Basics: Structure and components of a servo motor

The shaft and the winding form the structural core of a servo motor. They function as the rotor and the stator. Looking at the servo motor from the outside in, the stator (with the motor winding) is located below the housing. The latter consists of an electrically highly conductive material and can have various designs: The wire can vary in thickness or diameter, which in turn influences the winding intensity. The thinner the wire, the more and tighter windings can be implemented. These have a significant influence on the specifications of the motor. Decreasing wire thickness and increasingly tight windings yield the following effects:

• amplified magnetic field
• increased maximum torque
• higher countervoltage with increasing speed
• reduced efficiency
• increased waste heat, which requires appropriate cooling 

Cooling represents an essential part of a servo motor. In terms of applications, various forms of cooling come into question. They can work via air, oil or water. With water cooling, the highest nominal power can be implemented in a compact design. This means an increase in power density. Considering the increased costs entailed by higher space requirements as well as the loss of design flexibility, this increased power density is an important economic factor in the operation of any industrial machine.

Our Baumüller servo motors are available in different variants, which can also be designed without cooling. Especially for very dynamic requirements, however, water cooling should be selected. Oil (HLP-46 hydraulic oil) can also be used instead of water. In this case, the cooling effect is somewhat reduced compared to water depending on the size and operating mode of the motor. Liquid cooling saves space compared to air cooling (by eliminating the need for a fan) and also requires much less maintenance. This reduces costs for servicing and downtime. Water cooling is also particularly important in group installations that afford little space. If multiple motors are installed next to each other, they heat each other up. Liquid cooling effectively prevents this problem.

The servo structure of a drive system essentially consists of a stator and rotor or the combination of a motor winding and a motor shaft. The motor is driven by electrical energy flowing through the winding, creating an electromagnetic field that causes the shaft to rotate. Other important components include cooling and the servo controller. While the former is not essential, it is recommended for most industrial applications. Strictly speaking, the controller is not part of the motor, but is nevertheless essential for its precise operation.