2008 8 th IEEE-RAS International Conference on Humanoid Robots December 1 '" 3, 2008 / Daejeon, Korea WP1-28 Shock Absorbing Skin Design for Human-Symbiotic Robot at the Worst Case Collision Taisuke Sugaiwa I , Hiroyasu Iwata 2 , Shigeki Suganol J Humanoid Robot Institute, Waseda University, Japan, sugaiwa@Sugano.mech.waseda.acjp, sugano@wasedajp, 2 Waseda Institutefor Advanced Study, Waseda University, Japan, jubi@wasedajp Abstract- In this paper, we proposed a soft skin design method of human symbiotic robots which achieves collision safety in all collision situations. At the same time, soft skin design has to be optimized for the collision safety and the workability. Therefore we evaluate effectiveness of soft skin at each position on arm in longer-direction, and optimize its thickness along collision position. Firstly we discuss parameters for describing the collision between human and human-symbiotic robots, and identify the worst case collision including the out-of-control condition of the robots. Next we conducted actual collision experiments duplicating the worst case collision and apply the proposed method to soft skin covering of human-symbiotic robot "TWENDY-ONE". In consequence, TWENDY-ONE acquires both ofcollision safety and the workability. I. INTRODUCTION Human-symbiotic robots which can support human daily activities are greatly expected to be developed for a measure against labour shortages in aging societies. Human-symbiotic robots should have an anthropomorphic body (e.g. multi- finger hands, redundant arms) for the capability to achieve several tasks in human daily life; therefore the robots should be a kind of humanoid robot. However most of conventional humanoid robots mainly focused on imitation of human movement like bipedal walking, dancing and other motions, and they are not designed to enure human safety which is one of the most important function for human-symbiotic robots. Human-symbiotic robots will work in immediate proximity to humans in houses, welfare facilities, factories, and other places, and so accidental collisions may be occurred between human and the robots. Therefore collision safety which can assure low severity and probability of human injury at accidental collision is very important function for human- symbiotic robots. There are two kinds of researches on the collision safety of human-symbiotic robots. One focused on precise estimation of human injury severity at the collision (the collision means collision between human and robot in this paper) [1][2][3][4]. These researches had discussed that we can or cannot apply severity indices of automobile to the collision, and in consequence revealed difficulty to apply them to the collision by difference in mass, velocity and several conditions from 978-1-4244-2822-9/08/$25.00 ©2008 IEEE collision of automobile. A new severity index for the collision is expected to be developed. However there have ever been few actual cases of the collision, and we don't have enough information of potential human injury by the collision. And we can tell that it is very difficult to acquire the conclusive severity index for the collision. The other one focused on robot design method achieving the collision safety to reduce injury severity and probability of human [5][6]. Robot design architecture for the collision safety which uses shock absorbing skin and safety motion control scheme has been proposed in these researches. Soft skin covering on manipulator can absorb contact force at the collision. Safety motion control scheme can generates human- following motion or emergency motion stop based on collision detection with sensors. Effectiveness of these two functions collaboration was confirmed in these researches based on some criteria. On the other hand, if robot loses control of itself, one function of this collaboration makes no sense. In such situations, safety motion can't be generated by the motion control scheme, and only soft skin is effective for the collision safety. To assure the collision safety in all collision situations is very important ability of soft skin, and we can tell that it is necessary for the collision safety to design soft skin being enough effective in all collision situations. At the same time, soft skin design has trade-offproblem for the collision safety and workability to operate several tasks in human daily life. For the collision safety, human-symbiotic robots should have thick soft skin at wide area on its whole- body surface. For the workability, they should have wide movable range on each joint and large weight carrying capability. Because thick and wide soft skin covering reduces joint movable range and weight carrying capability, these two functional requirements make the trade-off problem for soft skin design. Based on these research backgrounds, we have two assignments for the collision safety skin design and describe them below; being enough effective in all collision situations solving trade-off problem for the collision safety and the workability 481