A Novel Pantographic Exoskeleton Based Collocated Joint Design With Application for Early Stroke Rehabilitation
Jiaoying Jiang, Wenjing Li, Kok-Meng Lee
Abstract
Motivated by the need to develop safe exoskeletons for collocated joint rehabilitation during the early stage of stroke recovery, this article presents a pantographic exoskeleton (PGE) capable of multi-degree-of-freedom motions in a single-joint collocated with the impaired joint. With minimum internal joint reactions in the presence of misalignment, the PGE “traces” the natural joint motion “like a pantograph” in the sagittal plane while performing in-bed rehabilitation, from which the joint parameters can be estimated for subsequent patient-specific motion training. An analytical model is presented to provide a rational basis for designing a collocated human-ankle/PGE mechanism, which has been numerically illustrated. The findings demonstrate that because the PGE joint do not restrict human ankle nature motion within the motion range of a typical ankle, it is less sensitive to joint misalignment as compared to conventional multijoint serial mechanisms that form a closed chain with the human limbs/joint. A prototype PGE has been designed; and its effectiveness for collocated ankle-joint manipulation has been experimentally investigated. Unlike conventional imaging methods that are prone to skin-marker errors and dependent on lumped-parameter approximations, the PGE directly measures the talus trajectory of the ankle-joint for characterizing its roll/slide motion and internal parameters.