A previous study from our laboratory showed that when soleus electro-myography was used to control the amount of plantar flexion assistance from a robotic ankle exoskeleton, subjects significantly reduced their soleus activity to quickly return to normal gait kinematics. We speculated that subjects were primarily responding to the local mechanical assistance of the exoskeleton rather than directly attempting to reduce exoskeleton mechanical power via decreases in soleus activity. To test this observation we studied ten healthy subjects walking on a treadmill at 1.25 m/s while wearing a robotic exoskeleton proportionally controlled by medial gastrocnemius activation. We hypothesized that subjects would primarily decrease soleus activity due to its synergistic mechanics with the exoskeleton. Subjects decreased medial gastrocnemius recruitment by 12% but decreased soleus recruitment by 27%. In agreement with our hypothesis, the primary reduction in muscle activity was not for the control muscle (medial gastrocnemius) but for the anatomical synergist to the exoskeleton (soleus). These findings indicate that anatomical morphology needs to be considered carefully when designing software and hardware for robotic exoskeletons.

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At moderate to fast walking speeds, the human ankle provides net positive work at high-mechanical-power output to propel the body upward and forward during the stance period. On the contrary, conventional ankle–foot prostheses exhibit a passiveelastic response during stance, and consequently, cannot provide net work. Clinical studies indicate that transtibial ampu-tees using conventional prostheses have higher gait metabolic rates than normal. Researchers believe that the main cause for these higher rates is due to the inability of conventional prostheses to provide suf-ficient positive power at terminal stance in the trailing leg to limit heel strike losses of the adjacent leading leg. In this investigation, we evaluate the hypothesis that a powered ankle–foot prosthesis, ca-pable of providing human-like ankle work and power during stance, can decrease the metabolic cost of trans-port (COT) compared to a conventional passive-elastic prosthesis. To test the hypothesis, a powered pros- thesis is built that comprises a unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. The prosthesis is shown to deliver the high mechanical power and net po-sitive work observed in normal human walking. The rate of oxygen consumption and carbon dioxide production is measured as a determinant of metabolic rate on three unilateral transtibial amputees walking at self- selected speeds. We find that the powered prosthesis decreases the amputee’s metabolic COT on average by 14% compared to the conventional passive-elastic prostheses evaluated (Flex-Foot Ceterus R
and Freedom In-novations Sierra), even though the powered system is over twofold heavier than the conventional devices. These results highlight the clinical importance of prosthetic interventions that closely mimic the mass di-stribution, kinetics, and kinematics of the missing limb.

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This paper presents a novel design for a 4 degree of freedom pneumatically-actuated upper-limb rehabilitation device. BONES is based on a parallel mechanism that actuates the upper arm by means of two passive, sliding rods pivoting with respect to a fixed structural frame. Four, mechanically-grounded pneumatic actuators are placed behind the main structural frame to control shoulder motion via the sliding rods, and a fifth cylinder is located on the structure to control elbow flexion/extension. The device accommodates a wide range of motion of the human arm, while also achieving low inertia and direct-drive force generation capability at the shoulder. A key accomplishment of this design is the ability to generate arm internal/external rotation without any circular bearing element such as a ring, a design feature inspired by the biomechanics of the human forearm. The paper describes the rationale for this device and its main design aspects including its kinematics, range of motion, and force generation capability.

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Gait training of stroke survivors can help in retraining their muscles and improving their gait pattern. Robot assisted gait training (RAGT) was developed for stroke survivors using ALEX and force-field controller, which use assist-as-needed paradigm for rehabilitation. In this paradigm undesirable gait motion is resisted and assistance is provided towards the desirable motion. The force-field controller achieves this paradigm by applying forces at the foot of the subject. Two stroke survivors participated in a 15-day gait training study each with ALEX. The results show that by the end of the training the gait pattern of the patients was improved towards healthy subjects gait pattern. Improvement is seen as increase in the size of the patientspsila gait pattern, increase in knee and ankle joint excursions and increase in their walking speed on the treadmill.

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This paper presents multi-criteria design optimization of parallel mechanism based force feedback exoskeletons for human forearm and wrist. The optimized devices are aimed to be employed as a high fidelity haptic interfaces. Multiple design objectives are discussed and classified for the devices and the optimization problem to study the trade-offs between these criteria is formulated. Dimensional syntheses are performed for optimal global kinematic and dynamic performance, utilizing a Pareto front based framework, for two spherical parallel mechanisms that satisfy the ergonomic necessities of a human forearm and wrist. Two optimized mechanisms are compared and discussed in the light of multiple design criteria. Finally, kinematic structure and dimensions of an optimal exoskeleton are decided.

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