US5823307A — Stiff actuator active vibration isolation system

Claim 1

Independent Claim 192 words

An active vibration isolation system for isolating a payload mass from a source of vibration, said active vibration isolation system comprising: a small mass; at least one stiff actuator having first and second opposed ends and variable in length between the first and second opposed ends, the first end coupled to said small mass and the second end coupled to the source of vibration; a passive isolator interposed between said small mass and said payload mass, wherein said stiff actuator, said small mass and said passive isolator are interposed between said payload mass and the source of vibration; a sensor coupled to said small mass to generate a sensor signal which is a function of the movement of said small mass; and circuitry coupling said sensor to said stiff actuator and receiving said sensor signal, said circuitry including compensation circuitry to alter said sensor signal such that said active vibration isolation system will be stable over a predetermined range of vibration frequencies and payload masses, said circuitry further including control circuitry coupled to said stiff actuator for varying the length of said stiff actuator as a function of said altered sensor signal.

Claim 2

Dependent Claim 192 words

An active vibration isolation system for isolating a payload mass from a source of vibration, said active vibration isolation system comprising: a small mass; at least one stiff actuator having first and second opposed ends and variable in length between the first and second opposed ends, the first end coupled to said small mass and the second end coupled to the source of vibration; a passive isolator interposed between said small mass and said payload mass, wherein said stiff actuator, said small mass and said passive isolator are interposed between said payload mass and the source of vibration; a sensor coupled to said small mass to generate a sensor signal which is a function of the movement of said small mass; and circuitry coupling said sensor to said stiff actuator and receiving said sensor signal, said circuitry including compensation circuitry to alter said sensor signal such that said active vibration isolation system will be stable over a predetermined range of vibration frequencies and payload masses, said circuitry further including control circuitry coupled to said stiff actuator for varying the length of said stiff actuator as a function of said altered sensor signal.

Claim 3

Dependent Claim 59 words

The active vibration isolation system as recited in claim 1, wherein said sensor signal is a velocity signal indicating velocity of said small mass, said circuitry including a velocity integrator for integrating said velocity signal to derive a displacement signal and having an output for said displacement signal, said compensation circuitry coupled to said output of said velocity integrator.

Claim 4

Dependent Claim 26 words

The active vibration isolation system as recited in claim 1, wherein said compensation circuitry includes a DC blocking circuit for blocking DC voltage from said sensor.

Claim 5

Dependent Claim 37 words

The active vibration isolation system as recited in claim 3, wherein said DC blocking circuit has the transfer function: ##EQU11## where S is the LaPlace transform operator and W 1 is a frequency of about 0.3 hertz.

Claim 6

Dependent Claim 58 words

The active vibration isolation system as recited in claim 1, wherein said compensation circuitry includes a lowfrequency compensation circuit with a transfer function: ##EQU12## wherein S is the Laplace transform operator, T C1 is apreselected first time constant and T C2 is a preselected second time constant which is about twenty times shorter than said first time constant.

Claim 7

Dependent Claim 26 words

The active vibration isolation system as recited in claim 5 wherein said sensor has a suspension frequency, T C1 being approximately matched to said suspension frequency.

Claim 8

Dependent Claim 34 words

The active vibration isolation system as recited in claim 1, wherein said compensation circuitry includes a lead phase increase circuit which adds phase lead in the frequency region of resonance of said passive isolator.

Claim 9

Dependent Claim 29 words

The active vibration isolation system as recited in claim 7, wherein said lead phase increase circuit comprises two series-connected analog lead lag stages having two poles and two zeroes.

Claim 10

Dependent Claim 58 words

The active vibration isolation system as recited in claim 1, wherein said compensation circuitry comprises a high frequency gain reduction circuit operating on said sensor signal to reduce the gain thereof to unity at a point in the frequency domain substantially less than the resonance frequency formed by spring constant of said stiff actuator and said small mass.

Claim 11

Dependent Claim 40 words

The active vibration isolation system as recited in claim 9, wherein said high frequency gain reduction circuit has a transfer function: ##EQU13## where S is the LaPlace Transform Operator and 1/TC3 is said unity gain point in the frequency domain.

Claim 12

Dependent Claim 49 words

The active vibration isolation system as recited in claim 10, wherein said high frequency gain reduction circuit comprises two series-connected lag lead circuits each having a pole at a first frequency prior to said unit gain point and a zero at a second frequency after said unity gain point.

Claim 13

Dependent Claim 44 words

The active vibration isolation system as recited in claim 1, wherein said compensation circuitry includes a notch filter circuit having a notch of low gain at a resonance frequency caused by the interaction of said small mass, said payload mass and said passive isolator.

Claim 14

Dependent Claim 208 words

An active vibration isolation system for isolating a payload from movement in first, second and third axes which are orthogonal to each other, said active vibration isolation system comprising: an intermediate mass; first, second and third stiff actuators having variable lengths respectively aligned with the first, second and third axes, each one of the first, second and third stiff actuators having a first end coupled to said intermediate mass and a second end coupled to a support susceptible to vibration; first, second and third sensors coupled to said intermediate mass and operable to sense movement along first, second and third directions, respectively, the first direction parallel with the first axis, the second direction parallel to the second axis, the third direction parallel to the third axis, said first, second and third sensors respectively generating first, second and third sensor signals; and circuitry coupled to said first, second and third sensors for generating a first control signal as a function of the first sensor signal, a second control signal as a function of the second sensor signal and a third control signal as a function of the third sensor signal, wherein the first, second and third control signals respectively govern operation of the first, second and third stiff actuators.

Claim 15

Dependent Claim 208 words

An active vibration isolation system for isolating a payload from movement in first, second and third axes which are orthogonal to each other, said active vibration isolation system comprising: an intermediate mass; first, second and third stiff actuators having variable lengths respectively aligned with the first, second and third axes, each one of the first, second and third stiff actuators having a first end coupled to said intermediate mass and a second end coupled to a support susceptible to vibration; first, second and third sensors coupled to said intermediate mass and operable to sense movement along first, second and third directions, respectively, the first direction parallel with the first axis, the second direction parallel to the second axis, the third direction parallel to the third axis, said first, second and third sensors respectively generating first, second and third sensor signals; and circuitry coupled to said first, second and third sensors for generating a first control signal as a function of the first sensor signal, a second control signal as a function of the second sensor signal and a third control signal as a function of the third sensor signal, wherein the first, second and third control signals respectively govern operation of the first, second and third stiff actuators.

Claim 16

Dependent Claim 33 words

The active vibration isolation system as recited in claim 13, wherein the first end of said first, second and third stiff actuator is coupled to said small mass by a separate shear decoupler.

Claim 17

Independent Claim 128 words

A method of actively isolating a payload from vibration, comprising the steps of: resting the payload on a passive isolator; coupling the passive isolator to a small mass which is at least one order of magnitude smaller than a predetermined range of payload masses; supporting the small mass from a base susceptible to vibration by at least one stiff actuator; sensing the movement of the small mass; generating a small mass sensor signal which is a function of the movement of the small mass; generating a control signal which is a function of the small mass sensor signal; applying the control signal to the stiff actuator; and responsive to said step of applying, varying a length of the stiff actuator, thereby reducing the vibration experienced by the payload.

Claim 18

Independent Claim 128 words

A method of actively isolating a payload from vibration, comprising the steps of: resting the payload on a passive isolator; coupling the passive isolator to a small mass which is at least one order of magnitude smaller than a predetermined range of payload masses; supporting the small mass from a base susceptible to vibration by at least one stiff actuator; sensing the movement of the small mass; generating a small mass sensor signal which is a function of the movement of the small mass; generating a control signal which is a function of the small mass sensor signal; applying the control signal to the stiff actuator; and responsive to said step of applying, varying a length of the stiff actuator, thereby reducing the vibration experienced by the payload.

Claim 19

Dependent Claim 21 words

The method as recited in claim 15, wherein the sensor signal is a function of the velocity of the small mass.

Claim 20

Dependent Claim 38 words

The method as recited in claim 16, and further comprising the steps of: integrating the sensor signal to obtain a small mass displacement signal; and deriving the control signal as a function of the small mass displacement signal.

Claim 21

Dependent Claim 44 words

The method as recited in claim 15, and further comprising the steps of: modifying the sensor signal to compensate for at least one resonant frequency of the active vibration isolation apparatus; and generating the control signal as a function of the modified sensor signal.

Claim 22

Dependent Claim 48 words

The method recited in claim 15, and further comprising the steps of: sensing the movement of the payload; generating a payload sensor signal as a function of movement of the payload; and generating the control signal as a function of the sensor signal and the payload sensor signal.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2001-10-19	2002-04-20	2002-10-20	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2005-10-19	2006-04-20	2006-10-20	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2009-10-19	2010-04-20	2010-10-20	$7700.00	Window Closed / Lapsed

Stiff actuator active vibration isolation system

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