Alignment-free digital videorecorder-servo concept

An alignment-free servo concept for video recorders is presented that uses a microprocessor for digital regulation in combination with a novel drum-motor-control concept. The system is also capable of doing some of the required mechanical adjustments by itself. This servo concept is based on a general-purpose microcontroller with an enhanced-purpose microcontroller timer structure for measuring time intervals and generating output signals with a resolution of about 1 μs. In addition to the microprocessor, only a few amplifiers are needed to convert the incoming signals into logic levels and the pulse-length-modulated regulation signals into analog values. The drum motor is a DC brushless type with only one optocoupler as signal reference. It is controlled by a custom IC. The following functions are covered by this implementation: (a) the optocoupler signal is decoded for commutating of the motor, generating the speed and phase signals for the microprocessor; and (b) the output stages incorporate three push-pull stages with current limiter, a voltage-controlled loop for the output current, and a thermal shutdown stage with hysteresis