GB2127610A

GB2127610A - Magnetic disc transducer arm

Info

Publication number: GB2127610A
Application number: GB08325453A
Authority: GB
Inventors: Marc Feller; James Bjordahl
Original assignee: KENNEDY Co
Current assignee: KENNEDY Co
Priority date: 1982-09-30
Filing date: 1983-09-22
Publication date: 1984-04-11
Also published as: DE3334206A1; FR2534054A1; GB2127610B; GB8325453D0; JPS5979469A

Abstract

Several magnetic heads 46 cooperate within a stack of discs 34 rotating on an axis 42. For track following a closed-loop servo system is responsive to signals from a magnetic head tracking the underside of the lowermost disc and controls the head position by means of an electromagnetic actuator which includes a coil 24. Coil 24 is mounted on the base arm 48 which carries the magnetic head feeding the servo. The arm 48, in common with arms 62 which carry the other heads 46, is mounted to swing about pivot 44. The placing of the sensing head and the coil 24 adjacent one another at the outer end of the arm 48 minimizes mechanical vibration and allows the use of high gain in the servo-system. <IMAGE>

Description

SPECIFICATION Magnetic disc drive system The present invention relates to magnetic disk drive systems, and more particulary to magnetic disk drive systems of the type in which a closedloop servo is employed to maintain a servo head in alignment with a desired servo track during a track following mode of operation.

Magnetic disk drive systems have been considerable development in the face of rapidly expanding technology in this area. Such systems typically employ one or more magnetic heads designed to float on an air bearing relative to the surfaces of one or more rotating magnetic disks.

The problem of how to mount the magnetic heads so that they may be quickly and accurately positioned and thereafter maintained at different selected locations adjacent the surface of the magnetic disks has resulted in two basic approaches to the problem. One such approach involves a linear actuator, while the other approach utilizes a rotary actuator.

A typical linear actuator employs a carriage that accesses the different tracks on the magnetic disks radially. The carriage, which supports the magnetic heads at one end and a voice coil at the other, may ride on precision-ground cylindrical ways and is usually a complex die casting optimized for stiffness and low mass. In operation, the carriage is subjected principally to extension and compression forces. The carriage resonant frequency and therefore the servo bandwidth can be relatively high, reducing sensitivity to shock.

However the linear actuator does not lend itself to compact designs, and the precision machining to fabricate the carriage and its ways makes this an expensive approach to magnetic head positioning.

Most rotary actuator designs employ a pivoting arm that carries the magnetic heads on one end and a coil at the other end. Such systems are discussed in an article entitled "Design of a Swinging Arm Actuator for a Disk File" by J.S.

Heath at pages 389-397 of the July 1976 issue of IBM Journal of Research and Development.

Such actuators provide for a smaller drive enclosure and are usually less expensive than linear actuators, although precision bearing must be used for the pivot. The arm is subjected to bending forces, which cause the system to exhibit less stiffness, lower resonant frequencies and reduced servo bandwidth. The coil must usually be placed near the pivot because of size limitations.

This results in a relatively poor mechanical advantage, requiring a relatively large coil.

Magnetic disk drive systems are typically designed to undergo two different modes of operation, the first of which is the seek or positioning mode and the second of which is the track following mode. During the seek or positioning mode of operation the linear or rotary actuator or other arrangement for mounting the magnetic heads is operated to position a selected magnetic head at a desired one of a plurality of tracks recorded on the adjacent magnetic disk surface. Thereafter, the actuator or other apparatus for positioning the heads is operated in a manner so as to keep the selected head aligned with the desired track, resulting in a track following mode of operation.During the seek or positioning mode, the drive system functions as a velocity control system designed to position the selected magnetic head at the desired track in the quickest and most efficient manner possible.

Flexure, movement or vibration of any mechanical linkages between the actuator mechanism and the magnetic heads can adversely affect the speed with which seeking may be accomplished.

During the track following mode of operation, a closed-loop servo system is typically employed in order to enable the selected magnetic head to follow a desired track. Where a separate servo head is employed in conjunction with a plurality of different servo tracks, the magnetic signals sensed by the servo head are processed by the closed loop servo system so as to generate an error signal in accordance with deviations of the servo head from the desired track. This error signal is applied to the actuator to adjust the position of the servo head until it locks onto the desired servo track.

Such closed-loop servo systems operating in the track following mode are second order control systems. Such things are flexure, movement or vibration within the mechanical coupling between the actuator and the servo head are major problems which may seriously affect the ability of the closed-loop servo system to operate in an efficient manner during the track following mode.

In the case of the rotary actuators previously described in which the actuator is coupled to one end of an arm having a pivot within a central portion thereof and magnetic heads mounted at the opposite end thereof, the arm comprises a relatively large beam having substantial low frequency resonance. The low frequency resonance of the beam together with Hertzian resonances in the pivot bearings combine to tend to make the closed-loop servo system oscillate. To compensate for this, the gain of the servo system is usually set at a relatively low value. This reduces the disturbing effects of the arm resonance and pivot bearing resonances, but at the expense of the efficiency of the servo system.

Accordingly, it would be desirable to minimize the effects of the mechanical coupling between the actuator and the servo head within the closed loop servo system. This suggests close coupling of the actuator and the servo head so as to minimize the mechanical coupling therebetween.

It is known in the art to provide various different arm configurations for mounting the magnetic heads adjacent magnetic disks. An example of this is provided by the arrangement shown in U.S.

Patent 4,185,309 in which an elongated arm having a pivotally mounted first end mounts the magnetic head at an opposite second end together with a band and spindle drive arrangement. However, systems such as the one shown in Patent No. 4,185,309 do not utilize a closed-loop servo system and do not address the problems which occur when such a system is used to accomplish a track following mode.

Accordingly, it would be desirable to provide a magnetic disk drive system in which a closed-loop servo system can be operated in relatively efficient, high-gain fashion during track following mode. More specifically, it would be desirable within such systems to minimize the effects of mechanical coupling between the actuator and the servo head.

Brief Description of the Invention The present invention provides a magnetic disk drive system in which a rotary actuator is closely coupled to the magnetic head so as to minimize the effects of resonance and mechanical flexure within the mechanical coupling between the two.

This is accbmplished by mounting the actuator coil and the servo head adjacent one another at one end of an elongated arm having an opposite end pivotally mounted to permit rotation of the arm relative to one or more rotatable magnetic disks. The close coupling of the actuator coil to the servo head and the other magnetic heads at the same end of the arm greatly minimizes the mechanical coupling therebetween. Virtually all of the resonance of the arm together with the effects of the pivot bearing resonances are removed from the closed-loop servo system, enabling the system to be operated in a high gain, highly efficient fashion.

In a preferred embodiment of a magnetic disk drive system in accordance with the invention, a plurality of magnetic disks are mounted for rotation on a common axis within a sealed, Winchester-type enclosure together with an arm assembly and a rotary actuator including a coil.

The arm assembly includes an elongated base arm mounted for rotation about one end thereof and having the coil and a magnetic servo head mounted adjacent each other at the opposte end of the base arm. A plurality of additional arms within the arm assembly are mounted on top of the base arm in stacked, spaced-apart relation so as to be rotatable about a common axis with the base arm. Magnetic read/write heads mounted at the opposite ends of the additional arms adjacent the servo head and the coil address the opposite surfaces of the various magnetic disks.The rotary actuator includes in addition to the coil a stationary arrangement which interacts with the coil and which includes three different elongated magnetic elements extending in generally parallel, spaced-apart relation between opposite magnetic end portions such that the coil surrounds the center one of the elongated elements between opposite permanent magnets mounted on the other two elongated elements. A closed-loop servo system includes a position demodulator coupled to the servo head to provide a position signal indicative of the position of the head relative to a desired servo track, a summing junction for combining the position signal with any external commands to provide an error signal, a compensator for damping the error signal to prevent oscillation and a power amplifier for amplifying the error signal prior to application thereof to the coil.

Brief Description of the Drawings The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings, in which: Fig. 1 is a block diagram of a closed-loop servo system utilized in a magnetic disk drive system according to the invention; Fig. 2 is a perspective view of a magnetic disk drive system in accordance with the invention which utilizes the servo system of Fig. 1; Fig. 3 is a top view of a portion of the magnetic disk drive system of Fig. 2; Fig. 4 is a front view of the rotary actuator used in the magnetic disk drive system of Fig. 2; Fig. 5 is a side view of the arm assembly of the magnetic disk drive system of Fig. 2 together with the rotary actuator of Fig. 4 shown partly in section; and Fig. 6 is a plan view of the base arm of the arm assembly shown in Fig. 5 together with the coil comprising a part of the rotary actuator of Fig. 4 and a magnetic servo head.

Detailed Description Fig. 1 depicts a closed-loop servo system 10.

The servo system 10 of Fig. 1 is of conventional design except for a mechanical coupling 12 which is optimized in accordance with the invention. The servo system 10 includes a magnetic head 14 which comprises a servo head in the present example. When the servo system 10 is operating in a track following mode, the head 14 has been positioned at a desired servo track on a magnetic disk as the result of a seek or positioning mode of operation. The servo system 10 functions to maintain the head 14 aligned with the desired servo track during the track following mode. The magnetic head 14 provides a signal which indicates among other things whether the head 14 is tracking on or is deviating from the desired servo track. This information is used by the servo system 10 in generating an error signal in accordance with the amount of deviation of the head 14 from the desired servo track.

The signal from the adjacent magnetic disk surface which is sensed by the magnetic head 14 is passed to a position demodulator 16. This signal which is of dibit, tribit, or similar format is demodulated by the position demodulator 16 so as to provide a position signal representing the position of the magnetic head 14 relative to the desired servo track. The position signal is applied to a summing junction 18 together with an external command signal. The summing junction 18 combines the position signal and the external command signal into an error signal. During the track following mode, the external command signal is of zero value, and consequently the summing junction 18 passes the position signal as an error signal to a compensator 20.

The compensator 20 which includes a low pass filter and several other filters provides an amount of damping needed to prevent the servo system 10 from going into oscillation. The error signal as damped by the compensator 20 is amplified by a power amplifier 22 prior to being applied to an actuator coil 24 forming a part of a rotary actuator 26 (shown in Fig. 2) which is described hereafter.

Application of the error signal to the actuator coil 24 causes the rotary actuator 26 to reposition the magnetic head 14 so that the head 14 is aligned with the desired servo track.

Every magnetic disk drive system has the mechanical coupling 12 representing the mechanical structure which couples the actuator coil 24 to the magnetic head 14. As such, the mechanical coupling 12 forms a part of the closed-loop servo system 10 and effects the performance thereof. Resonant vibrations, bearing resonances and other variables present in the mechanical coupling 12 have a direct effect on the performance of the closed-loop servo system 10 because they are coupled directly in the closedloop of the servo system.In the case of the prior art rotary actuators previously described in which the actuator is located at one end of an elongated arm having a central pivot point and an opposite end on which the magnetic head is mounted, both the resonant vibrations of the elongated arm and the rotary bearing resonances at the pivot affect the performance of the closed-loop servo system.

In such arrangements it is frequently necessary that the gain of the closed-loop servo system be reduced, thereby seriously affecting the overall efficiency of the servo system.

In accordance with the present invention the actuator coil 24 is closely coupled to the magnetic head 14 by being mounted on the same end of a positioning arm as the magnetic head 14 and in close proximity to the head 14. As a result the mechanical coupling 12 between the actuator coil 24 and the magnetic head 14 consists of a very small portion of the positioning arm having an insignificant amount of natural resonance and no bearing or similar resonances. As a result the mechanical coupling 12 forms an insignificant part of the closed-loop servo system 10. The gain of the servo system 10 may therefore by relatively high, resulting in high efficiency and excellent track following capabilities.

Fig. 2 depicts a magnetic disk drive system 30 in accordance with the inventor which utilizes the closed-loop servo system 10 of Fig. 1 The drive system 30 which is of the Winchester type has a generally rectangular housing 32 for rotatably mounting a plurality of magnetic disks 34 therein together with an arm assembly 36 and the rotary actuator 26. These elements are sealed within the housing 32 by a cover 38 which is shown partly broken-away in Fig. 2. A rear portion of the housing 32 has a finned plate 40 at the upper end thereof to facilitate dissipation of heat from the drive system 30. As seen in Fig. 3 which is a top view of a portion of Fig. 2 the magnetic disks 34 are mounted in conventional spaced-apart fashion for rotation about a common axis 42.The arm assembly 36 is mounted for rotation about an axis 44 which is spaced-apart from and generally parallel to the common axis 42 of the magnetic disks 34. The arm assembly 36 which is of elongated configuration mounts a plurality of read/write magnetic heads 46 at an opposite end thereof. Included among the read/write heads 46 is the magnetic head 14 of Fig. 1 which is mounted on a base arm 48 within the arm assembly 36 together with the actuator coil 24.

The magnetic head 14, which functions as a servo head, addresses the underside of a lowermost one of the magnetic disks 34 which has a plurality of servo tracks recorded thereon. The remaining ones of the read/write magnetic heads 46 are disposed adjacent the upper and lower sides of the other ones of the magnetic disks 34.

As seen in Fig. 3 the actuator coil 24 is secured to an outer end 50 of the base arm 48 by an opposite pair of nuts 52 and 54. Rotational movement of the arm assembly 36 is limited by an opposite pair of elastomeric stops 56 and 58 disposed in the paths of the nuts 52 and 54 respectively. A filter 60 which is visible in Figs. 2 and 3 forms a part of an air circulation and filtering system within the drive system 30.

The arm assembly 36 includes a plurality of upper arms 62 which are stacked on top of and coupled to the base arm 48 and to each other in spaced-apart relation. The base arm 48 which is of elongated configuration has an inner end 64 thereof opposite the outer end 50 which is pivotally mounted for rotation about the axis 44.

Each of the upper arms 62 has an inner end 66 pivotally mounted for rotation about the axis 44 and an opposite outer end 68 which mounts a different pair of the read/write magnetic heads 46.

The base arm 48 and each of the upper arms 62 has a printed circuit board 70 mounted on and extending along the length thereof. Each of the printed circuit boards 70 provides the necessary electrical connections between the heads 46 and a terminal board 72 which is coupled to the base arm 48 and to the upper arms 62 adjacent the inner ends 64 and 66 thereof. The terminal board 72 is coupled to a terminal board 74 via a flexible conductor ribbon 76. The terminal board 74 makes the appropriate connections between the magnetic servo head 14 and other portions of the closed-loop servo system 10 shown in Fig. 1. The board 74 also makes appropriate connections between the various read/write heads 46 and other circuitry for processing, storing and retrieving data on the various magnetic disks 34.

As shown in Fig. 4 the rotary actuator 26 includes the actuator coil 24 and a stationary magnetic structure 80 mounted within the rectangular housing 32. The magnetic structure 80 includes three different elongated elements or bars 82, 84 and 86 of iron or similar magnetic material. The bars 82 and 84 are mounted in generally parallel, spaced-apart relation by an opposite pair of spacers 88 and 9Q. The bars 84 and 86 are mounted in generally parallel, spacedapart relation by an opposite pair of spacers 92 and 94. The spacers 88 and 92 and adjacent portions of the bars 82. 84 and 86 are held together by a plurality of bolts 96 extending therethrough. In similar fashion the spacers 90 and 94 and adjacent portions of the bars 82, 84 and 86 are held together by a plurality of bolts 98 extending therethrough.A permanent magnet 100 of elongated configuration is mounted at 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 actuator coil 24 is mounted so as to surround and be slideable relative to the middle bar 84. As shown by a double headed arrow 104 in Fig. 4, the actuator coil 24 is slideable along the length of the bar 84 to permit rotation of the arm assembly 36 between the opposite limits defined by the stops 56 and 58. Energization of the coil 24 by the error signal produced by the closed-loop servo system 10 creates a magnetic field which interacts with the magnetic fields normally produced by the permanent magnets 100 and 102 so as to move the coil 24 along the bar 84 by an appropriate amount.

The arm assembly 36 is shown in Fig. 5 together with the rotary actuator 26. It will be seen from Fig. 5 that the actuator coil 24 is wound on a coil holder 106 which is in turn secured to the outer end 50 of the base arm 48 by the nuts 52 and 54. The coil holder 106 has an aperture 1 08 therein for receiving the bar 84 of the stationary magnetic structure 80. The outer ends 68 of the upper arms 62 are secured to the outer end 50 of the base arm 48 in spaced-apart relation by a plurality 6f spacers 110 disposed between the upper arms 62 and between the lowest one of the arms 62 and the base arm 48. A plurality of bolts 11 2 extend through the upper arm 62 and the spacers 110 and through the base arm 48 to complete the assembly.The inner ends 66 of the upper arms 62 are held spaced-apart from each other and from the inner end 64 of the base arm 48 by a plurality of spacers 114 disposed therebetween and having hollow interiors for receiving a central shaft 11 6. The shaft 116 is mounted by bearings (not shown) to provide rotation of the arm assembly 36 about the axis 44.

The base arm 48 is shown in greater detail in Fig. 6. As seen in Fig. 6 the base arm 48 is of elongated configuration between the opposite ends 50 and 64 thereof. The outer end 50 is coupled to the coil holder 106 by the nuts 52 and 54. The inner end 64 has a circular aperture 118 therein for receiving the central shaft 11 6 shown in Fig. 5. The magnetic head 14 is mounted on the outer end 50 of the arm 48 by a bolt 120. The outer end 50 is also provided with a pair of apertures 122 for receiving the bolts 112.

It will be appreciated from Fig. 6 that the actuator coil 24 and the servo head 14 are closely coupled by being mounted in close proximity to each other on the outer end 50 of the base arm 48. The mechanical coupling 12 in the servo system 10 of Fig. 1 consists of the small portion of the outer end 50 of the base arm 48 between the coil 24 and the magnetic head 14. This small portion does not involve any bearing resonances and undergoes a minimum of resonant vibrations so as to have an insignificant effect on the servo system 10.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. In a magnetic disk drive system having at least one magnetic disk, a magnetic head disposed adjacent the magnetic disk, an arm positioning actuator, and a closed-loop servo system responsive to signals sensed by the magnetic head to provide magentic head position error signals to the actuator, the improvement comprising an arm assembly pivotally mounted for rotation about a first end thereof and having an opposite second end thereof coupled to the actuator and to the magnetic head.

2. The invention set forth in claim 1 , wherein the actuator includes a coil and the arm assembly is of elongated configuration between the first and second ends thereof and mounts the coil at the second end thereof opposite the first end and the magnetic head at the side of the second end and adjacent the coil.

3. The invention set forth in claim 1, wherein the arm assembly comprises a base arm pivotally mounted at a first end thereof for rotation about an axis and having an opposite second end thereof coupled to the actuator and to the magnetic head and a plurality of additional arms coupled to the base arm and disposed above and spaced-apart from the base arm and from each other, each of the additional arms being rotatable about the axis at a first end thereof and having an opposite second end disposed adjacent the second end of the base arm and adapted to mount at least one magnetic head.

4. The invention set forth in claim 1, wherein the second end of the arm assembly is spaced apart from the first end thereof by a given distance and the magnetic head is spaced apart from the arm positioning actuator by a distance which is substantially less than the given distance.

5. The invention set forth in claim 1, wherein a surface of the at least one magnetic disk has a plurality of servo tracks recorded thereon, the magnetic head is disposed adjacent the surface of the at least one magnetic disk and the closed loop servo system is operative to provide to the arm positioning actuator a signal determined by the deviation of the magnetic head from a desired one of the servo tracks recorded on the surface of the at least one magnetic disk.

6. The invention set forth in claim 1, wherein the arm positioning actuator includes a coil mounted on the second end of the arm assembly, a magnetic structure mounted in a fixed location and including a pair of opposite end portions of magnetic material and three different intermediate portions of magnetic material extending between and coupled to the pair of opposite end portions, the three different interconnecting portions of the magnetic material being spaced apart from each other and a center one thereof receiving the coil thereon.

7. The invention set forth in claim 1, wherein the magnetic disk drive system has a plurality of magnetic disks rotatable about a first common axis and including the at least one magnetic disk, the arm assembly includes a plurality of elongated arms rotatable at first ends thereof about a second common axis spaced apart from the first common axis, each of the elongated arms having a second end opposite the first end thereof, and means coupling the second ends of the plurality of elongated arms together, the magnetic disk drive system has a plurality of magnetic heads including the magnetic head mounted on the second ends of the plurality of elongated arms and disposed adjacent different ones of the plurality of magnetic disks, the arm positioning actuator has a stationary portion and a movable portion coupled to one of the plurality of elongated arms at the second end of the arm, and the closed-loop servo system is coupled between one of the magnetic heads and the arm positioning actuator and is operative to provide to the arm positioning actuator signals determined by the deviation of the one of the magnetic heads from a desired position on the surface of one of the plurality of magnetic disks.

8. The invention set forth in claim 7, wherein the surface of the one of the plurality of magnetic disks has a plurality of servo tracks recorded thereon and the closed loop servo includes a position demodulator coupled to the one of the magnetic heads, a compensator coupled to the position demodulator and a power amplifier coupled between the compensator and the arm positioning actuator.