Three Modes of Servo Motor Brake

Users are often confused about electromagnetic braking, regenerative braking, dynamic braking, resulting in selecting the wrong accessories.

Three concepts

1. Dynamic brake is composed with dynamic brake resistor. It can shorten the mechanical feeding distance of servo motor by energy consumption braking when malfunction, emergency stopping, power off occurs.
2. Regenerative braking means that servo motor feedback the energy produced by braking during deceleration or stopping through inverter circuit to DC bus and is absorbed by RC (resistance-capacitance) circuit.
3. Electromagnetic braking locks the shaft of motor by mechanism equipment.
   

Differences

1. Regenerative braking can work only when servo operates normally. The motor cannot brake in some conditions, such as malfunction, emergency stopping, power off, etc. Dynamic brake and electromagnetic brake can work without power supply.
2. The regenerative braking can operate in system automatically, but dynamic braking and electromagnetic braking cannot operate without outer relay control.
3. Electromagnetic braking generally turns on after SV OFF; otherwise, it may cause the amplifier overload. Dynamic braking generally turns on after SV OFF or main circuit is shut off; otherwise, it may cause the dynamic braking resistor overheating.

Notes for accessories selection

1. Some systems (such as transmitter, lifting device, etc.) require that the servo motor can stop as soon as possible. But when malfunction, emergency stopping, power off occurs, servo has no regenerative braking and cannot decelerate the motor. Meanwhile, it is necessary to choose dynamic brake because mechanical inertia is too large. Select the dynamic brake according to the load, operating speed of motor and other factors.
2. To maintain the static position of mechanical equipment, some systems requires larger output torque provided by motor and the stopping time is longer. If self-lock function of servo is used, motor overheating or amplifier overload may occur. For this condition, it is suggested to use the motor equipped with electromagnetic braking.
3. Some servo have built-in regenerative braking unit, but if regenerative braking is used frequently, the DC bus voltage may become too high, so it is necessary to equip an additional regenerative braking resistor. Refer to the instructions of sample for the necessity to equip the regenerative braking resistor and about how much regenerative braking resistor can be equipped. Note that the number of braking on sample list is the data when the motor is without any load. In actual selection, first calculate the inertia ratio based on the load inertia of system and motor inertia on sample, then divide the braking number on sample list by (inertia ratio + 1) to get the required data which is the allowable braking number.