Abstract:
A position sensor for sensing the position of a moving part capable of actuating a plunger belonging to the sensor and more specifically a mechanism for orienting the plunger of the sensor. The sensor includes a guide that is rotationally orientable in a body about a first axis XX′ of rotation, and a plunger sliding without rotation in the guide along the axis XX′. A locator prevents rotation of the guide in the body about the axis of rotation, in a given angular position. The locator is fixed nonremovably in the body and possesses either several tabs spaced regularly about the guide and capable of fitting into one position groove to immobilize the guide or several position grooves in which one tab can fit to immobilize the guide. Such a position sensor may find particular application in detecting the positions of moving mechanical components.

Description:
FIELD OF THE INVENTION 
     The invention relates to a position sensor for sensing the position of a moving part capable of actuating a plunger belonging to the sensor. More specifically the invention discloses a mechanism for orienting the plunger of the sensor. 
     DESCRIPTION OF THE RELATED ART 
     A position sensor is a device designed to be actuated by a moving part, either because of the shape of its plunger or because of the force required to actuate it. 
     The position of the moving part is sensed by the mechanical action which the part exerts on the plunger when in contact with it. 
     Position sensors are usually fitted with miniature switches combining a reliable system of rapid switching with a sealed enclosure that confines the contacts in a neutral gas atmosphere favorable to the switching of low-level circuits up to high currents. The displacement of the plunger by the moving part actuates the miniature switch and closes or opens an electrical contact which signals the presence of the moving part. 
     The shape of that part of the plunger which comes into contact with the moving part is adapted both to the shape of the moving part whose position is to be detected and to the type of movement of the part. The reason for this is that, depending on the configuration of the mechanical system in which the sensor is inserted, the angle of attack defined between the direction of the movement of the moving part and the axis of the plunger, when contact occurs between the moving part and the plunger, can differ. 
     For example, if the displacement of the moving part is in the direction of the axis of the plunger, the free end of the plunger can simply be a hemispherical surface giving point contact with the moving part. With this same type of displacement, the free end of the plunger may be fitted with a ball able to pivot in the plunger in order to provide frictionless contact with the mechanical part, if the latter exhibits lateral movement with respect to the plunger axis. 
     In cases where the moving part exhibits a linear movement more or less at right angles to the plunger axis, the plunger comprises at its free end a roller oriented in the direction of movement of the part, the roller being integral with the plunger and being able to rotate about an axis of rotation perpendicular to the axis of the plunger. 
     FIG. 1 a  shows a partial section through a position sensor  10  according to the prior art, comprising a roller  12 , a guide  14  that can be rotationally oriented about a first axis XX′ of rotation, in a body  16  and a plunger  18  sliding without rotation in the guide  14  along this first axis XX′. 
     At the free end of the plunger is the roller  12  which is of circular cylindrical shape and can turn on a spindle or shaft  20  about a second axis YY′ of rotation, this second axis YY′ being colinear with the axis of revolution of the roller, and perpendicular to the first axis XX′. 
     When a moving part P travelling in a direction Dz approximately perpendicular to the first axis XX′ and to the second axis YY′ contacts the roller  12  on a point of its cylindrical surface situated above the second axis YY′, a first force F 1  is exerted by the moving part P on the periphery of the roller. This first force F 1 , transmitted to the plunger  18  through the shaft  20 , produces a component force F 2  in the direction of the first axis XX′. This component force F 2  causes the plunger  18  to slide down the guide  14 , and the roller  12  down two guide grooves  22  situated in the guide  14  on either side of the first axis XX′. 
     The sliding of the plunger down the guide takes place without rotation, the second axis YY′ of rotation of the roller  12  being maintained in the same direction throughout the sliding of the roller in the guide grooves  22 . 
     As it slides down the guide  14 , displaced by the component force F 2  towards the interior of the body, the plunger  18  actuates, via a rod  24 , an electric microswitch  26 . A return spring  28  is compressed during the displacement of the plunger towards the interior of the body. When the moving part P moves away from the roller, the plunger  18  is returned to its initial position by the return spring  28 . 
     The body  16  of the position sensor is mounted on a frame (not shown in FIG. 1 a ) and is thus immobilized in its position with respect to the direction of displacement of the moving part. As a consequence the roller  12  must be able to be oriented and maintained in its angular position about the first axis XX′ so that the second axis YY′, about which the roller revolves, is essentially perpendicular to the direction Dz of the movement of the moving part whose position is to be detected. Having the roller oriented in the direction of movement of the moving part ensures that the roller turns properly on its spindle and avoids lateral loads during contact with the moving part. 
     To this end, the lower part of the guide  14  comprises position grooves  30  distributed around its periphery at an angular pitch a about the first axis XX′. At the upper end of the body  16 , the sensor possesses a locator  32  which is fixed so that it cannot rotate in the body of the sensor and which is in the form of a washer with a tooth  34  designed to fit into one of the position grooves  30 . 
     The body has a screwthread  35  on its cylindrical outer surface on which a nut  36  is screwed to clamp the guide  14  and the locator  34  firmly to the body  16 . 
     FIG. 1 b  shows a perspective view of the guide  14  showing the position grooves  30  distributed around the periphery of the guide at-an angular pitch α of 45 degrees. 
     An angular position β of the guide grooves  22 , and consequently the angular position of the roller  12  sliding in these grooves with respect to a reference axis ZZ′ of the sensor passing through the first axis XX′ and through the middle of the tooth  34  of the locator  32 , will consequently be determined by the selection of one of the position grooves  30 , which contains the tooth  34 . 
     The drawing of FIG. 1 c  shows a simplified top-down view of the sensor taken on AA′, where the angular position β of the guide grooves  22  is approximately 90 degrees with respect to the reference axis ZZ′. In this configuration the second axis YY′ of the roller  12  shown in dashes in FIG. 1 c  will have turned through the angle β of 90 degrees with respect to its position in FIG. 1 a.    
     FIG. 2 a  shows a view of the principle of a position sensor  40  according to the prior art showing another mechanism for the angular positioning of a plunger  42  with respect to a fixed body  44  of the sensor. 
     The position sensor  40  comprises, as in the case of the sensor of FIG. 1 a,  a guide  46  that can be oriented rotationally about the first axis XX′ in the body  44 , with the plunger  42  sliding without rotation in the guide  46  along this first axis XX′. 
     In this embodiment the guide  46  has first holes  48  distributed radially with an angular pitch α about the first axis XX′. The axes of the holes all lie in the same plane perpendicular to the first axis XX′, and each hole  48  can be lined up with the open end of a second hole  50  in the periphery of the body  44 . 
     A locator in the form of a flexible circular collar  52  encircles the body  44  of the sensor around its periphery. FIG. 2 b  shows the collar  52  with a short rod  54  in its center which can be inserted into the second hole  50  of the body and into one of the first holes  48 - 1  of the guide lined up with the first. Selecting one of the second holes  48 - 2  and keeping it lined up with the first hole by means of the rod  54  ensures an angularly position β of the guide with respect to the sensor body. 
     The different mechanisms of angular positioning for sensors in the prior art have drawbacks as follows. 
     In operation, the sensor suffers impacts when contact occurs between the moving part and the roller. These repeated impacts produce vibrations in the sensor with the risk of loosening the locator from the sensor body. These vibrations can for example shake the collar  52  free from the sensor shown in FIG. 2 a  or slacken the nut  36  of the sensor shown in FIG. 1 a.    
     The loosening of the locator and the failure to keep the guide in position in the sensor body means that the roller is no longer oriented and the position sensing function is therefore no longer performed, with the consequences which this can engender in systems requiring a high degree of reliability of operation. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to reduce the problems of the prior art by proposing a position sensor for sensing the position of a moving part comprising: 
     a guide that is rotationally orientable in a body about a first axis XX′ of rotation, and a plunger sliding without rotation in the guide along this axis XX′; 
     a locator that prevents rotation of the guide in the body about the first axis of rotation, in a given angular position, characterized in that the locator is fixed nonremovably in the body and in that it possesses either several tabs spaced regularly about the guide and capable of fitting into one position groove to immobilize the guide or several position grooves in which one tab can fit to immobilize the guide. 
     In one embodiment of the position sensor according to the invention, the tab or tabs are designed to be bent to enable at least one tab to be inserted into a position groove of the guide, in order to prevent rotation of the guide in the body. 
     In a first variant of the sensor according to the invention, the locator possesses several tabs, two of these tabs bent, one into each of two position grooves of the guide thus preventing the guide from rotating in the body. 
     In another variant of the position sensor, the locator possesses one bendable tab and the guide several position grooves, the angular position of the guide being determined by the choice of one of the position grooves containing the single bent tab. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become apparent on reading the detailed description given thereof with reference to the attached drawings, in which: 
     FIGS. 1 a,    1   b,  already described, show a position sensor and its guide, respectively, according to the prior art; 
     FIG. 1 c,  already described, is a simplified top-down view of the sensor shown in FIG. 1 a;    
     FIGS. 2 a  and  2   b,  already described, show another position sensor and its locator, respectively, according to the prior art; 
     FIGS. 3 a  and  3   b  are a perspective view and a sectional view, respectively, of a position sensor according to the invention; 
     FIG. 3 c  is a perspective view of the guide of the sensor shown in FIG. 3 a,  according to the invention; 
     FIG. 3 d  is a simplified top-down view of the sensor shown in FIG. 3 a,  according to the invention. 
     FIG. 3 a  is a perspective view of a position sensor  60  according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The sensor comprises a guide  62  that is rotationally orientable about the first axis XX′ in a body  64  and a plunger  66  sliding without rotation in the guide  62  along the first axis XX′. As in the case of the position sensors shown in FIGS. 1 a  and  2   a,  the free end of the plunger projecting from the guide comprises the roller  12 , which is able to turn about the spindle  20  of second axis YY′ perpendicular to the first axis XX′. 
     FIG. 3 b  shows a section through the position sensor shown in FIG. 3 a,  on a plane passing through the first axis XX′ perpendicular to the second axis YY′ of the roller  12 . 
     The guide  62 , which is of circular cylindrical shape, possesses an upper part  68  and a lower part  70 , the upper part having a smaller diameter than the lower part which fits inside a first recess  72  in the body  64  of the sensor. 
     The first recess  72 , which is of circular cylindrical shape and coaxial with the first axis XX′, is open in one direction at one end  74  of the body  64 , situated towards the free end of the plunger, and in the other direction to a second recess  76 , coaxial with the first and of the same shape, with a diameter slightly smaller than that of the first recess, thus creating a circular shoulder  78  on which a washer  80  sits. 
     The second recess  76  is open to a third recess  82  through which a lower part  84  of the plunger  66  can pass as it slides inside the body  64 . 
     The lower part  70  of the guide is applied, via a base surface  86  perpendicular to its axis of revolution, against the washer  80 , thus keeping the guide in its longitudinal position on the first axis XX′ in the body of the sensor. 
     A washer-like locator  88  possesses an outer edge  90  and an inner edge  92 . The locator is crimped by its outer edge  90  into the body of the sensor, near its end  74 , coaxially with the first axis XX′. 
     The locator  88  is crimped into the body  64  of the sensor in such a way as to clamp the cylindrical lower part  70  of the guide between the said locator resting on a circular surface  94  resulting from the intersection of the upper part  68  with the lower part  70  of the guide, and the washer  80 . The guide is thus kept in its longitudinal position on the first axis XX′, such that it cannot be removed from the body of the sensor, between the locator  88  and the washer  80 . 
     Besides keeping the guide in its longitudinal position in the body of the sensor, the locator performs a second function of angular positioning in the body of the sensor about the first axis XX′. 
     For this purpose, the locator  88  possesses, on the one hand, notches  96  in its outer edge  90 , in order to make it rotationally nonremovable once crimped into the body  64  and, on the other hand, tabs  98  on its inner edge  92 , the tabs being spaced regularly at an angular pitch α about the first axis XX′, the faces of the tabs being parallel to the cylindrical surface of the guide. 
     The sliding of the plunger  66  in the guide  62  takes place without rotation because the second axis YY′ of the roller  12  is maintained in the same direction throughout the sliding of the plunger as the roller  12  slides in the upper part  68  of the guide, in two symmetrical guide grooves  100  situated on either side of the first axis XX′. 
     The two guide grooves  100  are continued towards the lower part  70  of the guide  62  as far as the circular surface  94 , in the form of two position grooves  102  narrower than the guide grooves, and each of which can take one of the tabs  98  of the locator  88  after bending. 
     FIG. 3 c  is a perspective view of the guide  62  comprising the two position grooves  102 . 
     Of the tabs  98 , FIG. 3 b  shows two  104  bent almost horizontal either side of the first axis XX′. The bent tabs  104  fitting into the two respective position grooves  102  in order to prevent the guide  62  rotating in the body  64  of the sensor. 
     The choice of which two tabs are bent  104  either side of the first axis XX determines the angular position of the guide with respect to a reference direction of the body (which is fixed to a frame) and consequently the angular position of the roller  12  with respect to this reference direction. 
     Specifically, the guide must be oriented in such a way that the two position grooves  102  are lined up with the two opposing tabs selected for bending. In this embodiment the locator  88  possesses eight tabs spaced at an angular pitch α equal to 45 degrees. The locator can therefore be oriented in the body with angular increments of 45 degrees. 
     The angular position β of the guide grooves  100  and consequently that of the roller  12  sliding in these grooves, with respect to the body of the sensor, will be determined by which two opposing tabs are selected to be bent into the two position grooves  102 . 
     The drawing of FIG. 3 d  is a simplified top-down view taken on BB′ of the position sensor  60 , showing the position of the roller  12  with respect to a reference axis VV′ passing through the first axis XX′ and the middle of a locking groove  106  laid in the body of the sensor parallel to the first axis XX′. 
     In this illustrative embodiment, the position sensor is fixed with respect to the direction of movement of the moving part by the way it is mounted on a frame  108 . For this purpose, the body of the sensor comprises on its circular cylindrical surface, a screwthread  110  and the locking groove  106  parallel to the first axis XX′. A position-defining washer  112  surrounding the body of the sensor comprises on its inner edge an internal bend  114  which fits into the locking groove  106  and an external bend  116  designed to be inserted into a cavity  118  in the frame  108 . Two nuts  120  and  122  screwed onto the body either side of the position-defining washer  112  clamp this washer against the frame so that the external bend  116  fits into the cavity  118  of the frame  108  and prevents the body of the sensor rotating in the frame. 
     Two lock washers (not shown in the Figure) can be placed between the clamping nuts  120  and  122  and the frame  108  in order to ensure that the fixing of the sensor to the frame is as reliable as possible. 
     The embodiment of the locator is not restricted to the example described and other pitches can be chosen within the limits of the possible ways of constructing the locator and the guide. For example, a pitch of 30 degrees results in a locator having 12 regularly spaced tabs. 
     The locator  88  will be made in a material that will allow the tabs to be bent almost horizontal and unbent to the initial vertical position to allow for the angular position of the roller to be changed a large number of times. As an example, the locator may be made of stainless steel. 
     The embodiments of the locator  88  and of the guide  62  are not restricted to the embodiments described. In other embodiments of the position sensor, the locator possesses several tabs and the guide a single position groove  102 , one of the bent tabs fitting into the single position groove  102 , which means that angular pitches a can be used that do not necessarily give rise to two opposing tabs on either side of the first axis XX′. 
     A wiper seal  124  situated at the lower end of the guide in an internal circular surface  126  of the said guide is held in position in the guide by the washer  80 . An O-ring  128  is placed in the second recess  76 . The wiper seal  124  and the O-ring  128  grip the plunger  66 , allowing it to slide inside the guide and inside the body of the sensor while preventing leaks between the inside of the sensor body and the external environment. 
     In other applications of the position sensor according to the invention, the moving part has a slot, the position of which must be detected. For this purpose the free end of the plunger projecting from the guide comprises a lever (not shown) integral with the plunger. As with the roller, the lever must be able to be oriented and in this application the lever must be oriented in the direction of the length of the slot of the moving part, so that it can fit into the slot of the moving part as it moves. The position sensor according to the invention is excellent in this type of application. 
     The position sensor according to the invention has many advantages over the position sensors of the prior art, namely: 
     reduced size owing to the disappearance of the systems for locking the locator, e.g. the locking nuts; 
     a limited number of parts, reducing the cost of manufacture and the reliability of the product; 
     ability to be used in numerous applications in civilian and military industry; 
     great reliability in use compared with sensors of the prior art.