Active stiffness variable series elastic actuator and control method thereof

Abstract

The application provides a double-motor driving and rigidity actively adjustable series elastic actuator and a control method thereof, which utilizes elastic elements to convert kinetic energy and potential energy, reduces system energy consumption, improves system energy utilization efficiency, improves dynamic performance of the actuator by introducing the elastic elements, strengthens the anti-impact capability of the system, and improves the safety of human-machine interaction; rigidity is controlled by changing the effective lever arm length between the end of the actuator and the elastic element, the deformation of the elastic element under the load of the actuator is measured, the transmission ratio of the system is calculated, the output torque is obtained, and the output force control of the actuator is further realized. The application utilizes double-motor driving and double-differential transmission mechanism to realize active adjustment of the output rigidity of the actuator system, and has a more extensive use scene and application range.

Description

Technical Field

[0001] This invention belongs to the field of robotics technology and involves multiple interdisciplinary technologies such as mechanics, computer science, rehabilitation kinematics, instrument science, control science, and sensor technology. Specifically, it relates to an active variable stiffness series elastic actuator and its control method. Background Technology

[0002] Modern rehabilitation medicine research shows that when the brain is damaged due to stroke, it possesses the ability to remodel itself to adapt to changing environments—this is neuroplasticity. Rehabilitation training can promote proper neural remodeling, helping stroke patients better recover limb movement. Rehabilitation robots, as an intelligent, automated, and powerful rehabilitation medical tool, are not only at the forefront of current robotics research but also a new interdisciplinary technology combining robotics and rehabilitation medicine. Compared to other robots, rehabilitation robots directly interact with humans; therefore, their performance must meet requirements such as compliant human-computer interaction, adaptability to individual differences, and safety in abnormal situations.

[0003] Series elastic actuators, as compliant joint actuators, are fundamental to endowing robots with inherent safety, enhancing situational awareness, and improving human-robot interaction capabilities. By connecting elastic elements in series at the motor and load ends, series elastic actuators transform torque control into faster-responding and more precise position control, while simultaneously strengthening the system's shock resistance and improving the safety of human-robot interaction. Currently, some research has been conducted based on series elastic actuators, including:

[0004] Patent CN105500368A proposes a disc-type series elastic actuator, which improves the power density and torque output performance of the system by setting inner and outer discs between the motor and the load and fixing three springs.

[0005] Patent CN115338901A proposes a series elastic actuator with continuously adjustable stiffness. By utilizing the self-locking characteristics of the lead screw and slider mechanism, the output stiffness of the system can be continuously adjusted, reducing energy consumption and effectively simplifying the overall structure of the actuator.

[0006] Patent CN113334356B proposes a passive stiffness series elastic actuator, which uses a cam structure and a leaf spring structure to achieve passive stiffness adjustment. The stiffness curve of the actuator series elastic components is customized by designing the cam shape and leaf spring structure dimensions.

[0007] The aforementioned patents all achieve passive stiffness changes in the actuator through the design of the position or size of the elastic element, but some problems still exist:

[0008] 1. The stiffness adjustment range of the drive is small, and the nonlinear adjustment method can easily make the system unstable;

[0009] 2. All drives use a passive stiffness adjustment method, making it difficult to achieve complete control over the stiffness of the drive's output torque. Summary of the Invention

[0010] To address the aforementioned issues, this invention proposes a dual-motor driven series elastic actuator with actively adjustable stiffness and its control method. By changing the effective lever arm length between the actuator end and the elastic element, stiffness controllability is achieved. By measuring the deformation of the elastic element under load and calculating the transmission ratio of the system, the output torque can be obtained, further enabling actuator output force control.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] An active variable stiffness series elastic actuator includes a power mechanism, a differential transmission mechanism, a variable stiffness mechanism, a housing, a control processing unit, a sensor unit, and a power module. The power mechanism is a dual-motor structure that provides power to the actuator. The differential transmission mechanism is mounted on the upper part of the power mechanism and connected to it to realize differential transmission with dual motor inputs. The variable stiffness mechanism is mounted on the top of the differential transmission mechanism through a threaded hole to realize real-time adjustment of the actuator stiffness and torque output. The sensor unit detects the rotation angle information of the dual motors and the rotation angle information of the output shaft. The power mechanism, the sensor unit, and the control processing unit are all connected to the power module.

[0013] The power mechanism includes a transmission ring gear motor, a sun gear motor, a base, a load-bearing base, a positioning bearing, a central gear, a central gear key, a central drive gear, and a ring gear drive gear. The transmission ring gear motor and the sun gear motor are mounted on the base. The output shafts are coaxially and tightly fitted with the ring gear drive gear and the central drive gear, respectively. The load-bearing base is coaxially mounted and fixed to the base. The positioning bearing is installed in the inner groove of the base. The central gear is coaxial with the positioning bearing. The central gear is coaxially mounted with the positioning bearing through the central gear key. The central drive gear meshes with the central gear.

[0014] The differential transmission mechanism includes a transmission gear ring, a planetary gear base, a base bearing, a sun gear, a sun gear key pin, three planetary gears, six limit bearings, three planetary gear fixed shafts, a planetary gear platform, and a platform bearing. The planetary gear base and planetary gear platform are fixedly installed through threaded holes. The lower part of the transmission gear ring is missing teeth and is coaxially installed and rotates with the load-bearing base. The sun gear is coaxially fitted with the center gear through the sun gear key pin. Three planetary gears are evenly distributed between the transmission gear ring and the sun gear, and are coaxially installed with the limit bearings and planetary gear fixed shafts fitted tightly on the planetary gear base and planetary gear platform, forming a differential transmission mechanism based on a planetary gear system. The planetary gear platform is connected to the outer ring of the platform bearing, and the platform bearing is coaxially connected to the upper part of the sun gear.

[0015] The variable stiffness mechanism includes a left variable stiffness gear ring, a right variable stiffness gear ring, a central platform, a central guide rail, a left bearing gear, a right bearing gear, a left platform rack, a right platform rack, a left receiving component, a right receiving component, a left deformation guide rail, a right deformation guide rail, a left compression platform, a right compression platform, a left mold spring, a right mold spring, and an output shaft. The left and right variable stiffness gear rings are longitudinally fixed to the upper part of the planetary gear platform through threaded holes. The left and right bearing gears are fixed to the upper part of the central platform through bearings. The central platform has threaded holes for fixing the central guide rail. The two sliders of the central guide rail are used to fix the left platform rack and the right platform rack, respectively. The left bearing gear meshes with the left variable stiffness gear ring and the left platform rack, respectively, and the right bearing gear meshes with the right variable stiffness gear ring and the right platform rack, respectively. The variable stiffness gear ring meshes with the right platform rack, and the positional difference between the variable stiffness gear ring and the bearing gear drives the platform rack to move linearly along the central guide rail. The left and right receiving parts are fixedly connected to the left and right platform racks, respectively. The left and right deformation guide rails are fixedly connected to the left and right receiving parts, respectively. The left and right compression platforms are fixedly installed on the sliders on the left and right deformation guide rails, respectively. Both the left and right compression platforms are provided with cylindrical sleeves. The left mold spring is coaxially fitted onto the outer surface of the cylindrical sleeve of the left compression platform, and its rear end is fixedly connected to the left compression platform. The right mold spring is coaxially fitted onto the outer surface of the cylindrical sleeve of the right compression platform, and its rear end is fixedly connected to the right compression platform. The upper end of the output shaft is fixed to the upper part of the outer shell.

[0016] The control processing unit comprises a data acquisition and storage unit and a control processor. The data processing unit acquires information such as the position and speed of the sensor unit, while the control processor processes the data acquired by the sensor unit and performs drive control functions for the geared ring motor and the sun gear motor.

[0017] The sensor unit includes two motor encoders and one output shaft encoder. The two motor encoders are fixed to the ends of the transmission gear ring motor and the sun gear motor, respectively, and transmit the motor's operating status to the motor controller in real time. The output shaft encoder is fixed to the end of the output shaft and is used to record the absolute position information of the output shaft in real time.

[0018] The power module provides energy to the sensor unit, control processing unit, transmission gear motor, and sun gear motor.

[0019] Furthermore, in the power mechanism, the central gear, the central drive gear, and the gear ring drive gear are on the same horizontal plane.

[0020] Furthermore, in the differential transmission mechanism, the upper part of the planetary gear base is provided with three arc-shaped bosses distributed at 120° for fixed connection with the planetary gear platform. Both the planetary gear base and the planetary gear platform are provided with three circular through holes distributed at 120° for installing and fixing six limit bearings respectively.

[0021] Furthermore, in the variable stiffness mechanism, a cuboid baffle is provided at the lower end of the output shaft to push the left compression platform and the right compression platform to move along the left deformation guide rail and the right deformation guide rail.

[0022] The present invention also provides a control method for an active variable stiffness series elastic actuator, comprising the following steps:

[0023] The output shaft encoder records the absolute position information of the output shaft in real time. By comparing the angular position information with that of the transmission gear ring motor encoder and the sun gear motor encoder, the relative displacement between the output shaft and the left and right compression platforms is calculated. Based on the effective lever arm length at this time, the external load applied to the driver is calculated. The external load is equal to the output force of the driver. At the same time, the difference in the revolution angle between the left variable stiffness gear ring, the right variable stiffness gear ring and the center platform drives the linear motion of the left platform rack and the right platform rack, thereby changing the position of the force point between the output shaft and the left and right compression platforms. The effective lever arm length between the output shaft of the control driver and the elastic element is adjusted in real time to achieve controllable system output stiffness.

[0024] By calculating the relative displacement between the output shaft and the compression platform, as well as the effective lever arm length at this time, the force condition of the driver can be obtained, thus achieving force control.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] 1. The active variable stiffness series elastic actuator designed in this invention utilizes elastic elements to convert kinetic energy and potential energy into each other, thereby reducing system energy consumption and improving system energy utilization efficiency. At the same time, the introduction of elastic elements also improves the dynamic performance of the actuator, strengthens the system's shock resistance, and enhances the safety of human-computer interaction.

[0027] 2. The active variable stiffness series elastic actuator designed in this invention achieves continuous and adjustable output stiffness of the actuator system by changing the effective lever arm length of the system. Compared with the fixed stiffness series elastic actuator, it can guarantee the force control accuracy at low stiffness and the force control bandwidth at high stiffness.

[0028] 3. The active variable stiffness series elastic actuator designed in this invention utilizes dual motors and a dual differential transmission mechanism to achieve active adjustment of the output stiffness of the actuator system, thus having a wider range of application scenarios and scope.

[0029] 4. The active variable stiffness series elastic actuator designed in this invention can realize the synchronous input of two motors, that is, either motor participates in the adjustment of the actuator stiffness and also participates in the output of the actuator system. Compared with other series elastic actuators that add stiffness adjustment motors, it significantly improves the overall input efficiency of the system. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the active variable stiffness series elastic actuator provided by the present invention.

[0031] Figure 2 This is a cross-sectional view of the active variable stiffness series elastic actuator provided by the present invention along the front view reference plane;

[0032] Figure 3 This is a three-dimensional view of the internal structure of the active variable stiffness series elastic actuator provided by the present invention.

[0033] Figure 4 This is a top view of the active variable stiffness series elastic actuator power mechanism provided by the present invention;

[0034] Figure 5 This is a three-dimensional view of the active variable stiffness series elastic actuator power mechanism provided by the present invention;

[0035] Figure 6 This is an internal top view of the active variable stiffness series elastic actuator differential transmission mechanism provided by the present invention.

[0036] Figure 7 This is a three-dimensional view of the internal structure of the active variable stiffness series elastic actuator differential transmission mechanism provided by the present invention.

[0037] Figure 8 This is a top view of the active variable stiffness series elastic actuator variable stiffness mechanism provided by the present invention;

[0038] Figure 9 This is a three-dimensional view of the active variable stiffness series elastic actuator variable stiffness mechanism provided by the present invention;

[0039] Figure 10This is a schematic diagram of the high stiffness state of the active variable stiffness series elastic actuator provided by the present invention.

[0040] Figure 11 This is a schematic diagram of the low-stiffness state of the active variable stiffness series elastic actuator provided by the present invention. Detailed Implementation

[0041] The technical solutions provided by the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] Reference Figure 1 , Figure 2 This invention provides an active variable stiffness series elastic actuator, comprising a power mechanism 1, a differential transmission mechanism 2, a variable stiffness mechanism 3, a housing 4, a control processing unit 5, a sensor unit 6, and a power module 7. The power mechanism 1 is a dual-motor structure that provides power to the actuator. The differential transmission mechanism 2 is mounted on top of the power mechanism 1 and connected to it to achieve differential transmission with dual motor inputs. The variable stiffness mechanism 3 is mounted on the top of the differential transmission mechanism 2 via a threaded hole, enabling real-time adjustment of the actuator's stiffness and torque output. The sensor unit 6 detects the rotation angle information of the dual motors and the rotation angle information of the output shaft. The control processing unit 5 processes the data from the sensor unit and controls the dual motors. The power module 7 supplies power to all mechanisms, units, and modules of the actuator.

[0043] Reference Figure 1 , Figure 2 , Figure 4 , Figure 5 The power mechanism 1 includes a transmission ring gear motor 1-1, a sun gear motor 1-2, a base 1-3, a load-bearing base 1-4, a positioning bearing 1-5, a central gear 1-6, a central gear key pin 1-7, a central drive gear 1-8, and a ring gear drive gear 1-9. The transmission ring gear motor 1-1 and the sun gear motor 1-2 are respectively mounted on the lower part of the base 1-3 through four positioning holes. The load-bearing base 1-4 is coaxially mounted and fixed to the base 1-3. The base 1-3 has an O-shaped inner groove at its center. The positioning bearing 1-5 is installed in the O-shaped inner groove of the base 1-3. The central gear 1-6 is coaxial with the positioning bearing 1-5 and is fixed by the central gear key pin 1-7. The central drive gear 1-8 is fixed to the output shaft of the sun gear motor 1-2 and meshes with the central gear 1-6. The ring gear drive gear 1-9 is fixed to the output shaft of the transmission ring gear motor 1-1. The central gear 1-6, the central drive gear 1-8, and the ring gear drive gear 1-9 are all on the same horizontal plane.

[0044] Reference Figure 1 , Figure 2 , Figure 6 , Figure 7The differential transmission mechanism 2 includes a transmission gear ring 2-1, a planetary gear base 2-2, a base bearing 2-3, a sun gear 2-4, a sun gear key pin 2-5, three planetary gears 2-6, six limit bearings 2-7, three planetary gear fixed shafts 2-8, a planetary gear platform 2-9, and a platform bearing 2-10. The transmission gear ring 2-1 meshes with the gear ring drive gear 1-9. The lower part of the transmission gear ring 2-1, which has missing teeth, is coaxially mounted with the load-bearing base 1-4, allowing them to rotate relative to each other. The base bearing 2-3 is coaxially connected to the upper part of the central gear 1-6. The planetary gear base 2-2 is connected to the outer ring of the base bearing 2-3. The sun gear 2-4 is fixedly connected to the upper part of the planetary gear base 2-2 via the sun gear key pin 2-5 and the shaft. The upper part of the planetary gear base 2-2 has three arc-shaped bosses distributed at 120° for fixing to the planetary gear platform 2-9. Both the planetary gear base 2-2 and the planetary gear platform 2-9 have three circular through holes distributed at 120° for mounting and fixing six limit bearings 2-7. The three planetary gears 2-6 are coaxially connected to the limit bearings 2-7 mounted on the planetary gear base 2-2 and the planetary gear platform 2-9 via the planetary gear fixing shaft 2-8. Three planetary gears 2-6 mesh with the transmission gear ring 2-1 and the sun gear 2-4, respectively. The planetary gear platform 2-9 is connected to the outer ring of the platform bearing 2-10, and the platform bearing 2-10 is coaxially connected to the upper part of the sun gear 2-4.

[0045] Reference Figure 1 , Figure 2 , Figure 3 , Figure 8 , Figure 9The variable stiffness mechanism 3 includes a left variable stiffness gear ring 3-1, a right variable stiffness gear ring 3-2, a central platform 3-3, a central guide rail 3-4, a left bearing gear 3-5, a right bearing gear 3-6, a left platform rack 3-7, a right platform rack 3-8, a left receiving component 3-9, a right receiving component 3-10, a left deformation guide rail 3-11, a right deformation guide rail 3-12, a left compression platform 3-13, a right compression platform 3-14, a left mold spring 3-15, a right mold spring 3-16, and an output shaft 3-17. The left and right variable stiffness gear rings 3-1 and 3-2 are fixed to the planetary gear platform 2-9 via centrally symmetrical limiting holes. The central platform 3-3 has equally spaced threaded holes and two symmetrical stepped cylindrical bosses. The equally spaced threaded holes are used to fix the central guide rail 3-4, and the stepped cylindrical bosses are used to install the left bearing gear 3-5 and the right bearing gear 3-6. The lower part of the central platform 3-3 is equipped with a stepped shaft, which is fixedly connected to the platform bearing 2-10, the sun gear 2-4, the base bearing 2-3, and the central gear 1-6, and connected to the base 1-3 through the positioning bearing 1-5. The left platform rack 3-7 and the right platform rack 3-8 are fixedly connected to the upper parts of the two sliders of the central guide rail 3-4, respectively. The left bearing gear 3-5 meshes with the left variable stiffness gear ring 3-1 and the left platform rack 3-7, respectively, and the right bearing gear 3-6 meshes with the right variable stiffness gear ring 3-2 and the right platform rack 3-8, respectively. The left bearing 3-9 and the right bearing 3-10 are fixedly connected to the left platform rack 3-7 and the right platform rack 3-8, respectively. The left bearing 3-9 and the right bearing 3-10 are provided with threaded holes and circular slots. The threaded holes are used to fix the left deformation guide rail 3-11 and the right deformation guide rail 3-12, respectively. The left compression platform 3-13 and the right compression platform 3-14 are fixedly installed on the sliders of the left deformation guide rail 3-11 and the right deformation guide rail 3-12, respectively. Both the left and right compression platforms 3-13 and 3-14 are equipped with cylindrical sleeves. The left mold spring 3-15 is coaxially fitted onto the outer surface of the cylindrical sleeve of the left compression platform 3-13, with its rear end fixed to the left compression platform 3-13. The right mold spring 3-16 is coaxially fitted onto the outer surface of the cylindrical sleeve of the right compression platform 3-14, with its rear end fixed to the right compression platform 3-14. The lower end of the output shaft 3-17 is equipped with a cuboid baffle plate, used to push the left and right compression platforms 3-13 and 3-14 along the directions of the left and right deformation guide rails 3-11 and 3-12. The upper end of the output shaft 3-17 is fixed to the upper part of the outer casing 4 by bearings and retaining rings.

[0046] Sensor unit 6 includes a drive gear ring motor encoder 6-1, a sun gear motor encoder 6-2, and an output shaft encoder. The drive gear ring motor encoder 6-1 is fixed to the end of the drive gear ring motor, and the sun gear motor encoder 6-2 is fixed to the end of the sun gear motor. They transmit the operating status of the two motors to the motor controller in real time. The output shaft encoder is fixed to the end of the output shaft and is used to collect the absolute position information of the output shaft.

[0047] The control processing unit 5 consists of a data acquisition and storage unit and a control processor. After the sensor unit completes the acquisition of information such as position and speed, it transmits it to the control processor. The control processor completes the processing of the data acquired by the sensor unit and the drive control functions of the gear ring motor and the sun gear motor.

[0048] The power module 7 provides energy to the sensor unit 6, the control processing unit 5, the transmission gear motor 1-1, and the sun gear motor 1-2.

[0049] Reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11Ultimately, the transmission ring gear motor 1-1 and the sun gear motor 1-2 generate torque, driving the ring gear drive gear 1-9 and the central gear 1-6 to rotate. The ring gear drive gear 1-9 drives the transmission ring gear 2-1 to rotate, and the central gear 1-6 drives the sun gear 2-4 and the central platform 3-3 to rotate. The angular difference in rotation between the transmission ring gear 2-1 and the sun gear 2-4 drives the rotation and revolution of the planetary gear 2-6. The revolution of the planetary gear 2-6 drives the left variable stiffness ring gear 3-1 and the right variable stiffness ring gear 3-2 to rotate, and the rotation of the central platform 3-3 drives the left bearing gear 3-5 and the right bearing gear 3-6 to revolve. The revolution of the left variable stiffness ring gear 3-1, the right variable stiffness ring gear 3-2, and the central platform 3-3 drives the output shaft 3-17 to rotate. Under the action of external load, relative displacement occurs between the output shaft 3-17 and the left compression platform 3-13 and right compression platform 3-14, thus exhibiting series elastic characteristics. The output shaft encoder 6-3 can record the absolute position information of the output shaft 3-17 in real time. By calculating the angular position information of the transmission gear ring motor encoder 6-1 and the sun gear motor encoder 6-2, the relative displacement between the output shaft 3-17 and the left compression platform 3-13 and right compression platform 3-14 can be obtained. Then, based on the effective lever arm length at this time, the external load applied to the driver is calculated. The external load is equal to the output force of the driver. At the same time, the difference in the revolution angle between the left variable stiffness gear ring 3-1, the right variable stiffness gear ring 3-2 and the central platform 3-3 drives the linear motion of the left platform rack 3-7 and the right platform rack 3-8, thereby changing the position of the force point between the output shaft 3-17 and the left compression platform 3-13 and right compression platform 3-14. The effective lever arm length between the output shaft 3-17 of the control driver and the elastic element is adjusted in real time, so as to realize the controllable output stiffness of the system. By calculating the relative displacement between the output shaft 3-17 and the compression platform, as well as the effective lever arm length at this time, the force situation of the driver can be obtained, thus enabling force control.

[0050] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. An active variable stiffness series elastic actuator, characterized in that, include: The system comprises a power mechanism, a differential transmission mechanism, a variable stiffness mechanism, a housing, a control processing unit, a sensor unit, and a power module. The power mechanism is a dual-motor structure that provides power to the driver. The differential transmission mechanism is mounted on top of the power mechanism and connected to it to achieve differential transmission with dual motor inputs. The variable stiffness mechanism is mounted on the top of the differential transmission mechanism via a threaded hole, enabling real-time adjustment of the driver stiffness and torque output. The sensor unit detects the rotation angle information of the dual motors and the rotation angle information of the output shaft. The power mechanism, sensor unit, and control processing unit are all connected to the power module. The power mechanism includes a transmission ring gear motor, a sun gear motor, a base, a load-bearing base, a positioning bearing, a central gear, a central gear key, a central drive gear, and a ring gear drive gear. The transmission ring gear motor and the sun gear motor are mounted on the base. The output shafts are coaxially and tightly fitted with the ring gear drive gear and the central drive gear, respectively. The load-bearing base is coaxially mounted and fixed to the base. The positioning bearing is installed in the inner groove of the base. The central gear is coaxial with the positioning bearing. The central gear is coaxially mounted with the positioning bearing through the central gear key. The central drive gear meshes with the central gear. The differential transmission mechanism includes a transmission gear ring, a planetary gear base, a base bearing, a sun gear, a sun gear key pin, three planetary gears, six limit bearings, three planetary gear fixed shafts, a planetary gear platform, and a platform bearing. The planetary gear base and planetary gear platform are fixedly installed through threaded holes. The lower part of the transmission gear ring is missing teeth and is coaxially installed and rotates with the load-bearing base. The sun gear is coaxially fitted with the center gear through the sun gear key pin. Three planetary gears are evenly distributed between the transmission gear ring and the sun gear, and are coaxially installed with the limit bearings and planetary gear fixed shafts fitted tightly on the planetary gear base and planetary gear platform, forming a differential transmission mechanism based on a planetary gear system. The planetary gear platform is connected to the outer ring of the platform bearing, and the platform bearing is coaxially connected to the upper part of the sun gear. The variable stiffness mechanism includes a left variable stiffness gear ring, a right variable stiffness gear ring, a central platform, a central guide rail, a left bearing gear, a right bearing gear, a left platform rack, a right platform rack, a left receiving component, a right receiving component, a left deformation guide rail, a right deformation guide rail, a left compression platform, a right compression platform, a left mold spring, a right mold spring, and an output shaft. The left and right variable stiffness gear rings are longitudinally fixed to the upper part of the planetary gear platform through threaded holes. The left and right bearing gears are fixed to the upper part of the central platform through bearings. The central platform has threaded holes for fixing the central guide rail. The two sliders of the central guide rail are used to fix the left platform rack and the right platform rack, respectively. The left bearing gear meshes with the left variable stiffness gear ring and the left platform rack, respectively, and the right bearing gear meshes with the right variable stiffness gear ring and the right platform rack, respectively. The variable stiffness gear ring meshes with the right platform rack, and the positional difference between the variable stiffness gear ring and the bearing gear drives the platform rack to move linearly along the central guide rail. The left and right receiving parts are fixedly connected to the left and right platform racks, respectively. The left and right deformation guide rails are fixedly connected to the left and right receiving parts, respectively. The left and right compression platforms are fixedly installed on the sliders on the left and right deformation guide rails, respectively. Both the left and right compression platforms are provided with cylindrical sleeves. The left mold spring is coaxially fitted onto the outer surface of the cylindrical sleeve of the left compression platform, and its rear end is fixedly connected to the left compression platform. The right mold spring is coaxially fitted onto the outer surface of the cylindrical sleeve of the right compression platform, and its rear end is fixedly connected to the right compression platform. The upper end of the output shaft is fixed to the upper part of the outer shell. The control processing unit comprises a data acquisition and storage unit and a control processor. The data processing unit acquires information such as the position and speed of the sensor unit, while the control processor processes the data acquired by the sensor unit and performs drive control functions for the geared ring motor and the sun gear motor. The sensor unit includes two motor encoders and one output shaft encoder. The two motor encoders are fixed to the ends of the transmission gear ring motor and the sun gear motor, respectively, and transmit the motor's operating status to the motor controller in real time. The output shaft encoder is fixed to the end of the output shaft and is used to record the absolute position information of the output shaft in real time. The power module provides energy to the sensor unit, control processing unit, transmission gear motor, and sun gear motor.

2. The active variable stiffness series elastic actuator according to claim 1, characterized in that, In the power mechanism, the central gear, the central drive gear, and the gear ring drive gear are on the same horizontal plane.

3. The active variable stiffness series elastic actuator according to claim 1, characterized in that, In the differential transmission mechanism, the upper part of the planetary gear base is provided with three arc-shaped bosses distributed at 120° for fixed connection with the planetary gear platform. Both the planetary gear base and the planetary gear platform are provided with three circular through holes distributed at 120° for installing and fixing six limit bearings respectively.

4. The active variable stiffness series elastic actuator according to claim 1, characterized in that, In the variable stiffness mechanism, a cuboid baffle is provided at the lower end of the output shaft to push the left compression platform and the right compression platform to move along the left deformation guide rail and the right deformation guide rail.

5. A control method for an active variable stiffness series elastic actuator, implemented based on the active variable stiffness series elastic actuator according to any one of claims 1-4, comprising the following steps: The output shaft encoder records the absolute position information of the output shaft in real time. By comparing the angular position information with that of the transmission gear ring motor encoder and the sun gear motor encoder, the relative displacement between the output shaft and the left and right compression platforms is calculated. Based on the effective lever arm length at this time, the external load applied to the driver is calculated. The external load is equal to the output force of the driver. At the same time, the difference in the revolution angle between the left variable stiffness gear ring, the right variable stiffness gear ring and the center platform drives the linear motion of the left platform rack and the right platform rack, thereby changing the position of the force point between the output shaft and the left and right compression platforms. The effective lever arm length between the output shaft of the control driver and the elastic element is adjusted in real time to achieve controllable system output stiffness. By calculating the relative displacement between the output shaft and the compression platform, as well as the effective lever arm length at this time, the force condition of the driver can be obtained, thus achieving force control.

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