Method for damping rotational oscillations of a load-handling element of a lifting device

Abstract

A method for damping rotational oscillations of a load-handling element of a lifting device is created, wherein at least one controller parameter is determined by a rotational oscillation model of the load-handling element as a function of the lifting height (l.sub.H) and wherein, to damp the rotational oscillation of the load-handling element at any lifting height (l.sub.H), the at least one controller parameter is adapted to the lifting height (l.sub.H).

Claims

1. A method for damping rotational oscillation about a vertical axis of a load-handling element of a lifting device via a damping controller having at least one controller parameter, wherein the load-handling element is connected to a suspension element of the lifting device by at least three holding elements, the method comprising: adjusting a length of at least one holding element between the load-handling element and the suspension element by the damping controller via at least one actuator, acting on the at least one holding element, determining at least one controller parameter by a rotational oscillation model of the load-handling element as a function of a lifting height; and adapting the at least one controller parameter to the lifting height to dampen the rotational oscillation of the load-handling element at any lifting height; exciting the load-handling element to rotationally oscillate at a certain lifting height of the load-handling element; sensing, at a same time, at least an actual angle of rotation of the load-handling element about the vertical axis and an actual actuator position; and from the sensed actual angle of rotation and the actual actuator position, identifying model parameters of the rotational oscillation model of the load-handling element at the given lifting height by an identification method.

2. The method according to claim 1, wherein the at least one actuator is hydraulically or electrically actuated.

3. The method according to claim 1, wherein at least four holding elements are provided between the load-handling element and the suspension element.

4. The method according to claim 1, wherein the at least one actuator comprises at least two actuators.

5. The method according to claim 4, wherein the at least one actuator comprises one actuator per holding element.

6. The method according to claim 1, further comprising measuring the lifting height with a camera system arranged on the suspension element or on the load-handling element or by a lifting drive of the lifting device.

7. The method according to claim 1, further comprising measuring the actual angle of rotation of the load-handling element with a measuring device arranged on the suspension element or on the load-handling element.

8. The method according to claim 7, wherein the measuring device comprises a camera system or a gyro sensor.

9. The method according to claim 1, wherein the identification method is a mathematical method.

10. The method according to claim 9, wherein the mathematical method includes an online least-squares method.

11. The method according to claim 1, wherein the damping controller comprises is a state controller.

12. The method according to claim 11, wherein the state controller has five controller parameters.

13. The method according to claim 1, wherein a desired angle of rotation (.sub.soll) of the load-handling element is specified and the desired angle of rotation (.sub.soll) of the load-handling element is attained in a specified angle range.

14. The method according to claim 13, wherein the specified angle range is 10.sub.soll+10.

15. The method according to claim 1, wherein the lifting device comprises a crane, the holding elements comprise cables and the load-handling element comprises a spreader.

16. A method for damping rotational oscillation about a vertical axis of a load-handling element of a lifting device by a damping controller having at least one controller parameter, wherein the load-handling element is connected to a suspension element of the lifting device by at least three holding elements, the method comprising: adjusting a length of at least one holding element between the load-handling element and the suspension element by the damping controller via at least one actuator acting on the at least one holding element, determining at least one controller parameter by a rotational oscillation model of the load-handling element as a function of a lifting height; and adapting the at least one controller parameter to the lifting height to dampen the rotational oscillation of the load-handling element at any lifting height, wherein the rotational oscillation model is a second-order differential equation having at least three model parameters.

17. The method according to claim 16, wherein the three model parameters are a dynamic parameter, a damping parameter, and a system gain parameter.

18. A method for damping rotational oscillation about a vertical axis of a load-handling element of a lifting device by a damping controller having at least one controller parameter, wherein the load-handling element is connected to a suspension element of the lifting device by at least three holding elements he, the method comprising: adjusting a length of at least one holding element between the load-handling element and the suspension element by the damping controller via at least one actuator acting on the at least one holding element, determining at least one controller parameter by a rotational oscillation model of the load-handling element as a function of a lifting height; and adapting the at least one controller parameter to the lifting height to dampen the rotational oscillation of the load-handling element at any lifting height, wherein anti-windup protection is integrated in the damping controller, wherein actuator limits of the at least one actuator are specified to the damping controller.

19. The method according to claim 18, wherein the actuator limits of the at least one actuator is comprise a maximum permissible actuator position, a maximum permissible actuator velocity, and a maximum permissible actuator acceleration of the actuator.

20. A method for damping rotational oscillation about a vertical axis of a load-handling element of a lifting device, wherein the load-handling element is connected to a suspension element of the lifting device by at least three holding elements, the method comprising: adjusting a length of at least one holding element between the load-handling element and the suspension element via at least one actuator acting on the at least one holding element, determining at least one parameter by a rotational oscillation model of the load-handling element as a function of a lifting height; and adapting the at least one parameter to the lifting height to dampen the rotational oscillation of the load-handling element at any lifting height; exciting the load-handling element to rotationally oscillate at a certain lifting height of the load-handling element; sensing, at a same time, at least an actual angle of rotation of the load-handling element about the vertical axis and an actual actuator position; and from the sensed actual angle of rotation and the actual actuator position, identifying model parameters of the rotational oscillation model of the load-handling element at the given lifting height by an identification method.

Description

(1) The present invention is explained in greater detail below with reference to FIGS. 1 to 4, which show advantageous embodiments of the invention as schematically illustrated examples without imposing restrictions. The figures show:

(2) FIG. 1: the basic structure of a lifting device by means of a container crane,

(3) FIGS. 2a and 2b: a load-handling element including load for showing rotational oscillation,

(4) FIG. 3: a part of a schematically illustrated lifting device,

(5) FIG. 4: a controller structure of a damping controller,

(6) FIG. 5: a state estimation unit.

(7) FIG. 1 shows an example of a lifting device 1 by means of a schematically illustrated container crane 2, which is used, for example, to load and unload ships in a port. A container crane 2 usually has a supporting structure 3, which is fixedly or movably arranged on the ground. In the case of movable arrangement, the supporting structure 3 can be arranged on rails for movement in the Y direction, for example, as schematically shown in FIG. 1. Because of this degree of freedom in the Y direction, the container crane 2 can be used flexibly with respect to location. The supporting structure 3 has a boom 4, which is fixedly connected to the supporting structure 3. A suspension element 5 is usually arranged on said boom 4, which suspension element 5 can be moved in the longitudinal direction of the boom 4, i.e. in the X direction in the example shown. For example, a suspension element 5 can be mounted in guides by means of rollers. The suspension element 5 is usually connected by means of holding elements 6 to a load-handling element 7 for picking up a load 8. In the case of a container crane 2, the load 8 is usually a container 9, in most cases an ISO container having a length of 20, 40, or 45 feet and a width of 8 feet. However, there are also load-handling elements 7 that are suitable for simultaneously picking up two containers 9 next to each other (dual spreaders). For the damping method according to the invention, the type and design of the load-handling element 7 is not further relevant, however; any embodiments of the load-handling element 7 can be used. The holding elements 6 are usually designed as cables, wherein in most cases four holding elements 6 are arranged on the suspension element 5, but more or fewer holding elements 6 can also be provided, but at least three holding elements 6. In order to pick up a load 8, such as a container 9, the lifting height l.sub.H between the suspension element 5 and the load-handling element 7 can be adjusted by means of a lifting drive 10 (see FIG. 3), for example in the Z direction as shown in FIG. 1. If the holding elements 6 are designed as cables, the lifting height l.sub.H is usually adjusted by means of one or more cable winches 10a, 10b, as shown schematically in FIG. 3. To manipulate loads 8 or containers 9, the lifting device 1 or the container crane 2 can thus be moved in the direction of three axes. Because of fast movement sequences, uneven load in the container 9, or wind influences, the load-handling element 7 arranged on the holding elements 6, with the container 9 arranged on the load-handling element 7, can be excited to oscillate, as presented below by means of FIGS. 2a and 2b.

(8) FIG. 2a schematically shows a suspension element 5, on which a load-handling element 7 including a load 8 is arranged by means of four holding elements 6. The coordinate system shows the degrees of freedom of the load-handling element 7. The straight double arrows symbolize the possible directions of movement of the load-handling element 7, wherein the movement in the Y direction occurs by movement of the entire lifting device 1 in the presented example, the movement in the X direction occurs by movement of the suspension element 5 on the boom 4 (lifting device 1 and boom 4 not shown in FIG. 1a), and the movement in the Z direction occurs by the changing of the lifting height l.sub.H by means of the holding elements 6 and a lifting drive 10 (not shown). The curved double arrows symbolize the possible rotations of the load-handling element 7 about the respective axes. Rotation about the X axis or the Y axis can be compensated by the user of the lifting device 1 or of the container crane 2 relatively easily and are not described in greater detail here. Rotation about the Z axis (i.e. about the vertical axis), as shown in FIG. 2b, is very disturbing, as mentioned above, because in particular rotational oscillation of the load-handling element 7 about the Z axis would impede or delay the positioning of a load 8 in a certain location, for example on the cargo bed of a track or of a rail car.

(9) According to the invention, a method is therefore provided by means of which such rotational oscillation of a load-handling element 7 about the vertical axis can be simply and quickly damped so that fast movement processes of the load-handling element 7 with the load 8 arranged thereon are enabled, which should contribute to an increase in the efficiency of goods manipulation. A detailed description of the method is provided below by means of FIGS. 3 and 4.

(10) Of course, the described embodiment of the lifting device 1 as a container crane 2 according to FIGS. 1 to 3 should be understood merely as an example. The lifting device 1 can also be designed in any other way for the application of the method according to the invention, for example as an indoor crane, rotating tower crane, or mobile crane. All that is important is the basic function of the lifting device 1 and that the lifting device 1 has the essential components for carrying out the damping method according to the invention, as described below.

(11) The essential components of a lifting device 1 are shown in FIG. 3, in this case by means of the components of a container crane 2. The parts essential to the invention are shown. The structure and mode of operation of such cranes have already been described, are well known, and therefore do not have to be explained in greater detail. According to a preferred embodiment of the invention, four holding elements 6a, 6b, 6c, 6d, which can be designed, for example, as high-strength cables, more particularly as steel cables, are arranged between the suspension element 5 (shown schematically with dashed lines in FIG. 3) and the load-handling element 7. A lifting drive 10 is provided for raising and lowering the load-handling element 7 in the Z direction, i.e. for adjusting the lifting height l.sub.H. In the example according to FIG. 3, the lifting drive 10 is formed by cable winches 10a and 10b, wherein two holding elements 6a, 6c and 6b, 6d, respectively, are wound on each cable winch 10a, 10b. Of course, other forms of the lifting drive are also conceivable. To carry out the method according to the invention, at least one actuator 11a, 11 b, 11c, 11 d is provided on at least one holding element 6a, 6b, 6c, 6d for changing the length of the holding element 6. However, it is advantageous if an actuator 11a, 11 b, 11c, 11d is provided on each holding element 6a, 6b, 6c, 6d. Four holding elements 6a, 6b, 6c, 6d each having one actuator 11a, 11 b, 11c, 11 d are preferably arranged on the lifting device 1, as can be seen in FIG. 3.

(12) In the case of a lifting drive 10 as shown in FIG. 3, the holding elements 6a, 6b, 6c, 6d are guided by means of deflecting rollers, which are arranged on the load-handling element 7. The free end of each of the holding elements 6a, 6b, 6c, 6d is fastened to a stationary holding point, for example on the suspension element 5. In this embodiment, an actuator 11a, 11b, 11c, 11d is preferably fastened to a stationary holding point, for example on the suspension element 5, and the free end of the holding elements 6a, 6b, 6c, 6d is fastened to the actuator 11a, 11b, 11c, 11d. Consequently, the length of a holding element 6a, 6b, 6c, 6d can be adjusted by adjustment of the actuator 11a, 11 b, 11c, 11d, whereby the distance between the suspension element 5 and the load-handling element 7 is also adjusted.

(13) An actuator 11a, 11b, 11c, 11d can be controlled by a damping controller 12 to change the length of the corresponding holding element 6a, 6b, 6c, 6d between the suspension element 5 and the load-handling element 7, and, in the event of this, preferably at least one desired actuator position s.sub.soll or one desired actuator velocity v.sub.soll can be specified to the actuator 11a, 11b, 11c, 11d. For the damping control, at least an actual actuator position s.sub.ist of the at least one actuator 11a, 11b, 11c, 11 d can be captured by the damping controller 12 (damping controller 12 not shown in FIG. 3). For example, the damping controller 12 can be designed as a separate component in the form of hardware and/or software or can be implemented in an existing crane control system. As described in detail below, the at least one actuator 11a, 11b, 11c, 11 d can be controlled by the damping controller 12 in such a way that, by the changing of the actuator position and/or actuator velocity, the load-handling element 7 is excited to rotationally oscillate (as symbolized by the double arrow in FIG. 3), or the at least one actuator 11a, 11b, 11c, 11d can be controlled in such a way that rotational oscillation of the load-handling element 7 is damped.

(14) In the presented embodiment, preferably the lengths of two diagonally opposite holding elements 6a, 6b between the suspension element 5 and the load-handling element 7 are increased by means of the corresponding actuators 11a, 11b and the lengths of the two other diagonally opposite holding elements 6c, 6d are decreased by means of the corresponding actuators 11c, 11d, or vice versa, to stimulate or damp rotational oscillation. However, it is also possible, for example, that only three holding elements 6 are arranged between the suspension element 5 and the load-handling element 7 and only one actuator 11 is arranged for changing the length of one of the three holding elements 6. It is only important that the length of at least one holding element 6a, 6b, 6c, 6d between the suspension element 5 and the load-handling element 7 can be changed by means of the at least one actuator 11a, 11b, 11c, 11 d so that rotational oscillation of the load-handling element 7 about the vertical axis, in FIG. 3 about the Z axis, can be stimulated or damped.

(15) An actuator 11a, 11b, 11c, 11 d can be implemented in any manner; a hydraulic or electrical embodiment that allows length adjustment is preferably used. If, as shown in FIG. 3, actuators 11a, 11b, 11c, 11 d are used in the form of hydraulic cylinders, the energy for actuating the actuators 11a, 11b, 11c, 11 d can be drawn from an existing hydraulic system, for example. However, an actuator 11a, 11b, 11c, 11 d can also, for example, be implemented as a cable winch and be electrically controlled, wherein the actuating energy can be drawn from an existing power grid. Other embodiments of an actuator 11a, 11b, 11c, 11d that are suitable for changing the length of a holding element 6 between the suspension element 5 and the load-handling element 7 are also conceivable. In particular, an actuator 11a, 11 b, 11c, 11d must handle the expected forces during the raising and lowering of a load 8. To effect a required length change of a holding element 6a, 6b, 6c, 6d under certain loading, an actuator 11a, 11b, 11c, 11 d can also have an additional speed-changing gearset, for example.

(16) To carry out the damping method according to the invention, it is provided that at least an actual angle of rotation .sub.ist of the load-handling element 7 about the Z axis (or vertical axis) can be sensed; for example, a measuring device 14 in the form of a camera system can be provided, wherein a camera 14a is arranged on the suspension element 5 and a measurement element 14b, which interacts with the camera 14a, is arranged on the load-handling element 7, or vice versa. However, the actual angle of rotation .sub.ist can also be measured in another way, for example by means of a gyro sensor. What is important is that a measurement signal for the actual angle of rotation .sub.ist is available, which measurement signal can be fed to the damping controller 12. It is also provided that the lifting height l.sub.H between the suspension element 5 and the load-handling element 7 can be sensed. For example, the lifting height l.sub.H can be sensed by means of the lifting drive 10, for example in the form of a position signal of a cable winch 10a, 10b, said position signal being available in the crane control system. The lifting height l.sub.H could also be obtained from the crane control system. However, the lifting height l.sub.H can also be sensed, for example, by means of the measuring device 14, for example by means of a camera system that can sense both the lifting height l.sub.H and the actual angle of rotation .sub.ist. Such measuring devices 14 are known in the prior art and therefore are not discussed in greater detail here.

(17) The individual steps of the damping method are described below by means of FIG. 4.

(18) FIG. 4 shows a block diagram of a possible embodiment of the control structure according to the invention, with a damping controller 12, which, as already explained, can be implemented either as a separate component or preferably in the control system of the lifting device 1, and with a controlled system 15, which is controlled by the damping controller 12. In the embodiment example shown, the damping controller 12 is implemented as a state controller 13. However, in principle any other suitable controller can be used. The controlled system 15 is the system described by means of FIG. 3. The setpoint of the damping controller 12 is a desired angle of rotation .sub.soll of the load-handling element 7 and the manipulated variable is preferably a desired actuator position s.sub.soll of the at least one actuator 11a, 11b, 11c, 11d. Alternatively, a desired actuator velocity v.sub.soll can be used as the manipulated variable instead of the desired actuator position s.sub.soll. As already described, the actual angle of rotation .sub.ist can be sensed by means of a measuring device 14, for example by means of a camera system. As feedback, at least the sensed actual angle of rotation .sub.ist of the load-handling element 7 is fed to the damping controller 12 (and, in the case of the use of the desired actuator velocity v.sub.soll as the manipulated variable, also the sensed actual actuator position s.sub.ist). It would also be conceivable to additionally sense an actual angular velocity {dot over ()}.sub.ist and to feed the same to the damping controller 12, whereby the damping control could be improved further. Of course, an actual angular velocity {dot over ()}.sub.ist or an actual angular acceleration {umlaut over ()}.sub.ist can also be derived from the sensed actual angle of rotation .sub.ist if necessary, for example by derivation with respect to time.

(19) The required actual values, in particular the actual angle of rotation .sub.ist and possibly derivatives thereof with respect to time, either can be directly measured or can, at least in part, also be estimated in an observer. An advantage of the use of actual values, such as an actual angle of rotation .sub.ist, estimated by means of an observer is that any measurement noise of measurement values of a measuring device 14, which measurement noise is undesired for the damping control, can thereby be avoided. This is the main reason why, in a preferred embodiment according to FIG. 3, the actual angle of rotation .sub.ist is measured by means of a measuring device 14 but nevertheless an estimated actual angle of rotation {circumflex over ()}.sub.ist is used for the damping control (an estimated actual angular velocity {dot over ({circumflex over ()})}.sub.ist could additionally be used; see FIG. 5). Any suitable and well known observers, such as a Kalman filter, that determine estimated values of the required actual values can be used in this case. Below, estimated values are marked with {circumflex over ()} where applicable.

(20) However, it should be noted that the controller structure is secondary for the damping method according to the invention and in principle any suitable controller could be used. The required actual values are then fed to the damping controller 12 as measured values or estimated values, depending on the implementation.

(21) The damping controller 12 has at least one controller parameter, preferably five controller parameters. By means of the one or more controller parameters, the characteristics of the control can be set, for example response behavior, dynamics, overshoot, damping, etc., wherein one of the properties can be adjusted by means of each controller parameter. If several properties should be influenced, a corresponding number of controller parameters is required. The system behavior of the controlled system can thus be adapted.

(22) To design a suitable damping controller 12, the controlled system, i.e. the technical system to be controlled (e.g. as shown in FIG. 3), must first be modeled. In the present case, the rotational oscillation behavior of the load-handling element 7 about the Z axis is modeled by means of a rotational oscillation model, for example by means of a second-order differential equation in the form {umlaut over ()}+{dot over ()}+=i.sub.s. The three model parameters of said rotational oscillation model are a dynamic parameter , a damping parameter , and a system gain parameter i.sub., which are defined, for example, as

(23) $=\frac{J_{}}{c_{}\left(1_H\right)}$
with the mass moment of inertia J.sub. of the load 8 together with the load-handling element 7 and

(24) $=\frac{d_{}}{c_{}\left(1_H\right)}$
with a spring constant c.sub. and a damping constant d.sub. of the oscillation system. The spring constant c.sub. is modeled in dependence on the lifting height l.sub.H.

(25) Said rotational oscillation model should be understood merely as an example. Other rotational oscillation models that are able to model or approximate the real rotational oscillation could also be used.

(26) The model parameters of the rotational oscillation model, for example , , and i.sub., can be known but are generally unknown. Therefore, the model parameters can be identified by means of an identification method in a first step. Such identification methods are well known, for example from Isermann, R.: Identifikation dynamischer Systeme, 2nd edition, Springer-Verlag, 1992 or Ljung, L.: System Identification: Theory for the User, 2nd edition, Prentice Hall, 2009, and therefore are not discussed in greater detail here. Common to the identification methods is that the system to be identified is excited with an input function (e.g. a step function) and the output variable is sensed and is compared with an output variable of the model. The model parameters are then varied to minimize the error between the measured output variable and the output variable calculated by means of the model. For possibly necessary identification, the damping controller 12 can be used to excite the load-handling element 7 with the load 8 arranged thereon to rotationally oscillate about the Z axis at a certain lifting height l.sub.H. For this purpose, a separate excitation controller, for example in the form of a bang-bang controller, can be implemented in the damping controller 12. By means of the bang-bang controller, the at least one actuator 11a, 11b, 11c, 11d is controlled, for example, with the maximum possible desired actuator velocity v.sub.soll in accordance with the actual angle of rotation .sub.ist of the load-handling element 7. This means that, for example, the at least one actuator 11a, 11b, 11c, 11d is controlled with the maximum possible negative actuator velocity v at an angle of rotation .sub.ist0 of the load-handling element 7 and the at least one actuator 11a, 11b, 11c, 11d is controlled with the maximum possible positive actuator velocity v at an angle of rotation .sub.ist0 of the load-handling element 7. In the case of an embodiment of the lifting device 1 according to FIG. 3 with four holding elements 6a, 6b, 6c, 6d and four actuators 11a, 11b, 11c, 11d interacting therewith, the excitation advantageously occurs oppositely, in that, for example, the actuators 11a, 11 b are controlled with the maximum possible positive actuator velocity v and the actuators 11c, 11d are controlled with the maximum possible negative actuator velocity v, or vice versa. The excitation to rotational oscillation can occur at any fixed lifting height l.sub.H of the load-handling element 7. From the stimulated rotational oscillation of the load-handling element 7, the damping controller 12 determines the model parameters of the implemented rotational oscillation model at the specified lifting height l.sub.H on the basis of the sensed actual angle of rotation .sub.ist of the load-handling element 7 and the sensed actual actuator position s.sub.ist of the at least one actuator 11a, 11b, 11c, 11d by means of an identification method. In the case of the rotational oscillation model above, the dynamic parameter and the damping parameter are preferably first determined, and thereafter the system gain parameter i.sub. is determined preferably at a standstill of the at least one actuator 11a, 11b, 11c, 11 d (actual actuator velocity v.sub.ist=0). According to one embodiment of the invention, a mathematical online least-squares method is used as an identification method to identify the model parameters, but the use of other methods, such as offline least-square methods or optimization-based methods, would also be conceivable.

(27) With the known (previously known or identified) model parameters, a damping controller 12 can then be designed for the rotational oscillation model. For this purpose, a suitable controller structure is selected, such as a PID controller or a state controller. Of course, every controller structure has a number of controller parameters K.sub.k, k1, that must be set by means of a controller design method in such a way that desired control behavior results. Such controller design methods are likewise well known and are therefore not described in detail. The frequency response method, the root-locus method, controller design by pole placement, and the Riccati method are mentioned as examples, and there are of course many other methods. However, neither the specific controller structure nor the specific controller design method is important for the present invention. The desired control behavior too can be selected essentially as desired for the invention, of course while taking into consideration stability criteria and other boundary conditions. For the invention, it is only important that the controller parameters are defined in dependence on the lifting height l.sub.H. This too can be accomplished in very different ways.

(28) It would be conceivable to identify the model parameters for different lifting heights l.sub.H and to then determine the controller parameters K.sub.k for each of the different lifting heights l.sub.H. In this way, characteristic curves of the controller parameters K.sub.k in dependence on the lifting height l.sub.H or characteristic maps in dependence on the lifting height l.sub.H and other variables, such as a mass moment of inertia J.sub., can be constructed. This would of course be very complex and impractical. Therefore, the controller parameters K.sub.k of the damping controller 12 are preferably specified as a relationship expressed by a formula, as a function of at least the lifting height l.sub.H and optionally other model parameters, thus for example K.sub.k=f(l.sub.H) or K.sub.k=f(l.sub.H, . . . ). Thus, the controller parameters K.sub.k have to be defined only for one lifting height l.sub.H and can then be converted to other lifting heights l.sub.H in a simple manner. However, it is also possible to calculate the controller parameters K.sub.k for different lifting heights l.sub.H offline from the relationship expressed by a formula and to create a characteristic curve or a characteristic map therefrom, which is then used subsequently.

(29) For the damping control, the controller parameters K.sub.k are adapted to the current lifting height l.sub.H in each time increment of the control, for example by read-out from a characteristic map or by calculation. The damping controller 12 then uses the adapted controller parameters K.sub.k to determine the manipulated variable, which is set by means of the at least one actuator 11a, 11b, 11c, 11d in the time increment in question. The controller parameters K.sub.k are adapted to the current lifting height l.sub.H in such a way that rotational oscillation of the load-handling element 7 can be optimally damped at any lifting height l.sub.H.

(30) In particular in the case of a lifting device 1 having a load-handling element 7, it is common to use different load-handling elements 7 or size-adjustable load-handling elements 7 for different loads 8, e.g. for containers of different size. Of course, this would directly affect the mass moment of inertia J.sub.. Therefore, it can be provided that the procedure above is carried out for different load-handling elements 7. Different controller parameters K.sub.k would thus be obtained for different load-handling elements 7.

(31) The method according to the invention is explained below by means of a specific embodiment example. A rotational oscillation model in the form {umlaut over ()}+{dot over ()}+=i.sub.s, as described above, is used. The model parameters of the rotational oscillation model, e.g. , , and i.sub., are identified for a certain lifting height l.sub.H as described. A state controller 13, as shown in FIG. 4, is used as the controller structure for the damping controller 12 because of the good control performance of said state controller. Five parameters K.sub.I, K.sub.P, K.sub.1, K.sub.2, K.sub.FF are provided as controller parameters K.sub.k. For the design of the state controller 13, the system to be controlled is brought into a state space representation by means of the rotational oscillation model, as the controlled system 15, for example in the form

(32) $\frac{d}{\mathrm{dt}}\left[\begin{array}{c}s\\ \\ \stackrel{.}{}\\ e_{}\end{array}\right]=\left[\begin{array}{cccc}0& 0& 0& 0\\ 0& 0& 1& 0\\ \frac{i_{}}{}& -\frac{1}{}& -\frac{}{}& 0\\ 0& -1& 0& 0\end{array}\right]\left[\begin{array}{c}s\\ \\ \stackrel{.}{}\\ e_{}\end{array}\right]+\left[\begin{array}{c}1\\ 0\\ 0\\ 0\end{array}\right]v$

(33) The actuator position s, the angle of rotation , the angular velocity {dot over ()}, and a deviation e.sub. between the desired angle of rotation .sub.soll and the actual angle of rotation .sub.ist are used as states of the system. The controller parameters K.sub.k were defined as follows as a function of the lifting height l.sub.H, which is found in the model parameters

(34) $=\frac{J_{}}{c_{}\left(1_H\right)}\mathrm{and}=\frac{d_{}}{c_{}\left(1_H\right)}.$
d.sub.0 is a damping constant of the closed control loop; i.e. the nearly undamped system is converted into a damped system by means of the damping controller 12. The parameters .sub.i determine the dynamics and the response behavior of the control loop and are linked to the system properties of the rotational oscillation model to be identified (the index i0 stands for the number of parameters of the damping controller; in the presented example, these are the parameters .sub.0, .sub.1, .sub.2). The damping constant d.sub.0 and the parameters .sub.i are preferably pre-parameterized or predefined but can be adapted by the user if necessary.

(35) $K_p=2d_0{}_0+{}_1+{}_2$$K_1=\frac{1}{i_{}{K}_p}\left(\left(2d_0{}_0{}_1{}_2+\left({}_1+{}_2\right){}_0^2\right)-K_p\right)$$K_2=\frac{1}{i_{}{K}_p}\left(\left(2d_0{}_0\left({}_1+{}_2\right)+{}_0^2+{}_1{}_2\right)-1-K_p\right)$$K_I=\frac{1}{i_{}{K}_p}\left({}_0^2{}_1{}_2\right)$$K_{\mathrm{FF}}=K_2+\frac{1}{i_{}}$

(36) In the damping controller 12, the controller parameters of the state controller 13 are then calculated by means of the current lifting height l.sub.H and used as the basis of the control in each time increment of the control. Thus, the rotational oscillation of the load-handling element 7 can be effectively damped during a lifting process, because the damping controller 12 automatically adapts to the current lifting height l.sub.H.

(37) As a manipulated variable of the control, the damping controller 12 can determine an actuator position s.sub.soll to be set or an actuator velocity v.sub.soll for the at least one actuator 11a, 11 b, 11c, 11d and output the same at an interface 16. For this purpose, the damping controller 12 receives the required actual values, such as the actual position s.sub.ist of the at least one actuator 11a, 11b, 11c, 11d and the actual angle of rotation .sub.ist of the load-handling element 7, via an interface 17. The derivative of the actual angle of rotation .sub.ist with respect to time can be determined in the damping controller 12 or is measured.

(38) Alternatively, a state estimation unit 20 (FIG. 5), in the form of hardware and/or software, can be provided, which determines estimated values for the required input variables of the damping controller 12, here for example an estimated actual angle of rotation {circumflex over ()}.sub.ist and an estimated actual angular velocity {dot over ({circumflex over ()})}.sub.ist, from measured actual values, e.g. of the actual angle of rotation .sub.ist of the load-handling element 7. The state estimation unit 20 can be implemented as a well known Kalman filter, for example. The rotational oscillation model can also be used in the state estimation unit 20 for this purpose.

(39) A desired angle of rotation .sub.soll of the load-handling element 7 is specified to the damping controller 12 and is attained by means of the damping controller 12. Normally a desired angle of rotation .sub.soll=0 is specified, and therefore rotational oscillations about a defined zero position are counteracted. However, a desired angle of rotation .sub.soll deviating therefrom can also be specified, and therefore the load-handling element 7 is controlled to this angle by the damping controller 12 and independently of the lifting device 1 and also rotational oscillations about this angle are damped. For example, a load 8, such as a container 9, can thus be rotated in a specified angle range and thus also loaded onto a cargo bed of an inaccurately positioned truck, for example. An additional device for rotating the load-handling element 7 about the vertical axis is not required for this purpose. Depending on the type and design of the lifting device 1 and the components thereof, an angle of rotation of the load-handling element 7 can be set in a range of, for example, 10 by the damping controller 12.

(40) According to an advantageous embodiment, anti-windup protection is integrated in the damping controller 12, wherein actuator limits of the at least one actuator 11, more particularly a maximum/minimum permissible actuator position s.sub.zul, a maximum/minimum permissible actuator velocity v.sub.zul, and a maximum/minimum permissible actuator acceleration a.sub.zul of the actuator 11, are specified to the damping controller 12. By means of said integrated anti-windup protection, the damping controller 12 can be adapted to the design of the one or more available actuators 11 of the lifting device 1. To damp the rotational oscillation of the load-handling element 7, the damping controller 12, as described, calculates a manipulated variable of the at least one actuator 11, such as the desired actuator velocity v.sub.soll. If said desired actuator velocity v.sub.soll exceeds a maximum permissible actuator limit, such as the actuator velocity v.sub.zul, the desired actuator velocity v.sub.soll is limited to this maximum permissible actuator velocity v.sub.ad. Without actuator limits or anti-windup protection, it could happen that, for example, the damping controller 12 calculates an excessively high desired actuator velocity v.sub.soll, which the at least one actuator 11 could not follow because of the design thereof. This would lead to a control error, and the damping controller 12, in particular the integrator integrated in the damping controller 12, would attempt to compensate said control error in that the manipulated variable, e.g. the desired actuator velocity v.sub.soll, would be increased further. This boosting of the damping controller 12 or in particular of the integrator integrated in the damping controller could lead to destabilization of the damping controller 12, which can be reliably avoided by the integrated anti-windup protection. In addition, a desired actuator acceleration a.sub.soll can also be calculated from the desired actuator velocity v.sub.soll and can be compared with a maximum/minimum permissible actuator acceleration a.sub.zul of the corresponding actuator 11a, 11b, 11c, 11d. If said maximum/minimum permissible actuator acceleration a.sub.zul is exceeded, this can likewise be taken into account with a limitation of the desired actuator velocity v.sub.soll. Thus, different embodiments and sizes of actuators 11a, 11b, 11c, 11d can be taken into account in the damping controller, whereby the method can be very flexibly applied to a wide range of lifting devices 1.