摘要
在印刷、医药和食品包装,以及电子元器件组装机械中,许多自动机械的执行机构是通过链传动实现的,如全自动模切机、书本包装机、医药食品封装机等。在这类机械中步进链传动系统作为执行机构,常用于将待加工物料或半成品输送到预期工位,以便该机械的其它装置在相应的工位完成所需的工艺加工。由于链在高速工况下处于频繁的启动和停歇状态,其动力学特征有别于等速工作链,惯性力是其主要的工作负荷。正是注意到现有理论研究中存在的不足,以模切机步进链传动系统为研究对象,对该类系统的动力学特性进行分析与研究。
基于多体动力学理论,建立步进链传动系统在计算机虚拟环境下的样机模型,并通过仿真计算与实验测试结果比较,验证该模型可较全面地反映该类系统的多种复杂影响因素,能够较精确地揭示其运动学和动力学特性。
在此基础上,基于虚拟样机技术,从运动学和动力学角度对一般链传动系统进行分析,通过仿真计算研究链轮滚子间啮入冲击、链节张力变化等问题,并考虑到各种附加动载荷作用,分析链条速度以及从动链轮角速度波动情况。
结合虚拟样机模型对步进链传动系统的动力学影响因素进行仿真分析,探讨链条在不同运动规律驱动下,链节的纵向加速度响应情况。重点研究弹簧刚度及预紧力对系统动力响应的影响,结果发现,撑紧弹簧以及链条松边是影响该类系统动力特性的重要因素之一,在该类系统的动力学分析中不容忽略;对该类系统采用非对称曲线进行步进运动规律设计,并根据具体的工况特点适当地布置牙排等集中质量,能够有效抑制减速段的惯性冲击,降低残余振动,提高定位精度。
根据步进链传动的运动特点,从动力学角度探讨适用于该类链传动系统运动规律的设计问题,分析常用运动规律的特性值及该运动规律下系统动力响应性能的优劣,得出一些有益的结论,可为该类系统的运动规律设计提供借鉴。
The chain drives as the executive mechanisms are applied to many automaticmachines such as the full-automatic mould-cutting machine, the book packagingmachine and the medicine and food inserting machine. In this kind of machinery, theintermittent chain drive system as executive mechanism is used to transport materialswaiting to be processed or semifinished products to expected work station in order toprocess by other device in system. Due to start and dwell frequently in high speedworkingcondition,thedynamiccharacteristicsofintermittentchaindrivearedifferentfrom constant speed chain drive and the inertial force is the main working load. Justconsidering the deficiency in current theoretical research, the intermittent chain drivesystem is taken as an object, its dynamic characteristics are analyzed and studied inthispaper.
Firstly, the virtual prototype model of intermittent chain drive is constructed inthe computer environment based on the multi-body dynamics theory. Compared withthe available experimental measurements, the simulation results are in reasonableagreement with the test results which validates that the model can reflect the complexinfluencing factors roundly and reveal the kinematical and dynamic characteristics ofthesystemaccurately.
In addition, from the perspective of the kinematical and dynamic characteristicsof the general chain drive, the meshing impact between the sprocket and roller, thestretching force in the chain links, are investigated by simulation as well as thevelocity of chain and the angular velocity of the driven sprocket consideringadditionaldynamicloads.
The dynamic influencing factors on intermittent chain drive are analyzed bysimulationbasedonthevirtualprototypemodel.Itisfoundthatthetensionspringandthe slack side of the chain are important that can not be neglected in the investigationon the intermittent chain drives. Additionally, it is observed that using theunsymmetrical curves, designed as the motion laws, can restrain the inertial impacteffectively in deceleration period, reduce the vibration amplitude and improve thepositioningprecision,whichisbetterthanthesymmetricalcurves.
Finally, based on the dynamic characteristics of intermittent chain drive system, the design of motion laws for the system is studied. The characteristic values and thedynamic responseofthis typechaindrivesystem underthemotionlaws areanalyzed.Some useful conclusions which can provide reference for the design of motion lawsareobtained.
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