Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a gas circulation fan for an excimer laser apparatus. More specifically, the present invention relates to a gas circulation fan for an excimer laser apparatus that emits laser, by circulating halogen gas such as fluorine gas. 
   2. Description of the Background Art 
   In a conventional excimer laser apparatus, rolling bearing has been used as a bearing for the laser gas circulation fan. Generation of an impurity gas resulting from a reaction between the halogen gas such as fluorine included in the laser gas and bearing lubricant, and generation of dust from rolling surface of the bearing ball, however, degraded laser gas, affecting the laser output. As a solution to this problem, recently, a magnetic bearing has come to be used. 
     FIG. 6  is a block diagram showing a configuration of a mechanical body unit and a controller of a conventional magnetic bearing apparatus for the gas circulation fan. Referring to  FIG. 6 , on a main shaft  1 , a fan  2  is attached, forming a rotary body  3 . Gas  21  is circulated, as fan  2  rotates in a chamber  20 . Rotary body  3  has one side pivotally supported by a magnetic bearing  41 , and the other side pivotally supported by a magnetic bearing  42 . Magnetic bearing  41  on one side includes an electromagnet  51  positioned in a housing  23  and supporting, in non-contact manner, one side of rotary body  3 , and a position sensor  61  detecting position of rotary body  3 . Magnetic bearing  42  on the other side includes an electromagnetic  52  positioned in a housing  24  and supporting, in a non-contact manner, the other side of rotary body  3 , and a position detection sensor  62  detecting the position of rotary body  3 . 
   Magnetic bearings  41  and  42  are connected to a controller  7  through cables  81  and  82 , respectively. Controller  7  includes a position detection sensor circuit  9  processing signals from position sensors  61  and  62  and converts an amount of displacement of rotary body  3  to a voltage ratio; an offset adjuster  10  electrically correcting position mechanical deviation from the center of the floating position of rotary body  3 ; a sensor feedback gain adjuster  11  adjusting gain of an output representing displacement of position detection sensor circuit  9 ; a filter circuit  12  for reducing bending natural frequency or the like of rotary body  3 ; a phase compensating circuit  13  for stabilizing control system; and a power circuit  14  supplying current to electromagnets  51  and  52 . 
   In the conventional magnetic bearings  41  and  42  shown in  FIG. 6 , when a characteristic of mechanical body unit  25  such as a bearing gap or a main shaft natural frequency changes because of variation in processing accuracy, for example, position detection sensor circuit  9 , offset adjuster  10 , sensor feedback gain adjuster  11  and filter circuit  12  must be finely adjusted to address the change of mechanical body unit  25 , and it has been difficult to maintain compatibility between mechanical body unit  25  and controller  7 . For example, when controller  7  fails and is exchanged by a new controller, various portions of controller  7  must newly be adjusted. This is very troublesome in adjusting and maintaining the apparatus, and has an influence on productivity of the apparatus. 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a gas circulation fan of an excimer gas laser apparatus, in which a mechanical body unit and a control circuit have full compatibility. 
   The present invention provides a gas circulation fan for an excimer laser apparatus in which laser gas in a chamber is circulated by fan rotation, including: a rotary shaft on which the fan is attached; a controllable magnetic bearing supporting, in non-contact manner, the rotary shaft; a control circuit controlling the controllable magnetic bearing; a motor for rotating the rotary shaft; and a compensator provided between the controllable magnetic bearing and the controlling circuit, compensating for characteristic variation resulting from individual difference of the controllable magnetic bearing. 
   As the variation in characteristics derived from individual difference is compensated in this manner, compatibility between the controllable magnetic bearing and the control circuit is established. 
   The compensator includes a detector detecting a sensor signal of the controllable magnetic bearing, an offset adjusting circuit correcting positional deviation from the center of the rotary shaft based on the sensor signal detected by the detector, a feedback gain adjusting circuit adjusting the gain of detection output of the detector, and a filter circuit for reducing proper oscillation of the rotary shaft. 
   Accordingly, proper oscillation of individual controllable magnetic bearing can be compensated for by the compensator, and compatibility between the controllable magnetic bearing and the control circuit is ensured. 
   Further, the gas circulation fan includes a housing accommodating the controllable magnetic bearing, and the compensator is provided in the housing. 
   As the compensator is accommodated in the housing of the controllable magnetic bearing, even when the control circuit fails, what is necessary is simply to replace the failed circuit with a new control circuit, and adjustment operation can be eliminated. 
   According to another aspect, the present invention provides a gas circulation fan for an excimer laser apparatus circulating laser gas in a chamber by fan rotation, including: a rotary shaft on which the fan is attached; a controllable magnetic bearing supporting, in a non-contact manner, the rotary shaft; a control circuit controlling the controllable magnetic bearing; a motor for rotating the rotary shaft; and an adjusting member for adjusting natural frequency of the rotary body rotating integrally with the rotary shaft. 
   In this manner, by the adjusting member for adjusting the natural frequency, variation in natural frequency of the mechanical body can be minimized. 
   Further, the adjusting member includes a weight detachably attached to the rotary shaft. 
   Thus, by adjusting the mass of the weight, variation of natural frequency can be suppressed. 
   Further, the adjusting member includes a female screw formed along the axial direction from one end surface side of the rotary shaft, and a natural frequency adjusting member having a male screw portion formed on an outer circumferential surface and moved forward/downward engaged with the female screw portion. 
   As the natural frequency adjusting member is provided, the addition of the center of gravity of the screw can be changed by changing the amount of screwing, and hence the natural frequency of the entire rotary shaft can be adjusted. 
   According to a still further aspect, the present invention provides a gas circulation fan for an excimer laser apparatus circulating laser gas in a chamber by fan rotation, including: a rotary shaft on which the fan is attached; a controllable magnetic bearing supporting, in a non-contact manner, the rotary shaft; a control circuit controlling the controllable magnetic bearing; and a motor for rotating the rotary shaft; wherein the control circuit includes a bandpass filter for removing natural oscillation frequency of the rotary shaft, and a frequency setting circuit for setting the set frequency of the bandpass filter to the natural frequency of the rotary shaft. 
   Therefore, even when the natural frequency of the rotary shaft varies, the frequency of the bandpass filter can automatically be adjusted on the side of the control circuit. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a configuration of the magnetic bearing for a gas circulation fan of an excimer laser apparatus in accordance with a first embodiment of the present invention. 
       FIG. 2  shows a configuration of a mechanical body unit and a relay representing a modification of the first embodiment of the present invention. 
       FIGS. 3A and 3B  represent configurations of the magnetic bearing for gas circulation fan of an excimer laser apparatus in accordance with a second embodiment of the present invention. 
       FIGS. 4A  to  4 D represent the main shaft natural frequency adjusting mechanism of the excimer laser apparatus in accordance with a third embodiment of the present invention. 
       FIG. 5  shows a filter tuning mechanism for attenuating main shaft natural frequency of the excimer laser apparatus in accordance with a fourth embodiment of the present invention. 
       FIG. 6  shows a configuration of a magnetic bearing for gas circulation fan of a conventional excimer laser apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a block diagram representing a configuration of a mechanical unit and an electrical configuration, of the first embodiment of the present invention. 
   Referring to  FIG. 1 , in the present embodiment, portions that have limited compatibility between mechanical unit  25  and controller  7  shown in  FIG. 6  are accommodated in relays  15  and  16 . More specifically, in the conventional example shown in  FIG. 6 , compatibility between mechanical body unit  25  and controller  7  has been limited by position detection sensor circuit  9 , offset adjuster  10 , sensor feedback gain adjuster  11  and filter circuit  12 . 
   Therefore, in the embodiment shown in  FIG. 1 , the circuit configurations that have limited the compatibility are accommodate in relays  15  and  16 . More specifically, relay  15  includes position detection sensor circuit  151 , offset adjuster  152 , feedback gain adjuster  153  and filter circuit  154 , while relay  16  includes position detection sensor  161 , offset adjuster  162 , feedback gain adjuster  163  and filter circuit  164 . Relay  15  is connected to magnetic bearing  41  by means of a cable  81 , and relay  16  is connected to magnetic bearing  42  by means of a cable  82 . Further, relay  15  is connected to controller  7  by means of a cable  83 , and relay  16  is connected to controller  7  by means of a cable  84 . Only phase compensating circuit  13  and power circuit  14  are provided in controller  7 . 
   Respective circuits in relay  15  are finely adjusted in accordance with the characteristics of magnetic bearing  41 , while relay  16  is finely adjusted in accordance with the characteristics of magnetic bearing  42 . Therefore, it becomes possible to attain compatibility between mechanical body unit  25  including relays  15  and  16  and controller  7 . When controller  7  fails, for example, repair is completed simply by exchanging controller  7 , which does not require any fine adjustment, and therefore, the adjusting operation can be eliminated. 
     FIG. 2  shows a modification of the mechanical body unit and the controller in accordance with an embodiment of the present invention. In the embodiment shown in  FIG. 2 , relays  15  and  16  shown in  FIG. 1  are combined to be one relay  15 . Relay  15  contains position detection sensor circuit  156 , offset adjuster  157 , feedback gain adjuster  158  and filter circuit  159  each having circuits corresponding to magnetic bearings  41  and  42 , the relay  15  is connected to magnetic bearings  41  and  42  by cables  81  and  82 , respectively, and the relay  15  is connected to external controller  7  by cable  83 . 
   In this embodiment also, position detection sensor circuit  156 , offset adjuster  157 , feedback gain adjuster  158  and filter circuit  159  that have limited compatibility between mechanical body unit  25  and controller  7  are accommodated in relay  15 . Therefore, compatibility between controller  7  and mechanical unit  25  including relay  15  can be attained. 
     FIGS. 3A and 3B  represent configurations of the mechanical unit and the controller in accordance with the second embodiment of the present invention. In the embodiment shown in  FIGS. 3A and 3B , position detection sensor circuit  151 , offset adjuster  152 , feedback gain adjuster  153  and filter circuit  154  constituting relay  15  shown in  FIG. 1  are provided on an inner substrate  30  within a housing  23 , while position detection sensor circuit  161 , offset adjuster  162 , feedback gain adjuster  163  and filter circuit  164  constituting relay  16  are mounted on an inner substrate  31  in a housing  24 . As respective circuit components are mounted on inner substrate  30  and  31 , relays  15  and  16  shown in  FIG. 1  can be eliminated, enabling further reduction in size. In this structure also, compatibility between mechanical body  25  and controller  7  can be attained. 
     FIGS. 4A  to  4 D represent a third embodiment of the present invention. When natural frequency of rotary body  3  including main shaft  1  varies because of processing accuracy error in manufacturing main shaft  1 , it becomes necessary to readjust frequencies of filter circuits  154 ,  164  and  159  in the relay in inner substrates  30  and  31 , to be in accordance with the natural frequency of rotary body  3 , as described in the first and second embodiments. 
   In contrast, in the embodiment shown in  FIGS. 4A  to  4 D, variation in proper oscillation of main shaft  1  is minimized, so as to eliminate adjustment of the set frequency of filter circuit  12 . More specifically, in the example shown in  FIG. 4A , a natural frequency adjusting weight  17  is attached to one end of main shaft  1 , and in the example shown in  FIG. 4B , natural frequency adjusting weight  17  is attached on the other side of main shaft  1 . By attaching natural frequency adjusting weight  17  on main shaft  1 , the mass is adjusted such that the natural frequency of main shaft  1  has a prescribed value (prescribed frequency of filter circuit  12  shown in FIG.  6 ). 
   Though natural frequency adjusting weight  17  is attached on one side or on the other side of main shaft  1 , it may be attached to other position. By this method, individual difference in natural frequency of rotary body  3  including main shaft  1  can be eliminated. Therefore, it becomes unnecessary to arrange filter circuit  12  in relays  15  and  16  or on inner substrates  30  and  31 , and a filter circuit can be arranged in controller  7 . Thus, readjustment of set frequency of filter circuit  12  becomes unnecessary. 
   In the example shown in  FIG. 4C , a natural frequency adjusting screw  18  is attached on one end surface of main shaft  1 , in place of natural frequency adjusting weight  17 . In this example, a female screw  22  is formed on one end of main shaft  1 , and natural frequency adjusting screw  18  having male screw formed therein is engaged therewith. By changing the amount of screwing of natural frequency adjusting screw  18 , the position of the center of gravity of the screw changes as shown in  FIG. 4D , and hence the natural frequency of main shaft  1  as a whole can be adjusted. 
     FIG. 5  shows configurations of mechanical body unit  25  and the controller in accordance with the fourth embodiment of the present invention. Similar to the third embodiment, in the present embodiment, when natural frequency of rotary body  3  including main shaft  1  varies because of processing accuracy error in manufacturing main shaft  1 , the filter frequency is automatically adjusted by a digital control circuit  19  of controller  7 . More specifically, in digital control circuit  19 , a filter tuning control circuit  26  sets the frequency of filter circuit  12  to an expected natural frequency of rotary body  3  and activates magnetic bearings  41  and  42 , and the frequency of filter circuit  12  is changed from a frequency little lower than the expected natural frequency of rotary shaft  3  to a frequency a little higher than the expected frequency, while measuring frequency characteristics at respective frequencies. Filter tuning control circuit  26  finds the frequency of filter circuit  12  at which the peak of proper oscillation becomes the smallest, and sets the thus found frequency as the prescribed frequency of the apparatus. By setting the frequency of the filter circuit  12  to the prescribed frequency thereafter, optimal control can automatically be attained. 
   Therefore, in accordance with the present embodiment, even when there is an individual difference in natural frequency of rotary body  3 , the filter frequency can automatically be adjusted by digital control circuit  19 . Therefore, it is unnecessary to take into consideration compatibility of mechanical unit  25 . 
   As described above, according to the embodiments of the present invention, full compatibility between the mechanical body and the controller can be attained. Therefore, it is expected that efficiency in operation is improved at the site of production, and maintenance is facilitated. For example, at the site of production, a plurality of mechanical bodies may be adjusted by using one controller. 
   Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Technology Category: 2