A flexible pneumatic muscle with controllable bending direction and its preparation method

Abstract

The present invention relates to the field of flexible drive technology, specifically a flexible pneumatic muscle with controllable bending direction and a preparation method thereof. The present invention solves the problem that the bending direction of existing flexible pneumatic muscles is uncontrollable. A flexible pneumatic muscle with controllable bending direction comprises a strip muscle body with a square cross-section and made of Ecoflex00‑50; a strip air cavity and a plurality of spherical air cavities are coaxially provided inside the strip muscle body; the front end of the strip air cavity is closed, and the rear end passes through the rear end surface of the strip muscle body; each spherical air cavity is cross-connected with the strip air cavity, and each spherical air cavity is arranged at equal distances; the rear end opening edge of the strip air cavity is sealed and docked with a trachea; four thermoplastic polyurethane elastomer grid structures and four serpentine electric heating coils made of nickel-chromium alloy resistance wire are buried inside the strip muscle body. The present invention is suitable for flexible robots.

Description

Technical Field

[0001] The present invention relates to the field of flexible drive technology, in particular to a flexible pneumatic muscle with controllable bending direction and a preparation method thereof. Background Art

[0002] With the development of flexible functional materials, 3D printing technology, and biomimetics, research in flexible robots has become a new area of ​​research. Flexible robots offer simple structures, ease of fabrication, low cost, and the ability to achieve large degrees of deformation. Furthermore, their all-soft material properties offer improved adaptability and biocompatibility compared to traditional machines, driving the rapid development of this field. The main actuation methods for flexible robots include pneumatic drive, hydraulic drive, flexible functional material drive, and stretch wire drive. Pneumatic drive is the most widely used and researched of these robots.

[0003] Flexible pneumatic muscles, as flexible actuators with output characteristics similar to biological muscles, are widely used in pneumatically driven flexible robots. They are lightweight, low-cost, easy to prepare, and have a high output force-to-weight ratio. They can generally achieve contraction and bending movements. However, when performing bending movements, existing flexible pneumatic muscles can only control the bending angle due to the limitations of their own materials and structures, but cannot control the bending direction, which limits their scope of application. Based on this, it is necessary to invent a flexible pneumatic muscle with controllable bending direction and a preparation method thereof to solve the problem of uncontrollable bending direction of existing flexible pneumatic muscles. Summary of the Invention

[0004] In order to solve the problem that the bending direction of existing flexible pneumatic muscles is uncontrollable, the present invention provides a flexible pneumatic muscle with controllable bending direction and a preparation method thereof.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A flexible pneumatic muscle with controllable bending direction, comprising a strip-shaped muscle body with a square cross-section and made of Ecoflex00-50; a strip-shaped air cavity and a plurality of spherical air cavities are coaxially opened inside the strip-shaped muscle body; the front end of the strip-shaped air cavity is closed, and the rear end passes through the rear end surface of the strip-shaped muscle body; each spherical air cavity is cross-connected with the strip-shaped air cavity, and each spherical air cavity is arranged at equal distances; the rear end opening edge of the strip-shaped air cavity is sealed and connected to the trachea; four thermoplastic polyurethane elastomer grid structures and four A serpentine electric heating coil wound with nickel-chromium alloy resistance wire; four thermoplastic polyurethane elastomer grid structures are parallel to the four side surfaces of the strip muscle body, and the four thermoplastic polyurethane elastomer grid structures are symmetrically distributed around the center line of the strip muscle body; four serpentine electric heating coils are arranged in parallel on the outside of the four thermoplastic polyurethane elastomer grid structures, and the four serpentine electric heating coils are symmetrically distributed around the center line of the strip muscle body; both ends of each serpentine electric heating coil pass through the rear end surface of the strip muscle body and are led outward.

[0007] A method for preparing a flexible pneumatic muscle with controllable bending direction (the method is used to prepare the flexible pneumatic muscle with controllable bending direction described in the present invention), the method is implemented by the following steps:

[0008] Step 1: Prepare a thermoplastic polyurethane elastomer grid structure; the specific steps are as follows:

[0009] Step 1.1: First, a grid-shaped groove is machined on the metal substrate using a laser marking machine. Then, the grid-shaped groove is polished smooth using a grinding machine. Then, the grid-shaped groove is filled with thermoplastic polyurethane elastomer powder.

[0010] Step 1.2: First, heat the metal substrate on an 80°C drying table for 10 minutes to melt the thermoplastic polyurethane elastomer powder in the grid-shaped channels into molten thermoplastic polyurethane elastomer. Then, cool the metal substrate at room temperature for 20 minutes to solidify the molten thermoplastic polyurethane elastomer in the grid-shaped channels into a thermoplastic polyurethane elastomer grid structure. Then, remove the thermoplastic polyurethane elastomer grid structure.

[0011] Step 2: Mix Ecoflex00-50 component A and Ecoflex00-50 component B in a mass ratio of 1:1 and stir evenly to prepare an Ecoflex00-50 prepolymer mixture; the Ecoflex00-50 component A is a platinum-catalyzed silicone rubber matrix; the Ecoflex00-50 component B is a platinum-catalyzed silicone rubber curing agent;

[0012] Step 3: Prepare a strip-shaped encapsulation layer; the specific steps are as follows:

[0013] First, the Ecoflex00-50 prepolymer mixture is injected into the mold, and then the thermoplastic polyurethane elastomer grid structure and the serpentine electric heating coil made of nickel-chromium alloy resistance wire are immersed in the Ecoflex00-50 prepolymer mixture, and then cured and formed to obtain a strip-shaped encapsulation layer;

[0014] Step 4: Prepare the casting mold;

[0015] The casting mold includes a flat box-shaped base and two U-trough-shaped shells; the upper end of the flat box-shaped base is provided with an opening; the notches of the two U-trough-shaped shells are butted against each other, and the two U-trough-shaped shells are embedded in the flat box-shaped base; the two U-trough-shaped shells and the flat box-shaped base together enclose a strip-shaped casting cavity;

[0016] Step 5: Prepare the air cavity mold;

[0017] The air cavity mold includes a wooden stick and a plurality of spheres with holes; each sphere with holes is sleeved on the wooden stick, and each sphere with holes is arranged at equal distances;

[0018] Step 6: Prepare the strip muscle body; the specific steps are as follows:

[0019] Step 6.1: Select four strip-shaped packaging layers and attach the first to third strip-shaped packaging layers to the bottom, left, and right sides of the strip-shaped casting cavity one by one;

[0020] Step 6.2: First pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity, then place the air cavity mold into the strip casting cavity, and then continue to pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity until the Ecoflex00-50 prepolymer mixture covers the air cavity mold, and then place the fourth strip encapsulation layer on top of the Ecoflex00-50 prepolymer mixture;

[0021] Step 6.3: First, heat the casting mold in a 60°C oven for 30 minutes to allow the Ecoflex 00-50 prepolymer mixture and the four strip-shaped encapsulation layers to solidify into one, thereby forming the strip-shaped muscle body. The casting mold is then allowed to cool at room temperature for 20 minutes. The flat box-shaped base is then peeled off from the strip-shaped muscle body, followed by peeling off the two U-grooved shells from the strip-shaped muscle body. The strip-shaped muscle body is then removed.

[0022] Step 7: First, a hole is opened on the rear end face of the strip muscle body, and then the wooden stick is pulled out through the hole. The hole and the cavity formed after the wooden stick is pulled out together constitute a strip air cavity. Then, each perforated sphere is squeezed out through the hole. The cavities formed after the perforated spheres are squeezed out constitute each spherical air cavity one by one. Then, the trachea is bonded to the edge of the rear end hole of the strip air cavity with an adhesive, thereby obtaining a flexible pneumatic muscle with controllable bending direction.

[0023] In the step 1, the metal substrate is made of aluminum and has a thickness of 3 mm.

[0024] In the step 2, the mass of Ecoflex00-50 component A and the mass of Ecoflex00-50 component B are both 30 g, and the stirring time is 5 min.

[0025] In step 4, the flat box-shaped base and the two U-groove-shaped shells are both made by 3D printing.

[0026] In the step 5, the sphere with holes is made of acrylic.

[0027] When working, it is equipped with a power supply and four switches. The four serpentine electric heating coils and the four switches are connected in series one by one to form four series branches. The two ends of each series branch are respectively connected to the two output ends of the power supply.

[0028] The specific working process is as follows: First, in the initial state, all four switches are off, the four serpentine heating coils are de-energized, and the four thermoplastic polyurethane elastomer mesh structures are in a solid state. At this point, the four thermoplastic polyurethane elastomer mesh structures exert a restraining force on the muscle strip, thereby limiting the stretchability of the muscle strip. Second, to initiate bending, two or three adjacent thermoplastic polyurethane elastomer mesh structures are selected as heating targets. The two or three switches corresponding to the heating targets are then closed, energizing and heating the two or three serpentine heating coils corresponding to the heating targets. The heat generated is transferred to the heating targets, melting them into a liquid state. This releases the restraining force exerted by the heating targets on the muscle strip, allowing the muscle strip to regain its stretchability in the direction corresponding to the heating targets. Next, air is inflated through the air tube into the strip air cavity and several spherical air cavities. Under the action of the air pressure, the muscle strip expands in the direction corresponding to the heating targets, thereby performing bending motion in the direction corresponding to the unheated thermoplastic polyurethane elastomer mesh structures. During this process, the bending angle can be controlled by controlling the air pressure. By selecting two or three different thermoplastic polyurethane elastomer grid structures as heating objects, bending movements in different directions can be achieved, thereby achieving control of the bending direction.

[0029] Compared with existing flexible pneumatic muscles, the flexible pneumatic muscle with controllable bending direction described in the present invention utilizes the influence of the physical state change of the thermoplastic polyurethane elastomer grid structure on the strip muscle body (when the thermoplastic polyurethane elastomer grid structure is in a solid state, the thermoplastic polyurethane elastomer grid structure exerts a restrictive force on the strip muscle body, thereby limiting the tensile properties of the strip muscle body. When the thermoplastic polyurethane elastomer grid structure is in a liquid state, the restrictive force of the thermoplastic polyurethane elastomer grid structure on the strip muscle body is released, thereby allowing the strip muscle body to restore its tensile properties), not only realizing the control of the bending angle, but also realizing the control of the bending direction, thereby effectively expanding the scope of application.

[0030] The present invention effectively solves the problem of uncontrollable bending direction of existing flexible pneumatic muscles and is suitable for flexible robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the three-dimensional structure of a flexible pneumatic muscle with controllable bending direction in the present invention.

[0032] Figure 2 It is a schematic diagram of the cross-sectional structure of a flexible pneumatic muscle with controllable bending direction in the present invention.

[0033] Figure 3 It is a schematic diagram of the three-dimensional structure of the metal substrate and the grid-shaped channel in the present invention.

[0034] Figure 4 It is a schematic diagram of the three-dimensional structure of the thermoplastic polyurethane elastomer grid structure in the present invention.

[0035] Figure 5 It is a schematic diagram of the three-dimensional structure of the serpentine electric heating coil in the present invention.

[0036] Figure 6 It is a schematic diagram of the cross-sectional structure of the strip-shaped encapsulation layer in the present invention.

[0037] Figure 7 yes Figure 6 Top view of .

[0038] Figure 8 It is a schematic diagram of the three-dimensional structure of the casting mold in the present invention.

[0039] Figure 9 It is a schematic diagram of the three-dimensional structure of the air cavity mold in the present invention.

[0040] In the figure: 1-strip muscle body, 2-strip air cavity, 3-spherical air cavity, 4-trachea, 5-thermoplastic polyurethane elastomer grid structure, 6-snake-shaped electric heating coil, 7-metal base, 8-grid-shaped channel, 9-strip encapsulation layer, 10-flat box-shaped base, 11-U-trough shell, 12-wooden stick, 13-sphere with hole. DETAILED DESCRIPTION

[0041] A flexible pneumatic muscle with controllable bending direction, comprising a strip-shaped muscle body 1 with a square cross-section and made of Ecoflex00-50; a strip-shaped air cavity 2 and a plurality of spherical air cavities 3 are coaxially opened inside the strip-shaped muscle body 1; the front end of the strip-shaped air cavity 2 is closed, and the rear end passes through the rear end surface of the strip-shaped muscle body 1; each spherical air cavity 3 is cross-connected with the strip-shaped air cavity 2, and each spherical air cavity 3 is arranged at equal distances; the rear end opening edge of the strip-shaped air cavity 2 is sealed and connected to a trachea 4; four thermoplastic polyurethane elastomer grid structures 5 and four A serpentine electric heating coil 6 is wound with a nickel-chromium alloy resistance wire; four thermoplastic polyurethane elastomer grid structures 5 are parallel to the four side surfaces of the strip muscle body 1, and the four thermoplastic polyurethane elastomer grid structures 5 are symmetrically distributed around the center line of the strip muscle body 1; four serpentine electric heating coils 6 are arranged in parallel on the outside of the four thermoplastic polyurethane elastomer grid structures 5, and the four serpentine electric heating coils 6 are symmetrically distributed around the center line of the strip muscle body 1; both ends of each serpentine electric heating coil 6 pass through the rear end surface of the strip muscle body 1 and are led outward.

[0042] A method for preparing a flexible pneumatic muscle with controllable bending direction (the method is used to prepare the flexible pneumatic muscle with controllable bending direction described in the present invention), the method is implemented by the following steps:

[0043] Step 1: Prepare a thermoplastic polyurethane elastomer grid structure 5; the specific steps are as follows:

[0044] Step 1.1: First, a grid-shaped groove 8 is machined on the metal substrate 7 using a laser marking machine, and then the grid-shaped groove 8 is polished smooth using a grinding device, and then the grid-shaped groove 8 is filled with thermoplastic polyurethane elastomer powder;

[0045] Step 1.2: First, heat the metal substrate 7 on an 80°C drying table for 10 minutes to melt the thermoplastic polyurethane elastomer powder in the grid-shaped channels 8 into a molten thermoplastic polyurethane elastomer. Then, cool the metal substrate 7 at room temperature for 20 minutes to solidify the molten thermoplastic polyurethane elastomer in the grid-shaped channels 8 into a thermoplastic polyurethane elastomer grid structure 5. Then, remove the thermoplastic polyurethane elastomer grid structure 5.

[0046] Step 2: Mix Ecoflex00-50 component A and Ecoflex00-50 component B in a mass ratio of 1:1 and stir evenly to prepare an Ecoflex00-50 prepolymer mixture; the Ecoflex00-50 component A is a platinum-catalyzed silicone rubber matrix; the Ecoflex00-50 component B is a platinum-catalyzed silicone rubber curing agent;

[0047] Step 3: Prepare the strip-shaped encapsulation layer 9; the specific steps are as follows:

[0048] First, the Ecoflex00-50 prepolymer mixture is injected into the mold, and then the thermoplastic polyurethane elastomer grid structure 5 and the serpentine electric heating coil 6 made of nickel-chromium alloy resistance wire are immersed in the Ecoflex00-50 prepolymer mixture, and then cured and formed to obtain a strip-shaped encapsulation layer 9;

[0049] Step 4: Prepare the casting mold;

[0050] The casting mold includes a flat box-shaped base 10 and two U-trough-shaped shells 11; the upper end of the flat box-shaped base 10 is open; the notches of the two U-trough-shaped shells 11 are connected to each other, and the two U-trough-shaped shells 11 are embedded in the flat box-shaped base 10; the two U-trough-shaped shells 11 and the flat box-shaped base 10 together enclose a strip-shaped casting cavity;

[0051] Step 5: Prepare the air cavity mold;

[0052] The air cavity mold includes a wooden stick 12 and a plurality of spheres 13 with holes; each sphere 13 with holes is sleeved on the wooden stick 12, and each sphere 13 with holes is arranged at equal distances;

[0053] Step 6: Prepare the strip muscle body 1; the specific steps are as follows:

[0054] Step 6.1: Select four strip-shaped encapsulation layers 9 and attach the first to third strip-shaped encapsulation layers 9 to the bottom, left, and right sides of the strip-shaped casting cavity in a one-to-one correspondence;

[0055] Step 6.2: First, pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity, then place the air cavity mold into the strip casting cavity, and then continue to pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity until the Ecoflex00-50 prepolymer mixture covers the air cavity mold, and then place the fourth strip encapsulation layer 9 on top of the Ecoflex00-50 prepolymer mixture;

[0056] Step 6.3: First, heat the casting mold in a 60°C oven for 30 minutes to solidify the Ecoflex 00-50 prepolymer mixture and the four strip-shaped encapsulation layers 9 into one, thereby forming the strip-shaped muscle body 1. The casting mold is then allowed to cool at room temperature for 20 minutes. The flat box-shaped base 10 is then peeled off from the strip-shaped muscle body 1, and the two U-grooved shells 11 are then peeled off from the strip-shaped muscle body 1 to remove the strip-shaped muscle body 1.

[0057] Step seven: First, a hole is opened on the rear end face of the strip muscle body 1, and then the wooden stick 12 is pulled out through the hole. The hole and the cavity formed after the wooden stick 12 is pulled out together constitute the strip air cavity 2. Then, each perforated sphere 13 is squeezed out through the hole. The cavities formed after the extrusion of each perforated sphere 13 constitute each spherical air cavity 3 one by one. Then, the trachea 4 is bonded to the edge of the rear end hole of the strip air cavity 2 with an adhesive, thereby obtaining a flexible pneumatic muscle with controllable bending direction.

[0058] In the step 1, the metal substrate 7 is made of aluminum and has a thickness of 3 mm.

[0059] In the step 2, the mass of Ecoflex00-50 component A and the mass of Ecoflex00-50 component B are both 30 g, and the stirring time is 5 min.

[0060] In step 4, the flat box-shaped base 10 and the two U-groove-shaped shells 11 are both manufactured by 3D printing.

[0061] In the step 5, the sphere 13 with holes is made of acrylic.

[0062] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A flexible pneumatic muscle with controllable bending direction, characterized by: The invention comprises a strip muscle body (1) with a square cross section and made of Ecoflex00-50; a strip air cavity (2) and a plurality of spherical air cavities (3) are coaxially opened inside the strip muscle body (1); the front end of the strip air cavity (2) is closed, and the rear end passes through the rear end surface of the strip muscle body (1); each spherical air cavity (3) is cross-connected with the strip air cavity (2), and each spherical air cavity (3) is arranged at equal distances; the rear end opening edge of the strip air cavity (2) is sealed and connected to a trachea (4); four thermoplastic polyurethane elastomer grid structures (5) and four nickel-chromium alloy A serpentine electric heating coil (6) wound with a resistance wire; four thermoplastic polyurethane elastomer grid structures (5) are parallel to the four side surfaces of the strip muscle body (1) in a one-to-one correspondence, and the four thermoplastic polyurethane elastomer grid structures (5) are symmetrically distributed around the center line of the strip muscle body (1); four serpentine electric heating coils (6) are arranged in parallel on the outside of the four thermoplastic polyurethane elastomer grid structures (5) in a one-to-one correspondence, and the four serpentine electric heating coils (6) are symmetrically distributed around the center line of the strip muscle body (1); both ends of each serpentine electric heating coil (6) pass through the rear end surface of the strip muscle body (1) and are led outward.

2. A method for preparing a flexible pneumatic muscle with controllable bending direction, the method being used to prepare the flexible pneumatic muscle with controllable bending direction as claimed in claim 1, characterized in that: This method is implemented using the following steps: Step 1: Prepare a thermoplastic polyurethane elastomer grid structure (5); the specific steps are as follows: Step 1.1: First, a grid-shaped groove (8) is processed on the metal substrate (7) using a laser marking machine, and then the grid-shaped groove (8) is polished smooth using a polishing device, and then thermoplastic polyurethane elastomer powder is filled into the grid-shaped groove (8); Step 1.2: First, the metal substrate (7) is placed on a drying table at 80°C and heated for 10 minutes, so that the thermoplastic polyurethane elastomer powder in the grid-shaped channel (8) melts into a molten thermoplastic polyurethane elastomer. Then, the metal substrate (7) is placed at room temperature and cooled for 20 minutes, so that the molten thermoplastic polyurethane elastomer in the grid-shaped channel (8) solidifies into a thermoplastic polyurethane elastomer grid structure (5). Then, the thermoplastic polyurethane elastomer grid structure (5) is taken out. Step 2: Mix Ecoflex00-50 component A and Ecoflex00-50 component B in a mass ratio of 1:1 and stir evenly to prepare an Ecoflex00-50 prepolymer mixture; the Ecoflex00-50 component A is a platinum-catalyzed silicone rubber matrix; the Ecoflex00-50 component B is a platinum-catalyzed silicone rubber curing agent; Step 3: Prepare a strip-shaped encapsulation layer (9); the specific steps are as follows: First, the Ecoflex00-50 prepolymer mixture is injected into the mold, and then the thermoplastic polyurethane elastomer grid structure (5) and the serpentine electric heating coil (6) made of nickel-chromium alloy resistance wire are immersed in the Ecoflex00-50 prepolymer mixture, and then cured and formed to obtain a strip-shaped packaging layer (9); Step 4: Prepare the casting mold; The casting mold comprises a flat box-shaped base (10) and two U-trough-shaped shells (11); the upper end of the flat box-shaped base (10) is provided with an opening; the notches of the two U-trough-shaped shells (11) are butted against each other, and the two U-trough-shaped shells (11) are embedded in the flat box-shaped base (10); the two U-trough-shaped shells (11) and the flat box-shaped base (10) together enclose a strip-shaped casting cavity; Step 5: Prepare the air cavity mold; The air cavity mold comprises a wooden stick (12) and a plurality of spheres with holes (13); each sphere with holes (13) is sleeved on the wooden stick (12), and each sphere with holes (13) is arranged at equal distances; Step 6: Prepare the strip muscle body (1); the specific steps are as follows: Step 6.1: Select four strip-shaped packaging layers (9), and attach the first to third strip-shaped packaging layers (9) to the bottom, left, and right sides of the strip-shaped casting cavity in a one-to-one correspondence; Step 6.2: First, pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity, then place the air cavity mold into the strip casting cavity, and then continue to pour the Ecoflex00-50 prepolymer mixture into the strip casting cavity, so that the Ecoflex00-50 prepolymer mixture covers the air cavity mold, and then place the fourth strip packaging layer (9) on top of the Ecoflex00-50 prepolymer mixture; Step 6.3: First, place the casting mold in a 60°C oven and heat it for 30 minutes to solidify the Ecoflex00-50 prepolymer mixture and the four strip-shaped encapsulation layers (9) into one body, thereby obtaining the strip-shaped muscle body (1). Then, place the casting mold at room temperature to cool for 20 minutes, then peel off the flat box-shaped base (10) from the strip-shaped muscle body (1), and then peel off the two U-groove-shaped shells (11) from the strip-shaped muscle body (1), thereby removing the strip-shaped muscle body (1); Step 7: First, a hole is opened on the rear end surface of the strip muscle body (1), and then the wooden stick (12) is pulled out through the hole. The hole and the cavity formed after the wooden stick (12) is pulled out together constitute the strip air cavity (2). Then, each perforated sphere (13) is extruded through the hole. The cavities formed after the extrusion of each perforated sphere (13) constitute each spherical air cavity (3) in a one-to-one correspondence. Then, the trachea (4) is bonded to the edge of the rear end opening of the strip air cavity (2) using an adhesive, thereby obtaining a flexible pneumatic muscle with controllable bending direction.

3. The method for preparing a flexible pneumatic muscle with controllable bending direction according to claim 2, characterized in that: In the step 1, the metal base (7) is made of aluminum and has a thickness of 3 mm.

4. The method for preparing a flexible pneumatic muscle with controllable bending direction according to claim 2, characterized in that: In the step 2, the mass of Ecoflex00-50 component A and the mass of Ecoflex00-50 component B are both 30 g, and the stirring time is 5 min.

5. The method for preparing a flexible pneumatic muscle with controllable bending direction according to claim 2, characterized in that: In step 4, the flat box-shaped base (10) and the two U-groove-shaped shells (11) are both manufactured by 3D printing.

6. The method for preparing a flexible pneumatic muscle with controllable bending direction according to claim 2, characterized in that: In the step 5, the sphere with holes (13) is made of acrylic.

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