Browse Prior Art Database

Air-Bearing-Supported Three-Degrees-Of-Freedom Fine Positioner

IP.com Disclosure Number: IPCOM000101305D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 6 page(s) / 224K

Publishing Venue

IBM

Related People

Hammer, R: AUTHOR [+3]

Abstract

Disclosed is a three-degrees-of-freedom fine positioning device which provides a high degree of positioning capability (resolution down to 0.2 mm, and acceleration up to 12 g's) for use in planar alignment tasks. When coupled with a standard industrial robot and external sensing, improvements in precision up to two orders of magnitude can be achieved. The device consists of a moving element (armature) that can support an end effector and be positioned over a+1 mm range in x and y, and rotated up to 1.75o in r about the z axis with respect to a fixed stator. Motion of the armature with respect to the stator is achieved with zero backlash, zero hysteresis, and zero friction by use of an air bearing suspension. Direct-drive linear motors (1) provide motion of the armature. (Image Omitted)

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 46% of the total text.

Air-Bearing-Supported Three-Degrees-Of-Freedom Fine Positioner

       Disclosed is a three-degrees-of-freedom fine positioning
device which provides a high degree of positioning capability
(resolution down to 0.2 mm, and acceleration up to 12 g's) for use in
planar alignment tasks.  When coupled with a standard industrial
robot and external sensing, improvements in precision up to two
orders of magnitude can be achieved.  The device consists of a moving
element (armature) that can support an end effector and be positioned
over a+1 mm range in x and y, and rotated up to 1.75o in r
about the z axis with respect to a fixed stator.  Motion of the
armature with respect to the stator is achieved with zero backlash,
zero hysteresis, and zero friction by use of an air bearing
suspension.  Direct-drive linear motors (1) provide motion of the
armature.

                            (Image Omitted)

      Previous devices which used springs for support of a moving
armature as is, either cantilevered flat springs for movement in X
and Y axes (1), or wire springs for X, Y, R motion (2), had several
deficiencies: notably, out-of-plane motion due to changing spring
length with motion-insufficient z axis stiffness due to buckling of
springs, causing undesirable position errors.  The present invention
eliminates these problems while providing a compact and robust device
with higher performance.

      Prior art which utilized an air-bearing-supported armature in a
2- degrees-of-freedom device (3), had a resolution of 12 mm and a
peak acceleration of 1 g over large areas (4).  In the present
invention, the device has a resolution of 0.2 mm with acceleration on
the order of 12 g's.

      The basic components of the device, i.e., armature, stator,
motor magnet assembly, and housing, are shown in Fig. 1.

      AIR BEARING: To maximize the available air-bearing surface area
(necessary to provide high load handling capability), both stator and
armature surfaces are planarized.  The stator surface is dominated by
motor teeth, recessed channels and pads (Fig. 2).  The air-bearing
film is supplied from four recessed orifices, each serving one
quadrant of the stator. The orifices are small holes in sapphire
plates mounted in recesses.  Sapphire is used to prevent wear of the
orifice by sub-micron particles in the filtered air stream.
Additional recessed pads, located around the perimeter of the raised
air-bearing surface and supplied through channels from the recessed
orifices, serve to increase roll stiffness.  The stator-to-armature
air bearing film thickness is typically 5-10 mm.

      STATOR: To planarize the air-bearing surface, the permeable
(1008 steel) motor pole faces (shown in Fig. 3) are flush-mounted in
the stator by brazing.  The air-bearing surface is ground, lapped and
polished to provide a smooth flat surface.  For thermal
considerations the stator is made of nonmagnetic stainless steel.
...