EP2510136B1 - Device intended for collecting solid debris in an electrolytic cell intended for the production of aluminium - Google Patents

Description

The invention relates to the production of aluminum by igneous electrolysis according to the Hall-Héroult method. It relates more particularly to a device for collecting solid debris immersed or floating in the electrolysis bath and the liquid metal, in particular sludge from the electrolytic bath and which accumulate on the bottom of the tank, as well as the remains of carbon and crust debris that originate in particular from the various operations performed before and during the removal of spent anodes.

Aluminum is produced industrially by igneous electrolysis, according to the well-known Hall-Héroult process, in electrolysis cells. The plants contain a large number of electrolysis cells arranged in line, in buildings called halls or electrolysis rooms, and connected electrically in series using connecting conductors, so as to optimize the ground occupation of the cells. factories. The cells are generally arranged to form two or more parallel lines that are electrically bonded together by end conductors. In each cell, the electrolyte bath and the liquid metal are contained in a tank, called an "electrolysis cell", comprising a steel box, which is lined internally with refractory and / or insulating materials, and a cathode assembly located at the bottom of the tank. Anodes, typically of carbonaceous material, are partially immersed in the electrolyte bath.

In operation, an electrolysis plant requires interventions on the electrolysis cells including, in particular, the replacement of spent anodes with new anodes, the removal of liquid metal and the additions or withdrawals of electrolyte. In order to carry out these interventions, the factories are generally equipped with one or more service units comprising a movable bridge that can be translated over and along the series of electrolysis cells, and one or more service modules. , each comprising a carriage, adapted to be moved on the movable bridge, and handling and intervention devices, such as shovels and hoists, commonly called "tools". These service units are often called "electrolysis service machines" or "MSE"("PTA" or "Pot Tending Assembly" or "PTM" or "Pot Tending Machine" in English). The service module generally comprises, attached to the carriage, a rotary frame, called tool turret, which is adapted to rotate about a vertical axis and is integral with said tools. Each tool can be attached to the end of a cable operated by a winch attached to said turret, or at the end an arm, the latter being telescopic and / or articulated.

One of the necessary interventions during the anode replacement is the cleaning of the area occupied by the spent anode and to be occupied by the new anode. This zone is essentially constituted by the bath and the liquid metal but can contain many solid debris that it is necessary to remove before setting up the new anode. During the electrolysis, a hard crust of fluorinated cryolite and alumina is formed on the upper surface of the bath. This crust has the advantage of retaining heat within the bath and therefore constitutes an effective heat-insulating envelope. But it is extremely hard and adheres to the wall of the anode block, so it is necessary to break it around the worn anode, to allow the extraction thereof. Typically, rupturing of the crust is carried out using tools such as piercers, called "crust breakers". Then, during the removal of the spent anode, an orifice in the crust is formed, which orifice is left vacant until the installation of the new anode and which we will call "anodic hole". Crust failure and handling of the spent anodic block inevitably lead to the formation of solid pieces or parts which float or remain suspended in the electrolysis bath, or which fall to the bottom of the tank. It is then necessary to collect them by means of a collection tool, commonly called "crust".

The European patent application EP-A-0 440 488 describes an example of a crust scoop associated with a particular vehicle, distinct from a service machine. The European patent application EP-A-0 618 313 describes, but in a little detail, an example of a service machine equipped with a device to ensure the rupture of the crust in the vicinity of a worn anode and the cleaning of the anode hole. The crust scoop commonly used is a clamp consisting of two buckets arranged symmetrically with respect to a substantially vertical plane and hinged, pivoting about two substantially horizontal axes, possibly merged. Each bucket has a leading edge, also called "blade", vis-à-vis the leading edge of the other bucket. To collect the debris, the crust scoop is immersed in the open position in the bath and then the crust scoop is passed from an open position to a closed position, using at least one actuator that acts either directly on a scoop. , or preferably on a linkage designed to bring the cups in a rotational movement substantially symmetrical with respect to each other, the solid debris between the two cups being thus trapped, while the liquid medium mixture of Electrolyte bath and molten metal can still escape, in particular through openings in the walls of the buckets.

Traditionally, the movement of opening and closing the crust is driven by the actuation of at least one pneumatic cylinder which acts on a linkage designed to transform the translation movement of the cylinder in two symmetrical movements of the buckets . Before placing the new anode in the cell, ensure that all crust and carbon debris in the anode hole has been removed. As some of them can rest on the bottom of the tank, it is necessary to plunge the scoop in the liquid medium consisting of the bath and the metal so that its leading edges are flush with the bottom of the tank. But as the leading edges of the buckets describe circular trajectories when the crust shovel closes to pick up the debris, the maneuvering of the shovel is very delicate, because the cathodic assembly which constitutes the bottom of the tank risks to undergo a significant damage during this operation. To avoid such deterioration, it would be necessary to impose on the axis or pivot axes of the buckets a position in altitude such that the leading edges of the buckets never touch the bottom of the tank during the maneuver, while being the most possible close to this bottom so that the cleaning is effective. However, this position is difficult to evaluate because there is no visual access to the bottom of the tank. On the other hand, this theoretical position makes, because of the circular circular blades, the crust scoop inefficient in the phases where they are furthest from the bottom of the tank, a part of the debris resting on the bottom of the tank risk of not being collected.

Thus, this cleaning operation of the anode hole using the crust shovel encounters two antagonistic difficulties: either it is too close to the bottom of the tank and, in this case, there is a risk of damaging it, or is too far away and cleaning is insufficient. Whatever the way of proceeding, there remains a significant risk of general instability of electrical and magnetic order in the operation of the tank, leading to a decline in efficiency of the installation.

The European patent application EP-A-1 178 004 proposes a solution likely to solve the problem explained in the preceding paragraph. This solution consists of using a bucket scoop mounted on a vertical arm but not to directly attach the frame secured to the axes of the buckets on said vertical arm. To this end, the chassis is split into a part called "excavator frame", which remains attached to the arm attached to the turret and a part called "bucket support frame", vertically movable relative to the door frame such that, the instantaneous center of rotation of the buckets being able to move while the arm remains stationary relative to the bottom of the tank, it is possible to give the leading edges of the buckets a substantially rectilinear trajectory. The shovel can be placed so that its leading edges are flush with the bottom of the tank during the entire operation of closing the shovel. However, such a solution results in a major complication of the excavator mechanism, with a complex bucket closure assembly comprising "a transmission rod of forces, one of whose ends is articulated [...] on the buckets [...] and whose other end is articulated on a rotating actuating rod, itself hinged to the support frame of the buckets, said rotating rod being mechanically connected to the excavator frame by means of a connecting rod compensation means articulated on the excavator frame, said rotary rod being moreover actuated in rotation by means of an actuating cylinder, whose point of application is integral with the support frame of the buckets ". Such a solution requires the introduction into the crust with numerous intermediate pieces intended to operate in a hostile environment and to undergo vibrations of high amplitude, in particular because of the stresses associated with the breakdown of the buckets. This involves frequent replacement of these parts subject to rapid wear.

The aim that the applicant has set was to achieve, without damaging the bottom of the tank, effective cleaning of the anode hole during the replacement of the anodes, while using a simple tool, easy to clean and maintain , and inexpensive in maintenance.

1. a) un moyen de fixation permettant de fixer ladite unité de collecte sur un support mobile apte à déplacer ladite unité de collecte au-dessus de la zone à nettoyer ;
2. b) une liaison actionnée par un premier actionneur qui impose à ladite liaison un déplacement par rapport audit support mobile suivant la direction verticale;
3. c) un châssis solidaire de ladite liaison;
4. d) au moins un godet articulé, pivotant autour d'un axe sensiblement horizontal, monté sur ledit châssis, présentant une lame sensiblement horizontale et actionné par un deuxième actionneur, solidaire dudit châssis, qui impose audit godet un mouvement de rotation autour dudit axe sensiblement horizontal,
   caractérisée en ce que ledit premier actionneur est relié à un système de pilotage programmable apte à :
   1. i) déterminer, directement ou indirectement, l'altitude dudit axe sensiblement horizontal et la différence d'altitude entre ladite lame dudit godet et ledit axe sensiblement horizontal;
   2. ii) définir, à partir des valeurs déterminées en i), le déplacement vertical qui doit être imposé à ladite liaison pour que l'altitude de ladite lame reste supérieure à une valeur prédéterminée;
   3. iii) définir et transmettre audit premier actionneur un flux de commande approprié, permettant audit premier actionneur d'imposer ledit déplacement vertical à ladite liaison.

A first object according to the invention is a collection unit intended to collect solid debris and sludge present in the liquid media of an aluminum production cell, such as the electrolysis bath and the liquid metal, in particular a crust scoop for cleaning anodic holes, comprising:

1. a) a fixing means for fixing said collection unit on a mobile support able to move said collection unit above the area to be cleaned;
2. b) a link actuated by a first actuator which imposes on said link a displacement relative to said movable support in the vertical direction;
3. c) a frame secured to said connection;
4. d) at least one articulated bucket, pivoting about a substantially horizontal axis, mounted on said frame, having a substantially horizontal blade and actuated by a second actuator, integral with said frame, which imposes on said bucket a rotational movement about said axis substantially horizontal,
   characterized in that said first actuator is connected to a programmable control system capable of:
   1. i) determine, directly or indirectly, the altitude of the said substantially horizontal axis and the altitude difference between said blade of said bucket and said substantially horizontal axis;
   2. ii) defining, from the values determined in i), the vertical displacement that must be imposed on said link so that the altitude of said blade remains greater than a predetermined value;
   3. iii) define and transmit to said first actuator an appropriate control flow, allowing said first actuator to impose said vertical displacement to said link.

• recueille les données, typiquement fournies par des capteurs de mesure, concernant ladite altitude dudit axe sensiblement horizontal et ladite différence d'altitude entre la lame du godet et l'axe sensiblement horizontal ;
• en déduit, typiquement à l'aide d'une mémoire informatique associée, une valeur de consigne qu'il faut imposer à l'altitude dudit axe sensiblement horizontal de façon à ce que l'altitude de la lame soit au moins égale à une valeur prédéterminée, ce qui permet d'éviter tout risque de contact entre ladite lame et un obstacle situé en dessous de ladite unité de collecte, par exemple le fond de cuve,
• émet un signal représentatif de ladite valeur de consigne en direction du convertisseur.

Said first actuator makes it possible to vertically move said link which, typically in the form of a rigid rod, a vertical sliding mast, or a cable, is integral with the collection unit. According to the invention, it imposes on the first actuator, also called "lifting actuator", particularly during the rotation of the bucket or buckets, an operating regime where the altitude of the axis of rotation of the bucket is imposed according to from that of the blade of the bucket. To do this, said first actuator is controlled during the rotation of said bucket by said programmable control system which advantageously comprises a control and control unit and a converter. The control and command unit:

• collects the data, typically provided by measurement sensors, concerning said altitude of said substantially horizontal axis and said difference in altitude between the blade of the bucket and the substantially horizontal axis;
• deduces, typically using an associated computer memory, a set value that must be imposed on the altitude of said substantially horizontal axis so that the altitude of the blade is at least equal to a value predetermined, which avoids any risk of contact between said blade and an obstacle located below said collection unit, for example the bottom of the tank,
• sends a signal representative of said setpoint towards the converter.

The converter translates said signal into a control stream and transmits said control stream to said first actuator. Depending on the nature of the actuator, the converter may for example be a servo-distributor associated with a cylinder or a variable speed drive associated with an electric motor. In the first case, the control flow is an oil flow to a cylinder chamber. In the second case, the control flow is an electrical signal, or a control current, whose characteristic properties (intensity (s), frequency (s), ...) affect the direction and speed of rotation of the motor. .

The altitude of the substantially horizontal axis and that of the blade can be measured directly by sensors but, because of the aggressive environment and the lack of accessibility, these direct measurements are advantageously replaced by calculations based on indirect measurements. Thus, said programmable control system can be connected to a first sensor for measuring the vertical displacement of said link relative to a reference level and to a second sensor making it possible to measure, directly or indirectly, the difference in altitude between the blade of the bucket and the substantially horizontal axis around which the bucket pivots . The reference level can be a fixed level defined in the repository of the electrolysis hall. It can also be linked to the mobile support on which the collection unit is fixed. In the latter case, it is obviously necessary to take into account a possible altitude variation of said mobile support. As regards the second sensor, a sensor can be used to determine the angular position of the bucket. To this end, if said second actuator is a cylinder that requires a rotation to said bucket by means of a connecting rod, a displacement sensor can be used to measure the displacement of the rod of said cylinder with respect to the body of said cylinder.

Advantageously, the characteristics of the control flow transmitted to the first actuator act on the direction and the intensity of the displacement to be performed by said first actuator: plus the difference found between the measured altitude of the substantially horizontal axis and its set altitude. is important, the stronger the intensity of the displacement imposed on the actuator.

1. a) recueille les données fournies par ledit premier capteur et ledit deuxième capteur ;
2. b) déduit de ces données, à l'aide d'un programme informatique basé sur un modèle cinématique décrivant la trajectoire de la lame dans un référentiel approprié, la valeur de consigne qu'il faut imposer à l'altitude de l'axe de pivotement du godet et
3. c) transmet audit convertisseur un signal (S) représentatif de ladite valeur de consigne.

Of course, it is possible to be more demanding on the control of the trajectory of the blade, since the efficiency of the collection unit decreases when the blade moves too far from the bottom of the tank. In a preferred embodiment of the invention, the set value to be imposed on the altitude of said substantially horizontal axis is defined so that the altitude of the blade is not only larger but also as close as possible to said value. predetermined. Advantageously, by making the measurements a large number of times and by performing at each measurement a corrective displacement of said link so that the substantially horizontal axis is at the set altitude allowing the blade to be at the desired altitude it is possible to impose on said blade a predetermined trajectory. To this end, said control and control unit is advantageously an industrial programmable controller which, multiple times, preferably at regular time intervals, typically a few tens of milliseconds,:

1. a) collects the data provided by said first sensor and said second sensor;
2. b) deduced from these data, using a computer program based on a kinematic model describing the trajectory of the blade in an appropriate frame of reference, the set value that must be imposed on the altitude of the axis of pivoting of the bucket and
3. c) transmits to said converter a signal (S) representative of said setpoint value.

Advantageously, the computer program implemented in said programmable logic controller is based on a kinematic model which describes a trajectory of the blade passing above, but not too far, from the bottom of the tank. This trajectory can be deduced from the theoretical profile of the bottom of the vessel by translation along a vector oriented vertically upwards and whose intensity corresponds to a predefined safety distance.

The collection unit according to the invention can be for example a "crust scoop" used for cleaning anode holes, comprising a frame and two buckets mounted on said frame, arranged symmetrically with respect to a substantially vertical plane and articulated , pivoting about two substantially horizontal axes, each bucket having a blade vis-à-vis the blade of the other bucket, the second actuator, integral with said frame, imposing each of said buckets a rotational movement substantially symmetrical relative said substantially vertical plane, so that solid debris between the two buckets are trapped by said buckets.

Preferably, so as to impose a fluid movement on the bucket (s), it is avoided that the second actuator, also called "closing actuator" or "closing actuator / opening" is chosen from pneumatic cylinders, because this type of cylinder does not control at any time the speed of rotation of the bucket during the closing phase of the bucket or buckets. One can choose an (electro) mechanical actuator but, preferably, one will choose a hydraulic cylinder powered by a circuit of which a portion is mounted in differential to ensure the buckets the breakdown function described below, which is essential for the excavators to buckets used in the cleaning of anodic holes.

To collect the debris, the collection unit, which is a crust scoop, is immersed in the bath while it is in the open position, then it is moved from an open position to a closed position, using the closing actuator acting on a linkage designed to bring the buckets in a rotational movement substantially symmetrical relative to each other. The solid debris between the two buckets are thus trapped, while the liquid medium, mixture of electrolyte bath and molten metal can still escape, in particular through openings in the walls of the buckets. Part of this liquid medium, which is very viscous, adheres to the wall of the buckets, so that the cups are covered with a gangue that must be removed after each passage of the crust in the tank because the buckets , very quickly fouled, become inoperative. To remove the maximum of bath and metal that cool and freeze by adhering to the surface of the cups, we realize a operation, called "bucket breakdown". In this operation, the bucket closure / opening actuator is used so that the edges opposite the buckets are driven at such a speed that their bringing into contact results in a sufficiently violent shock for that the cooled bath and metal is peeled off and ejected from the surface of said wells.

• ➢ un premier schéma, où les godets avancent lentement mais où le vérin de fermeture peut fournir des efforts suffisants pour permettre d'entraîner les débris solides rencontrés par les godets,
• ➢ un deuxième schéma, où il n'est pas nécessaire de transmettre des efforts, mais où il faut transmettre aux godets une énergie cinétique suffisante pour que la fonction de claquage puisse être remplie. Ce deuxième schéma correspond à un montage en différentiel analogue à celui qui est décrit un peu plus loin, dans l'exemple 1, lors du commentaire sur la descente rapide de l'unité de collecte, illustré en figure 5. Bien évidemment, les fonctions à remplir étant différentes, le circuit alimentant le second actionneur est différent de celui qui alimente le premier actionneur mais le principe du montage en différentiel reste le même.

Traditionally, particularly because it was well suited to the breakdown operation, the bucket closure / opening actuator consisted of one or more pneumatic cylinders. Here, in the context of the present invention, to ensure smooth movement of the buckets and to better control the trajectory of the blades, it is advantageous to replace the pneumatic cylinder or cylinders by at least one double-acting hydraulic jack connected to a supply circuit which has at least two operating diagrams for closing the buckets:

• ➢ a first diagram, where the buckets advance slowly but where the closing cylinder can provide sufficient effort to allow to drive the solid debris encountered by the buckets,
• ➢ a second diagram, where it is not necessary to transmit forces, but where it is necessary to transmit to the buckets a sufficient kinetic energy so that the breakdown function can be filled. This second diagram corresponds to a differential assembly similar to that described a little further, in Example 1, when commenting on the rapid descent of the collection unit, illustrated in FIG. figure 5 . Obviously, since the functions to be fulfilled are different, the circuit supplying the second actuator is different from that supplying the first actuator, but the differential mounting principle remains the same.

Previously, it was thought that an effective breakdown of the crust scoop could only be done pneumatically. Indeed, it was thought that, thanks to compressed air, it is much easier and quicker to impose on the buckets symmetrical rotational movements fast enough for the resulting shock to detach and eject the bath and metal during solidification on the surface of the buckets. In addition, the compressed air source already existed on the service machine. Finally, it was desired to avoid the implantation of hydraulic circuits in places that may be in the immediate vicinity of the electrolysis bath.

Here, in the context of this preferred embodiment of the invention, one chooses as second actuator one or more hydraulic cylinders. To prevent it (s) is (s) near the electrolysis bath, it can either be removed or said hydraulic cylinders and provide an intermediate piece acting on the linkage, or leave them near the buckets but protect them from projections. For example, it is possible to use the hydraulic power unit which is mounted on the service machine and which is already placed at a height, so that it is remote from the electrolysis bath, and to install the hydraulic circuit necessary for the operation of the cylinder (s). so that the part most exposed to the hostile environment is limited to the hoses that feed the compartments of the double-acting cylinder. To further improve the protection of this circuit portion vis-à-vis the hostile atmosphere and possible bath projections, we can use the excavator frame as a screen, by mounting the cylinder or cylinders above that and complete the protection of the hoses of the hydraulic circuit near said cylinders by vertical walls surrounding said cylinders and said hoses.

On the other hand, the fact of choosing for closing actuator one or more hydraulic cylinder (s) allows to dedicate the compressed air supplied by the onboard compressor of the service machine to other functions or, of preferably, to choose a compressor of lower capacity, therefore lighter, to equip said service machine.

In a first embodiment according to the invention, said first actuator, also called "lifting actuator", comprises an electric motor integral with said movable support, a link secured to said collection unit and coupled to said motor so that the rotation said electric motor causes the displacement of said collection unit through said connection, and said converter is a speed controller which transmits to said electric motor a control current, whose characteristics allow said electric motor to impose said vertical displacement to said link. Said electric motor may be the motor of an electric jack, said link being the rod of the jack supporting or being coupled with a vertical mast supporting said collection unit. It can also be the motor of an electric winch, said link being the cable supporting said collection unit. Example 2 described below illustrates such an embodiment.

In a second embodiment of the invention, said first actuator comprises at least one hydraulic jack which comprises a body integral with the movable support and a piston connected to a rod which acts as said link and said converter is a distributor mounted on the portion. of the hydraulic circuit which feeds with a controlled flow the rod side chamber of said hydraulic cylinder. Thus, at least when said second actuator is activated, the volume of oil in the rod-side chamber is imposed by said distributor, which advantageously is an electro-hydraulic servo-distributor servo-controlled and controlled by said programmable control system. Preferably, said distributor is a 4/3 servo-distributor, proportional action, electrically controlled.

In this second embodiment of the invention, said first actuator comprises at least one hydraulic jack that allows to move vertically said connection to which is attached the rest of the collection unit. Preferably, the manipulator arm of the collection unit is a telescopic arm, comprising a "mobile" mast sliding in a "fixed" arm, the stem of said hydraulic cylinder being secured to said "mobile" mast and the body of said hydraulic cylinder being secured to said "fixed" mast, connected to said mobile support, for example a tool turret fixed on a carriage capable of running along the beam of a traveling crane, so that said collecting unit can be moved and positioned at above the work area before descending to the anodic hole. A "symmetrical" solution, consisting in making the "mobile" mast integral with the body of the jack and the rod integral with the "fixed" mast secured to the movable support, is also possible. In both cases, the rise of the collection unit is done by supplying the shaft chamber with oil. In this second embodiment of the invention, a preferred embodiment comprises a distributor controlled by a programmable automaton which collects, at regular time intervals, typically a few tens of milliseconds, the altitude H of the substantially horizontal axis around which the bucket and the value L of displacement of the piston rod of the second actuator, deduced from these values, using an associated computer memory, the set value that must be imposed on the altitude of the axis of pivoting of the bucket and injects a signal towards said dispenser so as to decrease or increase the volume of the oil which feeds the chamber rod side and which is necessary to reach the correct altitude.

The first actuator may include a plurality of hydraulic cylinders. However, the control of the oil volume in each of the rod-side chambers is not easy, it is preferable to use as the first actuator a single cylinder whose chamber rod side is fed with a single slave valve .

The device according to the invention makes it possible in particular to carry out a debris collection by defining a safety distance between the bottom of the tank and the blade of the bucket or buckets: as soon as the estimated distance is less than this safety distance, the system pilot sends to the said distributor a setpoint which increases the volume of oil in the cylinder side chamber of the cylinder so as to impose the desired altitude to the piston and therefore the substantially horizontal axis of rotation of the bucket.

Advantageously, for the debris collection to be effective, it is also necessary that the distance between the blade of the bucket and the bottom of the tank is not too great: as soon as the estimated distance is greater than a predetermined limit distance, the control system sends a direction to the distributor that reduces the volume of oil in the cylinder side chamber of the cylinder. In Example 1 presented below, it acts only on the hydraulic circuit connecting the shaft-side chamber: when it is necessary to move the bucket away from the bottom of the tank, the proportional-action servo-distributor controls the oil flow sent under the required pressure in the stem chamber; when it has to be brought closer, it evacuates towards the reservoir a controlled flow of oil coming from the shaft-side chamber, which is under a pressure corresponding substantially to the weight of the collecting unit. In example 2, the variable speed drive used emits a control current which can act not only on the amplitude of the speed of rotation but also on the direction of rotation of the electric motor.

Preferably, the safety distance and the limit distance are chosen as close as possible. The bottom of the tank being generally flat, this amounts to imposing a rectilinear trajectory to the leading edge of the bucket. Of course, this trajectory can be defined more precisely, depending on the actual geometry of the bottom of the tank where the collection of debris must be performed. In practice, therefore, a target altitude for the bucket blade is defined and the programmable control system is associated with a computer memory programmed to provide, depending on the bucket angle directly or indirectly measured, the altitude of the bucket. set that must have the instantaneous center of rotation of said bucket. The target altitude for the blade is constant if the bottom of the tank is considered plane. It can be variable, depending on the position of the anode hole to be treated in the cell; this simply requires the use of a computer memory associated with the more complex control system, giving different setpoints depending on where the collection unit works. Thus, the device according to the invention makes it possible to position the bucket or buckets as close as possible to the cathode, thus to increase the efficiency of the debris collection operation without touching the bottom of the tank.

In practical terms, the collection unit, suspended from the moving carriage which moves along the traveling crane, is advantageously provided with a displacement sensor which makes it possible to to know at any time the altitude of the or substantially horizontal axes of rotation of the bucket or buckets. The displacement sensor may be a cable encoder or a laser range finder. The elevation of the bottom of the tank is itself known and can be checked regularly, for example by slowly lowering the collection unit placed in a predetermined position until the blade of the bucket touches the bottom of the tank. The bucket is generally defined by an axial wall, that is to say a regulated surface generated by a generatrix parallel to the pivot axis and based on an open directional curve, and two transverse walls. These transverse walls have a substantially rectilinear edge, which joins the ends of the open curve. The position of the bucket can be characterized by the angle α that this edge with the vertical. By denoting by d the distance from this edge to the pivot axis and by h the distance between the blade and the projection of the pivot axis on said edge, is known at any time, depending on the angle of α inclination of the edge relative to the vertical, the difference in altitude between the substantially horizontal axis and said blade, which is given by the expression: ΔZ = d cos α + h sin α. The angle of inclination is itself directly related to a dimensional characteristic of the actuator that rotates the bucket. For example, if it is a cylinder, the angle of inclination is directly related to the stroke of the cylinder rod.

In a preferred embodiment of the invention, the programmable control system is an industrial programmable logic controller (PLC) which collects at regular time intervals, typically a few tens of milliseconds, to using a first sensor, the altitude of the pivot axis of the bucket, and with the aid of a second sensor, the value of the stroke of the closing cylinder and deduced from these values, to the using a computer program based on a kinematic model describing the trajectory of the blade in an appropriate frame of reference, the set value that must be imposed on the altitude of the pivot axis of the bucket and accordingly drives the servo distributor to introduce or evacuate the volume of oil necessary to reach the correct altitude.

1. a) un schéma différentiel, où la chambre côté tige et la chambre côté piston sont connectées à ladite source de pression, permettant d'assurer la descente à grande vitesse du mât;
2. b) un schéma correspondant au repos, l'unité de collecte restant suspendue, le circuit étant aménagé de telle sorte que ladite unité de collecte peut se déplacer verticalement sans effort en cas de rencontre d'obstacle;
3. c) un schéma où la chambre côté tige est connectée à la source de pression, correspondant à la montée de l'unité de collecte;
4. d) un schéma en fonctionnement asservi, où la portion de circuit alimentant la chambre côté tige comprend un distributeur asservi en débit et piloté par un système de pilotage programmable comprenant une unité de contrôle et de commande qui recueille les données concernant l'altitude dudit axe sensiblement horizontal et la différence d'altitude entre la lame du godet et l'axe sensiblement horizontal, déduit de ces données la valeur de consigne qu'il faut imposer à l'altitude dudit axe sensiblement horizontal et émet un signal représentatif de ladite valeur de consigne en direction dudit distributeur.

Advantageously, said hydraulic cylinder is a double-acting cylinder whose rod is secured to the vertical mast and said collection unit, with a rod-side chamber capable of imposing at any time on said rod a vertical movement upwards and a piston-side chamber. able to impose at any time on said rod vertical downward movement, the two chambers being connectable, via at least one distributor, to a pressure source or a reservoir, the supply circuit comprising several circuit portions that allow the following hydraulic power supply schemes to be realized:

1. a) a differential diagram, where the rod-side chamber and the piston-side chamber are connected to said source of pressure, to ensure the descent at high speed of the mast;
2. b) a diagram corresponding to the rest, the collection unit remaining suspended, the circuit being arranged such that said collection unit can move vertically effortlessly in case of encounter obstacle;
3. c) a diagram where the rod-side chamber is connected to the pressure source, corresponding to the rise of the collection unit;
4. d) a slave operation scheme, wherein the circuit portion supplying the rod-side chamber comprises a flow-controlled distributor and controlled by a programmable control system comprising a control and command unit which collects the altitude data of said axis substantially horizontal and the difference in altitude between the blade of the bucket and the substantially horizontal axis, deduced from these data the set value that must be imposed on the altitude of said substantially horizontal axis and emits a signal representative of said value of setpoint towards said distributor.

In Example 1 presented below, we describe in more detail these different operating phases of the collection unit.

Another object according to the invention is a service module intended to be used in an igneous electrolysis aluminum production plant comprising a trolley and handling and intervention devices, characterized in that it also comprises a collection unit according to the invention, as described above.

Another object according to the invention is a service unit of an igneous electrolysis aluminum production plant comprising a traveling crane and characterized in that it also comprises at least one service module according to the invention, such as previously described.

Another object according to the invention is the use of a service module according to the invention for the interventions on electrolytic cells intended for the production of aluminum by igneous electrolysis, in particular for the cleaning of the anode holes, wherein said first actuator is driven by said programmable control system such that said one or more bucket blades follow a predefined path, typically located above and parallel to the bottom of the vessel.

1. a. on amène à l'aide des actionneurs de la MSE ladite unité de collecte, en position fermée, au droit du dit trou anodique, ledit premier actionneur étant au repos;
2. b. on actionne ledit premier actionneur en descente rapide jusqu'à une altitude prédéterminée, supérieure au niveau du bain situé dans la cuve, afin d'autoriser l'ouverture de l'unité de collecte ;
3. c. on actionne ledit deuxième actionneur de telle sorte qu'il ouvre les godets jusqu'à ce que lesdits godets atteignent une position ouverte de référence, typiquement proche de l'ouverture maximale permise par la course du deuxième actionneur;
4. d. on actionne ledit premier actionneur en descente « lente » jusqu'à une altitude prédéfinie; dans un mode de réalisation spécifique et préféré, l'altitude prédéfinie visée est l'altitude atteinte par un point représentatif de la liaison lorsque la lame du godet arrive en contact avec le fond de cuve. Ainsi, on actionne ledit premier actionneur en descente lente jusqu'à ce qu'on détecte le contact d'au moins une lame sur le fond de cuve; par exemple, si l'actionneur est un vérin hydraulique, on utilise un capteur permettant de détecter le moment où la pression dans le circuit d'huile qui alimente la chambre côté piston augmente brutalement, un capteur permettant de connaître l'angle d'ouverture du godet et un capteur de déplacement qui permet de connaître l'altitude de la liaison lors dudit contact ;
5. e. on définit, à partir de l'altitude atteinte en fin d'étape précédente, la hauteur à laquelle doit être ladite lame, en tenant compte d'une distance de sécurité et on en déduit la trajectoire que doit suivre ladite lame entre ladite position ouverte de référence et la position fermée;
6. f. on actionne ledit premier actionneur pour remonter ladite unité de collecte jusqu'au point origine de la trajectoire définie à l'étape précédente ;
7. g. on actionne ledit deuxième actionneur, ledit premier actionneur étant en mode asservi de façon à ce que la lame suive la trajectoire définie en e) ;
8. h. une fois l'unité de collecte fermée, on actionne le premier actionneur en mode montée puis, lorsque l'unité de collecte a atteint une certaine altitude, on utilise les actionneurs de la MSE pour déplacer l'ensemble vers une aire de réception des débris récoltés.

• La figure 1 illustre schématiquement une machine de service dans une salle d'électrolyse typique destinée à la production d'aluminium, vue en section.
• La figure 2 illustre un mode de réalisation particulier d'une unité de collecte, qui est une pelle à croûte, montée sur un mât de guidage vertical télescopique actionné par un vérin hydraulique.
• La figure 3 illustre, en perspective, l'embiellage et la pelle à godet du mode de réalisation de la figure 2.
• Les figures 4 à 7 illustrent, dans quatre configurations différentes, le schéma d'un circuit hydraulique alimentant le premier actionneur (vérin de levage) d'une unité de collecte selon l'invention. Ces configurations correspondent aux modes de fonctionnement suivants: repos (figure 4), descente rapide (figure 5), montée (figure 6) et fonctionnement asservi (figure 7).
• La figure 8 illustre schématiquement une unité de collecte selon l'invention, dans laquelle le premier actionneur est un vérin électromécanique.

Another object according to the invention is a method for cleaning an anode hole during the replacement of an anode, in which a collection unit according to the invention is used, said first actuator being mounted integral with a service machine and proceeds as follows:

1. at. using the actuators of the MSE said collection unit, in the closed position, to the right of said anode hole, said first actuator being at rest;
2. b. said first actuator is operated in rapid descent to a predetermined altitude, higher than the level of the bath located in the tank, to allow the opening of the collection unit;
3. vs. said second actuator is actuated so that it opens the buckets until said buckets reach a reference open position, typically close to the maximum opening allowed by the stroke of the second actuator;
4. d. said first actuator is operated in a "slow" descent to a predefined altitude; in a specific and preferred embodiment, the predefined target altitude is the altitude reached by a point representative of the connection when the blade of the bucket comes into contact with the bottom of the tank. Thus, said first actuator is actuated in a slow descent until the contact of at least one blade is detected on the bottom of the vessel; for example, if the actuator is a hydraulic cylinder, a sensor is used to detect when the pressure in the oil circuit that feeds the piston-side chamber increases sharply, a sensor to determine the opening angle the bucket and a displacement sensor which makes it possible to know the altitude of the link during said contact;
5. e. from the altitude reached at the end of the preceding step, the height at which said blade is to be defined, taking into account a safety distance, and the path to be followed by said blade between said open position reference and closed position;
6. f. said first actuator is actuated to raise said collection unit to the origin point of the trajectory defined in the preceding step;
7. boy Wut. said second actuator is actuated, said first actuator being in slave mode so that the blade follows the path defined in e);
8. h. once the collection unit is closed, the first actuator is actuated in mounted mode and, when the collection unit has reached a certain altitude, the actuators of the MSE are used to move the assembly to a debris receiving area. harvested.

• The figure 1 schematically illustrates a service machine in a typical electrolysis room for the production of aluminum, seen in section.
• The figure 2 illustrates a particular embodiment of a collection unit, which is a crust scoop, mounted on a telescopic vertical guide mast actuated by a hydraulic cylinder.
• The figure 3 illustrates, in perspective, the linkage and the bucket bucket of the embodiment of the figure 2 .
• The Figures 4 to 7 illustrate, in four different configurations, the diagram of a hydraulic circuit feeding the first actuator (lifting jack) of a collection unit according to the invention. These configurations correspond to the following operating modes: figure 4 ), fast descent ( figure 5 ), climb ( figure 6 ) and slave operation ( figure 7 ).
• The figure 8 schematically illustrates a collection unit according to the invention, wherein the first actuator is an electromechanical jack.

Electrolysis plants for aluminum production include a liquid aluminum production area that includes one or more electrolysis rooms. The electrolysis room (1) illustrated on the figure 1 comprises electrolysis cells (2) and a service machine (5). The electrolysis cells (2) are normally arranged in rows or rows, each row or line typically having more than one hundred cells. The cells (2) are arranged so as to clear a circulation aisle along the electrolysis room (1). The cells (2) comprise a series of anodes (3) provided with a metal rod (4) for fixing and electrically connecting the anodes to a metal anode frame (not shown).

The service unit (5) is used to perform operations on the cells (2) such as anode changes or the filling of ground bath feed hoppers and aluminum fluoride (AlF3). It can also be used to handle various loads, such as tank elements, pockets of liquid metal that are used during casting ("ladles") or anodes. It can also be used to clean the anode hole after removing a worn anode and before installing a new anode.

The service unit (5) comprises a movable bridge (6) which can be translated over the electrolysis cells (2), and at least one service module (7) comprising a movable carriage (8), said "tool holder", adapted to be moved on the movable bridge (6) and equipped with several handling and intervention devices (10), such as tools, among which may include the crust scoop (100 '). The tools are here mounted on vertical telescopic poles (9) attached to the movable carriage (8). As we have already seen, for example in the European patent application EP-A-0 440 488 a crust scoop may also be moved and operated from a vehicle other than a service machine. The invention applies to any collection unit, regardless of its mode of movement and placement above the work area.

The Figures 2 and 3 illustrate a particular embodiment of a collection unit (100), which is a crust scoop (100 ') attached to the end of a telescopic arm, at the end of the movable arm here called "shovel barrel" ( 11). The shovel shaft is a mobile vertical mast (9 ") sliding in a vertical mast (9 '), which itself moves vertically under the effect of an actuator (not shown), able to make faster movements while remaining integral with the tool turret of the mobile carriage (8) of a service module (7) The crustal scoop comprises a frame (110) provided with two buckets (120a and 120b) placed in substantially perpendicular to a substantially vertical plane and articulated, pivoting about two substantially horizontal axes (115a and 115b). Each bucket (120a, 120b) has a leading edge, or blade (128a, 128b) opposite the blade (128b, 128a) of the other bucket (120b, 120a) The second actuator is here in the form of two cylinders (200, 201) secured to the frame (110) , operating simultaneously, by imposing on each of the buckets, via a connecting rod (300, 300 '), a movement of substantially symmetrical rotation relative to the substantially vertical plane, so that the solid debris between the two buckets are trapped by said buckets. Until the present invention, the two actuators of the second actuator were pneumatic cylinders particularly well suited for the breakdown operation.

EXAMPLES OF REALIZATION EXAMPLE 1 (FIGS. 2 to 7)

The Figures 4 to 7 illustrate, in four different configurations, the diagram of a hydraulic circuit supplying the first actuator (50) of a collection unit according to the invention, which moreover possesses the characteristics described above ( Figures 2 and 3 ).

The first actuator (50), or lift cylinder, is a double acting cylinder (51) with a body (55) and a piston (56) associated with a rod (52). The rod (52) is integral with the collection unit (not shown on the Figures 4 to 7 ). The double-acting cylinder (51) has a stem-like chamber (53), called the lower one, capable of imposing at any moment on the vertical mobile mast (9 ") a vertical upward movement and a piston-like chamber (54), said upper , capable of imposing a vertical downward movement on the vertical mobile mast at any moment, The hydraulic circuit comprises two portions (63) and (64) which feed the two chambers (53) and (54) of the double-acting cylinder (51). The circuit can be connected, via a three-position distributor, called "direction distributor" (80), to the "pressure line" (P) and to the "return line" (R) of a hydraulic power plant. The direction distributor (80) is naturally in the position (802) which corresponds to the rest and can be excited to be put in one of the two other possible positions: the position (803) where the rod (52) of the cylinder makes lowering the collection unit and the position (801) where the cylinder rod raises said collection unit.

The circuit portion (64) includes a main branch (640) having one end connected to the directional distributor (80) and the other end connected to the piston chamber (54) of the actuator (51).

The circuit portion (63) includes a main branch (630) having one end connected to the directional distributor (80) and the other end branching into two sub-branches; each of which is equipped with a two-position distributor (81, 82), the first sub-branch (631 comprising 6310, 6311, 6312 and 6313) being associated with a holding valve (90), the second sub-branch ( 632 comprising 6320, 6321 and 6322) being associated with the electrohydraulic servo-distributor (83). The two sub-branches meet at their other ends to form the circuit portion (633) which feeds the rod chamber (53) of the jack (51).

The figure 4 illustrates the circuit when the lift cylinder is at rest. The direction distributor (80) is naturally in the position (802), which puts the two circuit portions (63) and (64) in connection with each other through their respective main branches (630) and (640). The distributor (82) is in the position (821) which blocks the circulation in the second sub-branch. Isolated by the distributor (82) in position (821) and by the non-conducting valve (90) (the piloting pressures of the connections (92) and (93) are insufficient to make it flow), the The stem chamber (53) is maintained, apart from any shock, at a substantially constant pressure, associated with the weight of the collection unit. The circuit branch (633) is equipped with a safety, integrated in the function of the valve of retainer (90) to limit the pressure in the stem chamber in the event of an impact.

The figure 5 illustrates the circuit when the lift cylinder is in rapid descent. The direction distributor (80) is energized to occupy the position (803), which places the two circuit portions (63) and (64) in communication with the pressure line (P) of the hydraulic power unit, the two portions of circuit (63) and (64) also communicating with each other via their respective main branches (630) and (640) at the direction distributor (80) when in this position (803). The distributor (82) is in the position (821) which blocks the circulation in the second sub-branch. The distributor (81) is in the position (811) and allows the operation of the check valve (90): as soon as the resultant of the forces due to the piloting pressures coming from one part of the branch (92) and on the other side of the branch (93) is greater than a certain value, the check valve (90) becomes "passing".

The check valve (90) is set to a critical value, typically close to 180 bar, so that, as soon as its piloting has sufficient pressure, it becomes free-running and the oil can flow from the stem-chamber ( 53) to the plunger chamber (54), via the branches (630) and (640), which communicate with each other at the direction distributor (80), placed in position (803). In this way, the flow of oil from the hydraulic unit is increased by the flow of oil from the piston chamber. If the x is the ratio (section of the piston chamber (54)) / (section of the shank (52)), the flow from the hydraulic unit is multiplied by x, so that with such a differential arrangement, the piston rod can descend with a speed x times faster than with a conventional assembly.

The figure 6 illustrates the circuit when the lift cylinder raises the rod (52). The direction distributor (80) is energized to occupy the position (801), which places the main branch (630) in connection with the pressure line (P) of the hydraulic power unit and the main branch (640) in communication with the reservoir from the hydraulic power plant, via the return line (R). The distributor (82) is in the position (821) and the distributor (81) is in the position (811). The pressurized oil passes through the main branch (630), passes through the distributor (81) in position (811) and joins the portions (6313) and (633) via the non-return valve (91), to supply the chamber -Storm (53). As the piston rises, the oil in the piston chamber (54) is discharged to the return line (R) of the hydraulic unit, via the main branch (640).

The figure 7 illustrates the circuit when the lift cylinder is activated in a slave mode when the collection of debris. The direction distributor (80) is energized to occupy the position (801), which places the main branch (630) in connection with the pressure line (P) of the hydraulic power unit and the main branch (640) in connection with the return line (R) of the hydraulic power station. The dispenser (82) is in the position (822) and the dispenser (81) is in the position (812). Depending on whether you want to raise or lower the cylinder, the servo-distributor is activated to be placed in the position (831) for the descent or (833) for the climb.

• le premier indique la distance (H) entre un niveau horizontal de référence (N) (par exemple une plate-forme de la tourelle porte-outils) et un point fixe du châssis (110') de l'unité de collecte (représenté sur la figure 7 par le niveau horizontal commun des axes de rotation des godets), ce qui permet de connaître l'altitude de l'axe (115') autour duquel pivote le godet (120') dont la forme est schématisée en pointillés;
• - le second indique la course (L) de la tige du vérin de fermeture (200'), lequel, par le biais d'une bielle commune (300'), commande l'ouverture et la fermeture des deux godets.

The servo-distributor is controlled by a programmable controller (84) which receives the indications provided by two sensors:

• the first indicates the distance (H) between a reference horizontal level (N) (for example a platform of the tool turret) and a fixed point of the frame (110 ') of the collection unit (shown on the figure 7 by the common horizontal level of the axes of rotation of the buckets), which makes it possible to know the altitude of the axis (115 ') around which pivots the bucket (120') whose form is schematized in dashed lines;
• - The second indicates the stroke (L) of the rod of the closing cylinder (200 '), which, through a common connecting rod (300'), controls the opening and closing of the two buckets.

At any value L of the piston stroke of the closing cylinder corresponds a determined opening angle of the buckets, equal to twice the angle (α) that the edge (129 ') of the bucket with the vertical. By designating the distance from this edge (129 ') to the pivot axis (115') and the distance between the blade (128 ') and the orthogonal projection of the pivot axis on said edge (129 '), the difference in altitude between the axis (115') and said blade, which is given by the expression: ΔZ = d cos α + h sin α, is known at all times.

Thus, at any position of the rod of the closing cylinder corresponds an altitude to which must be said axis so that the blade (128 ') is at an altitude greater than or equal to a given value corresponding to the theoretical altitude of the bottom tank increased by a certain margin of safety, typically one or a few tens of millimeters. The programmable control system is a programmable controller (84) associated with a computer memory (85) which enables it, as a function of the measurement values of (H) and (L) transmitted, to define a set altitude at the lifting jack (50). If the set altitude is greater than the effective altitude of the lift cylinder, there is a danger of collision between the bucket blade and the bottom of the vessel and the servo-distributor must be activated to a position (833) to quickly correct the trajectory of said blade. The programmable controller (84) sends a signal (S) to the servo-distributor (83), which is a proportional proportional servo-distributor, imposing on the circuit portion supplying the rod-side chamber an oil flow (Φ) that is all the more important that the deviation from the set position is large. The signal has characteristics that make it possible to move the movable member of the servo-distributor in a position of type (833) more or less advanced, depending on the flow rate of oil under pressure, the oil from the branches (630) and (632) and feeding the rod-side chamber via the branches (6321), (6322) and (633).

When, however, the set altitude is lower than the effective altitude of the lift cylinder (50), the servo-distributor must be activated to lower the altitude of the blade. The programmable controller (84) sends a signal (S) to the servo-distributor (83) to a configuration corresponding to a position (831), where the pressurized oil no longer supplies the side-rod chamber, which is connected to the return line (R), via the branches (65), (6321), (6322) and (633), the flow (Φ) for discharging the oil to the return line being controlled by the opening of the servo-distributor, which is controlled by the signal emitted by the PLC.

The programmable automaton (84) collects, at regular time intervals, typically a few tens of milliseconds, the altitude H of the pivot axis of the bucket and the value L of the stroke of the closing cylinder and deduces from these values, using a computer program based on a kinematic model that describes the trajectory of the blade in an appropriate frame of reference, the set value that must be imposed on the altitude of the pivot axis of the bucket and emits a signal (S) towards the servo-distributor (83) so as to introduce or evacuate the volume of oil necessary to reach the correct altitude.

The second actuator (200 '), here simply schematized essentially to illustrate the role it plays in the operating principle of the first actuator (50), the latter being controlled in particular according to the spatial configuration of said second actuator. This second actuator, whose body is integral with the rod (52) of the first actuator (50), is here a double-acting hydraulic cylinder connected to a supply circuit, a part of which allows differential mounting to ensure the breakdown function .

• On amène à l'aide des actionneurs de la MSE ladite unité de collecte, en position fermée, au droit du dit trou anodique, le vérin de levage étant au repos (configuration illustrée par la figure 4) ;
• On actionne le vérin de levage en descente rapide (configuration illustrée par la figure 5) jusqu'à une altitude prédéterminée, supérieure au niveau du bain situé dans la cuve, afin d'autoriser l'ouverture de l'unité de collecte;
• On actionne l'actionneur des godets, dit « vérin de fermeture », de telle sorte qu'il ouvre les godets jusqu'à ce qu'ils atteignent une position ouverte de référence, typiquement proche de l'ouverture maximale des godets permise par la course du dit vérin de fermeture.
• On actionne le vérin de levage en descente « lente » (alimentation spécifique de la chambre côté piston) jusqu'à ce qu'on détecte le contact d'au moins une lame sur le fond de cuve ; on utilise par exemple un capteur permettant de détecter le moment où la pression dans le circuit d'huile qui alimente la chambre côté piston augmente brutalement et un capteur de déplacement qui permet de relever l'altitude de la lame lors dudit contact;
• On définit à partir de cette altitude la hauteur à laquelle doit être ladite lame, en tenant compte d'une distance de sécurité et on en déduit la trajectoire que doit suivre ladite lame entre ladite position ouverte de référence et la position fermée;
• On actionne ledit vérin de levage pour remonter ladite unité de collecte jusqu'au point origine de la trajectoire définie à l'étape précédente (configuration illustrée par la figure 6);
• On actionne le vérin de fermeture, le vérin de levage étant en mode asservi de façon à ce que la lame suive la trajectoire définie précédemment (configuration illustrée par la figure 7) ;
• Une fois l'unité de collecte fermée, on actionne le vérin de levage en mode montée (configuration illustrée par la figure 6) puis, lorsque l'unité de collecte a atteint une certaine altitude, on utilise les actionneurs de la MSE pour déplacer l'ensemble vers une aire de réception des débris récoltés.

Thus, in order to clean an anode hole when replacing an anode, it is possible to use a collection unit according to the invention, as illustrated in FIG. Figures 2 to 7 , mounted on a vertical telescopic mast attached to an electrolysis service machine (MSE) and proceeds from the following subject:

• With the aid of the actuators of the MSE, said collecting unit is brought into the closed position in line with the said anode hole, the lifting cylinder being at rest (configuration illustrated by FIG. figure 4 );
• The lifting cylinder is actuated in rapid descent (configuration illustrated by the figure 5 ) to a predetermined altitude, higher than the level of the bath located in the tank, to allow the opening of the collection unit;
• The bucket actuator, called the "closing cylinder", is actuated so that it opens the buckets until they reach an open reference position, typically close to the maximum bucket opening allowed by the bucket. stroke of said closing cylinder.
• The lifting cylinder is actuated downhill "slowly" (specific supply of the piston-side chamber) until the contact of at least one blade is detected on the bottom of the tank; for example, a sensor is used to detect the moment when the pressure in the oil circuit which feeds the piston-side chamber increases sharply and a displacement sensor which makes it possible to raise the altitude of the blade during said contact;
• From this altitude is defined the height to which said blade should be, taking into account a safety distance and deduced the path that must follow said blade between said reference open position and the closed position;
• Said lifting cylinder is actuated to raise said collection unit to the origin point of the trajectory defined in the preceding step (configuration illustrated by FIG. figure 6 );
• The closing cylinder is actuated, the lifting cylinder being in slave mode so that the blade follows the path defined previously (configuration illustrated by the figure 7 );
• Once the collection unit is closed, the lifting cylinder is actuated in mounted mode (configuration illustrated by the figure 6 ) then, when the collection unit has reached a certain altitude, the actuators of the MSE are used to move the assembly to a reception area of the harvested debris.

EXAMPLE 2 (Figure 8)

The figure 8 schematically illustrates a collection unit, in which the first actuator (50) is an electric motor (53 ') fed by means of a circuit which makes it possible to control the rotation of said motor. Here, the electric motor is that of an electric cylinder (51 ') which imposes a vertical movement to the link (52 ') integral with the frame (110'). In a variant of this example, the electric jack is replaced by an electric winch, the link then being a cable connected to said frame, the vertical displacement thereof being for example guided by a guide device fixed on the movable support.

• le premier indique la distance (H) entre un niveau horizontal de référence (N) (par exemple une plate-forme de la tourelle porte-outils) et un point fixe du châssis (110') de l'unité de collecte (représenté sur la figure par le niveau horizontal commun des axes de rotation des godets), ce qui permet de connaître l'altitude de l'axe (115') autour duquel pivote le godet (120') dont la forme est schématisée en pointillés;
• le second indique la course (L) de la tige du vérin de fermeture (200'), lequel, par le biais d'une bielle commune (300'), commande l'ouverture et la fermeture des deux godets.

The motor (53 '), according to the control current (I) sent by the variable speed drive (83'), is at all times able to impose on the link (52 ') a vertical movement upwards or downwards at the required speed. The variable speed drive (83 ') is controlled by a programmable controller (84) which receives the indications provided by two sensors:

• the first indicates the distance (H) between a reference horizontal level (N) (for example a platform of the tool turret) and a fixed point of the frame (110 ') of the collection unit (shown on the figure by the common horizontal level of the axes of rotation of the buckets), which allows to know the altitude of the axis (115 ') around which pivots the bucket (120') whose form is schematized in dashed lines;
• the second indicates the stroke (L) of the rod of the closing cylinder (200 '), which, through a common connecting rod (300'), controls the opening and closing of the two buckets.

At any value L of the piston stroke of the closing cylinder corresponds a determined opening angle of the buckets, equal to twice the angle (α) that the edge (129 ') of the bucket with the vertical. By designating the distance from this edge (129 ') to the pivot axis (115') and the distance between the blade (128 ') and the orthogonal projection of the pivot axis on said edge (129 '), the difference in altitude between the axis (115') and said blade, which is given by the expression: ΔZ = d cos α + h sin α, is known at all times.

Thus, at any position of the rod of the closing cylinder corresponds an altitude to which must be said axis so that the blade (128 ') is at an altitude greater than or equal to a given value corresponding to the theoretical altitude of the bottom tank increased by a certain margin of safety, typically one or a few tens of millimeters. The programmable control system comprises a programmable controller (84) associated with a computer memory (85) which enables it, as a function of the measurement values of (H) and (L) transmitted, to define the set altitude of the substantially horizontal axis around which pivots a bucket. If the set altitude is higher than the effective altitude, there is danger of collision between the bucket blade and the bottom of the tank. The variable speed drive (83 ') is then activated in such a way that it can quickly correct the trajectory of the blade. The programmable controller (84) sends a signal (S) to the variable speed drive (83 '), which converts said signal into a current of command (I) which imposes said electric motor a direction of rotation and speed all the more important that the deviation from the set position is large. Conversely, when the set altitude is lower than the effective altitude, the variable speed drive (83 ') is activated in such a way that it can quickly correct the motor servo, to lower the altitude of the blade. The programmable controller (84) sends a signal (S) to the variable speed controller (83 ') which imposes on the motor a direction of rotation and a speed which is greater as the deviation from the set position is large. .

Claims (19)

1. A collection unit (100) designed to collect the solid debris and mud in the liquid media of a cell for producing aluminum, such as the electrolysis bath and the molten metal, in particular a crust shovel (100') designed for cleaning anode holes, comprising:

   a) a means of fixing to fix said collection unit onto a mobile support (5') able to move said collection unit above the zone to be cleaned;

   b) a connection (520) actuated by a first actuator (50) which causes said connection to move in relation to said mobile support in the vertical direction;

   c) a frame (110) interdependent of said connection;

   d) at least one articulated bucket (120a, 120b), swiveling around a substantially horizontal axis (115a, 115b), fitted to said frame, with a substantially horizontal blade (128a, 128b), said bucket being actuated by a second actuator (200, 201), interdependent with said frame, causing said bucket to adopt a rotary movement around said substantially horizontal axis,
   characterized in that said first actuator (50) is connected to a programmable control system (83 + 84 + 85 ; 83' + 84 + 85) able to:

   i) determine, directly or indirectly, the altitude of said substantially horizontal axis and the difference in altitude between said blade of said bucket and said substantially horizontal axis;

   ii) define, from the values determined in i), the vertical movement which must be applied to said connection so that the altitude of said blade remains at least equal to a predetermined value;

   iii) define and transmit to said first actuator a suitable control flow (Φ, I), so that the first actuator can apply said vertical movement to said connection.
2. Collection unit (100, 100') according to claim 1, characterized in that said programmable control system includes:

   a) an instrumentation and control unit which acquires the data relating to said altitude of said substantially horizontal axis and said difference in altitude between the bucket blade and the substantially horizontal axis, deduces from these data a set point to be imposed on the altitude of said substantially horizontal axis so that the altitude of the blade is at least equal to a predetermined value, which makes it possible to avoid any risk of contact between said blade and an obstacle located below said collection unit , typically the tank bottom, and emits a signal (S) representative of said set point;

   b) a converter that translates said signal into a control flow (Φ, I) and transmits said control flow to said first actuator.
3. Collection unit (100, 100') according to claim 1 or 2, characterized in that said programmable control system is connected to a first sensor making it possible to measure the vertical movement of said connection in relation to a reference level (N) and to a second sensor making it possible to directly or indirectly measure the difference in altitude between said blade (128a, 128b) of said bucket (120a, 120b) and said substantially horizontal axis (115a, 115b), for example a sensor making it possible to determine the angular position (α) of said bucket.
4. Collection unit (100, 100') according to claim 3, characterized in that said second actuator is a jack imposing a rotation on said bucket via a rod, and in that said means making it possible to indirectly measure the difference in altitude between said blade (128a, 128b) of said bucket (120a, 120b) is an incremental position sensor measuring movement (L) of the rod of said jack in relation to the body of said jack.
5. Collection unit (100, 100') according to claim 3 or 4, in which said instrumentation and control unit is an Programmable Logic Controller (or PLC) which:

   a) acquires the data provided by said first sensor and said second sensor at regular time intervals, typically a few tens of milliseconds;

   b) deduces from these data, using a computer program based on a kinematic model describing the trajectory of the blade in an appropriate reference frame, the value of the set point which it is necessary to impose on the altitude of the bucket's pivotal axis, and

   c) transmits to said converter a signal (S) representing said set point.
6. Collection unit (100, 100') according to claim 5, in which said computer program implemented in said programmable controller is based on a kinematic model describing a trajectory of the blade which is deduced from the theoretical profile of the tank bottom by translation along a vector oriented vertically upwards, the intensity of which corresponds to a preset safety distance.
7. Collection unit (100, 100') according to any of claims 1 to 6, characterized in that it includes a frame (110) and two buckets (120a, 120b) assembled on said frame, laid out symmetrically in relation to a substantially vertical plane and articulated, swiveling around two substantially horizontal axes (115a, 115b), each bucket having a blade (128a, 128b) opposite the blade of the other bucket, the second actuator, interdependent of said frame, imposing on each of said buckets a substantially symmetrical rotation movement in relation to said substantially vertical plane, so that the solid debris located between the two buckets is trapped by said buckets.
8. Collection unit (100, 100') according to any of claims 1 to 7, characterized in that said second actuator (200, 201, 200') is a hydraulic actuating cylinder fed by a circuit which has at least two operating configurations for closing the buckets:

   a) a first configuration, in which sufficient force is transmitted to the buckets to make it possible to entrain the solid debris encountered by the buckets,

   b) a second configuration, corresponding to a differential assembly, in which sufficient kinetic energy is transmitted to the buckets for the slamming function to be carried out.
9. Collection unit (100, 100') according to any of claims 2 to 8, characterized in that said first actuator includes an electrical motor (53') interdependent with said mobile support, a connection (52') interdependent with said collection unit and coupled to said motor so that the rotation of said electric motor causes the movement of said collection unit via said connection, in that said converter is a variable speed transmission (83') which transmits to said electrical motor a control current (I), whose characteristics allow the electric motor to impose said vertical movement via said connection.
10. Collection unit (100, 100') according to claim 9, in which said electric motor is the motor of an electromechanical jack and in which said connection is the rod of said electromechanical jack.
11. Collection unit (100, 100') according to claim 9, in which said electric motor is the motor of an electric winch and in which said connection is the cable of said winch.
12. Collection unit (100, 100') according to any of claims 2 to 8, in which said first actuator includes a hydraulic actuating cylinder (51) including a body (55) interdependent with said mobile support, said connection being the rod (52) of said hydraulic actuating cylinder, and in which said converter is a distributor mounted on the portion of the hydraulic circuit which supplies the chamber on the rod side of said hydraulic actuating cylinder with a controlled flow.
13. Collection unit (100, 100') according to claim 12 in which said distributor (83) is an electro-hydraulic servo-distributor with controlled flow to control the volume of oil inside the chamber on the rod side, preferably, an electrically-controlled proportional action servo-distributor.
14. Collection unit (100, 100') according to claim 12 or 13, in which said distributor (83) is controlled by a Programmable Logic Controller (84) which acquires, at regular time intervals, typically a few tens of milliseconds, altitude H of the swiveling axis (115') of the bucket and value L of the movement of the piston rod of the second actuator (200'), deduces from these values, using a related computing memory (85), the set point which it is necessary to impose on the altitude of the pivotal axis of the bucket and injects a signal (S) to said distributor (83) in order to decrease or increase the volume of oil which feeds the chamber on the rod side and which is necessary to reach the right altitude.
15. Collection unit (100, 100') according to any of claims 12 to 14, in which said hydraulic actuating cylinder (51) is a double-acting jack, the rod (52) of which is interdependent with said collection unit, with a chamber on the rod side (53) able to constantly impose on said rod a vertical movement upwards and a chamber on the piston side (54) able to constantly impose on said rod a vertical movement downwards, it being possible to connect the two chambers, via at least one distributor (80), to a source of pressure (P) or a tank (R), the feeding circuit including several portions of circuits which make it possible to provide the following hydraulic feed configurations:

    a) a differential configuration, where the chamber on the rod side (53) and the chamber on the piston side (54) are connected to the pressure source (P), allowing the mast to descend at high speed;

    b) a configuration corresponding to rest position, the collection unit remaining suspended, and the circuit arranged so that said collection unit can move vertically without effort should it encounter an obstacle;

    c) a configuration in which the chamber on the rod side (53) is connected to the pressure source (P), corresponding to the upward movement of the collection unit;

    d) a configuration under controlled operation, in which the portion of circuit feeding the chamber on the rod side includes a distributor (83) with controlled flow and controlled by a programmable control system including an instrumentation and control unit which acquires the data relating to the altitude of said substantially horizontal axis and the difference in altitude between the bucket blade and the substantially horizontal axis, deduces from these data the set point which it is necessary to impose on the altitude of said substantially horizontal axis and emits a signal representative of said set point to said distributor.
16. Pot tending module (7) designed to be used in a plant for the production of aluminum by igneous electrolysis and comprising a carriage (8) and handling and servicing devices (10), characterized in that it also includes a collection unit (100) according to any of claims 1 to 15.
17. Pot tending assembly (5) for a plant producing aluminum by igneous electrolysis including an overhead travelling crane (6) characterized in that it includes also at least one pot tending module (7) according to claim 16.
18. Use of a pot tending module (7) according to claim 16 for work on electrolysis cells (2) designed for the production of aluminum by igneous electrolysis, in particular for cleaning the anode holes, in which said first actuator is controlled by said programmable control system so that said substantially horizontal axis follows a predefined trajectory, typically located above and parallel with the tank bottom.
19. Process for cleaning an anode hole during anode replacement, in which a collection unit according to any of claims 1 to 15 is used, said first actuator being assembled interdependently with a pot tending machine (5); one proceeds as follows:

    a. using the PTA actuators, said collection unit is brought in closed position, in line with said anode hole, said first actuator being at rest;

    b. said first actuator is actuated to descend quickly as far as a predetermined altitude, higher than the level of the bath located in the tank, in order to authorize opening of the collection unit ;

    c. said second actuator is actuated so that it opens the buckets until said buckets reach a reference open position, typically close to the maximum opening permitted by the travel of the second actuator;

    d. said first actuator is actuated in "slow" descent mode as far as a preset altitude;

    e. from the altitude reached at the end of the previous stage, the height at which said blade must be is defined, taking a safety distance into account, and the trajectory that said blade must follow between said open reference position and the closed position is deduced;

    f. said first actuator is actuated to raise said collection unit up to the point origin of the trajectory defined in the previous stage;

    g. said second actuator is actuated, said first actuator being in controlled mode so that the blade follows the trajectory defined in e);

    h. once the collection unit is closed, the first actuator is actuated in raise mode; then when the collection unit has reached a certain altitude, the PTA actuators are used to move the unit towards a zone which receives the collected debris.

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