GB2166279A

GB2166279A - Method and apparatus for starting rotation of a disc-drive motor in a disc memory device

Info

Publication number: GB2166279A
Application number: GB08526314A
Authority: GB
Inventors: Roger R Sleger
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1984-10-25
Filing date: 1985-10-24
Publication date: 1986-04-30
Also published as: GB8526314D0; JPS61104472A; DE3537515A1

Abstract

To reduce the starting torque required from a disc-drive motor in a contacting-head disc memory device, a dithering motion is applied to the head assembly (8) of the device during the start-up of the disc-drive motor. This dithering motion is effected by using the head positioner motor and is continued at least until the head assembly (8) has lifted off the rotating disc (5). Also the effects of large variations of torque of disc-drive motors with respect to the rotational angle and of substantial variations in friction due to non-uniformity of the wear layer on the disc (Fig 3), are alleviated. <IMAGE>

Description

SPECIFICATION Method and apparatus for starting rotation of a disc-drive motor in a disc memory device This invention relates to a method and apparatus for starting rotation of a disc-drive motor in a disc memory device. More particularly, this invention relates to disc-drive motor start-up in a disc memory device of the type in which a head assembly contacts the surface of a recording media disc when the disc is not rotating but rides above the rotating disc during operation of the device; such disc memory devices are hereinafter referred to as contactinghead disc memory devices.

As the demand for physically smaller disc memory devices has grown, the use of smaller components has become necessary. Such small components often have functional limitations which must be overcome.

The disc-drive or spindle motor of a disc memory device is one of the major components of such a device. However, the smaller it becomes, the lower the starting torque. Of course, smaller spindle motors having higher starting torque may be designed. However, such motors typically require more power and produce more heat, both of which are substantial disadvantages in small-sized disc memory devices.

In a contacting-head disc memory device, considerably more starting torque is required of the spindle motor because of head-to-disc interface friction.

Such friction may vary with different head and disc media materials. The higher such friction becomes, the more starting torque is required of the spindle motor.

It is an object of the present invention to facilitate start up of the spindle motor of a contacting-head disc memory device.

According to one aspect of the present invention, there is provided a disc memory device of the type in which a head assembly rests in contact with the surface of the recording media disc when the disc is not rotating but rides above the disc when the latter is rotated by a disc-drive motor of the device, the disc memory device including dither means for applying dithering motion to the head assembly in a direction parallel to the plane of the recording-media disc, and start-up control means arranged to cause the dither means to effect dithering motion of the head assembly during start-up of the disc-drive motor.

The dithering motion of the head assembly reduces the torque required from the disc-drie motor to overcome break-away head-disc friction and this enables lower torque motors to be used than would otherwise be possible.

Preferably, the dither means is constituted by a head-assembly positioner motor of the device. It should be noted that the motor used to drive the head positioner in a disc memory device is usually a stepper motor having high start-up torque characteristics. Such characteristics are required for such motors to assure position accuracy over the selected track. Stepper motors designed for head positioner systems develop high torque to provide the inherent stiffness to resist track following errors introduced by mechanical vibration and the like. Thus, such high torque capability, which already exists in most contacting-head disc memory devices, now can be employed during a start-up routine to permit the use of smaller, low torque, low power disc-drive motors.

Stepper motor torque translates to dithering force as a function of the particular mechanical design of the head positioner system.

The application of dithering motion also alleviates the difficulties that are encountered due to the large variations of torque with respect to rotational angle which are typical of small, low cost spindle motors, even at operating speed. By continuing the dithered motion of the head assembly until the head has lifted off the disc, the effect of substantial variations in friction at the head-to-disc interface owing to nonuniformity of the wear layer on the disc surface is overcome.

According to another aspect of the present invention, there is provided a method of starting rotation of a disc-drive motor in a disc memory device of the type in which a head assembly rests in contact with the surface of a recording-media disc when the disc is not rotating but rides above the disc when the latter is rotated by the disc-drive motor, said method comprising the steps of applying dithering motion to the head assembly in any direction parallel to the surface of the recording media disc; simultaneously energising the disc-drive motor to apply a rotational force to the disc; and discontinuing the dithering force after the head assembly has moved out of contact with the disc.

A contacting-head disc memory device embodying the present invention will now be particularly described by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a perspective view, from above, of a head assembly of the disc memory device, the head assembly resting on the surface of a disc media of the device; Figure 2 is a cross-sectional view of the head assemblytaken on line A-A of Figure 1; and Figure 3 is a graph showing, as a function of rotation angle, both the torque exerted by a spindle motor of the disc memory device, and the torque required to overcome head-to-media friction forces.

The contacting-head disc memory device shown in Figures 1 and 2 includes a disc media 5 arranged to be rotated by a spindle motor (not shown), and a head assembly 8 movable radially of the media 5 by a head positioner motor (also not shown).

As illustrated in Figures 1 and 2, prior to start-up of the disc memory device, the head assembly 8 of the device rests on the disc media 5 above a track 17.

Upon application of a force to the disc media 5 or head assembly 8 tending to cause relative movement therebetween, the magnitude of the friction force at the interface 7 of the head assembly 8 and the disc media 5 depends primarily upon the magnitude of the perpendicular contact force Fn and the surface properties of the head assembly 8 and disc media 5. The friction force will, of course, always oppose the resultant of any forces applied to the head assembly 8 in a plane parallel to the surface of the media 5. Thus, rotation of the media 5 will set up a friction force Ff in a direction 14 or 15 depending on the sense of rotation.

In known prior art systems, in orderto initiate rotation of the media 5 in direction 19, the spindle motor (not shown) must develop enough torque to overcome by itself the friction force Ff. However, since Ff always opposes motion of the media 5 with respect to the head assembly 8, any motion of the head assembly 8 with respect to the media 5 in any direction in a plane parallel to the surface of media 5 in sufficient magnitude will overcome Ff. Thus, if some other force, Fal is applied to the head assembly 8 in any direction parallel to the surface of media 5 of a magnitude sufficient to overcome the magnitude of Ff, the torque required to rotate the media 5 beneath the head assembly 8 will be significantly less.

If, as illustrated, the force A takes the form of a dithering force applied alternately in opposite radial directions 10, 11 relative to the disc media 5 (that is, at right angles to the track over which the head assembly 8 is positioned), then, instantaneously, as the media 5 just begins to rotate, Ff has no tangential component. However, as the media 5 begins to rotate, the tangential component of Ff becomes non-zero, since the direction of movement of the head assembly begins to change from the radial. The head assembly 8 actually traces a zig-zag path of varying periodicity across several tracks on the media 5. Upon the head assembly8 lifting off the surface of the media 5, the dithered motion may be stopped or else continued until the disc is up to full speed.

The head positioner motor (not shown) can conveniently be used to supply the dithering force Fa The dithering displacement of the head assembly 8 need not be very great, being of the order of a few tracks of the media 5. The control of the dither motion is effected by the control means of the disc memory device controlling the head positioner motor in accordance with a start-up program.

From the foregoing, it will be appreciated that the tangential force FR developed by the spindle motor at the head assembly need not by itselt be great enough to overcome a frictional force of magnitude Ff.

Referring now to Figure 3, the spindle motor torque Tm for a typical small size, low cost spindle motor such as used for the spindle motor of the present disc memory device, varies periodically with rotational angle. Tm varies because of inherent design characteristics of such motors. As the media 5 rotates, more Tm is produced by the motor at some angles than at other angles, even after the motor reaches full operating speed. However, as the media 5 continues to rotate, it will accumulate energy in flywheel fashion and accelerate toward operating speed.

Referring again to Figure 3, the torque Tf required to overcome the tangential component of the headto-media friction forces varies erratically, sometimes exceeding Tm as shown at 30. Tf varies because of variable properties of the wear layer on the surface of the media 5. Again, however, with continued dithering of the head slider assembly 8 and with the accumulated inertial energy of media 5 acting as a flywheel, the spindle motor will continue to accelerate and reach full operating speed.

As the media 5 accelerates and the head assembly 8 begins to lift off of the surface of media 5, Tf begins to decrease substantially as shown at 32. When head assembly 8 has completely lifted off, Tf achieves a non-zero minimum value as shown at 34 which is related to the configuration of the airbearing surface of the head assembly 8.

It will be appreciated that the forces FR and FT referred to in Figures 1 and 2 are related to the torques Tm and Tf referred to in Figure 3, by the distance of the point on media 5 at which such forces are applied from the rotational center of the spindle motor.

From the foregoing, it can be seen that the described contacting-head disc memory device may employ a spindle motor having a low starting torque and commensurately lower power requirement, smaller size and cooler operation and may have high friction at the head-to-disc interface. Since high starting torque is not required of spindle motor, the motor parameters may be optimized for high efficiency at normal operating speeds which also reduces cost of the motor and thus the disc memory device.

Although in the afore-described disc memory device, the force Fa is applied in a radial direction, this force can be applied to the head assembly 8 in any direction in a plane parallel to the surface of the media 5. Thus virtually any head positioner configuration using either a linear or rotary motor can be used.

Claims

1. A disc memory device of the type in which a head assembly rests in contact with the surface of a recording-media disc when the disc is not rotating but rides above the disc when the latter is rotated by a disc-drive motor of the device, the disc memory device including: dither means for applying dithering motion to the head assembly in a direction parallel to the plane of the recording-media disc, and start-up control means arranged to cause the dither means to effect dithering motion of the head assembly during start-up of the disc-drive motor.

2. A disc memory device according to claim 1 wherein the dither means is constituted by a headassembly positioner motor of the device.

3. A disc memory device according to claim 1 or claim 2, wherein the dithering motion is in opposite radial directions relative to the recording media disc.

4. A disc memory device according to any one of the preceding claims, wherein the starting torque of the disc-drive motor is inadequate to initiate rotation in the absence of dithering motion of the head assembly.

5. A disc memory device according to any one of the preceding claims, wherein the control means is arranged to discontinue dithering motion of the head assembly upon the disc-drive motor reaching its full operating speed.

6. A disc memory device substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of starting rotation of a disc-drive motor in a disc memory device of the type in which a head assembly rests in contact with the surface of a recording-media disc when the disc is not rotating but rides above the disc when the latter is rotated by the disc-drive motor, said method comprising the steps of: applying dithering motion to the head assembly in any direction parallel to the surface of the recording media disc; simultaneously energizing the disc-drive motor to apply a rotational force to the disc; and discontinuing the dithering force after the head assembly has moved out of contact with the disc.

8. A method of starting rotation of a disc-drive motor in a disc memory device, said method being substantially as hereinbefore described with reference to the accompanying drawings.