AU753960B2 - Multi-level machine vibration tester marker pen - Google Patents

Description

PAGE- 1 MULTI-LEVEL MACHINE VIBRATION TESTER MARKER PEN This invention is a small low cost machine vibration tester with handheld operation for vibration testing and data recording by maintenance workers repairing or operating low cost and non-critical machinery which has a 'speed of rotation' typically less than 12000 rpm.

An advantage of the invention or vibration tester is simple operation and designed for on going use day after day on the factory floor. The only significantly simpler device is the variable length reed vibrometer, which is more time consuming to adjust and take amplitude readings. The vibrating reed of the variable length reed vibrometer is especially hard to observe in dark machinery spaces. In contrast my invention has an illuminated read-out to indicate the level of vibration amplitude for use in dark machinery spaces.

Maintenance workers traditionally disassemble machines to find the cause of observed or sensed excess machine vibration, increasing vibration amplitude over a time period, increasing acoustic emissions over a time period.

This often easily finds the cause for machine vibration problems including, loose rotating shafts in bearings, damaged rolling element bearings, bent shafts, loose components on rotating assemblies, plus others.

Sometimes visual inspection of disassembled parts will not verify imbalance of rotating assemblies, electrical faults in electrical alternating current motors, some V-belt drive problems, plus others as the cause of the excess vibration, etc.

The invention connected with a digital multimeter as described later in the can verify some of the above listed causes of vibration that are not obvious from a visual inspection of disassembled machine parts.

Much of the current machine vibration testing equipment is expensive and 0~40 sophisticated to scientific instrument standard and is not commonly used the majority of maintenance workers except on expensive machinery.

/V R A4/ Maintenance workers who repair and often operate machines are often PAGE- 2 pernanently working on site and often have the best time saving cost advantage to use machine vibration testing devices to assist in the testing and fault finding of machines.

The art of machine vibration monitoring in the 1930's was a variable length reed vibrometer wich was a siple reed spring, weight, holder with calibrated frequency scale device. This device only has a few dollars of parts. For the vibrometer the amplitude of vibration of the reed spring when at resonance, is an indication of machine vibration at the set frequency indicated on the scale, hence acting as a distorted accelerometer with air damping of the moving reed spring causing the distortion of amplitude at different frequencies. Therefore, the amplitude of the reed spring vibration is a measure of machine vibration amplitude but not necessarily in engineering units. While I believe air damping in the previous causes the distortion of amplitude at different frequencies, I do not wish tobe bound by this.

This invention is an upgrade of the variable length reed vibrometer using modern technology including computer technology and developments in software and the minimum of electronic components.

Most current machine vibration moioig devices use expensive calibrated transducers that convert the mechanical vibration into a voltage signal proportional to the mechanical vibration in engineering units of vibration (for example possibility mm/s RMS -velocity transducer, g acceleration transducer, etc.). The normally linearly calibrated vibration transducer outputting electrical signal is then conditioned and analysed by very sophisticated and complex computer type circuits, especially for FFTtoo, Fast Fourier Transform- analysis, and then displayed in engineering units of vibration, usually on a computer type screen. Many of these expensive vibration transducers are permanently mounted on the machine surface by various means such as epoxy, cyanoacrylate cement, threaded stud or permanent magnet, as opposed to the hand-held invention- Permanently mounting the vibration transducer greatly increases the likelihood of exact :35 repeatable results and reduces the likelihood of gross errors.

invention is hand-held when taking vibration readings which is only convenient for a quick look survey. Hand-held vibration readings can have errors and poor likelihood of exact repeatable results. The invention is only intended to indicate significant increases in vibration from the **to previous vibration reading. This method of concentrating on relative changes is cited as a more reliable indication of machine condition than PAGE- 3 some of the Machine Vibration Standards that relate to machine type and power or size. This also reduces the risk of false alarm type repairs caused by the poor likelihood of exact repeatable results when using the invention used as a hand-held vibration device. The operating condition of the machine subject to vibration testing can greatly affect machine vibration levels indicated. This applies especially to machines that can operate at different load conditions and this loading factor can be written on the machine surface with the vibration data as explained later in the text.

Excess machine vibration in some machines can cause repeated breakdowns and unreliability. If the cause of vibration is diagnosed and repaired a previous troublesome machine can become reliable again. In some machines a red LED illumination vibration level would indicate excess machine vibration.

Importantly the written data on the machine surface also acts as a memory aid to maintenance workers. As even small factories can have hundreds of machines. Every maintenance worker at some time has stood looking at troublesome machine wondering if the machine is vibrating more than when it was brand new or operating reliably.

These "engineering unit(s)" calibrated vibration transducers are expensive and easily damaged by rough treatment and thusly not favoured for day to day use by the majority of maintenance workers where any possible cost savings could easily be lost in purchase of replacement of damaged expensive monitoring equipment.

0 This present invention consists of the minimum hardware to give the operator a visual indication of a possible significant change in machine 30 vibration from a previously recorded vibration data.

On the occasions, when more information is required, the invention has the potential to provide this. If mass produced to a suitable level of conformity, so that suitable software could be written by the manufacturer and then an algorithuse to correct the utut rm heetonccici to indicate engineering units of vibrations and perform fast fourier analysis in engineering units. The invention includes a nonlinear vibration ~*transducer- non-linear as a function of fr-equency. This nonlinear output for the electronic circuit can be corrected by an algorithm. A laptop computer is most suitable because it is easily portable and readily available in many factories. This provides the option to use the invention connected Z- a laptop computer, to display the frequency components of maximum PAGE- 4 amplitudes and then predict the machine faults producing these specific frequency components.

The invention can be described as an hand-held machine vibration tester and writing instrument comprising of.

an housing approximately the size of a match box, fitted with an accessible on/off switch and electro-magnetic radiation shielding for the internal cavity, to contain an electronic circuit, and an electrical power source; a vibration probe mounted on the outside surface of a housing wall section; a piezo element mounted on the corresponding, inside surface of said housing wail section with a permanent hardening adhesive to form a buttered joint between the inside housing wall and the piezo element; a weight mounted on the said piezo element, with a permanent hardening adhesive to form a buttered joint between the weight and the piezo element; said electronic circuit for controllable electrical coupling the output from the said piezo element to drive an electronic display, exposed via the 25 housing; said electronic display is indicative of the levels of vibration amplitude, which deviates from other engineering vibration units to an algorithm -that is, a set of instructions for a computer; electrical connectors, so that temporary electrical leads can be connected for sampling the output from the electronic circuit; a liquid marking line writing pen body, attached rigidly to the housing, J5 so as to not obstruct use of the vibration probe; whereby the said vibration tester can he held by the pen body, urging the said vibration probe against a machine surface to test machine vibration and later, the pen body can be held to write data on the said machine surface.

PAGE- TO assist with understanding the invention, reference will now be made to the accompanying drawings which show some possible embodiments of the invention.

In the drawing figure 1 shows the construction and housing of the vibration transducer.

This basic invention can be constructed in several different embodiments, each having a 'characteristic graph' of a different form.

The kit form embodiment of the invention can be sold for home assembly The kit contains, a housing box, a vibration probe, a weight electronic components and Printed Circuit Board- PCB- to assemble an embodiment of the invention. The kit's transducer section is assembled by gluing the components supplied. The glue is two part mix epoxy resin. The components of the transducer section are a vibration probe, piezo, element,, weight, housing wall section. Referring to figure 1 shows a cross-section of a vibration transducer. The base of a small plastic housing box walsection 4is glued to the piezo element 2with the orientation crystal side to the wall section 4 while the brass mounting plate side has glued to it the 20 gm weight 1. At the outside corresponding position of the wall section 4 the flat side of the vibration probe 5 is glued. The two wires 3 from the piezo element are connected to the Field Effect Transistor -FET- preamnplifier circuit that is part of the electronic circuit.

The electrical output from the kit embodiment transducer is amplified by the FET preamplifier circuit to an output level that is capable of driving a multiple comparator circuit, or similar.

30 The kit embodiment vibration transducer is constructed to drive a "bargraph voltmeter" using comparator circuits. These comparator circuits illuminate, in order, four LED's coloured first lowest voltage, green, :9 .yellow, orange and red the highest voltage. In typical machine vibration applications the voltage is driven by an alternating current of many 3 5 frequency components.

The kit embodiment's LED electronic display is a very common type of circuit with very common electronic components and it is unexpected that such a simple circuit would produce a useful outcome when observed with the naked eye. The LED electronic display when observed with the naked eye blurs a rapidly changing vibration signal into the appearance of a steady display. The four LED electronic display de-emphasises small but PAGE- 6 rapid changes in the amplitude of any input signal. This can be an advantage over a numerical digitally driven display.

In another form of construction of the kit form embodiment the housing wall 4 is metal (conductive) and earthed to the electronic circuit -here enough epoxy resin must be placed to ensure the solder to wire 3 connection to the non-earthed side of the piezo, crystal does not short out the tranisducer. The housing earthed to the circuit provides electromagnetic shielding to the internal cavity. In this design a thicker and stronger metal plate wall section raises the natural frequency of the transducer but this also reduces the deflection of the crystal and the generated electrical signal output relative to the mechanical vibration magnitude.

To assist in understanding how the invention can function without always displaying vibration levels in engineering units, the experimental data obtained from tests is shown as a graph, for the kit embodiment vibration tester. An example is figure 2A.

The term 'characteristic graph' now to be used, is the graphic depiction of machine vibration, as measured by the invention, showing the patterns of the different coloured LED's activation, using frequency on the X-axis and amplitude in engineering units of vibration on the Y-axis.

The 'characteristic graph' for the kit embodiment vibration tester is shown in figure 2A. The 'characteristic graph shows the mmn/sec RMS in engineering units versus exciting sine wave frequency of a vibrating shaker table. The figure 2A shows the fr-equency range 30 to 200Hz.

(turning speed range of the most numerous factory floor machines). The best range for the kit embodiment vibration tester to operate at is the frequency range 30 to 200H1z. As fuirther explanation by experiment showed the natural frquency of the kit embodiment vibration tester is at 240 Hertz just above the 'characteristic graph' frequency range.

In the frequency range shown in figure 2A the LEDs illumination changing from green to red with increasing amplitude of sine wave form vibration at each specific frequency, shows a doubling (6 dB) or greater, in engineering units, of the vibration amplitude at each specific frequency on the Xaxis of the graph.

The experimentation was required because most comnmon machinery ration standards (example ISO Standard 2372-1974) relate to PAGE- 7 engineering units of vibration and the kit embodiment vibration transducer needs to demonstrate operation in the frequency range and vibration amplitude suitable for trending of slow speed typical factory machinery.

The ISO Standard 2372 used for machine vibration condition monitoring provides Standard Comparison in overall vibration for Class Two Machines, these are the most common in many factories. Typical examples are electric motors with 15 to 75kW output, generally medium machines without special foundations, rigidly mounted engines, or machines on special foundations up to 300W The ISO Standard 2372 provides guidance for evaluating levels of machine vibration in machines operating at frequencies of 10 to 200Hz.

Importantly this Class classification excludes prime movers or driven equipment in which a major vibration component is derived from reciprocating motion.

The following shows vibration levels associated with typical Class Two Machines approximating to nearest 1mm/tns RMS Good 0 1 mm/s RMS Satisfactory 1 3 mm/s RMS Unsatisfactory 3 7 mm/s RMS Unacceptable 7 mm/s RMS 25 As in figure 2A, at the 50 200Hz range, a simiflar pattern to the ISO Standard 2372 is now provided on the invention by a LED colour illumination pattern, changing as the vibration levels change ie.

Gireen 'llumination variation for different frequencies 1 -2 mm/s RMS *.Yellow illumination variation for different frequencies 1.5 4 mm/s RMS 30 Orange illumination variation for different frequencies 3 -4.5 mim/s RMS Red Illumination variation for different frequencies 5 mnis RMS The above information obtained by experiment shows the kit embodiment of the invention does not accurately follow the ISO standard, but the imoran point of the previous paragraphs is that the vibration tester is sensitive enough to detect machine vibration at the range specified in the ISO standard. The invention can also indicate changes in machine vibration level by changes in the illumination pattern of the LED's within the "good" to "uinacceptable" range. At a machine vibration level indicated by green illumination, or yellow illumination the vibration is difficult to see visually. This vibration is within or close to the "threshold of '~-~perception" for feel and audible sensing.

PAGE- 8 An increase in machine vibration indicated by the LED illumination pattern changing from green only to red illumination is a possible indication of a vibration amplitude increase of 6 dB or greater for a specific dominant frequency. A 6dB increase of vibration amplitude level over time typically (weeks/months/years) is considered "significant" in machine monitoring routines. It is an indication of a possible mechanical or electrical fault The Canadian Navy (described in Machinery Vibration- Measurement and Analysis by Victor Wowk ISBN 0-07-071936-5), use the 6dB as significant.

For a mass manufactured embodiment of the invention can be housed in a housing the size of a match-box, or smaller, made of plastic or metal. A reduction in the size of the housing would be easily achieved by using components purpose built. The vibration transducer part is comparable with the size of a piezo crystal stylus pick-up on a record player. The housing must have provision for shielding the electronic circuit from electro-magnetic fields to limit spurious signals not related to the vibration signal. Further size reduction of housing can be achieved by standard surface mount technology or a custom designed electronic chip. A mass produced embodiment of the housing could have the vibration probe 5 as an integral part of the housing 4 to lower construction costs of the housing. The housing must have provision to contain a battery and on/off switch mounting. The mass produced embodiments could have variations from the vibration tester's 'characteristic graph' as shown in figure 2A. All mass produced embodiments of the invention with a manufactured conformity should produce a common 'characteristic graph'. The manufactured conformity would extend to the design of the electronic 30circuit and the electronic components used in the manufacture of the A variable choice of small preamplifier circuit designs could be used to :0.:drive the LED display of the kit embodiment vibration tester, but each circuit would produce likely variations from the 'characteristic graph' Figure 2A.

The pen body is a necessary part of the inventions purpose during the act of.. taigvbration readings. The housing alone would be too small to hold firmly when taking vibration readings. The housing is rigidly attached to the pen body PAGE- 9 This paragraph lists some prior art details for typical commercial vibration transducers for comparison to the invention.

Typical commercial vibration transducers are usually mechanically isolated from the electronic circuit housing and display. These have their piezo crystal, or ceramic, in mechanical compression using a screw thread.

The piezo crystal compression and heavier construction provide greater mechanical stiffness- factor. This heavier construction has a high natural frequency- 20,000Hz- and has a 'flat frequency response in the lower frequency range 30-200Hz. (a 'flat frequency response' would be described by an audio engineer as desirable. An example of a flat fr-equency response graph is figure 2B). The natural frequency of the vibration transducer described in this paragraph when in a type permanent machine mounting situation, as opposed to hand-held, is typically 20,000 Hertz, depending on the transducers physical size. This 20,OOOHertz is many times above the normal operating fr-equency range that has a "flat"' frequency response.

To assist with understanding some possible applications of the invention, reference will now be made to the accompanying drawings, which show some possible applications of the invention.

In the drawings: Two modes of use of the invention are:- 25 Figure 3A. an example of vibration reading mode Figure 3B. an example of data writing mode.

Figure 3A. shows one example of a Invention being held to take a reading of the vibration level at a specific point on a section of machine surface.

Only a cut-off section of machine surface is drawn. The vibration probe is urging firmly against the machine surface and the reading is obtained by noting the colour(s) of the LED's 12 that are illuminated. The reading is designated as the highest voltage indicating colour illuminated. For example if green ,yellow and orange displays are illuminated as a steady pattern of illumination then or orange is the designated reading. The writing nib of the pen is protected with the end cap 10. The pen is hand held to take readings with the hand grasping the main body 11.

The main body 11I may be manufactured with product information printed upon the outside surface. Figures 3. Figures 4. and Figure 5. show a "PAINT PEN" logo printed on the outside surface of the paint/ink pen.

PAGE- The pocket clip 14 is only used when the invention is carried in the pocket of someone's clothing as they are walking around the factory.

Figure 3B. shows one example of the invention being used to write the vibration and other related data on a machine surface (only part cut-off machine surface drawn for simplicity). The writing end cap is removed exposing the writing nib 15. The hand grasps the main body I11 and writes as in the Figure 3B. An important ftiction of themarker is towrite an enclosed shape for example a circle, or star, or box to indicate the exact position of the vibration probe on the machine surface when taking readings. This is to ensure readings have likelihood of improved repeatable results all other criteria being equal. On some machine surfaces vastly different vibration readings can be obtained moving a vibration probe only a centimetre. The Figure 3B. shows a circle and already written as a permanent data on the machine surface. The would denote a "low" vibration reading of green LED illumination only.

It will be realized that the form of figure 3A. is not the only form of the invention but may include many possible aranemnt of which two further arrangements are shown. Three possible forms of mounting the electronics housing to a paint pen are shown in figures fig 4A.; fig 4B.; fig 4C. respectively. Note figure 4A. figure 4B. drawn without cap fitted. Referring to figure 4C. the electronic housing has the mean of being used as a cap 10 for the paint/ink nib sealing the nib from the outside air.

Advane in electronics test equipment in the recent years provide massive cost reductions in purchase price of digital multi-meters with frequency reading test function. The cost is now within the price range for many maintenance workers who regularly use a multi-meter to diagnose :6-JO electrical problems in machines. These frequency read-out multi-meters, can provide extra information often not previously available at low cost.

An added advantage is provision for a connection to a multi-meter to provide information relating to a possible dominant frequency. Thusly the invention can be used for simple digital frequency analysis at a low cost, 0 0035 adding to the information that the LED display provides. The simple digital "frequency analysis" works only where one fr-equency is dominant with a much larger amplitude over all other frequencies, within the 0working range as per 'characteristic graph'. This is determined by noting 0* th rqec edn ftenut-meter over a minute or so. If the multimeter frequency reading is constant this may be the one frquency dominant over other frequencies in the signal. Quantitatively the dominant

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1 frequency would have an amplitude in the order of at least 10 times, or PAGE- 11 over the next largest frequency. If the multi-meter frequency reading is constantly changing over a wide range the vibration signal is of a complex form in the frequency domain, and a more advanced frequency analysis in required. Thusly connection to a computer may be required to perform this advanced frequency analysis.

To assist in understanding the use of the invention with a multi-meter, reference will now be made to the accompanying drawing which shows one example of this application.

In the drawing: Figure 5 is one possible method of connection using customised electrical test leads. Referring to Figure 5. The Invention is held by the body 11 with the vibration probe 5 firmly urging against the vibrating machine surface.

The illumination of the LED 12 must be noted as activated. The multimeter 20 using a small audio/phono mono plug 16 is connected by electrical leads 17 to banana plugs 18. The banana plugs 18 are plugged into the multi-meter sockets. The multi-meter must be switched to frequency reading function and the digital readout represents machine surface vibration frequency detected by the Invention.

The multi-meter could be replaced with an interface device connected to a laptop computer running Fast Fourier Transform FFT software. One example of an interfacing device is a soundcard fitted in some computers.

One example of spectrum analysis or FFT software is the "Audiotester" available free for a trial period on the Internet. The web-site address has been www.sumuller.de/audiotester. This software is not suitable as an 30 algorithm as described in the "claims" as the amplitude of vibration is not converted to engineering units of vibration. This software includes a correction files facility that can correct the frequency response of the soundcard and front and back added devices. A correction file for a specific vibration tester is made by creating a text file. It is created by 35 reading numbers off the "frequency response graph" and typing these numbers into the computer. The computer uses this data and cubicalspline-interpolation to provide a corrected frequency response into the spectrum analyser mode. This is one of many methods to develop a suitable algorithm. The method described in this paragraph assumes the soundcard used has a linear or "flat" response. This "Audiotester" software displays graphically and uses dB units to display amplitude so a further Scomputation is required to display engineering units of vibration.

PAGE- 12 Practical experiments with the Kit Vibration Tester embodiment, subject to mechanical vibration and connected electrically to a laptop computer, running the "Audiotester" software, show a Kit Vibration Tester embodiment produces large enough voltages to be measured by the sound card interfaced to the test laptop computer.

Importantly in experiment, with the Invention, the "Audiotester" software proved accurate measuring in the frequency scale. The amplitude scale was less accurate,, but this is a less important criteria than having the frequency scale accurate. The fr-equency, in Hertz, relative to the turning speed of the machine is usually used to determine the mechanical or electrical fault ie imbalance, misalignment, single phasing etc.

Different types of engineering vibration units of displacement, velocity and acceleration are related by a nonlinear formula in the frequency domain. The different engineering units of vibration, for example velocity, acceleration and distance, are related linearly on log-log axis in the frequency domain. Changes in machine vibration indicated by illuminations of different coloured. LED's on the invention, within the frequency range of the 'characteristic graph', fall outside the frequency response of all these engineering units. The relationship between the readout of the vibration tester and engineering units is very complicated 25 thus the benefit in using a suitable algorithm.

F or a mass produced embodiment of the invention the software could be written by the manufacturer to provide the algorithm. One example of this algorithm displayed by a computer, could graphically display the frequency range of the relevant 'characteristic graph' and the vibration amplitude, in an engineering vibration unit of operator's own specified choice, ie acceleration, velocity, distance.

It is envisaged that the invention would be used for day to day testing in a typical factory. The invention connected to the laptop computer would 3 only be used on occasion, thusly the electrical leads 17 can be described as temporary electrical leads. The laptop computer is less likely to be damaged from a rough factory floor environment with this pattern of use.

It is envisaged the invention with connection to the multi-meter option, as described previously, would be used more than the laptop computer connection option.

PAGE- 13 It is important to note that for on-going consistent monitoring with this invention, models or embodiments with the same 'characteristic graph' would have to used at each designated location. The 'characteristic graph' for each embodiment of this invention would be sold with each device and listed with the specification listing.

The invention may provide machine vibration data to indicate many commnon machine problems, not limited to, but including, imbalance, coupling mis-alignment, resonance, belts and pulleys, bearings, electrical motor vibrations.

Claims (8)

1. A hand-held machine vibration tester and writing instruiment comprising: a housing approximately the size of a match box, fitted with an accessible on/off switch and electro-magnetic radiation shielding for the internal cavity, to contain an electronic circuit, and an electrical power source; a vibration probe mounted on the outside surface of a housing wall section; a piezo element mounted on the corresponding inside surface of the said housing wall section, with a permanent hardenig adhesive to form a buttered joint between the inside housing wall and the piezo element; a weight mounted on the said piezo element with a permanent hardeing adhesive to form a buttered joint between the weight and the piezo element; said electronic circuit for controllable electrical coupling to the output fr-om the said piezo element, to drive an electronic display exposed via the .2 housing; said electronic display is indicative of the levels of vibration amplitude, which deviate from other engineering vibration units but is related by an algorithm -that is a set of instructions for a computer; electrical connectors, so that temporary electrical leads can be connected for sampling the output from the electronic circuit; a liquid marking line writing pen body attached rigidly to the housing, 35 so as to not obstruct use of the vibration probe; whereby the said vibration tester can be held by the pen body, urging the said vibration probe against a machine surface to test machine vibration and later the pen body can be held to write data on the said machine surface. PAGE-

2. The machine vibration tester, of claim 1 wherein each predetermined level of vibration amplitude is indicated by an illumination of a different coloured light emmitting diode.

3.The machine vibration tester, of claim 2 wherein the electronic display can indicate four levels of vibration amplitude.

4. The machine vibration tester, of claim 3 wherein the electronic display has a red illuminating light emitting diode to indicate the highest level of vibration amplitude. machine vibration tester, of claim 4 wherein the electronic display has a green only illuminating light emitting diode to indicate the lowest level of vibration amplitude.

6. The machine vibration tester, of claim 4 to 6 wherein the electronic display changing from a green light emitting diode illumination to illuminate a red light emitting diode is indication of a possible dominant frequency increase in vibration amplitude by a nominal 6dB.

7. The machine vibration tester of claim 1 wherein has said temporary electrical leads that can be connected via an interfacing device to a computer.

8. The machine vibration tester of claim 1 wherein has means to display on the said computer, in engineering units of vibration for acceleration, velocity, or distance, each as a function of frequency, an output from the electronic circuit.

9. The machine vibration tester of several embodiments substantially as herein described with reference to the accompanying drawings. o• *.o RONALD ALEXANDER HIGGINS 28 AUGUST. 2002