Warm ventilation pipe air tightness detection device

Abstract

The utility model relates to the technical field of heating and ventilation detection engineering, in particular to an air tightness detection device for a heating and ventilation pipe. The device comprises a first sealing plate, a second sealing plate, a first swing arm, a second swing arm, a fan and a sensor, a first rope hole is formed in the first sealing plate; a second rope hole and an air inlet are formed in the second sealing plate; the first swing arm is rotationally connected with the first sealing plate, an included angle is formed between the first swing arm and the first sealing plate, and a first pulley is arranged at the free end of the first swing arm; the second swing arm is rotationally connected with the second sealing plate, an included angle is formed between the second swing arm and the second sealing plate, and a second pulley is arranged at the free end of the second swing arm; an air outlet of the fan is communicated with the air inlet; the sensor is connected with a first cable body and a second cable body, the first cable body and the second cable body are matched with the first pulley and the second pulley respectively, and the free end of the first cable body and the free end of the second cable body penetrate through the first rope hole and the second rope hole respectively and are movably connected with the first rope hole and the second rope hole in a sealed mode. According to the application, the circumferential positioning of the leakage point in the air pipe can be realized.

Description

Technical Field

[0001] This application relates to the field of HVAC testing engineering technology, specifically to a device for testing the air tightness of HVAC ducts. Background Technology

[0002] There are two methods for testing the tightness of duct systems: If the manufacturing and installation processes are guaranteed, the light leakage method can be used; for medium and high-pressure systems, the air leakage test method should be used. The duct leakage tester mainly consists of a high-speed fan, a flow meter, and a tilting manometer. The duct section to be tested is sealed, the high-speed fan is connected to the duct, and the duct is connected to the tester with a flexible hose. The tester fan is started, and the frequency converter is adjusted to gradually increase the fan speed and the pressure in the test section. When the pressure reaches the required test pressure, it is stabilized. At this point, the air leakage of the test section equals the fan's supplementary airflow, and the negative pressure reading is directly displayed on the tilting manometer.

[0003] Existing duct inspection devices can detect leaks along the length of the duct, but they cannot determine the exact location of leaks in the circumferential direction, and the accuracy of leak location needs to be improved. Utility Model Content

[0004] The purpose of this application is to provide a device for testing the air tightness of heating and ventilation ducts, which aims to solve at least one of the technical problems existing in the prior art.

[0005] This application is achieved through the following technical solution:

[0006] A heating ventilation duct air tightness testing device, comprising:

[0007] The first sealing plate is used to seal and connect with one end of the air duct structure, and the first sealing plate has a first rope hole.

[0008] The second sealing plate is used to seal the connection with the other end of the duct structure. The second sealing plate is provided with a second rope hole and an air inlet.

[0009] The first swing arm is rotatably connected to the first sealing plate. The length direction of the first swing arm forms an angle with the surface of the first sealing plate. The free end of the first swing arm is provided with a first pulley.

[0010] The second swing arm is rotatably connected to the second sealing plate. The length direction of the second swing arm forms an angle with the surface of the second sealing plate. The free end of the second swing arm is provided with a second pulley.

[0011] A fan, wherein the air outlet of the fan is connected to the air inlet;

[0012] The sensor is connected to a first cable and a second cable, which respectively cooperate with a first pulley and a second pulley. The free ends of the first cable and the second cable respectively pass through the first rope hole and the second rope hole and are movably and sealingly connected to the first rope hole and the second rope hole. The sensor is used to detect the wind pressure and / or wind speed in the duct structure.

[0013] This application provides a HVAC duct airtightness testing device. The device seals both ends of the duct under test using a first and second sealing plate. A fan pressurizes the duct from the air inlet, creating a sealed testing environment. A first and second swing arm guide a cable connected to a sensor within the duct via pulleys. The angle between the swing arm and the sealing plate allows the sensor to scan synchronously along the duct's axial and circumferential directions. When a leak is detected, the sensor, pulled by the cable, accurately locates the leak's axial position and circumferential angle, achieving precise leak location across the entire three-dimensional space of the duct. This innovative device employs a structure where the mechanical swing arm and cable move in tandem, solving the problem of traditional testing methods being unable to determine the location of circumferential leaks. The testing process eliminates the need for segmented disassembly of the duct, significantly improving testing efficiency and positioning accuracy. It is particularly suitable for rapid airtightness testing of long-distance HVAC ducts.

[0014] In some alternative embodiments, the sensor is configured as a wind pressure sensor;

[0015] Alternatively, the sensor may be configured as a flow rate sensor;

[0016] Alternatively, the sensor may be configured as a multimodal detection unit including a wind speed sensor and a flow velocity sensor.

[0017] In some optional embodiments, the first swing arm is equipped with a first rotation drive source, and in the working state, the rotation center axis of the first swing arm coincides with the axis of the duct structure; and

[0018] The second swing arm is equipped with a second rotation drive source. In the working state, the rotation center axis of the second swing arm coincides with the axis of the duct structure.

[0019] In some optional embodiments, the first rope hole is coaxially arranged with the duct structure, wherein the first swing arm has a first cable hole along its length, and the free end of the first cable passes through the first cable hole and the first rope hole in sequence; and

[0020] The second rope hole is coaxially arranged with the air duct structure, wherein the second swing arm has a second wire hole along its length direction, and the free end of the second rope passes through the second wire hole and the second rope hole in sequence.

[0021] In some optional embodiments, the first rotation drive source is connected to the first sealing plate, wherein the first rotation drive source and the first swing arm are connected by a gear structure.

[0022] In some optional embodiments, the second rotation drive source is connected to the second sealing plate, wherein the second rotation drive source and the second swing arm are connected by a gear structure.

[0023] In some alternative embodiments, both the first and second swing arms are configured as telescopic arms.

[0024] In some alternative embodiments, the free ends of the first and second cables are respectively connected to a winding wheel.

[0025] In some alternative embodiments, the winding wheel is equipped with a servo motor.

[0026] In some optional embodiments, the number of first pulleys is configured to be two, and the axes of the two first pulleys are arranged in parallel, with the distance between the two first pulleys being less than the diameter of the first cable; and

[0027] The number of the second pulleys is configured to be two, and the axes of the two second pulleys are arranged in parallel, with the distance between the two second pulleys being less than the diameter of the second cable.

[0028] Compared with the prior art, this application has the following advantages and beneficial effects:

[0029] This application provides a HVAC duct airtightness testing device. The device seals both ends of the duct under test using a first and second sealing plate. A fan pressurizes the duct from the air inlet, creating a sealed testing environment. A first and second swing arm guide a cable connected to a sensor within the duct via pulleys. The angle between the swing arm and the sealing plate allows the sensor to scan synchronously along the duct's axial and circumferential directions. When a leak is detected, the sensor, pulled by the cable, accurately locates the leak's axial position and circumferential angle, achieving precise leak location across the entire three-dimensional space of the duct. This innovative device employs a structure where the mechanical swing arm and cable move in tandem, solving the problem of traditional testing methods being unable to determine the location of circumferential leaks. The testing process eliminates the need for segmented disassembly of the duct, significantly improving testing efficiency and positioning accuracy. It is particularly suitable for rapid airtightness testing of long-distance HVAC ducts. Attached Figure Description

[0030] The accompanying drawings, which are included to provide a further understanding of the embodiments of this application and form part of this application, do not constitute a limitation on the embodiments of this application. In the drawings:

[0031] Figure 1A schematic diagram of the working state structure of the heating and ventilation duct air tightness testing device provided in this application embodiment;

[0032] Figure 2 This is a schematic diagram of the cooperation structure between the first sealing plate and the first swing arm provided in an embodiment of this application;

[0033] Figure 3 This is a schematic diagram of the cooperation structure between the second sealing plate and the second swing arm provided in an embodiment of this application;

[0034] Figure 4 for Figure 2 A magnified structural diagram of point A in the middle.

[0035] The attached diagram shows the markings and corresponding component names:

[0036] 1-First sealing plate, 2-Second sealing plate, 3-First swing arm, 4-Second swing arm, 5-Fan, 6-First cable body, 7-Second cable body, 8-First pulley, 9-Second pulley, 10-First rotation drive source, 11-Second rotation drive source, 12-Air inlet, 13-First rope hole, 14-Second rope hole, 15-Winding wheel, 16-First wire hole, 17-Second wire hole, 18-Sensor, 19-Elastic rubber tube, 20-Support cylinder, 21-Bearing. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this application are only for explaining this application and are not intended to limit this application.

[0038] like Figures 1-3As shown in the figure, this application provides a heating and ventilation duct air tightness testing device, which includes a first sealing plate 1, a second sealing plate 2, a first swing arm 3, a second swing arm 4, a fan 5, and a sensor 18; it is used to seal and connect with one end of the duct structure, and the first sealing plate 1 has a first rope hole 13; the second sealing plate 2 is used to seal and connect with the other end of the duct structure, and the second sealing plate 2 has a second rope hole 14 and an air inlet 12; the first swing arm 3 is rotatably connected to the first sealing plate 1, and the length direction of the first swing arm 3 forms an angle with the plate surface of the first sealing plate 1, and the free end of the first swing arm 3 is provided with a first... A pulley 8; a second swing arm 4 is rotatably connected to a second sealing plate 2, the length direction of the second swing arm 4 forms an angle with the surface of the second sealing plate 2, and a second pulley 9 is provided at the free end of the second swing arm 4; the air outlet of the fan 5 is connected to the air inlet 12; a sensor 18 is connected to a first cable 6 and a second cable 7, the first cable 6 and the second cable 7 respectively cooperate with the first pulley 8 and the second pulley 9, the free ends of the first cable 6 and the second cable 7 respectively pass through the first rope hole 13 and the second rope hole 14 and are movably and sealingly connected to the first rope hole 13 and the second rope hole 14, and the sensor 18 is used to detect the wind pressure and / or wind speed in the duct structure.

[0039] In use, first place the sensor 18 in the duct structure. Then, pass the free ends of the first cable 6 and the second cable 7 on the sensor 18 around the first pulley 8 and the second pulley 9, and pass them through the first rope hole 13 and the second rope hole 14 on the first sealing plate 1 and the second sealing plate 2, respectively. Elastic rubber tubes 19 can be installed between the first cable 6 and the second cable 7 and the first rope hole 13 and the second rope hole 14 to ensure the sealing of the first cable 6 with the first rope hole 13 and the second cable 7 with the second rope hole 14. Adjust the angles of the first swing arm 3 and the second swing arm 4 so that the sensor 18 is positioned at the desired angle in the circumferential direction. Connect the first sealing plate 1 and the second sealing plate 2 to the length of the duct structure. On the flanges at both ends of the duct, the first cable 6 and the second cable 7 are tensioned. The fan 5 is started, and the first cable 6 or the second cable 7 is pulled to make the sensor 18 move along the axial direction of the duct. When a suspected leak point is detected at a certain position in the axial direction of the duct, the position of the free end of the first cable 6 or the second cable 7 is marked. Then the first sealing plate 1 and the second sealing plate 2 are opened and the angles of the first swing arm 3 and the second swing arm 4 are adjusted, so that the angular position of the sensor 18 in the circumferential direction is changed, thereby detecting the circumferential wind pressure and / or wind speed at the axial position of the duct. For example, the first swing arm 3 and the second swing arm 4 are rotated 90° each time. The specific location of the leak point in the circumferential direction is analyzed through four measurement results.

[0040] This application provides a HVAC duct airtightness testing device. The device seals both ends of the duct under test using a first sealing plate 1 and a second sealing plate 2. A fan 5 pressurizes the duct from the air inlet 12, creating a sealed testing environment. A first swing arm 3 and a second swing arm 4 guide a cable connected to a sensor 18 within the duct via pulleys. The angle between the swing arms and the sealing plates allows the sensor 18 to scan synchronously along the duct's axial and circumferential directions. When a leak is detected in the duct, the sensor 18, pulled by the cable, can accurately locate the leak's axial position and circumferential angle, achieving precise leak location within the duct's three-dimensional space. This innovative device employs a structure where the mechanical swing arms and cable move in tandem, solving the problem of traditional testing methods being unable to determine the location of circumferential leaks. The testing process eliminates the need for segmented disassembly of the duct, significantly improving testing efficiency and positioning accuracy. It is particularly suitable for rapid airtightness testing of long-distance HVAC ducts.

[0041] In some alternative embodiments, sensor 18 is configured as wind pressure sensor 18; or sensor 18 is configured as flow velocity sensor 18; or sensor 18 is configured to include a multimodal detection unit comprising wind speed sensor 18 and flow velocity sensor 18.

[0042] In this embodiment, the sensor 18 can be flexibly configured according to detection requirements: when using the wind pressure sensor 18, it can directly monitor pressure changes in the duct and quickly identify the pressure drop area caused by leakage; when using the flow velocity sensor 18, it can accurately locate the leak point through abnormal airflow velocity, which is especially suitable for micro-leak detection; and when configuring a multi-modal detection unit, it can simultaneously collect pressure and flow data, significantly improve detection accuracy through cross-validation, and reduce the false alarm rate. This modular sensor 18 design enables the device to adapt to different operating conditions (such as high-pressure / low-speed ducts), ensuring basic leak detection functions while achieving a more comprehensive airtightness assessment through multi-parameter fusion analysis.

[0043] In some optional embodiments, the first swing arm 3 is equipped with a first rotation drive source 10, and in the working state, the rotation center axis of the first swing arm 3 coincides with the axis of the duct structure; and the second swing arm 4 is equipped with a second rotation drive source 11, and in the working state, the rotation center axis of the second swing arm 4 coincides with the axis of the duct structure.

[0044] In this embodiment, by using the first rotation drive source 10 and the second rotation drive source 11, when the sensor 18 detects a leak at a certain position along the axial direction of the duct structure, the sensor 18 can be rotated circumferentially around the duct structure by the first rotation drive source 10 and the second rotation drive source 11. This eliminates the need to disassemble the first sealing plate 1 and the second sealing plate 2 to adjust the circumferential position of the sensor 18, making the detection process more convenient and improving detection efficiency. Furthermore, the first rotation drive source 10 and the second rotation drive source 11 enable precise angle control, allowing the sensor 18 to perform dense scanning of suspicious areas, thus improving the accuracy of leak location.

[0045] In some optional embodiments, the first rope hole 13 is coaxially arranged with the duct structure, wherein the first swing arm 3 has a first wire hole 16 along its length direction, and the free end of the first rope body 6 passes through the first wire hole 16 and the first rope hole 13 in sequence; and the second rope hole 14 is coaxially arranged with the duct structure, wherein the second swing arm 4 has a second wire hole 17 along its length direction, and the free end of the second rope body 7 passes through the second wire hole 17 and the second rope hole 14 in sequence.

[0046] In this embodiment, by setting the first wire hole 16 and the second wire hole 17, the sensor 18 can be driven to rotate by the first rotation drive source 10 and the second drive source simultaneously during axial movement without the problem of wire winding. In this way, the movement path of the sensor 18 in the duct structure is a spiral, which can improve the comprehensiveness of detection.

[0047] In actual implementation, the first rotation drive source 10 is connected to the first sealing plate 1, wherein the first rotation drive source 10 is connected to the first swing arm 3 through a gear structure transmission; at the same time, the second rotation drive source 11 is connected to the second sealing plate 2, wherein the second rotation drive source 11 is connected to the second swing arm 4 through a gear structure transmission.

[0048] For details, please refer to Figure 4 The following is a detailed description using the first swing arm 3 as an example. The installation structure of the second swing arm 4 can be referenced from the installation structure of the first swing arm 3. A support tube coaxial with the first rope hole 13 is vertically fixed to the first sealing plate 1 and communicates with the first rope hole 13. A countersunk hole is opened at one end of the first swing arm 3. The first swing arm 3 is connected to the shaft hole of the support tube through the countersunk hole. The first wire hole 16 passes through the first swing arm 3 from the bottom of the countersunk hole along the length of the first swing arm 3. The support tube is provided with a shaft stop located in the large diameter section of the countersunk hole. A bearing 21 sleeved on the support tube is also provided in the large diameter section to improve the smoothness of rotation of the first swing arm 3 and the support tube. The bearing 21 is axially positioned through the end cap connected to the opening of the countersunk hole and the shaft stop on the support tube.

[0049] In some alternative embodiments, both the first swing arm 3 and the second swing arm 4 are configured as telescopic arms.

[0050] In this embodiment, by adjusting the length of the first swing arm 3 and the second swing arm 4, the sensor 18 can rotate on circumferences of different diameters, thereby adapting to the airtightness detection of duct structures of different sizes; at the same time, the telescopic arm structure, in conjunction with the rotation drive source, can achieve precise control of the detection radius of the sensor 18, ensuring that the sensor 18 maintains the optimal detection distance from the duct wall, thus avoiding both a decrease in sensitivity due to excessive distance and scratch damage caused by excessive close distance.

[0051] In some optional embodiments, the first swing arm 3 and the second swing arm 4 can both be configured as electrically controlled telescopic rods. When the first swing arm 3 and the second swing arm 4 rotate to different angles, the first swing arm 3 and the second swing arm 4 can be controlled to extend or shorten by different distances, thereby making the movement paths of the free ends of the first swing arm 3 and the second swing arm 4 more diverse and not limited to a standard circle. For example, they can be rectangles, which are more suitable for the detection environment of rectangular duct structures.

[0052] In some alternative embodiments, the free ends of the first cable 6 and the second cable 7 are respectively connected to the winding wheel 15.

[0053] In this embodiment, by rotating the winding wheel 15, the pulling of the first cable 6 and the feeding of the second cable 7 can be achieved simultaneously, which makes the operation more convenient and ensures that the first cable 6 and the second cable 7 are always in the initial tension state.

[0054] In some alternative embodiments, the winding wheel 15 is equipped with a servo motor.

[0055] In this embodiment, after configuring a servo motor for the winding wheel 15, the precise control of the sensor 18 path can be achieved by controlling the rotation speed of the servo motor and the rotation speeds of the first rotation drive source 10 and the second rotation drive source 11. This will help improve the accuracy and comprehensiveness of the airtightness detection of the duct structure.

[0056] In some optional embodiments, the number of first pulleys 8 is configured to be two, and the axes of the two first pulleys 8 are arranged in parallel, with the distance between the two first pulleys 8 being less than the diameter of the first cable body 6; and

[0057] The number of second pulleys 9 is configured to be two, and the axes of the two second pulleys 9 are arranged in parallel, with the distance between the two second pulleys 9 being less than the diameter of the second cable body 7.

[0058] In this embodiment of the application, by setting two first pulleys 8 and two second pulleys 9, the first cable 6 and the second cable 7 can pass between the two first pulleys 8 and the two second pulleys 9 respectively. In this way, when the first swing arm 3 and the second swing arm 4 rotate, the first cable 6 and the second cable 7 are not easy to detach from the first pulleys 8 and the second pulleys 9, thereby ensuring that the sensor 18 can move accurately along the preset path within the duct structure.

[0059] In the above description, the length direction of the duct structure can be understood as the axis of the duct structure.

[0060] The specific embodiments described above illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Although the description of this application is presented in conjunction with some embodiments, this does not mean that the features of this application are limited to this embodiment. On the contrary, the purpose of describing the application in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of this application. To provide a thorough understanding of this application, many specific details are included in the above description. This application may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of this application, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0061] It should be noted that in this specification, similar reference numerals and letters in the above figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, and are only for the convenience of describing this application and simplifying the description, 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, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this application, it should be noted that unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0062] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A device for testing the airtightness of heating and ventilation ducts, characterized in that, include: The first sealing plate (1) is used to seal and connect with one end of the air duct structure. The first sealing plate (1) has a first rope hole (13). The second sealing plate (2) is used to seal the connection with the other end of the air duct structure. The second sealing plate (2) is provided with a second rope hole (14) and an air inlet (12). The first swing arm (3) is rotatably connected to the first sealing plate (1). The length direction of the first swing arm (3) forms an angle with the plate surface of the first sealing plate (1). The free end of the first swing arm (3) is provided with a first pulley (8). The second swing arm (4) is rotatably connected to the second sealing plate (2). The length direction of the second swing arm (4) forms an angle with the plate surface of the second sealing plate (2). The free end of the second swing arm (4) is provided with a second pulley (9). A fan (5), the air outlet of which is connected to the air inlet (12); The sensor (18) is connected to a first cable (6) and a second cable (7). The first cable (6) and the second cable (7) are respectively engaged with the first pulley (8) and the second pulley (9). The free ends of the first cable (6) and the second cable (7) pass through the first rope hole (13) and the second rope hole (14) respectively and are movably and sealedly connected to the first rope hole (13) and the second rope hole (14). The sensor (18) is used to detect the wind pressure and / or wind speed in the duct structure.

2. The airtightness testing device for heating and ventilation ducts according to claim 1, characterized in that, The sensor (18) is configured as a wind pressure sensor (18); Alternatively, the sensor (18) may be configured as a flow rate sensor (18); Alternatively, the sensor (18) may be configured to include a multimodal detection unit comprising a wind speed sensor (18) and a flow rate sensor (18).

3. The airtightness testing device for heating and ventilation ducts according to claim 1, characterized in that, The first swing arm (3) is equipped with a first rotation drive source (10). In the working state, the rotation center axis of the first swing arm (3) coincides with the axis of the duct structure; and The second swing arm (4) is equipped with a second rotation drive source (11). In the working state, the rotation center axis of the second swing arm (4) coincides with the axis of the duct structure.

4. The airtightness testing device for heating and ventilation ducts according to claim 3, characterized in that, The first rope hole (13) is coaxially arranged with the duct structure, wherein the first swing arm (3) has a first wire hole (16) along its length direction, and the free end of the first cable (6) passes through the first wire hole (16) and the first rope hole (13) in sequence; and The second rope hole (14) is coaxially arranged with the air duct structure. The second swing arm (4) has a second wire hole (17) along its length direction. The free end of the second rope body (7) passes through the second wire hole (17) and the second rope hole (14) in sequence.

5. The airtightness testing device for heating and ventilation ducts according to claim 4, characterized in that, The first rotation drive source (10) is connected to the first sealing plate (1), wherein the first rotation drive source (10) and the first swing arm (3) are connected by a gear structure.

6. The airtightness testing device for heating and ventilation ducts according to claim 4, characterized in that, The second rotation drive source (11) is connected to the second sealing plate (2), wherein the second rotation drive source (11) and the second swing arm (4) are connected by a gear structure.

7. The airtightness testing device for heating and ventilation ducts according to claim 1, characterized in that, Both the first swing arm (3) and the second swing arm (4) are configured as telescopic arms.

8. The airtightness testing device for heating and ventilation ducts according to claim 1, characterized in that, The free ends of the first cable (6) and the second cable (7) are respectively connected to the winding wheel (15).

9. The airtightness testing device for heating and ventilation ducts according to claim 8, characterized in that, The winding wheel (15) is equipped with a servo motor.

10. The airtightness testing device for heating and ventilation ducts according to claim 1, characterized in that, The number of the first pulleys (8) is configured to be two, and the axes of the two first pulleys (8) are arranged in parallel, and the distance between the two first pulleys (8) is less than the diameter of the first cable (6); and The number of the second pulleys (9) is configured to be two, and the axes of the two second pulleys (9) are arranged in parallel, and the distance between the two second pulleys (9) is less than the diameter of the second cable (7).

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