JP2021104580A - Cutting device of plate-like body - Google Patents

Abstract

To allow the installation of a cutting device of a plate-like body in small space and improve a finishing accuracy of the cutting of the plate-like body.SOLUTION: A cutting device 10 of a plate-like body comprises a stage 20 in a plane view rectangle shape on which a work B including a plate-like body is placed, an open hole 26 penetrating through the stage 20 in a vertical direction, a suction device 70 in communication with the open hole 26 and for suctioning the work B to a top surface of the stage 20, four cutting blades 33, 33', 43 and 43' kept on standby, respectively, at standby positions at four corners of the stage 20, an operation device 30, 30', 40 and 40' for moving four cutting blades 33, 33', 43 and 43' from the standby positions in one direction of a plain view clockwise rotation or an anticlockwise rotation along four sides of the stage 20 and a groove 28 which is opened to the top surface of the stage 20 and through which the cutting blades 33, 33', 43 and 43' pass.SELECTED DRAWING: Figure 1

Description

The present invention relates to a plate-shaped body cutting device.

As a device for cutting plate-like bodies such as plywood, fiberboard, and gypsum board, for example, as described in Patent Document 1, a cutting blade such as a band saw or circular saw is arranged on a stage, and the plate is directed toward the stage. It is common to advance the shape. By advancing the plate-shaped body while reciprocating or rotating the cutting blade, the plate-shaped body is finished into a predetermined shape.

For example, in the manufacturing process of plywood formed by laminating veneers, there is an apparatus for cutting four sides around the plywood which is a work. This cutting device is provided with a transport device for advancing the work by a feed roll or the like, a stage arranged at two locations along the traveling direction, and a work depositing device arranged on the downstream side of the last stage. There is. In the first stage, two of the four sides of the work are cut along the first direction of travel, and then the work is turned 90 degrees to advance, and the remaining two sides in the last stage are turned. Cut along the direction of travel. The work that has been cut is deposited on the work stacking device, and is carried out to the next process in a state where a plurality of works are stacked. As described in Patent Document 2, a technique of a multi-blade circular saw in which a large number of cutting blades facing in the same direction are arranged in parallel is also disclosed.

Japanese Unexamined Patent Publication No. 10-249801 Japanese Unexamined Patent Publication No. 6-114803

The conventional plate-shaped cutting device has a problem that a large amount of space is required for its installation. That is, a plurality of stages must be arranged along the transport direction of the transport device, and the transport device needs to be turned 90 degrees on the way, and its installation tends to be restricted in place. ..

Further, in the conventional plate-shaped body cutting device, the lifting force from the cutting blade acting on the plate-shaped body on the stage is dealt with by the pressing force of the pressing roll arranged above the stage. However, since the cut portion covers a wide range of the peripheral edge of the plate-like body, it is difficult to reliably press the wide range so as not to rise.

Further, in the conventional plate-shaped body cutting device, two sides along the traveling direction are cut in the first step, and then the remaining two sides are cut in the next step. Due to variations in thickness, uneven thickness of individual plate-like bodies, or the flow of wood grain on the surface, the transport direction of the plate-like body is not linear, and although it is slight, it curves or meanders. May be done. Such slight turbulence in the transport direction of the work causes bending during cutting (a state in which the cutting line is slightly curved instead of a straight line), and causes a large error in the parallelism and squareness of the cutting line. there is a possibility. That is, when the plate-shaped body is conveyed by the roll, the finishing accuracy of the work may not be stable.

Therefore, the first problem of the present invention is to enable the plate-shaped body cutting device to be installed in a small space, and the second problem is to improve the finishing accuracy of cutting the plate-shaped body.

In order to solve the above problems, the present invention presents a stage having a rectangular shape in a plan view on which a work made of a plate-like body is placed, a through hole penetrating the stage up and down, and the work communicating with the through hole. A suction device that attracts the above stage to the upper surface of the stage, four cutting blades that stand by at the standby positions at the four corners of the stage, and four cutting blades from the standby position along the four sides of the stage. A plate-shaped cutting device including an operating device that moves the stage in either a clockwise direction or a counterclockwise direction and a groove that opens on the upper surface of the stage and through which the cutting blade passes is adopted.

Since we adopted an operating device that moves the four cutting blades in one direction, clockwise or counterclockwise in a plan view, along the four sides of the rectangular stage, the four sides of the work are cut all at once. , The plate-shaped cutting device can be installed in a small space. Further, since the suction device for sucking the work to the upper surface of the stage is adopted, it is possible to maintain the plate-like body so as not to be lifted from the stage when the four sides are cut all at once.

Further, the operating device moves each of the four cutting blades from the standby position to the second standby position located on the opposite side of the moving sides in the one direction along the four sides. The first operation of reaching and cutting the work, and the second standby by moving each of the four cutting blades from the second standby position along the four sides in a direction opposite to the one direction. It is possible to adopt a configuration in which the second operation of reaching the original standby position from the position and cutting the work is performed.

Here, the cutting blade is a disk-shaped rotary blade that rotates in a certain direction in both the first operation and the second operation, and the through hole may be opened in the groove. can.

Further, the through hole may adopt a structure in which the through hole opens in the groove in a longitudinal direction in the extending direction of the groove.

In each of these embodiments, the through hole may employ a configuration in which a counterbore is provided around the upper surface opening of the stage.

Further, in each of these aspects, the stage can adopt a configuration in which an inclined surface on which a cut piece is dropped is provided on the outside of the groove.

INDUSTRIAL APPLICABILITY According to the present invention, a plate-shaped body cutting device can be installed in a small space, and the finishing accuracy of plate-shaped body cutting can be improved.

Top view showing one embodiment of the present invention Left side view of FIG. Front view of FIG. Enlarged perspective view of the main part of FIG. Floor plan of the stage Floor plan of the stage Enlarged plan view of the main part of the stage Sectional view showing the vicinity of the end of the stage

Embodiments of the present invention will be described with reference to the drawings. In this embodiment, in a process of manufacturing a plywood formed by laminating a plurality of veneers, a plate-shaped cutting device 10 (hereinafter referred to as a plate-shaped body) that cuts four sides around the plywood before finishing to form a predetermined shape having a rectangular shape. , Simply referred to as the cutting device 10).

As shown in FIGS. 1 and 2, the cutting device 10 has a rectangular stage 20 in a plan view arranged in the middle of the traveling direction of the transport device 1. On the stage 20, one unfinished plywood (hereinafter referred to as work B) made of a plate-like body transferred by the transfer device 1 is placed. The plywood before finishing has a shape slightly larger than the predetermined shape of the plywood, and is finished in the predetermined shape by cutting the four peripheral sides. The finished plywood is deposited on the work stacking device and then carried out to the next process.

As shown in FIGS. 2 and 4, the transport device 1 is a belt conveyor in which an endless belt 2 is wound between a drive roller 3 and a driven roller 6. The drive roller 3 is rotated by a driving force from a drive source 4 such as a motor, and the belt 2 operates by the rotation. The movement amount and speed of the belt 4 can be controlled by a control mechanism included in the drive source 4. As the control mechanism, an encoder, a servo mechanism, or the like can be adopted. As a result, the upper side (conveying side) of the belt 2 moves from the driven roller 6 side to the driving roller 3 side by a predetermined distance, and the lower side (return side) returns from the driving roller 3 side to the driven roller 6 side. go. The work B is introduced onto the belt 2 from an introduction device (not shown) arranged on the belt 2 near the driven roller 6, and the work B advances toward the stage 20 by the operation of the belt 2 and is a control mechanism. By controlling the amount of movement of the belt 2 by the above, the belt 2 is stopped at a predetermined position on the stage 20.

Here, the position of the drive roller 3 in the height direction can be adjusted by the elevating device 5. By lowering the position of the drive roller 3 while the work B is stopped at a predetermined position on the stage 20, the work B is placed on the upper surface of the stage 20, and the belt 2 is placed below the upper surface of the stage 20. That is, it retracts to a position separated from the work B. Although not shown, the driven roller 6 is also provided with a similar lifting device 5, so that the driving roller 3 side and the driven roller 6 side lifting device 5 operate at the same time.

As shown in FIGS. 1 to 4, the stage 20 is composed of four stage members 21, 22, 23, 24, 25 that are movable in the lateral direction. The first stage 21 is a main stage located in the center. The second stage 22 and the third stage 23 are substages adjacent to the downstream side and the upstream side in the traveling direction of the transport device 1 with respect to the first stage 21. Further, the fourth stage 24 and the fifth stage 25 are left and right side stages adjacent to the first stage 21 in a direction orthogonal to the traveling direction of the transport device 1.

As shown in FIG. 4, the first stage 21 is arranged between the two belts 2 constituting the transport device 1. In this embodiment, the first stage 21 is fixed so as not to move with respect to the frame F, but is positioned along the traveling direction of the transport device 1 or along the direction orthogonal to the traveling direction. May be adjustable.

The second stage 22 and the third stage 23 are slidably supported via the slide unit 52 with respect to the rail 51 provided on the frame F and parallel to the traveling direction. Further, the second stage 22 and the third stage 23 each have a rack 55 on the lower surface side thereof, and a pinion 56 provided on the frame F side meshes with the teeth of the rack 55. Therefore, when the pinion 56 is rotated by the driving force from the drive source 57 such as a motor, the second stage 22 and the third stage 23 move together with the rack 55 along the traveling direction of the work B, respectively. As a result, the second stage 22 and the third stage 23 can be moved to the upstream side or the downstream side in the traveling direction. In this embodiment, the second stage 22 and the third stage 23 are controlled to move at the same time in opposite directions by the same distance, but the movement amount and the movement direction of both may be controlled separately. can. The movement amount and movement speed of the rack 55 accompanying the rotation of the pinion 56 can be controlled by a control mechanism such as an encoder and a servo mechanism also included in the drive source 57.

The fourth stage 24 and the fifth stage 25 are slidably supported via the slide unit 54 with respect to the rail 53 provided on the frame F and extending in the direction orthogonal to the traveling direction. Further, each of the fourth stage 24 and the fifth stage 25 is provided with a rack 58 on the lower surface side thereof, and a pinion 59 provided on the frame F side meshes with the teeth of the rack 58. Therefore, when the pinion 59 is rotated by the driving force from the driving source 57 such as a motor, the fourth stage 24 and the fifth stage 25 move together with the rack 58 in a direction orthogonal to the traveling direction of the work B, respectively. do. As a result, the fourth stage 24 and the fifth stage 25 can be moved toward the side away from the first stage 21 or toward the side closer to the first stage 21 along the direction orthogonal to the traveling direction. In this embodiment, the fourth stage 24 and the fifth stage 25 are controlled to move at the same time in opposite directions by the same distance, but the movement amount and the movement direction of both may be controlled separately. can. The movement amount and movement speed of the rack 58 accompanying the rotation of the pinion 59 can be controlled by a control mechanism such as an encoder and a servo mechanism also included in the drive source 57.

Each of the first to fifth stages 20 (21 to 25) is provided with a through hole 26 that vertically penetrates the stage 20. The through hole 26 is opened on the upper surface and the lower surface of the stage 20, and a counterbore 27 is provided around the upper surface opening. The counterbore 27 may be formed of a step portion slightly lower than the upper surface of the stage 20, or may be formed of a conical surface that gradually lowers from the outer edge side toward the axial center of the through hole 26.

A connected space 72 is provided in the lower part of each of the first to fifth stages 20 (21 to 25). The connected space is a closed space, the upper portion thereof communicates with the through hole 26, and the lower portion thereof communicates with the suction device 70 via the passage 71. By operating the suction device 70, the inside of the connected space 72 becomes a negative pressure state. As a result, the work B on the stage 20 is attracted to the upper surface of the stage 20. Here, since the counterbore 27 is provided around the upper surface opening of the through hole 26, the area on which the suction force acts becomes wider than the cross-sectional area of the through hole 26, and the suction force of the work B is appropriately adjusted. ing.

The through holes 26 are arranged evenly on the entire upper surface of the stage 20 so that the suction force of the work B is evenly close to the entire board surface. In this embodiment, in the first to third stages 21 to 23, the through holes 26 are linearly aligned along the direction orthogonal to the traveling direction of the work B, that is, the width direction of the stage 20, and are adjacent to each other. The through holes 26 in the row are staggered in position with respect to the width direction of the stage 20. Further, in the fourth and fifth stages 24 and 25, the through holes 26 are linearly aligned along the traveling direction of the work B, and the through holes 26 in adjacent rows are aligned with respect to the traveling direction of the work B. It has a staggered arrangement that is misaligned.

Four cutting blades 33, 33', 43, 43'are arranged at the four corners of the stage 20. As shown in FIGS. 1 and 5, the four cutting blades 33, 33', 43, 43'are a pair of cutting blades 33, 33'(hereinafter, first) that cut the sides along the traveling direction of the work B. A pair of cutting blades 43, 43'(hereinafter, referred to as a cutting blade 33 and a second cutting blade 33') and a pair of cutting blades 43, 43'(hereinafter, referred to as a third cutting blade 43 and a fourth cutting blade) that cut the sides along the width direction of the stage 20. It consists of a blade 43'). The first to fourth cutting blades 33, 33', 43, 43'are disk-shaped rotary blades that always rotate in a certain direction around the support axis.

The first cutting blade 33 and the second cutting blade 33'are controlled by the operating devices 30 and 30', respectively. As shown in FIGS. 1 and 2, the respective operating devices 30 and 30'are a guide rail 31 and 31'along the width direction of the stage 20 and a traveling device 32 moving along the guide rail 31 and 31'. , 32'and. A drive source such as a motor is provided in the traveling devices 32 and 32', and the traveling devices 32 and 32'can move in one direction or the other direction along the guide rails 31 and 31'by the driving force of the drive source. can. Further, since the traveling devices 32 and 32'are provided with another drive source (also a motor or the like) for rotating the support shafts of the first cutting blade 33 and the second cutting blade 33', the first cutting is performed. The blade 33 and the second cutting blade 33'can move along the guide rails 31, 31' while rotating around the support shaft.

Further, the third cutting blade 43 and the fourth cutting blade 43'are controlled by the operating devices 40 and 40', respectively. As shown in FIGS. 1 and 3, the respective operating devices 40 and 40'are a guide rail 41, 41' along the traveling direction of the work B and a traveling device 42 moving along the guide rail 41, 41'. , 42'and. A drive source such as a motor is provided in the traveling device 42, 42', and the traveling device 42, 42'can move in one direction or the other direction along the guide rails 41, 41'by the driving force of the drive source. can. Further, since the traveling devices 42 and 42'are provided with another drive source (also a motor or the like) for rotating the support shafts of the third cutting blade 43 and the fourth cutting blade 43', the third cutting is performed. The blade 43 and the fourth cutting blade 43'can move along the guide rails 41, 41' while rotating around the support shaft.

Further, as shown in FIGS. 4 to 7, the stage 20 is provided with a groove 28 that opens on the upper surface thereof. Specifically, at the upstream end of the second stage 22 and the downstream end of the third stage 23, the first cutting blade 33 and the second cutting are cut along the width direction of the stage 20, respectively. A groove 28 through which the blade 33'passes is provided one by one. Further, at the outer end in the width direction of the fourth stage 24 and the outer end in the width direction of the fifth stage 25, the third cutting blade 43 and the fourth cutting blade are located along the traveling direction of the work B, respectively. Grooves 28 through which 43'passes are provided one by one. Further, the upstream end and the downstream end of the fourth stage 24, and the upstream end and the downstream end of the fifth stage 25, respectively, have a first along the width direction of the stage 20. There are three grooves 28 through which the cutting blade 33 and the second cutting blade 33'of the above pass.

By the way, the distance between the second stage 22 and the first stage 21 of the third stage 23 is increased or decreased according to the size of the work B. Further, the distance between the fourth stage 24 and the first stage 21 of the fifth stage 25 is also increased or decreased according to the size of the work B. For example, in FIG. 5, the distance between the fourth stage 24 and the first stage 21 of the fifth stage 25 is w1 and w2, whereas in FIG. 6, the fourth stage 24 is matched with the work B. The distance between the stage 24 and the fifth stage 25 with the first stage 21 is expanded to w1'and w2'. At this time, the traveling lines of the third cutting blade 43 and the fourth cutting blade 43'are also aligned with the work B. Similarly, in FIG. 5, the distance between the second stage 22 and the first stage 21 of the third stage 23 is w3 and w4, whereas in FIG. 6, the second stage is matched with the work B. The distance between the stage 22 and the first stage 21 of the third stage 23 is expanded to w3'and w4'. At this time, the traveling lines of the first cutting blade 33 and the second cutting blade 33'are also aligned with the work B. In this embodiment, three grooves 28 are provided at both ends of the stage 20 in the width direction in the fourth stage 24 and the fifth stage 25, respectively, so that the second stage 22 and the third stage 23 are provided. It can correspond to three kinds of positions. By increasing the number of the grooves 28, the types of work B that can be handled can be increased.

Here, in FIG. 5, the first cutting blade 33 and the second cutting blade 33'that cut the sides along the traveling direction of the work B are located at the lower left and upper right standby positions in the drawing. Further, the third cutting blade 43 and the fourth cutting blade 43'that cut the side along the width direction of the work B are located at the upper left and lower right standby positions in the drawing.

When cutting the four sides of the work B, the operating devices 30, 30', 40, 40' are along the peripheral sides of the stage 20 as shown by the arrows a, b, c, and d in FIG. The cutting blades 33, 33', 43, 43'are moved counterclockwise in a plan view to reach a second standby position located on the opposite side of the moving sides. In the figure, the first standby position is indicated by a solid line, and the second standby position is indicated by a chain line. It is desirable that these movements be set so that the cutting blades 33, 33', 43, 43' start at the standby position, which is the starting point, and arrive at the second standby position, which is the ending point, at the same time. The operation of making the four cutting blades 33, 33', 43, 43'reach from the first standby position to the second standby position to cut the work B is hereinafter referred to as the first operation.

Further, each of the operating devices 30, 30', 40, 40'is in the direction opposite to the arrows a, b, c, d in FIG. 5, that is, in a clockwise direction along each side around the stage 20. The cutting blades 33, 33', 43, 43'can also be moved. That is, each cutting blade 33, 33', 43, 43'can be moved from the second standby position to the first standby position. Similarly, for these movements, the cutting blades 33, 33', 43, 43'are set to simultaneously start from the second standby position which is the starting point and arrive at the first waiting position which is the ending point at the same time. Is desirable. The operation of making the four cutting blades 33, 33', 43, 43'reach from the second standby position to the first standby position and cutting the work B is hereinafter referred to as a second operation.

In this way, by using the first operation and the second operation together, for example, a certain work B is cut on four sides by the first operation, and the next work B is subjected to the second operation. It is possible to set the moving directions of the cutting blades 33, 33', 43, 43'to be alternately alternated for each work B, such as cutting the four sides by the operation of. In this way, after cutting in one direction (for example, counterclockwise in a plan view) with respect to a certain work B is completed, each cutting blade 33, 33', 43, 43'stands by at the finished position. Then, for the next work B, cutting in another direction (for example, clockwise in a plan view) can be started from the finished position as a starting point. As a result, the working time can be shortened.

Here, each of the cutting blades 33, 33', 43, 43'is a disk-shaped rotary blade that rotates in a certain direction in both the first operation and the second operation. Therefore, as described above, when the first operation and the second operation are used together, even if the work B, which is a plate-like body, is in a so-called downcut state at the tip in the traveling direction of the blade in one direction. In the other direction, a so-called upper cut state may occur, which may induce the work B to float. However, in this embodiment, since the through hole 26 is opened in the groove 28, the work B is attracted to the upper surface of the stage 20 by the suction device 70 in the vicinity of the cutting line where the lifting is likely to occur, and the lifting is prevented. can do. Further, in this embodiment, since the through hole 26 in the groove 28 is opened in a longitudinal direction in the extending direction of the groove 28, the suction force of the work B in the vicinity of the cutting line is particularly increased, and the work B is particularly prevented from being lifted. It is effective. Chips can also be sucked through the through hole 26 in the groove 28.

Further, since the through holes 26 are arranged not only in the groove 28 but also in the entire area of the stage 20, even if the four sides around the work B are cut all at once, the entire plate surface of the work B is not biased in the stage. It is adsorbed on the upper surface of the work B so that the work B is less likely to be lifted. That is, in the present invention, instead of advancing the work B with respect to the position-fixed cutting blade as in the conventional case, the four cutting blades are moved all at once with respect to the work B adsorbed and fixed to the stage 20. Therefore, it is possible to eliminate that the variation in the traveling direction of the work B affects the finish of the cutting line. As a result, the finishing accuracy such as the parallelism and the squareness of the four sides at which the work B is cut can be remarkably improved without being affected by the variation in the material and thickness of the work B.

In this embodiment, as shown in FIGS. 1 and 8, a cutting piece B'and a chip discharging device 60 are provided along the widthwise edge of the fifth stage 25. The discharge device 60 is of the same belt conveyor type as the transport device 1. An endless belt 62 is wound between the drive roller 63 and the driven roller (not shown), and the drive roller 63 is rotated by a driving force from a drive source 64 such as a motor, and the rotation causes the belt 62 to rotate. It moves in the same direction as the traveling direction of the work B. Guide walls 65 are provided at both ends of the belt 62 in the width direction to prevent the cut pieces B'and chips that have fallen on the belt 62 from falling off to the side. The cut pieces B'and chips are transferred to the downstream side by the belt 62 and discharged. Along the belt 62, an inclined surface 29 for dropping the cut piece B'is provided on the outside of the groove 28 of the stage 20. As a result, the cut pieces B'and chips cut from the work B smoothly fall onto the belt 62.

The work B whose four sides have been cut is discharged to the next process by the transport device 1. The control of the movement amount when the work B is carried out is the same as the control when the work B is introduced onto the stage 20. In this embodiment, the belt 2 of the transport device 1 operates when the next work B is introduced onto the stage 20, and the finished work B is carried out at the same time by the operation. ..

In the above embodiment, the transport device 1 is a belt transport type, but the transport device 1 is not limited to this embodiment, and may be changed to, for example, a transport roll type transport device 1 that presses the work B from above and below. good. Further, a means of lowering the work B from above the stage 20 and placing it at a predetermined position on the stage 20 is also conceivable. Further, in this embodiment, the four cutting blades 33, 33', 43, 43'are the rotary blades of the circular saw, but the present invention is not limited to this embodiment, and for example, a strip-shaped blade that reciprocates in the vertical direction is used. It may be adopted. Even if a strip-shaped blade is adopted, both the first operation and the second operation can be supported by providing a mechanism or the like for reversing the direction of the blade. Further, the work B to be handled is not limited to the plywood as in this embodiment, and for example, the cutting device 10 of the present invention can be applied to various plate-shaped bodies such as a fiber plate and a gypsum board.

1 Transport device 10 Cutting device (plate-shaped body cutting device)
20 Stage 26 Through hole 27 Counterbore 28 Groove 29 Inclined surface 30, 30', 40, 40'Operating device 33, 33', 43, 43' Cutting blade 70 Suction device B Work B'Cut piece

Claims (6)

A rectangular stage (20) in a plan view on which a work (B) made of a plate-like body is placed, and
Through holes (26) that penetrate the stage (20) up and down,
A suction device (70) that communicates with the through hole (26) and attracts the work (B) to the upper surface of the stage (20).
Four cutting blades (33, 33', 43, 43') that stand by at the standby positions at the four corners of the stage (20), respectively.
An operating device that moves the four cutting blades (33, 33', 43, 43') from the standby position along the four sides of the stage (20) in either clockwise or counterclockwise direction in a plan view. (30, 30', 40, 40') and
A groove (28) that opens on the upper surface of the stage (20) and allows the cutting blades (33, 33', 43, 43') to pass through.
A plate-shaped body cutting device comprising. The operating device (30, 30', 40, 40')
A second position in which the four cutting blades (33, 33', 43, 43') are moved from the standby position in one direction along the four sides and are located on opposite sides of each of the moving sides. The first operation of reaching the standby position of the work (B) and cutting the work (B), and
The four cutting blades (33, 33', 43, 43') are moved from the second standby position along the four sides in the direction opposite to the one direction, and from the second standby position. The second operation of reaching the standby position and cutting the work (B), and
The plate-shaped body cutting device according to claim 1. The cutting blade (33, 33', 43, 43') is a disk-shaped rotary blade that rotates in a certain direction in both the first operation and the second operation, and the through hole (26) is said. The plate-shaped body cutting device according to claim 2, which is open in the groove (28). The plate-shaped body cutting device according to any one of claims 1 to 3, wherein the through hole (26) opens longitudinally in the groove (28) in the extending direction of the groove (28). The plate-shaped body cutting device according to any one of claims 1 to 4, wherein the through hole (26) is provided with a counterbore (27) around the upper surface opening of the stage (20). The plate-shaped body cutting apparatus according to any one of claims 1 to 5, wherein the stage (20) includes an inclined surface (29) on which a cutting piece (B') is dropped outside the groove (28). ..

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