  In this work, we introduce an advanced thermo-active variable impedance
module which builds upon our previous innovation in thermal-based impedance
adjustment for actuation systems. Our initial design harnessed the
temperature-responsive, viscoelastic properties of Polycaprolactone (PCL) to
modulate stiffness and damping, facilitated by integrated flexible Peltier
elements. While effective, the reliance on compressing and the inherent stress
relaxation characteristics of PCL led to suboptimal response times in impedance
adjustments. Addressing these limitations, the current iteration of our module
pivots to a novel 'shear-mode' operation. By conducting comprehensive shear
rheology analyses on PCL, we have identified a configuration that eliminates
the viscoelastic delay, offering a faster response with improved heat transfer
efficiency. A key advantage of our module lies in its scalability and
elimination of additional mechanical actuators for impedance adjustment. The
compactness and efficiency of thermal actuation through Peltier elements allow
for significant downsizing, making these thermal, variable impedance modules
exceptionally well-suited for applications where space constraints and actuator
weight are critical considerations. This development represents a significant
leap forward in the design of variable impedance actuators, offering a more
versatile, responsive, and compact solution for a wide range of robotic and
biomechanical applications.
