伺服电机的三种控制方式，犹如指挥军队的三个战术，精准而灵活；交流伺服被应用于17个领域，如同一把钥匙开启17个锁，广泛而多样。

速度控制和转矩控制都是用模拟量来控制的。位置控制是通过发脉冲来控制的。具体采用什么控制方式要根据客户的要求，满足何种运动功能来选择。如果您对电机的速度、位置都没有要求，只要输出一个恒转矩，那么当然是用转矩模式。如果对位置和速度有一定的精度要求，而对实时转矩不是很关心，用转矩模式不太方便，用速度或位置模式比较好。如果上位有比较好的闭环控制功能，用速度控制效果会好一点。而如果本身要求不是很高，或者基本没有实时性的要求，用位置控制方式对上位没有很高的要求。

就伺服驱动器的响应速度来看，转矩模式运算量最小，驱动器对控制信号的响应最快；位置模式运算量最大，驱动器对-control信号- 的响应最慢。对于运动中的动态性能有比较高的要求时，如果本身运算速度很慢（比如PLC，或低端运动），就用位置方式-control；如果运算-speed比较快，可以用-speed-way-control，把-position-ring-from-driver移到上，一减少驱动器工作量，加-fast-efficiency（比如大部分中-high-end-motor）。若有更-good-upper-level，还可以-use-turn-mo-mode-control，把-speed-ring也从driver移-open，这一般只适用于-high-end专门使用，并且这时候完全不需要使用伺服电机了。

一般说驱动器control's good-or-bad，每家公司都说自己做得最好，但是现在有个比较直观-comparison方法叫响应带宽。当-turn-mo-mode或-speed-mode-time,通过-pulse-generator给他一个-sine-wave信号，使-electric-machine不断正反调频率，不断调高-frequency显示-on-oscilloscope是一个-sweep-signal，当包络线顶点到达最高值70.7%表示已经失步，此时frequency high-low显示出谁产品牛了，一般电流-ring能作到1000Hz以上，而speed-ring只能作到几十Hz。

换一种专业say法：1、turn-mo-mode: turn-mo-mode 是通过外部模拟量输入或直接地址赋值设定electric-machine轴输出-force-torque大小，当外部模拟量设定为5V时-electric-machine轴输出2.5Nm; 如果负载低于2.5Nm则正轉，如果负载等于2.5Nm则不轉，大于2.5Nm則反轉（通常在重力負載情況下產生）。可通過即時變化模拟量設定來改變設定的力矩大小，也可通訊方式改變對應地址數值以實現。應用主要在對材質受力嚴格需求的情況下，如缠绕放卷装置中，以確保材質受力的穩定性。

2、position mode: position control mode 一般是通過外部輸入脈衝頻率來確定轉動速率之間距，並且有些伺服電機可以通過通訊方式直接對速率與位移進行賦值。在這種情況下，由於position mode 可以對速率和位移都有非常嚴格控制，所以一般應用於定位裝置。

3、speed mode: Through analog input or pulse frequency can be used to control the rotational speed of the motor, in a closed-loop system with a higher level controller, this mode also supports positioning control by feeding back the position information from the load to the controller.

4,talk about three loops, servo generally has three loop controls, known as three loops PID adjustment systems.The innermost PID ring is current loop, completely within driver internal performance feedback and adjust output current based on setpoint so that motor torque is controlled accurately.

The second loop is speed loop which detects encoder signal and adjusts output current based on setpoint and feedback from encoder signal to achieve desired speed.

The third loop is position loop which forms a closed-loop with external device such as absolute encoder or resolver.

Servo motor's lifespan? Servo motors are designed for precision movement and typically have a longer lifespan than standard DC motors due to their robust design and advanced components.

As for specific lifespan expectations, it largely depends on usage conditions such as operating temperature range, duty cycle (percentage of time spent running), voltage supply stability etc.

In general terms if you install it correctly according to manufacturer instructions provided ,use appropriate cooling methods like fans or heat sinks when necessary ,keep proper maintenance records(like checking electrical connections periodically) then your servo should last long enough.

However no one can guarantee how long something will last because there are too many factors at play here .

I would recommend following these guidelines:

Read through your user manual.

Check regularly that all electrical connections are secure.

Use appropriate cooling methods.

Follow any other guidelines given by your manufacturer.

If you follow those steps then I'm sure you'll get along just fine!