RoboteQ AX3500 user manual Important Notice, Connecting and Using the Encoder Function

Connecting and Using the Encoder Function

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 55. 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 56. Large distance computation example

Important Notice

Encoders do not report an absolute position value but a count that is relative to the point where the motor shaft was at power up. It is typically necessary to have the motors moved to a “home” position and reset the counters at that reference point.

86 AX3500 Motor Controller User’s Manual Version 1.9b. June 1, 2007