Measuring and testing – Testing of apparatus
Reexamination Certificate
1998-12-14
2001-01-30
Noori, Max (Department: 2855)
Measuring and testing
Testing of apparatus
C360S075000
Reexamination Certificate
active
06178835
ABSTRACT:
The present invention relates to a tool, apparatus and a method for testing a fixture.
The present invention has particular application to testing of a fixture which provides a mechanical support for a disk drive.
In a device having a movable arm, such as a hard disk drive, an arm which carries a read/write head is moved over the surface of a magnetic disk on which data is stored. The arm is driven to position the head over a selected location on the disk to enable the head to write data to the disk or to read data from the disk, as the case may be. Accurate location and seeks between locations are required of the arm. Any movement of the device as a whole can cause a positioning error.
The disk drive itself is mounted in a fixture which provides a mechanical support for the disk drive. The fixture might be, for example, a mounting within a housing for a personal computer. Such a fixture might alternatively be a bay in a tester rack
11
an example of which is shown in FIG.
1
. The tester rack
11
has plural bays or fixtures
12
each of which has a carrier
13
which carries a disk drive. Plural disk drives are mounted in the respective fixtures
12
of the tester rack
11
so that operation of the plural disk drives can be tested following manufacture and prior to the disk drives being sold or incorporated into a personal computer or other system using such a disk drive.
Ideally, movement of the movable arm of the device is completely independent of the fixture in which the device is mounted. However, in practice, this is not feasible. In particular, in practice, there is usually some mechanical coupling between the device and the fixture. This is a particular problem with a disk drive. For example, when a disk drive is mounted in a tester rack
11
as shown in
FIG. 1
, unless the drive is mounted in the fixture
12
with absolute rigidity such that it cannot move at all, movement of the arm of the device generates a reaction torque in the disk drive casing which results in a rotation of the disk drive casing in a direction opposite the movement of the arm. This reaction movement of the casing couples with the normal settle motion of the moving arm. This can give a false indication that the head mounted on the arm is in the correct position on the disk or “on track”. This false indication can allow track writing to start for example, the track writing being interrupted by the continuation of the motion of the arm. This causes an off-track motion of the head which in turn results in a “write fault” detect error. It has been found that the degree of motion coupling with the disk drive can vary between the fixtures
12
in which the various disk drives are mounted.
Because of the variability of the fixtures
12
, the fixtures
12
have conventionally been individually tested prior to their use in supporting disk drives when the disk drives are themselves being tested. To date, the fixtures
12
have been tested by inserting a disk drive and carrying out a series of write-fault measurements. However, this in itself produces numerous problems. First, the disk drives themselves are variable and do not provide a standard tool for measuring the variability of the fixtures
12
. Secondly, because of the variability of the disk drives used for testing the bays
12
, a very large number of measurements was required in order to provide some reasonable spread of results on which statistical analysis could be carried out, the process thus taking several hours to complete. In any event, the results obtained provided no real measure of the errors caused by the coupling of the arm motion with the reaction movement of the disk drive.
It is therefore an object of the present invention to provide improved means for testing a fixture which is used for mounting a device having a movable arm. Typically, such a device requires accurate location of the arm and seeks between locations such that movement of the device as a whole can cause a positioning error. The invention has particular applicability to testing fixtures which are used for mounting disk drives during testing of the disk drives, but the invention has general applicability to any fixture used for mounting a device having a movable arm.
According to a first aspect of the present invention, there is provided a tool for mounting in and testing a fixture used for mounting a device having an arm which is movable to selected locations by an actuator, the tool comprising: a movable member which is movable to mimic movement of an arm of a device mounted in the fixture; and, means for measuring movement of the tool in a fixture on which the tool is mounted as a reaction to movement of the movable member.
The tool provides a standard device which can be used for testing a fixture in a standard and repeatable manner.
In an embodiment, the movable member is arranged to move solely in a rotary direction about an axis. This is of particular application where the arm of the device normally mounted in the fixture is moved in a rotary direction by a rotary actuator.
The movable member may comprise a coil mounted for rotary movement about said axis, the tool further comprising a permanent magnet coupled magnetically to the coil such that the coil moves about said axis when a current is applied to the coil.
The coil in a preferred embodiment is a butterfly coil and the tool preferably comprises a permanent magnet for each wing of the coil.
A magnetically soft material is preferably mounted on the coil which acts with the permanent magnet to centralise the coil in the tool. Using a magnetically soft material, such as magnetically soft iron blocks, centralises the coil in a manner having a very low resonant frequency.
The measuring means may comprise an accelerometer for measuring the acceleration of the tool in a fixture in which the tool is mounted as a reaction to movement of the movable member.
The measuring means in an embodiment is arranged to measure rotary movement of the tool.
In a preferred embodiment, the measuring means comprises two accelerometers arranged on a line passing through the centre of rotation of the tool and on opposite sides of said centre of rotation such that the difference between the outputs of said accelerometers provides a measure of rotary movement of said tool only.
The tool may have detachable plates. These allow the overall size and/or mass and/or resonant frequency of the tool to be varied as required by using different side plates of different size, shape or profile.
According to a second aspect of the present invention, there is provided apparatus for testing a fixture used for mounting a device having an arm which is movable by an actuator, the apparatus comprising: a tool having a movable member which is movable to mimic movement of an arm of a device mounted in the fixture; means for measuring movement of the tool in a fixture on which the tool is mounted as a reaction to movement of the movable member; and, movement comparing means for comparing the movement of the movable member with movement of the tool in a fixture in which the tool is mounted as a reaction to movement of the movable member.
The apparatus preferably comprises: drive means for providing a drive signal to drive the movable member to move within a fixture; means for outputting a movement signal indicative of movement of the tool in a fixture in which the tool is mounted as a reaction to movement of the movable member; the movement comparing means comprising signal comparing means for comparing the drive signal with the movement signal; and, determining means for determining whether the fixture passes or fails on the basis of said comparison.
According to a third aspect of the present invention, there is provided a method of testing a fixture used for mounting a device having an arm which is movable by an actuator, the method comprising the steps of: inserting a tool having a movable member in said fixture; moving the movable member in the fixture to mimic movement of an arm of a device normally mounted in the fixture; measuring movement of the
Hearn Anthony R.
Orriss David J.
Havant International Limited
Noori Max
Pillsbury Madison & Sutro LLP
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