Abstract:
A device for suspending loads includes an adjusting device ( 1 ) to permit the position of loads to be adjusted for height and a structure ( 9, 11 ) of articulated bars which can be extended as a double pantograph. Connectors to the overlying structure and a connection to the suspended loads are provided. Combined horizontal ( 17 A,  1713; 17 C,  17 D) and vertical ( 28; 30 ) guides fixed to the connection means ( 12, 14 ). Corresponding pairs of terminal bars in the structure of articulated bars slide in the combined horizontal ( 17 A,  1713; 17 C,  17 D) and vertical ( 28; 30 ) guides.

Description:
FIELD OF THE INVENTION 
     This invention relates to a device for suspending loads from an overlying structure, such as a ceiling or the like, in particular for lighting equipment for theaters, photographic, cinema or television studios, studios in which the trafficked surface located below the suspended equipment is used by performers and supporting staff. 
     BACKGROUND OF THE INVENTION 
     The known devices, which comply with rigorous safety standards in order to prevent accidents, in particular arising from the fall of suspended loads (or a suspended load), comprise (see for example that described in Italian Utility Model application no. FI/93/U/109 lodged on the Jun. 10, 1993) a double pantograph structure and cable means to adjust the height of the load above the trafficked surface. Normally such pantograph structure terminates at the two ends in a corresponding pair of bars of appreciably shorter length in comparison with the other bars in the pantograph structure. For example the length of these terminal bars is less than one third that of the other bars, so that both the ends of such pantograph structure terminate in corresponding extension parallelograms which are appreciably reduced in size, the distal apex of which is pivoted to the overlying structure and the suspended load respectively. The apex opposite the distal apex of each of the terminal parallelograms can slide in, a corresponding vertical guide which is rigidly connected to both the overlying structure and the suspended load. In this way the system has limited rigidity in respect of transverse oscillations because of the play in the couplings between the bars in the terminal parallelograms in the vertical guides, play whose effect is amplified by the small size of the terminal bars. For these reasons known devices only permit the application of axial loads, e.g. a single lighting device whose center of gravity is vertically in line with the vertical axis of symmetry of the pantograph structure. To suspend several lighting devices as a whole without being concerned with this vertical alignment of the center of gravity of the whole, more complex and costly suspension devices (known as “hoists”) are instead used. 
     Furthermore, in known devices these pantograph structures are generally suspended below a lifting winch, which may be motor-driven, which pays out/reels in suspension cables. Because of the size of the winch this fact limits the amount by which the suspended load can be moved upwards. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The purpose of this invention is to avoid these disadvantages and in particular to provide a low cost device which will also suspend eccentric loads. The invention relates to a device comprising cable lifting means for adjusting the position of loads for height and an elongatable double pantograph structure; means for attaching the device to the overlying structure and means for attaching the device to the suspended loads are provided at the opposite ends of the double pantograph structure. According to the invention, in order to limit transverse oscillations of the suspended load the connection means incorporate corresponding combined horizontal and vertical guides within which there slide corresponding pairs of terminal upper and lower bars from the systems of articulated bars, the terminal bars having a length which is similar to or only slightly less than that of the other bars in the pantograph structure. In this way, because each of the bars in such pairs of terminal bars is attached to the attachment means by means of two spaced apart pins the double bar structure has good lateral rigidity, greater than that of known devices. The guides for the pairs of upper terminal bars can be located side by side and on opposite sides of the cable lifting means so that the dimensions of the means remain contained within the elongatable structure even when the load is completely lifted and the bars in each system lie alongside each other, permitting upward travel of the suspended load which is independent of the presence of the lifting means. 
     In a preferred form of construction the cable lifting means comprise a motor-driven winch and the connecting means to the overlying structure comprise an upper plate below which the winch is rigidly fixed. This plate has side wings which are folded back at right angles towards the base of the opposite sides of the winch, these wings incorporating slots forming the guides in which the pairs of upper terminal bars slide. 
     The attachment means to the overlying structure may comprise at least one carriage equipped with at least two pairs of wheels, the pairs being spaced apart in the direction in which the carriage travels; these carriages, at least one of which may be motor-driven, are located above the plate and act to guide the device with minimum transverse play on a rail attached to the overlying structure. In this way the device and the suspended load can easily be moved horizontally along that rail, the at least two pairs of wheels spaced apart or the presence of several carriages spaced apart providing transverse rigidity against oscillations in the vertical plane passing through the rail. 
     The upper plate together with the corresponding side wings define an enclosure in which an electrical unit controlling the motor/reduction gear, the unit regulating the useful travel of the suspended load, and an overload and cable breakage monitoring unit can also be installed in addition to the motor/reduction gear of the winch. 
     In a preferred embodiment the connecting means to the suspended load located at the proximal end of the pantograph structure to the suspended load comprise a lower plate parallel to the upper plate having opposing lateral wings extending upwards at right angles in which are provided slots forming the sliding guides for corresponding pairs of lower terminal bars of the two pantograph systems. A bar which extends vertically upward, at the top end of which a rocker lever is pivoted at an intermediate point thereof to the ends of which are connected the ends of the two lifting cables operated by the winch, is attached to the center of the lower plate, at the top. 
     In a preferred embodiment the pivoting bar for the rocking lever extends upwards as far as is possible compatible with the available height within the device when this has all been gathered upwards. Also, in the double pantograph structure of the device, corresponding intermediate articulations between the bars in each pantograph are preferably applied to the corresponding ends of one horizontal pin which extends from one pantograph to the other, and two cable openings guiding the lifting cables of the device are attached to at least one of the pins. Both the pronounced upward development of the vertical pivot bar, which increases the mass of the part of the device suspended below the point of attachment of the lifting cables, and the presence of the cable openings for the lifting cables, effectively help to oppose lateral deformations in the attitude (namely the angular inclination of the structure with respect to some reference) of the device, in particular those due to possible differences between friction in the articulations of the pantograph. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a diagrammatical side view of the whole of a device according to the invention with an applied suspended load, the load illustrated by an indicative line—in this case comprising a cross-member with two lighting units; 
     FIG. 2 is an enlarged side view of the device in FIG. 1 along II—II, 
     FIG. 3 is a partial cross sectional view of the upper part of the device taken along line III—III in FIG. 2; and 
     FIG. 4 is a partial perspective view of the device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in particular, the device for suspending loads from an overlying structure, such as a ceiling or the like, especially for lighting equipment for photographic or television studios, comprises a winch  1  (FIG. 1) to adjust the height of the position of lighting equipment  3 A,  3 B by means of two lifting cables  5 ,  7  and two systems  9 ,  11  of bars articulated to form a pantograph which extend from an upper horizontal plate  12  with vertical side wings  12 A,  12 B which are bent downwards to a lower horizontal plate  14  with side wings  14 A,  14 B which are bent upwards. Above upper plate  12  are fixed two carriages  16 ,  18  fitted with pairs of wheels  20  which are capable of moving with minimum play along a rail  22  fixed to a ceiling  23 . Lower plate  14  is suspended from cables  5 ,  7  of winch  1  by means of a rocker lever  24  which is pivoted at the center to a vertical bar  26  which is fixed to plate  14 , cables  5 ,  7  being fixed to corresponding opposite ends of rocker lever  24 . Lower plate  14  has fixing holes for the various systems for attachment to the suspended loads; for example in FIG. 1 a cross-member  28  to which lighting equipment  3 A,  3 B are fitted is fixed below plate  14 . 
     Intermediate bars  9 C,  9 D;  11 C,  11 D of pantograph systems  9 ,  11  define articulated parallelograms arranged with two opposite apices corresponding to an intermediate pin  13  for the bars in vertical alignment  5  and with two opposite vertices corresponding to corresponding lateral pins  15  in horizontal alignment. Pins  15  are common to the two pantograph systems and with the bars of systems  9 ,  11  form a vertically extendible cage. End bars  9 A,  913 ,  9 E,  917 ;  11 A,  11 B,  11 E,  11 F (see also FIG. 3) are articulated at one end to a pin  15  and at the other end (which is of a length slightly less than that of the intermediate bars) by means of a pin  17  which can slide in a corresponding horizontal slot  17 A,  1713 ;  17 C,  17 D. These slots are provided respectively in wings  12 A,  1213 ;  14 A,  14 B of upper and lower plates  12 ;  14 . Corresponding vertical slots  28 ;  30  within which corresponding pins  32  each fixed to a pair of outer bars  9 A,  913 ;  11 A,  11 B;  9 E,  9 F;  11 E,  11 F of pantograph systems  9 ,  11  can slide are provided in wings  12 A,  1213 ;  14 A,  14 B of upper plate  12  and lower plate  14  corresponding to the vertical sagittal plane of travel X—X of the device. In this way when the position of the suspended load is at any height each end bar is secured in the horizontal direction by pin  32  in vertical slot  28 ,  30  and in the vertical direction by pin  17  in corresponding horizontal slot  17 A,  1713 ;  17 C,  17 D. Given the dimensions of the end bars, these points of attachment are spaced well apart and the rigidity of the device is not substantially influenced by the play with which the pins  17 ,  32  engage the corresponding slots. This configuration enables the device to support loads whose overall center of gravity is located outside the sagittal plane of travel X—X. 
     Winch  1  (see FIGS. 2 and 3) comprises an electric motor  1 A and a motor/reduction gear  1  B located under upper plate  12 . Output shaft  34  of axis Y—Y from motor/reduction gear  16  extends from both sides of the motor/reduction gear. Corresponding pulleys  36 ,  38 , each of which comprises a pair of disks side by side between which one of lifting cables  5 ,  7  is wound into a spiral are keyed to shaft  34  on sides opposite the motor/reduction gear. The length of each cable  5 ,  7  leaving pulley  36 ,  38  is diverted by a corresponding first deviating idler pulley,  40 ,  42  turning on a shaft  45  and provided with a peripheral groove for the cable. Shaft  45  is supported by two plates  47 ,  49  located at the sides of the motor/reduction gear and fixed to wings  12 A,  12 B of plate  12 . Each cable  5 ,  7  then passes into the throat of a second deviating idler pulley  44 ,  46  and partly wraps round it. These second pulleys  44 ,  46  are mounted on corresponding shafts  44 A,  46 A which are also supported by plates  47 ,  49 ; the support for shafts  44 A,  46 A which is proximal to corresponding pulley  44 ,  46  is formed of a slot  47 A,  49 A made in corresponding plates  47 ,  49 , this slot being orientated along a line bisecting the angle of deviation of the corresponding cable around pulley  44 ,  46 . A corresponding spring  51 ,  53  transversely presses corresponding shaft  44 A,  46 A towards the vertex of the diversion angle to operate a corresponding monitoring microswitch  55 ,  57  when cable  5 ,  7  breaks or slackens, in order to operate an alarm device. Slot  47 A supporting shaft  44 A is also extended on the other side with respect to the shaft, a shaft which is normally supported on the head  59  of a pin  61  and is stressed by a compression spring  63 . This spring  63  is located between head  59  and a stirrup  65  fixed to plate  47  and preloaded by means of a nut  62  applied to the threaded terminal part of pin  61 . In this way, when the load applied to the suspension device exceeds a predetermined limit shaft  44 A slides in slot  47 A overcoming the action of the compression spring  63  and operates another monitoring microswitch  67  which activates an alarm device. 
     A device  69 , which is in itself known, is fitted to an extension of shaft  34  to limit the possible downward and upward travel of the suspended load. The device comprises a threaded shaft  71  which is coaxial with shaft  34  and is coupled to rotate together with it, an assembly  73  fitted with a threaded hole coupled to threaded shaft  71  to move along it as the shaft rotates and to bring about automatic interruption of the winch drive through end-of-travel microswitches  74 ,  75  when the predetermined travel limit for the load are reached. In particular the lower travel limit can be adjusted by moving microswitch  73  axially into a suitable position by means of a screw adjustment along shaft  77  parallel to shaft  71 . 
     In an improved embodiment, for the reasons described above pivot bar  126  (FIG. 4) for rocker lever  24  extends as far as possible upwards compatible with the height available within the device when this is completely gathered upwards. In addition to this, the corresponding intermediate articulations  128  of the bars in each pantograph in the double pantograph structure of the device are preferably attached to the corresponding ends of the same horizontal pin  130  which extends from one pantograph to the other, and two wire openings  132  guiding lifting cables  5 ,  7  of the device are fitted to at least some of the pins  130 . 
     While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.