KEYWORDS: Tunable filters, Feedback control, Control systems, Digital signal processing, Electronic filtering, Repetition frequency, Signal processing, Mirrors
In ground-based mid-infrared observations the background radiation must be removed. Chopping is a background removal method requiring fast switching of the observation field. For MIMIZUKU, the mid-infrared instrument for the TAO telescope, we have developed a cold chopper which switches the observing field by tilting a movable mirror inside MIMIZUKU, instead of tilting the large secondary mirror.
We require a short transition time, sufficient amplitude, high frequency and steadyness for observation in the chopper movement.
With Repetitive Control we significantly increase performance by iteratively improving a feedforward trajectory and continously adapting to changes in the nonlinear dynamics.
This allows for much shorter transition time (<30 ms) and more freedom in the design of a feedback controller. Furthermore, repetitive disturbances originating from the cryo-cooler can be countered thus improving stability on sky.
Controller design, stabilisation, choice of reference trajectory, real-time computability and performance trade-offs are subjects in this research.
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