Rotary head assembly

Details Rotary head assembly Rotary head assembly

1984-03-06

1985-06-25

Kilgore, Robert M.

Dynamic magnetic information storage or retrieval

Head

Head accessory

360 90, 360102, 360129, 226 97, G11B 1560, G11B 5008, G11B 1564, B65N 1732

Patent

active

045257574

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a rotary head assembly of a video tape recorder (hereinafter called VTR), and is more particularly intended to present a rotary head assembly capable of recording and reproducing picture images of high quality at high reliability, by lifting the tape up from the cylinder with the dynamic pressure built up by pump-out type spiral grooves so as to lessen the tape running load, tape damage and wear of the cylinder itself due to sliding and friction of the tape and also to stabilize the tape running.


BACKGROUND OF THE INVENTION

A rotary head assembly of a VTR is generally composed of an upper rotary cylinder 2 and a lower fixed cylinder 3 as shown in FIG. 1, and a magnetic tape runs at a constant speed being helically wound around the rotary head assembly of about 180.degree.. Numeral 4 refers to a step part (called lead hereinafter) which guides the running position of the tape in its widthwise direction. A video head 5 is fixed to the upper rotary cylinder 2 and rotates at high speed (1800 rpm in the VHS system VTR) to record and reproduce picture signals on the magnetic tape. Numerals 6, 7, 8, 9 are tape guide posts.
The behavior of magnetic tape on the rotary head assembly having such constitution appears to be simple, but is actually extremely complicated. FIG. 2 is a schematic model representing a sectional view of a conventional rotary head assembly and the behavior of magentic tape 1 on it. Since the upper rotary cylinder 2 rotates at high speed, an air film is formed between the tape 1 and the outer circumference of the upper rotary cylinder 3 due to inclusion of air, so that the tape 1 receives a buoyancy in the upper rotary cylinder area. In the lower fixed cylinder area, on the other hand, since the relative speed between the magnetic tape 1 and the outer circumference of the lower fixed cylinder 3 is extremely small (11.0 mm/sec in 6 o'clock mode of VHS system VTR), such air film is not formed, and the magnetic tape 1 slides while contacting with the outer circumference of the lower fixed cylinder. Meanwhile, the magnetic head 5, in order to exchange signals with the magnetic tape 1, slides at high speed on the magnetic tape at an adequate contact pressure. Therefore, on the rotary head assembly, the magnetic tape is subject to a buoyancy in the upper rotary cylinder area and runs almost without contact, whereas, in the lower fixed cylinder area, the tape runs while receiving a sliding frictional resistance. That is, the dynamic situations vary significantly depending on the position of the tape in its widthwise direction. Further, since the magnetic tape is wound around the rotary head assembly helically, its dynamic situations vary also in the longitudinal direction of the tape. In particular, at the contact terminal end between the magnetic tape and rotary head assembly, the contact surface area with the lower fixed cylinder is increased, and the tape buoyancy is inferior. Yet, the upper rotary cylinder and lower fixed cylinder are assembled almost coaxially, but the dynamic state of the tape differs significantly depending on the coaxiality and the difference in diameter of the two cylinders. In FIG. 2, numeral 11 is a shaft, on which the upper rotary cylinder 2 is fixed by way of a disc 10. Numerals 12, 13 are ball bearings which rotate and support said shaft, 15 is a spacer, and 14 is a collar to fix the ball bearings by preloading.
Thus, the magnetic tape runs on the rotary head assembly under complicated dynamic state, but involves the following problems. That is:
(1) Tape chirping due to sliding at lower fixed cylinder--this is a kind of frictional vibration accompanying the sliding between tape and cylinder, and vibrations of about hundreds to several kilohertz occur in a running tape. This phenomenon is likely to occur when the tape running speed is low and the ambient humidity is high, which gives rise to color unevenness of picture and jitters.
(2) Sticking of tape to upper and lower cylinders--generally, coarseness of tape surface

REFERENCES:
patent: 4012792 (1977-03-01), Bloom
patent: 4257076 (1981-03-01), Shimizu
patent: 4266255 (1981-05-01), Camras
patent: 4395745 (1983-07-01), Aarts

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