Abstract:
The mechanism for the acceleration of a projectile of a projectile loom has a torsion-bar launching mechanism (1) with a striker lever (3) which, at its end remote from the torsion bar (2), carries a striker piece (34) which, during launching, acts directly on an impact face (43) of the projectile (4). The projectile (4) for the loom has a casing formed of a hollow body and may be partially closed at the rear, as viewed in the direction of flight. The striker piece (34) can pivot on the striker lever (3) and has at least one striker face (33) which is aligned by an alignment member (5) so that at the instant just prior to triggering of the weft insertion the position of the striker face conforms to that of the impact face (43) of the projectile (4); that is, for example, the two are parallel. The transmitted impact energy is uniformly distributed over the impact face of the projectile (4), which advantageously reduces wear of the striker face ( 33) and impact face (43).

Description:
BACKGROUND OF THE INVENTION 
     The invention is concerned with a mechanism for the acceleration of the projectile of a projectile loom. It is further concerned with a projectile loom having the mechanism in accordance with the invention. 
     From the U.S. Pat. No. 4,922,967 a drive for the projectiles of a projectile loom is known in which a striker piece acts directly on the projectile guided in a straight guideway. The striker piece is fastened to a striker lever at the end of it remote from the torsion bar and moves along a practically circular path. The striker lever is in contact via the striker piece with the rear end of the projectile in the region of the impact face and accelerates it in a few milliseconds over a travel of a few centimeters with an acceleration of up to 30,000 m/sec 2  to velocities of up to 60 m/sec. The striker face on the striker piece as well as the impact face on the projectile are therefore subjected to heavy loads, which leads to corresponding wear. 
     SUMMARY OF THE INVENTION 
     The problem the invention seeks to solve is to create a mechanism for the acceleration of the projectile of looms which reduces the wear at the impact face of the projectile as well as at the striker face of the striker piece. In accordance with the invention the problem is solved by providing an active or passive alignment member which acts upon the striker piece and positions the striker piece in such a way that during the triggering of weft insertion a striker face on the striker piece is conformed to the shape of the impact face on the projectile. 
     The mechanism for accelerating the projectile of a projectile loom has a torsion-bar launching mechanism with a striker lever which, at the end of it remote from the torsion bar, includes a striker piece that acts directly upon the impact face of the projectile during launching. The projectile for the loom, which has a casing formed of a hollow body, may be partially closed at its rear end as viewed in the direction of flight. The striker piece can turn on the striker lever and has at least one striker face which is oriented by an alignment member in such a way that at the latest directly before, at or after the triggering of weft insertion the position of the striker face conforms to that of the impact face on the projectile as, for example, two faces lying in parallel or nearly in parallel. The impact energy is thereby transmitted to the projectile and uniformly distributed over its impact face. Wear of the striker face and impact face is thereby reduced. 
     As a further advantage, the definite positioning of the striker face permits the placement of the projectile in the launching mechanism with a small clearance between the striker face and the impact face, which reduces the blow against the impact face. 
     A further advantage is that during the phase of acceleration of the projectile the striker piece does not come into contact with the alignment member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows part of the launching mechanism of a projectile loom constructed in accordance with the invention and illustrates, in broken lines, the projectile after the launching; 
     FIG. 2 shows a side elevation of a striker lever with its striker piece and with the projectile, in different positions during and after the launching of the projectile; 
     FIG. 3a shows a striker lever with a T-shaped striker piece able to turn through a certain angle; 
     FIG. 3b shows the striker lever with the T-shaped striker piece turned; 
     FIG. 3c shows a view of the striker lever in the launching direction; 
     FIG. 3d shows a view of the T-shaped striker piece; 
     FIG. 4a shows a striker lever with a U-shaped striker piece; 
     FIG. 4b shows a longitudinal section through the striker lever with the U-shaped striker piece; 
     FIG. 5 shows a further form of a turnable striker piece; 
     FIG. 6a shows an alignment member with the mutual positions of striker piece and projectile just prior to and, in broken lines, during weft delivery; 
     FIG. 6b shows the action of the alignment member on the position of the striker piece during the stressing of the striker lever; 
     FIG. 6c also shows the action of an alignment member on the position of the striker piece during the stressing of the striker lever; 
     FIG. 7 shows the position of the striker piece relative to the projectile during acceleration of the projectile; 
     FIG. 8 shows a spring-like alignment member; 
     FIG. 9 shows a further alignment member; and 
     FIG. 10 shows an actively moved alignment member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a projectile accelerating mechanism 1 of a projectile loom generally indicated by reference numeral 1a but not otherwise illustrated in detail because such looms are well known to those skilled in the art. One end of a striker lever 3 is connected to the torsion bar 2 for pivotal movements therewith as the bar is torsionally stressed and unstressed. The other end of the striker lever 3 pivotally mounts a striker piece 34 forming a striker face 33. At the latest just prior to the triggering of the weft insertion the position of the latter conforms to that of the impact face 43 of the projectile 4. The projectile 4 has multiple guides in the launching direction and, after launching, enters a channel 10 formed through the shed of the loom by guide teeth 11 and in that manner carries in the weft yarn 14. The guide teeth are fitted to reed 13 of the loom. At its other end (not shown) torsion bar 2 is clamped firmly and at its other end is twisted and stressed. In FIG. 1 the spring-back of striker lever is represented by reference numeral 3&#39; and is shown in dotted lines. The projectiles 4 are brought into the launching position, one after another, with a pivotable projectile lever 7. Projectiles 4&#39; are moved from lever position 7&#39;, shown in dotted line, to the front of striker piece 34 on striker lever 3. In the case of known projectile looms the return transport of the projectiles 4&#39; to the projectile lever position 7&#39; is effected, for example, by a conveyor chain (not shown). 
     The launching of a projectile 4 and the turning motion of the striker lever 3 induced by torsion bar 2 are illustrated in FIG. 2. Two further positions are drawn in dotted lines at 3&#39; and 3&#34; and the position of reversal of the striker lever is at 3&#39;&#34;. The launching phase has practically concluded when the striker lever 3 has pivoted through the angle α, while the striker lever 3 continues to pivot through the angle β to the position of reversal 3&#39;&#34;. During the stressing of the striker lever it is moved back again into its starting position 3, while between the starting position 3 and at least one part of the range of angle α an alignment member 5 influences the position of striker piece 34. 
     In FIG. 3a striker piece 34 is supported by a bushing 35&#39; pressed onto a pin 35 so that it can pivot on striker lever 3 and it has a T-shaped flat striker face 33 which is widened in the launching direction. In the illustrated embodiment striker face 33 is in the launching position and perpendicular to the direction of launch. Launching positions of the striker face 33 which deviate from the perpendicular are also possible, the impact face 43 on the projectile being in each case parallel or approximately parallel to the striker face 33. The alignment member acts upon at least one face of the striker piece 34. Thus the area 37, for example, is suitable as a guideface for coming into contact with the alignment member 5. The stopface 36 as represented in FIG. 3b limits the angular play δ of the striker piece 34. FIG. 3c shows a view of the striker lever 3 with the striker piece 34 in the direction of launch. An embodiment is represented in FIG. 3d of a striker piece 34 having a striker face 33 and guideface 37. The striker piece 34 is preferably shaped so that it is counterbalanced as regards its pivoting about bushing 35&#39;. 
     FIGS. 4a and 4b show as a further embodiment a striker piece 34 made in the shape of a U. Functionally it is identical to the striker piece shown in FIG. 3a. The wide guideface 37 brings about a reduction in the surface pressure on the area touching the alignment member 5. A T-shaped widening of those regions of the guideface 37 which come into contact with the alignment member 5 can also be advantageously employed in the embodiment of FIG. 3d. 
     In FIG. 5 striker piece 34 is shaped as a turnable polygon; e.g. as a hexagon, so that the different faces of the polygon may serve; e.g. successively as the striker face 33 or the guideface 37 respectively. 
     FIG. 6a shows striker lever 3, associated striker piece 34 as well as the projectile 4 in the launching position. Alignment member 50 fixes the position of striker face 33 on striker piece 34 parallel or approximately parallel to impact face 43 on projectile 4. The definite position of the striker face 33 allows projectile lever 7 to place projectile 4 in the launching position so that the distance between the impact face 43 and the striker face 33 typically amounts to a fraction of a millimeter. Upon triggering, striker face 33 preferably contacts impact face 43 with a negligibly low velocity and at a negligible angle between the striker face and the impact face and projectile 4 is increasingly accelerated when the two are in mutual contact. The guidebeam 8 forces projectile 4&#39; along a linear path in the launching direction, whereas the striker piece 34&#39; describes a circular path. Thus, while maintaining contact striker face 33 slides vertically to the weft direction across the impact face 43. 
     FIG. 6b shows the striker lever 3 with the associated striker piece 34 after it has been fully stressed. It also shows different possible positions 34&#39;&#34;, 34&#34; and 34&#39; of the striker piece during the stressing of the striker lever. The striker piece 34 has an angular play δ and the shown positions 34&#39;, 34&#34; and 34&#39;&#34; of the striker piece were selected for illustration of the action of the guideface 51. Only one particular set of many possible positions, which are dependent upon the angular play δ, are shown. 
     As regards the influence upon the position of the striker piece 34, four ranges may be distinguished in the guide or alignment member 50. In the entry range σ&#39; the distance between the guideface 51 and the circular path about the center of rotation of striker piece 34 is reduced. Following a range σ&#34;, over which a constant distance is maintained, there is a further range σ&#39;&#34; over which the distance is reduced. Finally, over the range σ&#34;&#34;, the guideface 37 of striker piece 34 and guideface 51 come in contact with one another at least partially and without play to thereby fix the position of the striker piece. In the illustrated example guideface 51 of guide member 5 reduces the angular play δ of the striker piece 34 over the range σ&#39;&#34; in order to fix the striker piece in position free of play at range σ&#34;&#34;. It may also be advantageous to start the reduction of the angular play δ at ranges σ&#39; as well as π&#34;. 
     The striking of guideface 37 against guideface 51 during the stressing of striker lever 3 may be reduced or even eliminated if the impact angle of the two surfaces is relatively flat. The shape of guideface 37 on striker piece 34 may be subdivided into an entry range Γ, an alignment range Γ&#34; as well as a holding range Γ&#39;&#34;, as is shown in FIG. 3a, to enable low-impact cooperation of the two guidefaces 37 and 51. 
     In addition, the angular velocity of the striker lever 3 during stressing may be influenced with appropriately shaped cam discs, so that, for example, over the range where the two guidefaces 37 and 51 first make contact, the angular velocity is correspondingly low. 
     Impact between guidefaces 37 and 51 may be further reduced by making the alignment member 50 flexible, particularly in a direction perpendicular to the weft path of the projectile, for example, by constructing the alignment member of a soft material such as plastic or by resiliently supporting the alignment member 50. 
     FIG. 6c shows the striker lever 3 and the associated striker piece 34 after stressing has been concluded. It also shows different positions 34&#39;&#34;, 34&#34; and 34&#39; of the striker piece during the stressing of the striker lever 3. In contrast to FIG. 6b, the range σ&#34;&#34; over which the position of the striker piece 34 is fixed is lacking. As a result, striker piece 34 exhibits slight angular play in its starting position. 
     The position of the striker piece 34 relative to the projectile 4 during the acceleration phase of the projectile 4 is shown in FIG. 7. On leaving the position 340a at the start of acceleration, the striker piece moves relative to the projectile to the position of maximum acceleration 340&#34;. The acceleration of the projectile terminates at position 340&#39;&#34;. While maintaining contact, striker face 33 slides perpendicularly to the weft direction across impact face 43. At least from the start of acceleration at 340&#39; to the point of maximum acceleration at 340&#34; the center of gravity S of the striker piece in the direction of launch lies within impact face 43 of the projectile. Any tilting of the striker piece resulting in a loss of the flat, face-to-face contact should take place, at the earliest, towards the end of the acceleration of the projectile in the vicinity of position 340&#39;&#34;. 
     A further embodiment of an alignment member is shown in FIG. 8. The alignment member 52 is made like a spring; e.g. a leaf spring secured to a clamping member 53. The clamping member may also be resilient so that the alignment member 52 may be a rigid body. The alignment member 52 and clamping member 53 may of course form part of alignment member 50, for example, by having the alignment member define holding range σ&#34;&#34;. 
     Another embodiment of an alignment member is shown in FIG. 9. In the terminal phase of stressing striker lever 3, striker piece 34&#39; (shown in dotted lines) meets alignment member 54 at a preferably very low angular velocity. The further pivoting of the striker lever causes alignment member 54 to align striker piece 34. Resilient properties of the alignment member in the launching direction of projectile 4 are advantageous. 
     As shown in FIG. 10, striker piece 34 may alternatively be aligned with an active, motor-driven alignment member 55 which, for example, in the starting position of the striker lever prior to triggering the weft insertion, adjusts the inclination of the striker piece with a linear or pivotal motion.