Hyper-Redundant Manipulator Capable of Adjusting Its Non-Uniform Curvature with Discrete Stiffness Distribution

Hyper-redundant manipulators are widely used in minimally invasive surgery because they can navigate through narrow passages in passive compliance with the human body. Although their stability and dexterity have been significantly improved over the years, we need manipulators that can bend with appropriate curvatures and adapt to complex environments. This paper proposes a design principle for a manipulator capable of adjusting its non-uniform curvature and predicting the bending shape. Rigid segments were serially stacked, and elastic fixtures in the form of flat springs were arranged between hinged-slide joint segments. A manipulator with a diameter of 4.5 mm and a length of 28 mm had been fabricated. A model was established to predict the bending shape through minimum potential energy theory, kinematics, and measured stiffnesses of the flat springs. A comparison of the simulation and experimental results indicated an average position error of 3.82% of the endpoints when compared to the total length. With this modification, the manipulator is expected to be widely used in various fields such as small endoscope systems and single-port robot systems.

IMPROVED ANALYSIS OF A PROPPED CANTILEVER UNDER LATERAL VIBRATION

Continuous systems are sometimes analysed as lumped masses connected by massless elements. This reduces the structure’s degree of freedom and therefore simplifies the analysis. However this over simplification introduces an error in the analysis and the results are therefore approximate. In this work sections of the vibrating beam were isolated and the equations of the forces causing vibration obtained using the Hamilton’s principle. These forces were applied to the nodes of an equivalent lumped mass beam and the stiffness modification needed for it to behave as a continuous beam obtained. The beam’s stiffness was modified using a set of stiffness modification factors to . It was observed that by applying these factors in the dynamic analysis of the beam using the Lagrange’s equation, we obtain the exact values of the fundamental frequency irrespective of the way the mass of the beam was lumped. From this work we observed that in order to obtain an accurate dynamic response from a lumped mass beam there is need to modify the stiffness composition of the system and no linear modification of the stiffness distribution of lumped mass beams can cause them to be dynamically equivalent to the continuous beams. This is so because the values of the modification factors obtained for each beam segment were not equal. The stiffness modification factors were obtained for elements at different sections of the beam

Aeroelastic Optimization Design of the Global Stiffness for a Joined Wing Aircraft

Due to the complexity and particularity of the joined wing layout, traditional design methods for the global stiffness of a high-aspect wing are not applicable for a joined wing. Herein, a beam-frame model and a three-dimensional wing-box model are built to solve the global stiffness aeroelastic optimization design problem for a joined wing. The goal is to minimize the weight, and the constraints are the overall aeroelastic requirements. Based on a genetic algorithm, two methods for the beam-frame model and one method for the three-dimensional model are used for comparative analysis. The results show that the optimization method for a diagonal beam section and the optimization method for an exponential/linear combination function fit are adequate for optimizing and designating the joined wing global stiffness. The distributions obtained using the two methods have good consistency and are similar to the distribution of the three-dimensional model. The stiffness distribution data and the beam section parameters can be converted from each other, which is convenient for redesigning the structure parameters using the stiffness distribution data, and is valuable for engineering applications.

Design guidelines for bump-type compliant conical foil bearing

The integral bump foil strip cannot optimize the performance for the compliant conical foil bearing (CFB) as the uneven distribution of structural stiffness. To maximize the bearing characteristics, this paper proposed different bump foil schemes. Firstly, the anisotropy of CFB was studied based on the nonlinear bump stiffness model, and the circumferentially separated foil structure was proposed. Moreover, an axially separated bump foil structure with the variable bump length was introduced to make the axial stiffness distribution more compliant with the gas pressure. In addition, the effect of foil thickness was also discussed. The results show that CFB with integral bump foil exhibits obvious anisotropy, and the suggested installation angle for largest load capacity and best dynamic stability are in the opposite position. Fortunately, a circumferential separated bump foil can improve this defect. The characteristics of CFB with axial separated foil structure can be improved significantly, especially for that with more strips and the variable bump half-length design. The suitable bump and top foil thickness should be set considering the improved supporting performance and proper flexibility. The results can give some guidelines for the design of CFB.

Buckling Analysis of Piles in Multi-Layered Soils

Pile buckling is infrequent, but sometimes it can occur in slender piles (i.e., micropiles) driven into soils with soft layers and/or voids. Buckling analysis of piles becomes more complex if the pile is surrounded by multi-layered soil. In this case, the well-known Timoshenko’s solution for pile buckling is of no use because it refers to single-layered soils. A variational approach for buckling analysis of piles in multi-layered soils is herein proposed. The proposed method allows for the estimation of the critical buckling load of piles in any multi-layered soil and for any boundary condition, provided that the distribution of the soil coefficient of the subgrade reaction is available. An eigenvalue-eigenvector problem is defined, where each eigenvector is the set of coefficients of a Fourier series describing the second-order displaced shape of the pile, and the related buckling load is the eigenvalue, thus obtaining the effective buckling load as the minimum eigenvalue. Besides the pile deformed shape, the stiffness distribution in the multi-layered soil is also described through a Fourier series. The Rayleigh–Ritz direct method is used to identify the Fourier development coefficients describing the pile deformation. For validation, buckling analysis results were compared with those obtained from an experimental test and a finite element analysis available in the literature, which confirmed this method’s reliability.

The Influence of Nonhomogeneous Interlayer Stiffness on Dynamic Response of Orbit-Girder System under Moving Load

Based on the finite Fourier series method and the principle of energy variation, a method for calculating the dynamic response of an orbit-girder system is proposed, which is suitable for general spring boundary and nonhomogeneous interlayer stiffness distribution. Two numerical examples are given to verify the effectiveness of the proposed method under different moving load speeds and different stiffness distribution patterns. Based on this method, the influence of boundary conditions, interlayer stiffness degradation mode and degradation amplitude as well as the motion load on the dynamic response of the orbit-girder system is analyzed. A formula for calculating the peak value of additional dynamic response caused by interlayer stiffness degradation is proposed based on the nonlinear fitting method, and the factors affecting the additional response are analyzed. Results show that the variation of boundary conditions does not affect the additional dynamic response of the orbit-girder system. The mode of interlayer stiffness degradation and the degree of nonhomogeneous distribution have a significant influence on the peak of additional dynamic response. The additional dynamic response peak value of the orbit-girder system increases significantly with an increasing degree of nonhomogeneous degradation of the interlayer stiffness. The orbit-girder system has multiple critical speeds under the action of moving load. The magnitude of moving load has an important effect on the additional response peaks of the orbit-girder system. The additional response peaks increase approximately linearly with the increase of the motion load.

Research on Variable-Stiffness Mechanisms of Robot Wrists for Compliant Assembling-Clamping

The stiffness requirements of robot wrists vary with processes during automatic assembling-clamping of robots. The precision of robots moving workpieces to operating positions in the process of rigid localization is achieved if robot wrists equip with a large stiffness. The pose errors of workpieces in the process of compliant assembling-clamping can easily be compensated if robot wrists with a low stiffness is utilized. The present compliant wrist can not meet the stiffness requirements of different processes. A robot wrist with a large stiffness variation is proposed and its mechanisms of rigid localization and compliant assembling-clamping are studied. The pose models of wrists caused by deformations are established. The influences of wrist stiffness on the deformation of itself are researched. The mechanism of modulating wrist stiffness during compliant assembling-clamping is revealed. A structure of 3-DOF (degrees of freedom) robot wrist with a stiffness variation is proposed. The wrist stiffness is changed by modulating the pretension. The influences of pretensions and geometrical parameters on the variable-stiffness characteristics and the stiffness distribution of a wrist are researched. Finally, the experiments are carried out to verify the feasibility of the wrists finishing assembling-clamping operations by modulating the stiffness.

Voxelated three-dimensional miniature magnetic soft machines via multimaterial heterogeneous assembly

Small-scale soft-bodied machines that respond to externally applied magnetic field have attracted wide research interest because of their unique capabilities and promising potential in a variety of fields, especially for biomedical applications. When the size of such machines approach the sub-millimeter scale, their designs and functionalities are severely constrained by the available fabrication methods, which only work with limited materials, geometries, and magnetization profiles. To free such constraints, here, we propose a bottom-up assembly-based 3D microfabrication approach to create complex 3D miniature wireless magnetic soft machines at the milli- and sub-millimeter scale with arbitrary multimaterial compositions, arbitrary 3D geometries, and arbitrary programmable 3D magnetization profiles at high spatial resolution. This approach helps us concurrently realize diverse characteristics on the machines, including programmable shape morphing, negative Poisson’s ratio, complex stiffness distribution, directional joint bending, and remagnetization for shape reconfiguration. It enlarges the design space and enables biomedical device-related functionalities that are previously difficult to achieve, including peristaltic pumping of biological fluids and transport of solid objects, active targeted cargo transport and delivery, liquid biopsy, and reversible surface anchoring in tortuous tubular environments withstanding fluid flows, all at the sub-millimeter scale. This work improves the achievable complexity of 3D magnetic soft machines and boosts their future capabilities for applications in robotics and biomedical engineering.