Abstract:
The invention relates to a device for interrupting selectively a rotary translational movement, comprising a threaded elongated element ( 14; 114 ) and an element ( 112 ) having a female thread mating with the thread of the elongated element ( 14; 114 ), one of said elements ( 112, 14; 114 ) performing a translatory movement as far as at least a position defined by an end-of-travel stop ( 150 ) as a result of engagement with the other element, and said translating element being able to undergo momentary deformation upon reaching said at least one end-of-travel position ( 150 ) with the effect of being disengaged from the other element.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of International Application Number PCT/EP2005/053607 filed Jul. 25, 2005, now International Publication WO 2006/013172, and claims priority from Italian Patent Application Number TV2004 U 000036 filed Aug. 4, 2004, the contents of which are herein incorporated by reference.  
       DESCRIPTION  
       [0002]     The present invention relates to a device for interrupting selectively a rotary translational movement, which is in particular used in a device for limiting the number of rotations of a mechanical shaft in an actuating system for roller blinds.  
         [0003]     In many applications a device is required for interrupting a rotary translational movement in a selective manner, i.e. controlled and/or influenced by particular boundary conditions. Although complex systems for achieving this object are known (for example using electronic control), it is extremely convenient to have the possibility of a simple and reliable solution. In the following description reference is made to an exemplar case—a device for limiting the number of rotations of a mechanical shaft—while not wishing in any way to limit the scope of the invention.  
         [0004]     In an actuating system for roller blinds a mechanical shaft forms the main actuating member and it is required to control the rotational movement thereof. In particular, a very frequent method of control is based on the number of revolutions which the shaft performs in both directions. In said actuating systems the roller blind (curtain, shutter, etc.) is wound up on and unwound from a roller integral with the shaft such that control of the number of rotations may be converted into control of the end-of-travel position of the roller blind.  
         [0005]     The closest state of the art for this application may be regarded as being the device  1  described in the patent U.S. Pat. No. 3,718,215, now lapsed, from which cross-sectional figures are shown in  FIG. 1  and  FIG. 2 . A splined shaft  10 , which is integral with the mechanical shaft  55  to be controlled (shown in schematic form) and actuated by a motor  20 , engages with two gear wheels  12  in turn each engaged by means of a female thread on a threaded spindle  14  on which they are able to move longitudinally in both directions following their own rotation—see  FIG. 1 . Depending on the direction of rotation of the splined shaft  10  (and therefore the controlled shaft) one of the two gear wheels  12  reaches and pushes a control element  16  which operates an electric switch  18  (microswitch), varying the opening/closing condition thereof—cf. the upper switch in  FIG. 2 . The change of state of the switch  18  is detected by the device  1  and the motor  20  is stopped. The other gear wheel  12  instead moves in the opposite direction, if necessary reaching the end of the threaded spindle  14 . Clearly in the device  1  there are two sets of elements for being able to control the two directions of rotation of the mechanical shaft  55 . Springs  22  push the gear wheels  12  towards the thread of the threaded spindle  14 , allowing them to engage again when the latter reverses its direction of rotation. This occurs both when said wheels  12  are in contact with and push the control element  16  and when they are at the opposite end of the spindle  14  and are unscrewed therefrom—cf.  FIG. 2 . It should be noted that both the gear wheels  12  and the spindles  14  are made of metal. Moreover, it is clear that the gear wheels  12 , the threaded spindle  14  and the springs  22  form a device for interrupting selectively a rotary translational movement, precisely that of the wheels  12  on the threaded spindle  14 .  
         [0006]     The two threaded spindles  14 , respectively, extend longitudinally in the form of two rods  70   a ,  70   b , at the end of which a gear wheel  72   a ,  72   b  coaxial therewith is present. The wheels  72   a ,  72   b  are engaged respectively with two endless screws  74   a ,  74   b . Following installation of the motor it is envisaged adjusting the opening and closing end-of-travel positions. By means of the action of the motor, the roller blind is positioned in the desired opening position and, by means of a suitable implement, such as for example a screw driver, and assuming that the upper spindle  14  is used for adjusting the opening end-of-travel position, the endless screw  74   a  is turned until, by means of rotation of the rod  70   a  and therefore the upper spindle  14 , the upper gear wheel  12  trips the upper switch  18 , which causes stoppage of the motor  20 . The subsequent displacement of the roller blind into the closing position and the consequent definition of the position in which the lower gear wheel  12  trips the lower switch  18 , using the same method described above for the opening position, causes movement of the upper gear wheel  12  away from the upper switch  18  into a position determined by actuation of the closing end-of-travel stop. This latter position may vary depending on the type of shutter or curtain on which the motor has been mounted and depending on the requirements of the individual user. Upon subsequent opening of the roller blind, the motor will run until one of the wheels  12  actuates one of the switches  18 . Therefore the rest (or non-operative) position of the upper and lower wheels  12  may be situated anywhere along the spindle  14  and may be different depending on the adjustments made. Once adjustment has been completed, the screws  74   a,b  keep the spindles  14  fixed.  
         [0007]     The device  1  may be improved, so as to comprise a smaller number of parts, resulting in advantages in terms of weight, lesser complexity and lower cost.  
         [0008]     The object of the present invention is to improve the state of the art. This object is achieved with use of a device for interrupting selectively a rotary translational movement in accordance with the following claims. 
     
    
       [0009]     The advantages and characteristic features of the present invention will emerge more clearly from the following description of an embodiment, to be regarded solely by way of an example and as being in no way limiting. The description refers to the accompanying drawing in which:  
         [0010]      FIG. 1  shows a schematic cross-sectional view of a device according to the state of the art in a first position;  
         [0011]      FIG. 2  shows a schematic view of the device according to  FIG. 1  in a second position;  
         [0012]      FIG. 3  shows a schematic cross-sectional view of a device which comprises the present invention, in a first position;  
         [0013]      FIG. 4  shows a schematic view of the device according to  FIG. 3  in a second position;  
         [0014]      FIG. 5  shows a detail of the device according to the present invention;  
         [0015]      FIG. 6  shows a detail of a variant of the device according to the present invention;  
         [0016]      FIG. 7  shows an enlarged view of a detail contained in the inset Q of  FIG. 6 ;  
         [0017]      FIG. 8  shows a detail of another variant of the device according to the present invention;  
         [0018]      FIG. 9  shows a detail of another variant of the device according to the present invention;  
         [0019]      FIG. 10  shows a detail of another variant of the device according to the present invention;  
         [0020]      FIG. 11  shows a schematic cross-sectional view of a variant of the device shown in  FIG. 3 , in a first position;  
         [0021]      FIG. 12  shows a schematic view of the device shown in  FIG. 11 , in a second position. 
     
    
       [0022]     The reference number  100  denotes a limiting device which is based on and improves the abovementioned device  1 , the numbering of which is maintained with the addition of a suffix “1” for similar elements. The limiting device  100  therefore comprises a splined shaft  110 , integral with the shaft  155  to be controlled (shown schematically) and actuated by a motor  120 . Said shaft  110  engages with two gear wheels  112  each of which is in turn engaged by means of a female thread on a threaded spindle  114 , said shaft  110  being supported by two support flanges  150 . As in the case of the abovementioned patent, said wheels  112  may move axially on said spindle  114  in both directions following rotation thereof—cf.  FIGS. 3 and 4 —and with the same effect: they may reach and push a control element  116  which operates an electric switch  118  (microswitch), varying the opening/closing condition thereof and therefore stopping the motor  120 —cf. The upper switch in  FIG. 4 —or may move along the threaded spindle  114  in the opposite direction to the switches  118 . The two threaded spindles  114 —as in the case of the known art—are respectively connected coaxially to two rods  170   a ,  170   b , at the end of which there are gear wheels  172   a ,  172   b , coaxial therewith. The wheels  172   a ,  172   b  are engaged respectively with two endless screws  174   a ,  174   b . The adjustment of the end-of-travel stops after installation of the motor  120  (i.e. the initial definition of the position of the wheels  112  on the spindle  114 ) is performed as already described for the known art. Similarly the screws  174   a, b  keep the spindles  114  fixed after adjustment.  
         [0023]     A characteristic of the limiting device  100 —due to the special features of the present invention—is the absence of the springs  22  existing in the known art, resulting in the undoubted saving of material and greater simplicity in terms of production and assembly. In order to prevent the wheels  112  from being forced beyond the thread of the threaded spindles  114 , no longer managing to engage therewith so as to move in the opposite direction, they are cut along a radius—see  FIG. 5  where the cut has the reference number  113 . In the case where they are made of plastic, this is achieved without difficulty. Moreover, the distance between the flanges  150  and the end  115  of the thread on the spindles  114  is kept less than the thickness of the gear wheels  112 : in this way said wheels  112  are stopped by the flanges  150  before they are able to disengage definitively from the thread on the spindles  114  and, owing to the cut along their radius, they are deformed and splay slightly, rotating idle (see  FIG. 4 ). With reversal in the direction of the motor  120 , the wheel  112  reverses its direction of rotation and, engaging again on the thread of the spindle  114 , moves away from the adjacent flange  150 . A second characteristic feature of the present invention is to make all the rotating parts preferably from plastic, in particular the gear wheels  122  and the threaded spindles  114 . In this way these parts may be made by means of moulding, in an efficient and cost-effective manner (plastic has a lower cost and moulding parts from plastic is a less costly process).  
         [0024]     It is therefore obvious that this novel system for interrupting selectively a rotary translational movement—namely by means of deformation of the gear wheels  112 —achieves the predefined object and simplifies greatly production of the limiting device.  
         [0025]     An alternative solution may be to manufacture the abovementioned components from soft plastic or rubber, such that it is not required to cut them in order to obtain the necessary deformation.  
         [0026]      FIGS. 11 and 12  show a variant  1000  of the limiting device  100 , in which the same reference numbers used in  FIGS. 3 and 4  are maintained for identical parts and the end-of-travel adjustment mechanism (the two rods  170   a ,  170   b , the gear wheels  172   a ,  172   b  and the two endless screws  174   a ,  174   b ) are not shown. In this case the control elements  116  have an L shape and slide inside an opening of the support flange  150 . The electrical switches  118  are arranged outside the flanges  150  and are actuated (see upper switch in  FIG. 12 ) by one end  116   b  of the elements  116 . The rest of the device is functionally identical to the previous device. It should be noted that in this variant it is possible to establish the end-of-travel position of the wheels  112 —as an alternative to using the flanges  150  or the screws  174   a , b—by making use of the length of the ends  116   b  and the resistance of the body of the switches  118  to the control elements  116  (and therefore to the wheels  112 ).  
         [0027]     The cut  113  in the gear wheel  112  may be not only linear (see  FIG. 5 ) but also have a different progression, for example a V-shaped progression (see  FIG. 10 ) or transverse progression (see  FIG. 8 ). The configurations of the cut  113  shown in  FIGS. 8 and 10  are such that one or more teeth of the wheel  112  need not be eliminated completely, improving the grip of the latter on the splined shaft  110 . Grooves with different forms may obviously be envisaged.  
         [0028]     In this case the cut (or groove) interrupts the internal thread of the wheel  122 . A variant of the invention is shown in  FIGS. 6 and 7 . Instead of cutting the wheel  112 , it may be sufficient to form a groove  117  therein parallel to the teeth. In this way an annular zone  121  of the wheel  112  remains completely in contact with the thread—favouring an optimum grip—but its thickness is somewhat smaller so that it is able to expand when stressed and cause the wheel  112  to disengage from the thread of the spindle  114 .  
         [0029]     In order to allow the gear wheel  112  to jump on the thread of the spindle  114  into the end-of-travel position, not necessarily is it required to make a cut (or form a groove) in said wheel  112 . Another solution is shown in  FIG. 9 . The threaded spindle  114  is formed hollow and with a longitudinal cut  123  which interrupts its cross-section. When the wheel  112  forces the thread of the spindle  114 , the latter gives way, contracting (the cut  123  becomes narrower), and disengages from the wheel  112 . It may also be sufficient merely to cut longitudinally on the spindle  114 , which is not hollow, along a portion of its thread, a groove which is blind or may extend from one side to the other.  
         [0030]     Clearly the number of cuts or grooves may vary depending on the specific cases and consist of more than one. Moreover, it is possible to imagine a device where it is the spindle  114  which performs a rotary translational movement along the thread of a fixed female thread.  
         [0031]     The device for interrupting selectively a rotary translational movement according to the present invention may be applied to other mechanisms, for examples devices for detecting obstacles or brakes. The splined shaft  110  may be replaced by a smooth spindle which transmits, via elastic belts, the movement to the wheel  112 . Alternatively, the wheel  112  may be smooth instead of having teeth, possibly made of rubber, and in contact with a smooth spindle which causes it to rotate by means of friction. In certain cases it may be convenient to produce these elements using different materials, for example rubber on the outside and an internal thread made of plastic.  
         [0032]     It is understood that minor variations with respect to the proposed idea of the present invention are in any case included within the following claims.