JP2012115954A - Tank drilling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify and down-size the structure by operating a support arm so as to increase its diameter with the progress of cutting, and to improve the working efficiency by holding a cutting piece with hole formation by a cutting blade to reduce the hole formation time.SOLUTION: A tank drilling device includes: a movable body 25 rotatably pivoted on a shaft end of a spindle 9 at its base end part, fitted on a shaft body 23 with a cam surface 23a disposed on its leading end part to be axially movable, having a small outer diameter part inserted into a through-hole pierced in advance in a component attaching part and a large outer diameter part abutting on a through-hole peripheral edge, and formed with at least two gaps 25d; a first elastic member 29 energizing the movable body; at least two support arms 31, each being positioned within the gap 25d of the movable body to be swingably pivoted and having a support part 31d disposed on a leading end part of another arm part brought into sliding contact with the cam surface and an outer peripheral surface of the shaft body; and a second elastic member 35 disposed on one arm part side of each support arm and energizing each support arm such that the support part usually moves it toward the diameter reducing side positioned within the gap.

Description

  The present invention relates to a tank drilling device formed in a hole for attaching various parts such as a gauge and a sensor to a tank, particularly a vehicle fuel tank.

  When forming holes for mounting various parts such as gauges and sensors in tanks, especially fuel tanks for vehicles, in order to prevent cut pieces from falling into the tank and becoming dirty, It is desired to drill a hole so that the cut piece is taken out of the tank.

As a tank drilling device that enables removal of a cut piece, for example, a tank drilling device disclosed in Patent Document 1 is known. The tank drilling device mounts a cutter blade at a predetermined distance around a spindle as a rotation center to a drill unit that opens holes for mounting various parts at predetermined locations of a tank, and at the lower part of the spindle, It consists of a piston that moves up and down along the axis of the spindle, a piston rod fixed to the lower part of the piston, and a plurality of arms that are pivoted downward and equidistantly to surround the piston rod. A projection is provided on the inner side in the vicinity of the pivotally attached portion, and a lower end portion of the arm is provided on the outer side to form a claw portion. Further, a cam groove is provided in the piston rod so that the projection portion of the arm Engaging with the cam groove, the protrusion of the arm is pushed up or down by the vertical movement of the piston, and an expansion mechanism portion is provided in which the lower end of the arm is reduced or expanded, A cutter that inserts and expands an expansion mechanism portion into a lower hole that is opened at a predetermined position of the tank, expands the expansion mechanism portion, supports the lower surface portion of the lower hole, and rotates integrally with the spindle. The blade is brought into contact with the surface of the tank to open a hole having a predetermined diameter, and the cutting piece cut out by the cutter blade is held by the expansion mechanism.

  In the expansion mechanism in the conventional tank drilling device described above, a cylinder composed of a piston and a piston rod for expanding or reducing the diameter of the arm supporting the lower surface of the through hole is provided, and is loosely fitted to the spindle. It is configured to operate by supplying compressed air from the formed air pipe.

However, in the above punching device, the structure of the expansion mechanism portion becomes complicated and large, so that the hole could be formed only in a tank in which a through hole of a certain size was formed. . That is, when a small-diameter hole is formed in the tank, the through-hole also has a small diameter according to the formed hole, and in an enlarged expansion mechanism portion, the small-diameter through-hole is inserted and penetrated. It was difficult to form a hole having a desired size.

Further, the air pipe of the expansion mechanism portion needs to be configured to be loosely fitted to the spindle and not to rotate when the spindle rotates. For this reason, the expansion mechanism portion of the punching device provides rotational resistance by inserting the arm into the through hole of the tank and penetrating the arm and expanding the arm to support the lower surface portion of the through hole. Even if the spindle is rotated in this state and the drilling operation is executed, the air pipe is not rotated.

For this reason, prior to forming the hole in the tank, it is necessary to perform the insertion operation of the expansion mechanism portion with respect to the through hole and the support operation to expand the arm to support the lower surface portion, and it takes time for the hole formation work, The through hole formation work efficiency was poor.

Japanese Patent No. 3618693

  The problem to be solved is that the expansion mechanism part of the conventional drilling device requires an operating member such as a cylinder for expanding the arm diameter, so that the expansion mechanism part becomes complicated and large. It is difficult to form a small-diameter hole. Further, when the hole is formed by the rotating cutter blade, it is necessary to prevent the expansion mechanism portion from rotating with respect to the spindle of the drill unit, and the arm of the expansion mechanism portion is attached to the periphery of the through hole prior to the formation of the hole. It must be supported on the lower surface, and it takes time to form the holes, resulting in poor work efficiency.

  The first aspect of the present invention provides a tank hole in which a cutting blade provided at a required distance in a direction orthogonal to the axis from the axis of a spindle that is driven to rotate is rotated around the spindle to form a hole in a component mounting portion of the tank. In the opening device, the base end portion is rotatably supported with respect to the shaft end portion of the spindle, the shaft body is provided with a cam surface at the tip end portion, and the shaft body has a predetermined stroke in the axial direction. It has a small-diameter portion with an outer diameter that can be inserted into a through-hole that is pre-drilled in the component mounting portion, and a large-diameter portion with an outer diameter that abuts the periphery of the through-hole. A movable body having at least two gaps each having an axial length extending over a large diameter portion and a small diameter portion, and two pivotally supported so as to be slidable within the gap between the movable bodies. At the tip of the other arm that is in the shape of a bowl and is in sliding contact with the cam surface and the outer peripheral surface of the shaft body At least two support arms provided with support portions and one arm portion side of each support arm, and each support arm is always moved to the reduced diameter side where the support portion is located in the gap. A second elastic member to be urged, and each support by the other arm portion slidably contacting the cam surface and the outer peripheral surface of the shaft body as the movable body is moved to the proximal end side of the shaft body with respect to the shaft body The periphery of the through-hole can be supported by the respective support portions that swing the arm and move to the enlarged diameter side outside the gap.

According to a second aspect of the present invention, there is provided a tank hole in which a cutting blade provided at a predetermined distance in a direction orthogonal to the axis from a rotationally driven spindle is rotated around the spindle to form a hole in a component mounting portion of the tank. In the opening device, the base end portion is rotatably supported with respect to the shaft end portion of the spindle, the shaft body is provided with a cam surface at the tip end portion, and the shaft body has a predetermined stroke in the axial direction. It has a small-diameter portion with an outer diameter that can be inserted into a through-hole that is pre-drilled in the component mounting portion, and a large-diameter portion with an outer diameter that abuts the periphery of the through-hole. And a first elastic member that urges the movable body toward the distal end side of the shaft body. And a double hook-like shape that is pivotably supported in the gap of the movable body. At least two support arms supporting portion to the tip portion of the other arm portion in sliding contact provided on an outer peripheral surface of the cam surface and the shaft member,
A second elastic member that is provided on one arm portion side of each support arm and urges each support arm so that the support portion always moves to the reduced diameter side located in the gap. On the other hand, as the movable body is moved to the proximal end side of the shaft body against the elastic force of the first elastic member, each support arm is rocked by the other arm portion that is in sliding contact with the cam surface and the outer peripheral surface of the shaft body. The most important feature is that the periphery of the through-hole can be supported by the respective support portions that move to the diameter expansion side outside the gap.

  The present invention can hold the cut piece by gradually increasing the diameter of the support arm as the cutting progresses without providing an operating member such as a cylinder, thereby simplifying the structure and reducing the size. it can. Further, along with the formation of the hole by the rotating cutting blade, the peripheral edge of the through hole can be supported by the support arm to hold the cut piece, and the working efficiency can be improved by shortening the time for forming the hole.

It is a fragmentary perspective view which shows the components attachment part of the tank in which a hole is formed with a tank drilling apparatus. It is a front view of a tank drilling device. It is a center longitudinal cross-sectional view of a tank drilling apparatus. It is explanatory drawing which shows a tank hole initial stage. It is explanatory drawing which shows the state in the middle of a tank hole opening. It is explanatory drawing which shows the state at the time of completion | finish of tank drilling. It is explanatory drawing which shows the state which set the tank drilling apparatus to the removal jig | tool. It is explanatory drawing which shows the state which removed the cutting piece.

  The present invention relates to the other arm that is in sliding contact with the cam surface and the outer peripheral surface of the shaft body as the movable body moves toward the base end side of the shaft body against the elastic force of the first elastic member with respect to the shaft body. It is the best embodiment to enable the periphery of the through-hole to be supported by the respective support portions that are moved by the portions to swing the support arms to the diameter-expanded side outside the gap.

The present invention will be described below with reference to the drawings showing examples.
First, a description will be given of a vehicle fuel tank 5 as a tank provided with a component mounting portion 3 drilled by a tank drilling device 1 according to the present invention. As shown in FIG. 1, the vehicle fuel tank 5 is different. It is made of synthetic resin with a plurality of synthetic resin sheets laminated and attached, and on its upper surface, a number of components are attached to the vehicle fuel tank 5 according to various components such as gauges, various sensors, fuel pumps, etc. Part 3 is formed.

  The component mounting portion 3 is composed of a cylindrical portion 3c having a required outer diameter and height, a male screw 3a being turned on the outer peripheral surface, and an upper surface being closed by a closing plate 3b. In the central portion of the closing plate 3b, there is provided a recess 3e with a required depth, in which a through hole 3d having an inner diameter into which a small-diameter portion 25b of a movable body 25 described later can be fitted is formed in the central portion. . The opening 7 as a hole is formed by cutting the closing plate 3b along the inner peripheral surface of the cylindrical portion 3c. The recess 3e is set to a depth at which the cutting edge of the cutting blade 17 contacts the upper surface of the closing plate 3b when the lower surface of the large-diameter portion 25a of the movable body 25 described later contacts the upper surface of the recess 3e. The

  As shown in FIG. 2 and FIG. 3, the tank drilling device 1 for forming the opening 7 in the closing plate 3b is, for example, an arm of an industrial robot that is controlled to move in at least a three-dimensional direction (both not shown). An opening 7 is automatically formed in the component mounting portion 3 by being attached to the tip portion and controlling the movement of the arm.

  A spindle 9 is rotatably supported on a main body (not shown) of the tank drilling device 1, and a rotary shaft of an electric motor 11 provided on the main body is drivingly connected to the spindle 9. The spindle 9 is rotated at a required number of rotations by driving the electric motor 11.

  A rotating body 13 is fixed to the spindle 9, and the rotating body 13 is provided with a blade attachment arm 15 that extends in the radial direction with the spindle 9 as a rotation center. A cutting blade 17 that extends downward in the figure and coincides with the axis of the spindle 9 and has a blade edge of both blades or a single blade is attached to the tip of the blade mounting arm 15.

  A balancer member 19 is attached to the rotating body 13 on the side opposite to the blade mounting arm 15 and is adjusted so that the weight on the side opposite to the blade mounting arm 15 side coincides with the spindle 9 as a center.

  A shaft portion 19 a of an idle rotating body 19 having an axis coinciding with the spindle 9 is pivotally supported via a bearing 21 at the center of the rotating body 13. As the bearing 21, an angular bearing that receives loads in both the thrust direction and the radial direction is suitable.

A base end portion of the shaft body 23 is fixed to the lower portion of the idle rotating body 19, and a cam surface 23a having a gradually decreasing diameter toward the distal end is provided at a distal end portion (lower end side in the drawing) of the shaft body 23. Is formed. Further, a support hole 23b extending in the axial direction with a required length is formed in the axial direction intermediate portion of the shaft body 23.

A shaft end of a support shaft 27 supported by the support hole 23b is fixed to the movable body 25 supported so as to slide in the axial direction with respect to the shaft body 23, and the movable body 25 is It is moved in the axial direction with a stroke corresponding to the axial length of the support hole 23b. Further, the movable body 25 is always urged downward along the axis by the spring force of the first compression spring 29 as the first elastic member mounted on the shaft body 23.

The movable body 25 has a large-diameter portion 25a that contacts the upper surface of the recess 3e at the periphery of the through-hole 3d, and extends downward from the lower portion of the large-diameter portion 25a, and has an outer diameter that can be inserted into the through-hole 3d. A small-diameter portion 25b is formed, and the movable body 25 extending from the lower portion of the large-diameter portion 25a to the small-diameter portion 25b has three gaps 25d extending in the axial direction and communicating with the shaft hole 25c around the axis. On the other hand, they are formed at equal intervals.

Within each gap 25d, a support arm 31 is supported so as to be swingable about a shaft 33 provided at the lower portion of the large diameter portion 25a. On one arm portion 31a of each support arm 31, there is a protrusion 31b on which a second compression spring 35 as a second elastic member provided in a spring mounting hole 25e formed in the large diameter portion 25a is latched. It is formed.

The other arm portion 31c of each support arm 31 extends so as to contact the outer peripheral surface of the shaft body 23 and the cam surface 23a, and a claw portion 31d as a support portion is formed at the tip portion. Each support arm 31 has a reduced diameter side where the claw portion 31d is located in the gap 25d of the small diameter portion 25b by the spring force of the second compression spring 31 and the gap 25d against the spring force of the second compression spring 31. It is oscillated between the enlarged diameter side located outside.

  The large-diameter portion 25a of the movable body 25 is formed with a plurality (three in the illustrated example) of mounting holes 25f penetrating in a radial direction perpendicular to the axis line at equal intervals in the circumferential direction. The engagement pin 37 is supported in the hole 25f so as to move in the radial direction. Each engagement pin 37 is engaged with a protrusion 23c as an engaged portion, the tip of which is formed around the axis of the outer peripheral surface of the shaft body 23 by the spring force of the third compression spring 39 constituting the third elastic member. Energized as possible.

Next, the operation of forming the opening 7 by the tank punching device 1 configured as described above will be described.
First, the initial state of the tank drilling device 1 will be described. With respect to the shaft body 23, the movable body 25 is arranged such that the support shaft 27 is positioned at the tip of the support hole 23b by the spring force of the first compression spring 29. Moved to. In this state, the other arm portion 31c of each support arm 31 abuts on the small diameter side of the cam surface 23a of the shaft body 23 and swings so that the claw portion 31d is positioned on the reduced diameter side by the spring force of the second compression spring 35. Is done.

  Next, in order to form the opening 7 in the closing plate 3b in the component mounting portion 3 by the tank drilling device 1 described above, the arm of the work robot is controlled to move the tank drilling device 1 with its shaft 23 closed. It is inserted into the through hole 3d of the recess 3e in the plate 3b and moved so that the lower surface of the small diameter portion 25b of the movable body 25 contacts the upper surface of the recess 3e. In this state, the cutting edge of the cutting blade 17 is in contact with or as close as possible to the upper surface of the closing plate 3b. (See Figure 4)

  Next, in the above-described state, the electric motor 11 is driven while the tank drilling device 1 is pressurized at a required pressure with respect to the vehicle fuel tank 5, and the cutting blade 17 is rotated about the spindle 9 to close the closing plate. Start cutting 3b. When the shaft body 23 is gradually moved inward of the vehicle fuel tank 5 according to the cutting depth of the closing plate 3b as the cutting blade 17 cuts the closing plate 3b, the movable body 25 is The shaft body 23 is gradually moved upward in the illustrated axis against the spring force of the first compression spring 29.

Each support arm 31 has a spring force of the second compression spring 35 as the other arm 31c slides from the small diameter surface side to the large diameter surface side of the cam surface 23a as the movable body 25 moves relative to the shaft body 23. The claws 31d are rocked so as to gradually move toward the diameter-expanding side. Thereby, each claw part 31d which moves to the diameter expansion side is positioned on the lower surface side of the recess 3e at the periphery of the through hole 3d and can be supported.
(See Figure 5)

  In the final stage of the cutting operation of the closing plate 3 b by the cutting blade 17, the movable body 25 is further moved above the axis with respect to the shaft body 23 as the cutting of the closing plate 3 b progresses. At this time, each support arm 31 is kept in a swinging state in which each claw portion 31d is moved to the larger diameter side by the other arm portion 31c being brought into sliding contact with the outer peripheral surface of the shaft body 23 from the large diameter surface of the cam surface 23a. Be drunk. Further, when the movable body 25 moves upward with respect to the shaft body 23, the engagement pin 37 that is biased by the spring force of the third compression spring 39 and presses against the outer peripheral surface of the shaft body 23 is The body 23 is moved radially outward against the spring force of the third compression spring 37 by sliding contact with the protrusion 23c, and then moved radially inward by the spring force to get over the protrusion 23c. The pressure contact state with respect to the outer peripheral surface is maintained.

When the cutting operation of the closing plate 3b by the cutting blade 17 is completed and the cut piece 3f is cut out, the movable body 25 biased by the spring force of the first compression spring 29 has the engaging pin 37 at the protrusion 23c. It is moved to a position below the engaged axis. In this state, each support arm 31 is kept in a peristaltic state in which the claw portion 31d is moved to the enlarged diameter side by the contact of the other arm portion 31c with the outer peripheral surface of the shaft body 23. The peripheral edge of the through hole 3d in the cut piece 3f cut by 31d is supported, the cut piece 3f is prevented from coming out of the movable body 25, and the holding state is maintained, and the cut piece 3f falls into the vehicle fuel tank 5 To prevent. (See Figure 6)

After the opening 7 is formed in the component mounting portion 3 by the above-described action, the arm of the work robot is controlled to move so that the tank drilling device 1 is moved away from the component mounting portion 3 and the movable body 25 is moved. The cut pieces 3f that are inserted into and held by the claw portions 31d of the support arms 31 are removed from the openings 7.

In order to remove the cut piece 3f from the movable body 25, the tank drilling device 1 is moved and controlled so that the shaft body 23 is positioned between the arm portions 41a of the substantially U-shaped removal jig 41 in the plane. The upper surface of the movable body 25 is brought into contact with the portion 41a.

Next, when the tank punching device 1 is moved so that the movable body 25 is in pressure contact with the arm portion 41a in the above state, the engaging pin 37 whose tip is engaged with the projection 23c is moved along with this movement. The engagement is forcibly released by moving outward in the radial direction against the spring force of the third compression spring 39. As a result, the movable body 25 moves to the distal end side with respect to the shaft body 23 by the spring force of the first compression spring 29, and the claw portion 31d moves to the reduced diameter side of each support arm 31 along with the movement. As a result, the support of the claw portion 31b with respect to the cut piece 3f is released, and the cut piece 3f is detached from the movable body 25. (See Figs. 7 and 8)

  In the present embodiment, as the cutting plate 17 b is rotated by the rotating cutting blade 17, each support arm 31 is moved by the movable body 25 that moves relative to the shaft body 23, and each claw portion 31 d is moved to the diameter-expanded side. By swinging so as to move, the periphery of the through-hole 3d can be supported, and the cut piece 3f is held and prevented from falling into the vehicle fuel tank 5. For this reason, it is possible to reduce the size of the apparatus itself without using a cylinder that operates the arm supporting the lower surface of the peripheral edge of the through hole in the diameter increasing direction as in the case of the conventional expansion mechanism, and the small diameter opening 7 is also efficient. Can be formed.

When the movable body 25 is moved to a predetermined position with respect to the shaft body 23 at the end of cutting, the engaging pin 37 is engaged with the protrusion 23 c so that the movable body 25 is moved by the spring force of the first compression spring 29. The cutting piece 3f is held by the claw portion 31d of each support arm 31 by restricting the return, and the cutting piece 3f is prevented from falling into the vehicle fuel tank 5 and out of the vehicle fuel tank 5. It is possible to take out.

The above description is attached so that the movable body 25 is moved toward the distal end side of the shaft body 23 by the first compression spring 29 that urges the movable body 25 downward in the axis line corresponding to the invention described in claim 2. The support arm 31 is urged to swing in the direction in which the claw portion 31d is reduced in diameter. However, in claim 1, the first compression spring 29 is not an essential invention.

That is, in the invention of claim 2 in which the first compression spring 29 is provided, when the opening 7 is formed by the cutting blade 17, the weight of the movable body 25 relative to the upper surface of the recess 3 e and the first compression spring 29. A load according to the spring force acts, and the closing plate 3b is bent by the load, and the cutting accuracy of the opening 7 may be deteriorated. In order to avoid this, the invention of claim 1 does not provide the first elastic member, and when the opening 7 is cut, only the dead weight of the movable body 25 acts to reduce the bending of the closing plate 3b, thereby cutting the opening 7. Improve accuracy.

DESCRIPTION OF SYMBOLS 1 Tank drilling device 3 Component attachment part 3a Male screw 3b Closure board 3c Cylindrical part 3d Through-hole 3e Recess 3f Cutting piece 5 Vehicle fuel tank 7 as a tank 9 Opening 9 Spindle 11 Electric motor 13 Rotating body 13a Balancer member 15 Cutlery Mounting arm 17 Cutting blade 19 Spinning rotating body 19a Shaft portion 21 Bearing 23 Shaft body 23a Cam surface 23b Shaft support hole 23c Projection portion 25 as engaged portion Movable body 25a Large diameter portion 25b Small diameter portion 25c Hollow portion 25d Clearance 25e Spring mounting hole 25f Mounting hole 27 Support shaft 29 First compression spring 31 as first elastic member Support arm 31a One arm portion 31b Projection portion 31c Other arm portion 31d Claw portion 33 as support portion Shaft 35 As second elastic member Second compression spring 37 Engagement pin 39 Third compression spring 41 as a third elastic member Removal jig 41a Arm

Claims (6)

In a tank drilling device in which a cutting blade provided at a required distance in the direction perpendicular to the axis from the axis of the rotationally driven spindle is rotated around the spindle to form a hole in the component mounting portion of the tank.
A shaft body having a base end rotatably supported with respect to the shaft end of the spindle and a cam surface provided at the tip;
An outer diameter that is inserted into the shaft body so as to be movable in a predetermined stroke in the axial direction, and that has a small outer diameter portion that can be inserted into a through hole previously drilled in the component mounting portion and an outer diameter of the through hole. A movable body having a large-diameter portion, communicating with a shaft hole into which the shaft body is inserted, and having at least two gaps formed of axial lengths extending over the large-diameter portion and the small-diameter portion;
At least two supporting portions provided at the tip of the other arm portion that is slidably contacted with the cam surface and the outer peripheral surface of the shaft body in a two-rod shape that is pivotably supported in the gap of the movable body. A support arm of
A second elastic member provided on one arm portion side of each support arm and biasing each support arm so that the support portion always moves to the reduced diameter side positioned in the gap;
With
As the movable body moves relative to the shaft body toward the base end side of the shaft body, each support arm is oscillated by the other arm portion slidably contacting the cam surface and the outer peripheral surface of the shaft body to expand the diameter outside the gap. A tank drilling device that enables the periphery of the through-hole to be supported by the respective support portions that move to. In a tank drilling device in which a cutting blade provided at a required distance in the direction perpendicular to the axis from the axis of the rotationally driven spindle is rotated around the spindle to form a hole in the component mounting portion of the tank.
A shaft body having a base end rotatably supported with respect to the shaft end of the spindle and a cam surface provided at the tip;
An outer diameter that is inserted into the shaft body so as to be movable in a predetermined stroke in the axial direction, and that has a small outer diameter portion that can be inserted into a through hole previously drilled in the component mounting portion and an outer diameter of the through hole. A movable body having a large-diameter portion, communicating with a shaft hole into which the shaft body is inserted, and having at least two gaps formed of axial lengths extending over the large-diameter portion and the small-diameter portion;
A first elastic member for urging the movable body toward the distal end side of the shaft body;
At least two supporting portions provided at the tip of the other arm portion that is slidably contacted with the cam surface and the outer peripheral surface of the shaft body in a two-rod shape that is pivotably supported in the gap of the movable body. A support arm of
A second elastic member provided on one arm portion side of each support arm and biasing each support arm so that the support portion always moves to the reduced diameter side positioned in the gap;
With
Each support is supported by the cam surface and the other arm portion that is in sliding contact with the outer peripheral surface of the shaft body as the movable body moves toward the proximal end side of the shaft body against the elastic force of the first elastic member with respect to the shaft body. A tank drilling device that can support the periphery of a through-hole by means of each support portion that moves to the diameter expansion side outside the gap by swinging the arm. 3. The movable body according to claim 1, wherein a shaft end of a support shaft that is slidably supported in a support hole formed in the shaft body is fixed, and the movable body moves in an axial direction with respect to the shaft body. Tank drilling device supported as possible. 3. The tank drilling device according to claim 1, wherein the cam surface gradually decreases in diameter toward the tip of the shaft body. 3. The movable body according to claim 1, wherein an attachment hole extending in a direction orthogonal to the axis is formed in the movable body, and the engagement is urged by the third elastic member in the attachment hole. When a pin is attached and the movable body moves toward the base end side of the shaft body against the elastic force of the first elastic member, the pin is engaged with the engaged portion provided on the shaft body. A tank drilling device that can maintain the moving state of the movable body. In claim 5, when the moving state of the movable body with respect to the shaft body is maintained by the engagement of the engagement pin with the engaged portion, each support arm is in a peristaltic state in which each support portion has moved to the enlarged diameter side. Tank drilling device to be held.

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