Vibration Isolation Systems

Vibration Isolation SystemsBY PRINCESS J. THOMAS

Vibration

Unwanted part of society

Causes imbalance, noise, waste of energy and failure in machine parts

Two types of unwanted vibration:

Ground Vibration – vibration transmitted from the ground through suspension

Direct Disturbance – vibration caused by disturbances acting on an isolation table

Two solutions:

Passive Vibration Isolation

Active Vibration Isolation

Passive Vibration Isolation

Simple

Purely Mechanical

Springs – softens vibration

Dampers – terminates the oscillation in the system

Must be calibrated correctly for the required function

Negative Spring Stiffness Mechanism

New revolutionary concept

Magnets in attracting configuration (Carella et al.)

Compact spring to produce negative stiffness (Lee at al.)

Simple 6-DOF system consisting of a vertical-motion isolator, horizontal-motion isolator and a tilt-motion isolator (Platus)

Vertical-Motion Isolator

Spring KS

Two fixed flexures

Compressive force P to create negative stiffness KN

Equation can be made to approach zero when weight is applied

Horizontal-Motion Isolator

Placed on top of vertical-motion isolator

Consists of two fixed-free column

Behaves similarly to horizontal spring and a negative spring mechanism

Passive Vibration Isolator

Active Vibration Isolation System

Accommodates for 6-DOF most of vibration

Translational in x, y and z planes

Rotational – roll, pitch and yaw

More accurate than passive isolators

No resonance in active system

Active Vibration Isolation System

Spring connected to Active Vibration Control (AVC) system

Feedback circuit consists of:

Piezoelectric Accelerometer

Analogue Control Circuit

Electromagnetic Transducer

Active Vibration Isolation System

Different ways of designing an active vibration system

Two channel controller (Serrand and Elliot)

Passive system as a base (Platus)

Used in:

Semiconductor production industry

Aircraft and space applications

Optical devices

QUESTIONS???