WO1999038370A1

WO1999038370A1 - Method and device for cutting the stalks of crops

Info

Publication number: WO1999038370A1
Application number: PCT/NL1999/000052
Authority: WO
Inventors: Loretta Maria Van Kollenburg-Crisan; Dmitrij Andreevits Sjwed; Peter Christiaan Wennekes; Johannes George Kornet
Original assignee: INSTITUUT VOOR MILIEU- EN AGRITECHNIEK (IMAG-DLO)
Current assignee: INSTITUUT VOOR MILIEU- EN AGRITECHNIEK (IMAG-DLO)
Priority date: 1998-01-30
Filing date: 1999-01-29
Publication date: 1999-08-05
Anticipated expiration: 2000-07-30
Also published as: NL1008161C2; AU2302099A

Abstract

This invention relates to a method and a device for cutting the stalks of crops. The method comprises placing two electrodes (8, 9) in contact with the stalk (14) of a crop plant. An alternating voltage is then applied over the electrodes (8, 9) and the electrodes are moved transversely on the stalk (14). The electrodes (8, 9) can be moved towards one another in a pinching movement or can be set up in a fixed position and pushed through the stalk (14). Preferably, an alternating voltage with a frequency of between 300 kHz and 1 MHz, preferably of between 500 and 800 kHz, and an amplitude of between 200 V and 1 kV, preferably of between 500 V and 700 V, is used. At such high frequencies the device is not dangerous if it is touched by an operator. Frequencies of between 20 and 100 Hz, at amplitudes of between 100 V and 500 V, can be used for cutting by robot. With the method according to the present invention crop stalks, such as, for example, stalks of vegetables or plants, can be cut through effectively within 2 seconds when harvesting, when plucking leaves, when topping or pruning or when taking cuttings for propagation. The temperatures generated during this operation are sufficiently high to kill moulds, bacteria and viruses, so that the risk of contamination is minimised and a high processing rate is possible. The keeping qualities of the crops harvested in this way also improve.

Description

1

Method and device for cutting the stalks of crops

The application relates to a device and a method for cutting the stalks of crops When cutting the stalks of crops, such as the stalks of cucumbers or tomatoes, or when taking cuttings from a crop or otherwise cutting off stalks or stems the problem arises that viruses and bacteria can be disseminated via the fluid or the sap that remains behind on the blade used for this purpose Consequently, the blade has to be cleaned with a cleaning fluid after every cut in order to neutralise these viruses and bacteria However, there is still a risk of contamination Furthermore, the process described above leads to a relatively low processing rate

One aim of the present invention is to provide a method and device for cutting the stalks of crops with which the dissemination of undesired substances, such as moulds, is prevented and with which viruses and bacteria on the crop are killed

A further aim of the present invention is to provide a method and a device for cutting the stalks of crops with which a high processing rate can be obtained and with which cutting can be performed mechanically in a simple manner To this end the method according to the present invention is characterised by the following steps placing two electrodes in contact with a stalk; application of an alternating voltage over the electrodes and - moving the electrodes transversely on the stalk

By placing the electrodes in contact with a stalk a current flows through the stalk which very rapidly heats the cells of the stalk so that they vaporise The heat which is generated as a result is localised within a small area so that the cells at that point turn to steam and leave a cavity behind in the cell matrix The heat liberated is released to the steam and is not conducted further along the stalk By moving the electrodes perpendicularly to the stalk said electrodes come into contact with new cells which, once again, are vaporised as a consequence of the heating Initially the tissue of the stalk will have a relatively low resistance since the stalk contains a large amount of water When the water \ aponses the conductance will decrease, as a result of which the potential difference over the stalk increases When said potential difference is sufficientlv high a spark will jump between the electrodes w hen the air present betw een the electrodes is ionised The resultant heating is firsth a consequence of the resistance of the stalk itself and secondly is a consequence of the encrg\ stored in the spark, the contribution of the latter being the 2 greater of the two. This leads to very local heating, as a result of which the cells very rapidly disintegrate. With the aid of the method according to the present invention it is possible to cut through a stalk with a cutting time of less than 1.5 seconds, in particular with a cutting time of less than 1 second. With these times it has been found that viruses, moulds and bacteria on the electrodes are killed when harvesting cucumbers, peppers, truss tomatoes, lettuce, courgettes and aubergines and when plucking leaves or when topping or pruning thereof. The same has been found when taking cuttings for propagation and when harvesting flowers such as chrysanthemums, carnations, bouvardia, roses, orchids, etc. and pot plants such as, for example, the rubber plant. Furthermore, it has been found that the keeping qualities of crops, such as fruit, which have been harvested using the method according to the present invention improve substantially and. for example, that the keeping period is up to 5 days longer than that in the case of crops cut in the conventional way.

Preferably, an alternating voltage having a frequency of between 100 kHz and 1 MHz, preferably of between 500 and 800 kHz, with an amplitude of between 200 V and 1 kV, preferably of between 500 V and 700 V, is used with the method according to the present invention. It has been found that a very good cutting effect is obtained with an alternating voltage of the abovementioned frequency. At such high frequencies the user will not receive a shock should he/she accidentally touch the electrodes since such high alternating voltages do not cause any muscle contractions in the user.

In an alternative embodiment the alternating voltage has a frequency of between 20 and 100 Hz, preferably of between 40 Hz and 70 Hz, and an amplitude of between 100 V and 500 V, preferably of between 150 V and 300 V. These frequencies and amplitudes give a good cutting effect and are particularly suitable, for example, for use when cutting is carried out by robot, since in this case the risk of a user receiving a shock from the electrodes is very small.

In a further embodiment the electrodes are moved towards one another without coming into contact with one another. The electrodes can, for example, be constructed in the form of a pair of tongs with two arms which are hingeable towards one another, with a handle, which is insulated with respect to the electrodes, with an operating mechanism for switching on the source of alternating voltage. The tongs can have a stop to limit the mutual position of the arms such that the electrodes are not able to touch one another. Said stop can be omitted if the electrodes pass beneath one another. 3

The smallest distance between the electrodes is not less than 0.1 mm, preferably not less than 0.5 mm. On operation of the arms, an operator is able, for example via a switch, to switch on the source of alternating voltage when a stalk has been confined between the two electrodes in order to obtain the cutting effect. The electrodes of the device according to the present invention are preferably of virtually circular cross-section with a diameter of between 0.5 and 5 mm, preferably of between 1 and 2 mm. With such a cross-section an electrode is formed which is sufficiently thin to achieve a good cutting effect but at the same time has sufficient rigidity not to deform on coming into contact with the stalk. The circular periphery of the electrodes prevents the electrode surface from being damaged when the spark jumps between the two electrodes. Preferably, the electrodes are made of a metal which has a relatively high melting point, such as, for example, tungsten.

In another set-up the electrodes are held in a fixed position with respect to one another during cutting. In this case the cutting head can comprise two fixed electrodes which taper towards one another with a minimum distance between them of between

0.1 mm and 0.5 mm. A cutting head of this type can be pushed through a stalk of a plant while supplying the alternating voltage to the electrodes. An automated embodiment of a device according to the present invention comprises a control unit and a motorised arm, which is connected to the control unit and has the cutting head and an optical sensor at the end thereof. By detection of a plant with the aid of the optical sensor, the arm is able to position the cutting head close to a stalk. The voltage source is then activated by the control unit and the arm will cut off the stalk using the cutting head. Preferably, the arm also comprises a gripper so that the plant can be gripped tightly before the cutting head is operated. As a result the plant can be placed in a container, such as a vegetable crate, by the gripper after it has been cut off.

A few embodiments of the method and the device according to the present invention will be described in more detail by way of example with reference to the appended drawing. In the drawing:

Figure 1 shows a first embodiment of a device according to the present invention which can be operated manually,

Figure 2 shows a detail of the cutting head according to Figure 1, the electrodes having been placed in contact with a stalk,

Figure 3 shows a cross-section through the electrodes of the device according to 4

Figure 2 at the point in time when a stalk is cut through,

Figure 4 shows a cutting head with electrodes arranged in a fixed position, and

Figure 5 shows an automated cutting device according to the present invention.

Figure 1 shows a first embodiment of a device 1 according to the present invention with a cutting head 2 and a source of alternating voltage 3. The cutting head 2 comprises two arms 4, 5 with a handle 6 at the bottom thereof. An insulating tip 7, 7', which, for example, is made of a plastic, is fixed to the top of the arms 4, 5, which are hingeable with respect to one another. An electrode 8, 9 in the form of a wire is attached to each insulating tip 7, 7'. The wire electrodes 8, 9 are connected via respective cables 10, 1 1 to the source of alternating voltage 3. The arm 5 is provided with a stop 12, it being possible to adjust the gap between the electrodes 8, 9 when manually bringing the arms 4, 5 together by tightening said stop 12. An operating mechanism 13, such as, for example, a push button, is also mounted on the arm 5, which operating mechanism is also connected to the source of alternating voltage 3 in order to be able to switch this on or off. The source of alternating voltage 3 comprises, for example, a source of alternating voltage of the Valleylab Model SSE3, Solid-State Electrosurgery type, obtainable from Bentley Laboratories B.V., Energielaan 3, P.O. Box 169 Uden, The Netherlands. During operation the cables 10, 1 1 of the electrodes 8, 9 are connected to the monopolar output of the source of alternating voltage and. for example, a pure sine wave voltage is applied over the bipolar electrodes 8, 9. The most favourable cutting effect is obtained with a voltage of between 500 and 750 V. When cutting the stalks of cucumbers it has been found that the temperature in the stalk, at the location where the electrodes 8, 9, are in contact with this, can rise to 1083 °C, the other parts of the electrodes 8, 9 which are further away from the stalk not becoming any hotter than approximately 190 °C. With wire electrodes with a diameter of 1.6 mm adequate rigidity and a low degree of deformation were obtained during cutting, so that the gap between the electrodes, which was 0.5 mm, was not pinched closed. Moreover, the surface area of such cylindrical electrodes was sufficiently small to restrict cooling thereof.

Figure 2 shows the cutting head 2 in its partially closed state, the electrodes 8, 9 being in contact with a stalk 14. As shown in Figure 3, the axes 15, 16 of the electrodes 8, 9 are somewhat offset so that in the closed state the width of the air gap D between the electrodes is 0.1 mm.

Figure 4 shows an alternative cutting head 20 with two electrodes 21 , 22 arranged in 5 a fixed position. The electrodes 21, 22 are curved and taper towards one another so as to capture a stalk between them. The gap D between the two electrodes is, for example, 0.1 mm. The electrodes 21, 22 are fixed to an insulated handle 23 and are connected via cables 24, 25 to a power supply, which is not shown in Figure 4. A cutting head 20 of this type is particularly suitable for automated cutting, for example by means of a robot. For cutting it is necessary only to push the cutting head 20 against the stalk, after which the supply voltage is applied to the cables 24 and 25 and after which the electrodes 21 and 22 can be pushed perpendicularly to the stalk through the latter. During this operation the stalk is cut through and sealed by singeing, the temperatures rising so high that viruses, bacteria and moulds are killed, so that the risk of contamination when cutting the stalks is substantially reduced. The air gap D is sufficiently narrow to disintegrate fibres remaining behind after cutting, so that there is a self-cleaning effect.

Finally, Figure 5 shows a diagrammatic representation of an automated cutting device according to the invention provided with a mobile frame 26 on which a control unit 27 and the power supply 28 have been placed. The cutting device is provided with segmented arms 29 and 30 with a number of drive motors to enable the arms to be rotated about three axes of rotation. The arm 30 has a gripper 31 at one end for tightly gripping a plant 34. A cutting head 32 for cutting through a stalk 33 of the plant 34 is located below the gripper 31. With this arrangement the plant 34 is held by the gripper 31 and, after the stalk 33 has been cut through, can be placed in a container such as, for example, a crate. Preferably, the cutting head 32 is constructed in accordance with Figure 4. The arms 29 and 30 are controlled by means of an optical sensor 35, such as, for example, a CCD camera which is connected to the control unit 27. The presence of a plant 34 is detected by means of the camera 35 and the arms 29 and 30 are positioned such that the gripper 31 is placed around the plant 34 and the cutting head 32 is level with the stalk 33.

Claims

6Claims

1. Method for cutting stalks of crops, characterised by the following steps: placing two electrodes (8, 9; 21, 22) in contact with a stalk (14); - application of an alternating voltage over the electrodes (8, 9; 21, 22) and moving the electrodes transversely on the stalk (14).

2. Method according to Claim 1, characterised in that the alternating voltage has a frequency of between 300 kHz and 1 MHz, preferably of between 500 and 800 kHz, and an amplitude of between 200 V and 1 kV, preferably of between 500 V and 700 V.

3. Method according to Claim 1, characterised in that the alternating voltage has a frequency of between 20 Hz and 100 Hz, preferably of between 40 and 70 Hz, and an amplitude of between 100 V and 500 V, preferably of between 150 V and 300 V.

4. Method according to Claim 1, 2 or 3, characterised in that the electrodes are moved towards one another without touching one another.

5. Method according to Claim 1, 2 or 3, characterised in that the electrodes are held in a fixed position with respect to one another during cutting.

6. Device (1) for cutting stalks of crops, comprising a cutting head (2, 20, 32) with two electrodes (8, 9; 21, 22) located some distance apart and an alternating voltage source (3, 28) connected to the electrodes.

7. Device (1) according to Claim 6, provided with two arms (4, 5) which are hingeable towards one another, with a handle (6), which is insulated with respect to the electrodes, with an operating mechanism ( 13) for switching on the source of alternating voltage (3), wherein the smallest distance between the electrodes (8, 9) is not less than 0.1 mm, preferably not less than 0.5 mm.

8. Device according to Claim 7, characterised in that the arms have a stop ( 12) for limiting the mutual position of the arms (4, 5). 7

9. Device according to Claim 6, 7 or 8 characterised in that the electrodes (8, 9; 21, 22) have an at least virtually circular cross-section with a diameter of between 0.5 and 5 mm, preferably of between 1 mm and 2 mm.

10. Device according to Claim 6, or Claim 9 with reference to Claim 6, characterised in that the electrodes (21, 22) are positioned in a fixed position with respect to one another and essentially taper towards one another with a smallest distance (D) between them of between 0.1 mm and 0.5 mm.

11. Device according to one of the preceding claims, characterised in that the alternating voltage source operates at a frequency of between 300 kHz and 1 MHz, preferably of between 500 and 800 kHz, and an amplitude of between 200 V and 1 kV, preferably of between 500 V and 700 V.

12. Device according to one of Claims 6 to 10, characterised in that the alternating voltage source operates at a frequency of between 20 and 100 Hz, preferably of between 40 and 70 Hz, and at an amplitude of between 100 V and 500 V, preferably of between 150 V and 300 V.

13. Device according to one of Claims 5 to 12, characterised in that the device has a control unit (27), a motorised arm (29), connected to the control unit (27), with the cutting head (32) at one end and with an optical sensor (35), connected to the control unit for positioning the cutting head (31) close to a stalk (33) and for switching the voltage source (28) on and off.

14. Device according to Claim 13, characterised in that said device is also provided with a gripper (31 ) for gripping tight the crop attached to a stalk (33), prior to operation of the cutting head (32).

15. Device according to one of Claims 6 to 14, characterised in that the electrodes are made of a metal having a relatively high melting point, such as tungsten.