| Different from a conventional robot's motion, there is much coupling among joints in the motion of human (or other creature). Human have talent for passing the motion energy by these coupling. And also, human have talent for controlling and passing the motion by the limit and the flexibility of joints. Compared with robot, human can move with better efficiency. In our research, we simplified the mode of such motion transfer as a dynamics coupling mode of actuated joints and underactuated joints (or named as passive joints/free-joints). In order to simulate human's motion mode, the actuated joints drive those underactuated joints by dynamics coupling. The research on control of underactuated system is signality not only for research on bionic mechanics, but also for other field, for example, space robot, low-cost robot, including improving the performance of conventional robot at high speed.Due to the underactuated joints, the motion control of an underactuated system is much more difficult than that of a conventional system. The underactuated joints can't be controlled directly, so it is an incomplete controllable system. Smooth feedback control is invalid for such system. According to same reason, the motion plan for an underactuated system is much difficult. Because the underactuated joints are driven by dynamics coupling, the motion trajectory must content not only the kinematics constraints, but also constraints of dynamics coupling. Here is another important problem involved in: whether the feedback control can be realized in a real system? The generation of trajectory depends on dynamics strictly, and it is very difficult to adjusted and compensated by feedback control. If the error of dynamics model can't be compensated, maybe the trajectory generated will not be realized, even can't assure the stability. For the complexity and variety of nonlinear, it is difficult to find a universal and efficient method for different types of nonlinear system. |
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