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Apparatus for Enhanced GALVO Shaft Position Encoding

IP.com Disclosure Number: IPCOM000106703D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Lin, HT: AUTHOR

Abstract

Disclosed is a scheme for achieving significant improvement in galvo angular position repeatability and accuracy. Laser beam steering repeatability and accuracy can be improved significantly using an image projection method. This can be achieved without increase of galvo inertia and thus exhibit no response speed penalty.

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Apparatus for Enhanced GALVO Shaft Position Encoding

      Disclosed is a scheme for achieving significant improvement in
galvo angular position repeatability and accuracy.  Laser beam
steering repeatability and accuracy can be improved significantly
using an image projection method.  This can be achieved without
increase of galvo inertia and thus exhibit no response speed penalty.

      Galvos are used extensively in many Laser applications for
rapid beam steering (Steered Primary Laser Beam 6).  Analog
capacitive sensor is usually used for galvo angular shaft position
feedback.  These type of sensors usually can achieve accuracy and
repeatability of approximately 0.1% of maximum reading due to noise
and temperature considerations.  This is not adequate in some high
speed and high precision Laser beam steering applications.  Other
position encoding schemes are rarely employed due to increase of
galvo inertia and thus affecting system response time [*].  The
technique and apparatus described here can be used to improve galvo
angular position repeatability and accuracy but without these
disadvantages.

      This method uses a secondary focused Laser beam 1, a
cylindrical lens 2, special mask 3, photo sensors A and B (items 4
and 5) arranged as shown in the Figure.  The secondary focused light
source (e.g., Laser and Lens) reflected from the backside of the Beam
Steering Mirror 7 projects a rectangular image 8 onto the mask 3.
Patterns A and B on the mask are located at 90 degrees out of phase
to each other.  This arrangement gives information on the rotational
direction of the mi...