Abstract
Piezoelectric actuators have achieved remarkable progress in many fields, being able to generate forces or displacements to perform scanning, tuning, manipulating, tactile sensing or delivering functions. In this work, two piezoelectric PZT (lead zirconate titanate) bimorph actuators, with different tip contact materials, were applied as tactile sensors to estimate the modulus of elasticity, or Young’s modulus, of low-stiffness materials. The actuators were chosen to work in resonance, taking advantage of a relatively low resonant frequency of the out-of-plane vibrational modes, associated with a convenient compliance, proven by optical and electrical characterization. Optical measurements performed with a scanning laser vibrometer confirmed that the displacement per applied voltage was around 437 nm/V for the resonator with the lower mass tip. In order to determine the modulus of elasticity of the sensed materials, the stiffness coefficient of the resonator was first calibrated against a force sensor, obtaining a value of 1565 ± 138 N/m. The actuators were mounted in a positioning stage to allow approximation and contact of the sensor tip with a set of target materials. Electrical measurements were performed using the resonator as part of an oscillator circuit, and the modulus of elasticity of the sample was derived from the contact resonant frequency curve of the cantilever–sample system. The resulting sensor is an effective, low-cost and non-destructive solution compared to atomic force microscopy (AFM) techniques. Materials with different modulus of elasticity were tested and the results compared to values reported in the literature.
Highlights
Creating devices able to operate at the micrometre scale has been part of the scope of the vanguard of science and technology for many years
In order to perform these measurements, the platform and actuator were moved with the virtual instrument to approach the tip and identify the contact on a sample of polylactic acid material, commonly known as PLA, frequently used in 3D printing
Once the actuator was brought into contact with the PLA sample, three open-loop measurements were completed by moving the platform between the positions 7.15 and 7.75 μm in the z-axis direction
Summary
Creating devices able to operate at the micrometre scale has been part of the scope of the vanguard of science and technology for many years. Sensors and actuators have been usually driven by electrostatic [1], electromagnetic [2], thermal [3], piezoelectric [4] and Lorentz forces [5,6]. The use of piezoelectric excitation is challenging, since a considerable voltage is needed to achieve practical forces or displacements. In-plane piezoelectric actuators, using PZT (lead zirconate titanate) as a piezoelectric layer, have recently shown promising results: laser-machined [7] and thick-film. In general, have achieved remarkable progress in many fields [12,13], being able to generate forces or displacements to perform scanning, tuning, manipulating, tactile sensing or delivering functions [14,15]. Tactile sensing might be one of the most complex sensing modalities
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