Shed forming device for a weaving machine
09915013 ยท 2018-03-13
Assignee
Inventors
- Bram Vanderjeugt (Ypres, BE)
- Matthew Theobald (Whittonstall-northumb, GB)
- Daniel Skinner (Gosforth-Newcastle-upon-tyne, GB)
Cpc classification
International classification
Abstract
A shed forming device for a weaving machine comprising motion systems consisting of hooks that are moveable up and down, transmission elements to transmit the hook motion to a carrier for warp threads, a first force element to exert a downward-directed force on the carrier, and an energy buffer and a second force element to exert a force on an element of the motion system that results in an upward-directed force on the carrier so that the element is so deformed or displaced that the elements of the motion system are kept under tension.
Claims
1. Shed forming device for a weaving machine comprising a number of motion systems consisting of a plurality of elements, each comprising, at least one carrier movable up and down by a driving element to position one or more warp threads in a shed, and transmission elements to transmit the motion of each driving element to a carrier, wherein each motion system comprises a first force element that is connected on the one hand to a carrier and on the other hand to a fixed point to exert a downward-directed first force on the carrier, and wherein each motion system comprises a second force element and an energy buffer, wherein the first force exerted by the first force element brings about the build-up of a supply of energy in the energy buffer by deformation or displacement of at least one part of an element of the motion system, that each motion system comprises a stopper to prevent the displacement or deformation caused by the first force from exceeding a predetermined maximum, that the second force element is provided to transform the energy stored in the energy buffer into a tensioning force that is exerted on an element of the motion system and results in an upward-directed second force on the carrier, wherein at least one part of the latter element is so deformable or displaceable under the influence of the tensioning force that the elements of the motion system are kept under tension.
2. Shed forming device for a weaving machine according to claim 1, characterized in that each motion system comprises, at least one hook that is movable up and down by a driving element at least one carrier to position one or more warp threads in a shed, and transmission elements to transmit the motion of each hook to at least one carrier.
3. Shed forming device for a weaving machine according to claim 1, characterized in that the second force element is or comprises an energy buffer, and that the first force exerted by the first force element results in a force on the second force element that brings about the build-up of a supply of energy in the energy buffer.
4. Shed forming device for a weaving machine according to claim 1, characterized in that the energy buffer is an accumulator of potential energy, hydraulic energy or pneumatic energy.
5. Shed forming device for a weaving machine according to claim 1, characterized in that at least one element of each motion system is a tensioning element with a first tensioning part and a second tensioning part that are displaceable relative to one another, and that the second force element is provided to exert said tensioning force on at least one of these tensioning parts so that these tensioning parts are forced into a relative position in which the elements of the motion system are kept under tension.
6. Shed forming device for a weaving machine according to claim 5, characterized in that the tensioning parts are integrated into the motion system in such a way that the tensioning parts are forced into a first relative position by the tensioning force so that the elements of the motion system are kept under tension.
7. Shed forming device for a weaving machine according to claim 6, characterized in that the first and the second force element are preferably dimensioned such that the first force exerted by the first force element results in a force on at least one of the tensioning parts that moves these tensioning parts against the tensioning force into a second relative position.
8. Shed forming device for a weaving machine according to claim 7, characterized in that the displacement of the tensioning parts from the first relative position to the second relative position brings about the build-up of a supply of energy in the energy buffer.
9. Shed forming device according to claim 8, characterized in that the second force element comprises a spring element and that the displacement from the first relative position to the second relative position brings about an elastic deformation of the spring element.
10. Shed forming device for a weaving machine according to claim 7, characterized in that each motion system comprises a stopper to prevent the tensioning parts from being displaced by more than a predetermined second relative position under the influence of the first force.
11. Shed forming device for a weaving machine according to claim 5, characterized in that the tensioning element is a cord of the motion system, wherein a first cord section and a second cord section are at a distance from one another, above and below an intermediate cord section, respectively, and that the second force element exerts a tensioning force on one or both cord sections so that the first and the second cord sections are forced towards one another.
12. Shed forming device for a weaving machine according to claim 11, characterized in that the motion system comprises at least one pulley over which a pulley cord runs to transmit the motion of the driving element to the carrier, and that the tensioning element is a pulley cord.
13. Shed forming device for a weaving machine according to claim 11, characterized in that the second force element allows the intermediate cord section to be pulled taut so that this intermediate cord section in the taut state acts as the stopper to prevent the further increase in the distance between said cord sections.
14. Shed forming device for a weaving machine according to claim 5 characterized in that the tensioning element is a connector with two connector parts that form said tensioning parts and that the two connector parts are connected to a respective element of the motion system, or respectively to an element of the motion system and a fixed machine part.
15. Shed forming device for a weaving machine according to claim 14, characterized in that the one connector part comprises a head piece that is located displaceably in a locating space of the other connector part.
16. Shed forming device for a weaving machine according to claim 5, characterized in that each motion system comprises at least one pulley element with two pulleys positioned above one another to transmit the motion of the driving element to at least one carrier, that the pulley element comprises two pulley parts that are displaceable relative to one another so that the pulley element forms the tensioning element and the two pulley parts form said tensioning parts.
17. Shed forming device for a weaving machine according to claim 16, characterized in that an uppermost and a lowermost pulley cord respectively run over the two pulleys positioned above one another that the two ends of the uppermost pulley cord are displaceable by means of a respective driving element that the lowermost pulley cord is connected to one or more harness cords, and that the pulley element acts as a tensioning element in that the pulley element has an uppermost pulley part and a lowermost pulley part at a distance apart wherein the pulley parts are displaceable relative to one another and the second force element exerts a force on these pulley parts to reduce said distance.
18. Shed forming device for a weaving machine according to claim 5 characterized in that the tensioning element is a hook drivable by a driving element with two hook sections that are displaceable relative to one another which form the tensioning parts.
19. Shed forming device for a weaving machine according to claim 5 characterized in that the second force element is a tension spring element that exerts a tractive force on said tensioning parts of the tensioning element to pull these tensioning parts together, or is a pressure spring element that exerts a compressive force on one of said tensioning parts to force this tensioning part in the direction of the other tensioning part.
20. Shed forming device for a weaving machine according to claim 1, characterized in that the second force element is provided to permanently exert a tensioning force.
21. Shed forming device for a weaving machine according to claim 1, characterized in that the second force element is located in the motion system between the carrier and the driving element.
Description
(1) In order to further illustrate the characteristics of the invention, a detailed description is given below of a number of preferred embodiments of the inventive shed forming device. It should be clear that these are only examples of the many possible embodiments covered by the invention, and that this description can in no way be regarded as a limitation of the scope of the protection. In this detailed description, reference numbers are used to refer to the attached figures, wherein
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(13) A jacquard device according to this invention (see
(14) The jacquard device also comprises a series of motion systems to position the warp threads on a weaving machine during shed formation in the consecutive weaving cycles. Each motion system comprises two interacting hooks that can be carried by a respective knife (I), (II) of a set of knives. Each hook (1), (2) can also be selected by means of selection units not shown in the figures in order to be held at a fixed height and not carried by the corresponding knife (I), (II). The motion of the hooks (1), (2) are transmitted by the various elements of the motion system to one or more warp threads as explained further below. By appropriate selection or non-selection of each of the two hooks (1), (2) of a motion system, the warp threads can each be positioned in a number of possible positions during the consecutive weaving cycles. The selection units are controlled in order to position the warp threads in such a way that a fabric with the desired characteristics is woven.
(15) In order to transmit the motion of the hooks (1), (2) to the warp threads, each motion system has not only these hooks (1), (2) but also a pulley element (3) located below the hooks which has an uppermost pulley (30) and a lowermost pulley (31) that are joined together by means of a connecting piece (32). The two interacting hooks (1), (2) are connected to a respective end of an uppermost pulley cord (4) that extends downwards from the hooks (1), (2) and runs over the uppermost pulley (30). A lowermost pulley cord (5) extends downwards from the lowermost pulley (31) and runs over this pulley (31), one end of said cord being connected by means of a connecting element, called an anchor (6), to a fixed part (7) of the jacquard device, and the other end of said cord being connected via a harness connector (8) to a harness cord (9) which in turn is connected to a heddle (10) comprising a heddle eyelet (10a). Due to the fact that the warp threads extend through this heddle eyelet (10a), they can be positioned by the motion system. The heddle (10) is connected via a return spring (11) to a lower fixed part (12) that may or may not be connected directly to the solid world. The return spring (11) that here takes the form of a spiral spring thus exerts a permanent downward-directed force on the heddle (10) in order to be able to displace the heddle (10) quickly and reliably to a lower position.
(16) According to this invention, one or more of said elements (1-9) of each motion system can be designed as a tensioning element in order to keep the elements of the motion system under tension and/or to keep the vertical parts of the pulley cords (4), (5) and the harness cord (9) taut. A number of possibilities are presented below in a non-limitative way.
(17) In a first possibility (see
(18)
(19) Each anchor (6) is designed as an essentially L-shaped body with a vertical leg (6a) in which a channel is provided and in which the uppermost end of a lowermost pulley cord (5) is guided and secured, and which is vertically adjustably connected to a guideway (60a), (60b) of a partition (60) and which comprises a leg (6b) protruding to the side at its lower end. On the upper side of the leg (6b) protruding to the side is a finger (6c) protruding upwards (see in particular
(20) Mounted between two adjacent partitions (60) is a stop profile (61) that extends between the vertical surfaces in which the pulley cords (5) coupled to these two partitions (60) are located. Each stop profile (61) is located above the two anchors (6) of these pulley cords (5) in such a position that the fingers (6c) and the spiral springs (62) of these anchors (6) come into contact with the underside (61a) of the stop profile (61) when the anchors (6) are moved upwards on their guideway (60a), (60b). Each stop profile (61) is mounted by means of mounting elements (not shown in the figures) that allow the mounting height to be changed so that the height of the underside (61a) can be adapted to the motion systems with which it operates.
(21) The elastic properties of the spiral spring (62) and the return spring (11) are such that the downward force that the return spring (11) of the motion system exerts on the heddle (10) under normal operating conditions results in an upward force on the anchor (6) that is sufficient to pull the anchor (6) up via the harness cord (9) and the lowermost pulley cord (5)see
(22) Due to the function of the return spring (11), the spiral spring (62) is compressed against the underside (61a) and potential energy is built up in the form of elastic energy. This energy ensures a permanent downward-directed tensioning force on the anchor (6), and hence also on the end of the lowermost pulley cord (5) connected to said anchor. Under certain (undesirable) operating conditions, the return spring (11) (temporarily) exerts a reduced tractive force. This occurs if the return spring itself fails and no longer develops sufficient force, but also if blocking occurs in the motion system between the return spring (11) and the spiral spring (62), or if the inertia of the elements of the motion system results in the tension of the return spring not being (completely) transmitted (for example, in the event of collisions or vibrations) to the motion system. The return spring (11) is then no longer able to keep the motion system under tension. As soon as a smaller downward force than the maximum return spring force is exerted on the anchor (6), the spiral spring (62) can relax more and push the anchor (6) to a lower position so that the finger (6c) is no longer in contact with the bottom surface (61a) of the stop profile (61). As a result of this downward displacement of the anchor (6) and the attached end of the lowermost pulley cord (5), all vertical parts of the cords (4), (5), (9) of the motion system maintain their taut state. In this way the spiral spring (62) will keep the cords (4), (5), (9) taut even if the force exerted by the spiral spring (11) fails almost completely. This tensioning effect is achieved because the return spring (11) is at the outermost point of the motion system while the spiral spring (62) is located between the return spring (11) and the knives (I), (II) in the motion system.
(23) The motion systems shown in
(24) Mounted between two adjacent partitions (60) in each case is a similar stop profile (63) that extends between the vertical surfaces in which the pulley cords (5) coupled to these two partitions (60) are located. Each stop profile (63) is located above the two anchors (6) of these pulley cords (5) in such a position that the flat upper side of the leg (6b) protruding to the side of each of these anchors (6) comes into contact with a respective wing (63a), (63b) and deforms this wing when the anchor (6) is moved upwards on its guideway (60a), (60b). Each stop profile (63) is mounted by means of mounting elements (not shown in the figures) that allow the mounting height to be changed so that the height of the wings (63a), (63b) can be adapted to the motion systems with which they operate.
(25) The elastic properties of the deformable wings (63a), (63b) and the return spring (11) are such that the force that the return spring (11) of the motion system exerts under normal working conditions is sufficient to pull up the anchor (6) until the wings (63a), (63b) reach maximum deformation up against a respective bumper (63e), (63d). This is the situation of the anchor (6) of the second and fourth motion system in
(26) The function of the wings (63a), (63b) corresponds to the function of the spiral spring (62) in the embodiment shown in
(27) In a second possibility the jacquard device comprises motion systems with a pulley element (3) that is designed as a tensioning element.
(28) In the first embodiment, the intermediate section (32) is in two parts with an uppermost intermediate part (320) and a lowermost intermediate part (321). In
(29) The uppermost intermediate part (320) comprises a pin (320a) which at its end has a disc-shaped body (320b). Around the pin (320a) is a spiral spring (322). Inside the lowermost intermediate part (321) is a cylindrical chamber (321a, 321b) with an uppermost chamber section (321a) that broadens step-wise and transitions into a lowermost chamber section (321b) with a larger diameter, wherein the chamber (321a, 321b) is accessible via an axial passage extending from the uppermost end of the lowermost intermediate part (321) and terminating in the uppermost chamber section (321a).
(30) The pin (320a) of the uppermost intermediate part (320) extends via the passage into the wider lowermost chamber section (321b) of the lowermost intermediate part (321), while the disc-shaped body (320b) is fitted radially into the wider chamber section (321b) and the spiral spring (322) is located around the pin (320a) and extends from the upper side of the disc-shaped body (320b) into the narrower uppermost chamber section (321a). As the disc-shaped body (320b) can be displaced vertically in the wider chamber section (321b), the lowermost pulley (31) can also be displaced vertically relative to the uppermost pulley (30).
(31) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) and the lowermost pulley cord (5) on the lowermost pulley (31) that is sufficient to displace the lowermost pulley (31) to the furthest possible position relative to the uppermost pulley (30). In this position (shown in
(32) Under certain operating conditions, the return spring (11) may (temporarily) exert a reduced downward force on the heddle (10), or a blocking in the motion system above the heddle (10) or the inertia of the elements in the motion system may result in the tension of the return spring (11) not being (completely) transmitted, so that it could no longer be guaranteed that the cords (4), (5), (9) of the motion system could be kept taut if there were no tensioning element. Due to the presence of the pulley element (3) in the form of a tensioning element, this can be prevented as follows. Due to the reduced tractive force of the return spring (11), the downward force on the lowermost pulley (31) also becomes smaller, and this lowermost pulley (31) is displaced upward relative to the uppermost pulley (30) under the force of the spiral spring (322). The body (320b) of the uppermost intermediate part (320) is thereby displaced downwards into the wider chamber section (321b) of the lowermost intermediate part (321), to a new position in which the uppermost (30) and lowermost pulley (31) are closer together.
(33) This relative displacement of the uppermost (30) and lowermost pulley (31) reduces the vertical distance (A) between the uppermost (30) and lowermost pulley (31) from the maximum distancethe situation in
(34) The principle of a two-piece intermediate section (32) is applied also in the second embodiment of the pulley element (3) designed as a tensioning element, whereby both intermediate parts (323), (324) can be displaced relative to one another between two positions with different distances (A) between the pulleys (30), (31), and whereby a spring element (325) ensures that the pulleys (30), (31) are forced into the relative position with the minimum distance (A).
(35) Here the one intermediate part is an arm (323) that is connected at one end to the lowermost pulley (31), and at the other end has a recess (323a, 323e) consisting of two parts with different widths. The wider uppermost part (323a) transitions step-wise into the narrower lowermost part (323e) of the recess, so that two transverse edges (323b) are formed which border the lower end of the wider part (323a) of the recess. This wider part (323a) is bordered at the side by two parallel edges (323c) which transition into an arc-shaped upper edge. These parallel edges (323c) have projections (323d) facing towards one another that are only indicated in
(36) The other intermediate part is a sliding body (324) to which the uppermost pulley (30) is pivotably connected, and which is located in the wider uppermost part (323a) of the recess. The width of the sliding body (324) corresponds to the width of the wider part (323a) of the recess, while the sliding body (324) has a smaller height so that it is displaceable vertically in this part (323a) of the recess. The side edges of the sliding body (324) are shiftably restrained against the above-mentioned projections (323d).
(37) The narrower part (323e) is bordered at the lower end by an end edge (323f). Between the underside of the sliding body (324) and this end edge (323f) is a spring element (325) that is designed as an elastically deformable element with a zigzag-shaped form that is made, for example, of plastic. The non-deformed condition of this spring element (325) can be seen in
(38) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) and the lowermost pulley cord (5) on the lowermost pulley (31) that is sufficient to displace the lowermost pulley (31) to the furthest possible position relative to the uppermost pulley (30). In this position (shown in
(39) By analogy with the first embodiment, the presence of this pulley element (3) therefore prevents the vertical parts of the cords (4), (5), (9) not remaining taut in the event of a reduced tractive force of the return spring (11). This reduced tractive force here naturally also results in a reduced downward force on the lowermost pulley (31), so that the uppermost (30) and lowermost pulley (31) are displaced towards one another by the force of the spring element (325). The sliding body (324) is thereby displaced downwards into the wider part (323a) of the recess into a new position in which the uppermost (30) and lowermost pulley (31) are closer together.
(40) This relative displacement of the uppermost (30) and lowermost pulley (31) reduces the vertical distance (A) between the uppermost (30) and lowermost pulley (31) from the maximum distancethe situation in
(41) The principle described above is also applied in the third embodiment. Here the intermediate section (32) consists of two elongated connecting pieces (326), (327) that are pivotably connected to a respective pulley (30), (31). The two connecting pieces extend in a straight line in the vertical direction of the motion system and are joined to one another. The uppermost connecting piece (326) has a T-shaped coupling element (326a, 326b) that extends downwards beyond the free end of the connecting piece. The coupling element has a neck (326a) and an attached head piece (326b). The lowermost connecting piece (327) has an internal space (327a) in the vicinity of the free end that is limited at its upper end by an upper wall (327b) and at its lower end by a lower wall (327c). The internal space (327a) is accessible via a passage in the upper wall. The neck (326a) extends via this passage into the internal space (327a) while the head piece (326b) is located into the internal space (327a). This connection also allows a relative displacement of the pulleys (30), (31) in the vertical direction.
(42) Between the two pulleys (30), (31) is a one-piece spring body (328) with two elastically deformable flanks (328a), (328b) that form the connection between an uppermost bridge section (328c) and a lowermost bridge section (328d). The uppermost bridge section (328c) is connected to the uppermost pulley (30) while the lowermost bridge section (328d) is connected to the lowermost pulley (31). The non-deformed condition of this spring body (328) can be seen in
(43) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) and the lowermost pulley cord (5) on the lowermost pulley (31) that is sufficient to displace the lowermost pulley (31) to the furthest possible position relative to the uppermost pulley (30). In this position (shown in
(44) By analogy with the function of the first and second embodiment, a smaller downward force on the lowermost pulley (31) will result in the spring body (328) springing back so that the uppermost (30) and lowermost pulley (31) are displaced towards one another. The head piece (326b) is thereby displaced downwards into the internal space (327a) into a new position in which the uppermost (30) and lowermost pulley (31) are closer together. This relative displacement of the uppermost (30) and lowermost pulley (31) reduces the vertical distance (A) between the uppermost (30) and lowermost pulley (31) from the maximum distancethe situation in
(45) In a third possibility the jacquard device comprises motion systems with a harness connector (8) that is designed as a tensioning element. The harness connector (8) consists of a male connector part (81) connected to a pulley cord (5) and a female connector part (82) connected to one or more harness cords (9). These two connector parts (81), (82) can be coupled together to form the connection between the pulley cord (5) and the harness cords (9). The male connector part (81) comprises a predominantly cylindrical base (81a) that transitions into an elongated stem (81b) on which an elastically deformable head (81c) is formed at its end. The female connector part (82) comprises a locating space (820a) for the head (81c) of the male connector part (81) that is accessible via a channel that extends from one end of the connector part (82) and terminates in the locating space (820a). At the other end the female connector part (82) has a hook (821c) for the connection to one or several harness cords (9) (not shown in
(46) The stem (81b) of the male part (81) can be moved via the channel into the locating space (820a) until the head (81c) is in the intended coupling position in the locating space (820a) so that the male (81) and the female connector part (82) are coupled.
(47) In the male part (81) there is a cylindrical channel (81d, 81e, 81f, 81g) extending axially from one end that has four parts with different diameters that transition step-wise into one another: a first part (81d) that extends from the end, a second part (81e) whose diameter is larger than that of the first part (81d), a third part (81f) whose diameter is larger than that of the second part (81e) and which forms a motion space for the cylindrical body (84) that is connected to the pulley cord (5), as explained further below. Finally there is a fourth part (81g) whose diameter is smaller again than that of the third part (81f). The step-wise changes in diameter form inclined walls in the channel.
(48) The pulley cord (5) extends via the passage forming the first (81d) and the second part (81e) of the channel and into the widest third part (81f) where the pulley cord (5) is connected to a cylindrical body (84) located radially in this third part (81f) of the channel. The height of the cylindrical body (84) is smaller than the height of the third part (81f) of the channel, while the diameter of the cylindrical body (84) is only slightly smaller than that of the channel, and in any case larger than the diameters of the second (81e) and fourth part (81f) of the channel. The cylindrical body (84) can therefore be displaced up and down in the third part (81f) of the channel, between a lowermost position in contact with the inclined walls (81h) that border the lower end of the third part (81f) and an uppermost position in contact with the inclined walls (81i) that border the upper end of the third part (81f).
(49) Around the pulley cord (5) is a spiral spring (83) that extends axially from the upper side of the cylindrical body (84) into the second part (81e) of the channel where the uppermost end of the spiral spring (83) is in contact with the inclined wall (81j) that borders the upper end of the second part (81e) of the channel.
(50) As the cylindrical body (84) can be displaced vertically in the third part (81f) of the channel, the anchoring point of the pulley cord (5) can be displaced vertically relative to the male connector part (81).
(51) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) and the female connector part (82) on the male connector part (81) that is sufficient to displace the cylindrical body (84) in the third part (81f) of the channel against the spring force of the spiral spring (83), to its uppermost position in contact with the inclined walls (81i) that border the upper end of the third part of the channel (81f). In this state (shown in
(52) The spiral spring (83) permanently exerts a tensioning force so that a downward-directed force is exerted on the cylindrical body (84). The spiral spring (83) therefore acts here like a pressure spring.
(53) With a reduced tractive force of the return spring (11), the downward force on the male connector part (81) also becomes smaller, and this cylindrical body (84) is displaced to a lower position in the third part of the channel (81f) under the force of the spiral spring (83). This type of condition is shown in
(54)
(55) The end part (821) comprises a pin (821a) that has a disc-shaped body (821b) with a larger diameter at the end, and a spiral spring (83) around the pin (821a). In the basic part (820) under the locating space (820a) is a motion chamber (820b) that is accessible via a channel from the lowermost end of the basic part (820). The pin (821a) of the end part (821) extends via this channel into the motion chamber (820b). The disc-shaped body (821b) is located in the motion chamber (820b) and is displaceable axially in this space. The spiral spring (83) is supported at one end on an inclined wall (820c) and at the other end is in contact with the underside of the disc-shaped body (821b) and exerts an upward-directed force on the disc-shaped body (821b). The spiral spring (83) is a pressure spring.
(56) As the disc-shaped body (821b) can be displaced vertically in the motion chamber (820b), the anchoring point of the harness cord (9) can be displaced vertically relative to the basis part (820) of the female connector part (82), and hence also relative to the anchoring point of the pulley cord (5).
(57) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) on the end part (821) that is sufficient to displace the disc-shaped body (821b) in the motion chamber (820b) into its lowermost position in the motion chamber (820b) against the spring force of the spiral spring (83). In this state (shown in
(58) The spiral spring (83) permanently exerts a tensioning force so that an upward-directed force is exerted on the cylindrical body (821b). In the event of a reduced tractive force of the return spring (11), the downward force on the end part (821) also becomes smaller, and the disc-shaped body (821b) is displaced to a higher position in the motion chamber (820b) under the force of the spiral spring (83). The most extreme position in which the disc-shaped body (821b) has been displaced against the upper wall of the motion chamber is shown in
(59) In a fourth possibility the jacquard device comprises motion systems with a pulley cord (5) that is designed as a tensioning element. The pulley cord (5) consists of two separate cord sections (5a), (5b) that are connected to a respective end (50a), (50b) of a spiral spring (50) and to a respective end part (51a), (51b) of an intermediate cord (51) that extends through the axial space inside the spiral spring (50). In order to form the connections to the spiral spring (50), a loop is formed at the end of each cord section (5a), (5b) by bending over the cord end and fastening it to the parallel run of the same cord using a clamping element (52). The hook-shaped ends (50a), (50b) of the spiral spring (50) are hooked into the loops thus formed. The end part (51a), (51b) of the intermediate cord (51) are fastened using the same clamping elements (52) to the respective cord sections (5a), (5b) of the pulley cord (5).
(60) The length of the intermediate cord (51) between the anchoring points is such that the intermediate cord (51) is not taut when the spiral spring (50) is in its relaxed state (see
(61) Under normal operating conditions, the return spring (11) exerts a downward force via the harness cord (9) on the lowermost cord section (5b) of the pulley cord (5) that is sufficient to displace the cord section (5b) downwards relative to the uppermost cord section (5a) against the spring force of the spiral spring (50). In this state (