AbstractCompliant mechanisms (CMs) have presented its inherently advantageous properties due to the fact that CMs utilize elastic deformation of the elementary flexible members to transfer motion, force, and energy. Previously, the classic Euler–Bernoulli beam theory is the most used theory in terms of modeling large beam deflections in CMs. However, it has some assumptions that may decrease the modeling accuracy, such as ignoring the shear strain and the axial strain of cross sections. In this article, to take into account the shear and axial strains, we adopt the Timoshenko beam theory along with some modifications to consider the axial elongation. To simplify the complexity of the proposed governing boundary value problem (BVP), we transform the BVP into an explicit formulation and use weighted residual methods to numerically approximate the solution. We first focus on the single-beam deflection of a straight beam and an initially curved beam (ICB) using Euler–Bernoulli beam theory, Timoshenko beam theory, and solid mechanics to analyze the contributions of the influences of shear and axial strains in beam deflections. Then, we prove the feasibility of the proposed modeling strategy via mechanism synthesis for a bi-stable mechanism and an ICB-based parallelogram mechanism. Finally, the deduction of the mathematical model and the numerical results are provided along with brief analysis on the mechanical performances of the studied CMs.

AbstractThis article presents the design, development, and motion control of a novel flexible robotic laparoscope (FRL). The main structure of the FRL includes a two degrees-of-freedom (DOFs) continuum mechanism driven by two pairs of cable-pulley-driven systems, which are actuated by four miniature linear actuators. A constant-curvature model is employed on the kinematics modeling and analysis of the continuum mechanism with designed major arc notches. The bending control strategy of the continuum mechanism is proposed and realized based on its kinematics model and a feedforward compensation method considering its nonlinearity motion calibration with a suitable initial tension of the driven cables. Besides, the continuum mechanism is made of elastic nylon material through 3D printing technology. An experimental prototype is developed to test the effectiveness and feasibility of the FRL. The experimental results indicate that the FRL has good positioning accuracy and motion performance with potential applications in robot-assisted laparoscopic surgery.

AbstractBifurcation behavior analysis is the key part of mobility in the application of origami-inspired deployable structures because it opens up more allosteric possibilities but leads to control difficulties. A novel tracking method for bifurcation paths is proposed based on the Jacobian matrix equations of the constraint system and its Taylor expansion equations. A Jacobian matrix equation is built based on the length, boundary, rigid plate conditions, and rotational symmetry conditions of the origami plate structures to determine the degrees-of-freedom and bifurcation points of structural motion. The high-order expansion form of the length constraint conditions is introduced to calculate the bifurcation directions. The two kinds of single-vertex four-crease patterns are adopted to verify the proposed method first. And then, the motion bifurcations of three wrapping folds are investigated and compared. The results demonstrate the rich kinematic properties of the wrap folding pattern, corresponding to different assignments of mountain and valley creases. The findings provide a numerical discrimination approach for the singularity of rigid origami structure motion trajectories, which may be used for a wide range of complicated origami plate structures.

AbstractThis paper presents the kinetostatic analysis of pneumatic bending soft actuator coupling with revolute joint, aimed to discover the bending performance of soft actuator wearing on physical joint of human body as exoskeleton. First, a new pneumatic bidirectional bending soft actuator is designed and its mechanical characteristic is obtained by experimental tests. Then, the kinetostatic analysis based on the principle of virtual work is conducted on the proposed soft actuator in the cases of bending alone and coupling with revolute joint. Finally, the kinetostatic equations are solved, and thus the bending performance of the soft actuator bending alone or coupling with revolute joint is obtained. This research mainly reveals the influence of coupling constraint on bending motions of soft actuator and lays a theoretical foundation for the pneumatic bending soft actuator to be applied in assist exoskeletons.

AbstractThe tracking control of tendon-driven manipulators has recently become a hot topic. However, the flexible elastic tendon introduces greater residual vibration, making it more difficult to control the trajectory tracking of the manipulator. In this paper, a dynamics model of the elastic tendon-driven manipulator (ETDM) that considers motion coupling is established. A hierarchical sliding mode control (HSMC) method is proposed to realize the trajectory tracking control of the ETDM. On the basis of the Lyapunov design method, the actuator subsliding manifold is defined as the first sliding manifold. The first sliding manifold is then used to construct the joint side subsliding manifold. Furthermore, the total sliding manifold is established based on the joint side sliding manifold and the actuator's sliding manifold. The stability of the proposed HSMC is proved using the Lyapunov stability theory. Finally, simulations and experiments are performed on a two-degree-of-freedom ETDM tracking desired trajectories to demonstrate the effectiveness of the proposed HSMC method. The proposed HSMC exhibits higher tracking accuracy compared with proportional–integral–derivative, and adaptive second-order fast nonsingular terminal sliding mode (SOFNTSM) controls in the simulations. The introduction of different disturbances reveals that HSMC has better robustness than proportional–integral–derivative control. Experimental results show that the maximum error of trajectory tracking is less than 0.025 rad.