Mechanical finger joint miniature encoder mounting structure for improving control precision

Abstract

The embodiment of the invention provides a mechanical finger joint miniature encoder mounting structure for improving control precision, and belongs to the technical field of medical instrument robot dexterous hands and high-precision sensing. The structure comprises a hollow annular magnetic encoder, a customized mounting base and an error compensation mechanism. The MPT-8-20 series encoder is directly integrated on a rotating shaft of a finger joint through the customized mounting base; the mounting base is provided with a positioning interface which is precisely matched with an encoder shell and a joint part, so that the concentricity and a constant air gap of an encoder sensing unit and a rotating part are ensured; the error compensation mechanism is integrated in the base and is used for passively inhibiting installation errors and environmental interference. According to the invention, the measurement precision of less than 0.01 degree in an extremely limited space is realized based on a commercial encoder, high anti-interference performance and reliability are realized, the integration problem of high-precision and high-reliability pose feedback of the miniature dexterous hand joint is effectively solved, and the miniature dexterous hand joint is suitable for miniature dexterous hands.

Description

Technical Field

[0001] This invention relates to the field of robot dexterous hand and high-precision sensing technology, and in particular to a micro encoder mounting structure for mechanical finger joints to improve control accuracy. Background Technology

[0002] As a core component for robots to achieve precise operations, the accuracy of the position measurement of the finger joints of a dexterous robotic hand directly determines its grasping and manipulation performance. Currently, displacement sensing solutions applied to robotic finger joints mainly suffer from the following limitations:

[0003] While traditional photoelectric encoders offer high measurement accuracy, their complex internal structure, including grating disks, light-emitting elements, and photosensitive receiving elements, makes miniaturization difficult and prevents installation within the extremely space-constrained space of finger joints. Furthermore, they are highly sensitive to environmental cleanliness; dust, oil, and condensation can easily contaminate the optical path, leading to signal failure, poor reliability, and difficulty in stable operation in unstructured environments.

[0004] Magnetic encoders overcome the size and environmental adaptability limitations of photoelectric encoders to some extent, but they generally suffer from insufficient accuracy. Solutions using conventional Hall elements have limited resolution, making it difficult to meet the measurement requirements of less than 0.01° for ultra-high precision operations (such as precision assembly and minimally invasive surgical simulation). Furthermore, magnetic encoders are extremely sensitive to installation tolerances such as the concentricity between the magnet and the sensor, and the air gap distance. Within the millimeter-scale micro-joint space, even minute deviations in machining and assembly can introduce significant measurement nonlinearity errors, which are difficult to completely eliminate through subsequent calibration.

[0005] Existing miniature encoder mounting structures typically lack targeted error compensation designs. During actual operation of a robotic arm, continuous joint rotation, unavoidable impact vibrations, and thermal changes during operation can all lead to micro-deformation of the mounting base and changes in the relative position of the encoder, compromising the accuracy of the initial calibration, causing measurement drift, and ultimately resulting in a decline in the overall control performance of the dexterous hand.

[0006] Therefore, developing a joint encoder mounting structure that can adapt to extremely miniaturized spaces while achieving ultra-high measurement accuracy, high environmental tolerance, and long-term stability has become a key technological bottleneck in promoting the development of high-end dexterous hands. Summary of the Invention

[0007] In view of this, embodiments of the present invention provide a mechanical finger joint micro encoder mounting structure for improving control accuracy, which at least partially solves the problems of limited space, insufficient sensor accuracy, and significant environmental interference in the prior art for micro dexterous hand joints.

[0008] This invention provides a micro encoder mounting structure for mechanical finger joints to improve control accuracy, including a hollow ring magnetic encoder, a customized mounting base, and an error compensation mechanism;

[0009] The hollow ring magnetic encoder includes a built-in ring magnet and a sensor sensing unit.

[0010] The customized mounting base includes a bearing and a finger base;

[0011] The bearing is coaxially fixed with the rotating output shaft of the finger joint, and the outer end face of the finger base is provided with a first positioning stop for interference fit or adhesive fixation with the rotating inner ring of the encoder.

[0012] The finger base is connected to the base of the first finger phalanx.

[0013] According to one specific implementation of the present invention, the bearing is made of an alloy material with a low coefficient of thermal expansion and has a through hole in the middle for connection with the rotating output shaft.

[0014] According to a specific implementation of an embodiment of the present invention, the finger base is an asymmetrical structure, which is connected to the first finger bone base through a bearing on the other side, and the diameter tolerance zone of the second positioning stop is H7, forming a precision clearance fit with the encoder static housing.

[0015] According to one specific implementation of the present invention, the fine-tuning shim group is an annular copper foil shim with a thickness of 0.01mm, 0.02mm or 0.05mm. By selecting shims of different specifications and quantities and stacking them, the gap between the static shell end face and the second positioning stop end face can be adjusted.

[0016] According to one specific implementation of the present invention, the mounting structure is entirely encapsulated within the internal cavity of the mechanical finger joint, and its maximum radial mounting dimension does not exceed 20mm.

[0017] According to a specific implementation of an embodiment of the present invention, the MPT-8-20 series encoder integrated through the mounting structure achieves an absolute position measurement accuracy better than 0.01° at the finger joint.

[0018] According to one specific implementation of the present invention, the finger base is a hollow structure, and its inner cavity is used to thread tendon ropes or signal cables that drive the dexterous fingers.

[0019] The present invention has the following beneficial effects:

[0020] It boasts extremely high measurement accuracy, achieving an angle measurement precision better than 0.01°. Through precise positioning stop design, error compensation mechanism, and dedicated signal processing algorithm, it achieves the resolution and accuracy of a photoelectric encoder, while also possessing stronger environmental adaptability.

[0021] With a compact structure and high integration, the overall radial dimension is less than 20mm, perfectly fitting the extreme space constraints of miniature, dexterous finger joints and solving the problem of installing high-precision sensors in tiny spaces.

[0022] It boasts strong anti-interference capabilities and excellent stability. The integrated soft magnetic alloy shielding design effectively resists external stray magnetic field interference; the error compensation mechanism suppresses installation errors and axial movement during operation, ensuring long-term accuracy and stability.

[0023] Excellent thermal stability. A titanium alloy with a low coefficient of thermal expansion is used as the mounting base, and temperature compensation is performed by a signal processing unit, effectively reducing the impact of temperature changes on measurement accuracy and ensuring measurement consistency across the entire temperature range.

[0024] Installation and maintenance are simple. The modular design and high-precision positioning interface enable rapid encoder installation and replacement, significantly reducing assembly difficulty and maintenance costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the mounting structure for a miniature encoder for a finger joint and the components of this mounting structure.

[0027] Figure 2 This is a schematic diagram of a hollow ring magnetic encoder structure;

[0028] Figure 3 This is a schematic diagram of the finger base structure;

[0029] Figure 4 This is a schematic diagram of the base of the first phalanx;

[0030] Figure 5 This is a schematic diagram of the error compensation mechanism; Detailed Implementation

[0031] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0032] See Figures 1-5This embodiment provides a mechanical finger joint micro encoder mounting structure for improving control accuracy. The structure is integrated inside the finger joint to achieve high-precision joint angle measurement. The specific structure includes the following parts: a hollow ring magnetic encoder (100), a customized mounting base (200), an error compensation mechanism (300), and a signal processing unit (400).

[0033] Hollow ring magnetic encoder (100): adopts MPT-8-20 series, with an outer diameter of 20mm, an inner diameter of 8mm, and a thickness of 5mm. It includes a ring magnet (110) and a sensor array plate (120). The ring magnet (110) is made of neodymium iron boron material, with multiple pole pairs magnetized (number of pole pairs ≥ 16), and is connected to the rotating part through its inner ring (101). The sensor array plate (120) is integrated into the encoder static housing (102) and contains a high-sensitivity magnetic induction unit.

[0034] Customized mounting base (200): includes bushing connector (210) and finger base (220). The right end face of the finger base is machined with a first positioning stop (211) with a diameter of 20.00 mm (tolerance 0 to +0.01 mm) and a depth of 1 mm.

[0035] The bushing connector (210) is made of TC4 titanium alloy, with a height of 8mm, an outer diameter of 12mm, and an inner diameter of 6mm. It is connected to the encoder rotating inner ring (101) by an interference fit (interference amount of 0.005mm).

[0036] Finger base (220): made of 7075 aluminum alloy, adopts an "L" shaped ring bracket structure, with a height of 10mm and a maximum outer diameter of 22mm. Its left end face is machined with a second positioning stop (221), with a stop diameter of 20.02mm (tolerance +0.01~+0.03mm), which forms a precision clearance fit with the encoder static housing (102).

[0037] Error compensation mechanism (300): includes fine-tuning shim group (310).

[0038] Fine-tuning shim group (310): composed of annular copper foil shims of three thicknesses of 0.01mm, 0.02mm and 0.05mm, installed between the end face of the second positioning stop (221) and the encoder static housing (102), used to precisely adjust the axial installation position of the encoder to ensure the optimal air gap (0.5mm±0.05mm).

[0039] Preload assembly (320): includes 8 circumferentially distributed miniature disc springs (321), with an outer diameter of 3 mm, a wire diameter of 0.2 mm, and a free height of 0.8 mm. They are installed in an annular groove inside the housing fixture (220) to provide a continuous axial preload (approximately 5 N) to the encoder static housing (102) and suppress axial movement during operation.

[0040] Signal processing unit (400): Integrated on sensor array board (120), using ASIC dedicated chip, to acquire the original magnetic field signal with 24-bit precision, and to perform real-time interpolation (×1024) and temperature compensation (-40℃~+85℃) through built-in algorithm, and finally output 26-bit absolute angle value, which is communicated through SPI interface.

[0041] Installation and implementation process:

[0042] The bushing connector (210) is fitted into the joint output shaft (222) and circumferentially fixed by the pin (212) to ensure no relative rotation.

[0043] The encoder rotating inner ring (101) is pressed into the first positioning stop (211) of the bushing connector (210) to form an interference fit.

[0044] Install an appropriate amount of fine-tuning shims (310) on the end face of the second positioning stop (221) of the housing fastener (220). By trying different combinations of thicknesses, ensure that the air gap between the magnet and the sensor is 0.5mm ± 0.05mm after the encoder static housing (102) is installed.

[0045] The encoder static housing (102) is fixed to the first finger bone base (400) with industrial adhesive, and a soft magnetic alloy shield (230) is installed around the housing fixing part (220) to effectively isolate external stray magnetic field interference.

[0046] Connect the signal cable (410) to the interface of the signal processing unit (400) to complete the installation.

[0047] Measurement performance: After installation, actual measurements showed that the structure achieved a repeatability of 0.005° and an absolute accuracy of 0.008° within the joint rotation range (±180°), and the accuracy remained stable under vibration at a frequency of 100Hz and temperature changes from -20℃ to +60℃.

[0048] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A mounting structure for a miniature encoder on a mechanical finger joint to improve control accuracy, characterized in that, Includes a hollow ring magnetic encoder (100), a customized mounting base (200), and an error compensation mechanism (300). The hollow ring magnetic encoder (100) includes a built-in ring magnet (110) and a sensor sensing unit (120). The customized mounting base (200) includes a bearing (210) and a finger base (220); The bearing (210) is coaxially fixed with the rotating output shaft (222) of the finger joint, and the outer end face of the finger base is provided with a first positioning stop (211) for interference fit or adhesive fixation with the rotating inner ring (101) of the encoder (100); The finger base (220) is connected to the first finger phalanx base (400).

2. The micro encoder mounting structure according to claim 1, characterized in that, The bearing (210) is made of a low thermal expansion coefficient alloy material and has a through hole in the middle for connection with the rotating output shaft (222).

3. The micro encoder mounting structure according to claim 2, characterized in that, The finger base (220) has an asymmetrical structure and is connected to the first finger bone base (400) through the bearing (210) on the other side. The diameter tolerance zone of the second positioning stop (221) is H7, which forms a precision clearance fit with the encoder static housing (102).

4. The micro encoder mounting structure according to claim 3, characterized in that, The fine-tuning shim group (310) is an annular copper foil shim with a thickness of 0.01mm, 0.02mm or 0.05mm. By selecting shims of different specifications and quantities and stacking them, the gap between the end face of the static shell (102) and the end face of the second positioning stop (221) can be adjusted.

5. The miniature encoder mounting structure according to any one of claims 1 to 4, characterized in that, The mounting structure is entirely encapsulated within the internal cavity of the mechanical finger joint, and its maximum radial mounting dimension does not exceed 20mm.

6. The micro encoder mounting structure according to claim 5, characterized in that, The MPT-8-20 series encoder integrated through the aforementioned mounting structure achieves an absolute position measurement accuracy of better than 0.01° at this finger joint.

7. The micro encoder mounting structure according to claim 1, characterized in that, The finger base (220) is a hollow structure, and its inner cavity is used to thread tendon ropes or signal cables that drive the dexterous fingers.

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