Joints Damping Torque Test Of Extravehicular Activity Spacesuit Arm

Shenzhou VI spacecraft has successfully accomplished the flight task of "two astronauts, more days" last year and it is expected that Shenzhou VII will make astronauts'extravehicular walking possible next year. Qi Faren, the chief consultant of Shenzhou VI said that:"There are two greatest difficulties are about to be solved by Shenzhou VII after Shenzhou VI: the EVA (Extravehicular Activity) spacesuit (Shenzhou VI is IVA one, Inner Vehicular Activity) and the air brake cabin."Currently, the EVA spacesuit's design and processing has almost been completed. However, what is more important is to give EVA spacesuit an overall ground-based test. Comparing with IVA spacesuit, the difficulty of EVA one is that it has to provide more protection while keeping good movability performance so that astronauts will smoothly complete EVA tasks. Therefore, the movability performance testing equipment, especially the movability performance testing equipment for upper limbs is absolutely essential.In 2002 DLR-HIT Joint Robotics Laboratory cooperating with China Aerospace Medical Engineering Institute has developed China's first set of IVA spacesuit joint torque testing device. Keeping the original mechanical devices and hardware unchanged, this project will mainly focus on solving the kinematics and dynamic algorithm problem of 5-DOFs (Degree of Freedoms) spacesuit arm (IVA only has 3 DOFs) and meanwhile extending the software making it qualified both in testing EVA and IVA spacesuit arms.Because the length of spacesuits is the tangent function of the elbow angle instead of a constant, it is impossible to work out the inverse kinematics calculation with analytical method. As the EVA arm has two more DOFs than the IVA one, the inverse kinematics calculation which performs very well in IVA arm can't meet the need of EVA arm in algorithm theory, memory occupation and computational load. This paper solves the algorithm theory problem by converting both positions and poses to relative errors; reduces the memory occupation and computational load to several tenth by dividing the table-making and consulting into two separate parts: the former four joints and the fifth joint, thus solves the feasibility and real-time problem of the algorithm. The experimental results from the SGI (Silicon Graphics Incorporated) work station verify that the new algorithm can meet the testing system's need very well in calculation precision and real-time capability.The other difference of EVA arm is that it is much more heavier than the IVA one, so it is necessary to compensate every section's gravity when calculating the joint damping torque. This paper figures out every section's mass and its centroid location by using the simplified model and experimental correction, and finishes the gravity compensation by using iterative Newton-Euler dynamics formula, besides this paper also compensates the fixture's gravity, both of them are proved effective by experiments.In the end, the EVA arm joint damping torque test is carried out. The joint's angle-damping torque figure which comes from different tests with single clamping of every of the five joints under their rating pressure are given, and the repeated errors, reasons for the errors and improvement methods are analyzed. Finally the test result of the single joint and its comparison with the same joint tested with former method are also given, the validity of the algorithm is proved.