Bi-polar disk torquing system for a disk drive to free stuck transducers

A method for freeing for rotation a disk driven by a multiple stator pole, multi-phase DC motor in a disk drive when a transducer has stuck to a surface of said disk, forming a stuck transducer/disk assembly having a resonant frequency, comprising the steps of:

• commutating bi-polar DC power of a first frequency at a first approximation of said resonant frequency to successive phases of said multi-phase motor for a predetermined number of cycles to start said motor beginning with a random motor phase;
• multi-phase motor for zero crossings;
• commutating bi-polar DC power of a second frequency at a second approximation of said resonant frequency when at the end of said predetermined number of cycles at said first frequency no back EMF voltage zero crossing is detected;
• commutating said bi-polar DC power at said second frequency to successive phases of said multi-phase motor for a predetermined number of commutation cycles, and
• monitoring the back EMF voltage of said multi-phase motor for zero crossings to determine if said multi-phase motor is rotating.

A motor control circuit for energizing a multi-phase motor for rotating a hard disk of a disk drive when a transducer of a transducer actuator has adhered to a surface of said hard disk, joining said transducer actuator and said hard disk in a transducer actuator/hard disk assembly having a resonant frequency, said motor control circuit comprising:

• a. a sensorless multi-phase motor,
• b. circuit means for commutating bi-polar voltages from a DC power supply to successive phases of said sensorless multi-phase motor for a predetermined number of successive commutation cycles equal to a multiple of twice the number of motor phases plus one motor phase for producing bi-directional motor torquers at substantially the resonant frequency of said transducer actuator/hard disk assembly,
• c. means for maintaining excitation of said plus one motor phase for a predetermined time interval, and
• d. means for sensing the zero crossing of the back EMF voltage of said sensorless multi-phase motor during said predetermined time interval for indicating whether said motor is rotating.

A motor control circuit for energizing a multi-phase motor for rotating a hard disk of a disk drive when a transducer of a transducer actuator has adhered to a surface of said hard disk, joining said transducer actuator and said hard disk in a transducer actuator/hard disk assembly having a resonant frequency, said motor control circuit comprising:

• a. circuit means for commutating bi-polar voltages at a first frequency which is a first approximation of said resonant frequency, from a DC power supply to successive motor phases in each commutation cycle, for a predetermined number of successive commutation cycles equal to a multiple of twice the number of motor phases plus one to produce a bi-directional motor torque which is a stepped, substantially sinusoidal motor torque at substantially the resonant frequency of said transducer actuator/hard assembly, in which excitation of the final motor phase is held on while the back EMF of said motor is sensed to detect if rotation is produced;
• and
• b. means responsive to the back EMF voltage of said multi-phase motor for changing the frequency of said bi-polar voltage to a second frequency which is a second approximation of said resonant frequency, for a second predetermined number of cycles, to attempt to increase said bi-directional motor torque if said hard disk fails to rotate when energized with said bi-polar voltage at said first frequency.

A control system for freeing for rotation a disk assembly in a head/disk assembly of a disk drive when a transducer of the head/disk assembly is stuck to a surface of a disk, forming a stuck head/disk assembly, comprising:

• a. a sensorless multi-phase motor forming a part of said disk assembly for rotating said disk assembly;
• b. a motor control circuit for commutating bi-polar voltages at a selected frequency to successive phases of said motor for a predetermined number of successive commutation cycles equal to a multiple of twice the number of phases of said motor, and, after the last motor phase of the last commutation cycle of said predetermined number of commutation cycles, for applying and for maintaining for a time interval a voltage to a succeeding motor phase;
• c. means for sensing zero crossings of the back EMF voltage of said motor, at least during said interval of time, for indicating whether there is motor rotation, and
• d. means responsive to said means for sensing zero crossings, in the event no zero crossings are sensed, for initiating a second commutation of bi-polar voltages at a selected frequency to successive phases of said motor for a second said predetermined number of successive commutation cycles beginning with that motor phase which follows said succeeding motor phase in the succession of motor phases.

A control system for freeing for rotation a disk assembly in a head/disk assembly of a disk drive when a transducer of the head/disk assembly is stuck to a surface of a disk, forming a stuck head/disk assembly, comprising:

• a. a sensorless multi-phase motor forming part of said disk assembly for rotating said disk assembly;
• b. a motor control circuit for commutating bi-polar voltages at a selected frequency to successive phases of said motor, starting at random with a first phase of said motor to initiate a predetermined number of successive commutation cycles equal to a multiple of twice the number of phases of said motor, and, after the last motor phase of the last commutation cycle of said predetermined number of commutation cycles, for applying and for maintaining for a time interval a voltage to said first phase of said motor, said first phase of said motor following the last motor phase of the last commutation cycle of said predetermined number of commutation cycles;
• c. means for sensing zero crossings of the back EMF voltage of said motor, at least during said interval of time, for indicating whether there is motor rotation, and
• d. means responsive to said means for sensing zero crossings, in the event no zero crossings are sensed, for initiating a second commutation of bi-polar voltages at a selected frequency to successive phases of said motor for a second said predetermined number of successive commutation cycles plus one motor phase, beginning with that phase of said motor which follows said first phase of said motor.

A control system for freeing for rotation a disk assembly in a head/disk assembly of a disk drive when a transducer of the head/disk assembly is stuck to a surface of a disk, forming a stuck head/disk assembly, comprising:

• a. a sensorless multi-phase motor forming part of said disk assembly for rotating said disk assembly;
• b. a motor control circuit for commutating bi-polar voltages at a selected frequency to successive phases of said motor, starting at random with a first phase of said motor to initiate a predetermined number of successive commutation cycles equal to a multiple of twice the number of phases of said motor, and, after the last motor phase of the last commutation cycle of said predetermined number of commutation cycles, for applying and for maintaining for a time interval a voltage to said first phase of said motor, which first phase follows the last motor phase of the last commutation cycle of said predetermined number of commutation cycles;
• c. means for sensing zero crossings of the back EMF voltage of said motor, at least during said interval of time, for indicating whether there is motor rotation;
• d. means for recycling for a predetermined number of times said predetermined number of successive commutation cycles after each sensing for zero crossings when no zero crossings are found;
• e. means for sensing the polarity of the back EMF voltage after sensing of a zero crossing for determining the direction of motor rotation, and
• f. means responsive to a predetermined polarity of said back EMF voltage for commutating bi-polar voltages to rotate said motor.