Interpreting Control Charts

Shewart-Control Charts

Ahmed S. Shaban TA, Industrial Engineering Dept., Faculty of Engineering, Fayoum

University

Control Chart Zones

Out-of-Control Patterns

1- Freak

Out-of-Control Patterns

2- Freaks Pattern

Freaks Pattern Analysis

Freaks Pattern Analysis – Cont.

Example 1. Mark the out-of-control points

Example 1: Solution

Example 2. Mark the out-of-control points

Example 2: Solution

Example 3. Mark the out-of-control points

Example 3: Solution

Example 4. Mark the out-of-control points

Example 4: Solution

Out-of-Control Patterns

3- Shifts

Shift Pattern Analysis

Shift Pattern Analysis

An Example for Shifts

Example 5. Mark the out-of-control points

Example 5: Solution

Example 6. Mark the out-of-control points

Out-of-Control Patterns

4- Runs and Trends

Test1: Seven or more consecutive points are gradually

increasing

Test2: 10 out of 11 points are gradually increasing

Test3: Visual Judgment

Probability Calculations for Trends

First Approach

Probability Calculations for Trends

Second Approach

Trend Pattern Analysis

Trend Pattern Analysis – Cont.

Example 7. Mark the out-of-control points

Example 8. Mark the out-of-control points

Out-of-Control Patterns

5- Cycles

Cycles Pattern Analysis

Example 9. Mark the out-of-control points

Out-of-Control Patterns

6- Grouping

Grouping Pattern Analysis

Example 10. Identify the out-of-control pattern

Example 10. Solution

Out-of-Control Patterns

7- Instability

1. More than one-third of the points lie outside the center

± 1σ or more than 5 percent of the points fall in or

beyond the outer 1σ bands.

2. The chart has a steep, zig-zag pattern

Instability Pattern Analysis

Example 11. Identify the out-of-control pattern

Out-of-Control Patterns

8- Stable Mixture

Stable Mixture Pattern Analysis

Example 12. Identify the out-of-control pattern

Out-of-Control Patterns

9- Stratification

Test: More than 14 consecutive points fall in the C zone (±

1σ band).

Stratification Pattern Analysis

Example 13. Identify the out-of-control pattern

New Trends to Detect Control

Charts Patterns

• Statistical Approaches

• Artificial Neural Networks (ANN)

• Fuzzy Logic