Parallel six-degree-of-freedom motion platform with variable stiffness and stroke and motion control method thereof

Abstract

The application belongs to the technical field of multi-degree-of-freedom motion platforms, and provides a parallel six-degree-of-freedom motion platform with variable rigidity and stroke and a motion control method thereof, wherein a swing arm mechanism is added at the bottom of an electric cylinder of a six-degree-of-freedom parallel robot, the swing arm mechanism has two rotary joints, is respectively driven by a motor and a speed reducer, changes the layout of a lower hinge point, changes the diameter of a hinge circle and the inclination angle of the electric cylinder, changes the rotary rigidity, the lateral translational rigidity and the stroke in each direction of the platform, and avoids structural interference.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of six-degree-of-freedom motion platform, in particular to a parallel six-degree-of-freedom motion platform with variable stiffness and stroke and a motion control method thereof. BACKGROUND

[0002] The parallel six-degree-of-freedom motion platform (six-degree-of-freedom parallel robot) is a structural design of Stewart platform, which can simulate the motion posture of multiple degrees of freedom in space through the motion of the driving electric cylinder and is widely used in various training simulators, such as flight simulators, automobile driving simulators, earthquake simulators, satellites, missiles and other aircrafts, entertainment devices (dynamic movie shaking platform) and other fields.

[0003] The parallel six-degree-of-freedom motion platform is composed of a 6-6 parallel mechanism of two upper and lower platforms, six electric cylinders in the middle and six Hooke's hinges (or spherical hinges) on the upper and lower platforms. The lower platform is fixed, and the lower platform is connected to the upper platform through the six electric cylinders and Hooke's hinges. The Hooke's hinges or spherical hinges are located at the connection between the upper platform and the six electric cylinders, which play a key role in ensuring the normal operation of the platform and the overall structural stiffness. The extension and retraction of each electric cylinder realize the translation of the upper platform along X, Y and Z and the rotation of the upper platform around X, Y and Z.

[0004] Generally, the parallel six-degree-of-freedom motion platform is driven by a servo electric cylinder, and of course a hydraulic cylinder is used in the design of a heavy-load parallel six-degree-of-freedom motion platform. By controlling the extension and retraction of the six electric cylinders, the upper platform is driven to move in six degrees of freedom (X, Y, Z, α, β, γ) in space, so as to simulate various spatial motion postures. During the motion process, the corresponding position and speed command signals of each electric cylinder are calculated according to the motion state of the six-degree-of-freedom platform, so as to control the motion of the motion platform and ensure that it moves along the predetermined trajectory. When the motion platform reaches the required position, the speed command signal of each electric cylinder is given as zero, and the motion platform stops, achieving the purpose of point control. At the same time, during the motion process, a closed-loop control strategy is adopted to feedback the speed and displacement signals of each electric cylinder. The speed signal is used for the input of closed-loop control to track the speed, and the displacement signal is used for position feedback and monitoring, so as to meet the pose control of the motion platform.

[0005] Parallel six-degree-of-freedom motion platform is driven by six parallel servo electric cylinders, has the advantages of high transmission efficiency, high speed, strong load capacity, high rigidity and high precision, and is more and more widely applied to various industries. The load capacity, motion space, motion speed and acceleration of the parallel six-degree-of-freedom motion platform are difficult to consider in all aspects, if the large motion space is pursued, the load capacity needs to be sacrificed, and if the large transverse displacement acceleration is pursued, the rotational angle acceleration needs to be sacrificed. Moreover, these performance indexes of the parallel robot are determined after the overall design is determined, which leads to a single working task of a parallel six-degree-of-freedom motion platform. Under complex working conditions, a parallel six-degree-of-freedom motion platform is often difficult to meet the left and right working requirements, and needs to be designed to be low and the angle between the electric cylinder and the ground to be small when good transverse displacement stiffness or large transverse displacement is required, and needs to be designed to be high and the angle between the electric cylinder and the ground to be large when good rotational stiffness or large rotational angle is required. Or change the stroke of the electric cylinder to improve these performance indexes. When interference occurs at a certain position, there is no other way to avoid interference except limiting the stroke.

[0006] For example Figure 1 As shown in the figure, the horizontal motion ability and transverse stiffness of the upper platform are not ideal when the transverse component force is small, and the horizontal motion output ability and transverse stiffness are improved when the transverse component force is increased. Figure 2 When the transverse component force is small and the α and β force arms are large, the rotational stiffness is good, but when the transverse component force is increased, the α and β force arms are reduced, resulting in the problem of reduced rotational ability.

[0007] In addition, the structure interference and position singularity problem shown in Figure 3a , 3b is also a big problem in the design and use of six-degree-of-freedom parallel robots, for example, the structure interference between the upper platform and the electric cylinder and the interference between the hinge and the electric cylinder shown in FIG. 3. The structure interference problem belongs to the design defect problem, which will cause serious damage to the electric motion platform and is not allowed to occur. In the design of large-tonnage and heavy-load six-degree-of-freedom parallel robots, this structure interference may also cause serious safety accidents, which is not expected and not allowed to occur. SUMMARY

[0008] As a first aspect of the present application, a parallel six-degree-of-freedom motion platform with variable stiffness and stroke is provided, a swing arm mechanism is added at the bottom of the electric cylinder of the six-degree-of-freedom parallel robot, the swing arm mechanism has two rotary joints, respectively driven by a motor and a speed reducer, thereby changing the layout of the lower hinge point, changing the diameter of the hinge circle and the inclination angle of the electric cylinder, and thereby changing the rotational stiffness, transverse translational stiffness and stroke in each direction of the platform, and avoiding structure interference.

[0009] As the second aspect of the present application, the swing arm movement of the parallel six-degree-of-freedom motion platform with variable stiffness and stroke is proposed, and two working modes of the parallel six-degree-of-freedom motion platform are controlled:

[0010] The first mode: the lower hinge circle diameter is changed by the movement of the swing arm mechanism, and the extension amount of the electric cylinder is unchanged; wherein during the movement driving process, the lower hinge circle diameter is changed by driving the six swing arm mechanisms to make the same movement;

[0011] The second mode: the motion platform is fixed, and the extension amount of one or more electric cylinders is changed by the movement of the swing arm mechanism.

[0012] Therefore, in the two modes, the rotational stiffness, lateral translational stiffness, and stroke in each direction of the platform can be changed by adjusting the two rotary joints, thereby avoiding structural interference.

[0013] As the second aspect of the present application, the control method of the parallel six-degree-of-freedom motion platform with variable stiffness and stroke is proposed, and the hinge point coordinate calculation method is as follows:

[0014] First, define the coordinate system: let the center point of the base upper plane be O, establish a global coordinate system CoordOXYZ on the base center upper plane, and establish a local coordinate system CoordA on the center of the i-th base connecting lug hole i X i1 Y i1 Z i1 , and establish a local coordinate system CoordB on the center of the i-th lower hook joint base connecting lug hole i X i2 Y i2 Z i2 ;

[0015] By obtaining the movement angles of the two joints of the swing arm mechanism, the coordinates of the hinge point C i in the local coordinate system CoordB i X i2 Y i2 Z i2 are solved; the coordinates of the hinge point B i in the local coordinate system CoordA i X i1 Y i1 Z i1 are solved, and then the conversion relationship between the local coordinate system CoordB i X i2 Y i2 Z i2 and the local coordinate system CoordA i X i1 Y i1 Z i1 is obtained.

[0016] wherein the coordinates of the articulation point C i may be converted to the local coordinate system CoordA i X i1 Y i1 Z i1 by coordinate system conversion. Since the conversion relationship between the local coordinate system CoordA i X i1 Y i1 Z i1 and the global coordinate system CoordOXYZ is fixed and known, the coordinates of the articulation point C i may be further converted into the coordinates of the global coordinate system CoordOXYZ.

[0017] Therefore, in the first mode, the upper platform changes in height with the movement of the swing arm mechanism, but it remains horizontal, the X coordinate and the Y coordinate of the upper articulation point remain unchanged, and the Z coordinate can be solved. In the second mode, the coordinates of the upper platform articulation point remain unchanged.

[0018] Compared with the prior art, the parallel six-degree-of-freedom motion platform and the motion control method thereof proposed by the present application increase a swing arm mechanism at the bottom of the electric cylinder of the six-degree-of-freedom motion platform, the swing arm mechanism is configured with two rotary joints and is driven by a motor and a speed reducer respectively. By the movement of the swing arm mechanism, the diameter of the articulation circle and the inclination angle of the electric cylinder are changed, and then the rotational stiffness, the lateral translational stiffness and the stroke in each direction of the platform are changed, the structural interference is avoided, and the stability, reliability, safety and application range of the platform motion are improved.

[0019] It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be seen as being part of the inventive subject matter of the present disclosure unless otherwise stated. Additionally, all combinations of claimed subject matter can be seen as being part of the inventive subject matter of the present disclosure.

[0020] The foregoing and other aspects, embodiments and features of the present teachings can be better understood and appreciated from the following description of the embodiments of the present teachings, referenced by the appended drawings. Other aspects, embodiments and features of the present teachings will be apparent from the description of the embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings are not intended to be to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented with a like numeral for clarity. Not all components can be called out in each drawing. Embodiments of various aspects of the present teachings will now be described, by way of example only, with reference to the accompanying drawings in which:

[0022] Figure 1is a schematic diagram of the platform before and after adjustment of the lateral force in the prior art.

[0023] Figure 2 is a schematic diagram of the platform before and after adjustment of the rotating force arm in the α, β direction in the prior art.

[0024] Figure 3a 、 3b is a schematic diagram of the structural interference of the parallel six-degree-of-freedom motion platform in the prior art, wherein Figure 3a represents the structural interference between the upper platform and the electric cylinder, Figure 3b represents the structural interference between the hinged member and the electric cylinder.

[0025] Figure 4 is a schematic diagram of the parallel six-degree-of-freedom motion platform with variable stiffness and stroke of the embodiment.

[0026] Figure 5 is Figure 4 a schematic diagram of the swing arm mechanism in the parallel six-degree-of-freedom motion platform of the embodiment.

[0027] Figure 6 is Figure 4 a schematic diagram of the coordinate system definition of the parallel six-degree-of-freedom motion platform of the embodiment.

[0028] Figure 7 is Figure 4 an axonometric view of the initial position state of the parallel six-degree-of-freedom motion platform of the embodiment.

[0029] Figure 8 is Figure 4 a schematic diagram of the lower hinged circle expansion state of the parallel six-degree-of-freedom motion platform of the embodiment.

[0030] Figure 9 is Figure 8 an axonometric view of the parallel six-degree-of-freedom motion platform in the example lower hinged circle expansion state.

[0031] Figure 10 is Figure 4 a schematic diagram of the lower hinged circle contraction state of the parallel six-degree-of-freedom motion platform of the embodiment.

[0032] Figure 11 is Figure 10 an axonometric view of the parallel six-degree-of-freedom motion platform in the example lower hinged circle contraction state. DETAILED DESCRIPTION

[0033] In order to better understand the technical content of the present application, specific embodiments are described below with the accompanying drawings.

[0034] Aspects of the present application are described in the disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of this disclosure need not necessarily include all aspects of the present application. It should be understood that various concepts and embodiments introduced above and those described in more detail below can be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. Additionally, some aspects of the present disclosure can be used independently of any other aspects of the present disclosure, for any suitable purpose.

[0035] In combination Figures 4-6 As shown, the parallel six-degree-of-freedom motion platform according to the embodiments of the present disclosure includes a base 100, a motion platform 200, and electric cylinders 400 arranged between the base 100 and the motion platform 200. Each electric cylinder 400 is configured with an independent or centralized control board and a driving program for driving the multi-degree-of-freedom attitude adjustment of the motion platform 200 by controlling the extension and retraction of the electric cylinder 400, thereby realizing multi-degree-of-freedom motion simulation.

[0036] In combination Figure 4 As shown, the parallel six-degree-of-freedom motion platform further includes upper Hooke joint bases 600 arranged on the lower bottom surface of the motion platform 200. Correspondingly, each upper Hooke joint base 600 is correspondingly provided with a lower Hooke joint base 300, which is correspondingly supported on the upper end of the swing arm mechanism, and the lower end of the swing arm mechanism is supported on the upper surface of the base 100.

[0037] In combination Figure 4 , 5 , 6, six electric cylinders 400 are respectively configured with their corresponding upper Hooke joint bases 600, lower Hooke joint bases 300, and swing arm mechanisms. The upper and lower ends of each electric cylinder 400 are hingedly connected between the corresponding upper Hooke joint base 600 and lower Hooke joint base 300.

[0038] In combination Figure 4 , 5 As shown in the example, a first lug seat 310 is arranged below the lower Hooke joint base 300. Correspondingly, corresponding to the lower Hooke joint base 300 of each electric cylinder, the upper surface of the base 100 is provided with a second lug seat 110. The first lug seat 310 and the second lug seat 110 are arranged in a matched manner.

[0039] As shown in Figure 4 , 5 The swing arm mechanism arranged below each electric cylinder 400 is used to expand or shrink the lower hinged circle, so as to change the rotational stiffness, transverse translational stiffness, and stroke in each direction of the platform, and avoid structural interference.

[0040] The lower hinge circle in the embodiment of the present application refers to the hinge circle formed by the hinge point at the lower end of the electric cylinder. In the traditional fixed-position platform design, the diameter and position of the lower hinge circle are determined by the hinge hinge arranged on the lower platform and are fixed. Therefore, as described in the background of the present application, there are problems of rotation stiffness, transverse translation stiffness and stroke in each direction under complex working conditions. In the platform design proposed in the embodiment of the present application, a position-variable lower hinge point is arranged at the lower part of the electric cylinder to realize the design of a variable and adjustable lower hinge circle, the adjustment of rotation stiffness, transverse translation stiffness and stroke in each direction, and the design suitable for small and medium loads, especially for applications below 1T load, such as driving simulators, flight simulators, vehicle driving simulators, earthquake simulators, and dynamic movies, entertainment devices, etc.

[0041] In the optional embodiment, each swing arm mechanism is configured with two rotary joints, i.e., a first rotary joint (upper rotary joint) arranged at the first lug 310 and a second rotary joint (lower rotary joint) arranged at the second lug 110. Each rotary joint is driven to rotate by a motor driving mechanism. Thus, by the rotary motion of the two joints of the swing arm mechanism, the inclination angle of the electric cylinder and the diameter of the hinge circle are changed, and then the rotation stiffness, transverse translation stiffness and stroke in each direction of the platform are changed, avoiding structural interference.

[0042] As shown in Figure 4 , 5 , a swing arm 530 is arranged between the two rotary joints of each swing arm mechanism. The upper end of the swing arm 530 is provided with a first fork 531, and the lower end is provided with a second fork 532.

[0043] The first lug 310 is mounted inside the first fork 531.

[0044] The second lug 110 is mounted inside the second fork 532.

[0045] In the optional embodiment, the aforementioned motor driving mechanism includes a motor and a speed reduction mechanism. The motor and the speed reduction mechanism are coaxially arranged and coaxially arranged with the corresponding first lug 310 or second lug 110. In the optional embodiment, the output end of each speed reduction mechanism is connected to the corresponding lug through a key connection.

[0046] Specifically, the motor driving mechanism arranged at the position of the first lug 310 includes a first motor 511 and a first speed reduction mechanism 512. The first motor 511 is a stepping motor, the output shaft of which is connected to the input end of the first speed reduction mechanism 512. The first speed reduction mechanism 512 preferably adopts a planetary gear speed reduction mechanism, the output end of which is keyed to the rotation center of the first lug 310 to drive rotation and thereby adjust the rotation of the first rotary joint.

[0047] In an optional embodiment, the output shaft end of the first reducer 512 is inserted into the center of the first lug 310 by means of a key connection.

[0048] In an embodiment of the present invention, the first rotary joint and the second rotary joint are both composed of corresponding ear seats and motor drive mechanisms, which cooperate with the corresponding forks (531, 532) to realize the rotation drive of the joint.

[0049] Combination Figure 4 , 5 As shown, the motor drive mechanism arranged at the second ear 110 includes a second motor 521 and a first reducer 522. The second motor 521 can be a stepper motor, and its output shaft is connected to the input end of the second reducer 522. The second reducer 522 is preferably a planetary gear reducer mechanism, and its output end is keyed to the rotation center of the second ear 110 to drive rotation, thereby adjusting the rotation of the second rotary joint.

[0050] In an optional embodiment, the output shaft end of the second reducer 522 is inserted into the center of the first lug 310 by means of a key connection.

[0051] Combination Figure 4 , 5 As shown, in the design of the two rotary joints, the output shaft end of each reducer passes through the side hole of the corresponding first fork 531 or second fork 532, and then connects to the rotation center position of the corresponding lug.

[0052] It should be understood that, under the teachings of this invention, the rotation drive mechanism of the two rotary joints can be implemented using existing highly integrated drive mechanisms to achieve the rotation drive design of the joint position.

[0053] Therefore, combined Figure 5 , Figure 6 As shown, for the swing arm mechanism corresponding to the six electric cylinders set on the platform, by synchronously driving the first rotary joint and the second rotary joint, keeping the first rotary joint moving in the same direction and the second rotary joint moving in the same direction, the diameter of the lower hinge circle is changed, while the extension and retraction of the electric cylinder remains unchanged. This expands and shrinks the diameter of the lower hinge circle, thereby adjusting the rotational stiffness, lateral translational stiffness, and stroke in various directions to adapt to applications under complex working conditions, especially under the condition of large stroke in the horizontal lateral direction, balancing the contradiction between rotational stiffness and rotation angle.

[0054] like Figures 8-9The schematic diagram of the embodiment of the application shows the expanded state of the lower hinge circle of the parallel six-degree-of-freedom motion platform. By synchronously controlling the movement of the first rotary joints and the movement of the second rotary joints, the rotation speed and rotation angle of the six first rotary joints are consistent, and the rotation speed and rotation angle of the six second rotary joints are consistent. The tilt angle of the swing arm 530, i.e. the tilt angle of the swing arm mechanism, is adjusted to expand towards the edge of the base 110, thereby adjusting the tilt angle of the electric cylinder 400 and expanding the lower hinge circle.

[0055] As shown in Figures 10-11 The schematic diagram of the embodiment of the application shows the contracted state of the lower hinge circle of the parallel six-degree-of-freedom motion platform. By synchronously controlling the movement of the first rotary joints and the movement of the second rotary joints, the rotation speed and rotation angle of the six first rotary joints are consistent, and the rotation speed and rotation angle of the six second rotary joints are consistent. The tilt angle of the swing arm 530, i.e. the tilt angle of the swing arm mechanism, is adjusted to contract towards the center of the base 110, thereby adjusting the tilt angle of the electric cylinder 400 and contracting the lower hinge circle.

[0056] In combination with Figure 4 and Figures 7-11 Based on the proposed parallel six-degree-of-freedom motion platform with variable stiffness and stroke and its motion control process, the parallel six-degree-of-freedom motion platform of the application can be set in two working modes:

[0057] The first mode: the diameter of the lower hinge circle is changed by the movement of the swing arm mechanism, and the extension and contraction amount of each electric cylinder 400 remains unchanged. During the movement driving process, the six swing arm mechanisms are driven to move in the same way to change the diameter of the lower hinge circle, as shown in Figures 8-9 and Figures 10-11 After the diameter of the lower hinge circle is adjusted, the attitude of the upper platform, i.e. the attitude of the motion platform 200, can be adjusted by the amount of the driven electric cylinder 400. Thus, by controlling the motion attitude adjustment of the platform under the premise of the expanded or contracted hinge circle, the contradiction between the rotation stiffness and the rotation angle and the horizontal stroke is solved.

[0058] The second mode: the upper platform and the lower platform motion platform remain fixed, and the extension and contraction amount of one or more electric cylinders is changed by the movement of the swing arm mechanism.

[0059] In the design of parallel six-degree-of-freedom motion platform, we found through the actual process and test of the designed and used multi-degree-of-freedom platform that, due to the electric cylinder being usually determined according to the design parameters, the greater the size difference between the upper and lower hinge circles of the parallel six-degree-of-freedom motion platform, the greater the inclination angle of the electric cylinder, the better the lateral stiffness, and the worse the rotational stiffness. At the same time, the length of the electric cylinder is constant, the greater the size difference between the upper and lower hinge circles of the parallel six-degree-of-freedom motion platform, the greater the inclination angle of the electric cylinder, the greater the translational stroke, and the smaller the rotational stroke.

[0060] The present application changes the diameter of the hinge circle and the inclination angle of the electric cylinder by increasing the swing arm mechanism at the bottom of the electric cylinder of the six-degree-of-freedom motion platform, and driving the swing arm mechanism by two rotary joints driven by motors and reducers, thereby changing the rotational stiffness, lateral translational stiffness, and stroke in each direction of the platform, and avoiding structural interference.

[0061] Therefore, the rotational stiffness, lateral translational stiffness, and stroke in each direction of the platform can be changed by adjusting the two rotary joints, and structural interference can be avoided.

[0062] As a second aspect of the present application, a control method of a parallel six-degree-of-freedom motion platform with variable stiffness and stroke is proposed, a global coordinate system CoordOXYZ of the upper plane center of the base, a lower local coordinate system CoordA i X i1 Y i1 Z i1 and an upper local coordinate system CoordB i X i2 Y i2 Z i2 of the side hole center of the i th first ear seat are established, and the position coordinates of each hinge point in the motion state are calculated through hinge point coordinate system conversion and reverse connection.

[0063] As an optional embodiment, the position coordinates of each hinge point in the motion state are calculated through hinge point coordinate system conversion and reverse connection, and the process includes:

[0064] First, define the coordinate system: let the center point of the upper plane of the base be O, a global coordinate system CoordOXYZ of the upper plane center of the base, a lower local coordinate system CoordA i X i1 Y i1 Z i1 and an upper local coordinate system CoordB i X i2 Y i2 Zi2 ;

[0065] By obtaining the motion angles of the two rotary joints of the swing arm mechanism, the coordinates of the articulated point C i In the upper local coordinate system CoordB i X i2 Y i2 Z i2 of the coordinates, the articulated point B i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 of the coordinates, and then the conversion relationship between the upper local coordinate system CoordB i X i2 Y i2 Z i2 and the lower local coordinate system CoordA i X i1 Y i1 Z i1 is obtained.

[0066] Wherein, the coordinates of the articulated point C i can be converted to the coordinates of the lower local coordinate system CoordA i X i1 Y i1 Z i1 by coordinate system conversion; since the conversion relationship between the lower local coordinate system CoordA i X i1 Y i1 Z i1 and the global coordinate system CoordOXYZ is fixed and known, the coordinates of the articulated point C i can be further converted into the coordinates of the global coordinate system CoordOXYZ.

[0067] (1) Coordinate system definition

[0068] The global coordinate system CoordOXYZ of the upper plane of the base center, the lower local coordinate system CoordA i X i1 Y i1 Z i1 of the side hole center of the i-th second ear seat on the base, and the upper local coordinate system CoordB i X i2 Y i2 Z i2 established at the side hole center of the i-th first ear seat are constructed.

[0069] (2) Set the initial state of the platform

[0070] Combined with Figure 4 ,6 , 7, in the initial position state, the coordinates of the hinge point C i and the hinge point D i in the global coordinate system CoordOXYZ are known, and the coordinates of the hinge point Bi in the upper local coordinate system CoordB i X i2 Y i2 Z i2 are known; the coordinates of the hinge point Bi in the lower local coordinate system CoordA i X i1 Y i1 Z i1 are known.

[0071] wherein the hinge point C i represents the rotation center point of the bottom of the i-th electric cylinder 400 and the corresponding i-th lower hook joint base 300, and Bi represents the lower hinge point.

[0072] The hinge point D i represents the rotation center point of the top of the i-th electric cylinder 400 and the corresponding i-th upper hook joint base 600, and Di represents the upper hinge point.

[0073] In combination Figure 6 , the hinge point Bi represents the rotation center point of the first fork part 531 of the swing arm in the swing arm mechanism corresponding to the i-th electric cylinder 400 and the corresponding first ear seat 310 in combination.

[0074] The hinge point Ai represents the rotation center point of the second fork part 532 of the swing arm in the swing arm mechanism corresponding to the i-th electric cylinder 400 and the corresponding second ear seat 110 in combination. Since the second ear seat 110 is fixed on the base 100, the global coordinates of the hinge point Ai are known and remain unchanged.

[0075] The offset amount [△X, △Y, △Z, △α, △β, △γ] of the lower local coordinate system CoordA i X i1 Y i1 Z i1 from the global coordinate system CoordOXYZ is known.

[0076] (3) Hinge point coordinate conversion

[0077] As can be seen from Figure 4 , 6 , the second rotation joint (i.e., the lower rotation joint) and the first rotation joint (i.e., the upper rotation joint) of the swing arm mechanism rotate around the Y i1 and Y i2 axes of the two local coordinate systems, respectively, with rotation angles β1 and β2, respectively.

[0078] In the initial state, the hinge point Bi In the lower local coordinate system CoordA i X i1 Y i1 Z i1 , the coordinates of the hinge point C i1 are (x i1 , y i1 , z i ), and in the upper local coordinate system CoordB i X i2 Y i2 Z i2 , the coordinates of the hinge point C i2 are (x i2 , y i2 , z i ). After the swing arm mechanism rotates, the coordinates of the hinge point B i in the lower local coordinate system CoordA i1 X i1 Y i1 Z

[0079]

[0080] The coordinates of the hinge point C i in the upper local coordinate system CoordB i X i2 Y i2 Z i2 are calculated as follows:

[0081]

[0082] (4) Coordinate system conversion of the hinge point (lower hinge point coordinate calculation)

[0083] Based on the coordinates of the hinge point B i in the lower local coordinate system CoordA i X i1 Y i1 Z i1 (x' i1’ , y' i1 , z' i1 ), and the coordinates of the hinge point C i in the upper local coordinate system CoordB i X i2 Y i2 Z i2 (x' i2 , y' i2 , z' i2 );

[0084] In combination with the lower local coordinate system CoordA i X i1 Y i1Z i1 The offset [△X, △Y, △Z, △α, △β, △γ] of the global coordinate system CoordOXYZ, then the coordinates of the hinge point C i In the local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates of the hinge point C

[0085]

[0086] The coordinates of the hinge point C i The coordinates of the hinge point C

[0087]

[0088] Thus, the global coordinates of the lower hinge point are obtained, i.e. the coordinates of the hinge point C i The coordinates of the hinge point C

[0089] (5) Upper hinge point coordinate calculation

[0090] In the initial state, the hinge point D i The coordinates of the hinge point D i3 in the global coordinate system CoordOXYZ are (x i3 , y i3 , z i ), and the initial length of the electric cylinder is L.

[0091] In the first mode, the X and Y coordinates of the hinge point D i3 are unchanged, i.e. x’ i3 = x i3 , y’ i3 = y i , and the Z coordinate is calculated as follows.

[0092]

[0093] In the second mode, the coordinates of the hinge point D i are unchanged.

[0094] Therefore, in the first mode, the moving platform 200 as the upper platform changes in height with the movement of the swing arm mechanism, but remains horizontal, and the X and Y coordinates of the upper hinge point are unchanged, and the Z coordinate can be obtained by the process of the above embodiment. In the second mode, the coordinates of the upper hinge point of the moving platform 200 are unchanged.

[0095] Compared with the prior art, the parallel six-degree-of-freedom motion platform and the motion control method thereof have the following advantages: a swing arm mechanism is added at the bottom of the electric cylinder of the six-degree-of-freedom motion platform, the swing arm mechanism is provided with two rotary joints and is driven by a motor and a speed reducer respectively, the diameter of the hinged circle and the inclination angle of the electric cylinder are changed through the movement of the swing arm mechanism, and then the rotation stiffness, the lateral translation stiffness and the stroke in each direction of the platform are changed, the structural interference is avoided, and the stability, reliability, safety and application range of the platform movement are improved.

[0096] Although the present application has been disclosed with reference to preferred embodiments, it is not intended to limit the present application. Those skilled in the art can make various modifications and improvements without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be subject to the scope defined by the claims.

Claims

1. A parallel six-degree-of-freedom motion platform with variable stiffness and stroke, characterized in that, include: Base (100); Motion platform (200); An electric cylinder (400) is disposed between the base (100) and the motion platform (200); A swing arm mechanism is provided between the base (100) and the motion platform (200), corresponding to each electric cylinder (400) and located below the electric cylinder (400). Each swing arm mechanism is provided with the upper surface of the base (100) and extends toward the motion platform. The upper end of the swing arm mechanism is provided with a lower Hooke hinge base (300). The bottom of each electric cylinder (400) is supported and hinged to the lower Hooke hinge base (300) of the corresponding swing arm mechanism. An upper Hooke hinge base (600) is set on the lower bottom surface of the motion platform (200), and the upper and lower ends of each electric cylinder (400) are respectively hinged to the corresponding upper Hooke hinge base (600) and lower Hooke hinge base (300). Each electric cylinder (400) has a first rotary joint and a second rotary joint, which are located at corresponding positions on the upper surfaces of the lower Hooke hinge base (300) and the base (100), respectively. The first rotary joint and the second rotary joint are configured to expand or shrink the lower hinge circle of the parallel six-degree-of-freedom motion platform through consistent synchronous motion control, so as to adjust the rotational stiffness, lateral translational stiffness and stroke in each direction of the platform. The swing arm mechanism includes a swing arm (530), which is provided with a first fork (531) at one end and a second fork (532) at the other end. The first rotary joint and the second rotary joint are respectively provided at the positions of the first fork (531) and the second fork (532). The first rotary joint includes a first ear seat (310) and a motor drive mechanism arranged coaxially with the first ear seat (310). The first ear seat (310) is installed in the first fork (531). The output shaft end of the motor drive mechanism passes through the side hole of the first fork (531) and is connected to the rotation center position of the first ear seat (310) by a key connection. The second rotary joint includes a second ear seat (110) and a motor drive mechanism arranged coaxially with the second ear seat (110). The second ear seat (110) is installed in the second fork (532). The output shaft end of the motor drive mechanism passes through the side hole of the second fork (532) and is connected to the rotation center position of the second ear seat (110) by a key connection. By synchronously controlling the movement of the first rotary joint and the movement of the second rotary joint, the rotational speed and rotational angle of the six first rotary joints are made consistent, as are the rotational speed and rotational angle of the six second rotary joints. The tilt angle of the swing arm mechanism is adjusted to achieve the adjustment of the lower hinge circle of the parallel six-degree-of-freedom motion platform.

2. The parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to claim 1, characterized in that, A first ear seat (310) is provided below the lower Hooke hinge base (300). For each electric cylinder (400), a second ear seat (110) is provided on the upper surface of the base (100) corresponding to the lower Hooke hinge base (300); the first ear seat (310) is provided in conjunction with the second ear seat (110).

3. The parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to claim 1, characterized in that, Its features are, The motor drive mechanism includes a motor and a reduction mechanism arranged coaxially.

4. The parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to claim 3, characterized in that, The reduction mechanism is a planetary gear reducer.

5. The parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to any one of claims 1-4, characterized in that, The parallel six-degree-of-freedom motion platform is configured to operate in at least two modes, including: First mode: The diameter of the lower hinge circle is changed by the movement of the swing arm mechanism, while the extension and retraction of each electric cylinder remains unchanged; wherein, during the motion driving process, the diameter of the lower hinge circle is expanded or reduced by driving the six swing arm mechanisms to perform consistent synchronous movements. Second mode: The motion platform is fixed, and the extension and retraction of one or more electric cylinders is changed by the movement of the swing arm mechanism.

6. The motion control method for a parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to any one of claims 1-4, characterized in that, By constructing a global coordinate system on the upper plane of the base center, and the first coordinate system on the base... i The lower local coordinate system at the center of the side hole of the second ear and the first i A local coordinate system is established at the center of the side hole of the first ear seat. By transforming and reversing the coordinate system of the hinge point, the position coordinates of each hinge point in motion are calculated. The specific implementation process includes: Let O be the center point of the upper plane of the base. Construct a global coordinate system CoordOXYZ for the upper plane of the base center. i The lower local coordinate system CoordA at the center of the side hole of the second ear seat i X i1 Y i1 Z i1 and the i The upper local coordinate system CoordB is established at the center of the side hole of the first ear seat. i X i2 Y i2 Z i2 ; By obtaining the motion angles of the two rotary joints of the swing arm mechanism, the hinge point C can be solved. i In the upper local coordinate system CoordB i X i2 Y i2 Z i2 The coordinates of hinge point B i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates are then used to obtain the upper local coordinate system CoordB. i X i2 Y i2 Z i2 With the lower local coordinate system CoordA i X i1 Y i1 Z i1 The transformation relationship; Among them, hinge point C i The coordinates can be transformed to the lower local coordinate system CoordA through coordinate system transformation. i X i1 Y i1 Z i1 Due to the lower local coordinate system CoordA i X i1 Y i1 Z i1 Since the transformation relationship with the global coordinate system CoordOXYZ is fixed and known, the hinge point C is further... i The coordinates are converted into the global coordinate system CoordOXYZ, that is, the global coordinates of the lower hinge point after the motion are obtained; Finally, in different motion modes, the global coordinates of the upper hinge point are determined based on the positional changes of the motion platform of the parallel six-degree-of-freedom motion platform.

7. The motion control method for a parallel six-degree-of-freedom motion platform with variable stiffness and stroke according to claim 6, characterized in that, The specific calculation of the global coordinates of the upper and lower hinge points includes: (1) Definition of coordinate system Construct a global coordinate system CoordOXYZ on the upper plane of the base center, and the first coordinate system on the base... i The lower local coordinate system CoordA at the center of the side hole of the second ear seat i X i1 Y i1 Z i1 and the i The upper local coordinate system CoordB is established at the center of the side hole of the first ear seat. i X i2 Y i2 Z i2 ; (2) Set the initial state of the platform In the initial position state, in the platform's design parameters, hinge point C i and hinge point D i The coordinates of the global coordinate system CoordOXYZ are known, and the coordinates of the local coordinate system CoordB are known. i X i2 Y i2 Z i2 The coordinates are known; hinge point Bi is in the lower local coordinate system CoordA. i X i1 Y i1 Z i1 The coordinates are known; Among them, hinge point C i Let represent the rotation center point between the bottom of the i-th electric cylinder and the corresponding i-th lower Hooke hinge base, and let represent the lower hinge point; Hinge point D i Let represent the rotation center point between the top of the i-th electric cylinder and the corresponding i-th upper Hooke hinge base, and let represent the upper hinge point. Hinge point Bi represents the rotation center point where the first fork of the swing arm and the corresponding first ear seat of the swing arm are joined in the swing arm mechanism corresponding to the i-th electric cylinder; hinge point Ai represents the rotation center point where the second fork of the swing arm and the corresponding second ear seat of the swing arm are joined in the swing arm mechanism corresponding to the i-th electric cylinder. Lower local coordinate system CoordA i X i1 Y i1 Z i1 The offsets [△X, △Y, △Z, △α, △β, △γ] from the global coordinate system CoordOXYZ are known; (3) Coordinate transformation of hinge point The second and first rotary joints of the swing arm mechanism revolve around the Y-axis of two local coordinate systems, respectively. i1 and Y i2 Rotate, with rotation angles β1 and β2 respectively; In the initial state, hinge point B i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates are (x i1 y i1 , z i1 Hinge point C i In the upper local coordinate system CoordB i X i2 Y i2 Z i2 The coordinates are (x i2 y i2 , z i2 After the rotary joint of the swing arm mechanism moves, the hinge point B... i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates are calculated as follows: ； Hinge point C i In the upper local coordinate system CoordB i X i2 Y i2 Z i2 The coordinates are calculated as follows: ； (4) Coordinate system transformation of hinge points Based on hinge point B i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates are (x' i1’ y' i1 , z' i1 Hinge point C i In the upper local coordinate system CoordB i X i2 Y i2 Z i2 The coordinates are (x' i2 y' i2 , z' i2 ); Combined with the local coordinate system CoordA i X i1 Y i1 Z i1 The offsets [△X, △Y, △Z, △α, △β, △γ] from the global coordinate system CoordOXYZ are used to calculate the hinge point C. i In the lower local coordinate system CoordA i X i1 Y i1 Z i1 The coordinates are represented as: ； Then, hinge point C i The coordinates in the global coordinate system CoordOXYZ are represented as follows: ； Thus, the global coordinates of the lower hinge point are obtained, which is the hinge point C after the swing arm has moved. i Coordinates in the global coordinate system CoordOXYZ; (5) Calculation of the coordinates of the upper hinge point In the initial state, hinge point D i The coordinates of the point in the global coordinate system CoordOXYZ are (x i3 y i3 , z i3 The initial length of the electric cylinder is L; In the first mode, hinge point D i The X and Y coordinates remain unchanged, x' i3 =x i3 y' i3 =y i3 The Z-coordinate is calculated as follows: ； In the second mode, hinge point D i The coordinates remain unchanged.

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