SORTING MACHINE
United States Patent 3738484
A number of steeply inclined tapered slides are arranged for gravity assisted singulation and alignment of items such as rice grains that are introduced at the top from vibrating chutes that are gently inclined in the opposite direction. The chutes extend from a common vibrating feed tray and have adjustable entrance gates to equalize the flow rates of the items. A stationary hopper supplies the feed tray through a flexible coupling. At the bottom of each slide, a photoelectric viewer is arranged to operate an ejector for diverting grains having dark spots. A variable background is provided and is adjusted so that the signal induced thereby is identical to that of the mid-portion of an acceptable grain. Light sources are positioned both above and below the photoelectric means so as to provide extra illumination for the leading and trailing ends of each grain, thus to avoid spurious signals similar to those induced by dark spots but caused by the rounded ends of acceptable grains.
US Patent References:
Colour sorting machines
Fraenkel - December 1962 - 3066797
Random stream materials sorter
Hutter - April 1965 - 3179247
Apparatus for classifying objects according to their internal structure
Nelson - May 1968 - 3385434
SORTING APPARATUS
Wood - December 1969 - 3482686
Colour sorting machines
Fraenkel - December 1962 - 3066797
Random stream materials sorter
Hutter - April 1965 - 3179247
Apparatus for classifying objects according to their internal structure
Nelson - May 1968 - 3385434
SORTING APPARATUS
Wood - December 1969 - 3482686
Inventors:
Hoover, Michael C. (Houston, TX)
Long, William C. (Houston, TX)
Long, William C. (Houston, TX)
Application Number:
05/124320
Publication Date:
06/12/1973
Filing Date:
03/15/1971
View Patent Images:
Export Citation:
Assignee:
Mandrel Industries, Inc. (Houston, TX)
Primary Class:
Other Classes:
209/908
International Classes:
B07C5/342; B07C5/342; B07C1/04
Field of Search:
209/73,111.6,111.7,74 222/566
Primary Examiner:
Schacher, Richard A.
Claims:
What is claimed is
1. A semi-free-fall sorting apparatus for granular items, comprising:
2. An apparatus as recited in claim 1 wherein:
3. Apparatus as recited in claim 1 wherein:
4. The combination recited in claim 3, wherein said apparatus also includes:
5. The combination recited in claim 4, wherein said apparatus also includes:
6. The combination recited in claim 5, wherein:
7. The combination recited in claim 1, wherein said examining and sorting means includes;
8. The combination recited in claim 7 and adapted for the sorting of elongated gray-white rice grains as said items, wherein:
9. The combination recited in claim 7, wherein:
10. The combination recited in claim 7, wherein said receptacle means for receiving acceptable undiverted items includes:
1. A semi-free-fall sorting apparatus for granular items, comprising:
2. An apparatus as recited in claim 1 wherein:
3. Apparatus as recited in claim 1 wherein:
4. The combination recited in claim 3, wherein said apparatus also includes:
5. The combination recited in claim 4, wherein said apparatus also includes:
6. The combination recited in claim 5, wherein:
7. The combination recited in claim 1, wherein said examining and sorting means includes;
8. The combination recited in claim 7 and adapted for the sorting of elongated gray-white rice grains as said items, wherein:
9. The combination recited in claim 7, wherein:
10. The combination recited in claim 7, wherein said receptacle means for receiving acceptable undiverted items includes:
Description:
BACKGROUND OF THE INVENTION
This invention relates to sorting machines and particularly to such machines adapted for gravity assisted singulation of the items to be sorted.
Previously, sorting machines for tiny items such as grains of rice, have comprised rotating suction wheels or other rotation or reciprocation mechanisms for singulating (i.e. separating and aligning in serial order) the grains for individual viewing by photoelectric means. While most such machines have operated satisfactorily, their volume or time-rate of sorting per ton is low when compared with the rate that is achievable for items of larger size. To increase the sorting rate, it is usually necessary to arrange a large number of sorters in parallel. With rotating and reciprocating mechanisms such as are known to the prior art, the space that is required for parallel arrangement is extremely great and is usually out of proportion to the requirements of economy and efficiency.
Accordingly, it is an object of the invention to provide a compact high speed sorting apparatus for small items.
It is another object of the invention to provide such a sorting apparatus that is adaptable for parallel arrangement and operation of a large number in a small space.
SUMMARY OF THE INVENTION
These and other objects are provided in an apparatus described as follows. A number of steeply inclined tapered slides are arranged for gravity assisted singulation and alignment of items such as rice grains that are introduced at the top from vibrating chutes that are gently inclined in the opposite direction. The chutes extend from a common vibrating feed tray and have adjustable entrance gates to equalize the flow rates of the items. A stationary hopper supplies the feed tray through a flexible coupling. At the bottom of each slide, a photoelectric viewer is arranged to operate an ejector for diverting grains having dark spots. A variable background is provided and is adjusted so that the signal induced thereby is identical to that of the mid-portion of an acceptable grain. Light sources are positioned both above and below the photoelectric means so as to provide extra illumination for the leading and trailing ends of each grain, thus to avoid spurious signals similar to those induced by dark spots but caused by the rounded ends of acceptable grains.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view partly broken away of an apparatus according to the invention;
FIG. 2 is a right side elevation view, partly broken away, of the apparatus of FIG. 1;
FIG. 3 is an enlarged view taken along the plane of lines 3--3 of FIG. 2;
FIG. 4 is an enlarged cross sectional view taken along the plane of lines 4--4 of FIG. 2;
FIG. 5 is an enlarged view of a portion of the apparatus shown in FIG. 2;
FIG. 6 is a schematic view illustrating the operation of the invention;
FIG. 7 is a view illustrating a variation of the apparatus of FIG. 5;
FIG. 8 is an elevation view taken on the plane of lines 8--8 of FIG. 2; and
FIG. 9 is a sectional view taken on the plane of lines 9--9 of FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIGS. 1-4 there are shown a number of elongated, tapered slides 11, each of which has a central longitudinal generatrix 12 steeply inclined (e.g., 35° from the vertical) for gravity assisted separation of small granular items such as grains 13 of rice sliding downwardly thereon. In the art of sorting granular items, it is of the utmost importanct to be able to separate the items and space them out in serial order (i.e. "singulate") so that they may be viewed one at a time and so that a rejection operation takes effect only for the one grain that is defective. In the present invention the elongation of the slides 11 and their considerable vertical extent (e.g., about 40 inches in an actual machine) enlists the separation assistance of gravity in the following way. It is well known that falling bodies accelerate at a constant and substantial rate, so that if two bodies begin falling from the same point at slightly different intervals of time, it follows that the vertical separation between them increases as a function of the acceleration g of gravity and the square of the time (t 2 ) of fall. If two grains of rice are each 0.25 inches long, and one begins to fall at time t o and the other begins to fall 1 millisecond later (i.e., at time t 1 = t o + .001 sec.), then when the second grain has fallen 40 inches, its leading end must be spaced behind the leading end of the first grain by one-fourth inch. In other words, a suitable separation equal to the length of one rice grain can be achieved in a fall of 40 inches even when the grains begin to fall only 1 millisecond apart in time. This minimum time-spacing is equivalent to only about four ten-thousandths of an inch (0.0004 inches) in terms of the initial falling distance of one grain, i.e., when the second grain begins to fall, the first has already fallen 0.0004 inches. In 40 inches of fall, then, the initial spacing is increased nearly 6,000-fold, from 0.0004 to 0.2500 inches. The usefulness of gravity assistance for separating the grains is therefore evident.
In the present invention, the grains are expected to slide down the inclined slides 11 rather than falling perfectly freely, so of course the slight frictional retardation of the grains on the slide tends to diminish the separation achievable by gravity. However, dry friction does not increase substantially with velocity, so its effects may be reckoned as constant and slight. We have seen that for free fall the grains of rice must be spaced apart for time intervals of greater than 1 millisecond at the top of the slide. If the effect of friction adds merely another millisecond to this minimum requirement, there is little disadvantage, for by far the overwhelming bulk of grains coming into the top of each slide 11 are spaced apart in time for greater than 2 milliseconds. Besides the above consideration, the frictional effect of the inclined slides 11 is more than offset by the channeling effect of the tapering shape of the slide. In FIG. 3 it is shown how the slide has an upper-end cross section of U-shape defined by two side walls 14 and a rounded bottom portion 16 of a radius much larger than the transverse radius of a rice grain 13. About one-third of the way down from the top, the slide has narrowed to a bottom portion just precisely fitting the rice grain cross section, and the side walls have converged to define a close-spaced generally V-shaped cross section. Clearly, then even if two grains of rice fell into the upper end of the slide 11 at times less than 2 milliseconds apart, they would nonetheless strike different portions of the slide bottom and, what with the effect of impact forces and the jostling effect produced in the grains by the tapering sides 14, the grains are still constrained to align themselves one behind the other in serial order before they reach the bottom. In fact, it may be said that even if two grains begin their falls at precisely the same instant in time, it is substantially impossible for them to arrive at the bottom end of the slide 11 without being suitably spaced apart in serial order.
If the grains are to derive the maximum effect from their initial time spacing, they should begin their falls from a condition of zero vertical component of velocity. Also it is desirable to reduce impact effects of the grains in the upper end of the slides 11 as much as possible, which requirement calls for the smallest possible horizontal component of velocity as well. Ideally, the grains would drop into the upper part of the slide 11 from a portion of the structure (i.e., the chutes 17) in which they occupied a position at rest (zero velocity in any direction) at the instant immediately before the fall began. This condition is approximately achieved by giving the chutes 17 the gentlest possible slope downward at an inclination in the opposite direction from that of the associated slides 11. The minimum inclination of the chutes 17 is the least inclination at which the grains will slidingly migrate downwardly at a reasonable processing rate when the friction is reduced as by vibrating the chutes 17, as with eccentrically loaded vibrating motor means 18. The chutes 17 are also tapered somewhat, but still at their open ends permit the random showering of grains into the slides 11. A further effect that has been noted with this structural geometry is that bouncing grains strike one another and tend to thus damp or decrease the bouncing effect.
To make utmost use of the space saving structure of slides 11 and chutes 12, a large number of each are arranged in parallel, and the chutes 17 are mounted to extend from a common feed tray 19, from which the chutes are partitioned by adjustable gates 21. Four motors 18 are used in the illustrated device, attached to the tray 19 (only two are shown in FIG. 1). Because the induced vibrating effect varies from chute to chute as a function of mechanical and mass characteristics of the chute, and distance of the chute from the motor, the gates 21 are adjusted individually in actual operation until the rates of flow of grains in all of the chutes are equalized and optimum (about 50 lbs. per hour per chute).
Above the tray 19 is fixedly mounted a hopper 22 for reception of the grains, and a flexible coupling 23 connects the stationary hopper 22 with the vibrating tray 19, so that a closed conduit for the grains is formed from the upper opening 24 of the hopper to the gates 21 of the chutes 17. The slides 11 do not vibrate, nor do any other portions of the apparatus except the coupling 23, tray 19, chutes 17 and motors 18.
As illustrated in phantom in FIG. 2, the tapering of the slides 17 enables a double saving of space in that two full banks of slides 11 may be criss-crossed at the narrower portions thereof, while the wider chutes 17 are divided between two opposite sides of the machine and are abutted side-by-side.
At the bottom end of each slide 11, the rice grains shoot out with considerable velocity upon a trajectory or path 31 (FIG. 5) which is substantially a straight prolongation of the generatrix 12, at least in the region of the predetermined viewing zone 32 adjacent the end of the slide. Each grain 13 is also invariably oriented with its length along the path 31 and is thus viewed from the same angle by a photoelectric viewing means 33 of standard type, disposed at the side of path 31 and provided with lens means 34 to define the zone 32 of view.
Because rice grains are of generally gray-white coloring if acceptable, and are generally translucent, and because unacceptable grains are usually distinguishable by the appearance of dark spots visible from all sides under proper illumination through the translucent interior, it is necessary to illuminate and inspect each grain from only one of its longer sides. To obtain a voltage signal from the photocell 33 indicative of an acceptable grain, the present invention provides a light source 35 shielded from the viewing zone 32 and illuminating a generally gray-white background 36 which is rotatable on an axis 37 abnormal to path 31 so that the background shade can be matched with that of an acceptable grain, and the voltage level 40 of the photocell signal is the same when an acceptable grain is in view as it is when there is no grain in view (FIG. 6). As shown in FIG. 5, the background 36 is rotatable through about 90° by means of a bell crank 38 operated by a pin 39 sliding in a slot 41 on the bell crank and extending from a piston 42.
The illustrative apparatus is of the dark-trip type and provides a positive signal pulse 43 when a dark spot in an unacceptable grain passes through the viewing zone 32. However if the grain is illuminated from only one position adjacent the photocell 33, as is usual in the prior art, the rounded leading and trailing ends of the grain reflect a lesser amount of light to the photocell 33 than comes from the mid-portion of the grain. At the same time, the leading and trailing ends of the grain are cutting off the reflected light from the background 36. The viewing zone is of course as narrow as possible and extends for a considerably less distance in the direction of path 31 than the length of the rice grain, in order to obtain the maximum signal level from the smallest dark spot. But the result of this combination of conditions, when only a single lamp is used, is that the ends of the rice grain appear as dark spots to the photocell and cause spurious defect signals 47 even though the grain may actually have no dark spots.
The precise mechanism of this phenomenon is not fully understood, but it is believed to be caused partly by specular reflection at flat angles of illumination near the extreme tips of the grains, which denies entry of this portion of incident light into the interior of the translucent or "transluminescent" grain, from whence it would ordinarily be glowingly and diffusedly reflected back to the photocell. Since less light gets back from the grain ends, a spurious dark spot is signalled. Also believed to be a cause, is the fact that less light is directly reflected back to the photocell from irregularities on the surface of the ends of the grain, where the surface is at a different angle than that of the long stretch of the mid-portion of the grain. In any event, it has been found experimentally that with only one lamp for illumination, spurious signals do appear.
Accordingly, the invention contemplates the use of at least two light sources 51 and 52 mounted respectively above and below the viewing means 33, 34 so as to provide extra illumination to the ends of the rice grain. The leading end of the grain is given extra illumination by light source 52 to compensate for the loss in illumination that the leading end receives from light source 51. As for the mid-portion of the grain 13, the combined illumination it receives and reflects to the photocell from both light sources adds up to produce a signal of the same general voltage level as that received from the leading end as a result of the more direct illumination of light source 52 above. A similar effect is produced by light source 51 on the trailing end of the grain. The result is an undisturbed steady voltage level signal 40 as the acceptable grain enters the viewing zone, passes through it, and departs. Only if a grain with a true dark spot appears does the photocell produce a deviating positive signal 43 to initiate rejection of the defective grain.
Upon receiving a rejection signal 43, the programmed logic of an electronic controller 56 causes the operation of a compressed-air value 57 and nozzle 58 to emit a quick sharp brief jet or blast of air directed against the side of the grain 13 transversely to the path 31 so as to blow the defective grain along a deviating or deflected path 59 into a reject hopper 61. If, however, the grain 31 is not defective and no signal pulse 43 is produced, the grain continues along path 31 to an acceptable product tube 62, which is laterally elongated so as to be common to all channels, and may in turn be coupled to a bag or other packaging, transporting or storage apparatus.
In the illustrated apparatus, the light sources 35, 51 and 52 are fluorescent tubes operated at high frequency (e.g., 20 kilohertz) and having the ballasts synchronized as by a common coupling 60.
Occasionally, while the apparatus is operating, it is desirable to be able to sample the product that is being accepted in each individual channel of the machine. For this purpose, the tube 62 (FIGS. 8 and 9) is formed with a side opening 63, and a number of individual sampling tubes 64 are mounted to cover the opening 63 in the normal operating condition of the machine, but without interfering with the flow of grains downwardly through the tube 62. The sampling tubes 64 are pivoted as at 66 however, so that the upper ends 67 can be individually tipped inwardly to catch the grains and divert them outwardly through the now-protruding open lower ends 68 and into the hand of the sampler.
Referring now to FIG. 7, an alternative arrangement is shown for use with opague products that must be examined from both sides. A pair of photoelectric examining devices 33a and 33b are placed on opposite sides of the path 31 from slide 11, and each phototube has a pair of light sources 51a, 52a, 51b and 52b, respectively, associated therewith, above and below the phototube. Each phototube is directed toward a background 36a and 36b, respectively, shown in the FIGURE as fixed in position. Alternatively, adjustable backgrounds such as background 36 of FIG. 5 could be used. Finally, a compressed air-jet nozzle 58a is mounted above the viewing zone 32a, as shown.
This invention relates to sorting machines and particularly to such machines adapted for gravity assisted singulation of the items to be sorted.
Previously, sorting machines for tiny items such as grains of rice, have comprised rotating suction wheels or other rotation or reciprocation mechanisms for singulating (i.e. separating and aligning in serial order) the grains for individual viewing by photoelectric means. While most such machines have operated satisfactorily, their volume or time-rate of sorting per ton is low when compared with the rate that is achievable for items of larger size. To increase the sorting rate, it is usually necessary to arrange a large number of sorters in parallel. With rotating and reciprocating mechanisms such as are known to the prior art, the space that is required for parallel arrangement is extremely great and is usually out of proportion to the requirements of economy and efficiency.
Accordingly, it is an object of the invention to provide a compact high speed sorting apparatus for small items.
It is another object of the invention to provide such a sorting apparatus that is adaptable for parallel arrangement and operation of a large number in a small space.
SUMMARY OF THE INVENTION
These and other objects are provided in an apparatus described as follows. A number of steeply inclined tapered slides are arranged for gravity assisted singulation and alignment of items such as rice grains that are introduced at the top from vibrating chutes that are gently inclined in the opposite direction. The chutes extend from a common vibrating feed tray and have adjustable entrance gates to equalize the flow rates of the items. A stationary hopper supplies the feed tray through a flexible coupling. At the bottom of each slide, a photoelectric viewer is arranged to operate an ejector for diverting grains having dark spots. A variable background is provided and is adjusted so that the signal induced thereby is identical to that of the mid-portion of an acceptable grain. Light sources are positioned both above and below the photoelectric means so as to provide extra illumination for the leading and trailing ends of each grain, thus to avoid spurious signals similar to those induced by dark spots but caused by the rounded ends of acceptable grains.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view partly broken away of an apparatus according to the invention;
FIG. 2 is a right side elevation view, partly broken away, of the apparatus of FIG. 1;
FIG. 3 is an enlarged view taken along the plane of lines 3--3 of FIG. 2;
FIG. 4 is an enlarged cross sectional view taken along the plane of lines 4--4 of FIG. 2;
FIG. 5 is an enlarged view of a portion of the apparatus shown in FIG. 2;
FIG. 6 is a schematic view illustrating the operation of the invention;
FIG. 7 is a view illustrating a variation of the apparatus of FIG. 5;
FIG. 8 is an elevation view taken on the plane of lines 8--8 of FIG. 2; and
FIG. 9 is a sectional view taken on the plane of lines 9--9 of FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIGS. 1-4 there are shown a number of elongated, tapered slides 11, each of which has a central longitudinal generatrix 12 steeply inclined (e.g., 35° from the vertical) for gravity assisted separation of small granular items such as grains 13 of rice sliding downwardly thereon. In the art of sorting granular items, it is of the utmost importanct to be able to separate the items and space them out in serial order (i.e. "singulate") so that they may be viewed one at a time and so that a rejection operation takes effect only for the one grain that is defective. In the present invention the elongation of the slides 11 and their considerable vertical extent (e.g., about 40 inches in an actual machine) enlists the separation assistance of gravity in the following way. It is well known that falling bodies accelerate at a constant and substantial rate, so that if two bodies begin falling from the same point at slightly different intervals of time, it follows that the vertical separation between them increases as a function of the acceleration g of gravity and the square of the time (t 2 ) of fall. If two grains of rice are each 0.25 inches long, and one begins to fall at time t o and the other begins to fall 1 millisecond later (i.e., at time t 1 = t o + .001 sec.), then when the second grain has fallen 40 inches, its leading end must be spaced behind the leading end of the first grain by one-fourth inch. In other words, a suitable separation equal to the length of one rice grain can be achieved in a fall of 40 inches even when the grains begin to fall only 1 millisecond apart in time. This minimum time-spacing is equivalent to only about four ten-thousandths of an inch (0.0004 inches) in terms of the initial falling distance of one grain, i.e., when the second grain begins to fall, the first has already fallen 0.0004 inches. In 40 inches of fall, then, the initial spacing is increased nearly 6,000-fold, from 0.0004 to 0.2500 inches. The usefulness of gravity assistance for separating the grains is therefore evident.
In the present invention, the grains are expected to slide down the inclined slides 11 rather than falling perfectly freely, so of course the slight frictional retardation of the grains on the slide tends to diminish the separation achievable by gravity. However, dry friction does not increase substantially with velocity, so its effects may be reckoned as constant and slight. We have seen that for free fall the grains of rice must be spaced apart for time intervals of greater than 1 millisecond at the top of the slide. If the effect of friction adds merely another millisecond to this minimum requirement, there is little disadvantage, for by far the overwhelming bulk of grains coming into the top of each slide 11 are spaced apart in time for greater than 2 milliseconds. Besides the above consideration, the frictional effect of the inclined slides 11 is more than offset by the channeling effect of the tapering shape of the slide. In FIG. 3 it is shown how the slide has an upper-end cross section of U-shape defined by two side walls 14 and a rounded bottom portion 16 of a radius much larger than the transverse radius of a rice grain 13. About one-third of the way down from the top, the slide has narrowed to a bottom portion just precisely fitting the rice grain cross section, and the side walls have converged to define a close-spaced generally V-shaped cross section. Clearly, then even if two grains of rice fell into the upper end of the slide 11 at times less than 2 milliseconds apart, they would nonetheless strike different portions of the slide bottom and, what with the effect of impact forces and the jostling effect produced in the grains by the tapering sides 14, the grains are still constrained to align themselves one behind the other in serial order before they reach the bottom. In fact, it may be said that even if two grains begin their falls at precisely the same instant in time, it is substantially impossible for them to arrive at the bottom end of the slide 11 without being suitably spaced apart in serial order.
If the grains are to derive the maximum effect from their initial time spacing, they should begin their falls from a condition of zero vertical component of velocity. Also it is desirable to reduce impact effects of the grains in the upper end of the slides 11 as much as possible, which requirement calls for the smallest possible horizontal component of velocity as well. Ideally, the grains would drop into the upper part of the slide 11 from a portion of the structure (i.e., the chutes 17) in which they occupied a position at rest (zero velocity in any direction) at the instant immediately before the fall began. This condition is approximately achieved by giving the chutes 17 the gentlest possible slope downward at an inclination in the opposite direction from that of the associated slides 11. The minimum inclination of the chutes 17 is the least inclination at which the grains will slidingly migrate downwardly at a reasonable processing rate when the friction is reduced as by vibrating the chutes 17, as with eccentrically loaded vibrating motor means 18. The chutes 17 are also tapered somewhat, but still at their open ends permit the random showering of grains into the slides 11. A further effect that has been noted with this structural geometry is that bouncing grains strike one another and tend to thus damp or decrease the bouncing effect.
To make utmost use of the space saving structure of slides 11 and chutes 12, a large number of each are arranged in parallel, and the chutes 17 are mounted to extend from a common feed tray 19, from which the chutes are partitioned by adjustable gates 21. Four motors 18 are used in the illustrated device, attached to the tray 19 (only two are shown in FIG. 1). Because the induced vibrating effect varies from chute to chute as a function of mechanical and mass characteristics of the chute, and distance of the chute from the motor, the gates 21 are adjusted individually in actual operation until the rates of flow of grains in all of the chutes are equalized and optimum (about 50 lbs. per hour per chute).
Above the tray 19 is fixedly mounted a hopper 22 for reception of the grains, and a flexible coupling 23 connects the stationary hopper 22 with the vibrating tray 19, so that a closed conduit for the grains is formed from the upper opening 24 of the hopper to the gates 21 of the chutes 17. The slides 11 do not vibrate, nor do any other portions of the apparatus except the coupling 23, tray 19, chutes 17 and motors 18.
As illustrated in phantom in FIG. 2, the tapering of the slides 17 enables a double saving of space in that two full banks of slides 11 may be criss-crossed at the narrower portions thereof, while the wider chutes 17 are divided between two opposite sides of the machine and are abutted side-by-side.
At the bottom end of each slide 11, the rice grains shoot out with considerable velocity upon a trajectory or path 31 (FIG. 5) which is substantially a straight prolongation of the generatrix 12, at least in the region of the predetermined viewing zone 32 adjacent the end of the slide. Each grain 13 is also invariably oriented with its length along the path 31 and is thus viewed from the same angle by a photoelectric viewing means 33 of standard type, disposed at the side of path 31 and provided with lens means 34 to define the zone 32 of view.
Because rice grains are of generally gray-white coloring if acceptable, and are generally translucent, and because unacceptable grains are usually distinguishable by the appearance of dark spots visible from all sides under proper illumination through the translucent interior, it is necessary to illuminate and inspect each grain from only one of its longer sides. To obtain a voltage signal from the photocell 33 indicative of an acceptable grain, the present invention provides a light source 35 shielded from the viewing zone 32 and illuminating a generally gray-white background 36 which is rotatable on an axis 37 abnormal to path 31 so that the background shade can be matched with that of an acceptable grain, and the voltage level 40 of the photocell signal is the same when an acceptable grain is in view as it is when there is no grain in view (FIG. 6). As shown in FIG. 5, the background 36 is rotatable through about 90° by means of a bell crank 38 operated by a pin 39 sliding in a slot 41 on the bell crank and extending from a piston 42.
The illustrative apparatus is of the dark-trip type and provides a positive signal pulse 43 when a dark spot in an unacceptable grain passes through the viewing zone 32. However if the grain is illuminated from only one position adjacent the photocell 33, as is usual in the prior art, the rounded leading and trailing ends of the grain reflect a lesser amount of light to the photocell 33 than comes from the mid-portion of the grain. At the same time, the leading and trailing ends of the grain are cutting off the reflected light from the background 36. The viewing zone is of course as narrow as possible and extends for a considerably less distance in the direction of path 31 than the length of the rice grain, in order to obtain the maximum signal level from the smallest dark spot. But the result of this combination of conditions, when only a single lamp is used, is that the ends of the rice grain appear as dark spots to the photocell and cause spurious defect signals 47 even though the grain may actually have no dark spots.
The precise mechanism of this phenomenon is not fully understood, but it is believed to be caused partly by specular reflection at flat angles of illumination near the extreme tips of the grains, which denies entry of this portion of incident light into the interior of the translucent or "transluminescent" grain, from whence it would ordinarily be glowingly and diffusedly reflected back to the photocell. Since less light gets back from the grain ends, a spurious dark spot is signalled. Also believed to be a cause, is the fact that less light is directly reflected back to the photocell from irregularities on the surface of the ends of the grain, where the surface is at a different angle than that of the long stretch of the mid-portion of the grain. In any event, it has been found experimentally that with only one lamp for illumination, spurious signals do appear.
Accordingly, the invention contemplates the use of at least two light sources 51 and 52 mounted respectively above and below the viewing means 33, 34 so as to provide extra illumination to the ends of the rice grain. The leading end of the grain is given extra illumination by light source 52 to compensate for the loss in illumination that the leading end receives from light source 51. As for the mid-portion of the grain 13, the combined illumination it receives and reflects to the photocell from both light sources adds up to produce a signal of the same general voltage level as that received from the leading end as a result of the more direct illumination of light source 52 above. A similar effect is produced by light source 51 on the trailing end of the grain. The result is an undisturbed steady voltage level signal 40 as the acceptable grain enters the viewing zone, passes through it, and departs. Only if a grain with a true dark spot appears does the photocell produce a deviating positive signal 43 to initiate rejection of the defective grain.
Upon receiving a rejection signal 43, the programmed logic of an electronic controller 56 causes the operation of a compressed-air value 57 and nozzle 58 to emit a quick sharp brief jet or blast of air directed against the side of the grain 13 transversely to the path 31 so as to blow the defective grain along a deviating or deflected path 59 into a reject hopper 61. If, however, the grain 31 is not defective and no signal pulse 43 is produced, the grain continues along path 31 to an acceptable product tube 62, which is laterally elongated so as to be common to all channels, and may in turn be coupled to a bag or other packaging, transporting or storage apparatus.
In the illustrated apparatus, the light sources 35, 51 and 52 are fluorescent tubes operated at high frequency (e.g., 20 kilohertz) and having the ballasts synchronized as by a common coupling 60.
Occasionally, while the apparatus is operating, it is desirable to be able to sample the product that is being accepted in each individual channel of the machine. For this purpose, the tube 62 (FIGS. 8 and 9) is formed with a side opening 63, and a number of individual sampling tubes 64 are mounted to cover the opening 63 in the normal operating condition of the machine, but without interfering with the flow of grains downwardly through the tube 62. The sampling tubes 64 are pivoted as at 66 however, so that the upper ends 67 can be individually tipped inwardly to catch the grains and divert them outwardly through the now-protruding open lower ends 68 and into the hand of the sampler.
Referring now to FIG. 7, an alternative arrangement is shown for use with opague products that must be examined from both sides. A pair of photoelectric examining devices 33a and 33b are placed on opposite sides of the path 31 from slide 11, and each phototube has a pair of light sources 51a, 52a, 51b and 52b, respectively, associated therewith, above and below the phototube. Each phototube is directed toward a background 36a and 36b, respectively, shown in the FIGURE as fixed in position. Alternatively, adjustable backgrounds such as background 36 of FIG. 5 could be used. Finally, a compressed air-jet nozzle 58a is mounted above the viewing zone 32a, as shown.