Robust Vibration Isolation of a 6-DOF system using modal decomposition and sliding surface optimization

For a high-performance 6-DOF Active Vibration Isolation System (AVIS), the vibration isolation performance (transmissibility) is the most important criterion and the disturbance rejection performance (compliance) has lower priority. The strategy of combining modal decomposition and frequency-shaped sliding surface control is applied based on the measurement scheme of relative displacement and payload absolute acceleration. Modal decomposition decouples the six modes and calculates the equivalent sensor noises for each mode. The designed performances, transmissibility and sensitivities to the two sensor noises, depend solely on the sliding surface design. The sliding surface is optimized for each mode with predefined constraints which are derived from common industrial requirements. The regulator is designed to realize the designed transmissibility for each mode and to achieve low compliance. The numerical example of the sliding surface optimization gives better result than the manual design. This strategy designs the four performances step by step and iterative design is not necessary.