Modeling and analysis of an electro-pneumatic braided muscle actuator

The present study deals with static modeling and analysis of a novel electro-pneumatic braided muscle (EPBM) actuator. The EPBM actuator is a hybrid McKibben-type actuator, made of a dielectric polymeric bladder enclosed in a braided mesh sleeve. A continuum mechanics-based electromechanical model is developed to predict the response of the actuator for a combined pressure and voltage loading. The model also incorporates braid-to-braid frictional effects. The model agrees well with existing experimental results for the special case of zero input voltage. Parametric studies are subsequently performed for varying braid angle, input pressure, and voltage. Finally, the model is utilized to study the impact of fiber-reinforcement in the bladder on the actuator performance.

Systematic framework for performance evaluation of exoskeleton actuators

Wearable devices, such as exoskeletons, are becoming increasingly common and are being used mainly for improving motility and daily life autonomy, rehabilitation purposes, and as industrial aids. There are many variables that must be optimized to create an efficient, smoothly operating device. The selection of a suitable actuator is one of these variables, and the actuators are usually sized after studying the kinematic and dynamic characteristics of the target task, combining information from motion tracking, inverse dynamics, and force plates. While this may be a good method for approximate sizing of actuators, a more detailed approach is necessary to fully understand actuator performance, control algorithms or sensing strategies, and their impact on weight, dynamic performance, energy consumption, complexity, and cost. This work describes a learning-based evaluation method to provide this more detailed analysis of an actuation system for our XoTrunk exoskeleton. The study includes: (a) a real-world experimental setup to gather kinematics and dynamics data; (b) simulation of the actuation system focusing on motor performance and control strategy; (c) experimental validation of the simulation; and (d) testing in real scenarios. This study creates a systematic framework to analyze actuator performance and control algorithms to improve operation in the real scenario by replicating the kinematics and dynamics of the human–robot interaction. Implementation of this approach shows substantial improvement in the task-related performance when applied on a back-support exoskeleton during a walking task.

Two-chambers soft actuator bending and rotational properties for underwater application

<span>This paper presents a study on bending and rotational properties of two-chambers soft actuator for underwater application. Previous study demonstrated the actuator characteristics required to optimize the bending performance and its potential to perform underwater because of the actuator material. However, there is less study of the actuator performance underwater as well as how the actuator tips rotating during actuator bending motion. In this paper, three tests have been proposed which are comparisons of bending angle simulation and experiment in air environment, bending angle performance in air and underwater environment as well as rotational angle of actuator tip in air environment. The bending angle of soft actuator is measured based on displacement in horizontal and vertical axis and for rotational angle, gyro sensor has been used. Based on the analysis, it is proven that the fabricated soft actuator performs almost similar trend to the simulation. It is also demonstrated that the actuator performs almost double bending motion underwater environment compared to in air environment at the same pressure, and the actuator is able to rotate 90º in air environment with the supplied pressure 52 kPa.</span>

An experimental and numerical investigation on active compliant joint made by shape memory alloy actuator

In this paper, a novel active compliant joint for robotic and microdisplacement applications is investigated numerically and experimentally. The proposed actuator structure is simple and possesses a higher energy density compared to the available actuators. Experimental tests are performed employing the shape memory behavior of NiTi alloy by the electric current as a heating source. To verify the actuator performance, numerical models are simulated in a nonlinear finite element program through employing a user subroutine according to experimental tests. Finite element implementation of the proposed actuator is performed based on the constitutive equations developed in Boyd–Lagoudas phenomenological model. Comparing the test and numerical results revealed that the numerical model is successful in predicting the actuator response. Finally, based on the verified numerical model, the effects of different parameters, e.g. the compression spring stiffness on the actuator performance are studied, and an optimal design for the actuator structure is proposed.