Speaking of the performance requirements for industrial robots, it is nothing more than “fast, accurate and ruthless”. In fact, this is the requirement for robot joint servo motor. Today we will disassemble the meaning behind these three words.

Among them, the meaning of “fast” and “accurate” is well understood by everyone, which requires that the response speed of servo motor should be fast and the control accuracy should be high. And how to solve the word “ruthless”? In fact, when you think about it carefully, in addition to being fast and accurate, the rest of our requirements for the servo motor is strong overload capacity, that is, “ruthless”.

## Why does the servo motor require strong overload capacity?

Because the servo motor is mainly used to drive the motion of joints on the robot, it needs to run frequently forward and reverse for a short time. In the case of frequent forward and reverse rotation, load with certain inertia and very fast control speed, the requirements for overload capacity (overload torque and overload current) of servo motor are very high.

It can be seen from the above formula that when the actual servo motor is started with load, in addition to the loaded torque tload and friction coefficient kn, it will also be due to the load inertia J and angular acceleration D ω/ The influence of DT leads to the increase of starting torque. In particular, the faster the motor accelerates, D ω/ The greater DT, the same J, the greater te, and the stronger the torque overload capacity of the servo motor.

## How to measure the overload capacity of servo motor?

We all know that dynamometer should be used to measure the torque speed curve of motor, so as to obtain the torque output performance of motor. But there is a problem here, that is, the torque speed curve reflects the torque output capacity of the motor at constant speed, and can not reflect the overload capacity of the servo motor. In the operation of servo motor, the output force during continuous operation is not large, but large during startup and braking. If the motor is selected according to the torque speed curve, the power of the selected motor will be seriously amplified.

Therefore, to measure the instantaneous overload torque of the servo motor, it is still necessary to measure the dynamic torque curve of the motor. Especially for the servo driver design, the input dynamic current curve of the motor must be measured at the same time, and the current curve and torque curve must be synchronized in order to accurately capture the overload capacity characteristics of the servo motor.