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42 www.emersonct.com SM-EZMotion Module User Guide
Feedhold Decel/Accel
When the Feedhold destination is activated, the motor will
decelerate to a stop in the time specified by the
FeedholdDecelTime parameter. When feedhold is cleared,
the motor will accelerate back to speed in the same
specified period of time.
Feedhold is a means to halt the motor within a velocity
profile and then return to the profile later at the exact same
place in the profile. Feedhold does not ramp and does not
decelerate in terms of velocity. Instead, it stops by
decelerating time. For example, if the motor is running at
50 revs/second and feedhold is activated with 2 seconds
specified in the FeedholdDecelTime parameter, then the
motor will actually slow and stop in 2 seconds as measured
time (on a time/velocity profile) goes from 100% to 0%.
Travel Limit Deceleration
The value entered here is the deceleration ramp that is
used when a software or hardware travel limit is hit.
7.3.7 Current View
The Current View allows the user to configure Current
Level Flags and Current Limits for use in the application.
Figure 71: Torque View
Current Level
This parameter sets the activation point for the Current
Level Active source. If set to 100%, the Current Level
Active source will activate any time the Current Command
reaches or exceeds 100% continuous.
Current Limit
This parameter sets the value to which the Current
Command will be limited when the Current Limit Enable
destination is active. To make the Current Limit always
active, assign the Current Limit Enable destination to the
Initially Active source on the Assignments view.
7.3.8 Tuning View
The Tuning View contains all the parameters that are
adjusted to properly tune the motor/drive system. Figure 72
shows an example of the Tuning View.
Figure 72: Tuning View
Inertia Ratio
This parameter is the ratio between the load inertia and the
motor rotor inertia. The formula is defined as follows:
In order to calculate the Inertia Ratio, the user must first
calculate the load inertia. The load inertia is the inertia of
the load reflected to the motor shaft. Control Techniques
offers a free sizing software called CTSize that helps the
user calculate the load inertia. CTSize can be downloaded
from the Control Techniques’ website at no charge
(www.emersonct.com).
When entering the inertia ratio, if the exact ratio is not
known, it is better to enter a lower (more conservative)
value than to enter a “higher-than-actual” value. Higher
numbers in the Inertia Ratio amplify the gains of the
Velocity and Position Loop parameters described below.
The motor rotor inertia used in this calculation can be found
on the Motor Tab on the Motor/Encoder view in
PowerTools Pro EZ or in the SPMotor.ddf file that is
installed with PowerTools Pro EZ software.
Velocity Loop Bandwidth
The Velocity Loop Bandwidth is the theoretical bandwidth
of the velocity controller. It is important for the motor data
file to be accurate for ideal velocity performance, in
particular the Motor Inertia and Motor Current Constant
(Ke). Higher Velocity Loop Bandwidth values will result in
better response to change in velocity command, however
InertiaRatio
LoadInertia
RotorInertia
-----------------------------------=