JPH0439124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic head used for magnetic recording or reproduction of signals on a magnetic tape.

(Prior Art) The magnetic head used in a VTR records or reproduces signals by slidingly contacting the magnetic tape, but in order to perform these signal processings with high reliability, it is necessary to have the magnetic head slidingly contact the tape. It is necessary to bring the gap formed on the surface (contact surface) into sliding contact with the magnetic tape with stable surface pressure.

For this reason, conventional practice has been to form the contact surface 1 of the magnetic head into a smooth convex curved surface as shown in FIG. 3, and to provide the gap portion 2 at the center of the contact surface 1, that is, at the highest position. ing.

On the other hand, there are at least two types of cassette-type magnetic tapes currently in use: thin tapes and thick tapes, depending on the length of the recording time, and signals can be recorded and played back using the same VTR on either magnetic tape. It is. For example, in the Beta format standard, a thick tape called L500 (approximately 20μ thick) is used.
m) and a thin tape called L830 (approximately 12μ thick)
m) is standardized.

In order to stabilize the sliding contact between the magnetic head and the magnetic tape and obtain the desired signal reproduction output, it is necessary to form the contacting surface of the magnetic head into a predetermined shape as described below. That is, a cross section at the gap portion 2 perpendicular to the contact surface 1 and along the track width direction, as shown by the - line in FIG. The radius of curvature (hereinafter referred to as "aging") is such that the distribution of the wear rate (amount of wear per unit time) of the contact surface 1 due to the sliding contact of the magnetic tape (indicated by the group of arrows in Figure 2) is uniform. (The shape of the contact surface at this time is referred to as the "final worn shape").

The sliding contact pressure between the magnetic head and the magnetic tape, which has a contact surface with a final wear shape, has a uniform distribution along the cross section, so that the gap part and the magnetic tape maintain a constant pressure regardless of the running time. Sliding contact with
Faithful signal reproduction is achieved.

However, the aging radius of curvature differs between thin and thick tapes, and the radius of curvature r of the magnetic head is equal to the aging radius of curvature r ₁ for the thin tape.
When it is set to (for example, 0.9 mm), it is disadvantageous for the reproduction of thick tapes, and when it is set to the aging curvature radius r ₂ for thick tapes (for example, 1.4 mm), it is disadvantageous for the reproduction of thin tapes. Therefore, conventionally, the radius of curvature r in the cross section of the magnetic head in the track width direction was an abbreviation of r ₁ and r ₂ so that a signal reproduction output above a certain value could be obtained for any thickness of magnetic tape. It was set to an intermediate value.

(Problems to be Solved by the Invention) Since the contact surface 1 of the magnetic head gradually wears out due to long-term signal reproduction or recording, the radius of curvature r in the cross section in the track width direction as described above is r ₁ and
For a magnetic head set between _r2 , when thin tapes are frequently used, the radius of curvature r approaches _r1 , and when thick tapes are frequently used, the radius of curvature r approaches _r2 . It turns out.

Figure 4 shows qualitatively the changes in the radius of curvature, with the horizontal axis representing the tape running time immediately after the magnetic head was manufactured and the vertical axis representing the radius of curvature r of the magnetic head. The radius of curvature when
When r ₀ ′ (r ₁ < r ₀ ′ < r ₂ ), curve 40 shows the change in the curve radius when thick tape is used frequently, and curve 42 shows the change in the curve radius when thin tape is used frequently. .

Normally, thick tape is used more frequently, and the radius of curvature r in the track width direction of the contact surface of the magnetic head is
It is often close to r ₂ .

As the radius of curvature r approaches _r2 , it moves away from _r1 , so the recording and playback performance for thin tapes gradually deteriorates, and before r becomes equal to _r2 , sufficient playback output cannot be obtained, which is the permissible limit r. ₃ (point A in Figure 4), and faithful signal reproduction is no longer possible.

Therefore, the period T ₁ during which the radius of curvature r reaches the allowable limit r ₃ from the value r ₀ ' at the start of use of the magnetic head becomes the life of the magnetic head.

In order to extend the life of the entire VTR device, it is necessary to extend the life of the magnetic head, but as mentioned above, in VTRs that use magnetic tapes of different thicknesses,
There was a limit due to the change in curvature due to wear of the magnetic head.

(Means for Solving the Problems) The magnetic head according to the present invention has a radius of curvature r in a cross section in the track width direction that is smaller than or substantially equal to the aging radius r ₁ of the thin tape, and a thick magnetic head. The radius of curvature ra is set to a value r ₀ that is larger than the radius of curvature ra that provides the minimum permissible playback output for the tape.

Note that the radius of curvature r ₀ at the beginning of use of the head is smaller than r ₀ ' of a conventional magnetic head, so the signal recording and reproducing performance on thin tapes at the beginning of VTR use will be inferior to that of the conventional magnetic head. Thus, the applicant has completed the present invention by clarifying that the deterioration in performance at this time is negligible compared to the advantage of extending the life, which is a unique effect of the present invention.

(Function) First, the case where thick tape is used frequently will be explained. In this case, the radius of curvature r of the magnetic head according to the present invention is set to a value smaller than r ₁ or a value r ₀ approximately equal to r ₁ (see FIG. 4) at the beginning of use of the head. As shown by curve 4 in FIG. 4, the period T ₂ until the permissible limit r ₃ (point B in FIG. 4) is reached is longer than T ₁ in the case of the conventional magnetic head.

FIG. 5 shows the qualitative relationship between the radius of curvature r of the contacting surface in the cross section of the magnetic head in the track width direction and the recording output V, as revealed by the applicant through experiments and the like. The recording/reproduction output V indicates the maximum output value (mV _pp ) when a magnetic tape on which an input signal of a certain level is recorded is reproduced, and the minimum allowable output value is expressed as V ₀ . Curve 5 represents the change in the case of a thin tape, and curve 50 represents the change in the case of a thick tape. Both curves 5 and 50 have a peak point f,
Centering on the curvature radii r ₁ and r ₂ of d, the output characteristic with the smaller radius of curvature (left side) has a relatively gentle slope, but the output characteristic with the larger radius of curvature (right side) has a relatively sloped slope. It's getting urgent. This left-right asymmetry of the characteristic curve is universal regardless of the thickness of the magnetic tape, and the effects of the present invention are obtained based on this left-right asymmetric output characteristic, as in the later techniques.

In the magnetic head according to the present invention, since the radius of curvature r ₀ at the start of use is smaller than r ₀ ' in the conventional magnetic head, the recording/reproducing output at the start of use of the magnetic head (running time zero) V decreases (point c → point b in FIG. 5).

However, the recording/reproducing output V (point b) at this time is larger than the allowable limit output V ₀ (point a), and there is no problem in actual recording/reproducing.

However, in the case of a thick tape, the output (point b) at the start of use of the magnetic head exists in a region with a gentle slope to the left of the peak point d of the curve 50. The difference from the output (point c) is small, and the difference will decrease as the usage time progresses.

If the magnetic head is replaced with a thinner tape at this time, a sufficiently high output level can be obtained for the output at the start of use of the magnetic head (point e) and the output for a certain period thereafter (points e to g). On the other hand, in conventional magnetic heads, the output at the start of use (point g)
However, there has been a rapid decline since then.

Therefore, according to the magnetic head of the present invention, if the use of thin tape is taken into account, recording and reproducing performance can be obtained that is equal to or better than that of conventional magnetic heads. Conventionally, this radius of curvature r
The relationship between this and the recording/reproducing output V was not made clear, and the merits of setting the initial radius of curvature r ₀ smaller than r ₁ were not recognized at all. However, as is clear from Figures 4 and 5, the change in magnetic head performance as the radius of curvature r goes from r ₀ ' to r ₃ , and the process that the radius of curvature r goes from r ₀ to r ₃ . When comparing the changes in magnetic head performance that follow in the previous example, the latter is superior both in terms of life span and average performance up to the life span.

Next, a case where thin tape is used frequently will be explained. In this case, the radius of curvature r of the magnetic head converges from r ₀ to r ₁ as shown by curve 41 in FIG. 4, but as is clear from FIG. However, the output at the start of use (points e and b) is greater than the allowable limit output V ₀ , and the output continues to increase until reaching the convergence point r ₁ of the radius of curvature. Therefore, the problem of shortened life due to changes in the radius of curvature does not occur.

Regarding magnetic head performance, in the case of thin tape, the output (point e) at the beginning of use is:
Since it exists in a region with a gentle slope to the left of the peak point f of the curve 5, a level equal to or higher than the output (point g) at the start of use of a conventional magnetic head can be obtained.

In this case, even if the magnetic head is replaced with a thicker tape, the output (point b) at the beginning of use of the magnetic head will exceed the allowable limit output, and the output will continue to increase as the usage time passes. . In contrast, the output of the conventional magnetic head decreases from the output at the start of use (point c). Therefore, when the recording and reproducing performance of the magnetic head according to the present invention is compared with that of the conventional magnetic head, there is almost no difference in the average output performance up to the convergence point, and the difference can be ignored.

(Effects of the Invention) In the magnetic head according to the present invention, when a thick magnetic tape is frequently used, a longer life and higher recording and reproducing performance can always be obtained than in the conventional magnetic head. Furthermore, even when a thin magnetic tape is used frequently, its life and performance are not inferior to conventional magnetic heads.

Therefore, according to the magnetic head according to the present invention, when two types of magnetic tapes with different thicknesses are used together, the overall effect is that a longer life and better recording and reproducing performance can be obtained than before. Become.

(Example) The applicant confirmed the performance of the magnetic head according to the present invention using magnetic heads having various radii of curvature (r=2.4, 1.4, 0.9, 0.7 mm). FIG. 1 shows the shape of the contact surface 1 of the magnetic head used in the test.

Optical interference fringes were used to measure the radius of curvature r of the contact surface 1. As shown in FIG. 1, the interference fringes 3 are obtained in an elliptical shape with the gap portion 2 as the center, and by reading the order of the fringes on the l-l line in the track width direction, the interference fringes 3 can be obtained in a cross section in the track width direction. The radius of curvature r of the contact surface 1 is calculated.

Note that the aging radius of curvature r ₂ when using the thick tape L500 is 1.4 mm, and the aging radius of curvature r ₁ when using the thin tape L830 is 0.9 mm.

An oscilloscope was used to measure the recording/reproducing output V, and the output waveform for one track was compared with the output level.

For thick tape, use r=1.4mm magnetic head,
In the case of thin tape, the magnetic head with r=0.9 mm showed the maximum recording and reproducing output, and in these cases, a uniform output waveform was obtained over one track length.

Also, no matter which magnetic tape is used,
There is no big difference in the output level and output waveform between the head with r = _0.9 and the head with r = _0.7. ), it was confirmed that the recording/reproducing performance of the magnetic head was only slightly degraded (see FIG. 5).

Therefore, in the magnetic head of this embodiment, by setting the radius of curvature r 0 of the contact surface to 0.7 mm before use, the radius of curvature _{r 0} of the contact surface before use is set to 0.7 mm, which makes it possible to In comparison, it is possible to extend the lifespan with almost no drop in recording and reproducing performance. Note that the radius of curvature r ₀ of the contact surface does not necessarily need to be set for the entire surface of the contact surface, and a curved surface with a radius of curvature r ₀ of r 0 is formed only in the vicinity of the gap forming part, and the other parts are set with a different curvature. It can also be a curved surface.

It goes without saying that the configuration of each part of the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the technical scope of the claims.

[Brief explanation of drawings]

Fig. 1 is a plan view of optical interference fringes appearing on the opposing surface of the magnetic head, Fig. 2 is a sectional view of the magnetic head in the track width direction, Fig. 3 is an oblique view of the magnetic head, and Fig. 4 is a plan view of the magnetic head. FIG. 5 is a graph showing the change in the radius of curvature with respect to the tape running time. FIG. 5 is a graph showing the change in the recording/reproducing output with respect to the radius of curvature of the magnetic head. 1...Contact surface, 2...Gap portion, 3...Interference fringes.

Claims (1)

[Claims] 1 It is used for signal recording or signal reproduction on two types of magnetic tapes with different thicknesses, and the shape of the contact surface in a cross section along the track width direction and perpendicular to the contact surface that is to be in sliding contact with the magnetic tape is In a magnetic head having a convex curved surface, the radius of curvature of the contact surface in the cross section at least near the magnetic gap forming portion is such that the magnetic head slides against a thin magnetic tape for signal recording or signal reproduction. In this case, the radius of curvature r ₁ of the final friction shape that makes the distribution of friction velocity along the cross section of the magnetic head substantially uniform is smaller than or substantially equal to it, and the minimum permissible playback output for thick magnetic tape is A value r ₀ larger than the radius of curvature ra that will be obtained
A magnetic head characterized by being formed in.