The technology of servo motors has advanced significantly along with advances in industrial robots.
Interest in factory automation started growing in the United States from the 1950s, initially involving mechanisms such as belt conveyors, automatic machinery, and industrial robots. While early automated machinery and industrial robots tended to use hydraulics or pneumatics to control actuator positioning, they had problems in terms such as accuracy, operational reliability, the associated plumbing, and hydraulic fluid or air leaks.
Subsequently, the use of DC servo motors grew through the 1950s and 60s as their technology improved, and they began to be fitted in industrial robots in place of the troublesome hydraulic and pneumatic mechanisms.
AC servo motors, meanwhile, emerged in the 1980s. Their practical benefits include making robots smaller and lighter, and as a result, they now make up the bulk of servo motors used in modern industrial machinery.
Types of servo motors
Servo motors can be grouped into DC servo motors and AC servo motors
DC servo motors
These are servo motors driven with a brushed direct current (DC) motor. Although DC motors are easier to control than AC motors and were widely used in the past for their small size and low cost, advances in AC motor control technology has seen fewer opportunities for their use in recent times.
AC servo motors
These are servo motors driven with an alternating current (AC) motor. Although their control is more complex than that of DC motors, advances in control technology enabled them now to be the most common type of servo motor.
Depending on their drive mechanism, AC servo motors can be divided into synchronous motors (SMs) and induction motors (IMs). The difference is based on whether or not they have a permanent magnet.
SMs incorporate a permanent magnet. To increase motor output, the amount of permanent magnet usage (which are expensive) increases, and therefore makes them cost more. For this reason, they are widely used for low power applications (up to 10kW). However, with the emergence of high-performance permanent magnets in recent years, synchronous AC servo motors are now the default option.
IMs do not use permanent magnets and tend to be used in higher output applications (10kW or more).