Condition based monitoring by vibrational analysis

• US 6,321,602 B1
• Filed: 09/28/1999
• Issued: 11/27/2001
• Est. Priority Date: 09/28/1999
• Status: Expired due to Fees

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Rockwell Science Center LLC
• Inventors: Ben-Romdhane, Mohamed
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/406,350
• Time in Patent Office: 791 Days
• Field of Search: 73/660, 73/659, 73/593, 73/587, 73/579, 73/602, 73/116, 702/182, 702/183, 702/184, 702/185, 702/33, 702/35, 702/36, 702/56, 340/679, 340/682
• US Class Current: 73/660
• CPC Class Codes: F16C 19/52 with devices affected by abnormal or undesired conditions
• CPC Class Codes: G01M 13/028 Acoustic or vibration analysis
• CPC Class Codes: G01M 13/045 Acoustic or vibration analysis

Abstract

An apparatus and method monitors the condition of a bearing/shaft assembly by forming diagnostics based on spectral analysis of assembly'"'"'s vibration. Baseline parameters are determined by a microprocessor analysis of the vibration spectra, comparing actual peaks to the peaks predicted by a model. The microprocessor estimates rotation rate and preferably number of rolling elements by attempting to fit the model to the actual vibrational spectrum, by varying the assumptions. Baseline profiles are formed from one or more selected tones and preferably also harmonics thereof, to characterize the bearing/shaft assembly. The baseline profiles and parameters are compared against later acquired vibrational characteristics, and the comparison is used to diagnose bearing and/or shaft conditions.

Claims

1. A method for monitoring a condition of a rotating assembly having a shaft and a bearing, by analyzing the vibrations generated by the assembly'"'"'s motion, comprising:

analyzing a first spectrum of a vibration generated from the assembly, to determine the acceptable vibrational characteristics of the assembly while operating within acceptable parameters;

after said step of analyzing a first spectrum, analyzing a second spectrum of a vibration generated from the assembly at a later time, to determine the operating vibrational characteristics of the assembly;

determining from at least one of said first and second spectra a frequency of rotation of the shaft; and

comparing said operating vibrational characteristics with said acceptable vibrational characteristics to determine the condition of said assembly.

2. The method of claim 1, wherein said step of analyzing a second spectrum comprises determining a later frequency of rotation of said machine, associated with said later time;

and wherein said step of comparing said operating vibrational characteristics includes re-scaling at least one of the operating or acceptable vibrational characteristics to account for a ratio between said baseline and said later frequencies of rotation, thereby normalizing said at least one characteristic with respect to rotational frequency.

3. The method of claim 1, wherein at least one of said spectra is analyzed by:

converting a vibration signal from said machine into a digital representation by sampling, at a sampling frequency, a vibration signal and digitizing said signal; and

resampling the digital representation at a resampling frequency.

4. The method of claim 3, further comprising:

digitally filtering said digital representation.

5. The method of claim 1, further comprising:

Computing, based upon a measured vibration spectrum, an estimated number of rolling elements within the bearing of said assembly.

6. The method of claim 1, wherein said vibrational characteristics are compared by computing diagnostics based upon a defect indicator profile, said said defect indicator profile including a fundamental defect indicator tone and at least one harmonic thereof.

7. The method of claim 6, wherein said diagnostics are computed based on multiple defect indicators, said defect indicators chosen from the group consisting of an inner ring defect indicator profile, an outer ring defect indicator profile, a rolling element defect indicator profile, a cage train defect indicator profile, and a residue.

8. A method for monitoring a condition of a rotating assembly having a shaft and a bearing, by analyzing the vibrations generated by the assembly'"'"'s motion, comprising

sensing a vibration from the assembly;

transducing said vibration to obtain an electrical signal;

digitizing said electrical signal to obtain a digitized vibration signal;

digitally filtering said digitized signal;

resampling said filtered digitized signal;

transforming said filtered, digitized signal to a spectral transform representation to obtain a first spectrum representing the vibration from the assembly;

analyzing said first spectrum of the vibration generated from the assembly, to determine the acceptable vibrational characteristics associated with the vibration of the assembly while operating within acceptable design parameters;

after said step of analyzing a first spectrum, analyzing a second spectrum of a vibration generated from the assembly at a later time, to determine its operating vibrational characteristics at said later time; and

comparing said operating and acceptable vibrational characteristics to determine the condition of said machine, by a method comprising;

identifying at least one defect indicator profile in said first and second spectra, said indicator including the fundamental frequency and harmonics of a defect indicator tone;

computing diagnostics indicative of the condition of the machine based upon said defect indicator spectrum.

9. A system for monitoring the condition of a bearing, comprising:

a sensor for sensing a vibration of the bearing and producing a vibration signal;

a signal processor which receives said vibration signal from said sensor and produces a baseline spectrum of said vibration signal; and

a data processor, programmed to receive and store said spectrum of the vibration signal and to compare it to a second spectrum of vibration signal sampled at a later time, to detect deviations of the vibration signal from the baseline spectrum.

10. The system of claim 9, wherein said signal processor comprises:

an analog to digital converter (ADC) which samples the vibration signal from said sensors and converts it to digital data; and

a digital signal processor (DSP) which receives the digital data from said ADC and resamples the digital data.

11. The system of claim 10, wherein said digital signal processor also digitally filters said digital data and transforms said data into a frequency domain representation, to obtain a spectrum of said vibration signal.

12. The system of 11, wherein said digital signal processor digitally filters said digital data with a Finite Impulse Response (FIR) filter.

13. The system of 12, wherein said data processor is programmed to determine a fundamental rotational frequency of the bearing by analyzing a spectrum obtained from the vibration of said bearing.

14. The system of 13, wherein said data processor is further programmed to determine a number of rolling elements in the bearing by analyzing a spectrum obtained from said vibration, and to perform diagnostics based upon bearing defect indicators.

15. The system of 9 wherein said sensors are integrated with at least one of said signal processor and said data processor, and diagnostic data is transmitted via a wireless data channel.