基于高效的双输出函数脉冲发生机构的运动——动力学综合研究
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摘要
当今机构及机械系统设计的发展趋势是:高效节能、满足可持续发展的环保要求;柔性及可控与易调;对各种内部和外部不确定因素的自适应性以及智能化的主动控制。为此,高品质低成本的自调与可控机械、智能机械、仿生机械、微型机械或大型机械等即成为当前机械创新设计的主要方向。在机械学领域,连杆机构可视为其它基本机构的理论结构原型,其优势在于:a)低副结构的运动副元素易于精确制造,且承载能力较强;b)运动形式及其规律多样化。连杆机构从理论上讲不仅可以实现刚体运动的所有形式,而且可以满足任意要求的运动规律;c)在平面闭链机构中,对于同一原动件,可以产生多种不同形式、不同规律的运动输出。即可实现运动分解与合成的多种方案,以满足多用途的功能要求;d)运动规律易于调整和可控。即通过调整几何结构参数、或控制运动参数,使机构具有高的柔性与适应性;e)自由度的设置灵活。可为自调机械、智能机械等提供理想的原型。连杆机构的这些特点,有的已被大家所熟悉,并得到了广泛应用。而有的如多输出、易调与可控、自适应及多自由度设置等还未被充分认识。另一方面,连杆机构还存在许多不足:a)构件大多作变速运动,通常存在运动突变现象,且变化较为剧烈,使系统产生附加动载荷,引起振动、冲击、噪声等,以至机械效率降低;b)平面闭链机构中存在较多的过约束和约束的不确定性。对高效、高稳定可靠工作可能造成不良的影响和“障碍”;c)机构尺度综合方程的求解一直是一个难点;d)惯性力与惯性力偶矩不易平衡。其它问题还包括运动副的累积误差、摩擦分析,等等。但核心是动力学性能的优化问题。所以,寻求新的、性能良好、以及能够充分发挥上述优势特征的新型连杆机构,并在新的应用中不断完善与创新,使其能够高效率、高稳定的可靠工作,以满足现代科学技术发展的迫切要求,乃是当务之急。并有着重要的理论意义和工程应用价值。
    脉动无级变速器是一种有前途和潜力的机械式无级变速器,它的关键部分——脉冲发生机构即为连杆机构。其基本要求是:a)效率高且功率适用范围广;b)输出转速无级适时可调;c)高的稳定性(脉动度低、振动小等);d)既能满足多脉冲输出,又结构简单;e)可实现高速传动(曲柄转速一般为1500rpm)。为满足这些要求,不仅要充分应用和发挥连杆机构的优点,还要克服其不足,这正是连杆机构值得深入研究的内容。
    因此,本文以连杆机构为对象,以脉动无级变速器为结合点,以高效率、高稳定性为主要目标,从理论和方法上对其进行了深入系统的研究。论文的主要工作与
    
    成果体现在以下几个方面:
     (1)构建了脉动无级变速器新型传动机构——全铰链式的双输出脉冲发生机构。既充分应用了连杆机构的固有特点,又简化了系统结构。从根本上改变了现有脉冲发生机构的低效率、动力作用不连续及冲击较大的缺陷。依据脉动无级变速器的工作特性要求,应用机构结构综合理论讨论了以六杆运动链作为传动机构的可能方案;在此基础上,详细研究了双输出脉冲发生机构的结构型式特点及其类型的选择;进一步分析了双输出脉冲发生机构的几个基本运动学及动力学特性。
     (2)基于改善动力学性能、提高输出运动的平稳性,实现了六杆双输出函数脉冲发生机构按传动比要求的等价四杆机构的综合原理与方法。有效地解决了使双输出摇杆均具有相同脉动度及相似运动规律的机构尺度综合这一难题;并完成了该六杆机构基本结构与运动特性的分析研究。
     (3)建立了具有双运动输出的Ⅲ级函数发生机构的高阶运动参数综合模型,并结合应用同伦—连续优化方法,实现了该机构的运动-动力学优化综合。达到了通过按高阶运动参数综合,控制与改善机构动力学性能的目的。
     (4)开发并研制了不同于传统自由行程机构工作原理的具有自调自适应性的新型差动双制动块式自由行程机构。在分析了该机构的结构与力学特征的基础上,详细研究了其工作机理;并对其结构参数的确定原则进行了深入探讨;最后进行了该机构的原理及性能实验验证与分析。
    (5)完成了基于高效及高稳定性的双输出脉冲发生机构的自调结构创新设计。在提出了“零过约束基本杆组”概念的基础上,首次实现了无过约束机构设计运动副所有配置方式的确定方法,并建立了运动副最佳配置方案的选用原则。该方法可以推广应用于非零过约束设计。最后,通过消除或减少过约束的影响完成了系统的自调结构创新设计。
Linkage mechanism, seen as the theoretical structure model of all other basic mechanisms has some advantages in mechanical field: a). Easy manufacturing and high loading ability of pair element in lower pair structure; b). Diversities in movement pattern and regularity; c) various movement outputs of the same mechanical part in plane closed chain mechanism in terms of patterns and regularities; d). Easy adjustment and control in movement regularity; e). Flexible set-up of free degree. But some of these properties such as multiple output, easy adjustment and control and various free-degree sets still remain incompletely understood while other properties have been well known and extensively applied. In addition, drawbacks such as uncertain constraint and overconstraint of plane closed chain mechanisms, unknown solutions to synthesis equations of mechanism criterions and unstable movement of mechanism parts have been recorded.
    Impulse stepless speed regulator is a promising and potential mechanical stepless speed regulator. Its key part, impulse generator mechanism is the very linkage mechanism. To achieve high efficiency, adjustable rotating speed, high stability, various impulse output and simple structure as well as high-speed transmission, one is required to employ the advantages of linkage mechanism and overcome its weaknesses. The objective of this Ph.D. thesis was to study the linkage mechanism from the theoretical and methodological point of view in order to achieve high efficiency and stability.
    (1)A novel transmission mechanism called full turning-pair type of double output impulse generator mechanism was established, possessing the intrinsic properties of linkage mechanism and simplified systematic structure. Some drawbacks commonly seen in current impulse generator mechanisms, such as low efficiency, uncontinuity of driving force and higher impact were permanently overcome. In light of the requirements on the functional properties of impulse stepless speed regulator, a possibility that the six-link movement pair is used as a transmission mechanism was discussed by applying the synthesis principle of mechanism structure. In addition, focusing on the double output impulse generator mechanisms, their structural properties and selection programs for different models were studied in detail and the characteristics of some basic
    
    dynamics and motor mechanism were further analyzed.
    (2)The synthesis principle and methodology of identical-grade four link mechanism were proposed so that the functional generator mechanism with six-link and double output could meet the demands for the ratio of transmission to motion. The problems regarding the initial criterion synthesis were solved and analysis for basic structure and motor natures of the six-link mechanism was accomplished.
    (3)To control and improve the properties of mechanism dynamics, a synthetical parameter model of high-grade motion was created for three-grade functional generator mechanism with double output. Meanwhile, the optimization about motion and dynamics of the mechanism was carried out by employing homotopy-continuation method.
    (4)A novel differential and double brake-block overrunning speed clutch was developed. Its working mechanism was detailed based on the characterization of its structure and dynamics and the principle determining the structural parameters was probed. Analysis results indicated that this new clutch was self-adjustable and self-adaptable and differed from the conventional overrunning speed clutch in terms of motoring principle. Moreover, the principle and function of the new clutch were confirmed by in-house experiment.
    (5)To obtain high efficiency and high stability, the automatic adjusting function of double output impulse generator mechanism was innovated. The method and regulation to determine and select all possible variations of motion pairs were established which were applicable for the process when non free-degree element group in plane closed chain mechanism approached a zero over-co
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