On Vibration Suppression of a Tendon-Driven Soft Robotic Neck

Seshagopalan Thorapalli Muralidharan¹Randy Gomez²Georgios Andrikopoulos^1*

• ¹Mechatronics Unit, Robot Design Lab, KTH Royal Institute of Technology, Stockholm, Sweden
• ²Kabushiki Kaisha Honda Research Institute Japan, Wako, Japan

Tendon-Driven Continuum Actuators (TDCAs) offer compliant, lifelike motion but are prone to undesired vibrations along unactuated axes, particularly under load. This article presents a real-time control strategy for mitigating such vibrations in a 2-DoF TDCA-based soft neck, using the HARU social robot as a case study. The approach combines current-based tendon pretensioning, baseline PID control, and a novel Coupled Axis Indirect Vibration Suppression (CIVS) mechanism. CIVS uses high-pass filtered yaw acceleration from an inertial sensor to indirectly modulate tendon tensions via cross-axis coupling. A classical Sliding Mode Controller (SMC) is additionally implemented as a nonlinear benchmark for evaluating tracking performance under the same hardware constraints. Experimental results demonstrate a 53% reduction in yaw range and a 60% decrease in yaw acceleration area compared to baseline, while preserving compliance and simplicity. The method is well-suited for soft robotic systems where direct actuation is infeasible, particularly in human-interactive applications, while the results demonstrate the potential for achieving low-complexity and effective vibration suppression that can scale with future developments in soft robotics.