UV imprint fabrication of polymeric scales for optical rotary encoders

• Polymeric scale gratings for interferential rotary encoders were made by UV imprint.
• Acrylic trimethylolpropane ethoxylate photopolymer on PET substrate was used.
• Problems concerned with mould contamination or sticking to the polymer were absent.
• Replicated scales have demonstrated good reproducibility of Si mould features.
• Effective transmitted diffraction in the zero and first order was achieved.

Optical encoders are one of the most common displacement sensors. Scale gratings for such sensors are usually made of glass. However, polymers can offer several advantages such as lightweight, low cost fabrication and versatility in structures and grades. In this paper application of UV imprint technique to fabricate polymeric scale gratings for rotary encoders is reported. Experiments are performed by imprinting 3 μm layer of UV sensitive photopolymer coated on the substrate made of 200 μm PET film. Process of UV imprinting caused no problems concerned with mould contamination or sticking to the polymer. Optical microscopy and AFM measurements of replicated polymeric scales have demonstrated the absence of macro-defects and good reproducibility of Si mould features with lateral dimensions down to the order of hundreds of nanometers. Measurements of intensity distribution in transmitted diffraction pattern have showed an effective diffraction with most of the diffracted light intensity concentrated in the zero and first diffraction order as it is required for the application in optical rotary encoders employing interferential scanning principle. Commercialization of UV imprint technology would allow replacement of conventional glass scales at least in those applications where lightweight and low price of encoders are of great importance.