Intelligent condition monitoring and fault diagnostic system for preventative maintenance

Abstract

A system for condition monitoring and fault diagnosis includes a data collection function that acquires time histories of selected variables for one or more of the components, a pre-processing function that calculates specified characteristics of the time histories, an analysis function for evaluating the characteristics to produce one or more hypotheses of a condition of the one or more components, and a reasoning function for determining the condition of the one or more components from the one or more hypotheses.

What is claimed is: 
     
         1 . A system for automatic fault diagnosis comprising:
 a non-transitory data collection function that acquires time histories of selected mechanical or power variables for one or more of components of a device in response to deterioration in the operation of the device.   a non-transitory pre-processing function that calculates specified characteristics of the time histories;   a non-transitory analysis function for evaluating the characteristics to produce one or more hypotheses of a condition of the one or more components; and   a non-transitory reasoning function for determining faults of the one or more components or of the device from the one or more hypotheses.   
     
     
         2 . The system of  claim 1 , wherein at least one of the selected variables includes an actual voltage, torque, velocity, and position of the one or more components during a constant velocity section of a move sequence. 
     
     
         3 . The system of  claim 2 , wherein the pre-processing function operates to:
 request additional time histories if the position variables lack a certain range and minimum variance;   compute nominal torque from a model and residual torque as a difference between the nominal torque and the actual torque;   compute a mean and variance of the residual torque; and   compute a Fourier transform of the residual torque with respect to the position variables.   
     
     
         4 . The system of  claim 3 , wherein the analysis function operates to determine if the residual torque exceeds a threshold, report peak frequencies of the Fourier transform, and to determine a distance corresponding to an oscillation period of the residual torque. 
     
     
         5 . The system of  claim 4 , wherein the reasoning function operates to determine the presence of a fault, and to analyze the Fourier transform peaks to determine the fault. 
     
     
         6 . The system of  claim 1 , wherein the selected variables include a tracking error of the one or more components and the pre-processing function operates to compute a Fourier transform of the tracking error as one of the specified characteristics. 
     
     
         7 . The system of  claim 1 , wherein the selected variables include a tracking error and a force of the one or more components 
     
     
         8 . The system of  claim 1 , wherein the selected variables include an output of a disturbance observer for the one or more components. 
     
     
         9 . The system of  claim 1 , wherein the selected variables include a belt tension of the one or more components. 
     
     
         10 . The system of  claim 1 , wherein the selected variables include position and acceleration measurements at various points on the one or more components and the pre-processing function operates to calculate a Fourier transform of the position and acceleration measurements to obtain a power spectrum as one of the specified characteristics. 
     
     
         11 . A system for on-demand fault diagnosis comprising:
 a non-transitory data collection function that acquires time histories of one or more mechanical or power variables related to a component of a device on an on-demand basis;   a non-transitory pre-processing function that calculates specific characteristics of the time histories;   a non-transitory analysis function for evaluating the characteristics to produce one or more hypotheses about a condition of the component of the device; and   a non-transitory reasoning function for determining the condition of the component from the one or more hypotheses.   
     
     
         12 . The system of  claim 11 , wherein the one or more variables include positions and torques of the component as the device follows a predetermined trajectory. 
     
     
         13 . The system of  claim 12 , wherein the pre-processing, analysis, and reasoning functions operate to identify parameters of a rigid-body dynamic model of the device from the time histories. 
     
     
         14 . The system of  claim 11 , wherein the pre-processing, analysis, and reasoning functions operate to compare parameters of the rigid-body dynamic model representing properties of a joint of the device with baseline parameters of the joint to identify problems. 
     
     
         15 . The system of  claim 11 , wherein the one or more variables include a response of the device as the device moves to positions uniformly distributed on a grid and is excited by a swept-frequency harmonic signal. 
     
     
         16 . The system of  claim 11 , wherein the component of the device includes a motor and the one or more variables include steady state voltage and current values of the motor as the motor is commanded to produce a known force. 
     
     
         17 . The system of  claim 16 , wherein the analysis function operates to compute a winding resistance value for the motor, and to compute current and force residuals by substituting the steady state current values and the commanded force value into equations of a motor model simplified for static load conditions. 
     
     
         18 . The system of  claim 17 , wherein the reasoning function operates to compare the current and force residuals with set thresholds to identify a violation of the motor model. 
     
     
         19 . The system of  claim 11 , wherein the one or more variables include sine and cosine signal values of an encoder of the device as the device moves at a constant velocity. 
     
     
         20 . The system of  claim 19 , wherein the pre-processing function operates to compute a magnitude of an imaginary vector whose Cartesian coordinates are the sine and cosine values. 
     
     
         21 . The system of  claim 20 , wherein the analysis function operates to record maximum and minimum values of the sine and cosine signals and the imaginary vector. 
     
     
         22 . The system of  claim 21 , wherein the reasoning function operates to compare the maximum and minimum values to pre-set thresholds to determine a condition of the encoder. 
     
     
         23 . The system of  claim 11 , wherein the one or more variables include a dimension of a feature scanned by a mapper of the device. 
     
     
         24 . The system of  claim 23 , wherein the pre-processing, analysis, and reasoning functions operates to compare the scanned dimension with a known dimension of the feature to determine a condition of the mapper. 
     
     
         25 . The system of  claim 11 , wherein the one or more variables include a response of the device as the device moves to positions uniformly distributed on a grid and is excited by an impulse, step-frequency or swept-frequency harmonic signal. 
     
     
         26 . The system of  claim 25 , wherein the pre-processing, analysis, and reasoning functions operate to determine a stability measure of a controller of the device from the response. 
     
     
         27 . The system of  claim 11 , wherein the component includes a communication network connected to the device and the one or more variables include a topology of the network. 
     
     
         28 . The system of  claim 11 , wherein the one or more variables include an actual position of the component that causes a light beam to be cut, and wherein the analysis function operates to detect a shift in the actual position. 
     
     
         29 . The system of  claim 28 , wherein the light beam is produced by a beam mapper carried by the component and is cut by a fixed feature. 
     
     
         30 . The system of  claim 28 , wherein the light beam is fixed with respect to a work cell of the device and is cut by the component. 
     
     
         31 . The system of  claim 11 , wherein the one or more variables include a location and orientation of a station mapped by the device. 
     
     
         32 . The system of  claim 11 , wherein at least one of the selected variables includes a result of running a virus scan by the component.