WO1994020231A1

WO1994020231A1 - Optical sorter

Info

Publication number: WO1994020231A1
Application number: PCT/DK1994/000090
Authority: WO
Inventors: Ole KØSTER
Original assignee: Stormax International As
Priority date: 1993-03-05
Filing date: 1994-03-04
Publication date: 1994-09-15
Also published as: DK24693D0; DK169280B1; DK169280B3

Abstract

An optical sorter for grading oblong articles which are conveyed one at a time mutually spaced and usually placed perpendicular to the direction of conveyance on a conveyor belt. The optical sorter uses laser light and infra-red light sensors and an elctronic camera connected to data-processing equipment arranged to determine whether an article is to be accepted or rejected, and with at least one grading device (70) which is connected to an output from the data-processing equipment (50), and arranged to remove articles under the control of the data-processing equipment. In the new optical sorter the articles are conducted through a 'blanket' of light, preferably laser light, to determine the height or 'sweep' of each article, and the thickness of the article is measured by optical displacement sensors on the basis of distance measurements. In addition the measurements with the optical displacement sensors (44-47) are used to calculate the so-called 'propeller' distortion of the articles by calculating a plane through the three measuring-points and calculating the distance from a fourth measuring-point to the said plane. The objects are photographed by an electronic camera (52) and the data thus recorded are used to clculate the article's length, length variations, width, width variations, rounding, so-called 'banana' distortion, absolute colour and colour differences. The electronic measuring circuit is arranged to provide statistics on the deviations of the sticks (30) from the given limit values for a normal grading and if required for a second grading, and is arranged to display the results on the monitor screen (50).

Description

Title: Optical Sorter

Technical Field

The present invention relates to an optical sorter of the type specified in the preamble of claim 1 .

Background Art

Several machines for the control measurement and grading of articles, for example as described in DK-PS 1 55,274, are already known. An optical sorter in which the articles are conducted through a blanket of light emitted by a light source through a narrow slit in the first part of a device towards a photosensitive receiver in a second part of the device in order to determine the height of each article is known for example from EP-A-0,091 ,854 and EP-A-0,007,248. An optical inspection sys¬ tem using laser light to detect the quality of organic material, such as food, is known from WO-90/01 693.

The articles are primarily oblong articles such as chopsticks or ice-lolly sticks, especially made of wood.

Brief Description of the Invention

The object of the present invention is to develop an optical sorter which is on the one hand much easier for the user to operate than the types known so far and which on the other hand uses more sophisticated control measurement technology such that it will be a faster-operating sorter which grades on the basis of better, i.e. more accurate, measure¬ ments than the types already known.

This object is to be achieved with an optical sorter of the type specified in the introduction and characterised by the features specified in the characterising clause of claim 1 .

The articles are typically ice-lolly sticks which must preferably be as flat as possible. The data-processing equipment is arranged to monitor, on the basis of the above measurement, which involves four measuring points, two at each end of the article (such that the four measuring points should define a rectangle), that all the measurements are in the same plane. This makes it possible to monitor, more quickly than with any method known hitherto, that the article (in particular the ice-lolly stick) is flat.

Usually, the articles will be located perpendicular to the direction of motion of a conveyor belt.

The "sweep" measurement by the "blanket" of laser light measures the height, or more accurately the "shadow", of the article in a manner already known. If this height is greater than a given size, e.g. the thick¬ ness of an ice-lolly stick, it means that the article is curved either upwards or downwards and any such defect will be revealed by the "sweep" measurement irrespective of whether the curvature is convex or concave.

The measuring method described has a further advantage inasmuch as it involves no physical contact with the article and there are no moving parts in the measuring equipment itself. Only the conveyor with the articles is moving. This also makes it easier to adjust settings such as grading criteria while the sorter is operating.

The features specified in the dependent claims help to improve the functioning of the sorter, and in particular its measuring accuracy and operating speed. Brief Description of the Drawing

In the following the invention will be described in greater detail with reference to the accompanying drawings, in which

Fig. 1 shows an example of a preferred embodiment of an optical sorter according to the invention,

Fig. 2 shows the measuring chamber of the sorter viewed from the front,

Fig. 3 shows the first measuring section and a measuring chain,

Fig. 4 shows the second measuring section,

Fig. 5 shows the measuring chain viewed from above,

Fig. 6 shows the compressed air cylinders for removing faulty articles,

Figs. 7a and 7b show typical set-up displays,

Figs. 8a, 8b and 8c show typical displays for adjustment, and

Fig. 9 shows a typical display of the image which is formed by means of the camera.

Best Mode for Carrying Out the Invention

Fig. 1 shows an example of a preferred embodiment of the sorter ac¬ cording to the invention. The articles come from some feeder device not shown in the Figure, but which in practise is located to the right of the apparatus in Fig. 1 as indicated by the arrow 12, via a magazine, which functions as a storage vessel (buffer store). From there they are picked up by a slat conveyor not shown in the Figure. A brush is mounted to brush off any excess material, such that only one stick lies on each slat of the slat conveyor.

They then reach a transitional point where they are transferred from the slat conveyor to a new conveyor designated the measuring chain 22.

The manner in which this transfer is effected is that, above the system, there are a number of pins on a carrier wheel which from above guides the sticks over on to the measuring chain. In addition the sticks run or slide on rails 24 and in between certain lateral guides and from there they are carried on the measuring chain into the measuring chamber 26, which is surrounded by preferably black, matt wall panels to prevent undesired reflection of light.

Above the measuring chamber 26 is a monitor 50 where the operator can observe from the display, for example as shown in Figs. 7a, 7b, 8a, 8b, 8c and 9, the progress of the measuring process. The monitor is also used for the trial runs and adjustments of the sorter, in this case in conjunction with a track ball 55 which lies protected and partly hidden below the operating panel 60, which is furnished with start and stop buttons.

On the left of the measuring chamber is a box 70 with a pair of com¬ pressed-air cylinder pistons which remove the rejected or second-grade sticks from the chain conveyor. The operator can operate the machine manually with a hand wheel 80.

The measuring chain 22 is shown diagrammatically in Figs. 3 and 5, where for the sake of simplicity the actual links of the chain have not been drawn in, but the upward-projecting pins 23 are shown. The chain is typically a 3/8" (9,525 mm) chain which has a carrier pin 23 on every second link. The distance between the sticks 30, the so-called stick spacing, thus become 3/4" (19,050 mm). At each end the sticks are supported by two rails 24 as shown in Fig. 5, and are pushed forward by the carrier on the two measuring chains 22.

The measuring chain is preferably inclined so that the sticks are carried slightly upward.

In a preferred embodiment the new machine according to the invention comprises a chain conveyor with replaceable measuring chains which can be mounted on chain sprockets, preferably chain sprockets with two rows of teeth, such that the distance between the chains can be regu¬ lated to accommodate wooden articles of differing lengths.

In the measuring field, which is within the measuring chamber 26, va¬ rious different properties can be measured optionally, such as "pres¬ ence", "sweep", "propeller" distortion, "thickness", "length", "width", "banana" distortion, "colour", as explained in the following.

The electronic equipment operates at a speed which allows the monito- ring of - for example - 25 sticks a second, and the registration of several measurement values of a given property in several positions for each stick. The thickness, for example, can be measured at three adjacent points, as can be seen from the screen display in Fig. 8c.

The first measuring field could simply be used to detect the presence of a stick, for example by means of a photoelectric cell.

The sticks are preferably to be measured for curvature, which is also called "sweep", and the first measuring field therefore preferably con¬ sists of a laser sensor 32, for example a Type 2-12 laser sensor from the Japanese firm Keyence, i.e. a laser emitter and receiver. Through a narrow slit 36 the emitter beams a "laser blanket" which "hangs" vertic- ally across the measuring chain 22, and in the preferred embodiment the "laser blanket" measures 10 x 1 mm in cross-section. This produces a vertical measuring zone across the measuring chain. It measures both above and below the level, i.e. both above and below the stick 30. The laser emitter 32 and the laser receiver 32 are mounted one on each side of the rail 24 and the measuring chain 22 with the sticks 30 as sketched roughly in Fig. 5. A notch 34 in each rail 24 ensures that the laser beam can pass freely across and below the sticks 30. The actual measuring chain 22 is slightly below the sticks 30, as shown in Fig. 3. Close to the notch 34 is the outlet of a blowing nozzle not shown in the Figure, which blows the area clean at predetermined intervals. Appropriate exhaustion facilities have also been established. The nozzle typically blows for three seconds every half hour. The intervals are set according to the amount of dust generated by the product in question.

The next measuring section 42 preferably lies exactly three inches from the middle of the first measuring section 32, and this corresponds to the distances between a fixed, integral number of measuring positions. The distances are determined by the choice of chain, and normally a 3/8" chain link is used, i.e. a chain length of 7,62 cm or 3" has eight chain links with carrier pins on every second link, i.e. on four links, and has locations for four sticks on the intermediate links.

In this position lie four measuring cells 44, 45, 46, 47 as shown in Fig. 4, in the form of optical displacement sensors of a type developed in Denmark and distributed by Dansk Mikroelektronik (DME) under the name ODS 30. Each optical sensor consists of an emitter which emits an infra-red light beam, which strikes the stick 30 at a measurement centre, the centre point M1 , M2, which is a 1 mm round ring or circle, and a receiver, which registers the reflected light beam. This measures the distance down to the stick from each of the four sensors which are positioned in pairs on each side, two above the stick and two below the stick as shown in Fig. 4.

An associated electronic control circuit, which is based on known tech¬ nology and is therefore not described here in more detail, controls the four sensors such that they alternately work together in pairs, and such that they work as "master and slave". The distance from each sensor to a stick is normally set at about 30 mm. The sensors 44-47 are mounted by known means on slides not shown in the Figure, on spindles likewise not shown in the Figure, which make it possible to slide the sensors horizontally, and thus to alter the distances between the measurement centres Ml , M2, which are preferably positioned at each end of the stick, about 5-10 mm from the ends of the stick 30.

The distance down to the stick is measured on both sides, and below are the other two sensors 46, 47 which likewise measure the distance from the stick. On the basis of these measurements the thickness can be determined at both ends of the stick, and the points are usually as close to the rounded ends as possible, i.e. in practice they are spaced 6- 7 mm from the end of the stick. Since the thickness is measured in accordance with known principles for the measurement of thickness, the measurement principle will not be described in any detail here.

At the same time the uppermost measuring cells are used solely to measure whether a stick has been twisted into a form like that of a propeller. This is therefore called the "propeller" measurement. If a stick is twisted like a propeller, it cannot lie against the travel rails 24 at both ends and both sides. The measuring principle is such that the uppermost cells make two measurements at each end, and if there is a difference between the four measurement results, a plane is calculated through three of the measuring points and finally the distance from this plane to the fourth measurement point is calculated. This produces an expression of the stick's "propeller" distortion (i.e. its degree of torsion).

Thereafter, about twelve spaces (24 chain links) to the left in Fig. 2 is shown a centre line C which is the measurement centre for an electronic camera 52, and the remainder of the measurements are done with the camera. A partially screened light source 54 is mounted in the top of the measuring chamber beside the camera 52.

The camera 52 is recording a picture of the conveyor, i.e. the measuring chain with the sticks 30. As can be seen from Fig. 2, the centre line C of the camera is essentially perpendicular to the measuring chain 22. The measurement area is illuminated by the light 54 which is so sus¬ pended that it does not obscure the view of the camera, and so that direct reflections up into the camera are avoided. All rails and surfaces, especially in the measuring area, are painted black to prevent any inter¬ ference with the image of the sticks 30.

On the basis of the data which the camera records, the apparatus de¬ termines the length, width and the bending which is called the "banana" distortion of the stick, a fault which typically occurs if there is a knot or flaw in the wood) as well as its colour.

Each of the four measurements obtained by electronic image processing on the basis of the data recorded with the camera, is itself in turn the result of several measurements.

The length of the sticks is measured along several lines. A maximum length is recorded, as well as a length difference which is in fact an expression of the rounding at the end of the stick, making it possible to monitor that the rounding is correct. The measurement is made from an imaginary line on the stick to the curved or rounded end, and this indi¬ cates whether the rounding is correct.

The same applies to the width of the stick, which is a total width based on 32 measurements evenly spaced along the stick. A width difference is also measured, which is partly due to the rounding viewed from the other direction. The 32 width measurements will reveal if there are any excessively deep cuts into the edges. A comparison of the width of one area with the width of an adjacent area establishes whether the edge is straight.

The "banana" distortion is identified by measuring the distance from an "imaginary" straight line (which may be a line of symmetry for the stick or a line parallel with such a line of symmetry) to one or both of the side edges of the stick. If the side edge is curved, as viewed by the camera, the stick resembles a banana, and should be rejected.

The same applies to colour measurement. On the basis of a large num¬ ber of measurements regularly spaced along the stick, an absolute colour is measured, and at the same time a colour difference, on the basis of colour comparisons with the adjacent areas. A stick with a knot or flaw will normally be rejected because of excessive colour differences.

It is a condition for the acceptance of the stick that the colour differ¬ ences are no greater than a predetermined limit value. One can further¬ more define the criteria such that the absolute colour must lie within pre¬ determined limits, in practice one will often only specify a limit for how dark a stick may be, since light-coloured sticks have a directly appetizing effect.

After the measuring the measurement results are processed and com- pared with preset or learned values which may involve limit values for a first grading and a second grading, such that the sticks are divided into a Group 1 , Group 2 and Group 3. In practice this grading is effectuated on the conveyor belt by two pulse-controlled lubrication-free com- pressed-air cylinders which can operate at speeds up to 40 Hz, with pistons in plastic material.

The two compressed-air cylinders are placed a given number of positions after the measuring centre for the camera. This number must be precise¬ ly coordinated with the pulse control of the compressed-air cylinders. First, the processing of the measurement results must be concluded, such that the grade of a given stick has been determined, then at the exact moment when the stick has reached the grading station a pulse is emitted if the stick is to be ejected from the conveyor belt.

The cylinder piston is so mounted that it slides perpendicular to the direction of movement of the conveyor belt, and such that the piston can strike a stick on the belt with complete precision as it passes the piston. The stick which is to be rejected is thus ejected into a channel 71 which conducts it to the container for rejected sticks. Similarly, another piston has been mounted in a compressed-air cylinder which can eject a second-grade stick into a channel 71 for second-grade sticks which are then conducted along channels designed for the purpose to a destination for second-grading.

The compressed air used is preferably generated by a compressed-air system or a compressed-air bottle mounted in the space below the measuring chamber. Before the compressed air is conveyed to the appli¬ cation points, it is cleaned by passing through two filters, similarly mounted below the measuring chamber. Compressed air is used both for the above-mentioned compressed-air cylinders and for the flushing of the sensors. In addition, the whole electronics chamber with the camera electronics is subjected to slight overpressure to prevent pollution of the electronics and the camera, for example by dust from wood processing machinery located nearby.

Regular dust exhaustion and dust blowing has been installed, inasmuch as there are blowing nozzles close to the laser blanket, in order to clean the emitter and receiver lenses/windows 36. At the same time dust is exhausted from the area for distance measurement, which is performed by infra-red light.

In the preferred embodiment of the invention the whole machine can operate at a speed of 25 sticks a second. If necessary the compressed- air cylinder can reject 25 sticks a second.

On a monitor mounted above the measuring chamber the operator can observe which features are being measured and the limit values set for the various measurements and gradings.

With a track ball 55, which can be locked during normal operation, the operator can adjust the machine settings to the limit values required during grading.

On the monitor screen the operator can see the image registered by the camera 52. The operator can also choose between a number of func- tions and observe all the results of the measurement on the displays.

Figs. 7a and 7b shows the displays for a "basic set-up" menu used when the system is to be started up, and while the machine is inactive. From this menu the operator chooses which measuring cells are to be active and sets parameters for these cells. In this start-up menu the operator also specifies the chain type mounted on the machine. In the event that particularly wide articles are to be measured, a chain with a pin for every fourth link is used, such that the article spacing will be •I Vz " (i.e. 38, 1 mm), and all the stick positions normally used will be halved. Fig. 7b gives an overview of the various measuring cells, their positions in relation to the measuring chain, whether the cell is in use, and whether the grading is normal.

The display in Fig. 8a shows the data for the "sweep" cell: at the top it shows the chain position of the cell and where the measurement starts and ends; below are shown the direct measurements in the form of numerical values; and at the bottom is a "bar chart" which clearly illu- strates the measurement results for the last four articles, inasmuch as each of the low "bars" indicates a sweep measurement of an article, four measurements of each article, and the intervening four high "bars" represent the intermediate parts of the measuring chain without articles, i.e. the carriers.

Figs. 8b and 8c show corresponding displays for the calculation of "pro¬ peller" distortion (torsion) and the measurement of thickness respective¬ ly.

Fig. 9 shows a display indicating a measurement area with an article whose length, length variations, width, width variations, rounding, "banana" distortion, absolute colour and/or colour differences are calcu¬ lated by the data-processing system on the basis of the data from the camera 52.

Adjustments, such as changes in the limit values for normal grading and second-grading, can be made during continued operation of the sorter.

A statistics program calculates the number and/or percentages of art¬ icles that are rejected as a result of the different types of measurement. In the above drawings the articles shown as examples are all ice-lolly sticks, but it should be clear that the optical sorter can be used for several other kinds of articles in wood and plastic etc.

Claims

Claims.

1. An optical sorter for sorting or grading articles, especially oblong articles which are conveyed forward one at a time, mutually spaced, the optical sorter comprising light-emitting and light-receiving devices con¬ nected to data-processing equipment, to determine whether an article is to be accepted or rejected, and with at least one grading device which is connected to an output from the data-processing equipment, and arranged to remove articles under the control of the data-processing equipment, c h a ra cte ri se d in that the height/thickness of the article is measured by optical displacement sensors (44, 45, 46, 47) on the basis of distance measurements, and that the measurements with the optical displacement sensors (44 - 47) are used to calculate the article's so-called "propeller" distortion (i.e. the degree of torsion in the mainly flat article in relation to a plane surface) by calculating a plane through three measuring points, and calculating the distance of a fourth measuring point from the said plane.

2. An optical sorter as claimed in claim 1, characterised in that a picture of the articles is recorded by an electronic camera (52), and that the data thus recorded are used to calculate one or more of the following properties of the article: length, length variations, width, width variations, rounding, "banana" distortion, absolute colour and/or colour differences.

3. An optical sorter as claimed in claim 1 or2, c h a ra cte ris ed in that the articles are conducted through a "blanket" of light, preferably laser light, which is emitted by a light emitter through a narrow slit (36) in the first part of a device (32) to a photosensitive receiver in a second part of the device (32), in order to determine the height (thickness) or "sweep" of each article

4. An optical sorter as claimed in claim 1, 2 or 3, c h a r a ct e r¬ ised in that the measuring circuit is arranged to generate statistics on the sticks (30), deviations from the given limit values for normal grading and if required a second grading, and is arranged to display the results on the monitor (50).

5. An optical sorter as claimed in claim 3, ch aracte ri sed in that the articles (30) lie and slide upon rails (24), inasmuch as they are con¬ veyed forward by chains (22) with carrier pins (23), and that notches (34) have been made in the travel rails (24) so that the light blanket may pass unimpeded during measurement both above and below the articles (30).

6. An optical sorter as claimed in one or more of the above claims, c h a racterised in that the grading is effectuated by a number of pulse-controlled lubrication-free compressed-air cylinders with pistons in plastic material, preferably able to operate at speeds up to about 40 Hz.

7. An optical sorter as claimed in one or more of the above claims, c h a r a c t e r i s e d in that a compressed-air system has been so arranged as to supply the electronics chamber above the camera (52) with slight overpressure in order to prevent pollution in the electronics chamber.

8. An optical sorter as claimed in claims 3 and 6, c h a ra cte r¬ i s e d in that a jet nozzle has been installed close to the devices (32) which emit and receive a "light blanket" to measure the "sweep" of the articles, and where the said jet nozzle at regular intervals blows com- pressed air out to keep the light emitting devices (32) and in particular the slits (36) through which the light passes clean.

9. An optical sorter as claimed in claim 6, ch aracterised in that an exhaustion device has been mounted in the area near the displace¬ ment sensors (44, 45, 46, 47) in order to remove any dust particles.