A three-fingered dexterous manipulator with bolt dismounting function for space satellite

Abstract

The application discloses a three-fingered dexterous manipulator with bolt dismounting function for space satellites, and relates to the technical field of on-orbit maintenance of space robots. The manipulator comprises a palm part and three fully-driven finger parts, the palm part is provided with a first driving pair for independently driving finger deflection, and the second driving pair is arranged at each joint of the finger; a compliant self-centering module is arranged at the fingertip, the three fingertips can be buckled to form a size-adjustable wrench mouth frame, and the finger adopts quick dismounting modular design. According to the scheme, the motor current is collected in real time to realize online detection of the coaxiality of the bolt and the manipulator and the bolt and the screw hole by identifying the periodic change of the resistance during screwing; the eccentricity and the deflection are automatically corrected by low-force compliant alignment and active fine adjustment. The application solves the problems of the existing space manipulator, such as easy eccentricity of rigid clamping, lack of sensor coaxial detection, easy slipping and jamming during screwing, and inconvenient maintenance, and is suitable for high-precision and high-reliability dismounting operation of multi-specification bolts in the microgravity environment of satellites.

Description

Technical Field

[0001] This invention relates to the field of on-orbit maintenance manipulator technology, specifically to a three-finger dexterous manipulator for space satellites with bolt removal and installation functions. Background Technology

[0002] In on-orbit maintenance of space satellites, bolt removal and installation are core procedures for the repair and replacement of critical components such as solar panels and cabin connection structures, placing stringent requirements on the operational precision, environmental adaptability, and reliability of robotic arms. Existing space dexterous robotic arms mostly adopt single-finger independent drive or underactuated configurations, which, although possessing basic grasping functions, have significant shortcomings in bolt removal and installation scenarios.

[0003] Existing robotic arms mostly rely on rigid gripping structures and lack compliant adaptive mechanisms. When gripping nuts, they struggle to achieve self-centering, making them highly susceptible to misalignment between the bolt axis and the robotic arm's rotation axis due to even minor positional deviations. This is because rigid contact lacks radial compensation capability. In microgravity environments, weak contact force disturbances amplify initial alignment errors. Furthermore, robotic arm joint drives often employ friction drives or self-locking transmission structures, resulting in weak and lag-prone force feedback signals, making it impossible to detect misalignment in real time. This deficiency directly leads to uneven force distribution on the nut during tightening, with excessive load on one side. This not only exacerbates thread wear, stripping, and even seizing risks but also causes robotic arm vibration due to force imbalance, further amplifying the misalignment and severely impacting assembly and disassembly accuracy.

[0004] Meanwhile, existing robotic arms lack effective online coaxiality detection methods for bolt and screw hole alignment, relying heavily on vision sensors for attitude correction. The complex lighting conditions in the orbital environment, with occlusion and reflection interference, limit the accuracy of visual recognition, making it difficult to accurately capture minute deviations. Furthermore, vision-based solutions increase system complexity, power consumption, and potential failure points, resulting in insufficient reliability during long-term on-orbit operation. When there is a slight misalignment between the bolt axis and the screw hole axis, the thread may exhibit unilateral wedging. Existing robotic arms cannot promptly identify these signs of jamming and continue to output tightening torque, easily causing thread damage, component failure, or even joint damage due to torque overload, leading to on-orbit maintenance task failure.

[0005] In addition, the fingers of existing space robotic arms are mostly integrated fixed structures, which are difficult to disassemble and maintain. If a single finger fails, the entire machine needs to be disassembled and repaired, which cannot meet the requirements for rapid replacement in orbit. Moreover, the gripping mode is limited, and it can only rely on radial friction to fix the nut. When tightening bolts with high resistance, it is easy to slip off. It cannot take into account both precise gripping and high torque tightening conditions, and it is difficult to adapt to the bolt disassembly and assembly operations of space satellites with multiple specifications, high precision and high reliability.

[0006] For the reasons mentioned above, it is necessary to propose a three-finger dexterous manipulator with bolt assembly and disassembly functions for space satellites to solve the aforementioned problems. Summary of the Invention

[0007] The purpose of this invention is to address the deficiencies in the existing technology by providing a three-finger dexterous manipulator for space satellites with bolt assembly and disassembly functions.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A three-finger dexterous manipulator for space satellites with bolt assembly / disassembly functions includes a palm and fingers. The palm has multiple fingers, and each finger has a first drive joint that independently drives the corresponding fingers to rotate around a longitudinal axis. Each finger has multiple knuckles, and a second drive joint is provided at the hinge point between the knuckles, making the fingers fully driven. The manipulator collects real-time parameters of motor current or driving torque from each joint drive joint during the driving process. During bolt tightening, the manipulator detects changes in resistance as the fingers rotate around the longitudinal axis and at the finger joints by analyzing the real-time parameters. The periodic changes in resistance at each joint of the manipulator during tightening determine the coaxiality of the bolt and the manipulator, or the coaxiality of the bolt and the bolt hole.

[0009] Furthermore, the first drive unit includes a servo motor and a rotating base. The servo motor is fixedly installed inside the palm, and the output end of the servo motor is connected to the rotating base. The root of the finger is installed on the rotating base.

[0010] Furthermore, the second drive pair includes a servo motor and a gear pair. The gear pair includes at least a drive gear and a driven gear. The servo motor is fixedly installed in one side of the finger joint, and the driven gear is fixedly installed in the other side of the finger joint. The output end of the servo motor is connected to the drive gear. The drive gear meshes with the driven gear. The gear pair is a spur gear or a helical gear.

[0011] Furthermore, during the servo motor drive process, the reaction force of the three-finger robotic arm touching the object directly (through the gear pair) acts on the servo motor, causing the servo motor to generate changes in current or driving torque. The central controller then organizes, analyzes, and determines the collected feedback parameters.

[0012] Furthermore, the finger section has three segments, each including a base phalanx, a proximal phalanx, a distal phalanx, and a fingertip phalanx that are hinged together in sequence. The base phalanx is connected to the rotating base via a quick-release structure. The base phalanx has a plug-in ear at its base, and the plug-in ear has double positioning holes. The rotating base has a slot that mates with the plug-in ear, and the slot has a double pin positioning component that slides into the double positioning holes.

[0013] Furthermore, the end of the fingertip joint is provided with a compliant self-centering positioning module, which includes a guide groove and an elastic thin pad. The guide groove is provided at the distal end of the fingertip joint. The guide groove includes a V-shaped groove, an arc-shaped groove, or a composite groove combining V-shape and arc shape. An elastic thin pad is provided on the inner side of the groove opening of the guide groove.

[0014] Furthermore, the fingertips of the three fingers are connected end to end to form a wrench frame. The wrench frame connects and fixes the three fingers together through the fingertips, forming a wrench that mates with the nut of a bolt.

[0015] Furthermore, the fingertip joint is provided with a rotating block that controls the rotation around the long axis of the fingertip joint. The rotating blocks on the three fingertip joints are rotated and adjusted so that their different sized sides face the inside of the wrench frame, so that the wrench frame forms a switchable structure that can be matched with nuts of different sizes.

[0016] Furthermore, the method for determining the coaxiality of the bolt and the robot arm... When the bolt axis is coaxial with the overall rotation axis of the robot, the forces on the three fingertips are symmetrical and the radial load is balanced; this makes the current of the first drive pair motor at the root of the three fingers basically consistent, with very small fluctuations and weak periodic components; the current of each finger joint (second drive pair) is also stable and has similar amplitude.

[0017] When the bolt axis is misaligned / the robot arm is eccentric or off-axis, it can cause one fingertip to be "crushed" by the robot arm, while the other fingertip is "suspended" or "lightly touched" by the robot arm; the motor current at the base of the three fingers will show a significant inconsistency: one is too high, one is too low, and one is in the middle; as the robot arm rotates at a low speed (tightening the bolt), the eccentric load will periodically sweep across the three fingers, leading to: The currents of the three root motors exhibit periodic fluctuations with the same frequency and a phase difference of approximately 120°. And the fluctuation frequency is approximately equal to the rotation frequency of the robotic arm; The greater the fluctuation amplitude, the greater the eccentricity / coaxiality deviation.

[0018] The specific identification and judgment steps are as follows: S11: Low-force stable clamping, three fingers wrap around the nut with a small clamping force, the fingertip elastic pads are in close contact with slight pressure, the robot arm remains stationary, and the initial baseline current of the servo motor at the base of the three fingers is recorded; specifically: the bolt is clamped stably and low-force pre-tightened, the three fingers wrap around the nut with a low clamping force of 10%-30% of the rated clamping force, keeping the robot arm stationary and not rotating; the stationary baseline currents I10, I20, I30 of the first drive auxiliary motor of the three fingers and the stationary baseline currents Ij10, Ij20, Ij30 of the second drive auxiliary motor at the base of the finger joint are recorded respectively, and are collectively recorded as the baseline current Ibase.

[0019] S12: The robotic arm performs low-speed idle rotation without axial feed; the low-speed idle rotation detection is performed by placing the screw in an external constraint device under low-constraint support, clamping the nut with low preload when gripping the bolt, and directly performing low-speed idle rotation detection on the bolt and the robotic arm coaxiality in the receiving hole (external constraint device); the palm drives the three fingers to slowly rotate multiple times around the robotic arm's rotation axis, performing idle rotation without feed throughout the process; the real-time current of the first drive auxiliary motor at the base of the three fingers, the real-time current of the second drive auxiliary motor at each finger joint, and the real-time rotation angle θ of the robotic arm are monitored and collected in real time. (t) .

[0020] S13: Extract current characteristics and determine different shafts; based on the characteristic that the baseline current of different screw motor models differs, a dynamic difference ratio determination method is adopted to adapt to the detection needs of bolts of different specifications; for the real-time current of each motor collected, the current difference ΔI=I is calculated respectively. (t) -I base The relative rate of change of current ΔI / I base It also presets a proportional threshold; at the same time, it can perform bandpass filtering on the servo motor current of the second drive pair at the root of each finger, retain the components near the rotation frequency of the robotic arm, and extract the current fluctuation amplitude A1, A2, A3 and phase ϕ1, ϕ2, ϕ3 of each motor to assist in feature determination.

[0021] Coaxiality determination rule: If the relative rate of change of current ΔI / I of the motors of the first and second drive pairs of the three fingers is... base If all values ​​are less than the preset proportional threshold, and the current fluctuations are stable with no periodic fluctuations or obvious phase difference characteristics, then the bolt and the robot are determined to be coaxial.

[0022] Eccentricity and misalignment determination rule: If the relative rate of change of current ΔI / I of any one or more fingers motors is... base If the relative change rate of the three finger motors is significantly different and fluctuates periodically as the robotic arm continues to rotate, and the maximum amplitude of the motor current fluctuation exceeds the preset amplitude threshold and the phase difference between the fingers is close to 120°, it is determined that the bolt axis is not on the same axis as the robotic arm's rotation axis and there is dynamic eccentricity.

[0023] S14: Correction procedure for misalignment 1) Immediately reduce the clamping force to 5%–15% of the rated clamping force, so that the fingertip elastic pad can fully recover its deformation, allowing the nut to slide slightly within the robotic arm's jaws and releasing the rigid clamping constraint.

[0024] 2) Fingertip smooth self-centering alignment: Under low-force relaxation, the limiting and guiding effect of the fingertip guide groove, combined with the adaptive deformation characteristics of the elastic thin pad, guides the nut to automatically move towards the center of the robot arm, eliminating most of the eccentric deviation.

[0025] 3) Active fine-tuning of finger rotation base: The first drive pair controls the base of each finger to deflect at a small angle of ±2°-5°. Combined with real-time current feedback, a closed-loop adjustment is formed to continuously correct the alignment deviation until the relative change rate of current ΔI / Ibase of all motors of the three fingers drops below the preset ratio threshold, and the current fluctuation is uniform and stable without periodic fluctuations.

[0026] 4) Low-speed test run verification again: After fine-tuning, perform low-speed idling test without axial feed again. If the abnormal relative change rate of motor current and the eccentricity of periodic fluctuations completely disappear, the alignment and coaxiality are deemed qualified. Restore normal clamping force and prepare for formal tightening. If abnormal characteristics still exist, repeat the above steps of reducing force, self-centering and alignment, and angle fine-tuning until the coaxiality meets the standard.

[0027] Furthermore, the method for determining the coaxiality of the bolt and the threaded hole, The first 1-2 threads of the bolt are tapered and fit with the bolt hole with clearance. If the coaxiality is normal and there is no misalignment, the motor will show low torque, stable current and linear increase in angle with feed during the screwing process. If the bolt axis is misaligned (with a slight included angle), the thread will contact on one side, resulting in uneven load and wedging. This manifests as a sharp increase in the motor's current / torque, a halt in the angle increase, and the robotic arm exhibiting a "tightening" phenomenon. Spur gear transmissions lack self-locking and have low friction, so changes in current directly reflect the actual jamming force of the thread, without the self-locking protection of a worm gear.

[0028] The specific steps for determining the coaxiality of the bolt and the threaded hole are as follows: S21: Low-speed trial rotation stage. After coaxial alignment is completed, the robot moves with the bolt and aligns it with the screw hole. It starts to rotate at low speed and small feed, only turning the first 1-2 threads. S22: Monitor servo motor current and twisting angle, collect servo motor current of finger joints and root in real time, and record changes in the twisting angle of the robot arm. S23: Joint judgment of deviation based on three features 1) The current suddenly and significantly increases, far exceeding the current during normal turning. Specifically: I(t)>I base +ΔI th2 ΔI th2 : 30%–50% of the baseline current; If the duration is >0.2s, it is determined to have an off-center load risk; 2) The turning angle hardly increases anymore, and the screw becomes stuck and cannot be turned. 3) The difference in motor current among the three fingers increases, with the current on one side of the fingers being significantly higher; When deflected: if one side of the thread is in contact, the current at the corresponding finger joint / root will increase significantly; If any two of the above conditions occur simultaneously, it is determined that the bolt axis is misaligned with the bolt hole axis, and the bolt will become stuck. S24: Correction Procedure for Deviation and Jamming 1) Immediately stop turning in the forward direction, maintain slight downward pressure to prevent the bolt from coming off; 2) Reverse small angle retraction: Reverse the robotic arm 3°–10°, while reducing the clamping force to allow the fingertip elastic pad to fully reset; reduce the clamping force to 10%–20% of the rated force to allow the fingertip elastic pad to reset. 3) Compliant self-centering secondary alignment: Under low force conditions, the fingertip guide groove and elastic pad self-adjust to eliminate the slight misalignment angle between the bolt and the screw hole; 4) Try turning again at low speed: Turn the first 1-2 threads again at a low speed of 1-3° / s and with a small feed. Repeat the above judgment process. Try a maximum of 3 times. If it is still abnormal, alarm and stop the machine.

[0029] The advantages and beneficial effects of this invention are as follows: 1. Three-finger full drive and wrench frame dual mode: It can precisely grasp, transfer, insert and remove, and rigidly lock the nut, greatly improving the twisting and anti-slipping ability, and is suitable for complex operations in microgravity space.

[0030] 2. Smooth self-centering at the fingertips: The combination of V-shaped guide grooves and elastic thin pads allows for automatic alignment under low force, reducing eccentricity and misalignment, and preventing the threads from being stressed on one side, seizing, or damaged.

[0031] 3. Sensorless motor current sensing: Utilizing real-time feedback of servo motor current / torque, eccentricity and skewness are accurately identified through periodic characteristics. No additional sensors are required, resulting in a simple structure, high reliability, and low cost.

[0032] 4. Online coaxial detection and automatic correction: Empty rotation detection, low-speed trial rotation, and current closed-loop correction quickly eliminate eccentricity and slight deviation, prevent jamming and slippage, and significantly improve the success rate of on-orbit assembly and disassembly.

[0033] 5. Quick-release modular design for fingers: Faulty fingers can be quickly replaced on the track without disassembling the entire machine, reducing maintenance difficulty, shortening repair time, and extending the overall lifespan of the machine. Attached Figure Description

[0034] Figure 1This is an isometric drawing of the three-finger dexterous manipulator with bolt removal and assembly function of the present invention; Figure 2 This is an isometric view of the palm portion in this invention; Figure 3 This is an isometric view of the finger portion in this invention; Figure 4 This is a schematic diagram of the base phalanx and its internal driving structure in this invention; Figure 5 This is a schematic diagram of the proximal phalanx and internal driving structure in this invention; Figure 6 This is a schematic diagram of the distal phalanx, fingertip phalanx, and internal driving structure in this invention; Figure 7 This is a schematic diagram of the compliant self-centering positioning module in this invention; Figure 8 This is a top view of the fingertip joint clamping bolt in this invention; Figure 9 This is a schematic diagram of the integrated flange frame in this invention; Figure 10 This is a schematic diagram of the arrangement of the rotating block in this invention; Figure 11 This is a schematic diagram of the compliant self-centering mechanism in this invention; In the diagram: 1. Palm; 2. Fingers; 3. First drive pair; 4. Second drive pair; 5. Servo motor; 6. Rotating base; 7. Gear pair; 8. Drive gear; 9. Driven gear; 10. Base phalanx; 11. Proximal phalanx; 12. Distal phalanx; 13. Finger tip phalanx; 14. Quick-release structure; 15. Connecting ear; 16. Double positioning holes; 17. Slot; 18. Double pin positioning component; 19. Compliant self-centering positioning module; 20. Guide groove; 21. Elastic thin pad; 22. Wrench jaw frame; 23. Rotation. 24. Block; 25. Slide rail; 26. Motor compartment; 30. Motor compartment cover; 31. Base finger left plate; 32. Base finger right plate; 33. Base finger upper plate; 34. Base finger cover; 35. Proximal finger left plate; 36. Proximal finger right plate; 37. Proximal finger upper plate; 38. Proximal finger lower plate; 39. Distal finger left plate; 40. Distal finger right plate; 41. Distal finger lower plate; 42. Finger tip left plate; 43. Finger tip right plate; 44. Finger tip upper plate; 45. Finger tip lower plate; 46. Intermediate transmission gear; 47. Locking block; 48. Locking groove. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1: A three-finger dexterous robotic hand for space satellites with bolt assembly and disassembly capabilities, such as Figure 1-6 As shown, it includes a palm portion 1 and finger portions 2, wherein the palm portion 1 is provided with multiple finger portions 2, such as... Figure 1 The palm part 1 is equipped with a first drive pair 3 that independently drives the corresponding finger parts 2 to rotate and adjust around the longitudinal axis. In this embodiment, the palm part 1 is modularly connected to the robotic arm, and the entire robotic arm rotates around the longitudinal axis through the rotating part of the robotic arm to tighten the bolts. Figure 1 , 2 As shown, the palm part 1 includes a motor compartment 25, a compartment cover 26, and a first drive pair 3 arranged along the Z-axis inside the motor compartment 25. In this embodiment, the first drive pair 3 can be directly adopted as a servo motor 5, which is set along the Z-axis and its output shaft extends into the gap between the motor compartment 25 and the compartment cover 26. A rotating base 6 is set in the gap. The output end of the servo motor 5 of the first drive pair 3 is connected to one end of the rotating base 6, and its other end extends out of the range of the palm part 1 for mounting the finger part 2. The deflection of the finger part 2 is controlled by the first drive pair 3.

[0037] The finger portion 2 includes multiple phalanges. In this embodiment, three fingers are used as an example. The three finger portions 2 are arranged in a triangular shape on the palm portion 1. Figure 3 As shown, each finger segment 2 includes a base phalanx 10, a proximal phalanx 11, a distal phalanx 12, and a fingertip phalanx 13, which are sequentially hinged together. A second drive pair 4 is provided at the hinge points between the phalanxes, making the finger segment 2 a fully driven finger. The second drive pair 4 specifically includes a servo motor 5 and a gear pair 7. The gear pair 7 includes at least a drive gear 8 and a driven gear 9. The servo motor 5 is fixedly installed in one phalanx of the finger joint, and the driven gear 9 is fixedly installed in the other phalanx of the finger joint. The output end of the servo motor 5 is connected to the drive gear 8, and the drive gear 8 meshes with the driven gear 9. The gear pair 7 is a spur gear or a helical gear.

[0038] like Figure 4-6 As shown, the base phalanx 10 includes a left base plate 30, a right base plate 31, a top base plate 32, and a cover plate 33; the proximal phalanx 11 includes a left proximal plate 34, a right proximal plate 35, a top proximal plate 36, and a bottom proximal plate 37; similarly, the distal phalanx 12 includes a left distal plate 38, a right distal plate 39, a top distal plate 40, and a bottom distal plate 41; the phalanx 13 includes a left phalanx 42, a right phalanx 43, a top phalanx 44, and a bottom phalanx 45, so that the base phalanx 10, proximal phalanx 11, distal phalanx 12, and phalanx 13 all constitute a similar rectangular barrel-shaped structure.

[0039] The base joint 10 is hinged to the proximal joint 11. Specifically, the upper ends of the base left plate 30 and the base right plate 31 are hinged to the lower ends of the proximal left plate 34 and the proximal right plate 35 of the proximal joint 11. The servo motor 5 of the second drive pair 4 set at this hinge location is fixedly installed inside the rectangular barrel structure formed by the base joint 10. The gear pair 7 of this second drive pair 4 includes a drive gear 8 set at the output end of the servo motor 5 and a driven gear 9 fixedly installed on the hinge shaft of the proximal joint 11. Through the meshing of the drive gear 8 and the driven gear 9, the servo motor 5 drives the proximal joint 11 to rotate relative to the base joint 10. Since the meshing drive of spur gears or helical gears is used, this drive structure has the characteristics of simple structure, low friction interference, fast transmission response, easy control and retraction. At the same time, the change of motor current can directly reflect the joint obstruction.

[0040] Similarly, the hinge drive structure of the proximal phalanx 11 and distal phalanx 12 is as follows: the upper ends of the proximal left plate 34 and proximal right plate 35 of the proximal phalanx 11 extend upwards to the left and right sides of the lower part of the distal phalanx 12, and form hinges with the corresponding positions of the distal left plate 38 and distal right plate 39. A second drive pair 4 is set inside, which is similar to the structure in the aforementioned base phalanx 10 and proximal phalanx 11. A servo motor 5 and a drive gear 8 are set inside the proximal phalanx 11, and a driven gear 9 is fixedly set at the hinge shaft of the distal phalanx 12, and the drive is formed by meshing. The upper ends of the distal left plate 38 and distal right plate 39 of the distal phalanx 12 extend upwards to the left and right sides of the fingertip phalanx 13 and are used for hinges with it. The second drive pair 4 in this joint is slightly different from the aforementioned one. An intermediate transmission gear 46 is added between the drive gear 8 and the driven gear 9. The gear ratio can be changed by the intermediate gear to reduce speed and achieve the purpose of fine control of the fingertip rotation angle. Furthermore, in this embodiment, mounting end caps are provided at the joints of the fingers to restrict axial movement.

[0041] Through the above-mentioned fully driven finger structure design, the basic functions of the robot can be realized, such as: 1) grasping and transferring parts: such as small parts such as bolts, nuts, pins, clamping blocks, and washers; 2) adjusting and pre-positioning the posture of connectors: the clamping posture of connectors can be finely adjusted by independent control of three fingers; 3) inserting, removing and placing non-threaded parts: such as pins, positioning pins, buckles, and clamping plates; 4) compliant clamping and low-damage operation: suitable for fine operations near the thin solar panel and connector.

[0042] For example, when performing on-orbit maintenance on the solar panels of a space satellite, the maintenance involves not only tightening but also complex tasks such as grasping, transporting, attitude adjustment, insertion and removal, placement, and compliant docking. Therefore, this embodiment uses a three-finger dexterous manipulator, which can be widely adapted to space maintenance scenarios involving multiple objects, multiple attitudes, and multiple processes, and is suitable for tightening bolts.

[0043] The fully driven three-finger configuration enables precise twisting and anti-jamming under microgravity: This solution uses independent motor drives for each of the three fingers, combined with gear transmission, to achieve adaptive envelope gripping by the finger joints. This, along with the attitude deflection of the rotating base 6, precisely matches the position and thread specifications of the solar panel connector. The fully driven configuration allows independent control of each finger joint, enabling adaptive adjustment of the envelope shape according to the connector's shape. This overcomes the disturbance of weak contact forces under microgravity at the mechanical level, effectively solving the docking deviation problem. The rotating base 6 can actively adjust its working posture to ensure precise alignment of the twisting axis and the thread axis, preventing thread jamming. The combination of independent motor drives and gear transmission ensures precise output of twisting torque while maintaining gripping stability, significantly improving the reliability of on-orbit assembly and disassembly operations.

[0044] Example 2: In existing technologies, the finger structure of robotic arms is usually complicated in terms of connection methods, with intricate connecting parts and transmission components. This makes disassembly and replacement difficult and maintenance complex. If a problem occurs with a single finger, the entire robotic arm will become paralyzed. The complex structure makes it impossible to perform quick repairs, and usually, the arm can only be sent back to the ground for unified maintenance and replacement. This causes great trouble for use in orbit. This embodiment improves on this problem by modularizing the finger part 2 and connecting it to the rotating base 6 of the palm part 1 through a quick-release structure 14. In this way, when a problem is found with a finger part 2 during use in orbit, it can be easily disassembled and replaced in orbit, and the replacement is convenient and efficient.

[0045] Specifically, such as Figure 1 , 2 As shown, the base knuckle 10 and the rotating base 6 are connected by a quick-release structure 14. The rotating base 6 has an overall cuboid structure, with a connecting hole at one end for connecting to the servo motor 5 of the first drive pair 3 inside the palm part 1. The first drive pair 3 controls the rotating base 6 to swing around its drive shaft, thereby controlling the overall rotation of the finger part 2. The other end of the rotating base 6 forms a slot 17 for fixing the finger part 2. Specifically, the base knuckle 10 has a insertion ear 15 at its base, with double positioning holes 16 on the insertion ear 15. The rotating base 6 has a slot 17 that mates with the insertion ear 15, and the slot 17 has a sliding insertion double positioning hole. The double pin positioning component 18 of the positioning hole 16 and the slide rails 24 on both sides of the rotating base 6 are unlocked. After unlocking, the slide groove is pulled outward through the slide rails 24 to open the slot 17. After the slot 17 is extended, it provides space for the movement of the plug ear 15, so that the plug ear 15 can be released from the lock of the double pin positioning component 18, and then the entire finger part 2 can be removed. When replacing the spare finger part 2, the above order is reversed and reinstalled. The slot 17 moves back through the slide rails 24 and locks the plug ear 15 to form a fixation for the finger part 2. Then the position of the slot 17 is locked. After connecting the ribbon cable plug, the quick disassembly and installation steps can be completed. In this way, the faulty finger part 2 can be replaced on the rail.

[0046] Reduced on-orbit maintenance costs: In this embodiment, the finger connection structure adopts a quick-release structure 14 with slide rail 24 and double pin positioning, which can complete the finger installation without complicated alignment adjustments. During assembly, simply insert the finger part 2 and then push it into place along slide rail 24 to lock it in place, so that the double pin positioning part 18 can be inserted into the double positioning hole 16 to achieve locking, which greatly simplifies the ground assembly and on-orbit deployment process; when maintaining or replacing the finger later, only the fixed shaft needs to be removed to pull out the entire finger, without disassembling the whole machine or other modules; the quick-release structure 14 supports quick replacement of spare parts on-orbit, which significantly reduces the difficulty and operation time of disassembly and replacement in the space environment, and effectively reduces the maintenance cost throughout the entire life cycle.

[0047] Example 3: The improvement of this embodiment compared to Embodiment 1 lies in the structural improvement of the fingertip joint 13, such as... Figure 7 As shown, specifically, a compliant self-centering positioning module 19 is provided at the end of the fingertip joint 13, which includes a guide groove 20 and an elastic thin pad 21. The guide groove 20 is provided at the distal end of the fingertip joint 13. The guide groove 20 includes a V-shaped groove, an arc-shaped groove, or a composite groove combining V-shape and arc shape. An elastic thin pad 21 is provided on the inner side of the groove opening of the guide groove 20.

[0048] Figure 11 The left-middle figure shows the misalignment between the bolt axis and the threaded hole axis during rigid clamping. The structural improvement in this embodiment guides the connector towards the robot's tightening center when the three-finger clamping force is closed, reducing clamping eccentricity before tightening. The intermediate elastic thin pad 21 allows the connector to make slight radial clearance and small-angle compensation during the initial thread introduction stage, such as... Figure 11 As shown in the middle right figure, rigid clamping is used to avoid unilateral stress on the first 1-2 threads. The intermediate elastic thin pad 21 allows the connector to make slight radial clearance and small angle compensation during the initial thread introduction stage, thus avoiding unilateral stress on the first 1-2 threads due to rigid clamping.

[0049] Example 4: In this embodiment, the wrench frame is preferably formed after the compliant self-centering alignment described in Embodiment 3 is completed, which improves the anti-slipping ability during the formal tightening stage; the compliant alignment stage and the rigid locking stage are performed step by step. Specifically, in actual use, the finger part 2 can achieve a good clamping effect when independently controlling the clamping of the three sides of the nut, and the fingertip joint 13 applies radial clamping force to the nut; however, when the bolt is turned, especially when the bolt is tightened to the end, the clamping force formed by the radial pressure applied by the fingertip to the nut is difficult to fix well under the radial pressure as the bolt resistance increases, and slippage is likely to occur; for example Figure 8 As shown, the reason is that when the rotational resistance increases, the tangential component of the force on the clamping part increases sharply (e.g., Figure 8As indicated by the single arrow in the middle, the risk of slippage increases. At this point, the nut tends to rotate relative to the fingertip joint 13, and with the slight rotation of the hexagonal nut, the reaction force exerted by the nut on the fingertip joint 13 causes an outward expansion effect on the surrounding finger portion 2. Figure 8 (As indicated by the double arrows in the middle), if the finger part 2 cannot increase sufficient clamping force in time, it will eventually lead to slippage.

[0050] In other words, to avoid slippage, the radial pressure must be increased exponentially to resist the tangential force. If the radial pressure cannot resist the tangential force, the nut will easily slip. In practice, to make the robot arm more flexible, the best solution is to use a fully driven joint. However, due to the limited installation space, the joint motor of a fully driven joint is usually small, and its torque output is limited. When performing ordinary grasping operations in space, due to weightlessness, the relatively small torque servo motor 5 can still complete the grasping and transfer of the workpiece well. However, when facing the task of tightening bolts, this situation requires the servo motor 5 in the finger to output strong torque. That is to say, it is difficult for a normal robot arm finger 2 to have the function of tightening bolts if it is equipped with a relatively small torque servo motor 5.

[0051] To overcome the aforementioned shortcomings, namely the limitation of insufficient output torque of the servo motor 5, while still achieving good bolt tightening performance, the specific improvements in this embodiment include: the fingertips 13 of the three fingers 2 are sequentially connected end-to-end to form a wrench frame 22, as shown below. Figure 9 As shown, the wrench frame 22 connects and fixes the three finger parts 2 together through the fingertip joint 13 to form a whole. The wrench frame 22 forms a wrench that mates with the nut of the bolt, thereby rigidly locking the nut. In this embodiment, when facing the operation of tightening the nut of the bolt, the finger parts 2 can be spliced ​​together through their fingertip joints 13 to form a wrench frame 22. The inner dimensions of the wrench frame 22 match the nut specifications. During the tightening operation, if the tangential force increases and the nut tends to rotate, the wrench frame 22 forms a fixed frame structure. It restricts the rotation of the nut through the shape of the wrench, thereby avoiding relative rotation and limiting the outward expansion effect on the finger parts 2. During the entire tightening process, it is not necessary to increase the torque of the electrodes inside the finger parts 2. This embodiment provides an example of connecting the fingertips 13 of three fingers into one unit. Of course, this solution does not limit the form of connection and fixation between the fingertips 13. Other snap-fit ​​methods can also be used, that is, the tip of the fingertips 13 is inserted into the fingertip of the adjacent fingertips 13 and then the two are fixedly connected by snap-fit. The snap-fit ​​can be a motor specially set in the fingertip to control the locking and unlocking of the snap-fit, thereby conveniently realizing the connection and separation between the fingertips 13.

[0052] In this embodiment, when the fingertips 13 of the finger section 2 are separated, it is similar to a normal fully driven robotic arm and can perform various grasping and transfer operations. When facing the operation of tightening bolts, the three finger sections 2 are connected and fastened to form a wrench frame 22, so that they can be integrated as one unit. This can better overcome the tangential force. Even when the torque of the servo motor 5 in the finger joint is small, the bolt tightening operation can still be completed, effectively avoiding the risk of slippage.

[0053] Specifically, such as Figure 9 As shown, the end of the fingertip joint 13 is provided with a locking block 47, and the side of the fingertip joint 13 is provided with a locking groove 48 that cooperates with the locking block 47. Due to the design of the first drive pair 3, the deflection angle of the finger part 2 can be easily controlled. In use, the fingertip joint 13 is adjusted to a horizontal position, and all three fingers 2 are deflected and rotated at a certain angle through the first drive pair 3. The three fingertip joints 13 are sequentially locked into the locking groove 48 of the adjacent fingers through the locking block 47, thereby forming an integrated frame structure of the wrench frame 22. The space specifications inside the wrench frame 22 are adapted to the nut, so that when the nut is rotated under the same servo motor 5 output, it can resist a large radial force and avoid slippage. In this embodiment, since a smaller servo motor 5 can be used to complete the operation with a large torque requirement, it can save the purchase cost of a large torque servo motor 5 in actual production, and it is also suitable for installation in the space of a smaller finger joint. Furthermore, in order to better adapt to application scenarios with large tangential force, the slot 48 is preferably designed as a through slot 48 perpendicular to the direction of the upper fingertip plate 44 / lower fingertip plate 45. During installation, the fingertip joint 13 is in a horizontal position. By controlling other joints, the fingertip joint 13 is kept moving horizontally up and down, so that the locking block 47 at its end is vertically locked into the through slot 48, effectively increasing the strength and preventing the fingertip joints 13 from separating during screwing.

[0054] Example 5: In practical applications, for ease of use, bolts on space satellites are usually designed to be of the same specification or a small number of different specifications. To accommodate various bolt specifications in space satellites, this embodiment improves the structure of the fingertip joint 13 based on Embodiment 4. Specifically, as follows: Figure 10 As shown, a rotating block 23 is provided on the finger joint 13 for rotation control around the long axis of the finger joint 13. The rotating blocks 23 on the three finger joints 13 are rotated and adjusted so that their different sized sides face the inside of the wrench frame 22, so that the wrench frame 22 forms a switchable structure that can fit with different sized nuts. In actual use, the rotating block 23 can be set as a cuboid structure, and its rotation axis is also set off from its geometric axis. Thus, when controlling its rotation, the four sides of the rotating block 23 can form wrench frames 22 corresponding to four different sizes, greatly increasing its applicability.

[0055] Understandably, after controlling the rotation of the rotating block 23, it is necessary to keep its position locked to avoid slippage caused by rotation when tightening the bolt. Preferably, a worm gear transmission structure is set in the finger joint 13. The rotating block 23 is driven to rotate through the worm gear structure, thereby giving it a self-locking characteristic. This not only facilitates the switching of the various sides of the rotating block 23, but also locks it after the switching is completed, effectively preventing slippage during the tightening process.

[0056] Example 6: While three-finger robotic arms offer the advantage of flexibility, easily grasping various irregularly shaped objects and facilitating the handling and transfer of workpieces during on-orbit operation, they struggle with bolt tightening. Grabbing a bolt is easy, but tightening it is difficult. First, ensuring the bolt's axis is coaxial with the robotic arm's rotation axis is crucial. Tightening a bolt involves the robotic arm driving the entire arm's rotation; if the arm's axis is not coaxial with the bolt's, the tightening operation is impossible. Second, aligning the bolt with the threaded hole before screwing it in usually requires aligning the bolt end with the hole. However, in practice, even when the bolt end is aligned, a slight angle exists between the bolt's axis and the hole's axis, leading to increased uneven loading during tightening.

[0057] To address this issue, this embodiment comprehensively collects real-time parameters of motor current or driving torque fed back from each joint drive pair of the robotic arm during the driving process. During the process of the robotic arm tightening the bolt, the changes in resistance of the finger rotating around the longitudinal axis and the changes in resistance at the finger joints are detected by the real-time parameters fed back. During the tightening rotation, the coaxiality of the bolt and the robotic arm or the coaxiality of the bolt and the bolt hole is determined by the periodic change law of the resistance at each joint of the robotic arm.

[0058] During servo motor driving, the reaction force of the three-finger robotic arm touching an object is directly transmitted to the servo motor through gears, causing changes in current or driving torque. The central controller then processes, analyzes, and determines the collected feedback parameters. This embodiment focuses on constructing a closed-loop current / torque sensing and online coaxiality judgment system. This system enables the robotic arm to achieve high-precision coaxial detection, skew identification, and automatic correction without sensors (relying solely on motor electrical signals) in a microgravity, low-rigidity, and weak-feedback spatial environment. This avoids thread seizure, stripping, or damage to connectors, significantly improving the reliability of on-orbit assembly and disassembly in space.

[0059] Specifically, the palm part has three built-in first drive pairs (servo motors + rotating bases) that drive three fingers to deflect independently around the Z-axis; the second drive pairs in each joint of the finger part form a fully driven finger; the fingertip module is equipped with a compliant self-centering positioning module (V-shaped guide groove + elastic thin pad); and the servo motors are monitored, including real-time output current I, position θ, and speed ω.

[0060] During the tightening or clamping process, the robot arm comes into contact with the nut / screw hole, and the contact force is directly converted into the motor load torque through the fingertip → knuckle → gear pair → servo motor shaft: the motor current I is proportional to the load torque T.

[0061] When coaxial: the three fingers are subjected to symmetrical forces, I1≈I2≈I3, with small fluctuations and no periodicity.

[0062] When eccentric / skewed: One side experiences greater force than the other, resulting in a current difference > 0.3A. This current exhibits periodic fluctuations with a 120° phase difference as the robot rotates, with a frequency equal to the robot's rotational speed. The central controller extracts four characteristics in real time: average current, fluctuation amplitude, phase difference, and angle change rate, enabling automatic identification of coaxial / eccentric and aligned / skewed states. It should be understood that the above thresholds and specific values ​​are merely examples and can be preset or adaptively adjusted based on bolt specifications, thread size, clamping force, motor model, transmission ratio, and ground calibration results.

[0063] I. Bolt-Robot Coaxiality Inspection and Correction: S11: Low-force stable clamping The three fingers enclose the nut with 20% of the rated clamping force, and the thin elastic pads at the fingertips deform slightly to fit; the robotic arm remains stationary, and the baseline current of the three root motors is recorded: I 10 =0.22A, I 20 =0.21A, I 30 =0.23A; The joint baseline current Ij≈0.20A.

[0064] S12: Low-speed vortex detection This test involves placing the screw inside an external constraint device and testing it under low-constraint support conditions. In actual use in space, each bolt is placed in a storage hole one by one. When the three-finger robotic arm grasps the nut, the bolt is directly tested by air rotation in the bolt storage hole. The bolt storage hole is regarded as an external constraint device, which forms a guide hole for the bolt and provides low-constraint support, thereby enabling low-speed air rotation testing.

[0065] The robotic arm rotates 5 revolutions around the Z-axis at 2° / s without axial feed; real-time data acquisition: Root currents: I1(t), I2(t), I3(t); Joint currents: Ij1(t) ~ Ij9(t); Rotation angle: θ(t); S13: Coaxiality determination (parameter threshold can be set or changed) Coaxial: Current difference < 0.15A, fluctuation amplitude < 0.08A, no periodicity, pass the test.

[0066] Eccentricity is determined by current difference > 0.3A, fluctuation amplitude > 0.15A, and phase difference ≈ 120°.

[0067] Example (actual measurement in an eccentric scenario): I1: 0.45A (high), I2: 0.22A (medium), I3: 0.10A (low); as the rotation progresses, the current alternates between high and low, with a period of ≈3s (matching the rotation speed), indicating that the bolt is eccentric by 1.2mm.

[0068] S14: Automatic Eccentricity Correction Reduce the clamping force to 10% of the rated force, the elastic thin washer returns to its original position, allowing slight slippage of the nut; Smooth self-centering at the fingertips: V-groove + elastic washer guides the nut to move towards the center, eliminating about 80% of the off-center; Active fine-tuning: Controls finger base deflection ±3°, closed-loop adjustment to current difference <0.15A and fluctuation <0.08A; Secondary verification: Rotate freely for 3 more revolutions. The characteristic disappears, indicating coaxiality. Restore the rated clamping force.

[0069] II. Bolt-Thread Hole Coaxiality Inspection and Correction: S21: Low-speed trial spin After coaxial alignment, the robot arm with bolts is aligned with the screw hole, and the first two threads are screwed in at a feed rate of 1.5° / s and 0.1mm / s.

[0070] S22: Real-time monitoring Synchronous data acquisition: Current: I(t), Ij(t); Angle: θ(t), dθ / dt; S23: Skewness determination (combined three features) Thresholds: Current surge > 40% of baseline (ΔI > 0.08A), angle stagnation > 0.5s, three-finger current difference > 0.3A; any two conditions must be met to determine skewness or jamming.

[0071] For example: the current increases from 0.22A to 0.58A (+163%), the angle increases by only 0.8° in 3 seconds, I1=0.55A is much higher than I2=0.23A and I3=0.21A, indicating that the bolt is deflected by 1.8° and is about to jam.

[0072] S24: Automatic Deviation Correction 1. Stop rotating and maintain a downward pressure of 0.5N to prevent the bolt from coming loose; 2. Reverse the direction by 5°, reduce the clamping force to 15%, and the elastic pad will fully return to its original position; 3. Secondary self-centering: The fingertip adaptively adjusts under low force to eliminate minor deviations; 4. Retry: Try turning 2 turns at low speed, and retry a maximum of 3 times; if it is still abnormal, alarm and stop the machine to avoid physical damage.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites, characterized in that, The device includes a palm and fingers. The palm has multiple fingers, and each finger has a first drive pair that independently drives the corresponding fingers to rotate around the longitudinal axis. Each finger has multiple knuckles, and a second drive pair is provided at the hinge joint between the knuckles. The device comprehensively collects real-time parameters of the motor current or driving torque fed back from each joint drive pair during the driving process. During the screw-tightening process, the device detects the changes in resistance of the fingers rotating around the longitudinal axis and the changes in resistance at the finger joints by using the real-time feedback parameters. During the screw-tightening rotation, the device determines the coaxiality of the bolt and the device or the coaxiality of the bolt and the screw hole by observing the periodic changes in the resistance at each joint of the device.

2. The three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 1, characterized in that, The first drive unit includes a servo motor and a rotating base. The servo motor is fixedly installed inside the palm, and the output end of the servo motor is connected to the rotating base. The root of the finger is installed on the rotating base.

3. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 2, characterized in that, The second drive pair includes a servo motor and a gear pair. The gear pair includes at least a drive gear and a driven gear. The servo motor is fixedly installed in one side of the finger joint, and the driven gear is installed in the other side of the finger joint. The output end of the servo motor is connected to the drive gear. The drive gear meshes with the driven gear. The gear pair is a spur gear or a helical gear.

4. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 3, characterized in that, During the servo motor drive process, the reaction force of the three-finger robotic arm touching the object directly acts on the servo motor, causing the servo motor to generate changes in current or driving torque. The central controller then organizes, analyzes, and determines the collected feedback parameters.

5. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 1, characterized in that, The finger section has three segments, each of which includes a base phalanx, a proximal phalanx, a distal phalanx, and a fingertip phalanx that are hinged together in sequence. The base phalanx is connected to the rotating base via a quick-release structure. The base phalanx has a plug-in ear at its base, and the plug-in ear has double positioning holes. The rotating base has a slot that mates with the plug-in ear, and the slot has a double pin positioning component that slides into the double positioning holes.

6. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 5, characterized in that, The end of the fingertip joint is provided with a compliant self-centering positioning module, which includes a guide groove and an elastic thin pad. The guide groove is provided at the distal end of the fingertip joint. The guide groove includes a V-shaped groove, an arc-shaped groove, or a composite groove combining V-shape and arc shape. An elastic thin pad is provided on the inner side of the groove opening of the guide groove.

7. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 5, characterized in that, The fingertips of the three fingers are connected end to end to form a wrench frame. The wrench frame connects and fixes the three fingers together through the fingertips, forming a single unit. The wrench frame forms a wrench that mates with the nut of a bolt.

8. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 7, characterized in that, The fingertip joint is equipped with a rotating block that controls the rotation around the long axis of the fingertip joint. The rotating blocks on the three fingertip joints are rotated and adjusted so that their different sized sides face the inside of the wrench frame, so that the wrench frame forms a wrench with a switchable structure that can be matched with nuts of different sizes.

9. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 1, characterized in that, The method for determining the coaxiality of the bolt and the robot arm includes the following steps: S11: Low-force stable clamping. Three fingers grip the nut with a small clamping force, and the elastic pads at the fingertips apply slight pressure to maintain contact. The robotic arm remains stationary, and the initial current state of the servo motors at the base of the three fingers is recorded, which is the baseline current I of each motor. base ; S12: The robotic arm performs low-speed idle rotation without axial feed; the low-speed idle rotation detection is performed by placing the screw in an external constraint device under low-constraint support, with the palm driving the three fingers to slowly rotate multiple times around the robotic arm's rotation axis, performing idle rotation without feed throughout the process; the real-time current I of the servo motor at the base of the three fingers is monitored in real time. (t) ; S13: Extract current characteristics and determine different axes; Based on the characteristic that the baseline current of the motor differs when different screws are tightened, the current difference and proportional value of each finger servo motor are calculated in real time: ΔI=I (t) -I base The ratio of the relative rate of change of current is ΔI / I base Set a preset ratio threshold; If the relative rate of change of the motor current for the three fingers is ΔI / I base If all values ​​are less than the preset proportional threshold and the fluctuations are stable without periodic or regular fluctuations, then the bolt and the robot arm are determined to be coaxial. If the relative rate of change of the motor current of any one or more fingers is ΔI / I base If the current of each finger is greater than the preset ratio threshold and the relative change rate of the current of each finger is significantly different and shows periodic alternating fluctuations as the robot arm rotates, then it is determined that the bolt axis is not coaxial with the robot arm's rotation axis and there is eccentricity. S14: Correction procedure for misalignment 1) Immediately reduce the clamping force to allow the fingertip elastic pad to recover, allowing the nut to slide slightly within the robotic arm; 2) Fingertip compliant self-centering alignment: Under low force conditions, the fingertip guide groove and elastic pad guide the nut to move towards the center of the robot arm, eliminating most of the eccentricity; 3) Active fine-tuning of finger rotation base: Controls the small-angle deflection of the finger base, combined with current feedback, until the relative change rate of the current of the three motors is less than the preset proportional threshold and the current fluctuation is stable without obvious fluctuations. 4) Test rotation at low speed again: After the current returns to a stable level, restore the normal clamping force and prepare for formal tightening.

10. A three-finger dexterous manipulator with bolt removal and assembly function for space satellites according to claim 9, characterized in that, The method for determining the coaxiality of the bolt and the threaded hole includes the following steps: S21: Low-speed trial rotation stage. After coaxial alignment is completed, the robot moves with the bolt and aligns it with the screw hole. It starts to rotate at low speed and small feed, only turning the first 1-2 threads. S22: Monitor servo motor current and twisting angle, collect servo motor current of finger joints and root in real time, and record changes in the twisting angle of the robot arm. S23: Joint judgment of skewness based on three features: 1) The current suddenly and significantly increases, far exceeding the current during normal turning; 2) The turning angle hardly increases anymore, and the screw becomes stuck and cannot be turned. 3) The difference in motor current among the three fingers increases, with the current on one side of the fingers being significantly higher; If any two of the above conditions occur simultaneously, it is determined that the bolt axis is misaligned with the bolt hole axis, and the bolt will become stuck. S24: Correction procedure for skewness and jamming: 1) Immediately stop turning in the forward direction, maintain slight downward pressure to prevent the bolt from coming off; 2) Reverse small angle retraction: Reverse the robotic arm 3°–10°, while reducing the clamping force, so that the elastic pads at the fingertips can be fully reset; 3) Compliant self-centering secondary alignment: Under low force conditions, the fingertip guide groove and elastic pad self-adjust to eliminate the slight misalignment angle between the bolt and the screw hole; 4) Try turning again at low speed: Turn the first 1-2 threads again at low speed and small feed, and repeat the above judgment process.

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