In the field of power supply, the definition of servo motor is a rotary actuator or a linear actuator, which can accurately control the angle or linear position, speed and acceleration. It consists of a suitable motor coupled with sensors for position feedback, and also requires a relatively well-managed controller, which is usually a dedicated module specifically designed for servo motors.
Generally speaking, servo motors cannot be classified as a specific motor category, although the term "servo motor" is commonly used for motors that are suitable for closed-loop control systems. The servo motor is quite safe due to its closed-loop function and has advantages in many ways. Therefore, it can be used in applications such as robots, CNC machines and automated production sites. Compared with traditional stepper motors, they have many similarities and differences. These comparisons finally make this type of motor stand out in some applications.
For this type of motor, a servo motor with a synchronizer as its encoder was first developed. During wartime in the 1940s (during World War II), these systems did a lot of work in the development of radar and anti-aircraft guns. Simple servo motors can definitely use resistive potentiometers as position encoders, and they are only used at the simplest and cheapest level, so they compete fiercely with stepper motors.
However, due to design reasons, they are subject to wear and electrical noise in the potentiometer track. Although the position signal can be distinguished electrically to obtain the speed signal, PID controllers that can utilize this speed signal usually need to ensure a more accurate encoder, which will make the effect better.
At the same time, modern servo motors use rotary encoders, which can be absolute or incremental in design. Absolute encoders can determine position when powered on, but they are more complicated and expensive in cost, while incremental encoders are simpler, cheaper, and can operate at a faster speed. In fact, an incremental system usually combines its inherent ability to measure the rotation interval with a simple zero sensor to set its position at start-up like a stepper motor. Depending on the application, sometimes a motor with a separate external linear encoder is used instead of the servo motor. These motor plus linear encoder systems avoid errors in the transmission system between the motor and the linear carriage. Since they are no longer pre-packaged factory manufacturing systems, their design becomes more complicated in detail.
As mentioned earlier, the type of motor is not critical to the servo motor, and different types can be used. The simplest is that, due to their simplicity and low cost, the use of brushed permanent magnet DC motors has been welcomed by manufacturers. Small industrial servo motors are usually electronically commutated brushless motors, and the famous BLDC motors are also very popular on the market. For large industrial servo motors, AC induction motors are usually used, and variable frequency drives are usually used to control their speed. In order to achieve the final performance in a compact package, a brushless AC motor with a permanent magnetic field is used, which is an effective large-scale brushless DC motor.
If the servo motor is discussed in more depth, BLDC motor is a very popular type in the motor category. It is an abbreviation for brushless DC motor, also known as electronic commutation motor, also known as synchronous DC motor. Synchronous function BLDC motor is a synchronous motor that is driven by direct current through an inverter that sends out alternating current to excite each phase of the motor through a closed-loop controller. What does the controller do? At the same time, the controller provides current pulses to the motor windings to manage the torque and speed of the motor project.
Generally, the composition of a brushless motor system is basically the same as or even similar to a permanent magnet synchronous motor, abbreviated as PMSM, and the former can be considered a switched reluctance motor or an induction motor, but not a synchronous motor. Speaking of the advantages of brushless motors compared to brushed motors, the former design has a higher power to weight ratio, higher speed, better electronic control and lower maintenance costs.
As a result, based on these advantages, brushless DC motors are widely used in many scientific applications. By convention, common servo motors (DC and AC) are commonly used in robot science. Recently, AC servo motors have also been widely used because control has become easier than before, but these motors can still withstand better torque. At the same time, the price of servo motors is generally higher, so the standard sensor installed is an optical sensor with a selected resolution option.
Nowadays, some machine tool suppliers that produce machinery related to the machining center series are also trying to achieve multi-functionality, and the servo motor used in details is also expected to be multifunctional. Although they are not as flexible as machining centers, they are also very flexible in terms of motion control. Therefore, they are often used to customize specific tasks of a project.
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