EP0337339B1 - System for controlling a movement - Google Patents

Abstract

Movements of a portion of yarn during the piecing operation are regulated by means of a digital position controller. <IMAGE>

Description

This invention relates to a controllable movement system for moving an elongated structure, e.g. a thread, a fuse or a ribbon. The invention is especially designed for use in attaching devices for spinning machines, but is also not restricted to such applications.

State of the art

According to the current state of technology, attachments to spinning machines are controlled on a time-dependent basis. The individual processes, such as the switching on and off of motors, the actuation of clutches and solenoid valves, are determined with a time sequence Program controlled. The execution of the relevant actions is monitored by sensors such as limit switches, pressure switches, light barriers. This monitoring makes it possible to cancel certain processes when they have reached their destination and, if necessary, to start another process after the completion of a certain process (see DE 3634992 and CH 640576).

The type of control described comes from the technology of mechanical program switching mechanisms, in which the course of the program is determined by a series of cam disks, which are rotated by a motor at a constant speed. Modern microprocessor technology has adopted this structure directly. Instead of the shaft rotating at constant speed with the cam disks, only an internal time counter now occurs. Very complex processes are divided into individual, time-controlled and process-controlled processes that the microprocessor processes individually. This type of control is shown in the patent specification CH 640576 in FIG. 6.

• ― Der Fadenantrieb wird vor Erreichen der Endlage in den Schleichgang umgeschaltet und faehrt dann mit geringer Geschwindigkeit bis zur bestimmten Endposition. Diese Loesung entspricht der ueblichen Steuerungstechnik. Sie erbringt die gewuenschte Praezision der Endposition auf Kosten des erhoehten Zeitbedarfes.
• ― Die Fadenbewegung wird durch mechanische Hebel mit festen Anschlaegen erzeugt (siehe DE 3634992, Figur 3). Damit wird wohl der zurueckgelegte Weg praezise begrenzt, aber die Geschwindigkeit ist dem freien Spiel der Massen und Kraefte ueberlassen, was zu mangelhafter Reproduzierbarkeit der Zeitablaeufe fuehrt.

The described type of control now has the major disadvantage that any deviation in the speed, for example as a result of voltage fluctuations or motor warming, leads to significant deviations in the thread length, which is promoted by the drive in the given time. To avoid this, two measures are used:

• - The thread drive is switched to creep speed before the end position is reached and then moves along low speed to the certain end position. This solution corresponds to the usual control technology. It provides the desired precision of the end position at the expense of the increased time requirement.
• - The thread movement is generated by mechanical levers with fixed stops (see DE 3634992, Figure 3). This probably limits the distance covered, but the speed is left to the free play of the masses and forces, which leads to poor reproducibility of the time sequences.

German Offenlegungsschrift 2130690 describes a method according to which the length of the piece of thread spun back in an attachment process is controlled by counting pulses and these pulses are generated as a function of the rotation of a feed roller. The counting process is triggered by determining the end of the piece of thread to be fed back. Such a method only tries to determine the beginning and the end of the thread end movement.

It is the object of this invention to achieve a substantial improvement in the accuracy of movement systems for moving elongated structures.

The invention provides a system for controllably moving an elongated structure with a movable element, means for coupling the structure with the element and drive means for controllably moving the element. The invention is characterized in that the drive means has a control loop includes which can effect the continuous or pseudo-continuous regulation of the position of the movable element.

The drive means may advantageously include a motor with a rotatable shaft. The movable element can then be a roller, which is preferably rigidly coupled to the motor shaft.

The control loop can be a programmable device that can calculate a preprogrammed movement sequence on the basis of a determinable start position and a predetermined end position and that compares the actual sequence continuously or pseudo-continuously during the movement with this target sequence and forwards corresponding corrections to the drive means. The device can also be programmable with respect to the desired speed or acceleration.

Such devices are commercially available today, e.g. by Galil Motion Control, Inc., 1054 Elwell Court, Palo Alto, California under the designation MCC-3000 (Motion Control Chip Set). The theory and the mode of operation of such devices are in the publication "Motion Control by micro Processors" by Jakob Tal, which publication is available from Galil Motion Control, Inc.

• Figur 1: Eine schematische Darstellung eines Bewegungssystems gemaess dieser Erfindung,
• Figur 2: Einen Bewegungsablauf gemaess dem Stand der Technik fuer ein Ansetzverfahren beim Rotorspinnen,
• Figur 3: Ein Bewegungsablauf, welcher beim gleichen Verfahren durch ein Bewegungssystem gemaess dieser Erfindung erreichbar ist,
• Figur 4: Ein Geraet gemaess dieser Erfindung in Kombination mit einer Vorrichtung zur Bestimmung der Anfangsposition des Fadenendes,
• Figur 5: Eine Variante von Figur 4,
• Figur 6: eine Rotor-Spinn-Einheit (schematisch dargestellt),
• Figur 7: eine Steuerung zur Verwendung mit der Einheit gemäss Fig. 6, und
• Figur 8: ein Bewegungsdiagramm für ein von dieser Steuerung bewirktes "Fahrprogramm".

The invention is of particular advantage in connection with preparation processes in spinning machines. In such processes, it is known that it is necessary to precisely control the movement of a thread end, so that other operations (for example feeding fibers) are precisely controlled in connection with this Movement can be performed. This applies, for example, to the application of the rotor spinning process, for example, as was written in our USPS No. 4689945 (object 610), but also to the application of so-called nozzle and / or friction spinning, for example, as in our Switzerland. Patent applications Nos. 1695/87 and 4950/87 have been described. Such thread movements can very well be carried out with a system according to this invention, the movable element being formed by a rotatable roller and the coupling means being formed by a counter roller. In this case, only the first-mentioned roller is driven positively by the drive means, while the counter-roller is driven only by its contact with the first-mentioned roller. Such a pair of rollers is known per se from German Offenlegungsschrift 2711554. An embodiment of the invention will now be described in more detail as an example with reference to the drawings. It shows:

• FIG. 1: a schematic representation of a movement system according to this invention,
• FIG. 2: a motion sequence according to the state of the art for an attachment method in rotor spinning,
• FIG. 3: a movement sequence which can be achieved in the same method by a movement system according to this invention,
• FIG. 4: A device according to this invention in combination with a device for determining the starting position of the thread end,
• Figure 5: A variant of Figure 4,
• FIG. 6: a rotor-spinning unit (shown schematically),
• FIG. 7: a controller for use with the unit according to FIG. 6, and
• Figure 8: a movement diagram for a "drive program" effected by this control.

The description first refers to the diagram in FIG. 1. The thread 1 to be moved is clamped and conveyed by a drive roller 2 and a pressure roller 3. The thread end, not indicated, is guided by a guide, not shown, in a known manner, e.g. during rotor spinning through the extraction channel of the rotor spinning unit back into the rotor. The driving roller 2 sits on the shaft of a motor 4. An incremental rotary encoder 5 is arranged on the same shaft. The electronic power actuator 6 uses the supply voltage 8 to generate the regulated current 10 required to operate the motor. The current setpoint 9 is fed to this actuator by the digital position controller 7.

The digital position control device 7 receives as setting information signals on the one hand the target values for the target position 12 of the thread end, the desired speed 13 and the desired acceleration 14, on the other hand the output signal 11 of the incremental rotary encoder 5.

The position control device 7 calculates the speed assigned to each point of the route to be traveled from the setpoint signals input to it Speed setpoint. The same circuit determines the actual value of the position from the output signal 11 and the actual speed by differentiating according to the time. The control signal for the power actuator is determined from the three available values actual position, target speed and actual speed with the aid of known controller algorithms.

A suitable position controller for use on the position device 7 is available from the above-mentioned company Galil Motion Control, Inc. under the name Motion Control Chip Set MCC-3000.

The diagrams in FIG. 2 and FIG. 3 show the difference between the time-dependent and the route-dependent control of the thread feed. The speed (vertical axis) is shown in the left part by the solid line as a function of time. In the same diagram, the path covered is shown as a dashed line. In a suitable projection, the speed is shown as a function of the path on a separate diagram part on the right.

Figure 2 shows the conventional type of control. The movement process begins at time 1. After a phase of constant acceleration, the desired feed rate is reached in time 2 and then maintained until time 3. At this point the delay begins. If larger tolerances are accepted in the stopping point, this delay phase ends directly with the standstill. Since errors add up in this process, the approximation to the Desired end position normally carried out in creep speed. Switch to slow speed at time 4, the brake is applied at time 5 and the end position is reached at time 6.

In contrast, Figure 3 shows the route-dependent regulated process. Start-up and feed at constant speed up to changeover point 3 (initiation of the braking process) are basically the same as for the time-dependent control. The switchover point 3 is now determined not as a function of time, but as a function of the travel and the delay process is also regulated as a function of travel. The target point X is thus reached without loss of time and without irregularity in the movement sequence. The path-dependent control of the thread speed avoids scatter in the position of the thread end and in the length of time the thread end stays in the twist element and thus provides a reproducible attachment process.

The torsionally rigid coupling of the drive roller to the motor shaft is important for high accuracy of the thread movement. It is therefore advisable to mount the drive roller directly on the motor shaft or at least to connect both elements with a short, torsionally rigid coupling.

It is also important for the accuracy of the piecing process that the end of the piecing thread is precisely recorded as a reference for the entire movement. Two different methods are possible for this, which are shown in more detail in FIGS. 4 and 5.

The first method (Figure 4) is the end of the thread 30 after being drawn into the drive roller pair 31 (which corresponds to the roller pair 3, 2 shown in FIG. 1) and to be cut off at a certain distance. For this purpose, a suction pipe 32 is used in connection with a thread cutting device 33. This method is already known in connection with unregulated thread drives. Its disadvantage is that a clearly defined cut of the thread end is disadvantageous for the formation of the piecing. In this regard, a loosened thread end is cheaper, for example, as a result of a grinding process. However, when the thread is cut by grinding, the precisely defined distance between the drive roller and the cutting point is lost.

A second method proposed here (FIG. 5) is therefore based on a separate detection of the thread end. The thread 30 is separated by the grinding wheel 34. Then it is pulled back by the drive itself and passes a thread monitor 35 during this process, for example in the form of a photoelectric barrier. As soon as the end of the thread passes the barrier 35, the signal "no thread" arises, which in turn sets the value for the thread length in the drive control to the distance between the drive roller pair 31 and the photoelectric barrier 35. Relating to the Galil Motion Control Chip Set this signal corresponds to the command DH "Define Home".

The invention is not restricted to the described embodiment. For example, further electronic control loops are known as the variants mentioned by Galil Motion Control, Inc. A digital system based on microprocessor technology is advantageous, but an analog system is conceivable. The sequence shown in FIG. 3 is not essential to the invention. For example, in connection with a jet spinning process, it is not always important to control the recycling phase precisely. It would then under certain circumstances be sufficient to determine the starting position of the thread end and to pull the thread end by means of a movement system according to this invention from this starting position through a thread formation point, a piecing tool being formed by this thread formation point when pulling the thread end. A taxed movement in the sense of this invention then only takes place in one direction.

The invention is also not restricted to the use of rotatable elements. With the help of a linear drive e.g. a linear movement can be controlled and transmitted to a thread by means of a clamping element.

In order to clarify the potential application and advantages of the invention, the use already mentioned for application in a rotor spinning machine will now be explained in more detail with reference to FIGS. 6 and 7. FIG. 6 schematically shows a rotor spinning unit with a rotor 60, rotor bearing 62, housing 64, suction channel 66 and cover 68. The cover 68 can be moved relative to the housing 64 in order to close the housing (FIG. 6) or to open it and thereby the rotor to expose.

The cover 68 comprises a projection 70 which, when the housing is closed, extends into the open end of the rotor 60 protrudes. A feed channel 72 extends between a fiber feed (not shown) and an orifice 74 in the projection 70. Fibers can be conveyed into the rotor 60 in an air stream through the channel 72 to form a fiber ring in the rotor groove 76. The air flows between the rotor edge and the cover and out of the housing through the suction channel 66.

The cover 68 further comprises a withdrawal channel 78, through which the yarn formed can be withdrawn during normal operation and an auxiliary yarn 80 can be fed into the rotor 60 for attachment, as will be described below. A sensor 82 is also provided in the cover 68 and can respond to a signal generator 84 to trigger the feeding of fibers through the feed channel 72.

The signal generator 84, together with a pair of rollers 86, 88 and controller 90 (FIG. 7), is carried by a mobile attachment device, not shown. If necessary, the device can be positioned at the spinning position shown in FIG. 6 in order to carry out a preparation process. In this context, "attaching" is equated with "piecing", i.e. no difference is made between restarting spinning after a thread break and restarting after the machine has been switched off.

The pair of rollers 86, 88 corresponds to the pair of rollers 2, 3 (FIG. 1) - the roller 86 is rotated in operation by a motor 92 and the roller 88 is thereby held by a holder 80 (not shown) with the roller 86 in the sense " coupled "that the movement of the yarn 80 in the direction of its own length (at least in the nip line of the rollers 86, 88) by the Rotation of the roller 86 is determined. The movement of the 80 A yarn end will correspond to the movement in the nip line, provided, of course, that the yarn is kept stretched between the nip line and the yarn end. This can be ensured by inserting the yarn end 80 A into the extraction duct 78, an air flow being generated through the duct by the suction 66, provided that the speed of the yarn end does not exceed that of the air flow.

The armature of the motor 92 is rigidly connected to the roller 86 via a shaft 94 and is also connected to a tachometer 96, which emits signals to the controller 90. On the basis of these signals, the known properties of the motor 92 and setpoints determined by an input device 98, which define a predetermined “driving program”, the controller calculates the necessary power signal that is supplied to the motor 92 in order to run through the “driving program” via the motor .

For this purpose, the tachometer 96 emits a large number (eg 2000) of pulses per revolution of the motor shaft 94 to the control. This corresponds to a fine subdivision of the movement of the yarn into "digital sections" (eg with a diameter of the delivery roller of 12 mm and 2000 pulses per revolution, the tachometer transmits approx. 53 pulses per mm of yarn movement to the control). Under the above-mentioned conditions, the position of the yarn end can be determined continuously (or pseudo-continuously - with any accuracy depending on the effort), starting from a known starting position.

• ― einen Steuerprozessor 100
• ― einen digitalen Positionsregler 102 (in der Form eines Mikroprozessors) welcher ein "Fahrprogramm" in der Form von Sollwerten vom Prozessor 100 und Impulse vom Tachogeber 96 erhält,
• ― ein Leistungsteil 104, welcher ein Signal vom Prozessor 102 erhält und ein entsprechendes Leistungssignal an den Motor 92 abgibt, und
• ― einen Signalgeber 106, welcher die Speisung der Fasern über Geber 84 und Empfänger 82 auslöst.

The controller 90 includes:

• A control processor 100
• A digital position controller 102 (in the form of a microprocessor) which receives a "travel program" in the form of setpoints from the processor 100 and pulses from the tachometer 96,
• A power section 104, which receives a signal from the processor 102 and outputs a corresponding power signal to the motor 92, and
• - A signal transmitter 106, which triggers the feeding of the fibers via transmitter 84 and receiver 82.

The microprocessor 102 calculates both an actual speed and an actual acceleration for each “position” (position) of the “yarn end” and compares these values with the target values determined by the travel program. This comparison determines the output signal which is output to the power section and thereby defines the power signal delivered to the motor 92. This comparison is carried out for each new pulse by tachometer 96, so that the position control (position control) of the yarn end is "continuous" - the "continuity" can be increased by an increase in the number of pulses per revolution of the motor shaft - but this must be higher Accuracy can be bought through greater effort (especially in signal processing).

If lower accuracy is acceptable, this can be done by omitting the calculation of the acceleration (or even the speed) can be achieved for each position with a corresponding reduction in effort. Even under these circumstances, the system can be distinguished from the previously known proposals (eg JE 2711554) in that the known solutions do not include a control loop, but rely on the drive system to follow the control signals supplied to it. The new system will continuously check the response of the system to the control signals and improve it if necessary.

The signal processing in processor 102 is carried out according to algorithms determined by the manufacturer of the controller. Suitable controls are available from: GALIL, Palo Alto, California, USA and Hewlett Packard.

8 shows a time / path diagram for a system according to FIGS. 6 and 7, the position of the yarn end on the vertical axis and the time on the horizontal axis being shown. The "zero position" corresponds to the rotor groove 76 (FIG. 6). At time T the controller 90 emits a signal to trigger the fiber feed via the transmitter 84, the yarn end 80 A maintaining a predetermined distance A (FIG. 8 - for example 40 mm) from the rotor groove. At the time To, the end of the yarn lies in the draw-off channel 78, possibly in the rotor 60, the yarn being returned along the channel 78 also according to a program determined by the controller 90 in order to ensure the continuous stretching of the yarn.

At time T, before the completion of the formation of a Fiber ring in the rotor groove 76, the movement of the yarn is triggered to penetrate this ring. According to the program, this movement is carried out at a predetermined speed and is carried out at time T2, the position of the yarn end being continuously regulated as previously described.

It should be noted that the initiation of fiber feeding is a quick process, but its course is uncontrolled. It is triggered by a start signal, which simultaneously represents the reference point for the reference to the parallel thread feed process. The reference to this reference is temporal in nature.

When the thread feed is regulated, the control tasks are expediently divided into a control processor (100) and digital thread feed regulator (102). The process as a whole is triggered by processor 100. This processor can now give the start signal for both processes in a staggered manner, whereby the digital thread feed controller generates the required precision. However, it is also conceivable to compare the position of the thread parallel to the position control loop with a threshold value, which then starts the fiber feeding purely depending on the thread position.

Both processes are fundamentally coordinated by the processor 100, on the one hand, by starting the fiber feeding directly, on the other hand, entering the setpoint curve for the thread feed and also triggering it. In general, the thread feed starts earlier than the start the fiber feeding.

After a predetermined dwell time T, the controller 90 triggers the withdrawal of the yarn 80 at the time T. The withdrawal is carried out in two phases, namely a first phase P, which corresponds to the withdrawal of a predetermined withdrawn yarn length L at a predetermined speed, and a second subsequent phase, which is of indefinite duration but at a predetermined operating speed (production speed) higher than the yarn speed is during the first phase. The second phase is ended in that the yarn is delivered from the pair of rollers 86, 87 to the take-off system, not shown, of the machine.

It has been shown that when attaching a yarn to a rotor spinning machine, it is of the utmost importance for the quality of the attacher how the linear movement runs in an area that corresponds to the first rotor circumference.

There is a fiber ring in the rotor groove, the cross-section of which has not yet settled through continuous feeding and spinning, and which has a marked inhomogeneity due to the tearing with the attached thread. With the digitally controlled control, an individual adjustment can be made in precisely this size range, in the case shown the reduced take-off speed over the first rotor circumference L, see diagram in FIG. 8.

With digital technology, it is possible to move the thread in quick succession over lengths, which correspond to the circumference of the rotor 2, to be controlled precisely and to be linked to the fiber feed. A high degree of flexibility is also achieved through programmable control:

Every modification of the motion sequence is carried out in the software or by adjusting decade values. The mechanics can be used universally over a wide range or can be adapted to the conditions.

Last but not least, the price for a simple mechanical system is likely to be lower than for a fairly complex arrangement that has to be chosen in order to implement the handling of the yarn with the help of clamps, movable pliers and drive elements via stops and levers.

The quality of the attachment point in the yarn is immediately much better with the process of digital position control than with the conventional one with the automatic attachment machine. Although this result has been sought, the improvement in strength and uniformity is surprising, and it has not been expected to this extent by a person skilled in the art.

AA = automatic attachment (without servo component) servo component = device according to the invention.

The principle of the controlled yarn movement allows a controlled insertion of the thread end into the spinning unit in the whole area.

Because the yarn is always firmly coupled to the feed motor, and because the speed of the movement can always be adjusted to the technological needs with the controlled drive, the end can be inserted into the rotor through the extraction nozzle so that the air flow is always in an extended position worries. It is known that too fast a movement when entering the rotor space causes the yarn end to strike the opposite wall, which leads to changes in its structure which have a negative effect on the quality of the piecing.

Due to the quick regulation, the position of the Yarns always follow the target values, an insertion and extraction of the yarn end exactly coordinated with the fiber feed can be ensured without losing control of its exact position at some point.

In this way it is possible to always run the same distances - to be optimized in technological tests - for the individual phases of the piecing process at the same speed, and at the same time to switch on the fiber feed accordingly.

As mentioned before, the invention is not only applicable in connection with the rotor spinner. Where an elongated structure can be coupled to a drive system that can be controlled by a position control loop, this invention can be used to determine the movement of the structure.

It is not necessary for a pair of rollers to be provided for the delivery of the thread or another elongate structure. It is also conceivable that two non-rotatable clamping elements are attached to a lever, which move the thread on an arc or along a straight line. This swiveling movement only covers fractions of a full circle and therefore has to be resolved particularly finely. This applies analogously to a pair of linearly movable clamping elements.

In order to substantiate this statement, two further exemplary embodiments according to the invention will now be explained, both versions being suitable for use in an operating robot for a ring spinning machine.

Figure 9 shows the working head of a device 150 for the controlled formation of yarn turns around a body having a longitudinal axis P, e.g. a spindle 102 and a sleeve (not shown) carried by spindle 102. The device 150 comprises a carrier section 220, a C-shaped holder 222 and a C-shaped operating runner 224 (which can be rotated about the axis P in a track 226 formed by the holder 222). The operator runner has a ring gear 228 which meshes with two pinions 230, which in turn mesh with a ring gear 232 on a disk 231. The disk 231 is directly connected to the shaft (not shown) of a drive motor 234.

The operating rotor 224 is provided with a clamping device 241 (FIG. 10) which has a pin 242 with a clamping head 246 and a spring load 244 (indicated schematically). Pin 242 extends through a bore in the operator runner and protrudes from the bore at both ends. The spring load 244 exerts a prestress on the pin, which normally presses the clamping head 246 into contact with the underside of the operating rotor 224 and thus forms a clamping point K. By overcoming the spring load, the pin can be moved along the bore to open the clamping device.

In operation, a thread end to be moved with the clamping device 244 open is between the clamping head 246 and the Service runner 224 brought and held by closing the clamping device (connected to the service runner 224). A controlled winding operation can then be performed (after appropriate positioning of the elements) by starting the motor 234 and transmitting the rotation of the motor shaft to the operator rotor 224 via the pinion 230. The thread to be wound is dragged along by the clamping device (eg from a suitable storage device) and forms thread windings on the spindle 102 (or sleeve).

Figures 11, 12 and 13 show another controllable movement system for a thread. This system comprises two levers 172, 176, which are connected to one another via a pivot axis 174 with a motor drive (not particularly indicated). Lever 176 is connected to a housing 190 via a further pivot axis 188 (which is also provided with a motor (not indicated)). The latter is finally connected to a carrier 180 via a further, vertical pivot axis 178 (also with its own motor, not indicated). The lever 172 carries at its free end a holder 168 for the mouth part 167 of a thread store in the form e.g. a suction pipe 165, which is coupled to a suction system, not shown.

The stored thread F must be connected to an anchor point A. This location could, for example, be a clamping device according to FIG. 8. Figure 13 shows two other options. According to the first possibility (fully solid lines), the thread F is an auxiliary thread that was wound on a cop or on a sleeve after a thread break in order to enable the resumption of spinning. According to the Variant indicated by dashed lines, the thread F has been unwound from the yarn body of the cop 116 itself (after a search process). In both cases, the thread F has been threaded with a ring traveler carried by a spinning ring 106.

The motors of the axes 174, 178, 188 can now be started in order to move the mouth M of the part 167 in space in a controlled manner and to move the thread length between this mouth M and the rotor 108 accordingly. The suction system keeps the thread taut and the light width of the mouth M can be limited such that the predetermined (programmed) movement of the part 167 is converted into a corresponding specific movement of the thread.

FIG. 14 shows a block circuit diagram of a system for controlling the arrangements according to FIGS. 9 and 10 or FIGS. 11, 12 and 13, with a control system for the axes 174, 178, 188 each having to be provided in FIG. 11. Each drive motor MT has a shaft MW, which is coupled to the part to be moved (indicated by L in FIG. 14) and cooperates with an encoder E for determining the position (angular position) of the shaft. The motor MT is supplied with energy via an amplifier AMP, the power supplied by the amplifier being determined by a digital / analog converter DAC. The output signal of the converter DAC is controlled by a controller R, which in turn works in dependence on a comparator VGL.

The comparator VGL receives, on the one hand, a signal supplied by the encoder E, which corresponds to the actual position of the shaft MW, and, on the other hand, a setpoint, which is from the Program part PR is delivered. The controller R controls the motor MT in order to eliminate any deviations between the actual position (from the encoder E) and the target position (determined by the programming). The system can be designed such that the shaft moves from any start position with a predetermined driving characteristic to the end position defined by the programming.

When initializing the system, the sensor S indicates the position of the motor shaft MW or of the part L to be moved relative to a reference (e.g. a frame, not shown). Further movements of the motor MT or the shaft MW can be determined in relation to this initial position. In the complex system according to FIGS. 11, 12, 13, the movements of the three axes (shafts) 174, 178, 188 can be coordinated with one another in order to move the mouth part along a programmable path in space.

Claims (6)

1. A system for controlling the movement of a longitudinal object (30, 80), (e.g. a yarn, card sliver or a ribbon) with a movable element (2, 86), a means (3, 88) for coupling the object with the element (2, 86) and a driving means (4, 92) for controlling the movement of the element (2, 86), characterized in that the driving means (4, 92) comprises a control circuit for the continuous or pseudo-continuous control of the position of the movable element (2, 86) during its movement.

2. A system as claimed in claim 1, characterized in that the control (90) processes digital signals.

3. A system as claimed in claim 1 or 2, characterized in that the control circuit (90) controls the speed of the element (2, 86) at any controlled position of the element (2, 86).

4. A system as claimed in claims 1, 2 or 3, characterized in that the system is used in combination with a piecing device for a spinning machine and controls the movement of a yarn piece (30, 80) during the piecing process.

5. A system as claimed in claim 4, characterized in that the spinning machine is a rotor spinning machine and that the system controls the movement of the yarn (30, 80) both during the feedback in a spinning unit (60) and the drawing off of the yarn piece with the newly pieced yarn.

6. A system as claimed in claim 4, characterized in that the spinning machine is an air spinning machine and that the system is used for controlling (90) the movement of a yarn piece in a single direction through a yarn forming position.

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