Traversing hoists – Having means to prevent or dampen load oscillations – Antisway
Patent
1996-03-11
1998-10-20
Brahan, Thomas J.
Traversing hoists
Having means to prevent or dampen load oscillations
Antisway
212223, B66C 1304
Patent
active
058233695
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns a control device for automatically stopping the swiveling of cranes, which automatically stops the swiveling operation of a crane which has a suspended load, without any swinging of the load.
BACKGROUND ART
A technique of this type is described in a paper titled "Anti-Swing Control of the Overhead Crane Using Linear Feedback", by A. J. Ridout, Journal of Electrical and Electronics Engineering, Australia--IE Aust. & IREE Aust. Vol. 19, No. 1/2. In this paper, it is indicated that in cases where the upper end of a pendulum is decelerated at a constant acceleration in a state where there is no swinging of the pendulum, the pendulum can be stopped without swinging if the pendulum is stopped after the time corresponding to the period of the pendulum.
Specifically, in the case of a pendulum consisting of a degree of freedom of linear advance of x and a swinging angle of .theta., as is shown in FIG. 7, if there is no swinging of the load under the initial conditions, i. e., if .theta.=d.theta./dt=O, then, even if x is controlled from that point with a constant acceleration for the time of the period T of the pendulum, there will be no swinging of the load at the end, so that .theta.=d.theta./dt=O (see FIG. 8).
In Japanese Patent Application Kokai No. 3-18596, this characteristic of a pendulum is applied to rotary type cranes. The permissible conditions for the angular acceleration of swiveling based on the lateral bending strength of the boom are calculated from the swiveling radius of the suspended load, weight, inertial moment of the boom and permissible load of the boom, and swiveling is braked and stopped at a constant angular acceleration .beta. indicated by the following equation. is the swinging period of the suspended load, and n is the smallest natural number which is such that .beta. satisfies the abovementioned permissible conditions.
However, the rotary body and boom of an actual crane are elastic bodies; accordingly, even in the case of an angular velocity which causes no problems in terms of the strength of the boom, there is a possibility that flexing or elastic vibration may be induced in the rotary body or boom by such an angular velocity. Furthermore, if elastic vibration occurs, not only will the angular acceleration at the boom tip position not show a smooth deceleration as desired, but such elastic vibration may actually cause swinging of the suspended load. For example, FIGS. 9 (a) and 9 (b) illustrate cases in which a command for a constantly decelerating angular acceleration from steady swiveling in a suspended-load state at a certain boom attitude has been given. In FIGS. 9 (a) and 9 (b), the deceleration control time is different. In both FIGS. 9 (a) and 9 (b), the decelerating angular acceleration satisfies the boom strength conditions; however, in the case of FIG. 9 (a), where the deceleration time is short, elastic vibration is induced in the rotary body and boom of the crane, so that the boom tip shows considerable vibration. Accordingly, in a crane, the decelerating angular acceleration used to control the angular velocity of the boom tip is governed by the limiting value of the control system controlling the angular velocity of swiveling of the crane which takes such elastic vibration into consideration. In other words, even before the boom root stress reaches the point of yielding, elastic deformation results in a great change in characteristics with respect to the boom tip angular velocity control system, so that the limiting angular acceleration of the rotary body of the crane must be determined from the dynamic characteristics of the swiveling speed control system including such elastic deformation.
The present invention was designed in the light of such facts; the object of the present invention is to provide a control device for automatically stopping the swiveling of cranes which eliminates the effects of elastic vibration and thus insures good stopping precision.
DISCLOSURE OF THE INVENTION
The present invention is chara
Brahan Thomas J.
Kabushiki Kaisha Komatsu Seisakusho
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