GB1579741A

GB1579741A - Sorting of items into different classes

Info

Publication number: GB1579741A
Application number: GB9877A
Authority: GB
Original assignee: UK Secretary of State for Industry
Current assignee: UK Secretary of State for Industry
Priority date: 1978-01-09
Filing date: 1978-01-09
Publication date: 1980-11-26

Description

(54) IMPROVEMENTS IN OR RELATING TO SORTING OF ITEMS INTO DIFFERENT CLASSES (71) I, THE SECRETARY OF STATE FOR INDUSTRY, London do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the sortof items into two different classes from a mixture thereof, when a characteristic difference between the classes of item is that one class act as specular reflectors of a particular type of electromagnetic radiation while the other class act as diffuse reflectors of such radiation.

Particularly, though not exclusively, the invention is concerned with the sorting of plastics and paper items, (the term "paper" being intended herein also to encompass paper products such as cardboard and the like). Plastics items generally act as specular reflectors of electromagnetic radiation of wavelengths around 3 um in particular and otherwise in or near the visible range of wavelengths in general, while paper items act as diffuse reflectors in the same ranges.

In the area of municipal refuse management, both economic and environmental considerations make it increasingly desirable to reclaim those constituents of collected household refuse which can be put to good use. An important example of this is the reclamation of waste paper for re-processing, e.g. for use in the manufacture of paper boards, (in which case the reclaimed paper should contain less than 5% of contraries).

On the other hand, the high cost of refuse collection means that it is seldom practicable to make separate collections of potentially useful refuse constituents, rather it is normal to collect all the refuse together so that it is necessary for any constituents which it is desired to reclaim to be subsequently separated from the remainder of the refuse. In the case of reclaiming waste paper mechanical separation techniques already exist whereby the paper can be quite readily separated from the majority of other usual household refuse constituents.However, such techniques frequently result in films and sheets of flexible plastics in the collected refuse being separated from the remainder of the constituents along with the paper and there is consequently a need for a reliable automatic method of sorting out these two types of materials, sorting by hand being costly, time consuming and unpleasant. Such a method may be of value not only in the area of municipal refuse management but also in any other situation where items of paper and plastics have become mixed and it is desired to separate them.

In the first aspect the invention resides in a method of sorting items into two different classes from a mixture of the items, a characteristic difference between the classes of item being that one class act, relative to the other class, as specular reflectors of a particular type of electromagnetic radiation and have surfaces which are not entirely regular while the said other class act, relative to the said one class, as diffuse reflectors of such radiation, which method comprises the steps of;; (i) illuminating the items with a beam of radiation of the said type, (ii) providing relative movement between the beam and the items in a direction having a component normal to the direction of the beam, (iii) detecting fluctuations as a function of time in the intensity of the radiation reflected from the items, (iv) identifying from amongst such fluctuations pulses having both an intensity greater than a predetermined critical intensity and a duration smaller than a predetermined critical duration, which pulses are indicative of specular reflectors, and (v) separating items belonging to said one class from those belonging to the said other class in response to the identification of such pulses.

In a second aspect the invention resides in apparatus for sorting items into two different classes from a mixture of the items, a characteristic difference between the classes of item being that one class act, relative to the other class, as specular reflectors ofa particular type of electromagnetic radiation and have surfaces which are not entirely regular while the said other class act, relative to the said one class, as diffuse reflectors of such radiation, which apparatus comprises (i) a source of a beam of radiation of the said type to illuminate the items, (ii) means of providing relative movement between the beam and the items in a direction having a component normal to the direction of the beam, (iii) means for detecting fluctuations as a function of time in the intensity of the radiation reflected from the items, (iv) means for identifying from amongst such fluctuations pulses having both an intensity greater than a predetermined critical intensity and a duration smaller than a predetermined critical duration, which pulses are indicative of specular reflectors, and (v) means for separating items belonging to said one class from those belonging to the said other class in response to the identification of such pulses.

In the case when the two classes of items comprise paper and plastics items, the wavelength of the electromagnetic radiation employed is conveniently around 3 pom, or otherwise in or near the visible range of wavelengths, and may conveniently be produced by a laser.

In a preferred embodiment of the invention the items to be sorted are transported one by one, on a conveyor belt or the like, past a source of the electromagnetic radiation and a detector adapted to produce an electrical output signal the amplitude of which varies with the intensity of the radiation reflected from the source to the detector by the passing items. In such an arrangement it has been found that the amplitude fluctuations in the detector output when a diffuse reflector passes the source will be predominantly of relatively low frequency, while the amplitude fluctuations in the dctector output when a specular reflector passes the source will be predominantly of relatively high frequency, provided that the surface of the latter is not entirely regular; (this phenomenon is more fully described in the ensuing particular description).The identifying means in such an embodiment may thus perform its identification of the class to which each item belongs on the basis of a determination of the range of the dominant frequencies in the detector output. According to a further aspect of the invention, there is provided a waste materials management plant including apparatus according to the invention.

The invention will now be more particularly described, by way of example, with reference to the drawings filed with the pro.

visional specification in which: Figure 1 is a schematic pictorial representation of one embodiment of apparatus in accordance with the invention for separating films and sheets of flexible plastics from paper items e.g. in a municipal refuse sorting plant after separation from the remainder of the refuse constituents; Figure 2 schematically indicates the optical system of the sensing and control unit of Figure 1;and Figure 3 is a block diagram of the electronic section of the sensing and control unit of Figure 1.

Referring to Figure 1, the apparatus comprises a conveyor belt 1 upon which the paper and plastics items to be separated are deposited so as to be conveyed in the sense of arrow "A" one by one past a sensing and control unit 2 and a blower unit 3. The blower unit 3 comprises a constantly running blower whose discharge can either be directed by a nozzle 3A across the surface of the conveyor belt 1, or through a vent 3B directed away from the conveyor belt, depending upon the positioning of a flap 3C. The flap 3C is normally biased into its raised position in which the blower discharges through the vent 3B, but it can be lowered by the operation of a pneumatic actuator 4.The actuator 4 is itself controlled by the unit 2 so that whenever the latter senses the presence of a plastics item on the conveyor belt the flap 3C is lowered to direct the blower discharge through the nozzle 3A and across the surface of the belt to blow the item off the belt into a receptacle 5. When paper items are sensed however, the flap 3C is raised to direct the blower discharge through the vent 3B away from the conveyor belt, thereby allowing the paper items to continue along to the end of the belt whence they fall into a second receptable 6.

Referring now to Figure 2, the unit 2 comprises a laser 21 producing a beam "B" of radiation in the visible range which is directed down by a mirror 22 to illuminate a small area of the conveyor belt 1 and, in turn, the various items which are conveyed thereby. A portion of the laser light reflected by the items on the belt as they pass the unit 2 is collected by a lens 23 and focussed onto a silicon photodetector 24 whose output is fed to the electronic section indicated in Figure 3.

A filter 25 to pass only the wavelength of the laser light is also included.

The light reflected by each item on the belt as it passes the unit 2 is converted into a corresponding electrical signal by the photodetector 24 the amplitude and duration of which is dependant upon the intensity and duration of the received light. Paper is a diffuse reflector of visible light and of radiation of wavelengths around 3 pom and so the intensity of the light received by the photodetector from a paper item during its passage past the unit 2 will be reasonably constant. The amplitude of the corresponding electrical signal produced by the photodetector will consequently also be reasonably constant, with little or no high frequency amplitude fluctuation, the frequencies of what fluctuations there are being, of course, dependent upon the speed of travel of the conveyor belt.On the other hand the flexible plastics films and sheets initially mixed in with the paper are specular reflectors of visible light, and of radiation of wavelength around 3 ism with their crumpled surfaces behaving in effect as multi-facetted mirrors. Consequently, when one of these items passes the unit 2 it will reflect numerous short pulses of high intensity light to the photodetector, (although the mean reflectivity of the item may be low), with the result that the corresponding signal produced by the photodetector will consist of relatively high frequency amplitude fluctuations.

Thus by determining whether the dominant frequencies in the output of the photodetector at any time are relatively low or high it is possible to identify the material being sensed at that time as being either paper or plastics, and this is essentially the function carried out by the electronic section of the unit 2. To give some meaning to the terms "low frequency" and "high frequency" as used herein it is noted that from tests performed with apparatus of the type described operating with a conveyor belt speed of about 0.6m/sec it has been found that the dominant frequencies in the output of the photodetector when paper is being sensed are less than 15Hz while the dominant frequencies when flexible plastics films or sheets are being sensed are in the order of 120Hz and above.

Referring now to Figure 3, the output of the photodetector 24 is first fed to a low frequency filter 26 which filters out frequencies below about 2 or 3Hz to thereby reduce the possibility of spurious results arising from fluctuations in ambient lighting. The resulting signal is amplified at 27 and fed to low pass and high pass active filters 28 and 29 respectively, the path to the latter unit being via a high frequency filter 30 which filters out any amplifier noise, (above about lkHz). The signals from the active filters 28 and 29 are then fed to respective discriminators 31 and 32 each one of which is adapted to produce a logical "1 " output if the input to the discriminator is above a predetermined signal level and to produce a logical "0" output if below.Thus if paper is being sensed, so that the output of photodetector 24 is dominated by relatively low frequencies, the output of discriminator 31 should be "1" and the output of discriminator 32 should be "0", and if plastics is being sensed, so that the output of photodetector 24 is dominated by relatively high frequencies, the output of discriminator 31 should be "0" and the output of discriminator 32 should be "1".

The discriminators are both connected to a logic unit 33 which decides on the basis of the discriminator outputs whether the item being sensed is paper or plastics. If the logic unit identifies the item being sensed as plastics it sends a triggering pulse to an electro/ pneumatic converter 34 which in turn causes the pneumatic actuator 4 to lower flap 3C in the blower unit so that the item is blown off the conveyor belt. If the logic unit identifies the item being sensed as paper no signal is sent to the electrolpneumatic converter, thereby allowing the flap 3C to return to, or remain in, the raised position.

It is noted that, in the embodiment of the invention described above, the surface of the conveyor belt should act as a diffuse reflector of the laser light so that when the beam falls on the surface of the belt in between the conveyed items the apparatus reacts in the same manner as if paper was being sensed; i.e. the blower unit will not be actuated to blow across the belt unless and until a plastics item is sensed, and it will cease blowing across the belt as soon as the plastics item is removed from the belt.

As an alternative to the illustrated embodiment, it is possible to locate the radiation source and detector beneath the path of travel of the items to be sorted. In one suitable arrangement, the items are caused to travel down an inclined slide having in it an aperture through which the items are illuminated by the laser radiation.

Although the illustrated embodiment of the invention has been described above in terms of the separation of paper and plastics items, it will be appreciated that the apparatus will be equally applicable to the separation of other types of diffuse and specular reflectors of the laser light. In particular the separation of metal foils, (specular reflectors), from paper and other diffuse reflectors, (e.g. cloth, wood and rubber), is envisaged.

Furthermore, although a laser is preferred as the radiation source in the illustrated embodiment of the invention, since it produces an intense, well focussed beam and confers upon the optical system a marked insensitivity to source-detector distance and ambient lighting, it is believed that practical embodiments of the invention having the same function as that illustrated could be produced employing virtually any type of electromagnetic radiation source in or near the visible range of wavelengths, including, for example, an ordinary incandescent light bulb.

The illustrated embodiment employs a laser which produces radiation in the visible range. It has now been found that it can be preferable to use a laser which produces radiation in the infra-red range, for example at a wavelength of 3.39 tjm. At this wavelength the difference in efficiency of reflection between paper and plastics materials is more pronounced than in the visible range and this helps detection of pulses.

It has been found preferable, when working in the infra-red range, to use a concave mirror of diameter preferably in a range of 50 to 200 mm to focus the reflected radiation onto the photodetector. Such mirrors are more acceptable for focussing than are equivalent lenses because they are cheaper yet still have acceptable performance. In a preferred embodiment the laser beam is directed through a hole in the mirror to illuminate the items.

WHAT I CLAIM IS: 1. A method of sorting items into two different classes from a mixture of the items, a characteristic difference between the classes of item being that one class act, relative to the other class, as specular reflectors ofa particular type ofelectromagnetic radiation and have surfaces which are not entirely regular while the said other class act, relative to the said one class, as diffuse reflectors of such radiation, which method comprises the steps of:: (i) illuminating the items with a beam of radiation of the said type, (ii) providing relative movement between the beam and the items in a direction having a component normal to the direction of the beam, (iii) detecting fluctuations as a function of time in the intensity of the radiation reflected from the items, (iv) identifying from amongst such fluctuations pulses having both an intensity greater than a predetermined critical intensity and a duration smaller than a predetermined critical duration ,which pulses are indicative of specular reflectors, and (v) separating items belonging to said one class from those belonging to the said other class in response to the identification of such pulses.

2. A method according to claim 1 wherein the said one class of items which act as relatively specular reflectors consists of items having surfaces composed of a plastics material and the said other class of items which act as relatively diffuse reflectors consists of items having surfaces composed of paper.

3. A method according to claim l or 2 wherein the beam is of laser radiation.

4. A method according to claim 1, 2 or 3 wherein the wavelength of the radiation is either approximately 3 calm or is in the visible range.

5. A method according to claim 4 wherein the radiation is of wavelength 3.39 pm.

6. A method according to any preceding claim wherein said relative movement is at a velocity of approximately 0.6 m/sec.

7. A method according to any preceding claim wherein the said step of separating is effected by use of a blower to remove items detected as being or said one class of items from the vicinity of items of said other class.

8. A method of sorting items substantially as hereinbefore described with reference to the drawings accompanying the provisional specification.

9. An apparatus for sorting items into two different classes from a mixture of the items, a characteristic difference between the classes of item being that one class act, relative to the other class, as specular reflectors of a particular type ofelectromagnetic radiation and have surfaces which are not entirely regular while the said other class act, relative to the said one class, as diffuse reflectors of such radiation, which apparatus comprises (i) a source of a beam of radiation of the said type to illuminate the items, (ii) means for providing relative movement between the beam and the items in a direction having a component normal to the direction of the beam, (iii) means for detecting fluctuations as a function of time in the intensity of the radiation reflected from the items, (iv) means for identifying from amongst such fluctuations pulses having both an intensity greater than a predetermined critical intensity and a duration smaller than a predetermined critical duration, which pulses are indicative of specular reflectors, and (v) means for separating items belonging to said one class from those belonging to the said other class in response to the identification of such pulses.

10. An apparatus as claimed in claim 9 wherein the source of the beam of radiation is a laser.

11. An apparatus as claimed in claim 9 or 10 wherein the source can provide radiation of wavelength either approximately 3 pm or in the visible range.

12. An apparatus as claimed in claim 11 wherein the radiation is of wavelength 3.39 pm.

13. An apparatus as claimed in any one of claims 9 to 12 wherein the means for providing relative movement can establish a velocity of relative movement of approximately 0.6 m/sec.

14. An apparatus as claimed in any one of claims 9 to 13 wherein the means for providing relative movement comprises an inclined slide having in it an aperture through which the beam of radiation can be projected from beneath the slide.

15. An apparatus as claimed in any one of claims 9 to 14 wherein the means for detecting the reflected radiation comprises a concave mirror with a photodetector located at its focus.

16. An apparatus as claimed in claim 15 wherein the concave mirror has a hole in its surface through which in use the beam of radiation passes.

17. An apparatus as claimed in any one of claims 9 to 16 wherein the means for separ

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. difference in efficiency of reflection between paper and plastics materials is more pronounced than in the visible range and this helps detection of pulses. It has been found preferable, when working in the infra-red range, to use a concave mirror of diameter preferably in a range of 50 to 200 mm to focus the reflected radiation onto the photodetector. Such mirrors are more acceptable for focussing than are equivalent lenses because they are cheaper yet still have acceptable performance. In a preferred embodiment the laser beam is directed through a hole in the mirror to illuminate the items. WHAT I CLAIM IS:

1. A method of sorting items into two different classes from a mixture of the items, a characteristic difference between the classes of item being that one class act, relative to the other class, as specular reflectors ofa particular type ofelectromagnetic radiation and have surfaces which are not entirely regular while the said other class act, relative to the said one class, as diffuse reflectors of such radiation, which method comprises the steps of:: (i) illuminating the items with a beam of radiation of the said type, (ii) providing relative movement between the beam and the items in a direction having a component normal to the direction of the beam, (iii) detecting fluctuations as a function of time in the intensity of the radiation reflected from the items, (iv) identifying from amongst such fluctuations pulses having both an intensity greater than a predetermined critical intensity and a duration smaller than a predetermined critical duration ,which pulses are indicative of specular reflectors, and (v) separating items belonging to said one class from those belonging to the said other class in response to the identification of such pulses.

3. A method according to claim l or 2 wherein the beam is of laser radiation.

ating comprises a blower for removing items detected as being of said one class of items from the vicinity of items of said other class.

18. An apparatus substantially as hereinbefore described with reference to the drawings accompanying the provisional specification.

19. A waste materials management plant which includes apparatus as claimed in any one of claims 9 to 18.

20. A plurality of items which act as specular reflectors, the items having been sorted by a method according to any one of claims 1 to 8.

21. A plurality of items which act as diffuse reflectors, the items having been sorted by a method according to any one of claims 1 to8.