VIBROACUSTICAL DIAGNOSTIC IN SITU APPLICABLE TO AN MC CNC by nikeborome

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									 Traktori i pogonske mašine                                            Tractors and power machines



 Biblid: 0354-9496(2009) 14:1, p.82-87                                                  Nauþni rad
 UDK: 633.12:631.354 (497.115-17)                                                  Scientific paper




 VIBROACUSTICAL DIAGNOSTIC IN-SITU APPLICABLE
    TO AN MC 70 CNC VERTICAL MACHINING FOR
  DETERMINATION OF PREDICTIVE MAINTENANCE
                    SERVICE
                    Vl du V., Matache M1., Biriú S., Paraschiv G.2, Bungescu S.3

                                         SUMMARY
The usage of the spectral analysis (Fast Fourier Transform) ensures a great potential for the
reliability and maintainability increase for a large scale of components, assemblies and
systems. The “mechanical signature” is obtained by the means of the spectral analysis;
afterwards there is extracted information from the measured signal sample. In this paper will
be presented the correlation between the noise and the vibration (simultaneously measured),
obtained from the “mechanical signature” analysis and also will be revealed some of the
confidence factors for the vibro-acoustical diagnosis.
   Key words: vibration, noise, system, analysis, mechanical

       INTRODUCTION
Vibro-acoustical analysis uses external signal measurements of noise and vibrations to
diagnose the internal status or failures and also to detect the damages from the incipient
stadium. The analysis of the “mechanical signature” presents an important potential, being a
unique mean to increase reliability and maintainability of a large scale of components,
assemblies and systems. The signature analysis consists in extracting information from the
measured signal sample. The mechanical signature was identified by the means of FFT spectral
analysis.

       MATERIAL AND METHODS
The testing to demonstrate the utility of diagnostic services in the field of agricultural
machinery were made in SC ROMET Buzau by a joint team composed of experts from INMA
Bucharest and Bucharest UPB, making these measurements on a MC 70 CNC vertical
machining center.
Figure 1 is presented processing center which measurements were made and the equipment
mounted on it (currently transducer and accelerometers).


1 Vl du V., Matache M, INMA Bucharest; valentin-vladut@yahoo.com
2 Biriú S., Paraschiv G., P.U. Bucharest;
3 Bungescu S., USAMVB Timiúoara

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 Traktori i p/m      Vibroacustical diagnostic in-situ applicable to an              Vl du V., et al
 Tractors and p/m    mc 70 CNC vertical machining for …                   Vol.14.No.1.p.82-87, 2009.


On the main shaft of the car was fitted with two accelerometers to measure vibration directions
perpendicular to the main shaft, according to figure 2, and a revolution counter laser was
recorded by which the speed of rotation of central axis. Transducer was used for determining
magnetic mount.




  Fig. 1 - Vertical machining center MC 70
                     CNC




  Fig. 3 - Calibration of accelerometer and            Fig. 2 - Mounting the accelerometer and
transducer speed, that set of data acquisition           transducer speed on the central axis
                   sessions




                                                           Fig. 4 - Accelerometers and speed
                                                      transducer mounted on the centerline of the
                                                                           car




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 Traktori i p/m      Vibroacustical diagnostic in-situ applicable to an              Vl du V., et al
 Tractors and p/m    mc 70 CNC vertical machining for …                   Vol.14.No.1.p.82-87, 2009.




         Fig. 5 - Numerically controlled machine programming from the dashboard




                    Fig. 6 - Acquisition of data during processing of parts
       INVESTIGATION RESULTS AND DISCUSSIONS
Mechanical signature analysis using external measurements of noise and vibration signals to
diagnose the internal state or to detect defects and damage at the early stage.
Mechanical signature analysis has great potential, the only way to increase reliability and
mentenabilities a wide range of components, assemblies and systems.
Signature analysis is to extract information from the sample of measured signal. In this activity
has been identified mechanical signature using FFT spectral analysis.
The parameters used in the FFT analysis are:
   i Fmax = maximum frequency spectrum display (Hz)
   i n = number of frequencies in the spectrum.
Sampling rate (sampling rate) or rate of reading must be at least twice the maximum frequency
shown. Fe = 2Fmax, according to Shanon's theorem.
Duration of procurement is T = nmed / Fmax where med is the number of mediation.
Spectral resolution is the difference between 2 successive values of frequencies of the signal
spectrum. Increased resolution can be done by increasing the number of lines. Mathematically
speaking, it is equivalent to using a larger number of coefficients in Fourier series.
Resolution in vibration frequency spectrum is 'F = Fmax / N, where Fmax is the maximum
frequency shown, n is the number of spectrum lines.
Compressor was used to obtain spectra with FFT analysis: n = 400 lines, Fmax = 997.5 Hz.
Were made several measurements of vibrations induced in the shaft rotation speed of its
constant and the variable speeds in goal or task. Diagrams corresponding to these


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 Traktori i p/m      Vibroacustical diagnostic in-situ applicable to an              Vl du V., et al
 Tractors and p/m    mc 70 CNC vertical machining for …                   Vol.14.No.1.p.82-87, 2009.


measurements are listed below.
The value of RMS (root mean square - mean square) in acceleration, speed and movement is
the most used measure of the level of vibration or noise and therefore the spectra obtained for
such equipment were expressed.
   Measurement charts with accelerometer 1




Fig. 7- Power spectrum at N = 200 rpm (left) and N = 990 rpm (right), the axis x frequency in
               Hz, y-axis mean square value m/s2 acceleration, idling, accel. 1




    Fig. 8 - Power spectrum from N = 1000 rpm (left) and N = 2000 rpm (right), the axis x
        frequency in Hz, y-axis mean square value of acceleration m/s2 idling, accel. 1




    Fig. 9 - Power spectrum from N = 3000 rpm (left) and N = 5000 rpm (right), the axis x
       frequency in Hz, y-axis mean square value of acceleration m/s2 idling, accel. 1


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Traktori i p/m     Vibroacustical diagnostic in-situ applicable to an              Vl du V., et al
Tractors and p/m   mc 70 CNC vertical machining for …                   Vol.14.No.1.p.82-87, 2009.




   Fig. 10 - Power spectrum from N = 400 rpm (left) and N = 600 rpm (right), the axis x
     frequency in Hz, y-axis mean square value of acceleration m/s2 drill 8, accel. 1

  Accelerometer measurements chart 2




   Fig. 11 - Power spectrum from N = 200 rpm (left) and N = 100 rpm (right), the axis x
      frequency in Hz, y-axis mean square value of acceleration m/s2 idling, accel. 2




  Fig. 12 - Power spectrum from N = 2000 rpm (left) and N = 3000 rpm (right), the axis x
       frequency in Hz, y-axis mean square value of acceleration m/s2 idling, accel. 2




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 Traktori i p/m            Vibroacustical diagnostic in-situ applicable to an                     Vl du V., et al
 Tractors and p/m          mc 70 CNC vertical machining for …                          Vol.14.No.1.p.82-87, 2009.




       Fig. 13 - Power spectrum from N = 5000 rpm (left) and N = 400 rpm (right), the axis x
           frequency in Hz, y-axis mean square value of acceleration m/s2 idling, accel. 2




       Fig. 14 - Power spectrum from N = 400 rpm (left) and N = 600 rpm (right), the axis x
        frequency in Hz, y-axis mean square value of acceleration m/s2 drill 16, accel. 2
          CONCLUSION
Identification of mechanical signature is the most important part of diagnosis vibro-acoustic
spectra obtained as change may indicate a change in the state machine or equipment.
Identification of mechanical signature can be achieved by signal processing techniques such as
temporal analysis, Fourier analysis and analysis of CPB.
Following measurements on equipment type vertical machining center MC 70 CNC "were
obtained amplitude-frequency spectra (Fourier analysis), at different speeds and working
arrangements (to load and idling).

          REFERENCES
[1.]    B jenaru S., Vl du V., Ganga M., ú.a. - Analysis stage and the current study applied the theory of diagnosis for
        predictive maintenance, Research report, INMA Bucharest, 2007;
[2.]    B jenaru S., Vl du V., Ganga M., ú.a. - Developing experimental models, methods, techniques of spectral
        analysis in vibro-acoustical, Research report, INMA Bucharest, 2008;
[3.]    B jenaru S., Vl du V., Ganga M., ú.a. - Experimentation solution of vibration-noise ratio conditions in
        industrial systems for complex mechanical and mechatronic, Research report, INMA Bucharest, 2009;
[4.]    Marcel Dekker, Barron R.F. - Industrial Noise Control and Acoustics;
[5.]    Daniel R. Raichel - The Science and Applications of Acoustics 2nd Ed.

The paper received: 14.10.2009.                                                The paper received: 28.10.2009.


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