SERVO BASIC CONCEPTS.

What is a servo motor?

In 1960s, Yaskawa Electric had produced distinctive DC servo motors one after another and came to commercialize AC servo motors in 1983 while making a new trend in the motor industry. Now, after more than thirty years, almost 100% operators in factory automation industry apply AC servo motors. Yaskawa’s industrial robots also apply AC servo motors manufactured in-house for their joints.

Motors in general aim to work by rotating load continuously, however, servo motors also aim to respond to the target precisely and swiftly. By the way, do you know what “servo” means? The origin of the word is “servus” in Latin (or “slave” in English). Slaves obey the masters’ command and do as they are told. People started to use the word “servo” as it aims to control the target’s location, speed and route as it intended to.

Mechanism of AC servo motor

AC servo motor has a structure that holds three-phase windings in the stator, permanent magnets in the rotor and an angle detector on the opposite pulley side of the shaft. This detector plays an important role in AC servo motor. As a synchronous motor, it is essential for the normal drive of AC servo motor to know the magnetic poles created by the permanent magnets in the rotor precisely. The detector reads the information of the magnetic poles and pass it to controller side of the amplifier. By doing so, electric current flows through the three-phase windings correctly and the motor generates torque as commanded.

In addition, the detector provides the information of angle in order to control rotation speed and rotation angle of the rotor. The more accurate and detail the information of angle is, the more precise the control in speed and location becomes. The current Yaskawa’s servo motor (Σ-7 series) has 24bits resolution with the encoder functions as a detector, so that it can detect even a minute angle of sixteen-millionth of 360 degrees in circumference. For example, if you would compare it to the circumference of approx. 6,000m diameter, it can detect if the objects moves merely 2 cm.

From factory automation area to a wide range of industries

There is a wide range of AC servo motor applications. It started in factory automation area such as semiconductor and liquid crystal manufacturing equipment, electronic components mounting device, machine tool, textile machinery, packaging machinery, solar battery panel manufacturing equipment and industrial robot, and that it is expanded to medical equipment, amusement machine and automatic door installed at platforms of train stations. For example, LED manufacturing equipment applies multiple small-sized and high-performance AC servo motors as it requires high productivity and precision in positioning. There are expectations on LED lighting equipment to increase rapidly and on AC servo motors to be applied further in the future.