MODULAR STIFFNESS MODULATION IN 3D-PRINTED SOFT ACTUATORS FOR MECHANICAL TRAJECTORY PROGRAMMING

Soft pneumatic actuators (SPAs) offer safe, compliant interaction but are difficult to program for diverse motion trajectories without redesigning the actuator body or re-fabricating constraint layers. This paper introduces a modular trajectoryprogramming approach based on press-fittable, discrete strainlimiting layer (SLL) modules that can be reconfigured on a 3D-printed Zigzag SPA to tune stiffness and shape output on demand. We model the quasi-static behavior with a reducedorder Euler-Bernoulli formulation to identify an effective flexural rigidity that links SLL configuration to bending response, and we complement the model with finite-element simulations. Trajectory distinctness and shape variation are quantified using tip-path root-mean-square deviation (RMSD) and curvaturebased statistical distributions. Experiments with Dragon Skin and Dragon Skin + Ecoflex SLL combinations demonstrate more than 50 distinct tip trajectories, spanning simple bending, Scurves, and out-of-plane motion, substantially expanding the reachable workspace relative to conventional fixed-SLL SPAs. The approach is validated in three application demonstrations: a reconfigurable soft gripper, biomimetic finger-motion tracking, and an endoscope prototype where an S-shaped configuration reduces image distortion by 45.79% relative to conventional design that has only pure bending.