如果你看機器的教材，比如 robot modeling planing and control，其中講驅動器的一章一般會簡單介紹電流和電機輸出力矩的關系。但是這個力矩是電機輸出端的，不是連桿關節端，中間還有由于摩擦活著變形引起的消耗。在沒有關節力矩傳感器的情況下，用電流來計算電機輸出力矩，然后估計連桿端的力矩也是一個可以接受的選擇。 UR 機器人的各種觸停，柔性示教就是通過電流來估算力矩的。當力矩能夠被估計出來，并且通過機器人本身的動力學就可以知道在每種情形下對應需要的關節力矩，這樣就可以在力矩環 也就是電流環把動力學補償掉。所以就有了各種重力補償，柔性示教，觸停等等。我和我實驗室以前的一個同事也曾經用電流來估算一個手指的關節力矩。這種方法好處就是便宜，不足就是不準確，不十分安全。另外一種方法就是就是采用關節力矩傳感器，可以直接測量連桿端的力矩，然后在關節處可以采用速度環或者同樣的電流環來形成一個閉環力矩控制。有的機器人比如kuka lwr，在電機端和連桿端分別有力矩傳感器，不僅可以考慮到關節柔性變形引起的力矩消耗，也起到雙重安全保護的作用。 這種方式當然要準確很多，但是也貴了很多倍。這種柔性的協作機器人還有其他的幾種形式，有的也不需要力矩傳感器，但是驅動方式就完全不一樣。
If you look at the teaching material of machine, such as robot modeling planing and control, in which a chapter of drive will generally introduce the relationship between current and motor output torque. But the torque is the output of the motor, not the joint end of the connecting rod, and the consumption caused by the living deformation of friction in the middle. In the absence of joint torque sensor, it is acceptable to calculate the output torque of motor with current and estimate the torque of connecting rod end. UR robot's various touch and stop, flexible instruction is to estimate the torque through the current. When the torque can be estimated, and the dynamics of the robot itself can know the corresponding joint torque in every case, it can compensate for the torque in the torque loop, which is the current loop. So there are various kinds of gravity compensation, flexible instruction, touch stop, and so on. I and a former colleague of my lab have used electric current to estimate the joint torque of a finger. The advantage of this method is cheap, inadequacy is inaccurate, not very safe. Another way is to use the joint torque sensor to directly measure the torque of the connecting rod end, and then use the speed loop or the same current loop to form a closed loop torque control at the joint. Some robots, such as KUKA LWR, have torque sensors at the motor end and connecting rod end, which not only take into account the torque consumption caused by the joint flexible deformation, but also play a dual safety protection role. Of course, it's a lot more accurate, but it's a lot more expensive. There are several other forms of this flexible cooperative robot, and some do not need torque sensors, but the driving mode is completely different.