JP7628437B2 - Air Compressor - Google Patents

Description

The present invention relates to an air compressor that compresses outside air to generate compressed air and stores it in a tank, and is used to supply compressed air to pneumatic tools such as compressed air-driven nailers and air tackers.

An air compressor primarily comprises a compressor that compresses outside air to generate compressed air, a motor that drives the compressor, and a tank that stores the generated compressed air. When the motor is started, the compressor begins compression operation. The compressor generates compressed air by taking in outside air into a cylinder and compressing it with a piston that reciprocates within the cylinder. The compressed air stored in the tank is supplied to compressed air-driven pneumatic tools, such as nail guns and air tackers.

Air compressors for air tools such as nailers are controlled to stop the motor when the tank pressure reaches a specified stop pressure, and restart the motor when the tank pressure reaches a specified restart pressure. In recent years, air compressors with a feature that changes the restart pressure and stop pressure have been proposed with the aim of further improving the durability and reducing noise of air compressors (Patent Document 1).

JP 2017-036676 A

When the amount of work done using an air tool increases, the amount of compressed air consumed (air consumption) also increases. In such a case, in the air compressor disclosed in Patent Document 1, the "restart pressure" that restarts the motor and the "stop pressure" that stops the motor are set high in order to increase the amount of compressed air stored in the tank. Specifically, in the motor control of the air compressor, the restart pressure and stop pressure are changed so that they are proportional (linked) to the amount of air consumption.

However, the amount of work done using air tools is not always constant, and it is normal for the amount of work to vary over time (air consumption varies irregularly and significantly). When the amount of work varies over time like this, it is desirable to store compressed air even during periods when no work is being done. However, in the air compressor disclosed in Patent Document 1, when the operating period of no work begins, the stop pressure drops in conjunction with the air consumption, causing the compressor to stop in a short time and reducing the amount of compressed air stored. Thus, when the compressor is operated with the stop pressure reduced, the compressor stops immediately, significantly impairing the usability.

The objective of the present invention is to lower the stopping pressure of the air compressor to make it more durable, energy-efficient, and quiet, while avoiding air shortages so as not to impair the user experience.

This objective is achieved by having a compressor for compressing outside air to generate compressed air, a motor for driving the compressor, a tank for storing the generated compressed air, a tank pressure sensor for measuring tank pressure, an outlet for extracting compressed air from the tank, an outlet pressure sensor for measuring outlet pressure, and a controller for stopping the motor when the tank pressure reaches a stop pressure and restarting the motor when the tank pressure reaches a restart pressure, and the controller sets at least one of the stop pressure and the restart pressure based on the measured tank pressure and outlet pressure.

The air compressor may be an air compressor that performs motor control using either the first stop pressure or the second stop pressure as the stop pressure. In this case, in controlling the compression operation, the controller calculates the rate of change of the tank pressure from moment to moment based on the measured tank pressure, changes the restart pressure and the first stop pressure based on the rate of change of the tank pressure, calculates the second stop pressure based on the restart pressure, and adopts the higher of the first stop pressure and the second stop pressure as the effective stop pressure.

The controller of the air compressor may also increase or decrease the minimum filling pressure in controlling the compression operation according to the margin of the tank pressure during the previous operation period, and calculate the second stop pressure based on the restart pressure and the minimum filling pressure.

The controller of the air compressor may also set the lower limit of the restart pressure as the outlet pressure when controlling the compression operation.

In addition, the controller of the air compressor may increase or decrease the minimum filling pressure in controlling the compression operation according to the margin of tank pressure during the current operation period, and calculate the second stop pressure based on the restart pressure and the minimum filling pressure.

In the air compressor of the present invention, the controller sets at least one of the stop pressure and restart pressure based on the tank pressure and the outlet pressure. This allows the compressor to operate over a more flexible (lower) pressure range, resulting in quieter operation, energy savings, and longer life. Moreover, because at least one of the stop pressure and restart pressure is derived based on the tank pressure and the outlet pressure, the feeling of using the air compressor is not impaired.

In addition, in the air compressor of the present invention, the restart pressure and the first stop pressure are changed based on the rate of change of the tank pressure, and the second stop pressure is calculated based on the restart pressure, and the higher of the first stop pressure and the second stop pressure is adopted as the effective stop pressure. In this way, by introducing two stop pressures, making these stop pressures variable values, and using the higher of the two stop pressures as the effective stop pressure (the stop pressure that actually functions as an effective threshold), it is possible to achieve the excellent effect of preventing air shortages even if the amount of work is unevenly distributed over time.

In addition, in the air compressor of the present invention, the minimum filling pressure is a variable value that increases or decreases depending on the margin of the tank pressure during the previous operating period. (The minimum filling pressure is a pressure value used to derive the second stop pressure, and the second stop pressure is derived by adding the minimum filling pressure to the restart pressure.) In this way, by making the minimum filling pressure variable, it is possible to respond to variations in the temporal bias of air consumption.
In addition, by increasing or decreasing the current minimum filling pressure depending on the margin of tank pressure during the previous operating period, the previous amount of work can be reflected during the current operation, making it possible to avoid excess or shortage of pressure.

In addition, in the air compressor of the present invention, the lower limit of the restart pressure is set based on the outlet pressure. By referring to the outlet pressure in this way, it is possible to lower the pressure range in the compression operation control.

In addition, in the air compressor of the present invention, the minimum filling pressure in the current compression operation is a variable value that increases or decreases depending on the margin of tank pressure during the current operation period. This makes it possible to avoid air shortages more quickly.

FIG. 2 is a perspective view showing the appearance of an air compressor. FIG. 2 is a block diagram showing the functional configuration of an air compressor. FIG. 2 is a plan view showing an example of the layout of buttons and a display unit provided on an operation panel of an air compressor. FIG. 2 is a chart showing the principle of compression operation control utilizing restart pressure (consumption-linked). FIG. 4B is a chart showing a continuation of FIG. 4A. FIG. 4C is a chart showing a continuation of FIG. 4B. FIG. 2 is a chart illustrating the principle of compression operation control utilizing stop pressure (consumption-linked). FIG. 5B is a chart showing a continuation of FIG. 5A. FIG. 5C is a chart showing a continuation of FIG. 5B. FIG. 1 is a chart illustrating the principle of compression operation control using “restart pressure (consumption-linked)”, “stop pressure (consumption-linked)”, and “stop pressure (minimum filling)”. FIG. 13 is an image diagram illustrating the contents determined by "Condition 1", which is one of the certification conditions for the outlet setting value. 13 is an image diagram illustrating the contents that can be determined by "Condition 2," one of the certification conditions for the outlet setting value, and the contents that cannot be determined by Condition 2. FIG. 13 is an image diagram illustrating the contents determined by “Condition 4”, which is one of the certification conditions for the outlet setting value. FIG. 17 is an image diagram showing an example of the air supply capacity calculation process (S503 in FIG. 16). 4 is a flowchart showing a flow of a compression operation control process performed by an air compressor. 12 is a flowchart showing a subroutine of a pressure/pressure change rate acquisition process (S25) in FIG. 11 . 12 is a flowchart showing a subroutine of a tank pressure control range acquisition process (S27) in FIG. 11 . 14 is a flowchart showing a subroutine of an outlet setting value acquisition process (S207) in FIG. 13. 14 is a flowchart showing a subroutine of a pressure range acquisition process (S209) in FIG. 13. 12 is a flowchart showing a subroutine of an air supply capacity acquisition process (S29) in FIG. 11 . 12 is a flowchart showing a subroutine of a restart pressure acquisition process (S31) in FIG. 11 . 12 is a flowchart showing a subroutine of a stop pressure acquisition process (S33) in FIG. 11 . 12 is a flowchart showing a subroutine of the PFC/compressor control process (S35) in FIG. 11 .

(Air compressor configuration)
The configuration of an air compressor according to this embodiment will be described with reference to FIGS. 1 to 3.
FIG. 1 is a perspective view showing the appearance of an air compressor.
FIG. 2 is a block diagram showing the functional configuration of the air compressor.
FIG. 3 is a plan view showing an example of the layout of buttons and a display unit provided on an operation panel of an air compressor.

The air compressor of this embodiment includes a compressor 11 that generates compressed air, a motor 13 that drives the compressor 11, a Hall sensor 15 that detects changes in the rotational position of the rotor of the motor 13, a tank 17 that stores the generated compressed air, a tank pressure sensor 19 that measures the internal pressure of the tank 17, pressure reducing valves 1V, 2V that reduce the compressed air in the tank to a desired pressure and output it, outlets 1a, 1b provided downstream of the pressure reducing valve 1V, outlets 2a, 2b provided downstream of the pressure reducing valve 2V, outlet pressure sensors 1S, 2S that measure the outlet pressure, an operation panel 20 equipped with a display unit that displays various information and operation buttons, and a controller 30 that displays information on the operation panel 20 and controls the motor 13.

The compressor 11 is driven by the power of the motor 13. This compressor 11 takes in outside air into a cylinder and generates compressed air by compressing it with a piston that reciprocates within the cylinder with the power of the motor 13.

The motor 13 that drives the compressor 11 is, for example, an outer rotor type brushless motor. The motor drive may be sensored or sensorless, and may be a rectangular wave or a sine wave, with no particular limitation on the drive method. The type of motor is also not particularly limited, and may be, for example, a magnet motor or an induction motor.

The compressed air generated by the compressor 11 is stored in the tank 17. This tank 17 is provided with a tank pressure sensor 19 for measuring the tank pressure (internal tank pressure).

Of the pressure reducing valves 1V and 2V, the first pressure reducing valve 1V has a pressure adjustment knob 1D for adjusting the outlet pressure, and reduces the compressed air in the tank to a first set pressure (e.g., normal pressure of any value) before outputting it. The second pressure reducing valve 2V has a pressure adjustment knob 2D for adjusting the outlet pressure, and reduces the compressed air in the tank to a second set pressure (e.g., high pressure of any value) before outputting it. Hereinafter, the first pressure reducing valve 1V will be simply referred to as the "pressure reducing valve 1V." The second pressure reducing valve 2V will be simply referred to as the "pressure reducing valve 2V."

Outlets 1a, 1b, 2a, and 2b have air couplers to which an air hose of a pneumatic tool can be connected. Compressed air that has been decompressed by pressure reducing valve 1V can be taken out from first outlets 1a and 1b. Compressed air that has been decompressed by pressure reducing valve 2V can be taken out from second outlets 2a and 2b. Hereinafter, first outlets 1a and 1b will be simply referred to as "outlet 1." Second outlets 2a and 2b will be simply referred to as "outlet 2."

An outlet pressure sensor 1S for measuring outlet pressure (the pressure of compressed air taken out from the outlet 1) is provided near the outlet 1. This outlet pressure sensor 1S is provided, for example, downstream of the pressure reducing valve 1V, midway in the air flow path from the pressure reducing valve 1V to the outlet 1. Hereinafter, the pressure at the outlet 1 measured by the outlet pressure sensor 1S will be simply referred to as the "outlet 1 pressure."
An outlet pressure sensor 2S for measuring outlet pressure (the pressure of compressed air taken out from the outlet 2) is provided near the outlet 2. This outlet pressure sensor 2S is provided, for example, downstream of the pressure reducing valve 2V, midway in the air flow path from the pressure reducing valve 2V to the outlet 2. Hereinafter, the pressure at the outlet 2 measured by the outlet pressure sensor 2S will be simply referred to as the "outlet 2 pressure."

The operation panel 20 has an outlet 1 pressure display section 21, an outlet 2 pressure display section 22, a tank pressure display section 23, a power On/Off button 25 used to turn the air compressor on/off, an automatic On/Off button 27 used to switch the air compressor on/off automatically, and a panel MCU 29 that controls the above sections and is responsible for sending and receiving information to and from the controller 30.

The tank pressure display unit 23 displays the tank pressure obtained by the tank pressure sensor 19 after multiple moving average processing.
The outlet 1 pressure display unit 21 displays the outlet 1 pressure obtained by the outlet pressure sensor 1S after multiple moving average processing. Alternatively, the outlet 1 pressure when the later-described predetermined conditions (conditions 1 to 4) are satisfied (i.e., the outlet 1 set value (Pext1_mva[latest])) may be displayed.
The outlet 2 pressure display unit 22 displays the outlet 2 pressure obtained by the outlet pressure sensor 2S after multiple moving average processing. Alternatively, the outlet 2 pressure when the later-described predetermined conditions (conditions 1 to 4) are satisfied (i.e., the outlet 2 set value (Pext2_mva[latest])) may be displayed.

The operation panel 20 is equipped with an outlet 1 pressure display 21, an outlet 2 pressure display 22, a tank pressure display 23, a power On/Off button 25, and an automatic On/Off button 27, which are arranged in a layout such as that shown in FIG. 3 so that they can be seen and operated by the user.

The power On/Off button 25 is a button that is operated when performing motor control (compression operation control) according to the tank pressure, and when stopping this control. By operating the power On/Off button 25 of the air compressor and setting the power On, the system transitions to a mode in which the motor 13 is started/stopped according to the tank pressure.

The air compressor auto on/off button 27 is a button for switching the operation control mode of the air compressor between "auto on" mode and "auto off" mode.
In the "Auto Off" operation control mode, the stop pressure, which is the criterion for determining whether to stop the motor, is set to a predetermined fixed value (e.g., 4.5 MPa), and the restart pressure, which is the criterion for determining whether to restart the motor, is set to a predetermined fixed value (e.g., 4.1 MPa). These fixed reference values are used to control the stopping and restarting of compression operation.
In the "Auto On" operation control mode, the stop pressures (first stop pressure, second stop pressure) that serve as the criteria for determining whether to stop the motor are made variable, and the restart pressure that serves as the criteria for determining whether to restart the motor is made variable, and these variable reference values are used to control the stopping and restarting of compression operation.

In addition to the buttons described above, the operation panel 20 may be provided with a number of switches for changing the motor rotation speed, pressure range switching, etc., and the setting information set by these switches may be transmitted to the controller via communication so that the compressor operates in accordance with that information.
Furthermore, the operation panel 20 may be provided with a means for displaying the power On/Off state, and may display the current power On/Off state.
Furthermore, the operation panel 20 may be provided with a means for displaying the automatic On/Off state, and may display the automatic On/Off state.
Furthermore, the operation panel 20 may be equipped with a power supply voltage display and lamps for indicating various abnormalities in addition to the tank pressure display 23 and outlet pressure display units 21 and 22. In this case, each piece of display information is transmitted from the controller to the operation panel by communication, and each display is performed according to that information.

The controller 30 is responsible for controlling the operation panel 20 and the motor 13, and also detects the rotation speed of the motor 13 based on a signal from the Hall sensor 15, which detects changes in the rotational position of the rotor of the motor 13.

The controller 30 has a PFC circuit 31 (power factor correction circuit), an INV circuit 33 (inverter circuit), and a controller MCU 35 that controls these circuits 31 and 33. The PFC circuit 31 converts AC voltage from a commercial power source 41 into DC voltage. The INV circuit 33 generates a desired AC voltage from the DC voltage converted by the PFC circuit 31, and drives the motor 13. The compressor 11 performs compression operation when the motor 13 is driven. The controller MCU 35 controls the circuits 31 and 33, receives signals from the sensors 15, 19, 1S, and 2S, and transmits and receives signals to and from the panel MCU 29 of the operation panel 20.

(Outline of Compression Operation Control in Air Compressors)
Next, an overview of compression operation control in the air compressor having the above-mentioned configuration will be described.

The controller provided in the air compressor of this embodiment controls the motor that drives the compressor to stop when the tank pressure reaches the stop pressure, and to restart the motor when the tank pressure reaches the restart pressure. When the motor stops, the compression operation of the compressor stops, and when the motor restarts, the compression operation resumes.

In this control, the controller continues to monitor the tank pressure via the tank pressure sensor while the air compressor is powered on, and when the compressor is stopped (the motor is stopped), it determines whether the tank pressure has reached the restart pressure. On the other hand, when the compressor is operating (the motor is running), it determines whether the tank pressure has reached the stop pressure.

When the compressor is stopped, the controller changes the restart pressure, which is the criterion (threshold) for restarting the motor, based on the rate of change of the tank pressure. This restart pressure is proportional (linked) to the air consumption, so hereafter it will be referred to as the "restart pressure (consumption-linked)." The restart pressure (consumption-linked) is set based on the tank pressure and the outlet pressure.

On the other hand, when the compressor is operating, the controller sets two stop pressures (a first stop pressure and a second stop pressure) as candidates for the stop pressure that serves as the criterion (threshold) for stopping the motor, and adopts the higher of them as the effective stop pressure (the stop pressure that actually functions as an effective threshold). In other words, when the tank pressure reaches the adopted effective stop pressure, the controller stops the motor.

In this embodiment, while the compressor is operating, the first stop pressure is changed based on the rate of change of the tank pressure. Since this first stop pressure is proportional (linked) to the air consumption, hereinafter the first stop pressure is referred to as the "stop pressure (linked to consumption)." The stop pressure (linked to consumption) is set based on the tank pressure and the outlet pressure.

In addition, in this embodiment, the second stop pressure is calculated based on the restart pressure (consumption linked). Since this second stop pressure is a stop pressure value considered necessary to perform a minimum pressure filling (minimum filling), hereinafter the second stop pressure is referred to as the "stop pressure (minimum filling)." The stop pressure (minimum filling) is set based on the tank pressure and the outlet pressure.

(Principle of compression operation control using restart pressure (consumption linked))
Next, the principle of compression operation control using restart pressure (consumption-linked) will be described with reference to Figures 4A, 4B, and 4C. Figures 4A, 4B, and 4C are charts showing the principle of compression operation control using restart pressure (consumption-linked) when the compressor is stopped (motor is stopped).
FIG. 4A is a chart assuming a case where the air consumption by the pneumatic tool is constant (medium air consumption).
FIG. 4B is a chart showing a continuation of FIG. 4A, and is a chart showing a case in which the air consumption by the pneumatic tool fluctuates midway (air consumption decreases from a medium level to a low level), causing a drop in the restart pressure (consumption linked) midway.
FIG. 4C is a chart showing a continuation of FIG. 4B, and is a chart assuming a case where the tank pressure, which continues to decrease, reaches the restart pressure (consumption-linked) and actually restarts the motor.

In the assumed case shown in Figures 4A, 4B, and 4C, the controller performs the following steps (1) to (5) in order to determine whether or not to resume the paused compression operation. Note that the steps (1) to (5) described below correspond to the steps (1) to (5) shown in Figures 4A, 4B, and 4C.

(1) Measure the tank pressure value.
In this process, the pressure value of the tank pressure is measured based on the signal from the tank pressure sensor.

(2) Calculate the rate of change (slope) of pressure.
In this process, the rate of change (slope) of the tank pressure is calculated based on the current and previous tank pressure measurements. In the examples shown in Figures 4A, 4B, and 4C, the tank pressure decreases over time because compressed air is consumed by the air tool while the compression operation is stopped.

(3) Calculate the minimum reserve pressure.
In this process, the minimum reserve pressure is calculated based on the rate of change (slope) of the tank pressure calculated in (2) above and the minimum reserve time. The minimum reserve time is a predetermined time (e.g., about 20 seconds) and means the minimum time to ensure the current amount of work (rate of change). The minimum reserve pressure can be calculated using the following formula 1.
Formula 1: Minimum storage pressure = - rate of change of tank pressure x minimum storage time

(4) Convert the minimum reserve pressure into restart pressure (linked to consumption).
In this process, the restart pressure (consumption-linked) is calculated based on the minimum stockpile pressure calculated in (3) above and the lower limit of the restart pressure. The restart pressure (consumption-linked) can be calculated using the following formula 2. The lower limit of the restart pressure is set based on the outlet pressure (details will be described later).
Equation 2: Restart pressure (consumption-linked) = Minimum stockpile pressure + Lower limit pressure of restart pressure As can be seen from Equation 1 above and Equation 2 which uses the result of this equation, in this embodiment, the tank pressure and outlet pressure are used as basic data for calculating the restart pressure (consumption-linked). That is, in this embodiment, the controller sets the restart pressure (consumption-linked) based on the tank pressure and outlet pressure.

(5) Determination of whether to restart the compressor In this process, the tank pressure is compared with the restart pressure (consumption-linked), and if "tank pressure > restart pressure (consumption-linked)", it is determined that restarting the compressor is not necessary yet, and the motor is kept stopped (the compressor is kept stopped). In the example shown in Figures 4A and 4B, since "tank pressure > restart pressure (consumption-linked)", the motor is kept stopped (the compressor is kept stopped).
On the other hand, when "tank pressure ≦ start-up pressure (consumption-linked)", it is determined that the compressor needs to be restarted, and the motor is restarted to restart the compressor. In the example shown in Figure 4C, when "tank pressure ≦ start-up pressure (consumption-linked)" is met, the motor is driven (the compressor resumes operation).

(Principle of compression operation control using stop pressure (linked to consumption))
Next, the principle of compression operation control using the first stop pressure, "stop pressure (consumption-linked)" will be described with reference to Figures 5A, 5B, and 5C. Figures 5A, 5B, and 5C are charts showing the principle of compression operation control using the stop pressure (consumption-linked) when the compressor is operating (when the motor is driven).
FIG. 5A is a chart assuming a case where the air consumption by the pneumatic tool is constant (medium air consumption).
FIG. 5B is a chart showing a continuation of FIG. 5A, and assumes a case in which the air consumption by the pneumatic tool fluctuates midway (air consumption decreases from a medium level to a low level), causing the stop pressure (consumption linked) to decrease midway.
FIG. 5C is a continuation of FIG. 5B and illustrates a case in which the tank pressure continues to rise and reaches the stop pressure (consumption-linked), causing the motor to actually stop.

In the assumed case shown in Figures 5A, 5B, and 5C, the controller performs the following steps (1) to (5) in order to determine whether or not to pause compression operation. Note that the steps (1) to (5) described below correspond to the steps (1) to (5) shown in Figures 5A, 5B, and 5C.

(1) Measure the tank pressure value.
In this process, the pressure value of the tank pressure is measured based on the signal from the tank pressure sensor.

(2-1) Calculate the rate of change (slope) of pressure.
In this process, the rate of change (slope) of the tank pressure is calculated based on the current and previous tank pressure measurements. In the examples shown in Figures 5A, 5B, and 5C, compressed air is continuously supplied by the compression operation under conditions in which compressed air is consumed by the air tool, and the tank pressure increases over time.

(2-2) Calculate the rate of pressure change (slope) due to air consumption.
In this process, the air consumption pressure change rate is calculated based on the tank pressure change rate (slope) calculated in (2) above and the air supply pressure change rate. Note that there is a correlation between the tank pressure, motor rotation speed, and the air supply capacity of the compressor, and if the tank pressure and motor rotation speed are known, the air supply capacity of the compressor can be derived, and the air supply pressure change rate can be found based on that. The air consumption pressure change rate can be found using the following calculation formula 1.
Formula 1: Air consumption pressure change rate = Tank pressure change rate - Air supply pressure change rate

(3) Calculate the maximum storage pressure.
In this process, the maximum reserve pressure is calculated based on the air consumption pressure change rate calculated in (2-2) above and the maximum reserve time. The maximum reserve time is a predetermined time (for example, about 60 seconds) and means the maximum time to reserve the current workload (change rate) when the compressor is stopped. The maximum reserve pressure can be calculated using the following calculation formula 2.
Formula 2: Maximum storage pressure = -Air consumption pressure change rate x Maximum storage time

(4) Convert the maximum stockpile pressure into stop pressure (linked to consumption).
In this process, the stop pressure (consumption-linked) is calculated based on the maximum stockpile pressure calculated in (3) above and the lower limit of the stop pressure. The stop pressure (consumption-linked) can be calculated using the following formula. The lower limit of the stop pressure is set based on the outlet pressure (details will be described later).
Equation 3: Stop pressure (consumption-linked) = maximum stockpile pressure + lower limit pressure of stop pressure As can be seen from the above equations 1 and 2 and equation 3 which uses the results of these equations, in this embodiment, the tank pressure and outlet pressure are used as basic data for calculating the stop pressure (consumption-linked). That is, in this embodiment, the controller sets the stop pressure (consumption-linked) based on the tank pressure and outlet pressure.

(5) Determination of whether to stop compressor operation In this process, the tank pressure is compared with the stop pressure (consumption-linked), and if "tank pressure < stop pressure (consumption-linked)", it is determined that compressor operation needs to continue, and the motor is left running (the compressor is left running). In the example shown in Figures 5A and 5B, since "tank pressure < stop pressure (consumption-linked)", the motor is left running (the compressor is left running).
On the other hand, when "tank pressure ≧ stop pressure (consumption-linked)", it is determined that the compressor needs to be stopped, and the motor is stopped to stop the operation of the compressor. In the example shown in Fig. 5C, when "tank pressure ≧ stop pressure (consumption-linked)" is satisfied, the motor is stopped (the compressor is stopped).

(Outline of compression operation control using both "stop pressure (linked to consumption)" and "stop pressure (minimum filling)")
The above-mentioned "stop pressure (linked to consumption)" is a variable threshold value that varies depending on the magnitude of the time average of air consumption in the compression operation control. This compression operation control using the "stop pressure (linked to consumption)" is effective for continuous air consumption with almost no time bias in the air consumption, as shown in Figures 5A, 5B, and 5C.
However, when the air consumption is uneven over time, or when the air consumption is slow or rapid, problems such as air shortages occur, which significantly impairs the usability of the air compressor. In other words, if the threshold for the stop control of the compression operation relies only on the above-mentioned "stop pressure (consumption linked)," in sections where air is consumed, the stop pressure (consumption linked) will be high, but the pressure will not increase easily. Also, in sections where there is no air consumption, the stop pressure (consumption linked) will be low, and it will not be possible to store enough compressed air in the tank. Therefore, even if the time average of air consumption is large, the stop pressure will not increase, resulting in problems such as air shortages, which significantly impairs the usability of the air compressor.

In order to solve the problem described above of air shortages that occur when there is a time bias in air consumption, resulting in a poor usability of the air compressor, once the compressor starts, it is necessary to charge the compressor to a minimum pressure (minimum charge) from the pressure at that time (start-up pressure).

Therefore, in this embodiment, two concepts are introduced as stop pressures: the first stop pressure "stop pressure (consumption linked)" and the second stop pressure "stop pressure (minimum filling)", and the higher pressure is adopted as the effective stop pressure (the stop pressure that actually functions as an effective threshold). The "stop pressure (minimum filling)" is derived based on the pressure when the compressor is restarted (restart pressure), and is the stop pressure value considered necessary to perform the minimum pressure filling (minimum filling).

The "stop pressure (minimum fill)" is not a fixed value, but a variable value that varies according to the rate of air consumption (i.e., the time average rate of air consumption). In determining this "stop pressure (minimum fill)", in this embodiment, surplus pressure judgment criteria and insufficient pressure judgment criteria are set to measure the margin up to the lower limit pressure, and the value of the stop pressure (minimum fill) is optimized for the operation/stop cycle based on these criteria.

The principle of compression operation control using "restart pressure (consumption-linked)", "stop pressure (consumption-linked)", and "stop pressure (minimum filling)" will be explained below with reference to Figure 6. Figure 6 is a chart showing the principle of compression operation control using "restart pressure (consumption-linked)", "stop pressure (consumption-linked)", and "stop pressure (minimum filling)", and shows how the compressor repeatedly stops and restarts.

The main processes that occur when the compressor is stopped and running are explained in order, as shown in (1) to (6) in Figure 6.

(1) Stopped When the compressor is stopped, the tank pressure drops as air is consumed. When the tank pressure reaches the restart pressure (consumption-linked), the controller starts the motor and resumes compression operation.

(2) Driving [section n-1]
The main processes during operation in section n-1 are as follows:
(2-1) Change in Stop Pressure (Minimum Filling) The stop pressure (minimum filling) is increased or decreased depending on the margin of tank pressure during the previous operation in section n-2. Note that, in the embodiment shown in Fig. 6, the previous operation in section n-2 is not shown, so a specific description of the setting of the stop pressure (minimum filling) for the current operation in section n-1 is omitted.
(2-2) Change in Stop Pressure (linked to consumption) The stop pressure (linked to consumption) is changed according to the degree of air consumption, which changes from moment to moment. The principle of changing the stop pressure (linked to consumption) is as described above with reference to Figure 5.
(2-3) Measuring the tank pressure margin Based on the predetermined surplus pressure and underpressure criteria, the tank pressure margin up to the lower limit pressure based on the outlet pressure is measured. The method for setting the lower limit pressure will be described later.
The excess pressure criterion is a predetermined reference value that is used to determine the occurrence of excess pressure in the current operating section (section n-1) and to measure the degree of excess pressure. The measured degree of excess pressure is used to derive the stop pressure (minimum filling) in the next operating section (section n).
The underpressure criterion is a predetermined reference value that is used to determine the occurrence of underpressure in the current operating section and to measure the time during which the pressure is underpressure (underpressure time). The measured underpressure time is used to derive the stop pressure (minimum filling) in the next operating section (section n).
During operation in the current operating section (section n-1), the tank pressure is below the underpressure judgment criterion, and it is determined that underpressure is occurring in this section. In such a case, the minimum filling pressure [n] in the next operating section (section n) is increased according to the underpressure time (the time when underpressure occurred) in the current operating section (section n-1). The minimum filling pressure is the pressure value used to derive the stop pressure (minimum filling). As described below, the stop pressure (minimum filling) can be derived by adding the minimum filling pressure to the restart pressure in the next operating section (section n).
(2-4) Judgment on stopping compression operation During operation in this section n-1, the higher of the stop pressure (consumption-linked) and the stop pressure (minimum filling) is adopted as the effective stop pressure (the stop pressure that actually functions as an effective threshold).
When the rising tank pressure reaches the stop pressure (consumption-linked), the stop pressure (consumption-linked) at this time is not adopted as the effective stop pressure because "stop pressure (consumption-linked) < stop pressure (minimum filling)". In other words, at this point, the stop pressure (consumption-linked) does not function as the effective stop pressure, and the compression operation does not stop.
Then, when the tank pressure continues to rise and reaches the stop pressure (minimum fill), because "stop pressure (linked to consumption) < stop pressure (minimum fill)", the stop pressure (minimum fill) is adopted as the effective stop pressure, and compression operation is stopped at this point (the motor is stopped).

(3) Stopped When the compressor is stopped, the tank pressure drops as air is consumed. When the tank pressure reaches the restart pressure (consumption-linked), the controller starts the motor and resumes compression operation.
While the compressor is stopped, the restart pressure (linked to consumption) changes according to the degree of air consumption, but the restart pressure will not fall below a preset lower limit pressure (based on the outlet pressure). The lower limit pressure, which is the lower limit value of the restart pressure, will be described later.

(4) Driving [section n]
The main processes during operation in section n are as follows:
(4-1) Change in stop pressure (minimum filling) During operation in the previous section n-1, the tank pressure fell below the underpressure judgment criterion, so in operation in the current section n, the minimum filling pressure [n] is increased according to the underpressure time (the time when underpressure occurred). Then, the stop pressure (minimum filling) is calculated based on the minimum filling pressure [n] increased according to the underpressure time and the restart pressure in the current section n. As mentioned above, the restart pressure is derived based on the tank pressure and outlet pressure. The stop pressure (minimum filling) can be calculated using the following formula.
Formula: Stop pressure (minimum filling) = Minimum filling pressure + Restart pressure in current section As described above, in this embodiment, the tank pressure and outlet pressure are used as basic data for calculating the stop pressure (minimum filling). That is, in this embodiment, the controller sets the stop pressure (minimum filling) based on the tank pressure and outlet pressure.
(4-2) Change in Stop Pressure (Linked to Consumption) The stop pressure (linked to consumption) is changed according to the degree of air consumption, which changes from moment to moment.
(4-3) Measuring tank pressure margin Based on the predetermined surplus pressure and underpressure judgment criteria, measure the tank pressure margin up to the lower limit pressure.
During operation in the current operating section (section n), the minimum tank pressure exceeds the excess pressure judgment standard, and it is determined that excess pressure is occurring in this section. In such a case, the minimum filling pressure [n+1] in the next operating section (section n+1) is reduced according to the excess pressure in the current operating section (section n).
(4-4) Judgment for stopping compression operation During operation in the current section n, the higher of the stop pressure (linked to consumption) and the stop pressure (minimum filling) is adopted as the effective stop pressure (the stop pressure that actually functions as an effective threshold).
When the rising tank pressure reaches the stop pressure (consumption-linked), the stop pressure (consumption-linked) at this time is not adopted as the effective stop pressure because "stop pressure (consumption-linked) < stop pressure (minimum filling)". In other words, at this point, the stop pressure (consumption-linked) does not function as the effective stop pressure, and the compression operation does not stop.
Then, when the tank pressure continues to rise and reaches the stop pressure (minimum fill), because "stop pressure (linked to consumption) < stop pressure (minimum fill)", the stop pressure (minimum fill) is adopted as the effective stop pressure, and compression operation is stopped at this point (the motor is stopped).

(5) Stopped When the compressor is stopped, the tank pressure drops as air is consumed. When the tank pressure reaches the restart pressure (consumption-linked), the controller starts the motor and resumes compression operation.
While the compressor is stopped, the restart pressure (linked to consumption) changes according to the degree of air consumption, but the restart pressure will not fall below a preset lower limit pressure (based on the outlet pressure).

(6) Driving [section n+1]
The main processes during operation in section n+1 (processing within the range shown in the figure) are as follows.
(6-1) Change in stop pressure (minimum filling) During operation in the previous section n, the minimum tank pressure exceeded the surplus pressure judgment standard, so in operation in the current section n+1, the minimum filling pressure [n+1] is reduced according to the surplus pressure. Then, the stop pressure (minimum filling) is calculated based on the minimum filling pressure [n+1] reduced according to the shortage time and the restart pressure in the current section n+1. The stop pressure (minimum filling) can be calculated using the following formula.
Formula: Stop pressure (minimum filling) = Minimum filling pressure + Restart pressure in current section As can be seen from the formula above, in this embodiment, the tank pressure and outlet pressure are used as basic data for calculating the stop pressure (minimum filling). That is, in this embodiment, the controller sets the stop pressure (minimum filling) based on the tank pressure and outlet pressure.
(6-2) Change in Stop Pressure (Linked to Consumption) The stop pressure (linked to consumption) is changed according to the degree of air consumption.

(Specific compression operation control in air compressor)
Next, the compression operation control shown in Fig. 6 will be specifically described with reference to the flowcharts shown in Fig. 11 to Fig. 19. The configuration of the air compressor is shown in Fig. 2. Fig. 11 is a flowchart showing the flow of the compression operation control process performed by the air compressor, and Fig. 12 to Fig. 19 are flowcharts showing subroutines.

First, an initialization process is performed (S11 in FIG. 11).
In this process, the controller 30 sets and acquires the initial values of variables and states required for the following processes.

Next, the operation panel transmission/reception process is carried out (S13).
In this process, information is sent and received between the operation panel 20 and the controller 30. Specifically, information on the operation performed by the user on the operation panel 20 (power On/Off, automatic On/Off operation information) and the contents displayed on the operation panel 20 (tank pressure, outlet 1 pressure, outlet 2 pressure) are exchanged.

A receive buffer and a transmit buffer are prepared for sending and receiving information between the operation panel 20 and the controller 30. For example, the controller 30 receives operation information from the operation panel 20 (power on/off, automatic on/off operation information) and stores it in the receive buffer, and also transmits display information for the operation panel (tank pressure, outlet 1 pressure, outlet 2 pressure) stored in the transmit buffer to the operation panel 20.

Next, it is determined whether a control period has elapsed (S15).
In this determination process, the process waits for a certain period of time until the timing for performing control from step S17 onwards arrives (S15: No), and when the predetermined waiting period has elapsed, the control from step S17 onwards is started (S15: Yes). The waiting period in this determination process is set to, for example, 100 ms, taking into consideration the acquisition period of various pressure values. Note that, in order to reduce the burden on the controller MCU, the process structure may be such that this waiting period (control period) is a positive fraction of the acquisition period of various pressure values (for example, 200 ms).

Next, an operation information acquisition process is performed (S17).
In this process, the controller 30 refers to the reception buffer to obtain operation information for power On/Off and automatic On/Off.

Next, a pressure value acquisition process is performed (S19).
In this process, the controller 30 acquires the tank pressure from the tank pressure sensor 19, the outlet 1 pressure from the outlet pressure sensor 1S, and the outlet 2 pressure from the outlet pressure sensor 2S. The acquired data for each pressure value is used as base data for display on the operation panel, and is also used to acquire the outlet setting value and for calculation processing when automatic ON is enabled. Note that when acquiring pressure values from the pressure sensors 1S, 2S, and 19, the pressure sensor output voltage may be AD converted and the value acquired by the controller MCU 35 may be acquired as the pressure value, or a value converted to an easier-to-calculate value may be acquired as the pressure value.

Next, a pressure value for display calculation process is carried out (S21).
In this process, the controller 30 performs multiple moving averages for display of the information acquired in the pressure value acquisition process (S19) and stores the average in a transmission buffer. The tank pressure, outlet 1 pressure, and outlet 2 pressure data after calculation stored in the transmission buffer are transmitted from the controller 30 to the operation panel 20 and displayed on the displays 21, 22, and 23.

In addition, for the outlet pressure displayed on the outlet pressure display units 21 and 22, the outlet 1 set value and outlet 2 set value that have been certified and updated through the outlet set value acquisition process (S207 in FIG. 13) described below may be used as the display data on the outlet pressure display units 21 and 22.

Next, it is determined whether the power is set to On (S23).
If it is determined that the power is OFF (S23: No), the process of steps S13 to S21 is repeated again, whereas if it is determined that the power is ON (S23: Yes), the process proceeds to the next step (S25).

Next, a pressure/pressure change rate acquisition process is performed (S25).
In this process, the tank pressure change rate, outlet 1 pressure change rate, and outlet 2 pressure change rate are obtained based on the tank pressure, outlet 1 pressure, and outlet 2 pressure data obtained in the pressure value acquisition process (S19).

The specific process of the pressure/pressure change rate acquisition process in step S25 in FIG. 11 will be described below with reference to FIG. 12. FIG. 12 is a flowchart showing a subroutine of the pressure/pressure change rate acquisition process (S25) in FIG. 11.

In the subroutine of the pressure/pressure change rate acquisition process, first, a tank pressure LPF calculation (Ptank_lpf) is performed (S101).
Since the change in tank pressure when using an air tool is step-like on a micro level, the change rate is calculated after smoothing the change into a slope. Therefore, in the tank pressure LPF calculation, the tank pressure data acquired in the "Pressure Value Acquisition Process" (S19 in FIG. 11) is LPF-processed (output: Ptank_lpf). The pressure unit is [MPa]. For example, the time constant (e.g. 5 sec) is increased to smooth the step-like change, and an infinite impulse response LPF is used to save memory.

Next, a tank pressure change rate calculation (dPtank_lpf) is performed (S103).
This rate of change is used in the restart pressure acquisition process (S31) and the stop pressure acquisition process (S33) described below.
In this process, the pressure change rate is calculated from the previous and current updated values of Ptank_lpf obtained in the tank pressure LPF calculation (S101) and the control cycle (output: dPtank_lpf). The calculation formula is as follows. The change rate unit is, for example, [MPa/sec].
Formula: (Current Ptank_lpf - Previous Ptank_lpf) ÷ Control period

Next, a tank pressure moving average calculation (Ptank_mva[n]) is performed (S104).
This moving average value is used in the outlet setting value acquisition process (S207) described later.
In this process, the controller 30 performs a moving average process (for example, 10 control cycles = 1 sec) on the tank pressure data acquired in the pressure value acquisition process (S19 in FIG. 11). The pressure unit is [MPa].

Next, the outlet 1 pressure moving average calculation (Pext1_mva[n]) is performed (S105).
This moving average value is used in the outlet setting value acquisition process (S207) described later.
In this process, the controller 30 performs moving average processing (e.g., 10 control cycles = 1 sec) on the outlet 1 pressure data acquired in the pressure value acquisition process (S19 in FIG. 11). The pressure unit is [MPa]. In addition, past moving average values (e.g., past 40 control cycles (4 sec)) are stored in a buffer for later change rate calculation processing and outlet set value acquisition processing.

Next, the outlet 1 pressure change rate calculation (dPext1_mva[n]) is performed (S107).
This rate of change is used in the outlet setting value acquisition process (S207) described later.
In this process, the pressure change rate is calculated from the value of Pext1_mva 10 control cycles ago obtained in the outlet 1 pressure moving average calculation (S105), the current updated value, and the control cycle (output: dPext1_mva[n]). The calculation formula is as follows. The change rate unit is, for example, [MPa/sec].
Formula: (Pext1_mva[n] - Pext1_[n-10]) ÷ (control period x 10)
Also, for later outlet set value acquisition processing, past outlet 1 pressure change rates (for example, for the past 40 control cycles (4 seconds)) are stored in a buffer.

Next, the outlet 2 pressure moving average calculation (Pext2_mva[n]) is performed (S109).
This moving average value is used in the outlet setting value acquisition process (S207) described later.
In this process, the controller 30 performs moving average processing (e.g., 10 control cycles = 1 sec) on the outlet 2 pressure data acquired in the pressure value acquisition process (S19 in FIG. 11). The pressure unit is [MPa]. In addition, past moving average values (e.g., past 40 control cycles (4 sec)) are stored in a buffer for later change rate calculation processing and outlet set value acquisition processing.

Next, the outlet 2 pressure change rate calculation (dPext2_mva[n]) is performed (S111).
This rate of change is used in the outlet setting value acquisition process (S207) described later.
In this process, the pressure change rate is calculated from the value of Pext2_mva 10 control cycles ago obtained in the outlet 2 pressure moving average calculation (S109), the current updated value, and the control cycle (output: dPext2_mva[n]). The calculation formula is as follows. The change rate unit is, for example, [MPa/sec].
Formula: (Pext2_mva[n] - Pext2_[n-10]) ÷ (control period x 10)
Also, for later outlet set value acquisition processing, past outlet 2 pressure change rates (for example, for the past 40 control cycles (4 seconds)) are stored in a buffer.

This completes the subroutine for the pressure/pressure change rate acquisition process shown in FIG. 12. Note that in this embodiment, LPF processing and moving average processing are included in the pressure value calculation and change rate calculation, but these processes can be omitted by inserting an LPF circuit with an appropriate time constant between each pressure sensor 1S, 2S, 19 and the MCU controller 35.

Next, a process of acquiring the control range of the tank pressure is performed (S27 in FIG. 11).
Hereinafter, the specific processing of the tank pressure control range acquisition processing in step S27 in FIG. 11 will be described with reference to FIGS.
FIG. 13 is a flowchart showing a subroutine of the tank pressure control range acquisition process (S27) of FIG.
FIG. 14 is a flowchart showing a subroutine of the outlet setting value acquisition process (S207) of FIG.
FIG. 15 is a flowchart showing a subroutine of the pressure range acquisition process (S209) of FIG.

In the tank pressure control range acquisition process subroutine, first, it is determined whether the control mode is set to Automatic On or not (S201 in FIG. 13). The control mode is switched between Automatic On and Automatic Off by operating the Automatic On/Off button 27 on the operation panel 20.

If it is determined that the motor is automatically off (S201: No), the tank pressure threshold (stop pressure), which is the criterion for determining whether to stop the motor, is set to a predetermined fixed value (e.g., 4.5 MPa) (S203). Also, the tank pressure threshold (restart pressure), which is the criterion for determining whether to restart the motor, is set to a predetermined fixed value (e.g., 4.1 MPa) (S203).

On the other hand, if it is determined that Auto On is selected (S201: Yes), the tank pressure threshold (stop pressure), which is the criterion for determining whether to stop the motor, is made variable, and its upper limit is set to a predetermined upper limit (e.g., 4.5 MPa) (S205). Also, the tank pressure threshold (restart pressure), which is the criterion for determining whether to restart the motor, is made variable, and its upper limit is set to a predetermined upper limit (e.g., 4.1 MPa) (S205).

In this embodiment, the stop pressure and restart pressure in the case of automatic off are set to the same pressure values as the upper limit of the stop pressure and the upper limit of the restart pressure in the case of automatic on, but the former and the latter do not necessarily have to be set to the same pressure values. In other words, the stop pressure and restart pressure in the case of automatic off may be set to pressure values different from the upper limit of the stop pressure and the upper limit of the restart pressure in the case of automatic on.

Next, an outlet setting value acquisition process is performed (S207).
This process will be specifically described with reference to FIG.
Fig. 14 is a flowchart showing a subroutine of the outlet set value acquisition process (S207) of Fig. 13. The "outlet set value" is a pressure value used for various information processes in the air compressor (determining the lower limit of the restart pressure and the stop pressure, displaying the pressure on the outlet pressure display unit, etc.), and is the outlet pressure value when all of conditions 1 to 4 described below are satisfied.

When the air compressor is turned on, the outlet setting value for each outlet and the overall outlet setting value (representative outlet pressure, described below) are provisionally set to a predetermined value (e.g., 2.7 MPa). This setting process is performed during the initialization process (S11 in Figure 11).

After the air compressor is turned on, it is determined whether the outlet 1 pressure and the outlet 2 pressure each satisfy the following conditions 1 to 4. If all of conditions 1 to 4 are satisfied, it is assumed that no air tools are being used and the outlet pressure is stable, and the outlet pressure at that time is determined as the outlet set value.
(Condition 1) The outlet pressure must be a certain value lower than the tank pressure.
(Condition 2) The outlet pressure value is within a certain range for a specified period of time.
(Condition 3) The rate of pressure change is close to 0 for a predetermined period of time.
(Condition 4) When the motor is stopped (compression operation is stopped) and the outlet pressure is stable, the tank pressure change rate is 0 MPa/sec or more.

Below, we will explain each of the conditions 1 to 4 in detail.

(Condition 1) The outlet pressure must be a certain value lower than the tank pressure.
The outlet pressure, which is the secondary pressure of the pressure reducing valve, will not rise above the tank pressure (except in special cases such as mechanical malfunction), so unless the condition shown in the following formula, "the outlet pressure is a certain value lower than the tank pressure," is met, the outlet pressure at that time will not be adopted as the outlet set value (even if the pressure value and pressure change value at the outlet are stable). The "certain value" here is a predetermined value.
Tank pressure - outlet pressure ≧ constant value (e.g. 0.05MPa)

Condition 1 will be explained with a specific example shown in Figure 7. Figure 7 is an image diagram illustrating the contents to be determined in Condition 1. In the section a-g (the section from point a to point g) shown in Figure 7, the tank pressure (actually the moving average value (Ptank_mva[n]) fluctuates with the filling and consumption of compressed air. Note that in Figure 7, the solid line of the outlet pressure shows the progress of the actual pressure value at the outlet (actually the moving average value (Pext1_mva[n] or Pext2_mva[n])), and the dashed line shows the progress of the adopted outlet setting value (Pext1_mva[latest] or Pext2_mva[latest]).

In the section a-b among all sections shown in FIG. 7, the tank pressure and the outlet 1 pressure for normal pressure (the pressure at outlet 1, which is the secondary side of pressure reducing valve 1V) continue to rise at almost the same value at the same time. In the section a-b, the outlet 1 pressure does not reach the set pressure of pressure reducing valve 1V, and the outlet 1 pressure in this section does not satisfy condition 1. In other words, in the section a-b, the outlet 1 pressure is determined to be unstable and is not adopted as the outlet 1 set value. In such a case, the outlet 1 pressure display unit 21 of the air compressor may display, for example, 0, or may display a flashing pressure value (actually Pext1_mva[n]). After that, when point b is reached, the outlet 1 pressure reaches the set pressure of pressure reducing valve 1V, and then the outlet 1 pressure satisfies condition 1 "Tank pressure - outlet pressure ≧ constant value (for example, 0.05MPa)". In addition to condition 1, if conditions 2 to 4 are met, the outlet 1 pressure is determined to be stable, and the outlet 1 pressure at this time is adopted as the outlet 1 setting value (Pext1_mva[latest]).

In the section a-c, the tank pressure and the high-pressure outlet 2 pressure (the pressure at outlet 2, which is the secondary side of pressure reducing valve 2V) continue to rise at almost the same value at the same time. In the section a-c, the outlet 2 pressure does not reach the set pressure of pressure reducing valve 2V, and the outlet 2 pressure in this section does not satisfy condition 1. In other words, in the section a-c, the outlet 2 pressure is determined to be unstable and is not adopted as the outlet 2 set value. In such a case, the outlet 2 pressure display unit 22 of the air compressor may display, for example, 0, or may display a flashing pressure value (actually Pext2_mva[n]). After that, when point c is reached, the outlet 2 pressure reaches the set pressure of pressure reducing valve 2V, and then the outlet 2 pressure satisfies condition 1 "Tank pressure - outlet pressure ≧ constant value (for example, 0.05MPa)". In addition to condition 1, if conditions 2 to 4 are met, the outlet 2 pressure is determined to be stable, and the outlet 2 pressure at this time is adopted as the outlet 2 setting value (Pext2_mva[latest]).

After point d, the tank pressure temporarily drops as air is consumed, and in section ef, the tank pressure falls below the set pressure of pressure reducing valve 2V, resulting in the outlet 2 pressure fluctuating at approximately the same value as the tank pressure. Therefore, in section ef, condition 1 is not met, so the outlet 2 pressure at this time is determined to be unstable and is not adopted as the outlet 2 set value. Note that in section ef, which does not meet condition 1, the outlet 2 set value is not updated, but rather the most recently adopted outlet 2 set value is used and updated at regular intervals with the same value.

(Condition 2) The outlet pressure value is within a certain range for a specified period of time.
When air tools are used or the set pressure is changed (pressure adjustment of the pressure reducing valve), the outlet pressure changes, so the outlet pressure during such an unstable time is not adopted as the outlet set value. For example, if the 1-sec moving average pressure value (Pext1_mva[n] or Pext2_mva[n]) varies within 0.04 MPa (maximum - minimum) for 4 seconds (40 control cycles), it may be determined that condition 2 is met.

Condition 2 will be explained using the outlet 2 pressure shown in Figure 8 as a specific example. In Figure 8, the solid line for the outlet pressure shows the progress of the actual pressure value at the outlet (Pext2_mva[n]), and the dashed line shows the progress of the adopted outlet setting value (Pext2_mva[latest]).

Figure 8 is an image diagram showing examples of what can be determined by condition 2 on the upper side of the graph, and what cannot be determined by condition 2 on the lower side of the graph. The outlet 2 pressure shown by a solid line in the upper part of Figure 8 indicates the outlet 2 pressure for high pressure (the outlet 2 pressure that is the secondary side of pressure reducing valve 2V). Additionally, multiple rectangular frames shown by dashed lines in Figure 8 (hereinafter referred to as "judgment frames") each visually represent condition 2, with the horizontal width of the judgment frame visually indicating the "predetermined time" of condition 2, and the vertical width of the judgment frame visually indicating the "fixed width" of condition 2. Note that the "predetermined time" of condition 2 is a predetermined time, and the "fixed width" is a predetermined width.

In Fig. 8, for example, in section a, the outlet 2 pressure momentarily drops due to air consumption by the air tool. At this time, the fluctuation width of the outlet 2 pressure exceeds a certain width (vertical width of the judgment frame) within a predetermined time range (horizontal width of the judgment frame). Therefore, the outlet 2 pressure at this time does not satisfy condition 2, so the outlet 2 pressure is determined to be unstable and is not adopted as the outlet 2 set value.
In section b, there is no fluctuation in the outlet 2 pressure, and the fluctuation width of the outlet 2 pressure is within a certain width (vertical width of the judgment frame) within a predetermined time range (horizontal width of the judgment frame). Therefore, the outlet 2 pressure at this time satisfies condition 2, so if the other conditions 1, 3, and 4 are simultaneously satisfied, it is determined that the outlet 2 pressure is stable and is adopted as the outlet 2 set value.
In section c, the set pressure of the pressure reducing valve is adjusted and the outlet 2 pressure starts to gradually decrease. At this time, the fluctuation range of the outlet 2 pressure exceeds a certain range (the vertical width of the judgment frame) within a predetermined time range (the horizontal width of the judgment frame). Therefore, the outlet 2 pressure at this time does not satisfy condition 2, so it is determined that the outlet 2 pressure is unstable and is not adopted as the outlet 2 set value.
In section d, the outlet 2 pressure reaches the set pressure of the pressure reducing valve 2V, and the fluctuation is slight. At this time, the fluctuation width of the outlet 2 pressure is within a certain width (vertical width of the judgment frame) within a predetermined time (horizontal width of the judgment frame). Therefore, the outlet 2 pressure at this time satisfies condition 2, and if the other conditions 1, 3, and 4 are simultaneously satisfied, the outlet 2 pressure is determined to be stable and is adopted as the outlet 2 set value.
In sections a and c that do not satisfy condition 2, the outlet 2 setting value is not updated, but the most recently adopted outlet 2 setting value is used and updated with the same value at regular intervals.

(Condition 3) The rate of pressure change is close to 0 for a predetermined period of time.
In the case of a pressure reducing valve for normal pressure, the outlet pressure may return slowly immediately after the use of an air tool, and in such a case, there is a risk of slipping through the condition 2. Therefore, in order to exclude cases where the condition 2 is not met (such as when a normal pressure tool is used and the pressure return is slow immediately after use), if the condition "the pressure change rate is close to 0 for a predetermined time" is not met, the outlet pressure at that time is not adopted as the outlet set value. The "predetermined time" here is a time that is determined in advance. Whether or not the condition 3 is met can be determined based on, for example, "whether or not the absolute value of the pressure change rate based on the 1-sec moving average pressure value (dPext1_mva[n] or dPext2_mva[n]) is 0.04 MPa/sec or less for 4 sec (40 control cycles)."

Condition 3 will be described below by taking the outlet 1 pressure shown in the lower part of FIG. 8 as a specific example.
As shown in the outlet 1 pressure graph in Figure 8, when using a normal pressure air tool, the air that has escaped inside the tool during use is usually replaced by a large air flow rate due to the pressure difference before and after the pressure reducing valve, causing a stepwise drop in the outlet 1 pressure, but then the pressure after the pressure reducing valve (outlet pressure) gradually recovers to the pressure reducing valve set pressure according to the pressure difference. This latter gradual pressure recovery is very slow, especially with a normal pressure reducing valve. Condition 3 excludes cases where the rate of change of outlet pressure is like this.

In Figure 8, for example, in section A, the outlet 1 pressure momentarily drops due to air consumption by the air tool. At this time, the fluctuation range of the outlet 1 pressure exceeds a certain range (the vertical width of the judgment frame) within a specified time range (the horizontal width of the judgment frame). Therefore, the outlet 1 pressure in section A is excluded by condition 2, and is not adopted as the outlet 1 setting value (without having to determine condition 3).

Meanwhile, in section B, the outlet 1 pressure gradually recovers to the pressure reducing valve set pressure. This is a very slow change, especially with a pressure reducing valve for normal pressure. This gradual pressure recovery falls within the judgment frame of condition 2, so the outlet 1 pressure satisfies condition 2. However, the outlet 1 pressure in section B does not satisfy condition 3, "the rate of pressure change is close to 0 for a specified period of time," so it is determined to be unstable and is not adopted as the outlet 1 set value.

(Condition 4) When the motor is stopped (compression operation is stopped) and the outlet pressure is stable, the tank pressure change rate is 0 MPa/sec or more.
When a steady air release is continued using an air tool such as a duster, the outlet pressure will stabilize in a lowered state. In order to exclude cases where the outlet pressure stabilizes in a temporarily lowered state like this, if the condition "Tank pressure change rate is 0 MPa/sec or more" is not met, the outlet pressure at that time (even if the outlet pressure is stable) will not be used as the outlet setting value.

Note that it is expected that tank pressure will actually decrease due to factors such as natural attenuation. If such natural attenuation of tank pressure is taken into consideration, the threshold for the tank pressure change rate in condition 4 may be set to "negative, close to 0 MPa/sec."

Condition 4 will be explained using the normal outlet 1 pressure shown in Figure 9 as a specific example. Figure 9 is an image diagram illustrating the contents determined by condition 4. In Figure 9, the solid line for the outlet pressure shows the progress of the actual pressure value at the outlet (Pext1_mva[n]), and the dashed line shows the progress of the adopted outlet setting value (Pext1_mva[latest]).

With air tools such as nail guns, the pressure at the outlet changes (for a very short time) with each shot, but when a steady air consumption continues with a duster or the like, the outlet pressure remains stable for a long time (several seconds or more) as shown in Figure 9, so in such cases conditions 2 and 3 are not met. Therefore, condition 4 is used to determine whether air is being consumed based on the tank pressure, and such cases are excluded.

Figure 9 shows an example of a case where a duster is used to continuously and stably release air, but in the section of the judgment frame shown by the dashed line, the duster continues to release air in a stable state, satisfying conditions 2 and 3 described above. However, the tank pressure change rate in this section is negative, and does not satisfy condition 4, "Tank pressure change rate is 0 MPa/sec or greater," so this is not adopted as the outlet 1 setting value.

The assumed case shown in Figure 9 is a case where the tank pressure is dropping and the outlet pressure is stable, for example, when a duster is continuously used. In such a case, even if the outlet pressure is stable, the outlet pressure is not adopted as the outlet set value because it is not the outlet pressure set by the pressure reducing valve.
In addition, the cases that can be excluded by condition 4 are not limited to those mentioned above, and for example, a case in which the outlet pressure is stable even when pressure is leaking from the tank or the air hose or air tool connected to the outlet can also be excluded by condition 4. This is because such a situation is considered to be an abnormal state even if the outlet pressure is stable.

In this embodiment, condition 4 includes the requirement of "motor stopped state (compression operation stopped state)". However, even if the motor is driven (compression operation in progress), if it is possible to accurately grasp the amount of air supplied to the compressor, it is possible to accurately determine the threshold value of the tank pressure change rate used in condition 4 (0 MPa/sec in this embodiment). In other words, if it is possible to accurately grasp the amount of air supplied to the compressor, it is possible to accurately determine the threshold value of the tank pressure change rate used in condition 4, regardless of whether the compressor is operating or stopped.

It is determined whether or not all of the above conditions 1 to 4 are met for each of the outlet 1 pressure and the outlet 2 pressure (S311 to S314, S321 to S324 in FIG. 14).
When all of the conditions 1 to 4 are satisfied for the outlet 1 pressure (S311 to S314: Yes), the outlet 1 pressure at that time is recognized and updated as the outlet 1 set value (S317).
When all of the conditions 1 to 4 are satisfied for the outlet 2 pressure (S321 to S324: Yes), the outlet 2 pressure at that time is recognized and updated as the outlet 2 set value (S327).

The outlet 1 setting value thus certified and updated can be used as data for display on the outlet pressure display unit 21, and the outlet 2 setting value can be used as data for display on the outlet pressure display unit 22.

In this embodiment, the four conditions 1 to 4 described above are used in the judgment as to whether or not to adopt the outlet pressure as the outlet set value (S311 to S314, S321 to S324 in FIG. 14), but the conditions required for this judgment are not necessarily limited to the four conditions described above. That is, only one, two or three of conditions 1 to 4 may be used in the judgment as to whether or not to adopt the outlet set value. Furthermore, conditions 1 to 4 plus another condition may be used in the judgment as to whether or not to adopt the outlet set value.
Furthermore, the threshold value for each condition may be different for the outlet for high pressure and the outlet for normal pressure, for example.

Next, the certified and updated outlet 1 set value and outlet 2 set value are compared (S331). The maximum pressure value between the outlet 1 set value and the outlet 2 set value is adopted as the representative outlet pressure of the air compressor. In other words, if "outlet 1 set value ≧ outlet 2 set value" (S331: No), the outlet 1 set value is adopted as the representative outlet pressure of the air compressor (S333). On the other hand, if "outlet 1 set value < outlet 2 set value" (S331: Yes), the outlet 2 set value is adopted as the representative outlet pressure of the air compressor (S335).

The representative outlet pressure thus adopted, i.e., the maximum pressure value among the outlet 1 set value and outlet 2 set value, is used as the lower limit pressure (see the lower limit pressure shown in the chart in Figure 6). Note that the representative outlet pressure may be used as the lower limit pressure as is, or a buffer pressure (e.g., a margin of about 0.1 MPa) may be added to the representative outlet pressure to use as the lower limit pressure.

In the above embodiment, the maximum pressure value among the outlet 1 setting value and the outlet 2 setting value is adopted as the representative outlet pressure of the air compressor, and this representative pressure is used as the lower limit pressure, but the method of determining the representative outlet pressure is not limited to this. For example, a discrimination means such as a sensor that discriminates whether the outlet 1 and outlet 2 are in use or not may be provided for each of them, and when only one outlet is in use, the outlet setting value of the outlet that is in use may be adopted as the representative pressure.

Next, a pressure range acquisition process is performed (S209 in FIG. 13).
Fig. 15 is a flowchart showing a subroutine of the pressure range acquisition process (S209) of Fig. 13. In this pressure range acquisition process, as shown in Table 1, the upper and lower limit values of the restart pressure and the upper and lower limit values of the stop pressure are acquired as pressure ranges for compression operation control.

The principles for setting the upper and lower limits shown in Table 1 are as follows:

As described above in S201 of FIG. 13, if it is determined that Auto On is selected (S201: Yes), the tank pressure threshold (stop pressure), which is the criterion for determining whether to stop the motor, is made variable, and its upper limit is set to a predetermined upper limit (e.g., 4.5 MPa) (S205). In addition, the tank pressure threshold (restart pressure), which is the criterion for determining whether to restart the motor, is made variable, and its upper limit is set to a predetermined upper limit (e.g., 4.1 MPa) (S205).

In addition, the lower limit of the restart pressure (the lower limit of the restart pressure when the automatic pressure is on) is calculated based on the outlet set value (representative outlet pressure) acquired in the outlet set value acquisition process (S207). This calculation can be expressed by the following formula.
Restart pressure lower limit = outlet setting value + buffer pressure (e.g., a margin of about 0.1 MPa)

In addition, the stop pressure lower limit (the lower limit of the stop pressure when the automatic ON is selected) is calculated from the calculated restart pressure lower limit. This calculation can be expressed by the following formula.
Stop pressure lower limit = restart pressure lower limit + buffer pressure (e.g., a margin of about 0.2 MPa)

This completes the subroutine for obtaining the tank pressure control range shown in Figures 13 to 15.

Next, an air supply capacity acquisition process is performed (S29 in FIG. 11).
In this process, a process for calculating the air supply capacity is performed (S503 in FIG. 16). FIG 16 is a flow chart showing a subroutine of the air supply capacity acquisition process (S29) in FIG.

In the air supply capacity calculation process (S503 in FIG. 16), the air supply capacity of the compressor is calculated from the tank capacity, motor rotation speed, and tank pressure. In this embodiment, the tank capacity (the capacity of the tank 17) is determined in advance. The motor rotation speed can be detected based on a signal from the Hall sensor 15. The tank pressure can be detected based on a signal from the tank pressure sensor 19.

The air supply capacity calculation process will be specifically described with reference to Figure 10. Figure 10 is an image diagram showing an example of the air supply capacity calculation process.

The example shown in FIG. 10 is based on the premise that the controller has base data (correlation data of tank pressure-tank pressure change rate during pumping for a product with a motor of 2500 min ^-1 and a tank capacity of 16 L) in advance. In FIG. 10, the solid line indicates the change in air supply capacity of the base data used to calculate the air supply capacity. The dashed line indicates the change in the air supply capacity that the air compressor actually has. The air supply capacity is expressed as the tank pressure change rate [MPa/sec]. Note that in this embodiment, as an example of the base data, data of an air compressor (16 L product) equipped with a 16 L tank is used as the base data. Also, as an example of the air compressor in this embodiment, an air compressor of an 11 L product is assumed.

As shown in Figure 10, two air compressors with the same compressor and different tank capacities have the same air supply limit pressure. The air supply capacity at a certain tank pressure is proportional to the rotation speed and inversely proportional to the tank capacity.

Therefore, if the controller has base data in advance (correlation data between tank pressure and tank pressure change rate during pumping for a product with a motor of 2500 min ^-1 and a tank capacity of 16 L), the current air supply capacity of the air compressor can be calculated by using this base data as a reference and correcting it with the tank capacity and motor rotation speed.

Next, a restart pressure acquisition process is performed (S31 in FIG. 11).
In this process, a calculation process for acquiring the restart pressure (consumption linked) is performed (S601 in FIG. 17). FIG. 17 is a flow chart showing a subroutine of the restart pressure acquisition process (S31) in FIG.

In the calculation process for acquiring the restart pressure (consumption-linked), the restart pressure (consumption-linked) is constantly calculated while the compressor is stopped, based on the tank pressure change rate, the minimum storage time, and the restart pressure lower limit. This calculation process can be expressed by the following formula (also see the chart in Figure 4). As mentioned above, the restart pressure has upper and lower limits (see Table 1).
Restart pressure (linked to consumption) = - tank pressure change rate x minimum storage time + restart pressure lower limit

Next, a stop pressure acquisition process is performed (S33 in FIG. 11).
In this process, calculation processes are performed to obtain the stop pressure (consumption-linked) and the stop pressure (minimum filling) respectively (S701 to S705 in FIG. 18). FIG 18 is a flow chart showing a subroutine of the stop pressure obtaining process (S33) in FIG.

In the calculation process for acquiring the stop pressure (consumption-linked) (S701 in FIG. 18), the stop pressure (consumption-linked) is calculated based on the air supply capacity, the tank pressure change rate, the minimum reserve time, and the restart pressure lower limit while the compressor is running. This calculation can be expressed by the following formula (also see the chart in FIG. 5). As mentioned above, the stop pressure has upper and lower limits (see Table 1).
Stop pressure (linked to consumption) =
- (Tank pressure change rate - Air supply capacity) x Maximum storage time + Restart pressure lower limit

In the calculation process to obtain the stop pressure (minimum filling) (S703 in FIG. 18), the following steps (1) to (4) are executed in order. Please also refer to the chart in FIG. 6.

(1) While the compressor is operating, the surplus pressure criterion, underpressure criterion, and restart pressure lower limit are constantly calculated (surplus pressure criterion ≧ underpressure criterion ≧ restart pressure lower limit).

The excess pressure criterion and the underpressure criterion are determined, for example, based on the following equation.
Excess pressure judgment standard = Restart pressure lower limit + 0.1MPa
Underpressure judgment standard = Restart pressure lower limit + 0.05MPa

(2) While the compressor is operating, the stop pressure (minimum fill) is updated, as well as the shortage time (time when pressure was insufficient) and the minimum tank pressure (used to calculate the minimum fill pressure).

The "stop pressure (minimum fill)" can be calculated based on the following formula:
Stop pressure (minimum filling) =
Minimum filling pressure + restart pressure (the restart pressure when the current operation is started)

The "minimum tank pressure" is updated by monitoring the tank pressure from the start of the current operation. In other words, the minimum tank pressure value during the current operation is used as the minimum tank pressure.

The "shortage time" can be obtained by counting the time that the tank pressure falls below the underpressure criteria while the compressor is operating.

(3) When the compressor is stopped, the minimum filling pressure is updated.
The initial value of the minimum filling pressure is provisionally set to, for example, 1.0 MPa.
In the process of updating the minimum filling pressure, first, the margin pressure is calculated based on the formula "margin pressure=minimum tank pressure value-surplus determination reference pressure".
If "margin pressure >0", the stop pressure (minimum filling) is calculated based on the following equation (3-1).
On the other hand, when the margin pressure is not greater than 0 but the "shortage time is greater than 0", the stop pressure (minimum filling) is calculated based on the following equation (3-2).

(3-1) If margin pressure > 0
Minimum filling pressure (new) =
Minimum filling pressure (old) - margin pressure x specified decompression gain (provisional lower limit 0.2MPa)
(3-2) elseif insufficient time>0
Minimum filling pressure (new) =
Minimum filling pressure (old) + shortage time x specified boost gain (temporary upper limit 1.0MPa)

"Minimum filling pressure (new)" is the minimum filling pressure used to calculate the stop pressure (minimum filling) for the current operating section.
"Minimum filling pressure (old)" is the minimum filling pressure used to calculate the stop pressure (minimum filling) in the previous operating section.

In this way, in this embodiment, the minimum filling pressure is increased or decreased depending on the margin of tank pressure during the previous operating period, and this is reflected in the stop pressure (minimum filling) for the current compression operation. Note that the present invention is not limited to this, and the minimum filling pressure may be increased or decreased depending on the margin of tank pressure during the current operating period, and this may be reflected in the stop pressure (minimum filling) for the current compression operation. This makes it possible to avoid air shortages more quickly.

(4) When the compressor starts operating, the shortage time and minimum tank pressure are reset, the minimum tank pressure is set to the current tank pressure, and the shortage time is set to 0.

This completes the calculation process (S703 in Figure 18) to obtain the stop pressure (minimum filling).

Next, an effective stop pressure determination process is carried out (S705 in FIG. 18).
In this process, a calculation is performed to adopt the higher of the first stop pressure "stop pressure (consumption linked)" and the second stop pressure "stop pressure (minimum filling)" as the effective stop pressure (the stop pressure that actually functions as an effective threshold). This calculation is performed based on the following formula.
Effective stop pressure = Max (stop pressure (consumption linked), stop pressure (minimum filling))

This completes the subroutine for the stop pressure acquisition process shown in Figure 18.

Next, the PFC/compressor control process is carried out (S35 in FIG. 11).
The following description will be given with reference to Fig. 19. Fig. 19 is a flow chart showing a subroutine of the PFC/compressor control process (S35) in Fig. 11.

The PFC/compressor control process first performs the compressor on/off decision process (S801 in FIG. 19). In this process, while the compressor is stopped, the tank pressure is compared with the restart pressure (consumption-linked), and if "tank pressure < restart pressure (consumption-linked)", it is decided to operate the compressor. Also, while the compressor is operating, the tank pressure is compared with the effective stop pressure, and if "tank pressure ≧ effective stop pressure", it is decided to stop the compressor.

Next, the PFC-ON/OFF control process is performed (S803).
In this process, the motor 13 that drives the compressor 11 is controlled. That is, when it is determined in the compressor operation/stop determination process (S801) that "the compressor is operated," the PFC control is turned on. On the other hand, when it is determined that "the compressor is stopped," the PFC control is turned off.

Next, the compressor motor drive control process is carried out (S805).
In this process, the motor 13 is driven based on the CS signal.

This completes the PFC/compressor control process (S35 in Figure 11).

1a...first outlet, 1b...first outlet, 2a...second outlet, 2b...second outlet, 1D...pressure adjustment knob, 2D...pressure adjustment knob, 1S...first outlet pressure sensor, 2S...second outlet pressure sensor, 1V...first pressure reducing valve, 2V...second pressure reducing valve, 11...compressor, 13...motor, 15...hall sensor, 17...tank, 19...tank pressure sensor, 20...operation panel, 21...outlet 1 pressure display, 22...outlet 2 pressure display, 23...tank pressure display, 25...power on/off button, 27...automatic on/off button, 29...panel MCU, 30...controller, 31...PFC circuit, 33...INV circuit, 35...controller MCU, 41...commercial power supply

Claims (4)

A compressor for compressing outside air to generate compressed air;
A motor for driving the compressor;
A tank for storing the generated compressed air;
a tank pressure sensor for measuring the tank pressure;
an outlet for extracting compressed air from the tank;
an outlet pressure sensor for measuring an outlet pressure;
a controller that stops the motor when the tank pressure reaches a stop pressure and restarts the motor when the tank pressure reaches a restart pressure,
An air compressor that performs motor control using either a first stop pressure or a second stop pressure as the stop pressure,
The controller:
Calculating a rate of change in the tank pressure from moment to moment based on the measured tank pressure, and varying the restart pressure and the first stop pressure based on the rate of change in the tank pressure;
Calculating the second stop pressure based on the restart pressure;
An air compressor , characterized in that the higher of the first stop pressure and the second stop pressure is adopted as an effective stop pressure . The controller:
The minimum filling pressure is increased or decreased depending on the margin of tank pressure during the previous operation period.
calculating the second stop pressure based on the restart pressure and the minimum fill pressure;
2. The air compressor according to claim 1 . The controller:
The minimum filling pressure will be increased or decreased depending on the margin of tank pressure during this operation period.
calculating the second stop pressure based on the restart pressure and the minimum fill pressure;
2. The air compressor according to claim 1 . The controller sets the lower restart pressure limit based on an outlet pressure.
4. An air compressor according to claim 1, wherein the air compressor is a compressor having a first and second valves .