Flexible Endoscopic Robots
In article number 2200403, Shuxin Wang, Chaoyang Shi, and colleagues propose a novel distal continuum joint based on the hybrid pneumatic and cable‐driven approach, which ...achieves excellent bending characteristics in both flexible and rigid states, variable stiffness, and high loading capacity for flexible gastrointestinal endoscopy. The presented method demonstrates an effective and practical approach for flexible endoscopic robots to achieve flexibility for access and rigidity for operation.
Although robots tend to be as competitive as CNC machines for some operations, they are not yet widely used for machining operations. This may be due to the lack of certain technical information that ...is required for satisfactory machining operation. For instance, it is very difficult to get information about the stiffness of industrial robots from robot manufacturers. As a consequence, this paper introduces a robust and fast procedure that can be used to identify the joint stiffness values of any six-revolute serial robot. This procedure aims to evaluate joint stiffness values considering both translational and rotational displacements of the robot end-effector for a given applied wrench (force and torque). In this paper, the links of the robot are assumed to be much stiffer than its actuated joints. The robustness of the identification method and the sensitivity of the results to measurement errors and the number of experimental tests are also analyzed. Finally, the actual Cartesian stiffness matrix of the robot is obtained from the joint stiffness values and can be used for motion planning and to optimize machining operations.
•The effects of the parallel misalignment on spline stiffness is first considered.•The fillet-foundation stiffness is considered in the spline meshing stiffness.•The tooth stiffness is first ...modified.•The repeated calculation of energy from the body and tooth is removed.
Spline couplings are commonly applied in transmission systems for their high torque capability and efficiency. However, misalignment between the splines can lead to clearance, wear, and elastic deformation, affecting spline stiffness non-linearly. An improved method for calculating the lateral and angular stiffness of spline couplings considering parallel misalignment is proposed in this paper. The proposed method takes into account the fillet-foundation stiffness and modifies the tooth stiffness by removing the repeated calculation of energy. The accuracy and efficiency of the proposed method are verified through comparison with finite element (FE) results. The effects of spline torque, length, and misalignment on spline stiffness are also discussed. The analysis results show that both lateral and angular stiffness are affected by the phase angle of the parallel misalignment more than the magnitude. Furthermore, the misalignment has a greater influence on the spline stiffness in stages one and two than in stage three. The proposed method provides a more precise and efficient way to calculate spline stiffness under parallel misalignment, which can improve the design and optimization of spline couplings.
For fiber‐reinforced polymer structures, the out‐of‐plane stiffness is much lower than the in‐plane stiffness and is extremely prone to damage and instability. The potential of variable stiffness ...(VS) laminates was explored to enhance the stiffness in the thickness direction. Based on the finite strip method (FSM), a semi‐analytical solution for bending problems of laminates was derived, which is called the variable‐stiffness discrete strip (VSDS) method. By comparing with traditional constant stiffness (CS) laminates, the influence of design parameters of VS laminates on the bending shape and stress distribution of laminates under two load cases were studied. Combining the results of FE models, the accuracy of VSDS has been verified, and the strategy of VS layout configuration design to improve the bending resistance was proved.
Highlights
Variable stiffness discrete strips (VSDS) method was presented based on FSM.
Bending performances of VS laminates under two load conditions were studied.
The method has the ability to reduce the computation cost of bending problems.
The solutions of VSDS agree well with the results of FE models.
The improvement mechanism of VS laminates on bending resistance was explored.
Analysis diagram of finite strip method used in bending applications of VS composite laminates.
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•Realising a linear elastic oscillator using an inherently nonlinear stiffness configuration.•Achieving a strong geometrical nonlinear damping characteristic.•Prototyping a test-rig ...device for validation and damping insight.•Proposing an alternative design solution to classical linear oscillators.
This paper proposes a paradigm shift in the perspective of designing nonlinear oscillators, i.e., the exploitation of nonlinearity to achieve a linear behaviour to good engineering purposes. An elastic suspension with four inclined springs is studied, which has an inherently strong geometric nonlinear stiffness characteristic. Such a configuration has attracted remarkable research efforts in last couple of years, because, compared to other classical nonlinear spring configurations, it has more design parameters, which can be wisely selected to attain a tailored force–displacement characteristic. A particular relationship among these parameters is found so that the overall characteristic becomes exactly linear. Compared to the use of classical linear springs mounted along the direction of motion, the proposed configuration with inclined springs has the potential to allow more freedom in the dimensioning of an engineering device. Also, while the equivalent spring obtained is linear, the equivalent damping is not, and this has the potential advantage of practically realising a linear elastic behaviour with the benefit of geometrical nonlinear damping. Experiments are performed for validation on a prototype device, and results confirm the linear behaviour predicted by the theoretical analysis.
The combination of negative stiffness devices and inerters to traditional base isolators (TBI) and tuned mass dampers (TMD) does not exist in any state-of-the-art. Therefore, to pursue the research ...using the above-mentioned research scope, the negative stiffness inerter passive dampers such as negative stiffness inerter-based base isolators (NSIBI), negative stiffness base isolators (NSBI), negative stiffness inerter-based tuned mass dampers (NSITMD), and negative stiffness tuned mass dampers (NSTMD) are introduced in this paper. H2 and H∞ optimization methods are applied to derive the exact closed-form expressions for the optimal design parameters of these novel passive vibration dampers. Newton’s second law applies to derive the governing equations of motion of the controlled structures. The transfer function formation and Newmark-beta method are applied to determine the dynamic responses of the controlled structures analytically and numerically. Hence, H2 optimized NSIBI and NSBI have 45.98% and 46.71% more dynamic response reduction capacities than optimum TBI. In addition, H∞ optimized NSIBI and NSBI have 58.36% and 57.32% more dynamic response reduction capacities than optimum TBI. Furthermore, the optimum NSITMD and NSTMD have 0.42%, 10.84%, and 4.5%, 13.48% more dynamic response reduction capacities than traditional TMD. All the derivations are mathematically accurate.
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•Combination of NSD and inerters to TBI and TMD does not exist in state-of-the-art.•Negative stiffness inerter passive dampers are introduced.•H2 and H∞ optimized design parameters are introduced.•Vibration reduction capacities of NSIBI and NSBI are 45% more than TBI.•NSITMD and NSTMD have 10% more vibration reduction capacities than TMD.
Materials with Electroprogrammable Stiffness Levine, David J.; Turner, Kevin T.; Pikul, James H.
Advanced materials (Weinheim),
09/2021, Letnik:
33, Številka:
35
Journal Article
Recenzirano
Odprti dostop
Stiffness is a mechanical property of vital importance to any material system and is typically considered a static quantity. Recent work, however, has shown that novel materials with programmable ...stiffness can enhance the performance and simplify the design of engineered systems, such as morphing wings, robotic grippers, and wearable exoskeletons. For many of these applications, the ability to program stiffness with electrical activation is advantageous because of the natural compatibility with electrical sensing, control, and power networks ubiquitous in autonomous machines and robots. The numerous applications for materials with electrically driven stiffness modulation has driven a rapid increase in the number of publications in this field. Here, a comprehensive review of the available materials that realize electroprogrammable stiffness is provided, showing that all current approaches can be categorized as using electrostatics or electrically activated phase changes, and summarizing the advantages, limitations, and applications of these materials. Finally, a perspective identifies state‐of‐the‐art trends and an outlook of future opportunities for the development and use of materials with electroprogrammable stiffness.
Novel applications, such as soft robotics and haptics, require emerging material systems whose stiffness can be selectively programmed using an electrical input to increase performance and simplify designs. The state‐of‐the‐art materials with electroprogrammable stiffness are reviewed, categorizing them into those governed by electrostatics and phase‐changes, and identifying challenges and opportunities toward the next generation of stimuli‐responsive materials.
Soft robots have the appealing advantages of being highly flexible and adaptive to complex environments. However, the low‐stiffness nature of the constituent materials makes soft robotic systems ...incompetent in tasks requiring relatively high load capacity. Despite recent attempts to develop stiffness‐tunable soft actuators by employing variable stiffness materials and structures, the reported stiffness‐tunable actuators generally suffer from limitations including slow responses, small deformations, and difficulties in fabrication with microfeatures. This work presents a paradigm to design and manufacture fast‐response, stiffness‐tunable (FRST) soft actuators via hybrid multimaterial 3D printing. The integration of a shape memory polymer layer into the fully printed actuator body enhances its stiffness by up to 120 times without sacrificing flexibility and adaptivity. The printed Joule‐heating circuit and fluidic cooling microchannel enable fast heating and cooling rates and allow the FRST actuator to complete a softening–stiffening cycle within 32 s. Numerical simulations are used to optimize the load capacity and thermal rates. The high load capacity and shape adaptivity of the FRST actuator are finally demonstrated by a robotic gripper with three FRST actuators that can grasp and lift objects with arbitrary shapes and various weights spanning from less than 10 g to up to 1.5 kg.
A fast‐response, stiffness‐tunable (FRST) soft actuator is fabricated by hybrid multimaterial 3D printing. Owing to the thermomechanical properties of an embedded shape memory polymer layer, the actuator exhibits flexibility when heated and high stiffness (120 times stiffer than its purely elastomeric counterpart) when cooled. Assisted by Joule‐heating and fluidic cooling, the heating–cooling cycle is completed within 32 s.
For the purpose of isolating the low frequency vibration, a magnetic vibration isolator with the feature of high-static-low-dynamic stiffness (HSLDS) is developed in this paper, which is constructed ...by combining a magnetic negative stiffness spring (MNSS) with a spiral flexure spring (SFS) in parallel. The MNSS comprises three magnetic rings configured in attraction and is utilized to reduce the resonant frequency of the isolator. Then an analytical expression of magnetic negative stiffness (MNS) of the MNSS is deduced in terms of the current model, and an approximation to the MNS is further sought. To support the object, the axial positive stiffness of SFSs, which can behave with a smaller static deformation if a specified weight is applied, is analyzed with finite element method (FEM). After that, the governing equation of the isolator is established and solved via harmonic balance method (HBM). Finally, an experimental prototype is developed and tested. The experimental results demonstrate that the MNSS can reduce the resonant frequency of the isolator to expand the isolation frequency band to low frequency range; and the theoretical calculations and experimental results shows a good agreement.
•A passive isolator with the feature of high-static-low-dynamic stiffness is developed.•A magnetic negative stiffness spring is employed to lower the resonant frequency.•The damping property is improved considerably due to the usage of magnetic negative stiffness spring.•Prototype design and experimental results demonstrate the theoretical analysis.
•The NCM is comprehensively studied to design QZS for vibration isolation.•Hardening stiffness is preferred for better compensating the negative stiffness.•A confirmatory system is established to ...verify the effectiveness of the NCM and the isolation performance.
Various quasi-zero stiffness (QZS) vibration isolators have been emerged in recent years and applied successfully in low-frequency vibration isolation. However, in most cases, the general approach to achieving QZS is still limited to compensating the negative stiffness of the bistable structure by linear springs. Here, a nonlinear compensation method (NCM) for realizing QZS is developed and the corresponding methodology is systematically investigated. Specifically, for a certain negative stiffness structure (not limited to bistable structure), QZS can be obtained by utilizing hardening stiffness to compensate. A confirmatory QZS vibration isolation system is established to fully verify the effectiveness of the NCM. The confirmatory system exploits rhombus structure to generate nonlinear negative stiffness, which can be compensated by nonlinear positive stiffness (provided by repulsive magnets). The static analysis is completed to reveal the inherent stiffness compensation mechanism. The dynamic and experimental results demonstrate that the proposed QZS system has low resonant frequency and wide effective vibration isolation frequency band. The NCM has reference significance in realizing QZS and is beneficial to develop diversified low-frequency vibration isolators.
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