Parallel link unit and its control device
The parallel link unit with linear actuators and elastic members addresses the challenges of maneuverability and lifting in ultra-long robot arms, ensuring high output and convenience.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-08-30
- Publication Date
- 2026-03-13
AI Technical Summary
Existing ultra-long robot arms face challenges in maneuvering into confined spaces and lifting heavy objects while maintaining usability, with high-reduction ratio joints leading to significant movement slowdowns.
A parallel link unit comprising a first and second link, first and second intermediate links, and linear actuators with positioning means, along with elastic members and force sensors, allows for high output and convenience by controlling the relative positions and forces applied to the links.
The solution provides a robot arm with high convenience and output capabilities, enabling efficient movement and lifting of heavy objects without impairing usability.
Smart Images
Figure 2026045761000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a parallel link unit that can form an ultra-long robot arm by connecting multiple units and a control device thereof.
Background Art
[0002] Conventionally, an ultra-long robot arm formed by connecting multiple units has been known (see, for example, Non-Patent Document 1). According to this robot arm, it is possible to perform inspection work by entering a narrow and poorly visible environment with a camera attached to the tip of the arm.
[0003] By the way, the applicant is developing a robot that performs various operations in place of humans. As described in Non-Patent Document 2, this robot is attached to the tip of a crane mounted on the loading platform of a truck, transported to a work environment dangerous for humans such as high places, and performs various operations there.
Prior Art Documents
Non-Patent Documents
[0004]
Non-Patent Document 1
Non-Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0005] However, with a typical crane like the one described in Non-Patent Document 2, it is difficult to get a robot into a confined space. Also, the robotic arm described in Non-Patent Document 1 cannot lift heavy objects such as robots capable of performing various tasks.
[0006] Furthermore, if the joints (connections between units) of the robot arm described in Non-Patent Document 1 were replaced with high-reduction ratio, high-output ones, it might be possible to lift heavy objects like those of a robot capable of performing various tasks. However, it is thought that such measures would slow down the movement of the robot arm, significantly impairing its usability.
[0007] The present invention has been made in view of the above circumstances, and aims to provide a parallel link unit and a control device therefor that can be used as a robot arm that is highly convenient and has high output. [Means for solving the problem]
[0008] To solve the above problems, the parallel link unit according to the present invention is characterized by 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 of which is connected to an articulation 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 connecting the articulation formed by the first link and the first intermediate link and the articulation formed by the first link and the second intermediate link.
[0009] The positioning means of the parallel link unit described above may be a second linear actuator having a first movable 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 movable part.
[0010] The above-described parallel link unit may have a configuration in which the first link and the second link extend substantially vertically, 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.
[0011] The parallel link unit described above may further include an elastic member that generates a reaction force when compressed, having a first end and a second end, the first end being pivotably connected to a joint formed by a first link and a 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 positioning of the second end of the elastic member, which generates a reaction force when compressed, may be performed by a third linear actuator having a second moving part that moves along a second line segment. In this case, the second end of the elastic member can be connected to the second moving part.
[0013] An example of an elastic member that generates a reaction force when compressed is a compression-type gas spring.
[0014] The above-described parallel link unit may further include an elastic member that generates a reaction force when pulled, having a first end and a second end, the first end being pivotably connected to a joint formed by a first link and a 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 to the joint formed by the second link and the second intermediate link.
[0015] The positioning of the second end of the elastic member, which generates a reaction force when stretched, may be performed by a third linear actuator having a second moving part that moves along a second line segment. In this case, the second end of the elastic member can 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 uniaxial force sensor that measures the force applied to the first linear actuator.
[0018] In addition, in order to solve the above problems, a control device for a parallel link unit according to the present invention controls a first linear actuator and a second linear actuator, and 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.
Effect of the Invention
[0019] According to the present invention, it is possible to provide a parallel link unit and a control device thereof that can be a robot arm with high convenience and high output.
Brief Description of the Drawings
[0020] [Figure 1] It is a perspective view of a parallel link unit according to the first embodiment. [Figure 2] It is a diagram showing a usage mode of a parallel link unit according to the first embodiment. (A) shows the case where a robot arm is constituted by a parallel link unit alone, (B) shows the case where a robot arm is constituted by connecting a plurality of parallel link units, and (C) shows the case where a robot arm is constituted by connecting a plurality of parallel link units and a rotation unit. [Figure 3] It is a diagram showing a parallel link unit according to the first embodiment. (A) is a side view, (B) is a schematic side view, and (C) is a diagram for explaining the influence of a load. [Figure 4] It is a diagram for explaining the operation of a parallel link unit according to the first embodiment. [Figure 5]It is a diagram for explaining another operation of the parallel link unit according to the first embodiment. [Figure 6] It is a diagram for explaining yet another operation of the parallel link unit according to the first embodiment. [Figure 7] It is a diagram for explaining the operation of the parallel link unit according to the comparative example. [Figure 8] It is a perspective view of the parallel link unit according to the second embodiment. [Figure 9] It is a diagram showing the 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 the load. [Figure 10] It is a schematic side view of the parallel link unit according to the first modification example. [Figure 11] It is a schematic side view of the parallel link unit according to the second modification example. [Figure 12] It is a schematic side view of the parallel link unit according to the third modification example. [Figure 13] It is a schematic side view of the parallel link unit according to the fourth modification example. [Figure 14] It is a schematic side view of the parallel link unit according to the fifth modification example.
Modes for Carrying Out the Invention
[0021] Hereinafter, embodiments of the parallel link unit and its control device according to the present invention will be described with reference to the accompanying drawings.
[0022] [First Embodiment] Figure 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, unit 10A comprises 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 constitute a parallel link.
[0023] Unit 10A can be used alone to configure a robotic arm capable of moving heavy objects W into any environment (see Figure 2(A)), or multiple units can be used to configure an extra-long robotic arm (see Figure 2(B)). Furthermore, by combining Unit 10A with the rotary unit 70, an even more convenient extra-long robotic arm can be configured (see Figure 2(C)).
[0024] The base link 11 and output link 12 of unit 10A extend in the Z-axis direction (approximately vertical direction). Furthermore, the base link 11 and output link 12 are spaced apart from each other in the X-axis direction (approximately horizontal direction), 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] The first intermediate link 13 is connected to the base link 11 at one end so that it can swing around the Y-axis (an axis perpendicular to the X-axis and Z-axis). This swingable connection of links 11 and 13 forms the first joint 15.
[0026] The second intermediate link 14 is connected to the base link 11 at one end so that it can swing around the Y-axis. This swingable connection of links 11 and 14 forms the second joint 16. The second joint 16 is located approximately vertically below the first joint 15.
[0027] The first intermediate link 13 is connected to the output link 12 such that its other end can swing around the Y-axis. This swingable connection of links 12 and 13 forms the third joint 17.
[0028] The second intermediate link 14 is connected to the output link 12 such that its other end can swing around the Y-axis. This swingable connection of links 12 and 14 forms the 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 movable 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 movable part 32 can move in the Z-axis direction. The movement of the first movable part 32 is controlled by a control device (not shown).
[0030] As shown in Figure 3(A), the cylindrical first linear 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, i.e., the extension and retraction of the first linear actuator 20, is controlled by a control device that controls the second linear 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] The tip 22 of the first linear actuator 20 is connected to the fourth joint 18. In other words, the tip 22 of the first linear actuator 20 is connected to the output link 12 and the second intermediate link 14 so that it can swing around the Y axis.
[0032] The base end 21 of the first linear actuator 20 is connected to the first movable part 32 of the second linear actuator 30 so as to allow it to swing around the Y axis. This swingable connection forms a movable joint 33.
[0033] The movable 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 movable part 32 in the Z-axis direction under the control of a control device (not shown). In this embodiment, the second linear actuator 30 corresponds to the "positioning means" that positions the movable joint 33 (the base end portion 21 of the first linear actuator 20).
[0034] Figure 3(B) is a schematic representation of Figure 3(A). Figure 3(C) shows the output link 12 in Figure 3(B) with an extension 60 attached in the X-axis direction. As can be seen from these figures, unit 10A is an application of the Roberval mechanism conventionally used in devices such as balance scales. Therefore, when a load F1 of a heavy object W is applied to the position near the base of the extension 60, the force applied to the first linear actuator 20 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 the position near the tip of the extension 60. Similarly, torque applied to the output link 12 or the extension 60 around any axis has no effect on the first linear actuator 20.
[0035] In this embodiment, a single-axis force sensor (load cell) placed at the tip 22 of the first linear actuator 20 can measure the force applied to the first linear actuator 20. The force information obtained from this measurement is fed back to the control device described above.
[0036] In this embodiment, the control device includes a control stick. When the operator operates the control stick, a command corresponding to that operation is transmitted to the first linear actuator 20 and the second linear actuator 30. Preferably, the control stick is configured to transmit the force information that has been fed back to the operator in some way.
[0037] As will be explained in detail later, the first linear actuator 20 is mainly responsible for raising / lowering the output link 12, and the second linear actuator 30 is mainly responsible for changing the reduction ratio. For this reason, it is preferable that the first linear actuator 20 has relatively high responsiveness, and that the second linear actuator 30 can exert a relatively large force.
[0038] Next, the operation (change in posture) of unit 10A will be explained with reference to Figures 4 to 6. Note that some components have been omitted from these figures. The same applies to Figure 7, which shows the operation of a unit related to a comparative example.
[0039] Figure 4 shows the change in attitude of unit 10A when the first linear actuator 20 is operated while the movable joint 33 is maintained at the midpoint of the first line segment L1. When the control device retracts the first linear actuator 20 in accordance with the operator's input, the output link 12 rises (Figure (B) → (A)), and when the control device extends the first linear actuator 20, the output link 12 descends (Figure (B) → (C)).
[0040] Figure 5 shows the change in attitude of unit 10A when the first linear actuator 20 is operated while the movable joint 33 is maintained at the upper end of the first line segment L1 (= first joint 15). In this case as well, when the control device retracts the first linear actuator 20 in accordance with the operator's operation, the output link 12 rises (Figure (B) → (A)), and when the control device extends the first linear actuator 20, the output link 12 falls (Figure (B) → (C)). However, the amount of rise and fall of the output link 12 in Figure 5 is less than the amount of rise and fall in Figure 4. This indicates that the reduction ratio changes when the position of the movable joint 33 changes. The reduction ratio is maximum when the movable joint 33 overlaps the first joint 15 and minimum (= zero) when the movable joint 33 overlaps the second joint 16.
[0041] When the load is relatively large, the operator can activate the second linear actuator 30 via the control device to set a relatively large reduction ratio. This allows unit 10A to exert a large force (however, the change in attitude will be gradual). On the other hand, when the load is relatively small, the operator can activate the second linear actuator 30 via the control device to set a relatively small reduction ratio. This allows unit 10A to change its attitude quickly.
[0042] The operator can set the reduction ratio to zero via the control device when transporting unit 10A. This prevents damage to the actuator, reduction gear, load cell, etc., which are susceptible to shock, even if excessive force (shock) is applied to the output link 12 during transport, by preventing that force from being applied to the first linear actuator 20 itself or the load cell.
[0043] Furthermore, the operator can also set the reduction ratio to zero via the control device when resetting the load cell to zero. This makes it easy to create a state where 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 activates the second linear actuator 30 via the control device, the control device can also automatically activate the first linear actuator 20 to prevent the position of the output link 12 from changing. More specifically, the control device extends the first linear actuator 20 by an appropriate amount when the operator attempts to increase the reduction ratio (Figure 6(B)→(A)), and shortens the first linear actuator 20 by an appropriate amount when the operator attempts to decrease the reduction ratio (Figure 6(B)→(C)). This automatic control prevents unnecessary raising / lowering of the output link 12.
[0045] Similarly, the control device can also automatically compensate for fluctuations in the reduction ratio caused by the nonlinearity of the kinematics of the parallel link when the operator operates the first linear actuator 20 via the control device (when raising / lowering the output link 12) by operating the second linear actuator 30 by an appropriate amount.
[0046] In other words, the operator can independently control the motion of the output link 12 and the change in the reduction ratio (decoupling). The appropriate amount of control for this decoupling can be easily calculated by those skilled in the art using robotic kinematic calculations.
[0047] Furthermore, if the above-mentioned automatic control (de-interference) is not performed when the operator attempts to change the reduction ratio, the output link 12 will unnecessarily rise / fall, as shown in Figure 7.
[0048] [Second Example] Figure 8 shows a parallel link unit 10B according to a second embodiment of the present invention. As shown in the figure, unit 10B comprises 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. In other words, unit 10B differs from unit 10A in that it further comprises gas springs 40, 40, but is otherwise common to 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 which is the sleeve-side end and a tip end 42 which is the rod-side end that enters and exits the sleeve. In this embodiment, the gas springs 40,40 correspond to "elastic members".
[0050] The base ends 41 of the gas springs 40, 40 are connected to the second joint 16. That is, the base ends 41 of the gas springs 40, 40 are connected to the base link 11 and the second intermediate link 14 so that they can swing around the Y axis.
[0051] The tips 42 of the gas springs 40, 40 are connected to the third joint 17. That is, the tips 42 of the gas springs 40, 40 are connected to the output link 12 and the first intermediate link 13 so that they can swing around the Y axis.
[0052] Figure 9(B) is a schematic representation of Figure 9(A). Figure 9(C) shows the output link 12 in Figure 9(B) with an extension 60 attached in the X-axis direction. Unit 10B, like Unit 10A, applies a Roberval mechanism. Therefore, when a load F1 is applied near the base of the extension 60, the force applied to the first linear actuator 20 and gas springs 40, 40 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 near the tip of the extension 60.
[0053] The gas springs 40, 40 are most extended when the force applied between the base end 41 and the tip end 42 is less than a predetermined initial load, and they are compressed 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 these gas springs 40, 40 are used to perform weight compensation. This weight compensation reduces the force that the first linear actuator 20 must output to support the heavy object W. In other words, the power consumption of the first linear actuator 20 can be reduced.
[0054] [Differentiation] Although the first and second embodiments of the parallel link unit and control device according to the present invention have been described above, the configuration of the present invention is not limited to these.
[0055] (First variation) For example, the parallel link unit according to the present invention may be such that, as shown in Figure 10, the second linear actuator (guide 31 and first movable part 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 22 of the first linear actuator 20 is connected to the first movable part 32 of the second linear actuator. According to this modified unit 10C, similar to units 10A and 10B, the reduction ratio can be changed steplessly by operating the second linear actuator. In this modified example, the output link 12 corresponds to the "first link," and the base link 11 corresponds to the "second link." Also, in this modified example, the tip 22 corresponds to the "first end," and the base end 21 corresponds to the "second end."
[0056] (Second variation) In the parallel link unit according to the present invention, as shown in Figure 11, the tip portion 22 of the first linear actuator 20 may be connected to the third joint portion 17 instead of the fourth joint portion 18. In this modified unit 10D, similar to units 10A and 10B, the reduction ratio can be changed steplessly by operating the second linear actuator 30. However, in unit 10D, the load due to gravity acts in a direction that compresses the first linear actuator 20, so care should be taken to prevent buckling of the first linear actuator 20.
[0057] (Third variation) The parallel link unit according to the present invention may be equipped with a tension-type gas spring 40' that generates a reaction force when stretched, instead of a compression-type gas spring 40, as shown in Figure 12, for the parallel link unit 10E. The gas spring 40' has a base end 41' which is the sleeve-side end, and a tip end 42' which is the rod-side end 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. According to this modified example, unit 10E can perform weight compensation, similar to unit 10B. In this modified example, the gas spring 40' corresponds to an "elastic member".
[0058] (Fourth variation) The parallel link unit according to the present invention may be provided with a third linear actuator 50 similar to the second linear actuator 30 on the output link 12, as shown in Figure 13, for the parallel link unit 10F. The third linear actuator 50 includes a second movable part 51 that is movable in the Z-axis direction. The tip 42 of the gas spring 40 is connected to the second movable part 51 so that it can swing around the Y-axis, thereby forming a movable joint 52. The movable joint 52 can take any position on the second line segment L2 connecting the third joint 17 and the fourth joint 18 by moving the second movable part 51 in the Z-axis direction under the control of the control device. According to the modified unit 10F, the degree of self-weight compensation by the gas spring 40 can be adjusted by operating the third linear actuator 50 and changing the position of the movable joint 52. Furthermore, according to the modified unit 10F, 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) by operating the third linear actuator 50.
[0059] (Fifth variation) In the parallel link unit according to the present invention, as shown in Figure 14, parallel link units 10G and 10H, the base link 11 and output link 12 may be inclined by the same amount with respect to the Z-axis direction (=approximately vertical direction). In other words, the second joint 16 does not have to be approximately vertically below the first joint 15, and the fourth joint 18 does not have to be approximately vertically below the third joint 17. With a configuration like unit 10G, the range of motion upward is wider and the range of motion downward is narrower compared to unit 10A. On the other hand, with a configuration like unit 10H, the range of motion upward is narrower and the range of motion downward is wider compared to unit 10A. In other words, by inclining the base link 11 and output link 12 with respect to the Z-axis direction, the range of motion can be offset in either the vertical or vertical direction.
[0060] (Other variations) The means for positioning the first end of the first linear actuator 20 (for example, the base end 21 in the first embodiment) at an arbitrary 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 an arbitrary 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 42 in the fourth modified example) at an arbitrary position on the second line segment L2.
[0061] The elastic member for compensating for the self-weight is not limited to a compression or tension type gas spring. The elastic member 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 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 a 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) for measuring the displacement of the linear actuators 20, 30, and 50, (2) a force sensor (load cell) for measuring the force applied to the gas springs 40 and 40', and (3) a displacement sensor (e.g., an encoder) for measuring the displacement of the gas springs 40 and 40'. The location and type of sensors are not particularly limited in the present invention. Note that if the displacement sensor described in (1) or (3) is provided, the force sensor described in (2) is not necessary because the elastic force can be estimated by calculation from the output of the displacement sensor. However, a redundant configuration with both sensors can improve the accuracy, reliability, and fault tolerance of the measurement.
[0065] The base link 11 and output link 12 do not necessarily have to extend in a substantially vertical direction. In other words, the X-axis direction may be vertical, the Y-axis direction may be vertical, or a direction other than either axis may be vertical.
[0066] The above modifications can be combined with each other. For example, the third and fourth modifications may be combined to connect the tip 42' of the tension-type gas spring 40' to the second movable part 51. [Explanation of Symbols]
[0067] 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H Parallel Link Unit 11 Baselink 12 Output Links 13. First Intermediate Link 14. Second Intermediate Link 15. First joint 16. Second joint 17. Third joint 18. Fourth joint 20 First Linear Actuator 21 Base end (of the first linear actuator) 22 Tip (of the first linear actuator) 30. Second linear actuator 31 Guide 32 First Mobile Unit 33. Movable joint 40,40' Gas spring 41,41' Base end (of the gas spring) 42,42' (gas spring) tip 50 Third Linear Actuator 51 Second Mobile Unit 52 Movable joint
Claims
1. A parallel link consisting of a first link and a second link that are roughly parallel to each other, and a first intermediate link and a second intermediate link that are roughly parallel to each other, A cylindrical first linear actuator having a first end and a second end, the second end being connected to an articulation formed by the second link and the second intermediate link, Positioning means for positioning the first end of the first linear actuator at any position on a first line segment connecting 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, A parallel link unit characterized by having the following features.
2. The positioning means is a second linear actuator having a first moving part that moves along the first line segment, The first end of the first linear actuator is connected to the first moving part. The parallel link unit according to feature 1.
3. The first and second links 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. The joint formed by the second link and the first intermediate link is located approximately vertically above the joint formed by the second link and the second intermediate link. The parallel link unit according to claim 1 or 2, characterized in that it is the same as described in claim 1 or 2.
4. It further includes an elastic member that generates a reaction force when compressed, The elastic member has a first end and a second end, the first end being pivotably 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. The parallel link unit according to claim 3.
5. The positioning is performed by a third linear actuator having a second moving part that moves along the second line segment. The second end of the elastic member is connected to the second movable part. The parallel link unit according to feature 4.
6. The elastic member is a compression-type gas spring. The parallel link unit according to feature 4.
7. It further includes an elastic member that generates a reaction force when pulled, The elastic member has a first end and a second end, the first end being pivotably 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 to the joint formed by the second link and the second intermediate link. The parallel link unit according to claim 3.
8. The positioning is performed by a third linear actuator having a second moving part that moves along the second line segment. The second end of the elastic member is connected to the second movable part. The parallel link unit according to feature 7.
9. The elastic member is a tensile type gas spring. The parallel link unit according to feature 7.
10. The system further includes a single-axis force sensor for measuring the force applied to the first linear actuator. The parallel link unit according to claim 1 or 2, characterized in that it is the same as described in claim 1 or 2.
11. A control device for controlling a first linear actuator and a second linear actuator constituting the parallel link unit described in claim 2, When the second linear actuator is operated, the first linear actuator is operated so that the relative position of the second link with respect to the first link does not change as a result of the operation of the second linear actuator. A control device characterized by the following features.