DE102022205361A1 - Cable winch with pressure-dependent adjustment of at least one hydraulic motor - Google Patents

Abstract

The invention relates to a method for operating a hydraulic cable winch, with the cable winch comprising a rotatable cable drum which is in rotary drive connection with at least one hydraulic motor, with the at least one hydraulic motor being able to be supplied with pressurized fluid by means of at least one main pump, with at least one request signal (45; 46) is provided, which can be continuously changed by an operator of the cable winch, with the at least one hydraulic motor having a continuously adjustable displacement volume, with an actuating signal (14) being provided, by means of which the displacement volume of the at least one hydraulic motor can be adjusted, with the Cable winch comprises at least one first pressure sensor (36; 37), with which a load-side pressure can be measured on at least one hydraulic motor, with a pressure signal (62) being dependent on the measured value of the at least one first pressure sensor (36; 37). According to the invention, this Control signal (14) taking into account the at least ei a request signal (45; 46) in a plurality of calculation steps (50; 71; 73; 75; 76), wherein in a first calculation step (50) of said calculation steps (50; 71; 73; 75; 76) an associated outgoing signal (52) is limited by amount an associated incoming signal (51) is calculated for a current limit value (55), the current limit value (55) depending on the pressure signal (62).

Description

The invention relates to a method for operating a cable winch according to the preamble of claim 1.

From the DE 10 2010 055 718 A1 a hydraulic winch is known. The cable drum is driven by a hydraulic motor, which is supplied with pressure fluid from a main pump in an open hydraulic circuit. A switchable brake is also provided, with which the cable drum can be stopped. Such cable winches are often controlled purely hydraulically.

This results in the problem that vibrations can occur if the operator moves an operating lever very quickly or jerkily from zero in the direction of a maximum lowering speed. By adjusting the displacement volume of the hydraulic motor, the rope drum can be accelerated so much that the rope becomes load-free, even if the load is very heavy. If the load falls into the rope when braking later, the vibrations mentioned will occur. Furthermore, vibrations can be accommodated when the hydraulic motor hits its mechanical end stop for the minimum displacement volume, especially when this happens at high speed. This is also a possible consequence of the aforementioned jerky adjustment of the control lever of the cable winch.

An advantage of the invention is that such vibrations are avoided.

According to claim 1, it is proposed that the actuating signal is calculated in several calculation steps, taking into account the at least one request signal, wherein in a first calculation step of the calculation steps mentioned, an assigned outgoing signal is calculated by limiting the amount of an assigned incoming signal to a current limit value , whereby the current limit value depends on the pressure signal. The at least one request signal is generated by means of said operating lever. The displacement volume of the at least one hydraulic motor is set by means of the control signal.

The pressure signal corresponds to the load-side pressure on at least one hydraulic motor, ie the pressure that supports the load attached to the cable winch. The control signal is preferably proportional to the displacement volume of the at least one hydraulic motor. The relationship is preferably linear or approximately linear. Any variable with which the displacement volume of the hydraulic motor can be influenced can be used as the control signal. The control signal can be proportional to the pressure in the control cylinder of the hydraulic motor, for example, the displacement volume being adjusted with the control cylinder.

If there are several hydraulic motors, these are preferably connected hydraulically in parallel. The pressure on the load side is then the same for all hydraulic motors. Preferably, the several hydraulic motors are connected to the cable drum via a gearbox in a rotary drive connection in such a way that the total drive torque on the cable drum is equal to the sum of the individual drive torques on the individual hydraulic motors. All hydraulic motors are preferably controlled with the same actuating signal.

If several main pumps are provided, their displacement volumes are preferably set proportionally to one another, and they are most preferably set equal to one another if the main pumps are designed to be the same as one another. Several main pumps are preferably hydraulically connected in parallel so that they all feed into a single common line.

The at least one request signal can be a (preferably single) signal which can assume both positive and negative values. Such a signal is preferably specified as an electrical analogue value or as a digital value, with the sign indicating the direction of rotation of the cable winch. However, two separate signals for the two directions of rotation of the cable winch can also be provided. Such request signals are preferably generated in the form of a hydraulic pressure, in which case they are subsequently converted into a digital request signal which can be used within the framework of the calculation according to the invention. When the hoist drum is rotating, the associated demand signal is preferably proportional to the speed at which the hoist drum is rotating.

The method is preferably carried out in an automated manner, most preferably being carried out by an electronic control device which may comprise a programmable digital computer. The at least one hydraulic motor and the at least one main pump can be connected in an open or a closed hydraulic circuit.

The calculation steps mentioned are preferably carried out in rounds, with all calculation steps being carried out in each calculation round. The calculation rounds fol gene preferably according to a constant time cycle, the time cycle being, for example, 1 ms. At the beginning of each calculation round, the measured values of all sensors are determined as input variables for the calculation. The calculation process within a calculation round is preferably free of feedback, although it can otherwise be branched as desired. Calculation results from a calculation round can be used in subsequent calculation rounds in order to still enable feedback. At the end of a calculation round, the calculated actuating signal is output to the associated actuating means, for example the third pressure reducing valve, with the output value preferably remaining constant until the end of the next calculation round. A corresponding calculation program can be created, for example, with the Matlab Simulink software, which can convert graphic inputs into C program code. After compilation, the C program code can be executed on the programmable digital computer mentioned. It goes without saying that any programming language can be used, and the program code can be created manually.

The cable drum can preferably be stopped with a switchable brake. A two-value brake signal is preferably provided, with the switching state of the brake being dependent on the brake signal. The brake signal can be specified by the operator of the cable winch using a button or a switch. However, it is also conceivable that the braking signal is calculated from the request signal.

Advantageous developments and improvements of the invention are specified in the dependent claims.

It can be provided that the current limit value is exclusively dependent on the pressure signal and at least one constant parameter. Said dependency can contain derivations according to time and integrals over time, which are preferably calculated in a time-discrete manner. This preferably achieves a smoothing of the time profile of the current limit value in the case of a strongly fluctuating pressure signal.

It can be provided that the cable drum can be stopped with a switchable brake, the current limit value being constant when the cable drum is stopped with the brake, it being dependent on the pressure signal when the brake is open. This is intended to bring the system into a defined state when the brake is closed, so that when the brake is opened, the cable drum starts up smoothly and predictably.

Provision can be made for at least two first pressure sensors to be provided, with the pressure signal depending on the highest of the corresponding measured values. If a first pressure sensor fails or malfunctions, the cable winch can still be operated safely.

It can be provided that the pressure signal is formed by low-pass filtering from said highest measured value of the at least one pressure sensor. This is intended to achieve a smoothing of the time profile of the pressure signal. As a result, the excitation of vibrations is minimized. The highest measured value and/or the animal pass filtering is/are preferably carried out by a respective assigned calculation step within the framework of the round-by-round calculation method explained above.

It can be provided that the dependency between the current limit value and the pressure signal includes a linear dependency with exactly two parameters. The signal obtained by means of the linear dependency can be smoothed over time using a PT1 element or a low-pass filter in order to determine the current limit value.

Provision can be made for the current limit value to depend on the pressure signal in such a way that the displacement volume of the at least one hydraulic motor is limited in terms of amount to a value that is greater than the minimum displacement volume of the hydraulic motor when the current limit value is effective. This prevents the hydraulic motor from hitting the mechanical stop that limits the downward displacement volume. As a result, the excitation of vibrations is avoided.

According to the exemplary embodiment, a hydraulic motor is used whose displacement volume can be adjusted between a minimum displacement volume and a maximum displacement volume, with the direction of rotation of the cable winch being adjusted with a directional valve, in particular a 4/3-way valve. However, it is also conceivable that a hydraulic motor that can be adjusted beyond the displacement volume of zero is used, so that the directional control valve can be omitted. In the last-named case, the minimum displacement volume is zero, and what is important is the amount limitation mentioned. A control range around the displacement volume of zero is thus ruled out when the second limit value is effective. The first preferred case has the advantage that the pressure on the load side is permanently applied to the same working port of the hydraulic motor.

It can be provided that in a second calculation step, the difference is formed between an incoming signal that is dependent on the output signal of the first calculation step and a correction signal, with the control signal being dependent on the corresponding outgoing signal of the second calculation step, with the Correction signal is so dependent on the pressure signal that the pressure signal has an upper limit. This prevents excessively small displacement volumes being set on the hydraulic motor when very heavy loads are attached to the cable drum. It should be noted here that setting very small displacement volumes on the hydraulic motor can cause an extremely large increase in pressure. On the one hand, this ensures that the cable winch can hold the load, even if the operator requests a very high cable speed. Furthermore, a vibration excitation by pressure peaks is prevented. The correction signal preferably has only positive values. It is preferably subtracted from the signal entering the second calculation step. It goes without saying that every mathematically equivalent arithmetic operation should be covered by the protection, for example the addition of a negative correction signal.

Provision can be made for the correction signal to be calculated using a continuous linear controller, with the correction signal only being equal to the outgoing signal from the controller if the pressure signal is greater than a specified limit pressure, with the Correction signal is otherwise zero. As part of the calculation steps explained above, the controller is preferably calculated in a time-discrete manner, with intermediate values from a number of previous calculation steps being included in the calculation in a current calculation round. The controller is preferably a PID controller. Its I component is preferably set to zero if the pressure has fallen below the specified limit for a predetermined minimum period of time. The limit pressure corresponds approximately to the maximum desired pressure on the hydraulic motor on the load side.

It can be provided that the cable drum can be stopped with a switchable brake, the correction signal also being zero when the cable drum is stopped with the brake. This is intended to achieve a defined system behavior when the brake is released.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 einen hydraulischen Schaltplan der dem erfindungsgemäßen Verfahren zugrundeliegenden Seilwinde; und
• 2 ein Blockdiagramm, welches den Rechengang des erfindungsgemäßen Verfahrens darstellt.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

• 1 a hydraulic circuit diagram of the cable winch on which the method according to the invention is based; and
• 2 a block diagram showing the calculation process of the method according to the invention.

1 shows a hydraulic circuit diagram of the cable winch 10 on which the method according to the invention is based. The cable winch 10 has a rotatable cable drum 11 on which a cable, a chain or other traction means can be wound. A load 17 can be attached to the traction mechanism in order to raise or lower it, for example, against the effect of gravity. The present cable winch 10 is used, for example, in cranes with which very large loads are to be moved gently.

The cable drum 11 is in rotary drive connection with a hydraulic motor 12, with a non-rotatable coupling being provided in the simplest case. The hydraulic motor 12 is, for example, an axial piston machine with a bent-axis design. The displacement volume of the hydraulic motor 12 is continuously adjustable, in the present case an adjustment starting from a small minimum displacement volume in a single direction towards a maximum displacement volume or vice versa is provided. This has the advantage that the pressure 38 on the load side, which supports the load 17 against the force of gravity, is always present in the same pressure line 30, regardless of the operating state of the cable winch 10. For safety reasons, the load-side pressure 38 is measured with two first pressure sensors 36; 37 measured. The two end values of the displacement volume are preferably continuously adjustable by means of a mechanical end stop, and they are preferably set once in a fixed manner.

In the 1 and 2 are a total of four signal paths a; b; c; d, which are broken for the sake of clarity, with the same lower-case letters actually being connected to one another.

In the present case, the displacement volume is adjusted with the aid of a hydraulic motor controller 15, the hydraulic setpoint value 18 specified by means of the third pressure-reducing valve 13 (via the second signal path b) being essentially proportional to the displacement volume set. For example, the minimum Ver displacement volume is set when the hydraulic set point 18 is set to 28 bar, with the maximum displacement volume being set when the hydraulic set point 18 is set to 5 bar, the behavior therebetween being essentially linear. The following description is also based on these two exemplary pressure limit values of 28 bar and 5 bar.

A hydraulic operating lever 40 is also provided, which has a first and a second pressure-reducing valve 41; 42 includes, with which a first and a second control pressure 47; 48 can be generated. Depending on the direction of actuation of the operating lever 40, either the first or the second pressure reducing valve 41; 42 active. The operating lever 40 is presently designed in such a way that the first and the second actuating pressure 47; 48 could use a shuttle valve as a hydraulic target value 18 directly. According to the invention, however, this was not done in order to achieve the desired operating behavior of the cable winch 10 . When the deflection is zero, the operating lever 40 outputs a first or second actuating pressure 47; 48 from 5 bar, so that with direct motor coupling the maximum displacement volume would be set, so that the rope drum would rotate slowly or not at all. At maximum deflection of the operating lever 40, a first or a second actuating pressure 47; 48 of 28 bar output, so that the minimum displacement volume would be set with direct motor coupling, so that the cable drum 11 would rotate very quickly.

The first setting pressure 47 is measured with the second pressure sensor 43 , the second setting pressure 48 being measured with the third pressure sensor 44 . It goes without saying that the present invention can be used with a purely electric operating lever that outputs the measured values of the first or second pressure sensor almost immediately. For safety reasons, the present hydraulic design is preferred because by means of the first and second control pressure 47; 48 the directional valve 16 can be brought into a central position in which the cable drum does not move at all or only very slowly. This also happens if the entire hydraulic and electrical energy supply fails.

The hydraulic motor 12 is supplied with pressurized fluid by a main pump 31 . The pressurized fluid is preferably a liquid and most preferably hydraulic oil. The main pump 31 draws in the pressure fluid from a tank 33 and conveys it via the directional control valve 16 to the hydraulic motor 12, from where it flows back into the tank 33 via the directional control valve 16. Instead of the open hydraulic circuit shown, a closed hydraulic circuit can also be used. The directional control valve 16 has three positions. In the middle position, which is preloaded by return springs 83, the hydraulic motor 12 is clamped in an essentially hydraulically fixed manner. Targeted leaks to the tank 33 can be permitted in this case, so that when the brake 20 is closed, the pressure in the pressure line 30 is reduced. With the first control pressure 47, the directional control valve 16 is switched to the left position, with which the load 17 is lifted. The main pump 31 thus promotes against the action of gravity. With the second actuating pressure 48, the in 1 right position of the directional control valve 16 set, with which the load 17 is lowered. Here the pump promotes low-load, the weight of the load 17 being held by the throttle 19 in the directional control valve 16, the throttle being located in the return flow to the tank 33. The throttle 19 is designed so small that the speed of movement of the cable drum 11 is determined by the flow rate of the main pump 31 and the displacement volume of the hydraulic motor 12.

The main pump 31 is designed, for example, as an axial piston pump with a swash plate design. It preferably has a continuously adjustable displacement volume. This is set by a pump controller 34, with the delivery flow being able to be set, for example, proportionally to the position of the operating lever 40. It is conceivable that the flow rate is limited to a maximum value. The main pump 31 is driven by a drive motor 35, which can be designed, for example, as an internal combustion engine, in particular as a diesel engine.

Next is in 1 an auxiliary pump 32 is shown, with which the control oil supply for the operating lever 40, the third pressure reducing valve 13 and the switching valve 22 is to be symbolized. As shown, the pilot oil can be supplied with a separate auxiliary pump 32 . However, it is also conceivable that part of the pressure fluid delivered by the main pump 31 is used for the control oil supply.

The brake cylinder 21 of the brake 20 can be pressurized by means of the switching valve 22 . The brake cylinder 21 is designed as a single-acting cylinder, which activates the brake 20 in the depressurized state, so that the cable drum 11 cannot rotate. If pressure is applied to it, the brake 20 is released so that the cable drum 11 can be rotated by means of the hydraulic motor 12 . A stepless adjustment of the braking force is preferably not provided.

2 shows a block diagram which represents the calculation process of the method according to the invention. The calculation takes place in consecutive calculation rounds, which for example carried out at a constant time interval of 1 ms. At the beginning of each calculation round, the measured values of the first pressure sensors 36; 37, the second and third pressure sensors 43; 44 and the position of the brake switch 24 are read. The only output size of the in 2 The calculation process shown is the value of the actuating signal 14. This value is used, for example, to apply current to the coil of the first pressure-reducing valve 13 using pulse-width modulation (PWM). If the method is carried out with a number of hydraulic motors and accordingly with a number of first pressure-reducing valves 13 , all of the first pressure-reducing valves are controlled using the value of the single control signal 14 . In the period up to the end of the next round of calculations, this value is used to control the first pressure-reducing valve 13 in a time-constant manner.

According to a further embodiment of the present invention, the value of the control signal 14 can be used to calculate a target swivel angle of the hydraulic motor 12 . In such a case, an electro-proportional adjustment of the hydraulic motor is preferably used in 1 Replace system 13, 15 shown. During the electro-proportional adjustment of the hydraulic motor 12, a control force is applied to the control piston by a proportional magnet. The adjustment is then proportional to the current.

For this reason, it is clear to the person skilled in the art that this application does not relate to a specific type of adjustment of the hydraulic motor 12 and that the control signal, which is calculated by the patented method, by means of (or taking into account) the displacement volume of the at least one hydraulic motor 12 is adjustable, can be used in various ways.

the inside 2 The calculation process shown is essentially from left to right and is free of feedback within a calculation round. Intermediate values from earlier calculation rounds can be used within a calculation round in order to still enable feedback. This occurs, for example, within blocks 70; 71; 65; 61, for example to calculate derivatives with respect to time and integrals over time.

In the following, the calculation process within a calculation round based on the 2 explained. The selection unit 72 selects one signal from a group of three. The first request signal 45, namely the measured value of the second pressure sensor 43, is only selected if it is greater than the minimum value of 5 bar. The second request signal 46, namely the measured value of the third pressure sensor 44, is only selected if it is greater than the minimum value of 5 bar. Otherwise, a zero signal is selected, which always represents 0 bar. This makes use of the fact that the operating lever is designed in such a way that only one of the two control pressures can be above the specified minimum value. The zero signal is also always output when the brake switch 24 or the brake signal indicates a closed brake. The maximum displacement volume is then set on the hydraulic motor with the brake closed.

The selected signal forms the incoming signal 51 of a first calculation step 50. The corresponding outgoing signal 52 is equal to the incoming signal 51 if the incoming signal is smaller than a current limit value 55. Otherwise, it is equal to the current limit value 55. The determination of the current limit value 55 will be discussed further below.

Said outgoing signal 52 is smoothed with a PT1 element (https://de.wikipedia.org/wiki/PT1-Glied), so that excessively rapid changes in the request signal 46; 46 does not affect the setting signal 14. A correction signal 74 is then subtracted 73.

In limitation 75, the signal is limited to the value range from 0 bar to 28 bar in order to ensure that the hydraulic motor is not controlled with impermissible values. Values that are outside of the specified interval are replaced by the assigned interval limit. By means of the control pressure 76 found in this way, the current required to set the said control pressure 76 at the third pressure-limiting valve 13 , which forms the control signal 14 , is determined by means of a characteristic curve 76 .

If the limit value 55 is large enough and the correction value 75 is equal to zero, this calculation is essentially equivalent to a direct hydraulic coupling of the operating lever (No. 40 in 1 ) to the hydraulic motor (#12 in 1 ) via a shuttle valve.

The limit value 55 prevents the cable drum and thus the traction device from being accelerated faster than the gravitational acceleration by jerky adjustment of the operating lever towards the end position, as a result of which the load falling with gravity can no longer follow the traction device. This would result in a strong jolt when braking later, which could even result in the traction mechanism tearing. The correction value 75 is intended to prevent the pressure on the load side from being too great because the displacement volume set on the hydraulic motor is too small for very heavy loads.

A pressure signal 62 is used for both corrections, which is detected by the first two pressure sensors 36; 37 is determined. The two corresponding measured values are supplied to a maximum value calculation 60 so that only the higher of the two measured values in the pressure signal 62 is taken into account. This higher value is filtered with a low-pass filter 71, for example. The low-pass filtering 72 can take place in such a way that the pressure signal 62 is the mean value of the input signal of the low-pass filter 61 over a predetermined number of previous calculation rounds. When starting the system, the averaging is preferably initialized to zero. As a result, a pressure signal 62 is available very shortly after the system is started, which well represents the load on the cable drum.

As already explained, the system is equipped with a brake. While the brake stops the cable drum, the maximum displacement volume should be set on the hydraulic motor 12. This is initially achieved with the zero signal explained above, which is output by the selection unit 72 when the brake is switched on, even if the operating lever is deflected. The two corrections mentioned should only take effect when the brake signal 23 indicates a release of the brake over a fixed predetermined period of time. The timing control 65, the two first signal selections 66 and the controller release 67 are provided for this purpose. The inactivity of the two corrections is achieved by setting the current limit value 55 to 28 bar (corresponds to the smallest displacement volume of the hydraulic motor) and the correction value to zero. This means that the round-by-round calculation can be continued uninterrupted even during inactivity due to the active brake.

If the aforesaid short period of time has elapsed, the current limit value 55 is calculated from the pressure signal 62 by means of a linear dependency 64, with only two fixed parameters being taken into account here. These parameters are selected in such a way that the current limit value 55 is equal to zero (corresponds to the largest displacement volume) when the pressure signal 62 is equal to a desired maximum load pressure. The limit value would be 28 bar (corresponds to the smallest displacement volume) if the pressure signal 62 were equal to zero. It goes without saying that the pressure signal 62 is always somewhat greater than zero, even when the cable winch is free of load, since the weight of the traction means already causes a load pressure. As a result, the user can only set high speeds for the rope drum when it is carrying no load or only a small load.

The output signal of the linear dependency 62 is subjected to dynamic smoothing 78 before it is used as a limit value 55 . The dynamic smoothing 78 can be implemented as a PT1 element, for example.

The correction value 74 is calculated using a PID controller. The control deviation is determined from the difference between the desired maximum load pressure already mentioned above and the pressure signal 62 . However, the actuating signal of the classic PID controller (https://de.wikipedia.org/wiki/Regler#PID-Regler) is only used as a correction signal 74 if the pressure signal 62 is greater than the desired maximum load pressure . Otherwise no correction is required, with zero being used as the correction signal. As a result, the correction signal 74 always causes the cable drum to slow down and never accelerate it.

Reference List

a

first signal path

b

second signal path

c

third signal path

i.e

fourth signal path

10

winch

11

cable drum

12

hydraulic motor

13

third pressure reducing valve

14

control signal

15

motor controller

16

directional valve

17

load

18

hydraulic target value

19

throttle

20

brake

21

brake cylinder

22

switching valve

23

brake signal

24

brake switch

30

pressure line

31

main pump

32

auxiliary pump

33

tank

34

pump controller

35

drive motor

36

first pressure sensor

37

another first pressure sensor

38

load side pressure

40

operating lever

41

first pressure reducing valve

42

second pressure reducing valve

43

second pressure sensor

44

third pressure sensor

45

first request signal

46

second request signal

47

first set pressure

48

second control pressure

50

first calculation step

51

incoming signal of the first calculation step

52

outgoing signal of the first calculation step

55

current limit

60

Maximum value calculation

61

low pass filter

62

pressure signal

63

highest reading of the first pressure sensors

64

linear dependence

65

timing

66

first signal selection

67

controller release

70

PID controller

71

PT1 member

72

selection unit

73

second calculation step (subtraction)

74

correction signal

75

limitation

76

curve

77

loading pressure

78

dynamic smoothing

80

incoming signal of the second calculation step

81

outgoing signal of the second calculation step

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102010055718 A1 [0002]

Claims (10)

Method for operating a hydraulic cable winch (10), the cable winch (10) comprising a rotatable cable drum (11) which is in rotary drive connection with at least one hydraulic motor (12), the at least one hydraulic motor (12) being driven by at least one main pump (31 ) can be supplied with pressurized fluid, with at least one request signal (45; 46) being provided, which can be continuously changed by an operator of the cable winch (10), with the at least one hydraulic motor (12) having a continuously adjustable displacement volume, with a setting - signal (14) is provided, by means of which the displacement volume of the at least one hydraulic motor (12) can be adjusted, the cable winch (10) comprising at least one first pressure sensor (36; 37), with which a load-side pressure (38) on the at least one Hydraulic motor (12) can be measured, with a pressure signal (62) depending on the measured value of the at least one first pressure sensor (36; 37), characterized in that the control signal l (14) taking into account the at least one request signal (45; 46) is calculated in several calculation steps (50; 71; 73; 75; 76), wherein in a first calculation step (50) of said calculation steps (50; 71; 73; 75; 76) an assigned outgoing signal (52) is calculated by amount Limiting an associated incoming signal (51) to a current limit value (55) is calculated, the current limit value (55) depending on the pressure signal (62). procedure after claim 1 , wherein the current limit value (55) depends exclusively on the pressure signal (62) and at least one constant parameter. procedure after claim 2 , wherein the cable drum (11) can be stopped with a switchable brake (20), with the current limit value (55) being constant when the cable drum (11) with the brake (20) is stopped, with it depending on the pressure signal ( 62) is when the brake (20) is open. procedure after claim 2 or 3 , wherein at least two first pressure sensors (37; 38) are provided, wherein the pressure signal (62) depends on the highest (63) of the corresponding measured values. procedure after claim 4 , wherein the pressure signal (62) is formed by low-pass filtering (61) from said highest measured value (63) of the at least one pressure sensor (36; 37). Procedure according to one of claims 2 until 5 , wherein the dependency between the current limit value (55) and the pressure signal (62) includes a linear dependency with exactly two parameters. Procedure according to one of claims 2 until 6 , wherein the current limit value (55) depends on the pressure signal (62) in such a way that the displacement volume of the at least one hydraulic motor (12) is limited in terms of amount to a lower value that is greater than the minimum displacement volume of the hydraulic motor if the current Limit (55) is effective. Procedure according to one of claims 2 until 7 , wherein in a second calculation step (73), the difference between an incoming signal (80) dependent on the output signal (52) of the first calculation step (50) and a correction signal (74) is formed, the control signal ( 14) is dependent on the corresponding outgoing signal (81) of the second calculation step (73), the correction signal (74) being dependent on the pressure signal in such a way that the pressure signal has an upper limit. procedure after claim 8 , the correction signal (74) being calculated using a continuous linear controller (70), the correction signal (74) only being equal to the outgoing signal of the controller (70) if the pressure signal (62) is greater than a predetermined limit pressure, the correction signal (74) otherwise being zero. procedure after claim 9 , wherein the cable drum (11) can be stopped with a switchable brake (20), the correction signal (74) also being zero when the cable drum (11) is stopped with the brake (20).

Images