JP2008234705A - Eraser head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eraser head which can control a narrow erasing area and easily change its erasing magnetic field intensity. <P>SOLUTION: The eraser head includes permanent magnets, and composed of permanent magnets and yokes to guide the lines of magnetic force from both poles of the permanent magnets. A gap is formed at the tips of the yokes. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an erasing head used for signal erasing of a magnetic recording medium.

  There are two types of signal erasure in the magnetic recording medium: AC erasure in which an alternating magnetic field is gradually weakened to erase a signal, and DC erasure in which a saturation magnetic field is applied to cause saturation recording to erase a signal.

  DC erasing with a simple mechanism is often used for general tape recorders and video tape recorders. DC erasure is also used for servo signal recording on computer tape. There are two types of erasing heads used for DC erasing: a type in which a direct current (DC) current is caused to flow through a coil to generate a magnetic field of a certain intensity and a type using a permanent magnet, but current cost and cooling energy are not required The latter is advantageous. Patent Document 1 is an example of such an erasing head.

JP-A-62-243110

  Patent Document 1 proposes an erasing head including a cylindrical magnet core and a synthetic resin holder that is insert-molded so that the circumferential surface of the magnet core protrudes. However, since such an erasing head uses a wide ambient magnetic field generated by the magnet core, the erasing part of the magnetic tape cannot be precisely defined, and the magnetic tape is brought into contact with the magnet core for erasing. When it is desired to change the magnetic field strength, it is necessary to prepare a plurality of magnets having different magnetic flux densities, which is inconvenient in use.

  Therefore, the present invention provides an erasing head that can be controlled by narrowly limiting the erasing position and can easily change the erasing magnetic field strength.

  As a result of intensive studies on the erasing head, the inventors of the present invention can achieve the above-described object by forming the erasing head with the following configuration, thereby achieving the present invention.

  In other words, the erasing head includes a permanent magnet, which is composed of the permanent magnet and a yoke for guiding lines of magnetic force emitted from both poles of the permanent magnet, and has a gap at the tip of the yoke.

  A control mechanism for controlling the distance between the permanent magnet and the yoke is provided.

  Since the magnetic field lines coming out from both poles of the permanent magnet are guided by the yoke and a gap is provided at the tip of the yoke, a strong magnetic field can be generated in a narrow range in the gap portion, and the erasing location can be narrowly limited. In addition, since a control mechanism for controlling the distance between the permanent magnet and the yoke is provided, the magnetic field intensity generated in the gap can be easily changed by changing this distance.

  The present invention will be described below with reference to the drawings. FIG. 1 is a plan view of an erasing head as an example of the present invention. The erasing head 6 of this example includes a permanent magnet 1 that is a source of magnetic lines of force, a yoke 2 that guides magnetic lines of force generated from the magnetic poles of the permanent magnet 1, and a spacer 4 that is a mechanism that controls the distance between the permanent magnet 1 and the yoke 2. And a gap 3 formed at the tip of the yoke 2 and a holding body 5 for storing them.

  The magnetic field strength of the permanent magnet 1 is preferably 3000 Oe or more, and more preferably 5000 Oe or more. As such a permanent magnet 1, a neodymium magnet is preferably used. The flow of magnetic lines of force in the magnetic circuit formed by the permanent magnet 1 and the yoke 2 is as follows.

  The lines of magnetic force emitted from the N pole of one permanent magnet 1 pass through the yoke 2 and are guided to the gap 3 at the tip of the yoke 2. As the material of the yoke 2, a conventionally known material (pure iron, sendust, permalloy, etc.) having a large relative permeability is used. The yoke 2 is squeezed as it approaches the tip, a gap 3 is formed at the tip, and a strong magnetic field is formed in the space of the tip. The magnetic tape is conveyed while being in contact with the gap 3, and the magnetic layer is saturated and magnetized by a strong magnetic field in the tip space of the gap 3, thereby erasing the signal recorded on the magnetic layer. The magnetic field lines in the gap 3 return to the yoke 2 on the S pole side of the other permanent magnet 1 and converge to the S pole of the other permanent magnet 1. The lines of magnetic force emitted from the N pole of the other permanent magnet 1 converge to the S pole of one permanent magnet 1 through the yoke 2 on the side opposite to the yoke 2 forming the gap 3.

  The strength of the magnetic field generated in the gap 3 varies depending on the type of the permanent magnet 1 to be used, but as shown in FIG. 4, it also varies greatly depending on the width (w) and thickness (d) of the gap 3. Generally, a stronger magnetic field is generated as the width and thickness are reduced. The width and thickness of the gap 3 may be appropriately selected based on the required magnetic field strength, but considering the ease of processing and the like, the width (w) is preferably 0.1 to 2 mm, and the thickness (D) is preferably 0.1 to 5 mm. For example, when a neodymium magnet is used, the width (w) of the gap 3 is 0.5 mm, and the thickness (d) of the gap 3 is 5 mm, the magnetic field strength formed in the gap 3 is about 4 kOe at the maximum, and the thickness (d ) Is 0.5 mm, the maximum magnetic field strength is about 9 kOe.

  Furthermore, the strength of the magnetic field generated in the gap 3 can be easily controlled by changing the thickness of the spacer that controls the distance between the permanent magnet 1 and the yoke 2. As a method for controlling the distance between the permanent magnet 1 and the yoke 2, a conventionally known method such as control using a screw is used in addition to a method using a spacer. In addition, since the magnetic field is generated in a narrow gap, the portion to be erased can be narrowly limited.

  As a method of using the permanent magnet 1 in the magnetic circuit, in addition to the method of using two permanent magnets shown in FIG. 1, a magnetic circuit is formed by one permanent magnet as shown in FIGS. Also good.

It is a top view of the erase head of an example of the present invention. It is a top view of the erase head of another example of the present invention. It is a top view of the erase head of another example of the present invention. FIG. 3 is an enlarged plan view of a gap portion of an example erasing head of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Permanent magnet 2 Yoke 3 Gap 4 Spacer 5 Holding body 6 Erase head

Claims (2)

  An erasing head including a permanent magnet, the erasing head comprising the permanent magnet and a yoke for guiding lines of magnetic force emitted from both poles of the permanent magnet, and having a gap at a tip of the yoke.   The erasing head according to claim 1, further comprising a control mechanism that controls a distance between the permanent magnet and the yoke.

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