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Fast Laser Scanner to Detect Taper/ Rail of Sliders

IP.com Disclosure Number: IPCOM000121664D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 4 page(s) / 136K

Publishing Venue

IBM

Related People

Feliss, N: AUTHOR [+2]

Abstract

There is a current need for fast automatic inspecting the correctness of taper and rail-widths of sliders. Conventional laser scanners or laser microscopes exist for measuring sizes, shapes, and profiles, but conventional tools typically require careful sample alignment and are, thus, time-consuming. Described here is a double laser-beam scanning system that is insensitive to sample tilt and alignment, providing a fast measurement of taper and rail-widths, for example, measuring all 11 heads on a row in a few seconds.

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Fast Laser Scanner to Detect Taper/ Rail of Sliders

      There is a current need for fast automatic inspecting the
correctness of taper and rail-widths of sliders. Conventional laser
scanners or laser microscopes exist for measuring sizes, shapes, and
profiles, but conventional tools typically require careful sample
alignment and are, thus, time-consuming.  Described here is a double
laser-beam scanning system that is insensitive to sample tilt and
alignment, providing a fast measurement of taper and rail-widths, for
example, measuring all 11 heads on a row in a few seconds.

      The principle of the present invention is indicated in Fig. 1.
In a conventional laser scanner, a laser beam is scanned across the
reflective sample surface S perpendicular to the plane of Fig. 1, and
the reflected light is detected by a position sensor P.  If S is
moved down a distance H (Fig. 1a), the light spot on P moves down by
a distance of 2 H cos(g), where g is the grazing distance 2Ls, where
L is the distance from P to the illuminated spot.  Hence, the height
movement and the tilt both contribute to a signal at the position
sensor P, and it is not obvious how to measure just a small tilt
without having to adjust height.  The technique developed here
involves putting a positive lens to capture the reflected beam, and
to locate the position sensor at the focal length F from the lens; in
this case, if the sample surface S moves down by a distance H, the
spot on P will not move (Fig. 1c); however, if S tilts by a small
angle s, the spot at P moves down by a distance Fs.  Thus, the
technique shown in Fig.  1c is capable of measuring only tilting,
without any effect from displacement of S. However, we are interested
in measuring the angle between two reflective planes, without
worrying about the displacements and the tilts of each plane.  The
schematics to achieve this are indicated in Fig. 1d; here, the
reflected beams from S1 and S2, re spectively are captured by the
same converging lens, and detected by position sensors P1 and P2,
respectively, (these can be parts of a position sensor with a common
ground at the center), located at distance F from the lens.  The
corresponding output voltages, V1 and V2, respectively, are each
independent of the displacement of the sample, as already explained
in Fig. 1c.  Furthermore, the measured quantity is the difference
output D=(V1 - V2)/(V1 + V2); if the sample tilts by a small angle s,
both V1 and V2 change by the same amount 2Fs, and hence, D is
insensitive to sample tilt.  Indeed, for t...