A high-precision six-degree-of-freedom parallel mechanism

Abstract

The present invention discloses a high-precision six-degree-of-freedom parallel mechanism, comprising a moving mirror frame, a base plate, and six single-leg drive rods. In each single-leg drive rod, a ball joint bearing is rotatably disposed within a ball joint seat at the bottom of the moving mirror frame. The ball joint bearing is threadedly fixed to one end of a first connecting shaft, the other end of which is threadedly connected to the movable end of a piezoelectric actuator. One end of a second connecting shaft is fixed to the fixed end of the piezoelectric actuator by a screw, and the other end is threadedly fixed to one end of a linear bearing seat. The inner side of the other end of the linear bearing seat is threadedly fixed to the linear bearing, and the outer side is threadedly fixed to a locking bracket. The upper cylindrical surface of the coarse adjustment section screw passes through the locking bracket and the linear bearing, and is then threadedly connected to the linear bearing seat. The bottom end of the coarse adjustment section screw is fixedly connected to the base plate via an offset Hooke's hinge. The present invention can achieve six-degree-of-freedom adjustment of the moving mirror, greatly improving adjustment accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of precision instruments, and in particular relates to a high-precision six-degree-of-freedom parallel mechanism. Background Art

[0002] With the rapid advancement of optical technology, the application of optical systems is becoming more and more extensive, and the requirements for the imaging quality of the system are becoming higher and higher. The assembly accuracy of the optical system has become the main factor affecting the imaging quality of the system.

[0003] By consulting the literature, it is found that the Stewart parallel platform has the characteristics of high stiffness, strong load-bearing capacity, and high posture accuracy. It is widely used in aviation, aerospace, submarine operations, underground mining, manufacturing assembly and other industries. The practical application and theoretical research of parallel mechanisms have achieved a lot of research results.

[0004] For example, Chinese patent document CN107053144A discloses a six-degree-of-freedom platform structure, including an upper platform and a lower platform, between which an electric cylinder drive group is arranged. The electric cylinder drive group drives the upper platform to a predetermined position according to external control instructions.

[0005] Chinese patent document with publication number CN113386110A discloses a six-degree-of-freedom platform, including: a static platform, provided with a first ball joint mounting portion; a dynamic platform, provided with a second ball joint mounting portion; six motion branches, each motion branch having two ends connected to the first ball joint mounting portion and the second ball joint mounting portion respectively; wherein each motion branch is installed obliquely between the static platform and the dynamic platform.

[0006] However, the current six-degree-of-freedom platform cannot guarantee the precise positioning of the optical system assembly and adjustment, and cannot guarantee the relative position accuracy of the moving mirror and the other two stator mirrors. Summary of the Invention

[0007] The present invention provides a high-precision six-degree-of-freedom parallel mechanism, which can realize six-degree-of-freedom adjustment of the movable mirror to ensure the relative position accuracy of the movable mirror and the other two stator mirrors. Each single-leg driving rod adopts a coarse adjustment + fine adjustment method to ensure precise positioning during the debugging process, realize the confocal and co-phase of the movable mirror and the two stator mirrors, and improve the high-resolution image imaging quality of the spatial optical system.

[0008] A high-precision six-degree-of-freedom parallel mechanism comprises a moving mirror frame, a base plate, and six single-leg drive rods disposed therebetween; each single-leg drive rod comprises a ball joint bearing, a first connecting shaft, a fine adjustment segment assembly, a second connecting shaft, a coarse adjustment segment assembly, and an offset Hooke's joint;

[0009] The fine adjustment section assembly includes a piezoelectric actuator, and the coarse adjustment section assembly includes a linear bearing seat, a linear bearing, a locking bracket, and a coarse adjustment section screw;

[0010] Six ball joints are installed at the bottom of the movable mirror frame, and the ball joint bearings are rotatably arranged in the ball joints; the ball joint bearings are threadedly connected to one end of the first connecting shaft, and the other end of the first connecting shaft is threadedly connected to the movable end of the piezoelectric actuator; one end of the second connecting shaft is fixed to the fixed end of the piezoelectric actuator by a screw, and the other end is threadedly connected to one end of the linear bearing seat; the inner side of the other end of the linear bearing seat is threadedly connected to the linear bearing, and the outer side is threadedly connected to the locking bracket;

[0011] The upper cylindrical surface of the coarse adjustment section screw is provided with a thread, and the upper cylindrical surface passes through the locking bracket and the linear bearing and is connected to the thread of the linear bearing seat; the bottom end of the coarse adjustment section screw is fixedly connected to the base plate through an offset Hooke's hinge.

[0012] Furthermore, the ball joint bearing is of precision grade, the swing range of a single ball joint bearing is ±30°, and the swing accuracy range is ±2.5um.

[0013] Furthermore, the piezoelectric actuator includes an actuator movable end fixed to the first connecting shaft and an actuator fixed end fixed to the second connecting shaft;

[0014] The movable end of the actuator is used to drive the first connecting shaft to move axially. During the fine-tuning process, the piezoelectric actuator is driven by the control power supply to realize the small-stroke, high-precision axial telescopic movement of the single-leg driving rod. The piezoelectric actuator has its own displacement sensor to measure the axial displacement.

[0015] Furthermore, the piezoelectric actuator is an ultra-precision sensor with a resolution of sub-nanometer level and a fine adjustment stroke of 30 μm. The strain gauge sensor provided by the piezoelectric actuator achieves a closed-loop linearity of 0.15%.

[0016] Furthermore, one end of the inner hole of the linear bearing seat is a threaded hole, and the other end is a through hole;

[0017] The upper cylindrical surface of the coarse adjustment section screw passes through the through hole of the linear bearing seat and is threadedly matched with the threaded hole.

[0018] Furthermore, the fine adjustment section assembly also includes a laser rangefinder, and the laser rangefinder is detachably fixed to the side surface of the coarse adjustment section screw through a laser rangefinder bracket.

[0019] Furthermore, the laser rangefinder adopts a micro laser displacement sensor with a coarse adjustment section stroke of 10 mm, a linearity of ±0.1%, and a coarse adjustment section displacement accuracy of 10 μm.

[0020] Furthermore, a threaded through hole is formed on the side of the coarse adjustment section screw;

[0021] The side wall of the locking bracket is provided with two symmetrical straight slots for fixing the screw rod of the coarse adjustment section by screws in cooperation with the threaded through holes after the coarse adjustment;

[0022] The base of the locking bracket is provided with a plurality of waist-shaped holes and a notch. The plurality of waist-shaped holes are used to be fixed to the linear bearing seat by screws after the coarse adjustment of the coarse adjustment section screw rod, and the notch is used to avoid the laser emitted by the laser rangefinder.

[0023] Furthermore, the working process of the coarse adjustment segment component is:

[0024] The locking bracket is loosened and in a free state, and the screws fixing it to the linear bearing seat and the coarse adjustment section screw are released; the rotating linear bearing seat drives the coarse adjustment section screw to rotate, causing the single-leg drive rod to move axially; at the same time, the laser is emitted from the laser rangefinder outlet, hits the linear bearing seat and then reflects to the entrance, thereby measuring the displacement of the coarse adjustment section. After the coarse adjustment section is adjusted into place, the straight slot on the side of the locking bracket and the threaded through hole of the coarse adjustment section screw are screwed; at the same time, the top of the locking bracket is screwed to the linear bearing seat.

[0025] Furthermore, the offset Hooke's joint includes an upper Hooke's joint seat, a Hooke's joint shaft, a lower Hooke's joint seat and several Hooke's joint pressure plates; wherein the Hooke's joint shaft is fixed by the upper Hooke's joint seat and the lower Hooke's joint seat, and the upper Hooke's joint seat and the lower Hooke's joint seat are fixed by several Hooke's joint pressure plates and screws.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses a coarse and fine adjustment method. The coarse adjustment section is equipped with a laser displacement sensor, and the fine adjustment section has its own displacement sensor. The coarse adjustment section has a stroke of 10mm and an accuracy of 10μm. The fine adjustment section has a stroke of 30μm and an accuracy of 0.045μm. When the movable mirror frame platform is spliced ​​and adjusted with the other two stator mirrors, the platform's axial displacement accuracy can reach 1μm, and the tilt angle accuracy can reach 1".

[0028] 2. In the present invention, the coarse adjustment adopts a rotary linear bearing seat to drive the coarse adjustment section screw to rotate, so that the single-leg drive rod moves axially. The displacement sensor display value is used as a reference. A semi-automatic debugging method is adopted, which has a simple structure and low cost and can achieve the expected effect.

[0029] 3. The structure of the present invention is relatively simple and compact, with high overall rigidity. The six-bar parallel structure makes the adjustment mechanism have high rigidity. At the same time, the offset Hooke's hinge has a certain offset, which provides a large movable space and is convenient for installation and adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the overall structure of a high-precision six-degree-of-freedom parallel mechanism of the present invention.

[0031] Figure 2 Schematic top view of the movable mirror frame of the present invention.

[0032] Figure 3 It is a structural schematic diagram of the ball joint seat and the ball joint bearing in the present invention.

[0033] Figure 4 It is a cross-sectional schematic diagram of the single-leg driving rod in the present invention.

[0034] Figure 5 Schematic cross-sectional view of the piezoelectric actuator of the present invention.

[0035] Figure 6 It is a cross-sectional schematic diagram of the linear bearing seat in the present invention.

[0036] Figure 7 It is a structural schematic diagram of the locking bracket in the present invention.

[0037] Figure 8 Schematic diagram of the structure of the coarse adjustment section screw in the present invention

[0038] Figure 9 It is a cross-sectional schematic diagram of the coarse adjustment section assembly in the present invention.

[0039] Figure 10 It is a structural schematic diagram of the offset Hooke's hinge in the present invention.

[0040] Figure 11 It is a structural schematic diagram of the Hooke's hinge shaft in the present invention.

[0041] Figure 12 It is a structural schematic diagram of the bottom plate of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0043] like Figure 1 As shown, a high-precision six-degree-of-freedom parallel mechanism includes a moving mirror frame 1, six single-leg driving rods and a base plate.

[0044] like Figure 2 As shown, six bosses are provided at the bottom of the movable mirror frame 1, which are used to fix six ball joint seats 2 respectively.

[0045] like Figure 3 and Figure 4 As shown, each single-leg driving rod includes a ball joint bearing 3, a first connecting shaft 4, a fine adjustment section assembly, a second connecting shaft 6, a coarse adjustment section assembly and an offset Hooke's joint.

[0046] The fine adjustment section assembly includes a piezoelectric actuator 5. The coarse adjustment section assembly includes a linear bearing seat 7, a linear bearing 8, a locking bracket 9, a coarse adjustment section screw 10, a laser rangefinder bracket 11, and a laser rangefinder 12. The offset Hooke's hinge includes an upper Hooke's hinge seat 13, a Hooke's hinge shaft 14, and a lower Hooke's hinge seat 15.

[0047] In the embodiment of the present invention, the ball joint bearing 3 is of precision grade, the swing range of a single ball joint bearing is ±30°, and the swing accuracy range is ±2.5um, which can realize the rotation of the movable mirror around the axis.

[0048] The ball joint bearing 3 is rotatably arranged in the ball joint seat 2; the ball joint bearing 3 is threadedly connected to one end of the first connecting shaft 4, and the other end of the first connecting shaft 4 is threadedly connected to the movable end of the piezoelectric actuator 5; one end of the second connecting shaft 6 is fixed to the fixed end of the piezoelectric actuator 5 by a screw, and the other end is threadedly connected to one end of the linear bearing seat 7; the inner side of the other end of the linear bearing seat 7 is threadedly connected to the linear bearing 8, and the outer side is threadedly connected to the locking bracket 9.

[0049] The bottom of the coarse adjustment section screw rod 10 is threadedly connected to the upper Hooke's hinge seat 13, and the upper Hooke's hinge seat 13, the Hooke's hinge shaft 14 and the lower Hooke's hinge seat 15 are threadedly fixed by several Hooke's hinge pressure plates 16, and the Hooke's hinge shaft 14 is axially protected by several bearing covers.

[0050] like Figure 5 As shown, the piezoelectric actuator 5 includes an upper movable end 501 and a lower fixed end 502. The movable end 501 drives the first connecting shaft 4 axially. During fine-tuning, the power supply is controlled to drive the piezoelectric actuator 5 to achieve small-stroke, high-precision axial telescopic movement of the single-leg drive rod. The piezoelectric actuator 5 has a built-in displacement sensor that measures the axial displacement.

[0051] In this embodiment, the piezoelectric actuator 5 is an ultra-precision sensor with a sub-nanometer resolution and a fine-adjustment stroke of 30 μm. Its built-in strain gauge sensor achieves a closed-loop linearity of up to 0.15%. The calculated axial displacement accuracy is 0.045 μm at a stroke of 30 μm. Through precision simulation of the six-degree-of-freedom parallel mechanism, it was determined that when the movable mirror frame platform is spliced ​​and adjusted with the other two stator mirrors, the platform's axial displacement accuracy can reach 1 μm, and the tilt angle accuracy can reach 1″.

[0052] like Figure 6 As shown, a threaded hole 701 is provided at one end of the inner hole of the linear bearing seat 7, and a through hole 702 is provided at the other end.

[0053] like Figure 7 and Figure 8As shown, the sidewall of the locking bracket 9 is provided with two symmetrical straight slots 901, and the base is provided with three waist-shaped holes and a notch 902. The straight slots 901 are used to secure the coarse adjustment screw 10 via screws to the threaded through-holes 1002 after coarse adjustment. The waist-shaped holes are used to secure the coarse adjustment screw 10 to the linear bearing seat 7 via screws after coarse adjustment. The notch 902 is used to block the laser light emitted by the laser rangefinder 12.

[0054] like Figures 7 to 9 As shown, the axial part of the coarse adjustment section screw 10 passes through the linear bearing seat 7, the linear bearing 8, and the locking bracket 9 respectively. The cylindrical surface of the upper end of the coarse adjustment section screw 10 is provided with a thread 1001 and is connected to the threaded hole 701 of the linear bearing seat 7. The coarse adjustment section screw 10 fixes the laser rangefinder 12 to the side surface 1003 of the coarse adjustment section screw through the laser ranging bracket 11. A threaded through hole 1002 is also opened on the side surface of the coarse adjustment section screw 10, so that the locking bracket 9 and the coarse adjustment section screw 10 can be directly locked by screws after the coarse adjustment is in place.

[0055] In this embodiment, the laser rangefinder 12 is a micro laser displacement sensor with a coarse adjustment range of 10 mm and a linearity of ±0.1%. The displacement accuracy of the coarse adjustment range is calculated to be 10 μm.

[0056] During the coarse adjustment process, the locking bracket 9 is loosened and is in a free state, that is, the screw fixation with the linear bearing seat 7 and the coarse adjustment section screw 10 is released; the rotating linear bearing seat 7 drives the coarse adjustment section screw 10 to rotate, so that the single-leg drive rod moves axially along the coarse adjustment section screw 10, and at the same time, the laser is emitted from the outlet of the laser rangefinder 12, hits the linear bearing seat 7 and is reflected to the entrance, thereby measuring the displacement of the coarse adjustment section. After the coarse adjustment section is adjusted to the right position, the straight slot 901 on the side of the locking bracket 9 and the threaded through hole 1002 of the coarse adjustment section screw are locked with screws, and the top of the locking bracket 9 and the linear bearing seat 7 are locked with screws, which plays a circumferential fixing role while avoiding additional stress on the mechanism and affecting the mechanism accuracy.

[0057] like Figure 10 and Figure 11 As shown, the Hooke's hinge shaft 14 is secured by an upper and lower Hooke's hinge seats 13 and 15. Several Hooke's hinge pressure plates 16 are used in conjunction with screws to secure the upper and lower Hooke's hinge seats 13 and 15. Several bearing caps provide axial protection for the Hooke's hinge shaft 14. The two axes of the Hooke's hinge shaft 14 do not intersect at a point but are offset. This allows the offset Hooke's hinge to be screwed to the base plate without affecting screw tightening, and also allows for a wide rotation angle during two-axis rotation.

[0058] like Figure 12As shown, the base plate 17 is provided with 6 bosses 1701 for mounting 6 single-leg drive rods. A blind hole is provided in the middle of the boss 1701 to cooperate with the axial cylindrical clearance of the bottom end of the lower Hooke's hinge seat 15. The 4 threaded blind holes of each boss 1701 are fixed to each lower Hooke's hinge seat 15 by screws, thereby fixing each single-leg drive rod to the base plate 17.

[0059] In this embodiment, the ball joint bearing 3, the piezoelectric actuator 5, the linear bearing 8 and the laser rangefinder 12 are all commercially available components, and all meet the performance requirements of the present invention.

[0060] The high-precision six-degree-of-freedom parallel mechanism of the present invention is a combination of mechanical, electronic, and computer control technologies. Its use process is as follows: After the six-degree-of-freedom parallel mechanism is installed and the circuit is debugged, the system is turned on. First, a coarse adjustment method is used for adjustment, that is, the linear bearing seat 7 on the six single-leg drive rods is manually rotated to drive the six single-leg drive rods to perform large-scale, coarse-precision telescopic movement along the rod axis. The displacement is displayed by a laser displacement sensor for coarse adjustment. After the coarse adjustment is in place, the locking device is used to lock. Then, a fine adjustment method is used to drive the six piezoelectric actuators to respectively cause the six single-leg drive rods to perform small-scale, high-precision telescopic movement along the rod axis. Fine adjustment is performed using the displacement sensors provided by the actuators. After fine adjustment is in place, power is applied to maintain the position. By controlling the rotation of the ball joint bearing 3, the movable mirror can be rotated around the axis. The edge sensor on the side of the movable mirror is used to accurately control the movement and rotation of the movable mirror relative to the other stator mirrors. After the adjustment is in place, power is applied to maintain the position.

[0061] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-precision six-degree-of-freedom parallel mechanism, characterized in that: It comprises a movable mirror frame, a base plate and six single-leg driving rods arranged therebetween; each single-leg driving rod comprises a ball joint bearing (3), a first connecting shaft (4), a fine adjustment section assembly, a second connecting shaft (6), a coarse adjustment section assembly and an offset Hooke's hinge; The fine adjustment section assembly includes a piezoelectric actuator (5), and the coarse adjustment section assembly includes a linear bearing seat (7), a linear bearing (8), a locking bracket (9), and a coarse adjustment section screw (10); Six ball joint seats (2) are installed at the bottom of the movable mirror frame, and the ball joint bearing (3) is rotatably arranged in the ball joint seat (2); the ball joint bearing (3) is fixedly connected to one end of the first connecting shaft (4) by a thread, and the other end of the first connecting shaft (4) is fixedly connected to the movable end of the piezoelectric actuator (5) by a thread; one end of the second connecting shaft (6) is fixedly fixed to the fixed end of the piezoelectric actuator (5) by a screw, and the other end is fixedly connected to one end of the linear bearing seat (7) by a thread; the inner side of the other end of the linear bearing seat (7) is fixedly connected to the linear bearing (8) by a thread, and the outer side is fixedly connected to the locking bracket (9) by a thread; The upper cylindrical surface of the coarse adjustment section screw rod (10) is provided with a thread (1001), and the upper cylindrical surface passes through the locking bracket (9) and the linear bearing (8) and is connected to the thread of the linear bearing seat (7); the bottom end of the coarse adjustment section screw rod (10) is fixedly connected to the base plate through an offset Hooke's hinge.

2. The high-precision six-degree-of-freedom parallel mechanism according to claim 1, characterized in that: The ball joint bearing (3) is of precision grade, the swing range of a single ball joint bearing is ±30°, and the swing accuracy range is ±2.5um.

3. The high-precision six-degree-of-freedom parallel mechanism according to claim 1, characterized in that: The piezoelectric actuator (5) comprises an actuator movable end (501) fixed to the first connecting shaft (4) and an actuator fixed end (502) fixed to the second connecting shaft (6); The actuator moving end (501) is used to drive the first connecting shaft (4) to move axially; during the fine adjustment process, the piezoelectric actuator (5) is driven by the control power supply to achieve a small stroke, high-precision axial telescopic movement of the single-leg driving rod, and the piezoelectric actuator (5) is equipped with a displacement sensor to measure the axial displacement.

4. The high-precision six-degree-of-freedom parallel mechanism according to claim 3, characterized in that: The piezoelectric actuator (5) is an ultra-precision sensor with a resolution reaching sub-nanometer level and a fine adjustment stroke of 30 μm. The strain gauge sensor provided by the piezoelectric actuator (5) achieves a closed-loop linearity of 0.15%.

5. The high-precision six-degree-of-freedom parallel mechanism according to claim 1, characterized in that: One end of the inner hole of the linear bearing seat (7) is a threaded hole (701), and the other end is a through hole (702); The upper cylindrical surface of the coarse adjustment section screw (10) passes through the through hole (702) of the linear bearing seat (7) and is threadedly engaged with the threaded hole (701).

6. The high-precision six-degree-of-freedom parallel mechanism according to claim 1, characterized in that: The fine adjustment section assembly further comprises a laser rangefinder (12), and the laser rangefinder (12) is detachably fixed to the side surface of the coarse adjustment section screw (10) via a laser rangefinder bracket (11).

7. The high-precision six-degree-of-freedom parallel mechanism according to claim 6, characterized in that: The laser rangefinder (12) adopts a micro laser displacement sensor, the coarse adjustment section stroke is 10mm, the linearity is ±0.1%, and the coarse adjustment section displacement accuracy is 10um.

8. The high-precision six-degree-of-freedom parallel mechanism according to claim 6, characterized in that: A threaded through hole (1002) is also formed on the side of the coarse adjustment section screw rod (10); The side wall of the locking bracket (9) is provided with two symmetrical straight notches (901) for fixing the coarse adjustment section screw rod (10) by screws in cooperation with the threaded through hole (1002) after the coarse adjustment; The base of the locking bracket (9) is provided with a plurality of waist-shaped holes and a notch (902), wherein the plurality of waist-shaped holes are used for fixing the linear bearing seat (7) via screws after the coarse adjustment of the coarse adjustment section screw rod (10), and the notch (902) is used for avoiding laser light emitted by the laser rangefinder (12).

9. The high-precision six-degree-of-freedom parallel mechanism according to claim 8, characterized in that: The working process of the coarse adjustment segment component is: The locking bracket (9) is loosened and in a free state, and the screw fixation with the linear bearing seat (7) and the coarse adjustment section screw (10) is released; the linear bearing seat (7) is rotated to drive the coarse adjustment section screw (10) to rotate, so that the single-leg driving rod moves axially; at the same time, laser light is emitted from the exit port of the laser rangefinder (12), hits the linear bearing seat (7) and is reflected to the entrance port, thereby measuring the displacement of the coarse adjustment section. After the coarse adjustment section is adjusted to the right position, the straight slot (901) on the side of the locking bracket (9) and the threaded through hole (1002) of the coarse adjustment section screw (10) are screwed; at the same time, the top of the locking bracket (9) and the linear bearing seat (7) are screwed.

10. The high-precision six-degree-of-freedom parallel mechanism according to claim 1, characterized in that: The offset Hooke's hinge comprises an upper Hooke's hinge seat (13), a Hooke's hinge shaft (14), a lower Hooke's hinge seat (15) and a plurality of Hooke's hinge pressure plates (16); wherein the Hooke's hinge shaft (14) is fixed by the upper Hooke's hinge seat (13) and the lower Hooke's hinge seat (15), and the upper Hooke's hinge seat (13) and the lower Hooke's hinge seat (15) are fixed by the plurality of Hooke's hinge pressure plates (16) and screws.

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