Force-torque control is a robot control strategy that regulates the contact forces and moments a manipulator exerts on its environment, rather than commanding position alone. It uses force-torque sensing, typically at the wrist or in the joints, within a feedback loop so that the robot can maintain a desired contact force or yield compliantly to external loads. This is essential for tasks involving physical contact, such as assembly, polishing, and safe interaction with people.
- Force-torque control regulates the forces and moments a robot exerts on its surroundings rather than commanding position alone. It closes a Feedback Control loop around wrist or joint force sensing and is foundational to contact-rich Robot Manipulation and safe interaction.
Overview
- Pure position control struggles when a manipulator must touch its environment, because small position errors against a stiff surface produce large, potentially damaging forces.
- Force-torque control instead specifies a desired interaction force or a compliant relationship between motion and force, and uses sensed forces to adjust the commanded motion.
- It is closely related to impedance and admittance control, which shape the dynamic relationship between the robot and external loads.
Mechanisms
- A six-axis force-torque sensor, often at the wrist, measures the contact wrench applied through the end-effector.
- A controller compares the measured wrench to a reference and modulates joint torques or commanded positions to achieve the target interaction.
- Impedance control renders the robot as a virtual spring-damper, while admittance control maps measured force to a corrective motion.
- Accurate dynamic models and calibration remove the robot’s own inertial and gravitational forces so that only true contact forces are regulated.
Applications
- Precision assembly tasks such as peg-in-hole insertion and connector mating.
- Surface-following operations including polishing, deburring, and grinding.
- Collaborative robots that must remain safe and yielding when contacting people.
- Teleoperation and haptic systems that reflect contact forces back to an operator.