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1 – 10 of over 3000Canjun Yang, Weitao Wu, Xin Wu, Jifei Zhou, Zhangpeng Tu, Mingwei Lin and Sheng Zhang
Variable stiffness structure can significantly improve the interactive capabilities of grippers. Shape memory alloys have become a popular option for materials with variable…
Abstract
Purpose
Variable stiffness structure can significantly improve the interactive capabilities of grippers. Shape memory alloys have become a popular option for materials with variable stiffness structures. However, its variable stiffness range is limited by its stiffness in two phases. The purpose of this paper is to enhance the manipulation capabilities of tendon-driven flexible grippers by designing a wide-range variable stiffness structure.
Design/methodology/approach
Constitutive models of shape memory alloy and mechanical models are used to analyze the performance of the variable stiffness structure. A separated solution was used to combine the tendon-driven gripper and the variable stiffness structure. The feed-forward control algorithm is used to enhance the control stability of the variable stiffness structure.
Findings
The stiffness variable capability of the proposed variable stiffness structure is verified by experiments. The stability of the feedback control algorithm was verified by sinusoidal tracking experiments. The variable stiffness range of 8.41 times of the flexible gripper was tested experimentally. The interaction capability of the variable stiffness flexible gripper is verified by the object grasping experiments.
Originality/value
A new wide-range variable stiffness structure is proposed and validated. The new variable stiffness structure has a larger range of stiffness variation and better control stability. The new flexible structure can be applied to conventional grippers to help them gain stiffness variable capability and improve their interaction ability.
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Jiaqi Zhang, Ming Cong, Dong Liu, Yu Du and Hongjiang Ma
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…
Abstract
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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Xiaoyong Wei, Feng Ju, Bai Chen, Hao Guo, Dan Wang, Yaoyao Wang and Hongtao Wu
There is an increasing popularity for the continuum robot in minimally invasive surgery owing to its compliance and dexterity. However, the dexterity takes the challenges in…
Abstract
Purpose
There is an increasing popularity for the continuum robot in minimally invasive surgery owing to its compliance and dexterity. However, the dexterity takes the challenges in loading and precise control because of the absence of the shape tracking for the continuum robot. The purpose of this paper is to propose a new type of continuum manipulator with variable stiffness that can track the bending shape timely.
Design/methodology/approach
The low-melting-point alloy (LMPA) is used to implement the stiffness variation and shape detection for the continuum manipulator. A conceptual design for a single module is presented, and the principle of stiffness control based on the established static model is formulated. Afterward, a shape detection method is introduced in which the shape of the continuum manipulator can be detected by measuring the resistance of every LMPA. Finally, the effect of the proposed variable stiffness method is verified by simulation; the variable stiffness and shape detection methods are evaluated by experiments.
Findings
The results from the simulations and experiments indicate that the designed continuum manipulator has the ability of stiffness variation over 42.3% and the shape detection method has high precision.
Originality/value
Compared with conventional structures, the novel manipulator has a simpler structure and integrates the stiffness variation and shape detection capabilities with the LMPA. The proposed method is promising, and it can be conveniently extended to other continuum manipulators.
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Lei Zhang, Wendong Wang, Yikai Shi, Yang Chu and Xing Ming
To achieve variable stiffness, this paper aims to design a flexible actuator with variable stiffness by using the magnetorheological effect of magnetorheological fluid. The…
Abstract
Purpose
To achieve variable stiffness, this paper aims to design a flexible actuator with variable stiffness by using the magnetorheological effect of magnetorheological fluid. The variable stiffness actuator can well meet the safety requirements of human–robot interaction and be more adaptable to unknown or complex environments. The variable stiffness actuator designed in this study can realize the continuous and controllable change of stiffness compared with the existing actuator.
Design/methodology/approach
The principle of variable stiffness actuator is illustrated in detail; the three-dimensional model and mechanical model of the flexible actuator are provided. The magnetic field distribution of the actuator coil is analyzed, and the dynamic model of the actuator is provided.
Findings
Output torque test suggests that the magnetorheological fluid variable stiffness actuator (VSAMF) can output a stable torque which meets the designing requirements of the test; sinusoidal follow-up test shows that VSAMF can implement sinusoidal follow-up; variable stiffness test shows that VSAMF can achieve real-time variable stiffness adjustment; the crash test suggests that VSAMF can well protect machines when meeting obstacles.
Originality/value
In this paper, a new variable stiffness joint is proposed through changing the current to change the performance of the stiffness, and it can realize the continuous and controllable change of stiffness.
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This paper aims to investigate analytical solutions of natural frequencies and mode shapes of Euler-Bernoulli beams with step changes in the stiffness.
Abstract
Purpose
This paper aims to investigate analytical solutions of natural frequencies and mode shapes of Euler-Bernoulli beams with step changes in the stiffness.
Design/methodology/approach
In this work, analytical solutions for a beam with a single discontinuity was performed. Subsequently, based on an effective matrix formulation, the closed-form expressions of the single discontinuity beam could be conveniently extended to stepped beams with multiple stiffness discontinuities.
Findings
The results of the study show that the natural frequency of the beam can be adjusted by the local stiffness variation, and step location plays a significant role in free vibration responses.
Originality/value
The effects of the stiffness of the segment and step location on the natural frequencies of the stepped beams under different boundary conditions were examined using the proposed analytical scheme. This study provides insights into the design of variable-stiffness beam structures with the capability to adjust natural frequencies.
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Mingge Li, Zhongjun Yin, Xiaoming Huang, Jie Ma and Zhijie Liu
The purpose of this paper is to propose a casting process for the production of double-chamber soft fingers, which avoids the problems of air leakage and fracture caused by…
Abstract
Purpose
The purpose of this paper is to propose a casting process for the production of double-chamber soft fingers, which avoids the problems of air leakage and fracture caused by multistep casting. This proposed method facilitates the simultaneous casting of the inflation chamber and the jamming chamber.
Design/methodology/approach
An integrated molding technology based on the lost wax casting method is proposed for the manufacture of double-chamber soft fingers. The solid wax core is assembled with the mold, and then liquid silicone rubber is injected into it. After cooling and solidification, the mold is stripped off and heated in boiling water, so that the solid wax core melts and precipitates, and the integrated soft finger is obtained.
Findings
The performance and fatigue tests of the soft fingers produced by the proposed method have been carried out. The results show that the manufacturing method can significantly improve the fatigue resistance and stability of the soft fingers, while also avoiding the problems such as air leakage and cracking.
Originality/value
The improvement of the previous multistep casting method of soft fingers is proposed, and the integrated molding manufacturing method is proposed to avoid the problems caused by secondary bonding.
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Yongyao Li, Ming Cong, Dong Liu, Yu Du, Minjie Wu and Clarence W. de Silva
Rigid robotic hands are generally fast, precise and capable of exerting large forces, whereas soft robotic hands are compliant, safe and adaptive to complex environments. It is…
Abstract
Purpose
Rigid robotic hands are generally fast, precise and capable of exerting large forces, whereas soft robotic hands are compliant, safe and adaptive to complex environments. It is valuable and challenging to develop soft-rigid robotic hands that have both types of capabilities. The paper aims to address the challenge through developing a paradigm to achieve the behaviors of soft and rigid robotic hands adaptively.
Design/methodology/approach
The design principle of a two-joint finger is proposed. A kinematic model and a stiffness enhancement method are proposed and discussed. The manufacturing process for the soft-rigid finger is presented. Experiments are carried out to validate the accuracy of the kinematic model and evaluate the performance of the flexible body of the finger. Finally, a robotic hand composed of two soft-rigid fingers is fabricated to demonstrate its grasping capacities.
Findings
The kinematic model can capture the desired distal deflection and comprehensive shape accurately. The stiffness enhancement method guarantees stable grasp of the robotic hand, without sacrificing its flexibility and adaptability. The robotic hand is lightweight and practical. It can exhibit different grasping capacities.
Practical implications
It can be applied in the field of industrial grasping, where the objects are varied in materials and geometry. The hand’s inherent characteristic removes the need to detect and react to slight variations in surface geometry and makes the control strategies simple.
Originality/value
This work proposes a novel robotic hand. It possesses three distinct characteristics, i.e. high compliance, exhibiting discrete or continuous kinematics adaptively, lightweight and practical structures.
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Sadik Lafta Omairey, Peter Donald Dunning and Srinivas Sriramula
The purpose of this study is to enable performing reliability-based design optimisation (RBDO) for a composite component while accounting for several multi-scale uncertainties…
Abstract
Purpose
The purpose of this study is to enable performing reliability-based design optimisation (RBDO) for a composite component while accounting for several multi-scale uncertainties using a large representative volume element (LRVE). This is achieved using an efficient finite element analysis (FEA)-based multi-scale reliability framework and sequential optimisation strategy.
Design/methodology/approach
An efficient FEA-based multi-scale reliability framework used in this study is extended and combined with a proposed sequential optimisation strategy to produce an efficient, flexible and accurate RBDO framework for fibre-reinforced composite laminate components. The proposed RBDO strategy is demonstrated by finding the optimum design solution for a composite component under the effect of multi-scale uncertainties while meeting a specific stiffness reliability requirement. Performing this using the double-loop approach is computationally expensive because of the number of uncertainties and function evaluations required to assess the reliability. Thus, a sequential optimisation concept is proposed, which starts by finding a deterministic optimum solution, then assesses the reliability and shifts the constraint limit to a safer region. This is repeated until the desired level of reliability is reached. This is followed by a final probabilistic optimisation to reduce the mass further and meet the desired level of stiffness reliability. In addition, the proposed framework uses several surrogate models to replace expensive FE function evaluations during optimisation and reliability analysis. The numerical example is also used to investigate the effect of using different sizes of LRVEs, compared with a single RVE. In future work, other problem-dependent surrogates such as Kriging will be used to allow predicting lower probability of failures with high accuracy.
Findings
The integration of the developed multi-scale reliability framework with the sequential RBDO optimisation strategy is proven computationally feasible, and it is shown that the use of LRVEs leads to less conservative designs compared with the use of single RVE, i.e. up to 3.5% weight reduction in the case of the 1 × 1 RVE optimised component. This is because the LRVE provides a representation of the spatial variability of uncertainties in a composite material while capturing a wider range of uncertainties at each iteration.
Originality/value
Fibre-reinforced composite laminate components designed using reliability and optimisation have been investigated before. Still, they have not previously been combined in a comprehensive multi-scale RBDO. Therefore, this study combines the probabilistic framework with an optimisation strategy to perform multi-scale RBDO and demonstrates its feasibility and efficiency for an fibre reinforced polymer component design.
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Tianlei Wang, Fei Ding and Zhenxing Sun
Stiffness adjusting ability is essential for soft robotic arms to perform complex tasks. A soft state enables dexterous operation and safe interaction, while a rigid state enables…
Abstract
Purpose
Stiffness adjusting ability is essential for soft robotic arms to perform complex tasks. A soft state enables dexterous operation and safe interaction, while a rigid state enables large force output or heavy weight carrying. However, making a compact integration of soft actuators with powerful stiffness adjusting mechanisms is challenging. This study aims to develop a piston-like particle jamming mechanism for enhanced stiffness adjustment of a soft robotic arm.
Design/methodology/approach
The arm has two pairs of differential tendons for spatial bending, and a jamming core consists of four jamming units with particles sealed inside braided tubes for stiffness adjustment. The jamming core is pushed and pulled smoothly along the tendons by a piston, which is then driven by a motor and a ball screw mechanism.
Findings
The tip displacement of the arm under 150 N jamming force and no more than 0.3 kg load is minimal. The maximum stiffening ratio measured in the experiment under 150 N jamming force is up to 6–25 depends on the bending direction and added load of the arm, which is superior to most of the vacuum powered jamming method.
Originality/value
The proposed robotic arm makes an innovative compact integration of tendon-driven robotic arm and motor-driven piston-like particle jamming mechanism. The jamming force is much larger compared to conventional vacuum-powered systems and results in a superior stiffening ability.
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Ziyu Liao, Bai Chen, Tianzuo Chang, Qian Zheng, Keming Liu and Junnan Lv
Supernumerary robotic limbs (SRLs) are a new type of wearable robot, which improve the user’s operating and perceive the user’s environment by extra robotic limbs. There are some…
Abstract
Purpose
Supernumerary robotic limbs (SRLs) are a new type of wearable robot, which improve the user’s operating and perceive the user’s environment by extra robotic limbs. There are some literature reviews about the SRLs’ key technology and development trend, but the design of SRLs has not been fully discussed and summarized. This paper aims to focus on the design of SRLs and provides a comprehensive review of the ontological structure design of SRLs.
Design/methodology/approach
In this paper, the related literature of SRLs is summarized and analyzed by VOSviewer. The structural features of different types of SRLs are extracted, and then discuss the design approach and characteristics of SRLs which are different from typical wearable robots.
Findings
The design concept of SRLs is different from the conventional wearable robots. SRLs have various reconfiguration and installed positions, and it will influence the safety and cooperativeness performance of SRLs.
Originality/value
This paper focuses on discussing the structural design of SRLs by literature review, and this review will help researchers understand the structural features of SRLs and key points of the ontological design of SRLs, which can be used as a reference for designing SRLs.
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