Method and apparatus to detect sub-micron particles in a hard disk drive with optical pickup

A hard disk drive that includes an optical pick-up coupled to a head of a hard disk assembly (“HDA”). The head is located adjacent to a disk. The optical pick-up can sense the surface of the disk by detecting light reflected from the surface. The optical pick-up is coupled to a particle circuit that can distinguish between an embedded particle and a floating particle from the reflected light.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for distinguishing between an embedded particle or a floating particle on a disk of a hard disk drive.

2. Background Information

Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads can magnetize and sense the magnetic fields of the disk to write and read data, respectively. The heads are coupled to a pivoting actuator arm that has a voice coil motor.

Data is typically stored on tracks that extend radially across the disk surfaces. The voice coil motor can be energized to pivot the actuator arm and move the heads to different track locations. Each track is typically divided into a number of sectors.

The heads have air bearing surfaces that cooperate with an air flow within the hard disk drive to create air bearings. The air bearings prevent and/or minimize the mechanical wear between the heads and the surfaces of the disks. The strength of the magnetic field applied and sensed from the disk surface is an inverse function of the air bearing height. Consequently, it is desirable to minimize the air bearing height to optimize the magnetic performance of the heads.

To minimize contact between the disks and the heads it is desirable to manufacture the disk surfaces as smooth as possible. To insure that the disk surfaces comply with certain smoothness requirements, the disks are typically inspected with an apparatus commonly referred to as a disk certifier. There are various types of disk certifiers that operate with a stylus, a magnetic head and/or an optical detection system. In an optical based certifier a beam of light is reflected off the disk surface and then detected by an optical detection system. The detected reflected light is then analyzed to identify pits, particles and other anomalies on the disk surface. After inspection the disk is assembled into a sealed hard disk assembly (“HDA”).

Particles may be created during the operation of the drive. For example, mechanical contact between the heads and the disk surfaces may generate small particles on the order of 0.05 to 0.2 micrometers. The particles may float onto and scratch the disk surfaces. To date, there is no way to determine the cause of a disk surface scratch within an HDA. It would be desirable to provide an apparatus and method for determining the existence of floating particles within an HDA.

BRIEF SUMMARY OF THE INVENTION

A hard disk drive with an optical pick-up coupled to a head. The head is located adjacent to a disk. The optical pick-up is coupled to a particle circuit that can distinguish between an embedded particle and a floating particle on the disk.

DETAILED DESCRIPTION

Disclosed is a hard disk drive that includes an optical pick-up coupled to a head of a hard disk assembly (“HDA”). The head is located adjacent to a disk. The optical pick-up can sense the surface of the disk by detecting light reflected from the surface. The optical pick-up is coupled to a particle circuit that can distinguish between an embedded particle and a floating particle from the reflected light.

Referring to the drawings more particularly by reference numbers,FIG. 1shows an embodiment of a hard disk drive10of the present invention. The disk drive10may include one or more magnetic disks12that are rotated by a spindle motor14. The spindle motor14may be mounted to a base plate16. The disk drive10may further have a cover18that encloses the disks12.

The disk drive10may include a plurality of heads20located adjacent to the disks12. Each head20may have separate write (not shown) and read elements21(seeFIG. 2). The heads20are gimbal mounted to a flexure arm26as part of a head gimbal assembly (HGA). The flexure arms26are attached to an actuator arm28that is pivotally mounted to the base plate16by a bearing assembly30. The photo-transducer50may be mounted to flexure arm26, actuator arm28, baseplate16or other area of the drive10. Alternatively, the photo-transducer50may be mounted to the head, with or without need for a waveguide. A voice coil32is attached to the actuator arm28. The voice coil32is coupled to a magnet assembly34to create a voice coil motor (VCM)36. Providing a current to the voice coil32will create a torque that swings the actuator arm28and moves the heads20across the disks12.

The hard disk drive10may include a printed circuit board assembly38that includes a plurality of integrated circuits40coupled to a printed circuit board42. The printed circuit board40is coupled to the voice coil32, heads20and spindle motor14by wires (not shown).

As shown inFIG. 2, an optical pick-up44may be coupled to a head20. The optical pick-up44may include a lens46that is mounted to the head20and connected to a waveguide48. The proximal end of the waveguide48may be connected to a photo-transducer50such as a photodiode. The photodiode50provides an output signal with an amplitude that varies with the amount of light that impinges on the diode50. The lens46may focus light reflected from the disk surface into the waveguide48. The photo-transducer50may then detect the light. The light may be generated by a light source such as a laser diode52.

As shown inFIG. 3, the lens46may actually be an assembly that includes a near field lens or aperture54, and a far field lens or aperture56. The photo-transducer50may include an array of photodiodes that can be used to distinguish between near field and far field light. Floating particles tend to scatter light and are therefore more likely to reflect light into the far field. Embedded particles tend to reflect light into the near field. Separate fields allow the system to distinguish between embedded and floating particles. The array may also include a quadrature detector that can be used to determine the slope of any particle.

The photo-transducer(s)50can be connected to a particle circuit58that can process the output signal(s) of the transducer(s)50. By way of example, the particle circuit58may include a processor60connected to memory62. The processor60may be a digital signal processor (“DSP”) that also operates the disk drive. The processor60may operate a particle discrimination routine in accordance with instructions and data. The instructions and data may be stored in memory62. Although a processor60and memory62are shown and described, it is to be understood that the particle circuit58may be constructed with dedicated logic to perform the operation of distinguishing particles.

The processor60may be connected to the spindle motor to receive feedback data on the position of the disk relative to the lens46. This allows the processor60to correlate particle detection with disk position. The processor60may identify a particle as embedded when a certain output signal (particle detection) is provided by the transducer50on a repeatable basis (eg. repeatable run-out RRO), or floating when the output (particle detection) only occurs in a non-repeatable manner (eg. non-repeatable run-out NRRO).

The optical pick-up44can be implemented when trying to determine the cause of scratches on a disk surface. The HDA may be modified by replacing the head gimbal assembly of the drive with an assembly that includes the optical pick-up. The drive can then be operated so that the head flies adjacent to the disk and the optical pick-up44senses the disk surface. The particle circuit58can then identify floating particles that may be scratching the disk. The lens46, waveguide48and photo-transducer50of the optical pick-up may be designed to detect particles less than one micron. The apparatus and method allow for detection of surface scratch sources in an HDA environment.