GB2145271A - Magnetic head - Google Patents

Abstract

A rotating head cylinder includes a rotatable upper drum 2, a fixed lower drum 3 disposed opposite to the upper drum 2, a pair of magnetic heads 6, and a pair of rotation detecting magnets 8 cooperating with detection coils 11. The magnetic heads 6 and their respective magnets 8 are embedded in magnetic holders 5 to constitute respective integral units. <IMAGE>

Description

SPECIFICATION Magnetic head Field of the invention The present invention relates to a magnetic head in a rotating head cylinder.

Background of the invention A rotating head cylinder of the prior art is shown in Figures 1 and 2, where the cylinder consists of an upper drum 2 rotating about a shaft 1 and a fixed lower drum 3. Magnetic heads 6 which are held to their respective magnetic holders 5 are mounted with screws 7 to the surface 4 of the upper drum 2 that is opposed to the lower drum 3. Magnets 8 for detecting rotation are mounted separately by molded members 9 close to their respective heads 6 and at positions that are spaced a certain angle 6 from their respective heads 6 about the shaft 1.

Another head 12 that acts to detect rotation and has a coil 11 is mounted to the surface 10 of the fixed lower drum 3 which is opposed to the upper drum 2.

The head 12 is placed so as to be able to face the magnets 8 on the upper drum 2.

The head cylinder is rotated in synchronism with a reference signal which is the vertical synchronizing signal of 60 Hz contained in a video signal during recording of video signals. The reference signal is the control signal recorded at the lower fringe of a tape during reproduction. The video head assembly is equipped with a pulse generator to measure the rotational frequency or detect the phase.

This prior art device is capable of detecting the rotation of the upper drum 2 by means of its head 12 that reads the magnetic flux signal produced from the two magnets 8 which are mounted to the surface 4 of the upper drum 2 so as to be spaced 180 apart from each other as shown in Figure 2, the head 12 being mounted to the surface 10 of the lower drum 3.

This device has the disadvantage that the positions at which the magnets 8 are mounted must be shifted corresponding to the installation positions of the magnetic heads 6, because the heads 6 are mounted to the upper drum 2 with the screws 7, and because the magnets 8 are separately mounted to the upper drum 2 with the molded members 9 at positions spaced the certain angle 6 from the heads 6. Further, it is difficult to determine the angle 6 in mounting the magnets 8 serving to detect the rotation. Accordingly, the device is not assembled in an efficient way.

Summary of the invention In view of the foregoing difficulties associated with the prior art device, it is the main object of the present invention to provide a magnetic head in which magnets for detecting rotation can be always mounted at a given angle to their respective magnetic heads, and which dispenses with operations for adjusting the positions of the magnets after the components have been mounted.

The above object is achieved in accordance with the teachings of the present invention by providing a structure in which the magnetic heads and their respective rotation detecting magnets are imbedded in respectivei magnetic holders to constitute units.

Brief description of the drawings Figure 1 is a side elevation of a conventional rotating head cylinder; Figure 2 is a plan view taken along the surface 4 of the upper drum of Figure 1; Figure 3 is a side elevation of a rotating head cylinder according to the present invention; Figure 4 is a plan view taken along the surface 4 of the upper drum of Figure 3; Figure 5 is an enlarged view of one magnetic holder shown in Figures 3 and 4; and Figure 6 is a side elevation of the magnetic holder shown in Figure 5.

Detailed description of the invention Referring to Figures 3-6, there is shown a rotating head cylinder embodying the concept of the present invention. Those components of this head cylinder which are indicated by reference numerals 1 through 12 are the same as those of the aforementioned conventional device indicated by the same numerals. In the conventional device, as shown in Figure 2, the magnetic heads 6 are supported by their respective magnetic holders 5 and are mounted to the upper drum 2 with the screws 7. The magnets 8 for detecting rotation are mounted with the molded members 9 at positions spaced a certain angle 6 from their respective heads 6. The heads 6 and the magnets 8 are separately mounted to the upper drum 2.In the novel device, as shown in Figures 3 and 5, a magnetic head 6 and a rotation detecting magnet 8 spaced a certain angle 6 from the head 6 are imbedded in a magnetic holder 5 to constitute a unit, which is mounted to the upper drum 2 with a screw 7. Another unit constructed in the same way as the above unit is also mounted to the upper drum 2 with a screw 7.

As thus far described, in the novel device, the magnetic heads 6 and the respective rotation detecting magnets 8 are spaced the certain angle 6 from each other, and are imbedded in their respective magnetic holders 5, forming units, as shown in Figures 4 and 5. Therefore, it is possible to mount the magnetic heads 6 and the respective magnets 8 to the upper drum 2 while keeping the angular distance between them at the certain angle 6, irrespective of the positions at which the heads 6 are mounted.

In general, when magnetic heads such as the magnetic heads 6 are mounted, the opposed positions, the height, etc. are required to be determined with very high accuracy. In the present invention, the relative positional relation between the magnetic heads 6 and their respective rotation detecting magnets 8 is established during manufacture of the device. After these components are mounted to the upper drum 2, adjustment of positions including fine adjustment operations are dispensed with.

The operation for mounting the detecting magnets 8 can be effected simultaneously with the mounting of the magnetic heads 6 and hence no separate step is required for mounting the magnets 8. Further, since accurate assembly operations are performed only on the side of the upper drum 2, the number of assembly steps can be reduced.

In the device according to the invention, magnetic heads and their respective rotation detecting magnets are imbedded in their respective magnetic holders to constitute units and, accordingly, the magnetic heads and the magnets can be always mounted in an angularly spaced relation to each other. Further, after mounting these components, operations for adjusting the detecting magnets are not necessary. Consequently, the invention permits a magnetic head to be manufactured economically and with high accuracy.

While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit and scope of the following claims.

Claims (3)

1. In a magnetic head assembly having: an upper drum rotating about a shaft, a fixed lower drum disposed opposite to the upper drum, magnetic heads and their respective rotation detecting magnets which are supported on the surface of the upper drum that is opposed to the lower drum, and a rotation detecting head disposed on the surface of the lower drum that is opposed to the upper drum, the rotation detecting head having a coil, the improvement wherein the magnetic heads and their respective rotation detecting magnets are imbedded in respective magnetic holders to constitute respective integral units.

2. A magnetic head assembly as set forth in claim 1, wherein said units are secured to the upper drum by their respective screws.

3. A magnetic head assembly substantially as hereinbefore described, with reference to Figures 3 to 6 of the accompanying drawings.