机构运动学与动力学分析与建模 Ch00-3 刚体的位形 Configuration of Rigid Body Part1
刚体的位形可以用六个独立(坐标)参数完全描述:三个位置参数用于描述运动刚体上运动坐标系 { M } \left\{ M \right\} {M}原点 M M M在固定坐标系 { F } \left\{ F \right\} {F}的投影参数,三个转动参数用于描述运动坐标系 { M } \left\{ M \right\} {M}的基矢量相对于固定坐标系 { F } \left\{ F \right\} {F}的基矢量的姿态,而描述这种姿态的变换,则是需要确定矩阵 [ Q M F ] \left[ Q_{\mathrm{M}}^{F} \right] [QMF]。
因此为描述空间坐标系中任意一刚体的运动状态,首先需要描述刚体的位置矢量 R ⃗ M F \vec{R}_{\mathrm{M}}^{F} R MF与姿态矩阵 [ Q M F ] \left[ Q_{\mathrm{M}}^{F} \right] [QMF]
广义参考系坐标 Reference Coordinates
:为方便后续动力学方程的建立与推导,常用广义坐标矢量参数 q ⃗ M F \vec{q}_{\mathrm{M}}^{F} q MF来描述运动刚体的形位,其中:
q ⃗ M F = [ R ⃗ M F , θ ⃗ M F ] \vec{q}_{\mathrm{M}}^{F}=\left[ \vec{R}_{\mathrm{M}}^{F},\vec{\theta}_{\mathrm{M}}^{F} \right] q MF=[R MF,θ MF]- θ ⃗ M F \vec{\theta}_{\mathrm{M}}^{F} θ MF可以用多种方法来描述(通常包含3或4个角度参数 ),这些角度参数用于描述矩阵 [ Q M F ] \left[ Q_{\mathrm{M}}^{F} \right] [QMF]
对于刚体的运动状态而言,其运动坐标系的原点 M M M的位置矢量 R ⃗ M F \vec{R}_{\mathrm{M}}^{F} R MF表示与点的运动状态表示相同,因此需要探究如何用角度参数来描述转换矩阵。
3. 转换矩阵与旋转矩阵——刚体的位置与姿态描述
转换矩阵用于表述两个坐标系 { A : ( i ⃗ A , j ⃗ A , k ⃗ A ) } \left\{ A:\left( \vec{i}^A,\vec{j}^A,\vec{k}^A \right) \right\} {A:(i A,j A,k A)} 与 { B : ( i ⃗ B , j ⃗ B , k ⃗ B ) } \left\{ B:\left( \vec{i}^B,\vec{j}^B,\vec{k}^B \right) \right\} {B:(i B,j B,k B)}的基矢量之间的转换关系:
[ i ⃗ B j ⃗ B k ⃗ B ] = [ Q B A ] T [ i ⃗ A j ⃗ A k ⃗ A ] \left[ \begin{array}{c} \vec{i}^B\\ \vec{j}^B\\ \vec{k}^B\\ \end{array} \right] =\left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] i Bj Bk B =[QBA]T i Aj Ak A
其中,转换矩阵 [ Q B A ] T \left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}} [QBA]T表示坐标系 { B } \left\{ B \right\} {B}的基矢量在坐标系 { A } \left\{ A \right\} {A}中的表达,可将向量在不同的基矢量坐标系下进行表示。特殊的:若将基矢量替换成对应基矢量的向量投影,则可以表示为:两个原点重合的坐标系中,对同一向量的不同表达的转换关系;
上式也可以理解为:对坐标系 { A : ( i ⃗ A , j ⃗ A , k ⃗ A ) } \left\{ A:\left( \vec{i}^A,\vec{j}^A,\vec{k}^A \right) \right\} {A:(i A,j A,k A)}进行了 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]的旋转,此时将转换矩阵与向量的运算理解为张量与向量的运算,即得到了旋转后的向量在坐标系 { A } \left\{ A \right\} {A}中的表达,此时实际上,对原始坐标系 { A } \left\{ A \right\} {A}的基矢量同样进行了旋转,形成了新坐标系 { B } \left\{ B \right\} {B}的基矢量,其仍在坐标系 { A } \left\{ A \right\} {A}下表达。
[ r 1 A ′ r 2 A ′ r 3 A ′ ] = [ Q B A ] [ r 1 A r 2 A r 3 A ] \left[ \begin{array}{c} {r_{1}^{A}}^{\prime}\\ {r_{2}^{A}}^{\prime}\\ {r_{3}^{A}}^{\prime}\\ \end{array} \right] =\left[ Q_{\mathrm{B}}^{A} \right] \left[ \begin{array}{c} r_{1}^{A}\\ r_{2}^{A}\\ r_{3}^{A}\\ \end{array} \right] r1A′r2A′r3A′ =[QBA] r1Ar2Ar3A
目前,人们采用不同的角度参数 θ ⃗ \vec{\theta} θ 来对旋转矩阵进行描述
3.1 轴角变换
假设两个坐标系 { A } \left\{ A \right\} {A}与 { B } \left\{ B \right\} {B}的原点重合,其中坐标系 { B } \left\{ B \right\} {B}为坐标系 { A } \left\{ A \right\} {A}绕轴 v ⃗ F \vec{v}^F v F(单位向量)旋转 θ \theta θ所得到的。因此对于坐标系 { A } \left\{ A \right\} {A}中的点 P P P,经过转换后,得到点 P ′ P^{\prime} P′,此时点 P ′ P^{\prime} P′在坐标系 { B } \left\{ B \right\} {B}中的矢量投影与点 P P P在坐标系 { A } \left\{ A \right\} {A}中的投影分量相同。而在转换过程中,点 P ′ P^{\prime} P′在坐标系 { A } \left\{ A \right\} {A}中的表达发生变化,即有: [ P ′ 1 B , P ′ 2 B , P ′ 2 B ] = [ P 1 A , P 2 A , P 2 A ] \left[ {P^{\prime}}_{1}^{\mathrm{B}},{P^{\prime}}_{2}^{\mathrm{B}},{P^{\prime}}_{2}^{\mathrm{B}} \right] =\left[ P_{1}^{A},P_{2}^{A},P_{2}^{A} \right] [P′1B,P′2B,P′2B]=[P1A,P2A,P2A],因此对式 [ i ⃗ B j ⃗ B k ⃗ B ] = [ Q B A ] T [ i ⃗ A j ⃗ A k ⃗ A ] \left[ \begin{array}{c} \vec{i}^B\\ \vec{j}^B\\ \vec{k}^B\\ \end{array} \right] =\left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] i Bj Bk B =[QBA]T i Aj Ak A 有:
[ i ⃗ B j ⃗ B k ⃗ B ] T [ P 1 B P 2 B P 3 B ] = [ i ⃗ A j ⃗ A k ⃗ A ] T [ P 1 A P 2 A P 3 A ] ⇒ ( [ Q B A ] T [ i ⃗ A j ⃗ A k ⃗ A ] ) T [ P 1 B P 2 B P 3 B ] = [ i ⃗ A j ⃗ A k ⃗ A ] T [ P 1 A P 2 A P 3 A ] ⇒ [ i ⃗ A j ⃗ A k ⃗ A ] T [ Q B A ] [ P 1 B P 2 B P 3 B ] = [ i ⃗ A j ⃗ A k ⃗ A ] T [ P 1 A P 2 A P 3 A ] ⇒ [ Q B A ] [ P 1 B P 2 B P 3 B ] = [ P 1 A P 2 A P 3 A ] = [ P ′ 1 B P ′ 2 B P ′ 3 B ] \begin{split} &\left[ \begin{array}{c} \vec{i}^B\\ \vec{j}^B\\ \vec{k}^B\\ \end{array} \right] ^{\mathrm{T}}\left[ \begin{array}{c} P_{1}^{\mathrm{B}}\\ P_{2}^{\mathrm{B}}\\ P_{3}^{\mathrm{B}}\\ \end{array} \right] =\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] ^{\mathrm{T}}\left[ \begin{array}{c} P_{1}^{A}\\ P_{2}^{A}\\ P_{3}^{A}\\ \end{array} \right] \\ &\Rightarrow \left( \left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] \right) ^{\mathrm{T}}\left[ \begin{array}{c} P_{1}^{\mathrm{B}}\\ P_{2}^{\mathrm{B}}\\ P_{3}^{\mathrm{B}}\\ \end{array} \right] =\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] ^{\mathrm{T}}\left[ \begin{array}{c} P_{1}^{A}\\ P_{2}^{A}\\ P_{3}^{A}\\ \end{array} \right] \\ &\Rightarrow \left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] ^{\mathrm{T}}\left[ Q_{\mathrm{B}}^{A} \right] \left[ \begin{array}{c} P_{1}^{\mathrm{B}}\\ P_{2}^{\mathrm{B}}\\ P_{3}^{\mathrm{B}}\\ \end{array} \right] =\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] ^{\mathrm{T}}\left[ \begin{array}{c} P_{1}^{A}\\ P_{2}^{A}\\ P_{3}^{A}\\ \end{array} \right] \\ &\Rightarrow \left[ Q_{\mathrm{B}}^{A} \right] \left[ \begin{array}{c} P_{1}^{\mathrm{B}}\\ P_{2}^{\mathrm{B}}\\ P_{3}^{\mathrm{B}}\\ \end{array} \right] =\left[ \begin{array}{c} P_{1}^{A}\\ P_{2}^{A}\\ P_{3}^{A}\\ \end{array} \right] =\left[ \begin{array}{c} {P^{\prime}}_{1}^{\mathrm{B}}\\ {P^{\prime}}_{2}^{\mathrm{B}}\\ {P^{\prime}}_{3}^{\mathrm{B}}\\ \end{array} \right] \end{split} i Bj Bk B T P1BP2BP3B = i Aj Ak A T P1AP2AP3A ⇒ [QBA]T i Aj Ak A T P1BP2BP3B = i Aj Ak A T P1AP2AP3A ⇒ i Aj Ak A T[QBA] P1BP2BP3B = i Aj Ak A T P1AP2AP3A ⇒[QBA] P1BP2BP3B = P1AP2AP3A = P′1BP′2BP′3B
上式写明:坐标系 { B } \left\{ B \right\} {B}中,点 P P P与点 P ′ P^{\prime} P′之间的旋转关系。此时 P ′ P^{\prime} P′为运动刚体上的固定点,对点 P P P在坐标系 { B } \left\{ B \right\} {B}下的投影参数进行 [ Q B A ] T \left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}} [QBA]T旋转变化所得到的点 P ′ P^{\prime} P′在坐标系 { B } \left\{ B \right\} {B}下的投影参数。同时,对于 P P P与 P ′ P^{\prime} P′而言,其在某坐标系下表达的旋转关系是一致的,因此对于: [ Q B A ] [ P 1 A P 2 A P 3 A ] = [ P ′ 1 A P ′ 2 A P ′ 3 A ] \left[ Q_{\mathrm{B}}^{A} \right] \left[ \begin{array}{c} P_{1}^{A}\\ P_{2}^{A}\\ P_{3}^{A}\\ \end{array} \right] =\left[ \begin{array}{c} {P^{\prime}}_{1}^{A}\\ {P^{\prime}}_{2}^{A}\\ {P^{\prime}}_{3}^{A}\\ \end{array} \right] [QBA] P1AP2AP3A = P′1AP′2AP′3A 同样成立。
同理,利用几何关系对图进行分析,进而求得罗德里格旋转公式Rodrigues’ Rotation Formula
:
R ⃗ p ′ F = R ⃗ p F + ( v ⃗ F × R ⃗ p ′ F ) sin θ + 2 [ v ⃗ F × ( v ⃗ F × R ⃗ p ′ F ) ] sin 2 θ 2 = R ⃗ p F + v ⃗ ~ F R ⃗ p ′ F sin θ + 2 ( v ⃗ ~ F ) 2 R ⃗ p ′ F sin 2 θ 2 ⇒ R ⃗ p ′ F = [ E + v ⃗ ~ F sin θ + 2 ( v ⃗ ~ F ) 2 sin θ 2 ] R ⃗ p F = [ Q B A ] R ⃗ p F \begin{split} &\vec{R}_{\mathrm{p}^{\prime}}^{F}=\vec{R}_{\mathrm{p}}^{F}+\left( \vec{v}^F\times \vec{R}_{\mathrm{p}^{\prime}}^{F} \right) \sin \theta +2\left[ \vec{v}^F\times \left( \vec{v}^F\times \vec{R}_{\mathrm{p}^{\prime}}^{F} \right) \right] \sin ^2\frac{\theta}{2}=\vec{R}_{\mathrm{p}}^{F}+\tilde{\vec{v}}^F\vec{R}_{\mathrm{p}^{\prime}}^{F}\sin \theta +2\left( \tilde{\vec{v}}^F \right) ^2\vec{R}_{\mathrm{p}^{\prime}}^{F}\sin ^2\frac{\theta}{2} \\ &\Rightarrow \vec{R}_{\mathrm{p}^{\prime}}^{F}=\left[ E+\tilde{\vec{v}}^F\sin \theta +2\left( \tilde{\vec{v}}^F \right) ^2\sin \frac{\theta}{2} \right] \vec{R}_{\mathrm{p}}^{F}=\left[ Q_{\mathrm{B}}^{A} \right] \vec{R}_{\mathrm{p}}^{F} \end{split} R p′F=R pF+(v F×R p′F)sinθ+2[v F×(v F×R p′F)]sin22θ=R pF+v ~FR p′Fsinθ+2(v ~F)2R p′Fsin22θ⇒R p′F=[E+v ~Fsinθ+2(v ~F)2sin2θ]R pF=[QBA]R pF
而上式给出了:坐标系 { A } \left\{ A \right\} {A}中,点 P P P与点 P ′ P^{\prime} P′之间的转换关系。此时 P P P为运动刚体上的固定点,对点 P P P在坐标系 { A } \left\{ A \right\} {A}下的投影参数进行 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]旋转变化,所得到的点 P ′ P^{\prime} P′在坐标系 { A } \left\{ A \right\} {A}下的投影参数。
对罗德里格旋转公式进一步进行变换,将其改写为 [ Q B A ] = E + v ⃗ ~ F sin θ + 2 ( v ⃗ ~ F ) 2 ( 1 − cos θ ) \left[ Q_{\mathrm{B}}^{A} \right] =E+\tilde{\vec{v}}^F\sin \theta +2\left( \tilde{\vec{v}}^F \right) ^2\left( 1-\cos \theta \right) [QBA]=E+v ~Fsinθ+2(v ~F)2(1−cosθ),进而利用泰勒展开式,将旋转矩阵 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]进一步改写:
[ Q B A ] = E + θ v ⃗ ~ F + ( θ ) 2 2 ! ( v ⃗ ~ ) 2 + ( θ ) 3 3 ! ( v ⃗ ~ ) 3 + ⋯ + ( θ ) n n ! ( v ⃗ ~ ) n = e θ v ⃗ ~ \left[ Q_{\mathrm{B}}^{A} \right] =E+\theta \tilde{\vec{v}}^F+\frac{\left( \theta \right) ^2}{2!}\left( \tilde{\vec{v}} \right) ^2+\frac{\left( \theta \right) ^3}{3!}\left( \tilde{\vec{v}} \right) ^3+\cdots +\frac{\left( \theta \right) ^n}{n!}\left( \tilde{\vec{v}} \right) ^n=e^{\theta \tilde{\vec{v}}} [QBA]=E+θv ~F+2!(θ)2(v ~)2+3!(θ)3(v ~)3+⋯+n!(θ)n(v ~)n=eθv ~
可将轴角变换的转换矩阵写成指数形式。
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综合上述推导,可得到轴角变换的旋转矩阵 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]为:
[ Q B A ] = [ ( v 1 A ) 2 ( 1 − cos θ ) + cos θ v 1 A v 2 A ( 1 − cos θ ) − v 3 A sin θ v 1 A v 3 A ( 1 − cos θ ) + v 2 A sin θ v 1 A v 2 A ( 1 − cos θ ) + v 3 A sin θ ( v 2 A ) 2 ( 1 − cos θ ) + cos θ v 2 A v 3 A ( 1 − cos θ ) − v 1 A sin θ v 1 A v 3 A ( 1 − cos θ ) − v 2 A sin θ v 2 A v 3 A ( 1 − cos θ ) + v 1 A sin θ ( v 3 A ) 2 ( 1 − cos θ ) + cos θ ] \left[ Q_{\mathrm{B}}^{A} \right] =\left[ \begin{matrix} \left( v_{1}^{A} \right) ^2\left( 1-\cos \theta \right) +\cos \theta& v_{1}^{A}v_{2}^{A}\left( 1-\cos \theta \right) -v_{3}^{A}\sin \theta& v_{1}^{A}v_{3}^{A}\left( 1-\cos \theta \right) +v_{2}^{A}\sin \theta\\ v_{1}^{A}v_{2}^{A}\left( 1-\cos \theta \right) +v_{3}^{A}\sin \theta& \left( v_{2}^{A} \right) ^2\left( 1-\cos \theta \right) +\cos \theta& v_{2}^{A}v_{3}^{A}\left( 1-\cos \theta \right) -v_{1}^{A}\sin \theta\\ v_{1}^{A}v_{3}^{A}\left( 1-\cos \theta \right) -v_{2}^{A}\sin \theta& v_{2}^{A}v_{3}^{A}\left( 1-\cos \theta \right) +v_{1}^{A}\sin \theta& \left( v_{3}^{A} \right) ^2\left( 1-\cos \theta \right) +\cos \theta\\ \end{matrix} \right] [QBA]= (v1A)2(1−cosθ)+cosθv1Av2A(1−cosθ)+v3Asinθv1Av3A(1−cosθ)−v2Asinθv1Av2A(1−cosθ)−v3Asinθ(v2A)2(1−cosθ)+cosθv2Av3A(1−cosθ)+v1Asinθv1Av3A(1−cosθ)+v2Asinθv2Av3A(1−cosθ)−v1Asinθ(v3A)2(1−cosθ)+cosθ -
同理对于任意一已知旋转矩阵 [ Q B A ] = [ q 11 q 12 q 13 q 21 q 22 q 23 q 31 q 32 q 33 ] \left[ Q_{\mathrm{B}}^{A} \right] =\left[ \begin{matrix} q_{11}& q_{12}& q_{13}\\ q_{21}& q_{22}& q_{23}\\ q_{31}& q_{32}& q_{33}\\ \end{matrix} \right] [QBA]= q11q21q31q12q22q32q13q23q33 ,可计算出其轴角参数:
θ = a r c cos ( q 11 + q 22 + q 33 − 1 2 ) v ⃗ F = 1 2 sin θ [ q 32 − q 23 q 13 − q 31 q 21 − q 12 ] \begin{split} \theta &=\mathrm{arc}\cos \left( \frac{q_{11}+q_{22}+q_{33}-1}{2} \right) \\ \vec{v}^F&=\frac{1}{2\sin \theta}\left[ \begin{array}{c} q_{32}-q_{23}\\ q_{13}-q_{31}\\ q_{21}-q_{12}\\ \end{array} \right] \end{split} θv F=arccos(2q11+q22+q33−1)=2sinθ1 q32−q23q13−q31q21−q12
3.2 罗德里格变换Rodrigues’ Transform
结合上节所述内容,定义罗德里格参数Rodriguez Paremeters
为:
γ ⃗ F = v ⃗ F tan θ 2 = [ v 1 F v 2 F v 3 F ] tan θ 2 = [ γ 1 F γ 2 F γ 3 F ] \vec{\gamma}^F=\vec{v}^F\tan \frac{\theta}{2}=\left[ \begin{array}{c} v_{1}^{F}\\ v_{2}^{F}\\ v_{3}^{F}\\ \end{array} \right] \tan \frac{\theta}{2}=\left[ \begin{array}{c} \gamma _{1}^{F}\\ \gamma _{2}^{F}\\ \gamma _{3}^{F}\\ \end{array} \right] γ F=v Ftan2θ= v1Fv2Fv3F tan2θ= γ1Fγ2Fγ3F
进而将罗德里格旋转公式改写为:
[ Q M F ] = E + 2 1 + ( γ ) 2 ( γ ⃗ ~ F + ( γ ⃗ ~ F ) 2 ) , γ = ( γ ⃗ ~ F ) T γ ⃗ ~ F = tan 2 θ 2 \left[ Q_{\mathrm{M}}^{F} \right] =E+\frac{2}{1+\left( \gamma \right) ^2}\left( \tilde{\vec{\gamma}}^F+\left( \tilde{\vec{\gamma}}^F \right) ^2 \right) ,\gamma =\left( \tilde{\vec{\gamma}}^F \right) ^{\mathrm{T}}\tilde{\vec{\gamma}}^F=\tan ^2\frac{\theta}{2} [QMF]=E+1+(γ)22(γ ~F+(γ ~F)2),γ=(γ ~F)Tγ ~F=tan22θ
而罗德里格变换的旋转矩阵 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]为:
[ Q B A ] = [ 1 + ( γ 1 F ) 2 − ( γ 2 F ) 2 − ( γ 3 F ) 2 2 ( γ 1 F γ 2 F − γ 3 F ) 2 ( γ 1 F γ 3 F + γ 2 F ) 2 ( γ 1 F γ 2 F + γ 3 F ) 1 − ( γ 1 F ) 2 + ( γ 2 F ) 2 − ( γ 3 F ) 2 2 ( γ 2 F γ 3 F − γ 1 F ) 2 ( γ 1 F γ 3 F − γ 2 F ) 2 ( γ 2 F γ 3 F + γ 1 F ) 1 − ( γ 1 F ) 2 − ( γ 2 F ) 2 + ( γ 3 F ) 2 ] \left[ Q_{\mathrm{B}}^{A} \right] =\left[ \begin{matrix} 1+\left( \gamma _{1}^{F} \right) ^2-\left( \gamma _{2}^{F} \right) ^2-\left( \gamma _{3}^{F} \right) ^2& 2\left( \gamma _{1}^{F}\gamma _{2}^{F}-\gamma _{3}^{F} \right)& 2\left( \gamma _{1}^{F}\gamma _{3}^{F}+\gamma _{2}^{F} \right)\\ 2\left( \gamma _{1}^{F}\gamma _{2}^{F}+\gamma _{3}^{F} \right)& 1-\left( \gamma _{1}^{F} \right) ^2+\left( \gamma _{2}^{F} \right) ^2-\left( \gamma _{3}^{F} \right) ^2& 2\left( \gamma _{2}^{F}\gamma _{3}^{F}-\gamma _{1}^{F} \right)\\ 2\left( \gamma _{1}^{F}\gamma _{3}^{F}-\gamma _{2}^{F} \right)& 2\left( \gamma _{2}^{F}\gamma _{3}^{F}+\gamma _{1}^{F} \right)& 1-\left( \gamma _{1}^{F} \right) ^2-\left( \gamma _{2}^{F} \right) ^2+\left( \gamma _{3}^{F} \right) ^2\\ \end{matrix} \right] [QBA]= 1+(γ1F)2−(γ2F)2−(γ3F)22(γ1Fγ2F+γ3F)2(γ1Fγ3F−γ2F)2(γ1Fγ2F−γ3F)1−(γ1F)2+(γ2F)2−(γ3F)22(γ2Fγ3F+γ1F)2(γ1Fγ3F+γ2F)2(γ2Fγ3F−γ1F)1−(γ1F)2−(γ2F)2+(γ3F)2
- 罗德里格参数与欧拉参数的转换
[ γ 1 F γ 2 F γ 3 F ] = [ q 2 q 1 q 3 q 1 q 4 q 1 ] \left[ \begin{array}{c} {\gamma _1}^F\\ {\gamma _2}^F\\ {\gamma _3}^F\\ \end{array} \right] =\left[ \begin{array}{c} \frac{q_2}{q_1}\\ \frac{q_3}{q_1}\\ \frac{q_4}{q_1}\\ \end{array} \right] γ1Fγ2Fγ3F = q1q2q1q3q1q4
[ q 1 q 2 q 3 q 4 ] = [ 1 1 + γ 2 γ 1 F 1 + γ 2 γ 2 F 1 + γ 2 γ 3 F 1 + γ 2 ] \left[ \begin{array}{c} q_1\\ q_2\\ q_3\\ q_4\\ \end{array} \right] =\left[ \begin{array}{c} \frac{1}{\sqrt{1+\gamma ^2}}\\ \frac{{\gamma _1}^F}{\sqrt{1+\gamma ^2}}\\ \frac{{\gamma _2}^F}{\sqrt{1+\gamma ^2}}\\ \frac{{\gamma _3}^F}{\sqrt{1+\gamma ^2}}\\ \end{array} \right] q1q2q3q4 = 1+γ2 11+γ2 γ1F1+γ2 γ2F1+γ2 γ3F
3.3 方向余弦变换
由上节可知,转换矩阵 [ Q B A ] \left[ Q_{\mathrm{B}}^{A} \right] [QBA]表示坐标系 { B } \left\{ B \right\} {B}中的基矢量在坐标系 { A } \left\{ A \right\} {A}中的表达,即:
[ i ⃗ B j ⃗ B k ⃗ B ] = [ Q B A ] T [ i ⃗ A j ⃗ A k ⃗ A ] = [ q 11 q 12 q 13 q 21 q 22 q 23 q 31 q 32 q 33 ] T [ i ⃗ A j ⃗ A k ⃗ A ] \left[ \begin{array}{c} \vec{i}^B\\ \vec{j}^B\\ \vec{k}^B\\ \end{array} \right] =\left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] =\left[ \begin{matrix} q_{11}& q_{12}& q_{13}\\ q_{21}& q_{22}& q_{23}\\ q_{31}& q_{32}& q_{33}\\ \end{matrix} \right] ^{\mathrm{T}}\left[ \begin{array}{c} \vec{i}^A\\ \vec{j}^A\\ \vec{k}^A\\ \end{array} \right] i Bj Bk B =[QBA]T i Aj Ak A = q11q21q31q12q22q32q13q23q33 T i Aj Ak A
进而将转换矩阵内的元素展开:
[ Q B A ] T = [ i ⃗ A ⋅ i ⃗ B j ⃗ A ⋅ i ⃗ B k ⃗ A ⋅ i ⃗ B i ⃗ A ⋅ j ⃗ B j ⃗ A ⋅ j ⃗ B k ⃗ A ⋅ j ⃗ B i ⃗ A ⋅ k ⃗ B j ⃗ A ⋅ k ⃗ B k ⃗ A ⋅ k ⃗ B ] \left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}=\left[ \begin{matrix} \vec{i}^A\cdot \vec{i}^B& \vec{j}^A\cdot \vec{i}^B& \vec{k}^A\cdot \vec{i}^B\\ \vec{i}^A\cdot \vec{j}^B& \vec{j}^A\cdot \vec{j}^B& \vec{k}^A\cdot \vec{j}^B\\ \vec{i}^A\cdot \vec{k}^B& \vec{j}^A\cdot \vec{k}^B& \vec{k}^A\cdot \vec{k}^B\\ \end{matrix} \right] [QBA]T= i A⋅i Bi A⋅j Bi A⋅k Bj A⋅i Bj A⋅j Bj A⋅k Bk A⋅i Bk A⋅j Bk A⋅k B
进一步观察,可以将该矩阵转化为:
[ Q B A ] T = [ i ⃗ A ⋅ i ⃗ B j ⃗ A ⋅ i ⃗ B k ⃗ A ⋅ i ⃗ B i ⃗ A ⋅ j ⃗ B j ⃗ A ⋅ j ⃗ B k ⃗ A ⋅ j ⃗ B i ⃗ A ⋅ k ⃗ B j ⃗ A ⋅ k ⃗ B k ⃗ A ⋅ k ⃗ B ] = [ Q B i A Q B j A Q B k A ] = [ Q A i B Q A j B Q A k B ] \left[ Q_{\mathrm{B}}^{A} \right] ^{\mathrm{T}}=\left[ \begin{matrix} \vec{i}^A\cdot \vec{i}^B& \vec{j}^A\cdot \vec{i}^B& \vec{k}^A\cdot \vec{i}^B\\ \vec{i}^A\cdot \vec{j}^B& \vec{j}^A\cdot \vec{j}^B& \vec{k}^A\cdot \vec{j}^B\\ \vec{i}^A\cdot \vec{k}^B& \vec{j}^A\cdot \vec{k}^B& \vec{k}^A\cdot \vec{k}^B\\ \end{matrix} \right] =\left[ \begin{matrix} Q_{\mathrm{Bi}}^{A}& Q_{\mathrm{Bj}}^{A}& Q_{\mathrm{Bk}}^{A}\\ \end{matrix} \right] =\left[ \begin{array}{c} Q_{\mathrm{Ai}}^{B}\\ Q_{\mathrm{Aj}}^{B}\\ Q_{\mathrm{Ak}}^{B}\\ \end{array} \right] [QBA]T= i A⋅i Bi A⋅j Bi A⋅k Bj A⋅i Bj A⋅j Bj A⋅k Bk A⋅i Bk A⋅j Bk A⋅k B =[QBiAQBjAQBkA]= QAiBQAjBQAkB
其中, [ Q B i A Q B j A Q B k A ] \left[ \begin{matrix} Q_{\mathrm{Bi}}^{A}& Q_{\mathrm{Bj}}^{A}& Q_{\mathrm{Bk}}^{A}\\ \end{matrix} \right] [QBiAQBjAQBkA]中,每一项表示坐标系 { B } \left\{ B \right\} {B}中的基矢量在坐标系 { A } \left\{ A \right\} {A}下的表达,而 [ Q A i B Q A j B Q A k B ] . \left[ \begin{array}{c} Q_{\mathrm{Ai}}^{B}\\ Q_{\mathrm{Aj}}^{B}\\ Q_{\mathrm{Ak}}^{B}\\ \end{array} \right] . QAiBQAjBQAkB .中,每一项表示坐标系 { A } \left\{ A \right\} {A}中的基矢量在坐标系 { B } \left\{ B \right\} {B}下的表达。因此该形式的矩阵被称为方向余弦矩阵Direction Cosine Matrix
。
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