Multi-actuator system using single magnetic circuit

(24) Running day (62) Stamansbkans number (96) International filing day (86) Filing date for European patent application (30)

7811379-2, H 02 K 33/18 (11) Publication number 40h 44 I

Application received as

S3 Swedish patent application

D completed international patent application with number

Q converted European patenian application with number

77-11-07 US 849134

KB 3-A4 according to SIS 6130 13 al if ι38 0? Ιομαα (71) Applicant: International Business Machines Corporation Armonk NY US (72) Inventor: TR Patel San Jose Cal (74) 0mbud: Gasslander S (54) Name: Electromagnetic magnet headset arrangement comprising a plurality of independent circular flow gaps with a common permanent magnet (57) Summary:

Electromagnetic adjusting device having a plurality of independently movable apoles moving in circular flow gaps, which are magnetized in parallel from a single penane antenna. The adjusting device comprises, in addition to the peroanent magnet, which is attached to the *ⁿ plate down low reluctance », a plurality of pole cores and a low reluctance casing, which has a portion designed as a common pole plate and provided with a number of apertures corresponding to the pole cores. The casing runs from the surface contour of the pole plate to the plate and thus completely encloses the pole cores, coils and magnet. Each pole core has a rectangular base portion which abuts the permanent magnet and a cylindrical portion which extends into the pole plate and thus defines circular air gaps. Adjacent pole cores abut each other along one side to balance the magnetization of the pole cores. The longitudinal axis of the coil is smaller than the axial length of the circular air gap to allow the coil to remain within the gap at all times, thereby neutralizing any influence between the separate parallel flow paths emanating from the pen-magnet.

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(56) Publications cited:

US 3,487,241 (310-13)

US 3,924,146 (310-36)

7811379-2

The present invention relates generally to magnetic head arrangements and more particularly to those arrangements which contain special tone controlled setting means.

These adjusting means comprise a coil, so-called tone or guide coil, and the field of application in question determines the design of both the coil as well as the magnetic circuit and the manner in which the movement of the coil is transmitted to the part to be moved or adjusted. An application where such adjusting means have been used extensively is in connection with magnetic disk memories for aligning the magnetic head there relative to a selected concentric groove on a continuously moving magnetic disk. Here, in principle, the setting means must work in two modes, namely a track access mode and a track poverty. The track access mode is characterized by the coil being rapidly moved from one track position to another, which movement includes rapid acceleration and deceleration processes over time intervals that can be counted in milliseconds. The tracker mode is characterized by the coil moving only very small distances of the order of fractions of millimeters to follow the center line of a recorded track. The response time of the coil and the main carrier relative to signals generated by the corrective servo system becomes extremely significant as well as any conceivable external factor that could change the flow in the air gap or current in the coil.

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To increase the ability to record data with higher densities and the ability to align a magnetic head more precisely so that the track density can be increased has made it possible to create more compact disk memories by reducing both the number of discs in the pack and the use of smaller discs. 'Jetta has automatically resulted in a desire to have more compact main arrangements. The advantage of using more than one head per disk memory unit is obvious from an efficiency standpoint, provided it does not increase the cost of storing data or the cost of packing the disk memory. When a disk memory is provided with a plurality of heads, it is desirable to place the heads with the coil shafts in a plane so that, when the heads are mounted in the ski package, it becomes possible to remove the main unit and the coils themselves without also removing the relatively heavier magnetic structure. , see, for example, U.S. Patent 4.03ä, 411. The positioning of the coil shafts in the same plane allows the coils to be permanently mounted to the main carrier unit and the main disk unit so that a removal of the disk unit in a direction parallel to the plane of the coil shafts is facilitated.

By feeding each cylindrical pole core with the flow from a common permanent magnet into a device where the base of each pole core is in contact with both the magnet and a neighboring pole core, a more uniform magnetomotor force is obtained in each of the coils. It has been found, according to the present invention, that the ability of one coil to operate in a tracking mode is not counteracted by the other coil operating in track access mode, even if they share a common magnetic flux source.

The present invention relates to an adjusting means which has a single all individually magnetizable movable coils for moving separate main arm arrangements, wherein a common permanent magnet and pole cores are provided to allow all coils to be removed together with the disk pack. ^!4 has found that by using a common source of magnetization, i. a common permanent magnet, the size and position of the various individual pole cores, which define the inner boundary of the circular flow gap relative to the pole end, will result in a compact construction which allows the coils to be placed relatively tightly together with the coil shafts in a flat zone also containing the shaft for the disk pack. It has also been found that by placing adjacent pole cores so that adjacent surfaces have contact with each other, variations in the magnetic flux from the common perimeter magnet will be effectively balanced out in the pole cores.

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7811379

It is therefore an object of the present invention to provide a compact magnetic head arrangement with a plurality of coils, which are movable independently of one another in circular air gaps, the shafts of which lie in the same plane being fed with a uniform magnetic flow from a single permanent magnet.

It is a further object of the present invention to provide any magnetic head arrangement with a plurality of coils which are individually movable in separate flow gaps which are fed from a common permanent magnet, the movement of a coil in its circular gap in response to the magnetization of the coil does not adversely affect the function of another coil.

The above and other objects, features and advantages of the invention, as defined in the claims below, will become apparent from the following, more detailed description of a preferred embodiment illustrated in the accompanying drawings.

Fig. 1 is a perspective view of the improved magnetic head assembly of the present invention.

FIG. 2 is an embodiment of the present invention of FIG.

for use on a disk memory.

Fig. 3 shows another embodiment of the present invention where three coils are used.

Fig. 4 shows the device of Fig. 3 from above, illustrating in particular the radial notches in the pole pieces.

As can be seen from Fig. 2, the adjusting device comprises a plurality of individually movable coils 10a and 10b as well as the stationary arrangement 11, which has the task of defining the circular flow channels 12a and 12b in which the coils 1^r)a and 10b are located.

the leg stationary portion 11 comprises a rear plate 15, a permanent magnet 16, a plurality of pole cores 17a and 17b, and a housing 18, which is provided on one side with a plurality of circular openings 19a and 19b. Each opening 19 together with one of the pole cores 17 defines one of the circular flow gaps 12 in which the coil 10 is displaced. The remaining portion of housing 18 extends to the rear plate 15 and completely encloses the pole cores 17 and the permanent magnet 16.

As can be seen in Fig. 1, permanent magnet 16 is of rectangular shape and with its one surface 20 is attached to the rear plate 15 in a suitable manner. The opposite side 21 of the magnet 16 is arranged to abut against the pole cores 17, the axis of the cylindrical portion of the pole core perpendicular to the surface 20.

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The polar cores 1? apparently having a rectangular b aspect in 26 and a cylindrical portion 27. The base portion 26 is attached to the permanent magnet to provide a low reluctance transition between the permanent magnet and the pole core. The height of the base portion is sufficient to create a side surface 29 for each pole core, which side surface is in contact with the corresponding side surface of the adjacent pole core.

Theoretically, the magnetization of each pole is equal. In practice, however, some variation will occur in the magnetization of the base portion of each pole due to certain practical reasons. These variations can amount to plus / minus 10 ?. In principle, it is possible to obtain permanent magnetic materials with better tolerances, but the costs increase sharply with reduced tolerances. In addition, to simplify the manufacture of the magnetic block, it is not permanently magnetized until the entire structure has been assembled including the housing. The whole unit was then subjected to a very strong and theoretically uniform magnetic field, which charges the magnetic material.

In practice, neither the magnetic material nor the magnetizing field are uniform. Likewise, in practice, the reluctance at one contact point between a base and the magnetic surface is different reluctance at another contact point. By providing contact via a side surface with adjacent pole core, a magnetic shunt circuit is provided between the two parallel magnetic circuits. Such an arrangement ensures a greater uniformity of flow in the circular gap, as the flow rate in the cylindrical portion of the pole core near each circular gap is balanced. The reluctance of the contact surface formed between the side surfaces is considerably lower than the reluctance of any of the circular gaps.

The upper portion 27 of the pole core 17 is of cylindrical configuration and defines the inner diameter of the circular flow gap 12. In addition, the axis of this cylindrical portion 27 is generally perpendicular to the flat surface of the rectangular base 26.

As can be seen from Fig. 1, the cylindrical portion 27 is provided with three axially projecting grooves, which are displaced between one another 120 °. The purpose of these, grooves in the pole part 27 and the manner in which the coil 10 is attached to the magnetic head carrier, will be explained in detail later in connection with Fig. 2. Briefly, the coil 10 is attached to a ring 48 which is provided with three radially projecting disc members 49 which cooperate with the three axially arranged grooves 30. It should be noted that although only one coil with POOR QUALITY

7811379-2 ring shown in Fig. 1 there is in practice a coil with ring for each pole core.

The housing 18 has a portion 40 which forms the front pole piece of the adjusting device and is provided with a plurality of circular openings 19a and 19b, each defining the outer diameter of a circular flow gap 12. The remaining portion of the housing forms a low reluctance magnetic path. to the rear plate 15.

The thickness of this front pole piece 40 is sufficient to define together with one of the cylindrical pole members 27 a circular gap 12 having an axial length substantially longer than the axial length of the coil 10 so that the coil is always located within the gap 12 even at their end positions.

Fig. 2 illustrates an application using the adjusting device of Fig. 1 to set the magnetic heads at a magnetic disk memory. The disk memory is shown in principle in Figure 2 and comprises a plurality of disks 60 mounted on a rotatable shaft 61. The shaft 61 is provided with suitable storage devices 62, 63, which are secured to the stationary parts 64 and 65. A pair of carrier devices 66 and 67, comprising a plurality of heads with arms 68, are mounted on the fixed support parts 64, 65. be able to form part of a separable disk unit which is fully enclosed as close to that part of the main carrier mechanism which cooperates with the stationary part of the adjusting device.

Each magnetic head carrier is shown provided with a ring 48 to which the coil 12 is connected in the manner described in connection with Fig. 1. A suitable magnetization of the coil 12 from the adjusting servo system, shown in block form at 70, causes movement of the main carrier unit radially relative to the longitudinal axis of the shaft 61. It can be seen that the shown construction of the stationary part of the multi-coil adjusting device, in which the axes of the circular air gaps are in the same plane, allows the coil part of the adjusting device to be permanently coupled to the part which can be removed, since the whole the unit can be removed in a direction that is in the same plane as the coil shafts.

Since it is desirable to influence the magnetic head carrier unit via its center of gravity to avoid negative effects in the form of mechanical resonance, which may be caused by a variety of access operations, it is important to be able to vary the distance between the centers of gravity of the pole cores. The space between the disks in the axial direction on the shaft determines the distance ms lian the main carrier arm units on

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7811379-2 the adjusting unit, which in turn affects the design of this unit and thus becomes determinant of its center of gravity. To make the disc memory more compact, the balance between these spaces becomes important and interdependent.

The distance between the centers of gravity of the pole cores determines the amount of magnetizable material present in the area between the circular openings 10a and 19b. Since this area is particularly sensitive to the saturation and mutual influence of the poles, there is a tendency for the flow at this point in the gap to be relative to other parts of the gap. On this occurring, the existing part of the coil will react differently to other parts, resulting in a torque affecting the coil, the carrier and thus also the magnetic heads. This torque occurs along a line perpendicular to the axis of the coil and in the radial plane containing the area of ​​varying flux density. It has been found that the effect on the coil that results from the saturation tendency one within the area between the openings can be niniorated by placing one of the axial notches in the pole core adjacent to this area? ..

As the motion of the coil is transmitted to a portion to be adjusted by means of an arrangement similar to that shown in Figs. the movements of the coil as a result of the area between the circular openings tending to be saturated. As shown in FIG. 1 are the grooves in adjacent pole cores so located that they are adjacent to each other in this area and the two remaining radial grooves in each pole core are so located that the effect on the coil is balanced.

The result of such a design allows the center of gravity distance between the pole cores to be reduced, which automatically means greater flexibility in designing the distances between the disks, the location of the main carrier arm unit on the carrier and the design of the carrier itself.

Fig. 3 shows a setting device using multiple coils. The arrangement is similar to the two-coil arrangement shown in Fig. 1 except that there is a further pole core and the placement of the notches in the pole cores is different. As can be seen more clearly in Fig. H, the middle pole core 100 is provided with two notches 101 and 102 arranged diametrically against each other and in a plane containing the shafts for all circular pole parts. As can be seen, two additional notches 103, 10h can be used when the ring of the support unit, which is connected to the coil, is provided with four uniformly distributed ring elements.

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The operation of the device shown in Fig. 4 is identical to that described in connection with Figs. 1-3