VSB - Variable Stiffness Based on Bowden Cables: A Simple Mechanism for Soft Robotic Hands

Soft robotic hands compensate for uncertainty in perception and actuation by leveraging passive deformation in their intrinsically compliant hardware, facilitating robust and dexterous interactions with their environment. The ability to adjust the level of compliance during operation has the potential to further improve the performance of these hands by enabling novel interaction strategies. However, achieving variable stiffness mechanically typically requires significant engineering complexity, making these systems difficult to manufacture, prone to error, and expensive. We present a novel, very simple mechanism for achieving variable stiffness. This mechanism employs tendon-driven antagonistic actuation, with Bowden cables connecting elastic elements to servomotors. It supports compact actuator designs, while the Bowden cables facilitate flexible component placement within a robotic system. Following our approach, variable stiffness actuators can be easily manufactured at low-cost from readily available materials. Despite its simplicity, we demonstrate that our mechanism provides consistent and precise control over stiffness levels and contact torques, showcasing its potential for a broad range of applications in soft robotic systems.