This paper presents the design and analysis of a passive body weight (BW)-support lower extremity exoskeleton (LEE) with compliant joints to relieve compressive load in the knee. The biojoint-like mechanical knee decouples human gait into two phases, stance and swing, by a dual snap fit. The knee joint transfers the BW to the ground in the stance phases and is compliant to free the leg in the swing phases. Along with a leg dynamic model and a knee biomechanical model, the unmeasurable knee internal forces are simulated. The concept feasibility and dynamic models of the passive LEE design have been experimentally validated with measured plantar forces. The reduced knee forces confirm the effectiveness of the LEE in supporting human BW during walking and also provide a basis for computing the internal knee forces as a percentage of BW. Energy harvested from the hip spring reveals that the LEE can save human walking energy.

This paper presents the design concept of a weight-support lower-extremity-exoskeleton (LEE) with a compliant joint to relieve compressive load in the knee. Along with a leg dynamic model and a knee bio-joint model, a compliant exoskeleton knee-joint has been designed using topology optimization and experimentally evaluated. Results suggest that the gait-based design of a LEE can be divided into two parts in terms of knee angles; compliant coupling and body-weight support. The concept feasibility and dynamic models of the passive LEE design have been experimentally validated with measured plantar forces. Both simulation and experimental results agree with data in-vivo confirming the effectiveness of the LEE in supporting human body-weight during walking, and also provide a basis for computing the internal knee forces as a percentage of bodyweight.

This paper presents a dynamic model of a knee joint interacting with a two-link exoskeleton for investigating the effects of different exoskeleton designs on internal joint forces. The closed kinematic chain of the leg and exoskeleton has a significant effect on the joint forces in the knee. A bio-joint model is used to capture this effect by relaxing a commonly made assumption that approximates a knee joint as a perfect engineering pin-joint in exoskeleton design. Based on the knowledge of a knee-joint kinematics, an adaptive knee-joint exoskeleton has been designed by incorporating different kinematic components (such as a pin, slider and cam profile). This design potentially eliminates the negative effects associated with the closed leg/exoskeleton kinematic chain on a human knee. An investigation in the flexion motion of an artificial human knee joint is presented to compare performances of five exoskeleton designs against the case with no exoskeletons. Analytical results that estimate internal forces using the dynamic model (based on the properties of a knee joint) agree well with the experiments. These studies lead to an adaptive mechanism with a slider/cam as an alternative to pin joints for the exoskeleton, and illustrate the application of the model for designing an adaptive mechanism that minimizes internal joint forces due to a human-exoskeleton interaction.