A robust position measurement system for precision alignment of roll-to-roll printing using alignment patterns and light quantity

Roll-to-roll printing is a suitable technology for large-scale and high-speed mass production, and is a next-generation process technology that can be used to fabricate electronic devices and circuits by printing functional ink on a web, which is a flexible material like a film. As with lithography, roll-to-roll processing also must to achieve accurate layer-to-layer alignment in fabricating multi-layered circuits or devices. This alignment precision, in fact, is a critical factor in determining the integration and performance of printed electronics. As precise measurement of web positions is required to commercialize any process used to make printed electronics, a measurement system with an optical encoder with a precision on the level of micrometers was proposed in the preceding paper. However, it was not possible to measure the lateral positions of the web in the preceding paper because the phenomenon of the entire web being moved in the lateral direction could not be detected. In this paper, a measurement system that utilizes differences in the amount of light reflected from the alignment patterns depending on the web positions in the lateral direction is proposed for measuring the lateral positions of the web. This measurement system is a simultaneous web position measurement system for the moving direction and the lateral direction that uses only one optical sensor. It is also capable of detecting lateral deformation as well as lateral angle if two optical sensors are used. Since measurement noise can influence the measurement error, high measurement precision is obtained by adapting the Hilbert transform method, which is robust against noise. In addition, system reliability is verified through the linearity and repeatability of the experimentally measured signals.