PAFgrip: A Passive Grasp and Release Mechanism for Space Debris Capture

Japan Aerospace Exploration Agency (JAXA) is developing a debris capture device, HKK for active debris removal by utilizing a caging method to grasp the payload attachment fitting (PAF) of the upper stages of the rockets. The HKK can geometrically constrain all motions of the PAF, except for rotation around the symmetry axis of the PAF ring. To enhance the certainty of capture and complement form closure with a friction-based grip, an additional gripper, namely the PAFgrip, is proposed. This gripper is mounted at the end of the HKK arm; it passively grasps the PAF ring by converting the pushing force from the arm extension through a toggle mechanism. It can maintain the grasp without requiring a power supply, owing to its self-locking function. Additionally, a mechanism for adapting to variations in the thickness of the PAF ring has been designed. A passive release mechanism ensures that the PAF can be released without causing a significant reactive force, and a sensor system is implemented to detect the grasp state. Prototype testing validated that the PAFgrip can reliably grasp PAF rings with a thickness range of 1 mm using the extension force of HKK arm and hold on to the PAF against an external disturbance force of up to 80 N. Furthermore, the PAFgrip can release the PAF passively with a reactive force of less than 3 N, which is approximately 3% of the holding force.