WO1986000420A1

WO1986000420A1 - Method and device for non-contact detection of plants

Info

Publication number: WO1986000420A1
Application number: PCT/SE1985/000261
Authority: WO
Inventors: Anders WALLENA^oS; Carl Tyrén
Original assignee: Enpece Ab
Priority date: 1984-06-25
Filing date: 1985-06-24
Publication date: 1986-01-16
Also published as: SE8403364L; DK86586A; DK86586D0; AU4547985A; EP0215795A1; SE8403364D0; SE443050B

Abstract

In a method and a device for non-contact detection of plants (31), reflected light (6) is collected from a surface (5) by means of an optical system (7). The reflected light (6) is devided by means of a beam splitter (13) into two light beams (14, 15) each of which is filtered by an interference filter (16, 17) to a respective predetermined wavelength. Two photodiodes (18, 19) convert a respective wavelength (14, 15) into an electric signal (20, 21), each of these signals being amplified in a respective operational amplifier (22, 23). A divider (26) receives the two signals (20, 21) and divide them for emitting a ratio signal (27). This ratio signal (27) is compared in a comparator (28) with a preselected reference signal (29) for emitting an output signal (30) which indicates the presence/non presence of a plant (31) on the surface.

Description

METHOD AND DEVICE FOR NON-CONTACT DETECTION

OF PLANTS

The present invention relates to a method and a device for non-contact detection of plants.

In e.g. agriculture, forestry, horticulture and contiguous branches, there is a considerable need of making machines and equipment for use in growing crops automated and/or more effective. Examples of working operations which might be automated and/or made more efficient are row tracking, mechanical/chem¬ ical precision killing of weeds in growing crops, selective thinning, harvesting etc.

When hoeing row crops by means of hoeing machines it is today difficult to adjust the hoe or hoes later¬ ally, especially in undulated terrain and/or in terrain sloping heavily in one direction or the other. The guiding operation is at present carried out entirely manually or by means of simple guide wheels following a track previously made in the ground. Since none of these two guiding methods provide for sufficient accuracy, the rows must be wide in order to avoid damage to the crop. In such a case, it would be highly desirable to obtain automated row tracking or more efficient row tracking. This would also be the case in the planting and harvesting of vegetables in order to permit making the tractor drawing the planter or harvesting carriage driverless.

Weed killing in vegetable farming is today car¬ ried out almost exclusively by hand since there are few chemical preparations which have been approved. By a device for detecting the location of the plants it would be possible to perform an efficient mechanical or chemical weed killing operation between the plants in the longitudinal direction of the row.

When placing granulated parasiticidal agents. for instance in cabbage fields, use is today made of machines depositing the chemical in a continuous strip. Only about 10-30% of the chemical is dropped on the plants, the rest being wasted. The costs for the chemical preparations make a substantial part of the expenses of the grower. Thus, with a device for detecting the plants it would be possible to save about 70-90% of the chemical agent, entailing sub¬ stantial economic and environmental advantages. In the case of sugar beets, only a minor part of the sugar beet culture is thinned. This is so e.g. because the thinning machines available on the market do not pay regard to the size of the plants and the spacing between them. Manual thinning is carried out but to a minor extent and is too expensive. With a device for detecting the plants, it is possible to record both plant size and plant spacing with a view to hoeing undesired plants.

As will be appreciated from the above, there is a great need for a method and a device for non-contact detection of plants in order, for various purposes, to acquire information on the location and/or size of the plants.

This need has been met by the method according to the invention in that reflected light from a sur¬ face is collected and divided into at least two light beams which are filtered and converted into electric signals which are amplified and divided, the ratio signal being compared with a preselected reference signal to provide an output signal indicating the presence/non-presence of a plant on said surface.

The device based on this method is characterized by an optical system for collecting reflected light from a surface, a beam splitter for dividing the reflected light into at least two light beams, an interference filter for each of said light beams for filtration thereof to a predetermined wavelength, a photodiode for each of said wavelengths for conversion thereof into an electric signal, an operational amplifier for each of said signals for amplification thereof, a divider for receiving said two signals and dividing them to provide a ratio signal, and a comparator for comparing said ratio signal with a preselected reference signal to provide an output signal indicating the presence/non-presence of a plant on said surface.

The invention will be described in more detail hereinbelow with reference to the accompanying drawings, in which:

Fig. 1 is an optical/electric block diagram illu¬ strating the mode of operation of the device;

Fig. 2 schematically illustrates one of many conceivable applications of the invention; and

Fig. 3 is a diagram showing the intensity of reflection as a function of the wavelength.

The method and the device according to the inven¬ tion for non-contact "seeing" detection of plants are based on spectral signature. In the embodiment here described and illustrated, the detecting device is viewing two specific wavelengths in the reflection spectrum from the surface it is scanning at the moment. These two wavelengths have a characteristic intensity relation for plants, which is directly converted into the single output signal representing presence/non- presence of a plant or, shorter, plant/non-plant.

By simultaneously viewing other wavelengths in the reflection spectrum, it will also be possible to discriminate between different kinds of plants. Thus, the principle of detection is based on optical signature. The intensity relation between the wavelength 680 nm and 730 nm decides whether a plant should be indicated or not in the output signal of the detecting device. 680 nm is one of the wave¬ lengths of light which is heavily absorbed by the chlorophyll of the plant. The intensity of this wave- length therefore is very low in the reflection spectrum from a plant. 730 nm is a wavelength which the plant reflects very intensely. The intensity of this wave¬ length therefore is very high in the reflection spectrum from a plant.

This marked difference in the intensity of reflec¬ tion for these two wavelengths is unusual for objects other than plants, for which reason this principle of detection can yield highly reliable results. Fig. 3 is an example of this reflection spectrum from sugar beets or, more exactly, their tops.

The method and the device according to the inven¬ tion for non-contact detection of plants operate and are conceived in the following way. As schematically shown in Fig. 1, the detecting device, generally designated 1, is enclosed in a dust and moisture-proof casing 2. In the illustrated embodi¬ ment, the detecting device has a rotary scanner 3 with mirrors 4 sweeping the surface 5 to be detected. The light 6 reflected from the surface 5 is collected through the scanner 3 by an optical system 7. In the illustrated embodiment, this optical system has a diaphragm device 8 with two lenses 9 and two lenses 10, as well as an aperture 11 displaced between these two pairs of lenses in the common focus thereof for eliminating stray light from the reflected light 6. The optical system 7 also has a collecting device 38 with two lenses 12 for receiving the light 6, freed from stray light, and conducting it to a beam splitter 13.

The beam splitter 13 consists of a semi-reflecting mirror dividing the reflected light 6 into two light beams 14 and 15. Each of these two light beams 14 and 15, by a respective interference filter 16 and 17 of about 680 nm and about 730 nm, respectively, reaches a photodiode 18, 19 for conversion into electric signals 20, 21. The signals 20, 21 emitted by the photodiodes 18 ^' and 19 are amplified each by an operational amplifier 22, 23 of the FET type having constant gain and, after further amplification 1,10 or 100 times by amplifiers 24, 25 adjustable in parallel, are both supplied to an analogue divider 26 in which the 680 nm signal is inserted in the numerator. The output or ratio signal 27 from the divider 26 will thus reach its minimum when the detecting device is viewing a plant. A comparator 28 compares the ratio signal 27 from the analogue divider with a preselected reference signal 29 for providing an output signal 30 indicating the presence/non-presence of a plant 31 on the surface 5. The output signals 30 from the detecting device 1 may in turn be used as control signals in order, by the^' intermediary of a microcomputer, to control different types of means for processing and/or treating the detected plant 31 or other plants spaced therefrom by a predetermined distance, or the area surrounding said plants.

Fig. 2 shows one of many conceivable applications of the invention. More precisely, the detecting device 1 is here mounted on one side of a hoe 32 for hoeing row crops, for instance sugar beets 33. The hoe 32 is either drawn or carried by a tractor 34 and has a plurality of hoeing knives 35 for hoeing between the rows of crop 33. To prevent the soil loosened by the knives 35 from covering small plants, protecting discs 36 are used.

The detecting device 1 is so disposed on the hoe 32 that it will be located straight above a row of crop 33 immediately to the right of the hoe, or midway between two rows. In the illustrated embodi- ment, the hoe 32 is provided on either side with a steerable wheel 37. Through an operating mechanism (not shown), the wheels 37 are operably connected to and controllable by means of the detecting device 1. When the tractor 34 and the hoe 32 are advanced along the rows in the manner indicated in Fig. 2, the detecting device 1 successively detects the crop 33 in the row to the right of the hoe 32. Since the distance between the rows is constant and the- knives 35 are mounted with a mutual spacing corresponding to the distance between the rows, they will hoe the soil between the rows of crop 33. If, for some reason or other, the hoe 32 should depart from its right course, for instance if the ground is undulated and/or heavily sloping in any direction, the detecting device 1 will detect this circumstance by sensing that the crop 33 is not located straight underneath the scanner 3, whereby the detecting device 1 emits a control signal to the operating mechanism for steering the wheels 37 in the direction required to return the hoe 32 to its correct lateral position.

The ability of the optical detecting device 1 to detect plants with active or "dormant" photosynthesis makes it very versatile. As earlier mentioned, the detecting device in principle is an optical transducer which by means of two optical filters and two photo¬ diodes discriminates between plant and non-plant. The transducer can be made more or less sophisti¬ cated with a scanner as illustrated and described, or a stationary mirror, depending on the field of application. If the information from the detecting device and other transducers, for instance a transducer indicating the distance travelled, is processed by a microcomputer and its program, many different appli¬ cations can be obtained. The sole feature that distin¬ guishes the various applications from each other, is the program of the computer as well as the con- struction and mode of operation of the implements. In the application according to Fig. 2, the scanner 3 of the detecting device 1 is scanning sideways trans¬ versely of the direction of travel of the tractor 34 and the hoe 32. However, the scanner 3 can also be arranged for scanning in the longitudinal or the vertical direction. The latter application may be advantageous, for instance when topping sugar beets, in which case the scanner 3 may operate such that the detecting device 1 detects where the tops begin on the beet. This information may then be used for controlling a topper assembly which will correctly top every beet.

Naturally, the invention should not be considered restricted to the embodiments described above and illustrated in the drawings but may be modified in several ways within the spirit and scope of the accom¬ panying claims.

Claims

1. A method for non-contact detection of plants, c h a r a c t e r i z e d in that reflected light from a surface is collected and divided into at least two light beams which are filtered and converted into electric signals which are amplified and divided, the ratio signal being compared with a preselected reference signal to provide an output signal indicating the presence/non-presence of a plant on said surface.

2. Method as claimed in claim 1, c h a r a c - t e r i z e d in that said light beams are filtered to a wavelength of about 680 nm and about 730 nm, respectively.

3. Method as claimed in claim 1 or 2, c h a ¬ r a c t e r i z e d in that said surface is scanned for providing output signals indicating the location and/or size of the plants.

4. Method as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that the output signals are used as control signals for controlling means for processing and/or treating the detected plant or other plants spaced therefrom by a predeter¬ mined distance, or the region surrounding said plants.

5. A device for non-contact detection of plants (31), c h a r a c t e r i z e d by an optical system (7) for collecting reflected light (6) from a surface (5), a beam splitter (13) for dividing the reflected light (6) into at least two light beams (14, 15), an interference filter (16, 17) for each of said light beams for filtration thereof to a predetermined wave- length, a photodiode (18, 19) for each of said wave¬ lengths for conversion thereof into an electric signal (20, 21), an operational amplifier (22, 23) for each of said signals for amplification thereof, a divider 126) for receiving said two signals (20, 21) and divid¬ ing them to provide a ratio signal (27), and a comparator (28) for comparing the ratio signal (27) with a pre¬ selected reference signal (29) to provide an output signal (32) indicating the presence/non-presence of a plant (31) on said surface (5).

6. Device as claimed in claim 5, c h a r a c ¬ t e r i z e d in that the optical system (7) comprises a diaphragm device (8) having at least one lens (9) and at least one lens (10), and an aperture (11) dis¬ posed between said lenses in the common focus thereof for eliminating stray light from the reflected light (6); and a collecting device (38) having at least one lens (12) for receiving the light, freed from stray light, and conducting it to the beam splitter (13).

7. Device as claimed in claim 5 or 6, c h a r a c ¬ t e r i z e d in that the filters (16, 17) are adapted to filter the light beams (14, 15) emerging from the beam splitter (13) to a wavelength of about 680 nm and about 730 nm, respectively, and that the divider (26), after conversion of said wavelengths into corre¬ sponding signals (20, 21) in the photodiodes (18, 19) and amplification of these signals in the amplifiers (22, 23), is adapted to divide said signals with the 680 nm signal in the numerator.

8. Device as claimed in any one of claims 5-7, c h a r a c t e r i z e d in that a scanner (3) is disposed before the optical system (7) for scanning the surface (5) in order to establish the location and/or size of the plants (31).

9. Device as claimed in any one of claims 5-8, c h a r a c t e r i z e d in that means (35) for treating and/or processing the detected plant (31, 33) or other plants (31; 33) spaced therefrom by a predetermined distance, or the region surrounding said plants, are operably connected to and controlled by the detecting device (1).