A four-degree-of-freedom parallel mechanism for knee joint rehabilitation

Abstract

The present invention is a four-degree-of-freedom knee joint rehabilitation parallel mechanism, comprising a static platform, a dynamic platform, a first RRRRR branch chain, a second RRRRR branch chain, a UPS branch chain, and an input servo motor; the second RRRRR branch chain and the first RRRRR branch chain are distributed on the left and right sides of the front ends of the static platform and the dynamic platform, and the second RRRRR branch chain and the first RRRRR branch chain are both provided with an input servo motor; two UPS branches are symmetrically distributed on the left and right sides of the rear ends of the static platform and the dynamic platform; the four branches jointly realize two rotational degrees of freedom and two translational degrees of freedom of the dynamic platform relative to the static platform, the two translational degrees of freedom being used to fit the movement of the knee tibia relative to the femur; the two rotational degrees of freedom being used to fit the rotation of the knee tibia relative to the femur around a rotation axis perpendicular to the human sagittal plane and the external rotation movement of the knee tibia relative to the femur. This mechanism can accurately fit the variable axis movement of the human knee joint, reduce the human-computer interaction force generated during rehabilitation training, and improve comfort.

Description

Technical Field

[0001] The present invention belongs to the technical field of rehabilitation equipment, and in particular is a four-degree-of-freedom knee joint rehabilitation parallel mechanism. Background Art

[0002] The human knee joint is composed of the medial and lateral condyles of the femur, the medial and lateral condyles of the tibia, and the patella. The main function of the knee joint is to complete the flexion and extension movement of the human body in the sagittal plane, but the movement of the knee joint cannot be simply equated with rotation. The movement at the articular surface of the knee joint is mainly the rotation of the tibia relative to the femur around the rotation axis perpendicular to the sagittal plane. This rotation axis changes continuously with the different rotation angles of the knee joint, which manifests as the movement of the tibia relative to the femur. In addition, when the knee joint is flexed and straightened, the medial femoral condyle rotates internally, and the tibia rotates externally relative to the femur.

[0003] Existing knee rehabilitation devices do not consider the movement and external rotation of the tibia relative to the femur, but instead simply equate the movement of the knee joint to a single degree of freedom, rotational motion. Consequently, during rehabilitation training, there is a common mismatch between the mechanism's movement and the patient's knee joint movement, resulting in significant human-machine interaction forces during rehabilitation training, which can easily cause discomfort to the patient and even secondary injury. Patent application number 201820980471.7 discloses a knee rehabilitation training chair. The rehabilitation mechanism of the chair includes a thigh sleeve, two sets of calf sleeves, and a foot sleeve. The thigh sleeve and calf sleeve are connected by a first linkage assembly, and the calf sleeve and foot sleeve are connected by a second linkage assembly. The overall mechanism exhibits only rotational freedom, simply equating knee joint movement to rotation about a fixed axis. This ignores the movement and external rotation of the tibia relative to the femur, resulting in a poor fit with the knee joint and significant human-machine interaction forces during use. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a four-degree-of-freedom parallel mechanism for knee rehabilitation. This parallel mechanism features a virtual center of motion that matches the instantaneous center of motion of the knee joint. It also enables four-degree-of-freedom motion of the dynamic platform around the static platform, matching the variable axis motion of the knee joint. This reduces the human-machine interaction forces generated during knee rehabilitation training, improves patient comfort, and prevents secondary injuries.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A four-degree-of-freedom parallel mechanism for knee joint rehabilitation comprises a static platform, a dynamic platform, a UPS branch chain and an input servo motor; the mechanism is characterized in that the mechanism further comprises a first RRRRR branch chain and a second RRRRR branch chain; the second RRRRR branch chain and the first RRRRR branch chain are distributed on the left and right sides of the front ends of the static platform and the dynamic platform, and the second RRRRR branch chain and the first RRRRR branch chain are both provided with an input servo motor; the two UPS branches are symmetrically distributed on the left and right sides of the rear ends of the static platform and the dynamic platform; the four branches jointly realize two rotational degrees of freedom and two movement degrees of freedom of the dynamic platform relative to the static platform, and the two movement degrees of freedom are used to fit the movement of the tibia of the knee joint relative to the femur; the rotation axis of one rotational degree of freedom is always perpendicular to the sagittal plane of the human body, and is used to fit the rotation of the tibia of the knee joint relative to the femur around the rotation axis perpendicular to the sagittal plane of the human body; the rotation axis of the other rotational degree of freedom is perpendicular to the dynamic platform, and is used to fit the external rotation movement of the tibia of the knee joint relative to the femur.

[0007] Further, the first RRRRR branch chain includes a first RRRRR branch chain connecting rod No. 1, a first RRRRR branch chain connecting rod No. 2, a first RRRRR branch chain connecting rod No. 3 and a first RRRRR branch chain connecting rod No. 4; the upper end of the first RRRRR branch chain connecting rod No. 1 is rotatably connected to the static platform to form a rotating pair A1, the lower end of the first RRRRR branch chain connecting rod No. 1 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 2 to form a rotating pair B1, the lower end of the first RRRRR branch chain connecting rod No. 2 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 3 to form a rotating pair C1, the lower end of the first RRRRR branch chain connecting rod No. 3 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 4 to form a rotating pair D1, and the lower end of the first RRRRR branch chain connecting rod No. 4 is rotatably connected to the moving platform to form a rotating pair E1;

[0008] The second RRRRR branch chain includes a second RRRRR branch chain connecting rod No. 1, a second RRRRR branch chain connecting rod No. 2, a second RRRRR branch chain connecting rod No. 3, and a second RRRRR branch chain connecting rod No. 4; the upper end of the second RRRRR branch chain connecting rod No. 1 is rotatably connected to the static platform to form a rotational pair A2, the lower end of the second RRRRR branch chain connecting rod No. 1 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 2 to form a rotational pair B2, the lower end of the second RRRRR branch chain connecting rod No. 2 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 3 to form a revolving pair C2, the lower end of the second RRRRR branch chain connecting rod No. 3 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 4 to form a rotational pair D2, and the lower end of the second RRRRR branch chain connecting rod No. 4 is rotatably connected to the moving platform to form a rotational pair E2;

[0009] The rotation axes of the above-mentioned revolute pairs A1 and B1 are parallel, and the rotation axes of the revolute pairs C1, D1 and E1 intersect at one point. The intersection is the virtual motion center of the parallel mechanism, and the virtual motion center is used to fit the instantaneous motion center of the knee joint; the rotation axes of the revolute pairs A2, B2 and C2 are parallel, and at the same time parallel to the rotation axes of the revolute pairs A1 and B1; the rotation axes of the revolute pairs D2 and E2 are parallel and perpendicular to the moving platform.

[0010] Furthermore, the input servo motor located on the first RRRRR branch chain is installed at the upper end of the No. 1 connecting rod of the first RRRRR branch chain, and the output shaft axis of the input servo motor coincides with the rotation axis of the rotating pair A1; the input servo motor located on the second RRRRR branch chain is installed at the upper end of the No. 1 connecting rod of the second RRRRR branch chain, and the output shaft axis of the input servo motor coincides with the rotation axis of the rotating pair A2.

[0011] Furthermore, the first RRRRR branch chain connecting rod No. 2, the first RRRRR branch chain connecting rod No. 3 and the first RRRRR branch chain connecting rod No. 4 are all arc-shaped connecting rods, and the axes of the connecting holes at both ends of the arc-shaped connecting rods intersect at one point.

[0012] Furthermore, the UPS branch chain includes a ball joint connecting rod, a servo electric cylinder and a Hooke's joint connecting rod; the lower end of the Hooke's joint connecting rod is rotatably connected to the moving platform to form a U pair, the upper end of the Hooke's joint connecting rod is connected to the fixed end of the servo electric cylinder, and the push rod of the servo electric cylinder is connected to the lower end of the ball joint connecting rod to form a P pair; the upper end of the ball joint connecting rod is rotatably connected to the static platform to form an S pair.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. This mechanism utilizes four parallel branches, which improves fitting accuracy and facilitates motor placement. The four branches enable two translational degrees of freedom and two rotational degrees of freedom for the dynamic platform relative to the static platform. This four-degree-of-freedom motion fits the variable-axis motion of the knee joint. The position of the mechanism's virtual center of motion continuously changes with the dynamic platform's position, and the virtual center of motion fits the instantaneous center of motion of the knee joint. Two translational degrees of freedom remain within the human sagittal plane, fitting the movement of the knee tibia relative to the femur. The axis of rotation of one rotational degree of freedom is always perpendicular to the human sagittal plane, fitting the rotation of the knee tibia relative to the femur around an axis perpendicular to the human sagittal plane. The axis of rotation of the other rotational degree of freedom is always perpendicular to the dynamic platform of the parallel mechanism, fitting the external rotation of the knee tibia relative to the femur. This mechanism reduces the human-machine interaction forces generated during knee rehabilitation training and improves the motion incompatibility and reduced comfort caused by incomplete alignment of the joint axes during rehabilitation training.

[0015] 2. The mechanism has a simple structure and is easy to manufacture and assemble. The use of two UPS branches reduces redundant constraints in parallel and reduces singularities, further simplifying the mechanism's kinematics and improving its motion and force transmission performance. Only the first RRRRR branch in the entire mechanism contains curved rods, reducing the need for curved rods. Furthermore, since the UPS branch does not need to consider its coordination with the two RRRRR branches, the coordination accuracy requirements for the mechanism are lowered, significantly reducing the mechanism's manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0017] Figure 2 It is a structural schematic diagram of the static platform of the present invention;

[0018] Figure 3 It is a structural schematic diagram of the dynamic platform of the present invention;

[0019] Figure 4 Schematic diagram of the structure of the first RRRRR branch of the present invention;

[0020] Figure 5 Schematic diagram of the structure of the second RRRRR branch of the present invention;

[0021] Figure 6 This is a schematic structural diagram of the first UPS branch chain of the present invention;

[0022] Explanation of reference numerals: 1, static platform; 2, dynamic platform; 3, first RRRRR branch chain; 4, second RRRRR branch chain; 5, first UPS branch chain; 6, second UPS branch chain; 7, input servo motor; 8, virtual motion center;

[0023] 101. Static platform hinge support No. 1; 102. Static platform hinge support No. 2; 103. Static platform hinge support No. 3; 104. Static platform hinge support No. 4; 105. Static platform ring; 201. Dynamic platform hinge support No. 1; 202. Dynamic platform hinge support No. 2; 203. Dynamic platform hinge support No. 3; 204. Dynamic platform hinge support No. 4; 205. Dynamic platform ring; 301. First RRRRR branch chain No. 1 connecting rod; 302. First RRRRR branch chain connecting rod No. 2; 303, first RRRRR branch chain connecting rod No. 3; 304, first RRRRR branch chain connecting rod No. 4; 401, second RRRRR branch chain connecting rod No. 1; 402, second RRRRR branch chain connecting rod No. 2; 403, second RRRRR branch chain connecting rod No. 3; 404, second RRRRR branch chain connecting rod No. 4; 501, ball joint connecting rod; 502, servo electric cylinder; 503, Hooker's joint connecting rod. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present application is not limited thereto.

[0025] The present invention provides a four-degree-of-freedom knee joint rehabilitation parallel mechanism (hereinafter referred to as the mechanism), such as Figure 1 As shown, the mechanism includes a static platform 1, a dynamic platform 2, a first RRRRR branch chain 3, a second RRRRR branch chain 4, a first UPS branch chain 5, a second UPS branch chain 6 and an input servo motor 7; the second RRRRR branch chain 4 and the first RRRRR branch chain 3 are located on the left and right sides of the front end of the static platform 1 and the dynamic platform 2, and the first UPS branch chain 5 and the second UPS branch chain 6 are symmetrically distributed on the left and right sides of the rear end of the static platform 1 and the dynamic platform 2, and the upper and lower ends of the four branches are respectively connected to the static platform 1 and the dynamic platform 2; the four branches are used to realize the four-degree-of-freedom motion of the mechanism to fit the variable axis motion of the knee joint; the mechanism has a virtual motion center, the position of the virtual motion center changes with the posture of the dynamic platform 2, and the virtual motion center fits the instantaneous motion center of the knee joint. Through the parallel mechanism, the patient's knee joint is allowed to undergo rehabilitation training according to a predetermined trajectory.

[0026] like Figure 2 As shown, the static platform 1 includes a static platform ring 105, and four static platform hinge supports are evenly distributed at the bottom of the static platform ring 105, namely static platform No. 1 hinge support 101, static platform No. 2 hinge support 102, static platform No. 3 hinge support 103 and static platform No. 4 hinge support 104; the static platform No. 2 hinge support 102 has the same structure as the static platform No. 1 hinge support 101 and is located on the left and right sides of the front end of the ring 105, the static platform No. 1 hinge support 101 is rotatably connected to the upper end of the first RRRRR branch chain 3, and the static platform No. 2 hinge support 102 is rotatably connected to the upper end of the second RRRRR branch chain 4; the static platform No. 4 hinge support 104 has the same structure as the static platform No. 3 hinge support 103 and is located on the left and right sides of the rear end of the ring 105, the static platform No. 3 hinge support 103 is rotatably connected to the upper end of the second UPS branch chain 6, and the static platform No. 4 hinge support 104 is rotatably connected to the upper end of the first UPS branch chain 5.

[0027] like Figure 3As shown, the movable platform 2 includes a movable platform ring 205, and four hinge supports are evenly distributed at the bottom of the movable platform ring 205, namely movable platform hinge support No. 1 201, movable platform hinge support No. 2 202, movable platform hinge support No. 3 203 and movable platform hinge support No. 4 204; movable platform hinge support No. 2 202 and movable platform hinge support No. 1 201 are located on the left and right sides of the front end of the movable platform ring 205, movable platform hinge support No. 1 201 is rotatably connected to the lower end of the first RRRRR branch chain 3, and movable platform hinge support No. 2 202 is hinged to the lower end of the second RRRRR branch chain 4; movable platform hinge support No. 3 203 and movable platform hinge support No. 4 204 are symmetrically distributed on the left and right sides of the rear end of the movable platform ring 205, movable platform hinge support No. 3 203 is rotatably connected to the lower end of the first UPS branch chain 5, and movable platform hinge support No. 4 204 is rotatably connected to the lower end of the second UPS branch chain 6.

[0028] like Figure 4 As shown, the first RRRRR branch chain 3 is composed of four connecting rods, namely the first RRRRR branch chain connecting rod 1 301, the first RRRRR branch chain connecting rod 2 302, the first RRRRR branch chain connecting rod 303 and the first RRRRR branch chain connecting rod 4 304; wherein, the upper end of the first RRRRR branch chain connecting rod 1 301 is rotatably connected to the static platform first hinge support 101 to form a rotating pair A1, and the lower end of the first RRRRR branch chain connecting rod 1 301 is rotatably connected to the first RRRRR branch chain connecting rod 304. The upper end of the No. 2 link 302 of the R branch chain is rotationally connected to form a rotational pair B1, the lower end of the No. 2 link 302 of the first RRRRR branch chain is rotationally connected to the upper end of the No. 3 link 303 of the first RRRRR branch chain to form a rotational pair C1, the lower end of the No. 3 link 303 of the first RRRRR branch chain is rotationally connected to the upper end of the No. 4 link 304 of the first RRRRR branch chain to form a rotational pair D1, and the lower end of the No. 4 link 304 of the first RRRRR branch chain is rotationally connected to the No. 1 hinge support 201 of the movable platform to form a rotational pair E1;

[0029] like Figure 5As shown, the second RRRRR branch chain 4 includes a second RRRRR branch chain No. 1 connecting rod 401, a second RRRRR branch chain No. 2 connecting rod 402, a second RRRRR branch chain No. 3 connecting rod 403 and a second RRRRR branch chain No. 4 connecting rod 404; the upper end of the second RRRRR branch chain No. 1 connecting rod 401 is rotatably connected to the static platform No. 2 hinge support 102 to form a rotating pair A2, and the lower end of the second RRRRR branch chain No. 1 connecting rod 401 is rotatably connected to the second RRRRR branch chain No. 2 connecting rod 403. The upper end of the rod 402 is rotationally connected to form a revolute pair B2, the lower end of the second RRRRR branch chain No. 2 link 402 is rotationally connected to the upper end of the second RRRRR branch chain No. 3 link 403 to form a revolute pair C2, the lower end of the second RRRRR branch chain No. 3 link 403 is rotationally connected to the upper end of the second RRRRR branch chain No. 4 link 404 to form a revolute pair D2, and the lower end of the second RRRRR branch chain No. 4 link 404 is rotationally connected to the movable platform No. 2 hinge support 202 to form a revolute pair E2;

[0030] The rotation axes of the above-mentioned revolute pairs A1 and B1 are parallel, and the rotation axes of the revolute pairs C1, D1 and E1 intersect at one point, which is the virtual motion center 8 of the parallel mechanism. The virtual motion center 8 is used to fit the instantaneous motion center of the knee joint, and its position changes with the posture of the moving platform 2; the rotation axes of the revolute pairs A2, B2 and C2 are parallel, and at the same time parallel to the rotation axes of the revolute pairs A1 and B1; the rotation axes of the revolute pairs D2 and E2 are parallel and perpendicular to the moving platform 2, and are used for the external rotation movement of the tibia of the knee joint relative to the femur.

[0031] like Figure 6 As shown, the first UPS branch chain 5 includes a ball joint connecting rod 501, a servo electric cylinder 502 and a Hooke's joint connecting rod 503; the lower end of the Hooke's joint connecting rod 503 is rotatably connected to the movable platform No. 3 hinge support 203 through a Hooke's joint to form the U pair of the first UPS branch chain 5, the upper end of the Hooke's joint connecting rod 503 is connected to the fixed end of the servo electric cylinder 502, and the push rod of the servo electric cylinder 502 is fixedly connected to the lower end of the ball joint connecting rod 501. The servo electric cylinder 502 serves as the power source of the first UPS branch chain 5 and forms the P pair of the first UPS branch chain 5; the upper end of the ball joint connecting rod 501 is rotatably connected to the static platform No. 4 hinge support 104 through a ball joint to form the S pair of the first UPS branch chain 5; the upper and lower ends of the second UPS branch chain 6 are rotatably connected to the static platform No. 3 hinge support 103 and the movable platform No. 4 hinge support 204 respectively, and the connections of the remaining components of the second UPS branch chain 6 are the same as those of the first UPS branch chain 5.

[0032] The two input servo motors 7 are respectively located on the first RRRRR branch chain 3 and the second RRRRR branch chain 4. The input servo motor 7 located on the first RRRRR branch chain 3 is installed on the upper end of the first RRRRR branch chain connecting rod 301. The output shaft axis of the input servo motor 7 coincides with the rotation axis of the rotating pair A1, forming drive one; the input servo motor 7 located on the second RRRRR branch chain 4 is installed on the upper end of the first RRRRR branch chain connecting rod 401. The output shaft axis of the input servo motor 7 coincides with the rotation axis of the rotating pair A2, forming drive two; the servo electric cylinders of the first UPS branch chain 5 and the second UPS branch chain 6 are drive three and drive four respectively. The four drives make the parallel mechanism have four degrees of freedom.

[0033] Furthermore, the first RRRRR branch chain connecting rod No. 2 302, the first RRRRR branch chain connecting rod No. 303 and the first RRRRR branch chain connecting rod No. 4 304 are all arc-shaped connecting rods, and the axes of the connecting holes at both ends of the arc-shaped connecting rods intersect at one point.

[0034] The working principle and workflow of the present invention are:

[0035] Drive one and drive two respectively control the rotational movement of the first RRRRR branch chain No. 1 link 301 and the second RRRRR branch chain No. 1 link 401 relative to the static platform 1, and the servo electric cylinders of drive three and drive four control the movement of the first UPS branch chain 5 and the second UPS branch chain 6 by changing the extension and contraction amount, and the four drives jointly realize the four-degree-of-freedom movement of the mechanism; the parallel mechanism fits the variable-axis movement of the knee joint through four-degree-of-freedom movement, and the four degrees of freedom are two rotational degrees of freedom and two translational degrees of freedom of the dynamic platform 2 relative to the static platform 1. The two translational degrees of freedom are always located in the sagittal plane of the human body, and are used to fit the movement of the tibia of the knee joint relative to the femur; the rotation axis of one rotational degree of freedom is always perpendicular to the sagittal plane of the human body, and is used to fit the rotation of the tibia of the knee joint relative to the femur around the rotation axis perpendicular to the sagittal plane of the human body; the rotation axis of the other rotational degree of freedom is always perpendicular to the dynamic platform 2 of the parallel mechanism, and is used to fit the external rotation movement of the tibia of the knee joint relative to the femur.

[0036] In practical application, the static platform ring 105 is worn on the patient's thigh, and the dynamic platform ring 205 is worn on the patient's calf. The parallel mechanism's virtual motion center 8 corresponds to the knee joint's motion center. Four actuators jointly control the position and posture of the dynamic platform 2, allowing the patient's knee joint to undergo rehabilitation training along a predetermined trajectory. The parallel mechanism's motion mimics the variable axis motion of the human knee joint, reducing the human-machine interaction forces generated during knee rehabilitation training and addressing the incompatibility of motion and reduced comfort caused by incomplete joint axis alignment.

[0037] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A four-degree-of-freedom parallel mechanism for knee joint rehabilitation, comprising a static platform, a dynamic platform, a UPS branch chain, and an input servo motor; characterized in that: The mechanism also includes a first RRRRR branch chain and a second RRRRR branch chain; the second RRRRR branch chain and the first RRRRR branch chain are distributed on the left and right sides of the front end of the static platform and the dynamic platform, and the second RRRRR branch chain and the first RRRRR branch chain are both provided with input servo motors; two UPS branch chains are symmetrically distributed on the left and right sides of the rear end of the static platform and the dynamic platform; two rotational degrees of freedom and two translational degrees of freedom of the dynamic platform relative to the static platform are jointly realized by four branch chains, and the two translational degrees of freedom are used to fit the movement of the tibia of the knee joint relative to the femur; the rotation axis of one rotational degree of freedom is always perpendicular to the sagittal plane of the human body, and is used to fit the rotation of the tibia of the knee joint relative to the femur around the rotation axis perpendicular to the sagittal plane of the human body; the rotation axis of the other rotational degree of freedom is perpendicular to the dynamic platform, and is used to fit the external rotation movement of the tibia of the knee joint relative to the femur; The first RRRRR branch chain includes a first RRRRR branch chain connecting rod No. 1, a first RRRRR branch chain connecting rod No. 2, a first RRRRR branch chain connecting rod No. 3 and a first RRRRR branch chain connecting rod No. 4; the upper end of the first RRRRR branch chain connecting rod No. 1 is rotatably connected to the static platform to form a rotating pair A1, the lower end of the first RRRRR branch chain connecting rod No. 1 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 2 to form a rotating pair B1, the lower end of the first RRRRR branch chain connecting rod No. 2 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 3 to form a rotating pair C1, the lower end of the first RRRRR branch chain connecting rod No. 3 is rotatably connected to the upper end of the first RRRRR branch chain connecting rod No. 4 to form a rotating pair D1, and the lower end of the first RRRRR branch chain connecting rod No. 4 is rotatably connected to the moving platform to form a rotating pair E1; The second RRRRR branch chain includes a second RRRRR branch chain connecting rod No. 1, a second RRRRR branch chain connecting rod No. 2, a second RRRRR branch chain connecting rod No. 3, and a second RRRRR branch chain connecting rod No. 4; the upper end of the second RRRRR branch chain connecting rod No. 1 is rotatably connected to the static platform to form a rotational pair A2, the lower end of the second RRRRR branch chain connecting rod No. 1 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 2 to form a rotational pair B2, the lower end of the second RRRRR branch chain connecting rod No. 2 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 3 to form a revolving pair C2, the lower end of the second RRRRR branch chain connecting rod No. 3 is rotatably connected to the upper end of the second RRRRR branch chain connecting rod No. 4 to form a rotational pair D2, and the lower end of the second RRRRR branch chain connecting rod No. 4 is rotatably connected to the moving platform to form a rotational pair E2; The rotation axes of the above-mentioned revolute pairs A1 and B1 are parallel, and the rotation axes of the revolute pairs C1, D1 and E1 intersect at an intersection, which is the virtual motion center of the parallel mechanism. The virtual motion center is used to fit the instantaneous motion center of the knee joint; the rotation axes of the revolute pairs A2, B2 and C2 are parallel, and at the same time parallel to the rotation axes of the revolute pairs A1 and B1; the rotation axes of the revolute pairs D2 and E2 are parallel and perpendicular to the moving platform.

2. The four-degree-of-freedom knee joint rehabilitation parallel mechanism according to claim 1, characterized in that: The input servo motor located on the first RRRRR branch chain is installed at the upper end of the No. 1 connecting rod of the first RRRRR branch chain, and the output shaft axis of the input servo motor coincides with the rotation axis of the rotating pair A1; the input servo motor located on the second RRRRR branch chain is installed at the upper end of the No. 1 connecting rod of the second RRRRR branch chain, and the output shaft axis of the input servo motor coincides with the rotation axis of the rotating pair A2.

3. The four-degree-of-freedom knee joint rehabilitation parallel mechanism according to claim 1 or 2, characterized in that: The first RRRRR branch chain No. 2 connecting rod, the first RRRRR branch chain No. 3 connecting rod and the first RRRRR branch chain No. 4 connecting rod are all arc-shaped connecting rods, and the axes of the connecting holes at both ends of the arc-shaped connecting rods intersect at one point.

4. The four-degree-of-freedom knee joint rehabilitation parallel mechanism according to claim 1, characterized in that: The UPS branch chain includes a ball joint connecting rod, a servo electric cylinder and a Hooke's joint connecting rod; the lower end of the Hooke's joint connecting rod is rotatably connected to the dynamic platform to form a U pair, the upper end of the Hooke's joint connecting rod is connected to the fixed end of the servo electric cylinder, the push rod of the servo electric cylinder is connected to the lower end of the ball joint connecting rod to form a P pair; the upper end of the ball joint connecting rod is rotatably connected to the static platform to form an S pair.

Images