U.S. patent application number 12/201536 was filed with the patent office on 2009-03-05 for image forming apparatus with paper thickness detection unit and image forming method of the same.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Tokihiko ISE, Reiji MURAKAMI, Naofumi SOGA.
Application Number | 20090057995 12/201536 |
Document ID | / |
Family ID | 40406212 |
Filed Date | 2009-03-05 |
United States Patent
Application |
20090057995 |
Kind Code |
A1 |
MURAKAMI; Reiji ; et
al. |
March 5, 2009 |
IMAGE FORMING APPARATUS WITH PAPER THICKNESS DETECTION UNIT AND
IMAGE FORMING METHOD OF THE SAME
Abstract
An image forming apparatus of an embodiment of the invention
includes a paper feed cassette to contain a sheet on which an image
is to be printed, a pair of conveyance rollers to nip and convey
the sheet taken out from the paper feed cassette, a paper thickness
detection unit that is provided downstream of the sheet conveyed by
the pair of conveyance rollers and near a nip point between the
pair of conveyance rollers, has a rotator brought into contact with
the sheet, and detects a thickness of the sheet by a shift
generated when the sheet contacts with the rotator, a register
roller to align the sheet after the thickness of the sheet is
detected by the paper thickness detection unit, and a print
ejection mechanism that prints and fixes an image to the sheet
passing through the register roller and then ejects it.
Inventors: |
MURAKAMI; Reiji; (Kanagawa,
JP) ; ISE; Tokihiko; (Shizuoka, JP) ; SOGA;
Naofumi; (Shizuoka, JP) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
TOSHIBA TEC KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
40406212 |
Appl. No.: |
12/201536 |
Filed: |
August 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60969144 |
Aug 30, 2007 |
|
|
|
60971239 |
Sep 10, 2007 |
|
|
|
60972241 |
Sep 13, 2007 |
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Current U.S.
Class: |
271/262 ;
271/263 |
Current CPC
Class: |
B65H 2404/611 20130101;
B65H 2553/612 20130101; B65H 2801/06 20130101; B65H 2553/22
20130101; B65H 5/062 20130101; B65H 3/44 20130101; B65H 2557/2423
20130101 |
Class at
Publication: |
271/262 ;
271/263 |
International
Class: |
B65H 7/12 20060101
B65H007/12 |
Claims
1. An image forming apparatus with a paper thickness detection
unit, comprising: a paper feed cassette to contain a sheet on which
an image is to be printed; a pair of conveyance rollers to nip and
convey the sheet taken out from the paper feed cassette; a paper
thickness detection unit that is provided downstream of the sheet
conveyed by the pair of conveyance rollers and near a nip point
between the pair of conveyance rollers, has a rotator brought into
contact with the sheet, and detects a thickness of the sheet by a
shift generated when the sheet contacts with the rotator; a
register roller to align the sheet after the thickness of the sheet
is detected by the paper thickness detection unit; and a print
ejection mechanism that prints and fixes an image to the sheet
passing through the register roller and then ejects it.
2. The apparatus according to claim 1, wherein the paper thickness
detection unit detects a shift amount of the rotator as a voltage
value and detects the paper thickness.
3. The apparatus according to claim 2, wherein the paper thickness
detection unit samples the voltage value to obtain an average
value.
4. The apparatus according to claim 3, wherein the paper thickness
detection unit detects the paper thickness as a difference between
a voltage when the sheet does not contact with the rotator and a
voltage when the sheet contacts with the rotator.
5. The apparatus according to claim 4, wherein a distance D from a
nip point between the pair of conveyance rollers to a point where
the rotator contacts with the sheet is within a range of about 0 mm
to 10 mm.
6. The apparatus according to claim 5, wherein a pressing load P at
which the rotator contacts with the sheet is within a range of
about 60 g to 140 g.
7. The apparatus according to claim 4, wherein a fixing temperature
of the image in the print ejection mechanism is changed according
to the paper thickness detected in the paper thickness detection
unit.
8. An image forming apparatus with a paper thickness detection
unit, comprising: a plurality of paper feed cassettes to contain
sheets on which images are to be printed; a conveyance drive roller
and a conveyance driven roller that nip and convey the sheet taken
out from one of the plurality of paper feed cassettes; a first
conveyance guide provided at a side of the conveyance drive roller
and a second conveyance guide provided at a side of the conveyance
driven roller, which have openings at portions where the conveyance
drive roller and the conveyance driven roller contact with each
other, and guide the sheet conveyed by these rollers, a paper
thickness detection unit that is provided downstream of the sheet
conveyed by the conveyance drive roller and the conveyance driven
roller and near a nip point between the conveyance drive roller and
the conveyance driven roller, includes a rotator brought into
contact with the first conveyance guide and the sheet at a
specified pressing load, and detects a thickness of the sheet by a
shift generated when the sheet contacts with the rotator; a
register roller to align the sheet after the thickness of the sheet
is detected by the paper thickness detection unit; and a print
ejection mechanism that prints and fixes an image to the sheet
passing through the register roller and then ejects it.
9. The apparatus according to claim 8, wherein the paper thickness
detection unit detects a shift amount of the rotator as a voltage
value and detects the paper thickness.
10. The apparatus according to claim 9, wherein the paper thickness
detection unit samples the voltage value to obtain an average
value.
11. The apparatus according to claim 10, wherein the paper
thickness detection unit detects the paper thickness as a
difference between a voltage when the sheet does not contact with
the rotator and a voltage when the sheet contacts with the
rotator.
12. The apparatus according to claim 11, wherein a distance D from
a nip point between the pair of conveyance rollers to a point where
the rotator contacts with the sheet is within a range of about 0 mm
to 10 mm.
13. The apparatus according to claim 12, wherein a pressing load P
at which the rotator contacts with the sheet is within a range of
about 60 g to 140 g.
14. The apparatus according to claim 11, wherein a fixing
temperature of the image in the print ejection mechanism is changed
according to the paper thickness detected in the paper thickness
detection unit.
15. An image forming apparatus with a paper thickness detection
unit, comprising: a plurality of paper feed cassettes to contain
sheets on which images are to be printed; a conveyance drive roller
and a conveyance driven roller that nip and convey the sheet taken
out from one of the plurality of paper feed cassettes; a first
conveyance guide provided at a side of the conveyance drive roller
and a second conveyance guide provided at a side of the conveyance
driven roller, which have openings at portions where the conveyance
drive roller and the conveyance driven roller contact with each
other, and guide the sheet conveyed by these rollers, a paper
thickness detection unit that is provided downstream of the sheet
conveyed by the conveyance drive roller and the conveyance driven
roller and near a nip point between the conveyance drive roller and
the conveyance driven roller, includes a rotator brought into
contact with the first conveyance guide and the sheet at a
specified pressing load through an opening of the second conveyance
guide, and detects a thickness of the sheet by a shift generated
when the sheet contacts with the rotator; a register roller to
align the sheet after the thickness of the sheet is detected by the
paper thickness detection unit; and a print ejection mechanism that
prints and fixes an image to the sheet passing through the register
roller and then ejects it.
16. The apparatus according to claim 15, wherein the paper
thickness detection unit detects a shift amount of the rotator as a
voltage value, samples the voltage value to obtain an average
value, and detects the paper thickness.
17. The apparatus according to claim 16, wherein the paper
thickness detection unit detects the paper thickness as a
difference between a voltage when the sheet does not contact with
the rotator and a voltage when the sheet contacts with the
rotator.
18. The apparatus according to claim 17, wherein a fixing
temperature of the image in the print ejection mechanism is changed
according to the paper thickness detected in the paper thickness
detection unit.
19. An image forming method, comprising: taking out a sheet on
which an image is to be printed from a paper feed cassette; nipping
and conveying the taken-out sheet by a pair of conveyance rollers;
detecting a thickness of the sheet by a shift generated when a
rotator, which is provided downstream of the pair of conveyance
rollers to nip and convey the sheet and near a nip point between
the pair of conveyance rollers and is brought into contact with the
sheet, contacts with the sheet; aligning the sheet by a register
roller after the thickness of the sheet is detected; and ejecting
the sheet after an image is printed and fixed to the sheet passing
through the register roller.
20. The method according to claim 19, wherein at the detecting of
the thickness of the sheet, a shift amount of the rotator is
detected as a voltage value, the voltage value is sampled to obtain
an average value, and the paper thickness is detected.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on the benefit of the priority of
provisional application No. 60/969,144 filed on Aug. 30, 2007, the
benefit of the priority of provisional application No. 60/971,239
filed on Sep. 10, 2007, and the benefit of the priority of
provisional application No. 60/972,241 filed on Sep. 13, 2007. The
contents of these provisional applications are incorporated herein
by reference.
TECHNICAL FIELD
[0002] The present invention relates to an image forming apparatus,
and particularly to an image forming apparatus with a paper
thickness detection unit, and a method of the same.
BACKGROUND
[0003] Hitherto, in an image forming apparatus such as a
multi-function color copier (MFP), the types of media on which
color images or the like are printed are increased. Even when the
print medium is limited to paper, various paper sheets different
from each other in thickness or the like are used.
[0004] Incidentally, the paper types are generally classified by
paper weight (unit: g/cm.sup.2) indicating the weight per area. For
example, sheets of groups of 64 to 105, 106 to 163, 164 to 209, 210
to 256, and 257 to 300 are called standard paper, thick paper 1,
thick paper 2, thick paper 3, thick paper 4, respectively. These
paper weights are generally written on packages of sheets. The user
selects one of the written groups of the paper weights, so that a
print condition corresponding to the type of the paper is
automatically set.
[0005] However, the paper weight can be calculated from the density
and the paper thickness of a sheet, and the paper type can be
generally detected by measuring the paper thickness. Thus, there is
known an image forming apparatus with a paper thickness detection
mechanism that can detect the paper thickness.
[0006] One of these paper thickness detection apparatuses includes
a pair of conveyance rollers to convey a sheet, measures a
displacement amount of the conveyance rollers when the sheet passes
through between the conveyance rollers, and detects the paper
thickness from the displacement amount. That is, the conveyance
rollers are used also as the paper thickness detection rollers.
However, in this kind of apparatus, since the conveyance. rollers
have the function to convey the sheet, they are required to move
the passing sheet and must apply a specified pressure to the sheet.
Accordingly, the sheet whose paper thickness is detected is
pressed, and it is difficult to detect the accurate paper
thickness.
[0007] In another one of the paper thickness detection apparatuses,
a roller dedicated to paper thickness detection is provided in
addition to a conveyance roller, an opposite plate is provided to
be opposite to the roller, and a displacement amount of the paper
thickness detection roller, which is caused by a sheet entering
between the opposite plate and the paper thickness detection
roller, is measured to detect the paper thickness. However, in this
kind of apparatus, since the paper thickness detection roller is
not driven, when the sheet is made to enter the paper thickness
detection roller, unless the pressing force of the paper thickness
detection roller to the sheet is made small, the entering sheet is
buckled. However, when the pressing force of the paper thickness
detection roller is made small, holding by the paper thickness
detection roller becomes unstable, and an external vibration is
liable to exert an influence. Besides, when the pressing force of
the paper thickness detection roller is made small, the paper
thickness detection roller is likely to be bounded by an impact
generated when the sheet enters.
[0008] In a still another one of the paper thickness detection
apparatuses, for example, as disclosed in JP-A-2003-237982, in the
above paper thickness detection apparatus, a drive roller is
provided instead of the opposite plate, and this drive roller is
rotated in synchronization with the conveyance of the sheet.
However, in this kind of paper thickness detection apparatus, there
arise problems that the detection of accurate paper thickness
becomes difficult by the influence of vibration due to the rotation
of the drive roller when the paper thickness is detected, and the
cost is increased since the drive roller is required.
[0009] Incidentally, JP-A-7-187452 discloses a sheet conveying
apparatus in which a paper thickness detection roller is provided
downstream of a conveyance roller to convey a sheet contained in a
paper feed cassette and upstream of a register roller to align the
sheet.
SUMMARY
[0010] The present invention is made in view of the above, and
provides an image forming apparatus with a paper thickness
detection unit that has a simple structure, and can accurately
detect paper thickness without increasing the cost, and an image
forming method.
[0011] According to an aspect of the invention, an image forming
apparatus includes a paper feed cassette to contain a sheet on
which an image is to be printed, a pair of conveyance rollers to
nip and convey the sheet taken out from the paper feed cassette, a
paper thickness detection unit that is provided downstream of the
sheet conveyed by the pair of conveyance rollers and near a nip
point between the pair of conveyance rollers, has a rotator brought
into contact with the sheet, and detects a thickness of the sheet
by a shift generated when the sheet contacts with the rotator, a
register roller to align the sheet after the thickness of the sheet
is detected by the paper thickness detection unit, and a print
ejection mechanism that prints and fixes an image to the sheet
passing through the register roller and then ejects it.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective view showing the outline of a
multi-function color copier (MFP) of an embodiment of the
invention.
[0013] FIG. 2 is a view showing an example of a display screen of a
touch panel display 103 of an operation panel 102 when paper weight
is inputted.
[0014] FIG. 3 is a view showing the whole electrical rough
structure of the embodiment.
[0015] FIG. 4 is a view showing a rough structure of the MFP of the
embodiment of the invention in which the flow (supply, thickness
detection, print, post-processing) of a sheet is mainly
illustrated.
[0016] FIG. 5 is a view for explaining a relation between a
conveyance drive mechanism and a paper thickness detection
mechanism in the embodiment.
[0017] FIG. 6 is a view for explaining that a conveyance guide 301B
and the like can be separated from a conveyance guide 301A and the
like in a lateral direction.
[0018] FIG. 7 is a view for explaining that a conveyance driven
roller and the like can be separated from the conveyance guide 301B
in the embodiment.
[0019] FIG. 8 is a view showing a structure of a paper thickness
detection unit 124 in the embodiment.
[0020] FIG. 9 is a perspective view showing a structure of a
resistance change detection module 401, an arm 403 and a bearing
404 in the paper thickness detection unit 124.
[0021] FIG. 10 is a view showing an example of an output voltage of
a voltage detection circuit 406 when a sheet enters.
[0022] FIG. 11 is a view showing a relation between a sheet feed
mechanism and a conveyance drive roller 206A and a conveyance guide
301A.
[0023] FIG. 12 is a view showing a relation between an operation
timing of a paper feed drive motor and a paper thickness detection
timing in another embodiment for preventing vibration at paper
thickness detection.
[0024] FIG. 13 is a view showing a relation between the conveyance
guide 301A and frames 504a and 504b in a still another embodiment
for preventing vibration at paper thickness detection.
[0025] FIG. 14 is a view showing a connection relation between the
conveyance guide 301A and a stay 50 in a still another embodiment
for preventing vibration at paper thickness detection.
[0026] FIG. 15 is a view showing a relation between a holding
mechanism 309 and the conveyance guide 301B in a still another
embodiment for preventing vibration at paper thickness
detection.
DETAILED DESCRIPTION
[0027] Hereinafter, an embodiment of an image forming apparatus of
the invention will be described with reference to the drawings. In
the following, a description will be made on the assumption that
the image forming apparatus of the embodiment is a multi-function
color copier.
[0028] FIG. 1 is a perspective view showing an example of the outer
appearance of the multi-function copier of the embodiment of the
invention. An auto document feeder (ADF) 101 that is used also as a
document cover and automatically feeds sheet-like original
documents one by one is openably and closably provided at an upper
part of an apparatus body 100. An operation panel 102 including
various operation keys to instruct a copy condition and a copy
start, and various displays is provided at an upper front part of
the apparatus body 100. A touch panel display 103 that displays
various information to a user and can perform a specified input by
user's touch when input is required is provided on the side of the
operation panel 102.
[0029] A handle 104 is provided at the front of the apparatus body
100 and at a lower part of the operation panel 102 so that the
inside of the body can be opened at paper jam or the like.
[0030] Paper feed cassettes 111, 112, 113 and 114 are detachably
and attachably provided at a lower part of the apparatus body 100.
Sheets for color printing and sheets for monochrome printing, which
are equal to each other in size and are different from each other
in paper type, are contained in the respective paper feed
cassettes, and are selected and fed when printing is performed as
described later.
[0031] A post-processing apparatus 115 is put in contact with the
left side of the apparatus body 100. In the apparatus body 100, as
described later, a latent image is formed and is printed and fixed
to a sheet, and the sheet is subjected to processes such as
alignment and stapling in the post-processing apparatus 115, and is
ejected from a sheet ejection port 116. The sheet ejected from the
sheet ejection port 116 is loaded on a loading tray 117.
[0032] FIG. 2 shows an example displayed on the touch panel display
103. First, "Please select a sheet type" is displayed at an upper
part, and sheet types as display buttons are displayed below
it.
[0033] Buttons P0, P1 and P2 of standard paper (auto), standard
paper 1 and standard paper 2 are arranged and displayed at the
first stage, buttons of four types of thick papers, that is, thick
paper 1, thick paper 2, thick paper 3 and thick paper 4 are
displayed at the second stage. Buttons corresponding to types of
sheets other than the standard paper and the thick paper are
displayed at the third stage. In the example shown in FIG. 1, since
the four paper feed cassettes exist, for example, two types of
standard papers (standard paper 1 and standard paper 2) and two
types of thick papers (thick paper 1 and thick paper 2) are
supplied to these paper feed cassettes. The corresponding display
buttons P1, P2, TH1 and TH2 are displayed with black frames and can
be selected. The operator touches one of the black frame display
buttons, and then touches a setting display button S1, so that the
sheet to be recorded is determined.
[0034] The display button P0 of the standard paper (auto) is also
displayed with a black frame, and it is determined whether the
standard paper is standard paper 1 or standard paper 2. The
determined standard paper is supplied from the corresponding paper
feed cassette.
[0035] FIG. 3 shows an electrical rough structure of the embodiment
shown in FIG. 1. An MFP 119 includes a communication unit 120
connected to the outside through a network, a control panel control
unit 121 to control the whole control panel including the operation
panel 102 and the touch panel display 103 shown in FIG. 1, a
cassette sheet correspondence recognition unit 122 to previously
recognize types of sheets contained in the paper feed cassettes
111, 112, 113 and 114, a sheet supply control unit 123 to supply a
sheet of a type corresponding to the sheet type inputted to the
touch panel display 103 as explained in FIG. 2, a paper thickness
detection unit 124 to accurately detect the thickness of the sheet
supplied by the sheet supply control unit 123, a latent image
generation unit 125 to scan an original document when copying or
the like is performed in the MFP and to generate, for example, an
electrostatic latent image, a development transfer unit 126 to
develop the latent image formed in the latent image generation unit
125 with, for example, toner and to transfer the toner image to a
specified sheet, a fixing unit 127 to fix the transferred image by
a specified voltage, and a main control unit 128 to control the
respective units.
[0036] The fixing unit 127 includes a fixing process unit 127a to
perform a fixing process of an image to a specified sheet, and a
fixing temperature control unit 127b to control a fixing
temperature when the fixing process is performed.
[0037] FIG. 4 shows a rough structure of the MFP of the embodiment
in which the flow of a sheet is mainly illustrated.
[0038] The paper feed cassettes 111, 112, 113 and 114 contain
standard paper 1, standard paper 2, thick paper 1 and thick paper
2. The sheets contained in these paper feed cassettes are taken out
one by one by paper feed rollers 201, 202, 203 and 204 as the need
arises, and are supplied to a paper thickness detection conveyance
unit 205. The sheet supply control unit 123 shown in FIG. 3 also
includes a circuit to drive the paper feed rollers 201, 202, 203
and 204.
[0039] The paper thickness detection conveyance unit 205 includes
the paper thickness detection unit 124 to detect the thickness of a
conveyed sheet 118, and two pairs of conveyance rollers to convey
the sheet, that is, two conveyance drive rollers 206A and two
conveyance driven rollers 206B as described later. The sheet whose
thickness was detected by the paper thickness detection unit 124 of
the paper thickness detection conveyance unit 205 is conveyed, and
is aligned by a pair of register rollers 207a and 207b. The sheet
aligned by the register rollers 207a and 207b is supplied to the
development transfer unit 126. The electrostatic latent image
generated in the latent image generation unit 125 shown in FIG. 2
is developed with toner in the development transfer unit 126, and
is transferred to the conveyed sheet.
[0040] The sheet to which the toner image was transferred is
subjected to an image fixing process in the fixing unit 127, that
is, subjected to printing. The printed sheet is ejected from the
apparatus body 100 through some pairs of conveyance rollers 208,
and enters the post-processing apparatus 115. The sheet entering
the post-processing apparatus 115 is subjected to various
post-processes (not shown), such as stapling, in the
post-processing apparatus 115, is ejected from the sheet ejection
port 116, and is loaded on the loading tray 117.
[0041] Next, the paper thickness detection conveyance unit 205 in
this embodiment of the invention will be described. FIG. 5 shows a
sectional structure of the paper thickness detection conveyance
unit 205. The conveyance drive roller 206A is the roller, at least
the peripheral surface of which is formed of, for example, rubber,
and is rotated and driven by a conveyance drive motor 300. The
conveyance driven roller 206B has a peripheral surface formed of,
for example, plastic and is rotated in accordance with the rotation
of the conveyance drive roller 206A.
[0042] The sheet passes between a conveyance guide 301A and a
conveyance guide 301B. Roughly, the conveyance guide 301A has a
section of a "substantially inverse C" shape, and the conveyance
guide 301B has a section of an L-shape. The sheet 118 is conveyed
upward by the conveyance drive roller 206A and the conveyance
driven roller 206B. In order to enable the sheet 118 to be easily
removed when it is jammed on the way, the conveyance guide 301B can
be moved in a lateral direction, that is, an arrow 305
direction.
[0043] FIG. 6 is a sectional view of a state where the conveyance
guide 301B and the conveyance driven rollers 206B and 206B are
separated from the conveyance guide 301A and the conveyance drive
roller 206A. Further, FIG. 7 is a perspective view of a state where
the conveyance driven rollers 206B and 206B are separated from the
conveyance guide 301B in the lateral direction.
[0044] The conveyance guide 301A is provided with an opening 302a,
and the conveyance guide 301B is provided with an opening 302b. The
conveyance drive roller 206A and the conveyance driven roller 206B
are in contact with each other through the opening 302a and the
opening 302b. When the sheet 118 is supplied from the paper feed
cassettes 111 to 114, the sheet is nipped between the conveyance
drive roller 206A and the conveyance driven rolier 106B and is
conveyed in an arrow direction (upward). As described later, the
paper thickness detection unit 124 detects the thickness of the
sheet in the middle of this conveyance.
[0045] An opening 306 provided between the two openings 302b and
302b of the conveyance guide 301B shown in FIG. 7 is the opening
through which a bearing 404 (not shown in FIG. 7) of the paper
thickness detection unit 124 described later comes in contact with
the sheet 118.
[0046] As shown in FIG. 6, the conveyance guide 301B and the
conveyance driven roller 206B can be separated from the conveyance
guide 301A and the conveyance drive roller 206A. For example, when
the sheet 118 is jammed in the vicinity of a place between the
conveyance drive roller 206A and the conveyance driven roller 206B,
the conveyance guides 301A and 301B are separated from each other
as stated above, and the sheet can be removed.
[0047] Besides, as shown in FIG. 7, the conveyance guide 301B is
attached to the body by, for example, pressing springs 308a and
308b, and is pressed in an arrow C direction. On the other hand,
the conveyance driven roller 206B and a holding mechanism 309
thereof are provided independently of the conveyance guide 301B and
the like. The reason is to prevent as far as possible that the
vibration of the body described later is transmitted to the bearing
404 of the paper thickness detection unit 124 and, consequently,
exerts an influence on the paper thickness detection.
[0048] FIG. 8 shows the whole structure of the paper thickness
detection unit 124. The paper thickness detection unit 124 includes
a resistance change detection module 401, an arm 403 that rotates
around a fulcrum 402 of the resistance change detection module 401,
the bearing 404 provided at the leading end of the arm 403, and the
like. FIG. 9 is a perspective view showing a structure of the
resistance change detection module 401, the arm 403 and the bearing
404.
[0049] The bearing 404 is pressed at a specified pressure by a
not-shown spring or the like toward the direction of the conveyance
guide 301A and the conveyance drive roller 206A. A pressing load P
is, for example, 100 g. As shown in FIG. 5, a contact between the
sheet 118 and the bearing 404 is provided downstream of a nip point
between the conveyance drive roller 206A and the conveyance driven
roller 206B. A distance D from the nip point between the conveyance
drive roller 206A and the conveyance driven roller 206B to the nip
position between the sheet 118 and the bearing 404 is, for example,
about 6 mm.
[0050] If the pressing load P is made excessively large, when the
sheet enters between the conveyance guide 301A and the conveyance
guide 301B, the sheet 118 is not smoothly conveyed and is buckled.
Besides, if the pressing load P is excessively small, the bearing
404 is not suitably brought into contact with the sheet, the
bearing 404 is likely to be separated from the sheet by the
vibration of a drive system, and the bearing 404 is separated from
the sheet by an impact caused when the sheet 118 enters.
Accordingly, if the pressing load P is excessively low, it becomes
difficult to measure the accurate thickness of the sheet.
[0051] Besides, if the distance D is excessively large, the
position where the bearing 404 contacts with the sheet becomes
remote from the position where the sheet 118 is conveyed and
driven, that is, the contact position between the conveyance drive
roller 206A and the conveyance driven roller 206B. Since the
bearing 404 does not have the conveyance function of the sheet 118,
the conveyance force of the sheet becomes low at the position where
the bearing 404 contacts with the sheet 118 even in such a state,
and the normal conveyance of the sheet is likely to become
difficult. As stated above, in general, there is a relation among
the conveyance force of the sheet by the conveyance drive roller
206A and the conveyance driven roller 206B, the pressing load P of
the bearing 404, and the distance D.
[0052] Accordingly, although the pressing load P of the bearing 404
varies by the conveyance force of the sheet and the material and
structure of the bearing, the pressing load is preferably about 60
g to 140 g, and is more preferably about 80 g to 120 g. Besides,
although the distance D varies by the conveyance force and the
length of the contact portion between the conveyance drive roller
206A and the conveyance driven roller 206B, in general, it is
appropriate that the distance is about 0 mm to 10 mm. Further, the
distance D is preferably in the range of about 2 mm to 8 mm.
[0053] When the sheet 118 is conveyed along the conveyance guide
301A, the bearing 404 is rotated in a direction indicated by an
arrow 405a, and the arm 403 is shifted by the thickness of the
sheet 118, that is, is slightly turned in a direction of an arrow
405b. A magnet is provided near the fulcrum of the arm 403. A
magnetic resistance sensor using magnetic resistance whose
resistance value is changed correspondingly to the change of a
magnetic field is provided near the magnet.
[0054] An electric signal output of the magnetic resistance sensor
enters a voltage detection circuit 406, and its output voltage is
sampled, for example, ten times in a sampling circuit 407. The
reason why sampling is performed to average those values is that
the bearing 404 is moved in the arrow 405b direction by the
vibration of the apparatus and the conveyance of the sheet, so that
the value of the magnetic resistance is changed, and the output
voltage of the voltage detection circuit 406 is changed.
[0055] The voltage values sampled in the sampling circuit 407 are
averaged by the averaging circuit 408, and are inputted to a
voltage difference detection circuit 409. The voltage different
detection circuit 409 detects a difference between the averaged
voltage values. The voltage difference corresponds to the thickness
of the sheet 118. The magnetic resistance of the magnetic
resistance sensor functions in the direction in which the
resistance value is decreased when the sheet is conveyed, and the
output voltage value of the voltage detection circuit 406 is
decreased.
[0056] Setting is performed such that the voltage value detected by
the voltage detection circuit 406 is 1 mV when the thickness of the
sheet is 1 .mu.m. In general, since the thickness of standard paper
is about 100 .mu.m, the standard paper is detected to be about 100
mV. For example, voltage V0 before the sheet passes is made 3.3 V,
a value of about 1.35 V is made the center, and when the thickness
of the sheet is thick, the voltage value is changed in the
decreasing direction.
[0057] For example, it is assumed that the sheet 118 is nipped by
the bearing 404 in a period from time T1 to T2, and the sheet is
carried out at time T3 to return into the original state. As shown
in FIG. 10, when there is no sheet 118, the voltage detection
circuit 406 outputs the voltage of about V0. Also in this state,
the output value fluctuates by the vibration of the apparatus or
the like. The fluctuating output voltage value is sampled by the
sampling circuit 407, and the sampled values are averaged by the
averaging circuit 408. The averaged voltage value is sent to the
voltage difference detection circuit 409, and V0 is once stored
which is the voltage value when the sheet is not conveyed.
[0058] The sheet 118 is conveyed at time T1 and is nipped between
the bearing 404 and the conveyance guide 301A. The bearing 404 is
rotated as indicated by the arrow 405A, and is turned as indicated
by the arrow 405b. At this time, the value of the magnetic
resistance in the magnetic resistance sensor is decreased, and the
output value of the voltage detection circuit 406 becomes lower
than V0 after time T2 as shown in FIG. 10.
[0059] Even in the state where the sheet 118 is nipped between the
bearing 404 and the conveyance guide 301A and is moved, the bearing
404 is moved by the movement of the sheet 118 and the vibration of
the apparatus. The output voltage value of the voltage detection
circuit 406 is fluctuated by the movement of the bearing 404. These
voltage values are sampled, for example, ten times in the sampling
circuit 407 and are averaged by the averaging circuit 408. The
averaged value is inputted to the voltage difference detection
circuit 409, which is a voltage value V1 in the state where the
sheet 118 is inserted.
[0060] The voltage detection circuit 409 outputs, as the voltage
difference, the value obtained by subtracting the voltage value V1
from the previously detected voltage value V0. This value (V0-V1)
corresponds to the thickness of the sheet 118, and the thickness of
the sheet 118 is detected.
[0061] As stated above, when the paper thickness is detected as the
difference between the voltage values, not as the voltage value,
the offset of the voltage can be cancelled. Besides, such a problem
that the voltage value is changed by distortion of the conveyance
guide is removed. Accordingly, there is a merit that the paper
thickness can be further accurately measured.
[0062] Since the vibration given to the bearing 404 of the paper
thickness detection unit 124 exerts a bad influence on the detected
voltage value, it is preferable that the vibration is as small as
possible. One of main causes of the vibration is the vibration of
the conveyance drive motor 300 to rotate and drive the conveyance
drive roller 206A. Another one of the main causes of the vibration
is the vibration of a sheet pickup conveyance motor (not shown)
when the sheet is picked up from the paper feed cassette and is
conveyed.
[0063] In this point, in the foregoing embodiment of the invention,
the conveyance driven roller 206B, the holding mechanism 309
thereof and the conveyance guide 301B are provided independently of
the body, and these mechanisms are provided to be separable from
the conveyance drive roller 206A and the conveyance guide 301A.
Accordingly, according to this embodiment, there is a merit that
the influence of the vibration of the body exerted on the bearing
404 can be suppressed to be small.
[0064] As described above, in order to accurately detect the paper
thickness, it is desired that the vibration given by the body to
the bearing 404 of the paper thickness detection unit 124 is made
as small as possible.
[0065] Other embodiments of the invention for decreasing the
influence of the vibration exerted on the bearing will be described
below. In order to decrease the vibration given to the bearing 404,
these embodiments can also be combined.
[0066] Another embodiment of the invention relates to timings when
the sheet 118 is conveyed from the paper feed cassettes 111, 112,
113 and 114 and when the paper thickness is detected.
[0067] FIG. 11 shows a sheet paper feed mechanism, a structure of a
conveyance drive roller 206A and a conveyance guide 301A, and a
paper thickness detection mechanism. A paper feed drive motor 501
is a motor for picking up and conveying a sheet from a paper feed
cassette 201 by a sheet pickup roller 201P and paper feed rollers
201a and 201b.
[0068] The sheet is picked up from the paper feed cassette 111 by,
for example, the paper feed roller 201 and the sheet pickup roller
201P, and is conveyed to a position between the conveyance drive
roller 206A and a conveyance driven roller 206B through a paper
feed conveyance roller 208d, and then, the paper thickness is
detected in a paper thickness detection unit 124.
[0069] FIG. 12 shows a relation between the timing of paper feed
conveyance of the sheet and the timing of paper thickness
detection. FIG. 12(a) shows a conventional paper feed conveyance
timing, and shows that the paper feed drive motor 501 is driven in
a state of H. FIG. 12(b) shows the timing of paper thickness
detection, and the paper thickness is detected in a state of L,
that is, in a period Td. As shown in FIG. 12(a) and FIG. 12(b), the
timing of paper conveyance is irrelevant to the timing of paper
thickness detection.
[0070] In this embodiment of the invention, the paper feed
conveyance of the sheet is performed at the timing shown in FIG.
12(c). Also in this case, the state of H indicates that the paper
feed drive motor 501 is driven. As is apparent from FIG. 12(b) and
FIG. 12(c), in this embodiment, the paper feed drive motor 501 is
not driven in the paper thickness detection period Td. The paper
feed drive motor 501 is stopped in the paper thickness detection
period, and the vibration thereof is not transmitted to the bearing
404.
[0071] As described above, when the paper feed of the sheet and the
conveyance thereafter are not performed at the timing of paper
thickness detection, the paper feed drive motor can be stopped
during the paper thickness detection. As a result, the influence of
the vibration to the bearing 404 can be reduced.
[0072] Next, a still another embodiment for reducing the influence
of vibration of a motor and the like will be described with
reference to FIG. 11 and FIG. 13. FIG. 13 is a plan view
schematically showing a conveyance guide 301A and its peripheral
structure. In general, as shown in FIG. 14, the drive guide 301A is
fixed to a stay 503 by a screw 502, and the stay 503 is fixed to
frames 504a and 504b of an apparatus body. In this embodiment of
the invention, the conveyance guide 301A is not fixed to the stay
503, but is directly fixed to the frames 504a and 504b by support
members 505a and 505b.
[0073] The vibration of the conveyance drive motor 300 is generally
transmitted to the stay 503, is transmitted to the conveyance guide
301A, and is transmitted from the conveyance guide 301A to the
bearing 404 of the paper thickness detection unit. As in this
embodiment, when the conveyance guide 301A is directly connected to
the frames 504a and 504b, the vibration from the stay 503 to the
conveyance guide 301A can be suppressed.
[0074] Next, an embodiment for suppressing transmission of
vibration to a bearing 404 will be described with reference to the
drawings. FIG. 14 shows a structure in the embodiment. In general,
a conveyance guide 301A is fixed to a stay 503 by a screw 502.
Then, a vibration preventing material, for example, an elastic
rubber (bush) 507 is inserted between the stay 503 and the
conveyance guide 301A which are fixed by the screw 502.
[0075] The elastic rubber 507 suppresses the transmission of the
vibration, which is transmitted to the stay 503, to the conveyance
guide 301A. Accordingly, also by this, it is possible to prevent
the vibration of the motor and the like from being transmitted to
the conveyance guide, and the bearing 404 from the stay 503.
[0076] A still another embodiment for suppressing vibration
transmitted to a bearing 404 is shown in FIG. 15. A structure of
this embodiment suppresses the vibration which is transmitted from
a holding mechanism 309 of a conveyance driven roller 206B to a
conveyance guide 301B and is transmitted from the conveyance guide
301B to the bearing 404. In this embodiment, a vibration preventing
material, for example, an elastic rubber 508 is fixed to a part
where the holding mechanism 309 contacts with the conveyance guide
301B.
[0077] According to this embodiment, the vibration transmitted from
the conveyance driven roller 206B and the holding mechanism 309 to
the conveyance guide 301B can be suppressed.
[0078] When the thickness of the sheet is detected by the paper
thickness detection unit 124 as stated above, the thickness of the
sheet is reflected in the fixing temperature in the fixing unit 127
of FIG. 3.
[0079] The most frequently used standard paper is defined in the
range of paper weight of 64 to 105 g/cm.sup.2. However, in the case
of a high-speed color copier, it is difficult to cover the wide
range of paper weight by one kind of fixing temperature condition.
Then, in this embodiment, according to the paper thickness, the
paper with a thickness of up to 0.100 mm is identified as standard
paper 1, and the paper with a thickness exceeding 0.100 mm and up
to 0.130 mm is identified as standard paper 2.
[0080] When identified as standard paper 1, the temperature is
controlled to become 150.degree. C. to 175.degree. C. by the fixing
voltage control unit 127b of the fixing unit 127 shown in FIG. 3.
Besides, when identified as standard paper 2, the fixing
temperature is controlled to become about 160.degree. C. to
180.degree. C. by the fixing voltage control unit 127b.
[0081] When the type of the standard paper is not known, the user
touches the icon P0 shown in FIG. 2. Then, as stated above, the
paper thickness detection unit 124 operates to detect the paper
thickness. In this way, when the user merely touches the icon of
standard paper (auto), the fixing temperature is controlled to a
suitable temperature, and the excellent image printing is
obtained.
[0082] When the fixing temperature is not suitable for the sheet,
there occurs a low temperature offset in which the temperature is
low and the toner remains attached to the transfer roller, or a
high temperature offset in which the fixing temperature is so high
that the toner is peeled off. In such a case, the user touches the
icon P1 or the icon P2, and selects standard paper 1 or standard
paper 2.
[0083] As shown in FIG. 4, when the paper thickness detection unit
124 is provided on a common path after the sheet is conveyed from
the plural paper feed cassettes 111, 112, 113 and 114, the paper
thickness detection unit 124 can be used in common. Accordingly, it
is unnecessary to provide the paper thickness detection unit for
each of the paper feed cassettes.
[0084] Besides, in the embodiment shown in FIG. 4, at an upstream
side of the development transfer unit 126 located upstream of the
fixing unit 127, the sheet is aligned by the register rollers 207a
and 207b before the development and transfer are performed on the
sheet. The paper thickness detection is performed at a further
upstream side of the register rollers 207a and 207b. Accordingly,
there is a sufficient time from the detection of the paper
thickness in the paper thickness detection unit 124 to the change
of the fixing temperature, and excellent fixing can always be
performed according to the paper thickness. Besides, since the
sheet is aligned by the register roller before the development and
transfer are performed, after the paper thickness is detected, the
condition of the development and transfer, such as voltage, can be
easily set in accordance with the paper thickness, and an excellent
image can always be obtained.
[0085] In the embodiment, the description is given to the case
where the invention is applied to the multi-function color copier.
However, the invention can be applied not only to the
multi-function color copier, but also to another image forming
apparatus, such as a normal copier, a printer or a facsimile, which
includes an image generating unit to generate an image to be
printed on a recording sheet and specifies the type of a sheet to
be printed.
[0086] Obviously, many modifications and variations of this
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, this invention may be practiced otherwise than as
specification.
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