US3738484A

US3738484A - Sorting machine

Info

Publication number: US3738484A
Application number: US00124320A
Authority: US
Inventors: M Hoover; W Long
Original assignee: Mandrel Industries Inc
Current assignee: MANDREL IND INC US; Satake USA Inc; Mandrel Industries Inc
Priority date: 1971-03-15
Filing date: 1971-03-15
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12
Also published as: DE2212515A1; DE2212515C3; CA961804A; FR2129670A5; DE2265179A1; DE2265179C2; JPS5425265B1; BR7201481D0; NL7203430A; GB1354623A; DE2212515B2

Abstract

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

Elite States Patent [1 Hoover et a1.

1 SORTING MACHINE [75] Inventors: Michael C. Hoover; William C. Long,

both of Houston, Tex. [73] Assignee: Mandrel Industries, Inc., Houston,

Tex.

[22] Filed: Mar. 15, 1971 [21] Appl. No.: 124,320

[52] U.S. Cl. 209/73, 209/111.6 [51] Int. Cl. B07c 1/04, B070 5/342 [58] Field of Search 209/73, 111.6, 111.7,

[56] References Cited UNITED STATES PATENTS 877,322 1/1908 Gebler 226/566 3,066,797 12/1962 Fraenkel.... 209/111.6 3,179,247 4/1965 Hutter 209/74 3,385,434 5/1968 Nelson.... 209/111.6 3,482,686 12/1969 Wood 209/l1l.6 X

Primary Examiner-Richard A. Schacher Att0rney-Robert G. Clay 111 $73,484 June 12, 1973 [57] ABSTRACT 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 hav ing 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.

10 Claims, 9 Drawing Figures Pmmmm 3.738.484

sum 1 on;

UH HMHHQM gunman INVENTOR.

I MICHAEL C. HOOVER ATTORNEY PAIENIEI] Jim 2 I973 SW11 2 BF 4 INVENTOR,

MICHAEL C. HOOVER flaw/a ATTORNEY PAINTED- 3 man INVENTOR.

MICHAEL C. HOOVER AI'IORNEY msmwm z 5.738.484

SIHT HIF4 "REJECT" LEVEL NORMAL I SIGNAL RANGE 40 GOOD GOOD LIGHT GRAIN GRAIN MINOR MAJOR SPURIOUS DARK DEFECT DEFECT DEFECT GRAIN GRAIN SIGNALS INVENTOR.

MICHAEL G HOOVER BY flab/ea AT TOHNI. Y

E'II3 E SORTING MACHINE 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 ta-' pered 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 midportion 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. I 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 33 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 99 of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 14 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 of fall. If two grains of rice are each 025 inches long, and one begins to fall at time t and the other begins to fall I millisecond later (i.e., at time t t .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 I millisecond apart in time. This minimum time-spacing is equivalent to only about four tenthousandths 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 Vshaped 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 1 1 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 l7 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 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 ifa 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., 2O 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 36!), respectively, shown in the FIG- URE 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.

What is claimed is: l. A semi-free-fall sorting apparatus for granular items, comprising:

an elongated slide tapering downwardly to the diameter of said items and having a central longitudinal generatrix that is steeply inclined for gravity separation of said granular items sliding downwardly thereon, and for aligning said sliding items in serial order along a common path corresponding to said central generatrix;

the upper end of said slide having a gently rounded bottom portion as seen in cross-section along the line of said central generatrix, the curvature radius of said bottom portion being substantially greater than the mean radius of said granular items;

said slide tapering from upper to lower end so that the cross section along the direction of said central generatrix at the lower end displays a curved bot tom portion of curvature radius substantially in the same order as said mean radius of said granular items;

means for introducing said items in a random shower into the upper end portion of said slide; and

means for examining and sorting said items aligned in said serial order.

2. An apparatus as recited in claim 1 wherein:

said slide has spaced side walls extending from said curved bottom portion to define a U-shaped cross section at said upper end;

said side walls being angled to converge downwardly toward one another to define a generally V-shaped cross section at said lower end.

3. Apparatus as recited in claim 1 wherein:

said means for introducing said items to the upper end of said slide includes a vibrating tapered chute in the same vertical plane as said slide but gently inclined in the opposite direction so as to discharge said granular items into said slide with the least possible vertical component of velocity and a horizontal component of velocity oppositely directed to the horizontal velocity component that is to be induced in said items by said slide.

4. The combination recited in claim 3, wherein said apparatus also includes:

a plurality of said slides and said examining and sorting means arranged in parallel and a corresponding plurality of said chutes also in parallel;

said chutes extending from a common feeding tray mounted for vibration;

motor and eccentric mass vibrating means mounted to vibrate said tray and chutes; and

each of said chutes having an adjustable gate at the tray end thereof to equalize the flow rate of said items despite differences in the vibrating effect resulting from differences in the chutes and their distances from the vibrating means.

5. The combination recited in claim 4, wherein said apparatus also includes:

stationary hopper means mounted above said tray for reception of said granular items;

flexible coupling means between said hopper means and said tray;

said hopper means, flexible coupling means and tray being arranged to define a closed conduit for said granular items from the entrance to said hopper means to the opening of said adjustable gates to said chutes.

6. The combination recited in claim 5, wherein:

said slides are arranged in two criss-crossed banks;

the chutes for said respective banks extending from opposite sides of a feeder tray and hopper means;

said examining and sorting means being arranged in two corresponding banks beneath said slides.

7. The combination recited in claim 1, wherein said examining and sorting means includes;

photoelectric viewing means disposed beside said path for viewing a zone of said path no longer than the mean length of said granular items in their sliding orientation with respect to said slide;

at least two light sources disposed respectively above and below said photoelectric means along the length of said path;

ejection means adjacent said path for selectively diverting said items therefrom upon signal from said photoelectric means;

receptacle means on said path below said ejection means for receiving undiverted items;

a third light source positioned on the opposite side of said path from said viewing means and shielded from said viewing zone;

variable background means positioned adjacent said path directly opposite said viewing means and illuminated by said third light source and adjustable to induce a signal from said photoelectric means that is substantially identical to the signal induced by passage of the mid-portion of an acceptable one of said items;

said ejection means being adapted to operate only when the signal from said photoelectric means differs appreciably from said background-induced signal;

said background means including a flat-surfaced background uniformly colored in the same general color as said acceptable items;

said background being rotatably adjustable about an axis abnormal to said flat-surface so as to deepen or lighten the apparent shade of said background as viewed by said photoelectric means, thus to induce said signal identical with that of an acceptable item.

8. The combination recited in claim 7 and adapted for the sorting of elongated gray-white rice grains as said items, wherein:

said background is of generally gray-white color and is rotatable to reflect light to said photoelectric means in the same intensity as an acceptable grain of said rice;

said ejection means being calibrated to operate upon reception of a signal indicating a dark spot in one of said rice grains, said signal having a voltage amplitude level differing appreciably from that provided by said background.

9. The combination recited in claim 7, wherein:

two of said viewing means are provided on opposite sides of said path for viewing opaque items; and four light sources are provided, one above each viewing means, and one below each viewing means; and two background means are provided, each aligned with one of said viewing means and said viewing zone.

10. The combination recited in claim 7, wherein said receptacle means for receiving acceptable undiverted items includes:

a first elongated tube aligned on said path and having an opening in the upper side thereof; and

a second elongated tube pivoted on the upper side of said first tube so as to cover said opening in a normal position of said second tube aligned parallel to said first tube;

said second tube being pivotable to a sampling position wherein the upper end of said second tube intrudes through said opening into said first tube and diverts said acceptable items into said second tube for examination as a sample.

Claims

1. A semi-free-fall sorting apparatus for granular items, comprising: an elongated slide tapering downwardly to the diameter of said items and having a central longitudinal generatrix that is steeply inclined for gravity separation of said granular items sliding downwardly thereon, and for aligning said sliding items in serial order along a common path corresponding to said central generatrix; the upper end of said slide having a gently rounded bottom portion as seen in cross-section along the line of said central generatrix, the curvature radius of said bottom portion being substantially greater than the mean radius of said granular items; said slide tapering from upper to lower end so that the cross section along the direction of said central generatrix at the lower end displays a curved bottom portion of curvature radius substantially in the same order as said mean radius of said granular items; means for introducing said items in a random shower into the upper end portion of said slide; and means for examining and sorting said items aligned in said serial order.

2. An apparatus as recited in claim 1 wherein: saiD slide has spaced side walls extending from said curved bottom portion to define a U-shaped cross section at said upper end; said side walls being angled to converge downwardly toward one another to define a generally V-shaped cross section at said lower end.

3. Apparatus as recited in claim 1 wherein: said means for introducing said items to the upper end of said slide includes a vibrating tapered chute in the same vertical plane as said slide but gently inclined in the opposite direction so as to discharge said granular items into said slide with the least possible vertical component of velocity and a horizontal component of velocity oppositely directed to the horizontal velocity component that is to be induced in said items by said slide.

4. The combination recited in claim 3, wherein said apparatus also includes: a plurality of said slides and said examining and sorting means arranged in parallel and a corresponding plurality of said chutes also in parallel; said chutes extending from a common feeding tray mounted for vibration; motor and eccentric mass vibrating means mounted to vibrate said tray and chutes; and each of said chutes having an adjustable gate at the tray end thereof to equalize the flow rate of said items despite differences in the vibrating effect resulting from differences in the chutes and their distances from the vibrating means.

5. The combination recited in claim 4, wherein said apparatus also includes: stationary hopper means mounted above said tray for reception of said granular items; flexible coupling means between said hopper means and said tray; said hopper means, flexible coupling means and tray being arranged to define a closed conduit for said granular items from the entrance to said hopper means to the opening of said adjustable gates to said chutes.

6. The combination recited in claim 5, wherein: said slides are arranged in two criss-crossed banks; the chutes for said respective banks extending from opposite sides of a feeder tray and hopper means; said examining and sorting means being arranged in two corresponding banks beneath said slides.

7. The combination recited in claim 1, wherein said examining and sorting means includes; photoelectric viewing means disposed beside said path for viewing a zone of said path no longer than the mean length of said granular items in their sliding orientation with respect to said slide; at least two light sources disposed respectively above and below said photoelectric means along the length of said path; ejection means adjacent said path for selectively diverting said items therefrom upon signal from said photoelectric means; receptacle means on said path below said ejection means for receiving undiverted items; a third light source positioned on the opposite side of said path from said viewing means and shielded from said viewing zone; variable background means positioned adjacent said path directly opposite said viewing means and illuminated by said third light source and adjustable to induce a signal from said photoelectric means that is substantially identical to the signal induced by passage of the mid-portion of an acceptable one of said items; said ejection means being adapted to operate only when the signal from said photoelectric means differs appreciably from said background-induced signal; said background means including a flat-surfaced background uniformly colored in the same general color as said acceptable items; said background being rotatably adjustable about an axis abnormal to said flat-surface so as to deepen or lighten the apparent shade of said background as viewed by said photoelectric means, thus to induce said signal identical with that of an acceptable item.

8. The combination recited in claim 7 and adapted for the sorting of elongated gray-white rice grains as said items, wherein: said background is of generally gray-white color and is rOtatable to reflect light to said photoelectric means in the same intensity as an acceptable grain of said rice; said ejection means being calibrated to operate upon reception of a signal indicating a dark spot in one of said rice grains, said signal having a voltage amplitude level differing appreciably from that provided by said background.

9. The combination recited in claim 7, wherein: two of said viewing means are provided on opposite sides of said path for viewing opaque items; and four light sources are provided, one above each viewing means, and one below each viewing means; and two background means are provided, each aligned with one of said viewing means and said viewing zone.

10. The combination recited in claim 7, wherein said receptacle means for receiving acceptable undiverted items includes: a first elongated tube aligned on said path and having an opening in the upper side thereof; and a second elongated tube pivoted on the upper side of said first tube so as to cover said opening in a normal position of said second tube aligned parallel to said first tube; said second tube being pivotable to a sampling position wherein the upper end of said second tube intrudes through said opening into said first tube and diverts said acceptable items into said second tube for examination as a sample.