FI59653B - ELPNEUMATISK ELLER -HYDRAULISK OMVANDLARE ELLER LAEGEDON - Google Patents

Abstract

Disclosed is an electro-pneumatic or electro-hydraulic converter or actuator with a pneumatic or hydraulic nozzle-flap system or similar, which is controlled by an electric control signal. The electric control signal is a pulse sequence signal oscillating at a constant or variable frequency, the duty-cycle of which is varied proportionally to an input signal. The flap or similar is essentially arranged to oscillate in the linear range of its characteristic curve, so that it never completely opens or closes the nozzle or similar, which feature is provided by mechanical stoppers and/or by selecting said frequency sufficiently high. The invention thus provides a converter or actuator, with improved response speed and linearity and which shows minimal hysteresis.

Description

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Pat ^ och refisterstyrelsen * ^ Amek ^^ ToL29.05.81 (32) (33) (31) Fnrtuttjr utuellcwt— «ufird prtorfm (71) S-Installation, Pirkko-Liisa Seppänen komm.yhtiö, Pyssymiehenkatu 13, U063O Jyväskylä 63, Finland -Finland (FI) (72) Alpo Seppänen, Jyväskylä, Finland-Finland (Fl) (7 * 0 Forssen & Salomaa Oy (5 ^) Electro-pneumatic or hydraulic converter or positioner - Elpneu-matisk eller -hydraulisk omvandlare eller lägedon

The invention relates to an electro-pneumatic or hydraulic transducer or positioner which uses a pneumatic or hydraulic nozzle-flap system or the like, such as a spray pipe, and which is actuated by an electrical control signal.

The previously known electro-pneumatic or hydraulic transducers and positioners are generally based on the so-called for the use of a plunger. The force on said coil is approximately directly proportional to e.g. to the current signal applied to the coil. This known system is characterized by the following drawbacks:

Larger permanent magnet circuit and heavy moving coil system to provide sufficient force.

The relatively low resonant frequency due to the larger moving mass requires its special attenuations, which in turn leads to a reduction in the response speed, and the fact that the feedback loop is short extending only to the mechanical side and not to the electrical input signal level, causing inaccuracy in the system.

With regard to the state of the art incidental to the invention, reference is made to the following patents: 2,595,653: DE-AS 1,295,896, DE-OS 2,239,060 and 2,553,515, CH-PS 597,642 and US-PS 3,456,669.

It is an object of the present invention to provide a transducer or positioner in which the above disadvantages are largely avoided. It is a further object to provide a transducer or positioner in which the same structural elements as in previously known transducers and positioners can be used. Examples of such primary elements are the pneumatic nozzle-flap device.

In order to achieve the above and later objects, the invention is mainly characterized in that a pulse train oscillating at a certain fundamental frequency is used as said electrical control signal, in which a basic arranged to oscillate its characteristic curve in a substantially linear range so that said flap or the like, when operating, never completely closes or fully opens the nozzle, which is preferably achieved by selecting said fundamental frequency sufficiently high.

The transducer or positioner according to the invention achieves the following practically important advantages: the vibrating mass is made very small, which eliminates the vibration sensitivity and also the need for damping, whereby the response speed increases; - feedback (feedback), if needed, can be extended to an electronic level comparable to the input signal, thus improving frequency and linearity; - the desired nonlinearities, e.g. in connection with valve positioners, can be easily implemented with an electronic unit; - the change of direction is very simple; - the manufacturing accuracy of the mechanical components may be lower than in known analog solutions, because the control is in the form of a pulse and the feedback loop, if required, is substantially wider than known; - oscillating elements have minimal hysteresis (aftereffect) caused by rest friction.

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 shows a basic solution of an electro-pneumatic transducer according to the invention.

Figure 2 shows qualitatively the characteristic curve of the pneumatic nozzle-flap system of Figure 1.

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Figure 3 shows three control elements of the primary element.

Figure 4 shows an electro-pneumatic transducer according to the invention.

Figure 5 shows an electro-hydraulic actuator positioner according to the invention.

Figure 6 shows an electro-pneumatic valve positioner according to the invention.

The electro-pneumatic transducer according to Figure 1 comprises a nozzle-flap device, which is essentially known per se. This device comprises a flap 10 which is either flexible or bearing at one end at 11. The nozzle-flap device comprises a tube 15 with a choke 16 and an outlet nozzle 14 near the flap 10. A nozzle tube 15 is connected to the tube 17 by a pressure regulator 18 , from one of which the output pressure PQUt * of the transducer is taken. On the opposite side of the flap 10 to the nozzle 14 an electromagnetic coil 12 is arranged, the terminals 13 of which are supplied according to the invention According to the invention, within the basic period Tq corresponding to the fundamental frequency f, the duty-cycle of the pulse increasing and decreasing the pneumatic or hydraulic pressure is changed in proportion to the input signal 1 ^ according to Fig. 3. According to the upper curve of Fig. 3, a pulse τ ^ of amplitude IQ, which is e.g. a pressure-increasing pulse, is quite short compared to the duration of the basic period Tq, and thus in Fig. 1 the outlet pressure Pout is quite small. According to the middle figure, the pressure-increasing pulse is about 0.5 x T ^ and then PQUt is in the middle phases of its dynamic range. According to the lowest curve in Figure 3, the pressure-increasing pulse is relatively long in duration and thus the outlet pressure Pout is at the top of its dynamic range. In connection with the above, it must be emphasized that the pulses τ can, of course, also be pressure-reducing pulses.

Figure 2 illustrates the relationship of the adjustable pressure p to the supply pressure p

S

nozzle-flap system 10,14 as a function of nozzle gap s size. AS describes a normal linear operating range in which the transducers or positioners according to the invention also work best. Thus, the nozzle 14 does not close completely and does not open so as to enter the nonlinear lower part of the characteristic curve. In Figure 2, p / p * 1 naturally represents a position in which the flap 10 is fully closed and p / p 0 represents a position in which the flap 10 is fully open. In the converter according to the invention

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the primary element, i.e. e.g. the flap-nozzle device 10,14, is subjected to e.g. magnetically induced oscillating motion. Due to the electrical and mechanical quantities of the primary element and possibly the subsequent pneumatic or hydraulic amplifier unit 4 59653, such as resistance, inductance and moving springs and masses, the primary element does not have time to reach its extreme positions in its oscillating motion (Figure 2). Achieving said extreme positions is not even expedient, even on the basis of Figure 2, since this would impair the linearity of the system and the gain. In addition, it has been found in practice that the response speed of the transducer or positioner according to the invention increases to a certain limit as the fundamental frequency f increases.

According to Figures 4,5 and 6, the control systems shown therein use an electronic unit 20, which acts as a combined signal / pulse converter and a differential element (Σ). Due to the above, the pulses emanating from the electronic unit 20 tend to integrate in the mechanical and pneumatic or hydraulic circuits after the unit 20. This can be represented mathematically as k - p-JL fi dt

To J o where k is the proportionality factor, p is the pneumatic or hydraulic pressure,

Tq - basic period, τ «duration of the boost or drop pulse, I = electrical pulse quantity from the electronics unit (eg constant current of the magnetic circuit).

The electro-pneumatic transducer according to Fig. 4 comprises a pneumatic amplifier relay 21 to which a pneumatic supply pressure p is applied. By means of the nozzle-flap system 10,12,14 operating as described above, the outlet pressure PQUt is adjusted to be proportional to the input signal I. The feedback loop of the system includes a pneumatic bellows 27 and a member 37 that converts the force into an electrical signal. A feedback signal 1 ^ is supplied to the unit 20 via line 26. Based on the difference signal I ^ n - 1 ^, the control signal sää (τ) shown in Fig. 3 is generated.

Figure 5 shows an electro-hydraulic actuator positioner according to the invention. The positioner includes a hydraulic actuator cylinder 30 having a piston 31 and an arm 32 whose position or displacement dQut is the output signal. The system includes an element 28 for converting the position into an electrical signal, from which a feedback signal 1 to the unit 20 is passed via a line 26. The control system according to Fig. 5 comprises an oscillating jet 10 'according to the invention. The tubes 33a and 33b are connected to opposite sides of the piston 31 of the cylinder 30 so that according to the position of the nozzle 34 of the oscillating spray tube 10 ', the piston 31 of the operating cylinder 30 moves to a position corresponding to the control signal Ι (τ). This control system includes a hydraulic pump 29 with a suction basin 36.

Fig. 6 shows an electro-pneumatic valve positioner according to the invention, comprising a pneumatic amplifier relay 21, the pressure of which is applied to a diaphragm motor 22 acting as an actuator of the control valve 23. The positioner feedback loop includes a member 24 for converting the position of the valve 23 into an electric signal. ^ for unit 20.

The output of the system is, for example, the flow F controlled by the valve 23.

out

Although the current signal 1 (τ) is shown in Fig. 3 as a control signal, it should be noted that more than current can be used as the electrical signal. The same applies to the setpoint signal or the input signal 1 ^. If a current signal is used as the input signal, its range is eg 4 ... 20 mA.

As stated above, the fundamental frequency f may preferably be relatively high. In practice, in some applications, a suitable frequency range of about 30 ... 40 Hz has been found.

The following are claims within the scope of which the various details of the invention may vary within the scope of the inventive idea.

Claims (5)

59653 An electro-pneumatic or hydraulic transducer or positioner using a pneumatic or hydraulic nozzle-flap system (10,11,14) or the like such as a spray tube (10 ', 34,35) and wherein the flap (10) or the like (10) ') is acted upon by an electrical control signal, characterized in that said electrical control signal is a pulse chain oscillating at a certain fundamental frequency (fQ) (Ι (τ)), in which a fundamental period (Tq) corresponding to said fundamental frequency (f that the hydraulic output pressure (p or the equivalent (dt) changing pulse duration ratio (t / CT ^ -t)) and that said flap (10) or the like (10 ') is arranged to oscillate its characteristic curve (Fig. 2) in a substantially linear range (AS) so that that said flap (10) or the like (10 '), when in operation, never completely closes the nozzle (14) and does not fully open it, which is preferably achieved by selecting said fundamental frequency (fQ) high enough respectively. A transducer or positioner according to claim 1, characterized in that said fundamental frequency (fQ) is greater than about 30 Hz. Transducer or positioner according to claim 1 or 2, characterized in that the primary element is a pneumatic nozzle-flap combination (10, 14) known per se, which flap (10) is caused to oscillate by means of said pulse chain (Ι (τ)), which pulse chain (Ι (τ)) is applied to an electromagnetic coil (12) or the like arranged near the flap (10). Transducer or positioner according to Claim 1, characterized in that the primary element is an oscillating nozzle (10 '), the nozzle (34) of which oscillates the mouthpiece of the tubes (33a, 33b) leading to different sides of the piston (31) of the hydraulic cylinder (30). 35) in the context of. Transducer or positioner according to claim 1, 2, 3 or 4, characterized in that the fundamental frequency (fQ) of said electrical pulse chain (Ι (τ)) is in the range of 30 to 40 Hz. Transducer or positioner according to Claim 1, 2, 3, 4 or 5, characterized in that an electrical feedback device is formed from the output signal (p 1) of the transducer or on the basis of position (d) of the positioner actuator (22; 30, 31, 32). signal (1 ^), and that said feedback signal (1 ^) is applied to an electron age unit (20) adapted to act as a combined differential element (^) and a converter which converts the analog input signal (I ^ n) into said pulse chain (I ^ T )). 7 59653