OPERATION CONTROL DEVICE AND METHOD OF VACUUM PUMPS

Abstract

An operation control devices and operation methods thereof so as to eliminates the difficulties in such a case of introduction of vacuum sensors and/or inverter control is disclosed. The disclosure relates to a control of plural sets of vacuum pumps. In order to comply with the subjects to overcome the difficulties, the disclosure proposes to utilize current detection approach instead of direct pressure detection approach, while showing how to estimate a vacuum degree achieved under the operation of the pumps as well as presenting a method on the control of the number of pumps. It is also described how organically a current detecting device, a vacuum degree estimating device, a working pump control device and related methods to satisfy the subjects are linked. The usefulness of the disclosure is also revealed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in greater detail with reference to the preferred embodiments of the invention and the accompanying drawings, wherein:

FIG. 1 shows a whole constitution of the invention;

FIG. 2 is a figure sowing power (a current value) characteristic of a vacuum pump;

FIG. 3 illustrates a time chart as to an exemplary embodiment of the invention;

FIG. 4 illustrates a control flowchart as to an exemplary embodiment of the invention; and

FIG. 5 illustrates a prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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 made of.

FIG. 1 shows a whole constitution of the invention, wherein a vacuum tank 1 is depressurized by three vacuum pumps P_A, P_B and P_C. The vacuum pumps P_A, P_B and P_C are driven by motors M_A, M_B and M_C, respectively. There are placed electromagnetic open/close valves V_A, V_B and V_C between the vacuum tank 1 and each of the vacuum pumps P_A, P_B and P_C, respectively. Each of the vacuum pumps P_A, P_B and P_C is of a rotary displacement (volumetric) type such as of a scroll type or of a vane type, etc.

Each of the motors M_A, M_B and M_C is supplied with electricity from a power source 3. Since the speed control of each of the motors M_A, M_B and M_C is not performed, an inverter or the like is not prepared. Incidentally, each of the motors needs only to be an electric motor and the present invention is applicable to both AC motor and DC motor. In addition, a current-detecting means 5 detects the supplied current to each motor.

A control means 7 controls the operation and start/stop of the vacuum pumps P_A, P_B and P_C. The control means 7 includes a vacuum-degree-estimation means 9 to judge whether the current signal from the current-detecting means 5 reaches a threshold criterion value S which is set beforehand a target-vacuum value within a predetermined range and to judge whether the current signal from the current-detecting means 5 converges to the target vacuum (negative pressure) value with a predetermined span of time after the current signal reaches a threshold criterion value S, and a pump operation control means 11 to reduce the number of the pumps under operation when the vacuum-degree-estimation means 9 concludes that the threshold criterion value S or the target-vacuum value within a predetermined range is reached.

In case of the pump of a rotary displacement (volumetric) type such as of a scroll type or of a vane type, a power (current value) characteristic curve is shown as such a curve as in FIG. 2, wherein the curve includes a flat straight part and a mountain-shaped part, thereby the flat straight part corresponds to the current convergence by way of vacuum accomplishment and the mountain-shaped part means a large variation of the current.

Just after a commencement of depressurization of the vacuum tank 1, power (current value) is needed since the pumps have to compress and exhaust a high-pressure gas. In due course of depressurization process, the gas to be exhausted is disappears substantially. Therefore, the required power (current value) is lessened, while a negative pressure value in the vacuum tank converges to a substantially constant value less than or equal to 10² Pa to 10³ Pa.

By means of the aforementioned power (current) characteristics in such that the current value converges to a constant value P in connection with the depressurization process, the vacuum-degree-estimation means 9 judges whether the detected current reaches the aforementioned predetermined range from the constant value P minus α to the constant value P plus α, where α is allowance made for the fluctuation of measured values. The vacuum-degree-estimation means 9 also estimates the time when the detected current enters the range, namely, the time when the current reaches the aforementioned, predetermined-threshold-criterion value S. Further, the vacuum-degree-estimation means 9 concludes that the target vacuum (negative pressure) is completed, if the current is held within the range for a predetermined duration of time, for instance, several minutes.

On the other hand, the above constant value P is scheduled to be reset at a lower value as the operation hours of the vacuum pump P_A, P_B or P_C is accumulated. That is, the setting value P at the time of commissioning of the pumps is reduced to a value kP (P multiplied by a coefficient k) in such a manner that kP=0.9P, kP=0.8P and so on, where k is a parameter dependent of the operation hours of the vacuum pump P_A, P_B or P_C and k has a decreasing tendency in relation to increased operation hours.

More specifically, since a load demand for the vacuum pumps decreases gradually in proportion to the accumulated operation hours because of a running-in effect as to rotating and/or sliding wear-elements, a consideration for operation hours can give more accurate judgment on a vacuum-degree-completion. In addition, the consideration is given in such a manner that the aforementioned predetermined current range, whereby the threshold-criterion value S is regarded as reached, is lowered in connection with operation hours.

Judgment on whether the depressurized pressure reaches the threshold criterion value S, which is set beforehand the target-vacuum value, or the target-vacuum value is made by detecting the current to each of the motors M_A, M_B and M_C which drives each of the vacuum pumps P_A, P_B and P_C respectively. Therefore, the present invention can do without conventionally applied vacuum sensors for pressure detection of a vacuum tank and the present invention makes it possible to restrain equipment costs and brings a remarkable cost effectiveness especially in case in which special sensors of a dust-free type and/or a waterproof type are required, depending on the service condition as to a vacuum tank or a vacuum facility room.

When the depressurized pressure reaches the threshold criterion value S, which is set beforehand the target-vacuum value, the target-vacuum can be realized without operation of an unnecessary pump because the gas to be exhausted is reduced. When the target vacuum has been realized, the vacuum state can be held without operation of an unnecessary pump. Accordingly, it becomes possible to decrease the number of plural working vacuum pumps, to reduce the amount of power consumption as a result and to prolong maintenance intervals by stopping the operation of an unnecessary pump. In the control for operation and start/stop of the pumps, speed control equipment such as inverters and the like is not provided. Therefore, undesirable effects on surrounding equipment due to inverters are avoidable.

In succession, with reference to the time chart of FIG. 3 and the flowchart of FIG. 4, the explanation will be given about how the pump operation control means 11 reduces the number of the pumps under operation when the vacuum-degree-estimation means 9 concludes that the depressurized pressure reaches the threshold criterion value S.

As shown in FIG. 4, all the vacuum pumps P_A, P_B and P_C are under operation at the beginning (S1) and the vacuum pump P_A is chosen as a pump to be watched, and the current I_A thereof is monitored (S2). Whether the current I_A is within a range of P−α≦|_A≦P+α is judged (S3) and, in case in which the judgment is YES (affirmative), whether the duration thereof is not less than a predetermined time span t₀ is further judged (S4). If the judgment is YES (affirmative) in succession, then the target-vacuum is regarded as realized and the vacuum pumps P_B and P_C are stopped, while only the operation of the pump P_A is continued (S5).

It can be allowed to stop the vacuum pumps P B and P_C, without the judgment on whether the duration of the condition S4 is not less than a predetermined time span to, when it is judged whether the current I_A is within a range of P−α≦|_A≦P+α (S3) and the judgment is YES (affirmative), namely, when the depressurized pressure reaches the threshold criterion value S.

And while the monitoring of the current I_A is continued, whether I A exceeds P+α because of the deterioration of the vacuum state is judged (S6). If the I A becomes greater than P+α, then all the vacuum pumps P_A, P_B and P_C are operated again (S7). In succession, the pump to be monitored is shifted to the vacuum pumps P_B(S8) and the vacuum state is watched in such a manner that the current I_B for the pump P_B is watched by the same approach as the above-mentioned vacuum pump P_A is watched. In case in which the vacuum pump P_B is designated as the pump to be monitored, the pumps to be stopped are shifted to the pumps P_A and P_C and the only pump to be operated is shifted to the pump P_B(S9).

In the next stage, the pump to be watched is shifted to the vacuum pump P_C (S10), and the vacuum state is monitored watched in the same approach as the case where a vacuum pump P_A is used as a pump to be watched. In case where the vacuum pump P_C is designated as the pump to be watched, the pumps to be stopped are shifted to the pumps P_A and P_B and the only pump to be operated is shifted to the pump P_C (S11).

Therefore, as shown in FIG. 4, a pump operation control means 11 is constituted so that the control means 11 shifts a control step by a control step in such a manner that a control step A in the case where the vacuum pump P_A is used as a pump to be watched, a control step B in the case where the vacuum pump P_B is used as a pump to be watched, and a control step C in the case where the vacuum pump P_C is used as a pump to be watched.

A time chart of FIG. 3 shows the situation of the shifting, namely, a shift-circulation. After the pump P_A is started-up as a first pump to be operated, the pumps P_B and P_C are started with predetermined time-delays. And all the pumps are placed under operation. The time delays are provided in order to evade a large load, that is, an over-current due to the simultaneous starting of plural pumps.

A mark L in FIG. 3 means a point of time when the threshold criterion value S or the target-vacuum value is reached and the pumps other than the pump under watch are stopped. A mark M means a point of time when a detected current value goes out of the aforementioned predetermined range and, therefore, the pumps under suspension are now be restarted. The control action at the marks L or M is repeated also in case when the pump under watch is the pump P_B or P_C.

Moreover, in a case where any one of the vacuum pumps P_A, P_B and P_C is unable or difficult to be operated, the operation of the pump unable or difficult to be operated is skipped and the other next pump is designated as a pump to be watched. For instance, when the pump P_B is out of order or under maintenance, the pump to be monitored is shifted from the pump P_A to the pump P_C.

Furthermore, the electromagnetic open/close valves V_A, V_B and V_C are provided so as to hinder high pressure gas from flowing-back inside the vacuum tank by the vacuum pumps P_A, P_B and P_C. The valve V_A, V_B or V_C is opened respectively after the vacuum pumps P_A, P_B or P_C starts running.

In addition, it is not always necessary to stop simultaneously all the active pumps other than the pump under watch. It can be allowed to stop the pumps one by one so as to evade rapid change in pump-loads. Also, depending on the vacuum-degree requirement, it can be allowed to stop some pumps out of all the pumps other than the pump under watch.

In the above description on the embodiments, explanation has been given based on an example of three pumps. It goes without saying that the explanation stands in case of plural pumps such as a case of two pumps, four pumps and/or more pumps.

As mentioned above, by a method of controlling plural vacuum pumps, including the steps of designating a pump under watch, stopping the pumps other than the pump under watch and shifting the pump under watch one by one among the whole pumps, can be evaded a disadvantage that the operation unevenness among the plural pumps is incurred as a result of working a specific pump all the time and keeping the other pumps under suspension. Therefore, plural pumps are evenly employed and maintenance work for each pump is equalized. Thus, the increase in efficiency of maintenance work can be promoted.

The present invention eliminates the difficulties in such a case of introduction of vacuum sensors and/or inverter control. In addition, the present invention realizes the operation of plural vacuum pumps wherein the increase of facility costs is restrained, the maintenance frequency is reduced and the man-hour of repair work is lessened. As a conclusion, the present invention can be applicable to operation control devices and operation methods for plural vacuum pumps.

Claims

1. An operation control device of plural vacuum pumps for depressurizing gas inside at least one tank and/or chamber and so on, comprising: a current detecting means which detects a current flowing in a motor that drives the vacuum pumps; anda control means which reduces the number of the vacuum pumps under operation, while judging whether a target vacuum and/or substantially vacuum condition is reached, based on the situation that a current value detected by said current detection means converges within a predetermined range.

2. The operation control device of claim 1, wherein the control means further comprises a vacuum-degree-estimation means to judge that a threshold criterion value is reached when a current value of the motor under watch reaches the predetermined range, the threshold criterion value being predetermined in advance of a target-vacuum value and to conclude that said target-vacuum value is reached in case when the current value stays within the predetermined range for a predetermined span of time after the threshold criterion value is reached; wherein when the vacuum-degree-estimation means concludes that the threshold criterion value or the target-vacuum value within the predetermined range is reached, the number of the pumps under operation is reduced.

3. The operation control device of claim 1, wherein the target-vacuum value within the predetermined range is reset at a lower value as an operation hours of the vacuum pumps is accumulated.

4. The operation control device of claim 2, wherein the control means further comprises a pump operation control means; which designates one of the plural pumps as a pump under watch, stops at least one pump other than the pump under watch when said vacuum-degree-estimation means concludes, based on a current value of the motor driving the pump under watch, that said threshold criterion value or said target-vacuum value within the predetermined range is reached and shifts the pump under watch evenly one by one among the whole pumps.

5. The operation control device of claim 4, wherein in a case where any one of the vacuum pumps is unable or difficult to be operated, the operation of the pump unable or difficult to be operated is skipped and the other next pump is designated as a pump under watch.

6. An operation control method for plural vacuum pumps for depressurizing a gas inside at least one tank and/or chamber, comprising the steps of: detecting a current flowing into a motor that drives the vacuum pumps; andreducing the number of the vacuum pumps under operation, while judging whether a target vacuum and/or substantially vacuum condition is reached, based on the situation that a current value detected by said current detection means converges within a predetermined range.

7. The operation control method of claim 6, further comprising the steps of: designating one of the plural pumps as a pump under watch; judging that a threshold criterion value is reached when a current value of the motor under watch reaches the predetermined range, the threshold criterion value being predetermined in advance of a target-vacuum value; concluding that said target-vacuum value is reached in case when the current value stays within the predetermined range for a predetermined span of time after the threshold criterion value is reached; stopping at least one pump other than the pump under watch when it is concluded that said threshold criterion value and/or said target-vacuum value within the predetermined range is reached, based on a current value of the motor driving the pump under watch; and shifting said pump under watch evenly to the other next pump one by one among the whole pumps.