A novel vertical translational microactuator based on thin-film piezoelectric actuation is presented, using a set of four compound bend-up/bend-down unimorphs to produce translational motion of a moving platform or stage. The actuation material is a chemical-solution deposited lead–zirconate–titanate (PZT) thin film. Prototype designs have shown as much as 120 μm of static displacement, with 80–90 μm displacements being typical, using four 920 μm long by 70 μm legs. Analytical models are presented that accurately describe nonlinear behavior in both static and dynamic operation of prototype stages when the dependence of piezoelectric coefficients on voltage is known. Resonance of the system is observed at a frequency of 200 Hz. The large displacement and high bandwidth of the actuators at low-voltage and low-power levels should make them useful to a variety of optical applications, including endoscopic microscopy.
A novel three degree-of-freedom microactuator based on thin-film lead-zirconate-titanate (PZT) is described with its detailed structural model. Its central rectangular-shaped mirror platform, also referred to as the stage, is actuated by four symmetric PZT bending legs such that each leg provides vertical translation for one corner of the stage. It has been developed to support real-time in vivo vertical cross-sectional imaging with a dual axes confocal endomicroscope for early cancer detection, having large displacements in three axes (z, θx, θy) and a relatively high bandwidth in the z-axis direction. Prototype microactuators closely meet the performance requirements for this application; in the out-of-plane (z-axis) direction, it has shown more than 177 μm of displacement and about 84 Hz of structural natural frequency, when two diagonal legs are actuated at 14V. With all four legs, another prototype of the same design with lighter stage mass has achieved more than 430 μm of out-of-plane displacement at 15V and about 200 Hz of bandwidth. The former design has shown approximately 6.4° and 2.9° of stage tilting about the x-axis and y-axis, respectively, at 14V. This paper also presents a modeling technique that uses experimental data to account for the effects of fabrication uncertainties in residual stress and structural dimensions. The presented model predicts the static motion of the stage within an average absolute error of 14.6 μm, which approaches the desired imaging resolution, 5 μm, and also reasonably anticipates the structural dynamic behavior of the stage. The refined model will support development of a future trajectory tracking controller for the system.
Thin-film lead-zirconate-titanate (PZT) actuators are a potential enabling technology for autonomous micro-robots with locomotion abilities rivaling biological systems. Actuators capable of supplying the large forces and extended displacements needed to drive terrestrial micro-robotic locomotion have been designed and tested. These actuators use a combination of upward and downward unimorph bending to generate in-plane robotic joint motion. 500 μm by 100 μm actuators have demonstrated forces greater than 5 mN over almost 1 μm stroke length at just 20 V. These actuators can be leveraged to drive angular displacement of high-aspect ratio silicon flexures. Actuators are currently being integrated into flexural arrays to produce joint angles comparable to insects. Stacks of these silicon joint structures may be used to reinforce load-bearing capacity of the completed micro-robotic legs. Dynamic simulations of hexapedal and many-legged robots less than one centimeter in length utilizing these actuator-joint structures indicate potential payloads ranging from 50 to 200 mg, depending on the joint design, and walking speeds up to approximately 4 cm/s.
Multi-axis (z, θx, θy) micro-actuators based on thin-film lead-zirconate-titanate (PZT) for use in dual axes confocal microscopy are presented with their static and dynamic models. Prototype actuators have achieved as much as 430 μm of vertical displacement and ±10° of mechanical tilting angles in both θx and θy directions in a footprint of 3.2×3.2 mm. The experimental static displacements and transient response of the actuator were used to identify residual stresses in the thin films, dimensional variance due to fabrication limitation, and damping coefficients in the model. With the identified parameters, the model predicts the static displacements of the four corners of the stage with an average absolute error of 17.4 μm over five different voltage levels and shows a reasonable agreement with the experimentally measured transient dynamic data. These results will be used to develop closed-loop controller for the system.
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