Servo motors are among the most widely used variable speed drives in a range of different industries. With the different types of servo motors on the market, it’s relatively easy to find the right one for your application.
Essentially, a servo motor can be defined as a self-contained electrical device that converts electrical energy into mechanical energy. The motor enables parts of the machine to rotate with high efficiency and excellent precision. By working as part of a closed-loop control system, servo motors offer a considerable amount of varying torque. This happens by moving the output to the desired position.
Furthermore, various industries use servo motors in a host of different applications. Their compact size and powerful design make it easy for these little gadgets to perform precise control operations. RC servo motors are usually known as hobby servos because they’re designed for simplicity and consistency.
Microprocessors, power transistors, and the inclusion of three wires—power, ground, and control—add to these nifty motors’ popularity. Some types are also more affordable than others, making them ideal to use as hobby servos.
The most significant types of servo motors that feature high precision control that we’ll be highlighting in this article include the following:
Important Note: Assun Motor produces brushless DC servo motors. The intention of this article is to educate our readers on the differences between the 7 different types of servo motors.
7 Types of Servo Motor
DC Servo Motors
A DC servo motor is one of the more common servo motor types. With its rotary actuator, the motor enables precise control of position, velocity, and acceleration.
In a DC servo motor, there’s a permanent magnet shunt motor that supplies a field control similar to the armature-controlled permanent field motor. This ultimately provides the same motor performance which in turn specifies high stall torque. To achieve a decline in torque, simply amplify the speed.
While the speed regulation of this motor is considerably less, the stable magnet supplies turnaround that can be achieved by overturning the field voltage polarity. This is made possible by using split series field winding.
The key difference between a DC motor and an AC motor is that they have different power sources. While a DC servo motor generally relies on a separate DC source such as batteries, AC motors need an electric outlet.
A few common DC servo motor applications include:
- Machine tools
- Robotics
- Numerically controlled equipment
- Semiconductor devices
- Aircrafts
AC Servo Motors
AC servo motors are driven by alternating current and primarily consist of two basic parts—an outside stator and an inside rotor. They offer better control and also boast lower startup power demands. The control signal serves as the speed and direction of the rotation rather than setting the static position. This motor type has a gear mechanism to protect the rotation sensor.
A top reason to consider this motor is its wide customizability which allows for changing speed feedback and more torque. Furthermore, the positional rotation servo has an output shaft that lets the motor rotate at an impressive 180 degrees.
The motor primarily includes physical stops placed in the gear mechanism to prevent rotation. AC servo motor can be used as drive motor in the following applications:
- Automated conveyor belts and equipment
- Heavy industrial machinery
- Automation technology across various industries
- Washing machines
- Electric knife sharpeners
- Office equipment
- Ovens
- Water heater
Linear Servo Motors
A linear servo motor is a direct drive solution where the load is directly connected to the moving portion of the motor. This means that it produces velocity and force based on the actual current and voltage to produce a linear movement along the required axis. For the most part, linear servos use a rack and pinion mechanism to change their output.
Since the linear model features a continuous rotation servo motor, it can move in any direction indefinitely. It will change the required speed, depending on the command signals received. This happens when the motor offers a quick and accurate response because of the small armature inductive reactance.
Despite being available in multiple configurations, they all work more or less in the same way. For the most part, a linear servo motor is used in applications such as those listed below:
- Sliding doors
- Baggage handling machines
- Large-scale bulk materials transport
- Propelling the shuttle in looms
- Cranes for material handling
- Machines that pump liquid metal
Rotary Servo Motors
A rotary servo motor works by turning something in circles to function. This is different from the linear servo motor that uses a back-and-forth motion. Rotary servo motors are primarily used in food and beverage processing equipment such as electric food mixers that work by moving in circles.
They can be used in machines that mix ingredients or materials by moving in circles. Additionally, rotary servo motors can popularly be found in the following applications:
- Radio-controlled cars
- Toys
- Robots
- Aviation applications
Brushless Servo Motors
A brushless servo motor has a permanent magnet shunt control motor that rotates a fixed armature. This armature current eliminates the issues surrounding connecting the current to the moving armature. Essentially, an electronic controller replaces the brush assembly of a regular DC motor. In many instances, these servo motors are coupled with a type of encoder to activate the supply signal.
Since brushless servo motors are a specific subset of BLDC motors designed for applications that require precise position control as well as high speeds. Because the output is higher there’s much better torque speed and control. They are primarily used in CNC machinery.
Analog Servo Motors
For the most part, analog servo motors refer to the drives or amplifiers that are designed to operate an analog control circuit. Their control input is usually the conventional +/- 10 voltage signal speed or torque.
A common example of this type of servo motor is the cruise control function in a car. It measures servo motor speed and feeds the information back into a control circuit. This in turn adjusts the accelerator to maintain the chosen speed.
Advantages that make an analog servo a popular choice include affordability, lower power consumption, and low-frequency audible noise. Typical applications include the following:
- Sport-level cars and trucks
- Medical equipment
- Metrology applications that require low voltage
- Scale and sport aircraft
Digital Servo Motors
Digital servo motors use a small microprocessor to not only receive but also direct action at high-frequency voltage pulses. Typically, a digital servo sends almost six times the amount of pulses an analog signal does. Faster pulses provide consistent torque which produces faster and smoother response times. It’s worth noting that digital servos are noisier than their analog counterparts.
Higher-model airplanes and other more advanced hobby applications benefit from the use of digital servos. Other prominent applications that use digital servo motors:
- Home electronic devices
- Blu-ray disc devices use servos to extract and retract disc trays
Conclusion
Servo motors offer versatility and can be used to power anything from automation systems, mobile robots, and milling machines to automatic door openers. Additionally, servo motors can also be found in hobby stores because they are perfect for just about any type of hobby application.
The servo motor industry is expected to grow to U.S.$18.6 billion by 2027 as these motors are continuously being added to robotics and other modern applications. Additionally, energy-efficient equipment is also making use of different types of servo motors. With some servo motors being more affordable and readily available, it’s much easier for hobby enthusiasts to build their own applications to their own, unique requirements.
When looking for the perfect servo motor, consider the application and mechanical system you want to add it to. While experts suggest that brushless motors are more reliable, efficient, and quieter, it comes down to the application and budget you’re working with. Consider the features as well as the pros and cons of each motor before choosing the best one for your application!
Have you found our list of different types of servo motors informative? If so, please share it with friends, family, and colleagues who may be in the market for the perfect servo for work or hobby applications!
