High-precision six-degree-of-freedom parallel mechanism

Abstract

The invention discloses a high-precision six-degree-of-freedom parallel mechanism which comprises a movable mirror frame, a bottom plate and six single-leg driving rods. In each single-leg driving rod, a spherical hinge bearing is rotatably arranged in a spherical hinge seat at the bottom of the movable mirror frame; the spherical hinge bearing is in threaded fixed connection with one end of the first connecting shaft, and the other end of the first connecting shaft is in threaded connection with the moving end of the piezoelectric actuator; one end of the second connecting shaft is fixed with the fixed end of the piezoelectric actuator through a screw, and the other end is in threaded fixed connection with one end of the linear bearing seat; the inner side of the other end of the linear bearing seat is fixedly connected with the linear bearing through threads, and the outer side is fixedly connected with the locking bracket through threads; the cylindrical surface at the upper end of the coarse adjustment section screw rod penetrates through the locking bracket and the linear bearing and then is in threaded connection with the linear bearing seat; and the bottom end of the coarse adjustment section screw rod is fixedly connected with the bottom plate through an offset hooke joint. According to the invention, six-degree-of-freedom adjustment of the mover mirror can be realized, and the adjustment precision is greatly improved.

Description

Technical Field

[0001] The 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 installation 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. A large number of research results have been achieved in the practical application and theoretical research of parallel mechanisms.

[0004] For example, Chinese patent document with publication number 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, and the electric cylinder drive group drives the upper platform to a predetermined position according to an external control instruction.

[0005] A Chinese patent document with publication number CN113386110A discloses a six-degree-of-freedom platform, comprising: 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 of which has its two ends respectively connected to the first ball joint mounting portion and the second ball joint mounting portion; wherein each motion branch is obliquely installed 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 confocality and co-phasing of the movable mirror and the two stator mirrors, and improve the high-resolution image imaging quality of the space optical system.

[0008] A high-precision six-degree-of-freedom parallel mechanism comprises a moving mirror frame, a base plate and six single-leg driving rods arranged therebetween; each single-leg driving 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 joint seats are installed at the bottom of the movable mirror frame, and the ball joint bearing is rotatably arranged in the ball joint seat; the ball joint bearing is 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 with the thread of the linear bearing seat; the bottom end of the coarse adjustment section screw is fixedly connected with the bottom plate through an offset Hooke 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] Further, the piezoelectric actuator comprises 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 30um. 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 rod 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, the coarse adjustment section stroke is 10mm, the linearity is ±0.1%, and the coarse adjustment section displacement accuracy is 10um.

[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 notches for fixing the coarse adjustment section screw rod by screws in cooperation with the threaded through hole;

[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 for fixing with the linear bearing seat by screws after the coarse adjustment of the coarse adjustment section screw rod, and the notch is used for avoiding 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 with 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 driving rod to move axially; at the same time, the laser is emitted from the exit port of the laser rangefinder, hits the linear bearing seat and then reflects to the entrance port, 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 a plurality of 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 a plurality of Hooke's joint pressure plates and screws.

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

[0027] 1. The present invention adopts a coarse adjustment + fine adjustment mode. The coarse adjustment section is equipped with a laser displacement sensor, and the fine adjustment section has its own displacement sensor. The stroke of the coarse adjustment section is 10mm, and its accuracy is 10um. The stroke of the fine adjustment section is 30um, and its accuracy is 0.045um. When the movable mirror frame platform is spliced ​​and adjusted with the other two stator mirrors, the axial displacement accuracy of the platform can reach 1um, and the tilt angle accuracy can reach 1″.

[0028] 2. In the present invention, the coarse adjustment adopts a rotating linear bearing seat to drive the coarse adjustment section screw to rotate, so that the single-leg driving rod moves axially, and 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 is adopted to make the adjustment mechanism have high rigidity. At the same time, the offset Hook hinge has a certain offset and a large activity space, which is conducive to installation and adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The figure 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 It is a top view schematic diagram of the movable mirror frame in the present invention.

[0032] Figure 3 It is a schematic structural 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 It is a cross-sectional schematic diagram of the piezoelectric actuator in 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 schematic diagram of the structure of the locking bracket in the present invention.

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

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

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

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

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

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the 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, 6 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 distance measuring bracket 11 and a laser distance measuring instrument 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, the upper Hooke's hinge seat 13, the Hooke's hinge shaft 14 and the lower Hooke's hinge seat 15 are threadedly fixed through a plurality of Hooke's hinge pressure plates 16, and the Hooke's hinge shaft 14 is axially protected by a plurality of bearing covers.

[0050] like Figure 5 As shown, the piezoelectric actuator 5 includes an actuator movable end 501 at the upper end and an actuator fixed end 502 at the lower end. The actuator movable end 501 can drive the first connecting shaft 4 to move axially. During the fine adjustment process, the power supply is controlled to drive the piezoelectric actuator 5 to realize a small stroke and high-precision telescopic movement of the single-leg driving rod along the axial direction of the rod. The piezoelectric actuator 5 has a displacement sensor that can measure the axial displacement.

[0051] In this embodiment, the piezoelectric actuator 5 is an ultra-precision sensor with a resolution of sub-nanometer level and a fine adjustment stroke of 30um. The built-in strain gauge sensor can achieve a closed-loop linearity of up to 0.15%. The axial displacement accuracy is calculated to be 0.045um when the stroke is 30um. By performing precision simulation on the six-degree-of-freedom parallel mechanism, when the moving mirror frame platform is finally spliced ​​and adjusted with the other two stator mirrors, the axial displacement accuracy of the platform can reach 1um 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 side wall 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 be fixed by screws and threaded through holes 1002 after the coarse adjustment of the coarse adjustment section screw rod 10, the waist-shaped holes are used to be fixed by screws and linear bearing seat 7 after the coarse adjustment of the coarse adjustment section screw rod 10, and the notch 902 is used to avoid the laser emitted by the laser rangefinder 12.

[0054] like Figure 7 to Figure 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 upper cylindrical surface of the coarse adjustment section screw 10 is provided with a thread 1001 and is connected with the threaded hole 701 of the linear bearing seat 7. The coarse adjustment section screw 10 fixes the laser rangefinder 12 to the side 1003 of the coarse adjustment section screw through the laser rangefinder bracket 11. A threaded through hole 1002 is also opened on the side 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, the coarse adjustment section stroke is 10 mm, the linearity is ±0.1%, and the calculated coarse adjustment section displacement accuracy is 10 um.

[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 driving rod moves axially along the coarse adjustment section screw 10, and at the same time, the laser is emitted from the exit port of the laser rangefinder 12, hits the linear bearing seat 7 and then reflects 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 are locked with screws, and the top of the locking bracket 9 is locked with the linear bearing seat 7 with screws, which plays a circumferential fixing role while avoiding additional stress on the mechanism and affecting the mechanism accuracy.

[0057] like Fig.10 and Fig.11 As shown, the Hook hinge shaft 14 is fixed by the upper Hook hinge seat 13 and the lower Hook hinge seat 15, and the upper Hook hinge seat 13 and the lower Hook hinge seat 15 are fixed by a plurality of Hook hinge pressure plates 16 in cooperation with screws, and a plurality of bearing caps are used to provide axial protection for the Hook hinge shaft 14. The two axes of the Hook hinge shaft 14 do not intersect at one point, and have a certain offset, so that the offset Hook hinge can be installed on the bottom plate by screws without affecting the tightening of the screws, and a large rotation angle can be achieved when the two axes rotate.

[0058] like Fig.12As shown, the base plate 17 is provided with 6 bosses 1701 for mounting 6 single-leg driving rods, a blind hole is opened in the middle of the boss 1701 to cooperate with the axial cylindrical clearance at the bottom end of the lower Hooke's hinge seat 15, and 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 driving rod on 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 parts, 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, and its use process is as follows: the six-degree-of-freedom parallel mechanism is installed, the circuit is debugged, and the system is turned on. First, the coarse adjustment method is used for adjustment, that is, the linear bearing seat 7 on the six single-leg driving rods is manually rotated to drive the six single-leg driving rods to move along the axial direction of the rod with a large stroke and rough precision, and the displacement is displayed by the laser displacement sensor for coarse adjustment. After the coarse adjustment is in place, it is locked by the locking device. Then, the fine adjustment method is used to drive the six piezoelectric actuators to respectively make the six single-leg driving rods move along the axial direction of the rod with a small range and high precision, and the displacement sensor provided by the actuator is used for fine adjustment. After the fine adjustment is in place, it is powered on and maintained. By controlling the rotation of the ball joint bearing 3, the movement mirror can be rotated around the axis, and the movement and rotation of the movement mirror relative to other stator mirrors are accurately controlled by the edge sensor on the side of the movement mirror, and it is powered on and maintained after it is adjusted in place.

[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 protection scope 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 joint; The fine adjustment section assembly comprises a piezoelectric actuator (5), and the coarse adjustment section assembly comprises 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 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); 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 a locking bracket (9) and a linear bearing (8) and is connected to the thread of a linear bearing seat (7); the bottom end of the coarse adjustment section screw rod (10) is fixedly connected to the bottom plate via 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 30um. 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); After the upper cylindrical surface of the coarse adjustment section screw rod (10) passes through the through hole (702) of the linear bearing seat (7), it is threadedly matched 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 also includes a laser distance meter (12), and the laser distance meter (12) is detachably fixed to the side of the coarse adjustment section screw rod (10) via a laser distance measurement 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 stroke of the coarse adjustment section is 10 mm, the linearity is ±0.1%, and the displacement accuracy of the coarse adjustment section is 10 um.

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); The base of the locking bracket (9) is provided with a plurality of waist-shaped holes and a notch (902); the plurality of waist-shaped holes are used to be fixed to the linear bearing seat (7) by screws after the coarse adjustment of the coarse adjustment section screw rod (10); and the notch (902) is used to avoid 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 to be 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 is emitted from the exit port of the laser rangefinder (12), hits the linear bearing seat (7) and then reflects 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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