Process Capability
Janpu Hou
September 12, 2017
Process Capability
Computes process capability indices for a `qcc’ object of type “xbar” and plot the histogram.
Using xbar Chart for Center and StdDev
library(qcc)## Package 'qcc' version 2.7## Type 'citation("qcc")' for citing this R package in publications.data(pistonrings)
attach(pistonrings)
head(pistonrings)## diameter sample trial
## 1 74.030 1 TRUE
## 2 74.002 1 TRUE
## 3 74.019 1 TRUE
## 4 73.992 1 TRUE
## 5 74.008 1 TRUE
## 6 73.995 2 TRUEdiameter <- qcc.groups(diameter, sample)
q <- qcc(diameter[1:25,], type="xbar", nsigmas=3, plot=TRUE)
Cp = 1.7, Cpk = 1.66
process.capability(q, spec.limits=c(73.95,74.05))
##
## Process Capability Analysis
##
## Call:
## process.capability(object = q, spec.limits = c(73.95, 74.05))
##
## Number of obs = 125 Target = 74
## Center = 74 LSL = 73.95
## StdDev = 0.009785 USL = 74.05
##
## Capability indices:
##
## Value 2.5% 97.5%
## Cp 1.703 1.491 1.915
## Cp_l 1.743 1.555 1.932
## Cp_u 1.663 1.483 1.844
## Cp_k 1.663 1.448 1.878
## Cpm 1.691 1.480 1.902
##
## Exp<LSL 0% Obs<LSL 0%
## Exp>USL 0% Obs>USL 0%Cp = 1.7, Cpk = 1.66
process.capability(q, spec.limits=c(73.95,74.05), target=74.02)
##
## Process Capability Analysis
##
## Call:
## process.capability(object = q, spec.limits = c(73.95, 74.05), target = 74.02)
##
## Number of obs = 125 Target = 74.02
## Center = 74 LSL = 73.95
## StdDev = 0.009785 USL = 74.05
##
## Capability indices:
##
## Value 2.5% 97.5%
## Cp 1.7033 1.4914 1.9148
## Cp_l 1.7433 1.5548 1.9319
## Cp_u 1.6632 1.4827 1.8437
## Cp_k 1.6632 1.4481 1.8783
## Cpm 0.7856 0.6556 0.9154
##
## Exp<LSL 0% Obs<LSL 0%
## Exp>USL 0% Obs>USL 0%Cp = 0.341, Cpk = 0.301
process.capability(q, spec.limits=c(73.99,74.01))
##
## Process Capability Analysis
##
## Call:
## process.capability(object = q, spec.limits = c(73.99, 74.01))
##
## Number of obs = 125 Target = 74
## Center = 74 LSL = 73.99
## StdDev = 0.009785 USL = 74.01
##
## Capability indices:
##
## Value 2.5% 97.5%
## Cp 0.3407 0.2983 0.3830
## Cp_l 0.3807 0.3176 0.4439
## Cp_u 0.3006 0.2424 0.3588
## Cp_k 0.3006 0.2312 0.3700
## Cpm 0.3382 0.2960 0.3804
##
## Exp<LSL 13% Obs<LSL 12%
## Exp>USL 18% Obs>USL 16%Cp = 1.87, Cpk = 0.381
process.capability(q, spec.limits = c(73.99, 74.1))
##
## Process Capability Analysis
##
## Call:
## process.capability(object = q, spec.limits = c(73.99, 74.1))
##
## Number of obs = 125 Target = 74.05
## Center = 74 LSL = 73.99
## StdDev = 0.009785 USL = 74.1
##
## Capability indices:
##
## Value 2.5% 97.5%
## Cp 1.8736 1.6406 2.1063
## Cp_l 0.3807 0.3176 0.4439
## Cp_u 3.3665 3.0115 3.7215
## Cp_k 0.3807 0.3055 0.4559
## Cpm 0.4083 0.3377 0.4788
##
## Exp<LSL 13% Obs<LSL 12%
## Exp>USL 0% Obs>USL 0%