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Browse Prior Art Database

Shadowgraphic Technique for Measuring Small Motions

IP.com Disclosure Number: IPCOM000045367D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Hall, SA: AUTHOR [+3]

Abstract

The successful development of high-speed actuators for impact printing requires, for the evaluation of prototypes, a reliable and convenient technique to measure small, rapid displacements of mechanical parts. Ideally, the measurement technique should be linear, should interfere minimally with an actuator's dynamic performance, should accommodate easily a variety of prototype designs, and, for multi-piece actuators, should be able to monitor the motion of each piece independently.

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Shadowgraphic Technique for Measuring Small Motions

The successful development of high-speed actuators for impact printing requires, for the evaluation of prototypes, a reliable and convenient technique to measure small, rapid displacements of mechanical parts. Ideally, the measurement technique should be linear, should interfere minimally with an actuator's dynamic performance, should accommodate easily a variety of prototype designs, and, for multi-piece actuators, should be able to monitor the motion of each piece independently.

An optical technique is described in this article which meets all of the above objectives. For purposes of this discussion, it is assumed that the system to be studied is a wire-matrix actuator consisting of two pieces, a hammer 10 and a print wire 12, as shown in the figure. The area of interest of the actuator is illuminated by a laser or incandescent light source, and its silhouette, magnified if so desired, is imaged upon two screens 18 and 20 by means of one or more objective lenses 14 and a beamsplitter 16. Each screen is entirely opaque except for a small slit S(1) or S(2) which is carefully positioned with respect to the actuator's shadow. Located behind each slit is a photodiode 22 or 24 enveloped in an otherwise-dark enclosure, such that all of the light reaching the photodiode must pass through the slit. Consequently, as the hammer 10 moves back and forth, the front edge of its shadow travels across slit S(1), thereby modula...