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实验在两轴两框架小型光电稳定平台上进行,采用LuGre摩擦模型对扰动信号进行处理,转化为扰动摩擦力矩,使摩擦扰动可以根据不同的输入信号进行转化,目的是减小摩擦扰动对光电平台造成的影响,先进行Matlab/simulink仿真验证,然后搭建实验平台,在光电平台上进行实验,根据实验数据证实该方法可以有效减小摩擦力矩对平台伺服系统造成的影响。
参考需要仿真的稳定平台的结构参数,设置观测器与稳定平台伺服系统各参数取值如表1所示。
Item Parameters Value Sample period T/ms 0.1 Rotate inertia J/(kg·m2) 0.086 Torque coefficien K/(N·m·A−1) 0.718 Peak voltage U/V 12.2 Peak current I/A 17 Resistance R/Ω 1.8 Inductance L/mH 5.4 Table 1. Parameter selection of platform
经过对文中所研究的光电稳定平台进行离线辨识,测量有关数据,然后参考LuGre摩擦模型的数学结构,设置LuGre摩擦模型各参数取值如表2所示。
${\sigma _0}$ ${\sigma _1}$ ${\sigma _2}$ ${T_s}$ ${T_c}$ 200 8 0.01 0.15 0.06 Table 2. Parameter selection of LuGre friction model
考虑到在稳定平台实际应用过程中,低频大幅扰动可以通过调整平台伺服系统稳定回路相关增益进行扰动隔离,且有较好效果;高频小幅扰动通过稳定平台自身的惯性稳定和安装减震器方法也可以进行很好的隔离,而中频段是稳定平台控制系统较为薄弱的频段,故文中选择对
$ 10\;{\rm{Hz}},{0.03}^{°} $ 的中频扰动进行扰动补偿研究。为了提高仿真结果的准确程度,先验证文中提出的最小二乘角加速度估计算法的有效性,根据实际系统配置,将加速度估计环节输入信号设置为
$y = 3{t^2} + \omega $ ,其中$\omega $ 为白噪声信号,由于文章实验选用19位分辨率的DS-130光电编码器,经实测统计,得到该编码器的白噪声幅值为1×10−5 rad。输入信号如图6蓝线所示,经最小二乘角加速度估计之后的曲线如图6红线所示。可以看到,在经过二次微分引起的噪声放大影响后, FIR滤波器加速度估计环节的精度误差为$ \Delta a = 6.98\times{10^{ - 3}}\;{\rm{rad}}/{{\rm{s}}^2} $ ,根据公式(16),求出FIR滤波器的精度$ {\varepsilon}_{a}=0.167\;{\rm{rad}}/{{\rm{s}}}^{2} $ ,满足公式(16)提出的精度要求。图7蓝色部分表示将
$ 10\;{\rm{Hz}},{0.03}^{°} $ 的中频扰动信号输入给LuGre摩擦模型使其产生对应的摩擦力矩,该力矩加入稳定平台伺服系统时平台的速度响应图;红色部分表示经稳定平台角位置信息摩擦补偿之后的平台速度响应图。Figure 7. Load speed response diagram before and after compensation when 10 Hz,0.03° disturbance is applied
由图7可以看出,摩擦力矩作用于机构使得机构响应速度幅值为
$6.1\times{10^{ - 3}}\;{\rm{rad}}/{\rm{s}}$ ,但采用角加速度估计补偿之后,平台伺服系统的抗干扰能力有了很大的提升。经补偿后机构响应速度幅值仅为$2.5\times{10^{ - 3}}\;{\rm{rad}}/{\rm{s}}$ ,可见对$ 10\;{\rm{Hz}},{0.03}^{°} $ 的中频扰动产生的摩擦干扰该方法能实现很好的抑制效果。 -
由仿真验证结果,基于机构角位置信息的摩擦补偿可以有效抑制平台受到的摩擦扰动。为了进一步验证摩擦补偿方法在稳定平台中的实际应用效果,需要在实验平台上进行验证。
实验平台选择某两轴两框的稳定平台,针对平台方位轴系进行实验。该机构方位轴系转动惯量为0.315 kg·m2,方位电机选用直流有刷力矩电机,陀螺组件选择STM210型陀螺,方位测角元件选择绝对式光电编码器DS-130。陀螺与光电编码器的特性由表3、表4进行说明。
Parameters Value Measuring range/(°)·s−1 −400-400 Zero bias ≤20 Zero bias stability/(°)·h−1 ≤0.5 Bandwidth/Hz 131 Table 3. Main technical specifications of STM210 gyro
Parameters Value Resolution/(") 2.47 Precision/(") 9.89 Acquisition delay/ms 0.25 Data update cycle/ms 0.1 Table 4. Main technical specifications of DS-130 photoelectric encoder
文中对摩擦扰动的抑制能力的好坏直接关系到平台视轴稳像精度,所以实验以摩擦补偿方法对平台视轴稳像精度的提升程度为基准进行研究。
实验时,将稳定平台固定于模拟转台上方,给模拟转台输入
$ 10\;{\rm{Hz}},{0.03}^{°} $ 中频扰动信号,采样时间设置为0.04 s,统计20 s的稳定平台实验数据,图8(a)是在$ 10\;{\rm{Hz}},{0.03}^{°} $ 的信号作用下,平台方位轴系的稳像精度图:图8(b) 是在10 Hz,0.03°的信号作用下,平台方位轴系通过最小二乘加速度估计进行摩擦补偿后的稳像精度图。
Figure 8. Image stabilization accuracy of the platform before and after friction compensation when 10 Hz,0.03° disturbance signal is input
经过对实验数据进行分析处理,绘制平台受摩擦力矩影响的稳像精度图,对平台输入
$ 10\;{\rm{Hz}},{0.03}^{°} $ 扰动信号,经计算,得到补偿前平台稳像精度是26$\text{μ} {\rm{rad}}$ ,基于机构角位置信息进行加速度估计摩擦补偿之后,平台稳像精度达到了17$\text{μ} {\rm{rad}}$ ,性能提升了34.6%。实验结果表明,文中提供的扰动补偿方法可以切实提高稳定平台稳像精度,提升整体性能。
Friction observation compensation technology based on angular position information of photoelectric platform
doi: 10.3788/IRLA20210557
- Received Date: 2021-08-10
- Rev Recd Date: 2021-10-15
- Publish Date: 2022-06-08
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Key words:
- angular position information /
- friction torque /
- acceleration estimation /
- friction observation compensation
Abstract: In order to improve the image stability accuracy of the photoelectric servo stabilization platform, a compensation method of friction observation based on the running angle position information of the mechanism was proposed according to the principle of friction disturbance on the platform. Firstly, the precise control model of the photoelectric servo platform was established, and the friction torque of the platform was analyzed by using LuGre friction model, and then, the acceleration was estimated by the least square method based on the angular position information of the mechanism, and a disturbance observer based on the angular position information of the mechanism was designed to compensate the friction observation. Finally, the system simulation platform was established to perform simulation and experimental verification in Matlab/simulink. During the experiment, the mirror mechanism was installed on the simulation turntable, and a 10 Hz sinusoidal signal was applied to the turntable to compare and analyze the before/after experimental data of friction observation compensation. The experimental results show that when the simulation flight turntable moves sinusoidal at 10 Hz frequency, at friction observation of the before/after compensation, the image stabilization accuracy of the platform is reduced form 26 μrad to 17 μrad, and the performance is improved by 34.6%. This method can effectively enhance the anti-interference ability of the system, and improve the stability of the system.