Liquid crystal dispensing apparatus having integrated needle sheet

A liquid crystal dispensing apparatus includes a needle sheet formed as a unitary piece for dispensing liquid crystal material contained within a liquid crystal container through a nozzle by selectively contacting a needle. The needle sheet includes a needle contacting portion for contacting the needle and a coupling portion for coupling the liquid crystal container to the nozzle. Therefore liquid crystal material is prevented from remaining within the needle sheet and the needle sheet can be easily cleaned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal dispensing apparatus, and more particularly, to a liquid crystal dispensing apparatus having a needle sheet formed as a unitary piece, wherein liquid crystal material is prevented from remaining in the needle sheet and a cleaning process may be simplified.

2. Discussion of the Background Art

As portable electric devices such as mobile phones, personal digital assistants (PDA), notebook computers, etc., continue to be developed, small, light, and power-efficient flat panel display devices such as liquid crystal displays (LCD), plasma display panels (PDP), field emission displays (FED), vacuum fluorescent displays (VFD), etc., have become the subject of intense research. Due to their ability to be mass-produced, ease in driving, and superior image qualities, LCDs are of particular interest.

LCDs display information on a screen using refractive anisotropic properties of liquid crystal material. Referring toFIG. 1, an LCD1typically includes a lower substrate (i.e., a driving device array substrate)5connected to an upper substrate (i.e., a color filter substrate)3via sealant9. A layer of liquid crystal material7separates the lower and upper substrates5and3. A plurality of pixels (not shown) is formed on the lower substrate5and driving devices such as thin film transistors (TFTs) are formed on each of the pixels. A color filter layer is formed on the upper substrate3allowing the LCD to express color. Further, pixel electrodes and a common electrode are also formed on the lower and upper substrates5and3, respectively. An alignment layer is formed on both the lower and upper substrates5and3to uniformly align molecules within the layer of liquid crystal material7. The molecules within the layer of liquid crystal material may be selectively oriented by the driving devices. Accordingly, as the orientation of the molecules within the liquid crystal material is manipulated, the amount of light transmitted through portions of the LCD may be selectively controlled to convey information.

Fabrication processes for LCD devices may be roughly divided into a driving device array fabrication process, where driving devices are formed on the lower substrate5, a color filter fabrication process, where the color filter is formed on the upper substrate3, and a cell fabrication process. These fabrication processes will now be described with reference to FIG.2.

Referring toFIG. 2, in the driving device array substrate fabrication process (S101), a plurality pixel areas are formed at crossings of a plurality of gate lines and data lines formed on the lower substrate5and thin film transistors arranged in each pixel area are connected to gate lines and corresponding ones of data lines. Also, pixel electrodes are connected to each of the thin film transistors to drive the layer of liquid crystal material. Accordingly, the layer of liquid crystal material may be driven in accordance with a signal applied to the thin film transistor.

In the color filter fabrication process (S104), red (R), green (G), and blue (B) color filter layers for producing color and a common electrode are formed on the upper substrate3.

The alignment layer is formed on both the lower and upper substrates5and3, respectively. After being formed on the substrates, the alignment layer is rubbed to induce molecules within the layer of liquid crystal material to inherit a predetermined pretilt angle and alignment direction between the lower and upper substrates5and3(S102and S105). Subsequently, spacers are dispensed over the lower substrate5to maintain a uniform cell gap between the upper and lower substrates (S103). The sealant is applied to an outer portion of the upper substrate3(S106) and the lower substrate5is pressed and attached to the upper substrate3(S107).

The lower and upper substrates5and3are formed from glass substrates having an area larger in size than any individual panel areas. Accordingly, a plurality of corresponding panel areas are formed where driving devices and color filter layers are arranged within the attached glass substrates. Thus, in fabricating individual liquid crystal display panels, the attached glass substrates are cut into individual panels (S108). Subsequently, liquid crystal material is injected through a liquid crystal injection opening into the cell gap formed between the two substrates of each individual liquid crystal display panel (S109). After the liquid crystal material is injected, the liquid crystal injection opening is sealed (S109) and each individual liquid crystal display panel is inspected (S110).

To inject the liquid crystal material through the liquid crystal injection opening, a pressure difference between the exterior and the interior of the liquid crystal display panel is induced.FIG. 3illustrates a device used to inject liquid crystal material into cell gaps of liquid crystal display panels.

Referring toFIG. 3, liquid crystal material14is provided in a container12arranged within a vacuum chamber10that is connected to a vacuum pump (not shown) capable of creating and maintaining a vacuum within the vacuum chamber. A liquid crystal display panel moving device (not shown) is installed within the vacuum chamber10and moves separated liquid crystal display panels down from an upper portion of the container12toward the surface of the liquid crystal material14. In what is known as a liquid crystal injection method, the liquid crystal injection opening16of each liquid crystal display panel is arranged to contact the liquid crystal material. Subsequently, nitrogen gas (N2) is pumped into the vacuum chamber to increase the pressure therein from the initial vacuum pressure. As the pressure within the vacuum chamber10increases, the liquid crystal material14contacting the liquid crystal injection opening16is extruded (i.e., injected) into the cell gap of the liquid crystal display panel due to the pressure difference between the interior of the liquid crystal display panel and the interior of the vacuum chamber containing the pumped nitrogen gas. After the cell gap is completely filled with liquid crystal material14, the injection opening16is sealed using a sealant.

Injecting liquid crystal material according to the process described above is disadvantageous, however, at least for the following reasons.

First, the amount of time required to completely inject liquid crystal material14into the liquid crystal display panel1can be excessively long. For example, the cell gap between the driving device array and the color filter substrates is very narrow (e.g., on the order of a few micrometers) and, therefore, only a very small amount of liquid crystal material can be injected into the liquid crystal display panel at any time. Accordingly, injecting liquid crystal material into a typical 15-inch liquid crystal display panel using the injection process described above may take up to about eight hours. Thus, the time required to fabricate LCDs is unduly increased with the use of the liquid crystal injection process.

Second, the amount of liquid crystal material required by the liquid crystal injection method described above is exceedingly large. While only a small amount of liquid crystal is removed from the container12, a large amount of liquid crystal may become exposed to the atmosphere or to the nitrogen gas. Accordingly, a large amount of liquid crystal material reacts with, and can be contaminated by, nitrogen or other gases within the atmosphere. As a result, the cost of fabricating LCDs increases because liquid crystal material not injected into the liquid crystal display panel must be discarded after the injection process.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystal dispensing apparatus having an integrated needle sheet that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An advantage of the present invention provides a liquid crystal dispensing apparatus for dispensing liquid crystal material directly onto a glass substrate including at least one liquid crystal panel.

Another advantage of the present invention provides a liquid crystal dispensing apparatus capable of preventing the contamination of LCD devices, wherein the cleaning of a needle sheet may be simplified.

To achieve the advantages of the present invention, as embodied and broadly described, a liquid crystal dispensing apparatus may, for example, include a liquid crystal container for holding liquid crystal material to be dispensed, a gas input line, a case for receiving the liquid crystal container, a needle capable of being inserted into the liquid crystal container, wherein the needle is movable in up-and-down directions, a spring arranged at one end of the needle, a needle sheet arranged at a lower portion of the liquid crystal container to couple the liquid crystal container to the case, wherein a portion of the needle sheet contacts the needle and includes discharging hole that is opened/closed due to the up-and-down movement of the needle, and a nozzle coupled to a lower portion of the liquid crystal container via the needle sheet, wherein the nozzle includes a discharge opening for dispensing liquid crystal held in the liquid crystal container onto a substrate that includes at least one panel.

In one aspect of the present invention, the needle sheet may include a coupling portion for coupling the liquid crystal container to the case and the liquid crystal container to the nozzle.

In another aspect of the present invention, a needle contacting portion may be integrally formed with the coupling portion and contacting the needle.

In yet another aspect of the present invention, the needle contacting portion and end portion of the needle contacting the needle contacting portion may be formed of hard metal.

In still another aspect of the present invention, the needle sheet may be formed as a unitary piece such fine gaps within the needle sheet are removed. Accordingly, liquid crystal material does not remain within the needle sheet and contaminated liquid crystal material may be prevented from being dispensed onto a substrate. Further, contamination of LCD devices may be prevented while allowing the needle sheet to be easily cleaned.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In order to solve the problems of the aforementioned liquid crystal material injection methods, liquid crystal dispensing methods have been proposed. The liquid crystal dispensing method forms a liquid crystal layer by dispensing liquid crystal material directly onto a substrate and uniformly distributing the dispensed liquid crystal material over the entire surface of the substrate by pressing the substrate. The aforementioned liquid crystal dispensing method enables the liquid crystal material to be arranged on the substrate within a short period of time so that the process of forming a liquid crystal layer in large LCD panels may be performed quickly. Since a predetermined amount of liquid crystal material is dispensed on the substrate, consumption of liquid crystal material is minimized. Accordingly, costs of manufacturing LCDs may be reduced.

FIG. 4illustrates the fabrication of an LCD using a liquid crystal dispensing method according to one aspect of the present invention.

Referring toFIG. 4, the liquid crystal material may be dispensed prior to bonding a lower substrate105, on which driving devices may be formed with an upper substrate103, on which a color filter may be formed. Accordingly, liquid crystal material107may be dispensed on the lower substrate105, for example, in the form of a droplet. Alternatively, the liquid crystal material107may be dispensed on the upper substrate103. Regardless of which substrate supports the liquid crystal material107, during the bonding process, the substrate supporting liquid crystal material107should be arranged such that it is located under the other substrate, wherein the liquid crystal material107is arranged between the two substrates.

Sealant109may be dispensed along edges on the upper substrate103to bond the upper substrate103to the lower substrate105when they are pressed together. As the upper and lower substrates103and105, respectively, are pressed, the liquid crystal material107becomes spread so that a liquid crystal layer having a uniform thickness may be formed between the upper and lower substrate103and105. Subsequently, the bonded substrates may be separated into individual LCD panels. Accordingly, the liquid crystal dispensing method may dispense liquid crystal material107onto the lower substrate105prior to final assembly of the liquid crystal display panel101.

As is evident, the liquid crystal injection method illustrated inFIGS. 1-3differs from the liquid crystal dispensing method illustrated in FIG.4. For example, in injecting liquid crystal material, a glass substrate must be divided into individual panels to inject the liquid crystal while, in dispensing liquid crystal material, liquid crystal material is dispensed to individual panels from a glass substrate already processed and divided.

FIG. 5illustrates a flow chart of a method for fabricating LCD device using a liquid crystal dispensing method.

Referring toFIG. 5, driving devices (e.g., TFTs) and a color filter layer are formed on the lower and upper substrates, respectively, in respective TFT array fabrication and color filter fabrication processes (S201and S204), similar to the driving device array substrate fabrication and color filter fabrication processes shown in FIG.2. The lower and upper substrates may be provided as glass substrates including a plurality of individual panel areas. By incorporating the liquid crystal dispensing method in the fabrication of LCDs, glass substrates having an area up to 1000×1200 mm2or more (an area much larger than glass substrates fabricated using liquid crystal injection methods) may be efficiently processed into individual panels.

An alignment layer may be formed on the lower and upper substrates. Subsequently, the alignment layers may be rubbed (S202and S205) and liquid crystal material may be dispensed onto liquid crystal display panel areas within the lower substrate (S203). Also, sealant may be applied to outer portions of corresponding liquid crystal display panel areas within the upper substrate (S206).

Next, the upper and lower substrates may be disposed opposite each other and pressed and attached together via the sealant. When the two substrates are pressed, the dispensed liquid crystal material spreads uniformly over the entire surface of the panels (S207). By the aforementioned liquid crystal dispensing method, a plurality of liquid crystal display panels may be simultaneously formed within the attached upper and lower glass substrates. Next, the attached glass substrates may be cut (S208) to separate the plurality of individual LCD panels. The individual LCD panels may then be inspected (S209).

Manufacturing LCDs according to the aforementioned liquid crystal dispensing method is advantageous over the liquid crystal injection method illustrated, for example, inFIG. 2in that layers of liquid crystal material may be rapidly formed between the upper and lower substrates. The liquid crystal injection method shown inFIG. 2requires the injection opening to be sealed by the sealing material after injection is complete. However, in fabricating LCDs via the liquid crystal dispensing method, no injection openings exist that need to be sealed. In fabricating LCDs via the liquid crystal injection method, panels contact liquid crystal material within the container during injection. As a result, outer surfaces of the LCD panels become contaminated and a cleaning process is required. However, in fabricating LCDs via the liquid crystal dispensing method, liquid crystal material may be dispensed directly onto the substrate. As a result, outer surfaces of substrates are not contaminated with liquid crystal material and extra cleaning processes are not required. Accordingly, methods of fabricating LCDs that incorporate liquid crystal dispensing methods are less complex, more efficient, and have a greater yield than methods of fabricating LCDs that incorporate liquid crystal injection methods.

In fabricating LCDs via the liquid crystal dispensing method, the layer of liquid crystal material must be formed to a predetermined thickness, directly proportional to the size of the cell gap in the LCD panel. Accordingly, positions of the liquid crystal droplets and the amount of liquid crystal material they contain must be precisely controlled. Therefore, an apparatus for dispensing liquid crystal material in precisely arranged droplets each containing a precise amount of liquid crystal material is provided in accordance with the principles of the present invention.

FIG. 6illustrates the fabrication of an LCD using a liquid crystal dispensing method according to one aspect of the present invention.

Referring toFIG. 6, liquid crystal material107may be dispensed onto the lower substrate105(including a plurality of panel areas) using a liquid crystal dispensing apparatus120. In accordance with the principles of the present invention, the liquid crystal dispensing apparatus120may be arranged over the substrate105and, although not shown inFIG. 6, contains liquid crystal material to be dispensed.

Generally, the liquid crystal material107is dispensed onto the substrate in the form of a droplet. In a first aspect of the present invention, the substrate105may move in x- and y-directions at a predetermined speed while the liquid crystal dispensing apparatus120remains in a fixed position and dispenses liquid crystal material at predetermined times. As a result, droplets of liquid crystal material may be arranged on the substrate105and spaced apart from each other along x- and y-directions at predetermined intervals. In a second aspect of the present invention, the substrate105may remain in a fixed position while the liquid crystal dispensing apparatus120, moving in x- and y-directions, dispenses liquid crystal material onto the substrate. Similar to the effect of the preceding aspect, droplets of liquid crystal material may be arranged on the substrate105and spaced apart from each other along x- and y-directions at predetermined intervals. By the second aspect, liquid crystal material may, however, by dispensed non-uniformly onto the substrate105due to the movement of the liquid crystal dispensing apparatus120. Accordingly, the locations of, and amount of liquid crystal material contained in, droplets arranged on the substrate105may deviate from the predetermined locations and amounts. Therefore, dispensing liquid crystal material according to the first aspect is generally preferred over the second aspect.

FIGS. 7A and 7Billustrate a liquid crystal dispensing apparatus according to one aspect of the present invention.FIG. 7Aillustrates the liquid crystal dispensing apparatus when liquid crystal material is not dispensed.FIG. 7Billustrates the liquid crystal dispensing apparatus when liquid crystal material is dispensed.

Referring toFIGS. 7A and 7B, the liquid crystal dispensing apparatus may, for example, include a cylindrically shaped liquid crystal container124. In one aspect of the present invention, the liquid crystal container124may be made of a material a having a high moldability, high plasticity, and that is substantially non-reactive with liquid crystal material (e.g., polyethylene, etc.). Materials such as polyethylene, however, have a low strength and may therefore become easily deformed by applied stresses. When the liquid crystal container124is deformed, liquid crystal material cannot be dispensed precisely onto the substrate. Accordingly, the container124may be inserted within case122. In one aspect of the present invention, case122may be formed of a material having a high strength (e.g., stainless steel, etc.). Although not shown, a gas supply tube connected to an exterior gas supply unit may be arranged at an upper portion of the liquid crystal container124. Gas such as nitrogen (N2) may be provided by the exterior gas supply unit, transported through the gas supply tube, and arranged within portions of the liquid crystal container124not occupied by liquid crystal material107. Accordingly, the gas may press on the liquid crystal material107.

A needle sheet140may be provided at a lower portion of the case122. The needle sheet140may couple the case122and the liquid crystal container124together. Although not shown, a protrusion may extend from a lower portion of the liquid crystal container124and an opening may be formed within the case122to receive the protrusion. Accordingly, the protrusion of the liquid crystal container124may be inserted into the opening of the case122and coupled to the needle sheet140. Additionally, a nozzle145for dispensing predetermined amounts of liquid crystal material107within the liquid crystal container124may be coupled to the needle sheet140.

FIG. 8illustrates an exploded perspective view of region ‘A’ shown inFIGS. 7A and 7B.

Referring toFIG. 8, the needle sheet140may, for example, include a coupling portion141and a needle contacting portion143formed together as a unitary piece. In one aspect of the present invention, the coupling portion141may comprise a nut portion and a bolt portion. The protrusion (not shown) of the liquid crystal container124may be inserted into and coupled with the nut portion of the coupling portion141. The bolt portion of the coupling portion141may be inserted into and coupled with a nut portion of the nozzle145. A discharge hole142, through which the liquid crystal material107within the liquid crystal container124may be dispensed onto the substrate, may be formed within the needle contacting portion143of the needle sheet. In one aspect of the present invention, the discharge hole142functions enable liquid crystal material107to be transported outside the liquid crystal dispensing apparatus120. Accordingly, the discharge hole142may be opened/closed by a needle136such that liquid crystal material107within the liquid crystal container124may be allowed into/prevented from entering the discharge hole142. Liquid crystal material107allowed into the discharge hole142may then be dispensed onto the substrate.

According to the principles of the present invention, the nozzle145may comprise a supporting portion146that is coupled to the coupling portion141of the needle sheet140and a discharge opening147, through which liquid crystal material107within the liquid crystal container124may be dispensed onto the substrate. The bolt portion of the coupling portion141may be arranged within the supporting portion146. In one aspect of the present invention, a discharge tube (not shown), through which liquid crystal material may be dispensed onto the substrate, may be formed parallel to a portion of the discharge hole142arranged proximate the supporting portion146such that the discharge opening147may extend from the discharge tube. In one aspect of the present invention, liquid crystal material107may enter into the discharge hole142and be dispensed onto the substrate via the discharge opening147.

According to the principles of the present invention, the needle136may be inserted into the liquid crystal container124such that a first end of the needle136contacts the needle contacting portion143of the needle sheet140. In one aspect of the present invention, the first end of the needle136may be provided with a conical shape having dimensions substantially conformal to the perimeter of the discharge hole142. The first end of the needle may be inserted into the discharge hole142of the needle contacting portion143and close the discharge hole142.

According to the principles of the present invention, a second end of the needle136may be arranged near an upper case126of the liquid crystal dispensing apparatus120where a spring128and magnetic bar132are provided. The magnetic bar132maybe formed of a ferromagnetic or soft magnetic material. A gap controlling unit134may be connected to the needle136above the magnetic bar132. A solenoid coil130having, for example, a cylindrical shape may be arranged to surround at least a portion of the magnetic bar132. The solenoid coil130may be connected to, and receive electric power from, an electric power supply unit (not shown). Upon receipt of the electric power, the solenoid coil130may exert a magnetic force on the magnetic bar132.

In one aspect of the present invention, the needle136and the magnetic bar132may be spaced apart from each other by a predetermined distance, x. When the electric power is applied to the solenoid coil130, a magnetic force is exerted on the magnetic bar132to induce the needle136to contact the magnetic bar132. When the electric power is not applied to the solenoid coil130, the elastic force of the spring128pushes the needle136to its original position. By the movement of the needle136toward and away from the needle sheet143, the discharging hole142formed in the needle sheet140may be opened or closed. As the first end of the needle136and the needle sheet140may contact each other repeatedly, depending on the presence of electric power applied to the solenoid coil130, the first end of the needle136and the needle sheet140may become damaged. Accordingly, the first end of the needle136and the needle contacting portion143of the needle sheet140may be formed of a material that substantially resist deformation (e.g., a hard metal).

Referring toFIG. 7B, when electric power is applied to the solenoid coil130, the needle136is away from the needle sheet and the discharge hole is opened. Accordingly, nitrogen gas supplied to the liquid crystal container124presses on the liquid crystal material107and causes it to be dispensed via the nozzle145. The amount of liquid crystal material107dispensed depends upon the time during which the discharging hole142is open and the pressure of the nitrogen gas within the liquid crystal container. The time during which the discharging hole142is opened depends upon the distance, x, between the needle136and the magnetic bar132, the magnetic force exerted on the magnetic bar132by the solenoid coil, and the intrinsic elastic force of the spring128. The magnetic force exerted on the magnetic bar132is proportional to the winding number of the solenoid coil130or the magnitude of the electric power applied to the solenoid coil130. The distance, x, between the needle136and the magnetic bar132may be controlled by the gap controlling unit134.

In one aspect of the present invention, the solenoid coil130may be arranged around the needle136instead of around the magnetic bar132. Accordingly, the needle136may be formed of a magnetic material and be magnetized when electric power is applied to the solenoid coil130. Additionally, the magnetic bar132may be fixed in a particular position. Therefore, the needle136may move upward and downward to selectively contact the magnetic bar132.

As described above, the needle sheet140, which the needle136contacts to control the dispensing of the liquid crystal material107, may be provided as a unitary piece. Accordingly, the coupling portion141, coupling the liquid crystal container124to the case122and the nozzle145, and the needle contacting portion143that contacts the needle136are formed as a unitary piece. The following advantages may be realized when using the needle sheet of the present invention.

FIG. 9illustrates a needle sheet in a related art liquid crystal dispensing apparatus.

Referring toFIG. 9, a related art needle sheet240used in a liquid crystal dispensing apparatus comprises a first coupling portion241a, a second coupling portion241b, and a needle contacting member243arranged between the first and second coupling portions241aand241b. The first coupling portion241acouples the liquid crystal container124to the case122. The second coupling portion242bcouples the liquid crystal container124to the nozzle145. The needle contacting member243includes a discharge hole that may be opened/closed by needle136thereby allowing liquid crystal material to be selectively dispensed. The related art needle sheet240is provided as a plurality of separate components assembled together. In forming the related art needle sheet240, the separate components are assembled in a predetermined order as they are mounted onto the liquid crystal dispensing apparatus. As the separate components of the needle sheet240are assembled, however, fine gaps between the first coupling portion241a, the second coupling portion241b, and the needle contacting portion243may be formed. For example, fine gaps may be formed between the first coupling portion241aand the needle contacting portion243and between the second coupling portion241band the needle contacting portion243. As a result, liquid crystal material107is forced into, and remains within, the fine gaps.

Liquid crystal material remaining within the fine gaps increases ionic impurities and contaminates the liquid crystal material107forced out of the liquid crystal container124. Subsequently, the contaminated liquid crystal material is leaked to the nozzle245and dispensed onto the substrate. Therefore, the layer of liquid crystal material is contaminated and a specific resistance of the liquid crystal material increases to lower a voltage maintenance factor of the LCD device. Accordingly, LCD devices formed with a contaminated layer of liquid crystal material have a degraded quality.

In order to prevent the liquid crystal material dispensed from becoming contaminated, the needle sheet240must be cleaned after liquid crystal material is dispensed a predetermined number of times. Liquid crystal material may generally be removed by soaking the needle sheet240in a cleaning chamber filled with acetone and isopropyl alcohol and liquid crystal material is thereby removed. However, the acetone and isopropyl alcohol does not easily infiltrate the fine gaps between the first coupling portion241a, the second coupling portion241b, and the needle contacting portion243. Therefore, it becomes extremely difficult to completely remove the liquid crystal material remaining within the fine gaps. In order to completely remove the remaining liquid crystal material, the first and second coupling portions241aand241band the needle contacting portion243must be disassembled before they are cleaned. However, disassembling the needle sheet240is troublesome and time consuming to disassemble the needle sheet240into its constituent components.

According to the principles of the present invention, the needle sheet140is formed as a unitary piece such that fine gaps do not exist in the needle sheet140. Therefore, liquid crystal material does not remain in the needle sheet140to contaminate liquid crystal material dispensed onto the substrate. Additionally, when cleaning, there is no need for disassembling the needle sheet140thereby simplifying the cleaning process.

According to the principles of the present invention, the needle sheet140of the liquid crystal dispensing apparatus120may be provided as a unitary piece coupled to the liquid crystal container124and the nozzle145. Liquid crystal material does not remain on the needle sheet140after liquid crystal material is dispensed such that LCD devices do not include contaminated layers of liquid crystal material. Also, since the needle sheet is formed as a unitary piece, a step of cleaning may be simplified.