Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MAIL THICKNESS MEASURING APPARATUS
FIELD OF THE INVENTION
This invention relates to mail thickness measuring appa-
ratus, and in particular to such apparatus for use in high speed
mail handling machine.
BACKGROUND OF THE INVENTION
State-of-the-art mailing machines can perform such auto-
matic functions as handling mail of different sizes and thick-
nesses, envelope sealing, mail weighing, mail stamping, and mail
sorting. In developing machines with such functions, capable of
processing mail at high speeds of, for example, four or more
pieces per second, it becomes important if not essential that the
mail thickness is determined as soon as possible after the mail
begins its flow sequence. Knowing the thickness early is impor-
tant because there usually is a relationship between mail thick-
ness and mail weight, i.e., the thicker the mail, the more it
weighs. Typically, heavier mail must be processed slower than
lighter mail in a high speed processing environment. Hence, the
weight of the mail allows the computer which is controlling the
machine to slow the transport mechanisms when carrying heavy mail
and speed up the transport mechanisms when carrying lighter mail.
It is desirable to control transport velocity as a func-
tion of mail weight or mail thickness as soon as the mail pieces
begin their flow through the machine. Typically, the mail pieces
enter the system from a hopper in stacked form, and one of the
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first actions necessary is to separate an individual piece of mail from the
stack. The
mechanism for doing this is called a singulator and the action singulating.
Mail thickness sensors in prior art machines would typically position on top
of the
mail piece a follower connected to an optical system involving a light source
scanning
across an array of light detectors, the position of the light source being
determined by
the position of the follower, and the position of the light source determining
which
detector is activated. Mechanical systems have also been used.
These prior art systems suffer from one or more of the following shortcomings.
With optical systems, frequent maintenance is necessary to keep the optics
clean. A
mailing machine processing thousands of pieces of mail daily does not provide
a clean
environment for optical sensors. The signal output frequently was analog. This
meant
the use of an A/D convertor to translate the analog signal into a digital
signal that the
computer can process, which increased costs. Accuracy of thickness measurement
was
not always optimal. Especially with high speed processing, it is important to
be able to
measure the mail thickness in the range of 0.004-0.75 inches to an accuracy of
about
0.05 inches.
SUMMARY OF THE INVENTION
One object of an aspect of the invention is mail thickness measuring apparatus
capable of measuring the thickness of mail pieces being processed at high
speeds.
Another object of an aspect of the invention is a mail handling machine for
processing mail pieces of different thicknesses at high speeds wherein the
thickness
measurement is carried out early in the mail flow.
A further object of an aspect of the invention is thickness and measuring
apparatus for mail pieces that is capable of accurately measuring the mail
piece
thickness while the mail piece is being processed at high speed.
In accordance with one aspect of the invention, in a mailing machine capable
of
processing at high speed mail pieces supplied from a stack, mail thickness
measuring
apparatus is provided coupled to the singulator device that separates
individual mail
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pieces from the stack. By coordinating the thickness measuring function with
the
singulating function, the thickness of the mail pieces is determined as soon
as the flow
of individual mail pieces begins and thus the velocity of that flow can be
computer-
controlled for maximum efficiency and speed.
In accordance with another aspect of the invention, the thickness measuring
apparatus comprises a permanent magnet and a magnetic field detector system.
This
allows the system to operate accurately in a unclean environment, since the
presence
of dirt or contamination has virtually no effect on the magnetic field.
In accordance with still another aspect of the invention, a relatively simple
but
accurate thickness measurement system is employed, which outputs an absolute
encoded digital value which can be directly processed by a computer to control
the
velocity of the measured mail piece as it flows through the machine for
subsequent
sealing, weighing, stamping, and sorting if desired. In a preferred
embodiment,
connected to a follower which contacts the mail piece top is a permanent
magnet having
plural poled segments, the magnet position tracking that of the follower. The
magnet
traverses an array of magnetic field detectors which respond to selected
detected
magnetic fields, and in response outputs an absolute Gray encoded binary
number
which is unique for each subrange of mail thickness. Twenty accurate thickness
measurements can be made over a range of 0.004-0.75 inches to an accuracy of
0.05
inches. The resultant binary number can then be used to index into a lookup
table for
selecting an appropriate flow velocity sequence or profile for the measured
mail piece in
its subsequent processing through an automatic mail handling machine.
According to a further aspect of the invention, there is provided an apparatus
for
processing mail pieces comprising means for supplying multiple mail pieces, a
singulator for separating individual mail pieces, means for transporting mail
pieces from
the supplying means to the singulator, means operatively connected to the
singulator for
measuring the thickness of mail pieces singulated thereby and means downstream
of
the singulator for further processing of the mail, further transporting means
for
tranporting the single mail pieces to the further processing means, and means
for
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varying the velocity of the further transporting means in accordance with the
measured
thickness of each mail piece processed.
DESCRIPTION OF DRAWINGS
The invention will now be described in greater detail with respect to several
exemplary embodiments in connection with the accompanying drawings, wherein:
Fig. 1 is a schematic view of one form of magnetic sensor suitable for
measuring
mail thickness in accordance with the invention;
Fig. 2 is a table showing the binary coded and hex output for the sensor of
Fig. 1;
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Fig. 3 is a front schematic view of a typical mail hand-
ling machine employing the sensor of Fig. 1:
Fig. 4 is a detailed side view of the singulator and mag-
netic sensor schematically depicted in Fig. 3.
In the several figures, the same reference numerals are
employed to designate similar elements.
A suitable mail thickness sensor suitable for use in a
mail-handling machine, in an embodiment preferred for measuring
mail or letter thickness, is schematically illustrated in Fig. 1
and will be briefly described below. The sensor assembly com-
panies a fixed detector assembly 8, and a moving magnet 20. The
fixed detector assembly comprises seven Hall effect detectors 10-
16 arranged in a row spaced apart by a fixed center-to-center
spacing 18. Each detector has an active detecting area indicated
by reference numeral 27.
The magnet 20 moves in a straight line parallel to the
detector row separated by a gap 19. The preferred magnetic array
comprises two South (S) poles 22,24 separated by a North (N) pole
23. Additional N poles can be provided at the leading edge, pole
21, and at the trailing-edge, pole 25, of the assembly to sharpen
the field transitions. The magnet is moved by the mail piece
follower in the direction indicated by the arrow. The position
of the magnet 20 shown in solid lines is the start or zero thick-
ness position. In dashed lines are shown magnet positions 20'
and 20" in which the magnet would have been moved four and nine
units, respectively, to the right of its starting position.
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For the preferred geometry shown, with the active detector
area 27 equal to 0.05 inches, the detector spacing 18 equal to
0.2 inches (in the arrow direction), S pole 22 .025 inches long,
N pole 23 0.1 inches long, and S pole 24 0.15 inches long, the
detector array will output twenty different absolute Gray codes
over a mail thickness range of 0.004 to 1.0 inches with a worst
case resolution of ~ 0.05 inches. The output binary code
can be stored in a register 7, and subsequently retrieved by a
computer to be processed.
Fig. 2 is a table showing the output from each detector in
response to positions of the magnet 20. Basically, the detector
outputs a "0" when opposite a S pole, and a "1" when opposite no
field or a N pole. The column on the right, the Hex equivalent
of the adjacent binary coded output, shows that the output is
absolute, meaning no two codes are alike. The binary outputs
demonstrate Gray encoding, since no more than one bit changes for
adjacent magnet positions. The magnet is readily manufactured in
the geometry shown, and the detectors are commercially available
as inexpensive Hall-effect detectors. The gap spacing 19 would
be typically 0.04 inches. As previously mentioned, since the
moving part of the sensor is a magnet, and the fixed part the
Hall-effect detectors, a rugged sensor is obtained that will
withstand much abuse. Since magnetic fields are sensed, the
system is virtually immune to dirt and contamination. The direct
output of a binary-coded number eliminates the need for analog-
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to-digital conversion and reduces costs. The Gray encoding
ensures high resolution, reliable measurements.
In a practical embodiment, the detectors 10-16 are
mounted in a common holder or on a common support, with a seven
wire connector 6 for the output to the register 7.
Fig. 3 illustrates schematically the front end of the
mail handling machine, comprising a hopper 30 for receiving a
stack of mail pieces 31 for processing. A transport system com-
prising motor driven rollers 32 and a belt 33 picks out one or
more of the mail pieces 31 from the stack bottom and immediately
carries them under a singulator mechanism 35 which functions to
ensure that only a single piece of mail will thereafter be pro-
cessed at a time by the machine.
The singulator 35 may comprise any one of a number of
known mechanisms, provided that it includes a movable element
that follows the mail piece top. A preferred singulator com-
prises a four-bar linkage mechanism 36 which is pivoted on the
machine frame. A more detailed illustration is shown in Fig. 4.
The forward drive for the mail pieces, shown at 50, is supplied
by the belt or belts 32 which is mounted on the machine deck 37.
The four-bar linkage 36 comprises one or more reversely-driven
belts 38 rotating around pulleys 39 located at the corners of a
rhombus formed by the linkages 40. The rhombus is anchored at
pulley shafts 44 for pivotable movement on a support 41 extending
up from the machine frame. A compression spring 45 biases the
singulator 36 downward and applies a load onto the mail which it
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is helping to singulate. The reversely-driven belts 38 are typi-
cally interdigitated with the forward driving belts 32.
In operation, if more than one mail piece or overlapped
mail pieces enter the zone between the reversely-driven belts 38
and the forwardly-driven belts 32, while the bottom mail pieces
is driven forward to the right, any overlapping mail pieces are
driven backward. In this process, the bottom mail piece is
driven under the singulator nip, the lowermost portion of the
reversely-driven belts 38, causing an upwards push on the mechan-
ism. The rhombus 36 deforms to allow mail pieces of varying
thickness to pass under it while maintaining its outer circum-
ference. Thus, the rhombus 36 acts as a follower that moves up-
ward in the direction indicated by arrow 43 a distance propor-
tional to the mail thickness. The magnet array 20 depicted in
Fig. 1, which is fixed by plate 46 to the lower linkage bar 40,
likewise moves upward the same proportional distance. The Hall-
effect detector array 8 for the magnet array 20 is mounted on a
printed circuit board, which in turn is mounted on the fixed sup-
port 41. An optical sensor 47 is mounted in the deck 37 and
functions to detect the leading edge of the mail piece. When
detected, the sensor shuts down the forward and reverse drives
for an instant. Thus, the singulator upward motion stops. At
that point, the detector output to the register 7 stabilizes, and
the computer, shown at 51, also signalled by the sensor 47, polls
the register 7, retrieves the binary coded number stored therein,
and in turn stores it in an internal register. After a fixed
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time delay, typically 20 ms, the drive mechanisms are restarted
and the mail piece is carried forward, to the right, and is cap-
tured by a takeaway nip formed by driven roller 48 and spring-
biased idler 49, affixed to shaft 45, and is thus carried
downstream for further processing. If desired, a second sensor
(not shown) can be positioned downstream of the sensor 47 which
would operate similarly, i.e., detect the leading envelope edge,
stop the drives, and then restart them, all under computer con-
trol. This would allow a second mail thickness measurement to be
made of the same mail piece, and the second measurement averaged
with the first to ensure that unevenly stuffed envelopes do not
produce an erroneous weight indication.
As will be noted from the foregoing description, by asso-
ciating the thickness measuring sensor with a singulator mechan-
ism that follows mail pieces of varying thickness, the thickness
measurement is taken nearly simultaneously with the singulating
action, and thus early on in the mail handling process. Thus,
the computer is informed of the mail thickness and thus approxi-
mate weight at virtually the same time that each mail piece be-
gins its serial processing through the machine.
The use of the magnetic field operating sensors ensures
trouble free reliable operation even in the environment of high
mail throughput machines. Moreover, obtaining a binary coded
output directly reduces costs, and when the output is Gray en-
coded increases accuracy. The mechanism described, as il-
lustrated in the drawings, provides accuracy to 0.05 inches of
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the mail thickness. The resolution and range of measurable
thicknesses can be varied by adjusting the geometry of the detec-
for array and magnetic configuration or through the use of
linkages between the singulator and the magnet.
It will be understood that the invention is not limited
to the specific configuration of thickness sensor disclosed, and.
other configurations will also prove suitable. Moreover, the in-
ventions is not limited to the singulator mechanism specifically
disclosed, nor to the other details of the preferred embodiment
described.
While the invention has been described and illustrated in
connection with preferred embodiments, many variations and modi-
fications as will be evident to those skilled in this art may be
made therein without departing from the spirit of the invention,
and the invention as set forth in the appended claims is thus not
to be limited to the precise details of construction set forth
above as such variations and modifications are intended to be in-
cluded within the scope of the appended claims.
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