Diagnostic method for manufacturing processes

• US 6,859,756 B2
• Filed: 09/06/2002
• Issued: 02/22/2005
• Est. Priority Date: 09/06/2002
• Status: Active Grant

• Current Assignee: Shainin II LLC
• Original Assignee: Red X Holdings LLC
• Inventors: Allen, John R.
• Primary Examiner(s): Hoff, Marc S
• Assistant Examiner(s): TSAI, CAROL S W
• Application Number:
  US10/236,450
• Publication Number:
  US 20040049364A1
• Time in Patent Office: 900 Days
• Field of Search: 702 81- 84, 702182-185, 702/35, 702/155, 700108-110, 700/164, 700/125
• US Class Current: 702/183
• CPC Class Codes: B65G 2207/14 Combination of conveyors
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 19/41875 characterised by quality surveillance of production
• CPC Class Codes: G05B 2219/32189 Compare between original solid model and measured manufactured object
• CPC Class Codes: G05B 2219/32221 Correlation between defect and measured parameters to find origin of defect
• CPC Class Codes: G05B 2219/32222 Fault, defect detection of origin of fault, defect of product
• CPC Class Codes: G05B 2219/35223 Tolerance, consider tolerance in design, design for assembly
• CPC Class Codes: G05B 2219/37617 Tolerance of form, shape or position
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

A method for use in a system for diagnosing the causes of manufacturing defects involves process characterization. A set of forms is identified for a workpiece and for a piece of manufacturing equipment that acts upon the workpiece. The forms for the workpiece are preferably a hierarchic set of geometric forms. Each such geometric form corresponds to an aspect of the action of the manufacturing equipment upon the workpiece. A plurality of measurements is made on a defective workpiece following the hierarchical order of forms. The measurements are compared to a reference datum, and a deviation from the datum is computed. If the deviation exceeds a preselected threshold, an alert condition results, attributable to the action of the manufacturing equipment. Targeted adjustment corresponding to the action that caused the defect can then be made to the equipment.

Claims

1. A method for diagnosing a cause of deviation from an intended form in a workpiece produced by a manufacturing process, in which at least one form is defined for the workpiece and manufacturing equipment acts upon the workpiece according to the manufacturing process to impart the form, the method comprising the steps of:

defining a plurality of measurements for the workpiece, each relative to a respective reference datum;

taking the defined measurements for the workpiece;

generating a record of the measurements;

comparing the recorded measurements for each workpiece; and

inferring from the comparison of the measurements the existence of an alert condition associated with the action of the manufacturing equipment on the workpiece, wherein the measurements correspond to a hierarchic set of forms characterizing the workpiece, each form corresponding to an action of the manufacturing equipment, wherein the hierarchic set of forms comprises two categories;

a first category of forms characterizing the shape of a portion of the workpiece, and a second category of forms characterizing sets of portions of the workpiece.

2. The method according to claim 1, wherein the sets of portions of the workpiece comprise repeating portions.

3. The method according to claim 1, further comprising the step of plotting at least a subset of the recorded measurements in a graph prior to the step of inferring the existence of an alert condition.

4. The method according to claim 1, wherein the hierarchic set of forms comprises one selected from the group consisting of a point form, a path segment form, a path form and a surface form.

5. A method for identifying evidence of deviation from specification in a workpiece produced by a manufacturing process, the manufacturing process being performed by respective manufacturing equipment, the method comprising the steps of:

identifying a set of repeated portions of the workpiece, each instance of a repeated portion having a form, the form of one instance of a repeated portion being substantially similar to the form of the other instances;

for each instance of the repeated portion, making a set of measurements of the reproducible part relative to a respective reference datum;

comparing each set of measurements to a respective target range of values; and

based on the comparison, inferring the existence of evidence of deviation from specification, wherein the measurements relate to a hierarchic set of forms characterizing the workpiece, each form corresponding to an action of the manufacturing equipment.

6. The method according to claim 5, wherein the hierarchic set of forms comprises two categories:

a first category of forms characterizing the shape of a portion of the workpiece, and a second category of forms characterizing one or more portions of the workpiece.

7. The method according to claim 5, wherein the evidence of the deviation is a basis for indicating an alert condition.

8. The method according to claim 7, wherein the alert condition is based upon application of a preselected rule to the evidence.

9. The method according to claim 8, wherein the preselected rule comprises a deviation exceeding a threshold value.

10. The method according to claim 5, comprising the further step of storing the measurements in a computer data storage device.

11. The method according to claim 5, wherein at least a pair of instances of the repeated portion are contiguous in the workpiece.

12. The method according to claim 5, wherein the form comprises a shape of at least a portion of the workpiece.

13. A method for assessing a condition of a workpiece acted upon by manufacturing equipment, comprising the steps of:

identifying a set of forms, each form corresponding to an aspect of the action of the manufacturing equipment upon the workpiece;

for each form, making a plurality of measurements;

for each plurality of measurements, computing a respective deviation from a corresponding datum;

defining a deviation threshold; and

if a computed deviation exceeds the deviation threshold, inferring the existence of the condition attributable to the action of the manufacturing equipment on the workpiece associated with action corresponding to the form for which the deviation exceeds the threshold, wherein the set of forms comprises two categories;

a first category of forms that characterizes a geometric element of a portion of the workpiece, and a second category of forms that characterizes differences between workpieces.

14. The method according to claim 13, wherein the first category of forms comprises one selected from the group consisting of a point form, a path segment form, a path form and a surface form.

15. The method according to claim 13, further comprising the step of plotting the plurality of measurements for the plurality of forms on a single graph, prior to determining whether any computed deviation for each form exceeds a preselected threshold.

16. The method according to claim 15, wherein the graph comprises a representation of each plurality of measurements.

17. The method according to claim 15, wherein the graph comprises a representation of each plurality of measurements in relation to a respective form among a hierarchy of forms characterizing the workpiece, each form corresponding to an action of the manufacturing equipment.

18. The method according to claim 17, wherein the hierarchic set of forms comprises two categories:

a first category of forms characterizing the shape of a portion of a workpiece, and a second category of forms characterizing one or more portions of the workpiece.

19. The method according to claim 15, wherein the single graph comprises a geometric deviation chart.

20. The method according to claim 19, wherein the geometric deviation chart comprises a first region for comparing measurements corresponding to the hierarchic set of geometric forms, and a second region contiguous with the first, for recording the frequency of repetition of the forms that comprise portions of the workpiece.

21. The method according to claim 13, wherein the condition comprises an alert condition.

22. The method according to claim 13, wherein the plurality of measurements comprises at least three measurements.

23. The method according to claim 22, wherein the at least three measurements comprise exactly three measurements.

24. A method for detecting deviations from an intended form in a mechanical part, the deviations based upon computed differences between measured geometric properties with respect to a reference datum and defined threshold values, the deviations from an intended form caused by a machine tool operating on the mechanical part, the method comprising the steps of:

a. identifying a hierarchic set of geometric forms characterizing the mechanical part, each form corresponding to an action of the machine tool on the part;

b. categorizing the geometric forms from a lowest order to a highest order;

c. making a plurality of measurements corresponding to the lowest order form, each plurality of measurements made relative to a reference datum;

d. computing deviations based on differences between the plurality of measurements and the reference datum;

e. comparing the deviations with respective threshold values, the deviations exceeding threshold values indicating an alert condition; and

f. if an alert condition is present, inferring a deviation from the intended form, wherein the hierarchic set of geometric forms comprises two categories;

a first category of forms characterizing the shape of a portion of a workpiece forming the mechanical part, and a second category of forms characterizing one or more portions of the workpiece, wherein the second category of geometric forms comprises a surface defined by forms selected from the first category of shapes.

27. The method according to claim 24, wherein if no alert condition is present, performing the steps c-f for a higher order geometric form.

28. method according claim 24, wherein the first category of geometric forms comprises at least one selected from the group consisting of a segment, a line and a plane.

29. method according to claim 24, wherein the first category of geometric forms comprises at least one of the groups consisting of curvilinear segment, a closed curve and a surface.

25. A method for detecting deviations from an intended form in a mechanical part, the deviations based upon computed differences between measured geometric properties with respect to a reference datum and defined threshold values, the deviations from an intended form caused by a machine tool operating on the mechanical part, the method comprising the steps of:

a. identifying a hierarchic set of geometric forms characterizing the mechanical part, each form corresponding to an action of the machine tool on the part;

b. categorizing the geometric forms from a lowest order to a highest order;

c. making a plurality of measurements corresponding to the lowest order form, each plurality of measurements made relative to a reference datum;

d. computing deviations based on differences between the plurality of measurements and the reference datum;

e. comparing the deviations with respective threshold values, the deviations exceeding threshold values indicating an alert condition; and

f. if an alert condition is present, inferring a deviation from the intended form, wherein the step of checking for an alert condition is performed by plotting the plurality of measurements on a geometric deviation chart.

26. The method according to claim 25, wherein the geometric deviation chart comprises a first region for comparing measurements corresponding to the hierarchic set of geometric forms, and a second region contiguous or adjacent the first, for representing the frequency of repetition of the forms that comprise portions of the workpiece.