Abstract:
The invention relates to a yarn feeding device (F) for weaving or knitting machines whose winding element (W) is driven by an electric motor (M) controlled by an electronic speed control device (CU). According to the invention, the electric motor (M) is a synchronous motor, in particular, a permanent magnet (PM) motor with the speed control device (CU) provided for effecting a permanent vector control with the stator being sinusoidally acted upon. Continuously determined information pertaining to the relevant rotational position of the rotor (R) of the motor (M) is used in the speed control device (CU), which serves to perform permanent vector control, in order to adjust at least one predetermined rotational position (X 1,  X 2 ) of the winding element (W).

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a yarn feeding device and more specifically to the use of an electric synchronous motor for controlling a yarn feeding device.  
       BACKGROUND OF THE INVENTION  
       [0002]     The yarn feeding device known from EP 0 580 267 A1 comprises a pre-control device using the signals of a position sensor provided in the yarn feeding device in order to slowly drive the electric motor after switching off the electric motor by the speed control device until the winding element reaches a predetermined rotational position in relation to the housing. The control effort needed is considerable.  
         [0003]     The yarn feeding device as known from EP 0 327 973 A (U.S. Pat. No. 4,936,356) is provided with a detector fixed to the housing which detector can be actuated by a transmitter rotating with the winding element in order to adjust the winding element with slow rotational speed into a predetermined position relative to the housing when the speed control device has to switch off the electric motor. The predetermined position of the winding element e.g. may be appropriate in order to facilitate threading of the yarn through the yarn feeding device.  
         [0004]     U.S. Pat. No. 4,814,677 A generally discloses a field orientation control system of a permanent magnet motor operating by sinusoidal stator part actuation. The information on the momentary rotary position of the rotor is derived from measured stator voltages and stator currents. This is carried out without additional position sensors. The detected relative rotary positions of the rotor are used for the speed control and the torque control of the permanent magnet motor.  
         [0005]     The so-called brushless DC motor (BLDC) known from EP 10 52 766 A2 (U.S. Pat. No. 6,356,048) is employed as the drive source for the winding element of a yarn feeding device. The motor is designed without sensors. A control system is provided for controlling the torque and/or the speed of the motor. The control system calculates the commutation switching points for the stator parts in six angled positions which are distant by a respective 60° without a position sensor. In this case the zero crossing points of the backwards acting electromotoric force are determined which are induced in the stator windings by the rotation of the rotor magnets. In-between the six switching points, distributed about a full revolution, the position of the rotor remains unknown. The backwards acting electromotoric force is effected according to a trapezoidal course. This motor drive control principle does not allow a sufficiently accurate position control and position observation of the winding element because only predetermined rotary positions of the rotor are detected.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of the invention to provide a yarn feeding device of the kind as disclosed herein which allows in a structurally simple and controllable fashion an accurate position control and/or position observation of the winding element in order to selectively and precisely reproducibly adjust a predetermined rotary position of the winding element which rotary position is needed for an auxiliary function of the yarn feeding device.  
         [0007]     Additionally, this object can be achieved particularly expediently and simply by employing an electric synchronous motor for the control of the yarn feeding device, particularly a permanent magnet motor, which operates with permanent (continuous) stator vector control and sinusoidal stator actuation, in order to carry out the position control and/or position observation of the winding element in relation to the housing of the yarn feeding device, and to use for that purpose the information about the respective rotary position of the rotor which anyhow is needed for the permanent (continuous) stator vector control.  
         [0008]     The speed device equipped with the microprocessor detects permanently (continuously) the relative rotary position of the vector of the rotor which position corresponds to the momentary rotary position of the rotor. This is carried out to permanently (continuously) rotate the stator vector generated by the sinusoidal actuation of the stator part such that the desired speed and/or the desired torque is gained substantially steplessly. The information on the momentary rotary position of the rotor or the rotor vector, respectively, is used to adjust the winding element into the at least one predetermined relative position in the housing by using the fixed structural correlation between the rotor, the shaft and the winding element. This relative position e.g. is needed to thread the yarn by means of an automatic threading device without further checking the rotary position of the winding element, or to adjust the winding element into a position in which a manual threading process can be carried out without problems. Additionally or alternatively, the information by which during the permanent vector control of the rotor rotation is followed can be used to measure the wound on yarn length. The capacity of the microprocessor is sufficient without problems for this additional function. No sophisticated additional control circuits are needed, and also no costly sensor assemblies.  
         [0009]     The motor, expediently, is a permanent magnet motor which is available for fair costs and is efficient and takes up only minimal mounting space. Basically, however, also other types of synchronous motors may be used within the scope of this invention, like e.g. so-called reluctance motors, so even so-called “switched reluctance motors (SR)”. In principle, even a so-called BLDC (brushless DC motor) could co-operate with the speed control device according to the invention.  
         [0010]     In order to be able to permanently (continuously) and precisely follow the movement of the rotor, it is of advantage when the permanent magnets in the rotor are designed (e.g. formed), magnetised and/or configured (placed) such that the backward acting electromotoric force induced by the rotor in the stator winding follows a sinusoidal course. With the help of the sinusoidal course the respective rotor rotary position can be calculated accurately which is of advantage for the permanent (continuous) vector control, and which is very suitable as a side product also for the position control and/or position observation of the winding element relative to the housing.  
         [0011]     A calculating circuit is, expediently, contained in the speed control device, preferably in a microprocessor, which calculates the relative rotor rotary position with the help of the induced backwards oriented electromotoric force. The electromotoric force can be measured precisely in terms of its course and its magnitude.  
         [0012]     Additionally, if expedient, at least one rotary position sensor may be provided and connected to the speed control device. The signal of this sensor may be used in order to build up a holding torque by means of the motor control and to retain the winding element at the predetermined rotary position relative to the housing despite an externally acting rotary force, and in order to retrieve the rotary position of the winding element or the rotor, respectively, during a restart of the motor.  
         [0013]     Expediently, several relative rotary positions of the winding element within a 360° rotation of the winding element are programmed and can be selectively adjusted for correspondingly control stopping of the motor. That means that the winding element as well is stopped in the most suitable rotary position depending on the planned auxiliary function at the yarn feeding device. This relative rotary position can be selected completely arbitrarily.  
         [0014]     It is expedient to place the stator part in a predetermined rotary position in the housing. By this measure each desired relative position of the winding element, as e.g. programmed, can be set in relation to the housing already during assembly of the yarn feeding device, without the necessity to carry out further programming.  
         [0015]     By means of the determined permanent relative rotary position of the rotor during the vector control even the rotary travel of the winding element at least from the start to the end of a driving period can be measured without additional equipment parts, e.g. in order to precisely measure the wound on yarn length.  
         [0016]     Alternatively, the yarn length may be measured in the same fashion even between selected points in time or selected different relative rotary positions of the rotor, respectively, by evaluating the information about the momentary rotor rotation angle for this additional function.  
         [0017]     A predetermined relative rotary position of the winding element in relation to the housing may be a full yarn threading position in which an exit opening of the winding element is aligned with a threading path provided in the housing of the yarn feeding device. The on-board pneumatic threading device then may thread a new yarn without further interference by an operator.  
         [0018]     Alternatively, the predetermined rotary position of the winding element in relation to the housing and adjustment by means of the vector control may be a semi-threading position in which an exit opening of the winding element is positioned outside of shielding housing parts such that no obstacles hinder the manual gripping of the yarn e.g. for knotting the yarn to yarn material already provided on the storage surface, or such that the winding element does not have to be rotated manually into a position beneficial to this auxiliary function.  
         [0019]     An electronic yarn length measuring device can be supplied with the information on the rotor rotary positions during the vector control in order to e.g. derive precise information on the yarn consumption.  
         [0020]     In the case that additionally a position sensor for the winding element is provided in the yarn feeding device, e.g. in order to signal at least one position or to confirm a position, respectively, then this position sensor may be used for generating an aligning holding torque by means of the motor and in co-action with the speed control device. The holding torque retains the winding elements in the adjusted rotor position even if external forces tend to further rotate the winding element. The motor control is apt to adapt automatically to the magnitude of the acting external force in order to hold the winding element stationary.  
         [0021]     Expediently, the position sensor comprises permanent magnets distributed along the circumference of the winding element, and at least one detecting element fixed to the housing which responds to the passage of each permanent magnet. Preferably, a digitally operating Hall element is provided generating a digital signal whenever a permanent magnet is passing. However, particularly expedient is also an analogously operating Hall sensor responding respectively to one pair of adjacent permanent magnets in order to precisely monitor even rotation ranges of the winding element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     An embodiment of the invention will be explained with reference to the drawings wherein:  
         [0023]      FIG. 1  is a longitudinal section of a yarn feeding device comprising a synchronous electric motor of a permanent magnet type as a driving source for a winding element, and  
         [0024]      FIG. 2  is a cross-section of the yarn feeding device. 
     
    
     DETAILED DESCRIPTION  
       [0025]     A yarn feeding device F as shown in  FIG. 1  and  FIG. 2 e .g. is a weft yarn feeding device for a weaving machine (not shown). However, the invention can be applied to a yarn feeding device for a knitting machine (not shown) as well, the yarn feeding device e.g. then having a rotary yarn storage drum defining a winding element.  
         [0026]     The yarn feeding device F in  FIGS. 1 and 2  comprises a housing  1  with a housing bracket  2  containing additional components. A hollow shaft  3  is rotatably supported in a bearing  4  in the housing  1 . The shaft  3  stationarily supports by its free end a storage drum D which is positioned below the housing bracket  3 . In order to prevent that the storage drum D rotates together with the shaft  2  permanent magnets  12  are provided in the housing which magnetically co-act with not shown permanent magnets placed in the storage drum D.  
         [0027]     A rotor R is provided on the shaft  3 . The rotor co-acts with stator part S stationarily placed in the housing. The stator S is fixed by a positioning means  13  ( FIG. 2 ) in a predetermined rotary position.  
         [0028]     An electric motor control device CU containing a microprocessor MP e.g. is contained in the housing bracket  2 . The motor control device CU is connected for signal transmission to a yarn sensor assembly  8  and controls the speed, the torque and the rest periods of the electric motor M e.g. depending on the size of a yarn store formed by yarn windings on the storage drum D. Furthermore, a yarn threading path  9  is provided in the housing bracket  2  for co-action with a not shown, on-board pneumatic threading device in order to thread a new yarn entirely through the yarn feeding device. Furthermore, a withdrawal opening  7  for the yarn is placed at the housing bracket  2 .  
         [0029]     A winding element W having an exit opening  6  is fixed to the shaft  3 . The relative rotary position of the exit opening with respect to the rotor R is structurally fixed. The winding element W may be formed as a funnel-shaped disk  10  containing a not shown winding tube terminating at the exit opening  6 . At the winding element W permanent magnets  11  may be provided which are distributed along the circumference and which co-act with a detecting element H stationarily provided in the housing bracket  2 , e.g. with a digital or an analogous Hall sensor.  
         [0030]     The electric motor M is an electric synchronous motor, preferably a permanent magnet motor (a so-called PM-motor).  FIG. 2  illustrates the geometric distribution of permanent magnets PM in the rotor R and a schematic view of the stator part S (without stator windings provided therein).  
         [0031]     With the help of the speed control device CU and the microprocessor MP a permanent vector control of the motor M is carried out, i.e., the rotary position of the rotor vector is determined continuously without sensors, and the stator vector is rotated by a corresponding current actuation continuously such that the desired speed and an optimum development of the torque result. The actuation of the stator windings is carried out sinusoidally. The permanent magnets PM in the rotor R are designed (formed), magnetised and/or configured (placed) such that, furthermore, forced by the function, the backwards oriented electromotoric force in the stator windings resulting from the rotation of the rotor R in relation to the stator parts S will be induced with a sinusoidal course. With the help of the sinusoidal course of the induced electromotoric force the rotary position of the rotor vector is continuously determined. The stator vector is rotated according to the determination by actuation of the stator part. The information about the momentary rotary position of the rotor vector or the rotor, respectively, in relation to the stator windings or the stator part S, respectively, and the housing, furthermore is used for the position control and/or the position observation of the winding element W.  
         [0032]     Referring to  FIG. 2 a  predetermined rotary position X 1  of the winding element W is a so-called full threading position in relation to the housing  1 . In this full threading position the exit opening  6  of the winding element W is precisely aligned with the threading path  9  structurally integrated into the housing bracket  2 . In this predetermined rotary position X 1  the yarn while blown through the shaft  3  and out of the exit opening  6  is guided along the threading path  9  and finally is brought into the exit opening  7  without manual interference. However, a prerequisite for this function is that the winding element is stopped precisely at the predetermined rotary position X 1  when the electric motor M is stopped. For adjusting this rotary position X 1  now the permanently (continuously) present information on the rotary position of the rotor R in relation to the stator parts S or the housing, respectively, is used to precisely stop the winding element W at the predetermined rotary position X 1  by means of the speed control device CU, e.g. in case of a yarn breakage, as detected by not shown detectors.  
         [0033]     In  FIG. 2 , furthermore, a further predetermined rotary position X 2  is shown for the exit opening  6  of the winding element W. The rotary position X 2  is predetermined such that the exit opening  6  e.g. is stopped offset by 90° in relation to the housing bracket  2 , i.e. that the exit opening is not covered by any housing components hindering direct access.  
         [0034]     In case that a not shown yarn detector detects a yarn breakage situation while yarn material is still present on the storage surface of the storage drum D, the winding element will be stopped in the rotary position X 2  by means of the vector control of the electric motor M such that the then activated pneumatic threading device will present the blown-through yarn at an easily accessible position of the housing for being gripped by the operator. By a corresponding re-correlation of the signal generated by the yarn detectors the speed control device CU will have been informed beforehand in which of the e.g. two predetermined positions X 1 , X 2  the yarn winding element W has to be adjusted for a certain operating condition.  
         [0035]     The rotary position sensor  11 , H does not need to be used for this task. However, this sensor may assist, e.g. in order to prevent a undesired rotation of the winding element W when stopped at the respective position X 1  or X 2 , respectively. This means that then the speed control device CU will build a holding torque in the one or the other sense of rotation in order to locally retain the winding element despite the influence of external forces (the yarn tension or the like). Furthermore, the rotary position sensor  11 , H may be used for determining the rotary position of the rotor R and at the same time of the winding element W in case of a new operation start-up and as rapidly as possible.  
         [0036]     Furthermore, a yarn length measuring device can be interlinked with the speed control device CU in order to measure the length of the wound on yarn by means of the rotary travel Y of the winding element W.  
         [0037]     The respective predetermined rotary position X 1 , X 2  may be selected and adjusted arbitrarily, because the control permanently follows the movement of the rotor during operation of the motor and since the respective position information is present continuously. This means that neither the rotary positions X 1 , X 2 , nor further rotary positions of the winding element W as needed for other purposes have to be fixed beforehand either by the geometric relations between the stator S and the rotor R or by the geometric placement of the position sensor  11 , H. To the contrary any rotary positions can be freely adjusted or programmed, respectively, as they are best for the auxiliary functions of the yarn feeding device, e.g. for threading processes. The predetermined position X 2  e.g. even can be varied later by corresponding reprogramming, e.g. in a case in which at a weaving machine several yarn feeding devices have to be placed close to each other such that they might block the respective access e.g. to the position X 2  in  FIG. 2 . In such a case the position X 2  can be put to another location where comfortable access is possible for the operator despite the restriction by the several closely arranged yarn feeding devices.  
         [0038]     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.