Flexible shaft, and robot

Abstract

[Problem] To provide a flexible shaft capable of suppressing frictional force generated between an outer tube and an inner shaft, and a robot using the flexible shaft. [Solution] The present invention is provided with an inner shaft 21 and an outer tube having a through-hole 30 into which the inner shaft is inserted. At least a part of a wall body defining the through-hole of the outer tube is composed of a fluororesin. Grease is filled between an outer peripheral surface of the inner shaft and an inner peripheral surface of the through-hole.

Description

Flexible shaft and robot

[0001] The present invention relates to a flexible shaft and a robot using the flexible shaft.

[0002] A conventional flexible shaft for transmitting torque has been known, which includes an inner shaft and an outer tube, with the inner shaft inserted into the outer tube (see Patent Document 1). Flexible shafts are used in portable brush cutters and industrial machines with a torque transmission mechanism to transmit torque from a power source such as an engine to a rotating body such as a cutting blade.

[0003] Japanese Patent Application Laid-Open No. 2003-232330

[0004] The frictional force generated between the outer tube and the inner shaft reduces the torque transmission efficiency of the flexible shaft, so there is a demand for technology that can reduce the frictional force generated between the outer tube and the inner shaft in the flexible shaft.

[0005] In view of the above background, an object of the present invention is to provide a flexible shaft that can reduce the frictional force generated between an outer tube and an inner shaft, and a robot that uses the flexible shaft.

[0006] In order to solve the above problems, one aspect of the present invention comprises a flexible inner shaft (21), a through hole (30) into which the inner shaft is rotatably inserted, and a flexible outer tube (22), wherein at least a portion of a wall defining the through hole of the outer tube is made of fluororesin, and grease (35) is filled between the outer peripheral surface of the inner shaft and the inner peripheral surface of the through hole.

[0007] According to this aspect, the provision of the outer tube makes it possible to protect the inner shaft and surrounding objects. Furthermore, because the outer tube is made of a fluororesin with high sliding properties, it is possible to reduce friction that may occur between the outer tube and the inner shaft. In addition, it is possible to improve the durability of the flexible shaft.

[0008] In the above aspect, the grease preferably contains a fluororesin.

[0009] According to this aspect, it is possible to improve the durability of the flexible shaft while suppressing the frictional force that may occur between the outer tube and the inner shaft.

[0010] In the above aspect, the fluororesin contained in at least a portion of the wall that defines the through hole and the fluororesin contained in the grease are preferably made of the same material.

[0011] According to this aspect, it is possible to further reduce the frictional force that may occur between the outer tube and the inner shaft, and to further improve the durability of the flexible shaft.

[0012] In the above aspect, preferably, the inner shaft is formed by winding a wire (27) and includes a winding layer (28) that forms the outer circumferential surface of the inner shaft.

[0013] According to this aspect, the flexible inner shaft can be simply configured.

[0014] In the above aspect, preferably, a recess (37) for storing the grease is provided on at least one of the outer circumferential surface of the inner shaft and the inner circumferential surface of the through hole.

[0015] According to this aspect, it is possible to store grease for reducing the frictional force between the outer tube and the inner shaft.

[0016] In addition, in order to solve the above-mentioned problem, another aspect of the present invention is a robot equipped with the above-mentioned flexible shaft, comprising a drive unit capable of outputting torque in both directions, and a driven member connected to the drive unit via the flexible shaft and driven by the torque output by the drive unit.

[0017] According to this aspect, it is possible to provide a robot that transmits the torque output by the drive unit to a driven member via a flexible shaft, and that is capable of suppressing the frictional force that occurs between the outer tube and inner shaft of the flexible shaft.

[0018] According to the above aspects, it is possible to provide a flexible shaft that can reduce the frictional force generated between the outer tube and the inner shaft, and a robot that uses the flexible shaft.

[0019] 1 is a block diagram of a control device according to an embodiment; FIG. 2 is a side view showing (A) a first embodiment, (B) a second embodiment, and (C) a third embodiment of a flexible shaft; FIG. 3 is a side view showing a fourth embodiment of a flexible shaft; FIG. 4 is a graph showing the torsional rigidity characteristics of a flexible shaft according to the present invention; FIG. 5 is a graph showing the torsional rigidity characteristics of the flexible shafts of the first to third embodiments; and FIG. 6 is a graph showing the dependence of torque T on torsional angle θ for the flexible shaft of the third embodiment; and (A) a graph showing the derivative dT / dθ with respect to torsional angle θ of the graph in (A); and (C) a graph showing the second derivative with respect to torsional angle θ of the graph in (A).

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a flexible shaft according to the present invention and a robot equipped with the flexible shaft will be described in detail with reference to the drawings.

[0021] The robot 1 according to the present invention is a so-called articulated robot, and is equipped with a plurality of joints. Fig. 1 shows an example of the configuration of the robot 1 according to the embodiment. However, the configuration shown in Fig. 1 is merely an example, and the present invention is not limited to this configuration.

[0022] As shown in FIG. 1, the robot 1 includes a base 2, an intervening link 3 displaceably connected to the base 2, and a driven member 4 displaceably connected to the intervening link 3.

[0023] The base 2 is provided with a first driving device 6, a second driving device (not shown), and a control device 7 that controls the first driving device 6 and the second driving device independently.

[0024] The first driving device 6 is configured to be able to output torque in both directions and may be any of various motors including a main body 6A fixed to the base 2 and an output shaft 6B supported by the main body 6A and rotatable in both directions.

[0025] The second driving device is also configured to be able to output torque in both directions, and may be any of various motors having a main body fixed to the base 2 and an output shaft supported by the main body and rotating in both directions.

[0026] 3, the control device 7 is configured as a so-called microcomputer including a processor 7A such as a central processing unit (CPU), a storage device 7B such as an HDD or SSD, and a memory 7C such as a RAM or ROM. The control device 7 is configured so that the processor 7A reads necessary data and software from the storage device 7B and executes predetermined arithmetic processing in accordance with the software. The first drive device 6, the second drive device, and the control device 7 may each be supported by the base 2 via multiple members, or may be provided on a member other than the base 2.

[0027] As shown in Fig. 1 , the intervening link 3 is a rod-shaped member, and one end of the intervening link 3 is rotatably connected to the base body 2. In this embodiment, the intervening link 3 is pivotally supported on the base body 2 and rotatably supported relative to the base body 2. A gear box that converts rotation of the output shaft into rotation of the intervening link 3 relative to the base body 2 may be provided between the intervening link 3 and the output shaft of the second driving unit. However, the manner of connection between the intervening link 3 and the base body 2 is not limited to this manner. For example, the intervening link 3 may be rotatably supported on the base body 2 via the second driving unit by being directly coupled to the output shaft of the second driving unit.

[0028] The driven member 4 (also referred to as a driven member) is connected to the first driving device 6 via a transmission mechanism 10. The transmission mechanism 10 is interposed between the driven member 4 and the first driving device 6, and serves to transmit the rotation and torque output from the first driving device 6 to the driven member 4. The driven member 4 is driven by the rotation and torque output from the first driving device 6 transmitted by the transmission mechanism 10.

[0029] In this embodiment, the driven member 4 is connected to the intervening link 3 so as to be rotatable in both directions around the axis Y. The bidirectional torque output from the first driving device 6 is transmitted to the driven member 4 by the transmission mechanism 10, and the driven member 4 is driven to rotate in both directions relative to the intervening link 3.

[0030] 1 shows an example in which the rotation axis X of the intervenient link 3 relative to the base 2 and the rotation axis Y of the driven member 4 relative to the intervenient link 3 are perpendicular to the plane of the page and parallel to each other. However, the direction of the rotation axis X of the intervenient link 3 relative to the base 2 is not limited to this embodiment, and for example, the rotation axis X of the intervenient link 3 relative to the base 2 may be configured to be parallel to the plane of the page (e.g., in the up-down direction on the page).

[0031] The transmission mechanism 10 includes a single-axis actuator 11 supported by the intervening link 3 and converting the torque output from the first driving device 6 into axial force, a flexible shaft 12 interposed between the first driving device 6 and the single-axis actuator 11, and a displacement mechanism 13 that converts the axial force of the single-axis actuator 11 into a displacement of the driven member 4.

[0032] The single-axis actuator 11 is configured by a so-called ball screw that includes a screw shaft 15, a nut 16, and balls (not shown). When one of the screw shaft 15 and the nut 16 is rotated, the other moves linearly along the axis of the screw shaft 15. In this embodiment, the screw shaft 15 is supported by the intervening link 3 so as to be rotatable but immovable in the axial direction, and the nut 16 is supported by the intervening link 3 so as to be movable in the axial direction of the screw shaft 15 but immovable. In other words, the single-axis actuator 11 constitutes a conversion mechanism that converts the rotational motion (torque) of the screw shaft 15 into the linear motion (axial force) of the nut 16 and outputs it. Figure 2 shows the state of the robot 1 when the nut 16 moves due to the rotation of the screw shaft 15, as shown in Figure 1.

[0033] The flexible shaft 12 transmits the torque output from the first driving device 6 to the single-axis actuator 11. As shown in Fig. 4, the flexible shaft 12 includes an inner shaft 21 (also referred to as a shaft or a core) and an outer tube 22 (also referred to as an outer case or a casing).

[0034] As shown in Figures 4(A) to 4(C) and 5, the inner shaft 21 has a linear shape extending along an axis. The inner shaft 21 is flexible and configured to be bendable. The inner shaft 21 may be configured, for example, by a plurality of wires twisted to form a spiral. As shown in Figure 4(A), the inner shaft 21 may be configured by winding one or more layers of wire 26 around a single bendable core wire 25 (core wire).

[0035] As shown in FIGS. 4(B) and 4(C), the inner shaft 21 may be configured by first arranging several wires 27, such as steel wires, in a band shape and winding them in a direction that forms a predetermined pitch angle with respect to the axis to form a first winding layer 28, and then repeatedly arranging more wires 27 in a band shape and winding them in the opposite direction on top of the first winding layer 28 to form second and third winding layers 28.

[0036] In this embodiment, as shown in FIG. 4(C), the inner shaft 21 includes a first layer made up of wire 27 having a circular cross section wound over its entire length in one direction, a second layer made up of wire 27 having a circular cross section wound over its entire length in the opposite direction to the first layer, and a third layer made up of wire 27 having a circular cross section wound over its entire length in the opposite direction to the second layer.

[0037] Alternatively, the inner shaft 21 may be configured by connecting the ends of two mirror-symmetric shafts. For example, the inner shaft 21 may include a drive-side shaft provided on the drive side and a driven-side shaft provided on the driven side and having the same length as the drive-side shaft, in which the winding direction of the wire 27 constituting the drive-side shaft is opposite to the winding direction of the wire 27 constituting the driven-side shaft, and the end of the driven-side shaft and the end of the drive-side shaft are joined together.

[0038] Alternatively, the inner shaft 21 may have a core wire and a cylindrical small-diameter pipe with a through hole for inserting the core wire, and the small-diameter pipe may be configured so that it can be bent and deformed by providing a through hole at a desired position.

[0039] Alternatively, the inner shaft 21 may be formed of a plurality of link members 29 arranged in line along the axial direction and linearly connected to each other by universal joints, as shown in Fig. 5. It is desirable that the inner shaft 21 have inversion symmetry (mirror symmetry) about a plane passing through the axis. When the inner shaft 21 is formed of a small-diameter pipe with a through hole, it is desirable that the through hole be formed so as to have rotational symmetry about the axis and mirror symmetry about a plane including the axis.

[0040] 4A to 4C and 5, the outer tube 22 is cylindrical and has an inner hole 30 (through hole) through which the inner shaft 21 is inserted. The outer tube 22 is configured to be able to bend and deform, just like the inner shaft 21. The inner shaft 21 is slidably inserted into the inner hole 30 of the outer tube 22. In this way, the outer tube 22 protects the inner shaft 21 from dust and moisture.

[0041] Furthermore, because the outer tube 22 is provided, the flexible shaft 12 does not come into direct contact with surrounding objects such as the base body 2, the intervening link 3, or the driven member 4 during high-speed rotation of the inner shaft 21. This prevents the surrounding objects from being damaged and can protect them. Even when power is transmitted with multiple flexible shafts 12 bundled together, adjacent inner shafts 21 do not come into direct contact with each other, so that it is possible to prevent at least one of the inner shafts 21 from coming into contact with another adjacent inner shaft 21 due to high-speed rotation of the inner shaft 21 and being damaged.

[0042] When torque is applied to one end of the inner shaft 21 (for example, the end on the drive device side), the inner shaft 21 rotates relative to the outer tube 22. This transmits the torque to the other end of the inner shaft 21. In other words, the inner shaft 21 functions as a transmission member that transmits the rotation or torque input to one end to the other end.

[0043] The outer tube 22 may have any shape with an inner hole 30, such as a cylinder, a square tube, or a coiled tube, as long as it is flexible and can be bent. In this embodiment, the outer tube 22 is cylindrical. Since the inner shaft 21 and the outer tube 22 are configured to be flexible, the flexible shaft 12 is also configured to be flexible and can be bent.

[0044] The outer tube 22 is made of a fluororesin (polytetrafluoroethylene, PTFE). The entire outer tube 22 does not have to be made of a fluororesin, and at least a portion of the wall defining the inner hole 30 may be made of a fluororesin.

[0045] 4(C), it is preferable that grease 35 is filled between the outer peripheral surface of the inner shaft 21 and the inner peripheral surface that defines the inner hole 30 of the outer tube 22. However, this is not limited to this embodiment, and the grease 35 may be applied to either the outer peripheral surface of the inner shaft 21 or the inner peripheral surface that defines the inner hole 30 of the outer tube 22. It is preferable that the grease 35 has a higher viscosity than general-purpose lubricating oil.

[0046] The grease 35 preferably contains a fluororesin. In this embodiment, the grease 35 contains a fluororesin, which is the same material as the wall that defines the through-hole of the outer tube 22.

[0047] It is preferable that recesses 37 for storing grease 35 are provided on either the outer surface of the inner shaft 21 or the wall surface (inner circumferential surface) that defines the through hole of the outer tube 22. In this embodiment, the outer surface of the inner shaft 21 is formed from wires 27 that are arranged parallel to one another and have a circular cross section, so that recesses 37 are formed between the wires 27 of the winding layer 28 that define the outer surface, as shown in FIG. 4(C) . Grease 35 is stored in these recesses 37. However, the recesses 37 are not limited to this form, and for example, recesses 37 (grooves) extending in the circumferential direction may be formed on the inner circumferential surface that defines the through hole of the outer tube 22.

[0048] Fig. 6 shows the torsional rigidity characteristics (characteristic diagram) of the flexible shaft 12 according to this embodiment, which represent the relationship between the torsion angle θ of the inner shaft 21 and the torque T acting on one end of the inner shaft 21. As shown in Fig. 6, the flexible shaft 12 according to this embodiment has torsional rigidity characteristics in which the graph showing the relationship between the torsion angle θ and the torque T is symmetrical about the origin.

[0049] The smaller the slope dT / dθ of the graph in Figure 6, the easier it is for the inner shaft 21 to twist in response to the input torque T (i.e., softer), and the larger the slope, the harder it is for the inner shaft 21 to twist in response to the input torque T (i.e., stiffer).

[0050] As shown in Fig. 6, the flexible shaft 12 according to the present invention exhibits nonlinear characteristics, being soft when the torsion angle θ is small and becoming stiffer as the torsion angle θ increases. Hereinafter, the region of the graph including the point where the torsion angle θ is zero, where the slope dT / dθ is equal to or less than a predetermined threshold value Th, will be referred to as a first rigidity region D1, and the region of the graph where the slope dT / dθ is greater than the predetermined threshold value Th will be referred to as a second rigidity region D2. As shown in Fig. 6, the second rigidity region D2 corresponds to a region outside the first rigidity region D1 where the absolute value of the torsion angle θ is greater than that of the first rigidity region D1.

[0051] Since the slope dT / dθ of the graph for the second rigidity region D2 is larger than the slope dT / dθ of the graph for the first rigidity region D1, the second rigidity region D2 is also referred to as the high rigidity region and the first rigidity region D1 is also referred to as the low rigidity region.

[0052] The torsional rigidity characteristics of the inner shaft 21 have been discussed, for example, in Asano et al., "Measurement of Bi-directional Rotational Torsional Characteristics of Flexible Shafts" (Japan Society of Mechanical Engineers, Annual Meeting 2011, S111053) and Aida et al., "On the Torsional Characteristics of Flexible Shafts" ("Zairyo" Vol. 15, No. 153, pp. 410-417, 1996). According to Asano et al., in the first rigidity region D1, the wires 27 are not in sufficient contact with each other, and the wires 27 are generally free to deform, resulting in a small slope dT / dθ of the graph. On the other hand, in the second rigidity region D2, the wires 27 are constricted and come into contact with the wires 27 constituting the inner layer, generating a contact load due to the contact of the wires 27 with the inner layer. Therefore, in the second rigidity region D2, the contact load increases the torsional rigidity, resulting in a large slope dT / dθ of the graph.

[0053] The torsional rigidity characteristics of the flexible shaft 12, which is made up of wires 27 wound in alternating directions in each layer, depend on the parameters of the spacing between the wires 27 in each layer, the number of wires 27 constituting each layer, and the thickness of the wires 27. By adjusting at least one of these parameters, a flexible shaft 12 can be realized in which the graph showing the relationship between torque T and torsion angle θ is approximately symmetrical about the origin.

[0054] When realizing a flexible shaft 12 in which the graph showing the relationship between torque T and torsion angle θ is approximately symmetrical about the origin, for example, at least one (preferably two or more) of the parameters of the number of wires 27 constituting each layer and the thickness of the wires 27 may be selected, multiple flexible shafts 12 with different parameters may be prepared, the torsional rigidity characteristics may be measured, and the flexible shaft 12 in which the graph showing the relationship between torque T and torsion angle θ is most symmetrical about the origin may be selected.

[0055] Here, the graph being symmetrical about the origin means that within the range Θ of the torsion angle θ up to which plastic deformation occurs in the inner shaft 21, the point (θ, T(θ)) on the graph showing the relationship between the torque T and the torsion angle θ satisfies the following equation (1).

[0056]

[0057] In equation (1), δ may preferably be set to 0, except for T(θ)=0.

[0058] As shown in FIG. 1 , one end of the flexible shaft 12, more precisely, one end (input end) of the inner shaft 21, is connected to the output shaft 6B of the first driving device 6. The other end (output end) of the inner shaft 21 is coupled to the screw shaft 15 of the single-axis actuator 11. When the output shaft 6B of the first driving device 6 rotates, the inner shaft 21 rotates, and the screw shaft 15 of the single-axis actuator 11 rotates. This causes the nut 16 to move linearly along the axis of the screw shaft 15. In other words, when torque output from the first driving device 6 is input to the input end of the flexible shaft 12, it is output to the output end and transmitted to the single-axis actuator 11. The rotation transmitted to the single-axis actuator 11 is converted into linear motion by the single-axis actuator 11.

[0059] The displacement mechanism 13 includes a conversion link 40 provided between the driven member 4 and the single-axis actuator 11. One end of the conversion link 40 is rotatably coupled to the driven member 4 about a rotation axis Z1, and the other end is rotatably connected to the nut 16 about a rotation axis Z2. The rotation axis Z1 between the driven member 4 and the conversion link 40 is provided at a position different from the rotation axis Y between the driven member 4 and the intervening link 3. As shown in FIG. 1 , in this embodiment, the extension direction of the rotation axis Z2 between the conversion link 40 and the nut 16 is set to be perpendicular to the extension direction of the screw shaft 15.

[0060] 1 and 2, when the nut 16 moves due to rotation of the output shaft 6B of the first driving device 6, the driven member 4 rotates relative to the intervening link 3 in accordance with the movement of the nut 16. Note that, although the example shown in FIGS. 1 and 2 describes an example in which the driven member 4 is formed of a single member, the present invention is not limited to this embodiment. The driven member 4 may be formed of, for example, a plurality of members connected to each other so as to be rotatable or slidable.

[0061] The first driving device 6 can output torque in both directions, and the output shaft 6B can also rotate in both directions. Furthermore, the inner shaft 21 can rotate in both directions relative to the outer tube 22. Therefore, when the direction of action of the torque output by the first driving device 6 is reversed, the direction of movement of the nut 16 is also reversed, and the direction of rotation of the driven member 4 is also reversed. In the example shown in FIG. 2 , when the nut 16 moves to the right on the page, the driven member 4 rotates clockwise on the page. When the direction of the torque output by the first driving device 6 is reversed and the nut 16 moves to the left on the page, the driven member 4 rotates counterclockwise on the page.

[0062] Next, the effects of the flexible shaft 12 configured in this manner and the robot 1 equipped with the flexible shaft 12 will be described.

[0063] The inventors constructed the robot shown in FIG. 1 using various flexible shafts with different torsional stiffness characteristics (see, for example, FIGS. 7A to 7C). As a result, they found that the torque output to the driven member 4 sometimes depends on the direction and magnitude of the torque acting from the first drive unit 6. In such cases, since the torque output to the driven member 4 depends on the direction and magnitude of the torque acting from the first drive unit 6, it becomes necessary to take measures such as changing the rotation angle of the output shaft 6B depending on the direction and magnitude of the torque acting.

[0064] Therefore, the inventors of the present application conducted extensive research into why the torque output to the driven member 4 depends on the direction and magnitude of the torque acting from the first drive device 6. As a result, they concluded that this is because the torsional rigidity characteristics of the flexible shaft depend on the direction and magnitude of the torque acting. Therefore, the inventors of the present application evaluated the torsional rigidity characteristics of various flexible shafts.

[0065] Figures 7(A) to 7(C) show three examples (hereinafter referred to as Examples 1 to 3) of the torsional rigidity characteristics of flexible shafts obtained by evaluation. Figures 7(A) and 7(B) show the torsional rigidity characteristics of flexible shafts of Examples 1 and 2, respectively, according to conventional examples. Figure 7(C) shows the torsional rigidity of the flexible shaft 12 of Example 3 according to the present invention.

[0066] 7A to 7C, in each of the first to third examples of flexible shafts, when the torque T is zero and the torsional angle θ is zero (the origin), and torque is applied in a predetermined direction (hereinafter referred to as the positive direction), the torsional angle θ gradually increases. When the torsional angle θ reaches a predetermined angle threshold (hereinafter referred to as the positive angle threshold θu), the torsional rigidity increases rapidly, and it becomes difficult for the torsional angle θ to increase in response to an increase in the torque T.

[0067] When the torque is subsequently reduced to zero, as shown in Figure 7(A), in the flexible shaft of the first example, the torsion angle θ does not return to zero, but remains at a value that is significantly deviated from zero. Therefore, the flexible shaft of the first example has torsional rigidity characteristics in which the graph showing the relationship between the torsion angle θ and the torque T is asymmetric with respect to the origin.

[0068] On the other hand, as shown in Figures 7B and 7C, in the flexible shafts of the second and third examples, when the torsional angle θ exceeds the positive angle threshold θu and the torque is reduced to zero, the torsional angle θ becomes approximately zero. Furthermore, when torque is applied in the direction opposite to the positive direction (hereinafter referred to as the negative direction), the torsional angle θ gradually decreases. When the torsional angle θ reaches a predetermined angle threshold (hereinafter referred to as the negative angle threshold θd), the torsional rigidity increases, making it difficult to reduce the torsional angle θ. Thereafter, when the torque is increased to zero, the torsional angle θ becomes approximately zero.

[0069] 7B, in the flexible shaft of the second example, the absolute value of the positive angle threshold θu is different from the absolute value of the negative angle threshold θd, and therefore, in the flexible shaft of the second example, the graph showing the relationship between the torsional angle θ and the torque T has a torsional rigidity characteristic that is asymmetric with respect to the origin.

[0070] As shown in Figure 7 (C), the flexible shaft 12 of the third example has torsional rigidity characteristics in which the graph showing the relationship between the torsion angle θ and the torque T is symmetrical about the origin, and the absolute value of the positive angle threshold θu and the absolute value of the negative angle threshold θd are approximately equal.

[0071] As described above, the flexible shafts of the conventional examples (first and second examples) have torsional rigidity characteristics in which the graph showing the relationship between the torsion angle θ and the torque T is asymmetric with respect to the origin. In the flexible shaft of the first example, as shown in Figure 7(A), the graph showing the torsional rigidity characteristics does not pass through the origin and exhibits large hysteresis, which can cause problems in controlling the position of the driven member 4.

[0072] As shown in FIG. 7B, the graph showing the torsional rigidity characteristics of the flexible shaft of the second example passes through the origin, and the hysteresis is small.

[0073] However, in the flexible shaft of the second example, the absolute value of the positive angle threshold θu is different from the absolute value of the negative angle threshold θd, so when controlling the driven member 4, the control device 7 needs to change the rotation angle of the output shaft 6B and the magnitude of the torque output depending on the rotation direction of the output shaft 6B of the first drive device 6, i.e., the direction of torque action and the magnitude of the torque.

[0074] On the other hand, the flexible shaft 12 of the third example has torsional rigidity characteristics such that the graph showing the relationship between the torsion angle θ and the torque T is symmetrical about the origin, as shown in Figure 7(C). Therefore, the flexible shaft 12 of the third example (an embodiment of the present invention) can effectively transmit torque in both directions, regardless of the direction in which the torque acts. When controlling the driven member 4, the control device 7 can effectively control the drive of the driven member 4 without significantly changing the rotation angle of the output shaft 6B or the magnitude of the torque output, depending on the rotation direction of the output shaft 6B of the first drive device 6, i.e., the direction in which the torque acts and the magnitude of the torque.

[0075] Fig. 8(A) shows the torsional rigidity characteristics of the flexible shaft 12 according to the third example (embodiment), and Fig. 8(B) shows a graph of the derivative dT / dθ of the corresponding torque T versus the torsional angle θ. As can be seen from Fig. 8(B), in the flexible shaft 12 according to the third example (embodiment), the slope dT / dθ of the graph (i.e., the rate of change) is smaller than the threshold value Th in the region between the positive angle threshold value θu and the negative angle threshold value θd, and is larger in other ranges.

[0076] In addition, in FIG. 8C, the second derivative d of the torque T with respect to the torsional angle θ is ２ T / dθ ２ At the positive angle threshold θu, d ２ T / dθ ２ becomes a maximum, and d ２ T / dθ ２ Since the positive angle threshold θu and the negative angle threshold θd are respectively minimum, the positive angle threshold θu and the negative angle threshold θd can also be regarded as the torsion angle θ corresponding to the extreme value.

[0077] As shown in Figures 8A and 8B, the region between the positive angle threshold θu and the negative angle threshold θd corresponds to the first rigidity region D1, and the other region corresponds to the second rigidity region D2. As shown in Figure 6, the first rigidity region D1 includes points where the torsional angle θ is zero. In the first rigidity region D1, the torsional rigidity is lower than in the second rigidity region D2, and the inner shaft 21 is more likely to twist. On the other hand, in the second rigidity region D2, the torsional rigidity is higher than in the first rigidity region D1, and the inner shaft 21 is less likely to twist.

[0078] When an external load is applied to the free end of the driven member 4, torque is transmitted to the flexible shaft 12. When the robot 1 is mainly operated in the first rigidity region D1, the torsional rigidity is low, so the inner shaft 21 is easily deformed and impact forces are unlikely to be transmitted to the single-axis actuator 11. Therefore, by operating the robot 1 in the first rigidity region D1, it is possible to prevent impact forces from being transmitted to the single-axis actuator 11, and it is possible to effectively protect the single-axis actuator 11.

[0079] Furthermore, when the robot 1 is mainly operated in the first rigidity region D1 where the torsion angle θ is small, the flexible shaft 12 deforms in response to an external load, and the driven member 4 flexibly follows. In other words, the driven member 4 can be endowed with an appropriate springiness without the first driving device 6 controlling the driven member 4.

[0080] The outer tube 22 is made of a fluororesin having high slidability, which reduces friction that may occur between the wall surface that defines the through hole and the inner shaft 21.

[0081] 4, grease 35 is filled between the outer peripheral surface of the inner shaft 21 and the inner peripheral surface of the inner hole 30 of the outer tube 22. This further reduces friction that may occur between the inner shaft 21 and the outer tube 22.

[0082] Furthermore, by using grease 35, which has a higher viscosity than lubricating oil, it is possible to prevent leakage of lubricant from both ends of the outer tube 22. This reduces the frequency of maintenance such as replacing the flexible shaft 12 and replenishing lubricant between the inner shaft 21 and the outer tube 22.

[0083] Furthermore, in this embodiment, the grease 35 contains a fluororesin made of the same material as the fluororesin wall that defines the inner hole 30. This can further reduce friction that may occur between the inner shaft 21 and the outer tube 22. This reduces the frequency of replacing the flexible shaft 12 or replenishing the lubricant, and improves the durability of the flexible shaft 12.

[0084] In addition, recesses 37 for storing grease 35 are formed on the outer surface of the inner shaft 21 between the wires 27. Therefore, the rotation of the inner shaft 21 stirs and circulates the grease 35. This stirring and circulation helps to maintain the condition of the grease 35 in good condition. Furthermore, when the driven member 4 repeatedly reciprocates, as in the robot 1, the grease 35 between the outer surface of the inner shaft 21 and the inner circumferential surface of the inner hole 30 of the outer tube 22 is rarely pushed out in one direction. Therefore, the grease 35 can be well retained between the two, preventing them from running out of oil.

[0085] Although the description of the specific embodiments has been completed above, the present invention is not limited to the above-described embodiments and modifications, and can be implemented in a wide variety of variations. Furthermore, the specific configuration, arrangement, and quantity of each component and part can be appropriately changed within the scope of the present invention. Furthermore, some or all of the configurations of the above-described embodiments may be combined with each other. Meanwhile, not all of the components shown in the above-described embodiments are necessarily required, and can be selected as appropriate.

[0086] In the above embodiment, the inner shaft 21 has a torsional rigidity characteristic that is symmetric about the origin between the input torque and the torsional angle, but the present invention is not limited to the torsional rigidity characteristic being symmetric about the origin. In other words, it is sufficient that the inner shaft 21 has a torsional rigidity characteristic that is symmetric about the origin between the input torque and the torsional angle.

[0087] In the above embodiment, the graph showing the relationship between torque T and torsion angle θ being symmetric about the origin has been described as satisfying formula (1) within the range Θ of torsion angle θ up to which plastic deformation occurs in the inner shaft 21. However, this is not limiting, and for example, the graph showing the relationship between torque T and torsion angle θ being symmetric about the origin may be defined as satisfying formula (1) within the range Θ of torsion angle θ that can be generated by driving the first drive device 6. In other words, the control device 7 may limit the torque output by the first drive device 6 to be within the range of torsion angle θ that satisfies formula (1).

[0088] 1: Robot 4: Follower member 6: First driving device (driving device) 12: Flexible shaft 21: Inner shaft 22: Outer tube 27: Wire 28: Winding layer 30: Inner hole (through hole) 35: Grease 37: Recess

Claims

1. A flexible shaft comprising: a flexible inner shaft; and a flexible outer tube having a through hole into which the inner shaft is rotatably inserted, wherein at least a portion of a wall defining the through hole of the outer tube is made of fluororesin, and grease is filled between the outer peripheral surface of the inner shaft and the inner peripheral surface of the through hole.

2. The flexible shaft according to claim 1, wherein the grease contains a fluororesin.

3. The flexible shaft according to claim 2, wherein the fluororesin contained in at least a portion of the wall defining the through hole and the fluororesin contained in the grease are made of the same material.

4. A flexible shaft according to any one of claims 1 to 3, wherein the inner shaft is formed by winding a wire and has a winding layer that forms the outer surface of the inner shaft.

5. A flexible shaft according to claim 1 or 2, wherein a recess for storing the grease is provided on at least one of the outer circumferential surface of the inner shaft and the inner circumferential surface of the through hole.

6. A robot equipped with a flexible shaft according to any one of claims 1 to 3, comprising: a driving device capable of outputting torque in both directions; and a driven member connected to the driving device via the flexible shaft and driven by the torque output by the driving device.

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