Presented is a simple method combining a pre-stretching process with stencil lithography for high-resolution patterning of liquid metal wires on polydimethylsiloxane (PDMS) substrates. The PDMS substrate is pre-stretched to several times its original length before casting liquid metals, it is released and restores back to its original length after casting liquid metals through a stencil mask; hence, the width and spacing of the patterned liquid metal wires decrease simultaneously with the PDMS substrate. The degree to which the width and spacing of liquid metal wires decrease is approximately equal to the times that the PDMS substrate is pre-stretched. An ultraviolet-ozone surface modification method was used to enhance the adhesion between liquid metals and PDMS substrates, and an alternative method based on applying an external electric field was proposed to remove excess liquid metals over the stencil mask. Sub-30 µ m liquid metal wires were successfully patterned. As a demonstration, a liquid metal based flexible strain sensor was fabricated, the sensor exhibited excellent stretchability, stability, sensitivity and durability.

The machine vision measurement module is indispensable for the Modularized Flexible Precision Assembly Station (MFPAS), which is a fully automatic assembly system being developed at Dalian University of Technology (DUT). MFPAS consists of basic and additional modules, and are expected to be flexible, expandable, and re-configurable to adapt to a variety of parts with a large size range, requiring the machine vision measurement module to be able to achieve accurate measurement of position, as well as orientation of the parts with different size scale. An automatic zooming vision system was set up for evaluation and final integration in MFPAS. Pixel equivalent, principal point and orientation deviation of images were analyzed and experimentally studied using different magnifications of the lens. A new template with circular patterns of different diameters was designed for zoom-lens calibration. The experiments show that the measurement error caused by the variation of the pixel equivalent, principal point and orientation is estimated under 10 μm without online calibration. When high accuracy is required, online calibration can be employed during assembly. The evaluation results of the vision system with or without on-line calibration were given for a better trade-off between accuracy and efficiency during assembly.