Patent Application
20080080984
The present invention will now be described in greater detail with reference to the preferred embodiments of the invention and the accompanying drawings, wherein:
Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component described in these embodiments shall be only for explanation and shall not be construed as limiting the scope of the invention thereto, unless any specific mention is placed.
As shown in
The mechanical booster pump 5 is of a claw type vacuum pump 9, comprising a pair of pump rotors 11a and 11b, a gas suction port 13, and a gas discharge port 15. The mechanical booster pump 5 further comprise a pump casing (a housing) 17; wherein the pair of pump rotors 11a and 11b are built-in, and a rotating mechanism; wherein shafts 19 rotates the pump rotors 11a and 11b by transferring powers from a motor (not shown) as a power source to the rotors. In addition, the type of the exterior side vacuum pump 3 is not limited to a Roots-type and can be any other type of vacuum pumps such as a claw type, a screw type, a gear type and so on.
While the above-mentioned rotating mechanism makes the pump rotors 11a and 11b rotate in a reverse direction each other (as shown with the arrows S in
The pump rotors 11a and 11b have protrusive parts 21a and 21b like a claw (a nail of raptorial birds) respectively. And the protrusive parts 21a and 21b fit into counter-depressed parts 23b and 23a respectively. Thus, the fitting space forms a compression space 25.
The gas discharge port 15 has two openings, namely, a discharge opening for discharging a low compression gas (a DOLC) 27 and a discharge opening for discharging a high compression gas (a DOHC) 29. The DOLC 27 discharges the gas compressed within the mechanical booster pump at a stage of a lower compression ratio, while the DOHC 29 discharges the gas when a stage of a higher compression ratio is realized. In addition, the DOLC 27 is placed so that the gas inhaled through the gas suction port 13 is discharged before the gas is compressed into a compression space 25 formed by the pump rotors 11a and 11b. Further, the DOLC 27 is comprised of a first discharge opening for discharging a low compression gas 27a corresponding to the pump rotor 11a and a second discharge opening for discharging a low compression gas 27b corresponding to the pump rotor 11b.
In addition, while the cross-sectional area of the first discharge opening for discharging a low compression gas 27a is the same as that of the second discharge opening for discharging a low compression gas 27b, the cross sectional area of the openings 27a and 27b is formed more greatly than the cross-sectional area of the DOHC 29.
As shown in
Moreover, as shown in
Thus, by forming a discharge port on a casing-wall-surface vertical to the axes of the pump rotors 11a and 11b and on a casing-wall-surface parallel to the plane containing both axes of the pump rotors 11a and 11b, a mechanical booster pump 5 provided with a DOHC 29 and a DOLC 27 can be composed.
On a first low compression discharge passage 30 which communicatively connects the first discharge opening for discharging a low compression gas 27a and the exterior side vacuum pump 3, is provided an open/close valve 34, the opening/closing of which is controlled by the a controller 32. On the other hand, a second low compression discharge passage 36, which feeds the gas through the second discharge opening for discharging a low compression gas 27b, flows into the first low compression discharge passage 30 at the up-stream side of the valve 34. Moreover, a high compression discharge passage 38, which feeds the gas through the discharge opening for discharging a high compression gas 29, flows into a passage 30 at the down-stream side of the valve 34. Thus, the passages 30, 36 and 38 meet together and feed the gas toward the exterior side vacuum pump 3.
Here, an explanation as to the controller 32 will be given.
Pressure signals from the vacuum tank 7 or inlet pressure signals from the mechanical booster pump 5 are inputted into a controller 32 via a pressure sensor 40, and elapsed-time signals are inputted into the controller 32 from a timer 42.
At the beginning of gas discharging, the open/close valve 34 is opened, the exterior side vacuum pump 3 is started, and the mechanical booster pump 5 is consecutively started. In this way, the discharged gas from the first discharge opening for discharging a low compression gas 27a, the second discharge opening for discharging a low compression gas 27b, and/or the DOHC 29 is sent to the exterior side vacuum pump 3 through the first low compression discharge passage 30, the second low compression discharge passage 36, and/or the high compression discharge passage 38 respectively.
At a stage of operation wherein all the passages mentioned above are communicatively opened, a large amount of gas is discharged from the mechanical booster pump 5. The reason is that, at the stage mentioned above, the value of compression ratio is kept lower, and the discharging capability of the exterior side vacuum pump 3 is not deteriorated. Namely, the discharging resistance of the mechanical booster pump is restrained, and an increased pumping speed (discharging speed) is attained. And the exterior side vacuum pump 3 realizes a possible ultimate pressure (of medium vacuum) based on the capability of the exterior side vacuum pump 3 itself regarding compression action.
Thus, while the medium vacuum is realized without a deteriorated pumping speed, in a pressure range to the ultimate pressure of the exterior side vacuum pump 3, the power loss as well as the heat loss in the mechanical booster pump 5 can be reduced because of the lower compression ratio.
In a second stage, the controller 32 closes the open/close valve 34 by an input signal from the pressure sensor 40, when a predetermined ultimate pressure based on the capacity of the exterior side vacuum pump 3 is reached. Thus, a discharge from the first discharge opening for discharging a low compression gas 27a as well as from the second discharge opening for discharging a low compression gas 27b is intercepted, and the discharge only from the DOHC 29 remains. As a result, a differential pressure by the compression action of the compression space 25 in the mechanical booster pump 5 can be generated, and the mentioned differential pressure is added to the medium vacuum generated based on the capability of the exterior side vacuum pump 3. Consequently, a high vacuum, thereof pressure is lower than a pressure of the medium vacuum, can be attained.
When the medium vacuum is attained based on the capability of the exterior side vacuum pump 3, since the vacuum gas is substantially thin, an additional discharge through the compression space 25 in the mechanical booster pump 5 can bring a high vacuum without the difficulties of power loss or heat loss, whereas the difficulties can arise in case when a discharge is performed only through the DOHC 29 from an ambient pressure condition.
Then, the open/close valve 34 is closed, the differential pressure by a compression action of the compression space 25 of a mechanical booster pump 5 is added to the medium vacuum so as to lower a medium vacuum pressure. In this manner, a pressure P2 of a high vacuum condition is realized.
As described above, according to an embodiment of the present invention, by using a mechanical booster pump 5 provided with a discharge opening for discharging a low compression gas (a DOLC) 27, which discharges a gas of low compression ratio, and a discharge opening for discharging a high compression gas (a DOHC) 29, which discharges a gas of high compression ratio, an ultimate pressure is lowered and a high vacuum can be attained while a pumping speed is secured.
Next, an explanation on a second embodiment will be given.
In this second embodiment, an elapsed time signal from a timer 42, instead of a pressure signal from a pressure sensor 40, switches an open/close condition of the open/close valve 34.
A time t0 is defined as the time of beginning of gas discharging into the exterior side vacuum pump 3; through all the passages of the first low compression discharge passage 30, the second low compression discharge passage 36, and the high compression discharge passage 38 after the open/close valve 34 is opened, the exterior side vacuum pump 3 is driven, and further the mechanical booster pump 5 is driven.
A time t1 is defined as a time span in which the pressure of gas decreases from an ambient pressure P0 to a pressure P1 (medium vacuum pressure) on the condition that all the passages 30, 36 and 38 are fully communicatively open. Here, the time span (t1 minus t0) is to be predetermined by calculation based on the volume of the vacuum tank 7, the discharging capacity (swept volume) of the exterior side vacuum pump 3, the discharging capacity of the mechanical booster pump 5, driving conditions of each pump, the ambient temperature and so on.
When the controller recognizes, with a signal from the timer 42, that the time (t1 minus t0) has passed from the time t0, the open/close valve 34 is closed. Then, with the aid of a differential pressure due to the compression action of the compression space 25 of a mechanical booster pump 5, a lower pressure, namely, the high vacuum is realized at the time t2.
The second embodiment, as well as the first embodiment, makes it possible to improve the ultimate pressure toward a lower pressure, that is, to attain the high vacuum without deteriorating the pumping speed.
Moreover, in case of the use of the pressure sensor 40, because of dust, refuse particles, or water droplet in the vacuum tank 7 or gas passages, there is a risk of clogging and/or deterioration of the sensor 40, both of which can cause incorrect pressure detection. On the other hand, in case of the use of the timer 42, there is no difficulty of detection failure or deterioration. Therefore, highly reliable control can be performed.
In addition, in the first and second embodiments described above, it is explained that the controller 32 automatically opens and closes the open/close valve 34. However, as a matter of course, operators can manually open and closes the valve 34, based on their own judgment as to the values detected by the pressure sensor 40.
As for the mechanical booster pump 5, the explanation was given in consideration that the mechanical booster pump 5 is of a claw type vacuum pump 9. However, it goes without saying that the mechanical booster pump 5 can be of a Roots type pump or of a screw type pump other than of a claw type pump, so long as the mechanical booster pump 5 is provided with the DOLC 27 which discharges the gas of low compression ratio and the DOHC 29 which discharges the gas of high compression ratio.
Moreover, it should be noted that the explanation was given in consideration that the gas as a medium is any one of general gases including a specific gas such as air.
The present invention discloses an evacuation apparatus for evacuating a tank, a chamber and the like, wherein a mechanical booster pump is provided at the up-stream side of an exterior side vacuum pump so as to utilize the performance of the exterior side vacuum pump and improve an ultimate pressure of the exterior side vacuum pump without deterioration of pumping speed. And the present invention can be usefully applied to evacuation apparatuses.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2006-270047 | Sep 2006 | JP | national |
