CN112621806B

CN112621806B - Connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand

Info

Publication number: CN112621806B
Application number: CN202011531305.7A
Authority: CN
Inventors: 李剑锋; 孔源; 董明杰
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2020-12-23
Filing date: 2020-12-23
Publication date: 2022-06-07
Anticipated expiration: 2040-12-23
Also published as: CN112621806A

Abstract

A connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand belongs to the technical field of robots. The hand mainly comprises a base, a sliding seat, two under-actuated fingers and four connecting rod compensation mechanisms; two under-actuated fingers are arranged in the sliding seat, and each finger controls two joints of the finger through a motor; the sliding seat moves in the vertical direction in the base through the connecting rod compensation mechanism, so that the height of the tail end of the finger is compensated, and the function of linear track translation of the tail end of the finger is realized. The hand can automatically switch the grabbing mode, and not only can utilize the far finger section to linearly clamp the object on the workbench, but also can utilize the near finger section and the far finger section to self-adaptively envelope the objects with different shapes and sizes. The hand reduces the complexity of a control system through a mechanical structure, has the advantages of compact structure, high integration level, low manufacturing and maintenance cost and the like, and can be used as an end effector of an intelligent robot.

Description

Connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand

Technical Field

The invention belongs to the technical field of robots, and particularly relates to a structural design of a connecting rod sliding seat compensation type linear parallel clamp self-adaptive underactuated hand.

Background

With social progress and technological development, the application of the robot technology in daily life of people is more and more extensive. The performance of the robot hand, which is an important component of the robot, directly affects the working capacity of the robot. The robot hand is mainly divided into 3 types according to different application occasions and use functions: industrial grippers, multi-fingered dexterous hands and under-actuated hands.

The industrial gripper is a two-finger or multi-finger gripper without movable joints in the middle of fingers, has simple structure and reliable gripping, is mostly used in specific industrial environments, can only grip objects with characteristic shapes and sizes, and has poor universality. The multi-finger dexterous hand imitates the structural appearance of a human hand, each joint is provided with one driver, the sensors are rich, the functions are powerful, but the structure is complex, the control is difficult, the flexibility and the controllability of the mechanical arm are reduced, and the development cost of the mechanical arm is increased. The underactuated robot hand overcomes the defects of an industrial clamp holder and a multi-finger dexterous hand, utilizes less motors to drive more freedom degree joints, lightens the whole weight of a mechanism, reduces the complexity of a control system, has the advantages of compact structure, high integration level, low manufacturing and maintenance cost and the like, and is a research hotspot in the field of robot hands at present.

The robot hand can grasp an object mainly by pinching and holding, wherein the pinching is to grip the object with the end fingertips, and the holding is to envelop the object with a plurality of finger segments of the fingers. In the motion process of pinching and holding an object by a traditional underactuated hand, the motion track of the tail end of a finger is not linear, and the height between the tail end of the finger and the height of a working table top is constantly changed, so that the underactuated hand cannot grab a smaller object on the working table top on the premise of no complex control system, and the working range of the underactuated hand is limited.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand. The tail ends of the fingers can translate according to a linear track, and the objects on the workbench are clamped horizontally linearly by using the far finger sections; and the grabbing mode can be automatically switched according to the shape, size and position of the object, and the near finger section and the far finger section are used for self-adaptively enveloping the objects with different shapes and sizes. The hand has simple structure, low manufacturing and maintaining cost and large grabbing range, and can be used as an end effector of an intelligent robot.

The technical scheme of the invention is as follows:

the invention designs a connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand, which is characterized in that: the hand comprises a base, a sliding seat, two under-actuated fingers (a first finger and a second finger), and four connecting rod compensation mechanisms (a first connecting rod compensation mechanism, a second connecting rod compensation mechanism, a third connecting rod compensation mechanism and a fourth connecting rod compensation mechanism);

furthermore, the base is an under-actuated hand shell, the left side and the right side of the base are in contact with the sliding seat, the sliding seat can move in the vertical direction in the base, two sliding grooves are formed in the front side and the rear side of the base, and the connecting rod compensation mechanism can move in the horizontal direction in the sliding grooves; the sliding seat is mainly used for mounting two under-actuated fingers;

further, the under-actuated finger comprises a motor, a driving bevel gear, a driven bevel gear, a first gear, a second gear, a proximal finger section, a distal finger section, a first connecting rod, a second connecting rod, a first sliding rod, a second sliding rod, a spring, a transmission shaft, a proximal joint shaft, a distal joint shaft, a first shaft, a second shaft and a third shaft; the motor is fixedly connected with the sliding seat; the output shaft of the motor is fixedly connected with the driving bevel gear; the driven bevel gear is fixedly sleeved on the transmission shaft and is meshed with the driving bevel gear; the first gear is fixedly sleeved on the transmission shaft; the second gear is fixedly sleeved on the proximal joint shaft and is meshed with the first gear; the transmission shaft, the near-joint shaft and the first shaft are sleeved in the sliding seat; the transmission shaft, the proximal joint shaft, the distal joint shaft, the first shaft, the second shaft and the third shaft are parallel to each other; central points of the proximal joint shaft, the first shaft, the third shaft, the distal joint shaft and the second shaft are A, B, C, D, E respectively; segment AB equals segment CD; in the initial position, segment AD is equal to segment BC; in the initial position, line segments AB, BC, CD and AD form a parallelogram; one end of the proximal finger section is fixedly sleeved on the proximal joint shaft, and the other end of the proximal finger section is fixedly sleeved on the distal joint shaft; one end of the far finger section is sleeved on the far joint shaft, and the other end of the far finger section is fixedly sleeved on the third shaft; one end of the first connecting rod is fixedly sleeved on the first shaft, and the other end of the first connecting rod is sleeved on the second shaft; one end of the second connecting rod is fixedly sleeved on the second shaft, and the other end of the second connecting rod is fixedly sleeved on the third shaft; one end of the first sliding rod is sleeved on the first shaft; one end of the second sliding rod is sleeved on the third shaft and can generate relative displacement with the first sliding rod; the spring is sleeved on the first sliding rod and the second sliding rod, one end of the spring is fixedly connected with the first sliding rod, and the other end of the spring is fixedly connected with the second sliding rod;

further, the connecting rod compensation mechanism comprises a first compensation rod, a second compensation rod, a fourth shaft, a fifth shaft and a sixth shaft; the fourth shaft, the fifth shaft and the sixth shaft are parallel to the near joint shaft; the central points of the near joint shaft, the far joint shaft, the fifth shaft, the fourth shaft and the sixth shaft are respectively F, G, H, I, J; segment FI is equal to segment GH; line segment FG equals line segment HI; the line segments FI, FG, GH and HI form a parallelogram; one end of the first compensation rod is sleeved on the far joint shaft, the middle of the first compensation rod is sleeved on the fifth shaft, the other end of the first compensation rod is sleeved on the sixth shaft, and the first compensation rod can horizontally displace in the front sliding groove and the rear sliding groove of the base; one end of the second compensation rod is sleeved on the fourth shaft, and the other end of the second compensation rod is sleeved on the fifth shaft;

compared with the prior art, the invention has the following advantages and prominent effects:

the invention utilizes 2 under-actuated fingers to realize the self-adaptive gripping capability of the linear parallel clamp of the robot hand, and can utilize the object on the linear parallel clamp workbench of the far finger section and the object with different shapes and sizes of the near finger section and the far finger section to self-adaptively envelope the objects with different shapes and sizes according to the different shapes and sizes of target objects. The invention adopts an under-actuated mode, each finger drives two joints by using one driver, and the object can be stably grabbed without the feedback of a real-time electronic sensor through a purely mechanical feedback system; the invention has the advantages of compact structure, high integration level, low manufacturing and maintenance cost and large grabbing range, and is suitable for the end effector of the intelligent robot.

Drawings

FIG. 1 is an overall perspective external view of a connecting rod sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand designed by the present invention;

FIG. 2 is a front view of the embodiment shown in FIG. 1;

FIG. 3 is a left side view of the embodiment shown in FIG. 1;

FIG. 4 is a front view of the embodiment of FIG. 1 (not shown with parts);

FIG. 5 is an exploded view of the embodiment of FIG. 1;

FIG. 6 is a schematic diagram of the relative positions of the embodiment of FIG. 1, wherein in an initial state, quadrilateral ABCD is a parallelogram, quadrilateral FGHI is a parallelogram, and triangular BCE remains undeformed during the linear clamp phase;

FIG. 7 is a mechanical schematic of the embodiment shown in FIG. 1;

FIGS. 8 to 10 are schematic views (not shown in part) illustrating the operation of the linear flat object of the embodiment shown in FIG. 1;

fig. 11 to 13 are schematic diagrams (not shown in part) illustrating the operation process of the adaptive envelope object according to the embodiment shown in fig. 1;

fig. 14 is a schematic diagram of the action process of fig. 8 to 10 superimposed (not shown in partial parts), the motion track of the distal end of the distal finger segment is a straight line (top horizontal dashed line);

FIG. 15 is a schematic view of the action of FIGS. 11-13 superimposed (not shown in part);

FIG. 16 is a schematic exterior view of the linear clamped cylindrical object of the embodiment of FIG. 1;

FIG. 17 is a schematic diagram of the appearance of the adaptive enveloping cylindrical object of the embodiment of FIG. 1;

in fig. 1 to 17:

101-motor, 111-drive bevel gear, 112-driven bevel gear, 113-first gear,

114-second gear, 121-proximal finger section, 122-distal finger section, 123-first link,

124-second link, 125-first slide bar, 126-second slide bar, 127-spring,

131-drive shaft, 132-proximal joint shaft, 133-distal joint shaft, 134-first shaft,

135-second axis, 136-third axis, 1001-first finger, 1002-second finger,

2-sliding seat, 301-first compensation rod, 302-second compensation rod, 311-fourth axis,

312-fifth axis, 313-sixth axis, 3001-first link compensation mechanism,

3002-second link compensation mechanism, 3003-third link compensation mechanism,

3004 fourth connecting rod compensation mechanism, 4 base, 5 bearing,

61-first cylinder, 62-second cylinder.

Detailed Description

The present invention is described in detail with reference to the embodiments shown in the drawings, but it should be understood that these embodiments are not intended to limit the present invention, and those skilled in the art should understand that functional, methodological, or structural equivalents or substitutions made by these embodiments are within the scope of the present invention.

Referring to fig. 1 to 17, fig. 1 is an overall perspective external view of a connecting rod sliding seat compensation type linear parallel clamp adaptive underactuated hand designed according to the present invention; FIG. 2 is a front view of the embodiment shown in FIG. 1; FIG. 3 is a left side view of the embodiment shown in FIG. 1; FIG. 4 is a front view of the embodiment of FIG. 1 (not shown with parts); FIG. 5 is an exploded view of the embodiment of FIG. 1; FIG. 6 is a schematic diagram of the relative positions of the embodiment of FIG. 1, wherein in an initial state, quadrilateral ABCD is a parallelogram, quadrilateral FGHI is a parallelogram, and triangular BCE remains undeformed during the linear clamp phase; FIG. 7 is a mechanical schematic of the embodiment shown in FIG. 1; FIGS. 8 to 10 are schematic views (not shown in part) illustrating the operation of the linear flat object of the embodiment shown in FIG. 1; fig. 11 to 13 are schematic diagrams (not shown in part) illustrating the operation process of the adaptive envelope object according to the embodiment shown in fig. 1; fig. 14 is a schematic diagram of the action process of fig. 8 to 10 superimposed (not shown in partial parts), the motion track of the distal end of the distal finger segment is a straight line (top horizontal dashed line); FIG. 15 is a schematic view of the action process of FIGS. 11-13 superimposed (not shown with parts); FIG. 16 is a schematic exterior view of the linear clamped cylindrical object of the embodiment of FIG. 1; FIG. 17 is a schematic diagram of the appearance of the adaptive enveloping cylindrical object of the embodiment of FIG. 1;

the embodiment provides a link sliding seat compensation type linear parallel clamp self-adaptive under-actuated hand, which comprises two under-actuated fingers (a first finger 1001 and a second finger 1002), a sliding seat 2, four link compensation mechanisms (a first link compensation mechanism 3001, a second link compensation mechanism 3002, a third link compensation mechanism 3003 and a fourth link compensation mechanism 3004) and a base 4, and is shown in fig. 1 to 7;

the base 4 is an under-actuated hand shell, the left side and the right side of the base 4 are in contact with the sliding seat 2, the sliding seat 2 can move in the vertical direction in the base 4, two sliding grooves are formed in the front side and the rear side of the base 4, and the connecting rod compensation mechanism can move in the horizontal direction in the sliding grooves; the sliding seat 2 is mainly used for mounting two under-actuated fingers;

the under-actuated finger comprises a motor 101, a driving bevel gear 111, a driven bevel gear 112, a first gear 113, a second gear 114, a proximal finger section 121, a distal finger section 122, a first connecting rod 123, a second connecting rod 124, a first sliding rod 125, a second sliding rod 126, a spring 127, a transmission shaft 131, a proximal joint shaft 132, a distal joint shaft 133, a first shaft 134, a second shaft 135 and a third shaft 136; the motor 101 is fixedly connected with the sliding seat 2; the output shaft of the motor is fixedly connected with the driving bevel gear 111; the driven bevel gear 112 is fixedly sleeved on the transmission shaft 131 and meshed with the drive bevel gear 111; the first gear 113 is fixedly sleeved on the transmission shaft 131; the second gear 114 is fixedly sleeved on the proximal joint shaft 132 and meshed with the first gear 113; the transmission shaft 131, the near joint shaft 132 and the first shaft 134 are sleeved in the sliding seat 2; the transmission shaft 131, the proximal joint shaft 132, the distal joint shaft 133, the first shaft 134, the second shaft 135 and the third shaft 136 are parallel to each other; a, B, C, D, E are respectively set as the central points of the proximal joint shaft 132, the first shaft 134, the third shaft 136, the distal joint shaft 133 and the second shaft 135; segment AB equals segment CD; in the initial position, segment AD is equal to segment BC; in the initial position, line segments AB, BC, CD and AD form a parallelogram; one end of the proximal finger section 121 is fixedly sleeved on the proximal joint shaft 132, and the other end is fixedly sleeved on the distal joint shaft 133; one end of the distal finger section 122 is sleeved on the distal joint shaft 133, and the other end is sleeved and fixed on the third shaft 136; one end of the first connecting rod 123 is fixedly sleeved on the first shaft 134, and the other end of the first connecting rod is sleeved on the second shaft 135; one end of the second connecting rod 124 is fixedly sleeved on the second shaft 135, and the other end is fixedly sleeved on the third shaft 136; one end of the first sliding rod 125 is sleeved on the first shaft 134; one end of the second sliding rod 126 is sleeved on the third shaft 136 and can generate relative displacement with the first sliding rod 125; the spring 127 is sleeved on the first sliding rod 125 and the second sliding rod 126, one end of the spring is fixedly connected with the first sliding rod 125, and the other end of the spring is fixedly connected with the second sliding rod 126;

the connecting rod compensation mechanism comprises a first compensation rod 301, a second compensation rod 302, a fourth shaft 311, a fifth shaft 312 and a sixth shaft 313; the fourth shaft 311, the fifth shaft 312, the sixth shaft 313 and the proximal joint shaft 132 are parallel to each other; the central points of the proximal joint shaft 132, the distal joint shaft 133, the fifth shaft 312, the fourth shaft 311 and the sixth shaft 313 are respectively F, G, H, I, J; segment FI is equal to segment GH; line segment FG equals line segment HI; the line segments FI, FG, GH and HI form a parallelogram; one end of the first compensation rod 301 is sleeved on the far joint shaft 133, the middle of the first compensation rod is sleeved on the fifth shaft 312, and the other end of the first compensation rod is sleeved on the sixth shaft 313 and can generate horizontal displacement in the front and rear sliding grooves of the base 4; one end of the second compensation rod 302 is sleeved on the fourth shaft 311, and the other end is sleeved on the fifth shaft 312;

the specific operation principle of this embodiment is described below with reference to fig. 8 to 17:

in the present embodiment, the initial position is set to a state where the first link 123 is horizontal and the second link 124 is vertical, as shown in fig. 2.

The principle of under-actuated manual work is as follows:

(a) linear flat clamping process

Before the proximal finger section 121 and the distal finger section 122 are not in contact with an object, the motor 101 rotates forward to drive the driving bevel gear 111 to rotate, the driving bevel gear 111 drives the driven bevel gear 112 to rotate, the driven bevel gear 112 and the first gear 113 are fixedly connected to the transmission shaft 131, and the first gear 113 is meshed with the second gear 114 to drive the second gear 114 to rotate; the second gear 114 and the first link 123 are both fixedly connected to the first shaft 134, so as to drive the first link 123 to rotate; due to the existence of the spring 127, the first sliding rod 125 and the second sliding rod 126 cannot be displaced, so that the first connecting rod 123, the second connecting rod 124, the first sliding rod 125, the second sliding rod 126 and the spring 127 are seemingly connected together and can be regarded as one component; line segments AB, BC, CD and AD form a parallelogram, when the first connecting rod 123 rotates by an angle alpha, the near finger segment 121 also rotates by the angle alpha, and the far finger segment 122 only generates relative displacement relative to the sliding seat 2 and does not generate relative rotation, so that the function of flat clamping an object is realized;

meanwhile, the line segments FI, FG, GH, HI form a parallelogram, and when the proximal finger segment 121 rotates by the angle α, the second compensation lever 302 also rotates by the angle α; due to the kinematic characteristics of the parallelogram, the height at which point G rises in the vertical direction with respect to sliding seat 2 is equal to the height at which point H rises in the vertical direction with respect to sliding seat 2; and point G, H, J are collinear at three points, so that the elevation of point J in the vertical direction relative to slide block 2 is also equal to the elevation of point G in the vertical direction relative to slide block 2; because the point J of the first compensation rod 301 can only horizontally slide in the sliding groove of the base 4 and cannot vertically displace, the sliding seat 2 is driven to integrally descend in the base 4, the descending height of the sliding seat 2 relative to the base 4 in the vertical direction is equal to the ascending height of the far joint shaft 133 relative to the sliding seat 2 in the vertical direction, the point G only horizontally displaces relative to the base 4 and does not vertically displace, the tail end of the far finger section 122 always keeps the same height distance relative to the base 4, namely the tail end of the far finger section 122 translates according to a straight track;

when the distal finger section 122 contacts the object, the distal finger section 122 cannot rotate due to the blockage of the object, but the distal finger section 122 tends to reverse under the reaction force of the object; the motor is driven by a gear and a connecting rod to restrict the reverse rotation of the far finger section 122, so that the far finger section 122 is always kept in a vertical state relative to the sliding seat 2 and can clamp objects in parallel. The specific motion process of the linear flat clamping object is shown in fig. 8, 9 and 10;

when the object is released, the motor 101 rotates reversely, and the process is opposite to the process of linearly clamping the object, and is not described again.

(b) Adaptive object process

When the near finger section 121 and the far finger section 122 do not contact with the object, the under-actuated hand moves according to a linear horizontal clamping mode; when the near finger section 121 first contacts an object, due to the obstruction of the object, the near finger section 121 cannot rotate, the first connecting rod 123 continues to rotate under the driving of the motor 101, at this time, the spring 127 starts to deform, the first sliding rod 125 and the second sliding rod 126 generate relative displacement, the line segment BC lengthens, the first connecting rod 123 pushes the second connecting rod 124, and the second connecting rod 124 pushes the far finger section 122 to rotate around the point D to the direction close to the object, so that the self-adaptive enveloping function of the object is realized; in the self-adapting process, the proximal finger section 121 does not rotate relatively due to the obstruction of the object, so the connecting rod compensation mechanism does not work; the specific motion process of the adaptive envelope object is shown in fig. 11, fig. 12 and fig. 13;

when the object is released, the motor 101 rotates reversely, and the process is opposite to the self-adaptive object process, and is not described again.

In all the above cases, the device of the embodiment of the present invention can work normally.

The invention provides a connecting rod sliding seat compensation type linear parallel clamp self-adaptive underactuated hand which has the following beneficial effects:

1) the robot hand can automatically switch the grabbing mode according to different shapes and sizes of the grabbed objects, and realizes a composite grabbing mode of linear parallel clamping and self-adaptive enveloping;

2) the robot hand has the advantages of compact structure, high integration level and low manufacturing and maintenance cost, adopts a mechanical structure to reduce the complexity of a control system, and can be used as an end effector of an intelligent robot.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. The utility model provides a linear parallel clamp self-adaptation underactuated hand of connecting rod sliding seat repayment which characterized in that: the hand comprises a base, a sliding seat, two under-actuated fingers, namely a first finger and a second finger, and four connecting rod compensation mechanisms; the four connecting rod compensation mechanisms are a first connecting rod compensation mechanism, a second connecting rod compensation mechanism, a third connecting rod compensation mechanism and a fourth connecting rod compensation mechanism; the base is an under-actuated hand shell, the left side and the right side of the base are in contact with the sliding seat, the sliding seat can move in the vertical direction in the base, two sliding grooves are formed in the front side and the rear side of the base, and the connecting rod compensation mechanism can move in the horizontal direction in the sliding grooves; the sliding seat is mainly used for mounting two under-actuated fingers; the under-actuated finger comprises a motor, a driving bevel gear, a driven bevel gear, a first gear, a second gear, a near finger section, a far finger section, a first connecting rod, a second connecting rod, a first sliding rod, a second sliding rod, a spring, a transmission shaft, a near joint shaft, a far joint shaft, a first shaft, a second shaft and a third shaft; the motor is fixedly connected with the sliding seat; the output shaft of the motor is fixedly connected with the driving bevel gear; the driven bevel gear is fixedly sleeved on the transmission shaft and is meshed with the driving bevel gear; the first gear is fixedly sleeved on the transmission shaft; the second gear is fixedly sleeved on the proximal joint shaft and is meshed with the first gear; the transmission shaft, the near joint shaft and the first shaft are sleeved in the sliding seat; the transmission shaft, the proximal joint shaft, the distal joint shaft, the first shaft, the second shaft and the third shaft are parallel to each other; central points of the proximal joint shaft, the first shaft, the third shaft, the distal joint shaft and the second shaft are A, B, C, D, E respectively; segment AB equals segment CD; in the initial position, segment AD is equal to segment BC; in the initial position, line segments AB, BC, CD and AD form a parallelogram; one end of the proximal finger section is fixedly sleeved on the proximal joint shaft, and the other end of the proximal finger section is fixedly sleeved on the distal joint shaft; one end of the far finger section is sleeved on the far joint shaft, and the other end of the far finger section is fixedly sleeved on the third shaft; one end of the first connecting rod is fixedly sleeved on the first shaft, and the other end of the first connecting rod is sleeved on the second shaft; one end of the second connecting rod is fixedly sleeved on the second shaft, and the other end of the second connecting rod is fixedly sleeved on the third shaft; one end of the first sliding rod is sleeved on the first shaft; one end of the second sliding rod is sleeved on the third shaft and can generate relative displacement with the first sliding rod; the spring is sleeved on the first sliding rod and the second sliding rod, one end of the spring is fixedly connected with the first sliding rod, and the other end of the spring is fixedly connected with the second sliding rod; the connecting rod compensation mechanism comprises a first compensation rod, a second compensation rod, a fourth shaft, a fifth shaft and a sixth shaft; the fourth shaft, the fifth shaft and the sixth shaft are parallel to the near joint shaft; the central points of the near joint shaft, the far joint shaft, the fifth shaft, the fourth shaft and the sixth shaft are respectively F, G, H, I, J; segment FI equals segment GH; line segment FG equals line segment HI; the line segments FI, FG, GH and HI form a parallelogram; one end of the first compensation rod is sleeved on the far joint shaft, the middle of the first compensation rod is sleeved on the fifth shaft, the other end of the first compensation rod is sleeved on the sixth shaft, and the first compensation rod can generate horizontal displacement in the front sliding groove and the rear sliding groove of the base; one end of the second compensation rod is sleeved on the fourth shaft, and the other end of the second compensation rod is sleeved on the fifth shaft.