Novel telecentric fixed point mechanism for minimally invasive surgery

Abstract

The invention provides a novel telecentric fixed point mechanism for minimally invasive surgery, which comprises a base, a movable platform, two groups of planar branch chain assemblies, an arc branch chain assembly and a two-degree-of-freedom decoupling end effector, the two groups of planar branch chain assemblies are symmetrically arranged on the base, each planar branch chain assembly is a connecting rod group which is composed of six connecting rods and is provided with a parallelogram frame, and the arc branch chain assembly is provided with a parallelogram frame. The tail end of the plane branch chain assembly is connected and hinged to the movable platform, and the arc branch chain assembly comprises a semicircular arc guide rail and a rail sliding block matched with the arc guide rail in a sliding mode. A fixed point mechanism of a double-plane branch chain parallel configuration and a fixed point mechanism of a rotatable arc track configuration serve as parallel mechanism branch chains, over-constraint is formed in the mechanism, and the precision and rigidity of the mechanism are improved. The two planar branch chains are orthogonally and vertically arranged, the axes of the two driving joints are located in respective branch chain planes, are perpendicular to each other and coincide with each other, and a two-degree-of-freedom decoupling end executor is matched, so that the mechanism can realize four-degree-of-freedom movement which is completely decoupled.

Description

Technical Field

[0001] The invention relates to the technical field of minimally invasive surgical operations, and in particular to a novel telecentric fixed point mechanism used for minimally invasive operations. Background Art

[0002] Minimally invasive surgery (MIS) is a surgical technique that uses small trauma or small access routes to deliver instruments or chemicals into the human body to remove, repair or reconstruct lesions in the human body. Compared with traditional open surgery, which has problems such as large trauma (incision diameter is generally 12-16cm), large blood loss, easy infection of wounds and organs, and long recovery time, minimally invasive surgery has the advantages of minimal trauma (incision diameter is generally 0.5-1cm), less blood loss, high safety, less prone to postoperative infection, and short recovery time. Therefore, it has been widely popularized in recent years.

[0003] However, in minimally invasive surgery, there is a specific surgical constraint, that is, the surgical tool must pass through the incision point on the body surface, otherwise it will cause traction on the patient's wound and increase the size of the wound. Under this constraint, the surgical instrument can only have a maximum of 3 rotations and 1 movement, totaling four degrees of freedom. Therefore, this brings many difficulties to the doctor's manual operation. The more obvious problems are: it cannot move horizontally, which makes the operation less convenient, there is a fulcrum effect, and it causes hand-eye coordination. A better solution to these problems is to use a surgical robot with a remote center of motion (RCM) function to assist doctors in surgical operations. It has a remote center of motion (RCM) function to meet the constraint conditions, less traction on the patient's wound, and higher safety. It is equipped with a corresponding master-slave operating system and imaging equipment. By adopting a reasonable master-slave mapping and control strategy, it improves the intuitiveness and convenience of operation and eliminates the fulcrum effect.

[0004] At present, there are two main methods for surgical robots to realize the function of telecentric fixed points: algorithm constraint method and mechanism constraint method. Among them, the algorithm constraint method is to calculate the robot's target motion trajectory through the robot's inverse kinematics algorithm, and set corresponding constraints based on this, so that the motion trajectory of the robot's end instrument always passes through the telecentric fixed point. Under this method, the robot has high flexibility, a large range of motion, and can directly use existing commercial robot products; however, it relies on algorithm stability and has poor safety. Once an algorithm error occurs, it will cause great harm to the patient. The overall risk is too high and it is difficult to pass ethical review. It is rarely used in actual surgery. The mechanism constraint method is to constrain the two degrees of freedom of movement of the mechanism at the RCM point so that the end instrument can always pass the RCM point. This method has high stability and strong safety; it is more in line with the actual needs of surgery. The mechanism that can realize this constraint function is called the RCM mechanism. Its different configurations have different performance characteristics and can be applied to different surgical needs. Therefore, it is very meaningful to design and analyze its new configuration.

[0005] Existing solutions and shortcomings:

[0006] According to the composition of its opening and closing chain, the RCM mechanism can be divided into a series RCM mechanism, a parallel RCM mechanism and a hybrid RCM mechanism.

[0007] The serial RCM mechanism has been widely used in commercial surgical robots due to its simple structure and low difficulty in implementation. The most classic configurations are the double parallelogram configuration and the double pulley configuration based on its functional evolution. The Davinci minimally invasive surgical robot, the most successful surgical robot system in the world, adopts this configuration scheme. In academia, a lot of theoretical research and configuration evolution work have also been carried out. However, due to the excessive number of overall hinges, it is difficult to achieve a high level of accuracy, and it cannot meet the needs in some complex and delicate surgical fields. The second common serial configuration is the rotatable arc track configuration, which can achieve good RCM accuracy through precision-machined arc tracks and sliders. The Chinese University of Hong Kong has designed several prototypes based on this configuration; however, it is difficult to drive the degrees of freedom along the arc motion, and its own weight is large, so it is still mainly in the academic research stage. The third type of serial configuration is the multi-spherical connecting rod configuration, which has a large range of motion, diverse composition and evolution. Scholars from the University of Nebraska in the United States have designed a spherical gear connecting rod RCM prototype based on its evolution; however, its motion coupling is serious, resulting in its lack of safety and intuitiveness. According to the research and analysis of mechanism, the serial type of mechanism itself has a simple structure, a long link, and cumulative errors, resulting in generally poor accuracy and stiffness; and in summary, the defects of each serial RCM configuration are also more obvious, so the overall limitations of the serial RCM mechanism are relatively large.

[0008] The parallel RCM mechanism has a high structural complexity, and can eliminate the cumulative error between motion chains at the mechanism level; it has higher positioning accuracy and stiffness-to-mass ratio in essence. At present, there are many studies in the academic field. Its RCM configuration is mainly a double-plane branch parallel configuration. Its working principle is to intersect the rotation axes of two rotatable planar branches at one point. Under this geometric relationship, the intersection of the planes where the two branches are located must always pass through the intersection, thereby realizing the RCM characteristics. On this basis, teams such as Tianjin University, Shanghai Jiaotong University, Tsinghua University, and Delft University of Technology in the Netherlands have proposed related evolutionary configurations and prototypes. However, due to the complex structure of the branches and the many constraints and interferences between them, the parallel type of configuration either cannot meet the full-circle RCM motion of 4 degrees of freedom, or the workspace is small and the motion coupling is serious. It has not been used in the commercial field.

[0009] The hybrid RCM mechanism generally integrates the classic configurations of the previous serial RCM mechanism and the parallel RCM mechanism with some improvements. When designing, the posture adjustment motion required by the RCM mechanism is usually decoupled from the end device motion to simplify the kinematic calculation and reduce the degree of motion coupling. However, there are few related studies and solutions in this field. Among them, the more representative one is a hybrid RCM configuration proposed by Sungkyunkwan University in South Korea, which drives a double parallelogram branch chain through two UPS branches. It has a large working space and its accuracy is improved compared with the traditional double parallelogram serial configuration. However, due to the excessive number of hinges, it still cannot achieve high accuracy. In addition, the UPS branch chain with an equivalent spherical joint is used as the drive, and the mechanism is prone to singular configurations. Therefore, there is still room for improvement, but it reflects that the configuration research related to the hybrid RCM mechanism has great potential. Summary of the invention

[0010] 1. Technical issues to be solved

[0011] In view of the shortcomings of the prior art, the present invention provides a new telecentric fixed point mechanism for minimally invasive surgery, aiming to solve the problem that the RCM mechanism in the existing minimally invasive surgical robot system is difficult to simultaneously take into account good end positioning accuracy, good motion decoupling and a larger working space.

[0012] (II) Technical solution

[0013] To achieve the above objectives, the present invention is implemented through the following technical solutions: a new type of telecentric fixed point mechanism for minimally invasive surgery, the telecentric fixed point mechanism is installed on a robotic arm and is used to control the movement of surgical instruments. The telecentric fixed point mechanism includes a base, a moving platform, two groups of planar branch chain assemblies, an arc branch chain assembly, and a two-degree-of-freedom decoupling end effector. The two groups of planar branch chain assemblies are symmetrically arranged on the base. The planar branch chain assembly is a parallelogram frame composed of six connecting rods. The end connection of the planar branch chain assembly is hinged to the moving platform. The arc branch chain assembly includes a semicircular arc guide rail and a track slider slidably adapted on the arc guide rail. The two ends of the arc guide rail are pivotally connected to the base, and the track slider is connected to the moving platform. The two-degree-of-freedom decoupling end effector is arranged on the moving platform and is used to control the adjustment of the two degrees of freedom of rotation and feeding of the surgical instrument.

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

[0015] Preferably, the two-degree-of-freedom decoupling end effector includes a cylindrical gear, an autorotating gear, a feed gear, an autorotating motor, and a feed motor. The cylindrical gear is pivotally connected to the moving platform through a bearing. The outer surface of the cylindrical gear is provided with teeth at equal intervals in the axial and circumferential directions. The four sides of the teeth are all teeth that can mesh with the gears. The autorotating motor and the feed motor are fixed on the moving platform. The autorotating gear is meshed with the cylindrical gear in parallel and is connected to the output shaft of the autorotating motor. The feed gear is meshed tangentially with the axis of the cylindrical gear and is connected to the output shaft of the feed motor. The surgical instrument is arranged at the center of the cylindrical gear.

[0016] Preferably, the telecentric fixed point mechanism also includes two gravity compensation devices, which include a steel wire rope, a shell, a sliding block, a movable pulley, a fixed pulley, a spring, and a guide wheel. The lower part of the shell is coaxially connected to the end of the circular arc guide rail, and a slide rail for vertical sliding of the sliding block is provided in the shell. The movable pulley is arranged on the sliding block, one end of the steel wire rope is fixed to the back side of the circular arc guide rail, and the other end is fixed to the shell after passing through the guide wheel, the fixed pulley, and the movable pulley. The spring is arranged between the sliding block and the bottom of the shell, and a spirit level is arranged on the shell.

[0017] A displacement method of a telecentric fixed point mechanism comprises the following steps:

[0018] S1: The surgical instrument end coordinate system {P} and the telecentric fixed point mechanism fixed coordinate system {O} are taken as the initial posture;

[0019] S2: Feed depth d of surgical instrument relative to the entry point O after the telecentric fixed point mechanism moves w , the angle θ of the surgical instrument's rotation around its own axis w w , the angle θ between the projection line of the axis w on the fixed coordinate system xz, yz plane and the z axis x With θ y , these four variables reflect the posture of the instrument;

[0020] S3: The telecentric fixed point mechanism has three rotating joints and one moving joint driven by the motor. The rotation / movement amounts are represented by θ1, θ2, θ3, and d1 respectively; the plane where the planar branch chain component is located and its unit normal vector are represented by ∑ i and It means that since the two planes rotate around the axes of the driven joints 1 and 2 respectively, their Plücker coordinates in the coordinate system {O} can be expressed as:

[0021]

[0022] Where n oi Represents plane∑ i The position vector and normal vector between point O Since the two planes always pass through point O, n oi is always equal to 0, cθ and sθ represent cosθ and sinθ respectively, therefore, the Plücker coordinates of the intersection of the two planes (the straight line where the instrument axis w lies) can be calculated as:

[0023]

[0024] in

[0025] when -π / 2<θ1andθ2<π / 2

[0026] in is the unit vector of the line direction vector (the w vector of the coordinate system {P}), w o Represents the position vector and vector of the straight line relative to point O The cross product of the straight line can also reflect that the end instrument axis always passes through point O, and it can be further deduced that the angle between its projection line and the z-axis on the xz and yz planes is:

[0027]

[0028] Due to the existence of the arc branch chain assembly, the relative distance between the moving platform of the mechanism and the RCM point O is always fixed during the movement of the moving platform, and the moving platform cannot rotate around the instrument axis. Therefore, the end instrument installed on it will only move relative to it when the two series drive joints move; therefore, the feed depth d of the instrument relative to the entry point O is w The angle θ of the device's rotation around its own axis w depends only on the linear drive joint d1 and is equal in size. w It only depends on the rotation drive joint θ3 and is equal in size, so the forward and inverse kinematics of the mechanism can be obtained:

[0029]

[0030] Taking the derivative of the two ends of the positive kinematics, we can get:

[0031]

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

[0033] (III) Beneficial effects

[0034] The present invention provides a novel telecentric fixed point mechanism for minimally invasive surgery, which has the following beneficial effects:

[0035] 1. This new type of telecentric fixed point mechanism for minimally invasive surgery is based on the design method of over-constrained parallel mechanism. The fixed point mechanism of the dual-plane branch parallel configuration and the fixed point mechanism of the rotatable arc track configuration are used as parallel mechanism branches, forming over-constraints inside the mechanism, which improves the accuracy and stiffness of the mechanism. The two plane branches are arranged orthogonally and vertically, and the two drive joint axes are located in the planes of their respective branches and are perpendicular and coincident with each other. In combination with the two-degree-of-freedom decoupling end effector, the mechanism can achieve fully decoupled four-degree-of-freedom motion; by introducing the arc branch to limit the feeding freedom of the dual-plane branch, the moving platform is free of parasitic motion relative to the two rotational degrees of freedom, and then a drivable 2DOF decoupling parallel end effector is arranged on the moving platform to provide feeding and rotation of the instrument, so that the 4DOF kinematics are completely decoupled. Reduce the complexity of the control algorithm and improve intuitiveness and safety.

[0036] 2. This new type of telecentric fixed point mechanism used for minimally invasive surgery adopts an over-constrained design for the parallel part of the RCM mechanism. Two types of RCM mechanisms (arc RCM configuration and dual-plane RCM configuration) are used as branches of the parallel mechanism, and their RCM points overlap, so that the two moving motions of the parallel mechanism along the RCM point in the entire workspace are over-constrained. The over-constraint in the parallel mechanism can reduce the gap error of the branch chain and increase the stiffness of the mechanism, thereby improving the accuracy of the mechanism.

[0037] 3. This new type of telecentric fixed point mechanism for minimally invasive surgery adopts the design of a hybrid mechanism based on the characteristics of small inertia of RCM mechanism instrument feeding and rotation during surgery, and large inertia of posture adjustment. The two degrees of freedom with large inertia are driven by a large-size, high-load parallel mechanism, and the two degrees of freedom with small inertia are driven by a special gear rack composite mechanism installed in series on the parallel mechanism dynamic platform, making the mechanism more compact. At the same time, the degrees of freedom and complexity of the parallel mechanism are reduced; the branch chain parameters are optimized and designed, and the branch chain parameters are matched with each other under the premise of ensuring the performance of motion and force transmission, so as to jointly reduce the influence of internal constraints and mutual interference of each branch chain in the parallel part on the working space, so that the mechanism has a large motion space in a compact size. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is an axonometric diagram of the present invention in use;

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

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

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

[0042] Figure 5 It is the principle diagram of the RCM mechanism of the present invention;

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

[0044] In the figure: 1 base, 2 moving platform, 3 plane branch chain assembly, 4 arc branch chain assembly, 5 two-degree-of-freedom decoupling end effector, 6 gravity compensation device, 7 surgical instrument, 8 robotic arm, 31 drive motor, 32 connecting rod one, 33 connecting rod two, 34 connecting rod three, 35 connecting rod four, 36 connecting rod five, 37 connecting rod six, 41 arc guide rail, 42 track slider, 51 cylindrical gear, 52 bearing, 53 rotating gear, 54 feed gear, 55 rotating motor, 56 feed motor, 57 teeth, 61 wire rope, 62 housing, 63 sliding block, 64 movable pulley, 65 fixed pulley, 66 spring, 67 guide wheel, 68 level. DETAILED DESCRIPTION

[0045] The embodiment of the present invention provides a novel telecentric fixed point mechanism for minimally invasive surgery, such as Figure 1-6As shown, the telecentric fixed point mechanism is installed on a commercial six-degree-of-freedom cooperative robot arm 8. The robot arm 8 adjusts the telecentric fixed point mechanism to a suitable posture relative to the patient and then fixes it, serving as the frame of the telecentric fixed point mechanism. The telecentric fixed point mechanism is used to control the movement of the surgical instrument 7. During the operation, only the telecentric fixed point mechanism is performing the movement operation, which can provide a completely decoupled 4DOF movement, including the roll, pitch, axial feed and rotation of the end instrument 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 chain components 3, an arc branch chain component 4, and a two-degree-of-freedom decoupling end effector 5.

[0047] like Figure 2 As shown, two groups of planar branch chain assemblies 3 are symmetrically arranged on the base 1. The planar branch chain assembly 3 is a parallelogram frame composed of six connecting rods. The end of the planar branch chain assembly 3 is connected and hinged to the moving platform 2. The planar branch chain assembly 3 includes a driving motor 31, a connecting rod 1 32, a connecting rod 2 33, a connecting rod 3 34, a connecting rod 4 35, a connecting rod 5 36, and a connecting rod 6 37. The connecting rod 2 33, the connecting rod 3 34, the connecting rod 4 35, and the connecting rod 5 36 are hinged in sequence to form a parallelogram frame. The driving motor 31 is fixed on the base 1 and is hinged to the hinged part at the head end of the connecting rod 1 32. The tail end of the connecting rod 1 32 is coaxially hinged to the hinged end of the connecting rod 2 33 and the connecting rod 5 36. One end of the connecting rod 6 37 is hinged to the moving platform 2, and the other end is hinged to the connecting rod 3 34. The fourth link 35 and the fifth link 36 in the parallelogram frame are redundant and have no effect on kinematics, but they form over-constraints inside the branch chain, thereby increasing the overall stiffness of the branch chain and playing a limiting role, thereby avoiding collinear singularities between the links.

[0048] like Figure 2 As shown, the arc branch chain assembly 4 includes a semicircular arc guide rail 41 and a track slider 42 slidably adapted on the arc guide rail 41. The arc guide rail 41 can rotate around a fixed axis, and the two ends of the arc guide rail 41 are pivoted on the base 1. It has two rotational movements. The first rotational movement is achieved by installing the arc guide rail 41 on a pair of coaxial rotating joints. The pair of rotating joints are installed on the base 1, and the axis passes through the center of the arc guide rail 41. The second rotational movement is the rotation of the guide slider 42 on the arc guide rail 41 relative to the guide rail; the track slider 42 is connected to the moving platform 2. The arc guide rail 41 adopts a commercial guide rail formed by an integrated machine, which has good installation accuracy and overall rigidity compared to the split arc guide rail. The two-degree-of-freedom decoupling end effector 5 is arranged on the moving platform 2, and is used to control the adjustment of the two degrees of freedom of rotation and feeding of the surgical instrument 7.

[0049] like Figure 3As shown, the two-degree-of-freedom decoupling end effector 5 includes a cylindrical gear 51, a self-rotating gear 53, a feeding gear 54, a self-rotating motor 55, and a feeding motor 56. The cylindrical gear 51 is pivoted to the moving platform 2 through a bearing 52. The outer surface of the cylindrical gear 51 is provided with teeth 57 at equal intervals in the axial and circumferential directions. The four sides of the teeth 57 are all teeth that can mesh with gears. The self-rotating motor 55 and the feeding motor 56 are fixed on the moving platform 2. The self-rotating gear 53 meshes parallel to the cylindrical gear 51 and is connected to the output shaft of the self-rotating motor 55. The feeding gear 54 meshes tangentially with the axis of the cylindrical gear 51 and is connected to the output shaft of the feeding motor 56. The surgical instrument 7 is arranged at the center of the cylindrical gear 51. Combining the characteristics of the gear rack mechanism and the rotating gear mechanism, the end surgical instrument 7 can be provided with two degrees of freedom of axial feeding and self-rotation.

[0050] The cylindrical gear 51 is composed of a cylindrical surface that is first linearly rotated and cut with a rack profile, and then axially stretched and cut with a gear profile; the shaft has a center hole, and various types of surgical instruments, such as an endoscope, can be installed at one end of the shaft. Compared with the solution of serially driving each degree of freedom, this design can achieve decoupling and two-degree-of-freedom movement without interference during movement, and it is very compact. The shaft is installed in a circular track processed on the moving platform 2, and three PTFE sliding bearings are used to support the shaft and the instruments inside it. Two are installed on the track as fixed ends, and the other is installed on the shaft as a sliding end, which plays a three-point support role for the shaft to improve its axial accuracy and rigidity. The bearing 52 uses a PTFE sliding bearing. Compared with a rolling bearing, the PTFE sliding bearing can support both the linear and rotational movements of the shaft at the same time due to the low friction characteristics of its material itself, and can play a lubricating role in an oil-free state, thereby improving the cleanliness of the mechanism.

[0051] like Figure 4 As shown, the telecentric fixed point mechanism also includes two gravity compensation devices 6, which include a wire rope 61, a shell 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 shell 62 is coaxially connected to the end of the circular arc guide rail 41, and a slide rail for the sliding block 63 to slide vertically is provided in the shell 62. The movable pulley 64 is arranged on the sliding block 63. One end of the wire rope 61 is fixed to the back side of the circular 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 to the shell 62. The spring 66 is arranged between the sliding block 63 and the bottom of the shell 62.

[0052] During operation, the wire rope 61 drives the movable pulley 64, stretches the spring 66 and generates tension to compensate for the gravity torque applied to the coaxial rotating joint by the arc guide 41 and the two-degree-of-freedom decoupling end effector 5. The device is connected to the rotating joints on both sides of the arc guide 41 through three sets of bolts and nuts and a rotating shaft. In this way, 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 provided 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 1 32 joints of the two planar branch chain assemblies 3 are connected to the drive motor 31 as a drive joint, the plane where the planar branch chain assemblies are located can rotate around the joint axis under the drive of the drive motor 31, and the drive joint axes of the two planar branch chain assemblies are arranged vertically and intersecting at one point. The connecting rod 6 37 of the planar branch chain assembly is hinged with the moving platform 2 to form a joint, and the end joints of the two planar branch chain assemblies 3 are coaxially and reversely installed on the moving platform 2, and the equivalent installation points coincide. The common axis is the intersection of the planes where the two planar branch chain assemblies 3 are located, and the intersection always passes through the intersection of the two planar branch chain drive joint axes, so the two planar branch chain assemblies 3 together form a previously mentioned dual-plane branch parallel configuration RCM mechanism. The two degrees of freedom of the arc branch chain assembly 4 are: the rotation of the arc guide rail 41 around the coaxial rotating joint and the rotation of the track slider 42 on the arc guide rail 41 relative to the arc guide rail 41. The two rotational movements always pass through the center of the circle on 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, the branch chain also constitutes an RCM mechanism.

[0055] The RCM points of the two RCM mechanisms are overlapped, and the ends are connected through the moving platform 2. Since both RCM mechanisms constrain the two degrees of freedom required for the moving platform to leave the RCM point, each branch chain jointly over-constrains the moving platform 2. This over-constraint causes the moving platform 2 to receive the constraints of multiple branches at the same time when it deviates from the RCM point, making it difficult for the movement to occur. The design of the over-constrained parallel platform can reduce the gap error within the branch chain, so that the mechanism can improve the stiffness and accuracy while realizing the telecentric fixed point function.

[0056] The telecentric fixed point mechanism adopts a completely decoupled configuration design to improve safety during surgery and reduce the complexity of kinematic procedures. In medical practice, the position and posture of the instrument are often represented by four movements: the insertion length along the instrument axis and the rotation around the axis, the tilt angle around the entry point, and the swing angle. Therefore, compared with methods such as RPY angle and transformation matrix, it is more convenient and intuitive for doctors to use the above four movements to reflect the posture information. Therefore, this application proposes a displacement method for a telecentric fixed point mechanism, which describes the instrument posture by constructing these four variables in geometric space. Figure 6 As shown, the following steps are included:

[0057] S1: The surgical instrument end coordinate system {P} and the telecentric fixed point mechanism fixed coordinate system {O} are taken as the initial posture;

[0058] S2: Feed depth d of surgical instrument relative to the entry point O after the telecentric fixed point mechanism moves w , the angle θ of the surgical instrument's rotation around its own axis w w , the angle θ between the projection line of the axis w on the fixed coordinate system xz, yz plane and the z axis x With θ y , these four variables reflect the posture of the instrument;

[0059] S3: The telecentric fixed point mechanism has three rotating joints and one moving joint driven by the motor. The rotation / movement amounts are represented by θ1, θ2, θ3, and d1 respectively; the plane where the planar branch chain component is located and its unit normal vector are represented by ∑ i and It means that since the two planes rotate around the axes of the driven joints 1 and 2 respectively, their Plücker coordinates in the coordinate system {O} can be expressed as:

[0060]

[0061] Where n oi Represents plane∑ i The position vector and normal vector between point O Since the two planes always pass through point O, n oi is always equal to 0, cθ and sθ represent cosθ and sinθ respectively, therefore, the Plücker coordinates of the intersection of the two planes (the straight line where the instrument axis w lies) can be calculated as:

[0062]

[0063] in

[0064]

[0065] in is the unit vector of the line direction vector (the w vector of the coordinate system {P}), w o Represents the position vector and vector of the straight line relative to point O The cross product of the straight line can also reflect that the end instrument axis always passes through point O, and it can be further deduced that the angle between its projection line and the z-axis on the xz and yz planes is:

[0066]

[0067] Due to the existence of the arc branch chain assembly, the relative distance between the moving platform of the mechanism and the RCM point O is always fixed during the movement of the moving platform, and the moving platform cannot rotate around the instrument axis. Therefore, the end instrument installed on it will only move relative to it when the two series drive joints move; therefore, the feed depth d of the instrument relative to the entry point O is w The angle θ of the device's rotation around its own axis w depends only on the linear drive joint d1 and is equal in size. w It only depends on the rotation drive joint θ3 and is equal in size, so the forward and inverse kinematics of the mechanism can be obtained:

[0068]

[0069] Taking the derivative of the two ends of the positive kinematics, we can get:

[0070]

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

[0072] Schematic diagram of the working process of the telecentric fixed point mechanism: The overall hardware system of the telecentric fixed point mechanism includes: the host PC part, the hardware control part, and the sensor part. After the NDI optical sensor in the sensor part obtains the real-time position and posture of the mechanism, it sends a signal to the host PC through USB. The host computer analyzes the subsequent required movement of the mechanism and sends control commands to the Beckhoff embedded controller through the TCP / IP protocol. The embedded controller calculates the movement of each motor based on the kinematic algorithm and sends it to the driver through the Ethercat bus at a frequency of 1000Hz to ensure the real-time movement of the mechanism. The driver then converts these commands into current and voltage outputs to servo-drive the motor movement. The motor uses four Maxon DC servo motors, all equipped with high-precision reducers and encoders, thereby realizing high-precision drive of the proposed mechanism to meet the position accuracy requirements during surgery.

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

Claims

1. A novel telecentric fixed point mechanism for minimally invasive surgery, the telecentric fixed point mechanism being mounted on a robotic arm (8) and used to control the movement of a surgical instrument (7), characterized in that: The telecentric fixed point mechanism comprises a base (1), a moving platform (2), two groups of planar branch chain assemblies (3), an arc branch chain assembly (4), and a two-degree-of-freedom decoupling end effector (5). The two groups of planar branch chain assemblies (3) are symmetrically arranged on the base (1). The planar branch chain assembly (3) is a parallelogram frame composed of six connecting rods. The end of the planar branch chain assembly (3) is connected to the moving platform (2) and is hinged. The arc branch chain assembly (4) comprises a semicircular arc guide rail (41) and a track slider (42) slidably adapted on 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 decoupling end effector (5) is arranged on the moving platform (2) and is used to control the adjustment of the two degrees of freedom of rotation and feeding of the surgical instrument (7).

2. A novel telecentric fixed point mechanism for minimally invasive surgery according to claim 1, characterized in that: The planar branch chain assembly (3) comprises a driving motor (31), a connecting rod 1 (32), a connecting rod 2 (33), a connecting rod 3 (34), a connecting rod 4 (35), a connecting rod 5 (36), and a connecting rod 6 (37). The connecting rod 2 (33), the connecting rod 3 (34), the connecting rod 4 (35), and the connecting rod 5 (36) are hinged in sequence to form a parallelogram frame. The driving motor (31) is fixed on the base (1) and is hinged to the hinged part at the head end of the connecting rod 1 (32). The tail end of the connecting rod 1 (32) is coaxially hinged to the hinged end of the connecting rod 2 (33) and the connecting rod 5 (36). One end of the connecting rod 6 (37) is hinged to the moving platform (2), and the other end is hinged to the connecting rod 3 (34).

3. According to claim 1, a novel telecentric fixed point mechanism for minimally invasive surgery is characterized by: The two-degree-of-freedom decoupling end effector (5) comprises a cylindrical gear (51), a self-rotating gear (53), a feeding gear (54), a self-rotating motor (55), and a feeding motor (56). The cylindrical gear (51) is pivotally connected to the moving platform (2) through a bearing (52). The outer surface of the cylindrical gear (51) is provided with teeth (57) at equal intervals in the axial and circumferential directions. The four sides of the teeth (57) are all teeth that can mesh with gears. The self-rotating motor (55) and the feeding motor (56) are fixed on the moving platform (2). The self-rotating gear (53) meshes with the cylindrical gear (51) in parallel and is connected to the output shaft of the self-rotating motor (55). The feeding gear (54) meshes tangentially with the axis of the cylindrical gear (51) and is connected to the output shaft of the feeding motor (56). The surgical instrument (7) is arranged at the center of the cylindrical gear (51).

4. According to claim 1, a novel telecentric fixed point mechanism for minimally invasive surgery is characterized by: The telecentric fixed point mechanism also includes two gravity compensation devices (6), which include a steel 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 circular arc guide rail (41). A slide rail for the sliding block (63) to slide vertically is provided in the housing (62). The movable pulley (64) is arranged on the sliding block (63). One end of the steel wire rope (61) is fixed to the back of the circular 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 then fixed to the housing (62). The spring (66) is arranged between the sliding block (63) and the bottom of the housing (62). A level (68) is arranged on the housing (62).

5. A displacement method of a telecentric fixed point mechanism, characterized in that: The telecentric fixed point mechanism of claims 1 to 4 is adopted, comprising the following steps: S1: The surgical instrument end coordinate system {P} and the telecentric fixed point mechanism fixed coordinate system {0} are used as the initial posture; S2: Feed depth d of surgical instrument relative to the entry point 0 after the telecentric fixed point mechanism moves w , the angle θ of the surgical instrument's rotation around its own axis w w , the angle θ between the projection line of the axis w on the fixed coordinate system xz, yz plane and the z axis x With θ y , these four variables reflect the posture of the instrument; S3: The telecentric fixed point mechanism has three rotating joints and one moving joint driven by the motor. The rotation / movement amounts are represented by θ1, θ2, θ3, and d1 respectively; the plane where the planar branch chain component is located and its unit normal vector are represented by ∑ i and It means that since the two planes rotate around the axes of the driven joints 1 and 2 respectively, their Plücker coordinates in the coordinate system {0} can be expressed as: where n oi Represents plane∑ i The position vector and normal vector between 0 and The dot product of the two planes always passes through point 0, so n oi is always equal to 0, cθ and sθ represent cosθ and sinθ respectively, therefore, the Plücker coordinates of the intersection of the two planes (the straight line where the instrument axis w lies) can be calculated as: in in is the unit vector of the line direction vector (the w vector of the coordinate system {P}), wo represents the position vector of the line relative to the 0 point and the vector The cross product of the straight line can also reflect that the end instrument axis always passes through the 0 point, and it can be further deduced that the angle between its projection line and the z axis on the xz and yz planes is: Due to the existence of the arc branch chain assembly, the relative distance between the moving platform of the mechanism and the RCM point 0 is always fixed during the movement of the moving platform, and the moving platform cannot rotate around the instrument axis. Therefore, the end instrument installed on it will only move relative to it when the two series drive joints move; therefore, the feed depth d of the instrument relative to the entry point 0 is w The angle θ of the device's rotation around its own axis w depends only on the linear drive joint d1 and is equal in size w It only depends on the rotation drive joint θ3 and is equal in size, so the forward and inverse kinematics of the mechanism can be obtained: Taking the derivative of the two ends of the positive kinematics, we can get: Therefore, the forward and inverse kinematics and Jacobian of the telecentric fixed point mechanism are completely decoupled.

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