GB2403030A

GB2403030A - Magnetic suspension system

Info

Publication number: GB2403030A
Application number: GB0314487A
Authority: GB
Inventors: Guan Long Dong; David Lodge; Gabriel Louis Joachim
Original assignee: IFO
Current assignee: IFO
Priority date: 2003-06-20
Filing date: 2003-06-20
Publication date: 2004-12-22
Anticipated expiration: 2023-06-20
Also published as: GB2403030B; GB0314487D0

Abstract

A method of positioning an object 5 which is to be suspended in a magnetic suspension system. The magnetic suspension system comprises a supporting frame having an upper station 4 containing a permanent magnet 9, an electromagnet 6 and a sensor coil 7. The object 5 contains a second permanent magnet 10. The method comprises providing a spacer comprising first 41 and second 42 discrete spacing portions. The first spacing portion 41 is interposed between the object 5 and the upper station 4. The suspension system is then calibrated. The second spacing portion 42 is then interposed between the object 5 and the upper station 4 and the second spacing portion 42 is removed.

Description

MAGNETIC SUSPENSION SYSTEM

Field of the Invention

The present invention relates to a method of positioning an object to be suspended in a magnetic suspension system, as well as a spacer system for use therefor. The present invention also relates to a magnetic suspension system, a kit for use therewith and a calibration system therefor.

Background to the Invention

Magnetic suspension systems are known in the art and can be used for display purposes such as advertising or commercial displays; and/or educational purposes such as spinning globes.

A theoretically ideal system of this type would have a fixed support having an upper station containing a permanent magnet and a suspended object also having a permanent magnet and floating below the upper station of the fixed support. The permanent magnets are configured so as to attract one another in an upwards direction, countering the downwards gravitational force on the object. Hence a theoretical balance point is defined whereby in the absence of any external influences, controllers or fluctuations in the magnetic and gravitational forces, the object would be held steady in mid-air.

In fact, such a balance point is virtually impossible to maintain and so control systems are applied. For example DE 4210741, discloses a control system whereby fluctuations in the field provided by the permanent magnet in the object are interpreted by field effect sensors, and consequently the current to an additional electromagnet in the support frame is adjusted to provide an attractive or repelling force in order to prevent the object moving away from the balance point.

US 6,154,353 discloses such a system modified by the fact that the permanent magnets provide an attractive upwards force on the object slightly greater than the downwards force due to gravity. In this case the electromagnet in the upper station of the fixed support is employed to provide a small repelling force to provide a fine balance and establish what is called "a dynamic balance point" herein.

If the object moves away from this dynamic balance point, stationary sensors detect the change in the field caused by the positional variation of the permanent magnet in the object. If the field rises above a predetermined level the current to the electromagnet is increased and the repelling force consequently increases to push the object downwards. By extension, if the field falls below a certain value the current in the electromagnet is decreased such that the repelling force is reduced and the object is pulled upwards.

A dynamic balance point may also be established below the theoretical balance point such that the electromagnet provides an additional attracting force acting on the object's permanent magnet. This type of system is disclosed in GB Application 0213991.3.

In either system there is a discrete zone within which the object can be placed, such that the electronic control system of the apparatus can be turned on and capture the object and prevent it from falling to the ground or rising irrevocably to the upper I station of the device. The problem with such systems is that, in practice the user of the apparatus requires a degree of skill and practice to (a) place the object in the correct position (triggering the system to turn on); (b) release the object without imparting a force which might send the object out of the "control zone"; and (c) calibrate the apparatus.

Calibration for a typical magnetic suspension system consists of adjusting the electronic control circuit to activate the electromagnet control current at the proper time, that is, when the object is at the proper control zone position the system can be turned on. Another facet of the calibration procedure is the adjustment of the control circuit to the correct gain of the feedback loop, that is, the amount of attracting or repelling current needed per unit displacement of the object from the dynamic balance point.

The present invention seeks to alleviate one or more of the above problems.

Summary of the Invention

The current invention provides a spacer which has two functions allowing an object containing a permanent magnet to be suspended in a magnetic suspension apparatus with relatively little skill.

The first function of the spacer is to calibrate the apparatus to support the said object and establish the dynamic balance point. The second function of the spacer is to define a position for placement of the object such that the object will be captured by the apparatus and will not fall groundwards or rise irrevocably to contact the upper station of the device.

A variety of configurations of such a spacer are disclosed.

A further aspect of the invention is the facility to calibrate a single suspension system to a variety of different objects such that the suspended objects may be interchanged with ease.

Thus the current invention is an improvement on the functionality of magnetic suspension systems for use in the hands of non-skilled users. More specifically the invention is a spacer and a method for using the spacer to calibrate the apparatus and to set an object in the correct position in mid-air.

Figures In order that the present invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the prior art and the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig 1 is a general representation of a typical magnetic suspension system; Fig 2 is a cross sectional view of the upper station of a prior art system; Fig 3 is a cross sectional view of a theoretical system with the object held at the theoretical balance point; Fig 4 is a cross sectional view of a prior art system with the object held at a dynamic balance point above the theoretical balance point; Fig 5 is a cross sectional view of a system with the object held at a dynamic balance point below the theoretical balance point; Fig 6 is a cross sectional schematic view of a control zone within which a stationary object will be captured; Fig 7 is a perspective view of the first embodiment of a spacer according to the present invention; Fig 8 is a side view of a magnetic suspension system showing the operation of calibration spacing in accordance with one embodiment of the invention; Fig 9 is a side view of a magnetic suspension system showing the operation of the spacer to suspend the object in accordance with one embodiment of the invention; Fig 10 is a perspective view of an embodiment of a spacer for use with multiple objects; Fig 11 is a perspective view of a further embodiment of a spacer for use with multiple objects; Fig 12 is a perspective view of a third embodiment of a spacer for use with multiple objects; Fig 13 is a perspective view of a second embodiment of a spacer for use with a single object; Fig 14 is a block diagram showing an electronic circuit for holding an object at a dynamic balance point within a magnetic suspension system; and Fig 15 is a block diagram illustrating the control features of the calibration and suspension system, which are used in conjunction with the spacer embodiments.

Detailed Description

Fig 1 shows a typical manifestation of a magnetic suspension device. The frame (1) is divided into a stand (2), an arm (3) and a head unit (4). These may be constructed integrally or from several joined components. An object (5) is suspended below the head unit.

Fig 2 is a cross section of an embodiment of the unit demonstrated in Fig 1. Inside the head unit (4) is an air core electromagnet (6) which is controlled by a power application circuit which will be described later. A first permanent magnet (9) is mounted within the inner diameter of the electromagnet. Two magnetic field sensor coils (7) and (8) are mounted within the inner diameter of the permanent magnet (9) which in this example is of the ring or "doughnut" type. The windings of the electromagnet and the two sensor coils are coaxial and the axis of magnetization of the permanent magnet is substantially vertical.

The object (5) contains a second pemmanent magnet (10) which is orientated such that the two permanent magnets (9) and (10) are attracted to one another.

The sensor coils (7) and (8) serve to detect the strength of the magnetic field of permanent magnet (10) via suitable signal conditioning circuitry. Alternatively, sensors (7) and (8) may be any other type, e.g., hall sensors, flux gate sensors. etc. Fig 3 illustrates the concept of the theoretical balance point. In this theoretical example the electromagnet is switched off, the B field detector means is not shown, and permanent magnet (9) is a simple cylinder. The upwards force F1 provided by the attraction between the two permanent magnets (9) and (10) is exactly balanced by the downwards force F2 provided by the acceleration due to gravity acting on the object (5).

It is impractical under normal circumstances to provide a magnetic suspension unit which utilises the theoretical balance point to suspend an object, with power to the electromagnet normally off. This can be understood intuitively by seeing firstly it is very difficult to place the object exactly in position without any residual movement or forces on the object. Secondly, any perturbation or fluctuation in the ambient magnetic or gravitational fields or random microscopic motion of the object will result in an always decreasing or increasing upwards force on the object. Initial upward motion propels the object magnet towards the upper magnet. Conversely initial downward motion causes gravity always to be stronger than the decreasing upward magnetic pull, thus the object falls.

Fig 4 shows a prior art system (utilizing ferromagnetic flux line concentrators (9a) and I (1 Oa) ) whereby a dynamic balance point is established slightly above the theoretical balance point. To counter the increased attraction between the two permanent magnets (9) and (10) a small amount of current is caused to flow through the coil of I the electromagnet which establishes a repelling force between the electromagnet and the second permanent magnet (10) in the object (5). In this system the upwards force F3 caused by the attraction between the permanent magnets (9) and (10) is balanced by the sum of the downwards force F2 due to gravity and the repelling force F4 between the electromagnet (6) and the second permanent magnet (10).

In summary:

F1 = F2 to define the theoretical balance point F3 = F2 + F4 to define a dynamic balance point.

Still referring to Fig 4 it will be appreciated that in the steady state a small current is required to flow through the coils of the electromagnet (6) to maintain repelling force F4. If for any reason the steady state is disturbed the object might move either upwards or downwards from the dynamic balance point. When the object moves upwards the field (as detected by a sensor means (not shown) in the head unit), emanating from the second permanent magnet (10) in the object increases. When this increase reaches a certain value the current through the electromagnet is caused to increase, thus increasing the repelling force and pushing the object back downwards to the dynamic balance point. Conversely when the object moves downwards the field detected by the sensor means decreases. When this decrease satisfies predetermined conditions the current through the electromagnet is caused to reduce (or reverse) in such a way that the repelling force between magnet (10) and electromagnet (6) decreases and the object is restored to the dynamic balance point under the influence of the attraction between the permanent magnets (9) and (10) and the electromagnet (6).

Thus it can be seen that with a suitable control system, the object can be held substantially at a dynamic balance point indefinitely.

Fig 5 is a schematic of a different embodiment whereby the dynamic balance point is I located below the theoretical balance point. In this case the current through the windings of the electromagnet (6) flows in the reverse direction to that of Fig 4 to create an attractive force F5 between the electromagnet and the permanent magnet I (10) on the object. The electromagnet (6) is shown placed within the inner diameter of ring permanent magnet (10) and serves as an example of an alternative geometry to that shown in Fig 2. Sense coils (7) and (8) are placed around the outer diameter permanent magnet (10), also by way of example.

Because the object (5) is further from the head unit (4) containing permanent magnet (9) the attractive force F6 between the permanent magnets (9) and (10) is less than in the prior art example shown in Fig 4. In this case the dynamic balance point is defined by: F5+F6=F2 Where F2 is the gravitational force acting on the object.

In this embodiment of the invention the control system for the current passing through the windings of the electromagnet is substantially the same, except that when the object goes below the dynamic balance point (i. e. starts to fall) the current is caused to increase in such a way that dynamic balance is restored. When the object goes above the dynamic balance point the current is caused to reduce (or reverse).

In both of the above types of system, the range within which the system can control the object can be increased if the current through the electromagnetic coil can be reversed. Thus in the first system (Fig 4), where the dynamic balance point is above the theoretical balance point, if the object moves below the theoretical balance point for any reason, a reversed current through the coil (6) can be employed to retrieve the object and pull it back above the theoretical balance point. Similarly in the second system (Fig 5), if the object reaches a point above the theoretical balance point, a reversal of the current in electromagnet (6) can be employed to repel the object back below the theoretical balance point.

In practice, most modern systems have electromagnets with either one coil and means to send current in two directions; or two coils with mutually alternative current directions, so that the range of the control zone can be thus increased.

In any system, whether employing reversible current coils or not, there is an inherent zone wherein the object can be retained. If the object moves outside of such a "control zone" it will move irrevocably either down to the lower supporting surface under the influence of gravity; or up to the upper station under the primary influence of the two permanent magnets. Fig 6 illustrates such a control zone. The upper and lower vertical position limits reflect the minimum (or maximum reversed) and maximum value of current delivered to the electromagnet.

Objects of different mass or geometry will have different theoretical balance points and different control zones. The system of the current invention has a calibration mechanism that will import the dynamic balance point of the selected object, preferably a fixed fraction of the control zone below the theoretical balance point, typically 10%.

Any object and frame combination will have a defined theoretical balance point where the gravitational pull on the object is exactly balanced by the attraction between the permanent magnets in the upper station of the frame and the object respectively (see Fig 3). Furthermore, for a "below" system, there will be defined a desired dynamic balance point at which the electromagnet in the upper station of the frame will be supplied with a steady DC bias current to generate the extra force F5 and hold the object stably. Furthermore there will be an ideal mounting position where the object can be positioned, such that the control mechanism will be able to switch to the "on" state, capture the object and restore it to the dynamic balance point Thus in embodiments of the current invention, any given object which is provided with a permanent magnet in the upper region and is designed for use in a compatible suspension system, will be provided with a spacer which is precisely matched to the object in the context of the known suspension system. The spacer has two spacing portions.

Referring to Fig. 7, one embodiment of a spacer is shown. The spacer comprises a first cuboidal portion (41) abutting, at one end, with a second cuboidal portion (42).

The width of the first and second portions (41, 42) is the same but the height of the first portion (41) is greater than the height of the second portion (42). Therefore, while the sides and base of the first and second portions (41, 42) lie flush with one another, there is a step down from the top of the first portion (41) to the top of the second portion (42).

The first portion (41) is used to instruct the control system on the position of the dynamic balance point. This is accomplished by holding the object in position below the head (4) of the frame and using the spacer to set the distance between the lower surface of the head and the upper surface of the object as shown in Fig 8. With the user holding in one hand the object (5) to trap the spacer (41, 42) between the object (below) and the lower surface of the head (above), the user uses his second hand to follow a specified calibration procedure which typically involves manual input to the system e.g., pressing a button or turning a control knob. Typically the apparatus will acknowledge the calibration with an audible and /or visual indicator.

The second portion (42) of the spacer is then used to place the object in a position where the object can be released and will be safely captured by the control system.

As is the case in this embodiment, the second portion is typically narrower than the first as this ensures that when the object is released the attractive force of the two permanent magnets is greater than the downward force of gravity. This makes it easier for the user to accomplish because he/she will feel the upward force and feel confident to release the object. When the user is placing the object in position against the second spacer portion (42) the object will pass upwards through the space which was calibrated and defined by the first spacer portion. At that point the control electronics are triggered to the "on" state. When the object reaches and is touched to the second spacer portion and is then released the control electronics react and push the object into place at the desired dynamic balance point, without gravity taking over and pulling the object so far down that it falls. Fig 9 illustrates the operation of suspending the object using the second spacer portion.

It is to be appreciated that, in this embodiment, the first and second portions (41, 42) are differently sized elements (albeit joined together) that enable the suspension system to be calibrated to the object and the object to be positioned correctly for release. However, in other embodiments only a single element is required. For example, a single cuboidal portion having a height of a first dimension and a width of a second, different dimension can be used. The first dimension is used for the calibration step and the second dimension is used for the positioning step.

It will be appreciated that the more objects which the user accumulates for a given system, the more different pairs of spacers might be required, although it is sometimes possible to use different objects with the same spacer depending on the mass of the object and the volume and strength of the magnet in the object.

A second spacer embodiment is shown in Fig 10 and consists of two back to back units similar to that shown in Fig 9, rotatably connected. The spacer comprises first and second spacer units (45,46). The first spacer unit (45) comprises a first cuboidal portion (47), one end of which abuts the end of a second cuboidal portion (48). The second spacer unit comprises a third cuboidal portion (49), one end of which abuts one end of a fourth cuboidal portion (50). The two spacer units (45,46) are arranged on top of one another and an axle (51) extends between the first cuboidal portion (47) of the first spacer unit (45) to the third cuboidal portion (49) of the second spacer unit (46) such that the first and second spacer units, (45,46) are rotatable with respect to one another. As in the previous embodiment, the base of the first and second cuboidal portions (47,48) lie flush with one another and there is a step down from the top of the first cuboidal portion (47) to the top of the second cuboidal portion (48). Conversely, the tops of the third and fourth cuboidal portions (49,50) lie flush with one another and there is a step up from the base of the third cuboidal portion (49) to the base of the second cuboidal portion (50).

Although the length of the first, second and third cuboidal portions (47 to 50) are the same, they each have different heights and widths. The heights and widths of the respective cuboidal portions are shown in Figure 10 and can be summarised as follows.

A = height of first cuboidal unit (47), B = height of third cuboidal unit (49), C = height of second cuboidal unit (48), D = height of fourth cuboidal unit (50), E = width of first cuboidal unit (47), F = width of third cuboidal unit (49), G = width of second cuboidal unit (48), H = width of fourth cuboidal unit (50).

Each of the portions can be used for either the calibration operation or the suspension operation for a given object in a given suspension frame. Furthermore, dimension A can be added to B or D by mutual rotation of the first and third cuboidal portions (47,49); and similarly C can be added to B or D. Thus 12 different spacing combinations can be achieved from a single unit: A, B. C, D, E, F. G. H. A+B, A+D, C+B, C+D. This spacer can be fabricated from plastic, wood or any other (preferably non metallic) material.

A third embodiment is shown in Fig 11 and is of feeler gauge construction. The spacer (52) comprises first and second stacks (53, 54) of elongate leaves. Each stack (53, 54) of leaves is journalled at one end about which each leaf is independently rotatable. Each leaf of the unit rotates out of a housing (not shown) and has an appropriate dimension either as a calibration spacer or a positioning spacer for a given object and frame combination. It is used in exactly the same way as illustrated in Figs 8 and 9.

A fourth embodiment, which is shown in Figure 12 is a telescopic unit which can be extended to a required dimension within a given range. It consists of two barrels, inner (43) and outer (44) threaded one into the other as shown in Fig 12. A scale (45) on the inner barrel (43) read against the bottom edge of a window in the outer barrel (44) states the total dimension in the extendable direction and thus provide the correct spacing for the purpose.

A fifth embodiment of a spacer is shown in Fig.13. In this embodiment, the spacer comprises first (41) and second (42) cuboidal portions, abutting one another end to end. In this embodiment, the height and width of the second cuboidal portion (42) are less than the height and width of the first cuboidal portion (41). Each pair of opposing faces of the first and second cuboidal portions (41, 42) defines different dimensions.

Fig 14 illustrates the control circuit which holds the object in a state of levitation below the theoretical balance point. It will be appreciated that the functions outlined can be implemented via analogue circuitry or coded as numerical processing algorithms running on a Digital Signal Processor IC or a microprocessor IC; the appropriate digital/analogue inpuVoutput conversions derivable by those skilled in the art.

Coil sensor signals V7 and V8 are fed to a difference amplifier (20) whose output is integrated by leaky integrator (21) in order to transform the AC nature of the sensors' induced voltage signal to a quasi-DC signal with a decay constant of about 20 seconds. A portion of the signal from integrator (21) is summed via summation block (23) with a time differentiated portion, differentiator (22)'s output, to yield the object position plus velocity signal. One input of differential amplifier (24) is fed by the summation output (23). The output of differential amplifier (24) is fed to a power amplifier controller (25) which exercises a well-known algorithm based on the object's position and velocity status. The power controller (25) drives a power amplifier (26) to excite electromagnet (6) with the proper amount and direction of restoring force current to keep the object levitated. The power amplifier may be of any conventional type, e.g., bipolar dual-supply or single supply H-bridge types.

Each of these types may vary the current in a linear fashion or via pulse width modulation control.

The low frequency differential voltage variations e.g., less than 30 Hz, across electromagnet (6) are detected by differential amplifier (27) whose output is fed to leaky integrator (28). The time constant of integrator (28) is longer than that of integrator (21), and is summed with a DC bias level in summation block (29). Thus the output of (29) serves to set the reference level of current in electromagnet (6) to which the system will settle. If the DC bias is zero, the levitated object will be held with microscopic fluctuations very near the theoretical balance point. A constant DC bias of one polarity causes the system to settle at a dynamic balance point above the theoretical point; the opposite polarity causes the dynamic balance point to be at the preferred position below the theoretical balance point.

Fig 15 is a block diagram of the calibration circuit. Calibration is a system mode distinct from the normal operational mode, the user puts the system into calibration mode via a form of input, i.e. using the first portion (41) of the spacer as shown in Fig 8.

The levitation system with no object floating is normally held in a standby state, i.e., integrators (21) and (28) are continuously held in the reset state, their outputs are zero and the control system is effectively disabled and zero current is delivered to the power coil electromagnet (6). After entering calibration mode the object approaches the head from below, diff amp (20) amplifies the magnetic field rate of change signal and delivers a level to comparator (30) and when it exceeds a small fixed threshold the comparator (30) latches to the enable state of integrator (21). As the object approaches nearer to the head the integrator output increases. When the object comes to rest against the spacer, set to the dynamic balance point, a variable threshold level may be adjusted from high to low until it matches the object level, and at that point comparator (31) changes state, an audible/visual indicator is activated, and the level value is stored. Alternatively a button may be pressed to store the object level value, or in a further embodiment the system may determine that the object has come to rest against the spacer by detecting that there has been no rate of change of the object level for a few seconds and then automatically store the value. This level value reflects the strength of the magnetic field from the object magnet strength and gap (distance from the head) combination, and is used to set the gain of diff amp (20) which effectively sets the system feedback loop gain.

Upon completion of calibration, normal operational mode is active and the system is in the standby state. The system is now ready to capture an object for levitation. This is the point at which the second portion of the spacer is used to space the object from the upper station. When the object is released it will descend slightly and the spacer can be withdrawn, leaving the object stably suspended.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

1. A method of positioning an object to be suspended in a magnetic suspension system wherein the magnetic suspension system comprises a supporting frame having an upper station containing a permanent magnet, an electromagnet and at least one sensor coil and the object contains a second permanent magnet, the method comprising the steps of: providing a spacer comprising at least first and second discrete spacing portions, the spacing portions being matched to the object; interposing the first spacing portion of the spacer between the object and upper station and calibrating the suspension system to the object; interposing the second spacing portion of the spacer between the object and the upper station and thus positioning the object at a position where it will remain suspended when the second spacing portion is removed.

2. A method according to Claim 1 wherein the second spacing portion is smaller in the spacing dimension than the first spacing portion

3. A method according to Claim 1 or 2 wherein each spacing portion comprises a differently sized element and the elements are joined together.

4. A method according to claim 1 or 2 wherein the spacer comprises a single element, at least two of the dimensions of the element being differently sized and each discrete spacing portion corresponding to a dimension of the element.

5. A method according to any one of the preceding claims wherein the spacer comprises more than two discrete spacing portions, and wherein the method further comprises the step of, before interposing the first spacing portion, selecting the first and second discrete spacing portions that are matched to the object to be suspended.

6. A method according to Claim 5 wherein the spacing portions can be used in combination.

7. A spacer system for use with a magnetic suspension system comprising a supporting frame having an upper station containing a permanent magnet, an electromagnet and at least one sensor coil; and at least one object to be suspended, each object containing a second permanent magnet, the spacer system comprising a moveable spacer portion, the spacer portion being moveable so as to increase or decrease the spacing provided, the spacer portion being, in certain positions, for positioning an object for calibrating the suspension system to the object, and in other positions for positioning the same object to a position where the object will remain suspended when the spacer portion is removed.

8. A spacer system according to Claim 7 wherein the moveable spacer portion is telescopic in construction.

9. A spacer system according to claim 7, wherein the moveable spacer portion comprises a plurality of spacing leaves, the spacing leaves being arranged in a stack and journalled together such that each leaf is swingable about the journal independently of the other leaves in the stack so that the leaf protrudes from the stack.

10. A spacer system according to claim 9, further comprising a second spacer portion as defined in claim 9 connected to the first spacer portion.

11. A kit for use with a magnetic suspension system comprising a supporting frame having an upper station containing a permanent magnet, an electromagnet and at least one sensor coil; the kit comprising: an object to be suspended having a second permanent magnet mounted near its upper surface; and a spacer system, having at least two spacer portions, a first spacer portion for use for positioning the object for calibrating the suspension system to the object and a second spacer portion for positioning the object to remain suspended from the suspension system.

12. A magnetic suspension system comprising: a supporting frame having an upper station containing a permanent magnet, an electromagnet and at least one sensor coil; an object having a second permanent magnet mounted near its upper surface and which is designed to suspend unsupported from the upper station; and a spacer system having at least two spacer portions, the first spacer portion being for positioning the object for calibrating the suspension system to the object and the second spacer portion being for positioning the object at a position where the object will remain suspended when the second spacing portion is removed.

13. A kit according to claim 1 1 or a magnetic suspension system according to claim 12, wherein the spacer system is a spacer system according to any one of claims 7 to 10.

14. A calibration system for a magnetic suspension system comprising a supporting frame having an upper station containing a permanent magnet, an electromagnet and at least one sensor coil; and an object having a second permanent magnet mounted near its upper surface, which is designed to suspend unsupported from the upper station at a balancing position wherein the electromagnet is calibratable to support a particular object, the calibration system comprising: positioning means comprising a plurality of spacer portions; and detection means in the upper station to determine that the object has been placed in a balancing position.

15. A calibration system according to claim 14 further comprising a visual or audible indicator to confirm that the suspension system has been calibrated to the object.

16. A calibration system according to claim 14 or 15 wherein the means to determine that the object has been placed in a balancing position is a manual input means.

17. A calibration system according to claim 14 or 15 wherein the means to determine that the object has been placed in a balancing position is a detector.