JP3469378B2 - Electro-pneumatic converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric / pneumatic signal converter (hereinafter referred to as an electropneumatic converter) for controlling a pneumatic valve or the like by an electric input signal. About. [0002] For example, air pressure is used to drive a large control valve in the combustion control of a boiler such as a thermal power plant, and an electropneumatic converter uses electric signals (including pulse signals) 4 to 4. 20mA air signal 0.2-1.0kg / cm
Convert to ² . As the electropneumatic converter, there is one as shown in FIG. In the electropneumatic converter shown in FIG. 4, when the motor 60 is operated by an electric input, the circular cam 61 that rotates in conjunction with the rotation of the motor 60 rotates, thereby causing the nozzle 6 to rotate.
2. The back pressure of the booster relay 6
The signal is converted into an output air pressure signal by 6 and output. The nozzle 62 is attached to one end of the support plate 63, and the FB spring 64 and the FB bellows 65 displaceably support the support plate 63. In such an electro-pneumatic converter, the circular cam 61 is formed by approximating a deviation for each rotation angle to a straight line as shown in FIG. Such a circular cam is formed by punching with a cam mold, or by cutting a large and small disk by overlapping. However, in the case of a circular cam as shown in FIG. 5, it is necessary to accurately set the rotation angle and the offset position from the rotation shaft. In addition, the accuracy of each rotation angle is required for the manufacture of the mold, and the mold is expensive. In the case of cutting, the processing technique is restricted for the same reason. In either case, there is a problem that it is costly to manufacture a circular cam. Accordingly, the present invention has been made in view of such a problem, and an object of the present invention is to provide an electropneumatic converter which realizes a reduction in cam manufacturing cost. In order to achieve the above object, an electropneumatic converter according to the present invention comprises a rotatably supported drum, a drum driving means for driving the drum to rotate, and a pneumatic drive. A cylindrical cam plate formed of a strip-shaped thin plate having a shape corresponding to the characteristics of the output signal, and formed by making the thin plate into a cylindrical shape and fixed to a drum; a nozzle closely adjacent to the peripheral surface of the cylindrical cam plate; and a nozzle at one end. Is attached, the other end is fixed, and an elastic support is swingably supported in the extending direction of the cylindrical cam plate, and an urging member is engaged with the elastic support and supports the elastic support in the extending direction. A member and a bellows attached to the fixed end side of the elastic supporter with respect to the urging member and supporting the elastic supporter in the extending direction are provided. When the drum is rotated by the drum driving means (eg, a motor), the cylindrical cam plate fixed to the drum also rotates. Thus, for example, when the opening amount of the nozzle closed by the peripheral surface of the cylindrical cam plate increases, the back pressure of the nozzle decreases, the output air pressure of the booster relay receiving the back pressure of the nozzle decreases, and the return to the bellows decreases. The pressure decreases and the nozzle moves in the direction of extension of the cylindrical cam plate with the displacement of the elastic support, so that the cylindrical cam plate closes the nozzle again and the equilibrium position is maintained. On the other hand, when the nozzle is closed by the cylindrical cam plate, the opposite effect occurs, and
Again, the equilibrium position is maintained. [0008] In the electropneumatic converter of the present invention, the cylindrical cam plate is formed of a strip-shaped thin plate having a shape corresponding to the characteristics of the pneumatic output signal, and the thin plate is formed into a cylindrical shape. Since it is only one plate, the manufacturing cost of the cam can be reduced as compared with the conventional circular cam. In addition,
The shape of the cylindrical cam plate (that is, the strip-shaped thin plate piece) is determined by, for example, making the shape of one end edge of the thin plate piece into an inclined straight line because the nozzle follows the shape of the cylindrical cam plate and an output air pressure signal is obtained in accordance with the shape. In addition, the linearity of the output air pressure signal proportional to the motor rotation angle due to the electric input is improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments. FIG. 1 is a side view of a main part (motor rotation input mechanism) of the electropneumatic converter according to the embodiment, and FIG. 2 is a top view in which a nozzle portion is partially sectioned. A motor (drum driving means) 10
Is attached, and a drum 1 is attached to a rotating shaft 10a of the motor 10.
The cylindrical cam plate 12 is fixed to the drum 11. In this embodiment, as shown in FIG. 3B, the cylindrical cam plate 12 comprises a strip-shaped thin plate piece 12 having a shape corresponding to the characteristics of the air pressure output signal. On the other hand, as shown in FIG. 3A, the drum 11 has a cam mounting portion 11a having a step about the thickness of a thin plate piece. A thin plate piece 12 is wound around the cam mounting portion 11a and spot-welded at an appropriate place or fixed with screws. The thin plate piece 12 shown here has an inclined straight line 12a at one end in order to obtain the linearity of the output air pressure signal in proportion to the motor rotation angle due to the electric input. That is, a width difference (ΔH) is set between one end and the other end of the thin plate piece 12. The thin plate 12 is wound around the cam mounting portion 11a such that the inclined straight line 12a projects from the cam mounting portion 11a of the drum 11. Therefore, the thin plate piece 12 is
In the state of being wound and fixed around 1, the inclined straight line 12a forms one end edge of the cylindrical cam plate. The nozzle 30 is attached to one end of the holder 21, and is positioned so as to be close to the peripheral surface of the cylindrical cam plate 12 and face the edge 12 a of the cylindrical cam plate 12. On the other hand, a fulcrum plate 22 is attached to the other end of the holder 21, and the fulcrum plate 22 is fixed to the fixing bracket 20 with screws 23. Here, an elastic support is constituted by the holder 21 and the fulcrum plate 22. Accordingly, the holder 21 can swing in the direction of the arrow (extending direction of the cylindrical cam plate 12) about the fixed point (fulcrum) of the fulcrum plate 22, and the nozzle 30 can also be displaced in the same direction. FB for adjusting the displacement range of the nozzle 30
A spring 31 is provided, and one end of the FB spring 31 is
And the other end thereof is fixed to the fixing bracket 20 by a nut 32, respectively. Further, an FB bellows 33 that receives the feedback pressure of the output pressure output by the back pressure of the nozzle 30 and supports the holder 21 is provided in the holder 21 in parallel with the FB spring 31 on the fixed end side. The nozzle 30
As a circuit for converting the back pressure change into an output air pressure signal and outputting the output air pressure signal, and for providing the feedback pressure of the output air pressure to the FB bellows 33, for example, a circuit A surrounded by a chain line in FIG. 4 is used. In the electropneumatic converter configured as described above, when the motor 10 is operated by the electric input, the drum 11 rotates, and the cylindrical cam plate 12 fixed to the drum 11 also rotates.
Assuming that the cylindrical cam plate 12 rotates upward in the drawing from the state shown in FIG. 1, the edge 12a of the cylindrical cam plate 12 closing the nozzle 30 opens the nozzle 30, and the nozzle 30
Increases the amount of opening. As a result, the back pressure of the nozzle 30 decreases, the output air pressure of the booster relay decreases in response to the decrease of the back pressure, and the return pressure to the FB bellows 33 decreases. The nozzle 30 is displaced to the left in FIG. 1 around the center, and the nozzle 30 moves in the same direction accordingly. Then, the nozzle 30 becomes the cylindrical cam plate 1
2 again closes and the equilibrium position is maintained. On the other hand, when the cylindrical cam plate 12 rotates downward in the drawing, the nozzle 3
The amount of opening of the nozzle 30 decreases, and the back pressure of the nozzle 30 increases. Then, the output air pressure of the booster relay increases and the return pressure to the FB bellows 33 increases, so that the nozzle 30 moves rightward in FIG. 1, the nozzle 30 is opened from the edge 12a, and the equilibrium position is maintained. . As described above, in this embodiment, since the edge 12a of the cylindrical cam plate 12 has a linear shape corresponding to the characteristics of the pneumatic output signal, the rotation of the motor 10 by the electric input is linearly changed to the pneumatic output signal. Will be converted. In the above embodiment, the position of the fulcrum of the swing of the nozzle 30 is changed by changing the fixing position of the holder 21 to which the fulcrum plate 22 is attached with respect to the fixing bracket 20, so that the output air pressure per input rotation angle is changed. Characteristics can be changed. Further, in the above embodiment, the cylindrical cam plate 12
Although the shape of the edge 12a is an inclined straight line, by adopting another shape such as a shape exhibiting a sine wave characteristic,
It is also easy to convert the air pressure output characteristics. Further, in the above embodiment, the motor 10 is taken as the drum driving means, but the drum driving means is a pulse motor or a DC geared motor, and these are intermittently driven or driven by changing the number of pulses, so that the electric input is achieved. It is also possible to make the air pressure output characteristics per contact variable. The electropneumatic converter of the present invention has the following effects (1) to (3) because it is configured as described above. (1) The cylindrical cam plate is formed of a strip-shaped thin plate having a shape corresponding to the characteristics of the air pressure output signal. The thin plate is formed into a cylindrical shape, and the original state is merely a single plate. Compared with the conventional circular cam which requires the above-described shape accuracy, an expensive cam mold is not required for the manufacture of the cam, and a high processing cost is not required, so that the manufacturing cost of the cam can be reduced. (2) Since the nozzle follows the shape of the cylindrical cam plate and an output air pressure signal is obtained thereby, the linearity of the electric input / pneumatic output can be improved by, for example, making the shape of the edge of the cylindrical cam plate an inclined straight line. improves. (3) The cam deflection can be easily changed, and the control range can be limited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a main part (motor rotation input mechanism) of an electropneumatic converter according to one embodiment. FIG. 2 is a top view of a main part of the electropneumatic converter, in which a nozzle is partially sectioned. 3A is an enlarged view of a cylindrical cam plate in the electro-pneumatic converter, and FIG. 3B is a diagram showing a strip-shaped thin plate constituting the cylindrical cam plate. FIG. 4 is a main part configuration diagram of an electropneumatic converter according to a conventional example. FIG. 5 is an explanatory diagram of a circular cam in the conventional electropneumatic converter. DESCRIPTION OF SYMBOLS 10 Motor (drum driving means) 11 Drum 12 Cylindrical cam plate 12a Edges 21, 22 of cylindrical cam plate Elastic support 30 Nozzle 31 Spring (biasing member) 33 Bellows

Claims (1)

(57) Claims 1. A drum rotatably supported, a drum driving means for driving the drum to rotate, and a strip-shaped thin plate having a shape corresponding to the characteristics of an air pressure output signal. A cylindrical cam plate formed by fixing the thin plate piece to a drum and fixed to a drum; a nozzle closely approaching the peripheral surface of the cylindrical cam plate; and a nozzle attached to one end and the other end fixed to extend the cylindrical cam plate. An elastic support that is swingably supported in the direction, a biasing member that is locked to the elastic support and supports the elastic support in the extending direction, and the elastic support that is fixed by the biasing member. An electro-pneumatic converter, comprising: a bellows attached to an end side for supporting an elastic support in the extending direction.