228 publications from this institution
Hyper-redundant robots with slim bodies and redundant degrees of freedom (DoF) have shown promising applications for inspection and maintenance in confined environments. However, there is still lacking of effective methods to calibrate each section's positioning accuracy of hyper-redundant robots, limiting the ability of obstacle avoidance in confined environments. In this work, based on our 24-DoF hyper-redundant robot, a calibration method is proposed to improve the positioning accuracy of each section. To this end, a kinematic model is firstly established for the 24-DoF hyper-redundant robot. Then, a calibration model is further developed to calibrate the parameters of the kinematic model by simultaneously taking the position errors of each section into consideration. To verify the effectiveness of our method, three calibration simulations under different conditions are conducted, which demonstrate that our calibration method has better performance than existing methods on decreasing position errors of all sections. Further, with our calibration method, the average position error of the hyper-redundant robot decreases from 75.5188 mm to 14.3739 mm. Besides, the experimental results of a path-following experiment demonstrate that the motion precision of the hyper-redundant robot is improved by3 times after the calibration.
Twisting motion plays an important role in kinematics of soft robots. However, current twisting actuators usually suffer from complex mechanical design with multiple materials and undesired coupling with bending and stretching motions. In this letter, we propose a new class of soft twisting pneumatic actuators that purely rely on the freeform chamber geometry to achieve large bi-directional twisting rotations. The freeform chamber surface integrates geometric flexibility in the cross section, lateral profile, and axial chirality, which are parameterized as design variables. We develop a finite element analysis model and investigate the effect of the geometry parameters on the actuators' mechanical behavior. The actuator naturally undergoes combined twisting and axial motions, and achieves a bi-directional twisting rotation of 116.7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , blocking torque of 0.81 N · m, and energy density of 1907 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , well in line with the theoretical prediction. When it is constrained from axial motions, the actuator delivers pure twisting motion, achieving a bi-directional twisting rotation of 72.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , blocking torque of 0.56 N· m, and energy density of 925 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . This letter represents an important step toward leveraging the full potential of the freeform geometry design to create novel compact soft-bodied actuators and robots.
The application of soft robotics improves the compliance of robotic fingers, which, however, usually loses sufficient stiffness. Here, a biomimetic soft‐rigid hybrid (BSH) finger that can achieve both inherent compliance and autonomous lateral stiffness enhancement is proposed. Driven by pneumatic artificial muscles, the proposed two‐joined BSH finger can produce two flexion degrees of freedom (DOFs) and one lateral DOF motion. Imitating the human finger anatomy, the BSH finger is designed with elliptical bony ridges and eccentrically arranged ligaments. By leveraging the contact interference of the ridges and tensioning of the ligaments, the lateral stiffness of the BSH finger can be autonomously enhanced through finger flexion. During its natural stage, the lateral stiffness is relatively low to ensure mobility and compliance, while in its flexion stage, its lateral stiffness can increase to resist lateral deflection and high payload. To further investigate the advantages of the design, four BSH fingers are assembled into a robotic hand prototype with three grasping types including enveloping grasp, precise pinch, and power grasp. Experimental results demonstrate that the robotic hand prototype is capable of grasping various objects with a wide range of diameters, lengths, thicknesses, and weights, which will verify the effectiveness of the design methodology.
Pneu-net soft actuators, consisting of pneumatic networks of small chambers embedded in elastomeric structures, are particularly promising candidates in the society of soft robotics. However, there are few studies on the analytical modeling of pneu-net soft actuators, especially in the three-dimensional space. In this article, based on the minimum potential energy method and the continuum rod theory, we propose an analytical model and corresponding design approach for a class of generalized pneu-net soft actuators (gPNSAs) with both bending and twisting deformations by combining the geometric complexity and material elasticity. We experimentally verify our modeling approach and finally investigate the effects of geometric parameters, material properties, and external force on the deformations of gPNSAs, which can be used as a tool for the design of gPNSAs. We further demonstrate that our developed model can predict the deformations of gPNSAs made of multiple materials.
Dielectric elastomer actuators (DEAs) have shown great potentials for biomimetic soft robots. The inherent viscoelastic nonlinearities (such as creep and hysteresis) and the vibration dynamics of the DEAs may limit their motion accuracy in practical applications. However, few control efforts are made to handle these problems. In this paper, we propose a feedforward control approach for creep and vibration compensation of a dielectric elastomer actuator. To this end, a relative creep model of the DEA is first established, and a creep compensator based on the relative creep model is designed to eliminate the creep. Then, a vibration compensator based on a zero vibration input-shaping (ZVIS) technique is developed to suppress the vibrational dynamics of the creep-compensated DEA. The experimental results with the proposed control approach demonstrate that the creep of the DEA is reduced from 20% to less than 7%, and the overshoot of initially about 38.72% is almost completely removed.
No abstract is provided for this article.
Magnetostrictive actuators featuring high energy densities, large strokes, and fast responses are playing an increasingly important role in micro/nano-positioning applications. However, such actuators with different input frequencies and mechanical loads exhibit complex dynamics and hysteretic behaviors, posing a great challenge on applications of the actuators. Therefore, it is important to develop a dynamic model that can characterize dynamic behaviors of the actuators, including current-magnetic flux nonlinear hysteresis, frequency responses, and loading effects, simultaneously. To this end, a comprehensive model, which thoroughly considers the electric, magnetic, and mechanical domain, as well as the interactions among them, is developed in this paper. To validate the developed model, the parameters of the model are identified where the hysteresis of the magnetostrictive actuator is described, as an illustration, by the asymmetric shifted Prandtl-Ishlinskii model. The experimental results demonstrate that the comprehensive model presents an excellent agreement with dynamic behaviors of the magnetostrictive actuator.
In the practical applications of actuators, the control of their deformation or driving force is a key issue. Most of recent studies on dielectric elastomer actuators (DEAs) focus on issues of mechanics, physics, and material science, whereas less importance is given to the control of these soft actuators. In this paper, we underline the importance of a nonlinear dynamic model as the basis for a feedforward deformation control approach of a rubber-based DEA. Experimental evidence shows the effectiveness of the feedforward controller. The present study confirms that a DEA's trajectory can be finely controlled with a solid nonlinear dynamic model despite the presence of material nonlinearities and electromechanical coupling. The effective control of DEAs may pave the way for extensive emerging applications to soft robots.
