Baldor NextMove BX, Руководство по установке

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Getting Started
MN1258V4 08/2000
45
time
velocity
acceleration/deceleration rate
ACCEL
0
axis speed during move
SPEED
units of
measure
set by
SCALE
Ideal trapezoidal velocity profile
time
velocity
0
Typical actual velocity profile
Overshoot
Following error (positional lag)
Underdamped
Good
Ideal
Figure 4-12: Velocity Profiles
To reduce the onset of instability a damping term is incorporated in the servo loop algorithm, called
velocity feedback gain. Velocity feedback acts to resist rapid movement of the motor and hence
allows the proportional gain to be set higher before vibration sets in. (In some applications, the
velocity feedback is handled by the amplifier, called a velocity servo). The effect of too high
proportional gain, or too low velocity feedback gain is illustrated by the "Under damped" line in
Figure 4-12.
In NextMove BX, an alternative damping method is provided in the form of the derivative of the
error signal. Derivative action has the same effect as velocity feedback if the velocity feedback and
feedforward terms are equal. In torque controlled systems, derivative action is generally the
preferred term.
Below is a description of the servo loop terms and their effect on the response of an axis.
Proportional Gain : This acts directly on the difference between the actual position of the axis
and the desired position (following error). The larger the proportional gain the faster the axis will
respond, however large values of proportional gain will introduce oscillation and result in a large
settling times or in a worse case instability of the axis. Conversely, a small value of proportional
gain will result in the axes responding slowly and never reaching the desired position.