EP4056760B1 - Road finisher with levelling cascade control - Google Patents

Description

The present invention relates to a road finisher with a leveling system according to claim 1. The present invention also relates to a method for leveling a screed of a road finisher according to method claim 14.

Known road finishers are equipped with leveling systems that are used during a paving journey to compensate for unevenness in the subsoil that acts on the road finisher's chassis or directly on the screed of the road finisher. Based on the sensor measurements of a leveling system, the screed of the road finisher can be adjusted in height by means of a leveling cylinder, which has an extendable piston coupled to the screed, in order to produce a level paving layer.

In conventional leveling systems, when leveling is carried out using a stringline and distance sensor, the distance sensor is installed on the towing beam between a front towing point formed thereon, to which the piston of the leveling cylinder is attached, and the screed body towed by the towing beam, i.e. approximately at the level of the transverse distributor device in the direction of travel. From this position, the distance sensor detects neither the exact position of the rear edge of the screed behind it, which generally defines a screed height and which decisively determines the evenness of the installed covering, nor the influence of uneven ground on the front traction point. These imprecise sensor measurements do not reflect the profile of the existing subsoil so that the screed cannot be leveled based on this, which means that unevenness in the subsoil can be precisely compensated for.

DE 196 47 150 A1 discloses a road finisher with a leveling system that has a height control circuit as master controller that works on the basis of a measured height of the rear edge of the screed. This is configured to generate an actuating signal as a command signal for a towing point control loop designed as a slave controller, which based on this and with regard to a detected inclination of the towing arm of the screed actuates a hydraulic valve of a leveling cylinder coupled to the front towing point of the screed.

DE 100 25 474 B4 discloses a leveling system that uses a layer thickness control circuit as a master controller, from which an actuating signal based on a calculated actual layer thickness value and based on a layer thickness setpoint value emerges. This control signal specifies an inclination target value that can be supplied to a levelness control circuit designed as a follow-up controller. This evenness control circuit calculates and Based on an inclination of the towing arm detected during the paving journey, a control variable for controlling a leveling cylinder for adjusting the height of the screed.

In DE 196 47 150 A1 and DE 100 25 474 B4 the disturbing influence of the ground on a towing point position cannot be eliminated properly by means of the two-stage controller device. This is made more difficult by the use of inclination sensors, which are particularly susceptible to interference from uneven ground.

The object of the invention is to provide a road finisher with a leveling system that can be used to almost completely compensate for any disruptive influence of the subsoil on the tow point position of the screed. It is also the object of the invention to provide a leveling method for a road finisher that responds precisely to the existing subsurface profile.

This object is achieved by a road finisher according to claim 1 or by means of a method for leveling a screed of a road finisher according to claim 14. Advantageous developments of the invention are given by the dependent claims.

The invention relates to a road finisher with a screed for producing a paving layer on a subsoil on which the road finisher moves in the direction of travel during a paving run. To compensate for unevenness in the subsoil, the road finisher according to the invention comprises a leveling system for adjusting the height of the screed, the leveling system having a cascade control.

The cascade control comprises an outer control loop, which has a first controller (also referred to below as a screed controller), which is designed to, 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 target value of the screed height relative to it the predetermined reference to determine a target value of a towing point position of a towing point of the screed relative to the predetermined reference. The screed height here means in particular the height of a rear edge of the screed of the paving screed. The tow point position is preferably determined by a front end of the tow arm of the screed.

The cascade control system also includes an inner control loop, which has a second controller (also referred to below as a leveling cylinder controller), which is designed to, on the basis of a detected actual value of a leveling cylinder position of an extendable piston of a leveling cylinder that is attached to the towing point, and on the basis of a leveling cylinder held up to the second controller setpoint the leveling cylinder position to determine an actuating signal for the leveling cylinder, on the basis of which the leveling cylinder can be controlled.

According to the invention, the cascade control comprises either a middle control loop between the outer and the inner control loop, which has a third controller (also referred to below as the towing point controller), which is designed to, on the basis of a detected actual value of the towing point position of the towing point of the screed for the predetermined reference and on To determine the setpoint of the leveling cylinder position for the second controller on the basis of the setpoint of the tow point position determined by means of the first controller, or the cascade control has a tow point control between the outer and the inner control circuit, which is designed to do this on the basis of the setpoint determined by means of the first controller the traction point position of the traction point of the screed and in particular on the basis of a digital terrain model of the subsoil provided to the traction point control, on which the road finisher moves to produce the paving layer, to determine the target value of the leveling cylinder position for the second controller.

In the first alternative according to the invention, the cascade control comprises at least three control circuits, namely an outer, a middle and an inner control circuit, which are nested in one another to produce the actuating signal for the leveling cylinder. Using the three-stage cascade leveling system thus provided, in particular using the central control circuit, which responds directly to unevenness in the subsoil, an unknown traction point disturbance, which affects the traction point from the subsurface profile via the chassis of the road finisher, can be perfectly compensated.

The second alternative of the road finisher according to the invention provides a cascade control with integrated traction point control for improved leveling of the screed. The tow point control used for this forms a command control for the inner control loop and a follow-up control for the outer control loop and can almost completely compensate for the tow point disturbance on the basis of the digital terrain model provided, in which unevenness in the subsoil is taken into account as known.

With both alternatives, better compensation for unevenness in the ground is possible because both the influence of unevenness on the screed height and the influence of unevenness on the traction point mechanics are recorded directly and taken into account to generate the control signal for setting the leveling cylinder.

Both of the above-mentioned alternatives of the road finisher according to the invention make it possible for disturbing influences on the traction point position and the screed caused by unevenness in the subsoil to be precisely detected and accordingly almost completely corrected. This is primarily due to the fact that the leveling system is divided into several controlled/controlled system sections, which can be better designed with regard to their respective controlled/controlled system in order to almost completely compensate for any unevenness in the subsoil and other disturbance variables that occur in practice when leveling the screed to compensate.

The division of the coherent control section of the outer control loop into the above-mentioned alternatives, namely the combination of the superimposed inner and middle control loops or the combination of the inner control loop with the preceding traction point control, has a particularly positive effect on compensating for the unevenness of the ground. Each of these alternative combinations makes it possible for the combined controlled system of the outer control loop to be better controllable for the purpose of effective disturbance variable compensation due to its division into subsections.

The outer control loop preferably includes a controlled system whose output variable (controlled variable) is the detected actual value of the screed height relative to the predetermined reference and/or whose input variable is the detected actual value of the tow point position of the tow point of the screed relative to the predetermined reference. Alternatively, the input variable can be an actual value of the towing point position of the towing point calculated as a function of a detected actual value of the leveling cylinder position. The outer control circuit makes it possible to regulate the screed height with regard to the predetermined reference, for example a guide wire stretched next to the roadway.

A variant provides that the leveling system for the outer control loop has at least one first sensor, which is designed to detect the actual value of the screed height. This sensor is therefore also referred to below as a screed sensor. In particular, the first sensor is designed to detect a distance between the trailing edge of the screed and the predetermined reference. According to one embodiment of the invention, the first sensor is a distance sensor positioned in the area of a trailing edge of the screed for detecting a distance from the predetermined reference. For example, the sensor is attached to a side shifter of the screed. In this way, the actual height position of the screed can be precisely detected as a controlled variable, above all a height position of the rear edge formed thereon, and fed back to the first controller of the outer control loop. The outer feedback can be based on the feedback of the inner control loop, with the inner feedback preferably taking place more quickly, so that the disturbance variable compensation by means of the inner control loop or control loops and the control behavior of the outer control loop can be better matched to one another.

The inner control circuit preferably includes a controlled system whose output variable is the detected actual value of the leveling cylinder position of the extendable piston of the leveling cylinder attached to the towing point and/or whose input variable is the control signal for the leveling cylinder.

An advantageous variant provides that the leveling system for the inner control loop has at least one second sensor, which is designed to detect the actual value of the leveling cylinder position. This sensor is also referred to below as the leveling cylinder sensor. It is advantageous if the second sensor is a distance sensor positioned in the area of the leveling cylinder for detecting an extension path of the piston of the leveling cylinder. This means that the leveling cylinder position can be precisely recorded as a controlled variable, in particular the current extension path of the leveling cylinder piston, and fed back to the second controller of the inner control loop.

It is expedient if the middle control loop has a controlled system whose output variable is the detected actual value of the tow point position of the screed and/or whose input variable is the detected actual value of the leveling cylinder position.

According to one embodiment of the invention, the leveling system for the central control loop has at least one third sensor (also referred to below as the tow point sensor), which is designed to detect the actual value of the tow point position relative to the predetermined reference. It is expedient if the third sensor is a distance sensor positioned in the area of the towing point of the screed for detecting a distance from the predetermined reference. This means that the tow point position, which is directly influenced by unevenness, can be precisely recorded as a controlled variable and fed back to the third controller of the middle control loop.

In particular, the sensors for detecting the position of the screed and the tow point can be designed as path measuring sensors. The use of laser, ultrasonic, LIDAR and/or radar sensors would be conceivable. According to a preferred variant, at least one tachymeter arranged on the road finisher and/or a laser receiver attached to the assembly of screeds can be used as a measuring device for detecting the position of the screed and the tow point. It is conceivable that the tachymeter for target tracking of the predetermined reference is designed to be automatically adjustable in a motorized manner.

It would be conceivable that instead of two distance sensors installed at the trailing edge of the screed and at the tow point, a pitch sensor would be used in combination with a distance sensor. The distance sensor can be installed on the screed beam at any point between the rear edge of the screed and the towing point. The inclination sensor measures the angle of attack of the screed. Due to the known geometry of the screed, it is irrelevant at which position of the screed or the drawbar the inclination sensor is installed. If the sensor combination described here is used, the distances between the trailing edge of the screed and the towing point can be used as a reference (see the in Fig.2 distances y _bo and y _zp shown) can be determined by trigonometric calculations based on the measured angle and the measured distance. The structure and parameterization of the controller remain unaffected. This sensor configuration can also be used if an underground model is used as a reference (also referred to below as a virtual reference).

The cascade control preferably has at least one feedforward control of disturbance variables. It would be possible for the feedforward control to function on the basis of a calculated, indirect determination of at least one disturbance variable and/or on the basis of at least one directly measurable disturbance variable. Based on the feedforward feedforward, a manipulated variable, for example the manipulated variable for the towing point position, can be adjusted proactively by means of an upstream transfer function, instead of allowing the influence of the disturbance variable on the controlled variable present at the output.

It is conceivable that the disturbance variable control is equipped with at least one filter for smoothing calculated or recorded disturbance variables. In this way, the reaction of the controller functionally connected to the feedforward control can be dampened. Measurements of a subsoil profile recorded by means of a scanner and/or a digital terrain model can be used for the disturbance variables.

In particular, the cascade control includes a first feedforward control for the outer control loop and a second feedforward control for the middle control loop. This means that unevenness in the subsoil and/or other disturbance variables occurring during paving, for example disturbance variables relating to the mechanical and/or hydraulic systems of the road finisher, can be proactively compensated for in a fast-reacting manner, without them noticeably influencing the cascaded feedback of the controlled variables.

The respective disturbance variables can be activated and deactivated independently of one another, individually or together. It is conceivable that based on at least one process parameter measured on the road finisher during paving operation and/or based on a measured property of the paving layer produced, at least one disturbance variable triggering that responds directly or indirectly to the process parameter and/or the property of the paving layer can be automatically activated.

Preferably, the cascade control is supplemented by a layer thickness calculation module, which is designed to determine the target value of the plank height as a reference variable based on a determined current layer thickness of the paving layer produced and/or on the basis of a target value of the layer thickness of the paving layer to be produced that is held available to it for the outer control loop. With the help of this cascade control, the compensation of unevenness in the substrate can be completed by producing a desired layer thickness.

One variant provides that the layer thickness calculation module is configured to determine the layer thickness from a profile of the sensor measurements used for the leveling, possibly temporarily stored.

The actual value of the layer thickness can be determined using a layer thickness measuring system installed on the road finisher. It would be conceivable for the measurement results of at least one distance sensor to be used to determine the layer thickness produced, the measurement results of which are also used for the operation of the leveling system.

According to one variant, the reference is designed as a real physical reference (e.g. guide wire). In practice, however, a physical reference is not always available. In this case, a reference referred to here as "virtual" is used. This can be, for example, a rotating laser and a laser receiver mounted on the screed or a tachymeter that tracks a prism mounted on the screed. Typical distance sensors are not used for these two measurement methods, since the reference and sensor form a system.

From a practical point of view, an executable virtual reference is a mathematical model of the subsoil, which is available as a digital terrain model (DTM) or in another digital form (data from a (laser) scanner). When using such a reference, distance sensors continue to determine the distance to the ground and thus to the reference. In this case, the corresponding target distance for the screed and towing point to the ground is selected depending on the location so that the desired screed height is set. For the nominal value of the screed controller, r _bo ( x ) = z _bo applies _should ( x ) − z _ref ( x ) with r _bo ( x ) > 0 ∀ x . In the case of the traction point controller, the actuating signal of the screed controller is overlaid with the negative progression of the reference in order to achieve the traction point position desired by the screed controller.

The invention also relates to a method for leveling a paving screed of a road finisher in order to produce a paving layer on a subsoil on which the road finisher moves in the direction of travel during a paving run. According to the invention, unevenness in the subsoil is compensated for by means of a leveling system, which adjusts the height of the screed by means of a cascade control.

In the method according to the invention, an outer control loop of the cascade control uses a first controller to determine a setpoint value for a tow point position of a screed relative to a predetermined reference based on a detected actual value of a screed height relative to a predetermined reference and based on a setpoint value of the screed height that can be provided to the first controller as a reference variable Pull point of the screed relative to the predetermined reference.

Furthermore, an inner control loop of the cascade control uses a second controller to determine an actuating signal for the leveling cylinder based on a detected actual value of a leveling cylinder position of an extendable piston of a leveling cylinder attached to the traction point of the screed and on the basis of a setpoint value of the leveling cylinder position provided to the second controller for adjusting the height of the screed.

The method according to the invention provides that either a central control loop of the cascade control integrated between the outer and inner control loops is controlled by means of a third controller on the basis of a detected actual value of the towing point position of the towing point of the screed relative to the predetermined reference and on the basis of the setpoint value determined by means of the first controller the towing point position determines the target value of the leveling cylinder position for the second controller, or that a towing point control functionally integrated between the outer and the inner control circuit based on the target value of the towing point position of the towing point of the screed determined by means of the first controller and in particular on the basis of a digital signal provided to the towing point control Terrain model of the subsoil on which the road finisher moves to produce the paving layer, determines the target value of the leveling cylinder position for the second controller.

Accordingly, using the method according to the invention, the setpoint value of the leveling cylinder position provided as the reference variable for setting the leveling cylinder and thus also the required manipulated variable for the leveling cylinder are determined either by means of a three-stage, nested cascade control, i.e. using the superimposed first, second and third control circuits or on the basis of the outer and inner control loops and the traction point control formed in between. Based on both alternatives is one Better compensation for unevenness in the subsoil is possible because both the influence of unevenness on the screed height and the influence of unevenness on the traction point mechanism are recorded directly and taken into account to generate the control signal for setting the leveling cylinder.

The cascade control is preferably supplemented by at least one feedforward control. This can proactively respond to unevenness in the ground and other disturbance variables in order to determine the desired traction point and/or leveling cylinder position and reliably compensate for these by transmitting the associated disturbance variables to the screed controller, i.e. the controller of the outer control loop, and/or the traction point controller, i.e. the Controller of the middle loop, by means of a predetermined transfer function.

According to one embodiment, the cascade control is supplemented by a layer thickness calculation module, which determines the target value of the plank height for the outer control loop on the basis of a layer thickness of the paving layer that has been produced and/or on the basis of a target value of the layer thickness of the paving layer to be produced that is held available to it. For example, the layer thickness calculation module could use the leveling sensor signals to calculate the target screed height.

Fig. 1

einen Straßenfertiger zum Herstellen einer Einbauschicht auf einem Untergrund,

Fig. 2

eine isolierte, schematische Darstellung einer Einbaubohle des Straßenfertigers in einem Bezugskoordinatensystem,

Fig. 3

eine schematische Darstellung einer ersten Variante des erfindungsgemäßen Nivelliersystems für die Einbaubohle des Straßenfertigers, und

Fig. 4

eine schematische Darstellung einer zweiten Variante des erfindungsgemäßen Nivelliersystems für die Einbaubohle des Straßenfertigers.

Exemplary embodiments of the invention are explained in more detail with reference to the following figures. Show it:

1

a road finisher for producing an installation layer on a subsoil,

2

an isolated, schematic representation of a screed of the road finisher in a reference coordinate system,

3

a schematic representation of a first variant of the leveling system according to the invention for the screed of the road finisher, and

4

a schematic representation of a second variant of the leveling system according to the invention for the screed of the road finisher.

Technical features are given the same reference symbols throughout the figures.

1 shows a road finisher 1, which produces a paving layer 2 with a desired layer thickness S on a substrate 3, on which the road finisher 1 moves in a travel direction R during a paving run. The road finisher 1 has a levelable screed 4 for compacting the paving layer 2. The screed 4 has a pull arm 5, which at one front towing point 6 is connected to a leveling cylinder 7 attached to the chassis of the road finisher 1 . The leveling cylinder 7 can raise and lower the towing arm 5 at the front towing point 6 so that an angle of attack of the towed screed 4 can be set during the paving journey, with the screed 4 being raised or lowered in response thereto. In particular, unevenness 8 in the subsurface 3 can be compensated for by dynamic control of the leveling cylinder setting.

2 shows an isolated, schematic representation of the paving screed 4 in a reference coordinate system K, including the subsoil 3 and the dimensions relating to the screed geometry, which are associated with the Figures 3 and 4 are explained in more detail below.

3 FIG. 1 shows a leveling system 10A that is designed to level the screed 4. FIG. The leveling system 10A includes a cascade control 100A, which includes three superimposed control loops, namely an inner control loop 11, a middle control loop 12 and an outer control loop 13.

The outer control loop 13 has a first sensor H _bo (screed sensor), the inner control loop 11 has a second sensor H _nz (leveling cylinder sensor) and the middle control loop 12 has a third sensor H _zp (traction point sensor). Each of the three control circuits 11, 12, 13 thus has according to 2 each have a separate sensor. The sensors H _bo , H _nz , H _zp are configured to use the in 2 to measure the distances shown, in particular the extension path of the leveling cylinder s _nz , the screed height z _bo and the towing point position z _zp . Corresponding sensor signals y _bo , y _nz , y _zp are fed from the respective sensors H _bo , H _nz , H _zp as actual controlled variables to the three controllers C _bo , C _zp , C _nz .

According to 2 the cascade control 100A is supplemented by an optional feedforward control S1, S2, which is shown here schematically in dashed form.

First, the cascade control 100A is described in the following without feedforward control S1, S2. The three control loops 11, 12, 13 of the cascade control 100A are nested in one another. In the outer control loop 13, the screed height Z _bo is adjusted. The dynamic behavior of the "screed" controlled system is described by the transfer function G _bo . The output variable of this controlled system is the detected screed height Z _bo . The screed height Z _bo is determined by the screed sensor H _bo , which is located near a rear edge 14 of the screed (see Figures 1 and 2 ) is installed. The corresponding sensor signal y _bo is fed back to the controller C _bo . The input variable of the transfer function G _bo is the measured actual value of the tow point position z _zp . The corresponding target value of the tow point position r _zp is the actuating signal from the first Controller C _bo (screed controller) and is calculated from the set value of the screed height r _bo stored here and the sensor signal y _bo .

The actuating signal r _zp of the outer control loop 13 is the reference signal of the central control loop 12, which regulates the tow point position Z _zp with the aid of the tow point controller C _zp . The actual value of the tow point position z _zp is detected by the sensor H _zp , which determines the distance of the tow point from the reference L (for example a rope or guide wire stretched next to the roadway). The tow point position Z _zp is the output variable of the tow point mechanics G _zp . The resulting sensor signal y _zp is fed back to the traction point controller C _zp . The actuating signal of the traction point controller C _zp is the set value of the leveling cylinder position r _zp .

Thus, the actuating signal from the traction point controller C _zp represents the command variable of the inner control loop 11, the actual value of which is the leveling cylinder position s _nz . The inner control circuit 11 includes the leveling cylinder function G _nz as the controlled system, with the sensor H _nz detecting the leveling cylinder position and feeding it to the leveling cylinder controller C _nz . In this case, u _nz is the actuating signal of the leveling cylinder controller C _nz , which acts on the leveling cylinder 7 .

By means of the cascade control 100A described above, the disturbing influence of the subsoil d _zp on the tow point position Z _zp can be almost completely eliminated. In addition, due to the precise detection of the plank height Z _bo , this can be adjusted directly and the disturbance d _bo , which affects z _bo , can be better counteracted.

$${\mathrm{d}}_{\mathrm{zp}}={\mathrm{y}}_{\mathrm{zp}}+{\mathrm{z}}_{\mathrm{ref}}+{\mathrm{y}}_{\mathrm{nz}}-{\mathrm{s}}_{\mathrm{zp}0}$$

Based on the three sensor signals y _bo , y _nz , y _zp and in terms of in 2 The following relationships can be derived from the structure shown: $${\mathrm{e.g}}_{\mathrm{bo}}={\mathrm{y}}_{\mathrm{bo}}+{\mathrm{e.g}}_{\mathrm{ref}}$$

$${\mathrm{i.e}}_{\mathrm{zp}}={\mathrm{y}}_{\mathrm{zp}}+{\mathrm{e.g}}_{\mathrm{ref}}+{\mathrm{y}}_{\mathrm{na}}-{\mathrm{s}}_{\mathrm{zp}0}$$

Here d _zp is due to the interaction of the chassis fw with the ground 3, here in 2 Subsoil to _u , given. Thus d _zp = fw(z _u ) applies. Consequently, the ground profile can be calculated by the inverse function of the landing gear function. It applies $${\mathrm{e.g}}_{\mathrm{and}}={\mathrm{fw}}^{-1}\left({\mathrm{i.e}}_{\mathrm{zp}}\right).$$

Since the layer thickness s _es =z _bo -z _u applies, the layer thickness S _es can be determined using the relationships (1)-(3) from the three sensor signals y _bo , y _nz , y _zp . It applies $${\mathrm{s}}_{\mathrm{it}}={\mathrm{y}}_{\mathrm{bo}}+{\mathrm{e.g}}_{\mathrm{ref}}-{\mathrm{fw}}^{-1}\left({\mathrm{y}}_{\mathrm{zp}}+{\mathrm{e.g}}_{\mathrm{ref}}+{\mathrm{y}}_{\mathrm{na}}-{\mathrm{s}}_{\mathrm{zp}0}\right)$$

$${\mathrm{d}}_{\mathrm{bo}}={\mathrm{d}}_{\mathrm{zp}}$$

If the chassis influence is neglected, ie _zu ≈ d _zp is assumed, the following applies $${\mathrm{s}}_{\mathrm{it}}={\mathrm{y}}_{\mathrm{bo}}-{\mathrm{y}}_{\mathrm{zp}}-{\mathrm{y}}_{\mathrm{na}}+{\mathrm{s}}_{\mathrm{zp}0}$$

$${\mathrm{i.e}}_{\mathrm{bo}}={\mathrm{i.e}}_{\mathrm{zp}}$$

und $${\mathrm{s}}_{\mathrm{es}}\left(\mathrm{x}\right)={\mathrm{y}}_{\mathrm{bo}}\left(\mathrm{x}\right)-{\mathrm{y}}_{\mathrm{zp}}\left(\mathrm{x}-{\mathrm{s}}_{\mathrm{zh}}-{\mathrm{s}}_{\mathrm{bo}}\right)-{\mathrm{y}}_{\mathrm{nz}}\left(\mathrm{x}-{\mathrm{s}}_{\mathrm{zh}}-{\mathrm{s}}_{\mathrm{bo}}\right)+{\mathrm{s}}_{\mathrm{zp}0}$$

When implementing equations (5) and (6), the location dependency must be taken into account. That means it applies $${\mathrm{i.e}}_{\mathrm{bo}}\left(\mathrm{x}\right)={\mathrm{i.e}}_{\mathrm{zp}}\left(\mathrm{x}-{\mathrm{s}}_{\mathrm{zh}}\right)$$

and $${\mathrm{s}}_{\mathrm{it}}\left(\mathrm{x}\right)={\mathrm{y}}_{\mathrm{bo}}\left(\mathrm{x}\right)-{\mathrm{y}}_{\mathrm{zp}}\left(\mathrm{x}-{\mathrm{s}}_{\mathrm{zh}}-{\mathrm{s}}_{\mathrm{bo}}\right)-{\mathrm{y}}_{\mathrm{na}}\left(\mathrm{x}-{\mathrm{s}}_{\mathrm{zh}}-{\mathrm{s}}_{\mathrm{bo}}\right)+{\mathrm{s}}_{\mathrm{zp}0}$$

Thus the signals y _bo , y _nz , y _zp are recorded and the screed disturbance d _bo (x) at the waypoint x is calculated from the tow point disturbance _dzp of the previous waypoint x− _szh . The information regarding the paving thickness s _es (x) can be displayed to the operator, for example on a display at the outside control station of the screed.

In addition, the above cascade control 100A can be expanded by a layer thickness calculation module for layer thickness control, which can be provided with a target layer thickness as the desired layer thickness, on the basis of which the layer thickness calculation module calculates the target value of the plank height r _bo .

The special feature of the layer thickness calculation module is that the relationship between layer thickness and plank height is algebraic. This means that a change in layer thickness corresponds exactly to the same change in plank height. Two variants are conceivable for implementing a layer thickness control.

genutzt werden um den Sollwert der Bohlenhöhe r_bo direkt aus der gewünschten Schichtstärke zu bestimmen. Zur Berechnung der Sollbohlenhöhe r_bo aus der Sollschichtstärke r_es wird s_es = r_es und y_bo = r_bo in obige Gleichung eingesetzt. Anschließend wir bezgl. r_bo aufgelöst. Dies führt zu $$r_{\mathit{bo}}\left(x\right)=r_{\mathit{es}}\left(x\right)+y_{\mathit{zp}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)+y_{\mathit{nz}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)-s_{\mathit{zp}0}.$$

In the first variant, the current layer thickness is determined from the course of the sensor measurements and compared with the target layer thickness provided. This deviation is processed in the screed controller to change the screed height. In the second variant, the context $$s_{\mathit{it}}\left(x\right)=y_{\mathit{bo}}\left(x\right)-y_{\mathit{zp}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)-y_{\mathit{na}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)+s_{\mathit{zp}}$$

be used to determine the nominal value of the plank height r _bo directly from the desired layer thickness. To calculate the target pile height r _bo from the target layer thickness r _{es ,} s _es = r _es and y _bo = r _bo are used in the above equation. Then we regarding r _bo dissolved. this leads to $${\mathrm{right}}_{\mathit{bo}}\left(x\right)={\mathrm{right}}_{\mathit{it}}\left(x\right)+y_{\mathit{zp}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)+y_{\mathit{na}}\left(x-s_{\mathit{zh}}-s_{\mathit{bo}}\right)-s_{\mathit{zp}0}.$$

The difference between the cascade control and the cascade control extended by the layer thickness calculation module is essentially whether the user enters a target value for the plank height or for the layer thickness.

The cascade control 100A described above can be expanded by the in 2 Disturbance variable switching S1, S2 shown in dashed lines can be expanded. Information regarding the subsoil _zu and the resulting disturbances d _bo and d _zp are recorded and fed to the screed controller C _bo and the traction point controller C _zp , which use them to calculate the desired traction point and leveling cylinder position r _zp , r _nz in order to proactively Compensate for disturbance variables d _bo and d _zp without waiting for them to flow into the control variables Z _bo , Z _zp . The control signal calculation in the screed controller C _bo takes into account that the disturbance d _bo lags behind the disturbance d _zp with a dead time that depends on the paving speed. Both the computational determination of the disturbance variables d _bo and d _zp , as described above, and the direct measurement of the disturbance variables d _bo and d _zp using suitable measuring systems H _dbo and H _dzp (eg scanners, etc.) are possible. The measurement can be carried out both "online", ie during installation, and "offline", ie before installation, for example using a digital terrain model (DGM). Courses measured offline are stored in the control system.

The leveling method is not limited to any particular sensor technology. In particular, measuring systems such as tachymeters and/or laser receivers can be used to record the position of the screed and the tow point. An inclination sensor that measures the angle of attack of the screed would also be conceivable. One of the two ultrasonic sensors could be replaced by such a tilt sensor. The distance measured by the replaced sensor could then be determined by trigonometric relationships. As a result, it is also possible to deviate from the specified sensor positions at the towing point and the rear edge of the screed, which can have advantages in practice. The use of measuring systems without a fixed reference, for example a BigSki mounted on the drawbar 5 of the road finisher 1, which measures the distance to the subsurface 3 at different positions, could possibly also be used with a loss of accuracy.

With the 10A leveling system, the underground profile z _u is not known. z _u acts on the traction point 6 via the chassis fw and thus forms the unknown traction point disturbance d _zp = fw(z _u ). The middle control circuit 12 of the cascade control 100A, which regulates the tow point position Z _zp , is used in particular to compensate for this unknown tow point disturbance _dzp =fw(z _u ).

However, according to 4 a sufficiently accurate digital terrain model (DGM) is given _by this model and d _zp can be calculated using the chassis fw of the road finisher 1 . Thus, in the present case, the towing point 6 is influenced by a known disturbance. The consequence of this is that the middle control circuit 12 including the sensor H _zp is no longer required and can be replaced by a traction point control C' _zp . In addition, the information regarding z _u can be used for an optional feedforward control. The measuring devices H _dbo and H _dzp can consequently also be omitted.

wodurch der Steueralgorithmus für die Zugpunktsteuerung C'_zp gegeben ist. 4 Figure 12 shows the embodiment including a leveling system 10B with a digital terrain model (DTM) processing cascade controller 100B. The screed controller C _bo is in comparison to the basic version 3 almost unchanged. A difference to the variant shown 3 consists in the fact that, if a disturbance variable compensation is used, the disturbance d _bo in the screed controller C _bo is calculated from z _u . In contrast to the basic version according to 3 is the traction point controller C _zp in 4 no longer available, but is calculated by the traction point control C' _zp , which calculates a target value position r _nz of the leveling cylinder from the known subsurface profile z _u and the target position of the traction point r _zp . This calculation is based on equations (2) and (3). First, the actual values y _zp and y _nz are replaced by the corresponding setpoint values r _zp and r _nz . Equation (3) is then solved for _dzp . d _zp = fw(z _u ) applies. Substituting y _zp = r _zp , y _nZ = r _nz and d _zp = fw(z _u ) into equation (2) and solving for r _nz leads to $${\mathrm{right}}_{\mathrm{na}}=\mathrm{fw}\left({\mathrm{e.g}}_{\mathrm{and}}\right)-{\mathrm{right}}_{\mathrm{zp}}-{\mathrm{e.g}}_{\mathrm{ref}}+{\mathrm{s}}_{\mathrm{zp0}},$$

whereby the control algorithm for the tow point control C' _zp is given.

Claims (15)

1. Road finishing machine (1) with a screed (4) for producing a paving layer (2) on a subsoil (3) on which the road finishing machine (1) is moving in the laying direction (R) during a pavement drive, wherein the road finishing machine (1) comprises a leveling system (10A, 10B) for the height adjustment of the screed (4) for compensating irregularities (8) in the subsoil (3), wherein the leveling system (10A, 10B) includes a cascade control (100A, 100B) comprising an outer control loop (13) which includes a first control unit (C_bo) which is embodied to determine, on the basis of a detected actual value of a screed height (z_bo) of the screed (4) relative to a predetermined reference (L), and on the basis of a desired value of the screed height (r_bo) relative to the predetermined reference (L) which can be held available for it, a desired value of a pulling point position (r_zp) of a pulling point (6) of the screed (4) relative to the predetermined reference (L), and which comprises an inner control loop (11) which includes a second control unit (C_nz) which is embodied to determine, on the basis of a detected actual value of a leveling cylinder position (s_nz) of an extendable piston of a leveling cylinder (7) attached to the pulling point (6), and on the basis of a desired value of the leveling cylinder position (r_nz) held available for the second control unit (C_nz), a control signal (u_nz) for the leveling cylinder (7) by means of which the leveling cylinder (7) can be controlled,
   characterized in that
   the cascade control (100A) either comprises a central control loop (12) between the outer and the inner control loops (11, 13) that includes a third control unit (C_zp) which is embodied to determine, on the basis of a detected actual value of the pulling point position (z_zp) of the pulling point (6) of the screed (4) to the predetermined reference (L), and on the basis of the desired value of the pulling point position (r_zp) determined by means of the first control unit (C_bo), the desired value of the leveling cylinder position (r_nz) for the second control unit (C_zp), or that the cascade control (100B) includes a pulling point control (C'_zp) between the outer and the inner control loops (11, 13) which is embodied to determine, on the basis of the desired value of the pulling point position (r_zp) of the pulling point (6) of the screed (4) determined by means of the first control unit (C_bo), and in particular on the basis of a digital terrain model (DGM) of the subsoil (3) on which the road finishing machine (1) is moving for producing the paving layer (2), which model is held available for the pulling point control (C'_zp), the desired value of the leveling cylinder position (r_nz) for the second control unit (C_nz).
2. Road finishing machine according to claim 1, characterized in that the outer control loop (13) comprises a closed-loop controlled system (G_bo) whose output quantity is the detected actual value of the screed height (z_bo) of the screed (4) relative to the predetermined reference (L), and/or whose input quantity is the detected actual value of the pulling point position (z_zp) of the pulling point (6) of the screed (4) relative to the predetermined reference (L).
3. Road finishing machine according to claim 1 or 2, characterized in that the leveling system (10A, 10B) for the outer control loop (13) includes at least one first sensor (H_bo) which is embodied to detect the actual value of the screed height (z_bo).
4. Road finishing machine according to claim 3, characterized in that the first sensor (H_bo) is a distance sensor for detecting a distance to the predetermined reference (L) which is positioned in the region of a screed's trailing edge (14) of the screed (4).
5. Road finishing machine according to one of the preceding claims, characterized in that the inner control loop (11) comprises a closed-loop controlled system (G_nz) whose output quantity is the detected actual value of the leveling cylinder position (s_nz) of the extendable piston of the leveling cylinder (7) attached to the pulling point (6), and/or whose input quantity is the control signal (u_nz) for the leveling cylinder (7).
6. Road finishing machine according to one of the preceding claims, characterized in that the leveling system (10A, 10B) for the inner control loop (11) includes at least one second sensor (H_nz) which is embodied to detect the actual value of the leveling cylinder position (s_nz).
7. Road finishing machine according to claim 6, characterized in that the second sensor (H_nz) is a distance sensor positioned in the region of the leveling cylinder (7) for detecting the leveling cylinder position (s_nz) of the piston of the leveling cylinder (7).
8. Road finishing machine according to one of the preceding claims, characterized in that the central control loop (12) comprises a closed-loop controlled system (G_zp) whose output quantity is the detected actual value of the pulling point position (z_zp) of the screed (4), and/or whose input quantity is the detected actual value of the leveling cylinder position (s_nz).
9. Road finishing machine according to one of the preceding claims, characterized in that the leveling system (10A, 10B) for the central control loop (12) includes a third sensor (H_zp) which is embodied to detect the actual value of the pulling point position (z_zp) to the predetermined reference (L).
10. Road finishing machine according to claim 9, characterized in that the third sensor (H_bo) is a distance sensor for detecting a distance to the predetermined reference (L) which is positioned in the region of the pulling point (6) of the screed (4).
11. Road finishing machine according to one of the preceding claims, characterized in that the cascade control (100A, 100B) includes at least one disturbance variable feedforwarding (S1, S2).
12. Road finishing machine according to one of the preceding claims, characterized in that the cascade control (100A, 100B) is supplemented by a layer thickness calculation module which is embodied to determine, on the basis of an identified current layer thickness (S) of the produced paving layer (2), and/or on the basis of a desired value of the layer thickness (S) of the paving layer (2) to be produced which is held available for it, the desired value of the screed height (r_bo) for the outer control loop (13).
13. Road finishing machine according to claim 12, characterized in that the layer thickness calculation module is embodied to determine the layer thickness (S) from a progression of the sensor measurements employed for leveling.
14. Method of leveling a screed (4) of a road finishing machine (1) for producing a paving layer (2) on a subsoil (3) on which the road finishing machine (1) is moving in the laying direction (R) during a pavement drive, wherein irregularities (8) in the subsoil (3) are compensated by means of a leveling system (10A, 10B) which performs a leveling of the screed (4) by means of a cascade control (100A, 100B), wherein an outer control loop (13) of the cascade control (100A, 100B) determines, by means of a first control unit (C_bo), on the basis of a detected actual value of a screed height (z_bo) of the screed (4) relative to a predetermined reference (L), and on the basis of a desired value of the screed height (r_bo) relative to the predetermined reference (L) which can be held available for it, a desired value of a pulling point position (r_zp) of a pulling point (6) of the screed (4) relative to the predetermined reference (L), and wherein an inner control loop (11) of the cascade control (100A, 100B) determines, by means of a second control unit (C_nz), on the basis of a detected actual value of a leveling cylinder position (s_nz) of an extendable piston of a leveling cylinder (7) attached to the pulling point (6) of the screed (4), and on the basis of a desired value (r_nz) of the leveling cylinder position held available for the second control unit (C_nz), a control signal (u_nz) for the leveling cylinder (7) by means of which the leveling cylinder (7) is controlled for the height adjustment of the screed (4),
    characterized in that
    either a central control loop (12) present between the outer and the inner control loops (11, 13) of the cascade control (100A) determines, by means of a third control unit (C_zp), on the basis of a detected actual value of the pulling point position (z_zp) of the pulling point (6) of the screed (4) to the predetermined reference (L), and on the basis of the desired value of the pulling point position (r_zp) determined by means of the first control unit (C_bo), the desired value of the leveling cylinder position (r_nz) for the second control unit (C_zp), or that a pulling point control (C'_zp) present between the outer and the inner control loops (11, 13) of the cascade control (100B) determines, on the basis of the desired value of the pulling point position (r_zp) of the pulling point (6) of the screed (4) determined by means of the first control unit (C_bo), and in particular on the basis of a digital terrain model (DGM) of the subsoil (3) on which the road finishing machine (1) is moving for producing the paving layer (2), which model is held available for the pulling point control (C'_zp), the desired value of the leveling cylinder position (r_nz) for the second control unit (C_nz).
15. Method according to claim 14, characterized in that the cascade control (100A, 100B) is supplemented by at least one disturbance variable feedforwarding (S1, S2) and/or by a layer thickness calculation module which determines, on the basis of an identified layer thickness (S) of the produced paving layer (2), and/or on the basis of a desired value of a layer thickness (S) of the paving layer (2) to be produced which is held available for it, the desired value of the screed height (r_bo) for the outer control loop (13).

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