Vol.4 No.2 2011
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Research paper : Toward the use of humanoid robots as assemblies of content technologies (S. Nakaoka et al.)−90−Synthesiology - English edition Vol.4 No.2 (2011) achieved the size and weight reductions of the mechanical and electric systems.3.3 Improvement of the walking stabilization systemTo achieve a form similar to humans for the legs in HRP-4C, as seen in Fig. 4, the sole of the feet is smaller compared to the conventional bipedal robots, and the ankle-center is placed close to the heel. In bipedal robots, when the position of the zero-moment point (ZMP) of the sole approaches the edge of the sole, it topples along the edge[17]. Therefore, to prevent falling, it is necessary to keep the ZMP between the sole and floor accurately within the sole, but this becomes difficult to control as the surface area of the sole becomes smaller. We succeeded in obtaining sufficient stability by introducing the new walking stabilization system[18] based on the linear inverted pendulum tracking control that we have been studying as basic research to increase the ability of the bipeds to cover uneven ground.4 Motion expression support technology4.1 Issues in choreography of the movementIn addition to the form and appearance of the robot, the movement of the body is, of course, an important element of expression for the content. The function that will be basic for the content technology is that the robot engages in a series of movements designated by the content creator.The problem is how to choreograph such movements with the robot. In the life-size bipedal robot, the conventional method was to individually develop a program for some specific movements, or to set the commands for the basic preset movements. However, these were non-intuitive tasks that required specialized skills, and the resulting movements tended to be monotonous. Instead of such methods, an easy to understand, efficient method was needed to enable choreography of the various movements as desired by the creator.We shall take another look at the animation technology for CG characters. The humanoids and CG characters are similar in the point that the desired motion is choreographed to the human-like physical model. The CG character animation is a practical technology that has been used in many moving image contents over the years. Therefore, the technology to choreograph the humanoids in similar ways to the CG characters may be used realistically in the content technology of the humanoids.The basic methodology in CG animation is called the “key frame animation”. Here, “frame” means the images in sequential order that switches at tens of frames per second to generate the animation. In this method, the key frames are set when the character’s key poses are selected. The poses that fill the areas between the key poses are automatically created for the other frames. This results in the character’s motion. This allows choreographing detailed motions to the character directly, while skipping the between work. The setting of the poses that determine the motion is intuitive and easy to understand.While this method had been used in the software system intended for use in robots, it was insufficient for “bipedal” robots.In fact, most systems do not take into account the physical interaction between the robot and the floor in the real world, in processing the generation of the movement from the key poses. In such cases, the movement may be physically impossible for the robot to stay in balance on the feet, and the robot may fall when it is made to carry out the movement. This is the point that differs greatly between the robot and the CG character. In this system, if the robot is small and light and the relative sole size is large, the range where it can stay in balance without falling may be wide, and falls can be prevented depending on the adjustments of the key poses. Because of the size condition, the system was limited to the field of hobby robots, and it was not realistic for our purpose.The only system that considered the physical behavior Fig. 3 Cybernetic human HRP-4CName is “Miim”.Fig. 4 Size of left soles and the central position of the ankles of HRP-4C and HRP-2For comparison, the sole of HRP-4C is shown as dotted lines over the sole of HRP-2 on the right.Unit: mmHRP-2HRP-4CCenter of ankleCenter of ankle24013884105245

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