A two-rotation-one-transfer constrained parallel mechanism and a method for determining the end effector attitude.

Abstract

This invention provides a two-rotation-one-transfer constraint-free parallel mechanism and an end-effector attitude determination method, belonging to the field of robotics. It includes: a moving platform; a base comprising a first static platform and a second static platform, the second static platform being fixed relative to the first static platform and disposed between the moving platform and the first static platform; and three branches, each branch including a driving prismatic joint, a Hooke's joint, a first passive revolute joint, a second passive revolute joint, a first passive prismatic joint, a third passive revolute joint, and a second passive prismatic joint. The beneficial effects of this invention are: in a transverse state, the two-rotation-one-transfer constraint-free parallel mechanism, due to the branches bending towards the first static platform while changing the angle of the moving platform, reduces the distance between the moving platform and the first static platform, thus providing a certain degree of support for the branches and reducing the deformation of the moving platform relative to the first static platform under load, effectively increasing the longitudinal stiffness of the two-rotation-one-transfer constraint-free parallel mechanism.

Description

Technical Field

[0001] This invention belongs to the field of robotics technology and relates to a two-rotation-one-transfer constraint parallel mechanism and an end-effector posture determination method. Background Technology

[0002] Parallel robots offer advantages such as compact structure, high reliability, and large workspace. Furthermore, their inverse kinematics are easily calculated, effectively reducing the control complexity of the end effector. Therefore, they are widely used in medical, aerospace, and underwater vector thruster applications.

[0003] For example, an invention patent with application number CN202110402920.6 provides a two-rotation-one-transfer parallel mechanism, including a moving platform, a base, and three branches. The base includes a stationary platform, a redundant stationary platform, and multiple connectors connecting the stationary platform and the redundant stationary platform. The redundant stationary platform is located between the moving platform and the stationary platform, and has three through holes. The three branches connect the moving platform and the stationary platform. Each branch includes a driving moving pair, a first passive moving pair, a second passive moving pair, and a spherical pair. One end of each driving moving pair is movably connected to the stationary platform through the first passive moving pair, and the opposite end passes through a through hole of the redundant stationary platform and is rotatably connected to the moving platform through the corresponding spherical pair. The driving moving pair is also movably connected to the redundant stationary platform through the second passive moving pair.

[0004] In traditional 3-RPS and 3-PPS parallel mechanisms, the limitations of the ball joints make it difficult to meet the large pitch angle adjustment requirements of the end effector. Furthermore, in practice, the linear actuators such as the electric push rods driving the prismatic joints are generally quite long, resulting in an excessive distance between the moving and stationary platforms. This is especially problematic in the transverse configuration, where the moving platform, connected to the end effector, experiences excessive load and is prone to deformation, leading to decreased system rigidity and significant room for improvement. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the prior art by proposing a two-rotation-one-transfer constraint-free parallel mechanism that can effectively increase the longitudinal stiffness of the parallel mechanism, and also by proposing a method for determining the end attitude of the two-rotation-one-transfer constraint-free parallel mechanism.

[0006] The objective of this invention can be achieved through the following technical solution: a parallel mechanism with two rotations and one transfer over constraint, comprising:

[0007] Dynamic platform;

[0008] The base includes a first static platform and a second static platform, the second static platform being fixed relative to the first static platform and disposed between the moving platform and the first static platform;

[0009] The system comprises three branches, including a driving prismatic joint, a Hooke's hinge, a first passive rotary joint, a second passive rotary joint, a first passive prismatic joint, a third passive rotary joint, and a second passive prismatic joint. One end of the driving prismatic joint is connected to one end of the Hooke's hinge. The other end of the Hooke's hinge is rotatably connected to the moving platform via the first passive rotary joint. The other end of the driving prismatic joint is rotatably connected to the first stationary platform via the second passive rotary joint. The first passive prismatic joint is movably connected to the driving prismatic joint. The first passive prismatic joint is rotatably connected to the second passive prismatic joint via the third passive rotary joint, and is movably connected to the second stationary platform via the second passive prismatic joint.

[0010] In the above-mentioned two-rotation-one-transfer constraint parallel mechanism, the driving moving pair includes a linear driving body and a linear driving telescopic rod. The linear driving telescopic rod is telescopically connected to the linear driving body, and the linear driving body can drive the linear driving telescopic rod to extend and retract. The linear driving telescopic rod is connected to the end of the Hooke joint, and the linear driving body is rotatably connected to the first static platform through the second passive rotary joint.

[0011] In the above-described two-rotation-one-transfer-constrained parallel mechanism, the first passive rotary joint includes a bearing, and the end of the Hooke hinge is rotatably connected to the moving platform through the bearing.

[0012] In the above-mentioned two-rotation-one-transfer-through-constraint parallel mechanism, the second passive rotary pair includes a first rotary seat and a first rotary pin. The first rotary seat is connected to the linear drive body, and the first rotary pin is connected to the first stationary platform. The first rotary pin is rotatably connected to the first rotary seat.

[0013] In the above-mentioned two-rotation-one-transfer constraint parallel mechanism, the second static platform is provided with a guide hole, the linear drive body passes through the guide hole, and the linear drive body can move along the length direction of the guide hole when it rotates through the second passive rotary joint.

[0014] In the above-mentioned two-rotation-one-transfer-through-constraint parallel mechanism, the first passive moving pair includes a moving ring, which is sleeved on the linear drive body and can move along the length direction of the linear drive body, and the third passive rotation is connected to the moving ring pair.

[0015] In the above-mentioned two-rotation-one-transfer-through-constraint parallel mechanism, the second passive locating joint includes a slide rail and a slider. The slide rail is connected to the second static platform, and the third passive rotational joint is connected to the slider. The slider is movably connected to the slide rail.

[0016] In the above-mentioned two-rotation-one-movement constraint parallel mechanism, the third passive rotary pair includes a second rotary seat and a second rotary pin. The second rotary seat is connected to the slider, and the second rotary pin is connected to the moving ring. The second rotary pin is rotatably connected to the second rotary seat.

[0017] In the above-mentioned two-rotation-one-transfer constraint parallel mechanism, the three branches are distributed in an equilateral triangle at one end connected to the first static platform, and the three branches are distributed in an equilateral triangle at one end connected to the moving platform.

[0018] Secondly, an end-effector attitude determination method, based on the aforementioned two-rotation-one-transfer constraint parallel mechanism, includes the following steps:

[0019] Obtain the elongation of each branch and calculate the end pose using the following formula:

[0020] q1 = p z -rsinβ

[0021]

[0022]

[0023] In the formula, α is the angle of rotation of the moving coordinate system around the Z-axis, β is the angle of rotation of the moving coordinate system around the current Y-axis, γ is the angle of rotation of the moving coordinate system around the current X-axis, r is the radius of the moving platform, and p z Let {p} be the z-axis component of the coordinates of the origin p of the motion coordinate system in the static coordinate system {B}.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. In the horizontal position, the two-rotation-one-transfer-over-constraint parallel mechanism bends towards the first static platform as the branch changes the angle of the moving platform, thereby reducing the distance between the moving platform and the first static platform. This provides a certain support for the branch and reduces the deformation of the moving platform relative to the first static platform under load, effectively increasing the longitudinal stiffness of the two-rotation-one-transfer-over-constraint parallel mechanism.

[0026] 2. Compared with the traditional PPS parallel mechanism, the use of Hooke joints and rotary joints to replace ball joints improves the limitation of the ball joint on the pitch angle, effectively increasing the pitch angle to meet actual working requirements.

[0027] 3. The first rotating pin is rotatably connected to the first rotating seat, thereby driving the linear drive body to rotate relative to the first stationary platform. When the linear drive body drives the linear drive telescopic rod to extend, it rotates and approaches the first stationary platform, reducing the distance between the moving platform and the first stationary platform, reducing the deformation of the moving platform relative to the first stationary platform under load, and effectively increasing the longitudinal stiffness of the two-rotation-one-transfer constraint parallel mechanism.

[0028] 4. When the linear drive body rotates through the second passive rotary joint, it can move along the length direction of the guide hole. Therefore, the second stationary platform can guide the rotation direction of the linear drive body through the guide hole, thereby preventing the linear drive body from deviating and providing auxiliary support for the linear drive body.

[0029] 5. The movable ring is sleeved on the linear drive body and can move along the length direction of the linear drive body. When the linear drive body drives the linear drive telescopic rod to extend and retract and rotates relative to the first stationary platform, the movable ring moves along the length direction of the linear drive body, thereby realizing the movable connection between the linear drive body and the second stationary platform. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the two-rotation-one-transfer constraint parallel mechanism of the present invention.

[0031] Figure 2 This is a schematic diagram of the moving platform, base, and single branch of the present invention.

[0032] Figure 3 This is an exploded view of the moving platform, base, and single branch of the present invention.

[0033] Figure 4 This is a comparison diagram of the maximum pitch angle between the two-rotation-one-transfer over-constraint parallel mechanism of the present invention and the traditional PPS parallel mechanism.

[0034] Figure 5 This is a schematic diagram illustrating the working principle of the two-rotation-one-transfer parallel mechanism of the present invention.

[0035] In the figure, 100 is the moving platform; 200 is the base; 210 is the first static platform; 220 is the second static platform; 221 is the guide hole; 300 is the branch chain; 311 is the linear drive body; 312 is the linear drive telescopic rod; 320 is the Hooke hinge; 330 is the bearing; 341 is the first rotating seat; 342 is the first rotating pin; 350 is the moving ring; 361 is the slide rail; 362 is the slider; 371 is the second rotating seat; 372 is the second rotating pin. Detailed Implementation

[0036] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0037] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0038] Furthermore, in this invention, descriptions involving terms such as "first," "second," and "a" are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0041] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0042] like Figures 1-4 As shown, a two-rotation-one-transfer constraint parallel mechanism includes: a moving platform 100, a base 200, and a branch chain 300.

[0043] The base 200 includes a first static platform 210 and a second static platform 220. The second static platform 220 is fixed relative to the first static platform 210 and is disposed between the moving platform 100 and the first static platform 210.

[0044] The branch chain 300 comprises three components, including a driving sliding joint, a Hooke hinge 320, a first passive rotary joint, a second passive rotary joint, a first passive sliding joint, a third passive rotary joint, and a second passive sliding joint. One end of the driving sliding joint is connected to one end of the Hooke hinge 320. The other end of the Hooke hinge 320 is rotatably connected to the moving platform 100 via the first passive rotary joint. The other end of the driving sliding joint is rotatably connected to the first stationary platform 210 via the second passive rotary joint. The first passive sliding joint is movably connected to the driving sliding joint. The first passive sliding joint is rotatably connected to the second passive sliding joint via the third passive rotary joint and is movably connected to the second stationary platform 220 via the second passive sliding joint.

[0045] In this embodiment, when the two-rotation-one-transfer constraint parallel mechanism is in a horizontal position, the branch 300 bends towards the first stationary platform 210 while changing the angle of the moving platform 100, thereby reducing the distance between the moving platform 100 and the first stationary platform 210. This provides a certain support for the branch 300 and reduces the deformation of the moving platform 100 relative to the first stationary platform 210 under load, effectively increasing the longitudinal stiffness of the two-rotation-one-transfer constraint parallel mechanism.

[0046] It is worth noting that the two-rotation-one-shift constraint parallel mechanism is in a horizontal position during normal use (i.e., the center line of the base 200 is on the horizontal plane), and the longitudinal stiffness involved in the two-rotation-one-shift constraint parallel mechanism is the stiffness in the vertical direction in this state.

[0047] like Figures 1-4 As shown, based on the above embodiment, the driving moving pair includes a linear driving body 311 and a linear driving telescopic rod 312. The linear driving telescopic rod 312 is telescopically connected to the linear driving body 311. The linear driving body 311 can drive the linear driving telescopic rod 312 to extend and retract. The linear driving telescopic rod 312 is connected to the end of the Hooke joint 320. The linear driving body 311 is rotatably connected to the first static platform 210 through the second passive rotating pair.

[0048] Specifically, the linear drive element, including the linear drive body 311 and the linear drive telescopic rod 312, can be a pneumatic cylinder, a hydraulic cylinder, or an electric cylinder.

[0049] like Figures 1-4 As shown, based on the above embodiment, the first passive rotating pair includes a bearing 330, and the end of the Hooke hinge 320 is rotatably connected to the moving platform 100 through the bearing 330.

[0050] In this embodiment, such as Figure 4 As shown, Figure 4 The left side represents the maximum pitch angle that the moving platform 100 can achieve through the two-rotation-one-transfer constraint parallel mechanism. Figure 4 The right side shows the maximum pitch angle that the moving platform 100 of the traditional PPS parallel mechanism can achieve. Therefore, compared with the traditional PPS parallel mechanism, the use of Hooke's joint 320 in combination with a rotary joint to replace the ball joint improves the limitation of the ball joint on the pitch angle, effectively increasing the pitch angle and meeting the actual working requirements.

[0051] like Figures 1-4 As shown, based on the above embodiment, the second passive rotating pair includes a first rotating seat 341 and a first rotating pin 342. The first rotating seat 341 is connected to the linear drive body 311, and the first rotating pin 342 is connected to the first stationary platform 210. The first rotating pin 342 is rotatably connected to the first rotating seat 341.

[0052] In this embodiment, the first rotating pin 342 is rotatably connected to the first rotating seat 341, thereby driving the linear drive body 311 to rotate relative to the first stationary platform 210. When the linear drive body 311 drives the linear drive telescopic rod 312 to extend, it rotates and approaches the first stationary platform 210, reducing the distance between the moving platform 100 and the first stationary platform 210, reducing the deformation of the moving platform 100 relative to the first stationary platform 210 under load, and effectively increasing the longitudinal stiffness of the two-rotation-one-transfer constraint parallel mechanism.

[0053] like Figures 1-4 As shown, based on the above embodiment, the second static platform 220 is provided with a guide hole 221, the linear drive body 311 passes through the guide hole 221, and the linear drive body 311 can move along the length direction of the guide hole 221 when it rotates through the second passive rotary joint.

[0054] In this embodiment, when the linear drive body 311 rotates through the second passive rotary joint, it can move along the length direction of the guide hole 221. Therefore, the second stationary platform 220 can guide the rotation direction of the linear drive body 311 through the guide hole 221, thereby preventing the linear drive body 311 from deviating, and at the same time playing an auxiliary support role for the linear drive body 311.

[0055] like Figures 1-4 As shown, based on the above embodiment, the first passive moving pair includes a moving ring 350, which is sleeved on the linear drive body 311 and can move along the length direction of the linear drive body 311. The third passive rotation is connected to the moving ring 350.

[0056] Specifically, the opening of the moving ring 350 is adapted to the cross-sectional shape of the linear drive body 311.

[0057] In this embodiment, the movable ring 350 is sleeved on the linear drive body 311 and can move along the length direction of the linear drive body 311. When the linear drive body 311 drives the linear drive telescopic rod 312 to extend and retract and rotate relative to the first stationary platform 210, the movable ring 350 moves along the length direction of the linear drive body 311, thereby realizing the movable connection between the linear drive body 311 and the second stationary platform 220.

[0058] like Figures 1-4 As shown, based on the above embodiment, the second passive moving pair includes a slide rail 361 and a slider 362. The slide rail 361 is connected to the second static platform 220, and the third passive rotating pair is connected to the slider 362. The slider 362 is movably connected to the slide rail 361.

[0059] In this embodiment, when the linear drive body 311 drives the linear drive telescopic rod 312 to extend and retract and rotate relative to the first stationary platform 210, the slider 362 can slide along the slide rail 361. Therefore, the second stationary platform 220 can guide the rotation direction of the linear drive body 311 through the slider 362, thereby preventing the linear drive body 311 from deviating and realizing the active connection between the linear drive body 311 and the second stationary platform 220.

[0060] like Figures 1-4 As shown, based on the above embodiment, the third passive rotating pair includes a second rotating seat 371 and a second rotating pin 372. The second rotating seat 371 is connected to the slider 362, and the second rotating pin 372 is connected to the moving ring 350. The second rotating pin 372 is rotatably connected to the second rotating seat 371.

[0061] In this embodiment, the second rotating pin 372 is rotatably connected to the second rotating seat 371. When the linear drive body 311 drives the linear drive telescopic rod 312 to extend and retract and rotate relative to the first static platform 210, it guides the rotation direction of the linear drive body 311, thereby preventing the linear drive body 311 from deviating.

[0062] like Figures 1-4 As shown, based on the above implementation, the three branches 300 are arranged in an equilateral triangle at one end connected to the first static platform 210, and the three branches 300 are arranged in an equilateral triangle at one end connected to the moving platform 100.

[0063] Specifically, the three slide rails 361 and the slider 362 are centrally distributed at 120° on the second static platform 220.

[0064] like Figures 1-5 As shown, an end-effector attitude determination method is based on the aforementioned two-rotation-one-transfer constraint parallel mechanism. In the figure, {B} represents the coordinate system where the first static platform 210 is located, with the origin O; in the figure, {M} represents the coordinate system where the moving platform 1001 is located, with the origin p; Q1, Q2, and Q3 are three first passive rotary joints; r represents the radius of the moving platform 100.

[0065] Calculate the end-effector attitude using the formula shown below:

[0066] q1 = p z -rsinβ

[0067]

[0068]

[0069] The specific calculation process is as follows:

[0070] The coordinate transformation matrix uses the rotation matrix R = R(α,z)R(β,y)R(γ,x) of the ZYX Euler angles. First, the moving coordinate system is rotated by an angle α around the Z-axis, then by an angle β around the current Y-axis of the moving coordinate system, and finally by an angle γ around the current X-axis of the moving coordinate system.

[0071]

[0072] The vector representation of Q1, Q2, and Q3 in the moving coordinate system {M} is Q 1M =[r,0,0] T ; The vector p of the center p of the moving platform 100 in the static coordinate system {B} is [p x ,p y ,p z ] T Furthermore, the vector representation of Q1, Q2, and Q3 in the static coordinate system {B} is Q. iB =RQ iM +p=[Q iBX Q iBY Q iBZ ] T (i = 1, 2, 3); From the geometric constraints of the mechanism, we can obtain: Q 1BY =0; Calculation yields:

[0073]

[0074]

[0075] p y=-rcosβsinα

[0076] Furthermore, the displacement of the push rod can be deduced:

[0077] q1 = Q 1BZ =p z -rsinβ

[0078]

[0079]

[0080] It should be noted here that since the PRP in the middle of the two-rotation-one-transfer over-constrained parallel mechanism (3-(RPRP)PUR parallel mechanism) is over-constrained in this invention, it can be ignored in kinematic calculations and calculated according to 3-RPUR.

[0081] The two-rotation-one-transfer-constrained parallel mechanism operates as follows: by extending or retracting the drive sliding pair in the branch chain 300, the attitude of the end-effector 100 is adjusted to achieve pitch angle adjustment.

Claims

1. A parallel mechanism with two rotations and one transfer over constraint, characterized in that, include: Dynamic platform; The base includes a first static platform and a second static platform, the second static platform being fixed relative to the first static platform and disposed between the moving platform and the first static platform; The system comprises three branches, including a driving prismatic joint, a Hooke's hinge, a first passive rotary joint, a second passive rotary joint, a first passive prismatic joint, a third passive rotary joint, and a second passive prismatic joint. One end of the driving prismatic joint is connected to one end of the Hooke's hinge. The other end of the Hooke's hinge is rotatably connected to the moving platform via the first passive rotary joint. The other end of the driving prismatic joint is rotatably connected to the first stationary platform via the second passive rotary joint. The first passive prismatic joint is movably connected to the driving prismatic joint. The first passive prismatic joint is rotatably connected to the second passive prismatic joint via the third passive rotary joint, and is movably connected to the second stationary platform via the second passive prismatic joint.

2. The two-rotation-one-transfer constraint parallel mechanism as described in claim 1, characterized in that: The drive sliding joint includes a linear drive body and a linear drive telescopic rod. The linear drive telescopic rod is telescopically connected to the linear drive body, and the linear drive body can drive the linear drive telescopic rod to extend and retract. The linear drive telescopic rod is connected to the end of the Hooke's joint, and the linear drive body is rotatably connected to the first stationary platform through the second passive rotary joint.

3. The two-rotation-one-transfer constraint parallel mechanism as described in claim 2, characterized in that: The first passive rotating joint includes a bearing, and the end of the Hooke's hinge is rotatably connected to the moving platform via the bearing.

4. The two-rotation-one-transfer constraint parallel mechanism as described in claim 2, characterized in that: The second passive rotary joint includes a first rotary seat and a first rotary pin. The first rotary seat is connected to the linear drive body, and the first rotary pin is connected to the first stationary platform. The first rotary pin is rotatably connected to the first rotary seat.

5. A two-rotation-one-transfer constraint parallel mechanism as described in claim 2, characterized in that: The second stationary platform is provided with a guide hole, through which the linear drive body passes. When the linear drive body rotates via the second passive rotary joint, it can move along the length direction of the guide hole.

6. The two-rotation-one-transfer constraint parallel mechanism as described in claim 2, characterized in that: The first passive locating joint includes a locating ring, which is sleeved on the linear drive body and can move along the length direction of the linear drive body. The third passive rotary joint is connected to the locating ring.

7. The two-rotation-one-transfer constraint parallel mechanism as described in claim 6, characterized in that: The second passive locating joint includes a slide rail and a slider. The slide rail is connected to the second stationary platform. The third passive rotary joint is connected to the slider, and the slider is movably connected to the slide rail.

8. A two-rotation-one-transfer constraint parallel mechanism as described in claim 7, characterized in that: The third passive rotating pair includes a second rotating seat and a second rotating pin. The second rotating seat is connected to the slider, and the second rotating pin is connected to the moving ring. The second rotating pin is rotatably connected to the second rotating seat.

9. A two-rotation-one-transfer constraint parallel mechanism as described in claim 1, characterized in that: The three branches are arranged in an equilateral triangle at one end connected to the first static platform, and the three branches are also arranged in an equilateral triangle at one end connected to the moving platform.

10. A method for determining the attitude of an end effector, characterized in that, Based on the two-transfer-one-transfer constraint-free parallel mechanism as described in any one of claims 1-9, the steps include: Obtain the elongation of each branch and calculate the end pose using the following formula: q1=p z -rsinβ In the formula, α is the angle of rotation of the moving coordinate system around the Z-axis, β is the angle of rotation of the moving coordinate system around the current Y-axis, γ is the angle of rotation of the moving coordinate system around the current X-axis, r is the radius of the moving platform, and p z Let {p} be the z-axis component of the coordinates of the origin p of the motion coordinate system in the static coordinate system {B}.

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