Transcending the acceleration-bandwidth trade-off: Over-actuated precision motion stages with selective compliance and servo stiffness

In today’s precision positioning systems, there exists a fundamental trade-off between control bandwidth and achievable acceleration due to the structural material’s stiffness-to-weight ratio limit and existing control techniques. This trade-off severely limits the throughput of photolithography machines and wafer inspection systems for integrated circuit manufacturing, which directly depends on the acceleration and control performance of the wafer and photomask positioning stages. Aiming to break this trade-off and to enable new lightweight stages with further enhanced acceleration without sacrificing control performances, this paper proposes a novel hardware and control co-design paradigm for over-actuated precision positioning stages that integrates servo-stiffness and selected compliance. The key idea is to (a) stiffen the component’s flexible dynamics through servo-stiffness, i.e., actively control the structure’s flexible dynamics using additional actuators and sensors, and (b) smartly introduce structural compliance in the actively controlled flexible modes to reduce weight and to facilitate controller synthesis. A sequential design optimization framework for the proposed methodology is presented, and an over-actuated magnetically levitated planar motion stage embodying the proposed approach, which we call the FleXstage, is designed and built for performance evaluation. Simulation shows that the proposed design provides 24% reduced weight and 2.4 times control bandwidth improvement compared to a baseline lightweight stage, and experimental results of the FleXstage prototype align well with simulation predictions. These results demonstrate the feasibility and potential of the proposed methodology.