Dynamic optimisation of a crane load curve

Abstract

Means of controlling the lifting of a load suspended from a jib, carried by a crane mast, in particular means of determining: • as a function of the mass of the suspended load, a specified load factor quantifying an acceptable excess in relation to a predetermined maximum permissible load for said crane; • a maximum permissible lifting acceleration, as a function of the mass of the suspended load, the specified load factor and the position in distribution of the suspended load on the jib relative to the mast; • from lifting speed commands, optimized lifting speed commands intended to be executed by a drive device to move the suspended load in a lifting motion such that the acceleration relative to the lifting motion remains, in absolute value, less than or equal to the maximum permissible acceleration.

Description

[0001] The present invention relates to the field of cranes, and more specifically to tower cranes, and in particular to the monitoring of the maximum load moved.

[0002] According to a usual configuration, a tower crane comprises a vertical mast, a substantially horizontal boom carried by the mast and orientable in azimuth around the mast in a so-called orientation movement, as well as a trolley which is mounted mobile in radial translation along said boom thus carrying out a so-called distribution movement. The trolley carries a load, suspended from the trolley by a cable whose length can be modified by means of a winch which thus controls the vertical movement of said load, called lifting movement.

[0003] An essential characteristic of the crane is the maximum mass of the suspended load that the crane can move, based on an operating point defined by the distance of said load from the axis passing through the mast - called the distribution position - and by the mass of the load.

[0004] The maximum limit is typically described by means of a load curve, on a graph representing, on a first axis (conventionally on the abscissa), the distribution position and, on a second axis (conventionally on the ordinate), the mass of the load.

[0005] Conventionally, a tower crane has a monitoring and control system configured to limit the load lifting speed when the operating point approaches the load curve.

[0006] When the operating point reaches the load curve, the monitoring and control system stops the crane movements, in order to avoid any overshoot that is truly dangerous for the stability or structure of the crane.

[0007] For example, it is already known from documents US 9120650 and US 2008 / 275610 to implement control means ensuring that the acceleration of the suspended load does not exceed a maximum authorized acceleration, defined as a function of structural characteristics of the crane or the efficiency of its actuating means (motors or others), so as not to compromise the proper functioning or structural integrity of the crane. Document US 9120650 discloses the preamble of claim 1.

[0008] The load curve is generally established, with regard to the mechanical arrangement of the crane, on the one hand from a first limit called "static" which assumes that the crane is in a static mechanical state or in a permanent regime similar to a quasi-static regime (in particular with a lifting speed that is substantially constant, or zero), and on the other hand by also providing, in relation to this first static limit, a dynamic margin, which corresponds to a maximum exceedance tolerated in relation to this static limit, called load factor Ψ.

[0009] The said load factor Ψ makes it possible to take into account the additional stresses exerted on the boom, and more generally on the crane, when the suspended load is subjected to transient phenomena, for example at the start of a lifting movement, when the inertia of the suspended load is added to the weight of the said suspended load.

[0010] Safety standards, for example European standard EN 13001, require that the load factor Ψ remains below 30%.

[0011] In practice, the greater the load factor Ψ, i.e. the greater the safety margin imposed, the lower the maximum limit of the load that the crane can move.

[0012] This is why it is desirable, in order to improve the crane's performance, to reduce the load factor Ψ, without however compromising the operating safety of the crane.

[0013] It is thus known, for example from patent document EP-0 849 213, to implement control means, using a first load curve that is relatively restrictive in view of the potential capacities of the crane, and a second extended load curve. However, the second load curve can only be used for a predetermined reduced range of travel speed / acceleration, when the conditions for such an overshoot are met. In particular, provision is made for the use of a switch to select, depending on the circumstances, the appropriate load curve. The operator can thus manually force the control means to operate the crane using the second extended load curve. This solution is therefore based on the use of two predefined load curves and only partially optimizes the compromise between dynamic operating performance of the crane and load capacity, depending on the actual instantaneous capacities of the crane.

[0014] This is why there is still a need for improved and automated means, for tower cranes, of monitoring and controlling movements according to a load curve, offering an optimized compromise between load lifting capacity and dynamic operating performance.

[0015] One of the objects of the invention is to enable the taking into account, by improved monitoring and control means, of the capacity at a given moment of a crane, in particular a tower crane, to reduce the influence of dynamic factors and uncertainties to a determined level.

[0016] Another object of the invention is to provide means capable of taking into account, in order to determine the load factor, the capacities and performances of a crane to apply and control speed and acceleration instructions of the lifting motor.

[0017] Another object of the invention is to provide improved monitoring and control means for cranes capable of limiting the lifting movements of the payload, in speed and acceleration, by means of dynamic calculation rules depending on the current mechanical load, the range, the lifting speed and optionally other characteristic quantities of said crane.

[0018] One of the objects of the invention is to increase the lifting capacity of a crane, while ensuring a high level of safety.

[0019] One of the objects of the invention is to increase the dynamic performance of using a crane, while guaranteeing a high level of safety.

[0020] One of the objects of the invention is to provide improved means of monitoring and controlling cranes, which do not require, during their use, any action by the crane operator aimed at selecting from among several load curves the one adapted to the context to control the lifting movements of the load.

[0021] One of the objects of the invention is to provide improved means of monitoring and controlling a crane, using a single load curve to continuously adapt the speed and acceleration requested by the crane operator to comply with the dynamic constraints that the crane can withstand.

[0022] One of the objects of the invention is to provide improved crane monitoring and control means suitable for use in conjunction with the safety and cut-off devices usually deployed in a crane.

[0023] One or more of these objects are fulfilled by the device according to the independent claim. The dependent claims further provide solutions to these objects and / or other advantages.

[0024] More particularly, according to a first aspect, the invention relates to a method for controlling the lifting of a load suspended from a boom and having a mass, carried by a mast of a crane, in particular a tower crane. The invention can also be applied to other families of cranes - luffing jib crane, etc. - by transposing the calculations carried out according to the model of the invention to the geometry of said cranes.

[0025] The method comprises at least one step of determining, from lifting speed setpoints, optimized lifting speed setpoints intended to be executed by a motor device to move the suspended load in a lifting movement such that the acceleration relative to the lifting movement remains, in absolute value, less than or equal to a maximum authorized lifting acceleration, and it is remarkable in that it comprises the following preliminary steps: a first step of determining, as a function of the mass of the suspended load, a specified load factor quantifying an acceptable excess in relation to a predetermined maximum permissible load for said crane; and a second step of determining the maximum permissible lifting acceleration, as a function of the mass of the suspended load, the specified load factor and the distribution position of the suspended load on the boom relative to the mast.

[0026] The control method according to the invention makes it possible in particular to adapt the control of the crane according to the actual dynamics of the load.

[0027] The method therefore makes it possible to control the crane by taking into account the effects of the load when the latter is in a static or quasi-static mechanical state, but also in a transient state during which the inertial effects linked to the accelerations / decelerations of the load are observed.

[0028] In fact, during transient conditions, particularly at the start of lifting when the winch accelerates the load, a stress greater than the strict mass of the suspended load is exerted on the crane boom: the latter consequently undergoes the equivalent of a load heavier than that actually suspended from the winch, and therefore reacts with a pitching deformation greater than the deformation observed in quasi-static conditions.

[0029] The invention thus makes it possible to dynamically optimize the control of the crane with respect to the predetermined maximum permissible load for said crane, by limiting the lifting acceleration, as a function of current measurable parameters, such as the mass of the suspended load, and the distribution position of the suspended load.

[0030] Furthermore, optimization does not require any operator intervention.

[0031] While maintaining the same level of safety, the invention results in an improvement in the lifting capacity / dynamic performance compromise, compared to conventional approaches in which only the predetermined maximum permissible load for said crane would have been taken into account, or to approaches based on the use of two static maximum permissible load curves.

[0032] The process is also easily configurable to adapt to various needs, particularly with regard to the choice of the predetermined maximum admissible load.

[0033] The maximum permissible lifting acceleration can be determined using the following mathematical expression: gJ z x c 2 M + J z ψ 0 ∗ in which: x c corresponds to the distribution position of the suspended load; M corresponds to the mass of the suspended load; J z corresponds to a first-order stiffness and inertia model relative to the crane structure; Ψ 0 * is the specified load factor.

[0034] Thus, the method according to the invention makes it possible in particular to optimize the control of the crane, by dynamically limiting the acceleration, as well as the speed, of the suspended load, by means of a pre-established mathematical formula.

[0035] The specified load factor is determined, for example, by means of a maximum permissible load curve, corresponding to a limit load factor and a maximum static load.

[0036] Thus, a single maximum permissible load curve can be used, dynamically adapted to current real conditions by means of a mathematical formula allowing to take into account current real conditions, such as the mass of the suspended load or the distribution position of the suspended load.

[0037] This makes it possible to avoid exceeding the predetermined maximum permissible load for the crane, while approaching, in complete safety, as close as possible to said maximum permissible load.

[0038] The limit load factor can be determined from a first theoretical threshold depending on the theoretical load capacities supported by the crane and a second threshold depending on measurement uncertainties relating to the mass of the suspended load and / or the lifting movement of the suspended load.

[0039] The specified load factor can be obtained by multiplying the limit load factor by the ratio between the maximum static load corresponding to the maximum permissible load curve and the mass of the suspended load.

[0040] Thus, thanks to better control of the dynamic aspects permitted by the invention, it is possible to use a limit load factor approaching the limits set by the standards.

[0041] Advantageously, the optimized lifting speed instructions are determined so that their execution by the motor device to move the suspended load according to the lifting movement complies with the following condition: ∘ the lifting acceleration of the suspended load, in absolute value, remains less than or equal to the maximum authorized acceleration (L"MAX); in this case, said maximum authorized acceleration L"MAX corresponds to a theoretical acceleration which is calculated so as not to cause the dynamic factor considered to be exceeded; as well as one or more of the following additional conditions: ∘ the lifting speed of the suspended load, in absolute value, remains below a maximum authorized lifting speed, the maximum authorized lifting speed being determined according to the crane's capacity to brake the movements of the suspended load; and / or, ∘ the lifting speed of the suspended load, in absolute value, remains below a maximum safe lifting speed, determined according to the crane's capacity to withstand a sudden ground landing of the suspended load and / or an emergency stop; and / or, ∘ the lifting acceleration of the suspended load, in absolute value, remains below a maximum lifting acceleration achievable by the motor device; and / or, ∘ the lifting acceleration of the suspended load, in absolute value, remains above a minimum comfort lifting acceleration.

[0042] It is therefore possible to optimize both the safety of the crane, while optimizing the operating performance felt by the crane operator.

[0043] Optimized lifting speed setpoints can be determined so that the absolute value of the lifting speed of the suspended load increases, over a predefined period of time, along a ramp whose gradient corresponds to the maximum permissible lifting acceleration. Inertial effects can then be limited.

[0044] According to a second unclaimed aspect, the description relates to a computer program comprising instructions for carrying out the steps of the method according to the first aspect, when said program is executed by a processor.

[0045] Each of these programs may use any programming language, and may be in the form of source code, object code, or code intermediate between source code and object code, such as in a partially compiled form, or in any other desirable form. In particular, it is possible to use the C / C++ language, the ™< language of scripting languages, such as tel, javascript, python, perl which allow "on-demand" code generation and do not require significant overhead for their generation or modification.

[0046] According to a third unclaimed aspect, the description relates to a computer-readable recording medium on which is recorded a computer program comprising instructions for carrying out the steps of the method according to the first aspect.

[0047] The information carrier may be any entity or device capable of storing the program. For example, the carrier may comprise a storage means, such as a ROM, for example a CD-ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a floppy disk or a hard disk. Furthermore, the information carrier may be a transmissible medium such as an electrical or optical signal, which may be conveyed by an electrical or optical cable, by radio or by other means. The program according to the invention may in particular be downloaded from an Internet or Intranet network. Alternatively, the information carrier may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

[0048] According to a fourth aspect, the invention also relates to a crane, in particular a tower crane, suitable for implementing the method according to the first aspect. The crane comprises a mast supporting a boom on which is mounted a trolley intended to carry a suspended load having a mass, and means for controlling the lifting of the suspended load provided with means for determining, from lifting speed setpoints, optimized lifting speed setpoints intended to be executed by a motor device to move the suspended load in a lifting movement such that the acceleration relative to the lifting movement remains, in absolute value, less than or equal to a maximum authorized lifting acceleration. The means for controlling the lifting of the suspended load are further provided with: means for determining, as a function of the mass of the suspended load, a specified load factor quantifying an acceptable excess over a predetermined maximum permissible load for said crane; means for determining the maximum permissible lifting acceleration, as a function of the mass of the suspended load, the specified load factor and the distribution position of the suspended load on the boom relative to the mast.

[0049] The invention can also be applied to other families of cranes - luffing jib cranes, etc. - by transposing the calculations carried out according to the model of the invention to the geometry of said cranes.

[0050] Other features and advantages of the present invention will appear in the following description of embodiments, with reference to the appended drawings, in which: there figure 1 is an architectural diagram of a load lifting control system, according to one embodiment; figure 2 is a block diagram of the steps of a method for controlling the lifting of a suspended load, according to one embodiment; figure 3 represents a schematic diagram of the monitoring and control device, according to one embodiment of the invention; the figure 4 represents a block diagram used to describe a mechanical model of the oscillator type, used, according to an embodiment of the method according to the invention to determine the maximum authorized lifting acceleration; the figure 5 represents a diagram comprising a set of surface curves describing the maximum permissible lifting acceleration, as a function of the mass M of the load and the distribution position of the load, each surface curve corresponding to a specified load factor.

[0051] We refer to the figure 1 , on which is shown a system 1 for controlling the lifting of a suspended load 2.

[0052] This system is applicable to a 3 crane, and in particular to a 3 tower crane.

[0053] In reference to the figure 4 , it is conceivable to apply the system 1 to any type of crane 3 comprising a boom 4 which is yaw-orientable around a vertical axis (ZZ'), according to an orientation movement, and which is arranged so that the suspended load 2 is suspended from said boom 4 by a cable 5, and this in such a way that said crane 3 can modify the radial distance of said suspended load 2 relative to the vertical axis, according to a distribution movement, as well as the length of the cable 5 which connects the boom 4 to the suspended load 2, according to a so-called lifting movement, in order to be able to modify the altitude of the suspended load 2.

[0054] The crane 3 can thus form, for example, a luffing jib crane (tilting jib), a telescopic crane, or, particularly preferably, a tower crane.

[0055] In the following non-limiting example, the tower crane comprises a vertical mast 6, which materializes the vertical axis (ZZ'), a substantially horizontal boom 4 carried by the mast 6 and orientable in azimuth (yaw) around the mast 6, as well as a carriage 7 which is mounted mobile in radial translation along said boom.

[0056] The trolley 7 carries the load 2, suspended from the trolley by a cable 5 whose length can be modified by means of a winch.

[0057] In the following, for the sake of convenience of description, we will assimilate crane 3 to a tower crane, and the vertical axis (ZZ') to a mast 6.

[0058] The command control system 1 comprises in particular a piloting device 10, a monitoring and control device 20, a controller 30, and a command execution system 40.

[0059] The order execution system 40 typically comprises: a lifting motor device 41 coupled to the winch, capable of moving the load 2 in a lifting movement, according to instructions received; a distribution motor device 42 coupled to the carriage 7, capable of moving said carriage 7 in a distribution movement, according to instructions received; an orientation motor device 43 coupled to the boom 4, capable of moving said boom, and therefore the carriage 7 and the suspended load 2 in an orientation movement, according to the instructions received.

[0060] The command execution system 40 also comprises a measurement system 45 configured to deliver a set MES of physical and mechanical measurements, relating to the motor devices 41-42-43, to the load, as well as to the environment of the crane 3.

[0061] More particularly, the measuring system 45 comprises a set of sensors for measuring the mass of the load.

[0062] The measuring system 45 also comprises a set of sensors for determining, at each instant, the position, speed and acceleration of the main components of the command execution system 40, in particular the carriage 7, the boom 4, and the devices mechanically coupled to the load 2.

[0063] The control device 10 is configured to produce CMD lifting speed instructions as a function of interactions with a crane operator and to transmit said CMD lifting speed instructions to the monitoring and control device 20. The CMD lifting speed instructions may include in particular positioning, and / or speed, and / or acceleration instructions, intended in particular to be transmitted to the lifting motor device 41.

[0064] The control device 10 generally comprises a user interface, for example of the joystick type, which is intended to be manipulated by a crane operator to produce the lifting speed setpoints CMD. However, the lifting speed setpoints CMD can also be produced by other means, such as an automated control device.

[0065] The monitoring and control device 20 is coupled to the control device 10 to receive the lifting speed instructions CMD and to the measurement system of the command execution system 40 to receive the set MES of measurements.

[0066] The monitoring and control device 20 is configured to produce, as a function of the lifting speed setpoints CMD and the set of measurements MES, optimized lifting speed setpoints CMD' intended to be executed by the lifting motor device 41 to move the suspended load 2 in a lifting movement such that the acceleration relative to the lifting movement remains, in absolute value, less than or equal to a maximum authorized lifting acceleration L" MAX.

[0067] The controller 30 is coupled to the command execution system 40 and to the monitoring and control device 20 to receive the optimized lifting speed setpoints CMD'.

[0068] The controller 30 is configured to control the lifting motor device 41 belonging to the command execution system 40, according to the optimized lifting speed setpoints CMD'.

[0069] Typically, the controller 30 comprises automated control means, for example in a closed loop, in order to control, as a function of the information transmitted by the sensors of the measuring system and the information included in the optimized lifting speed instructions CMD', the positioning, speed and / or acceleration of the mechanical components of the command execution system 40.

[0070] We refer to the figure 2 , on which is represented a synopsis of the steps of a method, according to the invention, for controlling the lifting command of a load 2 suspended from a boom 4, carried by a mast 6 of a crane 3 (here a tower crane).

[0071] The method is in particular capable of being implemented by the command control system 1, previously described, and more particularly by the monitoring and control device 20.

[0072] During a first step 110, a specified load factor Ψ 0 * is determined, as a function of the mass M of the suspended load.

[0073] The specified load factor Ψ 0 * quantifies an acceptable excess over a predetermined maximum permissible load for the said crane. The specified load factor Ψ 0 * can be determined by means of a maximum permissible load curve, corresponding to a predetermined limit load factor Ψ 0 and a maximum static load.

[0074] In one embodiment, the limit load factor Ψ 0 is determined from a first theoretical threshold which is a function of the theoretical load capacities supported by the crane and a second threshold which is a function of measurement uncertainties relating to the mass of the suspended load and / or the lifting movement of the suspended load. The first theoretical threshold is typically defined according to a theoretical mechanical model of an ideal crane.

[0075] The load factor Ψ 0 limit is for example obtained by adding the first theoretical threshold and the second threshold. For example, if we consider a first theoretical threshold authorizing an excess of 10% of the maximum load, and a second threshold, an additional excess of 7.5% linked to measurement uncertainties, the load factor Ψ 0 limit is then equal to 10% + 7.5% = 17.5%.

[0076] The specified load factor Ψ 0 * can in particular be obtained by multiplying the predetermined limit load factor Ψ 0 by the ratio between, on the one hand, the maximum static load which corresponds to the maximum permissible load curve established for the limit load factor Ψ 0 , and on the other hand the effective mass M of the suspended load 2 handled by the crane 3 at the time considered.

[0077] Thus, for a given limit load factor Ψ 0, and therefore for a given basic maximum load curve, the lower the mass M of the suspended load 2, the higher the specified load factor Ψ 0 * will be.

[0078] The predetermined limit load factor Ψ 0 can in particular be chosen according to business rules, and / or vary according to the area of ​​use of the crane.

[0079] During a second step 120, a maximum authorized lifting acceleration L" MAX is determined, as a function of the mass M of the suspended load, the specified load factor Ψ 0 *, the distribution position X c of the suspended load 2 relative to the mast 6.

[0080] Preferably, the maximum permissible lifting acceleration L" MAX is also determined as a function of inertia components J z specific to the structure of the crane 3.

[0081] For example, the figure 5 represents a diagram comprising a set of surface curves describing the maximum authorized lifting acceleration L" MAX , expressed in g (1g corresponding to the acceleration of gravity), as a function of the mass M of the suspended load 2, expressed in kilograms, and the position in distribution X c of said suspended load, expressed in meters.

[0082] Each surface curve corresponds to a distinct specified load factor Ψ 0 *.

[0083] As a reminder, the limit load factor Ψ 0 used to determine the specified load factor Ψ 0 * can be freely chosen by the person responsible for configuring the crane.

[0084] In the example of the figure 5 , the set includes three surface curves corresponding to a specified load factor Ψ 0 * equal, respectively, to 0.15, 0.175, 0.2.

[0085] It is of course possible to use a set with a higher number of surface curves, so as to cover more finely and / or over a larger range different values ​​for the specified load factor Ψ 0 *.

[0086] Thus, during the second step 120, the maximum authorized lifting acceleration L" MAX can be determined, at any time, as a function of the mass M and the distribution position Xc, by determining by means of the surface curve corresponding to the specified load factor Ψ 0 *.

[0087] During a third step 130, optimized lifting speed setpoints CMD' are determined, from lifting speed setpoints CMD.

[0088] The optimized lifting speed instructions CMD' are intended to be executed by the lifting motor device 41 to move the suspended load 2 in a lifting movement in such a way that the acceleration specific to the lifting movement remains, in absolute value, less than or equal to the maximum authorized lifting acceleration L" MAX.

[0089] It should be noted that the maximum permissible lifting acceleration L" MAX is variable, depending on the load factor Ψ 0 * specified.

[0090] The maximum authorized lifting acceleration L" MAX is thus used as a value limiting the variations in speed of the suspended load, imparted by the motor device 41 at the origin of the lifting movement.

[0091] The optimized lifting speed instructions CMD' can further be determined, as a function of the lifting speed instructions CMD received from the control device 10, so that their implementation by the command execution system 40 also respects one or more of the constraints of the following non-exhaustive list: a maximum authorized lifting speed V MAX BRK, determined according to the crane's capacity to brake the movements of the suspended load 2, in particular to guarantee the safety of the braking of the load at all times; a maximum safe lifting speed V MAX SEC, determined according to the crane's capacity 3 to withstand a sudden ground placement of the suspended load 2 or an emergency stop, so as to ensure that the resulting dynamics remain within an acceptable envelope for the structure - said envelope being different from the nominal load curve; a maximum lifting acceleration L" SEC achievable by means of the lifting motor device 41; a minimum lifting acceleration L" MIN , called "minimum comfort acceleration", which is predetermined so as to set a lifting acceleration value which is high enough to ensure a certain comfort of lifting, but the value of which is low enough (in absolute value) to never endanger the crane; in practice, this minimum comfort acceleration can be used instead of the maximum acceleration L" MAX so as not to immobilize the crane unnecessarily.

[0092] We now refer to the figure 4 , on which is represented a principle diagram used to describe a mechanical model of the oscillator type, used, according to an embodiment of the invention, during the second step 120, to determine the maximum authorized lifting acceleration L" MAX.

[0093] The mechanical model presented below makes it possible to establish an inequality between the maximum authorized lifting acceleration L" MAX and the specified load factor Ψ 0 *. As long as this inequality is respected, the effective instantaneous load factor Ψ - corresponding to the load transport conditions at the instant considered - remains lower than the specified load factor Ψ 0 *. Thus, the static and dynamic load experienced at the instant considered by the crane never exceeds the maximum permissible overshoot fixed by the maximum permissible load curve.

[0094] The mechanical model can thus be described using the following mathematical expressions: J z θ ¨ = − Kθ + x c F z J z θ ¨ 0 = − Kθ 0 + x c F z 0 M L ¨ = F z − Mg M L ¨ 0 = F z 0 − Mg in which θ represents the pitch deflection angle of the boom 4 (i.e. the angle formed in pitch by the deformation of the boom 4 relative to the position of said boom when empty, due to the deformation by tilting bending of said boom 4 under the effect of the load); Δ F z = F z - Mg corresponds to the variation in vertical force linked to the load, F z being the vertical load at the instant considered; J z , K corresponds to a first-order stiffness and inertia model relative to the crane structure; more specifically, K corresponds to the stiffness of boom 4 in pitch bending, and Jz the inertia of boom 4 relative to its point of intersection with mast 6; M corresponds to the mass of the load; θ̃ = θ - θ 0 corresponds to the variation of the horizontal angle of the arrow; L̃ = L - L0 corresponds to the variation in load height directly proportional to the length of cable wound / unwound at the level of the lifting winch, or directly related quantity; we deduce: Jzθ˜¨=−Kθ˜+xcΔFz ML¨=ΔFz

[0095] It should be noted that the damping stiffness effect is neglected, since this does not amplify the dynamic effects of the deflection when the dynamic factor is significant - (as is the case in the load lifting phase or significant variation).

[0096] We can ask: − K θ ˜ + x c Δ F z ≤ x c Δ F z

[0097] Since M L ¨ = Δ F z and that consequently: x c Δ F z = x c M L ¨ we thus obtain the following mathematical expression: J z θ ˜ ¨ = − K θ ˜ + x c Δ F z ≤ Mx c L ˜ ¨

[0098] The effective instantaneous load factor Ψ corresponds to the quotient of the sum of the vertical acceleration of the suspended load - i.e. the acceleration of winding or unwinding of the cable - and the acceleration related to the pitch deflection of the crane boom, in the numerator, by the acceleration of gravity g, in the denominator, i.e. corresponds to the sum, related to the acceleration of gravity, of the vertical acceleration of the load and the acceleration related to the deflection of the boom 4. Thus, the effective instantaneous load factor Ψ can be described by the following mathematical expression: Ψ = L ˜ ¨ g + x c θ ˜ ¨ g Thus, we obtain the following inequality: Ψ = L ˜ ¨ g + x c θ ˜ ¨ g ≤ x c 2 M + J z gJ z L ˜ ¨

[0099] Therefore, if one chooses to limit the lifting acceleration L ˜ ¨ so that we respect: L ˜ ¨ < gJ z x c 2 M + J z Ψ 0 ∗

[0100] So we will necessarily have: Ψ = x c 2 M + J z gJ z L ˜ ¨ < x c 2 M + J z gJ z gJ z x c 2 M + J z Ψ 0 ∗

[0101] Either : Ψ < Ψ 0 ∗

[0102] Thus, the actual instantaneous load factor Ψ will always be less than the specified load factor Ψ 0 *.

[0103] In one embodiment, during the third step 130, the limitation of the lifting speed variations, i.e. the limitation of the lifting acceleration, with respect to the specified load factor Ψ 0 *, a limitation which makes it possible to impose the above inequality, is preferably obtained by the application of a ramp limiter type LIM function, more commonly referred to by the English expression “ramp limiter”. The ramp limiter type LIM function makes it possible to ensure that the speed variation requested at the input never exceeds a maximum acceleration threshold. Thus, the speed setpoint at the output of the LIM function respects the objective set by the designer.

[0104] In one embodiment, the LIM function describes a ramp whose slope corresponds to the maximum authorized acceleration L" MAX.

[0105] Also, for example, in response to a step of speed commands included in the CMD instructions, requested by the crane operator, the optimized CMD' instructions will include speed instructions to be applied, the value of which increases progressively, for a predefined period of time, following the ramp described by the LIM function, the slope of which corresponds to the maximum authorized acceleration L" MAX. In this way, the inertial effects are limited.

[0106] We now refer to the figure 3 , on which is shown a block diagram of the monitoring and control device 20, according to an embodiment of the invention. In this embodiment, the monitoring and control device 20 is configured to implement the lifting command control method, previously described, by means of the mathematical model as described previously, with regard to the figure 4 .

[0107] More particularly, the monitoring and control device 20 comprises a speed limiter module 210, an acceleration limiter module 220, and a braking and cut-off module 230 (noted SD&CUTF for “SlowDown & CUToFf”).

[0108] The speed limiter module 210 is configured to produce, for the acceleration limiter module 220, a higher CV lifting speed target setpoint, as a function of the CMD lifting speed setpoints, sent by the control device 10. The higher CV lifting speed target setpoint is determined by calculating the result of a limiter LIMv function for the value corresponding to the minimum between: the maximum authorized speed V MAX BRK, depending on the crane's ability to brake the movements of the suspended load; and, the maximum safe lifting speed V MAX SEC, determined according to the crane's ability to withstand sudden grounding of the suspended load and / or an emergency stop (braking and stopping of the lifting movement), so as to avoid jolts in emergency situations.

[0109] The acceleration limiter module 220 comprises a calculation module 240 of the maximum acceleration L" MAX , as a function of the specified load factor Ψ 0 *, the distribution position X c and the mass M.

[0110] The calculation module 240 may include means for reading in a preconfigured memory an abacus / a map corresponding to a set of surface curves as shown in the figure 5 .

[0111] Alternatively, the calculation module 240 may comprise calculation means using an explicit mathematical description, as described previously with regard to the figure 4 , to determine the maximum acceleration L" MAX .

[0112] The acceleration limiter module 220 is configured to determine the speed setpoint value applicable to the lifting motor 41, and gradually bring said speed setpoint to the higher lifting speed value CV, by applying as variation rate (slope VL" of the acceleration ramp), a value VL" which corresponds to the maximum between: ∘ on the one hand the minimum value between: ▪ the maximum lifting acceleration L" MAX determined by the calculation module 240; and, ▪ the maximum lifting acceleration L" SEC achievable by the lifting motor device 41 (so that the acceleration setpoint cannot exceed the hardware capacities of the lifting motor 41); the value thus retained at the time considered therefore advantageously corresponds to the most restrictive operating safety requirement, and consequently to the most unfavorable operating condition; ∘ and on the other hand a minimum lifting acceleration L" MIN , called “comfort lifting acceleration”.

[0113] The minimum lifting acceleration L" MIN corresponds to a minimum comfort acceleration for the crane operator to control. As indicated above, this minimum comfort acceleration is chosen to be low enough not to endanger the crane, while being high enough not to immobilize the crane unnecessarily, in particular when the calculated maximum lifting acceleration L" MAX is, occasionally, exceptionally low or abnormally low.

[0114] The chosen lifting acceleration value, applicable at the time considered, and therefore the slope VL" of the corresponding acceleration ramp, thus reflects the best possible compromise, taking into account operational safety requirements.

[0115] Advantageously, the acceleration limiter module 220 comprises means for limiting, over time, the lifting acceleration corresponding to the target lifting speed instructions CV received, by applying the LIM function of the ramp limiter type, describing a ramp whose slope corresponds to the value VL". The LIM function of the ramp limiter type makes it possible to restrict the speed variation requested at the input so that the lifting acceleration observed in absolute value remains lower than the value VL".

[0116] Preferably, the braking and cut-off module 230 is configured to ensure that the optimized instructions CMD' produced as a function of the acceleration instructions CA do not cause the load to move according to the distribution movement beyond a limit position XC MAX. If necessary, the cut-off module 230 modifies the optimized instructions CMD' so that the load does not exceed the limit position XC MAX after the implementation of the optimized instructions CMD'. It will be noted, more generally, that the invention preferably comes advantageously in superposition of the conventional safety devices making it possible to stop the movements of the crane in the event of the occurrence of a dangerous situation.

[0117] Thus, the optimized CMD' instructions can typically be transmitted to the crane's traditional safety and cut-off devices, which can therefore remain active in order to carry out their usual mission.

[0118] More particularly, the braking and cut-off module 230 can thus slow down the lifting motor 41 or even stop it when the load approaches, or even reaches, the predefined limit position XC MAX.

Claims

1. A method for controlling the command of the lifting of a load suspended from a boom and having a mass (M), carried by a mast of a crane, comprising at least a step of determining, from lifting speed setpoints (CMD), optimized lifting speed setpoints (CMD') intended to be executed by a motor device (41) for displacing the suspended load according to a lifting movement so that the acceleration related to the lifting movement remains, in absolute value, less than or equal to a maximum permitted lifting acceleration (L"MAX), said method being characterized in that it includes the following preliminary steps: • a first step (110) of determining, depending on the mass (M) of the suspended load, a specified load factor (Ψ0*) quantifying an acceptable exceedance related to a predetermined maximum allowable load for said crane; and • a second step (120) of determining the maximum permitted lifting acceleration (L"MAX), depending on the mass (M) of the suspended load, on the specified load factor (Ψ0*) and on the distribution position (Xc) of the load suspended on the boom with respect to the mast.

2. The method according to claim 1, wherein the maximum permitted lifting acceleration (L"MAX) is determined using the following mathematical expression: gJ z x c 2 M + J z ψ 0 ∗ wherein: xc corresponds to the distribution position of the suspended load; M corresponds to the mass of the suspended load; Jz corresponds to a model of stiffness and inertia of the first order related to the structure of the crane;3. The method according to any one of the preceding claims, wherein the specified load factor (Ψ0*) is determined by means of a maximum allowable load curve, corresponding to a limit load factor (Ψ0) and to a maximum static load.

4. The method according to claim 3, wherein the limit load factor (Ψ0) is determined from a first theoretical threshold dependent on the theoretical load capacities handled by the crane and from a second threshold dependent on measurement uncertainties related to the mass of the suspended load and / or to the lifting movement of the suspended load.

5. The method according to any one of claims 3 to 4, wherein the specified load factor (Ψ0*) is obtained by multiplying the limit load factor (Ψ0) by the ratio between the maximum static load corresponding to the maximum allowable load curve and the mass (M) of the suspended load.

6. The method according to any one of the preceding claims wherein the optimized lifting speed setpoints (CMD') are determined so that their execution by the motor device (41) for displacing the suspended load according to the lifting movement meets the following condition: ∘ the lifting acceleration of the suspended load, in absolute value, remains less than or equal to the maximum permitted lifting acceleration (L"MAX); as well as one or more of the following additional conditions: ∘ the lifting speed of the suspended load, in absolute value, remains lower than a maximum permitted lifting speed (VMAX BRK), the maximum permitted lifting speed (VMAX BRK) being determined depending on the capacities of the crane to slow down the movements of the suspended load; and / or, ∘ the lifting speed of the suspended load, in absolute value, remains lower than a maximum safety lifting speed (VMAX SEC), determined depending on the capacities of the crane to withstand a sudden lying of the suspended load on the ground and / or an emergency stopping; and / or, ∘ the lifting acceleration of the suspended load, in absolute value, remains lower than a maximum lifting acceleration (L"SEC) achievable by the motor device (41); and / or, ∘ the lifting acceleration of the suspended load, in absolute value, remains greater than a minimal lifting acceleration (L"MIN).

7. The method according to any one of the preceding claims wherein the optimized lifting speed setpoints are determined so that the absolute value of the lifting speed of the suspended load increases, over a predefined period of time, along a ramp whose slope corresponds to the maximum permitted lifting acceleration (L"MAX).

8. A crane, preferably a tower crane, including a mast supporting a boom on which is mounted a carriage intended to carry a suspended load having a mass (M), and means (20) for controlling the command of the lifting of the suspended load provided with means for determining, from lifting speed setpoints (CMD), optimized lifting speed setpoints (CMD') intended to be executed by a motor device (41) for displacing the suspended load according to a lifting movement so that the acceleration related to the lifting movement remains, in absolute value, less than or equal to a maximum permitted lifting acceleration (L"MAX), said crane being characterized in that the means (20) for controlling the command of the lifting of the suspended load are further provided with: • means for determining, depending on the mass (M) of the suspended load, a specified load factor (Ψ0*) quantifying an acceptable exceedance with respect to a predetermined maximum allowable load for said crane; • means for determining the maximum permitted lifting acceleration (L"MAX), depending on the mass (M) of the suspended load, on the specified load factor (Ψ0*) and on the distribution position (Xc) of the load suspended on the boom with respect to the mast.

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