3D print head for tubular member

Abstract

The present invention relates to the technical field of printing. Disclosed is a 3D print head for a tubular member. The 3D print head comprises a material chamber and a support rod, wherein the material chamber is provided with a feed port and a discharge port; and the support rod is arranged in the discharge port, the support rod is movably connected relative to the material chamber in the axial direction thereof, and the position of the support rod can be adjusted. In some embodiments, the support rod comprises a detachable front-end support section. In some embodiments, the support rod has an internal spatial structure. By means of the above structural configuration, the present invention can effectively prevent a tubular member from collapsing, thereby facilitating the improvement of the printing efficiency, improving the quality of the inner wall of the tubular member, and improving the structural adaptability.

Description

A 3D printing head for tubular components Technical Field

[0001] This invention relates to the field of printing technology, and in particular to a 3D printing head for tubular components. Background Technology

[0002] With the improvement of people's living standards and the increasing aging of society, the incidence of cardiovascular and cerebrovascular diseases is rising year by year and becoming increasingly prevalent among younger people. Cardiovascular disease is a disease with a high mortality rate in today's society. Data surveys show that cardiovascular disease ranks first among the overall health indicators of the Chinese population. The treatment of some cardiovascular diseases (such as aneurysms, arterial thrombosis, coronary artery bypass grafting, and traumatic vascular injuries) requires artificial blood vessel transplantation. Manufacturing artificial blood vessels that are biocompatible is key to treating these types of vascular diseases.

[0003] With the development of materials and processing technologies, it has become possible to manufacture biological blood vessels using artificial materials. Currently, artificial blood vessels are mainly manufactured through 3D printing, which uses additive manufacturing to build up the artificial blood vessels. However, because the printing material is in a molten state, the newly formed artificial blood vessels are relatively soft and prone to collapse, which limits the printing speed and thus affects printing efficiency.

[0004] In addition, the inner wall of artificial blood vessels is relatively rough, and it is easy to have unevenness and wrinkles, which affects blood transport and makes it easy to form thrombi.

[0005] Similarly, 3D-printed tubular components also suffer from some or all of the aforementioned defects. Summary of the Invention

[0006] To address the problems of easy collapse, low printing efficiency, and insufficient smoothness of the inner wall in existing 3D-printed tubular components, the purpose of this invention is to provide a 3D printing head for tubular components, so as to at least partially solve the above-mentioned problems.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A 3D printing head for tubular components includes a hopper and a support rod; the hopper has an inlet and an outlet; the support rod is arranged in the outlet, and the support rod is movably connected to the hopper along its axial direction and its position is adjustable

[0008] . In some preferred embodiments, the outlet is conical, and an annular gap for forming tubular components is formed between the lower inner wall of the outlet and the outer wall of the support rod.

[0009] In some preferred embodiments, a strut drive is further included, which is used to drive the support rod to move along its axial direction.

[0010] In some preferred embodiments, a sleeve is further included, which is fixedly connected to the hopper and is used to guide the support rod to move along its axial direction.

[0011] In some preferred embodiments, a sealing valve for preventing printing material from entering is further provided between the sleeve and the support rod.

[0012] In some preferred embodiments, there are two or more hoppers, including a central hopper and at least one peripheral hopper. The outlets of each hopper are coaxially arranged sequentially, and the support rod is arranged in the central hopper.

[0013] In some preferred embodiments, at least one of the peripheral hoppers is provided with a yarn feeding mechanism; the yarn feeding mechanism includes a yarn spool and at least one yarn bobbin; the yarn spool is rotatably connected relative to the peripheral hopper, and all the yarn bobbins are rotatably connected to the yarn spool, and the yarn bobbins are arranged circumferentially around the rotation center of the yarn spool.

[0014] In some preferred embodiments, the rotation axis of the wire spool coincides with the axis of the support rod.

[0015] In some preferred embodiments, the wire feeding mechanism further includes a wire spool drive component, which is fixedly installed relative to the peripheral hopper and is used to drive the wire spool to rotate.

[0016] In some preferred embodiments, the wire feeding mechanism further includes a wire spool frame, the wire spool frame being fixedly connected to the peripheral hopper, and the wire spool being rotatably connected to the wire spool frame.

[0017] By adopting the above technical solution, the beneficial effects of the present invention are as follows: The present invention, through the setting of the support rod, ensures that the tubular component continues to be supported after molding, thereby effectively preventing collapse and supporting higher printing speeds and improving printing efficiency; in addition, the support rod also makes the inner wall of the tubular component smoother. Furthermore, due to the setting of the filament feeding mechanism, the outer wall of the tubular component is covered with filament material, thereby improving the overall structural strength of the tubular component, which also prevents collapse and supports higher printing speeds and improves printing efficiency. Attached Figure Description

[0018] Figure 1 is a structural schematic diagram of Embodiment 1 of the present invention.

[0019] Figure 2 is a structural schematic diagram of Embodiment 2 of the present invention.

[0020] Figure 3 is a structural schematic diagram of Embodiment 4 of the present invention.

[0021] Figure 4 is a structural schematic diagram of Embodiment 5 of the present invention.

[0022] Figure 5 is a structural schematic diagram of Embodiment 6 of the present invention.

[0023] Figure 6 is a structural schematic diagram of Embodiment 6 of the present invention.

[0024] Figure 7 is a structural schematic diagram of Embodiment 7 of the present invention.

[0025] Figure 8 is a structural schematic diagram of Embodiment 8 of the present invention.

[0026] Figure 9 is a structural schematic diagram of Embodiment 9 of the present invention.

[0027] Figure 10 is a schematic diagram of the structure of Embodiment 10 of the present invention.

[0028] In the diagram: 1-hopper, 11-outlet, 12-outlet nozzle, 13-guide cylinder, 2-support rod, 3-support rod drive, 4-wire feeding mechanism, 41-wire spool, 42-wire drum, 5-sleeve, 6-wire spool drive, 201-internal space structure, 202-front end support section. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] It should be noted that in the description of this invention, the terms "upper," "lower," "left," "right," "front," and "rear," etc., indicate the orientation or positional relationship based on the description of the structure of this invention shown in the accompanying drawings. They are only for the convenience of describing this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0031] The terms "first" and "second" in this technical solution are merely designations for corresponding structures that are identical or similar, or that perform similar functions. They do not represent an arrangement of the importance of these structures, nor do they imply any ranking, comparison of size, or other meaning.

[0032] Furthermore, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two structures. For those skilled in the art, the specific meaning of the above terms in this invention can be understood in light of the overall concept of this invention and the specific context of this solution. Example 1

[0033] A 3D printing head for tubular components, as shown in Figure 1, includes a hopper 1 and a support rod 2.

[0034] The hopper 1 is used to store molten printing material. The hopper 1 has an inlet and an outlet 11, with the outlet 11 typically located on the bottom side of the hopper 1. Additionally, the hopper 1 is usually equipped with a pressurizing component to expel the stored molten printing material from the outlet 11 under pressure. The pressurizing component can be any pressurizing equipment used in the existing 3D printing field, such as screw extrusion, piston pressurization, or gas pressurization.

[0035] The support rod 2 is a straight rod-shaped structure and is arranged in the discharge port 11. For example, the upper end of the support rod 2 is fixed to the inner side of the top wall of the hopper 1. The diameter of the support rod 2 is smaller than the diameter of the discharge port 11, and the support rod 2 is usually coaxially arranged with the discharge port 11.

[0036] The lower end of the support rod 2 extends from the discharge port 11. A tapered discharge nozzle 12 with its smaller end pointing downwards is typically provided on the discharge port 11. This discharge nozzle 12 protrudes from the bottom surface of the hopper 1 and is usually integrally formed with the hopper 1. Furthermore, there is an annular gap between the inner wall of the lower end of the discharge nozzle 12 and the outer wall of the support rod 2. When the molten printing material stored in the hopper 1 is extruded through this annular gap, the required tubular component can be formed on the outer wall of the hopper 1 where the support rod 2 protrudes.

[0037] This design allows the printing material to exit in the form of a tubular component, and after exiting, it is supported by the support rod 2 (the part extending outside the hopper 1). This prevents the tubular component from collapsing on its sidewalls and also makes the inner wall of the tubular component smoother. Example 2

[0038] In this embodiment, based on Embodiment 1, a 3D printing head for tubular components is further equipped with a strut drive 3, as shown in Figure 2.

[0039] First, the support rod 2 is movably connected relative to the hopper 1 along its axial direction. For example, a through hole is provided on the side wall of the hopper 1 away from the discharge port 11 for the support rod 2 to slide in. The through hole is adapted to the diameter of the support rod 2. If necessary, a sealing element, such as a sealing ring, can be provided on the inner wall of the through hole.

[0040] The upper end of the support rod 2 extends through the through hole to the outside of the top surface of the hopper 1. The support rod drive 3 is fixed to the outside of the top wall or side wall of the hopper 1, such as a cylinder with a locking function, a hydraulic cylinder, or an electric cylinder. Its output end is connected to the upper end of the support rod 2 so that the support rod drive 3 can drive the support rod 2 to move along its axial direction. Of course, in other preferred embodiments, the support rod drive 3 can also be any device in the prior art that can output reciprocating linear motion, such as a screw conveyor, which drives the support rod 2 to rise and fall.

[0041] Thus, by setting up the support rod 2 and the strut drive 3, the strut drive 3 can drive the support rod 2 to move, thereby controlling the length of the support rod 2 extending from the nozzle 12, and thus changing the degree of support for the tubular component to adapt to different types of printing materials. Example 3

[0042] It is easy to understand that the strut drive component 3 in Embodiment 2 can also be omitted.

[0043] For example, the upper thread of the support rod 2 is screwed into the through hole at the top of the hopper 1. When it is necessary to adjust the length of the support rod 2 protruding from the discharge port 11, it is only necessary to screw the support rod 2 accordingly.

[0044] Alternatively, a bracket can be installed on the top of the hopper 1, with a rotating connecting nut on the bracket. The portion of the support rod 2 protruding from the top surface of the hopper 1 has an external thread that mates with the nut. A slider is fixed to the top of the support rod 2, and a corresponding groove is provided on the bracket to mate with the slider. Thus, when the nut is rotated, the support rod 2 can move along its axial direction, thereby adjusting the length of the support rod 2 protruding from the discharge nozzle 12. Example 4

[0045] In embodiments 2 and 3, the contact length between the support rod 2 and the printing material in the hopper 1 is relatively large. Therefore, when the support rod 2 moves axially, the support rod 2 experiences greater resistance from the printing material.

[0046] Therefore, in this embodiment, as shown in Figure 3, a sleeve 5 is also provided. The sleeve 5 is arranged inside the hopper 1 and is fixedly connected to the top wall of the hopper 1, for example by welding or threaded connection. The sleeve 5 is arranged coaxially with the through hole opened on the top wall of the hopper 1. The upper end of the support rod 2 passes through the sleeve 5 to the outside of the top of the hopper 1. That is, the sleeve 5 is used to guide the support rod 2 to pass through the hopper 1 in a direction away from the discharge port 11, thereby reducing the contact area between the support rod 2 and the printing material and reducing the resistance when it moves.

[0047] The lower end of the sleeve 5 is a certain distance from the discharge position of the discharge port 11, so that the printing material can come into timely and sufficient contact with the support rod 2 before being discharged.

[0048] Typically, a seal, such as a sealing ring, is provided between the sleeve 5 and the support rod 2 to prevent printing material from entering. A step or groove for installing the sealing ring is provided on the inner wall of the lower end of the sleeve 5.

[0049] It is easy to understand that the upper end of the sleeve 5 can also protrude from the hopper 1, and the strut drive 3 can also be fixed on the sleeve 5 in order to maintain the structural independence of the hopper 1.

[0050] It is easy to understand that sometimes the required tubular material is not necessarily a single-layer structure, but may be a multi-layer structure composed of different printing materials arranged sequentially from the inside out.

[0051] Therefore, there can be two or more hoppers 1, as shown in Figure 4. For example, there are two hoppers, and the discharge nozzles 12 of the two hoppers are arranged coaxially in sequence. Usually, the two hoppers are also nested in sequence. Typically, the inner hopper is called the center hopper 101, and the outer hopper is called the outer hopper 102. Usually, each of the two hoppers is equipped with a pressurizing device, and they discharge independently.

[0052] Of course, there can be two or more outer hoppers 102, which are also arranged in a nested manner. The discharge nozzles 12 configured in each hopper are also arranged in a coaxial manner, and there is an annular gap between the lower ends of the inner walls of each pair of adjacent discharge nozzles 12.

[0053] The support rod 2 is configured on the central hopper 101, and the support rod drive component 3 disclosed above or other supporting components such as nuts are also configured on the central hopper 101.

[0054] In use, the central silo 101 first discharges material under pressure to form the innermost layer of the tubular component. Then, the outer silos 102 discharge material sequentially from the inside to the outside, forming the various layers of the tubular component from the inside out, thus forming the required multi-layered tubular component. Example 6

[0055] It is easy to understand that, based on Embodiment 5, the peripheral hopper 102 is not necessarily used entirely for storing molten printing material. It can also be used to arrange the filament feeding mechanism 4. The filament feeding mechanism 4 is used to provide a reinforcing layer made of filament for the tubular component. This embodiment describes the configuration of the hoppers in detail as two, namely a central hopper 101 and a peripheral hopper 102. It is also easy to understand that the peripheral hopper 102 with the filament feeding mechanism 4 does not necessarily need to be equipped with a feed inlet and a pressurizing device. Of course, it can also be equipped with a feed inlet and a pressurizing device. At the same time, the peripheral hopper 102 is equipped with an openable and closable hopper cover, so as to facilitate the disassembly and assembly of the filament feeding mechanism 4, such as disassembling and assembling the filament spool 42 and cleaning up any residual printing material that affects the rotation of the filament spool 41.

[0056] As shown in Figure 5, the wire feeding mechanism 4 includes a wire spool 41 and a wire tube 42.

[0057] The wire spool 41 is annular and rotatably connected to the outer hopper 102. The axis of rotation of the wire spool 41 is usually coincident with the axis of the support rod 2. The wire drum 42 is the feeding drum for the wire material. It is rotatably connected to the wire spool 41, and the axis of rotation of the wire drum 42 is parallel to the axis of rotation of the wire spool 41. Of course, the axis of rotation of the wire drum 42 can also be perpendicular to the axis of rotation of the wire spool 41. In actual use, it is only necessary to ensure that the wire drum 42 can feed the wire material.

[0058] There is one or more (two or more) wire spools 42. When there are more than two wire spools 42, it is preferable that the revolution radius of each wire spool 42 is the same, and that each wire spool 42 is evenly arranged around the rotation center of the wire disc 41. Of course, when there are more than two wire spools 42, the revolution radius of each wire spool may not be exactly the same.

[0059] It is easy to understand that the filament feeding point of the spool 42 is typically at a certain distance from the tubular member formed on the support rod 2 in both the axial and radial directions. This makes it difficult for the filament fed from the spool 42 to wrap around the outer wall of the tubular member extruded from the discharge port 11. Therefore, the conical discharge nozzle 12 configured in the peripheral hopper 102 gathers the filament and guides it onto the outer wall of the tubular member.

[0060] Typically, the lower end of the discharge nozzle 12 configured in the outer hopper 102 is also formed with a cylindrical guide tube 13. The guide tube 13 enables the filament to adhere better to the outer wall of the tubular component. The guide tube 13 is usually integrally formed at the lower end of the discharge nozzle 12 configured in the outer hopper 102.

[0061] The rotating wire disc 41 enables the wire to automatically return to its correct position under tension when it becomes skewed.

[0062] The working process of the 3D printing head for tubular components provided in this embodiment of the invention is as follows: Before use, the required filament is wound onto the filament spool 42 (or the filament feeding mechanism 4 is replaced with a filament spool 42 containing the specified filament), and the filament is released from the guide cylinder 13; then, the central material hopper 101 is connected to the material delivery pipe, and the length of the support rod 2 extending from the discharge nozzle 12 configured in the central material hopper 101 is controlled by the strut drive 3. Then, the central material hopper 101 is driven by an external pressurizing device to extrude the molten printing material. The molten printing material is shaped into a tubular component under the action of the annular gap between the discharge nozzle 12 and the support rod 2, and then continues to grow while maintaining its shape under the support of the support rod 2. During the material discharge process of the tubular component, filament will adhere to it, so that the filament is released synchronously with its growth process, thereby forming a reinforcing structure composed of filament on the outer wall of the tubular component.

[0063] It is easy to understand that there can be two peripheral material bins 102, as shown in Figure 6. The peripheral material bin 102 located on the inner side is also used to arrange molten printing material, while the peripheral material bin 102 located on the outer side is used to arrange the feeding mechanism 4; or conversely, the peripheral material bin 102 located on the inner side is used to arrange the feeding mechanism 4, while the peripheral material bin 102 located on the outer side is used to arrange molten printing material.

[0064] When there are multiple peripheral material bins 102, each peripheral material bin 102 can be configured with molten printing material or a filament feeding mechanism 4 according to the required tubular component structure. Example 7

[0065] Based on embodiment 6, the wire feeding mechanism 4 further includes a wire spool drive 7, as shown in FIG7. The wire spool drive 7 is fixedly installed in the corresponding peripheral hopper 102. The wire spool drive 7 is used to drive the wire spool 41 to rotate. For example, the wire spool drive 7 is configured as a motor with gears, and a gear ring that cooperates with the gears is installed on the wire spool 41, thereby driving the wire spool to rotate through the wire spool drive 7.

[0066] With this configuration, during the growth of the tubular component, the wire spool drive 7 can drive the wire spool 41 to rotate, so that the wire can be wound in a spiral shape, thereby improving the reinforcement effect of the wire on the tubular component.

[0067] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention. Example 8

[0068] Based on the above embodiments, the support rod 2 includes a main support section 2 and a front support section 202 disposed near the discharge nozzle 12 and located in the tubular component forming area.

[0069] The front-end support section is connected to the main support section, and the two are separable.

[0070] The front support section is used to support and shape the inner wall of the tubular component during the forming process.

[0071] In some preferred embodiments, the front support segment is made of a soluble or biodegradable material.

[0072] In some preferred embodiments, the front support section is made of a metallic or high-strength material to form a reinforcing or bridging structure inside the tubular member.

[0073] In some preferred embodiments, a detachable connection structure, a disconnectable connection structure, or other separable connection structure is provided between the front-end support segment and the main support segment, so that the front-end support segment can be separated from the main support segment at a predetermined stage.

[0074] With this configuration, after the tubular component is formed, the main support section can be removed, while the front support section can be selectively left inside the tubular component or removed as needed, thereby improving structural adaptability. Example 9

[0075] Based on the above embodiments, the support rod 2 is provided with an internal space structure 201 for accommodating, guiding, or setting components.

[0076] In some preferred embodiments, the internal space structure is a hollow cavity and / or channel structure disposed inside the support rod 2.

[0077] In some preferred embodiments, the internal space structure includes a channel extending axially along the support rod 2.

[0078] In some preferred embodiments, the internal space structure may further include lateral openings, segmented channels, or combined channel structures communicating with the outside.

[0079] In some preferred embodiments, the internal space structure extends through at least a portion of the length of the support rod 2.

[0080] The internal space structure is used to provide spatial conditions for the setting, introduction, or formation of internal components of the tubular component during or after the molding process.

[0081] In some preferred embodiments, the internal space structure can also be used for gas flow, pressure balancing, or pressure regulation.

[0082] In some preferred embodiments, the internal space structure can remain closed during the forming process of the tubular component and can be gas-released or pressure-regulated at predetermined stages.

[0083] In some preferred embodiments, the inner wall of the internal space structure is provided with a low-friction structure and / or a sealing structure.

[0084] This configuration allows the support rod to support the tubular component while also providing conditions for internal structural design and pressure adjustment, thereby improving structural adaptability. Example 10

[0085] In some preferred embodiments, the front-end support segment is combined with the internal space structure.

[0086] In some preferred embodiments, the internal space structure extends through the front support section.

[0087] In some preferred embodiments, the front support section can be configured with components, reinforced with structural elements, or adjusted with pressure through the internal space structure.

[0088] In some preferred embodiments, the front-end support segment and the internal space structure can be implemented independently or in combination.

[0089] This design enables the support rod structure to have modular expansion capabilities, thereby improving its adaptability to different tubular component structural requirements.

Claims

Claims 1. A 3D printing head for tubular components, characterized in that... It includes a hopper and a support rod; the hopper has an inlet and an outlet; the support rod is arranged in the outlet, and the support rod is movably connected to the hopper along its axial direction and its position is adjustable.

2. The 3D printing head according to claim 1, characterized in that... The discharge port is conical, and there is an annular gap between the lower inner wall of the discharge nozzle and the outer wall of the support rod for forming a tubular component.

3. The 3D printing head according to claim 1, characterized in that... It also includes a strut drive component, which is used to drive the support rod to move along its axial direction.

4. The 3D printing head according to claim 1, characterized in that... It also includes a sleeve, which is fixedly connected to the hopper and is used to guide the support rod to move along its axial direction.

5. The 3D printing head according to claim 4, characterized in that... A seal is also provided between the sleeve and the support rod to prevent printing material from entering.

6. The 3D printing head according to any one of claims 1-5, characterized in that... The material hoppers are of two or more types, including a central material hopper and at least one peripheral material hopper. The discharge ports of each material hopper are arranged coaxially in sequence, and the support rod is arranged in the central material hopper.

7. The 3D printing head according to claim 6, characterized in that... At least one of the peripheral hoppers is provided with a wire feeding mechanism; the wire feeding mechanism includes a wire spool and at least one wire drum; the wire spool is rotatably connected to the peripheral hopper, the wire drums are all rotatably connected to the wire spool, and the wire drums are arranged circumferentially around the rotation center of the wire spool.

8. The 3D printing head according to claim 7, characterized in that... The rotation axis of the silk reel coincides with the axis of the support rod.

9. The 3D printing head according to claim 7, characterized in that... The wire feeding mechanism also includes a wire spool drive, which is fixedly installed relative to the peripheral hopper and is used to drive the wire spool to rotate.

10. The 3D printing head according to claim 7, characterized in that... The wire feeding mechanism also includes a wire spool frame, which is fixedly connected to the peripheral hopper, and the wire spool is rotatably connected to the wire spool frame.

11. The 3D printing head according to any one of claims 1 to 10, characterized in that, The support rod includes a main support section and a front support section located at one end near the discharge port. The front support section and the main support section are separable.

12. The 3D printing head according to claim 11, characterized in that, The front support section is used to support the inner wall of the tubular component during the forming process.

13. The 3D printing head according to claim 11 or 12, characterized in that, The front-end support section is made of a soluble or biodegradable material.

14. The 3D printing head according to claim 11 or 12, characterized in that, The front support section is made of metal or high-strength material.

15. The 3D printing head according to any one of claims 14, characterized in that, The front-end support section and the main support section are provided with a detachable connection structure, a disconnectable connection structure or other separable connection structure.

16. The 3D printing head according to any one of claims 1 to 10, characterized in that, The support rod has an internal space structure for accommodating, guiding, or setting components.

17. The 3D printing head according to claim 16, characterized in that, The internal space structure is a hollow cavity and / or channel structure set inside the support rod.

18. The 3D printing head according to claim 16 or 17, characterized in that, The internal space structure includes a channel extending axially along the support rod.

19. The 3D printing head according to claim 16 or 17, characterized in that, The internal space structure includes lateral openings that communicate with the outside.

20. The 3D printing head according to any one of claims 16 to 19, characterized in that, The internal space structure is used for gas flow, pressure balance, or pressure regulation.

21. The 3D printing head according to any one of claims 16 to 20, characterized in that, The inner wall of the internal space structure is provided with a low-friction structure and / or a sealing structure.

22. The 3D printing head according to any one of claims 11 to 15, characterized in that, The support rod is provided with the internal space structure as described in any one of claims 16 to 21.