Sensitivity of Balancing in Legged Systems Under Torque Constraint Variations

The balancing capabilities of a legged system can be influenced by several properties of the system itself, for instance, the strength of joint motors in a robot or muscle strength in living systems. In this work, the changes in the balancing capabilities of a legged system are evaluated as the joint actuator torque limits of the system change. The legged system is modeled with an inverted pendulum model with an actuated ankle and a finite foot size. The effect of variations of the ankle torque limits on the system balance stability is quantified through the local properties of Lagrange multipliers in optimization theory and are validated through numerical experiments. With the proposed method, the information on the balance stability boundary of a legged system is used to predict the balance stability characteristics of the system with altered joint torque limits, hence providing quantifiable guidelines to the design of such systems.

Control Solution for a Cable-Driven Parallel Robot With Highly Variable Payload

This paper deals with the design of a robust control scheme for a suspended Cable-Driven Parallel Robot (CDPR), composed of eight cables and a moving platform (MP), suitable for pick-and-place operations of heterogeneous objects with different shapes, sizes and masses, up to a total load of 700 kg. Dynamometers measure the force applied by each cable onto the moving-platform and are used to assess the payload mass at any time. In the proposed control solution, each motor of the CDPR is directly driven by a PD torque controller, which takes benefit of the real-time payload estimation in a feedforward term. In order to evaluate its performance, experiments on a typical pick and place trajectory are realized for different payloads. As a result, three control schemes: (i) a Proportional-Derivative (PD) torque controller; (ii) a PD controller with compensation of the MP mass only and (iii) a PD controller with real-time mass estimation and compensation are experimentally compared with respect to their positioning accuracy. It turns out that a good estimation of the payload is obtained in real-time thanks to the dynamometers. Moreover, the higher the payload mass, the more accurate the proposed controller with respect to its two counterparts.

Energy Absorption of Origami Crash Box: Numerical Simulation and Theoretical Analysis

Thin-walled tubes as energy absorption devices are widely in use for their low cost and high manufacturability. Employing origami technique on a tube enables induction of a predetermined failure mode so as to improve its energy absorption efficiency. Here we study the energy absorption of a hexagonal tubular device named the origami crash box numerically and theoretically. Numerical simulations of the quasi-static axial crushing show that the pattern triggers a diamond-shaped mode, leading to a substantial increase in energy absorption and reduction in initial peak force. The effects of geometric parameters on the performance of the origami crash box are also investigated through a parametric study. Furthermore, a theoretical study on the deformation mode and energy absorption of the origami crash box is carried out, and a good match with numerical results is obtained. The origami crash box shows great promise in the design of energy absorption devices.

Controlling Origami Stability Profile Using Magnets

Multi-stable structures and materials have attracted extensive research interests because they can provide a wide spectrum of adaptive properties and functionalities. Recently, origami has been identified as an important source for achieving multi-stability and has been exploited for developing unconventional mechanical metamaterials and metastructures. Once the crease pattern and the constituent materials have been specified for an origami structure, its multi-stability profile becomes unchangeable. On the other hand, a controllable profile would be desirable to endow the origami structures and origami metamaterials with further adaptability and versatility. This research investigates how to integrate magnets with origami to fundamentally alter the stability profiles. By embedding magnets into the origami facets or vertices, the magnetic potential energy would modify the original elastic potential energy landscape both quantitatively and qualitatively. Taking the stacked Miura-ori structures as examples, we show that different magnet assignments could either enrich the original bistable profile into a tri-stable or quad-stable profile, or simplify it into a mono-stable profile. Simultaneously, such magnet-induced evolutions of stability profile would trigger essential changes of the structure’s mechanical properties, which are promising to be used for developing multi-functional devices or metamaterials/metastructures. In this paper, in addition to the analyses, proof-of-concept design and prototype are presented. The results of this research would open up a new path for designing origami structures and metamaterials with controllable stability profiles that can be harnessed for many novel applications.

Liquid State Machine to Generate the Movement Profiles for the Gait Cycle of a 6 DOF Bipedal Robot in a Sagittal Plane

In this paper, a neuronal system with the ability to generate motion profiles and profiles of the ZMP in a 6DoF bipedal robot in the sagittal plane, is presented. The input time series for LSM training are movement profiles of the oscillating foot trajectory obtained by forward kinematics performed by a previously trained ANN multilayer perceptron. The profiles of objective movement for training are acquired from the analysis of the human walk. Based on a previous simulation of the bipedal robot, a profile of the objective ZMP will be generated for the y–axis and another for the z–axis to know its behavior during the training walk. As an experimental result, the LSM generates new motion profiles and ZMP, given a different trajectory with which it was trained. With the LSM it will be possible to propose new trajectories of the oscillating foot, where it will be known if this trajectory will be stable, by the ZMP, and what movement profile for each articulation will be required to reach this trajectory.

Kinematic and Workspace Modelling of a 6-PUS Parallel Mechanism

This article presents the kinematic analysis of a six-degree-of-freedom six-legged parallel mechanism of the 6-PUS architecture. The inverse kinematic problem is recalled and the Jacobian matrices are derived. Then, an algorithm for the geometric determination of the workspace is presented, which yields a very fast and accurate description of the workspace of the mechanism. Singular boundaries and a transmission ratio index are then introduced and studied for a set of architectural parameters. The proposed analysis yields conceptual architectures whose properties can be adjusted to fit given applications.

Three Approaches for Managing Stiffness in Origami-Inspired Mechanisms

Ensuring that deployable mechanisms are sufficiently rigid is a major challenge due to their large size relative to their mass. This paper examines three basic types of stiffener that can be applied to light, origami-inspired structures to manage their stiffness. These stiffeners are modeled analytically to enable prediction and optimization of their behavior. The results obtained from this analysis are compared to results from a finite-element analysis and experimental data. After verifying these models, the advantages and disadvantages of each stiffener type are considered. This comparison will facilitate stiffener selection for future engineering applications.

Modelling and Simulation of a Robotic System for Lower Limb Rehabilitation

As the life span increases and the availability of physicians becomes more and more scarce, robotic rehabilitation for post-stroke patients becomes more and more demanding, especially due to the repeatability character of the rehabilitation exercises. Both lower and upper limb rehabilitation using robotic systems have proved to be very successful in different stages of the rehabilitation process, but only a few address the immediate (critical) post-stroke phase, especially when the patient is hemiplegic and is unable to stand. The paper presents the kinematic modelling, singularity analysis and gait simulation for a new 4-DOF parallel robot named RECOVER used for lower limb rehabilitation for bedridden patients. The robotic system has been designed for the mobilization of the lower limb, namely the following motions: the hip and knee flexion and the plantar adduction/abduction and flexion/dorsiflexion. The kinematics has been studied and the singularity configurations have been determined to achieve a failsafe rehabilitation robot. Numerical simulations prove that the system can be used for gait training exercises in safe conditions.

Design of a Variable-Mobility Linkage Using the Bohemian Dome

The properties of the Bohemian dome are studied and it is found that for a particular type of Bohemian dome two different parameterizations based on the translation of circles can be obtained for the same surface, therefore, two different hybrid kinematic chains can be designed to generate the same Bohemian dome. These surface generators are reconfigurable and can generate two different surfaces each. Parameterizations for the secondary surfaces are obtained and studied. These hybrid kinematic chains are used to design a kinematotropic linkage with a total of 27 motion branches in its configuration space. The singularities in the configuration space are also determined using the properties of the surfaces. The resultant linkage offers an explanation of Wholhart’s queer-square linkage other than paper folding. The relationship between the properties of self-intersections in generated surfaces and the configuration space of the generator linkage is studied for the first time leading to the description of motion branches related to self-intersections of generated surfaces.

Multiphysics Modeling and Experimental Validation of Reconfigurable, E-Textile Origami Antennas

Physical deformation mechanisms are emerging as compelling and simple ways to adapt radio frequency (RF) characteristics of antennas in contrast to digital steering approaches acting on topologically fixed antennas. Concepts of physical reconfigurability also enable exceptional capabilities such as deployable and morphing antenna arrays that serve multiple functions and permit compact transport with ease. Yet, the emergent concepts lack broad understanding of effective approaches to integrate conformal, electrically conductive architectures with high-compliance foldable frameworks. To explore this essential interface where electrical demands and mechanical requirements may conflict, this research introduces a new class of origami-based tessellated antennas whose RF characteristics are self-tuned by physical reconfiguration of the antenna shape. E-textile materials are used to permit large antenna shape change while maintaining electrical conductivity. Dipole and patch antennas are considered as conventional antenna platforms upon which to innovate with the e-textile origami concept. Multiphysics modeling efforts establish the efficacy of foldable antenna geometries for broad tailoring of the RF characteristics. Experiments with proof-of-concept antennas confirm the large adaptability of wave radiation properties enabled by the reconfiguration of the e-textile origami surfaces. The results suggest that e-textile antennas can be integrated into clothing and mechanical structures, providing a non-invasive way of quantifying deformation for a wide range of applications.