M.Sc. Thesis: Jan Mundo on Extracting Low-Dimensional Control Variables for Movement Primitives
Supervisors: Elmar Rueckert, Prof. Dr. Jan Peters, Prof. Dr. Gerhard Neumann
Finished: 29. Oktober.2014
In robotics we often want to solve a multitude of different, but related tasks. Movement primitives (MPs) provide a powerful framework for data driven movement generation that has been successfully applied for learning from demonstrations and robot reinforcement learning. As the parameters of the primitives are typically high dimensional, a common practice for the generalization of movement primitives to new tasks is to adapt only a small set of control variables, also called meta parameters, of the primitive. Yet, for most MP representations, the encoding of these control variables is pre-coded in the representation and can not be adapted to the considered tasks. In this thesis, we want to learn the encoding of task-specific control variables also from data instead of relying on fixed meta-parameter representations. We use hierarchical Bayesian models (HBMs) to estimate a low dimensional latent variable model for probabilistic movement primitives (ProMPs), which is a recent movement primitive representation. We show on two real robot datasets that ProMPs based on HBMs outperform standard ProMPs in terms of generalization and learning from a small amount of data and also allows for an intuitive analysis of the movement. We also extend our HBM to a mixture model, such that we can model different movement types in the same dataset.