Actuator and robot, orthosis and haptic device including the same

Abstract

To provide an actuator capable of obtaining a larger stroke in a range in which excessive torsion does not occur.SOLUTION: An actuator includes: a plurality of wires each of which one end is engaged with a load; a support member to which each of the other ends of the plurality of wires is fixed; and a drive source for twisting the plurality of wires together by rotating the support member. A distance between the support member and the load is changed depending on the rotation of the support member. Each of the plurality of wires is fixed to the support member while twisted beforehand in the same torsional rotating direction. When the distance between the support member and the load is reduced, the plurality of wires are rotated and twisted together in the same rotating direction as the torsional rotating direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an actuator, and a robot, prosthetic, and haptic device equipped with the same. [Background technology]

[0002] Twisted string actuators (TSAs) are known that convert rotary motion into linear motion by twisting multiple wires together. In Patent Document 1, such an actuator is used as a drive source for driving the joints of a robot hand. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Pat. No. 4,843,921 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors have found the following problems with the actuator disclosed in Patent Document 1. In such actuators, if the number of rotations of the twisted wires is increased to increase the stroke, a condition called overtwisting occurs, in which the twisted wires are twisted into a coil. When overtwisting occurs, the stroke and torque fluctuations relative to the rotation become unstable, making it impossible to control the actuator. Therefore, there is a demand for an actuator that can obtain a large stroke within a range where overtwisting does not occur.

[0005] The present disclosure has been made in consideration of the above circumstances, and provides an actuator that can obtain a larger stroke within a range in which over-torsion does not occur. [Means for solving the problem]

[0006] An actuator according to one aspect of the present disclosure includes: a plurality of wires, each of which has one end engaged with a load; a support member to which the other ends of the plurality of wires are fixed; a drive source that rotates the support member to twist the plurality of wires, An actuator that changes a distance between the support member and the load in response to rotation of the support member, Each of the plurality of wires is fixed to the support member in a state where the wires are twisted in the same torsional direction in advance, When the distance between the support member and the load is reduced, the plurality of wires are rotated in the same rotation direction as the torsional rotation direction to be twisted together.

[0007] In an actuator according to one aspect of the present disclosure, each of the multiple wires is fixed to a support member in a state where the wires are twisted in the same torsional direction in advance. When the distance between the support member and the load is reduced, the multiple wires are rotated and twisted in the same rotational direction as the torsional direction. With this configuration, a larger stroke can be obtained within a range where the multiple wires do not overtwist.

[0008] The wires may be rotated in a direction opposite to the twisting direction from an untwisted state to twist the wires together, so that the position where the distance between the support member and the load is greatest is set as the operation start point. With this configuration, an even larger stroke can be obtained.

[0009] Each of the plurality of wires may be made of ultra-high molecular weight polyethylene, which can provide the wire with high strength.

[0010] Each of the plurality of wires may be a stranded wire formed by twisting a plurality of wires together. With this configuration, the wire can be made high strength.

[0011] The present disclosure may also be applied to a robot in which joints are driven by actuators according to the present disclosure. The prosthesis may be worn by a person and assists the movement of the person's joints, and may be driven by an actuator according to the present disclosure. The haptic device may be worn by a person and provides a virtual sense of touch to the person, and may be driven by an actuator according to the present disclosure. Effect of the Invention

[0012] The present disclosure makes it possible to provide an actuator that can obtain a larger stroke without causing over-torsion. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a side view illustrating a schematic configuration of the actuator according to the first embodiment. [Diagram 2] 1 is a graph showing changes in stroke and torque with respect to the number of rotations when twisting together wires W1 and W2 in Example 1. [Diagram 3] 13 is a graph showing changes in stroke and torque with respect to the number of rotations when twisting together wires W1 and W2 in Comparative Example 1. [Figure 4] 13 is a graph showing a change in effective stroke with respect to the pretwist amount. [Diagram 5] 1 is a graph showing a change in effective rotation speed with respect to the pretwist amount. [Figure 6] 4 is a graph showing changes in mechanical efficiency with respect to effective stroke in Example 1 and Comparative Example 2 shown in FIG. 2 and Comparative Example 1 shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, specific embodiments to which the present disclosure is applied will be described in detail with reference to the drawings. However, the present disclosure is not limited to the following embodiments. In addition, the following description and drawings are appropriately simplified for clarity of explanation.

[0015] (First embodiment) <Actuator configuration> First, an actuator according to a first embodiment will be described with reference to FIG. Fig. 1 is a side view showing a schematic configuration of an actuator according to embodiment 1. As shown in Fig. 1, the actuator according to this embodiment includes a pair of wires W1 and W2, a support member SP, and a motor MT.

[0016] 1, in the actuator, a motor MT rotates a support member SP, and wires W1 and W2 are twisted together to change the distance between the support member SP and a load LD. That is, the actuator according to this embodiment is one form of a twisted string actuator.

[0017] The actuator according to this embodiment drives, for example, the joints of a robot. The actuator may drive an accessory worn by a person to assist the movement of the person's joints. Alternatively, the actuator may drive a haptic device worn by a person to provide the person with a virtual haptic sensation.

[0018] As shown in Fig. 1, one end of each of the pair of wires W1 and W2 is engaged with the load LD. Here, "engagement" includes "fixing." In the example shown in Fig. 1, the pair of wires W1 and W2 twisted together is a single wire inserted into a through hole provided at the end of the load LD. On the other hand, the other end of each of the pair of wires W1 and W2 is fixed to a support member SP.

[0019] The pair of wires W1, W2 are, for example, resin wires. More specifically, the wires W1, W2 are, for example, made of ultra-high molecular weight polyethylene, which has excellent strength. With this configuration, the wires W1, W2 can have high strength.

[0020] Of course, the pair of wires W1 and W2 may be separate wires. The number of wires twisted together is not limited to two, and may be three or more. Furthermore, each of the wires W1 and W2 may be a twisted wire in which multiple wires are twisted together. With this configuration, the wires W1 and W2 can have high strength.

[0021] As described above, the support member SP supports the other ends of the pair of wires W1 and W2. The support member SP is connected to the rotating shaft of the motor MT and is rotated by the motor MT. When the support member SP is rotated in the direction of the arrow shown in the lower part of Fig. 1 in the state shown in the upper part of Fig. 1, the wires W1 and W2 are twisted together, and the distance between the support member SP and the load LD is reduced. In other words, the load LD is pulled toward the support member SP and approaches the support member SP.

[0022] On the other hand, when the support member SP is rotated in the direction opposite to the arrow in the state shown in the lower part of Fig. 1, the twisted wires W1 and W2 are untwisted and the distance between the support member SP and the load LD increases, as shown in the upper part of Fig. 1. In other words, the load LD moves away from the support member SP.

[0023] The motor MT is a drive source that rotates the support member SP to twist the wires W1 and W2. The motor MT is driven based on a control signal output from a motor control unit (not shown). The motor control unit includes a calculation unit such as a CPU (Central Processing Unit) and a storage unit such as a RAM (Random Access Memory) or a ROM (Read Only Memory) that stores various control programs and data. The control signal is, for example, a PWM (Pulse Width Modulation) signal. The drive source for rotating the support member SP is not limited to the motor MT, but may be, for example, an engine.

[0024] In the actuator according to this embodiment, the wires W1 and W2 are fixed to the support member SP in a state where they are twisted in the same torsional direction in advance. When the distance between the support member SP and the load LD is reduced, the wires W1 and W2 are rotated in the same rotational direction as the torsional direction to be twisted together. As will be described in detail later, this configuration allows a larger stroke to be obtained within a range where the wires W1 and W2 do not overtwist. Hereinafter, twisting the wires W1 and W2 in advance in order to fix them to the support member SP will be referred to as pretwisting.

[0025] In the actuator according to this embodiment, when the wires W1 and W2 are rotated to a certain extent in the direction opposite to the pre-twist of the wires W1 and W2 from a state in which the wires W1 and W2 are not twisted together, the distance between the support member SP and the load LD becomes maximum. Therefore, by setting this position as the operation start point, the effective stroke (hereinafter, effective stroke) can be made larger.

[0026] Furthermore, as will be described in detail later, in the actuator according to this embodiment, the reduction ratio of the actuator can be easily changed by changing the amount of pre-twist of the wires W1, W2. EXAMPLES

[0027] Examples and comparative examples of the actuator according to the first embodiment will be described below. However, the actuator according to the first embodiment is not limited to the following examples.

[0028] <Example 1> The wires W1 and W2 were twisted wires made by twisting two wires together. For each wire, a fishing line made of ultra-high molecular weight polyethylene with a total length of 100 mm and a diameter of 0.47 mm was used. The twist amount of the wires in the wires W1 and W2 was 34 turns, and the twist pitch was 2.9 mm. The twist amount of the wires is the pre-twist amount of the wires W1 and W2. Here, the pre-twist amount in Example 1 is conveniently set to 100%.

[0029] Starting from a state where the wires W1 and W2 are not twisted together, the wires W1 and W2 are rotated in the same direction as the pretwist of the wires W1 and W2 to obtain the stroke (positive stroke) within the range where overtwisting does not occur. On the other hand, starting from a state where the wires W1 and W2 are not twisted together, the wires W1 and W2 are rotated in the opposite direction to the pretwist of the wires W1 and W2 to obtain the stroke (negative stroke) within the range where overtwisting does not occur.

[0030] Here, Fig. 2 is a graph showing the change in stroke and torque with respect to the number of rotations of twisting the wires W1 and W2 in Example 1. The horizontal axis of Fig. 2 shows the number of rotations (times) of twisting. Here, the number of rotations in the same direction as the pretwist of the wires W1 and W2 (positive rotation) is shown as a positive value, and the number of rotations in the opposite direction to the pretwist of the wires W1 and W2 (negative rotation) is shown as a negative value. The upper vertical axis in FIG. 2 indicates stroke (mm), and the lower vertical axis in FIG. 2 indicates torque (Nm).

[0031] As shown in Figure 2, the positive stroke in the range where overtorsion does not occur was 46.6 mm at 20 rotations. On the other hand, the negative stroke in the range where overtorsion does not occur was 6.4 mm at -34 rotations. Here, as shown in FIG. 2, a peak stroke of -6.5 mm occurred at -15 rotations. Therefore, in the first embodiment, by setting the operation starting point at -15 rotations, an effective stroke of 53.1 mm is obtained.

[0032] As shown in FIG. 2, when over-torsion occurs, hysteresis occurs in the stroke and the torque fluctuation becomes unstable. Also, as shown in FIG. 2, with -15 rotations as the operation starting point indicated by the dashed line, rotation in a more positive direction than this is Example 1 (E1 in FIG. 2), and rotation in a more negative direction than this is the comparative example. This comparative example is referred to as Comparative Example 2 (C2 in FIG. 2). That is, in Example 1,

[0033] <Example 2> The wires W1 and W2 were twisted together by 24.5 turns at a twist pitch of 4.1 mm, and the other factors were the same as in Example 1. The pre-twist amount in Example 2 was 72%.

[0034] In Example 2, the positive stroke in the range where over-torsion does not occur was 37.5 mm at 21 rotations, while the negative stroke in the range where over-torsion does not occur was 17.5 mm at -33.5 rotations. Here, a peak stroke of -3.5 mm occurred at -10 revolutions. Therefore, in the second embodiment, an effective stroke of 41.0 mm is obtained by setting the operation starting point at -10 rotations.

[0035] <Example 3> The wires W1 and W2 were twisted together by 19.5 turns at a twist pitch of 5.1 mm, and the other conditions were the same as in Example 1. The pre-twist amount in Example 3 was 57%.

[0036] In Example 3, the positive stroke in the range where over-torsion does not occur was 37.0 mm at 22 rotations, while the negative stroke in the range where over-torsion does not occur was 21.0 mm at -33 rotations. Here, a peak stroke of -2.5 mm occurred at -7.5 revolutions. Therefore, in the third embodiment, an effective stroke of 39.5 mm is obtained by setting the operation starting point at -7.5 rotations.

[0037] <Example 4> The wires W1 and W2 were twisted together by 7 turns at a twist pitch of 14.3 mm, but the other conditions were the same as in Example 1. The pre-twist amount in Example 4 was 21%.

[0038] In Example 4, the positive stroke in the range where over-torsion does not occur was 35.0 mm at 26 rotations, while the negative stroke in the range where over-torsion does not occur was 34.0 mm at -32.5 rotations. Here, a peak stroke of -0.5 mm occurred at -4 rotations. Therefore, in the fourth embodiment, an effective stroke of 35.5 mm is obtained by setting the operation starting point at -4 rotation.

[0039] <Comparative Example 1> Except for the fact that the two strands of wires W1 and W2 were not twisted together, the procedure was the same as in Example 1. The amount of pre-twist in Comparative Example 1 was 0%. Here, Fig. 3 is a graph showing changes in stroke and torque with respect to the number of rotations of twisting the wires W1 and W2 in Comparative Example 1. The horizontal axis of Fig. 3 indicates the number of rotations (times) of twisting. The vertical axis on the upper side of Fig. 3 indicates the stroke (mm), and the vertical axis on the lower side of Fig. 3 indicates the torque (Nm).

[0040] As shown in Figure 3, the positive stroke in the range where overtorsion does not occur was 30.4 mm at 28 rotations. On the other hand, the negative stroke in the range where overtorsion does not occur was 32.1 mm at -28 rotations. Here, as shown in FIG. 3, in Comparative Example 1, the stroke at 0 rotations is the minimum of 0 mm, and no negative stroke peak occurs. Therefore, in Comparative Example 1, with 0 rotations as the operation starting point, an effective stroke of 30.4 mm (or 32.1) is obtained.

[0041] In Comparative Example 1 shown in Fig. 3, the rotation speed dependence of the stroke and torque is symmetrical with respect to 0 rotation, i.e., the y-axis, as the central axis. In contrast, in Example 1 and Comparative Example 2 shown in Fig. 2, the rotation speed dependence of the stroke and torque is asymmetrical with respect to -15 rotation, indicated by the dashed line, as the central axis. Specifically, as shown in Fig. 2, in Example 1, which is a rotation in the positive direction from -15 rotations, the effective stroke is larger than in Comparative Example 1, and in Comparative Example 2, which is a rotation in the negative direction from -15 rotations, the effective stroke is smaller than in Comparative Example 1.

[0042] Here, the positive stroke, negative stroke peak, and effective stroke of Examples 1 to 4 and Comparative Example 1 are shown together in Fig. 4. Fig. 4 is a graph showing the change in effective stroke with respect to the amount of pre-twist. The horizontal axis of Fig. 4 represents the amount of pre-twist (%), and the vertical axis represents the stroke (mm). In Fig. 4, Examples 1 to 4 are shown as E1 to E4, and Comparative Example 1 is shown as C1.

[0043] 4, in all of Examples 1 to 4, the effective stroke in the range where overtwist did not occur was greater than in Comparative Example 1. In addition, the greater the pretwist amount, the greater the positive stroke and negative stroke peaks, and as a result, the greater the effective stroke.

[0044] Next, Fig. 5 shows the rotation speeds corresponding to the positive stroke and negative stroke peaks shown in Fig. 4 for Examples 1 to 4 and Comparative Example 1. Fig. 5 is a graph showing the change in effective rotation speed with respect to the pretwist amount. The horizontal axis of Fig. 5 shows the pretwist amount (%), and the vertical axis shows the rotation speed (times). The effective rotation speed is the rotation speed corresponding to the effective stroke.

[0045] As shown in Figure 5, the larger the pretwist amount, the smaller the rotation speed corresponding to the positive stroke. On the other hand, the larger the pretwist amount, the more the rotation speed corresponding to the negative stroke peak shifts in the negative direction. Here, the negative shift in the rotation speed corresponding to the negative stroke peak is larger than the decrease in the rotation speed corresponding to the positive stroke, so the larger the pretwist amount, the higher the effective rotation speed becomes.

[0046] Next, Fig. 6 is a graph showing the change in mechanical efficiency with respect to the effective stroke in Example 1 and Comparative Example 2 shown in Fig. 2, and Comparative Example 1 shown in Fig. 3. The horizontal axis of Fig. 6 shows the effective stroke (mm), and the vertical axis shows the mechanical efficiency (%). Note that Example 1 corresponds to E1 in Fig. 2, which is a case where the rotor is rotated in the positive direction from -15 rotations shown by the dashed line in Fig. 2. Comparative Example 2 corresponds to C2 in Fig. 2, which is a case where the rotor is rotated in the negative direction from -15 rotations shown by the dashed line in Fig. 2.

[0047] As shown in FIG. 6, in Comparative Example 2, not only is the effective stroke small at a maximum value of 12.9 mm, that is, 12.9% (=12.9 mm / 100 mm×100), but the mechanical efficiency is also low. The mechanical efficiency of Comparative Example 1 peaks at an effective stroke of 10 mm, i.e., about 10%, and then gradually decreases. And, at an effective stroke of 20 mm or more, the mechanical efficiency of Comparative Example 1 is lower than that of Example 1. The maximum effective stroke of Example 1 is 30.4 mm, i.e., 30.4%.

[0048] In contrast, as shown in Fig. 6, in Example 1, not only is the maximum effective stroke large at 53.1 mm, i.e., 53.1%, but the mechanical efficiency is also stably maintained at a high value at effective strokes of 20 mm or more. Thus, it was found that Example 1 not only has a significantly superior maximum effective stroke value, but also has excellent mechanical efficiency.

[0049] The present disclosure is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present disclosure. [Explanation of symbols]

[0050] LD load MT motor SP Support member W1, W2 Wire

Claims

1. a plurality of wires, each of which has one end engaged with a load; a support member to which the other ends of the plurality of wires are fixed; a drive source that rotates the support member to twist the plurality of wires, An actuator that changes a distance between the support member and the load in response to rotation of the support member, Each of the plurality of wires is fixed to the support member in a state where the wires are twisted in the same torsional direction in advance, When reducing the distance between the support member and the load, the plurality of wires are rotated in the same rotation direction as the twisting rotation direction to twist them together. Actuator.

2. The plurality of wires are rotated in a direction opposite to the twisting direction from a state in which the plurality of wires are not twisted together, and the position where the distance between the support member and the load is the largest is set as an operation start point. The actuator of claim 1 .

3. Each of the plurality of wires is made of ultra-high molecular weight polyethylene.

3. The actuator according to claim 1 or 2.

4. Each of the plurality of wires is a stranded wire formed by twisting a plurality of wires together.

3. The actuator according to claim 1 or 2.

5. A joint is driven by the actuator according to claim 1 or 2. robot.

6. An orthosis worn by a person to assist movement of a joint of the person, 3. Driven by the actuator according to claim 1 or 2, Orthotics.

7. A haptic device that is worn by a person and provides a virtual haptic sensation to the person, 3. Driven by the actuator according to claim 1 or 2, Tactile devices.

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