JP3891261B2 - Air supply system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air supply system that can efficiently operate a compressor that generates compressed air used in various production facilities to save energy, and in particular , reduces air consumption in air-using equipment. The present invention relates to an air consumption measurement method and a measurement apparatus that can measure in real time, and an air supply system control method.
[0002]
[Related background]
In various production facilities, compressed air is used for air blow or as a drive source for an air cylinder. Compressed air is generated using a compressor, and is generally stored in an air tank, and then supplied to various loads (equipment for air use) such as an air cylinder through a predetermined piping system.
[0003]
In general, the pressure of the compressed air accumulated in the air tank is generally monitored, and the operation of the compressor is controlled in accordance with the pressure so that the compressed air of, for example, 0.7 MPa or more is added to the air tank, and thus the piping system. To ensure.
[0004]
[Problems to be solved by the invention]
By the way, when securing the compressed air to be supplied to the load as described above, the compressor is generally started when the pressure P of the compressed air in the piping system (air tank) decreases as shown in FIG. is doing. Then, the compressed air generated by the compressor is supplied to the air tank and further to the load via the piping system while increasing the pressure in the piping system, and is compressed and discharged from the compressor as shown in FIG. The air flow rate temporarily increases. That is, a large amount of compressed air is discharged from the compressor as much as the pressure of the compressed air in the piping system is increased.
[0005]
For this reason, the compressor will generate more compressed air than required by the load, and it cannot be denied that the energy consumption (power consumption) in the compressor will be great. Further, since the flow rate of the compressed air supplied to the load changes depending on the pressure, there is a problem in controlling the operation of the compressor simply by detecting the flow rate (volume flow rate or mass flow rate) of the compressed air.
[0006]
The present invention has been made in consideration of such circumstances, and the object thereof is to efficiently operate the compressor while ensuring the compressed air required by the air-using device and to save energy. It is to provide an air supply system .
[0007]
[Means for Solving the Problems]
In order to achieve the above-described object, the air supply system according to the present invention has a pressure P of compressed air and its mass (proportional to the number of moles n) in the piping system, the air gas constant R, the temperature T, and the piping. Focusing on the fact that when the volume of the system is V, [RT / V] is a proportional relationship with coefficient C,
A flow meter for determining the mass flow rate of compressed air supplied to the air used subject via pipeline from <a> compressor,
< b > a pressure gauge for obtaining a pressure of compressed air supplied to the air use object via the piping system;
< c > A differentiator for differentiating the pressure obtained by the pressure gauge to obtain the change,
< d > an air consumption detecting means for detecting an air consumption in the air use object based on a mass flow obtained by the flow meter and a pressure change obtained by the differentiator;
< e > Correction means for correcting the air consumption according to the temperature of the compressed air and / or the measurement time difference between the flow meter and the pressure gauge;
< f > control means for controlling the operation of the compressor according to the corrected air consumption;
It is characterized by comprising.
[0008]
Specifically, in the air consumption detection means, when the gas constant of air is R, the temperature is T, and the volume of the piping system is V, the mass flow rate Qin of compressed air obtained by the flow meter, From the change ΔP of the pressure P of the compressed air obtained by the pressure change detection means,
Qout = Qin−ΔP / (RT / V)
Is calculated as an air consumption amount. The air consumption amount (air amount) Qout is corrected according to the temperature of the compressed air and / or the measurement time difference between the flow meter and the pressure gauge, and the compressor is used with the corrected air consumption amount as a control amount. It is characterized by feedback control of the operation.
[0009]
Incidentally, the mass flow rate of the compressed air is detected by using a thermal flow meter including a heater element and a pair of temperature sensors provided in the flow direction of the compressed air across the heater element.
Note that the feedback control of the compressor includes a unit control for selectively driving these compressors when a plurality of compressors are used in parallel.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a compressed air supply device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an overall schematic configuration of a compressed air supply apparatus according to this embodiment, wherein 1a, 1b,... 1n are a plurality of compressors provided in parallel, and 2 are the compressors 1a, 1b,. It is an air tank as a buffer which stores the compressed air each supplied from 1n. The compressed air accumulated in the air tank 2 is supplied to a plurality of loads 4 a, 4 b, and 4 m each composed of an air blow mechanism, an air cylinder device, and the like via a predetermined piping system 3.
[0011]
The air tank 2 is provided with a pressure gauge 5 for detecting the pressure P of the compressed air accumulated in the air tank 3 and thus supplied to the piping system 3. The piping system 3 incorporates a flow meter 6 for detecting a mass flow rate Qin of compressed air supplied to the loads 4a, 4b, to 4m through the piping system 3.
The flow meter 6 for detecting the mass flow rate Qin is, for example, a thermal flow meter introduced in detail in Japanese Patent No. 3096820. That is, as shown in FIG. 2, the thermal flow meter is a heater composed of a heating resistor provided on a predetermined base B made of a silicon chip having a size of 2 mm × 2 mm × 0.5 mm, for example. The element structure is provided with a pair of temperature sensors Ru and Rd made of a resistance temperature detector in the fluid flow direction F with the element Rh interposed therebetween. Then, by utilizing the fact that the degree of diffusion (temperature distribution) of the heat generated from the heater element Rh changes due to the flow of the fluid (compressed air), the resistance value change due to the heat of the pair of temperature sensors Ru and Rd The mass flow rate Qin of the fluid is detected. In the figure, Rr is a temperature sensor made of a resistance temperature detector provided at a position away from the heater element Rh, and is used for measuring the ambient temperature T.
[0012]
In the compressed air supply apparatus configured as described above, the present invention is characterized by the pressure P of the compressed air detected by the pressure gauge 5 and the compressed air detected by the flow meter 6. In accordance with the mass flow rate Qin, the amount of compressed air used Qout at loads 4a, 4b, .about.4m is obtained as described below, and the operations of the compressors 1a, 1b, .about.1n are feedback controlled in accordance with the amount of usage Qout. The control system 10 is provided.
[0013]
That is, the control system 10 differentiates the pressure P of the compressed air in the piping system 3 detected by the pressure gauge 5 and obtains the time differential value [dP / dt] as a change ΔP of the pressure P. A change detecting means (differential means) 11 is provided. Further, the control system 10 includes coefficient means 12 for multiplying the pressure change ΔP by a predetermined coefficient (1 / C). The C is given as [RT / V] where R is the gas constant of air, T is the temperature, and V is the volume of the piping system.
[0014]
The control system 10 further includes a pressure change ΔP × (1 / C) multiplied by a predetermined coefficient (1 / C) by the coefficient means 12 and a mass flow rate Qin of the compressed air detected by the flowmeter 6. Compressed air consumption amount Qout in accordance with Qout = Qin−ΔP × (1 / C) = Qin−ΔP / (RT / V)
The difference means 13 to be obtained is provided. The amount Qout of compressed air determined in this way is given as a feedback control amount to the control unit 14 that controls the operation of the compressors 1a, 1b, .about.1n.
[0015]
In addition, what is necessary is just to employ | adopt conventionally methods, such as PID control, about the form of the operation control of the compressors 1a, 1b, and -1n by the control part 14. FIG. In addition to variably controlling the operation capability of each of the compressors 1a, 1b, to 1n, the number of units that selectively drive a plurality of compressors 1a, 1b, to 1n provided in parallel may be controlled. Needless to say.
[0016]
Here, the principle of the feedback control described above will be explained. The state of compressed air in the piping system 3 is expressed by PV = nRT (1) from the gas state equation where n is the number of moles of compressed air.
By transforming this state equation, the pressure P is changed to P = n × (RT / V) (2)
Can be expressed as When the temperature T of the compressed air is considered to be constant, the air constant R and the volume (volume in the piping system 3) V are constant, so that [RT / V] itself is constant. Therefore, the above equation (2) can be regarded as P = n × C (2a).
It can also be expressed as
[0017]
Here, by multiplying the number of moles n by the gas volume [22.4L] (constant) in the standard state, the volume A in the standard state of air in the pipe 3 is A = 22.4 × n.
Can be obtained as Therefore, if the above equation (2a) is expressed using this volume A,
P = A × (C / 22.4) (2b)
If the coefficient C is replaced as [C ′ = C / 22.4],
P = A × C ′ (2c)
Can be organized as.
[0018]
Here, when the above equation (2c) is differentiated by time t,
dP / dt = dA / dt × C ′ (3)
If the volume change [dA / dt] in the standard state of the air in the pipe is replaced with [Q], the above equation (3) is obtained.
dP / dt = Q × C ′ (3a)
Can be expressed as
[0019]
On the other hand, the volume change amount Q in the standard state of the air in the pipe is proportional to the change amount Qn of the air mass in the pipe, and the density ρ (constant) in the standard state of the air is Qn = Q × ρ (4)
Can be expressed as Therefore, substituting the above equation (4) into the previous equation (3)
dP / dt = Qn × (C ′ / ρ)
= Qn x C "(5)
Can be shown as That is, it can be found that the change amount Qn of the air mass in the pipe is proportional to the change ΔP (differential value; dP / dt) of the pressure P of the compressed air with respect to the coefficient C (C ″) described above.
[0020]
On the other hand, the amount of change Qn of the air mass in the pipe is determined by the discharge amount (mass flow rate) Qin of the compressed air that the compressors 1a, 1b,. The difference from the compressed air consumption (mass flow rate) Qout used by the loads 4a, 4b, to 4m, that is,
Qn = Qin−Qout (6)
Can be expressed as
[0021]
Then, if attention is paid to the above formulas (5) and (6), the amount of compressed air used Qout at the loads 4a, 4b, and 4m is
dP / dt (= ΔP) = Qn × C
= (Qin-Qout) x C
From the relationship
Qout = Qin− (dP / dt) / C
= Qin−ΔP / C (7)
Can be obtained as
[0022]
When there is no change in the pressure P of the compressed air, that is, when [dP / dt = 0], the discharge amount Qin of the compressed air discharged from the compressors 1a, 1b, ˜1n and the loads 4a, 4b, ˜4m Means that the amount of compressed air used Qout is equal to Qout [Qout = Qin]. Further, when the usage amount Qout of the compressed air used by the loads 4a, 4b, .about.4m is 0 [Qout = 0], the change of the pressure P of the compressed air is discharged by the compressors 1a, 1b, .about.1n. It corresponds to the discharge amount Qin of compressed air [dP / dt = Qin × C].
[0023]
Accordingly, the discharge amount (mass flow rate) Qin of the compressed air discharged from the compressors 1a, 1b,..., 1n to the piping system 3 is obtained using the flow meter 6, and the pressure P of the compressed air supplied to the piping system 3 is obtained. If the pressure change is detected using the pressure gauge 5 and the time change (time differential value; dP / dt) of the pressure is obtained as the change ΔP, the loads 4a, 4b, and 4m are used in accordance with the above equation (6). The used amount (mass flow rate) Qout of compressed air can be obtained. Then, if the operation of the compressors 1a, 1b, ˜1n is controlled in order to compensate for the use amount (mass flow rate) Qout of the compressed air used by the loads 4a, 4b, ˜4m, that is, the mass flow rate Qout is used as a control amount. If the operations of the compressors 1a, 1b, .about.1n are feedback-controlled, the compressed air in the piping system 3 can be kept substantially constant as shown in FIG.
[0024]
Therefore, it is not necessary to set the set pressure Pset of the compressed air to be supplied to the piping system 3 larger than the necessary pressure Pneed of the compressed air required by the loads 4a, 4b, to 4m. That is, the required pressure Pneed of the compressed air can be obtained without setting the compressed air set pressure Pset for the piping system 3 large in view of the pressure fluctuation of the compressed air accompanying the start-up of the compressors 1a, 1b,. The operation of the compressors 1a, 1b, to 1n can be efficiently feedback-controlled under the same set pressure Pset or a slightly higher set pressure Pset. Therefore, it is possible to significantly reduce the energy (electric amount) required for driving the compressors 1a, 1b, to 1n and to save energy.
[0025]
In a factory or the like to which such an air supply system is applied, it cannot be denied that air leaks from the piping system 3 to some extent. However, this air leak can also be detected as a total air consumption combined with the amount of air used by the target device according to the above-described system, so that the compressors 1a, 1b,. And the pressure of the compressed air in the piping system 3 can be kept stable.
[0026]
The present invention is not limited to the embodiment described above. For example, as a flow meter 6 incorporated in the piping system 3, when using a conventional differential pressure type, volume type, volume type, vortex type, ultrasonic type flow meter for volume flow rate measurement, for example, as shown in FIG. Thus, the volume flow rate Qv of the compressed air measured by the volume flow meter 6a is converted into the mass flow rate Qm according to the above-described gas state equation according to the pressure P and temperature T of the compressed air using the converter 6b. You can do it. In the case of using a mass flow meter, it is of course possible to use Coriolis mass flow meter in place of the thermal flow meter as described above.
[0027]
When the control system 10 is constituted by a microcomputer or the like, for example, as shown in the processing concept in FIG. 5, the pressure P of the compressed air obtained by the pressure gauge 5 is sampled at predetermined intervals [ In step S1, the mass flow rate Qin obtained by the flow meter 6 is sampled in synchronization with the sampling of the pressure P [step S2]. Next, a change ΔP of the pressure P between the sampling points is obtained [Step S3], and the pressure change ΔP is further multiplied by a predetermined coefficient 1 / C (= V / RT) [Step S4]. Then, from the mass flow rate Qin and the value ΔP (1 / C) obtained by coefficient processing of the pressure change ΔP, a use amount Qout of compressed air is obtained as a feedback control amount for the compressors 1a, 1b, to 1n [step S5]. You can do it.
[0028]
Further, here, it is considered that the temperature T of the compressed air is constant, and the feedback control amount Qin for the compressors 1a, 1b, .about.1n is obtained. However, when the temperature T varies, FIG. As shown, the correction means 15 may be used to correct the temperature of the compressed air use amount Qout obtained as described above. In the embodiment shown in FIG. 1, since the pressure gauge 5 and the flow meter 6 are installed in the vicinity of the air tank 2, the measurement results of both can be handled as having substantially no time difference. However, in practice, the pressure gauge 5 and the flow meter 6 may be installed at a distance from each other, and there may be a time difference in the measurement. Even in such a case, the correction means 15 may be used to correct the compressed air usage Qout.
[0029]
In the above-described embodiment, an example in which the compressor 1 is feedback-controlled has been described. However, it is also possible to use feedforward control such as predictive control. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0030]
【The invention's effect】
As described above, according to the present invention, since the operation of the compressor is controlled by focusing on the mass flow rate of the compressed air, the consumption amount of the compressed air supplied from the compressor to the air-use equipment via the piping system is controlled in real time. It is possible to measure and to easily optimize the pressure. As a result, it is possible to reduce the energy (electric power amount) required for driving the compressor and effectively save the energy. In addition, it is possible to achieve practically great effects such as simple and effective stable supply of compressed air.
[Brief description of the drawings]
FIG. 1 is an overall schematic configuration diagram of an air supply system according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a thermal flow meter for measuring a mass flow rate.
FIG. 3 is a diagram showing a state of pressure change of compressed air in a piping system under control of a compressor based on air consumption in the air supply system shown in FIG. 1;
FIG. 4 is a diagram showing another configuration example of a flow meter for measuring a mass flow rate.
FIG. 5 is a diagram showing an example of a procedure for calculating an air use amount (control amount) Qout by a microcomputer.
FIG. 6 is a diagram illustrating a change in pressure of compressed air and a change in discharge amount (flow rate) of compressed air from a compressor in a conventional air supply system.
[Explanation of symbols]
1a, 1b, ˜1n Compressor 2 Air tank 3 Piping system 4a, 4b, ˜4m Load 5 Pressure gauge 6 Flow meter 10 Control system 11 Differentiation means (ΔP calculation)
12 Coefficient means 13 Difference means

Claims (2)

A flow meter for determining the mass flow rate of compressed air supplied from the compressor to the air use target through the piping system;
  A pressure gauge for determining the pressure of compressed air supplied to the air use object via the piping system;
  A differentiator for differentiating the pressure obtained by the pressure gauge to obtain the change,
  An air consumption detecting means for detecting an air consumption amount in the air use target based on a mass flow rate obtained by the flow meter and a pressure change obtained by the differentiator;
  Correction means for correcting the air consumption according to the temperature of the compressed air and / or the measurement time difference between the flow meter and the pressure gauge;
  An air supply system comprising control means for controlling the operation of the compressor in accordance with the corrected air consumption. The flow meter for determining the mass flow rate of the compressed air comprises a thermal flow meter comprising a heater element and a pair of temperature sensors provided in the flow direction of the compressed air across the heater element. The air supply system described.

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