摘要
在主动隔振系统中,执行机构输出的主动控制力与系统隔振性能密切联系.为研究上述问题,本文通过建立优化目标函数对双层主动隔振系统进行优化来获得最优系统参数,分析优化前后双层主动隔振系统的隔振性能及主动控制力,验证优化方法的可性行.首先,从理论上研究了双层主动隔振系统在不同激励条件下的隔振性能,并分析了系统参数对主动控制力输出的影响.其次,建立综合性的优化目标评价系统的隔振性能,利用遗传算法优化目标函数.最后,利用模糊PID控制算法对双层主动隔振系统进行主动控制,对比优化前后的隔振性能及主动控制力,其结果表明:优化后,隔振对象的位移,与中间层的相对位移及主动控制力分别减小了32.7%,67.5%,55.4%.因此,双层主动隔振系统的优化设计方法是可行的.
双层隔振系统(DLVIS)因具有优越的隔振性能而引起广泛关
在众多的优化方法
查阅相关的文献可知,建立多目标优化函数, 利用遗传算法对双层主动隔振系统进行参数优化的研究相对较少.而本文的主要贡献是建立综合性的优化目标函数,利用遗传算法对双层主动隔振系统在全局范围内进行参数优化.
为提高系统的隔振性能,将执行机构(如

图1 双层隔振系统
Fig.1 Double layer vibration isolation system
(a)被动系统 (b)主动系统 (c) 主动系统
(a) passive system (b) active system (c) active system
当双层主动隔振系统受到外激励作用时,如
(1) |
其中,
,, |
,,, |
和分别为隔振对象和中间层的位移, 为隔振对象与中间层之间的相对位移, 为传递到基础的传递力.为传递函数,系统响应可表示为:
(2) |
联立和,可得和为:
(3) |
其中,j是虚数,
(4) |
其中,
,, |
. |
(5) |
其中,,,
, |
,. |
因此,和可表示为:
(6) |
(7) |
此外,,可表示为:
(8) |
传递到基础的力为,可表示为:
(9) |
将代入可得:
(10) |
联立和,有,可得:
(11) |
其中,为固有频率比,为激励频率比,为质量比,和为阻尼比,和为固有频率.将,和无量纲化,可得:
(12) |
其中,,, ,
(13) |
其中,,为的模,可表示为:
(14) |
其中,
(15) |
当双层主动隔振系统受到位移激励,如
(16) |
其中,,为隔振对象的位移,为隔振对象与中间层的相对位移.系统响应可表示为:
(17) |
其中,为传递函数,为的模,可表示为:
(18) |
由可知,幅值比与系统参数, ,,相关.系统阻尼比,对幅值比的影响如

(a) =1,=1.6,=0.1

(b) =1,=1.6,=0.1
图2 阻尼比,对幅值比的影响
Fig.2 The effect of andon
系统固有频率比与质量比对幅值比的影响如

(a) ,=0.1,=0.1
(b) =0.1,=0.1,=1.6
(a) ,=0.1,=0.1
(b) =0.1,=0.1,=1.6

(c) 对和的影响
(d) 对和的影响
(c) The effects of the on and
(d) The effects of the on and
图3 和对幅值比|Fa/F|的影响
Fig.3 The effects of the and on |Fa/F|
在主动控制过程中,系统因主动控制力输出饱和而无法实现最优隔振性能,因此,对双层主动隔振系统进行参数优化是非常有意义的.设计综合性的评价指标h(f)为:
(27) |
其中,≤1,,,为权重系数,且++=1,为主动控制力的输出饱和值.
采用遗传算法对目标函数h(f)进行优化,其中适应度函数选为h(f),据1.2分析,优化问题的数学模型为:
(28) |
利用模糊PID控制算法对双层主动隔振系统进行控制,比较其优化前后的隔振性能及主动控制力.考虑到各系统性能的均衡性,权重系数选为 =0.4,=0.3,=0.3.优化前后的系统参数如
主动隔振系统中,位移激励与力激励幅值分别为10 mm和500 N,频率为20~50Hz的随机激励.优化前后双层被动隔振系统的位移响应如

图4 优化前后被动隔振系统中被隔振对象的性能
Fig.4 The responses of the passive vibration isolation system before and after optimization
(a)上层位移 (b) 上层与中间层相对位移
(a) The displacement of top layer (b) The relative displacement
;between the top and immediate layers
为了进一步说明优化后双层主动隔振系统的优越性,主动隔振系统在优化前后的响应如

图5 优化前后主动隔振系统中被隔振对象的性能
Fig.5 The responses of the active vibration isolation system before and after optimization
(a)上层位移 (b)上层与中间层相对位移
(a)The displacement of top layer (b) The relative displacement between the top and immediate layers
主动控制力的输出曲线如

图6 优化前后主动控制力输出
Fig.6 The control force output of the active vibration isolation system before and after optimization

图7 优化前后系统性能对比
Fig.7 Comparison of DLVIS performance: before and after optimization
(a)双层被动隔振系统 (b)双层主动隔振系统
(a) Passive DLVIS (b) Active DLVIS
本文通过建立综合目标函数,采用遗传算法优化双层主动隔振系统,提高了双层隔振系统的隔振性能.从理论上推导了双层主动隔振系统在不同激励下的隔振性能,建立了由不同权重系数的子目标组成的综合目标函数,作为遗传算法的优化目标.通过数值仿真验证了优化后的双层主动隔振系统的优越性.结果表明,优化后,双层主动隔振系统中被隔振对象的位移与相对位移均能显著降低,主动控制力输出也下降55.4%.因此,本文采用遗传算法对双层主动隔振系统进行目标优化是可行的.
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