JPS6146897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video tape recorder (hereinafter referred to as VTR).
That's what it means. )'s rotating head assembly, which reduces tape running load and tape damage caused by tape sliding friction, as well as wear on the rotating cylinder itself, and enables high-quality image recording and playback with high reliability. The present invention provides a rotary head assembly that enables.

As shown in the example in Figure 1, the rotating head assembly of a VTR consists of an upper rotating cylinder 2 and a lower rotating cylinder 3, and a magnetic tape 1 is helically wound around the rotating head assembly at an angle of about 180 degrees and runs at a constant speed. . Reference numeral 4 denotes a stepped portion (hereinafter referred to as a lead) that guides the running position of the tape in the width direction. The video head 5 is fixed to the upper rotating cylinder 2, and is operated at high speed (for VHS VTRs).
It rotates at a speed of 1800 rpm) and records and plays back image signals on magnetic tape. 6, 7, 8, and 9 are tape guide posts.

The behavior of the magnetic tape on a rotating head assembly having such a configuration may appear simple at first glance, but it is actually extremely complex. FIG. 2 is a cross-sectional view of a conventional rotary head assembly and schematically shows the behavior of the magnetic tape 1 therein. Since the upper rotating cylinder 2 rotates at a high speed, an air film is formed between the magnetic tape 1 and the outer circumferential surface of the upper rotating cylinder 2 due to the air inflow effect, and the magnetic tape 1 receives a levitation force in the upper rotating cylinder section. receive. On the other hand, in the lower fixed cylinder section, the relative speed between the outer peripheral surfaces of the magnetic tape 1 and the lower fixed cylinder 3 is extremely small (in VHS system VTR6 mode).
11.1 mm/sec), an air film as described above is not formed, and the magnetic tape 1 slides in contact with the outer periphery of the lower fixed cylinder. Also, the magnetic head 5
slides on the magnetic tape at high speed under appropriate contact pressure in order to exchange signals with the magnetic tape 1. Therefore, on the rotary head assembly, the magnetic tape is subjected to a floating force in the upper rotary cylinder portion and travels almost without contact. On the other hand, in the lower fixed cylinder portion, the magnetic tape 1 runs while being subjected to sliding frictional resistance, and its dynamic situation varies greatly depending on the position in the width direction of the magnetic tape 1. Furthermore, since the magnetic tape is helically wound around the rotating head assembly, the mechanical conditions of the magnetic tape also change in the longitudinal direction. Also, the upper rotating cylinder and the lower fixed cylinder are assembled almost coaxially, but due to their coaxiality and the difference in diameter between them,
Naturally, the mechanical state of the tape is greatly influenced.
In FIG. 2, reference numeral 11 denotes a shaft, to which the upper rotating cylinder 2 is fixed via a disk 10. Further, 12 and 13 are ball bearings that rotatably support the shaft, 15 is a spacer, and 14 is a collar that applies preload to the ball bearing and fixes it.

Now, as mentioned above, the magnetic tape runs on the rotating head assembly under complicated mechanical conditions.
There are the following problems. In other words, (1) Tape squeal phenomenon caused by sliding on the lower fixed cylinder; it is a type of frictional vibration caused by the sliding between the tape and the cylinder, and vibrations of several hundred to several KHz occur in the running tape. do. This problem tends to occur when the tape running speed is low and in a high humidity atmosphere, resulting in color unevenness and jitter in the image.

(2) Phenomenon of tape adhesion to the upper and lower cylinders: In general, the surface roughness of the tape is on the order of several hundred Å and is extremely smooth, and the cylinder surface is also made of a smooth surface ( The surface roughness is 0.1~1S). When two extremely smooth surfaces are brought into contact in this way, they generally stick together. In the tape running system of a VTR, this phenomenon occurs when the tape adheres to the rotating head assembly, causing the tape to become unable to run. It is likely to occur in a humid atmosphere.

(3) Tape damage and wear caused by contact between parts of the rotating head assembly and the magnetic tape;
Not only will magnetic recording signals be lost due to tape damage, but the magnetic powder that falls off will accelerate wear on sliding parts, or accumulate in the head gap of the video head, causing a blockage that will make recording and playback impossible. become.

etc. All of these problems are caused by the magnetic tape contacting and sliding against the rotating head assembly, particularly the lower fixed cylinder.

On the other hand, with the trend towards smaller and lighter VTRs, in order to improve the signal recording density on magnetic tape, the conventional tapes coated with magnetic powder of iron oxide or chromium dioxide along with a resin binder have been replaced with so-called alloys. There is a trend toward using tape or vapor-deposited tape as magnetic tape. While the conventional tape magnetic surface is made of resin and magnetic powder,
In these new tapes, the tape magnetic surface is
Because it is a metal surface, the coefficient of friction when sliding against stainless steel, for example, increases from about 0.2 to about 0.5. Therefore, the above-mentioned problems associated with sliding in a rotating head assembly in which the magnetic surfaces are in sliding contact are brought into greater focus than with conventional tapes.

The present invention solves the above-mentioned problems of the conventional rotary head assembly and provides a rotary head assembly that enables high-quality image recording and playback with high reliability. 3rd to 6th
This will be explained using figures.

For things that are common to the configuration in Figures 1 and 2,
The same drawing numbers are given and explanations are omitted.

In the figure, 2a is the outer surface of the overlapping cylinder formed at the lower part of the rotating cylinder 2, and 3a is the inner surface of the overlapping cylinder formed at the upper part of the fixed cylinder ₃ . It forms a cylindrical surface. A pump-out type spiral group 21 is formed on the outer surface 2a of the overlapping cylinder of the rotary cylinder 2.

FIG. 4 shows a side view of the upper rotating cylinder in the above embodiment, and shows the spiral group 21.
It represents the pattern of In the figure, the blacked out areas indicate the grooves. In the figure, the blacked-out portion 16 is the groove, and the portion 17 is the land.

As the upper rotating cylinder rotates in the direction indicated by the thick arrow, the air inside the cylinder is blown out. Reference numeral 20 in FIG. 3 is a hole that communicates the space inside the rotary head assembly with the outside. In the configuration of the rotating head assembly of this embodiment, an upward air flow is generated by the spiral group 21 due to the rotation of the upper rotating cylinder 2, and air is further discharged to the outside from between the upper rotating cylinder and the lower fixed cylinder. The air gives a levitation force to the magnetic tape, and forms a uniform air film over the entire area on which the magnetic tape slides on the outer peripheral surfaces of the upper rotating cylinder 2 and the lower fixed cylinder 3, and the magnetic tape and the rotating head assembly. This avoids sliding contact between the tapes and realizes stable and smooth tape running.

Next, the principle of improving tape runnability in the present invention will be explained in more detail. FIGS. 5 and 6 show partial cross-sections of rotary head assemblies in a conventional configuration and an embodiment of the present invention, respectively. In the conventional rotating head assembly, as shown in Figure 5, the tape floats up to about 10μ at the top in the upper rotating cylinder, but in the lower fixed cylinder, the tape does not float at all and runs in contact with the tape. There is. This is due to the air pressure caused by the air bearing effect caused by the high speed rotation of the upper rotating cylinder.As shown by the arrow in the figure, some of the air pressure is from the upper end of the magnetic tape 1, and the rest is from the gap δ between the upper and lower cylinders.
This is because the air pressure flows out through the air (usually 0.1 to 1 mm) and does not reach the lower fixed cylinder part. In the rotating head assembly of the present invention (see FIG. 6), there is a spiral groove 21 between the upper rotating cylinder 2 and the lower fixed cylinder 3.
Since the structure is such that air is discharged to the outside,
The air pressure caused by the rotation of the upper rotating cylinder does not flow out through the gap _δ2 between the upper and lower cylinders, but rather, the air flow discharged by the spiral groove increases the air pressure that makes the magnetic tape levitate. The above-mentioned air pressure reaches the fixed cylinder section, thereby realizing floating running of the tape in the lower fixed cylinder section. By the way, the average air pressure required to levitate the tape in a normal VTR is 0.01 to 0.05 atg. To obtain this effect, the gap δ ₂ must be
Must be at least 50μ or less. Further, it is preferable that the axial length L of the spiral group be as large as possible. The optimal depth of the spiral groove depends on the gap _δ2 or the axial length L of the spiral group, but it also depends on the dimensions of the rotating head assembly of a normal VTR and the rotation of the upper rotating cylinder. Due to conditions such as speed, the desired effect cannot be obtained unless it is approximately 100μ or less. In setting the dimensions of these spiral grooves, publicly known materials (for example, Design of Gas
Bearings; DF Wilcock, MTI1972) may be used.

In this embodiment, the spiral group is provided on the upper rotary cylinder side, but it is clear that it may be provided on the lower fixed cylinder side. Furthermore, in this embodiment, a spiral groove is provided between the stepped cylindrical surface of the rotary cylinder and the cylindrical surface of the lower fixed cylinder, but vice versa, that is, the spiral groove is provided between the stepped cylindrical surface of the rotary cylinder and the cylindrical surface of the lower fixed cylinder. It is clear that a spiral group may be provided between the stepped inner cylinder surfaces.

As explained above, the rotating head assembly of the present invention generates floating force due to air pressure on the traveling magnetic tape not only in the upper rotating cylinder but also in the lower fixed cylinder part, thereby realizing stable and smooth tape running. This fundamentally eliminates tape squealing or tape adhesion phenomena, as well as tape damage and wear caused by sliding.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional rotary head assembly, FIG. 2 is a sectional view thereof, FIG. 3 is a sectional view of a rotary head assembly according to an embodiment of the present invention, and FIG.
5 is an explanatory diagram showing the behavior of the tape on the conventional rotary head assembly. FIG. 6 is an explanatory diagram of the fist movement of the tape on the rotary head assembly according to an embodiment of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Tape, 2... Rotating cylinder, 3... Fixed cylinder, 2a... Outer surface of polymerized cylinder, 3a... Inner surface of polymerized cylinder, 21... Spiral groove.

Claims (1)

[Scope of Claims] 1. A fixed cylinder having a cylindrical portion; a cylindrical portion disposed coaxially with the fixed cylinder and having substantially the same diameter as the cylindrical portion of the fixed cylinder; The rotating cylinder rotates relative to the fixed cylinder and supports the tape with the fixed cylinder, and the rotating cylinder and the fixed cylinder have overlapping cylindrical surfaces that fit into each other with a small gap. A spiral group is provided on either the outer surface or the inner surface of the cylinder facing each other, and the air discharged from the spiral group part by the rotation of the rotating cylinder is transferred to the opposing end surfaces of the rotating cylinder and the fixed cylinder. A rotary head assembly configured to discharge fluid to the outside from between. 2. The rotating head assembly according to claim 1, wherein the small gap is 50μ or less.