Joan Lobo-Prat

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.

SCRIPT Passive Orthosis: Design and technical evaluation of the wrist and hand orthosis for rehabilitation training at home

In this paper, a new hand and wrist exoskeleton design, the SCRIPT Passive Orthosis (SPO), for the rehabilitation after stroke is presented. The SPO is a wrist, hand, and finger orthosis that assists individuals after stroke that suffer from impairments caused by spasticity and abnormal synergies. These impairments are characterized in the wrist and hand by excessive involuntary flexion torques that make the hand unable to be used for many activities in daily life. The SPO can passively offset these undesired torques, but it cannot actively generate or control movements. The user needs to use voluntary muscle activation to perform movements and thus needs to have some residual muscle control to successfully use the SPO. The SPO offsets the excessive internal flexion by applying external extension torques to the joints of the wrist and fingers. The SPO physically interacts with the users using the forearm shell, the hand plate and the digit caps from the Saebo Flex, but is otherwise a completely novel design. It applies the external extension torques via passive leaf springs and elastic tension cords. The amount of this support can be adjusted to provide more or less offset force to wrist, finger, or thumb extension, manually. The SPO is equipped with sensors that can give a rough estimate of the joint rotations and applied torques, sufficient to make the orthosis interact with our interactive gaming environment. Integrated inertial and gyroscopic sensors provide limited information on the users forearm posture. The first home-based patient experiences have already let to several issues being resolved, but have also made it clear that many improvement are still to be made.

Evaluation of EMG, force and joystick as control interfaces for active arm supports

BackgroundThe performance capabilities and limitations of control interfaces for the operation of active movement-assistive devices remain unclear. Selecting an optimal interface for an application requires a thorough understanding of the performance of multiple control interfaces.MethodsIn this study the performance of EMG-, force- and joystick-based control interfaces were assessed in healthy volunteers with a screen-based one-dimensional position-tracking task. The participants had to track a target that was moving according to a multisine signal with a bandwidth of 3 Hz. The velocity of the cursor was proportional to the interface signal. The performance of the control interfaces were evaluated in terms of tracking error, gain margin crossover frequency, information transmission rate and effort.ResultsNone of the evaluated interfaces was superior in all four performance descriptors. The EMG-based interface was superior in tracking error and gain margin crossover frequency compared to the force- and the joystick-based interfaces. The force-based interface provided higher information transmission rate and lower effort than the EMG-based interface. The joystick-based interface did not present any significant difference with the force-based interface for any of the four performance descriptors. We found that significant differences in terms of tracking error and information transmission rate were present beyond 0.9 and 1.4 Hz respectively.ConclusionsDespite the fact that the EMG-based interface is far from the natural way of interacting with the environment, while the force-based interface is closer, the EMG-based interface presented very similar and for some descriptors even a better performance than the force-based interface for frequencies below 1.4 Hz. The classical joystick presented a similar performance to the force-based interface and holds the advantage of being a well established interface for the control of many assistive devices. From these findings we concluded that all the control interfaces considered in this study can be regarded as a candidate interface for the control of an active arm support.

Design and pilot validation of A-gear: a novel wearable dynamic arm support

BackgroundPersons suffering from progressive muscular weakness, like those with Duchenne muscular dystrophy (DMD), gradually lose the ability to stand, walk and to use their arms. This hinders them from performing daily activities, social participation and being independent. Wheelchairs are used to overcome the loss of walking. However, there are currently few efficient functional substitutes to support the arms. Arm supports or robotic arms can be mounted to wheelchairs to aid in arm motion, but they are quite visible (stigmatizing), and limited in their possibilities due to their fixation to the wheelchair. The users prefer inconspicuous arm supports that are comfortable to wear and easy to control.MethodsIn this paper the design, characterization, and pilot validation of a passive arm support prototype, which is worn on the body, is presented. The A-gear runs along the body from the contact surface between seat and upper legs via torso and upper arm to the forearm. Freedom of motion is accomplished by mechanical joints, which are nearly aligned with the human joints. The system compensates for the arm weight, using elastic bands for static balance, in every position of the arm. As opposed to existing devices, the proposed kinematic structure allows trunk motion and requires fewer links and less joint space without compromising balancing precision.The functional prototype has been validated in three DMD patients, using 3D motion analysis.ResultsMeasurements have shown increased arm performance when the subjects were wearing the prototype. Upward and forward movements were easier to perform. The arm support is easy to put on and remove. Moreover, the device felt comfortable for the subjects. However, downward movements were more difficult, and the patients would prefer the device to be even more inconspicuous.ConclusionThe A-gear prototype is a step towards inconspicuousness and therefore well-received dynamic arm supports for people with muscular weakness.

Design and control of an experimental active elbow support for adult Duchenne Muscular Dystrophy patients

Currently, a considerable group of adult Duchenne Muscular Dystrophy patients lives with severe physical impairments and strong dependency on care. Active arm supports can improve their quality of life by augmenting their arms residual motor capabilities. This paper presents the design and control of an experimental active elbow support specially made to investigate different control interfaces with adult DMD patients. The system can be controlled either with EMG or force signals which are used as inputs for an admittance-based controller. A preliminary test with a 22-year-old DMD patient with no arm function left, shows that the system is capable of successfully supporting the elbow flexion-extension movements using the low-amplitude EMG and force signals that still remained measurable.

New biomechanical model for clinical evaluation of the upper extremity motion in subjects with neurological disorders: an application case

Cervical spinal cord injury and acquired brain injury commonly imply a reduction in the upper extremity function which complicates, or even constrains, the performance of basic activities of daily living. Neurological rehabilitation in specialised hospitals is a common treatment for patients with neurological disorders. This study presents a practical methodology for the objective and quantitative evaluation of the upper extremity motion during an activity of daily living of those subjects. A new biomechanical model (with 10 rigid segments and 20 degrees of freedom) was defined to carry out kinematic, dynamic and energetic analyses of the upper extremity motion during a reaching task through data acquired by an optoelectronic system. In contrast to previous upper extremity models, the present model includes the analysis of the grasp motion, which is considered as crucial by clinicians. In addition to the model, we describe a processing and analysis methodology designed to present relevant summaries of biomechanical information to rehabilitation specialists. As an application case, the method was tested on a total of four subjects: three healthy subjects and one pathological subject suffering from cervical spinal cord injury. The dedicated kinematic, dynamic and energetic analyses for this particular case are presented. The resulting set of biomechanical measurements provides valuable information for clinicians to achieve a thorough understanding of the upper extremity motion, and allows comparing the motion of healthy and pathological cases.

Design of a perfect balance system for active upper-extremity exoskeletons

Passive gravity compensation in exoskeletons significantly reduces the amount of torque and energy needed from the actuators. So far, no design has been able to achieve perfect balance without compromising the exoskeleton characteristics. Here we propose a novel design that integrates an existing statically-balanced mechanism with two springs and four degrees of freedom into a general-purpose exoskeleton design, that can support any percentage of the combined weight of exoskeleton and arm. As it allows for three rotational degrees of freedom at the shoulder and one at the elbow, it does not compromise exoskeleton characteristics and can be powered with any choice of passive or active actuation method. For instance, with this design a perfectly balanced exoskeleton design with inherently safe, passive actuators on each joint axis becomes possible. The potential reduction in required actuator torque, power and weight, simplification of control, improved dynamic performance, and increased safety margin, all while maintaining perfect balance, are the major advantages of the design, but the integrated systems does add a significant amount of complexity. Future integration in an actual exoskeleton should prove if this tradeoff is beneficial.

Adaptive gravity and joint stiffness compensation methods for force-controlled arm supports

People with muscular weakness can benefit from arm supports that compensate the weight of their arms. Due to the disuse of the arms, passive joint stiffness increases and providing only gravity compensation becomes insufficient to support the arm function. Hence, joint stiffness compensation is also required, for which the use of active arm supports is essential. Force-based control interfaces are a solution for the operation of arm supports. A critical aspect of force-based interfaces, to properly detect the movement intention of the user, is the ability to distinguish the voluntary forces from any other force, such as gravity or joint stiffness forces. Model- and calibration-based strategies for the estimation of gravity and joint stiffness forces lack adaptability and are time consuming since they are measurement dependent. We propose two simple, effective and adaptive methods for the compensation of forces resulting from gravity and joint stiffness. The compensation methods are based on the estimation of the compensation force using a low-pass filter, and switching of control parameters using a finite state machine. The compensation methods were evaluated with an adult man suffering from Duchenne muscular dystrophy with very limited arm function. The results show that when gravity and joint stiffness forces were adaptively compensated the reachable workspace of the user was increased more than 50% compared to the workspace reached when only constant gravity compensation was provided.

Switching proportional EMG control of a 3D endpoint arm support for people with duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a disease resulting in progressive muscle degeneration. Active arm supports can improve the quality of life for people with DMD by augmenting the residual motor capabilities of their arm. As an extension of our previous study, this research aims at developing a EMG-based control interface to detect the users movement intention required to control more than 1-DOF. The interface switches between two horizontal and one vertical translations. Translations are proportionally controlled by EMG. The passive interaction torques measured between the arm and the active arm support, are used to make the robots endpoint resemble a gimbal mechanism. Hence decreasing the endpoints DOF from six to three by actively reducing the impedance of the rotational DOF. A preliminary evaluation of the control method has been carried out with one healthy subject, within a series of 2-D horizontal tracing and 3-D horizontal-vertical reaching tasks. A pilot study was also conducted with a boy with DMD controlling the device in a 2-D horizontal tracing task. Performance was evaluated in terms of path efficiency, smoothness, task completion rate and time. The results indicate that the control method is able to successfully detect the intention of the user and translate it into the intended movement. Furthermore, the reduction of the endpoints DOF, results in a simple yet functional controller able to support natural movements of the arm.

Design and control of the A-Arm: An active planar arm support for adults with Duchenne muscular dystrophy

Adults with Duchenne muscular dystrophy (DMD), due to their severe muscular weakness, cannot benefit from passive arm supports that only compensate for the weight of their arms. Active arm supports can potentially enable adults with DMD to perform activities of daily living, improving their independence, and increasing their participation in social activities. In this paper we present the A-Arm, an inconspicuous and simple planar active arm support for adults with DMD that can be controlled with force- or EMG-based interfaces. The A-Arm is intended to replace the arm rest of the wheelchair and assist during table top tasks such as computer, tablet, or smartphone use, writing and drawing, and the use of the wheelchairs joystick. In the force-based control interface we have implemented active compensation of the joint-stiffness forces using a measurement-based method to obtain an estimation of the voluntary forces of the user. A pilot evaluation with an adult with DMD (24 years-old, Brooke 5) has shown that the A-Arm was able to increase the functional workspace of the arm (from 100 cm2 to 190-200 cm2). We found that while force-based control was experienced by the participant as more fatiguing than EMG-based control, the movements with EMG-based control were less accurate. These preliminary results give promising perspectives for the use of simple active arm supports to increase the independence of people with DMD.