Characterization of the Variable Stiffness Actuator Fabricated of SMA/SMP and MWCNT/IL: PDMS Strain-Sensitive Heater Electrode

A microactuator that exhibited the variable stiffness function and the strain control was demonstrated by using the shape memory alloy (SMA), shape memory polymer (SMP), and the strain-sensitive stretchable heater polymer of multi-walled carbon nanotube/ionic liquid (IL): polydimethylsiloxane. The SMA filaments exerted the principal driving force and the SMP film modulated the elasticity of the actuator. To make the microfabrication of the actuator and the control feasible, we first demonstrated the use of a stretchable heater electrode, which accommodates 100% of the strain and low resistivity of 3.75
$m\Omega \cdot cm$
for the temperature control. The elasticity change of the SMP film was successfully realized by electrical heating, and the response was characterized. To obtain the strain without any additional implementation, we performed the self-sensing actuation. By developing the specified driver circuit, strain measurement was achieved while modulating the elasticity. Finally, we demonstrated the weight lifting of a microarm, a typical example to control the variable stiffness actuation.