CN212193202U - A gear differential underactuated three-joint manipulator - Google Patents

Abstract

The utility model discloses a gear differential underactuated three-joint manipulator, which comprises three-joint fingers; the three-joint fingers are arranged in 120 degrees, and each three-joint finger comprises a lower knuckle, a middle knuckle and an upper knuckle; the lower knuckle, the middle knuckle and the upper knuckle are connected through gear engagement, decoupling devices for realizing underactuation are respectively arranged on joint shafts at the joints of the lower knuckle, the middle knuckle and the upper knuckle, the lower knuckles of the three-knuckle fingers are respectively connected with a bevel gear transmission system through gears, the bevel gear transmission system is connected with a stepping motor, and the motion control of the three-knuckle fingers is realized by driving the bevel gear transmission system through the stepping motor. The utility model discloses simple structure, drive element are few, can the self-adaptation be grabbed the surface shape of object, and then realize harmless and reliable snatching.

Description

A gear differential underactuated three-joint manipulator

technical field

The utility model belongs to the technical field of mechanical production, in particular to a gear differential type under-actuated three-joint manipulator.

Background technique

With social development and technological advancement, robots are widely used in manufacturing, and the use of robots is even more attractive in space exploration where minimal maintenance requirements are emphasized. The manipulator or end effector is an important component of the robot. Initially, a single-degree-of-freedom gripper is used to complete some simple operations, such as welding, painting, assembly, etc. Although this type of gripper has a simple structure, convenient control, strong load capacity, High reliability, but this type of gripper has a single function and lacks flexibility, and can only work for specific tasks. Once the task changes, the end effector needs to be replaced. In this case, out of anthropomorphic imagination, multi-joint and multi-fingered dexterous hands have become the development trend of robot end effectors. However, due to the use of a large number of series joints, it leads to the disadvantages of complex structure, difficult control, poor load capacity and low reliability. Therefore, it is necessary to develop a grasping mechanism with a simple structure, few driving elements, and adaptively gripping the shape of the object.

Utility model content

The technical problem to be solved by the present invention is to provide a gear differential under-actuated three-joint manipulator in view of the above-mentioned deficiencies in the prior art, which has a simple structure, few driving elements, and can adapt to the surface shape of the object to be grasped, thereby realizing Non-destructive and reliable grabbing.

The utility model adopts the following technical solutions:

A gear differential underactuated three-joint manipulator comprises three three-joint fingers, the three three-joint fingers are arranged at 120°, and a decoupling device as an underactuated mechanism is respectively provided on the joint shaft of each three-joint finger; One end of the three three-joint fingers is respectively connected to the stepping motor through the drive transmission cylindrical gear through the bevel gear transmission system, and the bevel gear transmission system is driven by the stepping motor to realize the motion transmission and control of the three three-joint fingers.

Specifically, the three-joint finger includes an upper phalanx, a middle phalanx and a lower phalanx that are meshed and connected by gears in sequence; the upper phalanx and the middle phalanx are provided with upper phalanx drive gears at the joints, and the upper phalanx and the lower phalanx are provided at the joints. A middle finger drive gear is arranged, the other end of the lower finger is fixedly connected with the base finger support, and is connected with the bevel gear transmission system through the lower finger drive gear and the drive transmission cylindrical gear.

Further, a decoupling device is respectively provided on the joint shafts of the lower knuckle, the middle knuckle and the upper knuckle corresponding to the lower knuckle drive gear, the middle knuckle drive gear and the upper knuckle drive gear.

Further, the decoupling device at the lower knuckle is provided with a lower knuckle limiting device, the decoupling device at the middle knuckle is provided with a middle knuckle limiting device, and the decoupling device at the upper knuckle is provided with an upper knuckle limiting device. Knuckle limiter.

Further, the middle finger joint is provided with a middle finger joint transmission gear, the upper finger joint driving gear is meshed and connected with the middle finger joint driving gear through the middle finger joint transmission gear, and three lower finger joint transmission gears are sequentially arranged in the lower finger joint. In turn, the three lower knuckle transmission gears are meshed and connected with the middle knuckle drive gear.

Specifically, the bevel gear transmission system includes a first bevel gear, a second bevel gear, a third bevel gear and a fourth bevel gear; the second bevel gear and the third bevel gear are arranged in parallel, and the second bevel gear and the first bevel gear are meshed connection, the third bevel gear and the fourth bevel gear are meshingly connected; between the second bevel gear and the first bevel gear, between the first bevel gear and the fourth bevel gear, and between the fourth bevel gear and the third bevel gear The angles are all 120°.

Further, the input shaft of the stepping motor is connected with the first bevel gear, a drive cylindrical gear is arranged between the input shaft and the first bevel gear, the second bevel gear and the third bevel gear are connected by a connecting shaft, and the connecting shaft There is a second driving cylindrical gear on the upper part, the fourth bevel gear is connected with the third driving cylindrical gear through the connecting shaft, and each driving cylindrical gear passes through a driving transmission cylindrical gear and the lower knuckles set on the three three-joint fingers respectively. The drive gears are connected correspondingly.

Specifically, the decoupling device includes two friction plates that are in contact with each other, one side of the friction plates is connected with the shell of the three-joint finger, and the other side is connected with the adjusting screw through a spring.

Specifically, the stepper motor is arranged on the motor support, the bevel gear transmission system is arranged on three support plates, the motor support and the support plate are both fixed on the fixed plate, a holding plate is arranged above the support plate, and the holding plate Three base finger supports are arranged at intervals, and the base finger supports are respectively connected with the corresponding three-joint fingers.

Compared with the prior art, the present utility model at least has the following beneficial effects:

The utility model is a gear differential type under-actuated three-joint manipulator. Since the general fingers only need three joint knuckles to grasp objects, three three-joint fingers are used, and the distribution of 120° is beneficial to the uniform force of the entire manipulator. . The setting of the decoupling device at the joint can avoid the disordered state of movement of the entire finger during bending and straightening. The transmission system consists of 4 bevel gears meshing, which transmits power and also changes the direction of power.

Further, the setting of the three-joint finger structure is to meet the minimum finger joints required for grasping an object, so as to better grasp the object like a human finger.

Further, the decoupling device is a core device set under the structural design of the entire manipulator to complete the underactuated action. It can transfer the power to the next joint to continue the movement when the previous finger is still under a certain force.

Further, the differential gear structure is adopted between the joints, which can also meet a certain deceleration effect under the condition of achieving accurate transmission. Therefore, in addition to overcoming the frictional force of the decoupling device, a large torque can be obtained at the rear joints.

Further, the transmission system is arranged with four bevel gears according to a certain spatial structure. Mainly to transmit power to 3 three-jointed fingers distributed 120°. The four bevel gears are also equipped with power transmission spur gears. The structure of the entire bevel gear transmission system can not only meet the input of the power source, but also transmit the motion to the three mechanical fingers through the three power transmission cylindrical gears through transmission and changing the direction of movement.

Further, the purpose of the structural design of the decoupling device is to realize the core device of the underactuated structure, and the structure is simple. The friction force generated by the two friction plates under the pressure of the adjusting screw is the pre-tightening force that each joint needs to overcome when rotating, which can realize the sequential rotation of the joint fingers when grasping the object.

Further, the setting of each bracket of the whole manipulator can not only meet the spatial distribution of the bevel gear transmission system, but also meet the installation position of the motor and the installation of the 120° distribution of the three-joint fingers. It is the simple structure of the stent in the whole structure.

The utility model also discloses the operation method of the gear differential type under-actuated three-joint manipulator. The bevel gear transmission system rotates under the power input of the stepping motor, and at the same time changes the direction of the power, and transmits the power to the three-joint manipulator through the power transmission cylindrical gear. Knuckle fingers. At the same time, with the assistance of the limiting device and the decoupling device, the three-joint fingers transmit motion through the differential gear to realize the actions of opening and closing. The whole system is compact in structure and easy to operate.

To sum up, the utility model not only realizes the function of the manipulator, but also designs a novel transmission system structure and a differential gear transmission system in which the fingers rotate. By assembling different devices and structures, a new type of underactuated manipulator structure is designed. It not only meets the needs of the actual situation, but also proposes a new design concept and design method in the design of the manipulator structure. It is beneficial to the development of the entire manipulator industry and can promote the development of the robot structure.

The technical solutions of the present utility model will be described in further detail below through the accompanying drawings and embodiments.

Description of drawings

Fig. 1 is the structural representation of the utility model;

Fig. 2 is the finger model after the utility model has removed the base shell;

3 is a schematic diagram of the structure of the finger of the present invention;

4 is a schematic diagram of the rotating device of the present invention;

Fig. 5 is the gear transmission structure diagram of the utility model;

6 is a side view of the gear transmission structure of the present utility model;

7 is a schematic diagram of the spatial distribution position of the bevel gear of the present invention;

8 is a schematic diagram of the decoupling device of the present invention;

Fig. 9 is a kind of finger unfolding schematic diagram of the utility model;

10 is a schematic diagram of the adaptive grasping process of the present invention, wherein (a) is the initial position, (b) is the contact object of the lower knuckle, (c) is the contact object of the middle knuckle, (d) is the contact object of the upper knuckle .

Among them: 1. Motor support; 2. Stepper motor; 3. Base finger support; 4. Three-joint finger; 5. Retaining plate; 6. Supporting plate; 7. Fixed plate; 8. Input shaft; 9. Cone Tooth transmission system; 10. Drive transmission cylindrical gear; 11. Decoupling device; 12. Lower finger joint shaft; 13. Lower finger joint; 14. Middle finger joint shaft; 15. Middle finger joint; 16. Upper finger joint shaft; 17. Upper knuckle; 18-1. Lower knuckle drive gear; 18-2. Middle knuckle drive gear; 18-3. Upper knuckle drive gear; 19. Middle knuckle transmission gear; 20. Lower knuckle transmission gear; 23. 24. Second bevel gear; 25. Third bevel gear; 26. Fourth bevel gear; 27. Driving cylindrical gear; 28. Friction plate; 29. Spring; 30. Adjusting screw.

Detailed ways

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "horizontal", "upper", "lower", "front", "rear", "left", "right", The orientation or positional relationship indicated by "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one side", etc. is based on the drawings The orientation or positional relationship is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a reference to the present utility model. limits. In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first", "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

In the description of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it may be a movable connection, a fixed connection, It can also be a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

Please refer to FIG. 1 and FIG. 2 , a gear differential type underactuated three-joint manipulator of the present invention adopts gear transmission, adopts a decoupling device as an underactuated mechanism, and grasps through three three-joint fingers 4. The grasping method In order to grasp the inside of the finger, the whole mechanical finger has a small structure and simple control, which can meet the grasping and micro operation. include:

Motor support 1 , stepping motor 2 , base finger support 3 , three-joint fingers 4 , holding plate 5 , supporting plate 6 and fixing plate 7 . The motor support 1 and the three support plates 6 are respectively arranged on the fixed plate 7, the stepper motor 2 is arranged on the motor support 1, and the three support plates 6 are provided with a bevel gear transmission system 9. In the bevel gear transmission system 9 The transmission system is composed of four bevel gears with an indexing cone angle of 30°; the stepper motor 2 is connected to the bevel gear transmission system 9 through the input shaft 8; a holding plate 5 is provided above the support plate 6, and the three base fingers The supports 3 are arranged on the holding plate 5 at intervals and are used to fix the three three-joint fingers 4; the bevel gear transmission system 9 is respectively connected with the three three-joint fingers 4 through the decoupling device 11, and the stepping motor 2 passes through the bevel gear transmission system. 9. Control three three-joint fingers 4 for grasping operation.

Referring to FIG. 3 , the three-joint finger 4 includes an upper knuckle 17 , a middle knuckle 15 and a lower knuckle 13 . One end of the lower phalanx 13 is arranged on the base finger support 3, and is connected with the bevel gear transmission system 9 through the lower phalanx driving gear 18-1, and the other end is connected with one end of the middle phalanx 15 through the middle phalanx driving gear 18-2, The other end of the middle phalanx 15 is connected to the upper phalanx 17 through the upper phalanx drive gear 18-3, the middle phalanx 15 is provided with a middle phalanx transmission gear 19, and the upper phalanx drive gear 18-3 is connected to the upper phalanx through the middle phalanx transmission gear 19. The middle knuckle drive gear 18-2 is meshed and connected, the lower knuckle 13 is provided with three lower knuckle transmission gears 20 in turn, and the lower knuckle drive gear 18-1 is connected to the middle knuckle drive gear 18- 2 meshing connection; the lower knuckle drive gear 18-1 and the lower knuckle 13 are connected with the lower knuckle shaft 12, the middle knuckle drive gear 18-2 and the middle knuckle 15 are connected with the middle knuckle shaft 14, the upper knuckle drive gear 18- 3 and the upper knuckle 17 are connected with the upper knuckle joint shaft 16; the lower knuckle drive gears 18-1 corresponding to the three three-joint fingers 4 are respectively meshed with the bevel gear transmission system 9 through a drive transmission cylindrical gear 10, and the bevel gears are used. Transmission, the layout of three three-joint fingers and 4 positions are separated; in order to avoid the disordered state of movement of the whole finger during bending and straightening, a decoupling device is installed at the finger joints, the lower finger joint shaft 12, the middle finger joint shaft 14 A decoupling device 11 is respectively provided at the shaft 16 of the upper finger joint.

The finger has a certain adaptability of grasping shape. The finger parts are made of hard aluminum alloy, which has high strength, good rigidity and light weight, and the rotating pins are made of stainless steel. Brass sleeves are installed in the positioning holes of the fingers, and the brass sleeves can reduce the frictional resistance during the movement.

Please refer to FIG. 4 , the three base finger supports 3 are evenly distributed on the holding plate 5 at 120 degrees, and are respectively connected with a three-joint finger 4 , and the three three-joint fingers 4 of the underactuated manipulator can all wrap around the corresponding base finger The support 3 is relatively rotated, and can be rotated through 90 degrees, so that the three fingers rotate from the three-pointed center relative state to the state of touching the object to be grasped. The three base finger supports 3 fit together to form three included angles of 120 degrees in space, and cooperate with the 120-degree bevel gear transmission system to realize the movement and sequence control of the three three-joint fingers 4 .

5 and 6, the bevel gear transmission system 9 includes a first bevel gear 23, a second bevel gear 24, a third bevel gear 25, a fourth bevel gear 26 and a drive cylindrical gear 27; The three bevel gears 25 are arranged in parallel on the same shaft; the first bevel gear 23 is meshed with the second bevel gear 24 , the third bevel gear 25 is meshed with the fourth bevel gear 26 ; the second bevel gear 24 is meshed with the first bevel gear 23 The angle between the first bevel gear 23 and the fourth bevel gear 26, and the angle between the fourth bevel gear 26 and the third bevel gear 25 are all 120°, which realizes the synchronous movement of the three-joint fingers, and makes the three The joint fingers 4 are arranged at 120° in space. The three bevel gear shafts are respectively provided with cylindrical gears 27, which rotate together with the bevel gears.

A drive transmission spur gear 10 is provided between each three-joint finger 4 and the corresponding drive spur gear 27 on the bevel gear transmission system 9 , the drive spur gear 27 is meshed with the drive transmission spur gear 10 , and the three three-joint fingers 4 are The lower knuckle drive gear 18-1 is sequentially connected with the first bevel gear 23, the second bevel gear 24, the third bevel gear 25, and the fourth bevel gear 26 through the drive transmission spur gear 10 and the drive spur gear 27, respectively.

The input shaft 8 of the stepping motor 2 is connected with the first bevel gear 23 , a drive cylindrical gear 27 is arranged between the input shaft 8 and the first bevel gear 23 , and the second bevel gear 24 and the third bevel gear 25 are connected by The shaft is connected, the connecting shaft is provided with a second driving cylindrical gear 27, the fourth bevel gear 26 is connected to the third driving cylindrical gear 27 through the connecting shaft; the three driving cylindrical gears 27 are evenly distributed at 120°, and each driving cylindrical gear 27 are respectively connected with the lower knuckle drive gears 18-1 provided on the three three-joint fingers 4 through a drive transmission cylindrical gear 10 correspondingly in a meshing transmission connection. Four 120-degree transmission bevel gears are used, and the bevel gears and the corresponding driving cylindrical gears 27 are fixed together, and can rotate coaxially with the rotation between the bevel gears.

6 and 7, the stepping motor 2 is fixed on the motor support 1. After the input shaft 8 rotates, it drives the first bevel gear 23 and the driving cylindrical gear 27 fixed on the same shaft to rotate. The gear 23 meshes with the second bevel gear 24, so the second bevel gear 24 rotates with the first bevel gear 23 at the same time; since the taper angles of the first bevel gear 23 and the second bevel gear 24 are 30°, so the two The angle of intersection of the axes is 60°. The second bevel gear 24 and the third bevel gear 25 are on the same axis, so the third bevel gear 25 rotates coaxially with the second bevel gear 24, the fourth bevel gear 26 meshes with the third bevel gear 25, and the fourth bevel gear 26 also began to turn. Therefore, the first bevel gear 23 , the second bevel gear 24 , the third bevel gear 25 , and the fourth bevel gear 26 transmit the motion to the three three-joint fingers 4 through the three driving spur gears 27 to rotate.

Referring to FIG. 8, the decoupling device 11 includes a friction plate 28, a spring 29 and an adjustment screw 30; one side of the friction plate 28 is in contact with the shell of the three-joint finger, and the other side is connected with the adjustment screw 30 through the spring 29, and the adjustment screw 30 Compress the spring 29, so that the spring 29 produces a pre-tightening force; the spring 29 presses the friction plate 28, so that it is fixed and pressed with the knuckle shell. The three drive transmission spur gears 10 respectively transmit the motion to the three corresponding lower knuckle drive gears 8-1, and the decoupling device 11 fixed on the same joint shaft as the lower knuckle drive gear 8-1 rotates with the shaft, because the decoupling device 11 rotates with the shaft. There is friction between the friction plate in the coupling device and the shell of the lower knuckle 13. The lower knuckle 13 can rotate with the joint shaft 12 and the decoupling device 11 at the same time, which drives the lower knuckle 13 to rotate, and the lower knuckle 13 drives the whole Fingers turn.

Please refer to FIG. 3 and FIG. 9 , the rotation of the lower knuckle drive gear 8-1 drives the corresponding decoupling device 11 to rotate, the corresponding decoupling device 11 drives the lower knuckle 13 to rotate, and the lower knuckle 13 and the entire finger begin to circle around it. When the shaft rotates, after the lower knuckle touches the object, the friction force in the decoupling device 11 is not enough to overcome the object's blocking force on the lower knuckle, so the lower knuckle 13 stops rotating around the axis, and the lower knuckle drives the gear 8- 1 can still continue to rotate, driving the three lower knuckle transmission gears 20 to rotate, and then driving the middle knuckle driving gear 18-2 to rotate; the rotation of the middle knuckle driving gear 18-2 drives the decoupling device 11 at the middle knuckle joint to rotate, and the middle knuckle joint rotates. The friction force in the shell of the decoupling device 11 and the middle phalanx 15 drives the middle phalanx 15 to rotate, and the middle phalanx 15 and the upper phalanx start to rotate around the axis. After the middle phalanx touches the object, the friction in the decoupling device 11 corresponds to If the force is not enough to overcome the obstruction force of the object on the middle phalanx, the middle phalanx 15 stops rotating around the axis; similarly, the movement of the upper phalanx is pushed until the whole finger wraps the object. The remaining two three-joint fingers 4 work on the same principle. The three three-joint fingers 4 are also under-actuated, and their movements do not interfere with each other, and can grasp various irregular shaped objects.

After grasping the object, the stepper motor 2 continues to work, and the gear continues to rotate, which is equivalent to the idle rotation of the gear at this time. When the object is grasped, the motor fails or the power supply stops. Due to the frictional force of each joint, the fingers will not be released automatically.

When the grasping object needs to be released, the stepping motor 2 is reversed. When the power is transmitted to the lower knuckle driving gear 8-1, it is opposite to the previous rotation direction, and the lower knuckle driving gear 8-1 drives the corresponding solution The coupling device 11 rotates, the decoupling device 11 drives the lower phalanx 13 to rotate, the lower phalanx 13 and the entire finger begin to open around the axis, and after the lower phalanx touches the lower phalanx limit block, the The friction force is not enough to overcome the blocking force of the limit block on the lower knuckle, so the lower knuckle 13 stops rotating around the axis; then the lower knuckle driving gear 8-1 transmits the power to the middle knuckle through the three lower knuckle transmission gears 20 Drive gear 8-2; middle knuckle drive gear 8-2 drives the middle knuckle, the upper knuckle opens; after the middle knuckle touches the middle knuckle limit block, the middle knuckle stops rotating around the axis; then the power is transmitted through the middle knuckle The gear 19 is transmitted to the upper knuckle, and similarly, the upper knuckle is opened, and the mechanical finger returns to the initial open state.

In order to make the purposes, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. The embodiments described above are a part of the embodiments of the present invention, but not all of the embodiments. The components of the embodiments of the invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations. Accordingly, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

Please refer to Figure 10, which is an analytical model of the adaptive grasping process when the robot hand grasps a sphere placed on the palm. The initial positions of the three three-joint fingers 4 relative to the sphere are shown in Figure 10(a). The three three-joint fingers 4 start to move. After the lower phalanx touches the sphere, the lower phalanx stops moving when the blocking force of the sphere on the lower phalanx reaches the frictional damping force generated by the spring in the decoupling device, as shown in Figure 10(b). As shown in Figure 10(c) . There is friction in the friction plate of the upper knuckle joint decoupling device, and the upper knuckle continues to move until it touches the sphere, and the whole finger keeps the grasping posture. At this time, the positional relationship between the manipulator and the sphere is shown in Figure 10(d). Show.

The movements between the three fingers are also independent of each other. When none of the three fingers touch the object, all three fingers will move at the same time. When one finger stops moving due to the obstacle of touching the object, the other two fingers continue to move; When the object stops moving due to obstruction, the third finger continues to move; when the third finger stops moving due to the obstruction, all three fingers have already touched the grasped object. When continuing to move, the knuckles of the three hands start to move independently, so that they can grab various shaped objects with different geometric shapes.

The above content is only to illustrate the technical idea of the present utility model, and cannot limit the protection scope of the present utility model. Any changes made on the basis of the technical solution according to the technical idea proposed by the present utility model fall into the scope of the present utility model. within the scope of protection of the claims.

Claims (9)

1. A gear differential type underactuated three-joint manipulator is characterized by comprising three-joint fingers (4), wherein the three-joint fingers (4) are arranged in an angle of 120 degrees, and a joint shaft of each three-joint finger (4) is respectively provided with a decoupling device (11) serving as an underactuated mechanism; one end of each of the three-joint fingers (4) is connected with the stepping motor (2) through the driving transmission cylindrical gear (10) via the bevel gear transmission system (9), and the stepping motor (2) drives the bevel gear transmission system (9) to realize the motion transmission and control of the three-joint fingers (4).

2. The gear differential under-actuated three-joint manipulator according to claim 1, characterized in that the three-joint finger (4) comprises an upper knuckle (17), a middle knuckle (15) and a lower knuckle (13) which are connected in sequence by gear engagement; an upper knuckle driving gear (18-3) is arranged at the joint of the upper knuckle (17) and the middle knuckle (15), a middle knuckle driving gear (18-2) is arranged at the joint of the middle knuckle (15) and the lower knuckle (13), the other end of the lower knuckle (13) is fixedly connected with the base finger support (3), and is connected with the bevel gear transmission system (9) through the lower knuckle driving gear (18-1) and the drive transmission cylindrical gear (10).

3. The gear differential underactuated three-knuckle manipulator according to claim 2, wherein the lower knuckle (13), the middle knuckle (15) and the upper knuckle (17) of the lower knuckle drive gear (18-1), the middle knuckle drive gear (18-2) and the upper knuckle drive gear (18-3) are respectively provided with a decoupling device (11) on their knuckle axes.

4. The gear differential type underactuated three-knuckle manipulator according to claim 3, wherein a lower knuckle limiting device (12) is arranged on the decoupling device (11) at the lower knuckle (13), a middle knuckle limiting device (14) is arranged on the decoupling device (11) at the middle knuckle (15), and an upper knuckle limiting device (16) is arranged on the decoupling device (11) at the upper knuckle (17).

5. The gear differential underactuated three-knuckle manipulator according to claim 2, wherein a middle knuckle transfer gear (19) is arranged in the middle knuckle (15), the upper knuckle drive gear (18-3) is in meshed connection with the middle knuckle drive gear (18-2) through the middle knuckle transfer gear (19), three lower knuckle transfer gears (20) are sequentially arranged in the lower knuckle (13), and the lower knuckle drive gear (18-1) is in meshed connection with the middle knuckle drive gear (18-2) through the three lower knuckle transfer gears (20).

6. The gear differential under-actuated three-joint manipulator according to claim 1, characterized in that the bevel gear transmission system (9) comprises a first bevel gear (23), a second bevel gear (24), a third bevel gear (25) and a fourth bevel gear (26); the second bevel gear (24) and the third bevel gear (25) are arranged in parallel, the second bevel gear (24) is in meshed connection with the first bevel gear (23), and the third bevel gear (25) is in meshed connection with the fourth bevel gear (26); the angles between the second bevel gear (24) and the first bevel gear (23), between the first bevel gear (23) and the fourth bevel gear (26), and between the fourth bevel gear (26) and the third bevel gear (25) are all 120 degrees.

7. The gear differential type underactuated three-joint manipulator according to claim 6, wherein an input shaft (8) of the stepping motor (2) is connected with a first bevel gear (23), a driving cylindrical gear (27) is arranged between the input shaft (8) and the first bevel gear (23), a second bevel gear (24) and a third bevel gear (25) are connected through a connecting shaft, a second driving cylindrical gear (27) is arranged on the connecting shaft, a fourth bevel gear (26) is connected with the third driving cylindrical gear (27) through a connecting shaft, and each driving cylindrical gear (27) is correspondingly connected with a lower knuckle driving gear (18-1) arranged on three-joint fingers (4) through a driving transmission cylindrical gear (10).

8. The gear differential underactuated three-joint manipulator according to claim 1, characterized in that the decoupling device (11) comprises two friction plates (28) in contact with each other, one side of the friction plates (28) being connected to the outer casing of the three-joint finger (4) and the other side being connected to the adjusting screw (30) via a spring (29).

9. The gear differential type underactuated three-joint manipulator according to claim 1, wherein the stepping motor (2) is arranged on the motor support (1), the bevel gear transmission system (9) is arranged on the three support plates (6), the motor support (1) and the support plates (6) are fixed on the fixing plate (7), the holding plate (5) is arranged above the support plates (6), the three base finger supports (3) are arranged on the holding plate (5) at intervals, and the base finger supports (3) are respectively connected with the corresponding three-joint fingers (4).

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