User's Manual

PMAC User Manual

Setting Up a Motor 55

C003

000000000000000000011 111

MODES

DDRESS

HEX ($)

BINARY



LOW 16 BITS (4 HEX DIGITS) SPECIFY THE ADDRESS

WHEN HIGH 8 BITS ARE ZERO, ADDRESS IS USED IN NORMAL

MODE

I9=2 OR 3: PMAC REPORTS VARIABLE VALUE IN HEX



Figure 5 Address I-Variables

Ix02

AMP

ENC MOT

LIN ENC

LOAD

Encoder Table

X: $0720-$0739

Ix03

Ix04

FECP

Ix02 DAC output address

Ix03 POSITION loop feedback address

Ix04 VELOCITY loop feedback address

DACn

DACn+1

DAC Locations

Y: $C002-$C03B

ENCn

ENCn+1

Figure 6 PMAC Pulse and Direction Output

Accuracy vs. Stability

A sensor on the load (often a linear scale) provides a more accurate measure of position than a sensor on

the motor, because its accuracy is not affected by imperfections in the motor-load coupling. However, it

can also make the axis less stable, because these coupling imperfections (typically compliance and

backlash) are now inside the loop. A sensor on the motor, while less accurate provides better stability

because these imperfections are not inside the loop.

In many cases, it is possible to get both accuracy and stability by using sensors on both the motor and the

load. In a PMAC system, simply use the load encoder to close the position loop (for accuracy), using

Ix03 to point to this encoder; and use the motor encoder to close the velocity loop (for stability), using

Ix04 to point to this encoder.