Sensing One Nanometer Over Ten Centimeters: A Microencoded Target for Visual In-Plane Position Measurement

At the nanoscale, accurate control and position sensing are recurrent issues conditioning advances of technologies and instruments in diverse fields of application. Recent advances were reported that combine optical microscopy and computer vision for noncontact and multiaxis position sensing of end-effectors with a high accuracy. This article contributes to this domain by introducing a microencoded target aimed to high accurate (x, y, theta) measurements over an extended range. The microencoded target is designed to allow linear phase measurements, leading to high accuracy in position sensing, and unambiguous binary encoding leading to absolute position determination. In this way, ultimate performances and allowed measurement ranges are independent of each other and a current zone of observation can be registered with respect to the whole encoded area with an extra-large range-to-resolution ratio. Experiments reported in this article demonstrate a precision below 1 nm in lateral position and of 4 . 10(-6) rad. in rotation with an encoded target of more than 11 x 11 cm(2). The device demonstrated can be either inserted into experimental setups to allow accurate position control or used to calibrate in-plane displacements of one to three degrees of freedom actuators.