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Servomechanisms - Mechanical Inertia And Servomechanisms

antenna overshoot error oscillation

There is a similar overshoot problem that requires compensation by mechanical servomechanisms. If a servo is used to manipulate a massive object such as a radar antenna weighing 1,000 lb (454 kg) or more, the actuator must anticipate the antenna's approach to a newly-selected position. The inertial mass of the antenna will otherwise cause it to overshoot the desired alignment. When the feedback signal is compared with the input and the control electronics discovers the over-shoot, the antenna will reverse direction in an attempt to correct the new error. If the antenna overshoots again this may lead to a continuing oscillation called hunting where the antenna continually seeks a null but always turns too far before shutting down, requiring a continuing series of corrections. The resulting oscillation is very undesirable.

Servomechanisms must use very sophisticated electronic circuits that act as electronic anticipators of the load's position and speed to minimize instability while simultaneously maintaining a fast response to new instructions. Better servomechanism designs adjust the timing of error signals to provide just the right amount of anticipation under varying circumstances. The electrical phase-shift network needed to produce a stable servomechanism must be designed with great care.

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