Abstract. Rigid-flexible coupling is the development trend of lightweight parallel mechanisms. Different from traditional rigid parallel mechanisms, although the flexible components are light in weight, the large elastic deformation generated by the mechanism will affect the precision and stability of the movement. The elastic deformation of the flexible components makes the kinematic modeling challenging, which limits the application and promotion of such mechanisms. To solve the kinematic problems of such mechanisms and improve motion accuracy, this paper takes the rigid-flexible coupling parallel mechanism driven by elastic thin rods as the research object, proposes an inverse geometrico-static problem (IGP) solution, and conducts relevant motion tests to verify the correctness of the solution. Firstly, to solve the geometric relationship between the elastic thin rods and the end of the mechanism during the motion of the mechanism, the rigid-flexible coupling parallel mechanism driven by the elastic thin rods is rigidified and equivalent to a four-cable traction parallel robot, and the rationality of the rigidification equivalence is analyzed. Secondly, the kinematic/static coupling problem (geometrico-static problem) of the four-cable parallel robot is solved by the numerical iteration method, and a simulation example is analyzed, which shows that the cable length and Euler angle are cosine-like functions, the center of gravity distance is negatively correlated with the Euler angle amplitude, and the height and gravity of the end effector are independent of it. Thirdly, for the inverse kinematics problem of the rigid-flexible coupling parallel mechanism driven by elastic thin rods, a method combining the planar chain beam model and the kinematic model of the four-cable parallel robot is proposed. Finally, two experimental platforms are built to test and verify the accuracy of the above kinematic models. The test of the four-cable robot shows that the Fréchet distances of the target trajectories and the actual trajectories are relatively small (near 1), and the test of the rigid-flexible coupling parallel mechanism shows that the maximum errors between the target trajectories and the actual trajectories are all no more than 1.5 mm. The results all indicate that the target trajectories and the actual trajectories are highly consistent, which proves that the models and numerical iterative method are highly accurate. The method proposed in this paper can effectively solve the IGP of similar mechanisms and provide theoretical support for its practical application.

Abstract. Titanium alloy, as a material with high specific strength, is prone to severe tool wear during machining, leading to deterioration in the surface quality of the workpiece and presenting significant machining challenges. Therefore, to improve the machining quality of titanium alloy thin walls, the PCD (polycrystalline diamond) micro-end mill with straight peripheral and end cutting edges has been designed and fabricated for this specific task, and the key process factors relating to micromilling of Ti-6Al-4V thin walls have been studied in this paper. A method of identification of specific cutting force is proposed for a customized PCD micro-end mill using a mechanistic force model. Micromilling experiments have been carried out considering different cutting-edge rake angles and cutting fluids to identify the specific cutting force through a linear regression method. The surface roughness, tool wear, and thin-wall dimensional error have been also evaluated. Experimental results show that the specific cutting force has an approximately linear correlation with the cutting-edge rake angles. But the surface roughness, tool wear, and dimensional error have obvious nonlinear relations with the rake angles. Oil mist is the better processing fluid compared with dry cutting and jet cold air, which produces not only the smallest specific cutting force but also the smallest surface roughness value and dimensional error. When machining titanium alloy thin walls with a −45° cutting-edge rake angle tool, the oil mist lubrication process reduces the relative dimensional error from 7.1 % (observed under a dry-cutting process) to 4.5 %. This study provides theoretical and technical guidance for the machining of titanium alloy and other difficult-to-machine material components in the aerospace industry.

Abstract. In order to study the dynamic performance of a motorized spindle system more accurately and to consider the centrifugal effect, thermal effect of the angular contact ball bearing (ACBB) caused by high speed and influence of temperature rise on the dynamic viscosity of lubricating oil, a comprehensive stiffness model of a motorized spindle support bearing is established. Second, on this basis, combined with the Timoshenko beam theory and rotor dynamics, the dynamic model of the motorized spindle system is proposed using the finite element method. Finally, the influence of various factors on the dynamic characteristics of the high-speed motorized spindle system is studied and verified by experiments. The results show that the increase in the ball bearing preload and axial load could effectively improve the stability of the motorized spindle system, and the increase in the speed and thermal deformation of the ball bearing make the natural frequency and critical speed of the system decrease.

Abstract. This study introduces a novel bi-directional tuned mass damper (Bi-TMD) for tower cranes that is rear mounted and shares mass with the counterweight, overcoming the spatial and structural limitations of conventional designs. Unlike traditional top-mounted or mid-tower dampers, the proposed Bi-TMD is integrated into the counterweight, where movable masses on spring–damper units replace a portion of the concrete ballast. This design preserves the crane's lifting capacity while enabling bi-directional control of both sway and torsional vibrations. Finite-element simulations under Kaimal-spectrum fluctuating wind loads (ANSYS, 21 m s−1) show that the Bi-TMD, with a 5 % modal mass ratio, reduces peak tower-top acceleration and displacement by approximately 49 % and 24 %, respectively. Parametric studies yield three key findings: (1) the counterweight-mounted TMD provides effective vibration suppression, particularly for along-wind sway, without compromising structural integrity; (2) an optimal modal mass ratio of 3 %–4 % maximizes control efficiency and avoids local resonance, especially under cross-wind conditions; and (3) the rear-mounted Bi-TMD achieves 75 %–91 % of the performance of a mid-mounted TMD while avoiding spatial interference at the tower head. These results demonstrate that the Bi-TMD is as a practical and scalable solution for retrofitting existing cranes and for use in space-constrained environments.

Abstract. Statically balanced compliant mechanisms (SBCMs) can always maintain equilibrium without external forces and energy input, enabling accurate force and displacement transmission widely applied in engineering. However, structural designs to achieve high-efficiency torque and rotation transmission through neutral stability remain underdeveloped. In this paper, inspired by the azimuthal stability of the bendy straw in its bent state, we propose a statically balanced compliant torque coupling (SBCTC) composed of series-connected frustum shells. Numerical simulations based on the enlarged bendy-straw prototype to investigate the bending stability indicate that for SBCTCs with an identical outer radius, steeper base angles and larger radial differences are inclined to achieve bistability of the original extended and bent states. Based on geometrical characteristics from numerical results, a simplified beam model was built to accurately predict the bent state, enabling programmable SBCTC design. Subsequently, the bent SBCTC under torsion was also analysed through numerical simulations, which unveiled that all material elements experience periodic deformation along the closed circumferential path of the frustum shell. Simultaneously, the strain energy among material elements compensates for and coordinates with each other, thereby maintaining a constant total strain energy with an unchanged overall geometry during torsion. High-precision CT scanning technology was then employed on the physical prototype to quantitatively validate our numerical results and shape conservation. Finally, a specialised test platform was constructed here to test the torque transmission capabilities and limitations of the SBCTCs under different loads. As a result, our SBCTC can bend over 90° while maintaining a transmission efficiency of over 75 %, significantly surpassing existing industrial flexible couplings.

Abstract. This paper introduces a mobile mechanism inspired by three-dimensional Hilbert curves, comprising the Hilbert first-order curve mobile mechanism (HFCM) and the second-order curve mobile mechanism (HSCM). The HFCM, a bipedal system, utilizes seven actuated telescopic joints to replicate the geometric expansion–contraction behaviour of the first-order Hilbert curve. Featuring an amoeba-like adaptive morphology, this mechanism demonstrates high manoeuvrability in confined environments such as narrow pipelines and rubble zones through sequential segment actuation. Stability analysis, kinematic modelling, and experimental validation confirmed its capabilities for static walking, rotational motion, and stair negotiation on planar surfaces. The HSCM, designed based on the second-order Hilbert curve, underwent comprehensive gait planning and dynamic stability evaluation. ADAMS simulations validated its planar translation and omni-directional rotation performance under uniform mass distribution. This research establishes a novel design framework for reconfigurable mechanisms, with future work focusing on developing higher-order Hilbert curve-based systems and exploring their applications in disaster response robotics.

Abstract. Layer jamming structures (LJSs) are widely used as variable-stiffness components in collaborative robots to ensure safe human–robot interaction. However, existing analytical models often fail to adequately describe the mechanical behavior of LJSs with a large number of layers, particularly in capturing detailed stress distributions and deformations. This paper introduces a continuum-based layer jamming model (CLJM), which treats the LJS as a continuous medium under the assumption of infinitely many thin layers. The CLJM comprehensively analyzes internal stress distribution – including both shear and normal stresses – and deformation across different mechanical states (full jamming, half slipping, and full slipping). The model is validated through finite-element analysis (FEA) and experimental tests, showing strong agreement in both deformation response and stress profiles. The results demonstrate that the CLJM provides an effective and accurate theoretical tool for designing LJSs in variable-stiffness applications.

Abstract. Plants have evolved diverse strategies to survive and thrive in competitive natural environments. Their behaviours and mechanisms provide a rich source of inspiration for the design of innovative robots and have attracted growing attention from the robotics community over the past decades. Corresponding to the typical plant life cycle, this review introduces a new framework that categorizes plant-inspired robots into two main groups, i.e. robots inspired by on-plant and off-plant behaviours. Theoretically, all plant-inspired robots can be covered in this categorization framework. On-plant behaviours refer to movements exhibited by plants as monolithic living systems, and four categories of robots inspired by corresponding on-plant behaviours, including growth, gripping, trapping, and other specialized behaviours, are discussed. Off-plant behaviours involve movements of both parent plants and detached parts for seed dispersal. Robots inspired by three types of off-plant behaviours (wind dispersal, ballistic dispersal, and humidity-driven self-locomotion of seeds) are reviewed in detail. Furthermore, two conceptual research directions are proposed for the long-term development of the plant-inspired robots: (1) natural plant optimization re-inspired by robotics based on synthetic biology and (2) the development of exoplanet robots inspired by plant survival strategies. Due to their unique advantages, such as structural compliance, low cost, eco-friendliness, environmental adaptability, and responsiveness to stimuli, plant-inspired robots show application values in agriculture, biomedicine, environmental monitoring, and beyond. More advanced plant-inspired robots are expected to emerge in the upcoming future along with expanding knowledge of plant biology and growing research interest, which enables this review to be continuously refined and expanded.

Abstract. To help patients with unilateral limb movement disorders recover to normal life as soon as possible, this article, based on the principles of institutional innovation and analysis of existing designs, proposes the design of a novel linkage-type rehabilitation mechanism. This mechanism is designed to assist users in completing self-passive training by driving the affected limb with the healthy limb. The core of the mechanism is a single-degree-of-freedom linkage motion chain, which integrates a leg mechanism, an arm mechanism, and a back transmission mechanism. The main work of this paper includes the following: first, proposing the overall design concept of the rehabilitation mechanism and clarifying the synergistic working principle of each subsystem; second, designing an eight-bar leg mechanism based on human factor engineering data, whose end trajectory closely fits a normal gait trajectory; next, designing a six-bar arm mechanism that can work in coordination with the leg mechanism and a back transmission mechanism that ensures the cranks of the leg and arm mechanisms operate at a constant speed; and finally, conducting model simulation analysis and prototype experiments to verify the design. The results show that the rehabilitation mechanism can complete the predetermined coordinated movements. The contribution of this article is to provide a novel design for a rehabilitation mechanism, explore different development directions for similar products, and offer new ideas for the design of human–machine collaborative rehabilitation mechanisms.

Abstract. This paper focuses on the 4-PUU parallel mechanism with Schönflies motion, investigating its kinematic analysis and utilizing intelligent algorithms to solve its forward kinematics equations. Using screw theory as the mathematical framework, the number and nature of the degrees of freedom of the 4-PUU parallel mechanism are analyzed, proving that the mechanism can achieve 3T1R motion. The forward and inverse position kinematics equations are established with link lengths as constraints, and the velocity and acceleration equations of the mechanism are derived using the vector method. The forward kinematics equations of the mechanism are transformed into an unconstrained optimization problem, which is solved using an improved beluga whale optimization (BWO). To enhance the uniformity of the initial population distribution, a chaotic-opposition-based learning initialization strategy is introduced. Additionally, an elite strategy and a golden-sine-based position update mechanism are incorporated to improve the optimization capability of BWO. The integration of these strategies results in an enhanced optimization algorithm with superior global search ability. Given the mechanism's dimensional parameters, theoretical and motion simulations are conducted using MATLAB and Adams. The results indicate that the motion simulation curves from Adams closely match the numerical simulation curves from MATLAB, validating the theoretical derivation. Building on this, the improved beluga whale optimization (IBWO) algorithm, along with comparison algorithms (DEb1, ABC, PSO), is applied to solve the forward kinematics equations for interpolation points along the simulated trajectory. Numerical experiments demonstrate that IBWO outperforms the other comparison algorithms in solving the problem efficiently and accurately.