DE2002633C3 - Measuring arrangement for automatic and continuous measurement of the damping behavior - Google Patents

Description

The invention relates to a measuring arrangement for automatic and continuous measurement of the Damping behavior of a test object stressed by random vibrations for the purpose of determining the Fatigue limit during an operational process to be monitored.

When bodies are subjected to voluntary forces, certain internal vibrations are created in the Body built up when it tries to absorb the energy given to it. In some cases this can be him given energy exceed its physical limits and induce fatigue that leads to failure of the body. Bodies that are exposed to certain types of tension and stress are optimal should be provided with a suitable reinforcement in those areas that are susceptible to failure are subject to induced internal vibrations. However, in most cases it will be a failure only by using a procedure in which the body is cut open and then examined, established what led to the destruction of the body.

To determine fatigue strength curves of test specimens under static load, it is known (Maschinenbautechnik 1962, p. 593ff) to excite test specimens on a vibrating table with the aid of a random generator and to determine the number of vibrations until hairline cracks occur. By evaluating a large number of such tests on corresponding test specimens, a statement can finally be made about the probable number of load changes with an assumed load. However, it is not possible to make statements about the fatigue limit of a stressed body during the exercise.
In a further known measuring arrangement (Materialprüfung 1966, p. 262ff), it is proposed to reduce the measuring effort to combine a magnetic tape recorder with a computer.

In another known vibration test system (US-PS 31 57 045) test objects are mechanical

Exposed to stresses in the audio frequency range

and examined in certain frequency ranges. Again, there is no statement about the fatigue limit of one stressed body is possible even during the stress on the body.

According to a known method for measuring a physical quantity by means of an electrical device (DT-PS 8 37 476) several transducers attached to the test object are spatially separated from one another scanned and their curves are shown together on a cathode ray tube. A statement beyond the fatigue limit of the test piece can not be obtained.

In a known operational monitoring system for aircraft (DT-AS 16 23 888) the Transmission paths for the measured values converted into electrical signals are used several times, these Signals converted into digital signals and displayed in quasi-analog form. A statement about that

However, the fatigue limit of the monitored aircraft is not provided.

Various attempts have heretofore been made to obtain data necessary for the design fail-safe designs and / or for co-running

fenden monitoring can be used to initiate a process through which the created Forces can be eliminated or reduced, which would otherwise cause damage to the design could. Although there are many known devices for measuring the response of bodies or There are explanations for arbitrary vibrations, these are so complicated that one carries out the test The person cannot easily tell when, based on the data received, there has been a significant change in the Properties of the body or the execution results. Wind tunnel investigations, for example for flutter vibration investigations of dynamic models of vehicles have shown that decisions are not based on observation of the vehicle The time course of the relevant variables can be taken alone, since this is too complicated for the Observer could interpret more than the level of the signals. The stresses that occur are particularly critical near the flutter areas where ignorance of the attenuation trend and the Frequency can lead to destruction.

In many cases, examinations are only carried out in order to determine later by means of analysis whether the stability limits were incorrectly determined or whether the records were not long enough had been carried out in order to obtain characteristic values from them. Also were made out For security reasons, many records are longer than

Required carried out, so that valuable wind tunnel time was wasted.

There are also. Spectral analyzers for concurrent use have been developed in which attenuation laten can be obtained by measuring the bandwidth of the half-value point ^ However, this type of analysis requires a lot of time to obtain the exact attenuation values, and it leads to incorrect results for non-linear systems.

Correlation calculators have also been developed for on-line use in which attenuation data from the decrement of the autocorrelation function been received. However, these correlation calculators only give the attenuation for the amplitude of the Rms value of the random output or random output. To attenuation values at lower It takes a lot of time to obtain amplitudes, but attenuation values at higher amplitudes cannot can be obtained. Accordingly, correlation calculators can only be used with linear systems. Furthermore, the accuracy of the attenuation measurement is limited because, for. B. subtract two large numbers need to be to get a small number when the attenuation is small.

Another disadvantage of the known designs is that the attenuation indicators are not direct as electrical voltages that can be used in a control system.

The invention is based on the object of a measuring arrangement for automatic and continuous Measurement of the damping behavior of a test object stressed by random vibrations create through which from the measured values the fatigue limits of the test object already during of the measuring process can be determined.

The task is solved by the combination of the following features:

a) to determine the operational damping behavior of a DUT is in each case one by one Switch controlled measuring transducer device for positive half-waves or for negative half-waves each via a gate circuit and a switch to a measuring / holding circuit or connected for voltage comparison;

b) the output voltages of the measuring and holding circuit are in each case via sequence switch in the cycle of the timer pulses of a timer device the overall arrangement switched to output lines and

c) after a pulse sequence has elapsed, the switch is switched off via the gate circuit.

Arrangements and a scanning device are connected to the outputs for continuous averaging connected, to correct the displayed malfunction of the test objects is connected to the output of the Scanning device, a computer-based correction network is provided at the location of the objects to be measured.

The output data of the measuring arrangement are used to determine the safe working conditions of equipment suitable and make it possible to determine impending failure. The measurement is made while working equipment and the output signals obtained can be used in a control system in order to automatically correct dangerous abnormal observations.

In a particular application, the measuring arrangement results in different attenuation decrements Determined aircraft parts for those times in which there are arbitrary inputs, for example while taxiing, landing, taking off, during flight through turbulence or eddy zones (»The one during normal flight under boundary layer conditions. Such arbitrary inputs can also artificially generated using a random number generator. The determined damping decrement comes with a standard element on a dual track oscilloscope compared by the flight engineer. Variations can occur in terms of fatigue or the deterioration in stability can be interpreted.

The determined attenuation decrement signal can also be used as a control signal in an electrical control system of the aircraft used to be in dangerous situations instantly at a time that is shorter than the human reaction time to initiate a control process, for example when approaching to the so-called flutter limit. The determined damping decrement can also be saved and at the maintenance of the aircraft.

The measuring arrangement can also be used for flutter and vibration tests on dynamic models in the wind tunnel be used to determine the recording time required for statistical evaluations, whereby the test and analysis time can be reduced.

When using the measuring arrangement in the manufacture of certain parts of aircraft, automobiles, Spacecraft and the like can be discarded individual off-standard parts.

The measuring arrangement can also be used to display the operating status of systems that are in operation can be used, for example, in bridges and buildings that are excited by wind loads Vehicles excited by roughness of the road, etc.

As a general laboratory device, the measuring arrangement according to the invention can be used, to measure attenuation of nonlinear and linear systems. It can also be used as a device for classifying biological samples can be used.

An advantage of the measuring arrangement according to the invention is that a damping measurement during of the operation of the device under test can be obtained in the form of an electrical signal, which in turn is called Process control variable can be used. Measured values are also faster and more accurate than before methods used, regardless of whether the systems are linear or non-linear.

With the help of the measuring arrangement according to the invention, the effects of non-stationary influences recorded and automatically compensated.

The invention is explained below with reference to the drawing, for example.

F i g. Figure 1 is a simple representation of a body that is caused to respond to applied to vibrate arbitrary forces;

F i g. Fig. 2 is a diagram showing the vibrational states that exist in a given body egg are evoked when responding to forces applied to him;

F i g. 3 is a block diagram of the measuring arrangement; Fig. 4 is a timing diagram showing the working of the Measurement arrangement according to FIG. 3 is shown;

F i g. 5 is a diagram of a series of transition curves that occur in response to the outputs de

Measurement arrangement according to FIG. 3 can be obtained;

F i g. 6 is a diagram showing the attenuation data are shown, which by scanning the averaged outputs of the measuring arrangement according to FIG. 3 received will;

Figure 7 is a schematic view of a two stage Measuring arrangement;

F i g. Figure 8 is a schematic view of a multiple-entry modified embodiment a measuring arrangement;

Fig. 9 is a schematic representation of a measuring arrangement with a control system;

FIG. 10 is a diagram of an output obtained, for example, with the measuring arrangement of FIG. 9 can be obtained.

If a body according to FIG. 1 is exposed to arbitrary forces, vibrations are built up that are in According to the mechanical characteristics of the body can be damped. By connecting a vibration sensor transducer to the body according to FIG. 1, when exposed to arbitrary forces is, a vibration signal can be picked up, which is of the type as shown in FIG. 2 B is shown. The curve in this figure shows the vibrations of the body when responding on applied arbitrary forces.

When a single force is to be applied to the body and the body then responds to it the individual force is allowed to oscillate freely, the damping characteristics of the body would cause the vibration of the body to decay exponentially, as shown in FIG. 2a is shown. But when Arbitrary forces are continuously applied to the body, the oscillation deflections the body does not go back to zero and the body continues to vibrate at an irregular frequency that is determined by the sum of the arbitrary forces and the damping characteristics of the body.

By measuring the effect of the vibrations generated by the arbitrary forces you can using a concurrent or continuously effective measuring arrangement according to the invention Attenuation characteristics of the body can be obtained, so that valuable information regarding the mechanical characteristics of the body can be obtained.

Figure 3 is a block diagram of an automatic tracking measurement arrangement in accordance with the invention. This includes a switch 10, which controls a switch 12 to the input signal on a line 14 to a first transducer device 16 and to a second transducer device 18. One Reference voltage source 20 is provided in order to provide a reference voltage to the two devices 16 and 18 to put on. A gate circuit 22 or 24 is connected to the output of the comparison device 16 or 18, a switch 2f. or 28 to control which the input signal on line 14 to a holding circuit 30 or 32 applies. A reference voltage source 34 or 36 supplies a reference voltage to the holding circuit 30 or 32.

With the output of the Ihllcstromkrciscs 30 or 32 a / »- stage follower 38 or 40 is connected, which applies the test voltages to a plurality of output circuits 1, 2, 3 ... η . The switches 26 and 28, the input current circuit 30 and 32 and the / i-stage sequential switches 38 and 40 are all controlled by a /. The outputs 1, 2, 3... Π of the sequence switch 40 are coupled to the same outputs of the sequence switch 38.
With additional reference to FIG. 4, the mode of operation of the measuring arrangement according to FIG. 3 explained. The in F i g. Upper curve 15 shown in Figure 4 is an exploded view of the first three sensed vibrations of the type such

ίο in Fi g. 2b are shown. The voltage V _n T of the reference voltage source 20 is set to a suitable value of the input signal appearing on the line 14. The pulse or timer speed of the timer means 42 is then selected so that a number of samples are taken from the given input. An external start button is then actuated which causes switch 10 to turn switch 12 on and enables the input signal on line 14 to pass to transducer devices 16 and 18.

The transducer device 16 is set to provide an output signal when the voltage of the input applied to it reaches the reference voltage V _rc r. When the point A \ on the curve 15 is reached, the gate circuit 22 causes the switch 26 to be switched on in order to apply the input signal 15 appearing on the line 14 to the holding circuit 30. The output of the timer device 42 is also connected to the holding circuit 30 when the switch 26 is opened to cause the holding circuit 30 to generate a stepping output voltage which changes with each timer pulse in response to the instantaneous value of the input signal 15.

The timer signal input for the holding circuit 30 is shown in part 11 of FIG. 4, and it corresponds to points a 1, 12 a _n on curve 15 of part 1 of FIG. The timer pulses passing through the holding circuit 30 also cause the sequence switch 38 to change or change output lines with the voltage signal generated by the holding circuit 30. Accordingly, the output on line 1, in response to the input signal going through switch 26, corresponds to the first pulse shown in FIG. 4 is indicated in Part IV. The second picked up voltage, which corresponds to the voltage at point a ₂ , is applied to output 2 of sequence switch 38 and it appears as the first positive pulse that appears in part V of FIG. 4 is shown.

Similarly, the output voltage applied to the output 3 of the sequence switch 38 corresponds to the first pulse shown in part V of FIG. 4, and the voltage corresponding to the point a _n which appears at the n-lcn output of the switch 38 corresponds to that , which in part VU of FIG. 4 is represented by the first pulse. The number of samples n taken from a given input signal is generally chosen so that at least two positive intersections of the input signal are obtained.

The transducer device 18 is set so that s'c generates an output signal when the input signal 15 with its negative half-wool crosses the reference span, as it does at the point B \ in the part

fts 1 of FIG. 4 is shown. At dom point Βί the Gate circuit 24 that the switch 28 applies the input signal 15 on the line 14 to the holding circuit 32 which is also used by the timer 42 gc

controls is. where outputs for the lines 1, 2. 3 ... π of the sequence switch 40 corresponding to the points t> ~ "t> 2 ■. ■ b " are created in the manner as it is explained above with reference to the output of the switch 38. By turning on the switch 28, an off signal is still applied to the switch 10, whereby the switch 12 is turned off.

The outputs of the sequence switch 40 are directly coupled to the corresponding outputs of the sequence switch 38, so that the complete outputs on the lines 1, 2, 3 ... η comprise two pulses, the first of which is the output of the / 4 stage and the the second corresponds to the output of the β-stage, as it is in parts IV to VII of FIG. 4 is shown.

When each of the sequence switches 38 and 40 reaches the nth, ₅ output, an off signal is generated and applied to the gate circuit 22 and 24, respectively, to turn off the switch 26 and 28, respectively. Shortly after the sequence switch 40 begins its indexing process, an output 44 is generated _{which can be fed back to the ^ 0} outer start button of the switch 10 for single stage operation or which can be applied to a second stage to initiate two stage operation, as is referred to on F i g. 7 will be described.

For the sake of simplicity, the measuring arrangement according to FIG. 3 is referred to as a RANDOMDEC device. The various outputs of this device can be read in various ways. For example, an analog averaging circuit may be used so that the Ausgän- are _{averaged} 0} ge each line and approximate values of the period and the Dämpfungsdekrementes be obtained, as shown in F i g. 5 and 6 is shown. The one shown in FIG. Curves represent the typical voltage transitions of a RANDOMDEC output after passing through an averaging circuit. By scanning these outputs and displaying them on a cathode ray tube in time sequence, as shown in FIG. 6, both the period and the decrement of attenuation of the body under test can be conveniently determined.

The points 1, 2, 3 ... η according to FIG. 6A correspond to checking the outputs 1, 2, 3 ... Π taken from the RANDOMDEC device of FIG. 3 after they have been averaged to generate the stabilized output signals shown in FIG. By suitable calibration of the cathode ray tube display, the attenuation decrement can be read off very precisely as shown in FIG. 6B of the drawing. Using a suitable scale, the damping ratio can be read off directly instead of the damping decrement.

In Fig. 7, a two-step RANDOMDEC device is shown. In this embodiment, which includes a first RANDOMDEC device 50 and a second such device 52 of the type shown in FIG. 3, the outputs are connected in common to a set of output connections 1, 2, 3 ... π. The input signal applied to an input connection 54 is connected directly to the input of the two devices 50 and 52. When the first stage is started by an applied at 56 üußercs signal, the first stage 50 is actuated to a series of pulses to <, _s provide, as has been described above.

/ 11 after a certain predetermined time l'.ni'gung the first stage is made through this one Timing output 58 is generated to turn on the second stage which is a different set of Impulse creates corresponding later parts of the im Curve 15 shown in Part I of FIG. *. The timing output 60 of the second stage is to the first Stage fed back so that he is at the next peak works or becomes effective In this way, all peaks are included in the calculations.

Usually only two such devices are 50. 52 required to receive the decrement because the Graduated working time that is required is only slightly longer than one period. In certain laboratory applications it may be desirable to have more than one Consider period of decrement, in which case any number of stages in a similar fashion can be added to ensure that all Peaks gathered from pastures.

FIG. 8 shows a modified version with a multi-channel input which can be used to monitor many different conditions at the same time. In this embodiment, for example, inputs 1 and 2 are connected to a holding circuit '56 and 68, respectively, via a two-pole switch device 62 which is controlled by a timer device 64 and by on-off signals from the gate circuit 22 according to FIG. As described with reference to the circuits shown above, the output of the holding current circuit 66 and 68 is fed to an n-stage sequential switching device 70 or 72, which has a plurality of outputs 1, 2, 3 ... η for each input 1 or 2 creates. These outputs can be represented simultaneously in any suitable manner. If the comparison is made by a human operator, it may be useful to use a red light panel with a device for switching a cathode ray tube display at critical points for viewing. Multiple channels can also be used in critical cases to check the reliability of the measurement obtained. The multi-channel application shows the phase angle between the inputs as well as the attenuation and the period. This application of the invention is analogous to the cross-correlation of two signals, but it has the same advantages as those obtained with the RANDOMDEC mode of operation over the autocorrelation.

A complete measuring arrangement with a control system is shown in FIG. The entrance is in order Simplification of the explanation limited to two converters. It is to be understood, however, that any Number of transducers can be used in any suitable manner. Scndewandlcr 76 and 77 are arranged in a suitable manner so that they vibrate at critical points in the body; Sense aircraft 78. The Scndcwandler 76 unc 77 can voltmeter, Bcschlcunigimgsmcssci or any other suitable device designed to produce the desired size measure up.

The output of the Scndcwandlcrs 76 or, 77 win fed to a filer 80 or 81, which has a band size zting the signals to a segment of interest make. These signals are then fed to the RANDOM DEC device 82, which is continuously there Decrement determined. A scanner 86 is 7.1111 Sampling of the various outputs from center imaging assemblies 84 and 85 is provided and enabled the information required for a drawing up

direction 88 and a visual representation 90, if desired, the concurrently or continuously received Compare output with a previously recorded standard.

A standard selector 92 is provided for selecting a particular standard from a memory 94 which provides the appropriate reference voltage and timer setting to the RANDOMDEC device 82. The standard is then fed into the scanner 86 and the recording input | ₀ direction 88 and visual display 90 to provide an immediate indication of any deviation of the received input signals from those of the selected standard.

As in connection with Fig. 6 indicated, only the output of one is used to compare the attenuation averaged period of the signal is required. Adjacent outputs are usually also measured in order to Detect changes in period. For a failure other than the stability failure, i. H. for fatigue, loose connections etc, it may be desirable to look at all the exits to the entire RANDOM DEC drawing to be coordinated with a standard drawing.

By using a computer 100 responsive to the scanner 86, the measured Signal and the standard are compared. If voltages are outside the predetermined safety limits, a signal can be sent to one or more Correction networks 102 are sent back to perform an appropriate correction process. For example, a signal indicating the loss of stability could be used to signal a Servo device for reducing the energy supply to one or more machines or to the Switching on a standby system or activating one or more control surfaces.

In the operation of such a control system, the RANDOMDEC calculation would after processing a automatically run through a predetermined number of peaks again. This can be done conveniently by doing this occur that a counter is installed, which operates the external stop device after a predetermined Number of counts has been made.

In FIG. 10 is an example of the usefulness of the system of FIG. 9 shown. In this example, a standard is shown simultaneously with a detected signal X received at the time the tested body started to fail and a second sensed signal Z out of phase with the standard. The Fchler deviation of the sensed signal X from the standard shows very clearly the failure of the monitored body, while the phase shift ΔΦ of the second signal represents other deviations. This, of course, is another area of utility of the invention beyond simply determining the decrement of attenuation of a given implementation.

Various changes can be made within the scope of further embodiments of the invention. For example, the holding circuits from the circuit according to FIG. 3 can be omitted, however, this results in a certain loss of accuracy. Similarly, the timer device could a continuously running clock or the like that is simply switched on and not started, which is to some extent at the expense of timing. The averaging circuit can in its its simplest form can be a potentiometer. Furthermore, the RANDOMDEC device could work can be achieved by equivalent circuits in which fluidics components and / or digital computers can be used in place of the holding circuits.

Additionally, parallel RANDOMDEC devices can be used to reduce the attenuation on many different levels by offsetting the reference voltage values of each RANDOMDEC device at the same time to determine. The precision of the RANDOMDEC device could of course go further Saving the outputs of the sequence switch 38 and synchronizing these outputs with the Outputs of the sequence switch 40 can be improved. This would lead to a narrowing of the control of the Keep values around the mean. For linear and non-linear systems that are symmetric about zero, the working speed can be doubled by adding steps, which in the case of the negative value of the Reference voltage work, measured from the mean value. This can also be done by rectifying of the signal and doubling the number of steps that are at the positive reference level.

Further, additional accuracy can be obtained by adding a logical AND device to the external starter device, and a comparator device that is turned on when the input voltage is lower than the reference voltage. Without this, however, the system starts at b \ if the voltage is higher than the reference value when the external starting device is switched on. This can further be prevented by arranging a flip-flop and a switch between the switch 12 and the comparison device 18, which is switched on by the timing signal from the switch 26 and switched off by the timing signal from the switch 28.

For this purpose 4 sheets of drawings

Claims (3)

Patent claims: 1. Measuring arrangement for the automatic and continuous measurement of the Danipfungsver Behavior a self Random vibrations stressed the measurement for the purpose of determining the fatigue limit during an operational process to be monitored, g e marks by combining the following features: a) To determine the operational damping behavior of a test object, one is in each case a switch (10, 12) controlled measuring transducer device (16, 20) for positive half-waves or (18, 20) for negative half-waves via one gate circuit (22, 24) and one Switch (26, 28) to a respective measuring and holding circuit (30, 34) or (32, 36) for the purpose of Voltage comparison connected; b) the output voltages of the measuring and holding circuit (30, 34 or 32, 36) are each via sequential switches (38 and 40) in time with the timer pulses of a timer device (42) of the overall arrangement on output lines (1,2,3 ... η ) switched, and c) after a pulse sequence has elapsed, the switch (26, 28) is activated via the gate circuit (22, 24) each switched off. 2. Measuring arrangement according to claim 1, characterized in that arrangements (84, 85) and a scanning device (86) are connected to the outputs (1, 2, 3 .. η) for continuous averaging. 3. Measuring arrangement according to claims I and 2, characterized in that for correcting the displayed malfunction of the objects to be measured (76, 77) at the output of the scanning device (86) a computer (100) based correction network (102) is provided at the location of the test objects.