Vertical linkage multi-stage telescopic arm

Abstract

The utility model relates to the technical field of stacking, and discloses a vertical linkage multistage telescopic arm which comprises a carriage unit, a head section unit and a plurality of sliding units, the head section unit is connected to the carriage unit in a sliding mode, and a driving mechanism for driving the head section unit to move vertically is arranged on the carriage unit; the sliding unit close to the first section unit is connected to the first section unit in a sliding mode, and the other two adjacent sliding units are detachably connected in a sliding mode. The first section unit and the multiple sliding units achieve synchronous vertical movement through the corresponding synchronous chain assemblies. The problem that an existing stacking mechanism cannot achieve large-stroke stacking under the condition that the upper space is limited is solved. And through modular arrangement of the sliding units, mounting and dismounting work of the sliding units is facilitated, meanwhile, a flexible module increasing and decreasing function is achieved, and the applicability and practicability of the equipment are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to a vertical linkage multistage telescopic arm belongs to the field of stacking technology. BACKGROUND

[0002] In modern industrial production, stacking operation is a very common and important link. At present, the up-down stacking mechanism widely used in the market mostly adopts a straight-up straight-down operation mode. The working principle of this kind of traditional stacking mechanism is relatively simple, mainly through the vertical lifting and falling of the Z axis to realize the stacking and carrying operation of goods. In the conventional working environment, when the stacking stroke requirement is relatively small, they can complete the task relatively stably, and meet the production demand to a certain extent.

[0003] However, with the continuous expansion of industrial production scale and the increasing diversification of production scene, the performance requirements for the stacking mechanism are increasingly stringent. In many actual industrial production scenes, for example, some compactly laid-out workshops, or warehouses with strict restrictions on equipment installation height, when facing large-stroke stacking tasks, the traditional straight-up straight-down stacking mechanism has obvious defects. Because its Z axis will inevitably punch out of the top of the equipment during lifting, and extend a considerable distance out of the top of the equipment, which makes it impossible for this kind of stacking mechanism to realize large-stroke stacking operation in the working environment with limited overhead space. This limitation greatly limits the application range of the stacking mechanism, cannot meet the diversified stacking requirements, and thus has an adverse effect on the efficient operation of the entire production process.

[0004] In some electronic equipment manufacturing workshops, due to the installation of a large number of lighting equipment, ventilation ducts and other various production auxiliary facilities inside the workshop, the top space inside the workshop is extremely limited. In this case, if the traditional straight-up straight-down stacking mechanism is used, when the goods with a higher number of layers need to be stacked, the Z axis of the stacking mechanism will not be able to normally lift to the required height due to the insufficient overhead space, thus making the stacking work unable to proceed smoothly. Similarly, in some cold chain warehouses, in order to maximize the use of storage space, the goods shelves are usually installed very close to the ceiling, which also makes the traditional stacking mechanism face the problem of limited overhead space when stacking goods, and is difficult to meet the needs of the warehouse for efficient stacking of goods.

[0005] Therefore, developing a new type of stacking mechanism that can break through the limitation of overhead space and effectively realize large-stroke stacking operation has become an important problem to be solved in the current industrial field. UTILITY MODEL CONTENTS

[0006] The utility model discloses a vertical linkage multistage telescopic arm, which is used to solve the problem that the existing stacking mechanism cannot realize long-stroke stacking under the condition of limited upper space.

[0007] The above technical purpose of the utility model is realized by the following technical scheme:

[0008] A vertical linkage multistage telescopic arm comprises a drag plate unit, a first section unit and a plurality of sliding units, the first section unit is slidably connected to the drag plate unit, and the drag plate unit is provided with a driving mechanism for driving the first section unit to move vertically.

[0009] The sliding units close to the first section unit are slidably connected to the first section unit, and the other adjacent two sliding units are detachably connected.

[0010] The drag plate unit comprises a bottom base plate.

[0011] The first section unit and the sliding units comprise sliding base plates.

[0012] The synchronous chain assembly comprises two chain wheels arranged at the two ends of the sliding base plate respectively, each chain wheel is connected with a section of synchronous chain, the upper end of the two synchronous chains is connected through a chain tension block, the chain tension block is adjustably fixed on the sliding base plate of another sliding unit above, and the lower end of the two synchronous chains is fixed on the sliding base plate of the first section unit or the sliding base plate of another sliding unit below or the bottom base plate through a chain connecting block.

[0013] Through the above technical scheme, the driving mechanism can drive the first section unit to move up and down, then the plurality of synchronous chain assemblies are used to realize the synchronous movement of the other sliding units and the first section unit, and the telescopic arm can only extend downward and return to the original position upward as a whole, does not occupy the upper space of the telescopic arm, can be applied to more working places, especially the workshops or warehouses with insufficient space height; meanwhile, the number of sliding units can be appropriately increased or decreased according to the requirement, the more the number of sliding units, the greater the working length, and the sliding units are modularly arranged, which can facilitate the dismounting and mounting work, increase the adaptability and practicability, and reduce the production cost.

[0014] The utility model further sets up: the drive mechanism includes drive sprocket, the driven sprocket of setting at drive sprocket both sides and the drive chain of connecting on drive sprocket and driven sprocket, the both ends of drive chain are fixedly connected with the upper and lower end of the sliding base plate of first section unit through the tensioning assembly, drive sprocket is fixed on the output shaft of servo reducer, and the driven sprocket rotation rotation is connected on the bottom base plate, and servo reducer is fixed on the bottom base plate and is electrically connected with the controller. Tensioning assembly includes chain tensioning base fixed on the sliding base plate of first section unit, and the screw rod is sleeved in chain tensioning base, and one end of screw rod is fixed with pull rod, and pull rod is hung on the link of drive chain end, and the other end of screw rod is screwed with two lock nuts.

[0015] Through the above technical scheme, servo reducer drives drive sprocket to rotate, and the both ends of drive sprocket drive drive chain to move in the same direction, and drive chain drives first section unit to move relative to bottom base plate through tensioning assembly.

[0016] The utility model further sets up: bottom base plate and sliding base plate each are equipped with a group of concentric rollers and eccentric rollers on it;

[0017] One pair of symmetrically arranged guide rails are fixed on the sliding base plate, and the cross section of the guide rail is in trapezoidal shape, and the cross section of the groove of the roller is also in trapezoidal shape;

[0018] One guide rail on the sliding base plate is inserted on a group of concentric rollers on the sliding base plate or bottom base plate below it, and the other guide rail on the sliding base plate is inserted on a group of eccentric rollers on the sliding base plate or bottom base plate below it. Through the setting of eccentric rollers, the guide rail can be inserted on the roller, which facilitates the installation and disassembly of the sliding unit, thereby facilitating the increase and decrease of the sliding unit, and the existence of the eccentric rollers can prevent the guide rail from being stuck between the rollers.

[0019] The utility model further sets up: one side of the guide rail fixed on the sliding base plate of first section unit is equipped with two proximity sensors, one proximity sensor is fixed on the upper end of bottom base plate, and the other proximity sensor is fixed on the middle part of bottom base plate, and the proximity sensor is electrically connected with the controller. Through the proximity sensor, the corresponding guide rail position can be detected, when first section unit moves down, the upper proximity sensor cannot detect the existence of the guide rail first, and then when the lower proximity sensor also cannot detect the guide rail, it indicates that the limit position has been reached, and it cannot move down any more. Similarly, when first section unit moves up, the upper proximity sensor detects the guide rail, which indicates that first section unit has reached the limit position of moving up, and it cannot continue to move up.

[0020] The utility model further sets up: the lower part of bottom base plate is fixed with first pin block;

[0021] The upper part of the sliding base plate of the first section unit is fixed with a second pin block, and the first pin block is arranged opposite to the second pin block; the cooperation of the first pin block and the second pin block can limit the downward position of the first section unit, and can also prevent the first section unit from falling off the bottom base plate in an unexpected situation, thereby causing an accident.

[0022] The first pin block and the second pin block are each fixed with a damping buffer block; the damping buffer block can play a buffering role when the first section unit moves downward, improve the stability of the extension and contraction, and reduce contact noise.

[0023] The utility model further sets up: the side wall of sliding base plate is fixed with a pair of upward extending third pin block and a downward extending fourth pin block, and the fourth pin block is arranged close to the upper third pin block. When the sliding base plate moves, the fourth pin block on the upper side can only move between the two third pin blocks on the lower side of the sliding base plate, thereby limiting the moving range between the sliding units, and preventing the sliding units from separating from each other, thereby causing an accident and further improving the safety performance.

[0024] The utility model further sets up: the chain connecting block is formed with a half waist type hole, the half waist type hole is inserted on the end chain shaft of the synchronous chain, and the chain connecting block is fixed on the corresponding bottom base plate or movable base plate through screws;

[0025] The chain tensioning block comprises an integrally formed T-shaped block and a hook portion, and the shoulder portion of the T-shaped block is formed with a waist type groove;

[0026] The T-shaped block is inserted in the adjusting groove of the sliding base plate, a plurality of threaded holes are formed on the two side end faces of the adjusting groove, a screw is sleeved in the waist type groove, and the screw is screwed on the threaded hole, so that the T-shaped block is fastened; and the hook portion is hung on the end chain shaft of the synchronous chain;

[0027] The chain wheel is rotatably connected to the chain wheel seat, and the chain wheel seat is fastened to the end portion of the sliding base plate through screws.

[0028] The utility model further sets up: the opposite side of the hook portion is provided with a stop rod, the stop rod is detachably connected to the T-shaped block, and the two are connected through threads. By arranging the stop rod, the chain shaft of the synchronous chain can be prevented from being separated from the hook portion, the connection between the two is more stable, and the running stability of the entire telescopic arm is improved.

[0029] The utility model further sets up: the corresponding synchronous chain assemblies of the adjacent two sliding base plates are staggered. The synchronous chains are staggered, the distance between the adjacent two sliding units can be effectively reduced, the structure is more compact, and the size of the space occupied by the entire telescopic arm can be effectively reduced.

[0030] The utility model has the following advantages:

[0031] Compared with the prior art, the space adaptability is strong: the innovative vertical linkage design makes the telescopic arm only extend downward and return, perfectly avoiding the space limitation above, and is particularly suitable for the plant and warehouse with compact space, and significantly widens the application scenarios of the equipment.

[0032] Flexible variable working length: the modular sliding unit design is adopted, the number of sliding units can be flexibly increased or decreased as required.

[0033] Convenient installation and stable operation: the unique concentric roller and eccentric roller are matched with the trapezoidal guide rail design, which not only facilitates the installation and disassembly of the sliding unit, but also prevents the guide rail and the roller from being stuck, and ensures the stable operation of the equipment.

[0034] Optimized connection and compact structure: the chain connecting block and the chain tensioning block are carefully designed, which greatly facilitates the connection and adjustment of the synchronous chain and each component, the stop rod prevents the chain from falling off, and the connection stability is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the utility model;

[0036] Figure 2 It is a partial schematic diagram of the utility model's drag plate unit;

[0037] Figure 3 It is a partial schematic diagram of the utility model's first section unit;

[0038] Figure 4 It is a partial schematic diagram of the utility model's sliding unit;

[0039] Figure 5 It is a sectional view of the utility model;

[0040] Figure 6 It is an assembly schematic diagram of the utility model's sliding unit and synchronous chain assembly;

[0041] Figure 7 It is a schematic diagram of the utility model's synchronous chain assembly;

[0042] Figure 8 It is a schematic diagram of the utility model's chain connecting block;

[0043] Figure 9 It is a schematic diagram of the utility model's chain tensioning block;

[0044] Figure 10The schematic diagram of the folding state of the utility model.

[0045] Reference signs: 1, a drag plate unit; 11, a bottom base plate; 12, a proximity sensor; 13, a first pin block; 14, a damping buffer block;

[0046] 2, a first section unit; 21, a sliding base plate; 22, a second pin block; 23, a third pin block; 24, a fourth pin block;

[0047] 3, a sliding unit; 31, a concentric roller; 32, an eccentric roller; 33, a guide rail;

[0048] 4, a driving mechanism; 41, a driving sprocket; 42, a driven sprocket; 43, a driving chain; 44, a tensioning assembly; 45, a servo reducer;

[0049] 441, a chain tensioning base; 442, a screw rod; 443, a pull rod; 444, a locking nut;

[0050] 5, a synchronous chain assembly; 51, a sprocket; 52, a synchronous chain; 53, a chain tensioning block; 54, a chain connecting block; 55, a sprocket base;

[0051] 531, a T-shaped block; 532, a hook portion; 533, a waist-shaped groove; 534, a blocking rod;

[0052] 541, a half-waist-shaped hole. DETAILED DESCRIPTION

[0053] The specific embodiments of the utility model will be further described in detail below in combination with the drawings and examples. The following examples are used to illustrate the utility model, but not to limit the scope of the utility model.

[0054] The following references Figures 1 to 10 The embodiments of the utility model are explained as follows:

[0055] A vertical linkage multi-stage telescopic arm, as Figure 1 shown, comprises a drag plate unit 1, a first section unit 2 and a plurality of sliding units 3, the first section unit 2 is slidingly connected on the drag plate unit 1, and the drag plate unit 1 is provided with a driving mechanism 4 for driving the first section unit 2 to move vertically;

[0056] The sliding unit 3 close to the first section unit 2 is slidingly connected on the first section unit 2, and the other two adjacent sliding units 3 are detachably slidingly connected; the first section unit 2 and the plurality of sliding units 3 realize synchronous vertical movement through corresponding synchronous chain assemblies 5.

[0057] As Figures 2-4 shown, the drag plate unit 1 comprises a bottom base plate 11;

[0058] The first segment unit 2 and the sliding unit 3 include a sliding base plate 21; each of the bottom base plate 11 and the sliding base plate 21 is provided with a set of concentric rollers 31 and eccentric rollers 32.

[0059] A pair of symmetrically arranged guide rails 33 are fixed on the sliding base plate 21; the cross-section of the guide rail 33 is trapezoidal, and the cross surface of the groove of the roller is also trapezoidal.

[0060] One guide rail 33 on the sliding base plate 21 is inserted into a set of concentric rollers 31 on the adjacent lower sliding base plate 21 or base plate 11, and another guide rail 33 on the sliding base plate 21 is inserted into a set of eccentric rollers 32 on the adjacent lower sliding base plate 21 or base plate 11. The eccentric rollers facilitate the installation and removal of the sliding unit by inserting the guide rails into the rollers, thus facilitating the addition or removal of the sliding unit. At the same time, the presence of the eccentric rollers prevents jamming between the guide rails and the rollers.

[0061] The lower part of the base plate 11 is fixed with a first pin block 13;

[0062] The upper part of the sliding base plate 21 of the first segment unit 2 is fixed with a second pin block 22, and the first pin block 13 is set opposite to the second pin block 22. The downward movement position of the first segment unit can be restricted by the cooperation of the first pin block 13 and the second pin block, and at the same time, it can prevent the first segment unit from falling off the base plate in case of accident, causing an accident.

[0063] Each of the first pin block 13 and the second pin block 22 is fixed with a vibration damping buffer block 14. The vibration damping buffer block can buffer the first segment unit when it moves down, improve the stability of expansion and contraction and reduce contact noise.

[0064] like Figure 5 As shown, the drive mechanism 4 includes a drive sprocket 41, driven sprockets 42 disposed on both sides of the drive sprocket 41, and a drive chain 43 connected to the drive sprocket 41 and the driven sprockets 42. The two ends of the drive chain 43 are respectively fixedly connected to the upper and lower ends of the sliding base plate 21 of the first segment unit 2 through a tensioning assembly 44. The drive sprocket 41 is fixed on the output shaft of the servo reducer 45. The driven sprockets 42 are rotatably connected to the base plate 11. The servo reducer 45 is fixed on the base plate 11 and electrically connected to the controller.

[0065] like Figure 3 As shown, the tensioning assembly 44 includes a chain tensioning base 441 fixed on the sliding base plate 21 of the first segment unit 2, a screw 442 sleeved inside the chain tensioning base 441, a pull rod 443 fixed to one end of the screw 442, the pull rod 443 being hooked onto a link at the end of the drive chain 43, and two locking nuts 444 screwed to the other end of the screw 442.

[0066] The servo reducer drives the rotation of the driving sprocket, and the driving sprocket drives the two ends of the driving chain to move in the same direction, and the driving chain drives the first section unit to move relative to the bottom base plate through the tensioning assembly.

[0067] As shown in Figure 5 , Figure 6 , the synchronous chain assembly 5 includes two sprockets 51 respectively arranged at the two ends of the sliding base plate 21, each sprocket 51 is connected with a section of synchronous chain 52, the upper end of the two synchronous chains 52 is connected through a chain tensioning block 53, the chain tensioning block 53 is adjustably fixed on the sliding base plate 21 of the adjacent upper sliding unit 3, and the lower end of the two synchronous chains 52 is fixed on the sliding base plate 21 of the first section unit 2, the sliding base plate 21 of the adjacent lower sliding unit 3 or the bottom base plate 11 through a chain connecting block 54.

[0068] As shown in Figures 6-9 , the chain connecting block 54 is formed with a half-hip hole 541, the half-hip hole 541 is inserted on the end chain shaft of the synchronous chain 52, and the chain connecting block 54 is fixed on the corresponding bottom base plate 11 or movable base plate 21 through a screw;

[0069] The chain tensioning block 53 includes an integrally formed T-shaped block 531 and a hook portion 532, and the shoulder of the T-shaped block 531 is formed with a hip-shaped groove 533.

[0070] The T-shaped block 531 is inserted in the adjusting groove 211 of the sliding base plate 21, a plurality of threaded holes 212 are formed on the two side end faces of the adjusting groove 211, a screw is sleeved in the hip-shaped groove, and the screw is screwed on the threaded hole, so that the T-shaped block is fastened; the hook portion 532 is hung on the end chain shaft of the synchronous chain 52.

[0071] The sprocket 51 is rotationally connected to the sprocket seat 55, and the sprocket seat 55 is fastened to the end of the sliding base plate 21 through a screw.

[0072] The opposite side of the hook portion 532 is provided with a stop rod 534, the stop rod 534 is detachably connected to the T-shaped block 531, and the two are connected through threads. By arranging the stop rod, the chain shaft of the synchronous chain can be prevented from being separated from the hook portion, so that the connection between the two is more stable, and the running stability of the entire telescopic arm is increased.

[0073] As shown in Figure 1As shown, the guide rail 33 on the side of the sliding base plate 21 of the first section unit 2 is provided with two proximity sensors 12, one of which is fixed on the upper end of the bottom base plate 11, and the other is fixed on the middle part of the bottom base plate 11, and the proximity sensors 12 are electrically connected with the controller. The corresponding guide rail position can be detected through the proximity sensor, when the first section unit moves downward, the upper proximity sensor first detects that the guide rail does not exist, then when the lower proximity sensor also detects that the guide rail does not exist, it means that the limit position has been reached and cannot move downward any more; similarly, when the first section unit moves upward and the upper proximity sensor detects the guide rail, it means that the first section unit has reached the upper limit position and cannot continue to move upward.

[0074] A pair of upward extending third pin blocks 23 and a downward extending fourth pin block 24 are fixed on the side wall of the sliding base plate 21, and the fourth pin block 24 is arranged close to the upper third pin block 23. When the sliding base plate moves, the upper fourth pin block can only move between the two third pin blocks on the lower sliding base plate, thereby limiting the moving range between the sliding units and preventing the sliding units from separating from each other to cause accidents and further improving the safety performance.

[0075] The corresponding synchronous chain assemblies 5 of the adjacent two sliding base plates 21 are arranged staggered. The staggered arrangement of the synchronous chain can effectively reduce the distance between the adjacent two sliding units 3, the structure is more compact, and the size of the space occupied by the whole telescopic arm can be effectively reduced.

[0076] Working principle: the sliding plate unit is connected to the moving device of the corresponding stacker, when stacking is needed, the controller sends a command to the servo reducer, the servo reducer drives the driving chain wheel to rotate, the driving chain wheel drives the driving chain to move, and the driving chain drives the sliding base plate of the first section unit to move downward through the tensioning assembly;

[0077] When the first section unit moves downward, the first sliding unit connected thereto is driven to move downward through the synchronous chain assembly, and the second sliding unit above the first sliding unit is driven to move downward through the corresponding synchronous chain assembly of the first sliding unit, and so on, so that the multiple sliding units and the first section unit are synchronously moved downward, thereby realizing the downward extension of the telescopic arm, that is, the first section unit moves at a speed of 1v, the first sliding unit close to the first section unit moves at a speed of 2v, the second sliding unit moves at a speed of 3v, and so on.

[0078] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, some improvements and modifications can be made without departing from the technical principles of the present application, and the above-mentioned improvements and modifications should be regarded as the protection scope of the present application.

Claims

1. A vertical linkage multi-stage telescopic arm comprising a drag plate unit (1), a first section unit (2) and a plurality of sliding units (3), characterized in that: The first section unit (2) is slidingly connected to the drag plate unit (1), and the drag plate unit (1) is provided with a driving mechanism (4) for driving the first section unit (2) to move vertically; The sliding unit (3) close to the first section unit (2) is slidingly connected to the first section unit (2), and the other two adjacent sliding units (3) are detachably connected; The drag plate unit (1) comprises a bottom base plate (11); The first section unit (2) and the sliding unit (3) comprise a sliding base plate (21); The synchronous chain assembly (5) comprises two chain wheels (51) arranged at the two ends of the sliding base plate (21), each chain wheel (51) is connected with a section of synchronous chain (52), the upper end portions of the two synchronous chains (52) are connected through a chain tensioning block (53), the chain tensioning block (53) is adjustably fixed on the sliding base plate (21) of the other sliding unit (3) above, and the lower end portions of the two synchronous chains (52) are fixed on the sliding base plate (21) of the first section unit (2) or the sliding base plate (21) of the other sliding unit (3) below or the bottom base plate (11) through a chain connecting block (54).

2. A vertically linked multi-stage telescopic arm according to claim 1, wherein: The driving mechanism (4) comprises a driving chain wheel (41), a driven chain wheel (42) arranged on the two sides of the driving chain wheel (41) and a driving chain (43) connected between the driving chain wheel (41) and the driven chain wheel (42); the two ends of the driving chain (43) are fixedly connected with the upper and lower ends of the sliding base plate (21) of the first section unit (2) through a tensioning assembly (44), and the driving chain wheel (41) is fixed on the output shaft of a servo reducer (45).

3. A vertically linked multi-stage telescopic arm according to claim 1, wherein: Each of the bottom base plate (11) and the sliding base plate (21) is provided with a set of concentric rollers (31) and eccentric rollers (32); The sliding base plate (21) is fixed with a pair of symmetrically arranged guide rails (33).

4. A vertically linked multi-stage telescopic arm according to claim 3, wherein: The guide rail (33) on the sliding base plate (21) of the first section unit (2) is provided with two proximity sensors (12) on one side, one proximity sensor (12) is fixed on the upper end of the bottom base plate (11), and the other proximity sensor (12) is fixed on the middle part of the bottom base plate (11).

5. A vertically linked multi-stage telescopic arm according to claim 4, wherein: The lower part of the bottom base plate (11) is fixed with a first pin block (13); The upper part of the sliding base plate (21) of the first section unit (2) is fixed with a second pin block (22), and the first pin block (13) is arranged opposite to the second pin block (22); Each of the first pin block (13) and the second pin block (22) is fixed with a damping and buffering block (14).

6. A vertically linked multi-stage telescopic arm according to claim 5, wherein: A pair of upwardly extending third pin blocks (23) and a fourth pin block (24) are fixed on the side wall of the sliding base plate (21), the fourth pin block (24) is arranged close to the upper third pin block (23).

7. A vertically linked multi-stage telescopic arm according to claim 1, wherein: The chain connecting block (54) is formed with a half-hip hole (541), and the half-hip hole (541) is inserted on the end chain shaft of the synchronous chain (52). The chain tensioning block (53) comprises an integrally formed T-shaped block (531) and a hook portion (532), and a waist-shaped groove (533) is formed on the shoulder of the T-shaped block (531); The T-shaped block (531) is inserted into the adjusting groove (211) of the sliding base plate (21), a plurality of threaded holes (212) are formed on the two side end faces of the adjusting groove (211), and the hook portion (532) is hung on the end chain shaft of the synchronous chain (52).

8. A vertically linked multi-stage telescopic arm according to claim 7, wherein: The opposite side of the hook portion (532) is provided with a stop lever (534) which is detachably connected to the T-shaped block (531).

9. A vertically linked multi-stage telescopic arm according to claim 1, wherein: The corresponding synchronous chain assemblies (5) of the adjacent two sliding base plates (21) are arranged in a staggered manner.

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