CUT PILE TUFTING MACHINE CUTTING ELEMENTS

Abstract: A tufting machine in which knives (24) are mounted in an untensioned condition. The necessary tension between the knives and cooperating hooks (18) is provided by a cam surface (42) on the shank of the hook, and also by a scissor angle of substantially 4 DEG formed by inclining the hook and the knife towards one another. Each hook (18) is tilted about a horizontal axis parallel to the direction in which backing medium is fed through the machine so as to offset the cutting edge of the hook and reduce J-cutting.

Description: CUT PILE TUFTING MACHINE CUTTING ELEMENTS This invention relates to a cut pile tufting machine . In the production of cut pile tufted fabric, each reciprocating needle cooperates with a hook which seizes a loop of yarn from the needle and holds the loop until it is cut by a knife acting in scissors- like fashion against the side of the hook to form the pile. The cutting action occurs as the hook and knife oscillate along different paths. One example of a tufting machine which operates in this manner is disclosed in WO 96/36753. In order to generate pressure between a knife and a respective hook to provide the scissor like cutting action, the knives are mounted in a knife holder with a dual angle of inclination. This dual angle typically consists of a scissor angle of 4° and a pressure angle of 8 to 10°. The knife holders are then loaded into the machine and their position is then adjusted so that each knife flexes against the respective hook and is bent against the pressure angle back towards a vertical position. Each knife is thus bent into a curved configuration in which it is pretensioned against the respective hook. This generates the necessary tension in the knife, but also results in rapid wear of the knife and in wear of the cooperating surface of the hook. The tensioning of the knives against the hooks complicates the set up process. It also limits the number of knives that can be used in any one holder, as the force required to pretension the hooks in one holder becomes impractically high if too many hooks have to be pretensioned together. There are limitations on the loading of the knife against the hook since cutting occurs at a location adjacent to the throat of the hook and if contact occurs between the surface of the knife below the cutting edge and the surface of the hook behind the throat, the knife is said to be "heeling" against the hook and cutting either ceases or very rough cutting occurs. Moreover, the range of tension on the knife is limited in very fine gauge tufting machines since the pretensioning applied to the knife means that the face of the knife remains in contact with the cutting edge of the hook once the cutting edge of the knife has passed the cutting edge of the hook. This causes the knife to be bowed away from the hook towards an adjacent hook. In such fine gauge machines, a knife relief may be ground into the surface of the hook remote from the cutting surface to prevent or minimize such interference. Consequently, the required knife tension during cutting is difficult to attain with hooks of the prior art. Moreover, in fine gauge machines, the thickness of the yarns that may be cut may be limited because of the limitations of the tension that can be applied between the knives and hooks . In US 4,602,576, a proposal was made to remedy some of the aforesaid problems by proposing a hook having an inclined ramp on the face of the hook adjacent to the cutting edge, the ramp being a relief in the surface which acts as a cam surface to direct the knife as the knife oscillates adjacent to the throat of the hook. The cam surface is ground at an angle relative to the blade of the hook to increase the distance between the surface of the knife below the cutting edge and the surface of the hook behind the throat and to permit greater tension to be applied between the knife and the hook without resulting in "heeling" of the knife against the hook. As the flexed knife rides up the cam surface the distance between these surfaces will actually increase resulting in an increase in tension as the cutting edges approach each other. The proposal also was to provide an additional relief on the cutting edge of the hook as a continuation of the cam surface or at a slightly different slope to place the cutting edge substantially between the opposed surfaces of the blade of the hook in an effort to eliminate the "J cutting" problem. However, after unsuccessful attempts were made to develop hooks constructed in accordance with this proposal, efforts were abandoned. Also, this document does not address the above mentioned problems associated with tensioning the knives against the hooks. According to the present invention, a tufting machine comprises a housing, a needle bar which is reciprocably movable within the housing and on which a plurality of needles are mounted, whereby, in use, as a web of backing medium is fed through the machine, the needles reciprocate towards and away from the web to create loops of yarn on the opposite side of the backing medium; a plurality of hooks each associated with a respective needle and being reciprocably movable to grab each loop of yarn created by the respective needle, each hook having a bill and a shank on which a cutting edge is formed, the bill extending from the shank to define a throat therebetween; and a plurality of knives each having a cutting edge, associated with a respective hook but not being tensioned against the hook when the knife is in its position furthest from the cutting edge of the hook and being reciprocably movable for cutting the loops of yarn between the cutting edges of the hook and knife; each hook being inclined away from its respective knife in the direction in which the web moves through the machine at a scissor angle; whereby knife tension is increased by the scissor angle as the knife moves up the shank. The present invention provides a unique arrangement in which the knives are not pretensioned against the hooks. Instead, the pressure necessary for the cutting operation is generated by the scissor angle between the hook and knife. As the knives are not pretensioned against the hooks, the contact between the knives and hooks is greatly minimised, thus significantly reducing wear problems. As the knives are not pretensioned, they will not suffer from the problem in the prior art that the knife bows away from the hook, thereby removing the need to provide a knife relief in the surface of the hook remote from the cutting surface. A further consequence of the lack of pretensioning of the knives is that the only significant pressurised contact between the knife and the hook takes place between their respective cutting edges. This provides a self sharpening action for both the hook and the knife. The lack of pretensioning makes it easier to load the knives into the machine thereby facilitating the set up operation. Preferably each hook has a cam surface formed in the shank adjacent to the throat extending from a first thickness adjacent to the throat to a lesser thickness at a lower edge of the shank; whereby knife tension is increased as the knife rides up the cam surface. Thus, the tensioning of the knife is provided by both the cam surface and the scissor angle, so that the scissor angle can be reduced. The scissor angle is preferably at least 3° but the current preference is for an angle of substantially 4°. The scissor angle may be achieved by one of the hook and knife being mounted in a reference plane parallel to the direction in which the needles reciprocate and the direction in which the backing medium is fed through the machine while the other of the hook and knife is offset with respect to the reference plane by the scissor angle. However, a better scissor action is obtained when both the hook and the knife are inclined in opposition directions with respect to the reference plane each by substantially half of the scissor angle. The current preference is for the hook and the knife to be inclined by 2° in opposite directions with respect to this plane. Another unique aspect of this invention is a knife holder for a tufting machine, the knife holder comprising a housing and a plurality of knives mounted in the housing, the knives being mounted so as to be inclined at a scissor angle, but substantially not inclined at a pressure angle. As the present invention removes the need for pretensioning the knives, there is no need for the knives to have a pressure angle. Thus, the dual angle knives of the prior art are replaced by single angle knives . The projection of each knife from the holder is preferably less than 35mm, and more preferably less than 25mm. Again, the lack of requirement for pretensioning the knives allow shorter knives to be used. This offers a considerable improvement in the knife stiffness as the stiffness is proportional to the cube of the free length of the knife. Another problem encountered during cutting in a tufting machine results from the fact that the knives act against one face of the hook, and since the hook has a finite thickness, the leg of the yarn cut against the cutting surface of the hook is shorter than the other leg by an amount substantially equal to the thickness of the hook at the cutting edge. This is known as "J cutting". Thus, the pile fabric produced has unequal lengths projecting from the backing material and requires excessive tip shearing. In order to overcome this problem, each hook is preferably inclined about an axis parallel to the direction in which the web moves through the machine such that the top of the hook is tilted towards its respective knife. This tilts the cutting edge of the hook to a position where it is substantially mid-way between the top edges of the opposing faces of the hook, as a result of which each loop of yarn is cut substantially at its mid-point thereby reducing J- cutting and producing a carpet where the tufts are all of a substantially equal length. The angle of tilt of the hook is preferably 2°. This tilting of the hook provides the additional benefit that the cam angle presented by the cam surface to the knife is increased, thereby increasing the tension applied to the knife without unduly reducing the thickness and hence the strength of the hook adjacent to the cam surface. However, this feature also forms a further aspect of the present invention which is a tufting machine comprising a housing, a needle bar which is reciprocably movable within the housing and on which a plurality of needles are mounted, whereby, in use, as a web of backing medium is fed through the machine, the needles reciprocate towards and away from the web to create loops of yarn on the opposite side of the backing medium; a plurality of hooks each associated with a respective needle and being reciprocably movable to grab each loop of yarn created by the respective needle, each hook having a bill and a shank on which a cutting edge is formed, the bill extending from the shank to define a throat therebetween; and a plurality of knives each having a cutting edge, associated with a respective hook and being reciprocably movable for cutting the loops of yarn on the respective hook; each hook being tilted about an axis parallel to the direction in which the web moves through the machine such that the top of the hook is tilted closer to its respective knife than the bottom of the hook. As mentioned above, this allows the knife to cut substantially at the centre of the loop, thereby reducing the J-cutting effect. Preferably, the hook further comprises a cam surface formed in the shank adjacent to the throat and extending from a first thickness adjacent to the throat to a lesser thickness at the lower edge of the shank. The angle of tilt and the cam surface combine to tension the knife as it travels up the cam surface. The angle of tilt of the hook is preferably substantially 2°. An example of a tufting machine constructed in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Fig.l is a fragmentary perspective view of a portion of the tufting machine showing the needle bar, hook bar and knife bar; Fig.2 is a fragmentary perspective view of a portion of the hook bar and associated hooks as shown in Fig .1; Fig.3 is a side view of a single hook and knife pair; Fig.4A is a perspective view of a single hook and knife pair with the knife in its downward position and the hook in its extended position; Fig.4B is a view similar to Fig.4A with the knife in a raised position and the hook in a retracted position; Fig.5A-5D are schematic vertical sections through a single hook and knife pair in a set up position, an initial contact position, a cutting position and a final position respectively; Figs.6A-6D are plan views of the hook and knife pair in the same respective positions as in Figs.5A to 5D; and Fig. 7 is a schematic section through two hooks and knives showing the angle of tilt of the hooks. A portion of a cut pile tufting machine 10 is illustrated in Fig. 1 having a needle bar 12 carrying a plurality of needle modules including a body member 14 and a plurality of needles 16 extending therefrom mounted for reciprocation in cooperation with a respective oscillating hook 18 mounted within a module having a body member 20 which is fastened to a hook bar 22 for seizing loops of yarn from the needles. The body member has spaced apart parallel sides 21 adapted to substantially abut similar sides of adjacent modules as illustrated in Fig. 1. Cooperating with the hooks in a scissor-like fashion is a respective knife 24 mounted in a knife holder 26 secured to a knife bar 28 which oscillates in timed relationship with the oscillation of the hooks to cut the loops on the respective hooks. Each hook 18 includes an elongate blade or bill 30 having a beak 32 at the free end thereof and extending from a throat 34 formed at the junction of the blade 30 with a shank 36 having a mounting portion which is moulded within the body member 20. The underside of the bill 30 adjacent to and extending slightly from the throat 34 has a sharpened bottom edge 38 which conventionally acts as a ledger blade in cooperation with the oscillating knife 24 to cut loops of yarn on the bill as they approach the throat. The portion of the shank adjacent to the throat is ground at an incline to form a cam surface 40 which terminates at an edge 42 which is a continuation of the cutting edge of the blade, i.e., the intersection between the bottom edge 38 and the throat 34. The tufting machine described thus far is essentially a conventional modular tufting machine. In order to describe the distinction provided by the present invention, it is first necessary to define a Cartesian coordinate system. In this system, the x direction is the direction in which the backing medium moves through the tufting machine (in the drawings, the positive x direction being opposite to the - In ¬ direction of movement of the web) , the y direction is a transverse direction across the machine, i.e. the direction in which the row of needles is arranged, and the z direction is the direction in which the needles reciprocate which, in practice, will normally be the vertical direction. In general terms, and subject to the slight angles of incline specified below, the knives 24 are substantially planar and are positioned in planes parallel to the xz plane. The hooks 18 are similarly planar and are substantially parallel to the knives. The hooks and knives are both arranged to reciprocate in directions parallel to the xz plane. In the present invention, the hooks 18 are inclined by an angle α about the z axis towards the knife 24 bringing the beak 32 of the hook towards the knife as best shown in Figs. 4A and 4B. Similarly, each knife is inclined by an angle β in the opposite about the z axis as best shown in Fig. 4A. Typically, the angles a and β will be substantially 2°, such that each knife 24 and its respective hook 18 converge at an angle of 4 ° . The hook 18 is also tilted about the x axis by an angle γ so that the top of the hook is closer to the knife 24 than the bottom of the hook. The set up and cutting operations will now be described with particular reference to Figs. 4 to 6. In the set up position as shown in Figs. 5A and 6A, the knives 24 are loaded into the machine in an unstressed condition where a cutting edge 50 of the knife 24 lightly contacts the cam surface 40 of a respective hook 18 without tension. At this time, the hook is offset by 4° (the sum of angles and β)with respect to the knife 24. As shown in Fig. 6A, a part of the knife (shown as a dashed line) is directly below the shank of the hook. During operation the knives are reciprocate substantially in the z axis direction, while the hooks 18 rock to and fro in the xz plane in a generally horizontal manner to provide a relative line of motion 51 as shown in Figs. 4A and 4B. A slight movement of the hook 18 and knife 24 from the set up position of Figs 5A and 6A brings the hook and knife into initial contact in the position shown in Figs. 5B and 6B. In this position, the cutting edge 50 of the knife 24 makes initial contact with the cam surface 40 of the knife 18. Further movement of the knife 24 up the cam surface 40 to the cutting position shown in Figs. 5C and 6C begins to tension the knife 24. At this position, the cutting edge 50 of the knife 24 has travelled beyond the cam surface and cooperates with the cutting edge 38 of the hook 18 to cut the yarn on the hook. At this time further tension is applied between the knife 24 and hook 18 by virtue of the 4° scissor angle. The scissor angle creates a pressurised contact between the cutting edges which moves progressively across the cutting edges as the knife moves further with respect to the hook. The angling of the hook at angle γ brings the cutting edge 38 of the hook 18 between the top edges of the hook as shown in Fig. 7, such that the knife cuts the loop of yarn at a position substantially at the centre of the loop L, thereby reducing J cutting. As the knife 24 and hook 18 move to the final position as shown in Figs. 5D and 6D, the cutting edge 50 of the knife 24 passes the cutting edge 38 of the hook 18. At this stage, there will be a low pressure contact between the cutting edge 50 of the hook 18 and the face of the knife 24. This causes the knife 24 to be deflected away from the face of hook 18 as shown in Figs. 5D and 6D. However, because the knife is not pretensioned, the overall deflection of the knife 24 is minimal. There is therefore no need to provide a relief on the opposite face of the hook to allow for the bowing of the knife.

Claims: CLAIMS 1. A tufting machine comprising a housing, a needle bar which is reciprocably movable within the housing and on which a plurality of needles are mounted, whereby, in use, as a web of backing medium is fed through the machine, the needles reciprocate towards and away from the web to create loops of yarn on the opposite side of the backing medium; a plurality of hooks each associated with a respective needle and being reciprocably movable to grab each loop of yarn created by the respective needle, each hook having a bill and a shank on which a cutting edge is formed, the bill extending from the shank to define a throat therebetween; and a plurality of knives each having a cutting edge, associated with a respective hook but not being tensioned against the hook when the knife is in its position furthest from the cutting edge of the hook and being reciprocably movable for cutting the loops of yarn between the cutting edges of the hook and knife; each hook being inclined away from its respective knife in the direction in which the web moves through the machine at a scissor angle; whereby knife tension is increased by the scissor angle as the knife moves up the shank. 2. A machine according to claim 1, wherein each hook has a cam surface formed in the shank adjacent to the throat extending from a first thickness adjacent to the throat to a lesser thickness at a lower edge of the shank; whereby knife tension is increased as the knife rides up the cam surface. 3. A machine according to claim 1 or claim 2, wherein the scissor angle is at least 3°. 4. A machine according to claim 3, wherein the scissor angle is substantially 4°. 5. A machine according to any one of the preceding claims, wherein each hook and its respective knife are inclined in opposite directions with respect to a reference plane by substantially half of the scissor angle, the reference plane being a plane parallel to the direction in which the needles reciprocate and the direction in which the backing medium is fed through the machine. 6. A machine according to claim 5, wherein the hook and knife are each inclined by 2° with respect to the reference plane. 7. A machine according to any one of the preceding claims, wherein each hook is inclined about an axis parallel to the direction in which the web moves through the machine such that the top of the hook is tilted towards its respective knife. 8. A machine according to claim 7, wherein the hook is tilted at an angle of 2°. 9. A tufting machine comprising a housing, a needle bar which is reciprocably movable within the housing and on which a plurality of needles are mounted, whereby, in use, as a web of backing medium is fed through the machine, the needles reciprocate towards and away from the web to create loops of yarn on the opposite side of the backing medium; a plurality of hooks each associated with a respective needle and being reciprocably movable to grab each loop of yarn created by the respective needle, each hook having a bill and a shank on which a cutting edge is formed, the bill extending from the shank to define a throat therebetween; and a plurality of knives each having a cutting edge, associated with a respective hook and being reciprocably movable for cutting the loops of yarn on the respective hook; each hook being tilted about an axis parallel to the direction in which the web moves through the machine such that the top of the hook is tilted closer to its respective knife than the bottom of the hook. 10. A machine according to claim 9, wherein a cam surface is formed in the shank of the hook adjacent to the throat and extending from a first thickness adjacent to the throat to a lesser thickness at the lower edge of the shank. 11. A machine according to claim 9 or claim 10, wherein the angle of tilt of the hook is substantially 2 ° . 12. A knife holder for a tufting machine, the knife holder comprising a housing and a plurality of knives mounted in the housing, the knives being mounted so as to be inclined at a scissor angle, but substantially not inclined at a pressure angle. 13. A knife holder according to claim 12, wherein the length of each knife protruding from the knife holder is less than 35mm. 14. A knife holder according to claim 13, wherein the length of each knife protruding from the knife holder is less than 25mm. 15. A knife holder according to any one of claims 12 to 14, wherein the scissor angle is substantially 2°.

Inventors: BEVERLY IAN, BEVERLY, IAN
Applicants: SPENCER WRIGHT IND INC, SPENCER WRIGHT INDUSTRIES, INC.
Application year: 2000
Main classification: D05C15
IPC codes: D05C15