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目前,对于空间中光强或者电磁波的追踪常用的方式是采用光电传感器判别方向,并控制追踪系统进行追踪。以对太阳光追踪为例[1-4],常见的有重力式、电磁式和电动式,这些光电跟踪装置都使用光敏传感器如硅光电管,其传统的追踪系统控制策略有很大的改进空间。
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还是以视日追踪装置为例,选择性能熟悉、成本低的光敏电阻作为光电传感器。其工作原理是基于内光电效应,在半导体光敏材料两端装上电极引线,将其封装在带有透明窗的管壳里构成光敏电阻。
追踪机构如图 2所示,3只光敏电阻以正三角排列,它们之间由3块夹角为120°的挡板分隔,3只光敏电阻处于挡板根部,称其为三象限位置传感器。
通过改进,控制系统需要采集的模拟量由原先的4个变成了3个,通过3个电阻反馈的电压差值,可算出光源的相对位置,进而控制机械机构进行追踪。
三象限传感器电路设计采用3个光敏电阻串联,如图 3所示。当测得U1和U2后,可算出3只光敏电阻的分压,进而得到每只光敏电阻的相对受光情况,从而得到光源的偏差方向,完成测向功能。
光敏电阻内部电阻随光照射而变化,光度越强阻值越小(负光敏电阻)。将输出电压U1、U2分别送到处理器的ADC通道0和通道1进行采样,计算出光源偏离方向。图 4是光源从不同方位入射时的传感器照射情况。
当太阳光按图 4a所示方向入射时,${R_3}$受光照最强,其电阻最小,分压最低,对应${U_{{R_3}}}$最小;当太阳光按图 4b所示方向入射时,${R_1}$受光照最强,其电阻最小,分压最低,对应${U_{{R_1}}}$最小;当太阳光按图 4c所示方向入射时,${R_1}$、${R_3}$受等量光照,其电阻相同,分压相等,${U_{{R_1}}} = {U_{{R_3}}}$,此时追踪系统在水平方位上对准太阳。追踪系统垂直仰角的调整通过判断${U_1} - {U_2}$是否大于${V_{CC}}/3$来进行:
$$ \left\{ {\begin{array}{*{20}{l}} {{V_{CC}} - {U_1} > {U_2}\;\;\;\;\;{R_3}光照强, {R_1}光照弱, 光源偏右}\\ {{V_{CC}} - {U_1} < {U_2}\;\;\;\;\;{R_3}光照弱, {R_1}光照强, 光源偏左} \end{array}} \right. $$ $$ \left\{ {\begin{array}{*{20}{l}} {{U_1} - {U_2} > \frac{1}{3}{V_{CC}}\;\;\;\;\;{R_2}光照弱, 光源偏下}\\ {{U_1} - {U_2} < \frac{1}{3}{V_{CC}}\;\;\;\;\;{R_2}光照强, 光源偏上} \end{array}} \right. $$ 可得对应跟踪算法如图 5所示。
这样设计的目的是利用差分效果,当其中的某只电阻的阻值变化(光照变化)时,其余电阻即使光照未变化,它们的分压也会进行互补性改变,这样就提高了U1、U2的动态输出范围,进一步改善跟踪精度。而且电阻没有固定,光照强度适应能力好,使用器件少,控制系统需要采集的模拟量也由改进后的3个进一步优化成了2个,实现了硬件简化。
Improvement of Control Strategy of Tracking System Based on Photoelectric Sensor
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摘要: 该文提出了一种基于光电传感器的追踪系统控制策略改进方法。以视日追踪系统为例,使用新的三象限位置传感器替代原有四象限传感器测向,降低了系统成本及控制难度。利用差分效果将需采集的模拟量减少到两个,分别对应水平和俯仰两个维度的控制,相比原有的控制策略,控制逻辑更为简单,实时性和可靠性也可以保证。测试表明,该系统能实现在全空域范围内的点光源跟踪,可替代现有四象限视日追踪系统。通过更换末端传感器,此改进的控制策略还可用于空间中电磁波源的追踪,无论在军事领域还是民用领域均有极大的应用价值。Abstract: This paper presents an improved control strategy for tracking system based on photoelectric sensors. Taking the sun-tracking system as an example, the new three-quadrant position sensor is used to replace the original four-quadrant sensor for finding directions, which reduces the system cost and difficulties of controlling. The improved system control strategy uses the differential effect to reduce the analog quantities to two, corresponding respectively to the two-dimension control of the horizontal and vertical directions. Compared with the original control strategy, the proposed control logic is simpler, thus the real time and reliability can also be guaranteed. Tests explain that the system can realize the tracking of the point light source in the whole airspace and replace the existing four-quadrant sun-tracking system. By replacing the terminal sensor, the improved control strategy can also be used to track electromagnetic wave sources in space, which has great application value in both military and civil fields.
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