A large-stroke planar 2-DOF flexure-based positioning stage for vacuum environments

The growing demand from industry for high-precision systems introduces new challenges for positioning mechanisms. High accuracy and repeatability down\ud to the sub-micron scale are not uncommon. This is often combined with extreme environments, like high UV light sources, electron beams or vacuum. This\ud article focuses on the flexure mechanism for a largestroke planar XY-positioning system. Applications for such a flexure mechanism can be found in for example lithography, micromachining or microscopy

High precision optical fiber alignment using tube laser bending

In this paper, we present a method to align optical fibers within 0.2 μm of the optimal position, using tube laser bending and in situ measuring of the coupling efficiency. For near-UV wavelengths, passive alignment of the fibers with respect to the waveguides on photonic integrated circuit chips does not suffice. In prior research, it was shown that permanent position adjustments to an optical fiber by tube laser bending meets the accuracy requirements for this application. This iterative alignment can be done after any assembly steps. A method was developed previously that selects the optimal laser power and laser spot position on the tube, to minimize the number of iterations required to reach the target position. In this paper, that method is extended to the case where the absolute position of the fiber tip cannot be measured. By exploiting the thermal expansion motion at a relatively low laser power, the fiber tip can be moved without permanent deformation (only elastic strain) of the tube. An algorithm has been developed to search for the optimal fiber position, by actively measuring and maximizing the coupling efficiency. This search is performed before each bending step. Experiments have shown that it is possible to align the fiber with an accuracy of 0.2 μm using this approach

Laser forming for sub-micron adjustment: with application to optical fiber assembly

Laser forming is a method to deform a material by controlled local laser heating. In combination with a dedicated actuator topology, those deformations can be used for high precision alignment of components. This thesis applies this method to the alignment of optical fibers with respect to the waveguides on photonic integrated circuit chips. Recent advances in optical waveguide technology on these chips allow for wavelengths from UV to the visible range. However, the connection and assembly of the fibers requires an alignment accuracy of about 0.1 µm, which cannot be achieved using passive alignment. A fiber alignment actuator was developed that consists of a stainless steel tube. The tube can be bent locally by laser forming, resulting in a translation of the fiber tip. It has been found that there exists significant scattering of the magnitude and direction of the bending. Therefore, an alignment algorithm was developed that sets the optimal process parameters to iteratively converge to the optimal position with a minimum number of bending steps. Simulations and experiments using this algorithm show that the fiber tip reaches the target position within 15 steps, with an accuracy of 0.1 µ

Microtube laser forming for precision component alignment

A micro-actuator for precision alignment, using laser forming of a tube, is presented. Such an actuator can be used to align components after assembly. The positioning of an optical fiber with respect to a waveguide chip is used as a test case, where a submicron lateral alignment accuracy is required. A stainless steel tube with an outer diameter of 635 μm was used as a simple and compact actuator, where the fiber is mounted concentrically in the tube. An experimental setup has been developed to measure the fiber displacement in real time with a resolution better than 0.1 μm. In addition, this setup allows the axial and radial positioning of the laser spot over the surface of the tube. Several tube samples were (de)formed to move a fiber to a predefined position, using a laser with a wavelength of 1080 nm, a pulse length of 200 ms, and a power between 4 W and 10 W. On average of 18 laser pulses were required to reach the targeted position of the fiber with an accuracy of 0.1 μm. It has been found that increasing the laser power not only results in a larger bending angle but also in a larger uncertainty of this angle. The opposite is true for the radial bending direction, where the uncertainty decreases with increasing laser power.</jats:p

Polymer-filler interactions in poly(vinyl chloride) filled with glass beads: effect of grafted poly(methyl methacrylate)

Adhesion between filler and matrix has been studied using a model system composed of glass bead filled poly(vinyl chloride) (PVC). Stress-strain and volume-strain tests and scanning electron microscopy revealed that adhesion is improved by grafting poly(methyl methacrylate) (PMMA), which is known to be miscible with the PVC matrix, upon the surface of the glass beads. The best results were obtained when large amounts of grafted PMMA were used, leading to maximum stress of the composite, nearly as high as that of pure PVC.

Exact Constraint Design of a Two-Degree of Freedom Flexure-Based Mechanism

We present the exact constraint design of a two degrees of freedom cross-flexure-based stage that combines a large workspace to footprint ratio with high vibration mode frequencies. To maximize unwanted vibration mode frequencies the mechanism is an assembly of optimized parts. To ensure a deterministic behavior the assembled mechanism is made exactly constrained. We analyze the kinematics of the mechanism using three methods; Grüblers criterion, opening the kinematic loops, and with a multibody singular value decomposition method. Nine release-flexures are implemented to obtain an exact constraint design. Measurements of the actuation force and natural frequency show no bifurcation, and load stiffening is minimized, even though there are various errors causing nonlinearity. Misalignment of the exact constraint designs does not lead to large stress, it does however decrease the support stiffness significantly. We conclude that designing an assembled mechanism in an exactly constrained manner leads to predictable stiffnesses and modal frequencie