Control Techniques Epsilon EP-P, Reference Manual

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Epsilon EP-P Drive Reference Manual
191
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Revision A4 www.controltechniques.com
Consider the following before determining the Friction:
• The most consistent readings can usually be obtained at motor speeds higher than 500 RPM but lower test speeds can be
used if necessary.
• If your application has travel limits, it may be helpful to use an external position controller to prevent the axis from
exceeding the machine limits. Set up a trapezoidal profile as shown.
• In the procedure below, the Torque Command and Velocity Feedback parameters can be measured using the drive’s
analog outputs, PowerTools software.
• With vertical loads the test readings must be taken while travelling in the same direction.
• The use of the PowerTools graph feature or an oscilloscope may be needed for systems with limited travel moves to
measure the rapidly changing torque and velocity signals.
• If your system’s friction changes with operating temperature, perform this procedure at normal operating temperature.
Procedure for Determining Friction:
1. Run the motor at the low test speed (at least 500 RPM).
2. While at speed, note the Torque Command Actual value (TCL).
NOTE
If the friction loading of your system varies when operating at constant speed, due to a load or spring load that changes as
the motor rotates, use the lowest value measured.
3. Repeat Step 1 using a velocity at least two times the low speed.
4. While at speed, note the Torque Command Actual value (TCH).
5. Use the following formula to calculate the friction:
Where:
T
CH
= Torque Command Limited value at higher speed

T
CL
= Torque Command Limited at lower speed

RPM
H
= Higher RPM (velocity)

RPM
L
= Lower RPM (velocity)

FV = Friction value
The figure below shows the relationship of Torque Command to the Velocity Feedback. There is increased torque during the
Accel ramp (Ta), constant torque (Tc) during the constant velocity portion of the ramp and decreased torque (Td) during the
decel ramp.
Figure 146: Trapezoidal Velocity Waveform with Torque Waveform
Determining Inertia Ratio
Actual system Inertia Ratio is determined by accelerating and decelerating the load with a known ramp while measuring the
torque required.
L H
CL CH
RPM - RPM
) T - (T
FV ) 100 (
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