# US 4,396,966 A · Low mass actuator system for magnetic recording disks with half strength end poles

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- Number: US 4,396,966 A
- Document ID: US4396966A
- Status: Granted
- Kind: A
- Application number: 06/221,866
- Filed: 1980-12-31
- Granted: 1983-08-02
- Earliest claimed: 1980-12-31
- Assignees: International Business Machines Corporation
- Inventors: Robert A. Scranton; David A. Thompson; Thomas K. Worthington
- Web page: https://patentgrep.com/patent/US4396966A

## CPC

- H02K 41/031: {of the permanent magnet type}
- G11B 5/54: with provision for moving the head into or out of its operative position or across tracks
- G11B 5/5521: {across disk tracks (spiral track following G11B5/596)}
- H02K: DYNAMO-ELECTRIC MACHINES (dynamo-electric relays H01H53/00; conversion of DC or AC input power into surge output power {H03K3/53})
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

A linear motor adapted for driving a magnetic recording head reciprocably across the surface of a magnetic recording disk in a disk file has its stator located between the disks. The stator includes parallel magnetic yokes composed of plates extending parallel to the disks. At least one of the plates carries an array of regularly spaced and alternating magnetic pole elements, rigidly secured to one yoke with a gap extending between the yokes including the alternating poles providing a space within which the armature reciprocates, from one magnetic polarity to the opposite a plurality of times per reciprocation of the armature. End poles are provided at each end of the array, which are matched to collect the return flux from the adjacent distal pole to reduce fringing flux which emanates towards the disks and the recording heads.

## Claims

### Claim 1

In a magnetic recording disk file including at least one magnetic recording disk, and a magnetic recording head, said head being driven reciprocably generally parallel to said disk from its center to its periphery by a linear actuator having a stator, said stator being located adjacent to the surface of a said disk in said disk file, said stator being constructed of a pair of magnetic yokes comprising parallel plates extending parallel to said disk, with at least one of said yokes carrying an array of regularly spaced and alternating polarity magnetic pole elements including end poles at each end of said stator, the improvement comprising provision at the ends of said array of alternating equal magnetic strength pole elements of said flux gathering end poles composed of permanent magnetic material, said end poles having a flux producing capacity and polarity matched with about half the magnetic capacity of said alternating poles adjacent to said end poles, said end poles serving to collect the return flux from said alternating poles adjacent to said end poles of said stator, whereby fringing magnetic fields extending into the space adjacent to said stator in which said disk files are located is minimized.

### Claim 2 (depends on 1)

A disk file in accordance with claim 1, wherein said end poles produce substantially half the quantity of flux of said alternating equal poles.

### Claim 3 (depends on 1)

A disk file in accordance with claim 1 wherein said end poles are matched to collect the return flux from the adjacent alternating equal pole, whereby fringing flux which otherwise emanates towards the disk and recording head is reduced.

### Claim 4 (depends on 1)

A disk file in accordance with claim 1 wherein said stator is on the order of about 10 mm thick.

### Claim 5 (depends on 1)

A disk file in accordance with claim 1, wherein said actuator is adapted to be employed with a stack of at least two disks and said stator is thin enough to be located between a pair of said disks within said stack.

### Claim 6

In a linear actuator adapted for use with a magnetic recording disk file, said actuator having a stator, said stator being constructed of a pair of magnetic yokes comprising parallel plates, with at least one of said yokes carrying an array of regularly spaced and alternating polarity magnetic pole elements of substantially equal magnetic strength, plus, the improvement comprising provision at the ends of said array of alternating polarity equal magnetic strength pole elements of flux gathering end poles composed of permanent magnetic material, said end poles having a flux producing capacity matched with about half the magnetic capacity of poles adjacent to said end poles, said end poles serving to collect the return flux from said alternating poles adjacent to said end poles of said stator, whereby fringing magnetic fields extending into the space adjacent to said stator is minimized.

### Claim 7 (depends on 6)

A linear actuator in accordance with claim 6 wherein said stator is on the order of about 10 mm thick.

### Claim 8 (depends on 5, 6)

A disk file in accordance with claim 5 or 6 wherein said end poles produce half the quantity of flux of said alternating poles.

### Claim 9 (depends on 5, 6)

A linear actuator in accordance with claim 5 or 6, wherein said end poles are matched to collect the return flux from the adjacent alternating pole, whereby fringing flux which otherwise emanates outside of said stator is reduced.