YAGboss - Laser micro-sculpting of metal surfaces for the manufacture of high precision optical encoder scale

High-precision positioning is an important aspect of process control. In this context, high resolution positioning feedback provided by high accuracy optical position encoders (OPE) is an invaluable tool which is implemented on a wide range of automated systems where precise positioning is the key to successful applications or technology development. OPEs consist of two main elements: a scale and a read-head. Although OPE have been part of the industrial landscape for the last 30+ years, their current fabrication scheme is no longer in line with the requirements of increasingly more demanding applications such as electronic assembly or semiconductor manufacturing requiring nanometre resolution. Indeed, the mechanical embossing techniques traditionally used to manufacture the diffractive scales found in OPE are limited in resolution, whilst the alternative lithographic techniques are unsuitable for mass production and long scale lengths. This paper introduces a novel laser-based high precision micro-sculpting technique for the development of diffractive scales. It focuses on improving the scale's resolution whilst retaining commercially-viable process rates to realise the production of 100s of meters of sinusoidal surface features, 200nm±10nm deep and 4µm±0.1µm wide. In this paper, we investigate how the characteristics of the generated surface features (shape, width, depth) depend on the combination of laser parameters and processing atmosphere. Samples of 8µm-pitch scales marked on stainless steel are assessed by metrology and in conjunction with a read-head to evaluate their efficiency.