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Robots have been used to offset the limb weight through gravity compensation in upper body rehabilitation to delineate the effects of loss of strength and loss of dexterity, which are two common forms of post-stroke impairments. In this paper, we explored the impact of this anti-gravity support on the quality of movement during reaching and coordinated arm movements in a pilot study with two participants with chronic stroke. The subjects donned the Harmony exoskeleton which supported proper shoulder coordination in addition to providing gravity compensation. Participants had previously taken part in seven one-hour sessions with the Harmony exoskeleton, performing six sets of passive-stretching and active exercises. Pre- and post-training sessions included assessments of two separate tasks, planar reaching and a set of six coordinated arm movements, in two conditions, outside of and supported by the exoskeleton. The movements were recorded using an optical motion capture system and analyzed using spectral arc length (SPARC) and straight line deviation to quantify movement smoothness and quality. We observed that gravity compensation resulted in an increased smoothness for the subject with high level of impairment whereas compensation resulted in a reduction in smoothness for the subject with low level of impairment in the reaching task. Both participants demonstrated better coordination of the shoulder-arm joint with gravity compensation. This result motivates further studies into the role of gravity compensation during coordinated movement training and rehabilitation interventions.

In a previous study, a tethered pelvic-assist device (TPAD) was used to successfully retrain crouch gait in children with cerebral palsy by applying a downward force on the pelvis while walking on a treadmill. While the results of this study were promising, an important issue was to translate this training to the children in a more practical manner. This motivated the question in this letter whether a different intervention could result in similar improvements in the gait as seen with the TPAD. This is the motivation for this study, which compares the biomechanical differences in walking under the following two conditions. 1) The TPAD applies a pure downward force on the pelvis using tethers. 2) A weighted pelvic belt is used to apply the same downward force on the pelvis. In this case, the weight belt also increases the mass at the pelvis. A total of ten healthy subjects performed two separate experiments while walking on an instrumented treadmill. The whole-body kinematics were recorded using a motion-capture system, and the ground reaction forces were measured by the force plates embedded in the treadmill. We found no significant differences in the kinematic gait parameters of healthy subjects when the downward force, equivalent to 15% body weight, applied by the TPAD was replaced by a weighted pelvic belt having 15% body weight. However, the activation of the gastrocnemius muscle and the estimated maximum ankle torque, predicted by an inverted pendulum mathematical model, during the single support phase of walking, showed a higher increase with the weight belt when compared to a pure downward force. Thus, the weight belt, because of its simplicity, must be further considered as a more convenient candidate to translate the results of TPAD in children with cerebral palsy who suffer from crouch gait.

The viscoelastic properties of human soft tissue influence the nature of interaction at attachment points in wearable devices. Characterizing these properties is especially critical for understanding physical human-robot interaction (pHRI) for exoskeleton design, prosthetics, and similar fields. This paper presents the design and control of a novel actuated indenter for the measurement of human soft tissue properties. The accuracy of position (0.025 mm) and force (111 mN) measurements allows for repeatable and controlled tissue deformation and monitoring at 36 different angular locations (10° increments). Controlled indentation displacement with force feedback is used in three types of applications on a human subject’s forearm. The soft tissue stiffness profile, viscoelastic relaxation behavior, and frequency domain response are measured. The ability to perform multiple characterizations with one indenter device broadens the scope of a human-centered approach to design, modeling, and perception as they relate to pHRI interfaces.

Physical human-robot interaction (pHRI) interfaces are responsible for ensuring safe, comfortable, and effective force transfer between wearable devices and their users. However, analysis is often oversimplified by treating the human-robot attachment as a rigid connection and using gross load measurements. As a result, information about the distribution of forces across the human-robot contact surface is lost. In this paper, we present an analysis method to predict distributed loading across a pHRI interface based on a model with discretized elastic elements that account for compliance from human soft tissue and the robot attachment. Stiffness properties of a proxy upper arm are measured with an indenter and used in the pHRI interface model. The analysis is performed assuming a rigid arm model, consistent with the underlying assumption in literature, and repeated using the proposed compliant arm model with measured elastic properties. The distributed loading predicted by the pHRI interface model is validated with measurements from a sensorized upper arm cuff on the Harmony exoskeleton. Our results reveal that a model incorporating compliance at the human-robot attachment is necessary to improve prediction of distributed interface loads. This motivates the need for human-centered analysis which can enable finer control of interaction forces and help design more ergonomic attachment interfaces.

How best to attach exoskeletons to human limbs is an open and understudied problem. In the case of upperbody exoskeletons, cylindrical handles are commonly used attachments due to ease of use and cost effectiveness. However, handles require active grip strength from the user and may result in undesirable flexion synergy stimulation, thus limiting the robot’s effectiveness. This paper presents a new design, the Eminence Grip, for attaching an exoskeleton to the hand while avoiding the undesirable consequences of using a handle. The ergonomic design uses inverse impedance matching and does not require active effort from the user to remain interfaced with the exoskeleton. We compare the performance of the Eminence Grip to the handle design in a healthy subject target reaching experiment. The results show that the Eminence Grip achieves similar performance to a handle in terms of relative motion between the user and the exoskeleton while eliminating the requirement of grip force to transfer loads to/from the exoskeleton and avoiding stimulation of the flexion synergy. Taken together, the kinematic equivalence and improvement in ergonomics suggest that the Eminence Grip is a promising exoskeleton-hand attachment interface supporting further experiments with impaired populations.

In this work, we present and validate a novel inverse kinematics method for rehabilitation upper-limb exoskeletons that require joint coordination constraints. Starting from the conventional differential kinematics algorithm based on the inversion of the Jacobian matrix, we describe and test the improved algorithm based on the Projected-Gradient method, which takes into account inter-joint coordination constraints. The Harmony exoskeleton is used as a platform to demonstrate the method. In detail, we address the joint constraints needed to match anatomical shoulder movement and results show good performances of the proposed algorithm., https://youtu.be/x-EkavyAp_E

Much effort has been placed into the development of robotic devices to support, rehabilitate, and interact with humans. Despite these advances, reliably modeling the neuromuscular changes in human motion resulting from a robotic intervention remains difficult. This paper proposes a method to uncover the relationship between robotic intervention and human response by combining surface electromyography (sEMG), the musculoskeletal modeling platform OpenSim, and artificial neural networks (ANNs). To demonstrate the method, a one degree of freedom (DOF) elbow flexion-extension motion is performed and analyzed. Preliminary results show that while the robot provides assistance to the subject, it also appears to produce other unexpected responses in the movement. Further investigation using the new method reveals the neuromuscular effect of an unintended resistance to the subject’s motion applied by the robot as it enforces a speed slower than the subject selects. The characterization of the differences in expected and actual interaction is enabled by the method presented in this paper. Thus, the method uncovers previously obscured aspects of human robot interaction, and creates possibilities for new training modalities.

Hemiparetic gait is abnormal asymmetric walking, often observed among patients with cerebral palsy or stroke. One of the major features of asymmetric gait is excessive reliance on the healthy leg, which results in improper load shift, slow walking speed, higher metabolic cost, and weakness of the unused leg. Hence, clinically it is desirable to promote gait symmetry to improve walking. While there are no clear methods to achieve this goal, we are exploring new methods where we guide the pelvis to change the gait symmetry. This controller is designed to mimic the hands of a physical therapist holding the pelvis and guiding it to promote the usage of both legs during walking. In this paper, we show that the essence of this method can be demonstrated by promoting asymmetry in the gait of healthy subjects when walking with the device. The results showed that their kinematics and kinetics changed asymmetrically during the intervention. Subjects demonstrated asymmetric lateral ground reaction force to compensate for the lateral forces applied on the pelvis. Muscle activities increased on the targeted leg show the forced use of the leg which can be used for rehabilitation of patients with an asymmetric gait.

This work involves study of the first three natural frequencies of the perforated plates. The effect of the parameters which influence them have been studied. The parameters considered are the shape of perforations, pattern of the perforations, aspect ratio of the plate, dimensions of the plate, ligament efficiency and the mass remnant ratio (MRR). The study is focused on the effect of the most influencing parameter on the free vibrations.