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Method and Apparatus for Aligning and Registering a Two-Axis Linear Stepper Motor

IP.com Disclosure Number: IPCOM000104212D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 94K

Publishing Venue

IBM

Related People

Singletary, A: AUTHOR [+2]

Abstract

In a positioning system based on a two-axis linear stepper motor, electrical coils in the motor body (hereafter referred to as the "forcer") are aligned with a regular grid of features in the surface of a steel table or platen. Electromagnetic interactions between the motor coils and the features on the surface of the platen can be used to propel the forcer across the platen in both X and Y directions. In order for the most efficient interaction to be achieved, the forcer coils must be parallel to the X and Y axes of the grid of features on the platen. Motion and control of the forcer can be achieved in a range of discrete angular displacements, but the acceleration and positioning capabilities of the motor are degraded.

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Method and Apparatus for Aligning and Registering a Two-Axis Linear Stepper Motor

      In a positioning system based on a two-axis linear stepper
motor, electrical coils in the motor body (hereafter referred to as
the "forcer") are aligned with a regular grid of features in the
surface of a steel table or platen.  Electromagnetic interactions
between the motor coils and the features on the surface of the platen
can be used to propel the forcer across the platen in both X and Y
directions.  In order for the most efficient interaction to be
achieved, the forcer coils must be parallel to the X and Y axes of
the grid of features on the platen.  Motion and control of the forcer
can be achieved in a range of discrete angular displacements, but the
acceleration and positioning capabilities of the motor are degraded.
This alignment is difficult to achieve by hand due to the small
displacements involved and a tendency of the electromagnetic forces
to resist angular motion of the forcer.  This type of motor system
also has no provision for positional feedback.  It is, therefore,
very important to be able to identify a reference position and locate
the forcer very accurately.

      The disclosed method and apparatus consists of a configuration
of sensors and reference blocks and a method for using these to
ensure the precise location and alignment of the forcer from any
location on the platen surface and any angular configuration which
will allow movement and control of the forcer.

      The figure shows the configuration in which the sensors and
refer- ence blocks have been installed.  Three light beam sensors
have been used.  The X and Y limit sensors shine a beam across the
length of the platen near the left and front edges.  They are used to
provide coarse positioning feedback.

      The home sensor shines across the left front corner of the
platen at a 45 degree angle.  It is used in the final, fine
positioning.  The reference blocks are located beyond the beams of
the limit sensors in the lower left corner of the platen and are
precisely aligned to the grid of features on the platen.  These
blocks are spring-loaded in a direction normal to their primary axis.

The method for positioning and aligning the forcer is as follows:

      If the X limit sensor is clear, move the forcer in the nega-
tive X direction until the X limit sensor is broken and then stop as
quickly as possible.  Move the forcer in t...