A new telecentric fixed point mechanism for minimally invasive surgery

Abstract

The application provides a novel far-center fixed point mechanism for minimally invasive surgery, comprising a base, a moving platform, two sets of plane branch chain assemblies, a circular arc branch chain assembly and a two-degree-of-freedom decoupling end effector, the two sets of plane branch chain assemblies are symmetrically arranged on the base, the plane branch chain assembly is a linkage group with a parallelogram frame composed of six linkages, the end of the plane branch chain assembly is connected and hinged with the moving platform, and the circular arc branch chain assembly comprises a semicircular arc guide rail and a track slider slidingly fitted on the arc guide rail. The fixed point mechanism with a double-plane branch parallel configuration and the fixed point mechanism with a rotatable arc track configuration are used as parallel mechanism branches, over-constraint is formed in the mechanism, and the precision and rigidity of the mechanism are improved. The two plane branches are arranged orthogonally and vertically, the two driving joint axes are located in the respective branch planes and coincide with each other, and the two-degree-of-freedom decoupling end effector is matched, so that the mechanism can realize four-degree-of-freedom motion completely decoupled.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of minimally invasive surgery, in particular to a novel remote center of motion mechanism for minimally invasive surgery. BACKGROUND

[0002] Minimally invasive surgery (MIS) is a surgical technique that uses small incisions or minimal access to insert instruments or chemicals into the human body to remove, repair or reconstruct the lesions in the human body. Compared with the traditional open surgery, MIS has the advantages of minimal trauma (incision diameter is generally 0.5-1cm), less blood loss, high safety, less postoperative infection and shorter recovery time, etc. Therefore, MIS has been widely popularized in recent years.

[0003] However, in MIS, there is a specific surgical constraint condition, that is, the surgical tool must pass through the incision point on the body surface, otherwise it will cause the pulling of the patient's incision and increase the size of the incision. Under this constraint, the surgical instrument can have at most four degrees of freedom of movement, including three rotations and one movement. Therefore, this brings many difficulties to the doctor's hand operation. The more obvious problems are: unable to move horizontally, poor operation convenience, existence of fulcrum effect, hand-eye discoordination, etc. A better solution to these problems is to use a surgical robot with a remote center of motion (RCM) function to assist the doctor in surgical operation. The remote center of motion can meet the constraint condition, cause less pulling of the patient's incision, and have higher safety. In addition, it is equipped with a corresponding master-slave operation system and image equipment. By using reasonable master-slave mapping and control strategy, the operation intuitiveness and convenience are improved, and the fulcrum effect is eliminated.

[0004] Currently, there are two main methods to achieve the function of remote center of motion (RCM) for surgical robots: algorithm constraint method and mechanism constraint method. The algorithm constraint method calculates the target trajectory of the robot through the inverse kinematics algorithm of the robot, and sets the corresponding constraints based on this to make the motion trajectory of the end-effector of the robot always pass through the RCM. This method has high flexibility and a large range of motion, and can directly use existing commercial robot products. However, it relies on the stability of the algorithm, and has poor safety. Once an algorithm error occurs, it will cause great harm to the patient, and the overall risk is too great to pass the ethical review, so it is rarely used in actual surgery. The mechanism constraint method constrains the two degrees of freedom of the RCM mechanism at the RCM point, so that the end-effector can always pass through the RCM point. This method has high stability and strong safety, and is more in line with the actual needs of surgery. The mechanism that can achieve this constraint function is called RCM mechanism, and different configurations of the RCM mechanism have different performance characteristics and can be applied to different surgical needs. Therefore, it is meaningful to design and analyze new configurations of the RCM mechanism.

[0005] Existing solutions and drawbacks:

[0006] RCM mechanisms can be divided into serial RCM mechanisms, parallel RCM mechanisms, and hybrid RCM mechanisms according to their open and closed chain composition.

[0007] Serial RCM mechanisms have been widely used in commercial surgical robots due to their simple structure and low implementation difficulty. The most classic configuration is the double parallelogram configuration and the double pulley configuration based on its functional evolution. The world's most successful surgical robot system, Davinci minimally invasive surgical robot, adopts this configuration scheme. A large number of related theoretical research and configuration evolution work have been carried out in academia, but the overall number of hinges is too large, making it difficult to achieve high precision. In some complex and delicate surgical fields, it cannot meet the needs. The second common serial configuration is the rotatable circular arc track configuration, which can achieve good RCM precision through a precision machined circular arc track and a slider. Several types of prototypes have been designed by the Chinese University of Hong Kong based on this type of configuration. However, the driving difficulty of the degree of freedom along the circular arc is great, and the weight is large. At present, it is still mainly in the stage of academic research. The third type of serial configuration is the multi-spherical link configuration, which has a large range of motion and various composition and evolution methods. Scholars from the University of Nebraska have designed a spherical gear link RCM prototype based on its evolution. However, it has serious motion coupling, which affects its safety and intuitiveness. According to research and analysis in the field of mechanism, serial type mechanisms generally have poor precision and stiffness due to their simple structure and long chain links, which cause cumulative errors. Based on the above-mentioned defects of each serial RCM configuration, the overall limitations of serial RCM mechanisms are relatively large.

[0008] Parallel RCM mechanisms, while structurally complex, can eliminate cumulative errors between kinematic chains at the mechanics level; they inherently possess higher positioning accuracy and stiffness-to-mass ratio. Currently, there is considerable research in academia, with the primary RCM configuration being a two-plane branched parallel configuration. Its working principle involves intersecting the rotation axes of two rotatable planar branches at a single point. Under this geometric relationship, the line of intersection of the planes containing the two branches must always pass through this intersection point, thus achieving the RCM characteristics. Based on this, teams from Tianjin University, Shanghai Jiao Tong University, Tsinghua University, and Delft University of Technology in the Netherlands have proposed related evolutionary configurations and prototypes. However, due to the complex branch structure and numerous mutual constraints and interferences, parallel configurations either cannot satisfy full-circumference RCM motion with four degrees of freedom, or have a small workspace and severe motion coupling, and therefore have not yet been applied in the commercial field.

[0009] Hybrid RCM mechanisms generally integrate and improve upon classic configurations of series and parallel RCM mechanisms. Their design typically decouples the required attitude adjustment motions from the end-effector motions to simplify kinematic calculations and reduce motion coupling. However, current research and solutions in this field are limited. A representative example is a hybrid RCM configuration proposed by Sungkyunkwan University in South Korea, which uses two UPS branches to drive a double parallelogram branch. This configuration offers a large workspace and improved accuracy compared to traditional series double parallelogram configurations. However, due to the excessive number of hinges, it still cannot achieve very high accuracy. Furthermore, using UPS branches with equivalent ball joints as the drive mechanism makes it prone to singular configurations, indicating room for further improvement. Nevertheless, this demonstrates the significant potential for research into hybrid RCM mechanism configurations. Summary of the Invention

[0010] (a) Technical problems to be solved

[0011] To address the shortcomings of existing technologies, this invention provides a novel telecentric fixed-point mechanism for minimally invasive surgery, aiming to solve the problem that the RCM mechanism in existing minimally invasive surgical robot systems cannot simultaneously achieve good end-effector positioning accuracy, good motion decoupling, and a large workspace.

[0012] (II) Technical Solution

[0013] To achieve the above objectives, the present invention provides the following technical solution: a novel telecentric fixed-point mechanism for minimally invasive surgery, wherein the telecentric fixed-point mechanism is mounted on a robotic arm and used to control the movement of surgical instruments. The telecentric fixed-point mechanism includes a base, a moving platform, two sets of planar branch assemblies, an arc branch assembly, and a two-degree-of-freedom decoupled end effector. The two sets of planar branch assemblies are symmetrically arranged on the base. Each planar branch assembly is a parallelogram frame composed of six connecting rods. The ends of the planar branch assemblies are hinged to the moving platform. Each arc branch assembly includes a semi-circular arc guide rail and a track slider that slides on the arc guide rail. The two ends of the arc guide rail are pivotally connected to the base. The track slider is connected to the moving platform. The two-degree-of-freedom decoupled end effector is mounted on the moving platform and is used to control the adjustment of the surgical instrument's rotation and feed degrees of freedom.

[0014] Preferably, the planar branch assembly includes a drive motor, connecting rod one, connecting rod two, connecting rod three, connecting rod four, connecting rod five, and connecting rod six. Connecting rod two, connecting rod three, connecting rod four, and connecting rod five are sequentially hinged to form a parallelogram frame. The drive motor is fixed on the base and is hinged to the hinged part at the first end of the connecting rod. The tail end of connecting rod one is coaxially hinged to the hinged end of connecting rod two and connecting rod five. One end of connecting rod six is ​​hinged to the moving platform, and the other end is hinged to connecting rod three.

[0015] Preferably, the two-degree-of-freedom decoupled end effector includes a cylindrical gear, a rotating gear, a feed gear, a rotating motor, and a feed motor. The cylindrical gear is pivotally connected to the moving platform via bearings. The cylindrical gear has teeth at equal intervals in the axial and circumferential directions on its outer surface, and all four sides of the teeth are tooth profiles that can mesh with the gear. The rotating motor and the feed motor are fixed on the moving platform. The rotating gear meshes parallel to the cylindrical gear and is connected to the output shaft of the rotating motor. The feed gear meshes tangentially to the axis of the cylindrical gear and is connected to the output shaft of the feed motor. The surgical instrument is located at the center of the cylindrical gear.

[0016] Preferably, the telecentric fixed point mechanism further includes two gravity compensation devices. Each gravity compensation device includes a wire rope, a housing, a sliding block, a movable pulley, a fixed pulley, a spring, and a guide wheel. The lower part of the housing is coaxially connected to the end of the arc guide rail. The housing is provided with a slide rail for the sliding block to slide vertically. The movable pulley is mounted on the sliding block. One end of the wire rope is fixed to the back of the arc guide rail, and the other end passes through the guide wheel, the fixed pulley, and the movable pulley before being fixed to the housing. The spring is located between the sliding block and the bottom of the housing. A level is mounted on the housing.

[0017] A displacement method for a telecentric fixed-point mechanism includes the following steps:

[0018] S1: The initial pose is taken when the coordinate system {P} of the surgical instrument end point coincides with the fixed coordinate system {O} of the telecentric fixed point mechanism.

[0019] S2: After the telecentric fixed-point mechanism moves, the feed depth d of the surgical instrument relative to the incision point O. w The angle θ of the rotation of the surgical instrument around its own axis w w The angle θ between the projection line of axis w onto the xz, yz plane of the fixed coordinate system and the z-axis. x With θ y These four variables reflect the position and orientation of the instrument;

[0020] S3: The telecentric fixed-point mechanism has three rotary joints and one translating joint driven by a motor, and their rotation / translation amounts are represented by θ1, θ2, θ3, and d1, respectively; the plane in which the planar branch assembly is located and its unit normal vector are represented by ∑ i and This means that, since the two planes rotate around the axes of drive joints 1 and 2 respectively, their Plücker coordinates in coordinate system {O} can be represented as:

[0021]

[0022] Where n oi Represents the plane ∑ i Position vector and normal vector between point O The dot product of n is such that, since both planes always pass through point O, n... oi Since cθ and sθ are always equal to 0, and cθ and sθ represent cosθ and sinθ respectively, the Plücker coordinates of the intersection of the two planes (the straight line containing the axis w of the instrument) can be calculated as follows:

[0023]

[0024] in

[0025] when -π / 2 < θ1 and θ2 < π / 2

[0026] in It is the unit vector of the direction vector of the line (the w vector in coordinate system {P}), w o The vectors representing the position of the line relative to point O are: The cross product of the two lines, calculated using this straight line, also reflects that the axis of the end effector always passes through point O, and further, the angle between its projection line on the xz and yz planes and the z-axis can be derived as follows:

[0027]

[0028] Due to the presence of the circular arc branch assembly, the relative distance between the moving platform and the RCM point O remains constant during the movement of the mechanism, and the moving platform cannot rotate around the axis of the instrument. Therefore, the end effector mounted on it will only move relative to it when the two tandem drive joints move; thus, the feed depth d of the instrument relative to the infeed point O is... w Depends solely on the linearly driven joint d1 and all other joints being equal in size, and the angle θ by which the instrument rotates about its own axis w. w Since the rotational drive joint θ3 is constant and of equal magnitude, the forward and inverse kinematics of the mechanism can be derived as follows:

[0029]

[0030] Differentiating both sides of the forward kinematics yields:

[0031]

[0032] Therefore, the forward and inverse kinematics of the telecentric fixed-point mechanism are completely decoupled from the Jacobian.

[0033] (III) Beneficial Effects

[0034] This invention provides a novel distal immobilized point mechanism for minimally invasive surgery. It has the following beneficial effects:

[0035] 1. This novel telecentric fixed-point mechanism for minimally invasive surgery is based on an over-constrained parallel mechanism design method. It uses a fixed-point mechanism with a dual-plane branch parallel configuration and a rotatable circular arc track configuration as parallel mechanism branches, creating over-constraint within the mechanism and improving its accuracy and rigidity. By arranging the two planar branches orthogonally and perpendicularly, with the axes of the two drive joints located within their respective branch planes and perpendicular and coincident, and in conjunction with a two-DOF decoupled end effector, the mechanism can achieve completely decoupled four-DOF motion. By introducing a circular arc branch to restrict the feed degree of freedom of the dual-plane branches, the moving platform is free from parasitic motion relative to the two rotational degrees of freedom. Then, a driveable 2DOF decoupled parallel end effector is placed on the moving platform to provide instrument feed and rotation, thus achieving complete decoupling of the 4DOF kinematics. This reduces the complexity of the control algorithm and improves intuitiveness and safety.

[0036] 2. The novel telecentric fixed-point mechanism for minimally invasive surgery employs an over-constraint design in the parallel section of the RCM mechanism. Two configurations of the RCM mechanism (circular arc RCM configuration and double-plane RCM configuration) are used as branches of the parallel mechanism, and their RCM points are coincident. This over-constraints the two movements of the parallel mechanism along the RCM points throughout the workspace. The over-constraint in the parallel mechanism can reduce the gap error of the branches and increase the stiffness of the mechanism, thereby improving the accuracy of the mechanism.

[0037] 3. This novel telecentric fixed-point mechanism for minimally invasive surgery, based on the characteristics of the RCM mechanism during surgery—small inertia for instrument feeding and rotation, but large inertia for posture adjustment—adopts a hybrid mechanism design. The two degrees of freedom with large inertia are driven by a large-size, high-load parallel mechanism, while the two degrees of freedom with small inertia are driven by a specially designed gear and rack composite mechanism mounted in series on the moving platform of the parallel mechanism, making the mechanism more compact. This also reduces the degrees of freedom and complexity of the parallel mechanism; and the branch parameters have been optimized to ensure motion and force transmission performance while matching the branch parameters to reduce the impact of internal constraints and mutual interference of each branch in the parallel section on the workspace, allowing the mechanism to achieve a large motion space within a compact size. Attached Figure Description

[0038] Figure 1 This is an isometric view of the present invention in use.

[0039] Figure 2 This is a schematic diagram of the telecentric fixed point mechanism of the present invention;

[0040] Figure 3 This is a schematic diagram of the two-degree-of-freedom decoupled end effector structure of the present invention;

[0041] Figure 4 This is a schematic diagram of the gravity compensation device of the present invention.

[0042] Figure 5 This is a schematic diagram of the RCM mechanism of the present invention;

[0043] Figure 6 This is a schematic diagram illustrating the derivation of the kinematic model of the telecentric fixed-point mechanism of the present invention.

[0044] In the diagram: 1. Base, 2. Moving platform, 3. Planar branch assembly, 4. Circular arc branch assembly, 5. Two-degree-of-freedom decoupled end effector, 6. Gravity compensation device, 7. Surgical instrument, 8. Robotic arm, 31. Drive motor, 32. Link 1, 33. Link 2, 34. Link 3, 35. Link 4, 36. Link 5, 37. Connection 6, 41. Circular arc guide rail, 42. Track slider, 51. Cylindrical gear, 52. Bearing, 53. Rotating gear, 54. Feed gear, 55. Rotating motor, 56. Feed motor, 57. Tooth, 61. Wire rope, 62. Housing, 63. Sliding block, 64. Moving pulley, 65. Fixed pulley, 66. Spring, 67. Guide wheel, 68. Level. Detailed Implementation

[0045] This invention provides a novel distal immobilized point mechanism for minimally invasive surgery, such as... Figures 1-6As shown, the telecentric fixed-point mechanism is mounted on a commercially available six-DOF collaborative robotic arm 8. The robotic arm 8 fixes the telecentric fixed-point mechanism in place after adjusting it to a suitable position relative to the patient, serving as the frame for the mechanism. The telecentric fixed-point mechanism is used to control the movement of the surgical instrument 7. During the procedure, only the telecentric fixed-point mechanism performs the motion operations, providing fully decoupled 4DOF motion, including roll, pitch, feed, and rotation of the end-effector along the RCM point.

[0046] like Figure 1 As shown, the telecentric fixed point mechanism includes a base 1, a moving platform 2, two sets of planar branch components 3, a circular arc branch component 4, and a two-degree-of-freedom decoupled end effector 5.

[0047] like Figure 2 As shown, two sets of planar support components 3 are symmetrically arranged on the base 1. The planar support component 3 is a parallelogram frame composed of six connecting rods. The end of the planar support component 3 is hinged to the moving platform 2. The planar support component 3 includes a drive motor 31, connecting rod 1 32, connecting rod 2 33, connecting rod 34, connecting rod 4 35, connecting rod 5 36, and connecting rod 6 37. Connecting rod 2 33, connecting rod 34, connecting rod 4 35, and connecting rod 5 36 are hinged in sequence to form a parallelogram frame. The drive motor 31 is fixed on the base 1 and is hinged to the hinge part at the beginning of connecting rod 1 32. The end of connecting rod 1 32 is coaxially hinged to the hinge end of connecting rod 2 33 and connecting rod 5 36. One end of connecting rod 6 37 is hinged to the moving platform 2, and the other end is hinged to connecting rod 3 34. Links 4 (35) and 5 (36) in the parallelogram frame are redundant and do not affect the kinematics. However, they form over-constraints within the branches, which improves the overall stiffness of the branches and also serves as a limit, preventing collinear singularities between the links.

[0048] like Figure 2 As shown, the arc-shaped branch assembly 4 includes a semi-circular arc-shaped guide rail 41 and a track slider 42 slidably adapted to the arc-shaped guide rail 41. The arc-shaped guide rail 41 can rotate around a fixed axis, and its two ends are pivotally connected to the base 1. It has two rotational movements. The first rotational movement is achieved by mounting the arc-shaped guide rail 41 on a pair of coaxial rotary joints mounted on the base 1, with the axis passing through the center of the arc-shaped guide rail 41. The second rotational movement is the rotation of the track slider 42 on the arc-shaped guide rail 41 relative to the guide rail. The track slider 42 is connected to the moving platform 2. The arc-shaped guide rail 41 uses a commercially available guide rail that is machined in one piece, which has better installation accuracy and overall rigidity compared to a split arc-shaped guide rail. A two-degree-of-freedom decoupled end effector 5 is set on the moving platform 2 and is used to control the adjustment of the two degrees of freedom of the surgical instrument 7: rotation and feed.

[0049] like Figure 3As shown, the two-degree-of-freedom decoupled end effector 5 includes a cylindrical gear 51, a rotating gear 53, a feed gear 54, a rotating motor 55, and a feed motor 56. The cylindrical gear 51 is pivotally connected to the moving platform 2 via a bearing 52. The cylindrical gear 51 has teeth 57 evenly spaced axially and circumferentially on its outer surface. All four sides of the teeth 57 are tooth profiles that can mesh with the gear. The rotating motor 55 and the feed motor 56 are fixed on the moving platform 2. The rotating gear 53 meshes parallel to the cylindrical gear 51 and is connected to the output shaft of the rotating motor 55. The feed gear 54 meshes tangentially to the axis of the cylindrical gear 51 and is connected to the output shaft of the feed motor 56. The surgical instrument 7 is positioned at the center of the cylindrical gear 51. Combining the characteristics of a rack and pinion mechanism and a rotary gear mechanism, this design provides the end surgical instrument 7 with two degrees of freedom: axial feed and rotation.

[0050] The cylindrical gear 51 is constructed by first linearly rotating and cutting a cylindrical surface along a rack profile, and then axially stretching and cutting it along a gear profile. The shaft has a central hole, allowing the mounting of various surgical instruments, such as endoscopes, at one end. Compared to a series-driven design for each degree of freedom, this design achieves decoupled two-degree-of-freedom motion that does not interfere with each other during movement, and is very compact. The shaft is mounted within a circular track machined on the moving platform 2. Three PTFE sliding bearings support the shaft and its internal instruments: two are mounted on the track as fixed ends, and the other on the shaft as a sliding end, providing three-point support to improve its axial accuracy and rigidity. Bearing 52 is a PTFE sliding bearing. Compared to rolling bearings, PTFE sliding bearings, due to their low-friction properties, can simultaneously support both linear and rotational motions of the shaft and provide lubrication without oil, improving the cleanliness of the mechanism.

[0051] like Figure 4 As shown, the telecentric fixed point mechanism also includes two gravity compensation devices 6. Each gravity compensation device 6 includes a wire rope 61, a housing 62, a sliding block 63, a movable pulley 64, a fixed pulley 65, a spring 66, and a guide wheel 67. The lower part of the housing 62 is coaxially connected to the end of the arc guide rail 41. The housing 62 is provided with a slide rail for the sliding block 63 to slide vertically. The movable pulley 64 is mounted on the sliding block 63. One end of the wire rope 61 is fixed to the back of the arc guide rail 41, and the other end passes through the guide wheel 67, the fixed pulley 65, and the movable pulley 64 before being fixed to the housing 62. The spring 66 is located between the sliding block 63 and the bottom of the housing 62.

[0052] During operation, the wire rope 61 drives the pulley 64, stretches the spring 66, and generates tension to compensate for the gravitational torque exerted on the coaxial rotary joint by the arc guide rail 41 and the two-degree-of-freedom decoupled end effector 5. The device is connected to the rotary joints on both sides of the arc guide rail 41 via three sets of bolts and nuts and a rotating shaft. Thus, when the telecentric fixed-point mechanism is placed in different directions, the gravity compensation device 6 can adapt to the direction of gravity. A level 68 is installed on the housing 62. By determining the reading of the level 68, the gravity compensation device 6 can be fixed in the desired position by tightening the bolts.

[0053] Working principle:

[0054] like Figure 5 As shown, since the connecting rod 32 of the two planar branch components 3 is connected to the drive motor 31 as a drive joint, the plane on which the planar branch components are located can rotate around the axis of this joint under the drive of the drive motor 31, arranging the drive joint axes of the two planar branch components perpendicularly and intersecting at a point. The connecting rod 37 of the planar branch components is hinged to the moving platform 2, also forming a joint, so that the end joints of the two planar branch components 3 are coaxially and oppositely mounted on the moving platform 2, and the equivalent mounting points coincide. This common axis is the intersection line of the planes on which the two planar branch components 3 are located, and this intersection line always passes through the intersection point of the drive joint axes of the two planar branch components. Therefore, the two planar branch components 3 together form an RCM mechanism with a parallel configuration of two planar branches mentioned earlier. The two degrees of freedom of the arc branch assembly 4 are: the rotation of the arc guide rail 41 around the coaxial rotational joint and the rotation of the track slider 42 on the arc guide rail 41 relative to the arc guide rail 41. Both of these rotational movements always pass through the center of the arc guide rail 41. During the movement of these two degrees of freedom, the distance between the slider and the center of the guide rail remains unchanged. Therefore, this branch also constitutes an RCM mechanism.

[0055] By aligning the RCM points of these two RCM mechanisms and connecting their ends via a moving platform 2, and because both RCM mechanisms constrain the two degrees of freedom required for the moving platform to move away from the RCM point, each branch collectively creates an over-constraint on the moving platform 2. This over-constraint means that when the moving platform 2 moves away from the RCM point, it will simultaneously experience constraint forces from multiple branches, making such movement difficult. This design of an over-constrained parallel platform can reduce backlash errors within the branches, thereby improving the stiffness and accuracy of the mechanism while achieving the function of a telecentric fixed point.

[0056] The telecentric fixed-point mechanism employs a fully decoupled configuration design to improve surgical safety and reduce the complexity of kinematic procedures. In medical practice, the instrument's pose is typically represented by four motions: insertion length along the instrument axis, rotation about that axis, tilt angle around the entry point, and yaw angle. Therefore, compared to methods such as RPY angles and transformation matrices, using these four motions to reflect pose information is more convenient and intuitive for surgeons. This application proposes a displacement method for the telecentric fixed-point mechanism, describing the instrument's pose by constructing these four variables in geometric space. Figure 6 As shown, it includes the following steps:

[0057] S1: The initial pose is taken when the coordinate system {P} of the surgical instrument end point coincides with the fixed coordinate system {O} of the telecentric fixed point mechanism.

[0058] S2: After the telecentric fixed-point mechanism moves, the feed depth d of the surgical instrument relative to the incision point O. w The angle θ of the rotation of the surgical instrument around its own axis w w The angle θ between the projection line of axis w onto the xz, yz plane of the fixed coordinate system and the z-axis. x With θ y These four variables reflect the position and orientation of the instrument;

[0059] S3: The telecentric fixed-point mechanism has three rotary joints and one translating joint driven by a motor, and their rotation / translation amounts are represented by θ1, θ2, θ3, and d1, respectively; the plane in which the planar branch assembly is located and its unit normal vector are represented by ∑ i and This means that, since the two planes rotate around the axes of drive joints 1 and 2 respectively, their Plücker coordinates in coordinate system {O} can be represented as:

[0060]

[0061] Where n oi Represents the plane ∑ i Position vector and normal vector between point O The dot product of n is such that, since both planes always pass through point O, n... oi Since cθ and sθ are always equal to 0, and cθ and sθ represent cosθ and sinθ respectively, the Plücker coordinates of the intersection of the two planes (the straight line containing the axis w of the instrument) can be calculated as follows:

[0062]

[0063] in

[0064]

[0065] in It is the unit vector of the direction vector of the line (the w vector in coordinate system {P}), w o The vectors representing the position of the line relative to point O are: The cross product of the two lines, calculated using this straight line, also reflects that the axis of the end effector always passes through point O, and further, the angle between its projection line on the xz and yz planes and the z-axis can be derived as follows:

[0066]

[0067] Due to the presence of the circular arc branch assembly, the relative distance between the moving platform and the RCM point O remains constant during the movement of the mechanism, and the moving platform cannot rotate around the axis of the instrument. Therefore, the end effector mounted on it will only move relative to it when the two tandem drive joints move; thus, the feed depth d of the instrument relative to the infeed point O is... w Depends solely on the linearly driven joint d1 and all other joints being equal in size, and the angle θ by which the instrument rotates about its own axis w. w Since the rotational drive joint θ3 is constant and of equal magnitude, the forward and inverse kinematics of the mechanism can be derived as follows:

[0068]

[0069] Differentiating both sides of the forward kinematics yields:

[0070]

[0071] Therefore, the forward and inverse kinematics of the telecentric fixed-point mechanism are completely decoupled from the Jacobian.

[0072] Schematic diagram of the telecentric fixed-point mechanism's workflow: The overall hardware system of the telecentric fixed-point mechanism includes: a host computer PC, a hardware control unit, and a sensing unit. The NDI optical sensor in the sensing unit acquires the mechanism's real-time pose and sends signals to the host computer PC via USB. The host computer analyzes the required subsequent movements of the mechanism and sends control commands to the Beckhoff embedded controller via TCP / IP protocol. The embedded controller calculates the motion of each motor based on kinematic algorithms and sends it to the driver via the EtherCAT bus at a frequency of 1000Hz to ensure the real-time performance of the mechanism's movements. The driver then converts these commands into current and voltage outputs to servo drive the motors. The motors used are four Maxon DC servo motors, each equipped with a high-precision reducer and encoder, thus achieving high-precision drive of the proposed mechanism to meet the positional accuracy requirements during surgery.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel telecentric fixed-point mechanism for minimally invasive surgery, wherein the telecentric fixed-point mechanism is mounted on a robotic arm (8) for controlling the movement of surgical instruments (7), characterized in that: The telecentric fixed point mechanism includes a base (1), a moving platform (2), two sets of planar branch components (3), an arc branch component (4), and a two-degree-of-freedom decoupled end effector (5). The two sets of planar branch components (3) are symmetrically arranged on the base (1). The planar branch component (3) is a parallelogram frame composed of six connecting rods. The end of the planar branch component (3) is hinged to the moving platform (2). The arc branch component (4) includes a semi-circular arc guide rail (41) and a track slider (42) that is slidably adapted to the arc guide rail (41). The two ends of the arc guide rail (41) are pivotally connected to the base (1). The track slider (42) is connected to the moving platform (2). The two-degree-of-freedom decoupled end effector (5) is arranged on the moving platform (2) and is used to control the adjustment of the two degrees of freedom of the surgical instrument (7) in terms of rotation and feed.

2. A novel distal immobilized point mechanism for minimally invasive surgery according to claim 1, characterized in that: The planar branch assembly (3) includes a drive motor (31), a first link (32), a second link (33), a third link (34), a fourth link (35), a fifth link (36), and a sixth link (37). The second link (33), the third link (34), the fourth link (35), and the fifth link (36) are sequentially hinged to form a parallelogram frame. The drive motor (31) is fixed on the base (1) and is hinged to the hinged part at the head end of the first link (32). The tail end of the first link (32) is coaxially hinged to the hinged end of the second link (33) and the fifth link (36). One end of the sixth link (37) is hinged to the moving platform (2), and the other end is hinged to the third link (34).

3. A novel distal immobilized point mechanism for minimally invasive surgery according to claim 1, characterized in that: The two-degree-of-freedom decoupled end effector (5) includes a cylindrical gear (51), a rotating gear (53), a feed gear (54), a rotating motor (55), and a feed motor (56). The cylindrical gear (51) is pivotally connected to the moving platform (2) via a bearing (52). The cylindrical gear (51) has teeth (57) spaced axially and circumferentially on its outer surface. All four sides of the teeth (57) are tooth profiles that can mesh with the gear. The rotating motor (55) and the feed motor (56) are fixed on the moving platform (2). The rotating gear (53) meshes parallel to the cylindrical gear (51) and is connected to the output shaft of the rotating motor (55). The feed gear (54) meshes tangentially with the axis of the cylindrical gear (51) and is connected to the output shaft of the feed motor (56). The surgical instrument (7) is located at the center of the cylindrical gear (51).

4. A novel distal immobilized point mechanism for minimally invasive surgery according to claim 1, characterized in that: The telecentric fixed point mechanism also includes two gravity compensation devices (6). The gravity compensation device (6) includes a wire rope (61), a housing (62), a sliding block (63), a movable pulley (64), a fixed pulley (65), a spring (66), and a guide wheel (67). The lower part of the housing (62) is coaxially connected to the end of the arc guide rail (41). The housing (62) is provided with a slide rail for the sliding block (63) to slide vertically. The movable pulley (64) is set on the sliding block (63). One end of the wire rope (61) is fixed to the back of the arc guide rail (41), and the other end passes through the guide wheel (67), the fixed pulley (65), and the movable pulley (64) and is fixed on the housing (62). The spring (66) is set between the bottom of the sliding block (63) and the housing (62). A level (68) is set on the housing (62).

5. A displacement method for a telecentric fixed-point mechanism, characterized in that, The telecentric fixed-point mechanism according to any one of claims 1-4 includes the following steps: S1: Connect the surgical instrument end-effector coordinate system {P} to the telecentric fixed-point mechanism coordinate system {P}. When they coincide, they are used as the initial pose; S2: After the movement of the distal fixed-point mechanism, the surgical instrument's relative entry point feed depth Surgical instruments rotate around their own axis Angle of rotation axis The angle between the projection line on the xz, yz plane of the fixed coordinate system and the z-axis and These four variables reflect the position and orientation of the instrument; S3: The telecentric fixed-point mechanism has three rotary joints and one translating joint driven by a motor. Its rotational / translational ranges are respectively represented by... To represent; the plane in which the planar branch component is located and its unit normal vector are respectively represented by This indicates that, since the two planes rotate around the axes of drive joints 1 and 2 respectively, their coordinate system { The Plücker coordinates under} can be represented as: in Representing a plane and Position vector and normal vector between points The dot product, since the two planes always pass through... Point, therefore Equal to , They represent Therefore, the intersection of the two planes (the axis of the instrument) The Plücker coordinates of the line (where the line is located) can be calculated as follows: in in It is the direction vector of the line (in coordinate system {P}). The unit vector of (vector). Represents the line relative to The position vector of a point and the vector The cross product, calculated using this straight line, also reflects that the axis of the end effector always passes through... The point can be further deduced to have the following angle between its projection line on the xz and yz planes and the z-axis: Due to the presence of the circular arc branch assembly, during the movement of the mechanism's moving platform, its interaction with the RCM point... Since the relative distance remains constant and the moving platform cannot rotate around the instrument's axis, the end effector mounted on it will only move relative to it when the two tandem drive joints move; therefore, the relative entry point of the instrument... feed depth Depends only on the linear drive joint And they are all the same size, and the instruments rotate around their own axis. Angle of rotation Depends only on the rotation drive joint And since they are of equal size, the forward and inverse kinematics of the mechanism can be derived as follows: Differentiating both sides of the forward kinematics yields: Therefore, the forward and inverse kinematics of the telecentric fixed-point mechanism are completely decoupled from the Jacobian.

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