Sealant dispenser and control method thereof

Disclosed is a sealant dispenser for more precisely dispensing a sealant onto a substrate, and a control method thereof. The sealant dispenser includes 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. According to the principles of the present invention, because the nozzle and the syringe have substantially the same central axis, the response speed of the sealant to be dispensed is increased and the start point and the end point of paste pattern are more precisely dispensed. Also, by minimizing the distance between the nozzle and a measuring point provided by the distance sensor, it becomes possible to dispense the sealant at higher precision.

RELATED APPLICATION

This application claims the benefit of the Korean Patent Application No. P2004-0033395, filed on May 12, 2004, which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a sealant dispenser, and more specifically, to a sealant dispenser for more precisely applying (or dispensing) a sealant onto a substrate, and a control method thereof.

2. Background of the Related Art

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.

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.

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.

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.

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.

FIG. 1illustrates 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 syringe20for storing a sealant, and a nozzle32coupled to a lower portion of the syringe20, for discharging the sealant50.

A long bar-shaped bracket30is connected to the syringe20in a horizontal direction, and the nozzle is installed on the end of the bracket30. And, a distance sensor40for measuring a vertical distance between the nozzle32and the substrate10is installed in the vicinity of the nozzle32.

More specifically, the distance sensor40is spaced apart a predetermined distance (L) from the syringe20which is filled with the sealant. Here, the syringe20and the distance sensor40must 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.

Usually, an optical laser distance sensor is used for the distance sensor40. The bottom surface of the distance sensor has a “”, where a light emitting part42for emitting a laser beam46is installed on one side and a light receiving part44for receiving a laser beam46is on the other side.

Here, the light emitting part42emits a laser beam46towards the substrate, whereas the light receiving part44receives the laser beam reflected from the substrate. As such, the distance sensor40measures a distance between the substrate10and the nozzle32.

When the laser beam path is changed due to a flexure on the sealant-applied surface of the substrate10, the distance sensor measures the laser beam received to the light receiving part and transfers its measured value to a controller (not shown).

However, the related art sealant dispenser has the following problems.

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.

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.

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.

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

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.

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.

Another object of the present invention is to provide a high precision sealant dispenser and a control method thereof.

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.

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.

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.

Preferably, the sensor supporting part includes a coupling hole that the nozzle passes through.

More preferably, the coupling hole is disposed between the light emitting part and the light receiving part.

Preferably, the syringe and the outlet of the nozzle have substantially the same central axis.

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

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.

Preferably, the vertical distance between the substrate and the nozzle is maintained at a constant value.

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.

Preferably, the position detecting sensor and the nozzle are located each other at the opposite sides with respect to the substrate.

Preferably, the sealant dispenser further includes an adjusting part for adjusting the position of a syringe storing the sealant.

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.

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.

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.

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.

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.

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.

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.

Preferably, the vertical distance between the substrate and the nozzle is revised to maintain a constant value.

Preferably, the syringe and the nozzle for dispensing the sealant to the principal plane of the substrate have substantially the same central axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2is a front view illustrating key elements of a sealant dispenser according to the present invention;FIG. 3is a side view of a key element taking in the direction of arrow A inFIG. 2; andFIG. 4illustrates a detected position of a distance sensor which is photographed by a position detecting sensor, and a location of a nozzle.

Referring toFIG. 2 to 4, the sealant dispenser of the present invention includes a nozzle130for discharging a sealant while making a relative motion to a substrate110mounted on a stage, a syringe120coupled to the nozzle130, for storing the sealant, and a distance sensor140installed on both sides of the lower portion of the syringe120, for measuring a vertical distance from the principal plane of the substrate110to an outlet of the nozzle130.

The syringe120for 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 substrate110. Also, the nozzle130is coupled to one end of the syringe120, and the outlet of the nozzle130is installed in such a manner to have substantially the same central axis with the syringe120.

The sealant150in the syringe120travels 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.

The distance sensor140includes a light emitting part142for emitting a laser beam toward the substrate110, a light receiving part144for receiving a reflected laser beam from the substrate110, and a sensor supporting part145for supporting the light emitting part142and the light receiving part144.

The sensor supporting part145is installed above the light emitting part142and the light receiving part144, encompassing the lower portion of the syringe120. And, the sensor supporting part145is provided with a coupling hole148between the light receiving part144and the light emitting part142, so that the nozzle130passing through the coupling hole148is located between the light receiving part144and the light emitting part142.

Optionally, the sensor supporting part145can have a first sensor support supporting the light receiving part144and a second sensor support supporting the light emitting part142. That is, the light receiving part144and the light emitting part142are 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 part144and the light emitting part142.

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.

As can be seen inFIG. 3, the light emitting part and the light receiving part of the distance sensor140, and the syringe120are aligned in parallel to the principal surface of the substrate. In detail, if seen in the direction of arrow A inFIG. 2, the distance sensor140is installed symmetrically around the center of the syringe.

Preferably, the light emitting part142and the light receiving part144of the distance sensor140are 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.

The distance sensor140measures a vertical distance between the nozzle130and the substrate110to which the sealant150is applied. To this end, the light emitting part142of the distance sensor140emits a laser beam towards the substrate110, and the light receiving part144receives a reflected laser beam from the substrate110.

If the vertical distance between the substrate110and the nozzle130is changed due to a flexure on the surface of the substrate110, 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 part144, but also the phase of the laser beam is changed. Based on these changes, the distance sensor140measures the vertical distance from the nozzle130and the substrate110.

The measured vertical distance between the nozzle130and the substrate110is sent to a controller (not shown). Then, the controller (not shown) moves the nozzle130and the substrate110relatively 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.

Meanwhile, as shown inFIG. 2, a measuring point112on the substrate110from which a laser beam146is reflected is disposed a predetermined distance away from a position where the sealant150is applied. If the measuring point112and the position to which the sealant150is applied are coincident, the distance sensor140is interfered with its distance measurement by the sealant150applied to the substrate110. Thus, it is important that the measuring point112and the nozzle130are spaced apart at least at a minimum distance for the sealant not to interfere with the laser beam. Moreover, the measuring point112is preferably located on a front end of the nozzle, along the direction of the sealant application.

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.

Furthermore, a position detecting sensor170is installed below the substrate110and detects a horizontal distance between the nozzle130and the measuring point in which the laser beam emitted from the distance sensor140is reflected. Precisely speaking, the position detecting sensor170and the nozzle130are located at the opposite sides with respect to the substrate110.

Although a camera is preferably used as the position detecting sensor170, any type of sensor capable of detecting the position of the nozzle and the measuring point can be utilized.

As depicted inFIG. 4, a screen175photographed by the position detecting sensor170displays the nozzle and the measuring point.

Since the substrate110coated with the sealant150is a transparent glass, the measuring point112and the nozzle130are projected onto the substrate110. Hence, the position detecting sensor170regards a position on the substrate110where the nozzle130is projected as a place where the sealant150should be applied, and detects a distance d between the measuring point112and the nozzle130.

If the distance d between the measuring point112and the nozzle130is outside the predetermined allowable range, an adjusting part160mounted on the head unit adjusts the position of the syringe coupled to the nozzle.

Actually, the adjusting part160is connected to the syringe and minutely adjusts the coupling position of the syringe. The adjusting part160includes a motor to be able to adjust the coupling position and angle of the syringe120.

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.

FIG. 5is 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.

As can be seen inFIG. 5, the control method of the sealant dispenser is largely divided into three steps: a first set-up step (S100) 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 (S200) performed by the distance sensor, for setting a vertical distance between the substrate and the nozzle; and a sealant dispensing step (S300) for dispensing or applying a sealant to the position set in the first and second steps.

In the first set-up step (S100), 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.

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 (S110).

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 (S130).

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.

If a result of the first decision in step S130tells 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 (S200).

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 (S150). 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.

When the first set-up step (S100) 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 (S200) for setting the horizontal distance between the substrate and the nozzle.

In the second set-up step (S200), the distance sensor on the circumference of the lower portion of the syringe measures the vertical distance between the substrate and the nozzle (S210). 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.

Once the vertical distance is measured, it is decided as a second decision step whether the measured vertical distance falls within the allowable range (S230). 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 (S300).

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 (S250).

In the revision step S250, 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.

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 (S300). During the sealant dispensing step (S300), the syringe and the nozzle dispense the sealant while moving around substantially the same pivot.

The sealant dispenser and its control method have the following advantages.

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.

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.

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.

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.