Apparatus and method to calibrate servo sensors in a noisy environment

A method to calibrate a servo sensor disposed on a tape head disposed adjacent a moving magnetic tape, wherein said tape head is capable of communicating with servo logic, and wherein said servo logic is capable of communicating with a memory device, and wherein said magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, wherein said servo sensor detects said first recorded signal and said second recorded signal, and wherein a servo detector provides a servo signal comprising the ratio of the detected first recorded frequency and the detected second recorded frequency, and wherein an independent position sensor provides an IPS signal comprising the lateral position of said tape head with respect to the tape path, said method comprising the steps of:

• moving said magnetic tape;
• sampling said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• determining (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• calculating a transfer function using said (N) datapoints and a third order curve fitting algorithm;
• forming a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• setting a value for the maximum allowable residual error REMAX;
• computing (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• calculating the average residual error REAVG by averaging said (N) residual error values;
• determining if REAVG exceeds REMAX;
• and
• operative if REAVG exceeds REMAX, applying an offset to each of said (N) DPCAL(i) datapoints to form said second calibration curve;
• storing said second calibration curve at a first time in said memory device;
• providing said second calibration curve at a second time;
• using said second calibration curve to position said tape head adjacent said moving magnetic tape;
• and
• reading and/or writing information from and/or to said magnetic tape using said tape head.

An article of manufacture comprising a computer useable medium having computer readable program code disposed therein for calibrating a servo sensor disposed on a tape head disposed adjacent a moving magnetic tape, wherein said magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, wherein said servo sensor detects said first recorded signal and said second recorded signal, and wherein a servo detector provides a servo signal comprising the ratio of the detected first recorded frequency and the detected second recorded frequency, and wherein an independent position sensor provides an IPS signal comprising the lateral position of said tape head with respect to the tape path, the computer readable program code comprising a series of computer readable program steps to effect:

• sampling said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• determining (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• calculating a transfer function using said (N) datapoints and an (n)th order curve fitting algorithm, wherein (n) is equal to or greater than 1 and less than or equal to about 6;
• forming a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• setting a value for the maximum allowable residual error REMAX;
• computing (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• adjusting said first calibration curve to form a second calibration curve based upon said (N) residual error values.

An article of manufacture comprising a computer useable medium having computer readable program code disposed therein for calibrating a servo sensor disposed on a tape head disposed adjacent a moving magnetic tape, wherein said tape head is capable of communicating with servo logic, and wherein said servo logic is capable of communicating with a memory device, and wherein said magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, wherein said servo sensor detects said first recorded signal and said second recorded signal, and wherein a servo detector provides a servo signal comprising the ratio of the detected first recorded frequency and the detected second recorded frequency, and wherein an independent position sensor provides an IPS signal comprising the lateral position of said tape head with respect to the tape path, the computer readable program code comprising a series of computer readable program steps to effect:

• moving said magnetic tape;
• sampling said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• determining (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• calculating a transfer function using said (N) datapoints and a third order curve fitting algorithm;
• forming a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• setting a value for the maximum allowable residual error REMAX;
• computing (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• calculating the average residual error REAVG by averaging said (N) residual error values;
• determining if REAVG exceeds REMAX;
• and
• operative if REAVG exceeds REMAX, applying an offset to each of said (N) DPCAL(i) datapoints to form said second calibration curve;
• storing said second calibration curve at a first time in said memory device;
• providing said second calibration curve to said logic at a second time;
• using said second calibration curve to position said tape head adjacent said moving magnetic tape;
• and
• reading and/or writing information from and/or to said magnetic tape using said tape head.

A computer program product usable with a programmable computer processor having computer readable program code embodied therein to calibrate a servo sensor disposed on a tape head disposed adjacent a moving magnetic tape, wherein said magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, wherein said servo sensor detects said first recorded signal and said second recorded signal, and wherein a servo detector provides a servo signal comprising the ratio of the detected first recorded frequency and the detected second recorded frequency, and wherein an independent position sensor provides an IPS signal comprising the lateral position of said tape head with respect to the tape path, comprising:

• computer readable program code which causes said programmable computer processor to sample said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• computer readable program code which causes said programmable computer processor to determine (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• computer readable program code which causes said programmable computer processor to calculate a transfer function using said (N) datapoints and an (n)th order curve fitting algorithm, wherein (n) is equal to or greater than 1 and less than or equal to about 6;
• computer readable program code which causes said programmable computer processor to form a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• computer readable program code which causes said programmable computer processor to access a pre-determined value for the maximum allowable residual error REMAX for each of said (N) calculated datapoints;
• computer readable program code which causes said programmable computer processor to compute (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• computer readable program code which causes said programmable computer processor to adjust said first calibration curve to form a second calibration curve based upon said (N) residual error values.

A computer program product usable with a programmable computer processor having computer readable program code embodied therein to calibrate a servo sensor disposed on a tape head disposed adjacent a moving magnetic tape, wherein said tape head is capable of communicating with servo logic, and wherein said servo logic is capable of communicating with a memory device, and wherein said magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, wherein said servo sensor detects said first recorded signal and said second recorded signal, and wherein a servo detector provides a servo signal comprising the ratio of the detected first recorded frequency and the detected second recorded frequency, and wherein an independent position sensor provides an IPS signal comprising the lateral position of said tape head with respect to the tape path, comprising:

• computer readable program code which causes said programmable computer processor to move said magnetic tape;
• computer readable program code which causes said programmable computer processor to sample said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• computer readable program code which causes said programmable computer processor to determine (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• computer readable program code which causes said programmable computer processor to calculate a transfer function using said (N) datapoints and a third order curve fitting algorithm;
• computer readable program code which causes said programmable computer processor to form a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• computer readable program code which causes said programmable computer processor to access a pre-determined value for the maximum allowable residual error REMAX for each of said (N) calculated datapoints;
• computer readable program code which causes said programmable computer processor to compute (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• computer readable program code which causes said programmable computer processor to calculate the average residual error REAVG by averaging the values for RE(i);
• computer readable program code which causes said programmable computer processor to determine if REAVG exceeds REMAX;
• and
• computer readable program code which, if REAVG exceeds REMAX, causes said programmable computer processor to apply an offset to each of said (N) DPCAL(i) datapoints to form said second calibration curve;
• computer readable program code which causes said programmable computer processor to store said second calibration curve at a first time in said memory device;
• computer readable program code which causes said programmable computer processor to provide said second calibration curve at a second time;
• computer readable program code which causes said programmable computer processor to use said second calibration curve to position said tape head adjacent said moving magnetic tape;
• and
• computer readable program code which causes said programmable computer processor to read and/or write information from and/or to said magnetic tape using said tape head.

A tape drive for reading and/or writing information to a magnetic tape, wherein said magnetic tape comprises at least one or more continuous servo edges comprising an interface between a first recorded signal and a second recorded signal, comprising:

• a motion system capable of moving said magnetic tape alternatingly in a first direction and an opposing second direction along a first axis;
• a tape head capable of moving alternatingly in a third direction and an opposing fourth direction along a second axis, wherein said first axis and said second axis are substantially orthogonal,
• one or more servo sensors disposed on said tape head, wherein each of said one or more servo sensors are capable of detecting said first recorded signal and said second recorded signal;
• a servo detector, wherein said servo detector is capable of communication with each of said one or more servo sensors and with servo logic, and wherein said servo detector provides servo signals comprising the ratio of the detected first recorded signal and the detected second recorded signal;
• an independent position sensor, wherein said independent position sensor provides an IPS signal comprising a measurement of the lateral position of said tape head with respect to the tape path;
• a servo loop, wherein said servo loop is capable of moving said tape head in said third direction and in said fourth direction;
• a memory device;
• logic, wherein said logic is capable of communicating with said servo detector, said memory device, said independent position sensor, and said servo loop, said logic:
• sampling said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• determining (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• calculating a transfer function using said (N) datapoints and an (n)th order curve fitting algorithm, wherein (n) is greater than or equal to 1 and less than or equal to about 6;
• forming a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• setting a value for the maximum allowable residual error REMAX;
• computing (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• adjusting said first calibration curve to form a second calibration curve based upon said (N) residual error values.

A tape drive for reading and/or writing information to a magnetic tape, wherein said magnetic tape comprises at least one or more continuous servo edges comprising an interface between a first recorded signal and a second recorded signal, comprising:

• a motion system capable of moving said magnetic tape alternatingly in a first direction and an opposing second direction along a first axis;
• a tape head capable of moving alternatingly in a third direction and an opposing fourth direction along a second axis, wherein said first axis and said second axis are substantially orthogonal,
• one or more servo sensors disposed on said tape head, wherein each of said one or more servo sensors are capable of detecting said first recorded signal and said second recorded signal;
• a servo detector, wherein said servo detector is capable of communication with each of said one or more servo sensors and with servo logic, and wherein said servo detector provides servo signals comprising the ratio of the detected first recorded signal and the detected second recorded signal;
• an independent position sensor, wherein said independent position sensor provides an IPS signal comprising a measurement of the lateral position of said tape head with respect to the tape path;
• a servo loop, wherein said servo loop is capable of moving said tape head in said third direction and in said fourth direction;
• a memory device;
• logic, wherein said logic is capable of communicating with said servo detector, said memory device, said independent position sensor, and said servo loop, said logic:
• moving said magnetic tape;
• sampling said servo signal and said IPS signal to form servo signal/IPS signal data as said tape moves adjacent said servo sensor;
• determining (N) measured datapoints using said servo signal/IPS signal data, wherein each of the DPACT(i) members of said (N) datapoints comprises a measured servo signal and a corresponding measured IPS signal, wherein (i) is an integer greater than or equal to 1 and less than or equal to (N);
• calculating a transfer function using said (N) datapoints and a third order curve fitting algorithm;
• forming a first calibration curve comprising (N) calculated datapoints DPCAL(i) using said transfer function;
• setting a value for the maximum allowable residual error REMAX;
• computing (N) residual error values, wherein the residual error RE(i) for the (i)th one of said (N) calculated datapoints DPCAL(i) equals DPACT(i)−DPCAL(i);
• calculating the average residual error REAVG by averaging said (N) residual error values;
• determining if REAVG exceeds REMAX;
• and
• operative if REAVG exceeds REMAX, applying an offset to each of said (N) DPCAL(i) datapoints to form said second calibration curve;
• storing said second calibration curve at a first time in said memory device;
• recalling said second calibration curve at a second time;
• using said second calibration curve to position said tape head adjacent said moving magnetic tape;
• and
• reading and/or writing information from and/or to said magnetic tape using said tape head.