Stiff actuator active vibration isolation system

DETAILED DESCRIPTION The present invention solves the prior art problems by employing a small intermediate mass in its active vibration isolation system, distinct and elastically decoupled from the payload mass.
The small mass is at least one order of magnitude smaller than the payload mass.
At least one stiff actuator, such as a piezoelectric motor element, has a first surface coupled to the small mass and a second surface coupled to a source of vibration, such as the floor or an external case.
A passive isolator element, such as an elastomeric cup shaped isolator, couples the payload to the small mass.
A sensor is coupled to the small mass and generates a sensor signal which is a function of the movement of the small mass.
Circuitry receives the motion sensor signal and includes compensation circuitry such that the system will be stable over a predetermined range of vibration frequencies and payload masses.
The circuitry further includes drive circuitry that is coupled to the stiff actuator for varying the length of the stiff actuator as a function of the altered sensor signal.
Preferably, the small mass is isolated from vibration in each of the "X", "Y" and "Z" axes.
In a preferred embodiment, the small mass is housed within a case, and is suspended from the case in each of the "X", "Y" and "Z" axes by at least one stiff actuator in each direction.
In the instance where the stiff actuators are piezoelectric motor elements, the horizontally disposed stiff actuators are precompressed in order to avoid damage to the motor elements from tensile stress.
In a preferred design, each horizontal or radial piezoelectric motor element is placed between the small mass and a sidewall of the case on one side, and a compression assembly is placed on the other side of the small mass so as to exert compressive force from the case through the small mass to the piezoelectric motor element.
According to another aspect of the invention, each of the stiff actuators is coupled to the small mass or to the case using a shear decoupler that limits the exertion of shear stresses on the piezoelectric motors