December 1973
B73-10492
• NASA TECH BRIEF
Ames Research Center
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information
Service, Springfield, Virginia 2215 1. Requests for individual copies or questions relating to the Tech Brief program may
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546.
This document was prepared under the sponsorship of the National
Aeronautics and Space Administration. Neither the United States
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the
information contained in this document, or warrants that such use
will be free from privately owned rights.
the operator to present any one of 99 separate frames
of each right and left test film. A fiber-optic bundle
distributes the light from a central source to a diffus-
ing screen mounted just above the film-plane aperture.
The mechanical base permits rotating the optical
system precisely about the center of rotation of each
eye; the base is structurally rigid so that the vergence
angles of the optics are accurately determined. A ver-
gence-angle drive motor counterrotates two threaded
shafts through a miter gear arrangement; as the shafts
turn, blocks on the right and left sides of the base are
moved symmetrically inward or outward. The blocks
are rigidly supported by a set of fixed parallel rods
running from one side of the mechanical base to the
other. A platform with a V-groove cut into its curved
inner and outer edges is mounted over each driving
block, and a vertical drive pin attached to the top of
each block extends up through a slot in the platform
and moves back and forth as the driving block is
moved. A trolley mounted over each platform has
three V-shaped wheels which nm in the V-grooves;
the drive pins also extend into the trolleys, so that the
linear motion of the driving blocks is converted into
the curvilinear motion of the trolley mechanisms.
Each trolley is specially constructed to minimize fric-
tion and backlash.
The mechanical base permits vergence angle
changes from 22 degrees eso to 14 degrees exo for
each eye; interpupillary distance adjustments are
made by moving each driving block inward or out-
B73-10492
ward until the distance between the centers of the
radii of the curved tracks are equal to the interpupil-
lary distance of the subject. The X-Y adjustor for the
chin rest is also on the mechanical base. Alignment of
the apex of the subject's corneas is accomplished with
the aid of two small fixtures mounted on the outer
portions of the right and left optical systems; the
examiner sights across the fixtures and moves the
subject's head forward or backward by means of a
forehead adjustor.
All the subsystems of the electronic controls are
open-loop and solid-state-controlled and, with the
exception of the vergence angle drive, utilize dc
stepping motors as prime movers. Arrangement is
also made for readouts of each variable.
Note:
Requests for further information may be directed
to:
Technology Utilization Officer
Ames Research Center
Moffett Field, California 94035
Reference: TSP 73-10492
Patent status:
NASA has decided not to apply for a patent.
Source: Thomas A. Decker of
Baylor College of Medicine
under contract to
Ames Research Center
(ARC-10759)
Category 05
