Active vibration isolation system employing an electro-rheological fluid

Claim 2

A viscous damper comprising: (a) means for deriving a first signal representative of the velocity of relative motion between first and second elements connected by said viscous damper for the reduction of transmitted excitations therebetween; (b) means for deriving a second signal representative of the velocity of one of said first and second elements; (c) means for generating a command signal in response to the ratio of said second signal to said first signal; and (d) means for modulating the damping coefficient of the viscous damper in response to the command signal to approximate the vibration isolation characteristics of a "sky hook" type damper.

Claim 3

The viscous damper of claim 1 wherein the modulating means includes an actuator, an accumulator, means for fluidically coupling said actuator to said accumulator, with an electro-rheological fluid, and means for directing fluid flow through said coupling means in response to an applied voltage.

Claim 4

The active vibration isolation system of claim 1 wherein said viscous damper means generates damping forces substantially in accordance with the following equation: F.sub.d =C.sub.o [1+A(ABS(dX/dV))]dV where "F d " is the damping force, "C o " is a system constant, "A" is a system constant, "ABS" means `absolute value of`, "dX" is the payload velocity, and "dV" is the relative velocity of the payload with respect to the base.

Claim 5

An active vibration isolation system comprising: (A) means connectable to a payload and a base for generating a signal representative of the instantaneous ratio of the absolute velocity of said payload to the relative velocity between said payload and said base; and, (B) viscous damper means (i) including a servovalve through which an electro-rheological fluid can flow in response to a range of vibratory motions between said payload and said base, (ii) characterized by a variable instantaneous damping coefficient dependent on the viscosity of the electro-rheological fluid, (iii) for generating transmissibility characteristic substantially the same as a sky-hook type damper, and (C) and wherein said servovalve includes means for modulating the viscosity of the electro-rheological fluid in response to said generated signal and, thereby, modulating the variable damping coefficient of the viscous damper in response to said generated signal.

Claim 6

An active vibration isolation system comprising: (A) means connectable to a payload and a base for generating a signal representative of the instantaneous ratio of the absolute velocity of said payload to the relative velocity between said payload and said base; and, (B) viscous damper means (i) including a servovalve through which an electro-rheological fluid can flow in response to a range of vibratory motions between said payload and said base, (ii) characterized by a variable instantaneous damping coefficient dependent on the viscosity of the electro-rheological fluid, (iii) for generating transmissibility characteristic substantially the same as a sky-hook type damper, and (C) and wherein said servovalve includes means for modulating the viscosity of the electro-rheological fluid in response to said generated signal and, thereby, modulating the variable damping coefficient of the viscous damper in response to said generated signal.

Claim 7

The active vibration isolation system of claim 4 characterized by a differential equation of motion substantially in accordance with the following equation: M[(dX.sup.2 ]=[U-X]-C.sub.1 A[ABS(dX)](Δ) where "M" is the payload mass, "(dX 2 )" is the payload acceleration, "K" is the spring stiffness constant, "U" is the displacement of the base, "X" is the displacement of the payload, "C 1 " and "A" are system constants, "ABS" means the `absolute value of`, "dX" is the payload velocity, and "Δ" is plus or minus one (1).

Claim 8

The active vibration isolation system of claim 4 wherein the servovalve is a solid state servovalve.

Claim 9

The active vibration isolation system of claim 4 wherein said viscosity modulating means includes first and second conductive orificed elements, and a third insulative orificed element disposed between said first and second elements, and means for applying said generated signal between said first and second conductive elements, said viscosity modulating means characterized by a fluid path between said first and second elements and through said third element.

Claim 10

The active vibration isolation system of claim 7 wherein said generated signal is a voltage signal applied between said first and second elements substantially in accordance with the following equation: E.sub.c =(RC.sub.o) (1+GAIN (ABS dx/dv))/rA.sub.c.sup.2. where "E c is the voltage potential, "R" is an experimentally determined coefficient of proportionality, "C o " is the damping present when E c =0, "GAIN" is a scaling constant, "ABS" means `the absolute value of`, "dX" is the payload velocity, "dV" is the relative velocity of the payload relative to the base, "r" is the fluid path length between the first and second conductive elements, and "A c " is the effective payload supporting area of the viscous damper.

Claim 13

The method of claim 9 wherein the modulating step includes the steps of: (i) directing the flow of a fluid through an orificed element included in the viscus damper, said fluid having viscosity variable in response to a change in an electric field applied thereto, and (ii) applying the electric field in response to the command signal across said orificed element, and thereby modulating the damping coefficient of the viscous damper.

Claim 14

The method of claim 10 wherein the orificed element includes first and second conductive plates and a third insulative plate disposed therebetween, said first, second and third plates having orifices therethrough in fluidic communication, and said electric field applying step includes the step of applying an electric voltage between said first and second plates substantially in accordance with the following equation: E.sub.c =(RC.sub.o) (1+GAIN (ABSdx/dv))/rA.sub.c.sup.2 where "E c is the voltage potential, "R" is an experimentally determined coefficient of proportionality, "C o " is the damping present when E c =0, "GAIN" is a scaling constant, "ABS" means `the absolute value of`, "dX" is the payload velocity, "dV" is the relative velocity of the payload relative to the base, "r" is the fluid path length between the first and second conductive elements, and "A c " is the effective payload supporting area of the viscous damper.

Claim 15

A viscous damper for use with a substantially incompressible electro-rheological fluid, including a passive dissipation element comprising servovalve means for metering the flow of fluid therethrough and thereby providing damping pressure drops and resulting dissipation forces, said servovalve means comprising first and second conductive plate elements, substantially parallel to one another, in spaced relation and having opposing surfaces, and in contact with an insulative element disposed therebetween and defining means for directing fluid flow therethrough including first orifice means for directing fluid flow in a first direction through said first conductive element, second orifice means for directing fluid flow through said second conductive element, and third orifice means for directing fluid flow in a second different direction along said opposing surfaces, adjacent said insulative element, and between said first and second orifice means; and, wherein said insulative element defines a plurality of channels, each in fluid communication at one end thereof with one of the first orifice means and at the other end thereof in fluid communication with one of the second orifice means.

Claim 16

A viscous damper for use with a substantially incompressible electro-rheological fluid, including a passive dissipation element comprising servovalve means for metering the flow of fluid therethrough and thereby providing damping pressure drops and resulting dissipation forces, said servovalve means comprising first and second conductive plate elements, substantially parallel to one another, in spaced relation and having opposing surfaces, and in contact with an insulative element disposed therebetween and defining means for directing fluid flow therethrough including first orifice means for directing fluid flow in a first direction through said first conductive element, second orifice means for directing fluid flow through said second conductive element, and third orifice means for directing fluid flow in a second different direction along said opposing surfaces, adjacent said insulative element, and between said first and second orifice means; and, wherein said insulative element defines a plurality of channels, each in fluid communication at one end thereof with one of the first orifice means and at the other end thereof in fluid communication with one of the second orifice means.

Claim 17

The viscous damper of claim 12 further comprising a support receptacle including upper and lower chambers fluidically coupled by said servovalve means, said upper chamber including means for holding said incompressible electro-rheological fluid and means for supporting a payload, said lower chamber including means for storing said incompressible electro-rheological fluid at a substantially constant pressure such that pressure changes due to fluid volume changes are insubstantial, said servovalve means regulating the flow of said incompressible electro-rheological fluid between said upper and lower chambers.

Claim 18

The viscous damper of claim 13 wherein said means for supporting a payload includes a payload support in spaced relation to said first conductive element and a deformable wall of resilient elastomeric material bonded to the perimeter of said first conductive element and to said payload support for defining and fluidically sealing said upper chamber, wherein said upper chamber is of a volume which can vary with deflections of the conical wall in response to weight of a payload supported by the payload support and vibratory excitations applied thereto, wherein said incompressible electro-rheological fluid serves as a hydraulic fluid for the support of said payload.

Claim 19

The viscous damper of claim 14 wherein said lower chamber includes means for controlling the pressure of said incompressible electro-rheological fluid, said pressure controlling means including a diaphragm separating said lower chamber into first and second subchambers for respectively storing therein a substantially incompressible fluid adjacent said servovalve and a compressible fluid, said first and second subchambers having volumes which vary in response to pressure changes therein, wherein inertial forces caused by vibratory motion of the payload cause a reduction of volume in the upper chamber, causing, in turn, a pressure increase therein and a resulting pressure differential between said upper chamber and said first subchamber and a resulting flow of the electro-rheological fluid therebetween, and wherein said fluid flow damps said vibratory motion.

Claim 20

The viscous damper of claim 15 wherein said lower chamber comprises means for supporting a payload with substantially linear spring stiffness, and means for generating flow through said servovalve means and thereby generating dissipation forces in response to vibratory excitations applied thereto.

Claim 21

The viscous damper of claim 16 further including means for varying the dissipation forces in accordance with a feedback signal.

Claim 22

The viscous damper of claim 17 wherein said servovalve means is "solid state".

Claim 23

The viscous damper of claim 12 wherein said incompressible electro-rheological fluid includes a base and polymer grains having a coating of water suspended in the base, and is characterized by a viscosity which varies with the strength of an applied electrical field.

Claim 24

The viscous damper of claim 19 further comprising means for creating an electric field by applying a voltage potential between said first and second conductive elements.

Claim 25

The viscous damper of claim 20 wherein said voltage potential is applied in accordance with: E.sub.c =(RC.sub.o) (1+GAIN (ABS(dx/dv))/rA.sub.c.sup.2 where "E c is the voltage potential, "R" is an experimentally determined coefficient of proportionality, "C o " is the damping present when E c =0, "GAIN" is a scaling constant, "ABS" means `the absolute value of`, "dX" is the payload velocity, "dV" is the relative velocity of the payload relative to the base, "r" is the fluid path length between the first and second conductive elements, and "A c " is the effective payload supporting area of the viscous damper.

Claim 26

The viscous damper of claim 20 wherein the viscosity of the incompressible fluid varies in proportion to the applied electrical potential divided by the cube of the length of the fluid path between said first and second conductive elements.

Claim 27

The viscous damper of claim 12 wherein the plates are each on the order of 1.0 millimeter in thickness, and the insulative element is a plate of high resistivity on the order of 0.1 millimeter in thickness.

Claim 28

The viscous damper of claim 15 wherein said first and second orifice means include orifices for directing fluid flow through one of said first and second plates in a direction substantially perpendicular to the planes defined by said plates, said third orifice means includes a plurality of elongate channels connecting said orifices of said first orifice means to said orifices of said second orifice means for directing fluid flow in a direction parallel to the planes defined by said plates, whereby an extended fluid flow path is provided.