An external fixation orthotic mechanism with virtual center of motion characteristics

Abstract

This invention discloses an external fixation orthotic mechanism with virtual center motion characteristics, consisting of a moving platform, a stationary platform, three motion chains, and orthotic components. The three motion chains are distributed at 120° intervals along the circumference of the stationary platform, increasing the stability of the mechanism. The motion chains connect the moving platform and the stationary platform by threaded connection. By tightening the locking nut, the chains can be fixed to the stationary and moving platforms, making installation convenient, flexible, stable, and reliable. During orthotic treatment, the moving platform can drive the fixed component to rotate around the X and Y axes of the virtual coordinate system and move along the Z axis, increasing the orthotic flexibility and range, and ensuring that the axis of the orthotic component will not shift during the orthotic process, preventing misalignment. Based on the modular design concept, the external fixation orthotic mechanism of this invention can be used in series with some orthotic devices in clinical practice to achieve a wider range of orthotic functions and better orthotic effects.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, and more specifically, to an external fixation orthopedic mechanism with virtual center motion characteristics. Background Technology

[0002] Currently, there are many bone and joint deformity problems in orthopedic clinics. Since the introduction of Ilizarov orthopedic technology in the 1990s, the correction of skeletal deformities has made leaps and bounds. However, its component design has disadvantages such as simple configuration, many components, and time-consuming and laborious assembly, fixation and adjustment.

[0003] When correcting skeletal deformities, external fixators are involved in multi-degree-of-freedom rotation around a point in space and linear movement. Existing external fixation mechanisms, whether the Ilizarov frame, Taylor frame, or other bilateral, quadrilateral, or semi-ring types, cannot achieve virtual center movement. They require manual adjustment during use, which may lead to problems such as skeletal misalignment and insufficient correction. Furthermore, their structures have coupling characteristics, making it difficult to perform independent multi-degree-of-freedom spatial correction adjustments, thus affecting the treatment effect and the rehabilitation of patients with skeletal deformities. Summary of the Invention

[0004] The purpose of this invention is to design and develop an external fixation orthotic mechanism with virtual center motion characteristics. By combining a dynamic platform, a static platform and three motion chains, the external fixation orthotic mechanism can rotate around a virtual center point, which increases the flexibility and range of orthosis and improves the stability of the mechanism.

[0005] The technical solution provided by this invention is as follows:

[0006] An external fixation orthotic mechanism with virtual center motion characteristics includes:

[0007] A static platform, which is detachably fixed to the outside of the fixing component, and the height of the static platform is adjustable;

[0008] A moving platform is coaxially spaced from the stationary platform, and the moving platform is detachably fixed to the outside of the moving component;

[0009] The first branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to rotate around the x-axis of the virtual coordinate system;

[0010] The second branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to rotate around the y-axis of the virtual coordinate system.

[0011] The third branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to move along the z-axis of the virtual coordinate system;

[0012] The first branch includes:

[0013] The first motor is detachably fixed to the stationary platform;

[0014] An arc-shaped guide rail, one end of which is connected to the output end of the first motor, and the other end extends between the static platform and the moving platform;

[0015] A guide rail slider is slidably mounted on the arc-shaped guide rail;

[0016] The first electric push rod includes a fixed end and a pushing end, wherein the fixed end is connected to the guide rail slider and the pushing end is connected to the moving platform;

[0017] The interval between the first branch, the second branch and the third branch is 120°, and the radius of the arc of the arc-shaped guide rail is the same as the radius of the static platform.

[0018] The virtual coordinate system satisfies:

[0019] The origin is the center of the static platform, the x-axis is a horizontal line extending from the origin toward the first branch, the z-axis is a vertical line perpendicular to the static platform, and the y-axis is a horizontal line perpendicular to both the x-axis and the z-axis.

[0020] Preferably, the static platform includes:

[0021] First fixed ring; and

[0022] The first fixing pin has its two ends symmetrically arranged on the first fixing ring with the center of the ring, and the first fixing pin can selectively pass through the fixing member;

[0023] The second fixing ring is coaxially spaced from the first fixing ring, and the spacing is adjustable;

[0024] The first motor is detachably fixed on the second fixed ring, the center of the second fixed ring is the origin of the virtual coordinate system, and the first branch, the second branch and the third branch are all set between the second fixed ring and the moving platform.

[0025] Preferably, the moving platform includes:

[0026] The third fixed ring; and

[0027] The second fixing pin has its two ends symmetrically arranged on the third fixing ring with the center of the ring, and the second fixing pin can selectively pass through the moving member.

[0028] Preferably, the first branch further includes:

[0029] The first motor shaft connector is fixedly connected to the output end of the first motor.

[0030] One end of the arc-shaped guide rail is fixedly connected to the first motor shaft connector.

[0031] Preferably, the second branch includes:

[0032] The second motor is fixed on the second fixing ring;

[0033] The second motor shaft connector is fixedly connected to the output shaft of the second motor.

[0034] A fork-shaped head, which is rotatably disposed on the outside of the second motor shaft connector;

[0035] The second electric actuator has the same structure as the first electric actuator, with its fixed end connected to the fork-shaped head and its pushing end connected to the third fixed ring.

[0036] Preferably, the first branch further includes:

[0037] A slider connector, which is fixed to the guide rail slider;

[0038] The first sleeve has one end detachably mounted on the slider connector and the other end detachably mounted on the fixed end of the first electric push rod.

[0039] The first push rod connector has one end connected to the pushing end of the first electric push rod;

[0040] The first threaded rod has one end connected to the other end of the first push rod connector and the other end connected to the third fixed ring.

[0041] Preferably, the second branch further includes:

[0042] The second push rod connector has one end connected to the pushing end of the second electric push rod;

[0043] The second threaded rod has one end connected to the other end of the second push rod connector;

[0044] A first ball joint is disposed on the third fixed ring, and the first ball joint is connected to the other end of the second threaded rod.

[0045] Preferably, the third branch includes:

[0046] The second ball joint is disposed on the second fixed ring;

[0047] The third electric push rod has the same structure as the first electric push rod, and its fixed end is connected to the second ball joint;

[0048] The third ball joint is fixed on the third fixed ring, and the third ball joint is connected to the pushing end of the third electric push rod.

[0049] Preferably, the third branch further includes:

[0050] The third threaded rod has one end connected to the second ball joint;

[0051] The second sleeve has one end connected to the other end of the third threaded rod and the other end connected to the fixed end of the third electric push rod.

[0052] The third push rod connector has one end connected to the pushing end of the third electric push rod;

[0053] The fourth threaded rod has one end connected to the other end of the third push rod connector and the other end connected to the third ball joint.

[0054] Preferably, the rotation angles of the first and second motors are both -15° to 15°, the moving distances of the first, second, and third electric push rods are all 0 to 30 mm, and the length of the arc-shaped guide rail satisfies:

[0055]

[0056] In the formula, H is the length of the arc-shaped guide rail, and R is the radius of the arc-shaped guide rail.

[0057] The beneficial effects of this invention are as follows:

[0058] (1) The present invention designs and develops an external fixation orthotic mechanism with virtual center motion characteristics, which can be applied to the correction of human skeletal force lines. When the mechanism corrects skeletal force lines, it can rotate and move around the virtual center point in multiple dimensions, with a wide correction range. The correction process can be controlled by establishing serial communication between the host computer and the drive component to ensure the accuracy and flexibility of the correction. It can realize independent correction adjustment with multiple degrees of freedom in space, which has a positive impact on the postoperative rehabilitation of patients with bone and joint deformities.

[0059] (2) The present invention designs and develops an external fixation orthotic mechanism with virtual center motion characteristics, which combines three motion branches with a moving platform and a static platform, reducing the number of motion pairs, simplifying the configuration, and enhancing the stability of the mechanism. It can solve the problems of rotational misalignment and orthotic motion coupling that are common in current external fixation orthotic mechanisms. The height of the static platform is adjustable, making the mechanism more adaptable.

[0060] (3) The present invention designs and develops an external fixation orthotic mechanism with virtual center motion characteristics. When the mechanism is performing orthosis, the moving platform can drive the fixed component to rotate around the virtual coordinate system X and Y axes and move along the Z axis, which increases the orthotic flexibility and orthotic range, and ensures that the axis of the orthotic component will not deviate during the orthotic process, and the orthosis will not be misaligned. It realizes the accuracy of the mechanism's orthosis and the independent orthotic adjustment with multiple degrees of freedom in space, and improves the safe operation and quantitative precise control of the orthosis. Based on the modular design concept, the external fixation orthotic mechanism described in the present invention can be used in series with some orthotic instruments in clinical practice to achieve a wider range of orthotic functions and better orthotic effects. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the overall structure of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention.

[0062] Figure 2 This is a schematic diagram of the static platform described in this invention.

[0063] Figure 3 This is a schematic diagram of the structure of the moving platform described in this invention.

[0064] Figure 4 This is a schematic diagram of the structure of the first branch of the present invention.

[0065] Figure 5 This is a schematic diagram of the structure of the second branch of the present invention.

[0066] Figure 6 This is a schematic diagram of the structure of the third branch described in this invention.

[0067] Figure 7 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention rotating to one side around the x-axis of the virtual coordinate system.

[0068] Figure 8 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention rotating around the x-axis of the virtual coordinate system on the other side.

[0069] Figure 9 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention rotating to one side of the virtual coordinate system y-axis.

[0070] Figure 10 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention rotating around the y-axis of the virtual coordinate system on the other side.

[0071] Figure 11 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics described in this invention shortening along the z-axis of the virtual coordinate system.

[0072] Figure 12 This is a schematic diagram of the external fixation orthotic mechanism with virtual center motion characteristics as described in this invention extending along the z-axis of the virtual coordinate system. Detailed Implementation

[0073] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0074] like Figure 1 As shown, the external fixation orthotic mechanism with virtual center motion characteristics provided by the present invention includes:

[0075] The external fixation orthotic mechanism comprises a static platform 110, a movable platform 120, a first branch 130, a second branch 140, and a third branch 150. The static platform 110 is detachably sleeved on the outside of the fixed component 210 for positioning the mechanism. The movable platform 120 is coaxially spaced from the static platform 110 and is detachably sleeved on the outside of the moving component 220. The first branch 130, the second branch 140, and the third branch 150 are all telescopically arranged between the static platform 110 and the movable platform 120, with a 120° interval between them. The first branch 130 drives the external fixation orthotic mechanism to rotate around the x-axis of the virtual coordinate system, the second branch 140 drives the external fixation orthotic mechanism to rotate around the y-axis of the virtual coordinate system, and the third branch 150 drives the external fixation orthotic mechanism to move along the z-axis of the virtual coordinate system.

[0076] The virtual coordinate system satisfies:

[0077] The origin is the center of the static platform 110, the x-axis is a horizontal line extending from the origin toward the first branch 130, the z-axis is a vertical line perpendicular to the static platform 110, and the y-axis is a horizontal line perpendicular to both the x-axis and the z-axis.

[0078] like Figure 2As shown, the static platform 110 includes: a first fixing ring 111, a second fixing ring 112, and a first fixing pin 115. The second fixing ring 112 and the first fixing ring 111 have the same structure and are coaxially spaced apart. The second fixing ring 112 and the first fixing ring 111 are detachably connected by a threaded rod 113 and a nut. Threaded holes are evenly distributed on the first fixing ring 111 and the second fixing ring 112. The distance between the first fixing ring 111 and the second fixing ring 112 can be adjusted by rotating the threaded rod according to the distance between the fixing member 210 and the moving member 220. The two ends of the first fixing pin 115 are symmetrically arranged on the first fixing ring 111 around the center by a first fixing pin fastener 114, and are used to pass through the fixing member 210. The first fixing pin 115 and the second fixing ring 112 are respectively arranged on both sides of the first fixing ring 111.

[0079] The center of the second fixed ring 112 is the origin of the virtual coordinate system, that is, the center of the second fixed ring 112 is the virtual center point.

[0080] like Figure 3 As shown, the moving platform includes a third fixed ring 121 and a second fixed pin 122. The third fixed ring 121 and the first fixed ring 111 have the same structure. The two ends of the second fixed pin 122 are symmetrically arranged on the third fixed ring 121 with the center through the second fixed pin fastener 123, and are used to pass through the moving member 220. The second fixed pin 122 is arranged on the side of the third fixed ring 121 away from the second fixed ring 112.

[0081] like Figure 4As shown, the first branch 130 includes: a first motor 132, a first motor shaft connector 161, an arc-shaped guide rail 162, a guide rail slider 163, a slider connector 164, a first sleeve 133, a first electric push rod 134, a first push rod connector 135, and a first threaded rod 136. The first motor 132 is detachably fixed to the second fixed ring 112 via the first motor fixing member 131, forming a first rotating pair. The first motor shaft connector 161 is fixedly connected to the output end of the first motor. One end of the arc-shaped guide rail 162 is fixedly connected to the first motor shaft connector 161, and the other end extends between the static platform 110 and the moving platform 120, and the radius of the arc of the arc-shaped guide rail 162 is equal to that of the first fixed ring 112. The radii of the rings 111 are the same; the guide rail slider 163 is slidably disposed on the arc-shaped guide rail 162, forming a second revolute joint, which is essentially equivalent to a revolute joint rotating about an axis; the slider connector 164 is fixed on the guide rail slider 163; one end of the first sleeve 133 is connected to the slider connector 164 by a thread; the first electric push rod 134 includes a fixed end and a pushing end, the fixed end is connected to the other end of the first sleeve 133 by a thread, forming a sliding joint; one end of the first push rod connector 135 is connected to the pushing end of the first electric push rod 134; one end of the first threaded rod 136 is connected to the other end of the first push rod connector 135, and the other end is connected to the third fixed ring 121.

[0082] When the moving platform and the stationary platform are coaxial and parallel (i.e., the initial state of the external fixation orthopedic mechanism), the guide rail slider is in the middle position of the arc-shaped guide rail.

[0083] like Figure 5As shown, the second branch 140 includes: a second motor shaft connector 142, a second motor 143, a fork-shaped head 144, a second electric push rod 145, a second push rod connector 146, a second threaded rod 147, and a first ball joint 148. The second motor 143 is detachably fixed to the second fixed ring 112 via a second motor fixing member 141. The second motor shaft connector 142 is fixedly connected to the output shaft of the second motor 143. The fork-shaped head 144 is rotatably disposed on the outside of the second motor shaft connector 142, and the fork-shaped head 144 can rotate around the fork-shaped head 148. 44 rotates at the intersection point with the second motor shaft connector 142 to form a Hooke pair; the second electric push rod 145 has the same structure as the first electric push rod 134, and its fixed end is threadedly connected to the fork head 144 to form a sliding pair; one end of the second push rod connector 146 is connected to the pushing end of the second electric push rod 145; one end of the second threaded rod 147 is connected to the other end of the second push rod connector 146; the first ball joint 148 is disposed on the third fixed ring 121, and the first ball joint 148 is connected to the other end of the second threaded rod 147 to form a ball joint.

[0084] like Figure 6 As shown, the third branch 150 includes: a second ball joint 151, a third threaded rod 152, a second sleeve 153, a third electric push rod 154, a third push rod connector 155, a fourth threaded rod 156, and a third ball joint 157. The second ball joint 151 is disposed on the second fixed ring 112, forming a ball joint; one end of the third threaded rod 152 is connected to the second ball joint 151; one end of the second sleeve 153 is connected to the other end of the third threaded rod 152; the third electric push rod 154 has the same structure as the first electric push rod 134, and its fixed end is connected to the other end of the second sleeve 153, forming a sliding joint; one end of the third push rod connector 155 is connected to the pushing end of the third electric push rod 154; one end of the fourth threaded rod 156 is connected to the other end of the third push rod connector 155, and the other end is connected to the third ball joint 157. The third ball joint 157 is fixed on the third fixed ring 121, forming a ball joint.

[0085] The rotation angles of the first motor 132 and the second motor 143 are both -15° to 15°, and the moving distances of the first electric push rod 134, the second electric push rod 145, and the third electric push rod 154 are all 0 to 30 mm. The rotation angles of the motors and the moving distances of the electric push rods constitute the correction range of the external fixation orthotic mechanism. The length of the arc-shaped guide rail satisfies the following:

[0086]

[0087] In the formula, H is the length of the arc-shaped guide rail, and R is the radius of the arc of the arc-shaped guide rail. The radii of the arc-shaped guide rail 162, the first fixed ring 111, the second fixed ring 112 and the third fixed ring 121 can be customized according to the patient's body shape.

[0088] like Figure 7 As shown, when the external fixation orthotic mechanism rotates to the left around the virtual coordinate system X-axis, the center of the second fixed ring 112 is the virtual center point. The first branch 130 is the driving chain, and the second branch 140 and the third branch 150 are the driven chains, driving the first motor 132 to rotate forward, thereby driving the first branch 130 to rotate, locking the second motor 143. The second branch 140 rotates along the rotation axis 1 of the Hooke pair (the direction of the extension line of the output shaft of the second motor 143), and the third branch 150 rotates accordingly. The third electric push rod 154 extends, and the second electric push rod 145 shortens. Figure 8 As shown, when the external fixation orthotic mechanism rotates to the right around the virtual coordinate system X-axis, it drives the first motor 132 to reverse, locks the second motor 143, shortens the third electric push rod 154, and extends the second electric push rod 145. During the movement of the three branches, the orthotic force is transmitted to the moving platform 120 through the branches. The moving platform 120 can drive the moving component 220 to move around the virtual coordinate system X-axis.

[0089] like Figure 9 As shown, when the external fixation orthotic mechanism rotates to the left around the virtual coordinate system Y-axis, the second branch 140 is the driving chain, and the first branch 130 and the third branch 150 are the driven chains, driving the second motor 143 to reverse, locking the first motor 132, and causing the second branch 140 to rotate. The first branch 130 and the third branch 150 rotate accordingly, the second electric push rod 145 extends, and the first electric push rod 134 shortens; as shown... Figure 10 As shown, when the external fixation orthotic mechanism rotates to the right around the virtual center point Y-axis, it drives the second motor 143 to reverse, locks the first motor 132, shortens the second electric push rod 145, and extends the first electric push rod 134. The moving platform 120 can drive the moving component 220 to move around the virtual coordinate system Y-axis.

[0090] like Figure 11 As shown, when the external fixation orthotic mechanism moves upward along the Z-axis of the virtual coordinate system, it drives the first electric push rod 134, the second electric push rod 145, and the third electric push rod 154, locking the first motor 132 and the second motor 143, and extending the first branch 130, the second branch 140, and the third branch 150; conversely, as... Figure 12 As shown, the external fixation orthotic mechanism moves downward along the virtual center point Z-axis, the first branch 130, the second branch 140 and the third branch 150 shorten, and the moving platform 120 can drive the moving component 220 to move along the virtual coordinate system Z-axis.

[0091] This invention presents an external fixation orthotic mechanism with virtual center motion characteristics. By combining three motion chains with a dynamic platform and a static platform, the stability of the mechanism is increased, and installation is convenient and flexible. The height of the static platform is adjustable, making the mechanism more adaptable. Compared with existing external fixation orthotic mechanisms, it can realize virtual center motion, has fewer kinematic pairs, a simpler configuration, and is easier to control. It can solve the problems of rotational misalignment and orthotic motion coupling that are prone to occur in current external fixation orthotic mechanisms, and increases the flexibility and range of orthosis. The individual control of the three motion chains enables safe operation and precise quantitative control of the orthosis, and has a wider range of orthotic functions and better orthotic effects.

[0092] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. An external orthopedic fixation device having a virtual center of motion feature, characterized by, include: A static platform, which is detachably fixed to the outside of a fixed component, and the height of the static platform is adjustable, the static platform including a second fixed ring; A moving platform is coaxially spaced from the stationary platform, and the moving platform is detachably fixed to the outside of the moving component. The moving platform includes a third fixing ring. The first branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to rotate around the x-axis of the virtual coordinate system; The second branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to rotate around the y-axis of the virtual coordinate system. The third branch, which is retractably disposed between the static platform and the moving platform, is used to drive the external fixation orthopedic mechanism to move along the z-axis of the virtual coordinate system; The first branch includes: The first motor is detachably fixed to the stationary platform; An arc-shaped guide rail, one end of which is connected to the output end of the first motor, and the other end extends between the static platform and the moving platform; A guide rail slider is slidably mounted on the arc-shaped guide rail; The first electric push rod includes a fixed end and a pushing end, wherein the fixed end is connected to the guide rail slider and the pushing end is connected to the moving platform; The second branch includes: The second motor is fixed on the second fixing ring; The second motor shaft connector is fixedly connected to the output shaft of the second motor. A fork-shaped head, which is rotatably disposed on the outside of the second motor shaft connector; The second electric push rod has the same structure as the first electric push rod, with its fixed end connected to the fork-shaped head and its pushing end connected to the third fixed ring; The interval between the first branch, the second branch and the third branch is 120°, and the radius of the arc of the arc-shaped guide rail is the same as the radius of the static platform. The virtual coordinate system satisfies: The origin is the center of the static platform, the x-axis is a horizontal line extending from the origin toward the first branch, the z-axis is a vertical line perpendicular to the static platform, and the y-axis is a horizontal line perpendicular to both the x-axis and the z-axis. The rotation angles of the first and second motors are both -15° to 15°, the moving distances of the first, second, and third electric push rods are all 0 to 30 mm, and the length of the arc-shaped guide rail satisfies: ； In the formula, is the length of the arc-shaped guide rail, is the radius of the arc of the arc-shaped guide rail.

2. An external fixation orthopedic mechanism having a virtual center of motion feature as in claim 1, wherein, The static platform includes: First fixed ring; and The first fixing pin has its two ends symmetrically arranged on the first fixing ring with the center of the ring, and the first fixing pin can selectively pass through the fixing member; The second fixing ring is coaxially spaced from the first fixing ring, and the spacing is adjustable; The first motor is detachably fixed on the second fixed ring, the center of the second fixed ring is the origin of the virtual coordinate system, and the first branch, the second branch and the third branch are all set between the second fixed ring and the moving platform.

3. An external fixation orthopedic mechanism having a virtual center of motion feature as in claim 2 wherein, The moving platform includes: The second fixing pin has its two ends symmetrically arranged on the third fixing ring with the center of the ring, and the second fixing pin can selectively pass through the moving member.

4. The external fixation orthotic mechanism with virtual center motion characteristics as described in claim 3, characterized in that, The first branch also includes: The first motor shaft connector is fixedly connected to the output end of the first motor. One end of the arc-shaped guide rail is fixedly connected to the first motor shaft connector.

5. The external fixation orthotic mechanism with virtual center motion characteristics as described in claim 4, characterized in that, The first branch also includes: A slider connector, which is fixed to the guide rail slider; The first sleeve has one end detachably mounted on the slider connector and the other end detachably mounted on the fixed end of the first electric push rod. The first push rod connector has one end connected to the pushing end of the first electric push rod; The first threaded rod has one end connected to the other end of the first push rod connector and the other end connected to the third fixed ring.

6. The external fixation orthotic mechanism with virtual center motion characteristics as described in claim 5, characterized in that, The second branch also includes: The second push rod connector has one end connected to the pushing end of the second electric push rod; The second threaded rod has one end connected to the other end of the second push rod connector; A first ball joint is disposed on the third fixed ring, and the first ball joint is connected to the other end of the second threaded rod.

7. The external fixation orthotic mechanism with virtual center motion characteristics as described in claim 6, characterized in that, The third branch includes: The second ball joint is disposed on the second fixed ring; The third electric push rod has the same structure as the first electric push rod, and its fixed end is connected to the second ball joint; The third ball joint is fixed on the third fixed ring and is connected to the pushing end of the third electric push rod.

8. The external fixation orthotic mechanism with virtual center motion characteristics as described in claim 7, characterized in that, The third branch also includes: The third threaded rod has one end connected to the second ball joint; The second sleeve has one end connected to the other end of the third threaded rod and the other end connected to the fixed end of the third electric push rod. The third push rod connector has one end connected to the pushing end of the third electric push rod; The fourth threaded rod has one end connected to the other end of the third push rod connector and the other end connected to the third ball joint.

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