A six-axis force-torque sensor reports three forces (push and pull along x, y, z) and three torques (twist about each axis). Strain gauges inside a metal body deform minutely under load and change electrical resistance, which the electronics convert into newtons and newton metres.
This turns blind position control into force control. The robot can insert a shaft while wiggling until the resistance drops, polish a surface with a constant 20 N press regardless of part tolerance, or detect that it has hit something and stop.
It also enables hand guiding, where an operator pushes the tool and the robot follows. Many cobots achieve a similar effect with torque sensors in every joint instead of one sensor at the wrist.
