Enhancing End-user Engagement in Human-Robot Interaction by Performing LLM-driven Expressive Behaviors

We introduce a novel framework with strong generalization capabilities for enabling humanoid robots to perform semantically grounded, context-aware, and physically realizable expressive behaviors, with the goal of enhancing end-user engagement in open-world human–robot interaction (HRI). To achieve this goal, we develop a new LLM-based human cognition module that interprets user dialogues to infer latent intent and generates high-level multimodal behavior descriptions. These semantic representations are mapped to speech and motion outputs through a dual-stage embodied behavior generation pipeline. The pipeline consists of a shape adaptation module that maps human body motions into the robot's kinematic space, followed by a motion retargeting module that generates executable joint trajectories under physical constraints. Additionally, the modular architecture enables seamless integration of state-of-the-art generative models and serves as a practical testbed for evaluating expressive behavior generation in real-world settings. We validate this system on a 58-DoF humanoid platform through both controlled video-based studies and live HRI experiments. The results show significant improvements over rule-based and handcrafted baselines in terms of expressiveness, behavioral appeal, and user engagement. This work helps bridge the gap between high-level language understanding and low-level robot control, thereby enabling scalable and human-aligned expressive behavior generation for embodied agents.