CN1686056A - Femur center location method based on hand eye type robot - Google Patents

Abstract

A method based on the hand-eye robot for locating the center of femur includes calibrating the hand and eye of robot by Tsai method to obtain the their position transform relation, simultaneously moving the far end of femur and the camera fixed to the hand jaw of robot to make the center of fossa intercondyloidea in the vision field of camera in large covered spherical range, acquiring the data about said center and hand jaw state at each position, converting the data to the coordinate system based on robot, fitting the data to a spherical equation, and calculation.

Description

Femur center positioning method based on hand eye type robot

Technical field

The present invention relates to a kind of femur center positioning method, be used to not have the robot total knee replacement operation of CT based on hand eye type robot.Belonging to advanced makes and automatization's (medical science) field.

Background technology

In China, all there is every year thousands of serious arthritic need carry out the total knee replacement operation.Total knee arthroplasty is the implant surgery of typical Orthopeadic Surgery artificial prosthesis, its the most most important notion is to set up the accurate lower limb line of force, be that femoral head center, knee joint center (or intercondylar fossa center) and ankle joint center should be in same straight line, have only by the bone-culting operation that calculates and accurately measure just to make the lower limb line of force obtain to rebuild accurately.Present the determining of the determining of the lower limb line of force, corresponding prosthese position in the total knee replacement, and the sawing of cutting of thigh, tibia cut entirely and rule of thumb control grasp by the doctor, special-purpose locating template can only provide accuracy guarantee to a certain extent, anthropic factor is still very big, is main error sources.The advantage of robotic surgical is that it can improve line of force measurement and prosthese is laid precision, reduced destructiveness damage, shortening operating time to patient, helps postoperative patient to recover smoothly.

When determining the line of force of femur fragment, normal person's femoral head center is connected in the hip joint, can't directly measure to obtain its positional information, has only the positional information at intercondylar fossa center to obtain by directly measuring.Total knee replacement when determining the line of force of femur fragment be by marrow in bar and positioning guide plate, the anatomical axis of femur to internal rotation 5 to 7 degree, is obtained with indirect mode.This method is too dependent on doctor's clinical experience.With U.S. Robodoc operating robot is that the location technology of representative then needs special one-time positioning operation, on femur, implant sign titanium nail, reuse CT machine scanning femur, reconstruct the femur threedimensional model, virtual coordinate system by coupling threedimensional model place is realized femur location (Musits B. with the robot coordinate system, et al.Image-Driven Robot Assists Surgeons With Total Hip Replacements.Industrial ROBOT.1993.Volume 20, Issue 5:12-14).(Granted publication number: CN1179707C) problem that will determine the femoral head center is abstracted into the geometric model that point on the known sphere is found the solution the centre of sphere to Chinese invention patent " the femur localization method of robot total knee arthroplasty ", i.e. fixing hip joint (being the femoral head center) and mobile distal femur obtains the intercondylar fossa center point coordinate of diverse location under the observation of vision positioning system is so the femoral head center just can be regarded the centre of sphere of those intercondylar fossa central point place spheres that collect as.The weak point of this class localization method is: it is worked under the actionless situation of vision positioning system, this moment is because the restriction in the visual system visual field, distal femur can only move in very limited scope, and the femur center error ratio that calculates with centre of sphere method is bigger.

Summary of the invention

The objective of the invention is at the deficiencies in the prior art, propose a kind of femur center positioning method, solve the big problem of femur centralized positioning error in the robot total knee arthroplasty based on hand eye type robot.

Technical scheme of the present invention: method (the R.Y.Tsai and R.K.Lenz that at first utilizes Tsai, " A newtechnique for fully autonomous and efficient 3d robotics hand/eye calibration ", IEEETrans.Robot.Automat., vol.5, pp.345-358,1989.) hand eye type robot is carried out hand and eye calibrating, obtain the trick evolution relation of robot; Mobile simultaneously then distal femur and be fixed on camera on the robot hand makes the intercondylar fossa center when covering bigger sphere scope still within the field range at camera, in each station acquisition intercondylar fossa centre data and paw attitude; The intercondylar fossa centre data that collects is transformed into the paw coordinate system by the trick relation, utilizes the paw attitude data that it is transformed into basis coordinates system of robot down again, obtain all intercondylar fossa center coordinates under the same coordinate system; The problem of determining the femoral head center is abstracted into the geometric model that point on the known sphere is found the solution the centre of sphere, remove spherical equation of match with intercondylar fossa centre coordinate under the robot basis coordinates that obtains previously, determine the coordinate information at femoral head center with numerical computation method, realize the accurate location at femur center.

Femur center positioning method of the present invention mainly comprises following step:

1. utilize the method for Tsai that hand eye type robot is carried out hand and eye calibrating, obtain the trick evolution relation of robot, i.e. spin matrix and translation vector between robot hand coordinate system and the camera coordinates system.

2. gather intercondylar fossa centre coordinate and paw attitude data.Keep the femur center constant, go down on one's knees forward 90 the degree, mobile robot's paw makes the camera of tying up thereon over against distal femur intercondylar fossa center, gather intercondylar fossa centre coordinate and paw attitude data, the intercondylar fossa centre coordinate that obtain this moment is the coordinate under the camera coordinates system, and the paw attitude is the attitude under the basis coordinates system of robot.With this moment the femur position be benchmark, be moved to the left distal femur and make femur rotation 45 degree～60 degree, also be moved to the left robot hand simultaneously and make the intercondylar fossa center within the field range of camera, gather intercondylar fossa centre coordinate and paw attitude data.Similarly, more respectively to the right, three directions such as upper and lower move distal femur and robot hand, gather intercondylar fossa centre coordinate and paw attitude data.Measure intercondylar fossa centre coordinate and the paw attitude data that obtains 5 groups of diverse locations altogether.

3. the intercondylar fossa centre coordinate is transformed into basis coordinates system of robot down.At first the intercondylar fossa centre coordinate that collects is carried out the trick Coordinate Conversion by the trick evolution relation that step 1 obtains, be transformed into the robot hand coordinate system.Utilize the paw attitude data calculating paw coordinate system of this moment and the coordinate transform relation of basis coordinates system of robot then, obtain spin matrix and translation vector between two coordinate systems.At last the intercondylar fossa centre coordinate under the robot hand coordinate system further is transformed into basis coordinates system of robot down, so obtain the coordinate information of all intercondylar fossa centers under unified basis coordinates.

4. calculate the femoral head center with the sphere fitting process.The problem of determining the femoral head center is abstracted into the geometric model that point on the known sphere is found the solution the centre of sphere, utilize the intercondylar fossa centre data under the basis coordinates system of robot that obtains previously to remove spherical equation of match, obtain the centre coordinate of this sphere with the method for numerical computations, this sphere centre point is exactly the coordinate of femoral head center under basis coordinates system of robot, realizes the accurate location at femur center.

The present invention does not need to place sign titanium nail and takes the special positioning operation of CT section.During practical application, robot base should be fixed, and can move freely the motility of camera by utilizing the robot eye system, has enlarged effective range of activity of distal femur in traditional centre of sphere method, has improved centre of sphere method and has carried out the femur locating accuracy.In addition, by trick conversion etc. the intercondylar fossa centre coordinate unification under the different cameral coordinate system is transformed under the basis coordinates system of robot and calculates, algorithm principle is simple, complexity is low.

Utilize the femur targeting scheme in the positioning result design robot total knee arthroplasty of the present invention, by the robot executable operations, step is simple, has improved the femur positioning accuracy.

Description of drawings

Fig. 1 determines the principle model sketch map at femoral head center for the present invention.

Among Fig. 1: 1---the femoral head center, 2---the intercondylar fossa center, 3---camera, 4---robot hand, P ¹---distal femur initial position, P ²---the position after distal femur moves to left, P ³---the position after distal femur moves to right, P ⁴---the position after moving on the distal femur, P ⁵---the position after distal femur moves down, O _c-X _cY _cZ _cRepresent camera coordinates system, O _g-X _gY _gZ _gRepresent the robot hand coordinate system, O _r-X _rY _rZ _rRepresent basis coordinates system of robot.

The specific embodiment

In order to understand technical scheme of the present invention better, be described in further detail below in conjunction with drawings and Examples.

1. utilize the method for Tsai that hand eye type robot is carried out hand and eye calibrating, obtain the trick evolution relation of robot, i.e. spin matrix and translation vector between robot hand coordinate system and the camera coordinates system.The camera coordinates system that bidding obtains surely is respectively R with respect to the spin matrix and the translation vector of paw coordinate system _CgWith

2. gather intercondylar fossa centre coordinate and paw attitude data.Immobilized patients upper body and hip are to keep the femur center constant, and distal femur partly exposes.90 degree of going down on one's knees forward, note this moment, the distal femur position was initial position P ¹Mobile robot's paw makes the camera of tying up thereon over against distal femur intercondylar fossa center, gather intercondylar fossa centre coordinate and paw attitude data, the intercondylar fossa centre coordinate that obtain this moment is the coordinate under the camera coordinates system, and the paw attitude is the attitude under the basis coordinates system of robot.With this moment the femur position be benchmark, be moved to the left distal femur to P ²Make femur rotation 45 degree～60 degree, also be moved to the left robot hand simultaneously and make the intercondylar fossa center within the field range of camera, gather intercondylar fossa centre coordinate and paw attitude data.Similarly, more respectively to the right, upper and lower three directions move distal femur and robot hand, collection intercondylar fossa centre coordinate and paw attitude data.Measure intercondylar fossa centre coordinate and the paw attitude data that obtains 5 groups of diverse locations altogether.If distal femur is at each position P ⁱThe intercondylar fossa centre coordinate information that collects when (i=1,2,3,4,5) is the three-dimensional coordinate vector The paw attitude be six-vector wherein First three items (X _g ⁱ, Y _g ⁱ, Z _g ⁱ) be translational component, back three (RX _g ⁱ, RY _g ⁱ, RZ _g ⁱ) be attitude angle.Fig. 1 shows the principle model sketch map that the present invention determines the femoral head center, wherein P ¹Be distal femur initial position, P ², P ³, P ⁴, P ⁵Be respectively distal femur relative to the position of initial position after left and right, upper and lower four direction moves.

3. all intercondylar fossa centre coordinate unifications are transformed into basis coordinates system of robot down.As shown in Figure 1, O _c-X _cY _cZ _cRepresent camera coordinates system, O _g-X _gY _gZ _gRepresent the robot hand coordinate system, O _r-X _rY _rZ _rRepresent basis coordinates system of robot.At first with the intercondylar fossa centre coordinate under the camera coordinates system that collects

Be converted to the three-dimensional coordinate under the paw coordinate system

$\stackrel{\→}{P_g^i}=R_{\mathrm{cg}}{P}_c^i+\stackrel{\→}{T_{\mathrm{cg}}}$

Then by the paw attitude

Calculate the spin matrix R between paw coordinate system and the basis coordinates system of robot _Gr ⁱAnd translation vector

$R_{\mathrm{gr}}^i=\left[\begin{array}{ccc}\cos \left({\mathrm{RZ}}_g^i\right)& -\sin \left({\mathrm{RZ}}_g^i\right)& 0\\ \sin \left({\mathrm{RZ}}_g^i\right)& \cos \left({\mathrm{RZ}}_g^i\right)& 0\\ 0& 0& 0\end{array}\right]\left[\begin{array}{ccc}\cos \left({\mathrm{RY}}_g^i\right)& 0& \sin \left({\mathrm{RY}}_g^i\right)\\ 0& 1& 0\\ -\sin \left({\mathrm{RY}}_g^i\right)& 0& \cos \left({\mathrm{RY}}_g^i\right)\end{array}\right]\left[\begin{array}{ccc}1& 0& 0\\ 0& \cos \left({\mathrm{RX}}_g^i\right)& -\sin \left({\mathrm{RX}}_g^i\right)\\ 0& \sin \left({\mathrm{RX}}_g^i\right)& \cos \left({\mathrm{RX}}_g^i\right)\end{array}\right]$

$\stackrel{\→}{T_{\mathrm{gr}}^i}=(X_g^i,Y_g^i,Z_g^i)$

Again with the intercondylar fossa centre coordinate under the paw coordinate system Be converted to the three-dimensional coordinate under the basis coordinates system of robot

$\stackrel{\→}{P_r^i}=R_{\mathrm{gr}}^i\stackrel{\→}{P_g^i}+\stackrel{\→}{T_{\mathrm{gr}}^i}$

All intercondylar fossa centers have so just been obtained at the same coordinate system, i.e. coordinate information under the robot basis coordinates system.

4. calculate the femoral head center with the sphere fitting process.If the coordinate of femoral head center under basis coordinates system of robot is O _r=(x _r, y _r, z _r), the problem of determining the femoral head center is abstracted into the geometric model that point on the known sphere is found the solution the centre of sphere, remove the following spherical equation of match with the intercondylar fossa centre coordinate data under the basis coordinates system of robot that obtains previously:

(x-x _r) ²+ (y-y _r) ²+ (z-z _r) ²=R ²Obtain the centre coordinate (x of this sphere with the method for numerical computations _r, y _r, z _r) and radius R, this sphere centre point is exactly this femoral head center that not directly obtains coordinate, obtains the coordinate of femoral head center under basis coordinates system of robot thus, realizes the accurate location at femur center.

Claims (1)

1, a kind of femur center positioning method based on hand eye type robot is characterized in that comprising following concrete steps:

1) utilizes the method for Tsai that hand eye type robot is carried out hand and eye calibrating, obtain the trick evolution relation of robot, i.e. spin matrix and translation vector between robot hand coordinate system and the camera coordinates system;

2) gather intercondylar fossa centre coordinate and paw attitude data: keep the femur center constant, go down on one's knees forward 90 the degree, mobile robot's paw makes the camera of tying up thereon over against distal femur intercondylar fossa center, gather intercondylar fossa centre coordinate and paw attitude data, with this moment the femur position be benchmark, be moved to the left distal femur and make femur rotation 45 degree～60 degree, simultaneously also being moved to the left robot hand makes the intercondylar fossa center within the field range of camera, gather intercondylar fossa centre coordinate and paw attitude data, similarly, again respectively to the right, on, following three directions move distal femur and robot hand, gather intercondylar fossa centre coordinate and paw attitude data, measure intercondylar fossa centre coordinate and the paw attitude data that obtains 5 groups of diverse locations altogether;

3) the intercondylar fossa centre coordinate is transformed into basis coordinates system of robot down: at first the intercondylar fossa centre coordinate that collects is carried out the trick Coordinate Conversion by the trick evolution relation that step 1) obtains, be transformed into the robot hand coordinate system, utilize the paw attitude data calculating paw coordinate system of this moment and the coordinate transform relation of basis coordinates system of robot then, obtain spin matrix and translation vector between two coordinate systems, at last the intercondylar fossa centre coordinate under the robot hand coordinate system is transformed into basis coordinates system of robot down, so obtain the coordinate information of all intercondylar fossa centers under unified basis coordinates;

4) calculate the femoral head center with the sphere fitting process: the problem that will determine the femoral head center is abstracted into the geometric model that point on the known sphere is found the solution the centre of sphere, utilize the intercondylar fossa centre data under the basis coordinates system of robot that obtains previously to remove spherical equation of match, obtain the centre coordinate of this sphere with the method for numerical computations, this sphere centre point is exactly the coordinate of femoral head center under basis coordinates system of robot, realizes the accurate location at femur center.

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