Abstract:
A measuring cable travel sensor comprises a housing accommodating a measuring cable drum and a rotary spring operable to urge the cable drum in the direction of winding thereon a measuring cable. A rotary angle sensor is mounted to the housing on the outside thereof. The rotary angle sensor has a sensor shaft with a projecting end trunnion portion. The cable drum is fixed on the sensor shaft trunnion portion non-rotatably in concentric relationship thereon. The travel sensor is of a compact structure, in particular in its axial direction, and simple and inexpensive to produce.

Description:
FIELD OF THE INVENTION 
     The invention concerns a measuring cable travel sensor. 
     BACKGROUND OF THE INVENTION 
     Measuring cable travel sensors are travel or distance-measuring sensors operating on the principle of a measuring cable, with a housing which is suitable for use in industrial situations. A typical travel sensor of that kind comprises a precisely defined and positioned cable drum on to which a measuring cable is wound, generally only in a single layer on the drum. One end of the measuring cable is suitably fixed to the cable drum. The other free end of the measuring cable is secured to the body or article, the variation in the position of which is to be precisely measured. 
     When the movable body or article moves away from or towards the cable drum of the measuring cable travel sensor, the resulting angular movements of the measuring cable drum about its axis are converted into a precise travel or distance length by means of a rotary angle sensor which is non-rotatably coupled to the cable drum. A rotary torsion spring which is operatively connected to the cable drum, generally in coaxial relationship therewith, ensures that the measuring cable is wound on to the cable drum when the movable body whose position is to be measured moves towards the cable drum, thereby to ensure that the measuring cable is properly wound on to the drum and is kept in a reasonably taut condition. 
     It will be noted that measuring cable travel sensors of such a kind are used in the most widely varying technical situations and assemblies, for example for determining the position of an elevator cabin in an elevator shaft, for continuously monitoring the angular positions of ailerons, control elevators and vertical rudders in aircraft and the like. 
     In order to achieve the desired level of measurement accuracy for such a measuring cable travel sensor, it is necessary on the one hand to ensure absolute angular truth as between the measuring cable drum and the rotary angle sensor. That inter alia requires free unimpeded rotary movement of the cable drum of the measuring cable travel sensor, under all operating conditions, as any impediment to the rotation of the cable drum could grossly falsify the measurement result. Accordingly on the one hand the cable drum must be reliably and dependably supported to permit it to rotate freely and accurately while on the other hand there is no way in which the measuring cable drum could be permitted to have its rotary movement adversely affected for example by the cable drum rubbing or the like against the housing or another component as a consequence of a mechanical loading, thermally induced distortion or the like of one of the components of the assembly. 
     For that reason the housings for measuring cable travel sensors were hitherto composed of a plurality of stable metal parts, more specifically on the one hand tube portions and on the other hand end plates which were respectively screwed together in the appropriate configuration. 
     The production of injection-molded parts of plastic material or die-cast parts of light metal or alloy has been less wide-spread both for reasons of the number of items involved and also because of the inadequate degree of accuracy, in comparison with the use of end plates and tube portions which are produced by a procedure which involves cutting machining. 
     In order to provide an arrangement in which the cable drum is reliably supported and free to rotate, the cable drum has hitherto generally been non-rotatably arranged on a separate shaft which is supported in the housing of the measuring cable travel sensor, and that shaft on which the cable drum is disposed is non-rotatably connected to a trunnion portion of the shaft of the rotary position sensor not directly but by way of a coupling which can compensate for angular displacement. In that case, the rotary angle sensor itself was generally fixed on the outside of the housing so that only the projecting trunnion portion of the sensor shaft extends into the housing. 
     Such designs of measuring cable travel sensors are cost-intensive because of the metal parts for the housing, which are expensive to machine, and they are also relatively large in the axial direction because of the separate support arrangement for the cable drum and the consequentially necessary angle coupling transmission to the rotary angle sensor. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a measuring cable travel sensor which can be of a compact structural size, more especially in its axial direction, and which is simple and inexpensive to produce. 
     Another object of the present invention is to provide a measuring cable travel sensor which will afford accurate and reliable measurement results while nonetheless being of a simple design configuration. 
     Still another object of the present invention is to provide a measuring cable travel sensor which is of a robust structure such as to be capable of withstanding severe operating conditions. 
     Yet another object of the present invention is to provide a measuring cable travel sensor which affords the possibility of adaptation to different dimensional aspects in consideration of the operational situations in which it is to be employed. 
     In accordance with the principles of the present invention the foregoing and other objects are attained by a measuring cable travel sensor comprising a housing in which a measuring cable drum and a rotary spring are disposed. A rotary angle sensor is connected to the housing. The sensor has a shaft including a trunnion portion which projects out of the sensor. The cable drum is non-rotatably fixed in concentrically aligned relationship on the trunnion portion of the sensor shaft, in the axial longitudinal region of the trunnion portion where it projects from the sensor. 
     As will be appreciated from a description hereinafter in greater detail of a preferred embodiment of the measuring cable travel sensor according to the invention, a reduction in the size thereof in the axial direction is achieved by virtue of the elimination of the coupling referred to hereinbefore in connection with the previous designs. That is made possible by the avoidance of angular displacement as between the shaft of the cable drum and the sensor shaft, insofar as the cable drum is fitted on to the trunnion portion of the sensor shaft. In that respect, the cable drum does not have to be non-rotatably fixed directly on the sensor shaft, but it is possible also to use a concentric adaptor which is disposed therebetween. That can afford the advantage that the adaptor can project in the axial direction beyond the free end of the trunnion portion of the sensor shaft and can serve as a central, for example slotted entrainment means for the rotary or torsion spring which is disposed in the housing and which is axially spaced in relation to the cable drum. 
     The basic point of departure in terms of all stability considerations relating to the housing is thus the location of the connection between the rotary angle sensor and the housing. In order to permit inexpensive manufacture of the housing in the form of a molded or cast component of plastic material or light metal or alloy, more especially for example aluminum or ZN-casting, with the additional weight advantage that this entails, while affording adequate stability and strength, the housing comprises first and second half-shell portions which are fitted to each other, namely a shell portion which accommodates the rotary spring and a shell portion which accommodates the sensor, both of those being of a substantially cup-shaped configuration. 
     While however the rotary spring shell portion has a closed bottom, the sensor shell portion has a bottom region with a sensor opening through which the trunnion portion of the sensor shaft can project into the housing. The sensor itself is fitted to and secured to the sensor shell portion on the outside thereof. In the housing, the assembly comprising the adaptor and the cable drum is non-rotatably disposed on the trunnion portion of the sensor shaft by suitable mounting means such as clamping screws. 
     A very simple but nonetheless very strong and stable connection between the sensor shell portion and the sensor itself is achieved in accordance with another preferred feature of the invention by arranging on the inside of the sensor shell portion a stabilising ring in the form of a plate which comprises for example metal and which is of approximately the same size as the end face of the sensor or is of a somewhat larger outside periphery. 
     The stabilising ring is provided with screwthreaded bores and is screwed with a plurality of screws in a distributed array around the periphery, through the bottom of the sensor shell portion, using holding clips which mount the sensor to the sensor shell portion. For that purpose at its outside periphery the substantially cylindrical sensor has radially inwardly directed openings, preferably for example in the form of a peripherally extending annular groove, into which noses of the above-mentioned holding clips engage. When the sensor has a peripherally extending annular groove therein therefore instead of individual holding clips it is possible to use two semicircular ring clips which are each screwed to the internally disposed stabilising ring by way of a plurality of screw means. That affords a strong stable connection between the sensor and the sensor shell portion of the housing, with the connection in particular involving a substantial surface area such as not to allow strong torque forces acting at points. 
     In addition in accordance with a preferred feature of the invention the sensor shell portion is stiffened outside the region of contact of the stabilising ring therewith, with radially outwardly rising first radial ribs which are distributed over the entire periphery of the assembly. However the radial ribs do not extend continuously radially as far as the side walls of the sensor shell portion but terminate radially inwardly to such an extent that the casing of the cable drum which is of T-shaped or L-shaped cross-section can rotate radially outwardly of those first radial ribs, wherein the casing of the cable drum axially engages behind the radial ribs. It is only outside the region of the cable drum which rotates at that location that second radial ribs then in turn extend in an inclinedly rising configuration from the bottom of the sensor shell portion to the side walls thereof. 
     In accordance with another feature of the invention while the sensor shell portion, as considered in cross-section, has only one single region of the same depth and of the same free diameter, the spring shell portion is of a stepped configuration in the axial direction thereof. 
     The region of the spring shell portion which is of smaller diameter and which is of substantial depth in the axial direction thereof accommodates the rotary spring while the axially shallower but larger-diameter region which is therefore disposed radially around the smaller-diameter region corresponds to the dimensioning of the sensor shell portion and like same must accommodate the cable drum as, when considered in the axial direction, the plane of contact between the sensor shell portion and the rotary spring shell portion is disposed either in the region of the cable drum or in the region between the cable drum and the spring, but also in the larger-diameter region of the spring shell portion in order here to afford some play and clearance to allow for different axial lengths of the cable drum to permit different cable drums to be fitted to the arrangement. 
     The spring shell portion is also ribbed in a radial direction, but preferably with radial ribs which remain of the same height in their radial extent, more specifically both in the region of the bottom of smaller-diameter region and also in the region of the bottom part which extends therearound externally thereof. Arranged at the transition between the two regions of the spring shell portion are mounting pins or projections which are directed towards the sensor shell portion and on to which can be fitted a stop cover which closes off the end of the receiving region for accommodating the spring so that the spring is held at both faces thereof between the bottom part of the receiving region for accommodating the spring on the one hand and the above-mentioned cover on the other hand, and thus has a contact surface for supporting it at both faces of the spring. 
     In order to permit the peripheral casing portion of the cable drum to engage behind the first radial ribs of the sensor shell portion, as indicated above, the cable drum is of a T-shaped or L-shaped configuration when considered in cross-section, that is to say the radial plate member of the cable drum is not arranged on the end of the cable drum that is towards the sensor shell portion, but either centrally or on the end thereof, which is remote therefrom, in relation to the peripheral casing of the cable drum. 
     In addition the contact plane of the housing also extends through a cable entry connection portion which more particularly is preferably formed in one piece with the respective shell portions of the housing. The cable entry portion is preferably subdivided into a plurality of chambers which adjoin each other at different radial spacings relative to the axis of the housing so that, depending on the respective diameter of the cable drum in other aspects, cable guide elements for the cable entry can be selectively disposed in one chamber of the cable entry portion or another. 
     In accordance with a further preferred feature of the invention the housing is of a substantially quadrangular such as rectangular configuration in its external contour, wherein the screw means between the two shell portions constituting the housing are arranged in corner regions thereof, with the cable entry portion also being disposed in a corner region. That corner region also has the screw means between the different chambers which can be put to use of the cable entry portion. 
     In accordance with another preferred feature the housing and thus the entire measuring cable travel sensor can be secured in relation to other units and assemblies not by means of screws passing through the housing, which could give rise to problems in terms of maintaining sealing integrity, but instead the outside surfaces of the housing preferably have fixing grooves which are more preferably arranged parallel to the axial direction of the measuring cable travel sensor so that the housing of the measuring cable travel sensor can be fixed to the component supporting it by means of holding clips which can be screwed to that component, in a position of co-operating with the above-mentioned grooves. 
     As the cable entry portion is in operation heavily subjected to a wear loading by virtue of the cable sliding thereagainst, the cable entry portion is preferably generally provided with a spout-shaped cable guide portion which is fitted into the wall of the desired chamber of the cable entry portion, although it can also be formed in one piece therewith. The cable guide portion is preferably made from polyether ethylene ketone (PEEK) which is particularly resistant to high temperature and abrasion wear. PEEK can also be injection-molded or produced from the solid by cutting machining. 
     Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a view of an assembled measuring cable travel sensor according to the invention in axial section therethrough. 
     FIG. 2 a  shows a face view of a sensor shell portion forming part of the housing of the measuring cable travel sensor shown in FIG.  1 . 
     FIG. 2 b  shows a partly sectional side view of the sensor shell portion shown in FIG. 2 a.    
     FIG. 3 a  shows a face view of the spring shell portion forming part of the housing of the measuring cable travel sensor according to the invention, and 
     FIG. 3 b  shows a sectional side view of the shell portion shown in FIG. 3 a.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring firstly to FIG. 1, shown therein is a side view in cross-section of a measuring cable travel sensor according to the invention in the fully assembled condition, comprising generally a housing which is diagrammatically indicated at  1  and a rotary angle sensor  6  which is mounted to the housing  1  but of which only part is shown in FIG.  1 . The housing  1  is primarily formed by first and second half-shell portions, more specifically a shell portion  2  for mounting the sensor  6  on the outside thereof, referred to as the sensor shell portion, and a shell portion  3  for accommodating a rotary or torsion or spiral spring which is diagrammatically shown at  5  in FIG.  1 . The shell portions  2  and  3  are shown as a face view and a sectional view separately in FIGS. 2 a,    2   b  and FIGS. 3 a,    3   b  respectively, the view on to the respective sections in FIGS. 2 b  and  3   b  corresponding to that involved in FIG.  1 . 
     The two shell portions  2  and  3  of plastic material such as POM or PBTP produced as injection moldings are provided with a radial rib configuration which is disposed in the interior of the respective shell portion in order to ensure the highest possible level of stability for the assembly or the necessary stability with the minimum possible usage of material and the smallest possible wall thicknesses. In this arrangement the ribs extend radially in a radiating configuration at respective angular spacings of for example about 20°. 
     In the case of the sensor shell portion  2 , as FIGS. 2 a  and  2   b  show, the rib configuration is divided into two, as considered in a radial direction, as follows: 
     First, inwardly disposed radially extending ribs  23  rise in a radially outward region thereof and terminate in a tip which is at the same respective spacing for each rib  23 , from the center of the sensor shell portion  2 . That spacing is less than the inside diameter of the peripheral casing portion of the measuring cable drum which is indicated at  4  in FIG.  1  and which therefore rotates radially outwardly of the first radial ribs  23 . 
     At a spacing radially outwardly of the outer ends of the ribs  23 , second, radially outer radial ribs  27  in turn begin to rise from the inside outwardly. It will be seen from FIG. 2 b  however that the outer ribs  27  do not terminate free at the radially outward ends but go into side walls  26  of the sensor shell portion  2 . 
     As FIG. 2 b  more clearly shows, the radially inward, first radial ribs  23  begin at an annular ring  32  which also represents an annular rib which projects up from the bottom of the sensor shell portion  2 . It will be seen that the rib forming the annular ring  32  is smaller in height than the ribs  23  and  27 . The above-mentioned ribs are formed in one piece together with the bottom and the side walls, which extend therearound, of the sensor shell portion, and they are also formed in one piece with a cable entry portion  19  which, as shown in FIG. 2 a,  has a plurality of different cable entry chambers  30   a - 30   c.  The cable entry is selectively disposed in one of those chambers  30   a - 30   c  depending on the respective direction of extension of the cable, the length of the cable which is to be disposed on the cable drum  4 , and other relevant factors. For that purpose, a cable guide element  20  which must comprise a material such as for example PEEK that is highly resistant to abrasion wear and high temperature is to be arranged in one of those chambers which in addition must be provided with a bore for the cable to be passed therethrough. 
     Arranged centrally in the bottom of the main part of the sensor shell portion  2  which is of substantially square configuration in plan view and at the one side edge thereof in a corner region of the cable entry portion  19  with the cable entry chambers  30   a - 30   c  and thus in concentric relationship with the ribs  23 ,  27  and  32 , in the bottom of the sensor shell portion  2  is a circular sensor opening  16  through which in the assembled condition the centering collar or shoulder indicated at  8  in FIG. 1 of the externally mounted sensor  6  projects into the interior of the housing  1 . 
     In addition, provided in the bottom of the sensor shell portion  2  within the radial ring  32  are a plurality of bores  33  which more specifically are disposed at equal spacings relative to the center of the sensor shell portion  2 . The bores  33  are disposed in a support region which is diagrammatically indicated at  12 ′ and which serves for screw-mounting a stabilising ring which is indicated at  12  in FIG.  1  and which is put on to the bottom of the sensor shell portion  2  and the inside and outside diameters of which are so selected that the stabilising ring  12  preferably entirely covers the region between the outside periphery of the sensor opening  16  and the inside periphery of the radial ring  32 . The thickness of the stabilising ring  12  is smaller than or at a maximum equal to the height of the radial ring  32 . 
     Clips indicated at  13  in FIG. 1 which are disposed on the outside of the sensor shell portion  2  are screwed to the stabilising ring  12  through the bores  32  by means of screws which are screwed in from the exterior. The clips  13  bear against the outside surface of the end plate portion  25 , that is to say the bottom, of the sensor shell portion  2 , but at a spacing from that plate portion  25  they have a radially inwardly directed projection indicated at  13 ′ which preferably also extends over the entire peripheral region of the clips  13 . The clips  13  are each of a part-annular configuration. The projection  13 ′ fits into an annular groove in the outer periphery of the sensor  6  when the latter is fitted to the outside surface of the plate portion  25  in such a way that the centering shoulder or collar  8  of the sensor  6  fits into the opening  16  in the housing and a trunnion portion  7  forming a free end part of the shaft of the sensor  6  projects into the interior of the sensor shell portion  2  and thus into the interior of the housing  1 . 
     Using the part-annular clips  13  or also a larger number of individual clips which are no longer of a for example semicircular configuration makes it possible to avoid directly screwing the sensor  6  to the housing, for example with the stabilising ring  12  thereof, and thus avoids point loadings being applied to the sensor  6 . 
     Disposed in the corner regions of the sensor shell portion  2  are screw passages  34  which are also stiffened by individual ribs extending around each thereof. The sensor shell portion  2  is screwed through the screw passages  34  to the other shell portion, more specifically the spring shell portion  3  which has similar screw passages indicated at  34 ′ in FIG. 3 a,  when the shell portions  2  and  3  are assembled together. In that corner region in which the cable entry portion  19  is arranged on the main body part of the sensor shell portion  2 , the corresponding screw passage  34  is disposed at the level of a preferably central cable entry chamber  30   b  which is closed and cannot be used for cable entry but which only serves for stiffening and reinforcing purposes. 
     In addition the side walls  26  form on each two mutually opposite sides at mutually oppositely disposed positions fixing grooves  41   a,    41   b,    42   a,    42   b  which are directed inwardly, in perpendicular relationship in the side wall. In the fully assembled condition of the measuring cable travel sensor according to the invention, those fixing grooves serve to fix the sensor to a component (not shown) which supports it as part of the surrounding structure, by means of holding clips (also not shown) which can suitably engage into the respective fixing grooves  41   a,    41   b,    42   a,    42   b.  As the fixing grooves do not represent an opening which leads through into the interior of the housing  1 , a clip-type fixing of that kind is to be preferred to direct screwing which involves bores passing through the housing and opening into the interior thereof, quite apart from the fact that the forces involved are transmitted to the housing  1  in a more uniform fashion. 
     For that reason, the pairs of fixing grooves  41   a,    41   b  and  42   a,    42   b  respectively are arranged relatively close to a respective one of the sides of the housing and are only set back therefrom to such an extent that no collision occurs with the screw passages  34  which are provided in the respective corner regions and which are reinforced by annular ribs extending therearound. Preferably, associated with each of the pairs of fixing grooves  41   a  and  41   b  are side walls which are at an angle relative to each other. 
     Looking now in greater detail at FIGS. 3 a  and  3   b,  the spring shell portion shown therein basically differs from the sensor shell portion  2  in that the bottom of the spring shell portion  3  does not have an opening therethrough and, as considered in the cross-sectional view in FIG. 3 b,  the generally cup-shaped receiving region of the spring shell portion for accommodating the spring  5  is of a stepped configuration, with a central, deeper receiving region  5 ′ for accommodating the spring and a shallower receiving region  4 ′ for accommodating the measuring cable drum  4 , the region  4 ′ being of larger diameter than the smaller-diameter region  5 ′ and extending radially therearound. 
     It will be appreciated that, as shown in the sectional view in FIG. 1, the cable drum  4  is disposed entirely to the right of the plane of contact as indicated at  15  where the shell portions  2  and  3  meet, that is to say the cable drum  4  is disposed completely in the sensor shell portion  2 , but the shallow receiving region  4 ′ which is provided in the spring shell portion  3  is necessary so that if appropriate it is possible to use wider or larger cable drums  4 , depending on the respective situation of use involved. 
     In the case of the spring shell portion  3  the rib-forming radial ring  32 ′ projects at the inner periphery of the shallower receiving region  4 ′ for the cable drum  4  and radial ribs  27 ′ extend outwardly therefrom to the side walls  26 ′ to which they are integrally joined. In that arrangement the radial ribs  27 ′ do not rise in the radially outward direction but retain their height, generally the height of the radial ring  32 ′, over the whole of their radial extent. 
     The configuration of the fixing grooves  41 ′ a,    41 ′ b,    42 ′ a,    42 ′ b  and the cable entry portion  19 ′ with the various cable entry chambers defined thereby corresponds to that of the sensor shell portion  2  and likewise also the screw passages  34 ′. 
     The radially smaller but deeper receiving region  5 ′ for accommodating the rotary spring is disposed concentrically with respect to the center, that is to say with respect to the subsequent position of the trunnion portion  7  of the sensor shaft of the sensor  6 , and at its outer periphery has a raised peripherally extending annular flange  35  from which pins or projections  28  project. The pins or projections  28  thus face towards the free side of the spring shell portion  3  and are of a slotted configuration centrally in the longitudinal direction from their free end, in known manner. They serve for fitting on the plate-shaped contact or stop cover  9  which is shown in FIG.  1  and the outer periphery of which approximately corresponds to the inner periphery of the radial ring  32 ′. The annular flange  35  is arranged partially eccentrically along the inner periphery of the radial ring  32 ′, insofar as, as can be seen from FIG. 3 a,  the annular flange  35  is of a decreasing width over approximately a quarter of a circle, whereby there is a step in regard to the width in the annular flange  35  at a location at the periphery thereof. Arranged in that step in the width of the annular flange  35  is a blind hole which is indicated at  29  in FIG. 3 a  and which is also accessible from the inside of the spring shell portion  3 . The blind hole  29  serves for subsequently fixing the end of the wound spring  5  in the receiving region  5 ′, preferably by means of a pin or bolt which is fitted into the blind hole  29  and which is suitably connected to the end of the spring  5 , which is arranged at the outer periphery of the spring  5 . 
     The inner end of the winding of the spring  5  is fitted into the longitudinal slot in the entrainment trunnion portion  11  of an adaptor  10  which is fitted non-rotatably in aligned coaxial relationship on to the trunnion portion  7  at the end of the sensor shaft of the rotary angle sensor  6 , and is connected to the trunnion portion by means of a suitable clamping screw means, as can be seen from FIG.  1 . 
     Also arranged in the bottom of the inwardly disposed and deeper receiving region  5 ′ for accommodating the spring  5  are inner radial ribs  23 ′ which are also of a uniform height and which extend from an inner radial ring  36  outwardly into the peripheral walls of the deeper receiving region  5 ′. 
     Reference will again be made to FIG. 1 showing the measuring cable travel sensor in the assembled condition thereof. Illustrated therein is an end, provided with a rubber stopper  37 , of the measuring cable which is not shown in total but which is only indicated by the broken line  39  and at the end of which is disposed a fixing eye  38 . The measuring cable is wound on the periphery of the cable drum  4 . The cable drum  4  is non-rotatably connected in fixed angular relationship to the adaptor  10 , by the adaptor  10  passing through a central opening in the cable drum  4  and being screwed thereto in the axial direction. 
     In the end remote from the spring  5  the adaptor  10  has an axial bore for insertion of the trunnion portion  7  constituting the free end of the sensor shaft of the rotary angle sensor  6 . 
     Assembly of the measuring cable travel sensor takes place in the following sequence: 
     On the one hand the sensor  6  is secured to the sensor shell portion  2  by means of the stabilising ring  12  and the part-annular clips  13 . 
     On the other hand, firstly the cable drum  4  together with the measuring cable indicated at  39  is fixed to the adaptor  10 , and then on the one hand the cover  9  and on the other hand the spring  5  are then fitted on to the entrainment trunnion portion  11  of the adaptor  10 . That entire unit is now fitted into the spring shell portion  3  and in that case the outwardly disposed end of the spring  5  is also fixed in the blind hole  29  and the cover  9  is fitted on to the pins or projections  28  on the spring shell portion  3 . 
     The two pre-assembled half-shell portions, that is to say the sensor shell portion  2  with its associated components and the spring shell portion  3  with its associated components are then fitted together with insertion of the measuring cable into the required cable entry chamber  30   a  or  30   c  which are provided by suitably arranging a bore or a slot therein and fitting therein a cable guide element  20 . 
     After the two shell portions  2  and  3  have been screwed together by passing suitable screws through the screw passages  34 ,  34 ′, the assembly procedure is completed and the measuring cable travel sensor can be fixed to a component of surrounding structure by means of the fixing grooves  41   a,    41   b  and  42   a,    42   b  respectively and clips which fit thereto. 
     It will be appreciated that the above-described embodiment of the invention has been set forth solely by way of example and illustration of the principles thereof and that various modifications and alterations may be made therein without thereby departing from the spirit and scope of the invention.