Robotic control and force-feedback applications require multi-axial force and torque sensing. One possible implementation of future sensors is seen in fiber optic force torque sensors, since the signal demodulation may be located in some distance to the actual sensor and they also do not have to include any magnetic material. This article presents a fiber Bragg grating-based force and torque sensor with six degrees of freedom. The general setup resembles a Stewart platform. Its connecting beams are formed by the fiber used to measure the deformation of the transducer. The element creating stiffness may be of arbitrary form. We demonstrate how the sensor is realized and show results of all six force and torque measurements. We present a theoretical model of the sensor. The results in this work demonstrate the feasibility of a fiber-optic force-torque sensor.

No abstract

Quality control of microchemical products is based on the inspection of surface topography, film thickness and other optical constants. Especially for lab-on-chip applications, there is a strong demand for concurrent metrology and passive layer thickness observation. Chromatic confocal microscopy is a common method to reconstruct surface topographies, while thin film reflectometry is a technique for measuring film thicknesses. In this work, we present a combination of these two established techniques, simultaneously determining topography and film thickness. The proposed spectrometric measuring system captures confocal and thin film signals from a given sample. The extracted signals are analyzed according to a given model by a least-squares estimator in order to extract the parameters of interest. Finally, the sample's film thickness and topography are locally determined at the same time and with high precision. By scanning the sample surface laterally, both the surface topography and its film thickness can be reconstructed. The presented measurements performed at a test object exhibit excellent performance of the method.

The polarization-dependent reflection spectra of fiber Bragg grating (FBG) sensors in polarization-maintaining fibers are influenced by shear strain. This influence can be evaluated from a tensorial coupled-mode theory approach. Yet, this approach requires the numerical integration of the four coupled-mode equations. We present an easy to handle, completely analytical treatment of the polarization-dependent reflection spectra of FBGs. We derive the required equations and compare the results to the numerical integration of the four tensorial coupled mode equations.

No abstract