Grinding disc flatness detection device and detection method

Abstract

The present application relates to the technical field of levelness detection, and discloses a grinding disc flatness detection device and detection method, which comprises a circular table and a rotating table, a sliding plate is slidably arranged in the rotating table, and a positioning rod is vertically fixed to the outer end of the sliding plate; a rotating disc is rotatably arranged on one side of the sliding plate, and can drive the sliding plate to slide in the rotating table during rotation, so that the positioning rod approaches the rotating table to position the grinding disc; a sleeve is coaxially fixed to the bottom of the rotating table, and the sleeve is coaxially rotatably arranged in the circular table; the grinding disc flatness detection device and detection method can automatically rotate the rotating table with the positioned grinding disc, and move the detection mechanism relative to the grinding disc after positioning the grinding disc through rotation of the rotating disc, so that full-surface detection of the grinding disc is realized, and the coordination of the fixing, rotation and movement of the detection mechanism during the detection process is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of level detection, and in particular to a grinding disc flatness detection device and detection method. BACKGROUND

[0002] CMP grinding disc is the core consumable in the chemical mechanical planarization (CMP) process in semiconductor manufacturing, mainly used for trimming the surface of the polishing pad to ensure the uniformity and precision of the wafer surface. When modifying the surface of the grinding disc, the flatness of the grinding disc needs to be detected, and the relative movement of the detector and the grinding disc realizes full-surface sampling.

[0003] In the application file with publication number CN118274780A, a flatness detection device for grinding disc production is disclosed. By setting the adjusting mechanism, the servo motor and the first and second cylinders are controlled to realize accurate positioning of the detection mechanism. The flatness of the grinding disc in the circumferential direction is detected to ensure that the probe accurately contacts the measured area of the grinding disc for flatness detection. The horizontal adjusting member allows the detection mechanism to move accurately in the horizontal direction to adapt to the detection requirements of different positions, ensuring the accuracy and flexibility of the detection, so as to detect the flatness of the grinding disc in all directions.

[0004] However, the following problems exist in the use of the above-mentioned scheme. In the clamping of the grinding disc, the two-way cylinder clamps from both sides, which cannot ensure the concentricity of the grinding disc and the equipment positioning, and is prone to positioning deviation, resulting in the clamping center of the grinding disc and the clamping plate deviating, so that the circumferential trajectory of the probe is different from the actual center of the grinding disc when the adjusting mechanism rotates, affecting the detection accuracy. In the level detection, the fixing of the grinding disc, the movement and rotation of the detection mechanism need to rely on multiple independent driving systems such as servo motors, multiple cylinders and the like to cooperate with each other, resulting in poor coordination of the equipment, multiple vibration sources, multiple independent vibration sources in the detection, and vibration frequency and amplitude that cannot be coordinated and suppressed. It is easy to cause the vibration and interference of multiple vibration sources to be superimposed, resulting in a significant reduction in detection stability and poor detection accuracy. SUMMARY

[0005] The present application provides a grinding disc flatness detection device and detection method, which aims to solve the problem that the concentricity of the grinding disc and the equipment positioning cannot be ensured in the related art, and the fixing of the grinding disc, the movement and rotation of the detection mechanism need to rely on multiple independent driving systems to cooperate with each other in the level detection, resulting in poor coordination and multiple vibration sources.

[0006] The grinding disc flatness detection device and detection method of the present application comprises a circular table and a rotating table, a sliding plate is slidably arranged in the rotating table, and a positioning rod is vertically fixed to the outer end of the sliding plate.

[0007] One side of the slide plate is provided with a rotating disc rotatingly assembled in the rotating table, which can drive the slide plate to slide in the rotating table in rotation, so that the positioning rod approaches the rotating table to position the grinding disc;

[0008] The bottom of the rotating table is coaxially fixed with a sleeve, and the sleeve is coaxially rotatingly assembled in the interior of the circular table, which can rotate in the circular table along with the rotation of the rotating disc after the grinding disc is positioned;

[0009] The rotating table is provided with a detection mechanism above, one side of the detection mechanism is provided with a support, and the support is rotatingly assembled on the circular table, which can rotate on the circular table along with the rotation of the sleeve, so that the detection mechanism moves above the rotating table to detect the flatness of the grinding disc.

[0010] Preferably, the interior of the rotating table is provided with a circular cavity coaxially arranged with the rotating table and a plurality of side slots communicating with the circular cavity and arranged along the radial direction of the rotating table, the slide plate is slidingly assembled in the side slots, and the rotating disc is rotatingly assembled in the circular cavity.

[0011] Preferably, the bottom of the rotating disc is coaxially fixed with a rotating shaft rotatingly assembled in the sleeve, the bottom end of the rotating shaft is provided with a motor, the sidewall of the rotating disc is fixedly installed with an arc-shaped frame, a slide rod is slidingly assembled in the arc-shaped frame, and the slide rod is fixedly connected with the inner end of the slide plate.

[0012] Preferably, the interior of the circular table is provided with an inner cavity, the sleeve extends to the interior of the inner cavity, and the sidewall of the circular table is provided with an arc-shaped slot along the circumferential direction thereof.

[0013] Preferably, the detection mechanism comprises a detection cylinder, a detection head and a pressure sensor, the detection cylinder is vertically arranged directly above the rotating table, the detection head is slidingly assembled in the interior of the detection cylinder, and the pressure sensor is arranged between the detection head and the detection cylinder.

[0014] Preferably, the support comprises a mounting seat, a support column and a cross bar, the mounting seat is fixedly installed on the sidewall of the circular table, the support column is vertically rotatingly assembled in the mounting seat, the cross bar is arranged at the top end of the support column and can slide laterally on the support column, and the end of the cross bar away from the support column extends to the upper side of the rotating table and is fixedly connected with the detection cylinder.

[0015] Preferably, the top end of the support column is fixedly installed with a slide cylinder arranged along the radial direction of the rotating table, the cross bar is slidingly assembled in the interior of the slide cylinder, a fastening nut is threadedly connected in the slide cylinder, the bottom end of the fastening nut abuts against the cross bar, the end of the cross bar is fixedly installed with a lifting platform, and the detection cylinder is arranged on the lifting platform.

[0016] Preferably, the inside of the inner cavity is vertically rotatably provided with a transmission shaft, the transmission shaft is coaxially fixed with a first transmission gear and a second transmission gear, the diameter of the first transmission gear is larger than that of the second transmission gear, the outside of the sleeve is coaxially fixed with a gear ring engaged with the first transmission gear, the support is fixedly provided with an arc-shaped gear rack extending into the inner cavity and engaged with the second transmission gear.

[0017] Preferably, the circular table is fixedly provided with a locking cylinder, the locking cylinder is slidably provided with a locking block, the end of the locking block is spherical, the bottom of the rotating table is provided with a clamping groove matched with the locking block, the top end of the locking block is inserted into the clamping groove, and a spring is arranged between the locking block and the locking cylinder.

[0018] A grinding disc flatness detection method, comprising the following steps:

[0019] Step one: place the grinding disc above the rotating table;

[0020] Step two: rotate the rotating disc to push the sliding plate to slide in the rotating table, and the plurality of positioning rods push the grinding disc to the middle of the rotating table for center positioning;

[0021] Step three: continuously rotate the rotating disc to push the rotating table to rotate with the sleeve;

[0022] Step four: rotate the bracket driven by the sleeve to make the detection mechanism move against the grinding disc to detect the flatness of the grinding disc rotating with the rotating table.

[0023] In use, the grinding disc is centrally positioned by the plurality of positioning rods through the rotation of the rotating disc, the concentricity of the positioning rods and the rotating table is effectively ensured, the eccentric error is eliminated, and after the grinding disc is positioned, the rotating table overcomes the resistance of the locking assembly to rotate with the positioned grinding disc, the detection mechanism moves relative to the grinding disc, and then the full-surface detection of the grinding disc is realized, so that the positioning of the grinding disc, the rotation of the rotating table and the movement of the detection mechanism can be realized by separate driving, the coordination between the fixing, rotation and movement of the detection mechanism during the detection process is effectively improved, the investment in the driving system is reduced, the use cost is reduced, the vibration source is reduced due to the integration of the driving system, the vibration frequency of the rigid transmission components such as gears and racks is consistent, the vibration interference during the detection process is greatly reduced, the flatness detection stability and the accuracy of data are improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a perspective view of the present application.

[0025] Figure 2 is a front view of the present application.

[0026] Figure 3 is a sectional view of the present application.

[0027] Figure 4 is a schematic diagram of the internal structure of the rotating table of the present application.

[0028] Figure 5 is a schematic diagram of the internal structure of the circular table of the present application.

[0029] Figure 6 is a schematic diagram of the internal structure of the rotating table of the present application. Figure 3

[0030] Reference signs:

[0031] 10, pedestal; 11, circular table; 12, base; 13, inner cavity; 14, arc-shaped slot; 20, rotating table; 21, sleeve; 22, circular cavity; 23, side slot; 24, clamping slot; 30, positioning assembly; 31, sliding plate; 32, positioning rod; 40, driving assembly; 41, rotating disc; 42, rotating shaft; 421, motor; 43, arc-shaped frame; 44, sliding rod; 50, detection mechanism; 51, detection cylinder; 52, detection head; 60, support; 61, mounting seat; 62, support column; 621, sliding cylinder; 622, fastening nut; 63, cross rod; 631, lifting platform; 70, transmission assembly; 71, transmission shaft; 72, first transmission gear; 73, second transmission gear; 74, gear ring; 75, arc-shaped rack; 80, locking assembly; 81, locking cylinder; 82, locking block; 83, spring. DETAILED DESCRIPTION

[0032] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0033] As shown in Figures 1 to 5 , the flatness detection device for the grinding disc of the present application comprises a pedestal 10, a rotating table 20, a positioning assembly 30, a driving assembly 40, a detection mechanism 50, a support 60, a transmission assembly 70, and a locking assembly 80. The rotating table 20 is rotationally arranged on the pedestal 10, used for placing the grinding disc, and under the action of the locking assembly 80, the rotating table 20 cannot rotate on the pedestal 10 when the grinding disc is positioned. The positioning assembly 30 is located in the rotating table 20, capable of fixing the grinding disc under the action of the driving assembly 40. The detection mechanism 50 is arranged on the support 60, used for detecting the flatness of the grinding disc. The transmission assembly 70 is arranged in the pedestal 10, capable of driving the support 60 to rotate when the rotating table 20 rotates, realizing the full-surface detection of the grinding disc.

[0034] Reference Figure 1 , Figure 3 and​Figure 4 The pedestal 10 is composed of a circular table 11 and a base 12, the circular table 11 is fixedly installed on the top of the base 12, an inner cavity 13 is formed in the inside of the circular table 11 for the installation of the transmission assembly 70, and an arc-shaped slot 14 is formed in the side wall of the circular table 11 along the circumferential direction thereof to connect the inner cavity 13 with the outside of the circular table 11.

[0035] Referring to Figure 3 With Figure 4 A sleeve 21 is coaxially fixed to the bottom of the rotating table 20 and coaxially rotatably assembled in the inside of the circular table 11, a circular cavity 22 is formed in the inside of the rotating table 20 and is coaxially arranged with the rotating table 20, and a plurality of side slots 23 are arranged along the radial direction of the rotating table 20 and are connected with the circular cavity 22 to connect the circular cavity 22 with the outside of the rotating table 20.

[0036] Referring to Figures 1-4 The positioning assembly 30 includes a sliding plate 31 and a positioning rod 32, the sliding plate 31 is slidably assembled in the side slot 23, and the positioning rod 32 is vertically fixed to the outer end of the sliding plate 31 (i.e. the end located outside the rotating table 20), the positioning rod 32 can approach or move away from the rotating table 20 along with the sliding of the sliding plate 31, and the positioning rod 32 can position the grinding disc when approaching and can release the positioning of the grinding disc when moving away.

[0037] Referring to Figure 3 With Figure 4 The driving assembly 40 includes a rotating disc 41, a rotating shaft 42, an arc-shaped frame 43 and a sliding rod 44, the rotating disc 41 is rotatably assembled in the inside of the circular cavity 22, the rotating shaft 42 is coaxially fixed to the bottom of the rotating disc 41 and is rotatably assembled in the sleeve 21, the arc-shaped frame 43 is fixedly installed on the side wall of the rotating disc 41, the sliding rod 44 is slidably assembled in the arc-shaped frame 43 and is fixed to the inner end of the sliding plate 31 (i.e. the end located in the circular cavity 22), and the bottom end of the rotating shaft 42 is provided with a motor 421 located in the base 12 for driving the rotating shaft 42 to rotate, so that the rotating disc 41 rotates in the circular cavity 22, the sliding rod 44 is pushed by the arc-shaped frame 43 to drive the sliding plate 31 to slide along the side slot 23, and the positioning rod 32 approaches or moves away from the rotating table 20.

[0038] Referring to Figures 1-3 The detection mechanism 50 includes a detection cylinder 51, a detection head 52 and a pressure sensor, the detection cylinder 51 is vertically arranged above the rotating table 20, the detection head 52 is slidably assembled in the inside of the detection cylinder 51, and the pressure sensor is arranged between the detection head 52 and the detection cylinder 51, so that the pressure sensor can exert pressure on the detection head 52 along with the sliding of the detection head 52 in the detection cylinder 51, the pressure sensor can transform the pressure transmitted by the detection head 52 to detect the flatness of the grinding disc and to determine whether the flatness of the grinding disc is qualified.

[0039] Reference Figures 1-3 The support 60 comprises a mounting base 61 fixedly installed on the side wall of the circular table 11, a support column 62 vertically rotatably assembled in the mounting base 61, and a crossbar 63 arranged at the top end of the support column 62 and capable of sliding transversely on the support column 62, and the end of the crossbar 63 away from the support column 62 extends above the rotary table 20 and is fixed to the detection cylinder 51, so that the relative position of the detection cylinder 51 above the rotary table 20 can be adjusted in the movement of the crossbar 63, so that the detection mechanism 50 can better meet the detection of different grinding discs in the form of a disc or a ring.

[0040] The top end of the support column 62 is fixedly installed with a sliding cylinder 621 arranged in the radial direction of the rotary table 20, the crossbar 63 is slidingly assembled in the sliding cylinder 621, and a fastening nut 622 is threadedly connected in the sliding cylinder 621, and the bottom end of the fastening nut 622 is arranged in close contact with the crossbar 63, for fixing the crossbar 63, so as to adjust the position of the detection mechanism 50. The end of the crossbar 63 is fixedly installed with a lifting table 631, and the detection cylinder 51 is arranged on the lifting table 631 and can be lifted above the rotary table 20 under the driving of the lifting table 631, so that the detection head 52 approaches or moves away from the grinding disc.

[0041] Reference Figure 3 With Figure 5 The transmission assembly 70 comprises a transmission shaft 71, a first transmission gear 72, a second transmission gear 73, a gear ring 74, and an arc-shaped rack 75. The transmission shaft 71 is vertically rotatably assembled in the inner cavity 13. The first transmission gear 72 and the second transmission gear 73 are coaxially fixed on the transmission shaft 71, and the diameter of the first transmission gear 72 is greater than that of the second transmission gear 73. The gear ring 74 is coaxially fixed on the outside of the sleeve 21 and is engaged with the first transmission gear 72. The arc-shaped rack 75 is fixedly installed on the support column 62 and extends into the inner cavity 13 through the arc-shaped groove 14 and is engaged with the second transmission gear 73. The arc-shaped rack 75 is coaxially arranged with the support column 62, so that when the sleeve 21 rotates, the gear ring 74 is rotated, the first transmission gear 72 is pushed to rotate with the transmission shaft 71, the arc-shaped rack 75 is pushed by the second transmission gear 73, so that the support column 62 rotates in the mounting base 61, and then the crossbar 63 is rotated, so that the detection mechanism 50 moves above the rotating grinding disc, and then the grinding disc is detected.

[0042] Reference Figure 3 And Figure 6The locking assembly 80 comprises a locking cylinder 81, a locking block 82 and a spring 83. The locking cylinder 81 is fixedly installed on the circular table 11. The locking block 82 is slidingly assembled in the locking cylinder 81, and the end of the locking block 82 is spherical. The bottom of the rotating table 20 is provided with a clamping groove 24 matched with the locking block 82. The top end of the locking block 82 is inserted into the clamping groove 24. The spring 83 is arranged between the locking block 82 and the locking cylinder 81. The rotating table 20 and the circular table 11 are fixed by inserting the locking block 82 into the clamping groove 24. When the slide plate 31 and the positioning rod 32 are moved to position the grinding disc during rotation of the rotating disc 41 and the arc-shaped frame 43, the rotating table 20 will not rotate on the circular table 11. When the positioning rod 32 cannot continue to move after completing the positioning of the grinding disc, the rotating force of the rotating disc 41 overcomes the resistance of the spring 83, so that the locking block 82 is separated from the clamping groove 24 and completely enters the locking cylinder 81, thereby releasing the fixation between the rotating table 20 and the circular table 11, so that the rotating table 20 can rotate on the circular table 11 along with the rotation of the rotating disc 41.

[0043] A grinding disc flatness detection method, comprising the following steps:

[0044] Step one: place the grinding disc above the rotating table 20, so that the detection mechanism 50 is close to the grinding disc;

[0045] Step two: drive the rotating disc 41 to rotate by the motor 421 driving the rotating shaft 42, so that the slide plate 31 is driven to slide in the rotating table 20 by the arc-shaped frame 43 pushing the slide rod 44, so that the plurality of positioning rods 32 push the grinding disc to the middle of the rotating table 20 for center positioning;

[0046] Step three: the rotating disc 41 continues to rotate, and since the positioning rod 32 completes the positioning of the grinding disc, the slide plate 31 cannot continue to move, and then the slide plate 31 pushes the rotating table 20 to overcome the resistance of the spring 83 under the pushing of the arc-shaped frame 43, so that the sleeve 21 rotates in the circular table 11;

[0047] Step four: the sleeve 21 drives the gear ring 74 to rotate, and then drives the first transmission gear 72 and the second transmission gear 73 to rotate, so that the support column 62 is pushed to rotate by the arc-shaped rack 75, the bracket 60 is rotated, and the detection mechanism 50 is moved close to the grinding disc, so that the flatness of the grinding disc rotating with the rotating table 20 is detected.

[0048] The present application is by rotating the rotating disc 41, the plurality of positioning rods 32 center positioning the grinding disc, effectively ensure the concentricity of the positioning rods 32 and the rotating table 20, eliminate eccentric error, and after the grinding disc is positioned, the rotating table 20 overcomes the resistance of the locking assembly 80, rotates with the positioned grinding disc, moves the detection mechanism 50 relative to the grinding disc, and then realizes the full surface detection of the grinding disc, so that the positioning of the grinding disc, the rotation of the rotating table 20 and the movement of the detection mechanism 50 can be realized by separate driving, effectively improving the coordination between the fixing, rotation and movement of the detection mechanism 50 of the grinding disc during the detection process, reducing the investment of the driving system, reducing the use cost, and the integrated driving system reduces the vibration source, the vibration frequency of the rigid transmission components such as gears and racks is consistent, which can be better coordinated and inhibited through structure optimization, greatly reducing the vibration interference in the detection process, improving the stability of the levelness detection and the accuracy of the data.

[0049] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A flatness detection device for a grinding disc, comprising a circular table (11) and a rotating table (20), characterized in that, The inner part of the rotating table (20) is slidably equipped with a sliding plate (31), and the outer end of the sliding plate (31) is vertically fixed with a positioning rod (32); One side of the sliding plate (31) is provided with a rotating disc (41) which is rotatably equipped in the rotating table (20) and can drive the sliding plate (31) to slide in the rotating table (20) in rotation, so that the positioning rod (32) approaches the rotating table (20) to position the grinding disc; The bottom of the rotating table (20) is coaxially fixed with a sleeve (21), and the sleeve (21) is coaxially rotatably equipped in the inner part of the circular table (11), so that after the grinding disc is positioned, the sleeve (21) can rotate in the circular table (11) along with the rotation of the rotating disc (41); The upper part of the rotating table (20) is provided with a detection mechanism (50), one side of the detection mechanism (50) is provided with a support (60), and the support (60) is rotatably equipped on the circular table (11) and can rotate on the circular table (11) along with the rotation of the sleeve (21), so that the detection mechanism (50) moves above the rotating table (20) to detect the flatness of the grinding disc; The inner part of the rotating table (20) is coaxially provided with a circular cavity (22), and a side slot (23) is provided, the side slot (23) is provided in plurality and is communicated with the circular cavity (22) along the radial direction of the rotating table (20), the sliding plate (31) is slidably equipped in the side slot (23), and the rotating disc (41) is rotatably equipped in the circular cavity (22); The bottom of the rotating disc (41) is coaxially fixed with a rotating shaft (42), and the rotating shaft (42) is rotatably equipped in the sleeve (21), the bottom end of the rotating shaft (42) is provided with a motor (421), the side wall of the rotating disc (41) is fixedly installed with an arc-shaped frame (43), the arc-shaped frame (43) is slidably equipped with a sliding rod (44), and the sliding rod (44) is fixed with the inner end of the sliding plate (31); The inner part of the circular table (11) is provided with an inner cavity (13), the sleeve (21) extends into the inner cavity (13), and the side wall of the circular table (11) is provided with an arc-shaped slot (14) along the circumferential direction thereof; The detection mechanism (50) comprises a detection cylinder (51), a detection head (52) and a pressure sensor, the detection cylinder (51) is vertically arranged above the rotating table (20), the detection head (52) is slidably equipped in the inner part of the detection cylinder (51), and the pressure sensor is arranged between the detection head (52) and the detection cylinder (51); The support (60) comprises a mounting seat (61), a support column (62) and a cross rod (63), the mounting seat (61) is fixedly installed on the side wall of the circular table (11), the support column (62) is vertically rotatably equipped in the mounting seat (61), the cross rod (63) is arranged at the top end of the support column (62) and can slide laterally on the support column (62), and one end of the cross rod (63) away from the support column (62) extends to the upper part of the rotating table (20) and is fixed with the detection cylinder (51).

2. The disc flatness detection device according to claim 1, wherein The top end of the support column (62) is fixedly installed with a sliding cylinder (621), the sliding cylinder (621) is arranged along the radial direction of the rotating table (20), the crossbar (63) is slidingly assembled in the sliding cylinder (621), the sliding cylinder (621) is internally threadedly connected with a fastening nut (622), the bottom end of the fastening nut (622) is in close contact with the crossbar (63), and the end portion of the crossbar (63) is fixedly installed with a lifting platform (631), and the detection cylinder (51) is arranged on the lifting platform (631).

3. The disc flatness detection device according to claim 2, wherein The inside of the inner cavity (13) is vertically rotatably provided with a transmission shaft (71), the transmission shaft (71) is coaxially fixed with a first transmission gear (72) and a second transmission gear (73), the diameter of the first transmission gear (72) is larger than that of the second transmission gear (73), the outside of the sleeve (21) is coaxially fixed with a gear ring (74) engaged with the first transmission gear (72), the support column (62) is fixedly installed with an arc-shaped rack (75), and the arc-shaped rack (75) extends into the inner cavity (13) and is engaged with the second transmission gear (73) through the arc-shaped groove (14).

4. The disc flatness detection device according to claim 3, wherein The circular table (11) is fixedly installed with a locking cylinder (81), the locking cylinder (81) is slidingly assembled with a locking block (82) in the inside, the end portion of the locking block (82) is spherical, the bottom of the rotating table (20) is provided with a clamping groove (24) matched with the locking block (82), the top end of the locking block (82) is inserted into the clamping groove (24), and the spring (83) is arranged between the locking block (82) and the locking cylinder (81).

5. A method of detecting flatness of a polishing pad, suitable for use in the apparatus for detecting flatness of a polishing pad according to claim 4, characterized by, The steps include: Step one: place the grinding disc above the rotating table (20); Step two: rotate the rotating disc (41) to push the sliding plate (31) to slide in the rotating table (20), and the plurality of positioning rods (32) push the grinding disc to the middle of the rotating table (20) for center positioning; Step three: continuously rotate the rotating disc (41) to push the rotating table (20) to rotate with the sleeve (21) through the sliding plate (31); Step four: rotate the bracket (60) driven by the sleeve (21) to move the detection mechanism (50) against the grinding disc to detect the flatness of the grinding disc rotating with the rotating table (20).

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