Dynamic out-of-plane displacement measurement using the instantaneous analysis phase-shifting method
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TECHNICAL PAPER
Dynamic out-of-plane displacement measurement using the instantaneous analysis phase-shifting method Hong-Yih Yeh1 • Ying-Kai Hsu1 • An-Chi Wei1 • Ju-Yi Lee1 Received: 24 June 2020 / Accepted: 28 August 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents an instantaneous analysis shadow moire´ method for dynamic out-of-plane displacement measurement. The shadow moire´ method is widely applied to the measurement of the out-of-plane displacement, such as the deformation or warpage on the surface of the objects. Generally, the method of phase shifting is used to analyze the phases of the shadow moire´ fringes and to obtain the out-of-plane displacement. To generate accurate phase shifting, the grating must be moved step by step precisely. However, the step motion provided by the conventional mechanical device is neither accurate nor prompt. In this study, a novel stair-structured plate consisting of a series of 4-step-height sets is designed to produce shadow moire´ fringes with the quadrature phase. The quadrature-phase fringes are utilized to extract instantaneously the shadow moire´ phase for measurement of the dynamic out-of-plane displacement of an object. Experiments show that our method can effectively detect the dynamic out-of-plane displacement with a micrometric scale resolution and is capable of suppressing the discrepancy of displacement to 0.83 % . The proposed measurement method of the out-plane displacement is suitable for the pressure sensing or application of the tactile sensor.
1 Introduction Tactile sense is an essential function for a humanoid robot to acquire the force sensation on the interface between the robot and the object. Most of tactile sensors are composed of piezoresistive pressure sensors (Florez and Velasquez 2010). By means of measuring the change of the resistivity, the pressure sensor can detect how much it is pressed changing the out-of-plane displacement of the sensor. Moreover, sensors are fairly low cost, and easy to use but they are rarely accurate. There are several optical noncontact methods to solve accuracy problems. Liu and Lin (2013) proposed a three-point method for surface topography through measuring the out-of-plane displacement of an object with 0:1 l m accuracy. Liu’s method focused on the measurement of the surface profile of an object, and it is the static measurement of out-of-plane displacement. On the contrary, optical interferometer provides a precise and dynamic out-of-plane displacement measurement (Mohan et al. 1993; Van Haasteren and Frankena 1994). However, & Ju-Yi Lee [email protected] 1
many of them demand the coherent light sources. One of the further techniques free from coherent lights is the shadow moire´ method. The shadow moire´ technique with the typical phase-shifting algorithms (Perrin and Guilherme 2000) has been used to produce an optical noncontact method for surface topography measurement, outof-plane displacement measurement, deforma
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