KR20210072847A - System and method for controling needle with variable stiffness structure - Google Patents

Abstract

A needle control system having a variable stiffness structure according to the present invention includes a needle including an outer tube and an inner tube inserted to the inner side of the outer tube, and a needle control device for controlling the movement of the needle. The needle control device controls the rotational movement of the needle to change the stiffness of the needle, and according to the change in the stiffness of the needle, the curvature of the trajectory is controlled when the needle is inserted into the tissue.

Description

SYSTEM AND METHOD FOR CONTROLING NEEDLE WITH VARIABLE STIFFNESS STRUCTURE

The present invention relates to a needle control system and method having a variable rigidity structure, and more particularly, a needle control system and method for controlling the trajectory by modeling the relationship between the trajectory curvature of the needle and the stiffness of the needle to which the variable rigidity structure is applied. is about

Research on a method of changing and controlling bending rigidity and torsional rigidity by using a form in which a plurality of tubes are superimposed is being actively conducted in the field of robots. In particular, in a field such as minimally invasive surgery, it is important to appropriately control the rigidity of a tube having a very small size in order to precisely control a continuum robot needle in which a plurality of tubes are overlapped.

Minimally invasive surgery is performed by minimizing the incision area without open surgery. The incision site is small and there are few scars or sequelae, the exposure to bacterial infection is small, and the recovery is fast. Conventional surgical devices have a hard and fixed structure, so there is a problem in that it is difficult to navigate in the human body without damage to surrounding tissues. To overcome these limitations, a flexible continuum robot for minimally invasive surgery has been proposed.

In this minimally invasive surgery, the continuum robot is widely used because it can be miniaturized, but in an environment with a diameter of 3 mm or less, it is difficult to control the movement of the continuum robot because the moment arm is small and it is difficult to use a suitable micro actuator.

For needles in the form of continuum robots used in minimally invasive surgery, the accuracy of the distal tip reaching the target is particularly important. For example, if the position of the needle is incorrectly specified, a malignant tumor may not be detected during the biopsy, and healthy tissue is destroyed instead of cancerous tissue during brachytherapy, and the accuracy of treatment, examination, surgery, etc. decreases.

In order to improve the accuracy of the needle reaching the target, image-guided robotic systems are mainly used at present in combination with magnetic resonance imaging, ultrasound imaging or multi-imaging methods. Nevertheless, there are many constraining factors that cause the needle to deviate from its intended path, such as tissue inhomogeneity, organ deformation, respiration, and flow of body fluids.

US Registered Patent Publication No. 8715226 (2014. 5. 6)

The present invention has been devised to solve the problems of the prior art, and an object of the present invention is to provide a control method and system for steering a needle through modeling the relationship between stiffness and trajectory curvature in a needle having a variable stiffness structure.

In order to achieve the above object, according to an aspect of the present invention, as a needle control system having a variable rigidity structure, a needle including an outer tube and an inner tube inserted into the inner side of the outer tube and controlling the movement of the needle A needle including a needle control device, wherein the needle control device controls the rotational movement of the needle to change the stiffness of the needle, and the curvature of the trajectory is controlled when the needle is inserted into the tissue according to the change in the stiffness of the needle A control system is provided.

According to an embodiment of the present invention, as the stiffness of the needle decreases, there may be a relationship in which the curvature of the trajectory increases.

According to an embodiment of the present invention, at least one of the outer tube and the inner tube may include a plurality of regions having different rigidities.

According to an embodiment of the present invention, at least one of the outer tube and the inner tube may include a region in which a pattern is formed to reduce rigidity and a region in which a pattern is not formed.

According to an embodiment of the present invention, the outer tube may be made of a nitinol material, the inner tube may be made of a stainless steel material, and only the inner tube may include an anisotropic pattern.

According to an embodiment of the present invention, the needle control device controls the stiffness of the needle by changing the rotation angle of the inner tube, and as the rotation angle of the inner tube increases from 0° to 90°, bending of the needle The curvature of the trajectory in the direction may decrease.

According to an embodiment of the present invention, the needle control device may calculate the trajectory according to the change in the stiffness using a bicycle nonholonomic model (bicycle nonholonomic model).

According to another aspect of the present invention, as a needle control method having a variable stiffness structure, changing the stiffness of the needle by rotating the needle by a needle control device connected to the needle and changing the stiffness of the needle According to the method comprising the step of controlling the curvature of the trajectory when the needle is inserted into the tissue, the needle is provided with a needle control method comprising an outer tube and an inner tube inserted into the inner side of the outer tube.

According to an embodiment of the present invention, the step of changing the stiffness of the needle by rotating the needle includes controlling the stiffness of the needle by changing the rotation angle of the inner tube, As the rotation angle increases from 0° to 90°, the curvature of the trajectory in the bending direction of the needle may decrease.

According to an embodiment of the present invention, the method may further include calculating the trajectory according to the change in stiffness using a bicycle non-holonomic model.

A needle control system and method having a variable rigidity structure according to various embodiments of the present invention models the relationship between the stiffness of the needle and the trajectory curvature and enables precise trajectory control. In particular, it is possible to increase the target accuracy of the needle by adjusting the stiffness even in an environment inside the human body where space is limited and there is interaction with adjacent tissues. Through this, it is possible to reduce the damage to the surrounding tissue, it is possible to reduce the area that cannot be reached by expanding the curvature range of the needle trajectory. It enables safer minimally invasive surgery by limiting the insertion and rotation speed through needle control.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be.

1 shows a perspective view of a circular tube according to an embodiment of the present invention.
Figure 2 shows a perspective view of a tube structure having an asymmetric pattern according to an embodiment of the present invention.
3A and 3B are cross-sectional views of a circular tube having an asymmetric pattern of type A and type B, respectively, according to an embodiment of the present invention.
4 shows a rotational state of a circular tube having an asymmetric pattern of type A according to an embodiment of the present invention.
5A and 5B illustrate changes in bending stiffness ratio when the relative rotation angles of a plurality of circular tubes having asymmetric patterns of type A and type B are changed, respectively, according to an embodiment of the present invention.
6A and 6B respectively show a side view and a trajectory calculation model of an outer tube and an inner tube of a steerable needle according to an embodiment of the present invention.
7A and 7B respectively show a steerable needle control system implemented according to an embodiment of the present invention, and a change state of the needle trajectory curvature according to the needle rotation angle.
Figure 8 shows the needle trajectory according to the rotation angle of the inner tube in the yz plane according to an embodiment of the present invention and the standard deviation bar of the experimental results.
9A and 9B show graphs of the relationship between the stiffness of the needle and the curvature of the trajectory of the needle and the relationship between the rotation angle and the curvature of the trajectory of the needle, respectively, according to an embodiment of the present invention.
10 shows an example of needle trajectory control in which a steerable needle avoids an obstacle and reaches a target point according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Although the present invention has been described with reference to the embodiment shown in the drawings, which will be described as one embodiment, the technical idea of the present invention and its core configuration and operation are not limited thereby.

Robotic surgery allows for more precise control and can reduce unreachable areas. In particular, minimally invasive surgery using a robot uses a smaller incision, so it has a shorter recovery time and less risk of infection than traditional open surgery, so it is increasingly widely used.

In such minimally invasive surgery, a continuum robot capable of miniaturization is widely used, but in an environment with a diameter of 3 mm or less, it is difficult to control the movement of the continuum robot because the moment arm is small and it is difficult to use a suitable micro actuator.

As such, we propose a method for controlling the movement of the continuum robot by adjusting the rigidity of the continuum robot in an environment inside the human body where space is limited and there is interaction with adjacent tissues. A method and system for controlling the trajectory of a medical needle having a variable rigidity structure according to an embodiment of the present invention will be described as an example, but the present invention is not limited thereto, and if it is a tube structure having a variable rigidity structure, the trajectory is controlled. It can be applied without limitation.

1 shows a perspective view of a circular tube 100 according to an embodiment of the present invention.

Referring to FIG. 1 , a circular tube 100 made of two materials having different physical properties along the longitudinal direction and the circumferential direction of the circular tube 100 is shown. In this case, different physical properties may mean stiffness, and may be made of two or more materials having different physical properties. According to an embodiment of the present invention, the circular tube 100 may be configured in a form in which a part made of a flexible material (black part) and a part made of a hard material (white part) are alternately located along the circumference. For example, the flexible material may be a material such as rubber or an elastomer, and the rigid material may be a material such as a hard plastic or metal.

The steerable needle proposed in the present invention can change the rigidity by adjusting one or more of the rotation angle and the relative position by concentrically overlapping the inner and outer circular tubes of the shape as shown in FIG. 1 . The tube structure proposed in the present invention is described as an example of a circular shape, but is not necessarily limited thereto, and may be transformed into various hollow shapes capable of moving the relative positions between one or more inner tubes and outer tubes. In addition, a plurality of materials having different physical properties may be disposed along the longitudinal direction or the circumferential direction of each tube, and may be disposed by a combination of the circumferential direction and the longitudinal direction. For example, a plurality of materials having different physical properties may be disposed along the circumference of each tube in an oblique direction.

2 shows a perspective view of a tube structure 200 having an asymmetric pattern according to an embodiment of the present invention. According to an embodiment of the present invention, the tube structure 200 may be configured in a form in which a plurality of circular tubes are overlapped. A steerable needle may be constructed of such a tube structure.

As shown in FIG. 2, the tube structure 200 configured to have continuously varying rigidity according to an embodiment of the present invention is formed with an asymmetric pattern to be divided into parts having two or more different physical properties in the longitudinal direction and the circumferential direction. A tube may be provided. Referring to FIG. 2 , the tube on which the asymmetric pattern is formed is made of a hard material, such as metal, so that the patterned portion can be configured to dramatically reduce bending and torsional stiffness. For example, the tube in which the asymmetric pattern is formed may be made of a shape memory alloy such as nitinol or stainless steel, but is not necessarily limited thereto. The plurality of circular tubes having an asymmetric pattern includes an outer tube 210 and an inner tube 220 . Hereinafter, a form in which two circular tubes are overlapped is described as an example, but a form in which three or more tubes are overlapped is also possible, and the rigidity can be more precisely controlled by adjusting the relative positions between them.

The outer tube 210 is formed with a plurality of patterns 211 along the outer peripheral surface of the tube. These patterns 211 may be formed by, for example, laser processing equipment or a heat pad in a manner such as cutting processing, peeling processing, or local heat treatment. These are merely exemplary methods, and the pattern forming method is not limited thereto. The patterns 211 may be formed, for example, in an anisotropic pattern, but may be variously modified without any particular limitation in their shape.

According to an embodiment of the present invention, the patterns 211 of the outer tube 210 are a circumferential distance between the patterns (m ₁ ), a longitudinal distance between the patterns (l ₁ ), a width of the pattern (m ₂ ) and a pattern. can be determined by a parameter such as the height of l _{2 .} The patterns 211 of the outer tube 210 may be formed only in a circumferential direction along the outer circumferential surface, and may be divided into a pattern-formed area and a pattern-not-formed area. As shown in FIG. 2 , the bending rigidity and torsional rigidity of the outer tube 210 may be dramatically reduced in the region where the patterns 211 are formed. In the outer tube 210 , the region in which the patterns 211 are formed and the region in which the patterns 211 are not formed have a large difference in bending rigidity and torsional rigidity.

The inner tube 220 is formed with a plurality of patterns 221 along the outer peripheral surface of the tube. The patterns 221 may be formed by, for example, a laser processing device or a heat pad in a manner such as a cutting process, a peeling process, or a local heat treatment. The patterns 221 may be formed, for example, in an anisotropic pattern, but may be variously modified without any particular limitation on their shape.

According to an embodiment of the present invention, the patterns 221 of the inner tube 220 may also be determined by parameters such as a circumferential distance between patterns, a longitudinal distance between patterns, a width of a pattern, and a height of a pattern. The patterns 221 of the inner tube 220 may be formed in the same shape as the patterns of the outer tube 210 , but since they have a smaller diameter, parameters may be designed to decrease as the diameter decreases. In the inner tube 220, the patterns 221 may be formed only in a part of the circumferential direction along the outer circumferential surface, and the bending rigidity and torsional rigidity of the inner tube 220 may be dramatically reduced only in the region where the patterns 221 are formed. have. According to another embodiment of the present invention, the shape of the pattern of the inner tube 220 and the outer tube 210 may be different, and in particular, the ratio of the area in which the pattern is formed and the area in which the pattern is not formed is different in the circumferential direction. can be set.

The tube structure proposed in the present invention is described as an example of a circular shape, but is not necessarily limited thereto, and may be transformed into various hollow shapes capable of moving the relative positions between one or more inner tubes and outer tubes. In addition, a plurality of regions having different patterns may be disposed along the longitudinal direction or the circumferential direction of each tube, or may be disposed by a combination of the circumferential direction and the longitudinal direction. Here, examples of regions in which different patterns are formed may include regions in which a specific pattern is formed and regions in which no patterns are formed. The different patterns may be various patterns for varying the rigidity of the plurality of regions, and are not limited to a specific pattern. For example, a plurality of regions having different patterns may be arranged along the circumference of each tube in an oblique direction.

3A and 3B are cross-sectional views of a circular tube having an asymmetric pattern of type A and type B, respectively, according to an embodiment of the present invention. 3A and 3B are enlarged views of the cut surface 230 in order to confirm the circumferential direction pattern in more detail in the tube shown in FIG. 2 .

Referring to FIG. 3A , the outer tube 210 includes a region 213 in which patterns 211 are formed and a region 212 in which patterns are not formed along the circumferential direction. In the asymmetric pattern of type A according to an embodiment of the present invention, a plurality of patterns 211 are formed only in the middle portion obtained by dividing the semicircular portion into thirds in the cross section of the outer tube 210, and the pattern is formed in the remaining portion. The patterns 211 may be symmetrically formed on the opposite semicircle. The inner tube 220 has the same type A pattern as the outer tube 210, or only one of the inner tube 220 or the outer tube 210 may be patterned, and the relative pattern position is changed by rotation According to this, the rigidity of the continuum robot can be continuously changed.

Referring to FIG. 3B , the outer tube 210 includes a region 213 in which patterns 211 are formed and a region 212 in which patterns are not formed along the circumferential direction. In the asymmetric pattern of type B according to an embodiment of the present invention, only the middle portion obtained by dividing the semicircular portion into thirds in the cross section of the outer tube 210 is not formed, and the remaining both portions have a plurality of patterns 211 is formed, and patterns 211 may be symmetrically formed on the opposite semicircle. The inner tube 220 has the same type A pattern as the outer tube 210, or only one of the inner tube 220 or the outer tube 210 may be patterned, and the relative pattern position is changed by rotation According to this, the rigidity of the continuum robot can be continuously changed.

In the embodiment of type A and type B, parameters may be defined as shown in <Table 1>.

Here, d _i means the inner diameter of the outer or inner tube, and d _o means the outer diameter of the outer or inner tube. In addition, E means Young's modulus of the outer or inner tube, respectively, l ₁ is the longitudinal distance between patterns, l ₂ is the height of the patterns, m ₁ is the circumferential distance between the patterns, m ₂ is the width of the patterns means θ denotes the angle of an arc unit in the region where the pattern is formed, and n denotes the number of pattern units.

The asymmetric pattern shape of the outer tube and the inner tube is not limited to type A or type B, and may be transformed into a pattern and pattern arrangement form having various parameters according to the rigidity required for the tube structure, the range of change, and the like.

The rigidity of the tube structure formed by concentrically overlapping a plurality of tubes is controlled by at least one of a relative rotational movement and a translation movement of the plurality of tubes. As described above, each of the plurality of tubes of the tube structure is configured to have anisotropic properties in the circumferential direction and the longitudinal direction, so that the rigidity of the overlapping portion is changed during their rotational movement and parallel movement, relative longitudinal position, rotation By quantitatively adjusting parameters such as angle, it is possible to control to have desired rigidity.

4 shows a rotational state of a circular tube 400 having an asymmetric pattern of type A according to an embodiment of the present invention.

The circular tube 400 shown in FIG. 4 may be the above-described outer tube 210 or inner tube 220, and by rotating it, it is possible to control the rigidity of the tube structure. When the circular tube 400 of FIG. 4(a) is rotated counterclockwise by an angle ω, as shown in FIG. 4(b), the positions of the region 402 and the region 403 in which the patterns are not formed are rotate θ _p denotes an angle on the circumference formed by the region 403 in which the patterns are formed, and θ _u denotes the angle of the region in which the pattern is not formed. In this case, the direction of the load may measure the bending stiffness based on the (-y) direction. The measured stiffness is lowest when the outer and inner tube patterns coincide in the vertical direction based on the measurement direction of the stiffness, and the area where the pattern is not formed in the vertical direction based on the stiffness measurement direction coincides. In this case, the measured stiffness may be the greatest.

5A and 5B illustrate changes in bending stiffness ratio when the relative rotation angles of a plurality of circular tubes having asymmetric patterns of type A and type B are changed, respectively, according to an embodiment of the present invention.

Referring to FIG. 5A , when the rotation angles of the outer and inner tubes having the type A pattern are changed from 0° to 90°, respectively, the changed stiffness compared to the minimum stiffness is displayed as a ratio. _{For example, when changing the rotation angle (ω 1} , ω ₂ )=(0°, 0°) to (90°, 90°) of the outer and inner tubes with a type A pattern, the stiffness can differ by 2.10 times. have.

Referring to FIG. 5B , when the rotation angles of the outer and inner tubes having the type B pattern are changed from 0° to 90°, respectively, the changed stiffness compared to the minimum stiffness is displayed as a ratio. _{For example, when changing the rotation angle (ω 1} , ω ₂ )=(0°, 0°) to (90°, 90°) of the outer and inner tubes with a type B pattern, the stiffness can differ by 4.27 times. have. As illustrated in Figures 5a and 5b, it is possible to change the bending stiffness as a continuous function of forms depending on the rotational angle (ω ₂₎ of the inner tube 220, the rotation angle (ω ₁₎ and the outer tube 210 of the constant . Thus, that it is possible to angle of rotation (ω ₁₎ when adjusting the angle of rotation (ω ₂₎ to the scalable a bending stiffness (scalable) of and the outer tube (210) control of the inner tube (220) proposed by the present invention Able to know.

The steerable needle proposed in the present invention may be formed in a form in which a plurality of circular tubes are overlapped like the above-described tube structure. In particular, the steerable needle may consist of a tube structure in which a circular tube having two anisotropic patterns of an inner tube and an outer tube is superimposed.

In the case of a tube structure in which a circular tube having two anisotropic patterns is overlapped, the rigidity can be controlled by at least one of a relative rotational motion and a translational motion of the tube as described above. In the case of a needle having such a variable rigidity structure, when the needle is inserted into the human body, the trajectory is bent by the interaction with the surrounding tissue as the rigidity is changed through the relative rotation of the tube. Since the rigidity of the tube structure can be scalably controlled, the trajectory of the needle can be controlled by modeling the relationship between the rigidity and the curvature of the trajectory.

6A and 6B respectively show a side view and a trajectory calculation model of the outer tube and the inner tube of the steerable needle 600 according to an embodiment of the present invention.

Referring to FIG. 6A , the needle 600 may include an outer tube 610 and an outer tube 620 . According to an embodiment of the present invention, the outer tube 610 may be a circular tube made of nitinol with an outer diameter of about 2.0 mm and an inner diameter of about 1.8 mm. In addition, the inner tube 620 may be a round tube made of stainless steel with an outer diameter of about 1.65 mm and an inner diameter of about 1.35 mm. At this time, the inner tube 620 may be patterned to have an anisotropic distribution of bending stiffness along the radial direction as shown in FIG. 6A . The outer tube 610 may have a bevel tip as shown in FIG. 6A . The outer tube 610 is made of a material such as nitinol having a low rigidity, and the inner tube 620 is made of a material such as stainless steel having a high strength, so that the range of change in stiffness may be larger. The range of change in stiffness can be adjusted differently depending on the material for manufacturing the tube, the size (diameter, thickness, etc.) of the tube, and the pattern of the tube.

In the present invention, it is intended to propose a method of controlling the trajectory by controlling the stiffness of the needle through non-holonomic modeling of a steerable needle system, in particular, bi-cycle nonholonomic modeling. At this time, not only the insertion speed and rotation speed of the needle, but also an additional control input and the stiffness of the needle may be considered.

First, referring to Fig. 6b, the angle φ of the front wheel and the wheelbase l ₁ can be considered as variables of a standard kinematic bicycle, and the curvature k of the needle path is determined by the stiffness along the bending direction . Frame A is global coordinates, and frame B and frame C can each be considered as two wheels. Frame C and the needle tip may be positioned on the z-axis of frame B. As shown in FIG. 6B , the z-axis of the frame C has a difference from the z-axis of the frame B by an angle ?. Frame B and frame C are positioned at a constant distance from each other during needle insertion. u ₁ means the insertion speed of the needle along the z-axis of frame B, and u ₂ means the rotational speed along the z-axis of frame B. k means the curvature of the needle trajectory, and can be changed by the stiffness that varies depending on the rotational configuration of the inner tube.

,

,

,

로 표현될 수 있다. 또한, 프레임 B와 C는 서로에 대해 고정되어 있으므로,

이다. 파피안 제약식은 <수학식 1>과 같이 구해질 수 있다. Here, the Pfaffian constraints may be considered as follows. The origin velocity of frame B cannot be projected along the x and y axes of frame C, and the origin velocity of frame C cannot be projected along the x and y axes of frame C

,

,

,

can be expressed as Also, since frames B and C are fixed relative to each other,

to be. The Papian constraint can be obtained as in <Equation 1>.

Bicyclo non alone may take into account the space velocity V ₂ that is purely in the genomic model and pure space velocity V ₁ corresponding to the needle insertion corresponds to the rotation axis, dynamic model is expressed as <Equation 2>.

Here, u ₁ means the insertion speed of the needle along the z-axis of the frame B, u ₂ means the rotation speed along the z-axis of the frame B, k(t) means the curvature of the needle trajectory.

은 상수(constant)로 두고,

으로 둘 때, <수학식 3>과 같이 나타낼 수 있다. The kinematic model was also used to confirm the effect of varying stiffness.

is a constant,

When , it can be expressed as <Equation 3>.

,

으로 정의될 수 있다. here,

,

can be defined as

에 대해 동차 변환(homogeneous transformation)하는 경우, 동역학적 모델은 또한 <수학식 4>와 같이 나타낼 수 있다. Experimental data can be applied by using this as a discrete-time model. In the discrete time model, each time step k = 0, 1, 2, ... For , for T seconds

In the case of homogeneous transformation, the dynamic model may also be expressed as <Equation 4>.

At this time, the needle tip path vector may be defined as in <Equation 5>.

For example, when T = 1s and the needle insertion speed u ₁ = 6 mm/s, the dynamic model and the needle tip vector can be obtained as in Equation 6 below.

As described above, the Papian constraint can be applied as in <Equation 1>.

7A and 7B respectively show a steerable needle control system 700 implemented according to an embodiment of the present invention, and a change state of the needle trajectory curvature according to the needle rotation angle. By configuring the needle control system 700 as shown in Figure 7a, the dynamic model and the needle tip trajectory vector as described above can be confirmed.

Referring to Figure 7a, the needle control system 700 according to an embodiment of the present invention includes a needle control device 710 and a needle 720 consisting of a plurality of circular tubes. For example, as shown in FIG. 7A, the needle 720 may be composed of two circular tubes of an outer tube 610 and an inner tube 620, as shown in FIG. 6A, and the outer tube has no pattern, and the inner tube The tube may be a patterned circular tube. The outer tube 610 may have a bevel tip as shown in FIG. 6A . The needle control device 710 may control the movement of the tubes 610 and 620 by controlling the degree of rotation of the motor, the speed, and the degree and speed of the movement of the chuck. Each of the tubes 610 and 620 are supported by a chuck connected to a motor, and when each connected motor operates, each of the tubes 610 and 620 moves in parallel and rotationally, and the human tissue model 730 is moved in the insertion direction. For example, the human tissue model 730 may be made by mixing about 80% water, 19% gelatin, and 1% sugar to form an environment similar to the elasticity of the prostate cancer region. The needle control device 710 may include one or more processors, and the translational and rotational movements of the needles may be controlled by the one or more processors.

Referring to FIG. 7B , if the rigidity of the needle 720 is changed according to an embodiment of the present invention, the insertion path of the bevel tip may be modified. When a flexible needle 720 with a bevel tip is inserted into soft tissue, the asymmetry of the tip may cause the needle to warp. At this time, when the stiffness of the needle 720 is changed, the curvature of the needle may be changed. For example, the change in stiffness and curvature can be measured while inserting as much as 100 mm into the human tissue model 730 by setting _{the rotation angle θ R} of the inner tube in the needle 720 to 0°, 30°, 60°, and 90°, respectively. have. At this time, the insertion speed is u ₁ = 6 mm/s, the rotation speed is u ₂ = 0 mm/s, and it may be set to T = 1 s. In such a setting _{, the needle insertion state for each rotation angle θ R} is as shown in FIG. 7b , and the needle stiffness and the needle trajectory curvature for the _{rotation angle θ R can be obtained as shown in <Table 2>.} The flexural stiffness is determined by the rotational configuration of the inner tube, and the tendency of k can be derived from an energy-based model formula that combines tissue interaction, needle shape, and material properties.

Rotation angle θ _R 0° 30° 60° 90° Needle stiffness EI (kN mm ² ) 20.6 31.9 54.5 65.8 Curvature of the trajectory k(mm ^-1 ) 0.00330 0.00251 0.00197 0.00169

7B, when the needle is inserted into the human tissue model 730, the inner tube rotation angle θ _R of the needle 720 increases from 0° to 90°, the stiffness increases, and the bevel tip in the y direction increases. It can be seen that it is inserted in a less curved form. As such, by changing the rotation angle of the inner tube when inserting the needle into human tissue, or by appropriately modifying the rotation angle of the outer tube according to another embodiment, the degree of bending (degree of deformation) of the tip can be controlled, This allows placement of the needle tip in the desired tissue.

Figure 8 shows the needle trajectory according to the rotation angle of the inner tube in the yz plane according to an embodiment of the present invention and the standard deviation bar of the experimental results.

Referring to FIG. 8 , the needle trajectory predicted from the above-described bicycle non-holonomic model and the rotation angle θ _R of the inner tube are changed to a) 0°, b) 30°, c) 60° and d) 90°. When the standard horseshoe bars of the experimental results are shown.

As shown in FIG. 8 , when _{the needle is inserted into the human tissue model 730 by changing the rotation angle θ R} of the inner tube, the needle trajectory actually measured is the trajectory obtained according to the model proposed in the present invention and relatively small standard It can be seen that there is a deviation. Thus, by controlling the rotational configuration of the steerable needle to control the needle stiffness, the needle trajectory can be controlled.

9A and 9B show graphs of the relationship between the stiffness of the needle and the curvature of the trajectory of the needle and the relationship between the rotation angle and the curvature of the trajectory of the needle, respectively, according to an embodiment of the present invention.

According to an embodiment of the present invention, the stiffness of the steerable needle composed of two circular tubes is determined by the factors of the size of the inner and outer tubes, the material of the tube, and the angle formed by the pattern of the inner tube, and can be expressed together.

Here, E _o and E _i is the outside of the respective outer tubes and means the elastic modulus of the inner tube, D _o and D _i stands for the inner and outer diameter of each of the outer tube and, d _o and d _i respectively inner tube and inner diameter. Also, θ _h is the central angle of the inner tube pattern, and θ ₁ is the rotation angle determined by the rotation configuration of the inner tube. At this time, the outer tube is made of nitinol (E = 51.3GPa) and has an outer diameter of 2.0mm and an inner diameter of 1.8mm, and the inner tube is made of stainless steel (E = 188GPa) and has an outer diameter of 1.65mm and an inner diameter It can be configured with a diameter of 1.35 mm.

Referring to FIG. 9A , as described above, while changing the rotation angle of the inner tube to 0°, 30°, 60° and 90°, the results shown in <Table 2> inserted into the human tissue model 730 are linearly The relational expression between the fitted trajectory curvature and falseness can be obtained as shown in Equation (8).

Here, the stiffness can be expressed by <Equation 9> for _{the rotation angle θ i} of the inner tube as follows.

Accordingly, the trajectory curvature k can be expressed as <Equation 10> as a function of _{the rotation angle θ i of the inner tube.}

As a result, the relationship between the trajectory curvature k and the rotation angle θ _{i of the} inner tube can be shown as in FIG. 9B , and it can be confirmed that the rotational configuration of the inner tube determines the trajectory of the needle. Since the rotation angle (θ _i ) of the inner tube has the same rotation configuration as _{-θ i} and θ _i +π , it can be seen that it is sufficient to understand the relationship only in the range _{θ i ∈ [0°, 90°].}

In this way, it is possible to derive the relationship between the curvature of the needle trajectory according to the change in the stiffness of the needle composed of a plurality of tubes overlapped. Here, the relationship between the stiffness of the needle and the curvature of the trajectory has been described by taking the case where two circular tubes are overlapped as an example, but the present invention is not limited thereto. Through-path control can be applied. In particular, as shown in FIG. 10 , the path can be controlled by adjusting the stiffness so that the needle 720 moves away from the obstacle 20 from the start point 10 to the end point 11 .

As such, the method proposed in this specification has a much faster response speed than the method of changing the stiffness by electricity or heat, and can quickly and simply control the change in the stiffness of the needle. It can be particularly useful for improving the accuracy of the procedure and for minimally invasive surgery.

In the specific embodiments described above, elements included in the invention are expressed in the singular or plural according to the specific embodiments presented. However, the singular or plural expression is appropriately selected for the situation presented for convenience of description, and the above-described embodiments are not limited to the singular or plural component, and even if the component is expressed in plural, it is composed of a singular or , even a component expressed in a singular may be composed of a plural.

On the other hand, although specific embodiments have been described in the description of the invention, various modifications are possible without departing from the scope of the technical idea contained in the various embodiments. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the following claims as well as the claims and equivalents.

Claims (14)

A needle control system having a variable stiffness structure, comprising:
a needle including an outer tube and an inner tube inserted into the inner side of the outer tube; and
Including a needle control device for controlling the movement of the needle,
The needle control device controls the rotational movement of the needle to change the stiffness of the needle,
A needle control system, wherein the curvature of the trajectory is controlled when the needle is inserted into the tissue according to a change in the stiffness of the needle. According to claim 1,
The relationship in which the curvature of the trajectory increases as the stiffness of the needle decreases, a needle control system. According to claim 1,
At least one of the outer tube and the inner tube comprises a plurality of regions having different stiffnesses. According to claim 1,
At least one of the outer tube and the inner tube comprises a patterned region with reduced stiffness and an unpatterned region. According to claim 1,
The outer tube is made of nitinol material,
The inner tube is made of a stainless steel material,
and an anisotropic pattern only on the inner tube. 6. The method of claim 5,
The needle control device controls the stiffness of the needle by changing the rotation angle of the inner tube,
As the rotation angle of the inner tube increases from 0° to 90°, the curvature of the trajectory in the bending direction of the needle decreases, a needle control system. According to claim 1,
The needle control device for calculating the trajectory according to the change in stiffness using a bicycle nonholonomic model (bicycle nonholonomic model), a needle control system. A method for controlling a needle having a variable stiffness structure, the method comprising:
changing the stiffness of the needle by rotating the needle by a needle control device connected to the needle; and
Comprising the step of controlling the curvature of the trajectory when the needle is inserted into the tissue according to the change in the stiffness of the needle,
The needle includes an outer tube and an inner tube inserted into the inner side of the outer tube, needle control method. 9. The method of claim 8,
The relationship in which the curvature of the trajectory increases as the stiffness of the needle decreases, the needle control method. 9. The method of claim 8,
At least one of the outer tube and the inner tube comprises a plurality of regions having different stiffnesses, needle control method. 9. The method of claim 8,
At least one of the outer tube and the inner tube includes a patterned region with reduced rigidity and a non-patterned region. 9. The method of claim 8,
The outer tube is made of nitinol material,
The inner tube is made of a stainless steel material,
A needle control method comprising an anisotropic pattern only on the inner tube. 13. The method of claim 12,
The step of changing the stiffness of the needle by rotating the needle,
Controlling the stiffness of the needle by changing the rotation angle of the inner tube,
As the rotation angle of the inner tube increases from 0° to 90°, the curvature of the trajectory in the bending direction of the needle decreases, a needle control method. 9. The method of claim 8,
Further comprising the step of calculating the trajectory according to the change in the stiffness using a bicycle non-holonomic model, needle control method.

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