GB2335467A - Improved mechanical actuator - Google Patents

Improved mechanical actuator Download PDF

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Publication number
GB2335467A
GB2335467A GB9806169A GB9806169A GB2335467A GB 2335467 A GB2335467 A GB 2335467A GB 9806169 A GB9806169 A GB 9806169A GB 9806169 A GB9806169 A GB 9806169A GB 2335467 A GB2335467 A GB 2335467A
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Patent type
Prior art keywords
sheath
means
constriction
another
vessel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9806169A
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GB9806169D0 (en )
Inventor
Richard Martin Greenhill
Original Assignee
Richard Martin Greenhill
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Filing date
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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVO-MOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/08Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith characterised by the construction of the motor unit
    • F15B15/10Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith characterised by the construction of the motor unit the motor being of diaphragm type
    • F15B15/103Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith characterised by the construction of the motor unit the motor being of diaphragm type using inflatable bodies that contract when fluid pressure is applied, e.g. pneumatic artificial muscles or McKibben-type actuators
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B25HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25JMANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00Programme-controlled manipulators
    • B25J9/10Programme-controlled manipulators characterised by positioning means for manipulator elements
    • B25J9/1075Programme-controlled manipulators characterised by positioning means for manipulator elements with muscles or tendons

Abstract

Terminating and sealing pneumatic muscle actuators requires a retaining means. This invention provides a superior retaining design consisting of a retaining ring which clamps the expansible sheath to the expansible vessel and the terminator, obviating the need to transfer force from the expansible sheath to the terminator, and removing protrusions from the outside envelope of the muscle, permitting close-packing of moving actuators with considerably less interference.

Description

2335467 IMPROVED COMPONENT OF MECHANICAL ACTUATOR The present invention

relates to an artificial muscle and a mechanical actuator incorporating the muscle.

The present applicant's UK patent 2255961, dated 13 March 1992 discloses and claims a mechanical actuator including an artificial muscle or "traction element".

This muscle comprises an expansible vessel such as a tube, closed at each end, with means to introduce a fluid, such as air, under pressure, into the tube. The tube is made of expansible material such as rubber. Surrounding the tube is a braided sheath. As the fluid enters the tube, the increased pressure causes it to expand. This in turn causes the braided sheath to expand radially. The nature of the braiding is such that when it is expanded radially it is constrained to contract longitudinally. Thus a tensile force is generated between the points of attachment of the ends of the braided sheath. In the device termed a "Shadow Digit" disclosed in the inventor's patent referred to above, this force is used to cause relative movement of two pivotally interconnected beams.

In use, the air muscle is attached at one end to a f ixed point and at the other end to the piece to be moved. This needs to be done in such a way that the air muscle is extended, prior to the introduction of fluid under pressure. When fluid is introduced under pressure into the expansible vessel or tube, the walls of the vessel are stretched and expand. The expansion of the expansible vessel would occur both radially and longitudinally, but the attachment of the muscle under tension prevents longitudinal expansion, since the vessel is already stretched in that direction. Hence, only radial expansion can occur.

The braided sheath converts the radial expansion into a longitudinal contraction. It may also be used as the means of attachment to the structure which is to be acted on. It may be 9 looped back and secured by a contractible ring or other suitable tie to the end of the expansible vessel. Certain other materials which have the property of contracting axially when dilated radially may also be used instead of the braided sheath. For example a material moulded to form a diamondshaped lattice might be used. With these criteria, the selection of the sheath material is a simple matter for those skilled in the art. We use a braided sheath for example only, and refer to all such coatings as nthe sheath".

The present invention is an alternative means of construction of such devices.

Several improvements in use are claimed in that the muscle has a smooth exterior so that, for example, it is unlikely to catch or snag on other muscles or other objects which may be in contact with it; there is more flexibility in the method and location of attachment, and greater ease of construction; cost of construction should also be lower.

A human, or mammal, may have many different muscles packed closely together, able to slide against each other without damaging each other. Previous air muscle designs have generally been found to be unsuitable for use in a confined area where sharp or protruding parts of one muscle may cause damage to another, especially if they move relative to each other.

The present invention addresses this problem. The exterior of the device is smooth and is, in the main, formed by the braided sheath. Neither the means of attachment nor the means of supplying fluid to the expansible vessel make use of elements which protrude beyond the general line of the braided sheath. The tube which supplies fluid to the expansible vessel is situated within, and protected by, the braided sheath for all, or part of its length. It may be brought out of the braided sheath at a convenient point, well away from the moving part of the actuator.

The longitudinal contraction effected by the actuator is transmitted to the work by the braided sheath. In order to avoid the use of protruding or sharp or otherwise potentially damaging elements, the braided sheath is extended to any length which may be required or desired, to be attached to the work as preferred. Thus the braiding acts in much the same way as the tendon which attaches a human or mammalian muscle to the work (in the case of the human, the bone) to which force is to be applied.

The braiding may be attached to the work by clamping, bonding by glue or melting of elements, or any other means well known in the art.

The novel terminator gives rise to several improvements:- 0 Attachment of the actuator may be simpler, as the location and type of attachment may be varied by the end user.

& The ring does not need to be adjustable. Adjustable rings (such as the clips known as Jubilee clips) have several disadvantages; they are likely to be more expensive than simple rings; part of the clip may protrude inwards and may easily cause damage to the sheath or expansive vessel; under strain, the adjustment mechanism may fail, allowing the ring to expand.

0 Assembly of such actuators may be simpler, as compared to the looped sheath.

Repair of such actuators may be simpler, as compared to an actuator with a looped sheath.

The significant factor in the present invention is the shape and composition of the ring which compressively holds the elements which form the termination of the expansive vessel together.

In previous designs of air muscle, it would be necessary for such a ring to apply and sustain considerable force in clamping the elements which form the termination of the expansive vessel together. Commonly, one of these elements would have been part of the active elements of the actuator, while another would have been attached, directly or indirectly, to the work.

-4 Thus the ring would be required to clamp together firmly two or more elements under tensile strain which would, if not sufficiently clamped, come apart when the actuator was used.

The present invention avoids the necessity of such firm clamping by using the same element -- viz the braided sheath -- to perform two functions. In the central, active part of the muscle, the braided sheath is used to translate the radial expansion of the inner expansible vessel to longitudinal contraction of the assembly. On the other side of the ring, the continuing braided sheath simply acts as the means of attachment of the actuator (the muscle) to the work.

The ring may be needed to ef f ect the closure of the expansible vessel by clamping said vessel against the terminator, and may also act to clamp the tube or tubes used to fill and/or empty the vessel by compressing the terminator. However, the force required to perform these tasks has been found generally to be much less than that required for the firm clamping of elements under tensile strain referred to above.

Because this clamping force, then, is quite slight, it has been found by the present inventor that it is possible to obtain it merely by sliding the ring over the braided sheath and pushing it firmly into position. A suitable adhesive may be used to prevent it working loose as the actuator is used.

In the prior art, clamping means have been used to allow the ring to be forcibly contracted to clamp the elements under tensile strain. These means included a screw thread as on a Jubilee Clip or other hose clip, pliable ears which could be pinched together with pincers to close singleor double-eared clamps, crimping, and any other means to powerfully reduce the size of the ring while in position, so as to clamp the elements firmly together.

In general, these just-mentioned means required some element or other which protruded from the ring. In several cases these protrusions were quite sharply pointed, and therefore liable to cause damage. If a number of muscles constructed in this way were used in a confined space, without any means to separate them, and were to move relative to one another, they would be likely to jam against each other, and damage would also be likely.

In the present invention the ring may be smooth, such as a simple cylinder. It may also be contoured or shaped to avoid catching or snagging against other similar rings on similar muscles. For example the outer end that is to say the end away from the centre of the muscle, might be slightly conical or rounded inwards.

Because the clamping pressure of the ring does not need to be so great, the ring might be made of thinner, and/ or more flexible material, such as soft metal, plastic, heat-shrink plastic, a woven material, cord or thread, or any other material with sufficient tensile strength to prevent the walls of the expansible vessel from coming away from the terminator and allowing fluid under pressure to escape. Alternatively, the braiding itself may be constrained from expansion by fixing it with a suitable adhesive.

In order that the invention may be well understood, an example of it, which is given by way of example only, will now be described with reference to the accompanying drawings, in which:

Figure 1 is a view of a basic air muscle with loopedback sheath: and Figure 2 is an enlarged view of the same components at one end of the air muscle only, showing one example of the way in which it may be attached to the piece to be moved: and Figure 3 is a diagram to show how the air muscle needs to be fully stretched before fluid is introduced into it: and device.

Figure 4 is a cross sectional view of the proposed In more detail:- Figure 1 shows the general structure of the traction element or artificial muscle of the applicant's previous Patent already referred to.

Figure 2 is an enlarged view of the same components at one end of such a muscle only showing one example of the way in which it may be attached to the piece to be moved. Modifications to this muscle, on the means of securing the end of the active part of the muscle to the work and of the arrangement of the tube to introduce fluid under pressure into the expansible vessel, form the substance of the present patent application.

Figure 3 is a diagram to show how the air muscle needs to be extended longitudinally before fluid is introduced. The introduction of said fluid under pressure then causes the longitudinal contraction shown.

Figure 4 is a cross section of an example of an air muscle according to the present invention. A braided sheath 2 covers an expansible vessel 3 to form the main body and active part of the air muscle. The expansible vessel 3 is closed and made air-tight by the insertion of a terminator 4 at each end.

The braiding 2 and the expansible vessel 3 are held firmly against each terminator 4 by a ring 5. The presence of this ring 5 clamping the materials 2 and 3 against the terminator 4 prevents fluid from escaping from the expansible vessel 3.

When fluid such as air is introduced under pressure into the expansible vessel 3 (by means of the tube 6), the said vessel expands. This expansion is limited by the braiding 2, which translates the radial expansion into longitudinal contraction. The force of this contraction is applied to the work 7 to which the muscle is attached, by means of the extended braiding 2. There is no particular limit to the length of this braiding. It may be attached by any means to the work as convenient.

In order to fill the air muscle with fluid, and empty it again, a tube 6 is attached to one or both of the terminators 4. Other arrangements and fittings may be used to effect the flow of fluid into and out of the expansible vessel 3 to cause the muscle to operate. The tube 6 may pass through the braiding at any convenient point, which may be well away from the area where the active part of the muscle or muscles are.

Q

Claims (19)

Claims.
1. A mechanical actuator comprising: an expansible vessel having a
first and a second end; means for allowing flow of a fluid under pressure into and out of said vessel; means for converting radial expansion force of said expansible vessel into longitudinal contraction force, said means comprising a sheath surrounding the expansible vessel; fixtures for terminating and sealing said expansible vessel; retaining means for connecting said sheath to said fixtures, said retaining means being configured such that that the tensile force produced by the actuator is neither transmitted from said sheath to said fixtures nor transmitted from said sheath to said retaining means; means for attaching said sheath to structures to be acted on.
2. As in claim 1, wherein the terminating means for one end of the actuator comprises the apparatus used to allow flow of fluid under pressure into and out of the vessel.
3. As in claim 1, wherein the retaining means is any constriction of the braided sheath sufficient to ensure the sealing of the expansible vessel.
4. As in claim 1, wherein the longitudinal contraction force effected by the actuator is transmitted to the work through the braided sheath.
5. As in claims 1 and 4, wherein the sheath is extended to the structure to be acted on, and attached directly to that structure.
6. As in claims 1 and 4, wherein the sheath is attached to a flexible load-bearing element which is itself attached to the structure to be acted on.
7. As in claims 1 and 4, wherein a fastening or connector is attached to the braided sheath at a distance from the actuator, said fastening or connector serving to transfer tensile force to the structure to be acted on.
8. As in claims 1 and 3, wherein said constriction is produced by a smooth cylindrical band.
9. As in claims 1 and 3, wherein said constriction is produced by a conical band.
10. As in claims 1 and 3, where the retaining means is devoid of protrusions, so that multiple muscles may be packed together and may move relative to one another and in contact with one another without risk of piercing or abrasion from such protrusions.
11. As in claims 1, 3 and 4, wherein the means of supplying fluid to the expansible vessel does not protrude beyond the envelope of the sheath, so that multiple muscles may be packed together and may move relative to one another and in contact with one another without risk of piercing or abrasion from such protrusions.
12. As in claims 1, 3, 6 and 7, wherein the means of attachment does not protrude beyond the envelope of the sheath, so that multiple muscles may be packed together and may move relative to one another and in contact with one another
Cl without risk of piercing or abrasion from such protrusions.
13. As in claim 1, wherein no feature of the muscle protrudes beyond the envelope of the sheath, so that multiple muscles may be packed together and may move relative to one another and in contact with one another without risk of piercing or abrasion from such protrusions.
14. As in claims 1,3,8 and 9, wherein said constriction means is rigid.
15. As in claims 1,3,8 and 9, wherein said constriction means is a flexible sleeving.
16. As in claims 1,3,8 and 9, wherein said constriction means is a flexible sleeving whose diameter is reduced as part of the construction process to provide constriction.
17. As in claims 1,3,8 and 9, wherein said constriction means is a rigid sleeving whose diameter is reduced as part of the construction process to provide constriction.
18. As in claim 1, wherein the braided sheath is used to serve the role of the tendon in the mammalian musculature.
19. A mechanical actuator substantially as described herein with reference to Figures 1-4 of the accompanying drawing.
GB9806169A 1998-03-20 1998-03-20 Improved mechanical actuator Withdrawn GB9806169D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9806169A GB9806169D0 (en) 1998-03-20 1998-03-20 Improved mechanical actuator

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9806169A GB9806169D0 (en) 1998-03-20 1998-03-20 Improved mechanical actuator

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GB9806169D0 GB9806169D0 (en) 1998-05-20
GB2335467A true true GB2335467A (en) 1999-09-22

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7185580B2 (en) 2002-04-12 2007-03-06 Festo Ag & Co. Fluid-actuated contraction drive and associated contraction tube
DE102007017419B3 (en) * 2007-04-13 2008-05-29 Festo Ag & Co. Contraction drive, has fastening loop formed by fastening element, which is separated relative to string structure of contraction device and has opposed end sections firmly clamped together with contraction device in related clamping gap
EP1931882A1 (en) * 2005-09-02 2008-06-18 Martin Russell Harris A fluid transmission
CN105030389A (en) * 2015-07-25 2015-11-11 东北大学 Intelligent pneumatic muscle based on shape memory alloy spring

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4841845A (en) * 1986-09-22 1989-06-27 Theophile Beullens Hydraulic or pneumatic drive device
US5014600A (en) * 1990-02-06 1991-05-14 Welch Allyn, Inc. Bistep terminator for hydraulic or pneumatic muscle
US5351602A (en) * 1992-08-05 1994-10-04 The United States Of America As Represented By The Secretary Of The Army Jointed assembly actuated by fluid pressure

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4841845A (en) * 1986-09-22 1989-06-27 Theophile Beullens Hydraulic or pneumatic drive device
US5014600A (en) * 1990-02-06 1991-05-14 Welch Allyn, Inc. Bistep terminator for hydraulic or pneumatic muscle
US5351602A (en) * 1992-08-05 1994-10-04 The United States Of America As Represented By The Secretary Of The Army Jointed assembly actuated by fluid pressure

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7185580B2 (en) 2002-04-12 2007-03-06 Festo Ag & Co. Fluid-actuated contraction drive and associated contraction tube
EP1931882A1 (en) * 2005-09-02 2008-06-18 Martin Russell Harris A fluid transmission
EP1931882A4 (en) * 2005-09-02 2008-12-03 Martin Russell Harris A fluid transmission
US8220260B2 (en) 2005-09-02 2012-07-17 Martin Russell Harris Fluid transmission
DE102007017419B3 (en) * 2007-04-13 2008-05-29 Festo Ag & Co. Contraction drive, has fastening loop formed by fastening element, which is separated relative to string structure of contraction device and has opposed end sections firmly clamped together with contraction device in related clamping gap
CN105030389A (en) * 2015-07-25 2015-11-11 东北大学 Intelligent pneumatic muscle based on shape memory alloy spring
CN105030389B (en) * 2015-07-25 2017-03-01 东北大学 Based shape memory alloy spring intelligent pneumatic muscle

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GB9806169D0 (en) 1998-05-20 grant

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