Methods and apparatus for system fault diagnosis and control

Apparatus for diagnosing faults in a predetermined system, comprising:

• sensors for providing sensor data relative to the performance of the predetermined system,
• a domain specific knowledge base, including a plurality of rules in evidence-hypothesis form, which make assertions relative to the predetermined system,
• said knowledge base being free of information which makes inferences relative to the knowledge base,
• domain independent inference rules, including first and second levels of inference rules,
• means interconnecting said sensors, said domain specific knowledge base, and said domain independent inference rules,
• said first level of inference rules including means for testing evidence portions of selected rules of said domain specific knowledge base in response to said sensor data, and means responsive to successfully tested (fired) rules for making belief propagating inferences relative to the hypotheses of the domain specific rules,
• said second level of inference rules including means for determining which of the first level inference rules to apply when there is a choice,
• and means for outputting signals relative to at least certain of the domain specific rules which fire when their evidence portions are tested.

A method of diagnosing faults in a predetermined system, comprising the steps of:

• providing domain specific rules having confidence threshold (CFT) values, including rules in evidence-hypothesis form, to build a knowledge base of assertions relative to the predetermined system,
• providing data relative to the predetermined system,
• providing inference rules which make belief propagating inferences in response to the data, by selecting and applying the domain specific rules,
• propagating belief in the hypothesis of selected domain specific rules, in response to the data, by the step of interconnecting the domain specific rules, under the control of the inference rules, into a rule network of hypothesis nodes interconnected by evidence,
• said step of propagating belief including the steps of:
• (a) developing a confidence factor for each hypothesis node in the propagating step, using the confidence factors developed for supporting nodes,
• (b) comparing the developed confidence factor for each hypothesis node with the associated CFT value to determine when the present propagating path appears to be unproductive,
• (c) storing the information relative to an apparently unproductive path,
• and (d) returning to an apparently unproductive path in response to predetermined conditions, using the information previously stored to start at the point of previous termination,
• and outputting information in response to the belief propagating step.

A method of diagnosing faults in a predetermined system, comprising the steps of:

• providing domain specific rules, including rules in evidence-hypothesis form, to build a knowledge base of assertions relative to the predetermined system, said domain specific rules including values which assign relative weights to multiple pieces of evidence for a rule, and confidence factor assumption (CFA) values,
• providing data relative to the predetermined system,
• providing inference rules which make belief propagating inferences in response to the data, by selecting and applying the domain specific rules,
• propagating belief in the hypotheses of selected domain specific rules, in response to the data, by the step of interconnecting the domain specific rules, under the control of the inference rules, into a rule network of hypothesis nodes interconnected by evidence,
• said belief propagating step propagating belief without obtaining all of the evidence for a hypothesis of the steps of:
• (a) developing a confidence factor CF for each hypothesis node, (b) setting the weight of a missing piece of evidence to zero, (c) comparing the confidence factor CF with the CFA value, and (d) continuing without the missing evidence when CF exceeds the CFA value,
• and outputting information in response to the belief propagating step.