Servo control apparatus and method using absolute value input signals

A control system for a controlled variable representative of a system, wherein the system is characterized by an observable variable and wherein at least two values of the controlled variable correspond to a single value of the observable variable, the control system comprising:

• a signal source providing first and second values of the observable variable, the second value of the observable variable subsequent in time to the first value of the observable variable;
• mapping logic, the mapping logic receiving the first value of the observable variable and outputting a first and a second possible value of the controlled variable;
• a first estimator capable of estimating a future state of the system to be controlled, the first estimator receiving the first possible value of the controlled variable and producing a first predicted value of the observable variable responsive to the first possible value of the controlled variable;
• a second estimator capable of estimating a future state of the system to be controlled, the second estimator receiving the second possible value of the controlled variable and producing a second predicted value of the observable variable responsive to the second possible value of the controlled variable;
• and
• determining logic determining which of the first and second estimators more accurately predicts the second value of the observable variable.

A servo control system comprising the combination of:

• a signal source providing an error rate function f(y) corresponding to a displacement y, the displacement y characteristic of a system to be controlled
• a sampling circuit for sampling the value of f(y) at a sampling frequency of Xf to produce a function f(y)j;
• a map responsive to f(y)j to produce a positive value yj+ and a negative value yj−;
• a first estimator responsive to yj+ provide an estimated value ŷ1,j;
• a second estimator responsive to yj− to provide an estimated value ŷ2,j;
• and
• nonlinear logic responsive to ŷ1,j and ŷ2,j to generate an estimate ŷk of the displacement.

A method of estimating the value of an error signal in a servo control system, comprising the steps of:

• determining an error rate of the servo control system;
• sampling the error rate at a sampling frequency;
• using a nonlinear map to determine scalar position error values corresponding to each sampled error rate;
• generating positive and negative estimates of the absolute values of the scalar position error values;
• and
• using nonlinear logic to generate an estimate of an actual error signal based on the positive and negative estimates.

A servo system for positioning a magnetic head relative to a track which is movable relative to the head, the track having a succession of bursts of servo signals therealong and data signals between the bursts of servo signals, comprising the combination of:

• means responsive to the passage of the bursts of servo signals at the magnetic head for generating a first set of error signals;
• means responsive to the passage of the data signals at the magnetic head for generating a second set of error signals;
• and
• means responsive to the first and second sets of error signals for apply the position error signals from the first and second sets to correct the position of the magnetic head relative to the track,
• wherein the means responsive to the passage of the data signals at the magnetic head generates at least some of the second set of error signals by producing a pair of possible position error signal values in response to each sampling of the data track and processing the pair of possible position error signals values to choose one that best estimates position error of the magnetic head relative to the track.

A servo system for positioning a magnetic head relative to a track which is movable relative to the head, the track having a succession of bursts of servo signals therealong and data signals between the bursts of servo signals, comprising the combination of:

• means responsive to the passage of the bursts of servo signals at the magnetic head for generating a first set of error signals;
• means responsive to the passage of the data signals at the magnetic head for generating a second set of error signals;
• and
• means responsive to the first and second sets of error signals for applying the position error signals from the first and second sets to correct the position of the magnetic head relative to the track,
• wherein the means responsive to the passage of the data signals at the magnetic head generates each of the second set of error signals by generating a possible error signal during each of a succession of samplings of the data track and observing any changes in sign and absolute value of the possible error signal during the succession of samplings.