Arno H. A. Stienen

Self-Aligning Exoskeleton Axes Through Decoupling of Joint Rotations and Translations

To automatically align exoskeleton axes to human anatomical axes, we propose to decouple the joint rotations from the joint translations. Decoupling can reduce setup times and painful misalignment forces, at the cost of increased mechanical complexity and movement inertia. The decoupling approach was applied to the Dampace and Limpact exoskeletons.

Training modalities in robot-mediated upper limb rehabilitation in stroke: a framework for classification based on a systematic review

Robot-mediated post-stroke therapy for the upper-extremity dates back to the 1990s. Since then, a number of robotic devices have become commercially available. There is clear evidence that robotic interventions improve upper limb motor scores and strength, but these improvements are often not transferred to performance of activities of daily living. We wish to better understand why. Our systematic review of 74 papers focuses on the targeted stage of recovery, the part of the limb trained, the different modalities used, and the effectiveness of each. The review shows that most of the studies so far focus on training of the proximal arm for chronic stroke patients. About the training modalities, studies typically refer to active, active-assisted and passive interaction. Robot-therapy in active assisted mode was associated with consistent improvements in arm function. More specifically, the use of HRI features stressing active contribution by the patient, such as EMG-modulated forces or a pushing force in combination with spring-damper guidance, may be beneficial.Our work also highlights that current literature frequently lacks information regarding the mechanism about the physical human-robot interaction (HRI). It is often unclear how the different modalities are implemented by different research groups (using different robots and platforms). In order to have a better and more reliable evidence of usefulness for these technologies, it is recommended that the HRI is better described and documented so that work of various teams can be considered in the same group and categories, allowing to infer for more suitable approaches. We propose a framework for categorisation of HRI modalities and features that will allow comparing their therapeutic benefits.

Dampace: dynamic force-coordination trainer for the upper extremities

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.

Design of an electric series elastic actuated joint for robotic gait rehabilitation training

Robotic gait rehabilitation is at least as effective as conventional gait training in stroke survivors. Patients must be assisted as needed in order to improve affected gait patterns. The combination of impedance control and series elastic actuation is a viable actuation principle to be used for human robot interaction. Here, a new promising electric series elastic actuated joint is developed. The large torque bandwidth limit at 100 Nm is 6.9 Hz. With a total weight of 3.175 kg it is possible to directly mount the actuator on the exoskeleton frame. The actuator is capable of providing sufficient torque at normal walking speed. Full patient assistance during gait and free motions without impeding the gait pattern are possible. The actuator allows isometric measurements up to 100 Nm and the patients progress in robotic rehabilitation can be evaluated.

Design of a Rotational Hydroelastic Actuator for a Powered Exoskeleton for Upper Limb Rehabilitation

The goal of this study was to validate the suitability of a novel rotational hydroelastic actuator (rHEA) for use in our new rehabilitation exoskeleton for the upper limbs, the Limpact. The rHEA consists of a rotational hydraulic actuator and a custom-designed symmetric torsion spring in a series-elastic configuration. For rehabilitation therapy and impairment quantification, both compliant impedance control and stiff admittance control modes are possible. In the validation experiments, the torque bandwidth of the rHEA was limited to 18 Hz for a desired 20 N·m reference signal (multisine, constant spectrum) due the transport delays in the long flexible tubes between the valve and cylinder. These transport delays also required changes to existing theoretical models to better fit the models on the measured frequency response functions. The (theoretical) measurable torque resolution was better than 0.01 N ·m and the (validated) delivered torque resolution below 1 N· m. After the validation experiments, further iterative improvements resulted in a spring design capable of a maximum output torque of 50 N·m with an intrinsic stiffness of 150 N· m/rad and a slightly higher bandwidth. With the design locked, the maximum measurable isometric torque is 100 N ·m. In conclusion, the rHEA is suitable for upper limb rehabilitation therapy as it matches the desired performance.

Influence of Gravity Compensation on Muscle Activation Patterns During Different Temporal Phases of Arm Movements of Stroke Patients

Background. Arm support to help compensate for the effects of gravity may improve functional use of the shoulder and elbow during therapy after stroke, but gravity compensation may alter motor control. Objective. To obtain quantitative information on how gravity compensation influences muscle activation patterns during functional, 3-dimensional reaching movements. Methods. Eight patients with mild hemiparesis performed 2 sets of repeated reach and retrieval movements, with and without unloading the arm, using a device that acted at the elbow and forearm to compensate for gravity. Electromyographic (EMG) patterns of 6 upper extremity muscles were compared during elbow and shoulder joint excursions with and without gravity compensation. Results. Movement performance was similar with and without gravity compensation. Smooth rectified EMG (SRE) values were decreased from 25% to 50% during movements with gravity compensation in 5 out of 6 muscles. The variation of SRE values across movement phases did not differ across conditions. Conclusions. Gravity compensation did not affect general patterns of muscle activation in this sample of stroke patients, probably since they had adequate function to complete the task without arm support. Gravity compensation did facilitate active arm movement excursions without impairing motor control. Gravity compensation may be a valuable modality in conventional or robot-aided therapy to increase the intensity of training for mildly impaired patients.

Influence of haptic guidance in learning a novel visuomotor task

In (re)learning of movements, haptic guidance can be used to direct the needed adaptations in motor control. Haptic guidance influences the main driving factors of motor adaptation, execution error, and control effort in different ways. Human-control effort is dissipated in the interactions that occur during haptic guidance. Minimizing the control effort would reduce the interaction forces and result in adaptation. However, guidance also decreases the magnitude of the execution errors, which could inhibit motor adaptation. The aim of this study was to assess how different types of haptic guidance affect kinematic adaptation in a novel visuomotor task. Five groups of subjects adapted to a reaching task in which the visual representation of the hand was rotated 30 degrees. Each group was guided by a different force field. The force fields differed in magnitude and direction in order to discern the adaptation based on execution errors and control effort. The results demonstrated that the execution error did indeed play a key role in adaptation. The more the guiding forces restricted the occurrence of execution errors, the smaller the amount and rate of adaptation. However, the force field that enlarged the execution errors did not result in an increased rate of adaptation. The presence of a small amount of adaptation in the groups who did not experience execution errors during training suggested that adaptation could be driven on a much slower rate and on the basis of minimization of control effort as was evidenced by a gradual decrease of the interaction forces during training. Remarkably, also in the group in which the subjects were passive and completely guided, a small but significant adaptation occurred. The conclusion is that both minimization of execution errors and control effort drives kinematic adaptation in a novel visuomotor task, but the latter at a much slower rate.

Freebal: dedicated gravity compensation for the upper extremities

In most upper-extremity rehabilitation robotics, several components affect the therapy outcome. A common component is gravity compensation which alleviates upper-extremity movements. Gravity compensation by itself could improve motor control further or faster, separate from other effects of robotic therapy. To investigate the rehabilitation value of gravity compensation separately, we created the dedicated gravity compensation system, Freebal. The sling systems with ideal spring mechanisms in the Freebal are well suited for providing compensation forces. The device has steplessly scalable forces, a large range of motion with constant compensation forces, independent control of the compensation of the lower and upper arm, and low movement impedance. It also does not need external power, force sensors or active controllers. Finally, the Freebal can be easily moved, serviced and used in arm rehabilitation with either sitting or standing subjects.

Non-invasive control interfaces for intention detection in active movement-assistive devices

AbstractActive movement-assistive devices aim to increase the quality of life for patients with neuromusculoskeletal disorders. This technology requires interaction between the user and the device through a control interface that detects the user’s movement intention. Researchers have explored a wide variety of invasive and non-invasive control interfaces. To summarize the wide spectrum of strategies, this paper presents a comprehensive review focused on non-invasive control interfaces used to operate active movement-assistive devices. A novel systematic classification method is proposed to categorize the control interfaces based on: (I) the source of the physiological signal, (II) the physiological phenomena responsible for generating the signal, and (III) the sensors used to measure the physiological signal. The proposed classification method can successfully categorize all the existing control interfaces providing a comprehensive overview of the state of the art. Each sensing modality is briefly described in the body of the paper following the same structure used in the classification method. Furthermore, we discuss several design considerations, challenges, and future directions of non-invasive control interfaces for active movement-assistive devices.

Influence of gravity compensation training on synergistic movement patterns of the upper extremity after stroke, a pilot study

BackgroundThe majority of stroke patients have to cope with impaired arm function. Gravity compensation of the arm instantaneously affects abnormal synergistic movement patterns. The goal of the present study is to examine whether gravity compensated training improves unsupported arm function.MethodsSeven chronic stroke patients received 18 half-hour sessions of gravity compensated reach training, in a period of six weeks. During training a motivating computer game was played. Before and after training arm function was assessed with the Fugl-Meyer assessment and a standardized, unsupported circle drawing task. Synergistic movement patterns were identified based on concurrent changes in shoulder elevation and elbow flexion/extension angles.ResultsMedian increase of Fugl-Meyer scores was 3 points after training. The training led to significantly increased work area of the hemiparetic arm, as indicated by the normalized circle area. Roundness of the drawn circles and the occurrence of synergistic movement patterns remained similar after the training.ConclusionsA decreased strength of involuntary coupling might contribute to the increased arm function after training. More research is needed to study working mechanisms involved in post stroke rehabilitation training. The used training setup is simple and affordable and is therefore suitable to use in clinical settings.