In the nearly six decades since researchers began to explore methods of creating them, exoskeletons have progressed from the stuff of science fiction to nearly commercialized products. While there are still many challenges associated with exoskeleton development that have yet to be perfected, the advances in the field have been enormous. In this paper, we review the history and discuss the state-of-the-art of lower limb exoskeletons and active orthoses. We provide a design overview of hardware, actuation, sensory, and control systems for most of the devices that have been described in the literature, and end with a discussion of the major advances that have been made and hurdles yet to be overcome.

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Chronic hand impairment is common following stroke. While mass practice of movement has shown promise for rehabilitation, initial impairment of the hand may be too severe to permit even approximations of the desired movement. To facilitate movement, especially of pinch, we are building an exoskeleton to permit independent actuation of each of the three joints of the index finger. Separate actuators are used for flexion and extension, with closed-loop control of either force or position. In the future, a companion thumb exoskeleton will be developed to permit coordinated performance of pinch. This system will be used to assess strategies for optimizing rehabilitation of pinch and reach-to-pinch following stroke. The design of the actuated index fingerexoskeleton is presented here.

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This study presents preliminary results of a randomized controlled trial comparing a novel passive arm orthosis training system, the Therapy Wilmington Robotic Exoskeleton (T-WREX), with conventional self-directed upper extremity exercises. Chronic stroke survivors (n = 23) with moderate to severe upper limb hemiparesis trained three times per week for eight weeks with minimal supervision from an occupational therapist. Both groups demonstrated significant improvements in arm movement ability according to the Fugl-Meyer (3.7 point mean improvement in T-WREX group, p = 0.001, and 2.7 point improvement in control group, p = 0.003). Individuals who completed T-WREX training also demonstrated significant gains in self-rated quality of arm movement on the Motor Activity Log (p=0.05), and showed a trend towards greater gains on all clinical measures, although this trend was not significant at the current study size. Post-treatment surveys revealed a subjective preference for T-WREX training over conventional gravity-supported exercises. These preliminary results suggest that the T-WREX is a safe device feasible for clinical use, and effective in enhancing upper extremity motor recovery and patient motivation. Next steps are discussed.

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Robotic gait trainers are used all over the world for the rehabilitation of stroke patients, despite relatively little is known about how the robots should be controlled to achieve the optimal improvement. Most devices control complete joint trajectories and assume symmetry between both legs by either a position or an impedance control. However we believe that the control should not be on a joint level but on a subtask level (i.e. foot clearance, balance control). To this end we have chosen for virtual model control (VMC) to define a set of controllers that can assist in each of these tasks. Thus enabling the exoskeleton to offer selective support and evaluation of each substask during rehabilitation training. The bottleneck of the VMC performance is the ability to offer an end point impedance at the ankle as the arm between the joints is largest here. This endpoint impedance is evaluated in this paper to show the ability of our exoskeleton to offer the required moments to support all the gait functions defined in this paper. We have shown that it is possible to implement the VMCs necessary for selective support of gait functions using series elastic actuators with a non-linear transmission. For the vertical direction we measured an stiffness of 5 kN/m for all ranges at frequencies of up to 1 Hz as a near ideal spring. In the horizontal we measured op to 0.5 kN/m in the same frequency range. The crosstalk between the vertical and the horizontal directions has been shown to be small. This means that it is possible to selectively offer forces in either vertical or horizontal directions.

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According to reviews, training with upper-extremities rehabilitation robotics is at least as good as regular stroke rehabilitation, probably because the robotics increase the training intensity for the patients. As an alternative to the functional approach mimicking activities of daily living, targeted force-coordination training may also have its benefits. Our passive exoskeleton, the Dampace, has controlled braking on the three rotational axes of the shoulder and one of the elbow. It is designed to combine functional training of activities of daily living with force-coordination training. The Dampace exoskeleton can assist in identifying causes behind the movement disorders of stroke patients, tackle these causes with isolated force-coordination training, possibly simultaneously over multiple joints, and then integrate the isolated training back into a functional, task-specific training protocol. Not needing to align the Dampace axes to the human shoulder and elbow axes overcome some of the difficulties traditionally associated with exoskeletons. Although it adds more complexity, the reduction of setup times to a few minutes and the absence of static reaction forces in the human joints, are major advantages and have been well received by therapists and physicians. Controlled braking instead of actively assisting actuators, has the advantage of inherent safety and always actively participating patients, at the cost of not being able to assist movements or create all virtual environments.

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