Method for monitoring weft insertion in feeders of jet looms with fed thread pre-measuring unit

Abstract: A method for monitoring weft insertion which consists in setting, when a signal (UWSP) for counting the turns of thread that unwind from the feeder is missing one or more pulses with respect to the number of turns of the weft insertion request (TR) generated by the loom, a maximum time (TMRO), after which a microprocessor (µP), if no further counting pulses (UWSP) occurs, completes the release of the turns to be inserted (NSI-NSP) and/or the compensation of the turns (NS) that are present on the weft feeder and pre-measuring unit.

Description: The present invention relates to a method for monitoring weft insertion in feeders of jet looms with fed thread pre-measuring unit. Weft pre-measuring units are known and widely used in the field of jet weaving (air- or water-jet looms) which, inserted between the spool and the loom, have the specific task of feeding a preset length of thread, for each weft insertion, by releasing it from a weft reserve accumulated on the drum of the unit in the form of turns wound onto the drum and to also replace the released weft by winding onto the drum a corresponding amount of thread, so as to keep the weft reserve substantially unchanged (see e.g. WO-A 87 04151). As it will become better apparent from the detailed description that follows, a conventional system for feeding jet looms with a unit for pre-measuring the fed thread at each weft insertion uses a weft feeder and pre-measuring unit which comprises: a fixed drum, on which a windmilling arm winds the turns of thread that form the weft reserve; a weft retention finger for stopping the thread, which is associated with the fixed drum and is actuated electromagnetically in order to release the thread, allowing it to unwind from the drum, and to stop its unwinding when the pre-measured amount is reached; means for counting the turns of thread released at each weft insertion; means for counting the turns wound back onto the drum of the unit in order to restore the weft reserve; and a control microprocessor which receives a weft release signal from the loom and supervises the actuation of the weft retention finger, the counting of the unwound turns and the actuation of the motor that drives the windmilling arm that winds back the turns, restoring the weft reserve. In particular, in order to keep the weft reserve substantially invariant over time, the microprocessor processes the pulsed signals generated by a first optical sensor which detects the passage of the turns that unwind from the drum and, respectively, by a second magnetic sensor which provides one pulse at each turn of the windmilling arm that winds a corresponding turn onto the drum of the unit. For this purpose, the microprocessor compares the number of pulses of the signals generated by the first and second sensors and actuates accordingly the motor of the windmilling arm, making the number of pulses match so as to keep unchanged the weft reserve that is present on the drum of the feeder and pre-measuring unit. Correct control of the reserve by the above specified conventional system is ensured so long as the first and second sensors both provide the microprocessor with corresponding correct signals, but there are particular operating conditions in which this does not occur. In such cases, the conventional system is no longer capable of ensuring correct replenishment of the weft reserve. A typical condition in which the conventional system loses control of weft reserve replenishment occurs when, for any reason, one or more turns are unwound from the drum of the feeder and pre-measuring unit at an excessively low travel speed, hereinafter termed insertion speed. In this case, the circuit for detecting and amplifying the signal of the optical sensor designed to detect the turns that unwind from the drum (which is also described in detail hereinafter) can in fact eliminate the signal by interpreting it as noise and accordingly filtering it out by means of a high-pass filter. The filter is provided in order to eliminate light variations that are much slower than those caused by the rapid passage of the thread and are noise-related, such as for example variations in external light, the passage of grains of dust, vibrations of light reflected on the sensor caused by the operation of the unit, and the like. Many circumstances can make the insertion speed too low: for example, during normal insertion the weft can become entangled in the warp, or in the comb of the loom (if it is too dirty), and thus undergo sudden deceleration although the carrier fluid is fed at the maximum flow-rate. Likewise, during manual release of the weft the thread retained in the nozzle of the loom is propelled by a reduced flow, known as holding flow, at a pressure which is much lower than the normal weft release pressure: in this case also, the speed of the thread is reduced considerably. It is therefore evident that when one or more turns are unwound at an excessively low insertion speed, since the corresponding pulses produced by the optical sensor are no longer provided because the sensor does not effectively detect the passage of the turns, the feeder and measuring unit is depleted by a corresponding amount of reserve without restoring it, and can thus reach a condition in which it is completely empty, or at least a condition in which the presence of reserve is insufficient, forcing to stop the weaving process at least temporarily in order to manually start the reserve replenishment procedure. The aim of the present invention is to eliminate this severe drawback. Within this aim, an object of the present invention is to provide a method for monitoring weft insertion which is adapted to eliminate, or at least minimize, the possibility of depleting the weft reserve on the drum of the feeder and pre-measuring unit in any of the circumstances that can cause suppression of the signal of the sensor designed to detect the passage of the turns being unwound. Another important object of the present invention is to provide a monitoring method which is highly reliable and in particular is independent of the variation of several parameters of the weaving process, such as in particular the nature and count of the weft thread, the structure and operating speed of the loom, and the length of the thread required for each weft insertion. According to the present invention, this aim, these important objects and others which will become apparent from the following detailed description are achieved with a weft insertion monitoring method which has the specific characteristics stated in the appended claims. Substantially, the method according to the invention is based on the statistical prediction that every insertion request that arrives at the control and supervisor microprocessor is usually performed correctly regardless of whether the unwinding turn detection sensor has seen and reported or not the passage of all the turns to be inserted. In this manner, if the passage of a turn is not detected after a preset interval of time since the last pulse generated by the passage of a turn, or since the last insertion request, this failed detection is taken to mean that the requested turns have been inserted. In practice, the method according to the invention, based on this prediction, consists in programming the microprocessor so that it generates, upon an external command, respective interrupts upon variation in the signals produced by the turn winding and unwinding sensors and upon variation in the weft request signal produced by the loom; in assigning the routines of the interrupts of the signals of said sensors the task of decreasing and, respectively, incrementing the counters of the number of turns wound onto, and respectively unwound from, the drum of the unit, and of setting a timer to a value which is equal to the maximum time that elapses between the passage of one turn and the next; and in giving the routine of the weft request signal the task of ascertaining that the number of turns inserted as a consequence of the directly preceding request exceeds a preset minimum threshold and the task of compensating for any missing turns by subtracting them from the turns that are present on the feeder drum; said microprocessor being also adapted to generate a periodic internal interrupt whose routine has the task of checking whether the setting of the timer has expired or not in the interval between two turns, in order to compensate for said turns and set the number of released turns equal to the number of turns to be released, thereby indicating the end of the insertion. The characteristics, purposes and advantages of the weft insertion monitoring method according to the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, given by way of non-limitative example, wherein: Figure 1 is a block diagram of a conventional system for feeding and pre-measuring the weft for jet looms; Figure 2 is a circuit diagram of the circuit associated with the optical sensor for detecting the turns being unwound; Figures 3a-3b-3c-3d are flowcharts of the routines of the various interrupts generated by the supervisor microprocessor; Figures 4 and 5 are time charts of the signals that reach the supervisor microprocessor in case of correct and, respectively, irregular operation. With reference to Figure 1, SI generally designates a conventional system for feeding a weft thread F to a jet loom TE with pre-measurement of the thread fed at each insertion and unwound from a spool RO. The system SI uses, for this purpose, a weft feeder and pre-measuring unit, generally designated by the reference letter P, which comprises a fixed drum TA on which a windmilling arm BR, associated with a flywheel VO and actuated by a motor MO, winds a plurality of turns of thread which form a weft reserve RT. A weft retention finger DI for stopping the thread F is associated with the drum TA of the feeder and is actuated by an electromagnetic actuator AE in order to release the thread, allowing it to unwind from the drum TA, and to stop its unwinding when the pre-measured amount or length is reached. A microprocessor µP, designed to supervise the entire system SI, generates an output CE for controlling the electromagnet of the weft retention finger DI and another set of three outputs a, b, c for controlling the motor MO by means of a power interface (driver) MPD. A first optical sensor UWP, located at the output of the drum TA, is provided in order to count the turns that unwind from the drum and sends to the microprocessor µP its pulsed signals UWSP, processed beforehand in an amplification and filtration circuit CAF. A second magnetic sensor H provides the microprocessor µP with a pulse WSP at each rotation of the windmilling arm BR that winds a corresponding turn onto the drum TA, said magnetic sensor detecting the passage of a magnet M which is carried by the flywheel VO associated with the arm BR. The circuit CAF for amplifying and filtering the signal produced by the optical sensor UWP is now described with reference to Figure 2. Said sensor comprises an emitter diode LE and a receiver phototransistor FT, which produces, across its terminals, a weak current IR which is proportional to the amount of light received by reflection from a mirror, or the like, located on the drum TA of the unit P and which is struck by the light emitted by the diode LE. The current fed to the emitter diode is adjusted by an appropriate control circuit CRC which is designed to keep the current substantially constant. The weft thread F that unwinds from the drum intersects the beam of light that is incident on the mirror and reflected by it, causing an instantaneous decrease in the current IR emitted by the phototransistor. The current signal IR is amplified in an amplifier A1 at the output of which there is a corresponding signal S2 which is amplified in terms of voltage. In order to make the signal independent of noise caused by external light and/or other accidental factors which cause much slower variations than those produced by the passage of the turns of thread, the signal S2 is filtered in a high-pass filter A2 and the signal S3 that is present at the output of said filter is applied to a comparator A3, so that when signal S3 exceeds the reference threshold RF the positive pulse of the signal UWSP is produced. Otherwise, i.e., when S3 < RF, the pulse of the signal UWSP is suppressed. The microprocessor µP also receives the weft release request signal TR generated by the loom TE. When the microprocessor receives the request signal TR, it immediately energizes the actuator AE, which lifts the weft retention finger DI, allowing the unwinding of the turns of the weft reserve RT. At the same time, the loom TE, for example of the air-jet type, actuates the jets of the main nozzles and of the relay nozzles and inserts the weft in the shed. During weft insertion, the microprocessor, by means of the signals UWSP, is kept informed on the number of turns unwound from the drum TA of the pre-measuring unit P and when the requested number of turns has been reached it actuates the actuator AE with reversed polarity, causing the lowering of the weft retention finger DI and stopping the unwinding of the thread. At the same time, the microprocessor µP actuates the motor MO in order to replenish the turns of thread taken from the weft reserve RT, and at each wound turn it receives from the sensor H a corresponding signal WSP. In order to keep the weft reserve RT substantially invariant over time, the microprocessor compares the number of pulses of the signal UWSP with the number of pulses of the signal WSP and makes the number of the pulses substantially match. However, if one or more pulses of the signal UWSP are suppressed because S3 < RF due to one of the above noted reasons, the microprocessor loses control of reserve replenishment, and the reserve can become fully depleted, stopping the weaving process. In order to avoid this drawback, the present invention provides an insertion monitoring method which is independent of any checking of the match between the pulses of the signals WSP and UWSP and introduces the concept of the resetting, or lack thereof, of a counter within a preset time limit (timeout) elapsing from the passage of the last turn or from the actuation of the weft release request signal. In practice, with the method according to the present invention the microprocessor µP is programmed so as to generate (Figures 4 and 5), upon a command which originates externally, respective interrupts upon a variation (a negative one in the example of Figures 4 and 5) of the signals UWSP and WSP produced by the turn unwinding and rewinding sensors and upon a variation (a positive one in the example) of the weft request signal TR generated by the loom TE, and so as to internally generate a periodic control interrupt. With reference now to the flowcharts of Figures 3a, 3b, 3c and 3d, the parameters used in the various routines that the microprocessor performs for the various interrupts are defined hereafter: NS = number of turns present and wound on the drum TA of the feeder and pre-measuring unit P; NSI = number of turns required for the current insertion; NSP = number of turns released during the current insertion; TMRO = setting of a timer which corresponds to a preset time (timeout) elapsing from the passage of the last turn or from the actuation front of the weft release signal TR; FI = coefficient (1 <= FI <= 0) for evaluating whether the turns that are missing to complete the current insertion for should be compensated for or not. Using the above notations, the following interrupts are detected: interrupt in the signal UWSP (Figure 3a): the microprocessor starts a routine which has the following tasks: a) decrease the counter of the number of turns wound on the drum TA, setting NS = NS-1 , and correspondingly increment the counter of the number of turns released by the drum, setting NSP = NSP+1 ; b) setting the timer TMRO to the value equal to the maximum time that elapses between the passage of one turn and the passage of the next, said time being chosen greater than 2-3 times the average turn unwinding time (in the illustrated example, TMRO = 30 ms); interrupt of the signal WSP (Figure 3b): the microprocessor performs a routine whose sole purpose is to increment by one unit the number NS of the turns present on the drum; said signal in fact means that one turn has been wound onto the drum, and therefore the microprocessor sets NS = NS+1; interrupt of the weft release signal RA (Figure 3c): the microprocessor performs a routine which has the following tasks: a) check whether the turns inserted in the directly preceding insertion exceed the maximum required threshold, verifying the inequality NSP >= NSI.FI; b) if the result is positive, compensate for the turns that are missing for completion of insertion (NSI-NSP), subtracting said missing turns from the number of turns NS that are present on the drum TA; c) reset the counter for the turns NSP being released; d) set the timer TMRO; periodic interrupt (Figure 3d): the microprocessor performs a routine by means of which: a) it first of all checks the turn timeout condition, verifying the equality TMRO = 0. If this equality holds: b) the thread compensation condition expressed by the inequality NSP ≥ NSP.FI is verified; c) if this inequality also holds, the microprocessor compensates for the turns by setting NSP equal to NSI and this indicates the end of insertion. If instead TMRO ≠ 0, it is decreased. The above described periodic interrupt is executed with a preset and constant frequency, for example equal to 1 ms. The chart of Figure 4 plots the behavior over time of the variables involved in the monitoring method according to the present invention. Said chart is self-explanatory for the technician in the field and relates to an insertion of five turns NSI = 5 which occurs correctly without suppression of pulses of the sensor UWP. The chart of Figure 5, similar to the chart of Figure 4, instead illustrates an incorrect insertion in which although for example NSI = 5 and FI = 0.6, the pulses produced by the sensor UWP are only four. In this case, after the fourth pulse the timeout condition occurs, i.e., TMRO=0, so that the periodic interrupt, by positively verifying the condition NSP(=4)>NSI(=5).FI(=0.6)(=3), compensates for NS and NSP. Without altering the principle of the invention, the details of execution and the embodiments may of course be varied extensively, with respect to what has been described and illustrated by way of non-limitative example, without thereby abandoning the scope of the invention. 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 scope of each element identified by way of example by such reference signs.

Claims: A weft insertion monitoring method in systems (SI) for feeding looms (TE) of the jet type with a thread pre-measuring unit (P) which comprises a drum (TA) for accommodating a weft reserve (RT), a weft retention finger (DI), a windmilling arm (BR) for winding turns for replenishing the weft reserve, a first optical sensor (UWP) for detecting the turns of thread that unwind from the drum, a second magnetic sensor (H) for detecting the number of turns of the windmilling arm and a supervisor microprocessor (µP) which controls the weft retention finger (DI) and the motor (MO) of the windmilling arm (BR) and receives in input a weft request signal (TR) generated by the loom (TE) and first and second pulsed signals (UWSP-WSP) generated by said first and second sensors, which it compares, actuating the windmilling arm (BR) so as to make the number of pulses of said first and second signals match in order to keep the weft reserve (RT) substantially invariant; characterized in that it comprises the steps of determining, when said first signal (UWSP) is missing one or more pulses with respect to the number of turns of the weft request (TR), a maximum time (TMRO) after which the microprocessor (µP), if no further pulses (UWSP) from said first optical sensor (UWP) occur, completes the release of the turns to be inserted (NSI-NSP) and/or the compensation of the turns (NS) that are present on said drum (TA) of the pre-measurer (P). The monitoring method according to claim 1, characterized in that said maximum time (TMRO) is measured starting from the last pulse of the signal (UWSP) of said second optical sensor (UWP) or from the actuation front of the weft request signal (TR). The monitoring method according to claim 1, characterized in that said maximum time (TMRO) is 2-3 times longer than the average turn unwinding time. The monitoring method according to claim 1, characterized in that it comprises the steps of: programming said microprocessor (µP) so that it generates, under the external control of the signals (UWSP-WSP) of said first and second sensors (UWP-H) and of the weft request signal (TR) of the loom (TE), respective interrupts which occur upon a preselected variation of said signals; said microprocessor being also adapted to generate, by virtue of an internal command, an additional periodic interrupt; assigning to the routines of the signals of said first sensor (UWP) the task of decreasing (NS-1) the counter of the number of turns (NS) wound onto the drum of the feeder (P) and respectively of incrementing (NSP+1) the counter of the number of turns (NSP) unwound from said drum, and of setting a timer to said maximum time (TMRO) that is assumed to elapse between the passage of one turn and the passage of the next; assigning the routines of the weft request interrupt (TR) the task of checking whether the number of turns (NSP) inserted as a consequence of the directly preceding request exceeds or not a preset minimum threshold (NSP ≥ NSI.FI) and the task of compensating for any missing turns, subtracting them from the ones present on the drum (NS - (NSI-NSP) ), starting the insertion of the turns (NSP=0), setting the timer to said maximum time (TMRO); assigning the routine of said periodic interrupt the task of verifying whether the setting (TMRO) of the timer has expired or not during the interval between two turns in order to compensate for said turns and set the number of released turns equal to the number of turns to be released (NSP=NSI ), thus indicating the end of the insertion. The monitoring method according to claim 4, characterized in that the coefficient (FI) that determines said minimum preset threshold (NSI.FI) is changed automatically by the microprocessor (µP) according to the type of insertion requested. The monitoring method according to claim 4, wherein the interrupts generated by said first and second signals (UWSP-UWP) are produced at the negative variation of the pulses of said signals. The monitoring method according to the preceding claims, wherein said internal interrupt is executed with a perfectly periodic frequency. The monitoring method according to claim 6, characterized in that said periodic frequency is chosen equal to 1 ms.

Inventors: GOTTI LUCA, PEDRINI GIOVANNI, ZENONI PIETRO, GOTTI, LUCA, PEDRINI, GIOVANNI, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 2000
Main classification: D03D47
IPC codes: D03D47