Sudden changes in the dynamics of robotic tasks, such as contact with an object or the latching of a door, are often viewed as inconvenient discontinuities that make manipulation difficult. However, when these transitions are well-understood, they can be leveraged to reduce uncertainty or aid manipulation---for example, wiggling a screw to determine if it is fully inserted or not. Current model-free reinforcement learning approaches require large amounts of data to learn to leverage such dynamics, scale poorly as problem complexity grows, and do not transfer well to significantly different problems. By contrast, hierarchical planning-based methods scale well via plan decomposition and work well on a wide variety of problems, but often rely on precise hand-specified models and task decompositions. To combine the advantages of these opposing paradigms, we propose a new method, Act-CHAMP, which (1) learns hybrid kinematics models of objects from unsegmented data, (2) leverages actions, in addition to states, to outperform a state-of-the-art observation-only inference method, and (3) does so in a manner that is compatible with efficient, hierarchical POMDP planning. Beyond simply coping with challenging dynamics, we show that our end-to-end system leverages the learned kinematics to reduce uncertainty, plan efficiently, and use objects in novel ways not encountered during training.
Articulation motion models can also be seen as geometric constraints imposed on two or more rigid bodies. @cite_5 have proposed a method, , to learn geometric constraints encountered in a manipulation task from non-expert human demonstrations. @cite_7 @cite_4 developed an approach to learn geometric constraints governing relative motion between objects from human demonstrations. Their proposed approach can successfully learn geometric constraints even from noisy demonstrations. However, the use of custom force-sensitive hand-held tools to record human demonstrations restricts the generalizability of the approach to a wider set of tasks.
@cite_5 @cite_4 @cite_7
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Learning from demonstrations has been shown to be a successful method for non-experts to teach manipulation tasks to robots. These methods typically build generative models from demonstrations and then use regression to reproduce skills. However, this approach has limitations to capture hard geometric constraints imposed by the task. On the other hand, while sampling and optimization-based motion planners exist that reason about geometric constraints, these are typically carefully hand-crafted by an expert. To address this technical gap, we contribute with C-LEARN, a method that learns multi-step manipulation tasks from demonstrations as a sequence of keyframes and a set of geometric constraints. The system builds a knowledge base for reaching and grasping objects, which is then leveraged to learn multi-step tasks from a single demonstration. C-LEARN supports multi-step tasks with multiple end effectors; reasons about SE(3) volumetric and CAD constraints, such as the need for two axes to be parallel; and offers a principled way to transfer skills between robots with different kinematics. We embed the execution of the learned tasks within a shared autonomy framework, and evaluate our approach by analyzing the success rate when performing physical tasks with a dual-arm Optimas robot, comparing the contribution of different constraints models, and demonstrating the ability of C-LEARN to transfer learned tasks by performing them with a legged dual-arm Atlas robot in simulation. This letter introduces a method for recognizing geometric constraints from human demonstrations using both position and force measurements. Our key idea is that position information alone is insufficient to determine that a constraint is active and reaction forces must also be considered to correctly distinguish constraints from movements that just happen to follow a particular geometric shape. Our techniques can detect multiple plane, arc, and line constraints in a single demonstration. Our method uses the principle of virtual work to determine reaction forces from force and position data. It fits geometric constraints locally and clusters these over the whole motion for global constraint recognition. Experimental evaluations compare our force and position constraint inference technique with a similar position-only technique and conclude that force measurements are essential in eliminating false positive detections of constraints in free space.