ROAD FINISHING MACHINE WITH LEVELING CASCADE CONTROL

Abstract

A road finishing machine with a screed for producing a paving layer on a subsoil includes a leveling system for height adjustment of the screed for compensating for irregularities in the subsoil. The leveling system includes a cascade control having either a central control loop between outer and inner control loops that includes a control unit to determine, on the basis of a detected actual value of a pulling point position of a pulling point of the screed to a predetermined reference, and on the basis of a desired value of the pulling point position, a desired value of a leveling cylinder position, or a pulling point control between the outer and inner control loops to determine, on the basis of the desired value of the pulling point position of the pulling point of the screed, the desired value of the leveling cylinder position.

Claims

1. A road finishing machine comprising: a screed for producing a paving layer on a subsoil on which the road finishing machine is operable to move in a laying direction during a pavement drive; and a leveling system for height adjustment of the screed for compensating for irregularities in the subsoil, wherein the leveling system includes a cascade control comprising an outer control loop which includes a first control unit configured to determine, on the basis of a detected actual value of a screed height of the screed relative to a predetermined reference, and on the basis of a desired value of the screed height relative to the predetermined reference, a desired value of a pulling point position of a pulling point of the screed relative to the predetermined reference, and an inner control loop which includes a second control unit configured to determine, on the basis of a detected actual value of a leveling cylinder position of an extendable piston of a leveling cylinder attached to the pulling point, and on the basis of a desired value of the leveling cylinder position, a control signal for the leveling cylinder by which the leveling cylinder can be controlled; wherein the cascade control further comprises a central control loop between the outer and the inner control loops that includes a third control unit configured to determine, on the basis of a detected actual value of the pulling point position of the pulling point of the screed relative to the predetermined reference, and on the basis of the desired value of the pulling point position determined by the first control unit, the desired value of the leveling cylinder position for the second control unit, or a pulling point control between the outer and the inner control loops, the pulling point control configured to determine, on the basis of the desired value of the pulling point position of the pulling point of the screed determined by the first control unit, the desired value of the leveling cylinder position for the second control unit.

2. The road finishing machine according to claim 1, wherein the outer control loop comprises a closed-loop controlled system whose output quantity is the detected actual value of the screed height of the screed relative to the predetermined reference, and/or whose input quantity is the detected actual value of the pulling point position of the pulling point of the screed relative to the predetermined reference

3. The road finishing machine according to claim 1, wherein the leveling system for the outer control loop includes at least one first sensor configured to detect the actual value of the screed height.

4. The road finishing machine according to claim 3, wherein the first sensor is a distance sensor for detecting a distance to the predetermined reference which is positioned in the region of a screed's trailing edge of the screed.

5. The road finishing machine according to claim 1, wherein the inner control loop comprises a closed-loop controlled system whose output quantity is the detected actual value of the leveling cylinder position of the extendable piston of the leveling cylinder attached to the pulling point, and/or whose input quantity is the control signal for the leveling cylinder.

6. The road finishing machine according to claim 1, wherein the leveling system for the inner control loop includes at least one second sensor configured to detect the actual value of the leveling cylinder position.

7. The road finishing machine according to claim 6, wherein the second sensor is a distance sensor positioned in the region of the leveling cylinder for detecting the leveling cylinder position of the piston of the leveling cylinder.

8. The road finishing machine according to claim 1, wherein the central control loop comprises a closed-loop controlled system whose output quantity is the detected actual value of the pulling point position of the screed, and/or whose input quantity is the detected actual value of the leveling cylinder position.

9. The road finishing machine according to claim 1, wherein the leveling system for the central control loop includes a third sensor configured to detect the actual value of the pulling point position to the predetermined reference.

10. The road finishing machine according to claim 9, wherein the third sensor is a distance sensor for detecting a distance to the predetermined reference which is positioned in the region of the pulling point of the screed.

11. The road finishing machine according to claim 1, wherein the cascade control includes at least one disturbance variable feedforwarding.

12. The road finishing machine according to claim 1, wherein the cascade control is supplemented by a layer thickness calculation module configured to determine, on the basis of an identified current layer thickness of the produced paving layer, and/or on the basis of a desired value of the layer thickness of the paving layer to be produced, the desired value of the screed height for the outer control loop.

13. The road finishing machine according to claim 12, wherein the layer thickness calculation module is configured to determine the layer thickness from a progression of the sensor measurements employed for leveling.

14. A method of leveling a screed of a road finishing machine for producing a paving layer on a subsoil on which the road finishing machine is moving in a laying direction during a pavement drive, wherein irregularities in the subsoil are compensated by a leveling system which performs a leveling of the screed by a cascade control, wherein an outer control loop of the cascade control determines, by a first control unit, on the basis of a detected actual value of a screed height of the screed relative to a predetermined reference, and on the basis of a desired value of the screed height relative to the predetermined reference, a desired value of a pulling point position of a pulling point of the screed relative to the predetermined reference, and wherein an inner control loop of the cascade control determines, by a second control unit, on the basis of a detected actual value of a leveling cylinder position of an extendable piston of a leveling cylinder attached to the pulling point of the screed, and on the basis of a desired value of the leveling cylinder position, a control signal for the leveling cylinder by which the leveling cylinder is controlled for height adjustment of the screed, the method comprising: determining, by a third control unit of a central control loop present between the outer and the inner control loops of the cascade control, on the basis of a detected actual value of the pulling point position of the pulling point of the screed relative to the predetermined reference, and on the basis of the desired value of the pulling point position determined by the first control unit, the desired value of the leveling cylinder position for the second control unit; or determining, by a pulling point control present between the outer and the inner control loops of the cascade control, on the basis of the desired value of the pulling point position of the pulling point of the screed determined by the first control unit, the desired value of the leveling cylinder position for the second control unit.

15. The method according to claim 14, wherein the cascade control is supplemented by at least one disturbance variable feedforwarding and/or by a layer thickness calculation module which determines, on the basis of an identified layer thickness of the produced paving layer, and/or on the basis of a desired value of a layer thickness of the paving layer to be produced, the desired value of the screed height for the outer control loop.

16. The method according to claim 14, wherein determining the desired value of the leveling cylinder position for the second control unit by the pulling point control is further on the basis of a digital terrain model of the subsoil on which the road finishing machine is moving for producing the paving layer.

17. The road finishing machine according to claim 1, wherein the pulling point control is further configured to determine the desired value of the leveling cylinder position for the second control unit on the basis of a digital terrain model of the subsoil on which the road finishing machine is moving for producing the paving layer.

18. A leveling system for height adjustment of a screed of a road finishing machine, the screed for producing a paving layer on a subsoil on which the road finishing machine is operable to move in a laying direction during a pavement drive, the leveling system for compensating for irregularities in the subsoil and including a cascade control, the leveling system comprising: an outer control loop which includes a first control unit configured to determine, based on a detected actual value of a screed height of the screed relative to a predetermined reference, and based on a desired value of the screed height relative to the predetermined reference, a desired value of a pulling point position of a pulling point of the screed relative to the predetermined reference, and an inner control loop which includes a second control unit configured to determine, based on a detected actual value of a leveling cylinder position of an extendable piston of a leveling cylinder attached to the pulling point, and based on of a desired value of the leveling cylinder position, a control signal for the leveling cylinder which the leveling cylinder can be controlled; wherein the leveling system further comprises a central control loop between the outer and the inner control loops that includes a third control unit configured to determine, based on a detected actual value of the pulling point position of the pulling point of the screed to the predetermined reference, and based on the desired value of the pulling point position determined by the first control unit, the desired value of the leveling cylinder position for the second control unit, or a pulling point control between the outer and the inner control loop, the pulling point control configured to determine, based on the desired value of the pulling point position of the pulling point of the screed determined by the first control unit, the desired value of the leveling cylinder position for the second control unit.

19. The leveling system according to claim 18, wherein the cascade control includes at least one disturbance variable feedforwarding.

20. The leveling system according to claim 18, wherein the pulling point control is further configured to determine the desired value of the leveling cylinder position for the second control unit based on a digital terrain model of the subsoil on which the road finishing machine is moving for producing the paving layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the disclosure will be illustrated more in detail with reference to the following figures. In the drawing:

[0043] FIG. 1 shows a road finishing machine for producing a paving layer on a subsoil;

[0044] FIG. 2 shows an isolated schematic representation of a screed of the road finishing machine in a reference coordinate system;

[0045] FIG. 3 shows a schematic representation of a first variant of the leveling system for the screed of the road finishing machine according to the disclosure; and

[0046] FIG. 4 shows a schematic representation of a second variant of the leveling system for the screed of the road finishing machine according to the disclosure.

[0047] Technical features are always provided with the same reference numerals in the figures.

DETAILED DESCRIPTION

[0048] FIG. 1 shows a road finishing machine 1 that produces a paving layer 2 with a desired layer thickness S on a subsoil 3 on which the road finishing machine 1 is moving in a direction of travel R during a pavement drive. The road finishing machine 1 has a leveling screed 4 for compacting the paving layer 2. The screed 4 includes a pulling arm 5 which is connected, at a front pulling point 6, with a levelling cylinder 7 attached to the chassis of the road finishing machine 1. The leveling cylinder 7 can lift and lower the pulling arm 5 at the front pulling point 6 so that a set angle of the dragged screed 4 can be set during the paving drive, where in response thereto, the screed 4 is lifted or lowered. In particular, by a dynamic control of the leveling cylinder setting, irregularities 8 of the subsoil 3 can be compensated.

[0049] FIG. 2 shows an isolated, schematic representation of the screed 4 in a reference coordinate system K, including dimensions concerning the subsoil 3 and the screed geometry, which will be illustrated more in detail in connection with FIGS. 3 and 4 below.

[0050] FIG. 3 shows a leveling system 10A embodied to level the screed 4. The leveling system 10A comprises a cascade control 100A comprising three superimposed control loops, namely an inner control loop 11, a central control loop 12, and an outer control loop 13.

[0051] The outer control loop 13 includes a first sensor H.sub.bo (screed sensor), the inner control loop 11 a second sensor H.sub.nz (leveling cylinder sensor), and the central control loop 12 a third sensor H.sub.zp (pulling point sensor). Each one of the three control loops 11, 12, 13 thus includes each one separate sensor according to FIG. 2. The sensors H.sub.bo, H.sub.nz, H.sub.zp are configured to measure the distances represented in FIG. 2, in particular the extension path of the leveling cylinder s.sub.nz, the screed height z.sub.bo, and the pulling point position z.sub.zp. Corresponding sensor signals y.sub.bo, y.sub.nz, y.sub.zp are supplied from the respective sensors H.sub.bo, H.sub.nz, H.sub.zp to the three control units C.sub.bo, C.sub.zp, C.sub.nz as actual controlled variables.

[0052] According to FIG. 2, the cascade control 100A is supplemented by an optional disturbance variable feedforwarding S1, S2 which is here represented schematically in a dashed form.

[0053] First of all, the cascade control 100A will be described below without the disturbance variable feedforwarding S1, S2. The three control loops 11, 12, 13 of the cascade control 100A are interleaved. In the outer control loop 13, the screed height z.sub.bo is adjusted. The dynamic behavior of the closed-loop controlled system “screed” is described by the transmission function G.sub.bo. The output variable of this closed-loop controlled system is the detected screed height z.sub.bo. The screed height z.sub.bo is detected by the screed sensor H.sub.bo which is installed near a screed's trailing edge 14 (see FIGS. 1 and 2). The corresponding sensor signal y.sub.bo is supplied to the control unit C.sub.bo by feedback. The input variable of the transmission function G.sub.bo is the measured actual value of the pulling point position z.sub.zp. The corresponding desired value of the pulling point position r.sub.zp is the control signal of the first control unit C.sub.bo (screed control unit) and is calculated from the desired value of the screed height r.sub.bo and the sensor signal y.sub.bo held available here.

[0054] The control signal r.sub.zp of the outer control loop 13 is the reference signal of the central control loop 12 which adjusts the pulling point position z.sub.zp by means of the pulling point control unit C.sub.zp. The actual value of the pulling point position z.sub.zp is detected by means of the sensor H.sub.zp which determines the distance of the pulling point from the reference L (for example, a rope or guiding wire tensioned next to the roadway). Here, the pulling point position z.sub.zp is the output quantity of the pulling point mechanism G.sub.zp. The resulting sensor signal y.sub.zp is returned to the pulling point control unit C.sub.zp. The control signal of the pulling point control unit C.sub.zp is the desired value of the leveling cylinder position r.sub.zp.

[0055] Thus, the control signal of the pulling point control unit C.sub.zp represents the reference input of the inner control loop 11 whose actual value is the leveling cylinder position s.sub.nz. The inner control loop 11 comprises, as the closed-loop controlled system, the leveling cylinder function G.sub.nz, wherein the sensor H.sub.nz detects the leveling cylinder position and supplies it to the leveling cylinder control unit C.sub.nz. Here, u.sub.nz is the control signal of the leveling cylinder control unit C.sub.nz which acts on the leveling cylinder 7.

[0056] By means of the previously described cascade control 100A, the disturbing influence of the subsoil d.sub.zp on the pulling point position z.sub.zp can be nearly completely corrected. Moreover, due to the exact detection of the screed height z.sub.bo, it can be directly adjusted, and one can better counteract against the disturbance d.sub.bo which acts on z.sub.bo.

[0057] On the basis of the three sensor signals y.sub.bo, y.sub.nz, y.sub.zp and in view of the design presented in FIG. 2, the following correlations can be derived:

z.sub.bo=y.sub.bo+z.sub.ref   (1)

d.sub.zp=y.sub.zp+z.sub.ref+y.sub.nz−s.sub.zp0   (2)

[0058] Here, d.sub.zp is given by the interaction of the running gear fw with the subsoil 3, here in FIG. 2 subsoil z.sub.u. Thus, d.sub.zp=fw(z.sub.u) applies. Consequently, the subsoil profile can be calculated by the inverse function of the running gear function. The following applies:

z.sub.u=fw.sup.−1(d.sub.zp)   (3)

Since for the layer thickness, s.sub.es=z.sub.bo−z.sub.u applies, the layer thickness s.sub.es can be determined by means of the correlations (1)-(3) by the three sensor signals y.sub.bo, y.sub.nz, y.sub.zp. The following applies:

s.sub.es=y.sub.bo+z.sub.ref−fw.sup.−1(y.sub.zp+z.sub.ref+y.sub.nz−s.sub.zp0)   (4)

[0059] If the influence of the running gear is neglected, i.e., z.sub.u≈d.sub.zp is assumed, the following applies:

s.sub.es=y.sub.bo−y.sub.zp−y.sub.nz+s.sub.zp0   (5)

d.sub.bo=d.sub.zp   (6)

[0060] In the implementation of the equations (5) and (6), the location dependency is to be considered. This means, the following applies:

d.sub.bo(x)=d.sub.zp(x−s.sub.zh) and

s.sub.es(x)=y.sub.bo(x)−y.sub.zp(x−s.sub.zh−s.sub.bo)−y.sub.nz(x−s.sub.zhs.sub.bo)+s.sub.zp0

[0061] Thus, the signals y.sub.bo, y.sub.nz, y.sub.zp are recorded, and the screed disturbance d.sub.bo(x) is calculated at the way point x from the pulling point disturbance d.sub.zp of the previous way point x−s.sub.zh. The information with respect to the paving thickness s.sub.es(x) can be displayed to the operator, for example on a display at the external control stand of the screed.

[0062] Moreover, the above cascade control 100A can be extended by a layer thickness calculation module for the layer thickness control for which a desired layer thickness can be held available as a desired layer thickness based on which the layer thickness calculation module calculates the desired value of the screed height r.sub.bo.

[0063] The particularity of the layer thickness calculation module is that the correlation between the layer thickness and the screed height is algebraic. This means that a change of the layer thickness exactly corresponds to the same change of the screed height. To implement a layer thickness control, two variants are conceivable.

[0064] In the first variant, the current layer thickness is identified from the progression of the sensor measurements and compared to the desired layer thickness held available. This deviation is processed in the screed control unit to a change of the screed height. In the second variant, the correlation

s.sub.es(x)=y.sub.bo(x)−y.sub.zp(x−s.sub.zh−s.sub.bo)−y.sub.nz(x−s.sub.zh−s.sub.bo)+s.sub.zp0

can be utilized to determine the desired value of the screed height r.sub.bo directly from the desired layer thickness. To calculate the desired screed height r.sub.bo from the desired layer thickness r.sub.es, s.sub.es=r.sub.es and y.sub.bo=r.sub.bo are inserted in the above equation. Subsequently, a resolution is made with respect to r.sub.bo. This leads to

r.sub.bo(x)=r.sub.es(x)+y.sub.zp(x−s.sub.zhs.sub.bo)+y.sub.nz(x−s.sub.zh−s.sub.bo)−s.sub.zp0.

Thus, the difference between the cascade control and the cascade control extended by the layer thickness calculation module essentially is whether the user indicates a desired value for the screed height or for the layer thickness.

[0065] The above described cascade control 100A can be extended by the disturbance variable feedforwarding S1, S2 represented in a dashed line in FIG. 2. Here, information with respect to the subsoil z.sub.u and the resulting disturbances d.sub.bo and d.sub.zp are detected and supplied to the screed control unit C.sub.bo and the pulling point control unit C.sub.zp which use them for calculating the desired pulling point and leveling cylinder positions r.sub.zp, r.sub.nz to proactively compensate the disturbance variables d.sub.bo and d.sub.zp without waiting for them to have an influence on the controlled variables z.sub.bo, z.sub.zp. Here, in the control signal calculation in the screed control unit C.sub.bo, it is taken into consideration that the disturbance d.sub.bo lags behind with a dead time of the disturbance d.sub.zp depending on the paving speed. Both the calculated determination of the disturbance variables d.sub.bo and d.sub.zp as described above and the direct measurement of the disturbance variables d.sub.bo and d.sub.zp by means of suited measurement systems H.sub.dbo and H.sub.dzp (e.g., scanner and the like) are possible. Here, measurement can be accomplished both “online”, i.e., during paving, and “offline”, i.e., before paving, for example by means of a digital terrain model (DGM). Progresses measured offline are here stored in the controlling system.

[0066] The leveling method is not restricted to a certain sensor technology. To detect the screed and pulling point positions, in particular measurement systems, such as e.g., tachymeters and/or laser receivers, can be employed. An inclination sensor which measures the set angle of the screed would also be conceivable. One of the two ultrasonic sensors could be replaced by such an inclination sensor. The distance measured by the replaced sensor could then be determined by trigonometric relations. Thereby, one can also deviate from the defined sensor positions at the pulling point and the screed's trailing edge which can result in advantages in practice. The use of measuring systems without any fixed reference, for example, a “BigSki”™ mounted to the tow bar 5 of the road finishing machine 1 which measures the distance on the subsoil 3 at various positions, would possibly also be usable with losses of precision.

[0067] In the leveling system 10A, the subsoil profile z.sub.u is not known. z.sub.u acts, via the running gear fw, on the pulling point 6 and thus forms the unknown pulling point disturbance d.sub.zp=fw(z.sub.u). In particular to compensate this unknown pulling point disturbance d.sub.zp=fw(z.sub.u), the central control loop 12 of the cascade control 100A which adjusts the pulling point position z.sub.zp is employed.

[0068] However, if according to FIG. 4, a sufficiently precise digital terrain model (DGM) is given, z.sub.u is given by this model and d.sub.zp can be calculated by means of the running gear fw of the road finishing machine 1. Thus, the pulling point 6 is influenced by a known disturbance in the present case. The consequence is that the central control loop 12 including the sensor H.sub.zp is no longer required and could be replaced by a pulling point control C′.sub.zp. Moreover, the information with respect to z.sub.u can be used for an optional disturbance variable feedforwarding. The measuring means H.sub.dbo and H.sub.dzp can consequently also be omitted.

[0069] FIG. 4 shows the embodiment which comprises a leveling system 10B with a cascade control 100B which processes a digital terrain model (DGM). The screed control unit C.sub.bo is nearly unchanged compared to the basic design according to FIG. 3. A difference to the shown variant of FIG. 3 is that, if a disturbance variable feedforwarding is used, the disturbance d.sub.bo in the screed control unit C.sub.bo is calculated from z.sub.u. In contrast to the basic design according to FIG. 3, the pulling point control unit C.sub.zp in FIG. 4 is no longer present but is calculated by the pulling point control C′.sub.zp which calculates, from the known subsoil profile z.sub.u and the desired position of the pulling point r.sub.zp, a desired value position r.sub.nz of the leveling cylinder. This calculation is based on equations (2) and (3). First of all, the actual values y.sub.zp and y.sub.nz are replaced by the corresponding desired values r.sub.zp and r.sub.nz. Subsequently, equation (3) is resolved with respect to d.sub.zp. d.sub.zp=fw(z.sub.u) applies. The insertion of y.sub.zp=r.sub.zp, y.sub.nz=r.sub.nz and d.sub.zp=fw(z.sub.u) in equation (2) and a resolution with respect to r.sub.nz leads to

r.sub.nz=fw(z.sub.u)−r.sub.zp−z.sub.ref+s.sub.zp0   (7)

whereby the control algorithm for the pulling point control C′.sub.zp is given.

[0070] It is noted that the leveling system 10A, cascade control 100A, inner control loop 11, central control loop 12, outer control loop 13, and/or any other system, control, control loop, unit, control unit, controller, machine, screed, sensor, device, module, model, arrangement, feature, function, functionality, step, algorithm, operation, or the like described herein may comprise and/or be implemented in or by one or more appropriately programmed processors (e.g., one or more microprocessors including central processing units (CPU)) and associated memory and/or storage, which may include data, firmware, operating system software, application software and/or any other suitable program, code or instructions executable by the processor(s) for controlling operation thereof and/or for performing the particular algorithms represented by the various functions and/or operations described herein, including interaction between and/or cooperation with each other. One or more of such processors, as well as other circuitry and/or hardware, may be included in a single ASIC (Application-Specific Integrated Circuitry) or individually packaged or assembled into a SoC (System-on-a-Chip). As well, several processors and various circuitry and/or hardware may be distributed among several separate components and/or locations, such as a road finishing machine, a screed, a mobile unit or mobile computing device, or a remote server.