Mechanism and Machine Theory最新文献

Origami-inspired mechanisms are extensively utilized in aerospace, medical devices, and soft robotics due to their simplicity, reliability, and high fold-to-deploy ratio. However, actuating these structures for deployment remains challenging. This paper presents a design method for self-deployable origami utilizing the rigid-elastic coupling spherical mechanism. Initially, the rigid-elastic coupling spherical mechanism is designed by replacing one revolute joint of the rigid spherical mechanism with a V-shaped elastic nickel–titanium (Ni–Ti) alloy wire. We show that the rigid-elastic coupling spherical mechanism has equivalent kinematics to the associated rigid spherical mechanism, which is also the equivalent mechanism of the rigid-elastic coupling origami unit. By leveraging the elastic deformation of the Ni–Ti alloy wire in conjunction with the motion of the revolute joints, the rigid-elastic coupling mechanism acquires bistable characteristics, thereby enabling shape memory for self-deployment. The typical origami patterns, such as Miura-ori and Yoshimura-ori, are employed as design examples to showcase the performances of the associated self-deployable origami.

Profile modifications are a common practice to mitigate torsional dynamics and enhance mechanical efficiency in geared systems. Therefore, it is necessary to develop analytical tools that accurately predict the effect of such modifications on mesh stiffness and dynamic behavior of gear trains under both design and off-design conditions. This paper presents a novel analytical mesh stiffness model for spur gears that embodies conventional compliance phenomena with the effects of profile modifications and the enlargement of the line of action under load. The model accuracy is verified by comparing the results with FEM simulations. Subsequently, a dynamic model for spur gears incorporating time-varying backlash introduced by the modification is presented and validated using experimental data available in literature. Moreover, both the static and dynamic models are applied to conduct a sensitivity analysis of various profile modifications, aiming to capture the effects of intentional and unintentional deviations from the ideal involute profile. Notably, this type of analysis highlights the effects that modifications have on the harmonics associated with gear mesh stiffness and on the dynamic behavior of the system under varying loads. This exploration establishes the foundation for microgeometric optimizations of these types of system.

Gearboxes transfer rotational motion and handle precision functionalities in many fields, including aviation, wind turbines, and industrial services. Their health management is essential to minimize workforce risks, increase the level of safety, and avoid machine breakdowns. From this standpoint, the present experimental research work developed a convolutional neural network-based method for diagnosing different levels of tooth root cracks (25 %-50 %-75 %-100 %) for symmetric (20°/20°) and asymmetric (20°/30°) profiled gear pairs. A series of vibration experiments were performed on a one-stage spur gearbox to achieve this by using a tri-axial accelerometer under variable working loads. The main purpose of this experimental research study is to explore the influence of the tooth profile on spur gears’ vibration responses and whether utilizing an asymmetric tooth profile would positively impact a deep learning algorithm's classification accuracy to add to the enhancements it provides in terms of fatigue life, mesh stiffness, and impact strength. Experimental results revealed that the overall classification accuracy could be increased by 7.712 % by feeding the proposed deep learning model with vibration data measured using test samples with asymmetric teeth.

Load-bearing walking is a demanding activity for individuals engaged in field exploration, rescue operations, and military tasks. This study introduces a non-anthropomorphic passive lower-limb exoskeleton (NAPLE) aimed at augmenting human load-bearing capacities. NAPLE adopts a reconfigurable universal-cylindrical-revolution pair (U-C-R) mechanism in each leg to passively accommodate the walking gait, thereby circumventing the misalignment limitations of motion between humans and robots widely existing in anthropomorphic exoskeletons. The topology of the mechanism can be reconfigured to a U-R mechanism via a cylindrical pair regressed in the stance phase and recruited in the swing phase, which is intelligently and automatically regulated via a purely mechanical approach. Meanwhile, a gravity compensation spring was proposed to smooth the fluctuation of the center of mass of the load to further decrease the consumption of the wearer. Prototype testing demonstrated that NAPLE can transfer an average of 87.8 % of the load weighing 30 kg to the ground in the stance phase and an average of 42.4 % while walking.

This paper deals with the modeling, simulation, and experimental validation of a modified Gough–Stewart platform (MGSP) for vibration isolation, where the first six natural frequencies corresponding to the first six degree-of-freedom are nearly the same, enabling effective attenuation of the first six modes. The configuration is termed as dynamically isotropic and this work presents a geometry-based analytical approach to obtain the design parameters of the MGSP at its neutral position. The approach accommodates various payload configurations, including variable center of mass and mass/inertia properties. The validation of the design is demonstrated using a finite element software ANSYS${}^{\text{®}}$, and the model is further refined to incorporate flexural joints and structural damping. A prototype of the MGSP featuring flexural joints was tested, and it yielded experimental outcomes in close agreement with the finite element analysis results — the first six natural frequencies were close to the expected 29 Hz and vibration isolation of about 22 dB/octave. The close agreement among analytical, finite element, and experimental outcomes underscores the efficacy of our design approach and the suitability of an MGSP for micro-vibration isolation applications in spacecraft.

Optimization of hypoid gear contact performance is challenging due to its nonconvex nature and the handling of non-linear constraints involving complex gear contact behavior. In addition, the contact performance in the existing optimization schemes is highly reliant on the manufacturing quality, for example, the uncertain tooth form errors induced by machining tolerances and blade wear are usually ignored. To tackle these problems, a robust optimization methodology is proposed for hypoid gear contact performance. A finite element/contact mechanics model is established, which considers the stochastic tooth form errors following a Gaussian distribution model. The non-linear constraints are incorporated to avoid edge contact under loaded conditions, and tooth surface interference due to error. This methodology guarantees the feasible solution space and reduces the optimization complexity by the independent identification model. The identification model of the optimal solution is flexible in the parameter selection while keeping tooth depth. This non-deterministic problem is optimized based on the pattern search method. The Pareto front and design sensitivity analysis demonstrate the effectiveness and robustness of the proposed optimization methodology.

The surface accuracy of the deployable structure is crucial in determining the electromagnetic performance of the large satellite antenna. This paper proposes a comprehensive accuracy analysis framework for deployable structures considering clearances of spatial joints, geometric deviations, elastic deformations, external loads, and preloads, all of which can affect surface accuracy during the assembly process. Surface accuracy is calculated by combining the global equilibrium analysis of the deployable structure with the local equilibrium analysis of clearance-affected joints. First, a global elastostatic equilibrium analysis of the deployable structure is performed based on a unified mathematical formulation that describes the elasticity of beams and joints. Then, the local equilibrium analysis for the clearance-affected joints is transformed into a quadratic optimization problem through a linear-complementarity-based method. This method avoids the necessity for a combinatorial search for several traditional discontinuous contact configurations. Considering both global and local equilibrium in iterative analysis, the surface accuracy of the antenna is calculated. This integration avoids prior artificial assumptions about contact configurations of the joints. Finally, the proposed method is validated by comparing it with simulations and experimental results.

The generation of optimal reference trajectories poses a challenging problem for industrial machines due to the trade-off between execution speed and vibration amplitude. This paper presents a novel method for systematically planning smooth and robust S-curve trajectories of arbitrary order adapted to vibratory behaviour for high-speed operations. In particular, the minimum time trajectory featuring good continuity under kinematic bounds is designed utilizing an improved procedure based on the existence prediction of trajectory segments. A complete analytical solution for trajectories of orders up to five is then derived. Moreover, through an analysis of the dynamic response characteristics, a parameter tuning strategy based on modal properties is established, enabling further shaping of the acceleration profiles to remove the energy content around the resonances with lower sensitivity to modelling errors. Due to the embedded filtering effect, the optimized trajectories combine specific vibration cancellation with high-frequency attenuation while providing flexibility to balance competing objectives. Comparative experiments conducted on a robot transferring flexible beams demonstrate the effectiveness and robustness of the proposed methodology in reducing residual vibration and settling time under system uncertainties.

A rigid-flexible coupling model for the planetary gear system is developed, in which the flexibility of the ring gear, input shaft, and carrier are considered. Subsequently, rotational modal projection is proposed to simulate the meshing of the flexible ring gear at any angle of planet gear revolution, and the coordinate transformation equations are presented to establish the coupling between rigid body and rotating flexible body. These two approaches incorporate the pass effect into the coupling model. Additionally, a method employing pre-emphasized noise to simulate random excitations is introduced. The model is validated by comparing computed modal frequencies and dynamic responses with those from ANSYS software and experiment, respectively. Results indicate that the proposed method accurately simulates the modulation signal observed in the experiment. Closely matched resonances excited by random excitations are apparent in experimental and simulated acceleration spectra, highlighting the validity of the proposed method and aiding in the determination of operational system modes. In addition, analyses of parameter influences are conducted, which further reveal the dynamic characteristics of the system.

The paper describes two novel calculation methods that can predict the service life of linear guideways more accurately than the conventional method. The first method is based on a linear damage accumulation in each rolling contact, which can take into account changing load cycles for a statistically based long-term remaining service life estimation. Since this statistically based estimation still has some inaccuracies, a second method is proposed that uses a dynamic simulation model of the linear guideway to perform a model-based condition monitoring. With this method, a more accurate damage-based prediction of the remaining useful service life can be made in the short term. The dynamic model takes into account both the elasticity of the Hertzian rolling contact and the elasticities of the carriage and rail depending on the dynamic rolling element circulation. The model also includes a simplified pitting model which allows the actual pitting size to be calculated by comparing the simulated vibration behaviour with the measured vibration behaviour. The calculated pitting propagation velocity is used to estimate the remaining useful service life.