Robust linear control of a bending molecular artificial muscle based on spin crossover molecules
Résumé
Bending actuators represent a popular class of artificial muscles for which efficient closed-loop control is a remarkable challenge, due to the complexity of physico-chemical phenomena occurring during dynamic contraction. In this study, we investigate an electro-thermally actuated, bilayer bending actuator based on spin crossover molecules. While these artificial muscles can open-loop contract in several tens of seconds, we show that a simple closed-loop PID-control is able to reduce the response time to ca. 1.5 s, even with loads up to 5 times the actuator weight (i.e. a maximal load of about 343 mg). We demonstrate also satisfactory sine wave tracking performance. The relevance of this linear control approach applied to a nonlinear actuator is the consequence of the high sensibility of the actuator to the current, responsible for the Joule effect. Notably, the actuator roughly behaves like a second-order linear system, whose time “constants” decrease with current. Consequently, the natural speed improvement peculiar to the PID-controller is further amplified by this nonlinear effect, without any loss in stability of the closed-loop system.
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