Micron-scale adjusting mechanism for accurately positioning and adjusting high-precision reflector antenna

Abstract

The invention provides a micron-sized adjusting mechanism for accurately positioning and adjusting a high-precision reflector antenna, which is characterized in that a hollow motor is mounted on a supporting threaded rod of a compact thread differential adjusting mechanism, and a set of annular structure for realizing high-precision displacement through differential threads is tightly placed between the hollow motor and the threaded rod; the front end and the rear end of the adjusting mechanism are each provided with a ball head structure, so that the adjusting mechanism and the panel have the self-adaptive capacity in the assembling process. The compact thread differential adjusting mechanism achieves six-degree-of-freedom adjustment, and the precision requirements of the compact range panel in different installation and adjustment stages are met through manual coarse adjustment and electric fine adjustment. Space is fully saved, the hollow servo motor is used, the gap between the hollow servo motor and the shaft is utilized, two pairs of differential threads are designed to be matched, micron-sized Z-direction high-precision movement is achieved, and the assembling requirement of a compact range is met. And meanwhile, high bearing capacity, high adjustment resolution and long-term operation stability and reliability are achieved.

Description

Technical Field

[0001] This invention relates to a micron-level adjustment mechanism for precise positioning and adjustment of high-precision reflector antennas. The threaded differential adjustment mechanism is composed of a hollow motor and two pairs of nested differential threads, which can precisely adjust the supported object in six degrees of freedom, belonging to the field of spatial micro-displacement execution technology. Background Technology

[0002] Measuring antenna parameters or radar target scattering characteristics is an important research direction in my country's scientific and technological development, with the measurement accuracy of instruments playing a crucial role. Compact fields, as complex systems engineering integrating electromagnetic scattering theory, high-precision reflector manufacturing, and precision assembly technology, directly determine the high-frequency electrical performance of the system based on the surface accuracy of their reflectors. Large reflectors (tens to hundreds of square meters) require multi-panel splicing due to manufacturing limitations, and the higher the operating frequency, the higher the surface accuracy requirements. The overall surface accuracy must meet RMS < λ / 100 (RMS ≤ 0.03 mm for 100 GHz), and the splicing gap must be controlled within the range of 0.03 ± 0.015 mm. This places extremely high demands on panel support positioning and six-degree-of-freedom micron-level precision adjustment.

[0003] In existing drive schemes for reflective panel displacement actuators, hydraulic drives are difficult to meet long-cycle precision adjustment requirements due to medium leakage and compressibility; piezoelectric ceramics and magnetostrictive drives suffer from nonlinear hysteresis and low load defects; while current servo and stepper motor solutions, although possessing high load and linear micro-displacement output capabilities, mostly employ traditional solid motor structures, resulting in low space utilization and reliance on ordinary threaded drives that limit the accuracy ceiling. Using hollow servo motors can significantly save space through optimized structural design, and combined with differential threaded drive mechanisms, can further improve the resolution of micro-displacement adjustment, providing a compact and integrated new path for high-precision, high-resolution actuators required in tight-field applications.

[0004] To address the aforementioned technical bottlenecks, this invention proposes a six-degree-of-freedom precision adjustment mechanism that employs a hollow servo motor drive and differential screw transmission technology. This mechanism optimizes space utilization and enables nanometer-level precision adjustment while ensuring high load capacity, providing a new method for stable support and precise posture control of compact field reflective panels. Summary of the Invention

[0005] The purpose of this invention is to provide a micrometer-level adjustment mechanism for precise positioning and adjustment of high-precision reflector antennas, thereby improving the assembly accuracy and efficiency of compact field reflector panels. This compact threaded differential adjustment mechanism mounts a hollow motor on a supporting threaded rod, and a ring structure that achieves high-precision displacement via differential threads is tightly placed between the hollow motor and the threaded rod. The mechanism is compact, has high load-bearing capacity, and high resolution. The compact threaded differential adjustment mechanism also has a ball-head structure at both the front and rear ends, allowing for some self-adaptation between the adjustment mechanism and the panel during assembly. This compact threaded differential adjustment mechanism can achieve six degrees of freedom adjustment, and can meet the accuracy requirements of different assembly and adjustment stages of the compact field panel through manual coarse adjustment and electric fine adjustment. Specifically, the X and Y axes can be adjusted using adjusting bolts, the Z axis can be manually coarsely adjusted using a pair of locking nuts, and fine adjustment in the Z axis can be performed by driving the differential thread mechanism with a hollow motor.

[0006] This compact thread differential adjustment mechanism mainly consists of a front ball head support unit, a differential adjustment drive unit, and a rear adjustment locking unit, such as... Figure 1 and Figure 2 As shown.

[0007] The front ball joint support unit includes a front flange (1), a reverse clamping small flange (2), a front ball joint cover (3), a front ball joint (21), a ball joint fixing bolt (22), and a clamping flange (23). The front flange and the front ball joint cover are fixed together by a threaded pair, and their inner rings mate with the outer rings of the front ball joint, forming a ball joint motion pair. The reverse clamping small flange and the clamping flange are located at both ends of the front ball joint, clamping the front ball joint to form the front ball joint support unit. The ball joint fixing bolt connects the front ball joint to the front translation rod sleeve in the differential adjustment drive unit.

[0008] The other end of the front flange has a flange hole corresponding to the hole on the back of the reflective panel, which can be used to connect the panel to the compact threaded differential adjustment mechanism.

[0009] The differential adjustment drive unit includes a front translation rod sleeve (4), a backlash-free disc spring assembly (20), a transmission motor cover (5), a hollow motor moving end (6), an internal thread differential sleeve (7), a hollow motor fixed end (8), and a central threaded rod (13). The hollow motor fixed end is connected to the shoulder on the central threaded rod via a threaded pair. The outer side of the hollow motor moving end is connected to the transmission motor cover via a threaded pair. The transmission motor cover engages with the outer ring keyway of the internal thread differential sleeve via an inner ring keyway. The internal thread differential sleeve is divided into left and right halves, which are installed using threaded pairs through front and rear mounting holes. The threaded hole with a smaller inner diameter on the left side of the internal thread differential sleeve engages with the central threaded rod, and the threaded hole with a larger inner diameter on the right side of the internal thread differential sleeve engages with the front translation rod sleeve. The two sides of the cylindrical front end of the central threaded rod are flattened, and the front translation rod sleeve engages with the hole in the central threaded rod, retaining the Z-axis degree of freedom. The front end of the central threaded rod has a small boss machined on the top of the flattened cylindrical part. The bottom of the backlash-eliminating disc spring assembly is fitted on this boss, and the top of the assembly contacts the top of the inner hole of the front translation rod sleeve. During operation, it is kept compressed to provide backlash-eliminating force for the two sets of threaded engagement.

[0010] The rear adjustment and locking unit includes a support housing (10), adjusting bolts (9), a rear ball head cover (11), a rear adjusting nut (12), a rear ball head locking nut (14), a clamping bushing (15), a rear ball head (16), a guide support sleeve (17), a locking nut (18), and a front adjusting nut (19). The guide support sleeve mates with the central threaded rod hole, and one end of the rear ball head abuts against the shoulder of the guide support sleeve. Its position on the guide support sleeve is fixed by the clamping bushing and the rear ball head locking nut at the other end. The support housing and the rear ball head cover are connected by a threaded pair, and the inner ring mates with the outer ring of the rear ball head, forming a ball head kinematic pair. The support housing and the reflector back frame are fixed by welding. Therefore, the X and Y axis positions of the central threaded rod can be adjusted by four adjusting bolts. Each adjusting bolt is equipped with a locking nut, and the locking nut is used to lock the rod after adjustment. The guide support sleeve can move in the Z-axis direction for coarse adjustment of the Z-axis position. It has a front adjustment nut and a rear adjustment nut at both ends. After adjustment, the front adjustment nut and the rear adjustment nut are locked to fix the position.

[0011] The core design principle of this invention is to provide stable and highly accurate precision displacement; therefore, deformation caused by temperature changes and loads should be minimized. Considering these factors, the shaft is made of 17-4PH stainless steel, which has the advantages of high hardness, good dimensional stability, and a low coefficient of linear expansion. The internal thread differential sleeve uses C95400 aluminum bronze, which has excellent friction-reducing and debris-catching capabilities, and being a different material from the shaft, it reduces the risk of seizing and adhesion.

[0012] The advantages and benefits of this invention are as follows: (1) This invention saves space by using a hollow servo motor and utilizing the gap between the hollow servo motor and the shaft to design two pairs of differential thread fits to achieve micron-level high-precision Z-axis movement and meet the assembly requirements of the compression field.

[0013] (2) This invention adopts a double ball-head series structure, which has good adjustment flexibility and spatial six-degree-of-freedom adjustment function. It integrates manual coarse adjustment and electric fine adjustment modes: manual coarse adjustment can be achieved in the X and Y axis directions through a threaded transmission mechanism, while the Z axis direction is driven by a motor. The high resolution of the motor combined with the differential mechanism can achieve nanometer-level precision. With the addition of a sensor, automated precision closed-loop adjustment can also be achieved. Furthermore, it has a stroke of 3mm on this precision basis, while retaining the manual coarse adjustment function.

[0014] (3) The present invention is mainly designed based on the threaded pair transmission, which has high load capacity, high adjustment resolution and long-term operation stability and reliability. Attached Figure Description

[0015] Figure 1 This is an assembly drawing of a compact thread differential adjustment mechanism.

[0016] Figure 2 This is an isometric view of a compact thread differential adjustment mechanism.

[0017] Figure 3 This is a schematic diagram of the differential motion principle of a compact thread differential adjustment mechanism.

[0018] Figure 4 This is a diagram showing the internal thread fit relationship of a compact thread differential adjustment mechanism.

[0019] The labels and symbols in the diagram are explained as follows: Detailed Implementation

[0020] The present invention discloses a micron-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna, as shown in the figure. It mainly consists of a front-end ball head support unit, a differential adjustment drive unit, and a rear-end adjustment and locking unit.

[0021] The front ball joint support unit includes a front flange 1, a reverse clamping small flange 2, a front ball joint cover 3, a front ball joint 21, a ball joint fixing bolt 22, and a clamping flange 23. The inner rings of the front flange 1 and the front ball joint cover 3 mate with the outer ring of the front ball joint 21, forming a ball joint kinematic pair, providing a certain degree of freedom during assembly and adjustment. Both the front flange 1 and the front ball joint cover 3 are designed with corresponding holes for installing threaded pairs, thus ensuring the concentricity of the front flange 1 and the front ball joint cover 3 during assembly. The reverse clamping small flange 2 and the clamping flange 23 are located at both ends of the front ball joint. The outer ring of the reverse clamping small flange 2 mates with the inner ring of the front ball joint 21, and the inner ring of the reverse clamping small flange 2 mates with the outer ring of the front translation sleeve 4. The clamping flange 23 has a stepped through hole inside, and the protruding side inside the clamping flange 23 is in contact with the top of the ball joint fixing bolt 22, serving a limiting function. The ball head fixing bolt 22 passes through the through hole of the clamping flange 23 and mates with the center threaded hole of the front translation rod sleeve 4. After tightening, it serves to connect the front ball head support unit and the differential adjustment drive unit. The other end of the front flange 1 has a flange hole corresponding to the hole on the back of the reflector panel, which can connect the panel to the compact threaded differential adjustment mechanism.

[0022] The differential adjustment drive unit includes a front translation rod sleeve 4, a drive motor cover 5, a hollow motor moving end 6, an internally threaded differential sleeve 7, a hollow motor fixed end 8, and a central threaded rod 13. The two sides of the frontmost cylindrical part of the central threaded rod 13 are flattened. After the front translation rod sleeve 4 mates with the central threaded rod hole 13, it cannot rotate, retaining the Z-axis degree of freedom. The bottom of the hollow motor fixed end 8 has several threaded holes, and its bottom surface rests on the shoulder of the central threaded rod 13. The shoulder also has several corresponding holes. A threaded pair passes through the holes on the shoulder of the central threaded rod 13 and is tightened to the hollow motor fixed end 8, thus fixing the hollow motor fixed end 8. The outer side of the hollow motor moving end 6 has threaded holes, which connect to the drive motor cover 5 via a threaded pair. The drive motor cover 5 mates with the outer keyway of the internally threaded differential sleeve 7 via an inner ring keyway. When the hollow motor moving end 6 rotates, the drive motor cover 5 fixed to the hollow motor moving end 6 rotates synchronously, driving the threaded differential sleeve 7 to rotate together via the keyway. The smaller-diameter threaded hole on the left side of the internal threaded differential sleeve 7 has a threaded engagement with the central threaded rod 13, with a pitch of P1. The larger-diameter threaded hole on the right side of the internal threaded differential sleeve 7 has a threaded engagement with the front translation rod sleeve 4, with a pitch of P2. When the internal threaded differential sleeve 7 rotates one revolution in the forward direction, it moves outward by P1. Since the front translation rod sleeve 4 cannot rotate, it can only move in the Z direction. Therefore, when the internal threaded differential sleeve 7 rotates one revolution, the front translation rod sleeve 4 moves inward by P2 relative to the internal threaded differential sleeve 7. Therefore, after the hollow motor moving end 6 rotates one revolution, the actual displacement of the front translation rod sleeve 4 is P1-P2. Figure 3As shown in the diagram. Blue represents the central threaded rod, black the hollow motor, yellow the drive motor cover, orange the internal threaded differential sleeve, green the front translation rod sleeve, and gray the front ball joint support unit. The hollow motor moving end 6 is a high-precision servo motor with a positioning accuracy of 0.004°. Therefore, one rotation of the motor can be divided into 90,000 motion steps, and the final differential displacement generated by each step is... Assume P1 is P2 is Substituting the values, we can obtain the final differential displacement generated in each step as follows: Theoretically, nanometer-level adjustment precision can be achieved. The internal thread differential sleeve 7 is divided into left and right halves, with two pairs of flange holes at the front and rear. After alignment on the shaft, it is fixed by a threaded pair. This is to facilitate alignment of the two differential threads on the central threaded rod 13 and the front translation rod sleeve 4, and to allow for movement margin. The front end of the central threaded rod 13 has a small boss machined on the flattened cylindrical top. The bottom of the backlash-free disc spring assembly 20 is fitted onto this boss, and the top contacts the top of the inner hole of the front translation rod sleeve 4. Throughout the entire motion process, the backlash-free disc spring assembly 20 is in a compressed working state, providing a forward force to the front translation rod sleeve 4. The front translation rod sleeve 4 can transmit the force to the threaded drive with the internal thread differential sleeve 7, eliminating the thread backlash between the two. At the same time, the internal thread differential sleeve 7 is also subjected to a forward force. Under the action of this force, the thread fit clearance between the internal thread differential sleeve 7 and the central threaded rod 13 will also decrease.

[0023] The rear adjustment and locking unit includes a support housing 10, an adjusting bolt 9, a rear ball head cover 11, a rear adjusting nut 12, a rear ball head locking nut 14, a clamping bushing 15, a rear ball head 16, a guide support sleeve 17, a locking nut 18, and a front adjusting nut 19. The inner wall of the guide support sleeve 17 contacts the thread tip of the central threaded rod 13, ensuring their concentricity. Simultaneously, the central threaded rod 13 can move and rotate along the Z-axis within the guide support sleeve 17. The outer surface of the guide support sleeve 17 is cuboid, providing a flat contact surface for the adjusting bolt 9. The right end of the rear ball head 16 abuts against the shoulder of the guide support sleeve 17, and the left end abuts against the right end of the clamping bushing 15. The rear ball head locking nut 14 passes through the guide support sleeve 17 and abuts against the left end of the clamping bushing 15. Tightening the nut fixes the rear ball head 16 onto the guide support sleeve 17. The support housing 10 and the rear ball head cover 11 are connected by a threaded pair, and the inner ring of the support housing 10 and the rear ball head cover 11 mates with the outer ring of the rear ball head 16, forming a ball head kinematic pair, providing a certain degree of freedom for the assembly and adjustment process. The support housing 10 and the reflector back frame are fixedly connected by welding, so the X and Y axis positions of the central threaded rod can be adjusted by four mutually perpendicular adjusting bolts 9. There are four mutually perpendicular and symmetrical threaded holes on the right side of the support housing 10 near the end face. The four adjusting bolts 9 are screwed into the support housing 10 through the threads and contact the outer surface of the guide support sleeve 17. Each adjusting bolt 9 is equipped with a locking nut 18. The symmetrically distributed adjusting bolts 9 in the same direction can move the guide support sleeve 17 in that direction by coordinating the adjustment. After adjustment, the locking nut 18 is used to lock it. The guide support sleeve 17 can be moved in the Z-axis direction for coarse adjustment of the Z-axis position. There are front adjusting nuts 19 and rear adjusting nuts 12 at its two ends, respectively. After adjustment, the front adjusting nuts and rear adjusting nuts are locked to fix the position.

[0024] The following is a preliminary check of the thermal expansion, load, and lead error of the mechanism designed in this invention: (1) Thermal expansion error The coefficient of thermal expansion of 17-4PH stainless steel Approximately C95400 aluminum bronze has a coefficient of thermal expansion. Approximately This invention is primarily used for the precision assembly of multiple panels. Therefore, when the temperature changes, the overall support and the front half of the adjustment mechanism for all panels expand together, resulting in a coordinated change, and their impact can be ignored. Thus, we only need to consider the thermal expansion caused by the different Z-axis displacements at each support point.

[0025]

[0026]

[0027] That is, the differential travel generated per revolution The thermal expansion error, assuming a total travel of 30 revolutions, will result in a maximum thermal expansion error at different locations. Thermal expansion error.

[0028] (2) Load error The diameter of the central shaft is Therefore, the cross-sectional area is , length of force The elastic modulus of 17-4PH stainless steel The maximum expected load is The strain occurring in this shaft is approximately:

[0029] That is, when the shaft load fluctuates between 0-200N, the maximum output at different locations is... The strain error.

[0030] (3) Lead error Under ideal conditions, the lead generated by the motor in one revolution is:

[0031] However, due to inevitable machining errors during thread processing, the actual lead is:

[0032] This error actually places high demands on the machining of the shaft and the internal threaded sleeve, because differential machining only considers the difference in error. If the lead errors of the two sections are in the same direction and have the same magnitude, they will cancel each other out after differential machining; if the errors are out of direction, they will be amplified after differential machining. Therefore, it is necessary to choose to perform coaxial precision grinding on both thread sections under the same clamping conditions, and then perform mating and lapping after machining, so that the errors are correlated and can cancel each other out. The value should be minimized as much as possible. According to the table, the axial tolerance of the thread lead for grade 3 machining accuracy is... The longest threaded section of this invention is only 46mm, therefore the lead error is approximately... . In summary, even after considering the three types of errors mentioned above, the overall movement error of this precision adjustment mechanism remains at the micrometer level, ensuring the execution of precise displacement.

Claims

1. A micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna, characterized in that: The compact threaded differential adjustment mechanism features a hollow motor mounted on a supporting threaded rod, with a ring structure tightly placed between the hollow motor and the threaded rod to achieve high-precision displacement via differential threads. The mechanism also includes a ball-head structure at both the front and rear ends, enabling self-adaptation between the adjustment mechanism and the panel during assembly. The compact threaded differential adjustment mechanism consists of a front ball-head support unit, a differential adjustment drive unit, and a rear adjustment locking unit. It achieves six degrees of freedom of adjustment, meeting the precision requirements of different assembly and adjustment stages of the compact panel through manual coarse adjustment and electric fine adjustment. The X and Y axes are adjusted using adjusting bolts, while the Z-axis is coarsely adjusted manually using a pair of locking nuts, or finely adjusted using a differential thread mechanism driven by a hollow motor.

2. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 1, characterized in that: The front ball head support unit includes a front flange, a reverse clamping small flange, a front ball head cover, a front ball head, ball head fixing bolts, and a clamping flange; the front flange and the front ball head cover are fixed by a threaded pair and the inner ring of the ball head mates with the outer ring of the ball head, forming a ball head kinematic pair; the reverse clamping small flange and the clamping flange are located at both ends of the front ball head, respectively, clamping the front ball head to form the front ball head support unit; the ball head fixing bolts connect the front ball head to the front translation rod sleeve in the differential adjustment drive unit.

3. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 2, characterized in that: Both the front flange and the front ball head cover are designed with corresponding holes for installing threaded pairs, ensuring the concentricity of the front flange and the front ball head cover assembly.

4. A micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 2 or 3, characterized in that: The reverse clamping flange and the clamping flange are located at both ends of the front ball head. The outer ring of the reverse clamping flange mates with the inner ring of the front ball head, and the inner ring of the reverse clamping flange mates with the outer ring of the front translation rod sleeve. The clamping flange has a stepped through hole inside, and the protruding side inside the clamping flange is in contact with the top of the ball head fixing bolt, which serves as a limit function.

5. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 4, characterized in that: The other end of the front flange has a flange hole corresponding to the hole on the back of the reflective panel, which connects the panel to the compact threaded differential adjustment mechanism.

6. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 1, characterized in that: The differential adjustment drive unit includes a front translation rod sleeve, a backlash-free disc spring assembly, a transmission motor cover, a hollow motor moving end, an internal thread differential sleeve, a hollow motor fixed end, and a central threaded rod. The hollow motor fixed end is connected to the shoulder on the central threaded rod via a threaded pair. The outer side of the hollow motor moving end is connected to the transmission motor cover via a threaded pair. The transmission motor cover engages with the outer ring keyway of the internal thread differential sleeve via an inner ring keyway. The internal thread differential sleeve is divided into left and right halves, which are installed using threaded pairs through front and rear mounting holes. The threaded hole with a smaller inner diameter on the left side of the internal thread differential sleeve engages with the central threaded rod, and the threaded hole with a larger inner diameter on the right side of the internal thread differential sleeve engages with the front translation rod sleeve. The two sides of the cylindrical front end of the central threaded rod are flattened, and the front translation rod sleeve engages with the hole in the central threaded rod, retaining the Z-axis degree of freedom.

7. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 6, characterized in that: The front end of the central threaded rod is flattened and has a small boss machined on the top of the cylindrical part. The bottom of the backlash-free disc spring assembly is fitted onto the boss, and the top of the assembly contacts the top of the inner hole of the front translation rod sleeve, maintaining compression during operation.

8. The micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 1, characterized in that: The rear adjustment and locking unit includes a support housing, an adjusting bolt, a rear ball head cover, a rear adjusting nut, a rear ball head locking nut, a clamping bushing, a rear ball head, a guide support sleeve, a locking nut, and a front adjusting nut. The guide support sleeve mates with the central threaded rod hole, and one end of the rear ball head abuts against the shoulder of the guide support sleeve. Its position on the guide support sleeve is fixed by the clamping bushing and the rear ball head locking nut at the other end. The support housing and the rear ball head cover are connected by a threaded pair, and the inner ring mates with the outer ring of the rear ball head, forming a ball head kinematic pair. The support housing and the reflector back frame are fixed together by welding.

9. A micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 8, characterized in that: The inner wall of the guide support sleeve hole contacts the thread tip of the central threaded rod to ensure their concentricity. At the same time, the central threaded rod moves and rotates along the Z direction inside the guide support sleeve. The outer side of the guide support sleeve is a cuboid, providing a flat contact surface for the adjusting bolt.

10. A micrometer-level adjustment mechanism for precise positioning and adjustment of a high-precision reflector antenna according to claim 1, 8, or 9, characterized in that: The X and Y axis positions of the central threaded rod are adjusted by four mutually perpendicular adjusting bolts. There are four mutually perpendicular and symmetrical threaded holes on the right side of the support housing near the end face. The four adjusting bolts are screwed into the support housing through the threads and contact the outer surface of the guide support sleeve. Each adjusting bolt is equipped with a locking nut. The symmetrically distributed adjusting bolts in the same direction adjust the position of the guide support sleeve in a coordinated manner. After adjustment, the locking nut is used to lock the position. The guide support sleeve moves in the Z axis direction for coarse adjustment of the Z axis position. There are front and rear adjusting nuts at both ends. After adjustment, the front and rear adjusting nuts are locked to fix the position.

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