Procedure for damping the sway of the load of a crane

Abstract: Procedure for damping the sway of the load (2) moved by the carriage (1) of a crane, said load being suspended on at least one hoisting rope (3). The damping is achieved by using a discrete time control system whose control interval is varied in accordance with the hoisting rope length (L) while the control parameters remain constant.

Description: The present invention relates to a procedure for damping the sway of the load moved by the carriage of a crane, said load being suspended on at least one hoisting rope. In the control procedures currently used for damping the load sway in cases where the rope length may change during the lifting operation, several damping control parameters have to be trimmed during use. This trimming requires a large amount of computation. In addition, the trimming procedures currently used for damping the load sway require a precise determination of the position of the load. For this reason, in the currently used procedures a detector for measuring the load position must be placed on the load in many cases. DE-OS 1 531 210 discloses a procedure for damping the sway of a crane load. The carriage has to be moved with a fixed rope length. After stopping the carriage a correction signal is outputted after time corresponding to the square root of the fixed rope length. However, this procedure is not applicable in cases when the rope length of the crane is altered during the movement of the carriage. The object of the present invention is to eliminate the drawbacks referred to above. The procedure of the invention for damping the sway of the load of a crane is characterized by the features of claim 1. The preferred embodiments of the invention are presented in the other claims. In the procedure of the invention, no re-trimming of the control parameters is required. This reduces the amount of computation. Moreover, in the procedure of the invention, the load position needs not be determined. In the following, the invention is described in detail by the aid of an example by referring to the drawing attached, representing a simplified view of a carriage-and-load system. The figure shows a carriage 1, a load 2 and a hoisting rope 3. The carriage 1 moves on wheels 4 along rails 5. The hoisting rope 3 is wound on a reel 6. The mechanism moving the carriage 1 and the hoisting motor rotating the reel 6 are not shown in the figure. Suppose that the motor hoisting the load 2 works nearly ideally, in which case the desired hoisting or lowering speed of the load is achieved in a very short time (the time needed for acceleration is not taken into account). Suppose further that the hoisting or lowering speed changes relatively slowly as compared to the rest of the dynamics of the crane. Leaving the dynamics of the motor drives out of account, the dynamics of the carriage-and-load system depends on the hoisting rope length L, the mass m L of the load and the mass m T of the carriage. Thus the force f T in the figure corresponds to the ideal carriage control moment. Equation 1 represents the transfer function of an ideal moment controlled crane, where f T is the control force, x T is the carriage position, δ is the damping resulting from the linear friction, and The internal dry (coulomb) friction of the motor drives complicates the dynamics of the system and leads to non-linearities. By using fast tachometer feedback and a speed reference, these difficulties can be eliminated. In this way, the internal equations of the system are simplified. They are independent of the friction terms, the reaction forces resulting from the mass of the load, and therefore also of the masses. Since the load position and swing are controlled by a single control signal, a new artificial transfer function is formed, in which the swing angle  and the carriage position x T are added together. The adjustable artificial output is defined as Ω = x T + β , r T is a speed reference given by a computer and β is a weighting coefficient. Kv and Kα are parameters. The time constant of the simplified motor drive model is assumed to be zero. The angle  is the angle of the rope relative to the vertical direction. The system uses fixed-parameter control with a variable control interval. As the controller has fixed parameters, the control algorithm needs only be computed once. After that, only the control interval and the gain are varied in accordance with the hoisting rope length. The control interval is proportional to the square root of the rope length, as shown by equation 2. The constant parameters are preset for a given rope length, i.e. the reference length. The control interval is of the order of 100 ms. It is obvious to the person skilled in the art that different embodiments of the invention are not restricted to the example described above, but that they may instead be varied within the scope of the following claims. The damping procedure of the invention is also applicable in open systems. The discrete time control can be implemented e.g. using a computer with a suitable control program.

Claims: Procedure for damping the sway of the load, moved by the carriage of a crane, said load being suspended on at least one hoisting rope (3), wherein the length (L) of the hoisting rope is measured, characterized in that the length (L) of the hoisting rope varies during the movement of the carriage, that said procedure uses discrete time control, that the control interval of the discrete time control system is varied with the hoisting rope length (L) while the control parameters of the real crane system remain constant. Procedure according to claim 1, characterized in that the load position and swing are controlled by a single control signal, and that the control procedure employs a transfer function in which at least the swing angle () and the carriage position (x T ) are summed. Procedure according to claim 1 or 2, characterized in that the swing angle () and the carriage position (x T ) are summed by multiplying at least one of these factors by a weighting coefficient (β). Procedure according to one of claims 1 - 3, characterized in that the control interval is proportional to the square root of the length of the hoisting rope. Procedure according to one of claims 1 - 4, characterized in that the constant parameters are preset for a given hoisting rope length.

Inventors: VIRKKUNEN JOUKO, VIRKKUNEN, JOUKO
Applicants: KCI KONE CRANES INT OY, KCI KONECRANES INTERNATIONAL CORPORATION
Application year: 1990
Main classification: B66C13
IPC codes: B66C13