U.S. patent application number 15/098651 was filed with the patent office on 2016-11-03 for sheet conveying apparatus, and image forming apparatus.
The applicant listed for this patent is TOSHIBA TEC KABUSHIKI KAISHA. Invention is credited to Masao YAMAGUCHI.
Application Number | 20160318724 15/098651 |
Document ID | / |
Family ID | 57203995 |
Filed Date | 2016-11-03 |
United States Patent
Application |
20160318724 |
Kind Code |
A1 |
YAMAGUCHI; Masao |
November 3, 2016 |
SHEET CONVEYING APPARATUS, AND IMAGE FORMING APPARATUS
Abstract
In one embodiment, a sheet conveying apparatus has a first
conveying guide and a second conveying guide which is opposite to
the first conveying guide. The sheet conveying apparatus further
has at least one first concave portion. The first concave portion
is provided in the first conveying guide to be recessed in a
direction to separate from one surface of a sheet.
Inventors: |
YAMAGUCHI; Masao;
(Katsushika Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOSHIBA TEC KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
57203995 |
Appl. No.: |
15/098651 |
Filed: |
April 14, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65H 2601/521 20130101;
B65H 5/38 20130101; B65H 2404/52131 20130101; B65H 5/062 20130101;
B65H 2404/512 20130101; B65H 2404/5211 20130101 |
International
Class: |
B65H 5/38 20060101
B65H005/38; B65H 5/06 20060101 B65H005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2015 |
JP |
2015-093145 |
Claims
1. A sheet conveying apparatus, comprising: a first conveying guide
which is arranged at one surface side of a sheet to be conveyed; a
second conveying guide which is arranged opposite to the first
conveying guide, and at the other surface side of the sheet; and at
least one first concave portion which is provided in the first
conveying guide to be recessed in a direction to separate from the
one surface of the sheet.
2. The sheet conveying apparatus according to claim 1, further
comprising: at least one second concave portion which is provided
opposite to at least the one first concave portion, and in the
second conveying guide to be recessed in a direction to separate
from the other surface of the sheet.
3. The sheet conveying apparatus according to claim 2, wherein: a
plurality of sets of the facing first and second concave portions
are provided.
4. The sheet conveying apparatus according to claim 2, further
comprising: a plurality of sound absorption chambers each of which
is formed by the facing first and second concave portions.
5. The sheet conveying apparatus according to claim 4, wherein: the
plurality of sound absorption chambers have different lengths in a
conveying direction of the sheet.
6. The sheet conveying apparatus according to claim 5, wherein: the
first conveying guide has an inner surface which is opposite to the
one surface of the sheet, and a protrusion which is provided on the
inner surface to contact the sheet.
7. An image forming apparatus, comprising: an image forming device
which forms an image on a sheet; a first conveying path which
conveys a sheet on which the image is to be formed to the image
forming device, and discharges the sheet which has passed through
the image forming device; a second conveying path which conveys a
sheet formed with a document image for forming the image to a
reading position for reading the document image, and discharges the
sheet from the reading position; a first conveying guide which is
provided in at least one conveying path of the first and second
conveying paths, and is arranged at one surface side of the sheet;
a second conveying guide which is provided in the one conveying
path, and is arranged opposite to the first conveying guide, and at
the other surface side of the sheet; and at least one first concave
portion which is provided in the first conveying guide to be
recessed in a direction to separate from the one surface of the
sheet.
8. The image forming apparatus according to claim 7, further
comprising: at least one second concave portion which is provided
opposite to at least the one first concave portion, and in the
second conveying guide to be recessed in a direction to separate
from the other surface of the sheet.
9. The image forming apparatus according to claim 8, wherein: a
plurality of sets of the facing first and second concave portions
are provided.
10. The image forming apparatus according to claim 9, further
comprising: a plurality of sound absorption chambers each of which
is formed by the facing first and second concave portions.
11. The image forming apparatus according to claim 10, wherein: the
plurality of sound absorption chambers have different lengths in a
conveying direction of the sheet.
12. The image forming apparatus according to claim 11, wherein: the
first conveying guide has an inner surface which is opposite to the
one surface of the sheet, and a protrusion which is provided on the
inner surface to contact the sheet.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2015-093145, filed on Apr. 30, 2015, the entire contents of which
are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a sheet
conveying apparatus to convey a sheet along a conveying guide, and
an image forming apparatus having this sheet conveying
apparatus.
BACKGROUND
[0003] Conventionally, as a sheet conveying apparatus, an apparatus
in which a sound absorbing material is provided on an inner surface
of a conveying guide, in order to reduce noise at the time of
conveying a sheet is known. A concave portion so as to increase a
surface area of the sound absorbing material is provided, on a
surface of the sound absorbing material.
[0004] For example, in an image forming apparatus such as a copying
machine and a printer, when a sheet is conveyed along a conveying
guide, a friction sound is generated due to sliding contact between
a surface of the conveying guide and the sheet. In addition, a
collision sound is also generated between a sheet to be conveyed
and a conveying roller. In addition, a sound when a sheet to be
conveyed on a curved conveying path warps, and a sound when an edge
of the warped sheet abuts against a conveying guide, and so on are
also generated. In addition, a sound of a motor to drive a
conveying roller and a sound of a fan, and so on are generated.
[0005] In order to check a frequency characteristic of a sound
generated from a copying machine, a microphone was installed at a
position 1 m away from the front of the copying machine, and an
operation sound was measured when a document was fed via an
automatic document feeder of the copying machine. An example of the
result obtained by performing a frequency analysis of the measured
operation sound is shown in FIG. 17. In the graph of FIG. 17, a
vertical axis is a sound pressure level, and a horizontal axis is a
frequency. When FIG. 17 is seen, it is understood that the
operation sound at the time of conveying a document via the
automatic document feeder has a wide frequency band. That is, since
noise caused by the conveyance of a sheet is a sound in which the
above-described various sounds are mixed, its frequency band also
becomes wide.
[0006] For this reason, when a sound absorbing material is simply
provided on a conveying guide, as in the above-described
conventional image forming apparatus, though a sound of a specific
frequency band can properly be absorbed, but on the other hand, the
effect of absorbing a sound of the other frequency band can hardly
be expected. FIG. 18 shows a sound absorption characteristic when a
thickness of urethane foam that is a representative sound absorbing
material is changed. A vertical axis of the graph of FIG. 18 is a
vertical incident method sound absorptivity (an absorptivity
measured by a vertical incident method), and a horizontal axis is a
frequency. According to FIG. 18, in any cases of thicknesses, a
sound absorptivity shows a peak at about 2000 Hz. According to FIG.
18, it is understood that a sound absorption effect of a sound of a
frequency other than about 2000 Hz is small. That is, when a sound
absorbing material was only provided on the conveying guide, a
sound contained in a certain specific frequency band could be
reduced, but it was difficult to reduce the whole noises. In
addition, a sound absorbing material is used, and thereby the
number of components increases, and the manufacturing cost of the
apparatus becomes high.
[0007] Accordingly, the development of a sheet conveying apparatus
which can reduce a sound of a wide frequency band with an
inexpensive configuration has been desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic diagram showing an image forming
apparatus according to an embodiment.
[0009] FIG. 2 is a schematic diagram showing a sheet conveying
apparatus according to an embodiment.
[0010] FIG. 3 is an enlarged diagram showing the sound deadening
structure provided in the document conveying path of FIG. 2.
[0011] FIG. 4 is a sectional diagram along F4-F4 of FIG. 2.
[0012] FIG. 5 is a sectional diagram along F5-F5 of FIG. 2.
[0013] FIG. 6 is a sectional diagram showing a modification of FIG.
5.
[0014] FIG. 7 is a sectional diagram showing a modification of FIG.
5.
[0015] FIG. 8 is a sectional diagram showing a modification of FIG.
5.
[0016] FIG. 9 is a sectional diagram showing a modification of FIG.
5.
[0017] FIG. 10 is a schematic diagram showing an example of a
testing device for describing an attenuation amount of a sound by
the sound deadening structure of FIG. 3.
[0018] FIG. 11 is a graph showing the relation between an
attenuation amount and L/.lamda. described using the device of FIG.
10.
[0019] FIG. 12 is a diagram showing an attenuation amount
distribution when a length L of the absorption chamber of FIG. 3 is
set to 0.01 m.
[0020] FIG. 13 is a diagram showing an attenuation amount
distribution when the length L of the absorption chamber of FIG. 3
is set to 0.02 m.
[0021] FIG. 14 is a diagram showing an attenuation amount
distribution when the length L of the absorption chamber of FIG. 3
is set to 0.03 m.
[0022] FIG. 15 is a graph showing the change of an attenuation
amount when the length L of the sound absorption chamber of FIG. 3
is changed.
[0023] FIG. 16 is a schematic diagram showing a modification in
which a protrusion is provided on the upper guide plate of FIG.
6.
[0024] FIG. 17 is a graph showing a result obtained by performing a
frequency analysis of an operation sound of a conventional copying
machine.
[0025] FIG. 18 is a graph showing a characteristic of a
conventional sound absorbing material.
DETAILED DESCRIPTION
[0026] According to one embodiment, a sheet conveying apparatus has
a first conveying guide, a second conveying guide, and a first
concave portion. The first conveying guide is arranged at one
surface side of a sheet to be conveyed. The second conveying guide
is arranged opposite to the first conveying guide, and at the other
surface side of the sheet. The first concave portion is provided in
the first conveying guide to be recessed in a direction to separate
from the one surface of the sheet, by at least one. The first
concave portion extends a conveying space defined between the first
conveying guide and the second conveying guide, to cause an
acoustic impedance to be changed, for example, and thereby reduces
a sound generated at the time of conveying the sheet.
[0027] Hereinafter, further embodiments will be described with
reference to the drawings. In the drawings, the same symbols
indicate the same or similar portions. FIG. 1 is a schematic
diagram showing a copying machine 100 according to an embodiment of
an image forming apparatus. The copying machine 100 has an image
forming device 10 at an approximately central portion in a chassis
101. The image forming device 10 forms an image, based on a
document image read by a scanner 7 described later, or a document
image obtained from the outside. For example, the image forming
device 10 has a yellow image forming unit 10Y, a magenta image
forming unit 10M, a cyan image forming unit 10C, a black image
forming unit 10B. The image forming units 10Y, 10M, 10C, 10B of the
four colors are arranged together separately from each other in the
horizontal direction. Each of the image forming units 10Y, 10M, 1C,
10B has a photoreceptor that is an image carrier. The image forming
unit 10Y forms a toner image of yellow color on the photoreceptor,
using a toner of yellow color. The image forming unit 10M forms a
toner image of magenta color on the photoreceptor, using a toner of
magenta color. The image forming unit 1C forms a toner image of
cyan color on the photoreceptor, using a toner of cyan color. The
image forming unit 10B forms a toner image of black color on the
photoreceptor, using a toner of black color. Hereinafter, the
above-described toner image is simply called an image.
[0028] The copying machine 100 further has a transfer device, a
sheet feeding device, a sheet conveying device, a fixing device, a
sheet discharge device, and a reading device. The transfer device
has a transfer belt 1, and a transfer roller 3. The transfer belt 1
is an endless belt which is arranged along the respective
photoreceptors of the image forming units 10Y, 10M, 10C, 10B. The
above-described images of the four colors, for example, formed by
the image forming units 10Y, 10M, 10C, 10B are transferred from the
above-described respective photoreceptors to the transfer belt 1.
The transfer belt 1 runs while carrying the above-described image.
The sheet feeding device has a sheet feeding cassette 2 and a
pickup roller 2a. The sheet feeding cassette 2 houses a sheet P
(sheet) on which the above-described image is to be formed. The
pickup roller 2a picks up the sheet P from the sheet feeding
cassette 2, and feeds the sheet P to a main conveying path 8 (a
first conveying path) of the sheet conveying device. The sheet
conveying device has the above-described main conveying path 8. The
main conveying path 8 is a conveying path of the sheet P, from the
above-described sheet feeding device to the conveying device, via
the transfer roller 3 of the transfer device and the fixing device.
The main conveying path 8 conveys the sheet P to be fed by the
pickup roller 2a to a position of the transfer roller 3 of the
above-described transfer device. The transfer roller 3 is arranged
opposite to the transfer belt 1. The transfer roller 3 transfers
the above-described image carried by the transfer belt 1, from the
transfer belt 1 to the sheet P. The main conveying path 8 conveys
the sheet P to which the above-described image(s) has been
transferred to the fixing device. The fixing device is a fixing
unit 4 including a heat roller not shown, for example. The fixing
unit 4 fixes the image to one surface of the sheet P. The image is
finally formed on the sheet P, with the above-described processes
by the above-described respective devices. The main conveying path
8 conveys the sheet P formed with the image to the sheet discharge
device. The sheet discharge device has a sheet discharge tray 5 and
a sheet discharge roller 5a. The sheet discharge roller 5a
discharges the sheet P formed with the image to the sheet discharge
tray 5. The sheet discharge tray 5 holds the discharged sheet P.
The reading device has a document table 6 and the scanner 7. The
document table 6 supports a document D to be loaded on the surface
thereof. The document D is a sheet (sheet) on which a document
image for image forming by the above-described image forming device
is formed. The scanner 7 scans the document D supported on the
document table 6, to read the document image of the document D.
[0029] Further, the scanner 7 scans the document D to be fed to a
reading position of the document table 6 by an automatic document
feeder 110 described later, to read the document image of the
document D. Each of the above-described image forming units 10Y,
10M, 10C, 10B of the respective colors forms an electrostatic
latent image based on each color component of the document image
read by the scanner 7, on the above-described photoreceptor. Each
of the image forming units 10Y, 10M, 10C, 10B develops the
electrostatic latent image using the toner of each color, to form
the above-described toner image of each color, on the
above-described photoreceptor. The images formed on the respective
photoreceptors are transferred to the transfer belt, as described
above.
[0030] The sheet P is picked up from the sheet feeding cassette 2
by the pickup roller 2a, as described above, and is conveyed to the
transfer position by the transfer roller 3 of the transfer device,
and the fixing position by the fixing device, by the main conveying
path 8. As described above, the superposed image of the respective
colors carried on the transfer belt 1 is transferred to the sheet P
at the above-described transfer position by the transfer roller 3.
The sheet P on which the image has been transferred is further made
to pass through the fixing unit 4 by the main conveying path 8. The
toners of the respective colors of the above-described image which
has been transferred to the sheet P are melted by the fixing unit
4, and thereby are fixed to the sheet P. The sheet P formed with
the image is further discharged to the sheet discharge tray 5 by
the sheet discharge roller 5a, as described above.
[0031] The copying machine 100 further has an inversion conveying
path 9. When forming images on both surfaces of the sheet P, the
copying machine 100 reverses the sheet discharge roller 5a in the
state to sandwich the sheet P formed with an image on the
above-described one surface (a front surface). The sheet discharger
roller 5a is reversed, to lead the relevant sheet P to the
inversion conveying path 9. The inversion conveying path 9 feeds
the sheet P led by the sheet discharge roller 5a to the main
conveying path 9 again, in the front/back inversed state. The main
conveying path 8 conveys the sheet P in the front/back inversed
state to the transfer position by the transfer roller 3 of the
transfer device, and the fixing position by the fixing device, as
described above. Accordingly, an image is also formed on the other
surface (a back surface) of the sheet P.
[0032] FIG. 2 is a schematic diagram showing the automatic document
feeder 110 (hereinafter, referred to as the ADF 110) that is an
embodiment of a sheet conveying apparatus. The ADF 110 has a sheet
feeding tray 111, a sheet discharge tray 112, and a document
conveying device, as shown in FIG. 2. The sheet feeding tray 111
holds the document D. The document D held by the sheet feeding tray
111 is fed to a document conveying path 113 of a document conveying
device, by a sheet feeding roller not shown, for example. The
document conveying device has the above-described document
conveying path 113 (a second conveying path). The document
conveying path 113 conveys the document D fed from the sheet
feeding tray 111 to the above-described reading position. Further,
the document conveying path 113 discharges the document D which has
passed through the above-described reading position to the sheet
discharge tray 112. The sheet discharge tray 112 holds the
discharged document D. Further, the document conveying device of
the ADF 110 has a plurality of conveying rollers arranged along the
document conveying path 113, and sound deadening structures 20
described later which are arranged in the middle of the document
conveying path 13.
[0033] In the copying machine 100 having the above-described ADF
110, since the sheet P is conveyed in the chassis 101, and the
document D is conveyed in the ADF 110, the above-described
operation sound in accompany with the conveying operation is
generated. Since the copying machine 100 is generally installed in
an office and used therein, it is desirable to make the operation
sound like this small as much as possible.
[0034] For this reason, in the present embodiment, the sound
deadening structures 20 are respectively provided in the main
conveying path 8 and the inversion conveying path 9 each of which
conveys the sheet P in the chassis 101 of the copying machine 100,
and further in the document conveying path 113 which conveys the
document D in the ADF 110. By this means, sounds generated at the
time of conveying the sheets (the sheet P and the document D) can
be reduced, as a whole of the copying machine 100 including the ADF
110. Since the sound deadening structures provided in the
respective conveying paths 8, 9, 113, and sound deadening
mechanisms thereof are the same, in the following description, the
sound deadening structure 20 provided in the document conveying
path 113 of the ADF 110 will be described as a representative, and
the description of the sound deadening structures 20 provided in
the main conveying path 8 and the inversion conveying path 9 will
be omitted.
[0035] FIG. 3 is an enlarged sectional diagram of the sound
deadening structure 20 provided in the ADF 110 of FIG. 2. FIG. 4 is
a sectional diagram along F4-F4 of FIG. 2, and FIG. 5 is a
sectional diagram along F5-F5 of FIG. 2. In the present embodiment,
the sound deadening structures 20 are provided at two positions
along the document conveying path 113 (hereinafter, simply referred
to as the conveying path 113).
[0036] The above-described document conveying device of the ADF 110
has an upper guide plate 22 (a first conveying guide) and a lower
guide plate 24 (a second conveying guide). The upper guide plate 22
is arranged in the conveying path 113 at one surface side (for
example, an upper side in FIG. 4 and FIG. 5) of the document D to
be conveyed in the conveying path 113. The lower guide plate 24 is
arranged in the conveying path 113 at the other surface side (for
example, a lower side in FIG. 4 and FIG. 5) of the document D to be
conveyed in the conveying path 113. In the following description,
one surface and the other surface of the document D are sometimes
called conveying surfaces. Further, one surface side and the other
surface side of the document D are sometimes called one side of the
conveying surface and the other side of the conveying surface,
respectively. The above-described sound deadening structure 20 has
a structure obtained by performing a shape processing of the upper
guide plate 22 (first conveying guide), and the lower guide plate
24 (second conveying guide), for example. The upper guide plate 22
and the lower guide plate 24 respectively have flat inner surfaces
22a, 24a which are opposite to each other while sandwiching the
conveying surfaces of the document D therebetween, as shown in FIG.
4.
[0037] Specifically, as the sound deadening structure 20, at least
one concave portion 23 (a first concave portion) is provided to be
recessed in the direction to separate from the conveying surface of
the above-described document D, in the upper guide plate 22. The
concave portion 23 has a semi-cylindrical shape. Further, at least
one concave portion 25 (a second concave portion) is provided
opposite to the concave portion 23, and to be recessed in the
direction to separate from the conveying surface of the
above-described document D, in the lower guide plate 24. For
example, the concave portion 23 is formed so that a part of the
upper guide plate 22 is recessed from the inner surface 22a in the
direction to separate from the conveying surface of the document D.
For example, the concave portion 25 is formed so that a part of the
lower guide plate 24 is recessed from the inner surface 24a in the
direction separate from the conveying surface of the document D.
These two concave portions 23, 25 have the same shapes which are
plane symmetric to the conveying surface, and are provided in the
posture that the respective longitudinal axes thereof are along the
conveying direction of the document D. Accordingly, when the two
concave portions 23, 25 are faced to each other, a space with an
approximately columnar shape is formed in the middle of the
conveying path 113. This space functions as a sound absorption
chamber 30.
[0038] The above-described sound absorption chamber 30 is provided
in the middle of the conveying path 113, and thereby the sound
deadening structure 20 changes an area of a cross section of the
conveying path 113 cut along a plane orthogonal to the conveying
direction of the document D, along the conveying direction. The
cross-section area of the conveying path 113 is changed in the
middle thereof in this manner, to cause an acoustic impedance
thereof to be changed, and thereby it is possible to make the
conveying path 113 have a sound deadening function.
[0039] When a sound pressure of a sound to be propagated through
the conveying path 113 is p, a cross-section area of the conveying
path is S, and a particle velocity is .mu., an acoustic impedance Z
can be expressed as,
Z=p/S.mu..
[0040] For example, when the cross-section area of the conveying
path 113 is increased along the conveying direction of the document
D, and thereby the acoustic impedance is changed (is decreased), a
part of a sound is reflected (r1, r3) at positions (R1, R3 in FIG.
3) where the acoustic impedance is changed, and is returned in a
direction reverse to the conveying direction of the document D. By
this means, the sound to be propagated in the conveying direction
is decreased, and in addition, the reflected sound and the sound to
be propagated in the conveying direction interfere with each other,
and thereby the sound to be propagated in the conveying direction
attenuates.
[0041] In addition, when the cross-section area of the conveying
path 113 is decreased, and thereby the acoustic impedance is
changed (is increased), a part of a sound is reflected (r2, r4) at
positions (R2, R4 in FIG. 3) where the acoustic impedance is
changed, and is returned in a direction reverse to the conveying
direction of the document D. By this means, the sound to be
propagated in the conveying direction is decreased, and in
addition, the reflected sound and the sound to be propagated in the
conveying direction interfere with each other, and thereby the
sound to be propagated in the conveying direction further
attenuates.
[0042] As described above, the concave portion 23 and the concave
portion 25 are respectively provided in the upper guide plate 22
and the lower guide plate 24 defining the conveying path 23, and
the sound deadening structure 20 of the present embodiment is
formed by performing a shape processing of the upper guide plate 22
and the lower guide plate 24, to cause the cross-section area of
the conveying path 113 to be changed, and reduces the sound to be
propagated through the conveying path 113. Even if the sound
deadening structure 20 is provided at one position on the conveying
path, the sound deadening effect can be exerted, but the sound
deadening structures 20 are provided at a plurality of separate
positions (in the present embodiment, two positions) in the
conveying direction, as in the present embodiment, and thereby it
is possible to further enhance the sound deadening effect.
[0043] In addition, in the present embodiment, two sets of the
semi-cylindrical concave portions 23, 25 (sound absorption chambers
30) are provided in the conveying path 113, but the sound
absorption chambers 30 may be provided at a plurality of positions
in the width direction orthogonal to the conveying direction, as
shown in FIG. 6, for example. In addition, as shown in FIG. 7,
concave portions 27, 29 each having a rectangular sectional shape
are provided opposite to each other, and thereby a sound absorption
chamber 40 may be provided in the conveying path 113. Further, as
shown in FIG. 8, a plurality of the sound absorption chambers 40
may be provided in the conveying path 113 side by side in the
above-described width direction.
[0044] In addition, when a plurality of the sound absorption
chambers 30 (40) provided along the conveying direction are
arranged at the same positions in the width direction, the same
part of a leading edge in the conveying direction of the document D
to be conveyed comes to pass through the sound absorption chambers
30 (40) many times, and thereby there is a possibility that a
trouble such as folding and break is generated at the leading edge
of the document D. For the reason, as shown in FIG. 9, for example,
so that the same part of the leading edge of the document D does
not pass through the sound absorption chambers 30 (40) many times,
the sound absorption chambers 30 (40) which are continuously
provided in the conveying direction may be arranged so that the
positions thereof in the width direction are shifted. In addition,
in FIG. 9, the sound absorption chamber 30 is illustrated as a
sectional shape seen from the conveying direction, so that the
description is easily understandable. In addition, in FIG. 9, the
conveying direction of the document D is shown by an arrow T.
[0045] Hereinafter, an attenuation amount of a sound by the
above-described sound deadening structure 20 will be described
using a testing device 50 shown in FIG. 10. The testing device 50
has, in the middle of a sound propagation path 52 having a circular
sectional shape (a cross-section area S1), a columnar sound
absorption chamber 54 having a circular sectional shape of a
cross-section area S2 larger than the cross-section area S1. When a
length of the sound absorption chamber 54 along the sound
propagation direction (an arrow direction in the drawing) is L, a
ratio of the cross-section areas is m (=S2/S1), a wavelength of a
propagated sound is .lamda., and k=2n/.lamda., an attenuation
amount of a sound which is propagated in this device is expressed
as follows.
Attenuation amount=10log.sub.10{1+1/4(m-1/m).sup.2sin.sup.2kL}
(dB)
[0046] FIG. 11 is a graph showing the relation between the
above-described attenuation amount and L/.lamda.. A vertical axis
of this graph is an attenuation amount, a horizontal axis is
L/.lamda.. The graph of FIG. 11 shows a case in which the
cross-section area ratio m=10, and a case in which m=50, in
comparison with each other. In this case, it is assumed that a
temperature of the propagation path of the sound in the testing
device 50 was 30.degree. C.
[0047] According to FIG. 11, it is understood that as the
cross-section area ratio m of the propagation path is larger, the
attenuation amount of the sound becomes larger. That is, in order
to enhance the sound deadening effect, it is only necessary to make
the cross-section area S2 of the sound absorption chamber 54 larger
than the cross-section area S1 of the sound propagation path 52.
When the conveying path 113 of the document D is considered in
place of it, since a conveying space (a gap between the inner
surface 22a of the upper guide plate 22 and the inner surface 24a
of the lower guide plate 24) of the document D is very narrow, it
is easy to make the cross-section area of the conveying path 113
several tens times, by providing the sound absorption chamber 30
(40).
[0048] In addition, as can be understood from FIG. 11, when the
length L of the sound absorption chamber 54 is .lamda./2, .lamda.,
3.lamda./2, 2.lamda. . . . , the attenuation amount of the sound
becomes 0, and when L is .lamda./4, 3.lamda./4, 5.lamda./4 . . . ,
the attenuation amount becomes maximum. That is, the attenuation
amount of the sound changes depending on the relation between the
length L of the sound absorption chamber 54 and the wavelength
.lamda. of the sound. In other words, a plurality of the sound
absorption chambers are provided in the propagation path of the
sound, and the lengths L of the respective sound absorption
chambers are made different, and thereby it is possible to
attenuate a sound of a wide frequency band.
[0049] FIG. 12 shows an attenuation amount of the sound, when the
length L of the sound absorption chamber is set to 0.01 m, and a
frequency Hz of the propagated sound and the cross-section area
ratio m of the conveying path are used as parameters. According to
FIG. 12, it is understood that when the cross-section area ratio m
is set to 40, the attenuation amount of a sound of 8000-10000 Hz
becomes the largest.
[0050] FIG. 13 shows an attenuation amount of the sound, when the
length L of the sound absorption chamber is set to 0.02 m, and the
frequency Hz of the propagated sound and the cross-section area
ratio m of the conveying path are used as parameters. In addition,
FIG. 14 shows an attenuation amount of the sound, when the length L
of the sound absorption chamber is set to 0.03 m, and the frequency
Hz of the propagated sound and the cross-section area ratio m of
the conveying path are used as parameters. According to FIG. 13 and
FIG. 14, it is understood that when the cross-section area ratio m
is set to 40, the attenuation amount of a sound of 5000 Hz becomes
the largest.
[0051] As described above, the attenuation amount of the sound
changes depending on the cross-section area ratio m of the
conveying path. In addition, the length L of the sound absorption
chamber has an optimum value wherein an attenuation amount can be
made the largest in accordance with a frequency of the sound to be
attenuated. In other words, a plurality of the sound absorption
chambers are provided in the middle of the conveying path of a
sheet, and the lengths of the respective sound absorption chambers
are made different, and thereby it is possible to reduce a sound of
a wide frequency band.
[0052] FIG. 15 is a graph showing change of an attenuation amount
of the sound when the frequency Hz of the propagated sound and the
length L of the sound absorption chamber are used as parameters. A
vertical axis of this graph is an attenuation amount, a horizontal
axis is a length of the sound absorption chamber. At this time, the
temperature of the conveying path was set to 30.degree. C., and the
cross-section area ratio m was set to 10. According to this, when L
is changed, a sound of each frequency has at least one peak of the
attenuation amount, and it can be understood that an optimum value
of a length of the sound absorption chamber exists.
[0053] In a case of a sound of 1000 Hz, for example, an attenuation
amount becomes the largest, when the length L of the sound
absorption chamber is set to 0.087 m. In addition, in a case of a
sound of 5000 Hz, for example, an attenuation amount becomes the
largest, when the length L of the sound absorption chamber is set
to 0.017 m, 0.053 m, 0.087 m, 0.122 m. In addition, in a case of a
sound of 10000 Hz, for example, an attenuation amount becomes the
largest, when the length L of the sound absorption chamber is set
to 0.009 m, 0.026 m, 0.044 m, 0.061 m, 0.079 m, 0.096 m, 0.114 m,
0.131 m.
[0054] As described above, according to the present embodiment, the
cross-section area of the conveying path is changed in the middle
of the conveying path of a sheet, and thereby an acoustic impedance
is changed before and after the cross-section area is changed, and
accordingly it is possible to reduce the sound which is propagated
through the conveying path. In addition, at this time, a plurality
of the sound absorption chambers with different lengths, along the
conveying direction, of the sound absorption chambers for changing
the cross-section area of the conveying path are provided, and
thereby it is possible to reduce a sound of a wide frequency band.
In this case, it is not necessary to provide a sound absorbing
material on the conveying guide unlike a conventional one, and
thereby the number of components can be reduced, and the
manufacturing cost of the apparatus can be reduced. That is,
according to the present embodiment, it is possible to provide a
sheet conveying apparatus which can reduce a sound of a wider
frequency band with an inexpensive configuration, and an image
forming apparatus having this apparatus.
[0055] While certain embodiments have been described, these
embodiments have been presented by way of example only. For
example, in the above-described embodiment, the case that the
concave portions are respectively provided in the guide plates (the
upper guide plate 22 and the lower guide plate 25) at the both
sides of the conveying surface of a sheet, and thereby the sound
absorption chamber is provided in the middle of the conveying path
has been described. But the sound absorption chamber is not limited
to this, but the concave portion 23 is provided only in the upper
guide plate 22, and thereby a sound absorption chamber may be
provided between the concave portion 23 and the lower guide plate
24. That is, a shape and a size of the sound absorption chamber can
be designed optionally, and it is only necessary that a plurality
of sound absorption chambers with different lengths along the
conveying direction are provided. In addition, the concave portions
may not be the same shapes that are plane symmetrical with respect
to the conveying surface.
[0056] Further, a plurality of protrusions 60 may be provided on
the inner surface 22a of the upper guide plate 22, as shown in FIG.
16. A plurality of these protrusions 60 function so as to reduce an
area where a sheet to be conveyed contacts the inner surface 22a of
the upper guide plate 22. By this means, it is possible to reduce a
friction sound due to sliding contact between the sheet and the
upper guide plate 22. In addition, a plurality of these protrusions
60 may be an elongated rib continuous in the conveying
direction.
[0057] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *