RoboteQ user manual PID tuning in Speed Mode, AX3500 Motor Controller User’s Manual

PID tuning in Speed Mode

The Differential component of the algorithm computes the changes to the error from one 16 ms time period to the next. This change will be a relatively large number every time an abrupt change occurs on the desired speed value or the measured speed value. The value of that change is then multiplied by a user selectable Differential Gain and added to the out- put. The effect of this part of the algorithm is to give a boost of extra power when starting the motor due to changes to the desired speed value. The differential component will also greatly help dampen any overshoot and oscillation.

The Integral component of the algorithm perform a sum of the error over time. This compo- nent helps the controller reach and maintain the exact desired speed when the error is reaching zero (i.e. measured speed is near to, or at the desired value).

	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 67. 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 experimenta- tion.

The Roborun PC utility makes this experimentation easy by providing one screen for chang- ing the Proportional, Integral and Differential gains and another screen for running and monitoring the motors. First, run the motor with the preset values. Then experiment with different values until a satisfactory behavior is found.

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