Patent Publication Number: US-2022220676-A1

Title: Levelling system for a road construction machine

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2020/075731, filed Sep. 15, 2020, which is incorporated herein by reference in its entirety, and additionally claims priority from European Application No. EP 19 198 712.2, filed Sep. 20, 2019, which is incorporated herein by reference in its entirety. 
     Embodiments of the present invention refer to a levelling system and a road construction machine. Further embodiments refer to a method for levelling and to a computer program. In general, the present invention relates to the technical field of mobile road construction machines, in particular to a levelling system for road finishing machines, (road paver, asphalt paver) or milling machines. 
    
    
     BACKGROUND OF THE INVENTION 
     A road paver on a tracked or wheeled drive runs on a prepared foundation (road bed) onto which a street surface to be produced or road pavement to be produced is to be applied. As a rule the road pavement is a bituminous material, wherein however layers with sand or stone or concrete layers may also be added in. Provided behind the road paver, in the direction of travel, is a height-adjustable screed, and piled on its front side is a supply of the road paving material that is supplied and distributed by a conveyor device that makes sure that the amount of road paving material kept on the front side of the screed is adequate but is not too much. The height of the rear edge of the screed relative to the surface of the prepared foundation, which may also be formed by an old road pavement covering, establishes the thickness of the street surface produced prior to its subsequent further consolidation by rollers. The screed is held on a tow arm that is borne rotatably movable about a tow point arranged in the center area of the road paver, the height of the screed being determined by a hydraulic adjusting device. The height of the screed is controlled by at least one levelling system. Mobile milling machines, which are also referred to as so-called cold milling machines, comprise a rotatably mounted milling drum that is fixed with respect to its axis of rotation relative to the chassis of the milling machine. The milling machine has a front and a rear landing gear. Depending on the milling machine or milling machine type, one of the two landing gears (front or rear) can be manually adjusted to a fixed value in height. The corresponding other landing gear has a chassis height adjustment, which is controlled in response to a milling (cutting) depth control signal. 
     A known road paver (road finisher) is described for instance in EP 0 542 297 A1. The road finisher has, instead of a mechanical sensing runner for producing a level-control signal for a vertically adjustable plate, an ultrasonic control device with at least two, advantageously three, ultrasonic sensors which are arranged in the direction of movement of the road finisher at a considerable distance on the plate. By means of the ultrasonic sensor signals, the distances of each ultrasonic sensor from a reference surface are detected, those values which lie outside the plane by more than a predetermined distance, which plane is determined by the measurement points assigned to the remaining distances, being rejected as incorrect measurements. The evaluation device calculates the projected level at the rear edge of the plate with reference to the level signals, the mutual spacings between the sensors and the distance of a sensor from the rear edge of the plate. 
     Furthermore, EP 0 547 378 A1 describes an apparatus for controlling the cutting depth of a road grooving machine by vertical adjustment of both the front and rear travelling gear on the basis of a cutting depth control signal, which is generated by a tracer ski by sampling a reference plane, including at least three ultrasonic sensors arranged one behind the other in the direction of movement of the cutter, and an evaluation means for determining the distances between the ultrasonic sensors and a reference plane to derive therefrom an inclination signal as well as an averaged distance signal. The evaluation means controls the height of the two travelling gears such that the average distance of the cutter drum as well as the position of the machine relative to the reference plane are adjusted. 
     The U.S. Pat. No. 6,027,282 A describes a control device for controlling the application of a material which is adapted to be applied to a subgrade by means of a road finisher, said road finisher comprising a tractor and a floating screed, which is attached by means of at least one draw arm to the tractor in such a way that said screed is arranged behind said tractor in the direction in which the road finisher is moving when in operation, a first end of said at least one draw arm being secured to the tractor by means of a vertically adjustable coupling device, and a second end of said at least one draw arm being rigidly secured to the floating screed, said control device comprising a device for detecting the height of a screed edge in relation to a reference height, said screed edge being the rear lower edge of the screed in the direction of movement. The control device further comprises a device for detecting the inclination of said at least one draw arm in relation to a reference plane. A device for controlling the height of the vertically adjustable coupling device controls the height of said vertically adjustable coupling device on the basis of the detected inclination and the detected height of the rear lower edge of the screed. 
     While controlling a height of a screed, e.g. in order to adapt the thickness of the pavement to be applied, unevenness of the underground is often problematic. Therefore, there is the need for an improved approach. 
     SUMMARY 
     An embodiment may have a road construction machine, especially a paving machine or a milling machine, having a levelling system, the road construction machine including a chassis and a tool, the levelling system having: a first height sensor arrangement coupled to a first side of the tool or to a first side of the chassis of the machine and configured to determine a first distance information as first actual value for a distance to an underground or to an applied layer in reference to a reference point belonging to the first side of the tool or to the first side of the chassis; and a second height sensor arrangement coupled to the second side of the tool or to a second side of the chassis and configured to determine a second distance information serving as second actual value for a distance to the underground or to the applied layer in reference to the reference point belonging to the second side of the tool or to the second side of the chassis; and a first controller including a first independent controller loop configured to control a height position of the first side of the tool or of the machine chassis based on the first actual value and a first setpoint for the height position of the first side of the tool or of the chassis; and a second controller including a second independent controller loop independent from the first independent controller loop and configured to control a height position of the second side of the tool or of the chassis based on the second actual value and a second setpoint for the height position of the second side of the tool or of the chassis; and an additional sensor coupled to the tool or the chassis and configured to determine an actual reference value for either the first or the second side of the tool or either the first or the second side of the chassis, the actual reference value describing a height position of either the first or the second side of the tool or either the first or the second side of the chassis; wherein the first and the second controllers are configured to adapt the setpoint based on the actual reference value of the additional sensor, wherein a setpoint adaption performed by the first or the second controller takes place only either on the first side or the second side of the tool or of the chassis. 
     Another embodiment may have a method for performing a levelling for road construction machines, especially for a paving machine or a milling machine, the road construction machine including a chassis and a tool, the method having the steps of: determining a first distance information as first actual value for a distance to an underground or to an applied layer in reference to a reference point belonging to the first side of the tool or to a first side of the chassis using a first height sensor arrangement coupled to a first side of the tool or to the first side of the chassis; determining a second information serving as second actual value for a distance to the underground or to the applied layer in reference to the reference point belonging to the second side of the tool or to a second side of the chassis using a second height sensor arrangement coupled to the tool or to the second side of the chassis; controlling, using a first independent controller loop, a height position of the first side of the tool or of the first side of the chassis based on the first actual value and a first setpoint for the height position of the first side of the tool or of the first side of the chassis and controlling, using a second independent controller loop independent from the first independent controller loop, a height position of the second side of the tool or of the second side of the chassis based on the second actual value and a second setpoint for the height position of the second side of the tool or of the second side of the chassis; determining an actual reference value using an additional sensor coupled to the tool or to the chassis, the actual reference value describing a height position of the tool or of the chassis; and adapting either the first or the second setpoint based on said actual reference value. 
     Another embodiment may have a non-transitory digital storage medium having a computer program stored thereon to perform the method for performing a levelling for road construction machines, especially for a paving machine or a milling machine, the road construction machine including a chassis and a tool, the method having the steps of: determining a first distance information as first actual value for a distance to an underground or to an applied layer in reference to a reference point belonging to the first side of the tool or to a first side of the chassis using a first height sensor arrangement coupled to a first side of the tool or to the first side of the chassis; determining a second information serving as second actual value for a distance to the underground or to the applied layer in reference to the reference point belonging to the second side of the tool or to a second side of the chassis using a second height sensor arrangement coupled to the tool or to the second side of the chassis; controlling, using a first independent controller loop, a height position of the first side of the tool or of the first side of the chassis based on the first actual value and a first setpoint for the height position of the first side of the tool or of the first side of the chassis and controlling, using a second independent controller loop independent from the first independent controller loop, a height position of the second side of the tool or of the second side of the chassis based on the second actual value and a second setpoint for the height position of the second side of the tool or of the second side of the chassis; determining an actual reference value using an additional sensor coupled to the tool or to the chassis, the actual reference value describing a height position of the tool or of the chassis; and adapting either the first or the second setpoint based on said actual reference value, when said computer program is run by a computer. 
     Embodiments of the present invention provide a levelling system for a road construction machine, e.g. a paving machine or a road milling machine. The road construction machine comprises a chassis (machine body or machine frame) and a tool (e.g. screed or milling drum). The levelling system comprises a first height sensor arrangement, a second height sensor arrangement, a first controller, a second controller and an additional sensor. The first height sensor arrangement (e.g. a single sensor, like ultrasonic sensor or a support mechanism comprising a plurality of sensors) is coupled to a first side of the tool or to a first side of the chassis of the machine (e.g. the left side or the right side of the tool or of the machine) and configured to determine a first distance information, (e.g. a height value of the screed with respect to the underground) as first actual value (for a distance to an underground or to an applied layer) in reference to a reference point belonging to the first side of the tool or to the first side of the machine. The second height sensor arrangement, e.g. another ultrasonic sensor or another support mechanism comprising a plurality of sensors, is coupled to a second side of the tool or a second side of the chassis of the machine (the corresponding other side of the tool or of the machine, e.g. the left side or the right side of the tool or of the machine) and configured to determine a second distance information serving as second actual value (for a distance to the underground or to the applied layer) in reference to the reference point belonging to the second side of the tool or to the second side of the machine. The first controller comprises a first control loop configured to control a height position of the first side of the tool or of the machine chassis based on the first actual value and a first setpoint for the height position of the first side of the tool or of the machine chassis. The second controller comprises a second control loop configured to control a height position of the second side of the tool or of the machine chassis based on the second actual value and a second setpoint for the height position of the second side of the tool or of the machine chassis. The additional sensor (e.g. a cross slope sensor or a layer thickness measurement sensor system or a (laser based) 3D control system) is coupled to the tool or the machine chassis and configured to determine an actual reference value for either one side of the tool or either one side of the machine chassis (either the first side or the second side of the tool or of the machine), the actual reference value also describing a height position of either one side of the tool or either one side of the machine chassis (either the first side or the second side of the tool or of the machine). The first and/or the second controller or both controllers are further configured to adapt the setpoint based on the actual reference value of the additional sensor, whereby a setpoint adaption (adjustment) takes place only either on the first side or on the second side of the tool or of the machine. 
     The first side of the tool or of the (chassis of) the machine can be either the left side or the right side of the tool or of the machine (seen in the direction of travel of the machine). Correspondingly, the second side of the tool or of the (chassis of) the machine may be either the left side or the right side of the tool or of the machine (seen in the direction of travel of the machine). 
     Embodiments of the present invention are based on the finding that an additional sensor device (either cross-slope sensor, layer thickness measurement system or 3D control system or similar) can be used to form additional closed loop control of the set point of one of the control loops of the levelling system controlling the first or the second machine site. The additional sensor device would input into the control loop of one of the levelling systems with its own set point (slope, layer thickness, . . . ) whose output is an adjustment of the grade set point in the levelling system control loop. It is effectively a control loop within a control loop. This has the advantage that the smoothness performance of the slope control can be improved, while maintaining the proper thickness without compromising on smoothness. 
     According to embodiments, the road construction machine may be a paving machine, so the tool may be a screed. According to further embodiments, the road construction machine may be a road milling machine, so the tool may be a milling unit/milling drum, whereby the milling unit/milling drum is usually (rigidly, fixed) connected/coupled to the chassis (machine body or machine frame) of the road milling machine. For both implementations, the tool extends in parallel to the underground or the applied layer ( 22 ) and/or substantially perpendicular (e. g. 75° to 105°) to a driving direction of the road construction machine. 
     According to embodiments, the additional sensor comprises a cross slope sensor coupled to the tool or to the chassis of the machine and configured to determine an inclination of the tool or of the machine chassis transverse to the direction of travel of the road construction machine, wherein the actual reference value is derived from an actual inclination value. Here the first and/or the second controller may adapt its setpoint (first and/or second setpoint) such that the tool or the machine chassis has a predetermined inclination. 
     According to further embodiments, the additional sensor comprises a layer thickness measuring system configured to determine a thickness of the applied layer (when the road construction machine is a paving machine), wherein the actual reference value is derived from an actual layer thickness value. Alternatively, the additional sensor comprises a layer thickness measuring system (milling depth measuring system) configured to determine a thickness/depth of the milled underground (when the road construction machine is a milling machine), wherein the actual reference value is derived from an actual layer thickness value. Here, the first and/or the second controller may adapt its setpoint (first and/or second setpoint) such that a minimum and/or maximum thickness of the applied layer is maintained. 
     According to further embodiments, the additional sensor comprises 3D position determiner configured to determine a height position of the tool or of the chassis of the machine, wherein the actual reference value is derived from a height position value. Here, the first and/or the second controller may adapt its setpoint (first and/or second setpoint) such that minimum and/or maximum height position of the tool or of the machine chassis is maintained. 
     According to embodiments, the first height sensor arrangement comprises a plurality of first height sensors, which may be arranged (coupled to the first side of the tool or to the first side of the chassis of the machine) along the driving direction. This has the purpose that small unevenness can be compensated due to averaging. The plurality of first height sensors may be attached by a support mechanism, e.g. attached to the screed or to the tow arm (when the road construction machine is a paving machine) or to the chassis of the road construction machine (e.g. when the road construction machine is a milling machine). According to further embodiments, one or more first height sensors are arranged behind the screed or the milling drum (when seen within the driving direction), so that this first height sensor can measure a distance to the pavement. The height sensors arranged before the screed or the milling drum typically measure a distance to the underground. As already indicated, according to embodiments, the first height sensor arrangement/first height sensor is attached to the screed or to the tow arm (when the road construction machine is a paving machine) or to the chassis of the road construction machine (e.g. when the road construction machine is a milling machine). 
     Note, the second height sensor arrangement may also be implemented analogously to the first height sensor arrangement. According to embodiments, the second height sensor arrangement comprises a plurality of second height sensors, which may be arranged (coupled to the second side of the tool or to the second side of the chassis of the machine) along the driving direction. The plurality of second height sensors may be attached by a support mechanism, e.g. attached to the screed or to the tow arm (when the road construction machine is a paving machine) or to the chassis (machine body or machine frame) of the road construction machine (e.g. when the road construction machine is a milling machine). According to further embodiments, one or more second height sensors are arranged behind the screed or the milling drum (when seen within the driving direction), so that this second height sensor can measure a distance to the pavement. The height sensors arranged before the screed or the milling drum typically measure a distance to the underground. According to embodiments, the second height sensor arrangement/second height sensor is attached to the screed or to the tow arm (when the road construction machine is a paving machine) or to the chassis of the road construction machine (e.g. when the road construction machine is a milling machine). 
     The first height sensor arrangement can be either arranged on the left or on the right side of the machine (seen in the direction of travel of the machine). Correspondingly, the second height sensor arrangement may be either arranged on the left or the right side of the machine (seen in the direction of travel of the machine). 
     Another embodiment provides a road construction machine, especially a paving machine or a milling machine comprising the levelling system as described above. 
     Another embodiment provides a corresponding method for levelling. The method comprises the steps:
         determining a first distance information as first actual value for a distance to an underground or to an applied layer in reference to a reference point belonging to the first side of the tool or to the first side of the chassis of the machine (machine body or machine frame) using a first height sensor arrangement coupled to a first side of the tool or to the first side of the chassis of the machine;   determining a second information serving as second actual value for a distance to the underground or to the applied layer in reference to the reference point belonging to the second side of the tool or to the second side of the chassis of the machine (machine body or machine frame) using a second sensor coupled to the tool or to the second side of the chassis of the machine;   controlling, using a first controller loop, a height position of the first side of the tool or of the first side of the machine chassis based on the first actual value and a first setpoint for the height position of the first side of the tool or of the first side of the machine chassis and controlling, using a second controller loop, a height position of the second side of the tool or of the second side of the machine chassis based on the second actual value and a second setpoint for the height position of the second side of the tool or of the second side of the machine chassis;   determining an actual reference value for either the first or the second side of the tool or of the machine chassis, the actual reference value describing a height position of either the first or the second side of the tool or of the machine chassis using another sensor coupled to the tool or to the machine chassis; and   adapting either the first or the second setpoint based on the actual reference value.       

     This method may be performed by use of a computer program. 
     According to an embodiment, the method may be performed by use of a computer program. 
     Also for the method and the computer program as described above, the first side of the tool or of the (chassis of) the machine can be either the left side or the right side of the tool or of the machine (seen in the direction of travel of the machine). Correspondingly, the second side of the tool or of the (chassis of) the machine may be either the left side or the right side of the tool or of the machine (seen in the direction of travel of the machine). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
         FIG. 1 a    shows a schematic block diagram of a measurement system according to a basic embodiment; 
         FIG. 2 a , 2 b    show schematic illustrations of a road paving machine comprising a measurement system/levelling system according to embodiments; 
         FIGS. 3  show schematic views of a road paving machine for illustrating further embodiments; 
         FIGS. 4 a , 4 b    illustrate the use of the measurement system/levelling system in connection with a 3D control system according to an enhanced embodiment; and 
         FIG. 5  illustrates optional details for the measurement system/levelling system according to further embodiments; and 
         FIG. 6  show a schematic illustration of a road milling machine comprising a measurement system/levelling system according to embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Below, embodiments of the present invention will subsequently be discussed referring to the enclosed figures, wherein identical reference numerals are provided to objects having an identical or similar function, so that the description thereof is mutually applicable and interchangeable. 
       FIG. 1 a    shows a road construction machine  10  comprising at least a screed  15  as tool and a measurement system  1  to be used as input for the levelling system. The measurement system  1  comprises at least the following entities, namely a distance sensor  3 R, a distance sensor  3 L, an additional sensor  2 , here a cross slope sensor  2 , a right controller  5 R and a left controller  5 L. The road construction machine  10  may be a paving machine driving along the direction  10 D. 
     The distance sensor  3 R (arranged at the right side of the screed  15 ) as well as the distance sensor  3 L (arranged at the left side of the screed  15 ) may be ultrasonic sensors measuring a distance/height from a reference point or reference height to the underground  21  or to the newly applied pavement  22 . The sensor  3 R is marked by the R, since the sensor is arranged at one side, here the right side of the screed  15 . The sensor  3 L is consequently arranged on the other/left side. The sensors  3 R/ 3 L determines/monitors the respective distances DL/DR, e.g. to the underground, along one length position of the screed  15 . This length position for the sensor  3 R is marked by  15 R. The position  15 R may be selected along the width of the screed  15 , such that an even surface along the (entire) line  15 R can be scanned. For example, but not necessarily, the position  15 R is at the right end of the screed  15 . 
     Both distance sensors  3 L/ 3 R have the purpose to determine actual distance values DL/DR (here, actual height values). By use of the actual height/distance values the actual height positions of the two sides of the screed  15  can be monitored and height positions can be controlled. In detail, typically, both actual distance values DR/DL are compared to respective set points for the respective side, so that the tool  15  at the respective side can be adjusted with regard to its height in order to track the set point for the respective side. Expressed in other words, this means that two levelling systems of the controllers  5 L/ 5 R are used to control the height of the screed  15  and also have the inclination of the screed transverse to direction of travel  10 D of the road finishing machine  10 . This means that each machine side  10 L/R is controlled (levelled) separately, i.e. there are two independent levelling systems that have two independent control loops for the left and the right side of the machine  10 . 
     When two measurement/levelling systems are used at a road finishing machine  10 , i.e. each machine side  10 L/R is controlled (levelled) separately, it may happen that on one side  10 R of the machine (for instance on the right machine side  10 R) the evenness of the new pavement road surface  22  is good, whereas on the opposite machine side  10 L (left machine side), the evenness of the new road surface  22  is bad due to greater unevenness in the underground  21  to be paved. 
     To handle this problem, the idea is to control the set point of the control loop of the levelling system controlling the one machine side having the uneven underground  21 . As discussed above, the typical control loop (first and second controller  5 L/ 5 R) is based on a set point and a sensor feedback with the output of the levelling controller controlling the position of the tow point cylinder to keep the actual position at the set point. When now the set point is adapted based on the additional sensor device  2 , the additional sensor device  2  would input the control loop (second controller  5 L) of the levelling system  1  controlling the left machine side  10 L with its own set point (slope, layer thickness, . . . ) whose output is an adjustment of the grade set point in the levelling system control loop. Due to adapting the set point of the side having the uneven underground, it can be counter-railed that the uneven underground  21  is transferred to the new pavement  22 , since the set point is adjusted when the tool/screed  15  deviates from the desired path. By use of an inclination sensor  2  as additional sensor the deviation can be detected, when the inclination exceeds the desired position. Expressed from this point of view, this means that another measurement principle is used for validating the real control value, here the distance value measured by using the sensor  3 L. For the same principle other sensors than the cross-slope sensors  2  can be used, for example the layer thickness measurement system (not shown) can be used as well. Here, the layer thickness value forms the basis for adapting the set point of the control loop for the left machine side  10 L. According to another embodiment, an external height sensor, e.g. implemented using a so-called total station (prism/tachymeter) may be used as sensor  2 . For example, a height value for the screed, which is measured by the total station, may be used for adapting the set point of the control loop for the left machine side  10 L. 
     In this context, it is understood that it is also possible, that on the other side  10 L of the machine (left machine side  10 L) the evenness of the new pavement road surface  22  is good, whereas on the opposite machine side  10 R (right machine side), the evenness of the new road surface  22  is bad (also due to greater unevenness in the underground  21  to be paved). From the above description, it is understood that in this case the additional sensor device  2  would input the control loop (controller  5 R) of the levelling system  1  controlling the right machine side  10 R with its own set point (slope, layer thickness, . . . ) whose output is an adjustment of the grade set point in the levelling system control loop. 
     To sum up, the first and the second controller  5 L/ 5 R form the two control loops, namely one for the left and one for the right side, wherein, based on the sensor signal from the additional sensor  2 , the set point of one of the levelling control loops for the left or the right side will be adapted. 
     Regarding the sensors  3 L and  3 R it should be noted that these may be ultrasonic control units, as described in EP 0 542 297 A1 or EP 0 547 378 A1. These sensors typically use three or four ultrasonic sensors because of the fact that the ultrasonic sensors scan the surface at a plurality of widely spaced points, so that elongated bumps in particular are well-balanced. 
     Dependent on the distance to be measured, the sensor  3 R as a single sensor, like ultrasonic sensor, is arranged in front or behind the screed  15 . In order to enable that the sensor  3 R can measure the height of the screed with reference to the underground  21  or the new pavement  22 , the sensor  3 R is implemented as height sensor, i.e. measures a distance substantially perpendicular to the underground  21 . The position of the height sensor with respect to the screed  15 , and especially with respect to the rear edge of the screed  15  is (at least during operation) fixed so that by measuring the distance DR between the screed  15 /rear edge of the screed  15  and the underground  21 /new pavement  22  can be calculated. This can be done, e.g. by taking into account the offset between the mounting height of the sensor  3 R and the respective reference point of the screed  15 , e.g. the rear edge. 
     In order to enable that the position between the sensor  3 R and the reference of the screed  15  maintains at least during operation constant the sensor  3 R may be directly or indirectly attached to the screed  15 . Indirectly means that a support mechanism may be used or that the sensor  3 R or the corresponding support mechanism is attached to a tow arm of the screed  15 . 
     Regarding the slope sensor  2  it should be noted that same may be directly attached to the screed or somehow coupled to same, such that a cross slope (along the length of the screed  15  and transverse to the direction of travel  10 D of the machine  10 ) can be measured. 
     There are a number of different combinations of the set point control loop invention, as described in more detail below. 
     The present invention will be detailed below referring to the appended drawings.  FIG. 2 a    shows a road finishing machine  10  illustrated schematically in a side view, comprising a control platform  11 , a material bunker  12  and a screed  15 , which is movable attached to the machine chassis via two tow arms  13 L (left machine side) and  13 R (right machine side). During the paving drive, the road finishing machine  10  moves on the underground to be asphalted  21 , whereby paving material is transported from the material bunker  12  via a non-depicted conveyor device underneath the control platform  11  through the chassis of the road finishing machine  10  to the rear to the screed  15  by which it is processed into a new pavement layer  22 . 
     As shown in  FIG. 2 a   , at the right tow arm  13 R of the road paver  10  a support mechanism  60 R is arranged for a sensor system (measurement system/levelling system)  40 R, wherein this is advantageously arranged at two points at the tow arm  13 R. Advantageously, the main support mechanism  61 R is releasable secured both in the front region of the tow arm, for example in the immediate vicinity of the tow point, by means of a holder  62 R and in the rear region, for example in the immediate vicinity of the attachment of the screed  15 , by means of a holder  63 R. On the main support mechanism  61 , which extends along the direction of travel of the paver  10 , further releasable secured and along the main support mechanism  61 R slideable holders  64 R are arranged, by means of which individual distance sensors  41 R to  44 R of the sensor system (measurement system/levelling system)  40 R are held. For further (fine) adjustment of the outer distance sensors  41 R and  44 R further releasable secured and displaceable holders  65 R are provided. Advantageously, the main support mechanism  61 R consists of individual or individually connectable mechanical parts or even by means of a twisting mechanism rotatable items or even telescopic items in order to adjust the system in length individually. For known sensor and levelling systems, variable lengths in the range of 9 to 13 meters are common. 
     The sensor system  40 R shown in  FIG. 2 a    consists of four distance sensors  41 R to  44 R, but it is also conceivable that are only three distance sensors  41 R,  43 R and  44 R arranged, which scan an underground  21  still to be processed and a new pavement layer  22 . The sensor system  40 R thus comprises at least two distance sensors  41 R,  42 R and/or  43 R in front of the screed  15 , which scan the still to be processed underground  21  and determine distance values s 1 R, s 2 R and/or s 3 R to the underground  21  still to be processed, as well as a further distance sensor  44 R, which scan the newly laid or new built-in road surface  22  and determines a distance value s 4 R to the newly laid or newly installed road surface  22 . The basic structure of the sensor system  40 R shown schematically in  FIG. 2  essentially corresponds to the systems known from conventional technology. 
     The sensor system  40 R further comprises a levelling system control unit  45 R, consisting essentially of a process control unit  45 RA and an operating and monitoring unit (control and display device)  45 RB. The individual distance sensors  41 R to  44 R may be connected via cable connections  41   k  to  44   k  to the process control unit  45 RA, which reads in and processes the measured distance values s 1  R to s 4 R of the distance sensors  41 R to  44 R. Furthermore, the process control unit  45 RA controls the height position of the screed  15  as a function of the measured distance values s 1 R to s 4 R, that means the process control unit  45 RA functions as a leveling unit. Via the operating and monitoring unit  45 RB, an operator, for example the screed personnel, can set adjustments or changes to various parameters concerning the leveling or monitor them during the installation process. The operating and monitoring unit  45 RB serves as a so-called human-machine interface (HMI or MMI). In an advantageous variant, the process control unit  45 RA and the operating and monitoring device  45 RB are combined in one device or in one housing, that means components are integrated within one device or housing. 
       FIGS. 2 b   ,  3  and  4   a  show the road finishing machine (paver)  10  illustrated schematically in a bird view, comprising two sensor systems (measurement systems/levelling systems)  40 L and  40 R as described above, whereby each sensor system (measurement system/levelling system)  40 L and  40 R comprises four distance sensors  41 L/R . . .  44 L/R. With these two sensor systems (measurement systems/levelling systems)  40 L and  40 R each machine/tool side (left/right) is controlled (levelled) separately. 
     As shown in  FIGS. 2 b   ,  3  and  4   a , the road finishing machine  10  comprises furthermore an additional sensor device  200 ,  300  or  400 . The additional sensor device  200 ,  300  or  400  would input into the control loop of one of the sensor systems (measurement systems/levelling systems)  40 L or  40 R, controlling the left or right machine side  10 L/R with its own set point whose output is an adjustment of the grade set point in the levelling system control loop. 
     As shown in  FIG. 2 b   , the additional sensor device is a cross slope sensor  200 , which is arranged above the main screed  15 M, advantageously on a crossbeam attached to the screed  15 . The cross slope sensor  200  measures the inclination of the screed  15  transverse to the direction of travel of the road finishing machine  10 . As shown in  FIG. 3 , the additional sensor device is a layer thickness measuring system  300 , which is arranged at screed extensions  15 SL and  15 SR. It is also possible, that the layer thickness measuring system  300  is arranged at the main screed  15 M. The layer thickness measuring system  300  comprises distance sensors  302 L/R and  303 L/R, whereby the distance sensors  302 L and  303 L are arranged on the left machine side  10 L at a mechanical holder  305 L, and the distance sensors  302 R and  303 R are arranged on the right machine side  10 R at a mechanical holder  305 R. Distance sensors  302 L/R are arranged in front of the screed  15  and measure the distances to the underground to be asphalted  21 ; distance sensors  303 L/R are arranged behind the screed  15  and measure the distances to the newly applied road surface  22 . Out of the measurement signals from the distance sensors  302 L/R and  303 L/R a layer thickness control unit  310  calculates the layer thickness of the newly applied road surface  22  during the paving drive. 
     As shown in  FIG. 4 a   , the additional sensor device is a 3D control system  400 . Such a 3D control system  400  is described for instance in DE 199 51 296 C2 or DE 199 51 297 C1. Briefly described, the 3D control system  400  comprises a tachymeter (total station)  430  to determine the position of a reference point (prism  440 ), whereby the prism  440  is arranged above the screed  15 , advantageously as shown in  FIG. 4 a    at the rear edge of the screed extension  15 SR.  FIG. 4 b    shows the 3D control system  400  in more detail. A 3D operating and monitoring unit  420  receives signals  432  from the tachymeter (total station)  430  via an antenna  421  and sends these signals to a 3D process control unit  410 , which calculates the position of a correction point from the position of the reference point (prism  440 ) and the target stretch. 
     All described additional sensor devices  200 ,  300  or  400  may be coupled to the sensor system (measuring system/leveling system)  40 L or  40 R, so that in the control loop of the sensor system (measuring system/leveling system)  40 L or  40 R, the set point of the additional sensor devices  200 ,  300  or  400  is included. Coupling one of the additional sensor devices  200 ,  300  or  400  to the sensor system (measurement system/levelling system)  40 L or  40 R is effectively a control loop within a control loop. 
     The advantages of coupling one of the additional sensor devices  200 ,  300  or  400  to the sensor system (measurement system/levelling system)  40 L or  40 R is for instance improving the smoothness performance of the slope control and maintaining the proper thickness without compromising on smoothness. 
     As already described above, via the operating and monitoring units  45 LB and  45 RB, the operator, for example the screed personnel, can set adjustments or changes to various parameters concerning the levelling. For instance, the operator can make adjustments manually with regard to the set point of the sensor system (measurement system/levelling system)  40 L and/or  40 R, whereby the additional sensor device  200 ,  300  or  400  acts like a supervisory sensor or supervisory system. 
       FIG. 5  shows an additional wireless communication interface unit  70  arranged on the road finishing machine  10 , which is connected via a cable connection  70   k  to the process control unit  45 A of the levelling system control unit  45 L/R. Via the wireless communication interface unit  70 , the sensor system (measuring system/leveling system)  40 L or  40 R is able to wirelessly exchange data with a remote data server system  90  and/or a mobile device  80 , that is to say to wirelessly transmitting data to said devices  80  and  90  and receiving data wirelessly from these devices  80  and  90 . The mobile device  80  can be, for example, a laptop computer or a tablet PC or a smartphone or the like, wherein the mobile device  80  has a communication unit  85  in order to be able to communicate via corresponding wireless connection types such as WLAN, Bluetooth, etc. 
     For example, via connection links  71  or  72 , data such as measured distance measurements from the distance sensors  41  L/R . . .  44 L/R and/or data indicative of the height of the screed  15  sent to the mobile device  80  or over a network  95  to the data server  90  for logging calculation or evaluation purposes. As a result, a machine operator or construction site supervisor has an overview of the paving process and can react immediately in the event of problems such as the failure of a distance sensor. Furthermore, via a connection  71 ,  81  and  91 , data may also be sent from the mobile device  80  to the sensor system (measuring system/leveling system)  40 L or  40 R on the paver  10  or to the data server  90 , for example to set calculation parameters of the controller&#39;s calculation algorithm or to include data relating to the sensor system (measuring system/leveling system)  40 L or  40 R stored on the data server  90 . It is also conceivable in this context that calculations of the control device during the asphalt installation are not (only) carried out in the process computer unit(s)  45 LA/RA of the levelling system control unit  45 L/R, but (also) on the data server  90 , for which purpose a continuously existing data or communication connection between the process control unit(s)  45 LA/RA on the paver  10  and the data server  90  is a requirement. Also for remote maintenance purposes, the communication device  70 , the communication links  71 ,  72 ,  81  and  91  and the mobile devices  80  are suitable, for example, to remotely retrieve a status of the sensor system (measuring system/leveling system)  40 L or  40 R and/or to detect and resolve an occurring error of the sensor system (measuring system/leveling system)  40 L or  40 R. 
     Although embodiments of the invention have been explained with reference to a road finishing machine, it can also be used on road milling machines (as described above). 
       FIG. 6  shows a road milling machine  10  illustrated schematically in a side view, comprising a milling drum/milling unit  15  as tool, which is rigidly (fixed) connected/coupled to the chassis  17  (machine body or machine frame) of the road milling machine  10 . The road milling machine  10  has two front and two rear landing gears  16 F and  16 R, whereby in  FIG. 6  only the left front and the left rear landing gears  16 F and  16 R are shown. The road milling machine  10  comprises a sensor system  40 L, which consists of three distance sensors  41 L,  43 L and  44 R, which are coupled to the chassis  17  (machine body or machine frame) of the machine  10  and which scan an underground  21  still to be milled and a milled road surface  22 . The sensor system  40 L thus comprises at least two distance sensors  41 L and  43 L in front of the milling drum/milling unit  15 , which are arranged at a distance a from each other and scan the still to be milled underground  21  and determine distance values to the underground  21  still to be milled, as well as a further distance sensor  44 L, which is arranged at a distance a from sensor  43 L and scan the milled road surface  22  and determines a distance value to the milled road surface  22 . The basic structure of the sensor system  40 L shown schematically in  FIG. 6  essentially corresponds to the system known from conventional technology as described in EP 0 547 378 A1. The sensors  41 L,  43 L and  44 R scan the surface at a plurality of widely spaced points, so that elongated bumps in particular are well-balanced. 
     The sensor system  40 L further comprises a levelling system control unit (not shown in  FIG. 6 ), consisting essentially of a process control unit and an operating and monitoring unit (control and display device). The individual distance sensors  41 L,  43 L and  44 L may be connected via cable connections to the process control unit, which reads in and processes the measured distance values of the distance sensors  41 L,  43 L and  44 L. Furthermore, the process control unit controls the height position of the milling drum/milling unit  15  as a function of the measured distance values, that means the process control unit functions as a leveling unit. Via the operating and monitoring unit, an operator, for example the milling machine personnel, can set adjustments or changes to various parameters concerning the leveling or monitor them during the milling process. The operating and monitoring unit serves as a so-called human-machine interface (HMI or MMI). In an advantageous variant, the process control unit and the operating and monitoring device are combined in one device or in one housing, that means components are integrated within one device or housing. 
     As already described in relation to the road paving machine above, it is also conceivable that the road milling machine  10  illustrated schematically in  FIG. 6  comprises a further (second) sensor system (measurement systems/levelling systems)  40 R (not shown in  FIG. 6 ) on the other (right) machine side  10 R, which is similar to the sensor system (measurement system/levelling system)  40 L as described above. With these two sensor systems (measurement systems/levelling systems)  40 L and  40 R each machine/tool side (left/right) is controlled (levelled) separately. 
     The road milling machine  10  illustrated schematically in  FIG. 6  comprises furthermore an additional sensor device (not shown in  FIG. 6 ). The additional sensor device would input into the control loop of one of the sensor systems (measurement systems/levelling systems)  40 L or  40 R, controlling the left or right machine side  10 L/R with its own set point whose output is an adjustment of the grade set point in the levelling system control loop. 
     The additional sensor device is a cross slope sensor, which is arranged at the machine chassis  17 . The cross slope sensor measures the inclination of the machine chassis  17  and therefore the inclination of the milling drum/milling unit  15  transverse to the direction of travel of the road milling machine  10 . 
     Furthermore, it is also conceivable that the additional sensor device is a layer thickness measuring system (milling depth measuring system), which measures the layer thickness of the milled road surface during the milling drive. A road milling machine and method for measuring the milling depth is for instance described in US 2008/0152428 A1. 
     It is also conceivable that the additional sensor device is a 3D control system. Such a 3D control system is described for instance in DE 199 51 296 C 2  or DE 199 51 297 C1 by means of a paving machine. The 3D control system comprises a tachymeter (total station) to determine the position of a reference point (prism), whereby the prism may be arranged at the chassis (machine body or machine frame)  17  of the milling machine  10 . A 3D operating and monitoring unit receives signals from the tachymeter (total station) via an antenna and sends these signals to a 3D process control unit, which calculates the position of a correction point from the position of the reference point (prism) and the target stretch. 
     Regarding the milling machine, all described additional sensor devices may be coupled to the sensor system (measuring system/leveling system)  40 L or  40 R, so that in the control loop of the sensor system (measuring system/leveling system)  40 L or  40 R, the set point of the additional sensor devices is included (similar to the explanations with regard to the paving machine described above). Coupling one of the additional sensor devices to the sensor system (measurement system/levelling system)  40 L or  40 R is effectively a control loop within a control loop. 
     Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some one or more of the most important method steps may be executed by such an apparatus. 
     Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable. 
     Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed. 
     Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier. 
     Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier. 
     In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer. 
     A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, the digital storage medium or the recorded medium are typically tangible and/or non-transitionary. 
     A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet. 
     A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein. 
     A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein. 
     A further embodiment according to the invention comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver. 
     In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods may be performed by any hardware apparatus. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  Asphalt paver (road finishing machine)/Road milling machine 
           10 L/R Machine side (left/right) 
           11  Control platform 
           12  Hopper (material bunker) 
           13 L/R Tow arm (left/right) 
           14  Auger 
           15  Screed/Milling drum (milling unit) 
           15 M Main screed 
           15 L/R Length positions (left/right) for sensors 
           15 SL/SR Screed extensions (left/right) 
           15 LC/RC Screed extension control (left/right) 
           15 RE Screed rear edge 
           16 F/R Front and rear landing gear 
           17  Chassis (machine body or machine frame) 
           21  Underground to be asphalted/Underground to be milled 
           22  Newly applied road surface/milled road surface 
           40 L/R Sensor system (measurement system/levelling system) (left/right) 
           41 L/R,  44 L/R Distance sensors (left/right) 
           41   k  . . .  44   k  Cable connection 
           45 L/R Levelling system control unit (left/right) 
           45 LA/RA Process control unit (left/right) 
           45 LB/RB Operating and monitoring unit (left/right) 
           60 L/R Levelling system support mechanism (left/right) 
           61 L/R Main support mechanism (left/right) 
           62 L/R,  63 L/R Mechanical holders (left/right) 
           64 L/R,  65 L/R Slideable mechanical holders for distance sensors (left/right) 
           70  Wireless communication interface unit 
           70   k  Cable connection 
           80  Mobile device (laptop computer, smartphone or any other kind of mobile or portable device) 
           85  Communication unit 
           90  Data server system 
           71 , 72 , 81 , 91  Communication links 
           95  Network 
           200  Cross Slope Sensor 
           300  Layer Thickness Measuring System 
           302 L/R, 303 L/R Distance sensors (left/right) 
           305 L/R Mechanical holders for distance sensors (left/right) 
           310  Layer Thickness control unit 
           400  3D Control System 
           410  3D Process control unit 
           415  Screed width measuring device 
           420  3D Operating and monitoring unit 
           421  Antenna 
           430  Tachymeter (total station) 
           431  Measuring direction to prism 
           432  Data signal 
           440  Prism 
           441  Mechanical holder for prism 
           450  Screed width input unit 
           480  Steering control unit 
           481  Control signal for steering control unit DL/DR Actual height values (left/right)/Actual distance values (left/right) 
           1  Levelling system 
           2  Additional sensor 
           3 L/ 3 R Distance sensors (left/right) 
           5 L/ 5 R Controller (second/first)/(left/right) 
           10 D direction of travel of the machine 
         a Distance between two sensors