MEANS FOR PARKING READ/WRITE HEADS IN A DISC DRIVE USING THE BACK-EMF OF THE SPINDLE MOTOR TO OPERATE A STEPPER MOTOR

Electronic circuitry is provided to position the read/write heads (10) in a designated landing zone when the electrical power is removed from the drive (27). when power is removed from the drive, the stored energy of the rotating spindle motor (27) is used as a source of electrical power and timing pulses to the stepper motor (30) 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 (50) is provided to couple the power and clock pulses to selected windings of the stepper motor (30) in an order that will cause the stepper motor to rotate in the direction necessary to move the transducer heads (10) to a predetermined park position at the inner diameter of the disc whenever power is removed from the disc drive. Since the location of the heads at power down may not be known, the timing of the pulses in such that a sufficient number of steps will be taken to move the transducer heads to the parking zone within the time allotted even if power down occurred when the heads were at the outermost track. Step pulses will continue to be generated until the back EMF of the spindle motor is insufficient to generate such pulses. After the transducer heads are at the predetermined parking location, any additional steps will cause the actuator to contact a mechanical "inner crash stop" designed to prevent damage to the transducer heads from contact with the clamp which retains the discs.