Linear drive and six degrees of freedom platform

Abstract

The application provides a linear driver, an upstream shaft section of a rotating shaft is used as an output shaft of a rotating motor, a downstream shaft section of the rotating shaft is used as a screw shaft of a screw nut pair, and a plurality of position sensors are arranged between an extension of a motor housing and a nut.The linear driver of the application directly obtains the displacement between the motor housing and the nut through the position sensors between the extension and the nut, thereby greatly improving the displacement output control precision of the linear driver.The application also provides a six-degree-of-freedom platform, a base and a moving platform are connected through the linear driver to drive the moving platform.The six-degree-of-freedom platform of the application uses the linear driver with high-precision displacement output as a supporting leg to drive the moving platform, thereby improving the motion and positioning precision of the platform.

Description

Technical Field

[0001] The present invention relates to the technical field of precision instruments, and specifically relates to a linear driver and a six-degree-of-freedom platform. Background Art

[0002] A linear driver is an actuator that converts the rotational motion of a motor into linear motion through an internal precision mechanism. Most common linear drivers use ball screws to output displacement, while in application scenarios with high precision and small lead, a transmission mechanism with higher precision is required. The displacement output control accuracy of a linear driver depends not only on the displacement accuracy of the transmission mechanism itself, but also on the measurement accuracy of the displacement detection unit matched with the transmission mechanism. For example, in the solution disclosed in the patent "A Micro-lead Differential Planetary Roller Screw and Electric Cylinder" (WO2025228296A1), a differential planetary roller screw is adopted as the internal transmission mechanism, and the displacement accuracy of the screw can reach the sub-micron level or even the nanometer level. However, in the above solution, only a single linear sensor is provided to measure the output position of the differential planetary roller screw. The linear sensor is composed of components such as a grating ruler and a reading head, and its measurement process is subject to interference from factors such as vibration and thermal expansion, resulting in accuracy loss, which cannot match the high-precision measurement requirement of the differential planetary roller screw, leading to insufficient displacement control accuracy of the electric cylinder. Summary of the Invention

[0003] The objective of the present invention is to provide a linear driver to improve the measurement and control accuracy of its displacement output.

[0004] Another objective of the present invention is to provide a six-degree-of-freedom platform, which improves the motion and positioning accuracy of the platform by increasing the displacement driving accuracy of its support legs.

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

[0006] A linear driver is provided with a rotating shaft in a cylinder body. The upstream shaft section of the rotating shaft serves as the output shaft of the rotary motor, and the downstream shaft section of the rotating shaft serves as the screw shaft of the screw-nut pair. The shaft body of the downstream shaft section is sleeved with rollers and a nut in sequence along the radial direction. The downstream end face of the motor housing extends to the outer side of the peripheral wall of the nut to form an extension portion, and at least two sets of position sensors are arranged between the inner wall surface of the extension portion and the outer wall surface of the nut, and the position sensors are arranged at intervals along the circumferential direction and / or the axial direction of the nut.

[0007] A six-degree-of-freedom platform is provided with the above-mentioned linear driver between a base and a moving platform to drive the moving platform.

[0008] The linear actuator of the present invention mainly obtains the displacement between the motor housing and the nut directly by combining the position sensor between the extension and the nut through differential measurement. The differential measurement method greatly improves the measurement accuracy, making it match the displacement output accuracy of the high-precision lead screw and nut pair, thereby improving the displacement output control accuracy of the entire linear actuator.

[0009] The six-degree-of-freedom platform of the present invention mainly uses the linear actuator with high-precision displacement output as a support leg to drive the moving platform, thereby improving the motion and positioning accuracy of the platform. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a linear actuator;

[0011] Figure 2 A cross-sectional view of the first embodiment of the linear driver;

[0012] Figure 3 A cross-sectional view of another embodiment of a linear drive;

[0013] Figure 4 A schematic diagram of a six-degree-of-freedom platform after removing some linear actuators. Detailed Implementation

[0014] See Figures 1-3 The linear actuator shown has a rotating shaft 10 inside the cylinder. The upstream shaft section 11 of the rotating shaft 10 serves as the output shaft of the rotary motor 20, and the downstream shaft section 13 of the rotating shaft 10 serves as the lead screw shaft of the lead screw and nut assembly 30. Rollers 31 and nuts 32 are sequentially mounted on the shaft body of the downstream shaft section 13 in the radial direction. The downstream end face of the motor housing 21 extends to the outer side of the circumferential wall of the nut 32 to form an extension 211. At least two sets of position sensors 40 are provided between the inner wall surface of the extension 211 and the outer wall surface of the nut 32. The position sensors 40 are arranged at intervals along the circumference and / or axial direction of the nut 32.

[0015] In the above scheme, the shaft end of the rotating shaft 10 adjacent to the rotary motor 20 is defined as the upstream end. The rotary motor 20 and the lead screw and nut assembly 30 share a rotating shaft 10. The rotary motor 20 includes a rotor 23 mounted on the upstream shaft section 11 and a stator 22 mounted on the inner wall of the motor housing 21. The downstream end of the upstream shaft section 11 is provided with a radial bearing 111 arranged adjacent to it. The motor housing 21 and the nut 32 avoid each other. The motor housing 21 serves as the fixed end of the linear actuator, and the nut 32 serves as the output end of the linear actuator. The position sensor 40 measures the axial displacement relationship between the motor housing 21 and the nut 32. It is important to note that the displacement relationship between the motor housing 21 and the nut 32 is affected by factors such as temperature drift, vibration, and electromagnetic interference, resulting in sub-micron or nanometer-level differences from the theoretically calculated values. The displacement data measured by at least two sets of position sensors 40 in this solution undergoes differential calculation, eliminating common-mode errors caused by these factors. The measured distance change data between the motor housing 21 and the nut 32 effectively compensates for errors caused by lead screw backlash, pitch error, and elastic deformation, directly yielding the axial output distance of the linear actuator. Its measurement accuracy matches the displacement output accuracy of the high-precision lead screw and nut pair 30, significantly improving displacement measurement accuracy, anti-interference capability, and long-term operational stability, thereby truly achieving sub-micron and nanometer-level output control of the linear actuator. Furthermore, the rotary motor 20 and the lead screw and nut pair 30 share a common shaft 10, resulting in a compact structure, small space occupation, shortened transmission chain length, reduced transmission backlash and error accumulation caused by component installation, and improved dynamic response speed and transmission efficiency.

[0016] To ensure the displacement accuracy of the transmission mechanism, the lead screw and nut assembly 30 is a differential planetary roller lead screw, and the rollers 31 are a planetary roller assembly. This solution not only meets the nanometer-level output positioning requirements of the linear actuator but also possesses a large load-bearing capacity, making it suitable for a wide range of applications.

[0017] As a preferred option, such as Figure 3 As shown, the downstream end face of the extension 211 is adjacent to the upstream end face of the nut 32. The position sensor 40 includes a first component 41 disposed on the downstream end face of the extension 211 and a second component 42 disposed on the outer wall of the upstream end of the nut 32. The position sensors 40 are arranged at intervals along the circumference of the nut 32. In the above scheme, the first component 41 and the second component 42 are arranged adjacently at intervals. In this embodiment, the position sensor 40 preferably adopts a grating ruler assembly, wherein the first component 41 is a reading head and the second component 42 is a grating ruler. Preferably, two sets of position sensors 40 are provided, symmetrically arranged relative to the axis of rotation 10. Specifically, the first component 41 and the second component 42 of the two sets of position sensors 40 are respectively symmetrically arranged relative to the axis of rotation 10, which is beneficial to simplify the differential measurement algorithm and ensure measurement accuracy.

[0018] As another preferred option, such as Figure 2 As shown, the downstream end face of the extension 211 is adjacent to the downstream end face of the nut 32, and the position sensors 40 are arranged at intervals along the axial direction. In the above scheme, the position sensors 40 are disposed at both ends of the outer wall of the nut 32 along the axial direction. The nut 32 is inserted into the cavity enclosed by the extension 211, and the downstream end of the nut 32 is exposed at the opening of the downstream end of the extension 211 to avoid interference between the extension 211 and the output end of the linear driver. The position sensors 40 in this scheme have a large installation space, and the installation position can be freely selected. In addition to being arranged at intervals along the axial direction of the nut 32, they can also be arranged at intervals along the circumferential direction of the outer wall of the nut 32, or simultaneously arranged at intervals along its axial and circumferential directions. Adjusting the algorithm can meet the differential measurement requirements of the position sensors 40.

[0019] Preferred, such as Figure 2 As shown, a linear guide assembly or linear bearing 212 is provided between the inner wall of the extension 211 and the outer peripheral wall of the nut 32 to form an axial guiding fit, and the linear guide assembly or linear bearing 212 avoids the mounting position of the position sensor 40. Figure 2 The embodiment shown uses a linear bearing 212 to convert sliding friction into rolling friction, achieving a low-friction, high-rigidity linear guiding fit between the motor housing 21 and the nut 32.

[0020] More specifically, a bottom end cap 321 is provided on the downstream end face of the nut 32, and the downstream shaft segment 13 is located within the area enclosed by the nut 32 and the bottom end cap 321. A differential sensor 50 for measuring the axial displacement of the downstream end face of the rotating shaft 10 is provided on the inner bottom surface of the bottom end cap 321 adjacent to the downstream shaft end of the downstream shaft segment 13. The differential sensor 50 has at least 3 sets of probes, and the probes are evenly distributed circumferentially along the projection contour of the rotating shaft 10 on the bottom end cap 321.

[0021] In the above scheme, the probe of the differential sensor 50 is preferably a capacitive sensor or an eddy current sensor. The measurement data of each probe can be combined to obtain differential data of the axial distance between its measuring end face and the downstream shaft end face of the downstream shaft segment 13. The radial eccentricity and tilt angle data of the rotating shaft 10 can also be measured through differential calculation. That is to say, the differential sensor 50 can simultaneously measure the position and attitude of the rotating shaft 10 in the linear actuator, and form a closed loop with the measurement data of the position sensor 40, making the measurement data more comprehensive and accurate. In addition, as another embodiment, such as... Figure 3 As shown, an upstream position sensor 80 is also provided on the inner wall of the motor housing 21 adjacent to the upstream shaft end of the upstream shaft section 11. The upstream position sensor 80 is linked with the measurement data of the differential sensor 50 to further improve the measurement accuracy of the rotating shaft 10.

[0022] To further improve measurement accuracy, an encoder or circular grating sensor 70 is also provided on the shaft of the rotating shaft 10. Preferably, the encoder or circular grating sensor 70 is located at the upstream end of the upstream shaft segment 11. The encoder or circular grating sensor 70 is used to detect the rotation angle of the rotating shaft 10. Its rotation angle measurement data is combined with the axial displacement data obtained by differential measurement by the position sensor 40 to form a high-precision closed-loop feedback, thereby further improving the displacement control accuracy of the linear actuator.

[0023] As a preferred embodiment, a gearbox 122 is provided at the downstream end of the upstream shaft segment 11, and the gearbox 122 is connected to the downstream shaft segment 13 via a coupling 123. Machining a single, continuous shaft 10 is difficult and costly. Machining two shafts separately and connecting them into a shaft 10 via the coupling 123 significantly reduces the machining difficulty while ensuring the dimensional accuracy of the shaft 10. The gearbox 122 allows for easy adjustment of the output speed of the shaft 10, and when used with a differential planetary roller screw, it achieves speed compensation, compensates for differential transmission speed loss, and balances the accuracy and dynamic performance of the linear drive.

[0024] like Figure 2 As shown, the position sensor 40 includes a first component 41 disposed on the inner wall of the extension 211 and a second component 42 disposed on the outer wall of the nut 32. In this embodiment, the position sensor 40 is preferably a grating ruler assembly, wherein the first component 41 is a grating ruler and the second component 42 is a reading head, or the first component 41 is a reading head and the second component 42 is a grating ruler, the latter facilitating the fixing of the reading head's wiring harness to the extension 211.

[0025] Preferably, an electromagnetic brake assembly 90 is provided on the inner wall of the motor housing 21 adjacent to the upstream shaft end of the upstream shaft section 11. The electromagnetic brake assembly 90 enables the linear drive to lock when power is off, meeting the requirements of high safety performance scenarios.

[0026] The selection range for position sensor 40 and upstream position sensor 80 in this solution includes, in addition to the grating ruler assembly, laser interferometers, laser displacement sensors, spectral confocal sensors, capacitive sensors, eddy current sensors, LVDT differential displacement sensors, magnetic grating ruler assemblies, etc.

[0027] See Figure 4 The six-degree-of-freedom platform shown has a linear actuator, as described above, between the base 1 and the moving platform 2 to drive the moving platform 2.

[0028] A ball joint 213 is provided on the upstream outer end face of the motor housing 21 of the linear actuator and connected to the base 1. A Hooke joint or cross joint 323 is provided on the downstream outer end face of the nut 32 of the linear actuator and connected to the moving platform 2.

[0029] In the above scheme, the load-bearing capacity, rigidity, displacement resolution, and transmission accuracy of the linear actuator directly determine the positioning accuracy, dynamic performance, and operational reliability of the six-degree-of-freedom platform. This scheme, based on the transmission mechanism composed of the lead screw and nut pair 30, incorporates a differential measurement system composed of position sensors 40. This enables the overall positioning accuracy, stability, and anti-interference capability of the six-degree-of-freedom platform to reach the application level of semiconductor manufacturing equipment and precision optomechanical systems, truly achieving nanometer-level high-precision pose adjustment capabilities and broadening the high-precision application scenarios of the six-degree-of-freedom platform.

Claims

1. A linear driver, characterized in that: The cylinder body is provided with a rotating shaft (10). The upstream shaft section (11) of the rotating shaft (10) serves as the output shaft of the rotary motor (20), and the downstream shaft section (13) of the rotating shaft (10) serves as the lead screw shaft of the lead screw nut pair (30). The shaft body of the downstream shaft section (13) is fitted with rollers (31) and nuts (32) in sequence along the radial direction. The downstream end face of the motor housing (21) extends to the outer side of the circumferential wall of the nut (32) to form an extension (211). At least two sets of position sensors (40) are provided between the inner wall surface of the extension (211) and the outer wall surface of the nut (32). The position sensors (40) are arranged at intervals along the circumference or axial direction of the nut (32). The position sensors (40) measure the displacement data between the motor housing (21) and the nut (32) for differential calculation.

2. The linear driver according to claim 1, characterized in that: The lead screw and nut assembly (30) is a differential planetary roller lead screw, and the roller (31) is a planetary roller assembly.

3. The linear driver according to claim 1 or 2, characterized in that: The downstream end face of the extension (211) is adjacent to the upstream end face of the nut (32). The position sensor (40) includes a first component (41) disposed on the downstream end face of the extension (211) and a second component (42) disposed on the outer wall surface of the upstream end of the nut (32). The position sensors (40) are arranged at intervals along the circumference of the nut (32).

4. The linear driver according to claim 1 or 2, characterized in that: The downstream end face of the extension (211) is adjacent to the downstream end face of the nut (32), and the position sensors (40) are arranged axially at intervals.

5. The linear driver according to claim 1 or 2, characterized in that: A bottom end cap (321) is provided on the downstream end face of the nut (32). The downstream shaft segment (13) is located in the area enclosed by the nut (32) and the bottom end cap (321). A differential sensor (50) for measuring the axial displacement of the downstream end face of the rotating shaft (10) is provided on the inner bottom surface of the downstream shaft end adjacent to the downstream shaft segment (13) of the bottom end cap (321). At least three sets of probes of the differential sensor (50) are provided and the probes are evenly distributed circumferentially along the projection contour of the rotating shaft (10) on the bottom end cap (321).

6. The linear driver according to claim 1 or 2, characterized in that: A linear guide assembly or linear bearing (212) is provided between the inner wall of the extension (211) and the outer peripheral wall of the nut (32) to form an axial guiding fit, and the linear guide assembly or linear bearing (212) avoids the mounting position of the position sensor (40).

7. The linear driver according to claim 1 or 2, characterized in that: The shaft (10) is also equipped with an encoder or a circular grating sensor (70).

8. The linear driver according to claim 1 or 2, characterized in that: The downstream end of the upstream shaft segment (11) is provided with a gearbox (122), which is connected to the downstream shaft segment (13) via a coupling (123).

9. The linear driver according to claim 7, characterized in that: An encoder or circular grating sensor (70) is located at the upstream end of the upstream shaft segment (11).

10. The linear driver according to claim 1 or 2, characterized in that: An upstream position sensor (80) is also provided on the inner wall of the upstream shaft end of the upstream shaft section (11) adjacent to the motor housing (21).

11. The linear driver according to claim 4, characterized in that: The position sensor (40) includes a first component (41) disposed on the inner wall of the extension (211) and a second component (42) disposed on the outer wall of the nut (32).

12. The linear driver according to claim 1 or 2, characterized in that: An electromagnetic brake assembly (90) is provided on the inner wall of the motor housing (21) adjacent to the upstream shaft end of the upstream shaft section (11).

13. A six-degree-of-freedom platform, characterized in that: A linear actuator as described in any one of claims 1 to 12 is provided between the base (1) and the moving platform (2) to drive the moving platform (2).

14. The six-degree-of-freedom platform according to claim 13, characterized in that: A ball joint (213) is provided on the upstream outer end face of the motor housing (21) of the linear actuator and connected to the base (1). A Hooke joint or cross joint (323) is provided on the downstream outer end face of the nut (32) of the linear actuator and connected to the moving platform (2).

Images