Active vibration isolation system

A vibration isolation system comprising:

• a payload;
• a support;
• a passive isolation system for supporting said payload on said support;
• a geophone disposed so as to sense vibrational movement of said payload relative to said support, said geophone comprising a case, a proof mass suspended within the case, and means for measuring the relative velocity of the proof mass relative to the case and for producing an output signal that is proportional to said relative velocity by the expression S(X-Z), where S is the Laplace operator, X is the displacement of the case relative to said support, and Z is the displacement of the proof mass as the payload undergoes vibrational movement;
• circuit means coupled to said geophone for modifying said geophone output signal so that it is more nearly proportional to the actual velocity shown by the expression SX of said case and payload;
• a force transducer for applying a force to said payload in response to an input signal;
• and
• means for applying said modified geophone output signal as an input signal to said force transducer so as to cause said force transducer to apply a force to said payload in a direction in opposition to the direction of movement of said payload as it vibrates.

A vibration isolation system comprising:

• a payload mass;
• a support;
• a passive isolation system supporting said payload mass on said support;
• a geophone for sensing vibrational movement of said payload mass relative to said support and for producing an output signal in response to said movement, said geophone comprising a case adapted to vibrate with said payload mass, a proof mass suspended in said case so as to be capable of displacement relative to said case as said case undergoes vibrational movement, and means for measuring said relative displacement and providing in response thereto a geophone output signal that is represented approximately by the following equation using Laplacian notation:
• ##EQU11## where E.sub.v (s) represents the geophone transfer function, .beta.=gain in units of volts per inch per second, S=the Laplace operator, X is the displacement of the geophone case, Z is the displacement of the proof mass, S(X-Z) is the relative velocity of the proof mass relative to the geophone case, .xi..sub.g is the geophone fraction of critical damping, and w.sub.g is the proof mass resonant frequency;
• control circuit means responsive to said geophone output signal for modifying said geophone output signal so that the effective resonant frequency of said geophone is lower than the resonant frequency of said passive isolation system by at least one decade;
• a force transducer for applying a force to said payload mass in response to an input signal;
• and
• means for applying said modified geophone output signal as an input signal to said force transducer so as to cause said force transducer to apply a force to said payload mass in a direction in opposition to the direction of movement of said payload mass as it vibrates.

A vibration isolation system comprising:

• a payload mass;
• a support means supporting said payload mass so that said payload mass is subject to vibrational motion and will respond to application of a force opposing said vibrational motion, said support means comprising a passive isolation system;
• a geophone for sensing vibrational movement of said mass relative to said support and for producing a transducer output signal that varies as a function of the velocity of said payload mass as it undergoes vibrational motion relative to said support;
• circuit means responsive to said geophone output signal for modifying said geophone output signal;
• an electromagnetic force transducer for applying a force to said payload mass in response to an input signal;
• and
• means for applying said modified geophone output signal as an input signal to said force transducer so as to cause said force transducer to apply a force to said payload mass in a direction in opposition to the direction of movement of said payload mass as it vibrates;
• said circuit means being adapted to modify the output signal of said geophone so as to as to provide a compensated geophone transfer function represented as follows:
• ##EQU14## where:
• F(s) is the geophone transfer function, g(s) is the transfer function of said circuit means, T.sub.g is the geophone time constant, and S is the Laplace operator.

An active vibration isolation system comprising:

• a payload mass supported so as to be subject to vibrational motion and to respond to application of a force opposing said vibrational motion;
• a geophone for producing a velocity signal in response to vibrational motion of said payload mass;
• an electrically operated force transducer for applying a force to said payload mass in response to an input signal;
• circuit means responsive to said velocity signal for producing a control signal that provides a compensated geophone transfer function as follows:
• ##EQU15## where F(s) is the transfer function of the geophone, g(s) is the transfer function of the circuit means, T.sub.g =is the time constant for the geophone, and S is the Laplace operator;
• and
• means for applying said control signal as an input signal to said force transducer.

An active vibration control system for a payload that is supported relative to a supporting structure and is subject to undesirable vibration in a plurality of degrees of freedom comprising:

• a plurality of geophones mounted on said payload, each of said geophones being oriented to sense a velocity component of said payload in a predetermined one of several degrees of freedom and adapted to produce a geophone electrical output signal that varies as a function of the velocity component in said predetermined one degree of freedom;
• a plurality of force actuators each operable in response to an individual input signal for applying a force to said payload in opposition to vibrational motion of said payload in one of said degrees of freedom;
• a plurality of channel circuit means each adapted to produce a channel electrical output signal in response to an input signal;
• a plurality of means for applying said geophone output signals as input signals to said channel circuit means;
• and
• means for applying said channel output signals to said force actuators;
• said channel circuit means being adapted to modify said geophone output signals so that each of said channel circuit means output signals provides a compensated geophone transfer function that is represented approximately as follows:
• ##EQU16## where F(s) is the transfer function of one of said geophones, g(s) is the transfer function of the channel circuit means to which the output signal of said one geophone is applied, T.sub.g = is the time constant for said one geophone, and S is the Laplace operator.