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 slewed, 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 conveyor 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'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.

