Single-lens direct focusing 3D printing system for increasing focusing spot temperature

Abstract

The invention discloses a single-lens direct focusing 3D printing system for increasing the temperature of a focusing light spot, and belongs to the technical field of 3D printing. The system comprises a solar condensation light path subsystem and a photo-thermal 3D printing subsystem; the photo-thermal 3D printing subsystem comprises a wire feeding module and a printing module, the wire feeding module is used for providing printing supplies for the printing module, and the printing module comprises a three-axis movement mechanism and a printing platform. The three-axis movement mechanism is used for driving the printing platform to move on the horizontal plane and driving the circular point focusing type Fresnel lens to move up and down, the sun-tracking platform is connected with the double-axis tracking device, and the double-axis tracking device is used for driving the sun-tracking platform to rotate so that the sun-tracking platform can face the sun. The solar condensation light path subsystem is used for tracking, collecting and converging sunlight to the circular point focusing type Fresnel lens. The structure can reduce light energy loss and improve the temperature of a focusing light spot.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing, and particularly relates to a single-lens direct focusing 3D printing system for increasing the temperature of a focused light spot. Background Art

[0002] Single-lens direct focusing 3D printing uses a solar tracking and collection system to directly focus solar energy as the heat source for 3D printing forming. In the process of converging sunlight, multiple optical fibers are often used to refract sunlight for transmission. However, during the transmission process, the sunlight needs to be refracted multiple times by the optical fibers, resulting in serious heat loss. Now, a structure that can reduce light energy loss and increase the temperature of the focused light spot is proposed. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention provides a single-lens direct focusing 3D printing system for increasing the temperature of a focused light spot, and solves the above problems.

[0004] To achieve the above objectives, the present invention is realized through the following technical solutions: A solar concentrating light path subsystem and a photothermal 3D printing subsystem; The photothermal 3D printing subsystem includes a wire feeding module and a printing module. The wire feeding module is used to provide printing consumables for the printing module. The printing module includes a three-axis motion mechanism and a printing platform. The three-axis motion mechanism is used to drive the printing platform to move on a horizontal plane and drive a circular point-focusing Fresnel lens to move up and down. The heliostat platform is connected to a two-axis tracking device, and the two-axis tracking device is used to drive the heliostat platform to rotate so that the heliostat platform faces the sun; The solar concentrating light path subsystem is used to track, collect, and converge sunlight to a circular point-focusing Fresnel lens.

[0005] On the basis of the above technical solutions, the present invention also provides the following optional technical solutions: Further technical solution: The wire feeding module includes a wire feeder and a wire feeding nozzle. The wire outlet of the wire feeder is connected to the wire feeding nozzle through a wire feeding tube to ensure the accuracy of directional wire feeding. The wire feeder is provided with 3D printing wire materials. The wire feeding nozzle is fixed on a lens support through a universal clamp to ensure that the light spot always remains in the same position as the wire feeding nozzle.

[0006] Further technical solution: The wire feeder includes a control part and a driving part. The control part provides a visual parameter setting function to adjust parameters such as wire feeding speed, wire feeding interval, and wire returning speed to adapt to different printing requirements. The driving part performs wire feeding drive according to the instructions of the control part to ensure the accuracy and stability of wire feeding.

[0007] Further technical solution: The central control subsystem includes a power supply module and a control module. The power supply module includes a solar panel and a solar battery, and the solar panel is connected to the solar battery.

[0008] Further technical solution: The control module includes an industrial personal computer, and the industrial personal computer is connected to the solar concentrator optical path subsystem and the photothermal D printing subsystem.

[0009] Further technical solution: It includes a heliostat module, a converging module, and a light control module. The heliostat module includes a photoelectric sensor and a heliostat platform. There are four identical silicon photovoltaic panels on the photoelectric sensor, and the silicon photovoltaic panels are respectively placed in four quadrants divided by baffles. The converging module is installed on the heliostat platform, and the photoelectric sensor is installed on the converging module.

[0010] Further technical solution: The heliostat platform is connected to a two-axis tracking device. The two-axis tracking device is used to control the rotation of the heliostat platform. The photoelectric sensor is connected to the two-axis tracking device. The two-axis tracking device is connected to a square protection frame. The photoelectric sensor converts the optical signal into an electrical signal and collects it. After the electrical signal is collected, the data is transmitted to the main controller through an analog-to-digital conversion circuit. The main controller then releases a signal to drive the two-axis tracking device to move and adjust the position of the photoelectric sensor through corresponding analysis and comparison.

[0011] Further technical solution: The two-axis tracking device has two built-in motors. An electric push rod and a rotating central axis are respectively connected to the two-axis tracking device. Any one of the motors is connected to the rotating central axis and is used to drive the rotating central axis in the horizontal direction. The rotating central axis is hinged to the heliostat platform. The other motor is connected to the electric push rod and is used to drive the electric push rod to extend or shorten in the vertical direction. The electric push rod is slidably hinged to the heliostat platform through a bearing, and the azimuth angle is perpendicular to the elevation angle.

[0012] Further technical solution: The converging module includes a circular point-focus Fresnel lens and a lens bracket. The circular point-focus Fresnel lens is used to converge sunlight to create a heat source. The circular point-focus Fresnel lens is fixed to the lens bracket by a buckle. A photoelectric sensor is installed on the lens bracket, and the silicon photovoltaic panel in the photoelectric sensor is parallel to the circular point-focus Fresnel lens, so that when sunlight is perpendicularly incident on the photoelectric sensor, it is also perpendicularly incident on the circular point-focus Fresnel lens.

[0013] Further technical solution: The light control module includes a light shielding plate and a variable aperture. The light shielding plate is connected to the circular point-focus Fresnel lens. The variable aperture is installed on the bottom plate, and the bottom plate is fixedly connected to the lens bracket. The bottom plate is made of an aluminum alloy plate with a certain stiffness to ensure the parallelism of the variable aperture. A circular hole is provided in the middle of the light shielding plate, and the central axis of the variable aperture coincides with the central axis of the circular point-focus Fresnel lens.

[0014] Beneficial effects The present invention provides a single-lens direct focusing D printing system, which has the following beneficial effects compared with the prior art: When sunlight shines obliquely on the silicon photovoltaic panel, there is a deviation in the sunlight received by the photoelectric sensor. At this time, the four silicon photovoltaic panels receive different light intensities. When sunlight is vertically incident, the four silicon photovoltaic panels receive the same light intensity. When the light intensities received by each quadrant are different, different voltages are generated. The main controller collects the voltage deviation signal, and the analog-digital circuit amplifies the signal. According to the photoelectric tracking algorithm, it drives and controls the movement of the two-axis tracking device, and then makes the heliostat platform move in the horizontal and pitching directions until the sunlight is vertically incident on the photoelectric sensor, so that each silicon photovoltaic cell receives the same light. At this time, the heliostat platform faces the sun, and the heliostat is completed. After the heliostat is completed, the printing module and the converging module also face the sun, and the sunlight can be vertically incident on the circular point-focus Fresnel lens, thereby generating a high-energy and high-heat solar spot. At this time, the wire feeding module accurately sends the D printing consumables to the focused spot for fuse deposition forming. The direct focusing of a single large-area circular point-focus Fresnel lens greatly reduces the loss in light refraction. During this process, the wire feeding nozzle and the circular point-focus Fresnel lens move in coordination to achieve that when the focused spot moves, the wire feeding nozzle follows its movement, and the relative position between the focused spot and the wire feeding nozzle remains unchanged. Description of the drawings

[0015] Figure 1 It is a three-dimensional structure schematic diagram of the present invention.

[0016] Figure 2 It is an enlarged schematic diagram of the lens structure of the present invention.

[0017] Figure 3 It is a side view structure schematic diagram of the present invention.

[0018] Figure 4 It is a schematic diagram of the solar concentrating light path subsystem process of the present invention.

[0019] Figure 5 It is a schematic diagram of the light path incident angle of the present invention.

[0020] Figure 6 It is a schematic diagram of the photoelectric tracking algorithm of the present invention.

[0021] Annotation of reference numerals: Photoelectric sensor 1, heliostat platform 2, silicon photovoltaic panel 3, baffle 4, two-axis tracking device 5, rotating central axis 6, electric push rod 7, circular point-focus Fresnel lens 8, lens bracket 9, light baffle 10, variable aperture 11, bottom plate 12, printing platform 13, wire feeder 14, wire feeding nozzle 15, solar battery 16, industrial control all-in-one computer 17, square protection frame 18, three-axis motion mechanism 19, solar panel 20. Detailed implementation mode

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0024] Please refer to Figure 1 、 Figure 2 and Figure 5 , which is provided for the single-lens direct focusing 3D printing system for improving the temperature of the focused spot in the embodiment of the present invention, includes a square protection frame 18, and also includes: Solar concentrating optical path subsystem, which is used to track, collect and converge sunlight, so that parallel sunlight is focused to the photothermal 3D printing platform; Photothermal 3D printing subsystem, which accurately sends the printing consumables to the spot for melting and deposition, and the printing platform moves in the XY direction according to a preset path; Central control subsystem, which is used to supply power to the whole system and control the process parameters in each printing process through visual operation; The solar concentrating optical path subsystem includes a heliostat module, a converging module and a light control module. The heliostat module is used to determine the sun's azimuth so that the converging module always faces the sun; the converging module is used to collect and converge sunlight to generate a high-energy and high-heat sunlight spot; and the light control module is used to control the light flux; the heliostat module includes a photoelectric sensor 1 and a heliostat platform 2. Four identical silicon photovoltaic panels 3 are provided on the photoelectric sensor 1. The photoelectric sensor 1 is divided into four quadrants by a baffle 4, and the four silicon photovoltaic panels 3 are respectively placed in the four quadrants divided by the baffle 4. The converging module is installed on the heliostat platform 2, and the photoelectric sensor 1 is installed on the converging module.

[0025] Please refer to Figure 1 Specifically, the heliostat platform 2 is connected to the two-axis tracking device 5, the two-axis tracking device 5 is used to control the rotation of the heliostat platform 2, the photoelectric sensor 1 is connected to the two-axis tracking device 5, and the two-axis tracking device 5 is slidably connected to the square protection frame 18.

[0026] Please refer to Figure 6 Specifically, the photoelectric sensor 1 converts the optical signal into a voltage deviation signal through a voltage deviation calculation formula and collects it. After the voltage deviation signal is collected, the data is transmitted to the main controller through an analog-to-digital conversion circuit. The voltage deviation calculation method is as follows: The main controller drives the two-axis tracking device 5 to move according to the photoelectric tracking algorithm, adjusts the position of the photoelectric sensor 1 to face the sun directly, so as to increase the spot heat.

[0027] Please refer to Figure 3 Specifically, the two-axis tracking device 5 is built-in with two motors. An electric push rod 7 and a rotating central axis 6 are respectively connected to the two-axis tracking device 5 for making sunlight vertically incident on the circular point focusing Fresnel lens 8. Any one of the motors is connected to the rotating central axis 6 for driving the rotating central axis 6 to rotate in the horizontal direction. The rotating central axis 6 is hinged to the heliostat platform 2; Please refer to Figure 3 Specifically, the other motor is connected to the electric push rod 7 for driving the electric push rod 7 to extend or shorten in the vertical direction; the electric push rod 7 is slidably hinged to the heliostat platform 2 through a bearing.

[0028] Please refer to Figure 1 and Figure 2 Specifically, the converging module includes a circular point focusing Fresnel lens 8 and a lens bracket 9. The circular point focusing Fresnel lens 8 is used to converge sunlight to create a heat source. The circular point focusing Fresnel lens 8 is fixed on the lens bracket 9 through a buckle.

[0029] Please refer to Figure 2 and Figure 3 Specifically, a photoelectric sensor 1 is installed on the lens bracket 9. The silicon photovoltaic panel 3 in the photoelectric sensor 1 is parallel to the circular point focusing Fresnel lens 8, and is used for when sunlight is vertically incident on the photoelectric sensor 1, it is also vertically incident on the circular point focusing Fresnel lens 8.

[0030] Please refer to Figure 2 and Figure 3 Specifically, the light control module includes a light baffle 10 and a variable aperture 11. The light baffle 10 is connected to the circular point focusing Fresnel lens 8. The variable aperture 11 is installed on the bottom plate 12. The bottom plate 12 is fixedly connected to the lens bracket 9.

[0031] Please refer to Figure 2. Specifically, the bottom plate 12 is made of an aluminum alloy plate with a certain stiffness to ensure the parallelism of the variable aperture 11. The maximum diameter of the light passing aperture of the variable aperture 11 is 36 mm, and the minimum diameter is 1.8 mm. The material is aluminum alloy. A circular hole is provided in the middle of the light blocking plate 10. By placing light blocking sheets with different apertures on the circular hole, the circular point-focus Fresnel lens 8 is blocked to achieve the purpose of light shielding, reducing the light flux, and controlling the optical power. The central axis of the variable aperture 11 coincides with the central axis of the circular point-focus Fresnel lens 8. When the variable aperture 11 is closed, the aperture blades block the solar focused beam, and at this time the light flux is 0%. When the variable aperture 11 is opened, the aperture blades do not block the solar focused beam, and at this time the light flux is 100%. Thus, during the opening and closing process of the variable aperture 11, a change in the light flux from 0% to 100% can be achieved, and the optical power can be controlled. The specific optical parameters of the circular point-focus Fresnel lens 8 are as follows: Table 1 Optical Parameters of the Circular Point-Focus Fresnel Lens Please refer to Figure 1 and Figure 2 Specifically, the photothermal 3D printing subsystem includes a wire feeding module and a printing module. The printing module includes a three-axis motion mechanism 19 and a printing platform 13. The three-axis motion mechanism 19 is fixedly connected to the heliostat platform 2. The central position of the heliostat platform 2 coincides with the Y-axis center of the three-axis motion mechanism 19. The printing platform 13 is connected to the X-axis of the three-axis motion mechanism 19 to drive the printing platform 13 to move in the XY directions. The Z-axis on the three-axis motion mechanism 19 is fixedly connected to the lens support 9 to drive the circular point-focus Fresnel lens 8 to move in the up and down directions, providing conditions for studying the influence of different off-focus distances on the light spot. The wire feeding module includes a wire feeder 14 and a wire feeding nozzle 15. The wire outlet of the wire feeder 14 is connected to the wire feeding nozzle 15 through a wire feeding tube to ensure the accuracy of directional wire feeding. The wire feeder 14 is provided with 3D printing wire. The wire feeding nozzle 15 is fixed on the lens support 9 through a universal clamp to ensure that the light spot always remains in the same position as the wire feeding nozzle.

[0032] Please refer to Figure 1 and Figure 2, specifically, the wire feeder 14 includes a control part and a driving part. The control part provides a visual parameter setting function to adjust parameters such as wire feeding speed, wire feeding interval, and wire returning speed to adapt to different printing requirements. The driving part drives wire feeding according to the instructions of the control part to ensure the accuracy and stability of wire feeding. The driving power comes from a motor. The driving part consists of an adjustable pre-tightening force lever, a driving gear, and a driven gear. Among them, the adjustable pre-tightening force lever is used to tightly press the wire material, and the handle can be rotated to adjust the pressing degree. The 3D printing wire material enters through the feeding port on the wire feeder, then passes through the connecting pipe on the fixing block, and is sent out from the discharging port via the wire feeding wheel and the guiding wheel. The wire feeding wheel and the guiding wheel are respectively coaxially fixed on the driving wheel and the driven wheel. The limitation of the wire material diameter can be adjusted by adjusting the pre-tightening force lever.

[0033] Please refer to Figure 1 , specifically, the central control subsystem includes a power supply module and a control module. The power supply module includes a solar panel 20 and a solar battery 16. The solar panel 20 is connected to the solar battery 16. The solar panel 20 converts sunlight into direct current and transmits the electric energy to the solar battery 16 for storage. The battery can store chemical energy. When power is needed, the chemical energy stored in it is converted into electric energy for the device to use. The control module includes an industrial personal computer 17. The industrial personal computer 17 is connected to the solar concentrating optical path subsystem and the photothermal 3D printing subsystem, and is used to control the process parameters in each printing process through Mach3 software.

[0034] In the embodiment of the present invention, when sunlight shines obliquely on the silicon photovoltaic panel 3, there is a deviation in the sunlight received by the photoelectric sensor 1. At this time, the four silicon photovoltaic panels 3 receive different light intensities. When sunlight is vertically incident, the four silicon photovoltaic panels 3 receive the same light intensity. When the light intensities received by each quadrant are different, different voltages are generated. The main controller collects the voltage deviation signal, and the analog-digital circuit amplifies the signal. According to the photoelectric tracking algorithm, it drives and controls the movement of the two-axis tracking device, and then makes the heliostat platform 2 move in the horizontal and pitching directions until the sunlight is vertically incident on the photoelectric sensor 1, so that each silicon photovoltaic panel 3 receives the same light, and at this time the heliostat platform faces the sun to complete the heliostat. When the heliostat is completed, the printing module and the converging module also face the sun, and the sunlight can be vertically incident on the circular point-focusing Fresnel lens 8, thereby generating a high-energy and high-heat solar spot. At this time, the wire feeding module accurately sends the 3D printing consumables to the focusing spot for fused deposition molding. The direct focusing of the single-piece large-area circular point-focusing Fresnel lens 8 greatly reduces the loss in light refraction. During this process, the wire feeding nozzle 15 and the circular point-focusing Fresnel lens 8 move in coordination to achieve that when the focusing spot moves, the wire feeding nozzle 15 follows its movement, and the relative position between the focusing spot and the wire feeding nozzle 15 remains unchanged.

[0035] It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0036] The fixed connection referred to in this application means a connection where there is no relative movement after the parts or components are fixed. It is divided into two types: detachable connection and non-detachable connection.

[0037] (1) Detachable connection: The parts are fixed together by using screws, splines, wedge pins, etc. This type of connection can be disassembled during maintenance and will not damage the parts. However, the specifications of the connecting parts used must be correct (such as the length of bolts, keys, wedge pins), and tightened appropriately.

[0038] (2) Non-detachable connection: mainly refers to welding, riveting, and mortise fitting, etc. Since it needs to be forged, sawed, or oxy-cut to be disassembled during maintenance or replacement, the spare parts generally cannot be used a second time. At the same time, during the connection, attention should be paid to the process quality, technical inspection, and remedial measures (such as correction, polishing, etc.).

[0039] The sliding connection referred to in this application means that a component can slide along a linear trajectory, and the hinged connection referred to in this application means that a component can rotate along an axial constraint.

[0040] In some cases, the sliding connection and the hinged connection referred to in this application can also be damped, so that the component has the ability to maintain at the desired position.

[0041] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A single lens direct focusing 3D printing system for increasing the temperature of a focused light spot, characterized in that: include: Solar concentrating optical path subsystem and photothermal 3D printing subsystem; The photothermal 3D printing subsystem comprises a wire feeding module and a printing module, wherein the wire feeding module is used to provide printing consumables for the printing module, and the printing module comprises a three-axis motion mechanism (19) and a printing platform (13), wherein the three-axis motion mechanism (19) is used to drive the printing platform (13) to move on a horizontal plane and to drive the circular point-focusing Fresnel lens (8) to move up and down, and the heliostat platform (2) is connected to a dual-axis tracking device (5), and the dual-axis tracking device (5) is used to drive the heliostat platform (2) to rotate so that the heliostat platform (2) faces the sun; The solar concentrating optical path subsystem is used to track, collect and concentrate sunlight onto a circular point focusing Fresnel lens (8).

2. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 1, characterized in that: The wire feeding module comprises a wire feeding machine (14) and a wire feeding nozzle (15); a wire outlet of the wire feeding machine (14) is connected to the wire feeding nozzle (15) via a wire feeding tube to ensure the accuracy of directional wire feeding; a 3D printing wire is provided on the wire feeding machine (14); and the wire feeding nozzle (15) is fixed on a lens bracket (9).

3. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 2, characterized in that: The wire feeder (14) comprises a control part and a drive part, wherein the control part provides a visual parameter setting function so as to adjust the wire feeding speed, wire feeding interval and wire rewinding speed parameters to adapt to different printing requirements, and the drive part performs wire feeding driving according to the instructions of the control part.

4. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 1, characterized in that: The central control subsystem comprises a power supply module and a control module, the power supply module comprises a solar panel (20) and a solar storage battery (16), and the solar panel (20) is connected to the solar storage battery (16).

5. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 4, characterized in that: The control module comprises an industrial control all-in-one machine (17), and the industrial control all-in-one machine (17) is connected to a solar concentrating optical path subsystem and a photothermal 3D printing subsystem.

6. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 1, further comprising a light control module and a convergence module, wherein the light control module is used to control the light flux emitted by the convergence module, the heliostat module comprises a photoelectric sensor and a plurality of silicon photoelectric panels (3), the photoelectric sensor (1) is divided into a plurality of quadrants by a plurality of baffles (4), the plurality of silicon photoelectric panels (3) are respectively placed in the plurality of quadrants divided by the baffles (4), and the convergence module is mounted on the heliostat platform (2).

7. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 6, characterized in that: The dual-axis tracking device (5) is slidably connected to the square protection frame (18), and the photoelectric sensor (1) converts the optical signal into a voltage deviation signal through a voltage deviation calculation formula and collects the signal, wherein the voltage deviation calculation method is: After the voltage deviation signal is collected, the data is transmitted to the main controller through the analog-to-digital conversion circuit. The main controller releases a signal to drive the dual-axis tracking device (5) to move according to the photoelectric tracking algorithm, so as to adjust the position of the photoelectric sensor (1) so that the photoelectric sensor (1) always faces the sun.

8. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 7, characterized in that: The dual-axis tracking device (5) has two built-in motors. The dual-axis tracking device (5) is respectively connected to an electric push rod (7) and a rotating central axis (6). One motor is connected to the rotating central axis (6) and is used to drive the rotating central axis (6) to rotate in a horizontal direction. The rotating central axis (6) is hinged to the heliostat platform (2). The other motor is connected to the electric push rod (7) and is used to drive the electric push rod (7) to extend or shorten the vertical direction rod. The electric push rod (7) is slidably hinged to the heliostat platform (2) via a bearing.

9. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 6, characterized in that: The converging module comprises a circular point-focusing Fresnel lens (8) and a lens bracket (9); the circular point-focusing Fresnel lens (8) is used to converge sunlight to produce a heat source; the circular point-focusing Fresnel lens (8) is fixed on the lens bracket (9); a photoelectric sensor (1) is mounted on the lens bracket (9); a silicon photoelectric cell panel (3) in the photoelectric sensor (1) is parallel to the circular point-focusing Fresnel lens (8).

10. The single-lens direct focusing 3D printing system for increasing the temperature of the focused light spot according to claim 6, characterized in that: The light control module comprises a light blocking plate (10) and a variable iris (11), wherein the light blocking plate (10) is connected to a circular point-focusing Fresnel lens (8), the variable iris (11) is mounted on a base plate (12), the base plate (12) is fixedly connected to a lens bracket (9), a circular hole is provided in the middle of the light blocking plate (10), and the central axis of the variable iris (11) coincides with the central axis of the circular point-focusing Fresnel lens (8).

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