摘要
本文提出了一种新型的柔性隔振结构,该结构是基于柔性曲梁的力学特性而设计的.研究结果表明,该结构能通过轴向方向的负载来降低扭转方向的刚度,从而达到扭转方向的准零刚度特性,实现低频隔振.本文首先构建了柔性隔振结构的单元模型,并确定了单元模型轴向及扭转方向等关键静力特性,结果表明,该结构的单元模型能实现扭转方向的准零刚度特性,且轴向方向有较高的负载.然后,对不同结构参数的单元模型进行了动力学分析,确定了各结构参数对该结构动力学特性的影响,并利用有限软件对其进行了仿真分析,结果表明,该单元模型具有较好的隔振效果.最后,对构建的多层仿生柔性结构的隔振效率及隔振带宽进行了探讨.该结构具有柔性机构免装配、可整体加工、易小型化等特点,适用于精密光学仪器、机器人、卫星等具有扭转方向低频隔振的领域.
振动是大多数人类活动和工程应用中普遍存在的一种运动现象,例如我们能听到声音、能说话、能看见东西等,都与振动密切相
隔振器的种类可分为被动隔振器、半主动隔振器和主动隔振器.其中,被动隔振器结构简单,不需要外部能量,因此造价相对较低,是解决许多工程振动传动问题中最为常见的一种方案,但是一般的被动隔振存在一个明显的缺陷,对于传统的线性隔振器,只有当激励频率大于结构固有频率的倍时,才能实现振动隔离,因此实现低频隔振时,会遇到静变形过大和失稳的问
准零刚度实现的特点大都是利用正负刚度部件并联来实现准零特性,达到低频隔振,有较宽的隔振带宽.在准零刚度隔振结构中,正负刚度部件并联时,难免会存在装配或者摩擦等因素造成的误差,从而降低了隔振效率.本文提出了一种新型的连续的具有柔顺性的被动隔振器:在机构上,它具有柔性机构免装备、可整体加工、易于小型化等优
如

图1 单元模型结构示意图
Fig.1 Schematic diagram of element structure

图2 单元结构的三维模型图
Fig.2 3d model diagram of element structure
对单元模型的静力特性进行分析,

(a) 轴向力与轴向位移之间的关系
(a) The relationship between axial force and axial displacement

(b) 扭转角度与力偶距之间的关系
(b) The relationship between the torsion angle and the moment of couple
图3 单元模型的静力特性
Fig.3 Static characteristics of the element model
无预载时扭转恢复力偶距与扭转角度的关系为:
分析可知,模型的扭转方向刚度与模型的初始结构参数和轴向预载有关,即模型的扭转刚度函数可表示为.
式中,的单位为,的单位为.

(a) 单元模型在几种预载下扭矩与转角的关系
(a) The relationship between torque and rotation angle under several preloads of the element model

(b) 扭转刚度与预载的关系
(b) The relationship between torsional stiffness and preload
图4 轴向预载对单元模型扭转方向刚度的影响
Fig.4 Influence of axial preload on torsional stiffness of the element model
根据上一节中对静力学的分析可知,轴向预载和结构参数会对结构的刚度特性存在影响.轴向预载的不断增大,结构的扭转刚度会逐渐减少.对于实现柔性隔振结构扭转方向在扭转角度为零位置处的准零刚度特性,即在时,要求扭转刚度,再根据应用场合设计合理的初始参数与轴向预载.例如,负载确定的情况下设计合理的初始结构参数,或者结构参数确定的情况下确定负载.本节针对在中心距,夹角的初始结构参数的情况下实现扭转准零刚度.
通过数值分析和有限元仿真结果可知,该结构扭转方向准零刚度的实现需要较大的轴向负载,进而产生较大的轴向变形.为了减小轴向变形,保证轴向方向上能有足够的预载来达到扭转准零刚度条件,本文的一案例以在每根柔性曲梁的两端附加轴向弹簧的方式来实现.

(a) 有限元模型
(a) Finite element model

(b) 扭转方向的力矩和转角之间的关系
(b) The relationship between torque and rotation angle
图5 准零刚度单元结构
Fig.5 Quasi-zero stiffness element structure
根据第2节中描述的三维模型,利用有限软件进行仿真,将上下两个底板设置为刚体部件,下底板进行固定约束,各部件之间采用绑定连接.在这些约束条件下,对几种不同结构参数的单元模型进行模态分析,得到不同结构参数下的固有频率.

图6 不同类型单元模型的前二阶模态图
Fig.6 First-order and second-order modes of different cells
对单元模型的隔振性能进行分析,

图7 隔振结构简化模型
Fig.7 A simplified model of vibration isolation structure
当模型仅受到下底板扭转运动激励时,单元模型的动力学方程为:
当运动激励为简谐激励时,即,则上底板的响应可表示为,单元模型的隔振效率为:
以第1类结构参数下的单元模型为例,进行谐响应分析,通过振动幅频曲线分析其在不同的轴向预载下的隔振效率,如

(a) 第1类单元扭转方向隔振效率
(a) Vibration isolation efficiency of cell 1 in torsion direction

(b) 第1单元在不同轴向预载下的有效隔振范围
(b) Effective vibration isolation range of cell 1 under different axial preload

(c) 附加弹簧后准零刚度条件下的隔振效率
(c) Vibration isolation efficiency under the condition of quasi-zero stiffness after spring addition
图8单元模型的隔振性能
Fig.8 Vibration isolation performance of element model
柔性隔振结构还可以搭建多层结构来扩大隔振带宽,

图9 1-1组合的双层结构
Fig.9 1-1 combination of double layer structure
(a)1-1组合模型图
(a)Figure 1-1 combined model
;(b)Vibration isolation efficiency of 1-1 combined model
同样地,对其他类型的单元组合的隔振性能进行分析,探究结构参数对组合单元隔振区域的影响.

(a) φ与隔振区域的关系
(a) The relationship between and the vibration isolation region

(b) 中心距与隔振区域的关系
(b) The relationship between center distance d and vibration isolation region
图10 隔振区域与结构参数的关系
Fig.10 The relationship between vibration isolation area and structural parameters
多层隔振结构能够提高隔振效率,本案例为8层准零隔振单元组合的结构,其有限元模型图如

(a) 多层结构有限元模型图
(a) Finite element model of multilayer structure

(b) 多层结构的隔振效率
(b) Vibration isolation efficiency of multilayer structure
图11 多层结构
Fig.11 Multilayer structure
本文基于柔性曲梁的力学特性设计了一种新型的柔性隔振结构,并对其性能进行了研究.该结构能通过轴向方向的负载来降低扭转方向的刚度,从而达到扭转方向的准零刚度特性,实现低频隔振.根据研究结果与分析,本文的主要贡献如下:
1)本文提出的新型的柔性隔振结构,能通过利用结构轴向与扭转方向的耦合关系,从而实现扭转方向的准零刚度特性.增加轴向方向的负载会降低扭转方向的刚度,提高隔振效率.
2)讨论了关键结构参数对该仿生柔性隔振结构隔振性能的影响,在运动范围内,该结构的曲梁初始斜率越小,结构的轴向承载能力越大,扭转方向的起始隔振频率越小.该结构的曲梁距中心轴的距离越小,结构的轴向承载能力不变,扭转方向的起始隔振频率越小.
3)多层柔性隔振结构具有较好的低频隔振性能,准零隔振单元的多层结构理论上能实现全频率范围的有效隔振,本文提出的8层隔振结构,当隔振效率为50%时的起始隔振频率为2.3Hz,比单层隔振效果较好.
综上所述,本文提出的新型仿生柔性隔振结构能实现扭转方向的低频隔振,且有较大的轴向负载能力,适用于多种存在扭转低频隔振的领域.另外,该结构具有柔性机构免装配、可整体加工、易小型化等特点,应用的场合很广.
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