Multirate digital control system for use with a system having a linear transfer function, such as a head positioning system in a magnetic disc drive

A multirate digitally controllable hard disc storage system, including:

• a rotatable disc with positional information stored thereon;
• a read/write head for placement and retrieval of information storable on said disc;
• an actuator system having a linear transfer that positions said at least one read/write head adjacent said disc;
• and
• a multirate digital control system for controlling said actuator system, said multirate digital control system comprising:
• an estimator, coupled to receive sampled sensed positional information stored on said disc, and outputting a first control signal representing measured read/write head position, and outputting at least one second control signal representing estimated read/write head position;
• said first and second control signals being output at a multiple r of a rate of sampling said sensed positional information, wherein r.gtoreq.2, wherein the estimator outputs r-1 second control signals, and computational delay means for introducing a desired delay in said first and second output signals, said desired delay compensating at least in part for time necessary to compute said output signals, said estimator determining values for the first and second control signals at the rate of sampling said sensed positional information.

In a digital control system for use with a system having a linear transfer function, a method for generating actual and predictive data for positioning an element in the system based upon sampling sensed positional information stored in the system, the method comprising the following steps:

• (a) sampling sensed positional information at a sampling rate and computing a position measurement Y.sub.m ;
• (b) computing an output prediction error esterr;
• (c) qualifying said Y.sub.m measurement computed at step (a) with said output prediction error esterr computed at step (b);
• (d) calculating a first control value u(k,0) based upon esterr, as computed at step (b), and a precalculation based upon predicted states and generating a first control signal based on the first control value for repositioning the element in said system as needed;
• (e) calculating a current estimate using said esterr as computed at step (b);
• (f) calculating a second control value u(k,1), using said current estimate calculated at step (e);
• (g) calculating a prediction estimator, using said current estimate calculated at step (e) and using said second control value calculated at step (f);
• said steps (f) and (g) including introducing a desired delay in said first and second output signals, said desired delay compensating at least in part for time necessary to compute said first control value and said prediction estimator;
• and
• (h) generating a second control signal based on the second control value after an appropriate delay for repositioning the element in said system as needed.

For use with a hard disc storage system that includes a disc with positional information stored thereon, at least one read/write head for placement and retrieval of information storable on said disc, and an actuator system having a linear transfer function that positions said at least one read/write head adjacent said disc, a method for controlling said actuator system, said method comprising the following steps:

• (a) computing and outputting a position measurement of said read/write head at a sampling rate, said position measurement using samples of said positional information stored on said disc;
• (b) computing and outputting a prediction error associated with position of said read/write head at the sampling rate;
• (c) qualifying said measurement computed at step (a) with said output prediction error computed at step (b);
• (d) calculating a first control value based upon said output prediction error as computed at step (b), and a precalculation based upon predicted states, and applying the first control value to reposition said read/write head;
• (e) calculating a current estimate using said output prediction error as computed at step (b);
• (f) calculating a second control value using said current estimate calculated at step (e);
• (g) calculating a prediction estimator, using said current estimate calculated at step (e) and using said second control value calculated at step (f);
• said steps (f) and (g) including introducing a desired delay in said first and second output signals, said desired delay compensating at least in part for time necessary to compute said first control value and said prediction estimator;
• and
• (h) applying the second control value to reposition said read/write head after an appropriate delay.