International Business Machines Corporation

Steven Carter Wills

Alex Chliwnyj

David Lee Swanson

James Mitchell Karp

John Alexander Koski

Colleen Renee Stouffer

Christopher Robert Pandolfo

Robert Allen Hutchins

John James Gniewek

Dennis Peter Rienstra

Noise in a same-gap, frequency-based servo tape system is reduced by applying correlated noise factors, generated during calibration, to filtered data write signals. The resulting noise values are subtracted from filtered servo signals, at frequencies Fand F, to generate first and second noise-compensated servo signals at frequencies Fand F. In one embodiment, the Fand Fdata signals are filtered through two SOBP filters which output the magnitudes of the signals. The Fand Fservo signals are similarly filtered. In another embodiment, the Fand Fdata signals are filtered through two Goertzel filters which output the real and imaginary components of the signals and the Fand Fservo signals are similarly filtered through two other Goertzel filters. Correlated noise factors are applied to the outputs of the write data Goertzel filters and the results subtracted from the corresponding outputs of the servo Goertzel filters.

Noise reduction in same-gap servo in frequency-based servo tape systems

A method and apparatus to calibrate a servo sensor disposed on a tape head located adjacent a moving magnetic tape is disclosed where that magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, and where the servo sensor provides a servo signal, and where an independent position sensor provides an IPS signal. The method first samples the servo signal and the IPS signal, calculates a transfer function, and forms a first calibration curve. The method then forms an average residual error value. If that average residual error exceeds the maximum allowable residual error, then the method applies an offset to the first calibration curve to form a second calibration curve. That second calibration curve is saved for subsequent use during, for example, read/write/erase operations.

Apparatus and method to calibrate servo sensors in a noisy environment

Width of a write track for a magnetic tape head is measured by writing a foreground magnetic track signal on a magnetic tape having a dissimilar background signal. A magnetic tape read head is moved from beyond one edge, laterally across, and beyond the opposite edge of the foreground track signal. Logic detects the read head encountering the one edge and the opposite edge of the foreground track signal; and determines, from an independent position sensor, the width of the foreground track signal as the lateral distance between the lateral position of the read head at one edge, and at the opposite edge of the foreground track signal.

Measurement of write track width for magnetic tape head

A method to calibrate a transducer, whereby the transducer provides a first signal, and whereby a reference provides a reference signal. The first signal is sampled at a sampling rate comprising a reference frequency, and a digital measured first signal waveform is formed. The reference signal is sampled at the sampling rate, and a digital measured reference signal waveform is formed. The real and imaginary components of the measured first signal waveform are determined at (P) harmonics of the reference frequency. A filtered first signal waveform is formed using those real and imaginary components. The real and imaginary components of the measured reference signal waveform are determined at (P) harmonics of the reference frequency. A filtered reference signal waveform is formed using those real and imaginary components. A transfer function is formed using the filtered first signal waveform and the filtered reference signal waveform. A calibration curve is formed using that transfer function.

Apparatus and method to calibrate one or more transducers in a noisy environment

A method to calibrate a servo sensor disposed on a magnetic tape head disposed adjacent a magnetic tape, where that magnetic tape includes at least one servo edge comprising an interface between a first recorded signal and a second recorded signal, whereby the servo sensor is capable of detecting that first recorded signal and that second recorded signal, and whereby an independent position sensor provides an IPS signal comprising the position of the tape head with respect to the tape path. Applicants' method determines and uses initial servo signal information and initial IPS signal information to determine an initial transfer function. That initial transfer function is used to determine a positioning signal where the tape head is alternatingly moved in a first direction and an opposing second direction along a first axis as the tape moves along a tape path such that the position of the magnetic head along the first axis as a function of time comprises a periodic function having the positioning signal. Additional servo signals and additional IPS signals are sampled. Those sampled signals are used to determine a second transfer function.

Apparatus and method to calibrate a servo sensor

A method to calibrate a servo sensor disposed on a magnetic tape head disposed adjacent a magnetic tape moving along a tape path. The method measures a maximum and a minimum servo signal ratio, establishes target maximum and minimum servo signal ratios, and determines if the measured servo signal ratios include the target ratios. If the measured servo signal ratios include the target servo signal ratios, then the method forms a filtered servo signal waveform using the measured servo signal waveform. The method then uses the filtered servo signal waveform to calculate a transfer function which is saved for subsequent track following.

An apparatus and method to read and/or write information from and/or to a moving magnetic tape comprising one or more servo edges using a tape head comprising (N) servo sensors. Bach servo edge comprises an interface between a first recorded signal and a second recorded signal, where each of the (N) servo sensors detects that first recorded signal and that second recorded signal. The method calculates (N) target PES signals and provides (N) measured PES signals. Using the target and the measured PES signals, the method forms (N) weighted PES signals and averages those (N) weighted PES signals to form a Composite PES signal. That Composite PES signal is used to position the tape head.

Apparatus and method to read and/or write information to a magnetic tape medium

Dynamic tension control for tape transported along a tape path between supply and take-up reels, driven by supply and take-up motors, and having tachometers for determining linear speed of the tape. A controller accelerates the tape toward a target speed, initially operating the motors in static acceleration tension control; and if the linear speed of the tape is within a predetermined range of the target tape speed, operating the motors in composite tension control employing static tension control and delta velocity control.

Combined tension control for tape

Dynamic tension control for tape transported along a tape path between supply and take-up reels, driven by supply and take-up reel motors. Rotational angular velocities of the supply and take-up reels are determined from tachometers, and therefrom a linear speed for the tape at the supply reel, and a linear speed for the tape at the take-up reel are each determined. The tape linear speeds at the reels are compared to determine a delta velocity between the linear speeds. The motors are operated in accordance with a function of the delta velocity to provide a torque to at least one of the reels tending to reduce the delta velocity.

Delta velocity tension control for tape

A servo position detector and a method for detecting and following an index position displaced at an offset with respect to an edge of a servo track, an edge comprising an interface between two dissimilar recorded servo signals. The servo track has two edges on opposite lateral sides of a middle recorded servo signal, the edges separated by a predetermined distance. A servo read element has an active sensing region which is no more than and is substantially the entire predetermined distance separating the edges, thereby.sensing no more than two of the dissimilar recorded servo signals at one of the edges. An independent position sensor senses the coarse position of the servo read element, indicating which edge or which index position is aligned with the servo read element. Logic compares the two sensed servo signals to determine the ratio therebetween, and determines an error between the compared ratio and a predetermined ratio. The predetermined ratio is an offset from a centered on-edge ratio, and identifies the index position. The logic provides the servo position error with respect to the index position. A servo positioner moves the servo read element to reduce the servo position error.

Detection of indexed servo positions displaced from servo track edges

Servo errors can be avoided in a bi-directional reel-to-reel tape transport in which magnetic tape is moved in either of two opposite directions for data recording by providing a fine-line tachometer for each reel and a directly coupled tension sensor. Control of tape speed is implemented in a servo algorithm that uses tachometer inputs to determine parameter values for generating reel motor drive currents. If the linear velocity of both reels is the same then the tension output must be within a tolerable range. The directly coupled tension output provided an is indication of the actual current of the tension sensor. The difference between the linear velocities of the tape from each reel is calculated and monitored together with the tape tension. A trip level is set when an error occurs to stop tape motion and permit recovery without damaging the tape. The status of each outputs indicates the status of the tape velocity and whether the tape is slack or stretched on one reel which could cause a servo error which must be detected in order to prevent chopped blocks of data or data slivers. Motor problems may also be detected using the invention.

Servo error detection of bi-directional reel-to-reel tape drives using fine line tachometers

Servo elements contained within a tape head detect a lateral displacement the magnetic tape relative to the tape head and generate position error signals corresponding to such lateral displacement. To aid in servo monitoring, the position error signals are sampled at predetermined times and the samples output or stored in machine-readable form. Each sample is classified as bad if it exceeds a predetermined threshold. Samples are analyzed to determine, for each time a bad position error signal occurs, how many successive position error signals are also bad. Samples are also analyzed to determine the relationship between bad position error signals samples and total samples. This data may be used for a number of different purposes. For example, this information may be used to identify differences between performance on top and bottom servo edges, or problems with the servo writing mechanism. Performance variations among different servo elements may also be identified. Such data may also be used to help recognize large 'dropouts' or 'fades' in the tape media. Furthermore, the data may also be analyzed to yield an overall indication of the media surface and edge quality of the media. Importantly, this information may be employed to pinpoint servo read errors, distinguishing between media problems and servo element malfunctions. Data obtained in accordance with the invention may also be used to evaluate tape media, with one possible implementation applying a numerical rank to factory-new tape media and subsequently binning the media according to their numerical ranks.

System and method for monitoring and analyzing tape servo performance

A high resolution, independent position sensor is provided, having application in a magnetic tape drive and other environments in which a linear or angular position is to be monitored. Analog outputs from an inexpensive, low resolution optical encoder are processed to correct gain and offset distortions and are used as the basis for an interpolation process. If a code strip having a 127-micron grating is used, a resolution of about 0.125 microns can be achieved.

Optical position sensing device and method for sub-micron measurement

An improved and apparatus is provided in a tape drive for servo-controlling a tape head position relative to a magnetic tape as the magnetic tape travels past the tape head thereby reducing track mis-registration on the magnetic tape. Servo elements contained within the tape head detect a lateral displacement of the magnetic tape position relative to the tape head and generate position error signals corresponding to such lateral displacement. The position error signals are then filtered to generate a low frequency position error signal, a midrange frequency error signal, and position reliability signals. The tape head is then positioned by a head actuator according to the low frequency position error signal to adjust to the lateral movement of the magnetic tape. The midrange frequency error signal is compared to a distortion threshold to determine if errors exist due to tape edge vibrations or distortion of the magnetic tape. The position reliability signals are used to calculate an error density, which is then compared to a surface threshold to determine whether a surface defect exists on the magnetic tape.

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Tucson, AZ, United States of America

Steven Carter Wills