X-R 控制图

X-R 控制图

過程控制

a) 計算及繪畫控制限- 樣本容量低於 7時，極差並沒有 LCL

解释控制图解释控制图

U CL

LCL

Avg

U CL

LCL

Avg

Change in level

Change in variability

解釋控制圖 - 確定是否有不受控的情況

- 檢查過程記錄，找出並列明任何特殊原因。 - 再計算控制限。

控制上限(UCL)

中線

控制下限 (LCL)

控制上限 (UCL)

中線

控制下限 (LCL)

受控過程

不受擯過程

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

Test 1. One Point Beyond Zone A Test 2. Nine Points in a Row

on One Side of the Center Line

Test 3. Six Points in a Row Steadily

Increasing or Decreasing

Test 4. Fourteen Points in a Row

Alternating Up and Down

x

x

x

x

x

x

控制图失控检验控制图失控检验

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

UCL

LCL

A

A

BCCB

Test 5. Two Out of Three Points in

a Row in Zone A or Beyond

Test 6. Four Out of Five Points in

a Row in Zone B and Beyond

Test 7. Fifteen Points in a Row in Zone C

(Above and Below Centerline)

Test 8. Eight Points in a Row on Both

Sides of Centerline with None in Zone C

x x

x

x

x

x x

控制图的失控检验控制图的失控检验

UCL

LCL

A

A

BC

CB

控制图失控检验控制图失控检验One point above UCL

Two out of three successive point here or above

Four out of five successive point here or above

Seven out of eight successive point here or above

One point above LCL

Two out of three successive point here or bellow

Four out of five successive point here or bellow

Seven out of eight successive point here or bellow

3

2

1

-3

-2

-1

034.1%

13.6%

34.1%

13.6%

2.2%

2.2%

0.1%

0.1%

20100

Observation Number

UCL

LCL

20100

Observation Number

UCL

LCL

Seasonal Trends:These could be caused by systematic changes like: temperature, operator fatigue, voltage or pressure fluctuations, etc.

Mixtures:A clear indication is when most of the points are close to the control limits, and almost no points near the center line. These are usually due to underestimating the process variability or “over-control” , where operators intervene with the process frequently trying to respond to inherent variability instead of assignable causes. This also occurs when controlling two processes on the same chart.

控制图的趋势判断规则控制图的趋势判断规则

20100

Observation Number

UCL

LCL

151050

Observation Number

UCL

LCL

Changes in process means:These are usually due to the introduction of new operators, machines, procedures, etc. Can also happen because of process improvements.

Upward/Downward Trends:Continuous trending on the same direction. These are usually caused by component wear among others.


20100

Observation Number

UCL

LCL

“White Space”:Points tend to cluster around the mean. Usually caused by: (1) incorrect control limits (overestimating process variability), (2) continuous improvements paying-off. Limits should be recalculated when this situation is found.


製程控制對特殊原因採取的措施 1. 即時分析失控情況是非常重要的，以便

將不符合規格的產品減至最少；並取得新的數據作調查分析。

2. 特殊原因可以是正面或負面3. 在控制圖中，我們可能會在任何單值子

組中得到一個特殊原因的錯誤信息。

Example of OCAP in W7PT

X-R 控制图

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