Speedring Optimizes Mirror Design

ALGOR FEA HELPS SPEEDRING SYSTEMS, INC. OPTIMIZE MIRROR DESIGN

Mr. Ketabchi used a Compaq 386, 33MHz desktop computer to construct and analyze the mirror. He is shown here with the system.

Mr. Mehrdad Ketabchi, project engineer for Speedring Systems, Inc. of Rochester Hills, Michigan, recently completed a series of Algor FEA analyses aimed at optimizing the design of a critical component of an airborne sighting and guidance system. Development of the system is being funded by the British, French and German governments.

The component is a beryllium, nickel plated mirror, designed to operate in an airborne environment with critical static and dynamic performance requirements. The primary objectives of the analyses were to determine the optimal thickness and web construction of the mirror, in order to meet these requirements.

Four Analyses Performed

"Algor FEA software was used to create the model, then four analyses were performed," explains Mr. Ketabchi. "These included Constant Acceleration Analysis, to determine parallelism of lines of sight, flatness, and maximum stress under an acceleration of 1g; Frequency Analysis, to test the flexible modes of the mirror; Random Vibration Analysis, to determine maximum stress and displacement at frequencies of 5.5 to 1000 Hz; and Shock Analysis, to see the effects of a 20g half-sine pulse lasting 11 ms, and a 6g half-sine pulse lasting 100 ms."

The model consists of 1902 3-D solid elements and 3402 nodes, of which 16 are made inactive to simulate the mirror's two-zone, fixed mounting system. Twenty-four (24) nodal forces are used to simulate a tripod assembly that is mounted on the mirror.

The model of the mirror used in the analyses is shown. Note the complex design of the mirror's web construction.

The static analysis was performed on models with different thicknesses to determine an optimum thickness for the face-sheet and ribs. The optimized part measures 368 x 343 x 25.5 mm and weighs less than 2 Kg. It has a natural frequency above 700 Hz and maintains a 2 arc second parallelism on specified zones while subjected to 1g acceleration perpendicular to the plane of the mirror.

"Through our analyses we found stress and deflection levels acceptable under both constant acceleration and shock conditions," Mr. Ketabchi explains. "The random vibration analysis also indicated acceptable stress levels."

Quality Graphics

Mr. Ketabchi used Algor's SuperCap Animation and Presentation Software to create "slide show" images of the analysis results. The Pizazz Plus Screen Print Utility was then used to capture the images for output on an HP Paint Jet printer. The color images were included in a final written report.

Speedring Systems is involved in the design and manufacture of Metal Optics and Precision electromechanical systems for pointing, scanning and positioning. Currently, the company is developing the opto-mechanical design for the "International Solar Terrestrial Physics-Polar Satellite Visual Imaging Investigation (ISTP-PS VII)".