Synchronized spindle control for disk drives

Apparatus for controlling the angular position of a first index on a rotating disk of a first disk drive with respect to a second index on a rotating disk of a second disk drive comprising:

• first detecting means for detecting each revolution of said first index, said first detecting means outputting a first output signal in response to said detection of said first index signal;
• first comparing means coupled to said first output signal for comparing said first output signal to a first reference signal, said first comparing means providing a first error signal representing a difference between said first output signal and said first reference signal;
• first feedback means coupled to said first error signal and to a motor rotating said first disk for controlling the rotation speed of said motor;
• second detecting means for detecting each revolution of said second index, said second detecting means outputting a second output signal in response to said detection of said second index signal;
• second comparing means coupled to said second output signal for comparing said second output signal to a second reference signal, said second comparing means providing a second error signal representing a difference between said second output signal and said second reference signal;
• second feedback means coupled to said second error signal and to a motor rotating said second disk for controlling the rotation speed of said motor;
• third comparing means coupled to said first and second output signals for comparing said first and second output signals and providing a third error signal representing a difference between said first and second output signals;
• third feedback means coupled to said third error signal and to said motor of said second disk drive for controlling position of said second index with respect to said first index.

A method for synchronizing a plurality of disk drives comprising the steps of:

• designating one of said plurality of disk drives as a master drive;
• providing a first output signal from said master dirve representative of the angular position of a rotating disk on said master drive;
• designating the other of said plurality of disk drives as slave drives;
• providing an output signal from each of said slave drives representative of the angular position of a rotating disk on each of said slave drives;
• generating for each or said slave drives a first error signal representing a difference between said first output signal and said output signal of each said slave drive by comparing said first output signal to said output signal of each of said slave drives;
• controlling the rotation of said slave drives in relation to said first error signal such that the angular position of said slave drives is dependent on said first output signal.