Magnetic can sorter

Sidewalls of cans from one filling and closing line are magnetized to provide each with a north pole oriented toward the can top. Sidewalls of cans from another filling and closing line are magnetized to provide each with a south pole oriented toward the can top. These tagged cans are randomly merged into one line for further processing without mixing up can top orientations, for instance, for cooking in a conveyor-fed continuous cooker in order to keep the cooker operating nearer full capacity. Then, each can passes a magnetic sensing station where one (top) end of each can is investigated by a probe which senses whether that end is a north pole or a south pole. The sensing station commands a diverter downstream which shunts the cans sensed as having north pole ends into a different line from the cans sensed as having south pole ends.

BACKGROUND OF THE INVENTION 
Until a few years ago, most commercial canners practiced batch-wise cooking 
of canned foods. 
Then conveyor-fed continuous cookers were developed and marketed, 
principally by FMC Corporation. 
A typical continuous cooker accepts one continuous row of filled and sealed 
but unlabeled cans, rolls the cans on their sides in a helix extending 
from end to end on the cylindrical inner surface of a drum while applying 
heat to the cans, e.g. using high-pressure steam. 
The cans which have passed through the cooker are then typically cooled, 
palleted and warehoused. When the canner receives an order to ship, the 
palleted cans are withdrawn from storage, labeled with the desired 
labeling, boxed and shipped. 
Generally, a continuous cooker is configured to process one uniform size of 
can, for instance 303 .times. 404, one pound cans and substantial 
modifications are needed to switch can size. However, these continuous 
cookers are able to cook canned food quite rapidly, so rapidly in fact 
that generally two or more can filling and closing lines must serve one 
continuous cooker if the continuous cooker is to be run near full 
capacity. 
As a typical example, many filling and closing lines processing one pound 
food cans operate at an output rate of about 200 to 250 cans per minute, 
whereas a typical continuous cooker has an operating capacity of 600 1 
pound cans per minute. Thus, either such a continuous cooker must be fed 
by 2 or 3 can filling and closing lines, or run with a full volume of 
steam wastefully cooking only a few cans and a lot of empty space, or run 
in a batch-wise manner. 
The economics of commercial canning is such that both running a continuous 
cooker part full or as a batch-wise cooker is a losing proposition for 
both money and energy. 
For the typical large volume canner and for the typical small volume 
canner, the problem just outlined is unlikely to arise. 
The large volume canner can expect to be packing so much of one sort of 
food that it is feasible to feed their continuous cooker using two, three 
or several filling and closing lines each putting the same kind and grade 
of food in the same cans. 
The small volume canner lacks the expectation of being able to fully use a 
continuous cooker. Thus, such a unit is generally not part of a small 
canner's equippage. 
The problem of using a continuous cooker efficiently and profitably is most 
likely to arise for a medium volume canner. Such a canner may have 
operational peaks during which a continuous canner can be served by a 
plurality of filling and closing lines all processing the same kind and 
quality of food. However, at other times the volume or anticipated length 
of run may be insufficient to warrent operating more than one filling and 
sealing line to process a particular kind and quality of food. 
Faced with that potential, some medium-sized canners have acquired 
continuous cookers, used them efficiently at times and inefficiently at 
other times and have hoped increasing business volume would improve their 
efficiency. Other medium-sized canners have simply put off acquiring 
continuous cookers, despite their obvious advantages. 
While a medium-sized canner may not have the volume of one kind and quality 
of food to run several filling and sealing lines at once to can that food, 
it is likely to have sufficient business volume to be running two or more 
filling and sealing lines at once, each processing a different kind and/or 
quality of food. For instance, one line might be packing Grade A peas and 
another might be packing Grade B peas, or one might be packing cream-style 
corn while the other is packing whole-kernel corn. 
Prior to the present invention, others have made some efforts to find an 
acceptable way to serve a continuous cooker with the randomly mixed output 
of a plurality of filling and sealing lines that are processing foods of a 
different kind or quality. Basically, these efforts have centered about 
marking the cans from each line in an optically sensible manner. These are 
examples of what has been tried: brass-colored lids on one line's cans and 
silver-colored lids on the other line's cans; spots of highly reflective 
paint applied to the cans of one line, but not to those of the other; and 
different product codes embossed on the can lids. Sensing devices have 
ranged from simple brightness detectors through complex optical character 
readers. 
However, all these optical techniques have a common problem: at the point 
in the process where the mixed cans are to be separated, the cans most 
often are covered with beads of moisture, because they have just gone 
through a cooling spray and/or because they have cooled below the dew 
point of their environment and condensation has occurred thereon. Simply 
put, the moisture beads reflect light in a sufficiently unpredictable 
manner as to introduce an unacceptable level of uncertainty in a 
discrimination based on optical cues. 
These prior art systems have other undesirable features. Odd-colored lids 
are unacceptable to some of the canners' customers and to some ultimate 
consumers. Their use requires the canners to stock two or more colors of 
lids and to avoid mistakes in supplying the right color of lids to each 
canning line. Applied spots of paint or the like require spot applying 
machinery which can become fouled or exhausted of paint resulting in a 
number of identically-appearing intentionally spotless and unintentionally 
spotless cans becoming mixed, then unsortable. In addition, processing in 
a cooker can remove some paint spots applied under less-than-optimum 
conditions such as improper composition, mixing or drying of the paint. 
SUMMARY OF THE PRESENT INVENTION 
The present invention was devised to provide a reliable way of tagging cans 
and for sorting tagged cans from a mixture of cans. 
In practicing the preferred form of the invention, sidewalls of cans from 
one filling and closing line are magnetized to provide each with a north 
pole oriented toward the can top. Sidewalls of cans from another filling 
and closing line are magnetized to provide each with a south pole oriented 
toward the can top. These tagged cans are merged randomly into one line 
for further processing without mixing up relative can top orientations, 
for instance for cooking in a conveyor-fed continuous cooker in order to 
keep the cooker operating nearer full capacity. Then, each can passes a 
magnetic sensing station where one (top) end of each can is investigated 
by a probe which senses whether that end is a north pole or a south pole. 
The sensing station commands a diverter downstream which shunts the cans 
sensed as having north pole top ends into a different line from the cans 
sensed as having south pole top ends. 
A particular sensing probe and system is disclosed, as are variations 
calling for less and more magnetizing and diversion into more than two 
output lines. 
The principles of the invention will be further discussed with reference to 
the drawings wherein preferred embodiments are shown. The specifics 
illustrated in the drawings are intended to exemplify, rather than limit, 
aspects of the invention as defined in the claims.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS OF THE INVENTION 
In General 
The output of one can packing line 10 is magnetically tagged at a 
magnetizing station 12 interposed in the output conveyor 14 of that 
packing line. Typically, these cans are provided with a north pole N 
toward the can top. 
The output of another can packing line 16 is magnetically tagged at a 
magnetizing station 18 interposed in the output conveyor 20 of that 
packing line. Typically, these cans are provided with a south pole S 
toward the can top. 
The conveyors 14 and 20 merge at 22 to provide one row of a mixture of 
magnetically tagged cans. A conveyor 24 feeds the can mixture to a 
continuous cooker 26. The cans are conveyed through the continuous cooker 
26, whereupon the cans are cooled at 27 and accepted by a conveyor 28. 
A magnetic sensing device 30 stationed astride the conveyor 28 examines 
each passing can typically for whether the can being examined is 
presenting a north pole or a south pole toward the sensing device. 
Further downstream, the conveyor 28 splits into at least two conveyor lines 
32, 34 and a conventional can diverter 36 is provided at the fork. The 
diverter 36 is electronically linked to the sensing device 30, for 
instance by wire 38, to be operated by the output signal of the sensing 
device. 
In the instance shown, when each can sensed to have a north pole top 
reaches the diverter, it is shunted to the conveyor line 32, and when each 
can sensed to have a south pole top reaches the diverter, it is shunted to 
the conveyor line 34. 
As also depicted, a third conveyor line 40 may be provided for untagged 
cans or for occasional tagged cans whose pole strength is too low to 
permit a discrimination to be made and relied upon. 
In Particular 
In order to use the invention, the canner must run cans of magnetizable 
material, e.g. conventional tin plate, T.F.S. or the like and not cans 
made of e.g. all-plastics, foil/fiber helically wound composites, or 
non-magnetizable aluminum alloys. However, at least at present, the 
structural demands for rigidity upon vacuum-packed, sealed food cans 
practically dictate the use of steel sheet for such cans to avoid can 
collapse on initial exposure to high-pressure steam and later in the 
cooling step after cooking. 
After the cans are filled and closed in a top-end-up orientation, a 
conventional turning mechanism is used at 42 to place each can in a 
horizontal condition with all the top-ends pointed the same direction. 
The magnetizing stations preferably each include a permanent magnet 
including a set of two rails 44N, 44S arranged side-by-side and extending 
longitudinally of the respective conveyors 14, 20. The rails 44N, 44S are 
transversely spaced apart by an amount nearly equal to the longitudinal 
extent of the sidewall of the size of can being processed and the rails 
are preferably disposed at a downward slant greater than any slant the 
conveyor 14 or 20 may have. The permanent magnet should be so strong as to 
magnetize each can to saturation parallel to the can length. 
The rails 44N, 44S are preferably sufficiently long that each can which 
reaches the rails and rolls down their slant undergoes at least one 
complete revolution while rolling on the rails. 
Generally the cans are closely packed on the conveyors 14 and 20, but 
acceleration on the slanting rails causes each can, while it is being 
magnetized, to become spaced apart from its neighbors in the row. 
One might ask, why not just magnetize a flat end of each can rather than 
the cylindrical sidewall. One reason for the sidewall choice is the 
widespread practice of canning companies of using magnetically assisted 
conveyors. If, for instance, there is a substantial difference in the 
height of the cooker 26 inlet and the packing lines 10 or 16, or between 
the cooker 26 and the end of the processing line, one or more of the 
conveyors 14, 20, 22, 24, 28, 32, 34 will have an inclined section. In 
order to keep the cans being conveyed up or down the incline from 
slipping, it is conventional to place magnets under or in the conveying 
surface to press the cans into good tractive engagement with the conveying 
surface. As it is, use of a magnetically assisted conveyor disturbs the 
polarity of the can sidewalls, but does not destroy or reverse it. 
However, this practice would prevent a reliable separation from being made 
if the can ends rather than the can sidewalls were magnetically tagged. 
(It is possible to successfully use tagged ends if magnetic conveyors are 
not used, or if only one end of each can is ever presented toward a 
magnetic conveyor, and it is the opposite end of each can that is 
magnetically tagged.) 
It should be apparent that the apparatus and method of the invention can be 
successfully used only in instances where the top-bottom orientation of 
each can is not randomized at any point between the magnetizing station 
12, 18 and the magnetic sensing station 30. Thus, although each can may be 
tipped on its side and set back upright once or several times during 
processing, the orientation, can-for-can remains certain so long as each 
can has what was its top end, when it was magnetized, presented in the 
same direction at the magnetic sensing station. 
So far as it concerns the present invention, the main effect of 
magnetically aided conveying of the magnetically tagged cans is to produce 
local peaks and troughs in the pole strength of the magnetized cans, 
particularly at the can end which was presented toward the magnetically 
aided conveyor. Accordingly, it is desirable to present one can end toward 
the magnetically aided conveyor but always sense the polarity at the 
opposite end of the can. For instance, it may be decided, as an arbitrary 
convention, to sense the polarity by presenting the can top ends toward 
the sensing probe at the station 30, and to have magnetically conveyed the 
cans only while they were resting on the can bottom ends. Thus, the can 
magnetic pole that is most "damaged" during magnetically assisted 
conveying is not used for discrimination. Rather, the least "damaged" pole 
is sensed at station 30. 
Other factors and events such as the can sidewall seam (if any), the 
leading and trailing ends of the magnetic rails 44N, 44S, cooking heat, 
banging together of cans and the like can produce minor discontinuities or 
variations in pole strength. In general, these are not as significant as 
those resulting from magnetically assisted conveying, and in no event is a 
north pole end changed to a south pole end or vice versa by these factors 
and events. 
Typically, the continuous cooker 26 accepts the mixture of magnetically 
tagged cans in a continuous stream of cans which abut one another in a 
single row. The row of cans feeds into a spiral guide (indicated at 50) 
inside the cooker shell and roll in, or nearly in, contact with adjacent 
cans along the whole length of the guide 50. A spider (not shown) mounted 
inside the cooker presses the cans outwards into the guide. High-pressure, 
high-temperature steam, contained in the cooker body by suitable 
steam-locks heats the cans inside the cooker. The continuous rolling of 
the cans causes mixing and more even heat distribution within each can, 
speeding the cooking process. 
The cans which exit the cooker 26 pass a cooling station 27 on the conveyor 
28, where cool water sprays, total immersion in water, or the like cool 
the cans. 
At the sensing station, the conveyor 28 includes a higher speed section 52 
for providing a space in the order of one can diameter between adjoining 
cans so that the sensor can examine each can individually, with little 
interference from neighboring cans. 
There are a number of ways magnetic sensing could be carried out at 30. For 
instance, a coil placed adjacent the can path and connected to a current 
flow magnitude and direction indicating meter would have a current induced 
therein by passage of magnetized cans by the coil. In practice, the 
strength of the indication is proportional to the speed of the cans past 
the coil and the necessary speed for producing sufficient induced current 
strength for a reliable indication is inconveniently fast. 
Fortunately, there are other sensing techniques which are not dependent on 
speed of can travel past the sensor. The presently, preferred technique 
utilizes a Hall-effect sensor. 
As is well known, it is possible to use a chip of some semiconductor 
materials as a magnetic sensor. In order to do that, a voltage is applied 
across two opposing edges of the chip and two other opposing edges are 
connected to a current flow indicating device. When the sensor is brought 
near a magnetized object, the vector of electron flow across the 
semiconductor chip is changed, producing a corresponding change in the 
current flow indicated by the indicating device. Instead of placing the 
chip itself in proximity with the magnetized body, a probe of highly 
permeable magnetic core material such as permalloy may be connected to the 
chip and brought near the magnetized object. 
By preference, the probe includes a first, ring-shaped element to be 
brought into proximity with each can end, and a second element pointing 
into space away from the can. The preferred arrangement is shown in FIG. 
2, in which the chip 56 of FIG. 4 is served by a ring-shaped probe 58 and 
a rod-shaped other element 60. 
The sensing station further includes a can detector 62 subsystem for 
determining each point in time when the ring-shaped probe element should 
be taking a measurement. Typically, the can detector includes a photocell 
circuit 64 wherein interruption or reflection of a photocell beam cues the 
magnetic sensing station to make a measurement a fixed, brief time later. 
The object is to make the measurement when the ring-shaped probe element 
58 coincides with a can end of a can being conveyed through station 30. 
When the ring 58 is of substantially the same diameter as the can and the 
measurement is taken at the point that the circular probe and can end are 
substantially coaxial, whatever variation there is in pole strength 
angularly of the can longitudinal axis, is largely averaged out by the 
probe. 
Although the sorting device need not have a visual indicator of magnetic 
polarity, provided its sensor is connected in a command relation to a can 
diverter, a visual indicator permits easier adjustment and monitoring. 
Accordingly, a visual indicator 65 is provided. It may have a conventional 
circuit 66 for zeroing the indicator and a span adjustment 68 for 
adjusting the indicator needle swing to the scale range of the instrument. 
In that way, for instance, sensing an ideal north pole can swing the 
indicator needle all the way to the right on the scale and sensing an 
ideal south pole can swing the indicator needle all the way to the left on 
the scale. The amplified, zeroed and span-adjusted signal is also 
electrically compared at 70. If the can has its north pole toward the 
probe, the diverter 36 is signalled by the comparator to divert that can 
to the left onto the conveyor 32 when that can reaches the diverter 36. 
If, instead, the can has its south pole toward the probe, the diverter 36 
is signalled by the comparator to divert that can to the right. Odd cans 
whose sensed pole may be so damaged as to be indeterminate are shunted to 
a separate line 40 when they reach the diverter 36, upon detection of this 
anomaly at 71. In the preferred two-level system, each can sidewall is 
magnetized parallel to the can longitudinal axis so as to have a north 
pole toward one end of each can of one grade or quality of contents and a 
south pole toward the same end of each can of a second grade or quality of 
contents and the magnetic sorter simply looks for north ends and south 
ends. However, a somewhat less reliable two-level system could be run 
wherein only one of the two incoming streams of cans is magnetically 
tagged, either all north or all south, and the sorter looks for such tags. 
In that event, the discrimination process separates the cans by whether 
they are tagged or untagged. Such a variation is less reliable because 
only about half the magnitude of difference exists between the pole 
strength of an ideally tagged can and an ideally untagged can and pole 
damage can more easily result in some weakened tag cans being sorted with 
untagged cans. Of course, a minor amount of such mis-sorting can be 
tolerated if the food in both tagged and untagged cans is of the same 
kind, but that in the untagged cans is of a lesser grade, since the net 
result of a sorting error is, e.g. to put a can of Grade A peas in with 
the cans of Grade B peas and lose the incremental value of its true grade. 
Similarly, a three-level system can be run by integrating a line of north 
tagged cans, a line of south tagged cans and a line of untagged cans. 
Sensing and diverting is performed as with the preferred embodiment, 
except that a third class of cans will wind up on conveyor 40. For the 
same reasons as explained in regard to the just-described one tagged/one 
untagged two-level system, use of such a three-level system is best 
confined to instances where no great liability is caused by the occasional 
mis-sorting of a tagged can into the untagged group. An instance where 
such a three-level system could be used is where one filling and closing 
line is processing Grade A Fancy peas, a second line is processing Grade B 
peas and the third line is processing the lowest grade of peas. If the 
cans with the lowest grade of peas are the untagged ones, any mis-sorting 
is much more likely to shunt a can of Grade A Fancy or Grade B peas on to 
the conveyor for cans of lowest grade peas to the same, tolerable result 
as described with relation to the second two-level variation. 
Notice that the system just described is insensitive to whether the cans 
are hot or cold, wet or dry, light or dark, labeled or unlabeled and that 
the sensing is largely insensitive to the speed of travel of the cans 
through the sensing station. Accordingly, the system described overcomes 
problems in the art, is straightforward, easy and economical to use. 
It should now be apparent that the magnetic can sorter, as described 
hereinabove, possesses each of the attributes set forth in the 
specification under the heading "Summary of the Invention" hereinbefore. 
Because the magnetic can sorter can be modified to some extent without 
departing from the principles of the invention as they have been outlined 
and explained in this specification, the present invention should be 
understood as encompassing all such modifications as are within the spirit 
and scope of the following claims.