Diagnostic method for manufacturing processes

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.

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.    
   
   
       2 . The method according to  claim 1 , wherein the at least one form comprises a shape of at least a portion of the workpiece.  
   
   
       3 . The method according to  claim 1 , wherein the measurements correspond to a hierarchic set of forms characterizing the workpiece, each form corresponding to an action of the manufacturing equipment.  
   
   
       4 . 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, wherein the graph depicts deviations of the measurements from respective reference data.  
   
   
       5 . A method for identifying evidence of deviation from specification in a form produced in a workpiece by a manufacturing process, the manufacturing process being performed by respective manufacturing equipment, the method comprising the steps of: 
 identifying a set of measurable forms associated with the workpiece, each form corresponding to an action of the manufacturing equipment;    for each form, identifying a reference datum;    for each form, making a set of measurements of the form relative to the respective datum;    comparing each set of measurements to a respective target range of values; and    based on the comparison, inferring the existence of evidence of an alert condition,    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 a set of portions of the workpiece.    
   
   
       6 . 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.    
   
   
       7 . The method according to  claim 6 , further comprising the step of inferring an alert condition based upon the evidence of a preselected rule.  
   
   
       8 . The method according to  claim 7 , wherein the preselected rule comprises the deviation exceeding a threshold value.  
   
   
       9 . 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.    
   
   
       10 . 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, 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;    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.    
   
   
       11 . A method for characterizing the ability of a machine tool to reproduce a product without deviating from a specification intended for at least a portion of the product, the characterization based upon taking geometric measurements, the method comprising the steps of: 
 a. identifying a set of geometric forms present in the product;    b. selecting a first of the set of geometric forms;    c. making a plurality of measurements corresponding to the selected geometric form;    d. for each plurality of measurements, computing a deviation from a respective reference datum;    e. checking for an alert condition based on each of the respective deviations;    f. if an alert condition is present, adjusting the machine tool and repeating the method from step c iteratively until no further alert condition is found; and    g. if no alert condition is detected, repeating the method from step b and incrementing to the next form until all geometric forms have been selected.    
   
   
       12 . The method according to  claim 11 , wherein a first category of geometric form comprises at least one selected from the group consisting of a segment, a line and a plane.  
   
   
       13 . The method according to  claim 11 , wherein the geometric form comprises a surface defined by forms selected from the first category of geometric form.  
   
   
       14 . The method according to  claim 13 , wherein the first category of geometric forms comprises at least one of the groups consisting of curvilinear segment, a closed curve and a surface.  
   
   
       15 . The method according to  claim 11 , wherein the specification comprises at least one of the groups consisting of a spatial form and a temporal form.  
   
   
       16 . The method according to  claim 15 , wherein the spatial form comprises physical locations where the product is made.  
   
   
       17 . The method according to  claim 15 , wherein the temporal form comprises an interval of time.