EP1775252B1 - Method and device for the control of the load for a crane with foldable boom - Google Patents

Description

The present invention relates generally to tower cranes luffing jib. More particularly, this invention relates to a method of controlling the load of a luffing tower tower crane, as well as to a device for carrying out this method.

The figure 1 The attached drawing shows, very schematically, a tower crane luffing jib. Such a crane comprises, at the top of a mast symbolized by its vertical axis Z, an assembly rotating about this axis Z which comprises a luffing jib 2, a counter-jib 3 supporting a counterweight 4, a punch 5, and a tie rod Counter-deflection 6. The fixed length of the counter-boom 3 is designated d, while the reach of the crane, which depends on the angle of inclination α of the arrow 2, is designated by P.

Such a luffing jib crane requires for its operation, in particular to take into account the strength of its frame and the stability of the crane, to be used with a loading diagram, that is to say that each inclination angle α of the arrow 2, or each corresponding P-range, is associated with a maximum load to be lifted.

The loading pattern is established according to the crane stability conditions, the mast strength and the resistance of the slewing ring of the rotating assembly. These conditions require that a torque due to the load raised and the weight of the boom 2, which is of constant value with respect to the axis Z of the mast, not be exceeded.

To verify this condition relating to a constant torque, the simplest solution consists in measuring the force supported by the counter-balance rod 6 using a dynamometer 7, or a force measuring device. equivalent. It must then be verified, using the dynamometer 7, that the tensile force in the anti-jib tie 6 does not exceed a set value.

The variation of effort F in the dynamometer 7, as a function of the load moment M, can be written in the form of the equation: $$\mathrm{F}=\mathrm{M}/\mathrm{d}$$

ou, si l'on exprime la charge en fonction de la portée : $$\mathrm{charge}=\left(\mathrm{F}\times \mathrm{d}\right)/\mathrm{P}$$

The load moment being the product of the load by the span P, the preceding equation becomes: $$\mathrm{F}=\mathrm{P}\times \mathrm{charge}/\mathrm{d}$$

or, if one expresses the load according to the range: $$\mathrm{charge}=\left(\mathrm{F}\times \mathrm{d}\right)/\mathrm{P}$$

Curve A of the figure 4 represents the theoretical loading diagram, corresponding to this last equation, this theoretical curve A representing the load to be lifted as a function of the span P.

However, in order for the force in the counter-balance rod 6 to be really proportional to the moment of loading, as considered above, whatever the position of the arrow 2, the arrow 2, the counter-arrow must be 3 and the punch 5 are concurrent. However, by construction, it is technically difficult to articulate these three elements in one and the same point, located on the Z axis of the mast, and it is therefore forced to realize a crane construction in which the points of articulation of the boom 2, the counter-arrow 3 and the punch 5 are dissociated, as indicated by P1 and P2 on the figure 2 .

Under these conditions, which correspond to reality, the force measured in the counter-jib tie 6, for a given range and a given load, is different from the previously stated theoretical case.

ou, si l'on exprime la charge en fonction de la portée P : $$\mathrm{charge}=\left[\mathrm{F}\times \mathrm{d}\times \left(\mathrm{L}2/\mathrm{L}1\right)\right]/\mathrm{P}$$

ou encore : $$\mathrm{charge}=\left(\mathrm{L}2/\mathrm{L}1\right)\times \left[\left(\mathrm{F}\times \mathrm{d}\right)/\mathrm{P}\right]$$

The variation of force F in the dynamometer, as a function of the load moment M, can be written in this case: $$\mathrm{F}=\left[\mathrm{M}\times \left(\mathrm{The}2/\mathrm{The}1\right)\right]/\mathrm{d}$$

or, if one expresses the load according to the range P: $$\mathrm{charge}=\left[\mathrm{F}\times \mathrm{d}\times \left(\mathrm{The}2/\mathrm{The}1\right)\right]/\mathrm{P}$$

or : $$\mathrm{charge}=\left(\mathrm{The}2/\mathrm{The}1\right)\times \left[\left(\mathrm{F}\times \mathrm{d}\right)/\mathrm{P}\right]$$

In this case, the permissible load for a given range P is that of the theoretical case previously explained, multiplied by the ratio L2 / L1 between the lengths L2 and L1, respectively measured from the points of articulation P2 and P1. This relationship is reflected by the curve B on the loading chart of the figure 4 .

The load here is a function of the ratio L2 / L1, which is a ratio that is itself variable since the lengths L1 and L2 vary according to the range P. In particular, for the low ranges, therefore for a more strongly raised arrow 2, as shown in figure 2 we have: L2 <L1.

Conversely, for the largest litters, so for a lesser arrow 2, as shown by the figure 3 we have: L2> L1.

As a result, for a load moment M given, the force measured by the dynamometer is greater when the range P is maximum (arrow lowered) compared to what it is when the range P is minimal. (arrow up). In other words, the permissible load when the range is maximum will be lower than that which the crane could have lifted safely.

In other words, considering the loading chart of the figure 4 , we note that the curve B is always below the theoretical curve A, so that for a given P range the load is lower with the curve B. All the possibilities of the crane are not exploited and, in particular, the load at maximum range is less than it could be.

To illustrate the state of the art previously described, reference is here made to the patent US 5263597 , which shows a luffing jib crane, which may be a tower crane, however without counter-jib, with a tie rod connecting the end of the boom to a punch, and with a dynamometer or force measuring device placed on the pulling arrow, to measure the effort supported by this pulling. The effort measurement thus performed, combined with a pre-established loading diagram, allows here the control of the load of the luffing jib crane.

Telescopic boom cranes are also known, including truck-mounted cranes that are not tower cranes, for which various load curves are used depending on the state of elongation of the boom - see, for example, the patent. US 4039084 . This does not, however, address the particular problem, discussed above, which is unique to tower cranes luffing jib.

Based on the above, the present invention aims to optimize the loading pattern of a luffing jib tower crane, to use the crane frame at its maximum capacity, whatever the range.

For this purpose, the subject of the invention is essentially a method for controlling the load of a luffing jib tower crane, by using a pre-established loading diagram combined with a measurement of the force supported by the luffing rod. counter-boom of the crane, this method being characterized in that alternatively, depending on the range of the crane resulting from the position of its boom, at least two distinct load curves, or a first load curve used between the minimum range and intermediate range, and at least one other load curve, corresponding to a higher load moment, used between the intermediate range and the maximum range.

In a preferred embodiment of the method, object of the invention, said other load curve, used between the intermediate range and the maximum range, is a curve deduced by homothety of the first load curve, used between the range. minimum and intermediate range.

Thus, the invention consists, in principle, in creating a load curve C (see figure 4 ) whose theoretical torque is greater than that of the load curve B defined above, and which is deduced in particular from the curve B by a homothety, the two curves B and C being used alternately. More particularly, the change in the load curve is determined by the graph, and takes place at the point where the curve C intersects the curve A, in order not to put the crane in danger: the curve B is used between the minimum range Pm and the intermediate reach PO, and the curve C is used between this intermediate reach PO and the maximum reach PM.

The invention also relates to a device for controlling the load of a luffing tower tower crane, implementing the method defined above. This device is of the kind of those using at least a dynamometer or an equivalent force measuring device, associated with the jib against the jib, to measure the force supported by the tie rod; according to the invention, the at least one dynamometer, or the equivalent force measuring device, is provided with tripping means for a first effort corresponding to the first load curve, used between the minimum range and an intermediate range, and trigger means for at least one other force, greater than the previous one, corresponding to at least one other load curve, used between an intermediate range and the maximum range, means being provided to detect the passage of the arrow by the position corresponding to the intermediate range

In one embodiment of this device, the dynamometer is equipped with a first switch that is triggered for a greater force than the first load curve and at least one other switch that triggers for a greater effort than the one at least one other load curve, therefore to a force greater than the triggering force of the first switch. In particular, the dynamometer 7 can be equipped with two switches 11 and 12, the first switch 11 being used for the smallest ranges, and the second switch 12 was used for the largest ranges, up to the maximum range (PM) , the change of switch used being performed during the passage by the position of the arrow which corresponds to the aforementioned intermediate range (PO).

To detect the passage of the arrow by the position corresponding to this intermediate range, a possibility is that the lifting winch of the boom is equipped with a counting means of the turns of its drum, means that closes a switch of the kind "Limit switch" intervening for a determined number of turns, which corresponds to the passage through said intermediate range.

• en équipant la grue de deux dynamomètres distincts, intervenant respectivement pour les deux courbes de charge, au lieu d'un seul dynamomètre équipé de deux interrupteurs ;
• en plaçant le dynamomètre non pas sur le tirant de contre-flèche 6, mais sur le poinçon 5, ce qui constitue une solution équivalente car l'effort dans le poinçon est proportionnel à l'effort dans le tirant de contre-flèche ;
• en utilisant trois tronçons de courbe de charge, ou des tronçons plus nombreux, au lieu de deux courbes ;
• en utilisant tous moyens pour détecter le passage de la flèche relevable par la portée intermédiaire, provoquant le passage d'une courbe de charge à l'autre.

One would not depart from the scope of the invention, as defined in the appended claims:

• by equipping the crane with two separate dynamometers, intervening respectively for the two load curves, instead of a single dynamometer equipped with two switches;
• by placing the dynamometer not on the tie-rod 6, but on the punch 5, which constitutes an equivalent solution because the force in the punch is proportional to the force in the against-arrow tie;
• using three sections of load curve, or more sections, instead of two curves;
• using any means to detect the passage of the luffing boom by the intermediate range, causing the passage of a load curve to another.

Claims (7)

1. Method for adjusting the load of a luffing jib tower crane, by using a predetermined load diagram combined with a measurement of the force (F) borne by the counter jib tie bar (6) of the crane, characterized in that , depending on the jib radius (P) of the crane as a result of the position of its jib (2), at least two separate load curves are used alternately, either a first load curve (B) used between the minimum jib radius (Pm) and an intermediate jib radius (PO) and at least one further load curve (C), corresponding to a greater load moment (M), used between the intermediate jib radius (PO) and the maximum jib radius (PM).
2. Method according to claim 1, characterized in that said further load curve (C), used between the intermediate jib radius (PO) and the maximum jib radius (PM), is a curve obtained by homothetic transformation of the first load curve (B), used between the minimum jib radius (Pm) and the intermediate jib radius (PO).
3. Device for adjusting the load of a luffing jib tower crane for implementing the method according to claim 1 or 2, the device using at least one dynamometer (7) or an equivalent force measuring apparatus, associated with the counter jib tie bar (6) of the crane, for measuring the force (F) borne by this tie bar, characterized in that the dynamometer (7), which is at least one in number, or the equivalent force measuring apparatus, is provided with triggering means (I1) for a first force corresponding to the first load curve (B) used between the minimum jib radius (Pm) and an intermediate radius (PO) and triggering means (12) for at least one further force, greater than the aforementioned force, corresponding to at least one further load curve (C) used between an intermediate jib radius (PO) and the maximum jib radius (PM), means being provided for detecting the passage of the jib (2) through the position corresponding to the intermediate jib radius (PO).
4. Device according to claim 3, characterized in that the dynamometer (7) is fitted with a first switch (I1) which is triggered for a force greater than that of the first load curve (B) and at least one further switch (12) which is triggered for a force greater than that of at least one further load curve (C), namely at a force greater than the force for triggering the first switch (I1).
5. Device according to claim 4, characterized in that the dynamometer (7) is fitted with two switches (I1, I2), the first switch (I1) being used for the smaller jib radiuses (P) and the second switch (12) being used for larger radiuses, up to the maximum jib radius (PM), the switch used being changed at the time of passage through the position of the jib (2) which corresponds to the aforementioned intermediate jib radius (PO).
6. Device according to claim 3, characterized in that the crane is fitted with two separate dynamometers, being respectively activated for the two load curves (B, C).
7. Device according to any one of claims 3 to 6, characterized in that, for detecting the passage of the jib (2) through the position corresponding to the intermediate jib radius (PO), the luffing jib hoist (2) is fitted with a means for counting the revolutions of its drum, said means closing a switch of the "end of travel" type which is activated for a set number of revolutions, which corresponds to the passage through said intermediate jib radius (PO).

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