請(qǐng)教:伺服電機(jī)的結(jié)構(gòu)及工作原理

請(qǐng)教:伺服電機(jī)的結(jié)構(gòu)及工作原理
   謝謝

交流伺服電機(jī)的工作原理
　　伺服電機(jī)內(nèi)部的轉(zhuǎn)子是永磁鐵，驅(qū)動(dòng)器控制的U/V/W三相電形成電磁場(chǎng)，轉(zhuǎn)子在此磁場(chǎng)的作用下轉(zhuǎn)動(dòng)，同時(shí)電機(jī)自帶的編碼器反饋信號(hào)給驅(qū)動(dòng)器，驅(qū)動(dòng)器根據(jù)反饋值與目標(biāo)值進(jìn)行比較，調(diào)整轉(zhuǎn)子轉(zhuǎn)動(dòng)的角度。伺服電機(jī)的精度決定于編碼器的精度（線數(shù)）。
4. 什么是伺服電機(jī)？有幾種類(lèi)型？工作特點(diǎn)是什么？
答：伺服電動(dòng)機(jī)又稱(chēng)執(zhí)行電動(dòng)機(jī)，在自動(dòng)控制系統(tǒng)中，用作執(zhí)行元件，把所收到的電信號(hào)轉(zhuǎn)換成電動(dòng)機(jī)軸上的角位移或角速度輸出。分為直流和交流伺服電動(dòng)機(jī)兩大類(lèi)，其主要特點(diǎn)是，當(dāng)信號(hào)電壓為零時(shí)無(wú)自轉(zhuǎn)現(xiàn)象，轉(zhuǎn)速隨著轉(zhuǎn)矩的增加而勻速下降，
請(qǐng)問(wèn)交流伺服電機(jī)和無(wú)刷直流伺服電機(jī)在功能上有什么區(qū)別？

答：交流伺服要好一些，因?yàn)槭钦也刂疲D(zhuǎn)矩脈動(dòng)小。直流伺服是梯形波。但直流伺服比較簡(jiǎn)單，便宜。
永磁交流伺服電動(dòng)機(jī)

請(qǐng)教2樓:伺服電機(jī)編碼器為17位,定位精度能否達(dá)到360/131072度
         謝謝

我也想知道哦

編碼器的位數(shù)和定位精度的關(guān)系什么？謝謝

定位精度是指在一圈下的編碼器脈沖數(shù)所對(duì)應(yīng)的行程。

如果編碼器為17位，即13萬(wàn)線，則一圈的電機(jī)旋轉(zhuǎn)對(duì)應(yīng)100mm的位置移動(dòng)，定位精度為100mm/130000。

這是理論值，因?yàn)?，機(jī)械系統(tǒng)的精度很難與電氣控制系統(tǒng)來(lái)匹配。

Servomotors are available as AC or DC motors. Early servomotors were generally DC motors because the only type of control for large currents was through SCRs for many years. As transistors became capable of controlling larger currents and switching the large currents at higher frequencies, the AC servomotor became used more often. Early servomotors were specifically designed for servo amplifiers. Today a class of motors is designed for applica-tions that may use a servo amplifier or a variable-frequency controller, which means that a motor may be used in a servo system in one application, and used in a variable-frequency drive in another application. Some companies also call any closed-loop system that does not use a stepper motor a servo system, so it is possible for a simple AC induction motor that is connected to a velocity controller to be called a servomotor.
Some changes that must be made to any motor that is designed as a servomotor in-cludes the ability to operate at a range of speeds without overheating, the ability to operate at zero speed and retain sufficient torque to hold a load in position, and the ability to operate at very low speeds for long periods of time without overheating. Older-type motors have cooling fans that are connected directly to the motor shaft. When the motor runs at slow speed, the fan does not move enough air to cool the motor. Newer motors have a separate fan mounted so it will provide optimum cooling air. This fan is powered by a con-stant voltage source so that it will turn at maximum RPM at all times regardless of the speed of the servomotor. One of the most usable types of motors in servo systems is the permanent magnet (PM) type motor. The voltage for the field winding of the permanent magnet type motor can be AC voltage or DC voltage. The permanent magnet-type motor is similar to other PM type motors presented previously. Figure 11-83 shows a cutaway picture of a PM motor and Fig. 11-84 shows a cutaway diagram of a PM motor. From the picture and diagram you can see the housing, rotor and stator all look very similar to the previous type PM motors. The major difference with this type of motor is that it may have gear reduction to be able to move larger loads quickly from a stand still position. This type of PM motor also has an encoder or resolver built into the motor housing. This ensures that the device will accurately indicate the position or velocity of the motor shaft.

11.11.5.1 Brushless Servomotors The brushless servomotor is designed to operate without brushes. This means that the commutation that the brushes provided must now be provided electronically. Electronic commutation is provided by switching transistors on and off at appropriate times. Figure 11-85 shows three examples of the voltage and current waveforms that are sent to the brushless servomotor. Figure 11-86 shows an example of the three windings of the brushless servomotor. The main point about the brushless servomo-tor is that it can be powered by either ac voltage or dc voltage.
Figure 11-85 shows three types of voltage waveforms that can be used to power the brushless servomotor. Figure ll-85a shows a trapezoidal EMF (voltage) input and a square wave current input. Figure ll-85b shows a sinusoidal waveform for the input voltage and a square wave current waveform. Figure ll-85c shows a sinusoidal input waveform and a sinusoidal current waveform. The sinusoidal input and sinusoidal current waveform are the most popular voltage supplies for the brushless servomotor.
Figure 11-86 shows three sets of transistors that are similar to the transistors in the output stage of the variable-frequency drive. In Fig. ll-86a the transistors are connected to the three windings of the motor in a similar manner as in the variable-frequency drive. In Fig. 1 l-86b the diagram of the waveforms for the output of the transistors is shown as three separate sinusoidal waves. The waveforms for the control circuit for the base of each transis-tor are shown in Fig. ll-86c. Figure ll-86d shows the back EMF for the drive waveforms.

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