Circuit and method for controlling the parking and unparking of a read-write head

A disk-drive system, comprising:

• a disk having a peripheral edge and a surface;
• a platform disposed adjacent to the peripheral edge of the disk and raised with respect to the disk surface;
• a coil;
• an arm;
• a read-write head coupled to the arm;
• and
• a nondithering control circuit coupled to the coil and adapted to receive a current signal indicating a magnitude of a current flowing through the coil, the nondithering control circuit operable to cause the coil to park the read-write head by sensing a speed of the arm during measurement periods when the current signal indicates substantially zero current flows through the coil and, in response to the sensed speed, moving the read-write head from over the disk onto the platform at approximately a constant speed.

A method, comprising:

• during hard-park and hard-unpark operations of a read-write head,
• accelerating the read-write head to approximately a predetermined speed using a head-motor coil;
• sensing a current flowing through the coil;
• directly monitoring a back voltage across two nodes of the coil such that no circuit element is in series with the coil between the two nodes during measurement periods when substantially zero current flows through the coil;
• and
• when or after the head attains the predetermined speed, maintaining the speed of the head at approximately the predetermined speed in response to the back voltage.

A method, comprising:

• coupling a nondithered drive signal to a coil of a motor assembly to park a read-write head on a ramped platform;
• sensing a current flowing through the coil;
• uncoupling the drive signal from the coil to allow the current flowing through the coil to decay to approximately zero;
• during hard-park and hard-unpark operations of the read-write head when the sensed current is approximately zero, sampling a back voltage across the coil;
• adjusting the drive signal in response to the sampled back voltage;
• coupling the adjusted drive signal to the coil, the adjusted drive signal shifting the back voltage toward or maintaining the back voltage substantially at a predetermined level;
• and
• repeating the sensing, uncoupling, sampling, adjusting, and coupling the adjusted drive signal one or more times.

A disk-drive system, comprising:

• a disk having a peripheral edge and a surface;
• a platform disposed adjacent to the peripheral edge of the disk and raised with respect to the disk surface;
• a coil;
• an arm;
• a read-write head coupled to the arm;
• and
• a nondithering control circuit coupled to the coil and adapted to receive a current signal indicating a magnitude of a current flowing through the coil, the nondithering control circuit operable to cause the coil to unpark the read-write head by sensing a speed of the arm during measurement periods when the current signal indicates substantially zero current flows through the coil and, in response to the sensed speed, moving the read-write head from the platform to a position over the disk at approximately a constant speed.

A method, comprising:

• coupling a nondithered drive signal to a coil of a motor assembly to park a read-write head on a platform;
• sensing a current flowing through the coil;
• uncoupling the drive signal from the coil to allow the current flowing through the coil to decay to approximately zero;
• sampling a back voltage across the coil while the approximately zero current is flowing through the coil;
• adjusting the drive signal in response to the sampled back voltage;
• coupling the adjusted drive signal to the coil, the adjusted drive signal shifting the back voltage toward or maintaining the back voltage substantially at a predetermined level;
• and
• repeating the sensing, uncoupling, sampling, adjusting, and coupling the adjusted drive signal one or more times only during hard-park and hard-unpark operations of the read-write head.