Abstract:
The invention concerns a load balancing device consisting of a planetary or trochoidal mechanical differential speed reducer, arranged on a winch comprising two drums and enabling to balance the torque exerted on the drums. Thus, if a cable is improperly wound on one of th drums, the balancing device enables the tensile load exerted on each wire to remain identical. Such a device is particularly efficient to ensure security for a working platform operating on a building facade.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns a balancing device for traction forces, specifically intended for a hoist, that is supposed to simultaneously wind or unwind two or more traction cables, as well as a hoist fitted with such a device and a gondola equipped with at least one hoist as hereinabove. 
     Such hoists, particularly those comprising a twin winding organ, traction drums or traction sheaves where each of said organs carries its own cable, find numerous applications. Particularly in certain configurations they are employed for lifts or more specifically for gondolas engaged in the cleaning and/or upkeep of the facades of high-rise buildings. Such a gondola usually is held by four cables, a first pair of cables being arranged at a first short side of the gondola and the second pair of cables being arranged at the second short side of the gondola. Each pair of cables is wound/unwound from a hoist equipped with two drums, with each hoist having its own motor that is controlled independently of the other motor. Thus, the speed of winding/unwinding of each hoist is so adjusted by known mechanical, electric, or electronic means that each pair of cables is unwound or wound with the same speed and the gondola will remain horizontal. For the two cables of a given pair, to the contrary, since their winding or unwinding speed is controlled by a single hoist or by just one motor, said means cannot be employed to preserve their balance. An unbalance between the two cables of a pair may arise, for instance, when the winding of one of the cables on its drum is irregular and causes subsequent windings to be wound with a larger diameter than that of the windings of the other cable. In this case the cable being wound up on a larger diameter will tend to assume the full traction force, which may lead to 
     an unbalance of the gondola or, by rupture of this overly loaded cable, to risk for the workers riding this gondola. 
     A first mechanical means that allows an identical tensile stress to be preserved for the two cables of a given pair, even in a situation where one of the cables is poorly wound, consists of bringing the two cables together on one sheave. Such a device may be dangerous in the instance of rupture of one of the cables, since the other cable then becomes free, and the gondola is no longer held by either of the two cables. 
     According to other means, the two cables are attached to the two ends of a spreader while the center of this spreader is hinged to the suspension beam or to the gondola. This device will not encounter the drawback mentioned earlier, but now the difference in lengths that can be admitted between the two cables is limited by the length of the spreader. 
     In the two means described above, the balancing device—sheave spider or center of the spreader—is attached to the gondola or suspension beam in a single point, which in the final analysis is detrimental to the gondola&#39;s balance. FR-A-2 183 594 describes a device with differential for a crane lifting hoist. Using this device the operator controls sequentially rather than simultaneously a lifting operation and a mast telescoping operation. There is no indication anywhere in this document that the device permits a simultaneous actuation of both drums. 
     WO 88/05999 describes a differential device allowing the forces on two traction cables of a trawl to be balanced. This document explicitly describes that the operations of launching of the trawl as well as those of hauling it in do not involve the use of the differential device, which is put in operation, only during the fishing, that is, when the hoists are inactive. 
     SUMMARY OF THE INVENTION 
     The invention provides a force balancing device for a hoist intended for at least one pair of traction cables that will allow the drawbacks mentioned earlier to be avoided. 
     It is an objective of the invention to propose a hoist that is intended for at least one pair of traction cables and is fitted with at least one force balancing device that is capable of ensuring at all times the safety of the object suspended on the cables. 
     It is yet another objective of the invention to propose a gondola for facade upkeep that is fitted with at least one hoist equipped with a force balancing device. 
     These objectives are attained by a balancing device, a hoist, and a gondola having the characteristics mentioned in the independent claims, while specific embodiments or variants are described in the dependent claims. 
     The below description describes several embodiments of a device according to the invention, and should be read in conjunction with the attached drawing comprising the figures where 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevation of part of an installation for facade cleaning, 
     FIG. 2 is an end view of part of the installation of the preceding figure, 
     FIG. 3 is a view in longitudinal section of a first embodiment of a balancing device according to the invention, 
     FIG. 4 is a partly sectioned front view of the device of the preceding figure, 
     FIG. 5 is a view in longitudinal section of a second embodiment of a balancing device according to the invention, 
     FIG. 6 is a partly sectioned front view of the device of the preceding figure, and 
     FIG. 7 is a schematic representation of the operation of part of the device of FIGS.  5  and  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 and 2, one has a building  1  with a vertical facade  10  and a roof  11 , here represented as being a flat roof. Building  1  is equipped with an installation  2  for cleaning/upkeep of the facade  10  comprising a gondola  20  suspended from a first pair of cables  21  and a second pair of cables  22 , with two support beams  23  and  24  fixed on a frame  25  that preferably can move on the roof  11  so that the gondola  20  will be able to reach all of the facade  10 . 
     The gondola  20  that is shown here comprises more particularly two end faces  20 A and  20 B each carrying a hoist  3  allowing the gondola  20  to be raised or lowered along the facade  10 . The first hoist  3  comprises more particularly a first motor  30 , preferably an electric motor, a first reduction gear  31 , as well as two drums  32  and  33  mounted coaxially at the wall  20 A, while the second hoist comprises a second motor  34 , a second reduction gear  35 , and two further drums  36  and  37  mounted coaxially at the wall  20 B. The two drums  32  and  33  of the first hoist each take one cable  210  or  211 , respectively, of the first pair of cables  21  while the two drums  36  and  37  each take one cable  220  or  221 , respectively, of the second pair of cables  22 . The free ends of cables  210  and  211  of the first pair  21  are attached to the beam  23 , preferably detachably, while the free ends of cables  220  and  221  are attached in like manner to the beam  24 . 
     A control unit  38  supplies and controls each of the motors  30  and  34 . 
     Optionally and depending on the configuration that is selected for the drums, the gondola may also comprise two additional units shown schematically at  39  which are suitable for performing one of more of the following functions: changeover of the cables  210 ,  211  and  220 ,  221  distributed along an axis parallel to the axis of rotation of the drums, as shown in FIG. 1 in the space between the drums and the units  39 , to a configuration where each cable pair is arranged within a plane perpendicular to the above mentioned axis, as shown in FIG. 2, or, in another embodiment of the gondola that is not represented in the figures, to a plane parallel to said axis, in the section situated between the unit  39  and the beam  24 , level winding of each cable on its drum, and safety brake blocking the cable or cables when a cable rupture is detected. These different means are known in the art and will hence not be described in more detail here. 
     An irregular winding of one or several of the above cables on one or several of the drums mentioned may lead to an unbalance in the load distribution between the cables  210  and  211  or  220  and  221 , or to an unbalance of the gondola  20  that corresponds to an angular slippage about the longitudinal axis of roll R or an angular slippage about the transverse axis of pitch T, or to a combination of these two slippages. 
     In the embodiment represented, slippage about the axis T when present can be compensated by acting on the relative speeds of the two motors  30  and  34 , either by an organ for automatic detection of said slippage or manually via the control unit  38 . 
     Since the two drums  32  and  33  of the first hoist or the two drums  36  and  37  of the second hoist are controlled by a single motor  30  or  34 , respectively, it is not possible to compensate slippage about the axis R by the means just mentioned. 
     It is proposed to this effect according to the invention to instal a mechanical balancing device between the two drums,  32  and  33  or  36  and  37 , respectively, of each hoist. 
     According to a first embodiment, the balancing device consists of a mechanical differential reduction gear with three axles, as for instance the planetary gears  4  as shown in FIGS. 3 and 4. The device  4  comprises an input shaft  40  that is driven directly by the motor  30  or  34  or by the reduction gear  31  or  35 , as needed. A sun gear  41  is solidly mounted on the shaft  40 . One or several planet gears  42  engage, on one hand with the sun gear  41  and on the other hand with an external race  43  with internal teeth. The race  43  carries the drum  32  or  36  that is part of a lifting mechanism. Each of the planet gears  42  is pivoted on an axle  420 , while said axles are fastened to a flange  44  that freely pivots about the end of shaft  40 . Flange  44  carries the drum  33  or  37 . 
     Looking at FIG.  4  and assuming that the shaft  40  or sun gear  41  turns clockwise, while blocking the drum  32  or  36  or the race  43 , respectively, one can see that the flange  44  that carries the drum  33  or  37  also turns clockwise. If to the contrary one blocks the drum  33  or  37  or the flange  44 , respectively, one can see that the drum  32  or  36  turns counterclockwise while the shaft  40  turns clockwise. Thus, in order to obtain a simultaneous ascending or descending motion of the gondola according to the direction of rotation of the shaft, it will be necessary that the two cables of one pair be wound up in opposite directions onto the two drums, as seen in FIG.  4 . 
     The balancing device  4  for the traction forces functions as follows, in the situation where the two cables of one pair exert the same traction force on the two drums or identical torques are exerted, respectively, the two drums are rotated in opposite directions when the shaft  40  is rotated, and thus cause the gondola to ascend or descend, depending on the direction of rotation of shaft  40 . In a situation where one of the cables is wound up with a diameter that is different from that of the other cable, which causes the force exerted on one of the cables to be more important than that exerted on the other cable, then the drum holding the more highly taut cable will block and cause the motion performed by the other drum to continue until the difference in forces is made up and the forces exerted on the two cables are once more essentially identical. 
     One thus has a differential balancing device between the two drums which acts so that, when one cable is more highly taut than the other, the torque created on the drum by this taut cable causes the race or flange adjacent to this drum to become a fixed point of the device, thus allowing the other element, flange or race, as well as the adjacent drum to make up this difference in tension, no matter whether the drive shaft is driven or not. Through this device the two cables of a pair of cables are thus always subject to essentially identical traction forces, even if the speeds of rotation of the two drums are not identical. 
     Design versions of this device that differ from the one just described can be envisaged. For instance, the size ratios of the different gear wheels that are present may be different from what has been described or represented, just like known design variations of triaxial planet reduction gears, for instance, a number of planetary gears that is different from the number shown here, or another way of meshing of the gear wheels. 
     A second embodiment of a balancing device according to the invention is represented in FIGS. 5 and 6. This device, which is again a mechanical differential reduction gear with three axles, essentially corresponds to a trochoidal (cycloidal) reduction gear such as that known by the name of “Cyclo” (registered trade mark), a specific embodiment of which is described in EP 0 291 052. 
     This device  5  comprises an input shaft  50  that, like the shaft  40  of the preceding device, comes directly from the drive motor or from an intermediate reduction gear. The shaft  50  comprises an eccentric cyclindrical bearing surface  51  that is fixed on the shaft. The eccentric bearing surface causes eccentric rotation of a toothed wheel  52  that has a central cylindrical bore  520 , or equivalent means for rotation mounted on the eccentric bearing surface  51 , external teeth  521  of which a specific embodiment will be described in greater detail below, as well as a plurality of circular bores  522  regularly spaced along a diameter that is coaxial to the central bore  520  and to the teeth  521 . The device  5  additionally comprises an external race  53  with internal teeth  530  of which a specific embodiment will also be described below, and which in part engages with the teeth  521  of the wheel  52 . A flange  54  is freely pivoted on the shaft  50  and supports a plurality of protruding rods  540 , each of them corresponding to a bore  522  of the wheel  52 . It can be seen in the figure that the bores  522  have a larger diameter than the rods  540 ; this device of bores and rods actually serves to transpose the eccentric rotary motion of the wheel  52  to a concentric rotary motion of the flange  54  about the shaft  50 . To this effect the diameter of a bore  522  is equal to the diameter of a rod  540  plus the amount of eccentricity of the wheel  52 . One may have one or more sets of bores and rods for the transmission of this motion, and it is also feasible that one or several bores are arranged on the flange  54  while the corresponding rod or rods are attached to the wheel  52 . The external race carries the drum  32  or  36  which holds the cable  210  or  220 , respectively, while the flange  54  carries the drum  33  or  37  which holds the cable  211  or  221 , respectively. 
     FIG. 7 shows a preferred embodiment of part of the device just described, showing the engagement of wheel  52  in the race  53 . The race  53  has a plurality of semicylindrical bearings  531  each holding a roller  532  freely turning in said bearing  531 . In the example represented, the race  53  comprises twenty bearings  531  and as many rollers  532 . The eccentric wheel  32  has a plurality of semicylindrical bearings  523  on its periphery, the number of said cylindrical bearings here being one less than that of the rollers  532 . One will thus understand that, when the race  53  is blocked, one has one revolution of the eccentric wheel  52  for any nineteen revolutions of the shaft  50 , or one revolution of the flange  54  or of the drum  33  or  37  supported by this flange, for one revolution of the shaft  50 . When blocking the flange  54  or the drum  33  or  37 , or the wheel  52 , respectively, to the contrary, one has twenty revolutions of the race  53  or of the drum  32  or  36  supported by this race, respectively, for one revolution of the shaft  50 . 
     It is an advantage of a differential trochoidal balancing device according to this second embodiment described, over the planetary device according to the first embodiment described, that the ratio of speeds of the drums to the speed of the drive shaft is distinctly larger, so that it becomes possible with a trochoidal balancing device according to this second embodiment to omit placing a speed reduction gear  31  or  35  between the motor and the input shaft  50  of the balancing device. 
     Different design variants of a differential trochoidal balancing device can be envisaged; for instance, one can have a difference between the number of rollers  532  and the number of bearings  523  on the wheel  52  that is larger than one, for instance two or three. Likewise, the external teeth  521  of the wheel  52  and the internal teeth  530  of the race  53  may differ from those described here, that is, one may have conventional teeth  521  and  530  where one or several teeth are engaged simultaneously. The differential trochoidal balancing device may also be designed like that described in the document EP 0,291,052, that is, comprising several wheels  52  in parallel, and eccentrically offset so as to distribute the forces in a softer and more regular way. 
     Other types of reduction gear can also be provided to function as a balancing device. For instance, a reduction gear of the registered trade mark Harmonic Drive, or more generally a differential mechanical reduction gear of the kind found in a car could very well perform the desired function of balancing the traction forces. Generally, any differential mechanical reduction gear mounted between the two drums could be used as a balancing means. Preferably, so as to have a compact device, a triaxial reduction gear will be used. 
     A balancing device according to one or the other of the embodiments envisaged can be made more complete by adding a disconnecting means, for instance a latch which will allow facile unwinding of the cables from their drums when the gondola is at ground, on order to attach them to the suspension beams. 
     A balancing device according to one or the other of the embodiments envisaged can also be employed in a hoist fitted with two traction sheaves, rather than two drums; preferably, the traction sheaves will then be fitted with known means helping to make the cable adhere to a segment of the sheave&#39;s periphery. 
     The gondola described above, and shown in the figures, is conceived with the four cables, each fastened at one corner of the gondola, but other configurations for attachment of the cables can also be envisaged, for instance with the four cables aligned in a plane holding the longitudinal axis of the gondola. 
     Also, the gondola has been described with the hoists  3  mounted on board; but one could just as well have an installation where the two hoists  3  are arranged outside of the gondola, for instance on the structure  25  supporting the beams  23  and  24  or directly on these beams. In this embodiment one could even have a single hoist driven by just one motor, with the axle of the motor holding two sets of drums and each set of drums comprising a balancing device according to one or other of the embodiments described. Thus, a single hoist or a single motor shaft may very generally comprise several pairs of drums and/or traction wheels, each pair with its own balancing device. 
     The balancing device according to one or other of the embodiments described, like the hoist having such a balancing device, have been described and represented as employed with a gondola for the upkeep of a facade of a building; but both the balancing device and the hoist can be employed in many other applications.