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:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an operation-control device and an operation-control method of vacuum pumps such as a scroll pump, a vane pump and the like, especially to a case where plural set of vacuum pumps are provided. 
         [0003]    2. Description of the Related Art 
         [0004]    In conventional operation-control methods for vacuum pumps such as a scroll pump, a vane pump and the like, a frequency control by an inverter is introduced and the speed of an AC motor which drives a vacuum pump is controlled by using a signal of a pressure-sensor detecting a pressure of gas inside a vacuum tank to be depressurized. As for a pump load control by means of an inverter, a prior art, for instance, such as JP-A-H9-4591/1997 (hereafter, referred to as a patent document 1) has been known. 
         [0005]    As shown in  FIG. 5 , in the patent document 1 is illustrated a control-step constitution, wherein the speed of an AC motor  04 , which drives a vacuum blower (vacuum pump)  03  connected to a vacuum tank  01 , is controlled by a frequency converter (inverter)  05 , and the speed is increased when the operation differential pressure of the pump decreases and demand power goes down, while the speed is decreased when the operation differential pressure of the pump increases and demand power goes up; so that the input power poured into the motor driving the pump is kept constant. Further, the pressure P inside the vacuum tank  01  is detected for the estimation of vacuum condition. 
         [0006]    In the conventional operation-control approaches for the vacuum pump as shown in the patent document 1, a pressure (vacuum) sensor is used for estimating the vacuum condition, since the vacuum condition in the tank  01  is detected as pressure P. In case when dust and/or water droplets in the tank or the vacuum facility room adhere to the probe of the sensor, it is afraid that the signals are not accurate and unexpected failure may happen. Thus, special sensors of a dust-free type and/or a waterproof type are required in order to prevent the invasion of dust and/or water droplet. Consequently, there arises a problem of cost increase as to equipment and/or facility. 
         [0007]    Furthermore, a speed control inverter always accompanies electronic noise which causes undesirable problems to the surrounding electrical/electric equipment if it is nearby the inverter. 
         [0008]    On the other hand, in case where a constant vacuum condition is needed, for instance, in case where a highly depressurized vacuum condition is required in a vacuum chamber of semiconductor production devices, plural sets of vacuum pumps are provided. And even when one of the pumps is out of service due to failure or maintenance and exhaust ability is lessened, the remaining pumps hold the predetermined required vacuum condition. 
         [0009]    However, driving plural sets of pumps results in an increase of power consumption and maintenance costs. Furthermore, providing plural pumps may increase failure frequency of the pumps, maintenance frequency of the pumps along with affiliated facility and man-hours for repairing. 
       SUMMARY OF THE INVENTION 
       [0010]    In view of the above-stated background, the present invention is aiming at: eliminating the difficulties in such a case of introduction of vacuum sensors and/or inverter speed control; realizing 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; and providing an operation control device and an operation control method which are compatible with the just-stated aims. 
         [0011]    In order to resolve the problems mentioned above, the present invention provides an operation control device of plural vacuum pumps for depressurizing a gas inside at least one tank and/or vacuum facility room and so on, including: a current detecting means which detects a current flowing in a motor that drives the vacuum pumps; and a control means which reduces the number of the vacuum pumps actually under operation, while judging whether a target vacuum or substantially vacuum condition is reached, based on a situation that a current value detected by the current detection means converges within a predetermined range. 
         [0012]    According to the present invention, the current flowing in the motor is detected, and it is judged that a target vacuum or substantially target vacuum condition is realized when the current value converges within a predetermined range. Therefore, it is not necessary to provide with vacuum sensors for pressure detection of a vacuum tank as conventionally used, so that equipment costs can be restrained and a remarkable cost effectiveness can be obtained, especially in case where 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. 
         [0013]    Since the gas to be exhausted is reduced when a target vacuum or substantially target vacuum condition is realized, it is possible to hold the vacuum condition or to reach the target vacuum condition without operation of an unnecessary pump. Therefore, 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 effect due to inverters on surrounding equipment is avoidable. 
         [0014]    According to another constitution of the present invention, the control means of the operation control device further includes 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; in which 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. 
         [0015]    The another constitution of the above mentioned makes it possible to decrease the number of plural working vacuum pumps and to reduce the amount of power consumption as a result, because the target vacuum can be reached without large current after the depressurized pressure reaches the threshold criterion value. In addition, it is made possible that the number of pumps and the amount of power consumption are reduced after surely estimating that the target vacuum (negative pressure) is reached when the detected current stays for a predetermined span of time in the predetermined range. 
         [0016]    According to another aspect of the present invention, the target-vacuum value within the predetermined range is reset at a lower value as the operation hours of the vacuum pumps are prolonged. 
         [0017]    By the above constitution, more accurate judgment on a vacuum-degree-completion is carried out, while the operation hours are taken into consideration. Here, the consideration is given in such a manner that the aforementioned predetermined current range, whereby the threshold-criterion value is regarded as reached, is lowered in connection with operation hours. In addition, the reason of this lowering is that 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. 
         [0018]    Another aspect of the present invention is characterized in that the operation control device includes a pump operation control means, which designates one of the plural pumps as a pump under watch, stops at least one of the pumps other than the pump under watch when the vacuum-degree-estimation means concludes, based on a current value of the motor driving the pump under watch, that the threshold criterion value or the target-vacuum value within the predetermined range is reached and shifts the pump under watch evenly one by one among the whole pumps. 
         [0019]    According to a method of the present invention of controlling plural vacuum pumps, the method includes 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; thereby such operation manner can be evaded that a specific pump is always working, the other pumps are kept under suspension, and the operation unevenness among the plural pumps is incurred as a result. 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. 
         [0020]    Another constitution of the present invention is characterized in that, 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. 
         [0021]    The above constitution makes it possible to prevent operation unevenness among the plural sets of the vacuum pumps, since plural pumps are evenly employed and the operation hours of each pump are equalized. 
         [0022]    Another constitution of the present invention relates to an operation control method for plural vacuum pumps for depressurizing a gas inside at least one tank and/or chamber including the steps of: detecting a current flowing in a motor that drives the vacuum pumps; and reducing the number of the vacuum pumps actually 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 the current detection means converges within a predetermined range. 
         [0023]    According to the above constitution, the current to each motor which drives each corresponding vacuum pump is detected and it is judged that the target-vacuum or the substantial target-vacuum is realized when the current value converges within a predetermined range, resulting in that conventionally applied vacuum sensors for pressure detection of a vacuum tank or a vacuum facility room can be omitted, and the above constitution also makes it possible to restrain equipment costs and brings 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. 
         [0024]    Moreover, the above constitution makes it 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; since the gas to be exhausted is reduced when a target vacuum or substantially target vacuum condition is realized, it is possible to hold the vacuum condition or to reach the target vacuum condition without operation of an unnecessary pump. Still furthermore, in the control for operation and start/stop of the pumps, speed control equipment such as inverters and the like is not necessary. Therefore, undesirable effects due to inverters on surrounding equipment are avoidable. 
         [0025]    In connection with the above, still another constitution of the present invention can be given: an operation control method including 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 a 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 the 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; shifting the pump under watch evenly to the other next pump one by one among the whole pumps. 
         [0026]    According to the above described invention, it is made possible to decrease the number of plural working vacuum pumps and to reduce a power consumption as a result, because the target vacuum can be reached without large current after the depressurized pressure reaches the threshold criterion point value. In addition, the number of pumps and the amount of the power consumption are reduced after surely estimating that the target vacuum (negative pressure) is realized when the detected current stays for a predetermined span of time in the predetermined range. 
         [0027]    Moreover, according to the above constitution, is evaded disadvantage that the operation unevenness among the plural pumps is incurred as a result of working a specific pump at all the times 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. 
         [0028]    The present invention can provide an operation control device and operation method thereof so as to eliminate the difficulties in such a case of introduction of vacuum sensors and/or inverter. In addition, by the operation of plural vacuum pumps of the present invention, the increase of facility costs is restrained, the maintenance frequency is reduced and the man-hour of repair work is lessened. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The present invention will now be described in greater detail with reference to the preferred embodiments of the invention and the accompanying drawings, wherein: 
           [0030]      FIG. 1  shows a whole constitution of the invention; 
           [0031]      FIG. 2  is a figure sowing power (a current value) characteristic of a vacuum pump; 
           [0032]      FIG. 3  illustrates a time chart as to an exemplary embodiment of the invention; 
           [0033]      FIG. 4  illustrates a control flowchart as to an exemplary embodiment of the invention; and 
           [0034]      FIG. 5  illustrates a prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    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. 
         [0036]      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. 
         [0037]    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. 
         [0038]    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. 
         [0039]    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. 
         [0040]    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 10 2  Pa to 10 3  Pa. 
         [0041]    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. 
         [0042]    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. 
         [0043]    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. 
         [0044]    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. 
         [0045]    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. 
         [0046]    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. 
         [0047]    As shown in  FIG. 4 , all the vacuum pumps P A , P B  and P C  are under operation at the beginning (S 1 ) and the vacuum pump P A  is chosen as a pump to be watched, and the current I A  thereof is monitored (S 2 ). Whether the current I A  is within a range of P−α≦| A ≦P+α is judged (S 3 ) and, in case in which the judgment is YES (affirmative), whether the duration thereof is not less than a predetermined time span t 0  is further judged (S 4 ). 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 (S 5 ). 
         [0048]    It can be allowed to stop the vacuum pumps P B and P C , without the judgment on whether the duration of the condition S 4  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 (S 3 ) and the judgment is YES (affirmative), namely, when the depressurized pressure reaches the threshold criterion value S. 
         [0049]    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 (S 6 ). If the I A becomes greater than P+α, then all the vacuum pumps P A , P B  and P C  are operated again (S 7 ). In succession, the pump to be monitored is shifted to the vacuum pumps P B (S 8 ) 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 (S 9 ). 
         [0050]    In the next stage, the pump to be watched is shifted to the vacuum pump P C  (S 10 ), 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  (S 11 ). 
         [0051]    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. 
         [0052]    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. 
         [0053]    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 . 
         [0054]    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 . 
         [0055]    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. 
         [0056]    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. 
         [0057]    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. 
         [0058]    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. 
         [0059]    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.