GB2315341A - Controlling the gap between an electromagnet and an armature - Google Patents

Controlling the gap between an electromagnet and an armature Download PDF

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Publication number
GB2315341A
GB2315341A GB9704384A GB9704384A GB2315341A GB 2315341 A GB2315341 A GB 2315341A GB 9704384 A GB9704384 A GB 9704384A GB 9704384 A GB9704384 A GB 9704384A GB 2315341 A GB2315341 A GB 2315341A
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GB
United Kingdom
Prior art keywords
electro
magnet
current
gap
flux intensity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB9704384A
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GB2315341B (en
GB9704384D0 (en
Inventor
Malcolm Alexander Swinbanks
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems Electronics Ltd
Original Assignee
GEC Marconi Ltd
Marconi Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB9604429.2A external-priority patent/GB9604429D0/en
Application filed by GEC Marconi Ltd, Marconi Co Ltd filed Critical GEC Marconi Ltd
Priority to GB9704384A priority Critical patent/GB2315341B/en
Publication of GB9704384D0 publication Critical patent/GB9704384D0/en
Publication of GB2315341A publication Critical patent/GB2315341A/en
Application granted granted Critical
Publication of GB2315341B publication Critical patent/GB2315341B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D3/00—Control of position or direction
    • G05D3/12—Control of position or direction using feedback
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37389—Magnetic flux
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37425—Distance, range
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/42—Servomotor, servo controller kind till VSS
    • G05B2219/42065—Feedforward combined with pid feedback
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/49—Nc machine tool, till multiple
    • G05B2219/49276—Floating, air, magnetic suspension xy table, sawyer motor, xenetics

Abstract

An electro-magnet (11) is spatially coupled with respect to a support armature (15) by an operational gap (16) and their relative movement is automatically compensated by controlling a current (14) supplied to the electro-magnet (11). The current (14) and hence a magnetic field (F) are controlled by a current controller (13) which incorporates a transfer function and is operated in a feedforward path (19) by a signal (18) from a sensor (17) which detects variations in the gap (16) between the electro-magnet (11) and the support armature (12). The current controller (13) is also operated in a feedback path (22) by a signal (21) from a sensor (20) which detects variations in the flux intensity of the magnetic field (F). The operation of the current controller (18) by the sensors (17 and 20) controls the force by which the support armature (15) is attracted towards the electro-magnet (11), whilst maintaining the gap (16) at a desired value and inhibiting the transmission of vibration between the support armature (15) and the electro-magnet (11).

Description

APPARATUS AND METHOD FOR SPATIALLY COUPLING AN ELECTRO-MAGNET TO A SUPPORT ARMATURE This invention relates to an apparatus and method for spatially coupling an electromagnet to a support armature such that movement of either the electro-magnetic or support armature is automatically compensated for so that such movement is not substantially transferred between the electro-magnet or the support armature. Such apparatus are often referred to as support actuators.
At present, it is possible to couple a base to a vibrating load support armature using an electro-magnet mounted to the base, the electro-magnet when energised with a suitable fixed current produces a magnetic field which exerts an attraction force on the support armature so as to attract the support armature towards the electro-magnet when the support armature is positioned within the magnetic field. It should be understood that there is a physical gap between the support armature and the electro-magnet.
An electro-magnet can be considered as a dual input, single output device. The output being the attraction force exerted by the magnetic field on the support armature. The attraction force is dependent on the inputs, the first being a current which is used to energise the electro-magnet and the second being dependent on the magnitude of the gap. For example, the attraction force exerted on the support armature increases as the support armature is positioned closer to the electro-magnet, e.g. the magnitude of the gap is reduced, and decreases as it is positioned further from the electro-magnet, e.g. the magnitude of the gap is increased. The attraction force exerted by an electro-magnet on a support armature is analogous to a strong negative spring.
It is common practice to employ high gain feedback control on the electro-magnet in an attempt to convert the strong negative spring into a weak negative spring so that more precise control of the attraction force of the electro-magnet can be applied.
However, such high gain feedback cannot be maintained over an infinite bandwidth and in practice the gain of the feedback must ultimately roll-off towards zero with increasing frequency. The result of the roll off effect causes a change in phase and the weak negative spring then tends to behave more like a negative damper. This feeds energy into variations in the gap which can readily excite any structural resonance in the roll off frequency range. This in turn generates undesirable force variations on the support armature.
It is the object of this invention to obviate or mitigate this disadvantage.
According to a first aspect of the present invention there is provided an apparatus, comprising a current controller operable to produce a variable current, an electro-magnet connected to receive the variable current and to generate a magnetic field having a flux intensity dependant on the variable current, a support armature separated from the electro-magnet by an operational gap and supported by the magnetic field, a first control means arranged to detect variation in the operational gap and to operate the current controller dependant on variation in the operational gap, a second control means arranged to detect variation of the flux intensity and to operate the current controller dependant on variation of the flux intensity, and the first control means and the second control means being arranged to vary the current in the electro-magnet whereby the flux intensity of the magnetic field will maintain the operational gap substantially constant.
Preferably, the first control means may comprise a gap sensor arranged to detect variation in the operational gap, the first control means may also be arranged to generated a first control signal dependant on variation in the operational gap, and the first control signal may be arranged to operate the current controller. The first control means may be arranged in a feedforward path from the gap sensor to the current controller.
Preferably, the second control means may comprise a flux sensor arranged to detect the variation in the flux intensity, the second control means may also be arranged to generate a second control signal dependant on variation in the flux intensity, and the second control signal may be arranged to operate the current controller. The second control means may be arranged in a feedback path from the flux sensor to the current controller Operation of the controller may be determined by a transfer function of a relationship between the first control signal, the second control signal and the variable current applied to the electro-magnet, and the current controller may be arranged to produce the variable current dependant on the transfer function.
According to a second aspect of the present invention there is provided an apparatus for isolating vibration between a load and a support structure, comprising a current controller operable to produce a variable current, an electro-magnet connected to receive the variable current and to generate a magnetic field having a flux intensity dependant on the variable current, a support armature separated from the electro-magnet by an operational gap and supported by the magnetic field, the load supported from the support structure by the magnetic field between the electro-magnet and the support armature, a first control means arranged to detect variations in the operational gap and to operate the current controller dependant on variations in the operation gap, a second control means arranged to detect variations of the flux intensity and to operate the current controller dependant on variations of the flux intensity, and the first control means and the second control means being arranged to vary the current in the electro-magnet whereby the flux intensity of the magnetic field will maintain the operational gap substantially constant and inhibit transmission of vibration therebetween.
According to a third aspect of the present invention there is provided a method of spatially coupling a support armature with respect to an electro-magnet, comprising applying a current to the electro-magnet to generate a magnetic field having a flux intensity dependant on the current, and controlling an operational gap between the armature and the electro-magnet by detecting variation in the operational gap and detecting variation in the flux intensity, and varying the current dependant on the variation in both the operational gap and the flux intensity.
Preferably, the method may also comprise varying the current dependant on a transfer function of a relationship between a. variations in the operational gap, b. variations in the flux intensity, and c. the current applied to the electro-magnet According to a fourth aspect of the present invention there is provided a method of isolating vibration between a load and a support structure, comprising supporting a load from the support structure by a magnetic field across an operation gap between an armature and an electro-magnet, and controlling the operational gap by detecting variation in the operational gap and detecting variations in the flux intensity, and varying flux intensity of the magnetic field dependant on the variation both in the operational gap and the flux intensity.
The positioning and protection of these electro-magnets and support armatures is taught in our co-pending British Applications GB. A [that is British Application 9604973.9] and GB A [that is British Application 9604952.3] both filed on the 8th March 1996, the whole contents of each Application being incorporated herein by reference.
The invention is further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a feedforward section of an apparatus according to the present invention; Figure 2 illustrates a feedback section of the same apparatus, and Figure 3 illustrates a complete apparatus of the present invention comprising both feedforward and feedback sections given in Figures 1 and 2.
Given that an electro-magnet can be operably connected to receive an input current, that the electro-magnet can generate a magnetic field using such input current and that a support armature can be separated from the electro-magnet by an operational gap, the electro-magnet can be considered a dual input, single output device. That is the electromagnet has a single output in the form of a magnetic field having a flux intensity determined by both magnitude of the input current supplied to the electro-magnet and magnitude of the operational gap. For example, if the input current is constant, then variations in the gap will cause variations in the flux intensity of the magnetic field. This effect can be characterised mechanically as a negative spring.
Since the electro-magnet naturally has the characteristics of a negative spring, the electro-magnet is very difficult to control using high gain feedback, especially at high frequencies, due to the roll-off to unity of the gain with increasing frequency. Furthermore phase shifts, associated with the roll-off of the gain with increasing frequency, cause the electro-magnet to behave more like a strong negative damper which feeds energy into variations of the gap. Such negative damping will accordingly result in the electro-magnet transferring vibrations to the support armature. Negative damping will also excite any structural resonance in the roll-off frequency range and will thereby generate force variations on the support armature and consequent instability. The present invention avoids this problem by giving positive mechanical spring characteristics to the electro-magnet.
Referring to Figure 1, apparatus 10 comprises an electro-magnet 11 operably connected to an input current 12 via a current controller 13 and is arranged to generate a magnetic field F having a variable flux intensity according to a variable current 14 supplied by the current controller 13. The flux intensity is controlled to keep the electro-magnet 11 separated from a support armature 15 by an operational gap 16.
This is achieved by operably connecting a gap sensor 17 to the current controller 13, the gap sensor being arranged to produce a first control signal 18 representing variation in the gap 16, and by feeding the first control signal 18 forward along a feedforward control path 19 to the current controller 13 to control the variable current 14. A suitable gap sensor 17 can be any inductive proximity detector which is commercially available.
Referring to Figure 2, the control of the gap 16 can be improved still further by also using a flux sensor 20 to operate the current controller 13. The flux sensor 20 is arranged to detect variations in the flux intensity generated by the magnetic field F of the electromagnet 11 and to produce a high gain second control signal 21 representing the variations.
By feeding back the high gain second control signal 21 along a feedback control path 22 to the current controller 13, precision of control of the magnetic field F is made virtually independent of any variation in the gap 16. A suitable flux sensor 20 can be any Hall effect device which is commercially available.
Operation of the current controller 13 is determined by a transfer function of the observed relationship between the first control signal 18, the second control signal 21 and the variable current 14 applied to the electro-magnet 11 to generate the magnetic field F.
By determining the correct transfer function for the current controller 13, the feedforward control path 19 is biased so that the characteristics of the electro-magnet 11 are radically changed so that it behaves like a weak positive spring with phase shifts associated with increasing frequency causing the electro-magnet 11 to behave like a positive damper.
The feedforward control path 19 can have a very wide bandwidth, but the precision of control is dependent on the precision of the measurements used to determine the transfer function.
The high gain second control signal 21 provided along the feedback control path 22 further modifies the characteristics of the electro-magnet 11 to make it behave like an even weaker positive spring so that, when the high gain second control signal 21 rolls- off with increasing frequency, the associated phase shifts generate positive damping in the electromagnet 11 which extracts energy from any variations in the gap 16 in the roll off frequency range. Therefore any structural resonance in this frequency range will be damped and will not generate force variations on the support armature 15.
Figure 3, illustrates both the feedforward control path 19 and the feedback control path 22 applied to the electro-magnet 11 via the current controller 13, all references are the same as those used in Figures 1 and 2 and the associated description.
Appropriate variation of the current 14 applied to the electro-magnet 11, by using the first control signal 18 and the second control signal 21 to operated the current controller 13, causes the support armature 15 to levitate in a controlled position in the magnetic field F created by the electro-magnet 11. Thereby the electro-magnet 11 and the support armature 12 are coupled at a selected spacing, the operational gap 16, by the attraction of the magnetic field F.
If the support armature 15 is attached to a vibrating load, it will move with respect to the electro-magnet 11 and the gap 16 will vary. Such variations in the gap 16 are detected by the gap sensor 17 and the first control signal 18 is generated depending on the magnitude of variation of the gap 16. The first control signal 18 controls the input current 12 to generate the variable current 14 that in turn varies the strength of the magnet field F generated by the electro-magnet 11 thereby compensating for variations in the gap 16. In this manner the support armature 15 will be returned to its original position relative to the electro-magnet 11 by appropriate variation of the variable current 14.
Greater precision for maintaining the gap 16 can be achieved by providing the high gain second control signal 21 in feedback from the flux sensor 20 in the magnetic field F of the electro-magnet 11 to the current controller 13. Variations in the flux are measured a second control signal 21 is generated according to the variations and is used to vary the current 14 proportionally to the variations in the magnitude of the flux to maintain the gap 16.
The vibrating load may alternatively be attached to the electro-magnet 11 instead of the support armature 15.
This arrangement achieves high stability and, in the frequency range in which both controls are operating, the precision achieved is much higher than could be achieved by either control operating individually.

Claims (12)

1. An apparatus, comprising a current controller operable to produce a variable current, an electro-magnet connected to receive the variable current and to generate a magnetic field having a flux intensity dependant on the variable current, a support armature separated from the electro-magnet by an operational gap and supported by the magnetic field, a first control means arranged to detect variation in the operational gap and to operate the current controller dependant on variation in the operational gap, a second control means arranged to detect variation of the flux intensity and to operate the current controller dependant on variation of the flux intensity, and the first control means and the second control means being arranged to vary the current in the electro-magnet whereby the flux intensity of the magnetic field will maintain the operational gap substantially constant.
2. An apparatus, as in Claim 1, wherein the first control means comprises a gap sensor arranged to detect variation in the operational gap, the first control means also being arranged to generated a first control signal dependant on variation in the operational gap, and the first control signal being arranged to operate the current controller.
3. An apparatus, as in Claims 1 or 2, wherein the first control means is arranged in a feedforward path from the gap sensor to the current controller.
4. An apparatus, as in any preceding claim, wherein the second control means comprises a flux sensor arranged to detect the variation in the flux intensity, the second control means also being arranged to generate a second control signal dependant on variation in the flux intensity, and the second control signal being arranged to operate the current controller.
5. An apparatus, as in any preceding claim, wherein the second control means is arranged in a feedback path from the flux sensor to the current controller
6. An apparatus, as in Claims 2 to 5, wherein operation of the controller is determined by a transfer function of a relationship between the first control signal, the second control signal and the variable current applied to the electro-magnet, and the current controller is arranged to produce the variable current dependant on the transfer function.
7. An apparatus for isolating vibration between a load and a support structure, comprising a current controller operable to produce a variable current, an electro-magnet connected to receive the variable current and to generate a magnetic field having a flux intensity dependant on the variable current, a support armature separated from the electro-magnet by an operational gap and supported by the magnetic field, the load supported from the support structure by the magnetic field between the electro-magnet and the support armature, a first control means arranged to detect variations in the operational gap and to operate the current controller dependant on variations in the operation gap, a second control means arranged to detect variations of the flux intensity and to operate the current controller dependant on variations of the flux intensity, and the first control means and the second control means being arranged to vary the current in the electro-magnet whereby the flux intensity of the magnetic field will maintain the operational gap substantially constant and inhibit transmission of vibration therebetween.
8. An apparatus substantially as described herein with reference to any of the accompanying drawings
9. A method of spatially coupling a support armature with respect to an electro-magnet, comprising applying a current to the electro-magnet to generate a magnetic field having a flux intensity dependant on the current, and controlling an operational gap between the armature and the electro-magnet by detecting variation in the operational gap and detecting variation in the flux intensity, and varying the current dependant on the variation in both the operational gap and the flux intensity.
10. A method, as in Claim 9, comprising varying the current dependant on a transfer function of a relationship between a. variations in the operational gap, b. variations in the flux intensity, and c. the current applied to the electro-magnet.
11. A method of isolating vibration between a load and a support structure, comprising supporting a load from the support structure by a magnetic field across an operational gap between an armature and an electromagnet, and controlling the operational gap by detecting variations in the operational gap and detecting variations in the flux intensity, and varying flux intensity of the magnetic field dependant on the variation both in the operational gap and the flux intensity.
12. A method substantially as described herein with reference to any of the accompanying drawings.
GB9704384A 1996-03-01 1997-03-03 Apparatus and method for spatially coupling an electro-magnet to a support armature Expired - Lifetime GB2315341B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9704384A GB2315341B (en) 1996-03-01 1997-03-03 Apparatus and method for spatially coupling an electro-magnet to a support armature

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9604429.2A GB9604429D0 (en) 1996-03-01 1996-03-01 Support actuator
GB9704384A GB2315341B (en) 1996-03-01 1997-03-03 Apparatus and method for spatially coupling an electro-magnet to a support armature

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GB9704384D0 GB9704384D0 (en) 1997-10-01
GB2315341A true GB2315341A (en) 1998-01-28
GB2315341B GB2315341B (en) 2000-01-12

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GB9704384A Expired - Lifetime GB2315341B (en) 1996-03-01 1997-03-03 Apparatus and method for spatially coupling an electro-magnet to a support armature

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1385212A (en) * 1971-04-19 1975-02-26 Rohr Industries Inc Magnetic suspension and propulsion system
GB2259158A (en) * 1991-08-22 1993-03-03 Mtu Muenchen Gmbh Control device for electromagnetic suspension system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1385212A (en) * 1971-04-19 1975-02-26 Rohr Industries Inc Magnetic suspension and propulsion system
GB2259158A (en) * 1991-08-22 1993-03-03 Mtu Muenchen Gmbh Control device for electromagnetic suspension system

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GB2315341B (en) 2000-01-12
GB9704384D0 (en) 1997-10-01

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732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PE20 Patent expired after termination of 20 years

Expiry date: 20170302