This paper describes the design and control architectures for a novel active thoracolumbosacral orthosis targeted at correction of abnormal postures and treatment of the human spine, often seen in adolescent idiopathic or neuromuscular scoliosis. Our novel device is motivated by the current limitations of the rigid braces used for this purpose which do not adapt to changes in the skeletal system in response to treatment. In addition, the dynamic brace can open possibilities for new treatment methods which currently do not exist. Previous brace designs were not capable of providing dynamic controlled forces. Our design utilizes two Stewart-Gough platforms in series, each controlled independently, either in position or force modes. The design can provide controlled forces/torques on different regions of spine to modify the posture. Additionally, it can control the motion of different regions of the spine through independent position control of each platform using six parallel actuators. Both control methods were validated in benchtop tests. A range of motion study was also performed with a healthy subject wearing the device while the system was controlled in transparent mode.

Due to the complexity of the human musculoskeletal system and intra/intersubjects variability, powered exoskeletons are prone to human-robot misalignments. These induce undesired interaction forces that may jeopardize safe operation. Uncompensated inertia of the robotic links also generates spurious interaction forces. Current design approaches to compensate for misalignments rely on the use of auxiliary passive degrees of freedom that unavoidably increase robot inertia, which potentially affects their effectiveness in reducing undesired interaction forces. Assessing the relative impact of misalignment and robot inertia on the wearer can, therefore, provide useful insights on how to improve the effectiveness of such approaches, especially in those situations where the dynamics of the movement are quasi-periodic and, therefore, predictable such as in gait. In this paper, we studied the effects of knee joint misalignments on the wearer's gait, by using a treadmill-based exoskeleton developed by our group, the ALEX II. Knee joint misalignments were purposely introduced by adjusting the mismatch between the length of the robot thigh and that of the human thigh. The amount of robot inertia reflected to the user was adjusted through control. Results evidenced that knee misalignment significantly changes human-robot interaction forces, especially at the thigh interface, and this effect can be attenuated by actively compensating for robot inertia. Misalignments caused by an excessively long robot thigh are less critical than misalignments of equal magnitude deriving from an excessively short robot thigh.

This paper introduces the overall design of ALEX III, the third generation of Active Leg Exoskeletons developed by our group. ALEX III is the first treadmill-based rehabilitation robot featuring 12 actively controlled degrees of freedom (DOF): 4 at the pelvis and 4 at each leg. As a first application of the device, we present an adaptive controller aimed to improve gait symmetry in hemiparetic subjects. The controller continuously modulates the assistive force applied to the impaired leg, based on the outputs of kernel-based non-linear filters, which learn the movements of the healthy leg. To test the effectiveness of the controller, we induced asymmetry in the gait of three young healthy subjects adding ankle weights (2.3kg). Results on kinematic data showed that gait symmetry was recovered when the controller was active.

ALEX III is a bilateral exoskeleton for gait rehabilitation. It is an evolution of two previous prototypes - ALEX and ALEX II - developed at the University of Delaware. The new robot comprises a support platform and two robotic legs. Its unique characteristic is the possibility to actively control 12 degrees-of-freedom: 4 at the pelvis and 4 for each leg. This paper focuses on the design and fabrication of the robotic leg. Results from early evaluations are presented where the robotic leg is attached to a fixed frame and controlled with a zero-interaction controller.

As our robotics community advances its understanding toward the optimal design of robotic exoskeletons for human gait training, the question we ask in this paper is how the anterior lunge degree of freedom in the robotic exoskeleton affects human gait training. Answering this question requires both novel robotic design and novel protocols for human gait training to characterize this effect. To the best of the authors' knowledge, this is the first study to characterize the effect of an exoskeleton's degrees of freedom on human gait adaptation. We explored this question using the Active Leg EXoskeleton (ALEX) II. The study presented was performed using ALEX II under the following two configurations: 1) locking the anterior/posterior translation in the exoskeleton, while allowing other degrees-of-freedom (labeled as locked mode) and 2) keeping the anterior/posterior degree of freedom unlocked (labeled as unlocked mode). Healthy subjects walked at self-selected speeds on a treadmill and were trained to walk with a new gait template, scaled down from their normal template. While both groups showed adaptation and retention over a 26-min period following training, the unlocked group showed better performance in terms of adaptation and retention compared with the locked group.

This paper addresses an important question in the field of rehabilitation robotics that can help engineers to develop and optimize future gait training robotic exoskeletons. This question can be posed as follows: Do the exoskeleton's degrees-of-freedom at the pelvis affect human adaptation to new gait templates? More specifically, would additional degrees-of-freedom in the exoskeleton that allow the human trunk to translate and rotate, and the hips to abduct/adduct increase human gait adaptation with an exoskeleton?