U.S. patent number RE31,195 [Application Number 06/121,907] was granted by the patent office on 1983-04-05 for method and a device for ascertaining the degree of compaction of a bed of material with a vibratory compacting device.
Invention is credited to Heinz Thurner.
United States Patent |
RE31,195 |
Thurner |
April 5, 1983 |
Method and a device for ascertaining the degree of compaction of a
bed of material with a vibratory compacting device
Abstract
A device for ascertaining the degree of compaction of beds of
material with a vibratory compaction device as a function of the
vibratory amplitude of the motion of the compaction device at
selected frequencies is described. The amplitude of vibratory
motion of a compaction device is measured at a fundamental
frequency and at least the second harmonic of the fundamental
frequency and a ratio of the measured signals is computed. The
ratio or quotient of the two signals provides a representation of
the degree of compaction of the material being compressed by the
compaction device. The ratio or quotient may be utilized either as
a direct indication to an operator of the degree of compaction or
as a control signal in an automated servo control compaction
system.
Inventors: |
Thurner; Heinz (S-132 00
Saltsjo-Boo, SE) |
Family
ID: |
26656704 |
Appl.
No.: |
06/121,907 |
Filed: |
February 15, 1980 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
773783 |
Mar 2, 1977 |
04103554 |
Aug 1, 1978 |
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Foreign Application Priority Data
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Mar 12, 1976 [SE] |
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7603249 |
Aug 3, 1976 [SE] |
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7608709 |
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Current U.S.
Class: |
73/573 |
Current CPC
Class: |
E02D
3/046 (20130101) |
Current International
Class: |
E02D
3/046 (20060101); E02D 3/00 (20060101); G01M
007/00 () |
Field of
Search: |
;73/573,574,579,84,32A
;404/133 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Statistische Verfahren zur Datenverarbeitung . . . ", Thesis by
Prickhartz, published Oct. 1970..
|
Primary Examiner: Gill; James J.
Attorney, Agent or Firm: Birch, Stewart, Kolasch and
Birch
Claims
It is claimed:
1. A method for measuring the degree of compaction achieved in a
bed of material by a vibratory compaction device comprising the
steps of:
vibrating the compaction device against the bed of material to be
compacted to generate a characteristic signal of the vibratory
motion of the compacting device against said material, said
characteristic vibratory motion signal having a fundamental
frequency and a plurality of harmonic frequencies;
measuring the amplitude of said characteristic vibratory motion
signal at said fundamental frequency;
measuring the amplitude of said characteristic vibratory motion
signal for at least the second harmonic of said fundamental
frequency; and
comparing the measured amplitudes of said fundamental frequency and
said at least second harmonic frequency to ascertain the degree of
compaction of said bed of material.
2. The method of claim 1, wherein said step of comparing comprises
computing the quotient between the measured amplitude of said
fundamental frequency and said second harmonic frequency.
3. The method of claim 1, comprising the further steps of:
measuring the amplitude of the third harmonic of said
characteristic signal of said vibratory motion;
weighting and adding the measured amplitudes of the second and
third harmonic frequencies to provide a weighted sum thereof;
and
comparing the weighted sum with the measured amplitude of the
fundamental frequency to ascertain the degree of compaction of the
bed of material.
4. The method of claim 3, wherein said characteristic signal of
vibratory motion has both vertical and horizontal amplitude
components with respect to said bed of material and only said
vertical components are measured at said fundamental and harmonic
frequencies.
5. The method of claim 3, wherein said characteristic signal of
vibratory motion has both vertical and horizontal amplitude
components and both said vertical and horizontal amplitude
components at said fundamental and harmonic frequencies are
measured for comparison.
6. A system for measuring the degree of compaction achieved in a
bed of material by a vibratory compaction device comprising:
means for vibrating the compaction device against the bed of
material to be compacted;
transducer means for generating a characteristic signal of the
vibratory motion of the compacting device against said material,
said characteristic vibratory motion signal having a fundamental
frequency and a plurality of harmonic frequencies;
first filter means for filtering said fundamental frequency from
said characteristic frequency to obtain a fundamental amplitude
signal;
means for measuring the amplitude of said fundamental amplitude
signal;
second filter means for filtering at least one harmonic frequency
component from said characteristic signal to obtain a harmonic
frequency signal;
means for measuring the amplitude of said harmonic frequency
signal; and
means for comparing the amplitudes of said fundamental and harmonic
frequency signals to generate a signal representative of the degree
of material compaction of said material.
7. The system of claim 6, wherein said means for comparing
comprises divider means for determining the ratio between the
amplitude of said fundamental frequency signal and the amplitude of
said harmonic frequency signal.
8. The system of claim 6 further including:
third filter means for filtering an additional harmonic component
of said characteristic signal to obtain an additional harmonic
frequency signal;
means for measuring the amplitude of said additional harmonic
frequency signal;
means for adding the respective measured amplitudes of harmonic
signals; and
means for comparing the amplitude of the fundamental signal to the
sum of the amplitudes of the harmonic signals.
9. The system of claim 6 further including means for applying the
signal from said means for comparing to said means for vibrating to
control the degree of compaction. .Iadd. 10. A method for measuring
the degree of compaction achieved in a bed of material by a
vibratory roller of a compaction device comprising steps of:
vibrating the vibratory roller of the compaction device such that
said vibratory roller vibrates against the bed of material to be
compacted to generate a characteristic signal of the vibratory
motion of the vibratory roller against said material, said
characteristic vibratory motion signal having a fundamental
frequency and a plurality of harmonic frequencies;
measuring the amplitude of said characteristic vibratory motion
signal at said fundamental frequency;
measuring the amplitude of said characteristic vibratory motion
signal for at least the second harmonic of said fundamental
frequency; and
comparing the measured amplitudes of said fundamental frequency and
said at least second harmonic frequency to ascertain the degree of
compaction of said bed of material. .Iaddend..Iadd. 11. The method
of claim 10, wherein said step of comparing comprises computing the
quotient between the measured amplitude of said fundamental
frequency and said second harmonic frequency. .Iaddend..Iadd. 12.
The method of claim 10, comprising the further steps of:
measuring the amplitude of the third harmonic of said
characteristic signal and said vibratory motion;
weighting and adding the measuring amplitudes of the second and
third harmonic frequencies to provide a weighted sum thereof;
and
comparing the weighted sum with the measured amplitude of the
fundamental frequency to ascertain the degree compaction of the bed
of material. .Iaddend..Iadd. 13. The method of claim 12, wherein
said characteristic signal of vibratory motion has both vertical
and horizontal amplitude components with respect to said bed of
material and only said vertical components are measured at said
fundamental and harmonic frequencies. .Iaddend..Iadd. 14. The
method of claim 12, wherein said characteristic signal of vibratory
motion has both vertical and horizontal amplitude components and
both said vertical and horizontal amplitude components at said
fundamental and harmonic frequencies are measured for comparison.
.Iaddend..Iadd. 15. A system for measuring the degree of compaction
achieved in a bed of material by a vibratory compaction device
comprising:
roller means;
means for vibrating said roller means for compaction device against
the bed of material to be compacted;
transducer means for generating a characteristic signal of the
vibratory motion of said roller means of the compacting device
against said material, said characteristic vibratory motion signal
having a fundamental frequency and a plurality of harmonic
frequencies;
first filter means for filtering said fundamental frequency from
said characteristic frequency to obtain a fundamental amplitude
signal;
means for measuring the amplitude of said fundamental amplitude
signal;
second filter means for filtering at least one harmonic frequency
component from said characteristic signal to obtain a harmonic
frequency signal;
means for measuring the amplitude of said harmonic frequency
signal; and
means for comparing the amplitudes of said fundamental and harmonic
frequency signals to generate a signal representative of the degree
of material compaction of said material. .Iaddend..Iadd. 16. The
system of claim 15, wherein said means for comparing comprises
divider means for determining the ratio between the amplitude of
said fundamental frequency signal and the amplitude of said
harmonic frequency signal. .Iaddend..Iadd. 17. The system of claim
15, further including:
third filter means for filtering an additional harmonic component
of said characteristic signal to obtain an additional harmonic
frequency signal;
means for measuring the amplitude of said additional harmonic
frequency signal;
means for adding the respective measured amplitude of harmonic
signals; and
means for comparing the amplitude of the fundamental signal to the
sum of the amplitudes of the harmonic signals. .Iaddend..Iadd. 18.
The system of claim 15, further including means for applying the
signal from said means for comparing to said means for vibrating to
control the degree of compaction. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for
ascertaining the degree of compaction in a bed of material with a
vibratory compacting device. The invention is particularly related
to a method and a device for ascertaining the degree of compaction
by evaluating the signals from at least one transducer which is
responsive to the vibratory motion of the compacting device as well
as that of the bed being compacted.
2. Description of the Prior Art
It was previously known to estimate the degree of compaction
achieved with a compacting apparatus by controlling parameters such
as vibratory frequency, vibratory amplitude, compaction time etc.
in response to the observed degree of compaction. A serious
drawback in this context is the difficulty of finding physical
characteristics that are easy to measure, exhibit a significant
relationship to the degree of compaction achieved and lend
themselves to the control of the compacting device.
Natural physical characteristics such as soil density, soil
elasticity coefficient etc. are not possible to measure
continuously with simple devices. Several proposals have therefore
made use of the vibratory motion of the vibratory device and/or
that of the soil. By estimating the relationship between the force
or the energy developed by the vibrator in the compacting device
and the motion of the soil, it is possible to determine the nature
of the vibratory motion resistance of the soil.
A device of the last mentioned type is disclosed in British Pat.
No. 1372567 published Oct. 30, 1974. In FIGS. 17-19 and the
accompanying text in accordance with this previously known device,
two acceleration pick-up devices 147 sense the motion of the soil
and two strain gauges 158 sense the force of a vibrator 154-156. By
comparing the amplitudes of the output signals from the
acceleration pick-ups 157 and from the strain gauge 158, it is
possible to determine the nature of the vibratory motion resistance
of the soil and the result of the comparison can be used for
estimating or controlling the operation of the compacting
machine.
Another prior art device of a different type for estimating the
degree of compaction achieved with a vibratory device is disclosed
in U.S. Pat. No. 3,599,543 issued Aug. 17, 1971 to Kerridge. The
motion of a vibrating part, for example the roller, of a vibratory
roller may in accordance with said U.S. Patent be approximated by
an ellipse. From FIG. 1 of said U.S. Patent, it is apparent that
the major axis of the ellipse will increase with an increasing
number of passes to and fro over the soil. Therefore, the major
axis is used as a measure of the degree of compaction. In order to
determine the major axis of the ellipse, the vibratory motion of
the roller is sensed by a number of accelerometers the positions
and orientation of which are clearly indicated in FIGS. 2 to 4 of
the said U.S. Patent.
In another prior art device disclosed in U.S. Pat. No. 3,053,157,
it is suggested that the degree of compaction achieved with a
dynamic soil compacting apparatus be optimized by setting the
vibratory frequency at the resonance frequency of the system
comprising the dynamic soil compacting apparatus and the soil. To
this end, the vertical acceleration of a part of the compacting
apparatus is sensed by a transducer and is controlled in response
to the output signal of the transducer. However, this device does
not provide for any direct measurement or estimation of the
achieved degree of compaction.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to
provide a method and apparatus for accurately determining the
degree of compaction of a soil bed compacted by a vibratory
compaction device.
The present invention derives advantage of a quite surprising
discovery, namely, that in compacting a soil bed with a vibratory
compacting device a relationship exists between the achieved degree
of compaction of the soil or of the bed and the amplitude of the
vibratory motions of the compacting device, the amplitude of said
motions occuring at frequencies that correspond to harmonics of the
fundamental frequency of the vibratory motion. In accordance with
the invention, the amplitudes of the harmonics as well as the
amplitude of such a portion of the vibratory motion that has
substantially pure fundamental frequency are derived. The said
relationship will be strongly amplified when the amplitudes of the
parts of the vibratory motion which correspond to harmonics of the
fundamental frequency are compared to the amplitude of the part of
the vibratory motion which generally corresponds to the pure
fundamental frequency.
In order to be able to estimate the achieved degree of compaction,
only the vertical part of the vibratory movement is of primary
interest for most of the embodiments in accordance with the present
invention. However, estimation of the achieved degree of compaction
can, in accordance with the teachings of the present invention,
form part of a system for controlling the vibratory frequency, the
vibratory amplitude and/or other parameters of of a vibratory
compacting device. Primarily in such applications of the invention
parts of or all of the horizontal component of the vibratory motion
are (is) of primary interest.
BRIEF DESCRIPTION OF THE DRAWINGS
Specific embodiments of the invention will now be described by way
of example with reference to the Figures of the accompanying
drawings wherein elements which are not essential for the
understanding of the invention have been omitted for the sake of
clarity and in which:
FIG. 1 is a block diagram of an embodiment of the present invention
in accordance with which signals are derived by filtering and use
is made of signals having frequencies which correspond to the
fundamental frequency and to the second harmonic of the vibratory
motion of the compactor device;
FIG. 2 is a block diagram of an embodiment of the present invention
using filtering techniques for deriving signals having frequencies
which correspond to the fundamental frequency and the second and
third harmonics of the vibratory motion of the compactor
device;
FIG. 3 is a block diagram of the present invention when implemented
into a system for controlling parameters of a vibratory compacting
apparatus;
FIG. 4 is a block diagram of an embodiment of the present invention
adapted especially for use in vibratory roller machines having two
vibrating rollers;
FIG. 5 is a circuit diagram of a preamplifier which may be used as
for example amplifier AZ in FIG. 1;
FIG. 6 is a circuit diagram of a fundamental and harmonic filter
which may be used in the embodiment shown in FIG. 1;
FIG. 7 is a circuit diagram of a rectifier and a low pass filter
which are used together as amplitude sensing means L10 or L11 in
the embodiment shown in FIG. 1;
FIGS. 8 and 9 are a block diagram and circuit diagram,
respectively, of a divider used in connection with an analogue
signal processing technique, for example used as K11 in the
embodiment shown in FIG. 1;
FIG. 10 is a block diagram of a divider used in connection with a
digital signal processing technique and as an averager for deriving
the mean value over any selected interval, said averager being used
as K11 in FIG. 1;
FIGS. 11 and 12 are electrical circuit diagrams of the divider
shown in FIG. 10;
FIG. 13 illustrates the positioning of a transducer on a vibratory
roller machine; and
FIGS. 14-19 are diagrams illustrating the results achieved with an
embodiment in accordance with FIG. 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In FIG. 1, P1 represents a part of a vibratory compaction device
for compacting a bed of material which may for example comprise
soil, gravel, stone resulting from blasting operations, asphalt
etc. Part P1 contacts the soil and is imparted a vibratory motion
from a vibrator V1 of the vibratory compaction device. Vibrator V1
may comprise a mass which is rotating around an axis and has its
center of gravity positioned eccentric in relation to said axis.
For the sake of simplicity, it is supposed that said motion has a
certain fundamental frequency, FG, although it is within the scope
of the present invention that said motion may comprise several
components of mutual different fundamental frequencies.
The vibratory motion of part P1 is not only related to the motion
of the vibrator but also to the properties of the soil.
Accordingly, when the properties of the soil are changed as a
result of compaction, the vibratory motion of part P1 will
change.
As indicated in FIG. 1, transducer G11 is arranged for sensing the
vibratory motion during compaction of the soil. In order to
illustrate the connection between the transducer and part P1, said
elements are shown to be connected with each other by way of three
broken parallel lines. Transducer G11 is so constructed that is
responds to movements directed substantially only in one direction
and it is so mounted on the vibratory compaction device that it is
sensing substantially the vertical component of the vibratory
motion. It is then possible to derive from the transducer output
signals representative of said component and which herein will be
referred to as a motion component signal. Said motion component
signal is indicated by the output of the transducer and is supplied
to an amplifier AZ which amplifies said signal to a proper level
before it is further supplied to two band pass filters F10, F11.
Amplifier AZ also acts as an impedance transducer.
The upper band pass filter F10 shown in FIG. 1 is so tuned that its
passband lies around the fundamental frequency, whereas signals
having frequencies substantially lower than the fundamental
frequency as well as signals having frequencies above or
substantially at the second harmonic of the fundamental frequency,
are rejected. Therefore, the upper band pass filter can filter out
the fundamental component from the motion component signal and this
filtered fundamental component has a frequency that generally
corresponds to that of the fundamental frequency.
The lower band pass filter F11 of FIG. 1 is so tuned that its
passband lies around the second harmonic of the fundamental
frequency, whereas signals having frequencies that substantially
correspond to the fundamental as well as signals corresponding to
the third harmonic of the fundamental, are rejected. Therefore, the
lower band pass filter can filter out harmonics of the motion
component signal, said filtered harmonics having a frequency that
generally corresponds to the second harmonic of the fundamental. As
will become more apparent hereinafter, the existence of such
harmonic components are substantiated by FIGS. 14-19 and the
accompanying specification.
The output signal from the upper band pass filter F10, that is the
above mentioned fundamental component, is supplied to amplitude
determining means L10. The output signal from said amplitude
determining means represents the amplitude of the fundamental
component.
The output signal from the lower band pass filter F11, that is the
harmonic component, is supplied to amplitude determining means L11.
Amplitude determining means L11 generates an output signal
representing the amplitude of the harmonic component.
The output signal from amplitude determining means L10 and L11 are
supplied to a divider K11 which generates an output signal k11
representing the quotient of the amplitude of the harmonic
component and that of the fundamental. Output signal k11 may either
be supplied to a display unit (not shown) observed by the operator
of the compacting device or to a control device (not shown) for
controlling one or more parameters of the compacting device.
In addition to the fundamental component, only one harmonic is
filtered out from the motion component signal in the embodiment
shown in FIG. 1.
In certain applications, a better result may be achieved if more
than one harmonic component is filtered out.
The use of only one transducer as indicated in the embodiment
described in connection with FIG. 1 may under certain circumstances
have associated difficulties. It may be difficult to position the
transducer so that the motion component signal therefrom will have
optimum significance. Quite often, the position of the transducer
will be slightly eccentric or asymmetric in relation to vital parts
of compactor part P1. In certain circumstances, these drawbacks or
problems may at least partially be compensated by the use of two
transducers for sensing the vibratory movement of compactor part
P1. The position of the transducers are preferably so selected that
the transducers are placed symmetrically in relation to compactor
part P1 or vital parts thereof.
In FIG. 2, there is shown an embodiment wherein two transducers are
used and wherein the amplitude of two filtered harmonic components
of mutually different frequencies also are used. From each
transducer, a motion component signal representing substantially
the vertical component of the movement of each respective
transducer is derived. The two motion component signals are added
together and amplified in a preamplifier AZ. The output signal from
the preamplifier is supplied to three band pass filters F10, F11,
F12 the uppermost and the middle of which are constructed and
operated in the same manner as that described in connection with
the embodiment shown in FIG. 1.
The lowermost band pass filter F12 of FIG. 2 is so tuned that its
passband is lying around the third harmonic of the fundamental,
while signals having a frequency above or generally coinciding with
the fourth harmonic of the fundamental as well as signals having a
frequency below or a frequency generally coinciding with the second
harmonic of the fundamental, are rejected. This band pass filter
F12 can, therefore, filter out a harmonic component of the motion
component signal, said filtered harmonic component having a
frequency that generally coincides with the third harmonic of the
fundamental. This filtered harmonic component is fed to amplitude
determining means L12.
The output signals from amplitude determining means L11 and L12 are
supplied to a weighting and adding amplifier SA which forms an
output signal that represents a weighted sum of the amplitudes of
filtered harmonic components. In order to illustrate that the
signals are weighted when summed in the adder, the two inputs of
the amplifier are marked .alpha. and .beta., respectively. The
output signal from the amplifier as well as the output signal from
amplitude determining means L10 are supplied to a divider K12 which
generally operates in the same manner as divider K11 in the
embodiment shown in FIG. 1.
The output signal from divider K12 is accordingly representative of
the quotient between the weighted sum of the amplitude of the
filtered harmonic components and the amplitude of the filtered
fundamental component.
The embodiments described thus far make use of motion component
signals representing substantially the vertical component of the
motion of one or more transducers. However, transducers from which
a motion component signal representing generally a horizontal
component of motion may be derived, are also within the scope of
the present invention. Transducers of this kind are preferably used
in controlling the compacting device when it is necessary to derive
more information concerning the degree of compaction than can be
derived with only one motion component signal that represents
generally the vertical component of the motion of one or more
transducers. In FIG. 3, an embodiment of this kind is depicted.
In FIG. 3, there is shown two transducers G11 and G12 each having
two outputs marked X and Z respectively. A motion component signal
representing generally the vertical component of the motion of the
transducer is provided at output Z in a manner analogous to that of
FIGS. 1 and 2. At output X on each respective transducer a motion
component signal is derived which for each respective transducer
represents the horizontal component of the motion of the respective
transducer in a particular direction, namely, the X direction. The
output signal from the Z-outputs at the transducers are processed
by preamplifier AZ, by the three lower band pass filters shown in
FIG. 3 as well as by the three lower rectifiers L10, L11 and L12 in
the same manner as described in connection with FIG. 2. The output
signal from the X-outputs of the transducers are supplied to a
preamplifier AX. The output signal from preamplifier AX are
processed by the three upper band pass filters indicated in FIG. 3
as well as by the three upper rectifiers L10, L11 and L12 in the
same manner the output signal from preamplifier AZ of FIG. 2 is
processed.
The oblong block to the extreme right of FIG. 3 symbolizes a device
which on the basis of the amplitudes of the filtered fundamentals
and harmonics generates signals for ascertaining and controlling
the degree of compaction. In order to illustrate the various
operations performed by this device, it may be thought of as being
divided into six sections indicated in the drawing as AMP, FG, KX,
S, ZS and H, respectively. Section KZ provides one or more signals
in response to the amplitude of the signals which have been
filtered by the three lowermost band pass filters in FIG. 3.
Section KX provides one or more signals in response to the
amplitude of the signals which have been filtered by the three
uppermost band pass filters of FIG. 3. One or more of the signals
provided by sections KX and KZ may for example be of the same type
of signal k12 provided in the embodiment shown in FIG. 2.
Section AMP provides a signal for controlling the vibratory
amplitude of the compacting device in response to one or more
signals from section KX and/or section KZ. The output signal from
section AMP is supplied to a control circuit RAMP controlling the
vibratory amplitude of vibrator V1 in response to said output
signal as well as other existing information, if any.
In response to one or more signals from section KX and/or section
KZ, section H generates a signal which is supplied to a control
circuit RH controlling the speed by which the compacting device is
advanced. In response to this signal and other existing
information, if any, control circuit RH controls a propulsion
device M of the compacting device or of a vehicle drawing the
compacting device. Section S provides a combination of the signals
from sections KX and KZ to give an output 1.
In response to one or more signals from section KX and/or KZ,
section FG generates a frequency control signal which is supplied
to a frequency control circuit RF. This circuit is controlling the
frequency of vibrator V1 in the response to the frequency control
signal and other signals, if any, received by the frequency control
circuit from vibrator V1.
In the above described embodiments, the vibratory frequency of the
vibrator has been generally constant. Due to this it is possible to
tune the band pass filters once for all. If optimum results of the
compacting is desired, it may be required to vary the fundamental
frequency of the vibrator within a comparatively wide range and in
doing so it may be necessary to use band pass filters the band pass
range of which can be varied at the same rate with which the
fundamental frequency of the vibratory motions varies. To this end,
a frequency control circuit RF is provided having transducers for
sensing the vibratory motion of the vibrator. Frequency control
circuit RF is also provided with three outputs labelled F0, F1 and
F2. The output signals from these outputs are representative of the
fundamental frequency, the second and the third harmonic,
respectively, of the vibratory motion. The outputs are supplied to
the band pass filters to vary their pass bands in response to
variations in the fundamental frequency.
FIG. 3 and the accompanying description thereof should not be
regarded as an exhaustive description of a complete system for
controlling parameters of a vibratory compacting device. The
invention of FIG. 3 and the accompanying text is instead to
illustrate the manner in which the device in accordance with the
invention may form a part of such a system, namely, the part
required to make it possible to ascertain the degree of compaction.
The operation of the rest of the control system does not form part
of the present invention and will therefore not be described.
Tests conducted with a prototype in accordance with FIG. 1 proved
successful when using it in a vibratory roller machine having a
vibrating roller. However, results achieved when using it on one
vibratory roller machine having two vibrating rollers turned out to
be inconsistent, namely, sometimes good and sometimes less
successful. One reason for this is supposed to reside in the fact
that vibratory motions appearing in the soil as a result of the
vibratory motion of one of the rollers interfere with other
vibratory motions of the soil resulting from the vibratory motions
of the second roller.
Another reason for this may be that the chassis of the vibratory
roller machine provides a mutual interaction between the vibratory
motions of the rollers. At present, it is therefore supposed that
the embodiments according to FIGS. 1-3 are most suited to be used
in compacting devices that do not have two or more at least
partially independent parts P which are imparted a vibratory
motion.
The block diagram shown in FIG. 4 illustrates one embodiment of the
present invention which is especially adapted for vibratory roller
machines having two rollers. To a certain extent, the embodiment
shown in FIG. 4 is also adapted for other compacting devices having
two parts P1 and P2 which are imparted at least partially
independent vibratory motions of the same or of different
frequencies. The vibratory motions of part P1 is sensed by
transducers G11 and G12. These transducers are so constructed and
mounted that they operate in the same manner as the corresponding
transducers shown in FIG. 2. The output signals from transducers
G11 and G12 are added and amplified in means A1. The output signal
from means A1 is processed by three band pass filters F10, F11,
F12, three amplitude determining means L10, L11, L12, a weighing
and adding amplifier SA1 and a divider K12 in the same manner as in
the embodiment shown in FIG. 2. Output signal k12 from means K12 is
accordingly representative of the quotient between the weighted sum
of the filtered amplitudes of the harmonic components and the
amplitude of the filtered fundamental components.
The vibratory motion of part P2 is sensed by transducers G21 and
G22. These transducers are so constructed and mounted that they
operate in the same manner as transducers G11 and G12 in the
embodiment shown in FIG. 2. The output signals from transducers G21
and G22 are added and amplified in means A2. The output signal from
means A2 is processed by three band pass filters F20, F21, F22,
three amplitude determining means L20, L21 and L22, a weighting and
adding amplifier SA2 and means K22 in same way in which the output
signal from means AZ is processed in the embodiment shown in FIG.
2, as well as the way in which output signal from means A1 is
processed in the embodiment in FIG. 4. Output signal k22 from means
K22 is accordingly representative of the quotient between the
weighted sum of the amplitude of the filtered harmonic components
and the amplitude of the filtered fundamental component.
The output signals from amplitude determining means L10 and L20 are
supplied to an adding device A3 the output signal of which is
supplied to means Kb. The output signals from the weighting and
adding amplifiers are supplied to adding means A4 the output
signals of which are supplied to means Kb. Means Kb is of the same
type as means K12 or K22 and generates an output signal which is
representative of the quotient between two parameters; the first
one being the weighted sum of the four filtered amplitudes of the
harmonic components, the weighting coefficients being .alpha.1,
.beta.1, .alpha.2 and .beta.2; the second parameter being the sum
of the amplitude of the filtered fundamental components. Output
signal b from means Kb will accordingly be representative of the
relation between the said last mentioned weighted sum and said sum
of the amplitudes of the fundamental components.
Output signal k12 from means K12 and output signal k22 from means
K22 is supplied to adding means A5 which is of the same general
type as adding means A3 and A4 as well as to subtracting means A6.
Output signal s from adding means A5 will accordingly be
representative of the sum of k12 and k22 whereas output signal d
from subtracting means A6 will be representative of the difference
of k12 and k22. Output signals d and s are supplied to means KR
which is of the general type as means Kb. The output signal from Kr
will accordingly be representative of the quotient between the
difference of k12 and k22 and the sum of k12 and K22.
If the embodiment shown in FIG. 4 is used in for example a double
roller compacting machine for compacting asphalt, parameter r would
be indicative of the relative rate of the degree of compacting
during the passage in question. The increase of this parameter r in
consequence of a passage of the machine will empirically decrease
with an increasing number of passes over the material being
compacted. When the increase of the degree of compaction is
sufficiently small in relation to the total degree of compaction,
one knows that the achieved degree of compaction is near the
maximum one that can be achieved if the existing conditions remain
unchanged.
With a reasonable knowledge of the increase of the degree of
compaction in relation to the number of passes, parameter r in
combination with signal k12 and/or k22 will provide a measure of
the absolute degree of compaction, though each of k12 and k22 only
is indicative of a relative measure of the degree of compaction
provided by P1 and P2, respectively, during the pass in
question.
It is obvious to the man skilled in the art that several
modifications of the embodiment shown in FIG. 4 are within the
scope of the present invention. One or more of parameters b, d, s,
r may for example be omitted.
A prototype of an indicator of the degree of compaction achieved by
a vibratory roller has been manufactured in accordance with the
embodiment shown in FIG. 1. As transducer G11 for sensing the
vibratory motion an accelerometer of type 4393 manufactured by
Bruel & Kjaer was used. The output of the accelerometer, that
is signal AZ in FIG. 1, was amplified in a preamplifier the circuit
diagram of which is shown in FIG. 5. The preamplifier comprises
three integrated circuits ICI, manufactured by Fairchild and being
of type .mu.A776, a coupling capacitor having a capacitance of
0,1.mu.F, two resistors R1 having a resistance of 1 M.OMEGA., one
resistor R2 having a resistance of 10M.OMEGA., two resistors R3
each having a resistance of 10k.OMEGA., one resistor R4 connected
to a voltage source not shown, one resistor R5 having a resistance
of 10k.OMEGA. and one resistor R6 of 470k.OMEGA.. The reference
designation 8 indicated at each integrated circuit refers to the
corresponding terminal of the package as indicated on the
manufacturer's data sheet.
In FIG. 6, the circuit diagram of two band pass filters used in the
prototype in accordance with the embodiment of FIG. 1 is indicated.
The upper portion of the circuit diagram is a band pass filter
having a pass band lying around 25 Hz. The lower portion of the
circuit diagram of FIG. 6 refers to a band pass filter of the same
general kind but having a pass band lying around 50 Hz. The
relative band width of the band pass filters has deliberately been
made as identical as possible and is about 1/3.
A vibratory roller manufactured by Dynapac and having the model
number CH 47 was used and the fundamental frequency thereof was
about 25 Hz. The upper and lower portion of the circuit diagram of
FIG. 6 correspond to the upper and the lower band pass filters F10,
F11, respectively, of FIG. 1.
Each filter of FIG. 6 is built around an integrated circuit having
four separate operational amplifiers IC2 in the same package and
being manufactured by Motorola under the name MC 3403 P. The upper
filter which has a pass band lying around 25 Hz comprises eight
capacitors the capacitances of which are 100 nF each while the
lower filter which has its passband round 50 Hz comprises four
capacitors each having a capacitance of 100 nF. Besides a voltage
source, not shown, each filter comprises a number of resistors
R7-R19 having the following resistances: R.sub.7 =89 k.OMEGA.,
R.sub.8 =47 k.OMEGA., R.sub.9 =150 k.OMEGA., R.sub.10 =4,7
k.OMEGA., R.sub.11 =22 k.OMEGA., R.sub.12 =470 k.OMEGA., R.sub.13
=120 k.OMEGA., R.sub.14 =33 k.OMEGA., R.sub.15 =220 k.OMEGA.,
R.sub.16 =3,9 k.OMEGA., R.sub.17 =15 k.OMEGA., R.sub.18 =66
k.OMEGA.och R.sub.19 =560 k.OMEGA..
Reference is now made to FIG. 7 showing a circuit diagram of a
rectifier which is followed by a low pass filter. The combination
indicated in FIG. 7 has been used as amplitude determining means
L10 in the prototype built in accordance with the embodiment of
FIG. 1. The rectifier comprises an integrated circuit sold by
Motorola under the trade name MC 3403 P. This integrated circuit
comprises four separate operational amplifiers but only two thereof
are used in the rectifier. The two remaining operational amplifiers
in the package are used for amplitude determining means L11. The
rectifying operation is performed by two diodes connected over the
output of the left operational amplifier. In addition to a voltage
source, not shown, the rectifier comprises eight resistors each of
10k.OMEGA.. The low pass filter comprises a simple RC-combination
with a resistor R of 1,2 k.OMEGA. and a capacitor C of 1000
.mu.F.
Reference is now made to FIG. 8 showing a block diagram of a
divider used as divider K11 in the prototype built in accordance
with the embodiment of FIG. 1. The divider has two inputs A and B,
respectively, for receiving output signals from the lower pass
filter shown in FIG. 7. Input B is receiving the output signal of
the rectifier and low pass filter combination used for sensing the
amplitude of the filtered harmonic component, that is the
combination corresponding to L11 of FIG. 1. Input A is receiving
the output signal from the rectifier and low pass filter
combination used for sensing the amplitude of the filtered
fundamental component, that is the combination corresponding to L10
of FIG. 1. The divider operates with analogue signal processing
techniques and comprises a dividing circuit which delivers an
output signal the magnitude of which is proportional to the
quotient between the magnitude of the input signal on input B and
the magnitude of the input signal on input A.
The quotient between the amplitude of the filtered fundamental
component is of course relevant only in case the amplitude of the
fundamental component is higher than the noise or background level.
To this end the block diagram of FIG. 8 comprises a comparator and
a locking device the operation of which correspond to that of a
squelch control provided in a common tuner. In the comparator, the
amplitude of the filtered fundamental components is compared with a
predetermined reference amplitude ref and as a result of the
comparison a signal is supplied to the locking device. In response
to said signal, the locking device will pass the output signal from
the divider to the display only in case the input signal at input
A, that is the amplitude of the filtered fundamental component, is
sufficiently high.
Reference is now made to FIG. 9 showing the circuit diagram of a
divider provided with a comparator and a locking device in
accordance with the block diagram of FIG. 8 and used as divider K11
in the prototype manufactured in accordance with the embodiment of
FIG. 1.
The divider is built around two integrated circuits. One of these,
viz. IC2, is of the same type as that used in the filters and in
the rectifier. Circuit IC2 compares the input signal at input A
with a voltage which is tapped from a voltage divider comprising
resistors the resistance of which are 15k.OMEGA., 68k.OMEGA. and
12k.OMEGA., respectively, and generates and output signal which via
a resistor of 10k.OMEGA. is supplied to the base of a transistor
which is manufactured by ITT under the trade name of BY Y 59.
Accordingly, IC2, the resistors and the transistor will form the
comparator and the locking device shown in the block diagram of
FIG. 8.
The second integrated circuit IC3 is manufactured by Analog Devices
and is sold under the trade name AD532. This IC is so wired that it
provides an output signal the magnitude of which is proportional to
the input signal at input B divided by the input signal at input A.
The output signal from the integrated circuit IC3 is, via a
resistor R22 of 2.2k.OMEGA. and a variable resistor, connected to
an indicator which provides a visual indication when the transistor
is in its nonconducting state due to the existence of a signal from
IC2. When the transistor is in its saturated state in response to a
signal from IC2, the output signal from IC3 will be shunted to
earth via a resistor of 2.2k.OMEGA..
The divider described thus far operates with analogue signal
processing techniques. However, it is of course possible to use a
divider having digital signal processing techniques. In FIG. 10, a
block diagram of a divider of the last mentioned type is shown.
Input A of the divider is supplied with the output signal from
amplitude determining means L10 to which the filtered fundamental
component is supplied. Input B of the divider is supplied either
with the output signal from amplitude determining means L11 to
which the filtered harmonic component is supplied or with the
output signal from the weighting and adding amplifier with FIGS. 2
and 4.
A first voltage-to-frequency converter generates a first digital
output signal DA in the form of pulses, the repetition frequency of
which is dependent on the magnitude of the input signal to input A.
A second voltage-to-frequency converter generates a second ditital
output signal DB in the form of pulses, the pulse repetition
frequency of which is dependent on the input signal to input B. The
first and second output signal as well as a signal having a
frequency .function..sub.1 from an oscillator are supplied to a
digital divider which is generating a third digital output signal
DK in the form of pulses the pulse repetition frequency of which is
dependent on the quotient between the amplitude of the input signal
at input B and the input signal at input A. The third digital
output signal is supplied to a frequency divider dividing by a
factor N, where N is settable with the aid of a BCD switch which
also is controlling the corresponding factor N of a second
divider-by-N similar to the first mentioned divider. The second
divider-by-N is supplied with a signal having a frequency
.function..sub.2 from the oscillator and is generating in response
thereto a logic signal which is supplied to a gate. In response to
said logic signal, the gate will either block or pass to a counter
the digital output signal which is appearing in the form of pulses
and emanates from the first divider-by-N.
The logic signal from the second divider-by-N will shift its logic
level at time intervals which are proportional to N. Accordingly,
the gate will pass digital pulses from the first divider-by-N
during time intervals which are proportional to N. On the other
hand, the frequency of the digital pulses are inversely
proportional to N in consequence of the first divider-by-N.
Accordingly, the number of pulses supplied to the counter is
substantially independent of N provided the existing conditions
remain unchanged. From the above, it is clear that the
instantaneous pulse repetition frequency of DK will be
substantially proportional to the quotient between the magnitude of
the signal applied at input B and the magnitude of the signal
applied at input A. The count of the counter will, however, be
substantially proportional to a mean value of this quotient taken
during a time interval which is settable and also proportional to
N.
In FIGS. 11 and 12, there is shown a circuit diagram of a digital
divider provided with an averager of the type shown in FIG. 10.
The analogue input signals to inputs A and B are inverted and
amplified to a suitable level by way of two operational amplifiers
IC4A, IC4B manufactured by Fairchild and sold under the trade name
.mu.A 741. The output signals of the operation amplifiers are each
supplied to a voltage-to-frequency converter. Each
voltage-to-frequency converter IC5A, IC5B comprises an integrated
circuit manufactured by Intech and sold under the trade name
A-8400. The two integrated circuits are implemented with electrical
components the individual values of which differ between the two
integrated circuits so that the pulse repetition frequency of the
first digital output signal DA varies between 50 and 100 Hz while
the pulse repetition frequency of the second digital output signal
DB varies between about 0.5 and 50 kHz.
The digitally performed division of the frequencies of the pulse
trains is performed on the basis of and is controlled by a pulse
train having a constant frequency .function..sub.1 derived from an
oscillator provided with a frequency divider. The oscillator
comprises an integrated circuit manufactured by RCA under the trade
designation CD 4060. The oscillator frequency is 3276, 8 Hz and
this frequency divided by 2.sup.6 resulting in an .function..sub.1
equal to 51, 2 H and also by 2.sup.14 resulting in an
.function..sub.2 equal to 0,2 Hz.
The positive flank at input C provides via a capacitor of 100 pF
and a resistor 10k.OMEGA. a reset pulse to the JK flip-flops which
are manufactured by RCA under the trade name CD 4027. The diode is
used to shunt negative pulses to earth. The first one of the pulses
DA which occurs after the reset pulse will after inversion in an
inverter trigger a first JK flip-flop FF1. When JK flip-flop FF1 is
triggered, gate U1 will open and pass pulses from DB. When the next
pulse of DA arrives, the first flip-flop FF1 will again change its
state, close gate U1 and also change the state of a second
flip-flop FF2.
The Q terminal of flip-flop FF2 will then go low and will prevent;
in consequence of the wiring of the J and K inputs of flip-flop
FF1; that FF1 will be triggered by succeeding pulses on DA.
Flip-flops FF1 and FF2 are sold by Fairchild under the trade
designation CD 4027.
Accordingly, gate U1 will pass pulses from DB during one period of
DA once during each period of frequency .function..sub.1.
Pulse train DK comprises bursts of pulses the frequency of which
within the bursts is the same as the frequency of DB. One burst
will be provided during each period of frequency .function..sub.1
and will have a duration which is as long as a period of DA. The
number of pulses during one second is: ##EQU1##
This frequency is divided by 256 in a counter which is manufactured
by RCA and has the trade name CD 4520 thereby providing a pulse
train having a suitable frequency and pulses that are generally
uniformly distributed in time. The circuit comprises switches that
provide for manual selection between a single measurement and
indication of a mean value or a continuous measurement and
indication of successive mean values during successive time
intervals.
When the START button is depressed and the two movable contacts of
the mode switch are in the left position shown in the drawing, the
monostable flip-flop IC7 (RAC type CD 4098) will be triggered and
deliver a reset pulse at output Q for resetting the three decade
counters CD 4518, a pulse to a flip-flop formed by gates U2 and U3
which will go low and thereby provide a low level at input R of
oscillator IC6 which will begin to oscillate, as well as a pulse
which via OR-gates U6 and U7 is supplied at the PL inputs of
counters IC8 (RCA type CD 40192). Upon receipt of said pulse,
counters IC8 are set at a count N previously set at BCD.
Inputs LE of three drivers CD 4511 (RCA CD 4511) have low level in
consequence of gates U4 and U5. Therefore, the counting up of the
decade counters CD 4518 will be continuously displayed at the
display which comprises modules having the type designation FND
500. NAND gates U1-U5 and U8 as well as OR gates U6 and U7 are
manufactured by RCA under the designation CD 4011 and CD 4071,
respectively. The capacitance of the capacitors connected to IC6
and IC7 is 15nF and 150nF, respectively.
In response to incoming pulses of DK at input D and pulses having
the frequency .function..sub.2 from oscillator IC6, the counters
IC8 will start counting down from N. When a count of zero is
reached they will generate a pulse at each respective output
TC.sub.D. The pulse at the output of the upper counter will pass
through OR gate U7 to input PL of the upper counter to reset the
upper counter to a count of N again. In the same manner, the pulse
at output TC.sub.D of the lower counter will pass through OR gate
U6 and set the lower counter at a count of N. Moreover, the pulse
at output TC.sub.D will reset the flip-flop constituted by U2 and
U3. This will occur after N/.function..sub.2 seconds and will stop
oscillator IC6. The counts then appearing in decade counters CD
4518, that is the result of the performed measurement, will be
presented at the display.
In the continuous measuring and indicating mode, the movable
contacts of mode switch are in right position and the above
described operation sequence is started. However, the counting up
of the counters will not be displayed since LE will now go high
because the switch will now connect one input of U4 to a positive
potential.
When the first measurement is completed after N/.function..sub.2
seconds, U9 will deliver a TC.sub.D pulse which will bring one of
the inputs of U4 down to a low level and accordingly bring LE to go
down implying that the counts of the decade counters will be passed
and displayed. Said TC.sub.D pulse will also trigger the monostable
flip-flop whereafter the next sequence will start in the same
manner as were the START button depressed.
Accordingly, the last measurement taken will be presented at the
display until a new value has been measured.
As mentioned previously, the prototype has been tested on a
vibratory roller manufactured by Dynapac under the trade
designation CH 47. In order to illustrate the mounting of the
transducers, FIG. 13 illustrates a cross section of the roller and
adjacent elements thereof. The transducer was mounted at g11.
Concerning the rest of the elements shown in FIG. 13, reference is
made to the manufacturer's instruction manual describing model CH
47. The manual may upon request be supplied by the manufacturer. In
this context, it is worthwhile to note that the position of the
transducer is similar to the position of transducer T shown in FIG.
2 of U.S. Pat. No. 3,599,453.
If the above indicated roller CH 47 is to be provided with two
transducers in accordance with for example the embodiment shown in
FIG. 2 of the drawings, the second transducer may for example be
mounted at g12 as indicated in FIG. 13.
In FIGS. 14-16, the results of two tests performed with the above
mentioned single roller vibratory machine CH 47 on sand are
illustrated. These tests were conducted in Karlskrona in 1976.
The tests were conducted on a sand bed which was 1.5 meters high
and was provided between plinths which were used as a ground for a
hall construction. Due to the rather high and loose filling, the
bed ruptured after 3-4 passages which is indicated by the curve
representing test No. 1. The bed was thereafter loosened down to
about 60 cm with the aid of a caterpillar and test No. 2 was then
conducted.
In FIG. 14, the relative magnitude of the quotient between the
amplitude of the second harmonic and that of the fundamental is
shown as a function of the number of passages (1-18) over the bed.
The results have been derived by analysing tape recordings of the
signal achieved with the constructed prototype.
In FIG. 15, the result of density measurements taken after passages
Nos. 3, 6, 9 and 18 during test No. 1 is shown. The density has
been measured at three different levels ( =1-15 cm; =15-30 cm;
=30-40 cm) with the aid of a water volume meter.
In FIG. 16, the settlement of the bed surface is shown as a
function of the number of passages. The settlement was measured by
surface levelling.
In FIGS. 17-19, the results achieved with tests performed in
Biskopsberg 1975 on moraine with a vibratory tandem roller machine
manufactured by Dynapac under the trade name CC 20 are shown. This
roller had a fundamental frequency of about 50 Hz and the filters
F10, F11 were tuned accordingly.
In FIG. 17, there is shown the relative magnitude of the quotient
between the amplitude of the second harmonic and that of the
fundamental as a function of the number of passages (1-8). The
result has been derived by processing tape recordings of signals
generated by a prototype with 50 Hz and 100 Hz filters.
In FIG. 18, the results from density measurements are shown. The
density has been taken at three different levels ( =1-15 cm; =15-30
cm; =30-40 cm) after passages Nos. 2, 4 and 6, respectively with
the aid of a water volume meter.
In FIG. 19, the settlement of the bed surface is shown as a
function of the number of passages. The settlement has been
determined by way of surface levelling.
The test results exhibit a good correlation between the settlement
and the density of the bed and the relative magnitude of the
quotient between the amplitudes in questions. The small deviations
which are present can be attributed to imperfections of the
prototype and margins of error during measurements etc.
Accordingly, it is apparent that the previous mentioned
relationship between the degree of compaction of a bed and the
relative magnitude of the quotient really exists.
The above described embodiments may be varied and modified in
several ways within the scope of the present invention. The number
of harmonic components derived by filtering and having frequencies
which generally correspond to different harmonics of the
fundamental frequency need not necessarily be two. It is for
example possible to use the amplitude of filtered harmonics having
frequencies which correspond to the fourth harmonic of the
fundamental. However, tests performed in this direction indicate
that the amplitudes of the filtered fourth harmonics have generally
the same order as those of noise and background signals. Tests
indicate that it therefore, as a compromise between complexity on
the one hand and price on the other, is preferred to make use of
only such harmonic components which have a frequency corresponding
to the second harmonic of the fundamental.
In embodiments generally corresponding to that of FIG. 3, it is
moreover possible to derive, by filtering, a different number of
harmonic components from different motion components signals, for
example may two harmonic components with mutually different
frequencies be filtered out from the motion component signal at the
Z-outputs of the transducers in addition to only one harmonic
component that is filtered out from the motion component signal
derived at the X-outputs of the transducers.
For compacting devices having two or more vibrators with
sufficiently spaced apart fundamental frequencies, it is possible
to separate during the filtering each fundamental component and its
accompanying harmonic components from the rest of the fundamental
components and their accompanying harmonics. However, it is also
possible to filter out and make use of the fundamental components
in common and to filter out and make use of corresponding
harmonics, which must be of the same order, in common. If two or
more fundamental frequencies do not differ sufficiently nuch from
each other, it may be practically impossible to separate them from
each other, especially since they will exhibit a time dependent
variation caused by the construction of the compaction device or by
the achieved degree of compaction.
Provided that the amplitude of the fundamental component is
constant, it would also be possible to filter out and make use of
only one or more fundamental components. However, tests have
indicated that the amplitude of the filtered fundamental components
are not always constant. Moreover, the use of the quotient between
the magnitude of two signals filtered out from one and the same
transducer signal will simplify the calibration of the device for
measuring the degree of compaction in accordance with the present
invention.
Taking the quotient means that the influence of temperature, aging
etc. of the transducers and of other components will be
considerably reduced. The gain of the preamplifier may vary within
reasonable limits without affecting the quotient. The use of
filters which are of the same type and have the same relative band
width for deriving the fundamental and harmonic components by
filtering will, in combination with the forming of the quotient,
provide a substantial reduction of the way in which reasonably
small variations of the fundamental frequency of the vibratory
motion will affect the result of the measurement. If the filters
are detuned due to variations of the fundamental frequency, the
amplitude of the filtered components will experience a relative
decrease which is of substantially the same order of magnitude
because the degree of detuning is the same. Accordingly, it is
preferred to relate the magnitude of the amplitude of a filtered
harmonic component to that of the filtered fundamental
component.
It should be understood that the method and apparatus described
herein may be modified as would occur to one of ordinary skill in
the art without departing from the spirit and scope of the present
invention.
* * * * *