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Program for Simulating Direct Light Reflection

IP.com Disclosure Number: IPCOM000075906D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 7 page(s) / 160K

Publishing Venue

IBM

Related People

Appel, A: AUTHOR [+3]

Abstract

This program is a technique for determining the manner in which light is reflected from arbitrary reflective surfaces. Such determination is valuable in many situations. For example, it is advantageously employed in the automatic detection of the position in three-dimensional space of silicon wafers on an assembly line. By measuring the light which is reflected from a set of minute cavities which are either etched into or impressed on the wafer, the position of the wafer can be quickly determined for automatic processing.

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Program for Simulating Direct Light Reflection

This program is a technique for determining the manner in which light is reflected from arbitrary reflective surfaces. Such determination is valuable in many situations. For example, it is advantageously employed in the automatic detection of the position in three-dimensional space of silicon wafers on an assembly line. By measuring the light which is reflected from a set of minute cavities which are either etched into or impressed on the wafer, the position of the wafer can be quickly determined for automatic processing.

Where such automatic detection of position is desired, it is important to be able to determine in advance how light will reflect from the cavities. In addition, it is important to know how much light will be reflected from different angles and the sensitivity of the cavities to changes in orientation. Furthermore, a significant factor is the determination of the best shape of a cavity for a given purpose. The configuration of the cavities is generally that of a hollow pyramid where the base is a regular polygon. The pyramid may be truncated. In the application of the program, there are provided not only quantitative results but also an understanding as to certain optical properties of cavities.

In Fig. 1, there is shown the classical descriptive geometry solution to the determination as to how a light ray reflects from an arbitrary plane in space. Fig. 1 consists of two normal views and three auxiliary views. In order to accurately determine the reflected ray, the plane of reflection has to be found and only in this view can the angle of incidence be measured. The reflected ray then has to be projected back to the original views to ascertain as to how this reflected ray is reflected from any other surface. It is obvious, that the descriptive geometry solution is a difficult drafting problem. There are other graphical methods for solving this problem but they are less precise. The problem is solved herein by the program in an interactive computer graphics environment.

The program traces the path of reflected light throughout the hollow cavity and is general enough to be used with any combination of surfaces, not only those forming a hollow cavity. Accordingly, the program may be used to solve problems in optics, mechanical design, industrial design and lighting.

The basic technique used in conjunction with the program for determining the angle of the reflected ray is illustrated in Fig. 2. Therein, an incident ray is described by a point P(I), which is a starting point of the ray, and a direction. The real piercing point of this ray is found on all surfaces in the given set of surfaces.

A real piercing point must lie within the boundaries of the surface. Not all surfaces will have a real piercing point. The surface that the ray will reflect from has the real piercing point which is closest to point P(I) but not behind P(I). After determining as to which surface the ra...