如果你看机器的教材，比如 robot modeling planing and control，其中讲驱动器的一章一般会简单介绍电流和电机输出力矩的关系。但是这个力矩是电机输出端的，不是连杆关节端，中间还有由于摩擦活着变形引起的消耗。在没有关节力矩传感器的情况下，用电流来计算电机输出力矩，然后估计连杆端的力矩也是一个可以接受的选择。 UR 机器人的各种触停，柔性示教就是通过电流来估算力矩的。当力矩能够被估计出来，并且通过机器人本身的动力学就可以知道在每种情形下对应需要的关节力矩，这样就可以在力矩环 也就是电流环把动力学补偿掉。所以就有了各种重力补偿，柔性示教，触停等等。我和我实验室以前的一个同事也曾经用电流来估算一个手指的关节力矩。这种方法好处就是便宜，不足就是不准确，不十分安全。另外一种方法就是就是采用关节力矩传感器，可以直接测量连杆端的力矩，然后在关节处可以采用速度环或者同样的电流环来形成一个闭环力矩控制。有的机器人比如kuka lwr，在电机端和连杆端分别有力矩传感器，不仅可以考虑到关节柔性变形引起的力矩消耗，也起到双重安全保护的作用。 这种方式当然要准确很多，但是也贵了很多倍。这种柔性的协作机器人还有其他的几种形式，有的也不需要力矩传感器，但是驱动方式就完全不一样。
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.