Abstract:
A cable actuator comprising a chassis ( 1 ), a screw ( 2 ) mounted rotatably on the chassis and driven by an electric motor, a nut ( 4 ) engaging with the screw and associated with anti-rotation means such that a rotation of the screw, under the action of the motor, results in an axial movement of the nut, and two substantially parallel cables ( 10 ) coupled to the nut on either side of same. The cables are linked to an anchoring member ( 20; 30; 40 ) that is interposed between the nut and the cables, the anchoring member being secured to the nut while also being movable relative to same.

Description:
[0001]    The invention relates to a cable actuator comprising a screw/nut assembly, the nut of which is mobile in translation, and is coupled to a pair of cables. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cable actuators are known comprising a screw/nut assembly, the screw of which is rotated by an electric motor, and the nut of which is mobile in translation. The mobile element is coupled to one or more cables, in order to exert traction on the cables. 
         [0003]    A cable actuator of this type is known from document FR2809464, wherein the element in translation is the screw, whereas the nut is mobile in translation under the action of a motor. The cable passes into a bore in the screw, and is coupled by means of a tolerant fastener to the misalignments of the cable. 
         [0004]    In certain applications, in particular in robotic applications, the size of the actuator is highly critical, and it is important to ensure that this size is as small as possible. 
         [0005]    Cable actuators are known comprising a screw which is fitted such as to rotate, and is driven by an electric motor, with a nut cooperating with the screw and being associated with anti-rotation means, such that rotation of the screw under the action of the motor gives rise to axial displacement of the nut, and two parallel cables which are coupled to the nut on both sides of it. 
         [0006]    For the same course, this device makes it possible to reduce the size of the cable actuator. In fact, in the known cable actuators, in which the cable(s) is/are coupled to the screw which is displaced, the screw is designed to extend from both sides of the actuator. Thus, the general size would be at least 2C+L, where C is the course of the actuator, and L is the size of the nut. In the actuator according to the invention, this minimum size is now only C+L. 
       OBJECT OF THE INVENTION 
       [0007]    The object of the invention is to propose a cable actuator of the aforementioned type, which is tolerant to the various displacements and deformations which can interfere with its operation. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to achieve this objective, according to the invention a cable actuator is proposed comprising a screw which is fitted such as to rotate and is driven by an electric motor, with a nut cooperating with the screw and being associated with anti-rotation means, such that rotation of the screw under the action of the motor gives rise to axial displacement of the nut, and two parallel cables which are coupled to the nut on both sides of it, wherein, according to the invention, the cables are connected to an anchorage unit which is interposed between the cables and the nut, the anchorage unit being coupled to the nut, so as to permit relative movement between the nut and the anchorage unit. Thus, any misalignments of the cables are absorbed by movement of the anchorage unit, without subjecting the nut to stress. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be better understood by reading the following description of various embodiments of it, provided with reference to the figures of the accompanying drawings, among which: 
           [0010]      FIG. 1  is a partial view in perspective of a cable actuator according to a particular embodiment of the invention; 
           [0011]      FIGS. 2A and 2B  are operating diagrams of the cable actuator in  FIG. 1 , the nut being shown in the two end axial positions; 
           [0012]      FIG. 3  is a partial view in perspective of an actuator according to a particular embodiment, the nut of which is equipped with a pivoting anchorage unit; 
           [0013]      FIGS. 4A and 4B  are lateral views according to two perpendicular orientations, illustrating an actuator with an anchorage unit according to another particular embodiment, illustrating two situations of misalignment of the cables; 
           [0014]      FIGS. 5A and 5B  are lateral views according to two perpendicular orientations, illustrating an actuator with an anchorage unit according to another particular embodiment, illustrating two situations of misalignment of the cables; 
           [0015]      FIG. 6  is a schematic representation in perspective of another particular embodiment of a cable actuator according to the invention; 
           [0016]      FIG. 7  is a detailed view in perspective of a detail of the embodiment in  FIG. 6 ; 
           [0017]      FIG. 8  is a schematic representation in perspective of another particular embodiment of a cable actuator according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    With reference to  FIG. 1 , the cable actuator according to the invention comprises a chassis  1  on which a screw  2  is fitted so as to turn according to an axis X, whilst being rotated, in this case by an electric motor  3 . A nut  4  cooperates with the screw  2 , and is associated with an anti-rotation device  5  comprising two arms  6  which extend on both sides of the nut  4 , in order to support rollers  7  (only one can be seen in this case), which are fitted so as to turn according to an axis Y at right-angles to the axis X. The rollers  7  are engaged in longitudinal slots  8  which are provided in the chassis, and extend parallel to the axis X. The axis Y passes substantially into the center of the nut  4 . Thus, the nut is displaced axially under the effect of the rotation of the screw, without turning around the axis X. However, angular deviations are permitted around the axis Y, but also around an axis Z which is at right-angles to the axes X and Y. 
         [0019]    The nut  4  comprises means  9  for coupling of two cables  10   a,    10   b  which extend on both sides of the nut  4 , parallel to the axis X. In this case, the coupling means comprise two double flanges (only one can be seen in this case) which extend on both sides of the nut  4 . 
         [0020]    As illustrated in  FIGS. 2A and 2B , the cables  10   a  and  10   b  are each wound around a pulley  11 , the two pulleys  11  being integral with the same shaft  12  which is fitted such as to rotate according to an axis parallel to the axis Z. The shaft  12  is thus rotated once traction is exerted on the cables by displacement of the nut  4 . In a manner known per se, the cables  10   a  and  10   b  are kept taut, for example by placing the cables in a loop between two pulleys (as in document FR2809464), or, if only a one-way action is required, by means of a tension spring. 
         [0021]    Various causes can introduce disturbances which give rise to dissymmetry in the traction of the two cables  10 . In particular, the shaft  12  may not turn around an axis which is perfectly parallel to the axis Z, and can be subjected to axial or transverse offsettings. Similarly, it is known that if a ball screw or roller screw is used, the nut is liable to oscillate around a transverse axis, which is or is not included on the plane defined by the pair of cables (in particular, if the actuator is equipped with an anti-rotation device, such as the one shown in  FIG. 1 , the nut will oscillate around the axis Y), which will naturally induce dissymmetries in the traction of the cables  10   a,    10   b.    
         [0022]    In order to absorb these disturbances, and according to the invention, the nut  4  is equipped with an anchorage unit to which the cables are coupled directly, the anchorage unit being integral with the nut whilst being mobile relative to the latter, in order to absorb these disturbances, and ensure homogeneous traction of the two cables. 
         [0023]    According to a particular embodiment illustrated in  FIG. 3 , in this case the anchorage unit comprises a frame  20  which is fitted so as to pivot on the nut  4  according to the axis Y. The frame  20  comprises pivots  21  which are fitted so as to pivot on the frame around the axis Z (when the frame is straight as shown here). The cables  10   a  and  10   b  are coupled directly to the pivots  21 . Thus, the nut is free to oscillate around the axis Y without however giving rise to imbalance in the traction of the cables  10   a,    10   b.    
         [0024]    As a variant, it would be possible to couple the cables directly on the frame  20 , with the natural flexibility of the cables absorbing any rotation around the axis Z. 
         [0025]    According to another particular embodiment illustrated in  FIGS. 4A and 4B , the nut is once more associated with a frame  30  to which the cables  10   a  and  10   b  are coupled. However, the frame  30  is no longer fitted so as to pivot on the nut  4 , but is suspended on the nut by means of two rigid connecting rods  31  with ball ends. The connecting rods  31  extend on both sides of the nut  4 , the connecting rods preferably being coupled to the latter at coupling points which are symmetrical relative to the axis X (and are on the axis Y in  FIG. 4   a ). The cables  10   a  and  10   b  are coupled directly to the frame  30  at two symmetrical points (according to the axis Z in  FIG. 4B ). The two figures show how a frame  30  of this type makes it possible to absorb offsetting according to the axis Y of the axis of rotation of the shaft  12  ( FIG. 4A ), and offsetting of this same axis of rotation according to the axis Z ( FIG. 4B ). Angular offsetting of the said axis of rotation around the axis X or around the axis Y would be absorbed in the same manner by the mobility of the frame  31 . 
         [0026]    According to yet another embodiment illustrated in  FIGS. 5A and 5B , the frame  40  is now suspended on the nut by means of two naturally flexible portions of cable  41 . 
         [0027]    These portions of cable  41  can be connected simply to the nut and to the frame, without a ball connection. For example, their ends can be secured directly on the nut and on the frame, or form a loop around a spindle. 
         [0028]    In the embodiment represented in  FIG. 6 , the nut is connected rigidly (in this case by welding) to a frame  50  with a square form comprising bores with references  51  to  54  at each of its corners. Two square frames  60  and  70  each comprising a central orifice  61 ,  71  for passage of the screw  2  extending on both sides of the frame  50 . At each of their corners, the frames  60  and  70  comprise respective bores with the references  62  to  65  and  72  to  75 . The cable  10   a  and the counterpart cable  10   b  are wound around pulleys  11  and extend through bores in the frames  50 ,  60  and  70 . As shown in detail in  FIG. 7 , a first strand  80  of the cable  10   a  passes through the bore  51 , extends on the first face  55  of the frame  50  whilst running along the edge  56 , then passes through the bore  52 , and extends on the second face  57  of the frame  50  whilst running along the edge  56 , then passes once more through the bore  51 . The first strand  80  of the cable  10   a  then carries out a dead turn on the frame  50  and secures the cable  10   a  to the nut  104 . The first strand  80  of the cable  10   a  extends as far as the frame  60 , and carries out a dead turn on the latter through bores  62  and  63 , in order to exit through the bore  62 , and be wound around the pulley  111 . The second strand  81  of the cable  10   a  extends parallel to the first strand  80  as far as the frame  60 , and then carries out a dead turn on the latter through the bores  63  and  62  in order to exit through the bore  63 . The second strand  81  then carries out a dead turn on the frame  50  through the bores  52  and  51 , in order to exit through the bore  52 . The second strand  81  then engages in the bore in the frame  70 , and carries out a dead turn on the frame  70  through the bores  73  and  72 , in order to exit once more through the bore  73 , and be wound around the pulley  11 . The second strand  81  is then connected to the first strand  80 , and carries out a dead turn on the frame  70  through bores  72  and  73 , in order to exit through the bore  73  and join once more the first strand  80  which is engaged through the bore  51  in the frame  50 . The counterpart cable  10   b  follows a similar path through the bores  53 ,  54  of the frame  50 ,  64 ,  65  of the frame  60 ,  74  and  75  of the frame  70 . 
         [0029]    The cables  10   a  and  10   b  are thus connected to the nut  4  by an anchorage unit comprising the frames  60  and  70  and the cable strands  80 ,  81 . The frames  60  and  70  are suspended on the nut  4  by the cable strands  80  and  81  (which play the same part as the connecting rods  31  and the portions of cable  41  of the embodiments previously described) whilst being mobile relative to the nut. 
         [0030]    The blocking of the cables by means of dead turns is particularly useful when using cables made of synthetic material, in particular polyaramide strings, the crimping of which on the nut  104  is difficult to carry out. It will be appreciated that the use of dead turns in order to render the cables  10   a  and  10   b  integral with the nut (via the frame  50 ) as well as with the anchorage units (in this case the frames  60  and  70 ) is not limited to single dead turns, and the blocking effect can be reinforced by carrying out a plurality of dead turns by passing the cable several times through the same pair of bores. 
         [0031]    According to another particular embodiment represented in  FIG. 8 , the transmission by the cables  10   a  and  10   b  is carried out by means of a single cable loop  90 , the two strands of which, which form the cables  10   a  and  10   b,  are represented in lines with different thicknesses in order to facilitate understanding. This effect is obtained by modifying the embodiment of the dead turns on the frame  50 . The first strand  91  of the cable  90  (corresponding to the first strand  80  of the embodiment in  FIG. 6 ) is engaged through the bore  52  in the frame  50 , and extends on the first face  55  of the frame  50 , whilst running along an edge adjacent to the edge  56 , it then passes through the bore  53  and extends on the second face  57  of the frame  50 , whilst running along an edge  58  of the frame  50  parallel to the edge  56 , then passes through the bore  54 , before being engaged through the bore  65  in the frame  60 . The strand  91  then extends between the bore  65  and the bore  64 , exits once more via the bore  64 , and passes above the edge of the frame  60  in order to be wound around the pulley  11  and join once more the pulley  11  facing it, without being engaged in any of the frames  50 ,  60 ,  70 . The strand  91  then engages in the bore  74  in the frame  70 , in order to exit once more via the bore  75 , pass above the edge of the frame  70 , and extend as far as the bore  54  in the frame  50 . The strand  91  then engages through the bore  54  in the frame  50 , extends on the second face  57  of the frame  50  whilst running along an edge adjacent to the edge  58 , then passes through the bore  51 , and extends on the first face  56  of the frame  50  whilst running along the edge  56  of the frame  50 , then passes through the bore  52 , before engaging through the bore  63  in the frame  60 . The strand  91  then extends between the bore  63  and the bore  62 , exits once more via the bore  62 , and passes above the edge of the frame  60 , in order to be wound around the pulley  11  and join once more the pulley  11  facing it, without being engaged in any of the frames  50 ,  60 ,  70 . The strand  91  then engages in the bore  72  in the frame  70 , in order to exit once more via the bore  73 , pass above the edge of the frame  70 , and extend as far as the bore  52  in the frame  50 . 
         [0032]    This embodiment makes it possible to obtain a cable actuator, the variations of length and resilience of which have a uniform effect on the operation of the actuator. 
         [0033]    The invention is not limited to the preceding description, but incorporates all variants included in the scope of the invention defined by the claims. In particular, although in this case the anchorage unit is in the form of a frame, the anchorage unit can have any form once it is rendered integral with the nut, whilst being mobile relative to the latter. Any means for coupling the anchorage unit to the nut can be envisaged. 
         [0034]    In addition, although, in the examples illustrated, the anchorage unit is coupled to the nut by coupling means which are connected to the anchorage unit at two points which define a first axis transverse to the axis of rotation of the screw, with the cables being coupled to the anchorage unit at a second transverse axis which is perpendicular to the first transverse axis, the two transverse axes need not be perpendicular to one another, but simply oblique. 
         [0035]    Finally, if the misalignments of the cables are negligible, it is possible to dispense with an intermediate anchorage unit, and couple the cables directly to the nut.