Method of controlling a plurality of compressors

Abstract

Compressed gases are gathered from a plurality of compressors and employed if required. A pressure of compressed gas thus gathered is measured by a pressure sensor to generate a pressure signal, which is transmitted to a control. The signal is transmitted from the control to electromagnetic switches to control motors for the compressors to determine which of the compressors run.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of controlling a plurality of compressors.

[0002] Japanese Patent No. 2,875,702 discloses a method of controlling a plurality of compressors in a system in which compressed gases from a plurality of compressors are gathered into a pressure tank of which a required compressed gas is taken out.

[0003] When compressed gases outputted from compressors are supplied into a pressure tank of which the compressed gas is taken out in use, the compressors frequently start and stop, which results in failure in the compressors and burning damage in a motor if difference in pressure between the upper and lower limits is small.

[0004] Accordingly, with increase in the volume of the pressure tank, the upper limit of pressure is kept to 0.2 MPa higher than used pressure to increase difference between the upper and lower limits.

[0005] However, in this method, it operates for a long time to increase driving power thereby increasing running costs. The compressors are continuously operated at a high pressure to cause decrease in lives of the compressors.

[0006] Furthermore, rotation speed of the compressor is set depending on high upper limit pressure and it is necessary to decrease rotation speed during normal operation. So it operates with decreased amount of air, thereby decreasing efficiency of the compressors.

[0007] The compressors are cooled with cooling fans driven at low rotation speed thereby decreasing cooling effect. Thus, it causes decrease in lives of tip seals and bearings.

SUMMARY OF THE INVENTION

[0008] In view of the above disadvantages, it is an object of the invention to provide a method of controlling operation of compressors to increase the number of the compressors operated at low pressure closer to the lower limit and to decrease the number of the compressors operated at higher temperature closer to the upper limit, time for operation being decreased to decrease running costs to improve the lives of the compressors, tip seals and bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The above and other features and advantages of the invention will become more apparent from the following description with respect to embodiment as shown in appended drawings wherein:

[0010] FIG. 1 is a view which shows one embodiment of the present invention; and

[0011] FIG. 2 is a graph which shows a change in pressure to compressors in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] FIG. 1 illustrates one embodiment of the present invention.

[0013] Compressed gases, such as compressed air, outputted from a plurality of compressors are gathered into a pressure tank. A required amount of compressed air is taken out of the pressure tank and employed. The compressed gases are not always gathered into the pressure tank, but may be taken out of conduits directly.

[0014] In the embodiment as shown in FIG. 1, eight compressors 1 comprising C1 to C8 are driven by motors 2 comprising M1 to M8 respectively, Electromagnetic switches 3 comprising E1 to E8 turn the motors M1 to M8 on and off respectively.

[0015] At exits of the compressors 1, check valves 4 comprising V1 to V8 are provided to prevent running back of compressed air from the compressors 1 Compressed air through the check valves 4 is all fed into a pressure tank 5, of which compressed air used in an object 7 is taken out by opening and shutting a valve 6. To keep compressed air in the pressure tank 5 at a desired pressure, the compressors 1 are controlled on the basis of feedback by determination of compressed air in the pressure tank 5.

[0016] Pressure of compressed air in the pressure tank 5 is measured by a pressure sensor 8 to generate a pressure signal which is transmitted to a control 9 which has a determining portion 10 for determining the number of operating compressors and a selecting portion 11 for starting and stopping any of the compressors. Based on the pressure signal measured by the pressure sensor 8, the determining portion 10 determines the number of the operating compressors 1. Generally, the operating compressors are determined depending on the pressure signal between predetermined upper and lower limits.

[0017] In a preferred embodiment, each of the compressors 1 has approximately the same capability, and the pressure between the upper and lower limits are divided into pressure levels which are equal to the compressors 1 in number. The measured pressure signal is out of desired pressure level and reaches to the boundary of the pressure levels, thereby changing the number of the operating compressors 1.

[0018] Specifically, the measured pressure signal increases and reaches to pressure level higher than desired pressure level by one stage. Then, the number which is subtracted by one from the number of the operating compressors 1 is determined as a new number of operating compressors. Meanwhile, the pressure signal decreases and reaches to pressure level lower than desired pressure level by one stage. Then, the number which is added by one to the number of the operating compressors 1 is determined as a new number of operating compressors.

[0019] A signal of the number determined in the determining portion 10 is transmitted to the selecting portion 11 that selects which compressors start or stop. The selection is carried out with predetermined order of starting and stopping. Preferably, numeric order may be allotted to the compressors 1 which start and stop in the order. By the numeric order, any of the compressors 1 equally start and stop to avoid disadvantage that a specific compressor frequently starts and stops or is operating for a long time.

[0020] When the compressor 1 which starts or stops is selected in the selecting portion 11, a signal is transmitted to the operating portion 12 from which it is transmitted to the electromagnetic switches 3 which turn on or off power sources to the corresponding motors 2, so that the compressors 1 selected in the selecting portion 11 start or stop.

[0021] FIG. 2 is a graph that illustrates changes in pressure to the operating compressors 1 when the eight compressors 1 such as C1 to C8 are controlled. Compressed air in the pressure tank 5 between the lower limit such as 0.6 MPa and the upper limit such as 0.7 MPa is divided in pressure into eight stages which are equal to the compressors 1 in number to determine each pressure level. The lower and upper limits are set to level 0 and level 8/8 respectively, and 1/8 to 8/8 are set therebetween by dividing equally. Also, for example, desired pressure levels are set to 1/8 to 2/8. Continuous Nos. 1 to 8 are allotted to the eight compressors 1.

[0022] As shown in FIG. 2, first, until a pressure signal 13 measured by the pressure sensor 8 becomes the pressure level 1/8, the eight compressors 1 all run. Pressure rises, the pressure level reaches 1/8 at P1 beyond the lower limit 0, and a stop signal is transmitted from the control 9 to the electromagnetic switch E1 of the compressor No.1 (C1) via the operating portion 12 to stop the compressor No.1. The seven compressors Nos. 2 to 8 still run.

[0023] Pressure rises without compressed air to reach the pressure level 2/8 at P2, and then a stop signal is transmitted to the electromagnetic switch E2 for the compressor No.2 (C2) from the control 9 via the operating portion 12 to stop the compressor No.2. The six compressors Nos. 3 to 8 still run.

[0024] Pressure rises slightly without compressed air. Before it becomes the next pressure level 3/8, compressed air is used and the pressure level falls to 1/8 at P3, and a start signal is transmitted from the control 9 to the electromagnetic switch E1 for the compressor No.1 (C1) which initially stops, via the operating portion 12, so that the compressor No.1 starts. Thus, the seven compressors No.1 and Nos. 3 to 8 still run.

[0025] With compressed air, the pressure level falls, but does not reach 0. Thereafter, compressed air is not used, and pressure reaches to 2/8 at P4 again beyond the pressure level 1/8. A stop signal is transmitted to the electromagnetic switch E3 for the compressor No.3 (C3) from the control 9 via the operating portion 12. Thus, the six compressors No.1 and Nos.4 to 8 still run.

[0026] Compressed air is not used and the pressure level rises to 3/8 at P5. A stop signal is transmitted from the control 9 to the electromagnetic switch E4 for the compressor No.4 (C4) via the operating portion 12 to stop the compressor No.4. The five compressors No.1 and Nos. 5 to 8 still run.

[0027] Compressed air is not used and pressure rises, so that the pressure level reaches to 4/8 at P6. A stop signal is transmitted from the control 9 to the electromagnetic switch E5 for the compressor No.5 (C5) via the operating portion 12 to stop the compressor No.5. The four compressors No.1 and Nos. 6 to 8 still run.

[0028] Compressed air is not used and pressure rises, so that the pressure level reaches to 5/8 at P7. A stop signal is transmitted from the control 9 to the electromagnetic switch E6 for the compressor No.6 (C6), which stops. The three compressors Nos. 1, 7 and 8 still run.

[0029] Compressed air is not used, and pressure rises, so that the pressure level reaches to 6/8 at P8. A stop signal is transmitted from the control 9 to the electromagnetic switch E7 for the compressor No.7 (C7) via the operating portion 12 to stop the compressor No.7. The two compressors Nos. 1 and 8 still run.

[0030] Compressed air is not used and the pressure level rises, so that the pressure level reaches to 7/9 at P9. A stop signal is transmitted from the control 9 to the electromagnetic switch E8 for the compressor No.8 (C8) via the operating portion 12 to stop the compressor No.8. Only the compressor No.1 still runs.

[0031] Compressed air is not used and pressure rises, so that the pressure level reaches to 8/8 at P10. A stop signal is transmitted from the control 9 to the electromagnetic switch E1 for the compressor No.1 (C1), which stops. All the compressors do not run.

[0032] While compressed air is used and the pressure level falls below 7/8, all the compressors do not run yet.

[0033] Compressed air is used and the pressure level falls to 7/8 at P11. A start signal is transmitted from the control 9 to the electromagnetic switch E2 for the compressor No.2 (C2) which secondly stops, via the operating portion 12, to start the compressor No.2. The seven compressors No. 1 and Nos. 2 to 8 do not run yet.

[0034] Compressed air is used, and the pressure level falls to 6/8 at P12. A start signal is transmitted from the control 9 to the electromagnetic switch E3 for the compressor No.3 (C3) which thirdly stops, via the operating portion 12, to start the compressor No.3. The compressors No. 1 and Nos.4 to 8 do not run yet.

[0035] Compressed air is used and the pressure level falls to 5/8 at P13. A start signal is transmitted from the control 9 to the electromagnetic switch E4 for the compressor No.4 (C4) which stops fourthly, via the operating portion 12 to start the compressor No.4. The five compressors No.1 and Nos. 5 to 8 do not run.

[0036] Compressed air is used and the pressure level falls to 4/8 at P14. A start signal is transmitted from the control 9 to the electromagnetic switch E5 for the compressor No.5. (C5) which stops fifthly, via the operating portion 12 to start the compressor No.5. The compressors No.1 and Nos.6 to 8 do not run yet.

[0037] Compressed air is used and the pressure level falls to 3/8 at P15. A start signal is transmitted from the control 9 to the electromagnetic switch E6 for the compressor No. 6 (C6) which stops sixthly, via the operating portion 12 to start the compressor No.6. The three compressors Nos. 1, 7 and 8 do not run.

[0038] Compressed air is used and the pressure level fall to 2/8 at P16. A start signal is transmitted from the control 9 to the electromagnetic switch E7 for the compressor No.7 (C7) which stops seventhly, via the operating portion 12 to start the compressor No.7. The two compressors Nos. 1 and 8 do not run yet.

[0039] Compressed air is used and the pressure level fall to 1/8 at P17. A start signal is transmitted from the control 9 to the electromagnetic switch E8 for the compressor No.8 (C8) which stops eighthly, via the operating portion to start the compressor No.8. Only the. compressor No. 1 does not run yet.

[0040] Compressed air is used and the pressure level falls to 0/8 at P18. A start signal is transmitted from the control 9 to electromagnetic switch E1 for the compressor No.1 (C1) which stops ninthly, via the operating portion 12 to start the compressor No.1. All the compressors Nos. 1 to 8 run, and there is no compressor that does not run.

[0041] The foregoing merely relate to embodiments of the invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein:

Claims

1. A method of controlling a plurality of compressors, comprising the steps of:

gathering compressed gases outputted from said plurality of compressors which have approximately the same capability;

measuring pressure of a compressed gas thus gathered to transmit a pressure signal to control said plurality of compressors;

dividing the pressure of the compressed gas between upper and lower limits into a plurality of pressure levels which are equal in number to said compressors; and

determining which of the compressors run when the pressure signal reaches the boundary of said pressure levels.

2. A method as claimed in claim 1 wherein the compressed gases are gathered into a pressure tank from said plurality of compressors.

3. A method as claimed in claim 1 wherein the pressure of the gathered compressed gas is measured by a pressure sensor to generate a pressure signal.

4. A method as claimed in claim 1 wherein the compressed gas is air.

5. A method as claimed in claim 1 wherein the pressure signal is transmitted to a control which has a determining portion for determining the number of operating compressors and a selecting portion for starting and stopping any of the compressors.

6. A method as claimed in claim 5 wherein the pressure signal is transmitted from the control to electromagnetic switches via an operating portion, said electromagnetic switches being connected to motors for said compressors to turn on and off said compressors.

7. A method as claimed in claim 1 wherein the pressure rises to an upper pressure level to decrease the number of operating compressors, while the pressure falls to a lower pressure level to increase the number of operating compressors.

8. A method as claimed in claim 1 wherein continuous numbers are allotted to said plurality of compressors, any of the compressors being started and stopped in order of the numbers to change the number of operating compressors.