Dynamic Analysis of a Spherical Parallel Robot Used for Brachial Monoparesis Rehabilitation

This paper presents studies on the dynamic analysis of the ASPIRE robot, which was designed for the medical recovery of brachial monoparesis. It starts from the virtual model of the existing version of the ASPIRE robot, which is analysed kinematically and dynamically by numerical simulations using the MSC.ADAMS software. For this purpose, this paper presents theoretical aspects regarding the kinematics and dynamics of the markers attached to the flexible bodies built in a specifically developed MSC.ADAMS model. Three simulation hypotheses are considered: (a) rigid kinematic elements without friction in couplings, (b) rigid kinematic elements with friction in couplings, and (c) kinematic elements as deformable solids with friction in couplings. Experimental results obtained by using the physical prototype of ASPIRE are presented. Results such as the connecting forces in the kinematic joints and the torques necessary to operate the ASPIRE robot modules have been obtained by dynamic simulation in MSC.ADAMS and compared with those determined experimentally. The comparison shows that the allure of the variation curve of the moment obtained by simulation is similar to that obtained experimentally. The difference between the maximum experimental value and that obtained by simulation is less than 1%. A finite element analysis (FEA) of the structurally optimized flexion/extension robot module is performed. The results demonstrate the operational safety of the ASPIRE robot, which is structurally capable of supporting the stresses to which it is subjected.

On design sensitivities in the structural analysis and optimization of flexible multibody systems

The structural analysis and optimization of flexible multibody systems become more and more popular due to the ability to efficiently compute gradients using sophisticated approaches such as the adjoint variable method and the adoption of powerful methods from static structural optimization. To drive the improvement of the optimization process, this work addresses the computation of design sensitivities for multibody systems with arbitrarily parameterized rigid and flexible bodies that are modeled using the floating frame of reference formulation. It is shown that it is useful to augment the body describing standard input data files by their design derivatives. In this way, a clear separation can be achieved between the body modeling and parameterization and the system simulation and analysis.

A symbolic framework for flexible multibody systems applied to horizontal axis wind turbines

The article presents a symbolic framework that is used to obtain the linear and non-linear equations of motion of a multibody system including rigid and flexible bodies. Our approach is based on Kane's method and a nonlinear shape function representation for flexible bodies. The method yields compact symbolic equations of motion with implicit account of the constraints. The general and automatic framework facilitate the creation and manipulation of models with various levels of fidelity. The symbolic treatment provides analytical gradients and linearized equations of motion. The linear and non-linear equations can be exported to Python code or dedicated software. The application are multiple such as: time-domain simulation, stability analyses, frequency domain analyses, advanced controller design, state observers, digital twins, etc. In this paper, we describe the method we used to systematically generate the equations of motion of multibody systems. We apply the framework to generate illustrative onshore and offshore wind turbine models. We compare our results with OpenFAST simulations and discuss the advantages and limitations of the method. A Python implementation is provided as an opensource project.

Current Trends and Prospects in Compliant Continuum Robots: A Survey

Compliant continuum robots (CCRs) have slender and elastic bodies. Compared with a traditional serial robot, they have more degrees of freedom and can deform their flexible bodies to go through a constrained environment. In this paper, we classify CCRs according to basic transmission units. The merits, materials and potential drawbacks of each type of CCR are described. Drive systems depend on the basic transmission units significantly, and their advantages and disadvantages are reviewed and summarized. Variable stiffness and intrinsic sensing are desired characteristics of CCRs, and the methods of obtaining the two characteristics are discussed. Finally, we discuss the friction, buckling, singularity and twisting problems of CCRs, and emphasise the ways to reduce their effects, followed by several proposing perspectives, such as the collaborative CCRs.

Research on the Influence of Wheel Polygonization on Axle Stress

To study the influence of wheel polygonization on the dynamic stress of the wheel axle, a vehicle-track rigid-flexible coupling dynamic model was established. In the model, the wheelset, axle box, and track system were modelled as flexible bodies to consider the influence of elastic vibration. At the same time, the dynamic stress on key positions of the axle under the wheel polygonization excitation was measured on the high-frequency vibration test rig. The accuracy of the model was verified by comparison with the test results. The wheel axle stress under the excitation of the wheel polygonization with different orders, wave depths, and running speed was calculated. The results show that the wheel polygonization can increase the amplitude of the axle dynamic stress, and the larger the wave depth of the wheel polygonization, the larger the stress amplitude. When the wheel polygonization frequency is close to the frequency of the wheelset elastic vibration mode, the wheelset first-order bending and second-order bending modes have a great influence on the axle stress. The resonance vibration of the wheelset elastic modal can cause the dynamic stress on key positions of the axle increase sharply.

Collective dynamics in entangled worm and robot blobs

Living systems at all scales aggregate in large numbers for a variety of functions including mating, predation, and survival. The majority of such systems consist of unconnected individuals that collectively flock, school, or swarm. However, some aggregations involve physically entangled individuals, which can confer emergent mechanofunctional material properties to the collective. Here, we study in laboratory experiments and rationalize in theoretical and robophysical models the dynamics of physically entangled and motile self-assemblies of 1-cm-long California blackworms (Lumbriculus variegatus, Annelida: Clitellata: Lumbriculidae). Thousands of individual worms form braids with their long, slender, and flexible bodies to make a three-dimensional, soft, and shape-shifting “blob.” The blob behaves as a living material capable of mitigating damage and assault from environmental stresses through dynamic shape transformations, including minimizing surface area for survival against desiccation and enabling transport (negative thermotaxis) from hazardous environments (like heat). We specifically focus on the locomotion of the blob to understand how an amorphous entangled ball of worms can break symmetry to move across a substrate. We hypothesize that the collective blob displays rudimentary differentiation of function across itself, which when combined with entanglement dynamics facilitates directed persistent blob locomotion. To test this, we develop a robophysical model of the worm blobs, which displays emergent locomotion in the collective without sophisticated control or programming of any individual robot. The emergent dynamics of the living functional blob and robophysical model can inform the design of additional classes of adaptive mechanofunctional living materials and emergent robotics.