Abstract:
A laser projection system capable of irradiating a light beam for alignment is provided. The alignment laser projection system comprises a reflection unit, a moving reflection unit, irradiation units that irradiate light to the reflection unit and the moving reflection unit, a guide unit which drives the moving reflection unit, a housing which contains a driving unit, a control unit which controls the irradiation unit and the driving unit, and a display unit which displays control states. In irradiating a laser beam, the laser projection system resolves the problem of instable power supply and information transfer due to the damage in a cable apparatus caused by alternating movements of an irradiation unit such that it supplies stable alignment line in repetitive works.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a laser projection system, and more particularly, to an alignment laser projection system which can accurately align; working lines without being affected by interference that can occur internally during the working process of a machine tool. 
   2. Description of the Related Art 
   In order to construct an external ship body or an internal structure in a large structure such as a ship, a very wide steel plate is needed, but it is impossible in reality to produce such a wide steel plate. Accordingly, for that purpose, a plurality of steel plates of a predetermined area are joined by welding and then used. 
   Meanwhile, if the welding parts of steel plates are not accurately joined in a predetermined allowable error range, the strength of a predetermined part of a ship body produced based on the welding can be relatively weaker than other parts and due to this, the ship body may be broken. Accordingly, the welding between joining steel plates should be performed after an accurate welding line is formed. 
   However, the area of each steel plate joined by welding is also much wider than an ordinary area of a steel plate such that it is difficult to apply normal welding line forming methods, such as those using worker&#39;s eye measure or a measuring tape. Accordingly, in this case, a laser projection system shown in  FIGS. 1 and 2  is used for the alignment. 
   Generally, a laser projection system  1  comprises a housing  40  internally which has a laser irradiation unit, a driving unit container  50  which is coupled to one side of the housing  40  and internally has a driving unit  52 , an encoder container  60  which is coupled to the other side of the housing  40  and internally has an encoder  62 , a control unit  70  which is connected to the driving unit  52  and the encoder  62  and controls the driving unit  52 , and a display  80  which displays the situation controlled by the control unit  70 . 
   Inside the housing  40 , disposed are a ball screw  20  which can be extended or contracted in the direction from the center to either side with being held through penetration holes (not shown) formed on both sides of the housing  40 , a first irradiation unit  32  which is fixed to the center of the ball screw  20 , and at least one pair or more of second irradiation units  34  and  36  which are coupled to the ball screw  20  at symmetrical locations about the first irradiation unit  32 . Cables  33 ,  35 , and  37  are connected to the first and second irradiation units  32 ,  34  and  36 , respectively. 
   As the first and second irradiation units  32 ,  34 , and  36 , normal laser units are used respectively. 
   The cables  33 ,  35 , and  37  provide power from a power supply unit to the first and second irradiation units  32 ,  34 , and  36 , respectively. In addition, the first and second irradiation units  32 ,  34 , and  36  transmit information on respective moving distances to the control unit  70 . 
   The driving unit  52  is connected to one end of the ball screw  20  to extend or contract the ball screw and for this a stepping motor is usually employed. 
   The encoder  60  is connected to the other end of the ball screw  20 , and if the ball screw  20  is extended or contracted by the driving unit  52 , transmits information on this moving distance to the control unit  70 . 
   The control unit  70  controls start and end of operation of the driving unit  50 , and the driving range, receives information on the moving distance of the ball screw  20  measured by the encoder  60 , and displays the control situation for these on the display  80 . An ordinary terminal or CPU with a control function corresponds to this unit  70 . 
   The display  80  displays the situation controlled by the control unit  70 . An ordinary monitor corresponds to this, and of course, a touch screen can also, be used. 
   In the operation of the laser projection system having the structure described above, first, objects desired to be welded (A, B, C, D) are placed below or beside the laser projection system. Then, from the external power supply unit (not shown) through the respective cables  33 ,  35 , and  37 , power is supplied to the first and second irradiation units  32 ,  34 , and  36  connected to the, respective cables  33 ,  35 ,  37 . 
   If power is supplied, light beams irradiated by the first and second irradiation units  32 ,  34 , and  36  accurately indicate straight welding lines between the objects to be welded (A, B, C, D), and according to this, a worker performs welding work using a welder  90  and so on. 
   Meanwhile, in order to form an accurate welding line, if the driving unit  52  is driven, the ball screw  20  connected to the driving unit  52  is extended or contracted from the first irradiation unit  32  to the right-hand side or left-hand side. According to this, a pair of the second irradiation units  34  and  36  coupled to the ball screw  20  move to the right or to the left such that an accurate welding line can be adjusted and along thus aligned welding line, the welder welds the objects and then the desired structure can be produced. 
   However, when the prior art laser projection system with the structure described above are frequently used in welding fields, the ball screw  20  is extended or contracted particularly by the driving unit  52 , and according to this, the cables  35  and  37  connected to the second irradiation units  34  and  36  among the first and second irradiation units  32 ,  34 , and  36 , which move together with the ball screw  20 , frequently contacts with an inner wall surface of the housing  40  such that the cables  36  and  37  are frequently damaged. 
   These damages of the cables cause error in the location information of the irradiation units transmitted to the control unit through the cables such that it becomes impossible to align an accurate welding line originally desired and when the welding work is completed, this can directly cause serious damages to the finished structure. 
   In addition, it causes difficulties in providing power to respective irradiation units from the external power supply unit or a laser beam desired to irradiate itself is not generated. Accordingly, the laser projection system should be regularly inspected and frequently replaced and this becomes one of major factors for deterioration of the entire productivity. 
   This problem also occurs identically in all cases where a laser projection system with the identical structure is needed for more accurate position alignment, such as when the laser projection system is used for position alignment in manufacturing tires, and when an iron plate is manufactured in a predetermined shape after a blast furnace process. 
   SUMMARY OF THE INVENTION 
   The present invention provides a laser projection system which can form an alignment line at a desired accurate location even when a ball screw is frequently extended or contracted by a driving unit. 
   The present invention also provides a more economical laser projection system which can form a more accurate alignment line with a simpler structure. 
   According to an aspect of the present invention, there is provided an alignment laser projection system comprising: a housing wherein both sides of the housing are open and a permeation window is formed in the length direction at the bottom of the housing; a first side surface holding plate wherein an upper hole and a center hole are formed such that the central axis of each hole is the same as the central axis line in the length direction of the permeation window, and a pair of bottom holes are formed such that the central axis of each hole is in parallel with and level with the axis line in the length direction of the permeation window, and the two axes of the holes are symmetrical about the axis line of the permeation window, and the first side surface holding plate is coupled to one side surface of the housing: a second side surface holding plate where holes corresponding the upper hole and bottom holes of the first side surface holding plates are formed respectively and the second side surface holding plate is coupled to the other side of the housing; a center holding plate wherein holes corresponding to each of bottom holes of the first and second side surface holding plates are formed and the center holding plate is coupled to the inner center of the housing; a reflection unit which penetrates into and is coupled to each upper hole of the first and second side surface holding plates; a guide unit formed with a ball screw and a guide rod wherein both ends of each of the ball screw and the guide rod penetrate into and are coupled to respectively bottom holes of the first and second side surface holding plates; a pair or more of guide blocks which are disposed on locations symmetrical about the center holding plate, wherein the guide unit penetrates into and is coupled to a pair or more of the guide blocks; a driving unit which is coupled to one end of the ball screw and drives the ball screw; an encoder which is coupled to the other end of the ball screw and detects information on the movement of the ball screw; a first irradiation unit which is inserted into a central hole of the first side surface holding plate and irradiates light; a moving reflection unit which is coupled to a coupling member on the top of each guild block and protrudes above the central axis line of the permeation window in the length direction; a second irradiation unit which is coupled to the center holding plated by a coupling member and protrudes above the central axis line of the permeation window in the length direction; and a control unit which is connected to the driving unit, the encoder, and the first and second irradiation units and controls the same. 
   According to another aspect of the present invention, there is provided an alignment laser projection system comprising: a housing wherein both sides of the housing are open and a permeation window is formed in the length direction at the bottom of the housing; a first side surface holding plate wherein an upper hole is formed such that the central axis of the hole is the same as the central axis line in the length direction of the permeation window, and a pair of bottom holes are formed in the vertical direction on one location selected between two locations where the central axis of a lower bottom hole of the pair is in parallel with and level with the center of the axis line in the length direction of the permeation window and the first side surface holding plate is coupled to one side surface of the housing; a second side surface holding plate where holes corresponding the upper hole and bottom holes of the first side surface holding plates are formed respectively and the second side surface holding plate is coupled to the other side of the housing; a center holding plate wherein holes corresponding to each of bottom holes of the first and second side surface holding plates are formed and the center holding plate protrudes to the center from an inside side surface perpendicularly facing the length axis line of the permeation window, and is coupled to the inner center of the housing; a reflection unit which penetrates into and is coupled to each upper hole of the first and second side surface holding plates; a guide unit formed with a ball screw and a guide rail wherein both ends of each of the ball screw and the guide rail penetrate into and are coupled to respectively bottom holes of the first and second side surface holding plates; a pair or more of first guide blocks which are disposed on locations symmetrical about the center holding plate, wherein the ball screw of the guide unit penetrates into and is coupled to a pair or more of the guide blocks; a second guide block which is coupled to the bottom of each of the first guide blocks and slides along the guide rail; a driving unit which is coupled to one end of the ball screw and drives the ball screw; an encoder which is coupled to the other end of the ball screw and detects information on the movement of the ball screw; a moving reflection unit which is coupled to a coupling member on the top of each guild block and protrudes above the central axis line of the permeation window in the length direction; a second irradiation unit which is coupled to the center holding plated by a coupling member and is disposed above the central axis line of the permeation window in the length direction; a first irradiation unit which is inserted into a central hole of the first side surface holding plate and irradiates light; and a control unit which is connected to the driving unit, the encoder, and the first and second irradiation units and controls the same. 
   The penetration coupling of the ball screw and the guide block; a ball screw nut is used as a medium such that the rotational movement of the ball screw is converted into the rectilinear movement of the guide block. 
   Also, in the penetration coupling of the ball screw and the first guide block, a ball screw nut is used as a medium such that the rotational movement of the ball screw is converted into the rectilinear movement of the guide block. 
   The guide rail and the second guide block are an LM rail and an LM block, respectively. 
   The housing is one selected among a cylinder, a rectangular pillar and a polygonal pillar. 
   The permeation window of the housing is formed as a slit, or is tightly closed by a transparent material. 
   The reflection unit is formed with a photo conductive drum with an embedded reflection plate. 
   The ball screw is extended or contracted in both side directions, at the same time, from the center holding plate by the operation of the driving unit. 
   The driving unit is a motor. 
   The second irradiation unit is formed with a moving reflection unit. 
   The first and second irradiation units are laser units. 
   The moving reflection unit is formed with a prism. 
   The control unit further comprises a display to display a situation being controlled. 
   The display is formed with a touch screen. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a diagram of the entire structure of the prior art alignment laser projection system; 
       FIG. 2  is a detailed diagram of the structure of the prior art alignment laser projection system; 
       FIG. 3  is a diagram of the entire structure of an alignment laser projection system according to the present invention; 
       FIG. 4  is a detailed sectional view of an alignment laser projection system as a first preferred embodiment according to the present invention; 
       FIG. 5  is a detailed plan view of an alignment laser projection system as the first preferred embodiment according to the present invention; 
       FIG. 6  is a detailed sectional view of an alignment laser projection system as a second preferred embodiment according to the present invention; and 
       FIG. 7  is a detailed plan view of an alignment laser projection system as the second preferred embodiment according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 3 through 5  are a diagram of the entire structure, a detailed sectional view, and a detailed plan view, respectively, of a first preferred embodiment of a laser projection system according to the present invention. 
   The present invention basically comprises a housing  100  which contains a variety of apparatuses, a control unit  800  which controls the variety of apparatuses inside the housing  100 , a display  900  which displays a situation controlled by the control unit  800 . 
   Both sides of the housing  100  are open and on the bottom of the housing  100 , a permeation window  120  is formed in the length direction. 
   The permeation window  120  may be formed as a slit of a recess shape, or the recess shape slit may be closed with a transparent material. If only light can permeate through the permeation window  120 , any shape or material can be used. 
   Preferably, the permeation window  120  is formed to be shorter than the entire length of the housing  100  as shown, but of course, it can be formed the same as the entire length of the housing  100 . 
   Meanwhile, preferably, the shape of the housing is formed in a cylinder shape, but not limited to this, and it is obvious that the shape of the housing  100  can be any one selected among rectangular and polygonal pillars. 
   The reference numbers  150 ,  160 , and  170 , which are not described yet, indicate insertion grooves in protrusions protruding toward the central axis line of the housing  100  from the inner side surfaces so that a first side holding plate, a second side holding plate, and a center holding plate that will be explained later can be inserted and fixed. 
   To both the open sides of the housing, the first side surface holding plate  220  and the second side surface holding plate  240  are coupled and the center holding plate  260  is coupled to the internal center. 
   On the first side holding plate  220 , an upper hole  222 , a center hole  224 , and a pair of bottom holes  226  are formed. 
   The upper hole  222  and the center hole  224  are formed such that the central axis of each hole is the same as the central axis line in the length direction of the housing permeation window  120 . A pair of the bottom holes  226  are formed such that the central axis of each hole is in parallel with and level with the axis line in the length direction of the housing permeation window  120 , and the two axes of the holes are symmetrical about the axis line of the permeation window  120 . 
   That is, when both side surfaces of the housing  100  are taken as a base and if the permeation window  120  is at the bottom of the housing  110 , the upper hole  222  and the center hole  224  are formed respectively on a diameter line drawn in the upper direction from the permeation window  120 , and a pair of the bottom holes  226  are formed on an even level and on the right hand side and on the left hand side of the diameter line. 
   On the second side surface holding plate  240 , an upper hole  242  and a pair of bottom holes  246  corresponding to the upper hole  222  and a pair of the bottom holes  226  of the first side surface holding plate  220  are formed respectively. 
   The center holding plate  260  comprises a first holding plate and a second holding plate, which are protruding from inside side surfaces of the housing  100  in the central axis line direction of the housing  100  to face each other. In each of the first and second holding plates, holes corresponding to the bottom holes  224  and  226  of the first and second side surface holding plates  220  and  240  are formed. 
   Preferably, the shape of each holding plate is a fan shape and the part adjacent to the permeation window  120  is formed to be concave. 
   Inside the housing  100  according to the present invention, disposed are a guide unit  400 , a guide block  430  which is coupled with the guide unit  400 , first and second irradiation units  720  and  740 , a driving unit  620  which drives the guide unit  400 , an encoder  660  which measures movement of the guide unit  400 , and a moving reflection unit  760  and a reflection unit  300  that reflect light irradiated by the first irradiation unit  720 . 
   The guide unit  400  comprises a ball screw  424  and a guide rod  422  that are level with each other. The ball screw  424  has an operation structure by which the ball screw  424  can be extended or contracted in both directions (the left hand side and right hand side in the figure) from the center of the housing  100  where the center holding plate  260  is disposed, which is well known in the art and detailed explanation will be omitted. 
   The guide rod  422  prevents the guide block  430 , which will be explained later, from rotating together according to the rotational movement of the ball screw  424 , and allows the guide block  430  to perform rectilinear movement along a predetermined straight line axis. 
   Meanwhile, the guide rod  422  and the ball screw  424  penetrate into and are coupled to a pair of holes formed in each of the first and second side surface holding plates  220  and  240 . 
   A pair of penetration holes (not shown) are formed on both sides of the guide block  430  facing to each other so that the guide rod  422  and the ball screw  424  forming the guide unit  400  can penetrate into and be coupled to the holes. Preferably, a pair or more of the guide blocks  430  facing each other on symmetrical locations about the center holding plate  170  are coupled to the guide unit  400 . 
   In addition, it is desirable that by using a ball screw nut  434  as a medium, the guide block  430  and the ball screw  424  are coupled. This is because by the movement of a ball embedded in the ball screw nut  434 , the rotational movement of the ball screw  424  can be converted into the rectilinear movement of the guide block  430 , and in addition, the rectilinear movement of the guide block  430  can be implemented smoothly and precisely. 
   Together with this, it is desirable that for smooth movement of the guide rod  422 , a separate guide rod coupling member  432  is used as a medium also for coupling the guide block  430  and the guide rod  433 . 
   The moving reflection unit  760  is to reflect light irradiated by the first irradiation unit  720 , which will be explained later, and is coupled to the upper part of the guide block  430  by a separate coupling member  762 . In a state where the center of the moving reflection unit  760  corresponds to the axis line center of the housing permeation window  120  in the length direction, the moving reflection unit  760  protrudes over the permeation window  120 . 
   If only the moving reflection unit  760  can reflect light appropriately, it can be implemented not limited by any one type, but it is desirable that it is implemented by a prism. The protruding location may be either of the left hand side and the right hand side of the guide block  430 . 
   Of course, the kind of the coupling member  762  and the coupling method are not limited to any one and can be selected from a variety of types and methods. 
   Meanwhile, though only a pair of moving reflection units (including the guide block) on locations facing each other are shown in the figure, the number of moving reflection units can be changed in a variety of ways according to the conditions of a desired work field. Accordingly, when necessary, one or more pairs of moving reflection units, or a plurality of moving reflection units with the number of moving reflection units in one direction bigger than the number of moving reflection units in other direction can be formed. 
   The first irradiation unit  720  is a unit to irradiate light and an ordinary laser unit corresponds to this. The first irradiation unit  720  is inserted into and coupled to the center hole  224  of the first side surface holding plate  220  and is connected to the control unit  800 , which will be explained later, through a separate cable. 
   The second irradiation unit  740  is a separate irradiation unit to irradiate light and in the present invention, instead of the second irradiation unit  740 , the moving reflection unit described above can also be used. When a separate irradiation unit is used as the second irradiation unit  740 , it will have the same structure and connection as the first irradiation unit  720  described above, and when the moving reflection unit is used as the second irradiation unit  740 , it will have the same structure as the moving reflection unit  760  described above. 
   The driving unit  620  is coupled to one end of the ball screw  424  of the guide unit  400  to drive the ball screw  424 . Preferably, a stepping motor is used as the driving unit  620 , but not limited to this and any ordinary motor can be used. 
   The encoder  660  is coupled to the other end of the ball screw  424  of the guide unit  400  and is an apparatus to accurately detects such information as the rotation speed of the ball screw  424 , and to feed the information back to the control unit  800 . An ordinary optical encoder corresponds to this and is well known in the art. Accordingly, the detailed explanation will be omitted. 
   The reflection unit  300  reflects again light to the outside through the housing permeation window  120 , the light which is irradiated by the first irradiation unit  720  (if the second irradiation unit is a separate irradiation unit, the second irradiation unit is also included) and then reflected by the moving reflection unit. This re-reflection of light is conducted by a reflection plate (not shown) embedded in the reflection unit  300 . 
   The material and shape of the reflection plate are not limited to specific ones if only with a high reflection rate it can reflect most of irradiated light. 
   In addition, it is desirable that the reflection unit  300  is made with a photo conduct drum. The reflection unit  300  penetrates into and are coupled to each bottom hole  222  of the first and second side surface holding plates  220  and  240 . 
   The control unit  800  controls the first and second irradiation units  720  and  740  (when the second irradiation unit is formed as a moving reflection unit, the first irradiation unit), the driving unit  620 , and the encoder  660 . An ordinary terminal with an embedded CPU corresponds to this. 
   The display  900  displays the operational situation controlled by the control unit  800 . Of course, a touch screen that can control through direct contact by a user to the screen, as well as an ordinary display corresponds to this. 
   Meanwhile,  FIGS. 6 and 7  are a detailed sectional view and a detailed plan view, respectively, of an alignment laser projection system as a second preferred embodiment according to the present invention. Focusing on only those parts of the structure, which are different from the first embodiment described above, the second embodiment will now be explained. 
   On the first side surface holding plate  230 , an upper hole  232 , a center hole  234 , and a pair of bottom holes  236  are formed. The upper hole  232  and the center hole  234  are the same as in the first embodiment. A pair of the bottom holes  236  are formed in the vertical direction on one location selected between two locations where the central axis of a lower bottom hole of the pair  236  is in parallel with and level with the center of the axis line in the length direction of the housing permeation window  120 . 
   That is, when both side surfaces of the housing  100  are taken as a base and if the permeation window  120  is at the bottom of the housing  110 , the two holes  236  are formed vertically on one location selected between the left hand side and right hand side from a diameter line drawn in the upper direction from the permeation window  120 . 
   On the second side surface holding plate  250 , an upper hole  252  and a pair bottom holes  256  corresponding to the upper hole  232  and a pair of bottom holes  236 , respectively, of the first side surface holding plate  230  are formed. 
   On the center holding plate  270 , holes corresponding to each of the bottom holes  236  and  256 , respectively, of the first and second side surface holding plates  230  and  250  are formed. 
   A guide unit disposed inside the housing comprises a ball screw  524  on the top and a guide rail  522  at the bottom, and penetrates into and is coupled to each of the bottom holes  236  and  256  of the first and second side surface holding plates  230  and  250 . 
   The ball screw  524  penetrates into and is coupled to the first guide block  560 , and the bottom part of the first guide block  560  is coupled with a second guide block  540  which slides along the top surface of the guide rail  522 . 
   That is, with the first and second guide blocks  560  and  540  being coupled with each other, the first guide block  560  moves along the ball screw  524  and the second guide block  540  slides along the guide rail  522 . 
   Using a ball screw nut as a medium for coupling the first guide block  560  and the ball screw  524  is the same as in the first embodiment. Of course, the coupling method of the first and second guide blocks  560  and  540  may be selected among a variety of ways. 
   Meanwhile, it is desirable to use an ordinary LM guide formed with an LM block and an LM rail for the second guide block  540  and the guide rail  522 , respectively, because it can reduce friction in sliding and at the same time guarantee precise movement. 
   The remaining part of the structure of the second embodiment that is not described is the same as in the first embodiment and therefore the detailed description will be omitted. 
   Referring to the attached figures, the operation of the laser projection system according to the present invention having the structure described above will now be explained. 
   First, when power from an external power supply unit is supplied to the first and second irradiation units  720  and  740  (if the second irradiation unit is formed as a moving reflection unit, the first irradiation unit) and light is irradiated, the light irradiated by the second irradiation unit  740  is directly incident on the reflection unit  300 , and the light irradiated by the first irradiation unit  720  is reflected by the moving reflection unit  760  (if the second irradiation is formed as a moving reflection unit, the light irradiated by the first irradiation unit is all reflected on the moving reflection unit) and with the changed irradiation direction, is incident on the reflection unit  300 . 
   The light irradiated to the reflection unit  300  is reflected by the reflection plate embedded in the reflection unit  300  and its irradiation direction is changed (the arrow direction in  FIGS. 4 through 6 ) such that an alignment line is formed. If the light lines by the respective moving reflection units  760  do not match with a desired alignment line when the first irradiation unit  720  is taken as a base, the user can manipulate the control unit  800  so that the control unit  800  drives the driving unit  620  in one direction to rotate the ball screw  424 . Then, the rotation movement of the ball screw  424  is converted into the rectilinear movement of the guide block  430  and the moving reflection unit  760  comes close to or goes away from the center holding plate  260  of the housing  100 . According to this, the alignment line can be again adjusted accurately. 
   Even if the alignment line by the respective moving reflection units  760  do not match with a desired line, the user can drive the driving unit  620  in the reverse direction such that the line is appropriately adjusted. 
   Meanwhile, the control unit  800  displays information on the strength of the light irradiated by each of the irradiation units, information on the operation of the driving unit  620 , and information analyzed by the encoder  660  on the display  900  connected to the control unit  800 . If a touch screen is used as the display, the operation situation of the entire system can be controlled more precisely by the user checking the situation with the user&#39;s naked eye. 
   Optimum embodiments have been explained above and are shown. However, the present invention is not restricted to the above-described embodiments and many variations are possible within the spirit and scope of the present invention. The scope of the present invention is not determined by the above description but by the accompanying claims. 
   According to the present invention, for irradiation of an alignment laser beam, an irradiation unit which moves in a predetermined distance is formed with moving reflection units and a reflection unit and the accompanying cables are removed such that instability of power supply and information transfer due to damages in the cables is removed and a stable alignment line can be provided in repetitive works. 
   In addition, in the prior art a plurality of irradiation units disposed in the housing and directly irradiating lights should be used, but in the present invention, even when only one irradiation unit is used, a desired purpose can be well achieved such that the entire system is more economically constructed.