Adaptive robot control improves contact tasks by balancing stiffness and compliance
Imp-ACT: Adaptive Impedance Control and Action Chunking with Transformers to Learn Contact-Rich Manipulation from Demonstrations
Robotics
Summary
Robots doing tasks that involve touching and pushing need to be both strong and flexible in just the right ways. The authors developed a method called Imp-ACT that lets robots adjust their stiffness depending on the direction they are moving, so they don’t push too hard or too softly. They used a special controller during demonstrations to record this adaptive stiffness along with the robot’s movements and vision. Their approach helps robots successfully do tasks like wiping surfaces and plugging in cables while reducing unwanted forces and vibrations.
What this means in practice
- •For industrial robot programmers: Program robots to perform delicate contact tasks like assembly or cleaning with automatic adjustment of stiffness for better success and lower wear.
- •For robotic teleoperation operators: Enable teleoperators to record demonstrations that naturally include adaptive stiffness, improving robot compliance without manual stiffness tuning.
Authors
Luca Zanetti, Doganay Sirintuna, Idil Ozdamar, Pietro Balatti, Heng Zhang, Arash Ajoudani
Abstract
Contact-rich manipulation requires robots to balance accurate motion tracking with compliant interaction, yet most visual-action policies leave compliance fixed at the controller level. We present Imp-ACT, a methodologically grounded and practical approach to incorporating direction-dependent Cartesian stiffness modulation directly into demonstration collection, without manual stiffness selection or offline target reconstruction. During teleoperation, a self-tuning impedance controller adapts stiffness along the instantaneous direction of motion while maintaining compliance in orthogonal directions. The adapted stiffness is applied and recorded alongside visual observations and motion commands, capturing motion and compliance under the same dynamics. We implement this pipeline using Action Chunking with Transformer (ACT) to predict end-effector pose, gripper action, and motion-direction stiffness from visual, proprioceptive, and wrench observations. The performance of Imp-ACT is evaluated on wiping and plug insertion using both success rate and quantitative measures of contact behavior. Compared with fixed low- and high-stiffness baselines, Imp-ACT achieves comparable or higher success while maintaining low interaction forces. In wiping, it reduces contact-force vibration by approximately $29\times$ relative to the compliant baseline and $180\times$ relative to the stiff baseline. In plug insertion, it reduces forces orthogonal to the insertion direction by $43\%$ relative to the better fixed-stiffness baseline. These results highlight the benefit of maintaining sufficient stiffness along the direction needed for task execution while preserving compliance in other directions to limit contact forces and accommodate environmental constraints.