Browse Prior Art Database

Magnetic Sensor for 2-D Linear Stepping Motor

IP.com Disclosure Number: IPCOM000108847D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 6 page(s) / 249K

Publishing Venue

IBM

Related People

Brennemann, AE: AUTHOR [+4]

Abstract

Disclosed is a device for magnetically sensing the teeth on the platen of a Sawyer linear motor system. Signals are generated by the change in self-inductance of sensor coils as they move over the surface of the platen. These signals are encoded into coordinate locations of the motor relative to the platen. The sensors are relatively inexpensive to fabricate by using the same materials and techniques that are used in the manufacture of the Sawyer motors themselves.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 35% of the total text.

Magnetic Sensor for 2-D Linear Stepping Motor

       Disclosed is a device for magnetically sensing the teeth
on the platen of a Sawyer linear motor system.  Signals are generated
by the change in self-inductance of sensor coils as they move over
the surface of the platen.  These signals are encoded into coordinate
locations of the motor relative to the platen.  The sensors are
relatively inexpensive to fabricate by using the same materials and
techniques that are used in the manufacture of the Sawyer motors
themselves.

      Linear motors are well known to the robotics art.  It is also
known that pairs of linear motors may be combined to provide two axes
of motion (x-y) in mutually perpendicular directions.  Such a
two-axis motor or "forcer" (1) is moved across a flat platen
electromagnetically.  The forcer can be actuated in x or y separately
or in a vectorial combined direction.  It has the disadvantage that
it cannot be rotated about the z axis.  In fact, the forcer is
normally prohibited from rotating by the use of two motor sets for
each axis.

      Another disadvantage of the prior two-axis system is the
limited speed of the step motors.  While they have high acceleration
capability this cannot normally be utilized because of their
potential to stall when run open-loop. They are typically used for
application such as flatbed x-y plotters where speed is moderate and
the load is small, allowing open-loop operation.  However, when it is
required to move such motors precisely from one position to another
at high speed and under varying loads, a closed-loop system must be
used.  Various attempts have been made in this field.  For example,
pairs of sensors and lights have been used for detecting differences
in reflectance of orthogonal grid lines on a platen (2), and
measurements of the capacitance between the platen and an electrode
array have been  used (3) to determine the forcer position over a
platen.

      What would be desirable would be to:
      1)  have position sensors that are integral to the stepping
motors,
      2)  sense position directly off the platen teeth rather than
using laser interferometers and mirrors, or the like,
      3)  allow some rotation about the z axis,
      4)  provide sensors that are inexpensive to fabricate, that are
made of the same materials and fabricated with the same techniques as
the motors.

      The present invention satisfies these needs.  While the
following description relates generally to sensors for use on
two-axis (x-y) linear motors, the sensors are just as applicable to
single-axis linear motors. For use with two-axis motors, the sensors
of the present invention are attached to orthogonally arranged linear
motors.  They detect teeth in a platen to provide quadrature output
signals for both axes that vary with motor position.  The x,y, and Rz
displacements of the forcer above the platen can be determined
precisely allowing...