EP3390730A1

EP3390730A1 - System and method for determining a material entity to be removed from a pile and a control unit for a working machine comprising such a system

Info

Publication number: EP3390730A1
Application number: EP15910863.8A
Authority: EP
Inventors: Torbjörn MARTINSSON; Martin Magnusson
Original assignee: Volvo Construction Equipment AB
Current assignee: Volvo Construction Equipment AB
Priority date: 2015-12-18
Filing date: 2015-12-18
Publication date: 2018-10-24
Anticipated expiration: 2035-12-18
Also published as: CN108431336A; EP3390730B1; EP3390730C0; WO2017105308A1; US20180347154A1; EP3390730A4; CN108431336B

Abstract

The present invention relates to a system (18) for determining a material entity (32) to be removed from a pile (16) by means of an implement (12) of a material moving machine (10). The system (18) comprises means for generating a current pile shape (26) of the actual surface shape of the pile (16). Moreover, the system (18) is adapted to determine a nominal pile shape (28) of at least a portion of the pile (16). The nominal pile shape (28) is determined on the basis of at least the current pile shape (26) and information regarding the material type of the pile (16). Further the system (18) is adapted to determine a surplus volume (30) between the nominal pile shape (28) and the current pile shape (26) and the system (18) is adapted to determine the material entity (32) to be removed from the pile (16) on the basis of the surplus volume (30).

Description

SYSTEM AND METHOD FOR DETERMINING A MATERIAL ENTITY TO BE REMOVED FROM A PILE AND A CONTROL UNIT FOR A WORKING MACHINE COMPRISING SUCH A SYSTEM.

TECHNICAL FIELD

The present invention relates to a system for determining a material entity to be removed

5 from a pile according to the preamble of claim 1 . Moreover, the present invention relates

to a material moving machine comprising such a system. Further, the present invention relates to a method for determining a material entity to be removed from a pile.

Additionally, the present invention relates to a method for removing material from a pile.

10 BACKGROUND

A material moving machine may be used for a plurality of material moving operations. One example of such operations is moving material from a material pile. Purely by way of example, moving material from a pile may be carried out when performing re-handling of processed material. Non-limiting examples of a material moving machine may be a wheel 15 loader, an excavator or the like.

Generally, an operation of moving material from a material pile comprises: digging into the pile with an implement of the material moving machine, at least partially filling the

implement and moving the removed material to another location, e.g. by moving the 20 material moving machine.

In order to be able to appropriately dig into a pile and fill an implement with material, US 2015/0046044 A1 proposes a method which evaluates a set of possible attack poses for an implement in order to select an attack pose that results in an appropriate filling of the 25 implement.

Although the method presented in 2015/0046044 A1 is appropriate for many material moving operations, there is still a need for improvements of strategies for removing

material from a material pile.

30 SUMMARY

An object of the present invention is to obtain a system for determining a material entity to be removed from a pile which system can be used for an efficient material moving operation.

The above object is achieved by the system according to claim 1.

As such, the present invention relates to a system for determining a material entity to be removed from a pile by means of an implement of a material moving machine. The system comprises means for generating a current pile shape representing the actual shape of the pile. Moreover, the system is adapted to determine a nominal pile shape of at least a portion of the pile, the nominal pile shape being determined on the basis of at least the current pile shape and information regarding the material type of the pile. The system is adapted to determine a surplus volume between the nominal pile shape and the current pile shape. Further, the system is adapted to determine the material entity to be removed from the pile on the basis of the surplus volume.

The system according to the above implies that preferred attack poses may be chosen. Furthermore, the above system implies the possibility to maintain an appropriate pile shape during a material removing procedure. For instance, as compared to prior art solutions, the above system implies a reduced risk of having a deterioration of the pile during a material moving sequence. This in turn implies a more efficient and productive material moving operation, in particular if material is moved from the pile during an autonomous operation.

Moreover, by virtue of the face that the material entity to be removed is determined on the basis of the surplus volume between the nominal pile shape and the current pile shape, a material removal strategy can be selected in which the material to be removed, at least to some extent, slides into the implement. This is turn implies that material may be removed from the pile without necessarily having to force the implement through the pile in order to fill the implement. Instead, the implement may be moved relative to the pile and material will slide into the implement as the implement moves. As such, material may be removed from the pile with a relatively low energy consumption. Optionally, the information regarding the material type of the pile comprises a nominal angle of repose for the material type. The nominal angle of repose implies that the nominal pile shape may be determined in a straightforward manner. Optionally, the system is adapted to determine an excluding portion of the pile. Moreover, the system is adapted to determine a portion of the nominal pile shape which extends from the excluding portion in a direction determined by the information regarding the material type of the pile. Certain piles may for instance have a relatively planar portion, such as a planar top or a ramp extending from the bottom towards the top of the pile, and it has been realized that the surplus volume determination may be improved if such portions are excluded when determining a portion of the nominal pile shape by the information regarding the material type of the pile. In particular, such portions may be excluded when determining portion of the nominal pile shape using the nominal angle of repose.

Optionally, the system is adapted to determine a horizontal main extension direction of the excluding portion. Moreover, the system is adapted to determine a main material removal direction that is substantially parallel to the horizontal main extension direction.

If a pile comprises an excluding portion with a horizontal main extension direction, a material removing strategy may be determined which takes such a horizontal main extension direction into account. Such a strategy implies a reduced risk of obtaining an impaired pile, e.g a pile with crevices or the like.

Moreover, selecting a main material removal direction in accordance with the above indicates a material removal that eventually results in that the pile assumes a relatively conical shape which thereafter can be removed in a straightforward manner. Optionally, the excluding portion comprises a portion approximated by a line or a polygon, preferably a rectangle. Approximating the excluding portion with a line or a polygon implies that the general shape of the excluding portion may be determined in a straightforward manner. As a non-limiting example, the excluding portion comprises a portion approximated by a rectangle. Optionally, the pile has an extension in a vertical direction and the excluding portion of the pile is determined to be located above the nominal pile shape in the vertical extension. If the excluding portion is located in the above-mentioned position, the pile generally has a frustoconical shape. In such an event, it is generally beneficial to determine the surplus volume as a volume that is located between the envelope surface of the frustoconical shape and a nominal pile shape that extends from the excluding portion down to the bottom portion of the pile.

Optionally, the pile has a bottom portion, the system being adapted to determine if the excluding portion extends to the bottom portion. If the excluding portion extends to the bottom portion, the excluding portion generally forms a ramp up the pile.

Optionally, when the system determines that the excluding portion extends to the bottom portion, the system determines that the material entity to be removed from the pile comprises the excluding portion. As has been indicated hereinabove, the excluding portion may in the present case be regarded as a ramp that extends up the pile. In such an event, the ramp generally has a ramp inclination relative to a vertical axis which ramp inclination is less than the angle of repose for the pile material. As such, a relatively large portion of the ramp may be removed before the associated side of the pile assumes a configuration that approaches the nominal pile shape. As such, it may be suitable to start with removing portions of the ramp.

Optionally, the means comprises a perception assembly for generating the current pile shape, the perception assembly preferably comprising at least one of a camera and a laser sensor. A camera and/or a laser sensor imply appropriate means for generating the current pile shape.

Optionally, the means is adapted to generate a three-dimensional current pile shape representing the actual shape of the pile, the perception assembly preferably comprising at least one of a time-of-flight camera, a stereo camera, a structured light camera or an actuated laser range finder. A three-dimensional current pile shape implies an appropriate possibility to determine current pile shape as such, but also an appropriate possibility to determine a shape of a excluding portion. For instance, a three-dimensional shape of the excluding portion may be determined. Optionally, the system is adapted to determine the current pile shape and/or the nominal pile shape when material has been removed from the pile. When material has been removed from the pile, the shape of the pile generally changes. As such, in order to be able to determine the surplus volume in an appropriate manner, at least one of the current pile shape and the nominal pile shape may be re-determined after the material has been removed from the pile.

Optionally, the material entity is a material volume. Optionally, the implement has a maximum material loading capacity and the system is adapted to determine the material entity to be removed from the pile on the basis also of the maximum material loading capacity.

Purely by way of example, it is envisaged that, in one embodiment of the system, the current pile shape as well as the nominal pile shape are updated after every scoop of removed material. However, it is also envisaged that, in other embodiments of the system, the current pile shape and/or the nominal pile shape is updated less frequently, e.g. every fifth or tenth scoop of removed material. Further, in embodiments of the system, the frequency at which the current pile shape is updated differs from the frequency at which the nominal pile shape is updated. As a non-limiting example, the current pile shape may be updated more frequently than the nominal pile shape.

A second aspect of the present invention relates to a material moving machine, comprising an implement and a system according to the first aspect of the present invention. A material moving machine according to the second aspect may be used for removing material from a pile in an efficient manner.

A third aspect of the present invention relates to a method for determining a material entity to be removed from a pile by means of an implement of a material moving machine.

The method comprises:

- generating a current pile shape representing the actual shape of the pile,

- determining a nominal pile shape of at least a portion of the pile, the nominal pile shape being determined on the basis of at least the current pile shape and information regarding the material type of the pile, - determining a surplus volume between the nominal pile shape and the current pile shape, and

- determining the material entity to be removed from the pile on the basis of the surplus volume.

Optionally, the information regarding the material type of the pile comprises a nominal angle of repose for the material type.

Optionally, the method further comprises determining an excluding portion of the pile and determining a portion of the nominal pile shape which extends from the excluding portion in a direction determined by the information regarding the material type of the pile.

Optionally, the method further comprises determining a horizontal main extension direction of the excluding portion. Moreover, the method further comprises determining a main material removal direction that is substantially parallel to the horizontal main extension direction.

Optionally, the excluding portion comprises a portion approximated by a line or a polygon. Optionally, the pile has an extension in a vertical direction and the excluding portion of the pile is located above the nominal pile shape in the vertical extension.

Optionally, the pile has a bottom portion, the method comprises determining if the excluding portion extends to the bottom portion.

Optionally, upon determination that the excluding portion extends to the bottom portion, the method determines that the material entity to be removed from the pile comprises the excluding portion. Optionally, the pile has an extension in a vertical direction and the excluding portion of the pile is located above the nominal pile shape.

Optionally, the material entity is a material volume. Optionally, the implement has a maximum material loading capacity and the method comprises determining the material entity to be removed from the pile on the basis also of the maximum material loading capacity. A fourth aspect of the present invention relates to a method for removing material from a pile by means of an implement of a material moving machine.

The method comprises:

- determining a material entity to be removed from the pile using a method

according to the third aspect of the present invention and

- operating the implement so as to remove the thus determined material entity from the pile.

Optionally, the method further comprises determining the current pile shape and/or the nominal pile shape when material has been removed from the pile.

A fifth aspect of the present invention relates to a control unit for a working machine, the control unit being adapted to:

- generate a current pile shape representing the actual shape of the pile,

- determine a nominal pile shape of at least a portion of the pile, the nominal pile shape being determined on the basis of at least the current pile shape and information regarding the material type of the pile,

- determine a surplus volume between the nominal pile shape and the current pile shape, and

- determine the material entity to be removed from the pile on the basis of the

surplus volume.

Optionally, the working machine comprises an implement and the control unit is further adapted to issue a signal to the working machine to operate the implement so as to remove the thus determined material entity from the pile. BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples. In the drawings:

Fig. 1 is a schematic perspective view of a material moving machine and a pile; Fig. 2 is a schematic side cross-sectional view of one type of pile;

Fig. 3 is a schematic side cross-sectional view of another type of pile; Fig. 4 is a point cloud image of the Fig. 3 pile; Fig. 5 is a schematic perspective view of a further pile type;

Fig. 6 is a schematic perspective view of yet another pile type, and Fig. 7 is a flow chart of a method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will be described in the following for a material moving machine in the form of a wheel loader 10 such as the one illustrated in Fig. 1. The wheel loader 10 should be seen as an example of a material moving machine which could comprise a system according to the present invention and/or for which the method of the present invention may be used.

However, it is also envisaged that the present invention may be implemented in another type of material moving machine, such as an excavator (not shown) or a bulldozer (not shown). Moreover, it should be emphasized that although the invention is described hereinbelow with reference to a movable material moving machine, it is also envisaged that the moving machine may be a stationary moving machine. The Fig. 1 material moving machine 10 comprises an implement 12 which in the Fig. 1 embodiment is exemplified by a bucket. Moreover, the material moving machine 10 comprises an actuating arrangement 14 for lifting and/or tilting the implement 12. Purely by way of example, the actuating arrangement 14 may comprise a hydraulic actuator and/or an electric actuator (not shown in Fig. 1 ).

Purely by way of example, the implement 1 may be adapted to be moved, relative to the ground and/or relative to the remaining portion of the material moving machine 10, to thereby be loaded with material.

Fig. 1 further illustrates a pile 16 of material. Purely by way of example, the material may comprise sand, gravel, soil, pebbles, rocks or the like. In a material removal operation, the material moving machine is adapted to remove a portion of the pile 16 or, alternatively, the complete pile 16.

Fig. 1 also illustrates a system 18 for determining a material entity to be removed from the pile 16 by means of an implement of a material moving machine. In Fig. 1 , the material moving machine 10 comprises the system 18. However, it is also envisaged that the system 18 may be spatially separated from the material moving machine 10. Purely by way of example, the system 18, or at least parts of it, may be located in a stationary or moving object (not shown in Fig. 1 ) spatially separated from the material moving machine 10.

The system 18 comprises means for generating a current pile shape representing the actual shape of the pile 16. Such means may also be referred to as a current pile shape generator. As a non-limiting example, such means may comprise a perception assembly for generating the current pile shape. Purely by way of example, the perception assembly may comprise at least one of a camera and a laser sensor. The perception assembly may be used for generating an image of the actual shape of the pile 16 which image thereafter may be used for generating the current pile shape representing the actual shape of the pile 16. The means for generating a current pile shape may comprise a pile shape generation electronic control unit 19 that is adapted to receive information from the perception assembly and process the information thus received in order to generate the current pile shape. In the event that the means is adapted to generate a three-dimensional current pile shape, the perception assembly may comprise at least one of a time-of-flight camera, a stereo camera, a structured light camera or an actuated laser range finder such that a three-dimensional image of the surface pile 16 may be generated.

To this end, though purely by way of example, the image of the actual shape of the pile may be generated by a point cloud measurement of the pile 16 and optionally the surrounding area. For instance, such a point cloud measurement may be determined by collecting data with an actuated Sick LMS21 1 laser range finder or a Velodyne HDL-64E, after which the data are registered with a suitable algorithm such as 3D-NDT or ICP.

Moreover, a point cloud measurement may also comprise segmentation of the point cloud to isolate the points that belong to the pile 16. An example of such segmentation is described in WO2013043087A1 .

The Fig. 1 material moving machine 10 is presented with two implementations of the perception assembly 20. In the first implementation, a perception assembly 20' is attached to the material moving machine 10. Purely by way of example, and as is indicated in Fig. 1 , the material moving machine 10 may comprise a cabin 22 with a cabin top 24, wherein at least the portion of the perception assembly 20' of the first alternative is attached to the cabin top 24. However, it is also envisaged that the first alternative implementation of the perception assembly 20' may be attached to another portion of the material moving machine 10, such as the actuating arrangement 14 or, alternatively, the implement 12. For instance, the perception assembly 20' may be connected to the uppermost portion of the implement s.

In the second implementation of the perception assembly, a perception assembly 20" is not attached to the material moving machine 10. Moreover, though purely b way of example, the perception assembly 20" in accordance with the second implementation is spatially separated from the material moving machine 10. As non-limiting examples, the perception assembly 20" in accordance with the second alternative implementation may be located on a stationary object, such as a mast 26 or the like, or a perception assembly 20"' may be located on a moving object (not shown). By way of example only, the moving object may be an object that is capable of flying and that has one or more rotors, e.g. a helicopter or a quadcopter. In the event that a plurality of material moving machines (not shown in Fig. 1 ) removes material from the same pile 16, the material moving machines may use the same perception assembly; either a perception assembly 20' that is attached to one of the material moving machines or a perception assembly 20" that is not attached to any one of the material moving machines.

When the image of the actual shape of the pile has been generated, a current pile shape representing the actual shape of the pile 16 may be generated. Purely by way of example, the current pile shape may be the same as the generated image of the surface pile 16. However, it is also envisaged that the current pile shape is generated on the basis on the image of the pile surface. In other words, the current pile shape may be generated by further processing information obtained from the image of the pile surface. For instance, in the event that the image of the pile surface is generated by point cloud measurement of the pile 16, and optionally the surrounding area, as has been discussed hereinabove, the current pile shape may be constituted by the point cloud as such or, alternatively, the current pile shape may be generated by triangulation of the point cloud wherein triangles are formed between adjacent points in the point cloud. It is also envisaged that the current pile shape may be processed by applying a smoothing function to the points in the point cloud such that local discontinuities in the surface formed by the points of the point cloud are smoothen out when generating the current pile shape.

Irrespective of the implementation of the perception assembly, the pile shape generation electronic control unit 19 may preferably communicate with the perception assembly, e.g. via cables and/or via wireless communication. However, in implementations of the means for generating a current pile shape, the electronic control unit 19 and the perception assembly may form a unitary component that is adapted to transmit the current pile shape to another portion of the system 18.

The system 18 is optionally also adapted to receive information indicative of the material type of the pile 16. Purely by way of example, the system 18 may be adapted to receive input from an operator indicative of the material type. As another option, the system 18 may be able to determine the type of material by e.g. reading the weight of the material loaded into the implement, for instance using one or more weight sensors (not shown), determining the volume of the material loaded into the bucket, e.g. using the above- discussed image and/or the above-discussed surface model, determining the density of the material and from the density thus determined establish the type of material.

As a further option, the system 18 may be able to determine the type of material by determining the location of the bucket, e.g. using a GPS system or the like, and using data of the material at that location, e.g. using a database, a look-up table, and thus determine the type of material.

It should be noted that the information regarding the material need not necessarily include the type of material as such. As a non-limiting example, the information regarding the material may be an angle of repose that is determined to be appropriate for a plurality of material types, for instance a plurality of material types that are located in the vicinity of the pile 16. Thus, though purely by way of example, if a working machine is positioned in a specific geographical location, one strategy could be to assume that all piles in that location contains material with approximately the same angle of repose. On the other hand, it is also envisaged that the information regarding the material may comprise information as regards the actual material type.

In addition to determining the current pile shape, and as will be explained further hereinbelow, the system 18 is adapted to determine a surplus volume between a nominal pile shape and the current pile shape and determining the material entity to be removed from the pile on the basis of that surplus volume. To this end, the system may comprise a control unit 21 , for instance an electronic control unit, which is adapted to carry out the above procedure. In embodiments of the system 18, the control unit 21 and the pile shape generation electronic control unit 19 may be separate components and the control unit 21 may be adapted to receive information from the pile shape generation electronic control unit 19. However, it is also envisaged that embodiments of the system 18 may comprise a single control unit 21 a first portion of which forms part of the means for generating a current pile shape 26 and a second portion of which is adapted to determine the surplus volume and determining the material entity to be removed from the pile on the basis of that surplus volume. Purely by way of example, the control unit 21 may be an electronic control unit configured to run a first computer program that is adapted to receive information from the perception assembly 20 and generate a current pile shape 26 and also to run a second computer program that is adapted to receive information from the current pile shape 26 and determine the nominal pile shape, the surplus volume and the matehal entity to be removed from the pile 16.

Fig. 2 illustrates an example of a current pile shape 26. The current pile shape 26 may preferably be three-dimensional, but in order to simplify the description of the present invention, a two-dimensional cross-section of a current pile shape is illustrated in Fig. 2.

The system 18 is adapted to determine a nominal pile shape 28 of at least a portion of the pile. The nominal pile shape 28 is determined on the basis of at least the current pile shape 26 and information regarding the mate al type of the pile from which the current pile shape was generated.

A material type parameter that may be relevant when determining the nominal pile shape 28 is the nominal angle of repose a, viz the steepest angle relative to a horizontal plane to which a material can be piled without slumping, for the matehal loaded into the bucket 12.

Moreover, the system 18 is adapted to determine a surplus volume 30 between the nominal pile shape 28 and the current pile shape 26. Further, the system 18 is adapted to determine the material entity 32 to be removed from the pile on the basis of the surplus volume 30.

In Fig. 2, the material entity 32 is exemplified by a material volume. However, it is also envisaged that in other embodiments of the system 18, the material entity 32 may relate to another physical property of the material to be removed. Purely by way of example, the matehal entity 32 may relate to the weight of the material to be removed. When the matehal entity 32 relates to the material weight, the system 18 may be adapted to, based on the surplus volume 30 and possibly also on additional material properties such as the density, determine how the implement 12 should move in relation to the pile 16 in order to remove a preferred material weight.

In the example illustrated in Fig. 2, the pile extends down to a ground level 34 and the matehal entity 32 to be removed from the pile is chosen such that the material entity 32 has a bottom portion that is located relatively close to the ground level 34 and that the matehal entity 32 has one side 32' that is located relatively close to the nominal pile shape 28. It is generally preferred to choose the material entity 32 such that a portion thereof is located at, or at least close to, the ground level 34. By such a choice, once the material entity 32 has been removed from the pile, material of the pile that is located above the material entity 32 may start sliding downwards such that a new surplus volume is formed at a relatively low elevation. The new surface that is created by the material that has slid downwards will generally have a surface angle that is close to the angle of repose a.

It is generally preferred to choose the material entity 32 such the material entity 32 does not extend into the nominal pile shape 28 in order to avoid excessive sliding of material. However, in certain conditions, e.g. when the surplus volume is small 30, e.g. due to the fact that the current pile shape 26 is similar to the nominal pile shape 28, the material entity 32 may be allowed to extend into the nominal pile shape 28. In the Fig. 2 example, the nominal pile shape 28 has been determined by identifying the top portion 35 of the current pile shape 26 and generating a cone the inclination of which corresponds to the angle of repose and the apex of which is located at the top portion 35 of the current pile shape 26. Moreover, the implement 12 may have a maximum material loading capacity. For instance, the implement 12 may have maximum material loading volume and/or a maximum material loading weight. As s non-limiting example, the system may be adapted to determine the material entity 52 to be removed from the pile 16 on the basis also of the maximum material loading capacity.

Fig. 3 illustrates another implementation for determining the nominal pile shape 28. As for the pile illustrated in Fig. 2, a two-dimensional cross-section of a current pile shape is illustrated in Fig. 3. In the Fig. 3 implementation, the system 18 is adapted to determine an excluding portion 36 of the pile which should be excluded from a portion of the nominal pile shape 28 which portion is determined by the information regarding the material type of the pile, e.g. the nominal angle of repose a. As such, the system 18 is adapted to determine a portion of the nominal pile shape 28 which extends from the excluding portion 36 in a direction determined by the information regarding the material type of the pile 16. In the Fig. 3 example, the excluding portion 36 has a planar shape with a circumference 38 and the nominal pile shape 28 is determined by generating a surface with two ends, a first surface end being aligned with the circumference 38 of the excluding portion 36 and a second surface end being located on ground level 34. The surface extends from the circumference 38 to the ground level with the angle of repose a. As may be gleaned from Fig. 3, generating the nominal pile shape 28 in the above-discussed manner may result in a frustoconical nominal pile shape 28. If the current pile shape 26 comprises a plurality of points or nodes, for instance if the current pile shape 26 has been determined by a point cloud measurement as has been indicated hereinabove, the excluding portion 36 may be determined in accordance with the below example that is presented with reference to Fig. 4. In order to simplify the presentation of the below example, a two-dimensional image of points of a point cloud measurement is illustrated in Fig. 4. However, it should be reiterated that a point cloud may generally form a three-dimensional image of the actual pile.

Firstly, a set of bottom-edge points BEP and top-edge points TEP of the pile may be determined. If the point cloud has been triangulated, the bottom points can be selected as the boundary points that are close to the ground plane, and the top points are the remaining boundary points.

As a non-limiting example, bottom and top points can be selected based on the height of points in a local spherical neighbourhood of a relevant point, viz the points that are located within a sphere the centre of which is the relevant point and which sphere has a predetermined radius.

For instance, assume that z is the altitude of a point p and that z_m is the average altitude of the n points closest to p, z_b the minimum altitude of the neighbouring points and z_t the maximum altitude.

For point clouds that are unevenly distributed (for instance if the resolution varies over the pile) two thresholds t_b and t, could be used to avoid selecting points inside the pile as top or bottom points. To this end, if z is the globally lowest altitude of all the points in the point cloud and z is the highest altitude, i_faand i₍can be selected automatically as t_b = z + tol and t_t = 2 - tol, wherein tol indicates a tolerance. Purely by way of example, the tolerance tol may be set to a percentage of the height of the pile, wherein the height of the pile may be determined by subtracting z from 2, or the tolerance tol may have a fixed value, for instance 0.5m. A scaling factor t_z could be selected based on the average point density. Purely by way of example, using t_z = 0.75 has proved a relevant value in practice. Bottom points can be selected as the points that fulfil both of the following criteria z<z_m - tz(z_m - z_b) and z<t_b. In a similar vein, top points can be selected as the points that fulfil both of the following criteria z>z_m + t_z(z_t - z_m) and z>t_t.

Once the top-edge points TEP have been identified, for instance using the above procedure, a polygon may be fitted to the top-edge points TEP, which defines a base shape that the top-edge points TEP form. Non-limiting base shapes comprises a point, a line, a rectangle or a ramp.

Optionally, such a polygon can be projected to a maximum-likelihood plane, in order to flatten and/or smoothen the polygon. One way to do so is to apply principal component analysis to the set of top points and compute three eigenvalues λ₂> λ₃ and three corresponding eigenvectors e e₂, e₃. The top-edge points TEP can then be projected onto to the planar surface defined by the normal eigenvector e₃ and the in-plane eigenvectors βι and e₂. Fig. 5 illustrates a pile 16 that comprises an excluding portion 36. The system 18 may be adapted to determine a horizontal main extension direction 39 of the excluding portion 36. As a non-limiting example, the horizontal main extension direction 39 may be determined using the first in-plane vector βι, for instance by projecting the first in-plane vector βι onto a horizontal plane P.

Moreover, the system may be adapted to determine a main material removal direction 40 that is substantially parallel to the horizontal main extension direction 39. In the example illustrated in Fig. 5, the main material removal direction 40 extends in the same direction as the horizontal main extension direction 39 but in another example embodiment, the main material removal direction 40 could extend in a direction opposite of the horizontal main extension direction 39. Fig. 6 illustrates a pile that has a bottom portion located at ground level 34. As a non- limiting example, the system may be adapted to determine if the excluding portion 36 extends to the bottom portion as is the case in the Fig. 6 example.

A procedure for determine if the excluding portion 36 extends to the bottom portion may comprise a step of determining whether or not the at least a part of the excluding portion 36 determined is located at or at least close to any one of the bottom-edge points BEP that have been discussed hereinabove with reference to Fig. 4.

Purely by way of example, when the system determines that the excluding portion 36 extends to the bottom portion, the system determines that the material entity to be removed from the pile comprises the excluding portion 36.

Removing an excluding portion 36 that extends to the bottom portion, such as the ramp illustrated in Fig. 6, may be advantageous since the ramp generally deviates significantly from the nominal pile shape 28. Thus, the ramp generally comprises a significant amount of material that can be removed before reaching a pile shape that is close to the nominal pile shape 28.

However, for practical reasons, for instance if the excluding portion 36 that extending to the bottom portion is used as a ramp during an operation of removing material from the pile, it may be advantageous to use a material removal strategy that follows a constraint that the material entity to be removed from the pile should not include the excluding portion 36. As s non-limiting example, the system is adapted to determine the current pile shape and/or the nominal pile shape when material has been removed from the pile. Purely by way of example, it is envisaged that, the current pile shape as well as the nominal pile shape may be updated after every scoop of removed material. However, it is also envisaged that, in other embodiments of the system, the current pile shape and/or the nominal pile shape is updated less frequently, e.g. every fifth or tenth scoop of removed material. Further, in embodiments of the system, the frequency at which the current pile shape is updated is different from the frequency at which the nominal pile shape is updated. As a non-limiting example, the current pile shape may be updated more frequently than the nominal pile shape.

Finally, Fig. 7 illustrates a flow chart illustrating a method in accordance with the present invention. The method is directed to determine a material entity to be removed from a pile by means of an implement of a material moving machine. The method illustrated in Fig. 7 comprises

S1 . generating a current pile shape representing the actual shape of the pile, S2. determining a nominal pile shape of at least a portion of the pile, the nominal pile shape being determined on the basis of at least the current pile shape and information regarding the material type of the pile,

S3, determining a surplus volume between the nominal pile shape and the current pile shape, and

S4. determining the material entity to be removed from the pile on the basis of the surplus volume. It should be noted that the above method may be performed by the control unit 21 that have been presented hereinabove. Purely by way of example, such a control unit 21 may be adapted to receive information regarding the pile from another component, such as the perception assembly 20 that has been discussed hereinabove. It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made.

Claims

1. A system (18) for determining a material entity (32) to be removed from a pile (16) by means of an implement (12) of a material moving machine (10), said system (18) comprising means (19; 21 ) for generating a current pile shape (26) representing the actual shape of said pile (16), moreover, said system (18) being adapted to determine a nominal pile shape (28) of at least a portion of said pile (16), said nominal pile shape (28) being determined on the basis of at least said current pile shape (26) and information regarding the material type of said pile (16), said system (18) being adapted to determine a surplus volume (30) between said nominal pile shape (28) and said current pile shape (26), said system (18) being adapted to determine said material entity (32) to be removed from said pile (16) on the basis of said surplus volume (30).

The system (18) according to claim 1 , wherein said information regarding the material type of said pile (16) comprises a nominal angle of repose for said material type.

The system (18) according to any one of the preceding claims, wherein said system (18) is adapted to determine an excluding portion (36) of said pile (16), said system (18) being adapted to determine a portion of said nominal pile shape (28) which extends from said excluding portion (36) in a direction determined by said information regarding the material type of said pile (16).

The system (18) according to claim 3, wherein said system (18) is adapted to determine a horizontal main extension direction (39) of said excluding portion (36), said system (18) being adapted to determine a main material removal direction (40) that is substantially parallel to said horizontal main extension direction (39).

The system (18) according to any one of claims 3 or 4, wherein said excluding portion (36) comprises a portion approximated by a line or a polygon, preferably a rectangle.

6. The system (18) according to any one of claims 3 to 5, wherein said pile (16) has an extension in a vertical direction and said excluding portion (36) of said pile (16) is determined to be located above said nominal pile shape (28) in said vertical extension.

The system (18) according to any one of claims 3 to 5, wherein said pile (16) has bottom portion, said system (18) being adapted to determine if said excluding portion (36) extends to said bottom portion.

The system (18) according to claim 7, wherein, when said system (18) determines that said excluding portion (36) extends to said bottom portion, said system (1 8) determines that said material entity (32) to be removed from said pile (16) comprises said excluding portion (36).

The system (18) according to any one of the preceding claims, wherein said means comprises a perception assembly for generating said current pile shape (26), said perception assembly preferably comprising at least one of a camera and a laser sensor.

10. The system (18) according to claim 9, wherein said means is adapted to generate a three-dimensional current pile shape (26) representing the actual shape of said pile (1 6), said perception assembly preferably comprising at least one of a time-of- flight camera, a stereo camera, a structured light camera or an actuated laser range finder.

1 1 . The system (18) according to any one of the preceding claims, wherein said

system (18) is adapted to determine said current pile shape (26) and/or said nominal pile shape (28) when material has been removed from said pile (16).

12. The system (18) according to any one of the preceding claims, wherein said

material entity (32) is a material volume.

13. The system (18) according to any one of the preceding claims, wherein said

implement (1 2) has a maximum material loading capacity and said system (1 8) is adapted to determine said material entity (32) to be removed from said pile (16) on the basis also of said maximum material loading capacity.

14. A material moving machine (10), comprising an implement (12), said material moving machine (10) further comprising a system (18) according to any one of the preceding claims.

15. A method for determining a material entity (32) to be removed from a pile (16) by means of an implement (12) of a material moving machine (10), said method comprising :

- generating a current pile shape (26) representing the actual shape of said pile (16),

- determining a nominal pile shape (28) of at least a portion of said pile (16), said nominal pile shape (28) being determined on the basis of at least said current pile shape (26) and information regarding the material type of said pile (16),

- determining a surplus volume (30) between said nominal pile shape (28) and said current pile shape (26), and

- determining said material entity (32) to be removed from said pile (16) on the basis of said surplus volume (30).

16. The method according to claim 15, wherein said information regarding the material type of said pile (16) comprises a nominal angle of repose for said material type.

17. The method according to any one of claims 15 or 16, wherein said method further comprises determining an excluding portion (36) of said pile (16) and determining a portion of said nominal pile shape (28) which extends from said excluding portion (36) in a direction determined by said information regarding the material type of said pile (16).

18. The method according to claim 17, further comprising determining a horizontal main extension direction (39) of said excluding portion (36), said method further comprises determining a main material removal direction (40) that is substantially parallel to said horizontal main extension direction (39).

19. The method according to claim 17 to 18, wherein said excluding portion (36) is defined by a portion approximated by a line or a polygon.

20. The method according to any one of claims 17 to 19, wherein said pile (16) has an extension in a vertical direction and said excluding portion (36) of said pile (16) is located above said nominal pile shape (28) in said vertical extension.

21 . The method according to any one of claims 17 to 20, wherein said pile (16) has a bottom portion, said method comprises determining if said excluding portion (36) extends to said bottom portion.

22. The system (18) according to claim 21 , wherein, upon determination that said excluding portion (36) extends to said bottom portion, said method determines that said material entity (32) to be removed from said pile (16) comprises said excluding portion (36).

23. The method according to any one of claims 17 to 22, wherein said pile (16) has an extension in a vertical direction and said excluding portion (36) of said pile (16) is located above said nominal pile shape (28).

24. The method according to any one of claims 15 to 23, wherein said material entity (32) is a material volume.

25. The method according to any one of claims 15 to 24, wherein said implement (12) has a maximum material loading capacity, said method comprises determining said material entity (32) to be removed from said pile (16) on the basis also of said maximum material loading capacity.

26. A method for removing material from a pile (16) by means of an implement (12) of a material moving machine (10), said method comprising:

- determining a material entity (32) to be removed from said pile (16) using a method according to any one of claims 15 - 25 and

- operating said implement (12) so as to remove the thus determined

material entity (32) from said pile (16).

27. The method according to claim 26, wherein said method further comprises:

- determining said current pile shape (26) and/or said nominal pile shape (28) when material has been removed from said pile (16).

28. A control unit (21 ) for a working machine (10), said control unit being adapted to:

- generate a current pile shape (26) representing the actual shape of said pile (16),

- determine a nominal pile shape (28) of at least a portion of said pile (16), said nominal pile shape (28) being determined on the basis of at least said current pile shape (26) and information regarding the material type of said pile (16),

- determine a surplus volume (30) between said nominal pile shape (28) and said current pile shape (26), and

- determine said material entity (32) to be removed from said pile (16) on the basis of said surplus volume (30).

29. The control unit (21 ) according to claim 28, wherein said working machine (10) comprises an implement (12) and said control unit further being adapted to:

- issue a signal to said working machine (10) to operate said implement (12) so as to remove the thus determined material entity (32) from said pile (16).