Rigid-flexible coupled dexterous hand

Abstract

The invention discloses a rigid-flexible coupled dexterous hand which comprises a palm base and a plurality of finger units. Each finger unit comprises a finger base part, a fingertip module and a plurality of knuckles, and the finger base parts are fixedly mounted on the palm base; the fingertip module comprises a fingertip, a tendon, a fingertip base and a fingertip fixing frame, the tendon and the fingertip are made of flexible elastic materials, the fingertip is installed on the fingertip fixing frame, and the tendon is used for connecting the fingertip fixing frame and the fingertip base; for any finger unit, each knuckle of the finger unit comprises a knuckle support and a knuckle steering engine fixedly installed on the knuckle support, and a finger base steering engine is further fixedly installed on the finger base. And according to the sequence from the finger base to the fingertip, the finger base steering engine is used for controlling the movement of the first knuckle, the last knuckle steering engine is used for controlling the movement of the fingertip base, and the other knuckle steering engines are used for controlling the movement of the next knuckle.

Description

Technical Field

[0001] The present invention relates to the technical field of dexterous hands, and in particular to a rigid-flexible coupled dexterous hand. Background Art

[0002] As an important end effector of humanoid robots, compared with traditional manipulators that can only perform specific tasks, dexterous hands have the advantages and characteristics of high flexibility and strong versatility. They can endow robots with more precise operation capabilities and stronger environmental adaptability, and are an important way to promote humanoid robots towards general artificial intelligence. At present, the research on dexterous hands mainly focuses on dexterous hands composed of rigid materials and soft dexterous hands composed of artificial muscles.

[0003] Among them, dexterous hands composed of rigid materials often adopt a cable-driven method. The cable-driven dexterous hand often uses a motor as the driving device, and drives the cable through gear transmission or pulley transmission in cooperation with the motor to control each joint of the dexterous hand, and can achieve complex and high-precision motion control of the dexterous hand. Although the dexterous hand composed of rigid materials has the advantages of high energy conversion efficiency and good force control effect, its rigid structure has potential safety hazards in the process of manipulating fragile objects and performing human-machine interaction, and it is difficult to be applied to daily life tasks.

[0004] The soft dexterous hand composed of artificial muscles often adopts gas drive. The gas drive controls the opening and closing force and speed of the fingers by adjusting the air pressure, and has the advantages of fast response speed and simple structure. Although the soft dexterous hand composed of artificial muscles has the characteristics of convenient energy storage, good compliance, high safety, etc., its control dynamic performance is poor.

[0005] Therefore, there is an urgent need to design a rigid-flexible coupled dexterous hand that can balance control dynamic performance and safety performance to improve the adaptability to a wider range of application scenarios and more complex tasks. Summary of the Invention

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A rigid-flexible coupled dexterous hand includes a palm base and a plurality of finger units;

[0008] Each finger unit includes a finger base, a fingertip module and a plurality of phalanges. The finger base is fixedly installed on the palm base;

[0009] The fingertip module includes a fingertip, a tendon, a fingertip base and a fingertip fixing frame. The tendon and the fingertip are made of a flexible elastic material. The fingertip is installed on the fingertip fixing frame, and the tendon is used to connect the fingertip fixing frame and the fingertip base;

[0010] For any finger unit, each phalanx includes a phalanx bracket and a phalanx servo fixedly installed on the phalanx bracket, and a finger base servo is also fixedly installed on the finger base;

[0011] In the order from the finger base to the fingertip, the finger base servo is used to control the movement of the first phalanx, the last phalanx servo is used to control the movement of the fingertip base, and other phalanx servos are used to control the movement of the next phalanx.

[0012] In some embodiments, for any finger unit, the multiple phalanges include a first phalanx, a second phalanx and a third phalanx. The first phalanx includes a first phalanx servo and a first phalanx bracket, the second phalanx includes a second phalanx servo and a second phalanx bracket, and the third phalanx includes a third phalanx servo and a third phalanx bracket.

[0013] In some embodiments, the number of finger units is five, including one thumb unit and four ordinary finger units with the same structure.

[0014] In some embodiments, for the thumb unit, the finger base servo is used to control the flexion and extension movement of the first phalanx, the first phalanx servo is used to control the rotation movement of the second phalanx, the second phalanx servo is used to control the flexion and extension movement of the third phalanx, and the third phalanx servo is used to control the flexion and extension movement of the fingertip base.

[0015] In some embodiments, for the thumb unit, the directions of the output shafts of the finger base servo, the second phalanx servo and the third phalanx servo are all perpendicular to the direction when the thumb unit is straightened, and the direction of the output shaft of the first phalanx servo is the same as the direction when the thumb unit is straightened;

[0016] Moreover, the output shaft of the finger base servo is fixedly connected to the bottom side of the first phalanx bracket, the output shaft of the second phalanx servo is fixedly connected to the bottom side of the third phalanx bracket, and the output shaft of the third phalanx servo is fixedly connected to the bottom side of the fingertip base, so as to realize the control of the flexion and extension movement;

[0017] The output shaft of the first phalanx servo is fixedly connected to the bottom surface of the second phalanx bracket, so as to realize the control of the rotation movement.

[0018] In some embodiments, for any ordinary finger unit, the finger base servo is used to control the flexion and extension movement of the first phalanx, the first phalanx servo is used to control the lateral swing movement of the second phalanx, the second phalanx servo is used to control the flexion and extension movement of the third phalanx, and the third phalanx servo is used to control the flexion and extension movement of the fingertip base.

[0019] In some embodiments, for any ordinary finger unit, the direction of the output shaft of the finger base servo is the same as the direction when the ordinary finger unit is straightened, and the directions of the output shafts of the first phalanx servo, the second phalanx servo, and the third phalanx servo are all perpendicular to the direction when the ordinary finger unit is straightened;

[0020] The output shaft of the finger base servo is fixedly connected with a first bevel gear, and the bottom end of the first phalanx bracket is fixedly connected with a second bevel gear. The first bevel gear and the second bevel gear are engaged with each other and the included angle between them is 90 degrees, so as to transfer the movement of the servo output shaft to the first phalanx to control the flexion and extension movement of the first phalanx;

[0021] The output shaft of the first phalanx servo is fixedly connected to the middle of the side surface of the second phalanx bracket to control the lateral swing movement of the second phalanx;

[0022] The output shaft of the second phalanx servo is fixedly connected to the bottom side surface of the third phalanx bracket to control the flexion and extension movement of the third phalanx;

[0023] The output shaft of the third phalanx servo is fixedly connected to the bottom side surface of the fingertip base to control the flexion and extension movement of the fingertip base.

[0024] In some embodiments, a plurality of palm base servos are further installed on the palm base, and the plurality of palm base servos correspond to the plurality of finger units one by one;

[0025] Each palm base servo is provided with a steel wire, and a wire winding wheel is fixedly installed on the output shaft of the palm base servo;

[0026] One end of the steel wire is wound around the wire winding wheel, and the other end is fixedly connected to the side of the fingertip fixing frame facing the palm base;

[0027] The palm base servo is used to control the bending of the tendon through the steel wire.

[0028] Compared with the prior art, the beneficial effects of the rigid-flexible coupled dexterous hand provided by the present invention are as follows: Aiming at the technical defect that it is difficult for the existing dexterous hands to balance the control dynamic performance and safety performance, a unique design is adopted in the rigid-flexible coupling method, combining rigid phalanges and flexible fingertips and tendons, effectively weighing the control dynamic performance and safety performance; thus making this dexterous hand have better compliance and higher safety performance compared with the dexterous hand based on rigid materials, and have higher control precision and better dynamic control performance compared with the soft dexterous hand based on artificial muscles. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the rigid-flexible coupled dexterous hand provided by the present invention;

[0030] Figure 2 Schematic diagram of a normal finger unit;

[0031] Figure 3 Schematic diagram of a thumb finger unit;

[0032] Figure 4 Schematic diagram of the palm base servo and related structures;

[0033] Figure 5 Schematic diagram of the connection between two phalanges.

[0034] Explanation of the reference numerals in the drawings:

[0035] 1. First phalanx; 11. First phalanx bracket; 12. First phalanx servo; 13. Second bevel gear; 2. Second phalanx; 21. Second phalanx bracket; 22. Second phalanx servo; 23. Output shaft; 24. Hexagon bolt; 3. Third phalanx; 31. Third phalanx bracket; 32. Third phalanx servo; 4. Palm base; 41. Palm base servo; 42. Steel wire; 43. Winding wheel; 5. Finger base servo; 51. First bevel gear; 6. Finger tip; 7. Tendon; 8. Finger tip base; 9. Finger tip fixing bracket; 10. Normal finger unit; 20. Thumb unit. Specific embodiments

[0036] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the following further elaborates how the present invention is implemented in combination with specific embodiments.

[0037] Referring to Figure 1 and Figure 2 As shown, in a specific embodiment, the present invention provides a rigid-flexible coupled dexterous hand, including a palm base 4 and a plurality of finger units; each finger unit includes a finger base, a finger tip module and a plurality of phalanges, and the finger base is fixedly installed on the palm base 4; the finger tip module includes a finger tip 6, a tendon 7, a finger tip base 8 and a finger tip fixing bracket 9, the tendon 7 and the finger tip 6 are made of flexible elastic materials, the finger tip 6 is installed on the finger tip fixing bracket 9, and the tendon 7 is used to connect the finger tip fixing bracket 9 and the finger tip base 8; for any finger unit, each of its phalanges includes a phalanx bracket and a phalanx servo fixedly installed on the phalanx bracket, and a finger base servo 5 is also fixedly installed on the finger base; in the order from the finger base to the finger tip 6, the finger base servo 5 is used to control the movement of the first phalanx, the last phalanx servo is used to control the movement of the finger tip base 8, and other phalanx servos are used to control the movement of the next phalanx.

[0038] In addition, referring to Figure 2As shown, both ends of the tendon 7 can be connected to the fingertip base 8 and the fingertip fixing frame 9 on the upper and lower sides through straight notches. The fingertip 6 can be attached to the fingertip fixing frame 9 with glue, thus realizing the coupling of the rigid mechanism and the flexible mechanism. The tendon 7 and the fingertip 6 are made of flexible elastic materials, such as being cast with silicone; the rigid mechanisms such as the fingertip base 8 and the phalanx bracket can be obtained by 3D printing technology.

[0039] Preferably, for any finger unit, the multiple phalanges include the first phalanx 1, the second phalanx 2 and the third phalanx 3. The first phalanx 1 includes the first phalanx servo 12 and the first phalanx bracket 11. The second phalanx 2 includes the second phalanx servo 22 and the second phalanx bracket 21. The third phalanx 3 includes the third phalanx servo 32 and the third phalanx bracket 31.

[0040] Preferably, the number of finger units is five, including one thumb unit 20 and four ordinary finger units 10 with the same structure.

[0041] Further referring to Figure 3 As shown, for the thumb unit 20, the finger base servo 5 is used to control the flexion and extension movement of the first phalanx 1. The first phalanx servo 12 is used to control the rotation movement of the second phalanx 2. The second phalanx servo 22 is used to control the flexion and extension movement of the third phalanx 3. The third phalanx servo 32 is used to control the flexion and extension movement of the fingertip base 8.

[0042] Specifically, for the thumb unit 20, the output shafts of the finger base servo 5, the second phalanx servo 22 and the third phalanx servo 32 are all perpendicular to the direction when the thumb unit 20 is straightened. The output shaft of the first phalanx servo 12 is in the same direction as the direction when the thumb unit 20 is straightened. And, the output shaft of the finger base servo 5 is fixedly connected to the bottom side of the first phalanx bracket 11. The output shaft of the second phalanx servo 22 is fixedly connected to the bottom side of the third phalanx bracket 31. The output shaft of the third phalanx servo 32 is fixedly connected to the bottom side of the fingertip base 8, so as to realize the control of the flexion and extension movement. The output shaft of the first phalanx servo 12 is fixedly connected to the bottom surface of the second phalanx bracket 21, so as to realize the control of the rotation movement.

[0043] Referring to Figure 2 As shown, for any ordinary finger unit 10, the finger base servo 5 is used to control the flexion and extension movement of the first phalanx 1. The first phalanx servo 12 is used to control the lateral swing movement of the second phalanx 2. The second phalanx servo 22 is used to control the flexion and extension movement of the third phalanx 3. The third phalanx servo 32 is used to control the flexion and extension movement of the fingertip base 8.

[0044] Specifically, for any ordinary finger unit 10, the direction of the output shaft of the finger base servo 5 is consistent with the direction when the ordinary finger unit 10 is straightened, and the directions of the output shafts of the first phalanx servo 12, the second phalanx servo 22, and the third phalanx servo 32 are all perpendicular to the direction when the ordinary finger unit 10 is straightened; the output shaft of the finger base servo 5 is fixedly connected with a first bevel gear 51, and the bottom end of the first phalanx bracket 11 is fixedly connected with a second bevel gear 13. The first bevel gear 51 and the second bevel gear 13 are engaged with each other and the included angle between them is 90 degrees, so as to transfer the movement of the servo output shaft to the first phalanx 1 to control the flexion and extension movement of the first phalanx 1; the output shaft of the first phalanx servo 12 is fixedly connected to the middle of the side surface of the second phalanx bracket 21 to control the lateral swing movement of the second phalanx 2; the output shaft of the second phalanx servo 22 is fixedly connected to the bottom side surface of the third phalanx bracket 31 to control the flexion and extension movement of the third phalanx 3; the output shaft of the third phalanx servo 32 is fixedly connected to the bottom side surface of the fingertip base 8 to control the flexion and extension movement of the fingertip base 8.

[0045] It can be seen that the transmission design of this rigid-flexible coupled dexterous hand refers to the structure and function of the human hand, and two different transmission design methods are adopted for the thumb and ordinary fingers. Since the thumb of the human hand is located on the front side of the other four fingers and has the ability of opposition, it can perform opposition movement of approaching each other or opposition movement of moving away from each other with another finger or multiple fingers. Therefore, the thumb occupies an extremely important position among all parts of the human hand.

[0046] In this embodiment, the realization of the opposition ability of the thumb unit 20 is completed by the collaborative work of the rotational degree of freedom of the thumb unit 20 and the remaining flexion and extension degrees of freedom. Multiple flexion and extension degrees of freedom jointly realize the function of the thumb bending, while the rotational degree of freedom realizes the function similar to the palm joint in the human hand by the second phalanx 2 rotating around the output shaft of the first phalanx servo 12, expanding the movement range of the thumb unit 20 and enabling the thumb unit 20 to have the ability to complete opposition movement and anti-opposition movement.

[0047] For the ordinary finger unit 10, in order to improve the structural compactness, the transmission between the finger base servo 5 and the first phalanx bracket 11 is realized through two bevel gears, so as to realize the movement transmission of the flexion and extension degrees of freedom within a limited space. Multiple flexion and extension degrees of freedom jointly realize the function of finger bending; while the lateral swing degree of freedom realizes the lateral swing movement of the finger on the horizontal plane by the second phalanx 2 rotating around the output shaft of the first phalanx servo 12, making the movement of the dexterous hand finger more flexible and increasing the redundancy of the dexterous hand degrees of freedom at the same time.

[0048] Through the analysis of the human hand structure and finger function, this rigid-flexible coupled dexterous hand designs two different finger transmission methods, enabling the dexterous hand to have the ability to complete opposition movement and anti-opposition movement.

[0049] Further referring to Figure 4 as shown, preferably, a plurality of palm base servos 41 are further installed on the palm base 4, and the plurality of palm base servos 41 correspond to the plurality of finger units one by one; each palm base servo 41 is configured with a steel wire 42, and a wire winding wheel 43 is fixedly installed on the output shaft of the palm base servo 41; one end of the steel wire 42 is wound around the wire winding wheel 43, and the other end is fixedly connected to one side of the fingertip fixing frame 9 facing the palm base 4; the palm base servo 41 is used to control the bending of the tendon 7 through the steel wire 42.

[0050] In addition, the steel wire 42 can pass through the preset pores on the fingertip base 8 and then be fixedly connected to the fingertip fixing frame 9 to limit the movement range of the steel wire 42. By driving the wire winding wheel 43 to rotate forward or backward through the output shaft of the palm base servo 41, the stretching movement of the steel wire 42 can be controlled; when the steel wire 42 pulls the tendon 7, the tendon 7 is stressed and bent; when the pulling force of the steel wire 42 on the tendon 7 decreases, the tendon 7 returns under its own elastic force. In this way, reliable control of the fingertip bending degree of freedom is achieved, meeting the design requirements of the dexterous hand for compliance and safety performance.

[0051] It can be seen that in this embodiment, for any one finger, five servos are configured: the palm base servo 41, the finger base servo 5 and three knuckle servos. That is, each finger has five degrees of freedom, so that the rigid-flexible coupled dexterous hand exhibits kinematic characteristics and configurations similar to those of the human hand, achieving the purpose of dexterous movement.

[0052] In addition, in combination with the requirements of the dexterous hand for control accuracy and control dynamic performance, the rigid-flexible coupled dexterous hand adopts a drive design with a simple structure and integrated into the dexterous hand. The servo can adopt the HTS-20L type servo. Referring to Figure 5 as shown, when the servo is structurally connected to the driven structure, taking the second knuckle servo 22 of the thumb unit 20 and the third knuckle bracket 31 as an example, a threaded hole is opened at the lower end of the third knuckle bracket 31, and the third knuckle bracket 31 is fixed to the output shaft 23 of the second knuckle servo 22 through a hexagon bolt 24, so as to transmit the rotation of the output shaft 23 to the third knuckle bracket 31. In this way, the offset angle of each knuckle on the servo surface can be accurately controlled, and the movement transmission between the knuckles at all levels is simply and efficiently realized to achieve the opposition ability of the dexterous hand. Except for special cases (such as the finger base servo 5 of the ordinary finger unit 10 and the first knuckle bracket 11 are driven by two bevel gears), most of the servos and the structures they drive can adopt a similar way to realize the movement transmission.

[0053] The hardware control system of the rigid-flexible coupled dexterous hand can be composed of a control module, a communication module, an I / O module, a power supply module, a sensor module and a host computer. The control module can adopt the stm32f103 type microcontroller; the sensor module can include multiple visual and tactile sensors, which are respectively arranged at different positions of the dexterous hand. The control module is connected to each servo and sensor through serial communication respectively, and is physically connected to the host computer through USB. Using the serial port as the communication method, it sends the current motion states of each servo to the host computer, and at the same time receives the control instructions sent by the host computer to achieve the closed-loop control of the dexterous hand. The I / O module can send the control instructions of the remote controller to the control module to achieve the human-computer interaction function of the dexterous hand.

[0054] In summary, for the technical defect that the existing dexterous hands are difficult to balance the control dynamic performance and safety performance, the rigid-flexible coupled dexterous hand provided by the present invention adopts a unique design in the rigid-flexible coupling method, combining the rigid phalanges and the flexible fingertips 6 and tendons 7, effectively weighing the control dynamic performance and safety performance; thus making the dexterous hand have better compliance and higher safety performance compared with the dexterous hand based on rigid materials, and having higher control precision and better dynamic control performance compared with the soft dexterous hand based on artificial muscles.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A rigid-flexible coupled dexterous hand, characterized in that: It comprises a palm base (4) and a plurality of finger units; Each finger unit comprises a finger base, a fingertip module and a plurality of finger joints, wherein the finger base is fixedly mounted on the palm base (4); The fingertip module comprises a fingertip (6), a tendon (7), a fingertip base (8) and a fingertip fixing frame (9), wherein the tendon (7) and the fingertip (6) are made of soft elastic material, the fingertip (6) is mounted on the fingertip fixing frame (9), and the tendon (7) is used to connect the fingertip fixing frame (9) and the fingertip base (8); For any finger unit, each finger joint includes a finger joint bracket and a finger joint servo fixedly mounted on the finger joint bracket, and a finger base servo (5) is also fixedly mounted on the finger base; In order from the finger base to the finger tip (6), the finger base servo (5) is used to control the movement of the first finger joint, the last finger joint servo is used to control the movement of the finger tip base (8), and the other finger joint servos are used to control the movement of the next finger joint.

2. The rigid-flexible coupled dexterous hand according to claim 1, characterized in that: For any finger unit, the plurality of finger joints include a first finger joint (1), a second finger joint (2) and a third finger joint (3); the first finger joint (1) includes a first finger joint servo (12) and a first finger joint bracket (11); the second finger joint (2) includes a second finger joint servo (22) and a second finger joint bracket (21); and the third finger joint (3) includes a third finger joint servo (32) and a third finger joint bracket (31).

3. The rigid-flexible coupled dexterous hand according to claim 2, characterized in that: The number of the finger units is five, including a thumb unit (20) and four common finger units (10) with the same structure.

4. The rigid-flexible coupled dexterous hand according to claim 3, characterized in that: For the thumb unit (20), the finger base servo (5) is used to control the flexion and extension movement of the first finger joint (1), the first finger joint servo (12) is used to control the rotational movement of the second finger joint (2), the second finger joint servo (22) is used to control the flexion and extension movement of the third finger joint (3), and the third finger joint servo (32) is used to control the flexion and extension movement of the fingertip base (8).

5. The rigid-flexible coupled dexterous hand according to claim 4, characterized in that: For the thumb unit (20), the directions of the output shafts of the finger base servo (5), the second knuckle servo (22) and the third knuckle servo (32) are all perpendicular to the direction of the thumb unit (20) when it is straightened, and the direction of the output shaft of the first knuckle servo (12) is consistent with the direction of the thumb unit (20) when it is straightened; Furthermore, the output shaft of the finger base servo (5) is fixedly connected to the bottom side of the first finger joint bracket (11), the output shaft of the second finger joint servo (22) is fixedly connected to the bottom side of the third finger joint bracket (31), and the output shaft of the third finger joint servo (32) is fixedly connected to the bottom side of the fingertip base (8), thereby realizing the control of flexion and extension movement; The output shaft of the first knuckle steering gear (12) is fixedly connected to the bottom surface of the second knuckle bracket (21), thereby realizing the control of the rotary motion.

6. The rigid-flexible coupled dexterous hand according to claim 3, characterized in that: For any common finger unit (10), the finger base servo (5) is used to control the flexion and extension movement of the first finger joint (1), the first finger joint servo (12) is used to control the lateral swing movement of the second finger joint (2), the second finger joint servo (22) is used to control the flexion and extension movement of the third finger joint (3), and the third finger joint servo (32) is used to control the flexion and extension movement of the fingertip base (8).

7. The rigid-flexible coupled dexterous hand according to claim 6, characterized in that: For any common finger unit (10), the direction of the output shaft of the finger base servo (5) is consistent with the direction of the common finger unit (10) when it is straightened, and the directions of the output shafts of the first finger joint servo (12), the second finger joint servo (22) and the third finger joint servo (32) are all perpendicular to the direction of the common finger unit (10) when it is straightened; The output shaft of the finger base servo (5) is fixedly connected to a first bevel gear (51), and the bottom end of the first finger joint bracket (11) is fixedly connected to a second bevel gear (13), and the first bevel gear (51) and the second bevel gear (13) are meshed with each other and the angle between the two is 90 degrees, so that the movement of the servo output shaft is transmitted to the first finger joint (1) to control the flexion and extension movement of the first finger joint (1); The output shaft of the first finger joint steering gear (12) is fixedly connected to the middle part of the side of the second finger joint bracket (21) to control the lateral swing movement of the second finger joint (2); The output shaft of the second finger joint servo (22) is fixedly connected to the bottom side of the third finger joint bracket (31) to control the flexion and extension movement of the third finger joint (3); The output shaft of the third finger joint servo (32) is fixedly connected to the bottom side of the fingertip base (8) to control the flexion and extension movement of the fingertip base (8).

8. The rigid-flexible coupled dexterous hand according to claim 1, characterized in that: The palm base (4) is also equipped with a plurality of palm base steering engines (41), and the plurality of palm base steering engines (41) correspond one-to-one to the plurality of finger units; Each palm base steering engine (41) is equipped with a steel wire (42), and a winding wheel (43) is fixedly mounted on the output shaft of the palm base steering engine (41); One end of the steel wire (42) is wound on the winding wheel (43), and the other end is fixedly connected to a side of the fingertip fixing frame (9) facing the palm base (4); The palm base steering engine (41) is used to control the bending of the tendon (7) through a steel wire (42).

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