RoboteQ AX2550/2850 user manual Using the Encoder to Track Position

Installing, Connecting and Using the Encoder Mod-

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 position.

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 formula is as follows:

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

Destination= 50,050

Counter= 50,000

distance	at divider
50	1
25	2
12	4
6	8
3	16
1	32
0	64
0	128

FIGURE 87. Small distance computation example

Destination= 50,000

Counter= 45,000

distance	at divider
127	1
127	2
127	4
127	8
127	16
127	32
78	64
39	128

FIGURE 88. Large distance computation example

Important Notice

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