CA1052550A - Process for the manufacture of pile fabric - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention provides a process for the manufacture of a pile fabric by severing a selection of yarn strands appearing on one of the faces of at least one sheet of fabric, in which the severing is performed by means of a focused laser beam, characterised in that the zone of focus of the said beam is brought successively into contact with a determined portion of each of the said strands, on each occasion for a period of time sufficient to cause combustion of at least part of the fibres forming said strands.
The present invention also provides a device for the production of a pile fabric including means for producing a focused laser beam; guide means for successively placing the zone of focus of the beam into contact with the determined port-ions of strands, a selection of yarn strands appearing on one of the faces of at least one sheet of fabric, and drive means for moving the focus of the beam relative to the said determined strand portions.

Description

lOS;~550 The present invention relates to a process and device for the manufacture of pile fabric.
The cutting of yarn strands bonded to a fabric sheet is required in the manufacture of various piled fabrics. Among these may be mentioned in particular velvet, a combination known comm-~ 1 de r ~h~ ~a de rn~ercially~as VELCRO and comprising a hooked fabric for fastening to a looped fabric, and certain machine manufactured carpets.
In each case, the cutting of these strands comes up against pro-blems of knife wear.
It has recently been proposed to use a laser beam for cutting determined portions of yarn strands to form hooks on a band of looped fabric of approximately 5 cm in width. Two var-iations of the proposed solution are envisaged. One of these variations consists of transmitting a laser beam transversely to the band of fabric, focused in the central zone of the band at any given instant to cut one of the branches of the loop. The other of these variations consists of directing the laser beam ~ in the direction of the band and interposing a perforated mask to allow only part of the beam to pass. The results obtained by these processes are very mediocre as a large part of the energy of the laser beam is lost, so that in the case of plastics material the yarn is cut by fusion rather than by combustion. Consequently, the cut is not clean and the efficiency is very low. Moreover, such processes are suitable only for a very narrow band and are consequently unusable for wider fabrics such as those produced for clothes manufacture, such as velvet.
The cutting of a piece of fabric to obtain velvet constitutes one of the most delicate operations in the manufacture of this material. In the case of the finest velvets this operation is carried out with the aid of a knife fixed to a guide engaged in a column of fabric races or floats.
These columns consist of yarn strands disposed as - 1 - ~

lOS'~S50 transverse loops aligned to form c~lumns or ribs which are disposed side by side on the surface of the fabric sheet. An endless band is formed by sewing the two ends of one piece of fabric, in such a manner that the end of each column coincides with the end of an adjacent column, the knife is introduced at one end of a continuous column so formed, and the fabric band is made to move along so that all the transverse strands are cut. This is repeated until all the columns of races have been cut. This operation involves about twenty hours of ~ork for a piece of size 300 m x 0.70 m. The normal wear of the knife sometimes causes the loss of the piece of fabric, or at least its sale as a remnant. In this respect, a knife change during the cutting of any one piece of fabric leads to an apparent modification of the velvet reflection. The resultant loss of profit is very considerable.
This method of cutting velvet also suffers from not being able to be used in the cutting of synthetic yarn, so that nearly all the velvet at present produced in this manner is cotton, the knives used being unsuitable for cutting a piece of synthetic fabric. In addition to these disadvantages, the use of a knife constitutes an obstacle to increase of cutting speed, which is limited to between 3 and 5 m/s.
The object of the present invention is to at least partly remedy the disadvantages of the aforementioned solutions.
To this end, the present invention firstly provides a process for severing a selection of yarn strands appearing on one of the faces of at least one sheet of fabric, in which the sever-ing is performed by means of a focused laser beam, characterised in that the zone of focus of the said beam is brought successively into contact with a determined portion of each of the said strands, on each occasion for a period of time sufficient to cause combust-tion of at least part of the fibres forming said strands.

lOS~SSo The present invention also provides a device for accomplishing the process, characterised in that it comprises guide means for successively placing the zone of focus of the beam into contact with the determined portions of said strands, and drive means for moving the focus of the beam relative to the said determined strand portions.
The accompanying drawing is a diagrammatic represent-ation of way of example, of two embodiments of the process accord-ing to the invention.
Figure 1 is an elevation of a device for accomplishing one of these methods.
Figure 2 is a more detailed sectional view on the line II-II of Figures 1 or 3.
Figure 3 is a sectional view on the line III-III of Figure 2.
Figure 4 is a block diagram of the fluid control cir-cuit.
Figure 5 is a control diagram for the block diagram of Figure 4.
Figure 6 is a very diagrammatic representation of a modified detail of the first embodiment.
Figure 7 is an elevation of a device for accomplishing the second of these methods.
Figure 8 is a sectional view on the line VIII-VIII of Figure 7.
Figure 1 is a very diagrammatic illustration of a cutt-ing device for columns of races of a fabric T to obtain velvet.
This device is mounted on the frame of a well known machine des-igned to drive an endless band of fabric. This machine is shown only by its frame 1 without the drive mechanism for the band of fabric, as this mechanism does not fall within the scope of the present invention. It is sufficient for its understanding to 105~550 note that the direction of movement of the fabric is perpendicular to the plane of Figures 1 and 3, and is in the direction of its warp, although this example must in no way be considered limiting as the process described is equally applicable to the case in which the races are cut in the weft direction.
A pair of parallel tubular rails 2 (Figures 2 and 3) is fixed to the machine frame 1 by two lateral uprights 3 and 4 (Figure 1). This pair of rails carries a slidably mounted carr-iage 5 controlled by a worm 6 (Figures 1 and 2) driven by a pneumatic motor 7 (Figure 1). The carriage 5 is formed from two side plates 8 and 9 assembled with a certain gap therebetween by means of cross bars 10 and bolts 11. As shown in particular in Figure 2, the fabric band T is gripped between two pairs of rollers Rl, R2 and R3, R4 respectively. These rollers form the drive rollers for the fabric T and their respective speeds are chosen in such a manner that the drawing rollers Rl, R2 rotate slightly faster than the tensioning rollers R3, R4, so as to - produce a tension in the fabric T and so hold it against the shoes 8a, 9a.
The carriage 5 also comprises a pair of parallel tubular rails 12 which serve to guide a second carriage 13 kept in a mean position by two very weak centering counter springs 14 and 15 which operate in compression between the side pieces 8 and 9 respectively and the parallel neighbouring edge of the second carriage 13. As a modification, these springs could be elimin-ated as will be seen hereinafter. The position of the carriage 13 is detected by a fluid detector in the form of a block 16 with a milled slot 16a in which a screen 17 rigid with the carriage 13 engages. A discharge aperture is provided in the rim 16_ of the detector 16 and a receiving aperture is formed opposite the discharge aperture in the rim 16c of the detector. The quantity of air received by the receiving aperture is a function of the lQ5~550 penetration of the screen 17 in the slot 16a, and consequently of the position of the carriage 13 relative to the carriage 5.
The processing of this slgnal will be explained hereinafter.
The second carriage 13 carries a convergent lens 18 located on the axis of one of the branches 19 of a T duct 20 (Figure 2), the horizontal branch 21 of which is held between the side plates 8 and 9 of the carriage 5. This horizontal branch 21 is connected to an opening 22 in the side plate 9. A mirror 23 disposed at the intersection of the branches 19 and 21 and at 45 to their respective axes is fixed to the side plate 8 by a support 24 and two bolts 25. The horizontal branch 21 and opening 22 are aligned along the axis of a laser beam produced from a laser 26 and transmitted by two mirrors 27 and 28 by way of two lenses 39a and 39b. The characteristics of the laser used will be discussed hereinafter.
A nozzle 48 connected to a source of pressurised fluid (not shown) directs a jet of this fluid into the focus zone of the lens 18.
The carriage 5 also comprises a guide and safety mechanism consisting of an arm 29 of U section, rotatable about a rod 30 and stressed by a tension spring 31. The free end of this arm carries a guide 32, a disengagement cam 33 and a stop 34 for a reference spring 35 fixed to the second carriage 13.
This cam is engaged between the branches of the U cross-section of the arm 29 and is retained by a peg 29a engaged in an oval through aperture 33a in the cam. The thickness of this cam is less than the distance deparating the two parallel branches of the U cross-section of the arm 29. Consequently the cam 33 and guide 32 have two degrees of freedom with respect to the arm 29, laterally and longitudinally. The cam 33 comprises a further two lateral guides 33b designed for engagement in an aperture between two guides 13_, and 13_ seen in particular in Figure 3. A bar 36 105'~550 is pivoted to the first carriage 5 and comprises at one end a stop tooth 37 and at the other end a cam follower 38 consisting of a roller.
It has been stated heretofore that the position of the carriage 13 is detected by the detector 16. The pressure signals measured downstream of the receiving aperture in the rim 16c are characteristic of the depth of penetration of the screen 17 in the slot 16a. This receiving aperture in the rim 16c (Figures 4 and 5) is connected to the inlet of an operational amplifier 40, the amplified signal of which operates an analogue servo-valve 41 which controls the pneumatic motor 7 driving the carriage 5 in one direction or the other by means of the worm 6 in such a manner as to re-centre the carriage 5 in relation to the carriage 13.
Figure 5 shows the fluid control diagram used for pro-cessi~g the fluid signal obtained by means of the detector 16.
The circuit comprises the detector 16 fed by a source of compressed air 42, a filter 43 and a pressure reducer 44. The pressure in the outlet lines of the detector 16 is amplified by the operation-al amplifier 40, the outputs of which are connected to the servo-valve 41. This latter is connected to the compressed air source 42 by way of a bistable valve 45 and a lubricator 46 which adds oil mist to the air. The bistable valve is connected to a control switch 47. The outputs from the analogue servo-valve are connect-ed to the variable speed pneumatic motor 7 which drives the worm 6.
As shown in Figure 2, the laser beam is concentrated by the lens 18 to form a spot directed on to the guide 32 when this is held in the working position by the bar 36. The guide 32 is designed to engage in a column of races of the fabric T, so that the races are brought with precision to the spot where the laser beam is concentrated almost instantaneously. The guide 32 remains in its working position as long as the pressure exerted in the 10~i~550 direction of the arrow F resulting from the resistance of the columns of fabric races against the guide 32 is substantially balanced by the resistance of the reference spring 35. If this pressure increases, for example due to damage to the guide or for any other reason, the force exerted in the direction of the arrow F increases suddenly and pushes the cam 33 in this direction.
The follower 38 is then raised by the cam 33, and the arm 2g, thus disengaged from the stop tooth 37, is pulled sharply by the spring 31 into the position shown by the dashed and dotted line.
Conversely, if this pressure reduces, the reference spring 35 pushes the cam 33 in the direction opposite F and likewise raises the follower 38. The arm 29 is again disengaged from the stop tooth 37 and leaves the guide 32 of the race column.
While the fabric T moves fast under the shoes 8a and 9a, the guide 32 is subjected to lateral movements of variable ampli-tude and frequency. As the fabric passes by at a speed of the order of several metres per second, it is easy to understand that the column of races in which the guide is enga~ed undergoes lateral movements which could range from some tenths of a mm to some cm. The purpose of the guide is to perfectly follow these movements. Because of the rigid connection between the second carriage 13 and guide 32, all the lateral movements of the guide 32 result in similar movements of the carriage 13. The inertia of this latter is evidently chosen to low as possible so as not to offer even the smallest resistance to lateral movements. As the carriage 13 is rigid with the lens 18, and the laser beam rays encountering this lens are parallel, the laser spot constantly follows the guide 32 and consequently cuts the fabric races pre-cisely, despite the lateral oscillations which it undergoes as it passes by. At the same time, the nozzle 48 feeds a jet of fluid, which may be air, water or a neutral gas. The purpose of this fluid is to evacuate the combustion gases which reduce the i(~S~SSO

efficiency of the focused laser beam.
As a consequence of the movements of the carriage 13, the pressure transmitted by the detector 16 to the amplifier 40 varies proportionally, so that the amplified signal which appears at one or other of the outlets of the amplifier 40 moves the servo-valve 41 in one direction or the other proportionally to the signal value. Consequently the pneumatic motor 7 (Figure 1) is driven in one direction or the other at a speed proportional to the signal, and this motor movement is transmitted to the worm 6 and carriage 5.
The inertia of the circuit means that the motor 7 reacts only with a certain delay. Assuming that the carriage 13 is driven with an oscillating movement of small amplitude and at a frequency of the order of 20 to 50 Hz for example, the carriage 5 remains practically immobile as its movement corresponds to the mean of the movements of the carriage 13. If the oscillation frequency reduces and the amplitude increases, the carriage 5 indeed moves but because of the delay the amplitude of the movement is very small. In contrast, every movement of the carriage 13, however small it may be and providing it is not oscillating, is followed by an identical movement of the carriage 5O Because of this the passage from one column of races to the neighbouring column is rigorously followed by the carriage 5. This indicates why the springs 14 and 15 are optional, the carriage 13 being in any case centered by the fluid system.
It has been calculated that the power of the laser spot remains practically unchanged providing the relative movement between the mirror 23 and lens 18 does not exceed 2 mm in one direction or the other. As the optical system formed by the lens 18 and guide 32 is rigid with the same mobile member, the carriage 13, the spot behaves exactly as if the tissue passed by without any lateral movement. The fluid control circuit for the carriage lV5;~550 5 guarantees that the distance between the axis of the heam of parallel rays reflected by the mirror 23 and the optical axis of the lens 18 does not exceed the aforementioned 2 mm, so that the power at the level of the laser spot is substantially constant.
The advantage of the two-carriage mechanism described lies in the fact that the rapid lateral oscillations of small amplitude are faithfully reproduced by the second carriage 13, which a filtering phenomenon is produced between the second carriage 13 and the carriage 5. As the laser beam is formed of parallel rays, as though the source was located at infinity, the relative movements between the mirror 23 and lens 18 have no influence on the location of the spot but only on its power.
However, the reduction in power is not significant providing the distance between the two carriages 5 and 13 does not exceed + 2 mm, which can be guaranteed. The laser used in this applic-ation is a CO2-laser having a power of a few hundred W, and an emitted wavelength of 10.6 ~m. In the present e~ample, the dia-meter of the beam of paralleI rays emitted by the source of laser rays 26 is 8 mm. This beam traverses the first converging lens 39a of focal length F. The second converging lens 39_ of focal length 2F, which is at a distance 3f from the lens 39a, straigh-tens the diverging beam to form a parallel beam of 16 mm diameter.
The diameter of the spot _ is notably inversely proportional to the diameter D of the beam concentrated by the lens 18, _ being represented by the equation:
d = ~

where ~ is the wavelength emitted by the laser 26 and f the focal length of the lens 18. It is thus attractive to increase the diameter of the beam concentrated by the lens 18 as much as poss-ible within practical limits. The power obtained at the level of the spot is sufficient to increase the cutting speed to an lQ52550 order of magnitude several times greater than present speeds.
In practice, other constraints evidently reduce this laser per~ormance.
A blade 32a is provided on the guide 32 (Figure 2) after the point of impact of the laser spot on the guide 32 with respect to the direction F of movement of the fabric T. This blade 32a is provided to cut any filaments which had not been cut by the laser rays. This blade is however optional. In one unrepresented modification, the laser spot could be made to shift laterally relative to the guide 32 by a distance equal to the distance be-tween two neighbouring columns of races.
In the device illustrated in Figures 1 to 3, the beam axis is directed substantially perpendicular to the plane of the fabric T. Consequently approximately 50~ of the laser beam energy is lost because of the gaps separating the threads.
This lost proportion of energy could be considerably reduced by inclining the beam axis as shown in Figure 6, which 3~
- B shows the guide is~ with the fabric races, and the lens 18 and mirror 23 which have been inclined through an angle ~ about the lens focus, in a plane containing the guide 32. This device in-creases the time of passage of each thread through the focused laser beam by reducing by a like amount the time during which the beam falls in the gaps separating the threads.
Figures 7 and 8 show a device for carrying out the pro-cess according to the second method. There exist looms which simultaneously produce two fabric sheets Tl and T2 bonded to each other by a plurality of threads which are then cut to separ-ate the sheets and form piled surfaces on each sheet. Velvets and certain types of carpets can be obtained by this process.
The sheets may be separated either at the outlet of the loom or on a machine specially conceived for this purpose.

105;~55(~
Figures 7 and 8 show very diagrammatically a device which enables a laser to be used in such a case. The Figures show the sheets Tl and T2 firstly mutually parallel and then, after separation, mutually diverging to be wound on two storage rolls 51 and 52. The distance between the sheets Tl and T2 in the separation zone is defined very exactly by two rollers 53 and 54.
The laser 26 with its optical circuit is mounted absol-utely identically to the manner shown in Figure 1. The optical circuit terminates in a mirror 23' and a lens 18' carried by a carriage 55 slidably mounted on two rails 56 and 57 parallel to the rollers 53 and 54. The carriage 55 is connected to a drive mechanism comprising a motor 58 and a belt 59 held between the pulley 60 of the motor 58 and a pulley 61. A drive peg 62 is fixed under the carriage 55. This peg 62 is aligned with the axis joining the centres of the pulleys 60 and 61, and is engaged with a fork 63 rigid with the belt 59. This device enables the carriage 55 to be driven with a reciprocating movement, the tra-jectory of which is parallel to the trajectory of the laser beam, so that the line scanned by the point of focus of this beam is constantly kept between the rollers 53 and 54, so burning during its passage that portion of the threads joining the sheets Tl and T2 brought into contact with the beam almost instantaneously.
Again, a nozzle 64 connected to a source of fluid (not shown), for example air, projects this fluid into the focus zone of the beam.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for severing a selection of yarn strands disposed in parallel columns on one of the faces of a fabric web in which the severing is effected by a focused laser beam, said appar-atus comprising: means for displacing said web past a cutting station parallel to said columns; a laser generating a laser beam; optical means for training said beam transversely to the direction of separ-ation of said web upon the severing thereof; a reflector for reflec-ting said beam perpendicularly to said direction of said separation;
a convergent lens intercepting said reflected beam and positioned at said station for focusing the reflected beam at a point along the path of said web; a slide carrying said lens; means for guiding said slide transversely in the direction of separation; a guide element rigid with said slide for engagement in one of said columns for stretching same in the direction of separation and extending beneath the focus of said lens; and means connecting said guide element with said slide for kinetically coupling the focus of said lens to the displacements of the web whereby the focus of said beam successively contacts predetermined portions of each of the strands of the column engaged by said element to cause combustion of at least part of the fibers thereof.

2. A process for the manufacture of a pile fabric by severing a selection of yarn strands appearing on one of the faces of at least one sheet of fabric, in which the severing is performed by a focused laser beam focused by a convergent lens carried by a slide kinetically coupling the focus of the lens to the displacements of the web whereby the zone of the focus of the said beam is brought successively into contact with a determined portion of each of the said strands, for a period of time at each of said portions suffic-ient to cause combustion of at least part of the fibres forming said strands.

3. A process according to claim 2 in which the fabric comprises side by side columns or ribs of aligned looped strands, the strands being transverse to the length of the columns.

4. A process according to claim 2 in which the zone of focus is brought into contact with each of the strands by means of relative longitudinal movement of a guide connected to said slide within the column.

5. A process according to claim 3 or 4 in which the central portions of the columns are made to move successively past the cutting location in the zone of focus of the beam and the axis of the beam is inclined towards the surface of the fabric in a plane substantially perpendicular to the surface of the fabric and sub-stantially parallel to the direction of movement of the columns.

6. A process according to claim 2, 3 or 4 in which a jet of fluid is directed into the zone of focus of the beam to prevent combustion products reducing the efficiency of the beam.