Skill Learning from Human Demonstrations Using Dynamical Regressive Models for Multitask Applications

This paper is concerned with the motor skill learning from human demonstrations using the framework of dynamic regressive models (DRMs). The DRM-based motion planner is preferred as it generates the end-effector trajectory dynamically based on the current state of the end-effector. Within existing frameworks, a single DRM can learn a single motion profile. In addition, such learned DRMs from the data may not be stable. This paper addresses both these issues in a comprehensive manner. In this paper a single DRM has been used to encode human demonstrations involving multitask profiles and multiple task-equilibriums which is novel. We have introduced the idea that the learned DRM will generate human-like stable motion if the energy dissipation rate (EDR) of the generated trajectory follows that of the human demonstration. Thus, the DRM structure has been modified by adding a continuous guiding signal which can be called as the control signal. This signal has been derived using control theoretic principle to ensure asymptotic stability while maintaining the EDR equivalent to that of the human demonstration. The asymptotic stability of the learned DRM has been established by involving a nonmonotonic Lyapunov function consisting of first derivative of a quadratic function and the energy function associated with the DRM. The proposed framework can be learned using many existing regression techniques in this paper Gaussian mixture regression, locally weighted projection regression, and support vector regression techniques have been used successfully. During the pick and place tasks, human demonstrations involving multiple task profiles and multiple task-equilibriums are generated using a 7 DOF commercial robot manipulator. Experimental validations show that the DRMs learned using these three regression schemes are able to guide the robot along the multitask profiles in a stable manner.