舵机原理简析

天羽伏魔李帅 · 发表于 2013-10-6 21:36:35

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在坛里看到一篇舵机原理的英文简介连接，觉得不错，就翻译过来，共大家参考！水平有限，请勿拍我

Whats a Servo?什么是舵机

A Servo is a small device that has an output shaft. Thisshaft can be positioned to specific angular positions by sending the servo acoded signal. As long as the coded signal exists on the input line, the servowill maintain the angular position of the shaft. As the coded signal changes,the angular position of the shaft changes. In practice, servos are used inradio controlled airplanes to position control surfaces like the elevators andrudders. They are also used in radio controlled cars, puppets, and of course,robots.

舵机就是一种有输出轴的小传动装置。这个输出轴能够通过向舵机输入一个编码信号而定位到我们指定的角度位置。只要这个编码信号存在于信号输入线上，舵机就将保持输出轴的当前角度位置不变。一旦编码信号改变，输出轴的角度位置也将跟着改变。实际中，舵机被用于控制无线遥控飞机模型升降尾翼、方向尾翼等的位置，也被用于无线遥控车、玩具中，当然机器人中也有应用。

A Futaba S-148 Servo(舵机)

Servos are extremely useful in robotics. The motors aresmall, as you can see by the picture above, have built in control circuitry,and are extremely powerful for their size. A standard servo such as the FutabaS-148 has 42 oz/inches of torque, which is pretty strong for its size. It alsodraws power proportional to the mechanical load. A lightly loaded servo,therefore, doesn't consume much energy. The guts of a servo motor are shown inthe picture below. You can see the control circuitry, the motor, a set ofgears, and the case. You can also see the 3 wires that connect to the outsideworld. One is for power (+5volts), ground, and the white wire is the controlwire.

舵机在机器人技术中极其有用。正如上图所示，舵机体积小，控制电路被集成到内部，相对于其尺寸来说，舵机是极其有力的。例如Futaba S-148这样的标准舵机就拥有42 oz/inches 扭力，相对于其尺寸来说是极其强壮有力的。舵机能够将电能比例化地转化为机械负载，因此舵机在小负载的情况下不会消耗太多的电能。下图展示了一个舵机的组件，包括控制电路，电机，一组齿轮，以及舵机外壳。另外还有三根连接到外部的线，一根为电源线(+5v)，一根为底线，白色线为控制线（信号线）。

A servo disassembled.(舵机分解)

So, how does a servo work? The servo motor has somecontrol circuits and a potentiometer (a variable resistor, aka pot) that isconnected to the output shaft. In the picture above, the pot can be seen on theright side of the circuit board. This pot allows the control circuitry tomonitor the current angle of the servo motor. If the shaft is at the correctangle, then the motor shuts off. If the circuit finds that the angle is notcorrect, it will turn the motor the correct direction until the angle iscorrect. The output shaft of the servo is capable of travelling somewherearound 180 degrees. Usually, its somewhere in the 210 degree range, but itvaries by manufacturer. A normal servo is used to control an angular motion ofbetween 0 and 180 degrees. A normal servo is mechanically not capable ofturning any farther due to a mechanical stop built on to the main output gear.

那么，舵机是如何工作的呢？舵机的电机都会有一个控制电路，舵机的输出轴连接着一个电位器（可变电阻）。上图电路板的右上角就是电位器。控制电路通过这个电位器来监视舵机的当前角度。如果监视到输出轴在正确位置（控制电路会根据输入信号来得到正确的角度），就切断电机电源。如果监视到输出轴不在正确的位置，控制电路就启动电机往正确的方向旋转，直到达到正确的位置。舵机输出轴通常能够旋转的行程为180度或210度，但是不同的厂家不一样。普通舵机被用于控制0到180度的角度旋转动作，但是这个角度值的范围受主输出齿轮的机械限位的限制。

The amount of power applied to the motor is proportionalto the distance it needs to travel. So, if the shaft needs to turn a largedistance, the motor will run at full speed. If it needs to turn only a smallamount, the motor will run at a slower speed. This is called proportionalcontrol.

提供给电机的能量和电机需要行进的距离（角度）成正比。因此，如果输出轴需要转动一个大的角度，电机就会全速旋转；如果输出轴只需要转动一个小角度，则电机就会以一个较低的速度旋转，这就是比例控制。

How do you communicate the angle at which the servoshould turn? The control wire is used to communicate the angle. The angle isdetermined by the duration of a pulse that is applied to the control wire. Thisis called Pulse Coded Modulation. The servo expects to see a pulse every 20milliseconds (.02 seconds). The length of the pulse will determine how far themotor turns. A 1.5 millisecond pulse, for example, will make the motor turn tothe 90 degree position (often called the neutral position). If the pulse isshorter than 1.5 ms, then the motor will turn the shaft to closer to 0 degress.If the pulse is longer than 1.5ms, the shaft turns closer to 180 degress.

我们怎么知道舵机会转多少度呢？答案是靠控制线。旋转角度由控制线上的脉冲信号持续时间决定，这被称为脉码调制。舵机的控制信号为每20毫秒一次的方波脉冲。脉冲的宽度决定电机转多少。例如，一个宽度为1.5毫秒的脉冲会使电机旋转到90度位置（通常为称为中位）。如果脉冲小于1.5毫秒，电机将会带动输出轴旋转直到0度。如果大于1.5毫秒，电机将会带动输出轴旋转知道180度。

As you can see in the picture, the duration of the pulsedictates the angle of the output shaft (shown as the green circle with thearrow). Note that the times here are illustrative, and the actual timingsdepend on the motor manufacturer. The principle, however, is the same.

正如上图所示，脉冲持续的时间对应着输出轴旋转的角度（图中用绿色圆圈和箭头表示）。特别注意：此处的时间只是一个示例，具体的时间有电机生产商决定，但是原理都一样。