6-UPRU high-precision positioning platform and positioning method
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2026-02-03
- Publication Date
- 2026-05-26
Smart Images
Figure CN122077572A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of precision positioning and micro-manipulation equipment technology, and particularly relates to a 6-UPRU high-precision positioning platform and positioning method. Background Technology
[0002] In the field of high-precision positioning and micromanipulation equipment, six-degree-of-freedom parallel positioning platforms have become key equipment for high-end applications such as semiconductor precision manufacturing, micro-nano device assembly, high-precision alignment of optical components, and precision metrology, addressing submicron to nanometer-level accuracy requirements for centimeter-level travel and load ranges from tens to hundreds of Newtons. However, existing positioning devices adapted to this range generally suffer from multiple technical bottlenecks, making it difficult to balance accuracy, stability, and scenario adaptability. Among these, traditional solutions, represented by the 6-UCU configuration, exhibit particularly typical shortcomings, reflecting common problems across the industry.
[0003] First, motion coupling and derived errors limit the upper limit of accuracy. Existing equipment adapted to loads of tens to hundreds of Newtons mostly relies on helical pairs such as ball screws for driving the chain, and lacks effective linear guidance and decoupling mechanisms. This results in a strong coupling relationship between the axial displacement of the chain and its rotation around its own axis. In reciprocating motion with a stroke of centimeters, the additional axial displacement generated by the rotation of the chain increases with the load, forming complex derived errors. These errors are difficult to accurately describe using traditional kinematic models and require compensation through complex algorithms. This not only increases the difficulty of control but also easily leads to accuracy loss due to algorithm iteration lag, making it impossible to stably achieve submicron to nanometer-level positioning requirements.
[0004] Secondly, thermal errors and mechanical wear affect long-term stability. Under conditions of centimeter-level strokes and loads ranging from tens to hundreds of Newtons, the frictional heat generated by transmission components such as ball screws becomes more significant, and axial thermal deformation becomes a fixed source of error. Existing equipment mostly adopts a semi-closed-loop control mode, making it difficult to integrate direct displacement detection elements and unable to provide real-time feedback on thermal deformation errors, leading to drift in positioning accuracy. Simultaneously, the rigid contact pairs experience accelerated wear during long-term reciprocating motion within this load range, with a gradual increase in the fit clearance, further exacerbating accuracy degradation and failing to meet the long-term stable operation requirements of high-end applications.
[0005] Furthermore, achieving high precision remains costly. To approach submicron to nanometer-level precision with centimeter-level strokes and loads ranging from tens to hundreds of Newtons, existing equipment requires ultra-precision machining processes to control component tolerances. Additionally, key parameters such as ball screw lead and bearing clearance must be individually calibrated before assembly. This process relies on specialized high-precision equipment and complex procedures, significantly increasing production and assembly costs. Simultaneously, the complex control algorithms used to compensate for errors require high-performance controllers, further driving up the overall equipment cost and limiting its large-scale application in more high-end scenarios.
[0006] In summary, existing high-precision positioning devices, suitable for centimeter-level strokes and loads ranging from tens to hundreds of Newtons, generally face common problems such as "motion coupling and thermal errors limiting accuracy, mechanical wear affecting stability, and high cost in achieving high precision," making it difficult to meet the differentiated requirements for accuracy, stability, and cost in various high-end scenarios. Therefore, there is an urgent need to propose a systematic solution from a structural design perspective that balances high precision, high stability, and scenario adaptability within this load and stroke range, while controlling manufacturing costs. Summary of the Invention
[0007] The purpose of this invention is to provide a 6-UPRU high-precision positioning platform and positioning method. By integrating the dual-rotation joint configuration design with motion control compensation, a systematic solution with full-link collaboration is constructed. This not only solves the problems of clearance, friction and wear caused by rigid rotation joints in traditional configurations at the structural level, but also meets the accuracy and load requirements of different scenarios through multi-configuration adaptation. Combined with closed-loop feedback compensation, the positioning accuracy and long-term stability of the platform are significantly improved, achieving high-precision positioning from submicron to nanometer level, and meeting the differentiated needs of various high-end precision manufacturing and testing scenarios.
[0008] To address the problems existing in the background art, the present invention adopts the following technical solution:
[0009] A 6-UPRU high-precision positioning platform, the positioning platform includes a static platform, a moving platform, and six drive chains with identical structures and spatially symmetrical distribution. Both ends of the drive chains are connected to the static platform and the moving platform respectively through cross-axis Hooke joints.
[0010] The drive chain includes a sliding joint and a rotating joint. The sliding joint is connected to the stationary platform via a cross-shaped Hooke joint. One end of the rotating joint is connected to the sliding joint, and the other end is connected to the moving platform via a cross-shaped Hooke joint. The rotating joint can be a flexible rotating joint or a rigid rotating joint. Each drive chain integrates a fully closed-loop detection unit.
[0011] The flexible rotary joint is an integrated elastic structure of inner ring, leaf spring, and outer ring, with a symmetrical overall distribution. The outer ring of the flexible rotary joint is connected to the output shaft, and several leaf springs are arranged between the outer edge of the inner ring and the outer ring. Some of the leaf springs are connected to a cross-shaped Hooke hinge. Through the elastic deformation of the leaf springs between the inner and outer rings, it has a single rotational degree of freedom around the axial center. The resistance to linear deformation under axial force and the resistance to angular deformation under circumferential torsion of the flexible rotary joint are significantly different, with a functional difference in deformation resistance of up to 10 on the order of magnitude. 5 More than twice, the flexible rotary pair achieves relative torsion of the drive chain around its own axis through the bending deformation of its own elastic body, thereby completing the motion decoupling of the drive chain's torsional degree of freedom and axial translational degree of freedom around its own axis;
[0012] The rigid rotating pair is a backlash-free rigid bearing rotating mechanism based on a preload design. The axial preload force is applied through the preload structure to eliminate bearing clearance, and the rotational characteristics allow the drive chain to twist relative to itself around its own axis, thus completing motion decoupling.
[0013] Furthermore, the flexible rotary joint includes a cylindrical outer ring body. Several pairs of first leaf springs are arranged on the inner wall of the outer ring body. The first leaf springs are symmetrically distributed and extend towards the axial direction of the outer ring body and connect to form an annular connecting ring in the axial direction of the outer ring body. In addition, a second leaf spring is installed on the connecting ring between each pair of first leaf springs. The second leaf spring extends outward and is not connected to the outer ring body. When installing the flexible rotary joint, it is connected to the output shaft through the first connecting hole on the side wall of the outer ring body, and the second connecting hole on the second leaf spring is connected to the cross-shaped Hooke hinge.
[0014] Furthermore, the bearing types of the rigid rotating pair include angular contact ball bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings, and the structural forms include back-to-back angular contact ball bearing preload type, face-to-face angular contact ball bearing preload type, tapered roller bearing assembly preload type, needle roller bearing and thrust bearing combination preload type, and self-aligning roller bearing preload type.
[0015] Furthermore, the sliding pair includes a drive unit, a transmission mechanism, an actuating component, and a guiding mechanism; the actuating component is an output shaft, the drive unit outputs power and transmits it to the output shaft through the transmission mechanism, and the guiding mechanism is used to provide axial guidance and constrain the circumferential rotation of the output shaft, so that the output shaft can only move linearly along the axial direction, thereby achieving mechanical decoupling between the circumferential rotational degree of freedom and the axial translational degree of freedom.
[0016] Furthermore, the fully closed-loop detection unit includes a position detection component and a speed detection component. The position detection component is used to directly measure the actual displacement of the moving pair actuator; the speed detection component is used to detect the operating speed of the drive unit; the feedback signal of the speed detection component is used to suppress speed fluctuations of the drive unit, and the feedback signal of the position detection component is used to directly correct the displacement deviation of the actuator. The detection signals of both are synchronously fed back to the control system, together forming a position-speed fully closed-loop servo control architecture, which can compensate for transmission errors, thermal deformation errors and assembly gap errors in real time.
[0017] Furthermore, the drive unit of the sliding pair adopts a servo motor, the transmission mechanism adopts a ball screw, and the actuation component adopts an output shaft. The rotor of the servo motor is coaxially connected to the ball screw via a metal diaphragm coupling. One end of the ball screw is supported in the bearing housing by a bearing seat. The output shaft is rigidly connected to the screw nut on the ball screw. The external spline of the output shaft and the spline sleeve in the spline sleeve housing form a spline fit, which restricts the circumferential rotation of the output shaft and only allows it to move linearly along the axial direction, thus completing the mechanical decoupling of the sliding pair and the rotary pair.
[0018] Furthermore, the position detection component employs an absolute grating ruler and an absolute grating reading head; the absolute grating ruler 3-14 is fixed on the outer surface of the output shaft 3-10, with the grating ruler stripe direction parallel to the output shaft axis, and the absolute grating reading head is installed inside the moving pair. The absolute grating ruler and the absolute grating reading head work together to form a position detection unit, realizing the direct acquisition of the actual displacement of the output shaft.
[0019] Furthermore, the speed detection component employs an absolute encoder connected to the drive unit.
[0020] A method for positioning using a 6-UPRU high-precision positioning platform includes the following steps:
[0021] Choose between a flexible or rigid rotary pair depending on the application scenario;
[0022] Based on the target pose of the moving platform and the characteristic parameters of the selected revolute joint, the target lengths of the six drive chains are calculated through inverse kinematics. The drive unit drives the output shaft to move, and under the action of the guide mechanism, the output shaft can only move linearly along the axial direction. At the same time, the position detection component measures the actual displacement of the moving joint actuator. The speed detection component detects the running speed of the drive unit. The detection signals of both are synchronously fed back to the control system, which together form a position-speed fully closed-loop servo control architecture, which can compensate for transmission errors, thermal deformation errors and assembly clearance errors in real time.
[0023] During the spatial motion of the moving platform, the flexible rotating joint releases the torsional angle around the branch axis caused by the platform motion through its own elastic deformation, while the rigid rotating joint releases the torsional angle through the rotation of the backlash-free bearing. This achieves mechanical decoupling between the sliding joint and the rotating joint, avoids derivative motion, and simplifies the motion control logic.
[0024] The six drive chains work together to drive the platform to achieve precise positioning with six degrees of freedom, realizing high-precision positioning from submicron to nanometer level, and meeting the differentiated needs of various high-end precision manufacturing and testing scenarios.
[0025] Furthermore, the specific structural type of the rigid rotating pair is selected based on the load, stiffness, and space requirements.
[0026] The beneficial technical effects of this invention are as follows:
[0027] 1. The dual rotary joint configuration of this invention can be precisely adapted to different application scenarios. The flexible rotary joint, with its integrated molding structure and frictionless and gapless characteristics, avoids accuracy deviations caused by low-speed "creeping" and wear, and is easy to assemble and cost-effective. The rigid rotary joint eliminates gaps through pre-tightening design, taking into account both high load-bearing capacity and high dynamic response characteristics, and meeting the large stroke application requirements under different load conditions. The sliding joint and the two rotary joints work together to decouple the single-leg motion, simplify the kinematic model, eliminate additional errors, and improve motion transmission accuracy. The single-leg "position-velocity" dual closed-loop servo control ensures controllable errors and guarantees the stability of positioning accuracy through speed loop stabilization and position loop offset compensation.
[0028] 2. The 6-UPRU high-precision positioning platform provided by this invention has the characteristics of wide positioning accuracy coverage, compact structure, strong dynamic response adaptability, high long-term operation stability, and convenient installation. Through the integrated solution of dual configuration adaptation and motion control compensation, it meets the differentiated needs of various precision manufacturing and testing scenarios with submicron to nanometer precision requirements. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the overall structure of the 6-UPRU high-precision positioning platform provided in an embodiment of the present invention;
[0030] Figure 2 This is a schematic diagram of the driving branch structure provided in an embodiment of the present invention;
[0031] Figure 3 A schematic cross-sectional view of the drive branch (flexible rotating pair configuration) provided in an embodiment of the present invention;
[0032] Figure 4 A schematic cross-sectional view of the drive chain (rigid revolute joint configuration) provided in an embodiment of the present invention;
[0033] Figure 5 This is a schematic diagram of the static platform structure provided in an embodiment of the present invention;
[0034] Figure 6(a) is a schematic diagram of the flexible rotating pair structure provided in Embodiment 2 of the present invention;
[0035] Figure 6(b) is a schematic diagram of the flexible rotating pair structure provided in Embodiment 2 of the present invention;
[0036] Figure 7 This is a schematic cross-sectional view of a rigid rotating pair provided in Embodiment 2 of the present invention. Detailed Implementation
[0037] The following description, in conjunction with the accompanying drawings, provides a clearer and more complete account of a 6-UPRU high-precision positioning platform and positioning method provided by the present invention:
[0038] Example 1
[0039] This embodiment provides a 6-UPRU (where U represents a Hooke joint, P represents a prismatic joint, and R represents a revolute joint) high-precision positioning platform. The positioning platform includes a static platform 1, a moving platform 2, six identical drive chains 3 arranged symmetrically in space, and a cross-shaft Hooke joint 4. The specific assembly relationship and working principle of each component are as follows:
[0040] like Figure 1 , 5 As shown, both the static platform 1 and the moving platform 2 are integrally machined from high-strength aluminum alloy. All hinge points used to connect the cross-axis Hooke hinge 4 are evenly distributed along the circumference in three sets of two-point symmetrical arrangements to ensure the platform's force balance and motion stability. Both ends of the drive chain are connected to the static platform 1 and the moving platform 2 respectively through the cross-axis Hooke hinge 4.
[0041] Both the static platform 1 and the moving platform 2 are equipped with cylindrical connecting keys 1-1. The cylindrical connecting keys 1-1 are evenly distributed around the circumference in three groups of two-point symmetrical arrangement. The cross shaft of the cross-axis Hooke hinge 4 is fixedly connected to the static platform 1 and the moving platform 2 through the cylindrical connecting keys 1-1, realizing a reliable connection between the drive chain 3 and the platform. The static platform 1 is also equipped with a wire interface fixing platform 1-2, which is used to organize the cable of the drive chain 3 and avoid cable entanglement or interference during movement. The positioning platform is fixed to the external base through the mounting holes at the bottom of the static platform 1 to ensure the stability of the overall installation.
[0042] The drive chain includes a sliding joint and a rotating joint, with the following connection relationship: the sliding joint is connected to the stationary platform through a cross-shaped Hooke joint, one end of the rotating joint is connected to the sliding joint, and the other end is connected to the moving platform through a cross-shaped Hooke joint. The rotating joint can be a flexible rotating joint or a rigid rotating joint. Each drive chain integrates a fully closed-loop detection unit.
[0043] Specifically, the sliding pair includes a drive unit, a transmission mechanism, an actuator, and a guide mechanism; the actuator is an output shaft, the drive unit outputs power and transmits it to the output shaft through the transmission mechanism, and the guide mechanism is used to provide axial guidance and constrain the circumferential rotation of the output shaft, so that the output shaft can only move linearly along the axial direction, thereby achieving mechanical decoupling between the circumferential rotational degree of freedom and the axial translational degree of freedom.
[0044] The revolute joint is configured with two independent technical solutions to adapt to different practical application scenarios. One of them is a flexible revolute joint solution, which adopts an integrated elastic structure of 'inner ring-leaf spring-outer ring', integrally formed from high-strength alloy. The overall structure is symmetrically distributed. The outer ring of the flexible revolute joint is connected to the output shaft, and several leaf springs are set between the outer edge of the inner ring and the outer ring. Some leaf springs are connected to a cross-shaft Hooke hinge. Through the elastic deformation of the leaf springs between the inner and outer rings, it only has a single rotational degree of freedom around the axial center. This flexible revolute joint achieves relative torsion of the drive chain around its own axis through the bending deformation of its own elastic body, thereby completing the motion decoupling of the drive chain's torsional degree of freedom and axial translational degree of freedom around its own axis. Its motion process has no mechanical contact friction and no backlash, which can effectively avoid the wear problem and creep phenomenon that are common in rigid kinematic pairs. Meanwhile, this flexible rotary pair possesses structural characteristics of high axial stiffness and low circumferential stiffness. Specifically, under typical working conditions, its resistance to linear deformation under axial force differs significantly from its resistance to angular deformation under circumferential torsion, with a functional difference in deformation resistance of up to 10 on the order of magnitude. 5 This design, with a speed of over 10 times, ensures structural stability under axial loads while enabling low-resistance, flexible circumferential torsion. It balances platform load-bearing stability with torsional flexibility. The integrated structural design significantly simplifies assembly, reduces installation complexity and manufacturing costs, and provides structural support for extending positioning accuracy to the nanometer level. It is suitable for applications with stringent positioning accuracy requirements (nanometer-level precision), long-term high-precision stability, clear cost control needs, and moderate load and workspace requirements. Another option is a rigid rotating pair solution. This rigid rotating pair is a backlash-free rigid rotating mechanism based on a preload design. Its core uses a preload structure to apply axial preload force to eliminate bearing clearance. Bearing types include, but are not limited to, angular contact ball bearings. Tapered roller bearings, needle roller bearings, and self-aligning roller bearings, among others, come in structural forms including but not limited to back-to-back angular contact ball bearings with preload, face-to-face angular contact ball bearings with preload, tapered roller bearing assemblies with preload, needle roller bearings combined with thrust bearings with preload, and self-aligning roller bearings with preload. They achieve zero-travel rotation through the rigid rotational characteristics of the bearings, exhibiting high load capacity, high rigidity, and high dynamic response. Their rotational characteristics allow for relative torsion of the drive chain around its own axis, achieving motion decoupling. The overall structure possesses high load capacity, high rigidity, and rapid motion response, enabling the transmission of large axial loads and torques. They are suitable for applications requiring sub-micron level or similar positioning accuracy, higher load capacity, larger working space, and rapid dynamic response.
[0045] The drive chain integrates a fully closed-loop detection unit, which includes a position detection component and a speed detection component. The position detection component is used to directly measure the actual displacement of the moving pair actuator; the speed detection component is used to detect the operating speed of the drive unit. The feedback signal from the speed detection component is used to suppress speed fluctuations of the drive unit, and the feedback signal from the position detection component is used to directly correct the displacement deviation of the actuator. The detection signals of both are synchronously fed back to the control system, together forming a position-speed fully closed-loop servo control architecture, which can compensate for transmission errors, thermal deformation errors, and assembly gap errors in real time, ensuring high-precision positioning stability under different configurations from the motion control compensation level.
[0046] Example 2
[0047] This embodiment provides a 6-UPRU (where U is a Hooke joint, P is a prismatic joint, and R is a revolute joint) high-precision positioning platform, including a static platform 1, a moving platform 2, six identical drive chains 3 arranged symmetrically in space, and a cross-shaft Hooke joint 4. The specific assembly relationship and working principle of each component are as follows:
[0048] like Figure 1 , 5 As shown, both the static platform 1 and the moving platform 2 are integrally machined from high-strength aluminum alloy. All hinge points used to connect the cross-axis Hooke hinge 4 are evenly distributed along the circumference in three sets of two-point symmetrical arrangements to ensure the platform's force balance and motion stability. Both ends of the drive chain are connected to the static platform 1 and the moving platform 2 respectively through the cross-axis Hooke hinge 4.
[0049] Both the static platform 1 and the moving platform 2 are equipped with cylindrical connecting keys 1-1. The cylindrical connecting keys 1-1 are evenly distributed around the circumference in three sets of two-point symmetrical arrangements. The cross shaft of the cross-axis Hooke hinge 4 is fixedly connected to the static platform 1 and the moving platform 2 through the cylindrical connecting keys 1-1, realizing a reliable connection between the drive chain 3 and the platform. The static platform 1 is also equipped with a wire interface fixing platform 1-2, which is used to organize the cables of the drive chain 3 and avoid cable tangling or interference during movement. The positioning platform is fixed to the external base through the mounting holes at the bottom of the static platform 1 to ensure the stability of the overall installation.
[0050] The drive chain includes a sliding joint and a rotating joint, with the following connection relationship: the sliding joint is connected to the stationary platform through a cross-shaped Hooke joint, one end of the rotating joint is connected to the sliding joint, and the other end is connected to the moving platform through a cross-shaped Hooke joint. The rotating joint can be a flexible rotating joint or a rigid rotating joint. Each drive chain integrates a fully closed-loop detection unit.
[0051] Specifically, such as Figure 2As shown, each drive chain 3 is a layered rigid shell structure, which includes, from bottom to top, a motor mounting shell 3-1, an intermediate support shell 3-2, a bearing seat mounting shell 3-3, and a spline sleeve mounting shell 3-4. Each shell is rigidly connected by screws evenly distributed along the circumference. The positioning reference surface is precision ground to ensure that the coaxiality and perpendicularity errors of each shell meet the design requirements after assembly.
[0052] In this embodiment, the driving unit of the sliding pair adopts a servo motor, the transmission mechanism adopts a ball screw, the actuating component adopts an output shaft, and the guiding mechanism adopts a spline fit structure; the driving unit outputs power to the output shaft through the transmission mechanism, and the guiding mechanism is used to provide axial guidance and constrain the circumferential rotation of the output shaft, so that the output shaft can only move linearly along the axial direction, realizing the mechanical decoupling of the circumferential rotational degree of freedom and the axial translational degree of freedom; specifically, as shown in... Figure 3 As shown, the servo motor 3-5 is fixedly installed in the motor mounting housing 3-1 by screws. The rotor of the servo motor 3-5 is coaxially connected to the ball screw 3-8 via a metal diaphragm coupling 3-7. The metal diaphragm coupling 3-7 can effectively compensate for the coaxiality error between the servo motor 3-5 and the ball screw 3-8, and reduce vibration and error transmission during the transmission process. One end of the ball screw 3-8 is supported on the bearing housing 3-3 via the bearing seat 3-9. It adopts a back-to-back mounting method of angular contact ball bearings to bear the axial load of the drive chain 3 and ensure the stability of the ball screw 3-8 when rotating at high speed. The output shaft 3-10 is provided with an internal threaded hole. The screw passes through the screw nut of the ball screw 3-8 and engages with the internal threaded hole to realize the rigid connection between the screw nut and the output shaft 3-10. The external spline of the output shaft 3-10 and the spline sleeve in the spline sleeve mounting housing 3-4 form a high-precision spline engagement. This engagement strictly constrains the circumferential rotation of the output shaft 3-10, allowing it to only move linearly along the axial direction, thus completing the mechanical decoupling of the sliding pair and the rotary pair.
[0053] When a flexible rotating joint is used for assembly, the output shaft 3-10 has a stepped locating shoulder at its end. This shoulder is used to axially limit and coaxially position the flexible rotating joint 3-11a, preventing it from moving axially along the output shaft and ensuring precise alignment with the output shaft axis, thus avoiding eccentricity affecting the motion decoupling accuracy. A screw passes through the internal threaded hole of the flexible rotating joint 3-11a and the output shaft 3-10, and combined with the positioning and load-bearing function of the shoulder, a reliable rigid fixation is achieved between the flexible rotating joint 3-11a and the output shaft 3-10. The flexible rotating joint 3-11a is connected in series with the sliding joint and the upper cross-shaped Hooke hinge 4. In this embodiment, the flexible rotating pair is shown in Figures 6(a) and 6(b). The flexible rotating pair includes a cylindrical outer ring 11-1. Several pairs of first leaf springs 11-2 are arranged on the inner wall of the outer ring. The first leaf springs are symmetrically distributed and extend towards the axial direction of the outer ring and connect to form an annular connecting ring 11-3 in the axial direction of the outer ring. In addition, a second leaf spring 11-4 is installed on the connecting ring between each pair of first leaf springs. The second leaf spring extends outward and is not connected to the outer ring. When installing the flexible rotating pair, it passes through the first connecting hole 11-5 on the side wall of the outer ring. Connected to the output shaft, the second connecting hole 11-6 on the second leaf spring is connected to the cross-shaped Hooke hinge. The flexible rotating pair in this embodiment is integrally machined from a high-strength alloy and is an elastic motion unit that rotates purely around a single axis. Rotation is achieved by the bending deformation of the overall elastic body through the deformation of the first leaf spring and / or the rotation of the second leaf spring. There is no mechanical friction or backlash during the motion process. Its axial high stiffness and circumferential low stiffness structural characteristics allow the drive chain 3 to rotate relative to itself around its own axis, avoiding the torsional stress from being transmitted to the involute spline pair, preventing the tooth surface from jamming or wearing, and thus avoiding the positioning platform from jamming.
[0054] like Figure 4 As shown, when a rigid rotating pair is used for assembly, the end of the output shaft 3-10 is fixed to the rigid rotating pair 3-11b by an interference fit; the corresponding rigid rotating pair structure type can be selected according to the actual scenario, such as... Figure 7As shown, in this embodiment, the rigid rotating pair uses a back-to-back angular contact ball bearing A. The end of the output shaft 3-10 is fixed to the inner ring of the bearing in the rigid rotating pair 3-11b via an interference fit. The outer ring of the bearing is transition-fitted to the mounting base. A preload is applied axially through the preload structure 3-15 to completely eliminate bearing clearance. The specific preload structure form is not limited; the core is to completely eliminate the clearance between the bearing rolling elements and the inner and outer rings, achieving rigid rotation without backlash. The rigid rotating pair 3-11b is connected in series between the sliding pair and the upper cross-shaft Hooke hinge 4. The relative torsion of the drive chain 3 around its own axis is achieved through the backlash-free rotation of the bearing. It has high load-bearing capacity and fast response characteristics, and is suitable for scenarios with positioning accuracy requirements at the sub-micron level or similar, high load, and large stroke.
[0055] like Figure 4 As shown, each drive branch 3 integrates a fully closed-loop detection unit, which includes a position detection component and a speed detection component. The position detection component is used to directly measure the actual displacement of the moving pair actuator. In this embodiment, the position detection component uses an absolute grating ruler 3-14 and an absolute grating reading head 3-13. The speed detection component is used to detect the running speed of the drive unit. In this embodiment, the speed detection component uses an absolute encoder 3-6 coaxially connected to the servo motor. The spline sleeve mounting housing 3-4 is bolted to the outside of a precision-ground L-shaped adapter plate 3-12, on which the absolute grating reading head 3-13 is mounted. The outer surface of the output shaft 3-10 is precision-ground and then attached to... An absolute grating ruler 3-14 is attached, with its stripe direction parallel to the axis of the output shaft 3-10. High-precision positioning reference surfaces and specialized fixtures ensure installation accuracy. Together, they form a position detection unit, enabling direct acquisition of the actual displacement of the output shaft 3-10. An absolute encoder 3-6 is mounted on the tail of the servo motor 3-5 via a flange. The input shaft of the absolute encoder 3-6 is coaxially connected to the rotor of the servo motor 3-5, forming a speed detection unit. Signals from both the position and speed detection units are fed back to the control system, forming a position-speed closed-loop servo control system. This system can compensate in real time for thermal expansion, pitch error, and transmission chain deformation of the ball screw 3-8, ensuring stable positioning accuracy under both rotary pair configurations.
[0056] The working principle of this invention is as follows: During use, the corresponding rotary pair configuration (flexible rotary pair 3-11a or rigid rotary pair 3-11b) is selected according to the application scenario. The rigid rotary pair 3-11b can be further selected based on load, stiffness, and space requirements, including but not limited to back-to-back angular contact ball bearing preload type, face-to-face angular contact ball bearing preload type, tapered roller bearing assembly preload type, needle roller bearing and thrust bearing combination preload type, self-aligning roller bearing preload type, etc.). The 6-UPRU high-precision positioning platform is fixed to the external base via the static platform 1, and then... The control system first calculates the target lengths of the six drive chains 3 using inverse kinematics based on the target pose of the moving platform 2 and the characteristic parameters of the selected revolute joint. Then, the servo motor 3-5 drives the ball screw 3-8 to rotate, converting the rotational motion into high-rigidity linear motion of the output shaft 3-10 under the guidance and constraint of a high-precision involute spline joint. Simultaneously, the absolute grating ruler 3-14 and the absolute grating reading head 3-13 detect the actual displacement of the output shaft 3-10 in real time, combined with the speed signal of the servo motor 3-5 fed back by the absolute encoder 3-6. This constitutes a single-leg fully closed-loop control system, which corrects the pitch error of the ball screw 3-8, transmission chain deformation, and thermal expansion in real time. During the spatial movement of the moving platform 2, the flexible rotary joint 3-11a releases the torsional angle around the branch axis caused by the platform movement through its own elastic deformation, while the rigid rotary joint 3-11b releases the torsional angle through the rotation of the zero-backlash bearing. This avoids the involute spline guide joint from bearing to bear excessive torsional constraint stress, and effectively suppresses the low-speed "creeping" phenomenon (flexible configuration) or ensures high dynamic response characteristics (rigid configuration). This achieves mechanical decoupling between the single-leg sliding joint and the rotary joint, avoiding derivative motion. The motion control logic is simplified; ultimately, the six drive chains 3 work together to drive the drive platform 2 to achieve precise positioning of six degrees of freedom. Through the flexible adaptation of dual configurations and rigid rotating pairs with multiple structures and bearing types, the adaptable bearing types include, but are not limited to, angular contact ball bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings. The corresponding preload configurations include, but are not limited to, back-to-back angular contact ball bearing preload type, face-to-face angular contact ball bearing preload type, tapered roller bearing group preload type, and needle roller bearing and thrust bearing combination preload type, etc., to meet the accuracy, load and response speed requirements in different scenarios.
[0057] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.
Claims
1. A 6-UPRU high-precision positioning platform, characterized in that, The positioning platform includes a static platform, a moving platform, and six identical drive chains that are spatially symmetrically distributed. Both ends of each drive chain are connected to the static platform and the moving platform respectively via a cross-shaped Hooke hinge. The drive chain includes a sliding joint and a rotating joint. The sliding joint is connected to the stationary platform via a cross-shaped Hooke joint. One end of the rotating joint is connected to the sliding joint, and the other end is connected to the moving platform via a cross-shaped Hooke joint. The rotating joint can be a flexible rotating joint or a rigid rotating joint. Each drive chain integrates a fully closed-loop detection unit. The flexible rotary joint is an integrated elastic structure of inner ring, leaf spring, and outer ring, with a symmetrical overall distribution. The outer ring of the flexible rotary joint is connected to the output shaft, and several leaf springs are arranged between the outer edge of the inner ring and the outer ring. Some of the leaf springs are connected to a cross-shaped Hooke hinge. Through the elastic deformation of the leaf springs between the inner and outer rings, it has a single rotational degree of freedom around the axial center. The resistance to linear deformation under axial force and the resistance to angular deformation under circumferential torsion of the flexible rotary joint are significantly different, with a functional difference in deformation resistance of up to 10 on the order of magnitude. 5 More than twice, the flexible rotary pair achieves relative torsion of the drive chain around its own axis through the bending deformation of its own elastic body, thereby completing the motion decoupling of the drive chain's torsional degree of freedom and axial translational degree of freedom around its own axis; The rigid rotating pair is a backlash-free rigid bearing rotating mechanism based on a preload design. The axial preload force is applied through the preload structure to eliminate bearing clearance, and the rotational characteristics allow the drive chain to twist relative to itself around its own axis, thus completing motion decoupling.
2. The 6-UPRU high-precision positioning platform according to claim 1, characterized in that, The flexible rotary joint includes a cylindrical outer ring body. Several pairs of first leaf springs are arranged on the inner wall of the outer ring body. The first leaf springs are symmetrically distributed and extend towards the axis of the outer ring body and connect to form an annular connecting ring in the axis of the outer ring body. In addition, a second leaf spring is installed on the connecting ring between each pair of first leaf springs. The second leaf spring extends outward and is not connected to the outer ring body. When installing the flexible rotary joint, it is connected to the output shaft through the first connecting hole on the side wall of the outer ring body, and the second connecting hole on the second leaf spring is connected to the cross-shaped Hooke hinge.
3. The 6-UPRU high-precision positioning platform according to claim 1, characterized in that, The bearing types of the rigid rotating pairs include angular contact ball bearings, tapered roller bearings, needle roller bearings, and self-aligning roller bearings. The structural forms include back-to-back angular contact ball bearing preload type, face-to-face angular contact ball bearing preload type, tapered roller bearing assembly preload type, needle roller bearing and thrust bearing combination preload type, and self-aligning roller bearing preload type.
4. The 6-UPRU high-precision positioning platform according to claim 1, characterized in that, The sliding pair includes a drive unit, a transmission mechanism, an actuator, and a guide mechanism; the actuator is an output shaft, and the drive unit outputs power to the output shaft via the transmission mechanism. The guide mechanism is used to provide axial guidance and constrain the circumferential rotation of the output shaft, so that the output shaft can only move linearly along the axial direction, thereby achieving mechanical decoupling between the circumferential rotational degree of freedom and the axial translational degree of freedom.
5. A 6-UPRU high-precision positioning platform according to claim 4, characterized in that, The fully closed-loop detection unit includes a position detection component and a speed detection component. The position detection component is used to directly measure the actual displacement of the moving pair actuator; the speed detection component is used to detect the operating speed of the drive unit. The feedback signal from the speed detection component is used to suppress speed fluctuations of the drive unit, and the feedback signal from the position detection component is used to directly correct the displacement deviation of the actuator. The detection signals of both are synchronously fed back to the control system, together forming a position-speed fully closed-loop servo control architecture, which can compensate for transmission errors, thermal deformation errors, and assembly gap errors in real time.
6. A 6-UPRU high-precision positioning platform according to claim 4, characterized in that, The drive unit of the sliding pair adopts a servo motor, the transmission mechanism adopts a ball screw, and the actuation component adopts an output shaft. The rotor of the servo motor is coaxially connected to the ball screw via a metal diaphragm coupling. One end of the ball screw is supported in the bearing housing by a bearing seat. The output shaft is rigidly connected to the screw nut on the ball screw. The external spline of the output shaft and the spline sleeve in the spline sleeve housing form a spline fit, which restricts the circumferential rotation of the output shaft and only allows it to move linearly along the axial direction, thus completing the mechanical decoupling of the sliding pair and the rotary pair.
7. A 6-UPRU high-precision positioning platform according to claim 5, characterized in that, The position detection component uses an absolute grating ruler and an absolute grating reading head. The absolute grating ruler 3-14 is fixed on the outer surface of the output shaft 3-10, and the stripe direction of the grating ruler is parallel to the axis of the output shaft. The absolute grating reading head is installed inside the moving pair. The absolute grating ruler and the absolute grating reading head work together to form a position detection unit, realizing the direct acquisition of the actual displacement of the output shaft.
8. A 6-UPRU high-precision positioning platform according to claim 5, characterized in that, The speed detection component uses an absolute encoder connected to the drive unit.
9. A method for positioning using a 6-UPRU high-precision positioning platform according to any one of claims 2-8, characterized in that, Includes the following steps: Choose between a flexible or rigid rotary pair depending on the application scenario; Based on the target pose of the moving platform and the characteristic parameters of the selected revolute joint, the target lengths of the six drive chains are calculated by inverse kinematics. The drive unit drives the output shaft to move. Under the action of the guide mechanism, the output shaft can only move linearly along the axial direction. At the same time, the position detection component measures the actual displacement of the moving pair actuator; the speed detection component detects the running speed of the drive unit. The detection signals of both are synchronously fed back to the control system, which together form a position-speed fully closed-loop servo control architecture, which can compensate for transmission errors, thermal deformation errors and assembly gap errors in real time. During the spatial motion of the moving platform, the flexible rotating joint releases the torsional angle around the branch axis caused by the platform motion through its own elastic deformation, while the rigid rotating joint releases the torsional angle through the rotation of the backlash-free bearing. This achieves mechanical decoupling between the sliding joint and the rotating joint, avoids derivative motion, and simplifies the motion control logic. The six drive chains work together to drive the platform to achieve precise positioning with six degrees of freedom, realizing high-precision positioning from submicron to nanometer level, and meeting the differentiated needs of various high-end precision manufacturing and testing scenarios.
10. A method for positioning using a 6-UPRU high-precision positioning platform according to claim 9, characterized in that, The specific structural type of the rigid rotating pair is selected based on the load, stiffness, and space requirements.