جستجوی مقالات مرتبط با کلیدواژه "ربات اسکلت خارجی" در نشریات گروه "مکانیک"

The series elastic actuators make more comfort in the use of assistive exoskeletons. In this paper, an assistive controller is designed for a series-elastic-actuator-driven knee exoskeleton to restore normative mobility of individuals with weak muscles. The main target of the proposed controller is to modify the dynamics performance of the coupled human-exoskeleton system. In other words, the proposed controller modifies the relationship between the net muscle torque exerted by the human and the resulting angular motion. There are fewer sensors in the proposed intent-independent method relative to other methods. Moreover, there are less controller coefficients to regulate where these coefficients are extracted from a type zero Takagi-Sugeno-Kang fuzzy system. The performance of the controller is evaluated by simulations and experiments. The amplitude of the EMG signals decreased in a healthy person worn the SUT-KneeExo. Moreover, the proposed algorithm has a better performance in comparison with integral admittance shaping mothed and output feedback assistive controller. In other words, the amplitude of the integral admittance is more and the phase lag is less than other methods.

The Creation of reference trajectories and the ability to track them in the presence of disturbances and uncertainties are important issues in investigating the exoskeleton performance. One of the methods of trajectory planning is the central pattern generation algorithm. This algorithm will behave in a limit cycle and the temporal disturbances have quickly removed the system and create harmonious trajectories. In this paper, for the creation of reference trajectories of each joint, a combination of seven modified Hopfield oscillators is used which provides the ability to change the frequency and domain of walking. Online modification of robot joint reference trajectories is done by using the feedback error signal between desired zero momentum point and zero momentum point of the robot at any moment. In order to cope with the disturbances and uncertainty with the uncertain domain and achieve maximum efficiency in tracking robot reference trajectories, an adaptive dynamic fast terminal sliding mode controller is used due to the elimination of chattering phenomena, and finite-time convergence. Also, by moving the Upper link the maximum stability of the robot based on zero momentum point criterion is guaranteed. To achieve maximum performance, controller parameters, oscillator coefficients, and connections between them are optimized. Finally, the performance of the proposed method is compared with a sliding mode controller. The results demonstrate the superiority of the proposed method.

In this paper, finite-time active fault tolerant control based on adaptive back-stepping nonsingular fast integral terminal sliding mode control is proposed to control a lower limb exoskeleton in the presence of actuator fault. In order to detect, isolate and accommodate the actuator fault, a third-order super twisting sliding mode observer is used. To eliminate the chattering of conventional sliding mode, supper twisting sliding mode algorithm is applied, which leads to finite-time convergence and high precision in tracking the desired trajectories. Back-stepping term guarantees global stability based on Lyapunov theory. Upper limb motion is used to provide stability to robot's motion based on zero-moment point criterion. In order to attain maximum stability based on zero-moment point, minimize error in tracking the desired trajectories, increase the tolerance of the controller against actuator fault, controller, observer and upper limb trajectory parameters are optimally tuned based on harmony search algorithm. Performance of the proposed controller is compared with the performance of sliding mode controller with/without fault information. Simulation results reveal the effectiveness of the proposed controller in the presence of actuator fault, uncertainty and disturbance in comparison with sliding mode controller.

Disturbance and bounded uncertainty are the most important factors which can be degrade efficient performance of the lower limb exoskeleton. While sliding mode control is a robust control approach against such disturbances, however, by applying the boundary layer in spite of chattering phenomenon, robust performance becomes feeble. In order to overcome this drawback, high order sliding mode algorithms like supper twisting has been proposed in which, chattering phenomenon is mitigated by eliminating the boundary layer. In this paper, an adaptive supper twisting sliding mode control is proposed for a lower limb exoskeleton robot in which the sliding variable and its derivative tend to zero continuously in presence of the disturbance and bounded uncertainty. In addition, the desired trajectory of the upper limb is determined so that in each moment the stability of the robot is guaranteed based on zero momentum point criterion. To achieve maximum stability and minimum error in tracking of the desired trajectories, the controller parameters and the upper limb desired trajectory parameters are optimized using the Harmony Search algorithm. Robot is modeled in ADAMS and then control inputs are applied to the Adams model. Finally, Performance of two controllers is compared. Simulation results reveal the performance of the proposed controller is better than the optimal sliding mode controller.

Musculoskeletal disorders caused by heavy workloads are very common in workers, which negatively affects workers' health and productivity. In this regard, the idea of designing an exoskeleton robot is proposed. This robot is similar to a dress which worn on the user's body and parallels the body, accompanying and helping the person. In this paper, the parallel distributed compensation control method is proposed to be applied to a four degrees of freedom exoskeleton waist robot. Initially, the dynamical equations governing the system are extracted. According to the nonlinear nature of the system, the parallel distributed compensator controller is designed with a Takagi-Sugeno linearization approach. The closed loop system response of this controller is investigated in the Simulink environment of the MATLAB software. The results show that the Takagi-Sugeno linearization approach accurately estimates the nonlinear system, and also the proposed controller perfectly intercepts the optimal closed loop response

Reference trajectory tracking and guarding against system disturbances and uncertainties are the important factors in the realm of lower limb exoskeleton robots control. Sliding mode PID is one of the robust controllers, which has a sliding manifold in the form of the PID controller. Chattering is the substantial predicament of the PIDSMC so that boundary layer around the sliding manifold is applied to eliminate the phenomenon. In this step, not only the chattering phenomenon is not eliminated but the robustness of the controller is also mitigated. In this study, supper twisting PID sliding mode controller (STPIDSMC) was used to eradicate the chattering phenomenon and enhancing controller robustness. The STPIDSMC robustness is protected indigenously and without defining the boundary layer, and the chattering phenomenon is reduced. Furthermore, to meet the external disturbances and uncertainties with unlimited amplitude, adaptive active force control method is combined by STPIDSMC as a modifying input control loop. In the active force control approach, the control input is online modified based on the estimation of moment inertia of the robot links. In order to accomplish maximum performance, control parameters were optimized using harmony search algorithm. In the optimal state, the performance of the proposed controller has been compared with PIDSMC and STPIDSMC that revealed the priority of the proposed controller rather than other controllers. The results indicate that the three error criteria, ITAE, ITASE, and IASE experience significant reduction about 39, 48, and 66 percent respectively compared to STPIDSM.

This paper presents a comprehensive process of designing series elastic actuators to be used in active joints of assistive exoskeleton robots. In this process, the stiffness parameter of torsional spring is selected based on two main criteria to satisfy all the requirements of human motions. The first criterion is an appropriate frequency response for the actuator, according to human motion needs. The second criterion is to provide a sufficient protection of actuator hardware against collision and impact. By determining the desired value for the stiffness parameter, spring architecture is designed to have sufficient mechanical strength and provide the desired stiffness in practice while occupying a minimum space. Along with motor and gearbox, the designed spring is assembled in a module to be used in active joints of exoskeleton robots. The module is designed in a way that the spring can be detached easily and the motor and gearbox can be used as a stiff actuator as well. The considerations in the optimization of the spring and in the design of the module has led to a very compact series elastic actuator which can be used in different human motions such as stair ascend and descend, sit to stand and walking.

Lower extremity exoskeleton a motion assistive technology, has been developed in recent years. Generation of gait pattern is a fundamental topic in design of these robots. A usual approach in most of exoskeletons is to use a pre-recorded pattern used as look up table. There are some deficiencies in this method, including data storage limitation and poor regulation according to walking parameters. Therefore, it is required to modeling human walking pattern to use in exoskeletons. There are simple models for walking of healthy person and humanoid robots. Nevertheless, using these models may cause injury to joints of the patient or damage to robot motors due to physical limitation of the user’s body. In this paper, the physical limitations are represented as mathematical constraints. Considering these constraints, appropriate models are proposed for position of the joints. Then, inverse kinematics equations are used to generate joints angles. In this work, the model parameters consist of stride length and height, walking speed and length of user thigh and shin. The performance of the model is evaluated by implementing on Exoped robot. Satisfaction and convenience of the users demonstrates the good performance of the model.

In this paper, an optimal robust hybrid active force controller based on Harmony Search Algorithm is designed for a lower limb exoskeleton robot. Dynamic equations are derived using Lagrange method by considering three actuators on the hip, knee and ankle joints to track a specific trajectory. One of the major problems of exoskeleton robots is non-synchronization of movements and transfer of power between the robot and human body which affects the robot in form of disturbance. In order to mitigate the effect of disturbances and increase precision, combination of active force control (Corrective loop of control input) with position control is used as an effective and robust method. In the active force control, to elicit robust input control against disturbances, the moment of inertia of the links is estimated at each instant by minimizing the Criteria of ITAE and the control input rate, using the Harmony Search algorithm and the control input is modified. Also, two controllers are designed for the position control loop using sliding mode and feedback linearization methods. In order to validate the performance of the designed controllers, the robot is modeled in ADAMS and control inputs are applied to the Adams model. For appropriate comparison, all control parameters are optimized using the harmony search algorithm and then performance of position controllers are compared in hybrid and conventional (without the force control loop). Results indicate the outperforming of the hybrid sliding mode controller rather than to the other designed controllers.

Assistive exoskeletons are a category of wearable robots that provide a portion of the forces, required by users in performing different motions. Hence, the users will be able to perform the motions with less effort. Hitherto, different control algorithms for assistive exoskeletons are proposed and their various effects on the users’ performance are evaluated. Recently, the authors of the present paper have proposed a new control method, called output feedback assistive controller, for compliantly actuated exoskeletons. This method is independent from user’s intent, requires a very low number of sensors and possesses a simple model-free structure. This paper evaluates the effect of the output feedback assistive controller on the agility of the users. A knee physiotherapy robot is considered as a single joint exoskeleton. Connecting a series elastic actuator to the robot and implementing the output feedback assistive controller, the agility of the user is evaluated in a target following experiment. Two markers are displayed on a monitor to represent the actual and desired knee angles for the user. The user is asked to follow the desired angles by moving his/her leg. The accuracy of the user in following the target is measured and compared in two assisted and unassisted cases. The results clearly verify the positive effect of the output feedback assistive controller on increasing the user’s agility.

In this article, trajectory generation, control and hardware development of a knee exoskeleton robot is provided. The robot aims to help the individuals with lower extremity weakness or disability during the sit-to-stand movement. In the trajectory generation phase, a new method is proposed which uses a library of sample trajectories to predict the sit-to-stand movement trajectory based on the initial sitting conditions of the user. This method utilizes the theory of "dynamic movement primitives" to estimate the sit-to-stand trajectory. The trajectory generation method is tested on a library of human motion data which has been obtained in a laboratory of motion analysis. In the next step, an exponential sliding mode controller is used to guide the robot along the predicted trajectory. The controller and the trajectory generator are implemented on the exoskeleton robot. For the hardware development, the xPC Target toolbox of MATLAB software and a data acquisition card was used. Finally, the robot was tested on a male adult. The subjects were asked to wear the robot while doing several sit-to-stand movements from various sitting positions. According to the results, the average power which is required to be applied by the user’s knee, is less when the exoskeletons assists him.

Exoskeleton robot has attracted attention of many researchers because it realizes an old aspiration to attain a machine which is worn by man and maximizes his might via its powerful actuators. Thorough coordination between robot movements and that of user constitutes the greatest complexity of exoskeleton technology. Investigations showed that impedance control (IC) is suitable for this application but the present forms of IC are mostly dedicated to industrial robots which have significant differences with exoskeleton. In this article a versatile form of IC for the mentioned application is developed. Besides، according to perpetual uncertainties in load and measured force signals، for the first time an adaptive method for IC of exoskeleton robot is implemented. Simulating operation of robot in tracking user''s walking motion while carrying a load of 50 (Kg) and with uncertainties in load and measured forces، proves efficiency of the proposed control method. Tracking error during simulation is almost zero and torques needed at interfaces are immaterial.

Exoskeleton is a machine composed of a wearable anthropomorphic structure which noticeably magnifies user's might via its actuators. In this research, dynamic modeling and control system design for a lower limb type of this robot were done. In the literature at most a 1 DOF part of the robot is modeled and controlled which doesnt give a good insight on how all of the robot parts are controlled simultaneously. First, a suitable structure was chosen similar to that of UC Berkeley's BLEEX project. Then dynamic equations were derived in sagittal plane using the Newton-Euler method. By an experiment using Xsens system, gate kinematics data were measured and the inverse dynamics was simulated both in SimMechanics and on the model in MATLAB that proved accuracy of the derived model. Impedance control was investigated and some corrective remarks were included in that algorithm. Using this method the robot was controlled. It stabilized the system and the robot followed user's movement exactly. While a load of 50 kilograms was carried, mostly moments of less than 1 (Nm) were applied at each interface among man and robot.