The present invention relates to a method of manufacturing a head unit of a magnetic head to be mounted in a magnetic recording/reproducing apparatus such as a VTR.
A conventional method of manufacturing a head unit will hereinafter be described with reference to the appended figures. FIG. 3 is a side view of an example of a conventional head unit. As shown in FIG. 3, two right and left head chips 2 and 3 (hereinafter referred to as xe2x80x9cchipsxe2x80x9d) are bonded to a base 1. The chips 2 and 3 are formed of pairs of metal plates (cores) 5 and 6, respectively. Each pair is formed of two metal plates joined to each other and a coil 4 is wound around each metal plate.
Gaps 7 and 8 are gaps formed in the joints between the metal plates 5 and the metal plates 6 of the respective chips. Curved surfaces 2a and 3a are formed as the front faces of the chips 2 and 3. Gaps on the curved surfaces 2a and 3a are head gaps 7a and 8a, respectively. In the figure, GD indicates a gap depth dimension of the gaps 7 and 8 in the side portions of the chips 2 and 3.
The base 1 eventually is attached to a rotating cylinder (not shown in the figure), and the curved surfaces 2a and 3a of the front faces of the chips 2 and 3 slide on a magnetic tape. Numeral 9 indicates a rotation center of the rotating cylinder.
FIG. 4A is a front view of an example of chip front faces before they are ground. Though the following description is directed to the chip 3, the same is true for the chip 2. Numeral 10 indicates contour lines of the curved surface 3a of the chip 3, more specifically, contour lines of the curved surface 3a when the head gap 8a is seen from an extension of a straight line 11 extending between the head gap 8a and the rotation center 9 of the rotating cylinder as shown in FIG. 3. Numeral 12 indicates a vertex of the curved surface 3a. The vertex 12 corresponds to a center of the contour lines 10. Bo indicates a distance between the vertex 12 and the head gap 8a. Y indicates a difference of heights between the chip 2 and the chip 3 from a chip-attached surface 1a of the base 1, namely, a relative height (hereinafter referred to as xe2x80x9ca head relative heightxe2x80x9d) of the two chips 2 and 3. In other words, the head relative height corresponds to a difference in level between the chips in a direction orthogonal to a chip-traveling direction.
FIG. 5 is a perspective view showing a chip grinding process. In the grinding process, a head unit 13 including the chips 2 and 3 is installed in a rotating drum 14. Accordingly, the chips 2 and 3 rotate coincidentally with the rotating drum 14 (rotating in a direction indicated by an arrow b). The front faces of the chips 2 and 3 are ground during rotation with a grinding tape 15 brought into contact therewith. Since the grinding is carried out with the grinding tape 15 traveling vertically, the front faces of the chips are ground always with an unused surface of the grinding tape 15.
In such a grinding process, as shown in FIG. 4A, the vertex 12 as a reference used to indicate Bo shifts in a direction indicated by an arrow a depending on the grinding amount. FIG. 4B shows a state where the grinding of the chip front faces is completed after the foregoing grinding process. A comparison of FIGS. 4A and 4B shows that the vertex 12 in FIG. 4B shifts in the arrow a direction. In the figures, S indicates a shift amount of the vertex 12 during the grinding.
The portion of the vertex 12 is to be brought into an excellent state of contact with a magnetic tape. Thus, it is preferable that the vertex 12 be as close to the head gaps 7a and 8a as possible. Ideally, the vertex 12 falls on the head gaps 7a and 8a, namely, Bo=0. Hence, Bo is a key factor affecting magnetic head performance, and thus, in the manufacturing process, it is necessary to selectively use a magnetic head in which Bo falls within the range of predetermined standard values that meet a required level of performance.
However, in the conventional manufacturing method as mentioned above, the shift amount S of the vertex 12 varies depending on the type of a head unit, and thus it is difficult to make the value of Bo fall in a target range. This has been a factor allowing the manufacturing yield to be decreased.
This invention is intended to solve the conventional problem as mentioned above. It is an object of the present invention to provide a method of manufacturing a head unit, wherein a predetermined distance is obtained between a vertex of a curved surface as a chip front face and a head gap after the chip front face is ground.
In order to achieve the above object, a method of manufacturing a head unit with a plurality of head chips mounted on one base according to the present invention is characterized as follows. That is, with respect to a head chip of the plurality of head chips fixed to the base, assume a distance between a vertex of a curved surface as a front face of the head chip and a head gap is indicated as Bo, a gap depth dimension in the head chip as GD, a value of Bo before grinding the front face of the head chip as Bo1, a value of Bo after grinding the front face as Bo2, a value of GD before grinding the front face of the head chip as GD1, a value of GD after grinding the front face as GD2, a grinding amount corresponding to a difference between GD1 and GD2 as xcex94GD, and a head relative height that is a difference in height from the base between two adjacent head chips of the plurality of head chips as Y,
in processing the head chips in which the head relative height Y is Yxe2x80x2 with the grinding amount xcex94GD of xcex94GDxe2x80x2, a value of Bo1 corresponding to a target value of Bo2 is determined through: a relationship between Bo and GD that has been determined with respect to a head unit in which the head relative height is substantially equal to Yxe2x80x2; the target value of Bo2; and the value of xcex94GDxe2x80x2, and the value of Bo1 thus determined is used as Bo1 of the head chips in which the head relative height Y is Yxe2x80x2.
According to the foregoing method of manufacturing a head unit, grinding of the front faces of the head chips is conducted after Bo1 corresponding to the target value of Bo2 is determined. Hence, a head unit with the value of Bo2 falling within the range of standard values can be manufactured efficiently, and accordingly the yield can be improved.
In the foregoing method of manufacturing a head unit, it is preferable that the relationship between Bo and GD be predetermined in a form of a characteristic straight line. The foregoing method of manufacturing a head unit allows the value of Bo1 corresponding to the target value of Bo2 to be determined easily through a relative formula of the characteristic straight line, the target value of Bo2 and xcex94GD.
Furthermore, it is preferable that the characteristic straight line is a straight line showing a correlation between coordinate axes determined using a distribution of coordinates (GD1, Bo1) and (GD2, Bo2).
Furthermore, preferably, the target value of Bo2 is zero. According to the foregoing method of manufacturing a head unit, the value of Bo1 is determined with the target value of Bo2 set to zero as an ideal value, so that the value of Bo2 easily distributes itself in the vicinity of zero, and thus the yield can be improved. This provides an advantageous manufacturing method.
Furthermore, preferably, the head chip before grinding the front face is so formed that a target value of the distance between the vertex of the curved surface as the front face of the head chip and the head gap before the head chip is fixed to the base is set to the value of Bo1 corresponding to the target value of Bo2. The foregoing method of manufacturing a head unit allows the value of Bo1 to be obtained with high accuracy by bonding the chips to the base with as little inclination as possible.
Furthermore, preferably, in fixing the head chip to the base, a fixing angle of the head chip is adjusted so that Bo1 in the head chip is the value of Bo1 corresponding to the target value of Bo2. According to the foregoing method of manufacturing a head unit, variations caused during processing of a head chip before being fixed to a base can be adjusted through a fixing angle adjustment, and accordingly the accuracy of the value of Bo1 can be improved.