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VERSATILE OPTICAL ENCODER DISC FACILITY PRODUCES OPTIMUM RESULTS
Fundamentally, says the company, the degree of control required by the application determines the encoder disc's slot count and slot precision, and ultimately the manufacturing technology choice. Tecan has perfected many cost-effective manufacturing methods to produce burr and stress-free discs, with inherent mechanical strength and extreme levels of precision. The company selects one, or a combination of these technologies depending on the level of precision demanded, to produce the optimum price to performance ratio for the specific application. A recent example can be seen in the provision of a custom disc for a specialist designer and manufacturer of highly specialised torque transducer systems. Liaising with Tecan engineers the company realised that a demanding encoder requirement, in a sophisticated aerospace project, could be cost-effectively satisfied, while ensuring optimum opto-mechanical performance. Critical elements in the design and production of the encoder disc were the need to maintain mechanical strength under varying torque, speed and temperature conditions while ensuring fine optical resolution through high-accuracy apertures. This was achieved by employing a two-stage Photo Electroforming process, an extremely accurate technology where metal is 'grown' electrolytically atom by atom within a photolythographically defined resist mould. Initially, the disc is Photo Electroformed to a thickness of 20 micron, producing optical slots of the finest possible resolution. A second PEF stage is then carried out which leaves the high-accuracy slots as they are and selectively increases the thickness of the disc in other areas. The result is a single rigid part, with localised thickness variations across its surface to suit both optical and mechanical requirements. In this case, as opposed to traditional photo-film techniques, Tecan employed specialised high-resolution chrome-on-glass tooling to achieve optical aperture tolerances of ±1.6 micron. PEF discs are typically thinner, lighter and more robust than discs manufactured by other means. They feature slots with extremely smooth, yet optically sharp edges that facilitate a well-defined light pulse. Typical PEF tolerances are ±4 microns, and in some cases, ultra-high tolerances of ±2 microns or less can be achieved.
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