Contact-Aware Predictive Control of a Logarithmic-Spiral Soft Gripper: A Control-Oriented Reduced-Order Numerical Study

Logarithmic-spiral soft grippers couple tendon actuation, variable-curvature morphology, distributed contact, and frictional load support. This study evaluates a finite-candidate predictive force-shape (PFS) controller within a control-oriented reduced-order surrogate of a two-tendon gripper. PFS is compared with open-loop, fixed-tension, position-only, and hybrid force-shape controllers across multiple object geometries, simultaneous uncertainty, payload-friction conditions, transient loads, ablations, and parameter variations. In the nominal study, PFS produced a mean force RMSE of 7.26 N and a mean peak local force of 8.07 N, while the comparison implementations produced force RMSE values from 57.9 N to 99.3 N and peak forces near 30.6 N. This behavior involved a geometric tradeoff: PFS position RMSE was 0.088 m, compared with 0.073 m for PO and 0.074 m for HFS. The remaining numerical studies characterize how this tradeoff changes inside the surrogate. A matched higher-resolution verification at (N,Nc)=(60,48) preserved the principal force–position tradeoff: PFS yielded a mean force RMSE of 10.25 N and peak local force of 8.84 N, while PO and HFS retained lower position RMSE. Because the morphology and contact relations are phenomenological, the results are interpreted as reproducible numerical evidence rather than experimental validation or proof of physical superiority.