Dobby with correlated and superimposed cams for the desmodromic operation of weaving looms

Abstract: Dobby (1) for the desmodromic operation of warp frames (2) in weaving looms, comprising a plurality of coaxial cams (4,5;204,205) which are coupled together in pairs and correlated, for the positive operation, in both directions, of the lever mechanisms (2a) for operating the frames (2) of weaving looms, wherein each pair of cams (4,5;204,205) is associated with a pair of wheels (8,9;208,209) lying in axially staggered planes and rigidly connected to a rocker arm (7;207) for operating the arms (2a) of the frames (2), each pair of cams (4,5;204,205) being formed by a first cam (4;204), the dimensional profile of which is smaller than the dimensional profile of the other cam (5;205) of the pair, the locus of the points described by the smaller cam remaining always within the locus of the points described by the larger cam.

Description: The present invention relates to a dobby for the desmodromic operation of warp frames in weaving looms in which the rocker arms operating the arms of the frames are moved by series of cams of varying profile, one having smaller dimensions than the other one, which are superimposed on one another in the axial direction and act on wheels rigidly connected to said rocker arms and lying in staggered planes, the locus of the points described by the smaller cam always being contained within the locus of the points described by the larger cam. In the sector relating to the manufacture of weaving looms for the production of fabric by means of the interlacing of warp and weft yarns, it is known of the need to perform and control the alternating movement of the frames carrying the healds for guiding the warp yarns, with the smallest dimensions, the maximum speed and the largest possible load applicable. Hitherto machines, known as "dobbies", have been produced for the control of said alternating movement, said machines using cams which are correlated and arranged alongside or facing each other, with the cam follower consisting of opposition wheels and rocker arms connected to the lever mechanism for operation of the frame. These dobbies, however, have some major drawbacks: in fact those dobbies which are based on cams arranged alongside one another have a lower supportable load level since they use only partly the axial space theoretically available for wheel/cam contact. This is due to the fact that in said axial space it is necessary to house the elements for lateral supporting of the wheel hub; moreover, said machines require particular profiles or grids for transverse centring of the wheels with respect to the cams themselves. It is also known in the art of a particular solution, of the so-called "opposing cam" type, based on the use of one axis for each cam, said solution, however, requiring more costly manufacturing processes. In other words, the possibility of applying high loads during contact between cam and wheel is linked to the need to increase the dimensions and hence the space occupied by the wheels and cams, this increase in the dimensions, however, being in conflict with the need to limit the axial space occupied by the sets of cams and wheels which are keyed onto the drive shafts in accordance with a predetermined standard pitch within which two cams and two wheels must be housed. The a.m. prior art is disclosed into CH-A-260.546. The technical problem of the invention is therefore that of providing a dobby for the positive operation, in both directions, of warp frames of weaving machines, whereby, with the minimum axial space occupied, it is possible to use the maximum width of contact between wheel and cam and achieve perfect centring thereof, without the need for additional auxiliary elements or special profiles of the contact surfaces. This technical problem is solved by the dobby of claim 1. Advantageous embodiments are set out in claims 2-12. In a first embodiment each cam pair is associated with a pair of wheels of different diameter, which are rotationally rigid with the opposite faces of the rocker arm operating the arms of the frames so that each cam of smaller dimensions is associated with the wheel of larger diameter and each cam of larger dimensions is associated with the wheel of smaller diameter. In a second embodiment, each pair of cams is respectively associated with a pair of wheels which are rigidly connected to a rocker arm operating the arms of the frames and are arranged partially superimposed on one another in the axial direction, said wheels having an eccentric hole for coupling with a pin which is located inside the area where the said wheels are superimposed and on which the rocker arm is also pivotably mounted. Further details may be obtained from the following description, with reference to the accompanying drawings, in which: Fig. 1 is a schematic section along a horizontal plane of the dobby according to the invention; Fig. 2 is a schematic section along the plane indicated by II-II in Fig. 1; Fig. 3 is a plan view of a first embodiment of the rocker arms for operating the frame arms; Figs. 4 and 5 are sections along the plane indicated by IV-IV and V-V in Fig. 3; Fig. 6 is a view, in the axial direction, of the arrangement of the pairs of cams and wheels of the dobby according to Fig. 1; Fig. 7 is a section along the plane indicated by VII-VII in Fig. 6; Fig. 8 is a schematic view of a second embodiment of the dobby according to the invention; Figs. 9a and 9b are, respectively, an axonometric view in exploded form and a front view of an example of embodiment of the rocker arm; Figs. 10a and 10b are sections along the planes indicated by X-X a,b in Fig. 9b, respectively; Fig. 11 is a view of the set of cams and wheels in contact with the rocker arm in the lowered frame position; Fig. 12 is a view of the cams and wheels with the rocker arm in the raised frame position; Fig. 13 is a partial section showing the arrangement of rocker arms in the condition where the machine is at a standstill. As shown in Figures 1 and 2, the positive dobby 1 with cams for operation of frames 2 of weaving machines according to the invention essentially comprises a first shaft 3 which has coaxially keyed onto it pairs of cams 4 and 5 with a correlated profile which rotate together with the shaft 3, and a pin 6 which has mounted on it the rocker arms 7 for operating the lever mechanisms 2a of the frames 2 to which they are connected via the pin 7a. More particularly (Fig. 3) each rocker arm 7 has a bottom shaped part 7b, which has formed in it the hole 7c for keying onto the shaft 6. Each of the opposite faces of the shaped rocker-arm part 7b has moreover formed in it an inset circular seat 7d and 7f with respectively a smaller and larger diameter for partially containing corresponding wheels 8 and 9 of different diameter. Said wheels 8 and 9 are respectively formed by a hub 8a, 9a, rigidly connected to the rocker arm itself, about which there rotates, by means of barrel rollers or spheres or bushes 8b, 9b, an external ring 8c, 9c having its axis of rotation at 8d, 9d coinciding with that of the hub. In this way the wheels 8 and 9 are located in different planes and may therefore be actuated by a respective cam of each pair of cams 4 and 5. More particularly, the cam 4 has a profile of smaller dimensions than the profile of the cam 5 and, during rotation, the locus of the points described by the profile of the smaller cam 4 is always contained within the locus of the points described by the profile of the larger cam 5. The arrangement, in the axial direction, of cams and wheels (Fig. 6) is such that the cam 4 of smaller dimensions is always and solely associated with the wheel 9 of larger diameter and the cam 5 of larger dimensions is always and solely associated with the wheel 8 of smaller diameter. As can be seen from Fig. 7, this makes it possible to limit significantly the axial space occupied, but at the same time to keep the wheels 8 and 9 guided since each rocker arm 7 supports a pair of wheels and acts as a shoulder for containing and guiding the adjacent wheels without the need for additional auxiliary elements. Although it is envisaged that they should have different diameters, the wheels 8 and 9 could also have the same diameter, it being sufficient in this case to provide a corresponding seat on the rocker arm for both the wheels. Figures 8 to 13 show a second embodiment of the dobby according to the invention, in which the rocker arm 207 is obtained by means of two shaped profiles 207b and 207c which are bonded together; each of them has a portion 307b,307c connected to the hubs of the wheels 208,209 by welding or bonding and/or by means of the rivets 214. As illustrated in Figures 9b, 10a and 10b, each shaped profile 207b,207c forming the rocker arm 207 lies on the same plane as the wheel 209,208 of the other opposite supporting profile 207c,207b. In addition to this, it is obvious how coupling of the shaped profiles 207b,207c carrying respectively the wheels 208,209 is not performed by means of simple frontal contact, but by means of relative translation of one lever with respect to the other so as to cause the two wheels to be partially superimposed, with the external profile of each wheel facing the internal profile of each shaped profile forming the rocker arm 207. Each wheel 208,209 is also provided, inside its hub 208a,209a, with an eccentric hole 208e,209e for mounting onto the said pin 6 for pivoting of the rocker arm. The arrangement of the wheels is such that each of them makes frictional - or revolving - contact with the respective lower rocker-arm part 207 and each wheel is partially superimposed on the other wheel in the region of engagement with the pin 6, so that the external profile of one 208 of the two wheels 208,209 comes into contact with the external profile of one 204 of the two actuating cams of each pair 204,205, while the other wheel 209 comes into contact with the external profile of the other cam 205 of the same pair 204,205. Rotation of the correlated cams 204,205 thus causes rotation of the wheels 208,209 and the consequent pivoting of the rocker arm 207 about the pin 6 so as to pass from a position (Fig. 11) where the frame is lowered to a position (Fig. 12) where the frame is raised. It must be emphasized that each wheel 208 is guided axially by the lateral surfaces of the two faces of the larger cams 205 which retain it axially. The wheel 209 making contact with the larger cam 205 is in turn guided by its own rocker arm 207, on the one hand, and by the next rocker arm in the axial direction, on the other hand. From the figures it can be seen that one wheel 208 of each pair 208,209 has a shaped recess 212a coaxial with an identical shaped recess 212 formed on the corresponding rocker arm 207 and suitably shaped for coupling with an associated eccentric shaft 213 which passes throught it and which is actuated only after stoppage of the loom and removal, via known systems, of the shaft 3 with respect to the shaft 6. This permits (Fig. 13) levelling of the frames so as to bring all the frames into the position where they are all at the same height so as to reduce to a minimum the tension of the warp yarns, when the loom is at a standstill. In fact, the frames, if they were not levelled, would keep the yarns tensioned, causing elongation thereof when the loom is stopped and resulting in risks of defects in the fabric when the loom is started up again after stoppage. In this position of the rocker arm as well it can be seen how the wheel 208, in contact with the smaller cam 204, is guided axially by the two larger cams 205 which centre it axially. The sections in Figures 10a and 10b show in detail how the lever arm between the fulcrum 6 for pivoting of the rocker arm 207 and the centre 208d of the wheel 208 is obtained directly inside the wheel 208 without additional connection elements. From the figures it can also be seen that the hubs of the wheels 208,209 are fixed to the rocker arm 207 over the surface of contact between hub and rocker arm and that each hub is fixed to the other hub of the same rocker arm over the entire surface of contact between the two hubs and the assembly is such that the axial dimension of the part of the lever of the rocker arm 207 connected to the pin 207a does not have any effect on the axial width which can be used for the wheel/cam contact. It is therefore obvious how with the dobby according to the invention it is possible to obtain high loads with the minimum axial space occupied, making it possible moreover to use the maximum width of contact between roller and cam and achieve perfect centering thereof without the need for further auxiliary elements or special profiles of the contact surfaces.

Claims: Dobby (1) for the desmodromic operation of warp frames (2) in weaving looms, comprising a plurality of coaxial cams (4,5;204,205) which are coupled together in pairs and correlated, for the positive operation, in both directions, of the lever mechanisms (2a) for operating the frames (2) of weaving machines, each pair of cams (4,5;204,205) is associated with a pair of wheels (8,9;208,209) lying in axially staggered planes and rigidly connected to a rocker arm (7;207) for operation of the arms (2a) of the frames (2), each pair of cams (4,5;204,205) being formed by a first cam (4;204), the dimension of the profile of which is less than the dimension of the profile of the other cam (5;205) of the pair, characterized in that the locus of the points described by the profile of the smaller cam always remaining within the locus of the points described by the profile of the larger cam. Dobby according to Claim 1, characterized in that each face of said lever (7) has an inset seat (7d,7f) for partially containing one respective wheel of said wheels (8,9). Dobby according to Claim 1, characterized in that said wheels have a different diameter. Dobby according to Claim 1, characterized in that the cam (5) of larger dimensions and the cam (4) of smaller dimensions are respectively in contact with the wheel (8) of smaller diameter and the wheel (9) of larger diameter. Dobby according to Claim 1, characterized in that said wheels (8,9;208,209) are formed by a hub (8a,9a;208a,209a), rigidly connected to the respective rocker arm (7; 207) about which there rotates an external ring (8c;9c;208c,209c) actuated by said cams. Dobby according to Claims 1 and 5, characterized in that said wheels (208,209) are arranged partially superimposed on one another in the axial direction and rigidly connected to a rocker arm (207) for operating the arms (2a) of the frames (2), said wheels (208,209) having an eccentric hole (208e,209e) for coupling with a pin (6) which is located inside the area where the said wheels are superimposed and on which the rocker arm (207) is also pivotably mounted. Dobby according to Claim 1, characterized in that the lever of the rocker arm (207) consists of two shaped profiles (207b,207c) which are rigidly coupled to one another and rigidly connected to one side of the first and second wheel (208, 209), respectively. Dobby according to Claim 1, characterized in that said wheels (208,209) are formed by a hub (208a,209a) about which there rotates an external ring (208c,209c), said hub being rigidly connected to the respective rocker arm and provided with a hole (208e,209e) which is eccentric with respect to the centre of rotation (208d,209d) of the said external ring. Dobby according to Claim 1, characterized in that each wheel (208,209) lies in the same axially perpendicular plane as that in which the semi-lever (207c,207b) supporting the other wheel (209,208) lies. Dobby according to Claim 1, characterized in that the radius of the wheel (208,209) making contact with the actuating cam (204,205) is greater than the distance between the centre (208d,209d) of said wheel and the axis of the pin (6) for pivoting of the rocker arm (207). Dobby according to Claim 1, characterized in that at least one (208a) of the hubs of said wheels (208,209) rigidly connected to the rocker arm (207) has inside it a recess (212a) coaxial with a corresponding identical shaped recess (212) of the associated rocker arm (207), for insertion of an eccentric shaft (213) rotatable upon command when the machine is stopped, so as to allow alignment of the frames in a predetermined position. Dobby according to Claim 1, characterized in that the hubs of the wheels (208,209) are fixed to one another over their contact surface.

Inventors: BERETTA GIOVANNI, BERETTA, GIOVANNI
Applicants: BREVTEX SA
Application year: 1996
Main classification: D03C5
IPC codes: D03C5