Method for positioning a magnetic head and magnetic disk driving apparatus for implementing the method

Abstract: A magnetic disk driving apparatus comprises a driving section (34) for driving a magnetic head on a destination track, in response to an input drive instruction, a detecting section (12 to 28) for detect­ ing peak values of signal components corresponding to servo data read out from the magnetic disk by the magnetic head, and a controller (30) for generating a drive instruction in accordance with a plurality of selected peak values of the detected peak values to out put the generated instruction to said driving section.

Description: The present invention relates to a magnetic disk driving apparatus for accurately positioning a magnetic head on a destination track of a magnetic disk. In order to position a magnetic head on a destination track of a magnetic disk in a conventional magnetic disk device, the magnetic disk has been used on which, for example, a servo pattern is recorded. The servo pattern is comprised of, for example, two patterns, each of which exists at one side with respect to a track center. Two signals are read from the two patterns. When the magnetic head is positioned off from the center of a desired track, the signals read from the two patterns are such that the signal corresponding to one of the patterns has a peak value larger than the signal corresponding to the other pattern. On the other hand, when the head is positioned right over the center of the desired track, the signals corresponding to the patterns have an equal peak value. Thus, by moving the magnetic head until the signal corresponding to one of the patterns and the signal corresponding to the other of the patterns have equal peak values, the magnetic head can be positioned right over the center of a desired track. A known method for improving the positional accuracy of the magnetic head is one in which peak values obtained for each of the patterns are averaged for subsequent comparison. This method permits accurate measurement of the amount of positional deviation of the magnetic head from a given track center. On the other hand, if error signals arise due to the disturbance and disk deficiencies at the servo pattern portions, the signals read from the patterns and hence the average values could have abnormal values. This would move the magnetic head to an erroneous position. Prior art document US-A-4 380 034, which is the basis for the prior art portions of claims 1, 4 and 5, discloses a track centering servo pulse noise filter in which prerecorded pulses on a disk track's even and odd half tracks are sensed by the disk's read head, preamplified, DC biased, peak detected, and stored on a FIFO basis into a noise filter comprising two sets of N analog sample and hold cells, one set for the even pulses and one set for the odd pulses. The output of each even-pulse sample and hold cell is input to a summing junction to form an average of the last N pulses. The same is done with the outputs of the odd-pulse sample and hold cells. The two summing junctions are then input to a differential amplifier to form a position error signal to the disk head track centering servo system for keeping the head centered on the track. Further, prior art document IBM TECHNICAL DISCLOSURE BULLETIN, vol. 23, no. 7A, December 1980, NEW YORK US, page 2713; J.C. Dennison et al.: "Erroneous Position Error Signals Accommodation", relates to erroneous position error signal accommodation in a record storage apparatus having a flexible record medium. In applying a sector servo techniques to such a flexible record medium, the likelihood of a defect in a servo area is quite high. Further, a dust particle on a servo area can also radically change the value or magnitude of the servo read-back signal. The result is an erroneous position error signal (PES) which can cause the control circuit to move the transducer away from the track center line, resulting in marginal or unacceptable performance. This can be avoided, in large part, by scrutinizing the rate of change between the present PES value and the previous PES value. It is an object of the present invention to provide a magnetic disk driving apparatus for accurately positioning a magnetic head on a destination track of a magnetic medium. To solve this object the present invention provides a magnetic disk driving apparatus as specified in claim 1, 4 or 5. The magnetic disk driving apparatus comprising a driving section for driving the magnetic head on the destination track, in accordance with an input drive instruction, a detecting section for detecting peak values of signal components corresponding to servo data read out from the magnetic disk by the magnetic head, and a controller for generating a drive instruction on the basis of a plurality of peak values selected from among the peak values detected, and outputting the drive instruction to the driving section. A positioning method comprises the steps of the reading out, by the magnetic head, of servo data from the magnetic disk, in order to detect peak values of signal components corresponding to the servo data, generating a drive instruction on the basis of a plurality of peak values selected from among the peak values detected, and driving the magnetic head on the destination track, in accordance with the drive instruction. According to the magnetic disk driving apparatus, as described above, since abnormal values due to the deficiencies of the servo pattern surface of a recording disk and the disturbance are removed for subsequent average processing, the accurate positioning of the head is always possible. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram of a magnetic disk device according to a first embodiment of the present invention; Figs. 2A and 2B are flowcharts for explaining the operation of the first embodiment; Figs. 3A through 3C are diagrams for explaining position control; Fig. 4 is a block diagram of a magnetic disk device according to a second embodiment of the present invention; and Fig. 5 is a flowchart for explaining the operation of the second embodiment. First, a first embodiment of the present invention will be described with reference to Fig. 1. A magnetic disk 10 is rotated by spindle motor 8. As shown in Fig. 3A a servo pattern comprising two pattern, each of which exists at one side with respect to track center TC, is recorded on disk 10. In this embodiment, the disk is assumed to be a floppy disk, on whose servo data surface the servo pattern is embedded, of a so-called sector servo system. Magnetic disk 10 may be of servo-surface-servo type or may be a hard disk. In the servo-surface-servo type of magnetic disk, the servo data is read out from a recording surface different from a data recording surface or another magnetic disk by a special head which is drived by an actuator along with the magnetic read/write head. Magnetic heads 12 and 42 are supported by a carriage mechanism 34 to be positioned on destination tracks in accordance with a drive instruction from CPU 30. Signals corresponding to servo data 61-63 and 71-73 read from magnetic disk 10 by magnetic head 12, for example, are amplified in amplifier 14 and then applied to timing extractor 16. Timing extractor 16 generates various control signals from the amplified signals. Switch 15 is responsive to a switching control signal from timing extractor 16 to feed the amplified signals corresponding to servo data 61-63 in pattern A to a peak hold circuit (P/H) 18 and to feed amplified signals corresponding to servo data 71-73 in pattern B to a peak hold circuit (P/H) 20. Peak hold circuits 18 and 20 hold peak values of the amplified signals in response to hold control signals from timing extractor 16, respectively. The peak values held by peak hold circuits 18 and 20 are converted to digital data by analog-to-digital (A/D) converters 22 and 24 in accordance with conversion control signals from timing extractor 16, respectively, and then stored into fast-in fast-out (FIFO) memories 26 and 28 in accordance with write control signals from timing extractor 16, respectively. Upon the completion of reading out of the predetermined servo data, CPU 30 reads the peak values from FIFO memories 26 and 28 and adds separately these values. When the addition is completed, CPU 30 issues write control signals to store these peak values in FIFO memories 26 and 28. The number of pieces of the servo data is predetermined, and data on the number of the servo data are stored in registers 324 and 330 in memory 32. When the addition is completed for all the servo data, sum values A S and B S are stored in registers 322 and 328, respectively. In addition, average values A AV and B AV are calculated from the sum values A S and B S , respectively. The peak values are sequentially read out from FIFO memories 26 and 28 to select peak values falling within predetermined error E from the average values A AV and B AV . Average values are determined by the selected peak values again. Subsequently, a difference between the average values thus determined is calculated, and a drive signal is applied to carriage mechanism 34 in accordance with the difference. Through the carriage mechanism head 12 can be accurately positioned on a destination track. The operation of the first embodiment will be described with reference to Figs. 2A and 2B. Magnetic disk 10 is rotated by spindle motor 8. On disk 10 the same pattern as the servo pattern shown in Fig. 3A is recorded. When a seek instruction is input to CPU 30, the initialization is performed in step S2. For example, the values N A and N B are set to be 0. Also, values A S and B S are set to be 0. Magnetic head 12 is subjected to a speed control for movement to a destination track. When the head reaches near to the destination track, the control is switched from the speed control to the positioning control as shown in step S2 and the following steps. Assume now that head 12 is positioned on position 2 with respect to the destination track. In step S4, servo data 61-63 and 71-73 are read from magnetic disk 10 by head 12 to generate servo signal corresponding to servo data 61-63 and 71-73. The servo signal is amplified in amplifier 14, and the signal shown in Fig. 3C is obtained. The amplified servo signal is applied to timing extractor 16. Switch 15 responds a switch control signal from timing extractor 16 to apply signal components corresponding to servo data 61-63 in pattern A to peak hold circuit 18 and signal components corresponding to servo data 71-73 in pattern B to peak hold circuit 20. One of the signal components applied to peak hold circuit 18 is held therein in accordance with a hold control signal, and the held peak value is converted to digital data by A/D converter 22 in response to a conversion control signal from timing extractor 16. The converted peak values are stored into FIFO memory 26 in response to a write control signal in step S6. At this time, the value N A indicative of the number of pieces of the servo data is incremented by one. The same processes are carried out for the servo signal components corresponding to servo data 71-73 in pattern B. In step S8, a decision is made as to whether or not the reading and writing operations have been completed for all the servo data. If NO in step S8, then the operations of steps S4 to S8 are repeated. If YES in step S8, then step S9 will be performed. In step S9, a variable I is set to be "1". The number N A of the servo data 61-63 is stored in register 324. In step S10, peak value A I is read from FIFO memory 26 for addition to variable A S . In step S12, the read peak value A I is stored into memory 26 again. At the same time, the variable I is incremented by one. Subsequently, a decision is made in step S14 as to whether the variable I is equal to the number N A of the servo data or not. If not equal, then the operations of steps S10 to S14 are repeated. If equal (YES) in step S14, then step S16 is carried out. In step S16, an average value A AV (=A S /N A ) for the servo data in pattern A is calculated. Subsequently, variable I is initialized to one, and value N A is set to variable K A . The sum value A S is stored in register 322. In step S18, peak value A I is read from FIFO memory 26 again, and variable I is incremented by one. In step S20, a decision is made as to whether or not an absolute value of a difference between peak value A I and average value A AV is larger than predetermined error E. If the absolute value is smaller than error E, then step S26 is carried out. If the absolute value is larger than the error, then step S24 is carried out so that sum value A S is read out of register 322 and peak value A I is subtracted from sum value A S . The result of the subtraction is stored in register 322. Variable K A stored in register 326 is decremented by one. That is to say, of the peak values A61-A63 corresponding to the servo data 61-63, the peak values A61 and A63 are considered to fall within the margin of error E of average value A AV in step S20 and thus used for calculating the average value. On the other hand, peak value A62 due to the disturbance is excluded from the calculation of the average value because the result of the decision in step S20 based on the value A62 is YES. Subsequently, in step S26, a decision is made as to whether variable I is equal to number N A of data stored in register 324. If not equal, the step S18 is carried out again. If equal, then a new average value A AV is calculated from sum value A S and variable K A and stored in register 322. At the same time, variable I is set to be one. In steps S30 through S48, the same processes as those in steps S10 through S28 are carried out for the servo data 71-73 in pattern B. In this way, average values A AV and B AV are obtained. In step S50, difference D between average values A AV and B AV is calculated, and a drive control signal is determined in accordance with difference D. Carriage mechanism 34 is driven by the determined drive control signal. As a result, average value A AV of peak values A61-A63 and average value B AV of peak values B71-B73 are made equal to each other, so that magnetic heads 12 and 42 can accurately be positioned on the destination tracks. Next, a second embodiment of the magnetic disk driving apparatus of the present invention will be described. The arrangement of the second embodiment will first be described with reference to Fig. 4. In the second embodiment, like reference numerals are used to denote like portions in the first embodiment, and the description thereof will be excluded. In the second embodiment, peak values A61-A63 and B71-B73 corresponding to servo data 61-63 and 71-73 in servo patterns A and B are stored together in FIFO memory 46 in accordance with a write control signal from timing extractor 44 similar to extractor 16. CPU 50 similar to CPU 30 calculates differences between A61 and B71; A62 and B72; A63 and B73, and then drives carriage mechanism 34 in accordance with an average value C AV of the calculated differences. In the operation of steps S60 through S66 shown in Fig. 5 the same processes as those in steps S2 through S8 in the first embodiment are performed. In the second embodiment, single FIFO memory 46 is used, so that peak values A61-A63 and B71-B73 are alternately stored into FIFO memory 46. If the storage of the servo data into FIFO memory 46 is completed in step S66, then variable I is set to be one in step S67. Steps S68 through S72 are the same as steps S10 through S14 in the first embodiment. In the first embodiment the peak values are separately added while, in the second embodiment, a difference between peak values A61 and B71 is first obtained and then the difference is added to value C S in step S68. If, in step S72, it is decided that the addition is completed, then average value C AV is calculated and value C S is stored in register 482 in memory 48 similar to memory 32. Number N of the servo data has been stored in register 484 in step S74. When average value C AV is obtained, the same processes as those in steps S18 through S26 in the first embodiment are carried out for each difference obtained in step S68. As a result, even if error signals due to the disturbance, the deficiencies of magnetic disk 10, or the like are output from amplifier 14, they can be removed in steps S78 and S80. Sum value C S of normal differences alone is obtained in step S82, and then average value C AV is calculated in step S84. In step S84, a drive control signal is determined in accordance with average value C AV of the differences. Carriage mechanism 34 is driven in accordance with the determined drive control signal. As a result, magnetic heads 12 and 42 are accurately positioned on the destination tracks as shown in Fig. 3B.

Claims: A magnetic disk driving apparatus capable of accurately positioning at least one magnetic head on a destination track of a magnetic disk, comprising: detecting means (12 to 28; 12 to 22, 44 and 46) for detecting peak values of signal components corresponding to servo data read out from said magnetic disk by said magnetic head; control means (30; 50) for generating a drive instruction in accordance with a plurality of selected peak values from among the detected peak values from said detecting means; and driving means (34) for driving said magnetic head on the destination track in accordance with the drive instruction generated by said control means, wherein: said control means (30; 50) includes means for selecting said plurality of selected peak values from among the detected peak values, and for generating the drive instruction from said plurality of selected peak values including first and second selected peak values to output the generated instruction to said driving means, and said control means (30; 50) comprises: first selecting means (30), for calculating a first average value of first peak values of the detected peak values, and second selecting means (30), for calculating a second average value of second peak values of the detected peak values, characterized in that: said control means (30; 50) selects said plurality of selected peak values from among the detected peak values in accordance with each of the detected peak values, said first selecting means (30) selects, from among the first peak values, said first selected peak values which fall within a predetermined value with respect to the first average value; and said second selecting means (30) selects, from among the second peak values, said second selected peak values which fall within the predetermined value with respect to the second average value. An apparatus according to claim 1, characterized in that said control means (30; 50) comprises: means (30) for calculating a third average value from said first selected peak values; means (30) for calculating a fourth average value from said second selected peak values; difference calculating means (30) for calculating a difference between the third and fourth average values; and generating means (30) for generating the drive instruction in accordance with the difference. An apparatus according to claim 1, characterized in that said detecting means (12 to 28; 12 to 22, 44 and 46) comprises: reading means (12, 14) for reading out the servo data from said magnetic disk, by means of said magnetic head, to generate the signal components; timing extraction means (16) for extracting a switching control signal, first and second detect control signals, and first and second write control signals from the signal components; first FIFO memory means (26), for storing first peak values of the detected peak values; second FIFO memory means (28), for storing second peak values of the detected peak values; first peak detecting means (18, 22) for detecting the first peak values from the signal components, in response to the first detect control signal from said timing extraction means, and for writing the detected first peak values into said first FIFO memory means, in response to the first write control signal from said timing extraction means; second peak detecting means (20, 24) for detecting the second peak values from the signal components, in response to the second detect control signal from said timing extracting means, and for writing the detected second peak into said second FIFO memory means, in response to the second write control signal from said timing extraction means; and switching means (15) for selectively outputting the signal components to one of said first and second peak detecting means, in response to the switching control signal from said timing extraction means. A magnetic disk driving apparatus capable of accurately positioning at least one magnetic head on a destination track of a magnetic disk, comprising: detecting means (12 to 28; 12 to 22, 44 and 46) for detecting peak values of signal components corresponding to servo data read out from said magnetic disk by said magnetic head; control means (30; 50) for generating a drive instruction in accordance with a plurality of selected peak values from among the detected peak values from said detecting means; and driving means (34) for driving said magnetic head on the destination track in accordance with the drive instruction generated by said control means, wherein: said control means (30; 50) comprises means (50) for calculating respective difference between first and second peak values of the detected peak values, for selecting a plurality of selected differences from the calculated differences, for generating the drive instruction from the plurality of selected differences, and for outputting the generated instruction to said driving means, and said control means (30; 50) comprises: means (50) for calculating the respective differences between the first and second peak values, selecting means (50) for calculating an average value of the calculated respective differences, and means (50) for generating the drive instruction from the plurality of selected differences to output the generated instruction to said driving means, characterized in that said selecting means (50) selects said plurality of selected differences from the calculated differences in accordance with the calculated differences, and selects from the calculated respective differences the plurality of selected differences which fall within a predetermined value with respect to the average value. A magnetic disk driving apparatus capable of accurately positioning at least one magnetic head on a destination track of a magnetic disk, comprising: detecting means (12 to 28, 12 to 22, 44 and 46) for detecting peak values of signal components corresponding to servo data read out from said magnetic disk by said magnetic head; control means (30; 50) for calculating differences between respective first and second peak values of the detected peak values and generating a drive instruction in accordance with calculated differences; and driving means (34) for driving said magnetic head on the destination track in accordance with the drive instruction generated by said control means, characterized in that: said control means (30; 50) further comprises, selecting means (50) for calculating an average value of the calculated differences, and for selecting from the calculated differences the plurality of selected differences which fall within a predetermined value with respective to the average value; means for calculating an average value of the selected differences; and means (50) for generating the drive instruction from the average value of the selected differences so as to reduce the average value of the selected differences.

Inventors: SAKURAI TETSUJI C O PATENT DIV, SAKURAI, TETSUJI C/O PATENT DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: G11B5
IPC codes: G11B5, G11B21