GB2345440A

GB2345440A - Load support with adjustable pressure support surface.

Info

Publication number: GB2345440A
Application number: GB9927461A
Authority: GB
Inventors: Phillip Raymond Michael Denne
Original assignee: Advanced Motion Technologies LLC
Current assignee: Advanced Motion Technologies LLC
Priority date: 1998-11-21
Filing date: 1999-11-22
Publication date: 2000-07-12
Also published as: GB9825514D0; GB9927461D0

Abstract

Load support apparatus, typically embodied as a seat for bearing the weight of a user, having an enclosure defined at least in part by a flexible membrane 3 as the surface of the seat. Means 21 are provided for pressuring the enclosure from a source of compressed fluid, and for varying the pressure within the enclosure by means of a piston 1, diaphragm or bellows arrangement in communication with the enclosure. The side of the piston, diaphragm or bellows remote from the enclosure is also pressurised 20. Control means act to vary the pressure on either side of the piston, diaphragm or bellows in concordance with the movements applied to it by a electromagnetic actuator 12 whereby to create pressure differentials which assist in the movement of the actuator and which, when the actuator is stationary, counter-balance the load such that no actuator force is required to hold the load in the stationary position. The change in pressure can be used to simulate forces acting on the load.

Description

APPARATS FOR SUPPORTING A LOAD This invention is generally directed to apparatus for supporting a load and in particular to apparatus comprising an enclosure having a flexible membrane defining at least part of a boundary surface. Typically the upper surface of such an enclosure is formed by a pad whereby the load is supported on the membrane by control of the fluid pressure within the enclosure and pad. The invention is principally but not exclusively concerned with apparatus in which the human body is in contact with the flexible membrane of the enclosure.

It is known to use the adjustment of fluid pressure in a plurality of pads in order to create a subjective sensation of motion in a flight simulator. We refer, in particular, to the patents of Kron, for example, GB 1 405 333, GB 1 531 995, GB 1 561 351, US 4 059 909 and to our co-pending international patent application PCT/GB93/ 01788. In these inventions the human body is supported by air pressure in a series of pads in such a way that variation in the pad air pressure will alter the degree of contact of the body with a slab of special material within the volume of the pad.

The air pressures used in the pads are generally in the order of 0.1 bar, which makes the air support soft. The special material within the pad has a strong gradient of hardness with compression, so that by changing the air pressure in the pads the degree to which the body is brought into contact with the material may be altered and thus the apparent hardness of the supporting surface can be controlled.

(By the"hardness"of a material we mean the rate at which the opposing force increases as a body intrudes into its surface).

It is known that the brain interprets the hardness of a surface with which the skin is in contact as a measure of the force which is being applied or is about to be applied to the skin by that surface. Further, a human being quickly learns that force produces acceleration and that body motion can therefore be understood from the integration of such signals. It is therefore possible to produce false sensations of motion by contriving to apply an appropriate pattern of hardness variations, synchronised with visual and audible sensations. The illusion is the basis of the flight simulator"g seat".

The surface of the human skin is the largest organ of the body and it has the oldest and most basic connections to the brain. Signals reaching the brain from the skinsurface are not subject to rational processing prior to response and they cause immediate, subconscious and uncontrollable reactions that are fundamental to balance and survival. It follows that, by the control of skin sensations in a special seat, bed or couch it is possible to cause various, strongly influencing effects on the human psyche. These effects are the basis of a variety of other potential applications of the"g seat"technology.

A human being makes a continuous series of involuntary, subconscious body movements that may, with skilled interpretation, be used to. understand the mental state and emotional reactions of that person to the prevailing circumstances.

Having a method of controlling by electronic means the pressure in a plurality of pads that may form part of a seat or couch, it is possible to collect accurate information on the involuntary movements of a human being and to learn to interpret those movements appropriately, whether for psycho-medical purposes or otherwise.

A person makes many instinctive body movements when striving to control a vehicle, whether that vehicle is real or is a part of a computer game. A seat or couch having a series of monitored pads under pressure, allows instinctive movements to be detected and to be processed so as to have an effect on the progress of a computer game. It is considered that intuitive and subconscious interactions of this kind enhance the attraction of a computer game.

Forces applied to the chair or couch by which a person is supported may be transmitted to that person by pressure variations in pads (or cushions). It therefore follows that, by maintaining the pressure in the pads at a constant value by artificial means, the person may, within reasonable limits, be isolated from any perturbing forces applied to the chair or couch (by, e. g., vehicle motion). A controlled support of this kind might be used as the basis of a luxury seat or as part of a system for transporting injured persons or extremely-delicate objects.

The basic principles of an actively-controlled positioning and isolating system may also be applied to machine tools of extreme precision, such as those used to manufacture semiconductor devices. The technology is also applicable to precision optical components of several types.

The present invention therefore seeks to contrive means for the rapid and precise modulation of fluid pressure within an enclosure having a flexible membrane defining at least part of a boundary surface so as to control the attitude and position of a body supported thereby. The present invention further seeks to contrive a precise and sensitive means of controlling this fluid pressure so as to create skin sensations of various kinds. The present invention also seeks to contrive means by which the movements of a person supported by or pressed against the flexible membrane may be measured, so as to observe involuntary responses to stimuli or to effect instinctive control by body motion in place of, or in addition to, deliberate manual control. Another aim of the present invention is to contrive means by which the pressure in such an enclosure may be maintained constant when it would otherwise be caused to vary by limited external disturbances such as real motion of the supporting chair, couch or machine structure.

There are three ways in which the pressure within such an enclosure or pad may be varied ; firstly by changing the mass of fluid which it contains; secondly by varying the volume of the enclosure or pad, and thirdly by altering the temperature of the fluid which it contains. The method of varying pressure by temperature changes is, however, discounted for the purposes of the present invention since the amplitude of the variations we require and the rates of change of pressure that would be necessary cannot be practically achieved.

In previous devices relating to the pressure control of seat pads, especially those of Kron to which we have previously referred, the pressure is changed by variation of the mass of air within the pad. Kron teaches the use of a first external source of pressurised air at a higher pressure, a second external reservoir at a lower pressure (the atmospheric surroundings may be treated as such a reservoir) and the use of control valves positioned between each pad and the reservoirs of air at different pressures.

Our co-pending International patent Application PCT/GB93/01788 teaches the use of a piston or diaphragm operated by electromagnetic means to move air back and forth between the pad and an associated reservoir.

It will be understood that the weight of a person resting on the flexible membrane of such an enclosure or on a pad, or the natural body shape of a person constrained to fit tightly against a plurality of pads, will exert a force whose natural effect is to oppose the pressure in the pad (s), expelling as much air as possible. Whilst this is not a problem for Kron, whose apparatus allows a valve to be closed by a spring to prevent this deflating action without the continuous consumption of energy, it is a problem to those who prefer to use direct electromagnetic forces to control the pressure within the pad (s). If no remedial measures are applied, power is consumed by the electromagnetic actuators so as to maintain a force that supports the weight or constrains the position of the person.

Our co-pending application therefore discloses a means generally illustrated in Figure 1, by which a counterbalancing fluid pressure is applied to the side of the piston or diaphragm 1 from an external reservoir 2, this pressure corresponding to the equilibrium pressure within the enclosure having the flexible membrane or the pad 3 and causing the flexible membrane to act as part of a soft spring system in the absence of electromagnetic force.

This method, however, does not fully consider the requirement for some pads to operate at a mean pressure that is greater than the pressure needed in other pads.

E. g. if the person is in a sitting position the pads beneath the ischial tuberosities will carry the major part of the body weight and must therefore be inflated to a greater pressure. Co-pending international patent application PCT/GB93/01788 teaches that the reservoir pressure is common to all the pads but also says that the reservoir pressure applied to the side of the piston or diaphragm opposite to the pad is adjusted so as to return the piston or diaphragm to the median position. It will therefore be clear that, whether or not the reservoir is common to all pads, the result is that those pads carrying a heavier load are more collapsed than others.

Because the collapse of the pad transfers more weight on the flexible membrane to the harder underlying surface 6, the heavier areas of the body perceive a disproportionately-harder support before any pressure variation is applied. The method also has the disadvantage that the provision of an external reservoir results in a"soft"support that makes severe power demands on the electromagnetic actuators to stabilise the system.

The present invention provides apparatus for supporting a load, said apparatus comprising an enclosure having a flexible membrane defining at least part of its boundary surface and volume-varying means for varying the pressure within the enclosure whereby to exert a variable pressure on a load supported on the said flexible membrane, in which the volume varying means includes a movable member the displacement of which is controlled by forces generated electromagnetically and in which the movable member forms an inner boundary surface of the enclosure.

In the present invention a load is supported by at least one pressurisable pad comprising a sealed flexible membrane, the force on said membrane being modulated by the variation in pressure of fluid within the pad, the pressure variation being produced by a change in summated volume of the pad and an associated modulating apparatus, the modulating apparatus including a piston, diaphragm, bellows or expandable element, the piston, diaphragm, bellows or expandable element being moved by electromagnetic means, the quiescent or equilibrium pressure of fluid within the pad being adjustable by first separate means, the reaction of the quiescent or equilibrium pressure against the modulating apparatus being counterbalanced by second separate means.

In one embodiment of the present invention the movable member is a piston or a diaphragm or a bellows.

In another embodiment of the present invention the movable member forms an outer boundary surface of a variable-volume device wholly enclosed within the enclosure, the variable-volume device acting to vary the pressure within the enclosure by occupying a varying proportion thereof.

In some embodiments the flexible membrane defining at least part of the boundary surface of the enclosure is spaced from a substantially rigid surface into contact with which the flexible membrane may be brought by adjusting the pressure within the enclosure in dependence on the applied load.

In a preferred embodiment of the present invention the apparatus is adapted as a seat for a user in which the degree of contact with the said substantially rigid surface influences the perceived hardness of the seat to the user.

One aspect of the present invention provides apparatus for supporting a load, said apparatus comprising a first enclosure defined at least in part by a flexible membrane by which the load is supported, a second enclosure separated from the first enclosure by a movable partition, partition displacement means and first and second pressure adjustment means each associated with a respective enclosure and each being operable to vary the pressure of a fluid in the respective enclosure in concordance with the forces exerted on the partition by the partition displacement means in use of the apparatus.

Preferably the first and second pressure adjustment means comprise means for varying the mass of the fluid within each of the first and second enclosures. In one embodiment the partition is a piston, or a diaphragm or a bellows or a telescoping tube arrangement.

In another embodiment the first enclosure means has a substantially rigid surface arranged beneath the flexible membrane. Preferably the rigid surface has a gradient of hardness under compression.

In yet another embodiment the first pressure adjustment means is responsive to first control means whereby to establish a pressure within the first enclosure in dependence on the load on the flexible membrane.

Alternatively the volume of the enclosure or pad between the flexible membrane and the substantially rigid surface may be filled with a graded, compliant, porous material and the pressure adjusted to a chosen preset value representative of a standard load or of an average person.

It will of course be appreciated that the lower surface is not an essential feature of the present invention.

Preferably the apparatus further comprises sensing means for sensing the extent to which the flexible membrane is depressed by the load whereby to provide a signal to the first control means in dependence thereon. The sensing means may comprise contact pressure sensors.

The substantially rigid lower surface may be so arranged that the variation of pressure within the enclosure or pad transfers a differing fraction of the load onto that surface so as to produce a controlled, subjective impression of hardness.

Preferably the electromagnetic actuator is provided with a position-sensing means and the motion of the actuator is controlled so as to vary the pressure in the pad.

In still another embodiment of the present invention the second pressure adjustment means is operative in response to second control means to vary the mass of the fluid and hence the pressure in the second enclosure whereby to urge the partition to a selected position in the absence of forces exerted thereon by the partition displacement means.

In yet another embodiment the partition displacement means is an electromagnetic actuator. In this embodiment the apparatus may further comprise third control means for controlling the extent of displacement of the partition from the selected position.

In another embodiment sensing means may also be provided for sensing the extent of displacement of the partition from the selected position. In this embodiment the apparatus may further comprise monitoring means for monitoring the electrical current used by the third control means.

The monitoring means may act on the first and second control means in such a way that the current consumed in the displacement of the partition is reduced.

Preferably the selected position of the partition is a pre-selected starting position whereby the monitoring means acts on the said first and second pressure adjustment means so that the time integral of the current consumed in the displacement of the partition tends to a value of zero.

Preferably in the aforementioned embodiments including monitoring means acting on the first and second pressure adjustment means a signal is supplied from the monitoring means in advance of the electromagnetic actuation of the partition whereby to compensate for differential response times.

The effect of reducing the current used by the electromagnetic actuation means may also be achieved by alternatively providing a small passage connecting the volume enclosed by the enclosure or pad volume and the volume enclosed by the partition, so as to equalise the pressures over a period of time that is long in comparison with the period of the required pressure variations.

In one embodiment of the present invention the first enclosure means comprises a plurality of chambers and the first pressure adjustment means is operative to vary the pressure within the chambers independently of one another.

In another aspect of the present invention the apparatus of any of the aforementioned embodiments may be adapted so that at least the first enclosure or enclosures form part of a seat intended to support an animal or human being. In still another aspect of the invention the apparatus may be used to exert a variable force on the body or part of the body of an animal or human being. The apparatus may also be used to measure or otherwise monitor movement, including involuntary movement, of an animal or human being.

One use of the apparatus may be to simulate or accentuate the sensation of motion of an animal or human being. Another use may be to relieve or remove the sensation of motion to an animal or human being.

A further aspect of the invention provides for a method of isolating a load from external pertubations, said method comprising the steps of i) placing the load on a flexible membrane forming an outer surface of at least part of an enclosure of variable volume ii) varying the mass, and hence the pressure of a fluid within the enclosure in dependence on the magnitude of the load, and iii) varying the volume of the enclosure, and hence the pressure of the fluid in the enclosure in dependence on detected pertubations, whereby to vary the forces applied to the load by the membrane so as at least to reduce the forces acting on the load as a result of the said pertubations.

Still another aspect of the invention provides a method of applying varying forces to a load, said method comprising the steps of i) placing the load on a flexible membrane forming part of an outer surface of at least part of an enclosure of variable volume, ii) varying the mass of the fluid within the enclosure, whereby to vary the volume of the enclosure and iii) subsequently varying the volume of the enclosure and hence the pressure therein so as to generate pertubating forces on the membrane and hence on the load.

Various embodiments of the apparatus of the present invention will now be described by way of non-limiting example with reference to the figures 2 to 4 of the following drawings in which Fig. 1 is a cross-sectional view through the device of our co-pending International Patent Application PCT/GB93/01788 ; Fig. 2 is a roughly cross-sectional view through a first embodiment of the present invention Fig. 3 is a roughly cross-sectional view through a second embodiment of the present invention; and Fig. 4 is a roughly cross-sectional view through a third embodiment of the present invention.

Referring now to Figure 2 a cylindrical enclosure generally designated 23 is divided into a first enclosure 24 and a second enclosure 25 by a piston 1. The first enclosure 24 has an outer boundary surface comprising a flexible membrane 26 formed by a circular pad 3. A part of the lower surface of the pad 3 rests in contact with an annular block 6 of material providing a rigid surface 27. A cylindrical channel 28 is provided in the annular block 6 so as to provide fluid communication means between the pad 3 and the rest of the enclosure. It will also be understood that means are also provided in the lower surface of the pad 3 so as to provide fluid communication means between the flexible membrane 26 and the piston 1. Rigid surface 27 is provided with contact pressure sensors 7 so as to provide sensing means for determining when a load placed on the pad causes the flexible membrane to contact the rigid surface.

The piston 1 comprises a generally cylindrical hollow tube 29 formed around a cylindrical member 30 that is upstanding from the floor of the enclosure 23. The outer surface of the cylindrical tube has an outer annular element 31 contacting the inner surface of the enclosure 23 and forming the partition within the enclosure.

The inner surface of the hollow tube 28 is provided with electromagnetic actuators 12 for actuating movement of the piston in response to a control means 13. It will be understood that, for the purposes of saving on space, the hollow tube is arranged so as to be able to enter the channel 28 defined in the annular block 6 but that it does not occupy the whole channel 28 so as to allow fluid communication means between the upper surface of the annular element 31 forming the partition and the pad 3.

The cylindrical member 30, which is provided with a plurality of magnets for determining the position of the piston upon electromagnetic actuation, has ports 20 and 21 for introducing fluid into the enclosure 23. Port 21 is connected to a valve 4 that constitutes first pressure adjustment means for intr. oducing fluid from a reservoir 5 into enclosure 23 above the piston 1, that is, into the first enclosure 24. The valve 4 is operatively connected to a control means 9. Port 22 is connected to a valve 11 that constitutes second pressure adjustment means for introducing fluid from the reservoir 5 into the enclosure 23 below the piston 1, that is, into the second enclosure. Valve 11 is operatively connected to control means 10.

Control means 9 and 10 also act on respective valves 11 and 4 so that either may be used so that the piston 1 is be brought to an equilibrium position whereby the pressures in each enclosure 24,25 are equilibrated before commencement of the operation of the apparatus.

In operation, when a load is applied to the pad 3, a signal is received by control means 9 from sensing means 7 so as to cause the control means 9 to operate valve 4 to introduce fluid from the reservoir 5 into the first enclosure 24. The signal means 7 operate to indicate to the control means 9 when the load is in light contact with the rigid surface 27 so that the introduction of fluid may be discontinued.

Of course during this sequence the electromagnetic actuation means is operable via control means 13 to hold the piston in its starting position. Since however, power is thereby consumed control means 10 is arranged to operate valve 11 in response to a signal from control means 13 whereby to provide a counterbalancing pressure by introducing fluid into the second enclosure 25. The increased pressure in the second enclosure 25 thereby serves to reduce the power consumed by the electromagnetic actuation means in maintaining the position of the piston. The second control means 10 is arranged to act on the valve 11 in response to the time integral of the current from the control means 13 used for maintaining electromagnetic actuation so as to transfer fluid into or out of the second enclosure means. Ideally the time integral is maintained as close to zero as possible.

It will be understood that the apparatus can be used to apply a varying pressure to a load or a person whereby control means 13 acts on the electromagnetic actuators 12 to cause piston 1 to move from its starting or selected position to a new position. In this way the volume of the enclosure 24 is varied with a consequential change in the pressure of the fluid therein. A person can therefore experience a variation in the degree of hardness of the pad and thus perceive a force.

In this embodiment control means 13 also acts to signal to second control means 10 to act on valve 11 to transfer fluid into or out of the first and second enclosures whereby to counterbalance the forces acting on the piston in its new position. By sending the signal to the second control means 10 advance of the electromagnetic actuation of the piston the opposition to movement of the piston by concentration effects is reduced.

It will also be understood that the apparatus can be used to sense the movement of the load. The movement of a load or person leads to a change in the force applied to the pad and thus to a consequential change in the pressure within the first enclosure, so that this movement will be detectable by a change in the current in control means 13 in order to resist displacement of the piston 1. This change in current can be monitored by monitoring means (not shown) and therefore provides a measure of the movement of the load. When the load is formed by a person such an arrangement can be used for monitoring and interpreting the movements, including the involuntary movements, of a that person.

The apparatus can alternatively be used to compensate for the forces experienced by a person or load when the apparatus is moving whilst the load or person remains still on or in the apparatus. Forces due to such motion can also lead to pressure variations within the first enclosure means. The apparatus of Fig. 2 can be used to counteract such forces so that the person or load is thereby decoupled from them and experiences of a sensation of"floating". In this situation the control system 13 is arranged so that the electromagnetic actuators do not constrain the piston to a selected position but allow movement of the piston in such a way as to suppress the pressure changes within the first enclosure.

Referring now to Fig. 3, a second embodiment of the present invention comprises a cylindrical enclosure 23 which is divided into a first enclosure 24 and a second enclosure 25 by a bellows unit 15 forming part of a piston 1. The piston 1 comprises an annular plate with a centrally located orthogonal shaft which is slideably engaged with a cylindrical channel formed in cylindrical electromagnetic actuation means. Ports 21 and 20 provide for the first and second pressure adjustment means described above (not shown).

Referring now to Figure 4, a similar embodiment shows a different arrangement of the bellows within the enclosure 23.

Apparatus according to the present invention can be used for a variety of purposes. In particular, the apparatus can be used for removing or accentuating, or for relieving or removing the sensation of motion to an animal or human being. Such use can be directed to entertainment or training purposes. The apparatus may additionally be used for pleasurable purposes including erotic purposes.

The apparatus of the present invention can further be used for therapeutic purposes such as in stimulating reactions in persons of an autistic or otherwise mentally abnormal state so as to promote healing. Use of the apparatus to monitor the involuntary reactions of a person subjected to various stimuli may be useful for providing data evaluating the mental condition of that person. This data may have some use psycho-medical research.

Referring to Fig. 2 pressure in the pad 3 is varied by movements of the electromagnetic element 12 attached to a piston 1 and the first separate means 9 for adjusting the mass of fluid therein includes an external source of fluid at a higher pressure 5, an access to a low-pressure region (not shown) and a three-position valve 4, so as to establish the appropriate mean or equilibrium pressure. In order to provide an indication of that equilibrium condition, the variable-hardness supporting surface 6 within the pad is provided with a pressure-sensitive device 7. The signals from this device indicate the condition that obtains when the inner surface of the flexible pad is in light contact with the variable-hardness surface.

(The system is then most sensitive to changes in fluid pressure within the pad.) The control means 9 is arranged to modulate the valve 4 so as to achieve the correct equilibrium pressure at the start of the operating sequence. So as to compensate for air leaks, temperature changes and large changes in posture by the seat occupant, the control means 9 may also be arranged to carry out adjustments to the equilibrium pressure at appropriate intervals during the operating sequence.

When the seat or couch is occupied the equilibrium pressure within the pad is greater than atmospheric pressure, so a force is exerted on the electromagnetic pressure-modulating element 1, of whatever form that may consist. That force must be balanced by a counter-pressure applied to the other side of the modulating element. The second separate control means 10 is therefore arranged to modulate the position of a valve 11, in response to the time integral of the current from control means 13 driving the electromagnetic device 12, so as to transfer fluid mass into or out of the appropriate part of the pressure-modulating apparatus so as to maintain the time integral close to zero. It should be noted that this second separate control means compensates for all potential perturbations of the system and reduces the electrical power consumption to a minimum.

In some circumstances it may be appropriate for the first separate pressurising means described above to be simplified by contriving instead that the volume beneath the pad membrane and the underlying surface is filled with a graded, porous, compliant material and that all the pads are pressurised to a value (in the order of 0.1 bar) appropriate to an average person. The unequal distribution of load amongst the pads may then be accommodated to an acceptable approximation by special choice of the pad dimensions and of the filling material for pads in different positions.

In similar circumstances it may also be possible to simplify the second separate pressurising means of valve 11 and control means 10 by arranging instead for a slow, controlled leak of pressurising fluid between ports 20 and 21.

It will be understood that, over a time that is short in relation to the integration time of the second separate pressurising means, the pressure in the pad 3 is directly related to the displacement of the electromagnetic actuator as indicated by the position transducer. Conversely, a movement of a person supported on the pad causes a change in pressure that results in a tendency to move the piston, diaphragm or bellows. That tendency is resisted by the actuator control means 13, which changes the current in the actuator so as to correct any deviation from its commanded position. The change in current is therefore a measure of personal movement, which we wish to monitor as a second objective of our invention.

It will also be understood that pressure changes similar to those described above might be caused by the motion of the chair (or other pad system) whilst the person or load remained still. Such perturbations might result from vehicle motion, for example. When it is a requirement that the person shall be decoupled from such perturbing motions the control system is arranged to allow the electromagnetic actuators to move freely-or by servo action to compensate for frictional effects- in such a way that the pressure transient is suppressed. The result of maintaining the pressure in the pads constant is to produce a sensation of"floating"for the person supported by the pad system, which was a third objective of our invention.

Figure 3 shows another form of the invention in which the modulating element is a bellows unit 15 in a sealed protective container 14, which may also house the electromagnetic actuator 12. The pad volume 3 is pressurised to the correct equilibrium value via port 21, as previously explained, whilst the pressure in the sealed protective enclosure 14 is occasionally modified via port 20 by the valve 11 so as to minimise the system power consumption. (In the alternative, a slow leak may be arranged to exist between the volumes served by ports 20 and 21).

One of the advantages of the bellows construction is that there are no sliding seals.

Nevertheless, it will be understood that an expandable element bounded by bellows is shown by way of example only and the bellows surface might be replaced by two nested tubes having a sliding seal if that option is preferred for other reasons.

Either type of structure might be assembled from low-cost plastic mouldings.

Figure 4 shows an example of a form of the invention in which the volume within the pad is directly connected to the sealed rigid container 14, which also houses an electromagnetic actuator 12. Movements of the actuator cause the volume of an expandable element 16, of which the actuator forms a part, to increase and decrease in value. An increase in the volume of the expandable element causes a corresponding decrease in the volume that is common to the pad, thereby causing an increase in the pressure beneath the membrane of the pad-and vice versa. Ports 21 and 20 serve to control the mass of fluid within the pad volume and to balance the long-term mean of the pressure across the surface 1, as previously described. Again, it will be understood that an expandable element bounded by bellows is shown by way of example only and that the bellows surface might be replaced by two nested tubes having a sliding seal between them.

The pre-assembled actuator assembly, including the plastic end plate 22, might be arranged to screw into, or to snap seal into, the housing 14.

Features of the present invention include for each pad, means indicative of the degree to which the supporting membrane is depressed by the load upon it.

Preferably each pad includes within it an underlying surface, so arranged that the variation of pressure within the pad transfers a differing fraction of the load onto that surface so as to produce a controlled, subjective impression of hardness. Preferably the underlying surface within the pad is fitted with at least one contact pressure sensor and the pressure of the fluid within the pad is adjusted in accordance therewith by first separate means so as to establish a quiescent or equilibrium value appropriate to the load. (In the alternative the volume of the pad between the membrane and the underlying surface is filled with a graded, compliant, porous material and the pad is pressurised to a chosen preset value representative of a standard load or of an average person).

The electromagnetic actuator is preferably provided with a position-sensing means and the motion of the actuator is controlled so as to vary the pressure in the pad.

Preferably the time integral of the required deviations of the electromagnetic actuator from its mid position is arranged to have a value of zero. Preferably the magnitude and polarity of the current supply to the electromagnetic actuator is monitored and the balancing quiescent fluid pressure on the surface of the piston, bellows or expandable element is controlled by second separate means so as to maintain the time integral of the current close to zero. (In the alternative a small orifice is contrived to exist between the volume of the pressure pad and the internal volume of the modulating element, so as to equalise the pressures over a period of time that is long in comparison with the period of the required pressure variations.) It will be appreciated that in some applications of the invention the special surface giving the effect of modulated hardness is not required but that the principles of the design are not significantly modified thereby.

Claims

CLAIMS 1. Apparatus for supporting a load, said apparatus comprising an enclosure having a flexible membrane defining at least part of its boundary surface and volumevarying means for varying the pressure within the enclosure whereby to exert a variable pressure on a load supported on the said flexible membrane, in which the volume varying means includes a movable member the displacement of which is controlled by forces generated electromagnetically and in which the movable member forms an inner boundary surface of the enclosure.
2. Apparatus according to Claim 1, in which the movable member is a piston, diaphragm or bellows.
3. Apparatus as claimed in Claim 1 or Claim 2, in which the movable member forms an outer boundary surface of a variable-volume device wholly enclosed within the enclosure, the variable-volume device acting to vary the pressure within the enclosure by occupying a varying proportion thereof.
4. Apparatus according to any of Claims 1 to 3, in which the flexible membrane defining at least part of the boundary surface of the enclosure is spaced from a substantially rigid surface into contact with which the flexible membrane may be brought by adjusting the pressure within the enclosure in dependence on the applied load.
5. Apparatus according to Claim 4 adapted as a seat for a user, in which the degree of contact with the said substantially rigid surface influences the perceived hardness of the seat to the user.
6. Apparatus for supporting a load, said apparatus comprising a first enclosure defined at least in part by a flexible membrane by which the load is supported, a second enclosure separated from the first enclosure by a movable partition, partition displacement means and first and second pressure adjustment means each associated with a respective enclosure and each being operable to vary the pressure of a fluid in the respective enclosure in concordance with the forces exerted on the partition by the partition displacement means in use of the apparatus.
7. Apparatus according to Claim 6, in which the first and second pressure adjustment means comprise means for varying the mass of the fluid within each of the first and second enclosures.
8. Apparatus according to Claim 6 or Claim 7, in which the partition is a piston, or a diaphragm, or a bellows or a telescoping tube arrangement.
9. Apparatus according to any of Claims 6 to 8, in which the first enclosure has a substantially rigid surface arranged beneath the flexible membrane.
10. Apparatus according to Claim 9, in which the substantially rigid surface has a gradient of hardness under compression.
11. Apparatus according to any preceding Claim, in which the first pressure adjustment means is responsive to first control means whereby to establish a pressure within the first enclosure in dependence on the load on the flexible membrane.
12. Apparatus according to Claim 11, further comprising sensing means for sensing the extent to which the flexible membrane is depressed by the load, whereby to provide a signal to the first control means in dependence thereon.
13. Apparatus according to Claim 12, in which the said sensing means comprise contact pressure sensors.
14. Apparatus according to any of Claims 11 to 13, in which the second pressure adjustment means is operative in response to second control means to vary the mass of the fluid and hence the pressure in the second enclosure whereby to urge the partition to a selected position in the absence of forces exerted thereon by the partition displacement means.
15. Apparatus according to Claim 14, in which the partition displacement means is an electromagnetic actuator.
16. Apparatus according to Claim 15, further comprising third control means for controlling the extent of displacement of the partition from the selected position.
17. Apparatus according to Claim 16 further comprising position sensing means for sensing the extent of displacement of the partition from the selected position.
18. Apparatus according to Claim 16 or Claim 17, further comprising monitoring means for monitoring the electrical current used by the third control means.
19. Apparatus according to Claim 18, in which the said monitoring means acts on the said first and second pressure adjustment means in such a way that the current consumed in the displacement of the partition is reduced.
20. Apparatus according to Claim 19, in which the selected position of the partition is a pre-selected starting position whereby the monitoring means acts on the said first and second pressure adjustment means so that the time integral of the current consumed in the displacement of the partition tends to a value of zero.
21. Apparatus according to Claim 19 or Claim 20, in which the monitoring means supplies a signal to act on the first and second control means in advance of the electromagnetic actuation of the partition whereby to compensate for differential response times.
22. Apparatus according to any preceding Claim, in which the first enclosure means comprises a plurality of chambers and the first pressure adjustment means is operative to vary the pressure within the chambers independently of one another.
23. Apparatus according to any preceding claim, in which at least the first enclosure or enclosures form part of a seat intended to support an animal or human being.
24. Use of apparatus according to Claim 23, to exert a variable force on the body or part of the body of an animal or human being.
25. Use of apparatus according to Claim 24, to measure or otherwise monitor movement, including involuntary movement, of an animal or human being.
26. Use of apparatus according to Claim 25 to simulate or accentuate the sensation of motion to an animal or human being.
27. Use of apparatus according to Claim 25 to relieve or remove the sensation of motion to an animal or human being.
28. A method of isolating a load from external pertubations, said method comprising the steps of i) placing the load on a flexible membrane forming an outer surface of at least part of an enclosure of variable volume ii) varying the mass, and hence the pressure of a fluid within the enclosure in dependence on the magnitude of the load, and iii) varying the volume of the enclosure, and hence the pressure of the fluid in the enclosure in dependence on detected pertubations, whereby to vary the forces applied to the load by the membrane so as at least to reduce the forces acting on the load as a result of the said pertubations.
29. A method of applying varying forces to a load, said method comprising the steps of i) placing the load on a flexible membrane forming part of an outer surface of at least part of an enclosure of variable volume, ii) varying the mass of the fluid within the enclosure, whereby to vary the volume of the enclosure and iii) subsequently varying the volume of the enclosure and hence the pressure therein so as to generate pertubating forces on the membrane and hence on the load.
30. Use according to any of Claims 24 to 27 in therapy.
31. Apparatus substantially as herein described with reference to and as shown in accompanying figures 2 to 4.