HIGH-PRODUCTIVITY BOBBIN WINDING METHOD, AND DEVICES FOR ITS IMPLEMENTATION

Abstract: A high-productivity bobbin winding method comprising a variable-­ duration intervention cycle for restoring yarn continuity. Said cycle is divided into two parts, of which a first part is devoted to braking the bobbin and a second part is devoted to joining the yarn, between the commencement of the two parts there being interposed a delay which varies as a function of the time measured for the bobbin to come to rest during the preceding intervention cycle.

Description: This invention relates to a bobbin winding method and a device for implementing said winding method. The improvement according to the invention enables the productivity of the winding operation to be increased and unproductive times to be eliminated or shortened. The winding operation consists substantially of transferring the yarn from a starting package and winding it on a rigid tube in order to form a structure wound in the form of cross turns and known as a bobbin, and during said transfer clearing the yarn of its imperfections and defects such as lumps, groups, naps, weak points, flocks etc. Said defects are eliminated by cutting out the defective portion and joining the yarn ends. This joint can be made either by a proper knot such as a fishermans knot or a weavers knot produced by a mechanical knotter, or by a pneumatic or friction joint in which the fibres of the cut ends are untwisted, intermixed and then retwisted to thus restore continuity to the cut yarn without introducing the hardly relevant irregularity represented by an actual knot. The removal of yarn defects is commonly known as yarn clearing in that the defect is detected by a yarn clearer which is sensitive to yarn defects and can either itself break the continuity of the yarn or operate a separate cutting member. Any discontinuity in the yarn causes the bobbin to undergo braking so that it stops, the yarn ends are picked up by mobile suckers and moved to the joining devices or knotters, the joined yarn is returned to its normal position and winding is recommenced, the bobbin and its drive roller being driven up from rest to the operating speed, which is generally of 600-1600 m/minute. The winding speed is determined - within the limits of the possible winding machine performance - by the quality and count of the yarn to be wound. The overall productivity of the operation is determined by the winding speed, the time taken by the overall intervention cycle and the actual number of interventions to be made. It is therefore apparent that if a certain yarn is wound at a too high speed, the increased productivity resulting from the increase in speed is compromised by the down times deriving from the increase in the number of interventions required to restore the yarn continuity due to the greater number of yarn breakages. The bobbin is normally driven by a rotating roller - of right cylindrical or slightly tapering conical shape - which is kept in contact along a generatrix common to the two members. The technical problem with which the present invention deals derives from the fact that during the winding operation the rotating roller does not change its shape or size, whereas the bobbin continuously changes its size due to the increasing amount of yarn wound on it. If the drive takes place under perfect friction, the peripheral speed of the drive roller is substantially equal to the linear winding speed of the yarn. The yarn is guided so that it winds on the bobbin in a spiral arrangement using a yarn guide of various shapes or spiral grooves formed in the surface of the driving roller, in which the yarn slidingly engages. By the action of such devices, the yarn is distributed over the bobbin surface by means of periodical travel along the bobbin generatrix. The closer together the turns, the more dense is the bobbin and vice versa. As the size of the bobbin increases, the linear yarn winding speed is kept substantially constant - this being a necessary condition for proper outcome of the operation - but the angular speed of the bobbin decreases linearly. As the yarn travels along the contact generatrix in constant time, the number of turns wound for each travel stroke of the yarn guide reduces slightly but continuously for each wound layer. As the bobbin forms it acquires an ever increasing inertia because of the increase in mass and its progressive distancing from the axis of rotation. The first stage in the intervention cycle which commences with the cutting or tearing of the yarn by the passage of a defective portion through the yarn clearer is the braking of the bobbin so that its speed decreases to zero. The brake must therefore absord the kinetic energy possessed by the rotating bobbin, and its stoppage time is substanstially proportional to said kinetic energy. Generally, the bobbin is braked by a mechanical shoe brake - or equivalent type - operated by pressurised fluid such as compressed air, which is distributed by a solenoid valve which operates following the yarn discontinuity signal. The drive roller is provided with its own braking devices, such as an inverter acting on its drive motor. To prevent damage to the bobbin it is desirable that the two braking actions take place independently, by withdrawing the bobbin and roller away from each other when the yarn discontinuity signal occurs at the commencement of the intervention cycle (US-A-4 195 790). According to another approach, disclosed in US-A-4 163 358, which relates to the winding of yarn coming from open-end spinning units, the bobbin and driving roller are allowed to rotate under inertial force a longer time when the bobbin is larger, and the brake is caused to operate only when the inertial rotation of the bobbin driving roller is reduced to a level at which no damage of the yarn can occur. The operations subsequent to the bobbin stoppage, i.e. the steps for knotting the broken or interrupted yarn, can take place only when the bobbin is at rest. In the known art the intervention cycle is effected as shown in the scheme of Figure 1. The duration of the intervention cycle is fixed and is divided into a fixed time available for bobbin stoppage and a fixed time for executing the other operations to be carried out during the intervention. After the stoppage time has passed, the bobbin must be completely at rest because otherwise the other intervention operations cannot be properly carried out, for instance it would be impossible to grip the end of the yarn on the bobbin side if this is still rotating. The drive and control unit for the members which sequentially carry out the various operations of the intervention cycle is a mechanical system - such as a shaft provided with a series of cams so that when rotated, said cams sequentially provide the drives for the various members, which consequently operate in sequence (US-A-2 733 870) - or an equivalent electrical control system. In this arrangement, the various intervention operations are performed sequentially by various members operated in accordance with a program of operation initiation times which are rigid and cannot be changed. To be more precise, it should be noted that certain preliminary operations, such as moving the yarn suckers into the correct position for seeking and picking up the yarn ends (these suckers being in their rest position at the commencement of the intervention cycle), can commence while the bobbin is still moving, but the actual operations of the intervention cycle subsequent to braking can only commence when the bobbin is properly at rest. If the bobbins to be produced are small or if the operating speed is low, the time taken by those preliminary operations which can be carried out while the bobbin is still moving is longer than the bobbin stoppage time, and there are therefore no problems. The fixed time allowed for bobbin stoppage must therefore correspond to the time required for absorbing the maximum kinetic energy which the bobbin can possess, and thus to its maximum possible winding speed, its maximum possible size and its maximum possible density. This time must then be increased by a certain safety margin to take account of any reduction in the efficiency of the braking system. The current tendency in bobbin production is to increase the winding speed and to maintain it when producing large-diameter bobbins. It is apparent that the criterion of assigning a fixed available time for bobbin stoppage based on the maximum kinetic energy which it can assume leads in most cases to a considerable time wastage because this fixed assigned time is necessary only when the bobbin has reached its maximum sheduled size and rotates at the maximum speed scheduled for this size. This is very important because this time wastage - even if only of the order of a few seconds - is repeated during every intervention cycle for restoring yarn continuity, and this cycle can take place hundreds of times. The deriving technical problem with which the present invention deals is to assign a bobbin stoppage time within the intervention cycle which is no longer fixed but is variable, and corresponds substantially to the time which the braking device would require at any given moment to bring the bobbin to rest, this time depending on the kinetic energy of the bobbin at the moment of this operation. The present invention consists therefore of winding method and devices for its implementation. It is essential by based on: dividing the intervention cycle - and the control devices which implement it - into two separate parts, a first part for braking and stopping the bobbin and directly linked to the break in continuity of the wound yarn (and which hereinafter is called simply braking) and a second part for the further stages of the intervention cycle which have to be carried out when the bobbin is at rest (and which hereinafter is called simply joining), and interposing between the commencement of the first part and the commencement of the second part a variable delay which is to be determined at any given time, and which is implemented by a timer device which controls the commencement of joining with a time displacement corresponding to said delay, which is equal to a time assigned for halting the bobbin; measuring the state of progress in the formation of the bobbin and transmitting this to the unit for identifying the delay to be assigned; identifying the delay to be assigned at any given time on the basis of the state of progress in the formation of the bobbin - and transmitting this to the timer device which implements this delay between the commencement of braking and the commencement of joining. Before describing in detail the invention, some introductory considerations are necessary. Mechanical bobbin braking systems exert a practically constant braking torque as the speed varies, and consequently the time required to halt the bobbin is essentially proportional to the bobbin kinetic energy. The time required for stopping the bobbin is therefore unequivocally determined by its state of progress - once the braking torque of the braking device is known. The bobbin stoppage time, and the kinetic energy which it possesses, depend therefore both on initially assigned parameters, namely; yarn count initial tube size manner in which the yarn guide undergoes its travel strokes peripheral speed of the drive roller (which is substantially equal to the linear winding speed), which do not vary as the bobbin progresses, and also on the actual bobbin progress itself, which can be measured as the number of revolutions made by the drive roller from the commencement of bobbin formation, or the length of yarn already wound on the bobbin, or the useful time which has passed from said commencement. These three indications of the state of progress are all equivalent as they are related by strictly linear relationships. Other indications of the state of progress of the bobbin under formation can be the number of revolutions undergone by the bobbin, its angular speed, its diameter etc. The variation in the times required to halt the bobbin as a function of its state of progress is shown in Figure 2. Whichever of the aforesaid indications is used as the reference, the variation is always upwards with growth in the state of progress of the bobbin under formation. The characteristics of the present inventin will now be described, commencing from the division of the intervention cycle and its control devices. The first part of the intervention cycle, which commences on receipt of a signal indicating yarn discontinuity - either because it has been cut intentionally by the yarn clearer, or because it has broken naturally or because the feed package is empty - consists of the following main stages: raising the bobbin away from the drive drum braking the bobbin braking the drive roller. All these three operations are related to each other and are controlled either electrically, for example by means of a solenoid valve operating with compressed air, or mechanically by means of a rotary shaft provided with cams. The various operations concerned and the devices which implement them proceed without rigid time relationship with the second part of the intervention cycle. The second part of the intervention cycle can commence either simultaneously with the first - if no delay instruction has been transmitted by the delay identification unit - or with a delay in accordance with the instructions from said delay identification unit. The second part of the intervention cycle consists of the following main stages: moving the yarn suckers which seize the yarn ends on the bobbin side and the supply package side; sensing the presence of yarn; if there is no yarn present on the package side, operating the package changing devices and, when the package has been changed, seizing the ne yarn end on the package side; disenabling the command which has implemented the first part of the cycle: the brakes are released, and the bobbin and roller are again brought into contact; reversing the motion of the drive roller for a short time to allow the sucker which seizes the yarn end on the bobbin side to operate which a sufficient length of yarn to reach the knotter; inserting the yarn ends into the knotter; operating the knotter to make the join and then release the joined yarn (in the meantime the yarn seizing suckers can return to their rest position); restarting the drive roller. These stages of the second part can also be controlled mechanically, for instance by a rotary shaft provided with a series of cams which gradually operate the controls for the devices implementing the aforesaid steps, or by equivalent electrical or electronic devices. The state of progress of the bobbin under formation is measured in the following manner. The present invention is based on an empirical criterion which overcomes the complexity of the relationships between the winding parameters, which can vary with considerable frequency according to the type and count of the yarn being wound and according to the type of bobbin which any specific user may require. This criterion is based on the following considerations. During the formation of a bobbin the breaks in yarn continuity are very frequent and can amount to some hundreds. The stoppages and restarts succeed each other with some frequency, and if there is no influence by outside factors each stoppage takes a progressively longer time. The effective time which the bobbin has taken to come to rest during the preceding intervention cycle is therefore used as the empirical indication of its actual state of progress. During each intervention cycle the time between the moment in which the command for braking the bobbin is given and the moment in which the bobbin-at-rest sensor indicates that it has actually stopped is measured, and the measured value indicates the time required for the bobbin to come to rest. Operationally, the bobbin-at-rest state can be likened to the attaining of an absolute or relative speed value which is below a predetermined minimum value. By way of example, this sensor can consist of a relay coupled to a magnetic pick-up system with a polar wheel rigid with one of the rotary fixing centres of the bobbin carrier arm, or be in the form of equivalent sensors known in the art. The measured value of the state of progress of the bobbin expressed as the time required for the bobbin to effectively come to rest during the preceding intervention cycle is fed to the unit for identifying the time delay to be assigned. The delay to be assigned is identified in the following manner. A progressively increasing series of times to be left available for halting the bobbin will be assumed. For example, if the following time series is set: 2 seconds (not less than the time occupied by the preliminary operations which can be carried out while the bobbin is still moving), 3 seconds corresponding to a delay of 1 second, 4 seconds corresponding to a delay of 2 seconds, 5 seconds corresponding to a delay of 3 seconds, 6 seconds corresponding to a delay of 4 seconds, and so on. This series of times, or delays, is set as a series of times to be assigned by the identification unit. The criterion used in identifying the times or delays to be assigned for bobbin braking is that the time assigned should be greater than the time required for its effective stoppage. This criterion consists of increasing in absolute or percentage terms the stoppage time measured during the preceding cycle and then assigning, as the time available for braking in the next intervention cycle, the minimum term of the aforesaid time series example plus the said increase. If for example the chosen criterion consists of assigning a time available for braking which is not less than 120% of the effective stoppage time during the preceding intervention cycle, and if the series of values to be assigned is that stated heretofore by way of example, the values in seconds given in the following table are obtained: Consequently, the following series of pairs values is obtained: for T lim1 = 1.67 seconds, delay Δt₁ = 1 second for T lim2 = 2.5 seconds, delay Δt₂ = 2 second for T lim3 = 3.33 seconds, delay Δt₃ = 3 second and so on. In contrast, if the chosen criterion is to assign a time available for braking which is equal to the effective stoppage time during the preceding intervention cycle increased by 0.5 seconds, and the series of values to be assigned is that stated heretofore by way of example, the values in seconds given in the following table are obtained: there will be the following series of pairs of values: for T lim1 = 1.5 seconds, delay Δt₁ = 1 second for T lim2 = 2.5 seconds, delay Δt₂ = 2 seconds for T lim3 = 3.5 seconds, delay Δt₃ = 3 seconds and so on. Depending on the criterion used for assigning the times available for braking or the delays to be introduced for the commencement of the second part of the intervention cycle, a discrete series of pairs of increasing values is obtained to be fed into the memory of the main computer provided on the machine, or of the microprocessors provided in each winding station. The patterns of the stepped lines corresponding to the two sets of pairs of values are given in Figure 3. This criterion for assigning delays enables the time assigned for braking to be adapted to any pattern of the curve of Figure 2, and therefore does not require stoppage time calculations and/or experimental determinations to be made for sample bobbins in order to determined the series of limiting state of progress values beyond which the delay Δt n must be incremented, and which would need to be memorised in the memory. It is apparent that the more numerous and close together the terms of the increasing series of times and/or delays to be assigned for bobbin braking, the closer the stepped line corresponds to the curve of Figure 2, from which it deviates essentially by the applied increase, which itself depends on the required safety margin. The characteristics and advantages of the present invention will be more apparent from the description given hereinafter of a typical embodiment thereof with reference to Figures 4 and 5. The bobbin 1 under formation, the tube of which is engaged on fixing centres of a bobbin carrier arm 2, rests against a bobbin driving roller 3 which rotates at a constant speed, driven by a motor 4 by way of a toothed belt drive 5. The bobbin 1 is therefore rotated by the roller 3 and winds the yarn about itself, its diameter gradually increasing. The bobbin carrier arm 2 carries in its fixing centres a mechanical brake 6 operated pneumatically by compressed air through a solenoid valve 7. On the fixing centres of the bobbin carrier arm 2 there is provided a bobbin-at-rest sensor 8 which, when the bobbin 1 has stopped, feeds a pulse to a time measurement instrument 9 which is connected to the control for the solenoid valve 7 and measures for each intervention cycle the effective time interval between the actuation of the brake control solenoid valve 7 and the moment when the bobbin 1 comes to rest and the sensor 8 sends the pulse to the instrument 9. Each winding station - commonly known as the winding head or simply head - is provided with a control unit comprising a microprocessor MP which generates the commands and controls the operations of the winding head. Said microprocessor MP is operatively connected to the following: to the yarn sensor SENS which - when it detects a break in yarn continuity - tells the microprocessor MP that the intervention cycle has to commence; to the brake control FREN which operates the brake 6 by the solenoid valve 7 and operates the other members which implement the braking cycle; to the measuring instrument 9 from which it receives information relative to the effective braking time and therefore obtains the previously described "empirical" state of progress; to the inverter INV to which it feeds stop and start signals for the motor 4 and thus for the roller 3; and to the joining control GIUNZ which sequentially activates the various members of the joining device which implement the joining cycle. The delays with which GIUNZ is activated are determined by a timer device incorporated in the microprocessor MP but not indicated on the figure. The microprocessor MP is also connected to other winding head functions and also to the machine processor or head computer CT which controls the operation of the entire winding machine by information and control interchange with the various microprocessors MP. The procedure takes place in accordance with the following logic scheme. The microprocessor MP contains in its memory the set of pairs of values of limiting effective bobbin stoppage times and delays to be assigned; this set can be modified by command from the CT. At each commencement of formation of a new bobbin, the microprocessor MP zeroes the last recorded effective stoppage time relative to the completed bobbin. At an n tM break in the continuity of the yarn the bobbin/roller assembly is braked, each separately by its own brake, and the effective bobbin braking time T n is measured through sensor 8 and instrument 9. The command for commencing the second part of the n tM intervention cycle, governed by the unit GIUNZ, is given by the microprocessor MP with a time delay Δt determined on the basis of the effective stoppage time T n-1 and measured with a timer device. The effective bobbin stoppage time of the n tM intervention cycle is compared with the series of limiting of values T lim1 , T lim2 , T lim3 ... to find the minimum T lim value which is stil greater than the measured T n , and the corresponding Δt is used for the next (n+1) tM intervention cycle. This new Δt delay value is fed into the timer device and is valid for the next (n+1) tM cycle. This logic scheme is shown in Figure 5. A modification of this logic scheme is shown in Figure 6, in which the determination of the delay Δt to be used for the n tM intervention cycle is made - again by comparing T n-1 with the values of the set of T lim values - at the moment of the n tM break in yarn continuity. The advantages obtained by the present invention are apparent from the aforegoing description, namely: the possibility of varying the time available for bobbin braking means that winding can proceed at higher speeds and/or larger diameter bobbins can be wound without extending said braking time beyond that strictly necessary; any efficiency loss in the bobbin brakes with the passing of time can be compensated by varying the series of T lim values and/or the series of times available for stoppage; the winding speed and/or the diameter of the bobbins produced can be varied without modifying either the machine or the data stored in the machine processor memories; the winding machine can be automatically adjusted for any variation in winding parameters or efficiency of the braking device; the criterion for assigning the method safety margin can be varied by simply varying the T lim set contained in the memory.

Claims: 1. A bobbin winding method comprising cycles for restoring yarn continuity by which the bobbin is halted and the ends of the discontinuous yarn are joined together, said cycles being divided into two parts, of which the first part is devoted to braking the bobbin and the second part is devoted to joining the yarn ends, characterised in that between the commencement of the first part and the commencement of the second part of the yarn continuity restoring cycles there is interposed a variable time delay which is determined at any given time on the basis of the state of progress of the bobbin measured at the moment of the preceding cycle, said state of progress of the bobbin being defined by the amount of time required for the bobbin to come to rest in said preceding cycle. 2. A bobbin winding method as claimed in claim 1, characterised in that the time required for the bobbin to come to rest is measured by the time interval between the moment in which braking is applied to the bobbin and the moment in which a signal that the bobbin is at rest is given. 3. A bobbin winding method as claimed in claim 1 or 2, characterised in that the time delay to be interposed between the commencement of the braking part and the commencement of the joining part of the cycles is determined by comparing the amount of time required for the bobbin to come to rest in the preceding cycle with a series of predetermined limiting values of said amount of time required for coming to rest, and a delay time is adopted which corresponds to the minimum value in the series of limiting values of time which is still greater than the measured time required for the bobbin to come to rest in the preceding cycle. 4. A bobbin winding method as claimed in claim 3, characterised in that the series of delay time values to be introduced between the commencement of the two parts of the cycles consists of a discrete series of increasing time intervals. 5. A bobbin winding method as claimed in claim 4, characterised in that the first value of the series of delay time values is zero. 6. A device for carrying out the bobbin winding method of one or more of the preceding claims, comprising a bobbin driving member (3) and a brake (6) for braking the rotating bobbin (1) on detecting a yarn discontinuity, and a yarn joining device for joining together the ends of a discontinuous yarn, characterised in that it further comprises a device (9) for measuring the time required for the braked bobbin (1) to come to rest, and a control unit (MP) operatively connected to said measuring device (9) for receiving time measures therefrom and comprising a timer device for controlling operation of said yarn joining device with a variable time delay starting from the commencement of the bobbin braking, wherein said time delay is determined each time on the basis of the state of progress of the bobbin (1) at the moment of the preceding cycle, said state of progress being defined by the amount of time measured by said measuring device (9) in the preceding bobbin braking cycle. 7. A device as claimed in claim 6, characterised in that said measuring device (9) comprises a time measuring instrument connected to a bobbin brake control valve (7) and to a sensor (8) responsive to a bobbin rest condition, said instrument measuring the time interval between the actuation of said brake control valve (7) and the receiving of the signal from said sensor (8). 8. A device as claimed in claim 6, characterised in that said control unit (MP) comprises a microprocessor having stored therein a series of limiting values of times required for the bobbin (1) to come to rest as a function of the state of progress of the winding, and in that the microprocessor is programmed for determining said time delay by comparing the measured time required for the bobbin (1) to come to rest in the preceding cycle with said series of limiting values and by adopting a delay time value which corresponds to the minimum value in the series which is still greater than the measured time required for the bobbin (1) to come to rest in the preceding cycle.

Inventors: BADIALI, ROBERTO, COLLI, LUIGI, MARANGONE, NEREO
Applicants: SAVIO S.P.A.
Application year: 1988
Main classification: B65H63
IPC codes: B65H63, D01H4