WO2011101645A1

WO2011101645A1 - Resistance training apparatus with linear electromagnetic assembly

Info

Publication number: WO2011101645A1
Application number: PCT/GB2011/000235
Authority: WO
Inventors: Hugh-Peter Granville Kelly
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-20
Filing date: 2011-02-21
Publication date: 2011-08-25
Anticipated expiration: 2012-08-20
Also published as: GB201002916D0; GB2477972B; GB2477972A

Abstract

Resistance training apparatus (20) is disclosed comprising a linear electromagnetic assembly in which an armature (23), formed from one or more electrical conductors, is disposed for linear travel relative to an elongate stator (22) wherein the user of the apparatus may, in use, exert an exercise force in the direction of travel of one or both of the armature and the stator, the arrangement being such that electrical currents (27) circulating within the armature and the interaction of the magnetic fields arising therefrom with those provided by the stator, serve to provide an opposing force against the exercise force, wherein the said opposing force is caused to arise as a result of movement enforced by the user of the armature relative to the stator, and thus the induction of eddy currents in the armature, characterised in that the armature is constructed and arranged such that the eddy currents circulate around a complete circuit within the training apparatus.

Description

RESISTANCE TRAINING APPARATUS WITH LINEAR ELECTROMAGNETIC

ASSEMBLY

The following invention relates to an improved form of exercise apparatus, in particular one suitable for resistance training. By -resistance training is meant the exertion of force by a person over a chosen distance against an opposing resisting force or pulling force. The process, also commonly known as weight training, is used by athletes intent upon personal fitness and the development of muscle. It is also used as a form of remedial treatment for patients recovering from muscle injury or an operation.

An example of apparatus currently used for resistance training comprises a stack of weights slidable along vertical guidance rods and connected by a wire rope or similar means to a movable member upon which the athlete is to exercise force. Movement of the member by the athlete causes the stack of weights to rise, so affording a gravitational counter-force and thus resistance to the muscle or group of muscles being exercised. The resistance means is normally housed within a frame, or other suitable rigid structure.

The degree of resistance can be selected by adjusting the number of weights being lifted and/or the use of pulley wheel multiplier arrangements to augment or diminish the force. Repetitive use of such apparatus causes over time physiological changes to the user's muscle tissue and the development thereof.

The use of such apparatus, while effective, affords a relatively crude method of resistance training. For example, force is constantly present the moment the weights are lifted from their rest position, even if force for the exercise being undertaken is required ideally only over the chosen stroke. In addition, an inertial force is also required to accelerate the mass of the weights being lifted, an unwelcome extra burden at the commencement of an exercise. Above all, for many exercises the use of weights is dangerous.

Carelessness or mishandling, especially when large stacks of weights are being used by powerfully built athletes, can lead to severe accidents. (An example of such an exercise is the "bench press" in which the athlete raises above his/her chest a horizontal bar, laden with weights at each end.)

Several alternative methods have been proposed to address -at least to some extent- the limitations of using weights to provide the required resistance. These include the use of hydraulic cylinders, conventional electric motors used as brakes or electromechanical systems in conjunction with weights. All of these still suffer however from notable problems, whether by way of complexity, bulk or difficulty in implementation.

An additional proposed method, having significant advantages over all the foregoing, is the use of linear electric motors or long stroke solenoids, such as is disclosed in WO2010/044048, DE-3920727 and EP-1166826. In these, the linear motors -which are fitted into the exercise apparatus- themselves provide a direct resistance force to the athlete, thus eliminating the attendant disadvantages of certain of the other methods.

However, disadvantageously in each case, the linear motors -which are variously of the AC induction or DC permanent magnet types- require, in the general case, the supply to them of electrical power in order to provide the necessary forces against which the user may exercise. For certain types of exercise this may be appreciable, not least due to the varying degrees of inefficiency applicable in terms of their conversion of supplied electrical energy to mechanical force. Consuming electrical power in order to exercise is not ideal in terms of either energy conservation, or being a "green" solution.

Additionally, the cabling of electricity to linear motor resistance training systems may present practical problems and even, in some cases be unfeasible, for example if the gymnasium housing the system is in a remote location. It may also be undesirable from the point of view of safety. An additional and particularly serious consideration is that totally infallible electrical and/or electronic control is essential to ensure, for example, that there may be no risk whatsoever of a linear motor exerting sudden violent or unexpected forces.

A favourable means of providing resistance for resistance training is one which overcomes, or substantially overcomes, the aforesaid disadvantages.

According to the invention resistance training apparatus comprises a linear electromagnetic assembly in which an armature, formed from one or more electrical conductors, is disposed for linear travel relative to an elongate stator wherein the user of the apparatus may, in use, exert an exercise force in the direction of travel of one or both of the armature and the stator, the arrangement being such that electrical currents circulating within the armature and the interaction of the magnetic fields arising therefrom with those provided by the stator, serve to provide an opposing force against the exercise force, wherein the said opposing force is caused to arise as a result of movement enforced by the user of the armature relative to the stator, and thus the induction of eddy currents in the armature, characterised in that the armature is constructed and arranged such that the eddy currents circulate around a complete circuit within the training apparatus.

In a preferred embodiment, the complete circuit is contained within the armature.

Inasmuch that the circulation of the eddy currents takes place within the resistance training apparatus, it will be appreciated that the apparatus in itself, forms the complete circuit for their

circulation. No external connection is necessary. Thus all of the opposing training force experienced by the user arises just from the eddy currents, together with, when applicable, any running frictional or gravitational forces in play.

It will also be appreciated that in this arrangement, no electrical energy whatsoever is required for the user to obtain the required force against which to exercise, the mechanical energy necessary for this purpose deriving solely from the electrical energy generated by the exertions of the user. The use of gravitational weights to provide the desired opposing force is thus replaced by the use of electromagnetism, and advantageously the additional force required to overcome the inertia of weights at the start of a stroke is substantially avoided.

Preferably, the elongate stator comprises a rigid member along the length of which is located a series of permanent magnets arranged such as to produce a sequence of fields of alternating flux polarity along the direction of travel of the armature. The fields emanating from the stator induce eddy currents in the armature as it passes through them, which in turn results in the back electromotive opposing force against which the user may exercise.

(By way of explanation, a back electromotive force is a

characteristic associated with the forced passage of an electrical conductor through a magnetic field, the phenomenon being known as Lenz's law.)

It will be appreciated that in this arrangement, the opposing force only occurs when movement is caused; in the absence of movement there is no counter force.

Three significant advantages arise from the use of induced

electromagnetism to provide an opposing force rather than the use of weights. First, on account of the fact that the weight of a typical armature providing the necessary resistance is substantially less than that of the weights which would normally be used, any danger arising from using the apparatus is virtually eliminated. Indeed, because the permanent force resulting from raised weights is removed, the user can even "let go" during the exercise without any risk -as before- of weights crashing downwards. (By way of example, a travelling armature of the invention capable of providing a resistance force of 80Kgs weighs only 650 grams, in contrast with that actual weight.) A resistance system in accordance with the invention, capable of providing the same force as weights, can therefore be manufactured from far smaller and lighter components. A further advantage arising from the elimination of weights is, as aforesaid, the

reduction in the inertial forces necessary to achieve initial

movement.

A second and profound advantage arises inasmuch that the electrical currents generated by the linear electromagnetic assembly are in direct proportion to the rate of movement imposed by the user. Thus a user may simply tune the force exerted by him or her upon the movable member simply by varying the speed at which it is caused to move. Enforcing a slow motion results in a moderate force, and the converse with a fast motion. Any natural variance in the muscularity of the limb or group of limbs being trained is therefore accommodated—over the selected stroke- simply by varying the speed at which the force is exercised. This is clearly not possible with gravitational weight systems. Employing this regime enables muscles to be trained safely to exhaustion, a technique used to stimulate their growth. If a constant force is required, this is achieved by maintaining a steady motion. One further advantage lies in the fact that when using a stack of weights, the weight selected necessarily must be less than the maximum an athlete can raise. Thus muscles cannot be optimally exercised to the extreme. When using a resistance system of the invention, the athlete may self-raise the opposing force to the absolute maximum of which he/she is capable, simply by increasing the speed at which the movement is carried out. This is found in practice to be remarkably effective in the development of muscle tissue.

A significant third advantage, to be hereinafter explained in more detail, arises inasmuch that the force experienced by the user can also be regulated by controlling the flow of eddy currents within the conductor(s) comprising the armature and thus the opposing force arising. By this means, the force can for example, be increased from stroke to stroke, or from one set of exercises to the next, or be removed altogether in a desired direction.

WO 2010/044048 which discloses the use of a linear motor to provide a training resistance force, mentions that the same can, under certain circumstances, act as a linear generator for providing a net power output. It does not circulate generated eddy currents in a complete circuit within the apparatus but must be connected to the grid / an external load bank so that wiring must undesirably lead from the motor to a socket or equivalent. Wires are in any case required during the normal mode of operation.

In any electromagnetic assembly in which forced movement is effected of an armature relative to its stator, it is desirable in terms of mechanical symmetry for the axial line through which the said force is transferred to lie at the effective axial centre line of the stator. By this means, uneven bending moments are avoided and the force may be communicated evenly along the length of the stator to either end thereof.

In a preferred form of the invention, the stator of the linear electromagnetic assembly comprises a tube housing a series of axially magnetised cylindrical permanent magnets, arranged in such manner that their like poles are facing. By this means, the magnetic flux emanating from the poles is squeezed out radially for optimum interaction with the conductive means comprising the armature. Preferably, the magnets are each separated from their neighbours by a spacer. With appropriate selection of the axial length of the magnets and their spacers, this arrangement assists the aforesaid flux squeezing but at the lowest manufacturing cost per unit length of the stator. The spacers may be fabricated from steel or iron to assist further the said flux squeezing.

In its simplest first form, an armature of the invention suitable for use with a tubular stator of the described preferred form, may comprise one single conductor in the form of an electrically conductive sleeve for travelling co-axially along the length of the tubular stator. By virtue of its inherent conductivity and coaxial location over the stator, the sleeve acts as an extended short circuited turn enabling the circulation therein of eddy currents both circumferentially and longitudinally and thus the generation of back electromotive forces serving to provide an opposing force against the exercise force.

The sleeve can be connected directly to the member on which the user is exercising force, or by a wire rope or similar means. Ideally, the sleeve may be fabricated from aluminium, stainless steel or copper. The force required to move the sleeve is substantially proportional to its speed.

It will be appreciated in this arrangement, that the length of the armature circuit in which the eddy currents are generated and can flow, determines their extent and thus the magnitude of the training opposing force. Thus, by adjusting the effective circuit length, for example by using a circuit breaker as the adjuster, the force can be commensurately moderated, or increased. Alternatively, several independent circuits, made from individual conductors within the armature, may be utilised, the number selected similarly varying the overall effective length of the circuit, and the extent of the training opposing force.

While the force experienced by the user may be readily adjusted by self-regulated speed control, a coarser adjustment may therefore be realised by varying the effective overall length of the sleeve, and thus the overall length of the circuit in which the eddy currents can circulate. For example, according to a feature of this preferred form of the stator and armature of the invention, the sleeve may comprise a number of smaller discrete lengths or sub-sleeves, the number of which caused to be displaced along the length of the stator being readily selected manually by appropriate

linkage/coupling means. (This arrangement is akin to that used in current weight training machines in which—by the insertion of a peg- the number of weights raised is similarly selected by the user for any given exercise.)

It should be noted that in any embodiment making use of a sleeve for the armature, in practice eddy currents circulate therein both circumferentially and, to a lesser extent, longitudinally. In each case, they take the path of least electrical resistance.

It is desirable for the user of the equipment to enjoy the smoothest possible force while using the resistance means of the invention. In is therefore important to avoid cogging forces. By cogging forces is meant those varying mechanical forces which can arise in the direction of travel as a result of uneven salient magnetic attractions as an armature carrying induced eddy currents traverses the stator inducing them.

According to an aspect of this first form of armature of the

invention, the sleeve length, whether comprised of a single sleeve, a sub-sleeve, or multiples thereof, is so selected as to minimise the effect of cogging forces. In practice, this is realised by ensuring that the sleeve length -at least for smaller lengths- is substantially equal to the length of half a full magnetic pole pitch in the direction of travel, or to integral multiples thereof. (By substantially equal is meant within +-5% of the nominal length.)

It is well known that the eddy currents induced in an

electromagnetic linear assembly, such as described herein, are dependent upon the air gap in between the armature and the stator. The smaller the gap, the greater the effect of the stator fields upon the armature.

In an alternative means of adjusting the force provided by such a tubular sleeve armature, the same may be split along its length in the direction of travel in one or more places to permit the spacing between the armature and stator to be adjusted by the user. The eddy currents induced in the armature are thereby varied in accordance with the width of the air gap, and the force experienced varied commensurately. The gap may also be advantageously employed to prevent the circumferential circulation of eddy

currents, and thus further to control the force experienced by the user.

Any length or arrangement of sleeve worked vigorously along the length of a magnetic stator pole by an athlete during training will become hot. This is as a result of the eddy currents circulating therein. To assist heat dissipation, the sleeve or its sub-sleeves, may be in the form of a finned extrusion.

It is customary to install resistance training means within a rigid frame or the like. This can occupy an undesirably large footprint, especially for gymnasium equipment to be used at home. To avoid both this and the expense of such a frame, the stator -along which the armature is caused to travel- may be affixed by mountings at its ends to a wall or other similar structure, and supplied to the user as a "ready-to-fix and install" package. It is often the case that users of gymnasium equipment wish to monitor their strength during the performance of an exercise.

According to an aspect of the invention, sensors are provided for detecting the force exerted as the tubular sleeve is displaced along the length of its stator. Such means might comprise a load cell arranged to detect the pulling force exerted on the sleeve during motion, or the reduction/increase in effective weight of the stator resulting from the motion of the sleeve along it.

As an alternative to the use of a single sleeve or multiple sleeves, in a second form the conductors forming the armature of the linear electromagnetic assembly may instead consist of a series of annular electrical coils arranged together in a stack so as to form a

cylindrical sleeve for sliding along the length of the stator. The coils may be positioned contiguously, meaning one face against the face of the next and so on, or spaced apart, to suit the disposition and therefore the optimum cutting of the lines of force of the magnetic fields emanating from the stator. The coils may be appropriately interconnected to form a plurality of phases.

As the armature comprising the said coils is forced by the user to travel along the length of the stator, so eddy currents are induced in the coils. These eddy currents are permitted to circulate within the coils by a short-circuiter. This then acts to vary the effective length of the circuit in which the eddy currents may circulate, and the extent of the resulting training opposing force experienced. (It should be noted, in contrast to the foregoing sleeve arrangement, that in the case of the use of coils, eddy currents can only circulate circumferentially, typical coil wire diameters being too thin to permit any longitudinal circulation across their cross section.)

The eddy currents provide a powerful braking effect, in effect behaving in a similar manner as they do within the sleeve form of armature hereinbefore described. Practical tests show that a quite modest stack of sixteen coils, of total length just 350mm and running along a stator of diameter 38mm, is capable of providing resistance forces at reasonable speeds, say lm/s, which are in the region of 80-100 kgf, an ample resistance force for athletes to train against.

Naturally, it is desirable during any steady motion imposed by the athlete over a given stroke, for the resistance force arising from the aforesaid arrangement to be as consistent as possible. To this end, the disposition and sizing of the permanent magnets in the stator, and, as determined therefrom, the axial length and sizing of each coil comprising the armature, is selected such that the

instantaneous back-electromotive force arising from the product of the current generated in any one phase of the generator and the intensity of the flux causing the said current, added to the back electromotive forces arising from the products of the currents generated in other phases of the armature and similarly the intensity of the flux causing those said currents, is substantially constant. By this means, a substantially constant force is

experienced by the user at any given speed regardless of the displacement of the armature relative to the stator.

It will be appreciated that in the case of the use of the first form of the armature of the invention, namely the use of a simple tubular sleeve or a number of sleeves, the same provides a resistive force regardless of its direction of travel, the induction of eddy currents, in accordance with Lenz's law, always being such as to resist the direction of the enforced movement.

By contrast, a significant advantage arising from use of the second form of the armature of the invention is that were the coils of the armature to be open circuited, no currents would flow and

substantially no resistive force would result. By this means, the direction of motion in which resistance is experienced can similarly be controlled. Thus, should physical resistance be required for an exercise in one direction only, the coils may be short circuited by the short-circuiter only for movement in that direction. On the return stroke, the coils are open-circuited by a circuit breaker.

One such example of an exercise that can benefit from this

advantage is that known as the leg press. In this, the legs are extended against a resistance force -hitherto provided by weights. The preference for some athletes is for pressure to be experienced on the outwards stroke only and not on the return. Eddy currents are therefore permitted to flow in the coils during the extension stroke, but as a result of instant disconnection on the return stroke, no resistance is experienced, so allowing a rapid and danger-free return to the starting position.

The switch from connected to disconnected status, as determined by the direction of travel, can be controlled by the user, or by external switching means responsive to the direction of travel. Numerous means may be employed to detect the said change in direction. For example, a direction sensitive switch located on a wheel within the device which is caused to turn according to the direction of travel, or electronic detection means establishing by means of encoders the direction of travel, or means responsive to the presence and direction of currents flowing in the coils.

A further benefit arises from the use of an armature formed from coils. As opposed to directly short circuiting the coils, the degree of resistance afforded to the user can be conveniently and accurately varied simply by regulating the currents allowed to circulate in the coils. If, as in the standard case, the coils were to be short circuited, maximum resistance occurs. However if a load of variable electrical resistance is utilised, the physical resistance experienced can be reduced to suit the user. Indeed the ohmic load connected to the coils of the armature may be varied during and over the length of the stroke, and indeed from one set of strokes to the next, to provide a physical resistance profiled to suit the user.

In both the first and second forms of the armature of the invention, the eddy currents induced respectively in the tubular sleeve or the armature coils may be augmented by the use of a ferromagnetic sleeve. This is sited coaxially over the length of the sleeve or coils such as to draw out more orthogonally the lines of force emanating from the stator, and thus to improve their flux linkage with the conductive medium forming the armature. The eddy currents generated are consequently increased. This improvement can be exploited to increase the resistance force available to the user at no extra cost in terms of the permanent magnets used in the stator. Alternatively, smaller and therefore cheaper magnets may be used, but able to provide the same force to the user on account of the use of the ferromagnetic sleeve.

The sleeve may be profiled at one or more portions thereof in such manner as to ensure there is no significant net salient pole

attraction in the direction of travel between it and the permanent magnets of the stator, and thus to eliminate substantially any cogging effects during its travel along it.

As an alternative to the use of a ferromagnetic sleeve being affixed coaxially over the armature coils and thus travelling along with them, an elongate ferromagnetic sleeve, located coaxially over the entire length of the stator, but with sufficient space to permit the free passage of the armature, may be similarly used to draw out the lines of force emanating from the stator, and thus improve

performance. This has the secondary advantage of providing a magnetic shield inasmuch that the lines of flux are effectively contained within it.

It will be appreciated from the foregoing that the training force provided by the linear electromagnetic assembly of the invention is a resistance force opposing the motion imposed by the user. Such a type of force is useful in the concentric contraction development of muscle tissue, and as such is applicable to many exercises

performed in modern gymnasiums. For some exercises however, it is desirable to experience a resistance force on the outgoing stroke, and, dependent on the type of exercise, a pulling or pushing force on the return stroke, or vice-versa. This facilitates the eccentric contraction development of muscle tissue.

Where the armature comprises as aforesaid a number of coils, a circuit breaker may be used to open circuit the short circuited condition in which the coils normally operate, and instead connect them to a power source, given the availability of an external power supply.

According to an aspect of the invention, the circuit breaker may be used in such manner that the armature coils may on one stroke of an exercise be short circuited or connected to a suitable load to provide a resistance force opposing the exercise force, and on the other stroke of the exercise, be fed suitably commutated electrical currents in such manner as to produce an axial thrust reaction against the stator in the required direction.

By this means, during a full cycle, an athlete may in a passive mode enjoy the benefit of exercising against an opposing force -during which no power input is required- and then, on the return stroke, by means of using externally supplied electrical power, exercise in an active mode against a pulling or pushing force as required to suit the muscle or muscle group under development.

In this arrangement, inasmuch that a constant force is present irrespective of direction of motion, this mode emulates that effected by the use of weights.

The use of electronic monitoring devices in gymnasium equipment is gaining popularity. These can provide the user with detailed information as to the force they are exerting, the overall power generated and so on.

According to yet a further aspect of the invention, the electricity generated by the armature coils in any one session is recorded and displayed to provide the user with his/her overall performance. In addition, the instantaneous voltage or joules being generated may be displayed, for example by means of a light emitting diode bar code or an array of light bulbs, successively lit according to the athlete's output, or some other similar arrangement, thereby affording the athlete with immediate visual data as to his/her work output.

For the sake of economy in manufacture and neatness in realisation, it may be desirable to eliminate the need for running cables and the like from the travelling armature to external means used for illuminating the aforesaid light emitting bar code, and also to any controller used by the user to regulate the resistance force by adjusting the degree to which eddy currents may freely pass around the conductors comprising the armature.

According to an aspect of the invention, the said controller and the light emitting bar code, together with any battery storage means necessary to power the same, are together mounted upon the travelling armature. Thus the armature becomes a self-contained unit, a particularly attractive solution for home-use athletes. (The battery may be maintained charged by apportioning for this purpose some of the currents generated.)

It is a current fashion to introduce vibration, or rapid force variation between two limits, during a resistance training stroke, the

purported aim being to stimulate even further the growth of muscle tissue.

It has earlier been explained that in the form of armature employing coils as its conductors, a substantially smooth force is obtained by combining, for example in the case of a two phase system, the terms comprising the squares of the respective sinusoidal and cosine variations of each phase in force as the armature moves relative to the stator.

According to a further feature of the invention in which annular coils are used to form the conductors of the armature, selected coils of one phase may be fully or substantially short-circuited, and coils of the remaining phase(s) left fully or substantially open circuited. The effect is to remove one of the aforesaid terms governing the resistance force,, causing it to vary (in a two phase system) with the modulus of the single square of the sine of the phase angle. This results in a significant vibration, directly felt by the user, as the armature is forced to move relative to the stator.

In one embodiment of the invention, an exercise apparatus comprises a linear electromagnetic assembly in which an armature, formed from one or more electrical conductors, is disposed for linear travel relative to an elongate stator wherein the user of the apparatus may, in use, exert an exercise force in the direction of travel of one or both of the armature and the stator, the

arrangement being such that electrical currents circulating within the armature and the interaction of the magnetic fields arising therefrom with those provided by the stator, serve to provide an opposing force against the exercise force.

The invention will now be described with reference to the

accompanying drawings in which :

Fig 1 a shows conventional weight training apparatus, Fig 1 b shows resistance means according to the invention and Fig lc shows a further form of resistance means according to the invention. Figs 2 a,b & c show respectively a stator and one form of armature of the invention, and their assembly,

Fig 3 shows the relationship between speed and the resistance force experienced by an athlete using the apparatus, Figs 4a,b&c show additional means of varying the resistance force to suit the user,

Fig 5 shows the ideal minimum length of the armature, relative to the pole pitch of the stator,

Figs 6 a, b & c, show means for regulating the resistance force experienced according to the direction of travel,

Fig 7 shows the armature in the form of a finned sleeve, which may for example, be an extrusion,

Figs 8a & b show means for registering the force exercised by the athlete, Fig 9 shows apparatus of the invention in a form suitable for domestic use,

Fig 10 shows an alternative from of armature, and a method of controlling the force experienced by the user,

Fig 11 is a diagrammatic explanation of a method of achieving linearity of force for the arrangement shown in Fig 10,

Fig 12 shows the use of a controlled switch to determine the direction in which resistance force is effected,

Fig 13 shows a method of controlling the profile of force

experienced to suit the athlete, Fig 14 shows the use of a ferromagnetic sleeve to increase the flux linkage between the stator and armature,

Fig 15 show an alternative form of sleeve to that illustrated in Fig 14, Fig 16 shows an embodiment of the resistance means of the invention in an active linear motor mode,

Fig 17 is a system diagram showing instrumentation and power conversion means connected to the resistance means,

Fig 18 shows an armature of the invention carrying thereon display and force controlling means and

Fig 19 shows diagramatically a method of obtaining a vibratory opposing force.

By way of assisting an understanding of the present invention, a weight training arrangement typical of those currently in use is shown at 10 in Fig la. The arrangement comprises a base plinth 11 upon which are mounted two vertical guide rods 12 and 13. A movable stack of weights 14 is guided vertically by the two rods. A central pull rod 15 is connected by a wire rope 16 onto an exercise bar 17. The apparatus is suitable for exercising and developing the triceps muscles. The method of operation is as follows:

The athlete presses down upon the bar 17 with hand pressure, as shown by the arrows at each end of the bar, and so causes the stack of weights to rise. The degree of resistance is selected by means of the pin 18, which engages onto the pull rod 15 the required number of weights, and thus the gravitational counter- force experienced. Once the bar has been fully depressed, (and the weights are at their highest position), the user carefully allows the bar to rise, ready for the next repetition.

The apparatus of the invention is now described with reference to the apparatus shown at 20 in Fig lb.

A plinth 21 supports a cylindrical magnetic stator pole 22. A cylindrical and electrically conductive sleeve 23 is guided

concentrically by internal bearings (not shown) along the stator. The sleeve is connected to the exercise bar 17 by a wire rope 24, passing over pulleys 25 and 26 located at each end of the stator.

Operation is the same as the apparatus shown at 10. As the athlete presses down upon the bar, the conducting sleeve is caused to rise. Eddy currents (designated by the arrows 27) are induced in the sleeve which on account of its conductivity acts as a short circuited turn and thus permits them to circulate therein in such manner as to cause magnetic fields which oppose -along the length of travel- those emanating from the stator -in accordance with Lenz's law. Thus a resistance force is experienced by the user. Importantly the force is felt in both directions of travel, thus the apparatus -as shown- can be used to train both the athlete's biceps and triceps, according to the direction of movement imposed on the bar.

It will be appreciated that in this form no electrical currents need be supplied to the apparatus, the construction of the armature being such that eddy currents are self-induced within it and circulate freely by virtue of its own conductivity. It follows that the free flow of eddy currents in therefore confined to within the resistance training apparatus, no external connection is required.

It should be noted numerous designs of linear electromagnetic assemblies may be utilised for the purpose of the invention, an example of an alternative construction being that in which the stator comprises an elongate flat surface and the armature has a similar operative flat surface. The armature 23 faces the stator 22 and is guided by bearings to pass along the length thereof. Such an example is shown at Fig 1 c. However it will be appreciated in this particular case, a bending moment is created as force arises between the two, as shown by the arrow. By contrast, the

arrangement shown in Fig lb ensures the force between the armature and stator is coaxial, and thus is communicated evenly along the body of the stator to each end thereof. Referring to Figs 2, a, b & c, certain of the components of the apparatus of the invention are shown now in more detail. The stator is shown at 22 and comprises a series of permanent magnets 29, with like poles facing. The magnets 29 may be advantageously separated by spacers 30. The magnets and spacers are housed within a thin walled tube 28, as shown.

On account of the fact that like poles face one another, the lines of flux radiating from the pole of each magnet are forced to radiate out from the tube, as shown by the flux lines on the diagram. This is an effective method of obtaining the maximum performance from the magnetic energy stored in each magnet, as the flux of each is forced to pass through the side walls of the tube, and then into the armature sleeve, for the effective induction of eddy currents therein.

The sleeve 23 (for traversing up and down the stator) may be fabricated from any electrically conductive material of low

resistivity. In order to avoid cogging and lateral magnetic attraction between the sleeve and the stator, non ferromagnetic materials such as aluminium or copper are ideal, being conductive but not ferromagnetic. (In special cases a specific form of external

ferromagnetic sleeve may be placed over the armature sleeve, as is explained in more detail hereinafter.) The eddy currents induced in the given length of sleeve are shown in more detail at 31.

During motion, the force experienced by the athlete is in direct proportion to the speed of movement, in accordance with Fleming's right hand rule, as shown at 32 in Fig 3. (The flux vector is

designated as Θ, the force experienced F, and the eddy currents induced, i.) The greater the speed, v, the greater the induced eddy currents and thus the resistance force experienced.

Several significant advantages arise from the use of the

arrangement of the present invention. In the first instance, the use of heavy and potentially dangerous weights is avoided altogether. The weight of the sleeve 23 is typically only a fraction, eg a few percent, of a full magnet stack as would previously be used to provide the opposing force. Secondly, by controlling the speed at which the exercise is carried out, the athlete can gauge the

resistance he/she experiences to match his/her muscularity and/or available strength on the day of training. By way of example, when utilising a stator of diameter approximately 38mm, and an

aluminium sleeve of external diameter 50mm, enforcing a brisk movement can result in some 40-60 kgf of resistance force. A gentler movement can elicit a more modest resistance force of eg 5- 10 kgf. In addition, the speed and thus the resulting force can be varied over the length of the stroke, with adequate practice, again to suit the needs of the athlete.

A third advantage arises from avoiding the use of weights inasmuch that the entire apparatus, by which is meant both the

electromagnetic resistance means and the (unshown) frame supporting it, can be fabricated from a thinner gauge of steel saving both on material and transport costs. Gymnasiums equipped with the apparatus may be installed in buildings with normal flooring, as the tons of weight associated with using conventional weight stacks is avoided. One further but not immediately apparent benefit arises inasmuch that the apparatus is visually more acceptable to female athletes intent upon increasing their muscle size, power and stamina, but preferring in the process not to be ostensibly

demonstrating the same, as would be the case when raising an ample number of weights. In addition, the dangers of having to hold up a stack of weights at the end of a stroke are avoided, as all resistance falls to zero as soon as the desired movement is

completed. It will be appreciated from an understanding of the physics of operation of the resistance apparatus of the invention, the longer the sleeve, the greater the effective circuit length in which eddy currents are induced, and thus the greater the resistance force experienced. This can be exploited advantageously for providing a method of adjusting the said force, in a method similar to that which is available with weight stacks, as shown in Fig la. Such an arrangement is now described with reference to Fig 4.

A stator of the apparatus is shown at 22 in Figs 4a), b) and c) . In this case, the sleeve 23, rather than comprising one long length, is instead divided into sub-lengths 33,34,35 and 36. Joiners 37,38 and 39, such as clips or clip means, are used to enable the athlete to conjoin the sub-lengths to one another in order to provide a sleeve of the desired overall length (as shown in Fig 4b) . By this means, a heavily muscled athlete wishing to enjoy the maximum resistance can readily use all four sub-lengths, whereas a less powerful athlete can elect to use just one or two sub-lengths. A variation to this is shown at Fig 4 c), where the sub-sleeve 40 is the shortest, and 41, 42 and 43 each increase successively in length . By this means a logarithmic increase in force can be utilised to provide a very wide variation .

In all cases, it is desirable that, at least for shorter lengths, any sub-sleeve is arranged to be substantially the same in length, or an integral multiple thereof, of the axial length "I" occupied by one spacer and one magnet of the stator, as shown at 44 in Fig 5. By substantially the same is meant within +-5% of this length . By this means, cogging forces are substantially avoided. (By cogging forces is meant an uneveness in the magnetic resistance force experienced when the sleeve is caused to move at a constant velocity. )

It is well known that increasing the air gap between the armature and stator of an electromagnetic assembly affects their magnetic coupling, and thus their performance. The greater the gap, the less the performance. Two further methods of varying the resistance force, utilising this phenomenon, are now shown with reference to Figs 6 a) and c). In these cases, rather than varying the effective length of the sleeve, and thus the circuit length in which the eddy currents can circulate, the air gap between the sleeve and the stator is adjusted. A consequent change in the induced eddy currents is thereby effected.

Referring first to Fig 6 a), the sleeve 23 is provided in two halves 45 and 46, hinged along their length as shown at 47. This arrangement enables the sleeve to be opened to the desired extent to attenuate the eddy currents induced therein. This arrangement may be made to be directionally dependent, and thus to afford a resistance force to the athlete in one direction only, occasionally desirable for certain exercises. Such an arrangement is shown at 6 b), in which the two portions of the sleeve 45 and 46, are normally held open by a spring 48. In this mode, the sleeve may readily travel along the stator. By suitably connecting the sleeves onto the pull ropes 24 and 24a, as shown at 48a, the sleeves are brought together on the upstroke to 22 provide an operative resistance force. As soon as tension is released, the spring serves to open the sleeves, enabling the sleeve to fall freely in readiness for the next upstroke.

A further variation to this is shown at Fig 6 c) in which the sleeve is divided into three segments, but hinged together at 49 onto a base ring. In this case, the pull ropes (not shown) are used to bring the sleeves together, as shown at 50, to provide the desired resistance. In both the arrangements of Figs 6 a) and c), screw adjustment means (not shown), may be employed to adjust the extent to which the sleeves are brought together, and thus the maximum resistance force provided. (Although the example given here has shown the hinging of armature segments to vary the air gap, numerous alternative mechanical arrangements are possible to effect such a variation.)

In all of the foregoing examples of the operation and use of the apparatus of the invention, the armature has been depicted as a simple sleeve. However, the sleeve may become hot when worked along the stator vigorously by a fit athlete due to the circulation of the eddy currents therein. To dissipate this heat, the sleeve may be equipped with cooling fins, as shown by the profile in Fig 7. An aluminium extrusion is ideal for this purpose.

An issue important to any athlete embarking upon a protracted regime of resistance training is the ability to assess the progress being made. In the case of the use of conventional weight stack apparatus, as shown in Fig la, progress is self evident, being indicated by the number of weights that can be lifted.

A method of tracking progress when using apparatus of the present invention is illustrated in Fig 8a. The pull rope 24 passes around the pulley 25 and down to the exercise bar 17. The pulley itself is mounted on a bracket 51 which presses in turn on an electrical load cell 52. The load cell output is connected, as shown, to a meter 53 which indicates the force being exerted, and so provides a visual reference to the athlete of the progress being made. (In a simpler realisation of the same principle, the load cell and meter

arrangement can be replaced by a conventional spring balance, not shown).

The same principle is illustrated again with reference to Fig 8 b. In this case, the load cell 52 is mounted at the base of the stator rod 22. The reduction in the effective weight of the rod as the armature is being pulled upwards, is again indicated by a meter (not shown) connected to the load cell.

Referring to Fig 9, a design of the apparatus adapted for domestic use is shown generally at 53. Mounting brackets 54 and 55 are used at the upper and lower extents of the stator rod 22 to fasten the same to a wall, or other suitable structure. The armature sleeve 23 is caused to traverse along the length of the rod 22 by the home- athlete, who exercises force thereon by means of a bar 56 affixed to the armature. Compliant means may be incorporated within the apparatus in order to accommodate the natural slight arc defined by the movement of the hands when carrying out a biceps or triceps development exercise. In a first form, such means can be a slotted mounting coupling the bar to the armature, as shown at 57 in the inset drawing. In a second form, the lower mounting bracket may incorporate a slotted aperture, as shown in the inset drawing at 58, so permitting the lower end of the stator rod to move in and out in sympathy with the said arc transcribed by the armature. In this second form, the top mounting bracket is suitably hinged to enable this lower end in/out motion.

In all of the previous examples, and in the following various examples of the invention, protective shields (not shown) may be fitted around the stator rod or the whole apparatus (excepting the exercise bar and the cable leading down to it), to prevent any accidental contact between the stator and any external

ferromagnetic object accidentally brought close to it. The physical spacing of the shield from the rod may be arranged to ensure any externally detectable field is within safe statutory limits for those equipped with pace makers and the like.

The foregoing descriptions of the present invention have shown the use of one or more conductive cylindrical sleeves to form the armature of the linear electromagnetic assembly. This provides a simple, effective and economic solution. However, an alternative solution, having specific additional advantages is also feasible, and is now described with reference to Fig 10. The armature, rather than being a simple sleeve, is instead comprised of a number of electrical annular coils, indicated generally at 60. The coils may be placed one against the other to form in effect a contiguous set of windings. The method of operation is precisely the same as using the sleeve. Forced movement of the coils through the magnetic fields emanating from the stator induces eddy currents within them, and thus the creation of an opposing force. The magnetic pitch of the coils is arranged to match that of the magnets within the stator, such that coils of any one phase, as shown at 61,62 and 63, generate simultaneously currents of the same amplitude. The combined currents thus add together to provide an electromotive force which is appreciable and varies in amplitude in exactly the same manner as the single piece sleeve - according to the speed at which the coils are forced through the stator magnetic fields. The number of coils present determines the effective circuit length in which the eddy currents may circulate.

This arrangement provides, as with the sleeve, an electromagnetic brake, and thus again affords an opposing force to the user.

Maximum resistance is obtained by using a short-circuiter to short- circuit the coils, and substantially no resistance at all is obtained by leaving the coils open-circuited to render impossible the flow of eddy currents.

It will be apparent from this that the degree of resistance afforded by the coils of the armature can be readily controlled simply by controlling how many of them are short circuited or regulating the ohmic resistance presented across the coil terminals. This is shown in Fig 10 where ganged rheostats 64 and 65 are used to regulate the current flow through each set of coils. (At one end of travel, this acts as a short-circuiter inasmuch that zero resistance is presented to the coils and the emfs generated within them.) This provides a host of possibilities in that the athlete can adjust the resistance force very precisely to match his/her requirements, as well as benefiting from the linear relationship between speed and resistance force. If required, coarse adjustment can be effected by connecting in by circuit breakers or disconnecting whole coils within the circuit feeding the rheostats, as indicated -by way of example- in Fig 10 by the-breakers at 66 and 67. In effect, the breakers and the rheostats individually or together become circuit length adjusters.

It is important that the interaction of the eddy currents induced in the coils, and their inter-reaction with the magnetic fields emanating from the stator, is such as to provide a continuous smooth force. This is achieved as shown in Fig 11. The sizing and spacing of the permanent magnets is so selected as to ensure the f|ux distribution, F, along the length of the stator varies substantially sinusoidally with the phase angle Θ per pole pitch, as shown at 66. Similarly the number of turns in each coil, and the number of layers, is selected to ensure the emf generated, E, in each coils similarly varies sinusoidally, as shown at 67. From this, it will be appreciated that the force experienced by the coils of one phase, being the product of the induced emf E and the strength of the field F causing it, varies as the square of the sinusoid, ie EFsin²0. In the example of the armature shown in Fig 10, this is shown to comprise two phases, the second phase being spacially displaced by TT/2 of a full pole pitch along the length of the stator relative to the first phase. Thus, applying the same principles, the product of the flux and the induced emf applying to the second phase varies as EFcos²0. Adding these two forces gives a gross force of EFsin²9+EFcos²0 or EF(sin 9 +EFcos²6) = EF. Thus the force experienced is constant (at a given velocity) regardless of the position of the armature along the stator.

For those resistance training exercises where force is required in one direction only, it is a simple matter when using the coil constructed armature, to open circuit the armature coils in the opposite direction. Such an arrangement is shown in Fig 12. An athlete 68 is carrying out a leg press exercise by pushing on the movable plate 69. Two stator rods 70 and 71 are attached thereto as shown, and slidably pass through fixed armatures 72 and 73 to provide the necessary resistance force. A direction detector unit 74 determines which way the moving assembly is travelling, and on the outwards stroke (when resistance is required), closes the switches 75 and 76 by means of the relays, as shown.

As soon as pressure is released, and the athlete permits the footplate to move backwards towards him/her under the effect of gravity, the switches are opened and the footplate becomes free to travel back towards the athlete ready for the next repetition. This is a significant advantage over conventional systems as illustrated by the fact that especially powerful athletes can leg-push significant weights, eg hundreds of kilograms. The slightest slip or momentary muscle collapse however can result in the footplate crashing back towards the athlete in free-fall, with severe consequences.

In the arrangement as shown in Fig 12, the only return force is the relatively moderate gravitational weight of the moving assembly. Even this can be controlled by connecting a suitably high ohmic resistance across the switches when opened, such as to permit the flow of currents in the armatures just sufficient to dampen the rate of return movement.

For specific exercises, it may be advantageous when resistance training to profile by external means the force experienced by the athlete over the desired stroke. This may be achieved as shown in Fig 13. A linear encoder 77 is arranged to extend over the length of travel of the armature 78. A reading head 79 mounted on the armature provides positional information to a computer 80, or other similar control system. The desired profile 81 is called up, as 20 shown, defining the force to be experienced—as shown on the vertical axis- versus the position—as shown on the horizontal axis. As the armature 78 is caused by the athlete to traverse the stator 22, the computer regulates the flow of current through the

armature, by means of the regulator unit 82, according to the called up profile, so providing the desired profiled force over the selected stroke.

It is naturally desirable to achieve as much resistance force as possible from a given length of armature. To this end, a

ferromagnetic shroud as shown at 83 in Fig 14, may be located coaxially around the coils 84. The effect is to draw out the lines of flux more orthogonally from the stator 22, as shown schematically at 85. (Note, in practice the lines of force are confined to within the shroud and do not extend to any extent beyond it. They are indicated on the diagram in this manner for clarity only.) In the absence of the shroud, the flux lines tend to diverge as shown at 86, with a commensurate loss of induced electro motive force.

A disadvantage of employing a ferromagnetic shroud is the effect known as cogging. This occurs as a result of the ends of the sleeve being attracted to the nearest magnetic pole. An uneven force ripple is imposed upon the otherwise smooth force experienced by the armature. To mitigate this effect, each end of the shroud may be profiled, as shown at 87. (A method of such profiling is disclosed in USA patent no. 5,909,066. In this, a profiled ferromagnetic sleeve is also employed to carry out a similar function, but has only one peak and dip around its periphery. There is a consequent deliberate asymmetry of attraction between the sleeve and the rod, the purpose of this being to reduce the effective weight of the armature when used20 horizontally. In the case of the sleeve 87 of Fig 14, there is a plurality of dips and of peaks, so ensuring attraction of the sleeve to the stator is symmetrical.) Rather than fitting a ferromagnetic shroud over just the armature coils, a single piece cylindrical shroud may be located over the length of the whole stator, as shown at 88 in Fig 15.This similarly draws out the lines of flux from the stator, as shown at 89, but remains itself stationary. The shroud provides in addition a

protective magnetic screen, as substantially no lines of flux escape beyond it.

An advantage arising from the use of coils to form the armature is that they can operate both in a passive short-circuited mode as well as in an active powered mode. In the passive mode, which is the normal mode of operation of the apparatus of the invention, the short-circuiter is closed to permit eddy currents to circulate of their own volition as movement of the armature is enforced, so providing the opposing training force. In an active mode, a circuit breaker may be used to remove the short circuit condition and enable suitably commutated currents to be fed by a regulator to the armature coils to create magnetic fields for working axially against those of the stator to provide a pulling or pushing force against which the athlete can exercise.

This is illustrated at 90 in Fig 16, where an athlete 91, having pulled the armature in its passive mode on the first stroke of a cycle to one end against an induced eddy current opposing force, is now shown pushing on the return stroke against the stator rod 92, being itself driven outwards by the powered armature 93. In this case, the outward push force exerted is present whether there is relative movement between the stator and armature or not. This therefore provides a different mode of operation, similar to that of raising a stack of weights in which the resistance force is permanently present. (Exactly the same applies to the case where the athlete is required to pull against the force, as shown at 94 in Fig 16.) By this means, for certain desired exercises, muscles may be developed in both their contraction and eccentric phases.

It will be appreciated from reference to Fig 10, that usable

electricity is generated when the coils of the armature are

connected to the external rheostats 64 and 65, -that is when these are not at their extreme short-circuiter end of travel.

Referring to Fig 17, a schematic diagram is shown of a control system 95 connected to the said armature coils for displaying, and registering the electrical power generated by the athlete.

A first function of the control system is to provide a display such as on light bulbs 96 (or light emitting diodes -LEDs not shown) to indicate the power being generated by the athlete's efforts. The greater the effort expended in forcing the armature coils 97 along the stator 22, the more in number and/or brightness are the bulbs or LEDs lit up by him/her. This provides an instantaneous visual feedback to the athlete (as well as to any others observing his/her physical strength and prowess). A second function is to display in joules, as shown at 98, the instantaneous -or averaged- energy being generated. A third function is supply the generated electricity to dissipation means, as shown at 99.

The light bulb/LED display 96 naturally provides the athlete -by way of visual feedback- with a certain motivation to perform better, but this may be quite considerably increased by a fourth function of the control system. A card reader 100 is used to register the gym member using the apparatus, and records on his card and/or transmits to a central recording computer, the kilowatt hours dissipated over any given training session. The member may receive reward points according to his/her recorded efforts when working out.

Referring to Fig 18, rather than connecting the armature 98 to external display means, as shown in Fig 17, these may instead be mounted directly upon the armature as shown at 101. In this case, a light emitting diode (LED) strip 102 is mounted vertically along the length of the armature, and indicates the training force being exerted by successively lighting up the LEDs 102. In addition, an electronic control unit for controlling the flow of eddy currents induced in the armature coils, and thus the opposing force provided to the user, may similarly be mounted upon the armature, as shown at 103. Fitted on this are switches 104, 105 and 106, operable to control the mark space ratio of a switching signal 107, used to control the gates of switching field effect transistors (FETs) 108, as shown. These are connected across the coils of the armature as shown. (Their ac output may conveniently be first rectified, not shown, for feeding DC in switchable form across the FETs.) By this means, a self contained training module is presented, especially attractive for home-based training systems.

Referring to Fig 19, a method is shown schematically of using an armature formed from coils to present a vibrating force to the user. The variation in field strength along the length of the stator is shown schematically at 109, as is the emf induced at 110. As explained hereinbefore with reference to Fig 11, the opposing force generated is the product of the generated emf E and the field strength F causing it. When these waveforms are both substantially sinusoidal, their product varies as the square of the sine of these two signals. To obtain a vibration force, only one set of coils is short circuited . In this case, the cosine squared component of the opposing force (as again shown in Fig 11) is absent. This results in a considerably uneven opposing force 111, directly felt by the user, and which can advantageously facilitate the accelerated

development of muscle tissue.

Numerous variations will be apparent to those skilled in the art.

Claims

1. Resistance training apparatus comprising a linear electromagnetic assembly in which an armature, formed from one or more electrical conductors, is disposed for linear travel relative to an elongate stator wherein the user of the apparatus may, in use, exert an exercise force in the direction of travel of one or both of the armature and the stator, the arrangement being such that electrical currents circulating within the armature and the interaction of the magnetic fields arising therefrom with those provided by the stator, serve to provide an opposing force against the exercise force, wherein the said opposing force is caused to arise as a result of movement enforced by the user of the armature relative to the stator, and thus the induction of eddy currents in the armature, characterised in that the armature is constructed and arranged such that the eddy currents circulate around a complete circuit within the training apparatus.

2. Resistance training apparatus according to claim 1, in which the elongate stator thereof comprises a series of permanent magnets arranged such as to produce a sequence of fields of alternating flux polarity along the direction of travel of the armature.

3. Resistance training apparatus according to any of the preceding claims in which the opposing force experienced by the user is substantially proportional to the rate at which the user causes the armature to move relative to the stator.

4. Resistance training apparatus according to any of the preceding claims in which the stator of the linear electromagnetic assembly comprises a tube housing a series of axially magnetised cylindrical permanent magnets, arranged in such manner that their like poles are facing.

5. Resistance training apparatus according to claim 4 in which the magnets are each separated from their neighbouring magnets by a ferromagnetic spacer.

6. Resistance training apparatus according to any one of the preceding claims in which the armature of the linear

electromagnetic assembly comprises an electrically conductive tubular sleeve for travelling co-axially along the length of the stator, the conductive annulus provided by the sleeve acting as a short circuited turn to provide the circuit for the circulation of eddy currents therein and the generation of the opposing force.

7. Resistance training apparatus according to claim 6 in which the sleeve can be connected to the member on which the user is exercising force.

8. Resistance training apparatus according to claim 6 in which the sleeve is affixed directly to the member on which the user is exercising force.

9. Resistance training apparatus according to claim 6 in which an intermediate connecting member is used to convey force exercised by the user to the sleeve.

10. Resistance training apparatus according to claim 6 in which coarse adjustment to the force experienced by the user is obtained by varying the effective overall length of the sleeve.

11. Resistance training apparatus according to claim 10 in which the sleeve may comprise a number of smaller discrete lengths or sub- sleeves, each providing a short circuited turn to provide the circuit, the number of which caused to be displaced along the length of the stator being selectable by linkage/coupling means.

12. Resistance training apparatus according to any of claims 6 to 11 in which the length of the sleeve or sub-sleeve is within +-5% of the length of half a full magnetic pole pitch in the direction of travel, or to integral multiples thereof.

13. Resistance training apparatus according to any of the preceding claims, in which the force experienced may be regulated by the adjustment of the effective width of an air gap between the armature and the stator thereof.

14. Resistance training apparatus according to claims 6 to 13 in which the sleeve or sub sleeve is split along its length in the direction of travel in one or more places to permit the spacing between the armature and stator to be adjusted by the user.

15. Resistance training apparatus according to claim 6 to 14 in which the sleeve or its sub-sleeves, is in the form of a finned extrusion .

16. Resistance training apparatus according to any of the preceding claims in which the electromagnetic assembly and/or its mountings, is/are adapted with fixing points and/or brackets to enable the same to be affixed to a wall or similar structure.

17. Resistance training apparatus according to any of the preceding claims in which sensors are provided for detecting the force exerted by the user in causing relative movement between the armature and the stator.

18. Resistance training apparatus according to claims 1 to 5 in which the armature of the linear electromagnetic assembly

comprises a series of annular electrical coils arranged coaxially together in a stack so as to form a cylindrical sleeve for travelling along the length of the stator.

19. Resistance training apparatus according to claim 18 comprising a short-circuiter for short circuiting the coils of the armature to provide the circuit for the circulation of eddy currents.

20. Resistance training apparatus according to claim 19 wherein the short-circuiter is adapted to allow the user to select the number of coils short circuited and thereby the length of the circuit.

21. Resistance training apparatus according to claim 18,19 or 20 in which the coils are positioned contiguously or spaced apart, but in either case such that the magnetic pitch of the coils matches substantially the magnetic pitch of the stator magnets.

22. Resistance training apparatus according to claims 18-21 in which the disposition and sizing of the permanent magnets in the stator, and, as determined therefrom, the axial length and sizing of each coil comprising the armature, is selected such that the instantaneous back-electromotive force arising from the product of the current generated in any one phase of the generator and the intensity of the flux causing the said current, added to the back electromotive forces arising from the products of the currents generated in other phases of the armature and similarly the intensity of the flux causing those said currents, is substantially constant.

23 Resistance training apparatus according to any of claims 18 to 22, in which the flow of currents generated in the armature coils over a given stroke is regulated and/or profiled by a regulator such as to adjust to the desired extent the degree of resistance

encountered by the user and/or its direction.

24 Resistance training apparatus according to claim 23 in which the said flow of currents may also be varied by the regulator from one exercise or set of exercises to the next.

25 Resistance training apparatus according to claims 18-24 further comprising at least one switch for controlling the flow of currents generated in the armature coils according to the direction of travel of the armature relative to the stator.

26 Resistance training apparatus according to any of claims 18 to 25 further comprising a regulator for actively feeding commutated currents to the coils of the armature such as to provide a return force to the user in a direction opposite to the opposing force within a range of relative longitudinal positions of the armature and stator, irrespective of relative movement between the armature and the stator.

27. Resistance training apparatus according to claim 26 further comprising a circuit breaker for breaking the complete circuit when the regulator actively feeds commutated currents to the coils.

28. Resistance training apparatus according to any of claims 25, 26 or 27, in which the flow of currents fed by the regulator to the coils of the armature is regulated and/or profiled to provide to the desired extent the degree of resistance encountered and/or its direction.

29. Resistance training apparatus according to any of claims 26-28 in which the regulator may pre-position the armature at a

predefined location relative to the stator.

30. Resistance training apparatus according to any of claims 26-29 in which the apparatus is arranged such that for one cycle of an exercise comprising a first stroke and a return stroke, during the first stroke the resistance apparatus operates in a passive mode in which eddy currents circulate around the complete circuit, and on the return stroke, operates in an active mode in which the regulator actively feeds commutated currents.

31. Resistance training apparatus according to any of the preceding claims in which a ferromagnetic sleeve is affixed coaxially over the armature of the apparatus for travelling with it and in such manner as to enhance the flux coupling of the stator with the armature.

32. Resistance training apparatus according to claim 31 in which one or more portions of the sleeve is/are profiled such as to reduce any cogging effects.

33. Resistance training apparatus according to claims 1-32 in which a ferromagnetic sleeve is located coaxially over the stator and substantially the length of travel of the armature, but with an air gap between the two such as to allow free passage of the armature.

34. Resistance training apparatus according to any of the preceding claims in which a shroud is positioned around the operative components of the apparatus, but sufficiently spaced therefrom to ensure any externally detectable magnetic field is within safe limits.

35. Resistance training apparatus according to claims 18-34 in which the apparatus incorporates a device for recognizing the user using the apparatus, and records or effects the recording, of the kWH dissipated by the efforts of the user over any given period.

36. Resistance training apparatus according to claims 18-35 incorporating a device for incrementing a user specific variable reflecting the number of kWH dissipated.

37. Resistance training apparatus according to claims 18-36 in which one or more display devices are used to indicate the rate of effort expended by the user in exercising on the apparatus and/or the overall kWH -or its equivalent- dissipated by the efforts of the user over any given period.

38 .Resistance training apparatus according to claims 35 and 37 in which any controller used to regulate the flow of eddy currents generated within the armature and any performance display device, together with any battery storage means necessary to power the same, are together mounted upon the travelling armature.

39. Resistance training apparatus according to any of claims 18 to 38 in which, in use, selected coils of one phase may be fully or substantially short-circuited, and coils of the remaining phase(s) left fully or substantially open circuited.

40. Resistance training apparatus according to any of the preceding claims further comprising a circuit length adjuster for user selection of the total length of the complete circuit in the armature.

41. A method of exercising and/or the development of muscle using a resistance training apparatus comprising exerting an exercise force in the direction of travel of one or both of an armature of the resistance training apparatus and/or the stator of the resistance training apparatus, in which the armature is formed from one or more electrical conductors, and is disposed for linear travel relative to the stator, wherein magnetic fields arising from electrical currents circulating within the armature interact with magnetic fields provided by the stator thereby providing an opposing force against the exercise force wherein the said opposing force is caused to arise as a result of movement of the armature relative to the stator enforced by the exercise force exerted by the user and thus the induction of eddy currents in the armature, characterised in that the eddy currents circulate around a complete circuit within the resistance training apparatus.