Design and Evaluation of a Novel Torque-Controllable Variable Stiffness Actuator With Reconfigurability

Zhu, Yanghui; Wu, Qingcong; Chen, Bai; Dawen, Xu; Shao, Ziyan

doi:10.1109/tmech.2021.3063374

Cited by 49 publications

(14 citation statements)

References 41 publications

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“…By fitting many experimental data of middle and long-distance runners, sports researchers have found a high positive correlation between the athlete’s leg joints stiffness and motion state (Kuitunen et al , 2002). For active variable stiffness actuators, Zhu et al (2021) proposed the concept of reconfiguring the pulley block to make the actuator work in different torque and stiffness ranges, which allows the actuator to achieve a variety of passive stiffness behaviors. Zhang et al (2019) designed a flexible actuator with variable stiffness by using magnetorheological effect of the magnetorheological fluid.…”

Section: Introductionmentioning

confidence: 99%

A lightweight variable stiffness knee exoskeleton driven by shape memory alloy

Zhang

Cong

Liu

et al. 2022

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Purpose This paper aims to get rid of the traditional basic principle of using the motor as the variable stiffness drive source, simplify the structure of the exoskeleton and reduce the quality of the exoskeleton. This paper proposes to use shape memory alloys (SMA) as the variable stiffness drive source. Design/methodology/approach In this study, SMA is used to construct the active variable stiffness unit, the Brinson constitutive model is used to establish a dynamic model to control the active variable stiffness unit and the above active variable stiffness unit is used to realize the force control function and construct a lightweight, variable stiffness knee exoskeleton. Findings The dynamic model constructed in this paper can preliminarily describe the phase transformation process of the active variable stiffness unit and realize the variable stiffness function of the knee exoskeleton. The variable stiffness exoskeleton can effectively reduce the driving error under the high-speed walking condition. Originality/value The contribution of this paper is to combine SMAs to construct an active variable stiffness unit, build a dynamic model for controlling the active variable stiffness unit and construct a lightweight, variable stiffness knee exoskeleton.

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Section: Introductionmentioning

confidence: 99%

A lightweight variable stiffness knee exoskeleton driven by shape memory alloy

Zhang

Cong

Liu

et al. 2022

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“…As an alternative, some scholars have studied non-linear variable stiffness actuators, which use only one motor ( Thorson and Caldwell, 2011 ; Yu et al, 2013 ; Schepelmann et al, 2014 ; Shao et al, 2019 ; Hu et al, 2020 ; Shao et al, 2021b ). Usually, human-like characteristics (small torque and low stiffness and large torque and large stiffness) are considered in non-linear VSA ( Zhu et al, 2021 ). In the work of Thorson and Caldwell (2011 ), planetary gear mechanisms were introduced to obtain non-linear characteristics.…”

Section: Introductionmentioning

confidence: 99%

Anti-Disturbance Sliding Mode Control of a Novel Variable Stiffness Actuator for the Rehabilitation of Neurologically Disabled Patients

Feng

Shao

et al. 2022

Front. Robot. AI

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Lower limb exoskeletons are widely used for rehabilitation training of patients suffering from neurological disorders. To improve the human–robot interaction performance, series elastic actuators (SEAs) with low output impedance have been developed. However, the adaptability and control performance are limited by the constant spring stiffness used in current SEAs. In this study, a novel load-adaptive variable stiffness actuator (LaVSA) is used to design an ankle exoskeleton. To overcome the problems of the LaVSA with a larger mechanical gap and more complex dynamic model, a sliding mode controller based on a disturbance observer is proposed. During the interaction process, due to the passive joints at the load side of the ankle exoskeleton, the dynamic parameters on the load side of the ankle exoskeleton will change continuously. To avoid this problem, the designed controller treats it and the model error as a disturbance and observes it with the disturbance observer (DOB) in real time. The first-order derivative of the disturbance set is treated as a bounded value. Subsequently, the parameter adaptive law is used to find the upper bound of the observation error and make corresponding compensation in the control law. On these bases, a sliding mode controller based on a disturbance observer is designed, and Lyapunov stability analysis is given. Finally, simulation and experimental verification are performed. The wearing experiment shows that the resistance torque suffered by humans under human–robot interaction is lower than 120 Nmm, which confirms that the controller can realize zero-impedance control of the designed ankle exoskeleton.

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“…In order to overcome the fundamental limitation of conventional SEAs, a number of novel compliant actuators have been proposed [2], [17]- [26]. Variable stiffness actuator (VSA) is one of the most investigated examples.…”

Section: Introductionmentioning

confidence: 99%

“…As a consequence, these actuators are generally complicated and heavy, which increases the complexity of the control and makes their deployment in assistive robots difficult, especially in wearable assistive robots. Apart from VSAs, the introduction of nonlinear stiffness in SEAs [2], [21]- [26] also provides a promising solution to the limitation of conventional SEAs. But existing designs still show limitations in achieving nonlinear stiffness and improving adaptability to different applications in assistive robots.…”

Section: Introductionmentioning

confidence: 99%

“…However, the adjustable parameters in the arrangement of linear springs were not investigated and analysed in detail. Recently, some novel and reconfigurable designs that are able to generate nonlinear and adjustable stiffness behaviors were introduced in [25], [26]. But the reconfigurability and adjustable stiffness were achieved based on different and complicated winding methods of the pulley blocks, which results in limited model accuracy because of friction and make it more difficult to achieve satisfactory control performance in the pHRI.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Design, Modelling, and Control of a Reconfigurable Rotary Series Elastic Actuator with Nonlinear Stiffness for Assistive Robots

Qian,

Han,

Aguirre-Ollinger

et al. 2022

Preprint

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In assistive robots, compliant actuator is a key component in establishing safe and satisfactory physical humanrobot interaction (pHRI). The performance of compliant actuators largely depends on the stiffness of the elastic element. Generally, low stiffness is desirable to achieve low impedance, high fidelity of force control and safe pHRI, while high stiffness is required to ensure sufficient force bandwidth and output force. These requirements, however, are contradictory and often vary according to different tasks and conditions. In order to address the contradiction of stiffness selection and improve adaptability to different applications, we develop a reconfigurable rotary series elastic actuator with nonlinear stiffness (RRSEAns) for assistive robots. In this paper, an accurate model of the reconfigurable rotary series elastic element (RSEE) is presented and the adjusting principles are investigated, followed by detailed analysis and experimental validation. The RRSEAns can provide a wide range of stiffness from 0.095 N•m/ • to 2.33 N•m/ • , and different stiffness profiles can be yielded with respect to different configuration of the reconfigurable RSEE. The overall performance of the RRSEAns is verified by experiments on frequency response, torque control and pHRI, which is adequate for most applications in assistive robots. Specifically, the root-mean-square (RMS) error of the interaction torque results as low as 0.07 N•m in transparent/human-in-charge mode, demonstrating the advantages of the RRSEAns in pHRI.

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Design and Evaluation of a Novel Torque-Controllable Variable Stiffness Actuator With Reconfigurability

Cited by 49 publications

References 41 publications

A lightweight variable stiffness knee exoskeleton driven by shape memory alloy

A lightweight variable stiffness knee exoskeleton driven by shape memory alloy

Anti-Disturbance Sliding Mode Control of a Novel Variable Stiffness Actuator for the Rehabilitation of Neurologically Disabled Patients

Design, Modelling, and Control of a Reconfigurable Rotary Series Elastic Actuator with Nonlinear Stiffness for Assistive Robots

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