Abstract:
The rotation of a first element ( 3 ), for example an arm carrying a lighting unit, with respect to a second element ( 2 ), about an axis ( 12 ), is limited in both directions, with an angular travel which can exceed  360 ° , by an elastic element ( 13 ) comprising two coils wound in the same direction, each cooperating with a mobile stop piece integral in rotation with the first element ( 14, 15 ), the central part of the spring ( 13 ) cooperating with a fixed stop piece ( 16 ) integral with the second element ( 2 )

Description:
FIELD OF THE INVENTION 
     The present invention relates to stop pieces for limiting angular travel about an axis of a first element with respect to a second element. 
     Many articulated systems use such elements which are movable in rotation with respect to one another. 
     For matters relating to the occupation of the surrounding space or the transmission of power, data or fluids, the angular travel between these elements must be limited, in both directions of rotation, by stop pieces. 
     BACKGROUND OF THE INVENTION 
     Conventionally, these stop pieces are rigid, which results, depending on the masses and speeds of displacement of the elements, in sudden stops against stop pieces, which generate vibrations and are very often noisy. 
     Furthermore, the repeated shocks and the inertias brought into play rapidly bring the safety of the system into question. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to propose a flexible stop piece providing limitation of angular travel without shocks between two elements and a progressive braking of the movement of relative rotation between these two elements, whilst eliminating the abovementioned disadvantages of fixed stop pieces. 
     In order to achieve this, according to one aspect of the invention, the first element comprises an inner part extending coaxially with respect to the axis of rotation in a sleeve part of the second element, the stop piece furthermore comprising an elastic element with two helical coils both wound in the same direction and one on each side of a central connecting zone, disposed concentrically between the inner part and the sleeve part, each coil being terminated with an end part, the sleeve part comprising a first stop zone capable of coming to bear against the central zone of the spring, the inner part comprising at least a second and a third stop zone, each capable of coming to bear against a corresponding end part of the elastic element. 
     According to other more particular characteristics of the invention: 
     the second and third stop zones are offset angularly; 
     each coil is disposed around the inner part such that it is normally slack; 
     the end parts extend axially and/or radially. 
     The present invention also relates to an articulated system comprising at least one such flexible stop piece and typically at least one flexible pipe or conductor extending inside the first and second elements. 
     The present invention also relates to a medical equipment item comprising at least one such articulated system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the present invention will emerge from the following description of particular embodiments, given by way of illustration but in no way limitative and given with reference to the accompanying drawings in which: 
     FIG. 1 is a longitudinal cross section of an articulation arrangement with a flexible stop piece according to the invention; 
     FIGS. 2 and 3 respectively are top and front views of the spring of the arrangement shown in FIG. 1; 
     FIG. 4 is a diagrammatic view of a ceiling lighting unit incorporating a flexible stop piece according to the invention; and 
     FIG. 5 is a diagrammatic view in perspective and in partial cross section of another embodiment of an articulated assembly with a flexible stop piece according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1, snows an example of an articulation subassembly  1 , incorporating a flexible stop piece according to the invention, between a first element  2  and a second element  3 . 
     In the example of application shown in FIG. 4, the articulation subassembly with a flexible stop piece  1  is disposed between the base of an operational lighting  4  support arm  3  and an element  2 . The support arm  3  is mobile in rotation with respect to the element  2 , which is itself mounted in an articulated manner at the end of an arm  5  attached to a ceiling mount  6  which advantageously supports at least a second arm  7 . 
     Returning to FIG. 1, the base of the arm  3  is fixed to a head  9  which is attached to a swivelling tubular element  8  by means of bearings  9   a ,  9   b , in a sleeve  10  which is integral with the element  2 . 
     According to one aspect of the invention, at least one cable  11  for carrying electrical current and/or for the transmission of digital, electrical or optical data, and/or at least one pipe for the transfer of medical fluid (oxygen, vacuum, etc.) runs in the arm  3 , the tubular element  8 , and beyond the latter, in the element  2 . 
     The tubular element  8  and the sleeve  10  are coaxial with the axis  12 . The rotation of the arm  3 , about the axis  12  with respect to the element  2  is limited in a controlled manner by an elastic element with coils  13  cooperating selectively, as will be seen below, with stop pieces  14  and  15 , carried by the tubular element  8 , and  16 , carried by the stationary sleeve  10 . 
     As can be seen more clearly in FIGS. 2 and 3, the elastic element  13  is typically made from steel spring wire and comprises two zones  17   a ,  17   b  coiled in the same direction connected by an intermediate connecting branch  18  extending in a plane which is tangential to the cylinder formed by the coiled zones  17   a ,  17   b.    
     In the embodiment shown in FIGS. 1 to  4 , each coiled zone forms a complete turn extended by a half-turn and is terminated at an axial end  19   a ,  19   b , the axial ends  19   a ,  19   b  being substantially aligned with one another and diametrically opposed to the connecting branch  18 . 
     Referring again to FIG. 1, the elastic element  13  is slipped loosely over the tubular element  8  between the latter and the sleeve  10 , whilst being trapped by a pin forming a stop piece  16  mounted in the sleeve  10  and extending radially inwards between the two coils  17   a ,  17   b  in such a way as to cooperate selectively by lateral abutment with the intermediate branch  18  of the elastic element  13 . 
     Similarly, two stop pieces  14  and  15  are mounted inside the tubular element  8  and extend radially outwards from the latter in order to cooperate selectively in lateral abutment with the axial ends  19   a  and  19   b  of the elastic member. 
     In this way, when the arm  3  rotates about the axis  12 , with respect to the element  2 , it causes the end of one of the coiled zones of the elastic element  13  to rotate, by means of the pin  14  if the rotation is in the clockwise direction or by means of the pin  15  if the rotation is in the anticlockwise direction. 
     When the amount of rotation becomes large, the central branch  18  of the elastic element  13  comes to bear against the stationary pin  16 . From this moment on, the rotation of the tubular element  8  will begin to stress the elastic element, which will create an opposing torque progressively braking the movement of the arm until it is stopped completely. 
     The restitution of the energy stored in the elastic element  13  then brings the arm  3  backwards. The damping of the flexible stop piece can be adjusted by adjusting the stiffness of the elastic member  13 . 
     As will be understood from the above, depending on the direction of rotation of the arm  3  and of the tubular element  8 , only one coiled zone  17   a  or  17   b  of the elastic element  13  is stressed, the other coiled zone remaining unstressed. 
     The stressed coil is forced in the direction of the coiling and therefore in the direction of tightening the turns around the tubular element  8 . Total damping is therefore achieved when all of the turns of this coil are tightened on the tubular element  8 , thus eliminating any risk of exceeding the permissible stresses in the elastic element  13 . 
     According to one aspect of the invention, as shown in FIG. 1, the pins  14  and  15  are angularly offset, typically by 90 degrees. 
     This offset makes it possible to fix the total angular travel of the arm. The offset pins arrangement according to the invention makes it possible to obtain angular travels greater than 360 degrees, which is generally impossible with the conventional systems with simple fixed stop pieces. 
     In the simplified embodiment shown in FIG. 5, the coiled zones  17   a  and  17   b  of the elastic element  13  are limited to one turn and the stop zones integral with the inner tubular element  8  are in this case constituted by radial faces of angular openings  140 ,  150  formed in the tubular element  8  and into which the free ends,  19   a  and  19   b  penetrate, in this case folded back radially towards the inside of the elastic element  13 . The angular offset sought between the stop zones is provided by an angular offset of the openings  140  and  150  and/or by the angular extension of the latter. The stop zone with the outer tubular element  10  is in this case constituted, as before, by a pin  16  extending radially inwards and fitted in a radial hole formed in the element  10 . 
     Although the invention has been described with respect to a particular embodiment, it is not limited thereby but, on the contrary, is subject to modifications and variants which will be apparent to those skilled in the art in the context of the following Claims. 
     In particular, although one of its preferred applications is in suspended systems carrying medical equipment such as the lighting units mentioned above, operational microscopes, dispensing arms and mobile radiographic equipment, it can also be applied in other industrial fields for the general public, such as, for example, rotational heads for cameras or supports for rotating fans.