Abstract:
A heddle shaft is formed of shaft rods which have hollow ends containing inserts fixedly positioned therein and lateral supports which include projections that respectively extend into recesses in the inserts. Clamping screws, which can extend through the shaft rods, apply a compressive force to clamp the projections in place and create detachable corner connections between the shaft rods and the lateral supports.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a heddle shaft having detachable corner connections. More specifically, the invention relates to a heddle shaft wherein the shaft rods include hollow sections into whose hollow space, at each corner connection, a projection extending laterally from the lateral support fits in a plug-like fashion and is clamped by a clamping means. 
     Heddle shafts usually consist of four basic elements, namely two support rods and two lateral supports connected to the support rods. The point of connection of the support rods with the lateral supports is referred to as a corner connection. In the case of so-called sliderless heddle shafts, when a new warp is to be drawn in, the entire shaft packet is removed from the loom and brought into the drawing-in room. In order to remove the heddles and to draw in new heddles, one of the two lateral supports is usually disconnected. It is obvious that a corner connection wherein the lateral supports can be quickly and easily detached from the shaft rod, and which can be just as quickly reconnected, is advantageous for weaving, because in most cases a lateral support must be removed to draw in new warp threads. In addition, the mounted lateral support must be positioned very precisely in relation to the support rods. If this is not done, disturbances will occur in the weaving operation, causing considerable costs. 
     Many constructions are in use that meet both requirements. One of the most successful and simplest constructions is disclosed in DE 33 08 371. This construction is based essentially on a projection of the lateral support being braced in the hollow space of the shaft rod by means of a pressure screw. Similar designs operating with the same principle of a pressure screw are found in EP 0 189 216, EP 0 328 953 and DE 40 38 384. 
     A further construction, though not quite so easy to handle, uses a draw-screw and a wedge which is clamped directly or indirectly in the hollow space of the shaft rod. Such constructions are disclosed in GB 925 562, SU 288 681, JP H3-55865 and CH 404 580. Also proposed have been elements which are movable around a pivot for bracing in the hollow space of the shaft rod, e.g., in EP 0 502 383. JGM H2-132 681 discloses a U-shaped element that is used for clamping a projection of a lateral support, once again by means of a pressure screw. 
     All of these designs (and there are still more than those listed) have in common that a bracing in the hollow space of the shaft rod occurs which considerably stresses the lateral walls of the shaft rods. Since compared to this prestressing the operating tensions created by the upward and downward motion of the heddle shafts are relatively low, such constructions can be used without a problem up to medium rotational speeds. But the continuously increasing rotational speeds of the loom increase the operating tensions so much that, although no overload breakages occur, fatigue fractures occur fairly quickly. The insertion of elastic parts does not provide a solution, because the level of stress is not reduced by doing so; rather, if anything, it only results in a somewhat reduced fracture frequency. The reinforcement by means of a box-type insert, used in DE 40 38 384, is no longer sufficient at very high rotational speeds either. Only EP 0 189 216 in FIGS. 4 and 5 shows a projection that does not impact the lateral walls of the shaft rod with the initial tension of the clamping screw. On the other hand, the projection of the lateral support that fits into the shaft rod is subjected to strain with these forces. It is also known that it is out of the question to mount a thread with sufficient diameter in the projection of the lateral support for the forces required nowadays. Furthermore, the shaft rod is weakened too much by the slot needed for the screw. Thus, although these are the proper rudiments of a solution to the problem, the proposed design is not realizable in practice. 
     It is therefore an object of the present invention to create a detachable corner connection for a weaving frame which is able to absorb the bracing and/or prestressing forces which occur during assembling as well as the stresses occurring during operation, and which also allows simple detachment and simple remounting. 
     SUMMARY OF THE INVENTION 
     According to the invention, this object is achieved by means of a heddle shaft with detachable corner connections wherein the shaft rod of the heddle shaft is hollow at least one end and wherein the elongated lateral support adjacent each hollow at end includes a side projection which extends into the hollow end, wherein an insert element having a channel extending inwardly from a side thereof is fixedly attached to the shaft rod at each hollow end so that the side projection can extend into the channel, and a clamping mechanism is provided for clamping the lateral projection in the channel, this mechanism applying a force on the side projection which is generally parallel with the elongated lateral support. 
     According to the present invention the prestressing stress is separated in its action from the operating stress and, at the same time, the proven simple functioning with a pressure screw for bracing a projection of the lateral support in the hollow space of the shaft rod can be maintained. An insert having a channel is mounted into the hollow space of the shaft rod such that the channel, which can be provided by a U-shaped or a pincer-shaped portion of the insert, faces the side support and receives the projection of the lateral support. The projection of the lateral support is clamped in known manner, for example, with a pressure screw, in this channel. The thread for the pressure screw is situated in an upper leg of the pincer-shaped or U-shaped portion of the insert. In this way, and of course by appropriate sizing of the U-shaped or pincer-shaped portion, the entire prestressing force is absorbed in the insert according to the invention. The insert itself is attached in the shaft rod at its end opposite the U-shaped or pincer-shaped legs. This attachment now transfers only the forces from the operation of the heddle shafts, however, and does not have to absorb any prestress at all. In this way, the level of stress in the side walls of the shaft rods is reduced enough that fatigue fractures no longer occur. 
     It should be noted that the clamping screw which is preferably used in the invention can of course be replaced with other appropriate clamping means; the important thing is that the gripping and/or prestressing forces during mounting of the corner connection are transferred from the heddle shaft via the insert onto the projection of the lateral support whereby the entire gripping and/or prestressing force is absorbed by the insert. 
     The invention will now be explained in greater detail with reference to the attached figures, taken in conjunction with the following discussion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partially broken away corner connection part of a heddle shaft utilizing an insert according to the invention; 
     FIG. 2 shows a further embodiment of a corner connection utilizing a modified embodiment of an insert according to the invention; 
     FIG. 3 shows another embodiment of a corner connection utilizing an elastic bearing part arranged between the projection and the inventive insert; and 
     FIG. 4 shows a still further embodiment of a corner connection utilizing a further embodiment of an insert according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a partially broken away corner connection part of a heddle shaft with an insert 3 according to the invention. The insert 3 is connected within a hollow end 1a of a support rod 1 of the heddle shaft by means of rivets 4. The lateral support 2 includes a projection 5 which is attached by means of a screw 6 that is screwed into thread 9 in the first part 7 of the pincer-shaped portion of the insert. This screw 6 presses the projection 5, located in the channel between the first part 7 and a second part 8, against the second part 8 of the pincer-shaped portion of the insert. This part 8 also has an inclination 10 which ensures that the projection 5 of the side support 2 is drawn into the pincer-shaped portion of the insert 3 until the surface 11 of the projection 5 lies against the surface 12 of the insert 3. In this way, an exact positioning of the lateral support 2 is achieved in relation to the insert 3 and thus also the support rod 1. 
     FIG. 2 shows a further embodiment of the insert, in this instance designated by 3&#39;. The thread 9&#39; is inclined in relation to the axis of the lateral support 2&#39; and presses against an inclination 13 on the projection 5&#39;. The lower part 8&#39; of the pincer-shaped portion of the insert 3&#39; does not have an inclination in this case. The pressure of the screw 6&#39; is sufficient to press the lateral support 2&#39; against the insert 3&#39;. 
     FIG. 3 shows a further embodiment of a corner connection according to the invention whereby the insert 3 receives an elastic bearing part 14 which is intended to act in a vibration-reducing manner and is mounted around a projection 13 of the lateral support 2. The screw 6 acts on the projection 13 of the lateral support by means of a pad 15 that serves to protect the elastic part, and braces the projection according to the invention in the insert 3. The particular embodiment of insert to be used with the support rod of the heddle shaft is adapted to the materials of the insert and the support rod. The insert is preferably made of tempered steel. When the support rod consists of aluminum, the connection of the two parts is preferably achieved with rivets. If the support rod is made of steel, then welding will be the preferred method of connection. For support rods of plastic, glueing will be the connection method of choice. 
     FIG. 4 shows a corresponding embodiment of the invention with a pincer-shaped insert 3&#39; which is stressed when the two projections 7&#39; and 8&#39; are drawn together. For this purpose, the projection 5&#39; of the lateral support 2 has a bore 16 that a pressure screw 6&#39; penetrates. The screw 6&#39; is a draw-screw that fits into the thread 9&#39; in the projection 8&#39;. When the screw 6&#39; is tightened, the two projections 7&#39; and 8&#39; are drawn toward each other and thus clamp the projection 5&#39; of the lateral support 2 in the insert 3&#39;. The action according to the invention, namely the absorption of prestressing strains in an insert that is attached in the shaft rod without subjecting it to the prestressing strain, is thereby also achieved in this manner. 
     The connection method has no substantial influence on the function of the insert according to the invention. But it must take place in a manner that positions the insert firmly in the support rod and does not hinder the pincer-shaped part in the small deformation that results from the bracing of the projection of the lateral support by means of the pressure screw. 
     The corner connections shown in FIGS. 1-4 are of course examples that can be altered, modified or completed as desired. Thus, in particular the inserts shown in the figures, their connection with the hollow space walls of the support rods, as well as the clamping means chosen in the form of a screw, are not limited to the forms of execution shown. Thus, for example, it is also possible to weld, glue or screw the insert together with the hollow space walls of the support rod. The insert can also be a pincer in the true sense of the word, whose pincer legs can fit in clamping manner into corresponding reliefs of the projection. Instead of the aforementioned screw, it is also possible to use a tensile gripping mechanism comprising bolts, for example, or other suitable clamping means. It is essential to the invention that in the hollow space of the support rod, an insert is arranged that has a receptacle or channel for receiving a projection of the lateral support, which projection is held in the receptacle of the insert by gripping and/or prestressing forces acting at almost parallel to the lateral support.