Frictional self-locking passive variable stiffness flat single-plane robotic arm

Abstract

The application discloses a friction self-locking passive variable stiffness flat single-plane mechanical arm, which comprises a gradient interval disc assembly, a plurality of flat interval discs are sequentially and serially nested from a fixed end to a free end along an axial direction in a descending order, and the structure of the plurality of flat interval discs gradually changes along the axial direction according to a preset power function rule, and the plurality of flat interval discs deflect along a first direction or a second direction; a central flexible core body penetrates through the plurality of flat interval discs and is used for axial series connection of the flat interval discs; a tendon radius conversion module is arranged on one side of the fixed end of the gradient interval disc assembly and is used for smooth transition of the radius of the gradient interval disc assembly; when the plurality of flat interval discs move to a preset limit angle along the first direction or the second direction, self-locking occurs between adjacent flat interval discs, and the mechanical arm is switched from a low stiffness state to a high stiffness state. The application can realize passive switching of the stiffness state without an independent self-locking mechanism and active control, and is suitable for operation in a limited space such as a narrow gap.

Description

Technical Field

[0001] This invention relates to the field of flexible robot technology, specifically to a friction-self-locking passive variable stiffness flat single-plane robotic arm. Background Technology

[0002] Continuum robots rely on flexible segmented structures to achieve flexible bending deformation, giving them a certain advantage in confined space operations. Existing planar continuum robots suffer from the following problems: First, most existing continuums are composed of flat spacers of equal size and structure connected in series, resulting in uniform overall stiffness. This makes it difficult to create a differentiated stiffness distribution along the arm's axial direction, leading to sagging and swaying at the root when the arm extends a large length. Increasing the overall stiffness, however, results in insufficient end-effector compliance. Second, traditional continuums with angle limits rely solely on solid edges for mechanical hard limiting, restricting only the maximum bending angle and failing to achieve stiffness state switching. The robot remains in a single stiffness state throughout, limiting its operational capabilities. Third, continuum drives commonly employ tendon traction, with a large radius of tendon arrangement at the drive end and a small radius on the body side. The tendon routing exhibits an inclined angle, generating lateral forces during traction, increasing frictional losses, and causing uneven tension among multiple tendons, leading to bending motion deviations. Fourth, most flexible continuums are designed as multi-directional spatial swinging structures, exhibiting lateral torsion and multi-posture motion coupling problems, making them unsuitable for narrow, flat working conditions requiring only planar bending.

[0003] Therefore, there is an urgent need to develop a flat continuum robot with axial gradient stiffness, passive variable stiffness achieved by frictional self-locking, smooth tendon path, and stable single-plane motion. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a friction-self-locking passive variable stiffness flat single-plane robotic arm, aiming to solve at least some of the problems mentioned above.

[0005] In a first aspect, the present invention provides a friction-self-locking passive variable stiffness flat single-plane robotic arm, comprising: The gradient spacer assembly includes several flat spacers nested in series from a fixed end to a free end along the axial direction in descending order of size. The structure of the several flat spacers gradually changes along the axial direction according to a preset power function law. The several flat spacers deflect along a first direction or a second direction. A central flexible core extends through the plurality of flat spacers and is used for axial connection, lateral support and unloading reset of the flat spacers. The shaft of the gradient spacer assembly coincides with or nearly coincides with the shaft of the central flexible core. A tendon radius conversion module is disposed on one side of the fixed end of the gradient spacer assembly for continuous transition of the radius of the gradient spacer assembly; When the relative deflection angle between adjacent flat spacers is less than the preset limit angle, the robotic arm is in the initial state. When the several flat spacers move to the preset limit angle along the first direction or the second direction, the adjacent flat spacers self-lock, and the robotic arm switches from a low stiffness state to a high stiffness state. When the deflection angle of the plurality of flat spacers decreases from a preset limit angle to less than a preset limit angle, the adjacent flat spacers release their self-locking, and the robotic arm switches from a high-rigidity state to a low-rigidity state.

[0006] Furthermore, each of the plurality of flat spacer disks includes a bottom surface and an end surface opposite to the bottom surface, which are provided with protrusions. The bottom surface is provided with a groove for accommodating the protrusions of adjacent flat spacers; The groove is provided with a nested inner slope, and the protrusion is provided with a nested outer slope. When the adjacent flat spacer discs deflect to a preset limit angle along the first direction or the second direction, the nested inner slope and the nested outer slope of the adjacent flat spacer discs cooperate to form a friction contact pair, thereby achieving self-locking.

[0007] Furthermore, the slope angle α of the nested outer slope and the slope angle β of the nested inner slope satisfy α < β, and the slope angle α and the friction angle φ satisfy 0 < φ - α ≤ 5°.

[0008] Furthermore, both the nested outer ramp and the nested inner ramp are flat and touching surfaces, and are symmetrically arranged on the upper and lower sides of the flat spacer, so that when the robotic arm bends upward and downward, it can form inclined surface contact limit and friction self-locking.

[0009] Furthermore, the flat spacer is provided with a lateral limiting structure, which is used to constrain the movement of the plurality of flat spacers to deflect only in a first direction or a second direction, so that any one of the flat spacers is in the same plane as the other flat spacers when it deflects.

[0010] Furthermore, the flat spacer is a flat sheet structure of equal thickness, and the lateral limiting structure is located inside the groove.

[0011] Furthermore, tendon perforations are provided on the left and right sides of the bottom surface to accommodate tendon ropes; the tendon perforations are connected to the outside of the flat spacer through open rifts, and the width of the open rifts is smaller than the diameter of the tendon ropes, so that the tendon ropes can be inserted into the tendon perforations by lateral pressing and remain in the tendon perforations during traction.

[0012] Furthermore, the tendon radius conversion module is provided with a wiring channel for the continuous transition of the radius of the gradient spacer assembly; the wiring channel continuously transitions from the small arrangement radius position at the free end of the gradient spacer assembly to the large arrangement radius position at the fixed end; the wiring channel is provided with a flexible spring bushing for the tendon rope to pass through, which is used to reduce the friction between the tendon rope and the hole wall to reduce wear.

[0013] Furthermore, it also includes a driving device that, when the tendon rope is subjected to traction, drives the plurality of flat spacer discs to deflect along a first direction or a second direction.

[0014] On the other hand, the present invention also provides a friction-locking passive variable stiffness flat single-plane continuous robot, including a friction-locking passive variable stiffness flat single-plane continuous manipulator as described in any one of the claims.

[0015] The beneficial effects of this invention are: 1. This invention employs a multi-parameter tapering design based on power functions, allowing the dimensions of the flat spacer disc, the nesting depth, and the tendon guiding position to continuously vary along the axial direction, thereby creating a gradient stiffness distribution with relatively high proximal support and relatively good distal compliance. This design helps reduce local stress concentration that may be caused by abrupt changes in size and can, to a certain extent, balance anti-sagging ability and end-bending adaptability during long-distance overhangs.

[0016] 2. This invention utilizes the inclined surface contact and interface friction of adjacent flat spacers at their limit deflection positions for passive stiffness adjustment. The robotic arm remains relatively compliant within a small bending range to adapt to obstacle avoidance and posture adjustment requirements. When a local deflection reaches a preset limit angle, the inclined surfaces press against each other, forming a frictional constraint, which correspondingly increases the local stiffness of the structure, allowing it to be used for force-applying operations such as pushing, pressing, or pulling. The aforementioned stiffness state transition can be achieved through structural contact relationships and friction, thus eliminating the need for independent electronic or fluid stiffness adjustment devices.

[0017] 3. The tendon radius conversion module of the present invention is used to enable a continuous transition in the radius of the flat spacer arrangement between the robotic arm body and the drive device, and can reduce the friction between the tendon rope and the hole wall through a flexible spring bushing. This structure helps to reduce the lateral component force, transmission loss and tendon rope wear generated by oblique traction, and can improve drive smoothness and tension consistency of multiple tendon ropes. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0019] Figure 1This is a schematic diagram of the gradient spacer assembly of the robotic arm of the present invention. Figure 2 This is a schematic diagram of the overall structure of the present invention; Figure 3 This is an exploded view of the overall structure of the present invention; Figure 4 This is a schematic diagram of the flat spacer disk structure of the present invention; Figure 5 This is a schematic diagram of the tendon radius conversion module structure of the present invention; Figure 6 This is a schematic diagram of the single tendon drive module structure of the present invention; Figure 7 This is a schematic diagram of the present invention in a compliant obstacle-avoiding state; Figure 8 This is a schematic diagram of the present invention under the extreme self-locking force application state; In the diagram: 1. Nickel-titanium alloy tube; 2. Tendon rope; 3. Flat spacer disc; 301. Tendon perforation; 302. Open rift; 303. Lateral restraint structure; 304. Nested outer ramp; 305. Nickel-titanium alloy tube perforation; 306. Nested inner ramp; 307. Groove; 308. Protrusion; 4. Tendon radius conversion module; 401 is the tendon foramen tunnel; 402 is the embedded spring; 403 is the anterior support restraint; 404 is the driving side tendon perforation; 405 is the nesting hole; 406 is the nickel-titanium alloy tube perforation; 407 is the central shaft perforation. 408 is a perforation hole for the tendon on the side of the robotic arm body; 5. Front support; 6. Single tendon drive module; 601. Fixed housing; 602. Transmission screw; 603. Transmission drive wheel; 604. Transmission belt; 605. Transmission driven wheel; 606. Servo mounting screw; 607. Anti-rotation optical shaft; 608. Screw drive slider; 609. Structure fixed to the rear support; 610. Structure cooperating with the rear support; 611. Drive servo; 612. Fixed top cover; 613. Top cover mounting screw; 7. Rear support; 8. Central connecting shaft. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1-8As shown, a friction-self-locking passive variable stiffness flat single-plane robotic arm comprises: a gradient spacer assembly, a central flexible core, and a tendon radius conversion module 4. This embodiment also includes a fixed base assembly, consisting of a front support 5 and a rear support 7, and multiple single tendon drive modules 6 installed between the front support 5 and the rear support 7. The tendon radius conversion module 4 is located between the front support 5 and the gradient spacer assembly, used to connect the drive device and the robotic arm body. A central connecting shaft 8 passes through the central shaft perforation of the rear support, sequentially through the central shaft perforation of the front support, and is embedded in the central shaft perforation of the tendon radius conversion module 4 to maintain the coaxial relationship between the front support 5, the rear support 7, and the tendon radius conversion module 4.

[0023] In this embodiment, the main body of the robotic arm can be composed of 18 flat spacer discs 3 nested sequentially from the fixed end to the free end along the axial direction in descending order of size. The external dimensions, nesting depth, and tendon insertion positions of each flat spacer disc 3 gradually change along the axial direction of the robotic arm according to a preset power function law. Several flat spacer discs 3 deflect along a first direction or a second direction (specifically, the first direction is the direction in which the flat spacer discs 3 deflect upwards, and the second direction is the direction in which the flat spacer discs 3 deflect downwards). The relevant dimensions of the 18 flat spacer discs 3 are continuously set along the axial direction according to the power function parameters. To uniformly describe the variation law of each geometric parameter along the axial direction, a dimensionless axial coordinate s = x / L is defined, where L is the total length of the main body of the robotic arm (L = 638 mm in this embodiment), x is the axial distance from the root end, and 0 ≤ s ≤ 1. For any geometric parameter Pi(s) that gradually decreases along the axial direction, it can be represented by the following power function: (s)= +( - (1-s)^

[0024] In the formula, and Let be the values ​​of the i-th type of geometric parameter at the root and end points, respectively. This represents the corresponding power exponent. In this embodiment, This includes at least the outer contour width W of the robotic arm body, the outer diameter D of the flat spacer 3, the nesting ramp mating depth H, and the distribution radius R of the mounting holes for the tendon rope 2. The power exponents of each parameter... It can be independently configured according to the requirements of load-bearing, bending, and transmission performance, or it can be synchronously configured using a unified power exponent γ, so that the external dimensions, the contact fit dimensions of adjacent flat spacer discs 3, and the lever arm of the driving tendon change in a coordinated manner along the axial direction. Based on the sample data of the outer contour of the tail of an adult East Asian scorpion, when the total length of the main body L=638 mm and the root end width is... =70 mm, end width When the radius is 26 mm, the power exponent γ = 2.36 and the coefficient of determination for fitting are obtained. =0.987. When γ=2.36, the dimension decays relatively quickly near the root end and maintains a continuous transition between the middle and distal sections, which is beneficial for balancing the bending load capacity at the root end and the bending compliance at the distal end. Therefore, the root end flat spacer 3 is set with a larger width and nesting depth to improve its support and bending capacity; the distal end flat spacer 3 is set with a smaller width and nesting depth to obtain a relatively larger bending curvature and reduce the attitude adjustment resistance, thereby forming a basic stiffness distribution that continuously varies along the boom axis without setting an independent stiffness adjustment mechanism. When the value of γ increases, the parameter decays relatively quickly near the root end, the difference in size and stiffness between the proximal end and the middle and distal sections increases relatively, and the high stiffness area tends to concentrate at the root end, which is beneficial for improving the proximal end load-bearing and bending support capacity, and therefore can be used for operations with certain load or overhang length requirements; when the value of γ decreases, the parameter decays relatively slowly along the axial direction, and the stiffness transition is more uniform, which is beneficial for maintaining overall compliance and curvature continuity, and therefore can be used for fine operation or attitude adjustment in narrow spaces. By setting each Furthermore, the cross-sectional stiffness, contact constraint capability, and tendon rope lever arm can be adjusted accordingly while keeping the total length of the robotic arm and the end boundary dimensions unchanged.

[0025] In this embodiment, each of the plurality of flat spacer disks 3 includes a bottom surface and an end face opposite to the bottom surface with a protrusion 308. The bottom surface is provided with a groove 307, which is used to accommodate the protrusion 308 of the adjacent flat spacer disk 3 along the free end. The groove 307 is provided with a nested inner slope 306, and the protrusion 308 is provided with a nested outer slope 304. When adjacent flat spacer disks 3 reach a preset limit angle along the first direction or the second direction, the nested inner slope 306 and the nested outer slope 304 of the adjacent flat spacer disks 3 cooperate to form a friction contact pair, thereby achieving self-locking. The inclination angle of the nested slope is less than the friction angle of the material contact surface of the flat spacer disk 3, and a gap is reserved between two adjacent flat spacer disks 3 for relative deflection. The maximum bidirectional relative deflection angle (preset limit angle) of adjacent flat spacer disks 3 is limited to 7° to 10°. The flat spacer 3 can be made of thermoplastic materials such as polylactic acid (PLA), polyethylene terephthalate-1,4-cyclohexanediol (PETG), and acrylonitrile-butadiene-styrene copolymer (ABS). Under dry friction conditions, the static friction coefficient μs of the contact surface of the above materials is typically 0.30 to 0.50, corresponding to a friction angle φ = arctan(μs), which is approximately 16.7° to 26.6°. To balance contact self-locking and unloading reset, this invention adopts a low-margin self-locking design. The slope angle α of the nested outer ramp 304 and the slope angle β of the nested inner ramp 306 satisfy α < β, and the slope angle α and the friction angle φ satisfy 0 < φ - α ≤ 5°. In this embodiment, the slope angle α is 14°; calculated based on the lower limit of the static friction coefficient μs = 0.30, the friction angle φ is approximately 16.7°, and the minimum self-locking margin is approximately 2.7°. The inclination angle of the inclined plane can be adjusted according to the material, surface roughness, and actual friction coefficient. When the relative deflection angle of the adjacent flat spacers 3 is less than the preset limit angle, the robotic arm is in its initial state. The structure mainly relies on the central flexible core and the pre-tensioned tendon rope 2 to maintain continuity, and the overall structure presents a relatively compliant state. When the plurality of flat spacer discs 3 move to a preset limit angle along the first or second direction, the nested outer ramp 304 and nested inner ramp 306 in the corresponding direction come into contact with each other and are pressed together. The static friction formed by the contact normal force can suppress the relative slippage along the ramp, thereby constraining the continued deflection of the adjacent flat spacer discs 3 and increasing the local equivalent stiffness accordingly, thus realizing angle limiting and passive stiffness adjustment. When the adjacent flat spacer discs 3 self-lock, the robotic arm switches from a low stiffness state to a high stiffness state. When the deflection angle of the plurality of flat spacer discs 3 decreases from the preset limit angle to less than the preset limit angle, the adjacent flat spacer discs 3 release self-locking, and the robotic arm switches from a high stiffness state to a low stiffness state. After the external deflection load is released or the driving tendon rope 2 is released, the contact normal force of the ramp decreases accordingly, and the residual friction resistance decreases accordingly.The elastic restoring torque of the central flexible core and the return effect generated by the pre-tightening of the tendon rope 2 can be used to overcome residual friction, so that the adjacent flat spacer 3 tends to return to the initial position along the mating inclined surface. Therefore, structural reset can be achieved without setting an independent unlocking actuator.

[0026] In this embodiment, the nested outer ramp 304 and the nested inner ramp 306 are both flat and flat contact surfaces, and are symmetrically arranged on the upper and lower sides of the flat spacer 3, so that when the robotic arm bends upward and downward, it can form inclined surface contact limit and friction self-locking.

[0027] In this embodiment, the flat spacer 3 is provided with a lateral limiting structure 303. The lateral limiting structure 303 is used to constrain the movement of the plurality of flat spacers 3 to deflection only along a first direction or a second direction, so that any one of the flat spacers 3 is in the same plane as the other flat spacers 3 when deflection occurs. The lateral limiting structure 303 of the flat spacer 3 is used to constrain the lateral disengagement and non-target direction rotation of adjacent flat spacers 3, and cooperates with the preset tendon hole position, so that the main motion degrees of freedom of the robotic arm are concentrated in the specified plane. This structure helps to reduce lateral torsion and spatial multi-degree-of-freedom coupling, and can reduce the complexity of kinematic modeling and control debugging to a certain extent, and improve the posture stability when working in confined space. The flexible arm as a whole is limited to completing bidirectional bending and S-shaped recurving motion in a single vertical plane, without lateral swinging degree of freedom.

[0028] like Figure 4 As shown, each flat spacer disc 3 is preferably a flat sheet structure of uniform thickness, with its lateral width, nesting depth, and tendon hole position gradually changing along the axial direction, which can be generated in batches through parametric modeling. The flat spacer disc 3 has shoulder wings on both sides, with semi-open tendon perforations 301 on the shoulder wings; an open rift 302 is provided between the tendon perforation 301 and the outer side of the flat spacer disc 3. The width of the open rift 302 is smaller than the diameter of the adapted tendon cord 2, allowing the tendon cord 2 to be laterally pressed into the tendon perforation 301 and held within the hole during traction. Each flat spacer 3 in the base segment of the gradient spacer assembly has three tendon perforations 301 and an open rift 302 on each side. The flat spacers 3 in this segment are characterized by being wide and short, and their main function is to stabilize the main body of the robotic arm and prevent vibration and instability during bending. Each flat spacer 3 in the middle segment has two tendon perforations 301 and an open rift 302 on each side. The bending of this segment is affected by four tendon ropes 2. Compared with the flat spacers 3 in the base segment, the length is increased and the width is correspondingly reduced. Its main function is to lengthen the overall length of the robotic arm and increase the reach. Each flat spacer 3 in the terminal segment is characterized by being slender and long, and is only affected by two tendon ropes 2 on each side. The control is more precise and simple, so its function is to increase the accuracy of the terminal segment control.

[0029] In this embodiment, a central flexible core extends through several of the flat spacers 3, serving for axial connection, lateral support, and unloading / resetting of the flat spacers 3; the central flexible core is an elastic rod or elastic tube. In this embodiment, the central flexible core is a nickel-titanium alloy tube 1. The nickel-titanium alloy tube 1 and the flat spacers 3 are fixed using a combination of through-type assembly and axial limiting at both ends. The nickel-titanium alloy tube 1, with a diameter of 1.6 mm and a length of 638 mm, sequentially passes through the through holes in the centers of 18 flat spacers 3, and continues through the drive tendon radius conversion module 4, the front support 5, the central connecting shaft 8, and the rear support 7. Each mating component has a through hole of not less than 1.6 mm pre-drilled in its center. The bottommost flat spacer 3 is embedded in the positioning hole of the drive tendon radius conversion module 4, and the topmost spacer is clamped by a limiting ring with a diameter of 2 mm, thereby restricting the axial movement of the flat spacers 3 and preventing them from detaching.

[0030] In this embodiment, the tendon rope 2 passes through the tendon perforation 301 of the flat spacer 3 to drive the robotic arm body to produce bending deformation. It is symmetrically arranged on both sides of the robotic arm body and can be divided into medial tendon group, intermediate tendon group, and lateral tendon group according to the functional segment. Each group includes two symmetrically arranged tendons. The medial tendon group passes sequentially through the medial tendon perforation 301 on the base, middle, and terminal sections of the flat spacer 3 from the fixed end side and connects to the end of the robotic arm to adjust the bending state of the terminal section and the entire robotic arm. The intermediate tendon group passes sequentially through the intermediate tendon perforation 301 on the base and middle sections of the flat spacer 3 and connects to the end of the middle section, but does not pass through the terminal section of the flat spacer 3. The lateral tendon group passes through the lateral tendon perforation 301 on the base section of the flat spacer 3 and connects to the end of the base section, but does not pass through the middle and terminal sections of the flat spacer 3. The drive-side ends of the six tendon ropes 2 can pass through the tendon radius conversion module 4 and be connected to the lead screw drive slider 608 of the corresponding single tendon drive module 6. By adjusting the extension and retraction of each tendon rope 2, the effective length difference between the two sides of the tendon ropes 2 at the base, middle, and end sections can be changed, thereby adjusting the bending state of each section of the robotic arm.

[0031] The tendon radius conversion module 4 of this invention has a wiring channel inside for the continuous transition of the radius of the gradient spacer assembly. The wiring channel continuously transitions from a small arrangement radius position at the free end of the gradient spacer assembly to a large arrangement radius position at the fixed end. A flexible spring bushing for the tendon rope 2 to pass through is provided within the wiring channel to reduce friction between the tendon rope 2 and the hole wall, thereby reducing the lateral force generated by oblique traction, transmission loss, and tendon rope wear, and improving drive smoothness and tension consistency of multiple tendon ropes. The tendon radius conversion module 4 is connected to the fixed end of the gradient spacer assembly, and its internal wiring channel is used to achieve a smooth transition of the tendon arrangement radius.

[0032] like Figure 5 As shown, the tendon radius conversion module 4 is located on one side of the fixed end of the gradient spacer assembly, and in this embodiment, it is located between the main body of the robotic arm and the front support 5. The main body side has a tendon perforation 301, and the drive side also has a tendon perforation 301, which are connected through an internal tendon hole tunnel 401. Each channel gradually transitions from a small radius position on the main body side of the robotic arm to a large radius position where the single tendon drive module 6 is located, allowing the tendon rope 2 to smoothly change direction and radius before entering the drive device. A soft stainless steel tendon hole tunnel 401 can be installed inside the tendon hole tunnel 401, allowing the tendon rope 2 to pass through the inner cavity of the spring 402. The tendon hole tunnel 401 can bend accordingly with the curvature of the channel, providing continuous guidance for the tendon rope 2, thereby helping to reduce large-area direct friction between the tendon rope 2 and the printing hole wall, reducing traction resistance and wear. The inner diameter of the tendon hole tunnel 401 should preferably be larger than the diameter of the tendon rope 2, and its outer diameter can be adapted to the tendon hole tunnel 401 to reduce possible axial movement during use. The tendon radius conversion module 4 may also be provided with a nesting hole 405, a nickel-titanium alloy tube through hole 406, and a central shaft through hole 407 that mate with the main body of the robotic arm. The front support limiter can be inserted into the included angle gap of the through hole of the single tendon drive module 6 on the front support 5 to constrain the rotation of the tendon radius conversion module 4 relative to the front support 5 and maintain the alignment relationship between each tendon channel and the corresponding drive device.

[0033] like Figure 6As shown, the present invention also includes a driving device, which applies traction to the tendon rope 2, driving the plurality of flat spacer discs 3 to deflect along a first direction or a second direction. In this embodiment, the driving device is a single tendon driving module 6, including a fixed housing 601, a transmission screw 602, a transmission drive wheel 603, a transmission belt 604, a transmission driven wheel 605, an anti-rotation optical shaft 607, a screw-driven slider 608, a drive servo motor 611, and a fixed top cover 612. The drive servo motor 611 is installed inside the fixed housing 601, and its output shaft is connected to the transmission drive wheel 603; the transmission drive wheel 603 drives the transmission driven wheel 605 to rotate through the transmission belt 604, and the transmission driven wheel 605 is fixedly connected to the transmission screw 602, thereby driving the transmission screw 602 to rotate. The screw-driven slider 608 is threadedly engaged with the transmission screw 602 and is simultaneously sleeved on the two anti-rotation optical shafts 607. The anti-rotation optical shaft 607 restricts the slider's rotation around the lead screw axis, converting the rotational motion of the lead screw 602 into linear displacement of the lead screw-driven slider 608 along the axial direction. The drive end of the tendon cable 2 is fixed to the lead screw-driven slider 608; the tendon cable 2 tightens when the slider moves away from the main body of the robotic arm, and releases when it moves in the opposite direction. The ends of the lead screw 602 and the anti-rotation optical shaft 607 can be supported by the fixed housing 601 and the fixed top cover 612, which can be installed using the top cover fixing screw 613. The drive servo motor 611 can be connected using the servo motor fixing screw 606 to reduce the possibility of relative displacement of the servo motor caused by the drive reaction force. Multiple single tendon drive modules 6 are respectively set between the front support 5 and the rear support 7. By independently adjusting the displacement of each tendon rope 2, the robotic arm can bend in the corresponding direction. When the tendon rope 2 on one side of the target bending direction is tightened, the tendon rope 2 on the opposite side can be released or kept pre-tightened to reduce the slack of the tendon rope 2 and the return gap.

[0034] Before the robotic arm begins operation, each individual tendon drive module 6 can be adjusted to provide appropriate preload to the six tendon ropes 2, maintaining the robotic arm body in an initial state of near-straightness. When the tendon rope 2 corresponding to a certain bending direction is tightened and the opposite tendon rope 2 is released accordingly, the flat spacer 3 can sequentially deflect relative to each other under the constraint of the nickel-titanium alloy tube 1, causing the robotic arm body to form a continuous bend. By changing the displacement of each tendon rope 2, the bending direction and curvature can be adjusted.

[0035] like Figure 7 As shown, during the obstacle avoidance phase, the relative deflection angle of adjacent flat spacers 3 can be controlled within a preset limit angle, keeping the nested inner ramp 306 and nested outer ramp 304 in a state where they are not fully compressed. At this time, the robotic arm maintains relatively low structural stiffness and can be used to approach, bypass, or traverse narrow passages along the obstacle contour. When locally subjected to external contact, the flat spacers 3 still retain a certain relative rotational space, which helps to reduce the impact of contact between the robotic arm and the environment.

[0036] like Figure 8 As shown, after the end effector of the robotic arm reaches the target position, the corresponding tendon rope 2 can be tightened further, causing the local flat spacer 3, which needs to bear the load, to reach a preset limit deflection angle. At this time, the corresponding nested outer ramp 304 and nested inner ramp 306 fit together and form a self-locking constraint under the action of interface friction, thereby increasing the local stiffness of the robotic arm. This allows it to hook, push, or press the target component after bypassing the obstacle. During the force application process, the load can be transmitted through the end flat spacer 3, the ramp contact pair, the gradient spacer assembly, and the fixed base assembly.

[0037] After the operation is completed, the drive servo motor 611 can be controlled to rotate in the opposite direction to release the tightened side tendon rope 2 and restore the contralateral tendon rope 2 to its appropriate pretension. As the normal clamping force of the inclined plane decreases, the elastic restoring torque of the nickel-titanium alloy tube 1 can cause the adjacent flat spacer 3 to release its self-locking constraint and gradually return to the center, causing the robotic arm to tend to return to its initial posture. Thus, a continuous operation process of compliant obstacle avoidance, extreme deflection force application, and unloading and reset can be formed.

[0038] This embodiment also conducted a comparative experiment on the effect of different 3D printing materials on the frictional self-locking performance. The static friction coefficient of the printing materials was between 0.30 and 0.50, corresponding to a friction angle of approximately 16.7° to 26.6°. The nested ramps of the two flat spacers 3 were fully fitted together, and then a load was gradually applied laterally to determine the critical load required for the upper flat spacer 3 to slip or detach. The results showed that within the test load range, the flat spacers 3 made of the three materials did not slip or detach along the ramp; as the load continued to increase, the flat spacers 3 first showed local plastic deformation, while the frictional contact pair remained locked. This result indicates that under the existing structural dimensions and a ramp angle of 14°, the PLA, PETG, and ABS flat spacers 3 can all achieve stable self-locking, and the material differences did not change their main failure modes.

[0039] The present invention also provides a friction-locking passive variable stiffness flat single-plane robot, including the friction-locking passive variable stiffness flat single-plane continuous robotic arm described in any of the above claims.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A friction-self-locking passive variable stiffness flat single-plane robotic arm, characterized in that, include: The gradient spacer assembly includes several flat spacers nested in series from a fixed end to a free end along the axial direction in descending order of size. The structure of the several flat spacers gradually changes along the axial direction according to a preset power function law. The several flat spacers deflect along a first direction or a second direction. A central flexible core extends through the plurality of flat spacers and is used for axial connection, lateral support and unloading reset of the flat spacers. The shaft of the gradient spacer assembly coincides with or nearly coincides with the shaft of the central flexible core. A tendon radius conversion module is disposed on one side of the fixed end of the gradient spacer assembly for continuous transition of the radius of the gradient spacer assembly. When the relative deflection angle between adjacent flat spacers is less than the preset limit angle, the robotic arm is in the initial state. When the several flat spacers move to the preset limit angle along the first direction or the second direction, the adjacent flat spacers self-lock, and the robotic arm switches from a low stiffness state to a high stiffness state. When the deflection angle of the plurality of flat spacers decreases from a preset limit angle to less than a preset limit angle, the adjacent flat spacers release their self-locking, and the robotic arm switches from a high-rigidity state to a low-rigidity state.

2. The friction self-locking passive variable stiffness flat single-plane robotic arm according to claim 1, characterized in that, Each of the plurality of flat spacers includes a bottom surface and an end surface opposite to the bottom surface, which are provided with protrusions; The bottom surface is provided with a groove for accommodating the protrusions of adjacent flat spacers; The groove is provided with a nested inner slope, and the protrusion is provided with a nested outer slope. When the adjacent flat spacer discs deflect to a preset limit angle along the first direction or the second direction, the nested inner slope and the nested outer slope of the adjacent flat spacer discs cooperate to form a friction contact pair, thereby achieving self-locking.

3. The friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 2, characterized in that, The slope angle α of the nested outer slope and the slope angle β of the nested inner slope satisfy α < β, and the slope angle α and the friction angle φ satisfy 0 < φ - α ≤ 5°.

4. The friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 2, characterized in that, Both the nested outer ramp and the nested inner ramp are flat and touching surfaces, and are symmetrically arranged on the upper and lower sides of the flat spacer, so that when the robotic arm bends upward or downward, it can form inclined surface contact limit and friction self-locking.

5. A friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 2, characterized in that, The flat spacer is provided with a lateral limiting structure, which is used to constrain the movement of the flat spacers to deflect only in a first direction or a second direction, so that any one of the flat spacers is in the same plane as the other flat spacers when it deflects.

6. A friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 5, characterized in that, The flat spacer is a flat sheet structure of equal thickness, and the lateral limiting structure is located inside the groove.

7. A friction-self-locking passive variable stiffness flat single-plane robotic arm according to any one of claims 2-4, characterized in that, The bottom surface has tendon perforations on both the left and right sides to accommodate tendon ropes. The tendon perforations are connected to the outside of the flat spacer through open rifts. The width of the open rifts is smaller than the diameter of the tendon ropes, so that the tendon ropes can be inserted into the tendon perforations by lateral pressing and remain in the tendon perforations during traction.

8. A friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 1, characterized in that, The tendon radius conversion module has a wiring channel inside for the continuous transition of the radius of the gradient spacer assembly; the wiring channel continuously transitions from the small arrangement radius position at the free end of the gradient spacer assembly to the large arrangement radius position at the fixed end; the wiring channel is provided with a flexible spring bushing for the tendon rope to pass through, which is used to reduce the friction between the tendon rope and the hole wall to reduce wear.

9. A friction-self-locking passive variable stiffness flat single-plane robotic arm according to claim 1, characterized in that, It also includes a drive device that, when the tendon rope is subjected to traction, drives the plurality of flat spacers to deflect along a first direction or a second direction.

10. A friction-self-locking passive variable stiffness flat single-plane continuous body robot, characterized in that, Including a friction-self-locking passive variable stiffness flat single-plane continuous robotic arm as described in any one of claims 1 to 9.

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