Traversing hoists – Methods
Patent
1996-12-03
1998-09-15
Brahan, Thomas J.
Traversing hoists
Methods
212275, B66C 1900
Patent
active
058066950
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is a method for the control of a harmonically oscillating load, in which method the load is transferred from the initial state to the final state of the oscillation of the load and to the final velocity of the point of suspension by controlling the load with control sequences, which consist of consecutively performed acceleration pulses, in which method the beginning or initial states of the oscillation of the load and the beginning or initial velocity of the point of suspension are either measured or estimated, and in which method the desired final states of oscillation of the load and the desired final velocity of the point of suspension are set by a human operator or, in the case of an automatic crane, by a computer.
A method is already known from the publication "Suboptimal control of the roof crane by using the microcomputer," by S. Yamada, H. Fujikawa, K. Matsumoto, IEEE CH1897-8/83/0000-0323, pp 323-328, in which, at constant acceleration, variable acceleration and switching times are pre-calculated and tabulated for the load suspending apparatus so that, by using the acceleration and switching times, the velocity of the load suspending apparatus, the oscillating angle of the suspended load, and the angular velocity of the oscillation of the suspended load are steered from certain starting values to desired final values. In this method, the phase plane is divided into squares, and switching times for acceleration are calculated and entered for each phase plane square. Consequently, the system moves at the desired final velocity and the suspended load is in a stationary state. The method uses constant acceleration, and the acceleration switching times are adjusted to achieve the desired final result. When using this method, if all possible starting and finishing situations are allowed, the table will be extremely large. In the method presented in the publication in question, the acceleration pulses are, in terms of absolute value, constantly large or at the value zero. In addition, the duration of the acceleration pulses is calculated iteratively and not directly by calculation.
Furthermore, the magnitude of acceleration is partly determined so that, for example, the first acceleration pulse is, in terms of magnitude, the same as the third acceleration pulse. Considering the phase plane presentation, in the above publication the position of the centre point of the trajectory of the acceleration pulse is determined, but the length of the curve varies.
In addition a method is known which, by summing the oscillation-eliminating acceleration sequences known from patent publication U.S. Pat. No. 3,517,830, succeeds in forming a velocity instruction for the load suspending apparatus which guides the load suspending apparatus to the desired final velocity in such a way that the oscillating angle of the suspended load is zero and the angular velocity of the suspended load's oscillation is zero. The use of this method is limited by the requirement for a stationary beginning situation of the suspended load and by the need to achieve a particular final situation concerning the oscillating angle and angular velocity of the suspended load. The method is not therefore suited to the guiding of a suspended load's suspension apparatus and the angular velocity of the suspended load to desired, random situations from completely random beginning values. The solution presented in publication U.S. Pat. No. 3,517,830 requires stationary beginning and final situations and its disadvantage is that it does not allow control adjustments in mid-control, but the sequence must be carried through to the end.
The disadvantage of the known methods is that they do not offer a simple, calculationally-advantageous method of calculating the velocity instructions for a suspended load's suspension apparatus, which would guide the load's suspension apparatus to a desired random final velocity, and suspended load oscillating angle, and angular velocity of the suspended load oscillating angle, starting from random
REFERENCES:
patent: 4603783 (1986-08-01), Tax et al.
patent: 4756432 (1988-07-01), Kawashima et al.
patent: 5219420 (1993-06-01), Kiiski et al.
Brahan Thomas J.
Skinner, Jr. Joel D.
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