Multi-redundancy rotary transformer with zero alignment structure

Abstract

In order to overcome the defects of poor alignment effect and poor assembly manufacturability of the zero alignment structure in the existing multi-redundancy rotary transformer, the invention provides a multi-redundancy rotary transformer with a zero alignment structure, which consists of two brushless rotary transformers which are coaxially arranged in sequence, rotor rotating shafts of the two rotary transformers are connected in a blind hole and step shaft hole matching and bonding mode, and during adjustment, the shaft holes of the rotor rotating shafts of the two rotary transformers can be matched for rotation adjustment, so that zero positions of rotor assemblies of the two rotary transformers are aligned, coarse adjustment of the zero positions is achieved, and the adjustment efficiency of zero alignment is improved. Meanwhile, the shells of the two brushless rotary transformers are connected through a connecting shell, and the shells of the two brushless rotary transformers can be rotationally adjusted relative to the connecting shell, so that the zero positions of the stator assemblies of the two rotary transformers are aligned, and fine adjustment of the zero positions is achieved.

Description

Technical Field

[0001] The invention relates to a redundant rotary transformer. Background Art

[0002] The rotary transformer is an electromagnetic sensor that can accurately transmit angle and speed signals. It is mainly used in various servo feedback systems and places where angle and speed measurement and sensing are required, such as industrial servo drive systems, aerospace and other fields, to provide angle (speed) and other signals to the controller. The rotary transformer has high sensitivity and reliability, strong anti-interference ability, and is particularly suitable for occasions with relatively harsh environmental conditions such as high temperature, severe cold, humidity, high speed, and high vibration. However, once an abnormal situation occurs in the rotary transformer, it cannot be replaced in time or it is difficult to disassemble and assemble, so there is a need for redundant backup. In order to improve reliability, most of the rotary transformers are currently used for combined installation, but this brings about the problem of zero-position synchronization between the redundancies, and zero-position alignment is an extremely important factor for the redundant rotary transformer. How to quickly align the zero position, prevent deviation after alignment, and the processability of assembly are all urgent problems that need to be solved. Therefore, it is necessary to design a zero-position alignment structure for the redundant rotary transformer. However, the zero-position alignment structure of the redundant rotary transformer currently has the disadvantages of poor alignment effect and poor assembly processability. Summary of the invention

[0003] In order to solve the shortcomings of poor alignment effect and poor assembly processability of the zero-position alignment structure in the existing redundant rotator, the present invention provides a redundant rotary transformer with a zero-position alignment structure.

[0004] The technical solution of the present invention is:

[0005] The redundant rotary transformer with zero alignment structure is special in that:

[0006] It includes two brushless rotary transformers connected in series axially through a connecting housing;

[0007] A single brushless rotary transformer comprises a housing, a rotating shaft, a rotor assembly, a stator assembly, a transformer outer ring, a transformer inner ring and a bearing; one end of the rotating shaft is supported in the housing through a bearing, the rotor assembly and the transformer inner ring are fixedly mounted on the rotating shaft, and the stator assembly and the transformer outer ring are fixedly mounted on the inner wall of the housing so as to be respectively sleeved outside the rotor assembly and the transformer inner ring;

[0008] The housings of the two brushless rotary transformers connected in series are respectively recorded as a first housing and a second housing, the rotating shafts are respectively recorded as a first rotating shaft and a second rotating shaft, and the connecting housing used to connect the two brushless rotary transformers is recorded as a third housing;

[0009] The first rotating shaft is axially butted with the second rotating shaft and fixedly connected by means of shaft hole matching and bonding. During installation and adjustment, the zero position of the rotor assemblies of the two brushless rotary transformers is roughly adjusted by rotating the shaft holes of the first rotating shaft and the second rotating shaft, so that the zero position of the rotor assembly on the first rotating shaft and the rotor assembly on the second rotating shaft are relatively consistent;

[0010] The third shell is sleeved outside the first shell and the second shell, the first shell is in axial contact with the second shell, and the two ends of the third shell are fixedly connected to the first shell and the second shell through connecting flanges; the inner walls at both ends of the third shell are respectively provided with N first latch teeth and N second latch teeth evenly spaced along the circumference, and the outer side walls of the first shell and the second shell are respectively provided with N first guide grooves and N second guide grooves that match the N first latch teeth and the N second latch teeth one by one, a first annular groove is provided between the N first guide grooves and the connecting flange at the end of the first shell, and a second annular groove is provided between the N second guide grooves and the connecting flange at the end of the second shell; the N first latch teeth of the third shell are snapped with the first annular groove at the end of the first shell after passing through the N first guide grooves of the first shell, and the N second latch teeth of the third shell are snapped with the second annular groove at the end of the second shell after passing through the N second guide grooves of the second shell;

[0011] During installation and adjustment, the first latch tooth of the third shell passes through the first guide groove and then snaps into the first annular groove, and the second latch tooth of the third shell passes through the second guide groove and then snaps into the second annular groove. The rotation of the first latch tooth in the first annular groove can cause the first shell and the third shell to produce relative rotational movement, and the rotation of the second latch tooth in the second annular groove can cause the second shell and the third shell to produce relative movement, thereby causing the first shell and the second shell to produce relative rotational movement, thereby further aligning the zero position of the stator assembly fixed on the inner wall of the first shell and the stator assembly fixed on the inner wall of the second shell.

[0012] Furthermore, the radial edges of the first latch tooth and the second latch tooth are chamfered, and the distance between the first latch tooth and the second latch tooth is smaller than the distance between the first annular groove and the second annular groove, so that the first latch tooth and the first annular groove are interference fit, and the second latch tooth and the second annular groove are interference fit.

[0013] Furthermore, waist-shaped holes are provided on the connecting flanges on the first shell and the second shell for connecting with the third shell, and threaded holes corresponding to the waist-shaped holes on the first shell and the second shell are provided on the connecting flanges at both ends of the third shell.

[0014] Furthermore, the end of the first rotating shaft is designed as a blind hole, and an exhaust hole is opened on the side wall of the blind hole near the bottom of the blind hole. The end of the second rotating shaft is designed as a step shaft. The axial docking of the first rotating shaft and the second rotating shaft is achieved by coating adhesive on the step shaft and inserting it into the blind hole for bonding.

[0015] Furthermore, a wire outlet hole is provided on the side wall of the third shell, a wire groove is provided on the inner side walls of the first shell and the second shell, and the side walls of the opening ends of the first shell and the second shell are respectively provided with a first wire outlet hole and a second wire outlet hole that match the position of the wire outlet hole of the third shell. The input excitation lead wires of the transformer outer ring and the output lead wires of the stator assembly of the two brushless rotating transformers are all led to the first wire outlet hole and the second wire outlet hole through the wire groove, and finally led out from the wire outlet hole of the third shell.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The redundant rotary transformer of the present invention adopts a modular design and is composed of two brushless rotary transformers arranged coaxially in sequence. The rotor shafts of the two rotary transformers are connected by a blind hole and a stepped shaft hole matching + bonding method. During installation and adjustment, the rotor shafts of the two rotary transformers can be first rotated and adjusted through the matching shaft holes to align the zero positions of their rotor assemblies, thereby achieving coarse adjustment of the zero position and improving the adjustment efficiency of the zero alignment. At the same time, the shells of the two brushless rotary transformers (on the inner walls of which the stator assembly and the transformer outer ring are fixedly mounted) are connected via a connecting shell (referred to as the third shell), and the inner walls of the two ends of the third shell are provided with N circumferentially evenly distributed latches, and the outer walls of the two rotary transformer shells (respectively referred to as the first shell and the second shell) are provided with N guide grooves corresponding to the latches, and an annular groove is formed between the end of the guide groove and the flange at the end of the rotary transformer shell. When the latch of the connecting shell penetrates the guide groove and reaches the annular groove, the shells of the two rotary transformers can rotate in the annular groove relative to the connecting shell, thereby realizing relative rotation between the two rotary transformer shells and the stator assembly fixed on their inner walls and the transformer outer ring as a whole, so that the zero positions of the stator assemblies of the two rotary transformers can be aligned, and the zero position can be finely adjusted.

[0018] 2. In the present invention, the spacing of the latch teeth arranged on the inner wall of the connecting shell between the two brushless rotary transformers is smaller than the spacing of the annular grooves respectively located on the two brushless rotary transformers, so that an interference fit is formed between the latch teeth and the annular grooves. In this way, after the zero position is aligned and before the connecting screws are installed, the aligned zero position will not loosen or deviate, which facilitates the operation when tightening the screws and improves the assembly processability.

[0019] 3. The redundant rotary transformer of the present invention adopts a modular design and a simple and efficient zero-position alignment mechanism, which reduces the number of assembly parts. The dual functions of the latching teeth on the inner wall of the connecting shell (third shell) between the two rotary transformers and the screw fastening strengthen the locking property between the two rotary transformers, thereby improving the reliability and stability of the entire redundant rotary transformer. At the same time, if a single-redundancy rotary transformer fails in the same batch of redundant rotary transformer products, a new rotary transformer can be quickly reassembled and zero-aligned, thereby realizing the modular design of the redundant rotary transformer and improving the versatility of the redundant rotary transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of a dual-redundancy rotary transformer of this embodiment.

[0021] Figure 2 yes Figure 1 Isometric view of.

[0022] Figure 3 yes Figure 1 Schematic diagram of the structure of the first shell.

[0023] Figure 4 yes Figure 1 Schematic diagram of the structure of the second shell.

[0024] Figure 5 yes Figure 1 Schematic diagram of the structure of the third shell.

[0025] Reference numerals:

[0026] 1-first brushless rotary transformer; 11-first rotating shaft; 111-first positioning shoulder; 112-exhaust hole; 12-first housing; 121-first flange; 1221-first waist hole; 122-first guide groove; 123-first annular groove; 124-first outlet hole; 125-first stepped hole; 126-second stepped hole; 13-first rotor assembly; 14-first stator assembly; 15-first transformer outer ring; 16-first transformer inner ring; 17-first bearing; 18-first screw;

[0027] 2-second brushless rotary transformer; 21-second rotating shaft; 211-second positioning shoulder; 22-second housing; 221-second flange; 2221-second waist hole; 222-second guide groove; 223-second annular groove; 224-second outlet hole; 225-third stepped hole; 226-fourth stepped hole; 23-second rotor assembly; 24-second stator assembly; 25-second transformer outer ring; 26-second transformer inner ring; 27-second bearing; 28-second screw;

[0028] 3-third housing; 31-third flange; 311-first threaded hole; 32-fourth flange; 321-second threaded hole; 33-first latching tooth; 34-wire outlet hole; 35-second latching tooth. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0030] like Figure 1 As shown, the redundant rotary transformer of this embodiment includes a first brushless rotary transformer 1, a second brushless rotary transformer 2 and a third shell 3. The first brushless rotary transformer 1 and the second brushless rotary transformer 2 have the same structure and are arranged in sequence along the axial direction. The first brushless rotary transformer 1 and the second brushless rotary transformer 2 are zero-aligned and assembled through the third shell 3.

[0031] The first brushless rotary transformer 1 comprises a first rotating shaft 11, a first housing 12, a first rotor assembly 13, a first stator assembly 14, a first transformer outer ring 15, a first transformer inner ring 16 and a first bearing 17. The left end of the first rotating shaft 11 is supported on the first housing 12 by the first bearing 17 and is located inside the first housing 12. A first positioning shoulder 111 is designed in the middle of the first rotating shaft 11. The first rotor assembly 13 and the first transformer inner ring 16 are both sleeved on the first rotating shaft 11 and located on both sides of the first positioning shoulder 111. The first positioning shoulder 111 is used to perform axial positioning and is adhesively fixed to the first positioning shoulder 111. The first rotor assembly 13 and the first transformer inner ring 16 are connected by cables. The first stator assembly 14 is sleeved outside the first rotor assembly 13, and the first transformer outer ring 15 is sleeved outside the first transformer inner ring 16. A first outlet hole 124 , a first stepped hole 125 and a second stepped hole 126 are provided on the inner wall of the first shell 12 . The first stator assembly 14 and the first transformer outer ring 15 are axially limited by the first stepped hole 125 and the second stepped hole 126 and are glued and fixed to the inner wall of the first shell 12 .

[0032] The second brushless rotary transformer 2 includes a second rotating shaft 21, a second housing 22, a second rotor assembly 23, a second stator assembly 24, a second transformer outer ring 25, a second transformer inner ring 26 and a second bearing 29. The right end of the second rotating shaft 21 is supported on the second housing 22 by a second bearing 27 and extends out of the second housing 22. A second positioning shoulder 211 is designed in the middle of the second rotating shaft 21. The second rotor assembly 23 and the second transformer inner ring 26 are both sleeved on the second rotating shaft 21 and located on both sides of the second positioning shoulder 211. The second positioning shoulder 211 is used to perform axial positioning and adhesively fix to the second positioning shoulder 211, and the second rotor assembly 23 and the second transformer inner ring 26 are connected by cables. The second stator assembly 24 is sleeved outside the second rotor assembly 23, and the second transformer outer ring 25 is sleeved outside the second transformer inner ring 26. A second outlet hole 224 , a third stepped hole 225 and a fourth stepped hole 226 are provided on the inner wall of the second shell 22 . The second stator assembly 24 and the second transformer outer ring 25 are axially limited by the third stepped hole 225 and the fourth stepped hole 226 and are glued and fixed to the inner wall of the second shell 22 .

[0033] The first rotating shaft 11 in the first brushless rotary transformer 1 is axially connected with the second rotating shaft 21 in the second brushless rotary transformer 2 to realize the axial connection between the first brushless rotary transformer 1 and the second brushless rotary transformer 2. The first rotating shaft 11 and the second rotating shaft 21 are fixedly connected by shaft hole matching + bonding, for example Figure 1 As shown in , the right end of the first rotating shaft 11 is designed as a blind hole, and an exhaust hole 112 is opened on the side wall of the blind hole near the bottom of the blind hole. The left end of the second rotating shaft 21 is designed as a step shaft. By coating adhesive on the step shaft and inserting it into the blind hole for bonding, the axial docking of the first rotating shaft 11 and the second rotating shaft 21 can be achieved. When the first brushless rotary transformer 1 and the second brushless rotary transformer 2 are axially docked and assembled, the zero position of the first rotor assembly 13 of the first brushless rotary transformer 1 and the second rotor assembly 23 of the second brushless rotary transformer 2 can be roughly adjusted by rotating the axial holes of the first rotating shaft 11 and the second rotating shaft 21 to ensure that the zero positions of the two are aligned and relatively consistent. Finally, after the rough adjustment is completed, the connection between the two shafts is completed by adhesive to ensure the reliability of the connection.

[0034] like Figure 1 , 3-5, in order to realize the connection among the first shell 12, the second shell 22 and the third shell 3, a first flange 121 is provided at the left end of the first shell 12, and a first waist-shaped hole 1221 is provided on the first flange 121; a second flange 221 is provided at the right end of the second shell 22, and a second waist-shaped hole 2221 is provided on the second flange 221; a third flange 31 and a fourth flange 32 are provided at the left and right ends of the third shell 3, respectively, a first threaded hole 311 matching the position of the first waist-shaped hole 1221 is provided on the third flange 31, and a second threaded hole 321 matching the position of the second waist-shaped hole 2221 is provided on the fourth flange 32.

[0035] In the radial direction, the third housing 13 is sleeved outside the first housing 12 and the second housing 22, and the first housing 12 and the second housing 22 are axially arranged in the third housing 13 and the open ends are in contact. In the axial direction, the third housing 3 is arranged between the first housing 12 and the second housing 22, and is respectively connected to the first housing 12 and the second housing 22 through connecting flanges; the third flange 31 at the left end of the third housing 3 is butted with the first flange 121 at the left end of the first housing 12, and connected by inserting the first screw 18 into the first waist hole 1221 and the first threaded hole 311; the fourth flange 32 at the right end of the third housing 3 is butted with the second flange 221 at the right end of the second housing 22, and connected by inserting the second screw 28 into the second waist hole 2221 and the second threaded hole 321.

[0036] In order to achieve fine adjustment of the zero position, N first latch teeth 33 are evenly distributed along the circumference on the inner wall of the third housing 3 near the first housing 12, and N second latch teeth 35 are evenly distributed along the circumference on the inner wall of the third housing 3 near the second housing 22; accordingly, N first guide grooves 122 are evenly distributed along the circumferential direction on the outer wall of the first housing 12, which are matched with the first latch teeth 33, and each first guide groove 122 extends axially from the right end to the left end of the first housing 12; N second guide grooves 222 are evenly distributed along the circumferential direction on the outer wall of the second housing 22, which are matched with the second latch teeth 35, and each second guide groove 222 extends axially from the left end to the right end of the second housing 22. A first annular groove 123 is formed between the end of the first guide groove 122 on the first housing 12 and the first flange 121, and a second annular groove 223 is formed between the end of the second guide groove 222 on the second housing 22 and the second flange 221. N is an integer greater than or equal to 2, and in this embodiment, N=3.

[0037] In order to improve the assembly processability, the radial edges of the first latch tooth 33 and the second latch tooth 35 of the present invention are further chamfered. At the same time, the distance between the first latch tooth 33 and the second latch tooth 35 is smaller than the distance between the first annular groove 123 and the second annular groove 223, so that the first latch tooth 33 and the first annular groove 123 are interference fit, and the second latch tooth 35 and the second annular groove 223 are interference fit.

[0038] In addition, in order to prevent the screws from being loosened due to the fact that the grooves at the waist-shaped holes on the connecting flanges of the first shell and the second shell are not deep enough, resulting in the screws being higher than the overall length of the structure after assembly, which may cause collision. In this embodiment, circular bosses are processed on the outer surfaces of the connecting flanges of the first shell and the second shell, such as Figure 3 , 4 shown.

[0039] Before fine adjustment and assembly, the first stator assembly 14 and the first transformer outer ring 15 are fixedly installed in the first housing 12, and the second stator assembly 24 and the second transformer outer ring 25 are fixedly installed in the second housing 22. Then, the redundant rotor assembly assembled by rough adjustment is installed into the first housing 12 and the second housing 22, and then the following fine adjustment and assembly are performed:

[0040] The N first latching teeth 33 on the left inner wall of the third housing 3 are respectively inserted into the N first guide grooves 122 on the outer wall of the first housing 12 and then buckled into the first annular groove 123 .

[0041] Next, the N second latches 35 on the right inner wall of the third housing 3 are respectively inserted into the N second guide grooves 222 on the outer wall of the second housing 22 and buckled into the second annular groove 223, and rotated in the second annular groove 223 until the fine adjustment alignment requirements of the zero position between the margins of the second brushless rotary transformer 2 are met.

[0042] Through the above-mentioned installation and adjustment process, the zero position fine adjustment between the two redundancies of the first brushless rotary transformer 1 and the second brushless rotary transformer 2 can be unified. Since the first latch tooth 33 and the first annular groove 123, as well as the second latch tooth 35 and the second annular groove 223 are interference fit, they will not loosen or deviate after being rotated to zero during the installation and adjustment stage, and then they are tightened by the first screw to ensure the reliability and stability between the redundancies.

[0043] In order to lead out the cables, wire grooves are provided on the inner walls of the first shell and the second shell, a first wire outlet hole 124 is provided at the right end of the side wall of the first shell 12, a second wire outlet hole 224 is provided at the left end of the side wall of the second shell, and a wire outlet hole 34 is provided on the outer wall of the third shell 3.

[0044] The output lead wire of the first stator assembly 14 in the first brushless rotary transformer 1 is led to the first lead hole 124 through the wire groove and then led out from the lead hole 34 on the side wall of the third shell 3. The input excitation lead wire of the first transformer outer ring 5 is led out through the first lead hole 124 and then led out from the lead hole 34 on the side wall of the third shell 3 for external output.

[0045] The output lead wire of the second stator assembly 24 in the second brushless rotary transformer 2 is led to the second lead hole 224 through the wire groove and then led out from the lead hole 34 on the side wall of the third shell 3. The input excitation lead wire of the second transformer outer ring 25 is led out through the second lead hole 224 and then led out from the lead hole 34 on the side wall of the third shell 3 for external output.

[0046] The working principle of the dual-redundancy rotary transformer in this embodiment is to design the brushless rotary transformer with redundancy, and the working principle of a single brushless rotary transformer adopts the existing conventional form, which will not be repeated here.

Claims

1. A redundant rotary transformer with a zero alignment structure, characterized in that: It includes two brushless rotary transformers connected in series axially through a connecting housing; A single brushless rotary transformer comprises a housing, a rotating shaft, a rotor assembly, a stator assembly, a transformer outer ring, a transformer inner ring and a bearing; one end of the rotating shaft is supported in the housing through a bearing, the rotor assembly and the transformer inner ring are fixedly mounted on the rotating shaft, and the stator assembly and the transformer outer ring are fixedly mounted on the inner wall of the housing so as to be respectively sleeved outside the rotor assembly and the transformer inner ring; The housings of the two brushless rotary transformers connected in series are respectively recorded as a first housing and a second housing, the rotating shafts are respectively recorded as a first rotating shaft and a second rotating shaft, and the connecting housing used to connect the two brushless rotary transformers is recorded as a third housing; The first rotating shaft is axially butted with the second rotating shaft and fixedly connected by means of shaft hole matching and bonding. During installation and adjustment, the zero position of the rotor assemblies of the two brushless rotary transformers is roughly adjusted by rotating the shaft holes of the first rotating shaft and the second rotating shaft, so that the zero position of the rotor assembly on the first rotating shaft and the rotor assembly on the second rotating shaft are relatively consistent; The third shell is sleeved outside the first shell and the second shell, the first shell is in axial contact with the second shell, and the two ends of the third shell are fixedly connected to the first shell and the second shell through connecting flanges; the inner walls at both ends of the third shell are respectively provided with N first latch teeth and N second latch teeth evenly spaced along the circumference, and the outer side walls of the first shell and the second shell are respectively provided with N first guide grooves and N second guide grooves that match the N first latch teeth and the N second latch teeth one by one, a first annular groove is provided between the N first guide grooves and the connecting flange at the end of the first shell, and a second annular groove is provided between the N second guide grooves and the connecting flange at the end of the second shell; the N first latch teeth of the third shell are snapped with the first annular groove at the end of the first shell after passing through the N first guide grooves of the first shell, and the N second latch teeth of the third shell are snapped with the second annular groove at the end of the second shell after passing through the N second guide grooves of the second shell; During installation and adjustment, the first latch tooth of the third shell passes through the first guide groove and then snaps into the first annular groove, and the second latch tooth of the third shell passes through the second guide groove and then snaps into the second annular groove. The rotation of the first latch tooth in the first annular groove can cause the first shell and the third shell to produce relative rotational movement, and the rotation of the second latch tooth in the second annular groove can cause the second shell and the third shell to produce relative movement, thereby causing the first shell and the second shell to produce relative rotational movement, thereby further aligning the zero position of the stator assembly fixed on the inner wall of the first shell and the stator assembly fixed on the inner wall of the second shell.

2. The redundant rotary transformer with a zero alignment structure according to claim 1, characterized in that: The radial edges of the first latch tooth and the second latch tooth are chamfered, and the distance between the first latch tooth and the second latch tooth is smaller than the distance between the first annular groove and the second annular groove, so that the first latch tooth and the first annular groove are interference fit, and the second latch tooth and the second annular groove are interference fit.

3. The redundant rotary transformer with a zero alignment structure according to claim 1 or 2, characterized in that: The connecting flanges on the first shell and the second shell for connecting with the third shell are both provided with waist-shaped holes, and the connecting flanges at both ends of the third shell are respectively provided with threaded holes corresponding to the waist-shaped holes on the first shell and the second shell.

4. The redundant rotary transformer with a zero alignment structure according to claim 3, characterized in that: The end of the first rotating shaft is designed as a blind hole, and an exhaust hole is opened on the side wall of the blind hole near the bottom of the blind hole. The end of the second rotating shaft is designed as a step shaft. The axial docking of the first rotating shaft and the second rotating shaft is achieved by coating adhesive on the step shaft and inserting it into the blind hole for bonding.

5. The redundant rotary transformer with a zero alignment structure according to claim 4, characterized in that: A wire outlet hole is provided on the side wall of the third shell, a wire groove is provided on the inner side walls of the first shell and the second shell, and a first wire outlet hole and a second wire outlet hole matching the position of the wire outlet hole of the third shell are respectively provided on the side walls of the opening ends of the first shell and the second shell. The input excitation lead wires of the transformer outer rings of the two brushless rotary transformers and the output lead wires of the stator assembly are all led to the first wire outlet hole and the second wire outlet hole through the wire groove, and finally led out from the wire outlet hole of the third shell.

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