The Mode list in the Advanced Measurement Options area determines how PC-DMIS computes the nominals for a given point. PC-DMIS allows you to choose between FIND NOMS, MASTER, NOMINALS, VECTOR, and SET NOM AX.
If MODE = FIND NOMS is active, PC-DMIS pierces the CAD model to find the closest location on a CAD edge (or surface) to the measured point and sets the nominals to that location on the CAD element.
If MODE = MASTER is active, PC-DMIS uses the measured feature as the nominal, but PC-DMIS does not update the X, Y, Z and diameter data in the dialog box.
If MODE = NOMINALS is active, PC-DMIS compares the measured feature with the theoretical data in the dialog box. It uses the measured data for calculations.
If MODE = VECTOR is active, PC-DMIS uses your first three hits to calculate the appropriate vector to use for the feature. PC-DMIS does not adjust the location of the feature. You must take the hits with the Auto Features dialog box active.
If MODE = SET NOM AX, PC-DMIS updates the nominal point location and the nominal approach direction before each execution.
For each mode, see the more detailed description in the table below if you need more information.
If a nominal value is not known, simply select FIND NOMS from the list. While this option is active, every time a value is selected to be changed, PC-DMIS prompts you to take the appropriate measurements on the part to obtain the values needed.
FIND NOMS
When you select FIND NOMS from the Mode
list, PC-DMIS pierces the CAD model to find the closest location on a
CAD edge (or surface) to the measured point, and sets the nominals to
that location on the CAD element.
To find the nominals using CAD data:
Verify that PC-DMIS is set to Curve mode or Surface mode (available from the Graphic Modes toolbar), as is appropriate for the particular measurement routine.
Click on the desired CAD element in the Graphic Display window. PC-DMIS will pierce the CAD element to obtain the location, but will not create a feature. Once the desired elements have been selected, PC-DMIS automatically fills in the X, Y, Z and I, J, K values.
If the values are satisfactory, select the Create command button.
If you select the Measure check box, PC-DMIS measures the feature during creation. If you have not added clearance moves, this may cause a probe collision with the part.
If a hit is taken on the part while in FIND NOMS mode, PC-DMIS searches through the CAD elements and finds the nominal CAD information that is closest to the measured point. If necessary, PC-DMIS prompts you to take any additional hits on the part.
The next time the part is measured, PC-DMIS sets the nominal data to the nearest CAD element it can find. The mode switch is then reset to NOMINALS.
Using Find Noms with Fixed Probes
A Faro or Romer arm using a fixed probe doesn't generate good approach vectors. Because of this, PC-DMIS cannot easily determine where to look for the surfaces.
To improve vectors from fixed probes:
Place the fixed probe on the part.
Press the Hit button.
Move the probe away from the part along the approximate surface vector.
Press the End button.
PC-DMIS calculates and then uses the vector between the hit and the probe tip's position.
Also, because the default vector from a Faro arm uses the axis of the fixed probe, the more you position the vector normal to the surface, the more useful the vector is for Find Noms operations.
MASTER
If a point is created when the Mode list is set
to MASTER, then the next time the part is measured,
PC-DMIS sets the nominal data equal to the measured data. The Mode
list is then reset to NOMINALS.
NOMINALS
The NOMINALS option also requires to have nominal
data before the measurement process begins. PC-DMIS compares the measured
feature with the theoretical data in the dialog box. It uses the measured
feature for any necessary calculations.
VECTOR
The VECTOR option allows you to update only the
feature's vector during learn mode; it does not update the nominal XYZ
values.
This option is only available for the Vector Point and Surface Point Auto features.
This option helps you to set a feature's vector that you may not be able to obtain otherwise. With the dialog box open, take three hits on the feature. This determines its vector.
You can use this mode as long as the dialog box remains open. Once you close the dialog box, the option is not available for the feature in the Edit window.
Supported Features: Vector Point, Surface Point, Corner Point, Line, Plane, Circle, Ellipse, Round Slot, Square Slot, Notch Slot, Polygon, Cylinder, Cone, Sphere
SET NOM AX
The SET NOM AX option updates (or "sets")
the nominal point location and the nominal approach direction before each
execution. If you select an axis check box from the Location
area, the CAD surfaces will be pierced along that axis. Otherwise, the
update vector will be used.
This option is only available for the Vector Point and Surface Point Auto features.
The axis (or vector) selected tells PC-DMIS along which axis (or vector) the CAD surface will be pierced to find a new theo and target.
To select the SET NOM AX option:
Make sure the Show Extended Sheet Metal Option check box is selected. See "Show Extended Sheet Metal Options" in the "Setting Your Preferences" chapter.
If desired, select one of the axis check boxes from the Location area.
Click SET NOM AX from the Mode list in the dialog box.
When you are done defining the rest of the Auto feature, click the Create button. The FIND NOM AXIS is then set to either the axis or the vector selected.
The Edit window for option this reads: FIND NOM AXIS = TOG
TOG represents the axis or vector to which FIND NOM AXIS is set. Available options for TOG include XAXIS, YAXIS, ZAXIS, VEC and NONE.
If you don't select any axis, then the result reads FIND NOM AXIS = VEC by default.