The main indicators to measure the performance of the servo control system are system accuracy, stability, response characteristics, and operating frequency, especially in terms of frequency bandwidth and accuracy.
The frequency bandwidth is referred to as the bandwidth, which is specified by the frequency response characteristics of the system and reflects the rapidity of the tracking of the servo system. The larger the bandwidth, the better the speed. The bandwidth of the servo system is mainly limited by the inertia of the control object and the actuator. The greater the inertia, the narrower the bandwidth. The bandwidth of the general servo system is less than 15 Hz, and the bandwidth of the servo system of large equipment is below 1 to 2 Hz. Since the 1970s, due to the development of torque motors and high-sensitivity tachometers, the servo system has realized direct drive, eliminated or reduced nonlinear factors such as backlash and elastic deformation, and enabled the bandwidth to reach 50 Hz, and has been successfully applied. In long-range missiles, artificial satellites, precision command instruments and other places. The accuracy of the servo system is mainly determined by the accuracy of the measuring elements used. Therefore, high-precision measuring elements, such as precision potentiometers, self-aligning machines and resolvers, must be used in the servo system. In addition, additional measures can also be taken to improve the accuracy of the system, such as connecting the measuring shaft of the measuring element (such as a self-aligning machine) to the rotating shaft through a reducer, so that the rotation angle of the rotating shaft is enlarged to improve the relative measurement accuracy. The servo system that adopts this kind of scheme is called the fine measuring and rough measuring system or the double-channel system. The angle measuring circuit that meshes with the rotating shaft through the reducer is called the fine reading channel, and the angle measuring circuit directly taken from the rotating shaft is called the coarse reading channel.
AC Servo System Performance Index
The main control objective of the position servo system is that the output value quickly tracks the change of the command value.Different applications have different specific requirements for the servo system, but the general requirements are basically the same. Specifically, in mechatronic products, the performance requirements for the servo system mainly include:
(1) Positioning accuracy
The static error between the final positioning point of the system and the command target value is the positioning accuracy, and the positioning accuracy is a key index to evaluate the positioning accuracy of the position servo system. For the AC servo system with its own code disc and excellent performance, it should meet the positioning accuracy requirement of ±1 pulse.
(2) Speed regulation range
That is, the ratio of the highest speed to the lowest speed of the motor, expressed by D.
(3) Static characteristics of speed regulation?
For most loads, the harder the mechanical properties, the smaller the transient speed change when the load changes, and the more stable the work is, so it is hoped that the harder the mechanical properties, the better.
(4) Dynamic characteristics of speed regulation
Dynamic characteristics, that is, the transient characteristics of speed changes, mainly include two aspects: one is whether the acceleration and deceleration processes are fast, sensitive and without overshoot. This requires that the rotor inertia of the motor is small, the torque/inertia ratio is large, and the motor torque output per unit volume is large. The second is whether the speed of the system can be automatically adjusted and recovered quickly when the load suddenly increases and decreases suddenly.
Technical requirements for servo control system
1. System accuracy
Servo system accuracy refers to the degree of accuracy required by the output to reproduce the input signal, expressed in the form of error, which can be summarized as dynamic error, steady-state error and static error.
The stability of the servo system refers to the ability of the system to return to the original stable state when the disturbance acting on the system disappears; or the ability of the system to reach a new stable operating state when a new input command is given to the system.
3. Response characteristics
The response characteristic refers to the response speed of the output quantity following the change of the input command, which determines the working efficiency of the system. The response speed is related to many factors, such as the running speed of the computer, the damping and mass of the motion system, etc.
4. Working frequency
The operating frequency usually refers to the frequency range of the input signal allowed by the system. When the working frequency signal is input, the system can work normally according to the technical requirements; and when other frequency signals are input, the system cannot work normally.
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