CN111906488B

CN111906488B - Welding fixture

Info

Publication number: CN111906488B
Application number: CN202010907860.9A
Authority: CN
Inventors: 邵何兴; 张宾; 黄星丽
Original assignee: Anhui Jianghuai Automobile Group Corp
Current assignee: Anhui Jianghuai Automobile Group Corp
Priority date: 2020-08-31
Filing date: 2020-08-31
Publication date: 2021-08-27
Anticipated expiration: 2040-08-31
Also published as: CN111906488A

Abstract

The invention discloses a welding fixture, which comprises a mounting seat, a clamping frame and a switching driving mechanism, wherein the mounting seat is provided with two welding stations respectively corresponding to two welding postures of a workpiece to be welded, the clamping frame is used for bearing the workpiece to be welded, the clamping frame is rotatably mounted on the mounting seat along a left-right axial line, the switching driving mechanism is provided with a driving stroke and is used for driving the clamping frame to rotate, the two welding stations are both positioned on a rotating track of the workpiece to be welded on the clamping frame, the switching driving mechanism drives the clamping frame to rotate, and the workpiece to be welded on the clamping frame is respectively positioned on the two welding stations correspondingly at two limit positions of the driving stroke. According to the technical scheme provided by the invention, the clamping frame is driven to rotate by the switching driving mechanism with a driving stroke, so that the posture conversion of the welding fixture is completed.

Description

Welding fixture

Technical Field

The invention relates to the technical field of automobile final assembly assembling tools, in particular to a welding fixture.

Background

As is well known, welding is a common connection process in the mechanical industry, and in parts of a sub-assembly of an automobile body, when a large number of parts need to be welded on different welding surfaces, the parts of the automobile sometimes need to be turned over. The welding fixture is an important means for ensuring the precision of automobile parts, and a reasonable positioning and compressing mode is the key point of fixture design. Conventional fixtures are often designed for only one weld attitude, making welding of partial subassemblies difficult.

In current welding jig design structure, evenly design many places spacing bayonet socket on the rotation axis, rotate drive rotation axis through staff's hand handle and rotate, the rotation axis drives the anchor clamps body again and rotates, utilizes the foot to step on link mechanism and inserts the conversion that the spacing bayonet socket of difference realized the anchor clamps gesture. When the mechanism is used, workers need to use hands and feet, the operation difficulty is high, and the connecting rod can not be inserted into a required limiting bayonet at each time.

Disclosure of Invention

The invention mainly aims to provide a welding fixture, and aims to solve the problems that the existing welding fixture needs to be used by hands and feet and is difficult to operate.

In order to achieve the above object, the present invention provides a welding jig, comprising:

the mounting seat is provided with two welding stations which respectively correspond to two welding postures of the workpiece to be welded;

the clamping frame is used for bearing a workpiece to be welded and is rotatably arranged on the mounting seat along a left-right axial line; and the number of the first and second groups,

the switching driving mechanism is provided with a driving stroke and is used for driving the clamping frame to rotate;

the two welding stations are located on a rotating track of a workpiece to be welded on the clamping frame, the switching driving mechanism drives the clamping frame to rotate and corresponds to two limit positions of the driving stroke, and the workpiece to be welded on the clamping frame is located on the two welding stations correspondingly.

Optionally, the switching drive mechanism comprises:

a driving wheel fixedly mounted to one end portion of the clamping frame which faces upward from left to right; and the number of the first and second groups,

the belt transmission structure comprises a driving belt, the middle position of the driving belt is fixedly wound on the driving wheel, one end of the driving belt is a driving end, the driving end can move up and down to drive the driving wheel to rotate, and the up-down moving stroke of the driving end corresponds to the driving stroke.

Optionally, the belt transmission structure further includes a linear driving structure, the movable end of the linear driving structure can move up and down, the fixed end of the linear driving structure is disposed on the mounting seat, and the movable end is fixedly connected to the driving end.

Optionally, the linear drive structure comprises a drive cylinder;

welding jig still includes air feeder and intercommunication air feeder with drive actuating cylinder's gas circuit, be equipped with control button on the gas circuit for switch gaseous flow direction on the gas circuit, and then switch drive actuating cylinder's expansion end's activity direction.

Optionally, the other end of the driving belt is a limiting end;

the switching drive mechanism further includes:

the mounting frame is fixedly mounted on the mounting seat and provided with two mounting arms arranged at intervals in the front-back direction, one of the mounting arms is a limiting arm, and a through hole penetrates through the upper end face of the limiting arm;

the limiting screw rod extends along the vertical direction, the upper end of the limiting screw rod is fixedly arranged at the limiting end, and the thread section of the lower end of the limiting screw rod penetrates through the through hole; and the number of the first and second groups,

the limiting nut is sleeved on the threaded section of the limiting screw and is positioned below the limiting arm, and the upper end surface of the limiting nut is abutted against the lower end surface of the limiting arm so as to limit the moving stroke of the driving belt;

the fixed end of the linear driving structure is arranged on the other mounting arm.

Optionally, the welding jig further comprises an installation shaft extending in the left-right direction, and the installation shaft is rotatably installed on the installation base along the left-right axis;

the driving wheel is fixedly arranged at one end of the mounting shaft;

the clamping frame is fixedly arranged at the other end of the mounting shaft.

Optionally, a mounting sleeve ring is arranged in the middle of the driving wheel, and a mounting hole communicated with an inner cavity of the mounting sleeve ring is formed in the side surface of the mounting sleeve ring;

the mounting shaft is sleeved in the inner cavity of the mounting sleeve ring, and a locking groove is formed in the mounting shaft corresponding to the mounting hole;

the welding fixture further comprises a rotation stopping pin, and one end of the rotation stopping pin penetrates through the mounting hole and is inserted into the locking groove.

Optionally, the mounting shaft is provided with a locking section protruding from the end face of the driving wheel, the end face is opposite to one side of the clamping frame, an external thread is arranged on the outer side face of the locking section, a threaded locking ring is sleeved on the external thread of the locking section, and a key connection structure is further arranged between the locking section and the threaded locking ring.

Optionally, the clamping frame includes:

the clamping body extends along the left and right direction;

the two balancing weights are respectively arranged at the left end and the right end of the clamping body; and the number of the first and second groups,

the rotating ring is arranged on the clamping body;

wherein, the clamping body is rotatably arranged on the mounting seat.

Optionally, the lower end of the mounting seat is provided with a height-adjusting structure and/or a leveling structure.

In the technical scheme provided by the invention, the mounting seat is provided with two welding stations respectively corresponding to two welding postures of a workpiece to be welded, the clamping frame is used for bearing the workpiece to be welded, the clamping frame can be rotatably mounted on the mounting seat along a horizontal axis, the clamping frame is driven to rotate through a switching driving mechanism with a driving stroke, the workpiece to be welded on the clamping frame is respectively correspondingly positioned on the two welding stations corresponding to two limit positions of the driving stroke, and therefore the posture conversion of the welding fixture is completed.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.

FIG. 1 is a schematic perspective view of a welding fixture according to an embodiment of the present invention;

FIG. 2 is a schematic view of the switching shifter mechanism of FIG. 1;

FIG. 3 is a schematic view of the mount of FIG. 2;

FIG. 4 is a schematic view of the spacing structure of FIG. 2;

FIG. 5 is a perspective view of the drive wheel of FIG. 2;

FIG. 6 is a perspective view of the mounting shaft of FIG. 2;

FIG. 7 is a perspective view of the drive wheel and mounting shaft assembly of FIG. 2 in combination;

FIG. 8 is a perspective view of the drive wheel and mounting shaft of FIG. 7 shown engaged from another perspective;

FIG. 9 is a schematic view of the mount of FIG. 1;

FIG. 10 is a perspective view of the switching drive mechanism of FIG. 1 coupled to a mounting base;

FIG. 11 is a perspective view of the clamping frame of FIG. 1;

FIG. 12 is a schematic plan view of FIG. 11;

FIG. 13 is a perspective view of the mounting base and the switching drive mechanism of FIG. 1;

FIG. 14 is a schematic view of the first clamp attitude of FIG. 1;

fig. 15 is a schematic view of the second clamp attitude of fig. 1.

The reference numbers illustrate:

reference numerals	Name (R)	Reference numerals	Name (R)
				100	Welding fixture	1	Mounting seat
2	Clamping frame	3	Switching drive mechanism
				31	Driving wheel	4	Belt transmission structure
41	Driving belt	42	Driving cylinder
				43	Control button	44	Mounting rack
45	Limit screw	46	Limit nut
				47	Support pin	32	Mounting shaft
33	Mounting collar	34	Rotation stopping pin
				35	Threaded locking ring	21	Clamping body
22	Balancing weight	23	Rotating ring
				11	Base plate	12	Supporting plate
13	Adjusting bolt	14	First limit nut
				15	Anti-drop nut	16	First channel steel
17	Rib plate	18	Second channel steel
				19	Third channel steel	10	Mounting plate

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.

In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B" including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.

In the automobile body sub-assembly parts, when a large number of parts need to be welded on different welding surfaces, the automobile parts sometimes need to be turned over, but because most of the parts on the automobile are heavy, the efficiency of turning over and welding by using a cantilever crane is low, and the labor intensity of manual turning is high and unsafe. In view of the above, the present invention provides a welding fixture, and fig. 1 to 13 show an embodiment of the welding fixture according to the present invention.

Welding jig 100 includes mount pad 1, clamping frame 2 and switches actuating mechanism 3, mount pad 1 has two welding station that correspond respectively and wait to weld two welding postures of work piece, clamping frame 2 is used for bearing and waits to weld the work piece, clamping frame 2 along controlling to the axis rotate install in mount pad 1, it has a drive stroke to switch actuating mechanism 3, be used for the drive clamping frame 2 rotates, wherein, two welding station all is in on the rotation orbit of waiting to weld the work piece on clamping frame 2, it drives to switch actuating mechanism 3 clamping frame 2 rotates, corresponds on two extreme positions of drive stroke, wait to weld the work piece on clamping frame 2 and correspond respectively in two on the welding station.

In the technical scheme provided by the invention, the welding fixture 100 is connected with the switching driving mechanism 3 with a driving stroke through the clamping frame 2, the clamping frame 2 is driven to rotate, and the clamping frame 2 rotates to two limit positions corresponding to the driving stroke, so that workpieces to be welded on the clamping frame 2 are respectively positioned on two welding stations correspondingly, and the posture conversion of the welding fixture 100 is completed. The arrangement is realized without using hands and feet of staff, so that the operation of an operator is more convenient, and the adjustment with higher precision is ensured.

The clamping frame 2 is driven to rotate by the switching driving mechanism 3, and the driving form of the switching driving mechanism 3 may be various, for example, the switching driving mechanism 3 includes a gear pair and a motor, the motor drives a driving gear to rotate, the driving gear drives a driven gear to rotate, and the driven gear is connected to the clamping frame 2, so as to drive the clamping frame 2 to rotate, please refer to fig. 2, or as in this embodiment, the switching driving mechanism 3 includes a driving wheel 31 and a belt transmission structure 4, and the driving wheel 31 is fixedly installed at one end portion of the clamping frame 2 which is upward from left to right; the belt transmission structure 4 comprises a driving belt 41, the driving belt 41 has certain elasticity, the middle position of the driving belt 41 is fixedly wound on the driving wheel 31, one end of the driving belt 41 is a driving end, the driving end can move up and down, the driving wheel 31 is driven to rotate by the friction force between the driving belt 41 and the driving wheel 31, and the up-and-down moving stroke of the driving end corresponds to the driving stroke.

The switching driving mechanism 3 drives the driving wheel 31 to rotate through the movement of the driving end in the up-down direction, the movement of the driving end in the up-down direction can be realized by driving a half gear through a motor, the half gear is engaged with a rack set oppositely arranged on the left and right of the half gear for transmission, when the half gear rotates clockwise to be engaged with a rack on the left side, the half gear drives the rack set to move upwards, when the half gear rotates clockwise to be engaged with a rack on the right side, the half gear drives the rack set to move downwards, when the half gear rotates continuously, the engagement transmission process is repeated, so as to drive the rack set to move upwards and downwards, and the movement of the driving end in the up-down direction can be realized, please refer to fig. 2, also as in this embodiment, the belt transmission structure 4 further comprises a linear driving structure, and the moving end of the linear driving structure can move upwards and downwards, the stiff end of linear drive structure is located mount pad 1, expansion end fixed connection in the drive end, through linear drive structure drives driving band 41 makes driving band 41 drives the drive wheel rotation, so set up the structure more simple, the drive stroke is changeed and is controlled, does not need too high to make moreover and installation accuracy, makes things convenient for and makes and installs.

In order to make the linear driving structure easy to control and convenient to operate, in particular, referring to fig. 1 and 2, in this embodiment, the linear driving structure includes a driving cylinder 42, the welding fixture 100 further includes a gas supply device and a gas path communicating the gas supply device with the driving cylinder 42, the gas circuit is provided with a control button 43 for switching the flowing direction of the gas on the gas circuit, and further switches the moving direction of the movable end of the driving cylinder 42, when the movable end of the linear driving mechanism is required to move downwards, the control button 43 is pressed, the air supply device supplies air, the air flow pushes the movable end of the driving air cylinder 42 to move downwards, when the control button 43 is pressed again, the driving cylinder 42 is in the air outlet state, and the movable end of the driving cylinder 42 moves upwards, so that the operation is convenient and labor-saving.

Further, in order to adjust the rotation angle of the clamping frame 2 to a desired angle, the switching driving mechanism 3 is further provided with a limiting structure, so that the switching driving mechanism 3 has two limit positions of the driving stroke, please refer to fig. 2 and fig. 3, in this embodiment, the other end of the driving belt 41 is a limiting end; the switching driving mechanism 3 further comprises a mounting frame 44, a limit screw 45 and a limit nut 46, the mounting frame 44 is fixedly mounted on the mounting base 1, the mounting frame 44 is provided with two mounting arms arranged at intervals in the front-back direction, one of the mounting arms is a limit arm, a through hole is arranged on the upper end face of the limit arm in a penetrating manner, the limit screw 45 extends in the up-down direction, the upper end of the limit screw 45 is fixedly mounted on the limit end, a lower end thread section penetrates through the through hole, the limit nut 46 is sleeved on the thread section of the limit screw 45 and is located below the limit arm, the upper end face of the limit nut 46 is used for being abutted against the lower end face of the limit arm to limit the movable stroke of the driving belt 41, wherein the fixed end of the linear driving structure is arranged on the other mounting arm, and when the driving cylinder 42 moves downwards, the driving cylinder 42 drives the other end of the driving belt 41 to move upwards, in order to adjust the driving stroke, the limiting screw 45 is limited by the lower end surface of the limiting arm to stop moving in the upward movement process by adjusting the relative position of the limiting nut 46 relative to the limiting screw 45, and the driving stroke is correspondingly changed, so that the rotating angle of the driving wheel 31 is changed, and the limit position of the switching driving mechanism 3 can be accurately adjusted, so that the workpiece to be welded is at a proper welding angle.

Further, when the two welding stations are located on the rotation track of the to-be-welded workpiece on the clamping frame 2, in order to fix the driving wheel 31 relative to the mounting seat 1 and facilitate the determination of the welding stations, a fixing component may be disposed between the driving wheel 31 and the mounting frame 44, and the fixing component may also have a plurality of manners, for example, a plurality of threaded holes are disposed on the driving wheel 31, a mounting hole is also disposed on the mounting frame 44, a screw passes through the mounting hole and is in threaded engagement with the threaded hole, referring to fig. 2 and 3, in this embodiment, a plurality of grooves are disposed along the circumferential direction of the driving wheel 31, a through hole for the support pin 47 to pass through is disposed at the top center of the mounting frame 44, the support pin 47 is disposed through the through hole, a nut is sleeved on the upper end of the support pin 47, and is used to fix the support pin 47 on the mounting frame 44, the driving wheel 31 is seated on the supporting pin 47, when the driving wheel 31 needs to be fixed, the supporting pin 47 can be adjusted to be in a relative up-down position, the supporting pin 47 is seated in the groove on the driving wheel 31, and the nut is tightened to make the top of the supporting pin 47 abut against the groove, so that the driving wheel 31 can be further limited from rotating due to the driving belt 41 and the driving wheel 31, and the driving wheel 31 is positioned at a required preset angle.

In order to enable the switching mechanism to rotate synchronously with the clamping frame 2, please refer to fig. 2 and 8, in this embodiment, the welding fixture 100 further includes an installation shaft 32 extending in a left-right direction, the installation shaft 32 is rotatably installed on the installation base 1 along a left-right axis, the driving wheel 31 is fixedly installed at one end of the installation shaft 32, and the clamping frame 2 is fixedly installed at the other end of the installation shaft 32, so that the clamping frame 2 is conveniently connected with the driving wheel 31, so that the clamping frame 2 and the driving wheel 31 rotate synchronously.

In order to enable the driving wheel 31 to drive the mounting shaft 32 to rotate, a fixing and matching structure is disposed between the driving wheel 31 and the mounting shaft 32, and the fixing and matching structure may be in various manners, such as a threaded manner or a clamping manner, please refer to fig. 4 and 5, in this embodiment, a mounting collar 33 is disposed at a middle position of the driving wheel 31, a mounting hole communicating with an inner cavity of the mounting collar 33 is disposed on a side surface of the mounting collar 33, the mounting shaft 32 is sleeved in the inner cavity of the mounting collar 33, a locking groove is disposed on the mounting shaft 32 corresponding to the mounting hole, the welding jig 100 further includes a rotation stopping pin 34, one end of the rotation stopping pin 34 passes through the mounting hole and is inserted into the locking groove, so that the driving wheel 31 and the mounting shaft 32 are relatively stable, and the driving wheel 31 is prevented from idling relative to the mounting shaft 32, affecting the transmission effect.

In order to make the driving wheel 31 and the mounting shaft 32 more stable, another fixing structure is further provided between the driving wheel 31 and the mounting shaft 32, please refer to fig. 6, in this embodiment, the mounting shaft 32 has a locking section protruding from an end surface of the driving wheel 31 on a side facing away from the clamping frame 2, an external thread is provided on an outer side surface of the locking section, a threaded locking ring 21 is sleeved on the external thread of the locking section, a key connection structure is further provided between the locking section and the threaded locking ring 21, and the mounting shaft 32 and the driving wheel 31 are further fixed by the threaded locking ring 35 and the locking section being in threaded fit, so as to ensure a transmission effect.

Referring to fig. 9 to 11, in this embodiment, the clamping frame 2 includes a clamping body 21 extending in the left-right direction for clamping the workpiece to be welded, the clamping body 21 is rotatably mounted on the mounting base 1, because the clamping frame 2 has a large weight when rotating around the mounting shaft 32, the welding jig 100 may have an unstable center of gravity during rotation, so that the welding jig 100 may generate large shaking, in order to make the welding jig 100 more stable and not too large shaking amplitude during rotation, the clamping frame 2 further includes two balancing weights 22 respectively disposed at the left and right ends of the clamping body 21, and during adjustment of the clamping frame 2, referring to fig. 12 and 13, the clamping frame 2 further includes a rotating ring 23, the rotating ring 23 is disposed on the clamping body 21, and an operator steps on a control button 43, the driving air cylinder 42 is in an air outlet state, the rotating ring 23 is rotated, and the rotating motion stops when the driving air cylinder 42 rotates to the maximum working stroke, so that the clamp body is switched from a first clamp posture to a second clamp posture.

In order to better fix the mounting seat 1 and enable the mounting seat to be heightened and/or leveled, a heightening structure and/or a leveling structure are arranged at the lower end of the mounting seat 1, the heightening and/or leveling structure comprises a bottom plate 11, a support plate 12, an adjusting bolt 13, a limit nut 14, an anti-drop nut 15, a first channel steel 16, a rib plate 17, a second channel steel 18, a third channel steel 19 and a mounting plate 10, two ends of the bottom plate 11 are respectively provided with a foundation bolt mounting hole for fixing the bottom plate on the ground, the support plate 12 is connected with the bottom plate 11 through the adjusting bolts 13 at four positions, the adjusting bolt 13 and the bottom plate 11 are directly fixed through electric welding, and the height of the support plate 12 can be adjusted through the limit nut 14 and the anti-drop nut 15, so that the height of the whole mounting seat 1 is adjusted; two ends of the first channel steel 16 are fixed with the supporting plate 12 through electric welding; second channel-section steel 18 with third channel-section steel 19 all through the electric welding with first channel-section steel 16 is connected, first channel-section steel 16 second channel-section steel 17 with 19 two liang between the welding have everywhere the floor 17 plays and supports the reinforcing effect, mounting panel 10 is fixed in through the electric welding second channel-section steel 18 with on the third channel-section steel 19, so through adjusting stop nut 15 with adjusting bolt 13's relative position is increaseed and/or the leveling, simple structure and easily regulation.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A welding fixture, comprising:

the switching driving mechanism is provided with a driving stroke and used for driving the clamping frame to rotate, the switching driving mechanism comprises a driving wheel and a belt transmission structure, the driving wheel is fixedly mounted at one end part of the clamping frame, which faces upwards left and right, the belt transmission structure comprises a driving belt and a linear driving structure, the middle part of the driving belt is fixedly wound on the driving wheel, one end of the driving belt is a driving end, the driving end can move up and down to drive the driving wheel to rotate, the upward and downward moving stroke of the driving end corresponds to the driving stroke, the fixed end of the linear driving structure is arranged on the mounting seat, the movable end of the linear driving structure can move up and down, the movable end is fixedly connected to the driving end, and the linear driving structure comprises a driving cylinder;

the gas circuit is provided with a control button and is used for switching the flowing direction of gas on the gas circuit so as to switch the moving direction of the movable end of the driving cylinder, and the control button is arranged at the bottom of the mounting seat;

2. The welding fixture of claim 1, wherein the other end of the drive belt is a limit end;

the switching drive mechanism further includes:

3. The welding jig of claim 1, further comprising a mounting shaft extending in a left-right direction, the mounting shaft being rotatably mounted to the mounting base along a left-right axis;

the driving wheel is fixedly arranged at one end of the mounting shaft;

the clamping frame is fixedly arranged at the other end of the mounting shaft.

4. The welding fixture according to claim 3, wherein a mounting collar is arranged at the middle position of the driving wheel, and a mounting hole communicated with an inner cavity of the mounting collar is formed in the side surface of the mounting collar;

5. The welding fixture according to claim 4, wherein the mounting shaft has a locking section protruding from an end surface of the driving wheel facing away from the clamping frame, an external thread is provided on an outer side surface of the locking section, a threaded locking ring is sleeved on the external thread of the locking section, and a key connection structure is further provided between the locking section and the threaded locking ring.

6. The welding fixture of claim 1, wherein the clamping frame comprises:

the clamping body extends along the left and right direction;

the rotating ring is arranged on the clamping body;

wherein, the clamping body is rotatably arranged on the mounting seat.

7. The welding fixture of claim 1, wherein the lower end of the mounting base is provided with a height adjustment structure and/or a leveling structure.