GB2554971A

GB2554971A - Method for determining a degree of wear of a cooling device which is operated with at least one piston

Info

Publication number: GB2554971A
Application number: GB1710827.5A
Authority: GB
Inventors: Hubner Martin; Munzberg Mario
Original assignee: Hensoldt Optronics GmbH
Current assignee: Hensoldt Optronics GmbH
Priority date: 2016-07-08
Filing date: 2017-07-05
Publication date: 2018-04-18
Anticipated expiration: 2037-07-05
Also published as: DE102016112591B4; GB201710827D0; DE102016112591A1; GB2554971B

Abstract

The invention relates to a method for determining a degree of wear of a cooling device 3 which is operated with at least one piston, in particular for an infrared detector 2, wherein, during the operation of the cooling device 3, high-frequency shock pulses (SP(t)) are continuously detected by a structure-borne noise sensor 3, which can be of a piezoelectric or microelectromechanical type, in structure-borne noise signals emanating from the cooling device 3 and/or are extracted from the said structure-borne noise signals, and wherein at least one variable which characterizes the degree of wear of the cooling device 3 is continuously determined from the detected and/or extracted shock pulses (SP(t)). Preferably, in embodiments, the sensitive frequency range is approximately 20-40 kHz. A warning message may be output when a limit value of wear is exceeded.

Description

(71) Applicant(s):

1710827.5

05.07.2017 (32) 08.07.2016 (33) DE

Hensoldt Optronics GmbH

Carl-Zeiss-Strasse 22, Oberkochen 73447, Germany (72) Inventor(s):

Martin Hiibner

Mario Miinzberg (51) INT CL:

G01H 1/00 (2006.01) (56) Documents Cited:

GB 2173865 A WO 2010/074648 A1 JP 2011119589 A US 20140216159 A1 KR20050078296

EP 0107178 A2 WO 2008/144864 A1 JP 2011094920 A US 20050049835 A1 (58) Field of Search:

INT CL F25B, G01H, G01L, G01M Other: WPI; EPODOC (74) Agent and/or Address for Service:

Barker Brettell LLP

100 Hagley Road, Edgbaston, BIRMINGHAM, B16 8QQ, United Kingdom (54) Title of the Invention: Method for determining a degree of wear of a cooling device which is operated with at least one piston

Abstract Title: Using shock pulses to determine degree of wear of a cooling device operated with a piston (57) The invention relates to a method for determining a degree of wear of a cooling device 3 which is operated with at least one piston, in particular for an infrared detector 2, wherein, during the operation of the cooling device 3, highfrequency shock pulses (SP(t)) are continuously detected by a structure-borne noise sensor 3, which can be of a piezoelectric or microelectromechanical type, in structure-borne noise signals emanating from the cooling device 3 and/or are extracted from the said structure-borne noise signals, and wherein at least one variable which characterizes the degree of wear of the cooling device 3 is continuously determined from the detected and/or extracted shock pulses (SP(t)). Preferably, in embodiments, the sensitive frequency range is approximately 20-40 kHz. A warning message may be output when a limit value of wear is exceeded.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

1/2

09 17

Fig. 2

212 σ>

ο ο

C\J

Time [s]

Fig. 3

07 17

Description:

Method for determining a degree of wear of a cooling device which is operated with at least one piston

The invention relates to a method for determining a degree of wear of a cooling device which is operated with at least one piston, in particular for an infrared detector, and also to a method for monitoring a degree of wear of a cooling device which is operated with at least one piston. The invention furthermore relates to a measurement system for determining and/or monitoring a degree of wear of a cooling device which is operated with at least one piston.

Previous methods for diagnosing the remaining run time of piston-operated cooling devices, in particular rotary Stirling-type coolers for infrared detectors, are based either on a purely statistical analysis of the temporary run time profile compared with existing meantime-to-failure (MTTF) data or on the further analysis of state variables, such as power consumption or cooling-down times, which only indirectly provide information about the degree of mechanical wear of the cooler. Manufacturer data of this kind is generally not enough to be able to predict the time of malfunction in situ on the customer’s premises with a significantly higher degree of accuracy so that malfunction during operation can be precluded. Different and unpredictable malfunction situations of this kind in situ can be tolerated only with difficulty, especially in the case of surveillance sector or security sector applications which have to run without interruption.

In the case of the abovementioned cooling devices, it is desirable to detect wear, for example of ball bearings, or play, which occurs in the piston or in the eccentric of the shaft bearing for example, in order to be able to provide information about an imminent malfunction. It would have to be possible to detect, for example, wear-related striking of metal on metal for this purpose.

US 6,889,553 B2 specifies a method and an apparatus for detecting and measuring shock waves.

07 17

Furthermore, reference is made to https://en.wikipedia.org/wiki/Shock_Pulse_Method.

Proceeding from the above, the object of the present invention is to provide a method for determining a degree of wear of a cooling device of the kind mentioned in the introductory part which is operated with at least one piston, which method avoids the disadvantages of the prior art, in particular allows accurate prediction of the wear-related remaining service life of the cooling device.

According to the invention, this object is achieved by the features cited in Claim 1. The said claim proposes a method for determining a degree of wear of a cooling device which is operated with at least one piston or is piston-operated, in particular for an infrared detector, in which method, during the operation of the cooling device, high-frequency shock pulses are continuously detected in structure-borne noise signals emanating from the cooling device and/or are extracted from the said structure-borne noise signals, and wherein at least one variable which characterizes the degree of wear of the cooling device is continuously determined from the detected and/or extracted shock pulses.

In the case of the solution according to the invention, a structure-borne noise-based analysis of the shock pulses and/or shock transients, which are induced during operation, of a cooler establishes a direct link to the wear-related cause of a possible cooler defect. The state variable which can be derived from the present invention allows significant limitation of the inaccuracy in the diagnosis of the remaining run time of a cooling device, in particular for an infrared detector. This allows an accurate prediction to be made about the wear-related remaining service life of the cooler and therefore allows accurately determinable preventive replacement of a cooler assembly in order to avoid cooler malfunctions during operation. The wear-related shock pulses or shock transients to be detected occur in the event of metal striking metal within the batches affected by wear.

07 17

It is highly advantageous, when determining the at least one variable which characterizes the degree of wear of the cooling device, substantially or only those shock pulses which have a repetition rate or repetition frequency of ωο and/or 2 <do are taken into account, wherein <do is the rotational frequency, in particular of the piston-driven Stirling-type machine, with which the cooling device is operated.

In the case of a piston drive which is frequently used for cooling devices and is periodically accelerated (so-called rotating piston machine or reciprocating machine), the main components of the oscillating force, which act on shafts and bearings, are to be expected at the rotational frequency ω₀ with which the cooling device is operated (so-called primary force) and at 2 ω₀ (so-called secondary force). Investigations by the inventors have shown that the substantial contributions to the shock pulses occur at fundamental frequencies of ω₀ and/or 2 ω₀. In particular, the contribution at a repetition rate or repetition frequency of 2 ω₀ is dominant. Therefore, it is highly advantageous, when determining the variable which characterizes the degree of wear of the cooling device, to take into account substantially those shock pulses or the contributions thereof which occur at the repetition rates of ωο and/or 2 ωο.

The at least one variable which characterizes the degree of wear of the cooling device is determined by means of a frequency distribution from a number of shock pulses which are detected and/or extracted over a prespecified time period.

The individual detected pulses can be counted and therefore a number can be determined over a specific time period or a measurement window. To this end, a prespecified threshold of the amplitude level of the shock pulses to be counted can be defined and/or an amplitude distribution can be taken into account.

The at least one variable which characterizes the degree of wear of the cooling device can be determined from an integrated level of the detected and/or extracted shock pulses.

A clear measure of the degree of wear of the cooler can be provided owing to this measure.

07 17

It is advantageous when a frequency analysis, in particular a discrete Fourier transformation, of the detected and/or extracted shock pulses is carried out in order to determine the at least one variable which characterizes the degree of wear of the cooling device.

Therefore, a targeted frequency analysis or spectrum analysis or spectral analysis of the shock pulses or of envelope curves or enveloping curves of the shock pulses can be carried out, in particular of components at the fundamental frequency ω₀ and 2 ω₀, in order to ascertain the variable which characterizes the degree of wear of the cooling device.

According to the invention, it can be provided that:

- the structure-borne noise signal is preliminarily filtered by means of a high-pass filter or a band-pass filter;

- the shock pulses are demodulated from the structure-borne noise signal;

- the structure-borne noise signal or the shock pulses is/are rectified; and/or

- envelope curves or envelopes are formed around the shock pulses in order to detect and/or extract the shock pulses.

Shock pulses in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 35 kHz, can advantageously be detected in the structure-borne noise signal and/or extracted from the said structure-borne noise signal.

Shock pulses or shock transients of this kind which can indicate wear

07 17 phenomena, such as ball bearing damage or the like for example, and therefore can contribute to determining the degree of wear of the cooling device are detected owing to these measures.

The structure-borne noise signal can be recorded in the region of the cooling device, preferably on its housing.

The cooling device can be designed as a rotary Stirling-type cooler.

Claim 10 specifies a method for monitoring a degree of wear of a cooling device which is operated with at least one piston, in particular for an infrared detector, wherein the degree of wear of the cooling device is continuously determined by means of a method according to the invention, wherein the at least one variable which characterizes the degree of wear of the cooling device is continuously compared with at least one prespecified limit value, and wherein a warning message or the like is output when the at least one limit value is exceeded.

A possible malfunction of the cooler during operation can be predicted in a very accurate manner owing to these measures. A warning message or the like can be output when a prespecified limit value is exceeded. Accordingly, a defective cooler can be replaced in good time.

Claim 11 relates to a measurement system for determining and/or monitoring a degree of wear of a cooling device which is operated with at least one piston, in particular for an infrared detector, comprising at least one structure-borne noise sensor and at least one signal processing and evaluation unit which is connected to the at least one structure-borne noise sensor so as to communicate with it and which receives the structure-borne noise signals, which are recorded by the at least one structure-borne noise sensor, as input signals and which is designed to carry out a method according to the invention for determining and/or monitoring the degree of wear of the cooling device.

Accordingly, the invention specifies an integrated measurement system for determining the remaining run time of cooling devices, in particular rotary Stirling-type coolers for infrared detectors. The integrated measurement system comprising structure-borne noise sensor or acceleration sensor and signal processing means allows detection and separation or extraction of high-frequency shock pulses in the structure-borne noise signal of the coolers. Wear-related play and loose parts provide, in connection with the oscillating force effects of the Stirling-type piston drive, the kinetic energy for generating shock-generated shock waves in the cooler housing, the integrated level of said shock waves providing a clear measure of the degree of wear of the cooler.

07 17

The at least one structure-borne noise sensor can be sensitive in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 32 kHz or 35 kHz.

The at least one structure-borne noise sensor can be of piezoelectric or microelectromechanical design.

Conventional acceleration or structure-borne noise sensors are typically sensitive for frequencies of 10 Hz to 10 kHz. However, sensor devices of this kind are generally not suitable for detecting high-frequency shock pulses or shock transients. Special structure-borne noise sensors which are sensitive at frequencies of approximately 20 kHz to approximately 40 kHz, in particular of approximately 30 kHz to approximately 40 kHz, preferably of 32 kHz or 35 kHz, are required for detecting the highfrequency shock pulses.

Advantageous refinements and developments of the invention can be found in the dependent claims.

An exemplary embodiment of the invention is described in principle below with reference to the drawing.

In the drawing:

07 17

Figure 1 shows a block diagram for illustrating the method according to the invention;

Figure 2 is a schematic illustration of an arrangement comprising a cooling device, which is designed as a rotary Stirling-type cooler, and a structure-borne noise sensor; and

Figure 3 shows simplified graphs relating to the application of the method according to the invention in conjunction with the arrangement from Fig. 2.

Figure 1 shows a schematic illustration of a thermal imaging device 1 with an infrared detector 2 on which a cooling device 3, which is in the form of a rotary Stirling-type cooler and is operated with at least one piston 3a (see Figure 2) or lifting piston, is arranged on the said infrared detector in order to cool it. Further constituent parts of the thermal imaging device 1, such as an optical system or the like for example, are not illustrated in Figure 1. Furthermore, an acceleration sensor or structure-borne noise sensor 4 is arranged in the region of the piston-operated cooling device 3, in particular on its housing, not illustrated in any detail. The structure-borne noise sensor 4 is sensitive in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 32 kHz or 35 kHz, and can be of piezoelectric or microelectromechanical design. The structure-borne noise sensor 4 can be used to record a structure-borne noise signal in the region of the cooling device 3, preferably on its housing, not illustrated in any detail.

According to the invention, a method for determining a degree of wear of the cooling device 3 will now be specified, wherein, during the operation of the cooling device 3, high-frequency shock transients or shock pulses SP(t) (see Figure 3) are continuously detected in structure-borne noise signals emanating from the cooling device 3 and/or are extracted from the said structure-borne noise signals, and wherein at least one variable which characterizes the degree of wear of the cooling device 3 is continuously determined from the detected and/or extracted shock pulses SP(t).

07 17

When determining the at least one variable which characterizes the degree of wear of the cooling device 3, substantially or only those shock pulses SP(t) which have a repetition rate of ωο and/or 2 ωο are taken into account, where ωο is the rotational frequency with which the pistonoperated cooling device 3 is operated (also see Figure 2).

In the method according to the invention, shock pulses SP(t) can be detected in the structure-borne noise signal and/or extracted from the said structure-borne noise signal in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 35 kHz.

As is further clear from Figure 1, a signal processing and evaluation unit 5 which is connected to the structure-borne noise sensor 4 so as to communicate with it and which receives the structure-borne noise signals, which are recorded by the at least one structure-borne noise sensor 4, as input signals and which is designed to carry out the method according to the invention for determining the degree of wear of the cooling device 3 is provided. The signal processing and evaluation unit 5 can be integrated into the thermal imaging device 1. The structure-borne noise sensor 4 and the signal processing and evaluation unit 5 can together form a measurement system 6 for determining and/or monitoring a degree of wear of the cooling device 3, wherein the signal processing and evaluation unit 5 is further designed to carry out a method for monitoring the degree of wear of the cooling device 3, wherein the degree of wear is continuously determined by means of the method according to the invention for determining the degree of wear of the cooling device 3, wherein the at least one variable which characterizes the degree of wear of the cooling device 3 is continuously compared with at least one prespecified limit value, and wherein a warning message or the like is output by the measurement system 6 when the limit value is exceeded.

07 17

The at least one variable which characterizes the degree of wear of the cooling device 3 can be determined by means of a frequency distribution from a number of shock pulses SP(t) which are detected and/or extracted over a prespecified time period.

As an alternative or in addition, the at least one variable which characterizes the degree of wear of the cooling device 3 can be determined from an integrated level of the detected and/or extracted shock pulses SP(t).

A frequency analysis, in particular a discrete Fourier transformation, of the detected and/or extracted shock pulses SP(t) can be carried out in order to determine the at least one variable which characterizes the degree of wear of the cooling device 3.

Figure 1 sequentially illustrates the manner of signal conditioning in the signal processing and evaluation unit 5. A signal amplifier 4a can be connected between the structure-borne noise sensor 4 and the signal processing and evaluation unit 5 or a high-pass filter 7 (see Figure 2). The signals received by the structure-borne noise sensor 4 are preliminarily filtered by the high-pass filter 7, for example for frequencies of greater than 10 kHz. The said filter may also be a band-pass filter. The shock pulses SP(t) are then demodulated from the preliminarily filtered structure-borne noise signal in step S1. The structure-borne noise signal is then rectified in step S2, this being followed in step S3 by envelope curves (see Figure 3) being formed around the shock pulses SP(t). The number of shock pulses SP(t) is then ascertained in step S4 and/or targeted frequency analysis of the shock pulse envelope curves for components at the repetition frequencies ω₀ and 2 ω₀ is performed in step S5.

Figure 2 shows, in more detail, the cooling device 3 which is in the form of a rotary Stirling-type cooler and on which the structure-borne noise sensor 4 is arranged. The cooling device 3 has a piston 3a, a connecting rod 3b and a crank 3c. The raw measurement signals of the structure-borne noise sensor 4 are amplified by the signal amplifier 4a.

07 17

The variable a(t) which is output by the structure-borne noise sensor 4 or the signal amplifier 4a describes the time-dependent acceleration present in the raw measurement signal of the structure-borne noise sensor 4. This is given by: a(t) = a^Q + SPO), where a^t) represents the structure-borne noise vibration inherent in each lifting piston drive with ω₀ (primary force) and 2·ωο (secondary force) given by a^t)-ω²-[cos(m-t) + const.-cos(2-w-t)] and SP(t) represents the wearrelated shock pulses transients or shock pulses which are driven by the abovementioned vibrations a^t) and therefore have the corresponding repetition rate (see Figure 3).

Figure 3 shows, on the basis of synthetic measurement data, the relationships with an exemplary cooler rotation frequency or rotational frequency of ω₀ = 25 Hz, that is to say with a period duration of 40 ms.

In the graphs in Figure 3, the time in s is plotted on the horizontal axis and accelerations (a(t) and, respectively, SP(t)) in arbitrary units are plotted on the vertical axis. The curve a(t) shown in the upper part of Figure 3 exhibits shock pulse modulations or shock pulses.

In the middle part of Figure 3, the shock pulses SP(t) are illustrated after preliminary filtering and the demodulation in step S1.

Finally, the lower part of Figure 3 shows the shock pulses SP(t) as envelope curves after rectification of the said shock pulses in step S2 and after execution of step S3.

07 17

List of reference symbols:

Thermal imaging device

Infrared detector

Cooling device

3a Piston

3b Connecting rod

3c Crank

Structure-borne noise sensor

4a Signal amplifier

Signal processing and evaluation unit

Measurement system

High-pass filter

SP(t) Shock pulses a(t) Time-dependent acceleration

Demodulation

Rectification

Formation of envelope curves

Ascertaining of the number of shock pulses

Frequency analysis

Claims

Patent claims: 25 07 17

1. Method for determining a degree of wear of a cooling device (3) which is operated with at least one piston (3a), in particular for an infrared detector (2) , wherein, during the operation of the cooling device (3), high-frequency shock pulses (SP(t)) are continuously detected in structure-borne noise signals emanating from the cooling device (3) and/or are extracted from the said structure-borne noise signals, and wherein at least one variable which characterizes the degree of wear of the cooling device (3) is continuously determined from the detected and/or extracted shock pulses (SP(t)).

2. Method according to Claim 1, wherein, when determining the at least one variable which characterizes the degree of wear of the cooling device (3) , substantially those shock pulses (SP(t)) which have a repetition rate of ωο and/or 2 <do are taken into account, wherein <do is the rotational frequency with which the cooling device (3) is operated.

3. Method according to Claim 1 or 2, wherein the at least one variable which characterizes the degree of wear of the cooling device (3) is determined by means of a frequency distribution from a number of shock pulses (SP(t)) which are detected and/or extracted over a prespecified time period.

4. Method according to Claim 1, 2 or 3, wherein the at least one variable which characterizes the degree of wear of the cooling device (3) is determined from an integrated level of the detected and/or extracted shock pulses (SP(t)).

5. Method according to one of Claims 1 to 4, wherein a frequency analysis, in particular a discrete Fourier transformation, of the detected and/or extracted shock pulses (SP(t)) is carried out in order to determine the at least one variable which characterizes the degree of wear of the cooling device (3).

25 07 17

6. Method according to one of Claims 1 to 5, wherein:

- the structure-borne noise signal is preliminarily filtered by means of a high-pass filter (7) or a band-pass filter;

- the shock pulses (SP(t)) are demodulated from the structure-borne noise signal;

- the structure-borne noise signal is rectified; and/or

- envelope curves are formed around the shock pulses (SP(t)) in order to detect and/or extract the shock pulses (SP(t)).

7. Method according to one of Claims 1 to 6, wherein shock pulses (SP(t)) in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 35 kHz, are detected in the structure-borne noise signal and/or extracted from said structure-borne noise signal.

8. Method according to one of Claims 1 to 7, wherein the structure-borne noise signal is recorded in the region of the cooling device (3), preferably on its housing.

9. Method according to one of Claims 1 to 8, wherein the cooling device (3) is designed as a rotary Stirling-type cooler.

10. Method for monitoring a degree of wear of a cooling device (3) which is operated with at least one piston (3a), in particular for an infrared detector (2), wherein the degree of wear is continuously determined by means of a method according to one of Claims 1 to 9, wherein the at least one variable which characterizes the degree of wear of the cooling device (3) is continuously compared with at least one prespecified limit value, and wherein a warning message or the like is output when the at least one limit value is exceeded.

11. Measurement system (6) for determining and/or monitoring a degree of wear of a cooling device (3) which is operated with at least one piston (3a), in particular for an infrared detector (2), comprising at least one structure13 borne noise sensor (4) and at least one signal processing and evaluation unit (5) which is connected to the at least one structure-borne noise sensor (4) so as to communicate with it and which receives the structure-borne noise signals, which are recorded by the at least one structure-borne noise sensor (4), as input signals and which is designed to carry out a method according to one of Claims 1 to 10.

12. Measurement system (6) according to Claim 11, wherein the at least one structure-borne noise sensor (4) is sensitive in a frequency range of from approximately 20 kHz to approximately 40 kHz, in particular in a frequency region of approximately 35 kHz.

13. Measurement system (6) according to Claim 11 or 12, wherein the at least one structure-borne noise sensor (4) is of piezoelectric or microelectromechanical design.

25 07 17

Intellectual

Property

Office

Application No: Claims searched:

GB 1710827.5 1-13