As collaborative robots expand into manufacturing environments the issue of safe motion continues to be a concern. Current design approaches involve adding force sensors, torque sensors, and sometimes proximity sensors. These adders along with more complex software control algorithms mitigate most of the concerns and result in slower operation. Unfortunately, these additional sensors also add significant cost and complexity.
This technical document explores the use of calibrated motor current and internal compliance in harmonic gearing to produce a virtual torque sensor without adding torque sensing components. Understanding the internal compliance of the mechanical structure along with the motor torque characterization can yield two virtual torque sensors. The virtual torque sensors inside each joint might work in conjunction with one multi-degree of freedom force sensor on the robot reducing cost and complexity while providing the necessary safe operation.