JPH06193390A - Small aperture pipe excavating propeller - Google Patents

Abstract

PURPOSE:To bend the whole leading body unforcedly and correct the direction of a leading hole easily by connecting the head section and succeeding section of an internal casing by a universal joint composed of a spherical contacting section and the engaging section of a polygon. CONSTITUTION:A head section 73 is rotated and driven from a succeeding section 7b by universal axial bond in the head section 7a and succeeding section 7b of an internal casing, and the head section 7a and the succeeding section 7b are turned mutually under the state, in which both sections 7a and 7b are inclined at a specified angle, according to the conditions of excavation. A guide boring rod 20 is revolved and driven apart from the internal casing 7 first, and a guide hole is dug while the guide boring rod 20 is propelled forward. When the direction of excavation is corrected by a leading body 5, four pairs of cylinders 11 are used, length, in which the piston rods 12 of two bodies in four bodies are elongated and the rods of other two bodies are shortened, is controlled, and the internal casing 7 is turned and driven while hydraulic force, where the leading body 5 is directed at an arbitrary angle within the range of a practically sufficient solid angle, is applied to the leading body 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-diameter pipe excavator for excavating a small-diameter pipe line in the ground. More specifically, it consists of a leading pipe that digs into the soil to lead the pipe, and a propulsion device that pushes a small-diameter pipe into the drilling hole and pushes the leading pipe to propel it. The present invention relates to a small-diameter pipe excavating propulsion machine for forming a small-diameter pipe line such as a line pipe or a gas pipe, and more particularly to a device capable of changing the direction of the leading end portion of the leading pipe for correcting the direction of the leading hole.

[0002]

2. Description of the Related Art Conventionally, in order to form small-diameter pipes such as water supply and sewer pipes, distribution line pipes, communication line pipes, and gas pipes in the soil, the small-diameter pipes are guided to the inside of the soil. A small-diameter pipe excavation propulsion machine is used which is composed of a leading pipe to be excavated and a propulsion device that pushes a small-diameter pipe into the excavation hole to push it forward. The leading conduit is composed of a cylindrical outer casing having an excavating blade at the head and a cylindrical inner casing (auger) having spiral blades on the cylindrical outer surface, and in particular, minutely corrects the direction of the leading hole. To divide the outer casing into two
The head portion and the trailing portion are freely swingable by a structure of a spherical bearing so that the head portion can be slightly swung in a certain direction with respect to the trailing portion. In addition, the outer casing leading part and the inner casing are connected in one body in the rotating direction, and while excavating with the rotating excavating blade, the spiral blade of the rotating inner casing causes the excavated earth and sand to move backward together with water. It is flushed and discharged (Japanese Patent Publication No. 61-23356).

[0003]

According to the conventional small-diameter pipe excavating propulsion machine described above, when the head portion of the outer casing is swung, the inner casing of the cylindrical body is entirely bent or rotational power is applied. Since the force of refraction must be applied while being transmitted, it is necessary to make it easy to perform the swing. If it is impossible,
Due to the strong soil effect, it is difficult to correct the direction.

The present invention has been made under such a technical background, and is intended to solve the following technical problems.

According to the present invention, the head portion of the inner casing can be easily shaken so that the entire leading conductor is bent without difficulty, and the direction of the leading hole can be corrected accurately and easily without being affected by the soil quality. An object is to provide a small-diameter pipe excavation propulsion machine.

[0006]

The present invention adopts the following means in order to achieve the above object.

The small-diameter pipe excavation propulsion machine of the present invention comprises a tip conductor and a propulsion device for pushing a small-diameter pipe following the tip conductor, and the tip conductor is a cylindrical shape having an excavation blade at its head. The outer casing is composed of an outer casing and an inner casing having a feeding means for feeding rearward soil and the like, the outer casing being a rear portion of the outer casing and an outer portion rotatably coupled to the rear portion of the outer casing. A small-diameter pipe that is divided into a casing leading portion, the outer casing leading portion is integrally connected to the inner casing in the rotation direction, and the outer casing leading portion and the outer casing succeeding portion are connected by a spherical bearing. In the excavation propulsion machine, the inner casing is divided into an inner casing leading portion and an inner casing trailing portion, and the inner casing leading portion and the inner casing are separated. The single trailing portion, is characterized in that it is connected by a universal joint consisting of a spherical contact part and the polygonal engaging portion.

Further, the small-diameter pipe excavating propulsion machine of the present invention comprises a tip conductor and a propulsion device for pushing a small-diameter pipe following the tip conductor, and the tip conductor is a cylinder having an excavating blade at the head. It consists of a box-shaped outer casing and an inner casing that has a feeding means around it to send earth and sand backward.
The outer casing is divided into a trailing portion of the outer casing and a leading portion of the outer casing that is rotatably coupled to the trailing portion of the outer casing, and the leading portion of the outer casing is integral with the inner casing in a rotation direction. Is a small-diameter pipe excavator in which the outer casing leading portion and the outer casing trailing portion are connected by a spherical bearing, and the inner casing is divided into an inner casing leading portion and an inner casing trailing portion. , The inner casing leading part (7a) and the inner casing succeeding part (7)
An inner ball bearing (30) and an outer ball bearing (31) are respectively coupled to either of b), and the both ball bearings (30,
31) Smoothly curved ball receiving holes (30a, 31a) are provided in the inner ball bearing (30) and the outer ball bearing (31) at a plurality of locations on the outer peripheral surface and the inner peripheral surface, respectively, and are the same in the circumferential direction. The ball (32) is fitted in a pair of ball receiving holes (30a, 31a) facing each other in position.

Further, the small diameter pipe excavation propulsion machine of the present invention is
It consists of a lead conductor and a propulsion device for pushing a small-diameter pipe that follows the lead conductor, and the lead conductor has a cylindrical outer casing having an excavating blade at its head, and a feeding means for feeding earth and sand backward. And an outer casing having an outer casing trailing part,
The outer casing leading portion is rotatably coupled to the outer casing succeeding portion, and the outer casing leading portion is integrally coupled to the inner casing in the rotation direction, and is connected to the outer casing leading portion and the outer portion. The casing rear part is a small-diameter pipe excavator connected by a spherical bearing, and the inner casing is divided into an inner casing leading part and an inner casing trailing part, and the inner casing leading part (7a) and the One of the inner casing succeeding portions (7b) has a plurality of partially convex spherical surfaces, and the area other than the area of these partially convex spherical surfaces is engraved with an appropriate depth in the center direction. Division (7
a) and the other of the inner casing succeeding part (7b) have a plurality of partially concave spherical surfaces, and the areas other than the areas of these partially concave spherical surfaces project in the central direction with an appropriate thickness. I am trying.

[0010]

The inner casing leading portion is engaged with the succeeding portion of the inner casing in a polygonal mesh to transmit rotational power from the succeeding portion of the inner casing, and is guided by the spherical contact portion to be in contact with each other. The shaft at the leading portion of the casing and the shaft at the rear portion of the inner casing rotate smoothly while intersecting with each other.

Further, the inner casing leading portion meshes with the inner casing succeeding portion through balls of the apex of the polygon, the rotational power is transmitted from the inner casing succeeding portion, and the inner casing leading portion makes contact with each other through a ball. By the sliding and rotation of the point of point contact, the shaft of the leading part of the inner casing and the shaft of the succeeding part of the inner casing rotate smoothly while intersecting with each other.

Furthermore, in the inner casing leading portion, the interference portion around the spherical surface of the apex of the polygon meshes with the inner casing succeeding portion, and the rotational power is transmitted from the inner casing succeeding portion. The shaft of the inner casing leading portion and the shaft of the inner casing succeeding portion rotate smoothly while intersecting with each other by sliding in the area where they are in contact with each other and are in surface contact.

[0013]

EXAMPLES Example 1 Next, examples of the present invention will be described. As shown in FIG. 1, a propelling machine 4 made up of a jack, a hydraulic motor and the like for pushing the small diameter pipe 2 into the excavation hole 3 is installed in the excavated starting shaft 1. The propulsion unit 4 also includes a rotation drive unit that rotates the pushed small diameter tube 2. Since these are not the gist of the present invention, detailed description thereof will be omitted. The small diameter pipes 2 are successively inserted into the excavation holes 3 formed by the leading conductor 5 in advance.

FIG. 2 shows the details of the leading conductor 5. The front conductor 5 includes an outer casing 6 and an inner casing 7.
It is made of The outer casing 6 is composed of an outer casing leading portion 6a and an outer casing trailing portion 6b,
The outer casing top portion 6a further divided, are made from the front of the rotating portion 6a ₁ and the rear of the non-rotating portion 6a _2. The rotating portion 6a ₁ and the rear non-rotating portion 6a ₂ are rotatably connected via a bearing 8. The front rotating part 6a ₁
A drilling blade 6a ₃ is fixed and attached to the tip of the.
As digging edge 6a _3, axial disk cutters 6a _3a facing obliquely, various cutter according to soil like a disk cutter 6b _3a which axis is oriented in the radial direction is used.

A first partial spherical body 9 partially having a spherical surface at a rear portion of the rear non-rotating portion 6a ₂ via a connecting portion 9a.
b is axially connected. On the other hand, the outer casing succeeding portion 6b and the first spherical seat 10 are formed integrally with the outer casing succeeding part 6b, and the first partial partial spherical body 9b and the spherical seat 10 are formed.
Partially contact the outer surface of the spherical seat 10 to form a first spherical bearing.

A cylinder portion 11 of a hydraulic drive system is fixed to the outer casing rear portion 6b, and a piston rod 12 has a front end thereof via an omnidirectional joint 13 and a base end of the outer casing leading portion 6a. The non-rotating portion 6a ₂ is connected to a tilt lever 14 which is tiltably provided. In addition, the retaining pin 15 of the omnidirectional joint 13 is a pin for preventing the retaining pin 15 from coming off. Reference numeral 16 is a detector for detecting the axial displacement width of the outer casing leading portion 6a and the outer casing succeeding portion 6b.

The tip of the inner casing 7 is connected to the innermost diameter portion of the rotating portion 6a ₁ of the outer casing leading portion 6a. A spiral blade 17 is wound around the outer cylindrical surface of the inner casing 7. Inner casing 7
Is also divided into its leading portion 7a and its trailing portion 7b.
A front shaft joint 18 is joined to the rear end of the leading portion 7a. The rear portion of the front shaft coupling 18 is formed as a second partial spherical body 18a having a partially spherical surface. On the other hand, the inner casing succeeding part 7b has
A second spherical seat 19 is formed on the body, and the second partial spherical body 18a and the second spherical seat 19 are partially in spherical contact to form a second spherical bearing.

Although the second partial spherical body 18a and the second spherical seat 19 are connected as one body in the rotational direction, they can be swung freely within a certain solid angle range. It is shown in FIGS. Although the front portion 18a ₁ and the rear portion 18a ₂ of the second partial spherical body 18a is spherical, the center portion in the axial direction is provided with octagonal ridge 18a ₃ of the front portion 18a ₁ from octagonal ridge 18a ₃ And a spherical surface of the rear portion 18a ₂ are continuously connected by an arbitrary curved surface.
The radius of the spherical surface of the front portion 18a _{1 and the} rear portion 18a ₂ is the distance between the midpoint of each side of the ridgeline 18a ₃ and the center O shown in FIG. Further, the line extending in the axial direction through the midpoint of each side of the ridgeline 18a ₃ is a circle 18a as shown in FIG.
It is formed in a _4.

The inner peripheral surface of the front portion 19a of the second spherical seat 19 is generally a cylindrical surface as shown in FIGS. 3 and 4, but at eight positions at equal angles to the cylindrical surface. A ridge body 19b like a spline hole that projects toward the center and extends in the axial direction
And the ridges 19b circumscribe the ridgelines 18a ₃ in a direction orthogonal to the center of the ridgelines 18a ₃ of the second partial spherical body 18a. The inner surface of the ridge body 19b is a narrow area and thus may be a flat surface, but can be formed in a protruding curved surface. The corners of the octagonal ridge are formed on a spherical surface having a radius larger than that of the spherical surfaces of the front portion 18a ₁ and the rear portion 18a ₂ , and the inner peripheral surface 1 of the front portion 19a of the second spherical seat 19 is formed.
Although it is inscribed in 9d, it is sufficient that the corners and the inner peripheral surface do not interfere with each other, so that they may be always separated. The rear portion 18a ₂ of the second partial spherical body 18a is in spherical contact with the spherical portion 19c formed at the front end of the rear portion of the second spherical seat 19.

A guide boring rod 20 is inserted inside the inner casing 7, and a boring bit 21 is attached to the leading end of the guide boring rod 20. Further, a large diameter portion 7a ₁ having a slightly larger diameter is provided at the leading portion thereof, and the large diameter portion 7a ₁ is inscribed in the innermost diameter portion of the rotating portion 6a ₁ of the outer casing leading portion 6a and slides. Although it is rotatable, a gap of an appropriate width is provided between the inner peripheral surface of the inner casing 7 and the outer peripheral surface on the rear side of the large diameter portion 20a ₁ of the guide boring rod 20. Further, a rotation drive device and a propulsion device for rotationally driving the guide boring rod 20 independently of the inner casing 7 and propelling the guide boring rod 20 forward are installed in the starting stand 1.

The cylinder portion 11, the expandable piston rod 12, the omnidirectional joint 13, the tilting lever 1
The hydraulic drive device including 4 and the like is provided with four sets on a concentric circle, and two sets are provided point-symmetrically with respect to a point on the common axis of the outer casing 6 and the inner casing 7. Next, the operation of the first embodiment will be described. It is assumed that FIG. 2 shows a state in which the vehicle has dug a certain distance in the horizontal direction from the starting stand 1. While the guide boring rod 20 is rotationally driven independently of the inner casing 7 and is propelled forward,
The guide hole 30 is dug as shown in FIG. When correcting the direction of excavation by the leading conductor 5, the four sets of cylinders 11 are
To use.

Two piston rods 12 selected from among the four hydraulic drive units are extended, the piston rods of the other two units are contracted, and the lengths of the piston rods 12 and the contracted lengths are controlled to make the front conductor practically sufficient. An oil pressure is applied to the lead conductor that can be directed at any angle within the solid angle range. When the inner casing 7 is rotated while applying such a hydraulic force, the rotation portion 6a ₁ rotates the head portion 6a of the outer casing 6 of the inner casing 7 and one body, digging edge of the tip of the rotating portion 6a ₁ 6a _3a and the disc cutter 6a _3b rotate to start making holes for inserting the small diameter tube 2, push the small diameter tube 2 following the leading conductor 5, apply propulsive force to the leading conductor 5, The body 5 is advanced. When this excavation is carried out for a while, the non-rotating portion 6a of the outer casing leading portion 6a is caused by the above-mentioned hydraulic pressure.
_{The second} partial spherical body 9b is inclined at an angle θ with respect to the first spherical seat 10 which is one body in the outer casing succeeding portion 6b, so that the leading portion 6a of the outer casing 6 is rotated as shown in FIG. rotational centerline L ₁ parts 6a ₁ guide boring rods 2
It is inclined at an angle θ with respect to the rotation center line L _{2 of} 0.

In this state, the guide boring rod 20
A part of the outer peripheral surface of the outer casing is inscribed in the innermost portion of the rotating portion 6a ₁ of the outer casing leading portion 6a and slides, but does not apply a bending force to the guide boring rod 20. However, the hydraulic pressure applied to exceed θ is absorbed by the elasticity of the guide boring rod 20.

During the excavation, the leading portion 7 of the inner casing 7
Octa ridge line 18a of the second partial spherical body 18a, which is one in a
_{Since 3} and the protrusion 19b of the inner casing rear portion 7b mesh in the direction of rotation about the axis, the inner casing front portion 7a and the inner casing rear portion 7b rotate at a constant angular velocity. The second partial spherical body 18a has a circular shape on the cross section passing through the axis at the point where the ridge body 19b contacts.

Therefore, in the meshing position shown in FIG. 2, the inner casing leading portion 7a can freely rotate with respect to the inner casing succeeding portion 7b on the paper surface, and also on the surface perpendicular to the paper surface through the axis in FIG. When the inner casing leading portion 7a tries to rotate relative to the inner casing succeeding portion 7b, the front portion 18a ₁ and the rear portion 1 of the second partial spherical body 18a are
8a ₂ is a spherical surface, and the vicinity of the central portion thereof, that is, the vicinity of the octagonal ridgeline 18a ₃ is crowned so as not to interfere with the ridges 19b, so that it can freely rotate.

That is, since the inner casing leading portion 7a and the inner casing succeeding portion 7b are so-called universally axially coupled, the inner casing leading portion 7a receives the rotational drive from the inner casing succeeding portion 7b while As shown in 7, depending on the excavation conditions, the angle θ
Only tilted, they rotate together.

When the tip conductor 5 catches up with the head of the guide boring rod 20, next, the tip boring by the guide boring rod 20 is performed on the basis of the tip conductor 5 inclined by the angle θ, that is, using the tip conductor 5 as a guide. To do. Then, the guide boring rod 20 tends to excavate in that direction while gently bending while being inclined by the angle θ. By repeating such excavation alternately, excavation holes can be formed in a predetermined direction, and the direction can be corrected.

Second Embodiment FIG. 8 shows a second embodiment of the present invention, which is the second embodiment of the first embodiment.
Instead of the partial spherical body 18 a and the second spherical seat 19, the inner ball bearing 30 and the outer ball bearing 31 are the inner casing leading part 7
a and the inner casing rear portion 7b, respectively,
Both ball bearings 30 and 31 have inner surface ball bearings 30 and outer ball bearings 30a and 31b having smooth curved surfaces (a part of which has a spherical surface having a radius of curvature smaller than the distance from the center O shown in the figure). One ball 32 is fitted in a pair of ball receiving holes 30a, 31a provided at a plurality of positions, for example, eight positions, on the outer peripheral surface and the inner peripheral surface of 31, respectively, at the same position in the circumferential direction.

According to this embodiment, the inner casing leading portion 7a and the inner casing succeeding portion 7b are integrally united in the rotational direction at a constant velocity ratio, but the shaft of the inner casing leading portion 7a and the inner casing are connected. Within a range where the axis of the trailing portion 7b is slightly tilted, they tilt slightly.

Third Embodiment FIG. 9 shows a third embodiment of the present invention. In this embodiment, the second partial spherical body 18a has eight partial spherical surfaces 18a ₁ as outer spherical surfaces. Areas other than the area 18a ₁ are engraved with an appropriate depth in the central direction. On the other hand, the front surface 19a of the second spherical seat 19 is also provided with eight partial spherical surfaces 19a ₁ as concave surfaces.
Region other than the region of 9a _1, the bulges 19a ₂ of the appropriate thickness are provided in the central direction. In terms of solid angle, the partial spherical surface 18a ₁ is narrower than the partial spherical surface 19a ₁ .

According to this embodiment, the second partial spherical body 18
Although the a and the second spherical seat 19 form a universal joint within a certain solid angle range, when the rotation about the axis from the state shown in FIG. ₁ interferes with the protrusion 19a ₂ of the second spherical seat 19, and the inner casing leading portion 7a and the inner casing succeeding portion 7b thereafter rotate as a unit at a constant speed.

Other Embodiments Some embodiments of the present invention have been described, but the present invention is not limited to the above embodiments, and design changes are made within the scope of the gist of the present invention described in the claims. be able to.
For example, the guide boring rod 20 is not limited to the excavating blade at the head, and instead of the excavating blade, or together with the excavating blade, a cleaning water injection port can be attached, and a chemical spray that can inject a solidifying agent or the like that solidifies the soil. It can be replaced with other plural kinds of guide boring rods having a mouth.

As the universal joint, various types such as a gear type shaft joint in which tooth tips and tooth surfaces are roughly formed and inner teeth and outer teeth are meshed with each other, and other known bar field type shaft joints are also used. Can be deformed and applied.

[0034]

According to the small diameter pipe excavation propulsion machine of the present invention,
When swinging the head part of the outer casing, the head part of the inner casing is also shaken comfortably, the whole lead conductor bends reasonably, and it is easy to correct the direction of the lead hole without being affected by the soil quality. Can be done

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of burying a small-diameter pipe using a small-diameter pipe excavator of the present invention.

FIG. 2 is a sectional view showing an embodiment of a small diameter pipe excavation propulsion device of the present invention.

FIG. 3 is a cross-sectional view showing a main part of a universal joint of an inner casing.

FIG. 4 is a perspective view showing a second spherical seat.

FIG. 5 is a perspective view showing a second partial spherical body.

FIG. 6 is a side sectional view showing a coupling relationship between a second spherical seat and a second partial spherical body.

FIG. 7 is a cross-sectional view showing a process during excavation of a guide hole.

FIG. 8 is a sectional view showing another embodiment of the present invention.

FIG. 9 is a sectional view showing still another embodiment of the present invention.

[Explanation of symbols]

3 ... small diameter tube 5 ... lead body 6 ... outer casing 6a ... outer casing top section 6b ... outer casing trailing portion 6a ₁ ... rotating portion 6a ₂ ... non-rotating portion 6a ₃ ... digging edge 7a ... inner casing top section 7b ... side casing trailing portion 9b ... first partially spherical member 9b 10 ... first spherical seat 18a ... second partial spherical body 18a ₁ ... front portion 18a ₂ ... rear portion 18a ₃ ... ridge 18a ₄ ... circle 19 ... second spherical seat 19a ... Front part 19b ... Ridge body 19c ... Spherical part 30a, 31a ... Ball receiving hole 32 ... Ball

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Ichimaru, 1534, Karatsu Ichihara, Saga Prefecture, inside Yoshida Iron Works Co., Ltd. (72) Inventor, Hideomi Honda, 1534, Karatsu Ichihara, Saga Prefecture, Yoshida Iron Works, Ltd.

Claims (3)

[Claims] 1. A lead conductor, and a propulsion device for pushing a small-diameter pipe that follows the lead conductor, wherein the lead conductor has a cylindrical outer casing having an excavating blade at its head, and earth and sand etc. to the rear. An inner casing having a feeding means for feeding, the outer casing being divided into an outer casing trailing portion and an outer casing leading portion rotatably coupled to the outer casing trailing portion, The outer casing head portion is integrally connected to the inner casing in the rotation direction, and the outer casing head portion and the outer casing trailing portion are small-diameter pipe excavation propulsion machines connected by a spherical bearing, The inner casing is divided into an inner casing leading portion and an inner casing trailing portion, and the inner casing leading portion and the inner casing trailing portion are spherical surfaces. A small-diameter pipe excavator, which is connected by a universal joint composed of a contact portion and a polygonal meshing portion. 2. A lead conductor, and a propulsion device for pushing a small-diameter pipe that follows the lead conductor, wherein the lead conductor has a cylindrical outer casing having an excavating blade at its head, and earth and sand etc. to the rear. An inner casing having a feeding means for feeding, the outer casing being divided into an outer casing trailing portion and an outer casing leading portion rotatably coupled to the outer casing trailing portion, The outer casing leading part is a small-diameter pipe excavator that is integrally connected to the inner casing in the rotation direction, and the outer casing leading part and the outer casing succeeding part are connected by a spherical bearing. The inner casing is divided into an inner casing leading portion and an inner casing trailing portion, and the inner casing leading portion (7a) and the inner casing trailing portion ( In any one of b), the inner ball bearing (30),
Outer ball bearings (31) are respectively coupled, and ball receiving holes (30a, 31a) having smooth curved surfaces are provided on the both ball bearings (30, 31) on the outer circumference of the inner ball bearing (30) and the outer ball bearing (31). A ball (32) is fitted in each of a pair of ball receiving holes (30a, 31a) provided at a plurality of positions on the surface and the inner peripheral surface and facing each other at the same position in the circumferential direction. A small diameter pipe excavator. 3. A tip conductor, and a propulsion device for pushing a small-diameter pipe that follows the tip conductor, wherein the tip conductor has a cylindrical outer casing having an excavating blade at the top, and earth and sand etc. to the rear. An inner casing having a feeding means for feeding, the outer casing being divided into an outer casing trailing portion and an outer casing leading portion rotatably coupled to the outer casing trailing portion, The outer casing leading part is a small-diameter pipe excavator that is integrally connected to the inner casing in the rotation direction, and the outer casing leading part and the outer casing succeeding part are connected by a spherical bearing. The inner casing is divided into an inner casing leading portion and an inner casing trailing portion, and the inner casing leading portion (7a) and the inner casing trailing portion ( One of b) has a plurality of partial convex spherical surfaces, and the area other than the area of these partial convex spherical surfaces is engraved with an appropriate depth in the central direction, and the inner casing top portion (7a) and The other part of the inner casing succeeding part (7b) has a plurality of partially concave spherical surfaces, and the area other than the area of these partially concave spherical surfaces is projected with an appropriate thickness toward the center. Caliber excavator.