A Novel Laminar Jamming Mechanism for Variable-Stiffness Robotic Arms

A central problem in human–robot interaction is the risk of severe injury in humans in the event of a collision with a rigid robot arm. The introduction of variable stiffness into a robot arm mitigates the effects of impact and generates a safe interaction in its compliant state. An approach to vary the stiffness of members in a robotic arm is Laminar Jamming. In this article, a new lock/unlock mechanism for Laminar Jamming is proposed. The solution consists of a pneumatic actuator that drives a trapezoidal pin to interfere mechanically with the layers, and, in turn, changing the stiffness of the Laminar Jamming Structure. Additionally, frames are placed along the structure to avoid local buckling of the layers. Experiments and finite element simulations were carried out to study the mechanical performance of this new mechanism. Experiments show that the proposed mechanism reached a maximum stiffness ratio of 3.65, which is 15% higher than the stiffness ratio of an equivalent flat clamp mechanism. Experiments also demonstrate that the proposed mechanism does not show the stick-slip phenomenon that exists in the flat clamp mechanism. Computational case studies were carried out to investigate the effects of the angle of the trapezoidal pin, the number of frames, the direction of the transverse force and the behavior at high deflections. Simulations show that the 30° trapezoidal pin has the highest stiffness for pressures larger than 500 kPa, three frames placed along the Laminar Jamming generate the maximum stiffness ratio, the stiffness slightly varies when the transverse force changes direction, and the stiffness decreases with increasing deflection.