Grasp Synthesis for Digital Hands with Limited Range of Motion in Their Thumb Joints

For virtual evaluation of universal design products, it is necessary to synthesize natural grasps for various hands including those with limited range of motion (ROM). In this paper, we study synthesizing grasps for digital hands with limited ROM in their thumbs' joints. We apply a contact-region-based method for grasp synthesis to this problem. In our previous study, two types of grasps were observed under the limitation of the thumb's ROM. One was a type that used the lateral region of the thumb, and the other was a type that used he same contact regions as healthy hands. In this paper, grasps are synthesized for two objects using three hand models whose lengths are different. With the same input information as the healthy hand, it is not possible to synthesize the grasps for the ROM-limited hand. On the other hand, when grasps are synthesized by changing the information about grasping target points of the thumb and the palm, feasible grasps for the ROM-limited hand can be found. For a camera object, the grasp using the thumb's radial region is automatically synthesized without changing the specified contact region. Also, for a spray object, a grasp that uses the same contact region as the healthy hand is synthesized. These results demonstrate our method can synthesize natural grasps even for ROM-limited hands, which will contribute to universal product design.