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Conditional Neural Expert Processes for Learning Movement Primitives from Demonstration (2402.08424v2)

Published 13 Feb 2024 in cs.RO and cs.LG

Abstract: Learning from Demonstration (LfD) is a widely used technique for skill acquisition in robotics. However, demonstrations of the same skill may exhibit significant variances, or learning systems may attempt to acquire different means of the same skill simultaneously, making it challenging to encode these motions into movement primitives. To address these challenges, we propose an LfD framework, namely the Conditional Neural Expert Processes (CNEP), that learns to assign demonstrations from different modes to distinct expert networks utilizing the inherent information within the latent space to match experts with the encoded representations. CNEP does not require supervision on which mode the trajectories belong to. We compare the performance of CNEP against widely used and powerful LfD methods such as Gaussian Mixture Models, Probabilistic Movement Primitives, and Stable Movement Primitives and show that our method outperforms these baselines on multimodal trajectory datasets. The results reveal enhanced modeling performance for movement primitives, leading to the synthesis of trajectories that more accurately reflect those demonstrated by experts, particularly when the skill demonstrations include intersection points from various trajectories. We evaluated the CNEP model on two real-robot tasks, namely obstacle avoidance and pick-and-place tasks, that require the robot to learn multi-modal motion trajectories and execute the correct primitives given target environment conditions. We also showed that our system is capable of on-the-fly adaptation to environmental changes via an online conditioning mechanism. Lastly, we believe that CNEP offers improved explainability and interpretability by autonomously finding discrete behavior primitives and providing probability values about its expert selection decisions.

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Authors (2)
  1. Yigit Yildirim (7 papers)
  2. Emre Ugur (37 papers)
Citations (2)

Summary

  • The paper introduces CNEP, a framework that leverages gating mechanisms and multiple expert networks to enhance learning from multimodal demonstrations.
  • It outperforms baseline models by achieving faster convergence and more accurate trajectory generation in complex sensorimotor tasks.
  • Empirical results show CNEP’s strong generalization from limited demonstrations to novel tasks, advancing robotic skill acquisition.

Enhancing Learning from Demonstration with Conditional Neural Expert Processes

Introduction to Conditional Neural Expert Processes

Learning from Demonstration (LfD) forms a critical aspect of robotic skill acquisition. It allows robots to learn complex, multimodal sensorimotor trajectories from expert demonstrations, thereby facilitating adaptability and generalization to novel environments and tasks. Demonstrations, however, often present significant challenges due to their inherent variances and the multiple ways to achieve the same skills. Addressing these challenges, this paper introduces the Conditional Neural Expert Processes (CNEP) model, a novel LfD framework intended to refine the process of teaching robots by efficiently generalizing across different modes present in expert demonstrations.

Addressing the Challenges in Multimodal Demonstrations

Traditional approaches to LfD, such as Dynamic Movement Primitives (DMPs) and Gaussian Mixture Models (GMMs), have been foundational yet exhibit limitations with multimodal demonstrations. In contrast, CNEP leverages a gating mechanism and multiple expert networks to handle high-dimensional and multimodal data. This design allows for significantly improved modeling of complex, multimodal sensorimotor trajectories and promotes expert specialization. The CNEP framework outperforms the baseline Conditional Neural Movement Primitives (CNMP) model, offering faster convergence and enhanced modeling performance.

Architectural Contributions and Methodological Advances

The methodological advancements brought by CNEP are twofold. First, it introduces a novel architectural component comprising a gating mechanism alongside multiple expert decoders. This innovation allows for the automatic selection of the most appropriate expert for generating motion trajectories based on the provided demonstrations. Second, CNEP incorporates a unique loss function, which thrives on ensuring even utilization of all experts and assigning a high probability to expert selection. The loss function integrates reconstruction loss with components aimed at expert activation and selection, facilitating a balanced and effective training process. Empirical evidence demonstrates CNEP’s ability to outperform existing methods across a range of tasks, including enhanced interpretability and specialist expertise.

Experimental Validation and Results

The efficacy of the CNEP approach is demonstrated through several experiments, involving both artificially generated datasets and real-robot tasks. These experiments not only compare CNEP with traditional models like CNMP but also underscore its capability to efficiently handle variability and multimodality in demonstrations. Specifically, CNEP shows a notable capability in distinguishing among multiple modes of achieving skill and exhibits superior performance in generating trajectories that accurately reflect expert demonstrations , especially in scenarios involving obstacles.

Implications and Future Directions

The introduction of CNEP marks a significant advancement in the field of Learning from Demonstration. By addressing the challenges posed by multimodal and high-dimensional sensorimotor trajectories, CNEP paves the way for more adaptive and efficient robotic learning. Its capacity to generalize from a limited set of demonstrations to novel tasks and environments underscores the potential for broader application in real-world robotic systems. Looking ahead, further research might explore optimizing the number of experts as a hyperparameter for the model, potentially enhancing its adaptability and efficiency further.

Acknowledgments

The development of the Conditional Neural Expert Processes model was supported by TUBITAK and the European Union under the INVERSE project. The collaborative efforts of the research community and the constructive feedback received throughout the paper were instrumental in achieving the promising outcomes presented in this paper.

Conclusion

The Conditional Neural Expert Processes model represents a formidable advancement in Learning from Demonstrations technology. Through its innovative approach to handling the complexity and variability inherent in robot skill acquisition, CNEP stands out as a crucial step towards more natural, efficient, and adaptable robotic learning systems. With its proven efficacy and potential for further optimization, CNEP is poised to significantly influence future developments in the field of generative AI and robotic learning.

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