Installing, Connecting and Using the Encoder Mod-
140 AX2500/2850 Motor Controller User’s Manual Version 1.7. February 1, 2005
Using the Encoder to Track Position
The encoder module can be used to report the distance between the actual motor position
and a desired destination. The resulting measured “distance” can then be used by the con-
troller in the position mode to move the motor in the right direction until the destination is
reached. This movement is controlled by the PID position algorithm inside the controller
and is therefore best suited at tracking posit ion.
Since the controller uses a signed 8-bit value (-127 to +127) for the distance measurement
in the Position Mode, a special algorithm is used to convert the real distance which can be
much higher than -127 to +127 as both the counter and destination registers are 32-bit
wide.
The actual for mula is as follow s:
Distance = (Destination - Counter value) / Divider
Where: divider is a configurable parameter of value 1, 2, 4, 8, 16, 32, 64 or 127
If computed distance is less than -127, then reported distance is -127
If computed distance is larger than +127, then reported distance is +127
Important Notice
Destination= 50,050
distance at di vider
50 1
25 2
12 4
6 8
3 16
1 32
0 64
0 128
Counter= 50,000
FIGURE 87. Small distance computation example
Destination= 50,000
distance at di vider
127 1
127 2
127 4
127 8
127 16
127 32
78 64
39 128
Counter= 45,000
FIGURE 88. Large distance computation example