Traversing hoists – Having means to prevent or dampen load oscillations – Antisway
Patent
1997-04-15
1998-06-23
Brahan, Thomas J.
Traversing hoists
Having means to prevent or dampen load oscillations
Antisway
294 814, B66C 1306
Patent
active
057692505
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method and a control apparatus for damping swaying and skew of the loading element suspended from lifting drums of a crane and the load attached to it, and for precision positioning the same in the horizontal direction and in the direction of skew.
Rope-suspended loading elements and loads of a crane tend to sway when the crane is accelerated or decelerated. Swaying of the loading element of a container crane, in particular, is harmful, as the crane should be able to deposit containers with a relatively high accuracy.
A method and apparatus of the type described above are known, for example, from Finnish Patent Application No. 943 401 (Publication No. 96677). In this apparatus, the control of the crane is implemented by a control apparatus consisting of a mechanism beam comprising three mechanically interconnected control mechanisms provided with a motor and a brake. The outermost motors of the mechanism beam comprise double rope drums to which two auxiliary ropes are always connected in such a manner that when one auxiliary rope is unwound from the rope drum, the other auxiliary rope is wound onto it. When swaying is damped and ropes are wound from one drum to another, the mechanism beam is allowed to move in the horizontal direction. The mechanism beam can be further moved in the lateral direction by a third control mechanism, which is positioned in the middle of the mechanism beam and is connected through gearing to the mechanism beam without direct connection to the auxiliary ropes.
The control apparatus disclosed in the above-mentioned application is implemented mainly mechanically, and all directions of movement are mechanically bound to each other.
SUMMARY DESCRIPTION OF THE INVENTION
The object of the present invention is to improve the method and apparatus for controlling the loading element and load of a crane in order to simplify them mechanically, and to allow the control of each auxiliary rope to be controlled independently but even more accurately and reliably than before, which maximizes the control of the loading element.
This is achieved with a control method of the invention, and a control apparatus of the invention, which is characterized by using control mechanisms mounted in the crane, and four auxiliary ropes between the control mechanisms and the loading element.
The present invention is based on the use of four identical but mechanically independent control mechanisms whose control is implemented completely electrically; the control is based on the weighing information of each auxiliary rope and the rotation speed of the motor connected to the auxiliary rope or the drum. There is always a sufficient length of rope in store on a rope drum, which automatically compensates for the different geometry of the auxiliary ropes and the lifting ropes. The forces exerted on each auxiliary rope are adjusted according to instructions given by control logic circuits to prevent the loading element and the load suspended from it from swaying. Both the damping of sway and the precision positioning of the load can be implemented by means of the control apparatus and its control logic circuits. The mechanically simple solution described above is thus achieved with an electric control system.
An essential feature of the invention is the measurement of rope forces of the auxiliary ropes with weighing sensors, and the measurement of the rotation speeds of the motors with tachometers. On the basis of these measurements, target values are calculated for the motor control devices.
According to the invention, each control logic circuit comprises a force controller for achieving and maintaining a desired rope force, a speed controller based on the rotation speed for counteracting skewing of the rope drum and the shaft of the motor, and a preamplifier of the desired rope force for compensating for the effect of force feedback on the moment reference. This sensor arrangement is an essential difference between the present invention and the solution of Fi
REFERENCES:
patent: 3743107 (1973-07-01), Verschoof
patent: 4705180 (1987-11-01), Lamer et al.
Jussila Olavi
Sorsa Timo
Brahan Thomas J.
KCI Konecranes International Corporation
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