Interferometric device for the in-process measurement of diameter variation in the manufacture of ultraprecise spheres

Abstract

A novel device is presented which is designed for in-process measurements of the variation of the diameter of highly reflective spheres. Silicon spheres have been used for the new definition of the International System of Units (SI). Many spheres have to be processed, and the form of these objects, and thus the manufacturing process’s stability, needs to be controlled every day. Commercially available measurement equipment and even state-of-the-art spherical interferometers have reached their limits in terms of resolution, uncertainty, the complexity of their handling routines, measurement time and even financial investment. A novel setup has thus been designed after considering and selecting a special mechanical setup with a minimal measurement loop, stable optical sensors and a handling strategy which avoids collision and contact with the very valuable, superpolished spherical objects. Thus, the design minimizes the influence of the environment and reduces the measurement time at an equator with sub-nanometre resolution to 3 min. In addition, the analysis time is reduced to less than a minute.

Scientific Developments and New Technological Trajectories in Sensor Research

“…Historically, research and development (R&D) efforts in sensor technology have been funded as an adjunct to large application programs that required sensors [ 16 ]. Now, selected R&D investments support the development of new and improved sensors with effective research planning processes directed to users for specific applications [ 129 ]. The description here of new technological directions and characteristics of sensors, having improved performance capabilities and applications in different settings, can help policymakers to enhance the allocation of R&D investments in private and public research organizations for scientific and technological development, and technology transfer of new sensors in society [ 56 , 64 , 130 , 131 , 132 , 133 , 134 , 135 , 136 ].…”

Non-contact ultrasonic inspection by Gas-Coupled Laser Acoustic Detection (GCLAD)

“…Vibrometers represent a particular type of interferometers based on the Doppler effect (laser Doppler vibrometers 19 ): for effective ultrasound detection, the emitted laser beam is immediately split into two beams, one with an additional frequency component resulting from the passage through an acousto-optic modulator; the differences between the two beams in frequency terms, more evident because of the preliminary passage in the modulator, provide the speed of the particles on the surface rather than their displacement. Interferometric techniques are characterized by high sensitivity, broad band and point detection 20 . Optimization of the tools made these techniques usable even on not perfectly smooth or reflective surfaces 21 , 22 , finding applications in numerous industrial fields.…”

A Real-Time Automated System for Dual-Aperture Common-Path Interferometer Phase-Shifting

“…In-process measurement characteristics require high-speed, high-resolution, real-time measurement, and optical measurement systems provide reliable alternatives to perform measurements and monitoring. Interferometric approaches have been widely used for surface measurement because they can provide noncontact, high-resolution, and high-accuracy measurements [3][4][5]. Particularly, common-path interferometers such as Fizeau or Twyman-Green have been widely used for ex-situ surface measurement, however, for on-machine measurement it is necessary to reduce the influence of disturbances associated with the process [4,5].…”