A gapless elastic sleeve coupling

Abstract

The present application relates to the technical field of mechanical transmission, and discloses a gapless elastic sleeve coupling, which comprises a left half coupling, a right half coupling and a connecting assembly. A plurality of connecting holes are uniformly distributed on the flange faces of the left half coupling and the right half coupling and are arranged in pairs, the connecting holes are divided into first connecting holes and second connecting holes, one of the two opposite connecting holes is a first connecting hole, and the other is a second connecting hole. The connecting assembly comprises a transmission pin and a gland. The transmission pin is divided into a close connection part and an elastic connection part along the axial direction. The close connection part is closely connected with the first connecting hole. The elastic connection part is arranged in the second connecting hole and is sleeved with an elastic sleeve. The gland is arranged at the end of the elastic connection part and compresses the elastic sleeve along the axial direction, so that the elastic sleeve is deformed in the radial direction and is closely combined with the inner wall of the second connecting hole. The present application eliminates the rotary gap between the elastic sleeve and the connecting hole, realizes the transmission without backlash, has the buffering and damping capacity, and is convenient to install.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission technology, specifically to an elastic sleeve coupling, and more particularly to a backlash-free elastic sleeve coupling capable of achieving zero-backlash transmission. Background Technology

[0002] Couplings are key components in mechanical transmissions used to connect the driving shaft and the driven shaft to transmit torque. Flexible sleeve pin couplings are widely used in various power transmission applications due to their simple structure, easy installation, and certain buffering and vibration damping capabilities.

[0003] Traditional flexible sleeve pin couplings typically consist of a driving half-coupling, a driven half-coupling, a pin, and a flexible sleeve. One end of the pin is fixedly connected to the conical hole of one half-coupling via a conical surface, while the other end of the pin, fitted with the flexible sleeve, is inserted into the hole of the other half-coupling. To ensure easy installation, a clearance fit is usually used between the flexible sleeve and the half-coupling hole; for example, a clearance of 0.5mm to 1.0mm is left between the outer circle of the flexible sleeve and the pin hole. However, this clearance fit results in backlash during operation, which cannot meet the requirements of backlash-free transmission in high-precision applications.

[0004] While existing technologies employ methods to eliminate clearance through expansion sleeves, these are typically used for connections between couplings and drive shafts (such as expansion sleeve diaphragm couplings and expansion sleeve perforated couplings), rather than addressing the transmission clearance between the flange faces of the two half-couplings. Furthermore, existing elastic sleeve pin couplings rely on the locking force of the pin assembly to generate frictional torque at the contact surface, compressing the rubber elastic sleeve to transmit torque. However, due to the gap between the elastic sleeve and the pin hole, their buffering and vibration damping effects are limited, and zero-backlash transmission cannot be achieved.

[0005] In addition, the elastic sleeve needs to be replaced regularly after long-term use. In traditional structures, replacing the elastic sleeve often requires disassembling the pin. The pin and the half coupling are in a conical surface fit. Disassembly requires forceful striking, which can easily damage the threaded part of the pin.

[0006] To address the above problems, the present invention provides a backlash-free elastic sleeve coupling. Summary of the Invention

[0007] The present invention aims to solve the technical problem that there is a gap between the elastic sleeve and the connecting hole of the half coupling in the existing elastic sleeve pin coupling, which makes it impossible to meet the requirements of high-precision backlash-free transmission.

[0008] Meanwhile, this invention also aims to solve the technical problem that existing elastic sleeve couplings cannot achieve the conversion from clearance fit to interference fit between the elastic sleeve and the connecting hole while maintaining ease of installation.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A backlash-free elastic sleeve coupling includes a left half coupling, a right half coupling, and a connecting assembly. The left and right half couplings each have multiple connecting holes evenly distributed along the circumference of their flange faces, with the connecting holes of the left and right half couplings arranged opposite each other. The connecting holes are divided into a first connecting hole and a second connecting hole; one of the two opposite connecting holes on the left and right half couplings is the first connecting hole, and the other is the second connecting hole. The connecting assembly includes a drive pin and a pressure cap. The drive pin is axially divided into a tight-fitting connecting portion and an elastic connecting portion. The tight-fitting connecting portion is tightly connected to the first connecting hole, and the elastic connecting portion passes through the second connecting hole, with an elastic sleeve fitted on it. The pressure cap is located at the end of the elastic connecting portion, and the pressure cap axially presses against the elastic sleeve, causing the elastic sleeve to undergo radial expansion deformation and tightly fit against the inner wall of the second connecting hole.

[0010] Preferably, the tight connection part is a cone, the first connection hole is a conical hole that mates with the cone, the tight connection part passes through the first connection hole, and its outer end is threaded with a first screw, a first washer is fitted on the first screw, the first washer is disposed between the head of the first screw and the tight connection part, and the end face of the first washer away from the head of the first screw abuts against the flange face of the left half coupling or the right half coupling.

[0011] Preferably, the elastic connecting part is a cylinder coaxial with the tight connecting part, the elastic sleeve is a drum-shaped elastic sleeve, and the pressure cap is fixed to the outer end of the elastic connecting part by a second screw. The second screw passes through the pressure cap and is threaded to the outer end of the elastic connecting part, and the head of the second screw presses against the pressure cap.

[0012] Preferably, the pressure cap is provided with a first pin hole and a locking hole along the axial direction, and the outer end of the elastic connecting part is provided with a second pin hole. A stop pin is connected between the first pin hole and the second pin hole to limit the relative rotation between the pressure cap and the transmission pin.

[0013] Preferably, a retaining washer is fitted onto the second screw. The retaining washer is disposed between the head of the second screw and the pressure cap. The retaining washer has a vertically folded portion that engages with the retaining hole. The side of the retaining washer away from the vertically folded portion can be folded toward the head side of the second screw to prevent the second screw from loosening.

[0014] Preferably, the gland has a circular groove in the middle, the circular groove is fitted onto the outer end of the elastic connecting part, and the bottom of the circular groove has a through hole for the second screw to pass through.

[0015] Preferably, a second washer is also fitted onto the transmission pin, and the second washer is disposed between the pressure cap and the elastic sleeve.

[0016] Preferably, the flange surfaces of the left and right half couplings each have two connecting holes evenly distributed in the circumferential direction, one of which is the first connecting hole and the other is the second connecting hole.

[0017] First, it achieves backlash-free transmission. This invention uses a pressure cap at the end of the elastic connection of the transmission pin to compress the drum-shaped elastic sleeve axially, causing the elastic sleeve to undergo radial expansion deformation. This changes the clearance fit (or line contact) between the elastic sleeve and the inner wall of the second connecting hole to an interference fit (surface contact), thereby completely eliminating the rotational clearance between the elastic sleeve and the second connecting hole and meeting the requirements for backlash-free transmission in high-precision transmission applications.

[0018] Secondly, installation is convenient. During initial installation, the elastic sleeve and the second connecting hole maintain a clearance fit, making installation as easy as with conventional elastic sleeve couplings, requiring no special tooling or complex operations. After installation, radial tightening of the elastic sleeve can be achieved simply by tightening the second screw, making operation simple.

[0019] Third, it also has buffering and vibration reduction capabilities. While eliminating transmission backlash, this invention retains the elastic element characteristics of the elastic sleeve, which can absorb vibrations and impacts during transmission, playing a buffering and vibration reduction role and protecting other components in the transmission system.

[0020] Fourth, reliable anti-loosening. This invention restricts the relative rotation between the pressure cap and the transmission pin by using a stop pin. The stop washer is fixed to the transmission pin by engaging with the vertical folded part of the stop washer and the locking hole. Then, the arc-shaped edge of the stop washer is folded towards the head side of the second screw, forming a multi-layer anti-loosening structure. This effectively prevents the second screw from loosening during long-term operation and ensures a durable and reliable tightened state.

[0021] Fifth, it has a simple structure and low manufacturing cost. This invention achieves backlash-free transmission by adding only a few parts, such as a pressure cap, a stop pin, and a stop washer, to the traditional elastic sleeve coupling. The structural changes are minor, the manufacturing cost is low, and it is easy to promote and use. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view of the overall structure of the present invention; Figure 2 for Figure 1 A magnified view of the area at point X (rotated 90 degrees counterclockwise); Figure 3 This is a schematic diagram of the elastic sleeve in the compressed state and the side view of the head of the second screw with the stop washer folded towards it. Figure 4 This is a cross-sectional view of the structure of the pressure cap of the present invention; Figure 5 This is a cross-sectional view of the transmission pin of the present invention; Figure 6 This is a three-dimensional structural diagram of the stop washer of the present invention.

[0023] In the diagram: 1-Left half coupling, 2-Right half coupling, 3-Connecting assembly, 31-Drive pin, 311-Tight connection part, 312-Elastic connection part, 313-Second pin hole, 32-Gland, 321-First pin hole, 322-Snap hole, 323-Circular groove, 33-Elastic sleeve, 34-First screw, 35-First washer, 36-Second screw, 37-Stop pin, 38-Stop washer, 381-Vertical fold-up part, 39-Second washer, 41-First connecting hole, 42-Second connecting hole. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" or "linked" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0026] In the description of the embodiments of the present invention, it should be noted that the terms "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention 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. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0027] like Figure 1As shown, the present invention provides a backlash-free elastic sleeve coupling, comprising a left half coupling 1, a right half coupling 2, and a connecting assembly 3. The left half coupling 1 and the right half coupling 2 are respectively used to connect to the driving shaft and the driven shaft (the connection method can be conventional methods such as key connection or shrink sleeve connection, which are not limited in this invention). The left half coupling 1 and the right half coupling 2 each have multiple connecting holes evenly distributed along the circumference of their flange surfaces, and the connecting holes of the left half coupling 1 and the right half coupling 2 are arranged opposite to each other.

[0028] The connecting holes are divided into a first connecting hole 41 and a second connecting hole 42. On the left half-coupling 1 and the right half-coupling 2, one of the two opposite connecting holes is the first connecting hole 41, and the other is the second connecting hole 42. In other words, in each pair of opposite connecting holes, one half-coupling has the first connecting hole 41, and the other half-coupling has the second connecting hole 42.

[0029] like Figure 1 , Figure 2 , Figure 4 and Figure 5 As shown, the connecting assembly 3 includes a drive pin 31 and a pressure cap 32. The drive pin 31 is divided into a tight connection part 311 and an elastic connection part 312 along the axial direction. The tight connection part 311 is tightly connected to the first connecting hole 41, and the elastic connection part 312 passes through the second connecting hole 42, and an elastic sleeve 33 is fitted on the elastic connection part 312.

[0030] like Figure 1 As shown, the pressure cap 32 is disposed at the end of the elastic connection portion 312. The pressure cap 32 presses the elastic sleeve 33 axially, causing the elastic sleeve 33 to undergo radial expansion deformation and fit tightly against the inner wall of the second connection hole 42.

[0031] As a preferred embodiment of the present invention, such as Figure 1 , Figure 2 and Figure 5 As shown, the tight-fitting connection part 311 is a cone, and the first connecting hole 41 is a conical hole that mates with the cone. The tight-fitting connection part 311 passes into the first connecting hole 41, and a tight connection is achieved through the conical fit. The outer end of the tight-fitting connection part 311 (i.e., the end away from the elastic connection part) is threaded with a first screw 34. A first washer 35 is fitted on the first screw 34, and the first washer 35 is disposed between the head of the first screw 34 and the tight-fitting connection part 311, with the end face of the first washer 35 away from the head of the first screw 34 abutting against the flange face of the left half coupling 1 or the right half coupling 2. By tightening the first screw 34, the tight-fitting connection part 311 can be pulled tight and fixed in the conical hole.

[0032] like Figure 1 , Figure 2 and Figure 5As shown, the elastic connecting part 312 is a cylinder coaxial with the tight connecting part 311. The elastic sleeve 33 is a drum-shaped elastic sleeve, that is, its middle outer diameter is larger than the outer diameters at both ends. The elastic sleeve 33 can be made of elastic materials such as rubber. The pressure cap 32 is fixed to the outer end of the elastic connecting part 312 (i.e., the end away from the tight connecting part) by a second screw 36. The second screw 36 passes through the pressure cap 32 and is threaded to the outer end of the elastic connecting part 312, and the head of the second screw 36 presses against the pressure cap 32.

[0033] As a preferred embodiment of the present invention, such as Figure 1 , Figure 2 and Figure 4 As shown, the pressure cap 32 has a first pin hole 321 and a locking hole 322 arranged axially. The outer end of the elastic connecting part 312 is correspondingly provided with a second pin hole 313. A stop pin 37 is connected between the first pin hole 321 and the second pin hole 313. The stop pin 37 is used to limit the relative rotation between the pressure cap 32 and the transmission pin 31, ensuring that the pressure cap 32 will not rotate relative to the transmission pin 31 during the tightening of the second screw 36.

[0034] As a preferred embodiment of the present invention, such as Figure 1 , Figure 2 , Figure 3 and Figure 6 As shown, a retaining washer 38 is fitted onto the second screw 36. The retaining washer 38 is positioned between the head of the second screw 36 and the pressure cap 32. The retaining washer 38 has a vertically folded portion 381, which engages with a locking hole 322, thus fixing the retaining washer 38 relative to the pressure cap 32 and the drive pin 31. The side of the retaining washer 38 away from the vertically folded portion 381 (usually an arc-shaped edge) can be folded towards the head of the second screw 36 to prevent the second screw 36 from loosening. Through the above structure, a multi-layered anti-loosening system is formed: the retaining pin 37 prevents the pressure cap 32 and the drive pin 31 from rotating relative to each other; the vertically folded portion 381 engages with the locking hole 322 to prevent the retaining washer 38 from rotating; and the arc-shaped edge of the retaining washer 38 folded towards the head of the second screw 36 directly prevents the second screw 36 from loosening.

[0035] As a preferred embodiment of the present invention, such as Figure 4 As shown, a circular groove 323 is provided in the middle of the pressure cap 32. The circular groove 323 is fitted onto the outer end of the elastic connecting part 312, and a through hole is provided at the bottom of the circular groove 323 for the second screw 36 to pass through. The structure of the circular groove 323 allows the pressure cap 32 to be better positioned on the outer end of the elastic connecting part 312, ensuring that the pressure cap 32 applies uniform pressure to the elastic sleeve 33.

[0036] As a preferred embodiment of the present invention, such as Figure 1As shown, a second washer 39 is also fitted onto the transmission pin 31. The second washer 39 is positioned between the pressure cap 32 and the elastic sleeve 33. The function of the second washer 39 is to transmit the axial pressure of the pressure cap 32 more evenly to the end face of the elastic sleeve 33, preventing the pressure cap 32 from directly contacting the elastic sleeve 33 and causing local stress concentration or damage.

[0037] As a preferred embodiment of the present invention, such as Figure 1 As shown, the flange faces of the left half coupling 1 and the right half coupling 2 each have two connecting holes evenly distributed along their circumference. One is the first connecting hole 41, and the other is the second connecting hole 42. This utilizes two drive pins 31, with the two drive pins 31 installed in opposite directions (one inserted from left to right, the other from right to left), resulting in more stable torque transmission and meeting most transmission requirements. Of course, depending on the actual torque transmitted, three, four, or more connecting holes and corresponding drive pins 31 can be provided; this invention does not limit this.

[0038] Working process and principle explanation Initial installation status: During initial installation, the tight-fitting part 311 of the drive pin 31 is inserted into the first connecting hole 41 of the left half coupling 1 or the right half coupling 2, and the tight-fitting part 311 is tightened and fixed in the first connecting hole 41 by tightening the first screw 34. At this time, the elastic connecting part 312 of the drive pin 31, together with the elastic sleeve 33 sleeved on its outer side, is inserted into the second connecting hole 42 of the other half coupling. In the initial state, there is a clearance fit between the elastic sleeve 33 and the inner wall of the second connecting hole 42, that is, there is a certain gap between the two, so that the drive pin 31 can easily pass into the second connecting hole 42, which facilitates the overall installation of the coupling.

[0039] Clamping working state: After the coupling is installed in place, the pressure cap 32 is fitted onto the outer end of the elastic connecting part 312, so that the circular groove 323 of the pressure cap 32 mates with the outer end of the elastic connecting part 312 for positioning. The stop pin 37 is inserted into the first pin hole 321 of the pressure cap 32 and the second pin hole 313 of the elastic connecting part 312, so that the pressure cap 32 and the drive pin 31 are relatively fixed. The stop washer 38 is fitted onto the second screw 36, so that its vertical folded-up part 381 is engaged in the locking hole 322 of the pressure cap 32.

[0040] Then, the second screw 36 is passed through the through hole in the middle of the pressure cap 32 and threaded into the threaded hole at the outer end of the elastic connecting part 312. Tightening the second screw 36 causes its head to press against the pressure cap 32 via the stop washer 38. The pressure cap 32 moves axially toward the elastic sleeve 33, pressing against the end face of the elastic sleeve 33. Under axial pressure, the drum-shaped elastic sleeve 33 undergoes axial compression deformation. Based on the volumetric incompressibility of rubber-like elastic materials (Poisson's ratio close to 0.5), the elastic sleeve 33 undergoes radial expansion deformation during axial compression, with its central part expanding outwards.

[0041] As the second screw 36 is gradually tightened, the radial expansion of the elastic sleeve 33 gradually increases, and the gap between the outer wall of the elastic sleeve 33 and the inner wall of the second connecting hole 42 gradually decreases until it disappears. When the second screw 36 is tightened to the correct position, the outer wall of the elastic sleeve 33 and the inner wall of the second connecting hole 42 change from an initial clearance fit (or line contact) to an interference fit (surface contact), that is, the two achieve a tight fit without any rotational clearance.

[0042] Anti-loosening lock: After the elastic sleeve 33 is tightened in place, fold the side of the retaining washer 38 away from the vertical folded part 381 (usually the curved edge) towards the head side of the second screw 36, so that the retaining washer 38 is tightly attached to the head of the second screw 36, thereby preventing the second screw 36 from loosening due to vibration during long-term operation. At this point, the installation of the entire coupling is complete.

[0043] Work process: When the coupling is working, power is transmitted from the drive shaft to the left half of the coupling 1 (or the right half of the coupling 2), then through the transmission pin 31 to the other half of the coupling, and finally to the driven shaft. Because the elastic sleeve 33 and the inner wall of the second connecting hole 42 have an interference fit with each other, there is no rotational clearance, thus enabling high-precision, backlash-free transmission. Simultaneously, the elastic sleeve 33, as an elastic element, absorbs vibration and impact during torque transmission, playing a buffering and vibration-damping role.

[0044] Elastic sleeve replacement: When the elastic sleeve 33 needs to be replaced after long-term use, simply reset the folded part of the stop washer 38 and loosen the second screw 36 to release the pressure of the pressure cap 32 on the elastic sleeve 33. After the elastic sleeve 33 recovers its elastic deformation, it returns to a clearance fit with the second connecting hole 42. Pulling out the stop pin 37 and removing the pressure cap 32 allows for easy removal of the old elastic sleeve 33 and replacement with a new one. The entire replacement process does not require disassembling the transmission pin 31 or moving the half-coupling, making the operation extremely convenient.

[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0046] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A backlash-free elastic sleeve coupling, comprising a left half coupling (1), a right half coupling (2), and a connecting assembly (3), characterized in that, The left half coupling (1) and the right half coupling (2) each have multiple connecting holes evenly distributed along the circumference of their flange surfaces. The connecting holes of the left half coupling (1) and the right half coupling (2) are arranged opposite to each other. The connecting holes are divided into a first connecting hole (41) and a second connecting hole (42). Of the two connecting holes that are opposite to each other on the left half coupling (1) and the right half coupling (2), one is the first connecting hole (41) and the other is the second connecting hole (42). The connecting assembly (3) includes a drive pin (31) and a pressure cap (32). The drive pin (31) The structure is divided into a tight connection part (311) and an elastic connection part (312) along the axial direction. The tight connection part (311) is tightly connected to the first connection hole (41). The elastic connection part (312) is inserted into the second connection hole (42), and an elastic sleeve (33) is sleeved on the elastic connection part (312). The pressure cap (32) is disposed at the end of the elastic connection part (312). The pressure cap (32) presses the elastic sleeve (33) along the axial direction, so that the elastic sleeve (33) undergoes radial expansion deformation and fits tightly against the inner wall of the second connection hole (42).

2. The backlash-free elastic sleeve coupling according to claim 1, characterized in that, The tight connection part (311) is a cone, and the first connection hole (41) is a conical hole that mates with the cone. The tight connection part (311) passes through the first connection hole (41), and its outer end is threaded with a first screw (34). A first washer (35) is fitted on the first screw (34). The first washer (35) is located between the head of the first screw (34) and the tight connection part (311), and the end face of the first washer (35) away from the head of the first screw (34) abuts against the flange face of the left half coupling (1) or the right half coupling (2).

3. The backlash-free elastic sleeve coupling according to claim 2, characterized in that, The elastic connecting part (312) is a cylinder coaxial with the tight connecting part (311), the elastic sleeve (33) is a drum-shaped elastic sleeve, and the pressure cap (32) is fixed to the outer end of the elastic connecting part (312) by a second screw (36). The second screw (36) passes through the pressure cap (32) and is threaded to the outer end of the elastic connecting part (312), and the head of the second screw (36) presses against the pressure cap (32).

4. The backlash-free elastic sleeve coupling according to claim 3, characterized in that, The pressure cap (32) is provided with a first pin hole (321) and a locking hole (322) along the axial direction. The outer end of the elastic connecting part (312) is provided with a second pin hole (313). A stop pin (37) is connected between the first pin hole (321) and the second pin hole (313) to limit the relative rotation between the pressure cap (32) and the transmission pin (31).

5. The backlash-free elastic sleeve coupling according to claim 4, characterized in that, A retaining washer (38) is fitted on the second screw (36). The retaining washer (38) is located between the head of the second screw (36) and the pressure cap (32). The retaining washer (38) has a vertical folded portion (381). The vertical folded portion (381) is inserted into the locking hole (322). The side of the retaining washer (38) away from the vertical folded portion (381) can be folded toward the head side of the second screw (36) to prevent the second screw (36) from loosening.

6. The backlash-free elastic sleeve coupling according to claim 3, characterized in that, The pressure cap (32) has a circular groove (323) in the middle, which is fitted onto the outer end of the elastic connecting part (312). The bottom of the circular groove (323) has a through hole for the second screw (36) to pass through.

7. The backlash-free elastic sleeve coupling according to claim 3, characterized in that, A second washer (39) is also fitted on the transmission pin (31), and the second washer (39) is disposed between the pressure cap (32) and the elastic sleeve (33).

8. The backlash-free elastic sleeve coupling according to claim 1, characterized in that, The left half coupling (1) and the right half coupling (2) each have two connecting holes evenly distributed in the circumferential direction of the flange face, one of which is the first connecting hole (41) and the other is the second connecting hole (42).

Images