Holding device for piston position detector
The invention concerns a holding device, which is displaceably mounted on the outside of a fluid pressure cylinder, for a piston position detector, the holder is displaceable and lockable at any desired position on a longitudinal guide on the outside of the cylinder tube. 
     Such a holding device is previously known from DE-C-3 516 346 (Daimler-Benz AG). This previously known device comprises a bracket like holder with two hook shaped clamping elements, which are jointly displaceable along a tension rod associated with the fluid pressure cylinder. One of the clamping elements is provided with a radially extending holding plate. A casing, incorporating a piston position detector, is detachably mounted to the holding plate by means of two screws. The other clamping element, which is pivotable relative to the first clamping element, is provided, on the one hand, with a fastening screw for application against the tension rod and, on the other hand, with a clamping screw effective between the clamping elements. Upon tightening the clamping screw the two clamping elements pivot in opposite directions, so that the casing and a protruding tongue element of the second clamping element are pressed against the exterior of the cylinder tube under clamping action. 
     On the basis of the above mentioned prior art and other similar arrangements (U.S. Pat. No. 4,230,023, EP-A-0 125 992 and EP-A-0 309 304) the present invention achieves a simple and reliable holding device, which 
     includes the least possible number of screws or similar fastening elements; 
     enables simple detachment of the casing of the piston position detector also when the holder is positioned and fastened in the desired position; and 
     protects the casing (and thereby the piston position detector) against external influences. 
     A further object is to assure a fixation without play of the casing to the holding device with reproducable precision, so that the casing, and thereby the piston position detector, is placed in exactly the same position after detachment and remounting, yet another object is to facilitate a protected placing of a signal cable which is connected to the piston position detector, so that the latter is also protected against external influences. 
     The above stated objects of the invention are achieved with a holder having a U-shaped yoke, into which the casing is at least partly insertable, whereby the casing together with a piston position detector contained therein is protected by the surrounding yoke. Further, only two fastening means are needed. The first fastening means is used for the fixation of the two shank ends of the yoke to the mutually parallel guides. The second fastening means is used for the fixation of the casing in the inserted position in the yoke. It is essential that the casing can be detached from and remounted into the yoke, also when the latter is held in a fixed position by the first fastening means. 
     According to a preferred embodiment of the invention, the second fastening means includes a (second) fastening screw, which upon insertion of the casing between the shanks of the yoke is inserted transversally between the shanks, and which by means of an elastic sleeve (which is compressed axially and thereby expanded radially) engages between two stop means arranged at a longitudinal distance from each other on the casing. 
    
    
     The invention will be explained in greater detail below with reference to the accompanying drawing. 
     FIG. 1 is a perspective view of a cylinder tube (the end plates and the piston of the fluid pressure cylinder are not shown) with a holding device according to the invention displaceably arranged on the outside thereof, the holding device being partly cut away to show a casing for a piston position detector inserted therein; 
     FIG. 2 is a perspective view of the piston position detector casing; 
     FIG. 3 is a cross-section through the holding device in a vertical plane and through a fastening screw used for fastening said casing; and 
     FIG. 4 is a cross-section of FIG. 3. 
    
    
     In FIG. 1 is shown a cylinder tube 1 of a fluid pressure cylinder, where the cylinder end plates and piston are not shown. The cylinder tube 1 is preferably manufactured from a light metal alloy and has. The cylinder tube also has longitudinal beads 2 with through holes 3 therein for fastening screws (not shown) for the end plates and, on the other hand, a dovetail-shaped longitudinal bead 4, which at its longitudinal edges form undercut, mutually parallel guide slots 4a, 4b for a holding device 5 according to the invention displaceable along the cylinder tube. 
     The holding device 5 for a piston position detector includes a U-shaped yoke 6, the shanks 7 and 8 of which at their ends are formed with inwardly projecting gripping edges 7a, 8a, which engage the guide slots 4a, 4b. The yoke 6 may be made of metal but is preferably produced out of a rigid plastic material rendering the yoke a certain dimensional flexibility as well as good sliding properties relative to the guide slots 4a, 4b. The dimensional flexibility, which is also increased by the longitudinal weakenings 6a, 6b in the web portion, or top, 6c of the yoke adjacent to the respective shank, is utilized for the detachable fastening of a casing 9 incorporating a piston position detector at the inside of the yoke 6 between its shanks 7, 8. At one end, as seen lengthwise, the shanks are provided with bevels or recesses 7b, 8b in the respective corner area to enable the displacement of the yoke all the way to the associated cylinder end plate. The yoke 6, serving as holder, is thus displacable along the whole length of the cylinder tube 1 (for the positioning close to the second end plate, the yoke can be snapped out of the guide slots 4a, 4b and turned 180°, so that the bevelled corner portions 7b, 8b abut said second plate) and may be positioned and fixed in a desired position by means of a transverse fastening screw 10. When the transverse fastening screw 10 is tightened presses the shanks 7, 8 of the yoke are drawn towards each other in the area of the fastening screw 10, i.e. near one end of the yoke 6 close to the gripping edges 7a, 8a, so that the latter will frictionally engage the guide slots 4a, 4b and thereby fix the yoke 6 in a well-defined position. The head 10a of the fastening screw 10 is countersunk in a corresponding conical recess in the shank 8, while the threaded end portion (not visible in the figures) is in threaded engagement with a nut, which is non-rotatably guided in a recess at the outside of the opposite shank 7 (in the same way as the fastening screw shown in FIG. 3). 
     The casing 9, which contains a piston position detector (not shown) connected to a signal cable 11, is essentially box-shaped and dimensioned to fit into the yoke with its mutually parallel side surfaces between the shanks 7, 8. On the upper side of the casing is provided two transverse ridges 12, 13 serving as stop means forming therebetween a rectangular channel. Before inserting the casing 9 into the position shown in FIG. 1; a sleeve of a relatively stiff elastic material is placed in the C channel between the ridges 12, 13. Upon placing the casing 9 in position, a second transverse fastening screw 15 can be inserted through a hole in the shank 8 and through the central hole of the sleeve 14 to an opposite hole in the shank 7, where a nut 16 is non-rotatably arranged in a recess in the outside of the shank 7 for threaded engagement with the fastening screw 15. When the fastening screw 15 is tightened, the shanks 7, 8 are pressed together, so that they will be mutually parallel along the full length of the yoke 6 (by tightening of only the fastening screw 10 the shanks will diverge somewhat in the direction towards the rear opening through which the casing 9 is inserted). At the same time, the engagement of the gripping edges 7a, 8a to the guide slots 4a, 4b will increase, and the elastic sleeve will be compressed axially, so that it is somewhat deformed radially, thereby eliminating the play against the associated fastening screw 15. Thus, the casing 9 is fixed effectively without play in the inserted position inside the yoke 6. 
     Instead of placing the nut 16 in a recess in the shank 7, the nut 16&#39; (see FIG. 4) may be non-rotatably arranged in the rectangular slot between the ridges 12, 13, so that the nut 16&#39; engages directly with the end of the sleeve 14&#39; (and not via the shank wall). Hereby, a great deformation of the sleeve 14&#39; is assured. The free end portion 15&#39;a of the fastening screw 15&#39;, formed as a guiding pin, is guided with a close fit in a corresponding circular hole in the shank 7. To achieve the best possible fastening action, the nut 16&#39; is of square section, so that it will fit well into the rectangular slot between the ridges 12 and 13. 
     It is obvious that the second fastening screw 15 or 15&#39; can be loosened easily, so that the casing 9 can be withdrawn from the yoke 6 while the yoke is locked in a well-defined position by means of the first fastening screw 10. 
     If desired, the signal cable 11 may be protected by a covering strip (not shown), which is cut into a desired length (corresponding to the distance between the rear end of the casing 9 and the rear end plate) and snapped onto the dovetailed bead 4. At the same time, the casing 9, with the piston position detector contained therein, will be protected by the entirely or partly surrounding yoke 6. 
     The second fastening screw 15 may cooperate with the casing 9 in another way, e.g. without the intermediary of the sleeve 14 by direct cooperation with a transverse recess or hole in the casing. Alternatively, the ridges 12, 13 may be replaced by a number of upward projections distributed transversally in a suitable manner for the forming of stop means on both sides of the second fastening screw 15 (with or without a sleeve) or by fastening means formed in some other way. 
     Further, the mutually parallel guide slots 4a, 4b may be formed differently and do not have to be made in one piece with the cylinder tube. They may, e.g., be formed in a separate longitudinal rail or consist of two separate guide strips. The yoke 6 may likewise be modified, e.g. consisting of two parts with a longitudinal joint in the web portion. It should, however, be of sufficient length to contain a substantial part of the casing 9. Also, the latter may have a different external shape provided that it is entirely or partly insertable between the shanks of the yoke and is lockable in a well-defined position by means of the second fastening means. These second means may, e.g., consist of a fence bar, arresting pins or the like, being movable into locking engagement with the casing from the web portion 6c of the yoke.