SE537398C2 - Adjustable table - Google Patents

Abstract

_21- ABSTRACTAoJusTABLE oBJEcT An actuator for adjusting the length of an extensible member, the actuatorcomprising: a driving mechanism; a rotary member arranged to be driven about itsaxis by the driving mechanism selectively in a first direction and a second direction;and an eiongate flexible member supported by a constraint means for transmittingforce from the actuator to the extensibie member in order to adjust the lengththereof; the eiongate fiexibie member passing around and being engaged with therotary member such that rotation of the rotary member in the first direction causesthe eiongate flexible member to be extended and rotation in the second directioncauses the eiongate flexible member to be retracted. [Figure 5]

Description

109481ADJUSTABLE OBJECT The present invention relates to an apparatus for changing the length of amember, and in particular, but not exclusively, to an apparatus for adjusting thelength of a support for an object in order to adjust the height thereof above asurface. For example, the invention may be used to provide a height-adjustabletable. lt is often desirable to adjust the height of an object and in particularfurniture such as tables, chairs, beds. For example, the ideal height of a table maydepend on what it is being used for at a given time, or the height of the personusing it. As these factors may change over time, it is desirable to provide a tablewhere the height of the tabletop above the surface on which the table stands maybe adjusted.

Additionally, there is a demand for devices which can be height-adjustedduring use. For example, it may be desirable to provide a chair which can be raisedas the user is standing up.

Furthermore, there are numerous applications for supports, mounts, displaystands, etc. where it is desired to support something above the ground, whilst beingable to adjust its height.

The awareness of the importance of good ergonomics in relation tofurniture, tools and other products is increasing and as a result it is perceived thatthe desire is increasing for apparatus of many kinds which can be adjusted to suitthe user. lt is, of course, well known to provide such objects with one or more legswhose length may be adjusted in order to vary the height of the object. However,there remains the need to provide a practical and convenient system for the user toadjust the length of the legs at will.

GB 766805 discloses a vertically adjustable bed table. The table comprisesa tabletop supported on an inverted U-shaped tubular frame member, the openends of which each telescopically engage a rod. Within the U-shaped tubular framemembers are a pair of flexible members which each extend from their inner ends,near the middle of the U-shaped tubular frame member to their outer ends whichabut the two rods. When endwlse pressure is applied to the inner end of both the flexible members, they each move within the U-shaped tubular member thereby _2_ transmitting force to the rods causing them to telescopically slide out of the U-shaped tubular frame and thereby causing the table top to rise. ln order to apply endwise pressure to the inner ends of the flexible membersa screw is provided, one half of which is left hand threaded and the other half ofwhich is right hand threaded. The screw is parallel and adjacent the top of the U-shaped tubular frame. The screw is provided with two nuts which have lugs whicheach engage with the inner end of one of the flexible members through slotsprovided in the tubular member. The screw extends laterally to one side of thetable top and is provided with a handle for winding the screw.

Upon winding the screw the nuts are caused to move from a positionmidway of the tubular member outwardly to apply endwise pressure to the innerend of the two flexible members which causes the rods to telescopically slide out ofthe inverted U-shaped tubular member and thus causes the tabletop to rise.Rotation of the screw in the opposite direction moves the nuts back towards thecentre which removes the pressure from the end of the flexible members. As aresult of the weight of the table, the tabletop will lower.

Although this is an effective system, the present inventors have recognisedthat it is subject to a number of drawbacks, not least that the actuating mechanismtakes up a large amount of space and that the degree of extension possible isdetermined by its linear dimensions. Thus, in GB 766805 the maximum heightadjustment is dependent on the length of screw that the nuts travel along, which inturn depends on the size of the table top, or other surface This may cause aproblem if the surface to be raised is relatively small, for example a chair, or themaximum required height adjustment is relatively large.

According to a first aspect of the present invention there is provided anactuator for adjusting the length of an extensible member, the actuator comprising:a driving mechanism; a rotary member arranged to be driven about its axis by thedriving mechanism selectively in a first direction and a second direction; and anelongate flexible member supported by a constraint means for transmitting forcefrom the actuator to the extensible member in order to adjust the length thereof; theelongate flexible member passing around and being engaged with the rotarymember such that rotation of the rotary member in the first direction causes theelongate flexible member to be extended and rotation in the second direction causes the elongate flexible member to be retracted. -3_ The invention extends to a corresponding method and so, viewed from asecond aspect, the invention provides a method of adjusting the length of anextensible member comprising: providing an actuator comprising a drivingmechanism, a rotary member arranged to be driven about its axis by the drivingmechanism selectively in a first direction and a second direction, and an elongateflexible member supported by a constraint means for transmitting force from theactuator to the extensible member in order to adjust the length thereof, the elongateflexibie member passing around and being engaged with the rotary member at itsproximal end and being engaged with the extensible member at its distal end; anddriving the rotary member of the actuator in order to extend and/or retract theelongate flexible member to thereby adjust the length of the extensible member.

By avoiding the use of a linear system such as the screw in GB 766805, theactuator of the present invention may be far more compact and is capable ofproviding a much greater length adjustment for a given maximum linear dimension. lt will be appreciated that by extending the elongate flexible member, a forcefor extending the extensible member may be transmitted from the actuator to thatmember and by retracting the elongate flexibie member, a force for retracting theextensible member may be provided. The elongate flexible member may act directlyon the extensible member. However, additionally or alternatively, the position of theelongate flexible member may be used to control the degree of extension of theextensible member with some or all of the force to cause the change of length beingprovided from another source. For example, in the case of an object or device thatis to be raised or lowered, the weight of the object may be used to lower it, with theelongate flexibie member being used to oppose the weight in order to control itsdescent.

The provision of the elongate flexible member in a constraint means enablesthat member to transmit both tension and compression forces, in other words it maybe used both to push and pull. The constraint means may be straight, butcommonly it will contain bends to allow the force from the actuator to be directed asrequired. The constraint means may be a substantially rigid conduit. ln the case where the actuator of the invention is to be used to adjust theheight of an object, the extensible member may be a support, for example anadjustable leg, which may conveniently be telescopic. The invention may be applied in this same manner to any telescopic member. _4_ Thus, in a preferred form of the invention, the elongate flexible member isarranged to cause an adjustable support of an object to change its length. ln thecase of a telescopic leg, the elongate flexible member may act against a firstteiescoping part, whilst a second teiescoping part is constrained, such thatextension of the elongate flexible member causes the first teiescoping part toextend from the second teiescoping part.

The engagement of the elongate flexible member with the rotary memberpreferably comprises the former being wound around the latter. Thus, in a preferredform of the invention, when the rotary member rotates in a first direction about itsaxis the elongate flexible member Winds around the rotary member and when therotary member turns in a second direction about its axis the elongate flexiblemember unwinds from the rotary member, whereby as the proximal end of theelongate flexible member Winds around the rotary member the distal end of theelongate flexible member is retracted, which may be used to cause the height of theobject to be lowered, and as the proximal endof the elongate flexible memberunwinds from the rotary member the distal end of the elongate flexible member isextended, which may be used to cause the height of the object to be raised.

The part of the actuator containing the rotary member may be providedseparately from, and may be remote from, the object that is being raised. However,in preferred forms of the invention, the actuator and the member that is beingextended are components of the same object. For example, the actuator may formpart of a piece of furniture, or other apparatus, that is height-adjustable.

Thus, viewed from a third aspect, the present invention provides a heightadjustable object comprising an extensible member and a surface arranged to beraised and lowered by adjustment of that member and further comprising theactuator according to the first aspect of the invention, the actuator being arrangedto adjust the height of the object. Thus, there may be provided a table comprising atable top, legs and an actuator as described above, whereby the height of the tablemay be adjusted by means of the actuator acting on the legs.

Any preferred features of the actuator of the first aspect can be included inthe height adjustable device of the second aspect of the present invention. lt will be appreciated that the maximum height adjustment is not limited bythe size of the object being raised. For example, in the case of a table, the size ofthe tabletop does not significantly constrain the degree of height adjustment. The length of elongate flexible member which can wind and unwind from the rotary _5_ member dictates the maximum height change; however, the size of the rotarymember and the length of the elongated flexible member can be determined duringmanufacture of the actuator to suit final end use requirements. The rotary membercan be arranged to accommodate several turns of the elongate flexible memberaround it. Also the actuator can be more compact and less obtrusive as it does notneed to span the whole width of the table being raised. ln other words, the presentinvention provides an actuator which may have a small build-in width withpotentially a very long stroke (distance between the maximum extension of theelongate flexible member and the minimum extension of the elongate flexiblemember).

The driving mechanism can be manually powered, for example comprising ahandle for a user to turn, or electrically powered, when the driving mechanism maycomprise an electric motor. Where the driving mechanism comprises an electricmotor, this allows the user to raise and lower a device conveniently and withminimum effort. Additionally, the motor can be remotely controlled from a switchingunit mounted some distance away so that the motor does not need to be readilyaccessible to the user. This means that the actuator can be compactly housed in asingle housing underneath the device and does not need to protrude laterally from,or be near the edge of, a surface being raised. lf a DC motor is used, the actuatormay be controlled to operate in extension or retraction mode simply by changingthe polarity of the current supplied to the motor.

There are a number of alternatives of drive train arrangements fortransmitting the power to the rotary member. For example, the part of the drivingmechanism providing power may be directly engaged with the rotary member or thedriving mechanism may comprise a transmission between the source and the rotarymember. There may be a gear box, at least one gear, a belt or chain or anyworking combination of these components to connect the power source to therotary member. However, as discussed below, the transmission preferablycomprises a worm drive. v ln a preferred embodiment a braking means is provided to prevent the rotarymember rotating when the driving mechanism is not driving the rotary member.This prevents the length of the extensible member changing due to a weight orother force applied to it between height changing operations. The means could bea brake or clip provided on a leg of the device. However it is preferable for the braking system to be provided by the actuator itself as this can give a simpler and _6v_ more compact device which is easier to manufacture. The braking means in theactuator may comprise a ratchet mechanism. However, more preferably a wormdrive is used to transmit motion from the driving mechanism to the rotary memberand to provide a braking means.

As is well known, with a worm drive a braking effect is achieved because aworm drive with a small enough pitch cannot be back-driven i.e. the worm can drivethe worm gear but, because of the gear ratio, the worm gear cannot drive the worm.As a result when the worm is not driven the worm gear cannot rotate and thus theextension of the elongate flexible member cannot change. This ensures that theheight of the device is maintained between height adjustment operations. ln the case of an actuator that is for use with a table or similar object,preferably the actuator should have a braking mechanism which is sufficient toprevent movement when the actuator is not being driven when a force of 1500 N isapplied to the distal end of the elongate flexible member. More preferably, thebraking mechanism should be able to withstand 2000 N. ln the case of a wormdrive, a worm gear with a pitch of 6 to 8 mm is sufficient to withstand 1500 to 2000N. ln a more preferred embodiment the braking means is a worm drive with a wormgear with a pitch of no more than 4 mm.

When the driving means comprises a worm drive it is preferable for therotary member itself to comprise a worm gear. This again reduces the number ofparts and makes the actuator simpler. Alternatively the rotary member could beattached to or engaged with the worm gear. ln a preferred embodiment a gear is provided on the end of the worm andpreferably the gear is engaged with a driven gear. This arrangement provides acheap and easy to manufacture drive train.

Where an electric motor is employed, it is preferable that the driven gear ismounted on the output shaft of the electric motor and drives the gear on the wormby means of a belt. However, the gear may be driven directly or by means of anintermediate gear, or a secondary worm gear arrangement may be employed. ln a preferred embodiment the actuator further comprises an end limitdevice, -wherein the end limit device prevents the rotary member rotating about itsaxis more than a predetermined maximum amount in either direction. This isdesirable as it can prevent the actuator or a member adjusted by it from beingdamaged by over-extension or over-retraction of the elongate flexible member. lf the elongate member is over-extended the extensible member may be extended to _7_ a degree which causes damage to it or related components, for example by over-extending the legs of a table. Also, the elongate flexible member may become fullyunwound from the rotary member.

Thus, preferably there is provided a device which prevents an over-extension or over-retraction of the elongate flexible member. Preferably such an"end limit" device allows the rotary member to rotate more than 360° but without riskof damaging the actuator or the device being raised or lowered.

This may be achieved by any mechanism which stops the rotary memberturning past a predetermined maximum rotation in either direction. For example,the end limit device may be a static protrusion in engagement with the rotarymember which stops the rotary member rotating past a certain point in eitherdirection. lf the actuator is driven by an electric motor it is preferable to provide an endlimit device which cuts the power to the motor/once the rotary member reaches thepredetermined maximum rotation in the direction it is being turned. This alsoprevents the motor from being overloaded.

Preferably the end limit device comprises an upper and a lower (or a firstand a second) switch which when activated each stop the electric motor operatingin a respective direction. With such an arrangement the upper switch can stop themotor operating to turn the rotary member in a first direction and the lower switchcan stop the motor operating to turn the rotary member in a second direction.When the rotary member reaches a maximum rotation in the first direction theupper switch is activated and when the rotary member reaches a maximum rotationin the second direction the lower switch is activated.

Preferably the end limit device is arranged such that when the rotarymember is being driven in one direction to a predetermined position, the switchwhich prevents the motor driving the rotary member any further in that direction isactivated and when the rotary member is being driven in the opposite direction toanother predetermined position the other switch is activated which prevents themotor driving the rotary member any further in that direction. Once thepredetermined maximum rotation is reached the current to the motor is controlled toprevent any more rotation in that direction, but the motor can still operate in theother direction to cause rotation in the other direction. ln a preferred embodiment, the end limit device comprises an arm which follows a cam provided on the rotary member. Preferably the arm is provided on a _8_ pivot member which moves up and down as the arm moves up and down followingthe cam on the rotary member. Preferably when the rotary member is rotated apredetermined maximum amount in either direction the pivot member moves up ordown a maximum amount to activate the upper or lower switch. This provides asmall, simple and easy to manufacture device which prevents the rotary memberbeing driven more than a maximum amount in either direction.

Preferably, when the end limit device comprises an arm which follows a camon the rotary member, the end limit device comprises a spring which biases the armto follow the path of the cam. The spring may be made of, for example, plastics ormetal, with metal being preferred as it increases the working lifetime of the end limitdevice.

The rotary member is preferably generally toroidal and the end limit switch ispreferably located in the centre of the rotary member to minimise the size of theactuator.

The end limit switch of the preferred embodiment provides a simple, easy tomanufacture and compact means to prevent the actuator causing over-extension orover-retraction of the elongate flexible member.

The elongate flexible member of the actuator can be any member which canfollow a curved path whilst still transmitting a force along its length. lt is thereforedesirable for the elongate flexible member to be substantially incompressible. Forexample, the elongate flexible member may be a flexible hose, rod, etc with anycross section shape such as a circle, star, square or rectangle, but in a preferredembodiment the elongate flexible member comprises a spring. Preferably thethickness of the wire of the spring is equal to the pitch of the spring - i.e. it is aclosed-coil spring - which means that adjacent turns of the spring will be in contactand thus the spring will be substantially incompressible.

The invention has been described so far in terms of the elongate flexiblemember passing through a constraint means. This means may be any suitablestructure which prevents the elongate flexible member flexing or bowing out when aforce is applied at one end. For example, the constraint may be a guide, or conduitwith diameter slightly larger than the elongate flexible member or a cage throughwhich the elongate flexible extends. The constraint means ensures that a forceapplied at one end of the elongate flexible member will be transferred to the other end of the elongate flexible member. -9_ The actuator may comprise more than one rotary member with an elongateflexible member engaged with each rotary member. This means that a number ofelongate flexible members can be used to adjust the height of an object. Thus, forexample, each leg of a table may be adjusted simultaneously.

When the actuator comprises a plurality of rotary members it is preferablefor the rotary members to be driven by the same driving mechanism. Thisfacilitates the extension and retraction of the elongate flexible members by thesame amount at the same time. Additionally, the actuator comprises fewer parts.When the actuator comprises more than one rotary member being driven by thesame driving mechanism, the driving mechanism may comprise a single wormaround which the multiple rotary members are arranged.

As discussed above, one preferred application of the present invention is toprovide a height adjustable object where height is adjustable by means of theactuator. The height adjustable object can be any object which may need to beraised or lowered. For example it may be a table, chair, bed, hospital bed,treatment bed or any other item of furniture. The height of the object is preferablyadjusted by the action of the actuator on telescopic |eg(s).

Preferably, the height adjustable device is a table having between one andfour legs, although the table could have any number of legs. Also, each legpreferably has a corresponding elongate flexible member although more than oneelongate flexible member could be associated with each leg. ln a preferred embodiment, the legs .are substantially perpendicular to thesurface of the device being raised. Although, when the table comprises a pluralityof legs, the legs could be offset by a certain degree providing they still providesupport for the table and allow the surface of the table to be raised and lowered bythe actuator. The legs may all be offset from perpendicular by the same amount inthe same or opposite direction or the legs may be offset by different amounts. ln a preferred embodiment, the elongate flexible member extends from theactuator through an extendible leg of the object to a reaction surface in the leg suchthat when the elongate flexible member is extended, the elongate flexible memberis forced into the leg and the distal end of the elongate flexible member acts againstthe reaction surface which causes leg to extend and the object to rise. When theelongate flexible member is retracted it is pulled out of the leg which causes thesurface (e.g. table top) of the height adjustable device to lower. The object may lower due to its weight forcing the surface downwards as the elongate flexible _10- member is pulled out of the leg. Alternatively, the elongate flexible member may beattached to the reaction surface in the leg and as a result retracting the elongateflexible member would force the table top or other surface to lower by the action ofthe elongate flexible member pulling the reaction surface of the leg towards thesurface of the object. ln a preferred embodiment, the leg(s) comprise(s) at least two portionswhich can telescopically slide within each other. The number of such portions canbe more than two. When the number of telescopically slidable portions is two themaximum extension is just under double the height of one of the portions.

Viewed from a fourth aspect the present invention provides a method ofadjusting the height of an object, the object comprising a surface to be raised orlowered and an actuator comprising a driving mechanism, a rotary member and anelongate flexible member, the method comprising: rotating the rotary member aboutits axis by means of the driving mechanism, wherein rotating the rotary membercauses the elongate flexible member, which is connected to the rotary member, towind around or unwind from the rotary member, thereby retracting the distal end ofthe elongate flexible member as the elongate flexible member winds around therotary member causing the height of the surface of the device to be lowered andextending the distal end of the elongate flexible member as the elongate flexiblemember unwinds from the rotary member causing the height of the surface of thedevice to be raised.

Preferably the device comprises an end limit device and the method furthercomprises the end limit device preventing the rotary mechanism rotating about itsaxis more than a predetermined maximum amount in either direction. As describedabove this prevents the elongated flexible member being over-retracted or over-extended which may damage the actuator and/or the height adjustable device.

The method according to the fourth aspect of the invention may includeproviding and using all the features of the first and second aspect of the invention.

Certain embodiments of the present invention will now be described, by wayof example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view from above of a height adjustable tableaccording an embodiment of the invention; Figure 2 is a perspective view of the table of Figure 1 from below; Figure 3 is an enlarged cut-away perspective view of the connection between the table's surface and one of its legs; A-11-V Figure 4 is a perspective view of an actuator that forms part of the table ofFigure 1; Figure 5 is a perspective view of the actuator of Figure 4 with the casingremoved; Figure 6 is a perspective view of a section through of the actuator of Figure 4; Figure 7 is a perspective view of a toroidal rotor of the actuator; and Figure 8 is an enlarged view of an end limit switch associated with theactuator.

With reference to Figures 1 and 2, height-adjustable table 1 comprises awood laminate tabletop 2 supported on a steel frame 3. Mounted on the framebeneath the tabletop 2 is an actuator 20 that will be discussed in detail below. Theframe 3 has an H-shaped longitudinally extending support portion 4 attached byscrews to the underside of the table top 2 and two legs 5, 6. Leg 5 is connected to afirst end of the longitudinally extending portion 4 and leg 6 is connected to a secondend of the support portion 4. Each of the legs 5, 6 extends perpendicularly to theplane of the tabletop 2.

Each leg 5, 6 is connected to the longitudinally extending support portion 4of the frame 3 by means of connection portions 7 provided at opposite ends ofsupport portion 4. The legs are each formed from two separate hollow tubular parts- an upper leg portion 8 and a lower leg portion 9 - and a foot 10. The leg portions8, 9 are arranged to slide telescopically within and over each other respectively inorder to adjust the height of the table. The upper ends of the upper leg portions 8are attached to a respective conneoting portion 7. The bottom of each lower legportion 9 is mounted to the centre of foot 10 so that the foot extends laterally fromthe leg. ln Figures 1 and 2, one leg 6 is showniln a retracted position with the upperleg portion 8 received telescopically within the lower leg portion 9 so that the upperleg portion cannot be seen. The other leg 5 is shown in an extended position withonly a portion of the upper leg portion 8 within the lower leg portion 9. ln use, thelegs will always be extended by the same amount i.e. the height of the legs wouldbe equal; the legs are shown at different extensions in Figures 1 and 2 for thepurposes of illustration only.

Figure 3 shows in detail the attachment between one of the upper leg portions 8 and support portion 4 by means of a connection portion 7. The latter 130 _12- comprises a plastics moulding 11, which is received within a housing 12 formed inthe support portion. The moulding 11 has a ribbed cylindrical projecting portion 13which forms an interference fit within the top of the upper leg portion 8, therebysecuring the leg to the support portion 4.

A curved passageway is provided through the moulding 11 through whichpasses conduit 14. This extends from actuator 20 (from the right, as shown), alongthe inside of the support portion 4 and through the passageway into the leg.

As will be discussed further below, conduit 14 receives an elongate flexibleclosed-coil spring 24 (not shown in Figure 3) which extends from the lower legportion 9 to the actuator 20. The interior of conduit 14 has a low coefficient offriction to facilitate movement of the spring therethrough. The distal end of thespring engages with the lower leg portion such that extension of the spring withinthe conduit 14 will cause telescopic extension of the leg.

Figure 4 is an enlarged view of the actuator 20 showing its housing 19 towhich conduits 14 are connected. There can also be seen the part of the housingwhich contains an electric motor 21 and associated gears.

Figure 5 shows an enlarged view of the internal components of the actuator20. lt may be seen that electric motor 21 and its associated gears and toothed beltare arranged to drive a pair of symmetrically arranged toroidal rotors 23 by meansof a circumferential worm gear 27 formed at the lower part of each rotor. The drivetrain between the motor 21 and the worm gear 27 is provided by a driven gearwheel40 on the output shaft of the motor 21 which is engaged with a gean/vheel 41 on theworm 22 by means of a toothed belt 42. Gean/vheel 41 is formed integrally withworm 22.

The rotors further comprise an integrally formed drum 28 which engages thespring 24 passing around it. lt can be seen that the spring connected to the righttoroidal rotor is more wound in than the spring on the left-hand toroidal rotor. Thisis shown for lllustrative purposes only and in reality the springs will be woundaround the drums 28 by equal amounts. Activating the motor causes the drums 28to counter~rotate, thereby winding or unwinding the springs 24 around the drums28. This has the effect that the springs 24 both extend or retract simultaneously andat the same rate in response to the drive provided by the motor 21.

As may be seen from Figure 6, the housing 19 is shaped to locate the rotors23 and enable them to rotate freely as they are driven and to guide each spring from its conduit 14 around the respective drum 28. This is achieved by means of an _13- inverted L-shaped housing member 29 which is provided between the top of theworm gear 27 and the top of the drum 28 and which constrains the radial position ofthe spring 24.

The pitch of the worm gear 27 is low enough to cause the device to be self-braking by means of the worm drive, i.e. a force applied on the spring 24 cannotturn the motor 21 and so the springs 24 remain in the position to which they aredriven.

As discussed previously, each of the springs 24 is guided by conduit 14from the actuator 20 to a leg 5, 6. Conduit 14 prevents the springs 24 from bowingout or kinking Iaterally or horizontally as it is unwound from the actuator so thatforce may be transmitted from the actuator to the table legs.

Within the leg 5, 6 the spring 24 is constrained by the leg itself and itextends to the lower leg portion 9 where it acts against a reaction surface (notshown) so that extension of the spring 24 causes the lower leg portion 9 to bepushed away from the upper leg portion 8, thereby extending the leg 5, 6 andraising the table. Retraction of the spring 24 likewise allows the table 1 to lower.

As each of the springs 24 are extended and retracted by the same amountas the actuator 20 operates, the two legs 5, 6 rise and fall by the same amountthereby ensuring that the tabletop remains horizontal. lt will be appreciated that the height of the table 1 may therefore be simplyand conveniently controlled by switching the supply and polarity of current to theelectric motor 21 in order to drive the motor 21 forward or reverse as desired. (Theelectrical supply and switch are not illustrated.) ln order to prevent the actuator 20 over-extending or over-retracting thesprings 24, which could damage the actuator 20, the actuator 20 is provided with anend limit system, as shown in Figures 7 and 8.

Figure 7 shows a single toroidal rotor 23 in more detail. As described above,it comprises a drum 28 around which the proximal end of a spring 24 can be woundand a circumferential worm gear 27. Between the drum 28 and the worm gear 27 isa recess 30. Within the recess 30 is a spring connection member 31 to which theproximal end of the elongate spring 24 can attach to provide positive registrationbetween the rotor 23 and the spring 24. The inner surface of the drum 30 isprovided with a continuous spiral ridge 32 which forms a cam surface. lt extendstwo turns around the inner surface thus forming an upper ridge portion 33 which is radially further from the centre of the toroidal rotor 24 than a lower ridge portion 34. _14- Figure 8 shows a limit switch assembly 35 which is located inside, andengages with, the cam surface formed by the ridge 32 one of the toroidal rotors 23.lt is mounted to the housing 19 (not shown in Figure 8) and therefore is held in afixed location relative to the rotary motion of the toroidal rotor 23. (For the purposeof clarity the end limit switch is not shown in Figure 5.) The end limit switchassembly 35 comprises an end limit switch holder 36, a cam following arm 37 andpivoting switch activator 38. The end limit switch holder 36 holds a lowermicroswitch 39L and an upper microswitch 39U and a biasing spring 44. The upperswitch 39U is held in a position axially above the switch activator 38 and the lowerswitch 39L is held in a position axially below the switch activator 38. The spring 44biases the arm 37 radially outwardly and axially downwardly so that the arm 37follows the cam surface of ridge 32.

As the toroidal rotor 23 turns, the arm 37 follows the ridge as it spirals roundthe inside of the inner drum 28 which causes the arm 37 and switch activator 38 toaxially rise or descend depending on the direction of rotation of the toroidal rotor 23.

The lower ridge portion 34 is provided with a groove 51 in a locationdetermined to be aligned with the arm 37 when the toroidal rotor has reached itsmaximum travel one direction. The upper ridge portion 33 is provided with anumber of holes 52. ln one of the holes 52 is a pin (not shown). The location of thepin is determined to align with the arm 37 when the toroidal rotor 23 has rotated apredetermined maximum amount in the other direction. lt will be appreciated thatthis arrangement allows the degree of travel of the rotor 23, and hence the springs24 to be set to one of a number of alternatives, depending on where the pin isinserted.

When the table 1 is being lowered (i.e. the springs 24 are being woundaround the toroidal rotor 23) the arm 37 follows the ridge 32 which is spirallingdownwards, as a result the arm 37 and with it the switch activator 38 descends,which brings the switch activator towards to the lower microswitch 39L. When thearm 37 reaches groove 51, the switch activator 38 descends to a position at which itactivates the lower microswitch 39L. Activating the lower microswitch 39L preventsthe motor 21 turning any further in that direction. However, the motor 21 can still bedriven in the opposite direction. lf this is done, as the table 1 rises, once arm 37 isout of the groove 51, the switch activator 38 will have moved away from the switch39L thereby allowing the motor 21 to be driven again in the original direction, if desired. _15- lf the motor 21 continues to move in the direction to raise the table 1,eventually the arm 37 will reach the pin which is located in one of the holes 52. Atthis point the table 1 will have reached its maximum height and arm 37, followingridge 32 will have risen to bring switch activator 38 into contact with uppermicroswitch 39U, which it will activate. This prevents the motor 21 turning anyfurther in that direction and so the motor 21 can only be operated to cause the table1 to lower and thus move the arm 43 off the pin. lt will be appreciated that at the predetermined maximum rotation in eitherdirection, the groove or pin provides a step change in the profile of the ridge 32 tocause a step movement in the switch activator 38 to activate the microswitchsuddenly in order to prevent arcing of the switch Contacts. ln the embodiment shown in the Figures, the actuator has a built-in length(length of the housing containing the two rotary members) of 0.45 m and has astroke (distance between the maximum extension and minimum extension) of 0.8mfor each of the elongate flexible members (i.e. a stroke of 2 times 0.8 m).

The process of lowering and then raising the table 1 will now be described.lnitially the table 1 is in its fully raised position with only a comparatively small partof the upper leg 8 located within the lower leg 9, and thus the two springs 24 arewound out to a maximum amount from the drums 28 on toroidal rotors 23. Thismeans that a maximum length of each spring 24 is in each leg 5, 6. The spring 24is substantially incompressible and the actuator 20 is locked by means of the wormdrive. As a result each spring 24 holds the legs 5, 6 in their telescopically extendedconfiguration and hence holds the table 1 at its maximum height. ln thisconfiguration, the limit switch assembly 35 prevents the motor 21 from beingactuated to raise the table 1 further, as described above.

To lower the table 1, the motor 21 is activated to drive the output shaft in theappropriate direction. As previously described, this turns the toroidal rotors 23 andcauses each of the springs 24 to be wound inwards. This action causes each of thesprings 24 to be retracted out of the legs 5, 6 so that the upper leg portion 8telescopically slides further into the lower leg portion 9, thereby lowering the heightof the table 1. This continues either until the user determines that the table 1 is atthe desired lower position or when the motor 21 is de-activated in the mannerdescribed above by the limit switch assembly 35. When the table 1 is in itsminimum height configuration, the majority of each of the upper leg portions 8 is within the corresponding lower leg portion 9. _15_ ln order to raise the height of the table 1, the motor 21 is activated in theopposite direction. This causes each of the springs 24 to be wound out from theinner drum 28 of each toroidal rotor 23 which forces the springs 24 to extend in theleg 5, 6 by an equal amount on each side. This action creates a force against thereaction surface in the lower leg portion 9 which causes the table to rise. Thetabletop 2 rises until the desired height is reached or the limit switch assembly 35 prevents the maximum height from being exceeded.

Claims (29)

:

1. An actuator for adjusting the length of an extensible member, the actuatorcomprising: a driving mechanism; a rotary member arranged to be driven about itsaxis by the driving mechanism selectively in a first direction and a second direction;and an eiongate flexible member supported by a constraint means for transmittingforce from the actuator to the extensible member in order to adjust the lengththereof; the eiongate flexible member passing around and being engaged with therotary member such that rotation of the rotary member in the first direction causesthe eiongate flexible member to be extended and rotation in the second direction causes the eiongate flexible member to be retracted.

2. An actuator as claimed in claim 1, wherein the eiongate flexible member isarranged to act directly on the extensible member to provide the force to cause it to extend and retract.

3. An actuator as claimed in claim 1 or claim 2, the actuator being configured to adjust the height of an object supported by the extensible member.

4. An actuator as claimed in any preceding claim, wherein when the rotarymember rotates in a first direction about its axis the eiongate flexible member Windsaround the rotary member and when the rotary member turns in a second directionabout its axis the eiongate flexible member unwinds from the rotary member,whereby as the eiongate flexible member Winds around the rotary member thedistal end of the eiongate flexible member is retracted to cause the length of theextensible member to be reduced and as the eiongate flexible member unwindsfrom the rotary member the distal end of the eiongate flexible member is extended to cause the length of the extensible member to be increased.

5. An actuator as claimed in any preceding claim, wherein the actuatorcomprises a braking means to prevent the rotary member rotating when the driving mechanism is not driving the rotary member.

6. An actuator as claimed in claim 5, wherein the driving means and the braking means comprise a worm gear in meshing relationship with a worm. _18-

7. An actuator as claimed in claim 6, wherein the rotary member comprises theworm gear.

8. An actuator as claimed in claim 6 or 7, wherein a gear is provided on the end of the worm and wherein the gear is engaged with a driven gear by means of atoothed belt.

9. An actuator as claimed in any preceding claim, wherein the driven gear is driven by an electric motor.

10. An actuator as claimed in claim 9, wherein the driven gear is mounted on the output shaft of the electric motor.

11. An actuator as claimed in any preceding claim, wherein the actuatorcomprises an end limit device, wherein the end limit device prevents the rotarymember rotating about its axis more than a predetermined maximum amount in either direction.

12. An actuator as claimed in claim 11 when dependent on claim 9 or 10,wherein the end limit device comprises a first and a second switch each of which when activated stop the electric motor operating in a respective direction.

13. An actuator as claimed in claim 11 or 12, wherein the end limit switch comprises an arm which follows a cam provided on the rotary member.

14. An actuator as claimed in claim 13 wherein the arm is provided on a pivotmember which moves up and down as the arm moves up and down following thecam on the rotary member, wherein when the rotary member is rotated apredetermined maximum amount in either direction the pivot member moves up or down a maximum amount to activate the upper or lower switch.

15. An actuator as claimed in any preceding claim, wherein the flexible member comprises a spring. _19-

16. An actuator as claimed in claim 15, wherein the spring has a pitch equal to wire thickness.

17. An actuator as claimed in any preceding claim, comprising a plurality ofrotary members and an elongate flexible member connected to each rotary member.

18. An actuator as claimed in claim 17, wherein the plurality of rotary members are driven by the same driving mechanism.

19. A height adjustable object comprising an extensible member and a surfacearranged to be raised and lowered by adjustment of that member and furthercomprising the actuator of any preceding claim, the actuator being arranged to adjust the height of the object.

20. A height adjustable object as claimed in any preceding claim, wherein theactuator is arranged to adjust the height of an object having at least one leg and theelongate flexible member extends from the actuator through a leg of the object to a reaction surface in the leg.

21. A height adjustable object as claimed in claim 20, wherein the leg comprises at least two portions which can telescopically slide within each other.

22. A height adjustable object as claimed in claim 19, 20 or 21, wherein the height adjustable object is a table.

23. A method of adjusting the height of an object comprising the use of an actuator according to any preceding claim.

24. A method of adjusting the height of a object, the object comprising a surfaceto be raised or lowered and an actuator comprising a driving mechanism, a rotarymember and an elongate flexible member, the method comprising rotating the rotary member about its axis by means of the driving mechanism,wherein rotating the rotary member causes the elongate flexible member, which is connected to the rotary member to wind around or unwind from the rotary member, _20- thereby retracting the distal end of the elongate flexible member as the elongateflexible member Winds around the rotary member causing the height of the surfaceof the object to be lowered and extending the distal end of the elongate flexiblemember as the elongate flexible member unwinds from the rotary member causing the height of the surface of the object to be raised.

25. A method as claimed in claim 23 or 24, wherein the aotuator comprises anend limit device, the method further comprising the aotuator preventing the rotatingmechanism rotating about its axis any more than a predetermined maximum amount in either direction.

26. A method of adjusting the length of an extensible member comprising:providing an aotuator comprising a driving mechanism, a rotary member arrangedto be driven about its axis by the driving mechanism selectively in a first directionand a second direction, and an elongate flexible member supported by a constraintmeans for transmitting force from the aotuator to the extensible member in order toadjust the length thereof, the elongate flexible member passing around and beingengaged with the rotary member at its proximai end and being engaged with theextensible member at its distal end and driving the rotary member of the aotuator inorder to extend and/or retract the elongate flexible member to thereby adjust the length of the extensible member.

27. An aotuator for adjusting the length of an extensible member substantially as hereinbefore described with reference to any of Figures 1 to 8.

28. A height adjustable table substantially as hereinbefore described with reference to any of Figures 1 to 8.

29. A method of adjusting the height of an object substantially as hereinbefore described with reference to any of Figures 1 to 8.