Edge detection system and method for detecting edge

Abstract

The invention relates to an edge detection system (10) for a road paver (1) wherein the edge detection system (10) comprises a sensor unit (11) configured to emit a sequence of laser pulses (16) in a plurality of directions (17) such that the sequence of laser pulses (16) is reflected at a plurality of locations (18) of a surface (19) to be scanned. The sensor unit (11) is further configured to detect reflections of the laser pulse sequence (16) and to generate, based on said detected reflections, a polar coordinate signal representing polar coordinates, where the polar coordinates comprise the distance and the correlation angle. The edge detection system (10) is configured to convert the polar coordinate signal into a Cartesian coordinate signal representing Cartesian coordinates and to determine a position of an edge (28) in the surface (19) to be scanned relative to the Cartesian coordinate system (20) based on the Cartesian coordinate signal.

Description

Technical Field

[0001] The present invention relates to detecting edges as a reference for paving road surfaces. Background Art

[0002] Road pavements, such as asphalt layers, are usually laid using road pavers. In order to provide the desired course of the road pavement, in particular its side edges, a reference is used, along which the road paver, in particular its screed plate, can be guided. These references include lines or edges. Examples of edges used as references are curb edges, edges of previously laid pavement layers, or milled edges resulting from the removal of a pavement layer to be replaced. Guiding the road paver or the screed plate, or its extension, respectively, in the reference direction is still usually achieved by manual control by an operator. Further automation is needed. A challenging goal is to detect the direction of the reference. WO 2020 088782A1 discloses a sensor system for a construction machine, in particular a road paver, comprising a laser scanner. This is to be able to achieve tracking by manipulating the road paver or extending or retracting an extendable screed plate part. Summary of the invention

[0003] The object of the present invention is to provide an improved system or method for edge detection. Advantageous further developments are provided in the respective dependent claims. The invention discloses an edge detection system for a road paver. The edge detection system comprises a sensor unit, which is configured to emit a sequence of laser pulses in a plurality of directions so that the sequence of laser pulses is reflected at a plurality of positions of a surface to be scanned. The sensor unit is further configured to detect the reflections of the sequence of laser pulses and to generate a polar coordinate signal representing polar coordinates based on the detected reflections, wherein the polar coordinates comprise a distance value and an associated angle value. The edge detection system is further configured to convert the polar coordinate signal into a Cartesian coordinate signal representing Cartesian coordinates and to determine the position of an edge in the surface to be scanned relative to a Cartesian coordinate system based on the Cartesian coordinate signal. The conversion into a Cartesian coordinate signal enables some processing techniques which, in contrast to the methods of the prior art, do not require radiation intensity to work.

[0004] The surface to be scanned may be, for example, a foundation or part of a foundation on which a road paver is traveling or on which a road pavement is being laid. In addition to the sensor unit, the edge detection system may also include other components, such as a control unit. The components of the edge detection system may be interconnected, for example to transmit signals and / or exchange data. For example, the connections between the components of the edge detection system may include one or more Ethernet connections and / or one or more CAN bus connections. The edge detection system may include a plurality of sensor units. Each sensor unit may have an address, such as an IP address. The address may be statically programmed into each sensor unit or assigned to each sensor unit, for example by the control unit. For example, the control unit may be configured to assign addresses to one, several or all sensor units based on a connector, via which the individual sensor units are connected to the control unit.

[0005] The control unit may be configured to perform various functions of the edge detection system. For example, the control unit may be implemented as a separate electronic circuit or as part of a central control unit of a screed or a central control unit of a road paver. A laser pulse sequence may be understood as a laser signal containing a finite number of cycles, in particular one or more cycles.

[0006] In the following, the expression "function" will be used in the general mathematical sense. For example, it can be understood as a relationship between two sets, in which each element of the first set is assigned to an element of the second set accordingly. The association can be given, for example, by a mathematical formula or a plurality of, for example, discrete, ordered counterparts (e.g., coordinate pairs). The ordered pairs can each contain an independent variable (e.g., a first coordinate or an x-coordinate) and a value of the function (e.g., a second coordinate or a y-coordinate or a slope). The edge detection system can be configured to determine an interpolation function based on a Cartesian coordinate signal. The interpolation function can be regarded as a representation of the profile of the surface to be scanned. The characteristic position of the profile can be determined mathematically by curve drawing.

[0007] The edge detection system can be configured to determine the smoothed function based on an interpolation function and / or based on a Cartesian coordinate signal. Smoothing can avoid errors in the evaluation, such as errors caused by measuring noise in the function that is not smoothed. The smoothed function can contain multiple ordered pairs. For example, the ordered pair can each include a first coordinate or x coordinate as an independent variable and a second coordinate or y coordinate as the value of the function.

[0008] The edge detection system can be configured to differentiate the smoothed function and determine a derivative function. The derivative function can include a plurality of ordered pairs. For example, the ordered pairs can each include a first coordinate or an x-coordinate as an independent variable and a slope, such as the slope of the smoothed function at the corresponding independent variable or the corresponding x-coordinate, as the value of the function. Since the derivative function can represent the direction of the slope of the smoothed function, it is possible to determine where the directional change of the profile of the surface to be scanned is located by evaluating the derivative function.

[0009] The edge detection system can be configured to determine the smallest minimum value and / or the largest maximum value of the derivative function. For example, the derivative function can be differentiated once more and then the zero point of the resulting second-order derivative function can be determined. The edge detection system can also be configured to ignore the position where the value of the derivative function is less than a threshold when determining the smallest minimum value and / or the largest maximum value of the derivative function. This can avoid continuously outputting randomly distributed values ​​without obvious extreme values.

[0010] The edge detection system may be configured to determine an edge distance value based on the independent variable of the derivative function at the smallest minimum value and / or the largest maximum value, which edge distance value may represent an edge distance between an edge in the surface to be scanned and the sensor unit.

[0011] The sensor unit may also include a 2-D lidar sensor. The sensor unit may be configured to emit a sequence of laser pulses in the infrared spectrum. For example, the sensor unit may be configured to emit infrared laser pulses. The sensor unit may also include a photodiode. The photodiode may be configured to detect reflections of a sequence of laser pulses, such as reflections in the infrared spectrum and / or reflections of infrared laser pulses. The sensor unit or the edge detection system may be configured to determine a distance value based on a transit time measurement.

[0012] All directions of the plurality of directions may lie in the same plane. The sensor unit may, for example, comprise a rotating mirror. The mirror may be configured to deflect the laser pulse sequence in the infrared spectrum and / or the infrared laser pulse into a plurality of directions. The sensor unit or the edge detection system may also be configured to determine an angle value based on the orientation of the mirror. The rotation frequency of the mirror may be between 1 Hz and 100 Hz, in particular between 1 Hz and 50 Hz, particularly preferably between 1 Hz and 30 Hz. The rotation frequency of the mirror may, for example, be 15 Hz. The sensor unit and / or the edge detection system may be configured to evaluate a measurement value in a range between -35° and 35°.

[0013] The edge detection system may further comprise a second sensor unit and may be configured to distinguish the sensor unit from the second sensor unit based on its IP address. Alternatively or additionally, the edge detection system may be configured to distinguish the sensor unit from the second sensor unit based on a mounting location of the sensor unit and the second sensor unit (e.g., a side and / or lateral shield of the screed plate where it is mounted). Alternatively or additionally, the edge detection system may be configured to distinguish the sensor unit from the second sensor unit based on a connector by which the respective sensor unit is connected to other components of the edge detection system, such as the control unit.

[0014] The invention also relates to a screed for a road paver comprising an edge detection system of the above type. The screed may comprise at least one extension, preferably two extensions. The edge distance may be defined parallel to the extension direction of the extension. The movement of the extension or extensions may be controlled based on the output of the edge detection system.

[0015] The sensor unit may be arranged on one, several or all extensions on the screed. In particular, the side shields may be mounted on one, several or all extensions on the screed. One or more sensor units may be arranged at one of the side shields, respectively. One or more sensor units may be arranged at the extensions or at the side shields, respectively, so that the plane is at an angle with respect to the surface to be scanned, which angle is greater than 0° and less than 180°, in particular 90°.

[0016] The screed plate may have a path measuring device and / or a width control device. The path measuring device may be configured to determine the extension path of each extension portion. The width control device may be configured to set a predetermined target by moving one or several or all extension portions.

[0017] The invention also relates to a road paver or a screed of the above type comprising an edge detection system of the above type. The plane can form an angle greater than 0° and / or less than 180° with the direction of travel of the road paver, preferably an angle greater than 75° and / or less than 105°. In particular, the plane can be oriented orthogonally with respect to the direction of travel of the road paver.

[0018] The present invention also relates to a method for detecting an edge by an edge detection system of a road paver, wherein the edge detection system comprises a sensor unit. The method comprises: emitting a sequence of laser pulses in multiple directions by the sensor unit so that the sequence of laser pulses is reflected at multiple positions of the surface to be scanned; detecting the reflection of the sequence of laser pulses by the sensor unit; and generating a polar coordinate signal representing polar coordinates based on the detected reflection, wherein the polar coordinates include a distance value and an associated angle value. The method also comprises converting the polar coordinate signal into a Cartesian coordinate signal representing Cartesian coordinates, and determining the position of the edge of the surface to be scanned relative to the Cartesian coordinate system based on the Cartesian coordinate signal.

[0019] The surface to be scanned may be, for example, a foundation or a part of a foundation on which a road paver is travelling or on which a road surface is being laid.

[0020] The method may further include determining an interpolation function based on the Cartesian coordinate signal.

[0021] The method may further comprise determining a smoothed function based on the interpolation function and / or based on the Cartesian coordinate signal.For example, a smoothed function may prevent errors in the evaluation process which may be caused by measurement noise in an unsmoothed function.

[0022] The method may further comprise differentiating the smoothed function and determining a derivative function. Since the derivative function represents the trend of the slope of the smoothed function, the position of the direction change of the contour of the surface to be scanned can be determined by evaluating the derivative function.

[0023] The method may also include determining the smallest minimum value and / or the largest maximum value of the derivative function. For example, the derivative function may be differentiated once more and then the zeros of the second-order derivative function so determined may be determined. Determining the smallest minimum value and / or the largest maximum value of the derivative function may include ignoring locations where the value of the derivative function is less than a threshold value. This may avoid continuously outputting randomly distributed values ​​without obvious extreme values.

[0024] The method may further comprise determining an edge distance value based on the independent variable of the derivative function at the smallest minimum value and / or the largest maximum value, wherein the edge distance value may represent an edge distance between an edge in the surface to be scanned and the sensor unit.

[0025] The invention also relates to a method of operating a screed of a road paver, comprising a method of detecting an edge of the above-mentioned type and further comprising moving an extension of the screed based on the determined edge distance value.

[0026] The method may also include setting a target value for the edge distance value. The method may also include defining a plausibility window around the target value, wherein if the edge distance value is within the plausibility window, the extended portion is moved taking into account the determined edge distance value, and / or, if the determined edge distance value is outside the plausibility window, the extended portion is moved ignoring the determined edge distance value. The method may include calculating the difference between the target value and the determined edge distance value. Outside the plausibility window, according to the method, the difference between the target value and the edge distance value may be assumed to be zero.

[0027] Furthermore, the sensor unit may comprise a 2D lidar sensor. The emission of the laser pulse sequence may, for example, comprise emitting a laser pulse sequence in the infrared spectrum, such as infrared laser pulses. The method may further comprise detecting (in particular by means of a photodiode) a reflection of the laser pulse sequence, such as a reflection in the infrared spectrum and / or a reflection of the infrared laser pulse. The photodiode may be provided as part of the sensor unit. The method may comprise determining the distance value based on a transit time measurement (e.g. by means of the sensor unit or an edge detection system).

[0028] The method may comprise deflecting the laser pulse sequence in the infrared spectrum and / or the infrared laser pulse into a plurality of directions, for example by means of a rotating mirror. The rotating mirror may be provided as part of the sensor unit. The method may comprise determining the angle value based on the orientation of the mirror. The rotation frequency of the mirror may be, for example, between 1 Hz and 100 Hz, in particular between 1 Hz and 50 Hz, particularly preferably between 1 Hz and 30 Hz. The rotation frequency of the mirror may be, for example, 15 Hz. The method may comprise evaluating the measured values ​​in the range between -35° and 35°. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic side view of a road paver with an edge detection system is shown.

[0031] Figure 2 Shows Figure 1 Schematic top plan view of a road paver.

[0032] Figure 3 Shows Figure 1 and Figure 2 Schematic detail view of the rear of the road paver.

[0033] Figure 4 A schematic diagram of an interpolation function generated based on an exemplary distance measurement is shown.

[0034] Figure 5 Shown based on Figure 4 Schematic diagram of the smoothed function generated by the interpolation function.

[0035] Figure 6 Shown based on Figure 5 Schematic diagram of the derivative function generated by the smoothed function.

[0036] Figure 7 Shows Figures 1 to 3 Schematic diagram of the connections between the various components of a road finishing machine. DETAILED DESCRIPTION

[0037] exist Figure 1 , a road paver 1 is shown in a schematic side view. The road paver 1 may comprise a tractor 2. The road paver 1 may further comprise a screed 3. The tractor 2 may be configured to tow the screed 3. For this purpose, the road paver 1 may comprise a pulling arm 4. The road paver 1 may be configured to lay a road surface 5 to a foundation 6. The road paver 1 may be movable in a driving direction 7.

[0038] The screed plate 3 may also include side guards 8. The side guards 8 may be configured to limit the paving width 9 of the screed plate 3 (see Figure 2 ). In particular, the side guards 8 may be configured to limit the paving width 9 in a direction transverse to the driving direction 7. The road paver 1 may further comprise an edge detection system 10. The edge detection system 10 may comprise a sensor unit 11. The sensor unit 11 may be arranged at one of the side guards 8.

[0039] exist Figure 2 , a road paver 1 is shown in a schematic top view from above. It can now be seen that the screed plate 3 can include a base screed plate 12. Furthermore, as shown in the present embodiment, the screed plate 3 can include two extensions 13. The extensions 13 can be moved relative to the base screed plate 12, in particular in an extension direction 15. The extension direction 15 can be oriented transversely, in particular orthogonally, to the drive direction 7. By moving the extensions 13, the paving width 9 of the screed plate 3 can be adjusted. Figure 2 It can also be seen that the edge detection system 10 may include a second sensor unit 14. As shown in the present embodiment, the sensor unit 11 and the second sensor unit 14 may be arranged at opposite extensions of the screed 3, in particular at opposite side shields 8 of the screed 3.

[0040] exist Figure 3, components of the screed 3 and components of the edge detection system 10 are shown in more detail from a perspective viewed from behind. It can be seen that the sensor unit 11 can be configured to emit a laser pulse sequence 16. The sensor unit 11 can be configured to emit the laser pulse sequence 16 in a plurality of directions 17. In the embodiment shown, the sensor unit 11 can be configured to emit the laser pulse sequence 16 such that the laser pulse sequence 16 is reflected at a plurality of positions 18 on the surface to be scanned 19. In the embodiment shown, a part of the foundation 6 can be considered as the surface to be scanned 19.

[0041] The reflections of the laser pulse sequence 16 may be detected by the sensor unit 11. For example, the reflections of the laser pulse sequence 16 may be detected by a photodiode (not shown) of the sensor unit 11. The sensor unit 11 and / or the edge detection system 10 may also be configured to determine a distance of the corresponding position 18 from the sensor unit 11 based on the transmission time of the laser pulse sequence 16 and its reflections. The sensor unit 11 and / or the edge detection system 10 may be configured to generate polar coordinate signals based on the distance and the direction 17 of the corresponding laser pulse sequence. Each polar coordinate signal may represent the position of the corresponding position 18 relative to a polar coordinate system having an origin, which may be located, for example, inside the sensor unit 11.

[0042] The edge detection system 10 and / or the sensor unit 11 may also be configured to generate a Cartesian coordinate signal based on the polar coordinate signal. The Cartesian coordinate signal may represent the Cartesian coordinates of the respective position 18 relative to a Cartesian coordinate system 20. The origin of the Cartesian coordinate system 20 may be located inside the sensor unit 11, in particular at the point where the laser pulse sequence 16 is reflected in the corresponding direction 17.

[0043] The edge detection system 10 and / or the sensor unit 11 may be configured to determine an interpolation function 21 based on the Cartesian coordinate signal (see Figure 4 ). Figure 4 A schematic diagram of such an interpolation function 21 is shown as an example. The edge detection system 10 and / or the sensor unit 11 may also be configured to determine a smoothed function 22 based on the interpolation function 21 . Figure 5 A schematic diagram of such a smoothed function 22 is shown as an example. Furthermore, the edge detection system 10 and / or the sensor unit 11 may be configured to determine a derivative function 23 based on the smoothed function 22, in particular by differentiating the smoothed function 22. Figure 6 A schematic diagram of such a derivative function 23 is shown as an example.

[0044] Furthermore, the edge detection system 10 and / or the sensor unit 11 may be configured to determine the smallest minimum value 24 and / or the largest maximum value 25 of the derivative function 23. The edge distance value 26 may be determined based on the smallest minimum value 24 of the derivative function 23 and / or based on the largest maximum value 25 of the derivative function 23. In particular, the edge detection system 10 and / or the sensor unit 11 may be configured to determine the edge distance value 26 based on the smallest minimum value 24 of the derivative function 23 and / or based on the largest maximum value 25 of the derivative function 23. In the present embodiment, the smallest minimum value 24 of the derivative function 23 is used as a basis for determining the edge distance value 26, as will be explained in further detail below. In particular, the independent variable of the derivative function 23 at the smallest minimum value 24 of the derivative function 23 may be determined as the edge distance value 26. The edge distance value 26 may be regarded as representing an edge 28 in the surface 19 to be scanned (see also Figure 3 ) and the edge distance 27 between the sensor unit 11 (see Figure 3 ).

[0045] exist Figure 7 , the connections between the edge detection system 10 and the components of the screed plate 3 are schematically shown. It can be seen that the edge detection system 10 may include a control unit 32. The sensor unit 11 may be connected to a first connector of the control unit 32. The second sensor unit 14 may be connected to a second connector 34 of the control unit 32. The connection between the sensor units 11, 14 and the control unit 32 may, for example, be embodied as Ethernet. For example, the sensor unit 11 may have a static IP address, based on which the control unit 32 may identify the installation side of the sensor unit 11. Similarly, the second sensor unit 14 may have a static IP address, which may be different from the IP address of the sensor unit 11, and the control unit 32 may determine the installation side of the second sensor unit 14 based on the static IP address. Alternatively or additionally, the first connector 33 and the second connector 34 may each be assigned to one installation side. In this way, the control unit 32 may be configured to determine, based on the connector to which the respective sensor unit 11, 14 is connected, at which installation side each sensor unit 11, 14 is arranged.

[0046] The following will be based on Figures 1 to 7 The operation of the edge detection system 10 in cooperation with the road paver 1 is further explained in a general and exemplary manner. The following description mainly refers to the sensor unit 11. However, it should be clear that these descriptions also apply to the second sensor unit 14.

[0047] The sensor unit 11 may be arranged at the extension 13, in particular at the side shield 8. Figure 1, the sensor can be mounted such that a plane 29 in which the plurality of directions 17 lie is oriented at an angle 30 relative to the subgrade 6 and / or relative to the driving direction 7. By adjusting the angle 30, the distance between the surface 19 to be scanned of the subgrade 6 and the rear edge of the screed 3 can be adjusted. By adjusting the mounting height of the sensor unit 11, the width of the surface 19 to be scanned can be adjusted.

[0048] from Figure 3 It can be seen that according to this embodiment, the x-coordinate of the Cartesian coordinate system 20 or the independent variable of the function determined relative to the coordinate system 20 can be oriented parallel to the extension direction 15 of the extension part 13. Figure 3 The x-coordinate of the Cartesian coordinate system 20 becomes more positive. In the direction of decreasing paving width 9 ( Figure 3 In order to be able to use the same sensor unit for the sensor unit 11 and the second sensor unit 14, the x-coordinate of the coordinate system (not shown) (whose origin is located in the second sensor unit 14) can be oriented so that the x-coordinate becomes more positive in the direction of decreasing paving width 9.

[0049] As referenced above Figure 7 As explained, the edge detection system 10 can be configured to automatically recognize on which side of the screed 3 the sensor unit 11 and the second sensor unit 14 are arranged. To facilitate edge detection, the operator can set the type of edge to be detected, for example, an edge that is inclined upward or downward toward the outside should be detected. For example, during the setting of the respective sensor unit 11, 14, the edge detection system can provide the operator with a suggestion based on the initial measurement data. The operator can accept or change the suggestion. Depending on the operator's settings, the smallest minimum value 24 of the derivative function 23 or the largest maximum value 25 of the derivative function 23 can be sought during the determination of the edge distance value 26.

[0050] When the side guard 8 is positioned in the desired position relative to the edge 28 and the sensor unit 11 detects the edge, the operator can save the edge distance value 26 determined in this case as a target value. If the edge distance value 26 deviates from the target value, for example due to a steering movement of the road paver or due to the course of the edge, a deviation may occur, for example a difference between the target value and the edge distance value 26. The corresponding extension 13 can be controlled in such a way that the deviation is compensated.

[0051] When the edge definition is not clear, the determination of the edge distance value 26 as described above may result in alternating edge distance values ​​26. Unwanted consequences of this influence can be reduced by the inertia of the adjustment behavior of the screed 3, in particular the extension part 13. If the consequences of the above-mentioned influence are to be further reduced, the trend of the edge distance value 26 can be attenuated and smoothed by a suitable filter, for example a low-pass filter.

[0052] In addition, it may happen that an object appears in the surface to be scanned 19, which causes an inappropriate edge distance value 26 to be detected (for example, because the object causes a higher slope in the smoothed function 22). In order to reduce the consequences caused by such objects, the edge distance value can be checked for credibility before considering setting the extension part 13. For example, a credible window can be defined around the target value. If the edge distance value 26 is within the credible window, the calculated difference between the target value and the edge distance value 26 can be considered when setting the extension part 13. If the edge distance value 26 is outside the credible window, it can be assumed that the difference between the target value and the edge distance value 26 is 0, so that the edge distance value 26 judged to be unreasonable can be ignored when setting the extension part 13.

Claims

1. An edge detection system (10) for a road paver (1), wherein: The edge detection system (10) comprises a sensor unit (11) configured to emit a sequence of laser pulses (16) in a plurality of directions (17) such that the sequence of laser pulses (16) is reflected at a plurality of positions (18) of a surface (19) to be scanned, wherein the sensor unit (11) is further configured to detect reflections of the sequence of laser pulses (16) and to generate a polar coordinate signal representing polar coordinates based on the detected reflections, wherein the polar coordinates comprise a distance and an associated angle, The edge detection system (10) is configured to convert the polar coordinate signal into a Cartesian coordinate signal representing a Cartesian coordinate, and determine the position of an edge (28) in the surface to be scanned (19) relative to a Cartesian coordinate system (20) based on the Cartesian coordinate signal.

2. The edge detection system according to claim 1, wherein: The edge detection system (10) is configured to determine a smoothed function (22) based on the Cartesian coordinate signal.

3. The edge detection system according to claim 2, wherein: The edge detection system (10) is configured to differentiate the smoothed function (22) and determine a derivative function (23).

4. The edge detection system according to claim 3, wherein: The edge detection system (10) is configured to determine the smallest minimum value (24) and / or the largest maximum value (25) of the derivative function (23).

5. The edge detection system according to claim 4, wherein: The edge detection system (10) is configured to determine an edge distance value (26) based on the independent variable of the derivative function (23) at the smallest minimum value (24) and / or the largest maximum value (25), the edge distance value (26) representing the edge distance (27) between an edge (28) in the surface (19) to be scanned and the sensor unit (11).

6. The edge detection system according to any one of claims 1 to 5, wherein: The edge detection system (10) further includes a second sensor unit (14), and the edge detection system (10) is configured to distinguish between the sensor unit (11) and the second sensor unit (14) based on IP addresses of the sensor unit (11) and the second sensor unit (14).

7. A screed (3) for a road paver (1), comprising an edge detection system (10) according to any one of claims 1 to 6.

8. The ironing screed according to claim 7, further comprising at least one extension portion (13), wherein: The movement of the extension portion (13) can be controlled based on the output of the edge detection system (10).

9. The ironing screed according to claim 8, wherein: The output of the edge detection system (10) is an output representing an edge distance value (26).

10. The ironing screed according to claim 8, wherein: The edge detection system (10) is configured to control the movement of the extension portion (13) based on a target value representing a desired value of an edge distance value (26).

11. The ironing screed according to claim 10, wherein: The edge detection system (10) is configured to define a trusted window around the target value, and wherein the edge detection system (10) is configured to move the extension portion taking into account the determined edge distance value (26) if the determined edge distance value (26) is within the trusted window, and / or to move the extension portion (13) ignoring the determined edge distance value (26) if the determined edge distance value (26) is outside the trusted window.

12. A road paver (1) comprising an edge detection system (10) according to any one of claims 1 to 6 or a screed (3) according to any one of claims 7 to 11.

13. The road paver according to claim 12, wherein: The plane (29) of the road paver (1) and the travel direction (7) form an angle (30), which is greater than 0° and / or less than 180°.

14. The road paver according to claim 14, wherein: The angle (30) is greater than 75° and / or less than 105°.

15. A method for detecting an edge (28) by means of an edge detection system (10) for a road paver (1), wherein: The edge detection system (10) comprises a sensor unit (11), wherein the method comprises: The sensor unit (11) emits a sequence of laser pulses (16) in a plurality of directions (17), so that the sequence of laser pulses (16) is reflected at a plurality of positions (18) of the surface (19) to be scanned, detecting reflections of the laser pulse sequence (16) by means of the sensor unit (11), generating a polar coordinate signal representing polar coordinates based on the detected reflection, wherein the polar coordinates include a distance and an associated angle, converting the polar coordinate signal into a Cartesian coordinate signal representing a Cartesian coordinate, The position of an edge (27) in the surface to be scanned (19) relative to a Cartesian coordinate system (20) is determined based on the Cartesian coordinate signal.

16. The method of claim 15, further comprising determining a smoothed function (22) based on the Cartesian coordinate signal.

17. The method of claim 16, further comprising differentiating the smoothed function (22) and determining a derivative function.

18. The method according to claim 17, further comprising determining a smallest minimum value (24) and / or a largest maximum value (25) of the derivative function (23).

19. The method according to claim 18, further comprising determining an edge distance value (26) based on an independent variable of the derivative function (23) at the smallest minimum value (24) and / or the largest maximum value (25), wherein: The edge distance value (26) represents the edge distance (27) between an edge (28) in the surface (19) to be scanned and the sensor unit (11).

20. A method of operating a screed (3) of a road paver (1), comprising the method of detecting an edge (28) according to any one of claims 15 to 19, and further comprising moving an extension (13) of the screed (3) based on the determined edge distance value (26).

21. The method of claim 20, further comprising setting a target value for the edge distance value (26).

22. The method of claim 21 further comprising defining a trust window around the target value, wherein If the determined edge distance value (26) is within the trust window, the extended portion (13) is moved taking into account the determined edge distance value (26), and / or, if the determined edge distance value (26) is outside the trust window, the extended portion (13) is moved ignoring the determined edge distance value (26).

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