RoboteQ AX2550/2850 Recommended Encoder Types, Installing, Connecting and Using the Encoder Mod

Installing, Connecting and Using the Encoder Mod-

A Channel

1 Pulse

= 4 Transitions B Channel

= 4 Counts

Quadrature

Signal

Count Up Count Down

FIGURE 77. Quadrature encoder output waveform

The figure below shows the typical construction of a quadrature encoder. As the disk rotates in front of the stationary mask, it shutters light from the LED. The light that passes through the mask is received by the photodetectors. Two photo detectors are placed side by side at so that the light making it through the mask hits one detector after the other to produces the 90o phased pulses.

LED light source

Rotating encoder disk

Stationary mask

Photodetector

FIGURE 78. Typical quadrature encoder construction

Unlike absolute encoders, incremental encoders have no retention of absolute position upon power loss. When used in positioning applications, the controller must move the motor until a limit switch is reached. This position is then used as the zero reference for all subsequent moves.

Recommended Encoder Types

The module may be used with most incremental encoder module as long as they include the following features:

•Two quadrature outputs (Ch A, Ch B), single ended signal

•2.5V minimum swing between 0 Level and 1 Level on quadrature output

•5VDC operation. 100mA or less current consumption per encoder

More sophisticated incremental, encoders with differential outputs, index, and other fea- tures may be used but these additional capabilities will be ignored.

The choice of encoder resolution is very wide and is constrained by the module’s maxi- mum pulse count at the high end, and measurement resolution for speed at the low end.

132 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005