CN111243491A - Display panel and driving method and driving device thereof - Google Patents

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described through embodiments with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the basic idea disclosed and suggested by the embodiments of the present invention, are within the scope of the present invention.

Referring to fig. 1, a schematic diagram of a circular display panel provided in the prior art is shown. The number of pixels driven by the middle data line Dm of the circular display panel is the largest, and compared with the middle data line Dm, the number of pixels driven by any one edge data line Dy near the edge of the display panel is less than that of the middle data line Dm, so that the parasitic capacitance of the middle data line Dm is different from that of the edge data line Dy, and the light emitting current of the pixel circuit driven by the middle data line Dm is different from that of the pixel circuit driven by the edge data line Dy, so that the display brightness of the middle area and the edge area of the display panel is different.

In order to solve the problem of non-uniform display, fig. 1 adopts a capacitance compensation method, and a compensation capacitor Cd is disposed on the edge data line Dy lacking pixels for compensation, so that the parasitic capacitance of the edge data line Dy is close to or equal to the parasitic capacitance of the middle data line Dm, thereby improving the display uniformity. However, the area of the compensation capacitor Cd is large, and the compensation capacitor Cd occupies a large frame area, which affects the screen occupation ratio.

Referring to fig. 2, a schematic diagram of another display panel provided in the prior art is shown. The display panel comprises a first display area 1'A and two second display areas 1' B positioned on two sides of the first display area 1'A, wherein a non-display area above a diagram of the first display area 1' A is provided with a camera, a receiver and the like, so that the number of pixels driven by data lines of the first display area 1'A is less than that of pixels driven by data lines of the second display area 1' B, and the display brightness of the first display area 1'A and the second display area 1' B of the display panel is inconsistent.

In order to solve the problem of display non-uniformity, fig. 2 adopts a capacitance compensation method, and a compensation capacitor Cd is disposed on the data line of the display area one 1' a lacking pixels for compensation, so that the parasitic capacitance of the data line in the display area one 1' a is close to or equal to the parasitic capacitance of the data line in the display area two 1' B, thereby improving the display uniformity. However, the area of the compensation capacitor Cd is large, and the compensation capacitor Cd occupies a large frame area, which affects the screen occupation ratio.

The driving method provided by the embodiment comprises the following steps:

step S1, determining the parasitic capacitance Ci of the ith data line and the parasitic capacitance Cr of the reference data line, where the number Pr of pixel circuits in a column of pixel circuits driven by the reference data line is greater than or equal to the number Pi of pixel circuits in a column of pixel circuits driven by the ith data line, and i is greater than or equal to 1 and less than or equal to m.

As mentioned above, the number Pr of pixel circuits in one row of pixel circuits driven by the reference data line is greater than or equal to the number of pixel circuits in any other row of pixel circuits in the display area, so the reference data line is substantially a data line electrically connected to the pixel circuits in the row with the largest number of pixel circuits in the display area. One pixel circuit controls one sub-pixel to emit light.

After the reference data line is determined, the driving device acquires the parasitic capacitance of the reference data line and the parasitic capacitance of other data lines, the parasitic capacitance of the data line is related to the number of pixels driven by the data line, and the driving device determines the parasitic capacitance of the data line according to the number of pixel circuits driven by the data line. The optional determination of the parasitic capacitance Ci of the ith data line and the parasitic capacitance Cr of the reference data line includes: c is parasitic capacitance of the data line, P is the number of pixel circuits of a column of pixel circuits driven by the data line, and Cp is coupling capacitance between the pixel circuits and the data line electrically connected with the pixel circuits; the parasitic capacitance Ci of the ith data line and the parasitic capacitance Cr of the reference data line are calculated according to formula (1), wherein Ci is Pi Cp, and Cr is Pr Cp.

After the display panel is manufactured, the coupling capacitance between the pixel circuit and the data line electrically connected thereto is determined to be a constant value, and for any one pixel circuit, the coupling capacitance between the pixel circuit and the data line electrically connected thereto is Cp. The parasitic capacitance of one data line is the sum of the coupling capacitances of the data line and the pixel circuits driven by the data line, and based on the fact that the coupling capacitance between the pixel circuit and the data line electrically connected with the pixel circuit is known to be Cp, and the number P of the pixel circuits driven by one data line is also predetermined, the parasitic capacitance C of the data line can be calculated to obtain C ═ P × Cp.

It can be understood that there may be a plurality of reference data lines in the display area as shown in fig. 3, and compensation is performed only on the data lines other than the reference data lines without performing compensation on the plurality of reference data lines during compensation, and the number of pixel circuits driven by the data lines to be compensated is less than that driven by the reference data lines. Specifically, after the display panel is manufactured, the driving device finds out one or more reference data lines according to the number of the pixel circuits driven by each data line, and each data line to be compensated is compensated in a subsequent compensation process based on the relevant parameter of one of the reference data lines.

Step S2, obtaining a data voltage compensation value Δ Vi when the ith data line driving pixel circuit reaches the set luminance threshold value, according to the parasitic capacitance Ci, the parasitic capacitance Cr, and the data voltage Vr when the reference data line driving pixel circuit reaches the set luminance threshold value.

As described above, when it is known that the data voltage applied to the reference data line is Vr, the data voltage Vr of the reference data line drives the sub-pixels on the reference data line to emit light, the light emission brightness of the sub-pixels is defined as a set brightness threshold reached by the reference data line driving the pixel circuit by the data voltage Vr, and the other data lines are compensated, that is, the data voltages of the other data lines are compensated so that the light emission brightness of the sub-pixels on each data line is the set brightness threshold, and the set brightness threshold may be a fixed value or a brightness interval with a small range.

In this step, the parasitic capacitance Ci of the ith data line to be compensated and the parasitic capacitance Cr of the reference data line are determined, and the data voltage Vr of the reference data line and the set brightness threshold value that the pixel circuit needs to reach are also determined, then the original data voltage of the data line to be compensated is adjusted on the basis, wherein the original data voltage of the data line to be compensated is known, the pixel circuit of the data line to be compensated reaches the set brightness threshold value after adjustment, and at this time, the data voltage increment of the data line to be compensated is the data voltage compensation value Δ Vi of the data line to be compensated.

In step S3, data voltage compensation value Δ Vi of the ith data line is used for compensation to obtain data voltage Vi of the ith data line, where Vi is Vr + Δ Vi.

As described above, the original data voltages applied to each data line in the selectable display panel are Vr, and since the number of the pixel circuits of the data line to be compensated is smaller than that of the reference data line, the parasitic capacitance of the data line to be compensated is smaller than that of the reference data line, and the electric quantity charged into the pixel circuit by the data line is affected, the sub-pixel luminance of the data line to be compensated and the sub-pixel luminance of the reference data line under the same data voltage are different. Based on this, the original data circuit Vr of the ith data line to be compensated is adjusted, so that the pixel circuit driven by the ith data line reaches the set brightness threshold, and the data voltage compensation value of the ith data line is calculated to be Δ Vi, so that the data voltage applied to the ith data line after compensation is Vi, and Vi is Vr + Δ Vi. Therefore, the compensation of the pixel circuit columns lacking the pixel circuits is realized, so that the light-emitting current of the pixel circuit columns lacking the pixel circuits is basically the same as the light-emitting current of the pixel circuits driven by the reference data line, the light-emitting brightness of each pixel circuit control sub-pixel tends to be consistent, and the problem of uneven display is solved.

For the display panel shown in fig. 3, the shape of the display panel is the same as that of the display panel shown in fig. 2. Fig. 2 adopts a capacitance compensation method, and a compensation capacitor is disposed on a portion of a data line lacking a pixel, so that the parasitic capacitance of the data line is the same as that of a reference data line, wherein the compensation capacitor has a larger area and is generally disposed in a frame region, resulting in a wide frame. The display panel shown in fig. 3 adopts a data voltage compensation mode to adjust the input data voltage of the data line, so that the parasitic capacitance of the data line lacking the pixel is the same as that of the reference data line, the compensation capacitance does not need to be arranged on the data line lacking the pixel, the area of a frame area is correspondingly not additionally occupied, the frame can be obviously reduced, the narrow frame is realized, and the screen occupation ratio is further improved.

In the case of the circular display panel shown in fig. 5, the display panel has a circular shape as in the case of the display panel shown in fig. 1. In fig. 1, a capacitance compensation method is adopted, and a compensation capacitor Cd is disposed on an edge data line Dy lacking pixels, so that the parasitic capacitance of the edge data line Dy is the same as that of a reference data line Dm, wherein the compensation capacitor Cd has a larger area and is generally disposed in a frame area, resulting in a wide frame. The circular display panel shown in fig. 5 adopts a data voltage compensation mode to adjust the input data voltage of the data lines, so that the parasitic capacitance of the edge data lines lacking pixels is the same as that of the reference data lines, the compensation capacitance does not need to be arranged on the edge data lines lacking pixels, the area of a frame area is correspondingly not additionally occupied, the frame can be obviously reduced, the narrow frame is realized, and the screen occupation ratio is further improved.

In the embodiment of the invention, pixel circuit columns with less pixel circuits exist in a display area of a display panel, a data voltage compensation value delta Vi for driving the pixel circuits to reach a set brightness threshold value by an ith data line is obtained according to a parasitic capacitance Ci of an ith data line, a parasitic capacitance Cr of a reference data line and a data voltage Vr for driving the pixel circuits to reach the set brightness threshold value by the reference data line, the data voltage compensation value delta Vi is adopted to compensate the data voltage of the ith data line, the compensation for the ith column of pixel circuit columns lacking the pixel circuits can be realized, so that the luminous current of the pixel circuits driven by the ith data line is basically close to the luminous current of the pixel circuits driven by the reference data line, and the brightness of the sub-pixels driven by the ith data line is basically consistent with the brightness of the sub-pixels driven by the reference data line, the problem of display unevenness is improved. In addition, compared with a capacitance compensation scheme, the capacitance compensation is adopted for part of the data lines lacking the pixels, so that the capacitance of the data lines is the same as that of the reference data lines, wherein the compensated capacitance has a larger area and is usually arranged in a frame area.

For example, on the basis of the above technical solution, in optional step S2, obtaining a data voltage compensation value Δ Vi that the ith data line driving pixel circuit reaches the set luminance threshold according to the parasitic capacitance Ci, the parasitic capacitance Cr, and the data voltage Vr that the reference data line driving pixel circuit reaches the set luminance threshold includes:

wherein | Vth | is a threshold voltage of a driving transistor of the pixel circuit, Vref is a reference potential of the pixel circuit, and Cst is a storage capacitance of the pixel circuit;

and (3) calculating to obtain a data voltage compensation value delta Vi when the ith data line drives the pixel circuit to reach the set brightness threshold according to the formula (2).

As described above, the original data voltage Vr of any data line in the display area is Vr, and the data voltage Vr applied to the reference data line can make the luminance of the sub-pixels on the reference data line be the set luminance threshold. By using the above formula (2) to compensate the data voltage for the data line lacking the pixel circuit, the sub-pixel controlled by the pixel circuit column lacking the pixel circuit can reach the set brightness threshold.

Specifically, the data voltage compensation formula (2) is established as follows:

1) selecting a reference data line, wherein the parasitic capacitance of the reference data line is Cr, the data voltage is Vr, and the charged data voltage of the pixel is Vp, and the capacitance discharge quantity is expressed by formula (4), (Vr-Vpx Cr (4).

And determining the data line corresponding to the pixel circuit column with the largest number of pixel circuits in the display area as a reference data line, and calculating the parasitic capacitance Cr of the reference data line according to the number of the pixel circuits of the reference data line. The driving device sets the data voltage provided for the reference data line as Vr, and the voltage on the reference data line after the pixel is charged is Vp, so that the capacitance discharge amount of the reference data line is obtained by calculation as shown in formula (4).

2) Selecting data lines X with different numbers of pixel circuits driven by the reference data lines, wherein the parasitic capacitance of the data lines X is Cx, the data voltage is Vx, and the data voltage after the pixel is charged is Vp, and the capacitance discharge quantity of the data lines X is (Vx-Vp) × Cx (5).

The number of the pixel circuits driven by the data line X is smaller than that of the pixel circuits driven by the reference data line, the parasitic capacitance Cx of the data line X is obtained by calculating by the driving device according to the number of the pixel circuits of the data line X, and it can be understood that the pixel circuit columns with the same number as that of the pixel circuits driven by the reference data line do not need to carry out data voltage compensation. The driving device sets the data voltage provided for the data line X to be Vx, and the voltage on the data line X after the pixel is charged should be the same as the voltage on the reference data line after the pixel is charged, so that the luminance of the sub-pixel driven by the data line X is the same as the luminance of the sub-pixel driven by the reference data line, that is, the voltage on the data line X after the pixel is charged is Vp. The capacitance discharge amount of the data line X calculated in this way is shown in equation (5).

3) After the data line charges the storage capacitor Cst of the pixel circuit, the charge amount of the storage capacitor Cst is expressed by equation (6), (Vp- | Vth | -Vref) × Cst (6).

One pixel circuit is disposed corresponding to one sub-pixel and configured to control whether the sub-pixel emits light or not, and the pixel circuit includes a storage capacitor Cst. When the pixel circuit is charged by the data line, the potential of the storage capacitor Cst in the pixel circuit is changed from the reference potential Vref of the pixel circuit to near Vdata- | Vth |, and thus the voltage of the storage capacitor Cst is changed to Vdata- | Vth | -Vref. The voltage Vp on the charged data line is Vdata, and the charging amount of the storage capacitor Cst is calculated as shown in formula (6).

After the pixel is charged, the discharge amount of the capacitor on the reference data line should be equal to the charge amount of the storage capacitor Cst in the pixel circuit, so that the voltage Vp on the data line after the pixel is charged can be calculated as shown in formula (7).

In the display area, the capacitance discharge amounts of different data lines are generally consistent, so that the data voltage Vx of the data line X, which is the compensated data voltage of the data line X, can be calculated.

According to the formula (8), the compensated data voltage Vx of the data line X is related to its parasitic capacitance, the charged line voltage, and the reference data line parameter, and if the pixel charged data line voltage Vp is known as shown in the formula (7), the formula (7) is substituted into the formula (8), so as to obtain the equation (9) of the compensated data voltage Vx of the data line X. The influence of the unknown parameter Vp is eliminated in equation (9), and the compensated data voltage Vx of the data line X is converted into a correlation between its parasitic capacitance, pixel circuit parameter, and reference data line parameter.

The parasitic capacitance Cx of the data line X, the threshold voltage | Vth | of the driving transistor of the pixel circuit, the reference potential Vref, and the storage capacitance Cst, the parasitic capacitance Cr of the reference data line is a known parameter that can be determined after the panel is manufactured, and the input data voltage Vr of the reference data line is a known parameter that can be determined during the display phase, so Vx represented by equation (9) has been converted to be correlated with the known parameter of the display panel.

7) Obtaining the data voltage compensation value delta Vx of the data line X according to the formula (9),

when the original data voltages supplied to the data lines by the driving device are all Vr, the data voltage compensation value Δ Vx of the data line X obtained on the basis of Vr is Vx-Vr. It can be understood that, after the display panel is manufactured, the driving device obtains a data voltage compensation formula of the data line X according to the above steps, and performs data voltage compensation on the data line X according to the formula.

Specifically, in the display stage, the driving device obtains the original data voltage Va of the reference data line according to the display screen, calculates the data voltage compensation value Δ Vj of the data line j according to the Δ V formula, so as to obtain the compensated data voltage Vj of the data line j equal to Δ Vj + Va, and applies Vj to the data line j. The driving device can perform data voltage compensation on each data line by the method, and the luminance substrates of the compensated sub-pixels are consistent, so that the display uniformity is improved.

The display panel also comprises a scanning line which is arranged in a way of crossing the data line, the scanning line controls whether the corresponding row of pixel circuits is conducted, and the data line charges the conducted pixel circuits when the pixel circuits are conducted so as to enable the sub-pixels to emit light. The width of the scan line affects the threshold voltage of the driving transistor of the pixel circuit, and Vthr can be considered as the compensation of the scan line width to the threshold voltage Vth, so that when the data line is charged to the storage capacitor Cst, the Cst voltage substantially changes from Vref to near Vdata- | Vth | -Vthr, thereby obtaining the data voltage compensation formula (3). The data voltage compensation formula (3) provided in this embodiment considers the influence of the scan line width on the threshold voltage of the driving transistor of the pixel circuit, realizes the compensation of the scan line width on the threshold voltage Vth, and can further improve the accuracy of the data voltage compensation, thereby improving the display uniformity.

Optionally 0.2-0.4 of Vthr. The width of the scan line affects the threshold voltage of the driving transistor of the pixel circuit, and based on the current display panel size and the design of the scan line width, Vthr compensation for the threshold voltage Vth is about 0.2-0.4, and optionally 0.3.

Based on this, equation (3) differs from equation (2) in that: after the data line charges the storage capacitor Cst of the pixel circuit, the charge amount of the storage capacitor is (Vp- | Vth | -Vref-Vthr) × Cst, and the data voltage compensation value Δ Vx of the data line X is

Specifically, the derivation process of equation (3) differs from equation (2) in that:

step 3), after the data line charges the storage capacitor Cst of the pixel circuit, the charging amount of the storage capacitor is converted into a formula (6'), (Vp- | Vth | -Vthr-Vref) × Cst (6');

Step 7), obtaining a data voltage compensation value delta Vx of the data line X according to the formula (9'),

by adopting the data compensation formula to perform data compensation on the data line, the light-emitting current of the pixel circuit driven by the data line is basically close to the light-emitting current of the pixel circuit driven by the reference data line, and the brightness of the sub-pixel driven by the data line is basically consistent with that of the sub-pixel driven by the reference data line, so that the problem of uneven display is solved. In addition, compared with a capacitance compensation scheme, the data voltage compensation mode only needs the driving device to adjust the data voltage applied to the data line, the area of a frame area is not occupied, the frame can be obviously reduced, the narrow frame is realized, and the screen occupation ratio is further improved.

Based on the same inventive concept, embodiments of the present invention further provide a driving apparatus for a display panel, where the driving apparatus can be used to perform the driving method described in any of the above embodiments, and the driving apparatus can be implemented in a software and/or hardware manner and is configured in a non-display area of the display panel. The display panel comprises a display area, wherein the display area comprises m data lines and m columns of pixel circuits, one data line drives one column of pixel circuits, and m is a positive integer greater than 1.

C＝P*Cp (1)，

c is a parasitic capacitance of the data line, P is the number of pixel circuits of a column of pixel circuits driven by the data line, and Cp is a coupling capacitance between the pixel circuits and the data line electrically connected thereto.

wherein | Vth | is a threshold voltage of a driving transistor of the pixel circuit, Vref is a reference potential of the pixel circuit, and Cst is a storage capacitance of the pixel circuit.

wherein | Vth | is a threshold voltage of a driving transistor of the pixel circuit, Vref is a reference potential of the pixel circuit, Cst is a storage capacitance of the pixel circuit, and Vthr is a compensation threshold voltage. Optionally 0.2-0.4 of Vthr.

The optional driving device is also used for establishing a data voltage compensation formula in advance; the method comprises the following steps:

1) selecting the reference data line, wherein the parasitic capacitance of the reference data line is Cr, the data voltage is Vr, the data voltage after the pixel is charged is Vp, the capacitance discharge amount is formula (4),

(Vr-Vp)*Cr (4)；

2) selecting data lines X with different numbers of pixel circuits driven by the reference data lines, wherein the parasitic capacitance is Cx, the data voltage is Vx, the charged data voltage of the pixel is Vp, the capacitance discharge amount is formula (5),

(Vx-Vp)*Cx (5)；

3) after the data line charges the storage capacitor Cst of the pixel circuit, the charge amount of the storage capacitor Cst is expressed by equation (6),

(Vp-|Vth|-Vref)*Cst (6)；

7) Obtaining the data voltage compensation value delta Vx of the data line X according to the formula (9),

the specific implementation process of the optional pre-established data voltage compensation formula is as follows: after the data line charges the storage capacitor Cst of the pixel circuit, the charge amount of the storage capacitor is (Vp- | Vth | -Vref-Vthr) × Cst, and the data voltage compensation value Δ Vx of the data line X is,

in the embodiment of the invention, the data voltage of the data line is compensated, and the compensation of the ith pixel circuit column lacking the pixel circuit can be realized, so that the luminous current of the pixel circuit driven by the ith data line is basically close to the luminous current of the pixel circuit driven by the reference data line, the brightness of the sub-pixel driven by the ith data line is basically consistent with the brightness of the sub-pixel driven by the reference data line, and the problem of uneven display is solved. In addition, compared with a capacitance compensation scheme, the data voltage compensation mode does not need to occupy the area of a frame area, so that the frame can be obviously reduced, a narrow frame is realized, and the screen occupation ratio is further improved.

Based on the same inventive concept, an embodiment of the present invention further provides a display panel, as shown in fig. 3, including: a display area 1 and a non-display area 2; the display area 1 comprises m data lines 11 and m columns of pixel circuits 12, one data line 11 drives one column of pixel circuits 12, the m data lines 11 comprise an ith data line and a reference data line Dr, the number of the pixel circuits of one column of pixel circuits 12 driven by the ith data line is less than or equal to that of the pixel circuits of one column of pixel circuits 12 driven by the reference data line Dr, m is a positive integer greater than 1, and i is greater than or equal to 1 and less than or equal to m; the non-display region 2 includes the driving means 3 as described above, and the driving means 3 is configured to supply the data voltage Vi to the ith data line and supply the data voltage Vr to the reference data line Dr, where Vi is Vr + Δ Vi, and Δ Vi is a predetermined data voltage compensation value required when the ith data line driving pixel circuit reaches the set luminance threshold of the reference data line Dr, so that the light emission current Imi of the pixel circuit driven by the ith data line approaches the light emission current Imr of the pixel circuit driven by the reference data line.

The method comprises the following steps of performing verification through tests, selecting a data line i and a reference data line, wherein the number of pixel circuits of the data line i is different from that of the reference data line; the parasitic capacitance of the reference data line is 10pF, the parasitic capacitance of the data line i is 2pF, and the original data voltage applied to the data line is 4.2V.

For the reference data line, the pixel circuit driven by the reference data line during the display period has a light-emitting current Imr of about 1.0453 nA.

Before compensation, the data voltage applied to the data line i is 4.2V, and the pixel circuit driven by the data line i has an emission current Imi of about 2.67nA in the display period. Obviously, before compensation, the difference between the light emitting current of the pixel circuit driven by the data line i and the light emitting current of the pixel circuit driven by the reference data line is large, and thus the difference between the light emitting brightness of the sub-pixel driven by the data line i and the light emitting brightness of the sub-pixel driven by the reference data line is large, which results in uneven display.

After compensation, the data voltage applied to the data line i is the compensated data voltage 4.3663V, and the pixel circuit driven by the compensated data voltage is driven by the pixel circuit to have a light emitting current Imi of about 1.0477nA in the display phase. Obviously, after compensation, the difference between the light-emitting current of the pixel circuit driven by the data line i and the light-emitting current of the pixel circuit driven by the reference data line is smaller, so that the difference between the light-emitting brightness of the sub-pixel driven by the data line i and the light-emitting brightness of the sub-pixel driven by the reference data line is reduced, and the uniformity of the display brightness is improved.

The optional display panel is a circular display panel. As shown in fig. 5, in the circular display panel, the number of pixel circuits in the edge pixel circuit row is smaller than that of the pixel circuits in the middle pixel circuit row, and the data voltage compensation is performed on the pixel circuit row with the edge lacking pixel circuits by using a data voltage compensation method, so that the difference between the light-emitting luminance of the edge display pixels and that of the middle display pixels can be reduced, and the display uniformity can be improved. And the data voltage compensation mode does not need to occupy the area of the frame, so that a narrow frame can be realized, and the screen occupation ratio is improved.

In the embodiment of the invention, the data voltage of the data line is compensated, and the compensation of the ith pixel circuit column lacking the pixel circuit can be realized, so that the luminous current of the pixel circuit driven by the ith data line is basically close to the luminous current of the pixel circuit driven by the reference data line, the brightness of the sub-pixel driven by the ith data line is basically consistent with the brightness of the sub-pixel driven by the reference data line, and the problem of uneven display is solved. In addition, compared with a capacitance compensation scheme, the data voltage compensation mode does not need to occupy the area of a frame area, so that the frame can be obviously reduced, a narrow frame is realized, and the screen occupation ratio is further improved.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious modifications, rearrangements, combinations and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.