U.S. patent application number 12/711513 was filed with the patent office on 2011-02-10 for sheet mass measuring unit.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yukio Asari, Yusuke Mitsuya, Yoshihiko Naruoka, Toru Todoriki.
Application Number | 20110031683 12/711513 |
Document ID | / |
Family ID | 42634921 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110031683 |
Kind Code |
A1 |
Asari; Yukio ; et
al. |
February 10, 2011 |
SHEET MASS MEASURING UNIT
Abstract
A mass measuring unit includes two driving rollers vertically
separate from each other and intersecting the direction of
conveyance of a mail matter. Servo motors for driving the driving
rollers are connected to torque detection units. A control unit
controls motor control units to cause them to impart a rate
difference between the driving rollers to rotate the mail matter
during its conveyance, and to cause the torque detection units to
detect the torque values of the servo motors. The control unit
compares the thus detected torque values with the torque values of
the servo motors detected when the servo motors are idling without
rotating the mail matter, thereby measuring the mass of the mail
matter using a calculation unit.
Inventors: |
Asari; Yukio; (Yokohama-shi,
JP) ; Mitsuya; Yusuke; (Yokohama-shi, JP) ;
Naruoka; Yoshihiko; (Yokohama-shi, JP) ; Todoriki;
Toru; (Kawasaki-shi, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
42634921 |
Appl. No.: |
12/711513 |
Filed: |
February 24, 2010 |
Current U.S.
Class: |
271/264 |
Current CPC
Class: |
B07C 5/20 20130101; G01G
19/4148 20130101; G01G 19/005 20130101; G03G 2215/00742 20130101;
G01G 17/02 20130101; B07C 5/165 20130101 |
Class at
Publication: |
271/264 |
International
Class: |
B65H 5/06 20060101
B65H005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2009 |
JP |
2009-185952 |
Claims
1. A mass measuring unit for measuring a mass of a sheet of paper,
comprising: a conveyor path configured to convey a sheet of paper;
a rotation mechanism configured to rotate and forward the sheet of
paper along the conveyor path; a torque detection unit configured
to detect torque of the rotation mechanism; and a calculation unit
configured to calculate a mass of the sheet of paper, based on
torque of the rotation mechanism that is detected by the torque
detection unit when the rotation mechanism rotates the sheet of
paper, and torque of the rotation mechanism that is detected by the
torque detection unit when the rotation mechanism rotates no sheet
of paper.
2. The mass measuring unit according to claim 1, wherein the
rotation mechanism rotates the sheet of paper at substantially a
same conveyance rate before and after rotating the sheet of
paper.
3. The mass measuring unit according to claim 1, wherein the
rotation mechanism rotates the sheet of paper at substantially a
same conveyance rate and attitude before and after rotating the
sheet of paper.
4. A mass measuring unit for measuring a mass of a sheet of paper,
comprising: a conveyor path configured to convey a sheet of paper;
a rotation mechanism including a driving roller configured to
rotate in contact with the sheet of paper conveyed by the conveyor
path, and a motor configured to accelerate and/or decelerate the
driving roller to rotate and forward the sheet of paper along the
conveyor path; a torque detection unit configured to detect torque
of the motor; and a calculation unit configured to calculate a mass
of the sheet of paper, based on torque of the motor that is
detected by the torque detection unit when the rotation mechanism
rotates the sheet of paper, and torque of the motor that is
detected by the torque detection unit when the rotation mechanism
rotates no sheet of paper.
5. The mass measuring unit according to claim 4, wherein the
rotation mechanism further includes a driven roller configured to
be rotated by the driving roller and cooperate with the driving
roller to hold therebetween the sheet of paper conveyed by the
conveyor path.
6. The mass measuring unit according to claim 4, wherein the
driving roller rotates the sheet of paper, kept in contact with a
portion of the sheet of paper deviated from an imaginary center
line that extends in a direction of conveyance and passes through
the center of gravity of the sheet of paper conveyed by the
conveyor path.
7. The mass measuring unit according to claim 4, wherein the torque
detection unit monitors a current supplied to the motor to detect
the torque of the motor.
8. The mass measuring unit according to claim 4, wherein the
rotation mechanism rotates the sheet of paper at substantially a
same conveyance rate before and after rotating the sheet of
paper.
9. The mass measuring unit according to claim 4, wherein the
rotation mechanism rotates the sheet of paper at substantially a
same conveyance rate and attitude before and after rotating the
sheet of paper.
10. A mass measuring unit for measuring a mass of a sheet of paper,
comprising: a conveyor path configured to convey a sheet of paper;
a rotation mechanism including a first driving roller, a second
driving roller, a first motor, and a second motor, the first
driving roller rotating in contact with a surface portion of the
sheet of paper conveyed by the conveyor path, the second driving
roller being vertically aligned with and separate from the first
driving roller, the second driving roller rotating in contact with
another surface portion of the sheet of paper conveyed by the
conveyor path, the first and second motors independently
accelerating and/or decelerating the driving rollers such that the
driving rollers rotate at different rates, thereby rotating and
forwarding the sheet of paper along the conveyor path; a torque
detection unit configured to detect torque values of the first and
second motors; a storing unit configured to beforehand store torque
values of the first and second motors detected by the torque
detection unit when the rotation mechanism is idling under same
conditions as when rotating the sheet of paper, with no sheet of
paper conveyed by the conveyor path; and a calculation unit
configured to calculate a mass of the sheet of paper, based on
torque values of the first and second motors that are detected by
the torque detection unit when the rotation mechanism rotates the
sheet of paper during conveyance thereof, and the torque values of
the first and second motors stored in the storing unit.
11. The mass measuring unit according to claim 10, wherein the
rotation mechanism further includes a first driven roller and a
second driven roller configured to be rotated by the first and
second driving rollers, respectively, and to cooperate with the
first and second driving rollers to hold therebetween the sheet of
paper conveyed by the conveyor path.
12. The mass measuring unit according to claim 10, wherein the
torque detection unit monitors currents supplied to the first and
second motors to detect the torque values of the first and second
motors.
13. The mass measuring unit according to claim 10, wherein in the
rotation mechanism, the first and second driving rollers are
accelerated and decelerated to rotate the sheet of paper at
substantially a same conveyance rate before and after rotating the
sheet of paper.
14. The mass measuring unit according to claim 10, wherein in the
rotation mechanism, the first and second driving rollers are
accelerated and decelerated to rotate the sheet of paper at
substantially a same conveyance rate and attitude before and after
rotating the sheet of paper.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2009-185952,
filed Aug. 10, 2009, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for measuring
the mass of a paper sheet, such as a mail matter, and more
particularly, to an apparatus for measuring the mass of a paper
sheet conveyed at a relatively high rate, without stopping the
conveyance of the sheet.
[0004] 2. Description of the Related Art
[0005] Jpn. Pat. Appln. KOKAI Publication No. 2005-162407
(hereinafter, patent document 1), for example, discloses a mass
detection apparatus as an apparatus for measuring the mass of a
paper sheet during conveyance of the same. In the apparatus
disclosed in patent document 1, the rotational rate of a driving
roller provided along a conveyor path is varied to gradually vary
the conveyance rate of a paper sheet conveyed held between the
driving roller and a pinch roller, and a change in the torque
applied to the driving roller in accordance with the mass of the
paper sheet is detected, thereby calculating the mass of the paper
sheet based on the detection result.
[0006] By thus detecting variations in the torque of the driving
roller by increasing/decreasing the conveyance rate of a paper
sheet held between the driving roller and the pinch roller, the
mass of the paper sheet can be detected without stopping the sheet.
Accordingly, the apparatus disclosed in patent document 1 can
sequentially convey a large number of paper sheets at a relatively
high rate, thereby realizing relatively high processing
performance.
[0007] However, in the mass detection apparatus disclosed in patent
document 1, it is necessary to change the conveyance rate of each
paper sheet during conveyance thereof, and hence it is necessary to
provide a sufficient gap between successive paper sheets, which
inevitably reduces the throughput. Furthermore, in this apparatus,
the ratio of an increase in the inertia moment of the driving
mechanism comprising the driving roller itself subjected to
acceleration/deceleration control, the driving shaft of the driving
roller, and/or the rotor of a motor for driving the driving roller,
which inertia moment occurs when the driving mechanism conveys a
paper sheet, to the inertia moment of the mechanism when it conveys
no sheet, is extremely low. This inevitably reduces the mass
detection accuracy.
BRIEF SUMMARY OF THE INVENTION
[0008] It is an object of the invention to provide a paper sheet
mass measuring unit capable of highly accurately measuring mass of
a paper sheet and enhancing the throughput.
[0009] To attain the object, a mass measuring unit for measuring a
mass of a sheet of paper, according to an embodiment, comprises: a
conveyor path configured to convey a sheet of paper; a rotation
mechanism configured to rotate and forward the sheet of paper along
the conveyor path; a torque detection unit configured to detect
torque of the rotation mechanism; and a calculation unit configured
to calculate a mass of the sheet of paper, based on torque of the
rotation mechanism that is detected by the torque detection unit
when the rotation mechanism rotates the sheet of paper, and torque
of the rotation mechanism that is detected by the torque detection
unit when the rotation mechanism rotates no sheet of paper.
[0010] Further, a mass measuring unit for measuring a mass of a
sheet of paper, according to a modification of the embodiment,
comprises: a conveyor path configured to convey a sheet of paper; a
rotation mechanism including a driving roller configured to rotate
in contact with the sheet of paper conveyed by the conveyor path,
and a motor configured to accelerate and/or decelerate the driving
roller to rotate and forward the sheet of paper along the conveyor
path; a torque detection unit configured to detect torque of the
motor; and a calculation unit configured to calculate a mass of the
sheet of paper, based on torque of the motor that is detected by
the torque detection unit when the rotation mechanism rotates the
sheet of paper, and torque of the motor that is detected by the
torque detection unit when the rotation mechanism rotates no sheet
of paper.
[0011] Yet further, a mass measuring unit for measuring a mass of a
sheet of paper, according to another modification of the
embodiment, comprises: a conveyor path configured to convey a sheet
of paper; a rotation mechanism including a first driving roller, a
second driving roller, a first motor, and a second motor, the first
driving roller rotating in contact with a surface portion of the
sheet of paper conveyed by the conveyor path, the second driving
roller being vertically aligned with and separate from the first
driving roller, the second driving roller rotating in contact with
another surface portion of the sheet of paper conveyed by the
conveyor path, the first and second motors independently
accelerating and/or decelerating the driving rollers such that the
driving rollers rotate at different rates, thereby rotating and
forwarding the sheet of paper along the conveyor path; a torque
detection unit configured to detect torque values of the first and
second motors; a storing unit configured to beforehand store torque
values of the first and second motors detected by the torque
detection unit when the rotation mechanism is idling under same
conditions as when rotating the sheet of paper, with no sheet of
paper conveyed by the conveyor path; and a calculation unit
configured to calculate a mass of the sheet of paper, based on
torque values of the first and second motors that are detected by
the torque detection unit when the rotation mechanism rotates the
sheet of paper during conveyance thereof, and the torque values of
the first and second motors stored in the storing unit.
[0012] In the above-described invention, a sheet of paper is
rotated during its conveyance, and the torque of the rotation
mechanism is detected, and is compared with the torque of the
driving system beforehand measured under the same conditions but
without rotating any sheet of paper, thereby measuring the mass of
the sheet of paper. By virtue of this structure, the mass of each
sheet of paper can be measured while sheets of paper are
successively conveyed at high rate, and hence the conveyance
throughput can be enhanced, compared to the conventional case where
the mass of each sheet of paper is measured based on a change in
torque detected when each sheet of paper is accelerated and
decelerated along the conveyor path.
[0013] Further, in the above-described invention, since the mass of
each sheet of paper is measured based on a change in the torque of
the rotation mechanism detected when each sheet of paper is rotated
by the rotation mechanism, a relatively high torque due to a
relatively high rotation moment can be generated, and hence the
mass of each mail matter M can be measured at high accuracy,
compared to the conventional case where each sheet of paper is
accelerated and decelerated along the conveyor path.
[0014] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0015] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate an embodiment of
the invention, and together with the general description given
above and the detailed description of the embodiment given below,
serve to explain the principles of the invention.
[0016] FIG. 1 is a block diagram illustrating a mail matter
selection/pickup/stamp canceling apparatus that incorporates a mass
measuring unit according to an embodiment of the invention;
[0017] FIG. 2 is a schematic view illustrating an essential part of
the mass measuring unit incorporated in the apparatus of FIG.
1;
[0018] FIG. 3 is a block diagram illustrating a control system for
controlling the operation of the mass measuring unit shown in FIG.
2;
[0019] FIG. 4 is a view useful in explaining the operation of the
mass measuring unit shown in FIG. 2;
[0020] FIG. 5 is a graph illustrating examples of rate patterns of
the two driving rollers incorporated in the mass measuring unit
shown in FIG. 2;
[0021] FIG. 6 is a view useful in explaining the ratio of the
inertia moment of a mail matter to that of the driving system
incorporated in the mass measuring unit shown in FIG. 2;
[0022] FIG. 7 is a table illustrating examples of the sizes,
specific gravities, masses and the inertia moments of the
structural elements incorporated in the mass measuring unit shown
in FIG. 2; and
[0023] FIG. 8 is a table illustrating examples of inertia moment
ratios, to the driving system, of mail matters of various sizes,
the masses of which are measured by the mass measuring unit shown
in FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0024] An embodiment of the invention will be described in detail
with reference to the accompanying drawings.
[0025] FIG. 1 is a schematic block diagram illustrating a mail
matter selection/pickup/stamping apparatus 100 (hereinafter
referred to simply as "the apparatus 100") that incorporates a mass
measuring unit according to the embodiment of the invention.
[0026] The apparatus 100 comprises a supply unit 101, a mechanical
detection unit 102, an OCR scanner unit 103, a twisting/reversing
unit 104, a switchback unit 105, a stamp unit 106 and a
delivery/stacker unit 107. The apparatus 100 also comprises a
convey unit 108 for conveying mail matters M through the
above-mentioned units. The apparatus 100 also comprises an
operation panel (not shown) for instructing the apparatus to
perform various operations, to switch the operation mode and to
display abnormality.
[0027] The supply unit 101 simultaneously receives a plurality of
mail matters M of standard sizes, mass and widths (perpendicular to
the direction of conveyance) that fall within respective preset
ranges, picks up the matters one by one and supplies them to the
subsequent processing unit. The convey unit 108 includes a conveyor
path 1 that runs through the post processing units 102 to 107 to
convey each mail matter M to the units.
[0028] The mechanical detection unit 102 detects metals, foreign
materials and the like contained in a mail matter M conveyed by the
conveyor path 1 of the convey unit 8, and also detects simultaneous
pickup of two or more mail matters M, or a short gap between mail
matters. If the mechanical detection unit 102 determines that a
mail matter cannot be processed by any of the post processing units
103 to 107, it ejects the mail matter into a reject/stacker unit
(not shown). The mechanical detection unit 102 incorporates a mass
measuring unit 10, described later, for measuring the mass of each
mail matter M while each mail matter is conveyed.
[0029] Further, before a mail matter M reaches the mass measuring
unit 10, the mechanical detection unit 102 detects the length of
the mail matter M defined along the length of the convey path, and
the width of the same defined along the width of the convey path,
and detects, using a timing sensor (not shown), whether the front
end of the mail matter M has passed, thereby acquiring information
indicating the conveyance position of the mail matter M. Based on
the detected length, width and conveyance position, the mechanical
detection unit 102 operates the mass measuring unit 10 as described
later to measure the mass of the mail matter M. If the mass
measuring unit 10 detects that the mail matter M is extremely
heavy, the mail matter M is ejected into the reject/stacker unit
(not shown).
[0030] The OCR scanner unit 103 optically reads the surface of the
mail matter M and subjects the reading result to photoelectric
conversion, thereby acquiring, in the form of an image, delivery
information such as a postal code and an address on the mail matter
M. The OCR scanner unit 103 also detects whether a stamp is stuck
to (or printed on) the mail matter M, and where on the mail matter
M the stamp is stuck. Since the mail matters M supplied by the
supply unit 101 differ in orientation (namely, the mail matters M
may be upside down or reversed), the OCR scanner unit 103 includes
at least two scanner units for reading both sides of each mail
matter M.
[0031] The twisting/reversing unit 104 includes a
twisting/reversing path (not shown) for twisting the received mail
matter M through 180.degree. about its axis extending along the
conveyor path, thereby reversing the same during conveyance of the
same. Namely, the twisting/reversing unit 104 reverses only
front-back both sides of the mail matter M and does not reverse the
conveyance direction of the same. The twisting/reversing unit 104
also includes a bypass (straight path) for bypassing the
twisting/reversing path so as not to feed the mail mater M
thereto.
[0032] The switchback unit 105 includes two switchback mechanisms
(not shown) each for receiving the mail matter M and feeding the
same in the opposite direction. The switchback unit 105 also
includes a bypass (straight path) for bypassing the two switchback
mechanisms so as not to feed the mail matter thereto.
[0033] The stamp unit 106 includes a stamp hub (not shown) that
rotates in contact with one surface of the received mail matter M.
The stamp unit 106 brings the stamp hub into contact with the stamp
of the mail matter M to cancel the stamp. In the embodiment, the
stamp unit 106 includes only one stamp hub provided at one side of
the conveyor path 1, since the front-back sides and upper and lower
ends of all mail matters M fed to the stamp unit 106 are already
adjusted by the twisting/reversing unit 104 and the switchback unit
105.
[0034] The delivery/stacker unit 107 delivers the mail matters M
into preset zones and collects them in the zones in accordance with
the delivery information detected by the OCR scanner unit 103. The
delivery/stacker unit 107 includes a reject/stacker unit (not
shown) for preventing, for example, a mail matter M temporarily
kept in and fed from the switchback unit 105 from being
stamp-canceled by the stamp unit 106, and ejecting the same into
the ejected matter collecting unit.
[0035] The apparatus 100 constructed as above determines, for
example, whether the fee stamp read from the mail matter M by the
OCR scanner unit 103 is appropriate for the weight of the mail
matter M measured by the mass measuring unit 10. If the mail matter
M is determined to be short paid, it is rejected to be printed with
a canceling mark by the stamp unit 106.
[0036] FIG. 2 is a schematic view illustrating an essential part of
the mass measuring unit 10 for measuring the mass of each mail
matter M passing through the above-described mechanical detection
unit 102. FIG. 3 is a block diagram illustrating a control system
for controlling the operation of the mass measuring unit 10. FIG. 4
is a view useful in explaining the operation of the mass measuring
unit 2. FIG. 5 is a graph illustrating examples of rate patterns of
two driving rollers 2U and 2L, described later, incorporated in the
mass measuring unit 10.
[0037] Referring now to FIGS. 2 to 5, the structure and operation
of the mass measuring unit 10 of the embodiment will be
described.
[0038] The mass measuring unit 10 of the embodiment is
characterized in that it can measure the mass of each moving mail
matter M without stopping or decelerating it. Assume here that in
the embodiment, each mail matter M is conveyed upright through the
mechanical detection unit 102 (i.e., through the mass measuring
unit 10) as shown in FIG. 4. Namely, a handling plane, on which
each mail matter M is handled by the mass measuring unit 10 while
it is passed through the unit 10, is set vertical.
[0039] As shown in FIG. 2, the mass measuring unit 10 includes two
driving rollers 2U and 2L vertically separate from each other at
one side (at the front side in FIG. 2) of the conveyor path 1. The
two driving rollers 2U and 2L have rotation shafts 3U and 3L,
respectively, which substantially vertically extend separate from
each other and coaxial with each other. The driving rollers 2U and
2L rotate in contact with one side of each mail matter M conveyed
by the conveyor path 1. In other words, the two driving rollers 2U
and 2L are set rotatable in a preset direction to angularly move
(rotate) and forward each mail matter M along the conveyor path
1.
[0040] The rotation shafts 3U and 3L of the two driving rollers 2U
and 2L are coaxially connected, using couplings (not shown), to
servo motors 6U and 6L, respectively, for rotating the driving
rollers 2U and 2L at various rates.
[0041] With this structure, the mass measuring unit 10 of the
embodiment can independently rotate, at a desired rate in different
directions, the two driving rollers 2U and 2L that are vertically
(i.e., perpendicular to the direction of conveyance) separate from
each other, thereby rotating (angularly moving) each mail matter M
conveyed by the conveyor path 1, as is shown in, for example, FIG.
4.
[0042] Two driven rollers 4U and 4L are provided at the opposite
side (i.e., the rear side in FIG. 2) of the conveyor path 1, facing
the two driving rollers 2U and 2L, respectively.
[0043] Like the driving rollers 2U and 2L, the two driven rollers
4U and 4L have rotation shafts 5U and 5L, respectively, which
substantially vertically extend separate from each other and
coaxial with each other. The rotation shafts 5U and 5L of the two
driven rollers 4U and 4L are fixed to, for example, frames (not
shown) incorporated in the mechanical detection unit 102. Namely,
the two driven rollers 4U and 4L are set rotatable about the fixed
rotation shafts 5U and 5L, respectively.
[0044] More specifically, one driven roller 4U is set rotatable in
contact with the upper driving roller 2U. Similarly, the other
driven roller 4L is set rotatable in contact with the lower driving
roller 2L. The two driving rollers 2U and 2L are rubber rollers,
and the two driven rollers 4U and 4L are two-layer rollers each
formed of a sponge layer and a rubber layer.
[0045] Namely, the driven rollers 4U and 4L have cored bars (not
shown) connected to the rotation shafts 5U and 5L via bearings (not
shown), respectively. The sponge layers as first layers are
provided on the outer surfaces of the cored bars, and the rubber
layers as second layers are provided on the outer surfaces of the
sponge layers. Further, the rotation shafts 5U and 5L are fixed to
the mechanical detection unit 102 as mentioned above.
[0046] Accordingly, the sponge layers of the driven rollers 4U and
4L are deformed in accordance with the thickness of each mail
matter M whenever each mail matter M passes therebetween, whereby
each mail matter M is nipped by the two pairs of rollers 2U, 4U, 2L
and 4L. While the two driving rollers 2U and 2L are rotated, each
nipped mail matter M is conveyed, held therebetween.
[0047] Since the rotation shafts 5U and 5L of the driven rollers 4U
and 4L are separate from each other, the driven rollers 4U and 4L
can rotate independently of each other at different circumferential
velocities. This can prevent an undesired force from being exerted
on each mail matter M even when the portions of the mail matters M
to be brought into contact with the driven rollers 4U and 4L have
different thicknesses.
[0048] As shown in FIGS. 2 and 3, the servo motors 6U and 6L for
rotating the driving rollers 2U and 2L, respectively, are connected
to motor control units 7U and 7L and also to torque detection units
8U and 8L, respectively. Further, as shown in FIG. 3, a control
unit 110 for controlling the operation of the mass measuring unit
10 is connected to a timing sensor 111 for detecting passing of the
front end of each mail matter M conveyed toward the mass measuring
unit 10, and also connected to a memory 112 that stores a data
table, described later. The control unit 110 is further connected
to a calculation unit 120 for calculating the mass of each mail
matter M based on the detection results of the torque detection
units 8U and 8L.
[0049] The motor control units 7U and 7L control the rotational
rates of the servo motors 6U and 6L to rotate the two driving
rollers 2U and 2L at the same rate as the process rate of the
apparatus 100, i.e., as the conveyance rate of each mail matter M,
before it is fed to the mass measuring unit 10. When the timing
sensor 111 detects the passing of the front end of a mail matter M,
the control unit 110 of the mass measuring unit 10 controls the
servo motors 6U and 6L to rotate the two driving rollers 2U and 2L
as indicated by the rate patterns shown in, for example, FIG. 5.
The rate patterns for the driving rollers 2U and 2L are beforehand
stored as control data in the memory 112.
[0050] When the two driving rollers 2U and 2L have been rotated in
accordance with the rate patterns shown in, for example, FIG. 5 to
rotate a mail matter M, the torque detection units 8U and 8L detect
the currents supplied to the servo motors 6U and 6L, and refer to
the data table stored in the memory 112 to thereby detect the
torque .tau. of the servo motor 6U and 6L, respectively, based on
the detected currents.
[0051] Further, when no mail matters M are conveyed, the torque
detection units 8U and 8L detect the torque TO of the driving
rollers 2U and 2L detected when the servo motors 6U and 6L
accelerate and decelerate the driving rollers. The thus-obtained
torque TO of the driving rollers 2U and 2L is beforehand stored in
relation to time as a parameter in a data table (not shown) stored
in the memory 112.
[0052] When the mass measuring unit 10 constructed as the above is
used to measure the mass of a mail matter M, the control unit 110
rotates the driving rollers 2U and 2L in accordance with the rate
patterns shown in, for example, FIG. 5, so that the mail matter M
is conveyed while angularly moving along the vertical handling
plane defined between the driving rollers 2U and 2L and the driven
rollers 4U and 4L, as is indicated by the broken lines of FIG.
4.
[0053] At this time, the control unit 110 acquires information
concerning the conveyance position of the mail matter M from the
timing sensor 111, and starts control of angularly moving the mail
matter M based on the rate patterns shown in FIG. 5, when the front
end of the mail matter M is nipped between the driving rollers 2U
and 2L and the driven rollers 4U and 4L. In FIG. 4, reference
symbols M1 to M7 denote changes in the attitude of the mail matter
M conveyed in the direction T.
[0054] It is desirable that the rate patterns for the driving
rollers 2U and 2L be set so that at least the conveyance rates of
the mail matter M detected before and after it is angularly moved
are equal to each other, i.e., the conveyance rates of the mail
matter M detected before and after it passes through the mass
measuring unit 10 are equal.
[0055] In other words, it is desirable that the rate patterns for
the driving rollers 2U and 2L be set so that the same processing
time is required when the mail matter M is passed through the mass
measuring unit 10 while being angularly moved, and when it is
passed through the unit 10 without being angularly moved. Namely,
it is desirable that the mail matter M is passed through the mass
measuring unit 10 without delay of conveyance.
[0056] In the embodiment, the rate patterns are set so that the
mail matter M assumes the same attitude before and after it is
angularly moved, in addition to the setting of keeping the
conveyance rate constant before and after the angular movement. By
thus controlling the rotations of the two driving rollers 2U and 2L
based on the above-mentioned rate patterns, no change will occur in
the conveyance rate, and no skew or shift will occur in the
conveyance attitude.
[0057] To angularly move each mail matter M during its conveyance
as described above, it is necessary to accelerate and decelerate
the two driving rollers 2U and 2L in accordance with preset rate
patterns (shown in, for example, FIG. 5). In this case, when a mail
matter M is angularly moved as described above, loads are exerted
on the servo motors 6U and 6L to thereby increase the torque values
of the servo motors 6U and 6L. Changes in torque depend upon the
rate patterns of the driving rollers 2U and 2L, also upon the
inertia moment of the driving system itself that includes, for
example, the rotation shafts 3U and 3L of the driving rollers 2U
and 2L, couplings (not shown), and the servo motors 6U and 6L, and
upon the mass of each mail matter M as a rotation target. For
instance, when angularly moving (rotating) a relatively heavy mail
matter M, the servo motors 6U and 6L each require a relatively
great torque corresponding to the mass of the mail matter M.
[0058] Namely, when all mail matters M are angularly moved
(rotated) with the same rate pattern, the inertia moment of the
driving system is constant, and hence the torque values of the
driving rollers 2U and 2L vary in accordance with the mass of each
mail matter M. Therefore, the mass of each mail matter M can be
measured by monitoring changes in the torque values of the servo
motors 6U and 6L and comparing the monitored values with reference
values. In other words, by monitoring the current supplied to each
servo motors 6U, 6L, the mass of each mail matter M can be
measured.
[0059] For example, when the mass of a mail matter M is zero, i.e.,
when no mail matter M is conveyed, and the driving rollers 2U and
2L are rotated, without rotating any mail matter M, at the same
rate patterns as those employed when rotating a mail matter M, the
torque of each of the servo motors 6U and 6L varies only in
accordance with the rate patterns and the inertia moment of the
driving system. Namely, by storing, in the memory 112 in relation
to the rate patterns, data indicating the torque of each of the
driving rollers 2U and 2L detected with time when these rollers are
rotated with no mail matter inserted therebetween, reference values
used for measuring each mail matter M can be set.
[0060] When the mass of a mail matter M is actually measured, the
mail matter M is angularly moved during its conveyance by rotating
the driving rollers 2U and 2L in accordance with preset rate
patterns (as shown in FIG. 5), and the torque .tau. of the servo
motors 6U and 6L is monitored at preset time points during the
conveyance of the mail matter M. The torque .tau. detected at each
preset time point is compared with the torque TO stored as a
reference value in a data table included in the memory 112, thereby
determining the mass of the mail matter M from the difference
between the detected and reference torque values.
[0061] Referring now to FIGS. 6 to 8, a description will be given
of the advantage of the mass measuring unit 10 of the embodiment,
using example cases. Namely, conventional mass measurement, which
is performed based on a change in the torque of a driving system
that occurs when a mail matter is accelerated and decelerated along
a conveyor path without being rotated, will be compared with the
mass measurement performed by the mass measuring unit 10 of the
embodiment based on a change in the torque of a driving system that
occurs when a mail matter is rotated.
[0062] The inertia moment of the driving system of the mass
measuring unit 10 constructed as above, i.e., the inertia moment
when no mail matter M is angularly moved, is substantially equal to
the sum of the inertia moment (I.sub.M) of each of the two servo
motors 6U and 6L, the inertia moment (I.sub.R) of each of the four
rollers, i.e., the two driving rollers 2U and 2L and the two driven
rollers 4U and 4L, and the inertia moment (I.sub.L) of each of the
rotation shafts 3U and 3L of the driving rollers 2U and 2L.
Actually, however, the inertia moment of the driving system is
obtained by adding, to the sum of the above-mentioned inertia
moments, the inertia moments of the coupling members that couple
the driving rollers 2U and 2L to the rotation shafts 3U and 3L,
respectively.
[0063] Further, the inertia moments of a mail matter M that occur
when the mail matter M is angularly moved (rotated) is quantified
as follows:
I.sub.MG=m(b.sup.2+h.sup.2)/12 [0064] I.sub.MG: Inertia moment
around the gravity center of the mail matter M [0065] m: Mass of
the mail matter M [0066] b: Length of the mail matter M along the
conveyor path [0067] h: Height of the mail matter M
[0067] I.sub.MR=mL.sup.2 [0068] I.sub.MR: Inertia moment around the
rotation center of the mail matter M [0069] L: Distance between the
gravity center of the mail matter M and the rotation center of the
mail matter M
[0070] From the above two equations, the inertia moment of the mail
matter M that occurs when the mail matter M is rotated is given
by
m(b.sup.2+h.sup.2)/12+mL.sup.2
[0071] Namely, the ratio (hereinafter referred to as the "inertia
moment ratio") of the inertia moment of the mail matter M itself to
the inertia moment of the driving system that occurs when it does
not rotate the mail matter M is expressed by the equation shown in
FIG. 6.
[0072] Further, r/R in the equation of FIG. 6 is a coefficient used
for converting the inertia moment of the mail matter M into the
inertia moment of the driving system around its rotation shaft, r
being the radius of each of the driving rollers 2U and 2L, R being
the distance between the driving rollers 2U and 2L.
[0073] In contrast, when as in the prior art, the mass of a mail
matter is measured by accelerating/decelerating the driving rollers
while the mail matter is conveyed, the inertia moment of the mail
matter is determined only from the distance between the rotation
shaft and the mail matter, i.e., the radius r of each driving
roller and the mass m of the mail matter, regardless of the
position of the gravity center of the mail matter, the length of
the mail matter, and the height of the mail matter, since the mail
matter is not rotated.
[0074] Namely, the inertia moment of the mail matter itself is
given by
mr.sup.2
[0075] Accordingly, if acceleration/deceleration control is
performed by the mass measuring unit 10, without rotating the mail
matter as in the prior art, the inertia moment ratio can be
calculated by substituting the inertia moment (mr.sup.2) of the
mail matter in the equation shown in FIG. 6. However, in this case,
the inertia moment ratio is extremely low, and the difference in
the torque of each driving roller between the case of conveying the
mail matter and the case of conveying no mail matter is extremely
small, compared to the case where the mail matter is rotated as
mentioned above.
[0076] If the torque difference detected by the torque detection
units 8U and 8L of the mass measuring unit 10 is too small, the
mass of the mail matter cannot accurately be detected. This being
so, in order to realize highly accurate mass measurement, it is
very effective to rotate the mail matter M as a mass measurement
target to thereby increase changes in the torques of the
motors.
[0077] The advantage of the mass measuring method of the embodiment
will be described by comparing the inertia moment ratio obtained
when the mass measuring method of the embodiment is employed, with
the inertia moment ratio obtained when the conventional mass
measuring method is employed.
[0078] FIG. 7 is a table showing examples of the sizes of the
structural elements of the mass measuring unit 10, examples of the
specific gravities of the materials of the structural elements, and
examples of the inertia moments of the structural elements. The
examples of the structural elements of the mass measuring unit 10
were the core of a driving roller, the rotation shaft of the
driving roller, a coupling, the core of a driven roller and the
rubber layer of the driven roller.
[0079] FIG. 8 is a table showing the ratio of the inertia moment of
each mail matter M per 1 g to that of the driving system, which
ratio is obtained when mail matters M of various sizes are each
rotated by the mass measuring method of the embodiment. The average
of the inertia moment ratios calculated in consideration of the
ratio of the number of mail matters of each size to that of mail
matters of any other size was 66.1%.
[0080] In contrast, the corresponding inertia moment ratio obtained
by the conventional mass measuring method was as low as 1.7%.
Namely, the inertia moment ratio obtained by the mass measuring
method of the embodiment is twenty times or more the inertia moment
ratio obtained by the conventional mass measuring method.
[0081] As described above, the mass measuring method of the
embodiment can detect even a slight difference between mail matters
M as a large torque change, and hence can measure the mass of each
mail matter M with high accuracy.
[0082] A description will now be given of a specific example of
calculating the mass m of a mail matter M using the mass measuring
method of the embodiment.
[0083] The entire torque .tau.0 of the driving rollers 2U and 2L
detected when the driving rollers do not rotate a mail matter M,
i.e., when the driving rollers are idling, can be expressed by the
product of the above-mentioned inertia moment of the driving system
and the angular acceleration .omega. of the driving system as given
by the following equation:
.tau..sub.0=(2I.sub.M+4I.sub.R+2I.sub.L){dot over (.omega.)}
(1)
[0084] The angular acceleration {dot over (.omega.)} of the driving
system is detected at a certain point of time while the servo
motors 6U and 6L are accelerating or decelerating.
[0085] In another aspect, the entire torque TO of the driving
rollers 2U and 2L is proportional to a current value i.sub.M
supplied to the servo motors 6U and 6L as given by the following
equation:
.pi..sub.0=K.sub.M (2)
where K is a proportional constant.
[0086] From the equations (1) and (2), the following equation can
be derived:
K .omega. . = ( 2 I M + 4 I R + 2 I L ) i M ( 3 ) ##EQU00001##
[0087] On the other hand, the entire torque of the driving rollers
2U and 2L detected when they rotate a mail matter M is the sum of
the above-mentioned torque .tau.0 and an increase .DELTA..tau. in
torque due to the inertia moment of the mail matter M. Namely, the
entire torque (.tau.0+.DELTA.t) of the driving rollers 2U and 2L is
given by the following equation:
.tau. 0 + .DELTA..tau. = { ( 2 I M + 4 I R + 2 I L ) + ( m b 2 + h
2 12 + m L 2 ) r R } .omega. . ( 4 ) ##EQU00002##
[0088] In another aspect, the entire torque (.tau.0+.DELTA..tau.)
is proportional to a current supplied to the servo motors 6U and 6L
as given by the following equation:
.tau..sub.0+.DELTA..tau.=K(i.sub.M+.DELTA.i.sub.M) (5)
where K is a value unique to the driving system of the mass
measuring unit 10 of the embodiment. The current value applied at
this time is (i.sub.M+.DELTA.i.sub.M) obtained by adding a current
value .DELTA.i.sub.M corresponding to the increase in the torque
for rotating the mail matter M.
[0089] From the above equations (1) and (4), the following equation
is derived:
.DELTA..tau. = m ( b 2 + h 2 12 + L 2 ) r R .omega. . ( 6 )
##EQU00003##
[0090] Further, from the above equations (2) and (5), the following
equation is derived:
.DELTA..tau.=K.DELTA.i.sub.M (7)
[0091] Yet further, from the above equations (6) and (7), the
following equation is derived:
K .omega. . = m ( b 2 + h 2 12 + L 2 ) r R .DELTA. i M ( 8 )
##EQU00004##
[0092] From the above equations (3) and (8), the following equation
is derived:
m = ( 2 I M + 4 I R + 2 I L ) .DELTA. i M ( b 2 + h 2 12 + L 2 ) r
R i M ( 9 ) ##EQU00005##
[0093] Thus, the mass m of the mail matter M is calculated.
[0094] Namely, in the equation (9), the mass m of the mail matter M
is a function of the current value i.sub.M supplied to the servo
motors 6U and 6L when no mail matter is rotated, and the current
value .DELTA.i.sub.M supplied to the servo motors 6U and 6L when a
mail matter M is rotated. Accordingly, the mass m of the mail
matter M can be calculated by monitoring the currents supplied to
the servo motors 6U and 6L, using the torque detection units 8U and
8L.
[0095] As described above, in the mass measuring unit 10 of the
embodiment, a mail matter M is rotated during its conveyance, with
the conveyance rate unchanged, the torque values of the servo
motors 6U and 6L detected when they accelerate and decelerate the
driving rollers 2U and 2L to rotate the mail matter M are detected,
and the detection result is compared with the torque of the driving
system beforehand measured under the same conditions but without
rotating any mail matter, thereby measuring the mass m of the mail
matter M. By virtue of this structure, the mass of each of a
plurality of mail matters M can be measured while they are
successively conveyed at high rate. As a result, there are no
changes in the gap between adjacent mail matters, and hence the
conveyance throughput can be enhanced.
[0096] Further, in the above-described embodiment, since a
relatively high torque is generated by rotating each mail matter M
as a mass measuring target, to thereby enhance the resolution, the
mass of each mail matter M can be measured at high accuracy.
[0097] In addition, in the above-described embodiment, the mass of
each mail matter M is measured using the inertia moment detected
when each mail matter M is rotated. Therefore, if a mail matter M
that contains, for example, a metal chip such as a coin is
measured, it is detected that the mail matter M is unnaturally
heavy, i.e., contains a foreign material, and hence the mail matter
is rejected. Namely, this mail matter is regarded as a
to-be-rejected matter that cannot be processed in a later process,
and is rejected. Thus, the mass measuring unit 10 of the embodiment
positively rejects a foreign material contained mail matter M.
[0098] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiment shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
[0099] For instance, although in the above-described embodiment,
the torque detection units 8U and 8L monitor the currents supplied
to the servo motors 6U and 6L to detect the entire torque .tau. of
the servo motors 6U and 6L, the invention is not limited to this
structure. Alternatively, a measuring instrument (not shown), such
as a strain gauge, may be used to detect the torque .tau..
[0100] Further, although in the above-described embodiment, the
mass measuring unit 10 is incorporated in the apparatus 100, the
invention is not limited to this. Alternatively, a mass measuring
function may be included in another processing unit. For example,
if an attitude correction unit for correcting a conveyance attitude
(skew or shift) of a mail matter M is provided along the conveyor
path 1 extending through the apparatus 100, it may be made to have
the mass measuring function.
[0101] Furthermore, although in the above-described embodiment,
each mail matter M is rotated by producing a difference in the
rates of the two driving rollers 2U and 2L located across the
conveyor path 1, the invention is not limited to this, and only a
single driving roller may be used to rotate each mail matter M. In
this case, it is sufficient if the single driving roller is brought
into contact with the portion of the surface of a mail matter M
that is deviated from an imaginary center line extending through
the center of gravity of the mail matter M along the conveyor path,
and the driving roller is accelerated and decelerated. In any case,
to measure the mass of the mail matter M, it is sufficient if the
torque of the driving roller assumed when the mail matter M is
rotated can be detected by some means. Thus, any mail matter
rotation mechanism and any torque detection method may be
employed.
[0102] For example, although in the embodiment, the driven rollers
4U and 4L are opposed to the driving rollers 2U and 2L with a mail
matter M interposed therebetween, they are not essential elements
for the present invention. If the mail matter M is laid down and
conveyed horizontally, a guide plate member having a flat slippy
surface is provided on the lower surface of the convey path, and
the driving rollers 2U and 2L are pressed against the mail matter
M, the mail matter M can be rotated by performing rate control of
the driving rollers 2U and 2L.
[0103] Moreover, although in the embodiment, the driving rollers 2U
and 2L are used as a mechanism for rotating a mail matter M, a
driving belt, for example, which can be run along the convey path,
may be used instead of the driving rollers 2U and 2L.
[0104] In addition, although in the embodiment, the torque .tau.0
of the rotation mechanism detected when it is idling is used as a
reference value for measuring the mass of a mail matter, the
invention is not limited to this. Alternatively, test sheets having
various sizes and a certain weight may be supplied to the apparatus
100, whereby the outputs of the servo motors 6U and 6L of the mass
measuring unit 10 be recorded and used as measurement reference
values.
* * * * *