Instrument for detecting defects in rolling elements of bearings is described. Detection depends on rate at which rolling elements impact defect and establishes envelope amplitude of ball resonant frequency. Block diagram of instrument is provided and results obtained in conducting tests are reported

Burchill, R. F.

Frarey, J. L.

English

NASA Technical Reports Server

October 1972	 B72-10689 
• NASA TECH BRIEF Marshall Space Flight Center 
NASA Tech Briefs announce now technology derived from the U.S. space prog ram. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
New Detection Method for Rolling Element and Bearing Defects 
Input From
	
 
Vibration	 Frequency	 H	 Li .11.1Envelope	 Low Pass _______Band Pass	 Detector	 A Filter 
	
Pickup	
Filter 
inner mace	 I 
Defect	 I	 Detector	 ______	
Filter 
Low Pass	 Level
Band Pass tectr 
Outer Race 
Defect J____lIIIIiJ Detector
JI Jj 0 
Low Pass Level 
Band Pass
Filter
Detector
 Filter 
B	 II 
^4- Defect jj^ Detector Low Pass Level Bend Pass Filter Detector D 
Inner Race 
Defect (IRD) 
Outer Race 
Defect (ORD) 
Ball Defect
Surface Finish 
tDDCl---
Defect 
BD = A D 
Surface Finish Defect = A (B + C + D) as	 ORD = A C
(continued overleaf) 
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The purpose of the concept and related detector is to 
detect bearing defects at their very early stages. The 
detection concept is based on the fact that bearing defects 
excite the resonant (carrier) frequency of the rolling 
elements of the bearing as these rolling elements impact 
the defect. This resonant frequency is generally in the 
high frequency region of the spectrum. The rate at which 
the rolling elements impact the defect determines the 
envelope (modulation) amplitude of the ball resonant 
frequency. The rate and character of the resonant 
excitation is a function of the type of defect. By envelope 
detecting the resonant frequency and subsequently ana-
lyzing the character of this envelope signal, bearing detects 
may be detected and identified as to source. The 
following relates signal characteristics to bearing condition. 
Carrier Modulation Condition 
Low None Excellent 
Relatively high Ball defect signal Ball defect 
Relatively high Race defect signal Race defect 
Relatively high Random character Initial surface 
defect
A block diagram of an instrument to identify these 
conditions is shown in the figure. The input from the 
vibration pickup is filtered by a bandpass filter wide 
enough to pass the resonant frequency and all side 
bands. Next, it is envelope detected which results in only 
the envelope signal. This signal then goes through a low pass 
filter and level detector. If the level is above a given value, 
the output of the level detector is a logical "1", if not, 
output A is a logical 140". 
The envelope signal also is fed to three identical 
channels, the only difference being the center frequency 
of the bandpass filter. The filter must be wide enough to 
contain the defect signal for variations in speed. The 
output of each filter is a defect signal, if present, or low 
level random noise if not present. This signal is detected, 
filtered, and level detected. Outputs B, C, and  are "1",
if a signal is present, "0" if not present. The logical 
elements act on the output A, B, C, and D, shown by the 
Boolean equations in the figure. As can be seen, discrete 
defects are indicated by the presence of the ball resonance 
and one of the discrete defect signals. Surface finish 
defects are indicated by the presence of the ball resonance 
without any of the defect signals. Other logic relationships 
can be used to recognize combinations of bearing defects. 
Notes: 
1. In experiments conducted, the resonant frequency 
was located at 30 kHz and the defect signal (modula-
tion) at 867 Hz. An important feature is that 30 kHz is 
well beyond the normal frequency range utilized in 
vibration analysis. 
2. Information concerning this innovation may be of 
interest to the designers and manufacturers of non-
destructive test equipment and industrial inspection 
systems. 
3. Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B72-10689 
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention may be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: R. F. Burchill and J. L. Frarey of

Mechanical Technology, Inc.

under contract to
Marshall Space Flight Center

(MFS-2 1911) 
B72-10689	 Category 06 


New detection method for rolling element and bearing defects

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