Robotic variable stiffness joint based on SMA spring driven leaf spring

Abstract

The present invention discloses a robot variable stiffness joint based on an SMA spring-driven leaf spring, comprising a driving wheel and a driven wheel, a plurality of slider assemblies, a plurality of SMA spring assemblies and a leaf spring, wherein one end of each of the leaf springs is fixed on the inner side wall of the driven wheel, and the other end thereof is slidably connected in a second slide groove, the two ends of each of the SMA spring assemblies are respectively fixedly connected to the slider assembly and a shaft sleeve, and a heating element is provided on each of the SMA spring assemblies, and the change in the length of the SMA spring in the SMA spring assembly is controlled by heating the heating element, thereby controlling the distance that the slider assembly moves up and down in the first slide groove, so as to change the position of the leaf spring in the second slide groove, so that the leaf spring is bent at different positions, thereby achieving the purpose of variable stiffness.

Description

Technical Field

[0001] The invention relates to the technical field of robot variable stiffness joints, and in particular to a robot variable stiffness joint based on an SMA spring driving a leaf spring. Background Art

[0002] With the continuous development of robot technology, the scope of robot application is becoming more and more extensive, and the scenes of human-machine interaction are becoming more and more numerous. In order to ensure the safety of workers and reduce the occurrence of accidents in the process of human-machine collaborative work, there is an urgent need for a robot system that can be used in a human-machine collaborative environment and is environmentally friendly and safe for workers.

[0003] However, since the robot body and each joint are rigid, the stiffness is very large when a collision occurs, and the rate of increase is very fast, which is obvious for the damage to the robot or the person. In order to reduce the impact when a collision occurs and reduce damage to humans and machines, we usually add a soft medium to the robot body to buffer the collision, but this method has limited buffering and increases the mass and volume of the body, which is not conducive to the efficient operation of the robot. Variable stiffness elastic joints enable the robot system to bend appropriately when encountering an impact, just like human muscles, thereby buffering the energy generated by the collision, protecting and eliminating mechanical shocks and reducing mechanical damage to parts. The Chinese invention patent application with publication number CN111376306A discloses a "robot variable stiffness joint". When the adapter is under load, the side cover rotates relatively and causes the side cover pressure column to press the corresponding leaf spring to achieve force balance, meeting the joint flexibility requirements. However, the buffering effect of this structure is also limited. As robots and humans come into closer contact, improving the safety of human-machine interaction becomes the primary factor in future robot design. This requires that the robot's variable stiffness joints cannot be limited to the above-mentioned structural form. It is necessary to design another structural form of variable stiffness elastic joints to absorb external impacts and enhance the smoothness, stability and stronger environmental adaptability of the robot's movement. Summary of the invention

[0004] In response to the above technical problems, the present invention provides a robot variable stiffness joint based on an SMA spring driving a leaf spring, based on the principle that a spring made of SMA material will change in length as the temperature changes. The active variable stiffness of the leaf spring is achieved by changing the length of the SMA spring in the SMA spring assembly, thereby improving the smoothness and flexibility of the robot's movement.

[0005] In order to achieve the above technical objectives, the technical solution of the present invention provides a robot variable stiffness joint based on an SMA spring driving a leaf spring, comprising:

[0006] A driving wheel and a driven wheel, wherein the driving wheel and the driven wheel are connected by a fixed shaft, a sleeve is sleeved on one end of the fixed shaft close to the driving wheel, and a side end surface of the sleeve is fixedly connected to the driving wheel, a plurality of first slide grooves are provided on the driving wheel, and a guide rail is provided in each of the first slide grooves, and both ends of the guide rail are fixed on the driving wheel;

[0007] A plurality of slider assemblies, one end of each of the slider assemblies is slidably connected to the guide rail, the other end of each of the slider assemblies passes through the first slide groove and is disposed between the driving wheel and the driven wheel, and a second slide groove is provided on the end surface;

[0008] Multiple SMA spring assemblies and leaf springs, one end of each leaf spring is fixed on the inner wall of the driven wheel, and the other end is slidably connected in the second slide groove. The two ends of each SMA spring assembly are respectively fixedly connected to the slider assembly and the shaft sleeve, and each SMA spring assembly is provided with a heating element. By heating the heating element, the change in the length of the SMA spring in the SMA spring assembly is controlled, thereby controlling the distance that the slider assembly moves up and down in the first slide groove, so as to change the position of the leaf spring in the second slide groove, so that the leaf spring bends at different positions to achieve the purpose of changing stiffness.

[0009] Furthermore, the SMA spring assembly includes an SMA spring and a spring base, two ends of the spring base are respectively fixed to the slider assembly and the shaft sleeve, the SMA spring is embedded in the spring base in a spiral rotation, and the heating element is wound around the SMA spring.

[0010] Furthermore, it also includes a conductive component that provides electrical energy for heating the heating element.

[0011] Furthermore, the conductive component includes a first brush, a second brush and two plastic cups with copper foil, the two plastic cups with copper foil are sleeved on the fixed shaft at intervals, and the copper foils of the two plastic cups are respectively connected to an external power supply through wires, one end of the first brush and the second brush are respectively in contact with the copper foil on the two plastic cups, and the other ends of the first brush and the second brush are respectively fixed on the shaft sleeve and are respectively electrically connected to the heating element.

[0012] Furthermore, one end of the fixed shaft connected to the driven wheel is hollow, and a wire outlet is provided on the fixed shaft between the two plastic cups. The wire passes through the hollow end of the fixed shaft and then passes out from the wire outlet and is connected to the copper foil on the two plastic cups for conduction.

[0013] Furthermore, two annular grooves are arranged at intervals on the outer circumference of the fixed shaft, and the two plastic cups are arranged in the two annular grooves respectively.

[0014] Furthermore, the heating element is a resistance wire.

[0015] Furthermore, the slider assembly includes a first slider and a second slider, the first slider is connected to one end of the second slider by a screw, and the second slide groove is arranged on the other end surface of the second slider.

[0016] Furthermore, a bearing is sleeved on one side of the fixed shaft connected to the driven wheel, a motor steering wheel is fixed to the outer side of the driven wheel, the driven wheel is connected to the rear motor through the motor steering wheel, and the driving wheel is connected to the front motor.

[0017] Furthermore, the guide rail is a dovetail guide rail.

[0018] Compared with the prior art, the beneficial effects of the present invention mainly include:

[0019] The present invention provides a robot variable stiffness joint based on an SMA spring driven leaf spring, by arranging an SMA spring assembly, a slider assembly and a leaf spring between a driving wheel and a driven wheel, and arranging a heating element on the SMA spring assembly, and controlling the temperature of the SMA spring by heating the heating element to control the change in the length of the SMA spring, thereby controlling the up and down movement of the slider assembly in the first chute of the driving wheel to change the position of the leaf spring in the second chute, so that the leaf spring bends at different positions, and achieves the purpose of variable stiffness, thereby improving the smoothness and flexibility of the robot movement. The robot variable stiffness joint provided by the present invention is similar to the muscle flexible joint of the human body, and can provide better impact absorption and vibration energy absorption, so that the whole machine has good stability, allows the robot to adapt to more complex working conditions, reduce external impacts, and can protect the robot's parts and workers. At the same time, the use of SMA springs as driving elements makes the robot joint small in size, compact in structure, and light in weight, and does not affect the original maneuverability of the whole machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a front view of the variable stiffness joint of the robot according to the present invention;

[0021] Figure 2 is a rear view of the variable stiffness joint of the robot according to the present invention;

[0022] Figure 3 is a diagram of the internal structure of the variable stiffness joint of the robot of the present invention (the heating element is not shown);

[0023] Figure 4 It is a top view of the variable stiffness joint of the robot described in the present invention (the driven wheel, the second slider and the SMA spring assembly are ignored).

[0024] The specific markings in the figure are:

[0025] 1-driving wheel, 11-first slide slot, 12-guide rail, 13-second slide slot, 2-driven wheel, 21-motor steering wheel, 3-slider assembly, 31-first slider, 32-second slider, 4-SMA spring assembly, 41-SMA spring, 42-spring base, 5-leaf spring, 6-fixed shaft, 61-wire outlet, 7-bushing, 8-heating element, 9-conductive assembly, 91-first brush, 92-second brush, 93-plastic cup. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 intended to limit the present invention.

[0027] Before describing the specific embodiments of the present invention in detail, the principle on which the present invention is based is first explained: As is known to all, memory alloy material is a new type of functional material for motor oil that was gradually formed and developed in the 1960s, referred to as SMA. Its essence is that at a certain temperature, the material phase body will change from austenite to martensite. The memory alloy martensite in the initial state can be plastically deformed, and it can be restored to the initial state when the temperature is increased to a certain equilibrium or critical temperature. We call this ability to return to the initial state the memory effect. Its deformation is more than 20 times that of general elastic materials, the maximum recovery strain is 8%, and the recovery stress is 300-600MPa. SMA mainly includes three categories: nickel-titanium-based, copper-based and iron-based. Nickel-titanium-based is the best shape memory effect found so far. Its tensile strength is greater than 1000MPa, and its elongation is also greater than 20%. The recovery stress will increase accordingly. It has good stability, cyclicity, and excellent ability to resist corrosion and friction. It is a very excellent functional material.

[0028] Based on the principle that the length of a spring made of SMA material changes with temperature, the present invention designs a robot variable stiffness joint based on an SMA spring driving a leaf spring. The structure of the robot variable stiffness joint is shown in FIG. Figure 1 to Figure 4 As shown, it mainly includes a driving wheel 1, a driven wheel 2, a plurality of slider assemblies 3, a plurality of SMA spring assemblies 4, a plurality of leaf springs 5 ​​and a fixed shaft 6.

[0029] The driving wheel 1 and the driven wheel 2 are connected by a fixed shaft 6, and a shaft sleeve 7 is sleeved on one end of the fixed shaft 6 close to the driving wheel 1. The side end surface of the shaft sleeve 7 is fixedly connected to the driving wheel 1. A plurality of first slide grooves 11 are provided on the driving wheel 1, and a guide rail 12 is provided in each of the first slide grooves 11. Both ends of the guide rail 12 are fixed on the driving wheel 1.

[0030] One end of each of the slider assemblies 3 is slidably connected to the guide rail 12, and the other end thereof passes through the first slide groove 11 and is arranged between the driving wheel 1 and the driven wheel 2, and a second slide groove 13 is opened on the end surface.

[0031] One end of each of the leaf springs 5 ​​is fixed on the inner wall of the driven wheel 2, and the other end thereof is slidably connected in the second slide groove 13. The two ends of each of the SMA spring components 4 are respectively fixedly connected to the slider component 3 and the shaft sleeve 7, and each of the SMA spring components 4 is provided with a heating element 8. By heating the heating element 8, the change in the length of the SMA spring 41 in the SMA spring component 4 is controlled, thereby controlling the distance that the slider component 3 moves up and down in the first slide groove 11, so as to change the position of the leaf spring 5 in the second slide groove 13, so that the leaf spring 5 bends at different positions to achieve the purpose of changing the stiffness.

[0032] In the above technical solution, the SMA spring assembly 4 is fixed on the slider assembly 3 and the shaft sleeve 7, and the heating element 8 is wound on the SMA spring 41 of the SMA spring assembly 4. When the heating element 8 is energized to generate heat to heat the SMA spring 41, the length of the SMA spring 41 changes, thereby controlling the slider assembly 3 to move up and down in the first slide groove 11, so that the positions of the slider assembly 3 and the leaf spring 5 change. Then, when the current motor drives the driving wheel 1 to rotate, the leaf spring 5 bends at different positions in the second slide groove 13, thereby achieving the purpose of changing the stiffness.

[0033] When the heating element 8 is not energized, the temperature of the SMA spring 41 remains unchanged and does not deform. At this time, the slider assembly 3 is located at the very end of the leaf spring 5, and the stiffness of the entire robot joint is minimal. When the heating element 8 is energized to heat the SMA spring 41 to the maximum temperature, the SMA spring 41 stretches, causing the slider assembly 3 to rise to the root of the leaf spring 5. At this time, the entire robot joint is approximately rigid. The degree of heating of the SMA spring 41 is controlled by adjusting the temperature of the heating element 8, thereby affecting the change in the length of the SMA spring 41, so that the stiffness of the leaf spring 5 can be arbitrarily adjusted between the minimum and approximate rigidity, thereby achieving the purpose of variable stiffness of the robot.

[0034] It is understandable that the length of the first slide groove 11 and the temperature together affect the change in the length of the SMA spring 41 . In practical applications, the length of the first slide groove 11 can be specifically set according to the need for the change in the length of the SMA spring 41 .

[0035] In some specific embodiments, Figure 3As shown, the SMA spring assembly 4 includes an SMA spring 41 and a spring base 42, the two ends of the spring base 42 are respectively fixed on the slider assembly 3 and the shaft sleeve 7, the SMA spring 41 is embedded in the spring base 42 in a spiral rotation, and the heating element 8 is wound on the SMA spring 41.

[0036] Optionally, the robot variable stiffness joint further includes a conductive component 9 for providing electrical energy for heating the heating element 8 .

[0037] In some specific embodiments, the conductive component 9 includes a first brush 91, a second brush 92 and two plastic cups 93 with copper foil, the two plastic cups 93 with copper foil are sleeved on the fixed shaft 6 at intervals, and the copper foils of the two plastic cups 93 are respectively connected to an external power supply through wires, one end of the first brush 91 and the second brush 92 are respectively in contact with the copper foil on the two plastic cups 93, and the other ends of the first brush 91 and the second brush 92 are respectively fixed on the shaft sleeve 7 and are respectively electrically connected to the heating element 8.

[0038] Furthermore, one end of the fixed shaft 6 connected to the driven wheel 2 is hollow, and a wire outlet 61 is provided on the fixed shaft 6 located between the two plastic cups 93. The wire passes through the hollow end of the fixed shaft 6 and then passes out from the wire outlet 61 and is connected to the copper foil on the two plastic cups 93 for conduction.

[0039] Furthermore, two annular grooves are arranged at intervals on the outer circumference of the fixed shaft 6 , and the two plastic cups 93 are arranged in the two annular grooves respectively.

[0040] In some specific embodiments, the heating element 8 is a resistance wire.

[0041] In some specific embodiments, the slider assembly 3 includes a first slider 31 and a second slider 32 , the first slider 31 is connected to one end of the second slider 32 by screws, and the second slide groove 13 is arranged on the other end surface of the second slider 32 .

[0042] In some specific embodiments, a bearing is also sleeved on one side of the fixed shaft 6 connected to the driven wheel 2, a motor steering wheel 21 is fixed to the outer side of the driven wheel 2, the driven wheel 2 is connected to the rear motor through the motor steering wheel 21, and the driving wheel 1 is connected to the front motor.

[0043] In some specific embodiments, the guide rail 12 is a dovetail guide rail, and the first sliding block 31 slides up and down along the guide rail 12 .

[0044] In summary, the present invention provides a robot variable stiffness joint based on an SMA spring-driven leaf spring, wherein an SMA spring assembly 4, a slider assembly 3 and a leaf spring 5 are arranged between a driving wheel 1 and a driven wheel 2, and a heating element 8 is arranged on the SMA spring assembly 4. The temperature of the SMA spring 41 is controlled by heating the heating element 8 to control the change in the length of the SMA spring 41, thereby controlling the up and down movement of the slider assembly 3 in the first slide groove 11 of the driving wheel to change the position of the leaf spring 5 in the second slide groove 13, so that the leaf spring 5 is bent at different positions, thereby achieving the purpose of variable stiffness, thereby improving the smoothness and flexibility of the robot movement.

[0045] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A robot variable stiffness joint based on an SMA spring driven leaf spring, characterized in that: include: A driving wheel and a driven wheel, wherein the driving wheel and the driven wheel are connected by a fixed shaft, a sleeve is sleeved on one end of the fixed shaft close to the driving wheel, and a side end surface of the sleeve is fixedly connected to the driving wheel, a plurality of first slide grooves are provided on the driving wheel, and a guide rail is provided in each of the first slide grooves, and both ends of the guide rail are fixed on the driving wheel; A plurality of slider assemblies, one end of each of the slider assemblies is slidably connected to the guide rail, the other end of each of the slider assemblies passes through the first slide groove and is disposed between the driving wheel and the driven wheel, and a second slide groove is provided on the end surface; Multiple SMA spring assemblies and leaf springs, one end of each leaf spring is fixed on the inner wall of the driven wheel, and the other end is slidably connected in the second slide groove. The two ends of each SMA spring assembly are respectively fixedly connected to the slider assembly and the shaft sleeve, and each SMA spring assembly is provided with a heating element. By heating the heating element, the change in the length of the SMA spring in the SMA spring assembly is controlled, thereby controlling the distance that the slider assembly moves up and down in the first slide groove, so as to change the position of the leaf spring in the second slide groove, so that the leaf spring bends at different positions to achieve the purpose of changing stiffness.

2. A robot variable stiffness joint based on SMA spring driven leaf spring according to claim 1, characterized in that: The SMA spring assembly comprises an SMA spring and a spring base, two ends of the spring base are respectively fixed on the slider assembly and the shaft sleeve, the SMA spring is embedded in the spring base in a spiral rotation, and the heating element is wound on the SMA spring.

3. A robot variable stiffness joint based on SMA spring driven leaf spring according to claim 2, characterized in that: Also included is a conductive component for providing electrical energy for heating the heating element.

4. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 3, characterized in that: The conductive component includes a first brush, a second brush and two plastic cups with copper foil, the two plastic cups with copper foil are sleeved on the fixed shaft at intervals, and the copper foils of the two plastic cups are respectively connected to an external power supply through wires, one end of the first brush and the second brush are respectively in contact with the copper foils on the two plastic cups, and the other ends of the first brush and the second brush are respectively fixed on the shaft sleeve and are respectively electrically connected to the heating element.

5. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 4, characterized in that: One end of the fixed shaft connected to the driven wheel is hollow, and a wire outlet is provided on the fixed shaft between the two plastic cups. The wire passes through the hollow end of the fixed shaft and then passes through the wire outlet and is connected to the copper foil on the two plastic cups for conduction.

6. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 5, characterized in that: Two annular grooves are arranged at intervals on the outer circumference of the fixed shaft, and the two plastic cups are arranged in the two annular grooves respectively.

7. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 6, characterized in that: The heating element is a resistance wire.

8. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 1, characterized in that: The slider assembly includes a first slider and a second slider, the first slider is connected to one end of the second slider by a screw, and the second slide groove is arranged on the other end surface of the second slider.

9. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 1, characterized in that: A bearing is sleeved on one side of the fixed shaft connected to the driven wheel, a motor steering wheel is fixed on the outer side of the driven wheel, the driven wheel is connected to the rear motor through the motor steering wheel, and the driving wheel is connected to the front motor.

10. The robot variable stiffness joint based on SMA spring driven leaf spring according to claim 1, characterized in that: The guide rail is a dovetail guide rail.

Images