JPH0447915B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video tape recorder (hereinafter referred to as
Abbreviated as VTR. ) of the rotary head assembly.

Conventional technology In recent years, video technology has made remarkable progress. On the hardware side, efforts have been made to make it smaller and lighter, while on the software side, metal tapes with high S/N ratios that enable short wavelength recording have become available. It's being released. Among these, various improvements have been made to the rotary head assembly, which influences the input/output characteristics between the tape and the head interface.

Hereinafter, an example of the above-mentioned conventional rotary head assembly will be described with reference to the drawings. FIG. 3 shows a perspective view of a conventional rotary head assembly. In FIG. 3, 1 is a tape. 2 is a rotating member, 3 is a fixed member provided approximately on the same axis as the rotating member 2, 4 is a lead provided on the outer peripheral surface of the fixed member 3, 5 is a head, and 6 is a head attachment on the rotating member 2. It's a window. The operation of the rotary head assembly constructed as described above will be explained below. Tape 1 is 1000~
It runs while sliding on the rotating member 2 and fixed member 3 that rotate at 2000 rpm. Further, a lead 4 is provided on the outer circumferential surface of the fixed member 3 for the purpose of regulating the position of the tape 1 when it runs, so that the head 5 mounted on the rotating member 2 can accurately move helically over the tape 1. By scanning, reliable input/output of video signals via the tape 1 is realized. The head 5 is approximately number 10 from the outer peripheral surface of the rotating member 2.
It is held in a micron protruding manner to the outside.

However, in the configuration described above, the head on the rotating member rotates at high speed and contacts the tape, and a portion of the rotating member also slides into contact with the tape. At this time, abrasion occurs between the head and the tape and between the rotating member and the tape, and abrasion powder is generated. These abrasion particles repeatedly adhere to and fall off between the surface of the rotating member and the tape, accumulate and gradually grow. The abrasion powder on the rotating member that has grown through the steps described above forms a kind of built-up edge that slides relative to the tape at high speed (the outermost peripheral speed of the rotating member), and is magnetically attached to the tape. This can cause significant damage accompanied by layer peeling. As a practical matter, a mixture of magnetic powder generated by sliding contact with the tape and aluminum, which is a component of the rotating member, accumulates on the outer peripheral surface of the rotating member. On the other hand, on the rotating member side, the tape is made of Co, Ni, etc., which have high S/N characteristics.
When the main component is a metal component such as Co or Ni, it has a series of problems in that Co and Ni are harder than aluminum, which is the main component of the rotating member, so they are damaged by wear particles. As a method for solving the above problems, the present inventors constructed a pump-out type spiral groove 9 between the rotating member 7 and the fixed member 8, as shown in FIGS. 4 and 5. We have already proposed a rotating head assembly with a new configuration that uses air pressure generated by the rotational force of the rotating member 7 to levitate the tape by a minute amount (5 to 20 μm) over the entire circumference of the rotating head assembly (for example, in a special Gansho 57-117168).

Problems to be Solved by the Invention However, with the above configuration, as the functions of VTRs have expanded, the normal 2 to 3
When double the tape tension is applied, the tape cannot float sufficiently from the fixing member 8, and there is an extremely high possibility that wear and damage will occur. Furthermore, due to design constraints, it is impossible to adopt a spiral groove structure that has high discharge pressure characteristics that can sufficiently cope with these unusual driving conditions.

In view of the above-mentioned drawbacks, the present invention provides a highly reliable and durable rotating head assembly that minimizes damage to both the tape and the rotating body by realizing sufficient tape floating even in the face of rapid tension fluctuations. It is something.

Means for Solving the Problems In order to solve the above problems, the rotating head assembly of the present invention includes a pump-out type spiral groove on the opposing surfaces of the rotating member and the fixed member,
Regarding the difference Δr between the radius of the rotating member and the radius of the fixed member, T
where is the tape tension, R is the radius of the tape sliding part of the fixed member, E is the Young's modulus of the tape, a is the tape width applied to the rotating member, h is the tape thickness, then the critical diameter difference Δr _cr is Δr _cr = TR/Eah Define Δr as 1 to r _cr
The outer diameter of the rotating member is made larger than the outer diameter of the fixed member so that the range is three times as large.

Effects With the above-described configuration, the present invention causes more of the surface pressure caused by the tape tension acting on the surfaces of the rotating member and the fixed member to be applied to the rotating member on which dynamic pressure during rotation acts, and less to the fixed member. By this action, the surface pressure of the tape on the fixing member at the portion supported by the air pressure discharged by the spiral groove is reduced, thereby realizing smooth floating of the tape.

Embodiment A rotary head assembly according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view showing a rotary head assembly in a first embodiment of the present invention. In FIG. 1, 10 is a rotating member, 12 is a spiral groove provided on the lower end surface of the rotating member, and 11 is a fixed member. The outer diameter of the fixed member 11 is set smaller than the outer diameter of the rotating member 10 by Δr. Also, 13
14 is a lead, and 14 is a magnetic tape (hereinafter abbreviated as "tape").

The operating principle of the rotary head assembly constructed as described above will be explained below.
According to the theory of oil bearings, in a rotating cylinder,
When wrapping a thin strip of tape, dynamic pressure is generated in the area sandwiched between the tape and the cylinder due to the viscosity of the air, and as the gap between the tape and the cylinder becomes smaller, the pressure increases. Specifically, when the clearance is zero, the pressure becomes infinite. Therefore, even in the rotating head assembly, the behavior of the tape on the rotating member 10 follows the above-mentioned oil theory, and as long as the rotating member 10 is rotating, the tape will float. On the other hand, the lower cylinder is not directly affected by the pressure generated by the rotating member 10. The air pressure discharged from the spiral groove provided at the lower end of the rotating member 10 is discharged from the gap between the rotating member 10 and the fixed member 11, and enters the gap between the tape on the fixed member 11, where the pressure is relatively low, and reaches this part. Realizes tape flotation. Now, let's model and find the surface pressure due to the tape on the rotating member and fixed member having a radius difference Δr. For simplicity, consider the tape as a collection of thread elements. A tape of width w, thickness h, and Young's modulus E is applied to a rotating head assembly having a diameter difference of Δr as schematically shown in Fig. 2, with a tension of T so that a width of a is applied to the rotating member side. When the longitudinal stress of the tape that acts on the rotating member and fixed member when it is pulled is σ _a and σ _b , respectively, then from the force balance equation, h(σ _a・a+σ _b・b)=T……(1) Also, The difference in principal stress is expressed by the following formula: σ _a −σ _b =EΔr/R ...(2) Calculating σ _a and σ _b from formulas (1) and (2), from (1), T/h= σ _a・a+σ _b・b σ _b = (T/h−σ _a・a)/b …(3) Substituting (3) into (2)
σ _a −T/hb+σ _a・a/b−EΔr/R …(4) Therefore σ _a =EΔr/R+T/bh/1+a/b=EΔrb/R+T
/h/a+b...(5) Therefore, σ _b =-(EΔra/R)+T/h/a+b...(6) The average tension T _a of the tape on which σ _a acts is T _a = σ _a・a・h ...(7) Similarly, T _b =σ _b・b・h ...(8) Therefore, the average surface pressure acting on the rotating and fixed members
Since P _a and P _b are R≫∆r, P _a = T _a /a (R + ∆r) T _a /aR = σ _a・h/R = T/WR + E∆r・b・h/WR ² ...(9) P _b = T _b /bR=σb・h/R=T/WR−E・Δr・a・h
/WR ²
...(10) Here, when the surface pressure P _b on the fixed member is set to zero, the critical value Δr _cr of Δr is determined from equation (4) as follows: Δr _cr = TR/Eah ...(11). When Δr is set to be greater than Δr _cr determined by equation (11), surface pressure P _b basically does not act on the fixed member. If the design is such that the discharge pressure of the spiral groove is equal to T/wR under normal running conditions, by setting Δr = Δr _cr , the surface pressure that the spiral groove discharge pressure is responsible for is T/wR.
and the sum of the surface pressure T/wR covered by the diameter difference Δr _cr ,
In other words, it maintains non-contact with the fixed member up to 2T/wR. This means that even if the tension doubles, P _b
represents zero.

Furthermore, if Δr=2Δr _cr , P _b becomes zero even if the tension increases three times. If Δr is set too large, the tape will tilt significantly on the rotating head assembly, causing running problems. Therefore, r should not be set to more than three times r _cr .
Next, explanation will be given using specific numerical values.

Here, T=20g, R=20mm, E=0.1×
When 10 ⁴ N/mm, a=4mm, and h=0.02mm, Δr _cr =TR/Eah=0.05mm.

Further, if T=50g, Δr _cr =0.125mm.

The above theory also holds true for a rotating head assembly that does not have a spiral groove, but when combined with a spiral groove, Δr can be reduced by the estimated discharge pressure of the spiral groove, and from the opposite perspective, Δr is provided. This has the effect of allowing a large margin in the design of the spiral groove in the sense that the surface pressure P _b acting on the fixing member can be made smaller in appearance.

Effects of the Invention As described above, the present invention provides a pump-out type spiral groove on the opposing surfaces of a fixed member and a rotating member, and compares the radius of the rotating member with the radius of the fixed member by a certain amount Δr within a certain range. By setting it to a large value, the tape can be easily floated not only on the rotating member but also on the stationary member, thereby realizing stable and wear-free tape running.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of a rotating head assembly according to a first embodiment of the present invention, FIG. 2 is a perspective view for explaining the operation of FIG. 1, and FIG. 3 is a perspective view of a conventional rotating head assembly. , FIG. 4 is a front sectional view of a conventional rotary head assembly, and FIG.
FIG. 3 is a bottom view of the rotating member 7 shown in the figure. 10... Rotating member, 11... Fixed member, 12...
...Spiral Groove, 13...Lead, 14...
…Magnetic tape.

Claims (1)

[Scope of Claims] 1. A fixing member having a cylindrical portion, which has approximately the same diameter as the fixing member, is provided opposite to and adjacent to the fixing member, and is coaxial with the fixing member, and holds the magnetic head. a lead that is helically provided around the main axis of the fixed member around the entire circumference or a part of the fixed member; and a lead that is helically wound around the fixed member and the rotating member and along the lead. with respect to the radius difference Δr between the rotating member and the fixed member, T is the tension of the magnetic tape, R is the radius of the tape running portion of the fixed member, E is the Young's modulus of the magnetic tape,
Let a be the dimension of the portion of the magnetic tape that hangs over the rotating member in the width direction, h be the thickness of the magnetic tape, and define the critical diameter difference Δr _cr expressed as Δr _cr = TR/Eah, where Δr is the width of Δr _cr . The radius of the rotating member is set to be larger than the radius of the fixed member so as to be in the range of 1 to 3 times, and a pump-out type spiral groove is provided on one of the facing surfaces of the rotating member and the fixed member. rotating head assembly.