In the servo system, a compensation device (usually a compensation circuit) with linear characteristics is commonly used, which adopts series, feedback (or parallel), negative feedback, positive feedback, and a combination thereof to improve the characteristics of the system and improve the system. Quality of work. The following describes the characteristics of various compensation connection forms and related precautions.
Common linear compensation for servo systems1. Series compensation
Series compensation refers to the integration of appropriate compensation devices (circuits) in the main channel of the system (ie, the forward channel). as the picture shows.
The commonly used series compensation devices are composed of circuits, and there are passive compensation networks composed of only R, L, and C. There are active compensation networks composed of linear integrated amplifiers, all of which can transmit DC signals, so only the parts that transmit DC signals in series in the system line can play a corresponding role. If the system transmits a fixed frequency AC carrier signal, the above two types of compensation networks cannot be used.
There are many forms of commonly used compensation networks that are practical in engineering. As a series compensation of the system, some of them cannot be used because in the main channel of the system, circuits with pure differential links cannot be connected in series (ie, networks without zeros with s=0 are not connected in series), which will block the constant The effective transmission of the signal prevents the servo system from working effectively.
In order to improve the steady-state accuracy of the system, it is often adopted to improve the type of the system (ie, no difference), which requires the integration of the integral link in the forward main channel of the system, or the series PI regulator.
In case the system open-loop logarithmic amplitude-frequency characteristic (the system is the minimum phase system), as shown by curve 1 in Figure 5.40a. Under zero initial conditions, the response of the system to the input step signal can meet the dynamic quality requirements, but the steady-state accuracy of the system is not high; to improve the system steady-state accuracy, the system open-loop gain needs to be increased, and the system open-loop logarithmic amplitude frequency The characteristics are shown in curve 2 in Figure a, but the dynamic quality of the system does not meet the requirements. While increasing the system open-loop gain, serially connect a lag compensation
There are many factors that affect the servo system control, the most important of which are servos such as position, speed, acceleration and vibration. The control accuracy of the system is one of the most important technical indicators. The control accuracy of the servo system is affected by many factors. The key to the accuracy of the detection device is resolution. The development of modern science and technology, the use of high-precision servo systems is increasing. For example, the high-precision phase-locked speed control system requires the speed measurement error "i0~, while the general speed measuring generator speed measurement error is 2%. 0.02% range. The radar antenna servo system used to track satellites must have a tracking error of 1'.
Observing celestial radio telescopes requires a servo system error of "0.05'. Beginning to enter the home TV laser player, the radial motion of the laser needle is controlled by the servo system, and the position error of the system is ≤1胛. The above examples show that the accuracy of the servo system is higher, and the accuracy of the detection device they use will be higher. First, the detection device in the system can distinguish the error and provide an effective signal before talking about controlling the system. Therefore, the high precision of the detecting device is a prerequisite for realizing a high-precision servo system. However, servo systems for various purposes are diverse, and their accuracy requirements are also very inconsistent. Because of this, the types of detection devices used in servo systems are very complicated. This section only uses common analog speeds and A simple description of the angle measuring (displacement) device.
1. Angular velocity detection
In the speed servo system, the output of the system must have a device for detecting the angular velocity. In the position servo system, it is also often required to obtain the speed damping signal. Therefore, it is widely used in servo systems. The most used ones are various speed measuring generators. The relatively simple ones have speed measuring bridges. The more accurate ones are incremental code disks.
(1) Speed ​​measuring generator
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