FR2534054A1 - UNIT OF MAGNETIC DISCS - Google Patents

Abstract

THE INVENTION RELATES TO A MAGNETIC DISCS UNIT IN WHICH A CLOSED CHAIN SLAVE TRANSMITS ERROR SIGNALS TO A ROTATING ACTUATOR ACCORDING TO THE DEVIATIONS EXISTING BETWEEN A SERVING HEAD AND A SERVING TRACK CARRIED BY A ROTATING MAGNETIC DISK. THE ENDING HEAD 14 AND THE COIL 24 OF THE ACTUATOR ARE MOUNTED IMMEDIATELY TO ONE ANOTHER ON AN END 50 OF A BASE ARM 48 SWIVEL TO ITS OTHER END 64, IN ORDER TO MINIMIZE THE MECHANICAL COUPLING AND THE RESULTING MECHANICAL RESONANCES IN CLOSED CHAIN SLAPPING. FIELD OF APPLICATION: MAGNETIC DISC UNITS, ESPECIALLY OF THE WINCHESTER TYPE.

Description

The invention relates to disk drives

  magnetic systems, and more particularly

  magnetic devices of the type in which closed-loop servocontrol is used to maintain a slave head in alignment on a desired slave track during a

  operating mode tracking.

  Magnetic disk drives have grown considerably with the rapid expansion of technology in this field. Such units typically use one or more magnetic heads designed

  to float on a cushion of air compared to over-

  faces of one or more rotating magnetic disks.

  The problem posed by the mounting of the magnetic heads so that they can be positioned quickly and accurately, and then held in different selected positions near the surfaces of the magnetic disks,

  has been the subject of two main attempts at solution.

  One of these attempts is to use an actuator

  while the other uses a rotary actuator

ing.

  A typical linear actuator uses a carriage that radially accesses the different tracks of the magnetic disks. The carriage, which supports the magnetic heads at one end and a voice coil at the other end, can move on precisely rectified cylindrical paths and it is usually consists of a complex molded piece optimized to have

  a certain stiffness and a low mass

  The carriage is mainly subjected to extension and compression forces. The resonant frequency of the carriage and thus the width of the servo band

  can be relatively high, which reduces the sensitivity

  However, the linear actuator is not suitable for

  compact configurations, and pre-machining

  The decision required for the manufacture of the carriage and its guides makes this method of positioning the magnetic heads expensive. Most rotating actuators use a pivoting arm which carries the magnetic heads at one end and a coil at the other end. Such devices are described in an article entitled JS Heath's Design of a Swinging Arm Actuator for a Disk File. pages 389-397 of the July 1976 issue of IBM Journal of Research and Development Such actuators reduce the size of training bootcases

  and they are usually less expensive than action-

  Linear bearings, although a precision bearing must be used for the pivot The arm is subjected to bending forces, which decreases the rigidity of the device, its

  resonant frequencies and the width of his band of asser-

  The coil should usually be placed

  proximity to the pivot due to dimensional limitations.

  This results in a relatively low leverage effect,

  which requires a relatively big coil.

  Magnetic disk drives are gener-

  designed to work in two different modes of operation, the first being the search or positioning mode and the second being the tracking mode

  During search or positioning mode

  Alternatively, the linear or rotary actuator or other magnetic head mounting device is implemented to place a selected magnetic head on a desired one of a plurality of recorded tracks on the adjacent surface of the magnetic disk. or any other head positioning device is implemented to maintain the selected head in alignment with the desired track, resulting in a tracking mode of operation. During the search or positioning mode, unit behaves

  as a speed control device designed to posi-

  select the magnetic head chosen on the desired track,

  in the fastest and most efficient way possible.

  Bending, movement, or vibration of any mechanical linkage between the actuating mechanism and the magnetic heads may impair the speed with which the search

can be done.

  In the tracking mode, a closed-loop servo is generally used to allow the chosen magnetic head to follow a desired track.

  pendent is used with several different slave tracks.

  The magnetic signals picked up by the head are processed by the closed-loop servocontrol so that the latter produces an error signal corresponding to the deviations between the controlled head and the desired track. This error signal is applied to the signal. actuator to adjust the position of the slave head until it is

  fixed on the desired slave track.

  Such closed-loop servocontrol devices working in the tracking mode are second order control devices.

  such as inflection, movement or vibration

  both the mechanical coupling between the actuator and the head

  enslaved pose significant problems that can affect

  Seriously the ability of closed-loop servo to operate effectively during the tracking mode In the case of the rotary actuators described above, in which the actuator is connected to an end of an arm whose a central part comprises

  a pivot, the opposite end of which carries magnetic heads

  ticks, the arm constitutes a relatively large beam having a low resonance frequency This low

  resonance frequency of the beam, associated with the reso-

  hertzian bearings of the pivot bearings, tends to

  ler closed-chain servoing To compensate for this

  oscillation, the gain of the servo device is -

  usually set to a relatively low value This reduces the disturbing effects of arm resonance and pivot bearing resonances, but at the cost of

the effectiveness of the enslavement.

  It is therefore desirable to minimize the effects of mechanical coupling between the actuator and the slave head in the closed-loop servocontrol. This suggests a close coupling between the actuator and the slave head so that

  to minimize their mechanical coupling.

  It is known in the art to use a variety of

  its different arm configurations for mounting the magnetic heads in the immediate vicinity of the magnetic disks US Pat. No. 4,185,309 discloses an example of such an arrangement in which an elongated arm having a first end mounted so as to be pivotable, carries the magnetic head to an opposite second end, as well as a ribbon and spindle drive device. However, devices such as that described in the aforementioned patent do not use chain servo. closed and do not deal with the problems that arise when such a device is

  used to operate in tracking mode.

  It is therefore desirable to have a

  unit of magnetic disks in which a -asservisse-

  closed chain can be implemented in a relatively efficient manner, with a high gain, during the tracking mode.

  to minimize the effects of mechanical coupling between the

  neur and enslaved head in such units.

  The invention relates to a magnetic disk unit

  in which a rotating actuator is tightly coupled to the magnetic heads to minimize the effects of resonance and mechanical bending in the mechanical coupling between the actuator and the heads For this purpose, the actuator coil and the slave head are

  mounted one close to the other, at a first

  of an elongated arm whose opposite end is pivotally mounted so that the arm can rotate

  relative to one or more rotating magnetic disks.

  The tight coupling of the actuator coil with the slave head and the other magnetic heads, at the same

  end of the arm, significantly minimizes the mechanical coupling

  that between the actuator and the head The totality, practically

  the resonance of the arm and the effects of

  resonances of the pivot bearings is eliminated from the servo

  closed chain, which allows the device to

  operate with high gain and very effectively.

  In a preferred embodiment of a magnetic disk unit according to the invention, a plurality of magnetic disks are rotatably mounted on a common axis within a closed enclosure, of the Winchester type, an arm assembly and a rotating actuator comprising a coil being also mounted within the enclosure The arm assembly comprises an elongate base arm rotatably mounted about a first end thereof and carrying the coil and a head magnets mounted near each other at the opposite end of the arm A plurality of additional arms forming part of the arm assembly are mounted on top of the base arm so as to be stacked and spaced apart. others to rotate around a common axis with the base arm Magnetic read / write heads, mounted on opposite ends of the additional arms, close Immediate movement of the servo head and coil

  to opposite surfaces of the various magnetic disks.

  The rotating actuator comprises, in addition to the coil, a

  fixed device which interacts with the coil and which

  takes three different elongated magnetic elements extending approximately parallel to each other, spaced apart from each other between extreme portions

  magnetic opposites such as the coil surround the elem-

  centrally elongated, -between opposite permanent magnets

  mounted on the other two elongated elements

  Closed-loop system includes a position demodulator

  coupled to the servo head to produce a position signal representative of the position of the head relative to a desired servo track, a summing junction for combining the position signal with any external command to produce a signal of error, a compensator for damping the error signal to prevent oscillation, and a power amplifier for amplifying the signal

  error before it is applied to the reel.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which: FIG. 1 is a flowchart of a closed-loop servo device used in the magnetic disk unit according to FIG. 'invention; Figure 2 is a perspective view, partially cut away, of the magnetic disk unit according to the invention which uses the control of Figure 1; Figure 3 is a partial top view of the magnetic disk drive of Figure 2;

  FIG. 4 is a front view of the action

  rotating neurode used in the magnetic disk unit of Figure 2; FIG. 5 is an elevation of the arm assembly of the magnetic disk unit of FIG. 2,

  as well as the rotary actuator of FIG.

  partially cut; and FIG. 6 is a plan view of the base arm of the arm assembly shown in FIG. 5, as well as the coil forming part of the rotating actuator.

  of FIG. 4, and that of a magnetic servo head

ment.

  FIG. 1 represents a device 10 for

  Closed-chain service The slave device 10

  -sement of Figure 1 is of conventional design, except the presence of a mechanical coupling 12 which is optimized

  According to the invention the device 10 for servoing

  It comprises a magnetic head 14 which constitutes a head

  in the example described.

  tif 10 operates in tracking mode, the head 14 is placed on a desired servo track of a magnetic disk as a result of operation in

  search or positioning device 10 to assert-

  Its function is to maintain the head 14

  on the desired servo track during the

2534054-

  tracking mode The magnetic head 14 produces a signal indicating, inter alia, whether the head 14 follows the desired servo track or deviates from it This information is used by the device 10 to produce an error signal which corresponds to the amplitude of the gap between the head 14 and the desired servocontrol track The signal coming from the adjacent surface of the magnetic disk, which is picked up by the magnetic head 14, is transmitted to a position demodulator 16 This signal is of the dibit, tribit or the like format and is demodulated by the demodulator 16 to form a position signal representing the position of the magnetic head 14 with respect to the servo track

  The position signal is applied to a

  18 The summation junction 18 combines the position signal and the external control signal to produce an error signal SE. During the tracking mode, the signal of outside order is from

  zero value and, therefore, the junction 18 of

  tion transmits the position signal as a signal

of error to a compensator 20.

  The compensator 20, which comprises a filter

  low pass and several other filters, determines the

  study of the damping required to prevent the servo device 10 from oscillating The error signal as damped by the compensator 20 is amplified by a power amplifier 22 before being applied

  to an actuator coil 24 being part of an action-

  Turning 26 (shown in Figure 2) which will be described below The application of the error signal to the coil 24 acts on the rotary actuator 26 so that it repositions the magnetic head 14 so that the latter place in

  alignment on the desired servo track -

  Each unit of magnetic disks includes

  the magnetic coupling 12 representing the mechanical structure

  The mechanical coupling 12, as such, is part of the closed-loop servocontrol 10 and is responsible for the operation of the resonant vibrations.

  the resonances of the bearings and other variables presented

  In the case of rotary actuators of the prior art, described above, and in the case of the rotary actuators of the prior art, these effects have a direct effect on the behavior of the closed-loop servocontrol 10 because they are transmitted directly to the closed chain of the servocontrol 10. in which the actuator is placed at one end of an elongated arm having a central pivot point and whose end

  opposite door carries the magnetic head, the vibrations of

  In such devices, it is often necessary to reduce the gain of the closed-loop servocontrol, which is highly detrimental to the efficiency of the closed arm. of enslavement. According to the invention, the coil 24 of the actuator is closely coupled to the magnetic head

  14 being mounted on the same end of a posi-

  As a result, the mechanical coupling 12 between the coil 24 of the actuator and the magnetic head 14 consists of a very small portion of the positioning arm. having a resonance frequency of practically negligible resonance and no resonance

  As a result, the mechanical coupling

  that 12 constitutes a negligible part of the closed-loop servo The gain of the servo-control 10 can therefore be relatively high, which results in a high efficiency and excellent tracking possibilities

track.

  Figure 2 shows a disk unit 30

  magnetic devices according to the invention, which uses the servo

  The unit 30 is of the Winchester type having a substantially rectangular enclosure 32 in which a plurality of magnetic disks 34 are rotatably mounted,

  assembly 36 with arms and the rotary actuator 26 These ele-

  parts are hermetically sealed inside the enclosure 32 by a cover 38 which is shown partially broken away in FIG. 2 A rear part of the enclosure 32 comprises a plate 40 whose upper end has fins in order to favor the heat dissipation of the unit 30 As shown in FIG. 3 which is a top view of a portion of

  the unit shown in Figure 2, the magnetic disks

  The ticks 34 are mounted so as to be spaced apart

  and to be able to turn on a common axis.

  seems 36 arm is mounted so that it can turn

  on an axis 44 which is spaced from the common axis 42 of the dis-

  The arm assembly 36, which is of elongated configuration, carries a plurality of magnetic read / write heads 46 at an opposite end of this assembly. Among the magnetic read / write heads 46 are find the magnetic head 14 of Figure 1 which is mounted on a base arm 48 forming part of the assembly 36, and the coil 24 of the actuator The magnetic head 14, which assumes the function of a head of servo, is addressed to the underside of the lowest magnetic discs

  34 on which several servo tracks are recorded.

  Other magnetic heads 46 read /

  writing are arranged near the upper faces

  top and bottom of other magnetic disks 34.

  As can be seen in Figure 3, the

  coil 34 of the actuator is attached to an outer end

  50 of the base arm 48 by two opposing nuts 52 and 54 The rotational movement of the arm assembly 36 is limited by two opposing stops 56 and 58 made of elastomer,

  arranged on the paths of the nuts 52 and 54, respectively

  A filter 60, visible in FIGS. 2 and 3, is part of a circulation and filtration device.

  of air placed inside the unit 30.

  The arm assembly 36 includes a plurality of upper arms 62 which are stacked on top of the base arm 48 and which are connected thereto and to each other so as to be spaced apart from each other. The base arm

  48, which is elongate in shape, has an integral end

  64 of the outer end 50 which is rotatably mounted about the axis 44. Each of the upper arms 62 has an inner end 66 pivotable on the axis 44 and an outer end.

  opposite 68 which carries a different pair of magnetic heads

  46 read / write ticks The base arm 48

  and each of the upper arms 62 each carry a

  printed circuit board 70 which extends along its length.

  Each printed circuit board 70 establishes the con-

  electrical connections required between the heads 46 and an end plate 72 which is coupled to the base arm 48 and the upper arms 62, near their inner ends 64 and 66 The end plate 72 is coupled to an end plate 74 by a flexible ribbon The terminal board 74 makes the appropriate connections between the servo magnetic head 14 and other parts of the closed-loop servocontrol shown in FIG. 1. The plate 74 also makes appropriate connections between the various heads 46. read / write and other circuits for processing, storing and retrieving data carried by the various

magnetic disks 34.

  As shown in FIG. 4, the rotary actuator

  The magnetic strut 80 comprises three elongated elements or elongate bars 82, 84 and 86 made of iron or similar magnetic material. The bars 82 have a coil 24 and a stationary magnetic structure 80 mounted inside the rectangular enclosure 32. and 84 are mounted so as to be roughly parallel and

  spaced apart from each other by means of two spacers oppo-

  88 and 90 The bars 84 and 86 are mounted so as to be approximately parallel and spaced from one another to

  the aid of two opposite spacers 92 and 94

  toises 88 and 92 and the adjacent sections of the bars 82, 84 and 86 are held together by several bolts 96 passing through them In a similar manner, the spacers and 94 and the adjacent sections of the bars 82, 84 and 86 are held together by several bolts 98 therethrough An elongate magnet 100 of elongate configuration is mounted on the underside of the upper bar 82. A permanent magnet 102 of elongated configuration is mounted

  on the top of the lower bar 86.

  The coil 24 of the actuator is mounted

  to surround the middle bar 84 and to be able to

  smooth to it As indicated by the arrow 104

  double head of Figure 4, the coil 24 of the action-

  neur can slide along the bar 84 to allow the arm assembly 36 to rotate between the opposing limits defined by the stops 56 and 5.

  24 by the error signal produced by the control 10.

  closed chain generates a magnetic field that interacts with the magnetic fields normally produced by the permanent magnets 100 and 102 to move the coil

  24 along the bar 84 for a suitable distance.

  The arm assembly 36 is shown in the figure, as well as the rotary actuator 26. It appears in FIG. 5 that the coil 24 of the actuator is wound on

  a support 106 which is itself fixed on the outer end

  50 of the base arm 48 by the nuts 52 and 54

  support 106 of the coil has an opening 108 des-

  adapted to receive the bar 84 of the fixed magnetic structure 80 The outer ends 68 of the upper arms 62 are fixed to the outer end 50 of the base arm

  48, so as to be spaced apart, by means of several

  toises 110 arranged between the upper arms 62 and between the lower arm 62 and the base arm 48 Several bolts 112 pass through the upper arm 62 and the spacers 110 and through the base arm 48 to complete

  The inner ends 66 of the upper arms

  62 are kept spaced from one another and

  of the inner end 64 of the base arm 48 by several

  spacers 114 disposed between these ends and

  recessed internally to receive a central shaft 116.

-SJ 4 * 54

  This shaft 116 is mounted using bearings (not shown).

  felt) to rotate the arm assembly 36 around

of axis 44.

  The base arm 48 is shown in more detail in FIG. 6 As can be seen in FIG. 6, the base arm 48 is of elongated configuration

  between its opposite ends 50 and 64 The outer end

  The inner end 64 has a circular opening 118 for receiving the central shaft 116 shown in FIG. 5. The magnetic head 14 is mounted on the outer end 50. of the arm 48 by means of a bolt 120 The outer end 50 also has two openings 122 intended to receive the

bolts 112.

  It can be seen in FIG. 6 that the coil 24, the actuator and the servo head 14 are tightly coupled by being mounted in close proximity to one another on the outer end 50 of the base arm 48. The mechanical coupling 12 of the servocontrol 10 of

  Figure 1 is the small part of the

  50 of the base arm 48 between the coil 24 and the magnetic head 14 This small part is not the seat of any bearing resonance and is subjected to minimal resonant vibrations, so that it

  produces a negligible effect on servocontrol 10.

  It goes without saying that many modifications can be made to the described disk drive and

  shown without departing from the scope of the invention.

Claims (6)

  A magnetic disk unit having at least one magnetic disk (34), a magnetic head (14) disposed in close proximity to the disk, an arm positioning actuator (26), and a chain servo (10).   which reacts to signals detected by the magnetic head   to transmit error signals to the actuator   the position of the magnetic head, the unit being   characterized in that it comprises an arm assembly (36) which is rotatably and rotatably mounted about a first end and a second end opposite the preceding one is connected to the actuator and the magnetic head.   Disk drive according to claim 1, characterized in that the actuator comprises a coil (24) and that the arm assembly is of elongated configuration between its first and second ends and carries the coil at its second end, opposed to the first   end, as well as the magnetic head located on the.   side of the second end and adjacent to the coil.   Disk unit according to claim 1, characterized in that the arm assembly comprises a base arm (48) which is pivotably mounted at a first end (64) so as to rotate about an axis (44) and a second end (50), opposite   to the previous one, is coupled to the actuator and to the head -   magnetic, the assembly also comprising a plurality of additional arms (62) connected to the base arm and disposed above said base arm, at a distance from the latter and from each other, each additional arm being able to rotate about said axis, by a first end (66), and having a second opposite end (68) which is adjacent to the second end of the base arm and is adapted for mounting at least one magnetic head (46).   4 disk drive according to claim 1, characterized in that the second end of the arm assembly is spaced from its first end a given distance and in that the magnetic head is spaced from the arm positioning actuator. from a distance   substantially less than the given distance.   Disk drive according to claim 1, characterized in that several servo tracks   are recorded on one surface of the magnetic disc (s)   ticks, the magnetic head being placed in close proximity   mediate from the disk surface and enslavement to   closed chain acting to transmit to the action-   An arm positioning sensor is a signal determined by the gap between the magnetic head and a desired one of the servo tracks recorded on the surface of the disk. Disk unit according to Claim 1, characterized in that the positioning actuator of   arm comprises a coil (24) mounted on the second end   mity of the arm assembly, a magnetic structure (80) mounted in positiop fixed and having two extreme parts   opposites, in magnetic matter, and three inter-   different mediates (82, 84, 86) of magnetic material extending between the two opposite end portions and connected thereto, the three different intermediate parts of magnetic material being spaced apart   others and the central part carrying the coil.   Disk drive according to claim 1, characterized in that it comprises a plurality of magnetic disks (34) rotatable about a first common axis (42) and comprising said magnetic disk, the arm assembly comprising a plurality of elongate arms (62) rotatable by first ends (66) about a second common axis (44) spaced from the first common axis, each elongate arm having a second end (68) opposite the first end, means (110) 112) interconnecting the second ends of the elongate arms, the magnetic disk unit having a plurality of magnetic heads (46) which comprise the magnetic head mounted on the second ends of the elongated arms and which are arranged in close proximity to certain different , some discs   magnetic actuators, the arm positioning actuator com-   both a fixed part (80) and a movable part (24) connected   at the second end of one of the elongated arms, the asser-   closed-loop drive being coupled between one of the magnetic heads and the arm positioning actuator and having the function of transmitting signals to the actuator which depend on the gap between one of the magnetic heads and a desired position on the surface of one of the magnetic disks.   Disk unit according to Claim 7, characterized in that several servo tracks   are recorded on the surface of one of the magnetic disks.   and that closed-loop servocontrol   takes a position demodulator (16) connected to one of the   magnetic heads, a compensator (20) connected to the demodulator   position transmitter and power amplifier (22)   mounted between the compensator and the positioning actuator. arms.