- Email: [email protected]
Ultrasonic sensor for liquid-level inspection in bottles
ELSEVIER
Scn~or,
SENSORS ACTuATORS PH~CAL
und Aclu
Ultrasonic sensor for liquid-level inspection in bottles E. Vargas *, R. Ceres, J.M. Martin, L. Calderon "Uti/litO de Awol/ulrica Jlldllstrllli (IAI-CSIC), N·I/I, Km 22HOO, Argam/a del Re\', 28500 Mat/ml, Sl'am
Abstract In this paper, the development of it precise and dynamic ultrasonic dh,tance sensor to mea';ure the level of liquid In bottles for an industrial line IS descnbed. For this afJplication. optical, capacillve or mechanical means are not suitable. In the fir!!! pnrt the limitations ofaconventlonal pulllc--echo ranging system are dlscu'\sed. A strategy to measure the time of flight based on the envelope of the echo !'Jignal is performed, solving in a practical way the problem of the complex signal reflected from the malO !'lurface, meni~cu~ and internal walls of the bottleneck. Keyuords: UltraSOniC; Sensors. liquid level. Envelope
I. Introduction
The present work is related to the European ESPRIT project NETCIM (Cooperative Network for CIME Technologies in Europe). The Instituto de Automatica Industrial (JAI) is responsible for the implementation of an advanced winebottting plant. with functionalities of inspection, control and automation integrated by computer. The inspection tasks are focused on the level of filling. the correct placement ofcorks and protective covers using ultrasonic techniques (see Fig. I). This paper describes the strategies used in the implementatIon of the subsystem of the plant that will be used for the on-hne inspection of the filling level ofwinebotlles. To carry it out, we need to measure the level of liquid, with one millimetre resolution, considering the menhcus formauon 10 the liquid surface and the VIbration of the bottles produced by their movement through the conveyor belt. Distance and displacement measurements are a wellknown problem and have been studied for many years. Noncuntact teChniques are preferred in IOdustrial automation because of their inberent simplicity, and are a reqUIrement for this application. The most comwon of these techniques are of ultrasonic, laser and infrared types. In a first stage of the project. some tests were carried out to select the basic measurement technique and the corresponding transducers to be used. No satisfactory results were obtained with acommercial laser interferometer even in static tests. '" Corre'pondmg author. Tel.. +341 871 1900. Fax: +3418717050 E-maIl. evarga,@mcrcunolal C"IC,CS 0924·4247/97/$17.00 © 1997 ElscvlcrSclence S.A. All nght'i re,erved PI/ 80924-4247(96) 0 1421-5
Level
~.4~1 Plant
Fig
~.
ImpccLlOn and automallon system usmg ultra,onic'i
Laser and IR ,ensors were discarded because these types of devices are more appropriate for measurements of flat and opaque surfaces. presenting for our casc a hIgh degree of absorption and secondary reflection for some angles of IOcidence Other techniques like CCD were refused because of lighting problems aad tbeir high cost. Ultrasonic sensing has characteristics that make it advantageous in some situations compared with other non-contact sensing methods such as electromagnetic (includingoptical), electrical, magnetic, thermal, or pneumatic means. For sensing through some medi~, such as froth above liqUIds. aqueous media. fibres, loose granular mat.cnals and dense vapours, ultrasonic systems may provide the most practical if not the only possible means [ I J. The use of ultrasonics in distance measurement in air has been viewed with great interest because it is very inexpensive and can be used m polluted. smoky or dark environments. Therefore, we have selected ultrasonic techniques here. However. existing ultrasonic sensors only measure the distance to the closest object within their viewing angle (in our
{£ Varga~ etal.
VD'~
2: 2 _ 1,5
/SemUrsllllti A(./Iwtor:; A 61 (!1}f)7j 256-259
257
..
.i.. ·:::·~:::::r::::::::::::i::::::::::::t::::::::::: A
'..........
..: .
;
;
o : :::::'.: ::::(::::::::
•• .. •
·; : -:
••
·i···· :
;
.. .
:::j:::::::.:::: :i:"::::: ::::t::::::::::: 50 IJsec/dlv
Fig. 2, Echo envelope from nplane.
application the bottleneck), '0 we have built our own specific systeln.
2. Measurement technique and its limitations 2. J. MeaslIl'emellttechlliqlle
Reviewing the basis of pulse-echo techniques, the ultmsonic sensor measures the time of flight (Tal') of an ultrasonic pulse reflected from an object and calculates the distance between the tran,ducer and the object. Sound travels at around 340 10 s - I in air. The distance, d, from transducer to object is d=(V,I)J2
with
V, =331.5 +0.61T (10 s·,) where Tis the air temperature (OC). A good accuracy in the determmation of the Tal' is required to achIeve enough precision in the dIStance measurement; this is not a tnvial task, due to the shape ofthe signal supplied by the transducer corresponding to the echo signal [2].
The conventional method for determining the Tal' is to start a counter when the transducer is excited and to stop it when the signal echo achieves a fixed threshold. This method has a great uncertainty in the determination of echo anival due to the variations of echo signals in amplitude and shape with the distance and noise components. Some authors have developed systems with a dynamic detection threshold, but the amplitude of the echo SIgnal varies not only with the distance [3], but also with thc nature of the reflector, which in our application IS a complex and internal surface. We have chosen to work with the enve10pe of the echo signal. Becouse the carrier contains no information about the closest object and can be eliminated, this allows us to use a larger sample time and thus to obtain a Simpler and more reliable system, in agreement with some researchers [4,5). A single transducer is used which operates in pulse-echo mode, the transducer alternately being the transmitter and receive,. of ultrasound waves.
In order to determine the Tal' with a sufficient degree of accuracy, we have used a subsample interpolation. It consists of fitting a line to a series of points in the rise-time interval of the echo signal by a minimum likelihood method (only the poinls between V=O.I Vm" and V=0.9Vm" are used, Fig. 2). This line is intersected at 50% of the peak value of the echo signal (point A). This Tal' has a theoretical bias which must be compensated for in the process calibration. 2.2. Limitatiolls ofIhe melhod
The above strategy does not consider the shape of the reflector. There are, though, notable differences when the reflector has more than one reflecting surface that can produce interference phenomena. Due to the faclthat the object under inspection has acomplex geometry, the echo-signal reflection is the vectorial addition of multiple simple echoes [6], backscattered by the mam liqUid surface, the associated meniscus and the internal walls of the bottleneck. This phenomenon produces very different signal profiles when the bottle passes under the transducer, depending On the liquid level, the diameter of the bottleneck and the wavelength of the echo signal. Because of diffraction and interfering multiple echoes, the positive slope of the echo signal does not always correctly fit the linear model, which introduces deviations into the measurement (see Fig. 3(a), Liquid echo). Sometimes it can occur that although the signal fits correctly to the linear model, the obtained measurement is not correct. That situation is less probable. because it only occurs if the caniers of the returned echoe' arc in the same phase.
3. A practical approach In order to solve the explained problem, we have used the knowledge ofthe echo·signal's rise time (t,) to decide which measurements are valid and which not. The measurement IS considered valid if: (a) VmJl\ > V'hrc,hakl' (b) The rise time (t,) is such that II <1,<1, (TL" see Fig. 3(b», where II and I, are emplncal values and depend on the characteristic of the reflector. TheSE restrictions reduce the variance of the measurements. Additionally to the level measurement, the ultrasonic sensor is able to detect the presence of lhe bottle WIthout any
E, Vllrgm
258
l!t lI/. /Semor~ allli ACllwlor~ A 61
(J!)97) 256-259
Volts
'"15:- v_~J ~
(b)
'~
~
ro~.
ro
w
~
~
1~
1ro
457
TN
N° Sample (Ts=5J!5eC) Fig. 3 Two s,lInpl~ echo Mgndb from cOII~cculivc tr
measured by an analog voltage, digitized using the other channel of the A/D board. We have selected a piezoelectric ultrasonic transducer of 220 kHz, the E-188/220 from Massa Corporation. This transducer was selected for to its suitable Characteristics: high resolution in the measurement, reduced sensitiVity to environmental nOIse, narrow lobe of emission and adequate range for the applicatIOn. Another advantage of this transducer is that it can work as both transmitter and receiver, eliminating problems of parallax [7].
complementary sensor; the procedure to do this is the distance measurement to the top of the bottleneck. After a bottle is detected, II measurements of the liquid level are taken. To obtam the final estimated distance (~), we calculate the weighted average. The weIght is the value of the peak amplitude of the echo signal.
EV
lllo1lt
,d,
B=~ EVm,lx, ,=,
S. Experimental results and conclusions 4. Experimental set-up
In Fig. 4 we show some results obtained from one bottle at three different speeds ofthe conveyor belt, v, = 12 cm s- I (3600 bottles per hour), v, = 18 (5400) and v, =22 (6600). It is very difficult to give absolute figures because the accuracy depends on too many factors (the line velocity,the conveyor belt, etc.), but we can observe in Fig. 4 that the accuracy and consistency of the measurements lies within the range of tolerance at the three velocities. In all distances WIthin our operation range (20-170 mm measured from the bottleneck) sImilar satisfying resl'lts were obtained: 99.7% of the measurements achieve an accuracy of ±0.9 mm (worst case). This simple sensor tested in an mdustnal plant has a good accuracy and consistency, low cost and high reliability, having been implemented with a general-purpose computer.
The sensor consist of a PC compatible with an A/D board plug in one slot, the WBFlash12-2 from OMEGA, the transducer, the driver block, and the filter/amplifier. see Fig. 1. Three pulses at 220 kHz with 50 V amplitude excite the transducer with a pul,e rate frequency of 100 Hz; the echoes are amplified and demodulated by a full-wave rectifier. The demodulated signal curresponding to the echo envelope is then digitized by the AID board, with 12-bit resolution and a sampling rate of 200 ksmnples S-I. For each transmission 400 points are digitized, corresponding to a range of 340 mm from the transducer. The temperature for correction of the sound velocity is sensed by a platinum deVIce, whose resistance variation is
Static Distante at center = 31.5 mm
(mm)
::!q~~~~4d=,;':::::: ___m__ ..__= m- .. __ 31
~ ~:.:~_f__ ~_~~_
"1
305 -
I
I
1 2 3 4 5
I
I
I
I
-:~~
I
I
I
-+- v3
J
6 7 8 9 10 11 12 13 1415 1617 1819 20
N° of measurement Fig 4. Meusurcments obt.uncd from a. bOUle
(03
=0 30)
E Varf,lu,\ el ai, I SI!IUOI'f (/I/({ At'/I/ClIOl~ 11 6/ (/997) 256-25!.J
Aclmowledgemenls This research has been carried out at Instituto de Automatica Industrial within the Esprit Project (9901) NETCIM. E. Vargas would like to thank Agencia Espanola de Coopemci6n Internacional for their financial support of his Ph.D. atU.C.M.
References
rI J R. BrY.lol "lid R Bogner. Ultnl\OOlC .. urf.lce imJgmg in advcr.. c cnvirOnmcnl1>, IEEE TrailS. Somu UI(mw/llc~. 3/ (1984) 373-390 121 J,M. M..ulin, R, Cere.. and T. Frclre, Ultr.l\OmC ranging' envelope :lnaIY3l~ glvc~ unproved l.lccuracy • St'll\or Rei'.. 12 (1992) 17-21. [3 J T, Freire. Scgubmcllto y Anuli\l\ de Enlomm de SolduJura por Areo Automatlluda Mcdi.mtc Ullr.....onido\, Ph.D TlJe,\/,. Univcr\ldJd Complulcnloc de MJdnd. 1995. [41 K. Audcnllcrt, H. Pcrcm,m ... Y. KuwuhJrd and J van Colmpcnhoul, Accurate ranging of multlple object u:-.ing ultr..\olllc .. co..or.... /I1I. Conf Rolwlin and AII/OlI/lItIOJI, NICe, FIClI/ce, /992. pp. 1733-1738. [5] G. Bcnct,J,J, SCITJno. P J, Gil and M, Sanchc7, DC'lgnor In ultrJ'OIlIC ~en,or cqulpped wIth a f.Jull-lolcr.lnl rClll·tIlnc Ian for prace..:-- control llpplicalloO\ ,1m Symp lme'"gemIIlMflImentatuJ/l, Be/gil/Ill, 1993. 16] A Freedman. A mechllni.. m of acoustic echo formation, Acmt/w, 12
(1962). 171 P Shlrlcy, An IlIlroducllon 10 ultra!lomc "cn..mg, ( (989).
Se/lSOfl,
(Nov.)
~59
Ralll'}" Ceres was born in 1947 in Jaon, Spain. He graduated in phySICS (c1ectronic) from Universidad Complu'ense of Madrid in 1971 and received the Ph.D. degree in 1978. After a lirst stay, for one year, in the LAAS-CNRS in Toulou~e (France), he has been working at the Insututo de Automatica Industrial (IAI), a dependent of the Spamsh National Council for Science Research. For the period 1990-1991 he worked in an electronics company (Amelec) as R&D director. Since the beginning, Dr Ceres has developed research activtties on sensor ~ystems applied to different fields, such as continuous process comrol, machine tools, agriculture, robotics and dis~bled people. Onlhese topics he has published more than 70 papers and congress communications, and he has several patents in industrial exploitation. At present Dr Ceres is the Spanish delegate for the IMT (Brite-Euram) Commitlee and deputy scientific director of the IAI. Jose M. Mal'lln Abreu was born 111 1958 in Isla Cristina (Spain) He graduated In physics from the Universileit van Amsterdam in 1982 and received the doctoral degree in 1990 from the Universidad Complutense de Madrid. He has developed many research activities in the field of automation of processes and especially on the study of sensors (focused on ultrasonic sensors) and their processing and application. He has published many sciemific papers and holds several patents. He has also participated in different national and international sCientific programmes and congresses.
Biographies
Enrique A. Vargas Cabral was born 111 Concepci6n. Paraguay,lI1 1966. He graduated in electrical engll1eering in 1991 from the Faculdade de Engenharia Industrial (Sao Paulo, Brazil). He was a research engineer and assistant professor at the Department of Electrical Engineenng, Catholic University of Asunci6n, from 1992 until 1994. Currently, he 's working towards the Ph.D. degree 111 computer systems and sciences at the Umversldad Complutense de Madrid, and is carrying out work in the IAI. HIS current research interests are ultrasonics, signal-processing techniques, object recognition and classification
Leopoldo Calderon was born in 1947 in Lumbrales (Spain) He graduated iu physics from the Universidad de Sevilla 111 1974 and received the doctoral degree in 1984 from the Universidad Complutensede Madrid. SlI1ce 1974 DrCalder6n has been working in the Instituto de Automatica Industrial developing many re~earch activities in the field of automation of processes and especially on the study of sensors (focused on ultrasonic sensors) and their processing and apphcation. As a consequence of this activity, Dr. Calderon has published many scientific papers and IS author ofdifferent patents. He has also participated in different national and international scientific programmes and congresses.
Scn~or,
SENSORS ACTuATORS PH~CAL
und Aclu
Ultrasonic sensor for liquid-level inspection in bottles E. Vargas *, R. Ceres, J.M. Martin, L. Calderon "Uti/litO de Awol/ulrica Jlldllstrllli (IAI-CSIC), N·I/I, Km 22HOO, Argam/a del Re\', 28500 Mat/ml, Sl'am
Abstract In this paper, the development of it precise and dynamic ultrasonic dh,tance sensor to mea';ure the level of liquid In bottles for an industrial line IS descnbed. For this afJplication. optical, capacillve or mechanical means are not suitable. In the fir!!! pnrt the limitations ofaconventlonal pulllc--echo ranging system are dlscu'\sed. A strategy to measure the time of flight based on the envelope of the echo !'Jignal is performed, solving in a practical way the problem of the complex signal reflected from the malO !'lurface, meni~cu~ and internal walls of the bottleneck. Keyuords: UltraSOniC; Sensors. liquid level. Envelope
I. Introduction
The present work is related to the European ESPRIT project NETCIM (Cooperative Network for CIME Technologies in Europe). The Instituto de Automatica Industrial (JAI) is responsible for the implementation of an advanced winebottting plant. with functionalities of inspection, control and automation integrated by computer. The inspection tasks are focused on the level of filling. the correct placement ofcorks and protective covers using ultrasonic techniques (see Fig. I). This paper describes the strategies used in the implementatIon of the subsystem of the plant that will be used for the on-hne inspection of the filling level ofwinebotlles. To carry it out, we need to measure the level of liquid, with one millimetre resolution, considering the menhcus formauon 10 the liquid surface and the VIbration of the bottles produced by their movement through the conveyor belt. Distance and displacement measurements are a wellknown problem and have been studied for many years. Noncuntact teChniques are preferred in IOdustrial automation because of their inberent simplicity, and are a reqUIrement for this application. The most comwon of these techniques are of ultrasonic, laser and infrared types. In a first stage of the project. some tests were carried out to select the basic measurement technique and the corresponding transducers to be used. No satisfactory results were obtained with acommercial laser interferometer even in static tests. '" Corre'pondmg author. Tel.. +341 871 1900. Fax: +3418717050 E-maIl. evarga,@mcrcunolal C"IC,CS 0924·4247/97/$17.00 © 1997 ElscvlcrSclence S.A. All nght'i re,erved PI/ 80924-4247(96) 0 1421-5
Level
~.4~1 Plant
Fig
~.
ImpccLlOn and automallon system usmg ultra,onic'i
Laser and IR ,ensors were discarded because these types of devices are more appropriate for measurements of flat and opaque surfaces. presenting for our casc a hIgh degree of absorption and secondary reflection for some angles of IOcidence Other techniques like CCD were refused because of lighting problems aad tbeir high cost. Ultrasonic sensing has characteristics that make it advantageous in some situations compared with other non-contact sensing methods such as electromagnetic (includingoptical), electrical, magnetic, thermal, or pneumatic means. For sensing through some medi~, such as froth above liqUIds. aqueous media. fibres, loose granular mat.cnals and dense vapours, ultrasonic systems may provide the most practical if not the only possible means [ I J. The use of ultrasonics in distance measurement in air has been viewed with great interest because it is very inexpensive and can be used m polluted. smoky or dark environments. Therefore, we have selected ultrasonic techniques here. However. existing ultrasonic sensors only measure the distance to the closest object within their viewing angle (in our
{£ Varga~ etal.
VD'~
2: 2 _ 1,5
/SemUrsllllti A(./Iwtor:; A 61 (!1}f)7j 256-259
257
..
.i.. ·:::·~:::::r::::::::::::i::::::::::::t::::::::::: A
'..........
..: .
;
;
o : :::::'.: ::::(::::::::
•• .. •
·; : -:
••
·i···· :
;
.. .
:::j:::::::.:::: :i:"::::: ::::t::::::::::: 50 IJsec/dlv
Fig. 2, Echo envelope from nplane.
application the bottleneck), '0 we have built our own specific systeln.
2. Measurement technique and its limitations 2. J. MeaslIl'emellttechlliqlle
Reviewing the basis of pulse-echo techniques, the ultmsonic sensor measures the time of flight (Tal') of an ultrasonic pulse reflected from an object and calculates the distance between the tran,ducer and the object. Sound travels at around 340 10 s - I in air. The distance, d, from transducer to object is d=(V,I)J2
with
V, =331.5 +0.61T (10 s·,) where Tis the air temperature (OC). A good accuracy in the determmation of the Tal' is required to achIeve enough precision in the dIStance measurement; this is not a tnvial task, due to the shape ofthe signal supplied by the transducer corresponding to the echo signal [2].
The conventional method for determining the Tal' is to start a counter when the transducer is excited and to stop it when the signal echo achieves a fixed threshold. This method has a great uncertainty in the determination of echo anival due to the variations of echo signals in amplitude and shape with the distance and noise components. Some authors have developed systems with a dynamic detection threshold, but the amplitude of the echo SIgnal varies not only with the distance [3], but also with thc nature of the reflector, which in our application IS a complex and internal surface. We have chosen to work with the enve10pe of the echo signal. Becouse the carrier contains no information about the closest object and can be eliminated, this allows us to use a larger sample time and thus to obtain a Simpler and more reliable system, in agreement with some researchers [4,5). A single transducer is used which operates in pulse-echo mode, the transducer alternately being the transmitter and receive,. of ultrasound waves.
In order to determine the Tal' with a sufficient degree of accuracy, we have used a subsample interpolation. It consists of fitting a line to a series of points in the rise-time interval of the echo signal by a minimum likelihood method (only the poinls between V=O.I Vm" and V=0.9Vm" are used, Fig. 2). This line is intersected at 50% of the peak value of the echo signal (point A). This Tal' has a theoretical bias which must be compensated for in the process calibration. 2.2. Limitatiolls ofIhe melhod
The above strategy does not consider the shape of the reflector. There are, though, notable differences when the reflector has more than one reflecting surface that can produce interference phenomena. Due to the faclthat the object under inspection has acomplex geometry, the echo-signal reflection is the vectorial addition of multiple simple echoes [6], backscattered by the mam liqUid surface, the associated meniscus and the internal walls of the bottleneck. This phenomenon produces very different signal profiles when the bottle passes under the transducer, depending On the liquid level, the diameter of the bottleneck and the wavelength of the echo signal. Because of diffraction and interfering multiple echoes, the positive slope of the echo signal does not always correctly fit the linear model, which introduces deviations into the measurement (see Fig. 3(a), Liquid echo). Sometimes it can occur that although the signal fits correctly to the linear model, the obtained measurement is not correct. That situation is less probable. because it only occurs if the caniers of the returned echoe' arc in the same phase.
3. A practical approach In order to solve the explained problem, we have used the knowledge ofthe echo·signal's rise time (t,) to decide which measurements are valid and which not. The measurement IS considered valid if: (a) VmJl\ > V'hrc,hakl' (b) The rise time (t,) is such that II <1,<1, (TL" see Fig. 3(b», where II and I, are emplncal values and depend on the characteristic of the reflector. TheSE restrictions reduce the variance of the measurements. Additionally to the level measurement, the ultrasonic sensor is able to detect the presence of lhe bottle WIthout any
E, Vllrgm
258
l!t lI/. /Semor~ allli ACllwlor~ A 61
(J!)97) 256-259
Volts
'"15:- v_~J ~
(b)
'~
~
ro~.
ro
w
~
~
1~
1ro
457
TN
N° Sample (Ts=5J!5eC) Fig. 3 Two s,lInpl~ echo Mgndb from cOII~cculivc tr
measured by an analog voltage, digitized using the other channel of the A/D board. We have selected a piezoelectric ultrasonic transducer of 220 kHz, the E-188/220 from Massa Corporation. This transducer was selected for to its suitable Characteristics: high resolution in the measurement, reduced sensitiVity to environmental nOIse, narrow lobe of emission and adequate range for the applicatIOn. Another advantage of this transducer is that it can work as both transmitter and receiver, eliminating problems of parallax [7].
complementary sensor; the procedure to do this is the distance measurement to the top of the bottleneck. After a bottle is detected, II measurements of the liquid level are taken. To obtam the final estimated distance (~), we calculate the weighted average. The weIght is the value of the peak amplitude of the echo signal.
EV
lllo1lt
,d,
B=~ EVm,lx, ,=,
S. Experimental results and conclusions 4. Experimental set-up
In Fig. 4 we show some results obtained from one bottle at three different speeds ofthe conveyor belt, v, = 12 cm s- I (3600 bottles per hour), v, = 18 (5400) and v, =22 (6600). It is very difficult to give absolute figures because the accuracy depends on too many factors (the line velocity,the conveyor belt, etc.), but we can observe in Fig. 4 that the accuracy and consistency of the measurements lies within the range of tolerance at the three velocities. In all distances WIthin our operation range (20-170 mm measured from the bottleneck) sImilar satisfying resl'lts were obtained: 99.7% of the measurements achieve an accuracy of ±0.9 mm (worst case). This simple sensor tested in an mdustnal plant has a good accuracy and consistency, low cost and high reliability, having been implemented with a general-purpose computer.
The sensor consist of a PC compatible with an A/D board plug in one slot, the WBFlash12-2 from OMEGA, the transducer, the driver block, and the filter/amplifier. see Fig. 1. Three pulses at 220 kHz with 50 V amplitude excite the transducer with a pul,e rate frequency of 100 Hz; the echoes are amplified and demodulated by a full-wave rectifier. The demodulated signal curresponding to the echo envelope is then digitized by the AID board, with 12-bit resolution and a sampling rate of 200 ksmnples S-I. For each transmission 400 points are digitized, corresponding to a range of 340 mm from the transducer. The temperature for correction of the sound velocity is sensed by a platinum deVIce, whose resistance variation is
Static Distante at center = 31.5 mm
(mm)
::!q~~~~4d=,;':::::: ___m__ ..__= m- .. __ 31
~ ~:.:~_f__ ~_~~_
"1
305 -
I
I
1 2 3 4 5
I
I
I
I
-:~~
I
I
I
-+- v3
J
6 7 8 9 10 11 12 13 1415 1617 1819 20
N° of measurement Fig 4. Meusurcments obt.uncd from a. bOUle
(03
=0 30)
E Varf,lu,\ el ai, I SI!IUOI'f (/I/({ At'/I/ClIOl~ 11 6/ (/997) 256-25!.J
Aclmowledgemenls This research has been carried out at Instituto de Automatica Industrial within the Esprit Project (9901) NETCIM. E. Vargas would like to thank Agencia Espanola de Coopemci6n Internacional for their financial support of his Ph.D. atU.C.M.
References
rI J R. BrY.lol "lid R Bogner. Ultnl\OOlC .. urf.lce imJgmg in advcr.. c cnvirOnmcnl1>, IEEE TrailS. Somu UI(mw/llc~. 3/ (1984) 373-390 121 J,M. M..ulin, R, Cere.. and T. Frclre, Ultr.l\OmC ranging' envelope :lnaIY3l~ glvc~ unproved l.lccuracy • St'll\or Rei'.. 12 (1992) 17-21. [3 J T, Freire. Scgubmcllto y Anuli\l\ de Enlomm de SolduJura por Areo Automatlluda Mcdi.mtc Ullr.....onido\, Ph.D TlJe,\/,. Univcr\ldJd Complulcnloc de MJdnd. 1995. [41 K. Audcnllcrt, H. Pcrcm,m ... Y. KuwuhJrd and J van Colmpcnhoul, Accurate ranging of multlple object u:-.ing ultr..\olllc .. co..or.... /I1I. Conf Rolwlin and AII/OlI/lItIOJI, NICe, FIClI/ce, /992. pp. 1733-1738. [5] G. Bcnct,J,J, SCITJno. P J, Gil and M, Sanchc7, DC'lgnor In ultrJ'OIlIC ~en,or cqulpped wIth a f.Jull-lolcr.lnl rClll·tIlnc Ian for prace..:-- control llpplicalloO\ ,1m Symp lme'"gemIIlMflImentatuJ/l, Be/gil/Ill, 1993. 16] A Freedman. A mechllni.. m of acoustic echo formation, Acmt/w, 12
(1962). 171 P Shlrlcy, An IlIlroducllon 10 ultra!lomc "cn..mg, ( (989).
Se/lSOfl,
(Nov.)
~59
Ralll'}" Ceres was born in 1947 in Jaon, Spain. He graduated in phySICS (c1ectronic) from Universidad Complu'ense of Madrid in 1971 and received the Ph.D. degree in 1978. After a lirst stay, for one year, in the LAAS-CNRS in Toulou~e (France), he has been working at the Insututo de Automatica Industrial (IAI), a dependent of the Spamsh National Council for Science Research. For the period 1990-1991 he worked in an electronics company (Amelec) as R&D director. Since the beginning, Dr Ceres has developed research activtties on sensor ~ystems applied to different fields, such as continuous process comrol, machine tools, agriculture, robotics and dis~bled people. Onlhese topics he has published more than 70 papers and congress communications, and he has several patents in industrial exploitation. At present Dr Ceres is the Spanish delegate for the IMT (Brite-Euram) Commitlee and deputy scientific director of the IAI. Jose M. Mal'lln Abreu was born 111 1958 in Isla Cristina (Spain) He graduated In physics from the Universileit van Amsterdam in 1982 and received the doctoral degree in 1990 from the Universidad Complutense de Madrid. He has developed many research activities in the field of automation of processes and especially on the study of sensors (focused on ultrasonic sensors) and their processing and application. He has published many sciemific papers and holds several patents. He has also participated in different national and international sCientific programmes and congresses.
Biographies
Enrique A. Vargas Cabral was born 111 Concepci6n. Paraguay,lI1 1966. He graduated in electrical engll1eering in 1991 from the Faculdade de Engenharia Industrial (Sao Paulo, Brazil). He was a research engineer and assistant professor at the Department of Electrical Engineenng, Catholic University of Asunci6n, from 1992 until 1994. Currently, he 's working towards the Ph.D. degree 111 computer systems and sciences at the Umversldad Complutense de Madrid, and is carrying out work in the IAI. HIS current research interests are ultrasonics, signal-processing techniques, object recognition and classification
Leopoldo Calderon was born in 1947 in Lumbrales (Spain) He graduated iu physics from the Universidad de Sevilla 111 1974 and received the doctoral degree in 1984 from the Universidad Complutensede Madrid. SlI1ce 1974 DrCalder6n has been working in the Instituto de Automatica Industrial developing many re~earch activities in the field of automation of processes and especially on the study of sensors (focused on ultrasonic sensors) and their processing and apphcation. As a consequence of this activity, Dr. Calderon has published many scientific papers and IS author ofdifferent patents. He has also participated in different national and international scientific programmes and congresses.