WO1997020186A1

WO1997020186A1 - Sensor for detection and/or discrimination of objects

Info

Publication number: WO1997020186A1
Application number: PCT/AU1996/000751
Authority: WO
Inventors: Peter John Blyth; John Fabian Russell
Original assignee: Aquasmart Pty. Ltd.
Priority date: 1995-11-24
Filing date: 1996-11-25
Publication date: 1997-06-05
Also published as: JP2000501177A; NO982352L; AUPN681595A0; NO982352D0

Abstract

A sensor (1) suitable for the detection and discrimination of objects including: (i) a body (3) having an aperture (11) orientated in use to allow objects to pass therethrough; (ii) at least one light emitter (5) for projecting a band or beam of light (9) across the aperture; (iii) at least one light receiver (15) for detecting the amount of light passing across the aperture; wherein, in use, the profile of an object passing through the aperture is determined ratiometrically by measuring the instantaneous change in the light level caused by the occlusion of light by the passing object. The sensor is applicable to the detection and discrimination of feed pellets, with particular application to aquaculture.

Description

SENSOR FOR DETECTION AND/OR DISCRIMINATION OF OBJECTS

This invention relates to a sensor for the detection and discrimination of objects which may pass through the vicinity of the sensor. In particular, it is applicable to the detection and discrimination of feed pellets, with particular application to aquaculture.

It is to be appreciated however that the sensor according to the invention is not limited to the field of aquaculture however it is particularly applicable to describe the invention in those terms. The principles described below may however be used in different applications or modified for use in detection of other types of objects.

Wild species of fish, and by degrees, semi wild species of fish introduced into aquaculture farming systems exhibit a broad range of feeding cycles that reflect their particular diversification. The broad range of feeding cycles are often determined by exogenous and endogenous factors that may alter that particular pattern. Because of the vast variation between the feeding pattern of species involved in such aquacultures, it is difficult to match feed output to the preferred feeding pattern of that species. Therefore, it is difficult to maximise growth and feeding efficiency while minimising feed wastage. This is a major problem inherent in present fish feeding systems.

A number of automatic systems have been developed some of which may involve use of a sensor to detect the amount of food wastage. In general, such systems operate on a simple on/off system wherein a sensor may simply determine that the fish do not require feeding if the sensor is able to detect a certain amount of food wastage within the water. The sensor in such systems may not be sufficiently sophisticated to take into account various exogenous and endogenous factors that impose minor aberrations to the general feeding pattern of the species. It is an object of the present invention to overcome or at least alleviate one or more of the difficulties associated with such systems.

The present invention resides in a sensor, suitable for the detection and discrimination of objects including:

(i) a body having an aperture orientated in use to allow objects to pass therethrough;

(ii) one or more light emitters for projecting a band or beam of light across the aperture; (iii) one or more light receivers for detecting the amount of light passing across the aperture; wherein, in use, the profile of an object passing through the aperture is determined ratiometricaily by measuring the instantaneous change in the light level caused by the occlusion of light by the passing object.

Most preferably, the sensor includes one or more collimating mirrors to direct the light from the emitter(s) to the receiver(s).

Direct analysis of the object passing through the aperture has a certain amount of importance when determining the amount of feed that may be required for a particular system. In an aquaculture system, the sensor is able to determine the amount of feed that may be passing through a sample area. Generally, the sample area is at a depth below where the species may generally feed, and the sensor is positioned there accordingly. The amount of feed that passes through the aperture is able to provide an indication as to the quantity of food that is being consumed by the cultured species.

Other matter, such as faeces may also pass through the aperture of the sensor. Real-time analysis of the profile of the object passing through the aperture allows for discrimination between a known class of object, for example feed pellet, and other objects, for example fish faeces. The analysis should also be able to determine the rate of which the known class of object passes through the aperture to provide information relating to the volume of feed which has been consumed.

Preferably, the sensor is used in a system which also includes a control unit able to analyse the information obtained from the sensor. Such a system is described in co-pending Australian provisional application PN 6814 and subsequently Intemational application No.fcf/doq6/oo7 2the entire disclosure of which is incorporated herein by reference. Correct analysis of the information enables the correct amount of feed at the most appropriate time to distribute to the aquaculture system.

The sensor may include one or more light emitters. In a most preferred form only one light emitter is used, however in another preferred configuration two light emitters may be used. It is conceived that the sensor may include more than two light emitters depending upon the sensitivity requirement of the sensor. A corresponding number of light receivers may also be used. The sensor may, for example use a bank of light emitters, each able to emit a particular light beam.

The light emitter preferably emits infra-red radiation, but other light sources, such as visible light source, may also be used.

In order to obtain a parallel curtain of light crossing the aperture, one or more collimating mirrors is preferably used to reflect the light across the aperture. Corresponding collimating mirrors on the opposing side of the aperture reflect the light to one or more receivers.

The light emitter(s), light receiver(s), collimating mirrors and other associated circuitry are housed within a body. As the sensor is generally used underwater, the body should be rugged and watertight. The body generally involves a material transparent to the wavelength of light used by the sensor.

The general design allows different sensors with a range of apertures to be manufactured utilising common operating principles and manufacturing techniques. The body generally incorporates a planar configuration consisting of two opposing plates allowing the components of the sensor to be enclosed therein. The body may be fabricated from flat sheets, such as acrylic, polycarbonate or similar material either by machining or molding. The plates have recessed areas which enclose the collimating mirrors, the light emitters and receivers and accompanying electronic systems. The opposing sheets are bonded at the time of assembly to provide a completely water tight enclosure. The bonding technique may utilise adhesives, ultrasonic welding or any suitable method, including the use of fastening bolts.

Fish feed pellets are generally substantially cylindrical in shape and generally have an average length of from 10 to 16 mm with a diameter of from 8 to 14 mm. Therefore, it has been found that a preferred aperture size for a sensor used in such an application is from 40 to 80 mm, most preferably about 50 mm. The curtain of light reflected should cover the entire diameter of the aperture. Generally the aperture is circular, but may be of any configuration. Preferably, the depth of the curtain of light is from 0.5 to 2 mm, most preferably from 1 to 1.5 mm.

The sensor is preferably used in conjunction with a control unit and computer data storage media embodying software. The control unit allows for automatic gain control of the sensor to establish a standard received signal level when no object is passing through the aperture. This feature allows the sensor to compensate for turbidity variation of the medium through which the objects are passing and can be used to determine whether the sensor is blocked or partially blocked.

The sensor may be calibrated to establish an appropriate range that maximises definition of a sample of objects that are passed through the aperture. This may be done by recording wave form measurements of individual objects and storing a group mean and standard deviation. Outliers are rejected. Individual object wave form measurements can also be stored. Definition and discrimination of the calibrated object as opposed to any other foreign material is carried out by comparison of the wave form values of an uncaiibrated object compared to the calibrated values.

In a preferred embodiment of the invention, the wave form measurements used to calibrate the sensor include the width, height and area. Mean standard deviation of each of these measurements is calculated and stored for comparison with objects passing through the sensor during use.

The control unit may allow for automatic self calibration of the sensor. In such an embodiment, further gain control (based on statistic dispersion) determined by the user or the automatic computer algorithm may establish an appropriate dispersion around the mean (using confidence limits) so as to limit other foreign objects. Self calibration adjustment over time may be achieved by the automatic computer algorithm via parametric or non-parametric comparison of mean (dependent upon the average wave form of distribution), allowing system autonomy until change reaches a threshold and automatic adjustment occurs and/or the user is informed.

The sensor according to the invention may also allow calculation of the velocity of particles passing through the aperture and accordingly, difference in velocity may also be used for discrimination of objects.

It will be convenient to further describe the invention with reference to the accompanying drawings which illustrate some preferred embodiments of the invention. Other embodiments of the invention are possible and accordingly the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is a plan view of a sensor according to the invention. Figure 2 is a side view of the sensor of figure 1.

Figure 3 is an alternative view of a sensor according to the invention.

Figure 4 is an alternative sensor according to the invention with two light transmitters and two receivers.

Figure 5 illustrates a sensor incorporated in a sampling funnel.

Figures 6 and 7 are schematic diagrams of fish feeding systems incorporating a sensor according to the invention.

In figure 1 , the sensor (1) is shown having a rugged water proof body (3), specifically designed for underwater use.

The sensor of figure 1 includes an emitter (5) able to emit light to a collimating mirror (7). A typical path of parallel light waves (9) is shown in dot formation reflected across the aperture (11). The light waves are reflected by a receiving collimating mirror (13) to a light receiver (15). Electronic equipment may be retained in enclosures (17). Information may be transmitted to a control unit (not shown) by waterproof connector (19). The control unit may form part of a system in which the sensor may be used. The body is generally formed of two parts connected together by mounting holes (21).

Figure 2 illustrates a side view of figure 1 illustrating the relative thickness of the sensor.

An alternative, and preferred mirror configuration is shown in figure 3 wherein the light emitter (5) and receiver (15) are moved from the axis of the opposing part parabolic collimating mirrors (14) and (16). When the light emitter and the light receiver are placed on the centre line of a parabolic minor, there may be a small dip in the response curve due to the shadowing effect of the emitter and detector. Such a problem may occur in a sensor as shown in figure 1. Figure 2 shows the light emitter (5) directing light to part parabolic mirror (14) to direct a parallel beam of light (9) across the aperture (11). Corresponding receiving mirrors (16) reflect the light to a similarly offset receiver (15). Both the light transmitter and receiver are offset from the parallel beams of light.

The positioning of the light emitter and receiver result in a mirror curve which is now a section of a parabola off the axis. Path length and incidence angle effects may result in a non-linearity of light intensity across the measurement aperture. This has been compensated for by using opposing parabolic sections for the light emitter and light detector. A further source of non-linearity may relate to the fact that practical light emitters and light detectors are most sensitive on axis. Sensitivity off axis decreasing relative to the off axis angle. In order to minimise the angle at which any light ray leaves the emitter or enters the detector has been achieved by increasing the average distance between the light emitter and/or light detector and its associated mirror by the particular placement within the sensor body, thereby decreasing the subtended angle.

In order to increase linearity of the sensor, the emission angle of the emitter and reception angle of the receiver need not be directed to the point of the mirror that intersects the centre line of the aperture.

Figure 4 illustrates a further embodiment where two light transmitters (5) emit light onto two collimating mirrors (7). Plane mirrors (21) assist in reflecting the light to the collimating mirrors. Corresponding receiving collimating mirrors

(13) are able to reflect the light to two light receivers (15). A typical light ray path (9) is shown crossing a substantially square aperture (11). The sensor according to the present invention may be used in a fish feeding system. Typically, the sensor may be incorporated into a funnel shown in figure 5 to provide an adequate sampling area. The sensor (1) may be attached to a funnel (23) by use of bolts (25) and attached to ring (27). A cone (29) may be placed within the funnel to assist in ensuring that a sample of the object passes through the aperture (9) of the sensor. The funnel may be suspended by use of ropes (31).

Figures 6 and 7 illustrate the use of the funnel and the sensor where information is transferred to a central control unit (32) by lead (33). Fish (35) generally feed on pellets (37) from cannon feeder (38) (fig 6) or hopper feeder (39) (fig 7) above the sensor (1) and the sensor is able to determine the feeding habit of the fish by measuring the quantity of feed that may pass through the sensor. The sensor according to the present invention is able to be used to detect a sample or absolute amount of feed which passes through a population of fish. Its use is particularly applicable in a system, which is the subject of co¬ pending Australian provisional application PN 6814, and subsequently as International application

Finally it is to be understood that various alterations, modifications or additions may be introduced into the sensor of the present invention with departing from the spirit or ambit of the invention.

Claims

1. A sensor suitable for the detection and discrimination of objects including: (i) a body having an aperture orientated in use to allow objects to pass therethrough;

(ii) at least one light emitter for projecting a band or beam of light across the aperture;

(iii) at least one light receiver for detecting the amount of light passing across the aperture; wherein, in use, the profile of an object passing through the aperture is determined ratiometrically by measuring the instantaneous change in the light level caused by the occlusion of light by the passing object.

2. A sensor, according to claim 1 further including at least one collimating mirror to direct the light from the light emitter to the light receiver.

3. A sensor according to claims 1 or 2 wherein real-time analysis of the profile of the object passing through the aperture allows for discrimination between a known class of object and other objects passing through the aperture, and determination of the rate of which the known class of object may pass through the aperture.

4. A sensor according to claims 2 or 3 wherein the light emitter is able to transmit light to a collimating mirror to reflect a band of light of substantially uniform intensity across the aperture.

5. A sensor according to any one of the preceding claims wherein a further collimating mirror is able to reflect the band of light to said light receiver.

6. A sensor according to any one of the preceding claims wherein the light emitter(s) emit infra-red radiation.

7. A sensor according to any one of the preceding claims wherein the light emitter is placed within the body of the sensor and is offset from the direction of the light crossing the aperture, and positioned to transmit light to at least one parabolic or part parabolic collimating mirror to direct a parallel beam of light across the aperture to one or more opposing parabolic or part parabolic collimating mirror(s), able to reflect the transmitted light to the light receiver, which is offset from the parallel beam of light.

8. A sensor according to claim 1 including two light emitters, each able to transmit light to a corresponding collimating mirror to direct light across the aperture of the sensor.

9. A sensor according to any one of the preceding claims wherein the collimating mirror is formed from: (i) an acrylic sheet formed with a parabolic surface; and (ii) vacuum deposited aluminium.

10. A sensor according to any one of the preceding claims wherein the sensor is adapted to measure the volume of fish pellets passing through the aperture.

11. A sensor according to any one of the preceding claims wherein the aperture is from 40 to 80 mm in diameter.

12. A sensor according to any one of the preceding claims wherein the band of light is transmitted across the entire diameter of the aperture and has a depth of from 0.5 to 2 mm.

13. A sensor according to any one of the preceding claims wherein the light transmitter, light receiver, collimating mirror and any accompanying electronic systems are housed in a water tight body.

14. A sensor according to claim 1 substantially as hereinbefore described with reference to any one of the drawings.