EP0467783A1 - Pending charge movement control procedure, and arrangement for implementing the same - Google Patents

Abstract

The method makes it possible to control the movement of a swinging load suspended from a support which is horizontally mobile and moved from a departure point to an arrival point during a journey of predetermined duration (T). The movable support (40) is subject to a support movement law x(t) determined such that the movement of the swinging load (20) is regulated by a load movement law X(t) satisfying the following conditions: X''(t) is continuous and derivable according to the time variable t, X''(t) = 0 and X'''(t) = 0 for t>/=T. Use especially for port lifting engines such as cranes, gantries for buckets or for containers. <IMAGE>

Description

The present invention relates to a method for controlling the movements of a pendulum load suspended from a horizontally movable support.

The invention also relates to devices for its implementation.

The invention applies in particular to port lifting devices such as cranes, gantry cranes or containers.

In the industrial field of handling and lifting of loads, in particular of containers, a primary objective is to precisely move from one point to another a load suspended by cables to a mobile support, such as a motorized trolley, and in particular to obtain a zero swing of the load at the end of the journey.

However, the precision of the displacement depends essentially on the control and the damping of the oscillations of the load during the displacement.

A certain number of methods for controlling the movements of pendular loads already exist, but the operating times given by these methods depend on the period of the pendulum constituted by the suspended load.

• les mouvements sont calculés avant le démarrage du mouvement en fonction des longueurs pendulaires qui sont elles-mêmes variables pendant le mouvement, en particulier pour les appareils de levage. Le calcul des paramètres du mouvement doit donc être effectué avant la mise en route en faisant des approximations sur la longueur du pendule et sur la variation de celle-ci ;
• dans le cas de petits mouvements, les mouvements, liés à la période du pendule, sont nécessairement lents ;
• il est difficile de tenir compte de conditions initiales non nulles.

These methods have the following disadvantages in particular:

• the movements are calculated before the start of the movement as a function of the pendulum lengths which are themselves variable during the movement, in particular for lifting devices. The calculation of the movement parameters must therefore be carried out before start-up by making approximations on the length of the pendulum and on the variation thereof;
• in the case of small movements, the movements, linked to the pendulum period, are necessarily slow;
• it is difficult to take into account non-zero initial conditions.

These drawbacks mean that the movement precision, if it remains sufficient for handling bulk products, is insufficient for handling containers.

The object of the present invention is to remedy these drawbacks by proposing a method for controlling the movements of a pendulum load suspended from a horizontally movable support, and moved from a starting point to an ending point during a travel from predetermined duration, which allows for taking into account disturbances and pendulum length variations and which uses the power of the lifting device to the maximum in order to reduce travel times.

According to the invention, the mobile support is subjected to a law of displacement of the support x (t) determined so that the displacement of the pendulum load is governed by a law of displacement of load X (t) satisfying the following conditions:
X˝ (t) is continuous and differentiable
X˝ (t) = 0 and X ‴ (t) = 0 for t ≧ T (duration of the journey), t denoting time, X˝ the second derivative i.e. the acceleration of the load during its displacement and X ‴ the third derivative.

Thus, rather than imposing, as in the previous control methods, the displacement of the mobile support and searching for the particular parameters giving a zero swing at the end of the journey, the mathematical conditions according to the invention guaranteeing zero swing, it suffices to choose a displacement law that meets these conditions. We can then make a choice based on parameters such as maximum speed and maximum acceleration of the mobile support to determine the displacement law giving the shortest travel times.

γ étant l'accélération de la charge au cours du trajet.In an advantageous embodiment of the invention, the law of displacement of the support x (t) is chosen so that the pendulum load is subject to an acceleration law X˝ (t) governed by the relation $$\text{X˝ (t) =}\frac{\text{<figure-callout id="2" label="γ" filenames="imgf0003.png" state="{{state}}">γ</figure-callout>}}{\text{2}}\text{. (1 - cos}\frac{\text{2π}}{\text{T}}\text{. t),}$$

γ being the acceleration of the load during the journey.

This simple writing law meets the conditions for canceling load balancing set out above. Its dual integration also presents no particular difficulty in implementation.

According to another aspect of the invention, the device for controlling the movement of a pendulum load suspended from a horizontally movable support, implementing the method according to the invention, associated with a lifting machine comprising lifting means and steering means, is characterized in that it comprises control and processing means receiving, on the one hand, information representative of the length of the associated pendulum, of the swing angle and of the displacement of the mobile support respectively length acquisition means, angle acquisition means and displacement acquisition means, and in return issuing lifting orders and direction orders respectively intended for lifting means and direction means , said direction orders being calculated so as to satisfy the displacement law X (t) according to the method as defined above.

• la figure 1 est une vue d'une forme pratique de réalisation du dispositif de contrôle de déplacement selon l'invention,
• la figure 2 est une vue générale d'un engin de levage portuaire pouvant être équipé d'un dispositif selon l'invention,
• la figure 3 représente la loi d'évolution de la vitesse d'un chariot dans un dispositif de contrôle de déplacement, dans l'art antérieur,
• la figure 4 est un schéma qui illustre les différentes variables géométriques utilisées pour la description du procédé et du dispositif selon l'invention,
• les figures 5A, 5B et 5C représentent respectivement les lois d'évolution de l'accélération, de la vitesse et du déplacement d'une charge pendulaire, avec le procédé selon l'invention,
• la figure 6 est un schéma bloc illustrant le procédé selon l'invention.

Other features and advantages of the invention will become apparent in the description below. In the appended drawings, given by way of nonlimiting examples:

• FIG. 1 is a view of a practical embodiment of the movement control device according to the invention,
• FIG. 2 is a general view of a port lifting device which can be fitted with a device according to the invention,
• FIG. 3 represents the law of evolution of the speed of a carriage in a displacement control device, in the prior art,
• FIG. 4 is a diagram which illustrates the various geometrical variables used for the description of the method and the device according to the invention,
• FIGS. 5A, 5B and 5C respectively represent the laws of evolution of the acceleration, the speed and the displacement of a pendulum load, with the method according to the invention,
• FIG. 6 is a block diagram illustrating the method according to the invention.

We will now explain the displacement control method according to the invention, together with the description of the device implementing the method.

In a particular embodiment of a control device according to the invention illustrated in FIG. 1, the device for controlling the movement of a pendular load 20 suspended from a mobile support of a lifting machine 1 comprises a computer 4 receiving on the one hand, at input CL, information on the length of the pendulum from a position encoder 7, at input B, sway information from a camera 18, or any other optical analysis device, and at the CD input, information on the displacement of the mobile support or direction information, and delivering in return, at output SL, lifting orders transmitted to lifting means 6, 5, 8 of the lifting machine 1, and at output SD, direction orders transmitted to lifting means 1 direction 14, 15, 16.

The lifting means comprise a lifting drum 8 around which is wound a suspension cable 21 connected to the load 20, for example, a container, a reduction gear 5 and an electric motor 6, arranged according to well known techniques. The lifting motor 6, with which the lifting encoder 7 is associated, is controlled, via a control line 9 and an amplifier 10, either from a lifting control lever 2 or by the computer 4, through the aforementioned SL output.

The steering means comprise a steering roller 16 rolling on a horizontal steering rail 17 linked to the lifting machine, a reduction gear 15 and an electric motor 14 to which a direction encoder 13 is fixed. This steering motor 14 is controlled via a steering power line 12 and a power amplifier 11, either from a steering control lever 3, or by the computer 4, through the aforementioned SD output.

The swing angle is measured by a camera 18 secured to the movable support and the objective of which is directed vertically downwards, the pendulum load 20 being fitted with an optical beacon 19 emitting a beam directed upwards.

The general diagram of a container handling and lifting machine 30 that can be fitted with a movement control device according to the invention is given in FIG. 2.

The port lifting device 30 comprises, according to known techniques, a gantry 35 to which a horizontal boom structure 33 is connected. A mobile carriage 34 can be moved horizontally in a direction X along the arrow 33. A container 31 is suspended from the mobile carriage 34 by cables 32 whose variation in length allows the container 31 to move in a vertical direction Z.

• une phase d'accélération constante, de durée T1,
• une phase à vitesse constante, de durée T2,
• une phase de décélération constante, de durée T3.

Previous techniques for controlling the movements of lifting devices generally call for particular solutions of the differential equation of movement of a pendulum load. FIG. 3 illustrates a law of evolution of the speed V as a function of the time t of the point of suspension of the load when the latter is animated by a movement which can be broken down into:

• a constant acceleration phase, of duration T1,
• a phase at constant speed, of duration T2,
• a constant deceleration phase, of duration T3.

These particular solutions are functions of the pendulum period. One method of reaching an end point without swinging consists in calculating adequate acceleration times T1 and braking times T3 as a function of the length of the pendulum and the duration T2 of the phase at constant speed. The disadvantages of these techniques, travel time linked to the pendulum period, difficulty in taking into account initial conditions, in particular, are eliminated with the implementation of the control method according to the invention.

FIG. 4 illustrates the main geometric variables taken into account in the implementation of the method according to the invention. The variable x represents the horizontal displacement of the carriage or mobile support 40. A perpendicular load 41 is suspended from the mobile carriage 40 by a cable of length l . In a situation of rocking, the cable is inclined at an angle α relative to the vertical, the pendulum load 41 having a gap y relative to said vertical. The instantaneous displacement of the pendulum load 41 is represented by a variable X equal to the sum x + y.

   X˝(t) = 0 pour t≧T (durée du trajet)
      γ étant l'accélération maximale de la charge.An example of displacement law X (t) of the pendulum load 41 which satisfies the mathematical conditions according to the invention is associated with the following acceleration law: $$\text{X˝ (t) =}\frac{\text{γ}}{\text{2}}\text{(1 - <figure-callout id="2" label="cos" filenames="imgf0003.png" state="{{state}}">cos</figure-callout>}\frac{\text{2 π}}{\text{T}}\text{· T) for 0 ≦ t <T}$$

X˝ (t) = 0 for t ≧ T (journey time)
γ being the maximum acceleration of the load.

It is easy to verify that the resulting law of displacement X (T) satisfies the aforementioned conditions, namely:
the second derivative X˝ (t) is continuous and differentiable and X˝ (t) = 0 and X ‴ (t) = 0 for a time t ≧ T (duration of the journey).

   g étant l'accélération de la pesanteur.Furthermore, the displacement of the suspension point of the load 41, and therefore the displacement of the mobile support 40 is determined by expressing the dynamic balance of the pendulum load: $$\text{X˝ (t) =}\frac{\text{y}}{\text{l}}\text{(g}\sqrt{\text{1- (}\frac{\text{y}}{\text{l}}}\text{) ²- l˝)}$$

g being the acceleration of gravity.

Equation (1) calculates the displacement X (t) as a function of the maximum acceleration γ and the travel time T, while equation (2) calculates the difference y as a function of the derivative second l˝ of the instantaneous length of the pendulum associated with the load and the acceleration X˝ (t).

It is easily shown that the above considerations lead to the equation of the second degree in y , that is to say of the deviation of the load from the vertical, as follows:

The root with the sign of (-X˝) is the solution of equation (3).

From knowing the difference y and the displacement X, we can easily deduce x (t) as the evolution of l (instantaneous length of the pendulum) progresses.

The position x of the carriage 40 is determined, with reference to FIG. 1, using the encoder 13, for example an incremental encoder, mounted on the shaft of the steering motor 14.

The variable l is determined by the encoder 7 mounted on the shaft of the lifting motor 6 while the variable y is calculated from the angle α and the length l via the optical system constituted by the camera 18 and tag 19.

This tag 19 constitutes a light source which creates a light spot on the sensitive element of the camera 18 which in return delivers a signal proportional to the angle α.

Knowing the angle α and the length l , the computer 4 can then determine the theoretical value of the difference y and the instantaneous real position X of the pendulum load 41.

In fact, in a port lifting device, there are real situations of disturbances due for example to the effect of the wind or to an initial rocking.

We can take into account the initial swing or disturbances tending to spread the position of the pendulum load from the theoretical law of displacement X (t) by controlling the position of the load to its theoretical position, represented in the form of a block diagram 60 in FIG. 6.

   x_th représentant le déplacement théorique et K₁ε′₁ représentant la correction à apporter à ce déplacement théorique. Cette correction correspond à un effort d'amortissement de type visqueux.A first block 61 illustrates the calculation of the theoretical displacement X (t) according to the invention. This theoretical displacement X (t) is compared to the actual displacement X equal to the sum of the displacement x of the carriage 40 (Figure 4) and of the product l.sin α of the instantaneous length l of the pendulum and the sine of the swing angle α, this sum being represented by block 67. The difference ε1 between the theoretical displacement X (t) and the actual displacement X is derived at 62. The derivative ε′1 allows the calculation of the corrected displacement x of the carriage 40 according to the relation (block 63) below: $${\text{x =}}_{\text{xth}}\text{+ K₁ ε′1}$$

x _th representing the theoretical displacement and K₁ε′₁ representing the correction to be made to this theoretical displacement. This correction corresponds to a viscous type damping force.

avec

X′_th

: dérivée du déplacement théorique X_th

ε₂

: erreur de la boucle d'asservissement en x,

et K₂

: coefficient de correction.

This correction calculation is followed by a displacement control loop x comprising a calculation of a speed reference CV according to the following relation (block 64): $${\text{CV = X ′}}_{\text{th}}\text{+ K₂ε₂,}$$

with

X ′ _th

: derived from the theoretical displacement X _th

ε₂

: error of the control loop in x,

and K₂

: correction coefficient.

The speed is then regulated (block 65) at the level of the steering motor 14 (FIG. 1). The effective displacement x of the carriage causes a swinging of angle α (block 66). Such control ensured a substantially zero swing at the end of the pendulum load path.

FIGS. 5A, 5B and 5C respectively illustrate the laws of evolution of the acceleration X˝ (t), the speed X ′ (t) and the displacement X (t) of the carriage in the particular embodiment of the invention described above, with maximum acceleration γ = 0.6 m / s², travel time T = 10 s and an initial speed V _o zero.

The method according to the invention moreover allows a relative optimization of the duration T of the path of the pendulum load. For a given distance D to be covered, it is possible to vary the period T of the maximum acceleration continuously.

By way of example, for a path comprising an acceleration phase and a braking phase, the relationship linking the period T, the maximum acceleration γ and the distance D, is as follows: $$\text{D =}\frac{{\text{<figure-callout id="2" label="γ T2" filenames="imgf0003.png" state="{{state}}">γ </figure-callout>}}^{\text{T2}}}{\text{2}}$$

• limitations de vitesse,
• limitation d'accélération,
• limitation de puissance.

If one seeks to decrease the duration of the journey for a given distance, the maximum acceleration γ must increase. We are then limited by the mechanical performance of the lifting machine. One can in particular be led to consider the following limitations:

• speed limits,
• acceleration limitation,
• power limitation.

When the maximum speed of the carriage is reached, it is possible to insert between the phases acceleration and braking, a phase during which the displacement of the pendulum load will be carried out without swinging and at speed of VMAX speed.

• effet moteur au niveau du point de suspension de charge inférieur à FMAX,
• vitesse du point de suspension inférieure à VMAX.

In a practical embodiment of the invention, the following limitations have been taken into account:

• motor effect at the load suspension point lower than FMAX,
• suspension point speed lower than VMAX.

If the first limitation (VMAX) is not reached, the journey time T and the maximum acceleration γ can then be determined. On the other hand, if this limitation is reached, a phase at VMAX speed is undertaken. A maximum acceleration and a distance traveled at VMAX speed are also determined.

Of course, the invention is not limited to the examples described and shown and numerous modifications can be made to these examples without departing from the scope of the invention.

It is thus possible to determine a displacement law which optimizes the performance of the lifting devices fitted according to the invention, taking into account any additional limitations.

Claims (15)

Method for controlling the movement of a pendulum load (20, 41, 31) suspended from a horizontally movable support (40, 34) and moved from a starting point to an ending point during a journey of predetermined duration ( T), characterized in that the movable support (40, 34) is subjected to a support displacement law x (t) determined so that the displacement of the pendulum load (20, 41, 31) is governed by a charge displacement law X (t) satisfying the following conditions:
X˝ (t) is continuous and differentiable according to the time variable t,
X˝ (t) = 0 and X ‴ (t) = 0 for t ≧ T (journey time), t denoting time, X˝ the second derivative, i.e. the acceleration of the load during of its displacement and X ‴ the third derivative. Method according to claim 1, characterized in that the law of displacement of support x (t) is chosen so that the pendulum load is subjected to a law of acceleration X˝ (t) governed by the relation: $$\text{X˝ (t) =}\frac{\text{γ}}{\text{2}}\text{. (1 - cos}\frac{\text{2π}}{\text{T}}\text{. t)}$$

γ being the maximum acceleration of the load during the journey. Method according to claim 2, characterized in that it comprises the following steps: A) calculation of the instantaneous theoretical value of the displacement variable X (t) of the pendulum load (20, 31, 41) by double integration of the law of acceleration X˝ (t) and as a function of the initial speed ( _Vo ) of the pendulum load (20, 31, 41), B) calculation of the instantaneous theoretical value of the deviation y (t) of the load from the vertical, as a function of the instantaneous length (l) of the pendulum associated with the pendulum load (20, 31, 41), C) calculation of the theoretical nominal value of displacement x (t) of the mobile support (34, 40), knowing that x (t) = X (t) - y (t), from the results of the above-mentioned steps A) and B). Method according to claim 3, characterized in that it further comprises a step (AS) of controlling the real position of the pendulum load (20, 31, 41) to its theoretical position represented by the displacement variable X ( t). Method according to claim 4, characterized in that it further comprises the following acquisition steps:
AC1 / acquisition of the instantaneous length (l) of the pendulum,
AC2 / acquisition of the real displacement variable (x) of the mobile support (34, 40),
AC3 / acquisition of the angle (α) between the pendulum and the vertical,
and a step of calculating the real displacement (X) of the pendulum load, from the result of the aforementioned acquisition steps, followed by a step of calculating the error (E1) equal to the difference between the theoretical displacement X (t) and the real displacement X. Method according to claim 5, characterized in that it further comprises a step of determining a correction (CORx), said correction (CORx) being added to the theoretical displacement variable (x (t)) to obtain the setpoint effective displacement (x) of the mobile support (40). Method according to one of claims 2 to 6, characterized in that it further comprises a limitation from the speed of the mobile support (40, 34) to a maximum speed (VMAX) and in that, when said limitation is reached, a displacement phase at constant speed is executed. Method according to one of claims 2 to 7, characterized in that it further comprises a limitation of the force applied to the mobile support (40, 34) to a maximum force (FMAX). Method according to one of claims 2 to 8, characterized in that it further comprises a step of relative optimization of the duration of the path of the pendulum load (20, 41, 31). Device for controlling the movement of a pendulum load (20) suspended from a horizontally movable support (40, 34), implementing the method according to the invention, associated with a lifting machine (1, 30) comprising means for lifting (5, 6, 8) and steering means (14, 15, 16, 17), characterized in that it comprises control and processing means (4) receiving on the one hand information representative of the length (l) of the associated pendulum, of the swing angle (α) and of the displacement (x) of the mobile support (40) originating respectively from length acquisition means (7), from angle acquisition means (18) and displacement acquisition means (13), and in return issuing lifting orders and direction orders respectively to said lifting means (5, 6, 8) and said steering means (14, 15, 16, 17), said direction orders being calculated so as to satisfy the displacement law X (t) according to the claim on 1. Device according to claim 10, characterized in that the control and processing means (4) are arranged to control the movement (X) of the pendulum load (41) to the theoretical displacement setpoint (X (t)) from the length (l), displacement (x) of the mobile support (40) and swing angle (α) information. Device according to claim 11, characterized in that the control and processing means (4) are arranged to further carry out within the control loop the movement (X) of the pendulum load (20, 41), a slaving of the instantaneous position (X) of the mobile support (40) to a corrected value calculated by said control and processing means (4). Device according to one of Claims 10 to 12, characterized in that the means for acquiring the length (l) and the means for moving (x) the mobile support respectively comprise a lifting encoder (7) associated with the means for lifting (6, 5, 8) and a direction encoder (13) associated with the steering means (14, 15, 16). Device according to one of claims 10 to 13, characterized in that the angle acquisition means comprise, on the one hand, an optical beacon (19) secured to the pendulum load (20) and whose light beam is oriented upwards, and on the other hand, optical analysis means (18), such as a camera, directed downwards, secured to the mobile support and substantially vertical to said beacon (19) in the absence of swing of the pendulum load. Device according to one of claims 10 to 14, characterized in that the control and processing means comprise a programmable computer.

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