A Novel Pantographic Exoskeleton Based Collocated Joint Design With Application for Early Stroke Rehabilitation

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.