Variable stiffness and driving combined continuum robot and optimization design method thereof

Abstract

The invention belongs to the technical field of continuum robots, and discloses a variable-rigidity and driving combined continuum robot and an optimization design method thereof.The variable-rigidity and driving combined continuum robot comprises a second section, a middle transition section, a first section, a first section rope and a second section rope, and the second section and the first section are connected through the middle transition section; each of the second section and the first section comprises a plurality of wire guiding discs and a plurality of check rings, every two adjacent wire guiding discs are connected through the corresponding check ring to form a cylindrical pair joint, and the four first section ropes and the four second section ropes are evenly distributed relative to the center line of the continuum robot; the four first section ropes are used for driving two mutually perpendicular degrees of freedom of the first section, the four second section ropes are used for driving two mutually perpendicular degrees of freedom of the second section, and the second section and the first section move independently. The continuum robot does not need to be assembled, is flexible in movement, controllable in rigidity and small in friction force, and improves the interaction and sensing ability with the environment during operation.

Description

Technical Field

[0001] The invention relates to the technical field of robots, and in particular to a variable-rigidity and drive-combined continuum robot and an optimization design method thereof. Background Art

[0002] In modern medicine, natural orifice (or minimally invasive) surgical robots, as a new type of medical equipment, are gradually changing traditional surgical methods. Due to the problems of large trauma, slow recovery, and many sequelae in surgical operations, a natural orifice (or minimally invasive) surgical robot technology that improves surgical accuracy, reduces patient pain, and speeds up recovery has received widespread attention and has developed rapidly in recent years.

[0003] Existing surgical robots mostly use rigid instruments, which are greatly restricted when operating in narrow, unstructured environments. Doctors have difficulty operating to avoid squeezing human tissues; rigid instruments are not flexible enough, making it difficult to remove diseased tissues in special locations. Although we can add sensors to rigid surgical instruments to obtain some interactive information, this still poses a high safety hazard and does not change the shortcomings of rigid surgical instruments' lack of flexibility.

[0004] In order to make up for the shortcomings of traditional rigid surgical instruments, such as poor flexibility, limited operating range, and insufficient safety, flexible continuum surgical robot systems have begun to emerge. The advantages in materials and structure make continuum robots have better flexibility and adaptability than rigid robots, which helps to improve the safety of robots interacting with the human body and makes up for the shortcomings of rigid robots in environmental adaptability and operational safety.

[0005] However, existing continuum robots usually have contradictions between variable stiffness methods, sensing methods, and robot volume. Most variable stiffness methods, such as particle blocking, layer blocking, low-melting-point alloys, magnetorheological fluids, etc., require adding other components to the continuum robot to achieve changes in stiffness, which undoubtedly greatly increases the volume of the robot. For surgical robots, due to severe size limitations, it is difficult to integrate sensors to detect their bending angles, external forces, etc. Moreover, rigid sensors can easily cause interference between sensors and robots, as well as problems with the installation of sensors that change the mechanical properties of the continuum robot.

[0006] Secondly, friction and irregular deformation bring troubles to the control of continuum robots. There are two main types of friction: one is the common problem of rope-driven robots, that is, the friction between the rope and the hole; the other is the common problem of hinged joint continuum robots, that is, the friction at the hinge joint. The friction between the rope and the hole will show nonlinear changes with the size of the rope tension, the bending angle, and the direction of movement. The sudden change between the dynamic and static friction forces will bring hysteresis, sudden change and uncertainty to the control of the robot. Uneven friction at the hinge joint will bring uncertainty to the shape of the robot. The most common effect of this irregular deformation is that the constant curvature model is no longer applicable. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a continuum robot with variable stiffness and drive combined and an optimization design method thereof, which does not require assembly, has flexible movement, controllable stiffness, and low friction, thereby improving the interaction and perception capabilities with the environment during operation.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A variable stiffness and drive combined continuum robot comprises a second section, an intermediate transition section, a first section, a first section rope and a second section rope, the second section and the first section are connected via the intermediate transition section, the second section and the first section both comprise a plurality of wire reels and a plurality of stop rings, two adjacent wire reels are connected via the stop ring to form a cylindrical sub-joint, the first section rope and the second section rope are both four and are evenly distributed relative to the center line of the continuum robot, the four first section ropes are used to drive two mutually perpendicular degrees of freedom of the first section, the four second section ropes are used to drive two mutually perpendicular degrees of freedom of the second section, and the second section and the first section move independently of each other.

[0010] As a further configuration, the wire reel is a cylindrical sub-joint wire reel, the upper end face and the lower end face of the wire reel are two vertical arcs respectively, the stop ring is a flexible stop ring, and the middle transition section is obtained by stretching the wire reel along the axial direction.

[0011] As a further configuration, the wire reels of the second section and the first section are stacked with their central symmetry axes parallel to each other and adjacently rotated 90°, and the stop rings of the second section and the first section are stacked with their central symmetry axes parallel to each other and adjacently rotated 90°.

[0012] As a further configuration, the stop ring includes an inner ring and outer rings on both sides, the two end faces of the inner ring are respectively provided with inner ring steps, the two inner ring steps are respectively located at the two ends of the inner ring, the two end faces of the outer ring are respectively provided with outer ring steps, the two outer ring steps of each outer ring are respectively located at the two ends of the corresponding outer ring, the two outer rings have the same orientation and angle, a stop ring center hole is provided at the center of the inner ring, center hole threading holes are provided at both ends of the inner ring, the center hole threading holes are located at the inner ends of the inner ring steps, and a center hole threading hole is also provided at the center of the outer ring.

[0013] As a further configuration, the inner ring is connected to the previous wire reel and the next wire reel respectively through two inner ring steps, and the two outer rings of each stop ring are connected to the previous wire reel and the next wire reel through two outer ring steps.

[0014] As a further configuration, the first section is in the shape of a cylindrical tube as a whole, and the first section includes a base. The first section is arranged in sequence along the length direction of the continuum robot in the order of base, stop ring, wire reel, stop ring, wire reel, ... stop ring, the first section of rope passes through the base, the stop ring and the wire reel, and one of the endpoints of the first section of rope is located in the middle transition section.

[0015] As a further configuration, the second section is in the shape of a cylindrical tube as a whole, the second section includes an end, the second section is arranged in sequence along the length direction of the continuum robot in the order of a stop ring, a wire reel, a stop ring, a wire reel... a stop ring, and an end, the second section rope passes through the base, the middle transition section, the stop ring and the wire reel, and one of the endpoints of the second section rope is located at the end.

[0016] An optimization design method for a continuum robot with variable stiffness and drive is proposed. According to the structural design and geometric relationship of the continuum robot, the relationship between the deflection angle of a single joint and the sum of the changes of the driving ropes on the two opposite sides can be obtained:

[0017]

[0018] Among them, ΔΦ represents the deflection angle of a single joint, Δd l Indicates the change in the length of the left rope, Δd r represents the change in the rope length on the right side, n represents the number of joints in the bending direction, r is the radius of the cylindrical sub-joint, and β is the half angle of the contact arc between the two joints;

[0019] In order to maximize the variable stiffness range and resolution, ΔL l (ΔΦ)+ΔL r (ΔΦ) should be as large as possible, so the performance index is set: J = ΔL l (ΔΦ)+ΔL r (ΔΦ)

[0020] get:

[0021]

[0022] Among them, Const is a constant value, θ max is the maximum rotation angle of a single degree of freedom;

[0023] set up

[0024]

[0025] get

[0026]

[0027] Because β∈(0°,90°), is a positive constant; since ΔΦ∈(0°,2β), Hengzheng, Always negative; therefore, f(β,ΔΦ) increases with the increase of ΔΦ and decreases with the increase of β. The smallest possible β value should be selected.

[0028] As a further setting, the two orthogonal deflection directions of the dual-degree-of-freedom continuum robot are recorded as the pitch direction and the yaw direction, and the changes of the two pairs of rope lengths in the two directions affect each other; suppose the number of joints in the two directions is n; consider the influence of the movement of the yaw axis on the pitch axis, and give the relationship between the joint deflection angle affected by the orthogonal joint and the rope length on both sides:

[0029]

[0030] Overall deflection angle θ pit ,θ yaw and the total rope length change ΔL on both sides l_pit , ΔL r_pit The relationship between:

[0031]

[0032] In the other direction, the effect of the pitch axis movement on the change in the yaw axis rope length can be determined by simply swapping the subscripts "pit" and "yaw" in the above formula.

[0033] As a further setting, the transformation matrix of two adjacent joints is found directly through the geometric relationship Then the transformation matrix from the far end point to the base coordinate system is derived according to the composite transformation formula;

[0034] Transformation Matrix is defined as follows:

[0035]

[0036] in, represents the position of the {n+1} system in the {n} system; Each column is the projection of the xyz axis of the {n+1} system onto the xyz axis of the {n} system; n P {n+1}ORG represents the coordinates of the origin of the {n+1} system in the {n} system;

[0037] When n = 0, it is the robot base coordinate system;

[0038] The relationship between coordinate system {n} and coordinate system {n+1} is:

[0039] {n} Extension Z n , X n Translate to get {n'};

[0040] {n'} around Y' n Rotation get{n"};

[0041] {n"} around Z' n 'Rotate 90° (n is an even number) or -90° (n is an odd number) to get {n+1};

[0042] The transformation matrices generated in the above three steps need to be right-multiplied continuously;

[0043] First, calculate the translation from the {n} system to the {n'} system, which is essentially the projection of the length of the middle rope onto the two coordinate axes; temporarily assume that n is even;

[0044] Rope length:

[0045] Rope relative to Z n The deflection angle of the axis is:

[0046] Therefore, Z n The axis translation is:

[0047] Where H is the section height, H = H link +2C axial +T ring , H link is the wire reel height, C axial is the axial clearance of the stop ring, T ring is the thickness of the movable part of the stop ring;

[0048] X n The axis translation is:

[0049] When n is an odd number, use ΔΦ yaw Replace ΔΦpit ,

[0050] Next, calculate the transformation matrix, still assuming that n is even,

[0051]

[0052] Similarly, when n is an odd number, use ΔΦ yaw Replace ΔΦ pit ;

[0053] According to the composite transformation method, the transformation matrix between the two wire coils is:

[0054]

[0055] The beneficial effects of the present invention are:

[0056] 1. Compared with other configurations, the continuum robot has better isotropy, smaller torque pulsation when rotating around the central axis, and easier control of output force.

[0057] 2. The inconsistency of the change in rope length during bending can be used to actively change the stiffness, solving the contradiction between stiffness and flexibility in the structural design of the continuum robot.

[0058] 3. The driving mode and the variable stiffness method are combined into one, which solves the contradiction between the variable stiffness method and the volume of the continuum robot.

[0059] 4. The deflection angle of a single joint becomes larger than that of other configurations. Therefore, using a shorter length or a smaller number of joints can make the continuum robot have a larger deflection angle as a whole and have higher flexibility.

[0060] 5. There are no heat-generating components, which avoids the possible damage to human tissues and cells caused by heat.

[0061] 6. The continuum robot consists of only one part. The newly designed flexible stop ring not only solves the problem of relative sliding between the wire reels, but also enables the robot to be formed in one piece without the need for assembly, making production convenient.

[0062] 7. The cylindrical joint transforms the sliding friction at the original hinge joint into rolling friction, effectively solving the problem of different deflection angles of each joint due to different friction forces.

[0063] 8. The flexible stop ring limits the relative sliding of the cylindrical joints and improves the ability of the continuum robot to withstand bending and torque. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a stereogram of the present invention.

[0065] Figure 2 for Figure 1 Enlarged view of point A in the middle.

[0066] Figure 3 It is a three-dimensional view of the wire reel of the present invention.

[0067] Figure 4 It is a stereoscopic view of the intermediate transition section of the present invention.

[0068] Figure 5 It is a cross-sectional schematic diagram of the intermediate transition section of the present invention.

[0069] Figure 6 It is a perspective view of the end of the present invention.

[0070] Figure 7 It is a three-dimensional diagram of the base of the present invention.

[0071] Figure 8 It is a three-dimensional view of the stop ring of the present invention.

[0072] Fig. 9 It is an exploded view of the cooperation between the stop ring and the wire reel of the present invention.

[0073] Fig.10 This is a single-joint geometric relationship diagram of the single-degree-of-freedom continuum robot of the present invention.

[0074] Fig.11 This is a single-joint geometric relationship diagram of the single-degree-of-freedom continuum robot of the present invention (after deflection).

[0075] Fig.12 This is a single-joint geometric relationship diagram of the dual-degree-of-freedom continuum robot of the present invention.

[0076] Fig.13 This is a single-joint geometric relationship diagram of the dual-degree-of-freedom continuum robot of the present invention (after deflection).

[0077] Fig.14 Schematic diagram of the effect of the stop ring of the present invention.

[0078] Fig.15 It is the transformation matrix diagram solved by the present invention.

[0079] Fig.16 It is a schematic diagram of the position of the partial coordinate system of the continuum robot of the present invention.

[0080] Fig.17 It is a schematic diagram of the deflection movement of the stop ring of the present invention.

[0081] In the figure: second section 1, first section rope 11, intermediate transition section 2, transition section middle hole 21, transition section threading hole 22, transition section terminal hole 23, first section 3, second section rope 31, wire reel 4, wire reel middle hole 41, wire reel threading hole 42, base 5, base middle hole 51, base threading hole 52, end 6, end middle hole 61, end threading hole 62, threaded portion 63, final endpoint 64, stop ring 7, inner ring 71, outer ring 72, stop ring middle hole 73, middle hole threading hole 74, inner ring step 75, outer ring step 76. DETAILED DESCRIPTION

[0082] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0083] like Figure 1-Figure 9 , Fig.17 As shown, this embodiment discloses a variable stiffness and drive combined continuum robot, comprising a second section 1, an intermediate transition section 2, a first section 3, a first section rope 11 and a second section rope 31, wherein the second section 1 and the first section 3 are connected via the intermediate transition section 2, the second section 1 comprises an end 6, and the first section 3 is connected via the intermediate transition section 2. Figure 6 The upper end of the end portion 6 is provided with a threaded portion 63, the center of the end portion 6 is provided with an end hole 61, the end hole 61 also penetrates the threaded portion 63, the end portion 6 is also provided with an end threading hole 62 penetrating the upper and lower end surfaces thereof, and the end threading hole 62 is located at the periphery of the threaded portion 63. The first section 3 includes a base 5, referring to Figure 7 The center of the base 5 is provided with a base middle hole 51, and the base 5 is also provided with a base threading hole 52 that passes through its upper and lower end surfaces. The threaded portion 63 of the end 6 can be connected to different instruments through threads, such as surgical forceps, tissue detection sensors, and endoscopes. The use of threaded connection is also to achieve quick release and quick replacement during surgery. The base 5 is the starting point of the first section 3. The base 5 is directly inserted into a mechanism that accommodates the base 5. The 8 ropes that pass through the first section 3 and the second section 1 are all passed out of the base 5 and are respectively connected to the 8 motors in the mechanism that accommodates the base 5. Each motor will perform position control or force control on a rope individually.

[0084] Reference Figure 1 , the second section 1 and the first section 3 both include a plurality of wire reels 4 and a plurality of stop rings 7, the wire reels 4 are cylindrical sub-joint wire reels, the stop ring 7 is a flexible stop ring, and two adjacent wire reels 4 are connected by the stop ring 7 to form a cylindrical sub-joint. It should be emphasized that the continuum robot only includes one part except the transmission rope (the first rope 11 and the second rope 31), and the second section 1, the intermediate transition section 2, the first section 3, the wire reel 4, and the stop ring 7 are all names divided from the function, not from the parts. They are continuously stacked in structure and material, without specific part boundaries that can be specified, and specifically these parts are formed by 3D printing.

[0085] Reference Figure 3 The wire reel 4 is roughly a flat cylinder, and the upper and lower end surfaces of the wire reel 4 are two vertical arcs, which are the basis for each section of the continuum robot to present two degrees of freedom. There is a wire reel hole 41 in the center of the wire reel 4, and four wire reel threading holes 42 are arranged through the upper and lower end surfaces. The wire reels 4 are stacked in a manner that the central symmetric axes are parallel to each other and rotated 90 degrees adjacent to each other.

[0086] Reference Figure 8 The stop ring 7 includes an inner ring 71 and outer rings 72 located on both sides. The outer ring 72 is two symmetrical semicircular arcs separated by the inner ring 71. The two end faces of the outer ring 72 are respectively provided with outer ring steps 76. The two outer ring steps 76 of each outer ring 72 are respectively located at the two ends of the corresponding outer ring 72. The outer ring steps 76 are approximately triangular bosses. There is only one approximately triangular boss on each end face of the semicircular arc. The two outer rings 72 have the same direction and angle. The same direction means that the outer ring steps 76 on the same side point to the same direction (upward or downward). The same angle means that the two outer rings 72 have the same inclination angle. The two outer rings 72 of each stop ring 7 are connected to the upper wire reel 4 and the next wire reel 4 through the two outer ring steps 76. The center of the outer ring 72 is provided with a middle hole threading hole 74, and a avoidance is set to meet the structural strength of the middle hole threading hole 74 (avoidance refers to the arc-shaped protrusion in the middle of the outer ring 72, corresponding to the arc-shaped concave area on both sides of the inner ring 71). The avoidance destroys the integrity and continuity of the shape features of the outer ring 72 and the inner ring 71 , and its width is determined by the printing accuracy of the 3D printer.

[0087] The inner ring 71 has two protruding parts in the bending direction, specifically, the two end faces of the inner ring 71 are respectively provided with inner ring steps 75 (i.e., protruding parts), the inner ring steps 75 are approximately rectangular bosses, and the two inner ring steps 75 are respectively located at the two ends of the inner ring 71. The inner ring 71 has two concave areas that are squeezed out by the outer ring 72 in the direction perpendicular to the bending direction. The inner ring 71 is connected to the previous wire reel 4 and the next wire reel 4 respectively through the two inner ring steps 75. Like the outer ring 72, each end face of the inner ring 71 has and only has one approximately rectangular boss. The center of the inner ring 71 is provided with a stop ring middle hole 73, and the two ends of the inner ring 71 are provided with middle hole threading holes 74, and the middle hole threading holes 74 are located at the inner end of the inner ring steps 75. The transmission rope passing through the middle hole threading holes 74 of the inner ring 71 is used to realize the movement of the one degree of freedom at the stop ring 7, and the movement of the other degree of freedom is. The stop rings 7 are stacked in a manner that the central symmetry axes are parallel to each other and rotated 90° adjacently. The end portion 6 is fixedly connected to the stop ring 7 at three bosses on the edge; the base 5 is also fixedly connected to the stop ring 7 at three bosses on the edge.

[0088] There are four first rope sections 11 and four second rope sections 31 and they are evenly distributed relative to the center line of the continuum robot. The four first rope sections 11 are used to drive two mutually perpendicular degrees of freedom of the first section 3, and the four second rope sections 31 are used to drive two mutually perpendicular degrees of freedom of the second section 1. The second section 1 and the first section 3 move independently of each other.

[0089] The purpose of the outer ring 72 and the inner ring 71 is to prevent the two adjacent wire reels 4 from sliding relative to each other, which is crucial to the modeling and control accuracy of the continuum robot. The bending movement is achieved by the material flexibility of the outer ring 72 and the inner ring 71, and the symmetrical left-right bending movement is achieved by the tensile and compressive deformation in the opposite directions. This movement is equivalent to two cylindrical surfaces contacting each other and rolling without sliding. The purpose of setting the boss at the outer ring 72 and the inner ring 71 is to achieve the division of the two parts under the 3D printing technology. The height of the boss, that is, the width of the gap, is determined by the printing accuracy of the 3D printer. Similarly, the width of the gap between the outer ring 72 and the inner ring 71 is also determined by the printing accuracy of the 3D printer.

[0090] Reference Figure 4 , the intermediate transition section 2 is essentially a mechanism transformation of the cylindrical sub-joint wire reel 4. The intermediate transition section 2 is the wire reel 4 stretched axially to a suitable height, and the approximate shape of the intermediate transition section 2 can be obtained. The intermediate transition section is the end of the first section 3 of the continuum robot, and it is also the end point of the four transmission ropes that control the movement of the first section 3. In the upper and lower end faces of the intermediate transition section 2, which are projected as circles, four threading holes, transition section threading holes 22, which completely penetrate the entity of the intermediate transition section 2 are evenly distributed. The position of the transition section threading holes 22 is completely determined by the position of the wire reel threading holes 42 on the cylindrical sub-joint wire reel 4, that is, the hole centers of two transition section threading holes 22 are symmetrically distributed on a straight line at the highest point of a certain end face with respect to the central axis, and the other two transition section threading holes 22 are symmetrically distributed in the vertical direction of the straight line, and the distances from the hole centers of the four transition section threading holes 22 to the central axis are equal. Two transition section terminal holes 23 are provided on the cylindrical side wall of the intermediate transition section 2, each of which intersects with two transition section threading holes 22, but the two transition section terminal holes 23 do not intersect, and the openings of the holes are chamfered to accommodate the first knotted rope 11, which can be referred to Figure 5 The chamfer not only makes it easier to remove the head of the first rope 11 from the inside, but also can accommodate the volume of the head of the first rope 11 so that the head of the first rope 11 does not excessively affect the cylindrical appearance and smooth shape of the continuum robot. A transition section middle hole 21 is provided in the center of the middle transition section 2.

[0091] The first section 3 is in a cylindrical tubular shape as a whole, and the first section 3 is arranged in sequence along the length direction of the continuum robot in the order of “base 5, pitch axis flexible stop ring 7, wire drum 4, yaw axis flexible stop ring 7, wire drum 4, … yaw axis flexible stop ring 7”, and the first section rope 11 passes through the base 5, the stop ring 7 and the wire drum 4, and one of the end points of the first section rope 11 is located at the middle transition section 2.

[0092] One end of the four first ropes 11 that drive the first section 3 to perform bending movement enters the transition section threading hole 22 of the middle transition section 2 through the threading holes of each subunit of the first section 3, and then the first rope 11 is bent 90° and enters the transition section terminal hole 23 opened on the cylindrical side wall of the middle transition section 2, and the rope is knotted at the chamfer to fix the end of the first rope 11 in the chamfer.

[0093] The second section 1 is similar in structure to the first section 3, and is in the shape of a cylindrical tube as a whole. The second section 1 is arranged in the order of the pitch axis flexible stop ring 7, the wire drum 4, the yaw axis flexible stop ring 7, the wire drum 4... the yaw axis flexible stop ring 7, and the end 6 along the length direction of the continuum robot, and the pitch axis flexible stop ring 7 and the yaw axis flexible stop ring 7 are identical in structure. This statement only represents the difference in the direction of movement to achieve the two mutually perpendicular degrees of freedom of the second section 1. The centers of all subunits of the second section 1 and the first section 3 have openings to allow the cables and wires required by the end effector to pass through the center. The center hole runs through the second section 1 and the first section 3 of the continuum robot along the central axis of the wire drum 4 and the stop ring 7.

[0094] The second rope section 31 passes through the base 5 , the intermediate transition section 2 , the stop ring 7 and the wire reel 4 , and one of the end points of the second rope section 31 is located at the end 6 .

[0095] One end of the four second ropes 31 that drive the second section 1 to perform bending movement first enters the transition section threading hole 22 of the middle transition section 2 through the threading holes of each subunit of the first section 2, then enters the threading holes of each subunit of the second section 1 through the transition section threading hole 22 of the middle transition section, and finally passes through the end threading hole 62 of the end section 6 and is tied and fixed.

[0096] The overall working space of the robot can be adjusted by adjusting the size and number of the subunits of the second section 1 and the first section 2 of the continuum robot and the length of the intermediate transition section 2.

[0097] The bending motion of the continuum robot is driven by eight transmission ropes passing through the threading holes. In addition, since the bending motion of the continuum robot in this configuration will cause the elongation of the transmission ropes at the symmetrical position to be not equal to the shortening, the robot stiffness can be actively adjusted in the control based on this property, and the mapping relationship between the force on the robot end and the rope length difference can be obtained through the difference between the elongation and shortening.

[0098] Fig.17 A schematic diagram of the deflection motion of the flexible stop ring is given, and the deflection angles are 0 degrees, 10 degrees and 30 degrees respectively.

[0099] This embodiment discloses an optimization design method for a continuum robot with variable stiffness and drive. The single-degree-of-freedom model of the continuum robot is as follows: Fig.10 , Fig.11 As shown in the figure, the revolute joint is composed of cylindrical pairs that can only roll relative to each other. Among them, r is the radius of the cylindrical pair joint, β is the half angle of the contact arc between the two joints, and C d is the center distance of the contralateral threading holes, and ΔΦ is the joint deflection angle.

[0100] The single joint deflection angle ΔΦ and the length d of the two side ropes at this joint can be derived l d r The relationship between:

[0101]

[0102] The change in the length of the rope on both sides Δd l , Δd r It can be expressed as:

[0103]

[0104] Assuming that this single-degree-of-freedom continuum robot has a total of n joints, and assuming that the deflection angle of each joint is the same, the overall deflection angle θ of this degree of freedom and the total rope length change ΔL on the left and right sides can be derived: l , ΔL r The relationship between:

[0105] θ=nΔΦ

[0106]

[0107] From the above two formulas, we can find that the sum of the changes in rope length must not be 0.

[0108] The sum of the rope length changes expressed by ΔΦ is:

[0109]

[0110] It is precisely because the sum of the changes in the rope lengths on the left and right sides is not 0 that the stiffness of the continuum robot can be expressed as a function of the rope tension. The rope tension can be changed by actively controlling the torque of the motor, that is, different stiffnesses can be used to resist external loads, realizing the unification of the driving method and the variable stiffness method, and effectively reducing the outer diameter of the robot.

[0111] By analyzing the single-degree-of-freedom continuum robot, we can also get the limit rotation angle ΔΦ of each joint: max When the single joint deflection angle is the largest, there must be:

[0112]

[0113] That is, ΔΦ max =2β is the maximum deflection angle of a single joint, θ max =2nβ is the maximum rotation angle of single degree of freedom (limit rotation angle).

[0114] The two orthogonal deflection directions of the dual-degree-of-freedom continuum robot are denoted as the pitch direction and the yaw direction, and the changes of the two pairs of rope lengths in the two directions affect each other.

[0115] Assume that the number of joints in both directions is n (each retaining ring is a joint).

[0116] Consider the effect of the yaw axis movement on the pitch axis, refer to Fig.12 , Fig.13 As shown:

[0117] Among them, ▇ is a placeholder, indicating that it can be either l or r.

[0118] The relationship between the joint deflection angle affected by the orthogonal joint and the length of the rope on both sides is given as:

[0119]

[0120] Overall deflection angle θ pit ,θ yaw and the total rope length change ΔL on both sides l_pit , ΔL r_pit The relationship between:

[0121]

[0122] In the other direction, the effect of the pitch axis movement on the change in the yaw axis rope length can be determined by simply swapping the subscripts "pit" and "yaw" in the above formula.

[0123] Reference Fig.14 As shown in the figure, two arcs with the same curvature as the contact arc of the cylindrical joint are drawn through the midpoint of the flexible stop ring. The essential effect is to increase the joint height H, H = Hlink +2C axial +T ring Among them, H link is the wire reel height, C axial is the axial clearance of the stop ring, T ring The thickness of the movable part of the stop ring.

[0124] Directly find the transformation matrix of two adjacent joints through geometric relationships Then the transformation matrix from the far point to the base coordinate system is derived according to the composite transformation formula.

[0125] Transformation Matrix is defined as follows:

[0126]

[0127] in, represents the position of the {n+1} system in the {n} system; Each column is the projection of the xyz axis of the {n+1} system onto the xyz axis of the {n} system; n P {n+1}ORG Represents the coordinates of the origin of the {n+1} system in the {n} system.

[0128] When n=0, it is the robot base coordinate system.

[0129] Reference Fig.15 As shown, the relationship between the coordinate system {n} and the coordinate system {n+1} is:

[0130] {n} Extension Z n , X n Translate to get {n'};

[0131] {n'} around Y' n Rotation get{n"};

[0132] {n"} around Z' n 'Rotate 90° (n is an even number) or -90° (n is an odd number) to get {n+1};

[0133] Because Euler angles are used to describe the robot posture, the transformation matrices generated in the above three steps need to be continuously right-multiplied.

[0134] First, calculate the translation from the {n} system to the {n'} system, which is essentially the projection of the length of the middle rope onto the two coordinate axes. Assume for the moment that n is even.

[0135] Depend on Fig.13 It can be seen that the rope length is:

[0136] Rope relative to Z nThe deflection angle of the axis is:

[0137] Therefore, Z n The axis translation is:

[0138] Among them, H is the section height.

[0139] X n The axis translation is:

[0140] When n is an odd number, use ΔΦ yaw Replace ΔΦ pit .

[0141] Next, we calculate the transformation matrix. Assuming n is even, we have Fig.15 It can be seen that:

[0142]

[0143] Similarly, when n is an odd number, use ΔΦ yaw Replace ΔΦ pit .

[0144] According to the composite transformation method, the transformation matrix between the two wire coils is:

[0145]

[0146] Finally, consider some special wire reels, bases, intermediate transition sections and ends. Fig.16 As shown, the base coordinate {0} of the second segment of the continuum, i.e., the origin of the assembly, is marked on the base; the coordinate system {16} fixed on the middle segment can be obtained by solving the second segment; the coordinate system {16} is translated by one segment height toward the direction of the first segment without rotation to obtain the base coordinate {0} of the first segment; the coordinate system {16} fixed on the end can be obtained by solving the first segment; it is moved by one segment height toward the distal direction without rotation to obtain the final endpoint 64 (distal endpoint).

[0147] The transformation matrix of the second segment is Indicates that the transformation matrix of the first segment is If it means:

[0148]

[0149] Assuming that the system is not subject to external forces and ignoring the friction between the rope and the threading hole, the bending shape of the continuum robot can be approximated as an arc (piecewise constant curvature model), that is, the joint deflection angles on the same degree of freedom are equal everywhere. The simplified formula is:

[0150]

[0151] From the sum of the changes in rope length, we know that ΔL l (ΔΦ)+ΔL r (ΔΦ) should be as large as possible.

[0152] Therefore, the performance index

[0153] J=ΔL l (ΔΦ)+ΔL r (ΔΦ)

[0154] Since the outer diameter of the continuum is limited by the working environment, it can be seen that: rsinβ≤Const

[0155] Among them, Const is a value proportional to the outer diameter of the continuum robot and is a constant value.

[0156] get:

[0157]

[0158] set up

[0159]

[0160] Then there is

[0161]

[0162] Because β∈(0°,90°), is a positive constant. And because ΔΦ∈(0°,2β), Hengzheng, Therefore, f(β,ΔΦ) increases with the increase of ΔΦ and decreases with the increase of β.

[0163] Conclusion: Choose the smallest possible β and the largest possible number of joints n. The increase in joints will compress the node height and make the wire coil flat, such as Fig.16 shown.

[0164] The overall deflection angle θ of the degree of freedom and the total rope length change ΔL on the left and right sides l , ΔL r The relationship between and As big as possible.

[0165] Therefore, the performance index

[0166]

[0167] The outer diameter of the continuum robot should be as large as possible. The effect of ΔΦ in the formula is two-sided. When the resolution of one side of the rope increases, the resolution of the other side of the rope will inevitably decrease. Therefore, the effect of ΔΦ in the formula is not considered. Resolution refers to the movement of the rope by a small length. The place where the end of the rope is connected (i.e., the middle transition section or the base) will have a small deflection angle. The ratio of the change in rope length to the change in angle is defined as resolution. A large resolution means that the rope moves a relatively long distance, and the end deflection angle deflects a relatively small angle, which helps to control the deflection angle more precisely and can also reduce the required accuracy of the encoder that measures the rope change.

[0168] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A variable stiffness and drive combined continuum robot, characterized in that: The invention comprises a second section (1), an intermediate transition section (2), a first section (3), a first section rope (11) and a second section rope (31); the second section (1) and the first section (3) are connected via the intermediate transition section (2); the second section (1) and the first section (3) both comprise a plurality of wire reels (4) and a plurality of stop rings (7); two adjacent wire reels (4) are connected via the stop ring (7) to form a cylindrical sub-joint; the first section rope (11) and the second section rope (31) are both four and are evenly distributed relative to the center line of the continuum robot; the four first section ropes (11) are used to drive two mutually perpendicular degrees of freedom of the first section (3); the four second section ropes (31) are used to drive two mutually perpendicular degrees of freedom of the second section (1); and the second section (1) and the first section (3) move independently of each other.

2. A variable stiffness and drive combined continuum robot as claimed in claim 1, characterized in that: The wire reel (4) is a cylindrical sub-joint wire reel, the upper end face and the lower end face of the wire reel (4) are respectively two vertical arcs, the stop ring (7) is a flexible stop ring, and the intermediate transition section (2) is obtained by stretching the wire reel (4) along the axial direction.

3. A variable stiffness and drive combined continuum robot as claimed in claim 1, characterized in that: The wire reels (4) of the second section (1) and the first section (3) are stacked in a manner that their central symmetry axes are parallel to each other and are rotated 90 degrees adjacent to each other, and the stop rings (7) of the second section (1) and the first section (3) are stacked in a manner that their central symmetry axes are parallel to each other and are rotated 90 degrees adjacent to each other.

4. A variable stiffness and drive combined continuum robot as claimed in claim 1, characterized in that: The stop ring (7) comprises an inner ring (71) and outer rings (72) located on both sides. The two end surfaces of the inner ring (71) are respectively provided with inner ring steps (75), and the two inner ring steps (75) are respectively located at the two ends of the inner ring (71). The two end surfaces of the outer ring (72) are respectively provided with outer ring steps (76). The two outer ring steps (76) of each outer ring (72) are respectively located at the two ends of the corresponding outer ring (72). The two outer rings (72) have the same orientation and angle. A stop ring center hole (73) is provided at the center of the inner ring (71). Center hole threading holes (74) are provided at both ends of the inner ring (71). The center hole threading holes (74) are located at the inner ends of the inner ring steps (75). The center of the outer ring (72) is also provided with a center hole threading hole (74).

5. A variable stiffness and drive combined continuum robot as claimed in claim 4, characterized in that: The inner ring (71) is connected to the previous wire reel (4) and the next wire reel (4) respectively through two inner ring steps (75), and the two outer rings (72) of each stop ring (7) are connected to the previous wire reel (4) and the next wire reel (4) through two outer ring steps (76).

6. A variable stiffness and drive combined continuum robot as claimed in claim 1, characterized in that: The first section (3) is in the shape of a cylindrical tube as a whole. The first section (3) comprises a base (5). The first section (3) is arranged in the order of base (5), stop ring (7), wire reel (4), stop ring (7), wire reel (4), ... stop ring (7) along the length direction of the continuum robot. The first section rope (11) passes through the base (5), the stop ring (7) and the wire reel (4). One of the end points of the first section rope (11) is located at the middle transition section (2).

7. A variable stiffness and drive combined continuum robot as claimed in claim 6, characterized in that: The second section (1) is in the shape of a cylindrical tube as a whole. The second section (1) includes an end portion (6). The second section (1) is arranged in the order of a stop ring (7), a wire reel (4), a stop ring (7), a wire reel (4) ... a stop ring (7), and an end portion (6) along the length direction of the continuum robot. The second section rope (31) passes through a base (5), an intermediate transition section (2), a stop ring (7) and a wire reel (4). One of the end portions of the second section rope (31) is located at the end portion (6).

8. An optimization design method for a variable stiffness and drive-combined continuum robot as claimed in any one of claims 1 to 7, characterized in that: According to the structural design and geometric relationship of the continuum robot, the relationship between the deflection angle of a single joint and the sum of the changes in the driving ropes on both sides can be obtained: Among them, ΔΦ represents the deflection angle of a single joint, Δd l Indicates the change in the length of the left rope, Δd r represents the change in the rope length on the right side, n represents the number of joints in the bending direction, r is the radius of the cylindrical sub-joint, and β is the half angle of the contact arc between the two joints; In order to maximize the variable stiffness range and resolution, ΔL l (ΔΦ)+ΔL r (ΔΦ) should be as large as possible, so the performance index is set: J = ΔL l (ΔΦ)+ΔL r (ΔΦ) get: Among them, Const is a constant value, θ max is the maximum rotation angle of a single degree of freedom; set up get Because β∈(0°,90°), is a positive constant; since ΔΦ∈(0°,2β), Hengzheng, Always negative; therefore, f(β,ΔΦ) increases with the increase of ΔΦ and decreases with the increase of β. The smallest possible β value should be selected.

9. The optimization design method of the variable stiffness and drive combined continuum robot as claimed in claim 8, characterized in that: The two orthogonal deflection directions of the dual-degree-of-freedom continuum robot are recorded as the pitch direction and the yaw direction, and the changes of the two pairs of rope lengths in the two directions affect each other; suppose the number of joints in the two directions is n; consider the influence of the movement of the yaw axis on the pitch axis, and give the relationship between the joint deflection angle affected by the orthogonal joint and the rope lengths on both sides: Overall deflection angle θ pit ,θ yaw and the total rope length change ΔL on both sides l_pit , ΔL r_pit The relationship between: In the other direction, the effect of the pitch axis movement on the change in the yaw axis rope length can be determined by simply swapping the subscripts "pit" and "yaw" in the above formula.

10. The optimization design method of the variable stiffness and drive combined continuum robot as claimed in claim 9, characterized in that: Directly find the transformation matrix of two adjacent joints through geometric relationships Then the transformation matrix from the far end point to the base coordinate system is derived according to the composite transformation formula; Transformation Matrix is defined as follows: in, represents the position of the {n+1} system in the {n} system; Each column is the projection of the xyz axis of the {n+1} system onto the xyz axis of the {n} system; n P {n+1}ORG represents the coordinates of the origin of the {n+1} system in the {n} system; When n = 0, it is the robot base coordinate system; The relationship between coordinate system {n} and coordinate system {n+1} is: {n} Extension Z n , X n Translate to get {n'}; {n'} around Y' n Rotation get{n"}; {n”} around Z″ n Rotate 90° (n is an even number) or -90° (n is an odd number) to get {n+1}; The transformation matrices generated in the above three steps need to be right-multiplied continuously; First, calculate the translation from the {n} system to the {n'} system, which is essentially the projection of the length of the middle rope onto the two coordinate axes; temporarily assume that n is even; Rope length: Rope relative to Z n The deflection angle of the axis is: Therefore, Z n The axis translation is: Where H is the section height, H = H link +2C axial +T ring , H link is the wire reel height, C axial is the axial clearance of the stop ring, T ring is the thickness of the movable part of the stop ring; X n The axis translation is: When n is an odd number, use ΔΦ yaw Replace ΔΦ pit , Next, calculate the transformation matrix, still assuming that n is even, Similarly, when n is an odd number, use ΔΦ yaw Replace ΔΦ pit ; According to the composite transformation method, the transformation matrix between the two wire coils is:

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