The control of a 75 centimeter diameter Atacama Large Millimeter/submillimeter Array (ALMA) [1] nutating subreflector, or Nutator, to meet the specifications of 10 millisecond (ms) settle time and 1.3 arc-second pointing error involves tremendous challenges. The ALMA Nutator has been under development since 2003 [2], and we have improved its dynamic characteristics through robust PID control algorithm, increasing the open loop bandwidth to beyond 200Hz and shortening the settle time to 20 ms. A mode switching associate with model following control scheme is also presented, and expected to improve the settle time and pointing error.
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