GB2528884A

GB2528884A - Actuator

Info

Publication number: GB2528884A
Application number: GB1413696.4A
Authority: GB
Inventors: Robert Steven Pemberton
Original assignee: Texkimp Ltd
Current assignee: Texkimp Ltd
Priority date: 2014-08-01
Filing date: 2014-08-01
Publication date: 2016-02-10
Anticipated expiration: 2034-08-01
Also published as: GB201413696D0; GB2528884B

Abstract

An actuator, a fibre tensioner for creel incorporating such an actuator, a creel and a method of operating a fibre tensioner are provided. The actuator 100 comprises: a housing 102 comprising a chamber 104, the chamber 104 having an aperture 106 for fluid communication with a source of pressurised fluid; a piston 108 having a head 110 for bearing on a member (54 in Figure 7); and a stem 112 for slideable location within the chamber 104. The stem 112 is configured to extend from, and retract into, the actuator chamber 104. The stem 112 comprises a passage 116 having a fluid orifice 118 for fluid communication with the chamber 104. The passage 116 opens at the head 110 of the piston 108 into an expansion chamber 120. The expansion chamber 120 has at least one wall 122 which is moveable relative to the piston head 110 in response to a change in fluid pressure delivered to the actuator 100.

Description

ACTUATOR

The present disclosure relates to an actuator.

Background

Figure 1 shows a creel arrangement for the delivery of fibres in a material processing plant. There are many different designs of creel and the one shown in Figure 1 is merely a diagrammatic representation typical of the related art. The creel comprises a support structure 10 upon which are mounted a number of spindles 12, and upon the spindles 12 are carried holders 13 for tubes or bobbins 14. The holder is supported on the spindle by means of bearings or bushes so that it can rotate to deliver the fibre. The fibre 16 is typically fed from the tubes or bobbins 14, upon which the fibre is wound, to a processing area 18 where the fibres are processed to produce a desired article or fabric. Two support structures 10 are shown in parallel and delivering fibres 16 to the processing area 18.

Tension must be maintained in the fibre 16 as it is released from the bobbin 14 to ensure the quality of the final product.

Hence a fibre tensioner, and components thereof including an actuator, which can maintain a predetermined and desirable fibre tension are highly desirable.

Summary

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Accordingly there may be provided an actuator comprising: a housing comprising a chamber, the chamber having an aperture for fluid communication with a source of pressurised fluid; a piston, the piston having a head for bearing on a member; and a stem for slideable location within the chamber, and configured to extend from, and retract into, the actuator chamber; the stem comprising a passage having: a fluid orifice for fluid communication with the chamber the passage opening at the head of the piston into an expansion chamber, and the expansion chamber having at least one wall which is moveable relative to the piston head in response to a change in fluid pressure delivered to the actuator.

The moveable wall of the expansion chamber may be resiliently biased towards the piston head.

The moveable wall of the expansion chamber may be provided as a flexible diaphragm.

The moveable wall may be fixed to the piston head towards the periphery of the piston head to provide a seal between the piston head and the moveable wall.

The moveable wall may be provided with an engagement feature to fix the moveable wall to a complementary engagement feature on the piston head.

The moveable wall engagement feature may be provided as ring around the periphery of the moveable wall, the ring having a stepped profile configured to be fitted around a lip provided on the piston head, the lip having a greater outer diameter than the inner diameter of at least one region of the ring.

The actuator may be pneumatically or hydraulically activatable.

There may also be provided a fibre tensioner for a creel, the creel comprising a support frame which carries a holder rotatable about a rotational axis, the holder having a bearing surface; wherein the fibre tensioner comprises: an actuator according to the present disclosure; a moveable load arm; a load strap which, in use, is connected at one end to the support frame and connected at its other end to the load arm, is arranged relative to the holder to bear upon the holder bearing surface; and a control unit for controlling the actuator to adjust the load arm position to maintain a desired predetermined tension in the load strap, and thereby maintain a predetermined frictional resistance to the rotational motion of the holder.

The control unit may be configured to maintain a predetermined schedule of tension on the load strap, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder.

The load arm may be pivotably mounted to the support frame towards one end, and is engaged with the moveable wall of the actuator towards its other end, such that the action of the actuator rotates the load arm about the pivot point.

The holder may be configured to support and engage with a bobbin.

There may also be provided a creel comprising a support frame; a holder carried on the support frame and rotatable relative to the support frame; and a fibre tensioner according to the present disclosure wherein the load strap is connected at one end to the creel support frame, at its other end to the load arm, and arranged relative to the holder to bear upon the holder bearing surface.

The holder bearing surface may comprise a ring shaped track having a rotational axis coaxial with the holder rotational axis; the track being flanked on either side by a wall to maintain the load strap in a substantially constant position along the holder rotational axis.

The load strap may be arranged to bear on substantially a whole circumference of the bearing surface.

There may also be provided a method of operating fibre tensioner for a creel, the creel comprising a support frame and carrying holder rotatable about a rotational axis on the support frame, the holder having a bearing surface; and the fibre tensioner comprises an actuator which acts upon a moveable load arm; a load strap which in use is connected at one end to the creel, at its other end to the load arm, to be arranged relative to the holder to bear upon the holder bearing surface; wherein the method comprises the step of: operating the actuator to adjust the load arm position to tension the load strap, and thereby maintain a desired frictional resistance to the rotational motion of the holder.

The method may further comprise operating the actuator to adjust the load arm position to maintain a predetermined schedule of tension in the load strap, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder.

The predetermined schedule of tension may define one or more desired loads, a range of loads, or a gradient of loads, to be maintained throughout a predetermined period of operation of the fibre tensioner.

The load arm position may be adjusted in response to a change in tension in the load strap as the holder rotates to maintain a substantially constant tension in the load strap and thereby maintain a substantially constant frictional force between the load strap and the holder.

The method may include the steps of: a) determining the tension of fibre being drawn from the holder; b) determining if the tension is within a predetermined range of desired values; c) if the tension is outside of a predetermined range of desired values, operating the actuator to move the position of the load arm to increase or decrease tension in the fibre by increasing or decreasing tension in the load strap such that the fibre tension value approaches the predetermined range of desired values.

Hence there is provided an actuator for use with fibre tensioners for a creel, and a method for operating the fibre tensioners, in order to maintain a predetermined fibre release tension.

Brief Description of the Drawings

Examples of the present disclosure will now be described with reference to the accompanying drawings, in which: Figure 1 shows a known creel arrangement; Figure 2 shows an example layout of a fibre tensioner and creel of the present

disclosure;

Figure 3 shows a side view of the layout of Figure 2, as shown from the direction of arrow "A" in Figure 2; Figure 4 shows an example of a holder which, in use, is mounted to the fibre tensioner and the creel of the present disclosure as shown in Figures 2,3; Figure 5 shows an example of an actuator; Figure 6 shows an example of an actuator of the present disclosure; Figures 7 to 9 shows a mode of operation of the actuator of figure 6 in combination with the tensioner arrangement of figures 2 to 4.

Detailed Description

Figures 2 to 4 show a fibre tensioner 40 for a creel according to the present disclosure.

Features common to the related art are identified with the same reference numerals used to describe the features of Figure 1. Hence in the example shown in Figures 2 to 4, and as described with reference to figure 1, a holder 13 supports and engages with a tube or bobbin 14. The tube 14 carries fibre material 16 for delivery to a processing area 18. A side view as seen from the direction of arrow "A" in Figure 2 is shown in Figure 3. Details of the holder 13 are shown in Figure 4.

The fibre tensioner 40 comprises an actuator 100 and a moveable load arm 54. An actuator piston 108 extends from the actuator 100 to press against the load arm 54.

The fibre tensioner 40 further comprises a strap 56 which in use is connected at one end to the creel support frame 44 at an anchor point 58. At its other end, the load strap 56 is connected to the load arm 54, for example by a clamp or pin arrangement 60. The holder 14 incorporates a pulley 90, shown in Figure 4. The load strap 56 is arranged upon the pulley surface 50.

The load arm 54 is pivotally mounted to the support frame 44 towards one end 76 at a pivot point 78. The load arm 54 is engaged with the piston 108 of the actuator 100 towards the other end 80 of the load arm 54, such that the action of the piston 108 on the actuator 100 rotates the load arm 54 about the pivot point 78.

As shown in Figure 4, the pulley bearing surface 50 comprises a cylindrical (e.g. ring shaped) track 92 having a rotational axis 48 coaxial with the spindle 12, holder 13 and bobbin 14. The track 92 may be flanked on either side by a wall to maintain the load strap in a substantially constant position along the holder rotational axis. The load strap 56 may be arranged to bear on at least the full circumference of the bearing surface 50.

The load strap 56 may alternatively be arranged to bear on more than one circumference of the bearing surface 50. In the example shown in Figures 2 to 5, the load strap 56 bears on substantially a full circumference (i.e. 360 degrees) of the bearing surface 50 by virtue of being wrapped around the circumference of the bearing surface 50. It may also bear on 720 degrees or 1080 degrees by being wrapped two or three times respectively around the circumference of the bearing surface 50.

The tension system 40 further comprises a control unit 62 for controlling the actuator to adjust the force on the load arm 54 and load strap 56, and thereby maintain a predetermined frictional resistance to the rotational motion of the holder 14 as fibre is drawn off the tube 14.

The control unit 62 is operable to control a pressure regulator 68 via the signal connection 70. In turn the pressure regulator 68 is operable to govern the force applied by the actuator 100 by regulating a fluid pressure supply to the actuator 100. The regulator 68 is supplied by fluid at constant pressure from a pressure source (e.g. an air compressor 84). The actuator 100 may be pneumatically or hydraulically activatable.

As shown in Figures 2,3 an ultrasonic sensor 70 is provided which is operable to measure the distance between the sensor and the outer surface of the wound fibre 16 on the tube 14.

The control unit 62 is operable to compute the outer diameter of the fibre 16 wound on the tube 14 and hence the force required at the actuator to achieve the desired fibre tension.

Additionally, or alternatively, the tension in the fibre 16 may be measured directly with a load cell device. In such an example, the control unit 62 is operable to adjust the force applied by the actuator 100 to maintain the desired tension in dependence of the measured value of tension in the fibre 16 as the fibre 16 is drawn off the bobbin 14.

Figure 5 shows a known actuator 29 for use in moving, or at least reacting against, a member 30. The example of figure 5 is provided as background to the understanding of the merit of the actuator of the present disclosure.

In the example shown the member 30 is pivotable. The actuator 29 comprises a piston 31 which slides within a housing 32, the housing 32 having an opening 33 for the inlet of a pressurised air to move the piston 31.

Forces induced on the piston by pressurised air entering the opening 33 act on the end of the piston and are transmitted along its axis. Any misalignment of the forces on each end of the piston 31 causes a tilting action and results in increased sliding friction and wear. Friction between the piston 31 and walls of the housing 32 results in generally unacceptable force accuracy when displacements of the piston are required.

By contrast, Figure 6 shows an actuator 100 which is the subject of the present disclosure, as described briefly above in relation to Figure 2 to 5.

The actuator 100 comprises a housing 102 having a chamber 104. The chamber 104 is defined by an inner wall, or walls, of the housing 102. The chamber 104 has an aperture 106, of diameter d2, for the passage of pressure air into and/or out of the chamber 104.

As described above in relation to Figures 2 to 5, the actuator 100 is also provided with a piston 108 of external diameter dl, and having a head 110. The piston 108 also has a stem 112 configured for slideable location within the chamber 104, the piston 108 being configured to extend from, and retract into, the actuator chamber 104. The piston 108 is slideable in a direction aligned with a central axis 114 of the chamber 104.

The stem 112 has a passage 116 with an orifice 118 for the passage of air into and/or out of the passage 116 from and/or to the chamber 104. The passage 116 extends along the full length of the piston 108, opening at the head 110 of the piston 108 into an expansion chamber 120. The expansion chamber 120 has at least one wall 122 which is moveable relative to the piston head 110. For example, the moveable wall 122 may move away from and towards the piston head 110 (as shown in Figure 9, the extreme positions of the diaphragm being shown as 122, 122').

The moveable wall 122 of the expansion chamber 120 is provided as a flexible diaphragm. The diaphragm may comprise a synthetic rubber or other suitable material.

In the example shown, the diaphragm is provided with a bullet or nipple 130 which extends away from the outer surface of the diaphragm 122 away from the piston head 110. The moveable wall 122 of the expansion chamber 120 may be resiliently biased towards the piston head 110.

The diaphragm 122 may be fixed to the piston head 110 towards the periphery 124 of the piston head 110 to provide a seal between the piston head 110 and the diaphragm 122. In the example shown, the piston head has a circular shape (when viewed from above as shown in the figure, i.e. in the direction of arrow "A" shown in figure 6).

Viewed from the same direction, the diaphragm 122 also has a circular shape of diameter d3, complementary in size to the piston head 122. As shown in the cross sectional view of Figure 6, the cross section of the annular diaphragm is curved, permitting movement of the nipple relative to the position head by change of curvature in the flexible diaphragm In this example, the diaphragm 122 is provided with an engagement feature 126 to fix it to the piston head 110. The moveable wall engagement feature 126 is provided as ring 126 around the periphery 124 of the moveable wall 122, the ring 126 having a stepped profile configured to be fitted around the complementary engagement feature 128, provided as a lip 128 provided on the piston head 110. The outer diameter of the lip 128 is greater than the smallest inner diameter of the ring 126. Hence the ring 126 hooks over the lip 128 to hold the wall 122 onto the piston head 110. The diaphragm 122 and ring 126 may be integrally formed with one another of the same material, or manufactured separately and joined together. Since they are of a flexible construction, the ring 126 may be sufficiently deformable to allow it to stretch over the lip 128.

In addition, a clamp ring (not shown) may be fitted around the periphery of the engagement feature to urge the engagement feature 126 and lip 128 into contact, and hence prevent the engagement feature 126 becoming detached in pad or completely from the lip 128. Such a clamp ring would thus assist in maintaining a seal between the moveable wall 122 and piston head 110.

Alternatively or additionally, the diaphragm 122 may be directly bonded to the piston head 110, for example around the periphery 124 of the piston head 110.

Figures 7 to 9 illustrate a mode of operation of the actuator 100 and load arm 54. For clarity, details of the rest of the system are omitted from these figures.

Figure 7 shows the system at rest, illustrated in the figures as position "B", with the load arm 54 resting on the nipple 130 of the actuator. The load strap 56 may be unloaded (that is to say, slack, as shown in Figure 8) or lightly in tension between the load arm 54 and anchor point 58 on the creel support frame 44. The system is operable such that the control unit 62 may command the regulator 68 to pressurise the air in the actuator 100, and hence move the piston 108 and diaphragm 122 to thereby achieve a chosen tension in the load strap 56.

The piston 108 and diaphragm 122 will thus rise in response to the increased fluid pressure to move from position "B' to position "C, as shown in Figure 8. When the slack is taken up by the movement of the piston, minor further movements of the load arm 54 may be taken up by the diaphragm 122 (for example, moving between positions 122,122' as shown in Figure 9) without having to overcome the friction or inertia inherent in the sliding piston 108.

Figure 9 shows a position "D" of the load arm 54 where the arm 54 is higher than in position "C". In this case, the strap may have worn or stretched owing to extended use, causing the arm to rise. However, the actuator diaphragm 122 is still able to operate as before, and move between positions 122,122' as shown.

In operation, pressurising the air in the chamber 104, and hence the passage 116 and expansion chamber 120, will result in a force pushing the central nipple 130 upwards, the force being centred around the central axis 114 of the chamber 104.

The area of the annulus formed between diameter d3 (of the moveable wall 122) and diameter dl (of piston 108) is the same both for the piston head and the diaphragm 122. As force = pressure x area, the force produced due to the pressure on the diaphragm 122 within this annulus is exactly equal to the force produced on the piston head 110 in the same annulus. Consequently, the force produce by the pressure on the diaphragm 122 balances the force produced by the pressure on the piston head 110.

There is a linear relationship between the moment of force applied to the holder 13 through the strap 56 and the linear force applied by the actuator 100.

Fibre tension may be determined by dividing the moment of force by the outer diameter of the fibre material 16 wound on the tube 14. As the fibre 16 is delivered, the diameter of the remaining material wound on the tube will decrease.

As the fibre 16 is unwound from the tube 14, the force applied by the actuator 100 is decreased by the controller 62 to maintain a constant tension.

That is to say the control unit 62 of the fibre tensioner 40 may determine the tension of the fibre 16 being drawn from the holder. It may then determine if the tension is within a predetermined range of desired values, if the tension is outside of a predetermined range of desired values, the control unit 62 may then operate the actuator 100 to move the position of the load arm 54 to increase or decrease tension in the fibre 16 by increasing or decreasing tension in the load strap 54 such that the fibre tension value approaches the predetermined range of desired values.

The control unit 62 may be configured to maintain a predetermined schedule of tension on the load strap 56, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder 13. The predetermined schedule of tension may define one or more desired loads, a range of loads, or a gradient of loads, to be maintained throughout a predetermined period of operation of the fibre tensioner.

The device of the present disclosure is advantageous because the control unit 62 and actuator 100 work together to maintain a constant fibre tension. The device and method of the present disclosure provide a predictable fibre tension by minimizing the effects of friction and mass inherent in a traditional actuator. Such precision and constancy obviates the need for adjustment of individual tensioners. This speeds set up time and results in a more reliable creel assembly 44 and hence will result in fewer manufacturing quality issues because of poor tension control of the fibres 16.

The actuator 100 combines the benefits of a large initial displacement provided by the piston 108 relative to the housing 102, with the diaphragm 122 allowing small displacements with good force accuracy and response, which is due to its inherent low friction and mass.

Since the force produced by the actuator 100 is proportional to the air pressure supplied and the cross sectional area of the stem 112 and diaphragm of the piston 108, the dimensions of the components of the actuator may be accurately controlled during manufacture, to thereby produce a device which accurately responds to input air pressure.

Also, as the area within dl on the top of the piston is the same as the area on the bottom of the piston, no net forces act on the piston, and hence no net forces are transmitted through the piston 108 to the nipple 130. Hence sliding friction and wear at the interface of the stem 112 and the wall of the housing chamber 102 are reduced compared to that of the example actuator shown in figure 5.

Small displacements resulting from non-circularity of the pulley 90 or eccentricity of the pulley 90 in relation to the spindle 12, causing cyclical variations in tension as the bobbin or tube rotates, may thus be accommodated by the active fibre tensioner device

of the present disclosure.

Additionally, variations in load strap length and, in the longer term, movement due to wear and stretch of the load strap may also be accommodated by the active fibre

tensioner device of the present disclosure.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMSAn actuator comprising: a housing comprising a chamber, the chamber having an aperture for fluid communication with a source of pressurised fluid; a piston the piston having a head for bearing on a member; and a stem for slideable location within the chamber, and configured to extend from, and retract into, the actuator chamber; the stem comprising a passage having a fluid orifice for fluid communication with the chamber the passage opening at the head of the piston into an expansion chamber, and the expansion chamber having at least one wall which is moveable relative to the piston head in response to a change in fluid pressure delivered to the actuator.
2 An actuator as claimed in claim 1 wherein the moveable wall of the expansion chamber is resiliently biased towards the piston head.
3 An actuator as claimed in claim 1 or claim 2 wherein the moveable wall of the expansion chamber is provided as a flexible diaphragm.
4 An actuator as claimed in any one of the preceding claims wherein the moveable wall is fixed to the piston head towards the periphery of the piston head to provide a seal between the piston head and the moveable wall.
An actuator as claimed in claim 4 wherein the moveable wall is provided with an engagement feature to fix the moveable wall to a complementary engagement feature on the piston head.
6 An actuator as claimed in claim 4 wherein the moveable wall engagement feature is provided as ring around the periphery of the moveable wall, the ring having a stepped profile configured to be fitted around a lip provided on the piston head, the lip having a greater outer diameter than the inner diameter of at least one region of the ring.
7 An actuator as claimed in any one of the preceding claims wherein the actuator is pneumatically or hydraulically activatable.
8 A fibre tensioner for a creel, the creel comprising a support frame which carries a holder rotatable about a rotational axis, the holder having a bearing surface; wherein the fibre tensioner comprises an actuator as claimed in any one of claims 1 to 7; a moveable load arm; a load strap which, in use, is connected at one end to the support frame and connected at its other end to the load arm, is arranged relative to the holder to bear upon the holder bearing surface; and a control unit for controlling the actuator to adjust the load arm position to maintain a desired predetermined tension in the load strap, and thereby maintain a predetermined frictional resistance to the rotational motion of the holder.
9 A fibre tensioner as claimed in claim 8 wherein the control unit is configured to maintain a predetermined schedule of tension on the load strap, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder.
A fibre tensioner as claimed in claim 8 or claim 9 wherein the load arm is pivotably mounted to the support frame towards one end, and is engaged with the moveable wall of the actuator towards its other end, such that the action of the actuator rotates the load arm about the pivot point.
11 A fibre tensioner as claimed in any one of claims 8 to 10 wherein the holder is configured to support and engage with a bobbin.
12 A creel comprising a support frame; a holder carried on the support frame and rotatable relative to the support frame; and a fibre tensioner as claimed in any one of claims 8 to 11; wherein the load strap is connected at one end to the creel support frame, at its other end to the load arm, and arranged relative to the holder to bear upon the holder bearing surface.
13 A creel as claimed in claim 12 wherein the holder bearing surface comprises a ring shaped track having a rotational axis coaxial with the holder rotational axis; the track being flanked on either side by a wall to maintain the load strap in a substantially constant position along the holder rotational axis.
14 A creel as claimed in claim 12 or claim 13 wherein: the load strap is arranged to bear on substantially a whole circumference of the bearing surface.
A method of operating fibre tensioner for a creel, the creel comprising a support frame and carrying holder rotatable about a rotational axis on the support frame, the holder having a bearing surface; and the fibre tensioner comprises an actuator which acts upon a moveable load arm; a load strap which in use is connected at one end to the creel, at its other end to the load arm, to be arranged relative to the holder to bear upon the holder bearing surface; wherein the method comprises the step of: operating the actuator to adjust the load arm position to tension the load strap, and thereby maintain a desired frictional resistance to the rotational motion of the holder.
16 A method of operating a fibre tensioner for a creel as claimed in claim 15, wherein the method further comprises operating the actuator to adjust the load arm position to maintain a predetermined schedule of tension in the load strap, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder.
17 A method of operating a fibre tensioner as claimed in claim 16 wherein: the predetermined schedule of tension defines one or more desired loads, a range of loads, or a gradient of loads, to be maintained throughout a predetermined period of operation of the fibre tensioner.
18 A method of operating a fibre tensioner as claimed in any one of claims 15 to 17 wherein the load arm position is adjusted in response to a change in tension in the load strap as the holder rotates to maintain a substantially constant tension in the load strap and thereby maintain a substantially constant frictional force between the load strap and the holder.
19 A method of operating a fibre tensioner as claimed in any one of claims 15 to 18 which includes the steps of: a) determining the tension of fibre being drawn from the holder; b) determining if the tension is within a predetermined range of desired values; c) if the tension is outside of a predetermined range of desired values, operating the actuator to move the position of the load arm to increase or decrease tension in the fibre by increasing or decreasing tension in the load strap such that the fibre tension value approaches the predetermined range of desired values.
An actuator substantially as hereinbefore described and/or as shown in figures 2 to 9.
21 A fibre tensioner for a creel substantially as hereinbefore described and/or as shown in figures 2 to 9.
22 A creel substantially as hereinbefore described and/or as shown in figures 2 to 9.
23 A method of operating fibre tensioner for a creel substantially as hereinbefore described and/or as shown in figures 2 to 9.AMENDMENTS TO THE CLAIMS HAVE BEEN FtLED AS FOLLOWS:- 1 An actuator comprising: a housing comprising a chamber, the chamber having an aperture for fluid communication with a source of pressurised fluid; a piston the piston having a head for bearing on a member; and IC) F.... a stem for slideable location within the chamber, and 0 configured to extend from, and retract into, the actuator chamber; C) the stem comprising a passage having: a fluid orifice for fluid communication with the chamber the passage opening at the head of the piston into an expansion chamber, and the expansion chamber having at least one wall which is moveable relative to the piston head in response to a change in fluid pressure delivered to the actuator.2 An actuator as claimed in claim 1 wherein the moveable wall of the expansion chamber is resiliently biased towards the piston head.3 An actuator as claimed in claim 1 or claim 2 wherein the moveable wall of the expansion chamber is provided as a flexible diaphragm.4 An actuator as claimed in any one of the preceding claims wherein the moveable wall is fixed to the piston head towards the periphery of the piston head to provide a seal between the piston head and the moveable wall.An actuator as claimed in claim 4 wherein the moveable wall is provided with an engagement feature to fix the moveable wall to a complementary engagement feature on the piston head.6 An actuator as claimed in claim 4 wherein the moveable wall engagement LU feature is provided as ring around the periphery of the moveable wall, the ring having a stepped profile configured to be fitted around a lip provided on the piston head, the lip having a greater outer diameter than the inner diameter of at 0 least one region of the ring.CV) 7 An actuator as claimed in any one of the preceding claims wherein the actuator is pneumatically or hydraulically activatable.8 A fibre tensioner for a creel, the creel comprising a support frame which carries a holder rotatable about a rotational axis, the holder having a bearing surface; wherein the fibre tensioner comprises an actuator as claimed in any one of claims 1 to 7; a moveable load arm; a load strap which, in use, is connected at one end to the support frame and connected at its other end to the load arm, is arranged relative to the holder to bear upon the holder bearing surface; and a control unit for controlling the actuator to adjust the load arm position to maintain a desired predetermined tension in the load strap, and thereby maintain a predetermined frictional resistance to the rotational motion of the holder.9 A fibre tensioner as claimed in claim 8 wherein the control unit is configured to maintain a predetermined schedule of tension on the load strap, and thereby maintain a predetermined schedule of frictional resistance to the rotational motion of the holder.A fibre tensioner as claimed in claim 8 or claim 9 wherein the load arm is If, pivotably mounted to the support frame towards one end, and is engaged with the moveable wall of the actuator towards its other end, such that the action of the actuator rotates the load arm about the pivot point.11 A fibre tensioner as claimed in any one of claims 8 to 10 wherein the holder is CV) configured to support and engage with a bobbin.12 A creel comprising a support frame; a holder carried on the support frame and rotatable relative to the support frame; and a fibre tensioner as claimed in any one of claims 8 to 11; wherein the load strap is connected at one end to the creel support frame, at its other end to the load arm, and arranged relative to the holder to bear upon the holder bearing surface.13 A creel as claimed in claim 12 wherein the holder bearing surface comprises a ring shaped track having a rotational axis coaxial with the holder rotational axis; the track being flanked on either side by a wall to maintain the load strap in a substantially constant position along the holder rotational axis.14 A creel as claimed in claim 12 or claim 13 wherein: the load strap is arranged to bear on substantially a whole circumference of the 0 bearing surface.CV) 15 An actuator substantially as hereinbefore described and/or as shown in figures 2 to 9.16 A fibre tensioner for a creel substantially as hereinbefore described and/or as shown in figures 2 to 9.17 A creel substantially as hereinbefore described and/or as shown in figures 2 to 9.