CARRYING DEVICE FOR HOLDING AN OBJECT IN POSITION ON A BODY BY MEANS OF FRICTION

Abstract: A device for holding an object in position on a body (3) without having to work the body (3) in any way. The device comprises a retaining element in the form of a flexible strap (6) whose free ends can be fastened to each other by means of a folded joint. A separate clamping unit comprises two strap tensioners (5, 5′) each provided with a guide face (11, 11′) for the strap (6). The object also is provided with a guide face for the strap on the side facing away from the body. The length of the strap is such that the body and the object can be spanned doubly by the strap. The folded joint is clamped between a part of the strap which is on the side of the folded joint facing away from the body and a surface part which is supported from the body.

Description: The invention relates to a carrying device for holding an object in position on a body, comprising: a retaining element for gripping round the body; and a clamping device serving therefor. Such a carrying device is known from European Patent Application 0082257. Such a carrying device is in particular designed to hold in position an instrument such as a mirror in the vicinity of the front end of a barrel of a cannon, more particularly a tank gun. By means of such a mirror, deviations occurring in the barrel during use are detected, so that such deviations can be processed in the shooting procedure. In a carrying device according to the abovementioned known technique, the retaining element is designed in the form of an essentially annular carrier for the instrument in question. This annular carrier is provided with a platform formed integrally therewith, on which the instrument in question can be mounted. The annular part is open at a point, diametrically opposite said platform, so that the opposite ends of said annular carrier can be pulled towards each other by means of a set of adjusting screws, in order to fix the entire unit on a cannon barrel. The annular carrier is provided with internal screw thread, while it is necessary for the cannon barrel in question to be provided with corresponding screw thread on an outer periphery part thereof. In this way the annular carrier can be screwed onto the cannon barrel, and by means of the clamping device the whole unit can be fixed on the cannon barrel. It is often inadmissible or impossible in the field to provide a cannon barrel with external screw thread which is to serve to fit such an annular carrier on the cannon barrel. The object of the invention is to eliminate the above-described disadvantage, while ensuring that the object in question is held firmly in place on the body in question in the particular operational circumstances. The invention is based on the idea of holding a said object on a said body in the desired manner by means of friction forces, while adding a minimum of weight. To this end a carrying device of the above-described type is according to the invention characterized in that the retaining element is designed in the form of a flexible strap whose freeends are suitable for fastening to each other by means of a folded joint; the tensioning device is designed as a separate unit, comprising two separate strap tensioners each provided with a guide face for the said strap; on the side facing away from the side via which the object can be placed on the body in question,the object is provided with a guide face for said strap; and said strap is of such a length that the body in question and the object placed thereon can be spanned doubly by said strap when the latter is placed round the two strap tensioners. In order to simplify the fitting of a carrying device on a body of this type, a carrying device according to the invention is further characterized in that in each of the strap tensioners and on either side of the particular guide face thereof screw holes are drilled, into each of which a tensioning screw can bescrewed, while the central axis of each of the two screw holes of such a strap tensioner deviates over such an angle from the normal determined by the plane in which the main tensioning forces act on the guide face that the main tensioning force acting thereon has the tendency to make these two central axes run essentially parallel to each other. The invention can be used advantageously to hold an instrument such as a mirror in place on a body, such as the barrel of a tank gun, near the front end thereof, or to retain said barrel without it being necessary to prework said body or said barrel locally in any way with a cutting tool. A body or cannon barrel provided with one or more carrying devices according to the invention, spaced apart and in which the respective ends of a said strap are fastened to each other by means of a folded joint, are thereby fitted in such a way on said body or barrel that such a folded joint is held fast between a strap part on the side of said folded joint facing away from the body or barrel and a surface part which is supported from the body or the cannon barrel. More particularly, a body or cannon barrel on which a carrying device according to the invention is fitted is further characterized in that the surface parts where said body or barrel is in contact with one or more of said carrying devices have a surface roughness of Ra = 1 ± 0.5 µm. In addition, in a body or cannon barrel on which one or more carrying devices according to the invention are fitted a lubricant is applied to those points where a particular strap is pressed against the body or cannon barrel and also to those points where opposite parts of said strap come into contact with each other. A coefficient of friction for aluminium (parts of a carrying device) on steel of 0.2-0.5 can be achieved for the body or cannon barrrel if the body or cannon barrel surface part in question and a part of a particular carrying device placed thereon fit each other with a mutual tolerance which is less than 0.040 mm. The invention will be explained in greater detail below with reference to the drawing of a number of embodiments. In the drawing: Fig. 1 is a cross section of an essentially cylindrical body and a carrying assembly according to the invention fixed thereon; Fig. 2 is a side view along the Line II-II in Fig. 1 of a part of the essentially cylindrical body and the carrying assembly according to the invention fixed thereon; Fig. 3 is a side view similar to that shown in Fig. 2, where a part is shown in section along the Line III-III in Fig. 1; Figs. 4, 5, 6 and 7 are diagrams to illustrate the way in which a clamping strap is fitted in a carrying assembly according to the invention; and Fig. 8 is a diagram of a cross section similar to that shown in Fig. 1, to illustrate an alternative embodiment of a carrying assembly according to the invention. For the sake of simplicity the invention is explained below with reference to a carrying assembly illustrating the invention for holding in place a reference mirror on a cannon barrel. Such a mirror at the front end of a cannon barrel serves to detect deviations taking place in the barrel during use and to process said deviations in the shooting procedures. Such a mirror should be simple to fix against and on a cannon barrel of known dimensions, provided that at the point of such fixing coats of lacquer on the cannon barrel are stripped down to the bare cannon barrel material. It is also a requirement that no aids such as grooves, keyways, threaded holes, weld-on components etc. which would assist the fastening of the carrying assembly against and on the cannon barrel may be provided. A carrying assembly according to the invention is equipped to hold in position on a cannon barrel such a mirror and the accompanying mirror carrying system exclusively by means of friction, such a fastening being resistant to the movements and vibrations undergone by the barrel during and after the firing of missile. The embodiment of the invention shown in Figs. 1 to 3 is in particular intended to hold in position an object, more particularly a reference mirror system with a reference mirror 1 and a mirror-carrying structure 2, on a body with an essentially round cross section, more particularly a cannon barrel, a part 3 of which is shown in these figures. In this embodiment there are two objects of carrying assemblies which are spaced apart in the axial direction of the cannon barrel. Each such carrying assembly; in the embodiment shown comprises a frame 4 for carrying the mirror-carrying structure; a strap tensioning device 5 and a clamping strap formed into a closed loop 6. Each frame such as 4 is provided with a curved supporting face 7 whose curvature is matched to that of the corresponding surface part of the cannon barrel on which the frame in question has to rest. Each of the two strap tensioning devices is also provided with a similar curved supporting face 8. In the embodiment shown each such frame 4 is designed as a holder and for that purpose is provided with a central opening 9 in which is fixed a round flange 10, 10′ with a light drive; in order to prevent axial displacement of the mirror-carrying assembly, each of said flanges is provided with a projecting edge which rests against a corresponding shoulder part of the holder. Each of the frames 4, 4′ is also provided with an essentially cylindrical clamping strap guide face 11, 11′. Each of the strap tensioning devices 5, 5′ is in turn made up of two strap tensioners such as 12 and 12′, a tension screw holder 13, 13′, and tension screws 14, 14′; 15, 15′; 16, 16′; and 17, 17′. Each of the two carrying assemblies also comprises a clamping strap 18, 18′. As shown in greater detail in Figs. 4 to 7, each such clamping strap is laid as a closed loop around the two strap tensioners of a corresponding strap tensioning device, the cannon barrel and the frame opposite it. In order to prevent such a clamping strap from sliding in the axial cannon barrel direction, each clamping strap guide face 11, 11′ is provided with an upright edge such as that shown in greater detail in Fig. 3. Figs. 4 to 7 illustrate the way in which each of the two clamping straps is mounted and by means of folded joint connecting together the two free ends to a loop shown in Fig. 7 can pull the frame in question by means of the appropriate strap tensioning device firmly against the cannon barrel surface. Each of the frames 4, 4′ is made of aluminium, on account of its good coefficient of friction, the possibility of truing up, and the relatively low weight of such a frame. The tensioningscrew holders 13, 13′ are also made of aluminium, while the corresponding four steel tensioning screws serve to tighten the particular clamping strap by means of the appropriate metal strap tensioner. Viewed in the axial cannon barrel direction, each tensioning screw holder is provided with a tapered intermediate part. In order to prevent the tensioning screws from damaging the tensioning screw holder, provision is made, between every two adjacent tensioning screws which are screwed into the various strap tensioners of the same strap tensioning device, for a cold-rolled spring steel strip, one of which is indicated by 19 in Fig. 1. Each strip is provided with two holes in which the tensioning screws in question are placed. Each of these steel strips is also filled in a groove hollowed out in the tensioning screw holder, in such a way that the strip is fixed and cannot turn as well. The tensioning screws are, for example, made in the form of steel socket-head screws. The strap tensioners are made of, for example, ETG steel. On account of buckling due to the force exerted by the clamping strap, the tensioning screw holes of a particular strap tensioner are provided in such a way that the central axis of each of these two screw holes deviates over such a small angle from the normal determined by the plane on which the main tensioning forces act on the strap guide face of such a strap tensioner that this main tensioning force acting thereon has the tendency to make the two central axes of these holes run essentially parallel to each other. All this is designed in such a way that with maximum load the tensioning screw holes run essentially parallel to each other. When fitted, the tensioning screws produce a dynamically loaded joint in which the tension force is of primary importance. The fixing . torque greatly depends on the coefficient of friction between the types of material placed on each other and the surface condition thereof. In the absence of a firm joint, the pretensioning force does not increase during tightening of the tensioning screws until the play for all parts and connections is eliminated and these parts settle. During this settling the tension force decreases and has to be adjusted again. In view of the requirement that the weight of the carrying assembly taken as a whole should be as low as possible, use is made of relatively short steel socket-head screws. During fixing of the clamping straps it is assumed that during the pretensioning all those faces which could cause an uncontrollable friction are greased, as a result of which the coefficient of friction is reduced and the maximum pretension can be achieved with a lower fixing torque. Where the clamping strap runs doubly over the barrel (left and right in Fig. 1) large normal forces act, resulting in large friction force, so that on tensioning the clamping strap slides poorly over the barrel. That is why grease is applied locally between the barrel and the clamping strap and preferably also between the two parts of the clamping strap. This means that the tension which is produced in the clamping strap with the strap tensioner is transferred as completely as possible upwards to the object to be held fast and is not divided into a part which is not necessary to make the clamping strap slide over the barrel and a part which is subsequently left over to retain the object. Of course, the friction between the object and the barrel or between the tensioning device and the barrel must be as great as possible. Using a torque spanner, it is possible to build up the pretension in controlled fashion by turning all tensioning screws alternately with increasing torque of equal magnitude and tightening the relevant tensioners parallel relative to the tensioning screw carrier. The tensioning screw carriers are capable of withstanding the maximum forces which are exerted on them by the clamping straps, and such a tensioning screw carrier transmits the resultants of said forces to the gun barrel in question. To join the free ends of a clamping strap to each other a folded joint of the type shown schematically in Fig. 6 was selected. Here the free ends of the clamping strap are pushed into each other and when fitted the returning strap part acts to exert added pressure on the folded joint. With such a structure as that detailed in Fig. 7, this folded joint seen in its entirety is pressed down on during the maximum load of the clamping strap by the returning part of the strap, in such a way that, with the relatively large acting forces, this joint cannot open and, as a result of the normal forces developed, remains in place, so that, when sliding during the clamping of the clamping straps, a mutual counteracting friction force occurs, with the result that pulling open of the folded joint is counteracted. The clamping straps are made of spring strip steel. For obtaining a reproducible and optimum fastening of the whole assembly to a particular cannon barrel it is necessary for the friction between the tensioning screw surfaces and screw joints, and also the friction between the clamping straps and the cannon barrel, to be low and reproducible. The friction values can be influenced by means of lubricants. When the friction between the particular clamping straps and the cannon barrel is reduced as low as possible, the tension forces from the tensioning devices will be transferred from the tensioning direction in the optimum manner to a particular frame. In the embodiment described with reference to Figs. 1 to 3 the friction for holding the mirror and mirror carrier in position on the cannon barrel is caused by normal forces which for each carrying assembly act on two diametrically opposite places. If in the fitted state the pulling force developed in a clamping strap is indicated by Fs, the maximum normal force acting per carrying assembly on the cannon barrel in a "two-point-structure" of the type referred to above is equivalent to 1.73 Fs x 2 = 3.46 Fs. For optimum use of the forces Fs developed in a clamping strap, it is advisable for each carrying assembly to be designed as a "three-point structure", in which the points where the resulting normal forces act on the cannon barrel are mutually displaed over angles of 120 degrees. The total normal force developed per carrying assembly and acting on the gun barrel is then given by the equation 3 x 1.73 Fs = 5.2 Fs. An embodiment of such a three-point structure of a single carrying assembly is schematically shown in Fig. 8. Such an embodiment can, for example, be used advantageously if a relatively large or relatively heavy instrument has to be held in place on a cannon barrel. Such a structure has an auxiliary element 20 which serves as an additional frame, and which is also provided with a curved supporting surface whose curvature is matched to that of the particular surface part of the cannon barrel on which this auxiliary element has to rest, and with a clamping strap guide face. This auxiliary element is together with a frame 21, which is comparable to a frame such as 4 which is used in the embodiment shown in figs. 1 to 3, fastened to a platform 22 with facilities (not shown) in which the instrument in question can be fitted. If desired, a carrying assembly of the type shown in Fig. 8 can be combined with a second similar carrying assembly which is disposed displaced in the axial direction of the cannon barrel in such a way that the platform is carried at four points. In an alternative embodiment of the invention, a single carrying assembly and a single clamping strap would suffice. With it, a mirror can be retained with a single clamping strap on a barrel in a similar way to that described and illustrated with reference to the embodiments of Figs. 1 - 3.

Claims: 1. Carrying device for holding an object in position on a body, comprising: a retaining element for gripping round the body; and a clamping device serving therefor, characterized in that the retaining element is designed in the form of a flexible strap whose free ends are suitable for fastening to each other by means of a folded joint; the clamping device is designed as a separate unit, comprising two separate strap tensioners each provided with a guide face for said strap; on the side facing away from the side by means of which the object can be placed on the body in question, the object is provided with a guide face for said strap; and said strap is of such a length that the body in question and the object placed thereon can be spanned doubly by said strap when the latter is placed round the two strap tensioners. 2. Carrying device according to Claim 1, characterized in that in each of the strap tensioners and on either side of the particular guide face thereof screw holes are drilled, into each of which a tensioning screw can be screwed, while the central axis of each of the two screw holes of such a strap tensioner deviates over such an angle from the normal determined by the plane in which the main tensioning forces act on the guide face that the main tensioning force action acting thereon has the tendency to make these two central axes run essentially parallel to each other. 3. Carrying device according to Claim 2, characterized in that the tensioning unit between a particular pair of bores for said tensioning screws which cooperate with the same strap tensioner is provided with a tapered part. 4. Carrying device according to one of the preceding claims, characterized in that the object is designed as a holder along the periphery of which the said guide face for the said strap and a supporting face by means of which said object can be placed on the body in question are disposed spaced apart. 5. Carrying device according to one of the preceding claims, characterized by an auxiliary frame which is provided with a supporting face by means of which said auxiliary frame can be placed on the body in question, and is also provided with a guide face for said strap. 6. Carrying device according to Claim 5, characterized in that the object and the auxiliary frame are fixed to a platform with facilities in which a second object can be mounted. 7. Carrying device according to one of the preceding claims, characterized in that the guide face for said strap, forming part of an object is confined between two upright side edges which are designed to limit a shift in the transverse direction of said strap. 8. Carrying device according to one of the preceding claims, characterized in that the object is made of aluminium. 9. Carrying device according to one of the preceding claims, characterized in that the clamping device has a tensioning screw holder made of aluminium, in that two neighbouring tensioning screws which can cooperate with different strap tensioners are present and in that when said screws are screwed into the particular strap tensioners said screws rest on carrying faces of said tensioning screw holder by means of a spring steel strip, which steel strip is secured against turning in the tensioning screw holder. 10. Carrying device according to one of the preceding Claims 5 through 9, characterized in that the auxiliary frame is made of aluminium. 11. Body provided with at least one carrying device according to one of the preceding Claims 1 through 9, with the free ends of said strap being fastened to each other by means of a folded joint, and this folded joint being clamped between a part of said strap which is on the side of said folded joint facing away from the body and a surface part which is supported from the body. 12. Body provided with at least one carrying device according to one of the preceding Claims 4 through 10, with the free ends of said strap being fastened to each other by means of a folded joint, and this folded joint being clamped between a part of said strap which is on the side of said folded joint facing away from the body and a surface part which is supported from the body. 13. Body according to Claims 11 or 12, characterized in that the surface parts where said body is in contact with the carrying devices have a surface roughness of Ra = 1 ± 0.5 µm. 14. Body according to Claims 11, 12 or 13, characterized in that a lubricant is applied to those points where said strap is pressed against the body and also to those points where opposite parts of said strap come into contact with each other.

Inventors: BAUMANN, JACOB SIJBRAND
Applicants: B.V. OPTISCHE INDUSTRIE "DE OUDE DELFT"
Application year: 1987
Main classification: F16B2
IPC codes: F16B2, F41G1