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Optical Means of Sensing Position of a Sawyer Motor on a Magnetic Grid Surface

IP.com Disclosure Number: IPCOM000112479D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 159K

Publishing Venue

IBM

Related People

Brennemann, AE: AUTHOR [+4]

Abstract

Fig. 1. Dual wavelength optical Sawyer motor sensor. Fig. 1(a). Light &lambda.1 illuminates a Sawyer motor platen through a slit in a mask as detailed in Fig. 1(b). The platen grooves are filled with a material that is fluorescent at wavelength &lambda.2. An optical filter removes &lambda.1 so only light of wavelength &lambda.1 reaches the photodetector. The amount of light reaching the photo detector is determined by the position of the slit, Fig. 1(b) and the normalized output plotted in Fig. 1(c).

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Optical Means of Sensing Position of a Sawyer Motor on a Magnetic
Grid Surface

      Fig. 1.  Dual wavelength optical Sawyer motor sensor.  Fig.
1(a).  Light &lambda.1 illuminates a Sawyer motor platen through a
slit in a mask as detailed in Fig. 1(b).  The platen grooves are
filled with a material that is fluorescent at wavelength &lambda.2.
An optical filter removes &lambda.1 so only light of wavelength
&lambda.1 reaches the photodetector.  The amount of light reaching
the photo detector is determined by the position of the slit, Fig.
1(b) and the normalized output plotted in Fig. 1(c).

      Disclosed is a device for optically sensing the grid pattern of
magnetic teeth on the platen of a Sawyer linear stepping motor system

[1]  when the motor moves over the platen surface.  Signals,
generated in the sensor photodetectors from light produced at the
surface of the grid pattern, are processed for velocity and
displacement values for motor control purposes.  Either a single or a
pair of sensors are mounted on each axis of a motor to provide
independent control of each axis.  This device is similar in function
to those described in [1-8]  but differs in the principles of
operation.

      The principles of operation of this sensor are illustrated in
Fig. 1, with the basic components shown in Fig. 1(a).  The platen is
an array of magnetic square teeth of nominal width W spaced on
centers of 2W, surrounded by grooves of width W.  The grooves are
filled with a polymer or similar material that is fluorescent when
irradiated.  The remaining components are mounted on the motor and
collectively move in either the x-axis or y-axis relative to the
platen.

      A primary light source of wavelength &lambda.1 illuminates the
platen through a slit in the mask.  The fluorescent material absorbs
some of the primary wavelenghts and emits light at a longer secondary
wavelength &lambda.2.  Light emanating from the slit conssits of both
&lambda.2.  and the remainder of &lambda.1.  that is reflected from
the surface.  An optical filter with a sharp longer wave length
cutoff removes &lambda.1.  and allows &lambda.2.  to reach the
photodetector.  The amount of &lambda.2 is a function of the mask
slit dimensions and x-y position relative to the platen.

      The unidirectional operation of the sensor is illustrated in
Fig. 1(b) for a single slit of dimensions W x L(10W) with the
detector output shown in Fig. 1(c).  The detector output is
proportional to the light from the fluorescent material exposed
through the slit and the position of the slit along the y-axis.  As
shown, the slit is aligned with a row of 5 teeth and 5 fluorescent
squares corresponding to slit position y = 0 in Fig. 1(c) with the
output at 0.5 maximum.  Moving the slit in the y direction a distance
W, causes the output to increase from 0.5 maximum to the maximum.
Moving the slit farther in y form W to 2W, the output decreases from
maximum to 0.5 maxi...