Key Concepts
Servo motors come in a few different configurations. First there is the differentiation based on the commutation mechanism between Brushed and Brushless motors. Brushed motors tend to be less expensive to buy, but more expensive to maintain in the long run. The primary disadvantages of Brushed motors as compared with Brushless motors are as follows:
- High emissions of electro-magnetic interference (EMI) due to commutation noise from the brush mechanism
- Limited rotor speed due to wear on the brushes
- Limited brush life requires periodic maintenance
- Poor heat transfer, since the heat is generated mainly in the inner armature
Brushless DC Rotary and Linear Servo Motors
Brushless servo motors, referred to alternately as Brushless DC (BLDC), Permanent Magnet Synchronous Motors (PMSM) or AC Servo Motors, come in two basic configurations: rotary and linear. Linear servo motors tend to be more expensive, but they provide the most efficient conversion of current to force, and obviate mechanical conversion of rotary motor motion to linear load motion.
Linear Servo Actuator
Linear servo actuators are often provided as ready-made systems that combine a rotary servo motor with a linear actuator.
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Variable or Switched Reluctance Motor
Another type of servo motor that is sometimes used is the Variable Reluctance Motor (sometimes called Switched Reluctance Motor). This motor induces non-permanent magnetic poles on the ferromagnetic rotor, and torque is generated through magnetic reluctance. These motors are sometimes used since they have very high power density at low-cost.
Servotronix Experience
Servotronix's products are designed to drive linear servo motors as well as rotary servo motors. The CD Series 5 was one of the first servo drive families on the market to easily support both types of motors. Our ability to combine linear servo motor control with interface to high-resolution sine encoders has enabled us to provide unique solutions such as the SDU (shown below) that provided our customers with distinctive competitive advantages.
In addition to controlling brushless rotary and linear motors, we have developed servo drives for Variable Reluctance Motors. In this case, too, the development was triggered by a specific customer requirement. This characterizes Servotronix operations well: we provide solutions to our customer's specific requirements.
