Human arm dynamics can help robots assemble satellites

Damping is the process of reducing the amplitude of oscillations or vibrations by dissipating energy. It is essential for preventing excessive contact force from damaging the objects during assembly. The human arm can flexibly adjust its damping to perform various tasks safely and stably. For example, when holding a fragile thing, the human arm reduces its damping to avoid breaking it, while when pushing a heavy object, it increases its damping to exert more force.

The researchers mimicked this feature by designing a variable admittance controller for robots that can change their damping according to the contact conditions and the assembly requirements. The controller can also compensate for external disturbances and environmental uncertainties.

To test their method, the researchers built a dynamic data acquisition platform to capture human arm motion during assembly tasks. They used an ATI omega160 6D force sensor to measure the contact force between the human hand and the assembly parts and a Stereolabs ZED mini motion capture system to obtain the end velocity of the human arm. They analyzed the data and summarized the dynamic characteristics of the human component, as well as three contact patterns for satellite assembly: sliding contact, impact contact, and stable contact.

The researchers then applied their method to a robot manipulator that can assemble satellite components in space. They conducted simulations and experiments to evaluate the performance of their method under different scenarios and compared it with other compliance control methods. They found that their approach can effectively improve the safety, robustness, and adaptability of robot space assembly.

The researchers also verified their method through a ground experimental platform that simulated space satellite assembly. Their robotic platform could measure forces and torques at the end of a robotic arm in the X, Y, and Z directions. They applied the human-like variable parameter admittance controller to the robot satellite assembly experiment and successfully verified the effectiveness of their method.

Developing control strategies that emulate human-like behavior can significantly enhance the adaptability, precision, and controllability of robots that perform assembly and maintenance tasks in space. Nevertheless, more research is necessary to enable robots to accomplish flexible assembly tasks comparable to those performed by humans. Additionally, there is a need for durable and reliable robots that can withstand harsh space environments.

According to Zhihong Jiang, a professor at the Beijing University of Technology, advancements in humanoid control strategies hold important implications for the future of space exploration and development, further improving mission efficiency, safety, and reliability.

Study abstract:

On-orbit assembly has become a crucial aspect of space operations, where the manipulator frequently and directly interacts with objects in a complex assembly process. The traditional manipulator control has limitations in adapting to diverse assembly tasks and is vulnerable to vibration, leading to assembly failure. To address this issue, we propose a human-like variable admittance control method based on the variable damping characteristics of the human arm. By collecting the velocity and contact force of human arm operations in assembly, we analyze the damping change of human arm and establish the active compliance model based on S-type damping variation rule in assembly. Furthermore, 3 passive contact models are proposed between the end of the human arm and the environment: one-sided bevel contact, both sides bevel contact, and pin–hole contact. On the basis of these active and passive models, a typical space assembly task for a robot is designed, and a human-like variable admittance controller is established and simulated. Finally, we build a ground verification platform and complete different assembly tasks, thereby successfully verifying the safety, robustness, and adaptability of the human-like variable admittance control method.