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Traditional propulsion systems for autonomous underwater vehicles (AUVs) have several deficiencies, such as the invasion of the aquatic environment through the generation of noise and damage to the ecosystem, higher energy consumption, and a unidirectional thruster vector. The last characteristic constrains the maneuverability of the vehicle. This paper proposes a 3-DOF spherical 3 universal–cylindrical–universal and 1 spherical joint (3UCU-1S) parallel mechanism coupled to an artificial caudal fin to produce a vectored thruster for a biomimetic AUV (BAUV). First, the design and construction of the prototype are described. Then, the kinematics and dynamics analysis of the parallel mechanism is presented. Finally, a motion study shows the types of movements that can be achieved with the mechanism to perform flapping of the caudal fin in different directions.

A numerically efficient force distribution method for actuator saturation avoidance is proposed, which is applicable to two different types of the mechanisms with two degrees of actuator redundancy, parallel mechanism (PM) and cable-driven parallel mechanism (CDPM). The proposed method searches the optimal force solutions based on their geometric interpretation. Each actuator force with two degrees of actuator redundancy is expressed as a plane equation with respect to two intermediate variables. Thus, the optimal forces are found by searching for both the intersections between force planes and the common intersection points among those force planes. The proposed method for each of PM and CDPM is described. Then for two different exemplary mechanisms, the 2 T 2 R -type 4 -DOF CDPM with six actuation cables and for the 2 T 1 R -type planar 3- DOF PM with five active joints, comparative simulations moving along the spiral trajectory are conducted, employing three different methods, the proposed method and the other two typical off-line methods, the interior point method and the linear matrix inequality method. It is confirmed from those simulation results that the computational efficiency of the proposed method in finding their desired optimal force solutions is superior to the ones of the other two typical offline optimal searching methods and also sufficiently fast enough in real time applications.

The article proposes an approach for synthesizing hybrid (parallel-serial) manipulators with five degrees of freedom (5-DOF) using open kinematic chains. The method idea consists in taking an open kinematic chain, selecting a subchain within it, and replacing the subchain with a parallel mechanism. The article considers 5-DOF open chains and 3-DOF subchains, substituted for 3-DOF parallel mechanisms with the same motion pattern as the subchain. Thus, synthesized hybrid manipulators have a 3-DOF parallel part and a 2-DOF serial part. First, we grouped 26 structures of open chains with revolute and prismatic joints into five types and 78 subtypes. Next, for each type, we selected one subtype and presented several hybrid mechanisms that can correspond to it. We considered hybrid manipulators that included 3-DOF parallel mechanisms with planar, spherical, and other commonly used motion types. The suggested synthesis method is intuitive for a designer, and it does not need any mathematical formulations like screw theory or group theory approaches.

The large number of patients with ankle injuries and the high incidence make ankle rehabilitation an urgent health problem. However, there is a certain degree of difference between the motion of most ankle rehabilitation robots and the actual axis of the human ankle. To achieve more precise ankle joint rehabilitation training, this paper proposes a novel 3- P UU/ R parallel ankle rehabilitation mechanism that integrates with the human ankle joint axis. Moreover, it provides comprehensive ankle joint motion necessary for effective rehabilitation. The mechanism has four degrees of freedom (DOFs), enabling plantarflexion/dorsiflexion, eversion/inversion, internal rotation/external rotation, and dorsal extension of the ankle joint. First, based on the DOFs of the human ankle joint and the variation pattern of the joint axes, a 3- P UU/ R parallel ankle joint rehabilitation mechanism is designed. Based on the screw theory, the inverse kinematics inverse, complete Jacobian matrix, singular characteristics, and workspace analysis of the mechanism are conducted. Subsequently, the motion performance of the mechanism is analyzed based on the motion/force transmission indices and the constraint indices. Then, the performance of the mechanism is optimized according to human physiological characteristics, with the motion/force transmission ratio and workspace range as optimization objectives. Finally, a physical prototype of the proposed robot was developed, and experimental tests were performed to evaluate the above performance of the proposed robot. This study provides a good prospect for improving the comfort and safety of ankle joint rehabilitation from the perspective of human-machine axis matching.

In order to design and implement a high-precision Stewart platform to precisely adjust the position and posture of the secondary mirror of a space camera, the following measures were taken: firstly, the inverse mathematical model and ADAMS parametric model of the Stewart platform are established, which are the basis of structural optimization design; secondly, the structural parameters of Stewart platform are obtained through structure optimization design in ADAMS after determining the objective function; thirdly, a 50nm resolution driving strut based on brushless DC motor, ball screw, grating ruler and PI closed-loop control law is designed, which strongly guaranteed the six degrees’ resolution of the Stewart platform that mainly consist of 6 such high-resolution driving struts; finally, the accuracy of Stewart platform is tested via dual frequency laser interferometer and photoelectric autocollimator, and the test results show that the displacement resolution of the Stewart platform is 0.2 μ m, and the angular resolution is 1”, which meets the requirements of the index. The Stewart platform has been successfully applied to the space camera by tuning the secondary mirror precisely in 6 degrees of freedom in the optical alignment experiment, which lays a solid theoretical and practical foundation for on orbit application in future.

With the rapid development of new energy vehicle industry, the energy supply efficiency of a heavy electric truck becomes a key factor that restricts its wide application. This paper proposes a new 3T1R parallel mechanism with movement as its motion input, which can be used in the fast power exchange of the heavy electric truck. The 2-PCR parallel mechanism is modeled with the SolidWorks software. Its degrees of freedom are examined with the helix theory and validated with the modified G-K formula. The kinematics is solved primarily with the closed-loop vector method. The Matlab is employed to graphically determine the mechanism′s working space. The results indicate the mechanism possesses 4 degrees of freedom, 3 translations across the X, Y and Z axes and 1 rotational degree of freedom around the Z axis. The movement in the Y and Z directions is independent, and the freedom of rotation around the Z axis interferes with the movement in the X direction. The output point can not only move in the X direction but also drive its rotational angle when it moves in the X direction. Based on this mechanism, the 4PC-2R parallel mechanism is proposed for further optimization. The comparison of the two mechanisms shows that the 4PC-2R parallel mechanism is smoother. Finally, the mechanism′s parameters are refined with the genetic algorithm so as to expand the working space of the 4PC-2R mechanism. The practical application of the 4PC-2R parallel mechanism demonstrates that it has a streamlined structure, an expansive operational range and fluid motion characteristics, thus being safer and more effective for a heavy electric truck′s power exchange. 针对电动重卡的换电作业过程, 设计了一种以移动副作为输入的新型3T1R并联机构。利用SolidWorks软件完成了2-PCR并联机构的三维建模。基于螺旋理论对机构的自由度进行了深入分析, 并通过G-K公式对其分析结果进行了验证, 确保了理论分析的准确性; 采用闭环矢量法对其进行运动学求解; 针对2-PCR机构 X 方向移动和绕 Z 轴转动相互干涉这一不足, 对机构进行优化得到4PC-2R并联机构。对4PC-2R并联机构进行了相应的自由度分析和运动学求解, 通过2个机构的对比, 可知4PC-2R并联机构运动更平稳。运用遗传算法优化机构参数, 进一步扩大了4PC-2R机构的工作空间, 该机构用于电动重卡的换电装置上, 可以有效提高电动重卡的换电效率和安全性。

This paper presents a climbing robot (CR) designed for the purpose of pipeline maintenance, with capability to avoid the risks inherent in manual operations. In the design process, a three degree of freedom (DOF) parallel mechanism coupled with a remote center of motion (RCM) mechanism linkage mechanism were designed to serve as the CR’s climbing mechanism, which met the specific demands for climbing movements. The modified Kutzbach–Grübler formula and the screw theory were applied to calculate the DOFs of the CR. Then, the inverse and forward position analysis for the CR was derived. Furthermore, velocity and acceleration analysis of parallel mechanism were conducted and derived the Jacobian matrix, through which the singularity of parallel mechanism was analyzed. In order to evaluate kinematic performance of parallel mechanism, the motion/force transmission index (LTI) of workspace was calculated, which directed the followed dimensional optimization process. According to the optimization result, a prototype was constructed and a series of motion experiments were carried out to validate its climbing capability.

Earth-contact mechanism (ECM), a type of mechanism to keep the system in contact with the earth and to move with the terrain changes. This paper uses the virtual equivalent parallel mechanism (VEPM) to convert the terrain data into the kinematical variables of the moving platform in the VEPM, and further analyzes the performance of the VEPM at each terrain point. Then, the comprehensive performance of the VEPM is chosen as the optimization goal, and a task-oriented dimensional optimization approach combined with the particle swarm algorithm and the neural network algorithm is proposed. This paper conducted a comparative experiment to verify the superiority of the new approach in optimizing the ECM’s comprehensive performance, whose performance analysis also can be applied into the layout design of the ECM. This paper proposed an analysis method to construct the ECM’s performance map based on the digital terrain map, which helps the control system and operator to make the optimal control decision.

As research on parallel mechanisms with limited degrees of freedom (DOF) continues to grow, this paper introduces a novel 2UPU-2SPU parallel mechanism that features 2 Rotational and 2 Translational (2R2T) motion capabilities. The SPU branches are symmetrically positioned relative to the plane of the 2UPU branches, endowing the mechanism with a full-circle DOF that encompasses two rotations and two translations. One of the rotational DOF influences the characteristics of a constrained rotational freedom. This study conducts a kinematic analysis using screw theory to elucidate the DOF and derives the inverse kinematics of the mechanism. Furthermore, by employing motion/force transmission performance indicators and performance maps, the mechanical performance characteristics are analyzed. A mathematical model for optimizing mechanical performance using the Particle Swarm Optimization (PSO) algorithm is established, facilitating the design of specific mechanical devices. The mechanism boasts a large workspace, with the operational space varying as the moving platform rotates, making it suitable for applications requiring minimal rotational and lateral movements but significant longitudinal displacement.

The authors‘ previous research has demonstrated that parallel mechanisms (PMs) with hybrid branch chains (i.e., branch chains containing planar or spatial loops) can possess symbolic forward position (SFP) solutions and motion decoupling (MD). In order to further study the conditions of a three-chain six degrees of freedom (DOF) parallel mechanism with SFP and MD, this paper proposes one 6-DOF branch chain A and two 5-DOF branch chains B and C. Based on these, a class of four 6-DOF PMs with three branch chains is devised. The symbolic position analysis of three of four such PMs is performed consequently, featuring partial MD and SFPs, which reveals that if the position or orientation of a point on the moving platform can be determined by the position of the hybrid branch chain, the PM exhibits partial MD and SFP. Finally, the accuracy of the symbolized forward and inverse solution algorithms is verified through numerical examples. This research brings a new insight into the design and position analysis of 6-DOF PMs, particularly those with SFP and partial MD.