124 research outputs found

    Comparison of DC Motors and Dielectric Elastomer Actuators For Wearable Wrist Exoskeletons

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    Paralysis or loss of strength resulting from stroke requires patients to undergo extensive rehabilitation therapy. It is known that intensive therapy contributes significantly to recovery, but as the number of surviving stroke patients increases, it is difficult for clinics to provide patients with the optimal level of therapy. Robotic devices for wrist rehabilitation have been developed to lessen these problems, but at the moment they are physically large and must be used within a clinical setting. More benefit could be obtained if the devices were portable, so that they could be used by the patients on a daily basis. To reduce the size of these devices, other means of actuation need to be considered, as currently DC motors and the required transmission are too large and heavy. Dielectric elastomer actuators (DEAs) may provide a solution to the actuation problem. The focus of this thesis was to compare DC motors with DEAs for use in a wearable wrist exoskeleton to assist with stroke rehabilitation. A simple setup of the forearm, wrist, and hand was developed for testing DC motors and DEAs. For testing the DC motors, kinematic and dynamic models of the arm were created to develop an inverse dynamics controller used to control the movement of the hand. DEAs were fabricated and tested to determine their capabilities in terms of force and range of motion. Based on the data collected, an electromechanical model was optimized to characterize the behavior of the DEAs. The results show that a single DEA strip is not capable of providing the force or range of motion required for a wearable wrist exoskeleton. Future work can be done to improve DEA design so that they may actuate a wearable wrist exoskeleton or could also be considered for use in other wearable rehabilitation devices

    Dielectric Elastomer Sensors

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    Dielectric elastomers (DEs) represent a class of electroactive polymers (EAPs) that exhibit a significant electromechanical effect, which has made them very attractive over the last several decades for use as soft actuators, sensors and generators. Based on the principle of a plane‐parallel capacitor, dielectric elastomer sensors consist of a flexible and stretchable dielectric polymer sandwiched between two compliant electrodes. With the development of elastic polymers and stretchable conductors, flexible and sensitive dielectric elastomer tactile sensors, similar to human skin, have been used for measuring mechanical deformations, such as pressure, strain, shear and torsion. For high sensitivity and fast response, air gaps and microstructural dielectric layers are employed in pressure sensors or multiaxial force sensors. Multimodal dielectric elastomer sensors have been reported that can detect mechanical deformation but can also sense temperature, humidity, as well as chemical and biological stimulation in human‐activity monitoring and personal healthcare. Hence, dielectric elastomer sensors have great potential for applications in soft robotics, wearable devices, medical diagnostic and structural health monitoring, because of their large deformation, low cost, ease of fabrication and ease of integration into monitored structures

    Wearable Electromechanical Sensors and Its Applications

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    Wearable electromechanical sensor transforms mechanical stimulus into electrical signals. The main electromechanical sensors we focus on are strain and pressure sensors, which correspond to two main mechanical stimuli. According to their mechanisms, resistive and capacitive sensor attracts more attentions due to their simple structures, mechanisms, preparation method, and low cost. Various kinds of nanomaterials have been developed to fabricate them, including carbon nanomaterials, metallic, and conductive polymers. They have great potentials on health monitoring, human motion monitoring, speech recognition, and related human-machine interface applications. Here, we discuss their sensing mechanisms and fabrication methods and introduce recent progress on their performances and applications

    Pathological Tremor as a Mechanical System: Modeling and Control of Artificial Muscle-Based Tremor Suppression

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    Central nervous system disorders produce the undesired, approximately rhythmic movement of body parts known as pathological tremor. This undesired motion inhibits the patient\u27s ability to perform tasks of daily living and participate in society. Typical treatments are medications and deep brain stimulation surgery, both of which include risks, side effects, and varying efficacy. Since the pathophysiology of tremor is not well understood, empirical investigation drives tremor treatment development. This dissertation explores tremor from a mechanical systems perspective to work towards theory-driven treatment design. The primary negative outcome of pathological tremor is the undesired movement of body parts: mechanically suppressing this motion provides effective tremor treatment by restoring limb function. Unlike typical treatments, the mechanisms for mechanical tremor suppression are well understood: applying joint torques that oppose tremor-producing muscular torques will reduce tremor irrespective of central nervous system pathophysiology. However, a tremor suppression system must also consider voluntary movements. For example, mechanically constraining the arm in a rigid cast eliminates tremor motion, but also eliminates the ability to produce voluntary motions. Indeed, passive mechanical systems typically reduce tremor and voluntary motions equally due to the close proximity of their frequency content. Thus, mechanical tremor suppression requires active actuation to reduce tremor with minimal influence on voluntary motion. However, typical engineering actuators are rigid and bulky, preventing clinical implementations. This dissertation explores dielectric elastomers as tremor suppression actuators to improve clinical implementation potential of mechanical tremor suppression. Dielectric elastomers are often called artificial muscles due to their similar mechanical properties as human muscle; these similarities may enable relatively soft, low-profile implementations. The primary drawback of dielectric elastomers is their relatively low actuation levels compared to typical actuators. This research develops a tremor-active approach to dielectric elastomer-based tremor suppression. In a tremor-active approach, the actuators only actuate to oppose tremor, while the human motor system must overcome the passive actuator dynamics. This approach leverages the low mechanical impedance of dielectric elastomers to overcome their low actuation levels. Simulations with recorded tremor datasets demonstrate excellent and robust tremor suppression performance. Benchtop experiments validate the control approach on a scaled system. Since dielectric elastomers are not yet commercially available, this research quantifies the necessary dielectric elastomer parameters to enable clinical implementations and evaluates the potential of manufacturing approaches in the literature to achieve these parameters. Overall, tremor-active control using dielectric elastomers represents a promising alternative to medications and surgery. Such a system may achieve comparable tremor reduction as medications and deep brain stimulation with minimal risks and greater efficacy, but at the cost of increased patient effort to produce voluntary motions. Parallel advances in scaled dielectric elastomer manufacturing processes and high-voltage power electronics will enable consumer implementations. In addition to tremor suppression, this dissertation investigates the mechanisms of central nervous system tremor generation from a control systems perspective. This research investigates a delay-based model for parkinsonian tremor. Besides tremor, Parkinson\u27s disease generally inhibits movement, with typical symptoms including rigidity, bradykinesia, and increased reaction times. This fact raises the question as to how the same disease produces excessive movement (tremor) despite characteristically inhibiting movement. One possible answer is that excessive central nervous system inhibition produces unaccounted feedback delays that cause instability. This dissertation develops an optimal control model of human motor control with an unaccounted delay between the state estimator and controller. This delay represents the increased inhibition projected from the basal ganglia to the thalamus, delaying signals traveling from the cerebellum (estimator) to the primary motor cortex (controller). Model simulations show increased delays decrease tremor frequency and increase tremor amplitude, consistent with the evolution of tremor as the disease progresses. Simulations that incorporate tremor resetting and random variation in control saturation produce simulated tremor with similar characteristics as recorded tremor. Delay-induced tremor explains the effectiveness of deep brain stimulation in both the thalamus and basal ganglia since both regions contribute to the presence of feedback delay. Clinical evaluation of mechanical tremor suppression may provide clinical evidence for delay-induced tremor: unlike state-independent tremor, suppression of delay-induced tremor increases tremor frequency. Altogether, establishing the mechanisms for tremor generation will facilitate pathways towards improved treatments and cure development

    ウェアラブル応用として電気活性ポリマーを用いた歪みセンサーの作製、特性評価及びモデリング

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    The last decade has witnessed a shift in the research trends from hard and brittle to soft, flexible, and lightweight wearable devices. There is a fast-growing demand for wearable strain sensors amongst all existing electromechanical soft devices, due to their potential applications in areas like wearable electronics, soft robotics, human motion detection, fitness industries, rehabilitation, and human activity monitoring. Stretchability, sensitivity, life, and repeatability in the wide range are highly desirable for strain sensors. In order to achieve this goal electroactive polymer (EAP) based capacitive strain sensors have been explored as one of the potential candidates for their application in the area of wearable devices. An electronic type EAP-based strain sensor was fabricated by using silver-coated conductive fabric as an electrode and mixture of silicone rubber as a dielectric film. This sensor was showing linear behaviour but low capacitive range (pF) and less elasticity due to fabric electrode restrict its use in a wide range of applications. To overcome this problem Ionic type of EAP-based strain sensor was fabricated, and efforts were directed to prepare free-standing stretchable polymer films to make capacitance strain sensors while introducing conducting polymers to make hybrid films with controlled conductivity and carbon grease was used as an electrode. It was found that conducting composite film-based strain sensor can sustain millions of stretching and relaxing cycles, showing high linearity, negligible losses, very high stretchability, and sensitivity. Hyperelastic and viscoelastic modeling have been conducted for estimating different material losses. A crack growth approach has been proposed for predicting the life of the sensor. Complete electromechanical modeling has been proposed for analyzing sensor behavior in 3D space. Further uniaxial tensile testing data was used to estimate different material constants and for predicting sensor behavior in multiaxial loading. Open and fist hand gesture was also recognized.九州工業大学博士学位論文 学位記番号:生工博甲第444号 学位授与年月日:令和4年9月26日1 Introduction|2 Materials and Methods|3 Electronic polymer-based strain sensors|4 Ionic polymer-based strain sensors|5 Application in wearables|6 General conclusion and future prospects九州工業大学令和4年

    Feasibility and Reliability of a Commercially Available Stretch-Sensitive Sensor for Neck Movement

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    The ability to move the neck is usually a good indicator of neck health. However, the tools currently available to measure neck range of motion rely on gravity and the clinician\u27s ability to accurately line the instruments on specific landmarks of the body. This study explored whether a commercially available wearable sensor, C-Stretch® that is flexible and lightweight can capture the functional performance of cervical motion across testing sessions. Furthermore, an assessment of the C-Stretch® against Aurora NDI, an electromagnetic tracking system was explored to determine the feasibility of transforming raw capacitance data into degrees of motion. Finally, a survey explored the user’s experience with C-Stretch®. The C-Stretch® was able to monitor cervical motion across testing with good reliability for the Bag-Lift and poor reliability for the Bag-Slide and Star task (ICC2,1 0.57, 0.39, 0.37), respectively. The systems accuracy and agreement for rotational neck motion were evaluated. The C-Stretch® showed high correlation (r = 0.90-0.99, p \u3c 0.01) for areas of overlap and was accurate for both sessions with average RMSE values of 5.06° (95% C.I = 0.30° to 10.10°) for the first session and 5.34° (95% C.I = 0.10° to 10.79°) for the second session with respect to the electromagnetic tracking system. Overall, users tolerated the C-Stretch® and did not find it uncomfortable. This study highlights the feasibility of using wearable stretch sensors that are light, unobtrusive and comfortable for assessing functional performance of the cervical spine

    A Soft touch: wearable dielectric elastomer actuated multi-finger soft tactile displays

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    PhDThe haptic modality in human-computer interfaces is significantly underutilised when compared to that of vision and sound. A potential reason for this is the difficulty in turning computer-generated signals into realistic sensations of touch. Moreover, wearable solutions that can be mounted onto multiple fingertips whilst still allowing for the free dexterous movements of the user’s hand, brings an even higher level of complexity. In order to be wearable, such devices should not only be compact, lightweight and energy efficient; but also, be able to render compelling tactile sensations. Current solutions are unable to meet these criteria, typically due to the actuation mechanisms employed. Aimed at addressing these needs, this work presents research into non-vibratory multi-finger wearable tactile displays, through the use of an improved configuration of a dielectric elastomer actuator. The described displays render forces through a soft bubble-like interface worn on the fingertip. Due to the improved design, forces of up to 1N can be generated in a form factor of 20 x 12 x 23 mm, with a weight of only 6g, demonstrating a significant performance increase in force output and wearability over existing tactile rendering systems. Furthermore, it is shown how these compact wearable devices can be used in conjunction with low-cost commercial optical hand tracking sensors, to cater for simple although accurate tactile interactions within virtual environments, using affordable instrumentation. The whole system makes it possible for users to interact with virtually generated soft body objects with programmable tactile properties. Through a 15-participant study, the system has been validated for three distinct types of touch interaction, including palpation and pinching of virtual deformable objects. Through this investigation, it is believed that this approach could have a significant impact within virtual and augmented reality interaction for purposes of medical simulation, professional training and improved tactile feedback in telerobotic control systems.Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Centre EP/G03723X/

    Low cost angular displacement sensors for biomechanical applications - a review

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    In the general scientific quest for increased quality of life a natural ambition is to know more about human body kinematics. Varied knowledge can be extracted from sensors placed on human body and through associated biomechanical parameter evaluation the causal connection between different biomechanical parameters and medical conditions can be inferred. From a biomechanical point of view, one of the most important parameters within the human body is the amplitude of angular movements of joints. Although many angular sensors are used in industry, particular characteristics such as small size, flexibility and appropriate attachment methods must be taken into consideration when estimating the amplitude of movement of human joints. This paper reviews the existing low cost easy to manipulate angular sensors listed in the scientific literature, which currently are or could be used in rehabilitation engineering, physiotherapy or biomechanical evaluations in sport. The review is carried out in terms of a classification based on the sensors’ working principles and includes resistive, capacitive, magnetic and piezoresistive sensors
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