U.S. patent application number 10/590242 was filed with the patent office on 2007-11-29 for electrical positive yarn feeding device.
This patent application is currently assigned to MEMMINGER-IRO GMBH. Invention is credited to Friedrich Dinkelmann, Rolf Huss, Friedrich Weber.
Application Number | 20070272784 10/590242 |
Document ID | / |
Family ID | 34833028 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070272784 |
Kind Code |
A1 |
Huss; Rolf ; et al. |
November 29, 2007 |
Electrical Positive Yarn Feeding Device
Abstract
A yarn delivery device is provided with a motor-driven yarn
delivery wheel, wherein the rotated position of the yarn delivery
wheels is detected with high precision by means of an angle
encoder. The angle encoder has at least a resolution s which is
greater than the circumference of the yarn delivery wheel, measured
in millimeters. The resolution s is preferably greater than five
times (preferably 5.24 times) the value of the diameter of a
winding of the yarn delivery wheel. The yarn delivery wheel is
preferably looped by several (three to twenty) windings.
Inventors: |
Huss; Rolf; (Lossburg,
DE) ; Dinkelmann; Friedrich; (Rechberghausen, DE)
; Weber; Friedrich; (Herzogsweiler, DE) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Assignee: |
MEMMINGER-IRO GMBH
Jakob-Mutz-Strasse 7
Dornstetten
DE
72280
|
Family ID: |
34833028 |
Appl. No.: |
10/590242 |
Filed: |
January 26, 2005 |
PCT Filed: |
January 26, 2005 |
PCT NO: |
PCT/EP05/00736 |
371 Date: |
June 22, 2007 |
Current U.S.
Class: |
242/365.6 |
Current CPC
Class: |
D04B 15/48 20130101 |
Class at
Publication: |
242/365.6 |
International
Class: |
B65H 51/02 20060101
B65H051/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2004 |
DE |
10 2004 009 057.2 |
Claims
1. A yarn delivery device (1), in particular for knitting machines,
having a yarn delivery wheel (5), around which the yarn (9) to be
delivered loops in at least one winding (12) for conveying the yarn
(9), having an electric motor (14) which has a shaft (13) which is
connected, fixed against relative rotation, with the yarn delivery
wheel (5), having an angle encoder (17) for detecting the rotated
position of the yarn delivery wheel (5), wherein the angle encoder
(5) has an angular resolution (s) which is at least so large that
the ratio (s/d) between the angular resolution (s) and the diameter
(d) of the yarn delivery wheel (5) is greater than 3 mm.sup.-1.
2. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) is connected with the
shaft (13).
3. The yarn delivery device in accordance with claim 1,
characterized in that the shaft (13) is a shaft extending through
the electric motor (14), at one of whose ends the yarn delivery
wheel (5) is fastened, and on the other end (16) the angle encoder
(17).
4. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) is an incremental
encoder.
5. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) is an encoder.
6. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) is an optical step
sensor.
7. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) has an angular
resolution (s), which is at least so great that the ratio (s/d)
between the angular resolution (s) and the diameter (d) of the yarn
delivery wheel is greater than 5 mm.sup.-1.
8. The yarn delivery device in accordance with claim 1,
characterized in that the angle encoder (17) is connected to an
actual value input of a control loop (29).
9. The yarn delivery device in accordance with claim 8,
characterized in that the control loop (29) has a desired value
input which is designed for receiving external desired position
signals.
10. The yarn delivery device in accordance with claim 8,
characterized in that the control loop (29) is a PD regulator.
11. The yarn delivery device in accordance with claim 8,
characterized in that the control loop (29) is connected a tension
regulator (38) with a device for disturbance variable
compensation.
12. The yarn delivery device in accordance with claim 8,
characterized in that control loop (29) is connected with a yarn
tension sensor (37) for detecting the yarn tension.
13. The yarn delivery device in accordance with claim 12,
characterized in that a comparator circuit (32) is connected to the
yarn tension sensor (37), which compares the detected yarn tension
with a desired yarn tension and determines a desired position
signal from the comparison.
14. The yarn delivery device in accordance with claim 1,
characterized in that the electric motor (14) is connected to a
regulating circuit (34) which is set up for a dragging mode of
operation, in which the current supply to the electric motor (14)
causes a torque insufficient for independent yarn conveyance.
15. The yarn delivery device in accordance with claim 14,
characterized in that a control circuit (34) is provided, which
registers the revolutions of the electric motor (14) in the
dragging mode of operation by means of the angle encoder (17).
16. The yarn delivery device in accordance with claim 15,
characterized in that an allowance for the positive delivery mode
of operation is obtained from the registered revolutions.
18. The yarn delivery device in accordance with claim 16,
characterized in that the allowance is obtained from the registered
revolutions of several yarn delivery devices (1, 2, 3).
Description
[0001] The invention relates to a yarn delivery device, which is in
particular suitable for the positive delivery of yarn to knitting
machines, for example circular knitting machines.
[0002] In connection with knitting machines, also with circular
knitting machines, the stitch size of the stitches to be created by
the individual knitting systems is set by means of a precise
apportioning of the yarn running into the knitting stations. For
knitting smooth goods, this principle is well established by using
mechanically driven yarn feeding devices. In this connection an
electrical or electronic replacement of the rigid mechanical
coupling between the yarn delivery device and the knitting machine
has long been sought.
[0003] For example, U.S. Pat. No. 3,858,416 discloses a knitting
machine with an electrical yarn feeding device, which can be
alternatingly driven in a voltage-regulated manner or synchronously
with the main cylinder. For performing the latter type of
operation, a magnetic or other type of sensor is provided at the
main drive mechanism of the knitting machine, which generates a
sequence of pulses whose frequency corresponds to the speed of the
knitting machine. A frequency/voltage converter converts these
pulses to a voltage, which then is characteristic of the operating
speed of the knitting machine.
[0004] The motor driving the yarn feed wheel is connected with a
tachometer generator, which is also connected to a
frequency/voltage converter in order to provide a voltage which is
characteristic of the rpm of the motor. A comparator circuit
compares the voltages delivered by both frequency/voltage
converters and controls the motor of the yarn feeding device
accordingly.
[0005] Deviations between the desired deliveries and actual
deliveries can occur in principle in connection with such
arrangements, which have an effect on the quality of the knit
goods.
[0006] It has been attempted in various ways to drive yarn delivery
wheels electrically. For example, DE 38 24 034 C1 discloses the
driving of a yarn delivery wheel by means of a step motor.
[0007] It is not possible to switch step motors arbitrarily on and
off. Instead, it is necessary to maintain a defined operating
regimen when starting as well as slowing down, so that no step
errors occur.
[0008] Further efforts can be found in DE 15 74 430 for delivering
tape- or strip-shaped material, in particular yarn, to a user
location at a preset speed. An electrical drive motor is provided
to this end, whose shaft is connected with a delivery wheel. Here,
a clutch device allows an arbitrary connection and disconnection of
the delivery wheel from the drive motor. The delivery wheel is used
as the rpm measuring device. Voltage meters are arranged upstream
and downstream of the delivery wheel. In a set-up mode of operation
the delivery wheel is uncoupled from the motor shaft and the rpm of
the yarn delivery wheel then occurring are registered in order to
be made the basis for the later operation of the motor.
[0009] The activation of the clutch is required for taking up the
set-up operation. Resisting devices provided in the path of the
yarn also act in a braking manner on the yarn. Therefore, in the
case of knitting machines the amount of yarn provided is affected
by chance. The clutch has a moment of mass inertia, which is added
to the moment of mass inertia of the yarn delivery wheel and of the
motor.
[0010] Based on the foregoing, it is the object of the invention to
create a yarn delivery device suitable in particular for knitting
machines, particularly for knitting machines with changing yarn
requirements, and allows a high degree of delivery quality in the
process.
[0011] This object is attained by means of the yarn delivery device
in accordance with claim 1.
[0012] The yarn delivery device in accordance with the invention
has a yarn delivery wheel which is rigidly connected with an
electric motor and has a predetermined diameter. In this case the
yarn delivery wheel can have a round, as well as a polygonal cross
section. For example, it can be in the form of a rod cage. An
alternative is a one-piece yarn delivery wheel, deep-drawn from
sheet metal, whose circumference is provided with longitudinal
ribs, for example, so that it mimics the outer contours of a rod
cage. Other yarn delivery wheels are also possible. It can be
enveloped by a lap resting against the entire circumference. But
the lap can also touch only a portion of the delivery wheel
circumference and can be conducted, for example, over (fixed or
stationary) lift-off pins. An angle encoder, which is connected
with the yarn delivery wheel in a manner fixed against relative
rotation, is furthermore provided, which generates a signal which
identifies every rotated position of the yarn delivery wheel. In
this case a high angular resolution is essential, which is at least
high enough so that the ratio between the number of steps of the
angle encoder and the diameter of the yarn delivery wheel is
greater than three per millimeter. By angular resolutions above
this threshold limit the yarn delivery wheel can be positioned so
accurately that synchronous running between the yarn delivery
wheels and the knitting machine is achieved in all essential
operational states of the knitting machine. If the angular
resolution of the angle encoder is higher than the mentioned value,
and if the rotatory position of the motor is correspondingly set in
a position regulation loop, it is possible to start up, as well as
stop, a knitting machine with an electronic positive feeding
device, without the production of standing rows, which otherwise
would have to be feared. Standing rows are understood to be rows of
stitches having a different size than the remaining stitches in the
knit material.
[0013] Preferably the angle encoder is connected with the shaft of
the motor, wherein a shaft extending through the motor is provided
in a preferred embodiment, at whose one end the yarn delivery wheel
is arranged and on its other end the angle encoder. The angle
encoder preferably is an incremental encoder with a high increment
number. At a diameter of 40 mm, the angle encoder has at least 120
steps, i.e. an angular resolution of at least 3.degree..
Embodiments are preferred, wherein the ratio s/d (number of steps
to the diameter of the delivery wheel) is greater than five. ("the
number of steps" is understood to be the number of steps which can
be distinguished during one revolution by means of the angle
encoder). In such a case the angle encoder has a resolution of more
than 200 steps per revolution of the delivery wheel. This
corresponds to a resolution of at least 1.8.degree. or better. In
the preferred case s/d is greater than 5:24. In this way delivery
accuracies regarding the yarn delivery are obtained from the
position regulation loop, regardless of the respective yarn
delivery wheel diameter, in which delivery deviations are less than
0.6 mm. This results in error-free knitted goods, even if the
operating speed of the knitting machine is changed, i.e. it stops
or starts.
[0014] In this way an electronic positive yarn feeding device is
created by means of the high-resolution angle encoder, which not
only provides precise deliveries, but moreover can be remotely
controlled. For example, when producing patterned knit goods, it
can be switched on and off in a specific manner. In this way the
electronic positive yarn feeding device in accordance with the
invention renders obsolete friction-type yarn feeding devices,
which up to now had been used for this purpose. It allows an
improved control of the stitch size when producing patterned goods.
In a preferred manner the electronic positive yarn feeding device
is provided with a pulse sequence as the control signal, wherein
each one of the pulses corresponds to an angle step of the yarn
delivery wheel. For example, the angle step corresponds to an angle
step which corresponds to the angular resolution of the position
sensor. Preferably it is of such a size that it corresponds to a
yarn delivery path of 1 mm, preferably 0.6 mm. With each step
received by the yarn delivery device, the latter rotates the yarn
delivery wheel forward by a yarn length of 0.6 mm. A continuous
control of the amount of the delivery corresponding to the rotation
of the main cylinder of the knitting machine is possible in this
way. The positionally-controlled feeding device virtually acts in
the same way as a step motor-driven feeding device, wherein its
position control loop prevents the occurrence of step errors.
[0015] The yarn delivery device can preferably house a position
regulating device, which always compares the angular position of
the yarn delivery wheel detected by the angle encoder with a
desired signal and corrects deviations. In an expanded embodiment
the position regulating device can also be the part of a regulating
device for the traction tension. In this case a yarn tension sensor
is additionally provided, which detects the actual tension of the
yarn. If this deviates from a predetermined desired tension value,
appropriate positioning signals are generated, which are then
converted by the position regulating device. In this case the
tension regulating device is embodied as a PD regulator with
disturbance variable compensation. This means that the regulator
has a proportionally amplifying portion ("P"), as well as a
differentiating portion ("D"). A correcting value is determined
from the detected yarn tension, from the actual delivery speed, and
possibly from the motor currents, and is linked with the desired
tension value in order to correct it in such a way that permanent
regulation deviations caused by the regulating device
disappear.
[0016] In a further development, the yarn delivery device in
accordance with the invention has a first mode of operation, in
which it operates, depending on its embodiment, as a positive yarn
feeding device either tension-regulated or positionally regulated.
In an additional mode of operation, which can be called a dragging
mode of operation, the current of the electric motor is reduced to
such an extent that it no longer provides active yarn feeding. In
this case the motor current is set in such a way that all possible
locking moments of the electric motor are overcome and no drive
moment is generated, or at most a drive moment which is not
sufficient for feeding yarn. As far as the yarn-processing machine
is concerned, no positive yarn feeding device exists in this
operational state.
[0017] Instead, the yarn-processing machine is required to obtain
yarn from a yarn source, for example a bobbin creel. In this case
the drive moment of the electric motor is at most sufficiently
large so that this process is made easier. In this case the force
for pulling the yarn off the bobbin creel is only partially
provided by the yarn feeding device. Thus the yarn delivery wheel
is virtually disengaged from the motor shaft, at least to the
extent that it does not provide any feeding. The yarn-processing
machine, or its knitting system, can pull in the yarn against a
small resistance. A circuit connected to the electric motor, or the
incremental encoder, can precisely detect the amount of yarn
obtained and make it the basis for the further operation of the
yarn delivery device in the positive yarn-feeding mode.
[0018] Details of advantageous embodiments of the invention are the
subject of the drawings, the specification or the claims. Exemplary
embodiments of the invention are illustrated in the drawings. Shown
are in:
[0019] FIG. 1, several electronic, positionally-regulated yarn
feeding devices and their connection to a central control device,
in a schematic representation,
[0020] FIG. 2, the yarn feeding devices designed as
tension-regulated yarn feeding devices, connected to a central
control device, in a schematic representation,
[0021] FIG. 3, the yarn feeding devices in accordance with FIG. 1
with an additional dragging mode of operation, connected to a
central control device in a schematic representation,
[0022] FIG. 4, an angle encoder of a yarn feeding device in a
schematic representation,
[0023] FIG. 5, output signals of the angle encoder in accordance
with FIG. 4,
[0024] FIG. 6, an alternative embodiment of an angle encoder in a
schematic representation,
[0025] FIG. 7, a tension-regulated yarn feeding device with
disturbance variable compensation in a schematic representation,
and
[0026] FIG. 8, a modified angle encoder in a schematic perspective
representation.
[0027] A group of yarn delivery devices 1, 2, 3, which are
connected to a central control device 4, is illustrated in FIG. 1.
The control device 4 can be a central control device, it can be
part of a knitting machine, be a separate device or can be housed
in one of the yarn delivery devices 1, 2, 3. The yarn delivery
devices 1, 2, 3 are represented merely by way of example. If
required, only a single yarn delivery device 1 or a larger group of
yarn delivery devices can be provided.
[0028] The number of the yarn delivery devices 1, 2, 3 corresponds
to the number of yarns to be delivered to a yarn-processing
machine, for example a circular knitting machine, and therefore to
the number of knitting stations. They are substantially identically
constructed in respect to each other. Thus, the subsequent
description of the yarn delivery device 1 correspondingly applies
to the remaining yarn delivery devices, as well as possibly
further, non-represented yarn delivery devices.
[0029] The yarn delivery device 1 has a yarn delivery wheel 5
constituted, for example, by a deep-drawn sheet metal element. At
the top and bottom it can respectively be provided with an
outwardly projecting edge 6, 7, which constitutes a yarn inlet area
and a yarn outlet area. A yarn storage area arranged between them
can be provided with ribs 8. Yarn guide means, such as, for
example, a yarn inlet eye, a yarn outlet eye, a yarn brake, a knot
catcher and the like are arranged upstream and downstream of the
yarn delivery wheel 5. Moreover, yarn feeler levers or other yarn
monitoring devices can be provided as required.
[0030] A yarn is looped around the yarn delivery wheel 5 with a
least one, preferably several laps 11. The lap 11 comprises at
least one, however preferably several windings 12. In the course of
a rotation of the yarn delivery wheel 5, the yarn 9 runs onto the
storage area of the yarn delivery wheel at the upper edge 6, in the
process forms side-by-side located windings and, because of this,
pushes the lap 11 axially downward. The yarn delivery wheel 5 can
have a slight conicity for making this process easier. With the
yarn delivery wheel 5 running, the lap 11 is therefore continuously
in movement on the yarn delivery wheel 5.
[0031] The yarn delivery wheel 5 is connected with a shaft 13,
which is part of an electric motor 14. The connection is fixed
against relative rotation and preferably cannot be released by
operationally controllable means, such as clutches or the like. The
electric motor 14 preferably is a brushless d.c. motor with a low
moment of mass inertia, such as for example a drag-cup motor, a
pancake motor, or the like. With low dynamic demands it is also
possible to employ some other type of motor, such as for example a
brushless d.c. motor, a synchronous motor, or the like. In the case
of a brushless d.c. motor, the electric motor 14 contains Hall
sensors for the positive detection of its armature, for example in
accordance with FIG. 8, and appropriate electronic switches for
supplying the stator windings in accordance with the angle of
rotation of the motor, which is for example excited by a permanent
magnet. With such a motor the torque generated by the electric
motor 14 at the shaft 13 corresponds to the operating current
supplied via a supply line 15.
[0032] The shaft 13 is connected, either in the area between the
electric motor 14 and the yarn delivery wheel 5, or alternatively
at its end 16 which is remote from the yarn delivery wheel 5 and
projects out of the electric motor 14, with an angle encoder 17,
which is preferably designed as an incremental encoder or as an
analog encoder with high resolution. His step number s is the
number of steps which result in a single full resolution of the
shaft 13. In this case the angle encoder 17 preferably has at least
such a step number s that the ratio between the step number s and
the diameter d of the windings 12 preferably is greater than three,
preferably greater than five. In this way the error occurring in
the detection of the rotated position of the yarn delivery wheel 5
lies below a limit which could cause tracks in the knit material,
even with particularly hard (inelastic) yarns.
[0033] The structure of the angle encoder 17 is shown by way of
example in FIG. 4. In this case it is constituted by a synchro
resolver having an armature with an armature coil 18, whose
longitudinal axis extends transversely to its axis of rotation. In
FIG. 4 the axis of rotation extends perpendicularly in respect to
the drawing plane. The armature coil 18 is connected with a supply
coil 19, which is axially oriented and which receives an a.c.
excitation signal via a stationary outer coil, not further
represented. Two stator coils 21, 22, whose coil axes are radially
oriented and offset by 90.degree., detect the alternating field
generated by the armature coil 18. The signal course represented in
FIG. 5 result from this. Corresponding to the position of the
armature coil 8, the amplitudes of the voltages generated in the
stator coils 21, 22 increase or decrease in the shape of a sine or
cosine. For example, in the case of an angle of rotation P, a
positive voltage U.sub.1 is induced in the stator coil 21, and in
the stator coil 22 a negative voltage U.sub.2. A conclusion
regarding the angle of rotation P can be drawn from the voltages by
means of the arc-sine or arc-cosine function.
[0034] An alternative embodiment of an angle encoder is represented
in FIG. 6. It operates optically and has a first stationary disk 23
and a second disk 24, which is connected with the shaft 13. Both
disks are respectively provided with a pattern of lines 25, 26,
oriented in the radial direction. These form a light-dark pattern.
The spaces provided between the lines 25 or 26 are preferably
transparent. In a preferred embodiment the width of the lines and
of the gaps between them are identical. The lines 25, 26 can also
be slightly wider than the gaps. They furthermore agree in their
number. If the angle encoder is intended to detect not only the
number of revolutions, but also the direction of rotation, they
differ in their number preferably by one.
[0035] A light source 27, for example in the form of a light diode,
is provided for counting the steps, and is arranged on one side of
the disks 23, 24. A light-sensitive element 28, for example a
photo-resistor, a photo-transistor, or the like, is provided on the
oppositely located other side. If the direction of rotation is to
be detected, one or two further such photoelectric barriers are
provided, which pass light through the pair of disks at another
location.
[0036] FIG. 8 illustrates another modified embodiment of an angle
encoder with a rotatable permanent magnet M and four Hall sensors
21a, 21b, 22a, 22b arranged in the field of the latter. For
example, these have been switched together as a bridge. Angle
encoders of this type are installed anyway in some brushless
electric motors, for example, in order to control electronic
switches used for triggering the motor coil. If, by means of
evaluating the voltages occurring at the Hall sensors 21a, 21b,
22a, 22b, such an angle encoder 17 allows the resolution of a
revolution into a step number s, which is equal to or greater than
the step number determined under the above discussed conditions,
this angle encoder internal to the motor can be used as the
position sensor for the connected control loop. The brushless d.c.
motor becomes a virtual step motor in this way, which in contrast
to the known step motors does not make any step errors, even if no
particular changes in the rpm are taken into consideration. Such a
virtual step motor can be operated in the start/stop mode, without
meeting any special start-up regimens or shut-down regimens.
[0037] The signals emitted by the synchro resolver in accordance
with FIG. 4 or the optical sensor in accordance with FIG. 5 are
provided to a control loop 29 (FIG. 1) as actual position signals.
A comparator 31 is a part of the latter, which compares the actual
position signals from the angle encoder 17 with desired positions
of a preselection unit 32. Each existing deviation between the
desired position signal and the actual position signal is passed on
as an angle error signal via a branch 33 to a regulating circuit
34, which controls the electric motor 14 correspondingly in order
to bring the desired position signal and the actual position signal
into agreement.
[0038] The actual position signals of all yarn delivery devices 1
to 3 can be optionally conducted via appropriate lines 35 to the
control device 4. In this case the lines 35 can directly pass on
the signals from the angle encoders 17 in that they connect the
angle encoders 17 with the control device 4. It is also possible to
lay out the lines 35 as a data bus, which is connected via
appropriate interfaces to the angle encoders 17. This includes all
existing data buses, also single wire buses.
[0039] The control device 4 sends control pulses 36 to the
preselection unit 32 via a line 36. Thus the yarn delivery devices
1, 2, 3, which are to be operated parallel, can be parallel
controlled. In the present exemplary embodiment the control unit 4
issues individual pulses, wherein each single pulse of the rotation
of the electric motor 14 by one step corresponds to the angular
resolution of the angle encoder 17. If the angle encoder 17 is
constructed in accordance with FIG. 4, for example, and if it
contains an evaluation circuit connected to the stator coils 21,
22, which converts the signals derived from the stator coils 21, 22
into a signal of analog or digital nature, which unequivocally
characterizes the angle of rotation, the preselection unit 32 is
also correspondingly embodied. In this case it has a counter, for
example, which respectively counts from zero up to the maximum
number of steps of the angle encoder 17, and then starts over
again. In this way an analog or digital step-shaped signal of the
appropriate number of steps is created from the individual step
pulses delivered via the line 36. As soon as pulses are delivered
via the line 36, the electric motor 14 rotates. If no pulses
arrive, it stops. Observed from the outside, in this way the
electric motors 14 behave like step motors, which perform an
angular step for every pulse delivered via the line 36. But as a
result of the internal position regulation they are not subject to
step errors so that, different from common step motors, they can be
started and stopped without problems.
[0040] The yarn delivery devices 1 to 3 delivered up to now operate
as follows:
[0041] It is assumed that the yarn delivery devices 1 to 3 are
provided for a knitting machine, which is designed, for example, as
a Jacquard knitting machine or as a knitting machine with a
striping attachment. Each yarn delivery device 1, 2, 3 supplies a
knitting station with a respective yarn 9. If the respective
knitting stations are to be supplied with yarn, the control device
4 sends pulses to the appropriate preselection units 32, whereupon
the yarn delivery wheels 5 rotate appropriately. In the course of
this they follow the preset signal true to the angle, wherein
existing angular deviations in relation to the circumference of the
yarn delivery wheel are less than 1 mm, but preferably less than
0.6 mm. This is a result of the requirement that the ratio s/d is
greater than three, preferably greater than five, per millimeter.
By means of this it is achieved that possible angular errors fall
below other error effects. The sliding movement of the lap 11 on
the yarn delivery wheel 5 in particular can be a part of such error
effects. As long as the yarn delivery wheel 5 rotates, the lap 11
is downwardly displaced by means of the incoming yarn 9 in the
direction of the unwinding yarn. Because of the existing axial
sliding movement, a certain slippage of the lap 11 in the
circumferential direction also occurs, of course. This means that a
certain slippage of the yarn on the yarn delivery wheel 5 occurs.
It is preferred if the quotient of the circumference of the yarn
delivery wheel and the angular resolution s is less than this
slippage, for example less than 1 mm, preferably less than 0.6 mm.
A knitting machine equipped with such yarn delivery devices 1 to 3
can be started up from a stop, stopped again and again started,
without creating standing rows, i.e. rows of stitches of a
different sizes.
[0042] The delivery speed of the yarn 9 can be increased, reduced
or set to zero by means of the specific delivery of pulses via the
line 36. Thus, positive yarn delivery is possible in connection
with Jacquard knitting machines.
[0043] Expanding the embodiment so far described, the yarn delivery
devices 1 to 3 can be provided with yarn tension sensors 37, which
monitor the tension of the unwinding yarn. For example, the tension
sensors can be connected with the preselection unit 32 in order to
affect the allowance of the yarn. Otherwise, the above description
correspondingly applies. The same reference numerals are being
used. It is possible in connection with this embodiment to operate
the yarn delivery devices 1, 2, 3 in a tension-regulated mode of
operation, if required. For example, a yarn tension signal is
delivered via the line 36. The preselection unit 32 compares this
with the actual tension determined by means of the yarn tension
sensor and creates an appropriate desired position signal. This is
in turn converted by the control loop 29 into revolutions of the
yarn delivery wheel 5.
[0044] Such a yarn delivery device 1 to 3 can operate alternatively
as a positive yarn feeding device or as a tension-guided yarn
feeding device, i.e. can deliver yarn at a constant delivery rate
or a constant yarn amount.
[0045] FIG. 7 illustrates a complement for the yarn delivery device
1 to 3 in accordance with FIG. 2. Here, the preselection unit 32
and the regulating circuit 34 have been combined into a position
regulating device 38. At one input 39, the latter receives a
tension preselection signal. It receives an actual tension signal
from the yarn tension sensor 37. At a further input, the angle
encoder 17 delivers an actual position signal. The moment driving
and accelerating the yarn delivery wheel 5 is detected by means of
a current sensor 41 and reported back to an input 42 of the tension
regulator 38. Thus, the tension regulator 38 receives signals
regarding the speed of the running yarn, the accelerating or
braking torque acting on the armature of the motor, and the yarn
tension. It is embodied as a PD regulator. An error signal is
formed from the yarn speed, the yarn tension and the motor current,
which is applied to the PD regulators in the form of a disturbance
variable. In this way a robust regulator is created, whose
regulating deviation is small for nearly all occurring yarns,
regardless of their elasticity, and which very rapidly follows
changes in the preset signal at the input 39.
[0046] FIG. 3 illustrates a further development of the yarn
delivery device 1 to 3, based on the embodiment in accordance with
FIG. 1. Initially, reference is respectively made to the
description of the exemplary embodiment in accordance with FIG. 1,
including FIGS. 4 to 6. The following applies in amplification:
[0047] The regulating circuit 34 has an additional control input,
at which it can be deactivated as a regulating circuit and changed
to a dragging mode of operation. This control input is connected
with the control device 4 via lines 43 or an appropriate bus. As
soon as the regulating circuit 34 receives an appropriate signal
via the lines 43, it changes into a dragging mode of operation. In
this, the electric motor 14 is charged with a low current, which is
at least sufficient to overcome possible locking moments of the
electric motor 14. The latter is then "invisible" as far as the
yarn delivery wheel 5 is concerned, i.e. it does not hamper a
rotation of the yarn delivery wheel 5 because of a pull on the yarn
5. This corresponds to a virtual uncoupling of the electric motor
14 from the yarn delivery wheel 5. In this state the individual
yarn processing positions (knitting systems) can themselves obtain
yarn without being prevented from doing so by the electric motors.
The control device 4 registers the amount of yarn obtained via the
lines 35. A preselection value can be determined from the detected
values, which in the course of a subsequent positive operation is
delivered via the line 36 in the form of appropriate control
pulses.
[0048] It is also possible to create a slight driving torque in the
dragging mode of operation in order to make it easier for the
knitting stations to obtain yarn. However, the moment, or the
control currents of the electric motors 14, are so low that no
individual yarn conveyance as a result of supplying the electric
motors 14 with current takes place.
[0049] The high resolutions of the angle encoders 17 which exist in
addition to possible sensors at the electric motors, such as Hall
sensors, for example, also have a positive effect in the course of
detecting the amounts of yarn obtained by the knitting stations.
Regarding the measurement of the natural yarn usage in the dragging
mode of operation it is possible to provide a complete freedom from
stopping moments, something which is hardly possible with
conventional step motors.
[0050] A yarn delivery device is provided with a motor-driven yarn
delivery wheel, wherein the rotated position of the yarn delivery
wheels is detected with high precision by means of an angle
encoder. The angle encoder has at least a resolution s which is
greater than the circumference of the yarn delivery wheel 5,
measured in millimeters. The resolution s is preferably greater
than five times (preferably 5.24 times) the value of the diameter
of a winding of the yarn delivery wheel. The yarn delivery wheel is
preferably looped by several (three to twenty) windings.
REFERENCE NUMERALS
[0051] 1,2,3 Yarn delivery devices [0052] 4 Control device [0053] 5
Yarn delivery wheel [0054] 6,7 Edge [0055] 8 Ribs [0056] 9 Yarn
[0057] 11 Lap [0058] 12 Winding [0059] 13 Shaft [0060] 14 Electric
motor [0061] 15 Feed line [0062] 16 End [0063] 17 Angle encoder
[0064] 18 Armature coil [0065] 19 Supply coil [0066] 21, 22 Stator
coils [0067] 21a,21b,22a,22b Hall sensors [0068] 23, 24 Disks
[0069] 25, 26 Lines [0070] 27 Light source [0071] 28 Element [0072]
29 Control loop [0073] 31 Comparator [0074] 32 Preselection unit
[0075] 33 Branch [0076] 34 Regulating circuit [0077] 35 Lines
[0078] 36 Line [0079] 37 Yarn tension sensors [0080] 38 Tension
regulator [0081] 39 Input [0082] 41 Current sensor [0083] 42 Input
[0084] 43 Lines [0085] P Angle of rotation [0086] d Diameter [0087]
s Step number [0088] M Permanent magnets [0089] U.sub.1, U.sub.2
Voltage
* * * * *