JP2003141837A - Method for inspecting preservo signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the dropout of a preservo signal on a magnetic disk medium correctly. SOLUTION: The preservo signal is reproduced from a magnetic disk medium 1, the pulse average amplitude value of a prescribed pattern in a servo wedge is measured from that signal in a computer part 10, and the moving average value of the pulse average amplitude measuring values of M adjacent servo wedges is calculated for each servo wedge. From the pulse average amplitude measuring values and the moving average value, a moving average deviation rate is calculated and the dropout is decided on the basis of the result of comparing each of moving average deviation rate and a prescribed value. When a preservo signal waveform contains the dropout, the pulse average amplitude value of each of patterns in the peripheral servo wedges is rapidly lowered but the moving average value is not changed so much. Therefore, the moving average deviation rate is rapidly inclined to the minus side and the dropout can be detected.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk medium, and more particularly, to a magnetic disk medium on which a spare servo signal (pre-servo signal) for generating a servo signal is recorded.
The present invention relates to a method for inspecting a pre-servo signal. 2. Description of the Related Art A magnetic disk drive device that uses a disk-shaped disk as a recording medium and reads or writes information with a flying head while rotating the disk at a high speed is used as an external storage device of a computer. I have. The magnetic disk medium used in the present apparatus is basically provided with concentric tracks at regular intervals on its surface, on which digital information can be recorded and reproduced. In a magnetic disk drive, positioning of a magnetic head is performed based on a servo signal written on a magnetic disk medium. Conventionally, a servo track writer has been mainly used as a means for writing this. However, in recent years, the number of tracks per surface of a magnetic disk has been increasing, the load on a servo track writer has increased, and the inefficiency of this method has become noticeable. Therefore, a self-servo write system has been used as an alternative. This method is
After recording a spare servo signal (pre-servo signal) on a magnetic disk medium in advance and incorporating it into a magnetic disk drive device, the device itself generates an original servo signal based on this signal. Since the pre-servo signal is directly transferred from the master disk by the magnetic transfer method, a high throughput can be obtained. [0005] The recording format of the pre-servo signal is based on a so-called sector servo system. FIG. 2 shows a conceptual diagram of the sector servo system. Servo wedge W1 is a magnetic disk medium HD
One recording surface is arranged at equal intervals in the circumferential direction.
FIG. 3 shows an example of the signal pattern of the servo wedge W1 portion of the pre-servo signal. A pattern such as an address mark and a gap follows the synchronization burst.
For example, a synchronous burst is a pattern in which 2T patterns are continuous. The 2T pattern is a pattern in which magnetization transition occurs every two bits when one bit is set as the minimum magnetization transition interval. Since the magnetization pattern of the pre-servo signal has a uniform spread in the radial direction, there is no concept of a track. Incidentally, in principle, the characteristics of the pre-servo signal may be degraded or a defect may occur during the transfer process in some cases. For example, a gentle undulation may occur in the signal envelope. FIG. 7A shows one such signal.
It shows the waveform for the circumference. This is generally called modulation, and is caused by undulation of a gap with a master disk during transfer, non-uniformity of magnetic characteristics of a medium, and the like. FIG. 5 shows an example of a pre-servo signal waveform (for one round) including a defect D1 in which the signal amplitude locally decreases. Such a defect D1 is generally called a dropout. This occurs due to particles being mixed during transfer, scratches on the medium, and the like. Dropout is characterized by a sharp change in amplitude as compared to modulation. Since modulation and dropout are deeply related to servo performance, they are measured and inspected in a signal evaluation test of a magnetic disk medium. Of these methods, the following method is generally used for dropout inspection. First, the average pulse amplitude value of, for example, the synchronous burst portion is measured for all the servo wedges in one round. Next, each pulse average amplitude value is simply averaged to obtain a track average value. Then, for each servo wedge, the ratio between the pulse average amplitude value of the synchronous burst portion and the track average value is determined,
If this is less than the predetermined value, it is determined as dropout. This inspection uses a test apparatus and software, and the processing is performed almost automatically. [0010] The above-described conventional method for detecting a dropout in a signal evaluation test includes the following.
Since it was based on a relatively simple principle, there were the following problems. That is, when a strong modulation is included in the pre-servo signal waveform, a decrease in the amplitude due to the strong modulation is regarded as a dropout, which may cause an erroneous detection. Therefore, the reliability of the test results was not sufficient. It is an object of the present invention to provide a method for inspecting a pre-servo signal which has solved the above-mentioned problems. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a plurality of servo wedges in which a pre-servo signal for generating a servo signal is recorded by a sector servo method are provided. A method of inspecting the presence or absence of a dropout in which the amplitude of a preservo signal reproduced from the magnetic disk is locally reduced by rotating the magnetic disk medium having the method, wherein the preservo signal is reproduced from the magnetic disk medium, From the reproduced signal, a pulse average amplitude value of a predetermined pattern in each servo wedge is measured for all servo wedges in one round on the magnetic disk, and for each servo wedge, a pulse average amplitude of a plurality of adjacent servo wedges is measured. Calculate the moving average of the measured values,
For each servo wedge, a moving average deviation rate is calculated from the pulse average amplitude measurement value and the moving average value, and a dropout is determined based on a comparison result between the calculated moving average deviation rates and a predetermined value. It is characterized by doing. According to the above configuration, for each wedge of one turn of the pre-servo signal, a pulse average amplitude value of a predetermined pattern is measured, a moving average deviation rate is obtained, and this is compared with the predetermined value. On the other hand, when a dropout is included in the pre-servo signal waveform, the pulse average amplitude value of each pattern sharply drops in the surrounding servo wedge, but the moving average value does not change much. Therefore, the moving average deviation rate in the vicinity thereof sharply falls to the negative side. Therefore, dropout can be detected by setting the predetermined value to be compared to an appropriate negative value. Further, since the fluctuation of the amplitude due to the modulation is gradual, even if this is included in the signal waveform, the moving average deviation rate is hardly affected by the fluctuation. Therefore, erroneous detection of dropout due to modulation can be prevented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. 1, 2, 4, 6, and 7. FIG. FIG. 1 shows a configuration of a test apparatus of the present embodiment for inspecting a pre-servo signal. In FIG. 1, a magnetic disk medium 1 is a magnetic disk medium to be evaluated in which a magnetic film, a protective film, a lubricant, etc. are adhered to a disk-shaped aluminum substrate and preservo signals are transferred and recorded. . Spindle motor 2
Fixes the magnetic disk medium 1 to a rotating shaft, and rotates the magnetic disk medium 1 at high speed by its rotational movement. The head slider 3 has a magnetic head (not shown) as a reproducing element mounted on a surface facing the magnetic disk medium 1 and is supported by a head arm 6. One end of the head arm 6 is fixed to a positioner 4 as a positioning mechanism, and the head slider 3 moves to a predetermined position on the magnetic disk medium 1 as the positioner 4 moves. The head slider 3 is loaded and unloaded on the magnetic disk medium 1 by a load / unload mechanism (not shown). An output signal of a magnetic head (not shown) of the head slider 3 is input to a read amplifier 5 as an amplifying means, where an amplitude of about several hundred mVp-p is obtained. The output signal of the read amplifier 5 is input to an A / D converter 8, where it is sampled. A / D
The converter 8 is, for example, a flash A / D converter. A 1 GHz sampling clock is externally supplied, and converts an input analog signal into 8-bit digital data in synchronization with the clock. On the other hand, the output signal of the read amplifier 5 is also input to the gate signal generation circuit 7. Gate signal generation circuit 7
Incorporates a circuit for analyzing a pattern of a pre-servo signal, and generates a gate signal C1 based on the circuit. The gate signal C1 can be activated, for example, only while the signal of the synchronous burst portion of the specific servo wedge is being input, by setting the gate signal generation circuit 7. A waveform memory 9 is connected to an output side of the A / D converter 8. The waveform memory 9 is provided as means for temporarily storing sampling data, and the gate signal C1 is a storage permission signal. The computer section 10 controls the spindle motor 2, the positioner 4, and the gate signal generation circuit 7 under the control of a CPU, which will be described later, and reads the sampling data stored in the waveform memory 9 to perform data processing. It is a device for performing. As shown in FIG.
An external storage device (not shown) for storing a pre-servo signal test program as shown in FIG. 2 and a CP for executing the operation program of the test device shown in FIG. 2 including the test program
U, a memory (not shown) having an area for temporarily storing data and a work area for the CPU, a monitor (not shown) for displaying test results, an input device such as a keyboard and a mouse for receiving user input (Not shown) is provided. Next, the process of checking the pre-servo signal will be described with reference to the flowchart of FIG. In FIG. 4, S
1, 1 and S2 indicate the step numbers of the program. In step 1, various measurement conditions, for example, a radial position to be measured on the magnetic disk medium 1, the number of rotations of the spindle motor, the number Ml of moving average processing, and a threshold value Th1 for judging dropout are inputted from the input device. I do.
In step 2, the spindle motor 2 is started and waits until the rotation speed reaches a predetermined value. In step 3, the head slider 3 is moved to the first measurement radius position on the magnetic disk medium 1 and loaded at that position. As a result, the head slider 3 flies above the magnetic disk medium 1 while keeping a small gap, and the pre-servo signal is reproduced via the magnetic head. The reproduced signal is amplified by the read amplifier 5. Further, the output signal of the read amplifier 5 is sampled by the A / D converter 8, and the sampled data is output at a data rate of 1 GHz. In step 4, first, waveform data of the synchronous burst portion of the first wedge is obtained. Here, the first wedge is a wedge that gives a reference position of the magnetic disk medium 1, and is distinguished from the others by a specific signal pattern.
Also, the second signal is input in the order in which
Numbers are assigned in the order of wedge, third wedge,..., Nth wedge (N is the number of all wedges). In order to acquire the waveform data of the synchronous burst section of the first wedge, the computer section 10 sets the gate signal generation circuit 7. Then, the gate signal C1 becomes active when the input of the signal of the synchronous burst portion of the first wedge starts, and returns to inactive at the end of the synchronous burst portion. Then, the sampling data of the synchronous burst section of the first wedge is sequentially stored from the head address of the waveform memory 9. Then, the process proceeds to step 5 after the completion. In step 5, the average pulse amplitude value of the synchronous burst portion of the first wedge is calculated. Therefore, first, the sampling data in the waveform memory 9 is checked to search for positive and negative peaks of all the pulse waves. After each peak is determined, the voltage value at each peak is obtained by converting the value of the sampling data into the voltage value at the input of the A / D converter 8. Further, the potential difference between each positive and negative peak is obtained, and the average value is calculated. Further, this is stored in a memory (not shown). In step 6, all wedges (first to first wedges)
It is determined whether or not the processing for the Nth) has been completed. If the processing has not been completed yet, the wedge number is incremented by one, and the process returns to step 4 to perform the same processing for the corresponding wedge. If all wedges have been processed, the process proceeds to step 7. In step 7, the pulse average amplitude values of the synchronous burst portions of the first to Nth wedges are read from the memory, and the moving average value MV (n) (n = 1, 2,..., N) is calculated. The following formula is the calculation formula. ## EQU1 ## P = floor (M / 2) where V (n) is the pulse average amplitude value of the synchronous burst portion of the n-th wedge, M is the moving average score (odd number), and floor is
r (x) is the largest integer not exceeding x. V (n + k) = V (n + k−N) (n + k> N) V (n + k) = V (n + k + N) (n + k ≦ N) Further, the calculation result is stored in the memory. In step 8, the moving average deviation rate KR of the pulse average amplitude value of the synchronous burst section of the first to Nth wedges
(N) (n = 1, 2,..., N) is calculated. The following formula is the calculation formula. ## EQU2 ## At this time, the moving average deviation rate KR (n) has a positive or negative sign, and the absolute value increases as the amplitude value of the wedge differs from that of the surrounding wedges. In step 9, it is determined whether or not any of the first to Nth wedges has a moving average deviation rate smaller than the threshold Th1. If yes, go to step 10; if no, go to step 11. In step 10, a wedge signal having a moving average deviation rate smaller than the threshold Th1 is determined to be a dropout, and the information (a wedge number, a radial position, a message of dropout detection, etc.) is displayed on a monitor screen. In step 11, it is determined whether or not there is a next measurement radius position. If there is, the process returns to step 3 to move the magnetic head to a new measurement radius position and perform the same processing. If not, terminate the program. When the program ends, the inspection of the magnetic disk medium 1 ends. FIG. 6A shows a pre-servo signal waveform of one round when the dropout D1 exists. 6 (b) shows the signal waveform of FIG. 6 (a) based on the present inspection method, the pulse average amplitude value V (n) and the moving average value M of the synchronous burst portion of each servo wedge.
V (n) is calculated and plotted. The wedge number N = 200 and the moving average score M = 31. FIG. 6C is a plot of the moving average deviation rate KR (n). It can be confirmed that KR (n) sharply drops near the 60th wedge where the dropout exists. For example, if a threshold is set near Th1 in the figure,
This can be reliably detected. FIG. 7 (a) shows a pre-servo signal waveform of one round in which there is no dropout but the same level of modulation as in FIG. 6 (a) is applied. FIGS. 7B and 7C show the average pulse amplitude V of the synchronous burst portion of each servo wedge at this time.
(N), moving average value MV (n), and deviation rate KR (n)
Is plotted. In this case, the deviation rate KR (n)
Is almost flat over one round, so for example, T
If a threshold value is set near h1 (same as that of FIG. 6c), a dropout will not be erroneously detected. In this embodiment, the synchronous burst is selected as a pattern for measuring the average pulse amplitude value in the servo wedge, but other patterns (excluding gaps) are used.
It is also possible to select. As described above, according to the present invention, for each wedge of one turn of the pre-servo signal, the pulse average amplitude value of the synchronous burst section is measured, and the moving average deviation rate is obtained. Is compared with a predetermined value to detect the dropout. Therefore, even if the modulation is included in the signal waveform, it is hardly affected by the modulation, and the erroneous detection of the dropout can be prevented. As a result, a more reliable inspection result can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a test apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a sector servo system. FIG. 3 is a diagram illustrating a signal pattern of a servo wedge. FIG. 4 is a flowchart of a test program. FIG. 5 is a diagram illustrating an example of a waveform of a pre-servo signal. 6A is a diagram showing an example of a waveform (for one round) of a preservo signal, FIG. 6B is a diagram showing a pulse average amplitude value and a moving average of the same signal, and FIG. 6C is a moving average deviation of the same signal It is a figure showing a rate. 7A is a diagram showing another example of a waveform (for one round) of a preservo signal, FIG. 7B is a diagram showing a pulse average amplitude value and a moving average of the same signal, and FIG. It is a figure showing an average deviation rate. [Description of Signs] 1 Magnetic disk medium 2 Spindle motor 3 Head slider 4 Positioner 5 Read amplifier 6 Head arm 7 Gate signal generation circuit 8 A / D converter 9 Waveform memory 10 Computer section

Claims (1)

A pre-servo signal for generating a servo signal is generated by rotating a magnetic disk medium having a plurality of servo wedges recorded by a sector servo method and reproducing the pre-servo signal from the magnetic disk. A method for inspecting for the presence or absence of a dropout in which the amplitude of a signal locally decreases, wherein a preservo signal is reproduced from the magnetic disk medium, and from the reproduced signal, for all servo wedges in one round on the magnetic disk, A pulse average amplitude value of a predetermined pattern in each servo wedge is measured, and for each servo wedge, a moving average value of pulse average amplitude measurement values of a plurality of adjacent servo wedges is calculated. Calculating a moving average deviation rate from the pulse average amplitude measurement value and the moving average value, A method for inspecting a pre-servo signal, wherein a dropout is determined based on a comparison result between an average deviation rate and a predetermined value.