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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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FIGURE 4.4 Rough phase alignment based on 6 points probing.<br />

When the base vectors of the CMM coordinate axis are known, the probing point data, A1 to A6, can<br />

be transformed to the contact point data, to , considering the probe ball radius as<br />

A� 1<br />

A� 6<br />

A1� � A1 � r( az, bz, cz) A2� � A2 � r( az, bz, cz) A3� � A3 � r( az, bz, cz) A4� � A4 � r( ay, by, cy) A5� � A5 � r( ay, by, cy) A6� � A6 � r( ax, bx, cx) (4.15)<br />

where r is the effective radius of the probe ball.<br />

In order to complete the rough phase coordinate alignment, the origin of the CAD coordinate system<br />

with respect to the CMM coordinate system is also required. The origin, O�( O�x , O�y , O�z ) of the CAD<br />

coordinate system can be evaluated by observing that O�A� 1, O�A� 4, and O�A� 6 vectors are perpendicular<br />

to the Z�, Y�, and X� axes, respectively. Thus,<br />

O�A 1� • Z� � ( A1�� O�)<br />

• ( az, bz, cz) � 0<br />

O�A 4� • Y� � ( A4�� O�)<br />

• ( ay, by, cy) � 0<br />

O�A 6� • X� � ( A6�� O�)<br />

• ( ax, bx, cx) � 0<br />

(4.16)<br />

where A1� to A6� are the coordinates of the contact points around the reference block. Thus the origin<br />

point O�( O�x , O�y , O�z ) of the CAD coordinate system can be obtained from Equation 4.16.<br />

The relationship is therefore established between the CMM coordinate and the CAD coordinate and<br />

can be expressed using the transformation matrix T1 such that M � T1D is satisfied. In the matrix

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