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Displacement Measurement by a Linear Encoder Using a Diode Array

IP.com Disclosure Number: IPCOM000047746D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Prakash, R: AUTHOR

Abstract

A typical optical encoder consists of precisely spaced parallel lines and is attached to the workpiece for motion measurement. By counting the number of lines going past a fixed sensor, the displacement is computed. The accuracy of measurement depends largely on the precision of the encoder lines. Any stress that alters the geometry (e.g., spacing) of the lines degrades the measurement accuracy. The geometric distortion may be a result of the manufacturing process. An encoder embodiment is described herein where the accuracy depends far less on maintaining the geometry of the encoder; instead, accuracy depends upon the sensor (a diode array in this case). As illustrated in Fig. 1, three components constitute the measuring system. The encoder strip is attached to the workpiece and slides over the sensor array.

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Displacement Measurement by a Linear Encoder Using a Diode Array

A typical optical encoder consists of precisely spaced parallel lines and is attached to the workpiece for motion measurement. By counting the number of lines going past a fixed sensor, the displacement is computed. The accuracy of measurement depends largely on the precision of the encoder lines. Any stress that alters the geometry (e.g., spacing) of the lines degrades the measurement accuracy. The geometric distortion may be a result of the manufacturing process. An encoder embodiment is described herein where the accuracy depends far less on maintaining the geometry of the encoder; instead, accuracy depends upon the sensor (a diode array in this case). As illustrated in Fig. 1, three components constitute the measuring system. The encoder strip is attached to the workpiece and slides over the sensor array. The light-emitting diode (LED) array illuminates the lines in the encoder strip. The encoder strip has lines drawn at an angle of 45OE. These lines are transparent, while the background is opaque. The spacing of the lines is such that at any given time at least one and at most two lines intercept the sensor array. These lines must be of uniform thickness and parallel to each other. The diode array sensor has as many as 512 elements spaced 25 mm apart. The spacing of these elements is uniform. The operation is readily defined by taking an example along with the illustrations of Fig. 2. If the encoder strip is in a starting position as shown Stage I, Element 300 is being intercepted by the encoder. This value is stored in the microprocessor. Next, the encoder moves and reaches Stage II. At this time, e.g., Element 500 is being intercepted by line 5 and 10 is being i...