Note: Descriptions are shown in the official language in which they were submitted.
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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
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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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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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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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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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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
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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.
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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
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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
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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.
