WO2015128163A1

WO2015128163A1 - Method for detecting a node and/or a bud from a stalk of a graminaceous plant

Info

Publication number: WO2015128163A1
Application number: PCT/EP2015/052353
Authority: WO
Inventors: Harald RÖDEL; Cassio Da Silva Cardoso Teixeira; Antonio Cesar Azenha; Guilherme Ribeiro GRAY
Original assignee: Basf Se
Priority date: 2014-02-28
Filing date: 2015-02-05
Publication date: 2015-09-03

Abstract

The present invention relates to a method for detecting a node (5) and/or a bud (8) from a stalk (1) of a graminaceous plant comprising: obtaining a picture of at least a part of the stalk (1), showing the projection of a lateral view of the stalk (1), and analyzing the obtained picture, wherein the distance of a position of the outline of the projection of the lateral view from a straight line that is parallel to the longitudinal axis (X) of the stalk (1) as a function of the longitudinal position (L) of the stalk (1) is determined, the algebraic sign of the first derivation (f ) of this function (f) is calculated, and the longitudinal position (Ln) of the node (5) and/or the bud (8) is detected at such longitudinal position (Ln) where the first derivation (f ) changes its algebraic sign. Furthermore, the present invention relates to a corresponding system for detecting a node (5) and/or a bud (8).

Description

METHOD FOR DETECTING A NODE AND/OR A BUD FROM

A STALK OF A GRAMINACEOUS PLANT

The present invention relates to a method and system for detecting a node and/or a bud from a stalk of a graminaceous plant. In particular, the graminaceous plant may be sugar cane.

The seed of sugar cane is a dry one-seeded fruit or caryopsis formed from a single carpel, the ovary wall pericarp being united with the seed-coat testa. The seeds are ovate, yellowish brown and very small, about 1 mm long. Disadvantageously, the seed of sugar cane only germinates under specific environmental characteristics, such as a constant warm and humid climate conditions. Such climatic conditions are not found everywhere sugar cane is grown and therefore germination of sugar cane seed is not always guaranteed. For commercial agriculture, the seed of a sugar cane is not sown or planted, but instead, the cane is propagated vegetatively by planting a stem segment or part of a stalk or culm or seedling.

The stem of sugar cane, as well as the stem of graminaceous plants, comprises several nodes, from which new plants grow. The traditional planting process of sugar cane involves the reservation of an area of the crop to be used as a source of plants for replanting, since the nodes are comprised in the stem. The plants used for replanting are harvested and then cut in segments of approximately 20 to 50 cm, so that at least two nodes are present in each stem segment sett. Cutting the stems is needed to break apical dominance that otherwise causes poor germination when using full length uncut stems. The segments are cut to have at least two buds or at least two nodes; every node gives generally rise to one single bud to assure germination, because not every bud germinates.

Various machines used to cut sugar cane segments are not able to identify any characteristic in the stem, and therefore the precise position of the cut sites is determined at random. After cutting, the setts, which have one or more nodes, are disposed horizontally, over one another in furrows of the ploughed soil, which are generally wide at ground level and deep 40 to 50 cm wide and 30 to 40 cm deep, and then lightly covered with soil. Although this plantation technique is still being used until today, the whole process is relatively inefficient because many segments of two to four nodes have to be used to guarantee the germination. The consequence is that a large area for re-planting needs to be used, and therefore area that could be employed for the crop and production of alcohol or sugar has to be reserved for re-planting. Thus, there is a necessity to increase the efficiency of the planting technique of sugar cane.

In a more recent cultivation method from Syngenta called Plene®, nodes of less than 4 cm in length are separated from the stems, treated with Syngenta seed products and then planted to the field. The method is said to lead to a yield increase of up to 15%. However, the area required for multiplication is still very large. Similar cultivation methods are also described in WO 2009/000398, WO 2009/000399, WO 2009/000400, WO 2009/000401 and WO 2009/000402.

Furthermore, WO 2009/100917 describes a cutting machine and a method for cutting stem segments of a graminaceous plant. According to the method, a characteristic of the stem is identified using a sensor. The sensor is a pressure transducer sensor, a capacitive sensor, an ultrasound sensor, an X-ray sensor, a magnetic sensor or a microwave sensor. The characteristic of the stem is in particular a node. After the node has been identified, the stem is placed in a determined position for cutting, depending on the response of the sensor. The stem is then cut at a particular position depending on the presence of the identified characteristic, i.e. the presence of a node. A similar method is described in WO 2009/100916.

Furthermore, CH 70201 1 A2 describes a further cutting device for sugar cane stalks. In this case, the sugar cane stalk is conveyed in the longitudinal direction to a node detection unit detecting the nodes of the stalk of the sugar cane. A cutting unit is connected to a control unit so that the cutting unit is activated if a node area is positioned within the cutting unit, thereby cutting out a node area.

Moreover, WO 86/06576 describes a method and an apparatus for dividing plant materials. The method and apparatus relates to improvements in the micro propagation of plants. According to this method the plant is scanned to generate an image signal representative of the optically detectable structure. From the image signal, division locations are determined and a corresponding division signal is generated. In particular, the image signal is processed to produce a co-ordinate map of the structure. Based on this co-ordinate map, branch tips and nodes are identified. A cutting machine is then activated responsive to the division signal to divide the plant material at the detected locations.

Moreover, WO 2013/160241 A1 and WO 2013/160242 A1 describe a method for extracting buds from a stalk of a graminaceous plant. In the methods described therein, before cutting out a vegetal tissue comprising the bud, the position of the bud is automatically detected. For detecting the bud on the stalk, the stalk is irradiated with a laser beam, and the reflected electromagnetic radiation is detected by an optical sensor. It is the object of the present invention to provide a method and a system for detecting a node and/or a bud from a stalk of a graminaceous plant, wherein the bud or the node can be detected reliably with cost-effective equipment.

According to the invention, this object has been achieved by a system as defined in claim 1 and a method as defined in claim 8. Further features of this method and system are defined in the dependent claims.

Accordingly, the present invention provides a method for detecting a node and/or a bud from a stalk of a graminaceous plant comprising the steps of obtaining a picture of at least a part of the stalk, showing the projection of a lateral view of the stalk, and analyzing the obtained picture, wherein the distance of a position of the outline of the projection of the lateral view from a straight line is parallel to the longitudinal axis of the stalk as a function of the longitudinal position of the stalk is determined, the algebraic sign of the first derivation of this function is calculated and the longitudinal position of the node and/or the bud is detected at such longitudinal position where the first derivation changes its algebraic sign.

It has been found that the presence of natural dimensional variations of the geometry of the stalk causes the effect of noise in a picture of the stalk that has been taken for detecting a node or a bud. Therefore, direct analysis of the picture leads to false positive detections of nodes or buds. In order to improve the reliability of the detection of a node or a bud, the method of the present invention uses a curve obtained by the outline of the projection of the lateral view of the stalk. However, this curve is not directly used for detecting a node or a bud, but the first derivation of the function of this curve is used for such detection. It has been found that this method provides an improved reliability for the detection of a node or a bud from a stalk of a graminaceous plant. Furthermore, the necessary equipment for carrying out the method is cost- effective, as a camera that is commercially available may be used in connection with software for analyzing the picture obtained by the camera.

The data analysis may be carried out by a processor of the camera. In this case thresholds from which the changing angles will be considered as node or bud has to be set. For example, every stalk that enters the equipment resets the thresholds. Analyzing the first node or bud will then take some time, but once the first node or bud has been detected new thresholds for further nodes or buds of this stalk are generated to be used for detecting the further nodes or buds of the stalk.

In terms of the present invention, "stalk" or "stem" is the main trunk of the graminaceous plant, specifically a primary plant axis that develops buds and shouts. Usually, the stalk is essentially cylindrical. The cross section of the stalk is essentially ring-shaped having essentially a circular periphery. Furthermore, a longitudinal axis is defined to cross the center of the ring shaped cross section of the stalk perpendicular. Preferably the stalk has at least a diameter of 40 mm.

"Node" is the location in the stalk where the shoot, bud or gemma is formed in a graminaceous plant.

"Shoot", "bud" or "gemma" is the embryo, spore or germ of a graminaceous plant.

According to one embodiment, the longitudinal position of the node and/or the bud is detected at such longitudinal position where the absolute value of the first derivation of the function exceeds a predetermined first threshold. In particular, the longitudinal position of the node or the bud may be calculated from the longitudinal position where the first derivation changes its algebraic sign and the longitudinal position where the first derivation of the function exceeds the first threshold. For example, the change of the algebraic sign of the first derivation is a necessary, but not sufficient condition for this longitudinal position. Only if the first derivation of the function exceeds the first threshold in the neighborhood of the position where the first derivation changes its algebraic sign, this longitudinal position is taken as a position where a node or a bud occurs. The first threshold may be larger than 0.1 , corresponding to an angle of about 5° of the outline relative to the direction of the axis of the stalk, preferably larger than 0.27, corresponding to an angle of about 15° of the outline relative to the direction of the axis, and in particular larger than 0.47, corresponding to an angle of about 25° of the outline relative to the direction of the axis.

An alternative or additional sufficient condition for the detection of the longitudinal position of a node or a bud may be that the absolute value of the second derivation of the function exceeds a predetermined second threshold. The second threshold is, for example, when the function of the outline curve reaches its inflexion point, preferably changing direction, and in particular changing pattern to its opposite side from decreasing to increasing. The second threshold is, for example, larger than 0. According to a further embodiment, firstly the longitudinal position of the node is detected, secondly the stalk is rotated around its longitudinal axis, whereby a plurality of pictures of the stalk showing the projection of a lateral view of the stalk around this longitudinal position of the node is obtained at different circumferential angle positions of the stalk, and wherein the plurality of pictures is analyzed. In analyzing the pictures, the distance of a position of the outline of the projection from the longitudinal axis of the stalk at this longitudinal position is generated, and the circumferential angle position of a bud on the node is detected at that angle position where the largest distance of the outline of the projection from the longitudinal axis of the stalk occurs. Therefore, preferably first the node is detected and then the bud on the node is detected. In the method it may not be assured that a bud is shown on the projection of the lateral view of the stalk. If the bud on a node is directed in the direction of the camera, the outline of the lateral view will not show such a bud. In such a case the node will be detected by the method of the present invention. Then the stalk is rotated while pictures being taken. If enough pictures are taken, at least one picture will show the bud on the node. The circumferential angle position may then be obtained by analyzing the distance of the outline from the axis of the stalk. The picture having the largest radial distance from this axis corresponds to a perpendicular direction of a straight line through the bud to the axis relative to the direction from the axis to the camera. If it is known at which orientation the corresponding picture has been taken, the circumferential angle position of the bud is known.

In particular, the picture is obtained by placing the stalk between a light source emitting light in the direction of the stalk and a camera taking the picture of the stalk. In this case, a rather high contrast in the picture of the stalk may be obtained so that the curve of the outline of the stalk can clearly be detected. It is advantageous to know not only the position of a bud in the longitudinal direction of the stalk but also the circumferential angle position of the bud, if the vegetal tissue comprising the bud is to be cut out, so that the extraction of the bud can comprise as much vegetal tissue as necessary but as little vegetal tissue as possible.

According to a further embodiment, the stalk is conveyed to a camera for obtaining the picture, wherein radial forces are exerted to the stalk at adjacent positions along the longitudinal extension of the stalk, said exerted forces being controlled independently of one another to urge said stalk in a straight line before the picture is obtained. Therefore the stalks on which a node and/or a bud is detected are as straight as possible in order to reduce the noise that a curvature may create. In particular, the radial forces are exerted to the stalk by rollers, the rollers also conveying the stalk in the longitudinal direction of the stalk. Furthermore, the position of the rollers is detected for controlling the radial forces exerted to the stalk to bring the stalk in a straight line. In particular, the distance of the rollers from the longitudinal axis of the stalk is detected.

The system for detecting a node and/or a bud from a stalk of a graminaceous plant according to the present invention comprises a camera for obtaining a picture of at least a part of the stalk, showing the projection of a lateral view of the stalk, and an analyzing unit for analyzing the obtained picture, wherein the analyzing unit is adapted to determine the distance of a position of the outline of the projection of the lateral view from a straight line being parallel to the axis of the stalk as a function of the longitudinal position of the stalk, to calculate the algebraic sign of the first derivation of this function and to detect the longitudinal position of the node and/or the bud at such longitudinal position where the first derivation changes its algebraic sign.

The system of the present invention may be adapted to carry out the method of the present invention as described above. The system therefore provides the same advantages as the above described method.

In particular, the above-mentioned straight line may be exactly on the longitudinal axis of the stalk. Therefore, the function shows the radius of the stalk at a particular longitudinal position. According to an embodiment, the system further comprises a light source for emitting light and a conveyer for holding the stalk, said light source, said conveyer and said camera arranged so that the stalk that is carried by the conveyer is placed between the light source and the camera. Furthermore, a translucent screen may be placed between the light source and the stalk that is carried by the conveyer. Such light source and in particular such translucent screen will make sure that the picture taken by the camera has a high contrast between the representation of the stalk in relation to its background.

According to a further embodiment, the conveyer is adapted for conveying the stalk within the camera image capturing area. In addition, the conveyer may comprise pressure roller units arranged at adjacent positions along the longitudinal extension of the stalk for exerting radial forces to the stalk. The pressure roller units are coupled to a control unit for controlling the radial forces exerted by the pressure roller units to said stalk independently of one another so that the stalk is urged in a straight line. According to the system of the present invention any curve of the stalk may be corrected. The extension of a stalk may deviate from an ideal straight line. However, an exact detection of the position of a bud can be carried out more accurately if the stalk is straight. According to the system of the present invention the stalks conveyed to the main detection device are brought into a straight line. Therefore, straight stalks are provided if the stalks are originally not straight. Thus, the detection of the buds on the stalk can be improved. According to one embodiment, the pressure roller units comprise rollers for conveying the stalk in the longitudinal direction of the stalk and for exerting the radial forces to the stalk. In particular, these rollers are rotated by one or more drive motors, for example by step motors. Therefore, the rollers provide two functions: on the one hand, the driven rotation of the rollers conveys the stalk in the longitudinal direction. On the other hand, the rollers exert radial forces to the stalk independently of one another. In this case, the radial direction is defined based on the basically cylindrical shape of the stalk. The radial direction is, therefore, perpendicular to the direction of the longitudinal axis of the stalk. In particular, the rotation axis of each roller is perpendicular to the longitudinal extension of the stalk to be conveyed and the radial force exerted by each roller is directed perpendicular to the longitudinal extension of the stalk to be conveyed as well as perpendicular to the axis of the pressure roller. According to a further embodiment, the rollers are rubber and/or polymer coated in order to convey the stalk in the longitudinal direction by a friction force. A rubber or polymer coating can provide a very precise control of the stalk by the rollers without any slippage. The radial forces exerted to the stalk by the rollers are controlled to urge the stalk in a straight line as well as to provide a friction between the stalk and the rollers that is large enough to convey the stalk in the longitudinal direction of the stalk.

According to a further embodiment, each pressure roller unit comprises a pneumatic spring. Such pneumatic spring may be a metal bellow filled with compressed gas. Such springs may be used as an alternative to a metal wire spring.

According to a further embodiment, each pressure roller unit comprises a guided cylinder that is coupled to the roller, and said guided cylinder is actuated by the pneumatic spring. In particular, the control unit may be coupled with a valve for actuating the pneumatic spring in order to control the force exerted to the guided cylinder and thereby to the roller. In fact, the guided cylinder moves the roller against the stalk in order to exert the radial force to the stalk.

According to a further embodiment, the system comprises at least one turning unit for rotating the stalk around its longitudinal access. This turning unit may also comprise one or more rollers. However, the axes of these rollers are aligned to the longitudinal axis of the stalk, i.e. the axes are parallel to the longitudinal axis of the stalk. Once the longitudinal position of a node has been detected, the turning unit may be used for the detection of a bud on such node.

Embodiments of the present invention are now described with reference to the Figures. Figure 1 shows schematically the structure of an embodiment of the system for detecting nodes and/or buds from a stalk according to the present invention;

Figure 2 shows the arrangement of the stalk relative to the camera and a backlight source;

Figure 3 shows a perspective view of the conveyer;

Figure 4 shows a detailed view of the conveyer and the turning unit;

Figure 5 shows another view of the conveyer and the turning unit shown in Figure 4;

Figure 6 further illustrates the function of a pressure roller unit; Figure 7 shows a cross-section of a stalk with a bud;

Figure 8 shows a perspective view of the stalk shown in Figure 7;

Figure 9 shows a picture that has been taken in an embodiment of the method of the present invention; and

Figures 10 to 12 illustrate the analysis of the picture shown in Figure 9 in accordance with the embodiment of the method of the present invention. The first embodiment of the system and the method of the present invention is now described with reference to the figures:

Sugar cane plants are removed by chopping off with a machete in a height of approximately 2 m to 2.5 m. The removed top part of the sugar cane plants is disregarded. The below, remaining stalks are removed from the field by cutting them off closely above the ground. The stalks are cleaned and prepared for the extraction of the buds. As shown in Figure 1 , such stalk 1 is placed on a conveyer. The conveyer comprises a belt 2 driven by drive rollers 4 for conveying the stalk 1 in direction A. The stalk 1 can be fed to a camera 1 1 that is coupled an analyzing unit 6.

Furthermore, the conveyer comprises pressure roller units 3 to urge the stalk 1 essentially in a straight line, as it will be described in detail later. In addition, pressure roller units 3 may be adapted to convey the stalk 1 in direction A so that the belt 2 may be omitted in particular in the neighborhood of the camera 1 1.

A control unit 28 is coupled to drive rollers 4 and pressure roller units 3. It transfers data indicating the exact longitudinal position of each stalk 1 to the analyzing unit 6. Therefore, the analyzing unit 6 comprises data indicating at each time the position of each stalk 1 in the longitudinal direction.

Figure 2 shows the arrangement of the camera 1 1 and the stalk 1 in the position of the stalk 1 where the picture is taken by the camera 1 1 , i.e. within a camera image capturing area.

As described above, the conveyer conveys the stalk 1 to the camera 1 1 by means of the belt 2 or the pressure roller units 3. When the camera 1 1 takes a picture of a section of the stalk 1 , the conveyor does not convey the stalk 1 so that stalk 1 rests when the picture is taken. After the picture has been taken, the conveyer moves stalk 1 forward in the direction A so that a picture of another section of the stalk 1 can be taken. The control unit 28 controls, in particular, the pressure roller units 3 so that the pictures of the stalk 1 overlap so that pictures of the lateral view of the stalk 1 are taken over the whole stalk 1.

The camera 1 1 is positioned on one side of stalk 1. On the opposite side, a light source 7 is positioned, which emits light in the direction of the camera 1 1. Between the light source 7 and the camera 1 1 and between the light source 7 and the stalk 1 , a translucent screen is positioned. The translucent screen 18 will provide a homogeneous bright backlight for the picture of stalk 1 taken by camera 1 1. Therefore, the picture will have a high contrast between the representation of the stalk 1 and its background.

In the following, the conveyer comprising the pressure roller units 3 will be described in more detail with reference to Figures 3 to 6:

The conveyer comprises pressure roller units 3 arranged at adjacent positions along the longitudinal extension of the stalk 1 . The distance between the pressure roller units 3 may be in the range of 5 cm to 30 cm depending on the length of the stalk 1 and its curvature. The pressure roller units 3 comprise rollers 9. The rollers 9 are coated by a polymer or by rubber to provide a large friction force when contacting the surface of the stalk 1 . The rollers 9 are pivotally mounted on an axle and driven by a first drive motor 30.

Furthermore, each pressure roller unit 3 comprises a guided cylinder 33 that is movably mounted within a housing 34. The guided cylinder 33 is coupled to the axle that supports the roller 9. By movement of the guided cylinder 3 the roller 9 can be brought into contact with the surface of the stalk 1.

Moreover, each pressure roller unit 3 comprises a pneumatic spring 35 within the housing 34. The pneumatic spring 35 is coupled to the control unit 28. Therefore, control unit 28 can initiate movement of each guided cylinder 33 by means of each pneumatic spring 35. Furthermore, control unit 28 can control for each pressure roller unit 3 the radial force that each roller 9 exerts to stalk 1 independently.

Figure 6 shows the geometry of a roller 9 relative to stalk 1. The roller 9 contacts the circumferential surface of stalk 1 and is urged by force F against stalk 1. In order to convey the stalk 1 in the direction of the arrow A in the longitudinal direction of the stalk 1 , the roller 9 is driven by first drive motor 30 in the direction of arrow B. Therefore, the rotation axis of the roller 9 is perpendicular to the longitudinal extension of the stalk 1 as well as the conveying direction A. Furthermore, the radial force F exerted by roller 9 to the stalk 1 is directed perpendicular to the longitudinal extension of the stalk 1 as well as perpendicular to the axis of the roller 9.

Returning to Figures 3 to 5, it can be seen that the pressure roller units 3 are arranged at adjacent positions along the longitudinal extension of the stalk 1 as well as on different angle positions at one particular longitudinal position of the stalk 1 . In particular, at one longitudinal position of the stalk 1 , three rollers 9 contact the stalk 1 and exert a radial force F to the stalk 1 . The angle between the three rollers 9 at one longitudinal position of the stalk 1 may be 120°. The position of each roller 9 relative to the surface of the stalk 1 as well as the radial force F exerted by each roller 9 is controlled by the guided cylinders 33 and the pneumatic springs 35 of the pressure roller units 3 in connection with the control unit 28. The radial position of the rollers 9 and the exerted forces F are controlled by control unit 28 such that the stalk 1 is urged in a straight line. Therefore, by means of the pressure roller units 3 in connection with the control unit 28 the stalk 1 is brought in a straight line and at the same time conveyed in direction A to convey the stalk 1 to the camera 1 1 .

The system further comprises turning units 36 as shown in Figures 4 and 5. The turning units 36 are similar to the pressure roller units 3. However, turning units 36 comprise rollers 37 that have a different orientation. The axle of rollers 37 is parallel to the longitudinal extension of the stalk 1. Furthermore, the rollers 37 may also be moved in the direction of the surface of the stalk 1 by means of a guided cylinder 38 of each of the turning units 36. The guided cylinders 38 of turning units 36 are coupled with the control unit 28, so that the stalk 1 can be rotated around its axis by means of rollers 37 that are also driven by a second drive motor such as a step motor.

The operation of the system as described with reference to Figures 3 to 6 is as follows:

Firstly, the control unit 28 controls the pressure roller units 3 so that rollers 9 are in pressure contact with the surface of stalk 1 . Rollers 9 are then rotated by first drive motors 30 so that the stalk 1 is moved forward. Simultaneously, the radial position of rollers 9 is detected with respect to the longitudinal axis of the stalk 1 . The control unit 28 then controls the radial position of rollers 9 independently from each other, thereby exerting a radial force to the stalk 1 for bringing stalk 1 in a straight line. Figures 7 and 8 show a cross section and a perspective view of a stalk 1.

Usually the stalk 1 comprises nodes 5 that are ring-shaped and spaced apart from each other in the longitudinal direction of the stalk 1. Each node 5 comprises one bud 8. The buds 8 of consequent nodes are located approximately on opposite directions of the stalk 1.

In Figures 7 and 8 the stalk 1 is only shown partly, comprising one node 5 including one bud 8. The stalk 1 defines a longitudinal direction L and a straight line S that passes through the center M of the stalk 1 and the position of bud 8. However, it is mentioned that not all buds have the same circumferential angle position on the surface of stalk 1 .

In the following, further details of the embodiment of the system of the present invention are described with reference to embodiments of the method of the present invention referring to Figures 9 to 12:

As described above, the stalk 1 is conveyed to the camera 1 1 so that pictures of the lateral view of the stalk 1 are taken section by section. Figure 9 shows such a picture 12. The picture 12 shows the projection of the lateral view of the stalk 1 . Such projection shows a graphical representation 13 of the stalk 1 as well as a graphical representation 14 of a node 5.

This picture 12 is analyzed by analyzing unit 6 as follows:

Firstly, the longitudinal axis X of the stalk 1 is determined by means of the graphical representation 13 in picture 12. Then the outline O on one side of the longitudinal axis X is determined by means of picture 12. For determining the outline O the high contrast between the graphical representation 13 of the stalk 1 and the background is advantageous. Then the distance of a position of the outline O of the projection of the lateral view from the longitudinal axis X of the stalk 1 is determined as a function of the longitudinal position I of the stalk 1 . This function f is shown in Figure 10 by graph 15.

Thereafter, the first derivation of this function f is calculated. Figure 1 1 shows the first derivation f of this function f by graph 16. Then the longitudinal position IN is determined at which the algebraic sign of the first derivation f of the function f changes.

This longitudinal position IN is taken as the longitudinal position IN of the node 5.

Furthermore, this longitudinal position IN is the longitudinal position IN of the bud 8. By means of this procedure the longitudinal position of node 5 and/or the bud 8 is detected.

According to another embodiment, the longitudinal position IN of the node 5 and/or the bud 8 is detected at such longitudinal position where the absolute value of the first derivation f of the function f exceeds a predetermined first threshold. As can be seen from Figure 1 1 , the absolute value of the first derivation f at the transition to the node 5 is rather high. Therefore, a very high absolute value of the first derivation f of the function f indicates the presence of a node 5 and a bud 8. The first threshold may be larger than 0.1 , corresponding to an angle of about 5° of the outline relative to the direction of the axis, preferably larger than 0.27, corresponding to an angle of about 15° of the outline relative to the direction of the axis, and in particular larger than 0.47, corresponding to an angle of about 25° of the outline relative to the direction of the axis. According to a further embodiment, the longitudinal position IN of the node 5 and/or the bud 8 is detected by considering the change of the algebraic sign of the first derivation f of the function f as well as the absolute value of the first derivation f in the neighborhood of the longitudinal position IN. AS can be seen from Figure 1 1 , at the boundary and of the node 5 the absolute value of the first derivation f is rather high.

According to a further embodiment, the longitudinal position IN of the node 5 and/or the bud 8 is detected at such longitudinal position where the absolute value of the second derivation f" of the function f exceeds a predetermined second threshold. In this case, the second derivation f" is calculated by analyzing unit 6. Figure 12 shows the second derivation f" as a graph 17. As it can be derived from Figure 12, the absolute value of the second derivation f" is rather high at longitudinal positions of the node 5. The second threshold will be an indication that a node or bud has been reached. The second threshold is, for example, when the curve reaches its inflexion point, preferably changing direction, and in particular changing pattern to its opposite side from decreasing to increasing. The second threshold is, for example, larger than 0.

Again, the second derivation f may be considered for detecting the longitudinal position IN of the node 5 and/or the bud 8 in addition to the above-mentioned change of the algebraic sign of the first derivation f and/or the absolute value of the first derivation f of the function f.

According to the method of the present invention, not only the longitudinal position IN of the node 5 can be detected but also the circumferential angle position of a bud 8, as depicted in Figures 7 and 8. For detecting the circumferential angle position of a bud 8, firstly the longitudinal position IN of a node 5 is detected as described above. Then the stalk 1 is rotated around its longitudinal axis L by means of turning units 36. In particular, stalk 1 is rotated about a small angle that may for example be in the range of 1 ° to 10°. Then a picture is taken by camera 1 1 . Thereafter, stalk 1 is again rotated about this small angle, and again a picture is taken by camera 1 1 . Therefore, a plurality of pictures of the stalk 1 showing the projection of a lateral view of the stalk 1 around its longitudinal position of the node 5 is obtained at different circumferential angle positions of the stalk 1 . These pictures are analyzed, wherein the distance of a position of the outline O of the projection from the longitudinal axis X of the stalk 1 at the longitudinal position of a node 5 is generated. The circumferential angle position of a bud 8 on the node 5 is detected at such angle position where the largest distance of the outline O of the projection form the longitudinal axis X of the stalk 1 occurs. Once the longitudinal position IN as well as the circumferential angle position of a bud 8 have been detected as described above, the stalk 1 can be conveyed to a cutting device for cutting out a vegetal tissue comprising the bud 8. This is, for example, described in detail in WO 2013/160241 A1 and WO 2013/160242 A1.

List of reference signs:

1 stalk

2 belt

3 pressure roller unit

4 drive roller for belt

5 node

6 analyzing unit

7 light source

8 bud

9 rollers

10 initial cutting device

1 1 camera

12 picture

13 graphical representation of the stalk

14 graphical representation of the node

15 graph

16 graph

17 graph

18 translucent screen

28 control unit

29 machine table

30 first drive motor

31 motor

32 cutting device

33 guided cylinder

34 housing

35 pneumatic spring

36 turning units

37 rollers

38 guided cylinder

Claims

Method for detecting a node and/or a bud from a stalk of a graminaceous plant comprising:

obtaining a picture of at least a part of the stalk, showing the projection of a lateral view of the stalk, and

analyzing the obtained picture, wherein the distance of a position of the outline of the projection of the lateral view from a straight line that is parallel to the longitudinal axis of the stalk as a function of the longitudinal position of the stalk is determined, the algebraic sign of the first derivation of this function is calculated, and the longitudinal position of the node and/or the bud is detected at such longitudinal position where the first derivation changes its algebraic sign.

Method according to claim 1 , wherein the longitudinal position of the node and/or the bud is detected at such longitudinal position where the absolute value of the first derivation of the function exceeds a predetermined first threshold.

Method according to claim 1 or 2, wherein the longitudinal position of the node and/or the bud is detected at such longitudinal position where the absolute value of the second derivation of the function exceeds a predetermined second threshold.

Method according to any one of the preceding claims, wherein firstly the longitudinal position of the node is detected, secondly the stalk is rotated around its longitudinal axis whereby a plurality of pictures of the stalk showing the projection of a lateral view of the stalk around this longitudinal position of the node is obtained at different circumferential angle positions of the stalk, and wherein the plurality of pictures is analyzed, wherein the distance of a position of the outline of the projection from the longitudinal axis of the stalk at this longitudinal position is generated, and the circumferential angle position of a bud on the node is detected at such angle position where the largest distance of the outline of the projection from the longitudinal axis of the stalk occurs.

Method according to any one of the preceding claims, wherein the stalk is conveyed to a camera for obtaining the picture, wherein radial forces are exerted to the stalk at adjacent positions along the longitudinal extension of the stalk, said exerted forces being controlled independently of one another to urge said stalk in a straight line before the picture is obtained.

6. Method according to claim 5, wherein radial forces are exerted to the stalk by

rollers, said rollers also conveying the stalk in the longitudinal direction of the stalk.

7. Method according to claim 5 or 6, wherein the position of the rollers is detected for controlling the radial forces exerted to the stalk to bring the stalk in a straight line.

8. System for detecting a node and/or a bud from a stalk of a graminaceous plant comprising:

a camera for obtaining a picture of at least a part of the stalk, showing the projection of a lateral view of the stalk, and

an analyzing unit for analyzing the obtained picture, wherein the analyzing unit is adapted to determine the distance of a position of the outline of the projection of the lateral view from a straight line that is parallel to the axis of the stalk as a function of the longitudinal position of the stalk, to calculate the algebraic sign of the first derivation of this function, and to detect the longitudinal position of the node and/or the bud at such longitudinal position where the first derivation changes its algebraic sign.

9. System according to claim 8, further comprising a light source for emitting light and a conveyer for holding the stalk, said light source, said conveyer and said camera being arranged so that the stalk that is carried by the conveyer is placed between the light source and the camera.

10. System according to claim 9, further comprising a translucent screen that is placed between the light source and the stalk that is carried by the conveyer.

1 1 . System according to any one of claims 8 to 10, wherein the conveyer is adapted for conveying the stalk within the camera image capturing area.

12. System according to any one of claims 8 to 1 1 , wherein said conveyer comprises pressure roller units arranged at adjacent positions along the longitudinal extension of the stalk for exerting radial forces to the stalk, and said pressure roller units are coupled to a control unit for controlling the radial forces exerted by the pressure roller units to said stalk independently of one another so that the stalk is urged in a straight line.

13. System according to any one of claims 8 to 12, wherein said pressure roller units comprise rollers for conveying the stalk in the longitudinal direction of the stalk and for exerting the radial forces to the stalk.

14. System according to any one of claims 8 to 13, wherein the system comprises at least one turning unit for rotating the stalk around its longitudinal axis.

15. System for extracting buds from a stalk of a graminaceous plant comprising:

a detection device for detecting a bud on a stalk; and a cutting device for cutting out a vegetal tissue comprising the bud based on the detected position of the bud,

wherein the detection device comprises the system for detecting buds from a stalk of a graminaceous plant according to any one of claims 8 to 14.