3D printed soft spring actuator improves robot safety in human interaction
Design and Experimental Validation of a 3D Printed Torsional Series Elastic Actuator for Safe Human Robot Interaction
Robotics
Summary
Robots that work closely with people need to be safe and gentle. The authors created a soft, twistable spring part using 3D printing that helps robot joints absorb forces safely. They tested this part to make sure it bends predictably and works well with regular robot motors. Because the soft material also naturally reduces shaking, the robot can react smoothly when people touch or push it. This new design is cheaper and simpler to make than traditional metal parts, helping robots interact safely with humans.
What this means in practice
- •For robotics engineers: Build safer physical interaction joints by integrating low stiffness 3D printed TPU springs into robotic arms to prevent injury during human contact.
- •For prosthetics designers: Use affordable, flexible 3D printed torsional springs to create compliant, comfortable prosthetic joints that adapt safely to user movement and external forces.
Authors
Joel Hidalgo Pisco, Melissa Cobos Condo, Luigi Miranda, Dennys Paillacho
Abstract
Ensuring intrinsic safety in physical human robot interaction (pHRI) is a critical requirement for social and service robots. While Series Elastic Actuators (SEAs) offer hardware based compliance, traditional metallic designs often require complex, multi part assemblies. This paper presents the design, finite element analysis (FEA), and experimental validation of a low stiffness, torsional spring for SEAs, manufactured via 3D printed thermoplastic polyurethane (TPU). The compliant element exhibits a highly linear torque deformation response (Ks = 0.066 Nm/degree), matching numerical predictions with under 3% deviation, a variance attributed to FDM structural anisotropy. To accommodate external interactions using standard position limited servomotors, a hybrid position controller with torque threshold switching was implemented. Experimental evaluations demonstrate the system ability to accurately track non stationary trajectories and safely yield to external disturbances. Furthermore, the inherent material damping of the TPU acts as a passive low pass filter, preventing high frequency oscillations during control mode transitions. The proposed architecture offers a cost effective, reliable, and easily manufacturable solution for safe pHRI.