ROAD FINISHING MACHINE AND METHOD FOR LEVELLING A SCREED

Abstract

A road finishing machine comprises a screed for producing a paving layer on a subsoil on which the road finishing machine is movable in a laying direction, wherein the screed has a pulling arm fixed to the road finishing machine at a front pulling point by a levelling cylinder; at least one measuring means for performing a distance measurement, a storage means, and a controlling system. The controlling system is embodied to calculate a correction value in response to at least one distance measurement performed with respect to the subsoil and/or to a reference, which is performable at a measuring point in front of a front edge of the screed, to at least temporarily store the correction value in the storage means and calculate a desired levelling value for the measuring point taking into consideration the stored correction value, based on which the levelling cylinder of the screed is controllable.

Claims

1. A road finishing machine, comprising a screed for producing a paving layer on a subsoil on which the road finishing machine is movable in a laying direction along a laying section, wherein the screed is height-adjustable and has a pulling arm which is fixed to the road finishing machine at a front pulling point formed thereon by means of a levelling cylinder, at least one measuring means for performing at least one distance measurement, a storage means, a controlling system and a closed-loop controller means operatively linked thereto for adapting a setting of the levelling cylinder, wherein the controlling system is embodied to calculate a correction value in response to at least one distance measurement performed with respect to the subsoil and/or to a reference, which is performable at a measuring point located in front of a front edge of the screed in the laying direction, to at least temporarily store the correction value in the storage means and calculate, with a continued laying operation, a desired levelling value for the measuring point, taking into consideration the stored correction value, and wherein the levelling cylinder of the screed is controllable based on the desired levelling value when the front edge of the screed reaches the measuring point.

2. The road finishing machine according to claim 1, wherein the at least one measuring means is fixed at the pulling arm of the screed.

3. The road finishing machine according to claim 1, wherein the at least one measuring means is arranged in a region of the front pulling point of the pulling arm.

4. The road finishing machine according to claim 1, wherein the at least one measuring means comprises a first sensor for measuring a distance to the reference and a second sensor for measuring a distance to the subsoil.

5. The road finishing machine according to claim 4, wherein the first sensor and the second sensor have a same distance to the front edge of the screed in the laying direction.

6. The road finishing machine according to claim 4, wherein the controlling system is embodied to determine the correction value for the measuring point by means of the distance to the subsoil measured at the measuring point by means of the second sensor, minus the distance to the reference measured by means of the first sensor, and furthermore minus a pre-set altitude of the reference to the subsoil.

7. The road finishing machine according to claim 4, wherein the controlling system is configured to form, in an intermediate step, a difference of a pre-set desired basic levelling value and the stored correction value to derive the desired levelling value for the measuring point.

8. The road finishing machine according to claim 7, wherein the controlling system is configured to calculate, from the difference between the pre-set desired basic levelling value and the stored correction value, minus a distance to the reference currently measured by means of the at least one measuring means, the desired levelling value.

9. The road finishing machine according to claim 1, wherein the at least one measuring means comprises a plurality of sensors for measuring a distance to the subsoil and/or to the reference, wherein the controlling system is embodied to form, based on a plurality of distance measurements to the subsoil and/or to the reference performed simultaneously, a respective average value as a basis for the determination of the correction value.

10. The road finishing machine according to claim 1, wherein the controlling system is configured to multiply the calculated correction value with a compensation factor depending on a geometry of the screed.

11. The road finishing machine according to claim 1, wherein the road finishing machine includes, for detecting a covered section of the front edge of the screed, at least one path measuring means, wherein the calculation of the desired levelling value can be triggered by means of the controlling system, if the covered section of the front edge of the screed detected by the at least one path measuring means corresponds to a distance between the at least one measuring means and the front edge of the screed.

12. The road finishing machine according to claim 1, wherein the controlling system is embodied to continuously calculate correction values during a laying drive of the road finishing machine along the laying section, to store them and to employ the respective stored correction values to determine adapted desired levelling values.

13. The road finishing machine according to claim 1, wherein the controlling system is embodied to employ a GPS data-based subsoil data model to determine the correction value.

14. The road finishing machine according to claim 1, wherein the controlling system is embodied to calculate the correction value taking into consideration a piston position of the levelling cylinder currently set at the measuring point.

15. The road finishing machine according to claim 1, wherein the at least one measuring means is fixed to a tractor of the road finishing machine, wherein its measured values can be calculated with measured values of a further measuring means which is arranged at the pulling arm or at the screed to control a certain screed height.

16. A method for levelling a screed of a road finishing machine, the method comprising: calculating, using a controlling system of the road finishing machine, a correction value in response to at least one distance measurement of a measuring means performed with respect to a subsoil and/or to a reference, wherein the at least one distance measurement is performed at a measuring point located in front of a front edge of the screed in a laying direction; at least temporarily storing the correction value; calculating a desired levelling value for the measuring point with a continued laying operation, taking into consideration the stored correction value; and controlling at least one levelling cylinder of the screed, based on the desired levelling value, when the front edge of the screed reaches the measuring point.

17. A road finishing machine, comprising: a screed for producing a paving layer on a subsoil on which the road finishing machine is movable in a laying direction, wherein the screed is height-adjustable and has a pulling arm; a leveling cylinder that connects the pulling arm to a portion of the road finishing machine; at least one measuring sensor for performing at least one distance measurement, with respect to the subsoil and/or to a reference, at a measuring point located in front of a front edge of the screed in the laying direction; and a controlling system that is embodied to calculate a correction value based on the at least one distance measurement, at least temporarily store the correction value in a storage means and calculate a desired levelling value for the measuring point, taking into consideration the stored correction value, and wherein the levelling cylinder of the screed is controllable based on the desired levelling value when the front edge of the screed reaches the measuring point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the disclosure will be illustrated more in detail with reference to the following figures. In the drawings:

[0036] FIG. 1 shows a road finishing machine for producing a paving layer on a subsoil;

[0037] FIG. 2 shows a schematic isolated representation of the screed of the road finishing machine with a measuring means according to a variant of the disclosure;

[0038] FIG. 3 shows a schematic isolated representation of the screed with a measuring means fixed thereto according to another variant of the disclosure;

[0039] FIG. 4 shows a schematic representation of a control loop according to the disclosure for performing the levelling of the screed of FIGS. 2 and 3;

[0040] FIG. 5 shows a schematic isolated representation of the screed with a measuring means fixed thereto according to a further variant of the disclosure; and

[0041] FIG. 6 shows a schematic representation of a control loop for levelling the screed according to the variant of FIG. 5.

[0042] Equal components are always provided with equal reference numerals in the figures.

DETAILED DESCRIPTION

[0043] FIG. 1 shows a road finishing machine 1 that produces a paving layer 2 on a subsoil 3 on which the road finishing machine 1 is moving along a laying direction R during a laying drive. The road finishing machine 1 has a height-adjustable screed 4 for (pre-) compacting the paving layer 2. The screed 4 is fixed to a pulling arm 5 which is connected, at a front pulling point 6, with a levelling cylinder 7 at a tractor 22 of the road finishing machine 1. The pulling arm 5 serves as a lever to convert a variation of a levelling cylinder position into a corresponding change of an angle of attack of the screed 4, in particular to compensate irregularities 8 in the subsoil 3.

[0044] FIG. 2 shows, in an isolated schematic representation, the screed 4, the pulling arm 5, and the levelling cylinder 7. A measuring means 10 is arranged at the pulling arm 5 between a front edge 9 of the screed and the front pulling point 6. The measuring means 10 is embodied to perform at least one distance measurement to the subsoil 3 and/or to a reference 11. According to FIG. 2, the reference 11 is built as a guiding wire, the reference 11 taking an averaged height h.sub.11 above the subsoil 3. The reference 11 is tightened laterally of the road finishing machine 1 and provides a levelling function of the screed 4, as will be illustrated more in detail below.

[0045] In FIG. 2, the measuring means 10 has a first sensor 12 for measuring a distance y.sub.1 to the reference, and a second sensor 13 for measuring a distance y.sub.2 to the subsoil 3. Preferably, the first and the second sensors 12, 13 are positioned, in the laying direction R, at a same distance x.sub.9 to the front edge 9 of the screed 4. Thus, at a measuring point 14 according to FIG. 2, two distance measurements are performed, one to measure the distance y.sub.1, and one to measure the distance y.sub.2.

[0046] FIG. 2 furthermore shows that the measuring means 10 can detect, by means of the two sensors 12, 13, an irregularity 8 in the subsoil 3 at the measuring point 14 underneath the measuring means 10. The irregularity 8 represents a difference to the foundation P. To compensate the irregularity 8 of FIG. 2, a corresponding levelling of the screed 4 takes place when, in a continued laying operation in the laying direction R, the front edge 9 of the screed 4 arrives above the irregularity 8, i.e., at the measuring point 14. In other words, the levelling system according to the variant shown in FIG. 2 employed according to the disclosure responds to the irregularity 8 detected by means of the measuring means 10 at the measuring point 14 when the front edge 9 of the screed 4 has passed the distance x.sub.9 shown in FIG. 2.

[0047] FIG. 3 shows a variant for attaching the measuring means 10 of FIG. 2. The arrangement in FIG. 3 differs from FIG. 2 in that the measuring means 10 is directly positioned at the front pulling point 6. At this position, quasi at the front end of the pulling arm 5, the distances y.sub.1, y.sub.2 detected by means of the two sensors 12, 13, can particularly advantageously be employed to compensate irregularities 8 in the levelling of the screed 4 to produce an even paving layer 2 because at that point, the height of the pulling point 6 is exactly detected and not superimposed by the levelling changes of the screed 4.

[0048] FIG. 4 shows a levelling system 15 in a schematic representation. The levelling system 15 can employ the measured height values detected according to FIG. 2 and FIG. 3 to level the screed 4 to compensate irregularities 8 in the subsoil 3.

[0049] The levelling system 15 has a storage means 16, a controlling system 17, and a closed-loop controller means 18 operatively linked thereto for adapting a setting of the levelling cylinder 7. According to FIG. 4, the measured distances y.sub.1, y.sub.2 of the sensors 12, 13 are forwarded to the controlling system 17. Based on the measured distances y.sub.1, y.sub.2 and taking into consideration the set height h.sub.11 of the reference 11 above the foundation P, the controlling system 17 can determine a correction value K.

[0050] The controlling system 17 of FIG. 4 is embodied to determine the correction value K for the measuring point 14 by means of the distance y.sub.2 to the subsoil 3 measured at the measuring point 14 by means of the second sensor 13, minus the distance y.sub.1 to the reference 11 measured by means of the first sensor 12, and furthermore minus the pre-set height h.sub.11 of the reference 11. Furthermore, the controlling system 17 can be configured to continuously store the correction values K determined during the laying operation along the laying section in the laying drive direction R for the respective measuring points 14 in the storage means 16, so that the correction values K can each be employed when the front edge 9 of the screed 4 reaches the corresponding measuring points 14 along the laying section for the levelling of the screed 4.

[0051] FIG. 4 furthermore shows that a current laying speed V.sub.E of the road finishing machine 1 can be displayed to the controlling system 17 by means of a speed sensor 19. The laying speed V.sub.E transmitted to the controlling system 17 may be employed to determine the distance x.sub.9. According to FIG. 4, a path measuring means 20, such as a sensor, for the levelling system 15 can be provided, coupled thereto or as a functionally independent unit, to detect the distance x.sub.9 or a covered section of the front edge 9 of the screed 4 if the road finishing machine 1 is moving forward in the laying direction R during the laying drive.

[0052] FIG. 4 furthermore shows that a pre-set desired basic levelling value y.sub.1-Basis is forwarded to the controlling system 17. Furthermore, a compensation factor c can be stored in the controlling system 17 which possibly depends on a geometry of the screed 4.

[0053] The controlling system 17 of FIG. 4 is configured to determine, for each stored correction value K, the covered path, i.e., the covered section, which the screed 4, in particular the front edge 9 embodied thereon, has passed since the time of the storing. As soon as the covered section corresponds to the distance x.sub.9, the correction value K is subtracted from the desired basic levelling value y.sub.1-Basis by means of the controlling system 17. Optionally, the correction value K can previously be multiplied with the compensation factor c.

[0054] The desired basic levelling value y.sub.1-Basis can be manually set by an operator at a control panel of the road finishing machine, so that a desired height of the screed 4 can be accordingly adjusted for the laying operation. The height of the screed 4 can be manually determined by the operator or be measured by a non-depicted layer thickness sensor.

[0055] FIG. 4 furthermore shows that the desired levelling value y.sub.1-Soll determined for the measuring point 14 by means of the controlling system 17 taking into consideration the correction value K is forwarded to the closed-loop controller means 18. Furthermore, the measured distance y.sub.1 is forwarded to the closed-loop controller means 18. The closed-loop controller means 18 is embodied to calculate, by means of a difference between the desired levelling values y.sub.1-Soll calculated based on irregularities 8 and the distance y.sub.1 currently measured at the measuring point 14, a controller quantity u which is forwarded to an actuator 21. The actuator 21, for example a hydraulic drive component, thereupon determines an extension path s.sub.7 of the levelling cylinder 7, so that a pulling point height h.sub.6 can be adjusted to position the screed 4, in particular its screed's rear edge, at a desired height h.sub.bo.

[0056] FIG. 5 essentially shows the arrangement of FIG. 3, wherein the measuring means 10 according to FIG. 5 only includes the first sensor 12 for measuring the distance y.sub.1 to the reference 11. By means of the arrangement of FIG. 5, the correction value K can be calculated primarily by means of the distance y.sub.1 and by means of the extension path s.sub.7 of the levelling cylinder 7. For an irregularity 8 detected by means of the measuring means 10, the correction value K can be calculated from a sum of the distance y.sub.1, the height h.sub.11 to the reference 11, a distance h.sub.z of the first sensor 12 to the front pulling point 6, and the extension path s.sub.7 of the levelling cylinder 7, minus a height h.sub.zp, whereby a constructive height of a bottom side F of the running gear to the front pulling point 6 is given with the levelling cylinder 7 being retracted.

[0057] FIG. 6 shows a levelling system 15′ for the arrangement shown in FIG. 5 in a schematic representation. Here, the measured distances y.sub.1 and the detected extension paths s.sub.7 of the levelling cylinder 7 are continuously forwarded to the controlling system 17, based on which the correction value K is calculated and stored in the storage means 16 for each measuring point 14 along the laying section. The correction value K can be calculated by means of the above-described sum, minus the height h.sub.zp present when the levelling cylinder 7 is retracted. The desired basic levelling value y.sub.1-Soll stored for the controlling system 17 is calculated to the desired levelling value y.sub.1-Soll, minus the correction value K, which is forwarded to the closed-loop controller means 18 as an input quantity at the latest when the front edge 9 of the screed 4 has arrived at the measuring point 14 for the measured distance y.sub.1, wherein the closed-loop controller means 18 determines, from a difference of the calculated desired levelling value y.sub.1-Soll and the measured distance y.sub.1, the controller quantity u for the actuator 21 which accordingly adjusts the levelling cylinder 7 to level the screed 4.

[0058] As one skilled in the art would understand, the controlling system 17 and controller means 18 (e.g., controller) may individually or collectively include suitable hardware and software, such as one or more processors (e.g., one or more microprocessors, microcontrollers and/or programmable digital signal processors) in communication with, or configured to communicate with, one or more storage devices or media (such as the storage means 16, which may comprise a magnetic storage device, an optical storage device, a solid-state storage device, and/or any other suitable storage device) including computer readable program instructions that are executable by the one or more processors so that the controlling system 17 and/or controller means 18 may perform particular algorithms represented by the functions and/or operations described herein. The controlling system 17 and/or controller means 18 may also, or instead, include one or more application specific integrated circuits, programmable gate arrays or programmable array logic, programmable logic devices, or digital signal processors.