Sweeping robot

Abstract

A robot sweeper includes a main body, a pair of drive modules, and a cleaning module. The drive modules are respectively pivotally connected to the main body. The drive modules include a roller set and a drive device. The drive device is mechanically connected to the roller set and configured to drive the roller set to rotate about a first axis. The cleaning module is connected to the main body and at least partially located between the roller sets along the first axis.

Description

Technical Field

[0001] This invention relates to a robotic vacuum cleaner. Background Technology

[0002] With the development of technology, robotic vacuum cleaners have become a common household appliance. Due to their convenient and time-saving cleaning capabilities, robotic vacuum cleaners are also increasingly being used in cleanrooms.

[0003] In order to meet the environmental requirements of a cleanroom, in addition to having good cleaning capabilities, whether a robot vacuum cleaner generates dust during operation is also an important factor for users to consider.

[0004] Therefore, how to enable robotic vacuum cleaners to move lightly and avoid dust generation during operation is undoubtedly a topic of great importance to the industry. Summary of the Invention

[0005] One of the objectives of this invention is to provide a robotic vacuum cleaner that can more easily overcome the friction generated by the ground when turning, thereby improving the robot's mobility and reducing the chance of dust being stirred up during movement.

[0006] According to one embodiment of the present invention, a robotic vacuum cleaner includes a main body, a pair of drive modules, and a cleaning module. The drive modules are pivotally connected to the main body. Each drive module includes a roller assembly and a drive device. The drive device is mechanically connected to the roller assembly and configured to drive the roller assembly to rotate about a first axis. The cleaning module is connected to the main body and is at least partially located between the roller assemblies along the first axis.

[0007] In one or more embodiments of the present invention, the roller assembly includes a first roller and a first shaft. The first shaft extends along a first axis and connects to the first roller. The driving device includes a driving unit and a second shaft, the second shaft being parallel to the corresponding first axis. The driving module further includes a housing and a transmission structure. The housing is pivotally connected to the main body about a second axis, the second axis being parallel to the first axis. The housing has a space, within which the corresponding first shaft and the corresponding second shaft are at least partially located. The transmission structure is located within the space and mechanically connects the corresponding first shaft and the corresponding second shaft.

[0008] In one or more embodiments of the present invention, the housing described above is located between the cleaning module and the corresponding first roller.

[0009] In one or more embodiments of the present invention, the drive module further includes a second roller and a first support member. The first support member is pivotally connected to the housing about a third axis, the third axis being perpendicular to the first axis, and the second roller is pivotally connected to the first support member.

[0010] In one or more embodiments of the present invention, the second axis described above is at least partially located between the first roller and the corresponding second roller.

[0011] In one or more embodiments of the present invention, the above-described sweeping robot further includes at least one third roller and at least one second support member. The second support member is pivotally connected to the main body about a fourth axis, which is parallel to the third axis. The third roller is pivotally connected to the second support member, and the cleaning module is at least partially located between the second roller and the third roller.

[0012] In one or more embodiments of the present invention, the transmission structure described above includes a first rotating wheel, a second rotating wheel, and a belt. The first rotating wheel is connected to a first rotating shaft. The second rotating wheel is connected to a second rotating shaft. The belt connects the first rotating wheel and the second rotating wheel and is configured such that the second rotating wheel drives the first rotating wheel to rotate.

[0013] In one or more embodiments of the present invention, the drive module further includes a tensioner. The tensioner is at least partially located within a corresponding space and connected to a corresponding housing. The tensioner is configured to adjustably at least partially abut against a corresponding belt.

[0014] In one or more embodiments of the present invention, the tensioner includes a structural member, an adjusting portion, and a rotating portion. The structural member includes a first end and a second end opposite to each other, the first end being pivotally connected to a corresponding housing, and the structural member having a pressure surface located between the first end and the second end. The adjusting portion adjustably passes through and connects to the housing and is configured to at least partially press against the pressure surface. The rotating portion is rotatably connected to the second end and is configured to at least partially press against a corresponding belt.

[0015] In one or more embodiments of the present invention, the above-described robotic vacuum cleaner further includes a pair of elastic elements. The elastic elements are respectively connected between the main body and the corresponding housing, and the elastic elements elastically extend and retract along the extension and retraction direction, which is offset from the second axis.

[0016] In one or more embodiments of the present invention, the drive module further includes a cover and a sealing element. The cover connects to the housing to enclose the space. The sealing element seals between the housing and the cover.

[0017] In one or more embodiments of the present invention, the first rotating shaft and the corresponding second rotating shaft are offset from each other.

[0018] In one or more embodiments of the present invention, the driving unit described above is a motor.

[0019] In one or more embodiments of the present invention, the driving device described above is located away from the first axis.

[0020] In one or more embodiments of the present invention, the cleaning module described above includes a plurality of cleaning wheels. The cleaning wheels are separated from each other and are each configured to rotate about a fifth axis, which is parallel to the first axis.

[0021] The above-described embodiments of the present invention have at least the following advantages:

[0022] (1) Since the cleaning wheel is located at least partially between the rollers along the first axis, when the robot vacuum makes a turning motion on the ground, it can more easily overcome the friction generated by the ground on the cleaning wheel, thus improving the robot vacuum's mobility and reducing the chance of dust being stirred up during movement.

[0023] (2) Since the housing of the drive unit is pivotally connected to the main body around the second axis, and the second axis is at least partially located between the first roller and the corresponding second roller, the sweeping robot has the ability to cross obstacles.

[0024] (3) The drive module also includes a cover and a sealing element. The cover connects to the housing to enclose the space, while the sealing element seals between the housing and the cover. In this way, even if dust particles accumulate in the space of the housing after long-term use of the robot vacuum, these dust particles will not leak out from the space of the housing, thus effectively avoiding the chance of the robot vacuum accidentally polluting the environment. Attached Figure Description

[0025] Figure 1 This is a three-dimensional schematic diagram of a sweeping robot according to an embodiment of the present invention;

[0026] Figure 2 for Figure 1 A side view of a robotic vacuum cleaner;

[0027] Figure 3 for Figure 1 A bottom view of a robotic vacuum cleaner;

[0028] Figure 4 for Figure 1 An exploded view of the driver module;

[0029] Figure 5 for Figure 4 A front view of the shell;

[0030] Figures 6-8 for Figure 1 A simplified side view of a robotic vacuum cleaner crossing an obstacle along a first direction of movement;

[0031] Figures 9-10 for Figure 1 A magnified side view of a robotic vacuum cleaner crossing an obstacle along a second direction of movement.

[0032] Symbol Explanation

[0033] 100: Robotic Vacuum Cleaner

[0034] 110: Main Body

[0035] 120: Driver Module

[0036] 121: Roller Set

[0037] 121a: First roller

[0038] 121b: First shaft

[0039] 122: Drive unit

[0040] 122a: Drive unit

[0041] 122b: Second shaft

[0042] 123: Shell

[0043] 124: Transmission Structure

[0044] 124a: First rotating wheel

[0045] 124b: Second rotating wheel

[0046] 124c: Belt

[0047] 125: Second roller

[0048] 126: First support component

[0049] 127: Tensioner

[0050] 127a: Structural component

[0051] 127a1: First end

[0052] 127a2: Second end

[0053] 127b: Adjustment section

[0054] 127c: Rotating part

[0055] 128: Cover

[0056] 129: Sealing element

[0057] 130: Cleaning Module

[0058] 131: Cleaning wheel

[0059] 140: Third roller

[0060] 145: Second support component

[0061] 150: Elastic element

[0062] 200: Ground

[0063] 300: Obstacles

[0064] X1: First axis line

[0065] X2: Second axis

[0066] X3: Third axis

[0067] X4: Fourth Axis

[0068] X5: Fifth Axis

[0069] CS: Pressure surface

[0070] D1: First direction of movement

[0071] D2: Second direction of movement

[0072] DE: Direction of extension / retraction

[0073] SP: Space Detailed Implementation

[0074] The following describes several embodiments of the present invention with reference to the accompanying drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and elements will be shown in the drawings in a simple schematic manner, and in all drawings, the same reference numerals will be used to denote the same or similar elements. And, where feasible, features of different embodiments may be applied interchangeably.

[0075] Unless otherwise defined, all terms used herein (including technical and scientific terms) have their ordinary meanings, which are understandable to those skilled in the art. Furthermore, the definitions of the foregoing terms in commonly used dictionaries should be interpreted in the context of this specification as having the meaning consistent with the relevant field of this invention. Unless specifically defined, these terms will not be construed as having idealized or overly formal meanings.

[0076] Please refer to Figures 1-3 . Figure 1 A perspective view of a sweeping robot 100 according to an embodiment of the present invention is provided. Figure 2 For illustration Figure 1 Side view of the 100 robotic vacuum cleaner. Figure 3 For illustration Figure 1 A bottom view of the robotic vacuum cleaner 100. In this embodiment, as... Figures 1-3As shown, a robotic vacuum cleaner 100 includes a main body 110, a pair of drive modules 120, and a cleaning module 130. Figures 1-3 In the drawing, only the support structure of the main body 110 is shown. In reality, the main body 110 also includes a shell and other parts, but for the sake of brevity, these structures are not shown. Figures 1-3 In the middle. The drive module 120 is pivotally connected to the main body 110 and includes a roller assembly 121 and a drive device 122. The roller assembly 121 is configured to abut against the ground 200 (see ground 200). Figure 2 The drive unit 122 is mechanically connected to the roller assembly 121 and configured to drive the roller assembly 121 to rotate about the first axis X1, thereby moving the robotic vacuum cleaner 100 on the floor 200. The cleaning module 130 is connected to the main body 110 and is located at least partially along the first axis X1 between the roller assemblies 121. It is worth noting that because the drive unit 122 of the drive module 120 is located away from the first axis X1, sufficient space is available between the roller assemblies 121 to accommodate the cleaning module 130.

[0077] In practical applications, the cleaning module 130 includes multiple cleaning wheels 131. The cleaning wheels 131 are separate from each other and are each configured to rotate about a fifth axis X5, which is parallel to the first axis X1. When the robot vacuum cleaner 100 is placed on the ground 200, the cleaning wheels 131 also come into contact with the ground 200. More specifically, the cleaning wheels 131 are made of silicone, so when they come into contact with the ground 200, they can attract dust particles from the ground onto their surface through electrostatic induction, thus removing dust particles from the ground 200. In this way, the robot vacuum cleaner 100 can avoid dust generation when cleaning the ground 200. Moreover, since the cleaning wheels 131 can rotate about the fifth axis X5, they can also rotate relative to the main body 110 when the robot vacuum cleaner 100 moves on the ground 200, thereby reducing the resistance when the robot vacuum cleaner 100 moves and effectively improving its mobility.

[0078] Specifically, when the roller assembly 121 rotates in the same direction around the first axis X1, the robotic vacuum cleaner 100 can move on the ground 200 in either the first direction of movement D1 or the second direction of movement D2. Conversely, when the roller assembly 121 rotates in the opposite direction around the first axis X1, the robotic vacuum cleaner 100 can turn on the ground 200. As described above, the cleaning module 130 is at least partially located between the roller assemblies 121 along the first axis X1, meaning the cleaning wheels 131 are at least partially located between the roller assemblies 121 along the first axis X1. Therefore, when the robotic vacuum cleaner 100 turns on the ground 200, it can more easily overcome the friction between the ground 200 and the cleaning wheels 131, thus improving the robotic vacuum cleaner 100's mobility and reducing the chance of dust being stirred up during movement.

[0079] Please refer to Figure 4 . Figure 4 For illustration Figure 1 An exploded view of the driver module 120. In this embodiment, as... Figure 4 As shown, the roller assembly 121 includes a first roller 121a and a first shaft 121b. The first shaft 121b extends along a first axis X1 and connects to the first roller 121a. The drive device 122 includes a drive unit 122a and a second shaft 122b, the second shaft 122b being parallel to the corresponding first axis X1, and the first shaft 121b and the corresponding second shaft 122b being offset from each other. The drive module 120 also includes a housing 123 and a transmission structure 124. The housing 123 is pivotally connected to the main body 110 about a second axis X2, which is parallel to the first axis X1. The housing 123 has a space SP, within which the corresponding first shaft 121b and the corresponding second shaft 122b are at least partially located. The transmission structure 124 is located within the space SP of the housing 123 and mechanically connects the corresponding first shaft 121b and the corresponding second shaft 122b. In practical applications, the drive unit 122a can be a motor.

[0080] Furthermore, such as Figure 4As shown, the transmission structure 124 includes a first rotating wheel 124a, a second rotating wheel 124b, and a belt 124c. The first rotating wheel 124a is located within the space SP of the housing 123 and is connected to the first rotating shaft 121b. The second rotating wheel 124b is located within the space SP of the housing 123 and is connected to the second rotating shaft 122b. The belt 124c connects the first rotating wheel 124a and the second rotating wheel 124b and is configured such that the second rotating wheel 124b drives the first rotating wheel 124a to rotate. Specifically, when the drive unit 122 is started, the drive unit 122a causes the second rotating shaft 122b to rotate along with the second rotating wheel 124b. The second rotating wheel 124b then drives the belt 124c to drive the first rotating wheel 124a to rotate. Since the first roller 121a is connected to the first rotating shaft 121b, and the first rotating shaft 121b is connected to the first rotating wheel 124a, the first roller 121a also rotates due to the drive of the first rotating wheel 124a, thereby causing the sweeping robot 100 to move on the ground 200.

[0081] In this embodiment, such as Figure 4 As shown, the drive module 120 also includes a cover 128 and a sealing element 129. The cover 128 connects to the housing 123 to enclose the space SP, while the sealing element 129 seals between the housing 123 and the cover 128. In this way, even if dust particles accumulate in the space SP of the housing 123 after prolonged use, these dust particles will not leak out from the space SP, thus effectively preventing the robot vacuum 100 from accidentally polluting the environment. In practice, the sealing element 129 can be a sealant, but the present invention is not limited thereto.

[0082] Furthermore, such as Figures 1-4 As shown, the drive module 120 further includes a second roller 125 and a first support member 126. The first support member 126 is pivotally connected to the housing 123 of the drive module 120 about a third axis X3, and the third axis X3 is perpendicular to the first axis X1, and the second roller 125 is pivotally connected to the first support member 126. In this embodiment, the second axis X2 is at least partially located between the first roller 121a and the corresponding second roller 125.

[0083] Furthermore, the robotic vacuum cleaner 100 also includes at least one third roller 140 and at least one second support member 145. For example, such as Figures 1-3 As shown, the robotic vacuum cleaner 100 includes two third rollers 140 and two second support members 145. The second support members 145 are pivotally connected to the main body 110 about a fourth axis X4, which is parallel to the third axis X3, and the third rollers 140 are pivotally connected to the second support members 145. In this embodiment, the cleaning module 130 is at least partially located between the second rollers 125 and the third rollers 140.

[0084] Please refer to Figure 5 . Figure 5 For illustration Figure 4 A front view of the housing 123. In this embodiment, as... Figures 4-5 As shown, the drive module 120 also includes a tensioner 127. The tensioner 127 is at least partially located within the space SP of the corresponding housing 123 and is connected to the corresponding housing 123. The tensioner 127 is configured to adjustably at least partially press against the corresponding belt 124c.

[0085] More specifically, such as Figure 5 As shown, the tensioner 127 of the drive module 120 includes a structural member 127a, an adjusting portion 127b, and a rotating portion 127c. The structural member 127a includes a first end 127a1 and a second end 127a2, with the first end 127a1 pivotally connected to a corresponding housing 123. Furthermore, the structural member 127a has a pressure surface CS located between the first end 127a1 and the second end 127a2. The adjusting portion 127b adjustably passes through and connects to the housing 123 of the drive module 120 and is configured to at least partially press against the pressure surface CS of the structural member 127a, allowing the structural member 127a to rotate relative to the housing 123 via the pivot connection between the first end 127a1 and the housing 123. For example, the housing 123 has a threaded hole, and the adjusting part 127b at least partially includes a screw. The adjusting part 127b is adjustablely connected to the housing 123 via the screw coupling the threaded hole, thereby pressing against the pressing surface CS of the structural member 127a, causing the structural member 127a to rotate relative to the housing 123 to different degrees. Furthermore, the rotating part 127c is rotatably connected to the second end 127a2 of the structural member 127a and is configured to at least partially press against the corresponding belt 124c. Specifically, the user can adjust the part 127b to press against the pressing surface CS of the structural member 127a to cause the structural member 127a to rotate relative to the housing 123 to different degrees, thereby causing the rotating part 127c to press against the belt 124c to different degrees, so that the belt 124c maintains appropriate tension. When the belt 124c is driven, the rotating part 127c pressing against the belt 124c can roll relative to the belt 124c. In practical applications, the rotating part 127c can be a bearing, but the present invention is not limited thereto.

[0086] like Figures 1-5As shown, the robotic vacuum cleaner 100 also includes a pair of elastic elements 150. The elastic elements 150 are respectively connected between the main body 110 and the housing 123 of the corresponding drive module 120. The elastic elements 150 elastically extend and retract along the extension direction DE, and the extension direction DE is offset from the second axis X2. By elastically extending and retracting between the main body 110 and the corresponding housing 123 along the extension direction DE, the elastic elements 150 can apply a pulling force or a pushing force to the drive module 120. Since the extension direction DE is offset from the second axis X2, this pulling or pushing force can generate a bending moment on the drive module 120, thereby improving the overall structural strength of the housing 123 and the main body 110. For example, the elastic element 150 can be a spring, a shock absorber, or a damper, but the present invention is not limited thereto.

[0087] As described above, since the housing 123 of the drive module 120 is pivotally connected to the main body 110 about the second axis X2, and the second axis X2 is at least partially located between the first roller 121a and the corresponding second roller 125, the sweeping robot 100 has the ability to cross the obstacle 300. Please refer to... Figures 6-8 . Figures 6-8 For illustration Figure 1 A simplified side view of a robotic vacuum cleaner 100 crossing an obstacle 300 along a first direction of movement D1. In this embodiment, as... Figures 6-8 As shown, when the robotic vacuum cleaner 100 moves along the first moving direction D1 on the ground 200 and encounters an obstacle 300, the housing 123 of the drive module 120 rotates relative to the main body 110 around the second axis X2, changing the tilt angle of the housing 123 relative to the main body 110. The third roller 140, the first roller 121a, and the second roller 125 can then roll sequentially onto the obstacle 300, allowing the robotic vacuum cleaner 100 to easily cross the obstacle 300. It is worth noting that during the process of the robotic vacuum cleaner 100 crossing the obstacle 300, the first roller 121a of the mechanically connected drive unit 122a remains in contact with the ground 200 or the obstacle 300, thus preventing the robotic vacuum cleaner 100 from being unable to move due to the first roller 121a being suspended in the air. Furthermore, as mentioned above, since the elastic element 150 elastically extends and retracts between the main body 110 and the corresponding housing 123 along the extension direction DE, it helps to increase the ground contact of the first roller 121a.

[0088] Please refer to Figure 9 . Figure 9 For illustration Figure 1 A partially enlarged side view of the robotic vacuum cleaner 100 crossing the obstacle 300 along the second direction of movement D2. In this embodiment, as... Figure 9As shown, when the robotic vacuum cleaner 100 moves along the second direction of movement D2 on the ground 200 and encounters an obstacle 300, the second roller 125 will touch the obstacle 300 first. As mentioned above, the elastic element 150 can generate a certain bending moment on the drive module 120. In other words, the elastic element 150 can provide support for the second roller 125 to increase the ability of the second roller 125 to climb and cross the obstacle 300.

[0089] Please refer to Figure 10 . Figure 10 For illustration Figure 1 A partially enlarged side view of the robotic vacuum cleaner 100 crossing the obstacle 300 along the second direction of movement D2. In this embodiment, as... Figure 10 As shown, when the robotic vacuum cleaner 100 moves along the second moving direction D2, and the second roller 125 and the first roller 121a have crossed the obstacle 300 while the third roller 140 is about to fall off the surface of the obstacle 300, the elastic element 150 can absorb the impact force of the third roller 140 hitting the ground 200 through the elastic support of the main body 110, thereby providing shock absorption for the robotic vacuum cleaner 100 and improving the durability of the robotic vacuum cleaner 100.

[0090] In summary, the technical solutions disclosed in the above embodiments of the present invention have at least the following advantages:

[0091] (1) Since the cleaning wheel is located at least partially between the rollers along the first axis, when the robot vacuum makes a turning motion on the ground, it can more easily overcome the friction generated by the ground on the cleaning wheel, thus improving the robot vacuum's mobility and reducing the chance of dust being stirred up during movement.

[0092] (2) Since the housing of the drive unit is pivotally connected to the main body around the second axis, and the second axis is at least partially located between the first roller and the corresponding second roller, the sweeping robot has the ability to cross obstacles.

[0093] (3) The drive module also includes a cover and a sealing element. The cover connects to the housing to enclose the space, while the sealing element seals between the housing and the cover. In this way, even if dust particles accumulate in the space of the housing after long-term use of the robot vacuum, these dust particles will not leak out from the space of the housing, thus effectively avoiding the chance of the robot vacuum accidentally polluting the environment.

[0094] Although the present invention has been disclosed in conjunction with the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A robotic vacuum cleaner, comprising: main body; A pair of drive modules are pivotally connected to the main body, and each of the drive modules includes: Roller assembly; and A drive unit, mechanically connected to the roller assembly and configured to drive the roller assembly to rotate about a first axis; and A cleaning module, connected to the main body, and located at least partially along the first axis between the roller assemblies. The cleaning module includes multiple cleaning wheels that are separate from each other and configured to rotate about a fifth axis that is parallel to the first axis.

2. The sweeping robot of claim 1, wherein each of the roller groups includes a first roller and a first rotating shaft, the first rotating shaft extending along the first axis and connected to the first roller, each of the driving devices includes a driving unit and a second rotating shaft, the second rotating shaft being parallel to the corresponding first axis, and each of the driving modules further includes: A housing, pivotally connected to the main body about a second axis parallel to the first axis, the housing having a space in which the corresponding first and second pivots are at least partially located; and A transmission structure is located within the space and mechanically connects the corresponding first rotating shaft and the corresponding second rotating shaft.

3. The robotic vacuum cleaner of claim 2, wherein each of the housings is located between the cleaning module and the corresponding first roller.

4. The robotic vacuum cleaner of claim 2, wherein each of the drive modules further comprises: The second roller; and A first support member is pivotally connected to the housing about a third axis perpendicular to the first axis, and a second roller is pivotally connected to the first support member.

5. The robotic vacuum cleaner of claim 4, wherein the second axis is at least partially located between each of the first rollers and the corresponding second roller.

6. The robotic vacuum cleaner as described in claim 4, further comprising: At least one third roller; and At least one second support member is pivotally connected to the main body about a fourth axis parallel to the third axes, and the third roller is pivotally connected to the second support member. The cleaning module is at least partially located between the second roller and the third roller.

7. The robotic vacuum cleaner of claim 2, wherein each of the transmission structures comprises: The first rotating wheel is connected to the first rotating shaft; The second rotating wheel is connected to the second rotating shaft; and A belt connects the first rotating wheel and the second rotating wheel, and is configured such that the second rotating wheel drives the first rotating wheel to rotate.

8. The robotic vacuum cleaner of claim 7, wherein each of the drive modules further comprises: A tensioner, at least partially located within the corresponding space and connected to the corresponding housing, is configured to adjustably at least partially press against the corresponding belt.

9. The robotic vacuum cleaner of claim 8, wherein each of the tensioners comprises: A structural member includes a first end and a second end opposite to each other, the first end being pivotally connected to the corresponding housing, the structural member having a pressure surface located between the first end and the second end; An adjusting part, adjustablely passing through and connecting to the housing, and configured to at least partially abut against the abutting surface; and A rotating part is rotatably connected to the second end and configured to at least partially press against the corresponding belt.

10. The robotic vacuum cleaner as described in claim 2, further comprising: A pair of elastic elements are respectively connected between the main body and the corresponding housing. Each of the elastic elements elastically expands and contracts along the expansion and contraction direction, which is offset from the second axis.

11. The robotic vacuum cleaner of claim 2, wherein each of the drive modules further comprises: The cover, which connects to the shell to enclose the space; and A sealing element is used to seal between the housing and the cover.

12. The robotic vacuum cleaner of claim 2, wherein each of the first axes is offset from the corresponding second axis.

13. The robotic vacuum cleaner of claim 2, wherein each of the drive units is a motor.

14. The robotic vacuum cleaner of claim 1, wherein the drive units are located away from the first axis.

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