Page 2–16 SureServo2 User Manual – 1st Edition – 05/20/2021
Chapter 2: Installation
Monitoring DI/DO Codes ParametersAlarms Wiring
Calculation of the regenerative power when there is external torque and the motor does the
negative work.
1) Direction of motion of the object
2) Force direction of the motor
3) Regenerative power
Usually, the motor does positive work and the motor’s torque direction is identical to the
rotation direction. However, in some instances, the motor’s torque direction is opposite to
the rotation direction. This means the motor is doing negative work and the external power
is applied to the servo drive through the motor. For instance, if the external force direction
is identical to the rotation direction (such as vertical downward motion of the machine), the
servo system outputs more power to counterbalance the excessive external load (the weight
of vertical-mounted machine) in order to keep up with the specified target speed. In this case,
considerable power returns to the servo drive. When DC Bus cannot store more power, this
power is consumed by the regenerative resistor.
Example 2:
For a 400W motor (SV2L-204B) with an external torque load +70% of the rated torque (1.27
N·m), with rotation speed up to 3000 rpm, the required external regenerative resistance is:
2 x (0.7 x 1.27 Nm) x
3000 rev/min x 2 x π
60 sec/min
= 560W
So, a regenerative resistor of 560W and 40Ω is needed.
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