A robot variable stiffness joint

Abstract

The utility model discloses a kind of robot variable stiffness joints. Robot variable stiffness joint includes joint unit and adjusting unit. Joint unit includes input disc, output disc and closed collar, input disc is coaxially arranged with output disc, and the circumferential outer edge of closed collar is sealingly connected with input disc and output disc;Adjusting unit includes driving mechanism, just mechanism, variable stiffness mechanism and refrigeration mechanism, driving mechanism includes multiple memory spring linear actuators, linear hall sensor is built-in in memory spring linear actuator, and refrigeration mechanism is installed in the inside of memory spring linear actuator. The volume of the robot variable stiffness joint is reduced by using memory spring linear actuator in the application;Joint support is strengthened by closed collar;The overall stiffness change of joint is obtained by linear hall sensor probe.

Description

Technical Field

[0001] This utility model relates to the field of robotics technology, specifically to a variable stiffness joint for robots. Background Technology

[0002] With the rapid development of robotics technology, its application in fields such as industrial manufacturing, medical care, and home services is becoming increasingly widespread, significantly increasing the complexity and safety requirements of human-machine collaboration scenarios.

[0003] Traditional robot safety strategies often rely on rigid materials and high-energy-consuming drive systems. While these ensure basic stability, they suffer from the following technical bottlenecks: Existing solutions often employ high-power motors and redundant structures to achieve high load-bearing capacity, resulting in high system energy consumption, heavy weight, and difficulty in controlling manufacturing costs. For example, industrial robot joints largely rely on rigid transmissions, which maintain precision, but energy consumption surges during prolonged operation, limiting lightweight design. While rigid structures can improve load-bearing capacity, they lack flexible buffering mechanisms, making them susceptible to mechanical damage from sudden impacts. Furthermore, their low modularity necessitates complete disassembly for maintenance, leading to inefficiency. Existing control algorithms lack the ability to fuse multi-sensor data, making it difficult to achieve high-precision dynamic adjustments, especially prone to trajectory deviations under variable load conditions.

[0004] In summary, existing robot technologies suffer from technical problems such as high energy consumption, high cost, complex structure, and low practicality. Utility Model Content

[0005] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a variable stiffness joint for robots to solve the technical problems of high energy consumption, high cost, complex structure and low practicality in the prior art.

[0006] To achieve the above-mentioned technical objectives, this application adopts the following technical solution: This application provides a variable stiffness joint for a robot, including a joint unit and an adjustment unit.

[0007] The joint unit includes an input disk, an output disk, and a sealing collar. The input disk and the output disk are arranged coaxially opposite each other, and the sealing collar seals the outer edges of the input disk and the output disk in a sealing manner. The adjustment unit includes a drive mechanism, a stiffness adjustment mechanism, a stiffness change mechanism, and a cooling mechanism. The drive mechanism includes multiple memory spring linear actuators, which are circumferentially fixed to the side of the input disk facing the output disk. Each memory spring linear actuator has a built-in linear Hall sensor. One end of the stiffness adjustment mechanism is connected to the power output end of the memory spring linear actuator, and the other end is slidably connected to the stiffness change mechanism. The other end of the stiffness change mechanism is fixed to the side of the output disk facing the input disk. The cooling mechanism is installed inside the memory spring linear actuator.

[0008] In some embodiments of this application, the memory spring linear actuator includes a base, a copper cylinder, a heating wire, and a memory alloy spring. The base is fixed to the input disk, the copper cylinder is disposed in the inner cavity of the base, the heating wire is wound around the outer wall of the copper cylinder, one end of the memory alloy spring is connected to the base, and the other end is connected to the stiffening adjustment mechanism.

[0009] In some embodiments of this application, the cooling mechanism includes a semiconductor cooling chip, which is placed between the base and the copper cylinder and attached to the outer wall of the copper cylinder.

[0010] In some embodiments of this application, the stiffness adjustment mechanism includes a return spring, a piston, and an inner ring of the piston. The return spring is coaxially disposed inside the shape memory alloy spring and connected to the linear Hall sensor. The piston is disposed inside the copper cylinder and one end is connected to the shape memory alloy spring. The inner ring of the piston is connected to the other end of the piston and is slidably connected to the stiffness adjustment mechanism.

[0011] In some embodiments of this application, the piston includes a first piston section and a second piston section connected to each other. The diameter of the second piston section is smaller than the diameter of the first piston section. The end of the second piston section is provided with an external thread and is sleeved with the return spring through the external thread. The end of the first piston section is provided with an internal thread and is connected to the piston inner ring through the internal thread.

[0012] In some embodiments of this application, the memory spring linear actuator includes a magnet that is fixedly attached to the end of the second piston segment.

[0013] In some embodiments of this application, the variable stiffness mechanism includes a blade spring and a clamping seat. The clamping seat is fixedly installed on the output disk. One end of the blade spring is inserted into the clamping seat, and the other end is inserted into the inner hole of the piston inner ring and slides axially along the inner hole.

[0014] In some embodiments of this application, an angle detection mechanism is also included, which includes a single-turn absolute encoder read head, an encoder magnetic ring, and an encoder read head mounting ring. The encoder read head mounting ring is fixed on the side of the plurality of bases away from the input disk. The single-turn absolute encoder read head is mounted on the encoder read head mounting ring, and the encoder magnetic ring is fixed to the output disk.

[0015] In some embodiments of this application, a microcontroller is also included, which is electrically connected to the linear Hall sensor, the heating wire, and the cooling mechanism, respectively.

[0016] In some embodiments of this application, a connector is also included, the connector comprising a hollow shaft that extends through and connects the input disk and the output disk, and a vent hole is provided on the side wall of the hollow shaft, the vent hole communicating with the cavity of the memory spring linear actuator.

[0017] Compared with the prior art, the beneficial technical effects of the technical solution provided in this application include: This application significantly reduces the size of the variable stiffness joint of the robot by using a memory spring linear actuator as the power source for stiffness adjustment; it strengthens the joint support through a sealed collar, overcoming the problem of inaccurate joint encoder output data jumps caused by the wobbling between the input and output disks; and it obtains the overall stiffness change of the joint by detecting the position change of the stiffness adjustment mechanism through a linear Hall sensor probe. A cooling mechanism enables the joint to achieve a dual-mode operation, improving control accuracy and overcoming the problem of delayed adjustment time in pure heating mode to avoid overshoot. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the embodiments will be briefly described below: Figure 1 This is a schematic diagram of the structure of a robot variable stiffness joint according to an embodiment of this application; Figure 2 This is a schematic diagram of the structure of an output disk in an embodiment of this application; Figure 3 This is a cross-sectional view of a memory spring linear actuator according to an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a linear Hall sensor probe in an embodiment of this application.

[0019] Figure label: Input disk 100, output disk 200; Drive mechanism 300, base 310, Hall sensor probe sealing sleeve 320, Hall sensor probe 330, memory alloy spring 340, circular magnet 350, copper cylinder 360, sealing ring 370; Adjusting mechanism 400, return spring 410, piston 420, piston inner ring 430, piston sleeve 440; Variable stiffness mechanism 500, blade spring clamp 510, blade spring 520; Connector 600; 700 sealing collar; Angle detection mechanism 800, encoder magnetic ring 810, angle encoder 820; Semiconductor cooling chip 900. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] Those skilled in the art will understand that, in this specification, the term "comprising" is an open-ended expression, meaning that the stated feature is present but other features are excluded. Directional terms such as "upper," "lower," "left," and "right" refer to exemplary directions based on the accompanying drawings. Features specified as "first" or "second" implicitly include one or more of that feature. Singular expressions can also be used in plural forms. "Multiple" means two or more. The terms "installed," "connected," and "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection via an intermediate medium, and it can be a connection within two components. Furthermore, "linked" can include wireless connections.

[0022] The purpose of this application is to overcome the above-mentioned technical deficiencies and propose a variable stiffness joint for robots to solve the technical problems of high energy consumption, high cost, complex structure and low practicality in the prior art.

[0023] To achieve the above-mentioned technical objectives, this application adopts the following technical solution: like Figure 1 ~ Figure 4 As shown. This application provides a variable stiffness joint for a robot, including a joint unit and an adjustment unit.

[0024] The joint unit includes an input disk 100, an output disk 200, a connector 600, and a sealing collar 700. The input disk 100 and the output disk 200 are arranged opposite to each other, and a receiving cavity is formed between the input disk 100 and the output disk 200. The connector 600 is built into the receiving cavity and is fixedly connected to the input disk 100 and the output disk 200 respectively.

[0025] The adjustment unit includes a drive mechanism 300, a stiffness adjustment mechanism 400, a stiffness change mechanism 500, and a cooling mechanism disposed in the receiving cavity. The drive mechanism 300 includes multiple shape memory alloy (SMA) spring linear actuators, which are fixedly installed on the side of the input disk 100 facing the output disk 200. The number of the stiffness adjustment mechanism 400 and the stiffness change mechanism 500 is the same as the number of the drive mechanism 300. One end of the stiffness adjustment mechanism 400 is connected to the power output end of the SMA spring linear actuator, and the other end is slidably connected to the stiffness change mechanism 500. The other end of the stiffness change mechanism 500 is fixedly installed on the side of the output disk 200 facing the input disk.

[0026] Under the action of the SMA spring linear actuator, the stiffness adjustment mechanism 400 slides on the stiffness-changing mechanism 500, thereby changing the force point and effective length of the stiffness-changing mechanism 500, resulting in a torque angle between the input disk 100 and the output disk 200. The cooling mechanism is installed inside the SMA linear actuator base and is tangent to the outer wall of the copper cylinder, effectively cooling the SMA spring when it is heated to a certain temperature. The control unit uses a sliding mode control algorithm based on displacement feedback. This robot's variable stiffness joint is flexible, achieving the purpose of active stiffness change. This robot's variable stiffness joint allows the robot to adapt to more complex working conditions, reduces external impacts, protects both robot components and personnel, improves the smoothness and flexibility of robot movement, and controls the joint, adjusting the input power in real time.

[0027] like Figure 3 , Figure 4As shown, the SMA spring linear actuator includes a base 310, a Hall sensor probe sealing sleeve 320, a Hall sensor probe 330, a shape memory alloy (SMA) spring 340, a circular magnet 350, a copper cylinder 360, and a sealing ring. The copper cylinder is placed within the base. The base 310 is fixed to the inner end face of the input disk 100. The copper cylinder 360 is disposed within the inner cavity of the base 310, and one end of the copper cylinder 360 is positioned by a boss inside the base 310, while the other end is positioned by a... A sealing ring 370 is fixed at the opening of the base 310. The SMA spring 340 is disposed inside the copper cylinder 360. One end of the SMA spring 340 is pressed into the hole wall inside the base 310, and the other end is connected to the stiffening mechanism 400. The heating wire is wound around the outer wall of the copper cylinder 360, and the two connectors of the heating wire are respectively led out from the wire outlet holes on both sides of the base 310. The linear Hall sensor probe 330 is sealed by the Hall sensor probe sealing sleeve 3. The base 310 is wrapped with a sealing sleeve 320, which is secured to the top of the return spring 410 by friction. The wire of the Hall sensor probe 330 is led out through a circular hole near the end of the return spring 410 and connected to the Hall sensor element. The sealing sleeve 320 is made of resin to reduce the influence of temperature on the Hall sensor probe 330. The circular magnet 350 is glued to the top part of the piston 420 and is also present in the return spring 410. When the position of the circular magnet 350 changes, the voltage output of the Hall sensor probe 330 changes continuously due to the Hall effect. Therefore, based on this characteristic, the displacement change of the piston 420 pushed by the SMA spring 340 when it is heated can be effectively detected, directly reflecting the length change of the part of the leaf spring 520 that does not enter the piston in the copper cylinder cavity, thereby achieving precise adjustment of joint stiffness.

[0028] Compared to traditional displacement measurement using laser displacement sensors, this application uses a linear Hall sensor for displacement measurement. Considering the small size of the drive mechanism 300, the probe of the Hall sensor can enter the interior of the drive mechanism 300 to detect the displacement of the piston 420 in real time, achieving the effects of lightweight, convenience, and practicality.

[0029] The heating wire described in this application is a nickel-chromium alloy wire. By energizing the nickel-chromium alloy wire, it is heated, and then the SMA spring 340 inside the copper cylinder 360 is heated evenly through the transmission of electricity. This causes the length of the SMA spring to change, driving the stiffness adjustment mechanism 400 to slide on the stiffness change mechanism 500. This changes the point of action and effective length of the stiffness change mechanism 500, creating a torque angle between the input disk 100 and the output disk 200, making the joint flexible and achieving the purpose of active stiffness change.

[0030] The stiffness adjustment mechanism 400 described in this application includes a return spring 410, a piston 420, a piston inner ring 430, and a piston sleeve 440. The piston 420 includes the piston inner ring 430, which has a rectangular hole slightly larger than the leaf spring 520. This hole is mainly used to insert one end of the leaf spring into the rectangular hole. When the SMA spring 340 pushes the piston 420 to move, the piston moves on the stiffness adjustment mechanism 500 through the rectangular hole in the piston inner ring.

[0031] Furthermore, when the SMA spring 340 pushes the piston to move, the circular magnet 350 on the piston will also move accordingly. However, since the return spring 410 is fixed to the base by a pin, the distance between the Hall sensor probe 330 and the circular magnet will change. When the Hall sensor is powered on, the magnetic induction intensity between the Hall probe and the magnet will change, thereby changing the output voltage of the Hall sensor. Based on the change in output voltage, the change in displacement of the piston 420 can be determined. Thus, the displacement feedback data can be used in the sliding mode control of the control unit to adjust the input power.

[0032] The variable stiffness mechanism 500 described in this application includes a leaf spring 520 and a leaf spring clamping block 510. The leaf spring clamping block 510 is fixedly installed on the inner end face of the output disk 200. One end of the leaf spring 520 is inserted into the leaf spring clamping block 510, and the other end of the leaf spring 520 is inserted into the rectangular hole of the piston inner ring 430 and contacts the inner surface of the rectangular through hole. The distance between the end of the leaf spring 520 inserted into the leaf spring clamping block and the rectangular hole of the piston inner ring 430 is the effective length of the leaf spring.

[0033] Furthermore, since the inner surface of the rectangular through hole is an arc-shaped surface, during dynamic stiffness variation, the arc-shaped surface and the leaf spring 520 are in line contact rather than surface contact, which can reduce friction, avoid jamming caused by surface contact, and enhance the compliance of the variable stiffness joint.

[0034] The connector 600 described in this application connects the output disk 200 to the input disk 100, wherein a rolling bearing is connected to the output disk, so that the output disk moves under the drive of the input disk.

[0035] In this application, a sealed collar is added between the input disk 100 and the output disk 200. This collar strengthens the joint support and also overcomes the problem of inaccurate output data jumps of the joint encoder caused by the shaking between the input and output disks.

[0036] The angle detection mechanism 800 described in this application mainly includes an encoder magnetic ring 810 and a single-turn absolute angle encoder 820. The single-turn absolute angle encoder 820 can accurately measure the torsional angle Δθ of the variable stiffness joint. After determining the material and effective length of the leaf spring 520, the stiffness K of the variable stiffness joint can be obtained. Thus, the torque of the variable stiffness joint can be obtained through the formula τ=K·Δθ. This is equivalent to adding a one-dimensional torque sensor. For torque control of the variable stiffness joint, it is not necessary to establish an accurate dynamic model of the variable stiffness joint and use impedance control. Instead, torque feedback can be used. A similar force control effect can be achieved by using simple admittance control, realizing joint flexibility, constant torque, and drag teaching. This not only improves the torque control accuracy but also simplifies the control algorithm and reduces the complexity of the control system.

[0037] The semiconductor cooling chip 900 described in this application is installed inside the base 310 and outside the copper cylinder 360, tangent to the copper cylinder. Its two wires are led out from the wire outlet holes on both sides of the base 310. Compared with the traditional pure heating mode, the dual-mode proposed in this application also improves the control accuracy and overcomes the problem of delaying the adjustment time in the pure heating mode to avoid overshoot.

[0038] The control unit described in this application includes a sliding mode control algorithm based on displacement feedback. Sliding mode control is a nonlinear control method that designs a specific "sliding surface" so that the system state reaches that surface within a finite time and maintains a "sliding mode" on the surface. In the sliding mode, the system is robust to changes in internal parameters and external disturbances, meaning that the control performance does not depend on an accurate system model. In this algorithm, the sliding mode controller adjusts the input power in real time through position feedback from a linear Hall sensor, utilizing its robustness to handle the nonlinearity and hysteresis effect of the SMA spring.

[0039] Sliding mode control can be achieved by adjusting the sliding mode gain k and the integral coefficient. Boundary layer thickness These parameters balance control precision, response speed, and chatter level.

[0040] Compared with the prior art, the beneficial technical effects of the technical solution provided in this application include: This application strengthens joint support by designing a sealed collar 700 between the input disk 100 and the output disk 200. This also overcomes the problem of inaccurate joint encoder output data jumps caused by the wobbling between the input and output disks, resulting in a more perfect joint assembly and a significant reduction in overall joint wobbling during movement. A linear Hall sensor probe 330 and a circular magnet 350 are added to the drive mechanism 300 to detect position changes in the piston 420 in the stiffness adjustment mechanism 400, thereby obtaining the effective length change of the leaf spring 520 and ultimately the overall stiffness change of the joint. A semiconductor cooling chip 900 is added to the drive mechanism 300, enabling the joint to achieve a dual-mode operation, improving control accuracy and overcoming the problem of delayed adjustment time in pure heating mode to avoid overshoot. Finally, a sliding mode control algorithm is added based on existing technology. Specifically, the sliding mode controller adjusts the heating wire and cooling mechanism input power in real time through position feedback from the linear Hall sensor, utilizing its robustness to handle the nonlinearity and hysteresis effects of the SMA spring.

[0041] Those skilled in the art will understand that the steps, measures, and schemes in the various operations, methods, processes, and procedures discussed in this application can be alternated, modified, rearranged, decomposed, combined, or deleted.

[0042] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Any other corresponding changes and modifications made based on the technical concept of this application should be included within the scope of protection of the claims of this application.

Claims

1. A variable stiffness joint for robots, characterized in that, include: The joint unit includes an input disk, an output disk, and a sealing collar. The input disk and the output disk are arranged coaxially opposite each other, and the sealing collar seals the outer edges of the input disk and the output disk in a sealing manner. The adjustment unit includes a drive mechanism, a stiffness adjustment mechanism, a stiffness change mechanism, and a cooling mechanism. The drive mechanism includes multiple memory spring linear actuators, which are circumferentially fixed to the side of the input disk facing the output disk. Each memory spring linear actuator has a built-in linear Hall sensor. One end of the stiffness adjustment mechanism is connected to the power output end of the memory spring linear actuator, and the other end is slidably connected to the stiffness change mechanism. The other end of the stiffness change mechanism is fixed to the side of the output disk facing the input disk. The cooling mechanism is installed inside the memory spring linear actuator.

2. The robot variable stiffness joint according to claim 1, characterized in that, The memory spring linear actuator includes a base, a copper cylinder, a heating wire, and a memory alloy spring. The base is fixed to the input disk, the copper cylinder is disposed in the inner cavity of the base, the heating wire is wound around the outer wall of the copper cylinder, one end of the memory alloy spring is connected to the base, and the other end is connected to the stiffening adjustment mechanism.

3. The robot variable stiffness joint according to claim 2, characterized in that, The refrigeration mechanism includes a semiconductor refrigeration chip, which is placed between the base and the copper cylinder and attached to the outer wall of the copper cylinder.

4. The robot variable stiffness joint according to claim 2, characterized in that, The stiffness adjustment mechanism includes a return spring, a piston, and an inner ring of the piston. The return spring is coaxially disposed inside the shape memory alloy spring and connected to the linear Hall sensor. The piston is disposed inside the copper cylinder and one end is connected to the shape memory alloy spring. The inner ring of the piston is connected to the other end of the piston and is slidably connected to the stiffness adjustment mechanism.

5. The robot variable stiffness joint according to claim 4, characterized in that, The piston includes a first piston section and a second piston section connected to each other. The diameter of the second piston section is smaller than that of the first piston section. The end of the second piston section is provided with an external thread and is sleeved with the return spring through the external thread. The end of the first piston section is provided with an internal thread and is connected to the piston inner ring through the internal thread.

6. The robot variable stiffness joint according to claim 5, characterized in that, The memory spring linear actuator includes a magnet, which is fixedly attached to the end of the second piston segment.

7. The robot variable stiffness joint according to claim 4, characterized in that, The variable stiffness mechanism includes a blade spring and a clamping seat. The clamping seat is fixedly installed on the output disk. One end of the blade spring is inserted into the clamping seat, and the other end is inserted into the inner hole of the piston inner ring and slides axially along the inner hole.

8. The robot variable stiffness joint according to claim 2, characterized in that, It also includes an angle detection mechanism, which includes a single-turn absolute encoder reader, an encoder magnetic ring, and an encoder reader mounting ring. The encoder reader mounting ring is fixed on the side of the plurality of bases away from the input disk. The single-turn absolute encoder reader is mounted on the encoder reader mounting ring, and the encoder magnetic ring is fixed to the output disk.

9. The robot variable stiffness joint according to claim 2, characterized in that, It also includes a microcontroller, which is electrically connected to the linear Hall sensor, the heating wire, and the cooling mechanism.

10. The robot variable stiffness joint according to claim 1, characterized in that, It also includes a connector, which includes a hollow shaft that connects the input disk and the output disk. The side wall of the hollow shaft has a vent hole that communicates with the cavity of the memory spring linear actuator.

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