Method and means for parking read/write heads in a disc drive using the back- emf of the spindle motor to operate a stepper motor

Abstract From the Canadian patent

Electronic circuitry is provided to position the read/ write heads in a designated landing zone when the electrical power is removed from the drive. When power is removed from the drive, the stored energy of the rotating spindle motor is used as a source of electrical power and timing pulses to the stepper motor which drives the actuator of the disc drive. The power generated by the spindle motor as it spins down is referred to as "back EMF." A sequencer circuit is provided to couple the power and clock pulses to selected windings of the stepper motor in an order that will cause the stepper motor to rotate in the direction necessary to move the transducer heads to a predetermined park …