Innovation sometimes explodes onto the scene as a disruptive technology. More often, though, it arrives quietly in the form of continuous improvement that enhances performance and expands the scope of application capabilities. Sometimes evolutionary improvements are subtle, but once in a while they are game-changing.
When it comes to magnetic linear encoders, there have been steady improvements over the years in terms of resolution and linearity, enabling them to replace optical linear encoders in many applications at a fraction of the cost. One stubborn limitation, however, has been the trade-off between measuring performance and tape-to-sensor gap distance, sometimes called simply the gap distance or the ride height. Generally speaking, the higher the resolution and/or linearity specification, the smaller the allowable gap distance or ride height becomes. This reduction in ride height requires a corresponding tightening of machine tolerances in order to ensure that the maximum allowable gap distance is not exceeded.
Recent breakthroughs in magnetic encoder design and technology have resulted in a new class of linear encoder systems that offer greatly expanded ride height. For example, an incremental system with 1 μm resolution and a system accuracy of ± 10 μm required a typical maximum tape-to-sensor gap distance of 0.35 mm. Now, the new generation of encoder technology can deliver the same 1 μm resolution and a similar ± 12 μm system accuracy, but with a maximum gap distance of 1.0 mm, nearly a threefold increase in ride height. That means far better tolerance of variability in the gap distance as the machine goes through its motions.
What’s more, encoder functionality can be assured even when the gap distance increases to as much as 1.8 mm, albeit with some loss of accuracy at these extreme distances. The ability to tolerate expanded variation in ride height ensures that machine operation will not be disrupted by loss of the encoder signal, even when gap tolerances occasionally exceed design maximums. That translates directly into greater design freedom for the engineer, and more machine uptime with fewer nuisance stoppages for the end user.
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