A dual degree of freedom robotic wrist

Abstract

The application discloses a double-degree-of-freedom robot wrist and relates to the technical field of robots, which comprises a wrist main body, a rotating support fixedly arranged on the wrist main body, a swing support rotatably arranged on the rotating support around a first axis, a wrist support rotatably arranged on the swing support around a second axis, the first axis being perpendicular to the second axis, an installation cavity arranged in the wrist main body, a plurality of pull rope units connected with tendon ropes arranged in the installation cavity, a plurality of first tendon rope through holes communicating with the installation cavity arranged on the wrist main body, a plurality of second tendon rope through holes arranged on the wrist support, a first driving unit and a second driving unit arranged on the wrist main body, a first transmission member connected with the output end of the first driving unit, a second transmission member connected with the output end of the second driving unit, and the first transmission member and the second transmission member being connected with the two sides of the wrist support respectively.

Description

Technical Field

[0001] This invention relates to the field of robotics, specifically to a two-degree-of-freedom robotic wrist. Background Technology

[0002] The robot wrist is a crucial component of robotics technology. As a key joint connecting the robot arm to end effectors (such as grippers and grippers), its performance directly impacts the robot's operational flexibility, operational accuracy, and applicability. With the continuous expansion of robot applications from structured industrial environments to unstructured, human-robot collaborative environments, higher demands are being placed on the biomimetic, compact, lightweight, and motion decoupling capabilities of robot wrists.

[0003] In existing technologies, the methods for achieving two degrees of freedom of wrist movement (usually pitch / bending and yaw) are mainly divided into two categories: serial and parallel.

[0004] While parallel two-degree-of-freedom wrists improve load-bearing capacity and structural stiffness to some extent, most parallel wrist mechanisms suffer from motion coupling problems—the motions of the two degrees of freedom interfere with each other, resulting in complex kinematic and dynamic models and difficulty in control.

[0005] Furthermore, in chord-driven wrist systems, the chords often need to bypass joint structures, and their length varies considerably during wrist movement. This not only affects transmission accuracy and force transmission efficiency but also increases control complexity. Summary of the Invention

[0006] To address the technical problems existing in the background art, the present invention proposes a two-degree-of-freedom robotic wrist.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: A two-degree-of-freedom robot wrist includes a wrist body, a rotating bracket fixedly mounted on the wrist body, a swing bracket rotatably mounted on the rotating bracket about a first axis, and a wrist bracket rotatably mounted on the swing bracket about a second axis, wherein the first axis and the second axis are perpendicular to each other. The wrist body has an installation cavity, and the installation cavity has several pull rope units for connecting tendon ropes. The wrist body has several first tendon rope through holes that connect to the installation cavity, and the wrist support has several second tendon rope through holes. The wrist body is provided with a first drive unit and a second drive unit. The output end of the first drive unit is connected to a first transmission component, and the output end of the second drive unit is connected to a second transmission component. The first transmission component and the second transmission component are respectively connected to both sides of the wrist support. The first driving unit and the second driving unit apply driving force to both sides of the wrist support through the first transmission member and the second transmission member. When the first transmission member and the second transmission member drive in the same direction, the wrist support bends relative to the wrist body. When the first transmission member and the second transmission member drive in opposite directions, the wrist support swings relative to the wrist body.

[0008] Preferably, the first tendon cord through holes are arranged at intervals along the first axis direction, and the second tendon cord through holes are arranged at intervals along the second axis direction. Through the above improvements, the multiple tendon cords are arranged in a neat and orderly manner inside the wrist, effectively avoiding cross-entanglement and mutual interference, and ensuring that the length change of each tendon cord tends to be consistent and minimized during wrist bending or swinging, which significantly improves the stability of force transmission and control accuracy.

[0009] Preferably, the rotating bracket has a cable ties extending toward the wrist support, and the cable ties are located between the first and second tendon ligament through holes. Through the above improvements, the cable ties can provide precise path constraints and guidance for the tendon ligaments, effectively preventing the tendon ligaments from shifting, loosening, or interfering with the surrounding structure when the wrist is bent or tilted. This ensures that the length changes of each tendon ligament are stable and controllable, thereby significantly improving the repeatability of force transmission and the consistency of control response. The cable ties also protect the tendon ligaments and simplify the threading and assembly, making the overall structure more compact and reliable, without affecting the free range of wrist movement.

[0010] Preferably, the swing bracket has a threading channel running through it along the thickness direction, and the wire harness is inserted into the threading channel. Through the above improvements, the tendon cord is guided in a fully enclosed manner when passing through the swing bracket, which effectively avoids friction and wear between the tendon cord and the edge of the swing bracket, and ensures the stability and controllability of the tendon cord path during wrist movement, further improving the repeatability and control accuracy of force transmission.

[0011] Preferably, the wrist body is provided with a positioning protrusion, the first tendon cord through hole is provided in the positioning protrusion, and the rotating bracket is provided with a positioning groove for the positioning protrusion to be inserted. Through the above improvements, the accuracy of the rotating bracket installation and positioning is improved, and the connection rigidity between the wrist body and the rotating bracket is enhanced, effectively resisting the impact and vibration during the movement and improving the structural stability.

[0012] Preferably, the wrist support has a connecting protrusion extending horizontally along the first axis on the side wall opposite to the hinge center of the swing support, and the connecting protrusion is provided with a driving protrusion for connecting the first transmission component and the second transmission component. Through the above improvements, the force application points of the first transmission component and the second transmission component are moved away from the hinge center of the wrist support, increasing the driving arm, thereby obtaining a larger driving torque under the same driving force, improving the load capacity and response speed of the wrist, and separating the transmission connection point from the hinge center axially to avoid structural interference, making the force line distribution of the dual drive unit more reasonable, effectively ensuring the accurate realization of the two-degree-of-freedom decoupled motion, and further enhancing the overall compactness and transmission efficiency of the wrist.

[0013] Preferably, both the first and second transmission components include a first connecting portion connected to the actuating end of the first and second driving units, and a second connecting portion connected to the wrist support. The first connecting portion and the second connecting portion have a preset bending angle, so that the first and second transmission components are arranged in a bent rod shape. Through the above improvements, since the flexion, extension and swaying movements of the human wrist are not transmitted along a straight line, but are achieved through the oblique course of tendons such as the radial and ulnar flexor carpi radialis and flexor carpi ulnaris, the bent rod shape of the first and second transmission components changes the force transmission direction of the driving arm from a straight line to a broken line, simulating the envelope path of the tendon around the carpal bones, so that the force direction of the driving unit is closer to the physiological traction direction of human muscles.

[0014] Preferably, the driving protrusion is spherically shaped and connects the first transmission component and the second transmission component. The first and second transmission components are provided with spherical connecting parts. The actuating ends of the first and second driving units are connected to the first and second transmission components through the spherical connecting parts. Through the above improvements, the driving protrusion is set as a spherical structure and cooperates with the spherical connecting parts on the first and second transmission components to form a ball-joint flexible transmission connection. This adaptively compensates for changes in the angle and position of the transmission components during wrist flexion and swaying movements, avoids jamming and additional stress caused by rigid connections, significantly reduces the requirements for the processing and assembly accuracy of parts, and effectively improves the linearity of force transmission and the consistency of control response, further enhancing the smoothness of the two-degree-of-freedom decoupled motion.

[0015] Preferably, the first axis and the second axis intersect at the same point, and the intersection point is the swing rotation center of the swing bracket. Through the above improvements, the spatial convergence of the two-degree-of-freedom rotation axes is realized, which is highly similar to the structure of the human wrist joint and conforms to the principle of bionics. This makes the movement mode of the robot wrist more natural and smooth. Since the axes are at the same point, there is no offset when the wrist bends and swings, which avoids the generation of additional torque, effectively reduces the motion coupling effect, and the structure is compact, which reduces the error accumulation caused by joint gaps and improves the overall control performance.

[0016] Preferably, both the first drive unit and the second drive unit have mounting end faces facing the wrist body. The first transmission component and the second transmission component are rotatably connected to the mounting end faces. The wrist body has concave mounting grooves on both sides. The first drive unit and the second drive unit are disposed in the mounting grooves. Through the above improvements, the first drive unit and the second drive unit are embedded in the concave mounting grooves on both sides of the wrist body, and the transmission component is directly rotatably connected to the mounting end face of the drive unit. This effectively reduces the space occupied by the outward protrusion of the drive mechanism, making the overall structure more compact and flat, which is conducive to integrated installation in a narrow arm body space.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: A rotating bracket is fixed to the wrist body, a swing bracket is rotatably mounted on the upper rotating bracket around a first axis, and a wrist bracket is rotatably mounted on the swing bracket around a second axis perpendicular to the first axis. The two axes intersect precisely at a point. When the first and second driving units drive in the same direction, the first and second transmission components simultaneously apply equal torques in the same direction to both sides of the wrist bracket, causing the wrist bracket to rotate relative to the swing bracket around the second axis, completing a bending motion (pitch). When the two driving units drive in opposite directions, the transmission components on both sides generate torques in opposite directions on the wrist bracket. This torque difference is controlled by... The wrist brace transmits power to the swing brace, forcing the swing brace, along with the wrist brace, to rotate relative to the upward-rotating brace around the first axis, thus achieving a swaying motion (swinging). Since bending only involves a partial rotation of the wrist brace around the second axis, while swaying drives the entire swing brace to rotate around the first axis, the two movements are independent and do not interfere with each other, making the kinematic model simple and the control precision high. It is especially suitable for dexterous operation and coordination in bionic and human-machine collaborative scenarios. Furthermore, through the reasonable routing path of the first and second tendon cable through holes, the length change of the tendon cable during wrist movement is minimal, ensuring stable force transmission efficiency and transmission precision, and extending the service life of the tendon cable. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the internal structure of the wrist body of the present invention; Figure 3 This is a schematic diagram of the structure of the wrist body of the present invention; Figure 4 This is a schematic diagram of the structure of the rotating bracket, the swing bracket, and the wrist bracket of the present invention. Figure 5 This is a schematic diagram of the wrist support structure of the present invention; Figure 6 This is a schematic diagram of the structure of the first transmission component of the present invention; Figure 7This is a schematic diagram of the structure of the rotating bracket and the swing bracket of the present invention. In the diagram: 1. Wrist body; 2. Rotating support; 3. Swinging support; 4. Wrist support; 5. Mounting cavity; 6. Cable unit; 7. First tendon cable through hole; 8. Second tendon cable through hole; 9. First drive unit; 10. Second drive unit; 11. First transmission component; 12. Second transmission component; 13. Cable harness; 14. Cable threading channel; 15. Positioning protrusion; 16. Positioning groove; 17. Connecting protrusion; 18. Drive protrusion; 19. First connecting part; 20. Second connecting part; 21. Spherical connecting part; 22. Mounting end face; 23. Mounting groove; 24. First rotating shaft; 25. Second rotating shaft; 26. First rotating groove; 27. Second rotating groove; Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be understood that although the terms upper, middle, lower, top, one end, etc., appear in this document to describe various elements, these elements are not limited by these terms. These terms are only used to distinguish the elements from each other for ease of understanding, and are not used to define any directional or sequential restrictions.

[0021] like Figure 1-7 As shown, a two-degree-of-freedom robot wrist includes a wrist body 1, a rotating bracket 2 fixedly mounted on the wrist body 1, a swing bracket 3 rotatably mounted on the rotating bracket 2 about a first axis, and a wrist bracket 4 rotatably mounted on the swing bracket 3 about a second axis. When the rotating bracket is raised, the first axis and the second axis are perpendicular to each other and intersect at the same point, which is also the swing rotation center of the swing bracket 3. This achieves the spatial convergence of the two-degree-of-freedom rotation axes, which is highly similar to the structure of the human wrist joint and conforms to the principles of bionics. This makes the movement mode of the robot wrist more natural and smooth. Since the axes are at the same point, there is no offset when the wrist bends and swings, avoiding the generation of additional torque, effectively reducing the motion coupling effect. Moreover, the structure is compact, reducing the error accumulation caused by joint gaps and improving the overall control performance.

[0022] The swing bracket 3 has a first rotating shaft 24 arranged along a first axis and a second rotating shaft 25 arranged along a second axis. The rotating bracket 2 has a first rotating groove 26 for the first rotating shaft 24 to be inserted into, and the wrist bracket 4 has a second rotating groove 27 for the second rotating shaft 25 to be inserted into.

[0023] Specifically, the wrist body 1 has an installation cavity 5, and the installation cavity 5 has several pull rope units 6 for connecting tendon ropes. The wrist body 1 has several first tendon rope through holes 7 that connect to the installation cavity 5, and the wrist support 4 has several second tendon rope through holes 8. Through the reasonable routing path of the first tendon rope through holes 7 and the second tendon rope through holes 8, the length change of the tendon rope is minimized during wrist movement, ensuring stable force transmission efficiency and transmission accuracy, and extending the service life of the tendon rope.

[0024] The rope-pulling unit 6 can be configured to have a telescopic device at the front end of the drive motor.

[0025] Furthermore, the wrist body 1 is provided with a first drive unit 9 and a second drive unit 10. The output end of the first drive unit 9 is connected to a first transmission component 11, and the output end of the second drive unit 10 is connected to a second transmission component 12. The first transmission component 11 and the second transmission component 12 are respectively connected to both sides of the wrist support 4. The first drive unit 9 and the second drive unit 10 can be electric cylinders. The first drive unit 9 and the second drive unit 10 extend and retract to drive the first transmission component 11 and the second transmission component 12 to move.

[0026] The first drive unit 9 and the second drive unit 10 apply driving forces to both sides of the wrist support 4 through the first transmission component 11 and the second transmission component 12. When the first transmission component 11 and the second transmission component 12 drive in the same direction, the wrist support 4 bends, causing the wrist support 4 to rotate relative to the wrist body 1 around the second axis, completing the bending action (pitch). When the first transmission component 11 and the second transmission component 12 drive in opposite directions, the two transmission components generate torques in opposite directions on the wrist support 4. This torque difference is transmitted to the swing support 3 through the wrist support 4, forcing the swing support 3 and the wrist support 4 to rotate together around the first axis relative to the upward rotation support 2, thereby realizing the yaw action (swing). Since bending only involves the partial rotation of the wrist support 4 around the second axis, while yaw drives the entire swing support 3 to rotate around the first axis, the two movements are independent of each other and do not interfere with each other, making the kinematic model simple and the control precision high. It is especially suitable for dexterous operation and coordination in bionic and human-machine collaboration scenarios.

[0027] The first axis is set along the X-axis, and the second axis is set along the Y-axis.

[0028] like Figure 1 , Figure 2 , Figure 4 , Figure 5As shown, as a further explanation of the implementation of the first tendon cord through hole 7 and the second tendon cord through hole 8, the first tendon cord through hole 7 is arranged at intervals along the first axis direction, and the second tendon cord through hole 8 is arranged at intervals along the second axis direction, so that the multiple tendon cords are arranged in a neat and orderly manner inside the wrist, effectively avoiding cross-entanglement and mutual interference, and ensuring that the length change of each tendon cord tends to be consistent and minimized during the bending or swinging of the wrist, which significantly improves the stability of force transmission and control accuracy.

[0029] Specifically, the rotating bracket 2 has a cable tie frame 13 extending toward the wrist bracket 4, and the cable tie frame 13 is located between the first tendon ligament through hole 7 and the second tendon ligament through hole 8. The cable tie frame 13 can provide precise path constraint and guidance for the tendon ligament, effectively preventing the tendon ligament from shifting, loosening or interfering with the surrounding structure when the wrist is bent or tilted, ensuring that the length change of each tendon ligament is stable and controllable, thereby significantly improving the repeatability of force transmission and the consistency of control response. The cable tie frame 13 also plays a role in protecting the tendon ligament and simplifying the threading assembly, making the overall structure more compact and reliable, and without affecting the free range of wrist movement.

[0030] Furthermore, the swing bracket 3 has a threading channel 14 extending along the thickness direction, and the wire harness 13 is inserted into the threading channel 14, so that the tendon cord is fully guided when passing through the swing bracket 3, which effectively avoids friction and wear between the tendon cord and the edge of the swing bracket 3, and ensures the stability and controllability of the tendon cord path during wrist movement, further improving the repeatability and control accuracy of force transmission.

[0031] Preferably, the wrist body 1 is provided with a positioning protrusion 15, the first tendon cord through hole 7 is provided in the positioning protrusion 15, and the rotating bracket 2 is provided with a positioning groove 16 for the positioning protrusion 15 to be inserted, which improves the accuracy of the installation and positioning of the rotating bracket 2, and also enhances the connection rigidity between the wrist body 1 and the rotating bracket 2, effectively resisting the impact and vibration during the movement process and improving the structural stability.

[0032] like Figures 3 to 7 As shown, as a further explanation of the implementation of the wrist support 4 in conjunction with the first transmission member 11 and the second transmission member 12, the side wall of the wrist support 4 away from the hinge center of the swing support 3 has a connecting protrusion 17 extending horizontally along the first axis, and the connecting protrusion 17 is provided with a driving protrusion 18 for connecting the first transmission member 11 and the second transmission member 12, so that the force application points of the first transmission member 11 and the second transmission member 12 are far away from the hinge center of the wrist support 4, increasing the driving arm, thereby obtaining a larger driving torque under the same driving force, improving the load capacity and response speed of the wrist, and separating the transmission connection point from the hinge center axially to avoid structural interference, making the force line distribution of the dual drive unit more reasonable, effectively ensuring the accurate realization of the two-degree-of-freedom decoupled motion, and further enhancing the overall compactness and transmission efficiency of the wrist.

[0033] Furthermore, the drive protrusion 18 is spherically shaped and connects to the first transmission member 11 and the second transmission member 12. The first transmission member 11 and the second transmission member 12 are provided with spherical connecting parts 21. The actuating ends of the first drive unit 9 and the second drive unit 10 are connected to the first transmission member 11 and the second transmission member 12 through the spherical connecting parts 21. By setting the drive protrusion 18 as a spherical structure and cooperating with the spherical connecting parts 21 on the first transmission member 11 and the second transmission member 12, a ball-joint flexible transmission connection is formed. This adaptively compensates for changes in the angle and position of the transmission members during wrist flexion and swinging movements, avoids jamming and additional stress caused by rigid connections, significantly reduces the requirements for the processing and assembly accuracy of parts, and effectively improves the linearity of force transmission and the consistency of control response, further enhancing the smoothness of the two-degree-of-freedom decoupled motion.

[0034] In addition, both the first transmission component 11 and the second transmission component 12 include a first connecting part 19 connected to the actuating end of the first drive unit 9 and the second drive unit 10, and a second connecting part 20 connected to the wrist support 4. The first connecting part 19 and the second connecting part 20 have a preset bending angle, so that the first transmission component 11 and the second transmission component 12 are set in a bent rod shape. Since the flexion, extension and lateral movement of the human wrist does not transmit torque in a straight line, but is achieved by the oblique course of tendons such as the radial flexor carpi radialis and the ulnar flexor carpi ulnaris, the bent rod shape of the first transmission component 11 and the second transmission component 12 changes the force transmission direction of the drive arm from a straight line to a broken line, simulating the envelope path of the tendon around the carpal bones, so that the force direction of the drive unit is closer to the physiological traction direction of human muscles.

[0035] like Figures 1 to 3 As shown, as a further explanation of the installation of the first drive unit 9 and the second drive unit 10, both the first drive unit 9 and the second drive unit 10 have a mounting end face 22 facing the wrist body 1. The first transmission member 11 and the second transmission member 12 are rotatably connected to the mounting end face 22, and the wrist body 1 has concave mounting grooves 23 on both sides. The first drive unit 9 and the second drive unit are disposed in the mounting grooves 23. By embedding the first drive unit 9 and the second drive unit 10 into the concave mounting grooves 23 on both sides of the wrist body 1, and making the transmission member directly rotatably connected to the mounting end face 22 of the drive unit, the space occupied by the outward protrusion of the drive mechanism is effectively reduced, making the overall structure more compact and flat, which is conducive to integrated installation in a narrow arm body space.

[0036] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A two-degree-of-freedom robotic wrist, comprising a wrist body (1), characterized in that, A rotating bracket (2) is fixedly provided on the wrist body (1), a swing bracket (3) is rotatably mounted on the rotating bracket (2) around a first axis, and a wrist bracket (4) is rotatably mounted on the swing bracket (3) around a second axis. The first axis and the second axis are perpendicular to each other. The wrist body (1) is provided with an installation cavity (5), and the installation cavity (5) is provided with a plurality of pull rope units (6) for connecting tendon ropes. The wrist body (1) is provided with a plurality of first tendon rope through holes (7) that connect to the installation cavity (5), and the wrist support (4) is provided with a plurality of second tendon rope through holes (8). The wrist body (1) is provided with a first drive unit (9) and a second drive unit (10). The output end of the first drive unit (9) is connected to a first transmission component (11), and the output end of the second drive unit (10) is connected to a second transmission component (12). The first transmission component (11) and the second transmission component (12) are respectively connected to the two sides of the wrist support (4). The first drive unit (9) and the second drive unit (10) apply driving force to both sides of the wrist support (4) through the first transmission member (11) and the second transmission member (12). When the first transmission member (11) and the second transmission member (12) drive in the same direction, the wrist support (4) bends relative to the wrist body (1). When the first transmission member (11) and the second transmission member (12) drive in opposite directions, the wrist support (4) swings relative to the wrist body (1).

2. The dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The first tendon cord through holes (7) are arranged at intervals along the first axis direction, and the second tendon cord through holes (8) are arranged at intervals along the second axis direction.

3. The dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The rotating bracket (2) has a cable tie frame (13) extending toward the wrist bracket (4), and the cable tie frame (13) is located between the first tendon cord through hole (7) and the second tendon cord through hole (8).

4. The dual-degree-of-freedom robotic wrist according to claim 3, characterized in that: The swing bracket (3) has a threading channel (14) that runs through the thickness direction, and the wire harness (13) is inserted into the threading channel (14).

5. A dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The wrist body (1) is provided with a positioning protrusion (15), the first tendon cord through hole (7) is provided in the positioning protrusion (15), and the rotating bracket (2) is provided with a positioning groove (16) for the positioning protrusion (15) to be inserted.

6. The dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The wrist support (4) has a connecting protrusion (17) extending horizontally along the first axis on the side wall opposite to the hinge center of the swing support (3), and the connecting protrusion (17) is provided with a driving protrusion (18) for connecting the first transmission member (11) and the second transmission member (12).

7. A dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The first transmission member (11) and the second transmission member (12) each include a first connecting part (19) connected to the actuating end of the first drive unit (9) and the second drive unit (10), and a second connecting part (20) connected to the wrist support (4). The first connecting part (19) and the second connecting part (20) have a preset bending angle, so that the first transmission member (11) and the second transmission member (12) are arranged in a bent rod shape.

8. A dual-degree-of-freedom robotic wrist according to claim 6, characterized in that: The driving protrusion (18) is spherically shaped and connects the first transmission member (11) and the second transmission member (12). The first transmission member (11) and the second transmission member (12) are provided with spherical connecting parts (21). The actuating ends of the first driving unit (9) and the second driving unit (10) are connected to the first transmission member (11) and the second transmission member (12) through the spherical connecting parts (21).

9. A dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The first axis and the second axis intersect at the same point, and the intersection point is the swing rotation center of the swing bracket (3).

10. A dual-degree-of-freedom robotic wrist according to claim 1, characterized in that: The first drive unit (9) and the second drive unit (10) each have a mounting end face (22) facing the wrist body (1). The first transmission member (11) and the second transmission member (12) are rotatably connected to the mounting end face (22). The wrist body (1) has concave mounting grooves (23) on both sides. The first drive unit (9) and the second drive unit are disposed in the mounting grooves (23).

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