Patent Publication Number: US-4254941-A

Title: Automatic anti-fall device for manual or motorized lifting systems

Description:
The main U.S. Pat. Ser. No. 4,106,733, concerns automatic cable safety apparatuses used in power-driven lifting systems in order to prevent for example the fall of a scaffolding nacelle, which comprise a cable clamping jaw block which is kept open under the action of the load applied to the lifting cable and/or the action of an engaging device, and which is adapted to grip an auxiliary cable when the action of the load is to be transferred from the lifting cable on to the safety cable either in connection with an interruption of this action of the load on the lifting cable or in the event that the speed of the jaw block sliding on the cable in a given direction exceeds a relative speed limit, whereby the apparatus according to the invention simultaneously shuts off the motor(s) of the lifting system. This apparatus actually makes it possible to realize the scopes of the main patent (chiefly a tightening of the jaw block combined with a shutting off of the motor(s) of the system either by a breaking of the lifting cable or in the event that the speed of the jaw block gliding on the cable in a given direction exceeds a limit speed), but may exclusively be employed when an auxiliary cable is available in order to take up the load, not only, of course, in case of rupture of the lifting cable, but also by breaking down, or failure, of the corresponding hoist. 
     Now, although employing an auxiliary cable is always advisable (in some countries even compulsory), it is of an obvious interest, in order to avoid being confronted with an alternative of &#34;all or nothing&#34;, to dispose of an automatic anti-fall apparatus for motor lifting systems which is adapted to work, should an auxiliary cable fail, in cooperation with only one cable, whereby this cable may or may not simultaneously serve as lifting cable. 
     Besides, the apparatus according to the basic U.S. Pat. No. 4,106,733 is susceptible to be improved in connection with its reliability against an exceeding of said limit speed. 
     As a matter of fact, said apparatus improves, at least in relation with the automatic device releasing the self-tightening jaw block clamping the auxiliary cable, other apparatuses, having the same function, which comprise as well a conventional driving pulley running on the cable passing through the mechanism. In these other apparatuses the driving pulley is in fact so arranged that it causes a light deflection of the cable, but the cable groove arc along which the pulley leans against the cable--and consequently the pressure of the cable on the pulley and the adhesive force between cable and pulley--may decrease in an undetermined way owing e.g. to a swinging of the load; so that their releasing devices do not assuredly function by a linear speed of the cable (relatively to the driving pulley) being identical to the peripheral speed of the driving pulley, and as a consequence, the lowering speed of the load is not assuredly proportional to the angular speed of the inertia block (which is identical to the speed of the driving pulley). And in the absence of this proportionality there is no guarantee that a releasing of the cable clamping device will be effected exactly at the limit speed predetermined, and these devices, as well as the safety apparatuses which depend on them, may not be regarded as reliable as a safety apparatus should essentially be. 
     But if it is true that the apparatus according to the main U.S. Pat. No. 4,106,733 in an improvement on what was known--apart from other considerations, also because its reliability is not jeopardized by a swinging of the load, since the cable is pushed against a driving roller 26 (see FIG. 3) by a second roller 27--it is also true that the contact zone of the roller surface and of the cable surface--the latter being utterly uneven as it consists of spiral strands and strands of spiral steel wire--is practically represented by a line and does not assure constancy of friction between the cable and the roller 26 (which is to drive the releasing device of the cable clamping device). This is more especially true as this friction is likely to vary within very broad limits in relation, on the one hand, to the state of the cable surface, which may be lubricated or not, and then again, and above all, owing to the fact that it cannot be possibly prevented that the mechanism of the apparatus gets dirty, to a smaller or greater degree, even though it is enclosed in an absolutely tight case, because of dust, mud and the various (small) scraps normally present in a building site, as these foreign particles get lodged in the spiral grooves between adjacent strands and wires and are thus introduced into the apparatus by the cable itself. 
     This being the case, it is to be feared, actually only in the absence of those regular controls (comprising cleaning and greasing) which are prescribed, as a function of the working time (or also of the duration of inactivity), for all hoists and, a fortiori, for all safety apparatus, more particularly cable safety apparatus--that e.g. dust will mix with the lubricant and increase its viscosity, thus reducing more or less the speed of the roller driving the triggering device. 
     I--A second embodiment of the invention enables to obviate also these disadvantages by realising an apparatus adapted to perfectly perform its function under all working conditions. In this second improved embodiment, as hereafter described, are provided, together with means already employed in the first embodiment, several new means as they are set forth hereafter, respectively sub (a) and (b): 
     (a) 1. A cable clamping device with a pair of jaws exerting their action, started by a pretightening spring, on a cable going through the safety apparatus, wherein 
     1.1. either the jaws are reciprocally identical or one of them is U-shaped and comprises between its branches the other jaw, which is flat; 
     2. A releasing device of the cable clamping device, which allows the jaws to almost instantaneously come into contact with the cable, under the action of said pretightening spring, as soon as the critical speed is attained, wherein 
     2.1. at least one centrifugal inertia block rotates at an angular speed proportional to its longitudinal speed relatively to the cable passing through the safety apparatus, and is arranged in such a way that the centrifugal force developing therein displaces it radially so to bring about, through a system of links, a releasing of the self-tightening block; 
     3. A current interrupter, suited to break the circuit in the case of too great a lowering velocity depending or not on a wrong control from the operator; 
     (b) 1. A driving pulley actuating the releasing device, which consists of two symmetrical half-pulleys having a relatively great diameter and presenting each one half-groove fitting the contour of the cable, whereby these half-pulleys are pushed one against the other by several springs, and which rotates on a shaft provided with 
     1.1. a bearing, preferably a needle bearing, by means of which the shaft supporting the centrifugal inertia block under I--a.2.1. and the driving pulley under I--b.1 may turn with a very low friction; 
     2. A press sliding guide located parallel to the cable opposite the driving pulley under I--b.1 or else a press pulley (similar or not to pulley 27 of the basic U.S. Pat. No. 4,106,733 disposed in the same plane as the driving pulley, whereby the press element (guide or pulley) is provided with a semicircular groove having the same diameter as the cable and is urged by a spring toward the cable. 
     3. α. A coating material for the cable groove of the driving pulley under I-b.1, and, if desired, for the cable groove of the press pulley under I-b.2., which has a high coefficient of friction so that the driving pulley can turn without any rotative slipping between it and the cable; 
     β. A coating material for the cable groove of the press sliding guide under I-b.2. which has a low coefficient of friction and causes practically no power loss and no wear of the cable. 
    
    
     This second embodiment of the invention, in which are incorporated the improvements mentioned hereabove under I--b, is represented in the FIGS. 1--5 of the drawing. 
     FIG. 1 is a longitudinal section of the apparatus along line I--I; 
     FIG. 2 is a front view, partly in section, of the apparatus after removal of the front case plates; 
     FIG. 3 is a cross-section along line III--III of FIG. 4; 
     FIG. 4 is a back view after removal of the back case plate; 
     FIG. 5 is a view of a device preventing a manual (re)starting of motors while jaws 13, 13&#39; clamp the cable. 
     A third embodiment of the invention is represented in FIGS. 6-10 of the drawing, in which: 
     FIG. 6 is a section taken along the line A--A of FIG. 8; 
     FIG. 7 is an elevation view taken in the direction &#34;B&#34; of FIG. 8 in which the back plate 04 of casing 0 has been removed; 
     FIG. 8 is a cross sectional view taken on the line C--C of FIG. 6; 
     FIG. 9 is a front elevational view taken in the direction &#34;A&#34; of FIG. 8 of the device shown in FIGS. 6-8; and 
     FIG. 10 is a fragmentary view, partly in section, of the pin 16 which connects the cable clamping device of the invention with the winch-hoist A.L. 
    
    
     The second embodiment as represented in FIGS. 1-5 of the drawing will now be described. 
     0. The safety apparatus is enclosed in a main case 0a, formed by two symmetrical case plates 02,03, and in a separate case 0b, defined by case plate 03 and by a case plate 04 secured to case plate 03 in a conventional way (e.g. by means of screws), and comprises the following devices: 
     a cable clamping device 1; 
     a stopping device 5 of the motor(s) actuating the hoisting and/or pulling system; 
     an engaging device 2 of the cable clamping device 1 and eventually of the motor(s) stopping device 5; 
     an automatic releasing device 3 of the cable clamping device 1 and eventually of the motor(s) stopping device 5; 
     a driving device 4 of the automatic releasing device 3; 
     a manual releasing device 6 of the cable clamping device 1 and eventually of the motor(s) stopping device 5; 
     a setting device 7 of the automatic releasing device 3. 
     1. The cable clamping device 1, which is located in the main case 0a, consists--as in the embodiment described in the basic patent--of a self-tightening block 11 composed by 
     a pair of plates 12, 12&#39; (of the self-tightening jaw block 11), 
     a pair of cable clamping jaws 13, 13&#39;, 
     two pairs of jaw actuating levers 14, 14&#39;, 
     a jaw pretightening spring 15. 
     1.1. Plates 12, 12&#39; are identical and reciprocally connected, e.g. by distance pins (riveted). They support at their upper part two shafts 14a, 14&#39;a with which jaw actuating levers 14, 14&#39; are pivotable. 
     Plates 12, 12&#39; are linked up at their lower parts 12b, 12&#39;b e.g. through two bolts or pins (not shown) lodged in holes 12d with the load and/or with the case (whereby, in the latter alternative, the case is connected with the load). 
     1.2. Cable clamping jaws 13, 13&#39; are, also in this second improved embodiment of the safety apparatus, of the type employed in the embodiment described in the main U.S. Pat. No. 4,106,733 (that is of the `U`-type). 
     The lower inside portion of the `U`-jaw 13 and the lower side of the flat jaw 13&#39;--which can penetrate more or less between the branches of the `U`-jaw--have a semicircular section with the same diameter as the cable section and can clamp the cable on almost all its circumference. 
     1.3. Jaw actuating levers 14, 14&#39; are two by two identical and are located opposite each other on both sides of the `U`-jaw 13. They are solid with the two shafts 14a, 14&#39;a which are pivotably connected to plates 12. 
     These levers are also solid with two elongated cross-cams 13b, which have a section composed of two equal semicircles reciprocally shifted on the common diameter whereon they are placed on opposite sides. 
     Cross-cams 13b pass through corresponding apertures 13c in the two jaws and their form is such that, when levers 14 pivot anti-clockwise (FIG. 2), jaws 13, 13&#39; clamp the cable. 
     Levers 14 are provided with an extension 14b and to these extensions is pivotably connected a cross-piece 15a, which is under the thrust of jaw pretightening spring 15. Thus levers 14 tend to pivot with their shafts in the sense in which jaws 13, 13&#39; draw together. 
     It may be pointed out, in this connection, that the shafts 14a, 14&#39;a of jaw actuating levers 14 and the centers of the corresponding active portions of the apertures 14b in which cross-cams 13b are located, on the one hand, and the four centers of the semicircles of these apertures, on the other hand, form two articulate parallelograms, so that, while lever 14 and (consequently) lever 14&#39; pivot under the action of pretightening spring 15 and/or of cable friction on jaws, the jaws remain rigorously parallel to one another and to the cable. 
     It may be pointed out as well that the sides of these parallelograms are arranged in such a way that the reaction of friction developed on the cable (FIG. 2, upwards), owing to the pretightening action of spring 15, when the clamping block 11 slides along the cable (downwards), tends to pivot the jaw tightening levers 14, 14&#39; in the same direction as the pretightening spring. An automatic clamping of the cable is thus assured, and the cable is gripped with a force which is proportional, under static conditions, to the weight of the load, and, under dynamic conditions, to the kinetic energy of the same. 
     1.4. Jaw pretightening spring 15 is wound around a bar 15b, which has, at one end, a U-piece 15a resting on a cross-bar 15d fixed on both side plates 12, 12&#39;, and passes, at the other end, through a hole in cross-piece 15c. Thus spring 15 is compressed between U-piece 15a and cross-piece 15c and exerts on the latter a thrust urging jaw actuating lever 14 to pivot in counter-clockwise direction (FIG. 2) and bring jaws 13, 13&#39; together. 
     2. The engaging device 2 of cable clamping device 1 is composed of: 
     an engaging pawl 23 co-operating with an engaging cross-pin 22; 
     an engaging lever 52 actuated, by the intermediary of a link 21, by an engaging spring 24. 
     2.1. Engaging pawl 23 in order to cooperate with engaging cross-pin 22--which is secured to a second extension of jaw actuating levers 14 opposite the spring loaded first extension 14b--is located in the main case 0a together with the cable clamping device 1 and is solid with a shaft 23a pivotable in a bearing fixed to case plate 03. 
     Its free end is provided with a recess 23b  wherein engaging cross-pin 22 is normally retained, and shaft 23a is so set that pawl 23 may move away from engaging cross-pin 22 in a direction parallel to the longitudinal axis of jaw actuating lever 14. 
     2.2. Engaging lever 52, link 21 and engaging spring 24 are enclosed in the separate case 0b. Engaging lever 52 is solid with shaft 23a of engaging pawl 23 while it is pivotably connected to link 21. This link is disposed in a direction generally perpendicular to the longitudinal axis of engaging lever 52 and its other end is under the action of engaging spring 24, which rests on a pin fastened to case plate 03. Thus engaging lever shaft 23a tends to pivot, according to FIG. 4, clockwise and engaging pawl 23 is maintained in a position where engaging cross-pin 22 rests in recess 23b. 
     3. The automatic device 3 releasing, in case of emergency, cable clamping device 1, is enclosed in the same case 0b as engaging device 2, which is completely separate from the main case 0a and is thus perfectly protected from foreign matters introduced into the safety apparatus by the cable itself. The automatic releasing device is composed of: 
     a hub 31 of automatic releasing device 3; 
     a centrifugal inertia block 32; 
     a balance spring 33 of centrifugal inertia block 32; 
     a releasing toothed wheel 34. 
     3.1. Hub 31 is keyed on a driving shaft 41a, with which it co-operates to trnsmit to the other members of the automatic releasing device the movement of rotation generated by the relative movement of translation between the cable and a driving member 41 in the form of a wheel fixed on driving shaft 41a. 
     3.2. Centrifugal inertia block 32 consists of a flat piece of metal having approximately the form of a sector. It is secured (e.g. by means of an elastic ring 33c) to a sliding rod 33b which goes through it in a radial direction and which can slide in a hole bored radially through hub 31 and shaft 41a. 
     3.3 The balance spring 33 of centrifugal inertia block 32 is wound around sliding rod 33b on the opposite side of the inertia block and rests on nut(s) 33a screwed on the rod. As the inertia block is normally maintained in contact with hub 31 with a force equal to the difference between the force of spring 33 and the centrifugal force, and starts to move away from the hub as soon as the centrifugal force overbalances spring 33, it is apparent that by screwing down more or less nuts(s) 33a and thus varying the force exerted by spring 33, the critical speed can accordingly be varied. 
     3.4. Releasing toothed wheet 34 is pivotably mounted on a (cylindrical) projection 44a of the shell of a needle bearing 41b of driving shaft 41a between the plate 03 of the main case 0a and a flange of the shell. 
     This releasing wheel is provided, in the case considered by way of example, with six equidistant radial teeth 34c which are bent at their free end in an axial direction so that the internal side of their portions parallel to shaft 41a is close to the trajectory of the end of rod 33b which is on the side of the centrifugal inertia block 32. 
     Besides, this wheel 34 is provided with an extension 34b articulated to link 21 (which transmits the pull of engaging spring 24 to engaging lever 52). 
     4. The driving device 4 of the automatic releasing device 3 is composed of: 
     a driving member 41, 
     a driving shaft 41a, 
     a press sliding block (or a press roller) 45 with a press spring 46. 
     4.1. Driving member 41 consists mainly of a disc 47 and of two press rings 47a,47b enclosed in the main case 0a, in a same median plane with the cable clamping device. Disc 47 is solid with driving shaft 41a and is provided with several holes through which spring pins 43b may slide in an axial direction. Press rings 47a, 47b are similarly provided with holes allowing spring pins 43b to slide through freely, and bear each a half of a semicircular cable groove 47c arranged on their periphery. 
     It may be pointed out that the form of groove 47c, owing to the fact that the driving wheel 41 is halved whereby the halves are at an angle to one another, forms a semicircular groove with a slot, which notoriously has a driving coefficient more advantageous (almost three times as high) than a groove with a square section. 
     The press rings 47a, 47 b are pushed one against the other by compression springs 43 which are wound around spring pins 43b and exert their action on ring 47a directly and on ring 47b by the intermediary of the same spring pins 43b. Springs 43 are in fact compressed between ring 47a and a circlips or elastic washer 43a set at the near end of pin 43b so that a circlips 43c set at the far end of pin 43b pushes ring 47b towards ring 47a i.e. against the cable. 
     It may be observed that the pressure exerted on the cable can be modified, if desired, by substituting a nut for one, or for each, circlips, so as to compress springs 43 more or less. 
     4.2. The driving shaft 41a, whereon driving wheel 41 is keyed, as well as hub 31 (through which slides the rod 33b of the centrifugal inertia block 32), rotates in needle bearing 41b whose shell is lodged in a stiffened bracket 44b rigid with case plate 03, said bracket being rated for assuring a maximum rigidity. 
     4.3 Press sliding block 45 is located opposite to driving member 41 and is provided with a groove 45c having a curved profile and being set parallel to the cable, and with two oblong holes 45b perpendicular to the groove and slidingly connected to two guide pins 45a, fixed to plates 12, 12&#39; of self-tightening block 11. The sliding block can thus be pushed against the cable by a spring (e.g. leaf spring 46) so that the cable is pressed between the block and the bottom of the cable groove formed by the halves arranged on the periphery of press rings 47a, 47b (as well as between the lateral portions of the cable groove of driving wheel 41 owing to the thrust of compression strings 43). 
     Instead of press sliding block 45 a press roller, not represented, may be employed, the axle of which is slidingly connected to two oblong holes, perpendicular to the cable, in plates 12, 12&#39; of self-tightening block 11.) 
     5. Since also in this case the hoisting and/or pulling system is supposed to be actuated by one or more electric motors--although its driving could as well be effected either by any conventional motor (a hydraulic and/or pneumatic motor or an internal combustion engine etc.) or by hand --the device 5 for stopping the motor(s) consists of a circuit breaker 51, secured on the inside of case Ob, and of an extension of the same level 52 which co-operates in engaging the cable clamping device 1. This extension, during a normal working of the hoisting system, exerts on a push-button of circuit breaker 51 a thrust which prevents it to cut off the current. 
     The circuit breaker should appropriately be of the two-stroke type, which lets current through only at every second stroke of the push-button. 
     6. A manual releasing device 6 of the cable clamping device 1 and of the motor(s) stopping device 5 can be easily provided in order to offer a supplementary safety in the event that a hoist and/or its electric motor would break down, e.g. at a certain lifting height, and the electro-magnetic brake would fail to work, or that the hoist would not firmly clamp the cable, but would let is slide through at a speed not high enough to trigger off the cable clamping device and motor(s) stopping device. Such a manual releasing device may simply consist of a releasing handly or lever (not shown in the drawing) rigidly mounted, outside of case Ob, on an extension of the shaft 23a on which are fastened pawl 23 (engaging the cable clamping device 1) and lever 52 (engaging the motors stopping device 5). 
     It is apparent that a rotation of shaft 23a (FIG. 2: clockwise; FIG. 4: anti-clockwise) will cause the engaging cross-pin 22 to get our of recess 23b of pawl 23, thus releasing cable clamping device 1, and will simultaneously lift lever 52 from the push-button of circuit-breaker 51, thus interrupting the feeding of the motor(s). 
     7. The setting device 7 of the automatic releasing device 3 of the cable champing device 1 and of the motor(s) stopping device 5 consists of a short flat setting lever 71 with a hub fixed, outside main case Oa, to an extension of shaft 14a which is solid with jaw actuating lever 14. Lever 71 enables, against the action of jaw pretightening spring 15, to pivot lever 14 clockwise (FIG. 2), that is in the direction in which they loosen jaws 13, 13&#39; and in which the extension of engaging lever 52 presses down the push-button of circuit breaker 51. 
     La--the working of the automatic safety apparatus described above does not substantially differ from the working of the first embodiment of the invention as disclosed in the main U.S. Pat. No. 4,106,733. 
     1. The mechanism of the apparatus, when ready to work, is in a (stable) equilibrium configuration as represented in the drawing (FIGS. 1-4), wherein engaging pawl 23 is pushed against engaging cross-pin 22 by engaging lever 52 controlled by engaging spring 24 through link 21. Jaw pretightening spring 15, which exerts a thrust on extension 14b of jaw actuating levers 14, is thus prevented from pivoting jaw actuating levers 14 in the direction where jaw 13, 13&#39; draw closer together and grip the cable. 
     2. During a normal working of the hoisting and/or pulling system the above equilibrium configuration is not modified because, as long as the angular speed of driving shaft 41a, and of the system sliding rod 33b/centrifugal inertia block 32, is lower than the critical speed predetermined, the trajectory of the end of rod 33b adjacent to inertia block 32 does not intersect the inward (cylindrical) surface of the axial portion of the teeth of releasing wheel 34, and this wheel cannot trigger off, through the other members of releasing device 3, the cable clamping device 1 and the stopping device 5 of the motor(s). 
     3. At the very moment as, for a cause whatsoever, the (relative) up-speed of the cable and the angular speed of the system driving member 41 in the form of a wheel centrifugal inertia block 32 (FIG. 4: anti-clockwise)--these speeds being, owing to the invention, exactly proportional to one another--simultaneously exceed their respective critical values, the centrifugal force acting in inertia block 32 overbalances balance spring 33 so that the end of rod 33b which is adjacent to inertia block 32 is projected outwards and strikes against the one or the other axial portion 34c of releasing toothed wheel 34. This wheel is then bound to pivot sharply, thus causing, through the instrumentality of the members of the engaging device itself, engaging pawl 23 to pivot in the same direction (FIG. 2: clockwise) and to release engaging cross-pin 22. Thus jaw pretightening spring 15 is in a position to pivot jaw actuating levers 14 in the direction which corresponds to a reciprocal drawing nearer of cable clamping jaws 13, 13&#39;, and the friction developed on contact surfaces between jaws and cable rapidly increases up to the stopping, simultaneous and almost instantaneous, of cable clamping device 1, of the hoist and of the load hanging on the safety apparatus and/or the hoist. This stopping also coincides--in case of motor driven hoist(s) --with the stopping of the motor(s) because engaging lever 52, pivoting (FIG. 4: anti-clockwise) away from the automatic circuit breaker 51, lifts its free end from the push-button of same and does not prevent it any longer from switching off the current (or, generally: the feeding). Of course, lever 52 will thereafter be pulled back by engaging spring 24 to its precedent position where it presses down the push-button, but a current feeding will nevertheless not be restored, since the circuit breaker, as indicated hereabove, is opportunely of the two-stroke type. For normal operation of the hoisting and/or pulling system, the setting lever 71, as described hereabove sub 7, should be operated in order to again close and maintain closed the circuit (jaws 13, 13&#39; being then again open). It is apparent, however, that the same result could be attained by operating, instead, the manual releasing lever or handle mounted on shaft 23a, which might cause serious damages to the lifting and/or pulling system because jaws 13, 13&#39; would still be clamping the cable. The device shown in FIG. 5 prevents such an irregular operation. 
     It comprises a knee lever 25, pivoted on a pin 25a fixed (as engaging pawl 23) to case plate 03, and a spring 26 secured to a pin 26a, also fixed to case plate 03. The shape of knee lever 25 and the position of its pivot pin 25a are such that, when engaging pawl 23 normally engages cross-pin 22(dots-and-dashes configuration), the arms 25b and 25c remain idle on the one end on the other side of the free end of engaging pawl 23, while an automatic or manual releasing of jaw actuating levers 14 will cause arm 25b to turn (FIG. 5: clockwise) so that arm 25c gets to a position close by pawl 23 where it prevents it from pivoting away from cross-pin 22. 
     4. The setting of the automatic releasing device 3 of cable clamping device 1 and of the motor(s) stopping device 5 can be operated by means of setting lever 71 and of the same members of the engaging device 2 of cable clamping device 1. 
     Setting lever 71 (FIG. 2) by pivoting clockwise actually produces the following effects: 
     (a) jaw actuating levers 14, 14&#39; also pivot clockwise (downwards) and move jaws apart; 
     (b) the end of engaging lever 52, drawn back by engaging spring 24, presses--in the case of an electrically driven hoist--the push-button of circuit breaker 51 and closes the circuit; 
     (c) knee lever 25 returns, under the action of spring 26 to its idle position; 
     (d) the engaging cross-pin 22 secured to the free end of jaw actuating levers 14, 14&#39; also moves downwards and, sliding along a slanting surface 23d situated at the free end of engaging pawl 23, pushes this back (FIG. 2: dots-and-dashes line), against the thrust of engaging spring 24, until it is level with the recess 23b of the pawl. Thus this may be brought back to its initial position, owing to the pivoting motion that engaging spring 24 through link 21 imparts to engaging lever 52 and to shaft 23a, thus ratching the engaging cross-pin 22 and making inoperative the cable clamping block 11. 
     As jaws 13, 13&#39; do not clamp any longer the cable, this may be now inserted or pulled out and, conversely, the safety apparatus may freely slide up and down the cable. 
     II--The purposes of the invention according to the main U.S. Pat. No. 4,106,733 are also achieved, in an even more efficient way, through a third embodiment which may particularly be employed when the safety apparatus is to co-operate with a winch-hoist provided with two two-part pulleys. (U.S. Pat. No. 4,193,311) This winch-hoist comprises, in a preferred embodiment, two pulleys similar to the driving member 41 serving in the apparatus described above as second, improved embodiment of the present invention to actuate the releasing device 3 of the cable clamping device 1. The pulleys, consisting each, as it will be recalled, of two co-axial parts (13), (14) pushed against one another by several springs (16), (U.S. Pat. No. 4,193,311), are coupled by means of two toothed rims arranged on their periphery beside the cable groove, and at least one of them is driven, e.g. by a greater motor. 
     In this third, improved embodiment of the invention the centrifugal releasing device is driven by a driving member 41 in the form of a sprocket which meshes--directly or through one or more cog-wheels 42--the peripheral toothed rim of at least one pulley of the winch-hoist. It appears that by this means the speed of the cable (and of the load), which is identical with that of the toothed rim, is--and cannot but remain--proportional to the angular speed of driving shaft 41a (carrying inertia block 32), thus excluding any irregularity in the transmission of the movement which might derive, not only (by insufficient maintenance) from foreign bodies penetrating into the case, but from any cause at all: an absolute reliablity of the automatic releasing device 3 and of the security apparatus itself is thereby warranted. 
     This third, improved embodiment of the invention is described hereafter: 
     1. The mechanism of the automatic security apparatus comprises the same devices as the mechanism of the second, improved embodiment of the invention, but the driving shaft 41a of the driving device 4 of the automatic releasing device 3 is now actuated by the sprocket and cog-wheel(s) above mentioned. 
     FIG. 6 shows in a section along line A1, A2 of FIG. 8. 
     the cable clamping device 1 and in a view from `A` (the front plate 02 of casing 0 being removed) 
     the fram 01 of casing 0 and 
     the driving gear 4 of automatic releasing device 3:, 
     FIG. 7 is a view from `B` of FIG. 8 (the back plate 04 of casing 0 being removed) of 
     the engaging device 2 of the cable clamping and motor(s) stopping devices 1 5, respectively and of 
     the automatic and manual releasing devices 3 resp. 6 of said cable clamping and motor(s) stopping devices 1 5 respectively; 
     FIG. 8 shows in a section-view along line C 1  C 2  of FIG. 6 
     the cable clamping device 1, along line C 2  C of FIG. 6 
     the driving gear 4 of automatic releasing device 3, along line D 1  D 2  D 3  D of FIG. 7 
     the engaging device 2 of the cable clamping and motor(s) stopping device 1 5, respectively, and 
     the automatic and manual releasing devices 3 6, respectively of said cable clamping and motor(s) stopping devices 1 5, respectively is and in a side view from `E` of FIG. 9 
     the automatic motor(s) stopping device 5 and 
     the setting device 7 of the automatic and manual releasing devices 3 6, respectively, of said cable clamping and motor(s) stopping device 1 5; 
     FIG. 9 is a front view from `A` of FIG. 8 of the safety apparatus and, in particular, of 
     the automatic motor(s) stopping device 5, and of 
     the setting device 7 of the automatic and manual releasing device 3 6, respectively of said cable clamping device 1 and of motor(s) stopping device 5; 
     FIG. 10 shows the pin 16 connecting the cable clamping device 1 with the winch-hoist A. L. 
     O. A case O enclosing the mechanism comprises a frame 01, which may be secured (e.g. by means of bolts) to the case of hoist A. L., and a front plate 02, a partition plate 03 and a back plate 04, all secured (e.g. by means of screws) to frame 01 so to form two reciprocally tight half-cases Oa, Ob. 
     1. The cable clamping device 1, also consisting of a self-tightening block 11, is enclosed--with the driving gear 4 of the automatic releasing device 3--in half-case Oa (FIGS. 6 and 8) and, though the cable clamping jaws are, by way of example, of a different type (which could have been employed as well in the second, improved embodiment of the invention, as described hereabove), also comprises 
     a pair of plates 12 (of self-tightening jaw block ll, 
     a pair of cable clamping jaws 13, 
     two pairs of jaw actuating levers 14 and 
     a jaw pretightening spring 15. 
     1.1 The two identical plates 12, rigidly connected through distance pins 12a, bear two fixed pins or two shafts 14a on which or, respectively, with which jaw actuating levers 14 are pivotable. 
     Each plate 12 is provided, on the load side, with an extension 12b having a bearing 12c, and in these bearings 12c a pin 16 is fixed with a cross-hole 16a set out in such a way that the cable may freely get through. 
     By mans of this pin the self-tightening block 11 --when it is released either automatically by releasing device 3 or by the operator through the manual releasing device 6--takes up the load; that, again, either through the winch-hoist, if the load is attached to the case of said winch-hoist (whereby this is also secured, as seen above, to the frame 01 of the safety device), or directly if the load is attached immediately to pin 16 itself. 
     1.2 Cable clamping jaws 13 (which, as it has been mentioned hereabove, could also be similar to those employed in U.S. Pat. No. 4,106,733 as well as in the second, improved embodiment of the invention as described above, that is of a `U`-type) are in the present variant of the type first disclosed in the U.S. Pat. No. 2,585,101. They are symmetrical and have two grooves 13a arranged in their opposite elongated surfaces along their longitudinal axis, which have a semicircular section susceptible to clamp the cable on almost all its circumference. Besides they are provided with two pairs of half-pins 13b, which are shifted from one another along their common diameter in a direction parallel to the longitudinal axis of the jaws and which project from their lateral surfaces so to engage with jaw actuating levers 14. 
     1.3. Jaw actuating levers 14, all mutually identical, are located on either side of jaws 13, on the inside of plates 12 (to which they are pivotably connected on pins or with shafts 14a), and show two appertures shaped and arranged in such a way that they allow a (limited) pivoting movement of half-pins 13b and thus--by a lowering movement of the security apparatus along the cable--cause jaws 13 to get close to one another and to clamp the cable with a force which is proportional to the kinetic energy of the load. 
     1.4. Jaw pretightening spring 15--in an even simpler way than in the second, improved embodiment of the invention disclosed above--is wound up around the pins (or shafts) 14a of the two pairs of jaw actuating levers 14 and its ends push each on a stud 15a fixed to one lever of each pair, in a direction which urges these levers to bring jaws 13 close together and onto the cable 
     2. The engaging device 2 of cable clamping device 1 is enclosed--with the releasing device 3 which drives it and except its engaging levers 21--in half-case Ob. As this is completely separate--as stressed hereabove--from half-case Oa, which encloses cable clamping device 1, engaging device 2 is perfectly sheltered from foreign bodies brought into the safety device by the cable itself. 
     This device is composed by 
     a pair of engaging levers 21 of self-tightening block 11, 
     an engaging ratched sector 22, 
     an engaging pawl 23 and 
     an engaging pawl spring 24, 
     and is adapted to hold the engaging levers 21 of self-tightening block 11 (which are enclosed in the same half-case Oaas the cable clamping device 1) in a position corresponding to unclamped jaws, and that against the thrust of jaw pretightening springs 15. 
     2.1. The engaging levers 21 of self-tightening block 11 are rigidly mounted on an engaging shaft 21a, which may pivot in two bearings 21b arranged respectively in the front case plate 02 and in partition plate 03. 
     In order to unclamp jaws 13, while ratching at the same time engaging ratchet sector 22, these levers may be actuated by the operator through a setting lever (or handle) 71 of the automatic device 3 for releasing the cable clamping and motor(s) stopping devices 1 5, respectively, whereby this lever 71 is fastened outside of case 0 on to the same engaging shaft 21a. 
     2.2. Engaging ratchet sector 22 is also solid with engaging shaft 21a, on the opposite side relatively to partition plate 03 as the engaging levers 21 of self-tightening block 11, and at the opposite end of engaging shaft 21a relative to setting lever 71. 
     Its function--by a normal working of the hoisting and/or pulling system--is to co-operate with engaging pawl 23 in preventing spring 15 from urging jaws 13 into contact with the cable, and for this purpose its free end has a tooth with a surface 22a situated in one plane with the ratchet sector axis. 
     2.3. Engaging pawl 23 consists of a very elongated piece, which is pivoted at one end on partition plate 03, whereby its other end has a nose with a surface 23b, perpendicular to the longitudinal axis of the pawl, on which may rest the corresponding surface 22a placed on the end tooth of ratchet sector 22. 
     On the median portion of pawl 23 is transversely secured, on its side in proximity of partition plate 03, a butting plate 23e, which co-operates with a releasing cam disc 34 (disclosed hereafter)--in case the load speed would exceed the maximum speed pre-established--for releasing ratchet sector 22. 
     2.4. Engaging pawl spring 24 has a median portion wound up around a pin 24a fixed at partition plate 03, two straight portions urging the back side of pawl 23 so that its nose remains in front of the tooth of ratchet sector 22, and two end portions bent transversely to either side of pawl 23 in order to keep it exactly in the same plane of ratchet sector 22, thus preventing an accidental releasing of the latter. 
     3. The automatic releasing device 3 of the cable clamping and motor(s) stopping devices 1 5, respectively, (which is also perfectly sheltered in half-case Ob) is composed of 
     a driving disc 31, 
     a centrifugal inertia block 32, 
     a balance spring 33 of inertia block 32 and 
     a releasing cam disc 34. 
     3.1. The driving disc 31 is mounted at an end of the driving shaft 41a, which turns in a support 41b (preferably provided with a needle bearing) fixed on partition plate 03. At the periphery of this disc 31 is fixed a pin 32a on which centrifugal inertia block 32 may pivot (whereby the pivoting point is set near the back end of block 32), and, at a point almost diametrically opposed to pin 32a, a stud 33a transversely hole-bored on which rests balance spring 33 of inertia block 32. 
     3.2. Centrifugal inertia block 32 consists of several elongated plates, mutually superposed, and thus it is possible, by varying the number of these plates and simultaneously the compression rate of balance spring 33, to have the value of centrifugal speed changed in a wide range. These plates have a generally circular shape and their contour doesn&#39;t ever, at rest or by normal working, protrude beyond the contour of driving disc 31, so particularly not a nose 32b located approximately in the middle of the plates outer side. 
     Said plates are riveted together and are fixed to their pin 32a (located near their back end) e.g. through a circlips which can be set in the one or in the other of several transversal grooves of the pin. 
     3.3. The balance spring 33 of inertia block 32 is wound up on a pin 33b gliding in the transverse hole of stud 33a and being urged, by means of nuts 33c screwed at its free end, against the back end of the inertia block. 
     The force that nuts 33c exert on the back portion of inertia block 32 can thus be adjusted by more or less compressing balance spring 33 through nuts 33c in order to counterbalance the centrifugal force developed on the main (forward) portion of the inertia block, thus preventing nose 32b from projecting out the contour of driving disc 31 until the angular speed of the inertia block attains the value of the centrifugal speed as predetermined. 
     3.4. Releasing cam disc 34, which is located between partition plate 03 and driving disc 31, can pivot on a cylindrical extension 34a of the shell of the needle bearing 41b in which turns the driving shaft 41a rigidly supporting the driving disc 31. 
     Releasing disc 34 and driving disc 31 are therefore co-axial. 
     The releasing disc is provided, in the embodiment considered as an example, with six cams 34b as well as with six catches 34c disposed quite close to the contour of the driving disc (and corresponding each to one cam 34b). Then again, the position of the axis of releasing disc 34 is such that the (mutually coincident) trajectories of the ends of cams 34b are bound to be intersected by the salient edge of butting plate 23c of engaging pawl 23. 
     4. The driving gear 4 of automatic releasing device 3 is enclosed in the same half-case Oaas cable clamping device 1 and comprises 
     a driving member 41 in the form of a sprocket for actuating the driving disc 31; 
     a driving shaft 41a; 
     an idle cog-wheel 42 and 
     a shaft 42a of idle wheel 42. 
     4.1. Driving member 41 actuating the driving disc 31 is solid--for instance in the manner shown in FIG. 6 or else in another conventional manner--with the free end of the same driving shaft 41a with which is solid driving disc 31. This shaft 41a is pivotably connected with partition plate 03 by means of needle bearing 41b whose shell is fixed to the partition plate 03, so that a maximum rigidity is warranted. 
     4.2 &amp; 3. Idle cog-wheel 42 meshes, on one side, driving member 41 and, on the other side, a toothed rim which is integral with the peripheral portion of the driving pulley of winch-hoist A. L., and turns, also by means of a bearing, on a shaft 42a which is fixed to partition plate 03 in a known manner, for instance as shown in FIG. 8. On one threaded end of shaft 42a are screwed, respectively on the one and the other side of the partition plate, a nut with washer and a castle-nut. Thus it is possible, by screwing both nuts tight, to rigidly fix shaft 42a to the partition plate and so to ensure its parallelism relatively to driving shaft 41a. 
     5. The stopping device 5 of the motor(s) actuating the hoisting and/or pulling system, that is, in the example considered, electric motor(s)--though driving could as well be effected, as in the embodiment of the invention disclosed above, by any type of motors or by hand--consists of a circuit breaker 51, secured e.g. on the outside of the case, on front plate 02, and of a lever 52 for engaging circuit breaker 51. This engaging lever is transversally fixed to the free end of engaging shaft 21a, on which also are rigidly mounted the engaging levers 21 of self-tightening block 11 and the engaging pawl 23 of the same, and its end, during a normal working of the hoisting and/or pulling plant, exerts on the push button of the circuit breaker a pressure which hinders it from automatically breaking the electric circuit. The admission of the interruption of the current feeding the motor(s) depends then on a voluntary operation of the respective push-buttons of an electric control switch board or switch hand-box. 
     6. The manual releasing device 6 of cable clamping device 1--which is intended to ensure (for example if the working platform should come to a standstill at a certain hoisting height) a supplementary safety besides the one offered by the electro-magnetic brake of the brake-motor--consists, in the embodiment shown in FIGS. 6 to 10, of a releasing rod 61 with handle. 
     This releasing rod is guided by a bush 61a fixed to the frame 01 of the case and passes through a hole-bored stud 61b fixed to partition plate 03. As the end of said rod is normally kept close by engaging pawl 23, a short forward movement of rod 61 lets pawl 23 pivot (FIG. 7: anti-clockwise) against the thrust of pawl spring 24. Instead of releasing rod 61 might be employed a releasing handle rigidly mounted on the pivot pin 23a of engaging pawl 23, whereby pawl 23 is then itself solid with pivot pin 23a. 
     IIa--The working of this third, improved embodiment of the invention is substantially similar to the working of the second, improved embodiment of the same invention as previously disclosed: 
     1. The drawings (FIGS. 6 and 7) show the mechanism ready to work. Engaging pawl 23, controlled by pawl spring 24, co-opertes with engaging ratchet sector 22 and engaging levers 21 in preventing pretightening spring 15 from urging jaw actuating levers 14 to pivot in the direction in which jaws 13 are drawn closer together and clamp the cable. 
     2. The above equilibrium configuration remains unchanged as long as the hoisting and/or pulling plant works normally. The angular speed of driving disc 31 is then in fact lower, more or less, than the critical speed predetermined, and thus the forward position of inertia block 32, and in particular nose 32b, is held inside of the circumfernce of driving disc 31 by balance spring 33 (exerting a thrust on its back portion) and does not succeed to trigger off cable clamping device 1. 
     3. If the linear (down) speed of the load and the angular speed of the toothed rim of the driving pulley of winch-hoist A.L.--as well as the angular speed of driving disc 31 (FIG. 7: anti-clockwise), which is, in the present third embodiment of the invention, constantly proportional to the load speed--simultaneously exceed the respective critical values, the moment (relatively to pivoting pin 32a) of the centrifugal force acting on the forward portion of centrifugal inertia block 32 prevails over the moment of the force of balance spring 33 and projects said forward portion to the outside, so that the nose 32b on the outer side of the inertia block butts against the one or the other of the catches 34c which stand out of releasing cam disc 34. 
     One of the cams 34b of this disc then pushes back, against the action of pawl spring 24, the butting plate 23e of engaging pawl 23, and so the pawl itself, until the nose at the free end of the same disengages the surface 22a of the tooth of engaging ratchet sector 22. Thus pretightening spring 15 is in a condition to pivot jaw actuating levers 14 in the direction in which jaws 13 clamp the cable, and the friction force developing on the contact surfaces between jaws and cable rapidly increases up to the simulatneous, almost instantaneous stopping of cable clamping device 1 with the safety apparatus, of the winch-hoist (solid with the cable clamping device) and of the load hung thereon. This stopping coincides furthermore--in the case of a motor-driving--with the switching off of the motor(s). Jaw actuating levers 14, while pivoting (FIG. 6: upwards) under the action of pretightening spring 15, exert, in fact, a thrust on the engaging levers 21 of cable clamping device 1 and thus urge the engaging lever 52 of circuit breaker 51 (this lever being secured to the same engaging shaft 21a as engaging levers 21) in the direction in which said lever 52 is lifted from the push-button of the circuit breaker, thus allowing the current (or generally the fluid) to be automatically interrupted by the circuit breaker. 
     4. The automatic releasing device 3 of the cable clamping and motor(s) stopping devices 1 5, respectively can also be simply set by means of a setting device 7, consisting in the present embodiment of the invention of a setting lever 71 which is solid with the same engaging shaft 21a whereon is fixed the engaging lever 52 of circuit breaker 51. Said lever 71, while pivoting (FIG. 1: clockwise), produces in fact the following results: 
     (a) the engaging levers 21 of self-tightening block 11 (FIG. 6) also pivot clockwise (downwards) and, thus pivoting in the same direction jaw actuating levers 14, cause jaws 13 to move reciprocally apart; 
     (b) the free end of engaging lever 52 (FIG. 9) presses the push-button of circuit breaker 51 and closes the circuit; 
     (c) the engaging ratchet sector 22 (FIG. 7) pivots anti-clockwise and its cog, moving downwards, glides along a slanting surface 23d located at the free end of engaging pawl 23 and pushes this back, against the thrust of engaging spring 24, until the surface 22a of its cog gets on to a same plane with the corresponding surface of the nose of engaging pawl 23. This may then pivot, under the thrust of engaging spring 24, back to its initial position where it cogs ratchet sector 22 and consequently engages self-tightening block 11 through engaging levers 21, and circuit-breaker 51 through engaging lever 52. 
     The cable is thus free to pass through the apparatus and feeding may be controlled by means of the push-buttons of the switch-board or -handle. 
     It is obvious that the invention may not be limited to its embodiments as discovered and claimed, merely as examples, in the main U.S. Pat. No. 4,106,733 and in the present application for a patent of addition: various modifications of the devices described and claimed may be undertaken without passing the scope of the invention.