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为了检测两个轴系的平行度,必须首先测量出每个轴系的旋转轴线空间位置,然后比较两者的偏差值获得平行度误差。为保证测试精度需要两个轴线的检测以同一坐标系为基准,如何简单高效的以同一基准检测两个轴系的旋转轴线成为平行度检测的关键问题。传统转台轴系垂直度测量常用的自准直仪具有测量精度高、使用方便、行业应用广、认可度高的优势。为此,首选光电自准直仪作为测量设备,借用自准直仪配合基准反射镜测量轴系偏转角度的方法,采用一个自准直仪,在不移动位置保证基准不变的前提下分别测量出两个轴系的旋转轴线角度。光学准直角度测量原理是利用自准直仪发出的自准直光,经过被测系统上的反射镜反射后被自准直仪接收,比较发射光和反射光的角度差即可获知反射镜法线角度,对于机械旋转轴系上同轴安装的反射镜的法线即为机械旋转轴轴线。为此,采用自准直仪结合基准反射镜即可测量机械旋转轴系的轴线角度。
对于同轴系统,由于转台两轴系同轴安装,其轴线重合,在轴心安装传统的基准反射镜后,两个轴系的基准镜相互遮挡,这造成在不调整测试系统的前提下很难实现同一测试设备测量两个轴系轴线角度,为保证测试可信度一般采用多台测量设备,利用基准传递完成测试。但该方法所需测试设备多、测试系统构建复杂,基准传递难度大对测试人员要求较高,在加工工厂很难具备测试条件,也可采用先测量一个轴,拆除该轴系基准反射镜后再测量另一个轴的方法,但由于转台尺寸小,一方面拆装困难另一方面需对转台进行机械拆卸,势必造成转台移位,从而影响测量精度。为了保证测量精度,为其他更高精度要求的测量提供必要的技术积累,方案采用一次安装两个基准镜,在无需机械拆卸的前提下实现两个轴系的测量。并且,考虑到实际测试多在加工工厂装配过程开展,必须考虑测试方法的便捷性。为此,必须研究新的同轴转台旋转轴角度同轴度测试方案。
为了实现测试基准镜即可反射自准直仪信号,又可人为可控透射光线的目的,将靠近自准直仪一侧的基准镜,由传统的反射镜优化为一半反射一半透射,测试时在两个旋转轴上分别安装两个角度可调的基准镜,测量方法示意图如图4(a)所示。自准直仪与PAT机构通过工装保证两者相对固定不动。该方法主要对PAT轴系同轴度进行检测,因此测试时PAT机构先不安装液晶光栅,光栅引起的光轴精度需另行讨论。在安装液晶光栅的位置安装基准镜1和基准镜2,两个基准镜均有调整机构,可以调整镜面的二维角度。基准镜1采用普通的反射镜,基准镜2镜面如图4(b)所示,其一半为透射镜面,另一半为反射镜面,基准镜实物如图4(c)所示。
图 4 测量原理示意图。(a)测量系统组成;(b)基准镜2示意图;(c)基准镜实物图
Figure 4. Schematic diagram of measurement principle. (a) Composition of measurement system; (b) Schematic diagram of reference mirror#2; (c) Reference mirrors
理论上通过调整自准直仪的角度和基准镜的角度可以保证在轴系转动时,自准直仪上的光斑以视场中心为圆心做圆周转动,圆周的最小半径即为轴系晃动最大值,圆周中心即为轴系轴线位置。但实际测量时,由于结构调整能力和人员观察精度有限,而且在调整时轴系晃动自身造成光斑无规律跳动,很难调整到理想状态,为此采用数学拟合方法对数据进行处理,剔除轴系晃动误差和调整误差后拟合得到测试数据点的圆心作为轴系转动时的理论轴线位置。首先安装基准镜1并调整反射镜和自准直仪角度,保证轴系1转动时自准直仪上光斑绕一个较小的圆变化,同时圆心尽量靠近视场中心。然后安装基准镜2并遮挡其透射面,保证光不会透过基准镜2,然后保持自准直仪不动,只调整基准镜2的角度,使其状态与基准镜1基本一致。测量时,首先遮挡住基准镜2的透射面,使自准直仪发射的光只能通过基准镜2反射,旋转旋转轴2同时记录测量数据。随后保持PAT机构和自准直仪不动,打开基准镜2的透射面遮挡反射面,自准直仪发射的光可以透过基准镜2的透射面照射到基准镜1上反射后回到自准直仪,此时转动旋转轴1并记录数据。测量时自准直仪始终保持不动,因此测量得到的两轴轴线空间位置均以自准直仪的坐标系为基准,并且自准直仪测量的是反射镜法线角度,所以测得结果为轴线空间角度,因此两个轴线间的差即为两个轴系间的平行度误差。测量时自准直仪成像如图5所示,图5(a)为不遮挡基准镜2任何表面时,自准直仪同时对基准镜1和2成像图,图5(b)为遮挡基准镜2反射面时,自准直仪对基准镜1成像,图5(c)为遮挡基准镜2透射面时,自准直仪对基准镜2成像图。
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采用最小二乘法对数据进行拟合,对测量数据处理剔除轴系晃动和自准直仪及基准镜调整误差的影响,获得旋转轴系的轴线空间位置[9]。轴系转动时基准镜法线一定是绕着一个圆变化,为此采用圆拟合公式:
$$ {\left(x-{x}_{0}\right)}^{2}+{\left(y-{y}_{0}\right)}^{2}={r}^{2} $$ (1) 式中:(x, y)为测量数据在x轴和y轴上的数值;(x0, y0)为圆心坐标;r为圆的半径。拟合时误差值平方的优化目标函数为:
$$ S=\sum _{i=1}^{n}{\left[\sqrt{{\left({x}_{i}-{x}_{0}\right)}^{2}+{\left({y}_{i-}{y}_{0}\right)}^{2}}-r\right]}^{2} $$ (2) 式中:(xi,yi)i=1,2···, n为圆上测量点坐标;n为参与拟合的数据点个数。
对公式(2)改写为:
$$ A=\sum _{i=1}^{n}{\left({x}_{i}^{2}+{y}_{i}^{2}+a{x}_{i}+b{y}_{i}+c\right)}^{2}=0 $$ (3) 式中:
$ a=-2{x}_{0} $ ;$ b=-2{y}_{0} $ ;$ c={x}_{0}^{2}+{y}_{0}^{2}-{r}^{2} $ 。当a,b,c取得最小值时,应满足:
$$ \left\{ \begin{aligned} & \frac{\partial A}{\partial a}=2\sum _{i=1}^{n}\left({x}_{i}^{2}+{y}_{i}^{2}+a{x}_{i}+b{y}_{i}+c\right){x}_{i}=0\\& \frac{\partial A}{\partial b}=2\sum _{i=1}^{n}\left({x}_{i}^{2}+{y}_{i}^{2}+a{x}_{i}+b{y}_{i}+c\right){y}_{i}=0\\& \frac{\partial A}{\partial c}=2\sum _{i=1}^{n}\left({x}_{i}^{2}+{y}_{i}^{2}+a{x}_{i}+b{y}_{i}+c\right)=0 \end{aligned}\right. $$ (4) 对公式(4)进行推导,可得:
$$ \left\{ \begin{aligned} & a=\frac{{H}_{2}{M}_{12}-{H}_{1}{M}_{22}}{{M}_{11}{M}_{22}-{M}_{12}{M}_{21}}\\& b=\frac{{H}_{2}{M}_{11}-{H}_{1}{M}_{21}}{{M}_{12}{M}_{21}-{M}_{11}{M}_{22}}\\& c=\frac{1}{n}{\sum }_{i=1}^{n}\left({x}_{i}^{2}+{y}_{i}^{2}+{ay}_{i}+{by}_{i}\right) \end{aligned} \right. $$ (5) 其中:
$$ \left\{ \begin{aligned} & {M}_{11}=\left(n\sum _{i=1}^{n}{x}_{i}^{2}-\sum _{i=1}^{n}{x}_{i}\sum _{i=1}^{n}{x}_{i}\right)\\& {M}_{12}={M}_{21}=\left(n\sum _{i=1}^{n}{x}_{i}{y}_{i}-\sum _{i=1}^{n}{x}_{i}\sum _{i=1}^{n}{y}_{i}\right)\\& {M}_{22}=\left(n\sum _{i=1}^{n}{y}_{i}^{2}-\sum _{i=1}^{n}{y}_{i}\sum _{i=1}^{n}{y}_{i}\right)\\& {H}_{1}=n\sum _{i=1}^{n}{x}_{i}^{3}+n\sum _{i=1}^{n}{x}_{i}{y}_{i}^{2}-\sum _{i=1}^{n}\left({x}_{i}^{2}+{y}_{i}^{2}\right)\sum _{i=1}^{n}{x}_{i}\\& {H}_{2}=n\sum _{i=1}^{n}{y}_{i}^{3}+n\sum _{i=1}^{n}{x}_{i}^{2}{y}_{i}-\sum _{i=1}^{n}\left({x}_{i}^{2}{+y}_{i}^{2}\right)\sum _{i=1}^{n}{y}_{i} \end{aligned} \right. $$ (6) 根据公式(5)可获得拟合后的圆心坐标(x0, y0)和半径r。
$$ {x}_{0}=-\frac{a}{2},{y}_{0}=-\frac{b}{2},r=\frac{1}{2}\sqrt{{a}^{2}+{b}^{2}-4c} $$ (7) 轴系晃动误差t0由公式(8)计算得到:
$$ {t}_{0}=max\left[\sqrt{\left|{\left({x}_{i}-{x}_{0}\right)}^{2}+{\left({y}_{i}-{y}_{0}\right)}^{2}-{r}^{2}\right|}\right] i=\mathrm{1,2},3,\cdots ,n $$ (8) 即:
$$ {t}_{0}=\sqrt{{\left({x}_{max}-{x}_{0}\right)}^{2}+{\left({y}_{max}-{y}_{0}\right)}^{2}}-\sqrt{{\left({x}_{min}-{x}_{0}\right)}^{2}+{\left({y}_{min}-{y}_{0}\right)}^{2}} $$ (9) 式中:(xmax, ymax)和(xmin, ymin)分别为测量点中距离拟合圆中心最大值点和最小值点。采用最小二乘法分别对两组数据进行拟合后得到两轴晃动误差t1,t2和轴线空间角度坐标(x01, y01)和(x02, y02),两个轴系的平行度误差(x0′, y0′)为:
$$ \left\{ \begin{aligned} & {x}_{0}'=\left({x}_{01}-{x}_{02}\right)\\& {y}_{0}'=\left({y}_{01}-{y}_{02}\right) \end{aligned} \right. $$ (10) 综合同轴误差为:
$$ {\Delta }_{xy}=\sqrt{{x}_{0}^{\prime 2}+{y}_{0}^{\prime 2}} $$ (11) -
影响测量不确定度的因素很多,包括人为测量误差、检测工具精度、测量方法等引起的误差,其中人为误差随机性较强,在此重点讨论测量方法与检测工具引起的测量不确定度。通过对测量数据的最小二乘圆拟合可以得到拟合圆的圆心和半径,分别评价轴系的晃动误差和平行度误差。数据的准确性和可信性势必影响拟合结果的精度,为了评价测试结果的准确性,保证测量结果的置信度,把测量数据对拟合结果的影响进行分析。影响拟合结果的测量数据主要参数有数据点数量、分布均匀性、数据分布离散性、测试点准确性等[16-17]。
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理论上平面内不在同一直线上的三个点即可完全确定一个圆,但是在实际测量中受到轴系晃动的影响每个测试点会产生一定的随机误差,甚至有可能出现错误的测量值,所以数据点过少时测量点偏差会严重影响拟合精度。
采用自准直仪对轴系旋转进行测量时,各个测量点可以认为是相互独立的,在没有错误测量点时可假设各点精度相同,所以每个测试点相互独立且互不相关,因此有xmax,ymax,xmin,ymin之间互为不相关,每个参数的不确定度与测量不确定度ut相同且uxmax=uymax=uxmin=uymin=ut,则拟合圆心(x0,y0)的不确定度(u_x0,u_y0)为:
$$ \left\{ \begin{aligned} & {u}_-{x}_{0}=\sqrt{\sum _{i=1}^{n}{\left(\frac{\partial {x}_{0}}{\partial {x}_{i}}\right)}^{2}}{u}_{t}=\frac{1}{\sqrt{n}}{u}_{t}\\& {u}_-{y}_{0}=\sqrt{\sum _{i=1}^{n}{\left(\frac{\partial {y}_{0}}{\partial {y}_{i}}\right)}^{2}}{u}_{t}=\frac{1}{\sqrt{n}}{u}_{t} \end{aligned}\right. $$ (12) 由此可见,随着测量点数的增加,拟合圆心的不确定度降低,但随着测量点的增加测量效率降低,同时增加了错误测量点出现的机率,在实际测量中需根据测试误差需求和单点测试预估不确定度,综合选取测量点数。
测量时单点测量值受到轴系晃动影响产生随机摆动,另外计算精度和数据精度同样影响拟合结果,所以实际测量时各测试点数据不完全独立,拟合结果不确定度受到轴系晃动等影响,为综合评价测量点的影响,数据点数引起的不确定度误差用不确定度偏差比u∆表示,为轴系误差拟合值f0与轴系晃动最大值∆之比表示,即:
$$ {u}_{\Delta }=\frac{{f}_{0}}{\Delta } $$ (13) 用matlab对在随机轴系晃动作用下3~48个均布测试点时拟合圆心坐标不确定度偏差比u∆和轴系晃动拟合偏差unv进行了仿真分析。仿真时,根据测试点数量在每个测试点下分别取500组随机数据进行拟合分析,以该组所有结果最大值作为输入分析不同测试点数量时数据偏差,仿真结果曲线如图6(a)所示,u∆分解为x轴上分量u∆x和y轴上分量u∆y。可见,随机数据造成结果曲线产生一定的震荡,但其并不影响其总体变化规律,从结果可见测量点的数量对拟合圆圆心影响较大,测试点数少于5个时轴系晃动测试结果不确定度偏差比较大,当数量大于6后其偏差比优于0.3,当点数少于16点时拟合结果变化较大,大于16点后变化趋于平缓,其不确定度偏差比在0.2左右,48点时其不确定度偏差比约为0.1,且从数据变化趋势可见,随着测试点数的增加,拟合圆心不确定度偏差会更趋近于零,其规律与公式一致。测试点数对误差拟合结果标准差影响如图6(b)所示,看见其变化规律与不确定度偏差比相同。
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单个测试点的不确定度主要取决于测量仪器的测量精度utc和被测量值随机偏差utx,一般测量中测试仪器测量精度必须高于被测值至少3倍以上,但当被测值精度较高时测量仪器精度不足会对测量不确定度产生一定影响,因此单点测试可信度计算时以两个被测量值随机偏差和测试仪器测量精度的平方根与测量值随机偏差之差作为单点测量不确定度ut,即:
$$ {u}_{t}=\sqrt{{u}_{tc}^{2}+{u}_{tx}^{2}}-{u}_{tx} $$ (14) 由上式可见,当测量仪器测试精度远高于被测值时,单点测量不确定度趋近于零。设仪器测试精度与被测值随机偏差之比为k,则单点测量不确定度比uk可表示为:
$$ {u}_{k}=\frac{{u}_{t}}{{u}_{tx}}=\sqrt{1+{k}^{2}}-1 $$ (15) 其当k取0.1~1时uk变化曲线如图7所示,由图可见,随着测量仪器精度变大,单点不确定度比随之快速上升,当测量仪器精度与被测值精度接近时,其测量误差约为被测值的0.4倍。
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常规的不确定度分析基本都基于数据均匀分布的假设,但是在PAT系统装配阶段进行测试时尚未安装电机和角度编码器,测试时很难保证测试点分布均匀性,同时在测量时由于人员失误等因素也会造成测量点分布不均。当不存在轴系晃动等误差时,即使测量点分布不均匀但其依然在理想圆上,因此对拟合圆不确定度没有影响,但是由于单点测量不确定度的存在,当测量点分布不均时,会影响测试点偏离度的分布,造成局部测试点集中,从而影响拟合精度。为此分析数据分布偏均匀性对不确定度的影响。由图8可见在不同测试点数时数据分布偏差角度分别为5°、10°和15°时,拟合圆圆心不确定度比uf和方差比ufv,其中ufx和ufy为不确定度比uf在x轴和y轴上的分量,每个数据点均为500组随机数据拟合结果的最大值。由图8(a)与(b)结果曲线可见ufx和ufy随着偏角增大而增大,在15°时最大可达到约0.11。在同一偏离角度时不确定度随着测量点数增加而增大,这是由测试点数增加,相邻两测量点角度间隔减小,角度偏离引起的数据不均匀性变大造成的。由图8(c)可见,数据不均匀性对测量结果方差影响较小。
图 8 数据分布影响分析结果。(a) x轴不确定度比;(b) y轴不确定度比;(c)标准差比
Figure 8. Data distribution affects analysis results. (a) x axis uncertainty deviation ratio; (b) y axis uncertainty deviation ratio; (c) Standard deviation ratio
根据以上分析测试时平行度和轴系晃动测量不确定度uzt和uzh为:
$$ {u}_{zt}={u}_{zh}=\sqrt{{\left({u}_{\Delta }{u}_{tx}\right)}^{2}+{u}_{k}^{2}+{\left({u}_{f}{u}_{tx}\right)}^{2}} $$ (16) 式中:utx为被测量值随机偏差;uzt和uzh的单位与utx相同。
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采用matlab编写了拟合程序并对某双光栅PAT机构进行了检测,其同轴度要求优于10″。检测时自准直仪与PAT放置在同一光学平台上,PAT通过工装固定在光学平台上保持不动,此时两者间位置可保持不动,放置引起的误差较小。测试时转动到每个测试点后静止3~5 s再进行测量,减小操作引起的PAT检测误差。检测现场如图9(a)和图9(b)所示。测量时每个轴系在一周内平均分布了16个测量点,测量数据的拟合结果如图9(c)所示,图中蓝色点为两组测量数据点,两个圆形轨迹为基准镜法线旋转理论圆,中心两个红色点为两轴系轴线空间角位置点。根据拟合结果轴系1轴线角度坐标为(72.56″, −2.74″)轴系2轴线角度坐标为(76.70″, 0.14″),两轴平行度误差为(4.14″, 2.98″),综合平行度误差为5.1″,两轴系晃动误差分别为3.96″和3.12″。由不平行度和轴系晃动引起的两轴综合摆动误差按两轴平行度误差分别与两轴晃动误差平方根计算为(6.5″, 5.8″)。系统轴系晃动误差预估utx取为4″,该测试采用TriAngle的TA HS 300-57型自准直仪,测量精度为0.75″。测试时测量点数量取为16,测试点分布误差小于10°,则测量结果不确定度uh为:
图 9 测试现场及测试结果。(a)现场图#1; (b)现场图#2; (c)测试结果
Figure 9. Test site and test result. (a) Figure at the crime scene#1; (b) Figure at the crime scene#2; (c) Test result
$$ {u}_{h}=\sqrt{{\left(0.2\times 4\right)}^{2}+{0.01}^{2}+{\left(0.11\times 4\right)}^{2}} =0.8'' $$ (17) 可见,采用TA HS 300-57型自准直仪进行16点测量时,该方法测试精度完全满足系统平行度优于10″的测试要求。
系统完成液晶光栅装调后通过光学方法对系统轴系性能进行了标定,标定现场如图10(a)和图10(b)所示。在PAT机构前方安放平行光源,后端安装CCD相机,平行光管发射的平行光通过PAT机构后被后端CCD相机接收,CCD可以提取接收光斑的脱靶量从而测量出光轴偏差程度,测试前将三者光轴调为同轴。测试时首先通过电机和编码器驱动控制两个光栅旋转到零位位置,此时平行光管发射平行光经过PAT机构后在CCD上的成像光斑位于视场中心位置,然后沿相同方向同步旋转两个光栅,在不存在轴系晃动时,光斑会保持同一位置不动,当轴系晃动时其光斑会发射摆动,测量出光斑摆动角度即为两个轴系的综合晃动误差。图10(c)和图10(d)为两次PAT机构旋转1周并均匀取36个测量点后的CCD光斑位置分布图,可见系统综合轴系摆动误差在x轴和y轴上分量最大值测试1约为(5.82″, 5.48″),测试结果2约为(6.01″, 5.66″),与装配过程中测试结果偏差为(10%, 5.5%)和(7.6%和2.4%)。
Coaxiality measurement and uncertainty analysis of rotating shafts based on autocollimation
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摘要: 在激光通信和光电跟瞄系统中已经开始采用基于旋转光栅或光楔的指向-捕获-跟踪(Pointing, acquisition and tracking, PAT)机构对光轴进行角度调整,该结构质量轻、体积小,非常有利于系统的轻小型化。由于结构中两个旋转轴的平行度误差会严重影响PAT机构性能,因此在机械装配时需严格保证两轴平行度。针对旋转轴系轴线不易测量,传统测试方法精度不足,轴系晃动误差影响测量结果等问题,为了满足两轴平行度高精度检测的需求,文中提出基于自准直原理的旋转轴平行度测试方法,利用自准直光学特性,结合特殊设计的半反半透基准镜,采用数据拟合方法剔除轴系晃动的影响,得到旋转轴轴线空间位置,创新地实现了无需调整测试和被测设备即可在同一基准下测量两个平行轴系轴线角度和平行度。该方法只需一台测试设备,排除了传统多台测试设备联合测量时,基准传导与变换中的测量和变换误差,提高了测试精度和测试效率。首先,设计了基于自准直仪的测试系统,采用一台自准直仪测试两个轴系轴线空间位置,从而得到旋转轴同轴误差;然后,对测试结果不确定度进行了研究,分析了测试准确性及其影响因素;最后,采用该测试方法和测试系统,对某双液晶光栅跟瞄PAT机构的两轴平行度进行了测量,系统的实际测试表明两轴平行度测试误差小于10%,该方法可以有效地测量两个同轴旋转轴系的平行度,并且具有较高的测量精度和可信度。Abstract:
Objective In laser communication and photoelectric tracking systems, the pointing, acquisition and tracking (PAT) mechanism based on optional grating or wedge has been used to adjust the angle of the optical axis. This structure is light in weight and small in size, which is very beneficial to the lightweight and miniaturization of the system. Since the coaxiality error of the two rotating axes of the structure seriously affect the performance of the PAT mechanism, it is necessary to strictly ensure the parallelism of the two axes during mechanical assembly. For the cross-tracking frame gimbal, the precision of shafting angle position depends on the verticality of two axes, which can be measured by autocollimator with optical mirror. But in optional grating or wedge PAT system, the gimbal is characterized by two rotating axes coaxially arranged to drive two gratings to rotate respectively, and the test method for cross-tracking frame gimbal is not applicable. The existing parallelism measurement methods, such as contact measurement and non-contact measurement, are straight-line measurements, contact measurement includes micrometer measurement and three-coordinate measurement, and the required angular deviation between two rotating axes of a coaxial turntable can be obtained only after data conversion. When the diameter of the distribution circle is small, its accuracy is low, and there are problems such as inconsistent conversion standards, poor conversion data accuracy, and low confidence. Therefore, it is necessary to establish the methods for angle parallelism measurement of grating or wedge PAT system with high precision, high reliability and high convenience to solve the engineering problems in the process of gimbal test and assembly. Methods A non-contact optical measurement method is proposed, and it uses an autocollimator as the only reference to measure the axis angle of two coaxial shafting without moving the autocollimator and the test gimbal in the test (Fig.4). Data processing is used to eliminate the influence of shafting sloshing to get the spatial position of the rotating axes. By comparing the angular deviation of the two axes, the parallelism of the two rotating axes can be measured. A semi-reverse semi-transparent reference mirror is designed in order to solve the problem of mutual occlusion of mirrors (Fig.4). The semi-reflection semi-transmission reference mirror can reflect collimating laser when testing its own shafting and project self-collimating light when testing another shafting (Fig.5). The spatial position of the axis of the rotating shafting is obtained by fitting the measured data with a least squares. Then the influences of the number of data points (Fig.6), the uniformity of data distribution (Fig.7), the dispersion of data distribution (Fig.8) and the accuracy of test points on the accuracy of test results are analyzed. Results and Discussions The fitting program is compiled by MATLAB , and a double-grating PAT mechanism is tested, the required coaxiality is better than 10″. In the test, 16 measuring points data are measured by TAHS 300-57 autocollimator whose measuring accuracy is 0.75′, and the distribution error of measuring points is less than 10°. Then the uncertainty of the measurement result is 0.8″, and the measuring precision of this method fully meets the requirement. In the test the error of comprehensive parallelism is 5.1″, and the sloshing error of two shafting is 3.96″ and 3.12″ (Fig.9). The two-axis combined swing error caused by unparallelism and shafting sloshing is calculated as the square root of two-axis parallelism error and two-axis sloshing error respectively (6.5″, 5.8″). After the alignment of the liquid crystal grating, the performance of the system axis is calibrated by optical method. In the two tests, the maximum value of the swing error of the synthetic shafting on the x-axis and y-axis is about 5.82″ and 5.48″, and the maximum value of the swing error on the x-axis and y-axis is about 6.01″ and 5.66″ (Fig.10). The deviation between the assembly period and the test results is (10%, 5.5%, 7.6% and 2.4%) respectively. Conclusions In this study, a parallelism testing method based on auto-collimation principle is proposed, and a testing device is designed. It innovatively realizes that the angle and parallelism of two parallel shafting axes can be measured under the same reference without adjusting the test and the tested equipment. This method only needs one test equipment, which eliminates the measurement and transformation errors in the benchmark conduction and transformation when the traditional multiple test equipment is used for joint measurement, and improves the test accuracy and efficiency. Then the error link in the test is studied, and the uncertainty of the test method is analyzed. The method of the paper can solve the problem of high precision and high reliability parallelism measurement of PAT mechanism. It is used in an coaxial PAT gimbal with grating. Through the experiment and test, it is proved that the deviation between the test result and the final-state test result is less than 10%. It is proved that the testing precision is good and the parallelism between coaxial rotors can be effectively measured. -
Key words:
- PAT /
- coaxiality /
- data fitting /
- uncertainty /
- rotating shafting
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