コンデンサで制動された可動コイル式アクチュエータの周波数応答

概要

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The dynamic tracking system of a video tape recorder (VTR) uses a moving-coil head actuator. The head fluctuates at the mechanical resonant frequency which is higher than fundamental drive frequency, so damping of mechanical resonance is important.In voltage drive, short-circuit damping effectively reduces the Q factor of resonance. However, voltage-displacement sensitivity varies with the coils resistance. On the other hand, in current drive, short circuit damping is not effective, but current-displacement sensitivity does not vary with the coils resistance.In order to obtain fine tracking, both the Q factor and the sensitivity variation need to be reduced. Consequently, a capacitor damping is proposed in which the actuator is short-circuited by a capacitor. This damping method is expected to have the following characteristics: a) current drive around the fundamental drive frequency, and b) voltage drive at frequency around the mechanical resonance.The sensitivity variation of the proposed circuit with respect to load resistance, as well as the frequency response of an actuator driven by this circuit, have been investigated by using an equivalent circuit and circuit simulation program, SPICE. The experimental results confirm that the Q factor and the sensitivity variation have both been reduced.
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