. In this embodiment, phosphor bronze is used.
Referring to
FIG. 8
, the movable power feeder
57
will be described. The movable power feeder
57
is formed by laminating a first fastening plate
571
a
and a second fastening plate
571
b
such that the first fastening plate
571
a
is bent, at its X-direction side end,
180
degrees downwardly (to the Y direction) and continues into the second fastening plate
571
b
. A screw
579
is threaded into a screw hole
574
. A comer
571
c
is curved at an appropriate radius to prevent clacking.
As shown in
FIGS. 7
to
9
, an insertion guide
572
, in the form of a semicircular hopper that is open on the Z-direction side, is provided on the side opposite to the X-direction of the first fastening plate
571
a
. The end of the terminal
53
a
is guided by the insertion guide
572
and inserted into a holding member
573
. The holding member
573
communicates with the insertion guide
572
and has a semicircular tunnel-like space extending along the Z direction. The internal space defined by the holding member
573
is slightly smaller than the diameter of the terminal
53
a
of the halogen heater. The terminal
53
a
is fitted into this space and held by the holding member
573
and a surface of the second fastening plate
571
b.
As shown in
FIG. 8
, the screw
579
is threaded into the screw hole
574
formed on the X-direction side through the first fastening plate
571
a
and the second fastening plate
571
b
. The screw
579
engages the screw hole
574
threaded in the second fastening plate
571
b
. Thereby, the first fastening plate
571
a
is pressed into contact with the second fastening plate
571
b
and the terminal
53
a
of the halogen heater
53
is firmly secured. Consequently, the first fastening plate
571
a
, the second fastening plate
571
b
, and the terminal
53
a
become reliably electrically conductive.
On the Y-direction side of the insertion guide
572
, a rectangular apron guide
575
extends from the second fastening plate
571
b.
As shown in
FIGS. 8 and 9
, a frame
51
a is provided in the vicinity of the movable power feeder
57
, and a rectangular rotation stopper
576
extends toward the Y direction from the end opposite to the X direction of the second fastening plate
571
b
. The stopper
576
is placed along the nearby frame Sla and restricts the movement in the X direction of the first fastening plate
571
a
and the second fastening plate
571
b
. The frame
51
a
and the movable power feeder
57
are usually out of contact with each other.
As shown in
FIG. 7
, a supporting member
577
extends zonally toward the Y direction from the Z-direction side end near the fixing hole
574
. The first fastening plate
571
a
, the second fastening plate
571
b
, the guide
575
, and the rotation stopper
576
are out of contact with the frame
51
and supported only by the supporting member
577
.
As shown in
FIGS. 7 and 13
, a first conductive member
578
a
extends zonally from the Y-direction side end of the supporting member
577
toward the Z direction and perpendicularly to the Y direction while being fitted into a slot
578
g
of the frame
51
. A projection
578
h
provided at the end opposite to the Z direction of the first conductive member
578
a
is fitted into a hole
578
i
provided in the frame
51
, which limits movement of the first conductive member
578
a
in the Y direction. Further, a second conductive member
578
b
zonally extends from the Z-direction side end of the first conductive member
578
a
toward the Z direction and perpendicularly to the Y direction while being in contact with the frame
5
1
. The conductive members
578
a
,
578
b
extend along the shape of the frame
51
and apart from the heat roller
52
. In addition, a connecting member
578
c
is provided to be coplanar with the second conductive member
578
b
and to project from the Z-direction side end thereof toward the X direction. As shown in
FIGS. 5 and 13
, the connecting member
578
c
has a screw hole
578
j
in which a screw
578
d
is inserted for electrical connection to the power source. The connecting member
578
c
also has a pair of protrusions
578
k
that communicate with corresponding walls
5781
of the frame
51
to correctly position the connecting member
578
c
in the Z direction. When the screw
578
d
is threaded into the screw hole
578
j
, the projection
578
h
provided at the end of the first conductive member
578
a
is secured to the frame
51
, and thereby the movable power feeder
57
is firmly secured to the frame
51
.
In the movable power feeder
57
structured as described above, the first fastening plate
571
a
, the second fastening plate
571
b
, the guide
575
, and the rotation stopper
576
are out of contact with the frame
51
and supported by the supporting member
577
. On the other hand, since the supporting member
577
is made of a resilient material, the holding member
573
is shiftable in the Z direction due to its resilience. Thus, even when the terminal
53
a
moves in the Z direction, the holding member
573
shifts as the terminal
53
a
moves while firmly holding the terminal
53
a.
As shown in
FIG. 5
, the terminal
53
b
on the left side (Z-direction side) of the halogen heater
53
is secured to the fixed power feeder
58
.
FIG. 10
shows the fixed power feeder
58
as viewed from the Y direction. As shown in
FIG. 10
, the fixed power feeder
58
is formed by bending a thin plate made of highly conductive metals, such as phosphor bonze or stainless steel. In this embodiment, phosphor bronze is used.
As shown in
FIG. 10
, the fixed power feeder is formed by laminating a first fastening plate
581
a
and a second fastening plate
581
b
such that the first fastening plate
581
a
is bent
180
degrees downwardly (toward the Y direction) at its end opposite to the X direction and continues into the second fastening plate
581
b
. A screw
589
is threaded into a screw hole
574
. A corner
581
c
is curved on an appropriate radius to prevent clacking.
As shown in
FIG. 10
, an insertion guide
582
in the form of a semicircular hopper, that is open on the side opposite to the Z-direction, is provided on the side opposite to the X-direction of the first fastening plate. The end of the terminal
53
b
is guided and inserted into a holding member
583
. The holding member
583
communicates with the insertion guide
582
and has a semicircular space extending along the Z direction. The internal space defined by the holding member
583
is slightly smaller than the diameter of the terminal
53
b
of the halogen heater
53
. As shown in
FIG. 5
, the terminal
53
b
penetrates this space and is held by the holding member
583
and a surface of the second fastening plate
581
b.
As shown in
FIG. 5
, the fixed power feeder
58
is disposed on a frame
51
d
. A screw
589
passes through a screw hole
584
formed on the X-direction side through the first fastening plate
581
a
and the second fastening plate
581
b
, and is threaded into the frame
51
d
. By means of the screw
589
, the fastening plates
581
a
,
581
b
are immovably secured to the frame
51
while the terminal
53
b
of the halogen heater
53
is firmly held. Consequently, the fastening plates
581
a
,
581
b
and the terminal
53
b
become electrically conductive.
As shown in
FIG. 10
, a plate
587
extends toward the Z direction from the first fastening plate
581
a
of the fixed power feeder
58
. The plate
587
is provided with a boss hole
586
b
into which a boss (not shown) provided on the frame
51
d
is fitted. A notch
586
a
is also provided at the X-direction side end of the plate
587
. The notch
586
a
and the boss hole
586
b
prevent the second fastening plate from rotating.
A connecting member
588
extends zonally from the plate
587
toward the Z direction. A cord (not shown) is soldered to an opening
588
a
formed at the tip of the connecting member to receive power from the power source.
As described above, the fixed power feeder
58
secures the terminal
53
b
of the halogen heater
53
to the frame
51
d
while firmly holding the terminal
53
b
, and thereby supports the halogen heater
53
. Further, the power cord connected to the connecting member
588
ensures power supply to the halogen heater
53
.
In the printer
1
according to the embodiment, the maximum paper width is approximately 210 mm, and the heat roller
52
and the halogen heater
53
have substantially the same length in the paper width direction as the maximum paper width. Since the linear thermal expansion coefficient of quartz glass is approximately 5.5×10
−7
, the body
53
c
of the halogen heater
53
, when turned on and heated, is elongated approximately 0.05 mm due to the thermal expansion.
At the same time, when the halogen heater
53
is turned on and heated, its surface temperature is raised and the heat roller is heated from the inside. The surface temperature of the heat roller
52
is raised to approximately 200° C. The surrounding frame
51
is also heated to 160° C. The frame
51
is made of dimensionally stable PET (polyethylene terephthalate). The linear thermal expansion coefficient of PET is approximately 2.0×10
−5
. When the halogen heater
53
is heated, the distance between the movable power feeder
57
and the fixed power feeder
58
is elongated approximately 0.8 mm due to thermal expansion of the frame
51
(made of modified PPE (polyphenylene ether)).
In other words, thermal expansion causes a shift of approximately 0.8 mm between the halogen heater
53
and the frame
51
that supports the halogen heater
53
. Thus, when the halogen heater
53
is immovably supported by the frame
51
, as in the conventional case, quartz glass having low mechanical strength may break.
In the above-described embodiment, since the resilient supporting is member
577
absorbs mechanical strain, the halogen heater
53
is not affected or broken by the mechanical strain.
Further, since the terminals
53
a
,
53
b
of the halogen heater
53
are firmly held by the holding members
573
,
583
, respectively, even when the holding member
573
shifts in the Z direction, poor electric contact is not caused and stable power supply is reliably maintained.
A temperature fuse
578
f
will now be described. As shown in
FIG. 5
, the screw
578
d
passes through the screw hole in the connecting member
578
c
provided at the Z-direction side end of the movable power feeder
57
and is threaded into a fastening member
51
b
. The temperature fuse
578
f
is disposed on the Z-direction side (to the left in
FIG. 5
) of the fastening member
51
b
and in the vicinity of the surface of the heat roller
52
. One terminal of the temperature fuse
578
f
is inserted to be sandwiched between the connecting member
578
c
and the fastening member
5
lb. The other terminal of the temperature fuse
578
f
is inserted to be sandwiched between a fastening member
51
c
and a fastening plate
578
g
made of phosphor bronze. A screw
578
e
passes through the fastening plate
578
g
and is threaded into the fastening member
51
c
, and thereby the other terminal is securely held. The other end of the temperature fuse
578
f
is wired through a hole (not shown) formed in the frame
51
to the back in
FIG. 5
(in the Y direction) and connected to the power source (not shown).
As shown in
FIG. 5
, a temperature sensor
59
is disposed above (in a direction opposite to the X direction of) the central portion of the heat roller
52
. The temperature sensor
59
includes a thermister
59
a
for detecting a temperature and a thermister support
59
b
. The thermister support
59
b
, made of heat-resistant resin, for example, a PI (polyimide) tape, is fixed at its one end to the frame
51
and supports and urges the thermister
59
a
so as to make sliding contact with the heat roller
52
. The thermister
59
a
in sliding contact with the heat roller
52
measures the surface temperature of the heat roller
52
and sends a signal to the control unit
20
(FIG.
1
). In response to the signal from the thermister
59
a
, the control unit
20
controls the surface temperature of the heat roller
52
, when it is higher than a predetermined temperature, by turning off the halogen heater
53
or reducing output of the halogen heater
53
.
Faulty temperature control by the thermister
59
a
and the control unit
20
may cause the heat roller
52
to overheat, resulting in a reduction in image quality and a deformation of the frame
51
. When the heat roller
52
is in danger of overheating due to the faulty temperature control, the temperature fuse
578
f
interrupts power supply to the halogen heater
53
to prevent the heat roller
52
from overheating.
In the printer
1
according to the embodiment, the terminals
53
a
,
53
b
of the halogen heater
53
are fastened to the holding members
573
,
583
by means of screws
579
,
589
, and the fixed power feeder
58
is firmly secured to the frame
51
. Thereby, the halogen heater
53
is supported in a stable manner. Even when the halogen heater
53
is turned on and heats up rapidly and the frame
51
expands thermally, such expansion is absorbed by the supporting member
577
. Thus, the halogen heater
53
will not be broken due to mechanical strain on the halogen heater.
Further, by use of the halogen lamp
53
having high thermal efficiency, quick thermal fixing can be achieved.
Further, since the terminals
53
a
,
53
b
are firmly fastened to the holding members
573
,
583
of the movable power feeder
57
and the fixed power feeder
58
, electric connections are reliably established. Accordingly, poor contact due to contaminated contact surfaces, insufficient urging force, and improper sliding due to biting is not caused by the difference in hardness of metals, ensuring stable power supply over an extended period of time.
Especially, the movable power feeder
57
is integrally formed by the holding member
573
on the first fastening plate
571
a
that holds the terminal
53
a
and serves as an electrode, the supporting member
577
that supports the first fastening plate
571
and the holding member
573
, and a wiring member that includes the second fastening plate
571
b
, supporting member
577
, first conductive member
578
a
, and second conductive member
578
b
. The movable power feeder
57
can be manufactured easily and at low cost by punching a plate out of a thin phosphor bronze sheet and bending the plate.
In the above-described embodiment, although only one terminal
53
a
of the halogen heater
53
is supported by the movable power feeder
57
, the other terminal
53
b
may also be arranged in the same manner.
In addition, although the holding member
573
is integrally formed with the supporting member
577
that supports the holding member
573
, they may be separately formed.
In this case, the supporting member
577
may be formed as part of the frame
51
. As shown in
FIG. 11
, a supporting member
51
g is integrally molded with the frame
51
into a thin plate and makes the power feeder movable. The supporting member
51
g
has appropriate resilience so as to absorb strain and prevents a breakage of the halogen heater
53
when the frame
51
thermally expands. In this case, as the supporting member
51
g
is insulative, a fastening portion
571
c
is provided on the second fastening plate
571
b
and power is supplied to this portion using a flexible power cord. A ring-shaped terminal is soldered to the end of the flexible power cord. The screw
579
passes through the ring-shaped hole of the terminal and the screw hole
574
and is threaded into the supporting member
51
g
, and thereby electric connection is reliably established. With this arrangement, the same effects as obtained in the above-described embodiment can be obtained. The terminal
53
a
of the halogen heater
53
and the holding member
573
are electrically connected in a stable manner. At the same time, the halogen heater
53
is firmly supported by the frame
51
, while its resilience is used to absorb mechanical strain on the halogen heater
53
and prevent breakage thereof.
The terminals
53
a
,
53
b
of the halogen heater
53
are not necessarily linear or pin-shaped. They may be tape-shaped, J-shaped, or looped. In such cases, the holding member
573
may be flat, or fastening screws may be used to fasten the J-shaped or looped portion. The holding member
573
may be of any shape that supports the terminal
53
a
of the halogen heater
53
and ensure reliable electric connection.
The heater may be, instead of the halogen heater
53
, a glass tube supporting a Ni—Cr alloy or a ceramic heater. The invention can be applied to any type of heater that generates high heat, undergoes thermal expansion, and has low mechanical strength.
Claims
- 1. A thermal fixing device for use with a recording medium, comprising:a heat roller that heats the recording medium; a pressure roller disposed opposed to the heat roller that presses the recording medium into contact with the heat roller; a frame that supports the heat roller and the pressure roller; a heater disposed inside the heat roller and provided with terminals at opposite ends thereof that receive electric power; electrodes fixed to the terminals of the heater and supplying the electric power to the heater, at least one of the electrodes not being directly fixed to the frame; and a supporting member disposed between the at least one of the electrodes and the frame that supports the at least one of the electrodes such that the at least one of the electrodes and one of the terminals fixed to the at least one of the electrodes can jointly shift while maintaining electric contact therebetween.
- 2. The fixing device according to claim 1, wherein the supporting member absorbs a difference in elongation between the heater and the frame caused, during heat generation by the heater, by a difference in linear expansion coefficient between the heater and the frame.
- 3. The fixing device according to claim 1, wherein the supporting member is made of a resilient material that can resiliently deform and shift.
- 4. The fixing device according to claim 1, wherein the supporting member is made of a resiliently deformable conductive material and is integrally formed with at least one of the electrodes.
- 5. The fixing device according to claim 1, wherein the supporting member is a supporting portion that is integrally formed with the frame and is resiliently deformable.
- 6. The fixing device according to claim 1, wherein the heater is a halogen heater that includes a quartz glass tube.
- 7. The fixing device according to claim 1, wherein the terminal is a pin-shaped terminal that has a rigidity capable of supporting a body of the heater.
- 8. The fixing device according to claim 1, wherein the supporting member deformably supports only one of the electrodes connected to one of the terminals of the heater, and the other electrode is secured to the frame.
- 9. A thermal fixing device for use with a recording medium, comprising:a heat roller that heats the recording medium; a pressure roller disposed opposed to the heat roller that presses the recording medium into contact with the heat roller; a frame that supports the heat roller and the pressure roller; a heater disposed inside the heat roller and provided with terminals at opposite ends thereof that receive electric power; electrodes fixed to the terminals of the heater and supplying the electric power to the heater; and a supporting member disposed between at least one of the electrodes and the frame that supports the at least one of the electrodes such that the at least one of the electrodes can shift, the at least one of the electrodes including a first fastening plate and a second fastening plate that extend substantially parallel to each other.
- 10. The fixing device according to claim 9, wherein the first fastening plate and the second fastening plate are connected to each other by a curved portion.
- 11. The fixing device according to claim 10, wherein the first fastening plate, the second fastening plate and the curved portion are integrally formed and are laminated.
- 12. The fixing device according to claim 11, wherein the curved portion is curved at an appropriate radius to prevent cracking.
- 13. The fixing device according to claim 12, wherein the first fastening plate defines a holding member that holds the at least one of the terminals.
- 14. The fixing device according to claim 13, wherein the holding member defines a semicircular tunnel-like space that is slightly smaller than a diameter of the at least one of the terminals.
- 15. The fixing device according to claim 14, wherein the first fastening plate defines an insertion guide that guides the at least one of the terminals into the holding member.
- 16. The fixing device according to claim 15, wherein the insertion guide defines a semicircular hopper.
- 17. The fixing device according to claim 16, wherein the first fastening plate and the second fastening plate each define corresponding screw holes.
- 18. The fixing device according to claim 17, wherein the supporting member includes a screw insertable through the screw holes of the first fastening plate and the second fastening plate to press the first fastening plate, the second fastening plate and the at least one of the terminals into contact with each other.
- 19. The fixing device according to claim 18, wherein the supporting member includes a rectangular rotation stopper that extends perpendicular to a direction of extension of the first fastening plate and the second fastening plate, the rectangular rotation stopper restricting movement of the first fastening plate and the second fastening plate in the direction of extension of the first fastening plate and the second fastening plate.
- 20. The fixing device according to claim 19, wherein the supporting member includes a supporting element that extends perpendicular to the direction of extension of the first fastening plate and the second fastening plate and supports the first fastening plate, the second fastening plate and the rectangular rotation stopper.
- 21. An image forming apparatus, comprising:an image forming unit that forms an image onto a recording medium; and the fixing device according to claim 1, wherein the fixing device makes the image on the recording medium permanent.
- 22. The image forming apparatus according to claim 21, wherein the image forming unit includes:a photosensitive member; an exposure unit that forms an electrostatic latent image on the photosensitive member; a developing unit that supplies developer to the photosensitive member; and a transfer unit that transfers the developer on the photosensitive member to the recording medium.
Priority Claims (1)
Number |
Date |
Country |
Kind |
11-092287 |
Mar 1999 |
JP |
|
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
5974285 |
Tomatsu |
Oct 1999 |
|
Foreign Referenced Citations (1)
Number |
Date |
Country |
8-44233 |
Feb 1966 |
JP |