Abstract:
A dispenser includes a light emitter to emit a light beam toward a surface of a substrate, a light receiver to receive the light beam reflected from the substrate, and a coupling hole, between the emitter and receiver, to receive a lower section of a syringe. The emitter, receiver, and coupling hole may be provided in a single support structure, and the coupling hole is located between a light emitting plane of the emitter and a light receiving plane of the receiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/118,278, filed on May 9, 2008, which is a continuation of U.S. Pat. No. 7,540,924, filed on May 10, 2005. The contents of both documents are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    One or more embodiments disclosed herein relate to apparatuses and methods for applying a material such as a sealant onto a substrate. 
         [0004]    2. Background 
         [0005]    In general, liquid crystal display (LCD) is lighter and smaller by volume than a traditional image display device using cathode-ray tube (CRT). Therefore, making great strides in recent years, LCD has been widely applied in many display devices, such as computer monitors and TVs. 
         [0006]    In case of the LCD, there is a certain space between an upper substrate and a lower substrate, and the space is filled with liquid crystal. In order for the LCD to perform its operation at optimum state, a cell gap of the lower and upper substrates should be maintained uniformly. In addition, in order to prevent excessive liquid crystal dispensing or insufficient filling of the space, it is very important to have a good positioning precision of a sealant coating for sealing the upper and lower substrates, and a proper control on the amount of coating being supplied to the substrates. This is because if the cell gap is not uniform or if liquid crystal is applied too much or insufficiently, the screen uniformity over the entire screen of an LCD will be deteriorated. 
         [0007]    A sealant used to seal the space between the lower and the upper substrate not only maintains a uniform cell gap, but also seals the upper and the lower substrate. 
         [0008]    A sealant is applied to a substrate by means of a sealant dispenser. The sealant dispenser includes a stage on which the substrate is mounted, and a head unit provided with a nozzle for discharging the sealant. 
         [0009]    Here, the nozzle makes a relation motion to the substrate, and applies a sealant of a designated shape onto the substrate. In other words, the nozzle moves into X-axis and Y-axis directions relatively to the substrate, and applies the sealant onto the substrate. Also, the nozzle is movable into Z-axis direction to adjust its height with respect to the substrate. 
         [0010]      FIG. 1  illustrates a head unit of a related art sealant dispenser. As can be seen in the drawing, the head unit of the sealant dispenser includes a syringe  20  for storing a sealant, and a nozzle  32  coupled to a lower portion of the syringe  20 , for discharging the sealant  50 . 
         [0011]    A long bar-shaped bracket  30  is connected to the syringe  20  in a horizontal direction, and the nozzle is installed on the end of the bracket  30 . And, a distance sensor  40  for measuring a vertical distance between the nozzle  32  and the substrate  10  is installed in the vicinity of the nozzle  32 . 
         [0012]    More specifically, the distance sensor  40  is spaced apart a predetermined distance (L) from the syringe  20  which is filled with the sealant. Here, the syringe  20  and the distance sensor  40  must be installed in parallel because of their own volumes. Therefore, in order to put the nozzle communicated with the syringe as close as possible to the focal point of the distance sensor, the syringe and the nozzle must be installed in ‘L’ shape. 
         [0013]    Usually, an optical laser distance sensor is used for the distance sensor  40 . The bottom surface of the distance sensor has a “ ”, where a light emitting part  42  for emitting a laser beam  46  is installed on one side and a light receiving part  44  for receiving a laser beam  46  is on the other side. 
         [0014]    Here, the light emitting part  42  emits a laser beam  46  towards the substrate, whereas the light receiving part  44  receives the laser beam reflected from the substrate. As such, the distance sensor  40  measures a distance between the substrate  10  and the nozzle  32 . 
         [0015]    When the laser beam path is changed due to a flexure on the sealant-applied surface of the substrate  10 , the distance sensor measures the laser beam received to the light receiving part and transfers its measured value to a controller (not shown). 
         [0016]    However, the related art sealant dispenser has the following problems. 
         [0017]    Firstly, since the nozzle and the syringe are spaced a designated distance apart, the flow path of the sealant is bent in “L” shape. In detail, the distance sensor and the syringe of the related sealant dispenser are separately installed in the head unit while maintaining a designated distance from each other. This is why the flow path of the sealant has an “L” shape. 
         [0018]    In that light, the related art dispenser requires a high pressure for discharging the sealant, and the usage of a highly viscous sealant was limited. 
         [0019]    Secondly, according to the related art sealant dispenser, the nozzle is installed on the lower portion of the bracket, so that there is a great distance between the position on the substrate where the sealant is discharged and the position on the substrate where a laser beam is reflected. Therefore, the distance sensor cannot get an accurate a vertical distance from the point to which the sealant is actually discharged to the nozzle. 
         [0020]    Thirdly, since the flow path of the sealant in the related art sealant dispenser is in “L” shape, the sealant is relatively slowly discharged. Hence, it is not clear exactly where sealant dispensing starts and ends. 
       SUMMARY OF THE INVENTION 
       [0021]    Accordingly, the present invention is directed to a lighting optical system that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
         [0022]    An object of the present invention is to provide a sealant dispenser featuring a low pressure for dispensing the sealant, and a control method thereof. 
         [0023]    Another object of the present invention is to provide a high precision sealant dispenser and a control method thereof. 
         [0024]    Still another object of the present invention is to provide a sealant dispenser featuring an accurate control over the dispensing position and dispensing amount of a sealant by increasing the response speed of a sealant to be dispensed, and a control method thereof. 
         [0025]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0026]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a sealant dispenser, including: a stage on which a substrate is mounted; a nozzle for dispensing a sealant while making a relative motion with the substrate; a syringe coupled to the nozzle, for storing the sealant; and a distance sensor installed on both sides of a lower portion of the syringe, for measuring a vertical distance between a principal plane of the substrate and an outlet of the nozzle. 
         [0027]    Preferably, the distance sensor includes: a light emitting part for emitting a laser beam towards the substrate; a light receiving part for receiving a laser beam reflected from the substrate; and a sensor supporting part for supporting the light emitting part and the light receiving part. 
         [0028]    Preferably, the sensor supporting part includes a coupling hole that the nozzle passes through. 
         [0029]    More preferably, the coupling hole is disposed between the light emitting part and the light receiving part. 
         [0030]    Preferably, the syringe and the outlet of the nozzle have substantially the same central axis. 
         [0031]    More preferably, a focal point of a laser beam emitted form the distance sensor, the nozzle, and the syringe are arranged on the same axis. 
         [0032]    Preferably, the light emitting part and the light receiving part of the distance sensor are aligned in a straight line along the principal plane of the substrate, and the light emitting part and the light receiving part are combined as one body. 
         [0033]    Preferably, the vertical distance between the substrate and the nozzle is maintained at a constant value. 
         [0034]    Another aspect of the present invention provides a sealant dispenser, including: a stage on which a substrate is mounted; a nozzle for dispensing a sealant while making a relative motion with the substrate; a distance sensor for measuring a vertical distance between a principal plane of the substrate and an outlet of the nozzle; and a position detecting sensor for detecting a horizontal position of the nozzle on the principal surface of the substrate. 
         [0035]    Preferably, the position detecting sensor and the nozzle are located each other at the opposite sides with respect to the substrate. 
         [0036]    Preferably, the sealant dispenser further includes an adjusting part for adjusting the position of a syringe storing the sealant. 
         [0037]    Preferably, a measuring point on the principal plane of the substrate in which a laser beam from the distance sensor is reflected is disposed on a front end of the nozzle along the direction of the sealant application. 
         [0038]    More preferably, the nozzle and the measuring point maintain a minimum distance from each other so that the laser beam does not interfere with the sealant. 
         [0039]    Still another aspect of the present invention provides a control method of a sealant dispenser, which the method includes the steps of: in a position detecting sensor installed below a substrate, setting a horizontal position of a nozzle on a principal plane of the substrate; in a distance sensor installed on both sides of a lower portion of a syringe, setting a vertical distance between the substrate and the nozzle; and dispensing a sealant to the position being set. 
         [0040]    Preferably, the step for setting the horizontal position of the nozzle includes the sub-step of: measuring a horizontal distance between a measuring point on the substrate in which a laser beam is reflected and the nozzle; and deciding whether the measured horizontal distance falls within a predetermined allowable range. 
         [0041]    Preferably, the method further includes the step of: if the measured horizontal distance is outside the allowable range, revising the horizontal position of the nozzle. 
         [0042]    Preferably, the step for setting the vertical distance between the substrate and the nozzle includes the sub-steps of: measuring a vertical distance between the substrate and the nozzle; and deciding whether the measured vertical distance falls within a predetermined allowable range. 
         [0043]    Preferably, the method further includes the step of: if the measured vertical distance is outside the allowable range, revising the vertical distance between the nozzle and the substrate. 
         [0044]    Preferably, the vertical distance between the substrate and the nozzle is revised to maintain a constant value. 
         [0045]    Preferably, the syringe and the nozzle for dispensing the sealant to the principal plane of the substrate have substantially the same central axis. 
         [0046]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
           [0048]      FIG. 1  is a perspective view illustrating a head unit of a related art sealant dispenser; 
           [0049]      FIG. 2  is a front view illustrating key elements of a sealant dispenser according to the present invention; 
           [0050]      FIG. 3  is a side view of a key element taking in the direction of arrow A in  FIG. 2 ; 
           [0051]      FIG. 4  illustrates a detected position of a distance sensor photographed by a position detecting sensor, and a location of a nozzle; and 
           [0052]      FIG. 5  is a flow chart explaining a control method of a sealant dispenser according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
         [0054]      FIG. 2  is a front view illustrating key elements of a sealant dispenser according to the present invention;  FIG. 3  is a side view of a key element taking in the direction of arrow A in  FIG. 2 ; and  FIG. 4  illustrates a detected position of a distance sensor which is photographed by a position detecting sensor, and a location of a nozzle. 
         [0055]    Referring to  FIGS. 2 to 4 , the sealant dispenser of the present invention includes a nozzle  130  for discharging a sealant while making a relative motion to a substrate  110  mounted on a stage, a syringe  120  coupled to the nozzle  130 , for storing the sealant, and a distance sensor  140  installed on both sides of the lower portion of the syringe  120 , for measuring a vertical distance from the principal plane of the substrate  110  to an outlet of the nozzle  130 . 
         [0056]    The syringe  120  for storing a sealant is in conical shape of which the inside diameter decreases in the downward direction, and is installed perpendicularly to the surface of the substrate  110 . Also, the nozzle  130  is coupled to one end of the syringe  120 , and the outlet of the nozzle  130  is installed in such a manner to have substantially the same central axis with the syringe  120 . As shown in  FIG. 2 , the syringe is supported by a syringe coupler  320 . 
         [0057]    The sealant  150  in the syringe  120  travels along a straight flow path and is discharged from the nozzle. In result, the response speed of the sealant is increased according to a positive or negative pressure signal of a controller that controls the amount of the sealant to be applied, and the sealant can be applied to an accurate position on the substrate. Especially, since the start point and the end point of dispensing are set precisely, defect rate can be reduced markedly. 
         [0058]    The distance sensor  140  includes a light emitting part  142  for emitting a laser beam toward the substrate  110 , a light receiving part  144  for receiving a reflected laser beam from the substrate  110 , and a sensor supporting part  145  for supporting the light emitting part  142  and the light receiving part  144 . As shown in  FIG. 2 , light emitted from the light emitting party  142  is substantially perpendicular to a light emitting plane  342 . Light received by the light receiving part  144  is substantially perpendicular to a light receiving plane  344 . 
         [0059]    The sensor supporting part  145  is installed above the light emitting part  142  and the light receiving part  144 , encompassing the lower portion of the syringe  120 . And, the sensor supporting part  145  is provided with a coupling hole  148  between the light receiving part  144  and the light emitting part  142 , so that the nozzle  130  passing through the coupling hole  148  is located between the light receiving part  144  and the light emitting part  142 . As shown in  FIG. 2 , the coupling hole  148  receives a lower part of the syringe  120 . 
         [0060]    Optionally, the sensor supporting part  145  can have a first sensor support supporting the light receiving part  144  and a second sensor support supporting the light emitting part  142 . That is, the light receiving part  144  and the light emitting part  142  are separately installed on both sides of the lower portion of the syringe, and the lower portion of the syringe mounted with the nozzle is installed between the light receiving part  144  and the light emitting part  142 . 
         [0061]    Apart from the above constitutional elements, the present invention also includes a head unit structure in which the focal point of a laser beam emitted form the distance sensor, the nozzle, and the syringe are serially arranged on the same axis. 
         [0062]    As can be seen in  FIG. 3 , the light emitting part and the light receiving part of the distance sensor  140 , and the syringe  120  are aligned in parallel to the principal surface of the substrate. In detail, if seen in the direction of arrow A in  FIG. 2 , the distance sensor  140  is installed symmetrically around the center of the syringe. 
         [0063]    Preferably, the light emitting part  142  and the light receiving part  144  of the distance sensor  140  are combined as one body. However, this is for illustrative purposes only and the present invention is not limited thereto. As aforementioned, therefore, it is possible to install the light transmitting part and the light receiving part separately from each other, and put the nozzle therebetween. 
         [0064]    The distance sensor  140  measures a vertical distance between the nozzle  130  and the substrate  110  to which the sealant  150  is applied. To this end, the light emitting part  142  of the distance sensor  140  emits a laser beam towards the substrate  110 , and the light receiving part  144  receives a reflected laser beam from the substrate  110 . 
         [0065]    If the vertical distance between the substrate  110  and the nozzle  130  is changed due to a flexure on the surface of the substrate  110 , the height from a point of laser beam reflection is changed. Consequently, not only the laser beam is received at a different position on the light receiving part  144 , but also the phase of the laser beam is changed. Based on these changes, the distance sensor  140  measures the vertical distance from the nozzle  130  and the substrate  110 . 
         [0066]    The measured vertical distance between the nozzle  130  and the substrate  110  is sent to a controller (not shown). Then, the controller (not shown) moves the nozzle  130  and the substrate  110  relatively to each other until the vertical distance has a predetermined value. Examples of a driving means (not shown) for moving the substrate and the nozzle include a linear motor and a servomotor. 
         [0067]    Meanwhile, as shown in  FIG. 2 , a measuring point  112  on the substrate  110  from which a laser beam  146  is reflected is disposed a predetermined distance away from a position where the sealant  150  is applied. If the measuring point  112  and the position to which the sealant  150  is applied are coincident, the distance sensor  140  is interfered with its distance measurement by the sealant  150  applied to the substrate  110 . Thus, it is important that the measuring point  112  and the nozzle  130  are spaced apart at least at a minimum distance for the sealant not to interfere with the laser beam. Moreover, the measuring point  112  is preferably located on a front end of the nozzle, along the direction of the sealant application. 
         [0068]    However, the above-described embodiments are merely exemplary and are not to limit the present invention. In effect, the measuring point and the position to which the sealant is applied can be located within a predetermined allowable range. Also, the measuring point can be located in any position close to the nozzle, along the direction of the sealant application. 
         [0069]    Furthermore, a position detecting sensor  170  is installed below the substrate  110  and detects a horizontal distance between the nozzle  130  and the measuring point in which the laser beam emitted from the distance sensor  140  is reflected. Precisely speaking, the position detecting sensor  170  and the nozzle  130  are located at the opposite sides with respect to the substrate  110 . 
         [0070]    Although a camera is preferably used as the position detecting sensor  170 , any type of sensor capable of detecting the position of the nozzle and the measuring point can be utilized. 
         [0071]    As depicted in  FIG. 4 , a screen  175  photographed by the position detecting sensor  170  displays the nozzle and the measuring point. 
         [0072]    Since the substrate  110  coated with the sealant  150  is a transparent glass, the measuring point  112  and the nozzle  130  are projected onto the substrate  110 . Hence, the position detecting sensor  170  regards a position on the substrate  110  where the nozzle  130  is projected as a place where the sealant  150  should be applied, and detects a distance d between the measuring point  112  and the nozzle  130 . 
         [0073]    If the distance d between the measuring point  112  and the nozzle  130  is outside the predetermined allowable range, an adjusting part  160  mounted on the head unit adjusts the position of the syringe coupled to the nozzle. 
         [0074]    Actually, the adjusting part  160  is connected to the syringe and minutely adjusts the coupling position of the syringe. The adjusting part  160  includes a motor to be able to adjust the coupling position and angle of the syringe  120 . 
         [0075]    Alternatively, if the nozzle is stopped, a stage (not shown) supporting the substrate can be driven to adjust the horizontal distance between the nozzle and the substrate. 
         [0076]      FIG. 5  is a flow chart explaining a control method of the sealant dispenser according to the present invention. The control method of the sealant dispenser will now be described in greater detail below. 
         [0077]    As can be seen in  FIG. 5 , the control method of the sealant dispenser is largely divided into three steps: a first set-up step (S 100 ) performed by the position detecting sensor, for setting or specifying a horizontal position of the nozzle on the principal plane of the substrate; a second set-up step (S 200 ) performed by the distance sensor, for setting a vertical distance between the substrate and the nozzle; and a sealant dispensing step (S 300 ) for dispensing or applying a sealant to the position set in the first and second steps. 
         [0078]    In the first set-up step (S 100 ), when the syringe descends, the nozzle coupled to the syringe moves close to the surface of the substrate. Here, it is also acceptable for the nozzle to touch the surface of the substrate. 
         [0079]    Then, the position detecting sensor installed below the substrate photographs the measuring point on the substrate in which the laser beam reflects and the position of the nozzle, to detect the horizontal distance between the measuring point and the nozzle (S 110 ). 
         [0080]    Once the horizontal distance between the nozzle and the measuring point is detected, it is decided whether the measured horizontal distance is within the predetermined allowable range (S 130 ). 
         [0081]    Here, the allowable range indicates a user-specified range for an appropriate distance between the measuring point and the nozzle. Preferably, the allowable range is set up differently, depending on a kind of the sealant used and pressure/speed of dispensing the sealant. 
         [0082]    If a result of the first decision in step S 130  tells that the distance between the measuring point and the nozzle is within the allowable range, the method proceeds to a second set-up step for setting the vertical distance between the nozzle and the substrates (S 200 ). 
         [0083]    On the other hand, if the horizontal distance between the measuring point and the nozzle is outside the allowable range, the position of the nozzle is revised (S 150 ). In this revision step, the adjusting part mounted on the head unit revises the position of the syringe to make sure that the horizontal distance between the measuring point and the nozzle falls within the allowable range. After revising the position of the syringe, it is preferable to measure the horizontal distance between the measuring point and the nozzle again. 
         [0084]    When the first set-up step (S 100 ) for setting the horizontal position of the nozzle on the surface of the substrate is over, the method proceeds to the second set-up step (S 200 ) for setting the horizontal distance between the substrate and the nozzle. 
         [0085]    In the second set-up step (S 200 ), the distance sensor on the circumference of the lower portion of the syringe measures the vertical distance between the substrate and the nozzle (S 210 ). Because the procedure associated with the measurement of the vertical distance has been already described referring to the constitutional elements of the distance sensor, it will not be explained here. 
         [0086]    Once the vertical distance is measured, it is decided as a second decision step whether the measured vertical distance falls within the allowable range (S 230 ). If a result of the second decision tells that the vertical distance is within the allowable range, the sealant is discharged (or dispensed) through the outlet of the nozzle (S 300 ). 
         [0087]    However, if a result of the second decision tells that the vertical distance is outside the allowable range, the vertical distance between the nozzle and the substrate is revised (S 250 ). 
         [0088]    In the revision step S 250 , either the syringe coupled to the nozzle can be moved vertically with respect to the surface of the substrate, or the other way round (i.e., the substrate can be moved vertically with respect to the nozzle). Either way, the vertical distance between the substrate and the nozzle must maintain a constant value. 
         [0089]    When the vertical distance between the nozzle and the substrate falls within the allowable range through the revision, the sealant is discharged (or dispensed) through the outlet of the nozzle (S 300 ). During the sealant dispensing step (S 300 ), the syringe and the nozzle dispense the sealant while moving around substantially the same pivot. 
         [0090]    The sealant dispenser and its control method have the following advantages. 
         [0091]    Firstly, the syringe and the nozzle have substantially the same pivot according to the principles of the present invention, so that the flow path of the sealant becomes a straight line, which in turn lowers the pressure required for discharging (or dispensing) the sealant. This means that diverse kinds of sealants including a highly viscous sealant can be utilized. 
         [0092]    Secondly, the distance between the measuring point on the substrate in which the laser beam is reflected and the position to which the sealant is applied is minimized, so that the sealant can be applied more precisely. 
         [0093]    Thirdly, since the flow path of the sealant is a straight line, the response speed of the sealant to be dispensed is increased. Thus, a precise amount of the sealant can be applied to an accurate position. Especially, by setting the start point and the end point of dispensing more precisely, the defect rate is reduced markedly. 
         [0094]    Fourthly, by setting the distance between the nozzle and the distance sensor within the allowable range, the application of the sealant can be controlled more precisely, and replacement of the syringe can be done easily and quickly. 
         [0095]    The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.