CN210633318U

CN210633318U - Clamp structure for processing choke plug of glass mold

Info

Publication number: CN210633318U
Application number: CN201921601116.5U
Authority: CN
Inventors: 韩志强; 王春坊; 杨永贞; 顾俊华; 陈佳熠; 钱进
Original assignee: Changshu Jianhua Mould Technology Co ltd
Current assignee: Changshu Jianhua Mould Technology Co ltd
Priority date: 2019-09-25
Filing date: 2019-09-25
Publication date: 2020-05-29
Anticipated expiration: 2029-09-25

Abstract

The utility model provides a fixture structure of glass mold bulkhead processing usefulness, belongs to frock clamp technical field. Comprises a chassis, which is arranged on an index plate of a revolving frame of a machine tool, and the revolving frame is arranged on a movable platform of the machine tool; the anchor clamps base, the centering on its one side upper portion is established the first chamber of stepping down of milling cutter, the centering on opposite side upper portion is established the milling cutter second and is stepped down, and this milling cutter second step down the chamber and correspond with the first chamber of stepping down of milling cutter, wherein: the directions of the cavity opening of the first abdicating cavity of the milling cutter and the cavity opening of the second abdicating cavity of the milling cutter are opposite to each other and are respectively communicated with the outside; the first stop block and the first pressing block are arranged on the clamp base at positions corresponding to two sides of the first abdicating cavity of the milling cutter; the second stop block and the second pressing block are arranged on the clamp base at positions corresponding to two sides of the second abdicating cavity of the milling cutter respectively. The milling precision is guaranteed, and the quality of a choke plug finished product is guaranteed; labor force is saved; the tool operation intensity is reduced, the clamping efficiency is improved, and the good milling operation progress is embodied.

Description

Clamp structure for processing choke plug of glass mold

Technical Field

The utility model belongs to the technical field of frock clamp, concretely relates to anchor clamps structure of glass mold bulkhead processing usefulness.

Background

As known in the art, a primary mold and a forming mold are generally used for manufacturing bottle and jar type glass containers such as beer bottles, red wine bottles, soda bottles, various seasoning bottles and daily cosmetic bottles by a blow-and-blow method, a glass melt in a molten state is introduced into the primary mold, a glass container preform (which is conventionally called a primary blank in the industry) is blow-formed in the primary mold, and the primary blank is transferred to the forming mold by a manipulator and is blow-formed, so that a finished glass container is finally obtained. In order to ensure that the glass melt entering the preform is successfully blown into the preform, the preform is provided with a closure which is engaged with the preform during the blowing of the preform from the glass melt entering the preform, and which is removed from the preform. The choke plug has two functions: firstly, blowing gas to the glass melting gas entering the primary mold; and secondly, pressing to avoid the upward overflow of the glass melt from the primary mold during the blowing process of the blowing mechanism positioned below the primary mold.

Technical information on the bulkhead structure can be found in published chinese patent documents, such as CN203639314U (a bulkhead), CN204058229U (a bulkhead structure for glass mold preforms) and CN104803586B (an alternative glass mold bulkhead), among others.

As is further known in the art, the bulkhead has a shape and a structure that are different depending on the blank mold, but the bulkhead satisfies the connection requirement substantially the same as the valve body robot of the line and row machine structural system, and specifically, a valve body robot mating cavity, which is also called a valve body robot mating groove (hereinafter, the same) and is provided one on each of the corresponding both sides of the bulkhead, is generally formed in the bulkhead.

In order to ensure the fixed connection effect between the valve body manipulator adapting groove and the valve body manipulator, a milling cutter of a machine tool is usually required to be milled on the valve body manipulator adapting groove, and the process of clamping a choke plug on the machine tool and milling by the machine tool in the prior art is as follows: the choke plug is clamped by a worker in a transverse clamping mode, the milling cutter mills the valve body manipulator adapter groove on one side of the choke plug in a downward vertical state, and after the milling is finished, the worker takes down the choke plug and rotates the choke plug for secondary clamping by 180 degrees, so that the milling cutter mills the valve body manipulator adapter groove on the other side of the choke plug. One of the defects of the process is that the choke plug needs to be clamped twice when the milling processing of the two valve body mechanical arm matching grooves is finished on the choke plug, so that the processing precision is influenced due to frequent clamping, and the quality of a finished product of the choke plug is difficult to guarantee; secondly, because the operator needs to stare at the machine tool all the time in the whole milling process so as to clamp the workpiece for the second time without losing time, one operator has low efficiency and is not beneficial to saving precious labor resources; thirdly, since the milling process is performed in a longitudinal milling process, the reliability of clamping the bulkhead must be sufficiently ensured, which results in a high working strength for workers. In view of the foregoing, it is of positive significance to explore a clamp suitable for clamping a choke plug with a reasonable structure.

The published chinese patent documents do not contain technical information on a jig for processing a glass mold and a glass mold accessory, and examples thereof include CN101659015B (a jig for processing a glass mold), CN101891373B (a jig for a glassware mold), CN101891372B (a jig for a glassware mold), CN101898311B (a jig structure for milling a positioning reference surface on a glass mold blank), CN102380777B (a jig device for processing a glass mold), CN102443859B (a jig device for processing a glass mold), CN102350650B (a jig for processing a glass mold), CN102350651B (a jig device for processing a glass mold with improved structure), CN102689187A (a turntable type jig for processing a glass mold), CN102848039A (a jig structure for processing a glass mold punch cooling groove disposed on an electric discharge machine), CN102837213A (a jig structure for processing a glass mold), CN102848246A (a jig for processing a glass mold), and the like, CN102848245A (fixture structure for glass mold processing), CN103056695A (fixture structure for glass mold cavity and joint surface processing), CN103084771A (fixture structure for open-close type forming mold hinge welding), CN103273350B (fixture structure for parallel surface milling of glass mold), CN203031352U (external processing fixture of double-drop glass mold), CN205834843U (fixture for machining glass mold), and CN206253847U (fixture for spray welding of glass mold cavity), etc.

As long as it is clear from a reading of the above patent documents without limitation: the tool clamp has the special characteristic aiming at a certain product, a certain class of products, a processing technology of a certain product or a processing technology of a certain class of products, and therefore the tool clamp belongs to a non-standard device, wherein the non-standard device does not have international standards, national standards and industrial standard specifications, does not have technical universality or technical reference, and is usually manufactured in a specific mode by a manufacturer producing products or using a specific technology to produce products. The technical solutions described below have been created in this context.

Disclosure of Invention

The utility model aims at providing a help satisfying vertical clamp and adorn the requirement and need not to carry out the secondary and press from both sides the dress and can ensure to mill the machining precision and ensure the off-the-shelf quality of vexed head, be favorable to making a workman carry out the value to two at least machines and get to save valuable labour resource, be of value to showing that to alleviate workman press from both sides dress operation intensity and improve and press from both sides the anchor clamps structure of glass mold vexed head processing usefulness that dress efficiency and can embody good milling operation progress.

The utility model aims to provide a fixture structure for processing a glass mold choke plug, which comprises a chassis, wherein the chassis is arranged on an index plate of a revolving frame of a machine tool in a use state, and the revolving frame is arranged on a moving platform of the machine tool; the anchor clamps base, this anchor clamps base directly or indirectly constitute in chassis one side up has seted up a first chamber of stepping down I of milling cutter at the position placed in the middle on one side upper portion of this anchor clamps base, and has seted up a milling cutter second chamber of stepping down II at the position placed in the middle on the opposite side upper portion of anchor clamps base, and this milling cutter second chamber of stepping down II is corresponding with the first chamber of stepping down I of milling cutter, wherein: the directions of the cavity opening of the first abdicating cavity I of the milling cutter and the cavity opening of the second abdicating cavity II of the milling cutter are opposite to each other and are respectively communicated with the outside; the first stop block I and the first pressing block I are arranged on the clamp base at positions corresponding to two sides of the first abdicating cavity I of the milling cutter; and the second stop block II and the second pressing block II are arranged on the clamp base at positions respectively corresponding to two sides of the second abdicating cavity II of the milling cutter.

In a specific embodiment of the present invention, a chassis bolt fixing groove is formed in the upward side of the index plate in a spaced state, and the peripheral edge portion of the chassis is fixed to the index plate by a chassis bolt at a position corresponding to the chassis bolt fixing groove.

In another specific embodiment of the present invention, the cross-sectional shape of the chassis bolt fixing groove is a T-shape, and the chassis bolt is a T-shaped bolt.

In another specific embodiment of the present invention, a bulkhead center positioning post is fixed to the center of the upward side of the clamp base by a bulkhead center positioning post screw.

In another specific embodiment of the present invention, a first stopper limiting groove i recessed in the upper surface of the fixture base is formed in the fixture base at a position corresponding to the first stopper i, and a second stopper limiting groove ii recessed in the upper surface of the fixture base is also formed in a position corresponding to the second stopper ii; the first stop block I is fixed on the clamp base at a position corresponding to the first stop block limiting groove I through a first stop block fixing screw I, and the second stop block II is fixed on the clamp base at a position corresponding to the second stop block limiting groove II through a second stop block fixing screw II; one end of the first pressing block I is arranged on the clamp base through a first pressing block shaft screw I, and the other end of the first pressing block I is a free end; one end of the second pressing block II is arranged on the clamp base through a second pressing block shaft screw II, and the other end of the second pressing block II is a free end.

In a further specific embodiment of the invention, a first press block and presser foot engaging groove i is formed at the free end of the first press block i and on the side facing the first stop i, and a second press block and presser foot engaging groove is formed at the free end of the second press block ii and on the side facing the second stop ii.

In a more specific embodiment of the present invention, the first stop i and the second stop ii form a diagonal position relationship with each other; the first pressing block I and the second pressing block II mutually form a diagonally arranged position relation.

In yet another specific embodiment of the present invention, the clamp base is in the shape of a cube.

In a more specific embodiment of the present invention, the revolving frame is disposed on the moving platform in a state of rotating 90 ° clockwise or 90 ° counterclockwise.

In yet another specific embodiment of the present invention, the left end and the right end of the movable platform are each configured with a revolving frame base, and the left end and the right end of the revolving frame are respectively rotatably supported on the revolving frame base and are in transmission connection with a revolving frame driving mechanism disposed on the revolving frame base of the left end or the right end.

The utility model provides one of the technical effects of the technical scheme, because chassis and anchor clamps base have set gradually from bottom to top on the graduated disk that sets up on the revolving frame, owing to seted up milling cutter first abdication chamber I and milling cutter second abdication chamber II respectively in one side and the opposite side of anchor clamps base again, still owing to set up first dog I and first briquetting I respectively in the position that corresponds the both sides of milling cutter first abdication chamber I, and set up second dog II and second briquetting II respectively in the position that corresponds the both sides of milling cutter second abdication chamber II, therefore the process of milling processing need not to carry out secondary clamp in adapting the chamber to two corresponding valve body manipulators on the vexed head, can ensure and mill the processing precision, and ensure vexed head finished product quality; secondly, because two dividing plates can be arranged on the revolving frame of one machine tool and one fixture structure of the utility model can be arranged on each dividing plate, one worker can at least check on the two machine tools, which is very beneficial to saving precious labor resources; thirdly, the milling of the milling cutter of the machine tool to the corresponding two valve body manipulator adapting cavities on the choke plug can be completed only by once clamping, so that the clamping operation intensity of workers can be obviously reduced, the clamping efficiency is improved, and the good milling operation progress is embodied.

Drawings

Fig. 1 is a schematic view of an embodiment of the present invention.

Fig. 2 is a schematic view of the bulkhead shown in fig. 1 configured on a primary mold.

Detailed Description

In order to make the technical essence and advantages of the present invention more clear, the applicant below describes in detail the embodiments, but the description of the embodiments is not a limitation of the present invention, and any equivalent changes made according to the inventive concept, which are only formal and not essential, should be considered as the technical scope of the present invention.

In the following description, all the concepts related to the directions or orientations of up, down, left, right, front and rear are illustrated in fig. 1 and are based on the rest state, and thus, they should not be construed as particularly limiting the technical solution provided by the present invention.

With reference to fig. 1, a chassis 1 is shown, which chassis 1 is in use arranged on an index plate 211 of a turret 21 of a machine tool 2, while the turret 21 is arranged on a mobile platform 22 of the machine tool 2; the clamp base 3 is shown, the clamp base 3 is directly formed on the upward side of the chassis 1, but the clamp base 3 and the chassis 1 can also be processed into a split structure, the clamp base and the chassis 1 are fixed by screws, a milling cutter first yielding cavity i 31 is arranged at the middle position of one side upper portion (right side upper portion shown in fig. 1) of the clamp base 3, a milling cutter second yielding cavity ii 32 is arranged at the middle position of the other side upper portion (left side upper portion of position state shown in fig. 1) of the clamp base 3, and the milling cutter second yielding cavity ii 32 corresponds to the milling cutter first yielding cavity i 31, wherein: the directions of the cavity opening of the first abdicating cavity I31 of the milling cutter and the cavity opening of the second abdicating cavity II 32 of the milling cutter are opposite to each other and are respectively communicated with the outside; a first stop block I4 and a first pressing block I5 are shown, and the first stop block I4 and the first pressing block I5 are arranged on the clamp base 3 at positions corresponding to two sides of a first abdicating cavity I31 of the milling cutter; a second stop ii 6 and a second pressing block ii 7 are shown, which second stop ii 6 and second pressing block ii 7 are arranged on the fixture base 3 at positions corresponding to both sides of the second abdicating cavity ii 32 of the milling cutter, respectively.

As shown in fig. 1, since the opening of the first milling cutter relief cavity i 31 faces to the right and the opening of the second milling cutter relief cavity ii 32 faces to the left, the openings of the first milling cutter relief cavity i 31 and the second milling cutter relief cavity ii 32 are opposite in direction, and the first milling cutter relief cavity i 31 and the second milling cutter relief cavity ii 32 are U-shaped.

As shown in fig. 1, two index plates 211 are disposed on the revolving frame 21, the index plates 211 can be driven by a driving device disposed below the revolving frame 21 to rotate, for example, clockwise or counterclockwise by 90 °, and two index plates 211 are disposed, so that the clamp structure of the present invention has two sets, and can simultaneously clamp two plugs 8 illustrated in fig. 1. Furthermore, according to the common general knowledge, the mobile platform 22, which is the structural system of the machine tool 2, is movable from side to side so that the two bulkheads 8 clamped on the two clamp structures correspond in sequence to the positions of the milling cutters 23 of the machine tool 2 shown in fig. 1.

As shown in fig. 1, a base plate bolt fixing groove 2111 is formed at an interval on the upward side of the index plate 211, and the base plate 211 is fixed to the peripheral edge portion of the base plate 1 by a base plate bolt 11 at a position corresponding to the base plate bolt fixing groove 2111.

In this embodiment, the cross-sectional shape of the chassis bolt fixing groove 2111 is T-shaped, and the chassis bolt 11 is a T-bolt.

As shown in fig. 1, a bulkhead center positioning post 33 is fixed to the center of the upward side of the clamp base 3 by a bulkhead center positioning post screw 331, and the bulkhead center positioning post 33 is adapted to be engaged with the bulkhead positioning center hole 81 of the bulkhead 8 shown in fig. 1.

Continuing to refer to fig. 1, a first stopper limiting groove i 34 recessed in the upper surface of the fixture base 3 is formed in the fixture base 3 at a position corresponding to the first stopper i 4, and a second stopper limiting groove ii 35 recessed in the upper surface of the fixture base 3 is also formed in a position corresponding to the second stopper ii 6; the first stop block I4 is fixed on the clamp base 3 at a position corresponding to the first stop block limiting groove I34 through a first stop block fixing screw I41, and the second stop block II 6 is fixed on the clamp base 3 at a position corresponding to the second stop block limiting groove II 35 through a second stop block fixing screw II 61; one end of the first pressing block I5 is arranged on the clamp base 3 through a first pressing block shaft screw I51, and the other end of the first pressing block I5 is a free end; one end of the aforementioned second press piece ii 7 is provided on the jig base 3 by a second press piece shaft screw ii 71, and the other end of the second press piece ii 7 is constituted as a free end.

As shown in fig. 1, a first presser foot engagement groove i 52 is formed at the free end of the first presser piece i 5 on the side facing the first stopper i 4, and a second presser foot engagement groove ii 72 is formed at the free end of the second presser piece ii 7 on the side facing the second stopper ii 6.

As shown in fig. 1, the first stopper i 4 and the second stopper ii 6 are in a diagonally disposed positional relationship with each other; the first pressure piece I5 and the second pressure piece II 7 are also in a diagonally opposite positional relationship with each other.

In the present embodiment, the jig base 3 has a square shape; the turret 21 is provided on the movable platform 22 in a state of being rotated 90 ° clockwise or 90 ° counterclockwise. That is to say the turret 21 may be rotated 90 in a clockwise/counter-clockwise direction.

As shown in fig. 1, a revolving frame seat 221 is formed at each of the left and right ends of the movable platform 22, and the left and right ends of the revolving frame 211 are rotatably supported by the revolving frame seats 221 and are drivingly connected to a revolving frame driving mechanism (not shown) provided on the revolving frame seat 221 at the left or right end.

Continuing to see fig. 1, being on-line operation personnel and being on-duty personnel press from both sides vexed head 8 and locate the utility model discloses an on the anchor clamps structure 2, concrete process is as follows: firstly, aligning a choke plug central positioning hole 81 of a choke plug 8 with a choke plug central positioning column 33, correspondingly inserting the choke plug central positioning column 33 into the choke plug central positioning hole 81, respectively enabling valve body manipulator adapting cavities 82 on two corresponding sides of the choke plug 8 to correspond to a first abdicating cavity I31 of a milling cutter and a second abdicating cavity II 32 of the milling cutter, respectively, enabling a first stop block I4 and a second stop block II 6 to be respectively attached to a choke plug first stop foot 83 on two sides of the choke plug 8, namely limiting the choke plug first stop foot 83, then enabling a first pressing block matching groove I52 of a first pressing block I5 and a second pressing block matching groove II 72 of a second pressing block II 7 to be respectively attached to a choke plug second stop foot 84 on two sides of the choke plug 8 and corresponding to the choke plug first stop foot 83 by a machine operator through screwing and unscrewing operations of a first pressing block shaft screw I51 and a second pressing block shaft screw II 71, namely limiting the choke plug second stop foot 84, the first and second presser shaft screws i 51 and ii 71 are tightened, and the other bulkhead 8 is similarly clamped, and therefore, the description thereof will not be repeated.

After the clamping of the bulkhead 8 is completed, the driving device below the rotary base 21 drives the index plate 211 to rotate, so that the valve body manipulator matching cavity 82 is aligned with the milling cutter 23, and then the rotary frame driving mechanism driving the rotary frame 21 to rotate rotates the rotary frame 21 90 degrees in the direction indicated by the arrow in fig. 1, so that the cavity opening of the valve body manipulator matching cavity 82 faces upwards, and the milling cutter 23 can mill the valve body manipulator matching cavity. After the valve body manipulator matching cavity 82 on one side is milled, the revolving frame 21 reversely rotates under the action of the revolving frame driving mechanism, so that the opening of the valve body manipulator matching cavity 82 on the other side faces upwards, and the milling cutter 23 can mill the valve body manipulator matching cavity 82 on the other side. After the valve body manipulator adapting cavities 82 on two corresponding sides of one bulkhead 8 are machined, under the movement of the mobile platform 22, the other bulkhead 8 to be milled corresponds to the station where the milling cutter 23 is located, and the milling cutter 23 is used for milling the valve body manipulator adapting cavities 82 on two sides of the other bulkhead 8 in the same manner.

The milling cutter 23 of a above-mentioned lathe 2 is to clamping in the utility model discloses an in-process that two vexed heads 8 on one set of anchor clamps are structural mills processing, the personnel of looking at the machine can press from both sides the work of dress vexed head 8 to another lathe 2. After the two plugs 8 on one machine tool 2 have finished machining the valve body manipulator adapter 82, the plug 8 is removed by the operator in the reverse process and the other plug 8 to be milled is clamped.

Referring to fig. 2, fig. 2 shows a primary mold 9, the bulkhead 8 milled from fig. 1 is in a use state of being matched with the primary mold 9, and in a working state of the line machine, a valve body manipulator not shown in the figure is matched with the valve body manipulator matching cavity 82, since the process of using the valve body manipulator in matching with the valve body manipulator matching cavity 82 of the bulkhead 8 belongs to the prior art, for example, refer to the last paragraph of the specification of CN204058229U mentioned in the above background art column by the applicant, and thus, the description thereof is omitted.

To sum up, the technical solution provided by the present invention remedies the defects in the prior art, successfully completes the invention task, and faithfully embodies the technical effects mentioned in the above technical effect column by the applicant.

Claims

1. The clamp structure for processing the glass mould choke plug is characterized by comprising a base plate (1), wherein the base plate (1) is arranged on an index plate (211) of a rotary frame (21) of a machine tool (2) in a use state, and the rotary frame (21) is arranged on a moving platform (22) of the machine tool (2); anchor clamps base (3), this anchor clamps base (3) directly or indirectly constitute in chassis (1) one side up, the middle position on one side upper portion of this anchor clamps base (3) has seted up a milling cutter first chamber of stepping down I (31), and the middle position on the opposite side upper portion of anchor clamps base (3) has seted up a milling cutter second chamber of stepping down II (32), and this milling cutter second chamber of stepping down II (32) and the milling cutter first chamber of stepping down I (31) corresponding, wherein: the directions of the cavity opening of the first abdicating cavity I (31) of the milling cutter and the cavity opening of the second abdicating cavity II (32) of the milling cutter are opposite to each other and are respectively communicated with the outside; the milling cutter positioning device comprises a first stop block I (4) and a first pressing block I (5), wherein the first stop block I (4) and the first pressing block I (5) are arranged on a clamp base (3) at positions corresponding to two sides of a first abdicating cavity I (31) of the milling cutter; the second stop block II (6) and the second pressing block II (7) are arranged on the clamp base (3) at positions corresponding to the two sides of the second abdicating cavity II (32) of the milling cutter respectively.

2. The jig structure for glass mold bulkhead processing according to claim 1, wherein a chassis bolt fixing groove (2111) is opened at an interval on an upward side of the index plate (211), and a chassis bolt (11) is fixed to the index plate (211) at a position corresponding to the chassis bolt fixing groove (2111) at a peripheral edge portion of the chassis (1).

3. The jig structure for glass mold bulkhead processing according to claim 2, wherein the cross-sectional shape of the chassis bolt fixing groove (2111) is a T-shape, and the chassis bolt (11) is a T-bolt.

4. The clamp structure for glass mold bulkhead processing according to claim 1, wherein a bulkhead center positioning post (33) is fixed to a center position of an upward facing side of the clamp base (3) by a bulkhead center positioning post screw (331).

5. The jig structure for glass mold bulkhead processing according to claim 1, wherein a first stopper groove i (34) recessed in the upper surface of the jig base (3) is formed in the jig base (3) at a position corresponding to the first stopper i (4), and a second stopper groove ii (35) recessed in the upper surface of the jig base (3) is also formed in a position corresponding to the second stopper ii (6); the first stop block I (4) is fixed on the clamp base (3) at a position corresponding to the first stop block limiting groove I (34) through a first stop block fixing screw I (41), and the second stop block II (6) is fixed on the clamp base (3) at a position corresponding to the second stop block limiting groove II (35) through a second stop block fixing screw II (61); one end of the first pressing block I (5) is arranged on the clamp base (3) through a first pressing block shaft screw I (51), and the other end of the first pressing block I (5) is a free end; one end of the second pressing block II (7) is arranged on the clamp base (3) through a second pressing block shaft screw II (71), and the other end of the second pressing block II (7) is a free end.

6. The jig structure for glass mold bulkhead processing according to claim 5, characterized in that a first press piece presser foot fitting groove I (52) is formed at the free end of the first press piece I (5) and at a side facing the first stopper I (4), and a second press piece presser foot fitting groove (72) is formed at the free end of the second press piece II (7) and at a side facing the second stopper II (6).

7. The jig structure for glass mold bulkhead processing according to claim 1, 5 or 6, characterized in that the first stopper i (4) and the second stopper ii (6) are in a diagonally disposed positional relationship with each other; the first pressing block I (5) and the second pressing block II (7) mutually form a diagonally arranged position relation.

8. The structure of a clamp for the bulkhead processing of a glass mold according to claim 1, 4 or 5, characterized in that the clamp base (3) has a square shape.

9. The jig structure for glass mold bulkhead processing according to claim 1, characterized in that the turret (21) is provided on the moving platform (22) in a state of being rotated 90 ° clockwise or 90 ° counterclockwise.

10. The jig structure for glass mold bulkhead processing according to claim 9, wherein a turret base (221) is formed at each of left and right ends of the moving platform (22), and left and right ends of the turret (21) are rotatably supported on the turret base (221) and are drivingly connected to a turret drive mechanism provided on the turret base (221) at the left or right end.