Method for defining an optimized load curve for a crane, method and control device for controlling the load suspended from a crane on the basis of the optimized load curve

Abstract

This defining method comprises the steps of: —simulating a crane comprising: i) a boom made up of elements and ii) a lifting member that is able to move along the boom, —selecting several elements to be tested, maximum stresses, and several ranges along the boom, and —carrying out the following analysis steps of: •choosing a theoretical load, •calculating stresses brought about by the theoretical load in each element to be tested, •comparing these stresses with maximum stresses, •increasing or decreasing the theoretical load depending on whether stresses are less than or greater than the maximum stresses, •repeating the calculating step and the comparison step and the step of increasing or decreasing until the maximum theoretical load is found, and •recording i) the range and ii) the maximum theoretical load.

Claims

1. A controlling method, for controlling a lifting member of a crane, the controlling method comprising the following steps: providing a physical crane comprising a jib comprising a structure composed of several elements, and a lifting member configured to lift a load and is movable along the jib successively in several reaches; simulating, by a computer, the crane comprising at least: i) the jib comprising the structure composed of several elements, and ii) the lifting member which is configured to lift the load and which is movable along the jib successively in several reaches, a first selection step comprising selecting several elements to be tested, a second selection step comprising, for each element to be tested, selecting at least one respective predetermined maximum stress, a third selection step comprising selecting several reaches along the jib, and at each reach, carrying out the following analysis steps: a choice step comprising choosing a theoretical load to be suspended from the lifting member, a calculation step comprising calculating stresses which are induced by the theoretical load in each element to be tested, a comparison step comprising, for each element to be tested, comparing the calculated stresses with the respective predetermined maximum stresses, an incrementation step comprising incrementing the theoretical load if at least one of the calculated stresses is less than a respective predetermined maximum stress, a decrementation step comprising decrementing the theoretical load if at least one of the calculated stresses is greater than a respective predetermined maximum stress, repeating i) the calculation step and ii) the comparison step and one from iii) the incrementation step and iii) the decrementation step until finding the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, storing in a memory a group of values comprising i) the reach and ii) the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, and defining a load curve for the crane, the load curve indicating the maximum theoretical loads found as a function of the selected reaches, communicating to a monitoring device control signals to control at least one movement of the lifting member of the physical crane from: i) a lifting movement to lift a target load; and ii) a distribution movement to displace the lifting member to a target reach based on the target reach indicated by the load curve.

2. The controlling method according to claim 1, wherein the structure comprises a lattice, the elements comprising bars arranged to form the lattice.

3. The controlling method according to claim 1, wherein, during the third selection step comprising in selecting several reaches, the reaches are selected in a regular distribution along the jib.

4. The controlling method according to claim 3, wherein the reaches are spaced apart in pairs, by an interval comprised between 0.5% and 10% of the length of the jib.

5. The controlling method according to claim 4, wherein the reaches are spaced apart in pairs, by an interval comprised between 1% and 2% of the length of the jib.

6. The controlling method according to claim 1, wherein, during the calculation step comprising calculating stresses, said stresses are calculated for a stressing mode selected in the group constituted of traction, shear, compression, buckling, torsion and bending.

7. The controlling method according to claim 1, wherein, during the second selection step comprising selecting predetermined maximum stresses, each predetermined maximum stress is selected so as to be comprised between 90% and 100% of a respective permissible stress.

8. The controlling method according to claim 1, wherein the analysis steps are initially carried out for a largest selected reach, so as to find firstly the theoretical load for the largest selected reach, then in which, during the choice step comprising in choosing a theoretical load for each other selected reach, the theoretical load is chosen inducing, around one end of the jib opposite to the largest reach, a moment equal to the moment induced by the theoretical load found for the largest selected reach.

9. A monitoring method for monitoring a load suspended from a crane, the monitoring method comprising the steps of: providing a physical crane comprising at least: i) a jib, ii) a lifting member which is configured to lift a load and which is movable along the jib successively in several reaches, iii) an evaluation device configured to evaluate a magnitude representative of the load suspended from the lifting member, and iv) a measuring device configured to measure a magnitude representative of the instantaneous reach, providing a monitoring device comprising a memory containing a load curve defined by a definition method, comprising the following steps: simulating, by a computer, the crane comprising at least: i) the jib comprising the structure composed of several elements, and ii) the lifting member which is configured to lift the load and which is movable along the jib successively in several reaches, a first selection step comprising selecting several elements to be tested, a second selection step comprising, for each element to be tested, selecting at least one respective predetermined maximum stress, a third selection step comprising selecting several reaches along the jib, and at each reach, carrying out the following analysis steps: a choice step comprising choosing a theoretical load to be suspended from the lifting member, a calculation step comprising calculating stresses which are induced by the theoretical load in each element to be tested, a comparison step comprising, for each element to be tested, comparing the calculated stresses with the respective predetermined maximum stresses, an incrementation step comprising incrementing the theoretical load if at least one of the calculated stresses is less than a respective predetermined maximum stress, a decrementation step comprising decrementing the theoretical load if at least one of the calculated stresses is greater than a respective predetermined maximum stress, repeating i) the calculation step and ii) the comparison step and one from iii) the incrementation step and iii) the decrementation step until finding the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, storing in a memory a group of values comprising i) the reach and ii) the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, and defining the load curve for the crane, the load curve indicating the maximum theoretical loads found as a function of the selected reaches, evaluating, by means of the evaluation device, magnitude representative of the load suspended from the lifting member of the physical crane, measuring, by means of the measuring device, magnitude representative of the instantaneous reach, communicating to the monitoring device control signals intended to control at least one movement of the lifting member of the physical crane from: i) a lifting movement to lift a target load; and ii) a distribution movement to displace the lifting member to a target reach, comparing the target load with the theoretical load indicated for the target reach by the load curve, and a restriction step comprising in, if the target load is greater than said theoretical load indicated for the target reach, restricting said at least one movement of the lifting member of the physical crane.

10. The monitoring method according to claim 9, wherein the restriction step comprises: i) a preventing step in which said at least one movement of the lifting member is prevented, and ii) a warning step in which the monitoring device communicates an exceeding warning notifying that the target load is excessive for the target reach.

11. The monitoring method according to claim 9, wherein the evaluation device comprises at least one measuring member selected from the group constituted of an electronic encoder and a displacement potentiometer.

12. A monitoring device comprising: a memory containing a load curve defined by a definition method for defining the load curve, the method comprising the following steps: simulating a crane comprising at least: i) a jib comprising a structure composed of several elements, and ii) a lifting member which is configured to lift a load and which is movable along the jib successively in several reaches, a first selection step comprising selecting several elements to be tested, a second selection step comprising, for each element to be tested, selecting at least one respective predetermined maximum stress, a third selection step comprising selecting several reaches along the jib, and at each reach, carrying out the following analysis steps: a choice step comprising choosing a theoretical load to be suspended from the lifting member, a calculation step comprising calculating stresses which are induced by the theoretical load in each element to be tested, a comparison step comprising, for each element to be tested, comparing the calculated stresses with the respective predetermined maximum stresses, an incrementation step comprising incrementing the theoretical load if at least one of the calculated stresses is less than a respective predetermined maximum stress, a decrementation step comprising decrementing the theoretical load if at least one of the calculated stresses is greater than a respective predetermined maximum stress, repeating i) the calculation step and ii) the comparison step and one from the incrementation step and iv) the decrementation step until finding the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, defining the load curve for the crane, the load curve indicating the maximum theoretical loads found as a function of the selected reaches, storing in a memory a group of values comprising i) the reach and ii) the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses, and a physical crane comprising at least: i) a jib, ii) a lifting member which is configured to lift a load and which is movable along the jib successively in several reaches, iii) an evaluation device configured to evaluate a magnitude representative of the load suspended from the lifting member, and iv) a measuring device configured to measure a magnitude representative of the instantaneous reach, a calculation unit configured to carry out a monitoring method for monitoring a load suspended from a physical crane, the monitoring method comprising the steps of: evaluating, by means of the evaluation device, magnitude representative of the load suspended from the lifting member, measuring, by means of the measuring device, magnitude representative of the instantaneous reach, communicating to the monitoring device control signals intended to control at least one movement of the lifting member from: i) a lifting movement to lift a target load; and ii) a distribution movement to displace the lifting member to a target reach, comparing the target load with the theoretical load indicated for the target reach by the load curve, and a restriction step comprising, if the target load is greater than said theoretical load indicated for the target reach, restricting said at least one movement of the lifting member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be well understood and its advantages will also emerge in the light of the following description, given only by way of non-limiting example and with reference to the appended figures, in which identical reference signs correspond to structurally and/or functionally identical or similar objects. In the appended figures:

(2) FIG. 1 is a schematic view illustrating a portion of a crane comprising a monitoring device implementing a monitoring method in accordance with the invention, from a load curve defined according to a definition method in accordance with the invention,

(3) FIG. 2 is a flow chart illustrating a definition method in accordance with the invention;

(4) FIGS. 3 and 4 are schematic views illustrating the jib of FIG. 1 respectively during the two steps of the definition method of FIG. 2;

(5) FIG. 5 is a diagram showing a load curve defined according to the definition method of FIG. 2;

(6) FIG. 6 is a view of a monitoring method in accordance with the invention; and

(7) FIG. 7 is a view of a monitoring device in accordance with the invention and configured to implement the monitoring method of FIG. 6.

DESCRIPTION

(8) FIG. 1 illustrates a crane 1 comprising a jib 2 and a tower 3 which supports the jib 2. The jib 2 is hinged relative to the tower 3 in particular about an axis 2.3. The jib 2 comprises a structure 4. The structure 4 is composed of several elements 5. Each element 5 forms a structural element, that is to say an element of the structure 4.

(9) In the example of FIG. 1, the structure 4 comprises a lattice and the elements 5 comprise bars arranged to form this lattice. Each element 5 is here a segment of the structure 4 including several bars.

(10) The crane 1 further comprises a lifting member 8. The lifting member 8 is configured to lift a load 10. As shown in FIG. 1, the lifting member 8 here comprises a carriage, a hook, a block, a cable and an actuator configured to drive the cable and the carriage.

(11) Thanks to the actuator and the carriage, the lifting member 8 is movable along the jib 2 successively in several reaches L. The lifting member 8 is at the minimum reach when it is located as closest as possible to the tower 3. The lifting member 8 is at the maximum reach when it is located the farthest away from the tower 3.

(12) FIG. 2 illustrates a definition method 100 for defining a load curve for a crane 1. The definition method 100 comprises a simulation step 102, in which the crane 1 comprising the lifting member 8 and the jib 2 is simulated. The simulation step 102 may implement a computer-assisted drawing software in order to design the jib 2. In this simulation step, the structure 4 is broken down into several elements 5. This simulation step 102 may further be operated by means of a computer, not shown, which is equipped with a program designed for perform analytical calculations.

(13) The definition method 100 further comprises a selection step 104 of elements to be tested 6, in which several elements to be tested 6 are selected from the elements 5. In the example of FIG. 2, most of the elements 5 of the structure 4 are selected as elements to be tested 6. Here, 90% of the bars forming the lattice of the jib 2 may be selected. This step of selecting elements to be tested 6 may be operated by means of the computer.

(14) Furthermore, the definition method 100 comprises a selection step 108 of stresses, in which, for each element to be tested 6, predetermined maximum stresses are selected so as to define in a set of predetermined maximum stresses. For a crane 1 intended to serve in Europe, the maximum predetermined stresses may be selected at 90% of the permissible stresses imposed by the machine directive EC-89/392, the FEM.1.001 standard and the EN14439 standard.

(15) This selection step 108 of stresses may be operated by means of the computer, such that the set of predetermined maximum stresses may be stored in this computer. The predetermined maximum stresses may be selected so as to reach, for each element 5, a utilization rate of about 90%.

(16) The definition method 100 further comprises a step of selecting reaches L, in which several reaches L are selected along the jib 2. During this selection step 110 of several reaches L, the reaches L are selected in a regular distribution along the jib 2. The selected reaches L are spaced apart in pairs, by an interval 9 approximately equal to 1.5% of the length of the jib 2, here about 1 m. This selection step 110 of reaches may be operated by means of the computer.

(17) Then, in the definition method 100, at each reach L selected in step 110; the analysis steps 112 described below are carried out. The analysis steps 112 may be operated by means of the computer.

(18) To start, the analysis steps 112 are operated for a first reach L, for example for the largest selected reach (for example the maximum reach) along the jib 2. The analysis steps 112 comprise: a choice step 112.1, in which a theoretical load to be suspended from the lifting member 8 is chosen; this theoretical load is chosen arbitrarily, a calculation step 112.2, in which stresses which are induced by the theoretical load in each element to be tested 6 are calculated, here for several stressing modes among the traction, the shear, the compression, the buckling, the torsion and the bending; and a comparison step 112.3, in which for each element to be tested 6, the calculated stresses are compared with respective predetermined maximum stresses.

(19) Then, the analysis steps 112 comprise: either an incrementation step 112.41, in which if at least one of the calculated stresses is less than a respective predetermined maximum stress, the theoretical load is incremented; or a decrementation step 112.42, in which, if at least one of the calculated stresses is greater than a respective predetermined maximum stress, the theoretical load is decremented.

(20) Then, the analysis steps 112 comprise an iteration step 12.5, in which we repeat:

(21) i) the calculation step (112.2) and

(22) ii) the comparison step (112.3) and

(23) either iii) the incrementation step (112.41)

(24) or iii) the decrementation step (112.42)

(25) until finding the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses.

(26) The number of iteration steps 112.5 depends on the theoretical load chosen during the choice step 112.1 and on the increment of the theoretical load. A small increment will require more iteration steps 112.5 than a large increment, but a small increment will result in a defined theoretical load with more accuracy than a large increment.

(27) In order to minimize the number of required calculations, during the choice step 112.1 a theoretical load for each other reach, it is possible to choose the theoretical load inducing, around one end of the jib 2 opposite to the largest reach, a moment equal to the moment induced by the theoretical load found for the largest selected reach.

(28) After finding the maximum theoretical load for the reach L, the definition method 100 comprises a storing step 112.6, in which a group of values comprising i) the reach L and ii) the maximum theoretical load for which the calculated stresses are substantially equal to the respective predetermined maximum stresses is stored in a memory of the computer. Thus, a maximum theoretical load is associated to each reach L in the memory.

(29) Then, as indicated by the jib 111 in FIG. 2, the reach L is changed, then the analysis steps 112 are carried out again for the next reach, and so on for all the selected reaches L during the selection step 110.

(30) After carrying out the analysis steps 112 for all the selected reaches L, a set which contains the groups of values {reach L; maximum theoretical load} is obtained. This set of values allows defining an optimized load curve 50, shown in FIG. 5. Thus, after finding the theoretical load for each selected reach L, a definition step 114 consists in defining the load curve 50 indicating: on the ordinate axis: the payloads 10+8 (in metric tons), deducted from the found theoretical loads, on the abscissa axis: the reaches L (in meters).

(31) The payload 10+8 is here the sum of the found theoretical load and the mass of the lifting member 8 (carriage, hook, block, cable and actuator).

(32) For comparison, FIG. 5 illustrates a load curve 49 which has been obtained by a method of the state of the art while keeping the maximum load moment constant. The load curve 50 obtained by the definition method 100 in accordance with the invention is optimized relative to the load curve 49 of the state of the art. Indeed, the load curve 50 allows lifting heavier payloads at all the reaches L.

(33) Moreover, FIG. 3 illustrates a monitoring method 200, for monitoring the load suspended from the crane 1. The monitoring method 200 comprises a provision step 202, in which the crane 1 is provided, comprising:

(34) i) the jib 2,

(35) ii) the lifting member 8,

(36) iii) an evaluation device 20 which is configured to evaluate the mass of the load 10 suspended from the lifting member 8; the evaluation device 20 here comprises an electronic encoder, and

(37) iv) a measuring device 22 which is configured to measure the length of the instantaneous reach L.

(38) The monitoring method 200 further comprises a provision step 204, in which a monitoring device 24 is provided, shown in FIG. 7, comprising a memory 26 which contains the load curve 50 defined according to the definition method 100.

(39) As shown in FIG. 7, the monitoring device 24 further comprises a calculation unit 28 which is configured to carry out the monitoring method 200. In the example of the figures, the monitoring device 24 is integrated in a control system 25 installed on the crane 1.

(40) The control system 25 further comprises a stop control 29 and position sensors 27 which are configured to generate signals representative of the position of the carriage, the angular position of the jib 2 relative to the tower 3, the position of the hook, the position of the block and the position of the load 10, respectively.

(41) The monitoring method 200 further comprises the following steps: 206: evaluating, by means of the evaluation device 20, the mass of the load 10 suspended from the lifting member 8, 208: measuring, by means of the measuring device 22, the length of the instantaneous reach L, 210: communicating to the monitoring device 24 control signals intended to control at least one movement of the lifting member 8 from: i) a lifting movement to lift a target load; and ii) a distribution movement to displace the lifting member (8) to a target reach, 212: comparing the target load with the theoretical load indicated for the target reach by the load curve 50, and 214: if the target load is greater than said theoretical load indicated for the target reach, restricting the movement of the lifting member 8.

(42) In particular, the restriction step 214 comprises: i) a preventing step 214.1 in which said at least one movement of the lifting member 8 is prevented, and ii) a warning step 214.2 in which the monitoring device 24 communicates an exceeding warning notifying that the target load is excessive for the target reach.

(43) Of course, the present invention is not limited to the particular embodiments described in the present patent application, or to embodiments which are within the reach of those skilled in the art. Other embodiments may be envisaged without departing from the scope of the invention, starting from any element equivalent to an element indicated in the present patent application.