I am trying to understand the difference between joint torque sensors, and force sensors, in a robot arm. From what I understand, joint torque sensors estimate the torque at each joint, whereas a force sensor estimates the joint at the end-effector.
But isn't it true that you can use the joint torque sensors to estimate the force at the end-effector, using forward kinematics? And if so, then why would you need to use a force sensor, if you already have joint torque sensors? Or would you typically only have one, i.e. only a set of joint torque sensors, or only a single force sensor?
The reason I am questioning this is that at https://blog.robotiq.com/robotiq-ebook-summary-force-sensors-in-robotics-research, it says:
Force sensors are designed to detect forces applied between their base and sensing plate
But then at https://studywolf.wordpress.com/2013/09/02/robot-control-jacobians-velocity-and-force/, it says:
Jacobians allow us a direct way to calculate what the control signal is in the space that we control (torques), given a control signal in one we don’t (end-effector forces)
Therefore, it seems to me that joint torque sensors and force sensors do the same thing, and you would never need both of them. Is this correct? Or do they play complimentary roles?