Articulation modeling aims to infer movable parts and their motion parameters for a 3D object, enabling interactive animation, simulation, and shape editing. In this paper, we present Sketch2Arti, the first sketch-based articulation modeling system for CAD objects. Our key observation is that designers naturally communicate articulation intent through lightweight sketches (e.g., arrows and strokes) that indicate how parts should move, yet translating such sketches into articulated 3D models remains largely manual. Sketch2Arti bridges this gap by enabling users to specify articulation through simple 2D sketches drawn from a chosen viewpoint. Given a CAD model and user sketches, our approach automatically discovers the corresponding movable parts and predicts their motion parameters, allowing iterative modeling of multiple articulations on complex objects with fine-grained control. Importantly, Sketch2Arti is trained in a category-agnostic manner without requiring object category information, leading to strong generalization to diverse objects beyond existing articulation datasets. Moreover, for shell models lacking interior structures, Sketch2Arti supports controllable internal completion guided by user sketches, generating plausible internal components consistent with the existing geometry and predicted motion constraints. Comprehensive experiments and user evaluations demonstrate the effectiveness, controllability, and generalization of Sketch2Arti. The code, dataset, and the prototype system are at https://arlo-yang.github.io/Sketch2Arti.

翻译：铰接建模旨在推断三维物体的可动部件及其运动参数，从而实现交互式动画、仿真与形状编辑。本文提出Sketch2Arti——首个基于草图的CAD物体铰接建模系统。我们的核心观察是：设计师通过轻量级草图（如箭头和笔画）自然地传达铰接意图，指示部件应如何运动，但将此类草图转化为三维铰接模型仍主要依赖手动操作。Sketch2Arti通过允许用户从选定视角绘制简单二维草图来指定铰接关系，从而弥合了这一差距。给定一个CAD模型和用户草图，我们的方法能自动发现对应的可动部件并预测其运动参数，支持对复杂物体进行多次铰接的迭代建模，实现细粒度控制。重要的是，Sketch2Arti以类别无关方式训练，无需物体的类别信息，从而对现有铰接数据集之外的多样化物体展现出强泛化能力。此外，针对缺乏内部结构的壳体模型，Sketch2Arti支持在用户草图引导下进行可控的内部补全，生成与现有几何及预测运动约束一致的合理内部组件。全面的实验与用户评估证明了Sketch2Arti的有效性、可控性与泛化性。代码、数据集和原型系统见https://arlo-yang.github.io/Sketch2Arti。