CA1168470A - Procedure and device for measurement - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention refers to a procedure and a device for measur-ing the degree of compaction attained when compacting a foundation by means of a vibrating compaction tool. The movement of that part of the compaction tool which rests on the foundation is sensed and analysed. The time interval elapsing between successive passages of the movement signal through the zero point or other reference level is measured.
Alternatively, the ratio between the absolute values of the extreme positive and extreme negative values of the motion in relation to the said level is also measured. By means of the relative magnitudes of these time intervals and amplitude relationships respectively a quantity is formed which comprises a measure of the degree of compaction of the foundation. The invention also refers to electronic devices which sense the movement and calculate the time intervals and amplitude relationships and calculate a quantity as a function of these, which comprises a measure of the degree of compaction attained in the foundation.

Description

~id/p~r PROCEDVRE AND DEVICE FOR MEASUREMENT

Teehnleal_ar a to whieh the invention relates The present inven-tion refers to a procedure and a device for measuring the degree of compaction achievea when compacting a foundation by means of a vibrating compaction tool. The eompaetion tool may be a roller with at least one eylindrieal drum which is caused -to oseillate by means of an eccentric weight rotating inside it~

Baekqround to the invention and teehnieal standpoint _ If the degree of compaction achieved wi-th a vibrating compact-iny tool can be measured simply and continuously, and if the frequeney and amplitude of the vibration of the eompaction tool, as well as the speed with whieh the tool is moved aeross the foundation, ean be varied, it would be possible to eontrol the eompaetion tool with the aim of at-taining op-timal eompaetion~ The danger of termina-ting eompaction before a suffieient degree of compaction has heen attained, or eontinuing eompaction although a suffieient degree of ~ eompaetion has already been attained, could be minimized.
There has therefore long existed a neea for a simple, inexpen-sive and reliable continuously measuring eompaetion degree ; meter for vibrating tools. In the pa-tent literature there :~ are many more or less different proposed designs of eompaetion degree meters. Among -those tha-t may be of interest as a baekground to the present invention, the ones deseribed in ~ British pa-tent 1372567 and USA patents 3599543 and 4103554, . L for example, may be mentioned.
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, ~ P~Co2 ' t r Brief description and summar~ oE the inven-tion The invention is based on sensing at least the vertical component of the movement of that ~art of the compaction -tool which rests on the ~oundation and carries out compaction.
If the compaction tool is moved across a flat, homogeneous, extremely soft and completely resilient foundation, -the aforementioned ver-tical component of -the movement would be a purely sinusoidal movement with respec-t -to time for the majority oE conventional compaction tools. On the other hand, if the compaction tool is moved back and forth across a stre-tch of the foundation consisting of soil or asphalt then at least initially a gradual increase i~ rigidity would be achieved in the foundation. Owing to the dynamic interac-- tion between the compaction tool and the foundation, the aforemelltioned vertical movement would increasin~ly deviate in shape from the purely sinusoidal form with increasing rigidity of the foundation. This deviation from a sinusoidal form is -- if all parameters in the compaction tool remain constant -- directly related to -the dynamic characteristics of the foundation and primarily its rigidity.

Through the aforementioned USA patent 4103554 it is already known that from the output signal of a transducer which senses the aforementioned mo~ement it is possible to filter out subsignals t'ne frequency of which essentially coincides with the basic frequency of the vibration and its harmonics.
According to the aforementioned patents there exists a relationship between the amplitudes of these subsignals and the degree of compaction.

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~id/pl`R~3 -r Even though compaction me-ters according to USA patent 410355 often work well, at least in certain connections, they do have certain disadvantages. For example, if i-t is deslred to vary the vibration Erequency of the compaction tool it is necessary to have either exchangeable bandpass filters or bandpass filters with controllable passband Erequencies, which renders the meter more complicated and more e~pensive~
Another drawback is that it is based on the concept that the basic ~requency of -the vibration is the lowest frequency in the movement performed by the vibra-ting and compacting part of the compaction tool.

The present invention is hased on the insight -that the relative magnitudes of the time in-tervals be-tween at least certain successive passages through the zero point of the said movement, or signals from the transducer sensing -the movement, display a relationship with the degree of compac-tion of the foundation. The invention is also based on the insight that the basic Erequency of the vibration is not the lowest frequency of the movemen-t perEormed by the vibra-ting and compacting part of the compaction tool. Depending on the type o~ compaction tool, lower frequencies may exist in the movement, including t~ose depending on the degree oE compac-tion of the Eoundation as well as those having poor re-lationship with the degree of compaction and stemming princi-pally rom the design and operation of -the compaction tool.

According to -the invention the magnitude of the -time interval between two or more successive passages -through the zero point of a signal from a transducer which senses the movemen-t of a vibrating part of the compaction tool which comes into L contact with and compacts the foundation is measured. ~y means . ~

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r of the relative magnitudes oE the said time intervals a quantity is formed which cornprises a measure o:E the degree of compaction achieved in the foundation~ ~i.thout :Eurther explanation it will no doubt be realized that when usin~
suita~le time measurement devices it is not necessary to reset the compaction degree meter or adapt it to the vihration frequency.

The invention does no-t utilize the absolute amplitude of the movement, wi-th the result that any changes in the sensitivity of the transducer or the amplification of the signal on account of aging va.rying, -temperature, etc~ are of no signifi-cance. ~n the other hand, the relative amplitude oE -the movement can be utilized in certain versions of the invention.

Detailed description_of th _ vention The invention will be described mainly wi.th reference to a version for cases where the compaction tool consists of a roller with a cylindrical drum which is caused to oscillate by means of a weight rotating i.nside it which is eccentrically located in relation to -the symmetric axis oE the drum. The acceleration of the drum in a vertical direction is recorded by an accele.rometer mounted on one of the bearing houses of the eccentric shaft, cf. the previously mentioned USA patents 3599543 and 4103554.

Fig. 1 shows examples of signals from a transducer Fig. 2 shows the values of quantities Eormed by the relative magnitudes of successive time intervals between passa-L ges throu~h the æero point ,:

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Fig. 3 shows examples of signals from a transducer when -the roller has such a combination oE parameters (static load, dynamic load, total weight, frame rigidity, power transmission, e-tc.) tha-t a state of oscillation arises Fig. 4 shows in block diagram form the conflguration of a version of a device according to the invention Fig. 5 shows in hlock diagram form the configuration oE an additional version of a device according to the invention Shown in Fig. 1 are examples oE signals recorded Ln this way during the first, sixth and twelfth pass on a foundation consisting of non-cohesive soil. Owing to the clynamic inter-action between the various parts of -the roller and the foundation the signal will increasingly deviate in shape , from -the sinusoidal form obtained when the roller moves ; across a soft and completely resilient foundation as the rigidity of the foundation increases. This deviation frorn sinusoidal form is -- if all roller parameters are constant --related to the dynamic properties of the foundation and primarily its rigidity. The magnitude 1 - Tl/T2 or T~/T~ -1 as in Fig. 1 shows good significance when correlated with the degree o compaction according to studies -that have been conducted. An advantage of -this quantity is also tha-t it can be calculated to a high degree of accuracy with a comparatively simple electronic device. In practicet the parameter value is calculated as a mean value of a certain number of periods of the oscillation in order to get away from -the eEfect of i L cyclic variations in the zero level of the signal and random - - -- - - .. .

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r-variations in the signalO Fig. 2 shows the parameters 1 -~rl/T2 (curve A) and T2/Tl - 1 (curve s) as a function of the number of passes calculated from the recorded signals as shown in Fig. 1. The respective parameters have here been calculated as mean values over two periods. The result shows a parameter value increase which in princi.ple corresponds to the compaction degree increase with an increasing number of passes completed.

Certain cornbinations of roller parameters produce oscillation sequences like those in Fig. 3, which may be due to the drum performing clouble jumps or entering a state of rocking oscillation. In the lat-ter case this effect can be eliminated for the most part by recording the acceleration of hoth . sides of the drum simultaneously and carrying out the analysis - on the mean value of the two signals, i.e. the movement of the centrepoint of the drum is analysed. In these cases it is under all circumstances important -to calculate the para-: meter in question as the mean value of two periods or a multiple oE two periods. Normally, the parameter is calculat-., 20 ed as a mean value of a large number of pe:ri~cls in order to reduce the risk oE random variations.

A aevice which calculates and presen-ts t,he result according to the invention can be arranged in several differen-t ways.
Two different main versions may be distinguished, one which ` is based solely on analogue signal processing and one in which the actual calculation of the re].evant parame-ter takesplace digitally. Fig. 4 shows in block diagram form the configuration of a device according -to -this latte:r version.

~; 30 L An electrical signal which describes the movement of the _ _, _ _ _ _-- .. . ...... .. . . . .. .. .... . ... . . . . .

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r drum is generated in transducer tl), which may suitably consist of an accelerometer mounted vertically on the vibrat-ing part of the compaction tool~ In certain cases i-t may be advantageous for the the two transducers to be averaged in such a mannex that a signa] corresponding to the vertical movement of the centre of gravity of the vibra-ting portion is generated. ~isturbing low-frequency and high-frequency oscillations are Eiltered out in block (2)~ Low-requency oscillations arise hy the compaction tool -travelling over an uneven surface, or example, or hy the frame of the tool entering a state of oscillation. High-frequency disturbances arise as a result of resonance in the structure and bearing play. Block (3) detec-ts passages through the zero point in the signal. This block also contains a device which blocks the zero detector for a length of time corresponding to halE
the shortest period tnat can occur. This is to avoid spurious zero de-tection occurring on account of superposed high-fre-quency disturbances remaining after (2). Two outgoing signals which control two gates (5) and (6) go out from (3)~ Gate (5) is open and allows pulses Erom the clock (4) to pass through when the signal from (2) is above the zero level and gate (6) lets through clock pulses when the signal level is below zero, The pulses rom the gates are counted or a defi~ite period of time and s-tored in two registers (10) and (113. After the predetermined time the contents o-f the registers are transferred to a digital divider section, following which the registers are reset to zero and begin to count pulses afresh~ The predetermined time for forming the mean value can be generated by the transducer signal so that it comprises a definite multiple of the periodicity of the main oscillation, which can be implemented with a counter L (7) orr alternatively, the average time is determined by the , _, ... . . . . . , . . _ . . _ .. ... ... . . .... . . .. .. . . . ... .

~ld/pa~8 r clock via a counter ~8) so that mean value formation takes place for a definite time asynchronously with the periodicity of the oscillations of the compaction tool. In the divider section the two digital values are divided by each other, following which the parameter value (1 ra-tio) is calculated in block (12)~ The digital parameter value is presented on a display and/or a printer ((13) and (14)). The digital parts of the device (15) can be constructed from s-tandard TTL or CMOS components but may to advantage consist oE a micropro-cessor.

So far it has been assumed that the output signal from a transducer which senses a part of -the movement of the compac-tion tool at least after a certain signal processsing comprises a distorted sinusoidal siynal, in which -the distortion is due to the rigidityr etc. of the foundatioll. Theoretically, other transducers are conceivable which generate a sinusoidal signal superposed on a constant or nearly constant signal.
In theory at least, such a signal could in electrical form always be of the same polarity but of varying amplitude.
Theoretically~ it is also conceivable that a superposed signal arises on account of the compaction tool moving up or down an incline. In such cases the passages through the zero point o the signal, to the extent that they occur, naturally do not constitute a good point of departure for measuring the degree of compaction, According to the invention, however, the same technique can be applied as in the case of the distorted sinusoidal signal if times when the submovement signal coincides with a reEerence value or when it rises above or falls below a reference value are sensed or detected instead of the passages through the zero point of the signal.
L The requiremen-t here is that -the reference value comprises ' !

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the arithme-tical mean value of the submovement signal calcu-lated or obtained over a suitable length o time~ One me-thod of ensuring that such a reference value coincides with zero i~ of course high-pass filtra-tion of the submovement signal.
The passband of the high-pass filter should then allow signals with a considerably lower frequency than the funda-mental frequency of the vibration to pass through, and pre~erably also signals wlth a frequency which is a fraction oE the Eundamental frequency of the vibra-tion. On the other handl zero frequency and direct current components, i.e.
chiefly stationary components of the submovement signal, should be filtered out effectively.
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The simplest version of a procedure or a device according to the invention is based on the quantity 1 minus the relation-ship between the magnitudes oE two consecutive time intervals.
The transducer should preferably be oriented so that the polarity of the signal will be as in the example in Fig. l~
The ratios Tl/T2 and T3/T4 will then be less than one if T1 and T3 are defined as -times during which the signal level is above zero and a certain reference value respectively and T2 and T3 are defined as times during which the signal level is below the said level. In certain connections lt is preferable to measure several time intervals and form subquantities as above.
,'-The quantity used as a measure of -the degree of compaction is then formed as an arithmetical and/or geometrical mean value of the subquantities. Alternatively, all time intervals during which the signal is above zero or a reference value and the corresponding time interval during which the signal L is below the said value can first be summed individually Eor a definite perlod of time or a definite number of cycles, ~ollowing which the desired quantity ls calculated as I
minus the ratio between the two sums.

A more complicated version of the invention t'nan those so ~ar ~escribed is hased on also measuring and utilizing -the relative amplitudes of the acceleration motic>n as well. The relative amplitudes oE the accelera-tion motion are understood in this connection -to be the size relationship ~ between the maximum amplitudes of the rnotion, or ~eviations Erom the mean value in the event that the Mean value is no-t zero over an entire period, during the tlme interval between consecu-tive passages t'nrough the zero point and -times when the momentary value coincides with the mean va1ue respectively in -the said cases. In Fig. 1 the absolute amplitudes A1 and ; A2 during the timé intervals Tl and T2 respectively are ; shown. According to the invention, although the absolute values A1 and A2 in the accelerometer signal are measured, it is the relative magnitude~ which is o~ signi~icance ` ~ for the degree of compaction. Several flifferent functions of~
and the relative magnitude of -time intervals Tl and T2 are conceivable as an output quantity and measure of the clegree o~ compaction achieved, for example T2 - Tl ; ~T2 - Tl and ~ r2 - Tl Tl Tl ~ T2 Tl ~ T2 Other powers of ~ and Tl/T2 besides 1 are also conceivable. Shown in Fig. 2 as an example is the quantity (~-T2 - T1)/T1 as curve C. One version oE an alternative L version is described below.

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The movement o the drum is sensed and filtered by means of a transducer 16 and a filter 17 as in Fig. 5 in the manner described with reference to the version as in Fig. 4. Passage of -the signal through the zero point or other reEerence level is detected by a threshold detector 18. The maximum value of the signal between two passages through -the signal ero point is determined in a peak value detector 1~ which is reset every time the signal passes the reEerence level ~ which is detected by the threshold detector 1~. The maximum .~ 10 value is converted into a digital value by analogue~to digital conver-ter 20. In a corresponding manner -the minimum value of the signal between two passages of the reference level is sensed in block 21~ The minimum value is converted by the analogue-to-digi-tal conver-ter 22 into a di.gital value.
: Detecte~ passages through the reference level :in the form of pulses from 18 reset the maximum value detector 19 and the minimum value detector 21 to zero. The pulses from threshold detector 18 and the digital values from the converters 20 and 21 are connected to a processor 23. The value of -the output quantity in question is calculated in processor 23, v after which the value is presented on display unit 24.

It is easy for the expert to construct a device or carry out a procedure according to the invention with commercially . available discrete components and integrated circui-ts. From . manuals, data sheets and other information supplied by manufacturers and/or sellers of electronic components such as Texas ~nstruments, Fairchild, Motorola, etc~ it is evident which components can be used, such as threshold detectors, comparators, counters, dividers, multipliers, filters, ampli~iers, clocks, etc. It is also evident which modi:Eica-L tions and additions are needed to adapt the components to different frequency rangesO ~rom inEormation supplied by manufacturers and/or sellers of vibracing compaction tools such as vibratory rollers the data which the expert needs in order to apply the invention when compacting with -them will be evident. ~rom the aforementioned patents i-t is evident how transducers Eor sensing the movement oE the compaction tool can be mounted. From these, examples oE usable -trans-clucers are also evldent as well as how more than one trans-ducer can be used simultaneously in order to reduce -the effect of certain disturbances. It is therefore probably unnecessary -to specif~ cornponents and circuits in detail.

Summary The invention reEers to a procedure and a levice for measur-ing the degree of compaction attained when compactin~ a Eoundation by means oE a vibrating compaction tool. The movement o~ tha-t part of the compac-tion tool which rests on the ~oundation is sensed and analysed. The time interval elapsing between successive passages o~ the movement si~nal through the zero point or o-ther reference level is measllred.
Alternatively, the ratio between the absolute values of the extreme positive and extreme negative values oE -the motion in relation to the said level is also measured. By means of the relative magnitudes of these time intervals and amplitude relationships respectively a quan-tity is formed whicn comprises a measure of the degree of compaction of the foundation. The invention also refers to electronic devices which sense the movement and calculate the time intervals and ampli-tude relationships and calculate a quantity as a function of these, which comprises a ~easure of the degree of compaction L attained in the foundation.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 A procedure for measuring the degree of compaction attained when compacting a foundation with a compaction tool having a vibrating section which in contact with the foundation and moving along it compacts the foundation; in which connection a submovement signal representing at least the most rapidly varying vertical component of the movement of the compacting section is generated, characterized by sensing of points in time when the submovement signal coincides with a reference value and/or when the submovement signal is above or below a reference value, in which connection the said reference value at least for the most part coincides with the mean value of the submovement signal, and by the formation of a quantity as a function of the magnitude of the time interval during which the signal is larger and smaller than the reference value or the time interval between successive points in time during which the submovement signal coincides with the reference value, which quantity is used as a measure of the degree of compaction.

2 A procedure as in Claim 1, characterized in that the function is a constant reduced by the relationship between the magnitudes of two time intervals.

3 A procedure as in Claim 1, characterized in that the func-tion comprises a mean value formed as a constant reduced by the relationship between the sum of a number of time intervals during which the signal is above the reference value and the sum of the same number of time intervals during which the signal is below the reference value.

4 A procedure as in Claim 1, characterized in that the function comprises a mean value of a number of subfunctions each of which is the difference between a constant and the relationship between the magnitudes of two time intervals.

5 A procedure as in Claim 1, characterized in that the extreme positive and extreme negative values of the submove-ment signal are also sensed in relation to the reference level and that the quantity is formed as a function of the said extreme values also.

6 A device for measuring the degree of compaction attained when compacting a foundation with a compaction tool having a vibrating section which in contact with the foundation and moving along it compacts the foundation, in which connection a transducer on the compaction tool generates a submovement signal representing at least the most rapidly varying vertical component of the movement of the com-pacting section, characterized by sensing elements for sensing when the submovement signal is above and below a reference value and/or points in time when the submovement signal coincides with a reference value, in which connec-tion the said reference value at least for the most part coincides with the mean value of the submovement signal and by function-forming elements for the formation of a quantity as a function of the magnitude of the time interval during which the signal is larger and smaller than the reference value or the time interval between successive points in time during which the movement signal coincides with the reference value, which quantity comprises a measure of the degree of compaction.

7 A device as in Claim 6, characterized in that the function-forming elements form the quantity as a function of a constant reduced by the relationship between the magnitudes of two time intervals.

8 A device as in Claim 6, characterized in that the function forming elements form the quantity as a mean value calculated as a constant reduced by the relationship between the sum of a number of time intervals during which the signal is above the reference value and the sum of the same number of time intervals during which the signal is below the reference value.

9 A device as in Claim 6, characterized in that the function-forming elements form the quantity as a mean value of a number of subquantities, each of which comprises a function of the difference between a constant and the relationship between the magnitudes of the time intervals.

10 A device as in Claim 6, characterized by elements (19,20) for sensing successive extreme positive and extreme nega-tive values of the submovement signal during the time interval, and in that the function-forming elements (23) form the quantity as a function of the extreme values also.

PASS NO. 1 Fig. 1 Fig. 2 PASS NO.
Fig. 3 Fig. 4 Fig. 5