Patent Description:
Some robots, manipulators, or actuators have joint function parts that enable bending and extension. The bending structural body as shown in Patent Literature <NUM> is used as such a joint function part.

The bending structural body of Patent Literature <NUM> is configured by engaging a plurality of disk elements that are mutually swingable, and performs bending motion as a whole by swinging each disk element.

An actuation cable, which is a cord-like member, is inserted through and guided by each disk element. A bending operation of the bending structural body is performed by pulling the actuation cable.

However, the above-described conventional bending structural body has a complicated structure because the bending structural body connects a plurality of disk elements and inserts an actuation cable through each disk element.

<CIT> relates to a flexible, bendable drive module made of flexible members for its flexure. <CIT> relates to a bending structure which can secure sufficient flexibility and axial rigidity, and to provide a joint function part and an instrument for an operation support robot. <CIT> relates to an articulatable member having constrained motion, and related devices and methods and the articulatable member includes a distal end, a proximal end, an actuation member, and a constraint member. <CIT> relates to technique of robotic positioning of a work tool or sensor including a redundant robotic apparatus and methods of deploying them. <CIT> relates to a hollow lumen cable apparatus in which the hollow lumen cable is formed by helically winding inner and outer coils with the helices of each coil being in an abutting relationship and the outer coil inner peripheral diameter being less than the outer peripheral diameter of the inner coil.

The complicated structure of the bending structural body is the problem that needs to be solved.

The following disclosure serves a better understanding of the present invention. The invention provides a bending structural body, including: an inner cylinder which includes a first inner coil part and a first outer coil part, and in which wound parts corresponding to the first inner coil part are fitted to spaces between adjacent wound parts of the first outer coil part; an outer cylinder which covers at least part of an outer circumference of the inner cylinder with a space therebetween and includes a second inner coil part and a second outer coil part, and in which wound parts corresponding to the second inner coil part are fitted to spaces between adjacent wound parts of the second outer coil part; and a plurality of cord-like members in a circumferential direction which are inserted into and guided by the space between the inner cylinder and the outer cylinder in an axial direction.

According to the invention, the bending structural body capable of bending and restoring is able to be realized with a simple structure simply by arranging a cord-like member used for manipulation or the like in the space between the inner cylinder and the outer cylinder composed of the inner and outer coil parts. Moreover, it is possible to stabilize the posture by preventing the compression of the inner cylinder and the outer cylinder before and after bending, and reliably guide the cord-like member through the space between the inner cylinder and the outer cylinder.

The purpose of simplifying the structure of the bending structural body was achieved by arranging the cord-like member in the space between the inner cylinder and the outer cylinder composed of the inner and outer coil parts.

That is, a bending structural body (<NUM>) includes an inner cylinder (<NUM>), an outer cylinder (<NUM>), and cord-like members (9a, 9b). The inner cylinder (<NUM>) includes a first inner coil part (<NUM>) and a first outer coil part (<NUM>), and the corresponding wound parts (15a) of the first inner coil part (<NUM>) are fitted to the spaces (13b) between the adjacent wound parts (13a) of the first outer coil part (<NUM>). The outer cylinder (<NUM>) covers at least part of the outer circumference of the inner cylinder (<NUM>) with the space (<NUM>) and includes a second inner coil part (<NUM>) and a second outer coil part (<NUM>), and the corresponding wound parts (19a) of the second inner coil part (<NUM>) are fitted to the spaces (17b) between the adjacent wound parts (17a) of the second outer coil part (<NUM>). The cord-like members (9a, 9b) are inserted into and guided by the space (<NUM>) between the inner cylinder (<NUM>) and the outer cylinder (<NUM>) in the axial direction.

The bending structural body (<NUM>) may include edge members (7a, 7b) that are attached to both ends of either one or both of the outer cylinder (<NUM>) and the inner cylinder (<NUM>) for inserting the cord-like members (9a, 9b) into the first insertion holes (<NUM>).

In addition, the bending structural body (<NUM>) may include a flexible member (<NUM>) inserted through the first inner coil part (<NUM>) of the inner cylinder (<NUM>), and the edge members (7a, 7b) may each have the second insertion hole (<NUM>) for inserting the flexible member (<NUM>).

The cord-like members (9a, 9b) include a drive cord-like member (9a) for driving one edge member (7a) with respect to the other edge member (7b), and a guide cord-like member (9b) provided on both sides of the drive cord-like member (9a) in the circumferential direction to limit the path of the drive cord-like member (9a).

Either one or both of the drive cord-like member (9a) and the guide cord-like member (9b) may be used as current-carrying paths.

Further, in the bending structural body (<NUM>), the first inner and outer coil parts (<NUM>, <NUM>) of the inner cylinder (<NUM>) and the second inner and outer coil parts (<NUM>, <NUM>) of the outer cylinder (<NUM>) may be reversely wounded to each other.

<FIG> is a perspective view showing the bending structural body according to Example <NUM> of the invention. <FIG> is a perspective cross-sectional view of the same part. <FIG> is a plan view of the bending structural body with the edge member omitted. <FIG> is a cross-sectional view showing the inner cylinder and the outer cylinder of the bending structural body.

The bending structural body <NUM> of this example is applied to the joint function parts of various devices such as manipulators, robots, actuators, and the like for medical and industrial purposes, and is capable of relatively displacing device-side members coupled to both sides by bending and stretching operations.

This bending structural body <NUM> includes an inner cylinder <NUM>, an outer cylinder <NUM>, edge members 7a and 7b, drive wires 9a and guide wires 9b as cord-like members, and a flexible tube <NUM> as a flexible member.

The inner cylinder <NUM> is a double coil that is able to be elastically bent and restored in the axial direction, and includes a first outer coil part <NUM> and a first inner coil part <NUM>.

The first outer coil part <NUM> and the first inner coil part <NUM> each include a coil spring having elasticity. Materials for the first outer coil part <NUM> and the first inner coil part <NUM> may both be metal, resin, or the like. Also, the cross-sectional shapes of the wires of the first outer coil part <NUM> and the first inner coil part <NUM> are circular. However, the cross-sectional shape is not necessarily circular, and may be semicircular, elliptic, or the like. Also, the cross-sectional shapes, wire diameters, materials. or the like of the first inner and outer coil parts <NUM> and <NUM> may be different from each other.

The first inner coil part <NUM> has a smaller center diameter than the first outer coil part <NUM> and is screwed into the first outer coil part <NUM>. The center diameters of the first outer coil part <NUM> and the first inner coil part <NUM> are constant from one axial end to the other axial end. However, the center diameter of this first outer coil part <NUM> may also be changed in the axial direction.

The first outer coil part <NUM> has a plurality of pitches 13b as spaces separating axially adjacent wound parts 13a (between adjacent wound parts 13a) in the axial direction. The corresponding wound parts 15a of the first inner coil part <NUM> are fitted to the plurality of pitches 13b from inside. Due to this fitting, the wound part 15a of the first inner coil part <NUM> comes into contact with both of the adjacent wound parts 13a of the first outer coil part <NUM>.

On the other hand, the first inner coil part <NUM> has a plurality of pitches 15b as spaces separating axially adjacent wound parts 15a (between adjacent wound parts 15a) in the axial direction. The corresponding wound parts 13a of the first outer coil part <NUM> are fitted to the plurality of pitches 15b from outside. Due to this fitting, the wound part 13a of the first outer coil part <NUM> comes into contact with both of the adjacent wound parts 15a of the first inner coil part <NUM>.

Therefore, the inner cylinder <NUM> is restricted from being compressed in the axial direction.

The outer cylinder <NUM>, like the inner cylinder <NUM>, is a double coil that is able to be elastically bent and restored in the axial direction, and includes a second outer coil part <NUM> and a second inner coil part <NUM>. This outer cylinder <NUM> covers the outer circumference of the inner cylinder <NUM> with a space <NUM> therebetween. When the outer cylinder <NUM> is shorter than the inner cylinder <NUM>, the outer cylinder <NUM> partially covers the inner cylinder <NUM> in the axial direction. Therefore, the outer cylinder <NUM> may be configured to cover at least part of the outer circumference of the inner cylinder <NUM> with the space <NUM> therebetween.

The space <NUM> is defined between the second inner coil part <NUM> of the outer cylinder <NUM> and the first outer coil part <NUM> of the inner cylinder <NUM> in the radial direction. The radial dimension of the space <NUM> is set slightly larger than the wire diameters of the drive wires 9a and the guide wires 9b.

Thereby, the inner cylinder <NUM> and the outer cylinder <NUM> serve as guides for the drive wires 9a and the guide wires 9b. The radial dimension of the space <NUM> may be appropriately set within a range that ensures the function of guiding the drive wires 9a and the guide wires 9b.

The second outer coil part <NUM> and the second inner coil part <NUM> of the outer cylinder <NUM> are configured similarly to the first outer coil part <NUM> and the first inner coil part <NUM> of the inner cylinder <NUM>. However, the winding direction of the outer cylinder <NUM> may be the same as or reverse to the winding direction of the inner cylinder <NUM>.

When the winding directions of the inner cylinder <NUM> and the outer cylinder <NUM> are reversed (reversely wound), the inner cylinder <NUM> and the outer cylinder <NUM> are able to resist torsion in reverse directions, and the torsional rigidity of the bending structural body <NUM> as a whole is able to be improved.

Like the first outer coil part <NUM> and the first inner coil part <NUM> of the inner cylinder <NUM>, the second outer coil part <NUM> and the second inner coil part <NUM> include elastic coil springs and may be made of metal, resin, or the like. The cross-sectional shapes of the wires of the second outer coil part <NUM> and the second inner coil part <NUM> are circular, but not necessarily circular. Further, the cross-sectional shapes, materials, wire diameters, or the like of the second inner and outer coil parts <NUM> and <NUM> may be different from each other.

The second inner coil part <NUM> has a smaller center diameter than the second outer coil part <NUM> and is screwed into the second outer coil part <NUM>. The center diameters of the second outer coil part <NUM> and the second inner coil part <NUM> are constant from one axial end to the other axial end, but may be changed in the axial direction.

The second outer coil part <NUM> has a plurality of pitches 17b separating axially adjacent wound parts 17a (between adjacent wound parts 17a) in the axial direction. The corresponding wound parts 19a of the second inner coil part <NUM> are fitted to the plurality of pitches 17b from inside. Due to this fitting, the wound part 19a of the second inner coil part <NUM> comes into contact with both of the adjacent wound parts 17a of the second outer coil part <NUM>.

On the other hand, the second inner coil part <NUM> has a plurality of pitches 19b as spaces separating axially adjacent wound parts 19a (between adjacent wound parts 19a) in the axial direction. The corresponding wound parts 17a of the second outer coil part <NUM> are fitted to the plurality of pitches 19b from outside. Due to this fitting, the wound part 17a of the second outer coil part <NUM> comes into contact with both of the adjacent wound parts 19a of the second inner coil part <NUM>.

Therefore, the outer cylinder <NUM> is restricted from being compressed in the axial direction.

The edge members 7a and 7b are cylindrical and made of metal or the like. Note that the edge members 7a and 7b may have other shapes such as a prism shape. These edge members 7a and 7b are respectively attached to the axial ends of the outer cylinder <NUM> by an appropriate fixing method such as welding. Also, the edge members 7a and 7b may be attached to the axial ends of the inner cylinder <NUM>, or may be attached to the axial ends of both the inner cylinder <NUM> and the outer cylinder <NUM>.

Attachment of the edge members 7a and 7b to the outer cylinder <NUM> is performed on either one of the second inner and outer coil parts <NUM> and <NUM>. In this example, the edge members 7a and 7b are attached to the second outer coil part <NUM>.

The first insertion hole <NUM> and the second insertion hole <NUM> are provided through the edge members 7a and 7b in the axial direction. The first insertion hole <NUM> axially communicates with the space <NUM> between the inner and outer cylinders <NUM> and <NUM> for inserting the drive wires 9a and the guide wires 9b.

The second insertion hole <NUM> communicates with the interior of the inner cylinder <NUM> in the axial direction for inserting the flexible tube <NUM>. The second insertion hole <NUM> of this example is provided at the axial center of the edge members 7a and 7b and has a circular cross section.

The edge members 7a and 7b are respectively attached to the device-side members that are relatively displaced via the bending structural body <NUM>. For example, one edge member 7a is attached to the device-side member on the distal side, and the other edge member 7b is attached to the device-side member on the proximal side. These edge members 7a and 7b may be omitted. In that case, both ends of the outer cylinder <NUM> may be directly attached to the device-side members.

The drive wires 9a and the guide wires 9b are drive cord-like members and guide cord-like members made of metal or the like. The drive wires 9a and the guide wires 9b have flexibility to an extent that does not hinder the bending and restoration of the bending structural body <NUM>.

The cross-sectional shapes of the drive wires 9a and the guide wires 9b may be circular similar to the first insertion hole <NUM>, or may be a different shape such as an ellipse or a rectangle. The drive wires 9a and the guide wires 9b may be stranded wires, NiTi (nickel titanium) single wires, piano wires, articulated rods, chains, cords, strings, ropes, or the like as long as the drive wires 9a and the guide wires 9b are cord-like members.

The guide wires 9b are not limited to metal or the like, and may be made of resin. Further, the guide wires 9b may be column-shaped or rod-shaped members instead of cord-like members.

The drive wires 9a and the guide wires 9b are axially inserted through and guided by the space <NUM> between the inner and outer cylinders <NUM> and <NUM>. In this example, a plurality of drive wires 9a and guide wires 9b are provided at predetermined intervals in the circumferential direction. In addition, the drive wires 9a may be guided in a spiral shape around the axis instead of being guided straight along the axial direction.

The ends <NUM> of the drive wires 9a and the guide wires 9b are inserted through the first insertion holes <NUM> of the edge members 7a and 7b and pulled to the outside. The ends <NUM> pulled out from one edge member 7a are prevented from coming off by end processing.

The drive wires 9a enable one edge member 7a to drive the other edge member 7b. That is, the drive wires 9a bend the bending structural body <NUM> by being pulled in the axial direction, and are connected directly or indirectly to an operating mechanism not shown to be operated in the axial direction.

In addition, the operation in the axial direction means moving the drive wires 9a forward and backward in the axial direction. The number of drive wires 9a may be appropriately set according to the bending motion of the bending structural body <NUM>.

The guide wires 9b are provided on both sides in the circumferential direction of each drive wire 9a to limit the path of the drive wires 9a. The guide wires 9b regulate the displacement of the drive wires 9a in the circumferential direction. In this example, the guide wires 9b and the drive wires 9a restrict the mutual displacement in the circumferential direction, thereby limiting the path of the drive wires 9a.

The guide wires 9b may also function as the drive wires 9a. Also, the guide wires 9b may be omitted. Furthermore, one or both of the drive wires 9a and the guide wires 9b may be used as a current-carrying path. In addition, it is also possible to use the inner cylinder <NUM> as a current-carrying path.

The flexible tube <NUM> is a tubular member made of resin or the like, and is inserted through the first inner coil part <NUM> of the inner cylinder <NUM>. This flexible tube <NUM> has flexibility to an extent that does not hinder the bending and restoration of the bending structural body <NUM>. The ends of the flexible tube <NUM> are inserted through the second insertion holes <NUM> of the edge members 7a and 7b and pulled to the outside. Further, as a cord-like member, the flexible tube <NUM> may be provided for current-carrying only rather than for driving and for guiding.

The flexible tube <NUM> is fitted into the second insertion hole <NUM> at the end. As a result, the inner cylinder <NUM> is positioned via the flexible tube <NUM> with respect to the edge members 7a and 7b. One of the edge members 7a and 7b may be used as a reference for positioning. The outer cylinder <NUM> is attached and positioned to the edge members 7a and 7b.

Therefore, in this example, the space <NUM> which is positioned between the inner and outer cylinders <NUM> and <NUM> by the edge members 7a and 7b and through which the drive wires 9a and the guide wires 9b are inserted is defined accurately.

Inside the flexible tube <NUM>, a driving member such as an air tube and a push-pull cable for driving an end effector or the like is inserted. It should be noted that the flexible tube <NUM> may be omitted and a driving member such as an air tube and a push-pull cable, or other flexible members may be used as the flexible member. The flexible member itself such as the flexible tube <NUM> and the driving member may be omitted.

<FIG> is a cross-sectional <NUM> view showing the inner cylinder <NUM> when bent. Since the bending of the outer cylinder <NUM> is the same as the bending of the inner cylinder <NUM>, <FIG> may serve as reference. Therefore, reference numerals of the outer cylinder <NUM> are shown in parentheses in <FIG>.

When the bending structural body <NUM> of this example is in a straight state without being bent (when extended), as shown in <FIG>, the corresponding wound parts 15a of the first inner coil part <NUM> are fitted between the adjacent wound parts 13a of the first outer coil part <NUM> of the inner cylinder <NUM>. For the outer cylinder <NUM>, the corresponding wound parts 19a of the second inner coil part <NUM> are also fitted between the adjacent wound parts 17a of the second outer coil part <NUM>.

Therefore, in the bending structural body <NUM>, even if a compressive force acts in the axial direction, the first inner and outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the second inner and outer coil parts <NUM> and <NUM> of the outer cylinder <NUM> are prevented from being compressed, and are prevented from being compressed as a whole. By preventing compression in this way, the posture is stabilized without changing the length of the central part.

Moreover, when the inner cylinder <NUM> and the outer cylinder <NUM> are reversely wound, each of the inner cylinder <NUM> and the outer cylinder <NUM> is able to resist torsion in the reverse direction. Therefore, even if a torsional force acts, the torsion as a whole is suppressed and the posture is stabilized.

In this way, the bending structural body <NUM> has high compression resistance and torsion resistance, and is stable in posture, so as to obtain the stable space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> and reliably guide the drive wires 9a and the guide wires 9b by the space <NUM>.

The bending structural body <NUM> may be bent by an operator pulling any one of the drive wires 9a, and is able to be bent <NUM> degrees in all directions by pulling a combination of different pairs of drive wires 9a. By this bending, an end effector or the like of a manipulator, which is a device to which the bending structural body <NUM> is applied, may be oriented in a desired direction.

When any one of the drive wires 9a is pulled, as shown in <FIG>, the pitches 13b and 17b between the adjacent wound parts 13a and 17a of the first and second outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the outer cylinder <NUM> on the inside of the bending become smaller; and the pitches 13b and 17b between the adjacent wound parts 13a and 17a of the first and second outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the outer cylinder <NUM> on the outside of the bending become larger. As a result, the length of the central part of the inner cylinder <NUM> does not change even when bent, and the posture is stabilized.

At this time, the first and second inner coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the outer cylinder <NUM> are pushed out toward the outside of the bending. This extrusion of the first and second inner coil parts <NUM> and <NUM> is permitted by the enlarged pitches 13b and 17b between the adjacent wound parts 13a and 17a of the first and second outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the outer cylinder <NUM> on the outside of the bending. Therefore, the bending motion is able to be performed smoothly.

Moreover, during bending, the corresponding wound parts 15a and 19a of the first and second inner coil parts <NUM> and <NUM> continue to fit between the adjacent wound parts 13a and 17a of the first and second outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the outer cylinder <NUM>.

Therefore, as in the straight state, the bending structural body <NUM> is restrained from being compressed in the axial direction, restrained from fluctuating in the length of the central part from this point, and the posture is stabilized. Therefore, a stable space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> is able to be obtained, and the drive wires 9a and the guide wires 9b are reliably guided by the space <NUM>.

Further, when the second inner coil part <NUM> of the outer cylinder <NUM> is pushed out, the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> becomes smaller on the inside of the bending, and the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> becomes larger on the outside of the bending.

After bending, both the inner cylinder <NUM> and the outer cylinder <NUM> are reliably returned to the uncompressed straight state before bending, in which the first and second inner coil parts <NUM> and <NUM> are fitted between the adjacent wound parts 13a and 17a of the first and second outer coil parts <NUM> and <NUM>. Therefore, the drive wires 9a and the guide wires 9b are reliably guided by the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> in the same manner as before bending.

As described above, this example includes: the inner cylinder <NUM> which includes the first inner coil part <NUM> and the first outer coil part <NUM>, and in which corresponding wound parts 15a of the first inner coil part <NUM> are fitted to the pitches 13b between adjacent wound parts 13a of the first outer coil part <NUM>; the outer cylinder <NUM> which covers the outer circumference of the inner cylinder <NUM> with the space <NUM> and includes the second inner coil part <NUM> and the second outer coil part <NUM>, and in which the corresponding wound parts 19a of the second inner coil part <NUM> are fitted to the pitches 17b between adjacent wound parts 17a of the second outer coil part <NUM>; and a plurality of drive wires 9a and guide wires 9b in the circumferential direction which are inserted into and guided by the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> in the axial direction.

Therefore, in this example, by simply arranging the drive wires 9a and the guide wires 9b in the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM> that include the inner and outer coil parts <NUM>, <NUM>, <NUM>, <NUM>, it is possible to achieve the bending structural body <NUM> capable of bending and restoring through an operation of the drive wires 9a with a simple structure.

Moreover, in the bending structural body <NUM> of this example, compression of the inner cylinder <NUM> and the outer cylinder <NUM> are able to be prevented before and after bending. Therefore, the drive wires 9a and the guide wires 9b may be surely guided through the space <NUM> between the inner cylinder <NUM> and the outer cylinder <NUM>, and the motion based on the operation of the drive wires 9a is able to be stabilized.

The bending structural body <NUM> of this example includes the edge members 7a and 7b attached to both ends of the outer cylinder <NUM> for respectively inserting the drive wires 9a and the guide wires 9b into the first insertion holes <NUM>.

Therefore, the bending structural body <NUM> is able to position between the drive wires 9a and the guide wires 9b at both ends, and is able to more reliably guide the drive wires 9a and the guide wires 9b.

In addition, the bending structural body <NUM> of this example includes the flexible tube <NUM> inserted through the first inner coil part <NUM> of the inner cylinder <NUM>, and the edge members 7a and 7b have the second insertion holes <NUM> for inserting the flexible tube <NUM> in the axial center.

Therefore, in this example, the inside of the first inner coil part <NUM> of the inner cylinder <NUM> is able to be used as a path through which the flexible tube <NUM> is inserted. Moreover, since the inner cylinder <NUM> is positioned on the edge members 7a and 7b via the flexible tube <NUM> and the outer cylinder <NUM> is attached to the edge members 7a and 7b to be positioned, it is possible to reliably position between the inner and outer cylinders <NUM> and <NUM> to perform the bending motion smoothly. Moreover, the space <NUM> between the inner and outer cylinders <NUM> and <NUM> is able to be defined accurately to more reliably guide the drive wires 9a and the guide wires 9b.

Further, in this example, when the first inner and outer coil parts <NUM> and <NUM> of the inner cylinder <NUM> and the second inner and outer coil parts <NUM> and <NUM> of the outer cylinder <NUM> are reversely wound to each other, the inner cylinder <NUM> and the outer cylinder <NUM> are able to resist torsion in different directions to improve the torsional rigidity as a whole.

<FIG> is a plan view of the bending structural body according to Example <NUM> of the invention with the edge member omitted. In addition, in Example <NUM>, the same code is attached to the structure corresponding to Example <NUM>, and the repeated description is omitted.

In Example <NUM>, the centers of the inner cylinder <NUM> and the outer cylinder <NUM> are shifted. Others are the same as Example <NUM>.

In this example, by shifting the centers O and O' of the inner cylinder <NUM> and the outer cylinder <NUM>, the space <NUM> in one of the shifting directions is narrower than the other. The space <NUM> in one of the shifting directions is so narrow that the space <NUM> does not allow the drive wires 9a to be arranged. The drive wires 9a are arranged only in the space <NUM> on the other side in the shifting direction.

Claim 1:
A bending structural body (<NUM>), comprising:
an inner cylinder (<NUM>) which comprises a first inner coil part (<NUM>) and a first outer coil part (<NUM>), and in which wound parts (15a) corresponding to the first inner coil part (<NUM>) are fitted to spaces (13b) between adjacent wound parts (13a) of the first outer coil part (<NUM>);
an outer cylinder (<NUM>) which covers at least part of an outer circumference of the inner cylinder (<NUM>) with a space (<NUM>) therebetween and comprises a second inner coil part (<NUM>) and a second outer coil part (<NUM>), and in which wound parts (19a) corresponding to the second inner coil part (<NUM>) are fitted to spaces (17b) between adjacent wound parts (17a) of the second outer coil part (<NUM>); and
cord-like members (9a, 9b) which are inserted into and guided by the space (<NUM>) between the inner cylinder (<NUM>) and the outer cylinder (<NUM>) in an axial direction;
edge members (7a, 7b) attached to both ends of either one or both of the outer cylinder (<NUM>) and the inner cylinder (<NUM>) for inserting the cord-like member (9a, 9b) into a first insertion hole (<NUM>); and
a flexible member (<NUM>) inserted through the first inner coil part (<NUM>) of the inner cylinder (<NUM>) to position the inner cylinder (<NUM>) on the edge members (7a, 7b),
wherein each of the edge members (7a, 7b) has a second insertion hole (<NUM>) for inserting the flexible member (<NUM>) and fitting an end of the flexible member (<NUM>).