U.S. patent number 3,696,946 [Application Number 05/037,629] was granted by the patent office on 1972-10-10 for conveyor system having a plurality of carrier position sensors.
This patent grant is currently assigned to Burroughs Corporation. Invention is credited to Bernard B. Dinerman, James R. Hunter, Abe Mann, Franklin T. Schroeder.
United States Patent |
3,696,946 |
Hunter , et al. |
October 10, 1972 |
CONVEYOR SYSTEM HAVING A PLURALITY OF CARRIER POSITION SENSORS
Abstract
This disclosure relates to an automatic conveyor system having a
plurality of sensors to detect the positions of the conveyor
carriers so that the difference between a computed carrier position
and its actual position will be less than the maximum tolerable
error due to wear, stretch or slack in the conveyor belt or chain.
At the time an article or parcel is placed in the conveyor system,
its carrier designation and position of the destined receiving bin
are stored in a memory. During each incremental time period, the
contents of the memory are scanned and compared with counters
associated with each position sensor. When a comparison is
achieved, a signal is sent to the appropriate receiving bin to
actuate the corresponding carrier to unload its contents.
Inventors: |
Hunter; James R. (Chadds Ford,
PA), Dinerman; Bernard B. (Norristown, PA), Mann; Abe
(Bala Cynwyd, PA), Schroeder; Franklin T. (Phoenixville,
PA) |
Assignee: |
Burroughs Corporation (Detroit,
MI)
|
Family
ID: |
21895383 |
Appl.
No.: |
05/037,629 |
Filed: |
May 15, 1970 |
Current U.S.
Class: |
198/349.95;
209/900; 198/502.3 |
Current CPC
Class: |
B65G
47/50 (20130101); Y10S 209/90 (20130101) |
Current International
Class: |
B65G
47/50 (20060101); B65g 043/00 () |
Field of
Search: |
;214/11R,11M ;198/38
;209/73 ;246/187B,182R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
741,124 |
|
Nov 1955 |
|
GB |
|
1,124,964 |
|
Aug 1968 |
|
GB |
|
Primary Examiner: Forlenza; Gerald M.
Assistant Examiner: Johnson; R. B.
Claims
What is claimed is:
1. A conveyor system having a plurality of carriers to receive
articles from at least one input console for delivery to one of a
plurality of destined stations, and means for selectively
designating the destined station for each of said articles, said
system comprising:
console sensor means associated with each said input console and
being responsive to actuating means disposed on each of said
carriers for detecting the presence of said carriers as they
traverse said console, carrier counter means coupled to each of
said console sensor means for identifying by means of the count
therein relative to a designated reference carrier the specific
carrier into which an article is deposited by said console for
conveyance to a preselected destined station,
said plurality of destined stations being arranged in a
predetermined number of zones, zone sensor means located in each of
said zones and being responsive to said actuating means for
detecting the presence of said carriers in said zones, the location
of each of said stations in a given zone being specified by its
base distance to the zone sensor means in that zone, zone counter
means coupled to each of said zone sensor means for providing count
information including a count of the carriers that traverse each of
said zone sensor means relative to said reference carrier,
means adapted to receive said carrier count from said carrier
counter means and said base distance of said preselected destined
station and to generate therefrom conveyor position data,
comparator means coupled to receive said conveyor position data and
said count information from the zone counter means for the zone
encompassing said preselected destined station, said comparator
means comparing said data and said count information and providing
an output signal solely in response to the occurrence of identity
therein, said output signal being indicative of the arrival of said
specific carrier at said predetermined destined station.
2. A system as defined in claim 1 wherein said actuating means for
each of said carriers comprises a single means for actuating said
console sensor means and said zone sensor means, and the actuating
means for said designated reference carrier comprises an additional
actuating means, each of said carrier counter means and said zone
counter means being adapted to be reset to its initial state in
response to the double actuation of its associated sensor means by
said reference carrier.
3. A system as defined in claim 2 wherein said console sensor means
and said zone sensor means are photocells and said actuating means
are flags adapted to actuate said photocells.
4. A system as defined in claim 2 wherein said console sensor means
and said zone sensor means are reed switches and said actuating
means are magnets.
5. A system as defined in claim 1 further including unloading means
associated with each said destined station to unload a particular
carrier, said unloading means being adapted to be energized for a
predetermined period of time.
6. A system as defined in claim 1 wherein the respective base
distances of the stations in a given zone are measured in terms of
whole multiples of carrier pitch and fractions thereof expressed in
predetermined increments of carrier advancement in said conveyor
system.
7. A system as defined in claim 1 wherein each of said carriers
includes a plurality of compartments, said carrier counter means
further comprising means for providing in conjunction with said
carrier count a fixed number of bias increments as a function of
the particular compartment in said specific carrier in which an
article is deposited.
8. A system as defined in claim 7 further including an increment
position sensor operatively connected in said conveyor system for
supplying an output signal for each predetermined incremental
distance advanced by said carriers.
9. A system as defined in claim 8 wherein said increment position
sensor is a rotary incremental shaft encoder connected to the shaft
that drives the conveyor medium.
10. A system as defined in claim 8 wherein said zone counter means
comprises a zone conveyor position counter for providing said count
of the carriers that traverse each of said zone sensor means and a
zone increment counter which is coupled to said increment position
sensor, said zone increment counter being responsive to the output
signals from said increment position sensor and providing a count
of the incremental distances advanced by said carriers between the
times of detection of successive carriers by the associated zone
sensor means, said zone increment counter being adapted to be reset
to zero and the count in said zone conveyor position counter being
concurrently advanced by one in response to the actuation of the
associated zone sensor means by one of said carriers.
11. A system as defined in claim 5 wherein said unloading means
include a station solenoid decoder having a pair of input terminals
and an output terminal, the output signal from said comparator
means being applied to one of said input terminals, means for
providing to the other of said input terminals the designation of
said preselected destined station, said station having a
door-opener solenoid for unloading a carrier, and solenoid driver
means coupled to said output terminal of said station solenoid
decoder for actuating said door-opener solenoid.
12. A conveyor system having a plurality of carriers each including
a plurality of compartments for receiving articles from at least
one input console for delivery to one of a plurality of destined
stations, and means for selectively designating the destined
station for each of said articles, said system comprising:
console sensor means associated with each said input console and
being responsive to actuating means disposed on each of said
carriers for detecting the presence of said carriers as they
traverse said console, carrier counter means including compartment
increment fixed bias means coupled to each of said console sensor
means for identifying by means of the carrier count relative to a
designated reference carrier and increment bias the specific
carrier and compartment thereof into which an article is deposited
by a given console for conveyance to a preselected destined
station,
said plurality of destined stations being arranged in a
predetermined number of zones, zone sensor means located in each of
said zones and being responsive to said actuating means for
detecting the presence of said carriers in said zones, the location
of each of said stations in a given zone being specified by its
base distance to the zone sensor means in that zone, zone conveyor
position counter means coupled to each of said zone sensor means,
increment sensor means operatively connected for detecting
predetermined incremental distances advanced by said carriers, zone
increment counter means coupled to said zone sensor means and being
further coupled to said increment sensor means, said zone conveyor
position counter means and said zone increment counter means
providing respectively counts of the carriers that traverse said
zone sensor means relative to said reference carrier and the
incremental distances advanced by said carriers between the times
of detection of successive carriers by the associated zone sensor
means,
memory storage means adapted to provide in response to input data
relative to said preselected destined station the numerical
designation of said destined station and the base distance and zone
number assigned thereto,
conveyor position computing logic means coupled to receive said
carrier count and increment bias from said carrier counter means
and said base distance of said preselected destined station from
said memory storage means and to generate therefrom conveyor
position data, said memory storage means storing said last
mentioned data,
comparator means coupled to receive said conveyor position data
from said memory storage means and said counts from said zone
conveyor position counter means and said zone increment counter
means for the zone encompassing said preselected destined station,
said comparator means comparing said data and said last mentioned
counts and providing an output signal solely in response to the
occurrence of identity therein, said output signal being indicative
of the arrival of said specific carrier and compartment thereof at
said preselected destined station.
13. A system as defined in claim 12 further including means for
scanning during each said incremental advancement of said carriers
the computed conveyor position data stored in said memory storage
means for comparison in said comparator means with the counts in
the conveyor position counter means and said zone increment counter
means.
14. A system as defined in claim 12 wherein said memory storage
means is adapted to supply in response to input data relative to
said preselected destined station, the numerical designations and
corresponding base distances and zone numbers assigned to at least
one alternate destined station in addition to said preselected
destined station, said conveyor position computing logic means
generating conveyor position data for both said preselected
destined station and said alternate station.
Description
BACKGROUND OF THE INVENTION
This invention relates to an automatic conveyor system and more
particularly to a conveyor system having a plurality of sensors to
detect carrier location.
Conveyor systems, the type for which the present invention is
adapted, such as the United States Post Office Department (now the
U.S. Postal Service) Model Nos. 120 and 121 of the Letter Sorting
Machine (LSM) presently in use by the U.S. Postal Service, are
designed to sort mail, parcels and other objects which are received
from a plurality of input consoles for conveyance to a plurality of
output receptacles. An explicit requirement of such an automatic
conveying system is that the station address of the receptacle to
which the conveyed object is destined must somehow be correlated
with the conveying carrier and stored until the time that the
carrier reaches the destined receptacle. A particular conveying
system which has been successful in the past is one in which the
respective carriers were provided with mechanical escort memories
or code wheels which ride along a code track. When a particular set
of code wheels correspond to the code of a particular receptacle,
the carrier is dumped or otherwise unloaded. The mechanical escort
memory presently used in the LSM comprises code wheels associated
with each cart compartment of the carrier and code bars at each of
the output bins or receptacles for decoding the wheels. The code
wheels are attached to the carrier and move on tracks. Obviously,
it is extremely important that the letter cart door be opened at
the correct position with respect to the letter receptacle in order
to insure that the mail pieces will properly enter the receptacle.
The LSM carts are held in position and transported by a pair of
roller-chain conveyors. In the particular models of the LSM
referenced hereinbefore, the conveyor chains are each approximately
282 feet long and twelve operator input consoles for loading mail
into the carts are provided. Along the conveyor chain, 161 letter
carts are spaced on 21-inch centers. Thus, each cart is eighteen
inches in length and the carts are separated from each other by a
distance of three inches. Each letter cart contains twelve
compartments, spaced 1.5 inches from each other. The memory system
must have the capability of keeping track of twelve mail pieces per
letter cart in 161 letter carts per machine, or a total of 1,932
mail pieces. As a letter cart compartment advances through the LSM
it passes each of the 277 letter receptacles located along the 282
feet of conveyor. Taking into account the relationship between the
door latches of adjacent mail compartments and the
solenoid-actuated door link, together with the physical dimensions
of the solenoid actuator arm itself, it can be shown that in the
LSM the solenoid actuator arm must operate within a "window"
distance of about 1.19 inches of conveyor chain travel, if it is to
open the correct letter cart compartment door and not interfere
with or open the door on either side of it. Simply stated, the
problem is to know precisely where any letter compartment is to
within 1.19 inches along a 282 foot conveyor chain. The mechanical
escort memory system provides excellent reliability since there are
no effects on performance due to variations of machine speed or in
the location of the carrier. However, reliability decreases as the
size of the system is increased since the larger the number of
mechanical components involved, the greater failure rate becomes.
For example, in the LSM such a system includes 1,932 code wheel
assemblies, or 23,184 code wheels, and 278 code bar assemblies, or
3,058 code bars. In addition there are the mechanical supports and
guides required along a track of approximately 244 feet.
As distinct from mechanical escort memories described above, other
types of magnetic and electric memories have been provided for
automatic conveyor systems. Such memories may take the form of a
rotating drum or an electronic shift register where the receptacle
address is moved or shifted through the memory as the conveying
carrier moves along the conveyor system. When the address reaches a
location in the memory corresponding to the destined receptacle,
the carrier is unloaded. Again, the reliability of this type of
system decreases as the size of the system increases since chain or
conveyor slack or stretch can result in nonuniform carrier spacing
such that the array of addresses moving through the memory is no
longer analogous to the exact model of the conveyor system.
Certain automatic conveyor systems of the prior art have attempted
with some success to maintain some analogy between the memory cycle
and the conveyor cycle by synchronizing the starting positions of
the respective cycles. For example, a counting scheme may be
employed wherein a counter is started when a mail piece is inserted
into a certain letter cart and compartment. Since each letter
receptacle is a fixed distance from a certain operator console, the
motion of the letter cart conveyor chain can be used to generate
distance-travelled pulses. A shaft encoder can be attached to the
drive chain sprocket of the letter cart conveyor to generate a
pulse to correspond to any desired linear advancement of the chain.
The distance from a console to any letter receptacle can be
expressed by the number of pulses needed to reach the receptacle.
Such techniques are successful for relatively small conveyor
systems. However, as the size of the conveyor system increases,
clack due to wearing or stretching of the conveyor belt or chain
can approach the pitch or distance between successive carriers in
the conveyor system thereby substantially reducing the reliability
of the system. If the slack becomes greater than the pitch, the
system becomes inoperable. In connection with the LSM, it has been
found that the length of the conveyor chain of a fixed number of
links varies significantly because of manufacturing tolerances,
change in chain tension (stretch), and wear between pins and
bushings. Moreover in the afore-mentioned counting scheme,
occasional system recalibration as to distance counts from the
operator console to the letter receptacles would be ineffective,
because the chain wear would probably not be uniform along the LSM
282 foot conveyor length.
Another possible solution to the problem involves locating a
position sensor at each of the letter receptacles as well as one
sensor at each operator input console. Each sensor at the operator
console establishes the cart compartment of one of the plurality of
carts which is to receive a certain mail piece. A memory is
provided to retain this information and make it available to the
sensor located at the letter receptacle. The receptacle sensor then
waits for the correct letter cart and compartment to arrive at the
receptacle so that it can trigger the door actuator mechanism to
open the door. This type of system has the advantage that the
correct letter cart and compartment can be accurately located by a
letter receptacle regardless of chain stretch, wear or
manufacturing tolerances. In connection with the LSM chosen for
purposes of illustration, the disadvantage of this system is the
need for the large number of position sensors which total 289 and
the associated logic circuits and memory needed to service 1,932
letter cart compartments. The cost of such a system is prohibitive
and the large number of sensors and associated circuits effectively
decrease the overall system reliability.
It is, therefore, an object of the present invention to provide
improved automatic conveyor system.
It is another object of the present invention to provide an
automatic conveyor system wherein error will not result from slack
due to wearing or stretching of the conveyor belt or chain.
It is a further object of the present invention to provide an
automatic conveyor system which will be error free irrespective of
the length of the conveyor belt or chain. It is a still further
object of the present invention to provide an electronic system
which will operate reliably and economically over the entire
life-span of the equipment.
SUMMARY OF THE INVENTION
The above objects of the present invention are accomplished by
providing a counting scheme in combination with a plurality of
sensors distributed along the conveyor path in the area of the
respective receptacle bins such that the position of the individual
conveyor carriers can be specified as the movement of each carrier
relative to its nearest sensor. The spacing between the sensors is
chosen to be less than that distance in which the maximum tolerable
error can occur due to wearing, stretching or sagging of the
conveyor belt or chain. With relation to the models of the LSM
system referenced hereinbefore, the invention contemplates dividing
the 282 foot long conveyor-chain distance and the receptacle bins
it services into a plurality of zones, each monitored by a conveyor
position sensor. As indicated hereinbefore, assuming that in the
LSM system, a 1.19 inch "window" of distance must be furnished to
operate a letter cart compartment door properly, nine zones each
having a conveyor position sensor are required. Further assuming
that twelve operator consoles are present, 12 console position
sensors are also required. Obviously, the total number of sensors,
that is, 21, contemplated in this particular LSM system modified in
accordance with the present invention, is but a small fraction of
the 289 sensors required in the system described hereinbefore.
Each receiving bin is specified by the position at which the
corresponding carrier will be when adjacent to that bin when it is
required that the carrier deposit a package, letter or other
article therein. This position designation, along with the carrier
designation, is stored in a multi-word memory at the time that the
article is placed in the carrier at an input console and the
contents of this memory are periodically scanned for comparison
with counters associated with each of the sensors. When the
particular count associated with a particular sensor corresponds to
designated position stored in the memory, a signal is sent to
actuate a trip mechanism associated with the respective receiving
bin to trip the carrier causing it to deposit its article.
Provision can be made for storing positions of alternate
receptacles or receiving bins should the first specified bin be
full or otherwise incapable of receiving an article.
A feature, then, of the present invention resides in a conveyor
system having a plurality of sensors mounted along the conveyor
path in the area of the receiving bins and counters associated with
the respective sensors to designate the relative position of the
individual carriers as they pass each sensor.
Another feature of the present invention resides in the provision
of a multi-word memory to store the delivery designation for each
of the respective carriers and the means to compare the count
associated with each sensor with said delivery designation.
Still another feature of the present invention resides in the means
to provide for alternative designations for each of the respective
carriers should the first specified designation refer to a
receiving bin that is not capable of receiving additional
articles.
DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages and features of the present
invention will become more readily apparent from a review of the
following specification when taken in conjunction with the drawings
wherein:
FIG. 1 is a representation of a conveyor system employing the
present invention;
FIG. 2 is a schematic representation of the input, memory, and
comparator logic employed with the present invention;
FIG. 3 is a representation illustrating the manner in which carrier
positions are designated according to the present invention;
FIG. 4a, b and c are representations of memory word formats as
employed in the present invention;
FIG. 5 is a flow diagram of the input console polling sequence as
employed in the present invention;
FIG. 6 is a flow diagram of the computation routine employed in the
present invention; and
FIG. 7 is a flow diagram of the scan and compare routine as
employed in the present invention.
GENERAL DESCRIPTION OF THE SYSTEM
As illustrated in FIG. 1, which is a representation of the
reference LSM transport system, conveyor system 10 is adapted to
traverse zones or receptacle areas 11, . . . , 19 each of which
comprises a plurality of receptacle bins that are adapted to
receive parcels and other articles that were loaded into the
conveyor system from input consoles 31, . . . , 42. Corresponding
zone sensors 21, . . . , 29 are associated with the receptacle
areas 11, . . . , 19 respectively. Input console sensors 51, . . .
, 62 are associated with input consoles 31, . . . , 42
respectively. It should be readily apparent that the representation
of FIG. 1 is a simplified one. Carrier carts each having at least
one, and usually more than one, compartment while not shown in FIG.
1, are assumed to be affixed to and transported by the conveyor
medium 10. In the LSM referenced herein, each cart comprises twelve
compartments and the conveyor 10 is of the roller-chain type.
Similarly, the zones or receptacle areas numbered 1 through 9
include all of the receptacle bins -- each zone comprising
approximately the same number of bins.
Each of the individual carrier carts is provided with a sensor
actuating device. The respective sensors may just be photo-cells in
which case the sensor actuating device for each cart would be a
flag of sufficient dimension to interrupt the photo-cell. Or the
respective sensors may be mercury-wetted reed switches in which
case the sensor actuate devices would be magnets. Except for the
first carrier cart, each carrier would be provided with one sensor
actuating device; however, the first carrier cart is provided with
two such actuating devices to provide two closely spaced pulses to
synchronize the position of the first cart relative to the nearest
sensor. The distance of each receiving bin from its associated zone
sensor is then measured as a number of incremental units. As will
be explained in greater detail hereinafter, the increments or
incremental units represent a predetermined fixed advancement of
the carrier conveyor medium. The actual increment distance chosen
determines the system resolution, that is, the precision required
in locating the carriers. The smaller the bias increment, the
faster the memory access cycle that will be required. In the LSM,
an increment of one-sixth inch was found to be satisfactory.
Perhaps a better understanding of the manner in which each
receiving bin is addressed will be obtained by reference to FIG. 3
which is a diagrammatic representation of the position of the
respective receiving bins relative to the carrier carts as they
traverse the conveyor path. In FIG. 3, it is assumed initially for
purposes of explanation that each of the carriers contains only one
compartment adapted to hold only a single piece of mail and that
the parcel discharge occurs when the leading edge of the carrier
cart is aligned with the right edge of the receiving bin. Thus, as
illustrated in FIG. 3, carrier cart number 2 is in a discharge
position over bin number 8 and carrier cart number 5 is in a
discharge position over bin.
The mail carriers (C) are numbered sequentially, for example, from
0 to 160 inclusive in the LSM, relative to a reference carrier
which has the "0" designation. The only system requirement is that
the reference carrier be uniquely identified, for example, by means
of its double sensor actuating devices, and that on the basis of
this identification the numbers of subsequent carriers be
recognized.
The base distance (D) is a set of numbers which represent the
physical distance of the right edge of each bin or receptacle
relative to the nearest zone sensor which is the bin reference
point depicted in FIG. 3. As indicated in the table in the upper
part of FIG. 3, the distance measurements are made in terms of
numbers of nominal carrier pitches (distance between carriers) and
fractions of carrier pitches (carrier increments). In terms of the
one-sixth inch increments referred to hereinbefore in connection
with the LSM, the carrier pitch expressed in increments is 126,
corresponding to the 21-inch spacing between carriers.
The reference carrier position (R) defines the location of the
reference carrier relative to the bin reference point.
In FIG. 3 the carrier pitch scale used for the measurement of the
various parameters has been indicated. It should be noted that the
division of the carrier pitch into ten parts has been made solely
for ease of explanation. As indicated hereinbefore, the incremental
distance would normally be measured by monitoring carrier motion,
such as by the shaft encoder 20 depicted in FIG. 1. It will be
observed from FIG. 3 that the reference carrier position R will
have a relation to the positions of each of those carriers whose
right edges are in alignment with respective right edges of bins,
such that the difference between the reference carrier position and
the number designation of a given one of the last-mentioned
carriers is the base distance of the bin aligned therewith. Thus,
the base distance D.sub.3 of bin number 3 is just one carrier and
four carrier increments. When carrier number 5 is in a position
adjacent to bin number 3, the reference carrier position (position
of carrier 0) will be five carriers plus (one carrier plus four
increments) or six carriers plus four increments. Similarly, the
base distance D.sub.8 of bin number 8 is four carriers and four
increments relative to the nearest sensor. Again, the reference
carrier position R will be two carriers plus (four carriers plus
four increments) which is six carriers plus four increments. In
this manner, when the sum of the carrier number designation and the
base distance of its destined receptacle bin are equal to the
reference carrier position R, the given carrier is in the
appropriate discharge position adjacent to the destined receptacle
bin.
The description of FIG. 3 has thus far not taken into account the
fact that each of the carriers may comprise a plurality of
compartments. Consider the LSM wherein each carrier comprises 12
compartments displaced from each other by 1.5 inches or nine bias
increments, assuming that the selected bias increments are each
one-sixth inch. Under the conditions illustrated in FIG. 3, it has
been assumed that the first compartment of carrier 2 is in the
proper position to discharge into bin 8. If it is desired to empty
the second compartment of carrier 2 into bin 8, it is necessary to
advance the carriers in the direction of the arrow by nine bias
increments. At this point, actuation of the door on the second
carrier compartment will cause the contents thereof to be deposited
in bin 8. Similarly, if the twelfth compartment of carrier 5 is to
be deposited in bin 3, the carriers must advance 99 increments to
the right of the position depicted. This operation is described in
detail in connection with FIG. 2. At this point, however, the
following considerations will be helpful to the reader. If
information is placed in the 12th compartment of carrier 5 by
console 12, a compartment increment fixed bias of 99 increments,
provided by unit 621 in FIG. 2, will be added to the cart count of
the console counter 620 in FIG. 2. The cart count, namely 5, and
increment bias, 99, of the compartment are then added to the base
distance of the destined receptacle. In FIG. 2 such addition is
performed by the computing logic 82. If the destined receptacle is
the bin 3 of FIG. 3, it will be assumed that this bin has a base
distance of one carrier pitch and four increments. The total of six
carriers and 103 increments from this addition is referred to as
the "computed conveyor position" . When the count in the zone
counter associated with the bin reference sensor of FIG. 3 is
identical to the "computed conveyor position", the 12th compartment
of carrier 5 will be in position to unload its contents into bin
3.
DETAILED DESCRIPTION OF THE SYSTEM
A better understanding of the system will perhaps be obtained from
the review of the various memory word formats as illustrated in
FIGS. 4a, b, and c. The memory is designed to consist of 8,192
addresses each containing a 36-bit word. This memory is divided
into three segments. The first segment as illustrated in FIG. 4a
consists of addresses 0 to 1,023 and is adapted to contain the
numbers of three separate receiving bins designated as primary,
first alternative, and second alternative. In the event that only
one receiving bin is to be assigned to the keyboard address, the
remaining two receptacle numbers will be a repeat of the assigned
number. The second segment of memory is used to contain the base
distance data as illustrated in FIG. 4b. This data includes the
zone position sensor number controlling the particular receiving
bin, the carrier cart count and the carrier increment count, the
sign (plus or minus) to indicate whether the receiving bin is
downstream or upstream from the sensor, and redundancy bits to
provide a "no go" signal if the memory should lose its word. The
third segment of memory contains the corresponding computed
conveyor position data as illustrated in FIG. 4c. This data
represents the count that will be reached on the specific conveyor
position counter when it is time to open the carrier cart
compartment door when the cart is located above a specific
receiving bin. Since with the particular embodiment described,
there can be up to 1,932 parcels in transit toward the receiving
bins and since each parcel can be directed to go to any of three
different receiving bins it is necessary to store 5,796 words for
this purpose.
Having described the particular memory word formats, the system
itself will now be described with reference to FIG. 2. As
illustrated therein, console position sensors 51, . . . , 62 which
were discussed briefly in regard to FIG. 1, are connected to a
corresponding binary counters 510, . . . , 620 which are adapted to
be reset to zero upon the receipt of a double-pulse. It will be
remembered that the reference carrier 0 is provided with a double
trip mechanism for this purpose. This resetting action is used to
indicate the position of the reference cart relative to a
particular console sensor. Since the carriers or carts are usually
designated by successive numbers, it is convenient, although not
necessary, to arrange the count in the cart counter of a give
console to be the same as the cart number designation of the cart
being loaded thereby. With this arrangement, if cart 124 is being
serviced by a console, actuation of the console position sensor by
cart 124 will cause the count in the associated console cart
counter to also be 124.
In normal operation, the first console loads the first compartment
in the carrier cart, the second console loads the second
compartment of the carrier cart and so on where each carrier cart
is provided with a plurality of compartments. Since the second
compartment of each cart is a fixed distance downstream from the
first compartment, it is necessary to add a fixed bias to the cart
counter for each of the respective consoles upstream from the first
console. As indicated in FIG. 2, the incremental bias to be added
to the first console's cart count is provided by unit 511. The
incremental bias to be added to the 12th console count is provided
by unit 621. It will be understood that corresponding units would
be provided for each of the other consoles.
The output signals from the respective consoles are then applied to
cart counter multiplexer 81 for presentation to computing logic 82
in a sequential manner.
At the time that a parcel is placed in a conveyor cart compartment
the operator enters the designation of the destined receptacle bin
into the console keyboard. The respective signals from each console
are then supplied to keyboard multiplexer 70 for ultimate
presentation to memory 79. The entries from the respective console
keyboards will be in the form of binary coded decimal signals which
are converted to binary signals by converter 71. Translator 72,
which is programmed by control unit 78, recognizes and separates
the respective receptacle designation as primary, first alternative
and second alternative for appropriate placement in the respective
registers 73, 74 and 75 as indicated in FIG. 2. Format control
information is entered into control unit 78 by card reader 77 or
other appropriate input devices.
The first two segments of memory as described in relation to the
memory word formats are stored in memory 79. The third segment of
memory which contains the computed conveyor position data is stored
in memory 80. This memory receives the computed conveyor position
from computing logic 82 which is essentially an adder-subtractor
that adds or subtracts the particular base distance for a specified
receptacle bin to the polled console conveyor data. That is to say,
the computed data position for a particular parcel destined to a
particular receptacle bin is the cart count and increment bias of
the cart compartment in which the parcel has been placed plus the
base distance of the destined receptacle bin. The result is a
number that will appear on the specific conveyor position counter
when it is time to release the parcel into the destined receptacle
bin. It will be remembered from the discussion of FIG. 4b that the
base distance of the destined receptacle bin may be added or
subtracted as required by the sign that appears in the first bit of
the base distance memory word format.
Conveyor position computing logic 82 also has the ability to handle
cart count overflow. For example if the console cart count is 160
carts and 99 increments and if the base distance of the destined
receptacle bin is 3 carts and 51 increments, the total would be 163
carts and 150 increments. Assuming that the incremental distance
between adjacent carts is 126 increments, the incremental count
would be corrected to 1 cart and 24 increments and thus the total
would be 164 carts and 24 increments. Further assuming that the
total number of carts in the conveyor system is 161, the final
conveyor position would be obtained from subtracting that number
which final result would be three carts and 24 increments. This is
the number that is to be stored in memory 80. To arrive at this
result, computing logic 82 receives the base distance data from
memory portion 79 and the console cart count and increment bias
from counter multiplexer 81 as illustrated in FIG. 2.
As the respective carrier carts traverse the conveyor system, their
presence is detected by zone sensors 21, . . . , 29 as illustrated
in both FIGS. 1 and 2. It will be remembered that the first carrier
cart is a reference carrier and induces a double pulse in each of
the sensors to reset the respective counters. The system is
provided with an increment position sensor 20 which may just be a
rotary incremental shaft encoder connected to the shaft that drives
the conveyor system. This encoder will provide the pulse for each
incremental advancement of the conveyor system.
Each of the zone sensors 21, . . . , 29 is adapted to step
corresponding zone conveyor position counters 210, . . . , 290 at
the time that a cart is detected by the sensor. This step also
resets the corresponding increment counter. The respective
counters, thus, provide both a cart count and an increment count
for each of the respective zone sensors which are in turn supplied
to conveyor position counter multiplexer 83. The particular zone
counter data to be received by multiplexer 83 is determined by the
zone number presented to multiplexer 83 from memory 80 as
illustrated in FIG. 2. At the same time, the corresponding computed
conveyor position is transferred to solenoid bias logic 84 for
comparison with the received count from multiplexer 83 which
comparison is made by comparator 86. At the same time, the
receptacle bin number associated with the computed conveyor
position is presented from memory 80 to receptacle solenoid decoder
85. Should comparator 86 indicate identity in the data being
compared, solenoid decoder 85 will actuate the respective solenoid
driver 87 to open the corresponding carrier cart door.
A particular function of solenoid actuate-deactuate bias adder
logic is to maintain the solenoid in an open position for
sufficient time to trip the cart compartment door latch. To this
end, when a comparison is first achieved by comparator 86, zero is
added to the conveyor position count by adder logic 84. Logic 84
then adds nine increments to the count going to the comparator so
that comparator 86 will find a comparison for those nine
incremental counts thus maintaining the corresponding solenoid in
an open position for the appropriate period of time. At the end of
the ninth count, the solenoid will be released so as not to open
subsequent carrier compartment doors.
Memory 80 of FIG. 2 is adapted to be accessed through all of its
word locations in sequence so that all of the computed conveyor
positions will be compared with corresponding conveyor position
counters during each operation cycle. The maximum number of
accesses required for the system described would be 5,796 scan and
compare cycles plus 5 accesses per console for each of the 12
consoles. For a resolution increment of one-sixth of an inch and a
velocity of 21 inches per second, an appropriate memory would be
one with an access time of 1.2 microseconds. Thus, each operational
cycle of the scan and compare routine can be accomplished in 7.3
milliseconds. As the size or speed of the system is increased or
the increment resolution is made smaller, thereby requiring a
shorter operational cycle, faster memories are available for this
purpose.
OPERATION OF THE SYSTEM
The system control which is not expressly illustrated in FIG. 2 can
best be described in relation to FIGS. 5, 6, and 7 which are flow
diagrams respectively of the input console polling sequence, the
computation routine and the scan and compare routine. Both the
polling of the input console and the scanning and comparing of the
computed conveyor position with the zone conveyor position counter
are carried out during each incremental advancement of the conveyor
chain. Upon detection of the first incremental pulse from increment
sensor 20, the polling counter (not shown in FIG. 2) is preset to
one, keyboard multiplexer 70 is checked to see if the console
specified by the polling counter inserted a parcel. If no such
parcel was inserted the polling counter is checked to see if it
equals the total number of consoles. If that result is false the
polling counter is incremented and the subroutine of checking to
see if the parcel has been inserted is repeated.
As indicated to FIG. 5, if a parcel had been inserted before the
next poll, the system enters a computation routine in which the
keyboard input is translated into the primary, first alternate, and
second alternate destination receptacle registers. Then, the
terminus conveyor position counts for each of the destination
receptacles are computed and stored in memory according to the
routine illustrated in FIG. 6 and the polling sequence is reentered
to see if the polling count is equal to the total number of
consoles. When a polling counter does equal the total number of
input consoles, the scan and compare routine of FIG. 7 is
entered.
Referring now to FIG. 6, the computation routine will be described.
As illustrated therein, the translator memory of translator 72 of
FIG. 2 is read at the addresses specified by the console keyboard
input and the contents thus obtained are placed in respective
primary, first alternate and second alternate registers. The base
distance is also read therefrom and added to the polled console
conveyor position data. If the cart count in the sum is greater
than the total number of carts in the system then that cart count
is adjusted to accommodate overflow. Otherwise, the results of the
conveyor position computation, the associated receptacle number and
the zone number are stored in computed conveyor position memory 80.
At this point, memory 80 is checked to see if the first alternate
receptacle conveyor position count has been computed. If it has
been, the the second alternate receptacle conveyor position count
is checked to see if it has been computed. If that check is true,
then the sequence reenters the polling sequence as described in
reference to FIG. 5. If neither of the alternate receptacle
conveyor position counts have been computed or only one of them has
been computed, then base distance memory 79 is read at an address
specified by one or the other of the alternate receptacle registers
74 or 75 and the system reenters the computed conveyor position
routine as indicated in FIG. 6.
Referring now to FIG. 7, the scan and compare routine will be
described. It will be remembered from the discussion of FIG. 5 that
the scan and compare routine is entered each time after all of the
input console counters have been polled. At the beginning of the
routine, the memory address counter of memory 80 of FIG. 2 is
preset to the first address thereof to obtain a receptacle number,
a zone sensor number and a computed conveyor position. As was
explained above in reference to FIG. 2, the conveyor position
counter associated with the zone sensor of the zone specified is
then sampled and the counter reading is compared to the computed
conveyor position. If there is identity between the counter reading
and the computed position, the solenoid of the receptacle specified
is actuated. If the sampled conveyor position count equals the
computed conveyor position count plus nine increments, the solenoid
associated with the receptacle is deactuated but not until then.
The memory address counter memory 80 is then checked to see if it
specifies the end address of that memory. If it does not then the
address counter is incremented and the scan and compare routine is
repeated. Once the memory address counter does equal the end
address, the scan and compare routine is exited and the input
console polling sequence is reentered.
With the system thus described, the number of zone sensors can be
so chosen that the distance between adjacent sensors is less then
the minimum distance over which maximum tolerable error can occur
due to wearing, stretching or slack in the conveyor belt or
chain.
Data is available to indicate the order of magnitude of such error.
Normal manufacturing tolerance for a 105 inch section of chain is
plus or minus 0.015 inches for a maximum variation of 0.965 inches
in a 282 foot long chain. For the same length of chain, chain
stretch under a starting load of 300 pounds can amount to 1.125
inches. Wear at each pin and bushing can reach up to 0.005 inches
per pin over the entire life span of a chain for an amount of 11.2
inches of variation in the same length of chain. The accumulation
of these variations in a 282 foot chain could amount to a total of
13,290 inches. It will be observed that a major portion of this
variation is due to wear between pins and bushings.
A typical carrier cart as anticipated for the present invention
would have compartments spaced 1.5 inches apart. Assuming that the
door-opener solenoid is to be actuated for 1.5 inches of cart
compartment advancement, the maximum variation of chain length that
can be tolerated without the solenoid actuating the door catch of
either a later cart or earlier cart is approximately 0.732 inches.
Comparing this variation to the maximum variation for 282 foot
length chain, indicates that it is sufficient to place monitoring
sensors approximately 15.5 feet apart. These calculations are for
carrier velocity of 21 inches per second where the solenoid rise
time is 15 milliseconds and the fall time is 20 milliseconds.
While but one embodiment of the present invention has been
disclosed, it will be apparent to those skilled in the art that
additions and modifications may be made therein without departing
from the spirit and scope of the invention as claimed.
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