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Kp=10,Kv2=3
Although the system is more damped, it appears to be having a little trouble matching the velocity
of the target. Velocity feedback means substracting some component of the velocity
(Kv2 x velocity) from the torque. As Kv2 increases, the velocity feedback will cause a greater
velocity error in our system. To compensate for this we need to add some Velocity Feedforward
(Kvff).
Velocity Feedforward (Kvff)
SilverMax contains an internal target generator called the “Trajectory Generator”. In real time,
SilverMax calculates the motion profile defined by a given command and it’s parameters. On
each servo cycle, the “target” value is updated in the servo control loop. Similar to the Velocity
Feedback value, a “Target Velocity” value is calculated from the “target” value, instead of the
position value. This “target” value is used to compensate a lag in position that is induced by the
Velocity Feedback term.
The Velocity Feedforward gain value is set to adjust the required amount of the Velocity
Feedforward term. Velocity Feedforward is a positive feedback value used to “anticipate” the
velocity needs for the servo control loop. Setting the gain value to zero, prevents the Velocity
Feedforward term from being used. Usually, this gain value is set equal to the sum of the
Velocity 1 Feedback (Kv1) and Velocity 2 Feedback (Kv2) gain values.
Setting Kvff=3 in our system produces the following chart.
SilverMax User Manual
104
Revision 3.22