A Morphology-Driven Conceptual Design Framework for Passive Sit-to-Stand Assistive Mechanisms

Passive sit-to-stand (STS) assistive devices provide an affordable and reliable alternative to powered rehabilitation systems; however, their effectiveness depends on the kinematic compatibility between the mechanism and the user. Existing studies primarily focus on specific mechanism implementations, whereas systematic methodologies that translate human morphology and motion into conceptual mechanism designs remain limited. This paper proposes an integrated framework combining Human Kinematic Modeling (HKM) and Anthropometry-informed Mechanism Design (AMeD) for the conceptual design of passive STS assistive mechanisms. The HKM reconstructs the STS motion from user anthropometric dimensions using a simplified sagittal-plane kinematic model to derive hip trajectories, center-of-mass progression, and critical assistance phases. These motion descriptors are transformed into engineering requirements through motion abstraction and hierarchical engineering mapping, enabling the generation of alternative linkage concepts, virtual mechanism instantiation, motion compatibility assessment, and preliminary mechanism specification. For the illustrative reference case, based on a stature-derived anthropometric parameterization (H=1.73 m), the reconstructed hip trajectory exhibits horizontal and vertical excursions of approximately 0.422 m and 0.461 m, respectively, defining the target motion envelope for the virtual mechanism. The proposed HKM-AMeD framework establishes a traceable methodology that transforms user anthropometry and human motion into engineering design knowledge, providing a reproducible foundation for the early-stage development and evaluation of passive assistive mechanisms before detailed optimization and physical prototyping.