A back-pressure sensor is a transducer that detects and measures the instantaneous torque that a robot motor applies. The sensor produces a variable signal, usually a voltage , that changes in a linear manner as the torque varies.
When a robot motor operates, it encounters mechanical resistance. This resistance might depend on lifted mass, mechanical friction against a surface or within a system, or the opposition to applied force caused by electromagnetic interaction (as in an electric generator). Torque is the turning force that a robot motor delivers. It is important that a robot motor provide enough torque to overcome the resistance in external systems, but excessive torque can be destructive.
A robot motor produces a measurable back pressure that depends on the applied torque. The greater the torque, the greater the back pressure, and the greater the output of the back-pressure sensor. This output, called the back signal or back voltage, can be used in a feedback loop to reduce the torque applied by the motor. The loop configuration acts as a force limiter that minimizes the possibility of damage to objects handled by a robotic end effector. The force limiter can also reduce the chance of injury to personnel working around the robot.