Safety Filter for Underactuated Mechanical Systems With Time-Varying Constraints

The safety-critical control of underactuated mechanical systems (UMSs) with both collocated and noncollocated configuration constraints is considered in this article. Based on the popular safety filter (SF) method using high-order control barrier function-based quadratic programs (HOCBF-QPs), this article further overcomes the difficulties caused by the singularity points of time-varying constraints and the underactuation characteristic. Specifically, the time-varying problem is addressed by transforming it into an extended time-invariant one. Then, the existing high-order CBF (HOCBF) theory is applied to construct singularity-free HOCBFs for UMS. Next, a Lipschitz continuous SF is proposed to handle multiple constraints in a hierarchical manner. Finally, experiments are performed on a 3-degrees of freedom boom crane platform to validate the effectiveness.