Traversing hoists – Having random condition sensor combined with an indicator or... – Means determining overloading produced by load
Reexamination Certificate
1999-08-26
2001-12-11
Brahan, Thomas J. (Department: 3652)
Traversing hoists
Having random condition sensor combined with an indicator or...
Means determining overloading produced by load
C212S261000
Reexamination Certificate
active
06328173
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a crane having a hydraulically actuated jib system, at least one cylinder for actuating the jib system and an apparatus for monitoring the pressure in the cylinder, which indicates the crane loading, wherein the feed flow of hydraulic fluid to the cylinder is controllable by varying the cross-section of a valve.
When moving loads, the acceleration effects which occur can cause oscillations of the carrier structure of the crane or the load carried by the crane. For example, the situation may involve oscillations in a vertical direction when a load is moved in a vertical direction, that is to say when it is raised or lowered, and that movement is stopped. Such oscillations give rise to loading peaks in the carrier structure of the crane and/or uncontrolled movements of the load.
The conventional method of actively damping undesired oscillations is a regulation effect, wherein the oscillation is damped by an oscillation of the same frequency, which is phase-shifted through 180°. The method is particularly suitable for preventing the progressive build-up of oscillaticns, for example pendulum movements of loads which are being moved, in the case of portal cranes (see DE 42 38 795 A1). The time involved in determining the phase and frequency of the harmonic oscillation causing the problems is however relatively great. In particular loadings which suddenly occur are not alleviated precisely in their dangerous initial phase.
In comparison, for example DE 37 19 897 A1 has proposed that the dynamic overloadings which most frequently occur in the case of loading cranes for goods vehicles or trucks can be combated in terms of the cause thereof. In that respect, the cause is considered to be excessively fast displacement of the control lever for the hydraulic drive of a crane member. The great difference between the reference and actual values of the speed of the crane member or the reference and actual values of the valve cross-section, Without appropriate countermeasures, would cause an excessively fast change in the valve cross-section and thus excessively great acceleration of the crane. In accordance with the known proposal therefore the control signal is filtered, and the information about the position of the control lever and thus the desired final speed of the crane member is only transmitted with a delay to the control motor for varying the valve cross-section. A disadvantage with that method is in particular that it only corrects operating errors but it does not take account of the actual dynamic conditions These however are dependent not only on the control but on the respective configuration of the crane and the load as well as environmental influences (wind, or a sudden reduction or increase in load).
SUMMARY OF THE INVENTION
The object of the invention is a crane which is provided with real regulation which at the same time acts quickly, to avoid dynamic overloads.
In accordance with the invention that is achieved in that a signal is produced in dependence on the variation in pressure in relation to time which is detected in the cylinder or the variation in the loading of the piston guided in the cylinder in relation to time, which signal actuates the drive for adjusting the valve cross-section in the direction of a reduction in the detected variation in pressure or loading.
In contrast to the known apparatuses for oscillation suppression, in which excessively abrupt control signals are filtered, the regulation according to the invention is based on the measurement of a characteristic value with respect to the dynamic crane loading, with measurement being implemented directly at the crane. It is therefore not a matter of the crane operator being corrected, but of a counteracting effect only when dynamic loadings occur which threaten to endanger the carrier structure of the crane or result in undesired load movements, by virtue of the formation of a signal which actuates the drive for adjusting the valve cross-section in the direction of a reduction in the detected variation in pressure. The signal is thus independent of the reference value of the valve cross-section, which is defines by the position of a hand lever.
As the danger to the crane is basically greater with a higher level of loading, it can preferably be provided that the strength of the signal rises over-proportionally at higher pressure values.
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Lodige, H. et al.: “Aktive Schwingungsdämpfung Für Ungefederte Arbeitsmaschinen”, Ölhydraulik Und Pneumatik; Bd. 39, No. 3, Mar. 1, 1995, pp. 188-192, XP000492760.
Brahan Thomas J.
Palfinger Aktiengesellschaft
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
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