A Reconfigurable Nonlinear Rotary Series Elastic Actuator with Adjustable Stiffness

Abstract

The present invention discloses a reconfigurable non-linear rotary series elastic actuator with adjustable stiffness. The actuator includes an input component, an adjustable stiffness flexible component, an output component and a support component. The input component includes a direct drive motor, a motor fixing device, and an input ring, which is used to connect with an external driving force to transmit the external driving torque to the adjustable stiffness flexible component. The adjustable stiffness flexible component includes an axial spatial spring array composed of linear tension springs, which is used to endow the actuator with non-linear characteristics. The output component includes an output ring with adjustable anchor points and an actuator output link, which is used to implement the auxiliary training task in human-computer interaction. The axial spatial spring array can endow the actuator with adjustable stiffness characteristics through the adjustable anchor points designed by geometric parameters without replacing the hardware. The support component includes an actuator bracket, which is used to support the reconfigurable non-linear rotary series elastic actuator with adjustable stiffness.

Description

Technical Field

[0001] The present invention relates to the technical field of robots, and particularly relates to a reconfigurable non-linear rotary series elastic actuator with adjustable stiffness. Background Art

[0002] In recent years, assistive robots for stroke rehabilitation and ability enhancement have developed rapidly. In particular, gait-assist exoskeletons have shown outstanding performance in improving users' motor functions and enhancing their quality of life. In such applications, assistive robots must directly physically interact with humans. To improve the safety of physical human-robot interaction, actuator design is crucial. Compliance is a core performance indicator of assistive robots and is of great significance for improving dynamic adaptability, environmental robustness, and achieving safe interaction. Compared with rigid drive systems, flexible actuators are superior in aspects such as impact force absorption and external load perception. The series elastic actuator is the most representative flexible drive structure. By introducing an elastic element between the rigid actuator and the load, it realizes low output impedance, good backdrivability, impact resistance, and efficient and stable force transmission, significantly improving the safety of physical human-robot interaction.

[0003] On the premise of ensuring the safety of human-robot interaction, the design of series elastic actuators faces multiple requirements and challenges. First, it is necessary to have an inherent force sensing ability to achieve accurate measurement and adjustment of interaction forces, relying on clear and predictable torque-deformation characteristics. Second, human-robot interaction scenarios usually require the actuator to have low friction, small hysteresis, no dead zone, and bidirectional consistent force output to adapt to the control requirements of rapid direction switching. In addition, good compliance is also the key to ensuring comfortable and safe interaction, requiring the actuator to have low stiffness and large deformation ability. However, series elastic actuators usually use springs with fixed stiffness as the elastic elements for force transmission, resulting in fundamental limitations of the actuators. On the one hand, soft springs can produce high force control fidelity and low output impedance, but at the same time limit the force output range and bandwidth. On the other hand, hard springs will increase the force bandwidth but reduce the interaction compliance. Summary of the Invention

[0004] In view of the above problems, a reconfigurable non-linear rotary series elastic actuator with adjustable stiffness is provided, aiming to effectively solve the inherent limitations of the above series elastic actuators.

[0005] The purpose of the present invention is to propose a reconfigurable nonlinear rotary series elastic actuator with adjustable stiffness. The reconfigurable nonlinear rotary series elastic actuator has excellent mechanical properties, such as good compliance, low friction, small hysteresis, and sufficient force bandwidth and output force. The reconfigurable nonlinear rotary series elastic actuator has advantages in stiffness range, output torque, compactness, and light weight. At the same time, a compliant drive unit with compactness, light weight and high-precision force control capability is provided for a wearable exoskeleton robot. The problem to be solved by the present invention is achieved by the following technical solutions: A reconfigurable nonlinear rotary series elastic actuator with adjustable stiffness includes: an input component, the input component includes a quasi-direct drive motor, a motor fixing device, and an input ring, which is used to connect with an external driving force to transmit the external driving torque to an adjustable stiffness flexible component. An adjustable stiffness flexible component, the adjustable stiffness flexible component includes an axial space spring array composed of linear tension springs, which is used to give the driver nonlinear and adjustable stiffness characteristics. An output component, the output component includes an output ring and a driver output connecting rod, which is used to realize auxiliary training tasks in human-computer interaction. A support component includes a driver bracket for supporting the reconfigurable nonlinear rotation series elastic driver.

[0006] The quasi-direct drive motor integrates a 9:1 planetary reducer, a single-turn absolute encoder and a highly integrated driver, achieving smooth operation with large torque and facilitating the compact design of the reconfigurable nonlinear rotary series elastic driver. The quasi-direct drive motor is fastened to the motor fixing device by a hexagon socket screw. The output end of the quasi-direct drive motor is fixed to the rear end of the input ring by a hexagon socket screw. The quasi-direct drive motor drives the input ring to move and causes the linear tension spring to deform. The thin-walled bearing is installed between the output ring and the driver housing to reduce friction. The rotary encoder consists of a reading head and a permanent magnet ring. The permanent magnet ring is fixed to the output ring, and the reading head is fixed to the driver housing for real-time reading of the rotation angle of the output ring. The quasi-direct drive motor has a single-turn absolute encoder and the rotary encoder to measure the deflection angle of the axial space spring array by difference, and accurately calculate the output torque of the reconfigurable nonlinear rotary series elastic driver.

[0007] The axial space spring array is the core structure of the reconfigurable nonlinear rotation series elastic actuator. The input ring and the output ring are coaxially configured and coupled by a linear tension spring. The flange deep groove ball bearing is used to achieve relative rotation and reduce friction. The input ring and the output ring include an inner ring and an outer ring, respectively. The inner and outer rings are each configured with four groups of symmetrically distributed linear tension springs, and the phase angle between adjacent groups is 90°. When the input ring and the output ring undergo relative angular displacement, the linear tension spring always maintains a pre-tensioned state, and its tangential component force forms a synthetic torque in the rotation plane.

[0008] The purpose of designing the four groups of linear tension springs in the inner ring of the axial space spring array is to increase the output torque of the reconfigurable nonlinear rotation series elastic actuator and optimize the compactness of the structure. The four groups of springs in the outer ring of the axial space spring array are reconstructed into three different configurations by changing the initial deflection angle. The output ring includes an adjustable anchor point. Based on the design of the adjustable anchor point based on geometric parameters, the axial space spring array can achieve rapid switching of stiffness modes without hardware reconstruction. Through the multi-modal stiffness characteristics from nonlinear to quasi-linear, it covers the full working conditions from compliant interaction to high dynamic loads, significantly improving the task adaptability of the reconfigurable nonlinear rotation series elastic actuator in auxiliary robot scenarios such as rehabilitation training, gait correction and weight-bearing exoskeletons.

[0009] Compared with the prior art, the present invention has achieved the following technical effects: 1. The axial space spring array can give the reconfigurable nonlinear rotation series elastic actuator adjustable stiffness characteristics through adjustable anchor points designed based on geometric parameters without replacing hardware. 2. A flange deep groove ball bearing is installed between the input ring and the output ring to reduce the friction during the rotation of the axial space spring array. 3. The inner and outer rings of the input ring and the output ring are both installed with linear tension springs, which effectively improves the compactness and output torque of the reconfigurable nonlinear rotation series elastic actuator. 4. By adjusting the initial deflection angle of the axial space spring array, a high nonlinear to quasi-linear stiffness curve is achieved, thereby achieving task-oriented stiffness optimization. High nonlinear stiffness is suitable for applications such as assistance that require high low impedance and precise interactive force control; medium-low nonlinearity or low nonlinear stiffness is suitable for scenes such as gait correction and weight-bearing exoskeletons that require stable high-bandwidth output. 5. The single-turn absolute encoder of the quasi-direct drive motor and the rotary encoder are used to obtain the rotation angle of the axial space spring array by difference, and the output torque of the reconfigurable nonlinear rotary series elastic actuator is accurately calculated through the equivalent stiffness model. 6. The reconfigurable nonlinear rotary series elastic actuator achieves a balanced design between safety interaction, dynamic load adaptability and system integration through the coordinated optimization of stiffness, torque and mass, providing a highly compliant, strong drive and low inertia drive device for assistive robots. Brief Description of the Drawings

[0010] Figure 1 External view of the reconfigurable non - linear rotary series elastic actuator according to the present invention; Figure 2 Internal view of the reconfigurable non - linear rotary series elastic actuator according to the present invention; Figure 3 Exploded view of the reconfigurable non - linear rotary series elastic actuator according to the present invention; Figure 4 Exploded view of the axial space spring array according to the present invention; Figure 5 Distribution view of the linear tension spring according to the present invention; Figure 6 Schematic diagram of configuration 1 of the axial space spring array according to the present invention; Figure 7 Schematic diagram of configuration 2 of the axial space spring array according to the present invention; Figure 8 Schematic diagram of configuration 3 of the axial space spring array according to the present invention.

[0011] In the figures, the direct - drive motor 1, motor fixing device 2, input ring 3, linear tension spring 4, adjustable anchor 5, output ring 6, thin - wall bearing 7, rotary encoder 8, reading head 8.1, permanent magnet ring 8.2, actuator housing 9, actuator bracket 10, actuator output connecting rod 11, flange deep - groove ball bearing 12. Detailed Description of the Invention

[0012] The following is a further description of the present invention in conjunction with the attached Figure 1-8 drawings:

[0013] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0014] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and thus should not be construed as limiting the present invention.

[0015] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example: it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0016] As Figure 1 , Figure 2 and Figure 3 shown, the first embodiment of the present invention provides a reconfigurable non-linear rotary series elastic actuator with adjustable stiffness on the basis of the prior art, including: an input component, the input component includes a direct drive motor, a motor fixing device, and an input ring, which is used to connect with an external driving force to transmit the external driving torque to the adjustable stiffness flexible component. The adjustable stiffness flexible component, the adjustable stiffness flexible component includes an axial space spring array composed of linear tension springs, which is used to endow the actuator with non-linear and adjustable stiffness characteristics. An output component, the output component includes an output ring with adjustable anchor points and an actuator output link, which is used to implement the auxiliary training task in human-computer interaction. A support component, the support component includes an actuator bracket, which is used to support the reconfigurable non-linear rotary series elastic actuator.

[0017] Figure 1 is the external view of the reconfigurable non-linear rotary series elastic actuator. As Figure 1 shown, the reconfigurable non-linear rotary series elastic actuator is tightly fastened to the actuator fixing bracket by using socket head cap screws. A link is installed at the end of the output ring to implement the auxiliary training task in human-computer interaction.

[0018] Figure 2 is the internal view of the reconfigurable non-linear rotary series elastic actuator. As Figure 2 shown, the reconfigurable non-linear rotary series elastic actuator has a compact structure and a lightweight design, which is convenient for integrated application. The lightweight design of the reconfigurable non-linear rotary series elastic actuator helps the auxiliary robot to improve the motion flexibility and reduce the mechanical structure burden. At the same time, through the coordinated optimization of stiffness, torque and mass, an equilibrium design is achieved among safe interaction, dynamic load adaptability and system integration.

[0019] Figure 3 is the exploded view of the reconfigurable non-linear rotary series elastic actuator with adjustable stiffness. As Figure 3As shown, the collimation drive motor is tightly connected to the motor fixing device by hexagon socket head cap screws. The output end of the collimation drive motor is tightly connected to the rear end of the input ring by hexagon socket head cap screws. One end of the linear tension spring is connected to the input ring, and the other end is connected to the output ring. The end of the output ring is the output end of the reconfigurable non-linear rotational series elastic actuator. The rotary encoder consists of a reading head and a permanent magnet ring. The reading head is tightly connected to the actuator housing by flat head screws. The permanent magnet ring is tightly connected to the output ring by flat head screws. The rotary encoder is used to measure the output angle of the reconfigurable non-linear rotational series elastic actuator. The collimation drive motor is equipped with a single-turn absolute encoder to obtain the angle of the motor shaft. The difference between the single-turn absolute encoder of the collimation drive motor and the rotary encoder can calculate the deformation of the axial space spring array composed of linear tension springs. The actuator housing is tightly connected to the motor fixing device by hexagon socket head cap screws. The motor fixing device is designed with a positioning boss to improve the assembly accuracy and structural stability when connecting to the actuator housing.

[0020] As Figure 4 is the exploded view of the axial space spring array. As Figure 4 shown, the axial space spring array consists of an input ring, linear tension springs, flange deep groove ball bearings, and an output ring. The stepped shaft at the front end of the input ring has an interference fit with the inner ring of the flange deep groove ball bearing, and the outer ring of the flange deep groove ball bearing is press-fitted inside the output ring. The upper and lower ends of the linear tension spring are respectively connected to the input ring and the output ring to form an axial space spring array to achieve structural compliant coupling. Both the input ring and the output ring are composed of inner and outer rings, and linear tension springs are installed on the inner and outer rings of each. Adjustable anchor points are evenly distributed on the output ring. The output ring is designed with adjustable anchor points based on geometric parameters to change the initial deflection angle of the linear tension spring, so as to endow the reconfigurable non-linear rotational series elastic actuator with adjustable stiffness characteristics without replacing the linear tension spring.

[0021] As Figure 5 is the distribution view of the linear tension spring. As Figure 5 shown, the input ring and the output ring respectively include inner and outer rings. Each of the inner and outer rings is configured with four pairs of symmetrically distributed linear tension springs, and the phase angle between adjacent groups is 90°. The purpose of installing linear tension springs on the inner rings of the input ring and the output ring is to enhance the output torque of the actuator and improve the structural compactness. The purpose of installing linear tension springs on the outer rings of the input ring and the output ring is to change the initial deflection angle of the linear tension spring through adjustable anchor points, so that the reconfigurable non-linear rotational series elastic actuator can achieve non-linear and adjustable stiffness characteristics.

[0022] As Figures 6-8An axial space spring array of a linear tension spring at different initial deflection angles. As Figures 6-8 shown, as the initial deflection angle of the linear tension spring increases, the output stiffness of the reconfigurable non-linear rotational series elastic actuator shows an increasing trend. When the initial deflection angle of the linear tension spring is zero, the system exhibits highly non-linear stiffness characteristics, which are suitable for rehabilitation assistance tasks with high requirements for low impedance and high-precision force control. As the initial deflection angle of the linear tension spring increases, the output stiffness tends to be moderately non-linear or low non-linear, which is beneficial to improving the stability and bandwidth of torque output, and is suitable for scenarios such as gait correction and load assistance.

[0023] The above description is only a preferred embodiment of the present application and an explanation of the technical principles applied. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept.

Claims

1. A reconfigurable non-linear rotary series elastic actuator with adjustable stiffness, characterized in that, Comprising: An input component, the input component includes a direct-drive motor (1), a motor fixing device (2), an input ring (3), which is used to connect with an external driving force to transmit the external driving torque to the adjustable stiffness flexible component; the direct-drive motor (1) is stably installed through the motor fixing device (2), and its output end is connected to the input ring (3) to drive the adjustable stiffness flexible component to move; an adjustable stiffness flexible component, the adjustable stiffness flexible component includes an axial space spring array composed of linear tension springs (4), which is used to endow the reconfigurable non-linear rotational series elastic actuator with non-linear and adjustable stiffness characteristics; the four groups of linear tension springs in the inner ring of the axial space spring array increase the output torque of the reconfigurable non-linear rotational series elastic actuator and optimize the compactness of the structure; the four groups of springs in the outer ring of the axial space spring array are reconfigured into three different configurations by changing the initial deflection angle; when the initial deflection angle of the linear tension spring (4) is zero, the system exhibits highly non-linear stiffness characteristics, which is suitable for auxiliary tasks with high requirements for low impedance and high-precision force control; as the initial deflection angle of the linear tension spring (4) increases, the output stiffness tends to be medium non-linear or low non-linear, which is beneficial to improving the stability and bandwidth of torque output and is suitable for gait correction and load assistance; an output component, the output component includes an output ring (6) with an adjustable anchor point (5) and a driver output link (11), which changes the initial deflection angle of the linear tension spring through the adjustable anchor point and is used to realize the auxiliary training task in human-computer interaction; A support component, the support component includes a driver bracket (10), which is used to support the reconfigurable non-linear rotational series elastic actuator.

2. The reconfigurable non-linear rotary series elastic actuator with adjustable stiffness according to claim 1, characterized in that The input ring (3) and the output ring (6) are coaxially configured and coupled through the linear tension spring (4), and relative rotation is realized by using a flange deep groove ball bearing (12) to reduce movement friction; the input ring (3) and the output ring (6) respectively include inner and outer rings; four groups of symmetrically distributed linear tension springs are arranged on each of the inner and outer rings, and the phase angle between adjacent groups is 90°.

3. The reconfigurable non-linear rotary series elastic actuator with adjustable stiffness according to claim 1, characterized in that, The motor fixing device (2) is designed with a positioning boss to improve the assembly accuracy and structural stability when connecting with the driver housing (9).

4. The reconfigurable non-linear rotary series elastic actuator with adjustable stiffness according to claim 1, characterized in that The adjustable anchor points (5) are evenly distributed on the output ring (6) and are used to change the initial deflection angle of the linear tension spring (4), thereby endowing the reconfigurable non-linear rotational series elastic actuator with adjustable stiffness characteristics; the adjustable anchor points (5) are designed based on geometric parameters, and the axial space spring array can realize rapid switching of stiffness modes without hardware reconstruction, realizing multi-modal stiffness characteristics from non-linear to quasi-linear, covering the full working conditions requirements from compliant interaction to high-dynamic load.

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