RoboteQ AX2550/2850 user manual PID tuning in Speed Mode, PID algorithm used in Speed mode

Closed Loop Speed Mode

	Proportional
	Gain
Desired Speed	E= Error
-	dt
	dE

x

xΣ Output

Tachometer A/D

or

Optical Encoder

Measured Speed

Integral Gain

dE

dt

x

Differential

Gain

FIGURE 76. PID algorithm used in Speed mode

PID tuning in Speed Mode

As discussed above, three parameters - Proportional Gain Integral Gain, and Differential Gain - can be adjusted to tune the Closed Loop Speed control algorithm. The ultimate goal in a well tuned PID is a motor that reaches the desired speed quickly without overshoot or oscillation.

Because many mechanical parameters, such as motor power, gear ratio, load and inertia are difficult to model, tuning the PID is essentially a manual process that takes experimen- tation.

The Roborun PC utility makes this experimentation easy by providing a screen for changing the Proportional, Integral and Differential gains and another screen for running and monitor- ing the motors. Run first the motor with the preset values. Then experiment different val- ues until a satisfactory behavior is found.

In Speed Mode, the Integral component of the PID is the most important and must be set first. The Proportional and Differential component will help improve the response time and loop stability.

In case where the load moved by the motor is not fixed, you will need to tune the PID with the minimum expected load and tune it again with the maximum expected load. Then try to find values that will work in both conditions. If the disparity between minimal and maxi- mal possible loads is large, it may not be possible to find satisfactory tuning values.

Note that the AX2500/2850 uses one set of Proportional Integral and Differential Gains for both motors and therefore assumes that similar motors, mechanical assemblies and loads are present at each channel.

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