GRINDING APPARATUS AND GRINDING METHOD

BACKGROUND

The present disclosure relates to a grinding apparatus and a grinding method that grind objects such as a glass plate whose surface has been smoothened and a display plate used in a liquid crystal display.

In recent years, in addition to traditional mobile phones that simply have a voice communication function, advanced mobile phones (known as “smartphones”) that are also capable of functioning as mobile personal computers have become common. In many cases, a flat panel display (FPD) such as a liquid crystal panel or an organic EL electroluminescence) panel is used in the display unit of such a mobile terminal device. The surface (and rear surface) of a flat panel display (or hereinafter “display panel”) is subjected to grinding before attachment to a mobile terminal device. As one example, as shown in FIG. 11, during the grinding process for a liquid crystal panel produced by combining (i.e., sticking together) a color filter 15 and a TFT (Thin Film Transistor) substrate 16, the liquid crystal panel needs to be made both thinner and stronger. Both the color filter 15 and the TFT substrate 16 have a glass substrate as the main component.

A double-sided grinder is known as a grinder capable of carrying out grinding on a display panel. A double-sided grinder is capable of simultaneously grinding both surfaces of workpieces subjected to grinding by epicyclically moving planetary carriers with holding holes that hold the workpieces and grinding the workpieces in the holding holes between an upper surface plate and a lower surface plate. During grinding, a slurry (abrasive) supplied from the upper surface plate becomes interposed between the upper and lower surface plates, thereby enabling the surfaces of the workpiece to be ground.

As examples of techniques for grinding a workpiece, Japanese Laid-Open Patent Publication No. S61-230866 discloses the provision of a cutaway at an arbitrary position of a positioning hole to facilitate the removal of a workpiece when grinding is carried out on one surface of the workpiece (single-sided attachment), while Japanese Laid-Open Patent Publication No. 2001-198805 discloses a grinding apparatus that grinds a workpiece and has clearances (injection holes 5) provided at the four corners of a recess hole 2 formed in a substantially rectangular shape in a workpiece holder.

SUMMARY

However, when the fracture strength of a display panel that has been ground using a double-sided grinder was measured using a strength tester, as shown in FIG. 12, two types of fracture mode were found. FIG. 12A shows a fracture 21 that starts at an end surface and FIG. 12B shows a fracture 22 that starts at a mid-surface position. Fractures that start at an end surface occur prominently in strength tests according to a JIS method. Fractures that start at a mid-surface position occur prominently in strength tests according to a DIG method.

At present, the functionality of mobile terminal devices is advancing rapidly and the number of people carrying such mobile terminal devices is increasing. In keeping with such user trends, there is demand for display panels with even higher fracture strength.

The grinder disclosed in Patent Publication No. S61-230866 is not capable of raising the strength of the workpiece that has been ground and does not contribute to improving the strength of the workpiece. With the grinding apparatus according to Patent Publication No. 2001-198805, since there is contact between an end surface (side surface) of the workpiece and the edge of the recess hole 2 of the workpiece holding jig across a long region that includes the center of the edge, there is a reduction in the strength of the workpiece.

The present disclosure aims to prevent the occurrence of at least fractures that start at the end surface of a display panel during grinding with a grinding apparatus, such as a double-sided grinder, that uses planetary carriers.

A grinding apparatus according to an embodiment of the present disclosure includes: an upper surface plate; a lower surface plate disposed facing the upper surface plate and rotating in an opposite direction to the upper surface plate; a sun gear rotated by a same rotational shaft as the upper surface plate and the lower surface plate; an internal gear rotated by the same rotational shaft as the upper surface plate and the lower surface plate; and a planetary carrier in which a holding hole that holds a workpiece is formed and which revolves while rotating in engagement with the sun gear and the internal gear. The holding hole in the planetary carrier is provided with a cutaway in a side of the holding hole that contacts a side surface of the workpiece when the planetary carrier rotates.

According to the above embodiment of the present disclosure, by forming the cutaway, contact between the side surface of the workpiece and the edge of the holding hole of the planetary carrier during grinding is avoided or the contact length (or area) is reduced.

According to the above embodiment of the present disclosure, it is possible to prevent the occurrence of fractures that start at an end surface of a workpiece during grinding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a grinding apparatus according to a first embodiment of the present disclosure;

FIG. 2 is a perspective view useful in explaining planetary carriers of the grinding apparatus according to the first embodiment;

FIG. 3 is a plan view showing one example of a planetary carrier according to the first embodiment.

FIG. 4 is a cross-sectional view along a line A-A near clearances of a holding hole in a planetary carrier, in a state where a workpiece has been attached to the holding hole;

FIG. 5 is a diagram useful in explaining an example of the supplying of slurry to the grinding apparatus;

FIG. 6 is a schematic diagram useful in explaining an example operation of the grinding apparatus;

FIG. 7 is a diagram useful in showing a method of measuring the strength of a workpiece according to a JIS strength test;

FIG. 8 is a graph showing example relationships between fracture strength and cumulative failure rate;

FIGS. 9A and 9B are diagrams useful in explaining examples of results analyzed according to Taguchi methods, with FIG. 9A showing results for S/N ratio (stability) and FIG. 9B showing results for sensitivity (a characteristic value);

FIG. 10 is a graph showing a degree of improvement in average strength of the workpiece when grinding has been carried out according to more appropriate conditions;

FIG. 11 is a perspective view showing one example of a display panel; and

FIGS. 12A and 12B are diagrams useful in explaining types of fractures that occur for a display panel, with FIG. 12A showing a fracture that starts at an end surface and FIG. 12B showing a fracture that starts at a mid-surface position.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the appended drawings. Note that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted.

The following description is given in the order indicated below.

1. Introduction
2. First Embodiment (Planetary Carriers: Example of Provision of Clearances at Holding Holes)
3. Second Embodiment (Grinding Conditions: Example Where Control Factors are Set Appropriately)
1. Introduction

Out of the two fracture modes described earlier, the present inventors considered whether the cause of a fracture that starts at the end surface of a workpiece (see FIG. 12A) was the production of cracks in a side surface due to contact between the workpiece and a planetary carrier during grinding, resulting in insufficient strength. Accordingly, the present inventors investigated whether preventing contact between the side surface of a workpiece and the planetary carrier would be effective in preventing fractures that start at the end surface of the workpiece. This is described in detail below as the first embodiment.

Meanwhile, the present inventors also considered whether the cause of a fracture that starts at a mid-surface position on a workpiece (see FIG. 12B) was the production of minute cracks (or “microcracks”) in such surface by grains in the abrasive during grinding due use of sub-optimal grinding conditions, again resulting in insufficient strength. Accordingly, the present inventors arrived at the technical concept of optimizing the grinding conditions (i.e., calculating optimal values according to minimization) as an effective method of preventing fractures that start at a mid-surface position of a workpiece. This is described in detail below as the second embodiment.

2. First Embodiment
Example Configuration of Grinding Apparatus

The grinding apparatus according to the first embodiment of the present disclosure will now be described with reference to the drawings. In this first embodiment of the present disclosure, a double-sided grinder is given as an example of a “grinding apparatus” for the present disclosure. First, the configuration of this double-sided grinder as a grinding apparatus according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 3.

FIG. 1 is a perspective view schematically showing a grinding apparatus according to the first embodiment of the present disclosure. Note that planetary carriers have been omitted from this diagram. FIG. 2 is a perspective view useful in explaining planetary carriers of the grinding apparatus according to the first embodiment. FIG. 3 is a plan view showing one example of a planetary carrier according to the first embodiment.

As shown in FIGS. 1 and 2, the grinding apparatus according to the present embodiment includes an upper surface plate 1, a lower surface plate 2 disposed so as to face the upper surface plate 1, a sun gear 3, and an internal gear 4. These four gears (rotating bodies) are capable of being rotated with independently selected rotational velocities.

The upper surface plate 1 is an annular disc that presses display panels as workpieces from above, and rotates due to the rotational force of an upper surface plate rotating portion 1A being transmitted thereto. The lower surface plate 2 is an annular disc on which the workpieces are placed and rotates due to a rotational force being transmitted thereto from a lower surface plate bearing (not shown). The upper surface plate 1 and the lower surface plate 2 rotate in respectively opposite directions during grinding. For example, when the grinding apparatus is viewed from above, the direction of rotation D1 of the lower surface plate 2 is anticlockwise when the direction of rotation Du of the upper surface plate 1 is clockwise.

The sun gear 3 is an external gear positioned at the center of the upper surface plate 1 and the lower surface plate 2 and uses a tooth form of the same size as a tooth form of planetary carriers 5. The sun gear 3 is rotated by the same rotational shaft as the upper surface plate 1 and the lower surface plate 2. The internal gear 4 is an internal gear positioned around the outer circumference of the lower surface plate 2 and uses a tooth form of the same size as the tooth form of the planetary carriers 5. The internal gear 4 is rotated by the same rotational shaft as the upper surface plate 1 and the lower surface plate 2.

The planetary carriers 5 disposed between the upper surface plate 1 and the lower surface plate 2 are shaped as comparatively thin discs, have teeth (concave grooves) cut into the outer circumferential surfaces thereof, and revolve while rotating in engagement with the sun gear 3 and the internal gear 4. The direction of rotation Ds of the sun gear 3 and the direction of rotation Di of the internal gear 4 are the same, and the direction of rotation of the planetary carriers 5 is decided by the difference between the rotational velocities of the two gears. Steel plate, glass epoxy resin, vinyl chloride sheet, or the like is used as the material of the planetary carriers 5.

For example, if the sun gear 3 is rotating faster than the internal gear 4 (in the anticlockwise direction), the direction of rotation of the planetary carriers 5 will be the clockwise direction Dc1. Meanwhile, if the internal gear 4 is rotating faster than the sun gear 3 (in the anticlockwise direction), the direction of rotation of the planetary carriers 5 will be the anticlockwise direction Dc2. Note that if the rotation of the lower surface plate 2 is in the anticlockwise direction D1, rotation of the planetary carriers 5 in the clockwise direction Dc1 is “forward rotation”. Conversely, if the rotation of the lower surface plate 2 is in the anticlockwise direction D1, rotation of the planetary carriers 5 in the anticlockwise direction Dc2 is “backward rotation”.

As shown in FIG. 3, a plurality of holding holes 10 into which workpieces to be ground are inserted are formed in a flat surface part of each planetary carrier 5. Display panels of liquid crystal panels or the like that have been cut into individual pieces are inserted into the holding holes 10 of the planetary carriers 5 and are held therein during the grinding process.

The holding holes 10 are substantially rectangular in shape and are formed with the length direction thereof in parallel to the radial direction of the planetary carriers 5. Cutaways (or “clearances”) 11a, 11b are formed at substantially central parts (i.e., near the center) of two facing edges 10a, 10b in the length direction that form each holding hole 10. By forming cutaways, that is, the clearances 11a, 11b for a holding hole 10 in this way, contact between the side surfaces of a workpiece and the edges 10a, 10b in the length direction of the holding hole 10 in a planetary carrier 5 during grinding is avoided or the contact length (contact area) of such contact is reduced.

FIG. 4 is a cross-sectional view along a line A-A near the clearances 11a, 11b of a holding hole 10 in a state where a workpiece has been inserted into the holding hole 10. As one example, if the rotation of the planetary carriers 5 is backward rotation (in the anticlockwise direction Dc2), the workpiece will move and be pressed against the edge 10a (with the clearance portion 11a) side of the holding holes 10 due to an inertia force. The side surface of the workpiece is subjected to drag F from the edge 10a of the planetary carrier 5 contacted by such side surface, which can cause cracks to occur in the side surface of the workpiece.

In the present embodiment, as described above, by forming the clearances, contact between the side surfaces of a workpiece and the edges 10a, 10b of a holding hole 10 of a planetary carrier 5 during grinding is avoided or the contact length (or area) is reduced, which makes it possible to suppress the production of cracks compared to in the past.

Note that in the present embodiment, the holding holes 10 are formed slightly larger than a size into which a workpiece can fit perfectly. By doing so, a degree of play is provided between each holding hole 10 and a workpiece, resulting in fewer opportunities for contact between the edges of the holding hole 10 and the workpiece and further reducing the production of cracks.

Note that although the clearances 11a, 11b are formed as semicircular or oval arc-shaped cutaways in the example in FIG. 3, as other examples the clearances 11a, 11b may be a shape that uses three edges of a quadrangle or two edges of a triangle.

With the configuration described above, the planetary carriers 5 that hold the workpieces are epicyclically driven so that the workpieces are ground between the upper surface plate 1 and the lower surface plate 2, thereby enabling both surfaces of the workpieces to be simultaneously machined.

Example Operation of Grinding Apparatus

The operation of a grinding apparatus of the above configuration will now be described. FIG. 5 is a diagram useful in explaining an example of the supplying of slurry to the grinding apparatus. FIG. 6 is a schematic diagram useful in explaining an example operation of the grinding apparatus.

Normally, once the grinding process starts, slurry (abrasive) 7 supplied as shown in FIG. 5 falls through holes or the like formed in the upper surface plate 1 toward the lower surface plate 2. With the slurry 7 interposed between the upper surface plate 1 and the lower surface plate 2, relative movement is caused between the upper surface plate 1 or the lower surface plate 2 and the workpiece while applying the pressure P (see FIG. 6), and rolling, scratching, crushing, and the like of grains included in the slurry 7 are used to smoothly and precisely finish the surfaces of the workpiece.

Strength Tests

Measurement was carried out via strength tests on workpieces after grinding using a strength tester that operates according to the principles shown in FIG. 7. The example in FIG. 7 shows the principles of a JIS strength test. This JIS strength test has a liquid crystal panel, where the color filter 15 and the TFT substrate 16 are combined, mounted horizontally as a workpiece on two rod-like supports 18A, 18B that are 30 cm apart, for example. An object 17 equipped with protrusions is then lowered from above according to a specified method and the occurrence of cracks and the state of any fractures are observed. In addition, a DIG strength test (not shown) is executed in addition to the JIS method to measure the strength of the workpiece after grinding. Note that 11N is currently necessary as the target strength of display panels.

FIG. 8 is a graph showing the measurement results of a strength test (in this example, according to the JIS method) of a liquid crystal panel (see FIG. 11) for a case where the clearances 11a, 11b are provided on the holding holes 10 of the planetary carriers 5. The graphs in FIGS. 9A and 9B are so-called “Weibull distributions” that show examples of the relationship between fracture strength (N) and cumulative failure rate F(t) %. First, to find the strength before the provision of the clearances 11a, 11b, strength tests were carried out on 1,000 liquid crystal panels and found that liquid crystal panels with an insufficient fracture strength of 8N were present. On the other hand, by using the planetary carriers 5 in which the clearances 11a, 11b are provided, a fracture strength of 25N that is at least three times higher could be achieved. This satisfies the target strength of 11N that is currently demanded for display panels.

According to the first embodiment described above, by providing the clearances (cutaways) at the holding portions for workpieces provided on the planetary carriers, it is possible to achieve a large improvement in strength. As one example, a strength improvement of three times or higher was observed on a Weibull distribution.

3. Second Embodiment

The second embodiment of the present disclosure will now be described with reference to Table 1 and FIGS. 9A and 9B. As shown in Table 1, eight items were given as control factors for grinding and three levels were set for each of such items. Note that the items “specific gravity”, “granularity”, “flow rate”, and “slurry temperature” in the table relate to the slurry. The item “first four steps” indicates the time until the rotational velocities of the respective gears rise in four stages to a set velocities. The item “direction of rotation” shows the direction of rotation of the planetary carriers 5. The item “pressing force” is the pressure applied by the upper surface plate 1 (or the lower surface plate 2) onto workpieces. Note that when the rotational velocity of the lower surface plate 2 is 30 rpm, 35 rpm, and 40 rpm, as examples the rotational velocity of the upper surface plate 1 is 10.2 rpm, 11.9 rpm, and 13.6 rpm respectively.

TABLE 1

No.
Control Factor
Level 1
Level 2
Level 3

1
Specific Gravity
60 g/cm³
70 g/cm³
80 g/cm³

2
Granularity
1000
1500
3000

3
Flow Rate
10 cc/min
20 cc/min
30 cc/min

4
Slurry Temperature
22° C.
30° C.
40° C.

5
Rotational Velocity of
30 rpm
35 rpm
40 rpm

Lower Surface Plate

6
First Four Steps
5 minutes
11 minutes
15 minutes

7
Direction of Rotation
Forward
Backward
Backward

8
Pressing Force
9 kpa
12 kpa
15 kpa

FIGS. 9A and 9B show the results of analysis of Levels 1 to 3 using Taguchi methods. Note that due to testing circumstances, some of Levels 1 to 3 for the respective items in Table 1 differ to the levels of the corresponding items shown in FIGS. 9A and 9B. The graph in FIG. 9A shows the stability (S/N ratio) of the strength when the workpieces are manufactured as products. Meanwhile, the graph in FIG. 9B shows the strength (or sensitivity (a characteristic value)) for each item in the control factors. The direction marked as “Good” indicates higher stability or higher strength (sensitivity).

As shown by the histogram in FIG. 10, as a result of JIS strength tests, the average strength of the liquid crystal panel before optimization of the conditions of the respective items in the control factors was 10.9N. Next, by optimizing the conditions of the respective items so that the rotation of the planetary carriers 5 is “backward”, the slurry specific gravity is “70 g/cm³”, the slurry granularity is “#1500”, the start time is “19 minutes”, the rotational velocity of the lower surface plate is “35 rpm”, and the pressing force is “15 kpa”, a result where the average strength of the liquid crystal panels was 13.9N was obtained. This satisfies the target strength of 11N that is currently demanded for display panels and is an improvement of 25%.

Note that from the graphs in FIGS. 9A and 9B, it is possible to set the respective items at conditions where stability is high and it is possible to maintain strength. For example, as shown in the S/N ratio and sensitivity graphs, strength increases in the direction indicated as “Good”. However, since a slurry with a granularity of 1000 is easier to obtain than a slurry with a granularity of 1500, selecting such a slurry facilitates inventory management and the like during manufacturing. Also, if priority is given to productivity, “twelve minutes” may be selected for the first four steps. If it is desirable to reduce the damage to a product, “12 kpa” could conceivably be selected as the pressing force.

According to the second embodiment described above, by optimizing the conditions of the respective items in the control factors during grinding, or in other words, by optimizing the grinding conditions, it is possible to improve the strength of the workpieces.

Note that it is also possible to apply the method of optimizing the conditions of the respective items in the control factors during grinding according to the second embodiment to the grinding method that uses the planetary carriers in which clearances are formed according to the first embodiment. In such case, it is possible to obtain the effects of both embodiments.

In the first embodiment, the clearances (cutaways) formed at the holding holes of the planetary carriers are provided at two positions. However, there is normally a tendency for the load on the planetary carriers, that is, the load on the workpieces, to increase when the rotation of the planetary carriers is in the forward direction. Accordingly, it is possible to provide a cutaway only on one side of each holding hole, that is, the side that is contacted by the side surface of a workpiece when the planetary carriers rotate in the forward direction. It should be obvious that if the planetary carriers rotate in the backward direction, it is similarly possible to provide a clearance on the edge on the side that is contacted by the side surface of a workpiece. Note that when clearances are provided on two edges of a holding hole as shown in the first embodiment, it is possible to cope with grinding that switches between forward and backward rotation of the planetary carriers.

A grinding apparatus and a grinding method according to embodiments of the present disclosure have been described above for an example of a double-sided grinder. However, the present disclosure is not limited to a double-sided grinder and can be applied to any grinder that holds workpieces in planetary carriers and carries out grinding by pressing surface plates onto the workpieces.

Additionally, the present technology may also be configured as below.

(1) A grinding apparatus including:

an upper surface plate;

a lower surface plate disposed facing the upper surface plate and rotating in an opposite direction to the upper surface plate;

a sun gear rotated by a same rotational shaft as the upper surface plate and the lower surface plate;

an internal gear rotated by the same rotational shaft as the upper surface plate and the lower surface plate; and

a planetary carrier in which a holding hole that holds a workpiece is formed and which revolves while rotating in engagement with the sun gear and the internal gear,

wherein the holding hole in the planetary carrier is provided with a cutaway in a side of the holding hole that contacts a side surface of the workpiece when the planetary carrier rotates.

(2) The grinding apparatus according to (1),

wherein the holding hole is substantially rectangular and the cutaway is provided in an edge on the side of the holding hole that contacts the side surface of the workpiece when the planetary carrier rotates.

(3) The grinding apparatus according to (1) or (2),

wherein the cutaway is provided in the edge on the side of the substantially rectangular holding hole that contacts the side surface of the workpiece and also in another edge that faces the edge.

(4) The grinding apparatus according to (2) or (3),

wherein the edge on the side of the holding hole that contacts the side surface of the workpiece when the planetary carrier rotates corresponds to a length direction of a rectangle.

(5) A grinding method for a grinding apparatus which includes: an upper surface plate; a lower surface plate disposed facing the upper surface plate and rotating in an opposite direction to the upper surface plate; a sun gear rotated by a same rotational shaft as the upper surface plate and the lower surface plate; an internal gear rotated by the same rotational shaft as the upper surface plate and the lower surface plate; and a planetary carrier in which a holding hole that holds a workpiece is formed and which revolves while rotating in engagement with the sun gear and the internal gear,

the grinding method comprising:

having the holding hole in the planetary carrier provided with a cutaway in a side of the holding hole that contacts a side surface of the workpiece when the planetary carrier rotates, and

holding the workpiece in the cutaway-provided holding hole in the planetary carrier and grinding at least one surface of the workpiece between the upper surface plate and the lower surface plate.

In the present specification, the processing steps describing chronological processes may of course be processed in chronological order in accordance with the stated order, but do not have to be processed in that chronological order. Further, the processing steps may be processed individually or in a parallel manner (e.g., parallel processing or object-based processing).

The present disclosure is not limited to the above-described embodiments, and obviously may incorporate various modifications and applications within the scope of the patent claims.

Namely, because the above-described embodiments are specific preferred examples of the present disclosure, they are subject to various preferred technical limitations. However, the technical scope of the present disclosure is not limited to these embodiments unless such a limitation is specifically stated in the above description. For example, the used materials, used amounts, processing time, processing order, numerical conditions of the various parameters and the like are merely preferred examples. Further, the dimensions, shapes, and positional relationships illustrated in the drawings used in the present disclosure are also schematic representations.

The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2011-218469 filed in the Japan Patent Office on Sep. 30, 2011, the entire content of which is hereby incorporated by reference.

GRINDING APPARATUS AND GRINDING METHOD

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