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(11) | EP 0 031 937 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
An electro-pneumatic or electro-hydraulic transducer Elektropneumatischer oder elektrohydraulischer Wandler Transducteur électro-pneumatique ou électro-hydraulique |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to an electro-pneumatic or electro-hydraulic transducer, in which there is a pneumatic or hydraulic nozzle-flap system, which flap is controlled by an electric control signal, as described in the preamble of claim 1.
[0002] A transducer comprising the features of the preamble of claim 1 is known from US-A-3 099 995. In this known transducer, an oscillating control signal with variable duty-cycle is applied to the flap, and thereby it is ensured that the adjustment drive for the flap and the flap itself can have a smaller mass, and thus a high response speed can be achieved. The known transducer operates in the manner that the flap opens and closes alternatingly the nozzle. In order to ensure that the thus adjusted pressure corresponds to the duty-cycle of the electric control signal, the pressure in the pressure chamber upstream of the nozzle shall change between inlet pressure and atmospheric pressure, and this necessitates an extremely small pressure chamber. Due to the necessity to have a small pressure chamber, the known transducer is subject to considerable precision requirements and constructive restrictions. Besides, an increase of the frequency is limited by the size of the pressure chamber. Moreover, the customary nozzle-flap systems, i.e. systems with the usual dimensions, cannot be used in the known transducer.
[0003] It is the object of the invention to develop the transducer according to the preamble in such a way that the precision requirements with view to the nozzle-flap system are not so strict, in particular, that it becomes possible to structurally use the same nozzle-flap system commonly used in transducers.
[0004] This object is achieved according to the invention by means of the features in the characterizing portion of claim 1, i.e. it is achieved mainly by the fact that, during the operation of the transducer, the range of movement of the flap is limited to a specific range excluding the positions of completely closed or opened nozzle.
[0005] In the transducer of the invention, the input pressure or the atmospheric pressure need not be produced in its pressure chamber. Therefore the pressure chamber resp. the volume between the nozzle and the restricted inlet orifice can be much greater in the transducer of the invention than in the known transducer (US-A-3 009 995). An extensive correspondence of the duty-cyle of the applied electric control signal to the output pressure out is still ensured, namely by limiting the range of movement of the nozzle flap. The precision requirements to the design of a small pressure chamber are therefore not as strict as in the case of the known transducer, and the increase of the frequency is not limited by the volume of the pressure chamber.
[0007] Embodiments of the invention will now be described in detail, by way of examples only.
Figure 1 is an exemplary embodiment of an electro-pneumatic transducer.
Figure 2 is a qualitative representation of the characteristic curve of a pneumatic nozzle-flap system.
Figure 3 shows three electric control signals.
Figure 4 illustrates a second embodiment of the electro-pneumatic transducer.
Figure 5 illustrates a third embodiment of the electro-pneumatic transducer as provided to actuate a valve.
[0008] An electro-pneumatic transducer illustrated in Figure 1 comprises a nozzle-flap device, essentially known as such. This device comprises flap 10 made of flexible material or supported by bearings at 11. The nozzle-flap device comprises pipe 15 with throttle 16 forming a restricted inlet orifice and, near flap 10, nozzle 14. Nozzle pipe 15 the interior of which is forming a pressure chamber is connected by pipe 17 to variable- pressure tank (pressure P), where the output pressure Pout of the transducer is taken from. On the other side of flap 10, opposite to nozzle 14, there is an electromagnetic coil 12. An electric pulse sequence I(T), illustrated in Figure 3, oscillating at a certain basic frequence fo or alternately at a certain variable frequency f, and of an amplitude to as constant as possible, is conducted to terminals 13 of electromagnetic coil 12. In accordance with the invention, and as shown in Fig. 3, the duty-cycle TfTo of the pulse that raises and lowers the pneumatic or hydraulic pressure proportionally to input signal lin is varied within cycle period To corresponding to basic frequency fo. As illustrated in Figure 3, in its top curve, pulse Ti whose amplitude is 10 is very short compared with the cycle period To; therefore the output pressure Pout of Figure 1 is rather low. In the middle curve the pressure-raising pulse T2 is approx. 0,5xTo and Pout then is in the middle area of its dynamic range. In the bottom curve of Figure 3, the pressure-raising pulse T3 is relatively long, and output pressure Pout is in the top area of its dynamic range. It has been emphasized that pulses can of course be pressure-lowering pulses as well.
[0009] Figure 2 illustrates the ratio of the adjusted pressure P and the input pressure P as a function of the distance S between the nozzle 14 and the flap 10. A S illustrates the linear operation range, on which the transducers in accordance with the invention function. Thus nozzle 14 is never completely closed or opened much enough to enter the unlinear bottom section of the characteristic curve. In the figure, P/Pg=1 naturally represents the position in which flap 10 is completely closed, and P/Ps=0 represents the position in which flap 10 is completely open. In a transducer in accordance with the invention, the flap 10 is made to vibrate, for instance magnetically. Due to electrical and mechanical quantities, such as resistance, inductance, and the masses of the moving springs of the flap and the pneumatic or hydraulic amplifying unit possibly following it, the flap will not, when vibrating, reach the extreme positions (Figure 2). According to Figure 2, reaching the extreme positions is avoided, as this would impair the amplification factor or the system linearity. In practice it has also been found out that the response speed of a transducer in accordance with the invention will, to a certain extent, be increased as the basic frequency fo increases.
[0010] In transducer systems illustrated in Figures 4 and 5, there is an electronic unit 20, which works as a combined signal/pulse converter and as a difference organ (∑). Because of facts described above, pulses leaving the electronic unit 20 tend to integrate in mechanical and pneumatic or hydraulic circuits that follow unit 20. A mathematical representation of this phenomenon is:
where
K=proportionality factor
P=pneumatic or hydraulic pressure
To=basic cycle
T=length of the pulse raising or lowering the pressure
I=electrical pulse sequence leaving the electronic unit (e.g. a constant current of the magnetic circuit).
[0011] An electro-pneumatic system illustrated in Figure 4 comprises a device 21 comprised of the above described elements 15, 16, 17 and 18, to which the pneumatic input pressure Ps is brought. Output pressure Pout of the nozzle-flap system 10,14 operating as described above is adjusted so to be proportional to input signal lin. A feedback loop of the system comprises pneumatic bellows 27 and element 37 which converts the force of the bellows 27 into an electrical feedback signal l1. Feedback control l1 is conducted via wire 26 to unit 20. Control signal I(T) illustrated in Figure 3, is formed according to the difference signal lin-l1.
[0012] Figure 5 illustrates an electro-pneumatic transducer in accordance with the invention, as provided to actuate a valve 23. The system comprises the device 21, whose pressure Pout is conducted to diaphragm motor 22 actuating the control valve 23. The feedback loop of the system comprises an element 24 that converts the position of valve 23 into an electrical signal. This element 24 conducts the feedback signal 11 via wire 26 to unit 20.
[0015] By using a sufficiently high frequency the nozzle-flap system 10;14 can be made operate in the linear area AS shown in Figure 2 in such a way that nozzle 14 is never completely closed or opened. In some cases the lower limit of frequency fo is approx. 15 Hz. However, the most favourable frequency range from the point of view of the invention is over 30 Hz, for instance 30...40 Hz. In some cases the frequency can be of the order of 100 Hz.
[0016] If, for some reason, it is not desired to maintain the flap movement in said linear range by choosing a sufficiently high frequency fo, which, however, is usually the best solution, it is possible, in addition to a sufficiently high frequency, to use mechanical stoppers which limit the vibration amplitude of flap 10.
[0017] Although a basic frequency fo has been under consideration, it should be emphasized that the invention can also be applied in such a way as to make frequency f=1/T variable. Thus it is possible to maintain pulse τ constant and change the output pressure Pout by varying the cycle T=1/f and consequently also the duty-cycle
In the framework of the invention both the pulse length τ and cycle To or T can be varied for control purposes. In some applications amplitude lo can also be varied for control purposes.
1. An electro-pneumatic or electro-hydraulic transducer comprising a controlled pressure
chamber (15), which is pressurized through a restricted inlet orifice (16) and depressurized
by an electrically operated pneumatic or hydraulic nozzle-flap system (10, 11, 14)
which comprises a flap (10) and a nozzle (14), the movement of said flap (10) being
controlled by an electric control signal, wherein the electrical control signal is
a pulse sequence (I(T)) oscillating at a certain frequency (f or fo) in which pulse sequence the duty-cycle (τ/To) of the pulses is varied proportionally to an input signal (lin) and within the cycle period (To) corresponding to said frequency (f or fo) characterized in that said nozzle-flap system (10, 11, 14) has a characteristic
curve with a linear range (△ s), which curve is defined by the dependency of the relative
adjusted pressure (P/Ps) on the distance (S) between the nozzle (14) and the flap (10), and in that the movement
of said flap (10) during operation of the transducer is essentially limited to said
linear range (Δ S) of said characteristic curve (Figure 2) so that said flap (10)
never completely opens or closes the nozzle (14), which feature is provided by mechanical
stoppers and/or by selecting said frequency (f or fo) sufficiently high.
2. A transducer in accordance with claim 1, wherein said certain frequency (fo) is higher than approx. 30 Hz.
3. A transducer in accordance with claim 1 or 2, wherein said certain frequency (fo) of said pulse sequence (I(T)) is within the range 30...40 Hz.
4. A transducer in accordance with claim 1, 2 or 3, wherein an electromagnetic coil
(12) is provided for oscillating the flap (10).
5. A transducer in accordance with claim 1, 2, 3 or 4, wherein an electric feedback
signal (11) is formed from the output signal (Pout) of the transducer, and that said feedback signal (11) is conducted to an electronic unit (20) which is additionally fed with said input
signal (lin) in analog form and which provides said pulse sequence (I(T)) as difference signal (lin-l1).
1. Transducteur électro-pneumatique ou électro-hydraulique comportant une chambre
(15) à pression réglable, qui est mise sous pression à travers un orifice d'entrée
étranglé (16) et décomprimée par un mécanisme tuyère-volet pneumatique ou hydraulique
(10, 11, 14) actionné électriquement qui comprend un volet (10) et une tuyère (14),
le mouvement du volet (10) étant commandé par un signal de commande électrique, lequel
signal est une séquence d'impulsions (l(τ)) oscillant à une certaine fréquence (f
ou fo), séquence dans laquelle le cycle de service (τ/To) des impulsions varie proportionnellement à un signal d'entrée (lin) et à l'intérieur de la période (To) correspondant à ladite fréquence (f ou fo), caractérisé en ce que le mécanisme tuyère-volet (10, 11, 14) présente une courbe
caractéristique comprenant une portion linéaire (Δ S), courbe définie par les variations
de la pression réglée relative (P/Ps) en fonction de la distance (S) entre la tuyère (14) et le volet (10) et en ce que
le mouvement du volet (10) pendant le fonctionnement du transducteur est essentiellement
limité à ladite portion linéaire (Δ S) de la courbe caractéristique (figure 2) de
telle sorte que le volet (10) ne ferme ni n'ouvre jamais totalement la tuyère (14),
ce qui est assuré à l'aide de butées mécaniques et/ou en choisissant la susdite fréquence
(f ou fo) suffisamment élevée.
2. Tranducteur selon la revendication 1, caractérisé en ce que la fréquence (fo) est supérieure à environ 30 Hz.
3. Transducteur selon la revendication 1 ou 2, caractérisé en ce que la fréquence
(fo) de la séquence d'impulsions (I(T)) est comprise entre 30 et 40 Hz.
4. Transducteur selon la revendication 1, 2, ou 3, caractérisé en ce qu'une bobine
électromagnétique (12) est prévue pour faire osciller le volet (10).
5. Transducteur selon la revendication 1,2,3 ou 4 caractérisé en ce qu'un signal de
réaction électrique (11) est formé à partir du signal de sortie (Pout) du transducteur et en ce que ledit signal de réaction (11) est appliqué sur un circuit électronique (20) qui est alimenté additionnelle- ment
par ledit signal d'entrée (lin) sous forme analogique et qui élabore ladite séquence d'impulsions (l(τ)) en tant
qu'un signal de différence (lin-l1),
1. Elektro-pneumatischer oder elektrohydraulischer Wandler, der eine geregelte Druckkammer
(15) aufweist, die durch eine begrenzte Einlaßöffnung (16) unter Druck gesetzt wird
un den Druck abbaut durch ein elektrisch betätigtes pneumatisches oder hydraulisches
Düsenklappensystem (10, 11, 14), daß eine Klappe (10) eine Düse (14) aufweist, wobei
die Bewegung der Klappe (10) von einem elektrischen Steuersignal gesteuert wird, wobei
das Steuersignal eine Pulsfolge (I(T)) ist, die in einer bestimmten Frequenz (f oderfo) schwingt, in welcher Pulsfolge der Abeitszyklus (τ/To) der Impulse proportional zu einem Eingangssignal (lin) und innerhalb der Schwingungsperiode (To) entsprechend der Frequenz (f oder fo) verändert wird, dadurch gekennzeichnet, daß das Düsenklappensystem (10, 11, 14)
eine charakteristische Kurve mit einem linearen Bereich (Δ S) aufweist, wobei die
Kurve bestimmt wird von der Abhängigkeit des relativ eingestellten Druckes (P/Ps) auf der Strecke (S) zwischen der Düse (14) und der Klappe (10), sowie dadurch daß
die Bewegung der Kläppe (10) während des Betriebs des Wandlers im wesentlichen begrenzt
ist auf den linearen Bereich (Δ S) der charakteristischen Kurve (Fig. 2), so daß die
Klappe (10) die Düse (14) nie vollständig öffnet oder schließt, wobei diese Vorteil
durch mechanische Stopper und/oder ausreichend hohe Auswahl der Frequenz (f oder fo) erzielt wird.
2. Wandler nach Anspruch 1, dadurch gekennzeichnet, daß die bestimmte Frequenz (fo) höber ist als ca. 30 Hz.
3. Wandler nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die bestimmte Frequenz
(fo) der Impulsfolge (I(T)) im Bereich von 30 bis 40 Hz liegt.
4. Wandler nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß eine elektromagnetische
Spule (12) zum Oszillieren der Klappe (10) vorgesehen ist.
5. Wandler nach Anspruch 1, 2, 3 oder 4, dadurch gekennzeichnet, daß ein elektrisches
rückgeleitetes Signal (11) von dem Ausgangssignal (Pout) des Wandler gebildet wird und daß das rückgeleitete Signal (11) zu einer elektronischen Einheit (20) geführt wird, die zusätzlich mit dem Eingangssignal
(lin) an analoger Form versorgt wird und die die Impulsfolge (l(τ)) als Differenzsignal
(lin-l1) vorsieht.