RoboteQ AX3500 Connecting and Using the Encoder Function, Optical Incremental Encoders Overview

Optical Incremental Encoders Overview

SECTION 8

Connecting and

Using the

Encoder

Function

This section describes the Encoder input module that is built into the AX3500.

Optical Incremental Encoders Overview

Optical incremental encoders are a means for capturing speed and travelled distance on a motor. Unlike absolute encoders which give out a multi-bit number (depending on the reso- lution), incremental encoders output pulses as they rotate. Counting the pulses tells the application how many revolutions, or fractions of, the motor has turned. Rotation velocity can be determined from the time interval between pulses or by the number of pulses within a given time period. Because they are digital devices, incremental encoders will measure distance and speed with perfect accuracy.

Since motors can move in forward and reverse directions, it is necessary to differentiate the manner that pulses are counted so that they can increment or decrement a position counter in the application. Quadrature encoders have dual channels, A and B, which are electrically phased 90° apart. Thus, direction of rotation can be determined by monitoring the phase relationship between the two channels. In addition, with a dual-channel encoder, a four-time multiplication of resolution can be achieved by counting the rising and falling edges of each channel (A and B). For example, an encoder that produces 250 Pulses per Revolution (PPR) can generate 1,000 Counts per Revolution (CPR) after quadrature.

AX3500 Motor Controller User’s Manual 77