Method and device for controlling weft winding arm rotating signals in weft feeders for weaving looms

Abstract: The method consists in using, in order to detect the passage of at least one moving magnet (M) associated with the flywheel (VO) that rotates jointly with the weft winding arm, a first magnetic sensor and a second magnetic sensor (H1-H2) which are mutually spaced by a preset distance (D) and are adjacent to the circular path of the at least one magnet, and in sampling the signals (WSP1-WSP2) of the first and second sensors (H1-H2) in order to extract from them, as regards counting the number (NS) of turns wound on the drum (TA), transition criteria (DX → OUT; OUT → DX; and, vice versa, A ≥ N) which indicate that a complete rotation of said arm (BR) has occurred and that said number (NS) of turns has consequently increased or decreased.

Description: The present invention relates to a method and a device for controlling weft winding arm rotation signals in weft feeders for weaving looms, particularly feeders and pre-measurers for jet looms. In the field of weaving, weft feeders are known and widely used which, in the case of jet looms, also act as weft pre-measurers. In other words, these devices, inserted between the spool and the loom, have the specific task of feeding a preset length of thread for each weft insertion, releasing it from a weft reserve accumulated on a drum of its own, in the form of turns wound onto said drum, and of also replenishing the released weft by winding back onto said drum a corresponding amount of thread so as to keep the weft reserve substantially invariant. Typically, and as will become apparent from the detailed description that follows, a system for feeding jet looms with pre-measurer of the thread fed at each weft insertion, uses a weft pre-measurer and feeder 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 said fixed drum and is actuated electromagnetically in order to release the thread, allowing it to unwind from the drum, and in order 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 in order to replenish the weft reserve on the drum of the feeder/pre-measurer, and a supervisor microcontroller 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 for moving the windmilling arm that winds back the turns, replenishing the weft reserve. In particular, in order to keep the weft reserve substantially invariant over time, said microcontroller 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 the rotation signals of the weft winding arm by detecting the passage of a moving magnet which rotates rigidly with said arm and generating a pulse at each turn of said arm which winds a corresponding turn onto the drum of the feeder/pre-measurer. For this purpose, the microcontroller compares the number of pulses of the signals generated by said first and second sensors and accordingly activates the motor of the windmilling arm, making said number of pulses match so as to keep unchanged the weft reserve that is present on the drum of the feeder/pre-measurer (see e.g. US-A-471 541). Correct control of the reserve by the above-specified conventional system is ensured as long as said first and second sensors both provide the microcontroller with corresponding correct signals, but there are particular operating conditions in which this does not occur. In such cases, the system is no longer able to ensure correct replenishment of the weft reserve. A typical condition in which the system loses control of weft reserve replenishment occurs very easily when said second magnetic sensor provides incorrect signals which do not correspond to a full rotation of the weft winding arm and to the corresponding winding of a turn onto the drum of the feeder/pre-measurer. Said magnetic sensor, typically a Hall sensor, is in fact sensitive to the passage of the moving permanent magnet, which is usually supported by a flywheel which is arranged at the base of the drum of the feeder and rotates rigidly with the weft winding arm. Accordingly, in normal operating conditions, at each angular movement of the flywheel through 360°, the moving magnet passes in front of the sensor, which generates a corresponding pulsed signal corresponding to a full rotation of the weft winding arm around the drum of the feeder/pre-measurer on which said arm correspondingly winds a turn of thread. In abnormal operating conditions, however, the flywheel may oscillate and perform, with a reciprocating back-and-forth motion, a plurality of larger or smaller angular movements. These abnormal operating conditions occur, for example, when the controlled weft insertion of the feeder is highly irregular, for example in the weaving of narrow bands of fabric. In such cases, the weft winding arm is subjected to rapid decelerations and accelerations which characterize the steps for braking and restarting, respectively, and said dynamic stresses cause said transient oscillation. If the position of the sensor, at the instant being considered, lies within the angular sector of oscillation of the magnet carried by the flywheel, a pulse is produced at each transit of the magnet in front of the sensor, although the generated pulse does not mean that a turn has been wound. In this manner, the supervisor microcontroller incorrectly overcounts the number of turns wound onto the drum; accordingly, if this transient phenomenon occurs rather frequently, the reserve of weft turns wound onto the drum of the feeder can become depleted; this is a severe drawback, since it forces to stop the weaving process in order to manually restore said weft reserve. Likewise, an overcount of the wound turns with respect to those actually present on the drum of the feeder can occur, when the feeder/pre-measurer is not moving, due to pulses generated by the magnetic sensor in relation to angular movements imparted manually and inadvertently to said flywheel by an operator, for example while performing adjustments on the feeder or on the entire weft thread feed system. The aim of the present invention is substantially to eliminate the above-mentioned severe drawback, by providing a method and a device for controlling weft winding arm rotation signals which are adapted to select the signals produced by said magnetic rotation sensor, suppressing, as regards the correct counting of the turns wound onto the drum of the feeder/pre-measurer, the pulses of the signals not matched by an actual full rotation of the weft winding arm. Another important object of the present invention is to provide a control method and device which are extremely simple, functional and reliable, and in particular, are such as to not require substantial modifications to the existing circuit means provided to control the feeder/pre-measurer associated with the system for feeding weft to the jet loom. According to the present invention, these and other objects which will become better apparent from the detailed description that follows are achieved with a method and a device for controlling the rotation signals on the weft winding arm having the specific characteristics stated in the appended claims. Substantially, the invention is based on the concept of using, in order to detect the passage of at least one moving magnet associated with the flywheel which rotates jointly with the weft winding arm, a first magnetic sensor and a second magnetic sensor, which are mutually spaced by a preset distance and are adjacent to the circular path of said at least one magnet, and of sampling, with a frequency whose period is smaller than, or equal to, the minimum time between the fronts of two consecutive signal pulses, the signals of the first and second sensors in order to extract therefrom, as regards counting the number of turns wound on the drum of the feeder, transition criteria which indicate that a complete rotation of said arm has occurred and that said number of turns has consequently increased or decreased. Further characteristics and advantages of the method and the device according to the invention will become better apparent from the detailed description that follows 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 the weft thread to a jet weaving loom provided with a thread feeder/pre-measurer; Figure 2 is a schematic view of the device for controlling the rotation signals of the weft winding arm of said feeder/pre-measurer, according to one embodiment of the invention; Figure 3 is a time chart of the rotation signals generated by the control device of Figure 2; Figure 4 is a schematic view of the rotation signal control device according to a variation of the invention; Figure 5 is an enlarged-scale view of a detail of Figure 4; Figure 6 is a time chart of the rotation signals generated by the device of Figure 4. In Figure 1, the reference sign SI generally designates a typical system for feeding the weft thread F to a jet loom TE with pre-measuring of the thread fed at each insertion and unwound from a spool RO. The system SI uses, for this purpose, a weft feeder/pre-measurer, generally designated by P, which comprises a fixed drum TA on which a windmilling arm BR, associated with a flywheel VO and driven 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 in order to stop its unwinding when the pre-measured quantity or length is reached. A microcontroller MC, preset to supervise the entire system SI, generates an output CE for the actuation of the electromagnet of the weft retention finger DI and an additional set of three outputs a, b, c for actuating the motor MO by means of a power interface MPD (driver). A first sensor UWP of the optical type, located at the output of the drum TA, is provided for counting the turns that unwind from the drum and sends to the microcontroller MC its pulsed signals UWSP, processed beforehand in an amplification and filtering circuit CAF. Another sensor H, of the magnetic type, is provided in order to supply the microcontroller MC with a pulse WSP at each turn of the windmilling arm BR that winds a corresponding turn onto the drum TA; said magnetic sensor being sensitive to the passage of a magnet M which is carried by the flywheel VO associated with the arm BR. A weft release request signal TR, generated by the loom TE, also reaches the microcontroller MC. When the microcontroller receives said request signal TR, it immediately energizes the actuator AE, which raises the weft retention finger DI, allowing the turns of the weft reserve RT to unwind. At the same time, the loom TE, for example of the jet type, activates the blowers of the main nozzle and of the relay nozzles and inserts the weft in the shed. During weft insertion, the microcontroller, by means of the signals UWSP, is kept updated on how many turns are unwound from the drum TA of the pre-measurer P and when the required number of turns is reached it activates, with reversed polarity, the actuator AE, causing the lowering of the weft retention finger DI and stopping the unwinding of the thread. Simultaneously, the microcontroller MC activates the motor MO in order to replace the turns of weft taken from the weft reserve RT and receives from the sensor H, at each rewound turn, a corresponding signal WSP. In order to keep the weft reserve RT substantially invariant over time, the microcontroller compares the number of pulses of the signal UWSP with the number of pulses of the signal WSP, and makes the number of said pulses substantially coincide. However, when one of the above-cited reasons causes the sensor H to generate one or more pulses WSP which are not matched by the actual and corresponding winding of one or more turns of the reserve RT, the microcontroller MC loses control of the replenishment of said reserve, which can accordingly become completely depleted, stopping the weaving process. In order to avoid this drawback, according to a preferred embodiment of the present invention, there is a control device as shown in Figure 2, which comprises a first magnetic sensor H1 and a second magnetic sensor H2, or Hall sensors, which are supported by the fixed frame of the feeder/pre-measurer P and are arranged, so as to be spaced by a distance D, one after the other adjacent to the circular path of the moving magnet M, from which they are spaced by a gap, or height, H. With this arrangement, the signals WSP1 and WSP2 respectively generated by said sensors H1-H2 assume over time, for a constant rotation rate of the flywheel VO, the pattern shown schematically in the chart of Figure 3. Said chart shows that in every instant the reading or sampling of the pair of values that the signals WSP1-WSP2 assume allows to deduce univocally in which of the circular sectors SX-C-DX-OUT, shown in Figure 2, the moving magnet M is located; C being the central sector and SX and DX being the sectors to the left and to the right of the central sector relative to the clockwise direction of rotation of the magnet M, indicated by the arrow in Figure 2. By checking at successive times the transition of the state of the pairs of signals WSP1 and WSP2, it is also possible to detect the direction of rotation of the magnet M when it passes in the vicinity of the sensors H1-H2. For this purpose, assuming the clockwise rotation of the arrow of Figure 2 to be the operating direction, the microcontroller MC is programmed to sample said pair of signals with a rate f ≥ 1/DT, where DT is the minimum time between the fronts of two signal pulses at the maximum rotation rate of the flywheel VO, and in order to increase by one unit the variable NS that represents the number of wound turns when said microcontroller detects the state transition: a) DX → OUT, i.e., the passage of the magnet M from the sector DX to the sector OUT located to the right of the sector DX, verifying, for this purpose, the following equalities C=OUT and C1=DX , where C is the value of the pair of signals WSP1, WSP2 at the generic sampling instant t and C1 is the value of the same pair of signals at the sampling instant t1 that precedes t . Likewise, the microcontroller MC decreases by one unit the numeric variable NS when it detects the opposite transition: b) OUT → DX, verifying, for this purpose, the equalities C=DX and C1=OUT; this transition meaning that the last wound turn has unwound. This is equivalent to assigning to the signals of the transition given in item a) a positive value (unit increment of NS) and assigning to the signals of the transition given in item b) a negative value (unit decrease of NS). In this manner, in case of oscillation of the magnet M in the vicinity of the sensors H1-H2, the final signal which is useful for increasing or decreasing the number of turns NS is the algebraic sum of the positive and negative transition signals accumulated during the oscillation. Of course, if the operating rotation of the weft winding arm BR is counterclockwise, the transition OUT → DX causes the increase of the numeric variable NS and the opposite transition DX → OUT causes its decrease. In the embodiment of Figures 4 to 6 there are again two magnetic Hall-type sensors H'-H2 which are supported by the frame of the feeder/pre-measurer P, but they are mounted so that one is inverted with respect to the other, so that for example the sensor H' is sensitive to the lines of flux of a magnetic field orientated in the direction of the arrow F1 of Figure 5 and the sensor H2 is sensitive to the lines of force of a magnetic field orientated in the direction of the arrow F2 of the same figure. Correspondingly, the flywheel VO of the feeder P is provided with a permanent magnet Mo, preferably made of neodymium or samarium-cobalt, whose magnetic field has a polarity (N-S) which is orientated like the arrow F1 and therefore like the field to which the sensor H' is sensitive, and with a plurality of additional permanent magnets M1-M4 (for example four), all of which have a magnetic polarity which is opposite to the polarity of the magnet Mo and therefore matches the orientation of the arrow F2 of Figure 4 and the field to which the sensor H2 is sensitive; the magnets of the set M1-M4 being uniformly spaced by a constant angular pitch. With this arrangement, the sensor H' produces a signal pulse WSP1 only when the magnet Mo passes in its vicinity and likewise the sensor H2 produces a signal pulse WSP2 only when one of the magnets M1-M4 passes in its vicinity. Accordingly, the time chart of the rotation signals generated by the sensors H'-H2 (Figure 6) shows that between two consecutive pulses of the signal WSP1 there are always N pulses of the signal WSP2; the example shows four. Using A to designate a numeric variable which represents the number of pulses of the signal WSP2 that occur between a transition t1 of the signal WSP1 and the preceding transition to , the microprocessor µP of the device is programmed so as to increase by one unit the numeric variable NS that represents the number of turns when it verifies the inequality A ≥ N and so as to decrease by one unit said variable in the opposite case, when the inequality A < N occurs. In the second case, the flywheel VO in fact certainly has not made a full turn (in either direction) and therefore the winding of a turn is ruled out. This embodiment of the control device, differently from the one described previously with reference to Figures 2 and 3, does not allow to discriminate the direction of rotation of the arm BR and therefore is unable to detect the winding of an entire turn in the opposite direction with respect to the working rotation. Without altering the principle of the invention, the details of execution of the method and the embodiments of the device may of course be changed 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 method for controlling the rotation signals (WSP) of the weft winding arm (BR) in weft feeders (P) for weaving looms (TE), characterized in that it consists in using, in order to detect the passage of at least one moving magnet (M) associated with the flywheel (VO) that rotates jointly with the weft winding arm, a first magnetic sensor and a second magnetic sensor (H1-H2) which are mutually spaced by a preset distance (D) and are adjacent to the circular path of said at least one magnet, and in sampling the signals (WSP1-WSP2) of the first and second sensors (H1-H2) in order to extract from them, as regards counting the number (NS) of turns wound on the drum (TA), transition criteria (DX → OUT; OUT → DX; and, vice versa, A ≥ N) which indicate that a complete rotation of said arm (BR) has occurred and that said number (NS) of turns has consequently increased or decreased. The control method according to claim 1, characterized in that the sampling rate of said signals (WSP1-WSP2) has a period which is smaller than, or equal to, the minimum time elapsing between the fronts of two consecutive signal pulses. The method according to claims 1 or 2, characterized in that the transition criteria (DX → OUT and vice versa) which indicate that a complete rotation of the weft winding arm (BR) has occurred in a clockwise rotation direction, and vice versa, are verified by the equalities C = OUT; C1 = DX and vice versa; where C is the value of the pair of signals (WSP1-WSP2) at the generic sampling instant ( t ) and C1 is the value of the same pair of signals at the preceding sampling instant ( t1 ). The method according to claims 1 or 2, characterized in that the first and second sensors (H'-H2) are sensitive to magnetic fields having reverse polarities and produced by a magnet (Mo) and, respectively, by a plurality of magnets (M1-M2) carried by said flywheel (VO), and in that the criterion that indicates that a complete rotation of the weft winding arm has occurred is represented, for a preset direction of rotation of said arm (BR), by the occurrence of the inequality A ≥ N where A is a numeric variable which represents the detected number of intermediate pulses of the signal (WSP2) of the second sensor (H2) occurring between two consecutive pulses of the signal (WSP1) of the first sensor (H'), and N is the preset number of said intermediate pulses, which corresponds to the number of said plurality of magnets (M1-M2). A device for performing the control method according to anyone of claims 1 to 3, characterized in that it comprises two magnetic sensors (H1-H2) which are associated with the flywheel (VO) of the weft winding arm (BR), are arranged on the fixed drum of the feeder (P), are mutually spaced by a preset distance (D) and are adjacent to the path of a moving magnet (M) which is carried by said flywheel (VO) of the weft winding arm, and a microcontroller (MC) which is programmed so as to sample the signals (WSP1-WSP2) produced by both of said magnetic sensors (H1-H2) when said magnet (M) passes, verify said transitions which indicate that the weft winding arm has performed a complete turn in the working direction or in the opposite direction, and accordingly increase or decrease the number (NS) of turns that constitute the weft reserve (RT) wound onto the drum (TA) of said feeder/pre-measurer. The device for performing the control method according to anyone of claims 1, 2 and 4, characterized in that it comprises: first and second magnetic sensors (H'-H2), which are supported, so as to be mutually spaced by a distance (D), by the fixed frame of the feeder (P) and are arranged so that one is inverted with respect to other, so as to be sensitive to the lines of flux of magnetic fields correspondingly orientated in opposite directions; a first moving magnet (Mo), which has the same polarity as the lines of the field to which the first sensor (H') is sensitive, said first sensor being carried by the flywheel (VO) of the weft winding arm (BR) of said feeder/pre-measurer (P); a plurality of additional moving magnets (M1-M4), which are also carried by said flywheel (VO) and have the same polarity as the lines of the field to which the second sensor (H2) is sensitive; a microcontroller (MC), which receives in input the selective signals (WSP1-WSP2) generated by the first and second sensors when the first moving magnet (Mo) and, respectively, the plurality of further moving magnets (M1-M4) pass; said microcontroller being programmed to verify the inequality (A < N) and to increase or decrease the numeric variable (NS) that represents the number of turns wound onto the drum (TA) of the feeder. The device according to claims 5 or 6, characterized in that said first and second magnetic sensors are constituted by Hall sensors.

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, B65H51