Abstract
A method for controlling the elevation of a retaining device of a ground milling machine as well as to a ground milling machine. Essential for the invention is that the retaining device is held in an initial position at a distance from the underlying ground and is reset from a yield position.
Claims
1. A method for controlling the elevation of a retaining device of a ground milling machine, comprising the steps: a) holding the retaining device in an initial position at a defined holding distance above the underlying ground, so that the retaining device is not in contact with the underlying ground; b) starting the milling operation; c) if ground material presses against the underside of the retaining device from below with a vertical upward counterforce, maintaining the retaining device in the initial position with a retaining force up to a defined maximum retaining force; d) if the counterforce exceeds the maximum retaining force, releasing the retaining device for vertical upward displacement and a pushing of the retaining device upwards by the counterforce; and e) returning the retaining device towards the initial position when the counterforce falls below the maximum retaining force, wherein the retaining device is returned no farther than to the initial position of the retaining device.
2. The method according to claim 1, wherein at least one of the following steps precedes step a): placing the retaining device on the underlying ground and subsequently raising the retaining device until the initial position at the defined holding distance of the retaining device from the underlying ground is reached; measuring an operating variable associated with the height adjustment of the retaining device and setting the raised height of the retaining device until a target value of the operating variable associated with the height adjustment of the retaining device is reached that corresponds to a reaching of the defined holding distance of the initial position; measuring a distance variable that changes with the height adjustment of the retaining device in relation to the underlying ground and raising or lowering the retaining device until a distance variable is reached that corresponds to the defined holding distance of the initial position; and deriving an actual raised state of the retaining device with the aid of displacement sensors associated with lifting columns for traveling devices and/or with the aid of a displacement sensor associated with a lifting device of the retaining device and/or with the aid of a position sensor of the ground milling machine, and raising or lowering the retaining device until a target raised state of the retaining device is reached that corresponds to the defined holding distance of the initial position and/or until a target displacement value of the displacement sensor associated with the lifting device of the retaining device is reached that corresponds to the defined holding distance of the initial position while considering measurement data of the position sensor of the ground milling machine.
3. The method according to claim 1, wherein a pressure force acting in the vertical downward direction is actively applied in step c) in addition to the weight of the retaining device in order to hold the retaining device in the initial position at a defined holding distance above the underlying ground.
4. The method according to claim 1, wherein step d) comprises switching a pressure relief valve.
5. The method according to claim 1, wherein when there is a height adjustment of lifting columns connecting traveling devices to the machine frame, the elevation of at least one lifting column is monitored, in that a correction factor is determined if the elevation of the at least one lifting column is changed, and in that the correction factor is used to adapt the position of the retaining device in order to maintain the defined holding distance.
6. The method according to claim 1, wherein the retaining device is held in the initial position so that the defined holding distance above the underlying ground lies in a range of from 5 to 50 mm.
7. A ground milling machine for carrying out the method according to claim 1, comprising: a machine frame supported by traveling devices; an operating platform, from which the ground milling machine is operated; a milling device with a milling drum which is arranged inside a milling drum housing and which is rotatable about a rotation axis; a retaining device which is arranged in front of the milling drum in the milling direction and which is height-adjustable via an actuator; a drive engine, with which the drive power required for the milling and traveling operation is generated; wherein a positioning control unit is provided which regulates the actuator of the retaining device in such a manner: that it initially maintains the elevation of the retaining device in an initial position at a defined holding distance above the underlying ground during milling operation, so that the retaining device is not in contact with the underlying ground; that it keeps the retaining device in the initial position with a retaining force up to a defined maximum retaining force when ground material presses against the underside of the retaining device with a vertical upward counterforce from below; that it releases the retaining device for vertical upward displacement when the counterforce exerted on the retaining device by the ground material exceeds the maximum retaining force; and that it returns the retaining device towards, but no farther than, the initial position when the counterforce falls below the maximum retaining force.
8. The ground milling machine according to claim 7, wherein the positioning control unit comprises a setting mode so as to comprise at least one of the following features for raising the retaining device to the initial position: it uses an elevation of the retaining device when the retaining device is lowered to the underlying ground; and/or it incorporates measuring an operating variable associated with the height adjustment of the retaining device and setting the raised height of the retaining device until a target value of the operating variable associated with the height adjustment of the retaining device is reached that corresponds to the reaching of the defined holding distance; and/or it incorporates measuring a distance variable that changes with the height adjustment of the retaining device in relation to the underlying ground and raising or lowering the retaining device until a distance variable is reached that corresponds to the defined holding distance; it incorporates deriving an actual raised state of the retaining device with the aid of displacement sensors associated with lifting columns for traveling devices and/or with the aid of a displacement sensor associated with a lifting device of the retaining device and/or with the help of a position sensor of the ground milling machine.
9. The ground milling machine according to any one of claim 7, wherein it has a display device on the operating platform of the ground milling machine, which displays at least one of the following operating states: the retaining device is in its initial position; the retaining device is in contact with the ground; the retaining device is pushed upward beyond its initial position.
10. The ground milling machine according to claim 7, wherein it has a setting device on the operating platform of the ground milling machine, with which at least one of the following settings can be performed: setting the initial position of the retaining device; setting the maximum retaining force; switching between a ground contact mode and an initial position holding mode.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention is described in greater detail in the following based on the examples shown in the figures, which show schematically:
[0024] FIG. 1: a side view of a ground milling machine of the center-rotor type;
[0025] FIG. 2: a side view of a ground milling machine of the rear-rotor type;
[0026] FIG. 3: a frontal view of the milling device against the milling direction with the retaining device in the initial position;
[0027] FIG. 4: the frontal view from FIG. 3, in which ground material contacts the retaining device in its initial position from below;
[0028] FIG. 5: the frontal view of FIGS. 3 and 4, in which a clump of ground material pushes the retaining device upwards beyond the initial position;
[0029] FIG. 6: a schematic side view of the retaining device shown in FIGS. 3 to 5;
[0030] FIG. 7: a flow chart of a method according to the invention;
[0031] FIG. 8: a control loop for the illustration of the height adjustment of the retaining device in response to the action of external forces; and
[0032] FIG. 9: a flow chart for an adaptation of the initial position when a lifting column is adjusted.
DETAILED DESCRIPTION
[0033] Identical or functionally similar components are designated with identical reference numbers in the figures, while not every recurring component is necessarily designated in every figure.
[0034] FIG. 1 shows a ground milling machine 1 of the center-rotor type with a machine frame 4 supported by traveling devices 2 via height-adjustable lifting columns 3. Arranged on the machine frame 4 is an operating platform 5, from which an operator located on the operating platform can control the traveling and/or milling operation of the ground milling machine 1. The ground milling machine 1 further comprises a milling device 6 with a milling drum housing 7 and a milling drum 8 (merely suggested in FIG. 1) arranged inside the milling drum housing, as well as a conveyor belt 9 with which milled material can be loaded onto a transport vehicle. During milling operation, the ground milling machine travels over the underlying ground in the main working direction A, which in the present case is the forward direction of the ground milling machine 1, and mills the material in the underlying ground 14 at a milling depth FT. The milling drum housing comprises a retaining device 10 (merely suggested in FIG. 1) arranged in front of the milling drum 8 in the main working direction A, lateral shields 11, as well as a rear stripping shield 12, all of which are height-adjustable in the vertical direction and at least partially close off the milling drum housing to the front, the sides and the rear, for example in order to prevent milled material from flying around and to ensure a controlled transport of the material inside the milling drum housing.
[0035] FIG. 2 shows a ground milling machine of the rear-rotor type, reference being made here to the corresponding description of the ground milling machine 1 according to FIG. 1 in this regard. In contrast to FIG. 1, only the two rear traveling devices 2 are connected to the machine frame 4 via height-adjustable lifting columns 3 in the ground milling machine 1 according to FIG. 2. At the front, the ground milling machine 1 according to FIG. 2 has either a single wheel or a pair of wheels connected with each other via a pendulum axle.
[0036] The ground milling machines 1 according to FIGS. 1 and 2 further comprise a positioning control unit 13, which controls and regulates the height adjustment of the retaining device 12, as explained in greater detail below.
[0037] FIGS. 3, 4 and 5 are front views of the milling drum 6 against the main working direction A. In FIG. 3, the retaining device 10, which protrudes from the rest of the milling drum housing 7 in the main working direction A and which is connected here to a front delimiting wall 15 and is height-adjustable together with the same in the vertical direction via two hydraulic cylinders 16, is in its initial position. In this initial position, the retaining device is, with respect to its bottom edge 17, which in the present case is formed by runners, at a distance A in the vertical downward direction from the surface of the underlying ground 14. The retaining device 10 is thus in a slightly raised position and is thus not in contact with the underlying ground 14. In the present example, the specific distance A is 10 mm and can usually lie in the value range indicated above. As is evident from FIG. 3, the milling tools, which are arranged on the milling drum 8 behind the retaining device in the working direction A, engage the underlying ground. The raised initial position of the retaining device 10 is maintained by the two hydraulic cylinders 16, the extended position of which is controlled by the positioning control unit 13, as suggested by the dotted lines in FIGS. 3, 4 and 5.
[0038] During milling operations, it can occur that, due to the milling drum rotating against the direction of rotation of the traveling devices, ground material, in particular in the form of ground clumps 18, is lifted in the vertical upward direction in relation to the remaining ground surface and strikes the bottom edge 17 of the retaining device 10 in its initial position from below. This state is shown in FIG. 4. In this case, the positioning control unit 13 can now be designed so as to apply a retaining force which counteracts this vertically upward acting counterforce exerted by the ground material, i.e. presses downwards in the vertical direction, and thus initially keeps the retaining device 10 in the initial position.
[0039] However, if the counterforce produced by the ground material rising in the vertical upward direction exceeds a defined maximum retaining force, provision is made for the retaining device 10 to yield in the vertical upward direction, as shown in FIG. 5. Here, the retaining device is raised in relation to the remaining ground surface of the underlying ground 14 by the additional amount A+ relative to the initial position. In the present example, the extent to which the retaining device 10 can be pushed further upwards beyond the initial position is limited by a mechanical limiting stop. Provision is also made for the positioning control unit 13 to continue to apply the maximum retaining force to the retaining device 10 in the vertical downward direction by means of the hydraulic cylinders 16.
[0040] If the counterforce applied in the vertical upward direction by the ground material now falls below the maximum retaining force, the retaining device 10, controlled by the positioning control unit 13, returns to its initial position and reassumes its initial position shown in FIGS. 3 and 4. Thus, the retaining device 10 is lowered in the vertical downward direction only as far as the initial raised position in relation to the ground surface, and not down to the ground surface.
[0041] FIG. 6 illustrates, as an example, further details of the positioning control unit 13, as well as some essential elements of the ground milling machine 1. In the present example, it comprises several sensors 19, 20 and 21, the measuring signals of which are transmitted to a processing unit 23 with suitable control software. The sensor 19 is a displacement sensor integrated into the lifting column 3. Such a displacement sensor can be integrated in each of the provided lifting columns of the ground milling machine 1. With the aid of these sensor data, the positioning control unit 13 can thus ascertain the position of the machine frame and thus indirectly the position of the retaining device (at least partially). The sensor 20 is a distance sensor which is height-adjustable together with the retaining device 10. The distance sensor 20 thus ascertains the vertical distance of the retaining device 10 from the underlying ground. The sensor 21 is a displacement sensor inside the hydraulic cylinder 16 by means of which the retaining device 10 is height-adjustable in the vertical direction. In particular with the aid of this sensor, the positioning control unit 13 can thus track how far the retaining device 10 has been pushed upwards or downwards starting from a known position. The processing unit 23 of the positioning control unit 13 controls a hydraulic system supply unit 24 comprising, for example, a pump, a pilot valve or the like. With the aid of the hydraulic system supply unit 24, it is possible, for example, to produce the additional retaining force beyond the force of gravity. Alternatively, it is also possible to produce the retaining force by switching a hydraulic valve to a blocking position when a counterforce increases. Also provided is a pressure relief valve 25, which can be controlled, for example, by the processing unit 23 of the positioning control unit 13 or can also be designed to act purely mechanically. Via the pressure relief valve 25, it is possible, for example, to define the maximum retaining force specifically by means of the switching threshold of the pressure relief valve. FIG. 6 is to be understood merely as an example. Additionally or alternatively, pressure sensors or similar sensing means can, for example, also be provided inside the hydraulic system supply unit of the hydraulic cylinders 16 and the lifting columns 3.
[0042] FIG. 7 illustrates the essential method steps for controlling the position of the retaining device in accordance with the invention. A first essential aspect is that, in step 26, the retaining device 10 is held in the initial position during the milling operation, for example as described above. In the initial position, the retaining device is raised in relation to the underlying ground and is thus not in contact with the latter. Thus, the retaining device 10 does not drag over the ground when the ground milling machine 1 travels over the underlying ground in the working direction A during the milling operation. Step 27 involves starting the milling operation, which in the present case also includes a continuation of a milling operation. Here, the retaining device is still held in its raised initial position according to step 26, in particular in relation to the machine frame. It can now occur that the motion of the milling drum causes ground material to rise from below and press upwards against the retaining device with a counterforce. In the method shown in FIG. 7, step 28 then involves initially maintaining the retaining device in its initial position and applying thereon a retaining force, which is produced, e.g., by the weight of the retaining device or also by additional application of pressure by means of the hydraulic cylinder 16, and which counteracts this counterforce. However, if the counterforce exerted on the retaining device by the ground material in the vertical upward direction continues to increase and a maximum retaining force is exceeded, step 29 involves releasing the retaining device so that it now yields by a displacement upwards. This can include, for example, switching a pressure relief valve. This yielding motion is usually limited in the vertical upward direction, for example by means of a mechanical limiting stop. If the counterforce exerted by the ground material pressing against the retaining device in the vertical upward direction from below now decreases enough to fall back below the maximum retaining force, a returning of the retaining device towards the initial position finally occurs in step 30. This returning movement is limited in the vertical downward direction by the reaching of the initial position of the retaining device. The retaining device is thus not pressed down to the normal ground surface but only as far as the initial position, in which the retaining device is positioned at the defined holding distance A above the underlying ground.
[0043] Prior to the method steps described above, step 31 can also involve moving the retaining device to the initial position by means of further measures of the method. For this purpose, it is, for example, possible that, in order to ascertain the zero position, i.e. the position in which the retaining device contacts the ground surface, the retaining device is in step 31 initially placed on the underlying ground, which can be ascertained, for example, by a pressure fluctuation in the hydraulic system supply unit of the hydraulic cylinder 16, and is then raised by a defined distance, which can be measured, for example, with the aid of the sensor 21, until it reaches the initial position. Additionally or alternatively, it is also possible that the vertical distance of the retaining device from the underlying ground is measured and monitored by the distance sensor 20 and is ultimately used as a target variable for the height adjustment of the retaining device.
[0044] Each of the method steps described above can comprise the use of a correction variable, in particular for defining and monitoring the initial position of the retaining device, in the control and regulation of the position of the retaining device according to step 32. This can become relevant in particular when the ground milling machine 1 has a machine frame that is height-adjustable via lifting columns, since the adjustment of the lifting columns also results in a change in the position of the retaining device in relation to the underlying ground. In this case, provision can be made for the positioning control unit 13 to receive displacement data obtained via suitable displacement sensors of the lifting columns and to consider these data for the control and regulation of the position of the retaining device. Additionally or alternatively, it is also possible here to use a position sensor of the ground milling machine, with which in particular the horizontal position of the machine frame is monitored. Specifically, this can mean that, when the machine frame is lowered by retracting the lifting columns, which also results in a lowering of the retaining device indirectly connected to the machine frame, the retaining device is raised by the amount of the correction factor in order to remain in its initial position in relation to the ground surface, i.e. in order to still have the same vertical distance from the ground surface after the height adjustment of the machine frame.
[0045] FIG. 8 now in particular illustrates further details of an illustrative design of a control loop, in particular for the method steps 28 to 30. The starting point according to 33 is the currently set height of the retaining device in the vertical direction above the surface of the underlying ground. Starting from the current position, which is ascertained, for example, with the aid of one of the sensors 20 or 21, the positioning control unit 13 conducts a check 34 whether the current position of the retaining device deviates from the initial position A in the vertical upward direction (h>0). If there is such a deviation, the retaining device remains in this floating position, if necessary with an additional retaining force being applied. If, on the other hand, there is no such deviation, according to 36, the retaining device remains held or fixed in the initial position. At 37, a determined position of the retaining device is updated. The current position thus determined is fed back and the control loop described above is run again. The process described in FIG. 8 can be performed by the positioning control unit 13 continuously or also intermittently, for example in a timed manner.
[0046] FIG. 9 illustrates further details for the adaptation of the positioning of the retaining device or the determination of a correction variable for the adjustment of the retaining device in order to maintain the initial position, i.e. the vertical distance of the underside of the retaining device from the underlying ground, when the lifting columns 3, in particular in a ground milling machine 1 as shown in FIG. 1, are adjusted. The starting point here is a measurement 38 of the position of the lifting columns 3, in particular at least the lifting columns 3 connecting the traveling devices to the machine frame at the front right and the front left, respectively. This measurement 38 can be performed during the milling operation or also at the beginning of the milling operation. If, in step 39, the positioning control unit 13 determines a change in the lifting height of the right and/or front left lifting columns, the calculation of a correction factor or correction variable occurs in step 40 for the adjustment of the retaining device based on the new height information. For example, if the front lifting columns have been retracted, the correction factor is the correction variable by which the retaining device needs to be raised in order to reassume its initial position, i.e. the defined holding distance of the retaining device in relation to the ground surface in the vertical downward direction. In step 41, the retaining device is now raised or lowered based on the determined correction variable. If, on the other hand, no change in height is determined, the retaining device remains fixed in its current raised position in step 42. Subsequently, the control loop described in FIG. 9 is run again starting at step 38. It is possible here to run the process described in FIG. 9 continuously. However, the adaptive height adjustment of the retaining device due to a height adjustment of lifting columns as shown in FIG. 9 preferably occurs only if the lifting columns are actuated. This method also applies accordingly when the height of the rear lifting columns and/or of the front and rear lifting columns of a ground milling machine is adjusted.
