In 2025, members of the Mechanism and Machine Theory journal’s Editorial Board and many independent reviewers contributed their time and expertise in reviewing manuscripts. This process greatly benefits our editors, contributing authors, and ultimately our readers. In fact, the high standard and reputation of the journal is strongly shaped by the expert knowledge, generous time contribution, and commitment to mechanism and machine science of the body of reviewers. Both, Elsevier, the publisher, and the editor-in-chief of the journal, would like to publicly pay tribute to all of the 988 reviewers who completed a total of 2638 reviews during the year of 2025. We are extremely grateful for their outstanding contributions and we are look forward to working with them in 2026!
Deformable ball bearings play a critical role in harmonic drives, where the transmission principle relies on elastic deformation of thin-walled components. Classical models based on rigid rings or computationally expensive FEM approaches struggle to capture the dynamic behaviour required for accurate description and/or have too expensive simulation costs. This work presents a discrete flexible multibody modelling approach in which the inner ring, rolling elements, and a discretized outer ring are represented as interacting bodies connected by spring-damper systems, nonlinear Hertzian contacts, and beam-based homogenization and anchoring forces. The outer ring deformation is reconstructed dynamically by modelling each circumferential sector as a simply supported Euler-Bernoulli beam, enabling a computationally efficient yet physically consistent description of ring curvature, sector coupling, and preload effects. Dynamic analyses show the emergence of consistent and predictable deformation-induced interactions. The proposed formulation, exploiting the discrete flexible multibody approach, bridges the gap between simplified analytical models and full FEM, providing an efficient tool suitable for integration into complete harmonic drive simulations and offering improved capabilities for dynamic performance prediction, and health-monitoring applications.
Branched compliant mechanisms, characterized by complex configurations comprising serial branches intersecting at branch points, offer unique advantages in achieving complex motion and load transfer in engineering systems. This work presents a comprehensive analytical method for the dynamic analysis of such mechanisms, employing a systematic approach to describe their frequency response. The research extends an existing method based on the Euler-Bernoulli beam and transfer matrix theories to incorporate branch points, capturing also mechanisms with closed structural loops. Branch connectivity is described through an order-independent topology definition, ensuring unambiguous assignment of branches into the system matrix and accommodating arbitrary configurations and connectivity. The presented methodology is validated against two representative examples, capturing both distributed and concentrated compliance as well as against mechanisms reported in the literature, with comparison to FE simulation results highlighting its accuracy. The proposed analytical method accurately predicts the natural frequencies within the assumptions of Euler-Bernoulli beam theory while requiring significantly less computational effort and modeling time. This efficiency, combined with the demonstrated accuracy, makes the method well-suited for rapid dynamic analysis and iterative design optimization in engineering applications.
Due to steep slopes and low bearing capacity of lunar crater terrain, conventional planetary rovers are prone to sinking, becoming trapped and failing to climb. To address engineering exploration scenarios, a high-trafficability lunar rover wheel with passive-deformation capability is proposed based on a bionic concept. The wheel has bidirectional driving characteristics. In the forward direction, the wheel functions as a soil-walk wheel with low energy consumption and high moving efficiency. In the backward direction, the wheel functions as a soil-paddle wheel with high trafficability and strong ability to escape being trapped. By adjusting driving direction combination, the rover can enter and cross craters. The soil-paddle piece, which serves as a transformable wheel unit, is mainly composed of a main piece, deputy pieces, a limit plate and springs. The wheel deformation behavior is driven by the interaction between the wheel structure and terrain, without requiring additional actuators, thereby providing passive adaptability. Based on terramechanics theory, the deformation mechanism and wheel performance are analyzed, and size parameters are selected. Rover prototype tests conducted in a simulated lunar terrain environment verify wheel functionality.
This paper presents the design and experimental validation of a compact wrist mechanism with integrated compliant transmission for high-torque-density and variable-stiffness actuation. The proposed design employs a serial pitch–yaw configuration for enhanced dexterity while maintaining compactness and low mass. The wrist integrates harmonic drives with a novel compliant gear and a compliant cap, which embed torque sensing directly into the drivetrain, eliminating the need for external torque sensors. This integrated compliant transmission reduces system complexity and maintains necessary dynamic responsiveness. A dual-encoder scheme combined with transmission error compensation enables accurate torque estimation. Based on a stiffness controller, experimental validations demonstrate accurate torque control, actively controlled backdrivability, and wide-range variable-stiffness regulation. Comparisons with existing parallel-wrist designs confirm competitive torque density and torque-to-volume ratio while maintaining low mass. These characteristics indicate its potential to improve adaptability and operational efficiency in compact robotic systems such as SCARA robots, gantry robots, and humanoid limbs.
Closed-form solutions to the inverse kinematics problem of serial manipulators are typically derived using geometry tailored to specific robot architectures. Numerical methods are more general but lack exactness, depend on convergence, and provide limited structural insight.This paper presents an analytical framework for inverse kinematics based on the factorization of Denavit–Hartenberg (DH) transformations. The forward kinematics is expressed as a product of variable joint factors and constant link matrices. A recursive elimination procedure isolates joint variables by reducing the system into lower-order subsystems, where rotation axes are defined in a global inertial frame. At each step, a two-condition coaxiality test determines whether pairs of axes can be merged. After reduction, the remaining axes are classified into four structural classes, and the corresponding closed-form solver is selected: single-axis extraction (Class C1), the Paden–Kahan two-axis subproblem (Class C2), a distance-constraint decomposition (Class C3), or a structural certificate (Class C4) indicating that no global closed form in elementary functions exists. In this case, the framework also provides a decomposition into analytically tractable subproblems. The framework handles revolute and prismatic joints without structural modification. It is applied to three manipulators with different architectures: a 7–DOF NonSRS arm with wrist offset (Franka Emika Panda), an 8–DOF mixed-joint lower-extremity rehabilitation exoskeleton, and a 9–DOF mixed revolute-prismatic redundant manipulator. In all cases, the procedure yields either a complete analytical solution or a structural certificate, together with a decomposition that achieves machine-precision accuracy. A comparison with two reference baselines is included: the Pinocchio library and the IKFast symbolic generator, evaluating convergence, determinism, and structural coverage.
Recent developments in vibration control have demonstrated the Acoustic Black Hole (ABH), whereby a gradual reduction in the wavespeed along the ABH structure enhances broadband energy dissipation due to the increase in efficacy of viscoelastic damping materials. Thus far, the ABH has only been realised for the control of flexural waves, with the reduction in wavespeed usually achieved with a graded reduction in stiffness, via a tapered thickness or graded material properties. Unlike flexural applications, the torsional wavespeed cannot be modified by a tapered cross-section alone. In this paper, a torsional ABH is achieved with a metastructure that grades the ratio between torsional stiffness and inertia along the length. The torsional ABH is shown to achieve a significant reduction in the vibration of a cylindrical shaft over a wide frequency range. The proposed torsional ABH design is also shown to exhibit a frequency-dependent localisation of wave energy, commonly known as “rainbow trapping”. A series of parametric studies is used to investigate the relationship between the geometry of the proposed ABH design and both the control performance and the rainbow trapping.
This paper presents a dynamic modeling and identification framework for a Cable-Assisted Robotic System (CARS), developed to enhance the rigidity of serial industrial robots by adding tensioned cables. A robot model is coupled with elastic and dissipative cable contributions to derive a posture-dependent Cartesian frequency response function (FRF) of the combined robot-cable system. Cable stiffness and damping are experimentally identified through displacement-controlled cyclic tension tests, capturing the nonlinear and tension-dependent behavior of cables with different geometries. The robot joint stiffness and damping parameters are then identified based on experimental FRFs using particle swarm optimization (PSO) and are obtained locally for different robot postures within the workspace. The accuracy of the proposed model and identification approach is validated through impact hammer experiments performed under different pulley configurations and cable tensions, and it showed close agreement between simulated and measured FRFs, particularly at dominant modes. Finally, the validated model is used to optimize the locations of the cable-routing pulleys using a genetic algorithm (GA), showing that proper routing of the tensioned cables can further enhance the directional dynamic stiffness of the system.
With the diversification of space missions, planar antennas are facing severe challenges for larger apertures, scalability, and surface flatness. This paper proposes a plano-Bennett six-link mechanism (PBSLM) based on Miura-ori for an ultra-large two-dimensional deployable planar antenna, enabling single degree-of-freedom (DOF) deployment and a flat reflective surface. Firstly, by integrating the Miura-ori and a planar 4R mechanism, a valley-crease equivalence method is introduced to construct the PBSLM, eliminating hinges on the reflective surface and ensuring its flatness. Secondly, the kinematic characteristics of the mechanism is analyzed using screw theory. Moreover, the PBSLM is applied to longitudinal, lateral, and two-dimensional network array extensions, forming a single DOF ultra-large two-dimensional deployable planar antenna. 3D models of 2×2 and 3×3 two-dimensional deployable planar antennas are established, and kinematic simulations are conducted using ADAMS. Based on this, a 12×10 ultra-large two-dimensional deployable planar antenna is proposed, and its unfolding process is demonstrated. Finally, a 3×3 prototype model is fabricated for experimental validation. The results confirm that the proposed method enables single-DOF deployment while maintaining surface flatness, demonstrating the effectiveness and feasibility of the mechanism.
In five-axis machining of complex surfaces, the rotary-axis configuration directly governs nonlinear error, kinematic singularity, and dynamic performance. Existing studies usually investigated the above three issues separately and cannot synthesize the rotary-axis configuration from task-specific features. This paper reveals the topological mismatch between the physical rotary axes and the ideal elementary motion axes (EMAs) as the common kinematic origin of these three issues. It proposes a forward design framework in which the elementary motion manifold (EMM) extracted from workpiece toolpath directly drives the rotary-axis configuration synthesis. The directional velocity gain (DVG) is established as the unifying optimization criterion. Spectral decomposition of the EMM structure tensor yields the optimal non-orthogonal axis directions in closed form. A propeller blade case study confirms that the synthesized non-orthogonal configuration (β=84.73∘) avoids the kinematic singularity encountered by the conventional CA configuration and, relative to it, reduces the RMS orientation nonlinear error by 96.5% and the RMS angular acceleration by 88.0%. This work shifts the design paradigm from ‘structure adapts to task’ to ‘task defines structure’.
Morphing nose cones have attracted considerable attention due to their capability to adapt aerodynamic performance under varying flight conditions. This paper presents a systematic synthesis method of multi-layer parallel mechanisms for morphing nose cones. The type synthesis of 1R1T parallel mechanisms is first performed via the screw-theory-based graphical method, yielding several novel parallel mechanisms that constitute the fundamental motion unit of morphing nose cones. Then, multiple parallel mechanisms are assembled in a stacked configuration to form multi-layer parallel mechanisms. To achieve coordinated motion in multi-layer 1R1T parallel mechanisms, a coupling strategy is proposed, and a linkage-based coupling mechanism is developed to ensure deterministic motion transmission between adjacent layers. The kinematic model of the multi-layer parallel mechanism is formulated and then validated through numerical simulations. Finally, a 3D-printed prototype is fabricated to evaluate the deformation capability and load-carrying capacity of the proposed mechanism. The results validate the feasibility of the proposed multi-layer parallel mechanism. This work presents a systematic and extensible framework for the synthesis of novel multi-layer parallel mechanisms for complex morphing systems.
Traditional flexible robotic arms face limitations in rotational capability and effective torque transmission, restricting their use in tasks requiring continuous torsional operations. This paper presents a novel cable-driven flexible robotic arm with decoupled rotational capability. Firstly, a flexible robotic arm system is designed which integrates a flexible robotic arm with a flexible housing, bending drive module, rotary drive module, and an end effector. Among them, the flexible housing can not only adaptively bend along with the flexible robotic arm, but also be freely rotated by the rotary drive module. Then, the kinematic model is established to map actuator inputs to end-effector pose. Finally, experiments are carried out to validate repeatability accuracy, decoupling of bending and rotation, and maximum output torque. Moreover, some applications of the flexible robotic arm in various tasks are demonstrated. It is found that the arm with a flexible housing can be applied in complex environments. This novel design advances flexible robotic arm technology, offering a versatile solution for the continuous rotation tasks.
Rigid-body contact in nonsmooth multibody dynamics is highly sensitive to local geometric representation near active interfaces. Conventional LCP-based formulations often rely on dense polygonal meshes or first-order geometric queries, limiting computational efficiency and local contact fidelity. This work proposes a sparse signed-distance-field LCP approach, i.e., SSLCP, for accurate and efficient rigid-body contact simulation. In this formulation, a signed distance field (SDF) with sparse narrow bands is incorporated into a curvature-aware LCP framework. The sparse SDF serves as the rigid-body geometric substrate, reducing storage requirements and the geometric cost of repeated near-contact evaluation. A curvature-enhanced LCP further introduces local curvature information, improving contact accuracy while preserving computational efficiency. Accordingly, distance, normal, and curvature queries are confined to the active contact neighborhood rather than a dense volumetric model. Several benchmark tests verify the effectiveness of the present method. Results show that the improved contact-response accuracy is particularly evident at larger time step sizes. The proposed SSLCP method is an effective alternative tool for reliable simulation of complex rigid-body contact problems in engineering applications such as cams and gears.
The contact force between the pantograph and the overhead contact line is a key indicator of railway current collection performance. Conventional measurement techniques rely on instrumented pantographs with structural modifications, increasing system complexity and limiting practical implementation. This work proposes and experimentally validates a low-intrusive methodology to estimate the pantograph contact force using acceleration, displacement, and pressure measurements while avoiding force measurements.The estimation problem is separated into two frequency ranges. The very low-frequency component is reconstructed from the pressure signal of the pantograph uplift mechanism, while the remaining frequency content is obtained by solving an inverse dynamic problem based on displacement and acceleration measurements. Four estimation models are investigated: two model-based approaches (Kalman Filter and Moving Horizon Estimation) and two data-driven models (feedforward Neural Network and Long Short-Term Memory network). Model parameters and hyperparameters are optimised to ensure a fair comparison and fully exploit the models’ potential.The methodology is experimentally validated on a laboratory test bench with a real pantograph. Results show reconstruction of the contact force within the 0–20 Hz range defined by EN 50317.
Isomorphism detection is a problem that must be considered in the topology synthesis of kinematic chains (KCs). However, despite the numerous proposed detection methods, simultaneously achieving simplicity, intuition, and efficiency in these methods remains challenging. In light of this challenge, this paper proposes a comparison information method for isomorphism detection based on coding KCs information. Firstly, to digitally describe the KCs, a modified Joint-Joint adjacency matrix is proposed. Secondly, the concepts of joint code, link code, and connection relationship matrix are introduced, and their corresponding construction steps are summarized. Thirdly, based on the above three indexes, the isomorphism criterion is proposed, and the corresponding programming algorithm is established. Finally, nine types of planar KCs with only revolute joints including six-bar, seven-bar, eight-bar, nine-bar, 10-bar, 11-bar, 12-bar, 15-bar, and 28-bar with simple joints and multiple joints, are exemplified to verify the effectiveness of the proposed method. The method provides a new and efficient idea for isomorphism detection covering a wide range of applications –including metamorphic mechanisms – regardless of whether they contain simple joints or multiple joints or both.
