Mechanism and Machine Theory最新文献

To address the inevitable twisting issue of modular configurations with different morphological parameters, this paper takes conical Kresling units as the research object, and a novel multi-layer conical Kresling origami mechanism (MCKOM) for linear actuation is designed. The main body consists of m serially connected flat-foldable bistable units with the same chirality but different morphological parameters. The design objective of achieving pure linear actuation under torque drive is realized by introducing external systems. Kinematic coupling and inner product models are established and multi-objective optimization algorithms are employed to optimize the structure. Based on optimized values, simulation and experimental validation of the motion behavior are conducted using ABAQUS and prototypes. The results show that the total twist angle decreased by 10.076° and the inner product increased by 60,291.98 mm³. Furthermore, the crease vertices cutting eliminates the influence of internal pressure on the guiding plate's outward deviation and increases the folding ratio from 41.49 % to 48.88 % under experimental conditions. The proposed novel pure linear actuation mechanism can be applied in actuation scenarios that require the conversion of rotational motion into linear displacement.

Taking a pair of spur gears as the research object, a contact dynamic model of the spur gear system was established based on the theories of contact mechanics and multi-body dynamics. The characteristics of the model are such that it can describe the dynamic contact behavior of a gear pairs, the meshing action of gear pairs no longer depends on the stiffness model of single and double teeth undergoing alternating meshing, and the model can be visualized in real time. In the process of modelling, firstly, the mathematical model of spur gear is established. The spur gear dynamic model is then built. Finally, the vibration responses obtained by the three methods (the propose method, the lumped parameter method and the experimental method) are compared. It is found that the proposed method is more consistent with the experimental method than the traditional lumped parameter method, which verifies the validity of the contact dynamic model of spur gear transmission. The proposed model and research results lay the foundation for research fields such as performance analysis, design optimization and fault diagnosis of gear systems.

Load distribution in ball screws is characterized by non-uniformity, leading to imbalances in the contact load of the balls along the nut. This non-uniformity negatively impacts the stiffness, accuracy and service life of the ball screw. This work proposes a solution to reduce the ball screw load distribution non-uniformity through an optimization model and two implementation methods: the variable pitch method and the ball offset method. Both methods involve applying an initial preload in certain areas of the nut to compensate for load imbalance. A case study tests both methods and evaluates the implications of implementing the optimization model.

Results confirm the model’s ability to reduce the load distribution non-uniformity, with a ratio improvements up to 61%. Additionally, this optimization enhances stiffness by up to 78% and extends service life by up to 17 times. The study also identifies the model’s limits and possible adverse effects, concluding that the specific case conditions must be considered in the optimization process.

The integrated bearing-positioning parallel manipulator is an important mean for ground testing of space optical telescope before being launched into space. To ensure positioning accuracy, the manipulator requires a pose sensor for the end-effector measurement with six degrees of freedom (DOF), real-time, high-precision, and operation in a vacuum environment. However, it is challenging for the current pose sensor to simultaneously meet all these requirements. In this paper, a novel concept of six-dimensional pose sensor based on parallel mechanism is proposed. A new mechanism design approach is presented to achieve the large measurement range, real-time measurement performance, and high accuracy measurement based on performance atlas. First, the G_F sets synthesis is developed to optimize the configuration of pose sensor. Next, two new design indicators are proposed to evaluate the real-time and high accuracy performance. Mechanism parameters are optimized by combining with mechanism singularity analysis. To guarantee high measurement accuracy, a key-term separation identification method with double neural networks is presented. Experiments on 6-UPS pose sensor demonstrate the effectiveness of the proposed mechanism design and key-term identification approach.

During the early stages of design, mechanisms are commonly modeled as perfect joints assembled with infinitely rigid bodies. This representation enables the prediction of the system’s mobilities through a mobility analysis. However, traditional mobility analysis tools can be computationally expensive or lack critical information, such as the type or direction of mobilities. It hinders the generation of topology and configuration through generative design schemes.

In this paper, we propose an alternative approach to mobility analysis based on a real vector space representation of mobilities. Our method provides relevant information for early design steps while being computationally effective through a novel formulation of series and parallel assembly topological operations. A benchmark on four selected use cases highlights an acceleration of 3 to 4 orders of magnitude compared to traditional approaches. Additionally, design rules on the joints’ positions can be automatically generated with our approach. It enables the automation of the complete design process, including topology and configuration. As such, we provide guidelines to develop a generative design scheme dedicated to the synthesis of guiding mechanisms.

This paper delves into the generation of helical face gears using a grinding worm. It investigates the computerized generation process and explores the inherent geometric constraints associated with the application of a grinding worm for helical face gears. An approximate grinding method, tailored for helical face gears featuring large helix angles, is proposed, with an evaluation of the resulting theoretical deviations. Furthermore, a novel rapid computational approach for determining the bearing contact of helical face gear pairs is introduced and validated through Finite Element Analysis (FEA). The subsequent analysis comprehensively examines the effects of the machine tool positioning errors on tooth flank deviations, bearing contact, and transmission errors. A sensitivity matrix is developed to elucidate the relationship between machine tool positioning errors and the tooth flank deviations, leading to the proposition of a correction method for theoretical generating deviations. Finally, the paper introduces a tooth flank modification method for helical face gears and the meshing performance is highly improved.

In this work, mechanisms that admit efficient kinematic computations are studied. The computationally efficient mechanisms are a special class of linkages that their constraint equations contain lower-order terms than that of the ordinary linkages. The lower-order constraint equations are of low computational complexity and thus readily solved. In the paper, case studies are carried out for mechanisms up to 3 degrees of freedom (DOF) and some interesting kinematic results are revealed. Examples of computationally efficient mechanisms are also presented.

Intense competition between top-level track cycling athletes rEq.uires research to make optimisation possible. In this context, the energetic efficiency of roller chain drives is studied to improve understanding of loss sources and to propose improvements. Losses in chain drives are mainly caused by the meshing/un-meshing process of chain links on the sprockets. However, a preliminary study shows that losses caused by the motion of rollers along their associated tooth profile have a significant influence. The aim of this paper is therefore to explore this phenomenon. An original 2D quasi static model of a two-sprocket drive is presented. The global drive kinematics (including transmission error) is determined using specific sub-models for the tight and slack strands. A local sprocket sub-model is then introduced to calculate link tension, roller/sprocket contact force and roller location. This model can be used for different tooth profile geometries. Based on the results provided by the global and local model, the presented model calculates drive efficiency, considering the losses caused by meshing and roller motion. A comparison with literature is done to ensure the model validity.