Method for controlling a height adjustment of a stripping plate of a ground milling machine, and ground milling machine

Abstract

The present invention relates to a method for controlling a height adjustment of a stripping plate of a ground milling machine, in particular a stripping plate of a cold milling machine, during the working process, said method comprising the following steps of detecting the striking of the stripping plate against an obstacle; automatically triggering the height adjustment unit for lifting the stripping plate from a working position, in which the stripping plate is in contact with the underlying ground to be processed, to avoid a further collision with the obstacle; and automatically triggering the height adjustment unit for lowering the stripping plate back to the working position upon overcoming the obstacle.

Claims

1. A method to control height adjustment of a stripping plate of a ground milling machine during a milling process, the method comprising the following steps: a) indirectly detecting a collision of the stripping plate with an obstacle in a working direction from a working behavior and/or a traveling behavior of the ground milling machine with at least one sensor to detect an operating variable of the ground milling machine associated with the milling process and a control unit; b) automatically triggering a height adjustment unit to lift the stripping plate from a working position, in which the stripping plate is in contact with underlying ground, when the collision with the obstacle has been detected; and c) subsequently, automatically triggering the height adjustment unit to lower the stripping plate back to the working position.

2. The method according to claim 1, wherein the operating variable associated with the milling process comprises a travel drive operating variable and/or a milling drive operating variable of the ground milling machine.

3. The method according to claim 1, wherein step a) comprises at least one of the following features: the control unit monitors variation of an ascertained actual travel drive operating variable over time; the control unit compares an ascertained actual travel drive operating variable of the ground milling machine to a travel drive operating variable specified internally by the machine; the control unit monitors variation of an ascertained actual milling drive operating variable; the control unit compares an ascertained actual milling drive operating variable of the ground milling machine to a milling drive operating variable specified internally by the machine.

4. The method according to claim 3, wherein the ascertained actual travel drive operating variable comprises an actual speed and/or an actual acceleration and/or a variation of the actual speed and/or a variation of the actual acceleration of the ground milling machine relative to an external environment.

5. The method according to claim 3, wherein the travel drive operating variable specified internally by the machine and/or the milling drive operating variable specified internally by the machine is retrieved from a machine control of the ground milling machine.

6. The method according to claim 3, wherein the ascertained actual travel drive operating variable comprises a rotational speed of a track chain and/or a rotational speed of a wheel drive and/or an electrical operating variable and/or a swiveling angle of a travel-drive pump.

7. The method according to claim 3, wherein the ascertained actual milling drive operating variable comprises an actual rotational speed of a milling drum and/or an actual torque of a milling drum.

8. The method according to claim 3, wherein the milling drive operating variable ascertained specified internally by the machine comprises a target rotational speed of a milling drum and/or a target torque of a milling drum.

9. The method according to claim 1, wherein the at least one sensor detects speed and/or acceleration of the ground milling machine over ground.

10. The method according to claim 1, wherein the at least one sensor comprises at least one of a radar sensor, a laser sensor or an accelerometer.

11. The method according to claim 1, wherein the operating variable associated with the milling process comprises an actual distance traveled by the ground milling machine, and/or a an actual speed and/or a slip at a track chain and/or a wheel of the ground milling machine.

12. The method according to claim 1, wherein a switch-over from step b) to step c), in a time- and/or distance-shifted manner, is performed when it is ascertained, with the at least one sensor, that a defined minimum speed and/or a defined positive acceleration of the ground milling machine over ground in the working direction has been reached.

13. The method according to claim 1, wherein in step b) the stripping plate is lifted no further than up to a defined threshold value.

14. The method according to claim 2, wherein the operating variable associated with the milling process comprises the travel drive operating variable of the ground milling machine.

15. The method according to claim 2, wherein the operating variable associated with the milling process comprises the milling drive operating variable of the ground milling machine.

16. The method according to claim 6, wherein the electrical variable is an amperage.

17. The method according to claim 10, wherein the at least one sensor comprises at least the radar sensor.

18. The method according to claim 10, wherein the at least one sensor comprises at least the laser sensor.

19. The method according to claim 10, wherein the at least one sensor comprises at least the accelerometer.

20. The method according to claim 1, wherein the ground milling machine is a cold milling machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail below with reference to embodiment examples shown in the figures. In the schematic figures:

(2) FIG. 1 is a side view of a ground milling machine;

(3) FIG. 2 is an oblique perspective rear view of a milling drum box of the ground milling machine depicted in FIG. 1;

(4) FIG. 3 is a flow chart showing the sequence of the steps of the method for controlling the height adjustment of a stripping plate of a ground milling machine; and

(5) FIG. 4 is a graphic illustration of the relationship between individual operating parameters in the course of the method according to the invention.

DETAILED DESCRIPTION

(6) FIG. 1 shows a ground milling machine 1, which is in this case designed as a road or cold milling machine. The ground milling machine 1 has an operator platform 2, a machine frame 3, a drive engine 4 and traveling devices 6 connected to the machine frame 3 via lifting columns, said traveling devices in the present case being crawler tracks, although wheels may be employed as well. In working operation, the ground 8 to be milled off is removed in the working direction a by a milling drum 9 mounted for rotation about a horizontal rotation axis 10 extending transversely to the working direction a inside a milling drum box 7 that is connected to the machine frame 3 and is arranged centrally between the front and rear traveling devices 6. Via a discharge belt 11, milled material is transferred onto a transport vehicle, which is not shown, and is transported away by the latter. The invention similarly also relates in particular to rear rotor milling machines in which the milling drum is arranged in the rear region of the machine, to ground stabilizers, recyclers and surface miners.

(7) The ground milling machine 1 is provided with a sensor 18a, which is arranged on the machine frame 3. The position of the sensor 18a on the machine frame 3 is in this case shown merely schematically and may be varied according to the circumstances, i.e. depending on the type of ground processing machine used. It should, however, not be arranged in the dirt area or at an exposed position. The sensor 18a is therefore preferably arranged in particular in front of the milling drum box in the working direction, and in this area in particular at a location vertically below the machine frame 3. The sensor 18a may in particular be a radar sensor, a laser sensor, an accelerometer or any other type of sensor suitable for recording the speed or the acceleration, in particular the negative acceleration, of the ground milling machine 1 over ground. Additionally or alternatively, the sensor 18a may also be used to ascertain the rotational speed of the traveling devices 6. What is essential is that the sensor 18a is used to obtain a signal that directly and indirectly depends on the actual movement of the ground milling machine 1 in the working or milling direction a and varies as a function thereof. The sensor 18a thus ascertains an actual travel drive operating variable in the sense of an actual advancing parameter. Further, a sensor 18b is provided. Said sensor is arranged and designed such that it ascertains an actual milling drive operating variable. For this, it is positioned such that it ascertains at least one operating variable that depends on the milling process, for example the rotational speed of the milling drum. The ground milling machine 1 finally also comprises a machine control 18c. Via said control, target specifications for travel drive operating variables and milling drive operating variables are transmitted from the driver or other components and are processed for controlling the ground milling machine 1.

(8) The ground milling machine 1 further has a control 19 the function of which will be described below in connection with FIG. 2. The sensors 18a and/or 18b as well as the machine control 18c are connected to the control 19 via signal lines, either via a cable connection or via a wireless data transmission link.

(9) FIG. 2 is an oblique perspective rear view of a milling drum box 7 of the ground milling machine 1 depicted in FIG. 1, which is in this case depicted with the stripping plate 14 lowered to the stripping position during milling operation of the ground milling machine. The stripping plate 14 then contacts the milling bed 12 and scrapes horizontally over the milling bed in the working direction a. The stripping plate 14 can be lifted starting from this position, as will be described in more detail below.

(10) Lateral shields 23 delimit the milling drum box 7 to the two sides that are intersected by the rotation axis 10 of the milling drum 9. Milled material is transported away in the working direction to the front in a known manner. The rear side in the working direction a is essentially formed by the stripping device 30, which comprises a stripping plate 14, a height adjustment device with two actuators 15a and 15b in the form of hydraulic cylinders 15, and a stripping bar 27.

(11) In the embodiment shown, the stripping plate 14 has a lower plate 13a and an upper plate 13b. The lower plate 13a is mounted at the upper plate 13b such that it is longitudinally displaceable, and is shown in the lowered position in FIG. 2. Thus, only the lower part of the stripping plate 14 is height-adjustable in the present embodiment example. However, variants in which the stripping plate is designed as one integral piece and/or is height-adjustable as a whole are explicitly also encompassed by the invention.

(12) During working operation, the ground milling machine 1 mills the ground through rotation of the milling drum 9 using the chisel devices arranged thereon (not shown) and transports the loosened milled material away via the discharge belt 11 (see FIG. 1). A milled track 40 having milling edges 41 and a milling bed 12 is formed in the ground 8, with the depth of the milling bed 12 depending on the set depth of the ground milling machine 1. The stripping device 30 can be displaced using the height adjustment unit 15. The stripping plate 14 is then, for example, guided over the milling bed in the working direction a, scraping directly on the milling bed 12.

(13) If there is a ground obstacle 17 in the milling bed 12, such as an edge, a small step, a groove or the like, a collision of said obstacle 17 with the stripping plate, which is lowered in working operation 14, causes a halt or a delay in movement of the ground milling machine 1 in the working direction a. In other words, the machine is thus stuck in the working direction via the jammed stripping plate 14. This is solved in the manner described below by resorting to at least one of the sensors 18a or 18b for the detection of an actual travel drive operating variable and/or milling drive operating variable or an actual value and the machine control 18c, via which a target value, i.e. a theoretical travel and/or milling drive operating variable is ascertained and monitored, a comparison of which is detected by the control 19 and, if the control 19 detects a collision with an obstacle, by initiating a lifting movement of the stripping plate 14. Alternatively, the obstacle situation may also be detected by the control 19 via the progression of the actual travel and/or milling drive operating variable over time, in this case without resorting to the machine control 18c. The essential aspect here is that the control 19 is designed such that it triggers the height adjustment of the two adjusting cylinders 15a, 15b at the lower plate 13 in a self-acting manner to lift the stripping plate 15 from its working position, in which it is in contact with the ground 8 to be processed, as described above, to resolve the existing collision with the obstacle 17 and thus enable the ground milling machine 1 to continue the milling works in the working direction a. The control 19 is further designed to trigger the height adjustment unit 15a, 15b in a self-acting manner to subsequently lower the stripping plate 14 back to the working position.

(14) It is noted that the configuration according to the invention is also applicable to other ground processing machines, for example compact milling machines or recyclers and surface miners, as already mentioned. In contrast to the two-piece implementation with an upper plate 13b and a lower plate 13a as described herein, these may be equipped with a single-piece stripping plate 14, which can be swiveled upwards and downwards in its entirety through a height adjustment unit. When striking against an obstacle 17, the entire stripping plate 14 would then be brought from its working position to a position spaced from the ground 8 by the control 19.

(15) FIGS. 3 and 4 now illustrate the essential basic idea of the method according to the invention.

(16) FIG. 3 is a flow chart which illustrates the sequence of the steps of the method for controlling the height adjustment unit 15a, 15b of a stripping plate 14 of a ground milling machine 1 as shown, for example, in FIG. 1, during the working process of the ground milling machine 1. A first step 20 involves detecting the striking of the stripping plate 14 against an obstacle 17. In a subsequent step 21, the height adjustment unit 15a, 15b is triggered automatically to lift the stripping plate 14 from a working position, in which the stripping plate 14 is in contact with the ground 8 to be processed, to avoid a further collision with the obstacle 17. Upon overcoming or passing the obstacle 17, a further step 22 of automatically triggering the height adjustment unit 15a, 15b for lowering the stripping plate 14 back to the working position is finally carried out. The essential aspect here is the detecting in step 20. This is explained in more detail in FIG. 4.

(17) FIG. 4 depicts a number of progressions of travel drive operating variables and milling drive operating variables correlated to one another in a time domain. The abscissa respectively shows a common time axis t. In the uppermost graph 31, the actual advancing speed v (actual value) of the ground milling machine of FIG. 1 in the working direction a in m/s, ascertained, for example, via the sensor 18a, is plotted as an example of an actual travel drive operating variable of the ground milling machine 1. In graph 32, on the other hand, the amperage of a current applied to an adjusting magnet of a travel-drive pump is plotted as an example of a target specification of a travel drive operating variable. This target specification thus provides a signal with respect to a travel drive operating variable which depends on how fast, in consideration of the available settings, the ground milling machine should be moving over ground, or at least whether or not it should be accelerating. This signal can, for example, be ascertained or read from the machine control 18c directly via a sensor at the adjusting magnet. Alternatively, use can also be made here of the switching position of an operating element, for example a joystick. In other words: The specified travel drive operating variable is thus a specification signal which is acquired at and within the machine and determines the theoretical movement of the ground milling machine in the working or milling direction. In FIG. 4, this value remains constant throughout the complete time period, i.e. the driver has in the present case specified a constant traveling speed. From a machine-internal point of view, the ground milling machine 1 should thus be advancing in the working direction a at essentially constant speed throughout the time period shown in FIG. 4. However, this is not the case, as can be taken from 31. At the time t1, the stripping plate strikes against a ground obstacle, so that the machine is hindered from continuing its movement in the working direction a. This causes the advancing speed, as an example of an actual travel drive operating variable of the ground milling machine 1, to very quickly drop at and beyond the time t2 until the time t3, where the machine comes to a halt.

(18) This halt is ascertained via the control unit by ascertaining the behavior of the two curves 31 and 32 relative to one another, as shown in curve 33. It can be seen that the drop in advancing speed is accompanied by an abrupt increase in the quotient 31/32 starting at the time t1 and continuing beyond the time t2 until t3. At t2, this abrupt variation passes a variation threshold A. This variation threshold achieves a certain inertness of the overall system in order to prevent over-sensitive responsiveness of the control in the case of speed variations of the ground milling machine. Alternatively, it is also possible here to only resort to a variation of the speed progression according to 31 through ascertainment of the speed variation over time. However, simultaneous consideration of the target value from 32 enables the present collision event to be correlated more accurately.

(19) Curve 34 represents the lifting position of the stripping plate, i.e. the distance of the bottom edge of the stripping plate from the milling bed in the vertical direction. At the zero line of the abscissa, the stripping plate is thus in its stripping position. If the variation threshold is exceeded at the time t2, the control initiates a lifting of the stripping plate, which is performed until the time t4 is reached. For this, the control unit actuates the lifting cylinder(s) for height adjustment of the stripping plate, as indicated in curve 35. S here designates a control signal for a lifting movement (above the abscissa) and a lowering movement (below the abscissa).

(20) At the time t4, the ground milling machine 1 thus accelerates again, as can be seen from curve 31. This acceleration in the working direction a is interpreted by the control unit as a sign indicating that the stripping plate has overcome the obstacle at least in the vertical direction, i.e. the stripping plate has been lifted far enough. The control unit thus stops the lifting movement and, according to curve 35, switches over to lowering the stripping plate until, at the time t5, the stripping plate has returned to its initial position and thus rubs over the milling bed again.

(21) Finally, at the time t6, the ground milling machine has regained an actual advancing speed the machine should travel at according to the machine-internal specification.

(22) Curve 36 illustrates utilization of an actual milling drive operating variable, more specifically the torque applied to the milling drum, which may, for example, be ascertained via the sensor 18b. Said torque drops at the time t1 as the ground resistance counteracting the milling drum during the milling process decreases due to the halt of the ground milling machine. Alternatively, the rotational speed of the milling drum could be used as an actual milling drive operating variable as well, in which case the progression of the curve would be exactly inverted. The rotational speed of the milling drum increases in the case of a halt of the machine at the ground obstacle.