Towards Manipulator Task-Oriented Programming: Automating Behavior-Tree Configuration
Creators: name: Cao, Yue
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 460205
subject: Intelligent robotics

description: Task-oriented programming is a way of programming manipulators in terms of high-level tasks instead of explicit motions. It has been a long-standing vision in robotics since its early days. Despite its potential, several challenges have hindered its full realization. This thesis identifies three major challenges, particularly in task specification and the planning-to-execution transition: 1) The absence of natural language integration in system input. 2) The dilemma of continuously developing non-uniform and domain-specific primitive-task libraries. 3) The requirement for much human intervention.To overcome these difficulties, this thesis introduces a novel approach that integrates natural language inputs, eliminates the need on fixed primitive-task libraries, and minimizes human intervention. It adopts the behavior tree, a modular and user-friendly form, as the task representation and advances its usage in task specification and planning-to-execution transition. The thesis is structured into two parts – Task Specification and Planning-to-Execution Transition.Task specification explores the use of large language models to generate a behavior tree from an end-user's input. A Phase-Step prompt is designed to enable the automatic behavior-tree generation from end-user's abstract task descriptions in natural languages. With the powerful generalizability of large language models, it breaks the dilemma that stays with fixed primitive-task libraries in task generation. A full-process case study demonstrated the proposed approach. An ablation study was conducted to evaluate the effectiveness of the Phase-Step prompts. Task specification also proposes behavior-tree embeddings to facilitate the retrieval-augmented generation of behavior trees. The integration of behavior-tree embeddings not only eliminates the need for manual prompt configuration but also provides a way to incorporate external domain knowledge into the generation process. Three types of evaluations were performed to assess the performance of the behavior-tree embedding method.Planning-to-execution transition explores how to transit primitive tasks from task specification into manipulator executions. Two types of primitive tasks are considered separately: point-to-point movement tasks and object-interaction tasks. For point-to-point movement tasks, a behavior-tree reward is proposed to enable reinforcement learning over low-level movement while following high-level running order of the behavior tree. End-users only need to specify rewards on the primitive tasks over the behavior tree, and the rest of the process will be handled automatically. A 2D space movement simulation was provided to justify the approach. For object-interaction tasks, the planning-to-execution transition uses a large-language-model-based generation approach. This approach takes natural-language-described primitive tasks as input and directly produces task-frame-formalism set-points. Combined with hybrid position/force control systems, a transition process from primitive tasks directly into joint-level execution can be realized. Evaluations over a set of 30 primitive tasks were conducted.Overall, this thesis proposes an approach that advances the behavior-tree towards automated task specification and planning-to-execution transitions. It opens up new possibilities for building better task-oriented manipulator programming systems.