A servo control system is an operating system that automatically controls the mechanical motion of a testing device according to predetermined requirements. In many cases, a servo system specifically refers to a feedback control system where the controlled variable (the system's output) is mechanical displacement, displacement velocity, or acceleration. Its function is to ensure that the output mechanical displacement (or rotation angle) accurately tracks the input displacement (or rotation angle). The structural composition of a servo system is not fundamentally different from other forms of feedback control systems.
Key Indicators of Servo Control Systems
The main indicators for evaluating the performance of a servo control system are four aspects: control accuracy, stability, response characteristics, and operating frequency , especially bandwidth and accuracy.
Frequency bandwidth, or simply bandwidth, is defined by the frequency response characteristics of a system and reflects the tracking speed of a servo system. A larger bandwidth indicates better speed. The bandwidth of a servo system is primarily limited by the inertia of the controlled object and the actuator. Greater inertia results in a narrower bandwidth. Generally, the bandwidth of a servo system is less than 15 Hz, while the bandwidth of a large-scale equipment servo system is below 1-2 Hz.
Since the 1970s, the development of torque motors and high-sensitivity tachometers has enabled servo systems to achieve direct drive, eliminating or reducing nonlinear factors such as backlash and elastic deformation, achieving a bandwidth of 50 Hz, and successfully applying them in long-range missiles, artificial satellites, precision command instruments, and other applications.
The accuracy of a servo system is primarily determined by the accuracy of the measuring elements used. Therefore, high-precision measuring elements, such as precision potentiometers, synchros, and rotary transformers, must be employed in servo systems.
In addition, additional measures can be taken to improve the system's accuracy. For example, the measuring axis of the measuring element (such as a synchro) can be connected to the rotating shaft via a reducer, thus amplifying the rotation angle of the rotating shaft and improving relative measurement accuracy. Servo systems employing this approach are called fine/coarse measurement systems or dual-channel systems. The angle measurement circuit that meshes with the rotating shaft via the reducer is called the fine reading channel, while the angle measurement circuit that takes data directly from the rotating shaft is called the coarse reading channel.
