No abstract

No abstract

Exoskeletons and wearable robotic systems have advanced substantially over the last decade for gait assistance, rehabilitation and load-carrying purposes. Currently, there are commercially available devices with stiff actuators. However, these actuators cannot adapt to their unpredictable environments. Thus, compliant actuators like series elastic and variable stiffness actuators have been implemented in exoskeletons and active orthoses. This paper presents a novel design and experimental characterization of a compliant actuator with adjustable stiffness for a lower limb wearable ankle robot (VS-AnkleExo). The proposed actuator is designed to mimic the behavior of biological ankle and maximizes the compliance between user and robot during a gait cycle. The adjustable stiffness of actuator is achieved through a controllable transmission ratio mechanism. Both transparency and tracking performance experiments are performed to demonstrate reduced the user-robot interaction force and improved the tracking performance of the proposed actuator, respectively. Experimental results showed that interaction forces between the user and robot are minimized in the transparency experiments, while the actuators proposed are able to track the given torque signals at various frequencies in the tracking experiments.

Exoskeleton robots are generally used for rehabilitation and load-carrying applications. Stable and flexible walking with minimal energy consumption of the human body is achieved by the compliant operation of the human joints. Essentially, the stiffness of the human ankle joint varies continuously, while the stiffness of the knee and hip joints remains nearly constant during loading phases of the walking cycles. With inspiration from the human leg biomechanics, a new biomimetic compliant lower limb exoskeleton robot (BioComEx) was constructed and its preliminary experimental tests were carried out in this paper. A variable stiffness actuator was developed for the ankle joint of BioComEx, and series elastic actuator designs were employed in the knee and hip joints of the robot. The joint actuators of BioComEx were designed longitudinally in order to be embedded inside of the thigh and shank leg segments for the compactness. Separate force sensors were employed in each segment of the robot for the modularity of the control strategies. Since the exoskeletons can be used for both load-carrying and rehabilitation, the developed robot was tested in both human-in-charge and robot-in-charge modes, respectively. The robot needs to mimic movement of healthy user joints in the human-in-charge mode and maximize the compliance between the user and robot; thus, the interaction forces should be reduced as possible. Hence, a modular closed-loop impedance control algorithm was developed for this mode. On the other hand, in the robot-in-charge mode, the robot joints need to track predefined gait references to make the patient walk. PID position control algorithm was chosen for preliminary test of the robot in this mode. Experimental results show that BioComEx is sufficiently satisfactory for walking applications of healthy and paralyzed users.

Son zamanlarda insan-dış iskelet robot etkileşim alanında umut verici ilerlemeler kaydedilmektedir. Tipik bir fiziksel kullanıcı-robot etkileşimi olarak, sağlıklı bir kullanıcının performansını arttırmak ya da fonksiyonları azalmış olan kullanıcılara yürüme desteği ve yürüme rehabilitasyonu sağlamak amacıyla dış iskelet robotlar geliştirilmiştir. Bu cihazlar performans arttırma çalışmalarında kullanıcılara herhangi bir engel çıkarmadan ya da onların hareketlerini sınırlamadan insan anatomisi ile uyumlu bir şekilde ve aralarında minimum etkileşim kuvveti oluşturarak şekilde hareket etmelidirler. Özellikle askeri uygulamalarda dış iskelet robotun sırtına yerleştirilmiş bir yükün robotun kendi ağırlığı ile birlikte kullanıcıya hissettirilmeden taşınması gerekmektedir. Bu bağlamda bu çalışmada daha önceden Geyer, (2010) tarafından oluşturulmuş 2 boyutlu bir insan modeli geliştirilerek insan-dış iskelet robot üzerinde etkileşim kuvvetlerini azaltma çalışması yapılmıştır. Çalışma kapsamında öncelikli 3 boyutlu bir insan modeli oluşturulmuştur. Bu insan modeli iki ayak, iki alt ekstremite ve bir gövdeden oluşan toplam beş zincirden meydana gelmektedir. Gerçek insan modeline en yakın sonuçlar elde edebilmek için kütlesi yaklaşık 66,75 kg ve boyu 190 cm olan erkek bir bireyin düz bir zeminde yürüme verileri alınmış ve 1 m/s hız ile yürütülmüştür. Geyer, (2010) tarafından oluşturulmuş 2 boyutlu insan modeli 3 boyutlu olarak geliştirildikten sonra, bir dış iskelet robot modeli elde edilmiştir. İnsan modeli üzerine bu dış iskelet model giydirilerek yeni bir insan-dış iskelet robot model yapısı oluşturulmuştur. İnsan-dış iskelet robot model üzerinde ilk önce herhangi bir kontrol olmadan yürüme çalışması gerçekleştirilmiştir. Daha sonra eklemler (aya bileği, diz ve kalça) için tanımlanan bir geri besleme kuvvet/tork kontrolü insan-dış iskelet robot model üzerine uygulanmış ve elde edilen sonuçlar kontrolsüz durum ile karşılaştırılmıştır.

No abstract

According to human biomechanics study, ankle joint musculoskeletal structure constantly changes joint stiffness during walking. Being inspired by human biomechanics, an ankle exoskeleton robot with an adjustable stiffness, named VSAnkleExo was designed and by using Simulation Environment MATLAB/SimMechanics, its position tracking simulation tests were carried out in this study. VSAnkleExo is intended to be used for the purposes of walking aid and rehabilitation. An effective position control of the robot is required for these purposes. Therefore, in this study, before testing the recommended controllers on the real robot, the position control simulations were applied on MATLAB/SimMechanics model of the robot. It is not easy to obtain the mathematical model of the robot because VSAnkleExo has a complex structure. For this reason, the control methods that do not need the mathematical model of the robot are tested here. In this study, firstly, a robot model was created by using MATLAB/SimMechanics. Then, trajectory tracking experiments and response experiments with disturbance were carry out on the model in order to reveal the efficiency of proposed fuzzy logic controllers. Besides, these experiments were performed with conventional PID and the all experiment results were compared. Experimental results show that proposed fuzzy PD+PID controller can influentially decrease reference tracking errors and acquire appropriate control performance. Furthermore, the controller is robust against external forces.

 Variable stiffness ankle exoskeleton robot  Estimation of ankle joint stiffness value over EMG signals  Real-time implementation of EMG based ankle stiffness estimationFigure A. Impedance control of VS-AnkleExo and position control diagram of the stiffness adjustment mechanism to follow the estimated ankle stiffness valuePurpose: The purpose of this study is to estimate the ankle joint stiffness with using the ankle musculoskeletal model parameters obtained via EMG signals and to show the real-time implementation of these predicted stiffness values on an ankle exoskeleton robot (VS-AnkleExo). Theory and Methods:In this study, a musculoskeletal model approach was used to describe the behavior of the ankle joint. The model consists of a joint driven by two muscles that provide plantar-flexion and dorsi-flexion movements of the ankle. In order to obtain the muscle forces that provide the necessary movements of the ankle, it was used Mykin muscle model. The parameters in the Mykin model were found by the help of measured torque and EMG data obtained with different feature extraction methods such as Root Mean Square, Mean Absolute Value, Average Amplitude Change, Difference in Absolute Standard Deviation Value, v-Order, Log Detector, Zero Crossing and Slope Sign Change. The Mykin model parameters were changed according to the feature extraction methods. Therefore, a verification experiment was carried out to decide which signal processing method is the best, and it was decided that Slope Sign Change method is the most appropriate one. Then, the stiffness estimation of the ankle joint was performed by using the biomechanical parameters found with this method. Finally, the estimated stiffness value was sent to actuation unit of AnkleExo in real-time, and the process of applying the force feedback impedance control algorithm was carried out. Results:The test results obtained with the Slope Sign Change method show that the estimated ankle joint stiffness value varies continuously between 200 Nm/rad-700 Nm/rad. Furthermore, it has been observed that the interaction torque between the user and the exoskeleton robot can be kept about 25% lower levels while VS-AnkleExo follows the ankle position by constantly changing the stiffness value in real-time. Conclusion:The estimated ankle stiffness values revealed in this study match with the ankle stiffness values found in the literature. Besides, it is seen that lower interaction torques occurred between the user and the robot during imitation of the stiffness values of the ankle in a real-time implementation of an impedance control.