ASDA-B3 Installation Find the maximum regenerative energy: Eo = 0.74 joules (from the table above). Find the regenerative energy that can be absorbed by the capacitor: Ec = 8.42 joules (from the table above). 2 The required capacity of the regenerative resistor = 2Ч((N+1)Ч𝐸 0 −𝐸 𝑐 ) T = 2Ч((15+1)Ч0.74−8.42) 0.4 = 17.1 W From the calculation above, the required power of the regenerative resistor is 17.1 W, which is smaller than the specified capacity. In this case, the built-in 40 W regenerative resistor fulfills the need. In general, the built-in regenerative resistor can meet the requirement when the external load is not too great.
(b) Calculation of the regenerative energy when there is external torque and the motor does the negative work. (3) (1) (2) (1) Moving direction of the object; (2) Direction of torque; (3) Regenerative energy 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 energy is applied to the servo drive through the motor.
For instance, if the external force direction is identical to the rotation direction (such as downward motion of the vertically-mounted machine), the servo system outputs more power to counterbalance the excessive external force (the weight of vertically-mounted machine) in order to keep up with the specified target speed. In this case, considerable energy returns to the servo drive. When the DC Bus is full and cannot store more energy, this energy is consumed by the regenerative resistor. Example:
For the motor ECM-A3L-CY0604RS1 (400 W), when the torque of the external load is +70% of the rated torque (1.27 N-m) with rotation speed up to 3,000 rpm, the required external regenerative resistor is: 2 Ч (0.7 Ч 1.27) Ч ( 3000Ч2Чπ 60 ) = 558 W. So, a regenerative resistor of 560 W and 40Ω is needed. 2-21