Mechanical-electrical Optoisolator Transducer with current-to-frequency Conversion

Transcription

1 Mechanical-electrical Optoisolator Transucer with current-to-frequency onversion Ioan Marcel IURUŞ 1, Mihai DIMIAN, Arian GRAUR 3 1,,3 Ştefan cel Mare University of Suceava, Romania str.universitatii nr.13, RO-709 Suceava 1 marcelciurus@usv.ro, imian@ee.usv.ro, 3 arian.graur@usv.ro Abstract A novel esign for a mechanical-electrical transucer is presente in this article along with the preliminary testing of the transucer prototype. By using a Polaroi optocoupler as the motion sensor, this evice combines the transucer feature to convert mechanical signals to electrical ones with the optoisolator feature of galvanic separation between two voltage moules. Signal conitioning circuit is a current-to-frequency converter, while the obtaine signals are logically compatible an can be processe by a microprocessor. The evice is aime for application in the areas of automation an mechatronics. Inex Terms urrent-to-frequency conversion, Optical polarization, Optoelectronics, Polaroi optocoupler, Transucer I. INTRODUTION One of the present emans in the evelopment of inustrial processes is the rigorous control of the parameters for ifferent components of the machine-tools an inustrial robots [1]. The precise etermination of the component position, spee, an acceleration requires multi-isciplinary approaches which combine fine mechanics, electronics an information technology []. This article presents a novel esign for a mechanicalelectrical transucer base on a Polaroi optocoupler as the motion sensor. As photoelectrical conversions eliminate the influence of electromagnetic isturbances [3], this evice combines the transucer feature to convert mechanical signals to electrical ones with the optoisolator feature of galvanic separation between two voltage moules. The originality of our approach consists of replacing the isk or isks having transparent an opaque spaces, which are usually use in such evices for controlling the light beam, with a system of Polaroi filters (analyzer, polarizer) leaing to novel optoisolator coine as Polaroi optocoupler [4]. The Polaroi optocoupler can comman both igital an analog integrate circuits can be better miniaturize than optical transucers with isks. When the Polaroi optocoupler sens ata to a microprocessor, the optocoupler output river can be an analog-to-igital converter [5]. However the focus of this paper is on current-to-frequency converter since the rigorous knowlege of the movement parameters for the components of a machine-tool requires a conversion with a large number of bits. The rectangular impulses generate by this river can be counte with a microprocessor internal counter. II. PROPOSED SHEME The block iagram of the mechanical-electrical optoisolator transucer has the following parts: the river of the transmitter moule (T x ) of the Polaroi optocoupler, the Polaroi optocoupler LED-phototransistor an the river of the receiver moule (R x, ), which are represente in Fig.1. Figure 1. The block iagram of the mechanical-electrical optoisolator transucer with current-to-frequency conversion. The corresponing schematic iagram is presente in Fig.. The river of (T x ) moule is an inepenent current source, while the light source of the Polaroi optocoupler is a super bright white LED with the luminous intensity on the irection of the longituinal axis of (10365±6) mc for a 19mA current, where the current intensity is regulate with the linear P 1 potentiometer. A rotating P-polarizer Polaroi filter is attache to LED optical output an a fixe A analyzer Polaroi filter is attache to the photoreceiver optical input, both filters having a thickness of 0.7mm. A mechanical system is use for the axial assembly an the rotation/translation movement of these components. Figure. The schematic iagram of the mechanical-electrical optoisolator transucer with current-to-frequency conversion. 119

2 The optocoupler s photosensitive etector is a BPV11 silicone NPN Phototransistor [6] which functions uner conitions of open base circuit, having the emitter-collector voltage of 18V. The river of the (R x ) moule of the Polaroi optocoupler is a current-to-frequency converter. This river s T -B170 transistor has the function of converting the current intensity (I ) through the phototransistor into voltage. The omain of (V ) voltage in which (I ) current is converte iffers from that of the comman (V D ) voltage of the integrate circuits I.. - βe565. For conversion V V D, the operational amplifier I.. 1 -βa741 is use. I.. is a phase locke loop (PLL). Among the functional blocks of the PLL (βe565), we only use the voltagecontrolle oscillator (VO) in orer to make the voltagefrequency conversion. III. EXPERIMENTAL RESULTS In Table I, the measure values of electric current intensities (I ) are presente for selecte values of angle () between the polarizing planes of the two filters an istance () between (T x ) an (R x ) moules. The transfer characteristics families of the LED-phototransistor Polaroi optocoupler, I=I() =const. an I=I() =const., are plotte in Fig. 3 an Fig. 4, respectively. TABLE I. THE OUTPUT ELETRI URRENT INTENSITIES OF THE LED PHOTOTRANSISTOR POLAROID OPTOOUPLER EXPRESSED IN (ΜA), FOR DIFFERENT VALUES OF ANGLE (Α) BETWEEN POLARIZING (P) AND (A) PLANES AND OF THE DISTANE (D) BETWEEN (T X ) AND (R X ) MODULES. (mm) (DEG) Figure 4. The transfer characteristics family I =I () =const. of the LED phototransistor Polaroi optocoupler. In orer to quickly an accurately etermine the movement parameters for ifferent components of a machine-tool, the extreme values of the (I ) current nee to be known with high precision. This involves a precise knowlege of the extreme values taken by () an () [7]. Otherwise, the polarizing voltage of the T transistor junctions coul be inaccurately compute, an consequently, the transfer characteristic V =V (I ) of the current-to-voltage converter coul be iverte from the linear form. For the analysis of these processes, the omain of the values of istance () is a little larger than the one for which the river of the (R x ) moule was esigne. In Table II are renere the values of (V ) voltage corresponing to the (I ) currents from Table I. Voltage (V ) is measure between the collector an the transucer chassis groun. In Fig. 5, the transfer characteristic V =V (I ) of the current-to-voltage converter is graphically represente. To make this graphic, were use the values from Tables I an II. TABLE II. THE VOLTAGE (V ) EXPRESSED IN (V), FOR DIFFERENT VALUES OF ANGLE (Α) AND OF THE DISTANE (D) BETWEEN (T X ) AND (R X ) MODULES. (mm) (DEG) Figure 3. The transfer characteristics family I =I () =const. of the LED phototransistor Polaroi optocoupler. 10 Figure 5. The transfer characteristic V =V (I ) of the current-to-voltage converter.

3 TABLE III. THE VOLTAGE (V D ) EXPRESSED IN (V), FOR DIFFERENT VALUES OF ANGLE (Α) AND DISTANE (D) BETWEEN (T X ) AND (R X ) MODULES. (mm) (DEG) The (V D ) values of the voltage obtaine by converting the voltage from Table II using I.. 1 are shown in Table III. Voltage (V D ) is measure between the 7 pin of the βe565 an the transucer s chassis groun. In Fig. 6, the transfer characteristics of the voltage range converter are presente base on the ata from Tables I an III. In Table IV, there are presente the values of the frequency (f) obtaine after the conversion of voltages (V D ) by I... By graphically representing ata from Table III an IV, the transfer characteristic of the voltage-tofrequency converter is obtaine, as one can see in Fig.7. By using ata from Tables I an IV, the transfer characteristics families of the mechanical-electrical optoisolator transucer with the current-to-frequency conversion are obtaine. f=f() =const. an f=f() =const. are presente in Fig.8 an Fig. 9, respectively. Figure 6. The transfer characteristic V D =V D (V ) of the voltage range converter. TABLE IV. THE FREQUENY (F) EXPRESSED IN (HZ), FOR DIFFERENT VALUES OF ANGLE (Α) AND DISTANE (D) BETWEEN (T X ) AND (R X ) MODULES. (mm) (DEG) Figure 8. The transfer characteristics family f=f() =const. of the mechanicalelectrical optoisolator transucer with the current-to-frequency conversion. Figure 9. The transfer characteristics family f=f() =const. of the mechanicalelectrical optoisolator transucer with the current-to-frequency conversion. Figure 7. The transfer characteristic f=f(v D ) of the current-to-frequency converter. 11 IV. HARATERISTIS MODELING If the intensity of the current through the LED in Fig. is maintaine constant then the intensity of the light beam (I ο ) incient on the surface of the polarizer filter (P) is constant in time. Knowing that the intensity of the light beam is proportional with the square of the maximum value of the electrical fiel s intensity, accoring to Malus s law, one

4 can show that the epenence of the light beam s intensity (I) at the output of the analyzer filter (A) on the intensity of the light beam incient on the (P) filter, is given by the following relation: I = I cos (1) 0 where () is the angle between the polarizing plans of the two filters. In the case of the LED-phototransistor bipolar polaroi optocouplers, the current-illumination relation is a power law with exponent a 1. By taking also into account the inverse square istance law relating the etecte illumination to the raiation luminous intensity, the epenence of intensity (I ) of the electric current at the collector on angle () an istance () between (T x ) an (R x ) moules can be expresse as follows: cos + T I = k () where k is a proportionality constant specific to the optocoupler. Since the extinction ratio of real polarizer filter is not zero, an aitional parameter T was introuce in () to account for the transmission of the light beam through the system of Polaroi filters incient in case of extinction (=90 ); From the light characteristics of the n-p-n, BPV 11 phototransistor use in our experiments power coefficient a is foun to be equal to 1 when the emitter-collector voltage is 18 V. By using the experimental ata from Table I for the extreme cases =0 an =90 when =10mm, the values for the empirical constants (T) an (k) are obtaine. As a result, theoretical transfer characteristics () for our prototype reas as follows: cos I = 515mA mm (3) A comparison between the experimental transfer characteristics family measure for our Polaroi optocoupler prototype (see also Fig. 3) an the theoretical transfer characteristics family given by (3) is presente in Fig. 10. The measurement ata are represente by symbols an the theoretical characteristics by continuous lines. The signal processing of the (R x ) moule starts with T transistor which converts (I ) current into (V ) voltage. The transfer function of the current-to-voltage converter from Fig. can be expresse as follows: V = V β R I = (E.7V) β R I (4) A F 3 1 where V A is the potential at point (A) of the circuit from Fig. an β F is the forwar common emitter current gain an is equal to 364 for the transistor use in our evice. The omain of (V ) voltages is then converte into (V D ) voltages with I.. 1. In the case of operational amplifiers from Fig., the gain of the amplifier is given by. VD VDm R 5 + R P A = = (5) V V R M 4 where V M is maximum voltage at the inverting input of I.. 1, V Dm is minimum voltage at the output of I.. 1, an R P F 3 is resistance from the circuit of P potentiometer. It is apparent from (5) that the expression of the transfer function of the voltage range converter is: R 5 + R P VD = VDm + ( VM V ) (6) R 4 In the case of our prototype: T VM = E1.7V βf R3 k = 15V (7) an (E1.7V) ( R 7 + R P4 ) (R 4 + R 5 + R P) VDm = (R 6 + R 7 + R P4) R 4 R 5 + R P T E1.7V F R 3 k = 5.48V R β 4 M where ( M ) is the maximum istance between (T x ) an (R x ) moules. The resulting theoretical characteristic is plotte in Fig. 6 by continuous line an is in goo agreement with the experimental measurements. Figure 10. Graphical representation of the theoretical an the experimental characteristics families I =I () =const. of the LED phototransistor Polaroi optocoupler. Next, voltages (V D ) are converte into frequencies by I... The transfer function of the voltage-to-frequency converter is given by the following relation [9]: VA VD f (9) [0. (V V ) 0.3] R A B which is represente by continuous line in Fig. 7. By replacing in (9), the electrical potentials at points A an B with their expression of voltages E 1 an E (see Fig. ) the expression for frequency becomes: E1.7V VD f (10) [0.44 (E E ) 4.94V] R 1 From eqs. (), (4), (6), (7), (8) an (10), the following expression is erive for the frequency generate by the mechanical-electrical optoisolator transucer with currentto-frequency conversion as a function of the movement parameters () an (): M (8) 1

5 ( R + R ) 1 (R R R ) k R (R R ) cos T (E.7V) 7 P P βf P R 5 R P R 4 R 6 R 7 R P4 R 4 f (,) + + (11) [0.44 (E E ) 4.94V] R 1 In Fig.11 an Fig.1, the families of theoretical characteristics f=f() =const. an f=f() =const. compute by using (11) are plotte against the experimental transfer characteristics of our prototype for the optoisolator transucer with current-to-frequency. The theoretical curves are represente by lines while the experimental ata, which were also given in Figs. 8 an 9, are plotte as symbols. parameters of some components of ifferent mechanisms. In the case of the transucer presente in this paper, the etermination is possible when function (11) rigorously escribes the real movement of the (Tx) moule as compare to (Rx) moule. Figure 11. Graphical representation of the theoretical an the experimental characteristics families f=f() =const. of the mechanical-electrical optoisolator transucer with the current-to-frequency conversion. Figure 1. Graphical representation of the theoretical an the experimental characteristics families f=f() =const. of the mechanical-electrical optoisolator transucer with the current-to-frequency conversion. Although the expression (11) can be mathematically extene in the fiel of negative frequencies, as can also be seen from the previous Figures, the representations in this area o not actually have a physical meaning. A general view over the eformation of the experimental family characteristics f=f(, ) because of the saturation effect, emerging for small values of the () an () movement parameters, can be notice in the 3D representation from Fig.13. V. ANALYSIS OF BORDELINE ASES The role of position an movement transucers is to quickly an precisely etermine the positions of movement 13 Figure D graphical representation of the experimental characteristics families f=f(,) of the mechanical-electrical optoisolator transucer with the current-to-frequency conversion. This involves accurate knowlege of the extreme values that can be taken by () an () measures as well as the form of function (). In orer to analyze these processes, the omain of the values of istance () is a little bit higher than that for which the river of the (R x ) moule was esigne. When the istance () between (T x ) an (R x ) moules is smaller than that one for which the transucer s river was esigne, for small values of () angle the current through the phototransistor (I ) increases to the maximum amitte value. This increase brings the operation of the phototransistor (T ) in the neighborhoo of the saturation area. In this case, the transfer characteristic I =I (I B ) Vc=const. =I 1 (I ) Vc=const. becomes nonlinear. This phenomenon can be notice in the following cases: =84mm for =0 an =78mm for [0, 0 ], Table II. The nonlinearity characteristic I 1 =I 1 (I ) V=ONST. etermines the lack of linearity in the inferior part of the transfer characteristic V =V (I ) of the current voltage-to-voltage converter, Fig.5. At the same time, too big values of the (I ) current, etermines the entrance of the operational amplifier in the saturation area for small values of the input voltages which results in large values of the output voltages Fig.6. In this region, the transfer characteristic of the voltage converter becomes nonlinear. This saturation effect can be also foun in the case of the current-to-frequency converter for small values of the frequencies generate by the VO moule of I..., Fig. 8, 9, 13. Because of this effect, it is impossible for the transucer to perceive the moification of istance () an the () angle in the case of exceeing borer values. onsequently,

6 the movements of the component parts of the machine-tools will receive erroneous commans. Another borerline case is met when currents intensities become too small. This situation can be encountere if the values of () an () parameters become too big. In these conitions, the VO moule of I.. becomes unstable, generating a signal characterize by frequency leaps. At the same time, although the amplitue of the signal oesn t change, a consierable moification of the offset current appears as seen in Fig. 14 an 15. Figure 14. The shape of the signal emitte by the transucer, for a comman current of the river (R x ) foun at the inferior borer of the omain (I =6.5 μa). Figure 15. The shape of the signal emitte by the transucer, for a comman current of the river (R x ) foun uner the inferior borer of the omain (I =6.5 μa). This instability of VO moule will etermine the chaotic commaning of the machine-tools component parts. VI. ONLUSIONS The transucer propose by us, using a Polaroi optocoupler sensor is not affecte by electromagnetic isturbance. This sensor can be better miniaturize than optical sensors equippe with isk/isks with transparent an opaque areas. The electrical signals generate by the propose transucer are analog signals an contains more information than the signals emitte by optical sensors isk/isks. Signal conitioning circuit of the transucer is not a classic analog-to-igital converter. Its conversion rate is lower than a parallel analog-to-igital converter. Although slower, the propose current-to-frequency converter allows the conversion of a large number of bits on the output signal of the sensor. This conversion has the avantage to specify strict parameters of the components of machine-tools. Optical sensors isk/isks may work in binary coe, ecimal coe or Gray coe. The coe is require by way of realization of the isc. If the signal conitioning circuit is a classic analog-toigital converter it imposes the type of coing scheme of the transucer. By using the propose current-to-frequency converter, the transucer can work with any of the three coes. In this case, the type of coe will be etermine by the numerator processor. Due to the fact that this transucer oes not require the use of a processor to ecoe a specific coe, it offers the user a great freeom in esigning the system of comman an control of machine tools. Transucer s frequency output signal contains information relate to the value of the () an () movement parameters. The maximum frequency which can be generate by the VO moule of βe565 is fm=500 KHz an the minimum frequency accomplishes the conition fm fm/ [9]. These characteristics of I..., allow the obtaining of some high resolution transucers. The signal generate at the transucer s output is a function of f=f(,) type (11). Such a signal permits microprocessors to obtain complex information concerning the position, the movement irection, the spee an the acceleration of the component parts of the machine-tools. The transucer presente in this article functions for angles whose value is comprise in [0, 90 ] omain. This thing restricts the rotation movements of an engine to a certain number of revolutions. The number of revolutions epens on the omain in which the () angle can take values an on the characteristics of the mechanical system use at gearing own the rotation movement. The moification of istance () between the two moules can be also use to compensate the effects that appear because of LED ageing which is a part of the optocoupler. The optocoupler s internal structure allows for its miniaturization. These transucers are generally aime at automation an mechatronics applications. REFERENES [1] J. ora an J.K. Al-Tayie, "Enhance performance variablereluctance transucer for linear-position sensing", IEE Proc. Electric Power Applications, vol. 150, pp , Sept [] A. Drumea, A. Vasile, P. Svasta an I. Ilie, "Moelling an simulation of simple mechatronic system - position control solution base on linear variable inuctor isplacement transucer", Proc. IEEE n Electronics System-Integration Technology onf., Greenwich, GB, Sept. 008, pp [3] K. Tsubata, K. Suzuki, S. Mikami an E.I. Osawa, "Recognition of lawn information for mowing robots", Proc. IEEE 4th Int. onf. Autonomous Robots an Agents, Wellington, NZ, Feb. 009, pp [4] I.M. iuruş, "Optocuplor polaroi" (patent pening), OSIM Bucureşti, RO, a , 009. [5] D.A. Rauth an V.T. Ranal, "Analog-to-igital conversion. part 5", IEEE Instrumentation & Measurement Magazine, vol. 8, pp , Oct [6] [7] S. Brock an J. Deskur, "The problem of measurement an control of spee in a rive with an inaccurate measuring position transucer", Proc. IEEE 10th Int. Workshop on Avance Motion ontrol, Trento, IT, March 008, pp [8] I.M. iuruş, "LED-Photoresistor Polaroi Optocouplers", Proc. 3r Int. Symp. Electrical Engineering an Energy onverters, Suceava, RO, Sept. 009, pp [9] M. iuguean et al., "ircuite integrate liniare. Aplicaţii", Eitura Facla, Timişoara, RO, 1986, ch. 7, sec. 7., pp