六点定位--坐标系的基础理论
六点定位原理概念：
一个自由的物体，它对三个相互垂直的坐标系来说，有六个活动可能性，其中三种是移动，三种是转动。习惯上把这种活动的可能性称为自由度，因此空间任一自由物体共有六个自由度。
在空间直角坐标系中，刚体具有六个自由度，即沿X、Y、Z轴移动的三个自由度和绕此三轴旋转的三个自由度。拥六个合理分布的支承点限制工件的六个自由度，使工件在夹具中占据正确的位置，称为六点定位法则。
采用六个按一定规则布置的支承点，限制工件的六个自由度，使工件在机床或夹具中占有正确的位置。
未受约束的刚体，在空间的位置是不确定的，它具有六个自由度：绕X轴、Y轴、Z轴方向的3个转动自由度和沿X轴、Y轴、Z轴的三个平动自由度 。为使刚体在空间具有确定的位置，就必须限制其六个自由度。
定位就是用各种形状不同的定位元件，来限制工件的自由度。
关于“六点定位”的几个问题：
（1）定位限制自由度，几“点”定位不能机械地理解成几个接触点；
（2）限制自由度应理解为：
定位支承点与工件定位基准面始终保持紧贴接触;
（3）定位支承点数目原则上不应超过工件自由度数目；
（4）自由度被限制，是指工件在此方向上有确定的位置:
不考虑外力的影响（注：定位和夹紧的区别）;
（5）定位支承点是抽象的，通过具体定位元件来体现。
（6）工件应限制几个自由度，由工件加工技术条件来确定。
六点定位原理举例
3.在XOY平面内布置了3个支承点，工件被限制的自由度为三个：约束了两个旋转自由度（绕X，Y轴旋转）和一个平动自由度（沿Z轴移动）.
2.在XOZ平面内布置了2个支承点，工件被限制的自由度为二个： Z轴旋转和Y轴平移。
1.在YOZ平面内布置了1个支承点，工件被限制的自由度为一个：X轴平移。
此时，六个自由度完全锁定。
RE:
基准：零件上用以确定其它点、线、面位置所依据的那些点、线、面。
设计基准：零件图上用以确定点、线、面位置的基准。
定位基准：零件加工、测量和装配过程中使用的基准。分为工序基准、定位基准、度量基准和装配基准。
几点注意：
(1)作为基准的点、线、面在工件上不一定存在，而常常由基准面来体现；
(2)基准可以是没有面积的点或线，但基准面一定是有面积的；
(3)基准包含尺寸之间的联系和位置之间的关系（如平行度、垂直度等）。
RationalDMIS测量软件六点定位详解：
DMISMN/'Created by [深圳力合精密装备科技有限公司-090118] on 星期二, 七月 10, 2018', 4.0
UNITS/MM, ANGDEC, MMPS
WKPLAN/XYPLAN
PRCOMP/ON
TECOMP/ON
FLY/1.000000
MODE/PROG, MAN
SNSET/APPRCH, 2.000000
SNSET/RETRCT, 2.000000
SNSET/DEPTH, 0.000000
SNSET/SEARCH, 10.000000
SNSET/CLRSRF, 50.000000
RECALL/D(MCS)
SNSLCT/S(ROOTSN1)
GEOALG/BF, LSTSQR
GEOALG/ANGLB, DEFALT
GEOALG/CIRCLE, LSTSQR
GEOALG/ARC, LSTSQR
GEOALG/PLANE, LSTSQR
$$
$$
MODE/MAN
F(PT1)=FEAT/POINT,CART,8.326538,75.352898,35.000000,0.000000,0.000000,1.000000
$$ Empty Meas Block
MEAS/POINT, F(PT1), 1
ENDMES
F(PT2)=FEAT/POINT,CART,7.381094,27.180397,35.000000,0.000000,0.000000,1.000000
$$ Empty Meas Block
MEAS/POINT, F(PT2), 1
ENDMES
F(PT3)=FEAT/POINT,CART,89.036491,28.313187,35.000000,0.000000,0.000000,1.000000
$$ Empty Meas Block
MEAS/POINT, F(PT3), 1
ENDMES
F(PT4)=FEAT/POINT,CART,8.672945,0.000000,14.855032,-0.000000,-1.000000,-0.000000
$$ Empty Meas Block
MEAS/POINT, F(PT4), 1
ENDMES
F(PT5)=FEAT/POINT,CART,63.419529,0.000000,14.033564,-0.000000,-1.000000,-0.000000
$$ Empty Meas Block
MEAS/POINT, F(PT5), 1
ENDMES
F(PT6)=FEAT/POINT,CART,0.000000,25.224169,29.234194,-1.000000,0.000000,0.000000
$$ Empty Meas Block
MEAS/POINT, F(PT6), 1
ENDMES
F(PT1)=FEAT/POINT,CART,8.326538,75.352898,35.000000,0.000000,0.000000,1.000000
F(PT2)=FEAT/POINT,CART,7.381094,27.180397,35.000000,0.000000,0.000000,1.000000
F(PT3)=FEAT/POINT,CART,89.036491,28.313187,35.000000,0.000000,0.000000,1.000000
F(PT4)=FEAT/POINT,CART,8.672945,0.000000,14.855032,-0.000000,-1.000000,-0.000000
F(PT5)=FEAT/POINT,CART,63.419529,0.000000,14.033564,-0.000000,-1.000000,-0.000000
F(PT6)=FEAT/POINT,CART,0.000000,25.224169,29.234194,-1.000000,0.000000,0.000000
D(CRD1) = LOCATE/FA(PT1), FA(PT2), FA(PT3), FA(PT4), FA(PT5), FA(PT6)
$$ coordinate system Iteration
$$
$$
(ITR_START)
MEAS/POINT, F(PT1), 1
PTMEAS/CART, 8.326538,75.352898,35.000000,0.000000,0.000000,1.000000
ENDMES
MEAS/POINT, F(PT2), 1
PTMEAS/CART, 7.381094,27.180397,35.000000,0.000000,0.000000,1.000000
ENDMES
MEAS/POINT, F(PT3), 1
PTMEAS/CART, 89.036491,28.313187,35.000000,0.000000,0.000000,1.000000
ENDMES
MEAS/POINT, F(PT4), 1
PTMEAS/CART, 8.672945,0.000000,14.855032,-0.000000,-1.000000,-0.000000
ENDMES
MEAS/POINT, F(PT5), 1
PTMEAS/CART, 63.419529,0.000000,14.033564,-0.000000,-1.000000,-0.000000
ENDMES
MEAS/POINT, F(PT6), 1
PTMEAS/CART, 0.000000,25.224169,29.234194,-1.000000,0.000000,0.000000
ENDMES
F(PT1)=FEAT/POINT,CART,8.326538,75.352898,35.000000,0.000000,0.000000,1.000000
F(PT2)=FEAT/POINT,CART,7.381094,27.180397,35.000000,0.000000,0.000000,1.000000
F(PT3)=FEAT/POINT,CART,89.036491,28.313187,35.000000,0.000000,0.000000,1.000000
F(PT4)=FEAT/POINT,CART,8.672945,0.000000,14.855032,-0.000000,-1.000000,-0.000000
F(PT5)=FEAT/POINT,CART,63.419529,0.000000,14.033564,-0.000000,-1.000000,-0.000000
F(PT6)=FEAT/POINT,CART,0.000000,25.224169,29.234194,-1.000000,0.000000,0.000000
D(CRD1) = LOCATE/FA(PT1), FA(PT2), FA(PT3), FA(PT4), FA(PT5), FA(PT6)
KNPTR1 = ITERAT/(ITR_START), (ITR_FAIL), 0.010000, ABSL, 10,$
FA(PT1), ZAXIS,$
FA(PT2), ZAXIS,$
FA(PT3), ZAXIS,$
FA(PT4), YAXIS,$
FA(PT5), YAXIS,$
FA(PT6), XAXIS
(ITR_FAIL)
