AU2006203257B2

AU2006203257B2 - Method and device for adjusting the load of a luffing jib tower crane

Info

Publication number: AU2006203257B2
Application number: AU2006203257A
Authority: AU
Inventors: Jean-Pierre Gautier; Michel Lissandre
Original assignee: Manitowoc Crane Group France SAS
Current assignee: Manitowoc Crane Group France SAS
Priority date: 2005-08-02
Filing date: 2006-08-01
Publication date: 2011-05-19
Anticipated expiration: 2026-08-01
Also published as: FR2889513A1; CN1907836A; ES2373052T3; CN1907836B; FR2889513B1; AU2006203257A1; EP1775252A1; MY141274A; EP1775252B1

Description

Pool Section 29 Regulation 3.2(2) AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: Method and device for adjusting the load of a luffing jib tower crane The following statement is a full description of this invention, including the best method of performing it known to us: I METHOD AND DEVICE FOR ADJUSTING THE LOAD OF A LUFFING JIB TOWER CRANE The present invention relates generally to luffing jib tower cranes. More 5 particularly, this invention relates to a method for adjusting the load of a luffing jib tower crane, in addition to a device for implementing this method. Figure 1 of the accompanying drawings shows, very schematically, a luffing jib tower crane. Such a crane includes, at the top of a mast symbolized by its vertical axis Z, an assembly rotating about this axis Z which includes a luffing 10 jib 2, a counter jib 3 bearing a counterweight 4, a stay 5 and a counter jib tie bar 6. The fixed length of the counter jib 3 is denoted by d, whilst the radius of the crane which depends on the angle of inclination a of the jib 2, is denoted by P. To function, such a luffing jib crane needs to be used with a load diagram, i.e. a maximum lifting load is associated with each angle of inclination a of the jib 15 2 or with each corresponding radius P, in particular to take account of the resistance of its framework and the stability of the crane. The load diagram is created according to the conditions of stability of the crane, the resistance of the mast and the resistance of the slewing ring of the rotating assembly. These conditions require that a torque due to the load lifted 20 and to the weight of the jib 2, which is a constant value relative to the axis Z of the mast, is not exceeded. To check this condition relative to a constant torque, the simplest solution consists in measuring the force borne by the counter jib tie bar 6 using a dynamometer 7 or an equivalent apparatus for measuring force. It is therefore 25 necessary to check, using the dynamometer 7, that the tensile force on the counter jib tie bar 6 does not exceed a set value.

-2 The variation of force F in the dynamometer 7, depending on the load moment M, may be expressed in the form of an equation: 5 F = M/d If the load moment is the product of the load times the radius P, the preceding equation becomes: 10 F = P x load/d or, if the load is expressed according to the radius: 15 load = (F x d)/P The curve A of figure 4 shows the theoretical load diagram, corresponding to the latter equation, this theoretical curve A showing the load to be lifted, 20 depending on the radius P. However, so that the force on the counter jib tie bar 6 is actually proportional to the load moment, as considered above, whatever the position of the jib 2, 25 it is necessary for the jib 2, the counter jib 3 and the stay 5 to be convergent. Because of its construction, it is technically difficult to articulate these three elements at the same point, located on the Z axis of the mast and the construction of the crane is 30 therefore restricted to being such that the pivot points of the jib 2, the counter jib 3 and the stay 5 are separate, as indicated by P1 and P2 on figure 2. In these conditions, which correspond to a real-life 35 situation, the force measured in the counter jib tie bar 6 for a given radius and load is different from the aforementioned theoretical example.

-3 The force variation F in the dynamometer, depending on the load moment M, may be expressed in this case as: F = [M x (L2/Ll)]/d 5 or, if the load is expressed according to the radius P: load = [F x d x (L2/Ll)]/P 10 or even: load = (L2/Ll) x [(F x d)/P] In this case, the admissible load for a given radius P 15 is that of the aforementioned theoretical example, multiplied by the ratio L2/L1 between the lengths L2 and L1, respectively measured from the articulation points P2 and P1. This relationship is translated by the curve B on the load diagram of figure 4. 20 In this case, the load depends on the ratio L2/L1 which is itself a variable ratio since the lengths Ll and L2 vary according to the radius P. In particular for small radiuses, namely for a jib 2 lifted higher, L2 < L1, as 25 figure 2 shows. Conversely for larger radiuses, thus for a jib 2 lifted less, L2 > L1, as figure 3 shows. 30 As a result, for a given load moment M, the force measured by the dynamometer is greater when the radius P is at a maximum (lowered jib) relative to how it is when the radius P is at a minimum (raised jib). In other words, the admissible load at maximum radius will 35 be less than that which the crane would have been able to lift in complete safety. In other words, when considering the load diagram of figure 4, it is observed that curve B is always below 4 the theoretical curve A, thus for a given radius P the load is lower with curve B. The full potential of the crane is therefore not exploited and, in particular, the load at maximum radius is less than what it could be. To illustrate the state of the art described above, reference is made here to 5 US Patent 5263597 which shows a luffing jib crane, able to be a tower crane, but without a counter jib, with a tie bar connecting the end of the jib to a stay and with a dynamometer or force measuring apparatus positioned on the jib tie bar, to measure the force borne by this tie bar. The force measurement carried out in this manner, combined with a predetermined load diagram, allows, in this example, 10 the adjustment of the load of the luffing jib crane. Cranes with telescopic jibs are also known, in particular truck cranes which are not tower cranes, for which various load curves are used depending on the extended state of the jib - see for example US Patent 4039084. However, this does not respond to the particular problem, described above, which is particular 15 to luffing jib tower cranes. Proceeding from the aforementioned observations, the present invention aims to optimize the load diagram of a luffing jib tower crane, to utilize the framework of the crane to its maximum capacity, whatever the radius. To this end, in one aspect the present invention provides a method for adjusting 20 load of a luffing jib tower crane, by using a predetermined load diagram combined with a measurement of force borne by a counter jib tie bar of the crane, wherein, depending on radius of the crane as a result of the position of its jib, at least two separate load curves are used alternately, either a first load curve used between a minimum radius and an intermediate radius and at least one further load curve, 25 corresponding to a greater load moment, used between the intermediate radius and a maximum radius. In a preferred embodiment of the method, which is a subject of the invention, said further load curve, used between the intermediate radius and the maximum radius, is a curve obtained by homothetic transformation of the first 30 load curve, used between the minimum radius and the intermediate radius. Thus, in principle, the invention consists in creating a load curve C (see figure 4) of which the theoretical torque is greater than that of load curve B 5 described above and which is obtained, in particular, from the curve B by homothetic transformation, the two curves B and C being used alternately. More particularly, the changing of the load curve is determined by the graph and is carried out at the point where curve C intersects curve A so as not to put the 5 crane at risk: curve B is used between the minimum radius Pm and the intermediate radius PO and curve C is used between this intermediate radius PO and the maximum radius PM. A subject of the invention is also a device for adjusting the load of a luffing jib tower crane, implementing the method described above. This device is of the 10 type of those using at least one dynamometer or an equivalent force measuring apparatus, associated with the counter jib tie bar of the crane, for measuring the force borne by this tie bar; according to the invention the dynamometer, which is at least one in number, or the equivalent force measuring apparatus, is provided with triggering means for a first force corresponding to the first load curve used 15 between the minimum radius and an intermediate radius and triggering means for at least one further force, greater than the aforementioned force, corresponding to -6 at least one further load curve used between an intermediate radius and the maximum radius, means being provided for detecting the passage of the jib through the position corresponding to the intermediate radius. 5 In an embodiment of this device, the dynamometer is fitted with a first switch which is triggered for a force greater than that of the first load curve and at least one further switch which is triggered for a force 10 greater than that of at least one further load curve, namely at a force greater than the force for triggering the first switch. In particular, the dynamometer 7 may be fitted with two switches Il and 12, the first switch Il being used for the smaller radiuses and the second 15 switch 12 being used for the larger radiuses, up to the maximum radius (PM), the switch used being changed during the passage through the position of the jib which corresponds to the aforementioned intermediate radius (PO). 20 For detecting the passage of the jib through the position corresponding to this intermediate radius, one possibility consists in that the luffing jib hoist is fitted with a means for counting the revolutions of its 25 drum, a means which closes a switch of the "end of travel" type being activated for a set number of revolutions, which corresponds to the passage through said intermediate radius. 30 It would not constitute a departure from the scope of the invention, as defined in the accompanying claims: - to fit the crane with two separate dynamometers, being respectively activated for 35 the two load curves, instead of a single dynamometer fitted with two switches; - not to place the dynamometer on the counter jib tie bar 6 but on the stay 5 which -7 constitutes an equivalent solution as the force in the stay is proportional to the force in the counter jib tie bar; 5 - to use three, or more, load curve sections, instead of two curves; - to use any means for detecting the passage of the luffing jib through the intermediate 10 radius, causing the passage from one load curve to the other.

Claims

1. Method for adjusting load of a luffing jib tower crane, by using a predetermined load diagram combined with a measurement of force borne by a counter jib tie bar of the crane, wherein, depending on radius of the crane as a 5 result of the position of its jib, at least two separate load curves are used alternately, either a first load curve used between a minimum radius and an intermediate radius and at least one further load curve, corresponding to a greater load moment, used between the intermediate radius and a maximum radius. 10

2. Method according to Claim 1, wherein said further load curve, used between the intermediate radius and the maximum radius, is a curve obtained by homothetic transformation of the first load curve, used between the minimum radius and the intermediate radius.

3. Device for adjusting the load of a luffing jib tower crane for implementing 15 the method according to Claim 1 or 2, the device using at least one dynamometer or an equivalent force measuring apparatus, associated with the counter jib tie bar of the crane, for measuring the force borne by this tie bar, wherein the dynamometer, which is at least one in number, or the equivalent force measuring apparatus, is provided with triggering means for a first force corresponding to the 20 first load curve used between the minimum radius and an intermediate radius and triggering means for at least one further force, greater than the aforementioned force, corresponding to at least one further load curve used between an intermediate radius and the maximum radius, means being provided for detecting the passage of the jib through the position corresponding to the intermediate 25 radius.

4. Device according to Claim 3, wherein the dynamometer is fitted with a first switch which is triggered for a force greater than that of the first load curve and at least one further switch which is triggered for a force greater than that of at least one further load curve, namely at a force greater than the force for triggering the 30 first switch. 9

5. Device according to Claim 4, wherein the dynamometer is fitted with two switches, the first switch being used for the smaller radiuses and the second switch being used for larger radiuses, up to the maximum radius, the switch used being changed during the passage through the position of the jib which 5 corresponds to the aforementioned intermediate radius.

6. Device according to Claim 3, wherein the crane is fitted with two separate dynamometers, being respectively activated for the two load curves.

7. Device according to anyone of Claims 3 to 6, wherein, for detecting the passage of the jib through the position corresponding to the intermediate radius, 10 the luffing jib hoist is fitted with a means for counting the revolutions of its drum, a means which closes a switch of the "end of travel" type being activated for a set number or revolutions, which corresponds to the passage through said intermediate radius.

8. A method for adjusting load of a luffing jib tower crane substantially as 15 described herein with reference to the accompanying drawings.

9. A device for adjusting load of a luffing jib tower crane substantially as described herein with reference to the accompanying drawings. POTAIN WATERMARK PATENT & TRADE MARK ATTORNEYS P27488AU00