Parallel link unit and control device therefor

Abstract

A parallel link unit 10A according to the present invention comprises: a parallel link configured from a base link 11 and an output link 12 which are substantially parallel to each other, and a first intermediate link 13 and a second intermediate link 14 which are substantially parallel to each other; a cylindrical first linear motion actuator 20 with a distal end connected to a fourth joint part 18 formed by the output link 12 and the second intermediate link 14; and a second linear motion actuator 30 that positions a proximal end of the first linear motion actuator 20 at an arbitrary position on a first line segment connecting a first joint part 15 formed by the base link 11 and the first intermediate link 13 to a second joint part 16 formed by the base link 11 and the second intermediate link 14. According to the present invention, a parallel link unit that can form a highly convenient, high-power robot arm is provided.

Description

Parallel link unit and its control device

[0001] The present invention relates to a parallel link unit and a control device for the same, which can be connected in multiple units to form an ultra-long robot arm.

[0002] Ultra-long robot arms made up of multiple connected units have been known (see, for example, Non-Patent Document 1). This robot arm is capable of carrying out inspection work by inserting a camera attached to the tip of the arm into narrow, poorly visible environments.

[0003] The applicant has been developing a robot that performs various tasks in place of humans. As described in Non-Patent Document 2, this robot is attached to the tip of a crane mounted on the bed of a truck, and is transported to a work environment that is dangerous for humans, such as a high place, where it performs various tasks.

[0004] "New snake-like manipulator, Float Arm", [online], HiBot Co., Ltd., [Retrieved August 22, 2024], Internet <URL: https: / / www.hibot.co.jp / ja / products / float-arm / > "World's first! Humanoid heavy machinery equipped with an intuitive human-operated system (our technology) will be introduced to JR West's railway equipment maintenance.", [online], Jinki Ittai Co., Ltd., [Retrieved August 22, 2024], Internet <URL: https: / / prtimes.jp / main / html / rd / p / 000000036.000070266.html>

[0005] However, it is difficult for a general crane such as that described in Non-Patent Document 2 to allow a robot to enter a narrow environment. In addition, the robot arm described in Non-Patent Document 1 cannot lift heavy objects like a robot that can perform various tasks.

[0006] It should be noted that if the joints (connections between units) of the robot arm described in Non-Patent Document 1 were replaced with those with a high reduction ratio and high output, it might be possible to lift heavy objects like a robot capable of performing various tasks. However, if such a measure is taken, the movement of the robot arm would become sluggish, and it is thought that convenience would be greatly impaired.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a parallel link unit that can be used as a highly convenient and high-output robot arm, and a control device for the same.

[0008] In order to solve the above problems, a parallel link unit according to the present invention is characterized by including: parallel links constituted by first and second links that are substantially parallel to each other and first and second intermediate links that are substantially parallel to each other; a cylindrical first linear actuator having a first end and a second end, the second end being connected to a joint formed by the second link and the second intermediate link; and positioning means for positioning the first end of the first linear actuator at an arbitrary position on a first line segment that connects the joint formed by the first link and the first intermediate link and the joint formed by the first link and the second intermediate link.

[0009] The positioning means of the parallel link unit may be a second linear actuator having a first moving part that moves along the first line segment. In this case, the first end of the first linear actuator may be connected to the first moving part.

[0010] The parallel link unit may have a configuration in which the first link and the second link extend in a substantially vertical direction, the joint portion formed by the first link and the first intermediate link is located substantially vertically above the joint portion formed by the first link and the second intermediate link, and the joint portion formed by the second link and the first intermediate link is located substantially vertically above the joint portion formed by the second link and the second intermediate link.

[0011] The parallel link unit may further include an elastic member that generates a reaction force when compressed, the elastic member having a first end and a second end, the first end being swingably connected to a joint formed by the first link and the second intermediate link, and the second end being positioned on a second line segment connecting the joint formed by the second link and the first intermediate link and the joint formed by the second link and the second intermediate link.

[0012] The second end of the elastic member that generates a reaction force when compressed may be positioned by a third linear actuator having a second moving part that moves along the second line segment, in which case the second end of the elastic member may be connected to the second moving part.

[0013] An example of a resilient member that generates a reaction force when compressed is a compression type gas spring.

[0014] The parallel link unit may further include an elastic member that generates a reaction force when pulled, the elastic member having a first end and a second end, the first end being swingably connected to a joint formed by the first link and the first intermediate link, and the second end being positioned on a second line segment connecting the joint formed by the second link and the first intermediate link and the joint formed by the second link and the second intermediate link.

[0015] The second end of the elastic member, which generates a reaction force when pulled, may be positioned by a third linear actuator having a second moving part that moves along the second line segment. In this case, the second end of the elastic member may be connected to the second moving part.

[0016] An example of an elastic member that generates a reaction force when pulled is a tension-type gas spring.

[0017] The parallel link unit may further include a one-axis force sensor that measures a force applied to the first linear actuator.

[0018] In addition, in order to solve the above-mentioned problems, the control device for a parallel link unit according to the present invention controls the first linear actuator and the second linear actuator, and is characterized in that, when the second linear actuator operates, the first linear actuator is operated so that the relative position of the second link with respect to the first link does not change due to the operation of the second linear actuator.

[0019] According to the present invention, it is possible to provide a parallel link unit that can be used as a highly convenient and high-power robot arm, and a control device for the parallel link unit.

[0020] 1A is a perspective view of a parallel link unit according to a first embodiment; FIG. 1B is a diagram showing a usage mode of the parallel link unit according to the first embodiment, where (A) shows a case where a robot arm is formed using only a parallel link unit, (B) shows a case where a robot arm is formed by connecting multiple parallel link units, and (C) shows a case where a robot arm is formed by connecting multiple parallel link units and a rotation unit. 1B is a diagram showing a parallel link unit according to the first embodiment, where (A) is a side view, (B) is a schematic side view, and (C) is a diagram for explaining the influence of a load. 1C is a diagram for explaining the operation of the parallel link unit according to the first embodiment; 1D is a diagram for explaining another operation of the parallel link unit according to the first embodiment; 1E is a diagram for explaining yet another operation of the parallel link unit according to the first embodiment; 1F is a diagram for explaining the operation of a parallel link unit according to a comparative example; 1G is a perspective view of a parallel link unit according to a second embodiment; 1G is a diagram showing a parallel link unit according to the second embodiment, where (A) is a side view, (B) is a schematic side view, and (C) is a diagram for explaining the influence of a load. 1G is a schematic side view of a parallel link unit according to a first modified example; 1G is a schematic side view of a parallel link unit according to a second modified example. 10A to 10C are schematic side views of a parallel link unit according to a third modified example, a parallel link unit according to a fourth modified example, and a parallel link unit according to a fifth modified example.

[0021] Hereinafter, embodiments of a parallel link unit and its control device according to the present invention will be described with reference to the accompanying drawings.

[0022] 1 shows a parallel link unit (hereinafter also simply referred to as "unit") 10A according to a first embodiment of the present invention. As shown in the figure, the unit 10A includes a base link 11 and an output link 12 that are substantially parallel to each other, a first intermediate link 13 and a second intermediate link 14 that are substantially parallel to each other, a cylindrical first linear actuator 20, and a second linear actuator 30. The four links 11, 12, 13, and 14 form a parallel link.

[0023] The unit 10A can be used alone to form a robot arm that can move a heavy load W into any environment (see FIG. 2A), or multiple units can be used to form an ultra-long robot arm (see FIG. 2B). Furthermore, the unit 10A can be combined with a rotation unit 70 to form an even more convenient ultra-long robot arm (see FIG. 2C).

[0024] The base link 11 and output link 12 of the unit 10A extend in the Z-axis direction (approximately vertical). The base link 11 and output link 12 are spaced apart from each other in the X-axis direction (approximately horizontal), which is perpendicular to the Z-axis direction. In this embodiment, the base link 11 corresponds to the "first link," and the output link 12 corresponds to the "second link."

[0025] One end of the first intermediate link 13 is connected to the base link 11 so as to be able to swing about the Y-axis (= an axis perpendicular to the X-axis and Z-axis). This swingable connection between the links 11 and 13 forms a first joint portion 15.

[0026] One end of the second intermediate link 14 is connected to the base link 11 so as to be able to swing around the Y axis. This swingable connection between the links 11 and 14 forms a second joint 16. The second joint 16 is located approximately vertically below the first joint 15.

[0027] The other end of the first intermediate link 13 is connected to the output link 12 so as to be able to swing around the Y axis. The swingable connection between the links 12, 13 forms a third joint 17.

[0028] The other end of the second intermediate link 14 is connected to the output link 12 so as to be able to swing about the Y axis. This swingable connection between the links 12 and 14 forms a fourth joint 18. The fourth joint 18 is located approximately vertically below the third joint 17.

[0029] The second linear actuator 30 includes a guide 31 attached to the base link 11 and a first moving part 32 that is movable along the guide 31. The guide 31 extends in the Z-axis direction, similar to the base link 11. Therefore, the first moving part 32 is movable in the Z-axis direction. The movement of the first moving part 32 is controlled by a control device (not shown).

[0030] 3A, the cylindrical first linear motion actuator 20 has a base end 21 which is the end on the sleeve side, and a tip end 22 which is the end on the rod side that moves in and out of the sleeve. The movement of the rod in and out, i.e., the extension and contraction of the first linear motion actuator 20, is controlled by a control device that controls the second linear motion actuator 30. In this embodiment, the base end 21 corresponds to the "first end" and the tip end 22 corresponds to the "second end."

[0031] A tip end 22 of the first linear motion actuator 20 is connected to the fourth joint 18. That is, the tip end 22 of the first linear motion actuator 20 is connected to the output link 12 and the second intermediate link 14 so as to be able to swing around the Y axis.

[0032] The base end 21 of the first linear motion actuator 20 is connected to a first moving part 32 of the second linear motion actuator 30 so as to be able to swing about the Y axis. This swingable connection forms a moving joint part 33.

[0033] The moving joint 33 can take any position on the first line segment L1 connecting the first joint 15 and the second joint 16 by moving the first moving part 32 in the Z-axis direction under the control of a control device (not shown). In this embodiment, the second linear motion actuator 30 corresponds to a "positioning means" that positions the moving joint 33 (the base end 21 of the first linear motion actuator 20).

[0034] FIG. 3B is a schematic diagram of FIG. 3A. FIG. 3C shows the output link 12 of FIG. 3B to which an extension 60 extending in the X-axis direction is attached. As can be seen from these figures, the unit 10A utilizes a Roberval mechanism conventionally used in devices such as top-load balances. Therefore, the force applied to the first linear actuator 20 when a load F1 of a heavy load W is applied to a position near the base of the extension 60 is always equal to the force applied to the first linear actuator 20 when a load F2 of the same magnitude as load F1 is applied to a position near the tip of the extension 60. Similarly, torque applied around any axis to the output link 12 or the extension 60 has no effect on the first linear actuator 20.

[0035] In this embodiment, the force applied to the first linear motion actuator 20 can be measured by a uniaxial force sensor (load cell) disposed at the tip 22 of the first linear motion actuator 20. The force information obtained by this measurement is fed back to the control device described above.

[0036] In this embodiment, the control device includes a control stick. When the pilot operates the control stick, a command corresponding to the operation is transmitted to the first linear actuator 20 and the second linear actuator 30. The control stick is preferably configured to transmit the force information that has been fed back to the pilot in some form.

[0037] As will be explained in detail later, the first linear motion actuator 20 is mainly responsible for raising and lowering the output link 12, and the second linear motion actuator 30 is mainly responsible for changing the reduction ratio. For this reason, it is preferable that the first linear motion actuator 20 has a relatively high response speed, and it is preferable that the second linear motion actuator 30 be able to exert a relatively large force.

[0038] Next, the operation (posture change) of unit 10A will be described with reference to Figures 4 to 6. Note that some components are omitted in these figures. The same applies to Figure 7, which shows the operation of a unit according to a comparative example.

[0039] 4 shows the change in attitude of the unit 10A when the first linear actuator 20 is operated while the moving joint 33 is maintained at the intermediate position of the first line segment L1. When the control device retracts the first linear actuator 20 in accordance with the operator's operation, the output link 12 rises ((B) → (A) in the same figure), and when the control device extends the first linear actuator 20, the output link 12 descends ((B) → (C) in the same figure).

[0040] FIG. 5 shows the change in the attitude of the unit 10A when the first linear actuator 20 is operated while the moving joint 33 is maintained at the upper end of the first line segment L1 (=first joint 15). In this case, too, when the control device retracts the first linear actuator 20 in accordance with the operator's operation, the output link 12 rises ((B) → (A) in the same figure), and when the control device extends the first linear actuator 20, the output link 12 descends ((B) → (C) in the same figure). However, the amount of rise and fall of the output link 12 in FIG. 5 is less than the amount of rise and fall in FIG. 4. This indicates that the reduction ratio changes when the position of the moving joint 33 changes. The reduction ratio is maximum when the moving joint 33 overlaps the first joint 15 and minimum (=zero) when the moving joint 33 overlaps the second joint 16.

[0041] When the load is relatively large, the operator can operate the second linear actuator 30 via the control device so that the reduction ratio is relatively large. This allows the unit 10A to exert a large force (however, the attitude change is gradual). On the other hand, when the load is relatively small, the operator can operate the second linear actuator 30 via the control device so that the reduction ratio is relatively small. This allows the unit 10A to change its attitude quickly.

[0042] When transporting the unit 10A, the operator can set the reduction ratio to zero via the control device. This prevents damage to the actuator, reducer, load cell, etc., which are sensitive to shocks, caused by an excessive force (impact) being applied to the output link 12 during transportation, which would otherwise be applied to the first linear actuator 20 itself or the load cell.

[0043] Furthermore, when the operator resets the load cell to the zero point, he or she can similarly set the reduction ratio to zero via the control device. This makes it easy to create a state in which no force is applied to the load cell. In this case, it is preferable to fix the output link 12 with a mechanical element such as a brake or stopper, that is, to prevent the position of the output link 12 (= the relative position of the output link 12 with respect to the base link 11) from changing.

[0044] When the operator operates the second linear actuator 30 via the control device, the control device can also automatically operate the first linear actuator 20 so as not to change the position of the output link 12. More specifically, the control device extends the first linear actuator 20 by an appropriate amount when the operator attempts to increase the reduction ratio (FIG. 6(B)→(A)), and retracts the first linear actuator 20 by an appropriate amount when the operator attempts to decrease the reduction ratio (FIG. 6(B)→(C)). This automatic control can prevent unnecessary raising / lowering of the output link 12.

[0045] Similarly, when the operator operates the first linear actuator 20 via the control device (when raising / lowering the output link 12), the control device can automatically correct fluctuations in the reduction ratio caused by the nonlinearity of the kinematics of the parallel link by operating the second linear actuator 30 by an appropriate amount.

[0046] That is, the operator can operate the movement of the output link 12 and the change of the reduction ratio independently of each other (decoupling). Note that the appropriate amount of operation for decoupling can be easily calculated by a person skilled in the art using kinematic calculations in robotics.

[0047] If the automatic control (non-interference) is not performed when the operator attempts to change the reduction ratio, the output link 12 will rise / fall unnecessarily, as shown in FIG.

[0048] 8 shows a parallel link unit 10B according to a second embodiment of the present invention. As shown in the figure, the unit 10B includes a base link (first link) 11 and an output link (second link) 12 that are parallel to each other, a first intermediate link 13 and a second intermediate link 14 that are parallel to each other, a cylindrical first linear actuator 20, a second linear actuator (positioning means) 30, and gas springs 40, 40. That is, the unit 10B differs from the unit 10A in that it further includes gas springs 40, 40, but is otherwise identical to the unit 10A.

[0049] The gas springs 40, 40 are compression type gas springs that generate a reaction force when compressed. As shown in Figure 9(A), the gas springs 40, 40 have a base end 41 that is the end on the sleeve side and a tip end 42 that is the end on the rod side that goes in and out of the sleeve. In this embodiment, the gas springs 40, 40 correspond to the "elastic member."

[0050] The base ends 41 of the gas springs 40 are connected to the second joint portion 16. That is, the base ends 41 of the gas springs 40 are connected to the base link 11 and the second intermediate link 14 so as to be able to swing around the Y axis.

[0051] The distal end portions 42 of the gas springs 40 are connected to the third joint portion 17. That is, the distal end portions 42 of the gas springs 40 are connected to the output link 12 and the first intermediate link 13 so as to be able to swing around the Y axis.

[0052] 9(B) is a schematic diagram of FIG. 9(A). Also, FIG. 9(C) shows an extension 60 extending in the X-axis direction attached to the output link 12 of FIG. 9(B). Like unit 10A, unit 10B utilizes the Roberval mechanism. Therefore, the force applied to the first linear actuator 20 and gas springs 40, 40 when a load F1 is applied to a position near the base of the extension 60 is always equal to the force applied to the first linear actuator 20 and gas springs 40, 40 when a load F2 of the same magnitude as load F1 is applied to a position near the tip of the extension 60.

[0053] The gas springs 40, 40 are in a most extended state when the force applied between the base end 41 and the tip end 42 is less than a predetermined initial load, and are in a contracted state by an amount corresponding to the excess force when the force applied between the base end 41 and the tip end 42 exceeds the initial load. In this embodiment, the characteristics of the gas springs 40, 40 are utilized to perform weight compensation. This weight compensation makes it possible to reduce the force that the first linear actuator 20 must output in order to support the heavy load W. In other words, it is possible to reduce the power consumption of the first linear actuator 20.

[0054] [Modifications] Although the first and second embodiments of the parallel link unit and control device according to the present invention have been described above, the configurations of the present invention are not limited to these.

[0055] (First Modification) For example, a parallel link unit according to the present invention may be configured as shown in FIG. 10 , in which the second linear actuator (guide 31 and first moving portion 32) is provided on the output link 12 side, the base end 21 of the first linear actuator 20 is connected to the first joint 15, and the tip end 22 of the first linear actuator 20 is connected to the first moving portion 32 of the second linear actuator. According to the unit 10C of this modification, similar to the units 10A and 10B, the reduction ratio can be continuously changed by operating the second linear actuator. In this modification, the output link 12 corresponds to the "first link" and the base link 11 corresponds to the "second link." In addition, in this modification, the tip end 22 corresponds to the "first end" and the base end 21 corresponds to the "second end."

[0056] 11 , the parallel link unit according to the present invention may have the tip 22 of the first linear actuator 20 connected to the third joint 17 instead of the fourth joint 18. According to the unit 10D of this modification, similar to the units 10A and 10B, the reduction ratio can be continuously changed by operating the second linear actuator 30. However, in the unit 10D, because the load due to gravity acts in a direction that compresses the first linear actuator 20, care must be taken to prevent buckling of the first linear actuator 20.

[0057] (Third Modification) A parallel link unit according to the present invention may include a tension-type gas spring 40' that generates a reaction force when pulled, instead of the compression-type gas spring 40, as in a parallel link unit 10E shown in FIG. 12. The gas spring 40' has a base end 41', which is the end on the sleeve side, and a tip end 42', which is the end on the rod side that enters and exits the sleeve. The base end 41' is connected to the first joint 15, and the tip end 42' is connected to the fourth joint 18. The unit 10E according to this modification can perform weight compensation, similar to the unit 10B. In this modification, the gas spring 40' corresponds to the "elastic member."

[0058] (Fourth Modification) A parallel link unit according to the present invention may be configured as a parallel link unit 10F shown in FIG. 13 , in which a third linear actuator 50 similar to the second linear actuator 30 is provided on the output link 12. The third linear actuator 50 includes a second moving section 51 that is movable in the Z-axis direction. The distal end 42 of the gas spring 40 is connected to the second moving section 51 so as to be able to swing about the Y-axis, thereby forming a moving joint 52. The second moving section 51 moves in the Z-axis direction under the control of the control device, so that the moving joint 52 can assume any position on the second line segment L2 connecting the third joint 17 and the fourth joint 18. According to the parallel link unit 10F according to this modification, the degree of weight compensation provided by the gas spring 40 can be adjusted by operating the third linear actuator 50 to change the position of the moving joint 52. Furthermore, according to the unit 10F of this modified example, by operating the third linear actuator 50, the force of the gas spring 40 can also be used as a force to raise / lower the output link 12 (i.e., a force to assist the first linear actuator 20).

[0059] (Fifth Modification) In the parallel link unit according to the present invention, the base link 11 and the output link 12 may be inclined by the same amount relative to the Z-axis direction (i.e., the substantially vertical direction), as in parallel link units 10G and 10H shown in FIG. 14 . In other words, the second joint 16 does not have to be located substantially vertically below the first joint 15, and the fourth joint 18 does not have to be located substantially vertically below the third joint 17. With a configuration like unit 10G, the upward movable range is wider and the downward movable range is narrower than unit 10A. On the other hand, with a configuration like unit 10H, the upward movable range is narrower and the downward movable range is wider than unit 10A. In other words, by inclining the base link 11 and the output link 12 relative to the Z-axis direction, the movable range can be offset in either the up or down direction.

[0060] (Other Modifications) The means for positioning the first end of the first linear actuator 20 (for example, the base end 21 in the first embodiment) at any position on the first line segment L1 is not limited to the second linear actuator 30. The first end of the first linear actuator 20 may be manually positioned at any position on the first line segment L1. The same applies to the means for positioning the second end of the gas spring 40 (for example, the tip end 42 in the fourth modification) at any position on the second line segment L2.

[0061] The elastic member for weight compensation is not limited to a compression or tension gas spring, and may be, for example, a coil spring.

[0062] The number of first linear actuators 20 in the first embodiment etc. is not limited to one, but may be two or more. Similarly, the number of gas springs 40, 40' in the second embodiment etc. is not limited to two, but may be one or three or more.

[0063] The mounting position of the force sensor (load cell) for measuring the force applied to the first linear actuator 20 is not limited to the tip end 22 of the first linear actuator 20, but may be, for example, the base end 21 of the first linear actuator 20.

[0064] The parallel link unit according to the present invention may further include sensors other than the force sensor for measuring the force applied to the first linear actuator 20. Examples of such sensors include (1) a displacement sensor (e.g., an encoder) that measures the displacement of the linear actuators 20, 30, and 50, (2) a force sensor (load cell) that measures the force applied to the gas springs 40 and 40′, and (3) a displacement sensor (e.g., an encoder) that measures the displacement of the gas springs 40 and 40′. The present invention does not limit where and what sensors are disposed. Note that if the displacement sensor (1) or (3) is provided, the force sensor (2) is not necessary. This is because the elastic force can be estimated by calculation from the output of the displacement sensor. However, a redundant configuration including both sensors can improve measurement accuracy, reliability, and fault tolerance.

[0065] The base link 11 and the output link 12 do not have to extend in a substantially vertical direction. In other words, the X-axis direction may be the vertical direction, the Y-axis direction may be the vertical direction, or a direction other than either of the axial directions may be the vertical direction.

[0066] The above-described modified examples may be combined with each other. For example, the third modified example and the fourth modified example may be combined to connect the distal end portion 42' of the tension-type gas spring 40' to the second moving portion 51.

[0067] 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H Parallel link unit 11 Base link 12 Output link 13 First intermediate link 14 Second intermediate link 15 First joint section 16 Second joint section 17 Third joint section 18 Fourth joint section 20 First linear motion actuator 21 Base end section (of first linear motion actuator) 22 Tip section (of first linear motion actuator) 30 Second linear motion actuator 31 Guide 32 First moving section 33 Moving joint section 40, 40' Gas spring 41, 41' Base end section (of gas spring) 42, 42' Tip section (of gas spring) 50 Third linear motion actuator 51 Second moving section 52 Moving joint section

Claims

1. A parallel link unit comprising: a parallel link composed of a first link and a second link that are substantially parallel to each other and a first intermediate link and a second intermediate link that are substantially parallel to each other; a cylindrical first linear actuator having a first end and a second end, the second end being connected to a joint formed by the second link and the second intermediate link; and positioning means for positioning the first end of the first linear actuator at an arbitrary position on a first line segment that connects the joint formed by the first link and the first intermediate link and the joint formed by the first link and the second intermediate link.

2. The parallel link unit according to claim 1, wherein the positioning means is a second linear actuator having a first moving part that moves along the first line segment, and the first end of the first linear actuator is connected to the first moving part.

3. A parallel link unit as described in claim 1 or 2, characterized in that the first link and the second link extend in a substantially vertical direction, the joint formed by the first link and the first intermediate link is located substantially vertically above the joint formed by the first link and the second intermediate link, and the joint formed by the second link and the first intermediate link is located substantially vertically above the joint formed by the second link and the second intermediate link.

4. A parallel link unit as described in claim 3, further comprising an elastic member that generates a reaction force when compressed, the elastic member having a first end and a second end, the first end being swingably connected to a joint formed by the first link and the second intermediate link, and the second end being positioned on a second line segment connecting the joint formed by the second link and the first intermediate link and the joint formed by the second link and the second intermediate link.

5. The parallel link unit according to claim 4, characterized in that the positioning is performed by a third linear actuator having a second moving part that moves along the second line segment, and the second end of the elastic member is connected to the second moving part.

6. The parallel link unit according to claim 4, wherein the elastic member is a compression type gas spring.

7. A parallel link unit as described in claim 3, further comprising an elastic member that generates a reaction force when pulled, the elastic member having a first end and a second end, the first end being swingably connected to a joint formed by the first link and the first intermediate link, and the second end being positioned on a second line segment connecting the joint formed by the second link and the first intermediate link with the joint formed by the second link and the second intermediate link.

8. The parallel link unit according to claim 7, characterized in that the positioning is performed by a third linear actuator having a second moving part that moves along the second line segment, and the second end of the elastic member is connected to the second moving part.

9. The parallel link unit according to claim 7, wherein the elastic member is a tension type gas spring.

10. The parallel link unit according to claim 1 or 2, further comprising a one-axis force sensor for measuring the force applied to the first linear actuator.

11. A control device for controlling the first linear actuator and the second linear actuator that constitute the parallel link unit described in claim 2, characterized in that when the second linear actuator operates, the control device operates the first linear actuator so that the relative position of the second link with respect to the first link does not change due to the operation of the second linear actuator.

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