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Capability calculations for True Position

VinniUSMC
Has anyone come across this as a means of calculating Cpk of a true position?

http://documentation.statsoft.com/ST...tionCapability

I think it should be possible, but I'm not sure if this is the answer or not. I was thinking about how something along the lines of the complex plane (or vectors/trig) could be used to identify grouping of a positional tolerance based on its quadrant within a unit circle, and then could be used to calculate Cpk. It's not unheard of. The normal distribution of a multivariate system is calculable, so why wouldn't a statistic that is related to the normal distribution in 1 variable work for higher dimensions?

I'm thinking that there must be a way to calculate the variance of position based on the the quadrant it falls in. Whether it's a trigonometric function, or a complex function.

Anyone have any input as I dive into this blackhole?

Curiosity killed the cat, hopefully I'm not a cat.

Parents
  • The points where the relevant plane intersects the tolerance circle are determined. This means that the distance from the tolerance circle to point of balance can be calculated, in two directions. By dividing these distances by three standard deviations, two Cpk values are obtained.

    Those distances are calculated in V14 and V16, and assigned as dist1 and dist2, then divided for each angle by 3 std dev. It gives cpk1 and cpk2.

    By means of the calculated standard deviation and the distance between the two points of intersection, which makes up the tolerance zone in the relevant direction, Cp can be calculated for the orientation given by the plane in question.
    dist is the sum of abs(dist1) and abs(dist2). (T20)
    Idivided it by 3 std dev, but it's not explained in the text, maybe t should be std dev ?
    I don't know, I just try to help without really understanding Disappointed... I'm french !
  • in reply to JEFMAN
    1-(page 26) All measured locations are projected in the constructed plane.
    2-(page 28)By iteratively rotating the constructed plane through the point of balance in different directions, repeating the
    projection of the points in the different directions and repeating the evaluation of Cp and Cpk in each iteration, the
    orientation for the largest dispersion of the amount of points can be produced as a basis for Cp and the orientation
    where the tolerance violation is at its greatest as a basis for Cpk.

    I agree about cp, because the calculation is not described, but cpk1 and cpk2 match to the description.
    Not sure how calculate cpk from them, I understand it's the min...

    to the rescue Wink
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  • in reply to JEFMAN
    1-(page 26) All measured locations are projected in the constructed plane.
    2-(page 28)By iteratively rotating the constructed plane through the point of balance in different directions, repeating the
    projection of the points in the different directions and repeating the evaluation of Cp and Cpk in each iteration, the
    orientation for the largest dispersion of the amount of points can be produced as a basis for Cp and the orientation
    where the tolerance violation is at its greatest as a basis for Cpk.

    I agree about cp, because the calculation is not described, but cpk1 and cpk2 match to the description.
    Not sure how calculate cpk from them, I understand it's the min...

    to the rescue Wink
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