Road finishing machine with leveling cascade control

Abstract

To provide a road finisher with a leveling system capable of almost completely compensating for influences of subsoil disturbances at a screed pull point location.SOLUTION: A road finisher comprising a screed (4) for producing a pavement layer (2) on a subsoil (3) and moving in a paving driving direction (R) over the subsoil (3) includes a leveling system for adjusting a height of the screed (4) to compensate for irregularities (8) in the subsoil (3). The leveling system has cascade control.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a road finishing machine comprising a levelling system according to claim 1. Furthermore, the present invention relates to a method for levelling a screed of a road finishing machine according to method claim 14. [Background technology]

[0002] Known road finishers are equipped with leveling systems that are useful for compensating for subsoil irregularities that act on the driving gears of the road finisher or directly on the screed of the road finisher during paving operations. Based on sensor measurements from the leveling system, the screed of the road finisher can be adjusted in height by a leveling cylinder with an extendable piston coupled to the screed to produce a flat paving layer.

[0003] In conventional leveling systems, when leveling is achieved by means of a guide wire and a distance sensor, the distance sensor is attached to the towbar. The towbar is located between the forward pulling point, where the leveling cylinder piston is attached, and the screed body, which is dragged by the towbar. That is, the towbar is dragged in the driving direction, generally at the level of the lateral paving means. From this position, the distance sensor does not detect the exact position of the screed's trailing edge or the influence of ground irregularities at the forward pulling point. The trailing edge, located behind the screed, generally defines the screed height and accurately determines the horizontality of the generated pavement. However, these sensor measurements are inaccurate and do not provide an accurate profile of the current subsoil. Therefore, screed leveling results cannot be based on them and accurately compensate for subsoil irregularities.

[0004] DE 19647150 A1 discloses a road finishing machine having a leveling system including a height control loop as a pilot controller operating based on the measured elevation of the screed trailing edge, which is configured to generate a control signal as a reference signal for a pull point control loop embodied as a sequential control, which controls a hydraulic valve of a leveling cylinder connected to the forward pull point of the screed based on and taking into account the detected inclination of the screed pull arm.

[0005] DE10025474B4 discloses a leveling system using a layer thickness control loop as a pilot control unit, from which a control signal is generated based on a calculated actual layer thickness value and based on a desired layer thickness value. This control signal specifies a desired inclination value that can be held available for a levelness control loop embodied as a sequence control. This levelness control loop calculates a variable that is manipulated for controlling a leveling cylinder for screed height adjustment based on the actual inclination value that is held available for this purpose and on the inclination of the pulling arm detected during paving operations.

[0006] In DE 19647150 A1 and DE 10025474 B4, the influence of subsoil disturbances at the tension point location cannot be completely eliminated by the two-stage control method. This is exacerbated by the use of gradient sensors, which are particularly susceptible to disturbances due to subsoil irregularities.

[0007] It is an object of the present invention to provide a road finisher with a leveling system that is able to almost completely compensate for the effects of subsoil disturbances at the screed pull point location. It is also an object of the present invention to provide a leveling method for a road finisher that responds accurately to the current subsoil profile. Summary of the Invention [Means for solving the problem]

[0008] This object is achieved by a road finishing machine according to claim 1 or by a method for levelling the screed of a road finishing machine according to claim 14. Advantageous refinements of the invention are given by the dependent claims.

[0009] The present invention relates to a road finishing machine comprising a screed for producing a paving layer on a subsoil, over which the road finishing machine moves in the direction of travel during a paving operation. The road finishing machine according to the invention comprises a levelling system for adjusting the height of the screed to compensate for irregularities in the subsoil, the levelling system including a cascade control.

[0010] The cascade control comprises an outer control loop including a first control unit (hereinafter also referred to as screed control unit) which is embodied to determine a desired value of the pull point position of the screed with respect to a predetermined reference based on a detected actual value of the screed height of the screed with respect to a predetermined reference and based on a desired value of the screed height with respect to the predetermined reference that can be kept available for this purpose, where screed height means in particular the height of the trail edge of the screed. Preferably, the pull point position is determined by the front end of the pulling arm of the screed.

[0011] The cascade control further comprises an inner control loop including a second control unit (hereinafter also referred to as levelling cylinder control unit) which is embodied to determine a control signal for the levelling cylinder, by means of which the levelling cylinder can be controlled, based on a detected actual value of the levelling cylinder position of an extendable piston of the levelling cylinder attached to the tension point and based on a desired value of the levelling cylinder position which is kept available for the second control unit.

[0012] According to the invention, the cascade control comprises a central control loop between the outer and inner control loops, the central control loop comprising a third control unit (hereinafter also referred to as pull point control unit) embodied to determine a desired value of the levelling cylinder position for the second control unit on the basis of the detected actual value of the pull point position of the pull point of the screed relative to a predetermined reference and on the basis of a desired value of the pull point position determined by means of the first control unit; or the cascade control comprises a pull point control between the outer and inner control loops, the pull point control being embodied to determine a desired value of the levelling cylinder position for the second control unit on the basis of a desired value of the pull point position of the pull point of the screed determined by means of the first control unit and in particular on the basis of a digital terrain model of the subsoil over which the road finishing machine moves to produce the paving layer, the model being kept available for the pull point control system.

[0013] In a first alternative form according to the invention, the cascade control includes at least three control loops, one outer, one central and one inner, interleaved to generate the control signals for the levelling cylinders, providing a three-stage cascade levelling system that can fully compensate for unknown pull point disturbances acting on the pull point from the subsoil profile via the driving gear of the road finishing machine, particularly using the central control loop that responds directly to subsoil irregularities.

[0014] A second alternative form of road finishing machine according to the invention provides a cascade control with an integrated pull-point control for improved screed levelling, which forms a pilot control for the inner control loop and a sequence control for the outer control loop, and is therefore able to almost completely compensate for pull-point disturbances, taking into account known subsoil irregularities, based on a digital terrain model kept available.

[0015] Both alternatives allow better compensation of subsoil irregularities, since both the effect of the irregularities on the screed height and the effect of the irregularities on the pull point mechanism are directly detected and taken into account for generating the control signals that set the levelling cylinders.

[0016] Both of the above-mentioned alternative configurations of the road finishing machine according to the invention allow for accurate detection of the influence of disturbances on the pull point position and the screed caused by irregularities formed in the subsoil and for corresponding almost complete compensation, mainly because the levelling system is subdivided into multiple closed-loop and open-loop control system sections, each of which can be better designed with a closed-loop / open-loop control system in mind, to almost completely compensate for the current irregularities in the subsoil and other disturbance variables that actually occur in the screed levelling.

[0017] In particular, the subdivision of the coherent closed-loop control system of the outer control loop into the above-mentioned alternatives has a positive effect on the compensation of subsoil irregularities. This subdivision means the combination of a superimposed inner closed loop with a central closed loop, or the combination of an inner closed loop with a leading pull point control. Each of these alternative combinations allows the closed-loop control system with which the outer control loop is combined to be better controlled for effective compensation of disturbance variables due to their subdivision into partial sections.

[0018] Preferably, the outer control loop comprises a control system whose output quantity (control variable) is the detected actual value of the screed height of the screed relative to a predetermined criterion and / or whose input quantity is the detected actual value of the pull point position of the pull point of the screed relative to a predetermined criterion. Alternatively, the input quantity may be the actual value of the pull point position of the pull point, which pull point position may be calculated depending on the detected actual value of the levelling cylinder position. The outer control loop makes it possible to adjust the screed height taking into account a predetermined criterion, for example a guide wire strung adjacent to the roadway.

[0019] In one variant, the leveling system includes at least one first sensor for the outer control loop, which is embodied to detect the actual screed height. This sensor is therefore also referred to as the screed sensor below. In particular, the first sensor is embodied to detect the distance from the screed trail edge to a predetermined reference. According to one embodiment of the present invention, the first sensor is a distance sensor for detecting the distance to the predetermined reference, located in the area of ​​the screed trail edge. For example, the sensor is attached to the side pusher of the screed. This allows the actual height position of the screed to be accurately detected as a control variable, particularly the height position of the trail edge, and fed back to the first control unit of the outer control loop. The outer feedback may be built on the feedback of the inner control loop. Preferably, the inner feedback operates faster, so that the disturbance variable compensation and pilot operation of the outer control loop can be better coordinated with the inner closed loop or closed loop.

[0020] Preferably, the inner control loop includes a closed loop control system whose output quantity is the detected actual value of the leveling cylinder position of an extendable piston of a leveling cylinder attached to the tension point, and / or whose input quantity is a control signal for the leveling cylinder.

[0021] In one advantageous variant, the leveling system for the inner control loop includes at least one second sensor embodied to detect the actual value of the leveling cylinder position. This sensor is also referred to as the leveling cylinder sensor hereinafter. Advantageously, the second sensor is a distance sensor arranged in the area of ​​the leveling cylinder to detect the extension / retraction path of the leveling cylinder piston. This allows the leveling cylinder position to be accurately detected as a control variable, in particular the current extension / retraction path of the leveling cylinder piston, and fed back to the second control unit of the inner control loop.

[0022] Preferably, the central control loop comprises a closed loop control system whose output quantity is the detected actual value of the screed pull point position and / or whose input quantity is the detected actual value of the levelling cylinder position.

[0023] According to one embodiment of the present invention, the leveling system for the central control loop comprises at least one third sensor (hereinafter also referred to as pull point sensor) embodied to detect the actual value of the pull point position relative to a predetermined reference. Preferably, the third sensor is a distance sensor detecting the distance to a predetermined reference located in the area of ​​the pull point of the screed. This allows the pull point position, which is directly affected by irregularities, to be accurately detected as a control variable and supplied by feedback to the third controller of the central control loop.

[0024] In particular, sensors for detecting the screed and pull point positions can be implemented as position measurement sensors. Laser, ultrasonic, LIDAR, and / or radar sensors can be used. According to a preferred variant, at least one tachymeter provided on the road finishing machine and / or a laser receiver attached to the screed unit can be used as a measuring means for detecting the screed and pull point positions. The tachymeter can be implemented so that it can be automatically adjusted by a motor for target tracking according to a predetermined criterion.

[0025] Instead of two distance sensors installed at the screed trailing edge and at the pull point, it is conceivable to use a longitudinal gradient sensor combined with a distance sensor. The distance sensor can then be installed on the screed arm at any point between the screed trailing edge and the pull point. The gradient sensor measures the screed setting angle. Here, since the screed geometry is known, it is irrelevant where the gradient sensor is installed on the screed or tow bar. When the sensor combination described herein is used, the distance to the screed trailing edge and pull point reference (distance y represented in Figure 2) can be calculated. bo and y zp) can be determined by trigonometric calculations based on the measured angles and the measured distances. The configuration and parameterization of the control unit remain unaffected by this. This sensor configuration can also be adopted when using a subsoil model as a reference (hereinafter also referred to as virtual reference).

[0026] Preferably, the cascade control includes at least one disturbance variable feedforward, which can function based on the determination of at least one indirectly calculated disturbance variable and / or based on at least one directly measurable disturbance variable. By means of the disturbance variable feedforward, a manipulated variable, for example a manipulated variable relative to the pull point position, can be actively adapted. This adaptation is performed by an upstream transfer function instead of allowing the influence of the disturbance variable on the control variable present at the output.

[0027] The disturbance variable feedforward may be fitted with at least one filter for smoothing the calculated or detected disturbance variables, thereby damping the response of a control unit functionally connected to the disturbance variable feedforward. Measurements of the subsoil profile recorded by means of a scanner may be used for the disturbance variable feedforward and / or a digital terrain model may be used.

[0028] The cascade control includes, inter alia, a first disturbance variable feedforward for the outer control loop and a second disturbance variable feedforward for the central control loop, which allows subsoil irregularities and / or other disturbance variables occurring during paving operations, such as disturbance variables related to the mechanical and / or hydraulic systems of the road finishing machine, to be actively and quickly compensated for without appreciably affecting the cascade feedback of the control variables.

[0029] Each of the disturbance variable feedforwards can be individually and independently activated and deactivated, or jointly activated and deactivated. Based on at least one process parameter measured at the road finisher during a paving operation and / or based on a measured characteristic of the pavement layer being produced, it is contemplated that automatic activation of at least one disturbance variable feedforward that responds directly or indirectly to the process parameter and / or the characteristic of the pavement layer may be possible.

[0030] Preferably, the cascade control is supplemented by a layer thickness calculation module which is embodied to determine, as a reference input, a desired screed height value for the outer control loop based on the identified current layer thickness of the paving layer to be generated and / or based on a desired layer thickness of the paving layer to be generated that is kept available for this purpose. By means of this cascade control, compensation for subsoil irregularities can be completed by generating the desired layer thickness.

[0031] In one variation, the layer thickness calculation module is configured to determine the layer thickness from ongoing sensor measurements that are used for the leveling operation and are optionally temporarily stored.

[0032] The actual layer thickness can be determined by means of a layer thickness measurement system implemented in the road finishing machine. It is also conceivable to use the measurement results of at least one distance sensor for identifying the layer thickness to be produced, the measurement results of which also serve the operation of the leveling system.

[0033] According to one variant, the reference is designed as a real physical reference (e.g., a guide wire). However, in practice, a physical reference is not always available. In this case, a reference, referred to here as "virtual," is employed. This may be, for example, a rotating laser and laser receiver mounted on the screed, or a tachometer tracking prism mounted on the screed. In these two measurement methods, the reference and the sensor form a single system, so a typical distance sensor is not used.

[0034] From a practical point of view, the virtual reference according to the embodiment is a mathematical model of the subsoil, which exists as a digital terrain model (DGM) or in other digital form (data from a (laser) scanner). When using such a reference, a distance sensor still determines the distance to the subsoil, i.e. to the reference. In this case, depending on the position, the corresponding desired distance to the subsoil of the screed and pulling point is selected, and the desired screed height is adjusted accordingly. For the desired value of the screed control unit, the following formula can be applied: r bo (x)=z bo_soll (x)-z ref (x) where r bo (x)>0 ∀x (for all x). In the pull point control unit, the control signal of the screed control unit is similarly superimposed by a negative progression of the reference so as to reach the pull point position desired by the screed control unit.

[0035] The invention further relates to a method for levelling the screed of a road finishing machine, which produces a paving layer on the subsoil over which the road finishing machine moves in the laying direction during a paving operation. According to the invention, irregularities in the subsoil are compensated by means of a levelling system which adjusts the height of the screed by means of a cascade control.

[0036] In the method according to the invention, the outer control loop of the cascade control determines by means of the first control unit a desired value of the pull point position of the pull point of the screed relative to a predetermined criterion based on the detected actual value of the screed height of the screed relative to a predetermined criterion and based on a desired value of the screed height relative to the predetermined criterion which can be kept available for the first control unit as a reference input.

[0037] Furthermore, the inner control loop of the cascade control determines, by means of the second control unit, on the basis of the detected actual value of the levelling cylinder position of the extendable piston of a levelling cylinder attached to the tension point of the screed and on the basis of the desired value of the levelling cylinder position kept available for the second control unit, a control signal for the levelling cylinder by means of which the levelling cylinder is controlled for adjusting the height of the screed.

[0038] The method according to the invention provides that a central control loop of the cascade control present between the outer and inner control loops determines by means of a third control unit a desired value of the levelling cylinder position for the second control unit on the basis of the detected actual value of the pull point position of the pull point of the screed relative to a predetermined reference and on the basis of the desired value of the pull point position determined by means of the first control unit, or that a pull point control functionally integrated between the outer and inner control loops determines a desired value of the levelling cylinder position for the second control unit on the basis of the desired value of the pull point position of the screed determined by means of the first control unit and in particular on the basis of a digital terrain model of the subsoil over which the road finishing machine moves to produce the paving layer, the model being kept available for the second control unit.

[0039] Thus, by means of the method according to the invention, a desired value of the levelling cylinder position is determined, which serves as a reference input for the setting of the levelling cylinder. This desired value controls the required variables for the levelling cylinder. This desired value can be determined by a three-stage interleaved cascade control, i.e. by means of superimposed first, second and third control loops, or by means of an outer and an inner control loop with a pull point control implemented between them. With both alternatives, the influence of irregularities on the screed height and on the pull point mechanism can be directly detected and taken into account for generating the control signals for the setting of the levelling cylinder, thereby enabling better compensation of subsoil irregularities.

[0040] Preferably, the cascade control is supplemented by at least one disturbance variable feedforward, which can actively respond to subsoil irregularities and other disturbance variables in order to determine the desired values ​​of the pull point and / or the levelling cylinder position, and can reliably compensate for them by providing the relevant disturbance variables to the screed control unit, i.e. the control unit of the outer control loop, and / or the pull point control unit, i.e. the control unit of the central control loop, by means of a predetermined transmission function.

[0041] According to one embodiment, the cascade control is supplemented by a layer thickness calculation module that determines a desired screed height for the outer control loop based on the layer thickness of the paving layer to be produced, as determined during a paving run, and / or based on a desired value of the paving layer thickness that is kept available for that purpose. The layer thickness calculation module can, for example, use a leveling sensor signal to calculate the desired screed height.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 shows a road finishing machine for producing a paving layer on a subsoil. [Figure 2] FIG. 2 shows an isolated schematic view of the screed of the road finishing machine in the reference coordinate system. [Figure 3] FIG. 3 shows a schematic diagram of a first variant of a leveling system for a screed of a road finishing machine according to the invention. [Figure 4] FIG. 4 shows a schematic diagram of a second variant of a levelling system for a screed of a road finishing machine according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0044] In the drawings, technical features are always provided with the same reference numbers.

[0045] FIG. 1 shows a road finisher 1 for producing a paving layer 2 with a desired layer thickness S on a subsoil 3. Over the subsoil 3, the road finisher 1 moves in a direction of travel R during a paving operation. The road finisher 1 has a leveling screed 4 for compacting the paving layer 2. The screed 4 has a pulling arm 5 that is connected at a forward pulling point 6 to a leveling cylinder 7 attached to the chassis of the road finisher 1. The leveling cylinder 7 can raise and lower the pulling arm 5 at the forward pulling point 6, so that the setting angle of the trailing screed 4 can be set during a paving operation, and the screed 4 is raised and lowered accordingly. In particular, by dynamic control of the setting of the leveling cylinder, irregularities 8 (unevenness, variations) in the subsoil 3 can be compensated for.

[0046] Figure 2 shows an isolated schematic view of the screed 4 in a reference frame K. The reference frame K includes the dimensions and geometry of the screed relative to the subsoil 3, which will be explained in more detail below in connection with Figures 3 and 4.

[0047] 3 shows a leveling system 10A embodied to level a screed 4. The leveling system 10A comprises a cascade control 100A including three superimposed control loops: an inner control loop 11, a central control loop 12, and an outer control loop 13.

[0048] The outer control loop 13 is connected to the first sensor H bo (screed sensor), and the inner control loop 11 includes a second sensor H nz (leveling cylinder sensor), and the central control loop 12 includes a third sensor H zp (pulling point sensor). Thus, according to Figure 2, each of the three control loops 11, 12, 13 includes one separate sensor each. Sensor H bo , H nz , H zp is the distance shown in Figure 2, especially the extension path s of the leveling cylinder. nz , screed height z bo , and the tensile point position z zp The three control units C bo , C zp , C nz Each sensor H bo , H nz , H zp from the corresponding sensor signal y bo , y nz , y zp is provided as the actual control variable.

[0049] According to FIG. 3, the cascade control 100A is supplemented by optional disturbance variable feedforward S1, S2, here represented schematically by dashed lines.

[0050] First, a cascade control 100A in which the disturbance variable feedforward S1 and S2 are omitted will be described. The three control loops 11, 12, and 13 of the cascade control 100A are interleaved. In the outer control loop 13, the screed height z bo The dynamic behavior of the closed-loop control system "Screed" is determined by the transfer function G boThe output variable of this closed-loop control system is the detected screed height z bo Screed height z bo is a screed sensor H provided near the trail edge 14 of the screed bo (see Figures 1 and 2). The corresponding sensor signal y bo is fed back to the control unit C bo The transfer function G bo The input variables are the tensile point position z zp is the measured actual value of the corresponding pull point position r zp The desired value of is given by the first control unit C bo (Screed control unit) control signal, and screed height r bo and the sensor signal y bo It is calculated from

[0051] The control signal r of the outer control loop 13 zp is the reference signal for the central control loop 12, which is controlled by the pull point control unit C zp By means of the tension point position z zp Adjust the tension point position z zp The actual value of is determined by a sensor H that determines the distance of the pulling point from a reference L (for example, a rope or guide wire stretched adjacent to the roadway). zp Here, the pulling point position z zp is the tension point mechanism G zp The output quantity of the sensor signal y zp is the pull point control unit C zp Pull point control unit C zp The control signal for the leveling cylinder position r zp is the desired value.

[0052] Therefore, the pull point control unit C zp The control signal s represents the reference input of the inner control loop 11, and the actual value of the inner control loop 11 is the smoothing cylinder position s nz The inner control loop 11 is a closed-loop control system that controls the smoothed cylinder function Gnz Equipped with Sensor H nz detects the leveling cylinder position and sends it to the leveling cylinder control unit C nz where u nz is a leveling cylinder control unit C acting on the leveling cylinder 7. nz is a control signal.

[0053] By the method of the cascade control 100A described above, the pull point position z zp Subsoil in zp The effect of the turbulence of the screed height z can be almost completely compensated. bo Accurate detection of the screed height z bo You can directly adjust the z bo Disturbance d acting on bo can be better cancelled out.

[0054] Three sensor signals y bo , y nz , y zp Based on this, and considering the design shown in Figure 2, the following interrelationships can be derived:

[0055] z bo =y bo +z ref (1)

[0056] d zp =y zp +z ref +y nz -s zp0 (2)

[0057] where d zp is the subsoil 3, here the subsoil z in Figure 2 u , is given by the interaction of the running gear fw with d zp =fw(z u ) can be applied. As a result, the subsoil profile can be calculated using the inverse function of the running gear.

[0058] z u =fw-1 (d zp ) (3)

[0059] For the layer thickness, s es =z bo -z u is applicable, and the layer thickness s es are the three sensor signals y bo , y nz , y zp The relationship (1) to (3) can be used to determine the temperature. As a result, the following equation can be applied:

[0060] s es =y bo +z ref -fw -1 (y zp +z ref +y nz -s zp0 ) (4)

[0061] Ignore the effect of running gear, i.e. z u and d zp Assuming that and are approximately equal, the following equation is obtained:

[0062] s es =y bo -y zp -y nz +s zp0 (5)

[0063] d bo =d zp (6)

[0064] In the implementation of equations (5) and (6), the position dependency is taken into account, which means that the following applies:

[0065] d bo (x)=d zp (xs zh )

[0066] s es (x)=y bo (x)-y zp (xs zh -s bo )-ynz (xs zh -s bo )+s zp0

[0067] This causes the signal y bo , y nz , y zp is recorded, and the screed disturbance d at waypoint x is bo (x) is the previous waypoint xs zh The tension point disturbance d zp Pavement thickness s es Information regarding (x) can be displayed to the operator, for example, on a display on the screed's external control stand.

[0068] Furthermore, the above-described cascade control 100A can be extended by a layer thickness calculation module for layer thickness control, for which the desired layer thickness is calculated as a function of the screed height r calculated by the layer thickness calculation module. bo The desired layer thickness can be kept available based on the desired value of .

[0069] A feature of the layer thickness calculation module is that the correlation between layer thickness and screed height is algebraic. This means that a change in layer thickness corresponds exactly to the same change in screed height. Two variants are possible for implementing layer thickness control:

[0070] In the first variant, the current layer thickness is identified from ongoing sensor measurements and compared with the desired layer thickness, which is kept available. This deviation is processed in the screed control unit and results in a change in screed height. In the second variant, the screed height r bo The following equation can be used to determine the desired value of ρ directly from the desired layer thickness:

[0071] s es (x)=y bo (x)-y zp (xs zh -s bo )-y nz (xs zh-s bo )+s zp0

[0072] Desired layer thickness r es to desired screed height r bo To calculate s es =r es and y bo =r bo is inserted into the above equation, and r bo This leads to the following equation:

[0073] r bo (x)=r es (x)+y zp (xs zh -s bo )+y nz (xs zh -s bo )-s zp0

[0074] Therefore, the difference between a cascade control and a cascade control extended by a layer thickness calculation module is essentially whether the user indicates a desired value for the screed height or the layer thickness.

[0075] The cascade control 100A described above can be extended by disturbance variable feedforward S1, S2 shown in dashed lines in FIG. 3, where subsoil z u and the resulting disturbance d bo , d zp information about the screed control unit C bo and tension point control unit C zp Screed Control Unit C bo and tension point control unit C zp The information provided is used to calculate the desired pull point position r zp and the leveling cylinder position r nz These are used to calculate the control variables z bo , z zp The disturbance variable d is calculated without waiting for it to affect bo and d zpwhere the screed control unit C bo In the control signal calculation, the disturbance d bo is the disturbance d zp The delay relative to the dead time of the disturbance variable d bo and d zp is calculated and the appropriate measurement system H dbo and H dzp Disturbance variable d due to (e.g., scanner) bo and d zp Here, measurements can be achieved both "online", i.e. during paving, and "offline", i.e. before paving, for example by means of a Digital Terrain Model (DGM). The progress of the offline measurements is now stored in the control system.

[0076] The leveling method is not limited to a specific sensor technology. Measurement systems, such as tachometers and / or laser receivers, can be used to detect the screed position and the pull-off point position. A gradient sensor measuring the screed's set angle is also conceivable. One of the two ultrasonic sensors can be replaced with such a gradient sensor. The distance measured by the replaced sensor can then be determined by a triangular relationship. This allows for a sensor position that is different from that defined at the pull-off point and the screed's trail edge, which can actually be advantageous. Measurement systems without a fixed reference, such as the BigSki®, mounted on the towbar 5 of the road finishing machine 1 and measuring the distance above the subsoil 3 at various positions, can also be used in some cases, albeit at a loss of precision.

[0077] In the leveling system 10A, the subsoil profile z u is unknown. At tension point 6, z u acts through the running gear fw and therefore the unknown pull point disturbance d zp =fw(z u) is formed. In particular, this unknown tension point disturbance d zp =fw(z u ) to compensate for the tension point position z zp A central control loop 12 of the cascade control 100A is used to regulate

[0078] However, if a sufficiently accurate digital terrain model (DGM) is given, as in Figure 4, z u is given by this model, and d zp can be calculated by means of the running gear fw of the road finishing machine 1. In this case, the pulling point 6 is therefore subject to known disturbances. As a result, the sensor H zp The central control loop 12 including the pull point control C' is no longer needed. zp Furthermore, z u The information about H can be used for optional disturbance variable feedforward. dbo and H dzp can also be omitted.

[0079] 4 shows an embodiment including a leveling system 10B with a cascade control 100B that processes a digital terrain model (DGM). bo has changed little compared to the basic design according to Fig. 3. The difference with the variant shown in Fig. 3 is that when disturbance variable feedforward is used, the screed control unit C bo Disturbance d at bo Z u In contrast to the basic design according to FIG. 3, the pull point control unit C zp no longer exists, but the pull point control C' zp It is calculated by the pull point control C'. zp is the known subsoil profile z u and the desired position of the pulling point r zp From the desired position r of the leveling cylinder nz This calculation is based on equations (2) and (3). First, the actual value y zp and ynz the corresponding desired value r zp and r nz As a result, d zp Equation (3) is solved for d zp =fw(z u ) applies. In equation (2), y zp =r zp , y nz =r nz and d zp =fw(z u ) insertion and r nz By solving for zp The control algorithm is given.

[0080] r nz =fw(z u )-r zp -z ref +s zp0 (7)

Claims

1. A road finishing machine (1) comprising a screed (4) for producing a paving layer (2) on a subsoil (3), the road finishing machine (1) moving over the subsoil (3) in a laying direction (R) during a paving operation, the road finishing machine (1) comprises a levelling system (10A, 10B) for adjusting the height of the screed (4) to compensate for irregularities (8) in the subsoil (3), The leveling system (10A, 10B) includes a cascade control (100A, 100B), The cascade control (100A, 100B) controls the screed height (z) of the screed (4) relative to a predetermined reference (L). ｂｏ ) and for that purpose, the desired value of the screed height (r) relative to the predetermined reference (L) can be kept available. ｂｏ ) based on the predetermined reference (L), the desired value (r ｚｐ ) and a first control unit (C ｂｏ an outer control loop (13) including The detected actual value (s) of the leveling cylinder position of the extendable piston of the leveling cylinder (7) attached to the pulling point (6) ｎｚ ) and based on a second control unit (C ｎｚ ) the desired value of the leveling cylinder position (r ｎｚ ) based on which a control signal (u) for the leveling cylinder (7) is generated. ｎｚ ) and said second control unit (C) is embodied to determine a signal by which said levelling cylinder (7) can be controlled. ｎｚ 1. A road finishing machine (1) comprising an inner control loop (11) including: The cascade control (100A) comprises a central control loop (12) between the outer control loop (13) and the inner control loop (11), the central control loop detecting the detected actual value (z ｚｐ ) and based on said first control unit (C ｂｏ The desired value of the pull point position (r ｚｐ ) based on the second control unit (C ｎｚ ) to the desired value of the leveling cylinder position (r ｎｚ ) and a third control unit (C ｚｐ ), or The cascade control (100B) includes a pull point control (C') between the outer control loop (13) and the inner control loop (11). ｚｐ ), and the pull point control is provided by the first control unit (C ｂｏ ) the desired value (r) of the pull point position of the pull point (6) of the screed (4) determined by means of ｚｐ ) and in particular a digital terrain model (DGM) of the subsoil (3) over which the road finishing machine (1) moves to generate the pavement layer (2), and ｚｐ ) based on a model kept available for the second control unit (C ｎｚ ) the desired value of the leveling cylinder position (r ｎｚ ) a road finishing machine characterized in that it is embodied to determine

2. The outer control loop (13) is a closed loop control system (G ｂｏ ), the output quantity of which is the detected actual value (z) of the screed height of the screed (4) relative to the predetermined reference (L). ｂｏ ) and / or the input quantity is the detected actual value (z ) of the pull point position of the pull point (6) of the screed (4) relative to the predetermined reference (L). ｚｐ 2. A road finishing machine according to claim 1, characterized in that

3. The leveling system (10A, 10B) for the outer control loop (13) controls the screed height (z ｂｏ a first sensor (H) embodied to detect the actual value of ｂｏ 3. A road finishing machine according to claim 1 or 2, characterized in that it comprises at least one

4. The first sensor (H ｂｏ 4. A road finishing machine according to claim 3, characterized in that the distance sensor (L) is a distance sensor for detecting the distance to the predetermined reference (L) located in the region of the screed trail end (14) of the screed (4).

5. The inner control loop (11) is a closed loop control system (G ｎｚ ), the output quantity of which is the detected actual value (s) of the levelling cylinder position of the extendable piston of the levelling cylinder (7) attached to the pulling point (6). ｎｚ ) and / or its input quantity is the control signal (u) for the levelling cylinder (7). ｎｚ 5. A road finishing machine according to claim 1, wherein the first and second rollers are arranged parallel to each other.

6. The leveling system (10A, 10B) for the inner control loop (11) controls the actual value of the leveling cylinder position (s ｎｚ a second sensor (H ｎｚ 6. A road finishing machine according to claim 1, further comprising at least one

7. The second sensor (H ｎｚ ) is the leveling cylinder position (s ｎｚ 7. Road finishing machine according to claim 6, characterized in that it is a distance sensor arranged in the area of ​​the levelling cylinder (7) for detecting the position of the levelling cylinder (7).

8. The central control loop (12) is a closed loop control system (G ｚｐ ), the output quantity of which is the detected actual value (z ｚｐ ) and / or the input quantity is the detected actual value of the leveling cylinder position (s ｎｚ 8. A road finishing machine according to claim 1, wherein the first and second rollers are arranged parallel to each other.

9. The leveling system (10A, 10B) for the central control loop (12) calculates the actual value of the pull point position (z) relative to the predetermined reference (L). ｚｐ a third sensor (H ｚｐ 9. A road finishing machine according to claim 1, comprising:

10. The third sensor (H ｂｏ 10. A road finishing machine according to claim 9, characterized in that the distance sensor (L) is a distance sensor for detecting the distance to the predetermined reference (L) located in the area of ​​the pull point (6) of the screed (4).

11. 11. Road finishing machine according to any one of claims 1 to 10, characterized in that the cascade control (100A, 100B) comprises at least one disturbance variable feedforward (S1, S2).

12. The cascade control (100A, 100B) is supplemented by a layer thickness calculation module which calculates the desired screed height value (r ) of the outer control loop (13) based on the identified current layer thickness (S) of the paving layer (2) to be generated and / or based on a desired value of the layer thickness (S) of the paving layer (2) to be generated that is kept available for this purpose. ｂｏ 12. A road finishing machine according to any one of claims 1 to 11, characterized in that it is embodied to determine:

13. 13. A road finishing machine according to claim 12, characterized in that the layer thickness calculation module is embodied to determine the layer thickness (S) from ongoing sensor measurements used for leveling.

14. 1. A method for leveling a screed (4) of a road finishing machine (1) for producing a paving layer (2) on a subsoil (3) over which the road finishing machine (1) moves in a laying direction (R) during a paving operation, comprising: Irregularities (8) of the subsoil (3) are compensated by a levelling system (10A, 10B) which performs the levelling of the screed (4) by means of a cascade control (100A, 100B), The outer control loop (13) of the cascade control (100A, 100B) is a first control unit (C ｂｏ ) the detected actual value (z) of the screed height of the screed (4) relative to a predetermined reference (L). ｂｏ ) and for that purpose, the desired value of the screed height (r) for the predetermined reference (L) can be kept available. ｂｏ ) based on the predetermined reference (L), the desired value (r ｚｐ ) is determined, The inner control loop (11) of the cascade control (100A, 100B) is connected to a second control unit (C ｎｚ ) the detected actual value (s) of the levelling cylinder position of the extendable piston of the levelling cylinder (7) attached to the pulling point (6) of the screed (4). ｎｚ ) and based on said second control unit (C ｎｚ ) the desired value of the leveling cylinder position (r ｎｚ ) based on which a control signal (u) for the leveling cylinder (7) is generated. ｎｚ ) by means of which a signal is determined with which the levelling cylinder (7) is controlled for adjusting the height of the screed (4), The central control loop (12) existing between the outer control loop (13) and the inner control loop (13) of the cascade control (100A) is a third control unit (C ｚｐ ) by means of the detected actual value (z) of the pull point position of the pull point (6) of the screed (4) relative to the predetermined reference (L). ｚｐ ) and based on said first control unit (C ｂｏ the desired value of the pull point position (r ｚｐ ) based on the second control unit (C ｚｐ ) to the desired value of the leveling cylinder position (r ｎｚ ), or A pull point control (C') exists between the outer control loop (13) and the inner control loop (11) of the cascade control (100B). ｚｐ ) is the first control unit (C ｂｏ ) the desired value (r) of the pull point position of the pull point (6) of the screed (4) determined by means of ｚｐ ) and in particular a digital terrain model (DGM) of the subsoil (3) over which the road finishing machine (1) moves to generate the pavement layer (2), and ｚｐ ) based on a model kept available for the second control unit (C ｎｚ ) the desired value of the leveling cylinder position (r ｎｚ ) determining the

15. The cascade control (100A, 100B) is supplemented by at least one disturbance variable feedforward (S1, S2) and / or by a layer thickness calculation module, which calculates the desired screed height value (r ) of the outer control loop (13) based on the identified layer thickness (S) of the paving layer (2) to be generated and / or based on a desired value of the layer thickness (S) of the paving layer (2) to be generated, which value is kept available for this purpose. ｂｏ 15. The method of claim 14, further comprising determining:

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