Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
Inventory Control and Communication System
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. provisional
patent applications No. 60/108,843, filed November 18,
1998, entitled Inventory Management System, and U.S
provisional patent application No. 60/136,297, filed May
27, 1999, entitled Inventory Control and Communication
System.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
Inventory management systems are known which attempt
to keep inventory of stock items at an optimal level
based upon factors such as availability, possibility of
price increase, lag time to reorder, and predictability
of consumption rates. One such system is a Materials
Requirements Planning (MRP) system, which is the primary
manufacturing module of Enterprise Resource Planning
(ERP} systems. Inventory ordering is performed through
accurate forecasts of finished product demand and raw
material availability, among other factors. Such
systems, however, depend upon accurate market
forecasting. Another inventory system is known as a
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"Kanban" system, in which stock items are maintained with
minimum and maximum thresholds. When the minimum
threshold is reached, enough stock is ordered to bring
the quantity back up to the maximum threshold. Timely
examination of the stock item level is required, however,
to ensure that the stock does not run out, and to ensure
timely notification to a supplier to effect delivery.
It would be beneficial, therefore, to provide a
system which performs automatic replenishment of stock
through real-time polling of stock item quantity to avoid
the need for periodic manual inspection of quantity and
the need to maintain accurate market forecasts.
BRIEF SUMMARX OF THE INVENTION
An inventory control and communication system
provides automated real-time polling of stock levels and
ordering in a timely manner so that optimal stock levels
are maintained. A storage unit, or bin, is established
for each stock item. One or more transducers are
associated with each storage unit to produce a signal
indicative of the weight of the stock items stored in or
at the corresponding storage unit. The signals are
transmitted at regular intervals to a central inventory
server, which maintains information about transducer
location and the corresponding stock item, such as item
weight and supplier information. Inventory logic in the
central inventory server computes the quantity of each
stock item from the transducer signals and the weight of
the stock items. Inventory logic also includes threshold
values for the minimum and maximum quantity of each stock
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item. When the quantity of a stock item reaches the
minimum threshold, inventory logic sends an order to the
supplier to restore the stock item to the maximum
quantity threshold, or otherwise indicates that a reorder
is needed.
Inventory logic computes the quantity of the stock
item from the transducer signals and the known weight of
the predetermined stock item at the particular storage
unit. The transducers, such as strain gauges, are
disposed on or at each storage unit in such a manner so
as to be sensitive to the weight of the stock items at
the storage unit. Typically the strain gauges are
mounted on the beams or supports bearing the weight of
the storage unit, so as to detect shear, compression, and
tension forces in the beams or supports. A transducer
may be affected by multiple storage units. The inventory
logic apportions the component of force imposed from a
particular storage unit through precise positioning of
the transducer relative to the storage unit. Also,
multiple transducers may be used to measure the weight of
a single storage unit. The inventory logic aggregates
multiple readings so that a true quantity is computed
regardless of the positioning of the stock items in or at
the storage unit.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The invention will be more fully understood with
reference to the following detailed description and
drawings, of which:
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Fig. 1 is a block diagram of the inventory control
and communication system as defined by the present
invention;
Fig. 2 is a context diagram of the system of Fig. 1;
Fig. 3 is an exploded view of an item bin storage
unit as used in the present invention;
Fig. 4 shows the item storage bin of Fig. 3 with an
expansion plate;
Fig. 5 shows the expansion plate of Fig. 4 attached
to a sensor base;
Fig. 6a shows a rack storage unit as utilized in the
present invention;
Fig. 6b shows the rack storage unit of Fig. 6a with
shelves;
Fig. 7 shows a shelf storage unit having a plurality
of sensor arrays;
Fig. 8a shows a side view of a pallet storage unit;
Fig. 8b shows a top view of the pallet storage unit
of Fig. 8a;
Fig. 8c shows an alternate side view of the pallet
storage unit of Fig.,8a;
Fig. 9a shows a horizontal fluid storage unit;
Fig. 9b shows a vertical fluid storage unit;
Fig. 9c shows a transmitter and gas cylinder storage
unit;
Fig. l0a shows a plurality of wire spool storage
units;
Fig. 10b shows sensor placement on one of the wire
spool units of Fig. 10a;
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Fig. 11a shows a perspective view of a circuit board
transducer;
Fig. llb shows a top view of the circuit board
sensor of Fig. lla;
Fig. 12 is a block diagram of the database and query
GUI as used in the present invention;
Fig. 13 shows a block diagram of a storage
transmission node;
Fig. 14 shows a flowchart of the storage
transmission node logic; and
Fig. 15 shows the packet structure of the transducer
signal packet sent from the storage transmission node.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Fig. 1, a block diagram of the
inventory control and communication system 10 is shown as
defined herein. One or more storage units, such as bins
12, store a quantity of a predetermined item. The
quantity is proportional to the weight of the loaded bin
12. A transducer 14 senses the weight 16 of the bin 12,
and produces a transducer signal 18 indicative thereof.
The transducer signal 18 and the weight of the
predetermined item is then used by quantity computation
20 to compute the quantity of the item in the respective
bin 12. An item quantity signal 22 is sent to inventory
control 24 which compares the quantity to minimum
quantity thresholds for the particular item. If the
quantity of a particular item is below the minimum
threshold, inventory control 24 sends an order message 26
to a supplier to restock the item.
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Referring to Figs. 1 and 2, the inventory control
and communication system 10 as described above is shown
in the context of a customer facility 30. A plurality of
storage units 32 are located at a facility 30, such as a
warehouse or manufacturing site. Each storage unit 32 is
adapted to store a predetermined item 34 of a known
weight. The storage units 32, described further below,
may be bins, pallets, shelves, fluid tanks, wire spools,
or other storage apparatus, and may be mounted in rows on
a rack 34 or free standing, depending on the items so
stored. One or more transducers 36 are associated with
each storage unit, and located so as to sense the weight
of the stored items 34. Each transducer 36 is connected
to a storage transmission node 38, described further
below, and sends to the storage transmission node 38 a
transducer signal 18 indicative of weight. The storage
transmission node 38 builds a transducer signal packet
including one or more transducer signals according to a
predetermined protocol.
The transducer signal packet is sent to a central
inventory server 40, which receives transducer signal
packets from other storage transmission nodes 38 at the
facility 30. The central inventory server 40 is
connected to an inventory database 42 which stores
information about the item corresponding to each storage
unit. For each storage unit 32, the weight of the item
stored therein is maintained, as well as a minimum and
maximum quantity threshold quantity for each item. The
transducer signal packets are used to compute the
quantity of the item remaining in the storage units, and
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are compared to the minimum quantity threshold stored in
the inventory database 42.
The inventory database 42 also contains supplier
information for each item. The inventory server 40 will
send an order to the supplier by any suitable means, such
as via Internet 46, voice 48, cellular 44, or via paper
mail 50 by printing an order on the attached printer 52.
Alternatively, the inventory server 40 may send quantity
information without requesting an order.
The inventory server 40 has a graphical user
interface (GUI), described further below, for performing
various inventory query functions. The GUI can be
accessed locally through the server monitor 54, or
accessed remotely from another computer 56.
TRANSDUCERS
Each of the transducers 36 as defined herein is
operable to sense the weight, mass, or pressure of items
34 or substances contained in a storage unit 32. In a
preferred embodiment the transducer is a strain gauge,
and is attached to a load-bearing element supporting the
storage unit 32, typically from beneath. A strain gauge
provides a signal indicative of micromechanical
deformations on the surface of a rigid member in response
to forces applied thereto. A strain gauge disposed on a
load bearing member supporting a storage unit delivers a
signal indicative of the weight exerted by the items
contained in or at the storage unit.
The range of sensitivity of the strain gauges is
selected based on the weight of the predetermined item
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and the quantity range expected. The strain gauges are
affixed at a location which is subjected to forces
exerted by the weight of the bin to which they
correspond. The location at which the strain gauges are
affixed takes various forms, described further below,
depending upon the type of storage unit. The forces so
exerted include tension, compression, and shear. Through
appropriate calibration and signal amplification, the
strain gauge signal indicative of the weight exerted by a
particular storage unit can be used to accurately compute
the total weight. The quantity of individual items can
therefore be computed from the predetermined weight of
individual items.
More than one strain gauge may be employed to sense
the weight exerted by a particular storage unit.
Multiple strain gauges are used to provide positional
independence of the location of the item in or at the
storage unit. Items located at a particular side of the
storage unit may exert more force on that side. Multiple
strain gauges can provide an offset such that the
aggregate reading of all signals corresponding to a
particular storage unit provides an accurate measurement
of the total.
In alternative embodiments, other transducers may be
employed to provide a signal indicative of the weight in
or at a storage unit 32. Pressure sensitive resistors,
resilient supports which selectively obscure a portion of
a light beam, or electromechanical means such as a
variable resistor may be employed.
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STORAGE UNITS
The storage units 32 disclosed herein include
several embodiments depending upon the types of items so
stored. Referring to Fig. 3, a storage bin embodiment is
shown. A storage bin 60 is adapted to be mounted on a
support frame 62. The support frame 62 includes a center
spine 64, cantilever moment arms 66, 68, and bearing arms
70, 72. The cantilever moment arms 66 and 68 are
attached on top of the center spine 64 such that they
extend equidistantly therefrom, and may be formed of a
single piece. Bearing arms 70 and 72 are attached to the
end of the cantilever moment arms 66, 68.
Two strain gauges are attached to the moment arms 66
and 68, preferable at a location where the mechanical
deformations due to strain are the greatest, to maximize
sensitivity. This location is the point just beyond that
at which the moment arms 66, 68 extend from the center
spine 64. One strain gauge 74 is mounted on the top of
the moment arm 66, and measures increasing tension as the
moment arm 66 is pushed downward from the weight of the
bin 60 pushing against the bearing arm 70. The other
strain gauge 76 is mounted on the bottom of the opposed
moment arm 68, and measures compressive forces as the as
the moment arm 68 is pushed downward from the weight of
the bin 60. For maximum accuracy, the bin 60 and the
strain gauges 74, 76 are symmetrically mounted over the
support frame 62 and center spine 64. Since symmetrical
positioning provides that the neutral axis is at the
centerline of the support frame above the center spine
64, the aggregate strain gauge 74, 76 readings are
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independent of the left-to-right location of the items in
the bin. Further, strain gauges 74 and 76 are mounted
parallel to the axis of the moment arms 66 and 68,
providing for front-to-back positional independence of
the items in the bin 60.
Resilient couplings 78 are used to attach the
bearing arms 70, 72 to the bin 60. The resilient
couplings 78 eliminate unwanted lateral forces which can
affect the tension and compression sensed by the strain
gauges 74 and 76 by restricting force exerted by the bin
60 to a vertical direction: The resilient couplings 78
also serve to cushion sudden surges of force which can
interrupt accurate readings, such as from an object
dropped or thrown into the bin 60.
In alternate embodiments, shown in Figs. 4 and 5; an
anti-expansion plate 80 is attached between the resilient
couplings 78 and the support frame 62. The plate 80 is
constructed of the same material as the support frame 62.
Strain gauge readings will therefore remain unaffected
from thermal expansion resulting from different expansion
coefficients between. the bin 60 material and the support
frame 62 material.
In another embodiment, shown in Figs. 6a and 6b, a
rack storage unit adapted to store rigid, elongated items
is shown. Referring to Fig. 6a, each storage unit 82
comprises a portion of a load bar 84 apportioned into
individual storage units through separation stops 86.
Strain gauges 88, adapted to measure shear force, are
located at each of the separation stops 86 and also at
the ends of the load bar 84. The weight exerted on the
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load bar 84 by a particular storage unit 82 can be
apportioned by measuring the component of force sensed
from adjacent storage units based on the position of the
strain gauges 88.
Referring to Fig. 6b, a shelf sensing system is
shown similar to the embodiment disclosed in Fig. 6a.
Each storage unit comprises a shelf 90 adapted to store
free-standing items which do not require separation stops
to ensure that they do not slide into an adjacent storage
unit. Each shelf 90 is supported by a portion of the
load bar 84. Strain gauges 88 measure force such that
the weight exerted by a particular shelf 90 can be
apportioned by measuring the component of force sensed
from adjacent storage units 90.
Referring to Fig. 7, another embodiment is disclosed
which shows the apportionment of forces from adjacent
strain gauges. Two load bars 100, 102 are used to
provide front-to-rear positional independence of items.
Three independent forces F1-F3 are applied to storage
units 104, 106, 108, respectively. Force F1 bearing on
storage unit 104, for example is proportional to:
~(SG1A - SG2A)~ + ~(SG1B - SG2By
or, equivalently
((SG1A + SG1B) - (SG2A + SG2B)~
Summarizing the general case, for a load between strain
gauges SGn and SGn+1 on load bars A and B:
F(n) - ~ (SG(n)A + SG(n)B) - {SG (n+1)A + SG{n+1)B) ~
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The storage units 104, 106, 108 could be bins, elongated
stock racks, shelves, or other configurations of items.
Referring to Figs. 8a-8c, a pallet embodiment is
disclosed. Such pallets typically are used to store
large, heavy items and adapted to be manipulated by
mechanical means such as a forklift. A pair of base
beams 110 each support cantilever beams 112. The
cantilever beams 112 each support bearing posts 114,
which bear the load of items stored on pallet planks and
transmit forces downward onto the cantilever beams 112.
Strain gauges 118 are affixed to the surface of the
cantilever beams 112, at a point just before the beam 112
is attached to the base beams 110. Either tension or
compression in the beams 112 may be measured, depending
upon whether the strain gauges 118 are mounted on the top
or bottom side, respectively, of the beams. The strain
gauges are connected to a storage transmission node 38
located between the base beams.
In another embodiment fluid quantity is measured.
Referring to Figs. 9a-9c, fluid tanks are shown. Fig. 9a
shows a strain gauge 120 affixed to the bottom of a
horizontal liquid tank 122, such as a home heating oil
tank. A vertical tank 124 is shown in Fig. 9b. Strain
gauge 120 is affixed near the bottom of the tank such
that fluid level is proportional to forces detectable on
the surface of the tank caused by the pressure of the
fluid. The strain gauge 120 should be affixed away from
structural aspects such as seams and legs which may
affect the linearity of the response. Further, the
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transducer signal is processed to accommodate the
predetermined geometry of the tank, and may be processed
using additional information such as the temperature of
the fluid so stored. Fig. 9c shows attachment of a
storage transmission node 38 to a gas cylinder 126.
Figs. l0a-lOb show a wire spool embodiment. A
horizontal rod 130 is adapted to store a spool 132 of
wire. Fig. 10b shows the location of the strain gauge
134 and the sides 136 of the spool. The strain gauge 134
provides a signal which is indicative of the downward
force of the corresponding spool 132. The quantity of
wire remaining can be computed from the known weight of a
segment of the wire so stored.
In another embodiment, a strain gauge is affixed to
a printed circuit board (PCB) 140, as shown in Figs. lla
and llb. Direct affixation to a printed circuit board
facilitates electronic connections when the expected
force is within a range which can be tolerated by a
printed circuit board. Strain gauges 142 are glued or
soldered to the surface on opposed sides, to sense both
compression and tension. Alternatively, strain gauges
142 can be embedded within the board 140, as long as the
strain gauges are located at the zero point 144 at the
center of the board, so as to sense compression and
tension equally. Further, PCB fabrication techniques may
be used to fabricate strain gauge elements directly onto
a structural member, such as a beam or support,
supporting a storage unit.
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TRANSDUCER POLLING
As indicated above in Fig. 2, each strain gauge 36
is connected to a storage transmission node 38 local to
the storage units 32. Each storage transmission node 38
may be connected to strain gauges 36 corresponding to
multiple storage units. Readings from each of the strain
gauges 36 are transmitted to the central inventory server
40.
Referring to Fig. 13, a block diagram of the storage
transmission node 38 is shown. Each strain gauge 36 is
connected to a multiplexor 140. Multiplexor 140 polls
each strain gauge 36 and sends the signals to the
processor 142. The processor builds a transducer signal
packet containing the transducer signals. A node
address, identifying the storage transmission node, is
read from a DIP switch 144. The node address
distinguishes multiple storage transmission nodes which
may be sending transducer signal packets to the central
inventory server 40. The transducer signal packet 147 is
shown in Fig. 15, and includes the node address I46,
values for each strain gauge reading 148, and checksum
fields 150. The transducer signal packet is sent to a
radio transmitter 152 for transmission to the central
inventory server 40 through an antenna 154. The storage
unit node 38 is powered through a power supply/regulator
156, which may include a photovoltaic cell 157.
A flowchart of the storage transmission node logic
is shown in Fig. 14. The processor is initialized at
step 200 to begin polling at the first strain gauge. The
signal from the next strain gauge is read, as depicted at
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step 202. A value indicative of the signal is written to
the proper position in the transducer signal packet, as
shown at step 204. A sampling algorithm may be employed
to provide verification through multiple successive
reads. A check is made, as disclosed at step 206 to
determine if all strain gauges have been polled. If not,
iterate through each strain gauge in sequence, as
depicted in step 208. When all strain gauges have been
read, the storage transmission node address is read from
DIP switch 144, as depicted in step 210. Checksum and
header fields are written to the transducer signal
packet, shown in step 212. A pause far the next pseudo-
random transmission interval is performed, as disclosed
in step 214 and described further below. When the
transmission interval elapses, the transducer signal
packet is sent to the central inventory server 40, as
shown in step 216. The next pseudo-random transmission
interval is selected, as shown at step 218, and control
reverts to step 202.
SIGNAL PACKET TRANSMISSION
On a periodic basis, as indicated above with respect
to Fig. 1, each storage transmission node 38 polls each
transducer 36 connected to it in sequence to cause the
transducer to send the transducer signal 18. Each
storage transmission node 38, after polling each
transducer 36, builds and sends the transducer signal
packet to the central inventory server 40. In a
preferred embodiment, transmission to the inventory
server 40 is via a RF link 58 to an RF receiver 60, but
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can be by any suitable means, such as Internet, power
line, modem, LAN, WAN, IR, or other communication link.
Typically there will be a plurality of storage
transmission nodes 38 at a facility. Each of these will
be sending periodic transducer signal packets containing
the latest transducer polling sequence. Transmission
intervals to the inventory server 40 are therefore
staggered pseudo-randomly, to avoid collisions between
simultaneous transducer signal packets. Collisions which
do occur, however, are unlikely to repeatedly affect the
same storage transmission node, due to the pseudo-random
staggering. Since the pseudo-random staggering makes it
unlikely that a collision will repeatedly affect the same
transmission node, subsequent transducer signal packets
will ensure that the quantity counts remain current.
In a preferred embodiment, the storage transmission
nodes comprise transmit only radios. Such radios do not
require a two way protocol, therefore saving bandwidth.
Accordingly, a pseudo-random interval avoids collisions
without requiring a duplex protocol. Further, the
interval determination uses the address of the storage
transmission node, ensuring that two storage transmission
nodes will not collide on consecutive cycles.
Referring again to Figs. 1 and 15, upon receipt by
the central inventory server 40 the transducer signal
packet is used to compute the quantity of items stored in
each storage unit 32. For each storage unit, information
concerning the corresponding storage transmission node
38, and the corresponding transducer signal values from
the transducer signal packet (148 and 147 respectively,
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Fig. 15) are used to compute the total weight contained
in or at the storage unit. The quantity is determined
from the individual item weight. The quantity is
compared to minimum order threshold values, which
indicate when an order is to be generated. When the
quantity falls below the minimum threshold, an order is
generated to replenish the quantity to a maximum quantity
for the item. Also contained in the database 42 are
supplier information and order methods, such as Internet,
paper mail, or telephone, so that an automatic order may
be generated and sent.
The database 42 is also connected to a GUI for
various user interactions, shown in Fig. 12. The
database is populated through a serial port 160 from the
receiver 60 (Fig. 1). A main view screen 162 provides
options allowing a user to access the various functions
enumerated below. A single item detail view 164 screen
allows graphical information concerning quantity of
individual parts in relation to the minimum and maximum
quantity thresholds. A replenish report view screen 166
provides information concerning frequency of orders
placed for a particular item. A replenish request view
screen 168 allows a manual item order to be placed via e-
mail or fax. A storefront view screen 170 allows remote
Internet access. An export database view screen 172
allows downloading to a remote client. An error report
view screen 172 provides diagnostic feedback about system
functions. Other queries and access to the database can
be envisioned in addition to those enumerated here.
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Those skilled in the art should readily appreciate
that the programs defining the functions described herein
can be delivered to a computer in many forms, including,
but not limited to: (a) information permanently stored
on non-writable storage media (e. g., read-only memory
devices within a computer such as ROM or CD-ROM disks
readable by a computer I/0 attachment; (b) information
alterably stored on writable storage medial (e. g., floppy
disks, tapes read/write optical media and hard drives);
or (c) information conveyed to a computer through a
communication media, for example, using baseband
signaling or broadband signaling techniques, such as over
computer or telephone networks via a modem. The present
embodiments may be implemented in a software executable
out of a memory by a processor. Alternatively, the
presently described functions may be embodied in part or
in whole using hardware components such as Application
Specific Integrated Circuits (ASICs), state machines,
controllers or other hardware components or devices, or a
combination of hardware components and software.
Those of ordinary skill in the art should further
appreciate that variations to and modification of the
above-described methods and apparatus for providing
automated inventory computation and ordering may be made
without departing from the inventive concepts disclosed
herein. Accordingly, the invention should be viewed as
limited solely by the scope and spirit of the appended
claims.
