Point Target Radius Vs. Fixture Tolerance

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  • Point Target Radius Vs. Fixture Tolerance

    We have been using Point Target Radius in our iteritve alingment and I was wondering what should be used Point Target Radius and\or Fixture Tolerance. We set Point Target Radius at .0025 but have not used Fixture Tolerance set at all most of the time we use a 4 point plane and then 2 points for the offset and 1 point to stop the other axis. Another programer uses 3 point plane 2 point offset and 1 point stop axis but uses Fixture Tolerance set at .001. I thought you only used that if you use more then your 3 2 1 alighnment. Could someone tell me what way is better for a closer fit to the model. Thanks

  • #2
    I got this e-mail from hexagon if anyone else wants to know the answer I thought I would share what they sent to me. Thanks

    A solution for your issue has been suggested.

    The Point Target Radius is a lateral zone around the feature nominal location and is used to force a remeasure if the current measured coordinates are not within this zone as evaluated by the alignment solution for the current iteration. The fitting is done along the nominal vector, also relative to the current alignment solution, so the point target radius does not factor into the alignment solution. It does control the remeasure, so it has impact on the feature/coordinates input into to the solver.

    The Fixture tolerance also does not impact the convergence of the alignment solution. It is used to report the final result and to implement branching to a label when value is exceeded.

    HELP FILE content.

    Point Target Radius
    While you can easily see the location needed to measure a circle on a part, determining the exact location to measure a point on the surface isn't easily done. Without any visual indicators telling you where to measure the point, it is difficult to manually measure the point in an exact spot. The Point Target Radius specifies an imaginary tolerance zone (or target) the size of the radius, around each point. This allows you to take a manual hit anywhere within the indicated tolerance. If the measured point does not fall within this zone, PC-DMIS re-measures the point in DCC mode.

    Fixture Tolerance
    The Fixture Tolerance box allows you to type a fitting tolerance value against which PC-DMIS compares feature elements making up the iterative alignment to their theoretical values.
    If after fitting the measurement values to the theoretical values, one or more of the input features have an error along their assigned datum axis that exceeds this tolerance value, PC-DMIS automatically goes to the error label (if one exists). See "Error Label".
    If you don't provide an error label, PC-DMIS displays an error message showing the errors along each of the datums. You will have the choice to accept the datum as it is and continue with the rest of the part program, or to cancel the part program execution.
    PC-DMIS can only use the fixture tolerance value if you used more than the minimum number of points needed to create the feature. For example, if you are measuring a plane, the minimum number of points needed for that plane is usually three points. However, if you wanted to use the fixture tolerance value, you would need to measure at least four points. If you use only three points then only one solution exists and PC-DMIS cannot adjust or re-iterate.


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