A METHOD OF MEASURING A MINUTE FLYING HEIGHT OF AN OBJECT AND A MAGNETIC DISK APPARATUS

Abstract: In a magnetic disk apparatus according to the pre­ sent invention, a slider has a sliding surface (K) and a reflecting surface (M). The height of the reflecting surface (M) from the magnetic disk (1) is greater than that of the sliding surface (K) from the disk (1), when the slider (6) flys above the disk (1), so that there exists a minute difference in level between the sliding surface (K) and the reflecting surface (M). The flying height of the sliding surface (K) of the slider (6) from the magnetic disk is measured. When the magnetic disk (1) is rotated, the slider (6) flys from the disk (1). In this state, reference flying height, i.e., the flying height of the reflecting surface (M) from the magnetic disk (1) is measured by the optical interference pro­ cess. Then, the minute difference is subtracted from the measured reference flying height to obtain the flying height of the sliding surface (K) of the slider (6) from the magnetic disk (1). According to the inven­ tion, even if the minimum flying height of the sliding surface (K) of the slider (6) is shorter than 0.1 micro­ meter, the measurement can be effected by the optical interference process. In general, moreover, a minute flying height between a fixed datum plane and an object flying above the datum plane can be measured accurately.

Description: The present invention relates to a method of accurately measuring, for example, a very small flying height of a slider of a magnetic disk apparatus from a magnetic disk, and to a magnetic disk apparatus adapted to be used for the measurement of the minute flying height of the slider from the magnetic disk. Magnetic disk apparatuses are generally known as a typical example of external memory units of computers. In these apparatuses, a magnetic disk is coupled to a motor for rotation, and a slider is provided for movement above the disk. A magnetic head fixed to the slider moves together with the slider above the magnetic disk, whereby information is written in or read out of the disk. In the conventional magnetic disk apparatuses of this type, the magnetic head and slider must be kept from being in contact with the magnetic disk so that they fly at a substantially fixed, minute height from the disk. This is required because the disk will be damaged if touched by the magnetic head. If the head fails to be kept flying a minute height above the disk, moreover, errors may possibly occur while the information is being written in or read out of the disk. Described in Japanese Patent Disclosure JP-A-5864670 for example, is an apparatus in which a magnetic head and a slider are kept off a magnetic disk, flying at a substantially fixed, minute height from the disk. In this prior art apparatus, compressed air flows between the magnetic disk and the slider facing the same while the disk is rotating. An air bearing force caused by the compressed air flow acts as a dynamic lift on the slider, thereby flying the slider from the magnetic disk. At the same time, the slider is urged to be depressed toward the disk. When the force of depression balances with the dynamic lift, the head and slider fly and keep at the minute height from the disk. Recently a recording system has been developed which can record information with high recording density. In this system, for example, magnetic domains of a magnetic disk with a perpendicular magnetic recording medium are perpendicularly magnetized so that the information is recorded on the disk. For high-density information recording on the recording system of this type, a magnetic head must be kept at a flying height of 0.1 micrometer or less from the magnetic disk, and variation of the flying height must be restricted to a very small value. During manufacturing processes for the magnetic disk apparatuses, therefore, the flying height of the magnetic head or slider from the magnetic disk, which is very small, may sometimes suffer errors due to slight errors in assembly or slight difference in the shape of each manufactured slider. Thus, in manufacturing the magnetic disk apparatuses, the slider must be checked to see if its flying height is within a predetermined range. Since the flying height of the slider is as small as 0.1 micrometer or less, however, it cannot easily be measured by conventional methods. The optical interference process is among the methods of measuring a minute height. However, a distance shorter than 0.1 micrometer cannot be measured directly by this process. A known slider (JP-A-60-18870) has a glass plate for reflecting light to enable a measurement of the flying height. The glass plate is secured to the slider body by means of an adhesive. Thus when the plate is attached to the slider, a slippage may be caused therebetween, such that errors concerning the measurement of the flying height of the slider body can occur. An object of the present invention is to provide a method of accurately measuring a minute flying height between a fixed datum plane and an object flying above the datum plane. Another object of the invention is to provide a method of accurately measuring the flying height of a slider of a magnetic disk apparatus from a magnetic disk at the time of assembling the magnetic disk apparatus. Still another object of the invention is to facilitate inspection of products by a method of measurement for magnetic disk apparatuses, and manufacture magnetic disk apparatuses in which the flying height of a slider is predetermined. A further object of the invention is to provide a magnetic disk apparatus adapted for the measurement of a minute flying height of a slider from a magnetic disk. According to the present invention, there is provided a method comprising the features of claim 1. Further advantageous developments of the method according to the invention are directed to by the features of the subclaims 2 to 11. According to the invention there is further provided a magnetic disk apparatus comprising the features of claim 12. In general, moreover, a minute flying height between a fixed datum plane and an object flying above the datum plane can be measured accurately. This invention can be more fuly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram showing a magnetic disk apparatus; Fig. 2 is a perspective view showing an example of a slider of the magnetic disk apparatus shown in Fig. 1; Fig. 3 is a partial side view of the slider as taken in the direction of arrow X of Fig. 2; Fig. 4 is a block diagram showing a measuring apparatus according to an example of the present invention for effecting a method of measurement of the invention; Figs. 5 and 6 are plan views of the slider bearing thereon interference fringes produced during the measurement of the flying height of the slider on the measuring apparatus shown in Fig. 4; Figs. 7 and 8 are graphs showing the flying height of the slider measured on the measuring apparatus of Fig. 4; Fig. 9 is a graph showing a range of the flying height of a magnetic head measurable by the method of measurement of the invention; Fig. 10 is a perspective view of a slider of a magnetic disk apparatus according to a second embodiment of the invention; Fig. 11 is a plan view of the slider shown in Fig. 10 bearing thereon interference fringes produced during the measurement; Fig. 12 is a graph showing measurement results of the flying height of the slider obtained through analysis of the interference fringes shown in Fig. 11; Fig. 13 is a perspective view of a negative-pressure slider of a magnetic disk apparatus according to a third embodiment of the invention; Fig. 14 is a plan view of the slider shown in Fig. 13 bearing thereon interference fringes produced during the measurement; Fig. 15 is a perspective view of an example of a negative-pressure slider of the magnetic disk apparatus of the third embodiment, the slider having an inclined negative-pressure producing surface; and Fig. 16 is a side view of the negative-pressure slider shown in Fig. 15. In Fig. 1, showing a magnetic disk apparatus, numeral 1 designates a magnetic disk which comprises a substrate and a recording layer formed of a vertical magnetic recording medium on the substrate. Disk 1 is rigidly mounted on a turntable (not shown) fixed on shaft 2 which is coupled to motor 3. Thus, the disk can rotate together with shaft 2. Magnetic head 5, which is fixed to slider 6, is placed on magnetic disk 1. Slider 6 is supported by suspension mechanism 7 in a manner such that it can fly from disk 1 as the disk rotates. Mechanism 7 is coupled to carriage 9 by means of access arm 8. Carriage 9 is connected to linear actuator 10 so as to be movable in the radial direction of disk 1, as indicated by arrow 11. Motor 3 and actuator 10 are electrically connected to control unit 4 to which commands are applied from a keyboard (not shown). Thus, the motor and actuator are controlled by control signals delivered from unit 4. As shown in Figs. 2 and 3, three ridges 15, 16 and 17 are formed on that face of slider 6 opposed to magnetic disk 1, extending in the rotating direction of the disk as indicated by arrow A. Slanting surfaces 18, 19 and 20 are formed on the end edges of ridges 15, 16 and 17, respectively, on the upstream side thereof with respect to the rotating direction of disk 1. Sliding surfaces K of ridges 15 and 17 facing the magnetic disk are specularly polished. Reflecting surface M of ridge 16 facing the disk is provided on a slant so that fine difference s in the level is provided between surfaces K and M. Preferably, the maximum value of difference s ranges from 0.1 to 2 micrometers, since a distance shorter than 0.1 micrometer cannot be measured by the optical interference process. Magnetic head 5 includes yoke 21 attached to that end edge of reflecting surface M on the downstream side with respect to the rotating direction of magnetic disk 1, and coil 22 wound around the yoke. The tip end of yoke 21 is located substantially flush with the end edge of surface M so that transducing gap G is formed between yoke 21 and the edge. Thus, the respective end edges of sliding surfaces K and reflecting surface M on the downstream side and the tip end of yoke 21 of the magnetic head are all on the same plane. According to the apparatus described above, sliding surfaces K of slider 6 are in contact with magnetic disk 1 when the disk is at a standstill, and fly from the disk when the disk rotates. More specifically, when disk 1 rotates, a flow of compressed air is produced between the disk and sliding surfaces K of slider 6. An air bearing force caused by the compressed air flow acts as a dynamic lift on slider 6, thus flying the slider from disk 1. The higher the rotational frequency of disk 1, therefore, the greater the dynamic lift and the flying height of slider 6 will be. A spring or the like urges slider 6 to be depressed toward magnetic disk 1. As the force of depression matches the dynamic lift, sliding surfaces K of slider 6 flies at a substantially fixed, minute distance from disk 1. When slider 6 flies, surfaces K decline to the downstream side with respect to the rotating direction of disk 1, due to aerodynamics. If magnetic disk 1 is a perpendicular recording magnetic disk, in particular, the distance between the disk and magnetic head 5, i.e., the minimum flying height of sliding surfaces K of slider 6, is expected to be kept within 0.1 micrometer and subject to only very small variation. Magnetic disk apparatuses, as products, must be checked to see if the flying height is a predetermined value. This check is achieved by the optical interference process using measuring apparatus 31, which will be described below. As shown in Fig. 4, measuring apparatus 31 comprises measuring magnetic disk 32 made of transparent material, motor 33 for rotating disk 32, and optical interferometer 34. The interferometer includes light source unit 35 for applying a unicolor or white light beam to slider 6, beam splitter 36 interposed between unit 35 and disk 32, microscope 37 for observing interference fringes on sliding surfaces K and reflecting surface M of slider 6, and camera 38 for photographing the interference fringes. Using measuring apparatus 31, the flying height of slider 6 is measured as follows. As shown in Fig. 4, slider 6 supported by suspension mechanism 7 is arranged in measuring apparatus 31 in the same manner as when it is set in an actual magnetic disk apparatus. Measuring magnetic disk 32 is rotated at a speed not lower than a predetermined level. If the minimum flying height of slider 6, i.e., the lift of surface K above disk 1, is 0.1 micrometer or more, the flying height of sliding surfaces K can be measured directly by the optical interference process. When a light beam from light source unit 35 is directed to slider 6, interference fringes A and B are produced on sliding surfaces K and reflecting surface M, respectively, as shown in Fig. 5. Fringes A and B are observed through microscope 37 and photographed by camera 38. The flying height of sliding surfaces K is determined by fringes A on the basis of the optical interference process. The reference flying height of reflecting surface M, i.e., the lift of surface M above magnetic disk 1, is determined by fringes B. As shown in Fig. 7, moreover, minute difference s between the reference flying height of reflecting surface M and the flying height of sliding surfaces K is measured. In Fig. 7, symbol H indicates the position of the tip end of yoke 21 of magnetic head 5. If measuring magnetic disk 32 is rotated at a speed lower than the predetermined level, the flying height of slider 6 is extremely short. If the minimum flying height of slider 6 is shorter than 0.1 micrometer, no interference fringes appear on sliding surfaces K. According to the present invention, however, reflecting surface M has minute difference s in level from sliding surfaces K. Therefore, the reference flying height of reflecting surface M is equal to the sum of the flying height of sliding surfaces K and minute difference s, so that interference fringes B appears on surface M, as shown in Fig. 6. The reference flying height is determined by fringes B. Meanwhile, minute difference s is measured in the aforementioned manner. Thus, the flying height of sliding surfaces K is obtained by subtracting difference s from the reference flying height, as shown in Fig. 8. In Fig. 8, symbols C and D indicate the flying height of sliding surfaces K and the reference flying height of reflecting surface M, respectively. The minimum flying height of surfaces K is equivalent to the flying height of magnetic head 5, i.e., the height between the tip end of yoke 21 and magnetic disk 1. Symbol h₀ indicates the flying height of head 5. Thus, the flying height of slider 6 can be measured even if the minimum flying height of sliding surfaces K is smaller than 0.1 micrometer. Fig. 9 shows measurement results of the flying height of magnetic head 5. In Fig. 9, black spots indicate a measurable range according to the prior art method of measurement, while circles indicate that according to the method of the present invention. Thus, according to the invention, the flying height of the magnetic head can be measured to an extremely small value. Fig. 10 shows a second embodiment of the present invention. In this embodiment, three ridges 15, 16 and 17 have respective sliding surfaces K1, K2 and K3 flush with each other. Furthermore, the side ridges 15, and 17 have elongated stepped sections on which reflecting surfaces 23, 24 for measuring flying height are formed, respectively, so as to extend along their corresponding ridges. Surfaces 23 and 24 have minute difference s in level from sliding surfaces K1, K2, and K3. When measuring magnetic disk 32 is rotated to fly slider 60, therefore, interference fringes E appear on reflecting surfaces 23 and 24, as shown in Fig. 11. Like that in the first embodiment, the reference flying height of reflecting surfaces 23 and 24 is determined by fringes E, as shown in Fig. 12. Since minute difference s is a measured value, the flying height of sliding surfaces K1, K2 and K3 of slider 60 is obtained by subtracting difference s from the reference flying height of surfaces 23 and 24. Furthermore, in the embodiment described above, a rolling can be measured. Figs. 13 to 16 show a third embodiment of the present invention. According to this embodiment, the invention is applied to a magnetic disk apparatus which includes negative-pressure slider 70. Recess is formed in slider 70 on one side so that the slider 70 has a flat sliding surface 71 and a negative-pressure producing surface 72 which are opposed to the magnetic disk. When disk 1 is rotated, a dynamic lift acts on the sliding surface. On the other hand, surface 72 is subjected to a negative pressure, which acts as a force to depress slider 6. The dynamic lift and negative pressure are balanced with each other, and negative-pressure slider 70 is flied a substantially fixed, minute distance from magnetic disk 1. If the flying height of negative-pressure slider 70 is measured by the optical interference process, interference fringes J appear on specular negative-pressure producing surface 72, as shown in Fig. 14. As in the first and second embodiments, the reference flying height of surface 72 is determined by fringes J. The flying height of sliding surface 71 is obtained by subtracting the depth of depression of surface 72 from the reference flying height of surface 72. Even if negative-pressure producing surface 73 is a slanting surface, as shown in Figs. 15 and 16, the flying height of sliding surface 71 can be measured by the optical interference process, since surface 73 has a predetermined difference in level from surface 71. According to the method of measurement of the present invention, the flying height of slider 6 from magnetic disk 1 can be accurately measured by the optical interference process even though its minimum is less than 0.1 micrometer. This can be seen also from the measurement results of Fig. 9. Thus, it is easy to manufacture magnetic disk apparatuses in which the minimum flying height of the slider is a predetermined value less than 0.1 micrometer. In general, according to the present invention, a minute flying height between a fixed datum plane and an object flying above the datum plane can be measured accurately. If the light source used in the measurement by the optical interference process is a white-light source, the maximum of minute difference s is 2 micrometers. When using a unicolor-light source, difference s greater than 2 micrometers can also be measured. Moreover, the magnetic head may be a thin-film head.

Claims: A method of measuring a flying height of a slider (6, 60, 70), the slider (6, 60, 70) having a sliding surface (K, K1, K2, K3, 71) and a reflecting surface (M, 72, 73) both opposed to a magnetic disk (1), and the flying height being defined as a height between the sliding surface (K, K1, K2, K3, 71) and the disk (1) and being shorter than a reference height between the reflecting surface (M, 72, 73) and the disk (1) when the slider (6, 60, 70) flies above the disk (1), a predetermined minute difference (s) existing between the flying height and the reference height, said method comprising the steps of: measuring the reference height by an optical interference process; and subtracting the predetermined minute difference from the measured reference height to obtain the flying height, characterized in that, the reflecting surface (M, 72, 73) is a part of the surface of the slider (6, 60, 70) opposed to the magentic disk (1). The method according to claim 1, further comprising a step of measuring the flying height of a magnetic head (5) away from the magnetic disk (1) on the basis of the flying height of the sliding surface (K, K1, K2, K3, 71) of the slider (6, 60, 70), the magnetic head (5) being attached to said slider (6, 60, 70) and having the tip end of its yoke (21) in the plane of the sliding surface (K, K1, K2, K3, 71). The method according to claim 1 or 2, cha racterized in that the maximum of said minute difference (s) ranges from 0.1 to 2 micrometers. The method according to one of claims 1 to 3, characterized in that said reflecting surface (M, 72, 73) is provided on a slant. The method according to one of claims 1 to 4, characterized in that said reflecting surface (M, 72, 73) is adjacent to the sliding surface (K, K1, K2, K3, 71). The method according to one of the claims 1 to 5, characterized in that, said reflecting surface (M, 72, 73) is located in the central portion of the slider (6, 60, 70). The method according to one of the claims 1 to 6, characterized in that a ridge (15, 17) is formed on that face of said slider opposed to the magnetic disk (1), said ridge (15, 17) extending in the rotating direction of the magnetic disk (1), and said reflecting surface (M, 72, 73) is formed beside the ridge (15, 17) so as to extend along the ridge (15, 17). The method according to one of the claims 1 to 7, characterized in that said magnetic head (5) is a thin-film head. The method according to one of the claims 1 to 8, characterized in that said magnetic disk (1) includes a perpendicular magnetic recording medium as a recording layer. The method according to claim 1, charac terized in that said slider is a negative-pressure slider, and a recess is formed on one side so that the slider (70) has a sliding surface (71) and a specular negative-pressure producing surface (72) which are opposed to said disk (1), and in that the negative-pressure producing surface (72) is polished to act as the reflecting surface used to measure a flying height of the sliding surface (71). The method according to claim 10, charac terized in that said negative-pressure producing surface (72, 73) is a surface parallel to or slanted at an angle to the sliding surface (71) of the negative-pressure slider (70). A magnetic disk apparatus which comprises a magnetic disk (1) rotated by a motor (3) and a magnetic head (5) for writing in and reading information from the magnetic disk (1), a slider (6, 60, 70) fixing the magnetic head (5) and movable together therewith above the magnetic disk (1), said slider (6, 60, 70) having a sliding surface (K, K1, K2, K3, 71) adapted to fly above the magnetic disk (1) as the magnetic disk (1) rotates, and a reflecting surface (M, 72, 73), the height of the reflecting surface (M, 72, 73) from the disk (1), being greater than that of the sliding surface (K, K1, K2, K3, 71) from the disk (1), when the slider (6, 60, 70) flies above the disk (1) so that there exists a predetermined minute difference (s) in level between the sliding surface (K, K1, K2, K3, 71) and the reflecting surface (M, 72, 73) characterized in that the reflecting surface (M, 72, 73) is a part of the surface of the slider (6, 60, 70) opposed to the magnetic disk (1).

Inventors: KUBO, MASAHIRO PATENT DIVISION, OHTSUBO, YASUO PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: G11B5
IPC codes: G11B5, G11B33, G11B21