JPH04229408A - System for checking reading out signal waveform of magnetic head - Google Patents

Abstract

PURPOSE:To allow the exact inspection of a thin-film head which produces distorted reading out signals by selecting a pair of waveforms of a positive pole and negative pole from the reading out signals of a magnetic head to be inspected, forming images and determining a distortion quantity by making waveform analysis. CONSTITUTION:Test codes are written/read into and out of one round of the tracks of a magnetic disk by the magnetic head 1 to be inspected and the reading out signals are subjected to level regulation by a reading out AMP 34 and are inputted to an imaging module 51 of an imaging circuit 5 added through a switch 4. A pair of the waveforms of the positive pole and negative pole are selected out of the reading out signals and are imaged by the selection signal from a microprocessor 31 in the module 51. The imaging data are stored in an image memory 52, are read out at proper times and are subjected to the waveform analysis. The distortion quantity is determined The obtained distortion quantity is compared with a reference value. The quantity exceeding this value is decided to be defective. The distortion quantity and the defective list are outputted to an output section 312.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for checking a read signal waveform of a magnetic head in a magnetic head testing apparatus.

0002

2. Description of the Related Art After magnetic heads used in magnetic disk drives are manufactured, their write/read performance is tested.

An overview of a magnetic head testing device and testing method will be explained with reference to FIGS. 2(a) and 2(b). In Figure (a), 1 indicates a magnetic head to be inspected, 2 indicates a magnetic disk for inspection, and 3 indicates an inspection device.Under the control of a microprocessor (MPU) 31 provided in the inspection device 3, a write circuit (WC) is 32 outputs a test code of a predetermined frequency,
The level is adjusted by the write AMP 33, and the magnetic head 1 writes on a suitable track TR of the magnetic disk 1, and then reads it out. Read signal is read AM
It is input to the average value circuit (AVE) 34 through P34, and as shown in the figure (
b) As shown in Figure 3, the average value AVEU or AVEd of the peak values of each waveform in one track TT is calculated, and this average value is compared with a predetermined reference value in the test circuit (DET) 36 to determine whether the reference value has been reached. A magnetic head that does not perform is determined to be a defective product, and the defective product data is sent to the MPU and stored in the memory 311, and this is sent to the output section 31 in a timely manner.
2, and defective products are disposed of.

[0004] The above-mentioned test is performed by averaging the waveform of the readout signal for one track round, but it is unclear whether each individual waveform is normal or not. However, thin-film heads that have recently been widely used are small and have a fine structure, so they retain the influence of external magnetic fields received during the manufacturing process, which may distort the waveform of the read signal. When such a thin film head is used in an actual device, the written data cannot be read correctly and an error occurs.

FIGS. 3(a) and 3(b) show an example of distortion of a read signal waveform caused by a thin film head. Figure (a) shows the so-called undershoot h1, h2, in which the fall of the waveform exceeds the 0 value.If h1 or h2 is larger than the peak value H of the waveform, this may be an error. It is detected and becomes an error pulse pe. However, p is the correct pulse. In Figure (b), the vicinity of the peak of the waveform is crushed to create a concave part, resulting in two peaks.When the depth of the concave exceeds a certain limit, two peaks are created corresponding to the two peaks. The pulses pa, pb of are detected. If one pa is correct, the other pb becomes an error pulse. Additionally, if the depth w is excessive, or if the positions of pa and pb deviate significantly from their normal positions, both may not be detected depending on the threshold value or window width of the detection circuit, resulting in a so-called missing error. Sometimes. The distortion of the positional shift of the peak point of the waveform as shown in Figure (b) is a type of wiggle.
It is. However, some Uyghurs have a single peak waveform that shifts back and forth.

[0006]

Since the above-mentioned undershoot and wiggle of the read signal waveform cause errors, it is necessary to check this and eliminate defective products. However, the magnetic head inspection apparatus described above does not have this function, and it is difficult to precisely examine waveform distortion using analog circuits. Therefore, it is considered effective to use image processing methods that have recently advanced. SUMMARY OF THE INVENTION An object of the present invention is to provide a checking method for determining defective products by determining the amount of distortion in a read signal of a magnetic head using an image processing method.

[0007]

[Means for Solving the Problems] The present invention is a method for checking a read signal waveform in a magnetic head testing device in which a test code is written/read on one track of a magnetic disk by a magnetic head to be tested. Then, from the readout signal waveform of the magnetic head, at least one pair of positive and negative polarity waveforms is selected under the control of the microprocessor, and this waveform is imaged by an imaging circuit to create imaged data and stored in a memory. . The stored imaging data is waveform-analyzed by a microprocessor, and the amount of distortion such as undershoot or wiggle in the waveform of the readout signal is determined and compared with a reference value. A magnetic head having an amount of distortion exceeding a reference value is determined to be a defective product.

[0008]

[Operation] With the above configuration, in the checking method of the present invention, at least one pair of positive and negative waveforms selected from the readout signal of the magnetic head to be inspected is imaged by the imaging circuit, and the imaged data is The waveform is analyzed by a microprocessor, and the amount of distortion, such as the undershoot of the waveform and the depth of the concave part of the wiggle waveform, is determined and compared with a standard value, and a magnetic head with an amount of distortion that exceeds the standard value is determined to be a defective product. It is something to be judged.

In the above, the reason why a pair of positive and negative waveforms is selected is that the positive and negative waveforms are not necessarily symmetrical and are generally distorted separately.

[0010] Also, in order to accurately check waveform distortion, it is considered desirable to check a large number of waveforms, but since distortion due to the characteristics of the magnetic head appears in all waveforms, Selecting and checking a pair of negative waveforms will provide an accurate check in most cases. However, some waveform distortions are due to causes on the magnetic disk side, and if the selected waveform happens to be distorted due to this, it cannot be distinguished from the cause of the magnetic head, but the amount of distortion is very large. If there is an abnormality, such as when the value is large, another pair is selected and checked.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block configuration of an embodiment of the checking system of the present invention, which is obtained by adding a switch 4 and an imaging circuit 5 to the conventional magnetic head inspection apparatus shown in FIG. 2(a). Identical elements are given the same reference numerals.

The test code from the write circuit 32 shown in FIG. The level of the signal is adjusted by , and the signal is input to the imaging module 51 of the added imaging circuit 5 via the switch 4 . In the imaging module, the selection signal from the microprocessor (MPU) 31 selects one of the positive and negative polarities from among the readout signals.
Paired waveforms are selected and imaged. The imaged data is stored in the image memory 52, read out by the MPU at appropriate times, and subjected to waveform analysis through software processing to determine the size of the waveform undershoot h (see FIG. 3(a)) and the depth of the concave portion of the wiggle waveform w( The amount of deformation such as (see Fig. 3(b)) is calculated. The obtained amount of distortion is compared with a reference value, and those exceeding this value are determined to be defective, and the amount of distortion data and a list of defective products are output to the output section 312. However, in an abnormal case such as when the amount of distortion is very large compared to the reference value, it is necessary to select another pair of waveforms and perform the same check as above.

The above-mentioned imaging module 51 and image memory 52 are commercially available, and their structure and operation are well known, and the MPU processing program for analyzing the distorted waveform is also generally known, so a detailed explanation of these will be omitted. .

[0014]

As described above, in the present invention, at least one pair of positive and negative waveforms is selected from the read signals of the magnetic head to be inspected and imaged by the imaging circuit. Image data is waveform analyzed by a microprocessor to accurately determine the amount of distortion such as waveform undershoot and the depth of the recess in the wiggle waveform, and is checked by comparing it with a reference value. The effect of accurately inspecting a thin film head that has been distorted is significant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional magnetic head testing device and an explanatory diagram of a testing method.

FIG. 3 is an explanatory diagram of distortion occurring in a read signal waveform of a thin film head.

[Explanation of symbols]

1 Magnetic head (thin film head) 2 Magnetic disk 3 Conventional magnetic head inspection device 31 Microprocessor (MPU) 311 Memory (MEM) 312 Output unit 32 Write circuit (WC) 33 Write AMP 34 Read AMP 35 Average value circuit (AVE) 36 Inspection circuit (DET) 4 Switch 5 Imaging circuit 51 Imaging module 52 Image memory

Claims (1)

[Claims] Claim 1: In a magnetic head testing device that writes/reads a test code to/from one track of a magnetic disk using a magnetic head to be tested, a positive polarity and a positive polarity are determined by a read signal of the magnetic head under the control of a microprocessor. At least one pair of negative polarity waveforms is selected, the selected waveform is imaged by an imaging circuit to create image data, and the image data is analyzed by the microprocessor to determine the waveform of the readout signal. Reading of a magnetic head, characterized in that the amount of distortion of undershoot or wiggle is determined, the amount of distortion is compared with a reference value, and a magnetic head having an amount of distortion exceeding the reference value is determined to be a defective product. Signal waveform checking method.