DIGIVEX Little Drive Servoamplifier
63
PVD 3530 GB 01/2005
General characteristics of each predictor
Mass or gravity compensation (vertical axis)
The current value, in amps, required by the motor to move the mass at constant speed (average
between up and down) is introduced directly into the parameter.
Dry or "static" friction
The friction force is fixed, whatever the speed. Its direction is opposed to motion, the sign
therefore depends on the speed set point sign.
In this case too, the values are entered directly in amps, for the required motor current to
overcome friction.
The "threshold" expressed in rpm defines a speed "band" within which this compensation is zero.
The threshold is of the order of 1/1000th of maximum speed. This zone allows torque oscillation
to be reduced during rapid and repeated changes of the speed sign. This is the case, in
particular, at rest when there is a position loop.
"Dynamic" friction compensation
Friction proportional to speed, encountered on some mechanical components using fluids.
Value to enter: coefficient in amps / rpm.
Acceleration prediction
Depending on the total inertia (load and motor rotor) and on the desired acceleration, the torque
necessary is equal to: C =
Σ
J . d
ω
/ dt.
The set point is monitored therefore in order to send a set point that is proportional to inertia
(fixed) and to acceleration to the current control. This is one of the limits of the system; there is
no point in having a variation in the speed set point that is greater than the maximum possible
acceleration of the motor, given by d
ω
/ dt = peak torque /
Σ
J. Acceleration prediction is only
useful if there is a ramp on the speed reference.
The parameter used is tpr, prediction time, in milliseconds; tpr can vary between:
0 ms (no prediction)
t = td, start up time from 0 to maximum speed, with full drive current. There is then 100%
correction.
This manual was downloaded on www.sdsdrives.com
+44 (0)117 938 1800 - [email protected]
