WO2015105419A1

WO2015105419A1 - System for harvesting asparagus

Info

Publication number: WO2015105419A1
Application number: PCT/NL2015/050009
Authority: WO
Inventors: Adrianus Johannes Petrus Maria Vermeer
Original assignee: Cerescon Holding B.V.
Priority date: 2014-01-07
Filing date: 2015-01-07
Publication date: 2015-07-16
Also published as: PE20161312A1; EP3091828A1; NL2012055C2

Abstract

According to the present application, a harvesting method is proposed for harvesting asparagus that does not suffer from the practical problems of the prior art disclosure. This method is characterised by placing an RF antenna in grid locations on an earth dam being cultivated to contain a sand bed with a moisture gradient that is held constant by, in a free space above the earth dam, transmitting a signal through the antenna in a plurality of selected frequencies in a range of 1 - 10 GHz; constructing an image from received signals in the grid locations for the plurality of selected frequencies and detecting in designated grid locations, from absence of image signal in multiple of said selected frequencies, presence and height information of an asparagus spear having a moisture component.

Description

Title: System for harvesting asparagus

FIELD OF THE INVENTION

The present invention relates to a method and device for harvesting asparagus in a crop bed.

BACKGROUND OF THE INVENTION

Ever since the Roman days, asparagus are cherished as a major delicacy. One of their drawbacks even to date is that the harvesting is labor intensive. No satisfactory techniques have been available to efficiently register and extract the asparagus spears from the plant bed. As is well known, white asparagus grow undergrounds, typically in well prepared earth dams and the asparagus beds remain productive for circa 10 years.

Plant seedlings are typically placed in a sandy enclosure in the earth dam, with spaced rows with a pitch of typically 180 cm apart, minimal 165 and not more than 300 cm. The underground bodies of the asparagus plants are called crowns. The crown size increases as the asparagus ages, so the bed will eventually become completely filled with crowns and the width of the bed will start to enlarge. Asparagus spears will color violet if exposed to light, this process already starts as the spears reach the upper few cm under the sand surface. The coloring of asparagus is considered as a quality deterioration and reduces the commercial value. Furthermore, the head will slightly open (as a flower) as soon as the counter pressure of the sand reduces in the top area of the sand bed. This is also a value reduction. For these reasons, it would be very attractive if it were possible to harvest the asparagus while the spear heads were still 5 or more cm below the surface. For this, a subsurface detection method is required which cannot be provided by classical optical vision solutions.

EP2668837 discloses a detection system for detecting the underground spears of the asparagus by means of X-ray irradiation. X-ray radiators and detectors may be placed opposite to each other elongate the dams and by suitable tuning of the doses, the asparagus can be imaged and elected for harvesting by appropriate positioning of a harvesting tool.

While the concept of underground imaging of the asparagus may be advantageous, the disclosed technique is hardly suitable in practice due to hazard risks, not only for human operation but also for microorganisms necessary for biological vitality. Thus there still remains a challenge for providing a practical method and device able to suitably identify the asparagus to elect it for harvesting.

SUMMARY OF THE INVENTION

According to an aspect of the present application, a harvesting method is proposed for harvesting asparagus that does not suffer from the practical problems of the prior art disclosure. This method is characterized by

placing an RF antenna in grid locations on an earth dam being cultivated to contain a sand bed with a moisture gradient that is kept constant , in a free space above the earth dam, transmitting a signal through the antenna in a plurality of selected frequencies in in a range of 1 - 10 GHz; constructing an image from received signals in the grid locations for the plurality of selected frequencies and detecting in designated grid locations, from absence of image signal in multiple of said selected frequencies, presence and height information of an asparagus spear having a moisture component.

In certain aspects of the invention, the method comprises placing a compact single point (round) antenna in a free space alongside and above the earth dam, transmitting an electromagnetic signal through the antenna and detecting sand crack and/or asparagus spear head reflections extending alongside a top surface of the earth dam. An X-Y plane image is built up from a large number of measurements executed in a grid pattern. This can be done with impulse based time-of-flight radar reflections detection, but also by continuous wave radar based upon wave interference, known as "holographic subsurface radar imaging". The latter method has the advantage of higher resolution at a short range.

Without being bound to theory, it is believed that, due to a moisture distribution of the asparagus spear in the sand bed, an image signal is detectable in the selected scan with frequencies characteristic for the asparagus, which is detectable in a suitably conditioned sand bed cultivated in earth dams and having a moisture gradient that is kept constant by covering the earth dam in plastic.

According to another aspect of the invention, the method comprises placing an antenna in a free space alongside and above the earth dam, transmitting an electromagnetic signal through the antenna and detecting reflections extending alongside a top surface of the earth dam at different frequencies whereby the value of the frequency is reduced (in steps) from a high value of 5 to 10 GHz down to a lower value of 1 to 2 Ghz. As the frequency is reduced, the penetration depth will rise. The occurrence of reflection images at certain frequencies will render information on the subsurface depth position of the asparagus spear head.

According to another aspect of the invention, the method comprises placing an antenna in a free space adjacent the earth dam;

transmitting an electromagnetic signal in a direction of an asparagus; and detecting a heat signature of the asparagus.

The method is partly based on the insight that the typical elongated shape and vertical growth direction of the asparagus integrates reflections from a radar antenna from the side of the dam , rendering it suitable for X-Y position determination with a ground penetrating radar. The method is partly based on the insight that an asparagus forms sand cracks extending in planar direction in the earth bed that can be detected by radar reflection.

The method is partly based on the insight that the asparagus has a high water content that will be heated more than the dryer sand mass around the asparagus if exposed to microwave radiation in the same frequency range as the electromagnetic waves used for radar detection. The higher relative temperature rise of the asparagus can thus be detected.

The transmitting antenna and receiving antenna may be placed distanced from each other in a trench alongside the earth dam. The transmitting antenna and receiving antenna may be placed opposite each other in adjacent trenches bordering the earth dam. Multiple transmitting and receiving antennas may be placed alongside each other. The

transmitting and receiving antenna may be formed by the same structure.

FIGURES

Figure 1 shows a system of an agricultural vehicle provided with a radar section according to an embodiment of the invention;

Figure 2 shows a schematic arrangement of an asparagus detection system according to another embodiment of the invention;

Figure 3 shows another schematic arrangement of an asparagus detection system according to a further embodiment of the invention;

Figure 4 shows a schematic plan view for detection of an asparagus in a plane alongside the earth beds;

Figure 5 shows a schematic side view and reflection profile of crack detection;

Figure 6 shows a schematic side view of an alternative asparagus detection method. DETAILED DESCRIPTION

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly

understood by one of ordinary skill in the art to which this invention belongs as read in the context of the description and drawings. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some instances, detailed descriptions of well-known devices and methods may be omitted so as not to obscure the description of the present systems and methods. The term "length adjusted to the earth dam height" will be understood by a skilled person as a length of about 0.1 - 1 times an earth dam height, that is typically of a height that is sufficient to cover the asparagus spears, for instance of 10-50 cm. The adjustment entails an optimization to sufficient transfer of radiating energy to the asparagus to render a suitable detection of it have e.g. by integrated reflection over the length of the asparagus spear.

The term "upstanding direction" relates to the normal direction parallel to the direction of gravity. A "base plane" refers to a notional plane coinciding with trench bottoms adjacent the earth dam. It is also typically the base which functions for the vehicle to drive alongside the earth dams. Reflections "alongside" a top surface of an earth dam are caused by cracks that extend in a planar direction conforming to a protrusion of the

asparagus head, that pushes the earth up in a dome. It will be further understood that the terms "comprises" and/or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

Throughout the application, any function for carrying out the disclosed methods, in particular, as further clarified below: detecting a reflection (or attenuation), may be implemented in hardware and/or software and as structurally identifiable by the function it performs in the system; i.e. the function is physically implemented in hardware and/or software or information structures transmitted through the network. The function may be implemented by dedicated processing circuitry that processes input data read from system resources. These functions may be executed by one or more processors configured to perform operational acts in accordance with the present systems and methods, such as to provide control signals to the various other module components. The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments said forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the drawings, the size and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments are described with reference to schematic illustrations of possibly idealized and/or intermediate structures of the invention.

In Figure 1A, according to an aspect of the invention a system 100 is illustrated. An agricultural vehicle 150 is provided, in forward driving direction, with a radar section 160. The radar section is constructed to perform a holographic radar imaging method.

Principles of the method are known from Zhuralvlev, Holographic subsurface imaging radar for applications in Civil Engineering", IET

International Radar Conference. Xi'an, China, herein incorporated by reference. According to the illustrated embodiment, in more detail in Figure IB, a grid is scanned with by continuous wave radar devices 161-1..161-x and a holographic image is constructed from received signals in grid locations 34 of scan lines 34 for the plurality of selected frequencies.

The radar devices 161-x are provided as multiple RF antennas

163, e.g. four or more, mounted on designated scanning wheels 164. The radar section 160, comprising the scanning wheels 161-1..x, is moved, by the vehicle 150 alongside earth dams 3, so that a grid of concentric lines 33 is scanned, with multiple grid locations 34 , that are determined by interval times of the scanning radar devices 161.

According to an aspect of the present invention, scans are performed at multiple selected frequencies, e.g. at a lower frequency of e.g. 1 GHz, a middle frequency of e.g. 2.5 GHz and a higher frequency of e.g. 4 GHz, at continuous wave radar frequencies in the interval of 1-10 GHz. By scanning at the multiple frequencies, plural holographic images can be constructed at the plurality of selected frequencies. A presence of an asparagus spear can be derived from persistent absence of image signal in multiple of said selected frequencies, in the example, e.g. in all selected frequencies except a selected lower frequency. In addition, height

information of an asparagus spear having a moisture component can be derived, by relating the penetration depth of a selected frequency where the asparagus is detected.

Accordingly, from holographic images at a lower frequency, a presence can be detected, wherein, for higher frequencies and a corresponding penetration depth, height information of the asparagus spear head can be derived.

For example, in an earth dam 3 a moisture profile is kept substantially constant by covering the earth dam in plastic foil, by irrigation or by another controlled soil hydrology method. Accordingly, a moisture gradient ranges from moisture levels above 70% in the lower parts (e.g. below 50% of the dam height) of the sand bed, to below 30% in the higher parts (e.g. above 50% of the dam height. With an earth bed thus conditioned an asparagus spear with a moisture content can be detected in the holographic image at lower frequencies that penetrate the earth dam at sufficient depth, e.g. with a penetration depth of 10-30 cm. By also scanning at higher frequencies, the presence or absence of the image signal is indicative for depth information of the asparagus spear, in particular its end part, relative to the earth dam surface. E.g. if the asparagus spear is detected also at a higher frequency of e.g. 7 GHz, a depth location of the end part of the asparagus may be less than 4 cm.

In a further aspect of the invention, the vehicle is provided with a cutting tool 170, mounted on the back of the vehicle, relative to the forward driving direction; and a harvesting tool 180, mounted behind the cutting tool. The vehicle may operate at speeds of about 0.1- 4 m/s, which provides for sufficient time in constructing and analyzing the holographic image obtained from the scanning unit 160 by a unit arranged for constructing an image from detected signals of the detector devices 161 in the grid locations for the plurality of selected frequencies to provide presence and depth information of asparagus spears having a moisture component.

Figure 2 shows a schematic arrangement of an asparagus detection system according to another embodiment of the invention. In the figure a system 200 is shown for detecting and harvesting asparagus 6 from elongated earth dams 3. The asparagus 6 can be detected and harvested individually. The system 200 comprises a vehicle 5 suited for moving alongside the earth dam 3 of an asparagus bed. The vehicle 1 comprises an RF antenna 1 of elongated shape in direction, when in use in an upstanding direction, placed alongside the earth dam 3. The earth dam 3 is of suitable composition for harvesting asparagus, known to the skilled person. In particular, preferably the asparagus 6 is enclosed in sand. The vehicle 5 further comprises a location detection means comprised in a controller 4 to detect the antenna position on a length coordinate alongside the earth dam. Such detection means may be any suitable detector, e.g. by GPS,

triangulation, speed measurement incorporated in the vehicle or length measurement relative to a fixed origin. The RF antenna is coupled to controller 4 arranged for supplying an electric signal to the antenna 1 , to have it radiating with a suitable frequency that may range from few MHz to several of GHz, depending on optimization and local conditions. A reflection of the transmitting field signal may be detected, in the embodiment by a receiving antenna 2. When detecting the reflection, the controller 4 may derive the asparagus position on a coordinate alongside the earth dam 3, in particular an x-y coordinate on a base plane.

Figure 3 shows another schematic arrangement an asparagus detection system 300 that functions in a transmission arrangement for detecting an x-y coordinate (i.e. a coordinate on a base plane) according to an embodiment of the invention. In the embodiment a cart 5 is formed by an inverted U-shape provided with transport wheels, transversally enclosing the dam 3 and suitably forming a frame for aligning an RF transmission antenna 1 in a free space alongside an earth dam 3 of an asparagus bed, the antenna being of elongated shape, the antenna being of a length adjusted to the earth dam height. The term "length adjusted to the earth dam height" will be understood by a skilled person as a length of about 0.1 - 1 times an earth dam height, that is typically of a height that sufficient to cover the asparagus spears, for instance of 10-50 cm. In the embodiments of Figure 2 and Figure 3 a head position height may be detected of the asparagus spear 6 relative to a base (i.e. z-position in the figure), from a detection signal as a function of step height wherein the antenna is placed in an upstanding direction at a plurality of step heights relative to a base plane the earth dam. The step heights can be attained by vertical displacement of the antenna or by plural antennas that are offset in the Z-direction. By distinguishing the signal profiles of beams that traverse an asparagus, and the profiles that do not do so because the antenna is placed above the heads of the asparagus spears, a height detection of the head, i.e. distal end of the asparagus spear is detected.

When the radar beam transverses the dam 3, the signal changes due to a differing dielectric constant and also reflects upon the interface of the materials with that difference. The asparagus spear, consisting for a larger part of water, differs considerably from the sand enclosure that surrounds it, so that the EM wave speed is detectably changed. In an embodiment, this can be measured by measuring pulses (traces) in the nanosecond ranges. Instead of constructing a visual image, the positions of individual asparagus can be derived by beforehand knowledge of the asparagus bed. Alternatively a method can be applied known as a

Frequency modulated continuous wave method, wherein a frequency modulated signal is sent. When the beam traverses an asparagus, a difference in signal propagation time is measured as a frequency shift or phase shift relative to a reference signal. This may lead to simpler signal analysis. Alternatively a method can be applied known as subsurface holographic radar imaging wherein a continuous wave is transmitted interfering with reflecting waves or phase shifted waves and thus forming patterns that are detected by a receiving antenna.

Figure 4 shows a schematic plan view for detection of an asparagus in a plane alongside the earth beds. In the embodiment multiple receiving and emitting antennas are depicted, to receive multiple signals in transillumination mode resulting in substantially parallel raypaths in the case of homogeneous subsurface media. This setup is a simple and quick way to locate anomalies. Although the Figure 4 embodiment receives signals from a plurality of emitters and receivers, the setup may be simplified by carrying out the measurement in time shift mode, with shifted positions.

Figure 5 shows a schematic side view (A) and reflection profile (B) of crack detection. In this embodiment, an antenna 1 is moved along a length direction of the earth dam 3 in a free space above it, transmitting an electromagnetic signal through the antenna 1 and detecting sand crack reflections extending alongside a top surface of the earth dam in receiver 2. Reflections "alongside" a top surface of an earth dam 3 are caused by cracks 33 that extend in a planar direction conforming to a protrusion of the asparagus head, that pushes the earth up in a dome 31.

In the embodiment, the antennas 1, 2 may be of a dipole type placed in the x-direction (i.e. elongate the earth dam), or alternatively Y direction (transversal to the earth dam). Parallel placed receiver antennas may detect the receiver signal, wherein the positions of the asparagus may be detected in a diagonal beam path. By combining the signals of plural detectors, exact X-Y positions can be measured. This technique may also be known as 'time-slicing', wherein reflection profiles may be registered on subsequent heights of the asparagus bed , for example, on heights of - 10, - 15, -20 cm from a top surface of the earth dam 3. In analyzing the reflection profiles at subsequent heights, the asparagus heads may be identified, by circular profiles in the reflection scan.

In addition, by combining the information of plural scans, a vertical insertion height can be identified for suitable harvesting at a desired height of the asparagus spear 7. An addition advantage is by combining different height profiles, an inclination of the asparagus spear 6 can be easily detected.

Figure 6 shows a schematic side view of an alternative asparagus detection method that can be combined with any of the preceding embodiments. Depending on the specific antenna arrangement, the heads of the asparagus may be yet difficult to discern, possibly from other small irregularities such as stones or humus, due to poor resolution of the ground penetrating radar. Also, the radar might miss an asparagus head that is already grown out of the sand surface. A problem is posed since increasing the resolution by using higher frequencies will lead to lesser penetration depth of the electromagnetic signal. This may be solved by measuring at radio frequencies of about 2 - 10 GHz, wherein the penetration depth may be smaller than 15 cm. However, due to the frequency range generally known as microwaves, the asparagus heads will rise in temperature . In the embodiment, the cart 5 is provided with an infrared detector 8. In addition or alternatively to placing an RF receiver antenna 2 in a free space adjacent the earth dam and transmitting an electromagnetic signal by emitter 1 in a direction of an asparagus 6, a heat signature of the asparagus 6 is detected by IR detector 8.

Finally, the above-discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to specific exemplary embodiments thereof, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the scope of the present systems and methods as said forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims.

In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in the claims do not limit their scope; several "means" may be represented by the same or different item(s) or implemented structure or function; any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage and are deemed explicitly disclosed by the subject application.

Claims

1. A harvesting method for detecting and harvesting asparagus from elongated earth dams, the earth dams being cultivated to contain a sand bed with a moisture gradient that is held constant, comprising by the steps of placing an RF antenna in grid locations on an earth dam in a free space above the earth dam, transmitting a signal through the antenna in a plurality of selected frequencies in a range of 1 - 10 GHz; constructing an image from received signals in the grid locations for the plurality of selected frequencies and detecting in designated grid locations, from an image signal in multiple of said selected frequencies, presence and depth information of an asparagus spear having a moisture component.

2. The method for harvesting asparagus according to claim 1, wherein

an RF antenna is aligned in a free space alongside an earth dam of an asparagus bed, the antenna being of elongated shape, the antenna being of a length adjusted to the earth dam height; an electric signal is supplied to the RF antenna, and a reflection of the transmitted field signal is detected, thereby detecting the asparagus spear position relative to the antenna.

3. The method for harvesting asparagus according to claim 1 or 2, wherein the antenna is placed in an upstanding direction at a plurality of step heights relative to a base plane the earth dam; and deriving a head position height of the asparagus spear relative to a base from a detection signal as a function of step height.

4. The method for harvesting asparagus according to any of the preceding claims further comprising placing an antenna in a free space adjacent the earth dam; transmitting an electromagnetic signal in a direction of an asparagus; and detecting sand crack reflections extending alongside a top surface of the earth dam.

5. The method for harvesting asparagus according to any of the preceding claims further comprising placing an antenna in a free space adjacent the earth dam; transmitting an electromagnetic signal in a direction of an asparagus and detecting a heat signature of the asparagus.

6. The method for harvesting asparagus according to any of the preceding claims further comprising placing the transmitting antenna and receiving antenna distanced from each other in a trench alongside the earth dam.

7. The method for harvesting asparagus according to any of the preceding claims further comprising placing the transmitting antenna and receiving antenna opposite each other in adjacent trenches bordering the earth dam.

8. The method for harvesting asparagus according to any of the preceding claims further comprising placing multiple transmitting and/or receiving antennas alongside each other in a direction alongside the earth dam and deriving a length coordinate of the asparagus spear alongside the earth dam from a detection signal as a function of a detection signal from the multiple transmitting and receiving antennas.

9. The method for harvesting asparagus according to any of the preceding claims wherein the transmitting and receiving antenna may be formed by the same structure.

10. A system for detecting and harvesting asparagus from elongated earth dams comprising;

- a vehicle suited for moving alongside an earth dam of an asparagus bed;

- the vehicle comprising a scanning unit provided with multiple RF antennas; - the vehicle further comprising a location detection means to detect the antenna position on a length coordinate alongside the earth dam;

- the RF antenna coupled to a controller arranged for transmitting the antenna with an electric signal, to have it radiating at selected frequencies in a range of 2 - 10 GHz;

a detector for detecting a reflection of the transmitting field signal; and a

- unit arranged for constructing an image from detected signals of the detector in grid locations for the plurality of selected frequencies to provide presence and depth information of an asparagus spear having a moisture component.

11. A system according to claim 10, further comprising an IR camera, placed relative to the top surface of the earth bed and arranged to detecting a heat signature of the asparagus head when transmitting the alternating electric signal.