A lightweight series elastic actuator with adjustable stiffness

Abstract

The present invention belongs to the technical field of actuators for exoskeleton robots, and discloses a lightweight series elastic actuator with adjustable stiffness, including: a driving turntable seat, on which a first mounting horizontal shaft and a second mounting horizontal shaft are fixed on opposite side surfaces, and a hollow rotating output shaft is arranged on the first mounting horizontal shaft; a flexible side driving input pulley, which is installed on one side of the driving turntable seat through a fixed support; a plurality of flexible side crank-link mechanisms slidably connected to one side of the driving turntable seat, and one side of each of them is hinged to the outer wall of the hollow rotating output shaft; a stiffness adjustment side input pulley, which is sleeved on the second mounting horizontal shaft through a hollow rotating shaft seat; a plurality of stiffness adjustment crank-link mechanisms slidably connected to the other side of the driving turntable seat, one side of each of them is hinged to the outer wall of the hollow rotating shaft seat, and the other side of each of them is connected to the other side of the corresponding flexible side crank-link mechanism through a spring. This actuator not only has a simple structure, light weight, and a large output stiffness range, but also has a simple stiffness adjustment method.

Description

Technical Field

[0001] The present invention relates to the technical field of actuators for exoskeleton robots, and more particularly to a lightweight series elastic actuator with adjustable stiffness. Background Art

[0002] Currently, during the process of human-robot collaborative operation, it is inevitable for contact and even collision to occur between humans and robots. Therefore, how to ensure that the impact force does not harm the human body is crucial, and quickly reducing the joint stiffness of the robot is one of the most feasible solutions. When the robot performs precise positioning or trajectory control, users always expect the joint stiffness of the robot to be very large to ensure the end positioning accuracy, which requires quickly increasing the joint stiffness. Therefore, in the human-robot interaction operation environment, it is essential to adjust the stiffness of the robot joints in real time.

[0003] For example, exoskeleton robots are used to assist the rehabilitation training of disabled patients. To improve the stability and safety of human-robot physical interaction, the joint interaction actuator should have a certain yield compliance. There are two strategies for providing compliance: the active strategy and the passive strategy. The active strategy uses force / torque feedback and control algorithms to simulate the compliance behavior without adding flexible components (such as springs or other elastic bodies). However, when the sensor fails, the active strategy cannot provide safe interaction. Subsequently, by introducing elastic elements, elastic actuators based on the passive strategy were proposed. Compared with the active strategy, the elastic elements provide a lower mechanical impedance for the passive elastic actuator, making it inherently safe. In addition, the inherent flexibility allows force / torque control to be converted into a position control problem, which can be used to improve the performance of force / torque control.

[0004] Existing passive elastic actuators can be divided into fixed-stiffness actuators (FSAs) and variable-stiffness actuators (VSAs). Fixed-stiffness actuators usually use actuators and elastic elements with fixed mechanical structures. The flexible behavior of fixed-stiffness actuators is usually designed based on preset working conditions, which limits the response bandwidth, torque control accuracy, energy storage capacity, and dynamic adaptability to the environment. Therefore, variable-stiffness actuators are designed to overcome the above limitations. There are many strategies used in variable-stiffness actuators: 1) changing the spring preload, such as MACCEPA and MACCEPA 2.0; 2) changing the effective length of the spring; 3) changing the transmission ratio between the spring and the actuator output, such as AwAS-II and vsaUT; 4) changing the configuration of the elastic element, such as JASR and RVSA. The variable stiffness enables the actuator to better adapt to different scenarios. However, this requires directly driving additional mechanisms such as gear transmission mechanisms or rack and pinion transmission mechanisms by motors to achieve stiffness adjustment, as shown in CN113414760B and CN103192406A, which makes the design of the actuator more complex and increases the weight, not meeting the requirements of joint lightweight design. And the elastic damper based on the change of spring preload is usually lighter and easier to control. In addition, compared with variable-stiffness actuators based on other principles, this actuator has better compatibility and smoother stiffness adjustment. However, the elastic damper based on the change of spring preload generally uses a single elastic element, which limits its stiffness adjustment range.

[0005] To reduce the impact of the joint actuator on the body mass distribution, the weight of the actuator should be as light as possible. Recent studies have reported various methods for reducing the weight of exoskeletons, such as algorithm compensation and using lightweight materials such as carbon fiber. In particular, Bowden cable drive (such as CN114831857A) as a power transmission unit has been widely used in exoskeletons due to its light weight and high load capacity.

[0006] Therefore, how to provide a lightweight stiffness-adjustable series elastic actuator based on the principle of changing spring preload, which has simple structure and stiffness adjustment, can increase the output stiffness range, and is lightweight at the same time, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a lightweight stiffness-adjustable series elastic actuator based on the principle of changing spring preload, which has simple structure and stiffness adjustment, can increase the output stiffness range, and is lightweight at the same time.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A lightweight stiffness-adjustable series elastic actuator, comprising:

[0010] A driving turntable base, on opposite sides of which are respectively fixed a first mounting horizontal shaft and a second mounting horizontal shaft, and a hollow rotary output shaft is sleeved on the first mounting horizontal shaft;

[0011] A flexible side driving input pulley, which is detachably mounted on one side of the driving turntable base through a fixed support. A steel wire rope is wound around the flexible side driving input pulley, and the hollow rotary output shaft is located between the fixed support and the driving turntable base;

[0012] A flexible side crank - connecting rod mechanism, which is a plurality of uniformly distributed and slidably connected on one side surface of the driving turntable base. One side of each flexible side crank - connecting rod mechanism is hinged to the outer wall of the hollow rotary output shaft;

[0013] A stiffness - adjusting side input pulley, which is sleeved on the second mounting horizontal shaft through a hollow rotating shaft seat, and a steel wire rope is wound around the stiffness - adjusting side input pulley;

[0014] A stiffness - adjusting crank - connecting rod mechanism, which is a plurality of uniformly distributed and slidably connected on the other side surface of the driving turntable base. One side of each stiffness - adjusting crank - connecting rod mechanism is hinged to the outer wall of the hollow rotating shaft seat, and the other side of each stiffness - adjusting crank - connecting rod mechanism is connected to the other side of the flexible side crank - connecting rod mechanism through a spring.

[0015] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a lightweight and stiffness-adjustable series elastic actuator. Among them, the wire rope on the flexible side is driven by a motor and a gearbox. When the wire rope drives the flexible side drive input pulley to rotate, the flexible side drive input pulley drives the drive turntable seat to rotate together. The drive turntable seat drives the flexible side crank-link mechanism to rotate together. The flexible side crank-link mechanism slides on the drive turntable at the same time and stretches the spring, causing the hollow rotary output shaft to rotate, thereby realizing the flexible movement of the corresponding joint of the robot. Therefore, the flexible side crank-link mechanism and the spring can provide the inherent compliance of the actuator. When it is necessary to increase the output stiffness of the actuator, the wire rope on the stiffness side drives the stiffness adjustment side input pulley to rotate. The stiffness adjustment side input pulley drives the stiffness adjustment crank-link mechanism to rotate. At the same time, the stiffness adjustment crank-link mechanism slides on the drive turntable seat and pulls the spring, increasing the stretching length of the spring, that is, increasing the pre-tightening force. At the same time, the spring will pull the flexible side crank-link mechanism to slide synchronously on the drive turntable seat, and then transmit the force to the hollow rotary output shaft to make it rotate. Therefore, for the series elastic actuator of the present invention, the crank-link of the stiffness adjustment and the flexible part share an output shaft, and the spring preload is adjusted through the stiffness adjustment crank-link mechanism to achieve the adjustment of the actuator stiffness, making the stiffness adjustment method simpler. In addition, the series elastic actuator of the present invention uses multiple springs, increasing the range of the actuator output stiffness and improving the application range of the actuator. In addition, the present invention uses a wire rope as the power input of the actuator, without setting mechanisms such as motors and gear transmissions on the actuator, making the structure of the actuator not only simple but also lighter in weight, meeting the requirement of the lightweight of the robot actuator.

[0016] Further, a plurality of mounting posts are fixedly spaced on one side surface of the drive turntable seat. A plurality of mounting ear plates are evenly fixed on the outer peripheral side wall of the fixed support. Each mounting ear plate is detachably connected to its corresponding mounting post. Each flexible side crank-link mechanism is disposed between two adjacent mounting posts.

[0017] The beneficial effect of adopting the above technical solution is that there is a certain gap between the fixed support and the drive turntable seat, which is convenient for accommodating the hollow rotary output shaft and the flexible side crank-link mechanism.

[0018] Further, the flexible side drive input pulley is fixed on the side surface of the fixed support away from the drive turntable seat by bolts.

[0019] The beneficial effect of adopting the above technical solution is that it is easy to disassemble and assemble between the flexible side drive input pulley and the fixed support.

[0020] Further, each flexible side crank-link mechanism includes:

[0021] The first linear guide rail is fixed on one side surface of the driving turntable seat, and a first slider is slidably connected to the first linear guide rail;

[0022] The first connecting plate is fixed on the first slider, and one end of the first connecting plate is connected to one end of the spring;

[0023] Link A, one end of Link A is hinged to one end of the first connecting plate, and the other end of Link A is hinged to the outer wall of the hollow rotating output shaft.

[0024] The beneficial effect of adopting the above technical solution is that when the steel wire rope drives the flexible side drive input pulley to rotate, the flexible side drive input pulley drives the driving turntable seat to rotate together. The first connecting plate slides on the first linear guide rail through the first slider, and under the action of the spring, drives the hollow rotating output shaft to output flexible torque through Link A.

[0025] Further, a first connecting column is fixed at a position close to one end of the first connecting plate. A first bearing is sleeved on the first connecting column. A first sleeve hole is formed at one end of Link A, and the first sleeve hole is sleeved on the outer ring of the first bearing;

[0026] A plurality of first connecting ear plates are uniformly fixed on the outer wall of the hollow rotating output shaft. A second connecting column is fixed on the first connecting ear plate. A second bearing is sleeved on the second connecting column. A second sleeve hole is formed at the other end of Link A, and the second sleeve hole is sleeved on the outer ring of the second bearing.

[0027] The beneficial effect of adopting the above technical solution is that it is easy for Link A to swing smoothly on the first connecting plate and the first connecting ear plate, reducing the jamming phenomenon.

[0028] Further, the stiffness adjustment side input pulley is fixed on the side surface of the hollow rotating shaft seat far from the driving turntable seat through bolts.

[0029] The beneficial effect of adopting the above technical solution is that it is easy to disassemble and assemble between the stiffness adjustment side input pulley and the hollow rotating shaft seat.

[0030] Further, each of the stiffness adjustment crank-link mechanisms includes:

[0031] The second linear guide rail is fixed on the other side surface of the driving turntable seat, and a second slider is slidably connected to the second linear guide rail;

[0032] The second connecting plate is fixed on the second slider. One end of the second connecting plate is fixed with a linkage rod, and the rod end of the linkage rod far from the second connecting plate is connected to the other end of the spring;

[0033] Link B, one end of the Link B is hinged to the other end of the second connecting plate, and the other end of the Link B is hinged to the outer wall of the hollow rotating shaft seat.

[0034] The beneficial effect of adopting the above technical solution is that when the wire rope drives the stiffness adjustment side input pulley to rotate, the second connecting plate slides on the second linear guide through the second slider, and the second connecting plate drives the spring to stretch through the linkage rod, adjusting the stretching length of the spring, that is, adjusting the pre-tightening force of the spring. Furthermore, the spring pulls the second connecting plate to slide on the first linear guide through the first slider, and drives the hollow rotating output shaft to output torque with greater stiffness through the Link A.

[0035] Further, a third connecting column is fixed at a position near the other end of the second connecting plate. A third bearing is sleeved on the third connecting column. A third sleeve hole is opened at one end of the Link B, and the third sleeve hole is sleeved on the outer ring of the third bearing;

[0036] A plurality of second connecting ear plates are uniformly fixed on the outer wall of the hollow rotating shaft seat. A fourth mounting column is fixed on the second connecting ear plate. A fourth bearing is sleeved on the fourth mounting column. A fourth sleeve hole is opened at the other end of the Link B, and the fourth sleeve hole is sleeved on the outer ring of the fourth bearing.

[0037] The beneficial effect of adopting the above technical solution is that the Link B can swing smoothly on the second connecting plate and the second connecting ear plate, reducing the jamming phenomenon.

[0038] Further, a first encoder magnetic ring is sleeved on the end of the hollow rotating output shaft near the driving turntable seat. A first magnetic encoder is fixed on one side of the driving turntable seat, and the probe of the first magnetic encoder corresponds to the position of the first encoder magnetic ring;

[0039] A second encoder magnetic ring is sleeved on the end of the hollow rotating shaft seat near the driving turntable seat. A second magnetic encoder is fixed on the other side of the driving turntable seat, and the probe of the second magnetic encoder corresponds to the position of the second encoder magnetic ring.

[0040] The beneficial effect of adopting the above technical solution is that the encoder can detect the angle θ between the driving turntable seat and the hollow rotating output shaft, and the angle α between the driving turntable seat and the hollow rotating shaft seat in real time, providing a calculation basis for the output torque of the driver.

[0041] Further, the weight of the driver is 0.41 kg, and the output stiffness range is 0 - 988 Nm / rad.

[0042] The beneficial effect of adopting the above technical solution is that the driver is light in weight and has a large output stiffness range, meeting the requirements of the exoskeleton robot driver. Brief Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0044] Figure 1 It is a schematic assembly structure diagram of a first perspective of a lightweight stiffness-adjustable series elastic actuator provided by the present invention.

[0045] Figure 2 It is a schematic assembly structure diagram of a second perspective of a lightweight stiffness-adjustable series elastic actuator provided by the present invention.

[0046] Figure 3 It is a schematic exploded structure diagram of a first perspective of a lightweight stiffness-adjustable series elastic actuator provided by the present invention.

[0047] Figure 4 For Figure 3 It is a schematic enlarged structure diagram of the local part A in

[0048] Figure 5 It is a schematic exploded structure diagram of a second perspective of a lightweight stiffness-adjustable series elastic actuator provided by the present invention.

[0049] Figure 6 For Figure 5 It is a schematic enlarged structure diagram of the local part B in

[0050] Figure 7 It is a schematic diagram of the flexible side crank-link mechanism and the stiffness adjustment crank-link mechanism in the present invention. Detailed Embodiments

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0052] See Figures 1-6 , the embodiments of the present invention disclose a lightweight stiffness-adjustable series elastic actuator, which is used to improve the compliance of the exoskeleton robot joint interaction, thereby improving the robustness and safety of the robot. The actuator includes:

[0053] The driving turntable base 1 (is rotatably installed on the housing of the driver), and a first mounting horizontal shaft 2 and a second mounting horizontal shaft 3 are respectively fixed on opposite sides of the driving turntable base 1. A hollow rotary output shaft 4 is sleeved on the first mounting horizontal shaft 2;

[0054] The flexible side driving input pulley 5, the flexible side driving input pulley 5 is detachably installed on one side of the driving turntable base 1 through a fixed support 6. A steel wire rope is wound around the flexible side driving input pulley 5, and the steel wire rope is driven by a motor and a gearbox (not shown) on the exoskeleton robot. The hollow rotary output shaft 4 is located between the fixed support 6 and the driving turntable base 1;

[0055] The flexible side crank - connecting rod mechanism 7, the flexible side crank - connecting rod mechanism 7 is a plurality of (preferably 4) evenly distributed and slidably connected on one side surface of the driving turntable base 1. One side of each flexible side crank - connecting rod mechanism 7 is hinged to the outer wall of the hollow rotary output shaft 4;

[0056] The stiffness - adjusting side input pulley 8, the stiffness - adjusting side input pulley 8 is sleeved on the second mounting horizontal shaft 3 through a hollow rotating shaft seat 9. A steel wire rope is wound around the stiffness - adjusting side input pulley 8, and the steel wire rope is driven by a motor and a gearbox (not shown) on the exoskeleton robot;

[0057] The stiffness - adjusting crank - connecting rod mechanism 10, the stiffness - adjusting crank - connecting rod mechanism 10 is a plurality of (preferably 4) evenly distributed and slidably connected on the other side surface of the driving turntable base 1. One side of each stiffness - adjusting crank - connecting rod mechanism 10 is hinged to the outer wall of the hollow rotating shaft seat 9, and the other side of each stiffness - adjusting crank - connecting rod mechanism 10 is connected to the other side of the flexible side crank - connecting rod mechanism 7 through a spring 11.

[0058] Wherein, a plurality of mounting columns 12 are fixedly spaced on one side surface of the driving turntable base 1, and a plurality of mounting ear plates 61 are evenly fixedly arranged on the outer peripheral side wall of the fixed support 6. Each mounting ear plate 61 is detachably connected to its corresponding mounting column 12, and each flexible side crank - connecting rod mechanism 7 is placed between two adjacent mounting columns 12. The flexible side driving input pulley 5 is fixed on the side surface of the fixed support 6 away from the driving turntable base 1 through bolts.

[0059] In the above - mentioned embodiment, each flexible side crank - connecting rod mechanism 7 includes:

[0060] The first linear guide 71, the first linear guide 71 is fixed on one side surface of the driving turntable base 1, and a first slider 72 is slidably connected on the first linear guide 71;

[0061] The first connecting plate 73, the first connecting plate 73 is fixed on the first slider 72, and one end of the first connecting plate 73 is connected to one end of the spring 11;

[0062] The connecting rod A74 has one end hinged to one end of the first connecting plate 73 and the other end hinged to the outer wall of the hollow rotary output shaft 4.

[0063] Specifically, a first connecting column 731 is fixed at a position near one end of the first connecting plate 73. A first bearing 13 is sleeved on the first connecting column 731. A first sleeve hole is formed at one end of the connecting rod A74, and the first sleeve hole is sleeved on the outer ring of the first bearing 13;

[0064] A plurality of first connecting ear plates 41 are uniformly fixed on the outer wall of the hollow rotary output shaft 4. A second connecting column 411 is fixed on the first connecting ear plate 41. A second bearing 14 is sleeved on the second connecting column 411. A second sleeve hole is formed at the other end of the connecting rod A74, and the second sleeve hole is sleeved on the outer ring of the second bearing 14.

[0065] In the above embodiment, the stiffness adjustment side input pulley 8 is fixed on the side of the hollow rotating shaft seat 9 away from the driving turntable seat 1 by bolts.

[0066] Each stiffness adjustment crank - connecting rod mechanism 10 includes:

[0067] A second linear guide 101 is fixed on the other side of the driving turntable seat 1. A second slider 102 is slidably connected to the second linear guide 101;

[0068] A second connecting plate 103 is fixed on the second slider 102. One end of the second connecting plate 103 is fixed with a linkage rod 104, and the end of the linkage rod 104 away from the second connecting plate 103 is connected to the other end of the spring 11;

[0069] A connecting rod B105 has one end hinged to the other end of the second connecting plate 103 and the other end hinged to the outer wall of the hollow rotating shaft seat 9.

[0070] Specifically, a third connecting column 1031 is fixed at a position near the other end of the second connecting plate 103. A third bearing 15 is sleeved on the third connecting column 1031. A third sleeve hole is formed at one end of the connecting rod B105, and the third sleeve hole is sleeved on the outer ring of the third bearing 15;

[0071] A plurality of second connecting ear plates 16 are uniformly fixed on the outer wall of the hollow rotating shaft seat 9. A fourth mounting column 161 is fixed on the second connecting ear plate 16. A fourth bearing 17 is sleeved on the fourth mounting column 161. A fourth sleeve hole is formed at the other end of the connecting rod B105, and the fourth sleeve hole is sleeved on the outer ring of the fourth bearing 17.

[0072] In another embodiment of the present invention, a first encoder magnetic ring 18 is sleeved on the end of the hollow rotary output shaft 4 close to the driving turntable base 1, and a first magnetic encoder 19 (encoder A) is fixed on one side surface of the driving turntable base 1. The probe of the first magnetic encoder 19 corresponds to the position of the first encoder magnetic ring 18;

[0073] A second encoder magnetic ring 20 is sleeved on the end of the hollow rotating shaft seat 9 close to the driving turntable base 1, and a second magnetic encoder 21 (encoder B) is fixed on the other side surface of the driving turntable base 1. The probe of the second magnetic encoder 21 corresponds to the position of the second encoder magnetic ring 20.

[0074] In the above embodiment of the present invention, all structures of the driver are manufactured by a numerically controlled machine tool, its weight is 0.41 kg, and the output stiffness range is 0 - 988 Nm / rad.

[0075] 1) Refer to Figure 7 , the theoretical derivation of the principle of variable stiffness of the series elastic driver of the present invention is as follows:

[0076] The stiffness of the series elastic driver constructs a theoretical model based on the following assumptions.

[0077] Assumption 1: All components of the crank - connecting rod mechanism are rigid.

[0078] Assumption 2: The stiffness of all springs is constant.

[0079] Assumption 3: The friction of the system is 0.

[0080] The pair of series crank - connecting rod mechanisms is composed of the crank - connecting rod mechanism of the flexible driver unit (i.e., the flexible - side crank - connecting rod mechanism in the present invention) and the crank - connecting rod mechanism of the stiffness - adjusting unit (i.e., the stiffness - adjusting crank - connecting rod mechanism in the present invention). When a deflection angle is generated between the driving turntable base and the hollow rotary output shaft (i.e., θ≠0), the tension of the spring will generate a torque on the output shaft, and encoder A is used to measure the deflection angle θ. Therefore, the torque acting on the hollow rotary output shaft is related to its rotation angle θ. To ensure sufficient safety, a limit point (a limiter, such as setting a corresponding stop post on the linear guide) is added at one end of the crank - connecting rod mechanism, so that the movement of the slider is limited. At this time, the torsion angle of the hollow rotary output shaft is also limited, and its movement range is (0, θ max .

[0081] Assume that the length of link A of the flexible driver unit is l a , and the length of link B of the stiffness - adjusting unit is l b . According to the crank - connecting rod structure of the flexible driver, its kinematic equation can be expressed as:

[0082]

[0083] Here, (0, y p ) represents the position coordinates of the connection axis P of the crank and the slider relative to the output shaft axis O. The output torque of the actuator can be expressed as:

[0084]

[0085] N represents the number of springs. The number of springs in the crank - connecting rod mechanism of the flexible actuator shown is 4, that is, there are 4 spring forces. F s,i represents the elastic force of the i - th spring, and r eq,i represents the equivalent moment arm of the i - th spring relative to the output shaft, and:

[0086] r eq,1 = r eq,2 = r eq,3 = r eq,4 = r eq (θ) (3)

[0087] In addition, the spring force can also be expressed as a relationship between the spring stiffness k s,i and the spring elongation l s,i , that is:

[0088] F s,i = k s,i l s,i (4)

[0089] Based on the actuator structure, it can be inferred that:

[0090] l s,1 = l s,2 = l s,3 = l s,4 = l s (θ, α) (5)

[0091] According to Equation (1), l s can also be expressed as:

[0092]

[0093] s(α) is the pre - stretched length of the spring, which can be applied by the crank - connecting rod mechanism of the stiffness adjustment unit, and its expression is:

[0094]

[0095] Here, α 0 represents the initial deflection angle of the output rod of the stiffness adjustment unit, which is defined as the position of the slider of the crank - connecting rod mechanism of the stiffness adjustment unit at the proximal limit point. Therefore, the spring pre - tightening force varies with the deflection angle α.

[0096] In addition, according to the literature, the equivalent moment arm r of the spring force of each crank - connecting rod mechanism of the flexible actuator acting on the output shaft torque eq can be expressed as:

[0097]

[0098] According to the definition of stiffness, the relationship between the torque increment of the output shaft and the equivalent rotational stiffness k eq and the rotational angle increment can be expressed as:

[0099] δT = k eq ·δθ (9)

[0100] Let:

[0101]

[0102] Then, taking the partial derivative of formula (9) gives:

[0103]

[0104] Let:

[0105]

[0106]

[0107] Then, the equivalent stiffness k eq is expressed as:

[0108]

[0109] According to formula (6), when θ ∈ [0, θ max , the following conclusion can be drawn:

[0110]

[0111] θ max represents the maximum deflection angle of the output shaft. Since (11) is an even function of θ, it can be obtained that when θ ∈ [-θ max , θ max , the stiffness of the actuator increases with the increase of the absolute value of the deflection angle of the output shaft. Similarly, the stiffness of the output shaft also increases with the increase of the pre - stretched length l s,i of the spring. According to formula (6) and formula (7),

[0112] when α ∈ [α min , α 0 (15)

[0113] Here, α minIt represents the deformation angle when the slider in the stiffness adjustment unit is at the farthest limit point position.

[0114] 2) Reconstruction of the stiffness range

[0115] In this design, the stiffness range of the flexible actuator depends on 4 linear factors, namely the stiffness of the spring (k s,i ), and 2 non-linear factors (f 1 , f 2 ). By changing the equivalent parallel stiffness of the spring the lower and upper limits of the stiffness of the flexible actuator can be changed, indicating that the present invention only needs to replace the spring to change the stiffness range of the flexible actuator, enabling the flexible actuator to adapt to different working environments. Therefore, theoretically, the stiffness range of the flexible actuator can be from 0 to ∞. However, due to the limitations of the physical properties of the material, the maximum output stiffness of the stiffness-variable flexible actuator is approximately 988 Nm / rad.

[0116] The principle of the output torque of the inherent flexibility output by the actuator is as follows:

[0117] The wire rope on the flexible side is driven by the motor and the gearbox. When the motor and the gearbox drive the wire rope and the wire rope drives the flexible side drive input pulley to rotate, the flexible side drive input pulley drives the drive turntable seat to rotate together. The first connecting plate slides on the first linear guide through the first slider, and under the action of the spring, drives the hollow rotating output shaft to output flexible torque through link A, realizing the movement of the corresponding joint of the robot.

[0118] The principle of the output torque of the actuator outputting a large range is as follows:

[0119] The wire rope on the rigid side is driven by the motor and the gearbox. When the motor and the gearbox drive the wire rope and the wire rope drives the stiffness adjustment side input pulley to rotate, the second connecting plate slides on the second linear guide through the second slider. The second connecting plate drives the spring to stretch through the linkage rod, adjusts the stretching length of the spring, that is, adjusts the pre-tightening force of the spring. Then the spring pulls the second connecting plate to slide on the first linear guide through the first slider, and drives the hollow rotating output shaft to output torque with a larger stiffness through link A.

[0120] The present invention provides a lightweight series elastic actuator for changing the spring preload based on a crank connecting rod. The stiffness adjustment and the crank connecting rod of the flexible part are coupled by a spring and share a rotating shaft (equivalent to sharing a crank). Moreover, the spring preload is adjusted by a stiffness adjustment crank connecting rod mechanism to continuously adjust the stiffness of the actuator, making the stiffness adjustment method simpler. In addition, the series elastic actuator of the present invention adopts four parallel springs, which increases the range of the output stiffness of the actuator and expands the application range of the actuator. Further, the present invention uses a steel wire rope as the input of the power of the actuator without setting up mechanisms such as motors and gear transmissions on the actuator, making the structure of the actuator not only simple but also lighter in weight, meeting the requirement of lightweight of the robot actuator.

[0121] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple. For the relevant parts, reference can be made to the descriptions in the method part.

[0122] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A lightweight stiffness-adjustable series elastic actuator, characterized in that, it includes: A driving turntable seat (1), on the opposite sides of the driving turntable seat (1), a first mounting horizontal shaft (2) and a second mounting horizontal shaft (3) are respectively fixed, and a hollow rotating output shaft (4) is sleeved on the first mounting horizontal shaft (2); A flexible side driving input pulley (5), the flexible side driving input pulley (5) is detachably mounted on one side of the driving turntable seat (1) through a fixed support (6), a steel wire rope is wound around the flexible side driving input pulley (5), and the hollow rotating output shaft (4) is located between the fixed support (6) and the driving turntable seat (1); A flexible side crank-link mechanism (7), a plurality of the flexible side crank-link mechanisms (7) are evenly distributed and slidably connected to one side surface of the driving turntable seat (1), and one side of each flexible side crank-link mechanism (7) is hinged to the outer wall of the hollow rotating output shaft (4); A stiffness adjustment side input pulley (8), the stiffness adjustment side input pulley (8) is sleeved on the second mounting horizontal shaft (3) through a hollow rotating shaft seat (9), and a steel wire rope is wound around the stiffness adjustment side input pulley (8); A stiffness adjustment crank-link mechanism (10), a plurality of the stiffness adjustment crank-link mechanisms (10) are evenly distributed and slidably connected to the other side surface of the driving turntable seat (1), one side of each stiffness adjustment crank-link mechanism (10) is hinged to the outer wall of the hollow rotating shaft seat (9), and the other side of each stiffness adjustment crank-link mechanism (10) is connected to the other side of the flexible side crank-link mechanism (7) through a spring (11); Each of the flexible side crank-link mechanisms (7) includes: A first linear guide (71), the first linear guide (71) is fixed on one side surface of the driving turntable seat (1), and a first slider (72) is slidably connected on the first linear guide (71); A first connecting plate (73), the first connecting plate (73) is fixed on the first slider (72), and one end of the first connecting plate (73) is connected to one end of the spring (11); Link A (74), one end of the link A (74) is hinged to one end of the first connecting plate (73), and the other end of the link A (74) is hinged to the outer wall of the hollow rotating output shaft (4); Each of the stiffness adjustment crank-link mechanisms (10) includes: A second linear guide (101), the second linear guide (101) is fixed on the other side surface of the driving turntable seat (1), and a second slider (102) is slidably connected on the second linear guide (101); A second connecting plate (103), the second connecting plate (103) is fixed on the second slider (102), a linkage rod (104) is fixed at one end of the second connecting plate (103), and the rod end of the linkage rod (104) far from the second connecting plate (103) is connected to the other end of the spring (11); Link B (105), one end of the Link B (105) is hinged to the other end of the second connecting plate (103), and the other end of the Link B (105) is hinged to the outer wall of the hollow rotating shaft seat (9).

2. A lightweight stiffness-adjustable series elastic actuator according to claim 1, wherein, A plurality of mounting posts (12) are fixedly spaced on one side surface of the driving turntable seat (1), and a plurality of mounting ear plates (61) are evenly fixedly arranged on the outer peripheral side wall of the fixed support (6). Each of the mounting ear plates (61) is detachably connected to its corresponding mounting post (12), and each of the flexible side crank-link mechanisms (7) is disposed between two adjacent mounting posts (12).

3. A lightweight stiffness-adjustable series elastic actuator according to claim 1, wherein, The flexible side drive input pulley (5) is fixed to the side surface of the fixed support (6) away from the driving turntable seat (1) by bolts.

4. A lightweight stiffness-adjustable series elastic actuator according to claim 1, wherein, A first connecting column (731) is fixed at a position near one end of the first connecting plate (73). A first bearing (13) is sleeved on the first connecting column (731). One end of the Link A (74) is provided with a first sleeve hole, and the first sleeve hole is sleeved on the outer ring of the first bearing (13); A plurality of first connecting ear plates (41) are evenly fixedly arranged on the outer wall of the hollow rotating output shaft (4). A second connecting column (411) is fixed on the first connecting ear plate (41). A second bearing (14) is sleeved on the second connecting column (411). The other end of the Link A (74) is provided with a second sleeve hole, and the second sleeve hole is sleeved on the outer ring of the second bearing (14).

5. A lightweight stiffness-adjustable series elastic actuator according to any one of claims 1-4, wherein, The stiffness adjustment side input pulley (8) is fixed to the side surface of the hollow rotating shaft seat (9) away from the driving turntable seat (1) by bolts.

6. A lightweight stiffness-adjustable series elastic actuator according to claim 1, wherein, A third connecting column (1031) is fixed at a position near the other end of the second connecting plate (103). A third bearing (15) is sleeved on the third connecting column (1031). One end of the Link B (105) is provided with a third sleeve hole, and the third sleeve hole is sleeved on the outer ring of the third bearing (15); A plurality of second connecting ear plates (16) are evenly fixedly arranged on the outer wall of the hollow rotating shaft seat (9). A fourth mounting column (161) is fixed on the second connecting ear plate (16). A fourth bearing (17) is sleeved on the fourth mounting column (161). The other end of the Link B (105) is provided with a fourth sleeve hole, and the fourth sleeve hole is sleeved on the outer ring of the fourth bearing (17).

7. A lightweight stiffness-adjustable series elastic actuator according to any one of claims 1-4, 6, wherein, A first encoder magnetic ring (18) is sleeved and fixed at the end of the hollow rotary output shaft (4) close to the driving turntable seat (1), and a first magnetic encoder (19) is fixed on one side surface of the driving turntable seat (1), and the probe of the first magnetic encoder (19) corresponds to the position of the first encoder magnetic ring (18); A second encoder magnetic ring (20) is sleeved and fixed at the end of the hollow rotating shaft seat (9) close to the driving turntable seat (1), and a second magnetic encoder (21) is fixed on the other side surface of the driving turntable seat (1), and the probe of the second magnetic encoder (21) corresponds to the position of the second encoder magnetic ring (20).

8. A lightweight stiffness-adjustable series elastic actuator according to any one of claims 1-4, 6 Characterized in that the weight of the actuator is 0.41 kg, and the output stiffness range is 0-988 Nm / rad.

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