EP0378870A1

EP0378870A1 - Tensioning device with adjustable action for adjusting the tension of threads fed to textile machines, in particular to knitting machines

Info

Publication number: EP0378870A1
Application number: EP89203127A
Authority: EP
Inventors: Bruno Pogliani
Original assignee: Santoni SpA
Current assignee: Santoni SpA
Priority date: 1988-12-16
Filing date: 1989-12-08
Publication date: 1990-07-25
Also published as: JPH02216249A; IT8822977A0; IT1228042B

Abstract

The tensioning device comprises at least two wheels (3, 4) with a peripheral race, rotatably installed, with substantial parallel axes, on a support (5), at a certain distance from each other. The support (5) can be orientated by being revolved around an axis substantially parallel to the axis of the wheels (3, 4), in order to move the wheels from a position in which they are not into contact with the thread (2) and are on opposite sides relatively to it, to a position of peripheral engagement with the thread (2).

According to the angle of orientation of the support (5), the thread (2) engages a longer, or shorter, portion of the peripheral race of the wheels (3, 4), running according to an "S"-shaped, or "Z"-shaped trajectory. The larger or smaller extent of engagement determines a larger or smaller value of rolling friction, and therefore a higher or lower thread tension. By means of a programmed movement of the support (5), the thread tension value during processing can be varied according to a programmed schedule.

Description

The present invention relates to a tensioning device, with adjustable action, for controlling the tension of threads fed to texile machines, in particular to knitting machines.
It is known that the tension with which one or more thread(s) is(are) fed to a textile machine is one among the most important factors for a high-quality product to be obtained. In case of a knitting machine, e.g., the correct tension of the thread is essential if a certain loop density has to be achieved.
In many cases, it is important that this tension can be modified during the course of processing, in order to obtain article portions with different characteristics, or differently shaped products in the various component parts thereof.
The most traditional tensioning devices are constituted by two mutually facing plates, between which the thread is caused to run according to a diametrical direction, with one of said two plates being fixed, and the other one being kept urged by a spring against the fixed plate, so as to generate a certain resisting force against the movement of the running thread. By adjusting the force applied by the spring, the resisting action, and consequently the tension of the thread downstream the tensioning device can be varied.
Also tensioning devices are known, which are composed by a revolving disk, on which a pressure wheel rolls, with the axis of said pressure wheel being perpendicular to the axis of the disk. The thread is caused to run between the wheel and the disk, undergoing a pressure action by the wheel urged against the disk. The position of the wheel in the direction of its own axis -- i.e., in the radial direction of the disk -- can be controllably varied, together with the position of thread, so as to change the running speed of the thread, which corresponds to the peripheral speed of the disk at the point in which said disk is engaged by the thread. Inasmuch as the disk revolves at an angular speed which is a function of the processing speed of the textile machine, a suitable adjustment of the radial position of the wheel on the disk makes it possible not only the amount of thread fed during an unit time, but also the tension under which the thread is fed to the textile machine, to be adjusted.
Also other devices, e.g., of magnetic type, are known, some of which make it possible the tension of the thread to be progressively varied according to a preestablished program, by means of gearwheels or of suitably controlled electrical micromotors.
One of the drawbacks which are generally observed in these devices known from the prior art is the excessive stress applied to the thread, which is often a thread with elastic characteristics, coated, and hence delicate, with the typical characteristics of said thread being possibly varied.
Furthermore, the rubbing of the thread between surfaces stationary relatively to the same thread causes dirt, or -- when used -- paraffin, to deposit and accumulate, with the value of friction undergoing changes, and the regularity of tension being jeopardized. It should be also pointed out that in case of wheel/disk tensioning devices, a certain rubbing is generated owing to the fact that the surfaces the thread comes into contact with, do not roll according to parallel axes, but according to mutually perpendicular axes.
The purpose of the present invention is therefore of providing a tensioning device with adjustable action, for controlling the tension of thread fed to textile machines, in particular to knitting machines, which overcomes these drawbacks and above all makes it possible a delicate action to be exerted on the thread, which does not practically cause a rubbing and a deposition of dirt, or of any other foreign substances, which may alter the tension parameters and/or the characteristics of the thread.
Within the scope of the above stated purpose, the present invention also aims at providing a tensioning device which makes it possible the tension of the thread to be adjusted within a wide range of values, with the adjustment being furthermore extremely precise, with the values set from time to time being kept constant without changes.
These purposes are achieved according to the instant invention by means of a tensioning device with adjustable action for controlling the tension of threads fed to textile machines and in particular to knitting machines, which comprises friction means suitable for coming into contact with the thread in order to determine the feeding tension thereof, characterized in that said friction means comprise at least two guide wheels rotatably supported at a certain distance from each other by a support, which can be orientated by being revolved around an axis substantially parallel to the axis of revolution of the wheels, with said wheels being positioned mobile on the trajectory of the thread in order to engage said thread at various angular positions of said support according to a winding angle variable as a function of the angular position of the support and in order that respective loops of the thread are formed, with discordant concavities.
Advantageously, the device can be provided with two wheels positioned on the support on opposite sides relatively to the axis of revolution of the same support, so that the thread, when is engaged by the wheels, runs along an "S"-shaped trajectory or a "Z"-shaped trajectory, with different angle values as the value of the angle of orientation of the support increases.
One will understand that with the tensioning device according to the present invention the thread, which, during its movement into contact with the wheels, causes the wheels -- idling on their support -- to revolve, only undergoes an action of rolling friction, and not of sliding friction, the action of rubbing of the thread, and therefore its wear, being reduced as compared to the traditional devices.
The possibility that the tension may vary owing to the presence of accumulated dirt (paraffin, loosened fibres, and so forth) does not exist any longer, because the same rotation of the wheels prevents any accumulation of dirt, rendering the system reliable with no need for maintenance or servicing.
By varying the angle of incidence of the thread relatively to the guide wheels, i.e., by differently orientating the support, the rolling friction value, and consequently the tension applied to the thread, varies smoothly and progressively. As a consequence, the tension can be adjusted with precision. The controlled change in tension can take place according to a programmed schedule, as a function of the need by the textile machine, with said tension being increased, or decreased, according to a pre-established law.
Further details and advantages of the instant invention will be clearer from the following disclosure thereof, relevant to some examples of practical embodiment of the invention, as illustrated for merely indicative purposes, and which is no way are limitative of the same invention, in the hereto attached drawings in which:

Figure 1 shows a partial elevation view of a tensioning device according to the instant invention in a first form of practical embodiment thereof, applied for exemplifying purposes to a knitting machine;
Figures 2a, 2b, 2c, 2d are schematic plan view of the device according to the present invention, in various positions corresponding to a same number of values of thread tension;
Figure 3 is a partially sectional, partially schematic view of a different form of practical embodiment of a device according to the present invention;
Figure 4 and 5 show further possible forms of practical embodiment of a device according to the present invention.

Referring to the figures of the hereto attached drawing tables, one will observe that the tensioning device 1 with adjustable tensioning action according to the present invention essentially comprises friction means, capable of determining the tension of the thread 2, and formed by at least two guide wheels 3 and 4 guiding the thread 2, and rotatably supported, at a certain distance from each other, by a support 5, which preferably is in the form of a plate with a rectangular outline.
The wheels 3 and 4 are provided with a peripheral race in order to secure the guide of the thread 2, and are positioned on a same side relatively to the support 5, with their respective axes being substantially parallel to each other, and perpendicular to the plane of the support 5.
The support 5 is supported with possibility of being orientated by means revolutionary movements around an axis 6, which is substantially parallel to the axes of the wheels 3 and 4. The orientation axis 6 preferably coincides with the axis of symmetry of the support 5, and the wheels 3 and 4 are symmetrically positioned on opposite sides relatively to the orientation axis 6. The device 1 is so positioned, that the wheels 3 and 4 result to be mobile along the trajectory of the thread 2, in order to engage said thread while it is being unwound from a cheese, or from another thread package, and is fed a textile machine.
In Figure 1 the exemplifying case is depicted of a knitting machine 7, to which the thread 2 comes running through the tensioning device 1.
In said figure, an electronic control unit used in order to control the machine is schematically shown and indicated by the reference numeral 8, which electronic control unit is suitable for sending to the various elements of the machine the necessary commands for a determined processing sequence. From this unit 8, through the interface 9 a set of commands are derived for orientating the support 5 as a function of the requirements of the machine, i.e., in order to fit the tension of the thread 2 to the specific processing requirements, as we'll see later on.
In the example shown in Figure 1, the orientation of the support 5 is achieved by means of a stepper motor 10, so associated with the same support that this latter is integral with the shaft 11 of the motor 10. The motor receives the commands which command it to rotate in either directions, in a per se known way, from the electronic control unit 8 through the interface 9 and the line 12, as a function of the required specific program of adjustment of the tension of the thread.
In order to better understand how such an adjustment is carried out, reference is made now to Figures 2a, 2b, 2c, 2d.
In Figure 2a, the support 5 is orientated in an angular position in which the wheels 3 and 4 are disengaged from the thread 2, are are at opposite sides relatively to said thread. The thread 2 substantially runs through the central point between the wheels 3, 4. Under these conditions, the device 1 does not supply any tension to the thread 2, and the only tension to which said thread is subject is the tension generated by the free unwinding from the thread package.
When the support 5 is revolved in clockwise direction, at a certain time the thread 2 comes into contact with the wheels 3 and 4, along a certain arc of the periphery of said wheels, as shown, e.g., in Figure 2b, with the thread thus forming respective loops with discordant concavities.
When the support 5 is revolved by a further angle in clockwise direction, the thread 2 remains into contact with the wheels 3 and 4, and the value of the contact arc, or angle, progressively increases, as shown in Figures 2c and 2d; with the trajectory along which the thread runs more assuming a more and more marked "S"-shape, or "Z"-shape.
One will understand that when the angle of contact, or of winding, of the thread 2 with/around the wheels 3 and 4, varies, also the friction conditions generated on the thread 2 by the same wheels, and therefore the tension applied to said thread varies, increasing when the contact angle increases, and decreasing with decreasing contact angle values. The variation takes place progressively and smoothly, so that by progressively controlling the angle of orientation of the support 5, a tension can be applied ot the thread, which varies according to the desired schedule during the course of the processing; for instance, a certain value of thread tension can be fixed during a certain processing step, and then a different, higher, or lower, tension can be given to the thread, by revolving the support 5 by a certain angle in the required direction.
It should be observed that the generated friction is of rolling type, so that a rubbing of the thread 2, and consequently a noticeable wear thereof, does not occur. Therefore, the thread undergoes a delicate action, which does not alter the characteristics thereof. Also curing the step of passage fom the condition of Figure 2a to the condition shown in Figure 2b, a rubbing does not take place, in that as soon as the thread 2 comes into contact with the wheels 3 and 4 these latter start rotating, supplying a first, slight increase in tension. As one may observe from the figures, the rotation of the wheels 3 and 4, which continues throughout the time of ccntact with the thread 2, is in opposite directions.
Advantageously, the wheels 3 and 4 are made from a hard material, such as, e.g., a ceramic material, steel, or hard plastics, and are installed on the support by means of pivots, bearings or sleeves suitable for accomplishing the minimum friction during revolution.
Thanks to the rotation of the wheels 3 and 4 during the step of tensioning of the thread 2, accumulations of dirt, or of any other materials which may possibly modify the friction conditions, and consequently alter the tension values, are prevented. A device according to the instant invention makes it hence possible constant tension conditions to be achieved, with no need for cleaning or servicing operations, throughout the time during which the support 5 remains orientated according to a certain angle.
The orientation of the support 5 can be obtained of course by resorting to a number of different means, instead of using a stepper motor 10.
In Figure 3, a pneumatic system of actuation of the support 5 is schematically shown, which comprises a piston 13 inside a cylinder 14. The piston 13 is subject to the pressure applied by a fluid on the one side thereof, and to the action of a return spring 15 on its other side. The fluid is fed by a pressurized fluid source 16. The stem 17 of the piston 13 is connected with the shaft of orientation of the support 5, e.g., through a toothing 19 provided on the stem 17, which engages a pinion 20 integral with the support orientation shaft. By varying the pressure of the fluid inside the cylinder 14, e.g., by means of a control valve 21, in its turn controlled by the electronic control unit 8, 9, the position of the piston 13 and consequently the angular position of the support 5 can be modified, with the tension of the thread 2 being consequently modified.
In case of a hosiery knitting machine, the command of the variation of the tension of the thread could also be derived from the main cylinder of the machine, through suitable mechanical devices.
Therefore, by means of a device according to the instant invention the tension of a thread fed to a textile machine can be increased or decreased as desired, or can be kept constant, in an extremely simple way, and within a wide range of values. It should be observed that on the support 5 also further wheels engaged by the thread could be installed, which would produce an increase in thread tension owing to the higher value of the generated rolling friction, even if the increase in friction generated by the additional wheels would not be modified by the change in orientation of the support 5, but would remain constant, in that the configuration of the trajectory of the thread between the inlet and outlet wheels would remain constant.
The hereinabove disclosed and illustrated device is suitable for operating on any planes, whether vertical, horizontal, or inclined, a matter of fact which renders particularly wide the range of applications of said device.
The orientation of the support 5 could also be performed by means of a spring system, or by means of a manual system, without thereby departing from the scope of the present invention.
The axis of orientation of the support 5 could also be positioned differently from as shown. For example, not necessarily does it coincide with the axis of symmetry of the support 5, and it could lay somewhere else between the wheels 3 and 4. It could also coincide with the axis of revolution of either of the wheels 3 and 4 (see Figure 4), or it could be in such a position that the wheels 3 and 4 are both positioned on a same side relatively to the orientation axis (Figure 5).
Advantageously, the wheels 3, 4 could be supported in an interchangeable way, so that they can be replaced by wheels different in weight, material or size, with the tension parameters being consequently varied. For example, wheels could be used, which are made from sintered plastics, or ceramic materials, for small tensions; and wheels made from special steel, or from another, relatively high-weight, material, in case larger tensions are required. Obviously, on a same support also wheels different from one another could be installed in order to obtain intermediate tension values.

Claims

1. Tensioning device with adjustable action for controlling the tension of threads fed to textile machines and in particular to knitting machines, which comprises friction means suitable for coming into contact with the thread in order to determine the feeding tension thereof, characterized in that said friction means comprise at least two guide wheels rotatably supported at a certain distance from each other by a support, which support can be orientated by being revolved around an axis substantially parallel to the revolution axis of said at least two wheels, with said wheels being positioned mobile on the trajectory of the thread in order to engage said thread at various angular positions of said support according to a winding angle variable as a function of the angular position of the support and in order that respective loops are formed by the thread, with discordant concavities.

2. Device according to claim 1, characterized in that said wheels are positioned on opposite sides relatively to the axis of orientation of the support.

3. Device according to claim 1, characterized in that the wheels are positioned on a same side relatively to the axis of orientation of the support.

4. Device according to claim 1, characterized in that the axis of orientation of the support coincides with the axis of revolution of one of the wheels.

5. Device according to claim 1 or 2, characterized in that the wheels are positioned symmetrically relatively to the axis of orientation of the support.

6. Device according to one of the preceding claims, characterized in that the support can be orientated in at least one angular position in which the wheels are disengaged from the thread and lay on opposite sides relatively to it.

7. Device according to one of the preceding claims, characterized in that a stepper motor is associated with the support in order to control the orientation of said support, with said stepper motor being commanded by an electronic control unit to rotate in either directions, as a function of the schedule of change of thread tension values.

8. Device according to one of the preceding claims from 1 to 6, characterized in that a device for pneumatic actuation is associated with the support, which pneumatic actuation device comprises a piston subject to a fluid pressure variable as a function of the desired thread tension, with the stem of said piston being linked with the support hinging axis in such a way that to a translational movement of the stem a revolutionary movement corresponds of the support.

9. Device according to one of the preceding claims, characterized in that the wheels are installed on said support in an interchangeable way.

10. Device according to one of the preceding claims, characterized in that the support bears wheels different from each other.

11. Textile machine, in particular knitting machine, comprising at least one thread tensioning device with adjustable action, according to one or more of the preceding claims.