Servosila recently completed a challenging project called "Tracking Telescope" that we would like to tell about.
A customer, an established telescope manufacturer, required a very high precision of motion control at very low speeds for a two-axis direct-drive telescope fixture. The fixtures are equipped with Servosila SC-25C servo drives and Renishaw 26bit optical encoders.
The telescopes are about 2meters long and are pretty heavy due to powerful optics. The positioning tolerance requirement is ~1.0 arc-second which calls for about 21bits of effective positioning accuracy with the 26bit encoders.
Furthermore, since celestial objects keep moving, this accuracy has to be maintained while tracking objects moving at speeds of up to 2.0 degrees per second. This corresponds to RPMs in the range of Zero to 0.30 RPM. Moving at such low speeds is a challenge in its own right.
An extensive use of Servoscope simulation software helped identify an envelop of configuration parameters that allowed the SC-25C servo drives to meet or exceed the tolerance requirements as well as the tracking performance requirements. It took a clever application of Velocity Feed Forward Signal in a PID loop to make such tracking possible.
We are soon publishing a technical paper that records the experiences and details a tuning procedure for Servosila SC-25C servo drives that resulted in the required performance.
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