What does high and low inertia mean in a servo motor?

What are the inertia, high and low inertia, small, medium and large inertia in servo motors? This article will explain them in detail.

A servo motor is an engine that controls the operation of mechanical components in a servo system. The rotor speed of a servo motor is controlled by an input signal and can respond quickly. In an automatic control system, it is used as an actuator and has the characteristics of a small electromechanical time constant, high linearity, and a starting voltage. It can convert the received electrical signal into an angular displacement or angular velocity output on the motor shaft.

1. Inertia

Inertia is the measure of the inertia of a rigid body rotating around an axis, and the moment of inertia is a physical quantity that characterizes the size of the rigid body's rotational inertia. It is related to the mass of the rigid body and the distribution of the mass relative to the rotating axis. (A rigid body refers to an object that will not change in an ideal state). When choosing a servo motor, the motor inertia is also an important indicator of the servo motor. It refers to the inertia of the servo motor rotor itself, which is very important for the acceleration and deceleration of the motor. If the inertia cannot be matched well, the motor will move very unsteadily.

2. High and low inertia

1. Low inertia

Low inertia means that the motor is relatively flat and long, and the spindle inertia is small. When the motor performs high-frequency reciprocating motion, the inertia is small and the heat is small. Therefore, low-inertia motors are suitable for high-frequency reciprocating motion. However, the torque is generally relatively small.

2. High inertia

The servo motor with high inertia is relatively large and has large torque, which is suitable for the occasions of large torque but not fast reciprocating motion. Because the driver needs to generate a large reverse drive voltage to stop the large inertia when moving at high speed, the heat is very large.

3. Advantages of small, medium and large inertia

Generally speaking, small inertia motors have good braking performance, quick response to starting, acceleration and stopping, and good high-speed reciprocating performance, and are suitable for some light load and high-speed positioning occasions, such as some linear high-speed positioning mechanisms. Medium and large inertia motors are suitable for large loads and occasions with relatively high stability requirements, such as some circular motion mechanisms and some machine tool industries.

If the load is relatively large or the acceleration characteristic is relatively large, and a motor with small inertia is selected, it may cause great damage to the motor shaft. The selection should be based on factors such as the size of the load, the size of the acceleration, etc. The general selection manual has relevant energy calculation formulas.

The best value for the servo motor driver to control the response of the servo motor is that the ratio of the load inertia to the motor rotor inertia is one and the maximum value cannot exceed five times. Through the design of the mechanical transmission device, the load can be controlled.

The ratio of inertia to motor rotor inertia is close to one or smaller. When the load inertia is really large and the mechanical design cannot make the ratio of load inertia to motor rotor inertia less than 1,500 times, a motor with a larger motor rotor inertia can be used, which is the so-called large inertia motor. When using a large inertia motor, to achieve a certain response, the capacity of the driver should be larger.

The above is the explanation of high and low inertia of servo motor inertia. I hope it can be helpful to you.