Patent Publication Number: US-2023160156-A1

Title: Self-propelled milling machine, as well as method for controlling a self-propelled milling machine

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/998,108, filed Aug. 20, 2020, which was a continuation of U.S. patent application Ser. No. 16/424,660, filed May 29, 2019, which was a continuation of U.S. patent application Ser. No. 15/807,631, filed Nov. 9, 2017, and further claims benefit of German Patent Application No. 10 2016 222 589.8, filed Nov. 16, 2016, each of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates to a self-propelled milling machine and a method for controlling a self-propelled milling machine in accordance with claims as submitted herewith. 
     The self-propelled milling machine, specifically, road milling machine, surface miner or recycler, comprises a machine frame with a longitudinal axis, a chassis with wheels or tracked ground-engaging units which support the machine frame, as well as a controller for the travelling and milling operation and a height-adjustable working drum. A slewable last or single transport conveyor of specified length is arranged in front of or behind the working drum as seen in the direction of travel of the milling machine, where said transport conveyor is slewable automatically about, as a minimum, an essentially vertical first axis laterally under a slewing angle. Such milling machines are known from EP 2 700 748. 
     The milling machine comprises a controller for the travelling and milling operation, as well as a working drum for the milling of, for example, a road pavement. A transport conveyor device comprising, as a minimum, one transport conveyor is located in front of or behind the working drum as seen in the direction of travel. Depending on where the transport conveyor is arranged, the milling machine is in the following called a front-loading/rear-loading milling machine. The transport conveyor may be stewed, relative to the longitudinal axis of the milling machine, laterally under a specifiable slewing angle to the left or right and may be adjustable in height via a specifiable elevation angle. The transport conveyor comprises a discharge end at which the milling material is unloaded, due to the conveying speed and the elevation angle, onto the loading surface of a transport vehicle via a flight path in the form of a parabolic trajectory. 
     A problem consists in the fact that the operator of the milling machine also needs to control loading of the loading surface by adjusting the slewing angle, the elevation angle, where appropriate, and/or the conveying speed of the transport conveyor and, by doing so, is distracted from the actual task of carrying out the milling operation. A correction of the slewing angle may be required, for example, when altering the direction of travel of the milling machine or of the transport vehicle. 
     In case of a rear-loading milling machine, problems also arise in coordinating the milling machine with the transport vehicle especially since the transport vehicle needs to drive behind the milling machine in reverse travel. An even higher level of stress results for the operator of the milling machine as he needs to control the milling process in forward travel on the one hand and needs to monitor loading of the transport vehicle behind the milling machine as seen in the direction of travel on the other hand, and in the process needs to control mainly the slewing angle and the elevation angle, where appropriate, and/or the conveying speed of the transport conveyor device. 
     The transport conveyor may be longer than the actual milling machine and usually measures approx. 5 m to approx. 8 m in length. 
     An automatic control of the slewing angle is specified from EP 2 700 748 which enables the operator of the milling machine to concentrate on the milling operation and on driving along a specified milling track. The milling machine can thus be moved in the direction of travel similar to a vehicle with a towed single-axle trailer. 
     BRIEF SUMMARY 
     Proceeding from such prior art, it is an object of the invention to create a self-propelled milling machine, as well as a method for controlling the milling machine in which a simplified execution of the loading process can be realized in any operating situation. 
     The invention advantageously specifies that a control system, at least as a function of a virtual trajectory for positioning the transport conveyor which is freely specifiable in a stationary coordinate system that is independent of the position and alignment of the machine frame, controls, by means of open-loop control or closed-loop control, at least the slewing angle of the transport conveyor automatically in such a fashion that a reference point of the transport conveyor, preferably the discharge end of the transport conveyor or the point of impingement of the worked-off milling material, always remains on the specified trajectory in the case of a change in position of the machine frame within the coordinate system. 
     The reference point, for example, the discharge end of the transport conveyor or the point of impingement of the worked-off milling material, is guided in an advantageous manner along a trajectory that is freely specifiable and is deter-mined virtually within a coordinate system that is stationary relative to the ground surface. In this arrangement, the reference point of the transport conveyor is a virtual or real locus on the transport conveyor or in the extended axis of the same which represents the position of the transport conveyor. 
     With the position and alignment of the milling machine within the coordinate system and the course of the trajectory in the coordinate system being known, the control system can determine the slewing angle of the transport conveyor to be currently adjusted relative to the milling machine by means of calculation in such a fashion that, for example, the discharge end of the transport convey-or or the point of impingement of the worked-off milling material, respectively, always remains on the specified trajectory. 
     To initialize the automatic open-loop control or closed-loop control process, the coordinate system may be determined relative to the machine frame, for example, by determining the starting position of the machine as the origin of the coordinate system. In this arrangement, the slewing axis of the transport conveyor relative to the machine frame may, for example, form the reference point of the milling machine for the starting position. The Y-alignment of the coordinate system may then, for example, extend parallel to the longitudinal axis of the machine frame. During the initialization, the trajectory determined in the coordinate system should preferably extend through the current position of the reference point, for example, of the discharge end or the point of impingement, respectively. 
     The coordinate system or the trajectory, respectively, is aligned relative to the milling machine during initialization only, and is stationary after the initialization and therefore independent of the machine position. After the initialization, the machine thus moves in said determined coordinate system. 
     In the case of closed-loop control, the trajectory may be considered as command variable, the change in position of the milling machine as disturbance variable, and the slewing angle as controlled variable. 
     As a result, the control system can minimize the distance between the reference point of the transport conveyor and the trajectory by controlling the slewing angle. 
     It is preferably specified for the control system to continuously detect the current position and alignment of the machine frame in the coordinate system and to determine the slewing angle to be adjusted as a function of the position of the stationary trajectory relative to the machine frame or to the reference point of the transport conveyor. 
     A position determination is continuous also when performed in specified time intervals, for example, at a frequency of 1 Hz. 
     In a particularly preferred embodiment, it is specified that the position of the trajectory relative to the stationary coordinate system is alterable in the control system, and that the control system recalculates the slewing angle to be adjusted in case of an altered position of the trajectory in the coordinate system. 
     This offers the advantage that the operator can determine the position of a trajectory not only at the beginning of a milling process but can also alter the same during the operation without having to simultaneously give up the automatic adjustment of the slewing angle. 
     To this effect, the control system may comprise a control operating element or an input device, respectively, operable by the operator, by means of which a different trajectory is determinable in the coordinate system in the case of a desired change in the position of the current trajectory, or by means of which the alignment of the current trajectory in the coordinate system is slewable about a preset virtual axis of rotation extending essentially orthogonal to the ground surface. 
     The operator can therefore enter a fundamentally altered trajectory into the control system on the one hand, or can alter the alignment of a trajectory already preset in the coordinate system. 
     An altered course of the trajectory may also take the form of, for example, the existing trajectory being shifted in parallel if, for example, the means of transport is not driving in the extended axis of the milling track but in parallel to the milling track. 
     When rotating the preset trajectory about a virtual axis of rotation, the axis of rotation may be adjustable, in the extended axis of the transport conveyor, in a range between the discharge end of the transport conveyor and the calculated point of impingement, with the vertical axis of rotation preferably extending through the discharge end or the calculable point of impingement. 
     In an advantageous embodiment, it is specified for the control system to comprise an image-displaying device which graphically represents, as a minimum, the relative position of the currently selected trajectory in relation to the transport conveyor and/or to the longitudinal axis of the machine frame and/or to the position of the loading surface of the means of transport. 
     The visual representation of the trajectory enables the operator to monitor the automatic control of the slewing angle and, should the need arise, to alter the direction and the course of the trajectory by means of the control operating element. 
     To calculate the current position and alignment of the machine frame in the coordinate system, the control system may continuously detect the steering angle and the distance travelled, or the steering angle and the current travel speed, or may continuously detect, by means of GPS sensors, the position and alignment of the machine frame relative to the coordinate system. 
     In addition, different steering modes may also be taken into consideration in the calculation such as, for example, the coordinated steering of all wheels or tracked ground-engaging units by means of steering both axles in the same or in opposite directions or steering a single axle only. 
     The control system may, for example, determine the orthogonal distance a of a reference point on the machine frame, preferably on the longitudinal axis, to the trajectory, and the angle between the longitudinal axis of the machine frame and the trajectory. 
     The transport conveyor may be inclinable about a second axis extending orthogonal to the first slewing axis under a specified elevation angle, where the control system additionally continuously controls the slewing angle of the slewable transport conveyor automatically as a function of at least one of the following parameters, namely, the longitudinal and transverse inclination of the machine frame, the advance speed, the elevation angle of the transport conveyor and the conveying speed of the milling material, in such a fashion that, in any steering situation during forward travel or reverse travel, the slewable transport conveyor assumes a specified slewing angle in which the reference point of the transport conveyor is, essentially, guided along the trajectory. 
     The transport conveyor may also be inclinable about a second axis extending orthogonal to the first slewing axis under a specified elevation angle, where the transport conveyor discharges the milling material onto the loading surface of the means of transport at a specified conveying speed. In addition to the slewing angle of the slewable transport conveyor, the control system may control, by means of open-loop control or closed-loop control, the elevation angle and/or the conveying speed of the transport conveyor automatically in such a fashion that the reference point of the transport conveyor always remains on the specified trajectory in the case of a change in position of the machine frame within the coordinate system. 
     It may additionally be specified for the control system to continuously locate the position of the loading surface in the coordinate system in order to always keep the reference point of the transport conveyor, for example, the discharge end or the point of impingement along the specified trajectory within the loading surface. 
     The control system may comprise, as a minimum, one detector which, with the steering mode being known, directly or indirectly detects the steering angle specified by the steering controller and the distance travelled, or the steering angle and the travel speed. 
     The control system may receive signals from a distance measuring device by means of which the distance to a means of transport is detectable. 
     In a preferred embodiment, it is specified for the control system to comprise an image-capturing device which creates a real or virtual view from the perspective of the operator or from the bird&#39;s eye perspective, preferably above the virtual axis of rotation of the trajectory, where the control system inserts the virtual trajectory into the image created by the image-capturing device and displayed on the image-displaying device. 
     The trajectory is preferably a straight line or a curve with a specified curve radius. The trajectory may finally also, for example, be a curve progression following the course of the road which is definable as a function of a distance travelled or within the parameters of a selected coordinate system. 
     The straight line or curve may be entered in a relative or absolute coordinate system through, for example, a mathematical function, a curve progression through, for example, a position data field in the form of coordinate data related to the coordinate system. 
     The invention furthermore relates to a method for controlling a self-propelled milling machine. 
     Further advantageous features can be inferred from the description. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Hereinafter, embodiments of the invention are illustrated in more detail with reference to the drawings. 
       The following is shown: 
         FIG.  1    represents a rear-loading road milling machine, 
         FIG.  2    represents a front-loading road milling machine, and 
         FIG.  3    represents a schematic representation of a starting position of the milling machine in the coordinate system, as well as the automatic control of the slewing angle in the case of a change in position of the milling machine, 
         FIG.  4    represents a schematic representation according to  FIG.  3    with a different position of the trajectory, 
         FIG.  5   a    represents the slewability of the trajectory about a virtual slewing axis, 
         FIG.  5   b    represents the parallel shift of a trajectory, 
         FIG.  5   c    represents a curve-shaped trajectory, 
         FIG.  6    represents an example of the calculation of the slewing angle to be adjusted, and 
         FIG.  7    represents a schematic circuit diagram of the control and detection device. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to self-propelled milling machines, specifically to road milling machines but also to surface miners and recyclers. 
       FIG.  1    shows the example of a rear-loading milling machine  1   b  in which the transport vehicle  10  travels behind the milling machine in reverse travel. 
     Provided that sufficient space is available on the side next to the milling machine  1   b , the means of transport  10 , for example, a truck, may also be moved next to the milling machine  1   b  in forward travel. 
       FIG.  2    shows a milling machine using as an example a front-loading road milling machine  1   a . The milling machine  1   a ,  1   b  comprises a machine frame  2  which is supported by a chassis  4  comprised of, for example, tracked ground-engaging units or wheels, said chassis  4  being connected to the machine frame  2  via no less than two height adjustment devices in the form of lifting columns  5 . As can be inferred from  FIG.  2   , the embodiment specifies four lifting columns  5  by means of which the machine frame  2  can be brought into a specifiable plane that extends preferably parallel to the road surface  6  which the tracked ground-engaging units of the chassis  4  stand on. 
     The milling machine  1   a  shown in  FIG.  2    comprises, between the tracked ground-engaging units of the chassis  4  as seen in longitudinal direction of the milling machine  1   a , a working drum  22 . 
     The working drum  22  may be adjustable in height via the lifting columns  5  supporting the machine frame  2  or relative to the machine frame  2 . 
     The milling machines  1   a ,  1   b  may comprise steerable tracked ground-engaging units and/or wheels. 
     Other designs of a milling machine  1   b  may also feature the working drum  22 , for example, at the height of the rear tracked ground-engaging units or wheels of the chassis  4 , as is also depicted in  FIG.  1   . 
     A transport conveyor  12  for transporting away the milled-off milling material may also be arranged at the front end  7  or at the rear end  8  of the milling ma-chine  1   a ,  1   b.    
     The directions of travel of the respective vehicles are each indicated in  FIGS.  1  and  2    by arrows  48 . 
     In the embodiment according to  FIG.  2   , the milling material  14  milled off by the working drum  22  is transferred, via a first transport conveyor  11 , to a second, slewable transport conveyor  12  which unloads the milling material  14  onto the loading surface  15  of the means of transport  10 . As a function of the conveying speed of the transport conveyor  12 , the milling material  14  is not immediately unloaded at the discharge end  13  of the transport conveyor  12 , but the milling material  14  rather follows a parabolic trajectory so that the point of impingement  16  on the loading surface  15  is located at a distance from the free discharge end  13  of the transport conveyor  12  in the extended axis of the same. The transport conveyor  12  can be slewed about a slewing angle α from a neutral position to the left or to the right via piston-cylinder units  18  in order to be able to unload the milling material  14  onto the loading surface  15  even when cornering or in the event of the transport vehicle  10  driving in an offset track. In addition, the operator of the milling machine  1   a ,  1   b  can adjust the elevation angle of the transport conveyor  12  by means of a piston-cylinder unit  20 . The elevation angle has an influence on the parabolic trajectory of the milled material  14  and on the position of the point of impingement  16 , as has the conveying speed of the transport conveyor  12 . 
     In this context, the point of impingement  16  signifies the point at which the milling material  14  discharged by the transport conveyor  12  impinges on the loading surface  15  of the means of transport  10 . In addition to the slewing angle of the transport conveyor  12 , said point of impingement  16  is also a function of the inclination and the conveying speed of the transport conveyor  12 , as well as, to a lesser extent, of the height of the loading surface  15  and the filling state of the same. With the slewing angle α of the transport conveyor  12  being known, the point of impingement  16  can therefore be calculated with sufficient accuracy. For a more accurate calculation, the parameters of elevation angle and/or conveying speed and/or properties of the means of transport  10  may continue to also be taken into consideration. 
     The currently adjusted elevation angle about a horizontal axis  21 , or the slewing angle α about a vertical slewing axis  23 , respectively, as well as the current steering angle are reported to a control system  24  which may furthermore comprise, as a minimum, one detector  26  which continuously detects the position of the loading surface  15 . Said detector  26  may be arranged either at the milling machine  1   a ,  1   b , at the end facing the transport conveyor  12 , or at the free discharge end  13  of the transport conveyor  12 . 
     Furthermore, further detectors generally known from prior art may be in place, which directly or indirectly detect the current slewing angle and the elevation angle of the transport conveyor  12 . A direct detection may be effected at the slewing axis  23 , an indirect detection may be effected, for example, when the slewing/elevation angles are adjusted by means of piston-cylinder units  18 ,  20 , and a path measuring system monitors the position of the piston-cylinder units  18 ,  20 . Said position can then be assigned to a specific slewing/elevation angle. 
     The control system  24  may be integrated into the controller  3  for the travelling and milling operation operated by the operator or may, as a minimum, be connected to the same in order to, where appropriate, also obtain data on the travel speed, the distance travelled and/or a detected steering angle of the milling machine  1   a ,  1   b  and the conveying speed of the transport conveyor  12 . 
     The control system  24  uses a stationary coordinate system independent of the position and alignment of the machine frame  2  which is initialized at a start of the milling process and stored in the control system  24  in a memory  58 . The control system  24  controls the slewing angle α of the transport conveyor  12  automatically as a function of the current position of the milling machine  1   a ,  1   b  and a trajectory  25  specified in the coordinate system. The coordinate sys-tem is stationary vis-à-vis the ground surface  6  but may, during initialization, be determined in the control system  24  based on the starting position of the milling machine in that it is, for example, determined in relation to the current position of the machine during initialization. For example, the position of the machine frame  2  or of a part of the machine, for example, the position of the slewing axis  23 , respectively, may be placed in the origin of the coordinate sys-tem. As is depicted in the drawings, the origin may also be placed at an offset to the position of the slewing axis  23  or in any other position the distance of which from the slewing axis  23  is known. The alignment of the machine frame  2 , that is, the longitudinal axis  9  may be placed parallel to the Y-axis of the co-ordinate system. 
     A freely specifiable virtual trajectory  25 , for example, in the form of a straight line, as can be inferred from the embodiments according to  FIGS.  3  to  5     a , may be entered in the control system  24  and integrated and stored in the stationary coordinate system. In the figures, the continuously drawn representation shows a starting position, whereas the dotted representation shows the situation after a change in position of the machine frame  2  or of the loading surface  15 , respectively. By means of the current machine position in the coordinate system and the fixed trajectory  25  in the coordinate system, the control system  24  can control, by means of open-loop control or closed-loop control, the slewing angle α of the transport conveyor  12  about the vertical slewing axis  23  automatically in such a fashion that, in the case of a change in position of the machine frame  2 , a reference point of the transport conveyor  12  is always kept on the trajectory specified. Most appropriately, such reference point is, for example, the discharge end  13  of the transport conveyor  12 . 
       FIG.  3    shows a simple embodiment in which the longitudinal axis  9  of the machine frame  2  of the milling machine  1   a  and the longitudinal central axis  17  of the transport conveyor  12  are aligned rectilinearly to one another in the starting position, that is, the current slewing angle α of the transport conveyor  12  is zero relative to the machine frame  2 . 
     In the extended axis of the transport conveyor  12  beyond the discharge end  13 , the point of impingement  16  on the loading surface  15  of the means of transport  10  is shown which, in the starting position, is also aligned collinearly to the longitudinal central axis  17  and the longitudinal axis  9 . 
     In  FIGS.  3  and  4   , the coordinate system is aligned, with its Y-axis, parallel to the longitudinal axis  9  of the machine frame  2 , with the origin being depicted at an offset to the slewing axis  23  for better visualization, so that the starting position of the machine in  FIG.  3    has the coordinates (x, 0). It is preferred, however, to determine the origin of the coordinate system automatically in relation to a fixed reference point of the machine frame, for example, the slewing axis  23 , with the Y-axis being aligned in parallel to the longitudinal axis  9  of the machine frame  2 . Alternatively, the Y-axis may, for example, be aligned parallel to the longitudinal axis  17  of the transport conveyor  12 . 
     Proceeding from such situation, in which the machine frame  2 , the transport conveyor  12 , the means of transport  10  and the specified trajectory  25  are collinear, the situation is depicted in dotted lines in  FIG.  3    in which the milling ma-chine  1   a  is required to drive around a manhole cover  42 . The process results in a change in the position and alignment of the machine frame  2  in the determined coordinate system. By means of the continuous detection of said changes in position and alignment, the control system  24  can automatically establish and control, by means of closed-loop control, the required alteration of the slewing angle α for the transport conveyor  12 . It can be inferred from the dotted representation that despite the change in the position of the milling machine  1   a , due to this control process, the point of impingement  16  of the milling material always remains on the trajectory  25 . 
     It is understood that, in lieu of the point of impingement  16 , a different reference point to the transport conveyor  12  which is a function of the slewing movement of the transport conveyor  12  may also be selected such as, for example, the discharge end  13 , or a different reference point on the transport conveyor  12  or in the extended axis of the same. 
       FIG.  4    shows a starting position in which the milling machine  1   a , the transport conveyor  12  and the means of transport  10  are initially aligned collinearly but the specified trajectory  25  has been altered in such a fashion that it extends, proceeding from the starting position depicted, obliquely to the longitudinal axis  9  of the machine frame  2  and the longitudinal central axis  17  of the transport conveyor  12 . Such intervention may be effected, for example, when the operator of the milling machine perceives that the means of transport  10  is performing a steering movement and is therefore no longer moving collinearly to the longitudinal axis  9  of the machine frame  2  or the transport conveyor  12 , respectively. Such a situation may arise, for example, when the means of transport  10  enters a bend ahead of the milling machine  1   a ,  1   b.    
     After both the means of transport  10  and the milling machine  1   a  have changed their positions, it is apparent that, in this case also, the stewing angle α can be controlled, by means of closed-loop control, automatically without any intervention by the operator in that, in this case, the point of impingement  16  follows the altered trajectory  25  automatically during the forward travel of the milling machine  1   a.    
       FIGS.  5   a ,  5   b ,  5   c    show further embodiments in which the operator can vary the position of the trajectory  25  within the coordinate system. 
     An operating element  27  is specified for this purpose which is connected with the control system  24 . In the case of a desired change in the position of the current trajectory  25 , an altered course of the trajectory  25  in the coordinate system is determinable via the operating element  27  in that, for example, the trajectory  25  is rotated in the coordinate system ( FIG.  5   a   ) or shifted in parallel ( FIG.  5   b   ). The control element  27  may, for example, comprise a rotary switch which is rotatable in two directions for the purpose of rotating the trajectory, and is movable laterally to the left or right for the purpose of parallel shifting. Furthermore, the operating element  27  may comprise an input device. Alternatively, an input of data may be effected via an input device of the controller  3  not depicted. 
     If a different, for example, a curved trajectory  25  ( FIG.  5   c   ) or a curve progression is to be entered, the input of data may also be effected via the operating element  27 . 
     In  FIG.  5   a   , the current trajectory  25  is slewed about a preset virtual axis of rotation  19  extending essentially orthogonal to the ground surface  6 . The vertical axis of rotation  19  may be adjustable in the extended axis of the transport conveyor  12  preferably in a range between the discharge end  13  and the calculated point of impingement  16 , where, however, the virtual axis of rotation  19  is to preferably extend through the discharge end  13  ( FIGS.  1  and  6   ) or through the point of impingement  16  ( FIGS.  2  and  4   ). It may furthermore be specified that the position of the virtual axis of rotation  19  can be altered by the machine operator via the operating element  27 . 
     The parallel shift of the trajectory  25  depicted in  FIG.  5   b    may be required, for example, at the beginning of the milling work when the system is prepared for loading onto a means of transport  10  driving parallel to the milling track. 
     During initialization, the trajectory  25  is collinear to the longitudinal axis  9  of the machine frame  2  and is then shifted in parallel in the coordinate system prior to the start of the milling process in such a fashion that it is collinear to the longitudinal central axis of the means of transport  10 . 
     An image-displaying device  30  may graphically represent, as a minimum, the relative position of the currently selected trajectory  25  in relation to the transport conveyor  12  and/or to the longitudinal axis  9  of the machine frame  2  and/or to the position of the loading surface  15  of the means of transport  10 , provided that a location of the position of the loading surface  15  is specified. 
     In addition, an image-capturing device  28  may be specified which creates a real or virtual view from the perspective of the operator or from the bird&#39;s eye perspective in the form of an image. The bird&#39;s eye perspective is preferably created above the virtual axis of rotation  19  of the trajectory  25 . The control system  24  may insert the virtual trajectory  25  into the image created by the image-capturing device  28  and displayed on the image-displaying device  30 . 
     The milling machine  1   a  represented schematically in  FIG.  6    by continuously drawn lines shows the starting position in which a coordinate system X, Y is defined relative to the milling machine. In this embodiment, the specified trajectory  25  is on one axis with the longitudinal axis  9  of the machine frame  2  in the starting position. When the milling machine  1   a  begins to move, the distance travelled by the milling machine and the steering angle adjusted in the process are continuously detected via sensors  50  to  52 . 
     The distance travelled by a reference point on the machine frame  2 , for example, the slewing axis  23 , and the altered alignment of the machine frame  2  relative to the Y-axis of the coordinate system (angle β) can be determined from these data. The position and alignment of the machine frame  2  of the milling machine in the coordinate system X, Y defined during initialization can thus be determined unambiguously. In conjunction with the position and alignment of the trajectory  25  which is also determined unambiguously in the coordinate system, the slewing angle α can thus be determined in such a fashion that the reference point, which in  FIG.  6    is the end  13  of the transport conveyor  12 , is located on the trajectory  25 . 
     In this context, it may be specified for the control system  24  to continuously establish the altered position data in the coordinate system X, Y of the milling machine  1   a  in relation to the starting position. 
     Alternatively, this process may be performed iteratively, that is, following control to adjust the current slewing angle, a new coordinate system (X′, Y′) may be defined at a “new” position of the milling machine (represented in dotted lines) in that the current position is adopted as the starting position. The position of the trajectory is then translated relative to said new coordinate system X′, Y′ and stored, and in the case of a further change in the position of the milling machine, the relative movement of the milling machine is established in the new coordinate system X′, Y′. 
     In  FIG.  6   , an example is depicted as to how the slewing angle α can be calculated in the coordinate system Y, X. For this purpose, reference points A, B are determined at the machine frame  2  which have the coordinates A=(x1, y2) and B=(x2, y2) in the coordinate system X, Y. The reference point A may, for example, be the slewing axis  23 . In  FIG.  6   , the reference point A would have the co-ordinates x1, 0; it is understood, however, that the reference point A may also have the coordinates (0, 0) in relation to the coordinate system X, Y. In the embodiment according to  FIG.  6   , the trajectory  25  is a straight line which may be entered in the coordinate system X, Y via a linear equation. 
       FIG.  6    shows a starting situation in which the longitudinal axis of the machine frame  2 , the longitudinal central axis  17  of the transport conveyor  12  and the trajectory  25  are collinear. When, following initialization, the milling machine  1   a  has moved to the position of the reference points A′ (x1′, y1′) and B′ (x2′, y2′), the distance a to the trajectory  25  can be calculated as follows: 
     In an initial step, the angle β between the longitudinal axis  9  of the machine frame  2  and the trajectory  25  extending parallel to the Y-axis of the coordinate system X, Y needs to be determined, where the length between the reference points A and B is given with  11 , and the length of the opposite cathetus b in the right-angled triangle in which the length  11  forms the hypotenuse is calculated from the difference of the x-coordinates of the reference points B′ and A′ as follows: 
         b=|x 1′− x 2′|
 
     For the dotted position of the milling machine, the angle β between the longitudinal axis  9  and the Y-axis of the coordinate system, and therefore the trajectory  25  then results in: 
       β=arcsin[( x 1′− x 2′)/ l 1]
 
     For the calculation of the slewing angle α to be adjusted, the distance a of the reference point A′ to the trajectory  25  results from: 
         a=|x 1′− x 1|,
 
     where x1 is also the constant x-coordinate of the trajectory  25 . 
     The angle α to be adjusted results from the sum of the previously determined angle β and the angle γ, where γ is the angle between the longitudinal central axis  17  of the transport conveyor  12  and the trajectory  25  resulting from the adjustment of the slewing angle β. 
     With the given length l2 between the slewing axis  23  and the reference point of the transport conveyor  12  projected on the coordinate system, the angle γ can be calculated as: 
       γ=arcsin( a/ 12).
 
     In the embodiment according to  FIG.  6   , the reference point of the transport conveyor  12  is the discharge end  13  of the transport conveyor where the virtual axis  19  may also be specified. 
     Instead of determining the position of two reference points on the machine frame A, B, it may also be specified to determine the position of a single point only if the angular change of the longitudinal axis  9  of the machine frame relative to the starting position is additionally determined based on the distance travelled and the steering angles adjusted in the process. The angle β can thus be determined directly. 
       FIG.  7    shows a possible structure of the control system  24  within the controller  3  and the elements interacting with the same. In this arrangement, proceeding from a starting position of the milling machine  1   a ,  1   b  during the initialization for tracking the change in position of the milling machine  1   a ,  1   b , the control system  24  may receive signals  50  to  55  from the controller  3  or directly from corresponding detectors. 
     The controller  3  may specifically transmit to the control system  24  signals  50  relating to the steering angle and steering mode, signals  51  relating to the travel speed, signals  52  relating to the distance travelled, signals  53  relating to the current slewing angle, signals  54  relating to the conveying speed of the transport conveyor  12 , as well as signals  55  relating to the elevation angle of the transport conveyor. 
     The control system  24  additionally receives signals from the image-capturing device  28 , the control operating element  27 , and in turn emits video signals to the image-displaying device  30 . 
     Moreover, the control system  24  may comprise, in all embodiments, a monitoring device  34  which compares the calculated slewing angle α with a specified maximum slewing angle range for the slewing angle and, in the case of the maximum possible or permissible slewing angle being exceeded, generates an alarm signal for the operator and/or a stop signal for the milling machine  1   a ,  1   b.    
     Notwithstanding the above, the monitoring device  34  may also generate an alarm signal for the operator or a stop signal for the milling machine  1   a ,  1   b  if the maximum possible or permissible slewing angle range of the transport conveyor is not sufficient to follow the trajectory. 
     The control system  24  also emits, via a CPU processor unit  68 , the open-loop control or closed-loop control signal, respectively, for the slewing angle α to activate the piston-cylinder units  18  for adjusting the slewing angle, where the monitoring device  34  may be interposed. 
     Moreover, the control system  24  may, besides activating the piston-cylinder units  18 , additionally also perform the activation of the piston-cylinder units  20  and/or an alteration of the conveying speed of the transport conveyor  12 . 
     The automatic control of the slewing angle α is effected in such a fashion that the reference point of the transport conveyor  12  always remains on the trajectory  25 . 
     In the process, the calculation of the slewing angle α is effected on the basis of the known dimensions of the machine frame  2  and the transport conveyor  12 , and the data of the coordinate system stored in the memory  58 , and the trajectory  25 . 
     When the initialization process is started, the position of the coordinate system may be determined in the memory  58 , and a trajectory  25  to be specified may be selected or altered and stored in the coordinate system. During initialization, the coordinate system is aligned preferably parallel to the longitudinal axis  9  of the machine frame  2 , and the origin of the coordinate system is placed, for example, on the slewing axis  23 . There is also always the possibility to re-determine the origin and alignment of the coordinate system X, Y relative to the machine frame  2  and to thus reinitialize the coordinate system as shown, for example, in  FIG.  6    with the coordinate system X′, Y′. During initialization, the longitudinal axis  9  of the machine frame  2 , as well as the longitudinal central axis  17  of the transport conveyor  12 , as well as the loading surface  15  of the means of transport  10 , are preferably aligned collinearly. 
     Different trajectories  25  can be selected and positioned in the coordinate sys-tem via the operating element  27 . In the simplest case, the trajectory is a straight line. The position of the trajectory  25  in the coordinate system can be altered by means of the operating element  27 ; as shown in  FIG.  4   , the trajectory  25  can, for example, be slewed about the virtual vertical slewing axis  19 . 
     The information on the trajectory  25  entered, for example, via the control element  27  or via an input device of the controller  3 , as well as, where appropriate, the video signals of the image-capturing system  28  may be emitted to the image-displaying device  30  in a combined fashion so that the operator can monitor the automatic operation of the slewing angle control starting after the initialization of the milling machine  1   a ,  1   b  on the image-displaying device  30  and, should the need arise, can influence the orientation of the trajectory  25  by means of the control operating element  27 . 
     Moreover, the control system  24  may receive signals from a distance-measuring device  40  by means of which the distance to a means of transport  10  following behind or driving ahead is detectable. 
     The control system  24  may continuously detect the position of the loading surface  15  and/or the transport conveyor  12  by means of the image-capturing system  28  or a non-optical electronic location system  62  which supplies data for determining the position of the loading surface  15  and for display on the image-displaying device  30  in relation to the machine frame  2  or to the transport conveyor  12 . The information from the image-capturing system  28  may be evaluated by means of image-analysing methods which are known for themselves. An example of a non-optical electronic location system is a radio-frequency identification system (RFID) which additionally offers the possibility to identify a specific loading surface  15  of a specific means of transport  10 . 
     When locating the loading surface  15  by means of RFID, stationary RFID tags may be used at the means of transport  10 , specifically, at the loading surface  15 . 
     Alternatively or additionally, signals from a GNSS device  56 , for example, GPS, GLONASS, Galileo, may be entered for position determination. The machine frame  2  preferably possesses, as a minimum, two GNSS receivers  64 ,  66  attached in different positions on the machine which, in addition to the position, also determine the alignment of the machine frame  2 . 
     The trajectory  25  is determined in the memory  58  relative to the coordinate system by means of, for example, the operating device  27 . During initialization, the trajectory  25  may, for example, initially be determined relative to the machine frame  2 . The coordinates of the trajectory  25  in the GNSS coordinate system can therefore be established and transferred into the memory  58  based on the position of the trajectory  25  in relation to the coordinates of the ma-chine frame  2  or the slewing axis  23 . 
     As soon as the milling machine  1   a ,  1   b  changes its position, the altered GNSS position coordinates of the machine and the machine alignment are detected while the coordinates of the trajectory within the GNSS coordinate system re-main unchanged. The relative movement between the machine frame  2  and the trajectory  25 , as well as the angular change between the trajectory  25  and the longitudinal axis  9  of the machine frame  2  can thus be established and, as a result, the slewing angle α controlled in such a fashion that the reference point of the transport conveyor  12  is on the coordinates of the trajectory  25 . 
     In case of a change in the course of the trajectory  25 , it is necessary to change the coordinates describing the trajectory  25 . 
     Determination of the machine position and of the alignment of the same is known prior art. 
     Two GPS sensors  64 ,  66  are shown in  FIG.  4   , for example, by means of which it is possible to determine the position and to determine the alignment of the machine frame  3 .