Skip to contents

Process capability indices (parametric)

Source: R/qcs.cp.r
qcs.cp.Rd

Calculates \(Cp\), \(Cpm\) using the formulation described by Kerstin Vannman(1995).

Usage

qcs.cp(
  object,
  parameters = c(u = 0, v = 0),
  limits = c(lsl = -3, usl = 3),
  target = NULL,
  mu = 0,
  std.dev = 1,
  nsigmas = 3,
  k = 1,
  contour = TRUE,
  ylim = NULL,
  ...
)

Arguments

object

qcs object of type "qcs.xbar" or "qcs.one".

parameters

A vector specifying the u and v parameters values. If parameters = c(u=0, v=0), the Cp indice is calculed; If parameters = c(u=1, v=0), the Cpk indice is calculed; If parameters = c(u=0, v=1), the Cpm indice is calculed; If parameters = c(u=1, v=1), the Cpmk indice is calculed.

limits

A vector specifying the lower and upper specification limits.

target

A value specifying the target of the process. If it is NULL, the target is set at the middle value between specification limits.

mu

A value specifying the mean of data.

std.dev

A value specifying the within-group standard deviation.

nsigmas

A numeric value specifying the number of sigmas to use.

k

A numeric value. If the capacity index exceeds the k value, then the process is capable.

contour

Logical value indicating whether contour graph should be plotted.

ylim

The 'y' limits of the plot.

...

Arguments to be passed to or from methods.

References

Montgomery, D.C. (1991) Introduction to Statistical Quality Control, 2nd ed, New York, John Wiley & Sons.
Vannman, K (1995) A Unified Approach to Capability Indices. Statitica Sinica,5,805-820.

Examples

library(qcr)
data(pistonrings) 
xbar <- qcs.xbar(pistonrings[1:125,],plot = TRUE)

mu <-xbar$center
std.dev <-xbar$std.dev
LSL=73.99; USL=74.01
qcs.cp(parameters = c(0,0),limits = c(LSL,USL),
      mu = mu,std.dev = std.dev,ylim=c(0,1))
#>     Cp  delta  gamma 
#> 0.3407 0.1176 0.9785 
#calculating all the indices
qcs.cp(object = xbar,parameters = c(0,0), limits = c(LSL,USL),ylim=c(0,1))

#>     Cp  delta  gamma 
#> 0.3407 0.1176 0.9785 
qcs.cp(object = xbar,parameters = c(1,0), limits = c(LSL,USL),ylim=c(0,1))

#>    Cpk  delta  gamma 
#> 0.3006 0.1176 0.9785 
qcs.cp(object = xbar,parameters = c(0,1), limits = c(LSL,USL),ylim=c(0,1))

#>    Cpm  delta  gamma 
#> 0.3382 0.1176 0.9785 
qcs.cp(object = xbar,parameters = c(1,1), limits = c(LSL,USL),ylim=c(0,1))

#>   Cpmk  delta  gamma 
#> 0.2984 0.1176 0.9785