JPH05189893A - Information recording/reproducing system - Google Patents

Abstract

PURPOSE:To obtain an information recording/reproducing system which can be secured easily and firmly to a linear motor and which can generate flux effectively while reducing cost. CONSTITUTION:Holes 33a, 33b are made at two positions through a back yoke 33 of a magnetic circuit constituting a linear motor for moving a carriage base 1 mounting an optical head, and positioning pins 36 provided on a drive chassis 32 are fitted in the holes 33a, 33b thus regulating the position. Under such position regulated state, the back yoke 33 is secured through screws 37 to the drive chassis 32 so that external force is received by the screws 37 and the positioning pin 36 thus enhancing impact resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the optical recording / recording of information.
The present invention relates to an information recording / reproducing apparatus having a structure in which a carriage equipped with an optical head for reproduction is moved by a linear motor.

[0002]

2. Description of the Related Art A conventional information recording / reproducing apparatus is disclosed in Japanese Patent Laid-Open No.
A holding member on which an objective lens and the like (optical head) are mounted, as in the optical information recording / reproducing device disclosed in Japanese Patent Laid-Open No. 13139.
There is a structure in which a (carriage) is moved along a recording surface of an optical disk by a linear motor. The linear motor includes a coil fixed to a holding member and a magnetic circuit including a magnet and a yoke fixed to a frame.

[0003]

In the conventional optical information recording / reproducing apparatus described above, the end of the yoke of the linear motor is fixed to the frame by a plurality of screws, but it is relatively thick.
Since the heavy yoke is fixed only with screws,
When an external force is applied, the screw easily loosens, which may affect the driving of the linear motor.

Further, since the yoke and the magnet are long pieces extending in the moving direction of the holding member, the magnetic flux increases from the center to both ends in the moving direction,
Since a through hole for penetrating the screw is formed at the end of the yoke, the magnetic flux loss is large and the space efficiency is reduced.

Further, the yoke is generally manufactured by cutting or casting, and the manufacturing cost is high, but it is necessary to form a through hole or the like for penetrating the screw, which further increases the cost. ..

An object of the present invention is to provide an information recording / reproducing apparatus which can be easily and surely fixed to a linear motor, effectively generate a magnetic flux, and can reduce the cost.

[0007]

In order to achieve the above object, the present invention movably supports a carriage carrying an optical head for optically recording and reproducing information, and both sides of the carriage are supported. In an information recording / reproducing apparatus in which the carriage is moved by a linear motor composed of a fixed coil and a pair of magnetic circuit bodies fixed to a base body, at least 2 of the magnetic circuit bodies are provided.
It is characterized in that a hole at a location and at least two pins provided on the base body are fitted to regulate the position, and the magnetic circuit body is fixed to the base body by a screw in the state where the position is regulated.

Further, the present invention is characterized in that the number of the screws for fixing the magnetic circuit body to the base is one.

Further, the invention is characterized in that the screw penetrates a substantially intermediate position of the magnetic circuit body in the carriage movement direction and is screwed into the base body.

Further, a yoke constituting the magnetic circuit is
It is characterized by being formed by laminating thin plates of magnetic material.

[0011]

According to the above means, the magnetic circuit body is screwed in the state where the hole of the magnetic circuit body and the pin of the base body which compose the linear motor are fitted and the position is regulated. It is possible to prevent the screw from loosening due to the restriction of the pin, the driving by the linear motor is stable, the shock resistance is excellent, and the reliability is enhanced.

Further, since the magnetic circuit body can be fixed to the base body with one screw, the number of fixing screws can be reduced as compared with the conventional case, so that the workability is improved and the cost can be reduced.

Further, since the penetrating portion of the one screw is provided in the portion where the magnetic flux is the smallest in the magnetic circuit, the magnetic flux loss can be reduced and the space efficiency can be improved.

Further, since the yoke is formed by laminating thin sheets of magnetic material, the yoke can be easily manufactured, and since the thin plate can be easily processed, small holes can be formed easily and the cost can be reduced. Can be achieved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall perspective view of an embodiment of the present invention, FIG. 2 is an exploded perspective view of a main portion of FIG. 1, and FIG. 3 is an explanatory view of a method of fixing a deflecting prism. Information is recorded optically. The carriage base 1 on which an optical head (not shown) for reproduction is mounted has an objective lens for a light beam emitted from a light source (not shown).
A deflection prism 2 for deflecting in the direction (not shown) is bonded. Here, the deflection prism adhesion surface 3 of the carriage base 1 is formed so that the lower surface of the deflection prism 2 excluding the edge portion 2a of the deflection prism 2 contacts as shown in FIG. When adhering, the deflecting prism 2 is pressed against the adhering surface 3 of the deflecting prism, whereby the angles of the deflecting prism 2 around the x-axis and the y-axis in the figure and the position in the z-axis direction are determined. Also, the angle around the z-axis, the x-axis direction, y
The axial position is determined by using a jig 4 having a zy plane and a zx plane as shown. After the deflection prism 2 is bonded to the deflection prism bonding surface 3 by using a UV curable adhesive (not shown) with the position and angle of the deflection prism 2 determined by the deflection prism bonding surface 3 and the jig 4, The jig 4 is removed.

By adopting the above-mentioned bonding method, the following effects can be obtained. First, of the surfaces of the deflection prism 2, only one surface is in contact with the carriage base 1. Therefore, even if the carriage base 1 is distorted or warped due to a temperature change or the like after adhesion, The influence is less likely to be transmitted to the deflecting prism 2, and therefore, the position and the angle of the deflecting prism 2 are less likely to change due to the warp or warp of the carriage base 1. Secondly, since the edge portion 2a of the deflecting prism 2 is weaker in strength than other portions, excluding this portion from the adhesive surface causes warping or the like on the deflecting prism adhesive surface 3 due to temperature change or the like. However, the deflection surface 2b of the deflection prism 2 is less likely to be distorted or warped.

FIG. 4 is a perspective view of a holding portion of the objective lens actuator, and a known objective lens actuator forming an optical head is installed in the central portion of the carriage base 1. An annular seat 5 is formed on which a spherical seat (not shown) for tilt adjustment comes into contact. Further, holes 7 and 8 through which three screws 6 for adjusting and holding the objective lens actuator are held are formed. Here, when adjusting the tilt of the objective lens actuator, one of the screws is the annular seat 5
Must be movable in the radial direction. Further, the objective lens actuator must prevent rotation of the objective lens about the optical axis so that the tracking direction does not tilt when adjusting the tilt. For this reason, two of the holes 7 and 8 are circular hollow holes 7, and one of them is an oval hole 8 having a width substantially equal to the screw outer diameter.

FIG. 5 is an explanatory view showing the installation relationship between the bearing and the shaft rail. As shown in FIG. 1, the carriage base 1 is provided with a bearing 11a for a pair of shaft rails 10a and 10b which are guide members. , 11b, and is movable in the radial direction of the optical disk (not shown). The bearings 11a and 11b are made up of two bearings each consisting of six bearings, as shown in FIG. 5, at two locations on one shaft rail 10a and at one central portion on the other shaft rail 10b. The five bearings 11a are fixed to the carriage base 1 by the following method.

That is, in each of the five bearings 11a, as shown in FIG. 6, the inner circumference of the inner ring 11a-1 is inserted into one end 12a of the bearing shaft 12, and the end surface of the inner ring 11a-1 has the end surface thereof. Flange part 13 provided on
Abutted against. The other end 12b of the bearing shaft 12 is inserted into an insertion hole 14 provided in the carriage base 1. Here, the outer diameter of the flange portion 13 is larger on the surface 13b contacting the carriage base 1 than on the surface 13a contacting the inner ring 11a-1 of the bearing 11a. This is because the surface 13a that abuts the inner ring 11a-1 of the bearing 11a comes into contact with the outer ring 11a-2 of the bearing 11a when the outer diameter is increased, which hinders the rotation of the bearing 11a, and the carriage base 1 side. This is because it is difficult to hold the inclination of the bearing shaft 12 with respect to the carriage base 1 small if the outer diameter of the surface 13b that comes into contact with is small.

The bearing shaft 12 and the bearing
Adhesion can be considered as a fixing method between the inner ring 11a-1 of 11a and the insertion hole 14 of the carriage base 1. However, in the case of adhesion, the bearing shaft 12 and the inner ring 11a-1 of the bearing 11a are fixed.
Since the fit of the insertion hole 14 of the carriage base 1 and the clearance fit must be a clearance fit, the inner ring 11a of the bearing 11a
-1 and the coaxiality between the insertion hole 14 of the carriage base 1 become large. For this reason, the fit between the bearing shaft 12 and the inner ring 11a-1 of the bearing 11a and the insertion hole 14 of the carriage base 1 should be fixed by press fitting as an interference fit with the inner ring 11a-1 of the bearing 11a.
The coaxiality between the insertion holes 14 of the carriage base 1 can be reduced.

Here, four of the five bearing shafts 12 are press-fitted in a direction from the outside to the inside of the carriage base 1, whereas only one bearing shaft 12 goes from the inside to the outside of the carriage base 1. Pressed in the direction. This is because, by arranging in this way, three of the five bearing shafts 12 have the same press-fitting direction, and the remaining two bearing shafts 12 have the same press-fitting direction. This is because the press-fitting direction is only two, and the press-fitting work only needs to be performed twice, which improves the assembling property. Further, as another reason, when the bearing shaft 12 which is press-fitted only in the direction from the inner side to the outer side of the carriage base 1 is press-fitted from the outer side to the inner side of the carriage base 1 without changing the position of the bearing 11a, The insertion hole 14 must be provided inside the bearing 11a. When the carriage base 1 is attached to both ends of the carriage base 1 in the carriage movement direction like the other four bearings 11a, the insertion holes 14 are formed in the carriage base 1.
Although it does not interfere with the objective lens actuator mounted on the carriage 1, since this one bearing 11a is located at the approximate center of the carriage base 1 in the carriage movement direction, the wall surface for forming the insertion hole 14 serves as the objective lens actuator. This is to avoid the problem of interference.

Next, a method of mounting the remaining one bearing 11b of the six bearings to the carriage base 1 will be described below. As shown in FIG. 2, the bearing 11b is fixed to the carriage base 1 via a leaf spring 20 which is a pressing means. This is because by biasing the bearing 11b toward the shaft rail 10b by the leaf spring 20, the entire carriage base 1 is biased against the shaft rail 10a with which the four bearings abut, and the carriage is subjected to disturbance, cushioning, etc. This is to prevent the object from moving or rotating in a direction other than the original moving direction.

Here, since the leaf spring 20 has a shape extending in the carriage movement direction, when the spring portion is bent at a slight angle with respect to the mounting portion like a normal leaf spring, Since the carriage base 1 forms the plate spring fixing portion, the carriage base 1 becomes large in the carriage movement direction. Therefore, in the present embodiment, the leaf spring 20 is formed in a state where the spring portion 20a is bent at a substantially right angle with respect to the mounting portion 20b, and the leaf spring fixing portion 1 is provided on the surface of the carriage base 1 perpendicular to the carriage movement direction.
forming a. Here, when the spring portion 20a and the mounting portion 20b are formed substantially at right angles, if the rigidity of the mounting portion 20b is weak, the spring portion 20a is likely to be twisted in an unnecessary direction. It is fixed by a screw n1 in a state of being sandwiched between the leaf spring fixing portion 1a of the base 1 and the holding plate 21.

Next, another feature of the leaf spring 20 will be described. It is necessary to position the objective lens on the disk recording surface during focusing and tracking pull-in of the objective lens, and a detection photointerrupter 22 which is an optical means for holding the carriage is installed. It is necessary to attach a light blocking plate to the carriage for blocking the detection optical path. Therefore, in the leaf spring 20, the light shielding plate portion 20c is formed by further bending the mounting portion 20b at a right angle. Therefore, since it is not necessary to newly provide a light shielding plate, the number of parts is reduced, and since it is not necessary to form the light shielding plate fixing portion on the carriage base 1, the shape is simplified and the cost can be reduced.

Next, a method of attaching the pair of coils 25 to the carriage base 1 will be described. As shown in FIGS. 1 and 2, the coil 25 is a bobbinless coil in which a wire is wound in an air-core state and impregnated with an epoxy resin or the like to increase rigidity, and is a coil mounting plate formed by a metal plate such as aluminum.
It is fixed to the 26 with an adhesive such as a highly rigid epoxy resin. The coil mounting plate 26 is fixed to the carriage base 1 with screws 27. The coil 25 is not directly adhered to the carriage base 1, but is fixed by a screw 27 via a coil mounting plate 26. The deflection prism 2 and the bearing 11 are attached to the carriage base 1.
Since relatively expensive parts such as a and 11b are fixed, when the coil 25 is directly adhered and disconnection occurs due to some accident, the deflection prism 2, the bearings 11a and 11b, etc. are fixed to the carriage base 1. This is to prevent damage caused by discarding the whole.

A carriage lock pin 28 is fixed to the coil mounting plate 26. This is to fix the carriage so that it will not move when the optical disk drive is not in operation.
(Not shown) is formed so as to fit with the carriage lock pin 28. In this embodiment, the carriage lock pin 28 is formed of a metal plate different from the coil mounting plate 26, but it may be formed by bending a single metal plate integrally with the coil mounting plate 26.

Further, the coil mounting plate 26 of the carriage base 1
As shown in FIG. 2, since the protrusion 1b is formed in the fixed portion, there is a gap between the coil mounting plate 26 and the wall surface of the carriage base 1. Where this coil mounting plate
A flexible cable 30 for supplying power to the seek coil 25 and the objective lens actuator is attached between the carriage 26 and the carriage base 1. Therefore, one surface of the carriage base 1 can be shared as a mounting surface for the two parts of the coil mounting plate 26 and the flexible cable 30, so that the space of the carriage case 1 can be saved and the shape thereof can be simplified. ..

Although the structure of the carriage has been described above, in the present embodiment, the carriage base 1 is made of resin, which is conventionally made of metal such as aluminum die cast. As a result, the carriage base 1 is significantly reduced in weight, and the weight of the movable portion of the carriage is reduced.
The seek time can be shortened. In addition, when the resin is used to lower the rigidity than before and causes resonance or the like, it is preferable to use a resin containing a carbon fiber filler. Further, when the molded product is made of resin, the parts such as the bearing shaft 12 and the leaf spring 20 can be insert-molded to greatly improve the assembling property.

As shown in FIG. 1, the carriage constructed as described above has two shaft rails on which the permanent magnet 31 and a magnetic circuit formed by a yoke, which will be described later, and the bearings 11a and 11b abut. It is attached to the drive chassis 32 that is the base in a state of being combined with 10a and 10b.

The structure of the magnetic circuit and the method of mounting it on the drive chassis 32 will be described below. First, the magnetic circuit is formed of a permanent magnet 31 and two yokes of a back yoke 33 and a front yoke 34. The permanent magnet 31 is fixed to the back yoke 33, and the front yoke 34 is a coil of the carriage base 1. The linear motor is formed by being coupled to the back yoke 33 while penetrating the air-core portion of 25. The linear motors are provided on both sides of the carriage base 1 and drive the carriage in the disk radial direction. The back yoke 33 and the front yoke 34 are formed by punching and stacking thin metal plates such as a thin silicon steel plate which is a magnetic material. Therefore, when the coil 25 is energized, the generation of eddy current in the yoke is reduced, and a linear motor with small loss becomes possible. Further, since the yoke is manufactured by punching a sheet metal, the cost is significantly reduced as compared with the case where the yoke is manufactured by cutting or casting like a general yoke. When the yoke is manufactured by punching a sheet metal, burrs are likely to occur. Therefore, when the entire lower surface of the yoke is fixed by abutting against the drive chassis 32, the yoke may be attached in an inclined state.

In addition, since the back yoke 33 and the permanent magnet 31 are generally at the same height in the structure of the linear motor, if the two are fixed by adhesion or the like, the permanent magnet 31 is fixed due to variations in accuracy. May protrude from the bottom surface of the. Therefore, if the entire lower surface of the yoke is fixed by abutting against the drive chassis 32, it may be mounted in an inclined state.To prevent this, the permanent magnet 31 should be smaller than the back yoke 33 in height. Therefore, the thrust of the linear motor is reduced.
On the other hand, as shown in FIG. 1, the lower surface of each back yoke 33 is fixed by abutting it on the three lands (only one linear motor side is shown in the figure) 35a and 35b provided on the drive chassis 32. , The land portions 35a and 35b are connected to the back yoke 33.
The above problem can be solved by making the size and the shape of the lower surface of the abutting edge portion where the burr is not contacted.

Next, the positioning of the back yoke 33 formed by the three lands 35a and 35b within the mounting plane is performed by the two positioning pins 36 provided on the drive chassis 32.
By The back yoke 33 is formed with a positioning hole 33a having a diameter substantially equal to the outer diameter of the positioning pin 36 and an oval positioning elongated hole 33b having a width substantially equal to the outer diameter, and the hole 33a and the elongated hole 33b. Are fitted to the positioning pins 36 and positioned. Back yoke positioned as above
33 is fixed by one screw 37 to the screw hole formed in one land portion 35b. In the fixing, the screw 37 is screwed into the drive chassis 32 while penetrating through the magnetic circuit in a substantially intermediate position in the carriage movement direction, so that the screw 37 is provided in a portion where the magnetic flux is the smallest in the magnetic circuit. Can be suppressed. Generally, the back yoke is positioned and fixed to the drive chassis by two screws, respectively. By adopting the above positioning and fixing method, the number of screws is reduced, so that the cost is reduced and the workability is improved. To do.

Next, a method of fixing the shaft rails 10a and 10b to the drive chassis 32 will be described. As shown in FIG. 1, the drive chassis 32, which is the base body, has a shaft rail positioning portion for positioning the shaft rails 10a and 10b in two directions perpendicular to the carriage movement direction (only one end side of the shaft rail is shown in the figure. 40) are provided at positions corresponding to the vicinity of both ends of the two shaft rails 10a and 10b, respectively. The shaft rails 10a and 10b are positioned by the shaft rail positioning portion 40, and are pressed against the shaft rail positioning portion 40 by the shaft rail fixing spring 41. Shaft rail fixing spring
One 41 is formed so as to press the ends of the two shaft rails 10a and 10b.
Press both ends of. Both shaft rail fixing springs 41 have the same shape. The tip of the shaft rail pressing portion of the shaft rail fixing spring 41 is bent at a substantially right angle to form a flat surface 41a that is substantially vertical to the carriage moving direction. The flat surface 41a causes the shaft rails 10a and 10b to move in the carriage moving direction due to an impact or the like. It prevents it from slipping.

Further, since the shaft rail fixing spring 41 is attached to the drive chassis 32 by the two screws 42, it does not rotate within the plane in which the shaft rail fixing spring 41 is attached. By the way, the width of the shaft rail pressing portion 41b of the shaft rail fixing spring 41 is smaller than the width of the screw fastening portion 41c. This is because the screw fastening portion 41c of the shaft rail fixing spring 41 forms a hole through which the screw 42 penetrates, and therefore it is necessary to widen the width to some extent, while the shaft rail pressing portion 41b is widened accordingly. This is because it is necessary to lengthen the shaft rails 10a and 10b, which causes a layout problem.

As described above, the two shaft rails 10
When the ends of a and 10b are pressed by one shaft rail fixing spring 41, especially at the inner peripheral side end of the shaft rails 10a and 10b on the optical disk side, the shaft rail fixing spring 41 and a known spindle motor for rotating the optical disk are used. May interfere with the layout. Therefore, Fig. 7 (a)
In this embodiment, as shown in the plan view of the spindle motor portion of FIG. 7 and the front view of the spindle motor of FIG. 7B, the rotor portion 46 portion of the spindle motor 45 and the screw fastening portion of the shaft rail fixing spring 41 are vertically moved. It is laid out so that it overlaps. Generally, in a spindle motor 45, a rotor portion 46 including a turntable on which an optical disc is placed is rotatably supported by a bearing with respect to a spindle base 47, and the spindle base 47 is driven by three screws 48 in a drive chassis. It is fixed at 32. A printed circuit board 49 is fixed on the upper surface of the spindle base 47,
Coils, Hall elements, etc. are arranged and wired on the printed circuit board 49. For this reason, it is difficult to make the printed board 49 smaller than the outer diameter of the rotor portion 46, but it is not a problem to cut a part of the spindle base 47 smaller than the outer diameter of the rotor portion 46. Therefore, in this embodiment, a part of the spindle base 47 is cut out to be smaller than the outer diameter of the rotor portion 46, and the screwed portion of the shaft rail fixing spring 41 is arranged in the space, so that the shaft rail fixing spring 41 and the spindle motor are Prevents 45 from interfering.

Next, when the carriage moves in the disk radial direction, it becomes uncontrollable due to some influence, and when it receives an overcurrent and collides with another member within the limit of the carriage moving range, it is placed on the carriage or the carriage. A damper 50 that absorbs shock so as not to break the objective lens actuator will be described. As shown in FIG. 1, the damper 50
Is fixed to the side surface of the shaft rail positioning portion 40 provided on the drive chassis 32. The damper 50 is formed of a viscoelastic member such as rubber and collides with the wall surface of the carriage base 1 to relieve the shock when the carriage runs away.

The positional relationship between the damper 50 and the bearings 11a and 11b for supporting the carriage will be described with reference to the front view of the damper portion of FIG. 8A and the side view of the damper portion of FIG. 8B. The bearing 11a and the damper 50 are arranged at positions where they do not overlap each other in a plane perpendicular to the central axis of the shaft rail 10a. Therefore, when the carriage is at the limit of the movement range, the damper 50 can be arranged in the same row as the bearing 11a in the carriage movement direction, and can be arranged so as to contact the one side surface 1c of the carriage base 1. Become. Since it is necessary for the damper 50 to absorb a large impact, it is necessary to secure a sufficient thickness in the carriage movement direction. However, by arranging the dampers in the above positional relationship, the damper 50 having a sufficient thickness can be laid out efficiently in a space-efficient manner.

[0039]

As described above, according to the present invention,
The magnetic circuit body that constitutes the linear motor is positionally regulated by pins and screwed, so it has excellent shock resistance and reliability, and the magnetic circuit body can be fixed with a single screw. It is possible to reduce the number of screws, improve workability and reduce costs, and since the screw can be installed at a position where magnetic flux loss in the magnetic circuit can be minimized, space efficiency can be improved, Further, since the yoke that constitutes the magnetic circuit body is formed by laminating thin sheets of magnetic material, it is easy to manufacture and the cost can be reduced. Therefore, the linear motor can be easily and surely fixed. Therefore, it is possible to provide an information recording / reproducing apparatus capable of effectively generating magnetic flux and reducing the cost.

[Brief description of drawings]

FIG. 1 is an overall perspective view of an embodiment of a carriage support mechanism of an information recording / reproducing apparatus of the present invention.

FIG. 2 is an exploded perspective view of a main part of FIG.

FIG. 3 is an explanatory diagram of a method of fixing a deflection prism.

FIG. 4 is a perspective view of a holding portion of an objective lens actuator.

FIG. 5 is an explanatory view showing an installation relationship between a bearing and a shaft rail.

FIG. 6 is an exploded perspective view of a supporting portion of a bearing.

FIG. 7 is a configuration diagram showing an installed state of a spindle motor and a shaft rail fixing spring.

FIG. 8 is a configuration diagram showing an installed state of a damper and a bearing.

[Explanation of symbols]

1 ... Carriage base (carriage), 25 ... Coil,
31 ... Permanent magnet, 32 ... Drive chassis, 33 ... Back yoke, 34 ... Front yoke, 33a ... Hole, 33b ... Long hole, 35a, 35b ... Land portion, 36 ... Positioning pin, 37
…screw.

Front page continuation (72) Inventor Takehide Ohno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A coil, which movably supports an optical head for optically recording / reproducing information, is fixed to both sides of the carriage, and a pair of magnetic circuit bodies fixed to a base. In the information recording / reproducing apparatus in which the carriage is moved by the linear motor configured by, at least 2 provided in the magnetic circuit body.
Information recording / reproducing, characterized in that the hole at a certain position and at least two pins provided on the base body are fitted to regulate the position, and the magnetic circuit body is fixed to the base body by a screw in the state where the position is regulated. apparatus. 2. The information recording / reproducing apparatus according to claim 1, wherein the number of the screws for fixing the magnetic circuit body to the base is one. 3. The information recording / reproducing apparatus according to claim 2, wherein the screw penetrates a substantially intermediate position of the magnetic circuit body in the carriage movement direction and is screwed to the base body. 4. The yoke which constitutes the magnetic circuit body is formed by laminating thin sheets of magnetic material.
Information recording / reproducing device.