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感知结构设计采用阵列排布结构形式如图 2a所示,对于单个FBG而言,其受力分析如图 2b所示。
依据FBG的工作原理,温度通过标定可理解为常数,即得到FBG仅与应力应变敏感的函数关系,则波长的改变量Δλ与应变ε的函数关系有:
$ \Delta \lambda=(1-p) \varepsilon \lambda_0 $
(1) 式中, λ0为初始波长,p为应力系数。
由图 1可知, x轴方向为厚度方向,也是施力方向,产生的摩擦力为z方向,设力的大小为F,感知模块为正方形,故长度均为d,则FBG的应变量可表示为:
$ \Delta d=\frac{2(1+\rho) F}{E \Delta x} $
(2) 式中,Δd为x轴方向的延长率,E为杨氏模量,ρ表示泊松比。沿y轴的力F与Δd的正比系数为k,则代入(2)式有:
$ k=\frac{E d \Delta x}{2 d(1+\rho)} $
(3) 由于材料因受力的应变一般不会特别大,可近似看作α≈β,则:
$ \Delta d^{\prime}=\Delta d \cos \beta $
(4) 故应变可写为:
$ \varepsilon=\frac{1}{\sqrt{2} k d} F \cos \beta $
(5) 应变传感单元主要受力的大小和力的作用影响,而由于FBG阵列是正交排布的,所以,无论在哪个方向,产生最大偏转角度都存在一组FBG对齐夹角不大于45°,这也是正交排布的原因。
基于正交光纤光栅阵列的负载感知系统研究
Research on load sensing system based on orthogonal fiber grating array
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摘要: 为了避免在装配中夹持力过大损坏产品或太小产生滑落的问题,采用了光纤传感智能感知的方法,设计了一种基于正交光纤光栅阵列的负载感知系统。感知模块采用光纤光栅两两相互垂直的方式排布,获取夹持平面两个正交方向的横向剪切力,从而分析夹持状态。实验中采用两个5.0cm×5.0cm的橡胶块制成负载感知模块,通过仿真定量分析了不同参量对夹持控制的影响程度,得到了光纤光栅的有效长度与敏感度成正比、与空间分辨率成反比的规律。结果表明,垂向灵敏度为31.4pm/N,水平灵敏度为29.9pm/N, 该系统可实时获取被夹持物的受力变化。该结果对智能调节控制是有帮助的。Abstract: In order to avoid the problem that the clamping force is too large to damage the product during assembly or too small to cause slipping, a method of intelligent sensing of fiber sensing was adopted, and a load sensing system based on orthogonal fiber grating array was designed. To analyze the clamping state, the sensing modules were arranged in a way that the fiber gratings were perpendicular to each other to obtain the transverse shear force in two orthogonal directions of the clamping plane. Two 5.0cm×5.0cm rubber blocks were used to make the load sensing module in the experiment. The effect of different parameters on the clamping control was analysed, and the results show that the effective length of the fiber grating is proportional to the sensitivity and inversely proportional to the spatial resolution. The results show that the vertical sensitivity is 31.4pm/N, and the horizontal sensitivity is 29.9pm/N. It can be seen that the system can obtain the force changes of the clamped objects in real time, which is helpful for intelligent adjustment and control.
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Key words:
- fiber optics /
- orthogonal array /
- load sensing /
- structural design
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