ASDA-M Chapter 2 Installation
Revision December, 2014
2-11
(b) When the external load torque exists, the motor is in reverse rotation.
Usually, the motor is in forward rotation, which means the torque output direction of
the motor is the same as the rotation direction. However, in some applications, the
direction of torque output is different from the rotation. In this situation, the motor is in
reverse rotation. The external energy goes into the servo drive through the motor. The
diagram below is one of the examples. When the motor is in constant speed, it is
positive torque in most of the time and a huge amount of energy rapidly transmits to
regenerative resistor.
Negative torque: TL × Wr TL: external load torque
For safety reasons, please calculate it by considering the safest situation.
For example, when the external load torque is the +70% rated torque and the rotation
reaches 3000 r/min, then take 400W (the rated torque is 1.27Nt-m) as the example,
the user has to connect the regenerative resistor which is 2 × (0.7× 1.27) × (3000 × 2 × π
／60) = 560W.
(2) Simple Selection
Choose the appropriate regenerative resistor according to the allowable frequency
and empty load frequency in actual operation. The so-called empty allowable
frequency is the frequency of continuous operation when the servo motor runs from
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