CN116687712A - A Knee Crossed Four-bar Exoskeleton and Its Design Method Based on Image Registration - Google Patents

Abstract

The utility model belongs to the field of exoskeleton robots, and discloses a knee joint crossed four-bar exoskeleton and a design method based on image registration, wherein the knee joint crossed four-bar exoskeleton comprises a thigh part, a shank part, a thigh and shank connecting part and a driving part, the thigh part and the shank part are connected through the thigh and shank connecting part, the driving part is used for driving the thigh and shank connecting part to drive the thigh part and the shank part to move, the thigh part, the shank part, a driving connecting rod piece and a driven connecting plate form a crossed hinge four-bar mechanism, and the length of the hinge crossed four-bar mechanism is designed according to an acquired skeleton X-ray image. The exoskeleton can be well applied to the scenes such as medical rehabilitation and carrying assistance, J-shaped curve priori knowledge is added in the process of solving the knee joint instantaneous center curve, the solving is quick, the data dependence degree is small, a four-bar mechanism schematic diagram is designed according to the characteristics of the anterior and posterior cruciate ligaments of the knee joint, and the designed mechanism has the function of artificial knee joint through X-ray image mapping mechanism parameters.

Description

A Knee Crossed Four-bar Exoskeleton and Its Design Method Based on Image Registration

technical field

The invention belongs to the field of exoskeleton robots, and in particular relates to a knee joint cross four-bar exoskeleton and a design method based on image registration.

Background technique

In the face of the aging society, the knee joint is prone to problems, and it is necessary to quickly design a suitable exoskeleton for knee joint exercise and rehabilitation. Knee joint exoskeleton has always been a research hotspot in the field of robotics. Knee joint rehabilitation training can be completed through knee joint exoskeleton, saving labor time.

At present, most of the exoskeletons of the knee joint are heavy, and most of the designs are designed by collecting motion data outside the body. This method cannot observe the real motion state inside the bone.

Chinese invention CN202110610808.1 discloses a personalized and customized high-compliance knee exoskeleton design method, which discloses the solution method of the ICR curve in the specification, which solves the problem of obtaining the instantaneous center curve in the Chinese utility model CN209850913U, but According to its claims and descriptions, the X-ray images taken are too dense, and the patient's body tissue suffers more radiation, and the calculation method is too dependent on the number of shooting angles of the patient. Moreover, the patent does not carry out the registration process of the pictures of each angle, which increases the error of the instantaneous center curve of the knee joint, and there is no design analysis and engineering feasibility verification of the principle and structure of the mechanism.

Contents of the invention

The purpose of the present invention is to provide a knee cross four-bar exoskeleton and its design method based on image registration, so as to solve the above-mentioned technical problems.

In order to solve the above-mentioned technical problems, the specific technical scheme of a kind of knee joint cross four-bar exoskeleton and its design method based on image registration of the present invention is as follows:

A knee cross four-bar exoskeleton, comprising a thigh part, a lower leg part, a leg connecting part and a driving part, the thigh part and the lower leg part are connected by a leg connecting part, and the driving part is used to drive the leg connecting part Drive the movement of the thigh parts and the lower leg parts, the thigh parts include thigh parts, the lower leg parts include calf parts, the thigh parts include active link parts, driven connecting plates, the thigh parts, calf parts, and active link parts The cross hinge four-bar mechanism is formed by the parts and the driven connecting plate, and the length of the hinge cross four-bar mechanism is designed according to the collected bone X-ray images.

Further, the thigh component includes a thigh baffle, a thigh piece, a thigh bearing seat, a thigh connecting piece, and a thigh fixing plate. The thigh baffle includes four symmetrically arranged waist holes. The thigh fixing plate and the thigh baffle Fixedly connected through the waist hole, the thigh part and the thigh baffle are fixedly connected through the thigh connecting part, the thigh bearing seat is fixed on the thigh part, the thigh fixing plate is fixed on the thigh, and the thigh part is opposite to the thigh during installation Fixed, the thigh piece has two sections of arc-shaped profile thigh piece arc A and thigh piece arc B, the thigh piece arc A is tangent to the rounded corners at both ends, the length is 80-120mm, the thigh piece Arc B is tangent to the rounded corners at both ends, and the length is 25-60mm.

Further, the lower leg parts include lower leg parts, lower leg baffles, lower leg connectors, bushings, lower leg bearing seats, lower leg optical shafts, and lower leg fixing plates. The lower leg upper boards include four symmetrically arranged waist holes. The calf fixing plate and the calf baffle are fixedly connected through the waist hole, the calf part and the calf baffle are fixedly connected through the calf connecting part, the calf bearing seat is fixed on the calf baffle and the calf part, and the shaft sleeve is connected to the calf On the bearing seat, the optical axis of the shank is in the middle of the shank bearing seat, the shank fixing plate is fixed on the shank, the shank part is fixed relative to the shank during installation, and the shank part has an arc-shaped profile at both ends Calf arc A and calf arc B, the calf arc A is tangent to the rounded corners at both ends, and the length is 30-50 mm, and the calf arc B is tangent to the rounded corners at both ends, and the length is 35-60 mm.

Further, the connecting parts of the large and small legs include an active link, a driven connecting plate, and a pin shaft. One end of the active link is installed on the thigh part, and the other end is installed on the optical axis of the calf, and is positioned between the calf bearing seat and Between the bushings, the driven connecting plate is in the shape of a rounded rectangle, four connecting holes are opened around it, and two large holes are opened at both ends of the center line of the long side, and the driven connecting plate and the lower leg bearing seat pass through the pin connect.

Further, the driving part includes a worm gear reducer and a motor, the worm gear reducer is fixed on the thigh part of the thigh part, the motor is arranged above the worm gear reducer, and a rectangular groove is opened below the worm gear reducer The active link is fixedly connected to the output shaft of the worm gearbox through a rectangular notch, and the active link can swing periodically in the rectangular notch driven by the motor.

The present invention also discloses a design method based on image registration of a knee cross four-bar exoskeleton, comprising the following steps:

Step 1: As shown in Figure 14, under the medical X-ray machine, take X-ray images of the femur not moving and the tibia bending at angles of 0°, 30°, 60°, 90°, and 120°;

Step 2: Preprocessing the obtained image data;

Step 3: Add marker points on the preprocessed image. The specific steps of step 3 are as follows: select 6 points on the femur with obvious changes in the curvature of the contour curve as marker points in turn, and select 3 points on the tibia with obvious changes in the curvature of the contour curve The points of the i-th image are used as marker points in turn, the point set of the i-th image is represented as S _i , and the coordinates of the j-th point of the i-th X-ray image are marked as where i=1,2,3,4,5; j=1,2,3...9;

Step 4: Carry out image registration based on the added marker points;

Step 5: Calculate the instantaneous heart curve of the knee joint based on the registered image;

Step 6: Calculate the length of each member of the four-bar mechanism;

Step 7: Set the calculated bar length as the parameter corresponding to the actual bar.

Further, the step 2 includes the following specific steps:

Step 2.1: Convert the collected image data in DICOM format to data in JPG format using a computer programming language;

Step 2.2: Correct the size of the image using the scale factor μ, and enhance the contrast of the image using a power transform.

Further, said step 4 includes the following specific steps:

Step 4.1: Keep the points of each picture relatively unchanged, and register all the pictures to the first picture;

Step 4.2: Register the points Pi (i=1, 2...6) on the femur, use the 0° mark point as the point set, and the registration error is Loss. The formula used is as follows:

where /> Step 4.3: Establish a coordinate system with the third point of each picture as the coordinate origin. There are three parameters in the registration process, which are the translation in the x-axis direction The amount of translation in the y-axis direction /> The angle θ ⁱ of rotation around the origin is represented by a coordinate transformation matrix. Each point set undergoes coordinate transformation, and the coordinate transformation matrix and coordinate transformation are as follows:

S _i T _i ;

Step 4.4: Take the registration error Loss as the objective function, θ, tx, ty, as the optimization variables There are 12 variables in total, the constraint condition is st, and the constraint condition adopted is as follows: />

Step 4.5: Select an optimization algorithm to solve the above target programming problem, save the optimal variables solved and visualize the registered point set.

Further, said step 5 includes the following specific steps:

Step 5.1: Use the cubic spline interpolation method to calculate the motion trajectory L ⁷ , L ⁸ , L ⁹ composed of P _i ⁷ , P _i 8 , P _i ⁹ (i=1, 2, ³ , 4, 5);

Step 5.2: Calculate the instantaneous rotation centers of the femur and tibia at five moments, calculate an instantaneous rotation center I _i (x _c , y _c ) for each picture, and calculate points 7, 8, and 9 in pairs for each picture 3 instantaneous centers of rotation The normal slope of points 7, 8, and 9 on the curve in the i-th 8th image is recorded as /> Among them, jk=78,79,89, which are averaged, and the specific calculation method is as follows:

Step 5.3: Change the parameters of the cubic curve _L0 from the coordinates of _Ii to obtain the instantaneous center curve L of the knee joint. The curve used is a curve within a limited range, in the shape of a "J", _L0 : y= ^ax3 + ^bx2 + cx+d, where the parameter constraints and the range of the curve are as follows: where />

Step 5.4: The optimization objective of the design curve L is i=1,2,3,4,5, dist represents the distance between two points, where the coordinates of Q _i are /> where /> and r _i is /> In the i-th element, the elements taken in the r vector are composed of the angles at which the X-ray pictures are taken, not limited to the above-mentioned 5 angles;

Step 5.5: Select an optimization algorithm to solve the equation of the decision variable X=[a, b, c, d] to determine the curve L, and solve the knee joint instantaneous center result.

Further, said step 6 includes the following specific steps:

Step 6.1: Design the cross four-bar linkage mechanism, the lengths are l ₁ , l ₂ , l ₃ , l ₄ , and set the bar length constraints. The specific constraints are as follows:

45mm<l ₁ <65mm

80mm<l ₂ <120mm

70mm＜ ₁₃ ＜110mm

35mm＜ ₁₄ ＜60mm

l ₂ + l ₄ ≤ l ₁ + l ₃ ;

Step 6.2: Evenly take 10 points in the instantaneous center curve L of the knee joint, L _ci (x _ci , y _ci ), the instantaneous center curve of the mechanism is composed of intersection points, and the angle between l ₂ and l ₁ of the four-bar mechanism is The instantaneous center L _ci (x _ci ,y _ci ) at α, where i=1,2,3...10, the value of α is in Taking 10 values evenly, L _ci (x _ci , y _ci ) is solved by a system of linear equations in six variables. The specific calculation method is as follows:

Step 6.3: Define the objective function That is, the average distance difference between the instant center curve of the knee joint and the calculation of the instantaneous center estimation of the rod, with the intersection point of rod 1 and rod 2 as the origin, the whole mechanism rotates γ around the origin, and the decision variable is X=[γ,l ₁ ,l ₂ ,l ₃ ,l ₄ ], use the optimization algorithm to solve all rod lengths.

A knee-joint cross four-bar exoskeleton of the present invention and its design method based on image registration have the following advantages: the designed exoskeleton based on image data of the present invention has fast design speed, high design precision, and design The structure is both lightweight and easy to maintain. It can be effectively used on patients who need rehabilitation training for the knee joint. The design method in the present invention extracts key information, calculates quickly, and the effect meets expectations. The cross four-bar mechanism adopted is well in line with the characteristics of the anterior and posterior cruciate ligaments of the human body, and has high bionicity. The designed exoskeleton can Combined with intelligent control algorithm to plan the trajectory of exoskeleton.

Description of drawings

Fig. 1 is the overall schematic diagram of the exoskeleton described in the present application;

Fig. 2 is a schematic diagram of a partial side view of the exoskeleton described in the present application;

Fig. 3 is a partial schematic diagram after disassembly of the exoskeleton calf baffle described in the present application;

Fig. 4 is a schematic diagram of the opening slot of the exoskeleton worm gearbox described in the present application;

Fig. 5 is a schematic diagram of the exoskeleton thigh baffle described in the present application;

Fig. 6 is a schematic diagram of the exoskeleton thigh part described in the present application;

Fig. 7 is a schematic diagram of the exoskeleton calf baffle described in the present application;

Fig. 8 is a schematic diagram of the exoskeleton lower leg part described in the present application;

Fig. 9 is a schematic diagram of the driven connecting plate of the exoskeleton described in the present application;

Fig. 10 is a schematic diagram of the active linkage of the exoskeleton described in the present application;

Fig. 11 is the schematic diagram of the cross four-bar mechanism of the design method described in the present application;

Figure 12 is a schematic diagram of the distribution of the anterior and posterior cruciate ligaments of the design method described in the present application;

Fig. 13 is a flowchart of the design method described in the present application;

Fig. 14 is a schematic diagram of bone image acquisition of the present application;

Figure 15 is a diagram of the X-ray image point marking sequence number of the design method described in the present application;

Fig. 16 is an effect diagram of X-ray image registration of the design method described in the present application;

Fig. 17 is a schematic diagram of solving the instantaneous heart curve of the knee joint according to the design method described in the present application;

Fig. 18 is the instantaneous heart curve of the knee joint by the method designed in the present application.

In the figure: 1. thigh baffle; 2. thigh fixing plate; 3. active connecting rod; 4. calf baffle; 5. calf fixing plate; ; 72, shank part arc B; 8, pin shaft; 9, driven connecting plate; 10, thigh part; 101, thigh part arc A; 102, thigh part arc B; 11, worm gear reduction box; 111, rectangular groove 12, thigh connector; 13, thigh bearing; 14, shaft sleeve; 15, calf bearing seat; 16, calf optical axis; 17, motor.

Detailed ways

In order to better understand the purpose, structure and function of the present invention, a knee cross four-bar exoskeleton and its design method based on image registration will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the exoskeleton of the present invention includes a thigh part, a calf part, a thigh connecting part and a driving part. and lower leg movement.

As shown in FIGS. 1 and 2 , the thigh parts include a thigh baffle 1 , a thigh member 10 , a thigh bearing seat 13 , a thigh connector 12 , and a thigh fixing plate 2 . The thigh baffle 1 includes four symmetrically arranged waist holes, the thigh fixing plate 2 and the thigh baffle 1 are fixedly connected through the waist holes, and the height can be adjusted along the direction of the waist holes. The thigh piece 10 and the thigh baffle 1 are fixedly connected through the thigh connecting piece 12 , and the thigh bearing seat 13 is fixed on the thigh piece 10 . The thigh fixing plate 2 is fixed on the thigh, and the thigh parts are fixed relative to the thigh during installation.

As shown in Figure 6, the thigh piece 10 has two sections of arc-shaped profile thigh piece arc A101 and thigh piece arc B102. B102 is tangent to the rounded corners at both ends, and the length is 25-60mm.

As shown in FIGS. 1-3 , the lower leg component includes a lower leg member 7 , a lower leg shield 4 , a lower leg connector 6 , a shaft sleeve 14 , a lower leg bearing seat 15 , a lower leg optical axis 16 , and a lower leg fixing plate 5 . The lower leg baffle 4 includes four symmetrically arranged waist holes, the lower leg fixing plate 5 and the lower leg baffle 4 are fixedly connected through the waist holes, and the height can be adjusted along the direction of the waist holes. The shank part 7 and the shank baffle 4 are fixedly connected by the shank connector 6, the shank bearing seat 15 is fixed on the shank baffle 4 and the shank part 7, the shaft sleeve 14 is connected to the shank bearing seat 15, and the shank optical axis 16 is on the shank bearing Seat 15 is in the middle. The shank fixing plate 5 is fixed on the shank, and the shank part is fixed relative to the shank during installation.

As shown in Figure 8, the calf part 7 has a calf part arc A71 and a calf part arc B72 with arc-shaped profiles at both ends. B72 is tangent to the rounded corners at both ends, and the length is 35-60mm.

The large and small leg connecting parts include active link 3, driven connecting plate 9, pin shaft 8, one end of active link 3 is installed on the thigh part, the other end is installed on the calf optical axis 16, and is positioned on the calf bearing seat 15 and shaft Set of 14 between. The driven connecting plate 9 is a rounded rectangular shape, four connecting holes are arranged around it, and two large holes are arranged at the two ends of the long side midline. The driven connecting plate 9 is connected with the shank bearing seat 15 by a pin shaft 8 .

The drive components include a worm gear reducer 11 and a motor 17 . The worm gear reducer 11 is fixed on the thigh part 10 of the thigh part, the motor 17 is arranged on the top of the worm gear reducer 11, and there is a rectangular notch below the worm gear reducer 11, and the active link part 3 is connected with the worm gear through the rectangular notch 111. The output shaft of the worm reduction box 11 is fixedly connected, and the active link 3 can periodically swing in the rectangular notch driven by the motor 17 .

There are threaded holes at the two ends of the thigh connector 12 and the shank connector 6, and the connections between the components are not described and all adopt threaded or bolted connections.

The thigh part 10 in the thigh part, the calf part 7 in the calf part, the active link part 3 and the driven connecting plate 9 constitute a cross hinge four-bar mechanism. The length of the hinge cross four-bar mechanism is designed according to the collected bone X-ray images, and the collected images are not less than two.

When the device of the present invention is installed on the knee joint of the lower limbs of the human body, the motor 17 drives the active link part 3 to move through the worm gear reducer 11. Due to the movement law of the hinge cross four-bar mechanism, the calf moves under the fixed traction of the calf to achieve auxiliary The purpose of the patient's movement.

Fig. 2 is an overall side view of the exoskeleton. The worm gear reducer 11 is fixed on the thigh part 10, and the motor 17 drives the active link part 3 to swing periodically. The rectangular notch 111 shown in Fig. 4 provides movement space for the swing.

Figures 5 and 7 are schematic diagrams of the structure of the thigh baffle 1 and the calf baffle 4. When the patient wears it, the thigh and calf lean against it. The thigh baffle 1 and the calf baffle 4 are provided with four small holes, which can be passed through Adjust the thigh fixing plate 2 and the calf fixing plate 5 to determine the best wearing position.

Figures 6, 8, 9, 10, and 11 are the schematic diagram of the cross four-bar mechanism and the design parameters corresponding to the actual rods. The distances l ₁ , l ₂ , l ₃ , and l ₄ in the figure are the distances between the center holes. The distance _l1 in 8 is the distance from a hole to the center hole of the bearing on the lower leg part 7, the distance _l2 in Figure 10 is the distance between the center holes of the active link bearings, and the distance _l3 in Figure 6 is the distance between the upper leg parts The distance between the bearing center holes on 10, the distance _l4 in Fig. 9 is the distance between the bearing center holes of the driven connecting plate 9.

As shown in Figure 13, the design method is described in detail below in conjunction with the accompanying drawings:

Step 1: As shown in Figure 14, under the medical X-ray machine, take X-ray images of the femur not moving and the tibia bending at angles of 0°, 30°, 60°, 90°, and 120°;

Step 2: Preprocessing the obtained image data, the specific steps are as follows:

Step 2.1: Convert the collected image data in DICOM format to data in JPG format using a computer programming language;

Step 2.2: Use the proportional coefficient μ to correct the size of the image, and use power transformation to enhance the contrast of the image;

Step 3: Add marker points on the preprocessed image, the specific steps of step 3 are as follows:

Select 6 points on the femur with obvious changes in the curvature of the contour curve as marker points in turn, and select 3 points on the tibia with obvious changes in the curvature of the contour curve as marker points in turn. The marker map is shown in Figure 15. The point set of the i-th picture Denoted as S _i , the coordinates of the jth point of the i-th X-ray image are marked as Wherein i=1,2,3,4,5; j=1,2,3...9.

Step 4: Carry out image registration based on the added marker points, the specific steps are as follows:

Step 4.1: Keep the points of each image relatively unchanged, and register all images to the first image.

Step 4.2: Register the points P _i (i=1, 2...6) on the femur, use the 0° mark point as the alignment point set, and the registration error is Loss, and the formula used is as follows:

where />

Step 4.3: Establish a coordinate system with the third point of each picture as the coordinate origin. There are three parameters in the registration process, which are the translation in the x-axis direction The amount of translation in the y-axis direction /> The angle θ ⁱ of rotation around the origin is represented by a coordinate transformation matrix. Each point set undergoes coordinate transformation, and the coordinate transformation matrix and coordinate transformation are as follows:

Step 4.4: Take the registration error Loss as the objective function, θ, t _x , t _y as the optimization variables There are 12 variables in total, and the constraint condition is st, and the constraints adopted are as follows:

Step 4.5: Select an optimization algorithm to solve the above target programming problem, save the optimal variables solved and visualize the registered point set. As shown in Figure 16, it is the effect diagram after registration.

Step 5: Calculating the instantaneous heart curve of the knee joint based on the registered image, the specific steps of the step 5 are as follows:

Step 5.1: Use the cubic spline interpolation method to calculate the motion trajectory L ⁷ , L ⁸ , and L ⁹ composed of P _i ⁷ , P _i ⁸ , and P _i ⁹ (i=1, 2, 3, 4, 5).

Step 5.2: Calculate the instantaneous center of rotation of the femur and tibia at five moments, each image can calculate an instantaneous center of rotation I _i (x _c , y _c ), and combine points 7, 8, and 9 in pairs for each image 3 instantaneous centers of rotation can be calculated The normal slope of points 7, 8, and 9 on the curve in the i-th 8th image is recorded as /> Among them, jk=78,79,89, which are averaged, and the specific calculation method is as follows:

Step 5.3: Change the parameters of the cubic curve _L0 from the coordinates of _Ii to obtain the instantaneous center curve L of the knee joint. The curve used is a curve within a limited range, in the shape of a "J", _L0 : y= ^ax3 + ^bx2 + cx+d, where the parameter constraints and the range of the curve are as follows: where />

Step 5.4: The optimization objective of the design curve L is i=1,2,3,4,5, dist represents the distance between two points, where the coordinates of Q _i are /> where /> and r _i is /> The i-th element in the r vector is composed of the angles at which the X-ray pictures are taken, and is not limited to the above-mentioned 5 angles. The schematic diagram of the optimization function is shown in Figure 17.

Step 5.5: Select an optimization algorithm to solve the equation of the decision variable X=[a,b,c,d] to determine the curve L, and solve the result curve of the knee joint instantaneous center as shown in Figure 18 .

Step 6: Calculate the length of each rod of the four-bar mechanism, and the specific steps of the step 6 are as follows:

Step 6.1: Design the intersecting four-bar linkage mechanism. The design inspiration is shown in Figure 12 and Figure 11. The lengths are l ₁ , l ₂ , l ₃ , and l ₄ , and the rod length constraints are set. The specific constraints are as follows:

45mm<l ₁ <65mm

80mm<l ₂ <120mm

70mm＜ ₁₃ ＜110mm

35mm < l ₄ < 60mm.

l ₂ +l ₄ ≤l ₁ +l ₃

Step 6.2: Evenly take 10 points in the instantaneous center curve L of the knee joint, L _ci (x _ci , y _ci ), the instantaneous center curve of the mechanism is composed of intersection points, and the angle between l ₂ and l ₁ of the four-bar mechanism is The instantaneous center L _ci (x _ci ,y _ci ) at α, where i=1,2,3...10, the value of α is in Taking 10 values evenly, L _ci (x _ci , y _ci ) is solved by a system of linear equations in six variables. The specific calculation method is as follows:

Step 6.3: Define the objective function That is, the average distance difference between the instant center curve of the knee joint and the calculation of the instantaneous center estimation of the rod, with the intersection point of rod 1 and rod 2 as the origin, the whole mechanism rotates γ around the origin, and the decision variable is X=[γ,l ₁ ,l ₂ ,l ₃ ,l ₄ ], use the optimization algorithm to solve all rod lengths.

Step 7: Set the calculated bar length as the parameter corresponding to the actual bar.

The above description is only a preferred embodiment of the present invention. Ideally, the instantaneous heart curve of the knee joint can be accurately obtained by taking X-ray pictures from two angles. The invention is shown above by way of suitable examples, but it is not intended to limit the invention itself. Compared with the existing exoskeleton design, the invention has the advantages of fast speed, clear design parameters, light structure and reliable results.

It can be understood that the present invention is described through some embodiments, and those skilled in the art know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, the features and embodiments may be modified to adapt a particular situation and material to the teachings of the invention without departing from the spirit and scope of the invention. Therefore, the present invention is not limited by the specific embodiments disclosed here, and all embodiments falling within the scope of the claims of the present application belong to the protection scope of the present invention.

Claims (10)

1. A knee cross four-bar exoskeleton, comprising a thigh part, a calf part, a thigh connection part and a drive part, the thigh part and the calf part are connected by a thigh connection part, and the drive part is used to drive the thigh The connecting part drives the thigh part and the calf part to move, and it is characterized in that, the thigh part comprises a thigh part (10), the calf part comprises a calf part (7), and the thigh connecting part comprises an active link part (3), from The movable connecting plate (9), the thigh member (10), the calf member (7), the active link member (3), and the driven connecting plate (9) form a cross hinge four-bar mechanism, and the hinge cross four bar mechanism The length of the mechanism is designed according to the acquired bone X-ray images. 2. Knee joint cross four-bar exoskeleton according to claim 1, is characterized in that, described thigh part comprises thigh baffle plate (1), thigh part (10), thigh bearing block (13), thigh connector ( 12), the thigh fixing plate (2), the thigh baffle (1) includes four symmetrically arranged waist holes, the thigh fixing plate (2) is fixedly connected with the thigh baffle (1) through the waist holes, the The thigh piece (10) and the thigh baffle (1) are fixedly connected through the thigh connecting piece (12), the thigh bearing seat (13) is fixed on the thigh piece (10), and the thigh fixing plate (2) is fixed on the thigh When installing, the thigh part is fixed relative to the thigh, and the thigh part (10) has two arc-shaped contours, thigh part arc A (101) and thigh part arc B (102), and the thigh part arc A (101) is tangent to the rounded corners at both ends and has a length of 80-120 mm. The thigh member arc B (102) is tangent to the rounded corners at both ends and has a length of 25-60 mm. 3. The knee-joint cross four-bar exoskeleton according to claim 2, characterized in that, the shank parts include a shank (7), a shank baffle (4), a shank connector (6), a shaft sleeve (14 ), shank bearing seat (15), shank optical axis (16), shank fixing plate (5), described shank baffle plate (4) comprises four waist holes arranged symmetrically, described shank fixing plate (5) and shank The baffle (4) is fixedly connected through the waist hole, the shank (7) and the shank baffle (4) are fixedly connected through the shank connector (6), and the shank bearing seat (15) is fixed on the shank baffle (4) ) and the shank (7), the bushing (14) is connected to the shank bearing (15), the optical axis of the shank (16) is in the middle of the shank bearing (15), and the shank fixing plate (5 ) is fixed on the calf, and the calf part is fixed relative to the calf during installation, and the calf part (7) has a calf part arc A (71) and a calf part arc B (72) with arc-shaped profiles at both ends, The calf arc A (71) is tangent to the rounded corners at both ends and has a length of 30-50 mm. The calf arc B (72) is tangent to the rounded corners at both ends and has a length of 35-60 mm. 4. The knee joint cross four-bar exoskeleton according to claim 3, characterized in that, the connecting parts of the thighs and legs comprise active linkages (3), driven connecting plates (9), pins (8), One end of the active link (3) is installed on the thigh member, and the other end is installed on the optical axis (16) of the lower leg, and is positioned between the lower leg bearing seat (15) and the shaft sleeve (14). The driven connecting plate (9) is a rounded rectangular shape, four connecting holes are arranged around, and two large holes are arranged at the two ends of the center line of the long side, and the driven connecting plate (9) and the shank bearing seat (15) pass through the pin shaft (8 )connect. 5. The knee joint cross four-bar exoskeleton according to claim 4, characterized in that, the drive components include a worm gear reducer (11) and a motor (17), and the worm gear reducer (11) is fixed on the thigh part On the thigh piece (10), the motor (17) is arranged above the worm gear reducer (11), and a rectangular notch is opened below the worm gear reducer (11), and the active link (3) Through the fixed connection of the rectangular notch (111) to the output shaft of the worm gear reducer (11), the active link (3) can periodically swing in the rectangular notch driven by the motor (17). 6. A design method based on image registration of the knee cross four-bar exoskeleton according to any one of claims 1-5, characterized in that, comprising the steps of: Step 1: As shown in Figure 14, under the medical X-ray machine, take X-ray images of the femur not moving and the tibia bending at angles of 0°, 30°, 60°, 90°, and 120°; Step 2: Preprocessing the obtained image data; Step 3: Add marker points on the preprocessed image, the specific steps of step 3 are as follows: Select 6 points on the femur with obvious changes in the curvature of the contour curve as marker points in turn, and select 3 points on the tibia with obvious changes in the curvature of the contour curve as marker points in turn. The point set of the i-th picture is denoted as S _i , The coordinates of the jth point of the X-ray image are marked as where i=1,2,3,4,5; j=1,2,3...9; Step 4: Carry out image registration based on the added marker points; Step 5: Calculate the instantaneous heart curve of the knee joint based on the registered image; Step 6: Calculate the length of each member of the four-bar mechanism; Step 7: Set the calculated bar length as the parameter corresponding to the actual bar. 7. The design method based on image registration according to claim 6, wherein said step 2 comprises the following specific steps: Step 2.1: Convert the collected image data in DICOM format to data in JPG format using a computer programming language; Step 2.2: Correct the size of the image using the scale factor μ, and enhance the contrast of the image using a power transform. 8. The design method based on image registration according to claim 6, wherein said step 4 comprises the following specific steps: Step 4.1: Keep the points of each picture relatively unchanged, and register all the pictures to the first picture; Step 4.2: Register the points Pi (i=1, 2...6) on the femur, use the 0° mark point as the point set, and the registration error is Loss. The formula used is as follows: where /> Step 4.3: Establish a coordinate system with the third point of each picture as the coordinate origin. There are three parameters in the registration process, which are the translation in the x-axis direction The amount of translation in the y-axis direction /> The angle θ ⁱ of rotation around the origin is represented by a coordinate transformation matrix. Each point set undergoes coordinate transformation. The coordinate transformation matrix and coordinate transformation are as follows: /> S _i T _i ; Step 4.4: Take the registration error Loss as the objective function, θ, tx, ty, as the optimization variables There are 12 variables in total, the constraint condition is st, and the constraint condition adopted is as follows: /> Step 4.5: Select an optimization algorithm to solve the above target programming problem, save the optimal variables solved and visualize the registered point set. 9. The design method based on image registration according to claim 6, wherein said step 5 comprises the following specific steps: Step 5.1: Use the cubic spline interpolation method to calculate the motion trajectory L ⁷ , L ⁸ , L ⁹ composed of P _i ⁷ , P _i 8 , P _i ⁹ (i=1, 2, ³ , 4, 5); Step 5.2: Calculate the instantaneous rotation centers of the femur and tibia at five moments, calculate an instantaneous rotation center I _i (x _c , y _c ) for each picture, and calculate points 7, 8, and 9 in pairs for each picture 3 instantaneous centers of rotation The normal slope of points 7, 8, and 9 on the curve in the i-th 8th image is recorded as /> Among them, jk=78,79,89, which are averaged, and the specific calculation method is as follows: Step 5.3: Change the parameters of the cubic curve _L0 from the coordinates of _Ii to obtain the instantaneous center curve L of the knee joint. The curve used is a curve within a limited range, in the shape of a "J", _L0 : y= ^ax3 + ^bx2 + cx+d, where the parameter constraints and the range of the curve are as follows: where /> Step 5.4: The optimization objective of the design curve L is i=1,2,3,4,5, dist represents the distance between two points, where the coordinates of Q _i are /> where /> and r _i is /> In the i-th element, the elements taken in the r vector are composed of the angles at which the X-ray pictures are taken, not limited to the above-mentioned 5 angles; Step 5.5: Select an optimization algorithm to solve the equation of the decision variable X=[a, b, c, d] to determine the curve L, and solve the knee joint instantaneous center result. 10. The design method based on image registration according to claim 6, wherein said step 6 comprises the following specific steps: Step 6.1: Design the cross four-bar linkage mechanism, the lengths are l ₁ , l ₂ , l ₃ , l ₄ , and set the bar length constraints. The specific constraints are as follows: 45mm<l ₁ <65mm 80mm<l ₂ <120mm 70mm＜ ₁₃ ＜110mm 35mm＜ ₁₄ ＜60mm l ₂ + l ₄ ≤ l ₁ + l ₃ ; Step 6.2: Evenly take 10 points in the instantaneous center curve L of the knee joint, L _ci (x _ci , y _ci ), the instantaneous center curve of the mechanism is composed of intersection points, and the angle between l ₂ and l ₁ of the four-bar mechanism is The instantaneous center L _ci (x _ci ,y _ci ) at α, where i=1,2,3...10, the value of α is in Taking 10 values evenly, L _ci (x _ci , y _ci ) is solved by a system of linear equations in six variables. The specific calculation method is as follows: Step 6.3: Define the objective function That is, the average distance difference between the instant center curve of the knee joint and the calculation of the instantaneous center estimation of the rod, with the intersection point of rod 1 and rod 2 as the origin, the whole mechanism rotates γ around the origin, and the decision variable is X=[γ,l ₁ ,l ₂ ,l ₃ ,l ₄ ], use the optimization algorithm to solve all rod lengths.