The present invention relates to a set of a rapier bar for weaving machines, comprising a toothed rack, which is made of fibre-reinforced plastic, with a plurality of teeth, and a gear wheel for these weaving machines, for engaging on this rapier bar.

Rapier weaving machines comprise one or more rapiers for inserting weft threads in a shed between warp threads, to form a fabric. These rapiers are mounted on rapier bars and are moved by means of this rapier bar through the shed in the rapier weaving machine. The rapier bars to which this invention relates are provided with a toothed rack for driving this motion.

The most important function of the rapier is to position the weft.

On the one hand this weft has to be positioned correctly in the weft direction. For the drive, the teeth of a gear wheel must be able to engage accurately in the teeth of the toothed rack of the rapier bar. For guiding and carrying the rapier, the rapier bar must be configured to be sufficiently stiff, straight and flat.

Furthermore, this weft has to be positioned correctly in the vertical direction and in the warp direction. For guiding and carrying the rapier, the rapier bar must also in this case be configured to be sufficiently stiff, straight and flat.

In order to be able to produce ever faster weaving machines, there is a need to make said rapier bar lighter, yet stiff enough to ensure correct positioning of the rapier.

An example of a rapier bar with a toothed rack that is mounted in a holder profile is known from DE 1 535 491 Al. In this case the toothed rack is glued in the holder profile, but this is quite a weak joint. In DE 1 710 293 Bl it is therefore proposed to provide the toothed rack with side walls, so that a better glued joint can be produced. However, this has the drawback that extra material is required for these side walls of the toothed rack, so that the assembly of toothed rack and tooth profile is heavier.

In EP 0 394 639 Al and DE 101 20 954 Al, the toothed racks are not provided with side walls. By means of a die, the toothed racks are formed from a plate, so that they are given a wavy profile. In addition they are provided with well-considered fibre reinforcement so as to be able to make the whole rapier bar lighter. As stated in EP 0 394 639 Al, a toothed rack of this kind is still mounted in a holder profile to ensure the necessary stiffness.

In DE 196 08 254 Al, the bottom of the holder profile is omitted so as to be able to produce a lighter rapier bar. However, said rapier bar is quite complex, and expensive to make.

In W02020/148605A1, an alternative lighter rapier bar is described and illustrated.

The aim of the present invention is to provide another alternative lighter rapier bar.

This aim is achieved by providing a set of: a rapier bar for weaving machines, comprising a toothed rack, which is made of fibre-reinforced plastic, with a plurality of teeth; and a gear wheel for these weaving machines, for engaging on the rapier bar; wherein the teeth comprise basic teeth and adapted teeth and wherein said adapted teeth are mounted in a middle zone centrally in the toothed rack, from which, seen relative to said basic teeth of the toothed rack that are mounted in adjacent zones, adjacent to the middle zone, material is omitted at least partially on the tooth flanks, so that the contact ratio, as determined with the finite element method, remains greater than 1.2.

By omitting material on the tooth flanks, at the level of this omitted material, the contact surface between teeth of the gear wheel and teeth of the toothed rack will be reduced during use thereof in a weaving machine. In order to guarantee good, durable operation, it is important that at any moment, teeth will still engage with one other.

The contact ratio is a measure of the overlapping action of the teeth of the toothed rack relative to the teeth of a gear wheel engaging thereon.

As is known, in practice, for plastic teeth this contact ratio is greater than the contact ratio E _a calculated with the known formula where: dai is the diameter of the tip circle of the gear wheel; dbi is the diameter of the base circle of the gear wheel; h _a 2 is the tip height of the teeth of the toothed rack;

- xi is the coefficient of profile displacement of the gear wheel; m is the module of the gear wheel; di is the diameter of the pitch circle of the gear wheel; and a is the pressure angle.

This theoretical calculation is thus not directly applicable to plastic teeth.

Instead, the contact ratio for plastic teeth can, as is known, be verified using the finite element method.

This contact ratio can be determined approximately, as described in T. Jabbour, et al., Real contact ratio and tooth bending stress calculation for plastic/plastic and plastic/steel spur gears, Mechanics & Industry 22, 30 (2021). This approximate calculation was also verified in this article using the finite element method.

When material is omitted at the level of contact surfaces between teeth of the rapier bar and teeth of the gear wheel, the contact ratio should of course be reduced accordingly.

Toothed racks of known rapier bars are always designed so that the contact ratio is somewhat greater than 1.2.

With omission of material on the tooth flanks, the contact ratio may remain unchanged, or may decrease. When this contact ratio is decreased on omission of this material, it is important that the material is only removed to the extent that this contact ratio in the middle zone still remains greater than 1.2. In the adjacent zones the contact ratio is then definitely greater than 1.2.

Research has shown that the omission of material in this middle zone does not hamper the proper operation of a set of said rapier bar and gear wheel in a weaving machine. Figs. 2-4 show, in schematic representations in a graph, in each case on a horizontal axis the number of the teeth (T) in a toothed rack, so that this represents the toothed rack seen over the length. Fig. 4 shows, on a vertical axis, the wear (W) of these teeth (T) in mm after a certain time has passed. It is clear that the teeth (T) in a middle zone (C) are less liable to wear than teeth (T) in the adjacent zones (O). It can be seen in Fig. 2 that the accelerations (A) - plotted on the vertical axis in m/s ² - to which these teeth (T) are subjected are somewhat higher in these adjacent zones (O) than in the middle zone (C). These higher accelerations (A) occur at lower speeds (V) of the toothed rack, as can be seen in Fig. 3, where the speed (V) in m/s is plotted on the vertical axis.

In a preferred embodiment, the carrying capacity of the teeth in the middle zone is at least 50.5% of the carrying capacity of the basic teeth in the adjacent zones, preferably at least 51%, even more preferably at least 52% and very preferably at least 55%.

Regarding the carrying capacity, preferably both the root stress OF and the Hertzian contact stress GHZ should be taken into account.

The root stress OF of the teeth in the middle zone is then preferably at least 50.5% of the root stress OF of the basic teeth in the adjacent zones, more preferably at least 51%, even more preferably at least 52% and very preferably at least 55%.

It is also known for this root stress OF that with regard to plastic teeth, this cannot be calculated directly with the classical formulae from the standards for toothed gearing. For plastic teeth, this root stress OF may however be calculated as described in T. Jabbour, et al., Real contact ratio and tooth bending stress calculation for spur gears, Mechanics & Industry 22, 30 (2021), with: where:

- Wtr is the transverse load; an is the pressure angle; hr is the bending moment arm;

- F is the face width of the teeth of the toothed rack; and

SF is the thickness of the teeth of the toothed rack in the critical section (whose tangent to the tooth neck makes an angle of 30° with the tooth centre line).

Furthermore, the Hertzian contact stress GHZ of the teeth in the middle zone is then preferably at least 50.5% of the Hertzian contact stress GHZ of the basic teeth in the adjacent zones, more preferably at least 51%, even more preferably at least 52% and very preferably at least 55%. It is also known, for this Hertzian contact stress GHZ, that with regard to plastic teeth, this cannot be calculated directly with the classical formulae from the standards for toothed gearing.

However, for plastic teeth, the Hertzian contact stress GHZ can be calculated as described in H.G.H. van Melick, Tooth-Bending Effects in Plastic Spur Gears, Geartechnology September/October 2007, 58-66, with: where: ais is the load distribution factor, which is the percentage of the load that is carried by the tooth for which the Hertzian contact stress is being calculated;

- F is the force; where E _g and E _p denote the elastic modulus and u _g and Up are the Poisson ratios of the gear wheel and the toothed rack, respectively;

- b is the width of the teeth of the gear wheel; and Rtip is the tip radius of the gear wheel.

The middle zone preferably occupies at most 40% of the total length of the toothed rack. More preferably this middle zone occupies at least 20% of the total length of the toothed rack.

The rapier bar is more preferably constructed symmetrically.

In a first specific embodiment the omitted material is omitted over the full width of the adapted teeth.

Then complete contact surfaces between these adapted teeth and teeth of the gear wheel are omitted. The number of teeth of the toothed rack that are in contact with teeth of the gear wheel is decreased in the middle zone relative to the adjacent zones. The contact ratio is also decreased as a result.

The remaining tooth profile then preferably remains equal over the full width of the teeth, but may alternatively also vary, seen in the transverse direction.

Even more specifically, the omitted material amounts to the complete adapted teeth. Preferably said basic teeth are then mounted in the middle zone, alternating with the adapted teeth. Corresponding tooth spaces in a toothed rack of this kind are then fused to a broadened tooth space, extending between remaining basic teeth.

In production, it is a simple matter to omit complete teeth, for example during production in a mould, omitting a complete tooth by filling the cavity for forming said tooth in the mould.

Alternatively, in the middle zone, material is omitted for alternating tooth flanks for successive adapted teeth.

In a simple variant, the remaining tooth profile is the same, seen in the transverse direction. However, it is also possible to vary the width of the adapted teeth in omitted tooth flanks. Thus, for example seen over the width of an adapted tooth, the one tooth flank may be omitted on a left side of the adapted tooth, whereas on the right side of the adapted tooth the other tooth flank is omitted.

In a further specific embodiment, the omitted material seen in the transverse direction occupies a central zone of the adapted teeth.

The contact surface between these adapted teeth and teeth of the gear wheel is then decreased. The flank width of these adapted teeth is decreased relative to the flank width of basic teeth.

Preferably, on either side of the central zone of the adapted teeth, the tooth profile of these adapted teeth then remains unchanged.

In this way, in the middle zone, one and the same number of teeth of the toothed rack then remains in contact with the gear wheel as in the adjacent zones. The contact ratio remains the same in these zones. Alternatively, however, this tooth profile may also still vary, seen over the width of the adapted teeth, for example by omitting material on the tooth flanks on either side of the central zone. More specifically, for example material may also be omitted on alternating tooth flanks on both sides.

A rapier bar of a set according to the present invention may be produced in various known ways, for example such as using the production methods for manufacturing the rapier bars according to the cited prior art. The omitted material may for example be omitted in post-processing, or in production of a toothed rack in a mould, an adaptation of this mould may be provided, or in injection moulding of a toothed rack, injection moulding of this material could be avoided, etc.

In a preferred embodiment, the rapier bar comprises a holder profile, which demarcates a mounting cavity with a bottom and vertical walls relative to the bottom. The toothed rack is then arranged in the mounting cavity.

This toothed rack may for example be manufactured separately by injection moulding and may be glued in the holder profile. Alternatively, it may for example be manufactured as described and illustrated in W02020/148605A1.

In the case of a rapier bar with a said holder profile, this holder profile is preferably made of fibre-reinforced plastic.

The gear wheel of a set according to the present invention is preferably made of metal.

Said gear wheel could alternatively for example also be made manufactured from a suitable plastic.

Furthermore, the aim of the present invention is also achieved by providing a weaving machine that comprises a set according to the present invention.

The present invention will now be explained in more detail on the basis of the following detailed description of a preferred embodiment of some rapier bars according to the present invention. The purpose of this description is exclusively to give illustrative examples and to present further advantages and features of the invention, and so is not to be interpreted as a limitation of the field of application of the invention or of the patent rights claimed in the claims.

In this detailed description, reference numbers are used for referring to the appended drawings, where

- Fig. 1 shows a set of a gear wheel and a rapier bar according to the present invention in side view;

- Fig. 2 shows schematically, in a graph, the acceleration to which a toothed rack from a set according to the invention is subjected in use in a weaving machine, distributed over the length thereof;

- Fig. 3 shows schematically, in a graph, the speed of a toothed rack from a set according to the invention in use in a weaving machine, distributed over the length thereof;

- Fig. 4 shows schematically, in a graph, the wear of a toothed rack from a set according to the invention in use in a weaving machine after a period of time;

- Fig. 5 shows a toothed rack from a set according to the invention in crosssection;

- Fig. 6 shows a holder profile for a rapier bar from a set according to the invention in cross-section;

- Fig. 7 shows an embodiment of a rapier bar from a set according to the present invention with a toothed rack from Fig. 5 and a holder profile from Fig. 6 in cross-section;

- Fig. 8 shows half of a toothed rack of a set according to the present invention in cross-section;

- Fig. 9 shows a part of the toothed rack from Fig. 8 in more detail;

- Fig. 10 shows the part of the toothed rack from Fig. 9 in top view;

- Fig. 11 shows a part of an alternative embodiment of a toothed rack of a set according to the present invention in cross-section;

- Fig. 12 shows the part from Fig. 11 in perspective;

- Fig. 13 shows a part of an alternative embodiment of a toothed rack of a set according to the present invention in cross-section;

- Fig. 14 shows the part from Fig. 13 in perspective. The set shown in Fig. 1 comprises a rapier bar (1) and a gear wheel (2) for engaging in this rapier bar (1) in order to drive it in a weaving machine.

As shown in Fig. 7, the rapier bar (1) comprises a holder profile (4) in which a toothed rack (8) is mounted.

The holder profile (4) is made of fibre-reinforced plastic. This is possible, for example, by production methods by which holder profiles from said prior art are manufactured.

For example a thermoset or a thermoplastic may be selected as plastic, e.g. epoxy, polyester, vinyl ester, polyurethane, etc.

As reinforcing fibres, for example carbon fibres may be selected, and/or aramid fibres and/or glass fibres. These reinforcing fibres are preferably arranged mainly in the longitudinal direction of the holder profile (4), in a fibre fraction between 50% and 80%. Optionally a fraction of reinforcing fibres may also be arranged at an angle relative to the longitudinal direction. This fraction is then preferably between 40% and 55%.

Optionally, during manufacture, a peel-off layer of nylon or polyester fabric may be applied on the surface. A thin polymer layer may also be co-extruded on the holder profile (4). Reinforcing fibres in directions other than the longitudinal direction may thus be arranged in the form of woven or nonwoven cloth on the outer side of the holder profile (4) and/or in the mounting cavity (5) on the inside of the holder profile (4), in order to increase the bending stress of the holder profile (4). This fibre- reinforced cloth may for example be 0.15 mm thick, so that on applying said cloth, on the inside and on the outer side of a basic profile of 0.8 mm thick, together a holder profile (4) of 1.1 mm thick can be formed.

The holder profile (4) comprises a bottom (6) and two vertical side walls (7) on either side of the bottom (6), which together demarcate a mounting cavity (5). The toothed rack (8) is fitted in this mounting cavity (5). This may for example be done by gluing.

Fig. 8 shows a half toothed rack (8). A half toothed rack (8), made identically, is fitted abutting on the half shown in the mounting cavity (5), with the part of the middle zone (A) shown abutting on each other. In this way, the toothed rack (8) is built up symmetrically and mounted in the holder profile (4).

The toothed rack (8) is also made of fibre-reinforced plastic. This may also be for example by production methods with which toothed racks from the cited prior art are manufactured.

As plastic, preferably thermoplastic material is selected, for example such as polyamide 6, polyamide 6.6, polyamide 12, PPA, PPS, PEEK.

As reinforcing fibres, preferably carbon fibres are selected. In the teeth (9, 10, 11, 12, 13) themselves, these reinforcing fibres are applied with arbitrary orientation. For wear resistance, these reinforcing fibres are aligned tangentially to the surface, but with arbitrary orientation.

The gear wheel (2) is made of metal. More specifically, for example case-hardening steel (16Mcr5) may be selected for said gear wheel for a weaving machine for carpet weaving and for example a fully hardened steel (42CrMo4V) may be selected for said gear wheel for a weaving machine for velvet.

Said gear wheel (2) could alternatively for example also be made of a suitable plastic.

The toothed rack (8) comprises in each case a middle zone (A), centrally in the toothed rack (8) and adjacent zones (B), which are positioned on either side of the middle zone (A). The middle zone (A) accounts for at least 20% and at most 40% of the total length of the toothed rack (8).

The toothed rack (8) also comprises in each case basic teeth (9) and adapted teeth (10, 11, 12, 13). Basic teeth (9) are fitted in the adjacent zones (B). The middle zone (A) comprises adapted teeth (10, 11, 12, 13), which may optionally be interchanged with basic teeth (9).

At ends of the toothed rack (8), in outer zones, besides the adjacent zones (B), optionally teeth may be omitted, for fastening a rapier (3) on the rapier bar (1).

The toothed rack (8) is preferably built up symmetrically.

For the adapted teeth (10, 11, 12, 13), in each case seen relative to the basic teeth (9), material (14) is omitted at least partially on the tooth flanks (15, 16). This material (14) is omitted in such a way that when the contact ratio is affected, this contact ratio nevertheless always remains greater than 1.2. Moreover, the material (14) is in each case omitted in such a way that the carrying capacity of the teeth (9, 10, 11, 12, 13) in the middle zone (C) is still about 55% of the carrying capacity of the basic teeth

(9) in the adjacent zones (O). In a comparable manner, by omitting more material or less material, alternative embodiments are also elaborated wherein the carrying capacity of the teeth (9, 10, 11, 12, 13) in the middle zone (C) is at least 50.5% or at least 51%, or at least 52% or even at least 55% of the carrying capacity of the basic teeth (9) in the adjacent zones (O).

In the first embodiment illustrated (see Figs. 8-10), in each case a basic tooth (9) is mounted alternately in the middle zone (C) and the material (14) of a following tooth

(10) is omitted completely, so that an extended tooth space (18) is formed, which extends between 2 basic teeth (9). The middle zone (C) may furthermore also comprise one or more basic teeth (9) following each other, which demarcate one and the same tooth space (17), such as the basic teeth (9) in the adjacent zones (O). Because in this embodiment, for the adapted teeth (10), the complete tooth (10) is omitted, the corresponding tooth flanks (15, 16) and therefore also the complete contact surfaces with the gear wheel (2) are also lost. The number of teeth (9) that are in contact with teeth (20) of the gear wheel (2) is decreased in the middle zone (C) relative to the adjacent zones (O). The contact ratio is also decreased as a result.

In the second embodiment illustrated (see Figs. 11-12), for successive adapted teeth (11, 12), material (14) is omitted on alternating tooth flanks (15, 16). Moreover, alternating ordinary tooth spaces (17) and extended tooth spaces (19) are delimited by these adapted teeth (11, 12). The rest of the tooth profile remains the same in each case over the full width of the teeth (11, 12). Also in this embodiment, with the omitted material (14), the corresponding tooth flanks (15, 16) and therefore also the complete contact surfaces with the gear wheel (2) are lost. Here too, the contact ratio is decreased accordingly.

In the third embodiment illustrated (see Figs. 13-14), material (14), seen in the transverse direction, is omitted in a central zone of the adapted teeth (13). The contact area between these adapted teeth (13) and teeth (20) of the gear wheel (2) is decreased. The flank width of these adapted teeth (13) is decreased relative to the flank width of the basic teeth (9). On either side of the central zone of the adapted teeth (13), there is no further change in tooth profile. In the middle zone (C), in this third embodiment, one and the same number of adapted teeth (13) remains in contact with teeth (20) of the gear wheel (2) as the number of basic teeth (9) that remain in contact with teeth (20) of the gear wheel (2) in the adjacent zones (O) in use. The contact ratio remains the same in the different zones (C, O).

In alternative embodiments, combinations may also be made from the various embodiments shown and/or the tooth profile may also vary over the width of the adapted teeth (10, 11, 12, 13).