CN110663092B

CN110663092B - Cable for robot

Info

Publication number: CN110663092B
Application number: CN201780090794.7A
Authority: CN
Inventors: 崔洪硕; 梁永勳; 朴弘根; 梁勋喆; 黄炫珠; 姜敏秀
Original assignee: LS Cable Ltd
Current assignee: LS Cable and Systems Ltd
Priority date: 2017-05-31
Filing date: 2017-10-25
Publication date: 2021-04-23
Anticipated expiration: 2037-10-25
Also published as: KR102348281B1; WO2018221793A1; KR20180131219A; CN110663092A; JP2020520068A; EP3633692A4; EP3633692B1; EP3633692A1

Abstract

The present invention relates to a robot cable, and the robot cable according to the present invention includes: a center fill; at least one inner cable core surrounding the center filler; at least one first filler surrounding the center filler and disposed between the inner cable cores; an inner binder tape made of an unsintered (unsintered) fluororesin, surrounding and binding the inner cable core and the first filler; at least one outer cable core surrounding an outer side of the inner tie wrap; at least one second filler disposed outside of the inner tie wrap; an outer binder tape for binding the outer cable core and the second filler, the outer binder tape being made of unsintered fluororesin; a shielding layer disposed outside the external ligature band; and the sheath is arranged on the outer side of the shielding layer.

Description

Cable for robot

Technical Field

The present invention relates to a robot cable, and more particularly, to a robot cable that is used for an industrial robot and that has greatly improved durability against repeated twisting and bending life.

Background

Generally, an industrial robot performs various operations such as welding, painting, and transfer on a production line of machine parts. Such an industrial robot is connected to a central control unit or the like via a robot cable, receives necessary electric power via the robot cable, and further receives and transmits information and the like necessary for various operations.

However, during such work, the industrial robot continues to move or move, and thus a fatigue load such as repeated tension, torsion, bending, or the like is applied to a cable for a robot connected to the industrial robot.

In this case, the conductor of the cable for the robot may be broken, and when the production line is stopped due to the broken cable, a loss of time and cost for replacing the cable may occur. Therefore, a robot cable ensuring high durability is required.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a robot cable that can significantly improve durability and fatigue life even when used in an environment that frequently undergoes torsion, bending, or the like.

Technical scheme for solving problems

In order to solve the above problems, the present invention can provide a cable for a robot, comprising: a center fill; at least one inner cable core surrounding the center filler; at least one first filler surrounding the center filler and disposed between the inner cable cores; an inner binder tape made of an unsintered (unsintered) fluororesin, surrounding and binding the inner cable core and the first filler; at least one outer cable core surrounding an outer side of the inner tie wrap; at least one second filler disposed outside of the inner tie wrap; an outer binder tape for binding the outer cable core and the second filler, the outer binder tape being made of unsintered fluororesin; a shielding layer disposed outside the external ligature band; and the sheath is arranged on the outer side of the shielding layer.

In this case, the inner cable core may be provided with: a first conductor formed by twisting a plurality of first wires at a predetermined first pitch; and a first insulating layer disposed outside the first conductor, and the first pitch may be 15 to 30 times an outer diameter of the first conductor.

In addition, the outer cable core may be provided with: a second conductor formed by twisting a plurality of second wires at a predetermined second pitch; a cable core formed by twisting a plurality of the second conductors at a predetermined third pitch; and a second insulating layer disposed at an outer side of the cable core, the second pitch may be 15 to 50 times an outer diameter of the second conductor, and the third pitch may be 10 to 30 times the outer diameter of the cable core.

And, a yield strength increase rate of the first wires of the inner core and the second wires of the outer core may be 1% to 30%.

In addition, the Unsintered fluororesin may be composed of an Unsintered Polytetrafluoroethylene (Unsintered PTFE) resin.

Here, the inner and outer tie wraps may have a coefficient of friction between 0.05 and 0.2.

In addition, the first filler may have an outer diameter corresponding to an outer diameter of the inner cable core, and the second filler may have an outer diameter corresponding to an outer diameter of the outer cable core.

Here, the outer diameter of the first filler may have an outer diameter of 80% to 120% of the outer diameter of the inner cable core, and the outer diameter of the second filler may have an outer diameter of 80% to 120% of the outer diameter of the outer cable core.

In this case, at least one of the center filler, the first filler, and the second filler may be formed by knotting elastic yarn (elastic yarn).

Also, the elastic yarn may be composed of polyester yarn (polyester yarn).

In addition, an additional binding tape may be further disposed between the shielding layer and the sheath.

In this case, the additional tie wrap may be composed of unsintered ptfe (unsintered polytetrafluoroethylene) resin.

In this case, the sheath may be formed by tube type (tube type) extrusion.

In order to solve the above problems, the present invention can provide a cable for a robot, including: a plurality of inner cable cores disposed on the outer peripheral surface of the center filler having a circular cross section; an inner binding band for binding the outside of the inner cable core; a plurality of outer cable cores disposed on an outer peripheral surface of the inner banding band; an outer binding band for binding the outside of the outer cable core; a shielding layer disposed outside the external ligature band; and a sheath disposed outside the shield layer, the inner and outer straps being composed of unsintered fluororesin having a friction coefficient of 0.05 to 0.2.

Effects of the invention

According to the robot cable of the present invention, durability and fatigue life can be significantly improved even when the cable is used in an environment where torsion, bending, or the like is frequently received.

Further, according to the robot cable according to the present invention, durability is improved, and process interruption occurring in an industrial site can be minimized, so that loss due to process interruption can be minimized.

Drawings

Fig. 1 is a cross-sectional view showing an internal structure of a robot cable according to an embodiment of the present invention.

Fig. 2 and 3 are graphs showing the rate of change in resistance of the number of twists according to the example and the comparative example according to the present invention.

Fig. 4 is a graph comparing the difference in coefficient of friction when the banding band according to the present invention and the conventional banding band are applied.

Fig. 5 is a graph comparing the change in the Pull-out force (Pull-out force) of the example according to the present invention and the comparative example.

Fig. 6 is a graph showing the resistance change rate (%) of the number of twists according to the example and the comparative example to which the present invention relates.

Detailed Description

Hereinafter, a robot cable according to an embodiment of the present invention will be described in detail with reference to the drawings.

Fig. 1 is a cross-sectional view showing an internal structure of a robot cable 100 according to an embodiment of the present invention.

Referring to fig. 1, the robot cable 100 includes: a center filler 20; at least one inner cable core 10 surrounding said center filler 20; at least one first filler 22 surrounding said center filler 20 and disposed between said inner cable cores 10; an inner binder 30 surrounding and binding (binding) the inner cable core 10 and the first filler 22, the inner binder 30 being composed of unsintered (unsintered) fluororesin; at least one outer cable core 40 surrounding the outside of the inner tie wrap 30; at least one second filler 50 disposed outside the inner tie wrap 30; an outer binder 32 binding the outer cable core 40 and the second filler 50, the outer binder 32 being composed of an unsintered (unsintered) fluororesin; a shielding layer 60 disposed outside the outer banding band 32; and a sheath 70 disposed outside the shield layer 60.

In the robot cable 100, the inner cable core 10 may be configured as a communication cable core for receiving and transmitting information with the outside, and the outer cable core 40 may be configured as a power cable core for supplying power.

Specifically, the inner cable core 10 is provided with: a first conductor formed by twisting a plurality of first wires 12 at a predetermined first pitch (pitch); and a first insulating layer 14 disposed outside the first conductor.

The first wire 12 may be made of copper (copper) or the like, and the first insulating layer 14 covering the first conductor made of the first wire 12 may be made of Polyethylene (PE, Polyethylene) or High Density Polyethylene (HDPE), or the like.

However, when the first wire 12 is subjected to the above-described steps to form the inner cable core 10, a tensile stress remains in the first wire 12. In this way, when a tensile pre-strain (tensile pre-strain) indicating a large tensile force remains in the first wire 12 after the inner cable core 10 is formed, the yield strength of the first wire 12 can be increased, for example, by 30% or more.

As described above, if the yield strength of the first wire material 12 increases, the fatigue life of the first wire material 12 decreases, and thus damage such as cracks (cracks) may occur in the first wire material 12. Such damage to the first wire 12 can be expressed by a resistance change rate (%) that changes the resistance.

That is, the relatively high resistance change rate (%) means that the first wire 12 is damaged by cracks or the like in a large amount, and in a serious case, the wire is broken.

Fig. 2 is a graph showing the rate of change in resistance of the number of twists according to the example and the comparative example relating to the present invention. The example shows the wire rod in which the increase rate of yield strength after the inner cable core 10 is formed is 1% to 30%, and the comparative example shows the wire rod in which the increase rate of yield strength after the inner cable core 10 is formed exceeds 30%. In the graph of fig. 2, the horizontal axis represents the number of twists (× 1000), and the vertical axis represents the rate of change in resistance (%).

As shown in fig. 2, in the case of the above-described example, even when the number of twists exceeds 10000 times, the resistance change rate is approximately 7%, and thus it is understood that the resistance change rate is very small. From this, it is understood that the wire rod of the example has very little damage such as cracks, and that the wire rod of the example has relatively little pre-strain, and the yield strength increase rate is 30% or less, that is, 1% to 30%.

On the contrary, in the case of the comparative example, it is found that the resistance change rate is substantially 13% or more when the number of twists exceeds 10000, and the resistance change rate is relatively very large. From this, it is understood that in the case of the wire rod of the comparative example, damage such as a very large number of cracks relatively occurs, and from this, it is also understood that in the wire rod of the comparative example, the pre-strain is relatively large, and the increase rate of the yield strength exceeds 30%.

Therefore, it is known that the fatigue life is increased as the pre-strain is decreased after the wire rod is processed, and that the fatigue life can be indirectly predicted by the increase rate of the yield strength or the resistance change rate after the wire rod is processed.

Therefore, after the wire rod is processed, the fatigue life can be increased by determining the rate of increase in yield strength or the rate of change in resistance in accordance with a predetermined critical value. For example, in the present invention, a case where the increase rate of the yield strength after processing the wire rod is 1% to 30%, that is, 30% or less or a case where the resistance change rate is 1% to 25%, that is, 25% or less may be set as the critical value.

The inventors of the present invention conducted experiments to confirm the factors affecting the rate of change in resistance of the wire rod, and fig. 3 shows the results.

Fig. 3 is a graph showing the rate of change in resistance of the number of twists according to the example and the comparative example according to the present invention. The example refers to a wire rod forming a cable core ("composite type") in which a plurality of wire rods are twisted at a predetermined pitch and such a plurality of conductors are twisted again at a predetermined pitch, and the comparative example refers to a conductor ("composite type") in which a plurality of wire rods are twisted at a predetermined pitch. In the case of the comparative example and the example, the entire outer diameter was formed to be the same.

At this time, comparative example 1 was formed such that the pitch of the wire rods was larger than that of comparative example 2. For example, the pitch of the wires of comparative example 1 is approximately 18mm, and the pitch of the wires of comparative example 2 is approximately 12 mm. In the graph of fig. 3, the horizontal axis represents the number of twists (× 1000), and the vertical axis represents the rate of change in resistance (%).

As shown in fig. 3, when the rate of change in resistance (%) increased by the number of twists was observed for the wire rods of examples after the collective and composite processing, it was found that the wire rods were remarkably superior to those of comparative examples.

That is, in the case of the wire rod of the above example, even when the number of twists exceeds 10000 times, the resistance change rate (%) was about 12%, and thus it was found that the resistance change rate was very small.

On the contrary, it is found that the resistance change rate (%) exceeds approximately 25% when the number of twists exceeds approximately 2000 times in the case of passing only the wire rod of comparative example 2 of the integrated type.

On the other hand, in the case of the wire rod of comparative example 1, when the number of twists exceeded 10000 times, the rate of change in resistance (%) was approximately 23%, which is superior to that of comparative example 2, but the rate of change in resistance was larger than that of example.

As a result, it was found that the rate of change in resistance was relatively minimum when passing through the integrated type and the composite type in the case of processing the wire rod. In addition, in the case of passing only the collective type, it is known that the resistance change rate is smaller as the pitch of the wire is relatively larger.

As shown in fig. 1, the first conductors of the inner cable core 10 may be formed in a collective type. In this case, the first pitch of the first wires 12 may be 15 to 30 times the outer diameter of the first conductor. If the ratio is less than 15 times, the rate of change in resistance of the first wire 12 exceeds 25%, or the rate of increase in yield strength exceeds 30%. On the contrary, if it is more than the above-mentioned 30 times, the pitch is too long to properly form the first conductor into a circular shape.

That is, in the case where the first pitch of the first wires 12 is in the above range, the yield strength increase rate of the first wires 12 of the inner cable core 10 is 1% to 30%, and the resistance change rate (%) is 1% to 25%.

On the other hand, a center filler 20 is provided in the center of the inner cable core 10. The center filler 20 functions to keep the robot cable 100 in a circular shape together with a first filler 22 and a second filler 50, which will be described later.

In the case of the existing cable, the filler is composed of a PVC wire (PVC string), Polyethylene (PE), Ethylene Propylene Diene Monomer (EPDM), or the like.

In the case of the existing cable, when the cable is subjected to bending or torsion, friction occurs between the insulator and the filler of the cable core without slipping (slip), and at this time, relatively more stress is applied to the cable core, so that damage or disconnection of the conductor may occur.

The following [ table 1] shows the results of measuring the electric resistance of the inner cable core 10 after 50 ten thousand times of the torsion test for the examples and comparative examples having the same structure. The embodiment is a case where the center filler 20, the first filler 22, and the second filler 50 are formed by twisting elastic yarns (elastic yarns) formed of polyester yarns (polyester yarns), and the comparative example shows a case where the center filler is formed of EPDM. The inner cores 1 to 5 are arbitrarily numbered for the inner core 10 shown in fig. 1.

[ Table 1]

	Resistance (m.OMEGA.) of comparative example	Resistance of the example (m.OMEGA.)
			Inner cable core 1	18.27	7.1
Inner cable core 2	18.05	7.6
			Inner cable core 3	37.5	8.2
Inner cable core 4	16.06	7.1
			Inner cable core 5	28.07	7.5

In table 1, the critical value may vary depending on the place where the cable is installed, the working process, the request of the customer company, and the like, but is approximately 8.25m Ω.

In this case, it is understood that the resistance values of all the inner cable cores are equal to or greater than the critical value and do not satisfy the reference value in the case of the comparative example.

In contrast, in the case of the above-described example, the maximum resistance value was 8.2m Ω, and all satisfied the reference value. In the case of this example, the filler is made of a yarn (yarn) having high stretchability, and therefore, even in the case of twisting or the like, only a relatively small stress is transmitted to the inner cable core, and an increase in resistance due to damage by the internal stress can be prevented.

Accordingly, in the present invention, at least one of the center stuffing 20, the first stuffing 22 and the second stuffing 50 may be formed by kinking elastic yarn (elastic yarn), which may be composed of polyester yarn (polyester yarn).

As shown in fig. 1, the center filler 20 is located at the center, and at least one inner cable core 10 and a first filler 22 are disposed along the outside of the center filler 20.

In the drawings, the number of the inner cable cores 10 is represented as five, and the number of the first fillers 22 is represented as three, but this is merely an example and may be appropriately modified.

On the other hand, since the inner cable core 10 and the first filler 22 are formed in a circular shape together, the first filler 22 preferably has outer diameters corresponding to the outer diameters of the inner cable core 10.

Since the outer diameter of the inner cable core 10 can be determined according to the working environment to which the robot cable 100 is applied, it is preferable that the outer diameter of the first filler 22 is determined to correspond to the outer diameter of the inner cable core 10.

For example, the outer diameter of the first filler 22 may have an outer diameter of 80% to 120% of the outer diameter of the inner cable core 10.

If the outer diameter of the first filler 22 is relatively too large, pressure is applied to the inner cable core 10 during twisting, and the first conductor of the inner cable core 10 may be damaged, for example, by disconnection. Further, if the outer diameter of the first filler 22 is relatively too small, the first filler cannot be formed into a circular shape.

On the other hand, the inner banding band 30 surrounds and bands the inner cable core 10 and the first filler 22, playing a role of maintaining a circular shape.

In the conventional cable, a nonwoven fabric or a sintered (sintered) fluororesin is used as a binding tape. However, when the sintered fluororesin is used, the strength and the friction coefficient are relatively high, and when torsion or the like acts on the cable, the stress cannot be absorbed but is transmitted to the inner cable core. Further, when torsion or the like acts on the cable, there is a possibility that the inner cable core is damaged due to friction between the binding tape and the inner cable core.

Therefore, in the present invention, the inner band 30 may be composed of an unsintered (unsintered) fluororesin having a relatively small friction coefficient and strong lubricity.

For example, the unsintered fluororesin may be composed of an unsintered ptfe (unsintered polytetrafluoroethylene) resin. At this time, it was confirmed that the inner tie wrap 30 was constituted to have a friction coefficient of 0.05 to 0.2. The band 30 having such a friction coefficient can realize a soft sliding when the cable is subjected to a torsion, and can minimize a friction damage between the band and the outer cable core 40, thereby greatly improving durability of the cable.

Fig. 4 is a graph comparing the difference in coefficient of friction when the band B according to the present invention and the conventional band a are applied.

Fig. 4 shows a case where the bandage B according to the present invention is made of an unsintered ptfe (unsintered polytetrafluoroethylene) resin, and a case where a conventional bandage a is applied shows a case where a sintered (sintered) fluororesin is applied.

As shown in fig. 4, it was found that the coefficient of friction was approximately 0.146 μ when the conventional tie wrap a was applied, whereas the coefficient of friction was 0.092 μ when the tie wrap B according to the present invention was applied, a reduction in the coefficient of friction of approximately 37% was achieved.

On the other hand, fig. 5 is a graph comparing the change in the drawing force (N) in the example according to the present invention and the comparative example.

Fig. 5 shows a case where the inner binding tape 30 is composed of an unsintered ptfe (unsintered polytetrafluoroethylene) resin in the example, and a case where a sintered (sintered) fluororesin is used as the binding tape in the comparative example. The drawing force is defined as a force (N) consumed by friction with the outer cable core when the inner cable core (pullout) is pulled. That is, the inner ligature 30 provides a relatively large pulling force to increase the frictional force between the inner cable core and the outer cable core, and the inner ligature 30 provides a relatively small pulling force to decrease the frictional force between the inner cable core and the outer cable core. In fig. 5, the horizontal axis represents the length (mm) of the inner cable core drawn out, and the vertical axis represents the force (N) consumed.

As can be seen from fig. 5, in the case of the comparative example, the force consumed decreases as the length of the inner cable core is pulled out increases. For example, it is known that the force consumed when the length of the inner cable core is pulled out to be approximately 100mm is approximately 30N to 35N.

In contrast, it is understood that the force consumed is smaller in the case of the example than in the case of the comparative example. For example, when the length of the inner cable core is pulled out to be approximately 100mm, the force consumed is approximately 15N, and it is found that the force is reduced by approximately 50% to 57% as compared with the comparative example.

It is understood that in the case of the mobile electric power communication cable 100 according to the present invention, since frequent movement frequently causes twisting, bending, and the like, the smaller the pulling force, the smaller the friction force between the inner core and the outer core due to the inner bandage 30, and the better the durability and fatigue life.

On the other hand, referring to fig. 1, at least one outer cable core 40 and at least one second filler 50 are provided outside the inner tie wrap 30.

In this case, the outer cable core 40 may be formed by the collective and composite processes described above.

For example, the outer cable core 40 may be provided with: a second conductor, a plurality of second wires 42 twisted at a predetermined second pitch; a cable core formed by twisting a plurality of the second conductors at a predetermined third pitch; and a second insulation layer 44 disposed outside the cable core.

At this time, the second pitch is 15 to 50 times the outer diameter of the second conductor, and the third pitch is 10 to 30 times the outer diameter of the cable core.

In addition, in the case where the second pitch and the third pitch of the second wires 42 are in the above-mentioned ranges, the yield strength increase rate of the second wires 42 of the outer cable core 40 is 1% to 30%, and the resistance change rate (%) is 1% to 25%.

On the other hand, the second filler 50 may have outer diameters respectively corresponding to the outer diameters of the outer cable cores 40, and for example, the outer diameter of the second filler 50 may be 80% to 120% of the outer diameter of the outer cable core 40.

In addition, the second fillers 50 may be formed by knotting elastic yarn (elastic yarn), which may be composed of polyester yarn (polyester yarn).

The description of such second filler 50 is similar to that of the first filler 22 described hereinbefore, and thus, a repetitive description will be omitted.

In the drawings, the number of the outer cable cores 40 is eight and the number of the second fillers 50 is one, but this is merely an example and may be appropriately modified.

On the other hand, the outer binder tape 32 binds the outer cable core 40 and the second filler 50, and is composed of an unsintered (unsintered) fluororesin. At this time, the unsintered fluororesin may be composed of an unsintered polytetrafluoroethylene (ptfe) resin, and the outer tie tapes 32 may have a friction coefficient of 0.05 to 0.2.

The description of such an outer tie wrap 32 is similar to that of the inner tie wrap 30 described hereinbefore, and so duplicate description is omitted.

A shielding layer 60 is provided on the outside of the outer tie wrap 32. The shield layer 60 may be formed in a metal tape shape or a metal braid shape by applying a material such as copper, aluminum, a copper alloy, or an aluminum alloy. The shielding layer 60 functions as follows: the communication characteristics of the communication cable based on electromagnetic wave shielding are maintained, or the cable is protected from an impact from the outside.

On the other hand, a sheath 70 is provided outside the shield layer 60. The sheath 70 serves as an outermost layer of the mobile electric power communication cable 100, does not expose the internal components and the like described above to the outside, and serves to protect the internal components from external impact.

In this case, in the case of the conventional cable, the sheath is extruded by a press type extrusion molding, but this method involves a problem that pressing marks of the sheath are generated in the conductor or the shield layer inside after the extrusion.

Therefore, in the present invention, in the case of extruding the sheath 70, the molding is performed by tube type extrusion. The step of inserting the internal components into the sheath 70 and pressing the same in a state in which the sheath 70 is prepared in a tube form in advance can prevent the conductor or the shield layer in the interior from being pressed by the sheath after pressing.

On the other hand, as shown in fig. 1, an additional tie wrap 34 may be further provided between the shielding layer 60 and the sheath 70. By providing the additional banding band 34, it is possible to further reduce the internal friction when the robot cable 100 is subjected to torsion or bending, etc.

At this time, the additional banding band 34 is composed of unsintered ptfe (unsintered polytetrafluoroethylene) resin, and has a friction coefficient between 0.05 and 0.2. The description of the additional ligature 34 is similar to that of the inner and

outer ligatures

30, 32 described hereinbefore, so that duplicate description is omitted.

In fig. 6, an example is a cable having the structure of fig. 1 described previously, and a comparative example shows a case where a sheath is formed by pressure extrusion using High Density Polyethylene (HDPE) or EPDM as a filler and sintered fluororesin as a tie tape. In fig. 6, the horizontal axis represents the number of twists (× 1000) and the vertical axis represents the rate of change in resistance (%).

As shown in fig. 6, it is understood that in the case of the cable according to the comparative example, when the number of twists reaches approximately 20000 to 25000, the resistance change rate exceeds 25% which is a reference value.

On the contrary, in the case of the cable according to the embodiment of the present invention, even when the number of twists exceeds 500000, the resistance change rate does not exceed 5.0% and is significantly lower than 25% which is the reference value.

While the present invention has been described with reference to the preferred embodiments, those skilled in the art to which the present invention pertains can implement the present invention with various modifications and alterations without departing from the spirit and scope of the present invention as defined in the appended claims. Therefore, if the modified embodiment substantially includes the constituent elements of the claims of the present invention, it should be considered to fall within the technical scope of the present invention.

Claims

1. A cable for a robot, comprising:

a center fill;

a plurality of inner cable cores surrounding the center filler;

at least one first filler surrounding the center filler and disposed between the inner cable cores;

an inner binder tape which surrounds and binds the inner cable core and the first filler in a contact state and is composed of an unsintered fluororesin;

a plurality of outer cable cores surrounding the outer circumferential surface of the inner banding band in a contact state;

at least one second filler disposed outside of the inner tie wrap;

an external binding band for binding the external cable core and the second filler, and the external binding band is made of unsintered fluororesin;

a shielding layer disposed outside the external ligature band; and

a sheath disposed outside the shielding layer,

the inside cable core is provided with: a first conductor formed by twisting a plurality of first wires at a predetermined first pitch; and a first insulating layer disposed outside the first conductor, the first pitch being 15 to 30 times an outer diameter of the first conductor.

2. The robot cable according to claim 1,

the outside cable core is provided with: a cable core, a plurality of second conductors twisted at a predetermined third pitch; and a second insulating layer provided outside the cable core,

the second conductor is formed by twisting a plurality of second wires at a predetermined second pitch,

the second pitch is 15 to 50 times an outer diameter of the second conductor,

the third pitch is 10 to 30 times an outer diameter of the cable core.

3. The robot cable according to claim 2,

a yield strength increase rate of the first wires of the inner cable core and the second wires of the outer cable core is 1% to 30%.

4. The robot cable according to claim 1,

the unsintered fluororesin is composed of an unsintered PTFE resin.

5. The robot cable according to claim 1,

the inner and outer tie bands have a coefficient of friction between 0.05 and 0.2.

6. The robot cable according to claim 1,

the first filler has an outer diameter corresponding to the outer diameter of the inner cable core and the second filler has an outer diameter corresponding to the outer diameter of the outer cable core.

7. The robot cable according to claim 6,

the outer diameter of the first filler has an outer diameter of 80% to 120% of the outer diameter of the inner cable core, and the outer diameter of the second filler has an outer diameter of 80% to 120% of the outer diameter of the outer cable core.

8. The robot cable according to claim 1,

at least one of the center filler, the first filler, and the second filler is formed by kinking an elastic yarn.

9. The robot cable according to claim 8,

the elastic yarn is composed of polyester yarn.

10. The robot cable according to claim 1,

an additional binding belt is further arranged between the shielding layer and the sheath.

11. The robot cable according to claim 10,

the additional tie wrap is comprised of an unsintered PTFE resin.

12. The robot cable according to claim 1,

the jacket is formed by tubular extrusion.

13. A cable for a robot, comprising:

a plurality of inner cable cores disposed on the outer peripheral surface of the center filler having a circular cross section;

an inner banding band for banding the outside of the inner cable core in a contact state;

a plurality of outer cable cores disposed in a contacting state on an outer peripheral surface of the inner banding band;

an outer binding band binding an outer portion of the outer cable core in a contact state;

a shielding layer disposed outside the external ligature band; and

a sheath disposed outside the shielding layer,

the inside cable core is provided with: a conductor in which a plurality of wires are twisted at a pitch of 15 to 30 times an outer diameter of the conductor; and an insulating layer disposed outside the conductor,

the inner and outer bands are composed of an unsintered fluororesin having a friction coefficient of 0.05 to 0.2.