APPARATUS FOR MONITORING THE CONDITION OF A MACHINE

• US 20150226603A1
• Filed: 09/11/2013
• Published: 08/13/2015
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: S.P.M. Instrument AB
• Original Assignee: S.P.M. Instrument AB
• Inventors: Hedin, Lars-Olov Elis
• Granted Patent: US 9,772,219 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01M 13/028 Acoustic or vibration analysis
• CPC Class Codes: G01M 13/045 Acoustic or vibration analysis
• CPC Class Codes: G05B 19/4069 Simulating machining process on screen G05B19/4068 takes precedence
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence

Abstract

A method for analyzing the condition of a machine, and an apparatus for analyzing the condition of a machine are described.

Claims

1. An apparatus for analysing the condition of a machine having a part (7,8) rotatable with a speed of rotation (f_ROT), comprising:

a transducer (10) for generating an analogue measurement signal (SEA) in response to machine vibration so that said analogue measurement signal (SEA) includes a vibration signal signature (SD) having

a vibration frequency (f_SEA) which is lower than an upper frequency limit value (f_SEAmax) and

at least one vibration signal repetition frequency (f_D) and

a vibration signal amplitude;

an A/D converter (40, 44) adapted to generate a digital measurement signal (S_MD, S_R) having a sequence of sample values (S_MD, S_R) dependent on the analogue measurement signal (S_EA), said digital measurement signal (S_MD, S_R) having a first sample rate (f_S), wherein said first sample rate (f_S) is at least twice said upper frequency limit value (f_SEAmax);

a digital peak value detector adapted to generate output peak values (A_PO) dependent on said sequence of sample values (S_MD, S_R);

a peak value discriminator being adapted to sort said output peak values (A_PO) into corresponding amplitude ranges during a measuring session;

a measuring session controller adapted to control a variably settable duration (T_Meas) of said measuring session;

a condition value generator adapted to generate a first condition value (LR_D) in response to said sorted output peak values (A_PO) and said duration (T_Meas) so that

said first condition value (LR_D) is indicative of a first amplitude value (A_LRD) having a first predetermined occurrence rate, and so that

said first condition value (LR_D) is based on a selected first temporal portion of the digital measurement signal (S_MD, S_R);

the apparatus further comprising

a decimator adapted to generate a decimated digital signal (S_RED;

S_RED1;

S_RED2) in dependence of said digital measurement signal (S_MD, S_R) so that the decimated digital signal (S_RED;

S_RED1;

S_RED2) has a reduced sampling frequency (f_SR1;

f_SR1); and

a Fourier Transformer adapted to generate a transformed signal in dependence of a selected second temporal portion of said decimated digital signal (S_RED;

S_RED1;

S_RED2) so that said transformed signal is indicative of said vibration signal repetition frequency (f_D);

said apparatus being arranged to

coordinate the generation of said transformed signal with the generation of the first condition value (LR_D) so that

the selected second temporal portion of said decimated digital signal (S_RED;

S_RED1;

S_RED2) is based substantially on said selected first temporal portion of the digital measurement signal (S_MD), and so that said selected first temporal portion of the digital measurement signal (S_MD) is generated during the variably settable duration (T_Meas) of said measuring session.

2. The apparatus according to claim 1, wherein

the condition value generator is adapted to generate a second condition value (HR_LUB) in response to said sorted output peak values (A_PO) and said duration (T_Meas) so that

said second condition value (HR_LUB) is indicative of an second amplitude value (A_HRLUB) having a second predetermined occurrence rate (f_C2), and so that

said second condition value (HR_LUB) is based on said selected first temporal portion of the digital measurement signal (S_MD, S_R).

3. The apparatus according to claim 1, further comprising

an analyzer having

a first analyzer input for receiving said first condition value (LR_D);

a second analyzer input for receiving said second condition value (HR_LUB);

wherein

the analyzer is adapted to generate a status signal indicative of whether the condition of the machine is normal or abnormal in dependence on said first condition value (LR_D) and said second condition value (HR_LUB).

4. The apparatus according to claim 3, further comprising

an apparatus input for receiving a signal indicative of a detected speed of rotation (f_ROT) associated with said rotatable part (7,8);

a third analyzer input for receiving said signal indicative of a detected speed of rotation (f_ROT);

a fourth analyzer input for receiving a bearing frequency factor value (OR, IR, FTF, BS); and

a fifth analyzer input for receiving said transformed signal;

wherein

the analyzer is adapted to generate a status signal indicative of the nature of, and/or cause for, an abnormal machine condition in dependence of said speed of rotation signal (f_ROT), said bearing frequency factor value (OR, IR, FTF, BS) and said transformed signal.

5. The apparatus according to claim 3, further comprising

an apparatus input for receiving a signal indicative of a detected speed of rotation (f_ROT) associated with said rotatable part (7,8);

a third analyzer input for receiving said signal indicative of a detected speed of rotation (f_ROT);

a fourth analyzer input for receiving a bearing frequency factor value (OR, IR, FTF, BS); and

a fifth analyzer input for receiving said transformed signal;

wherein

the analyzer is adapted to generate a status signal indicative of a probable location of an incipient damage in dependence of

said speed of rotation signal (f_ROT),

said bearing frequency factor value (OR, IR, FTF, BS) and

said transformed signal.

6. The apparatus according to claim 3, further comprising

an apparatus input for receiving a signal indicative of a detected speed of rotation (f_ROT) associated with said rotatable part (7,8);

a third analyzer input for receiving said signal indicative of a detected speed of rotation (f_ROT);

a fourth analyzer input for receiving a bearing frequency factor value (OR, IR, FTF, BS); and

a fifth analyzer input for receiving said transformed signal;

wherein

the analyzer is adapted to extract said at least one vibration signal repetition frequency (f_D) from said transformed signal; and

the analyzer is adapted to generate a frequency factor estimate (f_fEST) in dependence on said at least one vibration signal repetition frequency (f_D) and said detected speed of rotation (f_ROT); and

the analyzer is adapted to compare the generated frequency factor estimate (f_fEST) with a stored plurality of frequency factors (F_fstore1, F_fstore2, F_fstore3, . . . F_fstoren); and

wherein

the analyzer is adapted to generate a status signal indicative of a probable location of an incipient damage in dependence of said frequency factor comparison.

7. The apparatus according to claim 1, further comprising:

an associator adapted to associate

said first condition value (LR_D) with

said transformed signal.

8. The apparatus according to claim 1, further comprising:

a digital rectifier (270) adapted to perform a rectification so as to generate a rectified digital signal (SR) dependent on said digital measurement signal (SMD); and

wherein

the digital peak value detector is adapted to generate the output peak values (APO) dependent on said rectified digital signal (SMD, SR); and

said decimator is adapted to perform said decimation on the rectified digital signal (SR) so as to achieve said decimated digital signal (SRED;

SRED1;

SRED2) having a reduced sampling frequency (fSR1;

fSR1).

9. The apparatus according to claim 8, wherein:

the digital rectifier (270) is adapted to perform a full-wave rectification so as to generate a rectified digital signal (SR) dependent on said digital measurement signal (SMD) including absolute values of said sequence of sample values (S_MD, S_R).

17. The apparatus according to claim 2, further comprising

an analyzer having

a first analyzer input for receiving said first condition value (LR_D);

a second analyzer input for receiving said second condition value (HR_LUB);

wherein

the analyzer is adapted to generate a status signal indicative of whether the condition of the machine is normal or abnormal in dependence on said first condition value (LR_D) and said second condition value (HR_LUB).

10. An apparatus for analysing the condition of a machine having a part (7) rotatable with a speed of rotation (f_ROT), comprising

an input (42) for receiving an analogue measurement signal (S_EA) indicative of a vibration signal signature (S_D) having a vibration frequency (f_SEA) and at least one repetition frequency (f_D);

an A/D converter (40, 44) adapted to generate a digital measurement signal (S_MD) having a sequence of sample values dependent on the analogue measurement signal, said digital measurement signal (S_MD) having a first sample rate (fS), wherein said vibration frequency (fSEA) is assumed to be lower than half of the first sample rate (fS);

a digital rectifier (270) adapted to perform a rectification so as to generate a rectified digital signal (SR) dependent on said digital measurement signal (S_MD);

a digital peak value detector adapted to deliver output peak values (APO) on a peak value detector output dependent on said rectified digital signal (S_R);

a peak value discriminator being adapted to sort said output peak values (A_PO) into corresponding amplitude ranges during a measuring session;

a measuring session controller adapted to control a duration (T_Meas) of said measuring session;

a condition value generator adapted to generate a first condition value (LR_D) in response to said sorted output peak values (A_PO) and said duration (T_Meas) so that said first condition value (LR_D) is based on a selected first temporal portion of the digital measurement signal (S_MD);

the apparatus further comprising

a decimator for performing a decimation of the rectified digital signal (S_R) so as to achieve a decimated digital signal (S_RED;

S_RED1;

S_RED2) having a reduced sampling frequency (f_SR1;

f_SR2); and

a Fourier Tranformer adapted to generate a transformed signal in dependence on a selected second temporal portion of said decimated digital signal (S_RED;

S_RED1;

S_RED2);

said apparatus being arranged to

coordinate the generation of said transformed signal with the generation of the first condition value (LR_D) so that the selected second temporal portion of said decimated digital signal (S_RED;

S_RED1;

S_RED2) is based substantially on said selected first temporal portion of the digital measurement signal (S_MD).

11. An apparatus for analysing the condition of a machine having a part (7) rotatable with a speed of rotation (f_ROT), comprising

an input (42) for receiving an analogue measurement signal (S_EA) indicative of a vibration signal signature (S_D) having a vibration frequency (f_SEA) and at least one repetition frequency (f_D);

an A/D converter (40, 44) adapted to generate a digital measurement signal (S_MD) dependent on the analogue measurement signal, said digital measurement signal (S_MD) having a first sample rate (f_S), the first sample rate being at least twice (k) said vibration frequency (f_SEA);

a digital rectifier (270) adapted to perform full-wave rectification so as to generate a rectified digital signal (S_R) dependent on said digital measurement signal (S_MD);

a smoothing stage (TOP-3) adapted to generate a smoothened digital signal (S_Smooth) dependent on said rectified digital signal (S_R);

said smoothing stage (TOP-3) being adapted to adjust an output sample amplitude value (S<sub>SOUT—

i</sub>) upwards in dependence on

the amplitude of the corresponding input sample amplitude value (S<sub>SIN—

i</sub>) and in dependence on

the amplitude of temporally adjacent input sample amplitude values (S<sub>SIN—

i−

1</sub>, S<sub>SIN—

i+1</sub>);

an asymmetric digital filter for generating an asymmetrically low pass filtered signal (S_ASYM) in response to the smoothed digital signal (S_Smooth);

the asymmetric digital filter being adapted to generate the asymmetrically filtered signal (S_ASYM) so that

in response to a detected positive time derivative of the smoothed digital a first settable filter value (k) is set to a first value (KRise); and

in response to a detected negative time derivative of the smoothed digital signal said first settable filter value (k) is set to a second value (kFall);

a peak value detector (330) adapted to deliver output peak values (A_PO) on a peak value detector output (333) in response to said detected peak values (A_P); and

wherein

said peak value detector is adapted to limit the delivery frequency of said output peak values (A_P, A_PO) such that said output peak values (A_P, A_PO) are delivered at a maximum delivery frequency of f_dP, wherein

f_dP=f_s/e

where f_S is said first sample rate, and e is an a number higher than two.

Advantageously, the smoothing stage will eliminate “

dents”

in the rectified signal, and it will do so by always adjusting the amplitude upwards. Thus, whereas the rectified signal may include a sampled value having significantly lower amplitude that its neighbour samples, the signal from the smoothing stage will always be smooth. Whereas such a smoothing effect may also be achieved by means of a median-value-filter, the median-filter would also reduce the top amplitude value of the output signal in relation to the top value of the rectified input signal. Hence, whereas a median-filter would make the signal more smooth, the smoothing stage as defined above will not only make the signal more smooth, but it will also maintain the amplitude values of the highest detected amplitudes in the rectified signal.

12. The apparatus according to claim 11, wherein the smoothing stage includes

a first peak sample selector (TOP-3) adapted to analyze v consecutive received sample values, and to identify the highest amplitude of these v consecutive received sample values, and to deliver v consecutive output sample values with at least one of the v consecutive output sample values having an adjusted amplitude value, said adjustment being an amplitude increase,

wherein, v is an integer having a value of about fs/f_SEA.

13. The apparatus according to claim 11, wherein the smoothing stage includes

a first peak sample selector which is adapted to receive a plurality of temporally consecutive sample values;

and

identify the amplitude of a selected sample value from among said received plurality of consecutive sample values; and

analyze

the amplitude of the selected sample value,

the amplitude of the sample immediately preceding the selected sample value and

the amplitude of the sample succeeding the selected sample value; and

deliver an output sample value in response to said selected sample value so that said output sample value has an amplitude corresponding to the highest amplitude detected in said analysis.

14. The apparatus according to claim 11, wherein:

the asymmetric digital filter is adapted to generate the asymmetrically filtered signal (S_ASYM) so that

in response to a detected positive time derivative of the smoothed digital signal (S_Smooth) the asymmetrically filtered signal (S_ASYM) will have a positive time derivative substantially equal to that of the smoothed digital signal (S_Smooth); and

in response to a detected negative time derivative of the smoothed digital signal (S_Smooth) the asymmetrically filtered signal (S_ASYM) will have a comparatively slow response.

15. The apparatus according to claim 11, further comprising a decimator, a fourier transformer and a measuring session controller as previously defined.

16. The apparatus according to claim 15, wherein

said apparatus is arranged to coordinate the generation of said transformed signal with the generation of the first condition value (LR_D) so that

the selected second temporal portion of said decimated digital signal (S_RED;

S_RED1;

S_RED2) is based substantially on

said selected first temporal portion of the digital measurement signal (S_MD), and so that

said selected first temporal portion of the digital measurement signal (S_MD) is generated during the variably settable duration (T_Meas) of said measuring session.