光电编码器英文介绍..doc

直线和旋转编码器、解角器结构和原理 Linear and Rotary Encoders An encoder is an electrical mechanical device that can monitor motion or position. A typical encoder uses optical sensors to provide a series of pulses that can be translated into motion, position, or direction. Figure 10-109 shows a diagram and picture of rotary encoders. The diagram in Fig. 10-109b shows that the disk is very thin, and a stationary light-emitting diode (LED) is mounted so that its light will continually be focused through the glass disk. A light-activated transistor is mounted on the other side of the disk so that it can detect the light from the LED. The disk is mounted to the shaft of a motor or other device whose position is being sensed, so that when the shaft turns, the disk turns. When the disk lines up so the light from the LED is focused on the phototransistor, the phototransistor will go into saturation and an electrical square wave pulse will be produced. This figure shows an example of the square wave pulses that are produced by the rotary encoder. This type of disk was used in early applications but the size of the holes in the metal disk limited the amount of accuracy that could be obtained. As more holes were cut in the disk, it became too fragile for industrial use.  FIGURE 10-108 Example of Hall-effect switches. These switches are used for positioning applications such as indicating when a door is open or closed or if a safety guard is in place. Incremental Rotary EncoderAn encoder with one set of pulses would not be useful since it could not indicate the direction of rotation. Most incremental encoders have a second set of pulses that is offset (out of phase) from the first set of pulses, and a single pulse that indicates each time the encoder wheel has made one complete revolution. Figure 10-110 shows an example of the two sets of pulses that are offset. Since the two sets of pulses are out of phase from each other, it is possible to determine which direction the shaft is rotating b