Naohiro Uyama

Impedance-based contact control of a free-flying space robot with a compliant wrist for non-cooperative satellite capture

This paper presents the impedance-based contact control of a free-flying space robot utilizing a compliant wrist for non-cooperative satellite capture operation. An open loop impedance control law based on contact dynamics model is introduced to realize a desired coefficient of restitution defined between a manipulator hand of a space robot and a contact point on a free-flying target. The coefficient of restitution and the damping ratio are expressed as a function of contact and impedance parameters; and hence, the impedance parameters are tuned by setting a desired coefficient of restitution and a desired damping ratio. The collision experiment using twodimensional microgravity emulator, called air-floating test bed, verifies that the proposed open loop control law is capable of realizing a desired coefficient of restitution with fairly small errors.

Impedance-based contact control of a free-flying space robot with respect to coefficient of restitution

This paper presents an impedance-based contact control of a free-flying space robot with respect to the coefficient of restitution. Since no object is constrained in space, the contact between two objects in orbit must be treated carefully so as to prevent the objects from inducing undesired contact force and post-contact relative motion. As a solution to this issue, the authors propose a contact control method for a free-flying space robot based on the impedance control with respect to the coefficient of restitution. The coefficient of restitution is used as a reference value to tune the impedance parameters and is formulated through dynamic consideration to include both the impedance parameters and contact parameters in the coefficient of restitution. The fundamental experiment is conducted to verify the proposed control method, using a ground-based manipulator to realize the impedance control, and a fixed wall as a target surface. The experimental results showed that the proposed control method successfully controlled the coefficient of restitution between two bodies.

Virtual mass of impedance system for free-flying target capture

This paper discusses the target motion around the contact in the satellite capture operation using a free-flying space robot. The contact force has the potential for pushing the target beyond the manipulator reach or making the target have a tumbling motion. An impedance control is useful to prevent the robot hand from pushing the target. However, the relationship between the dynamics parameters, contact characteristics, and target motion have not been clarified yet. In this paper, virtual mass of impedance system (VMI) model is proposed to represent the influence of the hand impedance on the target motion. Using this model, the condition to prevent the robot pushing the target away is clarified.

Integrated experimental environment for orbital robotic systems, using ground-based and free-floating manipulators

On-ground experiment for space robotic system is essential to validate constructed robotic system prior to launch. This paper presents an integrated on-ground experimental environment for orbital robotic system. The experimental environment utilizes an air-floating testbed to realize two-dimensional micro-gravity environment on ground. As manipulation system, the constructed environment adopts a ground-based manipulator and a free-floating robot. In order to verify the emulated micro-gravity environment, two cases are tested: the impulse-momentum relationship between a ground-based manipulator and a free-floating target, and the conservation of momentum in a free-floating robot. Both results conclude the validity of the constructed experimental environment for on-ground micro-gravity emulation.