CN113562227B

CN113562227B - Crate, boxing robot workstation and boxing method

Info

Publication number: CN113562227B
Application number: CN202111125333.3A
Authority: CN
Inventors: 王金涛; 王化明; 朱维金
Original assignee: Weifang Xinsong Robot Automation Co ltd
Current assignee: Weifang Xinsong Robot Automation Co ltd
Priority date: 2021-09-26
Filing date: 2021-09-26
Publication date: 2022-01-07
Anticipated expiration: 2041-09-26
Also published as: CN113562227A

Abstract

The invention belongs to the technical field of material storage and transportation, and particularly relates to a crate, a boxing robot workstation and a boxing method. The crate comprises a crate body and elastic supports, the bottom of the crate body is provided with an opening and a plurality of elastic supports, and the opening is used for a lifting port when sheet workpieces are stacked or unstacked in the crate body; the boxing robot workstation comprises a robot, an intelligent end pick-up, a transfer trolley, a lifter and a crate, wherein the intelligent end pick-up is arranged at the executing tail end of the robot, the lifter is arranged on the transfer trolley, and when the crate is stacked or unstacked, the lifter extends out of an opening at the bottom of a box body and lifts a thin plate workpiece to enable the thin plate workpiece to be in a bent state. The invention avoids the collision and friction between the thin plate workpiece and the crate caused by the space motion trail precision of the cleaning robot, and is suitable for stacking and unstacking the thin plates of the cleaning robot and the end effector thereof in the crate.

Description

Crate, boxing robot workstation and boxing method

Technical Field

The invention belongs to the technical field of material storage and transportation, and particularly relates to a crate, a boxing robot workstation and a boxing method.

Background

Conventionally, a cleaning robot is used to pack or unpack thin plate workpieces, such as liquid crystal display panels, organic EL display panels, and solar cell panels, into or from boxes, and the thin plate workpieces need to be stored in a crate and transported. When the thin plate workpieces are stacked or unstacked, because the surfaces of the thin plates are smooth, the thin plates are stacked in multiple layers and are mutually compressed, air between the plates is extruded and discharged, the thin plates are mutually attached and adhered together, and when the thin plates are disassembled and processed, double materials are often caused by the adhesive, so that the actual production is influenced. For magnetic thin plate material distribution, magnetic force sheet separation equipment is generally adopted, and the problem of magnetic force sheet separation of thin plates can be effectively solved. However, when the robot is used for carrying and disassembling the non-magnetic thin plates and stacking or unstacking the non-magnetic thin plates in the crate, the non-magnetic thin plates are still difficult to separate, and the non-magnetic thin plates are usually separated by air blowing and separated by brushes, but the two modes are low in efficiency and poor in reliability. In addition, in the boxing process of the robot, the robot generates dust due to collision and friction between the thin plate workpiece and the crate caused by the precision of the space motion track of the robot, and the thin plate workpiece is polluted.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a crate, a boxing robot workstation and a boxing method, so as to solve the problems that the sheet bar-shaped sheets are difficult to separate in the process of stacking or unstacking the sheet bar-shaped sheets in the crate, and the sheet bar-shaped sheets are polluted by dust generated by collision and friction between the sheet bar-shaped sheets and the crate in the boxing process.

In order to achieve the purpose, the invention adopts the following technical scheme:

the crate comprises a crate body and elastic supports, wherein an opening and a plurality of elastic supports are arranged at the bottom of the crate body, and the opening is used for a lifting port when thin plate workpieces are stacked or unstacked in the crate body.

In a possible implementation manner, the box body is of a rectangular structure and comprises a bottom plate, and two short side plates and two long side plates which are arranged on the bottom plate, wherein the opening is arranged at the center of the bottom plate; the elastic support is of a strip-shaped structure and is arranged on the bottom plate along the width direction.

In one possible implementation, the inner side walls of the two short side plates are coated with a resilient high-friction coating.

The boxing robot workstation comprises a robot, an intelligent end pick-up, a transfer trolley, a lifter and a crate, wherein the crate comprises a crate body and elastic supports, and the bottom of the crate body is provided with an opening and a plurality of elastic supports;

the intelligent end effector is arranged at the executing tail end of the robot and used for picking up thin plate workpieces and stacking or unstacking the thin plate workpieces in the crate;

the transfer trolley is used for transferring the crates;

the lifter is arranged on the transfer trolley, and when the crate is stacked or unstacked, the lifter extends out of the opening at the bottom of the crate and lifts the sheet workpiece, so that the sheet workpiece is in a bent state.

In one possible implementation manner, the lifter comprises a lifter flexible supporting surface and lifter flat supporting surfaces symmetrically arranged on two sides of the lifter flexible supporting surface; a lifter flat support surface lower than the lifter flexible support surface for positioning the bottom of the crate; the lifter flexible supporting surface is used for lifting the thin plate workpiece.

In a possible realization, the top of the trolley is provided with a trolley upper support surface, which supports the crate during transport.

In a possible implementation manner, the box body is of a rectangular structure and comprises a bottom plate, and two short side plates and two long side plates which are arranged on the bottom plate, wherein the opening is arranged at the center of the bottom plate; the elastic support is of a strip-shaped structure and is arranged at the bottom of the bottom plate along the width direction.

Another embodiment of the present invention provides a boxing method using the boxing robot workstation, which comprises the following steps:

1) placing the crate on a transfer trolley, wherein an opening at the bottom of the crate corresponds to the lifter;

2) the lifter extends out, the crate is lifted through the lifter flat supporting surface, and the lifter flexible supporting surface extends out of the opening at the bottom of the crate to the crate;

3) the robot picks up the thin plate workpiece to stack in the crate through the intelligent end pick-up, the thin plate workpiece is supported by the flexible supporting surface of the lifter to form a bending state, and therefore two ends of the thin plate workpiece are not contacted with the inner walls of two ends of the crate;

4) after the stacking is finished, the lifting device retracts into the transfer trolley, so that the bottom of the crate is contacted with the supporting surface on the transfer trolley of the transfer trolley, meanwhile, the sheet workpiece completely falls into the crate, and the two ends of the sheet workpiece are contacted with the inner walls of the two ends of the crate.

The invention has the advantages and beneficial effects that:

1. the bottom of the crate provided by the invention is provided with the elastic support, so that the crate plays a role in damping in the transportation process; the bottom of the crate is provided with an opening, which is convenient for the stacking or unstacking process; the strip-shaped thin plate in the plate strip-shaped plate in the crate is automatically positioned in the transportation process and is suitable for the clean environment of a photoelectric field.

2. The boxing robot workstation provided by the invention can avoid the collision and friction between the sheet workpiece and the crate caused by the spatial motion trajectory precision of the cleaning robot, and is suitable for the cleaning robot to stack and unstack the sheets in the crate through the end effector.

3. According to the boxing robot workstation provided by the invention, in the process of stacking or unstacking the lath-shaped thin plates in the lath box, the middle part of the thin plate workpiece forms the convex arch shape through the lifter, so that two ends of two layers of thin plate workpieces are staggered to form a section of air gap, the thin plate workpieces are prevented from being adhered and adhered to each other, the thin plate workpieces are easy to separate, and the working efficiency is improved.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is an isometric view of a crate in an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a crate in an embodiment of the present invention;

FIG. 3 is an isometric view of a boxing robotic workstation in accordance with another embodiment of the present invention;

FIG. 4 is a top view of a boxing robotic workstation in another embodiment of the present invention;

FIG. 5 is an enlarged view taken at I in FIG. 4;

FIG. 6 is a cross-sectional view A-A of FIG. 4;

FIG. 7 is an enlarged view taken at II in FIG. 6;

in the figure: 1. robot, 2, intelligent end pick-up, 3, sheet workpiece, 4, transfer car, 5, lifter, 6, support surface on the transfer car, 7, lifter flat support surface, 8, lifter flexible support surface, 9, crate, 91, short side plate, 92, long side plate, 93, elastic support, 94, bottom plate, 95, opening, 41, transfer car, 42, transfer car.

Detailed Description

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

The crate is used for storing and transporting thin plate workpieces, and is used for damping vibration in the transportation process through elastic support; the collision between the two ends of the sheet workpiece and the interior of the box body can be avoided in the stacking or unstacking process of the crates. Referring to fig. 1-2, the crate comprises a box body and elastic supports 93, wherein the bottom of the box body is provided with an opening 95 and a plurality of elastic supports 93, and the opening 95 is used as a lifting port for stacking or unstacking thin plate workpieces 3 in the box body.

In the embodiment of the invention, the box body is a cuboid structure and comprises a bottom plate 94, two short side plates 91 and two long side plates 92, wherein the two short side plates 91 and the two long side plates 92 are arranged on the bottom plate 94, and an opening 95 is arranged at the center of the bottom plate 94; the elastic support 93 has a strip structure and is disposed on the bottom plate 94 along the width direction. The plurality of elastic supports 93 are arranged at equal intervals along the length direction, and play a role in absorbing shock during transportation.

Further, the inner side walls of the two short side plates 91 are coated with an elastic high-friction coating, such as fluororubber, so that when the two short sides of the sheet workpiece 3 are in contact with the two corresponding short side plates 91, no dust is generated, and a clean environment is ensured.

The crate provided by the embodiment of the invention is used for storing and transporting the thin plate workpiece 3, and plays a role in damping the vibration during the transportation process through the elastic support 93 at the bottom; the bottom of crate is equipped with opening 95, makes things convenient for the stack or breaks a jam in-process to lift sheet metal work piece 3 through lifting equipment to make sheet metal work piece 3 be in the bending condition, thereby leave the clearance between the both ends that make sheet metal work piece and two short side boards 91, prevent that the both ends of sheet metal work piece 3 from colliding with two short side boards 91 and producing the dust, guarantee the clean environment of vanning of sheet metal work piece 3. The thin plate workpiece in the crate is automatically positioned in the transportation process, and is suitable for the clean environment of the photoelectric field. In this embodiment, the thin plate workpiece is a strip-shaped thin plate of a photovoltaic enterprise, such as a glass substrate, a spacer, and the like.

Based on the design thought, another embodiment of the invention provides a boxing robot workstation, which can avoid collision and friction caused by the spatial motion track precision of a cleaning robot and is suitable for stacking and unstacking thin plates of the cleaning robot and an end effector thereof. Referring to fig. 3-7, the boxing robot workstation comprises a robot 1, an intelligent end effector 2, a transfer trolley 4, a lifter 5 and a crate 9, wherein the crate 9 comprises a crate body and elastic supports 93, and the bottom of the crate body is provided with an opening 95 and a plurality of elastic supports 93; the intelligent end effector 2 is arranged at the executing tail end of the robot 1 and is used for picking up the thin plate workpieces 3 and stacking or unstacking the thin plate workpieces in the crate 9; the transfer trolley 4 is used for transferring and transporting the crates 9; the lifter 5 is arranged on the transfer trolley 4, and when the crate 9 is stacked or unstacked, the lifter 5 extends out of the opening 95 at the bottom of the box body and lifts the thin plate workpiece 3 and the crate 9, so that the thin plate workpiece 3 is in a bent state.

Referring to fig. 3, in the embodiment of the present invention, the box body is a rectangular parallelepiped structure, and includes a bottom plate 94, and two short side plates 91 and two long side plates 92 disposed on the bottom plate 94, and the opening 95 is a rectangular structure and is disposed at a central position of the bottom plate 94; the elastic support 93 has a strip structure and is disposed at the bottom of the bottom plate 94 along the width direction.

Referring to fig. 3, in the embodiment of the present invention, the lift 5 includes a lift flexible supporting surface 8 and lift flat supporting surfaces 7 symmetrically disposed on both sides of the lift flexible supporting surface 8; the lift flat support surface 7 is lower than the lift flexible support surface 8 for positioning the bottom of the crate 9; the lifter flexible supporting surface 8 is used for lifting the thin plate workpiece 3, so that the thin plate workpiece 3 forms a convex arch at the middle part. In this embodiment, the lifter flexible supporting surface 8 is an arc-shaped curved surface protruding upward, and the lifter flat supporting surface 7 is a plane with the same height.

In the embodiment of the invention, the transfer vehicle 4 can move in any direction on the ground, and preferably, the transfer vehicle 4 is an AVG vehicle. The top of the transfer trolley 4 is provided with a transfer trolley upper support surface 6, which transfer trolley upper support surface 6 supports the bottom of the crate 9 during transport. The lifter 5 may be driven by a cylinder, or any other lifting means, which is not limited herein. In this embodiment, the robot 1 is a vertical articulated cleaning robot.

In another embodiment of the invention, the intelligent end effector 2 comprises three groups of sequentially arranged suckers, and the curved adsorption of the sheet workpiece 3 is realized through the height difference of the three groups of suckers. When the robot 1 stacks or unstacks the thin plate workpieces 3 in the crate 9 through the intelligent end effector 2, firstly, the crate 9 is lifted through the lifter flat supporting surface 7 of the lifter 5, so that the crate 9 is separated from the upper supporting surface 6 of the transfer trolley; and the thin plate workpiece 3 is lifted and supported by the lifter bending supporting surface 8, so that the thin plate workpiece 3 is in a bending state, two ends of the thin plate workpiece 3 are not in contact with two short side plates 91 of the crate 9, collision and friction between the thin plate workpiece 3 and the crate 9 caused by the spatial motion trajectory precision of the cleaning robot can be avoided, and the device is suitable for stacking and unstacking thin plates of the cleaning robot and an end pick-up thereof in the crate 9. On the other hand, the lath-shaped thin plates are stacked or unstacked in the crate, and the middle of the thin plate workpiece 3 forms an upwards-convex arch through the lifter 5, so that two ends of two layers of thin plate workpieces are staggered to form a section of air gap, the thin plate workpieces are prevented from being adhered and adhered to each other, the thin plate workpieces are easily separated, and the working efficiency is improved.

Based on the above design concept, another embodiment of the present invention provides a boxing method, which is completed by using the boxing robot workstation in any one of the above embodiments, and specifically includes the following steps:

1) placing the crate 9 on the trolley 4, the opening 95 at the bottom of the crate 9 corresponding to the lifter 5;

2) the lift 5 extends to lift the crate 9 through the lift flat support surface 7, and the lift flexible support surface 8 extends from the opening 95 at the bottom of the crate 9 into the crate 9;

3) the robot 1 picks up the thin plate workpieces 3 through the intelligent end pick-up device 2 to stack in the crate 9, the thin plate workpieces 3 are supported through the flexible supporting surface 8 of the lifter to form a bending state, so that two ends of the thin plate workpieces 3 are not contacted with the inner walls of two ends of the crate 9, and a gap d is formed between two ends of the thin plate workpieces 3 and a short side plate 91 of the crate 9, which is shown in fig. 6-7, wherein a first transfer trolley 41 in fig. 6 is in a stacking state;

specifically, the intelligent end effector 2 comprises three groups of suckers which are sequentially arranged, and the bent adsorption of the sheet workpiece 3 is realized through the height difference of the three groups of suckers. That is, the height of the group of suction cups positioned in the middle is lower than the height of the suction cups positioned at both sides, so that the middle part of the sheet workpiece 3 is raised upward after the picking is completed;

4) after the palletizing is finished, the lifter 5 retracts into the transfer trolley 4, so that the bottom of the crate 9 is contacted with the upper support surface 6 of the transfer trolley 4, and simultaneously, the thin plate workpiece 3 completely falls into the crate 9, and the two ends are contacted with the inner walls of the two ends of the crate 9.

In this embodiment, the upper support surface 6 of the transfer trolley can lift the crate 9 below the floor 94 of the crate 9 in the packing mode of the crate 9. The transfer trolley 4 with the lifting function is driven to a position where the robot 1 enables the intelligent end effector 2 to adsorb the thin plate workpiece 3. The lift 5 lifts relative to the trolley 4, the lift flat support surface 7 moving from a lowered position to a raised position, contacts the floor 94 of the crate 9 and lifts. The lifter flexure support surface 8 can lift the thin plate workpiece 3 to form a convex camber on the middle of the thin plate workpiece 3. At this time, the lifter flat supporting surface 7 is under the bottom plate 94 of the high-position liftable crate 9, and the lower surfaces of the two ends of the lowest layer of thin plate workpiece 3 are effectively supported by the elastic supports 93. The two short sides of the sheet workpiece 3 contain a certain gap d with the two corresponding short sides 91, see fig. 7; the two long sides of the thin-plate workpiece 3 and the two corresponding long side plates 92 each have a certain gap l, as shown in fig. 5. The clearance that two minor faces of sheet metal work piece 3 correspond with two short side boards 91 and the clearance of two long sides and two long side boards 92 that correspond of sheet metal work piece 3, the robot 1 of being convenient for lets intelligent end effector 2 adsorb sheet metal work piece 3 and packs into a box, pile up neatly or unstack etc. carries out the operation of a plurality of sheet metal work pieces 3 vanning and unpacking the case. The crate 9 may be provided with a plurality of layers of sheet work pieces 3 from top to bottom, in this embodiment only two layers. The thin-plate workpiece 3 conforms to the thin-plate theory of thin-plate structural mechanics. Therefore, the multilayer thin plate workpiece 3 forms a convex arch in the middle, the end parts of the two thin plates are staggered, a small air gap is formed between the two thin plates at the end part, the problem of mutual adhesion of the thin plates is effectively solved by the two small air gaps, and the thin plates are easy to separate when being detached and processed, so that the working efficiency is improved. The reverse process to the binning mode is the unpacking process.

And switching between a crate transportation mode and a crate unpacking mode, wherein the lifting of the crate 9 is changed from the lifter flat supporting surface 7 to the trolley upper supporting surface 6 during the lowering of the lifter 5 relative to the trolley 4 with the lifting function. The lifter flexible supporting surface 8 gradually descends to reduce the flexibility of the thin plate workpiece 3, and finally the lower surface of the lowest layer of the thin plate workpiece 3 is effectively supported by the elastic support 93.

Referring to fig. 6, taking the second trolley 42 as an example, when the crate 9 is in the transport mode, the upper trolley support surface 6 of the second trolley 42 can lift the underside of the floor 94 of the crate 9, the flexible lifter support surface 8 is slightly lower than the upper trolley support surface 6, and the lifter 5 is housed in the trolley 4. The lower surface of the lowest-layer thin plate workpiece 3 is effectively supported by the elastic support 93. Two short sides of the thin plate workpiece 3 and two corresponding short side plates 91 are respectively extruded to form contact friction counter-force positioning, so that the thin plate workpiece 3 is prevented from moving in the length and width directions and rotating in a horizontal plane. The crate 9 may be arranged with a plurality of layers of sheet work pieces 3 from top to bottom. At this time, the two long sides of the thin plate workpiece 3 and the two corresponding long side plates 92 respectively have a certain gap l, as shown in fig. 5. In the transportation process of the crate, the sheet workpiece 3 cannot generate relative collision and dust in the crate 9, and the sheet workpiece 3 is guaranteed to be transported in a clean environment.

According to the boxing method, the middle part of the thin plate workpiece is provided with the convex arch through the lifter, so that two ends of the two layers of thin plate workpieces are staggered to form a section of air gap, the thin plate workpieces are prevented from being adhered and adhered to each other, the thin plate workpieces are easy to disassemble, and the working efficiency is improved. Meanwhile, the collision and friction between the sheet workpiece and the crate caused by the spatial motion trajectory precision of the cleaning robot can be avoided, and the cleaning robot is suitable for stacking and unstacking the sheets of the cleaning robot and the end effector thereof in the crate.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A boxing robot workstation is characterized by comprising a robot (1), an intelligent end pick-up (2), a transfer trolley (4), a lifter (5) and a crate (9), wherein the crate (9) comprises a box body and elastic supports (93), and the bottom of the box body is provided with an opening (95) and a plurality of elastic supports (93);

the intelligent end effector (2) is arranged at the executing tail end of the robot (1) and is used for picking up thin plate workpieces (3) and stacking or unstacking the thin plate workpieces in the crate (9);

the transfer trolley (4) is used for transferring the crates (9);

the lifter (5) is arranged on the transfer trolley (4), and when the crate (9) is stacked or unstacked, the lifter (5) extends out of the opening (95) at the bottom of the crate body and lifts the thin plate workpiece (3), so that the thin plate workpiece (3) is in a bent state.

2. A boxing robot workstation in accordance with claim 1, wherein the lift (5) comprises a lift deflection support surface (8) and lift flat support surfaces (7) symmetrically arranged on both sides of the lift deflection support surface (8); a lifter flat supporting surface (7) is lower than a lifter flexible supporting surface (8) and is used for positioning the bottom of the crate (9); the lifter flexible supporting surface (8) is used for lifting the thin plate workpiece (3).

3. A boxing robot workstation in accordance with claim 1, wherein the top of the transfer trolley (4) is provided with a trolley upper support surface (6), the trolley upper support surface (6) supporting the crates (9) during transportation.

4. A boxing robot workstation in accordance with claim 1, wherein the box body is of a rectangular parallelepiped structure and comprises a bottom plate (94) and two short side plates (91) and two long side plates (92) arranged on the bottom plate (94), the opening (95) is arranged at the center of the bottom plate (94); the elastic support (93) is of a strip-shaped structure and is arranged at the bottom of the bottom plate (94) along the width direction.

5. Boxing robotic workstation according to claim 4, wherein the inner side walls of both the short side plates (91) are coated with a resilient high friction coating.

6. A boxing method using a boxing robotic workstation as claimed in any one of claims 1 to 5, comprising the steps of:

1) placing the crate (9) on the transfer trolley (4), wherein an opening (95) at the bottom of the crate (9) corresponds to the lifter (5);

2) the lifter (5) extends out, the crate (9) is lifted through the lifter flat supporting surface (7), and the lifter flexible supporting surface (8) extends out of the opening (95) at the bottom of the crate (9) into the crate (9);

3) the robot (1) picks up the thin plate workpieces (3) through the intelligent end pick-up device (2) and stacks the thin plate workpieces in the crate (9), the thin plate workpieces (3) are supported through the flexible supporting surface (8) of the lifter to form a bending state, and therefore the two ends of the thin plate workpieces (3) are not in contact with the inner walls of the two ends of the crate (9);

4) after the stacking is finished, the lifter (5) retracts into the transfer trolley (4), so that the bottom of the crate (9) is contacted with the supporting surface (6) on the transfer trolley of the transfer trolley (4), and simultaneously, the thin plate workpiece (3) completely falls into the crate (9), and the two ends of the thin plate workpiece are contacted with the inner walls of the two ends of the crate (9).

7. A boxing method according to claim 6, wherein the intelligent end effector (2) comprises three groups of suction cups arranged in sequence, and the curved suction of the sheet workpiece (3) is realized by the height difference of the three groups of suction cups.