JPH053650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an improvement in a rotary head assembly for a magnetic recording/reproducing device.

[Conventional technology]

FIG. 6 shows the configuration of a rotary head assembly using a hydrodynamic bearing in a conventional VTR.

In this figure, numeral 1 denotes a head for recording and reproducing information on a video tape, and is attached to a rotating cylinder 2. The rotating cylinder 2 is fixed to the radial flange 7 with screws 2A. Reference numeral 3 denotes a fixed cylinder, and a lead 3A for guiding the running of the tape is formed on the outer circumferential surface of the cylinder. Reference numeral 4 denotes a fixed shaft, which is fixed to the fixed cylinder 3 by a method such as press fitting or shrink fitting. The outer periphery of the upper and lower parts of this fixed shaft 4 has a spiral
Grooves 5 and 6 are formed, and a radial flange 7
A radial fluid bearing is constructed between the bearing medium (for example, oil) 8. Further, although not shown, a spiral groove is formed on the end face of the fixed shaft 4, and forms a thrust fluid bearing between it and the thrust flange 9 via a bearing medium (for example, grease) 10. .

This thrust flange 9 is a radial flange 7
It is fixed by screw 7A. The radial flange 7 has a rotary transformer 1 on the rotating side of a cylindrical rotary transformer that transmits, receives, and amplifies signals.
1 is fixed by a method such as adhesion. Also,
A fixed side rotary transformer 12 forming a pair therewith is fixed to the fixed cylinder 3 by a method such as adhesive.

Reference numeral 13 denotes a stator of a motor for driving the rotating cylinder 2, which is fixed to the fixed cylinder 3 by adhesive or screwing.

Reference numeral 14 denotes a rotor magnet of the drive motor, which is bonded to a rotor case 15, and the rotor case 15 is fixed to the radial flange 7 by bonding or screwing.

Reference numeral 16 is a retaining ring for preventing the rotary cylinder 2 from slipping off when the VTR is being transported. Although not shown, a grounding brush is usually in contact with the thrust flange 9 to prevent noise from entering the recording/reproducing head 1.

[Problem that the invention seeks to solve]

A rotating head assembly using a conventional spiral groove bearing is constructed as described above, so when an external force is applied to the rotating body due to a change in tape tension or external vibration, the rotating body will whirl around. The radial load capacity moment was 0 because no special consideration was given to the positions of the two radial bearings 5 and 6 provided on the fixed shaft 4, the center of gravity of the rotating part, and the mounting height of the head. There was a problem in that the deflection of the head was increased by the difference between the position, the center of gravity of the rotating part, and the mounting height of the head.

The present invention has been made to solve these problems, and an object of the present invention is to provide a rotating head assembly with improved rotational accuracy.

[Means for solving problems]

The rotary head assembly of the magnetic recording and reproducing apparatus according to the present invention is arranged such that the position where the radial load capacity moment of the two radial bearings is 0, the center of gravity of the rotating part, and the height position of the rotary head are approximately aligned. This is what I did.

[Effect]

The rotary head assembly in this invention comprises two
Since the position where the radial load capacity moment of each radial bearing is 0, the center of gravity of the rotating part, and the head height position are almost the same, the overturning moment of the rotating body due to disturbance can be suppressed to a minimum. , the influence of the whirling of the head can be minimized.

[Embodiments of the invention]

An embodiment of the present invention shown in FIG. 1 will be described below.

In this figure, reference numeral 17 denotes a rotary center of gravity position adjustment weight attached to the rotor case 15, and by adjusting its weight, the center of gravity position of the rotating body is adjusted to almost match the height position of the head. .
In addition, this rotational center of gravity position adjustment weight can be calculated so that the mass moment becomes 0 at the head height position, or can be calculated through preliminary experiments.
It is also possible to form it integrally with other rotating members, for example the rotor case 15. That is, the rotor case 15 can be integrated by increasing the thickness of a portion of the rotor case 15 in accordance with the calculated weight.

The rest of the configuration is the same as the conventional one, so the explanation will be omitted.

Further, FIG. 2 shows details of the bearing portion of the above embodiment in order to explain the operation of the above embodiment.

In this figure, A is the spiral groove, bearing width of the radial upper bearing 5, B is the bearing width of the lower bearing 6, O is the position where the radial load capacity moment is 0, and a is from point O to the center of the upper bearing 5. b is the dimension from point O to the center of the lower bearing 6, fa and fb are the dimensions of the radial bearings 5 and 6 when the rotating cylinder of the rotating head assembly is rotating.
shows the axial distribution of the pressure generated in the

Figure 3 shows the dynamic model of Figure 2, where Fa is the resultant force of the pressure distribution fa, and Fb
is the resultant force of the pressure distribution fb and indicates the radial load capacity. Also, M is overturning (rotation) due to disturbance.
Indicates a moment.

In this case, M=Fa·a+Fb·b holds true.
In order to keep the point O, where the radial load capacity moment is 0, unchanged regardless of the overturning moment, it is sufficient to set Fa/Fb=b/a. In this case, M=2Fa·a=2Fb·b, and as the overturning moment M increases or decreases, the radial load capacities Fa and Fb increase or decrease.

On the other hand, in a spiral groove radial bearing, the radial load capacity is F=
It is expressed as η・ω・R ⁴ /(ΔR) ²・ε.

Here, η is the viscosity of the lubricating fluid, ω is the rotational angular velocity,
R is the radius of the rotating body, ΔR is the bearing radial clearance, ε is the eccentricity, and is the dimensionless load capacity, which depends on the groove angle, the ratio of groove back width to groove width, groove depth, radial clearance, and bearing width. It is a constant determined by

Now, if the conditions of the radial bearings 5 and 6 in Fig. 2 are the same except for the bearing widths A and B, then Fa/
Fb=A/B. Therefore, if A/B=b/a, the position O point where the radial load capacity moment is 0 remains unchanged. Also, radial bearing width A, B
If they are made equal, a=b is obtained from A=B, and point O becomes the midpoint of the bearing span (a+b) of the radial bearings 5 and 6.

If the O point where the radial load capacity moment is 0 matches the head height position, head 1
rotates with the least amount of deflection in response to external disturbances (overturning moment). This state is shown in FIG.

In this figure, a thin solid line indicates a state in which no load is applied, and a thick solid line indicates a state in which a load is applied. Further, O indicates a position where the radial load capacity moment is 0, 1A indicates a head height position that coincides with the above-mentioned O point, and 1B indicates a head height position that does not coincide with the above-mentioned O point. In addition, X ₁ is 1A
_X2 is the amount of head deflection for 1B.

In this case, X _{1 <<}

Further, the force generated on the rotating body due to disturbance etc. can be divided into parallel load and couple load (rotational load).

Figure 5A shows the rotational runout of the head caused by a parallel load, Figure 5B shows the rotational runout caused by a couple load, and Figure 5C shows the rotational runout caused by both of the above loads. Each shows the rotational runout.

In these figures, thin solid lines and dotted lines indicate a state in which no load is applied, and thick solid lines and dotted lines indicate a state in which a load is applied.

Further, 18 is the rotation axis of the rotating part, 19 is the head height in this invention, 20 is the conventional head height,
21 is the center of gravity position of the rotating part, arrow 22 is the parallel load,
Arrow 23 indicates the couple load, Y ₁ indicates the rotational run-out amount of the head when the center of gravity of the rotating part and the height of the head match, that is, the amount of rotational runout of the head in this invention, and Y ₂ indicates the center of gravity of the rotating part and the height of the head. This shows the amount of rotational runout when the positions do not match, that is, in the conventional system, and it is clear that Y ₁ << _{Y 2} . As mentioned above, the rotational runout of the head can be minimized by matching the point O, where the radial load capacity moment is 0, with the head mounting height position, and by matching the center of gravity of the rotating part with the head height position. It can be done.

In addition, in the above embodiment, the case where only the bearing widths A and B are set was explained, but the important point is that Fa/Fb is determined by the radial load capacity ratio and the bearing position.
As long as = b/a is kept constant, point O remains unchanged.

〔Effect of the invention〕

Since the present invention is constructed as described above, a rotary head assembly with high rotational accuracy can be obtained at low cost.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing one embodiment of the present invention, Fig. 2 is an explanatory drawing showing details of the bearing portion of the above embodiment, Fig. 3 is a model diagram showing the dynamic model in Fig. 2, and Fig. 4 Figure 5A, B, C is a principle diagram showing the amount of head deflection due to the difference between the head position and the O point.
6 is a dynamic model diagram showing the correlation between the center of gravity position and the amount of rotational runout, and FIG. 6 is a sectional view showing the conventional configuration. In the figure, 1 is the head, 2 is the rotating cylinder, 3 is the fixed cylinder, 4 is the fixed shaft, and 5 and 6 are the spiral cylinders.
7 is a radial flange, 11 and 12 are rotary transformers, 13 and 14 are drive motors, and 17 is a rotary center of gravity position adjustment weight. In addition,
The same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Two spiral bearings constituting a radial bearing.
A fixed cylinder that supports a fixed shaft equipped with a groove bearing and is rotatably supported by the fixed cylinder having a tape-shaped recording medium guide portion on its outer periphery and the spiral groove bearing, and is compatible with the tape-shaped recording medium. A rotary cylinder that supports a magnetic recording/reproducing head,
A rotating head assembly for a magnetic recording/reproducing device, characterized in that a position where the radial load capacity moment of the radial bearing is 0, a center of gravity of the rotating section, and a height position of the magnetic recording/reproducing head are substantially coincident. . 2 The radial load capacity acting on one radial bearing is Fa, the radial load capacity acting on the other radial bearing is Fb, and the dimension from the center of one radial bearing to the position where the radial load capacity moment is 0 is a, Claim 1, characterized in that Fa/Fb=b/a is satisfied, where b is the dimension from the center of the other radial bearing to the position where the radial load capacity moment is 0. A rotary head assembly for the magnetic recording and reproducing apparatus described above.