Electrostatic-pneumatic converter

Abstract

Electrostatic-pneumatic converter with an electrostatic control device comprising a ground electrode (2) and a control electrode (4) designed as a movable rocker, electrically insulated from the ground electrode (2), which is actuated by a control voltage (U_St) applied between the ground electrode (2) and the control electrode (4), and with a valve device (40) comprising an inlet (42) for supplying fluid under a pre-pressure (Pv), an outlet nozzle (44) arranged in flow communication with the inlet (42) and an outlet (17) arranged in flow communication with the inlet (42), characterized in that the control electrode (4) forms at least a partial gap (3) with the ground electrode (2), the gap size of which is variable depending on the control voltage (U_St) applied between the control electrode (4) and the ground electrode (2) by a current source (5),that the opening cross-section of the outlet nozzle (44) is influenced by the gap size, wherein the output pressure (Pa) is controllable as a pneumatic output signal at the output (46) depending on the control voltage (U_St), wherein the value of the pneumatic output signal is adjustable from a minimum to a maximum value, and that the control electrode (4) comprises a compensating mass (6) and an adjoining impact plate (8) and is mounted between the compensating mass (6) and the impact plate (8) on a rotary axis (10) at the mass electrode (2).

Description

[0001] The invention relates to an electrostatic-pneumatic converter for converting an electrical control voltage into a pneumatic output signal.

[0002] DE 44 20 741 A1 discloses an electro-pneumatic transducer with a closing element, air inlets and outlets, at least one of which can be closed by the closing element. The transducer, controlled by an electrical signal, generates a pneumatic signal by moving the closing element and thus a change in air pressure in a signal air line. The mechanically bistable closing element requires an electrical energy supply to perform switching operations, but not to maintain a position. The electro-pneumatic transducer enables the conversion of an supplied electrical signal into a corresponding pneumatic signal by using an electrically operated closing element to control an air supply and thus provide corresponding air pressure fluctuations in a pneumatic signal line.

[0003] DE 100 47 705 A1 discloses a microvalve for controlling fluid flows, comprising at least one valve element for actuation by means based on an electrostatic operating principle, wherein the means include at least one so-called Comb-Drive actuator. The valve element of the microvalve is pivotably mounted at a bearing point in the manner of a rocker and is biased by spring means towards an initial position. Depending on the position of the rocker, one of two outlets is closed and the other of the two outlets is opened. Such a switching valve is therefore not capable of varying the pressure at the outlets.

[0004] EP 1 574 724 A1 relates to a pneumatic microvalve with a valve chamber arrangement and several valve channels through which compressed air can flow into and out of the valve chamber arrangement, and at least one of which can be closed by the valve element arrangement. Within the valve chamber arrangement, at least one surface has a coating with a lower surface energy density than the oil contained in the compressed air. The pneumatic microvalve is lubricated by small oil droplets. A piezoelectrically actuated tongue inside a chamber opens or closes air channels in the side of the chamber. The upper and lower surfaces of the piezoelectrically actuated tongue and the sides of the chamber are covered with an oil-repellent coating.

[0005] The invention is therefore based on the objective of providing an electrostatic-pneumatic converter by which an electrical control voltage applied to the converter can be converted into a pneumatic output signal, the value of which can be adjusted from a minimum to a maximum by means of the control voltage.

[0006] The electrostatic-pneumatic converter according to the invention comprises an electrostatic control device, which includes a ground electrode and a control electrode designed as a movable rocker, electrically insulated from the ground electrode, which is actuated by a control voltage applied between the ground electrode and the control electrode, and a valve device, which includes an inlet for supplying fluid under a pre-pressure, an outlet nozzle arranged in flow communication with the inlet, and an outlet arranged in flow communication with the inlet, wherein the converter is characterized in that the control electrode forms at least a partial gap with the ground electrode, the size of which of the gap can be changed depending on the control voltage applied between the control electrode and the ground electrode by a current source, and that the opening cross-section of the outlet nozzle is influenced by the size of the gap.wherein the output pressure is controllable as a pneumatic output signal at the output depending on the control voltage. According to the invention, the value of the pneumatic output signal is adjustable from a minimum to a maximum value, wherein the control electrode comprises a compensating mass and an adjoining impact plate and is mounted on a rotary axis on the mass electrode between the compensating mass and the impact plate.

[0007] Such a converter is suitable for applications where precise conversion of the control voltage into a pneumatic output signal is crucial. An example of such an application is an electrostatic-pneumatic converter for controlling a positioner in pneumatically actuated control valves. Since the control electrode comprises a counterweight and an adjacent baffle plate, the converter's continuous response is advantageously improved because the control electrode can react to the control voltage with virtually no inertia. Because mass compensation occurs around the axis of rotation, the converter system is position-independent.

[0008] In the converter according to the invention, the control electrode is plate-shaped and extends over the outlet nozzle, wherein the opening cross-section is advantageously directly dependent on the gap size.

[0009] According to an advantageous embodiment of the electrostatic-pneumatic converter according to the invention, the axis of rotation of the control electrode is formed by a sharp edge of the mass electrode, whereby precise bearing of the rocker formed from the balancing mass and the impact plate is achieved with minimal mechanical means.

[0010] In a further advantageous embodiment of the electrostatic-pneumatic converter according to the invention, a spring device is provided that presses the control electrode against the edge, further stabilization of the rocker formed by the counterweight and the impact plate is achieved with minimal effort, particularly if the spring device comprises a spring guided on a bolt. Furthermore, parasitic torques on the rocker can be eliminated in this way.

[0011] In this design, the current supply to the control electrode can be provided via the bolt and the spring, so that no further components are required for the current supply.

[0012] In a further advantageous embodiment of the electrostatic-pneumatic converter according to the invention, if the impact plate has a honeycomb structure, the weight of the impact plate is reduced, thereby improving the responsiveness and continuous reaction of the electrostatic-pneumatic converter according to the invention. Furthermore, the reduction in mass achieved through the honeycomb structure on the upper surface results in good vibration resistance and insensitivity to acceleration.

[0013] If, according to a further advantageous embodiment of the electrostatic-pneumatic converter according to the invention, the impact plate consists of electrically conductive ceramic and a dielectric and insulating layer made of insulating ceramic is provided on one side of the impact plate facing the ground electrode, it is advantageously achieved that the mutually facing surfaces of the impact plate and the ground electrode can be made extremely flat and smooth, whereby errors in the voltage-pressure conversion of the electrostatic-pneumatic converter according to the invention can be avoided.

[0014] According to a further advantageous embodiment of the electrostatic-pneumatic converter according to the invention, the spring can be rotated by the bolt so that the spring force application to the control electrode can be adjusted.

[0015] According to an advantageous embodiment of the electrostatic-pneumatic converter according to the invention, a finely adjustable stop is provided which limits the movement of the impact plate away from the ground electrode or the rocker opening, which contributes to the safety of the electrostatic-pneumatic converter according to the invention because the rocker cannot leave the working area.

[0016] In the electrostatic-pneumatic converter according to the invention, if the baffle plate interacts directly with the outlet nozzle, the gap between the outlet nozzle and the control electrode is wedge-shaped, since the lower surface of the baffle plate is at an angle to the opening of the outlet nozzle. On the other hand, the sealing tightness of this design of the valve assembly is quite sufficient for a number of applications.

[0017] The sealing tightness of the electrostatic-pneumatic converter is improved by providing a ball between the outlet nozzle and the control electrode, which ensures a tight seal regardless of the angle between the control electrode and the outlet nozzle.

[0018] In a further embodiment of the electrostatic-pneumatic converter according to the invention, the outlet nozzle is height-adjustable and thus the gap is adjustable, whereby the electrostatic-pneumatic converter according to the invention can be easily adjusted to different applications.

[0019] According to a further advantageous embodiment of the electrostatic-pneumatic converter according to the invention, a pre-throttle is arranged at the inlet of the valve device, being under the pre-pressure, whereby it is advantageously ensured that the pre-pressure is so low that a reliable adjustment function is given.

[0020] If, advantageously, the pre-choke comprises an interchangeable threaded bushing which is screwed into a thread in the ground electrode, it is achieved that the electrostatic-pneumatic converter according to the invention can be easily converted to different applications.

[0021] Further advantages, features and application possibilities of the present invention will become apparent from the following description in conjunction with the exemplary embodiments shown in the drawings.

[0022] The description, claims, and drawing use the terms and associated reference numerals listed below. In the drawing, this means: Fig. 1 a sectional view along line AA of Fig. 2 by an electrostatic-pneumatic converter according to an embodiment of the invention; Fig. 2 a top view of the electrostatic-pneumatic converter according to Fig. 1; Fig. 3. A perspective view of the ground electrode with the control electrode; . Fig. 4 another sectional view along line B - B of Fig. 2 through the electrostatic-pneumatic converter to Fig. 1; Fig. 5 a detailed representation of detail B of Fig. 3; Fig. 6 a detailed representation of the valve assembly according to a first embodiment of the valve assembly; and Fig. 7 A detailed representation of the valve assembly according to a second embodiment of the valve assembly.

[0023] Fig. Figure 1 shows a cross-sectional view along line AA of Fig. 2, which shows a top view of the electrostatic-pneumatic converter according to Fig. Figure 1 shows the electrostatic-pneumatic converter according to Fig. 1 thus comprises an electrostatic control device comprising a ground electrode 2 and a control electrode 4 designed as a movable rocker, electrically insulated from the ground electrode 2, which is actuated by a control voltage U_St applied between the ground electrode 2 and the control electrode 4 by a current source 5. The control electrode 4 forms at least a partial gap 3 with the ground electrode 2, the size of which is variable depending on the electrical control voltage U_St applied between the control electrode 4 and the ground electrode 2, wherein the output pressure Pa is controllable as a pneumatic output signal at output 46 depending on the control voltage U_St.

[0024] The ground electrode 2 and the control electrode 4 are made of electrically conductive material, for example, electrically conductive ceramic or aluminum. The ground electrode 2 and the control electrode 4 are electrically connected to a voltage source 5 and are electrically insulated from each other by a dielectric and insulating layer 7 on the side of the control electrode 4 facing the ground electrode 2.

[0025] The control electrode 4 comprises a counterweight 6 and an adjoining baffle plate 8 and is mounted between the counterweight 6 and the baffle plate 8 on a pivot axis 10 at the ground electrode 2, the weight of the counterweight 6 up to the pivot axis 10 being equal to the weight of the baffle plate 8 up to the pivot axis 10. The baffle plate 8 is made of electrically conductive ceramic and has a honeycomb structure with recesses 12. The movement of the baffle plate 8 away from the ground electrode 2 is limited by an adjustable stop 14, which is formed by the underside 16 of an adjusting screw 18. The pivot axis 10 of the control electrode 4 is a sharp edge 11 of the ground electrode 2.

[0026] A spring assembly 20 presses the control electrode 4 against the edge 10, with the impact plate 8 being securely and pivotably mounted on the ground electrode 2. The spring assembly 20 consists of a spring 22 guided on a bolt 24. This arrangement allows current to be supplied to the control electrode 4 via the bolt 24 and the spring 22.

[0027] The spring 22 is connected on one side to the ground electrode 2 and on the other side to the bolt 24, so that the spring 22 can be rotated by the bolt 24 in order to adjust the spring force application to the control electrode 4.

[0028] The impact plate 8 is coated on its underside opposite the ground electrode with a thin ceramic insulating layer 28, wherein the ground electrode 2 and the control electrode 4 form the capacitor for the electrostatic drive.

[0029] The electrostatic-pneumatic converter according to Fig. 1 is completed by a cover 30 made of electrically insulating material, which carries the spring device 20, as shown in Fig. 1 is shown.

[0030] Fig. Figure 3 shows a perspective view of the ground electrode 2 with the control electrode 4. Two guide pins 32, 34 are provided for lateral guidance of the impact plate 8 on the ground electrode 2, as shown in the Fig. 4 and Fig. 5 is shown, are stored in insulating sleeves 36, 38, penetrate the impact plate 8 and are anchored in the ground electrode 2.

[0031] The electrostatic-pneumatic converter further comprises a valve assembly 40, which includes an inlet 42 for supplying fluid at a pre-pressure Pv, an outlet nozzle 44 arranged in flow communication with the inlet 42, and an outlet 46 arranged in flow communication with the inlet 42. The opening cross-section of the outlet nozzle 4 is influenced by the size of the gap 3, with the opening of the outlet nozzle being controlled by movement of the rocker arm.

[0032] A pressure-controlled inlet 48 is arranged at inlet 42, comprising a replaceable threaded bushing 50 that is screwed into a thread 52 in the ground electrode 2. The supply pressure Pv is therefore supplied via the inlet 48.

[0033] The control electrode 4 forms the gap 3 with the outlet nozzle 44, which can be continuously changed depending on the electrical control voltage U-St applied between the control electrode 4 and the ground electrode 2 by a current source 5, whereby the output pressure Pa can be controlled as a pneumatic output signal at the output 46 depending on the control voltage U-St.

[0034] The gap between the outlet nozzle 44 and the control electrode 4 is according to Fig. 7 is wedge-shaped, so that the outlet nozzle 44 cannot be completely closed.

[0035] In the exemplary embodiment according to Fig. 6 a ball 54 is provided between the outlet nozzle 44 and the control electrode 4, which ensures the tight closing of the outlet nozzle 44 regardless of an angle between the control electrode 4 and the outlet nozzle 44.

[0036] The outlet nozzle 44 is used in both versions according to Fig. 6 as well as in the execution according to Fig. 7 height-adjustable, so that the gap can be adjusted.

[0037] The function of the electrostatic-pneumatic converter according to the invention is described below. The magnitude of the control voltage U_St, applied between the ground electrode 2 and the control electrode 4, controls the output signal pressure Pa. When the control voltage U_St, applied between the ground electrode 2 and the control electrode 4, generates an electrostatic force that attracts the control electrode 4 towards the ground electrode 2, the gap 3 between the control electrode 4 and the ground electrode 2 is reduced, and the output pressure Pa at the outlet 46 is increased. When the outlet nozzle 44 is closed, the output pressure Pa is equal to the inlet pressure or the pre-pressure Pv, so that the output pressure Pa can vary between the inlet pressure Pv and almost zero.

[0038] The force equilibrium is established between the electrostatic force of the capacitor acting on the rocker arm and the pneumatic force of the valve assembly 40 with pre-throttle 48 and outlet nozzle 44 acting on the rocker arm. The following parameters are adjustable to set the force equilibrium: the diameter of the pre-throttle 48 and the outlet nozzle 44, the area of ​​the capacitor formed by the ground electrode 2 and the control electrode 4, the thickness of the insulating layer 28, and the lever arm between the axis of rotation 10 and the outlet nozzle 44. Reference symbol list 2 Ground electrode 3 slits 4 Control electrode 5 Power source 6 leveling compound 8 Impact plate 10 Rotation axis 11 edge 12 Exclusion 14 attacks 16 Underside 18 Adjusting screw 20 Spring assembly 22 spring 24 bolts 28 Insulating layer 30 lids 32 guide pin 34 guide pin 36 Insulating sleeve 38 Insulating sleeve 40 Valve assembly 42 Entrance 44 Outlet nozzle 46 Exit 48 Forethrocer 50 threaded bushing 52 threads 54 balls

Claims

[1] Electrostatic-pneumatic converter with an electrostatic control device comprising a ground electrode (2) and a control electrode (4) designed as a movable rocker, electrically insulated from the ground electrode (2), which is to be actuated by a control voltage (U_St) applied between the ground electrode (2) and the control electrode (4), and with a valve device (40) comprising an inlet (42) for supplying fluid under a pre-pressure (Pv), an outlet nozzle (44) arranged in flow communication with the inlet (42) and an outlet (17) arranged in flow communication with the inlet (42), characterized by, that the control electrode (4) forms at least a partial gap (3) with the ground electrode (2), the size of which of the gap is variable depending on the control voltage (U_St) applied between the control electrode (4) and the ground electrode (2) by a current source (5), that the opening cross-section of the outlet nozzle (44) is influenced by the size of the gap, wherein the output pressure (Pa) is controllable as a pneumatic output signal at the output (46) depending on the control voltage (U_St), wherein the value of the pneumatic output signal is adjustable from a minimum to a maximum value, and that the control electrode (4) comprises a compensating mass (6) and an adjoining impact plate (8) and is mounted on a rotary axis (10) on the ground electrode (2) between the compensating mass (6) and the impact plate (8). [2] Converter according to claim 1, characterized by, that the control electrode (4) is plate-shaped and extends over the outlet nozzle (44). [3] Converter according to claim 1, characterized by , that the axis of rotation (10) of the control electrode (4) includes an edge (11) of the ground electrode (2), and that a spring device (20) is provided which presses the control electrode (4) against the edge (11). [4] Converter according to claim 3, characterized by , that the spring assembly (20) comprises a spring (22) which is guided on a bolt (24). [5] Converter according to claim 4, characterized by , that the current supply to the control electrode (4) is via the bolt (24) and the spring (22). [6] Converter according to claim 3, 4 or 5, characterized by , that the spring force of the spring (22) is adjustable by the bolt (24) in order to adjust the spring force application to the control electrode (4). [7] Converter according to any one of claims 1 to 6, characterized by, that the impact plate (8) has a honeycomb structure. [8] Converter according to any one of claims 1 to 7, characterized by , that the impact plate (8) consists of electrically conductive ceramic and a dielectric and insulating layer (28) of insulating ceramic provided on one side of the impact plate (8) facing the mass electrode (2). [9] Converter according to any one of claims 1 to 8, characterized by , that an adjustable stop (14) is provided which limits the movement of the impact plate (8). [10] Converter according to any one of claims 1 to 9, characterized by , that the gap (3) between the outlet nozzle (44) and the control electrode (4) is wedge-shaped. [11] Converter according to any one of claims 1 to 10 characterized by , that a ball (54) is provided between the outlet nozzle (44) and the control electrode (4) which ensures a tight seal regardless of an angle between the control electrode (4) and the outlet nozzle (44). [12] Converter according to any one of claims 1 to 11, characterized by , that the outlet nozzle (44) is height-adjustable and thus the gap (3) is adjustable. [13] Converter according to any one of claims 1 to 12, characterized by , that a pre-choke (48) is arranged at the inlet (42) under the pre-form. [14] Converter according to claim 13, characterized by , that the pre-throttle (44) includes an interchangeable threaded bushing (50) which is screwed into a thread (52) in the ground electrode (2).

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