User guide

Xenus Plus User Guide Operational Theory
Copley Controls 21
2.5.3: Velocity Mode and Velocity Loop
Velocity Loop Diagram
As shown below, the velocity loop limiting stage accepts a velocity command, applies limits, and
passes a limited velocity command to the input filter. The filter then passes a velocity command to
the summing junction. The summing junction subtracts the actual velocity, represented by the
feedback signal, and produces an error signal. (The velocity loop feedback signal is always from
the motor feedback device even when an additional encoder is attached to the load.) The error
signal is then processed using the integral and proportional gains to produce a current command.
Programmable digital filters are provided on both the input and output command signals.
Inputs
In velocity mode, the velocity command comes from one of the following:
The drive’s analog or PWM inputs.
A network command, CAN, or RS-232 Serial.
A CVM control program.
The drive’s internal function generator.
In position mode, the velocity command is generated by the position loop.
Velocity Loop Limits
The velocity command is limited based on the following set of parameters designed to protect the
motor and/or the mechanical system.
Limiter
Description
Velocity Limit
Sets the maximum velocity command input to the velocity loop.
Acceleration Limit
Limits the maximum acceleration rate of the commanded velocity input to the velocity loop.
This limit is used in velocity mode only.
Deceleration Limit
Limits the maximum deceleration rate of the commanded velocity input to the velocity loop.
This limit is used in velocity mode only.
Fast Stop Ramp
Specifies the deceleration rate used by the velocity loop when the drive is hardware
disabled. (Fast stop ramp is not used when drive is software disabled.) If the brake delay
option is programmed, the fast stop ramp is used to decelerate the motor before applying
the brake.
Note that Fast Stop Ramp is used only in velocity mode. In position mode, the trajectory
generator handles controlled stopping of the motor. There is one exception: if a non-latched
following error occurs in position mode, then the drive drops into velocity mode and the Fast
Stop Ramp is used.
For more information, see Following Error Fault Details (p. 51 ).
Velocity
Command
Current
Command
Velocity Limiter
Velocity Loop
Feedback (Derived Velocity)
Limits:
Velocity
Acceleration*
Deceleration*
Emergency Stop Deceleration*
*Not used when velocity loop is controlled by position loop. See "Velocity Loop Limits" for details.
Velocity Integral Gain (Vi)
Velocity Proportional Gain (Vp)
Limited
Velocity
+
-
+
+
Filter
Filter