To adapt to the development trend of digital control, most motion control systems use stepper motors, DC motors, or fully digital AC servo motors as actuators. Although these three are similar in control methods, they differ in performance and application. Dalan Motor will now compare the advantages and uses of these three types.
AC servo motor
advantage:
(1) It has no brushes or commutator, so it is reliable in operation and requires little maintenance.
(2) Stator windings are relatively easy to dissipate heat.
(3) Low inertia makes it easy to improve the speed of the system.
(4) Suitable for high-speed and high-torque working conditions.
DC servo motor
advantage:
DC servo motors specifically refer to brushed DC servo motors. These motors are expensive and complex in structure, have high starting torque, a wide speed range, and are easy to control. However, they require maintenance, which is inconvenient (replacing carbon brushes), generates electromagnetic interference, and has environmental requirements. Therefore, they can be used in cost-sensitive general industrial and civilian applications.
DC servo motors do not include brushless DC servo motors—these motors are small in size, light in weight, have high output power, fast response, high speed, low inertia, smooth rotation, and stable torque, but their power is limited and cannot be made in large quantities. They are easily made intelligent, and their electronic commutation method is flexible, allowing for square wave or sine wave commutation. These motors are maintenance-free, eliminating carbon brush wear, and have high efficiency, low operating temperature, low noise, minimal electromagnetic radiation, long lifespan, and can be used in various environments.
use:
(1) Actuator drive in various digital control systems.
(2) Power drives that require precise control of constant speed or precise control of speed change curves.
According to the magnitude of motor inertia, they can be divided into:
(1) Small inertia DC motor - Automatic drilling machine for printed circuit boards
(2) Medium inertia DC motor (wide speed range DC motor) – Feed system of CNC machine tools
(3) High inertia DC motors – spindle motors for CNC machine tools
(4) Special types of low-inertia DC motors
Stepper motor
advantage:
(1) The angle of rotation of the motor is proportional to the number of pulses;
(2) The motor has the maximum torque when it stops (when the windings are energized).
(3) Since the accuracy of each step is between 3% and 5%, and the error of one step will not accumulate to the next step, it has good positional accuracy and motion repeatability.
(4) Excellent start-stop and reverse response;
(5) Because there are no brushes, the reliability is high, so the lifespan of the motor depends only on the lifespan of the bearings;
(6) The motor's response is determined solely by digital input pulses, thus allowing for open-loop control, which simplifies the motor's structure and reduces control costs.
(7) Even by simply connecting the load directly to the motor shaft, it can rotate synchronously at extremely low speeds;
(8) Since the speed is proportional to the pulse frequency, it has a relatively wide range of rotational speeds.
defect:
(1) Improper control can easily lead to resonance;
(2) It is difficult to operate at high speeds;
(3) It is difficult to obtain a large torque;
(4) It has no advantage in terms of volume and weight, and its energy efficiency is low;
(5) Exceeding the load will disrupt synchronization, and high-speed operation will produce vibration and noise.
In summary, AC servo systems outperform stepper motors in many aspects. However, stepper motors are often used as actuators in less demanding applications. Therefore, the design of a control system must comprehensively consider factors such as control requirements and cost to select an appropriate control motor.
