Mechanism and Machine Theory最新文献

英文中文

Identification of non-circular profiles in hydrodynamic journal bearings 识别流体动力轴颈轴承中的非圆形轮廓

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-19 DOI: 10.1016/j.mechmachtheory.2024.105819

Hydrodynamic bearings, especially cylindrical radial plain journal bearings, are widely utilized in industry for their high load capacity and low friction energy losses. However, these bearings are prone to faults such as wear and ovalization, which can deform their circular profile and affect their vibrational response. Detecting these faults is essential to reduce their impact on production. This study introduces a methodology to identify hydrodynamic bearings with non-circular profiles. The bearing model and its numerical solution are implemented using the Finite Volume Method, with the effects of failures incorporated into a rotating system modeled by the Finite Element Method. A dataset is generated to reflect three common failure conditions in industrial applications: wear, ovalization, and a combination of ovalization with wear. The authors used this dataset to train a Multilayer Perceptron (MLP) neural network, which can identify the bearing profile shape based on specific attributes of the dynamic responses. The identification tests for the three fault conditions demonstrated high accuracy, particularly in distinguishing between ovalization and wear.

流体动力轴承，尤其是圆柱径向滑动轴承，因其高承载能力和低摩擦能量损失而被广泛应用于工业领域。然而，这些轴承很容易出现磨损和椭圆化等故障，从而使其圆形轮廓变形并影响其振动响应。检测这些故障对于减少其对生产的影响至关重要。本研究介绍了一种识别非圆形轮廓流体动力轴承的方法。轴承模型及其数值解决方案采用有限体积法实现，故障影响纳入有限元法建模的旋转系统中。生成的数据集反映了工业应用中的三种常见故障条件：磨损、椭圆化以及椭圆化与磨损的组合。作者利用该数据集训练了多层感知器（MLP）神经网络，该网络可根据动态响应的特定属性识别轴承轮廓形状。对三种故障条件的识别测试表明其准确性很高，尤其是在区分椭圆化和磨损方面。

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引用次数: 0

Design and tension distribution optimization of a 9-DOF cable-driven parallel spray-painting robot with 3 degrees of redundancy 具有 3 个冗余度的 9-DOF 拉索驱动并联喷涂机器人的设计和张力分布优化

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-19 DOI: 10.1016/j.mechmachtheory.2024.105818

This paper presents a 9-DOF cable-driven parallel spray-painting robot (CDPSR) with 3 ° of redundancy (DORs) for automated spraying on large, curved surfaces and proposes a feasible cable tension region (FCTR) calculation algorithm for multi-redundant robots. The end effector of the CDPSR consists of two moving platforms connected by a spherical hinge and driven by 12 cables, enabling 9 DOFs of motion (3 for translation and 6 for rotation). Given that the CDPSR has three DORs, a multi-dimensional FCTR vertex calculation algorithm is introduced. The FCTR is an adjacent, continuous, and closed convex hull in every dimension; therefore, the vertices of the FCTR can be determined sequentially and dimensionally. For DOR=3, the vertices on one face of the convex polyhedron are first determined and then extended to adjacent faces until the polyhedron is closed. An experimental prototype of the proposed robot was constructed and experiments on spray trajectory planning and FCTR calculation validation were conducted. The results of the simulations and experiments verified the motion performance of the CDPSR and the accuracy and efficiency of the FCTR calculation algorithm.

本文介绍了一种具有 3 °冗余度（DOR）的 9 DOF 拉索驱动并联喷涂机器人（CDPSR），用于在大型曲面上进行自动喷涂，并提出了一种适用于多冗余机器人的可行拉索张力区域（FCTR）计算算法。CDPSR 的末端效应器由两个移动平台组成，通过球形铰链连接，并由 12 根缆绳驱动，可实现 9 DOF 运动（3 个用于平移，6 个用于旋转）。鉴于 CDPSR 有三个 DOR，因此引入了多维 FCTR 顶点计算算法。FCTR 在每个维度上都是一个相邻、连续和封闭的凸壳，因此，FCTR 的顶点可以按顺序和维度确定。当 DOR=3 时，首先确定凸多面体一个面上的顶点，然后扩展到相邻面，直到多面体闭合。构建了拟议机器人的实验原型，并进行了喷雾轨迹规划和 FCTR 计算验证实验。模拟和实验结果验证了 CDPSR 的运动性能以及 FCTR 计算算法的准确性和效率。

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引用次数: 0

Design and optimization of compliant constant-torque mechanisms utilizing arbitrary pre-curved beams 利用任意预弯梁设计和优化顺应式恒扭矩机构

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-18 DOI: 10.1016/j.mechmachtheory.2024.105803

Compliant constant-torque mechanisms (CCTMs) have the potential to be used in precise manipulation and (force or torque) balance devices. In this paper, we propose two types of CCTMs utilizing varying-curvature beams. The stiffness-combination compliant constant-torque mechanisms (SC-CCTMs) are designed by combining positive-stiffness structures and negative-stiffness structures, whereas direct-zero-stiffness compliant constant-torque mechanisms (DZS-CCTMs) are designed by using zero-stiffness structures. In this paper, we develop a comprehensive methodology to analyze the mentioned CCTMs. Based on the methodology, a straight beam and a varying-curvature beam are optimized for negative stiffness and positive stiffness respectively to design SC-CCTMs. Besides, a constant-curvature beam is optimized for zero stiffness to design DZS-CCTMs. Then, the optimized SC-CCTM has the characteristic of adjustable constant-torque, and the optimized DZS-CCTM has a smaller preload range and a wider constant-torque range compared to existing results. Finally, the kinetostatic model has been verified using finite element method (FEM), with an error of less than 3% compared to FEM. The prototype of the optimized DZS-CCTM and SC-CCTM have been fabricated and tested to further verify the feasibility of the proposed design methodology.

顺应式恒转矩机构（CCTM）有望用于精确操纵和（力或转矩）平衡装置。在本文中，我们提出了两种利用变曲率梁的 CCTM。刚度组合顺应式恒转矩机构（SC-CCTMs）是通过组合正刚度结构和负刚度结构设计的，而直接零刚度顺应式恒转矩机构（DZS-CCTMs）则是通过使用零刚度结构设计的。在本文中，我们开发了一种综合方法来分析上述 CCTM。根据该方法，我们分别对负刚度和正刚度的直梁和变曲率梁进行了优化，从而设计出 SC-CCTM。此外，还对恒定曲率梁进行了零刚度优化，以设计 DZS-CCTM。与现有结果相比，优化后的 SC-CCTM 具有恒扭矩可调的特点，优化后的 DZS-CCTM 具有更小的预载范围和更宽的恒扭矩范围。最后，运动静力学模型已通过有限元法（FEM）验证，与 FEM 相比，误差小于 3%。优化后的 DZS-CCTM 和 SC-CCTM 原型已经制作完成并通过测试，进一步验证了所提设计方法的可行性。

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引用次数: 0

Simulating fatigue damage on planar mechanisms considering wear in revolute joints with clearance 模拟平面机构的疲劳损伤，考虑有间隙的旋转接头的磨损问题

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-17 DOI: 10.1016/j.mechmachtheory.2024.105805

Clearances and wear are present in almost all mechanisms. Their presence leads to degradation of the dynamic behavior of the mechanisms, involving the appearance of vibrations, noise, high forces at the joints, and an increasing fatigue damage.

To simulate this problem, a flexible multibody model is proposed to efficiently determine the stresses involved, thus avoiding the high computational costs associated with the finite element method. The model considers the mechanical interactions and material degradation processes that affect the stress state, providing a more accurate estimation of fatigue damage. In this work, a methodology is proposed for estimating fatigue damage in mechanisms with clearance joints without the need of simulating all the cycles actually performed.

The proposed methodology is applied to a planar slider-crank mechanism in which the fatigue undergone by the connecting rod is considered. Results show that clearances strongly affect the fatigue damage of the links. Furthermore, the effect of wear changes the linear behaviour of fatigue damage with respect to the number of cycles, generally producing a higher damage, and changing the critical damage zones in some cases.

间隙和磨损几乎存在于所有机构中。为了模拟这一问题，我们提出了一种灵活的多体模型，以有效确定所涉及的应力，从而避免与有限元法相关的高计算成本。该模型考虑了影响应力状态的机械相互作用和材料降解过程，能更准确地估计疲劳损伤。在这项工作中，提出了一种估算带间隙接头机构疲劳损伤的方法，而无需模拟实际执行的所有循环。结果表明，间隙对连杆的疲劳损伤有很大影响。此外，磨损的影响会改变疲劳损伤与循环次数的线性关系，通常会产生更高的损伤，并在某些情况下改变临界损伤区。

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引用次数: 0

An integrated design method for piezo-actuated compliant mechanisms considering configurations, flexure elements, and actuators 考虑构型、挠性元件和致动器的压电致动顺变机构综合设计方法

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-17 DOI: 10.1016/j.mechmachtheory.2024.105808

With the wide application of piezo-actuated compliant mechanisms (PACM) in the nano-positioning domain, it has been a crucial and challenging issue to design optimal PACMs with various design objectives and constraints. In this paper, an integrated design method for the planar PACMs is developed to realize their comprehensive performance optimization, considering the key factors, including mechanical configurations, flexure elements, and piezoelectric actuators (PEA). This method can effectively consider the complicated coupled dynamics between compliant mechanisms and actuators and further accurately predict the actual performance of the PACMs. Utilizing the Pareto optimality idea, the method can efficiently find the performance limits of various alternative configurations and offer the most appropriate design solutions for practical engineering applications. Two nano-positioning stages used for atomic force microscope (AFM) imaging are designed from alternative combinations of four configurations, five types of actuators, and twelve types of flexure hinges to illustrate the detailed design procedures. The results of the finite element analysis (FEA) and experiments finally verify the performance of the designed stages and validate the effectiveness of the proposed design method.

随着压电致动顺从机构 (PACM) 在纳米定位领域的广泛应用，如何在各种设计目标和约束条件下设计出最佳的 PACM 一直是一个关键且具有挑战性的问题。本文开发了一种平面 PACM 的集成设计方法，以实现其综合性能优化，其中考虑了机械配置、挠性元件和压电致动器 (PEA) 等关键因素。该方法可有效考虑顺从机构与致动器之间复杂的耦合动力学，并进一步准确预测 PACM 的实际性能。利用帕累托最优思想，该方法可以有效地找到各种备选配置的性能极限，并为实际工程应用提供最合适的设计方案。为了说明详细的设计步骤，我们设计了用于原子力显微镜（AFM）成像的两个纳米定位平台，由四种配置、五种致动器和十二种挠性铰链的备选组合而成。有限元分析（FEA）和实验结果最终验证了所设计平台的性能，并验证了所提出设计方法的有效性。

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引用次数: 0

Multiple lubricated joints with long and short bearings in multibody mechanical systems - Modeling, simulation, and performance analysis 多体机械系统中带有长短轴承的多重润滑接头 - 建模、模拟和性能分析

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-16 DOI: 10.1016/j.mechmachtheory.2024.105815

This study examines the effect of multiple lubricated imperfect long and short bearings on the performance of a multibody mechanical system. Unlike the typical assumption of a single perfect or imperfect lubricated joint due to modeling difficulties, this research considers the practical impacts of clearances in multiple joints. While unlubricated joints generally cause significant performance issues, lubricants reduce these effects, creating more localized peaks. The findings show that as the number of lubricated joints increases, both the magnitude and frequency of these peaks rise. In systems with multiple journal bearings, torque peaks become more noticeable due to the additional degrees of freedom introduced by the clearances. These degrees of freedom amplify acceleration, leading to higher lubricant reaction forces, which in turn require greater motor torque peaks to maintain the system's kinematics. Shorter lubricated joints exhibit more severe peaks than longer ones, mainly due to side leakage causing axial pressure variation and reduced damping capacity. The study highlights the need to replace idealized joints with imperfect ones for more accurate modeling of practical systems.

本研究探讨了多个润滑不完全的长短轴承对多体机械系统性能的影响。与因建模困难而通常假设的单一完美或不完美润滑接头不同，本研究考虑了多个接头间隙的实际影响。虽然未润滑的接头通常会导致严重的性能问题，但润滑剂会减少这些影响，从而产生更多局部峰值。研究结果表明，随着润滑接头数量的增加，这些峰值的幅度和频率都会上升。在具有多个轴颈轴承的系统中，由于间隙带来的额外自由度，扭矩峰值变得更加明显。这些自由度放大了加速度，导致润滑油反作用力增大，进而需要更大的电机扭矩峰值来维持系统的运动学特性。较短的润滑接头比较长的接头表现出更严重的峰值，这主要是由于侧漏导致轴向压力变化和阻尼能力降低。这项研究强调，需要用不完美的接头取代理想化的接头，以便对实际系统进行更精确的建模。

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引用次数: 0

A wearable robot for lower limb fracture reduction and rehabilitation: Design and experimental verification 用于下肢骨折复位和康复的可穿戴机器人：设计与实验验证

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-16 DOI: 10.1016/j.mechmachtheory.2024.105806

Most current orthopedic robots focused on fracture reduction surgery with limited involvement in postoperative rehabilitation training. However, post-surgical orthopedic rehabilitation training directly impacts the recovery of mobility, ambulation, and limb function in patients. Here, we propose a six degree-of-freedom (DoF) parallel robot that can perform fracture reduction surgery as well as postoperative rehabilitation training for lower limb. The actuation system is switchable to reduce the weight in fixed status and reuse the actuation units for lowering treatment costs. An optimal parameter design based on multi-objective optimization is presented for maintaining lightweight and high stiffness. The wearable robot has a 1.7 kg weight in electric mode and 1.3 kg in manual mode, with >80 kg payload. A hierarchical control strategy with three control modes is developed to meet the requirements of different stages of fracture treatment. Our preliminary experiments on bone models demonstrated the potential effectiveness of the proposed wearable robot for lower limb fracture reduction and rehabilitation training.

目前的矫形机器人大多侧重于骨折复位手术，对术后康复训练的参与有限。然而，手术后的骨科康复训练直接影响着患者的移动、行走和肢体功能的恢复。在此，我们提出了一种六自由度（DoF）并联机器人，它既能进行骨折复位手术，也能进行下肢术后康复训练。执行系统是可切换的，以减轻固定状态下的重量，并重复使用执行单元以降低治疗成本。基于多目标优化的最佳参数设计可保持轻质和高刚度。可穿戴机器人在电动模式下重量为 1.7 千克，在手动模式下重量为 1.3 千克，有效载荷为 80 千克。我们开发了一种具有三种控制模式的分层控制策略，以满足骨折治疗不同阶段的要求。我们在骨骼模型上进行的初步实验表明，所提出的可穿戴机器人在下肢骨折复位和康复训练方面具有潜在的有效性。

引用次数: 0

Experimental and numerical analyses of grid couplings in quasi-static and dynamic conditions 准静态和动态条件下网格耦合的实验和数值分析

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-15 DOI: 10.1016/j.mechmachtheory.2024.105807

Grid couplings typically comprise flexible, spring-like elements connecting two toothed hubs. They are used in heavy machinery to transmit power from prime movers to driven parts, even in the presence of positioning errors and deviations. The main objective of this paper is to introduce a comprehensive three-dimensional model, which can be used to predict coupling stiffness characteristics and load distributions at the spring/hub tooth contacts. The modelling principles are presented with emphasis being placed on the spring/hub contact simulation based on a combination of finite elements and Winkler elastic foundations. A series of comparisons with experimental evidence from a specific test rig are shown, which prove the validity of the model and its applicability to industrial couplings.

栅格联轴器通常由连接两个齿形轮毂的柔性弹簧元件组成。它们用于重型机械中，将动力从原动机传输到从动部件，即使存在定位误差和偏差。本文的主要目的是介绍一个全面的三维模型，该模型可用于预测弹簧/轮毂齿接触处的联轴器刚度特性和载荷分布。本文介绍了建模原理，重点是基于有限元和温克勒弹性基础组合的弹簧/轮毂接触模拟。一系列与特定测试台实验证据的比较结果证明了该模型的有效性及其对工业联轴器的适用性。

引用次数: 0

Construction method for circular arc elements in rational absolute nodal coordinate formulation 有理绝对节点坐标法中圆弧元素的构造方法

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-15 DOI: 10.1016/j.mechmachtheory.2024.105811

The Rational Absolute Nodal Coordinate Formulation (RANCF) element nodal coordinates and weights can be obtained through a rational Bézier description, which is relatively cumbersome for engineering applications. In this paper, a method for directly defining RANCF elements is proposed for circular arc geometric configurations. In this method the nodal coordinates and weights can be expressed directly by the position coordinates of geometric configurations. By utilizing position coordinates in defining RANCF elements for a geometric configuration, it becomes easier to adjust continuity conditions between elements and apply constraint equations during the preprocessing phase before simulation initiation. As a result, there is no longer a need to use knot multiplicity in NURBS representation to adjust continuity conditions. To address the arbitrary and diverse definitions of RANCF elements, a parameterization method for RANCF elements is proposed, along with an assessment criterion and an optimal parameterization method for RANCF circular arc elements. Numerical examples are presented to compare the performance of various parametric RANCF circular arc elements. The results demonstrate that convergence can be achieved by using fewer optimal parametric elements.

有理绝对节点坐标法（RANCF）元素的节点坐标和权重可通过有理贝塞尔描述获得，但这种方法在工程应用中相对繁琐。本文针对圆弧几何构型提出了一种直接定义 RANCF 元素的方法。在这种方法中，节点坐标和权重可以直接用几何构型的位置坐标来表示。利用位置坐标定义几何构型的 RANCF 元素后，在模拟开始前的预处理阶段，调整元素之间的连续性条件和应用约束方程变得更加容易。因此，不再需要使用 NURBS 表示法中的节点多重性来调整连续性条件。针对 RANCF 元素定义的任意性和多样性，提出了 RANCF 元素的参数化方法，以及 RANCF 圆弧元素的评估标准和最优参数化方法。通过数值示例比较了各种参数化 RANCF 圆弧元素的性能。结果表明，使用较少的最优参数元素就可以实现收敛。

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引用次数: 0

A new formulation for the dynamics of rigid bodies with unilateral interactions 具有单边相互作用的刚体动力学新公式

IF 4.5 1区工程技术 Q1 ENGINEERING, MECHANICAL

Mechanism and Machine Theory

Pub Date : 2024-10-15 DOI: 10.1016/j.mechmachtheory.2024.105809

A new approach is introduced for modelling multibody systems with unilateral interactions. We focus on the simulation of the forward dynamics problem. The dynamic and kinematic steps are solved with two different formulations. First, a four-point-mass model is used to represent the rigid body dynamics, avoiding the use of rotational coordinates. Therefore, the nonlinear inertial terms do not appear explicitly in the formulation. However, there are constant distance constraints between the point masses. The velocities of the point masses are obtained by solving the dynamics with this model. The angular velocity of the rigid body can be calculated from such velocities. Then, the kinematic problem is solved using the rigid body representation that fully embeds the constant distance constraints. Thus, the proposed approach can improve the accuracy of the dynamic problem with unilateral contact since the nonlinear inertial terms do not enter the formulation explicitly. The constraints appear explicitly in the dynamics representation, but they are linear there. In the position update, they are embedded exactly through the model change back to the angular velocity-based minimum coordinate formulation.

我们引入了一种新方法来模拟具有单边相互作用的多体系统。我们的重点是模拟前向动力学问题。动力学和运动学步骤采用两种不同的公式进行求解。首先，使用四点质量模型表示刚体动力学，避免使用旋转坐标。因此，非线性惯性项并没有明确出现在公式中。不过，点质量之间存在恒定距离约束。点质量的速度可通过使用该模型进行动力学求解获得。刚体的角速度可以根据这些速度计算出来。然后，使用完全包含恒定距离约束的刚体表示法来解决运动学问题。因此，由于非线性惯性项不会明确进入公式，因此建议的方法可以提高单侧接触动态问题的精度。这些约束条件明确出现在动力学表征中，但它们是线性的。在位置更新中，它们通过模型变化准确地嵌入到基于角速度的最小坐标表述中。

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