An automatic loading device for lamp holders of light boxes

Abstract

The utility model relates to the technical field of lamp box lamp holder subassembly assembly, disclose a kind of automatic feeding device of lamp box lamp holder, including rack, feeding mechanism, distributing mechanism and rotary assembly mechanism;Feeding mechanism is located on rack, and it is used for continuously conveying lamp holder subassembly one by one;Distributing mechanism is located at the discharging end of feeding mechanism, distributing mechanism is used to receive the lamp holder subassembly output by feeding mechanism, and it is transferred to feeding station one by one;Rotary assembly mechanism is located on rack, and it is used to transfer the lamp holder subassembly on feeding station to assembly station and assemble. The utility model can solve the problems of automatic feeding and rotary assembly lamp holder subassembly, improve the efficiency and quality of assembly.

Description

Technical Field

[0001] This utility model relates to the field of light box lamp head assembly technology, specifically to an automatic feeding device for light box lamp heads. Background Technology

[0002] In today's advertising displays, lighting decorations, and many other fields, light boxes, as a common device, play a crucial role. A light box comprises multiple lamp head components, and the rational layout and precise installation of these components directly determine the lighting effect, display quality, and overall performance of the light box. During the assembly of the light box lamp head components, because multiple components need to be installed, and the position of each component within the light box has strict requirements, it is essential to ensure that their positions correspond accurately to achieve the ideal lighting and display effect. To achieve this positional correspondence, it is often necessary to rotate the lamp head components to adjust their angle and orientation to meet design requirements.

[0003] However, in current actual production of lightbox lamp head components, loading and rotation assembly mainly rely on manual labor. This results in low assembly efficiency, and the precision of manual rotation assembly is difficult to guarantee. Different operators have different operating habits and skill levels, making it difficult to accurately adjust the lamp head component to the required angle and position each time, leading to deviations and affecting the overall quality of the lightbox. Furthermore, prolonged manual operation easily leads to operator fatigue; as fatigue increases, the probability of operational errors also rises, further reducing assembly efficiency and product quality.

[0004] In view of the shortcomings of the existing technology, it is necessary to develop an automatic lamp head feeding device to realize the automated feeding and rotation assembly of lamp head components, thereby improving assembly efficiency and quality. Utility Model Content

[0005] (a) Technical problems to be solved

[0006] This utility model provides an automatic feeding device for lamp head of a light box, which can at least solve the technical problem of how to automatically feed and rotate the lamp head assembly to improve assembly efficiency and quality.

[0007] (II) Technical Solution

[0008] To solve the above-mentioned technical problems, this utility model provides the following technical solution: an automatic feeding device for lightbox lamp heads, comprising:

[0009] frame;

[0010] The feeding mechanism, located on the frame, is used to continuously feed the lamp head assemblies one by one;

[0011] The material sorting mechanism is located at the discharge end of the material feeding mechanism. The material sorting mechanism is used to receive the lamp head components output by the material feeding mechanism and transfer them one by one to the loading station.

[0012] A rotary assembly mechanism, mounted on the frame, is used to transfer lamp head assemblies from the loading station to the assembly station for assembly.

[0013] Further, the aforementioned material distribution mechanism includes:

[0014] The material distribution block is located on one side of the feeding mechanism and is used to receive the lamp head assembly output by the feeding mechanism.

[0015] The material dispensing chuck and the connected translation drive and material dispensing rotation drive are used to clamp or release the lamp head assembly. One of the translation drive and the material dispensing rotation drive is located on the frame, and the other is connected to the material dispensing chuck for transmission.

[0016] The translation drive is used to drive the material distribution clamp to move back and forth between the material distribution block and the loading station. The material distribution block is provided with a clearance recess for the material distribution clamp to be inserted. The material distribution rotation drive is used to drive the material distribution clamp to flip.

[0017] Further, the aforementioned material dispensing chuck includes:

[0018] The first clamping arm is disposed on the clamping drive member and is provided with a limiting groove. The limiting groove is used to accommodate part of the lamp head assembly and limit the position of the lamp head assembly. A clearance opening is provided on one side of the limiting groove. The clearance opening extends outside the first clamping arm and is used to allow the lamp head assembly to be inserted into the limiting groove.

[0019] The second clamping arm and the clamping drive are located on the output end of the translation drive or the material distribution rotation drive. The output end of the clamping drive is connected to the second clamping arm. The clamping drive is used to drive the second clamping arm to move toward or away from the first clamping arm in order to clamp or release the lamp head assembly in the limiting groove.

[0020] Further, the aforementioned material supply mechanism includes:

[0021] The storage platform is located on one side of the material distribution block and is equipped with a material trough with openings at both ends. The material trough is used to accommodate several lamp head assemblies.

[0022] The pusher block and drive assembly are mounted on the frame and are connected to the pusher block and / or storage platform. The drive assembly is used to drive the pusher block and storage platform to move relative to each other so that the pusher block is positioned opposite the material trough and slides along the material trough from one end opening to the other end opening, thereby pushing the lamp head assemblies in the material trough one by one onto the distribution block.

[0023] In a further configuration, at least two material slots are evenly spaced on the aforementioned storage platform. The driving assembly includes a first driving member and a second driving member mounted on the frame. The first driving member is driven to the storage platform and is used to drive the storage platform to move along the arrangement direction of the material slots so that any material slot is positioned relative to the distribution block, and the pusher block is positioned relative to the distribution block. The second driving member is driven to the pusher block and is used to drive the pusher block to slide along the corresponding material slot so as to push the lamp head assemblies in the material slot one by one onto the distribution block.

[0024] Furthermore, the aforementioned pusher block is vertically slidably mounted on the output end of the second drive component.

[0025] Furthermore, the aforementioned rotary assembly mechanism includes:

[0026] The transfer chuck and the transfer rotation drive are used to clamp or release the lamp holder assembly. The transfer chuck is connected to the transfer chuck and is used to drive the transfer chuck to rotate.

[0027] The horizontal drive and the lifting drive are connected. One of the horizontal drive and the lifting drive is mounted on the frame, and the other is connected to the transfer rotary drive. The horizontal drive is used to drive the transfer rotary drive and the transfer chuck to move back and forth between the loading station and the assembly station. The lifting drive is used to drive the transfer rotary drive and the transfer chuck to move up and down toward the loading station or the assembly station.

[0028] Further configuration: the aforementioned lifting drive unit is provided in two parts, which are connected together. One lifting drive unit is located on the output end of the horizontal drive unit, and the output end of the other lifting drive unit is connected to the transfer rotation drive unit.

[0029] (III) Beneficial Effects

[0030] Compared with the prior art, the automatic feeding device for light box lamp heads provided by this utility model has the following beneficial effects:

[0031] The lamp head provided by this utility model achieves fully automated operation of the lamp head assembly from feeding to loading to rotating assembly by setting up a feeding mechanism, a dispensing mechanism and a rotating assembly mechanism. This effectively improves assembly efficiency and quality, reduces production costs, and ensures the accuracy and stability of loading and assembly. Attached Figure Description

[0032] Figure 1 This is a perspective view of the automatic feeding device for the light box lamp head in the embodiment;

[0033] Figure 2 This is a schematic diagram of the feeding mechanism and the distributing mechanism in the embodiment;

[0034] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0035] Figure 4 This is a schematic diagram of the material distribution clamp and the rotary assembly mechanism in the embodiment.

[0036] Icon labels:

[0037] 1. Machine frame; 11. Loading station;

[0038] 2. Feeding mechanism; 21. Storage platform; 211. Material trough; 212. Opening; 22. Pushing block; 23. Drive assembly; 231. First drive component; 232. Second drive component;

[0039] 3. Material distribution mechanism; 31. Material distribution block; 311. Relief recess; 32. Material distribution clamp; 321. First clamping arm; 3211. Limiting groove; 3212. Relief opening; 322. Second clamping arm; 323. Clamping drive component; 324. Mounting plate; 33. Translation drive component; 34. Material distribution rotation drive component;

[0040] 4. Rotary assembly mechanism; 41. Transfer chuck; 42. Transfer rotation drive component; 43. Horizontal drive component; 44. Lifting drive component;

[0041] 5. Lamp holder assembly; 6. Position detection component;

[0042] 7. Positioning mechanism; 71. Positioning block; 72. Positioning block drive component. Detailed Implementation

[0043] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0044] This utility model provides an automatic feeding device for lamp head of a light box, which solves the problem of how to automatically feed and rotate the lamp head assembly 5, thereby improving assembly efficiency and quality.

[0045] See Figure 1 As shown, Figure 1 The above is a perspective view of the automatic feeding device for light box lamp heads in the embodiment. The automatic feeding device for light box lamp heads includes a frame 1, a feeding mechanism 2, a distributing mechanism 3, and a rotating assembly mechanism 4.

[0046] The feeding mechanism 2 is installed on the frame 1 and is used to continuously feed the lamp head assemblies 5 one by one.

[0047] The material distribution mechanism 3 is installed at the discharge end of the material feeding mechanism 2. The material distribution mechanism 3 is used to receive the lamp head assemblies 5 output by the material feeding mechanism 2 and transfer them one by one to the loading station 11.

[0048] The rotary assembly mechanism 4 is mounted on the frame 1. The rotary assembly mechanism 4 is used to transfer the lamp head assembly 5 on the loading station 11 to the assembly station for assembly.

[0049] The above technical solution for the lamp head achieves fully automated operation of the lamp head assembly 5 from feeding to loading to rotating assembly by setting up a feeding mechanism 2, a distributing mechanism 3, and a rotating assembly mechanism 4. This effectively improves assembly efficiency and quality, reduces production costs, and ensures the accuracy and stability of loading and assembly.

[0050] See Figure 1 and Figure 2 As shown, Figure 2 This is a schematic diagram of the feeding mechanism and the distributing mechanism in the embodiment. In one embodiment of the distributing mechanism 3, the distributing mechanism 3 includes a distributing block 31, a distributing clamp 32, a translational drive 33, and a distributing rotational drive 34. The distributing block 31 is located on one side of the feeding mechanism 2 and is used to receive the lamp head assembly 5 output by the feeding mechanism 2. The distributing clamp 32 is used to clamp or release the lamp head assembly 5. The translational drive 33 and the distributing rotational drive 34 are connected, and one of the translational drive 33 and the distributing rotational drive 34 is mounted on the frame 1 by means of screwing or welding, while the other is connected to the distributing clamp 32 in a transmission manner. The translational drive 33 is used to drive the distributing clamp 32 to move back and forth between the distributing block 31 and the loading station 11; the distributing block 31 has a clearance recess 311 for the distributing clamp 32 to be inserted, and the distributing rotational drive 34 is used to drive the distributing clamp 32 to rotate. Thus, the material distribution mechanism 3, through the coordinated operation of the material distribution clamp 32, the translation drive 33, and the material distribution rotation drive 34, can accurately transfer the lamp head assemblies 5 output by the feeding mechanism 2 one by one to the loading station 11, ensuring the continuity and accuracy of loading and improving assembly efficiency. During the material distribution process, the material distribution rotation drive 34 can flip the material distribution clamp 32 so that the lamp head assemblies 5 on the material distribution block 31 can smoothly enter the material distribution clamp 32.

[0051] The aforementioned translation drive 33 can use an existing telescopic cylinder, and the material distribution rotation drive 34 can use an existing rotary cylinder.

[0052] See Figure 2As shown, a positioning detection component 6 can be installed on the material distribution block 31. The positioning detection component 6 is used to detect whether the lamp head assembly 5 has been conveyed to the material distribution block 31, so as to control the material distribution clamp 32, the translation drive component 33 and the material distribution rotation drive component 34 to work together to transfer the lamp head assembly 5 on the material distribution block 31 to the loading station 11.

[0053] See Figure 2 and Figure 3 As shown, Figure 3 for Figure 2 The enlarged schematic diagram at point A shows that, in one embodiment of the material dispensing chuck 32, the material dispensing chuck 32 includes a first clamping arm 321, a second clamping arm 322, and a clamping drive member 323. The first clamping arm 321 is mounted on the clamping drive member 323 by means of screwing or welding. The first clamping arm 321 has a limiting groove 3211. The limiting groove 3211 is used to accommodate part of the lamp head assembly 5 and restrict the position of the lamp head assembly 5. A clearance opening 3212 is opened on one side of the limiting groove 3211, which extends outside the first clamping arm 321 and is used for inserting the lamp head assembly 5 into the limiting groove 3211. The clamping drive member 323 is mounted on the output end of the translation drive member 33 or the material dispensing rotation drive member 34 by means of screwing or welding, and the output end of the clamping drive member 323 is connected to the second clamping arm 322 by means of screwing or welding. The clamping drive 323 is used to drive the second clamping arm 322 to move toward or away from the first clamping arm 321 to clamp or release the lamp head assembly 5 in the limiting groove 3211. In this way, the dispensing chuck 32 can stably clamp and fix the lamp head assembly 5 in the limiting groove 3211 of the first clamping arm 321, preventing the lamp head assembly 5 from shifting or falling off during the transfer process. In addition, the design of the limiting groove 3211 further ensures the positional accuracy of the lamp head assembly 5.

[0054] The aforementioned clamping drive 323 can use an existing clamping cylinder.

[0055] See Figure 1 and Figure 2 As shown, the first clamping arm 321 can be slidably connected to the mounting plate 324 of the clamping drive component 323, and then fixedly connected to the mounting plate 324 by a bolt and nut assembly. Thus, since the movement trajectory of the second clamping arm 322 remains unchanged, sliding the first clamping arm 321 can adjust the minimum distance between the first clamping arm 321 and the second clamping arm 322 to accommodate lamp head assemblies 5 of different thicknesses, thereby improving the versatility of the material dispensing chuck 32.

[0056] See Figure 1 , Figure 2 and Figure 3As shown, in one embodiment of the material feeding chuck 32, the feeding mechanism 2 includes a storage platform 21, a pusher block 22, and a drive assembly 23. The storage platform 21 is located on one side of the material feeding block 31 and has a material trough 211 with openings 212 at both ends. The material trough 211 is used to accommodate a plurality of lamp head assemblies 5. The drive assembly 23 is mounted on the frame 1 by means of screwing or welding and is drively connected to the pusher block 22 and / or the storage platform 21. The drive assembly 23 is used to drive the pusher block 22 and the storage platform 21 to move relative to each other, so that the pusher block 22 is positioned opposite the material trough 211 and slides along the material trough 211 from one end opening 212 to the other end opening 212, thereby pushing the lamp head assemblies 5 in the material trough 211 one by one onto the material feeding block 31. In this way, the storage platform 21 can store multiple lamp head components 5 at one time through the material trough 211 and restrict the conveying trajectory of the lamp head components 5 on the storage platform 21. Combined with the pusher block 22 and the drive component 23, the lamp head components 5 can be continuously fed one by one, which improves the efficiency and stability of the feeding and provides a reliable guarantee for subsequent feeding and assembly operations.

[0057] See Figure 1 and Figure 2 As shown, in one embodiment of the drive assembly 23, at least two material slots 211 are evenly spaced on the storage platform 21. The drive assembly 23 includes a first drive member 231 and a second drive member 232. The first drive member 231 and the second drive member 232 are mounted on the frame 1 by means of screwing or welding. The first drive member 231 is driven to the storage platform 21 and is used to drive the storage platform 21 to move along the arrangement direction of the material slots 211, so that any material slot 211 is positioned relative to the distribution block 31. The pusher block 22 is positioned relative to the distribution block 31. The second drive member 232 is driven to the pusher block 22 and is used to drive the pusher block 22 to slide along the corresponding material slot 211, so as to push the lamp head assemblies 5 in the material slot 211 one by one onto the distribution block 31. In this way, at least two material troughs 211 can hold more lamp head components 5, which is more convenient for subsequent automatic feeding; and the coordinated work of the first drive component 231 and the second drive component 232 enables the feeding mechanism 2 to flexibly select different material troughs 211 to feed the material blocks 31, which improves the flexibility and adaptability of the feeding and meets different production needs.

[0058] The first driving component 231 and the second driving component 232 mentioned above can both use existing linear drive mechanisms such as servo motor-screw nut linear modules, and their output ends are connected to the storage platform 21 and the pusher block 22 by means of screwing or welding.

[0059] See Figure 2As shown, in one embodiment of the pusher block 22, the pusher block 22 is slidably connected to the output end of the second drive member 232 along a vertical direction. Thus, since the production depth of the material trough 211 may have errors, resulting in slight differences in the production depth of different material troughs 211, the pusher block 22 may interfere with the bottom of some material troughs 211. The vertical sliding design of the pusher block 22 allows it to adapt to material troughs 211 of different depths, effectively avoiding problems such as poor material pushing or interference between the pusher block 22 and the bottom of the material trough 211 due to depth mismatch.

[0060] See Figure 1 , Figure 2 and Figure 3 As shown, based on any of the above embodiments, the automatic lamp head feeding device further includes a positioning mechanism 7. The positioning mechanism 7 includes a positioning block 71 and a positioning block drive 72. The positioning block 71 is located above the opening 212 at one end of the material trough 211 near the material distribution block 31. The positioning block drive 72 is mounted on the frame 1 by means of screwing or welding, and is connected to the positioning block 71 in a transmission manner. The positioning block drive 72 is used to drive the positioning block 71 to move up and down relative to the material trough 211 to loosen or press the lamp head assembly 5. Thus, when the feeding mechanism 2 outputs a lamp head assembly 5 onto the distribution block 31, the positioning block drive 72 drives the positioning block 71 to press the lamp head assembly 5 at the opening 212 of the material groove 211 near the distribution block 31, preventing the feeding mechanism 2 from outputting the next lamp head assembly 5. This effectively avoids the situation where the feeding mechanism 2 sends the next lamp head assembly 5 onto the distribution block 31 before the distribution mechanism 3 has transferred the lamp head assembly 5 from the distribution block 31, thus squeezing the lamp head assembly 5 off the distribution block 31.

[0061] The aforementioned positioning block drive 72 can use an existing telescopic cylinder.

[0062] See Figure 1 and Figure 4 As shown, Figure 4This is a schematic diagram of the material distribution clamp and rotary assembly mechanism in one embodiment. In one implementation of the rotary assembly mechanism 4, the rotary assembly mechanism 4 includes a transfer clamp 41, a transfer rotary drive 42, a horizontal drive 43, and a lifting drive 44. The transfer clamp 41 is used to clamp or release the lamp holder assembly 5. The transfer rotary drive 42 is driveably connected to the transfer clamp 41 and is used to drive the transfer clamp 41 to rotate. The horizontal drive 43 and the lifting drive 44 are connected; one of the horizontal drive 43 and the lifting drive 44 is mounted on the frame 1 by screwing or welding, while the other is driveably connected to the transfer rotary drive 42. The horizontal drive 43 drives the transfer rotary drive 42 and the transfer clamp 41 to move back and forth between the loading station 11 and the assembly station. The lifting drive 44 drives the transfer rotary drive 42 and the transfer clamp 41 to move up and down toward the loading station 11 or the assembly station. Thus, through the coordinated work of the transfer chuck 41, the horizontal drive 43 and the lifting drive 44, the rotary assembly mechanism 4 can accurately transfer the lamp head assembly 5 on the loading station 11 to each of the required positions. Combined with the transfer rotary drive 42, it can precisely adjust the lamp head assembly 5 to the required angle one by one, thereby realizing automatic rotary assembly and improving assembly efficiency and quality.

[0063] The aforementioned horizontal drive component 43 can use existing linear drive mechanisms such as servo motor-lead screw nut linear modules, the lifting drive component 44 can use existing telescopic cylinders, the transfer rotation drive component 42 can use existing rotary cylinders, and the transfer chuck 41 can use existing clamping cylinders.

[0064] See Figure 1 and Figure 4 As shown, based on the above embodiment, there are two lifting drive components 44 connected together. One lifting drive component 44 is mounted on the output end of the horizontal drive component 43 by means of screwing or welding, while the output end of the other lifting drive component 44 is connected to the transfer rotation drive component 42 by means of screwing or welding. Thus, the heights of the loading station 11 and the assembly station may be different; the two lifting drive components 44 allow for graded lifting and lowering of the transfer chuck 41, accommodating at least two different heights.

[0065] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An automatic feeding device for lightbox lamp heads, characterized in that, include: frame; A feeding mechanism, mounted on the frame, is used to continuously feed lamp head assemblies one by one; The material sorting mechanism is located at the discharge end of the feeding mechanism. The material sorting mechanism is used to receive the lamp head assemblies output by the feeding mechanism and transfer them one by one to the loading station. A rotary assembly mechanism is mounted on the frame and is used to transfer the lamp head assembly from the loading station to the assembly station for rotary assembly.

2. The automatic feeding device for lightbox lamp heads according to claim 1, characterized in that, The material distribution mechanism includes: A material distribution block is located on one side of the feeding mechanism, and the material distribution block is used to receive the lamp head assembly output by the feeding mechanism; The material dispensing chuck and the connected translation drive and material dispensing rotation drive are provided. The material dispensing chuck is used to clamp or release the lamp head assembly. One of the translation drive and the material dispensing rotation drive is located on the frame, and the other is connected to the material dispensing chuck for transmission. The translation drive is used to drive the material dispensing clamp to move back and forth between the material dispensing block and the loading station. The material dispensing block is provided with a clearance recess for the material dispensing clamp to be inserted. The material dispensing rotation drive is used to drive the material dispensing clamp to flip.

3. The automatic feeding device for light box lamp heads according to claim 2, characterized in that, The material dispensing chuck includes a first clamping arm, a second clamping arm, and a clamping drive. The first clamping arm is disposed on the clamping drive and has a limiting groove. The limiting groove is used to accommodate part of the lamp head assembly and restrict the position of the lamp head assembly. A clearance opening is provided on one side of the limiting groove, which extends outside the first clamping arm and is used for inserting the lamp head assembly into the limiting groove. The clamping drive is disposed on the output end of the translation drive or the material dispensing rotation drive. The output end of the clamping drive is connected to the second clamping arm. The clamping drive is used to drive the second clamping arm to move toward or away from the first clamping arm to clamp or release the lamp head assembly in the limiting groove.

4. The automatic feeding device for light box lamp heads according to claim 2 or 3, characterized in that, The feeding mechanism includes: A storage platform is located on one side of the material distribution block and is provided with a material trough with openings at both ends. The material trough is used to accommodate several of the lamp head assemblies. The pusher block and the drive assembly are mounted on the frame and are connected to the pusher block and / or the storage platform. The drive assembly is used to drive the pusher block and the storage platform to move relative to each other, so that the pusher block is positioned opposite the material trough and slides along the material trough from one end opening to the other end opening, thereby pushing the lamp head assemblies in the material trough one by one onto the distribution block.

5. The automatic feeding device for light box lamp heads according to claim 4, characterized in that, At least two material slots are evenly spaced on the storage platform. The driving assembly includes a first driving member and a second driving member mounted on the frame. The first driving member is driven to the storage platform and is used to drive the storage platform to move along the arrangement direction of the material slots so that any of the material slots is positioned relative to the distribution block. The pusher block is positioned relative to the distribution block. The second driving member is driven to the pusher block and is used to drive the pusher block to slide along the corresponding material slot so as to push the lamp head assemblies in the material slot one by one onto the distribution block.

6. The automatic feeding device for light box lamp heads according to claim 5, characterized in that, The pusher block is slidably mounted vertically on the output end of the second drive unit.

7. The automatic feeding device for lightbox lamp heads according to any one of claims 1, 2, 3, 5 and 6, characterized in that, The rotary assembly mechanism includes: The transfer chuck and the transfer rotation drive are provided. The transfer chuck is used to clamp or release the lamp head assembly, and the transfer rotation drive is connected to the transfer chuck and is used to drive the transfer chuck to rotate. A horizontal drive and a lifting drive are connected, one of which is mounted on the frame and the other is connected to the transfer rotary drive. The horizontal drive is used to drive the transfer rotary drive and the transfer chuck to move back and forth between the loading station and the assembly station. The lifting drive is used to drive the transfer rotary drive and the transfer chuck to move up and down toward the loading station or the assembly station.

8. The automatic feeding device for light box lamp heads according to claim 7, characterized in that, The lifting drive unit is provided in two parts, which are connected together. One of the lifting drive units is located on the output end of the horizontal drive unit, and the output end of the other lifting drive unit is connected to the transfer rotation drive unit.

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