Device for measuring the reserve of weft and for indicating weft breakage in weft feeders for textile machines, and weft feeder including said device

Abstract: Device comprising a first reed (A) which is subjected to the force applied by a variable number of turns of the reserve (RTM) and a second reed (B) which is subjected to the force applied by a constant number of turns which is equal to the depletion threshold of the reserve (RTm). The first and second reeds have the same elastic rigidity and are inserted in the base of the drum (12) of the feeder with one of their ends. Transducer means (30-31) are associated with each reed to measure the value of the resultants of the forces acting on the respective reeds, and processing means (UP) are provided to calculate the variation in the distance between the point where the resultant of the forces affecting the first reed (A) is applied and the insertion section of the first reed as the number of turns of the reserve (RT) varies and to emit a reserve residual measurement signal which is proportional to this distance.

Description: The present invention relates to a device for measuring the reserve of weft and for indicating weft breakage in weft feeders for looms and textile machines in general, and to a weft feeder which includes said device. It is known that weft feeders are devices provided with a fixed drum on which a windmilling arm winds multiple turns of thread that constitute a reserve of weft. The turns unwind from the drum when requested by the loom or textile machine, and before the reserve is depleted, the rotating arm winds more turns so as to constantly feed the weft reserve; a series of undulating rods causes the axial advancement of the fed turns from the base to the tip of the drum of the feeder. A detection device, which is sensitive to the presence of the reserve turns, activates the rotating arm when the number of said turns of the reserve decreases below a preset limit. Mechanical or optical detection devices are already known, for example from EP-A-171 516; the former are based on the use of a mechanical thread sensing probe which is capable of emitting a useful signal when the feeler part loses contact with the turns, whereas the latter are based on the use of one or more light beam emitters that cooperate with corresponding light beam receivers which are sensitive to the degree of reflection or blocking that the presence of the turns of thread produces on said light beams. Both of these known detection devices have numerous drawbacks. In particular, mechanical feeler devices are scarcely reliable, especially in the presence of low-count threads, due to the very narrow extent of the useful motion of the feeler. Their operation is accordingly easily affected by the presence of foreign matter, dust, and the like, and in any case requires accurate operations for adjusting the feeler, whose action must also be set according to the type of thread being used. Optical devices in turn have the severe drawback that they are particularly sensitive to the presence of foreign matter, dust, and the like, and that they are also highly sensitive to the nature and color of the thread being used, since the light reflection index depends on these factors; said devices are also equally sensitive to the type and intensity of the ambient lighting. Both of said known devices, whether mechanical or optical, furthermore have the drawback that they provide an indication of the "all or nothing" type, whereas current sophisticated control systems for looms and textile machines require an actual measurement of the residual reserve in order to adapt the various parameters of the production process to the actual amount of said reserve. Furthermore, dedicated devices must be installed in order to indicate weft breakage, since optical and mechanical devices of the above mentioned type are unable to simultaneously provide distinct signals that indicate weft presence and weft breakage. Accordingly, the structure of the control circuits associated with detection devices is more complicated and more prone to false indications. A principal aim of the present invention is essentially to eliminate the above described drawbacks of known types of mechanical and optical detection devices and within the scope of this general aim has the following important and particular objects: -- to provide a device that is capable of actually measuring the amount of residual weft that is present on the drum of the feeder and to provide a signal which is optionally proportional to the actual amount of the residual weft reserve; -- to provide a device which is fully insensitive to the presence of foreign matter, dust, and production residues, and is fully insensitive to the type and color of the thread being used and to ambient lighting; -- to provide a device that is capable of providing distinct weft reserve measurement and weft breakage signals; -- to provide a device that has a very simple structure, minimum bulk, and high reliability, and whose use does not entail significant structural modifications of the weft feeder to which it is applied. According to the present invention, this aim, these objects, and others are achieved by a device for measuring weft reserve and for indicating weft breakage which has the specific characteristics outlined in the appended claims. Substantially, the invention is based on the concept of measuring the variable elastic deformation of a first reed which is subjected to the force applied by a variable number of turns of the reserve and of correlating this deformation to the constant elastic deformation of a second reed which is subjected to the force applied by a constant number of turns which is equal to the reserve depletion threshold, in order to obtain a value that corresponds to the shift of the point of application of the resultant of the forces that act on the first reed as the number of turns that act on said reed varies. Both reeds are inserted at the base of the drum and lie parallel to the axis of the drum along its outer surface; the first reed is substantially as long as the maximum axial extension of the reserve of turns, and the second reed is substantially as long as the minimum axial extension of said reserve. The resultant Fa of the forces that act on the first reed is applied at a point of the reed which is spaced from the respective insertion section by an extent La which is variable. Likewise, the resultant Fb of the forces that act on the second reed is applied at a point of the reed which is spaced from the respective insertion section by an extent Lb which is constant. If the reeds are equally rigid, the following relation holds: Fa/La = Fb/Lb and accordingly: La=Fa . Lb/Fb Since Lb is constant, it is possible to obtain the value La, which is proportional to the amount of the residual reserve of weft turns, if the resultants Fa and Fb are known. Pairs of strain gauges (electrical resistance strain gauge) associated with the respective insertion sections of said first and second reeds measure the instantaneous value of said resultants, and pairs of operational amplifiers, which cooperate with a processing unit, calculate expression (2) to provide the measured value of the residual reserve of weft, which is directly proportional to the value La. If the force Fb that acts on the second reed becomes zero, this indicates weft breakage. The characteristics, purposes, and advantages of the device according to the present invention will become apparent from the following detailed description thereof, given with reference to the accompanying drawings provided by way of non-limitative example, wherein: figure 1 is a partially sectional view of a weft feeder with the weft reserve measurement and weft breakage indication device according to the invention; figure 2 is an enlarged-scale view of a detail of figure 1, illustrating in detail the first and second reeds of the device; figure 3 is an enlarged-scale view of a further detail of figure 1, schematically illustrating the distribution of the forces that act on the first and second reeds of the device; figure 4 is an electric block diagram of the system for measuring the forces that act on the reeds and of the unit for processing the measured data and for emitting the weft reserve measurement signal and the weft breakage signal. In the drawings, the reference numeral 10 generally designates a weft feeder of the type which comprises a fixed base 11 and a fixed drum 12 on which a windmilling hollow arm 13, associated with an equally hollow drive shaft 14, winds multiple turns of thread f that unwinds from a spool, not shown; said turns constitute a weft reserve RT. When requested by the loom or other textile machine, the thread unwinds from the drum, reducing the reserve RT until a preset minimum value RT m is reached; once this value has been reached, or before it is reached, the measurement and control device, generally designated by the reference numeral 15, activates the arm 13 to wind additional turns on the drum and restore the maximum reserve RT M . In a per se known manner, a system of undulating rods 16 moves the turns of thread from the base to the tip of the drum 12 until the reserve RT is completed. The drum 12 is supported, by means of a supporting plate 12a, by a support 17 which is fixed and rigidly coupled to the base 11 by pairs of oppositely arranged magnets 19 which are located, according to a known arrangement, on the support 17 and on a fixed disk 20 which is rigidly coupled to the base 11; the support 17 is freely rotatably mounted, with the interposition of bearings 21, on an extension of the drive shaft 14. According to the present invention, the device 15 for measuring and controlling the reserve of weft RT comprises a first reed A and a second reed B a respective end whereof is inserted in the plate 12a of the drum. The reeds A and B lie parallel to the drum 12 and along its outer surface, passing through corresponding openings 22-23 provided at the base of the drum 12. The length T of the reed A is at least equal to, and preferably greater than, the maximum axial extension of the reserve RT M of turns on the drum 12; the length t of the reed B is at least equal to, and preferably slightly greater than, the minimum axial extension RT m of the reserve of turns on the drum 12 (figure 2). Both reeds A and B are preferably made of steel plate, have the same elasticity modulus and the same rigidity, and are subjected to the force produced by the turns of thread of the reserve which are wound on them. The force applied by the turns on the reed A varies according to the variations of the reserve of thread RT wound on the drum 12 and decreases as said reserve decreases; the force applied by the turns of thread on the reed B is constant, since the number of turns -- equal to the minimum reserve -- that act on said reed is constant. With reference to figure 3, the resultant Fa of the forces that act on the reed A is applied at a point P of the reed which is spaced by an extent La from the insertion section of said reed; the length of the portion La is variable in a substantially linear manner with respect to the value of the resultant Fa. Likewise, the resultant Fb of the forces that act on the reed B (which lies at right angles to the reed but is shown parallel thereto due to graphical requirements) is applied at a point p which is spaced by an extent Lb from the insertion section of said reed; the extent Lb is constant, like the value of the resultant Fb. Respective pairs of strain gauges 30 and 31 are applied at the insertion section of each reed, are connected according to respective known bridge arrangements PS A -PS B (figure 4), and are supplied by a voltage Vcc; their outputs are connected to corresponding operational amplifiers AMP A -AMP B which provide in output signals which are proportional to the resultant Fa and to the resultant Fb respectively. Since the rigidity of the reeds A and B is the same, the following relation is true at all times: Fa/La = Fb/Lb By means of this relation, a processing unit UP, which is operatively connected to the amplifiers AMP A -AMP B , calculates in real time the value of the variable La, which is proportional (minus a factor of 0.5) to the remainder of the reserve RT of turns, assuming that: La = Fa.Lb/Fb For this purpose, the processing unit UP comprises: an input A/D converter 32, which is operatively connected to the output of the operational amplifiers AMP A -AMP B ; a timer T; a microprocessor µp which calculates expression (2); and an output D/A converter 33, which provides an analog signal S that is equal to the measurement of the reserve of weft that is present on the drum 12. The minimum value of the reserve is reached when Fa = Fb ; however, the device is capable of providing signals that are useful for causing the advance startup of the arm 13 before the minimum value of the reserve is reached. For example, it is possible to produce the advance startup of the arm 13 by making the advance time proportional to the beat rate of the loom, so as to take into account the response delays in order to avoid exceeding the minimum reserve residual. The condition Fb = 0 occurs if the weft thread breaks, and in this case the processing unit UP issues a stop signal SA for the entire loom-feeder assembly. The operational amplifiers AMP A -AMP B are located on board the supporting plate 12a of the drum 12. Due to the presence of the thread f in the region between the base and the tip of the drum 12, the cables c1-c2 that connect the output of said amplifiers to the processing unit UP, which is generally installed externally with respect to the feeder 10, and the cable AL that supplies the Vcc to the amplifiers and to the strain gauge bridges PS A and PS B , cannot be transferred outside the drum 12, which is rigidly coupled to the plate 12a. The problem is advantageously solved by means of the sliding-contact arrangement shown in figure 1, according to which a rotating commutator 40 provided with sets of three annular tracks 41-42 is arranged on the drive shaft 14 at the arm 13. Corresponding fixed sliding contacts 43-44 cooperate with the annular tracks 41-42 and are connected to respective cable portions which are rigidly coupled to the fixed support 17 at one end and to the fixed base 11 at the other end; said fixed base can include the processing unit UP or have a multiple connector that is suitable to allow the connection of said processing unit if it is located outside the feeder 10. According to an alternative but more complicated system, the power for supplying the strain gauge bridges and the amplifiers can be transferred electromagnetically in a per se known manner, by means of a transformer whose primary winding is located outside the drum and whose secondary winding is located inside said drum, whereas the data present at the output of the operational amplifiers is transmitted to the control system, located outside the drum 12, by means of optical emitters which are arranged inside the drum and by means of receiving phototransistors which are located outside said drum. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims: Device (15) for measuring weft reserve and for indicating weft breakage in weft feeders (10) which comprise a drum (12) on which a windmilling arm (13) winds multiple turns of thread (f) which constitute a thread reserve (RT), characterized in that it comprises: a first reed (A) which is subjected to the force applied by a variable number of turns of the reserve (RT) and a second reed (B) which is subjected to the force applied by a constant number of turns which is equal to the depletion threshold of the reserve (RT), said first and second reeds having the same elastic rigidity and being inserted in the base of said drum (12) with one of their ends such that said reeds lie parallel to the axis of the drum and along its outer surface; transducer means (30,31) which are associated with each reed to measure the value of the resultants (Fa,Fb) of the forces that act respectively on said reeds; and processing means (UP) for calculating the variation in the distance (La) between the point (P) where the resultant (Fa) of the forces affecting the first reed (A) is applied and the insertion section of said first reed as the number of turns of the reserve (RT) varies and for emitting a reserve residual measurement signal (S) which is proportional to said distance. Device according to claim 1, wherein the first and second reeds are inserted in the base of the drum and extend in the feeding direction of the weft on the drum parallel to the axis of and along the outer surface of the drum such that La = Fa.Lb/Fb where La is the distance between the point (P) where the resultant of the forces affecting the first reed (A) is applied and the insertion section of said first reed; Fa and Fb are the resultants of the forces acting respectively on the first reed (A) and on the second reed (B); and Lb is the distance between the point (p) where the resultant of the forces affecting the second reed (B) is applied and the insertion section of said reed. Device according to claims 1 and 2, characterized in that said first and second reeds (A,B) lie parallel to the axis of the drum (12) of the feeder (10) and outside said drum so as to receive the forces applied by the turns of the reserve (RT) wound on said drum. Device according to claims 1 to 3, characterized in that the axial length (T) of said first reed (A) is at least equal to the maximum axial extension (RT M ) of the reserve of turns of thread and in that the axial length (t) of the second reed (B) is at least equal to the minimum axial extension (RT m ) of the reserve of turns of thread. Device according to the preceding claims, characterized in that the transducer means for measuring the value of the resultants (Fa,Fb) on the respective reeds (A-B) are constituted by pairs of strain gauges (30,31) which are connected according to respective bridge layouts (PS A , PS B ) whose outputs are connected to corresponding operational amplifiers (AMP A ,AMP B ) which provide in output signals that are proportional to the resultant (Fa) of the forces that act on the first reed (A) and, respectively, to the resultant (Fb) of the forces that act on the second reed (B). Device according to claims 1 and 5, characterized in that the processing means (UP) comprise: an input A/D converter (32) which is operatively connected to the output of the operational amplifiers (AMP A ,AMP B ), from which it receives signals that are proportional to the resultants (Fa,Fb) that act on the first reed (A) and on the second reed (B) respectively; a microprocessor (µP) which is programmed so as to calculate in real time the ratio (Fa/Fb) between said resultants and multiply the result of said ratio by the constant value of the distance (Lb) between the point (p) where the resultant (Fb) affecting the second reed (B) is applied and the insertion section of said reed, obtaining the instantaneous value of the distance (La) between the point (P) where the resultant affecting the first reed is applied and the insertion section of said reed; and an output D/A converter (33) which is suitable to provide an analog signal (S) which is proportional to said ratio of the resultants and is equal to the weft reserve (RT) that is present on the drum (12). Device according to claim 6, characterized in that said microprocessor (µP) is also programmed to make the process computer (UP) emit a signal (SA) for stopping the loom-feeder unit when, due to the breakage of the weft thread (f), the resultant (Fb) of the forces that act on the second reed (B) becomes zero. Weft feeder (10) for textile machines, comprising a fixed base (11), a fixed drum (12) on which a windmilling hollow arm (13), associated with a hollow drive shaft (14), winds multiple turns of thread which constitute a reserve of weft (RT), characterized in that it comprises a weft reserve measuring device (15) which includes a first reed (A) and a second reed (B) which are inserted at the base of the drum (12) and lie parallel to the axis of said drum and along its outer surface, the length (T) of said first reed being at least equal to the maximum axial extension of the reserve of turns (RT M ), the length (t) of the second reed being at least equal to the minimum axial extension of the reserve of turns (RT m ); in that said reeds have respective pairs of strain gauges (30,31) which are connected in a bridge layout (PS A ,PS B ) and cooperate with respective operational amplifiers (AMP) which are supported by a base plate (12a) of the drum and are suitable to provide respective signals which are proportional to the resultants (Fa,Fb) of the forces that the turns of the reserve (RT) apply to said first and second reeds; and in that said signals and the power for supplying the strain gauge bridges (PS A ,PS B ) and the operational amplifiers are transferred to a processing unit (UP) which is external to the feeder (10) by means of sliding contacts (41,42,43,44) which are supported by a rotating commutator (40) that is rigidly coupled to the drive shaft (14) of the feeder (10). Feeder according to claim 8, wherein, as an alternative, said signals and said supply power are transmitted to the processing unit (UP) by transmission means which entail no electrical contact; said transmission means being optical and electromagnetic respectively.

Inventors: ZENONI PIETRO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1995
Main classification: B65H51
IPC codes: D03D47, B65H51