Apparatus using information about the extent of errors in sensed data for performing as a control function at least one of adjusting the position of a magnetic head to improve alignment relative to a track and selecting from two or more data signals a data signal having the least amount of errors is shown. The apparatus uses information about the extent of errors to perform a control function for reproducing the data stored in predetermined storage locations in a storage media. The apparatus positions a transducer for sensing from predetermined storage locations stored data containing at least one constraint. The transducer generates a first signal representative of the data containing at least one constraint stored in the sensed data and any errors introduced into the sensed data during the sensing. An input device, preferably in the form of a detector is responsive to the first signal for generating a control signal containing information about the extent of errors in the sensed data and for extracting a data signal. The control signal is used for performing the above control functions. A method for using information about the extent of errors for a control function to improve the extracted data stored at the predetermined storage locations is also shown.
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0. 35. A method comprising:
(a) detecting both stored data and at least two servo bursts, the stored data including at least one constraint; and
(b) sensing additional data via a transducer while positioning the transducer at least partly based on both a data-error-indicative quantity derived from the stored data and a position-error-indicative quantity derived from the servo bursts.
0. 46. A data handling system comprising:
at least one transducer configured to sense from a first data storage surface both stored data and
at least two servo bursts, the stored data including at least one constraint; and
at least one actuator configured to position the transducer(s) at least partly based on both a data-error-indicative quantity derived from the stored data and a position-error-indicative quantity derived from the at least two servo bursts.
29. A method for using information about an extent of errors in a storage system comprising:
positioning a first transducer for sensing data from first storage locations having stored data containing at least one constraint;
positioning a second transducer for writing data to second storage locations;
producing from the first transducer a first signal representative of the sensed data containing the at least one constraint from the first storage locations and information about errors in the sensed data;
generating in response to the first signal a control signal containing information about the extent of errors in the sensed data;
extracting from the first signal a data signal; and
receiving the control signal and performing a control function in response thereto to reduce a position error of the first transducer by an amount determined by the extent of errors in the sensed data and simultaneously to reduce a position error of the second transducer, the control function being performed as the first signal is produced.
28. A method for reading and writing data in a storage system comprising:
positioning a read element with respect to a first storage medium storing data to be sensed;
positioning a write element with respect to a second storage medium for writing data, the write element and the read element having a predefined spatial relationship with respect to each other;
sensing the first storage medium with the read element to generate a first signal representative of stored data containing at least one constraint and errors introduced during the sensing;
from the first signal, extracting a data signal and generating a control signal containing information about an extent of errors in the first signal;
determining a direction of a position error correction from the first signal; and
based on the control signal and the direction of the position error correction, simultaneously adjusting the positions of the read and write elements with respect to the first and second storage media, respectively, while maintaining the redefined spatial relationship between the read and write elements.
23. A data acquisition and recording system comprising:
a first transducer for detecting signals from a first storage medium embodying data to be acquired, the first transducer defining a first tracking relationship with respect to the first storage medium;
a second transducer for recording signals to a second storage medium, the second transducer defining a second tracking relationship with respect to the second storage medium, the first and second transducers having a defined spatial relationship relative to each other;
data recovery circuitry coupled to receive signals detected by the first transducer, the data recovery circuitry deriving recovered data from the detected signals, the data recovery circuitry deriving a measure of errors of the detected signals in relation to the recovered data in a substantially continuous manner, the measure being responsive to an accuracy of the first tracking relationship; and
a servo controller coupled to the data recovery circuitry to receive the measure and generate a position error signal in response to the measure, the position error signal having a magnitude representing a magnitude of a correction to be made to adjust the first and second tracking relationships.
25. Apparatus for extracting and recording data signals comprising:
a first transducer for sensing a first storage medium and generating a first signal representative of data containing at least one constraint from the first storage medium and any errors in the sensed data identified using the at least one constraint, the first transducer defining a first tracking relationship with respect to the first storage medium;
a second transducer for recording data on a second storage medium, the second transducer defining a second tracking relationship with respect to the second storage medium, the first and second transducers having a defined spatial relationship relative to each other;
an input device responsive to the first signal for generating a control signal containing information about the errors in the sensed data and for extracting a data signal; and
an output device operatively coupled to the input device for receiving the control signal and for performing a control function in response thereto to improve an accuracy of the first and second tracking relationships as a function of an extent of errors in the sensed data, the control function being performed as the first transducer generates the first signal.
1. A data acquisition and recording system comprising:
a first transducer for detecting signals from a first storage medium embodying data to be acquired, the first transducer defining a first tracking relationship with respect to the first storage medium;
a second transducer for recording signals to a second storage medium, the second transducer defining a second tracking relationship with respect to the second storage medium, the first and second transducers having a fixed spatial relationship with respect to each other;
data recovery circuitry coupled to receive signals detected by the first transducer, the data recovery circuitry deriving recovered data from the detected signals, the data recovery circuitry deriving a measure of errors of the detected signals in relation to the recovered data in a substantially continuous manner, the measure being responsive to an accuracy of the first tracking relationship; and
a servo controller coupled to the data recovery circuitry to receive the measure and generate a position error signal in response to the measure as the data recovery circuitry derives data from the detected signals, the position error signal being indicative of corrections determined for the first and second tracking relationships.
10. A data acquisition and recording system, comprising:
a read head for reading a signal representative of data from a first data storage surface, the read head defining a first relative positional relationship with respect to first data storage structures on the first data storage surface;
a write head for recording data on a second data storage surface, the write head defining a second relative positional relationship with respect to second data storage structures on the second data storage surface, the read head and the write head having a fixed spatial relationship relative to each other;
data processing circuitry coupled to receive signals detected by the read head, the data processing circuitry deriving data from the detected signals and generating a measure of errors in the detected signals relative to the derived data, the measure varying with misalignments in the first relative positional relationship in a predetermined manner; and
a servo control system for maintaining the first and second relative positional relationships, the servo control system receiving the measure of errors and generating a position error signal for adjusting positions of the read head and the write head, the position error signal being generated in response to the measure of error while the data processing circuitry derives data from the detected signals.
26. Apparatus for extracting and recording data signals comprising:
a first transducer for sensing a first storage medium and generating a first signal representative of data containing at least one constraint from the first storage medium and any errors in the sensed data identified using the at least one constraint, the first transducer defining a first tracking relationship with respect to the first storage medium;
a second transducer for recording data on a second storage medium, the second transducer defining a second tracking relationship with respect to the second storage medium, the first and second transducers having a fixed spatial relationship relative to each other;
an input device responsive to the first signal for generating a control signal containing information about the errors in the sensed data and for extracting a data signal; and
an output device operatively coupled to the input device for receiving the control signal and for performing a control function in response thereto to improve an accuracy of the first and second tracking relationships as a function of an extent of errors in the sensed data
wherein the output device is responsive to the control signal to produce a dynamic servo signal to improve an accuracy of the first and second tracking relationships, and wherein the dynamic servo signal is substantially continuously supplied.
24. A data acquisition and recording system, comprising:
a read head for reading a signal representative of data from a first data storage surface, the read head defining a first relative positional relationship with respect to first data storage structures on the first data storage surface;
a write head for recording data on a second data storage surface, the write head defining a second relative positional relationship with respect to second data storage structures on the second data storage surface, the read head and the write head having a fixed spatial relationship relative to each other;
data processing circuitry coupled to receive signals detected by the read head from the first data storage surface, the data processing circuitry deriving data from the detected signals and generating a measure of errors in the detected signals relative to the derived data, the measure varying with misalignments in the first relative positional relationship between the read head and the first data storage structure in a predetermined manner; and
a servo control system for maintaining the first and second relative positional relationships, the servo control system receiving the measure of errors and generating a position error signal in response to the measure of errors for adjusting positions of the read head and the write head, the position error signal having a magnitude representing a magnitude of the adjustment of position of the read head.
27. Apparatus for extracting and recording data signals comprising:
a first transducer for sensing a first storage medium and generating a first signal representative of data containing at least one constraint from the first storage medium and any errors in the sensed data identified using the at least one constraint, the first transducer defining a first tracking relationship with respect to the first storage medium;
a second transducer for recording data on a second storage medium, the second transducer defining a second tracking relationship with respect to the second storage medium, the first and second transducers having a fixed spatial relationship relative to each other;
an input device responsive to the first signal for generating a control signal containing information about the errors in the sensed data and for extracting a data signal; and
an output device operatively coupled to the input device for receiving the control signal and for performing a control function in response thereto to improve an accuracy of the first and second tracking relationships as a function of an extent of errors in the sensed data,
wherein the first transducer includes a magnetoresistive element, the first storage medium has storage locations including a track having a center line, the magnetoresistive element is positioned at a slight offset from the center line of the track in a known direction establishing a predetermined sensor offset, the output device is responsive to the control signal to generate a position error signal representing the magnitude and direction in which the first and second transducers are to be moved to improve magnetoresistive element alignment relative to the track.
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comparing the extracted data signal containing at least one constraint with an expected data signal containing at least one constraint; and
generating in response thereto the control signal.
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“This is a continuation of application Ser. No. 09/187,770, filed Nov. 6, 1998, now U.S. Pat. No. 6,381,088, allowed, the disclosure of which is hereby incorporated by reference in its entirety.”
1. Field of the Invention
The invention relates generally to using information about errors for improving extracted data sensed from stored data and more specifically relates to apparatus for using information about the extent of errors wherein a transducer is used to sense stored data having at least one constraint from predetermined storage locations. The transducer generates a signal containing at least one constraint and any errors introduced into the sensed data during the sensing. An input device, which in the preferred embodiment is a detector, is responsive to the signal from the sensor to generate a control signal containing information about the extent of errors and extracts a data signal. An output device is responsive to the control signal to perform a control function to effectively improve the extracted data signal as a function of the extent of errors in the sensed data. In addition, the transducer may have at least two sensors or two transducers may be used to produce a first signal and second signal which is applied to the input device to extract a first data signal and a second data signal wherein the output device is responsive to the control signal and to the first data signal and second data signal to derive a data signal therefrom having the least number of fewer errors averaged over an appropriate interval as the logical operation. Another example of a derivation is an output signal from a first data signal and a second data signal generated by forming a weighted average of the first data signal and the second data signal, as a logical operation, with the weights determined by means of a control signal so as to produce an output signal of the least number of fewer errors. Other derivations are well known to those skilled in the art of deriving an improved data output signal from several sensed signals of the same stored data.
A “flexure” is a flexible loading device that supports a head/slider assembly and is operatively mounted at the end of a loading arm in a head stack assembly.
A “head” is a fabricated device, which typically is in the form of a microchip, that contains one or more transducers or sensors or transducers having elements that function as read and/or write elements.
A “head/slider” is a fabricated element comprising a head and slider that is mounted onto a flexure for loading onto a rotating surface.
A “head/arm assembly” is an arm containing flexures and a head/slider assembly located at one end thereof. The end of the loading arm supporting the head/slider assembly may be articulated.
A holographic memory is a memory in which information or data is stored in the form of holographic images in photographic emulsion or other recording media.
A “position error signal” is a signal representing that a disc head is off track, and the magnitude and direction thereof; and the processing of this signal results in an adjustment of or repositioning of the head relative to predetermined storage locations by an actuator.
A “PRML” is an acronym for “partial response maximum likelihood” that is a method of generating and decoding the analog signal that records data at predetermined storage locations such as along a data track.
A “sensor” is a device for reading or reproducing information stored on a recording media such as for example, an inductive magnet, magnetoresistive (“MR”) element, an optical detector, e.g. charged coupled device (“CCD”), for responding to information stored on an optical storage medium.
A “slider” is a device that supports the head and forms an air bearing between the head and rotating surface to keep the head flying over the rotating surface, which typically is a magnetic disc, at the correct height and carries the electrical leads from the head to the flexure.
A storage medium is a storage device which may be a two dimensional medium such as a magnetic tape, rotating magnetic memory, an optical disc or a three dimensional medium such as a holographic memory.
A “transducer” is a device for interacting with a treated surface for recording and reproducing information on the treated surface. As used herein, the term “transducer” is intended to cover an inductive head, a write transducer, magnetoresistive elements, read transducers, lasers, optical sensors, microphones, CCD devices and the like. Sometimes the term “sensor” is used interchangeably with the term “transducer”, and in the context of this invention, a sensor is a read element or read transducer.
Chart I set forth below is a listing of actual head and disc drive parameters for the years 1997 and 1998 and of the forecasted parameters for the future showing the head technology and disc drives in which the present invention has utility:
CHART I
Areal
Read Track
Density
Width
Head
Year
(Gb/sq in)
KTPI
KBPI
(Microinches)
Technology
1997
2.64
12.5
201
54
MR
1998
4.10
16.0
256
42
MR, GMR
2000
10.00
30.0
334
22
GMR
2003
40.00
61.0
659
17
GMRT
2005
80.00
86.0
926
8
GMRT
Note:
MR is a magnetoresistive head.
GMR is giant magnetoresistive head wherein the sensor is formed of a material that utilizes spin-dependent scattering of electrons for sensing data stored at the predetermined storage electrons, an example of which is set forth in the IBM RESEARCH BULLETIN dated Aug. 21, 1998 and as shown at the IBM Website www.research.ibm.com.
GMRT is an advanced giant magnetoresistive head wherein the sensor is responsive to read track widths of less than 20 microinches.
Chart II set forth below is a listing of areal density, the KBPI×TPI for such areal density and the magnetic bit sizes for the applicable areal density in which the present invention has utility:
CHART II
Magnetic Bit Size-
Magnetic Bit Size-
Bits per inch ×
(Length)
(Width)
Tracks per inch
(Micrometers)
(Micrometers)
48 kbpi × 2100 tpi
10.000
0.710
150 kbpi × 6600 tpi
3.100
0.150
400 kbpi × 25 ktpi
0.800
0.064
800 kbpi × 50 ktpi
0.400
0.032
1,000 kbpi × 100 ktpi
0.300
0.015
Information about data errors is itself a valuable signal and can be determined in response to signals produced by the head, transducer or sensor. The information about data errors can be used to dynamically and rapidly adjust the state of the sensor (such as its position relative to a data track), so as to improve operation of the information storage system.
The apparatus of the present invention provides for using a transducer for sensing from predetermined storage locations stored data containing at least one constraint. The at least one constraint in the data may be in many forms. For the purpose of this invention, a constraint is some aspect of data, or an encoding of the data, or signal generated from the data, such that what is received from the transducer can be compared in some way with what was expected to be received so as to ascertain the extent of the difference. Often, the differences are due to some external effect on the signal carrying the data. The constraint may be an analog constraint, such as a limitation on the frequencies that can appear in the signal or the properties of the signal waveform. The constraints may be digital such as from an encoding process such as a parity check code or an error-correcting code (“ECC”).
Generally, encodings that introduce or impose constraints on signals have the property that the bit string resulting from the encoding is a subset of all possible bit strings of the same length. An appearance of a disallowed bit string, i.e. one that would not be produced by the encoding, in the process of receiving the signal containing the data, shows that the recovered data violates the constraint.
Accordingly, by determining the manner in which the constraint is violated, for example with an ECC, then any errors and extent of errors introduced into the signal can be ascertained, and this information used in accordance with the teachings of this invention.
An example is a Reed-Solomon type ECC encoding of a bit sequence. The ECC encoding will include both the data and the “syndrome” computed from the data (the bit sequence). This has the property that only a subset of the bit sequences, whose length is the length of the data plus the syndrome, is possible. If a signal containing the ECC encoded data is received, the decoding will reveal whether a correct sequence of data bits and syndrome bits is received or not. If not, than the extent of the errors in the signal can be determined, up to some number of errors that depends on the details of the ECC method.
Thus, by using the knowledge about the at least one constraint imposed on the first signal, a control signal containing information about the extent of errors can be immediately generated and used to perform a control function in accordance with the teachings of this invention.
Sensors that respond to digital data that is recorded for storage in an information storage system can generate signals that are responsive both to actual data and to errors in reading that data. The system can dynamically determine in response to signals produced by the head, transducer or sensor, both the actual data and information about those errors.
Analog techniques used for encoding individual bits and sequences of bits can be used to determine both the probable actual data and one or more measures of deviation from error-free retrieval of that actual data, e.g. PRML encoding techniques for storing and retrieving data.
PRML encoding techniques are used to encode data as it is stored on a disc drive as is well known in the art. During reading of a segment of data stored in PRML form using the state-of-the-art apparatus and method, the signal being read by the head, transducer or sensor, e.g., an MR head, is sampled at periodic intervals. The sample points are picked to be synchronous with the signal and sampling occurs at points where the signal is expected to take on specific values.
The present invention resides in apparatus and methods for using information about the extent of errors in sensed data for performing as a control function of at least one of adjusting the position of a transducer, such as a magnetic head, to improve alignment relative to a track and deriving from two or more data signals a data signal having the least amount of errors. The apparatus and method use the information about the extent of errors to perform a control function for reproducing the data stored in predetermined storage locations in a storage media.
The present invention is based on the sensing of recorded information or data on a storage media. The sensed or reproduced data contains errors introduced into the first signal during sensing of the information or data as a result of the transducer or sensor being offset from the predetermined storage locations, such as a track.
If the information or data as recorded or stored contains an error, the sensed data likewise includes such errors in the data. Such errors in the record data are different than any errors introduced into the sensed data as the same is being sensed which is the disclosure and teachings of this invention.
Referring now to
In the pictorial representation of
The data containing at least one constraint may take the form of a number of data encoding techniques which have a known relationship with the data associated with the constraint. Use of error coding techniques enable the true data to be determined with greater likelihood than erroneous data, notwithstanding errors, such as clutter or noise, which can interfere with correct reading of data in an information storage system.
A transducer 26 is positioned for sensing the predetermined storage locations 24 and generates a first signal representative of the data containing at least one constraint stored in the predetermined storage locations 24 and any errors introduced into the sensed data during the sensing. The first signal is shown by lead 30.
A input device, sometimes referred to herein as a detector, 34 is responsive to the first signal 30 for applying the sensed data signal shown by lead 38 to a control signal generating device, shown generally by box 42, for generating a control signal containing information about the extent of errors. The control signal is used for performing a control function as described hereinbelow. The input device 34 extracts a data signal shown as 56 as the reproduced data.
The control signal generating device 42 generates a control signal containing information about the extent of errors which may be used to perform the control function of controlling an adjusting element 48. The adjusting element 48 is operatively coupled to the transducer 26 by an actuatable assembly as represented by dashed line 52. The adjusting element 48 through the actuatable assembly shown by dashed line 52 adjusts or repositions the transducer 26 in a direction to position the transducer 26 in a direction to improve alignment relative to the predetermined storage locations 24.
In a preferred embodiment, the adjustment element 48 includes an actuator, such as for example that actuator 104 in
The transducer 26 of
In addition the transducer 26 may be a first transducer including at least two sensors for concurrently sensing the predetermined storage locations and generating a first signal and a second signal each representative of the data containing the at least one constraint from the predetermined storage locations and any errors introduced into the sensed data during the sensing. In such event, the input device extracts a first data signal and a second data signal as the reproduced data. In addition, the input device 34 applies the first signal and second signal to the control signal generating device 42 to generate a control signal. In this embodiment, the control function is responsive to the control signal and at least one of the first data signal and the second data signal to perform at least one of generating a dynamic servo signal and deriving from the first data signal and the second data signal a data signal containing the least amount of errors.
The block diagram of
The output device 76 reproduces the extracted data signal from the sensed data as shown on lead 80. Concurrently, the control signal and extracted data signal are applied to output device 76 as shown by lead 74. In addition, the control signal as shown by lead 82 is used to produce a dynamic servo signal which are used to improve alignment of the transducer 62 relative to the predetermined storage locations on the recording media 60. In this embodiment, the dynamic servo signal are in the form of substantially continuous servo signals, or position error signals applied to a servo control, all of which are represented by dashed line 82, to improve alignment of the transducer 26 relative to predetermined storage locations on the recording media 60.
The block diagram of
The apparatus illustrated in
If the structure of the transducer does not permit a read and write to occur at the same time, then the dynamic servo signal is disabled for the period approximately equal to a write period. Circuits for performing these functions are well known to persons skilled in the art.
The block diagram of
Concurrently, the input device applies the control signal to an adjusting element 144 via lead 142. In this embodiment, the adjusting element generates a dynamic servo signal which are applied to an actuator 150 via lead 146 to mechanically adjust the position of the transducer 110 to improve alignment between the transducer 110 relative to the predetermined storage locations. In the alternative the adjusting element 144 can generate an adjusting signal which can be used to electrically shift one of or both of one of or of two or more sensors the operating characteristics of one of the two or more sensors to reduce the extent of errors introduced into the sensed data. An example of such a transducer and structure thereof is discussed hereinbelow in connection with FIG. 3E.
The apparatus illustrated in
Referring now to
In
In
In the pictorial representation of
In the pictorial representation of
When the transducer 26 of
As discussed above in the Background, the future disc drive systems are to have track widths that are smaller in width. The read track widths are less than 50 microinches and smaller, and the magnetic bit sizes on the stored surface 22 for magnetically recording the data are also becoming smaller. As a result, precise head/track alignment is very important in reducing errors in the sensed data read from a predetermined storage locations or track containing the stored data containing at least one constraint and the apparatus described in
In a preferred embodiment, the surface 22 is a magnetic recording surface of a magnetic disc and the track 160 includes a material responsive to electromagnetic fields so as to read or write the data bits thereon, and such magnetic discs and techniques for reading and writing magnetic data are well known in the art.
Although embodiments of the invention are described with regard to storage and retrieval of digital data using magnetic discs, the invention has wide applicability to other forms of data storage, such as for example optical discs, laser disc, digital video discs, holographic memories and the like. In general, the invention includes all those embodiments in which reading or writing data is responsive to a state of the art sensor with regard to an information storing medium.
In
In
In
The schematic diagram of
The transducer 26 in this embodiment is in the form of two shielded MR elements. One example of such a transducer is an MR element which is referred to as the Dual-Stripe MR Head offered for sale by Headway Technologies, Inc., of Milpitas, Calif.
In the alternative, the transducer 26 may be formed of two MR elements having a conductive shield as illustrated in FIG. 3E.
If such a transducer was used in the apparatus illustrated in
The MR element may be a single transducer 174. It is also envisioned that in alternative embodiments, the transducer may include three (or more) read sensors and/or two or more write transducers. Such a structure would permit monitoring of and/or deriving of sensed data containing the at least one constraint from all elements.
The detector in this embodiment is capable of responding to the control signal containing the at least one constraint and to the extracted first data signal and second data signal developed from the at least two transducers to derive a data signal having the least number of fewer errors. In this manner the reproduced data is the extracted data signal having the least amount of errors. In addition, the control signal containing information about the extent of errors can be used to develop position error signals for a servo system as described herein.
There is no requirement that the transducer 26, which in this embodiment is a disc head, include any particular number of read sensors, such as additional MR elements similar to MR elements 176 and 178.
This invention is also effective using only a single MR head, such as for example MR element 176, as discussed in connection with FIG. 7.
The output signal of each MR element 176 and 178 provides the sensed data containing the at least one constraint and any errors introduced into the sensed data during sensing. These signals are applied via their respective read amplifiers 250 and 252 and the outputs of the read amplifiers 250 and 252 are the first signal and second signal. In the preferred embodiment, the first signal and the second signal appear on output shown by element 248 in the form of a time-varying electromagnetic signal, e.g. a voltage signal, responsive to positions of the corresponding MR elements 176 and 178 relative to the predetermined storage locations or data track 164.
Each read amplifier 250 and 252 receives the first signal and second signal representative of the sensed data containing at least one constraint from its associated MR element 176 and 178. The read amplifiers 250 and 252 each amplify the signal and perform any other required signal processing. Such signal processing may be for example conditioning the signal, converting the signal to another format, e.g. a quantized digital format or a remodulated format such as PCM.
The outputs 256 from the read amplifiers 250 and 252 (including the output from the summing amplifier 254 if required) are applied to a detector 260 which in turn, generates a control signal containing information about the extent of errors. In this embodiment, the detector 260 applies the control signal containing information about the extent of errors to an adjusting circuit 270 which generates position error signals developed from the control signal.
In the embodiment of
In this embodiment, the error detector 260 generates a unified control signal which is applied to the adjustment element 230 to determine separate signals for horizontal displacement, angular orientation and vertical displacement of the transducer relative to the predetermined storage locations, such as a track.
In
The other position error signal from the servo amplifier 172 is applied via lead 284 to a fine micropositioner 286 which may be an articulated end of an arm 232 for micromoving or microactuating of the head/arm assembly to position the same to improve head alignment with or to achieve substantial alignment relative to the predetermined storage locations or data track 164.
The block diagram of
Another control function is shown by Step 318 comprising using the control signal containing information about the extent of errors to generate a dynamic servo signal as illustrated by lead 318 and applying the same to the adjustment element to position the transducer using position error signal derived from the control signal to improve alignment of the transducer relative to the predetermined storage locations.
In the preferred embodiment of the present invention the method includes adjusting a magnetic transducer having at least two reading transducers or read elements with a servo system operatively coupled thereto for receiving as the dynamic servo signal derived from the control signal containing information about the extent of errors. The magnetic transducer is adjusted in a direction to position the magnetic transducer in improved alignment relative to the predetermined storage locations.
In the preferred embodiment, the at least two read transducers generate a first signal and a second signal and the Step 310 for deriving the sensed data signal having the least number of fewer errors performs the deriving step using sensed data.
It is envisioned that variations of this method may be used for adjusting the position of a transducer having a plurality of transducers relative to predetermined storage locations containing data being sensed by the transducer.
In the method illustrated in
In current state-of-the-art practice, a signal received from a transducer, such as for example in a rotating magnetic memory system, is processed using a technique known as Partial Response Maximum Likelihood (“PRML”). There are several known PRML encoding methods. The methods known as PR4 and EPR4 are commonly used. The example set forth hereinbelow is for use of the PR4 method. Use of other PRML encoding methods are similar.
In PR4 processing, the signal is sampled by an analog-to-digital converter (“ADC”) at periodic intervals. The sampling is done synchronously with the signal. Since a PR4 encoding method is being used, only 3 values are expected which, for purposes of this example, are termed 1,0 and −1, if there were no noise decreasing the signal-to-noise ratio or other effects on the signal, such as non-linear transition shifts (hereinafter referred to collectively as the “Signal Deterioration Effects”), perturbing the signal. These values correspond to specific outputs of the ADC which correspond to voltages in the signals and these would be deemed the observed values of the signal. Due to the Signal Deterioration Effects, the observed values produced by sampling will differ from the 3 expected values described above. For example, instead of a voltage corresponding to a 1, as the expected value, a voltage that is 0.9 times this amount might be observed. The fact that only voltages corresponding to the 3 expected values 1,0 and −1, would occur only under ideal conditions represents one example of a constraint on the signal that is used to generate information about the extent to which a transducer is not aligned with a track center.
Over repeated observations, the contributions of the Signal Deterioration Effects to signal errors will contribute about the same amount of error independent of the degree of head/track misalignment. Other of these effects, such as head lift, only occur rarely and are mostly of short duration. Therefore, over repeated observations the errors due to head/track misalignment are observable.
In accordance with the teachings of the present invention, such a signal would be a control signal containing information about the extent of errors which could be used to perform a control function as described herein.
One feature associated with use of PRML encoding is that only certain sequences of values can occur within the encoded signal or the signal containing at least one constraint. For example, in the PR4 method, not all sequences of the expected 3 values of 1,0 and −1 will occur. The “maximum likelihood” part of the PRML encoding is used to choose a best estimate, based on the possible sequences of these values, of the theoretical values that the observed values can represent. The fact that only certain sequences of symbols will occur, and not others, is another at least one constraint that is used to estimate the extent of error.
As is well known in the art of PRML decoding, alternate sequences of possible decoded data sequences are saved until the sequence exhibiting the least extent of errors can be determined. This allows the choice of that sequence exhibiting the least extent of errors as that sequence with the maximum likelihood of having been the original recorded data sequence. The extent of error measure for the chosen sequence is then available to use in the invention as at least one component of the control signal of the invention.
In light of these constraints, the observed values are compared with known or expected values. As discussed above the observed values may differ from the expected values due to the Signal Deterioration Effects. For example, one such effect may be due to the transducer rising temporarily to a greater height than normal off the disc surface due to encountering an aspersion, and then settling back to normal transducer flying height sometimes referred to as “head flying height”. By computing or comparing the differences between the observed values and the expected values, the differences can be used to generate a control signal containing information about the extent of errors.
As the transducer or head passes over a track, each observation can be combined with a specific number of previous observations and the oldest observation can be dropped so that the degree of error or extent of error calculated represents that specific number of most recent observations. In this way, a dynamic signal or nearly continuous signal corresponding to the degree of misalignment can be generated and such signal represents a control signal containing information about the extent of errors.
In this method, the control signal is being derived from current data, that is defined to be data that is satisfying a read request to a disc drive or data in the same track preceding a write sequence to a disc or to a track on the disc.
The step 306 of generating a control signal also performs the step of extracting the PRML encoding from the first signal and compares the observed PRML encoding of the extracted PRML encoding with an expected PRML encoding and generates the control signal from the difference between the observed PRML encoding and the expected PRML encoding.
It is also envisioned that the teachings of this invention have utility by using the method for using information about the extent of errors in combination with servo burst signals generated from prerecorded servo bursts. The method comprises the steps of: (a) positioning a first transducer for sensing prerecorded servo bursts and predetermined storage locations having stored data containing at least one constraint and generating in response to the prerecorded servo bursts servo burst signals and in response to the stored data a first signal representative of the data containing at least one constraint from the predetermined storage locations and any errors introduced into the sensed data during the sensing; (b) producing in response to the servo burst signals a position error signal; (c) generating in response to the first signal a control signal containing information about the extent of errors in the sensed data and extracting a data signal; and (d) receiving said position error signals and said control signal and adjusting with an adjusting element in the intervals between the servo burst signals the transducer in response to the position error signals to position the transducer in a designated alignment relative to said predetermined storage locations and performing in the intervals between the servo burst signals and in response to the control signal containing information about the extent of errors a control function to improve the extracted data signal as a function of the extent of errors.
The method can also include in the step of positioning including a transducer having at least two read elements that generate the servo burst signals and a first signal and a second signal each representative of the sensed data and any errors introduced into the sensed data during said sensing. The step of receiving is responsive to the first signal and the second signal to generate the control signal and for extracting a first data signal and a second data signal. The control function between servo burst signals performs with an output device at least one of receiving the control signal for generating a dynamic servo signal to improve alignment of the transducer relative to the predetermined storage locations on said surface and being responsive to the control signal and at least one of the first data signal and the second data signal to derive therefrom a data signal containing the least amount of errors. The method in the step of positioning also includes the transducer being a magnetoresistive element.
The response curve 330 shows that the BER curve is substantially flat about −12 microinches to about +12 microinches from the track center line of a track having a width of approximately 50 microinches. The curve 330 includes two minimum points 342 and 344 that correspond to the right and left boundaries of the track, respectively. Between the minimum points 342 and 344 and across the track width, head/track misalignment does not produce a significant number of errors.
The portion of the curve 330 extending beyond minimum points 342 and 344 rapidly slopes up as the relative horizontal displacement of the transducer increases from the center line of the trace. At these points on curve 330, a slight change of misalignment produces a significant change in the extent of errors.
The solid line curve 338 is a plot of the average extent of errors as a function of transducer position relative to the center line of the track in a manner similar to the BER curve 330. The solid line curve 338 is an idealized extent of error curve and beyond the minimum points 342 and 344 follows the BER curve 330. However, at the range of 12 microinches to about +12 microinches from the center line depicted by numeral 340, curve 318 demonstrates that a slight change in alignment produces a significant increase in the average extent of errors. This information about the extent of errors is used as the control signal and for generating a dynamic servo signal.
In the state of the art magnetic recording systems, the servo burst produces servo signals at the a rate of about 8,000 to 10,000 servo signals per second. In the present invention, the dynamic servo signal produced from a control signal containing information about the extent of errors using the teachings of the present invention result in a sampling rate significantly higher than the sampling rate of the state-of-the-art servo systems.
As a result of the above, apparatus for producing the control signal containing information about the extent of errors can be used in combination with the known Servo Burst Method. In such a combination, the control signal is used to generate substantially continuous feedback signals containing information about the extent of errors and applying the same to an actuator for positioning the read/write heads to maintain head/track alignment such that the position error signals from the apparatus are used during the intermittent open loop servo operation between or in the intervals between the servo burst signals of the Servo Burst Method. In the Servo Burst Method, the sensing of a recorded servo burst is used to produce a servo signal for adjusting the head position relative to the data track.
As discussed hereinbefore, a single MR element any be used as the read transducer in practicing this invention. In the instance where a single MR element is used as the transducer, the sensed data containing at least one constraint and information about errors can be used to determine the magnitude of adjustment required by the adjusting element. However, the direction of the adjustment is difficult to derive from the sensed data containing at least one constraint and information about errors. In the prior art Servo Burst Method, the servo burst signal can be used to develop position error signals containing information about the magnitude and direction of adjustment.
In the present invention, the control signal can contain the information required to make such an adjustment of an MR element by using the control signal containing information about the extent of errors for the apparatus having a single MR element as the reading transducer.
If the MR element is maintained slightly offset to one side of the center line, this slight misalignment produces a high average extent of errors. Referring to curve 338 of
The apparatus disclosed herein using a transducer that is a magnetoresistive sensor in a system where the predetermined storage locations is a track having a center line and the adjusting element is adjusted to position the sensor at a slight offset from the center line of the track in a known direction establishes a predetermined sensor position. In such an apparatus, the output device is responsive to the control signal containing information about the extent of errors to generate a position error signal, compensated by the predetermined sensor position, representing the magnitude and direction in which the adjusting element is to move said sensor to improve sensor/track alignment.
Thus, one servo control method for a single MR element or single sensor is to maintain the head slightly to one side of the track center between servo bursts. A small offset will provide reproduced data having substantially the same number of errors after PRML processing as compared to an ideal alignment of the head with the track. This is due to the BER in the output of a PRML processing not changing significantly as is evidenced from curve 330 in FIG. 7. As the predetermined sensor position approaches track center, the MR element or single sensor position will be corrected so as to slightly increase its displacement from track center. As the displacement is observed to increase beyond a given amount, the head position is adjusted to decrease the displacement. This method maintains the MR element alignment or single sensor between an upper and lower limit.
If the MR element or single sensor is nearer the center line of the track than a minimum displacement, then the direction of the offset becomes unknown. In such event, an adjustment is made to move the head slightly to the left. If the displacement is observed to increase, then the MR element or single sensor was to the left, otherwise the MR element was right. In this event, the adjustment may have reduced the observed offset to zero. This method can be repeated as soon as the offset is observed as shown on the curve 338 of FIG. 7.
In
The idealized extent of errors curve 338 shows the shape of the average extent of errors over a set of samples during PRML processing. As described herein, a new value can be obtained each time a new sample is obtained, which is in the range of 10,000 to 15,000 samples between each pair of servo bursts. This is sufficient to generate a nearly continuous servo signal, and is the preferred method in this invention.
Thus, slight changes to the MR element position which increase or decrease track offset can be used to generate information about the direction of track offset.
The first curve 410 shows the relationship between BER and head position for a first read transducer and the second curve 412 shows the relationship between the BER and horizontal head position for a second read transducer.
The response curves 410 and 412 are typical of the response curves produced using the transducer 26 having two insulated MR elements 176 and 178 in FIG. 5. This information can be used to generate a position error signal for practicing this invention.
If a transducer 26 is used having two unshielded MR elements as depicted in
The actual waveform 506 shows changes in the time-varying electromagnetic value on the second axis 504 with time on the first axis 502 as actually measured by the transducer. The actual response waveform includes a plurality of sample points 520 indicating actual sample values of the time-varying electromagnetic value determined by the PRML technique.
The ideal waveform 512 shows changes in the time-varying electromagnetic value on the second axis 504 with time on the first axis 502 as the same would be measured by the sensor for an ideal case of bit-encoding and bit-decoding. The ideal response waveform 512 includes a plurality of sample points 520 indicating ideal sample values of the time-varying electromagnetic value determined by the PRML technique.
In general, the actual response waveform 506 differs from the ideal response curve 512. The transducer receives the actual values for the actual sample points 520 and a comparator compares those values with the ideal sample values, and determines a set of sequences of data bits most likely to have produced the actual values for the actual sample points 520.
It is envisioned for one embodiment that the PRML encoding technique can be selected as a constraint for the data signal for practicing this invention in the following manner. The signal from the sensors, e.g., MR elements, can be sampled at twice the normal sampling rate or higher. After PRML decoding, using sample points as discussed hereinabove, the difference between the observed PRML encoding waveform from the sensor, e.g., MR head, and the expected PRML encoding as derived from the error corrected output data is computed. This computation provides information about the extent of errors in the sensed data signal and can be used for the control signal. Such computation is available using the computational capacity of state-of-the-art microprocessors and digital signal processors.
The following are examples of determining error rates using PRML processing: (a) The average amount by which the observed values of samples differs from the expected values of these samples, when averaged over a span of samples, which span of samples may range from a few tens of samples to a thousand or more samples; (b) the average amount of the squares of the above difference over the same range of sample sizes; (c) the average amount of squared differences between a PRML signal re-encoded from the error-corrected data output of the invention and the sensed signals, properly aligned in time, applied to each of the first data signal and second data signal that is input to the PRML decoders, to provide a measure of extent of error measurement that corresponds to the data stream produced by each PRML decoder and from which the control signal is composed; The advantage of this is that the best estimate of the expected PRML signal is that output signal that has been derived from the first data signal and the second data signal and has subsequently been PRML decoded, and possibly further error corrected as the best data output signal from the invention; and (d) other functions of these differences for these sample sizes.
When two MR elements are employed, a control signal is calculated for each in the above described manner. Then a function of all of these individual control signals combines then to produce and output control signal, there are many ways to combine the signals. The simplest is to subtract the first control signal from the second control signal and use the result as the control signal.
The method applies to the step of positioning using a transducer or transducers including transducers having two or more read elements to sense predetermined storage locations having stored data containing at least one constraint. The method utilizes the apparatus described herein above and is based on predetermined storage locations containing data being already written on or within a storage media.
At flow point 600, the sensor is positioned proximate to the predetermined storage locations or data track and is ready to read a sequence of data bits. At flow point 602, the transducer responds to the sequence of data bits and produces a first signal. At flow point 604, the detector or input device processes the first signal by comparing the first signal having at least one constraint with the expected signal containing the at least one constraint to generate the control signal containing information about the extent of errors. The flow point 606 also extracts the data signal from the first signal.
At flow point 606, the extracted data signal and the control signal containing information about the extent of errors may be used as shown by flow point 610 for electrically deriving a data signal having the least number of errors from multiple data signals and to produce the so derived data signal as the reproduced data 614. The extracted data can be used as the reproduced data as shown by lead 612.
At flow point 620, an adjusting element responds to the control signal containing information about the extent of errors to generate position error signals that are used to adjusting the position of the head such that the head is positioned in improved alignment relative to the predetermined storage locations or data track thereby continuing the read process as shown by flow point 640 extending back to flow point 600.
In the schematic diagram of
Each of the MR elements 176 and 178 produce an output signal appearing on leads 248 comprising the sensed data containing the at least one constraint and any errors introduced into the sensed data during sensing. The signal from MR element 176 is applied as an input to read amplifiers 250 and 254 while the signal for MR element 178 is applied to read amplifiers 252 and 254. The output of read amplifier 254 represents the sum of the signals produced by MR elements 176 and 178. The output of read amplifiers 250 and 252 represents the signal produced by MR elements 176 and 178, respectively.
The output signals of read amplifiers 250,252 and 254 each separately provide the sensed data containing the at least one constraint and any errors introduced into the sensed data during sensing. Each of the read amplifiers 250, 252 and 254 amplifies the signal and performs any other required signal processing and generates a first signal representative of data containing the at least one constraint from said predetermined storage locations and any errors introduced into the sensed data during sensing. Each of the read amplifiers 250, 252 and 254 applies its respective output as the first signal to parallel detectors.
Specifically, the first signal from read amplifier 254, which is a sum of two signals sensed by the MR elements, is applied as an input to a sum data extraction and error circuit 700 that produces an extracted data signal on output 710 representing the sum of the two signals sensed by the MR elements 176 and 178, and a control signal having information about the extent of errors which appears on output 720.
Similarly, the first signal from read amplifiers 250 and 252, which are the signals sensed by the MR elements 176 and 178, respectively, are applied as an input to a left data extraction and error circuit 702 for the sensed signal from MR element 176 and to a right data extraction and error circuit 704 for the sensed signal from MR element 178, respectively. The left data extraction and error circuit 702 produces an extracted data signal on output 712 extracted from the first signal from MR element 176 and a control signal having information about the extent of errors which appears on output 722.
The right data extraction and error circuit 704 produces an extracted data signal on output 714 extracted from the first signal from MR element 178 and a control signal having information about the extent of errors which appears on output 724.
In this embodiment, the sum data extraction and error circuit 700 generates a unified control signal while the left data extraction and error circuit 702 and the right data extraction and error circuit 704 each generate a control signal containing information about the extent of errors in each received signal.
In the embodiment of
The control signals 720, 722 and 724 are concurrently applied to the selection controller 723 and to a servo controller 724. The selection controller is responsive to the control signals to generate the processing control signal 736 applied to the data multiplexor 732 as described herein before.
The servo controller 723 generates position error signals from the control signals and applies the same via lead 726 to a servo amplifier 728. The servo amplifier 728 applies the servo signals representing the magnitude and direction of the adjustment required to improve alignment between the MR elements and data track 160.
The embodiment illustrated in
The multidisc storage system illustrated in the diagrammatic representation of the
As illustrated in
In
When the disc surfaces are on the same disc, physical conditions which introduce errors into the sensed signal, e.g., thermal expansion, bending or the like, affect both surfaces more or less equally thereby reducing errors between the transducers sensing data from surfaces on the same the rotating disc. When the disc surfaces are on different discs driven by a common spindle, physical conditions which introduce errors into the sensed signals, e.g., spindle wobble, affect both discs more or less equally thereby eliminating some errors between the transducers sensing data from surfaces on different rotating disc.
The transducers 764, 766, 768 and 770 sense the stored data and apply the sensed signals to their respective read amplifiers 782, 784, 786 and 788, respectively.
The outputs from each of the read amplifiers 782, 784, 786 and 788 are applied parallel to an input device 974 which derives a single extracted data signal therefrom which appears as output 798. The input device 794 generates a control signal containing information about the extent of errors from the plurality of first signals, and generates a dynamic servo signal which appear on lead 806. The control signal on lead 806 is applied to actuator 804 to adjust the position of one or more of the transducers 764, 766, 768 and 770 to improve transducer alignment relative to a track on the disc surface. The control signal shown in arrow 808 may be used in a manner similar to
As illustrated in
As a result of the high manufacturing tolerances necessary to achieve current track densities, and of operating environmental conditions introducing thermal and other effects that cause the transducer to transducer alignment to vary over time, information about the position of a transducer on a second disc surface is not sufficient to accurately control the position of the transducer on the first surface so as to be able to align that transducer with the required accuracy over a track on the first disc surface.
The apparatus of
Such additional information may be obtained from one or more of the other disc surfaces storing data in the disc drive. When the disc surfaces are on the same disc, the sensed data from the first transducer's reading is particularly useful, e.g., can be used to generate a single control signal to adjust both transducers to improve alignment of both transducers relative to its associated track. During manufacturing of a disc drive, a manufacturing step called “servowriting” is used in which servo burst are written for every track and every surface. It is envisioned as part of this invention to align tracks on opposite surfaces of the same discs, so that the track centers on the first surface are somewhat offset from the track centers on the second surface during servowriting. Thus, when a transducer on one surface is well aligned with a track on the first surface, the transducer on the opposite surface is somewhat misaligned with a track on the opposite surface. When this occurs, the relationship between the transducer and track on the opposite surface is such that the extent of errors is large.
As shown in
It is also envisioned to write the servo burst on opposite surfaces of a disc so that the servo burst on one surface are positioned half-way between pairs of servo bursts on the other surface which can be easily accomplished during servowriting. As a result, information from the servo burst on the second surface can be provided to the control device 794 during the intervals between generation of information from servo burst on the first surface. These control signals may be used in the intervals between the servo burst signals to adjust transducer position relative to a track on a nearly continuous basis.
It is envisioned that the teachings of the apparatus, method and system as disclosed has application in storage systems in which the storage medium is moved in relation to the transducer, including magnetic disc drives, both hard and floppy disc application, in magnetic tape drives, magnetic card stripes or the like. Any storage apparatus which utilizes magnetic responses, including magnetic induction, magneto-resistive sensors, including “giant magnetoresistive” transducer, “colossal magnetoresistive” transducer and spin-valve transducer are deemed to be within the teaching of the present invention.
In addition, it is envisioned that the teachings hereof would have utility for storage systems employing electric and other forces as sensed by an appropriate probe such as is used in atomic force microscopes and other microscanning devices.
In addition, it is envisioned that the teaching hereof would have utility for optical data storage or other storage systems including holographic memories which record and reproduce stored data in predetermined storage locations.
All of the above are envisioned to be useful for practicing the invention as disclosed herein.
Gaines, R. Stockton, Despain, Alvin M.
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