and  plays a role in collision avoidance. To determine the

order of measuring points is to minimize the measuring time. Generally, the number of guide points is 2 or  3. The reason is to minimize the inspection error and to move the probe for normal direction. For the collision of probe, to use the three guide points is lucrative, but for the measuring time, to use the two guide points is favorable. In this study, the entering direction of probe is decided by two guide points. (Fig.9(a)) There  are external guide points(Pi) and internal guide points(Pt).

Pti (x, y, z) Pi   g Ni (x, y, z)

Pii (x, y, z) Pi   g Ni (x, y, z)

exist in characteristic of touch-type inspection equipment, the feature may be not separated into the surface information. There is not easy to cope with this situation.

In   the  above,

g  represents   the   distance   from the

Therefore,  in  this  research,  the  inspection  feature    is

measuring point to the guide point. The measuring order of inspection points is applied to TSP-algorithm to decrease the total measuring time. (Fig.9(b)) Eq.(3) shows the objective function.

n

E  (3)

i1

(n: Number of measuring points)

Where n is the total number of measuring points, (xi, yi, zi) is the coordinate of measuring point and E is the total moving distance of probe. If the sequence of measuring points is determined for minimizing E, the probe path is determined accordingly.

assorted   and   organized   as   in   Fig.10.   At   first,  the

inspection object is pided into analytic geometries and free-form geometries. The analytic geometries are separated no more and left the single surface. In other words, the general characteristic feature could be constituted by several single inspection features and classified. In occasion of inspecting the single surface, it is gotten the result of inspection corresponding to six geometric tolerances. In case of inspecting two or more single geometry which is integrated geometries, it is gotten the result of inspection corresponding to four geometric tolerances related to each other.

Single Geometry

Integrated Geometry

Pt1

Fig.9 The probe path determination ( (a) Probe path using two guide points, (b) Measuring sequence by minimum distance calculation)

4. Inspection Feature

4.1 The classification of inspection feature

Generally, the geometric information of CAD or the characteristic feature which is possible to be pided in manufacturing step is used as the inspection feature.[11][12][13] When the inspection is executed using touch-type inspection equipment such as CMM or OMM , the inspection method by feature-unit has not proposed yet except the method of position error discrimination to measure the classified feature by points-unit.  Although the inspection object has the single feature of CAD/CAM, the inspection feature is separated into the surface information for measuring in more detail. Because the

direction or range which is impossible to measure   could

Fig.10 Geometric feature classification for inspection

4.2 OMM using inspection features

It is decided the workpiece to represent the process of determination measuring points by the  classification of feature in Automatic Mode and it agrees with the object to perform the inspection in experiment. Fig.11 shows the result of feature classification for  workpiece. In STEP 1, there are separated features by the classification for machining feature. In other words, there are structured the characteristic features as Island 1(F1), Pocket 1(F2) and Slot 1(F3). In STEP 2, the object is pided into the inspection feature again. S1~S5 are determined by the approaching direction of probe and there are features which are not made by the method of machining feature classification but they exist surely in the object after machining. These features are needed certainly when the inspection is performed. Fig.12 shows the inspection feature by the method of inspection feature