Four-wheel magnetic wheel driving mechanism for inspection robot running along double-circular tube track

Abstract

The application belongs to the technical field of inspection robots, and particularly discloses a four-wheel magnetic wheel driving mechanism for an inspection robot running along a double-circular-pipe track, which comprises a three-degree-of-freedom driving frame, the three-degree-of-freedom driving frame comprises a rotaryly connected arm frame connecting frame and a rotary arm frame connecting frame, the other ends of the arm frame connecting frame and the rotary arm frame connecting frame are rotaryly connected with the middle parts of corresponding driving connecting cross arms, magnetic driving units are arranged above the ends of the driving connecting cross arms, respectively, and an inspection robot body is detachably connected below the arm frame connecting frame and / or the rotary arm frame connecting frame, the magnetic wheels of the magnetic driving units are magnetically connected with the circular steel pipes of the double-circular-pipe track, and the explosion-proof motor drives the magnetic wheels to roll along the double-circular-pipe track, the center of gravity of the whole formed by the four sets of magnetic wheel driving units and the inspection robot body is close to the double-circular-pipe track, the risk of the robot falling off the double-circular-pipe track when vertically climbing is greatly reduced, vertical climbing, stable pitching and horizontal turning are realized, and stable operation is ensured.

Description

Technical Field

[0001] This invention belongs to the field of inspection robot technology, and specifically discloses a four-wheel drive magnetic suction wheel drive mechanism for an inspection robot that runs along a double circular tube track. Background Technology

[0002] The refining and reforming unit is a crucial component of an oil refinery. To ensure its safe and stable operation, most inspections are currently conducted manually. However, due to the high steel frame of the reforming unit, reaching 70-80 meters in some areas, and the dense piping and confined space, manual inspections rely primarily on steel ladders to reach the inspection site. This presents challenges such as high labor intensity, unpleasant odors, and the harsh outdoor environment of extreme temperatures. While inspection robots can address these issues, the large vertical climbs, horizontal turns, and pitching / bending movements involved in the inspection process pose a risk of detaching from the dual-circular-tube track, thus failing to meet inspection requirements. Furthermore, due to factors such as stress deformation of materials during manufacturing and installation, and thermal expansion and contraction in the outdoor environment, it is difficult to maintain precise parallelism between the two tracks and the spacing between the circular tubes. This results in deflection when passing through the two sections of the circular tube, compromising stable operation. Summary of the Invention

[0003] To address the problems in the background art, this invention discloses a four-wheel magnetic suction wheel drive mechanism for an inspection robot that runs along a double-circular tube track. The mechanism includes a three-degree-of-freedom drive frame and a magnetic suction drive unit. The magnetic suction wheel of the magnetic suction drive unit is magnetically attracted to the circular tube track and is movably connected to the three-degree-of-freedom drive frame, ensuring that the inspection robot can run stably along the double-circular tube track and meet the inspection requirements.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0005] A four-wheel drive mechanism for an inspection robot that runs along a double-circular-tube track. The double-circular-tube track includes a first circular steel tube and a second circular steel tube arranged in parallel. It includes a three-degree-of-freedom drive frame and an explosion-proof motor. The three-degree-of-freedom drive frame includes a rotatably connected boom connecting frame and a slewing boom connecting frame. The boom connecting frame and the slewing boom connecting frame are each capable of rotating around a horizontally arranged central axis. The other ends of the boom connecting frame and the slewing boom connecting frame are rotatably connected to the middle of a drive connecting crossarm via vertically arranged connecting shafts. The drive connecting crossarm is located on the first and second circular steel tubes. Between the boom connecting frame and / or the slewing boom connecting frame, the inspection robot body is detachably connected via a connector below. Above the end of the drive connecting crossarm, a magnetic drive unit is respectively provided. The magnetic drive unit includes a magnetic wheel and a frame. The frame has an n-type structure. One end of the frame adjacent to the drive connecting crossarm is fixedly connected to the drive connecting crossarm. The magnetic wheel is rotatably arranged between the opposite faces of the corresponding frame. The magnetic wheel is magnetically connected to the first or second round steel pipe. The output shaft of the explosion-proof motor is driven by the magnetic wheel to drive the magnetic wheel to roll along the double round pipe track.

[0006] Furthermore, the four-wheel drive mechanism of the inspection robot running along the double circular tube track has a side guard wheel rotatably connected to one end of the frame away from the corresponding drive connection crossarm, and the side guard wheel makes rolling contact with the first circular steel tube or the second circular steel tube.

[0007] Furthermore, the four-wheel drive magnetic chuck of the inspection robot running along the double-circular tube track has a matching key and keyway between the output shaft of the explosion-proof motor and the magnetic chuck. Under the action of the key and keyway, the magnetic chuck can move along the axial direction of the output shaft of the explosion-proof motor to adapt to the track gauge deviation of the double-circular tube track.

[0008] Furthermore, the four-wheel drive mechanism of the inspection robot running along the double circular tube track has an annular groove formed in the middle of the annular wall of the magnetic suction wheel, and the wall of the annular groove is matched with the first or second circular steel tube.

[0009] Furthermore, the four-wheel drive mechanism of the inspection robot running along the double-circular tube track includes a front drive connecting crossarm located at the front end of the boom connecting frame and a rear drive connecting crossarm located at the rear end of the slewing boom connecting frame. The angle between the front drive connecting crossarm and the boom connecting frame and the angle between the rear drive connecting crossarm and the slewing boom connecting frame are adjustable.

[0010] Furthermore, the four-wheel drive mechanism of the inspection robot running along the double-circular tube track includes a servo motor as its explosion-proof motor. The servo motor is installed in the explosion-proof motor cavity of the variable-diameter cylindrical structure. The large-diameter end of the explosion-proof motor cavity is sealed to the explosion-proof rear cover, and the small-diameter end of the explosion-proof motor cavity is sealed to the connecting flange. The output end of the servo motor passes through the connecting flange and is connected to one end of the output shaft for transmission. An explosion-proof copper sleeve and a bearing are provided between the output end of the servo motor and the inner wall of the small-diameter end of the explosion-proof motor cavity.

[0011] Compared with the prior art, the beneficial effects of the present invention are:

[0012] This invention discloses a four-wheel magnetic drive mechanism for an inspection robot that runs along a double-circular tube track. It includes a three-degree-of-freedom drive frame and an explosion-proof motor. The three-degree-of-freedom drive frame includes a rotatably connected boom connecting frame and a rotary boom connecting frame. The other ends of the boom connecting frame and the rotary boom connecting frame are rotatably connected to the middle of corresponding drive connecting crossarms. The drive connecting crossarms are positioned between a first circular steel pipe and a second circular steel pipe. Magnetic drive units are respectively arranged above the ends of the drive connecting crossarms. The inspection robot body is detachably connected to the bottom of the boom connecting frame and / or the rotary boom connecting frame via connectors. The magnetic wheels of the magnetic drive units are magnetically connected to the first or second circular steel pipe. The output shaft of the explosion-proof motor is driven by the magnetic wheels, driving them to roll along the double-circular tube track. Four sets of magnetic drive units are arranged on one side of the double-circular tube track, and the inspection robot body is on the other side. The center of gravity of the entire system, consisting of the magnetic wheel drive unit and the inspection robot body, is close to that of the double-tube track, greatly reducing the risk of the robot falling off the track during vertical climbing. Furthermore, the magnetic wheels of the four magnetic drive units provide sufficient magnetic force, fully utilizing the friction of each wheel to convert it into driving force, thus improving the robot's safety factor against falling while running along the vertical track. The three-degree-of-freedom drive frame has three degrees of freedom. When the inspection robot bends horizontally along the double-tube track, the three-degree-of-freedom drive frame can sway its angle. The inner and outer explosion-proof motors rotate according to a set speed ratio, and the inner and outer magnetic wheels move at different speeds. By setting the speed, it can adapt to the spacing and parallelism errors of the tube track, ensuring that the magnetic wheels adhere to the steel tube track without constraint, enabling vertical climbing, as well as smooth pitching and horizontal turning. This solves the problem of the robot's flexible deviation when passing through two sections of tubes, ensuring stable operation. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the overall structure of the four-wheel drive magnetic chuck drive mechanism of the inspection robot of the present invention;

[0015] Figure 2 yes Figure 1 A schematic diagram of the axonal structure of a three-degree-of-freedom drive frame;

[0016] Figure 3 yes Figure 1 Exploded view of the three-degree-of-freedom drive frame;

[0017] Figure 4 yes Figure 1 Exploded view of the magnetic attraction drive unit;

[0018] Figure 5 yes Figure 1 A partial cross-sectional view of the magnetic attraction drive unit;

[0019] Figure 6 yes Figure 1 A cross-sectional view of the explosion-proof motor.

[0020] Figure 7 A schematic diagram of the vertical climbing state of the inspection robot in this invention;

[0021] Figure 8 This is a schematic diagram of the horizontal bending state of the inspection robot in this invention;

[0022] In the above diagram: 01-Three-degree-of-freedom drive frame; 02-Magnetic drive unit; 03-Explosion-proof motor; 04-Double circular tube track; 05-Circular steel tube track frame; 06-Inspection robot body;

[0023] 101-Drive connecting crossarm; 102-Cross roller bearing; 103-Connecting shaft; 104-Bearing waterproof cover; 105-Locking nut; 106-First boom connecting frame; 107-Second boom connecting frame; 108-Bottom connecting frame; 109-Clamp; 110-Spherical bearing; 111-Spherical bearing connecting rod; 112-Slewing boom connecting frame; 113-Split cover; 114-Split seat; 115-Copper sleeve;

[0024] 201-Magnetic chuck; 202-Frame; 203-Ball bearing; 204-Bearing cap; 205-Side guard wheel; 206-Hex socket head cap screw;

[0025] 301-Explosion-proof rear cover; 302-Explosion-proof motor cavity; 303-Servo motor; 304-Explosion-proof copper sleeve; 305-Bearing; 306-Connecting flange; 307-Skeleton seal; 308-Output shaft; 309-Explosion-proof plug; 310-Screw; 311-Screw sealing ring; 312-Large sealing ring; 313-Small sealing ring; 314-Cable sealing ring; 315-Cable tip;

[0026] 401 - First round steel pipe; 402 - Second round steel pipe. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details. It should be noted that the four-wheel drive magnetic suction wheel drive mechanism of the inspection robot running along the double-circular tube track is controlled by the inspection robot's main control system. The control system is not an innovative point of the present invention, therefore, the control system will not be described in detail.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0030] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, 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 present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0031] Combined with appendix Figure 1-6This invention details a four-wheel drive magnetic chuck mechanism for an inspection robot that runs along a double-circular-tube track. The double-circular-tube track 04 includes a first circular steel tube 401 and a second circular steel tube 402 arranged in parallel. The bottoms of the first circular steel tube 401 and the second circular steel tube 402 are respectively fixedly connected to a circular steel tube track frame 05 arranged above them via connecting rods. The circular steel tube track frame 05 does not interfere with the movement of the four-wheel drive magnetic chuck mechanism of the inspection robot that runs along the double-circular-tube track. It includes a three-degree-of-freedom drive frame 01 and an explosion-proof motor 03. The three-degree-of-freedom drive frame 01 includes a rotatably connected boom connecting frame and a rotary boom connecting frame 112. The boom connecting frame and the rotary boom connecting frame 112 are connected by a joint bearing 110 and a joint bearing connecting rod 11. 1. Rotary connection: The boom connecting frame and the slewing boom connecting frame 112 can rotate around a horizontally set central axis respectively. The boom connecting frame includes a first boom connecting frame 106 and a second boom connecting frame 107 detachably connected by screws. The first boom connecting frame 106 and the second boom connecting frame 107 together form a rectangular boom connecting frame. The other end of the boom connecting frame is rotatably connected to the middle of the front drive connecting crossarm through a vertically set connecting shaft 103. The other end of the slewing boom connecting frame 112 is rotatably connected to the middle of the rear drive connecting crossarm through another boom connecting frame and the vertically set connecting shaft 103. Cross roller shafts are respectively set between the connecting shaft 103 and the rear drive connecting crossarm and between the connecting shaft 103 and the front drive connecting crossarm. The upper end of the connecting shaft 103 passes through the first boom connecting frame 106 and is screwed with a locking nut 105. The lower end of the connecting shaft 103 is fitted with a bearing waterproof cover 104. The drive connecting crossbeam 101 is located between the first round steel pipe 401 and the second round steel pipe 402. The inspection robot body 06 is detachably connected to the lower part of the boom connecting frame via a bottom connecting frame 108 and a clamp 109, and / or the inspection robot body 06 is detachably connected to the lower part of the rotating boom connecting frame 112 via a split cover 113, a split seat 114, and a copper sleeve 115. Magnetic drive units 02 are respectively provided above the ends of the drive connecting crossbeam 101. The magnetic drive units 02 include magnetic wheels 201 and frames 202. The magnetic roller 201 is made of neodymium iron boron high-strength magnetic material and laminated with steel plate to overcome the defect of high-strength magnetic material being easily broken by impact. The frame 202 has an n-type structure. One end of the frame 202 adjacent to the drive connection crossbeam 101 is fixedly connected to the drive connection crossbeam 101 by hexagonal screws 206. The magnetic roller 201 is rotatably set between the opposite surfaces of the corresponding frame 202. The magnetic roller 201 is magnetically connected to the first round steel tube 401 or the second round steel tube 402. The output shaft 308 of the explosion-proof motor 03 is connected to the magnetic roller 201 to drive the magnetic roller 201 to roll along the double round tube track 04. The end of the output shaft 308 is rotatably connected to the corresponding frame 202 through ball bearing 203. The end of the ball bearing 203 is fitted with a bearing cap 204.

[0032] like Figure 1 and Figure 7 As shown, taking the horizontal arrangement of the double-tube track as an example, four sets of magnetic wheel drive units 02 are set on one side of the double-tube track, and the inspection robot body 06 is on the other side of the double-tube track. In this way, the center of gravity of the whole formed by the four sets of magnetic wheel drive units 02 and the inspection robot body 06 is close to the double-tube track. At the same time, the magnetic attraction between the magnetic wheels 201 of the four sets of magnetic wheel drive units 02 and the steel tube is equivalent to pressure to provide sufficient friction, which improves the safety factor of the robot in preventing it from falling off the vertical track and greatly reduces the risk of the inspection robot falling off the double-tube track when climbing vertically.

[0033] like Figure 8 As shown, the four-wheel drive mechanism of the inspection robot running along the double-circular tube track of this invention has three degrees of freedom, which can adapt to the spacing error and parallelism error of the circular tube track, ensuring that the magnetic chuck 201 adsorbs the steel tube track without constraint and provides sufficient magnetic attraction force. When the inspection robot running along the double-circular tube track makes a horizontal turn, the drive mechanism can deflect by an angle. The explosion-proof motors 03 of the inner and outer rings rotate according to the set speed ratio, and the magnetic chuck 201 of the inner and outer rings move at different speeds to achieve smooth turning. This solves the problem of the robot having a flexible deviation when passing through two sections of circular tubes and ensures stable operation.

[0034] As an optional design, such as Figure 4 and Figure 5 As shown, the preferred four-wheel drive mechanism of the inspection robot running along the double circular tube track has a side guard wheel 205 rotatably connected to one end of the frame 202 away from the corresponding drive connection crossbeam 101. The side guard wheel 205 rolls in contact with the first circular steel tube 401 or the second circular steel tube 402. When running in a horizontal bend, if the magnetic suction wheel 201 rotates abnormally and there is a risk of it derailing, the side guard wheel 205 can apply a force to the magnetic suction wheel 201 to prevent it from derailing, thus playing a certain safety protection role.

[0035] As an optional design, such as Figure 5 As shown, the preferred four-wheel drive mechanism of the inspection robot running along the double circular tube track has a matching key and keyway between the output shaft 308 of the explosion-proof motor 03 and the magnetic wheel 201. Under the action of the key and keyway, the magnetic wheel 201 can move along the axial direction of the output shaft 308 of the explosion-proof motor 03 to finely adjust the distance between the two magnetic wheels 201 at both ends of the same drive connection crossarm, so as to adapt to the track gauge deviation of the double circular tube track 04.

[0036] As an optional design, such as Figure 4 and Figure 5As shown, the preferred four-wheel drive mechanism of the inspection robot running along the double circular tube track has an annular groove formed in the middle of the annular wall of the magnetic suction wheel 201, and the wall of the annular groove is matched with the first circular steel tube 401 or the second circular steel tube 402.

[0037] As an optional design, the preferred four-wheel drive mechanism of the inspection robot running along the double-tube track includes a front drive connecting crossarm 101 located at the front end of the boom connecting frame and a rear drive connecting crossarm 101 located at the rear end of the rotary boom connecting frame 112. The angle α between the front drive connecting crossarm 101 and the boom connecting frame and the angle β between the rear drive connecting crossarm 101 and the rotary boom connecting frame 112 are adjustable. When the inspection robot running along the double-tube track bends horizontally, the three-degree-of-freedom drive frame 01 can sway the angle and adjust the size of angles α and β. As shown in Figure 8, the explosion-proof motors of the inner and outer rings rotate according to the set speed ratio, and the magnetic wheels of the four sets of magnetic wheel drive units 02 move at different speeds to make smooth turns.

[0038] As an optional design, such as Figure 6 As shown, the preferred four-wheel drive mechanism of the inspection robot running along the double-circular tube track includes an explosion-proof motor 303, which is a servo motor 303. The servo motor 303 is housed in an explosion-proof motor cavity 302 with a variable-diameter cylindrical structure. The servo motor 303 and the explosion-proof motor cavity 302 are connected by screws 310. An explosion-proof plug 309 and a screw sealing ring 311 are also provided between the explosion-proof motor cavity 302 and the screws 310. The two ends of the explosion-proof motor cavity 302 are fixedly connected to the explosion-proof rear cover 301 and the connecting flange 306 by screws. The explosion-proof rear cover 301 has a through hole for the cable of the servo motor 303 to pass through. A cable sealing ring 314 and a cable nozzle 315 are provided in the through hole. A large sealing ring 312 is provided between the contact surface of the large diameter end and the explosion-proof rear cover 301, and a small sealing ring 313 is provided between the contact surface of the small diameter end of the explosion-proof motor cavity 302 and the connecting flange 306, which serves to prevent explosion, seal and waterproof. The output end of the servo motor 303 passes through the connecting flange 306 and is connected to one end of the output shaft 308. The other end of the output shaft 308 is keyed to the magnetic chuck 201. An explosion-proof copper sleeve 304, a bearing 305 and a skeleton seal 307 are provided between the output end of the servo motor 303 and the inner wall of the small diameter end of the explosion-proof motor cavity 302. The explosion-proof copper sleeve 304 and the bearing 305 are installed in the explosion-proof motor cavity 302, which serves to prevent explosion and support the rotation of the output shaft 308.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A four-wheel magnetic wheel driving mechanism for a robot for inspection along a double circular tube track, the double circular tube track comprising a first circular steel tube and a second circular steel tube arranged in parallel, characterized in that: The three-degree-of-freedom driving frame comprises a rotaryly connected arm frame connecting frame and a rotary arm frame connecting frame, the arm frame connecting frame and the rotary arm frame connecting frame can rotate around a horizontally arranged central axis, the other ends of the arm frame connecting frame and the rotary arm frame connecting frame are rotaryly connected with a middle part of a driving connection cross arm through a vertically arranged connecting shaft, the driving connection cross arm is arranged between a first circular steel pipe and a second circular steel pipe, a patrol robot body is detachably connected below the arm frame connecting frame and / or the rotary arm frame connecting frame through a connecting piece, a magnetic attraction driving unit is arranged above an end of the driving connection cross arm, the magnetic attraction driving unit comprises a magnetic attraction wheel and a frame, the frame is an n-shaped structure, one end of the frame adjacent to the driving connection cross arm is fixedly connected with the driving connection cross arm, the magnetic attraction wheel is rotaryly arranged between opposite surfaces of the corresponding frame, the magnetic attraction wheel is magnetically connected with the first circular steel pipe or the second circular steel pipe, an output shaft of an explosion-proof motor is in transmission connection with the magnetic attraction wheel to drive the magnetic attraction wheel to roll along a double circular pipe track, four sets of magnetic attraction wheel driving units are arranged on one side of the double circular pipe track, the patrol robot body is arranged on the other side of the double circular pipe track, and the gravity center of the whole formed by the four sets of magnetic attraction wheel driving units and the patrol robot body is close to the double circular pipe track.

2. The four-wheel magnetic wheel driving mechanism for the inspection robot running along the double-circular track according to claim 1, characterized in that in One end of the frame away from the corresponding driving connection cross arm is rotaryly connected with a flange wheel, and the flange wheel is in rolling contact with the first circular steel pipe or the second circular steel pipe.

3. The four-wheel magnetic wheel driving mechanism for the inspection robot running along the double-circular track according to claim 1 or 2, characterized in that: A key and a key groove are arranged between the output shaft of the explosion-proof motor and the magnetic attraction wheel, under the action of the key and the key groove, the magnetic attraction wheel can move along the axial direction of the output shaft of the explosion-proof motor to adapt to the track gauge deviation of the double circular pipe track.

4. The four-wheel magnetic wheel driving mechanism for the inspection robot running along the double-circular track according to claim 3, characterized in that: A ring groove is formed in the middle of the annular wall surface of the magnetic attraction wheel, and the wall surface of the ring groove is arranged in matching with the first circular steel pipe or the second circular steel pipe.

5. The four-wheel magnetic wheel driving mechanism for the inspection robot running along the double-circular track according to claim 3, characterized in that: The driving connection cross arm comprises a front driving connection cross arm arranged at the front end of the arm frame connecting frame and a rear driving connection cross arm arranged at the rear end of the rotary arm frame connecting frame, and the included angles between the front driving connection cross arm and the arm frame connecting frame and between the rear driving connection cross arm and the rotary arm frame connecting frame can be adjusted.

6. The four-wheel magnetic wheel driving mechanism for the inspection robot running along the double-circular track according to claim 3, characterized in that: The explosion-proof motor comprises a servo motor, the servo motor is arranged in an explosion-proof motor cavity in a variable-diameter cylindrical structure, a large-diameter end of the explosion-proof motor cavity is sealingly connected with an explosion-proof rear cover, a small-diameter end of the explosion-proof motor cavity is sealingly connected with a connecting flange, an output end of the servo motor penetrates through the connecting flange and is in transmission connection with one end of an output shaft, and an explosion-proof copper sleeve and a bearing are arranged between the output end of the servo motor and the inner wall of the small-diameter end of the explosion-proof motor cavity.

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