Elastically and Plastically Foldable Electrothermal Micro‐Origami for Controllable and Rapid Shape Morphing

Integrating origami principles within traditional microfabrication methods can produce shape morphing microscale metamaterials and 3D systems with complex geometries and programmable mechanical properties. However, available micro‐origami systems usually have slow folding speeds, provide few active degrees of freedom, rely on environmental stimuli for actuation, and allow for either elastic or plastic folding but not both. This work introduces an integrated fabrication–design–actuation methodology of an electrothermal micro‐origami system that addresses the above‐mentioned challenges. Controllable and localized Joule heating from electrothermal actuator arrays enables rapid, large‐angle, and reversible elastic folding, while overheating can achieve plastic folding to reprogram the static 3D geometry. Because the proposed micro‐origami do not rely on an environmental stimulus for actuation, they can function in different atmospheric environments and perform controllable multi‐degrees‐of‐freedom shape morphing, allowing them to achieve complex motions and advanced functions. Combining the elastic and plastic folding enables these micro‐origami to first fold plastically into a desired geometry and then fold elastically to perform a function or for enhanced shape morphing. The proposed origami systems are suitable for creating medical devices, metamaterials, and microrobots, where rapid folding and enhanced control are desired.An elastically and plastically foldable micro‐origami is developed and tested to create controllable and functional 3D shape morphing systems with multiple active degrees of freedom. The work demonstrates a versatile design–fabrication–actuation method to achieve rapid folding, enhanced control, and function in different atmospheric environments, enabling applications in microrobots, medical devices, and metamaterials.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/2/adfm202003741.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/1/adfm202003741-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163442/3/adfm202003741_am.pd

A Model-Free On-Off Iterative Adaptive Controller Based

Abstract-An on-off iterative adaptive controller has been developed that is applicable to servo systems performing repeated motions under extremely strict power constraints. The motivation for this approach is the control of piezoelectric actuators in autonomous micro-robots, where power consumption in analog circuitry and/or for position sensing may be much larger than that of the actuators themselves. The control algorithm optimizes the switching instances between 'on' and 'off' inputs to the actuator using a stochastic approximation of the gradient of an objective function, namely that the system reach a specified output value at a specified time. This allows rapid convergence of system output to the desired value using just a single sensor measurement per iteration and discrete voltage inputs. I. INTRODUCTION INIATURIZATION of sensors and actuators through developments in Microelectromechanical Systems (MEMS) technology can enable very low-power, small footprint implementation of a variety of engineered systems. Piezoelectric and electrostatic actuators are two of the most common mechanisms for generating motion in MEMS devices and act as capacitive loads with very small intrinsic power consumption. For instance, a 1 nF piezoelectric actuator operating at 20 V and 20 Hz requires only about 18 µW of power. However, in many cases actuators may face a changing environment or feature nonlinear behavior requiring a servo control system, in which actuator power can be easily exceeded by the power consumption of drive and sensing circuitry. To minimize power consumption of a complete servo control system for micro-scale piezoelectric or capacitive actuators, it is desirable to utilize switching ('on-off') control to avoid inefficiencies in driving circuits To perform low-power servo control the problem of selecting transition times of an on-off input sequence is converted to a model-free adaptive control problem with the adaptive controller based on the simultaneous perturbation stochastic approximation (SPSA) developed by Spall et al. [10], [11], [12], For power minimization in micro-robotics this controller has several benefits which include: a need for only one sensor measurement per motion, the ability to perform computation between steps to reduce processor requirements, and effectiveness in the presence of noisy sensors. A model-free approach was selected because the piezoelectric actuators targeted are highly nonlinea