Abstract:
A spot welding device for a nuclear fuel skeleton, which is assembled by spot-welding guide tubes for control rods and a instrumentation tube for measuring a state of an inside of a nuclear reactor to a spacer grid that has a plurality of cells formed in a thickness direction of a plate-shaped frame for inserting fuel rods, has a instrumentation tube hole formed at a center, and has four guide tube holes formed symmetrically above and below the instrumentation tube hole. The device includes: a welding gun including: a body, a first holder and a second holder extending from a side of the body and having respective electrodes facing each other at ends, respectively, and a driving unit disposed on the body and adjusting a distance between the electrodes; and a robot connected to the welding gun and having a rotary joint for rotating the welding gun.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a welding device and, more particularly, to a spot welding device for nuclear fuel skeleton which welds guide tubes for control rods and a instrumentation tube for measuring the state inside a nuclear reactor to a spacer grid supporting fuel rods in the nuclear reactor. 
         [0003]    2. Description of the Related Art 
         [0004]    A nuclear fuel skeleton is a frame for keeping fuel rods and for checking the reaction state of nuclear fuel in a nuclear reactor of a nuclear power plant. The skeleton is composed of spacer grids having a plurality of cells for fuel rods, guide tubes for control rods to be put into holes formed in the spacer grids arranged with a predetermined distance therebetween, and a instrumentation tube for measuring the state inside a nuclear reactor. The spacer grid is an important part of a nuclear fuel that fixes and supports fuel rods with uranium therein with predetermined force at predetermined distances and improves heat transfer from a nuclear reactor to a coolant. 
         [0005]    A fuel assembly is formed by putting fuel rods into the spacer grid cells of the skeleton and nozzles to both ends of the skeleton, and although it depends on the particular models of power plants, approximately one hundred seventy-seven fuel assemblies are used for about four years in nuclear reactors under Koran standard nuclear fuel regulations. 
         [0006]    As shown by the Chernobyl nuclear accident in the Soviet Union in 1986, a nuclear power plant requires very strict safety protocols. In particular, the nuclear fuel skeleton requires durability against extreme conditions for a long period of time in a nuclear reactor, so it is very important to perform many examinations in the process of manufacturing the nuclear fuel skeleton in order to achieve a high quality product. 
         [0007]    The spacer grids, guide tubes, and instrumentation tube of a skeleton are formed by bulging or welding. TIG welding has been used as the welding method in the related art. All the processes of TIG welding are manually carried out in a closed chamber filled with an argon gas due to the properties of the Zirconium Alloy that is a material for spacer grids and tubes (guide tubes and instrumentation tube). This is because If TIG welding is performed in a standby state, the metal at the welded portion combined with oxygen is broken due to the metallic properties of Zirconium Alloy, so bonding is impossible. 
         [0008]    Another reason for the requirement of manual welding is that it is difficult to set a welding angle due to narrow spaces between spacer grids, guide tubes, and a instrumentation tube, and inter-electrode contact is created at other portions of a skeleton during the process. Further, because there is a need for welding at over forty points within each grid when assembling one skeleton, the welding process is difficult. 
         [0009]    Additionally, another reason for the requirement of manual welding of spacer grids, guide tubes, and a instrumentation tube, is that a skeleton with even a slight defect cannot be reused; thus the defect causes an economic loss. 
         [0010]    Accordingly, for those reasons, it has been required to automate the process of assembling a skeleton that necessarily has low productivity and is expensive. 
         [0011]    To address the above, the applicant(s) has applied for a patent titled “Robot spot welding machine for nuclear fuel skeleton and spot welding method using that”, which has been disclosed in Korean Patent No. 10-0526721. 
         [0012]    The patent is shown in  FIGS. 1 to 3 . The registered patent will be simply introduced and the necessity of improving the structure of welding gun will be described hereafter mainly about the matters not solved by the registered patent. 
         [0013]    First,  FIG. 1  is a front view showing the entire configuration of a welding device of the registered patent. 
         [0014]    The robot spot welding device of the registered patent largely includes: a welding bench  200  with fixing frames  220  arranged at predetermined distances from each other to correspond to the gaps between spacer grids  110  constituting a skeleton  100 ; a robot  300  having a welding gun  350  and arranged in parallel with the welding bench, that is, on the rear side of the bench in the figures; electrodes inserted in guide tubes  120  and a instrumentation tube  130  to weld the spacer grids  110  and the guide tubes  120  to each other and the spacer grids and the instrumentation tube  130  to each other; and an loading table  500  aligned with the welding bench  200  to put the tubes  120  and  130  horizontally into holes  117   a,    117   b,    117   c,    117   d,  and  119  formed in the spacer grids  110  to align with the height of the holes these devices. 
         [0015]    The side with the welding bench  200  where the loading table  500  is positioned is defined as an ‘upper part’ and the opposite side is defined as a ‘lower part’ hereafter for the convenience of description. 
         [0016]    As described above, the types of nuclear fuel skeletons depend on the types of power plants, and manufacturers.  FIGS. 2A and 2B  shows a spacer grid  111  of a guardian type assembly for KSNP that has been used in the past of the grids for the skeleton. Though not used now, the arrangement of guide tubes and a instrumentation tube in the spacer grid is the same as that in the spacer grid of a PLUS7 assembly for KSNP shown in  FIG. 10 , which is generally used at present. 
         [0017]    As can be seen from the front view of  FIG. 2A , the grid  111  is formed by laser welding on plates made of Zirconium Alloy and arranged across each other. Springs  115   a  for fixing fuel rods F are formed in cells  115  formed by the grid plates. 
         [0018]    Further, as can be seen from the side view of  FIG. 2B , two dimples  115   b  are formed on the wall of each of the cells  115  for firmly fixing the fuel rods F, that is, total eight dimples are formed. 
         [0019]    As holes for inserting tubes in  FIG. 2A , a hole  119  for a instrumentation tube  130  and holes  117   a,    117   b,    117   c,  and  117   d  for guide tubes  120   a,    120   b,    120   c,  and  120   d  are formed. 
         [0020]    In  FIG. 2B , the welding points of the tubes  120  and  130  and the grid  111  are indicated by ‘W’, and according to TIG welding of the related art, welding is performed not inside the cells, but at the outsides where both ends of the cells and the tubes are in contact with each other. 
         [0021]    Such a configuration allows for automation of welding of a spacer grid, which has been performed manually in the past. 
         [0022]    However, as can be seen from  FIG. 3 , it is impossible to weld the instrumentation tube  130  with the welding gun  350  selected in the registered patent due to interference with the guide tubes, particularly, the guide tube  120   d  in the entrance of the welding gun, after welding the upper guide tubes  120   c  and  120   d.    
         [0023]    Accordingly, in order to weld the instrumentation tube  130  and all the guide tubes  120   a,    120   b,    120   c,  and  120   d  with the welding gun  350 , it is required to follow the welding sequence of the lower guide tubes  120   a  and  120   b,  the instrumentation tube  130 , and the upper guide tubes  120   c  and  120   d.  Further, welding or repairing of the instrumentation tube  130  or the lower guide tubes  120   a  and  120   b  for several purposes including maintenace, after the upper guide tubes  120   c  and  120   d  are welded, has to be performed manually. Therefore, there is a need for developing a welding gun that can weld the instrumentation tube  130  or the lower guide tubes  120   a  and  120   b,  even if the upper guide tubes  120   c  and  120   d  are welded, regardless of the welding sequence. 
         [0024]    The guardian type assembly for KSNP is not used any more, and the PLUS7 assembly for KSNP shown in  FIG. 10  is used now. Sleeves that can be combined with guide tubes and a instrumentation tube are inserted in advance at the positions for the guide tubes and the instrumentation tube in the spacer grid of the PLUS7 assembly for KSNP, as can be seen from  FIG. 10 , so the electrode of a welding gun is not directed to the inside of the spacer grid in welding, but welding is performed at the positions W where the sleeves and the guide tubes or the sleeves and the instrumentation tube overlap each other. Therefore, it is also required to change the direction of the electrode of the welding gun according to the related art shown in  FIG. 9 . 
         [0025]    The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art. 
         [0026]    Documents of Related Art 
         [0027]    Korean Patent No. 10-0526721 (registered on 31 Oct., 2005) 
       SUMMARY OF THE INVENTION 
       [0028]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention is intended to propose a spot welding device for a nuclear fuel skeleton which has a welding gun that can be arranged without interference with previously welded tubes so that guide tubes for control rods and a instrumentation tube for measuring the state inside a nuclear reactor are welded to a spacer grid for supporting fuel rods in the nuclear reactor. 
         [0029]    In order to achieve the above object, according to one aspect of the present invention, there is provided a spot welding device for a nuclear fuel skeleton, which is assembled by spot-welding guide tubes for control rods and a instrumentation tube for measuring a state of an inside of a nuclear reactor to a spacer grid that has a plurality of cells formed in a thickness direction of a plate-shaped frame for inserting fuel rods, has a instrumentation tube hole formed at a center, and has four guide tube holes formed symmetrically above and below the instrumentation tube hole. The spot welding device includes: a welding gun  1100  including: a body, a first holder  1110  and a second holder  1120  extending from a side of the body and having respective electrodes  1115  and  1125  facing each other at ends, respectively, and a driving unit  1130  disposed on the body and adjusting a distance between the electrodes; and a robot connected to the welding gun and having a rotary joint for rotating the welding gun, in which the first holder  1110  may have a bend  1111  bent in an extension direction from the body, a distance M between the guide tubes may be larger than a horizontal thickness T of the bend  1111 , the second holder  1120  may have a stepped portion  1121  where height changes, and a shortest distance S between the stepped portion  1121  and the bend  1111  may be larger than a cross-sectional diameter D of the guide tubes. 
         [0030]    The first holder  1110  may have a horizontal extension, the bend  1111 , and a first electrode  1115  sequentially from a joint with the body, and a vertical distance H 2  between a horizontal line passing through a center of the first electrode  1115  and a bottom of the horizontal extension may be larger than a vertical distance H 1  between a horizontal line passing through a center of the instrumentation tube and an upper horizontal tangent line of an upper guide tube. 
         [0031]    The second holder  1120  may have an upper extension  1123 , the stepped portion  1121 , a lower extension  1124 , and a second electrode  1125  sequentially from the body, and a vertical distance K between a horizontal line passing through a center of the second electrode  1125  and a bottom of the upper extension  1123  may be larger than a radius of the guide tubes, so that when a guide tube far from the welding gun  1100  is welded, the welding gun  1100  is not interfered with by an adjacent guide tube. 
         [0032]    The welding gun may be a single welding gun so that a robot with a low capacity can be used to move the welding gun, and accordingly, it is possible to reducing the manufacturing cost of the welding device. 
         [0033]    The spot welding device for a nuclear fuel skeleton according to the present invention has the following advantages. 
         [0034]    First, it is possible to perform welding without interference by previously welded tubes, so processes manually achieved when there is interference by previously welded tubes can be automated, and accordingly, it is possible to considerably reduce the work process, time, and cost. 
         [0035]    Second, since it is possible to perform welding without interference by previously welded tubes, welding can be systematically performed regardless of the welding sequence. 
         [0036]    Third, since a single welding gun is used, the entire weight of the welding gun is reduced and a robot with a low capacity can be used, so that it is possible to reduce the costs for manufacturing and maintenance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
           [0038]      FIG. 1  is a front view showing the entire shape of a robot spot welding device for a nuclear fuel skeleton of the related art. 
           [0039]      FIGS. 2A and 2B  are a front view and a side view, respectively, showing a spacer grid for the robot spot welding device for a nuclear fuel skeleton of the related art and a welding device of the present invention. 
           [0040]      FIG. 3  is a front view showing interference with a welding gun of the robot spot welding device for a nuclear fuel skeleton of the related art by a previously welded guide tube. 
           [0041]      FIG. 4  is a front view showing the entire shape of a welding gun of a spot welding device for a nuclear fuel skeleton according to the present invention. 
           [0042]      FIG. 5  is a front view showing that the welding gun of the spot welding device for a nuclear fuel skeleton according to the present invention can weld a instrumentation tube without interference by a guide tubes. 
           [0043]      FIG. 6  is a front view showing that the welding gun of the spot welding device for a nuclear fuel skeleton according to the present invention can weld a guide tube without interference by an adjacent guide tube. 
           [0044]      FIG. 7  is a table comparing the differences between the welding gun of the present invention and a welding gun of the related art. 
           [0045]      FIG. 8  is a plan view showing the welding gun of the present invention and a welding gun of the related art. 
           [0046]      FIG. 9  is a plan view showing the process of welding by a dual gun of welding guns according to the related art. 
           [0047]      FIG. 10  is a schematic side view of a spacer grid for an improved skeleton. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    Hereinbelow, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the drawings, the same reference numerals will refer to the same or like parts. 
         [0049]    The present invention provides a welding device achieved by improving a welding gun  350  used in the robot spot welding device for a nuclear fuel skeleton of an existing patent. The present invention is not used only for the entire welding system for which the welding device of existing patents and may be used within a wide variety of contexts as long as there is a requirement to put a welding gun between tubes, which are fixed in parallel by a welding device, for combining a plurality of tubes in parallel, without interference by previously installed tubes. 
         [0050]    The entire configuration and shape of the present invention will be described first with reference to  FIG. 4 , the principle of avoiding interference by a guide tube  120  using the components of the present invention will be described with reference to  FIGS. 5 and 6 , the differences from the related art will be clearly described with reference to  FIG. 7 , and then the advantages of a single gun, and other configurations and effects of the present invention will be described with reference to  FIGS. 8 and 9 . 
         [0051]      FIG. 4  is a front view showing the entire shape of a welding gun  1100  except for a robot in a spot welding device of a nuclear fuel skeleton according to the present invention. 
         [0052]    In  FIG. 4 , a body corresponding to a main frame of the welding gun  1100  is positioned at the right side and a driving unit  1130  is disposed at the lowermost portion of the body. The position of the driving unit  1130  is not limited, but when the driving unit  1130  is a servo motor, the right lower end in  FIG. 4  is appropriate for the position of the driving unit  1130 . The advantages of the driving unit  1130  when it is a servo motor will be described below. Further, it is assumed that the driving unit  1130  is a servo motor in the following description. Further, it should be noted that a pneumatic pressing type is not excluded. 
         [0053]    Though not shown in detail, a ball screw, a bearing, a belt, or other power transmission parts, and a cooling circuit, and a transformer, which allow for spot welding while pressing both sides of the welding points with first and second electrodes  1115  and  1125  by transmitting power from a servo motor, may be disposed in the body. 
         [0054]    A first arm  1150  and a second arm  1160  extending to the left from the body at the right side in  FIG. 4  and support a first holder  1110  and a second holder  1120 , respectively. 
         [0055]    The first electrode  1115  and the second electrode  1125  for pressure spot welding are connected to the ends of the first holder  1110  and the second holder  1120 , respectively. For pressure spot welding, the first electrode  1115  and the second electrode  1125  face each other, and in  FIG. 4 , the first holder  1110  bends, thereby enabling first electrode  1115  and the second electrode  1125  at the ends to face each other. 
         [0056]    The portion where the first holder  1110  bends is referred to as a bend  1111 . As in  FIG. 4 , the bend  111  is formed not suddenly, but smoothly curved to be inserted into a space between adjacent tubes. However, as can be seen from  FIG. 4 , if the bend  1111  is sufficiently small in width, it can be inserted between parallel tubes even if it is bent at a right angle, so it may be formed at the right angle. The thickness, however, has to be determined within a predetermined range, because not only wires for supplying electricity, but the cooling circuit for cooling are disposed in the holder. 
         [0057]    Though not shown in detail, the body is connected to a robot. The robot moves the entire welding gun  1100  close to of away from positions to be welded. Further, though not shown in the drawings, the robot may have a plurality of joints to smoothly move the welding gun  1100 , in which one of the joints can rotate and the rotation changes the up-down position relationship between the first holder  1110  and the second holder  1120  of the welding gun  1100 . That is, the welding gun  1100  has a rotary joint that can vertically rotate by 180 degrees. 
         [0058]    In the following description, there is provided the principle of capable of inserting the welding gun  1100  between previously welded guide tubes due to the shape of the welding gun described above. 
         [0059]      FIGS. 5 and 6  show a structure capable of inserting the welding gun  1100  according to the present invention between previously welded tubes without interference by the tubes, as an effect of the shape of the welding gun  1100 . Further, the effects of the welding gun  1100  according to the present invention will be made clearer by the table comparing the welding gun  1100  with the welding gun  350  of the related art. 
         [0060]      FIG. 5  is a plan view showing that both ends of a vertical cross-section of a instrumentation tube are welded and pressed by the first electrode  1115  and the second electrode  1125 . A servo motor type may be used for pressing the ends. The servo motor type can precisely control the pressing force regardless of the position of the welding gun  1100 , as compared with a pneumatic type. Further, the pneumatic type increases the weight of the welding gun  1100  due to a pneumatic cylinder and various parts for pneumatic control, but the servo motor type reduces the weight of the welding gun  1100  because it uses a motor having an appropriate capacity. 
         [0061]    Further, a servo welding gun that applies pressing force using a servo motor can be more precisely synchronized with a robot via a program and can more quickly approach an object to be welded by a short stroke. Further, pressing force, which is one of three important factors including the time for which a welding current is supplied in resistance spot welding, can be controlled, so the welding strength can be further improved. 
         [0062]    When a pneumatic gun is used, an unstable area is caused due to the shock of electrodes in the early stage of contacting and pressing. However, using a soft touch type controlling a servo gun can minimize the aforementioned shock by a pneumatic gun. 
         [0063]    The shape of the welding gun  1100  of the present invention is described with reference to  FIG. 5 . The welding gun  1100  includes: a body; a first holder  1110  and a second holder  1120  that extend from a side of the body and have respective electrodes  1115  and  1125  facing each other at ends; and a driving unit  1130  disposed on the body and adjusts the distance between the electrodes, in which the first holder  1110  has a bend  1111  bending from the body, the horizontal distance M between guide tubes  120  is larger than the horizontal thickness T of the bend  1111 , the second holder  1120  has a stepped portion  1121  where height changes, and the shortest distance S between the stepped portion  1121  and the bend  1111  is larger than the cross-sectional diameter D of the guide tubes. 
         [0064]    Referring to  FIG. 3 , in the welding gun of the related art, the horizontal distance M between guide tubes is smaller than the horizontal thickness of the portion corresponding to the bend  1111 . Accordingly, the condition that the horizontal thickness of the bend  1111  has to be smaller than the horizontal distance between the guide tubes  120  is one of the necessary conditions for excluding interference by previously welded guide tubes. 
         [0065]    An additional necessary condition is that the shortest distance S between the bend  1111  and the stepped portion  1121  has to be larger than the diameter D of the guide tubes. Comparing  FIGS. 3 and 5 , the necessity of the additional necessary condition is made clear. Although the bend  1111  and the stepped portion  1121  are substantially in parallel in  FIG. 5 , they do not need to be parallel and a necessary condition is only that the shortest distance between them has to be larger than at least the diameter of the guide tubes. 
         [0066]    Accordingly, the necessary condition that the welding gun  1100  can approach a welding point of the instrumentation tube  130  to weld the instrumentation tube  130  even with the guide tubes  120  welded first is consequently satisfied. 
         [0067]    Interference by the guide tubes  120  welded first can be finally excluded by the additional condition, in which it is required to compare the heights shown in  FIG. 5 . 
         [0068]    Referring to  FIG. 5 , the first holder  1110  has a horizontally extension, the bend  1111 , and the first electrode  1115  sequentially from the first arm protruding from the joint with the body of the welding gun and the vertical distance H 2  between the horizontal line passing through the center of the first electrode  1115  and the bottom of the horizontal extension has to be larger than the vertical distance H 1  between the horizontal line passing through the center of the instrumentation tube and the upper horizontal tangent line of an upper guide tube. 
         [0069]    Accordingly, even if the upper guide tubes  120   c  and  120   d  are welded first, it is possible to weld the instrumentation tube  130  with the welding gun  1100  without replacing the welding gun  1100 . Alternatively, it is also possible to weld the skeletons of models other than the PLUS7 assembly for KSNP without replacing a welding gun. 
         [0070]    The guide tubes  120  may interfere with the welding gun  1100  in another case, that is, when a welding gun is interfered with by adjacent guide tubes in welding, which are arranged horizontally in parallel. That is, when one guide tube is welded, there is a need for preventing a previously welded guide tube from interfering with the welding gun  1100 . 
         [0071]    Conditions for this purpose are shown in  FIG. 6 . Describing the configuration of the second holder  1120  in detail to explain those conditions, the second holder  1120  has an upper extension  1123 , a stepped portion  1121 , a lower extension  1124 , and a second electrode  1125  sequentially from the body. The vertical distance K between the horizontal line passing through the center of the second electrode and the bottom of the upper extension  1123  has to be larger than the radius of the guide tube, which is a condition for excluding interference between adjacent guide tubes. 
         [0072]    Obviously, as shown in  FIG. 3 , there is a structure capable of excluding interference with the welding gun  350  of the related art when another guide tube is welded, as shown in the table of  FIG. 7 . 
         [0073]    However, the configuration for excluding such interference is different from that for the welding gun  350  of the related art, in that it is required to remove the problem using the shapes of the first holder  1110  and the second holder  1120  of the welding gun  1100 . 
         [0074]    The differences between the characteristics of the present invention described above and a welding gun of the related art are shown in  FIG. 7 . 
         [0075]    As the conditions shown in  FIGS. 5 and 6  are satisfied, the welding order becomes free. That is, in the related art, it is required to perform welding in the order of welding the lower guide tubes  120   a  and  120   b  first, and then weld the instrumentation tube  130  at least before welding the upper left guide tube  120   c,  but according to the present invention, welding can be achieved even if it starts with any one of the upper and lower components, unlike the related art. 
         [0076]    For this purpose, however, another component is provided to a robot and that is a rotary joint. The configuration of an automated robot or rotary joints of a robot are well known in the art, so the detailed description is not provided. The important thing in this configuration is the fact that there is a need for a rotary joint, and referring to the table of  FIG. 7 , it is possible to know that the welding gun has been rotated downward by 180 degrees to weld a lower guide tube in the right upper section. 
         [0077]    That is, it is possible to weld a lower guide tube by rotating the welding gun by 180 degrees, even if the upper guide tube and the instrumentation tube have been welded already. Accordingly, when there is no rotary joint, the lower guide tubes have to be welded at least before the upper guide tubes are welded. 
         [0078]    However, even if there is no rotary joint, there is no priority in welding order between the lower guide tubes  120   a  and  120   b  and the instrumentation tube  130  because of the structure of the first holder  1110  and the second holder  1120 . 
         [0079]    On the other hand, for reference, the guardian assembly for KSNP shown in  FIGS. 2A and 2B  is not used any more, and the PLUS7 assembly for KSNP shown in  FIG. 10  is used now. The largest difference between the spacer grids of the two assemblies is that the guide tube  120  and the instrumentation tube  130  are welded to the spacer grid of the PLUS7 assembly for KSNP through the sleeves  113   a  combined with the grid in advance. Accordingly, the welding points W are positioned not inside the grid, but at the outer walls of the sleeves  113   a  protruding outside the grid, and instead of an insertion type, a straight type may be selected for the shapes of the first electrode  1115  and the second electrode  1125 . 
         [0080]    Referring to  FIG. 9 , in the spacer grid of the PLUS7 assembly for KSNP, welding should be performed at portions inserted in the spacer grid, so there is a need for a single welding gun or a dual welding gun for insertion at both sides of the spacer grid, as can be seen from the welding gun  350  of the related art. This is because electrodes that are inserted in opposite directions are both needed. 
         [0081]    However, when the spacer grid for a PLUS7 assembly for KSNP shown in  FIG. 10  is used, the welding points W are positioned on the outer walls of the sleeve  113   a,  so the electrodes may be formed straight, and accordingly, welding can be achieved by one single welding gun, as achieved by the welding gun of the related art. 
         [0082]    Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.