JP2017137802A - Fluid compression device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid compression device that can suppress noise caused by a rapid change of rotational frequency of a motor while supplying fluid having stable pressure.SOLUTION: A fluid compression device includes: a compressor body for compressing fluid; a motor for driving the compressor body; an inverter for controlling the rotational frequency of the motor; a control circuit for controlling the motor and the inverter; and a tank for storing the fluid compressed by the compressor body. When the compressor body is stopped, the pressure of the fluid in the tank is reduced and lowering prediction time until lowering to predetermined return pressure is less than a predetermined threshold value, the control circuit starts the compressor body at target rotational frequency and then increases the rotational frequency to required rotational frequency.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fluid compression apparatus.

  There exists patent document 1 as background art of this invention. In Patent Document 1, each of a plurality of compressors is started / stopped, and for a compressor that collects the discharge air of the compressors in an air tank, “calculate the pressure change per predetermined time in the air tank, `` Calculate and predict the time when the pressure in the air tank reaches the lower limit of the predetermined pressure range due to the calculated pressure change per predetermined time, and start the stopped compressor when the calculated and predicted time is shorter than the predetermined time. '' It is described.

JP-A-11-287188

  In the method described in Patent Document 1, since the stopped compressor is started at a normal rotation speed when the predicted operation time is shorter than a predetermined time, noise cannot be suppressed with a sudden rotation speed change. .

  In view of the above problems, an object of the present invention is to provide a fluid compression apparatus capable of suppressing noise accompanying a sudden change in rotational frequency of a motor while supplying a fluid having a stable pressure.

  In order to solve the above problems, the present invention controls a compressor body that compresses a fluid, a motor that drives the compressor body, an inverter that controls a rotation frequency of the motor, and the motor and the inverter. And a tank for storing the fluid compressed by the compressor body, and the control circuit is determined in advance because the compressor body is stopped and the pressure of the fluid in the tank is reduced. When the predicted lowering time until the pressure falls to the return pressure is smaller than a predetermined threshold, the fluid is characterized by increasing the rotational frequency to the required rotational frequency after starting the compressor body at the target rotational frequency. A compression device is provided.

  According to the present invention, it is possible to provide a fluid compression device capable of suppressing noise accompanying a sudden change in the rotational frequency of a motor while supplying a fluid having a stable pressure.

It is a top view which shows the external appearance of the inverter type fluid compression apparatus in Example 1 of this invention. It is a flowchart which shows the program of the inverter type fluid compression apparatus in Example 1 of this invention. It is a flowchart which shows the program of the inverter type fluid compression apparatus in Example 2 of this invention. It is a graph which shows the change of the pressure and rotation frequency when there are many amounts of used air in a prior art. It is a graph which shows the change of the pressure and rotation frequency when there are many amounts of use air in Example 1. FIG. It is a graph which shows the change of the pressure and rotation frequency when there are many amounts of used air in Example 2. FIG. It is a graph which shows the change of the pressure and rotation frequency when there is little amount of used air in a prior art. It is a graph which shows the change of the pressure and rotation frequency when the amount of used air in Example 1 is small. It is a graph which shows the change of the pressure and rotation frequency when the amount of used air in Example 2 is small. It is a graph which shows the relationship between the starting timing in Example 2, and a target rotational frequency.

  Embodiments of the present invention will be described below with reference to the drawings.

  Embodiment 1 of the present invention will be described below with reference to FIGS. 1, 2, 4, 5, 7, and 8. FIG.

  FIG. 1 shows the overall configuration of an inverter type fluid compression apparatus in this embodiment. The inverter type fluid compression apparatus (compression apparatus 7) of FIG. 1 mainly includes a compressor body 1 that compresses a fluid such as air, a motor 2 that drives the compressor body 1, and an inverter that controls the rotational frequency of the motor 2. 3 and a tank 5 for storing air compressed by the compressor body 1. The control circuit 4 has a function of sending a command for controlling the rotation frequency of the motor 2 to the inverter 3. The control circuit 4 controls the compressor body 1 by controlling the operation / stop of the motor 2 and the rotation frequency. A pressure sensor 6 for detecting the pressure of the internal fluid is attached to the tank 5. Information on the pressure of the fluid in the tank 5 obtained from the pressure sensor 6 is transmitted to the control circuit 4. The compression device 7 according to this embodiment has the configuration as described above.

  Next, control processing of the compression device 7 in the present embodiment will be described with reference to FIGS. FIG. 2 is a flowchart showing the control processing of this embodiment. This control process is performed every predetermined sampling period (for example, 200 ms).

  In step 1, the current pressure P (t) in the tank 5 is measured at a constant sampling period Ts.

  Next, in step 2, it is determined whether or not the compressor body 1 is currently stopped. If “Yes” is determined, the process proceeds to step 3. If “No” is determined, the process proceeds to Step 12.

In Step 3, the pressure change ΔP in the tank is calculated by Equation 1 using the current pressure P (t) and the pressure P (t-1) one second before.
(Formula 1)
ΔP = [P (t) -P (t-1)]
After calculating the pressure change ΔP, the process proceeds to step 4 to calculate the pressure change rate K per unit time. The pressure change rate K is calculated by Equation 2.
(Formula 2)
K = ΔP / Ts
In step 5, it is determined whether or not the pressure change rate K calculated in step 4 is a negative value, that is, whether or not the pressure is decreasing. If "No" is determined, the process proceeds to step 21 and returns. If “Yes” is determined, the process proceeds to step 6.

In the next step 6, the amount of air used Qu per sampling period Ts is calculated. The amount of air used Qu is calculated by Equation 3 using the differential pressure ΔP, the tank volume V, and the time T. Here, T = 1 second.
(Formula 3)
Qu = (592 * | ΔP | * V / T)
In step 7, the required rotation frequency Fn of the compressor main body 1 is calculated according to the used air amount Qu calculated in step 6. The rotation frequency Fn is calculated by Equation 4 using the conversion coefficient N. Here, N is a constant. That is, the required rotational frequency Fn becomes larger as the amount of air used Qu increases. Thus, during normal operation, even when the amount of air used is large, the pressure in the tank 5 does not decrease, and it is possible to supply air with a stable pressure. Note that a predetermined lower limit is set for the rotation frequency Fn, and when the amount of air used Qu is small and the value calculated by Equation 4 is less than the predetermined lower limit, Fn = predetermined lower limit To do.
(Formula 4)
Fn ＝ N * Qu
In the next step 8, a predicted decrease time Td during which the pressure drops to the return pressure is calculated. The predicted decrease time Td is calculated by Equation 5 using the return pressure Pmin, the current pressure P (t), and the pressure change rate K. That is, the predicted decrease time Td is a time obtained by dividing the pressure difference between the return pressure Pmin and the current pressure P (t) by the pressure change rate K.
(Formula 5)
Td = (Pmin-P (t)) / K
In step 9, it is determined whether or not the predicted decrease time Td calculated in step 8 is smaller than a predetermined threshold value of Td (for example, 2 seconds). If it is determined “No”, the process proceeds to step 21 and returns. If it is determined as “Yes”, the process proceeds to Step 10.

  In step 10, the compressor main body 1 is started, and the operation state of the compressor main body 1 is set as starting.

  In the next step 11, the target rotational frequency Fref shown in Formula 6 is obtained using the necessary rotational frequency Fn obtained in step 7 and the predicted decrease time Td, and the compressor body 1 is started at the target rotational frequency Fref. The target rotation frequency Fref is a value smaller than the necessary rotation frequency Fn. For this reason, when the compressor body 1 is started, a sudden change in the rotational speed can be suppressed, and the generation of noise can be suppressed.

At this time, by dividing Fn by the value obtained by dividing the predicted fall time Td by 0.2 (1/10 when the threshold is 2 seconds), which is the same value as the sampling period Ts, for example, the required rotation frequency Fn is obtained. It is possible to moderate the rotation frequency change until it reaches. That is, the larger the required rotational frequency Fn, the larger the target rotational frequency Fref, and the shorter the predicted decrease time Td, the larger the target rotational frequency Fref. Further, as shown in steps 13 to 17 below, the target rotation frequency Fref changes from the value at the time of activation so as to approach the necessary rotation frequency Fn after activation. Note that a predetermined lower limit is set for the target rotation frequency Fref in the same manner as Fn, and when the value calculated by Equation 6 is smaller than the predetermined lower limit, Fref = the predetermined lower limit. In this case, Fref has the same value as Fn.
(Formula 6)
Fref = Fn / (Td / 0.2)
After starting at the target rotational frequency Fref, the routine proceeds to step 21 and returns.

  If “No” is determined in Step 2, the process proceeds to Step 12 to determine whether or not the compressor body 1 is being activated. If “No” is determined, the process proceeds to step 19. If “Yes” is determined, the process proceeds to step 13. Changes in the target rotation frequency Fref during startup will be described in steps 13 to 17 below.

  In step 13, the pressure change ΔP in the tank is calculated by Equation 1 using the current pressure P (t) and the pressure P (t-1) one second before.

  After calculating the pressure change ΔP, the process proceeds to step 14 to calculate the pressure change rate K. The pressure change rate K is calculated by Equation 2.

  In the next step 15, a predicted decrease time Td in which the pressure drops to the return pressure is calculated. The predicted decrease time Td is calculated by Equation 5 using the return pressure Pmin, the current pressure P (t), and the pressure change rate K.

In step 16, the target rotation frequency Fref shown in Equation 7 is obtained using the estimated decrease time Td obtained in step 15, the current compressor rotation frequency Fc, and the necessary rotation frequency Fn, and the rotation frequency of the compressor body 1 is calculated. Is changed from the compressor rotational frequency Fc to the target rotational frequency Fref. At this time, similarly to step 11, (Fn−Fc) is divided by a value obtained by dividing the predicted fall time Td by, for example, 0.2 (1/10 when the threshold is 2 seconds) which is the same value as the sampling period Ts. Thus, it is possible to moderate the rotation frequency change until the required rotation frequency Fn is reached. That is, when the predicted decrease time Td is long, the rotation frequency change becomes gradual, and noise can be suppressed. On the other hand, when the predicted decrease time Td is short, it is possible to supply air with a stable pressure by quickly increasing the rotation frequency.
(Formula 7)
Fref = Fc + ((Fn-Fc) / (Td / 0.2))
In the next step 17, it is determined whether or not the current compressor rotational frequency Fc is equal to or higher than the necessary rotational frequency Fn. When it determines with "No", it moves to step 21 and returns. If “Yes” is determined, the process proceeds to step 18.

  In step 18, the operation state of the compressor body 1 is set as normal operation, the process proceeds to step 21 and the process returns.

  If it is determined as “No” in step 12, the process proceeds to step 19 to determine whether or not the compressor body 1 is in normal operation. When it determines with "No", it moves to step 21 and returns. If it is determined as “Yes”, the process proceeds to Step 20.

  In step 20, constant pressure control, that is, control for changing the rotation frequency Fn according to the amount of air used Qu from Equation 4, is performed, and the process returns to step 21 and returns.

  According to the above control, when ON-OFF operation is performed with an inverter type compressor, the compressor is started before reaching the return pressure, and the rotational frequency is gradually increased every 0.2 seconds (sampling period Ts). be able to. Therefore, the pressure in the tank does not become equal to or lower than the return pressure, air with a stable pressure can be supplied, and noise due to a sudden change in rotational speed can be reduced.

  The effects of this embodiment when the amount of air used is large will be described with reference to FIGS.

  Here, in the conventional technology, when the estimated time to the return pressure is not calculated, the compressor is started when the amount of air used is large, so that the pressure in the tank returns for a while from the start. It may drop below the pressure and may not be able to provide air at a stable pressure.

  Further, in the prior art, as in Patent Document 1, even if the predicted time to the return pressure is calculated, the inverter control is not performed, and the rotational frequency is increased rapidly when the compressor is started. The rotation frequency changes suddenly and noise cannot be suppressed.

  Even if inverter control is performed in the prior art, unlike the present embodiment, control for increasing the rotational frequency little by little is not performed. For this reason, when the amount of air used is large, the rotational speed is instantaneously increased to increase the pressure, and the pressure rises above the return pressure. In addition, since the rotational speed is decreased instantaneously thereafter, the rotational frequency changes rapidly, and noise cannot be suppressed.

  More specifically, when the predicted time until the return pressure is not calculated in the prior art, the pressure starts to reach the return pressure Pon as shown in FIG. In addition, since the operation is started at the rotation speed of the normal operation, the rotation frequency increases rapidly. According to the present embodiment, as shown in FIG. 5, the estimated time to the return pressure is calculated, and the compressor is started in advance before the pressure is reduced to the return pressure, so that the stable pressure is maintained so as not to fall below the return pressure. Air can be supplied.

  Next, the effect of this embodiment when the amount of air used is small will be described with reference to FIGS.

  When the predicted time until the return pressure is not calculated in the prior art, the rotation starts after the pressure reaches the return pressure Pon as shown in FIG. 7, and the rotational frequency increases rapidly. Even if inverter control is being performed, if the amount of air used is small, the pressure rapidly increases, so the rotational frequency is rapidly decreased to return the pressure to the return pressure. For this reason, the pressure in the tank rises rapidly, and the rotation frequency changes abruptly, so that noise cannot be suppressed. According to the present embodiment, as shown in FIG. 8, the predicted time until the return pressure is calculated, and the air at a stable pressure is set so as not to fall below the return pressure by starting the compressor in advance before the pressure is reduced to the return pressure. Can be supplied. Further, in this embodiment, control for increasing the rotation frequency little by little is performed, and noise can be suppressed because there is no sudden change in the rotation speed.

  A second embodiment of the present invention will be described with reference to FIGS. 1, 3, 4, 6, 7, 9, and 10.

  FIG. 1 shows the overall configuration of the inverter compressor in the present embodiment, and the description thereof is omitted because it is the same configuration as in the first embodiment.

  Next, the control processing of the present embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing the control processing in this embodiment. The description of the same flow as that of the first embodiment is omitted. Similar to the first embodiment, this control process is performed every predetermined sampling period (for example, 200 ms).

  In the present embodiment, the processing in step 8 is different from that in the first embodiment.

In this embodiment, in step 8, the threshold value (starting timing) of the predicted decrease time Td is determined with reference to FIG. The threshold value of the predicted decrease time Td is calculated by Equation 8 using the necessary rotation frequency Fn. Here, f (Fn) is a function that monotonously increases with respect to Fn. That is, the threshold value of Td increases monotonously with the required rotation frequency Fn and also monotonously increases with the amount of air used. As shown in FIG. 10, by changing the threshold value (start timing) of Td according to the amount of air used (required rotational frequency Fn), the required rotational frequency Fn increases when the amount of air used is large. The threshold increases and starts slowly. On the other hand, since Fn decreases when the amount of air used is small, the threshold value of the predicted decrease time Td decreases, the start-up is delayed, and the compressor body 1 is operated near the return pressure. Further, since the rotational frequency Fref determined by the mathematical formulas 6 and 7 becomes smaller as the Td threshold value becomes larger, the amount of air used increases, and even if the required rotational frequency Fn increases, the rotational frequency Fref can be started with a smaller rotational frequency Fref.
(Formula 8)
Td threshold = f (Fn)
Since the processes other than step 8 are the same as those in the first embodiment, description thereof is omitted.

  The effect of the present embodiment will be described. In this embodiment, the start timing is made variable according to the amount of air used, so that even when the amount of air used is large, the pressure in the tank 5 does not become lower than the return pressure, and the pressure is more stable compared to the first embodiment. Air can be supplied. Furthermore, a sudden change in the rotation frequency of the compressor can be suppressed.

  From here, the start-up timing of the compressor will be described with reference to FIG. According to the present embodiment, when the amount of air used is large, the activation timing can be advanced by increasing the Td threshold value in order to suppress a rapid change in the rotation speed, and the activation can be gradually and slowly performed with a small rotation frequency. When the amount of air used is small, if the start timing is early, the pressure is higher than the return pressure and becomes a constant or higher pressure.Therefore, by reducing the Td threshold and delaying the start timing, Operation is possible, and electric power can be reduced.

  Based on the change in the start timing of the compressor, the effect of the present invention on the amount of air used will be described.

  First, the effects of this embodiment when the amount of air used is large will be described with reference to FIGS. 4 and 6. In the prior art, when the predicted time until the return pressure is not calculated as shown in FIG. 4, the start is started after the pressure reaches the return pressure Pon. According to the present embodiment, as in the first embodiment, as shown in FIG. 6, the predicted time until the return pressure is calculated, and the compressor is started in advance before the return pressure is lowered, so that the return pressure is not lowered. In this way, air with a stable pressure can be supplied. Compared with Example 1, it is possible to increase the Td threshold value to accelerate the start timing and start the compressor so that the rotational speed can be slowly increased without falling below the return pressure. Noise can be further suppressed as compared with Example 1.

  Next, the effects of this embodiment when the amount of air used is small will be described with reference to FIGS. In the prior art, when the predicted time until the return pressure is not calculated, the operation starts after the pressure reaches the return pressure Pon as shown in FIG. 7, and the rotational frequency increases rapidly. Even if inverter control is being performed, if the amount of air used is small, the pressure rapidly increases, so the rotational frequency is rapidly decreased to return the pressure to the return pressure. For this reason, the pressure in the tank rises rapidly, and the rotation frequency changes abruptly, so that noise cannot be suppressed. According to the present embodiment, as in the first embodiment, as shown in FIG. 9, the predicted time until the return pressure is calculated, and the compressor is started in advance before the return pressure is lowered, so that the return pressure is not lowered. In this way, air with a stable pressure can be supplied. Further, in this embodiment, control for increasing the rotation frequency little by little is performed, and noise can be suppressed because there is no sudden change in the rotation speed. Also, compared with the first embodiment, the Td threshold value is decreased to delay the timing at the time of starting the compressor, thereby preventing a sudden change in the rotational speed and suppressing noise, and the pressure in the tank at the time of starting. Therefore, it is possible to reduce the electric power required for starting the compressor as compared with the first embodiment.

  The embodiments described so far are merely examples of the implementation of the present invention, and the technical scope of the present invention is not limitedly interpreted by these embodiments. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Compressor body 2 Motor 3 Inverter 4 Control circuit 5 Tank 6 Pressure sensor 7 Compressor

Claims (8)

A compressor body that compresses fluid, a motor that drives the compressor body, an inverter that controls the rotation frequency of the motor, a control circuit that controls the motor and the inverter, and a compressor body that is compressed A tank for storing fluid,
The control circuit is configured such that the compressor main body is stopped, the pressure of the fluid in the tank is decreased, and a predicted decrease time until the pressure decreases to a predetermined return pressure is smaller than a predetermined threshold value. In this case, after the compressor main body is started at the target rotation frequency, the rotation frequency is increased to a necessary rotation frequency.   2. The fluid compression apparatus according to claim 1, wherein the predicted drop time is a time obtained by dividing a pressure difference from a current pressure of the fluid in the tank to a return pressure by a rate of change in pressure per unit time.   The fluid compression apparatus according to claim 1, wherein the required rotational frequency becomes a larger value as the amount of air used increases.   The fluid compression device according to claim 1, wherein the target rotation frequency becomes a larger value as the required rotation frequency is larger.   The fluid compression apparatus according to claim 4, wherein the target rotation frequency becomes a larger value as the predicted decrease time is shorter.   2. The fluid compression device according to claim 1, wherein the control circuit gradually increases the rotation frequency as the predicted decrease time is longer after the compressor body is started at the target rotation frequency.   The fluid compression apparatus according to claim 1, wherein a threshold value of the predicted descent time changes according to an amount of air used.   8. The fluid compression apparatus according to claim 7, wherein a threshold value of the predicted decrease time increases as the amount of air used increases.

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