Page 322 - Sensors and Control Systems in Manufacturing

Advanced Sensors in Pr ecision Manufacturing
susceptible to electromagnetic interference, and are therefore useful 279
for information processing and display in measurement and control
systems. Their ability to rapidly scan a series of patterns provides
additional manufacturing automation opportunities when light and
dark patterns are placed in concentric rings in a disk. Figure 6.3 illus-
trates a portion of such a disk that can be rigidly attached to a shaft or
an object and housed in an assembly containing optical sensors for
each ring (Fig. 6.4). The assembly, called an optical encoder, automatically

FIGURE 6.3 Detection of movement direction in directional encoders: (a) by
means of two outputs with 90° phase shift; (b) output electronic circuit;
(c) additional marker for absolute positioning.

Coded disk Photodetectors

Digital
Output
Sensing shaft

θ

Optical focusing system
FIGURE 6.4 Principle of absolute position encoders for linear and rotary
movements.