Computer-implemented method and apparatus for monitoring statistical process control data

• US 5,392,226 A
• Filed: 06/17/1993
• Issued: 02/21/1995
• Est. Priority Date: 06/17/1993
• Status: Expired due to Term

• Current Assignee: ICOM Incorporated
• Original Assignee: ICOM Incorporated
• Inventors: Hamilton, Jeffrey L.
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Pipala, Edward J.
• Application Number:
  US08/078,462
• Time in Patent Office: 614 Days
• Field of Search: 364/188, 364/514, 364/551.01, 364/552, 395/100, 395/102, 395/118
• US Class Current: 702/81
• CPC Class Codes: G05B 21/02 electric

Abstract

A computer-implemented method and apparatus for monitoring a process operating under statistical process control (SPC). The computer displays a "target control chart" to represent SPC data from the process. The target control chart comprises a Specification Limits ball graphically depicting the specifications limits for the process, a Control Limits ball graphically depicting the control limits for the process, and a Data Population ball graphically depicting one or more characteristics of a sample population of the measured data values for the process. Once defined, the Specification Limits ball remains static, and its display is not altered. The Control Limits ball may be static, or may be re-positioned and re-sized as additional measured data values are included in the sample population. The Data Population ball is dynamic and is re-positioned and re-sized as additional measured data values are included in the sample population. The position of the Data Population ball on a Y axis of the target control chart is calculated by averaging all measured data values in a specified study length or moving window of the sample population. The diameter of the Data Population ball is calculated by determining a standard deviation of all measured data values in the specified study length or moving window of the sample population.

Claims

1. A process monitoring apparatus, comprising:

(a) means for collecting measured data values representing one or more characteristics of a process at discrete intervals during its operation;

(b) means for storing the measured data values in a memory; and

(c) means for displaying a target control chart on a monitor, wherein the target control chart comprises a Specification Limits ball graphically depicting specification limits for the process, a Control Limits ball graphically depicting control limits for the process, and a Data Population ball graphically depicting one or more characteristics of a sample comprising at least one of the and wherein the Specification Limits ball, the Control Limits ball and the Data Population ball are displayed on the monitor in a manner to represent an interrelation between the specification limits for the process, the control limits for the process, and the characteristics of the sample, so that an ideal environment is represented by concentrically overlaying the Specification Limits ball, Control Limits ball and Data Population ball.

2. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for re-positioning and re-sizing the Data Population ball and Control Limits ball as additional measured data values are included in the sample.

3. The apparatus as set forth in claim 1 above, further comprises:

(1) means for updating the sample with additional measured data values;

(2) means for calculating an average of one or more of the measured data values in the sample;

(3) means for calculating a standard deviation of one or more of the measured data values in the sample; and

(4) means for re-drawing the target control chart when the additional measured data values cause the Data Population ball to be altered.

4. The apparatus as set forth in claim 3 above, wherein the means for re-drawing comprises:

(i) means for calculating a position of the Data Population ball on a Y axis of the target control chart by averaging one or more of the measured data values in the sample; and

(ii) means for calculating a size of the Data Population ball by determining a standard deviation of one or more of the measured data values in the sample.

5. The apparatus as set forth in claim 3 above, wherein the means for re-drawing comprises:

(i) means for calculating a size of the Control Limits ball by determining a standard deviation of one or more of the measured data values in the sample; and

(ii) means for calculating a position of the Control Limits ball on a Y axis of the target control chart using the standard deviation.

6. The apparatus as set forth in claim 3 above, further comprising means for triggering an alarm on the computer when the measured data values exceed the specified specification or control limits.

7. The apparatus as set forth in claim 1 above, wherein the means for collecting comprises means for sampling the data values at a specified time interval.

8. The apparatus as set forth in claim 1 above, wherein the means for collecting comprises means for sampling the data values at an occurrence of a specified event.

9. The apparatus as set forth in claim 1 above, further comprising means for defining how many measured data values to include in the sample.

10. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for scaling a Y axis for the target control chart to reflect a viewport determined by the specification limits, wherein the scaled Y axis maximizes the resolution of the measured data values being viewed.

11. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for sizing the Specification Limit ball.

12. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for displaying the Specification Limit ball with its center positioned at a Setpoint on a Y axis of the target control chart.

13. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for displaying the Specification Limit ball with its center positioned at a center of a Y axis of the target control chart when no Setpoint is specified.

14. The apparatus as set forth in claim 1 above, wherein the means for displaying further comprises means for displaying the Control Limit and Data Population balls at a scale relative to the Specification Limit ball.

15. A method for monitoring a process, comprising:

(a) collecting measured data values representing one or more characteristics of a process at discrete intervals during its operation;

(b) storing the measured data values in a memory; and

(c) displaying a target control chart on a monitor attached to a computer, wherein the target control chart comprises a Specification Limits ball graphically depicting specification limits for the process, a Control Limits ball graphically depicting control limits for the process, and a Data Population ball graphically depicting one or more characteristics of a sample of at least one of the measured data values, and wherein the Specification Limits ball, the Control Limits ball and the Data Population ball are displayed on the monitor in a manner to represent an interrelation between the specification limits for the process, the control limits for the process, and the characteristics of the sample, so that an ideal environment is represented by concentrically overlaying the Specification Limits ball, Control Limits ball and Data Population ball.

16. The method as set forth in claim 15 above, wherein the displaying further comprises the step of re-positioning and re-sizing the Data Population ball and Control Limits ball as additional measured data values are included in the sample.

17. The method as set forth in claim 15 above, further comprising the steps of:

(1) updating the sample with additional measured data values;

(2) calculating an average of one or more of the measured data values in the sample;

(3) calculating a standard deviation of one or more of the measured data values in the sample; and

(5) re-drawing the target control chart when the additional measured data values cause the Data Population ball to be altered.

18. The method as set forth in claim 17 above, wherein the re-drawing step comprises the steps of:

(i) calculating a position of the Data Population ball on a Y axis of the target control chart by averaging one or more of the measured data values in the sample; and

(ii) calculating a size of the Data Population ball by determining a standard deviation of one or more of the measured data values in the sample.

19. The method as set forth in claim 17 above, wherein the re-drawing step comprises the steps of:

(i) calculating a size of the Control Limits ball by determining a standard deviation of one or more of the measured data values in the sample; and

(ii) calculating a position of the Control Limits ball on a Y axis of the target control chart using the standard deviation.

20. The method as set forth in claim 17 above, further comprising the step of triggering an alarm on the computer when the measured data values exceed the specified specification or control limits.

21. The method as set forth in claim 15 above, wherein the collecting step comprises the step of sampling the data values at a specified time interval.

22. The method as set forth in claim 15 above, wherein the collecting step comprises the step of sampling the data values at an occurrence of a specified event.

23. The method as set forth in claim 15 above, further comprising the step of defining how many measured data values to include in the sample.

24. The method as set forth in claim 15 above, wherein the displaying step further comprises the step of scaling a Y axis for the target control chart to reflect a viewport determined by the specification limits, wherein the scaled Y axis maximizes the resolution of the measured data values being viewed.

25. The method as set forth in claim 15 above, wherein the displaying step further comprises the step of sizing the Specification Limit ball.

26. The method as set forth in claim 15 above, wherein the displaying step further comprises the step of displaying the Specification Limit ball with its center positioned at a Setpoint on a Y axis of the target control chart.

27. The method as set forth in claim 15 above, wherein the displaying step further comprises the step of displaying the Specification Limit ball with its center positioned at a center of a Y axis of the target control chart when no Setpoint is specified.

28. The method as set forth in claim 15 above, wherein the displaying step further comprises the step of displaying the Control Limit and Data Population balls at a scale relative to the Specification Limit ball.