A robot variable stiffness joint

Abstract

The present invention discloses a variable stiffness joint for a robot, which comprises a joint unit and an adjustment unit. The joint unit includes an input disk, an output disk and a connecting member. The input disk and the output disk are arranged oppositely to form a receiving cavity. The connecting member is disposed in the receiving cavity and fixedly connected to the input disk and the output disk respectively. The adjustment unit includes a driving mechanism, a stiffness adjustment mechanism and a variable stiffness mechanism disposed in the receiving cavity. The driving mechanism includes a plurality of SMA spring linear drivers. One end of the stiffness adjustment mechanism is connected to the power output end of the SMA spring linear driver, and the other end thereof is slidably connected to the variable stiffness mechanism. The other end of the variable stiffness mechanism is fixedly installed on the side surface of the output disk facing the input disk. The present invention solves the technical problem that in the existing variable stiffness joints for robots, most of them use motors as the power source for stiffness adjustment, resulting in larger equipment weight and axial dimensions.

Description

Technical Field

[0001] The present invention relates to the technical field of robotic variable stiffness joints, and particularly to a robotic variable stiffness joint. Background Art

[0002] With the continuous development of robot technology, the scope of robot applications is becoming wider and wider, and the scenarios of human-robot interaction are also increasing. To ensure the safety of humans in human-robot collaboration and reduce damage to equipment and the environment, variable stiffness joints have been designed as one of the safety strategies.

[0003] The existing structural types of robotic variable stiffness joints are numerous, but most of them use motors as the power source for stiffness adjustment, which has no advantages in terms of structural size and weight, resulting in a relatively large weight and axial dimension of the equipment. Summary of the Invention

[0004] Therefore, it is necessary to propose a robotic variable stiffness joint, which uses an SMA spring linear actuator as the power source for stiffness adjustment to solve the technical problem of relatively large weight and axial dimension of the equipment caused by most existing robotic variable stiffness joints using motors as the power source for stiffness adjustment.

[0005] To achieve the above technical objectives, the technical solution of the present invention provides a robotic variable stiffness joint, including a joint unit and an adjustment unit. The joint unit includes an input disk, an output disk, and a connecting member. The input disk and the output disk are arranged opposite to each other, and a receiving cavity is formed between the input disk and the output disk. The connecting member is disposed in the receiving cavity and is fixedly connected to the input disk and the output disk respectively. The adjustment unit includes a driving mechanism, a stiffness adjustment mechanism, and a variable stiffness mechanism disposed in the receiving cavity. The driving mechanism includes a plurality of SMA spring linear actuators, and the plurality of SMA spring linear actuators are fixedly installed on the side of the input disk facing the output disk. The number of the stiffness adjustment mechanism and the variable stiffness mechanism is the same as that of the driving mechanism. One end of the stiffness adjustment mechanism is connected to the power output end of the SMA spring linear actuator, and the other end thereof is slidably connected to the variable stiffness mechanism. The other end of the variable stiffness mechanism is fixedly installed on the side of the output disk facing the input disk. The SMA spring linear actuator can make the stiffness adjustment mechanism slide on the variable stiffness mechanism to change the force application point and effective length of the variable stiffness mechanism, so as to generate a torque angle between the input disk and the output disk, realizing variable stiffness.

[0006] Further, the SMA spring linear actuator includes a sleeve - type base, a copper cylinder, a heating wire, and an SMA spring. The base is fixed to the inner end face of the input disk. The copper cylinder is disposed in the inner cavity of the base. One end of the copper cylinder is positioned by a boss inside the base, and the other end is fixed by a sealing ring disposed at the opening of the base. The SMA spring is disposed inside the copper cylinder. One end of the SMA spring is pressed against the hole wall inside the base, and the other end is connected to the stiffness - adjusting mechanism. The heating wire is wound around the outer wall of the copper cylinder, and the two connectors of the heating wire are respectively led out from the wire - outlet holes on both sides of the base.

[0007] Further, the stiffness - adjusting mechanism includes a piston and a piston inner ring disposed inside the piston. The piston is disposed inside the copper cylinder. One end of the piston away from the piston inner ring is connected to the SMA spring. The other end of the piston is internally provided with an internal thread adapted to the external thread of the piston inner ring. A rectangular through - hole for inserting the variable - stiffness mechanism is provided at the center inside the piston inner ring. Under the action of the SMA spring, the piston moves, thereby driving the piston inner ring to slide on the variable - stiffness mechanism.

[0008] Further, the piston is composed of a first piston and a second piston. The diameter of the second piston is smaller than that of the first piston. The outside of the second piston is provided with a thread, and a return spring is sleeved outside the thread. The piston sleeve is sleeved outside the return spring on this side. The other side of the return spring is inserted into the inside of the SMA spring, and the pull - ring on the other side is fixed in the bottom hole of the base through a pin. The end face of the piston sleeve away from the first piston is connected to the SMA spring.

[0009] Further, the inner - hole surface of the rectangular through - hole is an arc - shaped surface.

[0010] Further, the variable - stiffness mechanism includes a leaf spring and a clamping seat. The clamping seat is fixedly installed on the inner end face of the output disk. One end of the leaf spring is inserted into the clamping seat, and the other end of the leaf spring is inserted into the rectangular through - hole and contacts the inner - hole surface of the rectangular through - hole.

[0011] Further, the robot variable - stiffness joint further includes an angle - detection mechanism for measuring the torsional angle between the input disk and the output disk.

[0012] Further, the angle - detection mechanism includes a single - turn absolute encoder head, an encoder magnetic ring, and an encoder - head mounting ring. The encoder - head mounting ring is fixed on the side of the plurality of bases away from the input disk. The single - turn absolute encoder head is installed on the encoder - head mounting ring. The encoder magnetic ring is fixed on the inner end face of the output disk.

[0013] Further, the SMA spring linear actuator further includes a temperature control unit, which includes an intelligent temperature controller and a temperature sensor. The intelligent temperature controller is installed on the encoder head mounting ring. The input end of the temperature sensor contacts the SMA spring, and the output end of the temperature sensor is electrically connected to the input end of the intelligent temperature controller.

[0014] Further, the connecting member is a hollow shaft, and vent holes are provided at the portion of the hollow shaft corresponding to the SMA spring linear actuator.

[0015] Compared with the prior art, the beneficial effects of the present invention mainly include:

[0016] A variable stiffness joint of a robot provided by the present invention uses an SMA spring linear actuator as a power source for stiffness adjustment, and can reduce the axial dimension from about one hundred millimeters in the prior art to more than thirty millimeters, greatly reducing the volume of the variable stiffness joint of the robot, making the entire device structure compact, light in weight and highly practical, and can be applied to scenarios such as robotic arms and robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is an overall structural schematic diagram of the variable stiffness joint of the robot of the present invention;

[0018] Figure 2 is a structural schematic diagram of the variable stiffness joint of the robot of the present invention with the input disk removed;

[0019] Figure 3 is a cross-sectional view of the SMA spring linear actuator of the present invention;

[0020] Figure 4 is a schematic diagram of the variable stiffness mechanism of the present invention;

[0021] Figure 5 is a partial schematic diagram of the bearing of the variable stiffness joint of the robot of the present invention.

[0022] As shown in the figure:

[0023] 100 - input disk;

[0024] 200 - output disk;

[0025] 300 - drive mechanism, 310 - base, 320 - copper cylinder, 330 - heating wire, 340 - SMA spring, 350 - sealing ring, 360 - temperature control unit, 361 - intelligent temperature controller, 362 - temperature sensor;

[0026] 400 - Stiffness - adjusting mechanism, 410 - Piston, 411 - First piston, 412 - Second piston, 420 - Inner piston ring, 421 - Rectangular through - hole, 430 - Return spring, 440 - Piston sleeve, 450 - Pin;

[0027] 500 - Variable - stiffness mechanism, 510 - Leaf spring, 520 - Clamping seat;

[0028] 600 - Connecting piece, 610 - Bearing, 620 - Snap ring;

[0029] 700 - Angle - detecting mechanism, 710 - Single - turn absolute encoder head, 720 - Encoder magnetic ring, 730 - Encoder head mounting ring. Detailed implementation mode

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] As Figures 1 - 2 shown, the present invention provides a robot variable - stiffness joint, which includes a joint unit and an adjustment unit. The joint unit includes an input disk 100, an output disk 200 and a connecting piece 600. 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 connecting piece 600 is disposed in the receiving cavity and is fixedly connected to the input disk 100 and the output disk 200 respectively. The adjustment unit includes a driving mechanism 300, a stiffness - adjusting mechanism 400 and a variable - stiffness mechanism 500 disposed in the receiving cavity. The driving mechanism 200 includes a plurality of SMA spring linear drivers. The plurality of SMA spring linear drivers are fixedly installed on the side of the input disk 100 facing the output disk 200. The number of the stiffness - adjusting mechanism 400 and the variable - stiffness mechanism 500 is the same as that of the driving mechanism 200. One end of the stiffness - adjusting mechanism 400 is connected to the power output end of the SMA spring linear driver, and the other end thereof is slidably connected to the variable - stiffness mechanism 500. The other end of the variable - stiffness mechanism 500 is fixedly installed on the side of the output disk 200 facing the input disk. Thus, under the action of the SMA spring linear driver, the stiffness - adjusting mechanism 400 can slide on the variable - stiffness mechanism 500, thereby changing the force - applying point and the effective length of the variable - stiffness mechanism 500, so that a torque angle is generated between the input disk 100 and the output disk 200. This robot variable - stiffness joint has flexibility and achieves the purpose of active variable stiffness. This robot variable - stiffness joint can enable the robot to adapt to more complex working conditions, reduce external impacts, protect both the components of the robot and the human, and also improve the smoothness and flexibility of the robot's movement.

[0032] The robot variable stiffness joint described in the present invention above uses an SMA spring made of a shape memory alloy material to form an SMA spring linear actuator, and uses this SMA spring linear actuator as the power source for stiffness adjustment. Compared with the existing use of a motor as the power source for stiffness adjustment, the axial dimension can be reduced from the original approximately one hundred millimeters to more than thirty millimeters, making the robot variable stiffness joint of the present invention have a compact structure, small volume, and light weight, enhancing its practicability, and can be widely applied to scenarios such as robotic arms and robots.

[0033] The following further describes each component of the robot variable stiffness joint described in the present invention.

[0034] As Figure 2 shown, in this embodiment, there are a total of three sets of the SMA spring linear actuators (that is, the drive mechanism 300), which are fixedly distributed in the radial direction of the inner end face of the input disk 100 at a 120° angle in a plane. Correspondingly, there are also three sets of the stiffness adjustment mechanism 400 and the variable stiffness mechanism 500. Each set of the variable stiffness mechanism 500 is arranged at the power output end of the corresponding drive mechanism 300.

[0035] Specifically, as Figure 3 shown, the SMA spring linear actuator (that is, the drive mechanism 300) includes a sleeve - type base 310, a copper cylinder 320, a heating wire 330, and an SMA spring 340. The base 310 is fixed to the inner end face of the input disk 100. The copper cylinder 320 is arranged in the inner cavity of the base 310. One end of the copper cylinder 320 is positioned by a boss inside the base 310, and the other end is fixed by a sealing ring 350 arranged at the opening of the base 310. The SMA spring 340 is arranged inside the copper cylinder 320. One end of the SMA spring 340 is pressed against the hole wall inside the base 310, and its other end is connected to the stiffness adjustment mechanism 400. The heating wire 330 is wound around the outer wall of the copper cylinder 320, and the two connectors of the heating wire 330 are respectively led out from the wire - outlet holes on both sides of the base 310.

[0036] Preferably, the heating wire 330 is a nickel - chromium alloy wire. By energizing the nickel - chromium alloy wire to make it heat up, and then through the transfer of the copper cylinder 320, the SMA spring 340 inside the copper cylinder 320 is evenly heated, so that the length of the SMA spring changes, driving the stiffness adjustment mechanism 400 to slide on the variable stiffness mechanism 500, changing the action point and effective length of the variable stiffness mechanism 500, generating a torque angle between the input disk 100 and the output disk 200, making the joint flexible, and achieving the purpose of active variable stiffness.

[0037] Specifically, the stiffness adjustment mechanism 400 includes a piston 410 and a piston inner ring 420 disposed inside the piston 410. The piston 410 is disposed inside the copper cylinder 320, and one end of the piston 410 away from the piston inner ring 420 is connected to the SMA spring 340. An internal thread adapted to the external thread of the piston inner ring 420 is provided inside the other end of the piston 410. A rectangular through hole 421 for inserting the variable stiffness mechanism 500 is provided at the center inside the piston inner ring 420. When the SMA spring 340 drives the piston 410 to move, the piston inner ring 420 slides on the variable stiffness mechanism 500 through the cooperation of the internal thread of the piston 410 and the external thread of the piston inner ring 420.

[0038] Preferably, the piston 410 is composed of a first piston 411 and a second piston 412. The diameter of the second piston 412 is smaller than that of the first piston 411, and a thread is provided on the outside of the second piston 412. A return spring 430 is sleeved outside the thread. A piston sleeve 440 is sleeved outside this side of the return spring 430. The other side of the return spring 430 is inserted into the SMA spring 340, and a pull ring on the other side is fixed in the bottom hole of the base 310 through a pin 450. One end face of the piston sleeve 440 away from the first piston 411 is connected to the SMA spring 340.

[0039] Specifically, as Figure 4 shown, the variable stiffness mechanism 500 includes a leaf spring 510 and a clamping seat 520. The clamping seat 520 is fixedly installed on the inner end face of the output disk 200. One end of the leaf spring 510 is inserted into the clamping seat 520, and the other end of the leaf spring 510 is inserted into the rectangular through hole 421 and contacts the inner hole surface of the rectangular through hole 421.

[0040] Preferably, the inner hole surface of the rectangular through hole 421 is an arc surface. During dynamic stiffness variation, the arc surface and the leaf spring 510 are in line contact rather than surface contact, which can reduce friction, avoid the jamming phenomenon caused by surface contact, and enhance the compliance of the variable stiffness joint.

[0041] Specifically, the robot variable stiffness joint further includes an angle detection mechanism 700 for measuring the torsional angle Δθ between the input disk 100 and the output disk 200.

[0042] Furthermore, as Figure 2As shown, the angle detection mechanism 700 includes a single-turn absolute encoder head 710, an encoder magnetic ring 720, and an encoder head mounting ring 730. The encoder head mounting ring 730 is fixed to the side of the plurality of bases 310 away from the input disk 100. The single-turn absolute encoder head 710 is mounted on the encoder head mounting ring 730, and the encoder magnetic ring 720 is fixed to the inner end face of the output disk 200. The torsional angle Δθ can be accurately measured by the angle detection mechanism 700. Then, after determining the material and effective length of the leaf spring 510, the stiffness K of the variable stiffness joint can be obtained. Thus, through the formula τ = KΔθ, the torque of the variable stiffness joint can be obtained, which is equivalent to adding a one-dimensional torque sensor. For the torque control of the variable stiffness joint, it is not necessary to establish an accurate dynamic model of the variable stiffness joint for impedance control, but only torque feedback can be used, and a simple admittance control can achieve a similar force control effect, realizing joint flexibility, constant torque, drag teaching, etc. This not only improves the torque control accuracy, but also simplifies the control algorithm and reduces the complexity of the control system.

[0043] Specifically, the SMA spring linear actuator further includes a temperature control unit 360. The temperature control unit 360 includes an intelligent temperature controller 361 and a temperature sensor 362. The intelligent temperature controller 361 is mounted on the encoder head mounting ring 730. The input end of the temperature sensor 362 is in contact with the SMA spring 340, and the output end of the temperature sensor 362 is electrically connected to the input end of the intelligent temperature controller 361. The temperature of the SMA spring 340 is transmitted to the intelligent temperature controller 361 through the temperature sensor 362, and the deformation of the SMA spring 340 is controlled by adjusting the temperature through the intelligent temperature controller 361.

[0044] Specifically, as Figure 5 shown, the connecting member 600 is a hollow shaft. The input disk 100 and the output disk 200 are respectively assembled at both ends of the connecting member 600 through bearings 610 located at both ends of the connecting member 600, and their outer end faces are positioned by snap rings 620. The hollow shaft is provided with air vents at the part corresponding to the SMA spring linear actuator (i.e., the driving mechanism 300) for introducing compressed air, and a plurality of openings are provided at the other end for cables to pass through.

[0045] The working principle of a robot variable stiffness flexible joint based on SMA spring drive with angle detection provided by the present invention is as follows:

[0046] The heating wire 330 is energized to heat the copper cylinder 320, so that the SMA spring 340 in the copper cylinder 320 is evenly heated. At the same time, the temperature is adjusted by the external intelligent temperature controller 361 to control the deformation and elongation of the SMA spring 340, thereby driving the piston 410 to slide in the copper cylinder 320. The piston inner ring 420 is sleeved on the leaf spring 510. The input torque of the input disk 100 is transmitted to the output disk 200 through the contact between the arc surface of the piston inner ring 420 and the leaf spring 510. The sliding stroke of the piston 410 changes the effective length of the leaf spring 510 under force. The free end of the leaf spring 510 with a structure similar to a cantilever beam bends and deforms after being stressed, so that a torsional angle is generated between the input disk 100 and the output disk 200, making the joint flexible. When the same torque is input, the change in the effective length of the leaf spring 510 directly changes the amount of bending deformation of the leaf spring 510, resulting in a change in the torsional angle between the input disk 100 and the output disk 200, thereby changing the stiffness of the joint; after stopping heating, compressed air is introduced into the air vent of the hollow shaft to directly blow the inner cavity of the SMA spring linear actuator (i.e., the driving mechanism 300) to accelerate heat dissipation. After cooling, the SMA spring 340 completely shortens and resets under the tension of the return spring 430.

[0047] In addition, the torsional angle Δθ between the input disk 100 and the output disk 200 can be measured by the built-in high-precision single-turn absolute encoder head 710. Then, when the material property and effective length of the leaf spring 510 are determined, the stiffness K of the variable-stiffness joint is determined. At this time, the torque τ of the joint can be obtained by the formula τ = KΔθ.

[0048] In summary, a robot variable-stiffness flexible joint based on SMA spring drive with angle detection provided by the present invention has the following advantageous features:

[0049] 1. By controlling the temperature of the heating wire 330, the present invention drives the change in the length of the SMA spring 340, thereby changing the position of the piston 410 on the leaf spring 510 to change the effective length of the leaf spring 510, and further changing the stiffness of the leaf spring 510, realizing the active variable stiffness of the variable-stiffness joint, which can improve the smoothness and flexibility of the movement of the variable-stiffness joint, ensure the safety of people in human-robot collaboration, reduce equipment damage, and reduce expenses;

[0050] 2. The present invention uses the SMA spring linear actuator (i.e., the driving mechanism 300) as the power source for stiffness adjustment, so that the variable-stiffness joint is reduced to more than thirty millimeters in the axial dimension, with a compact structure, small volume, light weight, strong practicability, and can be applied to scenarios such as robotic arms and robots;

[0051] 3. The present invention can accurately measure the deflection angle through the angle detection mechanism 700. After determining the material and effective length of the leaf spring 510, the stiffness K of the variable stiffness joint can be obtained. Further, the torque can be calculated, which is equivalent to adding a one-dimensional torque sensor. For the torque control of the variable stiffness joint, it is not necessary to establish an accurate dynamic model of the variable stiffness joint for impedance control, but torque feedback can be used. Only simple admittance control can achieve a similar force control effect, realizing joint compliance, constant torque, teaching by dragging, etc. This not only improves the torque control accuracy but also simplifies the control algorithm and reduces the complexity of the control system.

[0052] The specific implementation manners of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A robot variable stiffness joint, characterized in that, It includes a joint unit and an adjustment unit; The joint unit includes an input disk, an output disk and a connecting member. The input disk and the output disk are arranged oppositely, and a receiving cavity is formed between the input disk and the output disk. The connecting member is disposed in the receiving cavity and fixedly connected to the input disk and the output disk respectively; The adjustment unit includes a driving mechanism, a stiffness adjustment mechanism and a stiffness change mechanism disposed in the receiving cavity. The driving mechanism includes a plurality of SMA spring linear drivers. The plurality of SMA spring linear drivers are fixedly installed on the side of the input disk facing the output disk. The number of the stiffness adjustment mechanism and the stiffness change mechanism is the same as that of the driving mechanism. One end of the stiffness adjustment mechanism is connected to the power output end of the SMA spring linear driver, and the other end thereof is slidably connected to the stiffness change mechanism. The other end of the stiffness change mechanism is fixedly installed on the side of the output disk facing the input disk; The SMA spring linear driver can make the stiffness adjustment mechanism slide on the stiffness change mechanism to change the force application point and the effective length of the stiffness change mechanism, so that a torque angle is generated between the input disk and the output disk, realizing variable stiffness; Wherein, the SMA spring linear driver includes a sleeve-shaped base, a copper cylinder, a heating wire and an SMA spring. The base is fixed to the inner end face of the input disk. The copper cylinder is disposed in the inner cavity of the base. One end of the copper cylinder is positioned by a boss inside the base, and the other end is fixed by a sealing ring disposed at the opening of the base. The SMA spring is disposed inside the copper cylinder. One end of the SMA spring is pressed against the hole wall inside the base, and the other end thereof is connected to the stiffness adjustment mechanism. The heating wire is wound around the outer wall of the copper cylinder, and two connectors of the heating wire are respectively led out from the wire outlet holes on both sides of the base.

2. The variable stiffness joint of a robot according to claim 1, characterized in that The stiffness adjustment mechanism includes a piston and a piston inner ring disposed inside the piston. The piston is disposed inside the copper cylinder. One end of the piston away from the piston inner ring is connected to the SMA spring. An internal thread adapted to the external thread of the piston inner ring is provided inside the other end of the piston. A rectangular through hole for inserting the stiffness change mechanism is provided at the center inside the piston inner ring. Under the action of the SMA spring, the piston moves, thereby driving the piston inner ring to slide on the stiffness change mechanism.

3. The variable stiffness joint of a robot according to claim 2, characterized in that, The piston is composed of a first piston and a second piston. The diameter of the second piston is smaller than that of the first piston. A thread is provided on the outside of the second piston. A return spring is sleeved on the outside of the thread. The piston sleeve is sleeved on the outside of this side of the return spring. The other side of the return spring is inserted into the SMA spring. The pull ring on the other side is fixed in the bottom hole of the base by a pin. The end face of the piston sleeve away from the first piston is connected to the SMA spring.

4. The variable stiffness joint of a robot according to claim 3, characterized in that, The inner hole surface of the rectangular through hole is an arc surface.

5. The variable stiffness joint of a robot according to claim 3, characterized in that The variable stiffness mechanism includes a leaf spring and a clamping seat. The clamping seat is fixedly installed on the inner end face of the output disk. One end of the leaf spring is inserted into the clamping seat, and the other end of the leaf spring is inserted into the rectangular through hole and contacts the inner hole surface of the rectangular through hole.

6. The variable stiffness joint of a robot according to claim 1, wherein The robot variable stiffness joint further includes an angle detection mechanism for measuring the torsional angle between the input disk and the output disk.

7. The robot variable stiffness joint according to claim 6, wherein The angle detection mechanism includes a single-turn absolute encoder head, an encoder magnetic ring, and an encoder head mounting ring. The encoder head mounting ring is fixed on the side of the plurality of bases away from the input disk. The single-turn absolute encoder head is mounted on the encoder head mounting ring, and the encoder magnetic ring is fixed on the inner end face of the output disk.

8. The variable stiffness joint of a robot according to claim 7, characterized in that, The SMA spring linear actuator further includes a temperature control unit. The temperature control unit includes an intelligent temperature controller and a temperature sensor. The intelligent temperature controller is mounted on the encoder head mounting ring. The input end of the temperature sensor contacts the SMA spring, and the output end of the temperature sensor is electrically connected to the input end of the intelligent temperature controller.

9. The variable stiffness joint of a robot according to claim 1, characterized in that The connecting member is a hollow shaft, and a vent hole is provided at a position on the hollow shaft corresponding to the SMA spring linear actuator.

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