Abstract:
The invention relates an apparatus for hoisting and handling equipment wherein the apparatus includes locking members having a locking block ( 30 ) carried by each telescopic element and including clamping member which is clamped in a rest position, an immobilization piece ( 40 ) carried by each element outside the element carrying a block configured to cooperate with the clamping member.

Description:
The present invention relates to the technical field of telescopic booms or jibs for cranes, whether installed on fixed installations or carried by mobile structures, whether self-propelled or not. 
     BACKGROUND OF THE INVENTION 
     In the above technical field, telescopic jibs are generally mounted on a turntable that is steerable in azimuth relative to a carrier structure, and the turntable carries a jib that is tiltable in elevation, the jib being made up of at least three distinct telescopic elements. 
     The first element is referred to as a “base” element and is generally connected to the elevation tilt axis, the second element is referred to as an “intermediate” element, and the third element is referred to as an “end” element and usually carries at least one jib head sheave. These three elements are intended to enable the length of the jib to be adjusted, so as to vary the distance or length between the elevation adjustment axis and the jib head sheave over which a cable passes and is guided, which cable is wound in or out from a base winch in order to vary the height of a load suspended from the portion of the cable that extends beyond the jib head sheave. 
     Initially, implementing a jib of the above type required the existence of technical means suitable for making it possible to adjust telescoping while under load so as to make it possible to adjust jib length relative to the vertical through a determined point relative to which a load was to be lifted, lowered, put into position, or removed. 
     To be able to perform such a function, it was necessary to provide relative sliding means between the telescopic elements capable of accommodating the stresses that arise while telescoping under load, and it was necessary to implement telescoping means that were particularly powerful in order to overcome the friction induced by sliding under load. 
     Such means are particularly expensive, they must be designed to be very robust, and they need to be subjected to very thorough maintenance so that the essential or prime function of the crane can be carried out in complete safety. Furthermore, such means represent considerable weight to the detriment of the functional capacity of the jib. 
     For some time, attempts have been made to emphasize prior telescoping while unloaded, while nevertheless still having the possibility of enabling the stroke of one element to be telescoped under load. Such a method makes it possible to install telescoping power that enables the unloaded jib to be set to length while nevertheless retaining the possibility of modifying said length over the stroke of a single element at reduced load. That method has the advantage of not straining the locking and unlocking members. 
     That technique consists in determining a priori the length that needs to be conferred to the jib so that from the site on which it stands it can reach a position vertically above the point where a load is to be picked up or put down, or indeed a locus which this point is capable of following, e.g. a portion of a circle, and then in adjusting the length of the jib accordingly. 
     To enable those techniques to be implemented, an actuator is placed inside a telescopic jib, which actuator is suitable for performing rectilinear displacement in both directions, and is connected, for example, to the base element and movable relative to the end element. 
     In general, such an actuator is constituted by a double-acting hydraulic actuator of single predetermined stroke which corresponds generally to the longest retraction or extension stroke that can be performed by any of the moving elements, naturally excluding the base element which is considered as being fixed. 
     The above technical means need to satisfy two basic requirements. 
     The first is to be able to hold the telescopic elements in a mutually locked configuration both in the retracted position and in the extended position. 
     The second is the need to be able to engage selectively by any one of the telescopic elements to release it from the position it is occupying and then drive it to a desired new position in which it must again be locked. 
     To make that possible, the prior art has various proposals. 
     Mention can be made of application EP 0 476 225 which mentions implementing a telescoping head carried by the actuator and suitable for causing locking blocks to be retracted or extended relative to complementary housings presented by the internal ends of the telescopic elements which are also interconnected in the retracted position by other selectively controllable members which need to be actuated synchronously. 
     That document would not appear to specify how the elements are caused to be locked together in the extended position. 
     In any event, it should be observed that that technology uses a series of locking members and engagement members which are superposed and which need to be fed with energy in the form of a fluid under pressure, which energy must be delivered in accurately synchronized manner in order to obtain the desired result which, by way of example, when performing outward telescoping, necessarily requires the following to be performed in sequence: the element concerned is engaged; the element is unlocked; the element is caused to slide relative to the others into its new position; in which position it must again be locked. 
     Mention can also be made of German application DE 4 344 795 in which, between the actuator and each of the telescopic elements, there are provided engagement means of the same kind as in the above-described application, and locking means which are constituted by engaging pins that need to be controlled separately during retraction in order to release one element relative to another. 
     Although that technology appears to be technically simpler than the technology of the preceding application, it nevertheless requires two types of control member to be implemented that are capable selectively of connecting the actuator to any one of the elements to be displaced, and of releasing said element that is to be displaced relative to the next element. 
     Such a requirement means that specific control circuits need to be established and moving members need to be present that are specific to each of those functions, and as a result, overall the telescoping apparatus is cumbersome to install, to put into operation, and to maintain, and it is not possible for it to claim any genuine savings in weight or mass compared with the solution proposed in application EP 0 476 225. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     The object of the invention is to propose a novel telescoping technique and novel means for implementing it so as to be able to perform the above functions in complete safety while using equipment of reduced weight. An object of the invention is to be able to transfer the weight saving obtained in this way to the benefit of jib construction, thereby enabling the effectiveness of the jibs to be reinforced without it being possible overall to consider that the total mass has changed to such an extent as to reduce functional capacity. 
     The invention proposes a novel technique and novel implementation means making it possible from a combination of two mutually co-operating technical means to perform both functions comprising firstly causing the actuator to operate in temporary manner to engage or to couple with one of the telescopic elements in order to apply thrust thereto, and secondly to release the telescopic element from the element which surrounds it so as to allow relative displacement between the elements, and conversely the opposite functions when it is appropriate to lock in the desired new position any one of the elements that have been moved so that it can then be decoupled from the actuator. 
     To achieve the above objectives, the method of the invention consists in: 
     implementing on each element other than the base element a locking block including a clamping member having a clamped rest position; 
     causing the clamping member of each block to co-operate with at least one fixed-position immobilization piece belonging to the element disposed concentrically outside the element carrying the block; and 
     causing the actuator to carry a member suitable for acting selectively on each of the locking blocks for the purposes of temporarily coupling or engaging them and for positively unclamping them; 
     by positive action firstly to connect said actuator to said block and secondly to neutralize the action of the clamping member on the immobilization piece; and 
     by retraction firstly to immobilize said block relative to the clamping piece and secondly to release the actuator relative to said block. 
     The invention also provides telescoping apparatus capable of implementing the above method, wherein: 
     the locking members are constituted by: 
     a locking block carried by each element other than the base element, and including a clamping member having a clamped rest position; and 
     at least one immobilization piece of fixed position belonging to the outer element disposed concentrically about the element carrying a block and designed to co-operate with the clamping member of said block; 
     and the driver means on the actuator comprise a single engagement member suitable: 
     for selectively engaging any one of the blocks to couple the actuator temporarily to the element carrying said block; and 
     for taking positive action to neutralize the clamping member of said block so as to release it relative to the immobilization piece. 
     The invention also provides a jib implementing the above means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other characteristics appear from the following description made with reference to the accompanying drawings which show embodiments and implementations of the invention as non-limiting examples. 
     FIG. 1 is a diagrammatic view showing an example of the jib to which the means of the invention apply. 
     FIG. 2 is a diagrammatic elevation view in section showing a telescopic jib of the invention. 
     FIG. 3 is a fragmentary perspective view on a larger scale showing a structural detail. 
     FIG. 4 is a perspective view showing the structure of FIG. 3 in greater detail. 
     FIG. 5 is a fragmentary section view in elevation and at a different scale on plane V—V of FIG.  4 . 
     FIG. 6 is a fragmentary perspective view analogous to FIG.  4 . 
     FIG. 7 is a fragmentary perspective view similar to FIG. 6 but with more parts omitted. 
     FIG. 8 is a fragmentary diagrammatic elevation view in section on a larger scale showing certain characteristic details. 
     FIG. 9 is a perspective view at a different scale showing a structural detail. 
     FIG. 10 is a diagrammatic elevation view on a smaller scale showing an operating position. 
     FIG. 11 is an elevation view in section corresponding to FIG. 5, but showing another characteristic position. 
     FIG. 12 is an elevation view in section substantially on plane XII—XII of FIG.  4 . 
     FIG. 13 is a fragmentary perspective view of a member in a structural variant. 
     FIGS. 14 and 15 are diagrammatic elevation views in section analogous to FIG. 2, but showing two variant embodiments. 
     FIG. 16 is a fragmentary elevation view in section at a different scale showing a variant embodiment of one of the component elements of the apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an application of the invention to a crane of the self-propelled mobile type. Such an example is given purely by way of illustration, since the invention can be implemented equally well on a crane that is installed in a fixed location, or to any analogous installation. 
     The crane of FIG. 1 comprises a platform or frame  1  carried by running members  2 , e.g. in conventional manner by a plurality of steering and driving wheel sets. The platform or frame  1  carries a driver&#39;s cab  3  which also houses one or more hydraulic and/or driving engine units. The frame  1  carries stabilizing outriggers  4  closed to its front and rear portions so as to ensure a stable base when the crane is in use. 
     The platform  1  also carries a turntable  5  which is steerable in azimuth about a vertical axis x-x′. The turntable  5  has a horizontal tilt shaft  6  carrying a jib  7  which can be tilted in elevation by means of an actuator  8 . 
     The jib  7  is made up of telescopic elements, e.g. four such elements, comprising a first or base element  9  carried directly on the shaft  6 . The elements  10  and  11  are known as intermediate elements, while the element  12  is an end element and carries at least one jib head sheave  13 . 
     The jib  7  also has at least one cable or the like  14  that is wound on and/or off a winch  15  and that passes over the sheave  13  beyond which a cable serves to suspend a load  16 . 
     The turntable  5  is also fitted with a jib cab  18  for controlling the means that actuate the jib such as the actuator  8 , the winch  15 , and telescoping means  19  included inside the jib  7  and represented by dashed lines in FIG.  1 . 
     Telescoping means such as  19  should be considered broadly as forming part of the prior art, with means of the invention being provided to make it possible with such telescoping means  19  to retract or extend each of the moving telescopic elements individually, i.e. the elements  10 ,  11 , and  12 , and to lock each of them in an extended position and also in a retracted position. 
     The means of the invention make use of apparatus suitable for enabling the telescoping method of the invention to be implemented as described below with reference in particular to FIG.  2 . 
     Such apparatus comprises firstly the actuator  19  which is designed in such a manner as to possess firstly a bearing point  20  associated with the base element  9 , and secondly a moving element  21  capable of being driven so as to move along a rectilinear stroke in either direction parallel to the axis y-y′ of the jib. The actuator  19  is preferably in alignment on said axis. 
     In an embodiment, the actuator  19  is constituted by a double-acting hydraulic actuator having a single stage or a single stroke, with a rod  22  secured to the bearing point  20  and a cylinder  23  connected to the moving element  21  and adapted to be carried by the end element  12  with the possibility of guiding its displacement relative thereto. This can be achieved, for example, via a leg  24  provided with wheels or the like  25  and suitable for running along a guide track (not shown). 
     For the person skilled in the art, implementing an actuator  19  of the type described above can be considered as posing no problems with respect to hydraulic feed even though it is in upside-down position, and that is why the pipes for feeding the two chambers of such an actuator are not shown in the drawings. 
     Similarly, the drawing does not show any bearing pieces or shoes or spacers interposed to provide support and guidance in relative sliding between the various moving elements such as  12 ,  11 , and  10  and in particular the base element  9 . 
     In the example shown, the moving element  21  is constituted by a telescoping head which is advantageously integrated in the end bearing of the actuator cylinder  23  opposite from its end wall. 
     The telescoping apparatus of the invention also comprises firstly locking members acting between the telescopic elements to prevent them from moving relative to one another when in the retracted position or the extended position, and secondly means carried by the actuator for the purpose of controlling said locking members. 
     In FIGS. 2 to  7 , it can be seen that the locking members comprise a locking block  30  carried by the inner end portion of each telescopic element  10 ,  11 , or  12 . As can be seen in FIGS. 3 and 4, each locking block  30  defines a well  31  opening out in the top face  32  of the block  30  and also into a cage  33  containing a clamping member  34  having a clamped rest position and constituted by two jaws  35  which are continuously urged towards each other by resilient members  36  (FIG.  5 ). The jaws  35  are placed facing each other via facing active faces which are situated on either side of a longitudinal midplane P-P′ containing the axis y-y′. 
     Each block  30  also has a plunger  37  designed to co-operate with the jaws  35 . For this purpose, the plunger  37  has a shank  37   1  guided in the well  31 , and an actuating face  37   2  facing towards the face  32 . The shank  37   1  is extended by a head  37   3  located inside the cage  33  to co-operate via sloping faces  38  with ramps  39  that face each other on the jaws  35 . 
     In a structural detail, shown in FIG. 8, all of the above-described locking members  30  for the telescopic elements are organized in such a manner that the actuation faces  37   2  of the plungers  37  are in alignment on a line or a plane such as L which is parallel to the axis y-y′. 
     For this purpose, and because of the offset that exists between the positions of the various locking blocks  30  due to the differences in section between the elements  10 ,  11 , and  12  that carry them, the various plungers  37  are provided with respective shanks  37   1  of different lengths such that the face  37  of each plunger lies in the plane or on the line L when the clamp  34  is in its clamping position, as described below. 
     Each locking member also comprises at least one immobilizing piece  40  of fixed position and belonging to the telescopic element immediately surrounding the telescopic element carrying the locking block  30  with which it is to co-operate. 
     This immobilization piece  40  is advantageously constituted by a segment of a bar designed to be held captive by and clamped between the facing faces of the jaws  35 . To improve this function, the facing faces of the jaws  35  are advantageously shaped so as to be complementary to the flanks of the piece  40  against which the jaws  35  are urged by the springs  36 . Advantageously, and as can be seen in FIG. 9, the piece  40  is constituted in the form of two racks having asymmetrical teeth  41  formed as opposing pairs along two longitudinal edges of the piece. Each asymmetrical tooth has a face  42  that is substantially orthogonal to the longitudinal axis of the piece  40  and a sloping face  43 . The piece  40  is carried by the telescopic element in such a manner that the faces  42  look towards the head of the jib. Because of this double-rack shape, the facing faces of the jaws  35  are provided with shapes  44  that are complementary to the teeth  41  (FIG.  7 ). To allow the piece  40  to pass, each block  30  has a notch  45  in its bottom portion (FIG.  4 ). 
     Each piece  40  is fixed to the corresponding telescopic element so that when it co-operates with the block  30  corresponding to the telescopic element inside it they define a fixed position. Thus, as shown in FIG. 2, each element  9 ,  10 , and  11  possesses on its inside two immobilization pieces  40  defining two co-operation positions for the locking block  30  corresponding to the immediately inner element, i.e.  10 ,  11 , and  12 , respectively. These two positions correspond respectively to the retracted position determined by the immobilization piece  40   1  and to an extended position determined by the immobilization piece  40   2 . 
     In the meaning of the invention, it should be considered that each element  9 ,  10 , or  11  can also have other immobilization pieces such as  40   3  each serving to define a respective intermediate position. 
     In a variant embodiment, as represented in FIG. 8 by chain-dotted lines, the immobilization piece  40  can in fact be constituted by a continuous bar  40   4  running along the entire working length of each element  9 ,  10 , or  11 , or along some of them, so as to make it possible to define not only extreme retracted and extended positions, but also n intermediate positions, as described below. Under such circumstances, the bar  40   4  complies with the structural details described above for the piece  40 . 
     The apparatus of the invention also comprises means carried by the actuator  19  for controlling the above-described members. Such means are given an overall reference  50  (FIGS. 2,  5 , and  8 ) and they are said to be “moving” since they are mounted on the telescoping head  21  carried by the actuator cylinder  23  in the example shown. In one embodiment, these means  50  comprise a member  51  suitable for occupying two relative positions under drive from a driver member  52 . The first of these positions is a retracted position and the second is an engagement or coupling position where the member  51  is capable of co-operating with the locking block  30  of any one of the moving telescopic elements  10 ,  11 , or  12 . 
     In the invention, the member  51  is also designed to act on the clamping member  34  of each block  30  so that by taking positive action it neutralizes the clamping function of the member  34  and thus releases the locking block  30  from the immobilization piece  40  with which it co-operates. Thus, the member  51  is designed to perform two functions which take place as described below. 
     In an advantageous embodiment, the member  51  is constituted by a pin, e.g. formed by the piston rod of an actuator constituting the driver member  52 . In such an embodiment, the driver member comprises an actuator cylinder  53  which is fixed to the telescoping head  21  in such a manner that the pin  51 , when in its extended position, can be engaged in the well  31  of one of the locking blocks  30 , thereby exerting thrust on the corresponding plunger  37 . 
     The apparatus of the invention can also advantageously make use of a read cell (FIGS. 2 and 8) carried by the telescoping head  21  and suitable for assessing the presence of position markers  61  fitted to the inside walls of the elements  9 ,  10 , and  11 , as shown in FIG.  2 . 
     The positions of the markers  61  are determined to correspond to the positions of the immobilization pieces  40   1  and also to a position p of maximum retraction in which the actuator  19  is out of operation. The cell  60  is also designed to detect the presence of position markers  62  which are provided to correspond to the immobilization pieces  40   2 . Naturally, intermediate position markers could be provided in association with the pieces  40   3  or with some of the positions that can be defined by a piece  40   4 . 
     The apparatus described above makes it possible to implement a telescoping method which, in accordance with the invention, takes place as follows. 
     Starting from a retracted telescoping position, the locking block  30  of each moving telescopic element, i.e.  10 ,  11 , and  12 , co-operates with the corresponding immobilization piece  40   1  carried by the immediately outer element, i.e. respectively  9  for the element  10 ,  10  for the element  11 , and  11  for the element  12 , in the relationship shown in FIG.  5 . In this position, the springs  36  in each block  30  urge the jaws  35  against opposite sides of the corresponding immobilization piece  40  which is firmly held captive. As a result, each element is prevented from moving axially relative to the immediately outer element surrounding it and cannot be subject to any rearward sliding, even if the jib is tilted in elevation, given the shape of the teeth  41  of the double rack  40 . 
     In this situation, all of the telescopic elements are immobilized relative to one another in a retracted position and they remain immobilized in a state of passive security, given that the clamping members  40  are of a type that is damped when in the rest position. 
     By way of example, the actuator  19  can occupy its out-of-service position shown in chain-dotted lines and corresponding to the position marker p, the actuator then being in its maximally retracted state. 
     When it is appropriate to proceed with extension telescoping, e.g. to extend the end element  12 , the actuator  19  is controlled so as to move the telescoping head  21  until it comes up to the corresponding locking block  30 , with this position being detected by the reader sensing the position marker  61  carried by the telescopic element  12 . 
     When the telescoping head  21  places the pin  51  in register with the locking block  30 , the driver  52  is powered so as to extend the pin  51  which is thus caused to penetrate into the well  31 . The result of this action is to couple the head  21  in temporary manner with the block  30  and consequently to link the actuator  19  with the end telescopic element  12 . 
     The driver  52  is powered so that the pin  51  extends to an extent such that it bears against the actuation face  37   2  of the plunger  37  which moves against the opposing action of the springs  36  to cause the jaws  35  to move apart, thereby releasing the immobilization piece  40 . 
     Thus, initially, the pin  51  temporarily selects the actuator  19  and the moving element to be moved, and subsequently releases the moving element from the immediately outer element relative to which it was previously immobilized. 
     The actuator  19  is then caused to move e.g. in the direction of arrow f 1  (FIG. 2) depending on the sequence being implemented, so that its extension causes the moving element  12  to be moved in the same direction, thus being telescoped into its extended position. The actuator  19  operates until the cell  60  detects the position marker  62  carried by the element  11 . Under such circumstances, the driver  52  is powered so as to retract the pin  51 . In this respect, the driver  52  can be of the single-acting type as shown in the drawing or it can be of the double-acting type. Naturally, any other type of driver member can be implemented to perform the same function. 
     As the pin  51  is retracted, it begins by withdrawing sufficiently to release the force applied to the plunger  37  so that it can retract and allow the action of the springs  36  to become preponderant, thereby closing the jaws  35  and clamping them on the immobilization piece  40   2  presented by the element  11  to face them in the present circumstance (FIG.  10 ). 
     Continued retraction of the pin  51  then leads to it being extracted completely from the well thus decoupling it from the locking block  30 , so that the temporary connection between the telescopic head  21  and said block is ended. 
     The extended telescoping element, in this case the element  12 , is thus again immobilized relative to the element surrounding it, in this case the element  11 , while the actuator  19  is decoupled therefrom and can be controlled to move in the opposite direction so as to return to the position p. 
     It should be observed that during this extension telescoping, guided relative movement between the actuator  19  and the element  12  is made possible because of the leg  24  and the wheels  25 . 
     As can be seen from the above, a single engagement member carried by the actuator, and a single locking block carried by each element suffice for each stroke to be imparted to a moving element to enable said stroke (whether an extension stroke or a retraction stroke) to be performed: firstly by temporary coupling between the actuator and the element that is to be moved; secondly by releasing or unlocking the element to be moved relative to the element surrounding it; thirdly by moving said element to be moved; fourthly by immobilizing said moved element in the desired new position; and fifthly by decoupling said element and the actuator  19  which can then be returned to its original position, or to an active position in order to run the same sequence of events with another moving element such as  11 , or  10 . 
     The proposal of the invention serves clearly to simplify the locking, engaging, and actuation means by causing each of them to perform two functions, and in particular by causing the pin  51  to perform two functions, while nevertheless ensuring that all of the sequences can be performed with positive security that occurs automatically. 
     The two functions performed enable the size of the technical means implemented to be reduced and thus enable the mass thereof to be reduced. Other things remaining equal, such a saving can then be taken advantage of in order to reinforce the structure of the telescopic elements so as to increase their strength and thus improve the functional characteristics thereof under load. 
     Naturally, the method of the invention as described with reference to the extension stroke of element  12  can be performed in similar manner for the retraction stroke of that element, with the exception of the functional sequence specific to the direction in which the actuator  19  is moved. 
     Also naturally, similar sequences can be performed when it is desired to impart a retraction or an extension stroke to any of the other moving elements, and in this case specifically the intermediate elements  10  and  11 . 
     In this respect, it should be observed that the sequence described above can be performed under exactly the same conditions for each of the elements, given that the plungers  37  are structurally organized so that they all lie in the same plane or on the same line L which corresponds to the trajectory that can be followed by the pin  51  and to its extension stroke for performing the two functions of coupling the telescoping head  21  with the block  30  and of neutralizing the clamping effect performed by the clamp  34 . 
     In an advantageous disposition of the invention, the block  30  is mounted in floating manner in or on the telescopic element that carries it. As shown in FIGS. 3 and 5, such a floating mount can be established, for example, by providing the block with grooves  63  for co-operating with a housing  64  formed in the corresponding telescopic element so as to leave clearance J extending transversely to the longitudinal axis y-y′. Such a floating mount has the advantage of allowing co-operation between the members  30  and  40  and  30  and  50  to be accommodated in spite of any possible lateral movements of the telescopic elements. To this end, it is advantageous to provide for a frustoconical bearing surface  31   a  to constitute the entrance to the well  31 . 
     To ensure that the co-operation position is nevertheless indexed, the head  37   3  advantageously includes a finger  37   4  or the like for co-operating, in the unlocked position of the jaws  38 , with a complementary slot  65  formed longitudinally in the top face of the piece  40  (FIG.  11 ). 
     FIGS. 4,  6 ,  7 ,  12 , and  13  show that in another advantageous disposition, each block  30  can be provided with means that immobilize the jaws against any opening displacement other than that under the control of the plungers  37 . To this end, the two jaws  35  are bracketed by two staples  66  disposed in the block  30  with springs  67  interposed to urge them to engage the jaws via their facing tines  68 . Each staple has at least one spur  69  with a sloping ramp  70  placed to co-operate vertically with at least one complementary projection  71  presented by the head  37   3 . Thus, when the head  37   3  is moved downwards by the member  50 , the projection  71  acts on the ramp  70  which pushes back the staple so as to release the jaws  35  for subsequent opening displacement under drive from the head  37   3 . 
     FIG. 14 shows a variant embodiment in which the actuator  19  is constituted by a wormscrew  80  which is connected to the fixed portion  20  via a motor and gearbox unit  81 , which fixed portion  20  can advantageously constitute a bearing for one of the ends of the screw whose other end is mounted in a box  82  carried by the leg  24 . The telescoping head  21  then constitutes a tapped body  83  co-operating with the wormscrew  80  and which is prevented from rotating, for example by guide rails  84  connecting the fixed bearing  20  to the box  82 . In this manner, rotation of the screw  80  in one direction or the other enables the telescoping head  21  to be moved in one direction or the other as represented by arrow f 2  in the same manner as produced in the preceding embodiment by operating the actuator  22 - 23 . 
     FIG. 15 shows another variant embodiment in which the actuator  19  is constituted by an endless chain  90  carried by sprocket wheels  91  and  92 , one of which is a return wheel and the other is a drive wheel given that it is connected to a motor member  93  such as a hydraulic or an electrical motor associated with a gearbox. 
     The sprocket wheels  91  and  92  are preferably carried by a beam structure  94  performing the above requirements of being secured to the fixed point  20  and serving to guide displacement relative to the element  12  by means of a leg  24  and wheel(s)  25 . 
     In another variant, the telescoping head  21  can advantageously be constituted merely by the body  53  of the motor that actuates the pin  51 . 
     It should be considered that the pieces  40  and the block  30  and indeed the means  50  could be disposed in manners other than that shown, for example they could be placed on the top internal generator lines of the elements  9  to  11 . 
     In the invention, provision can be made to constitute each driver  51  in the form of a telescopic actuator having two rods, one that performs the coupling function and the other that performs the function of controlling the plungers  37 . An embodiment is shown in FIG. 16 where the body  53  defines a cylinder  95  containing a piston  96  extended by a rod  97  for penetrating in the well  31  so as to take on the function of coupling with the block  30 . The rod  97  defines a cylinder  98  containing a secondary piston  99  which is extended by a rod  100  whose function is to act on the face  37   2  of the plunger  37 . Thick dashed lines in FIG. 16 show that the cylinders  95  and  98  can constitute double-acting actuator cylinders. The invention is not limited to the embodiments described and shown since various modifications can be made thereto without going beyond the ambit of the invention.