100-Metodos-de-Qualidade-Total

226 100 METHODS FOR TOTAL QUALITY MANAGEMENT
Table 1 Report sheet errors
Date Shift No. sheets n No. errors c Errors/sheet w
3/5 6 x 2 3 6 2.00
2 x 10 3 4 1.33
6 x 2 3 5 1.66
2 x 10 3 3.00
6/5 6 x 2 1 0 0
9/5 6 x 2 3 6 2.00
2 x 10 3 8 2.66
10/5 6 x 2 3 1 0.66
2 x 10 3 3 1.00
11/5 6 x 2 3 4 1.33
2 x 10 3 2 0.67
12/5 6 x 2 3 2 0.67
13/5 6 x 2 1 1.00
16/5 6 x 2 3 1 0.33
2 x 10 3 0 0
17/5 6 x 2 3 3 1.00
2 x 10 2 6 2.00
18/5 6 x 2 3 2 0.67
2 x 10 3 3 1.00
19/5 6 x 2 3 2 0.67
2 x 10 2 1 0.50
20/5 6 x 2 3 3 1.00
4/5
Total 22 58 C = 66
Benefits
It can be difficult to separate out random variation (often called common
cause or non-assignable variation) from real variation caused by changes to
the process. U charts are a way of doing this for the number of defects with
a sample size that varies by more than + 2 5 per cent.
Example
For data on report sheet errors see Table 1. The resulting U chart is given
in Figure 1.
- C 66
CL = U = =
n 58 = 1.14
K = 3VYi = 3.2
upper control limit = 0 + ..!I n
-
K
lower control limit =
U -
Yn
Refere n ce
T.P. Ryan (1989) Statistical Methods for Quality Improvement. New York: Wiley Interscience.