What is the difference between a servo motor and a regular motor?

What is the difference between a servo motor and a regular motor?

1. Motor Type Classification

1.1 DC Motors

DC motors can be classified into brushed DC motors, brushed DC geared motors, brushless DC motors, and brushless DC geared motors. As the names suggest, the difference between DC motors and brushed DC motors is that the output shaft of a brushed DC motor has a speed reducer installed. The speed reducer significantly decreases the motor’s speed, but significantly increases its output torque.

DC motors have a wide speed range and smooth speed regulation characteristics. They also have strong overload capacity and high starting and braking torque.

1.2 Stepper Motor

A stepper motor is a type of electric motor that converts electrical pulse signals into corresponding angular or linear displacement. For each input pulse signal, the rotor rotates by one angle or moves forward one step. The output angular or linear displacement is proportional to the number of input pulses, and the rotational speed is proportional to the pulse frequency. Therefore, stepper motors are also called pulse motors.

Stepper motors are classified into three types: permanent magnet (PM), reactive (VR), and hybrid (HB). Permanent magnet stepper motors are generally two-phase, with smaller torque and size, and a step angle typically of 7.5 or 15 degrees. Reactive stepper motors are generally three-phase, capable of achieving high torque output, with a step angle typically of 1.5 degrees, but with significant noise and vibration. They were phased out in developed countries such as Europe and America in the 1980s. Hybrid stepper motors combine the advantages of permanent magnet and reactive motors. They are further divided into two-phase and five-phase: two-phase stepper motors typically have a step angle of 1.8 degrees, while five-phase stepper motors typically have a step angle of 0.72 degrees. This type of stepper motor is the most widely used.

Stepper motors can adjust their speed by changing the pulse frequency over a wide range. Typical applications include CNC machine tools, plotters, rolling mills, and recorders. In summary, the characteristics of stepper motors are:

(1) Fast start, forward and reverse rotation, stop, and speed adjustment over a wide range

(2) Small displacement per pulse, high step angle accuracy, and no missed steps

(3) Large output torque, directly supporting the load

1.3 Servo Motors

Servo motors place greater emphasis on closed-loop control compared to the previous motor types. Generally, servo motors have dedicated servo motor drivers. Servo motors can be divided into DC servo motors and AC servo motors.

2. Main Differences Between Servo Motors and Ordinary Motors

2.1 The main differences between servo motors and ordinary motors lie in their control methods, accuracy and response performance, and application scenarios. Servo motors use a closed-loop control system, enabling high-precision positioning and rapid dynamic response; ordinary motors typically use open-loop control, suitable for power output applications where high precision is not required.

2.2 Control Principles and Methods

Servo motors use closed-loop control: The motor position/speed is monitored in real time through feedback devices such as encoders. The controller adjusts the output based on the deviation between the feedback and the target value, achieving precise control.

Ordinary motors mostly use open-loop control: There is no real-time feedback during operation; the speed is mainly changed by adjusting the input voltage or current, and the control accuracy depends on the mechanical structure.

2.3 Performance Differences

Control Accuracy: Servo motor positioning accuracy can reach the micrometer level or even higher (e.g., ±0.01 pulses), while the speed control accuracy of ordinary motors is generally only around ±5%. 1.2. Dynamic Response: Servo motors have millisecond-level response times, enabling rapid start-up, stopping, and adjustment; ordinary motors have relatively slow responses and are significantly affected by load changes.

1.3. Overload Capacity: Servo motors have weak overload capacity; even slight overloads will trigger an alarm and shutdown to protect the motor; ordinary motors can withstand loads exceeding their rated torque for short periods, but prolonged overloads may cause damage.

2.4 Structure and Application

· Structural Complexity: Servo motors integrate encoders, dedicated drivers, etc., resulting in a complex structure; ordinary motors typically only contain basic components such as stators and rotors, resulting in a simpler structure.

· Cost: Servo motors are more expensive due to the added feedback and control equipment; ordinary motors are less expensive.

· Application Scenarios: Servo motors are widely used in high-precision control fields such as CNC machine tools, industrial robots, and automation equipment; ordinary motors are mainly used in applications where precision and response speed requirements are not high, such as fans, pumps, and assembly lines.‌‌