Parallel link mechanism and industrial robot

Abstract

The parallel link mechanism (16) comprises: a support member (36); a connection joint (38); a first arm (40a) interconnecting the support member and the connection joint, the first arm comprising a first intermediate joint (50a) and a first drive rod (42a) rotatable about a first axis (44a); a second arm (40b) interconnecting the support member and the connection joint in parallel with the first arm, the second arm comprising a second intermediate joint (50b) and a second drive rod (42b) rotatable about a second axis (44b), the first and second axes defining a reference plane (54); wherein the parallel link mechanism is configured to adopt a state (68) in which the first and second drive rods are crossed, the connection joint is positioned on a primary side (70a) of the reference plane, and the first and second intermediate joints are positioned on an opposite secondary side (70b) of the reference plane.

Description

Technical Field

[0001] This disclosure relates generally to industrial robots. Specifically, it provides parallel linkage mechanisms and industrial robots including such parallel linkage mechanisms. Background Technology

[0002] Industrial robots are used in a wide range of automation applications. In many applications, industrial robots are used to load workpieces onto machines and unload them from machines after the machines have performed operations on the workpieces. Loading workpieces in this way can be referred to as caretakership.

[0003] US 5522275 A discloses an industrial robot used as a press intercom. The industrial robot includes: a base disposed in the space between two presses; a pair of arms rotatably mounted to the base; a pair of forearms rotatably mounted to the arms, the ends of the forearms being hinged about a common axis; a forearm extension rotatably supporting a wrist; and a tool flange attached to the wrist for supporting a gripping member. Summary of the Invention

[0004] One object of the present invention is to provide an improved parallel linkage mechanism for industrial robots.

[0005] Another object of the present invention is to provide an improved industrial robot.

[0006] These objectives are achieved by the parallel linkage mechanism according to the appended claim 1 and the industrial robot according to the appended claim 8.

[0007] The present invention is based on the understanding that by providing a parallel linkage mechanism comprising two parallel arms that interconnect a support member and a connecting joint in parallel, and wherein the two drive links of the arms can be oriented upward relative to their actuation axes, and the connecting joint can be positioned very close to the support member, both a small footprint and an increased range of motion of the parallel linkage mechanism can be achieved.

[0008] According to a first aspect, a parallel linkage mechanism for an industrial robot is provided, the parallel linkage mechanism comprising: a support member; a connecting joint; a first arm interconnecting the support member and the connecting joint, the first arm including a first intermediate joint and a first drive rod interconnecting the support member and the first intermediate joint; a first actuator arranged to drive the first drive rod to rotate relative to the support member about a first axis; a second arm interconnecting the support member and the connecting joint parallel to the first arm, the second arm including a second intermediate joint and a second drive rod interconnecting the support member and the second intermediate joint; and a second actuator arranged to drive the second drive rod to rotate relative to the support member about a second axis, the second axis and the first axis defining a reference plane; wherein the parallel linkage mechanism is configured in an adopted state in which the first drive rod and the second drive rod are intersected, the connecting joint is positioned on a primary side of the reference plane, and the first intermediate joint and the second intermediate joint are positioned on opposite secondary sides of the reference plane.

[0009] Parallel linkages provide a large working range for the connecting joint. By extending the first and second arms, the connecting joint can be positioned away from the supporting member. In a parallel linkage where the first and second drive rods are crossed and the first and second intermediate joints are positioned on the secondary side, the connecting joint can be positioned at least very close to the reference plane, or even across the reference plane to reach its secondary side. This capability of the parallel linkage, compared to a parallel linkage where the intermediate joint is always positioned on the primary side of such a reference plane, enables a significantly reduced footprint and a significantly increased range of motion for the connecting joint. The combination of a small footprint and a large range of motion makes the parallel linkage ideal for use in maneuvering operations in confined spaces, and / or allows such spaces to be manufactured narrower to reduce the overall footprint of applications such as press applications involving two machine presses managed by an industrial robot between two machine presses. However, industrial robots incorporating the parallel linkage according to the first aspect can be used in many applications beyond press applications.

[0010] The state in which the first and second drive rods of the parallel linkage mechanism intersect and the first and second intermediate joints are positioned on the secondary side of the reference plane can be referred to as the compact state. The first and second drive rods can intersect as seen in the direction along the first axis.

[0011] The first actuator and the second actuator can be rotary actuators. The first axis and the second axis can be horizontal.

[0012] The first and second axes can be parallel. In these cases, the first and second arms can be substantially planar or planar, thus contributing to the compactness of the parallel linkage mechanism.

[0013] The length of the first drive rod between the first axis and the first intermediate joint can be between 80% and 120% of the distance between the first axis and the second axis, such as between 90% and 110% of the distance between the first axis and the second axis, such as between 95% and 105% of the distance between the first axis and the second axis. This allows the first drive rod to be substantially maintained within or within the occupancy area of ​​the support member, for example, within the reference plane and in a direction parallel to the first axis, when the first intermediate joint is positioned on the reference plane. The length of the second drive rod can be substantially equal to or equal to the length of the first drive rod.

[0014] The first drive rod can move in a first plane transverse to the first axis, and the second drive rod can move in a second plane transverse to the second axis. In these cases, the support member can be positioned between the first and second planes. This variation of the parallel linkage mechanism also contributes to its compactness. For this variation, the first and second axes can be parallel or non-parallel.

[0015] The parallel linkage mechanism may also include a first driven link and a second driven link, wherein the first driven link interconnects the first intermediate joint and the connecting joint, and the second driven link interconnects the second intermediate joint and the connecting joint.

[0016] The first and second driven links can be positioned between the first and second planes. This variation also contributes to the compactness of the parallel linkage mechanism.

[0017] The support member may include an aperture in a reference plane between the first and second axes. The aperture may be arranged to receive a connecting joint. When the connecting joint is received in the aperture, it can thus be linearly positioned between the first and second axes. By designing the support member in this way, the parallel linkage mechanism can be in a very compact state, in which the first and second drive rods are crossed and the first and second intermediate joints are positioned on the secondary side of the reference plane. In this state, the aperture may even allow the connecting joint to move from the primary side across the reference plane to the secondary side.

[0018] The parallel linkage mechanism may also include a balancing device configured to assist the first actuator in counteracting the gravity acting on the first drive rod.

[0019] According to the second aspect, an industrial robot is provided, comprising a parallel linkage mechanism and an end effector according to the first aspect. The industrial robot can be mounted vertically such that the reference plane is horizontal and the primary side is vertically below the reference plane.

[0020] Industrial robots may also include a base and a base actuator, the base actuator being arranged to drive a support member to rotate relative to the base about an axis of the support member. The base actuator may be a rotary actuator. Where the support member is not rotatable relative to the base, the support member may constitute the base of the industrial robot or form part of the base of the industrial robot.

[0021] The axis of the supporting member can be transverse to the reference plane. Therefore, the axis of the supporting member can be vertical or not.

[0022] Industrial robots may also include a series linkage mechanism connected between the connecting joint and the end effector. A base, parallel linkage, series linkage mechanism, and end effector form an example of a manipulator. In addition to the manipulator, industrial robots may also include an electronic control system for controlling the manipulator, such as controlling any of its actuators.

[0023] In some alternative variations, the industrial robot does not include a series linkage mechanism. In such variations, the end effector can be located at the connection joint.

[0024] The tandem linkage may include a third drive rod and a third actuator, the third actuator being arranged to drive the third drive rod to rotate about a third axis relative to each of the first and second arms. The third actuator may be a rotary actuator.

[0025] The third axis can coincide with the connecting joint. This variation contributes to the compact design and agile performance of industrial robots. The third axis can also be parallel to the first axis.

[0026] The tandem linkage may further include a fourth drive link and a fourth actuator, the fourth actuator being arranged to drive the fourth drive link to rotate relative to the third drive link about a fourth axis. The fourth actuator may be a rotary actuator. The fourth axis may be parallel to the third axis.

[0027] The tandem linkage may also include a fifth drive rod and a fifth actuator, the fifth actuator being arranged to drive the fifth drive rod to rotate relative to the fourth drive rod about a fifth axis. The fifth actuator may be a rotary actuator. The fifth axis may be transverse to the fourth axis. Attached Figure Description

[0028] Other details, advantages, and aspects of this disclosure will become apparent from the following description, which is given in conjunction with the accompanying drawings, in which:

[0029] Figure 1 A schematic representation of a side view of an industrial robot used in an application, based on an example.

[0030] Figure 2 A schematic representation of a side view of an industrial robot;

[0031] Figure 3 A schematic representation of a partial perspective side view of an industrial robot;

[0032] Figure 4 A schematic partial side view of an industrial robot in a compact configuration; and

[0033] Figure 5 schematic representation Figure 4 A partial top view of an industrial robot. Detailed Implementation

[0034] The following will describe parallel linkage mechanisms and industrial robots including such parallel linkage mechanisms. The same or similar reference numerals will be used to denote the same or similar structural features.

[0035] Figure 1 The diagram schematically illustrates a side view of an industrial robot 10 used in application 12 according to an example. This example industrial robot 10 includes a fixed base 14, a parallel linkage 16, a series linkage 18, and an end effector 20. The industrial robot 10 also includes an electronic control system 22. The base 14, parallel linkage 16, series linkage 18, and end effector 20 constitute an example of the manipulator of the industrial robot 10.

[0036] Figure 1 A Cartesian coordinate system 24 for reference purposes is also shown. In this example, the Z-axis of coordinate system 24 is vertical. The control system 22 is configured to control the operation of the manipulator, for example, by using commands regarding coordinate system 24.

[0037] The specific and non-limiting example of application 12 includes a first machine press 26a and a second machine press 26b. The first machine press 26a includes a first bed 28a and a first slide 30a, the first slide 30a being movable relative to the first bed 28a to press a workpiece 32 between them in a first manner. The second machine press 26b includes a second bed 28b and a second slide 30b, the second slide 30b being movable relative to the second bed 28b to press the workpiece 32 between them in a second manner, different from the first manner. The distance between the first bed 28a and the second bed 28b can be, for example, at least 2 m, such as 5 m to 6 m.

[0038] Industrial robot 10 is horizontally positioned between the first machine press 26a and the second machine press 26b. Industrial robot 10 can, for example, pick up workpiece 32 from the first bed 28a after pressing by machine press 26a and place workpiece 32 on the second bed 28b. After pressing by the second machine press 26b, workpiece 32 can be picked up again by industrial robot 10, or it can be picked up by another industrial robot (not shown), for example... Figure 1 The right side of the second machine, press 26b.

[0039] In this example, the industrial robot 10 is top-mounted. This allows the first machine press 26a and the second machine press 26b to be arranged horizontally close to each other. As shown, the space between the first machine press 26a and the second machine press 26b is very limited. Figure 1 A straight line 34 extending between the first bed 28a and the second bed 28b is also shown. Line 34 is mentioned again later in the description.

[0040] Figure 2 A schematic side view of the industrial robot 10 is shown, and Figure 3 A schematic partial perspective side view of an industrial robot 10. (Common Reference) Figure 2 and Figure 3 The parallel linkage 16 includes a support member 36, a connecting joint 38, a first arm 40a, and a second arm 40b. In this example, the first arm 40a and the second arm 40b are substantially located in a common plane (here, the XZ plane of coordinate system 24). Therefore, the parallel linkage 16 in this example is substantially planar.

[0041] The first arm 40a interconnects the support member 36 and the connecting joint 38. The first arm 40a includes a first drive rod 42a, which is rotatably connected to the support member 36 for rotation about a first axis 44a. The parallel linkage 16 also includes a first actuator 46a for driving the first drive rod 42a to rotate about the first axis 44a. In this example, the first arm 40a also includes a first driven rod 48a, which is rotatably connected to the first drive rod 42a at a first intermediate joint 50a. Thus, the first drive rod 42a interconnects the support member 36 and the first intermediate joint 50a, and the first driven rod 48a interconnects the first intermediate joint 50a and the connecting joint 38. The first intermediate joint 50a provides relative rotation between the first drive rod 42a and the first arm 40a about a first intermediate axis 52a. The first intermediate axis 52a is parallel to the first axis 44a here.

[0042] The second arm 40b interconnects the support member 36 and the connecting joint 38 parallel to the first arm 40a. The second arm 40b includes a second drive rod 42b rotatably connected to the support member 36 for rotation about a second axis 44b. The parallel linkage 16 also includes a second actuator 46b for driving the second drive rod 42b to rotate about the second axis 44b. In this example, the second arm 40b also includes a second driven rod 48b rotatably connected to the second drive rod 42b at a second intermediate joint 50b. Thus, the second drive rod 42b interconnects the support member 36 and the second intermediate joint 50b, and the second driven rod 48b interconnects the second intermediate joint 50b and the connecting joint 38. The second intermediate joint 50b provides relative rotation between the second drive rod 42b and the second arm 40b about a second intermediate axis 52b. The second intermediate axis 52b is parallel to the second axis 44b here. The second driven rod 48b is rotatably connected to the first driven rod 48a at the connecting joint 38.

[0043] By controlling the operation of the first actuator 46a and the second actuator 46b, the connecting joint 38 can move in a plane (here, the XZ plane of coordinate system 24). Figure 2 and Figure 3 In this configuration, for example, as seen in a direction parallel to the first axis 44a, the first drive rod 42a and the second drive rod 42b intersect. Because the first drive rod 42a and the second drive rod 42b intersect, the parallel linkage 16 is compact in the X direction (here, the horizontal direction).

[0044] The first axis 44a and the second axis 44b define a reference plane 54. In this example, the first axis 44a and the second axis 44b are parallel, but they can also lie in and define the reference plane 54 if they are not parallel. In this example, the first axis 44a, the second axis 44b, and the reference plane 54 are all horizontal.

[0045] Figure 2 The distance 56 between the first axis 44a and the second axis 44b is shown, and Figure 3 The length 58 of the first drive rod 42a is shown. In this example, the length 58 is equal to the distance 56. The length 58 of the first drive rod 42a can be defined as the distance between the first axis 44a and the first intermediate axis 52a. The length of the second drive rod 42b, defined in a corresponding manner, is also equal to the distance 56.

[0046] The support member 36 in this example is generally V-shaped. The support member 36 includes a bore 60 between the first axis 44a and the second axis 44b.

[0047] The parallel linkage 16 in this example also includes a balancing device 62. The balancing device 62 assists the first actuator 46a in counteracting gravitational loads acting on the first drive rod 42a, such as the weight of the serial linkage 18 and the workpiece 32. The balancing device 62 may, for example, include a spring-biased piston-cylinder assembly that interconnects the support member 36 and the first drive rod 42a.

[0048] The industrial robot 10 in this example also includes a base actuator 64, which is arranged to drive the support member 36 to rotate relative to the base 14 about the support member axis 66. However, the industrial robot 10 in this example can move between the first machine press 26a and the second machine press 26b without actuation of the base actuator 64. The base actuator 64 can be used, for example, to reorient the parallel linkage 16 to, for example, align it with the YZ plane of coordinate system 24.

[0049] In this example, the serial linkage 18 interconnects the parallel linkage 16 and the end effector 20. The serial linkage 18 and the parallel linkage 16 are both substantially located in a common plane (here, the XZ plane of coordinate system 24).

[0050] The example of the serial linkage 18 includes a third drive rod 42c and a third actuator 46c, the third actuator 46c being arranged to drive the third drive rod 42c to rotate about a third axis 44c relative to each of the first arm 40a and the second arm 40b. The third axis 44c is parallel to the first axis 44a. In this example, the third axis 44c coincides with a connecting joint 38. Therefore, at the connecting joint 38, each of the first driven rod 48a, the second driven rod 48b, and the third drive rod 42c can rotate relative to each other about the third axis 44c. The third actuator 46c can, for example, drive the third drive rod 42c to rotate about the third axis 44c relative to the first driven rod 48a.

[0051] The example tandem linkage 18 also includes a fourth drive link 42d and a fourth actuator 46d, the fourth actuator 46d being arranged to drive the fourth drive link 42d to rotate relative to the third drive link 42c about a fourth axis 44d. Here, the fourth axis 44d is also parallel to the first axis 44a.

[0052] The example of the tandem linkage 18 also includes a fifth drive link 42e and a fifth actuator 46e, the fifth actuator 46e being arranged to drive the fifth drive link 42e to rotate relative to the fourth drive link 42d about a fifth axis 44e. The fifth axis 44e is transverse to the fourth axis 44d here. Furthermore, in this example, the fifth axis 44e intersects the fourth axis 44d. In this example, an end effector 20 is connected to the fifth drive link 42e.

[0053] Each of actuators 46a-46e and 64 is a rotary actuator. Using only rotary actuators 46a-46e and 64 enables a more compact and cost-effective design of the industrial robot 10 compared to using one or more linear actuators. The cable routing to the respective actuators 46a-46e is also simplified by using rotary actuators. Furthermore, since the first actuator 46a and the second actuator 46b operate in parallel, the torque provided can be relatively low.

[0054] Because the parallel linkage 16 and the sequential linkage 18 are essentially located in a common plane (here, the XZ plane), the industrial robot 10 is very compact in the direction transverse to this plane (here, the Y direction). Due to the intersection of the first drive link 42a and the second drive link 42b, the parallel linkage 16 enables the industrial robot 10 to provide a large working range for the end effector 20 in confined spaces. The industrial robot 10 also features a low-complexity design.

[0055] Figure 4 The diagram schematically illustrates a partial side view of the industrial robot 10 in state 68. State 68 may be referred to as the compact state. In state 68, the first drive link 42a and the second drive link 42b are intersected, the connecting joint 38 is positioned on the primary side 70a of the reference plane 54, and the first intermediate joint 50a and the second intermediate joint 50b are positioned on the secondary side 70b of the reference plane 54, opposite to the primary side 70a. Figure 4 In this configuration, the first drive rod 42a and the second drive rod 42b point upwards from the reference plane 54. In this example, where the reference plane 54 is horizontal and the industrial robot 10 is top-mounted, the primary side 70a is vertically below the reference plane 54. In state 68, the connecting joint 38 can be positioned very close to the support member 36. The parallel linkage mechanism 16 thus provides an excellent combination of compactness and the accessibility of the connecting joint 38 to the support member 36. Figure 4 In this configuration, the connecting joint 38 can be driven even further upwards and into the aperture 60, aligning the connecting joint 38 with the reference plane 54. In this way, the reach and compactness of the parallel linkage mechanism 16 are further improved.

[0056] Refer again Figure 1The ability of the parallel linkage 16 in state 68 enables the industrial robot 10 to rapidly move the end effector 20 between the first bed 28a and the second bed 28b without having to cross the line 34 between them and without rotating the support member 36 about the support member axis 66. The ability of the base actuator 64 and the support member 36 to rotate relative to the base 14 about the support member axis 66 is therefore optional. Furthermore, the combination of the parallel linkage 16 with the serial linkage 18, and the ability of the parallel linkage 16 in state 68, enables improved motion performance within the first machine press 26a and the second machine press 26b.

[0057] Common Reference Figure 2 , Figure 3 and Figure 4 Since the length 58 of the first drive rod 42a is equal to the distance 56 between the first axis 44a and the second axis 44b, when the first drive rod 42a rotates back towards the primary side 70a around the first axis 44a (in... Figure 4 When the direction is counterclockwise, the first intermediate axis 52a will not extend outside the second axis 44b (in the counterclockwise direction). Figure 4 (From center to left). The first drive rod 42a can therefore be maintained within the horizontal occupancy area of ​​the support member 36.

[0058] Figure 5 A partial top view of the industrial robot 10 is schematically shown. Also in Figure 5 In the middle, the parallel linkage mechanism 16 is in state 68. From Figure 5 It can be understood that the first drive rod 42a is movable in a first plane 72a transverse to the first axis 44a, and the second drive rod 42b is movable in a second plane 72b transverse to the second axis 44b. In this example, the first plane 72a and the second plane 72b are vertical and parallel. Figure 5 As shown, the support member 36 is positioned between the first plane 72a and the second plane 72b, here completely positioned between the first plane 72a and the second plane 72b. Furthermore, both the first driven rod 48a and the second driven rod 48b are positioned between the first plane 72a and the second plane 72b, here completely positioned between the first plane 72a and the second plane 72b. Figure 5 As shown, on one side is the support member 36, and on the other side are the first driven rod 48a and the second driven rod 48b, forming an X shape as seen in a direction transverse to the reference plane 54 (e.g., along the axis 66 of the support member). Figure 5 These described features also contribute to the compact design of the parallel linkage 16.

[0059] While this disclosure has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to what has been described above. For example, it should be understood that the dimensions of the components can be changed as needed. Therefore, the invention is intended to be limited only by the scope of the appended claims.

Claims

1. A parallel linkage mechanism (16) for an industrial robot (10), the parallel linkage mechanism (16) comprising: Supporting components (36); Connector (38); A first arm (40a) interconnects the support member (36) with the connecting joint (38). The first arm (40a) includes a first intermediate joint (50a) and a first drive rod (42a), which interconnects the support member (36) with the first intermediate joint (50a). A first actuator (46a) is arranged to drive the first drive rod (42a) to rotate about a first axis (44a) relative to the support member (36); The second arm (40b) is parallel to the first arm (40a) and interconnects the support member (36) with the connecting joint (38). The second arm (40b) includes a second intermediate joint (50b) and a second drive rod (42b), which interconnects the support member (36) with the second intermediate joint (50b). as well as A second actuator (46b) is arranged to drive a second drive rod (42b) to rotate relative to the support member (36) about a second axis (44b), the second axis (44b) and the first axis (44a) defining a reference plane (54). The parallel linkage mechanism (16) is characterized in that it is configured in a state (68) in which the first drive rod (42a) and the second drive rod (42b) are crossed, the connecting joint (38) is positioned on the primary side (70a) of the reference plane (54), and the first intermediate joint (50a) and the second intermediate joint (50b) are positioned on the opposite secondary side (70b) of the reference plane (54).

2. The parallel linkage mechanism (16) according to claim 1, wherein the first axis (44a) is parallel to the second axis (44b).

3. The parallel linkage mechanism (16) according to claim 2, wherein the length (58) of the first drive rod (42a) between the first axis (44a) and the first intermediate joint (50a) is between 80% and 120% of the distance (56) between the first axis (44a) and the second axis (44b).

4. The parallel linkage mechanism (16) according to any one of the preceding claims, wherein the first drive rod (42a) is movable in a first plane (72a) transverse to the first axis (44a), wherein the second drive rod (42b) is movable in a second plane (72b) transverse to the second axis (44b), and wherein the support member (36) is positioned between the first plane (72a) and the second plane (72b).

5. The parallel linkage mechanism (16) according to any one of the preceding claims further includes a first driven rod (48a) and a second driven rod (48b), the first driven rod (48a) interconnecting the first intermediate joint (50a) with the connecting joint (38), and the second driven rod (48b) interconnecting the second intermediate joint (50b) with the connecting joint (38).

6. The parallel linkage mechanism (16) according to claims 4 and 5, wherein the first driven rod (48a) and the second driven rod (48b) are positioned between the first plane (72a) and the second plane (72b).

7. The parallel linkage mechanism (16) according to any one of the preceding claims, wherein the support member (36) includes a aperture (60) in the reference plane (54) between the first axis (44a) and the second axis (44b), the aperture (60) being arranged to receive the connecting joint (38).

8. An industrial robot (10) comprising a parallel linkage mechanism (16) according to any one of the preceding claims and an end effector (20).

9. The industrial robot (10) according to claim 8 further includes a base (14) and a base actuator (64) arranged to drive the support member (36) to rotate relative to the base (14) about the axis (66) of the support member.

10. The industrial robot (10) according to claim 9, wherein the axis (66) of the support member is transverse to the reference plane (54).

11. The industrial robot (10) according to any one of claims 8 to 10 further includes a serial linkage (18) connected between the connecting joint (38) and the end effector (20).

12. The industrial robot (10) of claim 11, wherein the serial linkage (18) includes a third drive rod (42c) and a third actuator (46c), the third actuator (46c) being arranged to drive the third drive rod (42c) to rotate about a third axis (44c) relative to each of the first arm (40a) and the second arm (40b).

13. The industrial robot (10) according to claim 12, wherein the third axis (44c) coincides with the connecting joint (38).

14. The industrial robot (10) according to claim 12 or 13, wherein the third axis (44c) is parallel to the first axis (44a).

15. The industrial robot (10) according to any one of claims 12 to 14, wherein the serial linkage (18) further comprises a fourth drive rod (42d) and a fourth actuator (46d), the fourth actuator (46d) being arranged to drive the fourth drive rod (42d) to rotate about a fourth axis (44d) relative to the third drive rod (42c).

16. The industrial robot (10) according to claims 14 and 15, wherein the fourth axis (44d) is parallel to the third axis (44c).

17. The industrial robot (10) according to claim 15 or 16, wherein the serial linkage (18) further comprises a fifth drive rod (42e) and a fifth actuator (46e), the fifth actuator (46e) being arranged to drive the fifth drive rod (42e) to rotate about a fifth axis (44e) relative to the fourth drive rod (42d).

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