Stiff actuator active vibration isolation system

An active vibration isolation system for isolating a payload mass falling within a predetermined range of payload masses from a vibrating base on which the payload mass is supported, comprising:

• a small mass which is at least one order of magnitude less than said predetermined range;
• at least one stiff actuator having first and second faces and a variable length between said first and second faces, said stiff actuator changing said variable length responsive to receiving an actuator control signal, said first face of said stiff actuator coupled to said small mass and disposed in parallel to an axis passing through said small mass and said second face of said stiff actuator coupled to the base;
• a passive isolator interposed between said small mass and said payload mass and disposed in axial opposition to said stiff actuator, wherein said stiff actuator, said small mass and said passive isolator are interposed between said payload mass and the source of vibration;
• and
• a geophone mounted on said small mass for measuring the absolute velocity thereof and generating a velocity signal, circuitry coupled to said geophone and said stiff actuator for receiving said velocity signal, integrating said velocity signal to obtain a displacement signal, and generating said actuator control signal as a function of said displacement signal, wherein said active vibration system is interposed between said payload mass and a vibration source.

An active vibration isolation system, comprising:

• a passive isolator mount adaptable to support a payload having a payload mass falling within a predetermined range of masses, said payload exerting a force on said passive isolator mount along a first axis;
• at least one payload velocity sensor coupled to said payload for sensing an absolute velocity of said payload in a direction parallel to said first axis;
• a small mass supporting said passive isolator mount and disposed in opposition to said payload mass, said small mass preselected to be at least one order of magnitude less than said predetermined range of masses;
• at least one small mass velocity sensor coupled to said small mass for sensing an absolute velocity of said small mass in a direction parallel to said first axis;
• at least a first stiff actuator disposed adjacent said small mass and in opposition to said passive isolator mount, a length of said first stiff actuator aligned with said first axis and variable as a function of a control signal applied thereto;
• and
• a controller having inputs coupled to said sensors and at least one output which is coupled to said first stiff actuator, said controller operable to control said first stiff actuator to compensate for vibration of said payload with said control signal, said control signal generated by said controller as a function of input signals appearing on said inputs from said sensors.

An active vibration isolation system for isolating a payload from vibrations in a support, comprising:

• an external case having sidewalls defining a cavity;
• a small mass dimensioned to be at least partially received in said cavity such that said case is spaced from said small mass on all sides, said small mass being preselected to be at least one order of magnitude smaller than a preselected range of payload masses, said small mass adaptable to be coupled to a payload mass;
• passive isolator coupling said small mass with said payload mass;
• at least first and second axes disposed at an angle to each other and intersecting said sidewalls and a load axis;
• for each of said first axis, said second axis and said load axis, at least one stiff actuator having a variable length which varies according to a control signal applied thereto, said stiff actuator disposed such that said variable length thereof is parallel to a respective axis, said stiff actuator used in spacing said mass from said case;
• for each axis, a sensor joined to said small mass and operable to produce a velocity signal;
• and
• compensation circuitry for receiving said velocity signals from said sensors and generating a respective plurality of control signals in response thereto, said compensation circuitry applying said control signals to respective ones of said stiff actuators to change the variable lengths thereof.

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.

A method of actively isolating a payload from vibration, comprising the steps of:

• coupling a payload to at least first and second stiff actuators, each stiff actuator having a variable length aligned with a respective axis, the axes disposed at an angle to each other;
• sensing a movement of the payload in each of first and second directions respectively parallel to ones of the axes;
• generating a first control signal as a function of the movement in the first direction;
• generating a second control signal as a function of the movement in the second direction;
• applying the first and second control signals, respectively, to the first and second stiff actuators;
• responsive to said step of applying, varying the lengths of said first and second stiff actuators by amounts equivalent to the amounts of movement sensed in the first and second directions, respectively;
• decoupling the shear force on the first stiff actuator caused by varying the length of the second stiff actuator;
• and decoupling the shear force on the second stiff actuator caused by varying the length of the first stiff actuator.

An active vibration isolation system for isolating a payload, comprising:

• at least first and second stiff actuators having variable lengths aligned with respective first and second axes, said first and second axes disposed at an angle to each other, first ends of said first and second stiff actuators coupled to said payload, second ends of said first and second stiff actuators coupled to a base susceptible to vibration;
• first and second sensors coupled to said payload mass and operable to sense movement related to said payload mass in first and second directions, respectively, said first direction parallel with said first axis, said second direction parallel to said second axis, said first and second sensors respectively generating first and second sensor signals;
• and
• circuitry coupled to said first and second sensors for generating a first control signal as a function of said first sensor signal and for generating a second control signal as a function of said second sensor signal.

A method of isolating a payload from vibration of a base which supports the payload, the method comprising the steps of:

• coupling a passive isolator between the payload and a small mass;
• coupling at least one stiff actuator between the small mass and the base wherein said stiff actuator, said small mass and said passive isolator are interposed between said payload mass and the base, the stiff actuator having a variable length aligned with an axis;
• using a geophone to sense a velocity related to the payload in a direction parallel to the axis;
• responsive to said step of using the geophone, generating a velocity signal;
• integrating the velocity signal to obtain a displacement signal;
• generating a control signal as a function of the displacement signal;
• applying the control signal to the stiff actuator;
• and responsive to said step of applying, varying the length of the stiff actuator in order to decrease the vibration experienced by the payload.

An active vibration isolation system, comprising:

• a passive isolator adapted for supporting a payload;
• a small mass which is at least one order of magnitude smaller than a predetermined range of payload masses, said small mass coupled to said passive isolator and disposed in opposition to said payload;
• a sensor coupled to said small mass and generating a small mass sensor signal as a function of the movement of the small mass;
• circuitry coupled to said sensor and adaptable to generate a control signal as a function of the small mass sensor signal;
• and
• at least one stiff actuator interposed between a source of vibration and said small mass, said circuitry coupled to said stiff actuator for applying said control signal thereto, a length of said stiff actuator varying as a function of said control signal to thereby lessen the vibration experienced by said payload.