Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ATTORNEY FILE NO. 3C9414.PAT
CANADIAN PATENT APPLICATION
TITLE: TRAY UNSTACKER AND CONVEYING SYSTEM
FIELD OF THE INVENTION:
The present invention relates generally to tray handling and conveying equipment, and in
particular to such equipment de~igne~l to separate stacks of trays for placement and
transport individually on a conveyor.
BACKGROUND OF THE INVENTION:
Various types of trays are well known in the art for transporting goods for sale to a retail
location. Such trays, typically molded plastic or wire, are popularly used in the food
industry for transportation of the food products and for display thereof at a grocery store.
A typical example would involve trays used to transport loaves of bread wherein the
loaves of bread are arranged on the trays after which the individual trays are stacked in a
suitable cart. The carts provide for transporting of the bread to the food retail location
and in many cases serve also as the display from which the loaves are sold the consuming
public. After the trays are empty they are stacked and returned to the bakery for reuse.
Currently, the stacks of trays must be unstacked and placed individually on a conveyor
for conveying to the particular tray loading equipment. Unfortunately, manual labor is
required to unstack the trays due to the unevenness of their stacking, and their tendency to
cling together, especially in the case of wire trays. Accordingly, it would be very
desirable to have a m~l~hine that provides for automating of the lm~t~ckin~ process and
for placing of the lln~t~ked trays individually on a conveyor for subsequent reloading
thereof.
SUMMARY OF THE INVENTION:
The present invention concerns a machine for nn~t~e~in~ stacks of trays and individually
placing them on a conveyor. A conveyor is also shown for transporting of the individual
trays to a tray loading device while ~ lL;~ g a mhlilllulll spacing and plcvenlillg
contact there bclweell.
The unstacking m~hine includes an intake conveyor for transporting a plurality of stacks
of trays to a lm~t~ ing area. The intake conveyor includes a means for regulating the
movement of each stack of trays to the unloading area. With a stack positioned in the
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un.et~ing area a tray ~In~t~çking head is moved vertically downward onto the top most
tray. The tray lln.ctacl~ing head incl~ldes a plurality of substantially horizontally oriented
cylinders for operating tray contActing heads in a holizolllal direction. The horizontal
cylinders are operated to extend the tray contacting heads outwardly for contact at
perimeter locations of the tray to be un.~tAç~ed. Each tray contacting head is designed to
be able to contact the tray at any of generally three di~elenl points thereon. The
extension ofthe horizontal cylinders is ",~ ;"ed and the lifting head is then moved
vertically upwardly. A sensing means provides for determining whether or not a tray has
been succes~fillly carried along with the lifting head. If the sensing means determines that
no such tray has been lifted, the head can be dropped a second time for repeated attempts
at selecting a tray. If after a given number of attempts a tray is not successfully lifted, the
entire stack from which selection of a tray was attempted, is rejected and sent further
along the intake conveyor to a rejection location. The rejected stacks can be m~nll~lly
inspected and reintroduced to the intake conveyor.
If a tray has been successfully lifted, then a pair of tray c~t~.hing means below the lifted
tray are operated inwardly after which the horizontal cylinders are retracted causing the
tray to fall a short distance onto the catçlling means. A fast acting push cylinder is
positioned horizontally for contActing an edge of the tray as it rests on the tray catçhing
means. When operated, the push cylinder kicks the tray on to a loading conveyor
extçntlin~ parallel to the un~tac.~ing apparatus. The loading conveyor is positioned to
catch the tray as it is ejected from the tray unstacker. The tray cat~hing means can then be
operated outwardly to permit the tray selecting head to move downward for selecting
another tray. Thus, the process is repeated until the particular stack of trays has been
~l;",;l~A~e~, after which a further stack is moved into the un~t~çlring area.
The loading conveyor includes along the length thereof a plurality of groups of three
switches. Each group of three switches includes associated therewith two stopping
means. The switches and stop means provide for preventing of "shingling" of the
individual trays as they are moved towards the loading means. Shingling can occur when
a following tray rides up on top of, or is forced below, a leading tray due to the leading
tray being stopped. Ideally, the trays, as they move along the loading conveyor, should
remain spaced a particular distance so that there is no contact there between and,
therefore, no chance for ~hingling to occur. Also, with the trays l~ lAi~ing separated by a
uniform distance, it is much easier for the loading appa~ s to then subsequently select
and load each tray. Otherwise, if the trays become entangled on the loading conveyor,
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they must be m~nll~ily separated before they can be loaded. The three switches operate
the two stop means wherein if all three switches are made by overlaying trays, the stop
means are extended upwardly above the plane of transport of the trays along the conveyor
for stopping thereof. If either of the leading two switches becomes open as a result of a
tray passing over the switch and permitting opening thereof, the two stop means are
retracted below the level of travel of the trays permitting their further progress along the
conveyor. The three switches and two stop means operated thereby, are positioned along
the conveyor with respect to the size of the trays so that a desired minim~ t~nce is
",~ ed between all ofthe trays. Each set ofthree switches and two stop means
operate independently with respect to the other sets of switches and stop means. In fact,
each of the groups of three switches and two stop means operate autonomously and are
not controlled by a master control means, such as progl~llllllable logic controller. Thus,
the assembly wiring and overall cost of the anti .~hingling loading conveyor of the present
invention can be substantially reduced.
DESCRIPTION OF THE DRAWINGS:
A further underst~nrling of the structure, function, operation, objects and advantages of
the present invention can be had by referring to the detailed description of the prerelled
embodiment below which refers to the following figures, wherein:
Fig's. lA and lB show a side plan view of the present invention.
Fig. 2 shows an end plan view along lines 2-2 of Fig. 1 A.
Fig. 3 shows a top plan view along lines 3-3 of Fig. lA.
Fig. 4 shows an enlarged side plan view of the unstacking head of the present invention.
Fig. 5 shows a cross-sectional top plan view along lines 5-5 of Fig. 4.
Fig. 6 shows an end plan view along lines 6-6 of Fig 4.
Fig. 7 shows an enlarged partial of cross-sectional view of the lm~t~ ing head and a tray.
Fig. 8 shows an enlarged partial cross-sectional view of the un.ct~ç~ing head cont~cting a
tray for lifting thereof.
Fig. 9 shows a partial cross-sectional view of the head contacting a tray at an alternate
point thereon.
Fig. 10 shows a top plan view along lines 10-10 of Fig. 8.
Fig. 11 shows a front plan view of the present invention where an lln.~t~ç~ing head has
contacted a tray perimeter rim.
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Fig. 12 shows a front plan view ofthe present invention where an .ln~tacl~in~ head in
contact with a wire tray.
Fig. 13 shows an enlarged side plan partial cross-sectional view along lines 13-13 of Fig.
4.
Fig. 14 shows a front plan view of the present invention wherein a tray has been lifted to a
lifting head top position.
Fig. 15 shows a front plan view of the present invention wherein a tray has been dropped
onto the tray c~tçhine means.
Fig. 16 shows a flow diagram describing the process of lln~t~c~ing a tray.
Fig. 17 shows a side plan view of the anti-~hingling loading conveyor of the present
invention.
Fig. 18 shows a top plan view along lines 18-18 of Fig. 17.
Fig. 19 shows a top plan view of a pair of llnst~çl~ine machines ofthe present invention
arranged for discharging trays onto a common anti-~hineling loading conveyor.
DETAILED DESCRIPTION:
The tray lln~t~ r ofthe present invention, is seen in Fig.'s1A-lB, and generally referred
to by the numeral 10. Unstacker 10 in~ dçs a tray supplying conveyor 12 having an in
feed end 12A and an outlet end 12B. Conveyor 12 in~ludes a frame 14 having a plurality
of driven friction rollers 16 mounted therein. As seen by also l~rt;l~ing to Fig.'s 2 and 3,
conveyor 12 includes a stop consisting of a horizontally mounted drive cylinder 18
conne~ g to stop plate 20. Conveyor 12 also includes a pair of tray arranging gates 22
pivotally mounted thereto and driven by drive cylinders 24. Gates 22 each include tray
cont~cting side surfaces 26 and tray stop ends 28. Gates 22 define a tray lln~t~c~in~ area
30 having a tray sensing means 32 such as a proximily switch. Outlet end 12B also
includes further tray sensing means 34 and 35.
As seen by also referring to Fig's. 4-12, appalalus 10 includes a vertically operable tray
lifting head 36 secured to a frame 38. Conveyor 12 passes through frame 38 and beneath
head 36 wherein head 36 is positioned above conveyor llnst~r~ing area 30. Specifically,
head 36 is secured to a cylinder 40 and a pair of guide rods 42, which cylinder 40 and rods
42 are in tum secured to a plate 43 suspended from frame 38. Head 36 includes a central
mounting portion 44 consisting primarily of four vertical plates fomming plate pairs 44a
and 44b secured to a top horizontal plate 44c. Four L-shaped mounting brackets 45 are
pivotally secured by pins 46 extçn~ing between their respective plate pairs 44a and 44b.
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Brackets 45 each have a horizontal portion 45h and a vertical portion 45v. Each vertical
portion 45v has a stop end 45s. A horizontally oriented drive cylinder 47 is secured on
one end to each of the vertical portions 45v of the four brackets 45. Each cylinder 47 is,
in turn, secured to a tray cont~cting head 48. Four rect~n~ r stop brackets 49 are
secured to head top plate 44c adjacrnt stop ends 45s. Heads 48 are also secured to guide
rods 50 that extend within brass housings 52, which housings 52 are secured to horizontal
bracket portion 45h. Head 36 has a head down switch 53 having a tray contacting loop
53a pivotally secured thereto. A head up sensing proximity switch 54 is suspended from
frame 38 by a bracket 54a for determining the full up position of head 36.
As seen particularly in Fig. 6, contact heads 48 include a depth gauge block 55 having a
bottom tray cont~cting bottom surface 55a, a tray edge cont~rting plate 56 and a tray
hook plate 58. Each contact plate 56 includes a horizontally r~tenl1ing point 60, and each
hook plate 58 inrllldes an operative end consisting of a semi-circular groove 62 extçn-ling
holiGolllally adjacçnt a bottom end 64 thereof. It can be seen that point 60 extends
horizontally at a level above groove 62.
As seen by ler~llh~g to Fig. 2, unstacker 10 incl-ldes a fast acting push cylinder 66 secured
to frame 38. Cylinder 66 includes a tray contact head 67 and is secured to frame 38 at a
level equivalent with a pair of tray c~tçhing means 68. Tray c~tçhing means 68 each
include a drive cylinder 70 secured to frames 38 for providing motion to a pair oftray
holders 72. Holders 72 include tray supporting edges 74 and 76.
A transport conveyor 78 extends adjacrnt and parallel to conveyor 12. Transport
conveyor 78 includes a continuously driven chain 79 e~cten-ling along drive rh~nnrl~ 80
and return ch~nn~l~ 82. Conveyor 78 further inrhldçs a tray deflecting shield 84positioned above and a~j~crnt a tray landing area 85.
It will be understood by those of skill, that the various drive cylinders of the present
invention whether pneumatically or hydraulically driven require control valves and tubing
for providing connection to a source or sources of colllpressed air or hydraulic fluid.
Also, as is well understood by those of skill, the operation of such cylinder control valves,
and hence the cylinders, is re~ ted by a control means. Specifically, the control means,
such as a proglallllllable logic controller, will typically receive inputs from plo~illlily or
limit switches or other such sensing means ~djac~nt to cylinders, or applopliate moving
part operated thereby. Such sensing means, thus, provide for determining the extension or
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position of the associated cylinder or moving part for properly re~ ting the operation of
the present invention by the control means, as desired. Therefore, as the structure,
function and operation of such control components are well within the underst~n~ing of
the relevant level of skill in the art, for the purpose of facilitating the underst~n(ling of the
structure and operation of the present invention, such components are not included in this
description or figures hereof.
The operation of tray unstacker 10 of the present invention can be understood by also
referring to Fig's. 13, 14 and 15. As seen in Fig. 13, with a stack of trays ST in position in
n~t~ç~er area 30, head 36 is operated downward by cylinder 40 wherein heads 48 come
into contact with a top tray T. More particularly as seen in Fig's. 5-9, cylinders 47 then
extend to provide contact of head 48 with tray T. As seen in Fig's 8 and 9, it will be
appreciated that head 48 has generally two or three opportunities for successfully
cont~cting tray T and providing for lifting thereof. Specifically, hook portions 58 fall
partially within the grate holes 90 of the top tray T. Subsequent extension of cylinders 48
provide for contacting of hook portion grooves 62 with a cross-member 92 of the top tray
T. It can be understood that the landing point, and hence the extension position of heads
48, can vary. This contact portion 58 with groove hook 62 may be forced and heldagainst a tray rib 92 or an outer most edge rib 94. The depth at which hook groove 62
falls within a hole 90 below a top surface 96 of the particular tray T is determined by
block 55. It can be seen in Fig. 10 that block 55 is sized to span at least one of the grate
holes 90 and across at least two ribs 92. Thus, the position of surface 55a with respect to
hook end 64 determines the depth of insertion thereof. It can also be understood that such
trays T can become warped. Thus, one or more of the contact heads 48 may fail to be
positioned when cylinders 47 extend such that a hook is below the top tray surface 96
within one of the grate holes 90. In such a condition, point 60 provides an alternate means
of lifting contact with the tray by pushing against a perimeter edge 98 of the tray. As seen
in phantom outline in Fig. 8, a yet further gripping or holding contact point is possible
wherein groove 62 is pushed against the top rim of perimeter edge 98. Thus, head 48
provides for several opportunities for s~lccessfully cont~ctin~ and holding a plastic tray T.
Fig. 12 shows an example of a wire tray W having a wire cross strand 99 thereof being
contacted and held by hook groove 62. It will be understood that groove 62 can directly
contact strand 99 or be pushed there against with the flat portion of plate 58 directly
above groove 62. Alternatively, head 48 can extend so that point 60 can is positioned just
below perimeter wire 99a, or groove 62 can catch and hold perimeter wire 99a if head 48
extends that much above the surface of tray W. Thus, as with a plastic tray, the particular
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structure of head 48 can provide for a plurality of points of gripping contact with a wire
tray W.
As seen in Fig. 12, with the extension of cylinders 47 m~int~ined, lift cylinder 40 is
operated to move head 36 upward above the level of holders 72. C~tçhing means 68 are
then e~te.n~e~, as seen in Fig. 15. Cylinders 47 are then retracted thereby releasing tray T
to fall downward and on to holder edges 74 and 76 of holders 72. As seen by referring to
Fig. 2, push cylinder 66 is then extended rapidly to push or kick tray T on to parallel
conveyor 78. Thus, such process is a dynamic wherein the tray T is hurled offof holders
72, whereby it is deflected by shield 84 onto tray landing area 85 of conveyor 78.
It can be appreciated that cylinders 47 along with guides 50 and housings 52 are carried
with brackets 45 as they pivot about their respective pins 46. Brackets 45, and hence
cylinders 47, guides 50 and housings 52 can pivot between a free h~nging position
somewhat below the horizontal, as seen in Fig. 4, and a more horizontal tray cont~cting
position as depicted in Fig. . It will be understood that the extent to which brackets 45
can pivot downward is determined by the respective bracket stop ends 45s thereofcontacting each corresponding stop bracket 49. Thus, it can be seen that each cylinder 47
and its associated guide can "float" and thereby adapt to the geometry of each tray. Such
adaptability is important as each tray can, as stated above, become warped, i.e. not planar.
Therefore, each head 48 will be able to be positioned along the surface of the tray to
better insure contact in a grate hole or perimeter edge thereof for permitting a successful
lifting operation. It has been found that cylinders 47 and their associated guides should
preferably float through an arc of approx;.~.~t~ly 20 degrees exten~ling between the
horizontal and a point below the horizontal.
A more detailed underst~n~lin3~ of the process of lln~t~c~ing a tray as controlled by a
programmable logic controller, or the like, can be seen by referring to Fig. 16. At start
block 100 it is assumed that head 36 is in the full up position, as determined by sensor 54,
that c~tçhing means 68 are fully retracted and that contact head cylinders 47 are fully
retracted. At block 102 sensor 32 is checked to determine if a stack of trays is present in
the lln~t~cking area 30. If a tray is not present, that is, switch 32 is nnm~dç, at block 104
stop plate 20 is retracted by operation of piston 18 and gates 22 are oscillated by
operation of pistons 24. The sensor 32 is continually checked at block 106 and if it is
made then the process follows on to block 108. If however, at block 106 sensor 32 is not
made, a counter is incremented at block 110. If a predetermined number of cycles are
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attempted at block 112 i.e., that the counter is counted out, there is then an indication that
a blockage exists or that no trays are present. Thus, at block 114 a visual and/or audio
alarm can be activated to indicate the need for operator intervention.
If at block 108 a stack of trays are determined to be present in the ~-n~t~ ing area 30 then
head 36 is operated by cylinder 40 downward to contact a top tray. At block 116 the
control meçh~ni~m determines whether or not switch 53 has been made. If switch 53 has
not been made a counter is incremented at block 118, and then at block 120 the control
determines if the counter has counted out a preset number of cycles. If not, the cycle is
allowed to repeat and head 36 is raised and again lowered to attempt to propelly contact a
tray. It will be appreciated, that a top tray can be resting at an angle that would not permit
proper contact with head 36. Thus, if after a predetermined number of increments at
block 120 it is determined that a successful contact with a tray is not possible, then the
entire stack is rejected. The rejection process basically involves determining at block 122
if sensor 34 is made. If it is, then a stack of trays presumably occupies the area there
above and an audio and/or visual alarm is activated at block 124 to provide for operator
intervention for removing rejected stacks of trays from the outlet end 12B of conveyor 12.
It can be understood that sensor 35 can also be used to automatically signal that conveyor
end 12b is full. If however sensor 34 is llnm~de and therefore indicating room for a
rejected stack to occupy, gates 22 are opened at block 126 after which at block 128 the
control determines whether or not sensor 34 is made at block 128. If it is not, a counter is
incremented at block 130 and at block 132 the control questions whether or not the
predetermined the number of increments has been counted out. If it has not, gates 22 are
again opened at block 126 and it is again determined whether or not sensor 34 has been
made. If after a predetermined number of increments switch 34 is not made, then at block
134 an audio and/or visual alarm is activated to request operator intervention. This
situation could occur where the stack has somehow become caught and cannot flow fully
out of ~In~t~çl~ing area 30 to out take conveyor end 12B. If sensor 34 is determined to be
made at block 128, then gates 22 are closed, block 136, after which stop plate 26 is
retracted, block 138, to permit movement of a further stack into l-n~t~cking area 30. The
control then monitors sensor 32, block 140, and if it is made, indicating the presence of a
stack in the lln~t~ ing area 30, stop plate 20 is extçn-led7 block 142, to prevent
movement of a further stack of trays into the lln~t~e~ing area 30. Thus, with a stack in the
n~t~çking area 30 the cycle can again return to block 100 . If at block 140, after a
suitable delay, sensor 32 is not made, then a counter is incremented at block 144 after
which the control at block 146 determines the number of increments. If the predetermined
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number of increments have not occurred, then stop 24 is operated to retract again at block
138 and after which sensor 32 is again monitored to determine if it has been made, i.e.,
that a stack has moved into the lln~t~c~ing area 30. If after the predetermined number of
attempts and sensor 32 is not made, then a suitable audio and/or visual alarm is activated
at block 148 for requesting operator intervention. Typically, operation of an alarm at
block 148 would indicate that there are no further stacks of trays, or possibly that a tray
stack has somehow become entangled and not able to move into the lln~t~çl~ing area from
conveyor intake end 12A.
Referring again to block 116, if switch 53 is made then cylinders 47 are operated to
extend, block 150, for providing contact between contact heads 48 and the top most tray
ofthe stack. At block 152 cylinder 40 is operated to lift head 36 upward. At block 154
the control determines whether or not head up switch 54 is made. If switch 54 is not
made, this situation would indicate that a tray is possibly entangled with a lower tray and
not permitting cylinder 40 to fully retract. Thus, at block 156 a counter is incremented,
after which at block 158 if the counter has not counted out, the control retracts cylinders
47 at block 160 after which the sequence of blocks 150, 152, and 154 is again attempted.
If however at block 158 the counter has counted out, then cylinders 47 are retracted at
block 162 and the stack rejection process of blocks 122-142 is implemented. If at block
154 head up switch 54 is made, then the control queries at block 164 whether or not the
down switch 53 has become unmade. It will be appalelll to those of skill that such a
situation would indicate that a tray has not been succes~fi-lly carried with head 36. Thus,
a contact head or heads 48 may not have had sufficient contact with the tray to permit its
successful lifting upward from the stack. If switch 53 is unm~de, such picking process is
repeated providing a counter at block 156 has not counted out. If the counter is counted
out, then a defective tray is indicated and the entire stack is rejected as per the sequence of
blocks 122-142. If both the head up and head down switches 54 and 53 respectively are
made, indicating a tray has been sllccç~fi-lly selected, lifted and held in a subst~nti~lly
horizontal position, cylinders 70 are then operated to extend holders 72, at block 166. At
block 168 the control determines whether or not holders 72 have been fully extended. If
not, the same retry procedure described for decision blocks 154 and 164 is implemented.
If holders 72 are succes~fiully extended, then cylinders 47 are retracted at block 170 for
releasing of a tray held thereby. At block 172 the control determines if switch 53 has been
unmade, that is, that wire loop 53a has become free to rotate to its normal position
slightly below the plane of the lifted tray, thereby indicating successful release of the tray
held by head 36. If successful release does not occur, then the incrementing and possible
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stack rejection sequence as above described for blocks 154, 164, and 168 is implemented.
If however switch 53 is unmade at block 172, then the control determines at block 174
whether or not the landing 85 area of conveyor 78 is in condition to receive a tray. A
more detailed explanation of the means by which such detel lllinalion regarding the landing
area of a conveyor 78 is made is contained herein below. It will be apparent to those of
skill that if the receiver section is not clear, the control waits until such signal is made. If
the tray receiving area is clear then cylinder 66 is actuated at block 176 to kick or push a
tray into the receiving area. At block 178 the control determines whether or not the tray
has landed successfully at the tray receiving area of conveyor 78. Again, a fuller
explanation of the means for determining such succes~fi-l receiving of a tray will be
described in greater detail herein below. If the control determines that a tray was not
succes~fi-lly received, then an appropl iate audio and/or visual alarm is directly operated at
block 180. It has been found that if a tray is not successfully received on conveyor 78, it
is preferable not to include a counter and try to again kick the tray by operation of cylinder
66, as such further attempts generally lead to mechanical damage of the trays and/or the
unstacker itself. If a tray is successfully received on conveyor 78 at block 182, the process
can go to start and be repeated for the selecting of a further tray offthe stack present in
the unstacking area 30.
It can be seen that holder edge 74 is slightly narrower than holder edge 76. It has been
found that a slightly narrower edge 74 is desirable to provide for clearance of a tray as it is
lifted there past by head 36. This additional clearance was found to be necessary as the
trays were generally found to be positioned slightly towards edge 74 rather than edge 76.
As seen in Fig's. 17 and 18, conveyor 78 includes a plurality of sets of switches and stops.
Four such sets are shown wherein switches A, B and C; A1, B 1 and C 1; A2, B2 and C2;
and A3, B3 and C3 are electrically interconnected over lines L, L1, L2 and L3 respectively
to stops D and E; D1 and E1; D2 and E2; and D3 and E3, respectively. All such "A", "B"
and "C" switches are operated by spring mounted lever arms 104 that normally extend
above the top surface 102 of conveyor 78 over which trays T travel. All of the "D" and
"E" stops include a drive cylinder 105 secured vertically to one longitudinal side of
conveyor 78 for driving a stop arm or fingerlO6 between a tray stopping position above
conveyor surface 102 and a retracted tray flow position below surface 102. Trays T1-T7
are shown on conveyor surface 102.
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Conveyor 78 functions to transport the individual trays placed thereon by an unstacker 10
to loading equipment, not shown, that reloads the trays with goods, such as loaves of
bread. Since the trays, and especially wire ones, have a tendency, to become entangled, it
is very important that a minimllm ~ t~n~e between the trays be m~int~ined as they are
transported along conveyor 78. That is, the trays must not be allowed to come in contact
with each other. Typically the trays have a tendency to "shingle" wherein a following tray
will ride up or be forced under the next tray in front of it, if the movement of that
downstream tray is stopped. Fnt~ngled trays can co,-,pro"lise the operation of conveyor
78. Also, the loading equipment requires that the trays arrive individually so that they can
be properly loaded. Thus, the plurality of sets of stops and switches along the entire
length of conveyor 78 from the point at which trays are placed individually thereon to the
loading equipment, function to prevent such tray contact. The operation thereof can be
understood wherein each "A","B" and "C" group of switches are wired to their respective
"D" and "E" stops such that if all such switches are made, then the respective two stops
are operated so that arms 106 thereof extend to their tray stopping position. However, if
any one of the two leading "A" or "C" switches becomes nnm~ ., then the associated
stops "D" and "E" are operated to retract arms 106 thereofbelow conveyor surface 102.
Thus, for example, trays Tl and T2 "make" switches A,B and C wherein the lever arms
106 thereof are held downward in a horizontal or closed orientation, and therefore, arms
106 of stops D and E are ~.~tçnded upward stopping tray Tl and any further tray, not
shown, that may run against stop E. However, if trays are being consumed by the loading
equipment, then at least one of a group of three A', B' or C' dow"sllealll switches, not
shown, will open as a tray passes there above and permits a lever arm 106 to spring
upward to its normal angular or open position. As a result thereof the associated stops
will move their arms downward pe~ g tray movement. This switch opening and stop
retraction can then progress along conveyor 78 in a chain reaction manner. Fig. 17 will be
understood to be a "snapshot" of such a sequence wherein It will be assumed that switches
A3 and C3 have become open as a tray has moved from a position there above. Thus,
stops D3 and E3 are retracted as at least one of the switches A3, B3 or C3 is open. Trays
T7 and T6 have moved in the direction of arrow A along conveyor 78 wherein switch C2
has become open as a result of tray T6 moving there past. Thus, Stops D2 and E2 are
retracted as well because, again, at least one switch of the three, namely the C2 switch,
has become open. As a consequence thereof, Trays T~ and T4 can now move along
conveyor. However, stops Dl and El remain extended as tray T4 has not moved muchand continues to make switches Al and Cl, and tray T3 is Iying above and making switch
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B1. Likewise, stops D and E are extended as trays T2 and T1 are making switches A, B
and C.
It will be appleciated by those of skill, that the "C" switches provide for closer spacing of
the trays as they move along conveyor 78. Without a "C" switch a tray would have to
travel past an "A" switch before the preceding stops could be lowered. Also, it will be
understood that the ~i~t~nce between an "A" or "B" switch and its closest upstream stop,
"D" or "E" stop respectively, is greater than one tray length so that in a static situation
when a stop extends, it does not do so when a tray is there above. In a typical
embodiment where the trays are 24 inches long the distance between the stops "D" and
"E" is generally 30 inches. Such distance also serves to space the trays a sufficient
distance from a dynamic point of view to provide for smooth operation of conveyor 78 yet
maximize the volume of trays that can be carried thereby. In addition, each set of three
switches and two stops operate and are controlled autonomously. Thus, anti-~hinglin~ or
back pressure controlling conveyor 78 is made far less costly to m~nllf~ctllre than if such
control means along the length thereof required overall coordination and control thereof.
A plurality of un~t~ckers 10 can be used to feed a common conveyor. As seen in. Fig. 17,
a pair of lln~t~ Prs U1 and U2 are positioned on opposite side of a common conveyor
250. Conveyor 250 is the same as conveyor 78, but includes switches Y1, Z1, X2, Y2
and Z2, and a stop 252. Switches Y1, Z1, X2, Y2 and Z2 are ofthe type previouslydescribed having spring operated lever arms 104 normally held at an angle above the tray
traveling surface of conveyor 250. Stop 252 is secured to conveyor 250 and includes a
mounting portion 254. A drive cylinder 256 and a stop arm 258 are pivotally secured to
portion 254 and drive cylinder 256 includes a piston 260 pivotally secured to an extension
of arm 258. ~ ~n~in~ areas 264 and 266 on conveyor 350 provide for receiving trays
pushed thereon by unstackers U1 and U2 respectively.
The operation and coordination of unstackers U1 and U2 call be understood wherein, a
control means for Un~t~ç~er U1 looks to see if switch Y1 is unm~de. If so, then a tray
can be discharged therefrom onto area 264. It will be appreciated that the Y1 interference
switch is the one that the control means looks at in block 174 of the flow chart of Fig. 16
to determine that a tray was succes~fi-lly discharged onto conveyer 78. Thus, as per the
flow chart of Fig. 16, and in the present example, if switch Y1 is made, it is assumed that
the tray discharge operation was successful. If tray T10 is successfully pushed onto
conveyor 250 it will land on the operating arm of switch Y1 and make that switch, and
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unstacker Ul will not discharge a further tray at this point in time. Tray 10 will then
travel in the direction of the arrow in Fig. 19. In the prerelled embodiment, Unstackers
Ul and U2 operate independently, that is, their sim-llt~neous operation is not necessarily
required or coordinated by a common control means. Thus, one unstacker can operate if
the other is shut down. Therefore, unstacker U2is not directly "aware" that unstacker Ul
has placed tray T10 on conveyor 250. If unstacker U2is prepared to eject a tray from the
holders thereof onto conveyor 250, it looks at the X2 switch to see if it is open, i.e.
Ilnm~de. If so, then stop 252is operated wherein piston 260is extended by cylinder 256
whereby arm 258is positioned, as seen in the phantom outline thereof, to extend into the
path of travel of the trays along conveyor 250. Stop 252is operated if switch X2is open,
as such indicates there is no tray present making switch X2 whereby arm 258 will be clear
to move into position to stop any oncoming tray in a position that would not interfere with
the discharge of a tray into area 266. In other words, an open switch X2 indicates that
there exists a sufficient gap between arm 258 and any tray coming its direction that has
been discharged by unstacker U1 so that stop 252 can be operated in sufficient time to
stop such an oncoming tray. Therefore, in this present description, if tray T10 has been
discharged but has not yet traveled sufficiently to make switch X2, arm 258 will stop tray
T10. Unstacker U2 then looks to switches Y2 and Z2 which are interference switches. If
no tray is making either the Y2 or the Z2 switches then unstacker U2 can safely discharge
a tray onto area 266 as no tray is present therein and stop 252is blocking the travel of
any tray therein. If tray T10 is making switch X2 at the time control looks at that switch,
as represented by phantom line T10', then unstacker U2 will wait until tray T10 has
cleared switch Z2. However, if tray T10 subsequently makes switch X2 after switch X2is
first looked at, then the control for unstacker U2 ignores switch X2 and looks only at
switches Y2 and Z2. It can be seen that with tray T10 at the T10' position switch Zl will
be made. Switch Zl is, as with switch Yl, an interference switch whereby lln~t~cker Ul
will not discharge a further tray if either switch Yl or Z 1 switch is made. As a necessity
of the rolegoing, switches Yl and Z1 are spaced apart a distance that is less than a full
tray length. This spacing provides for at least an instant of ~imlllt~neous making of both
switches by a tray as it travels along conveyor 250. Otherwise, if the spacing was greater
than a tray length, the controller for un~t~ç1~r Ul could receive erroneous information
that a tray had cleared the Yl and Zl switches, whereas it was actually temporarily
positioned there between. When a tray is discharged from unstacker U2 clamp 252is
opened. Thus, such a discharged tray T12 and tray T10 will move along conveyor 250. If
however, the first stop E down stream thereof is extended, as the result of switches A, B
and C being made, tray T12 will stop at the position shown and will be making switch Z2.
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Since clamp 252 has opened tray T10 will move along conveyor 250 an will eventually
make both switches X2 and Y2. When this happens, the control for unstacker U2 will
close clamp 252 wherein arm 258 will contact the side of tray T10, as represented by tray
T10 being at position T10". Thus, it can be appreciated that switches X2, Y2 and Z2 will
be operating as back pressure or anti-~hinglin~ switches in the manner of switches A, B
and C. Switch Z1 is positioned so that it will also be made when tray T10 is making
switched X2 and Y2. The~efole, unstacker U1 will not discharge a further tray until
switch Z 1 is l~nm~de. It will be appal elll to those of skill that the use of one l-n.st~ç~er 10
will always involve at least two switches "Y" and "Z", the "X" switch being necessary if a
further unstacker 10 is situated upstream therefrom.
