multi-DOF Structure Research Articles

Design of a Multi-DOF Structure Based on Dynamic Analysis and Autonomous Operation Algorithm

Aiming at the problem of sandy soil collection, a multi-DOF mechanical structure is improved. Manipulator is developed by optimizing the integral middle boom to telescopic arm, and an automatic quick coupler is designed which is between the manipulator and the operating unit. The multi-DOF structure is analyzed based on dynamic theory, and the results of the limited operation range and the cylinder driving force are obtained, which could provide a theoretical basis for the structural design and the cylinder selection. An autonomous operation algorithm for sandy soil collection is proposed. The angle discretization method is adopted to improve collection efficiency. The model prototype is established to carry out the experimental verification. Through the test, the device in remote operation mode shows great performance in working conditions, and the autonomous operation algorithm can reduce the working intensity and risk of the operator and improve the efficiency of sandy soil operation.

Mechanical Structural Design and Actuation Technologies of Powered Knee Exoskeletons: A Review

Robot knee exoskeletons can not only help the rehabilitation training function of the elderly and disabled patients, but also enhance the performance of healthy people in normal walking and weigh-bearing walking by providing sufficient torques. In recent years, the exoskeletons of knee joints have been extensively explored. The review is to summarize the existing research results of mechanical structure design and actuation technologies, propose the future development trend, and promote the further development of the powered knee exoskeletons, related theories, and engineering applications. In this study, the mechanical structures of knee exoskeletons are first illustrated. Their mechanical structures are classified into two types: simple mechanical structures with one purely rotary DOF and biological geometry-based multi-DOF structures. Subsequently, the actuation design of wearable knee exoskeletons includes conventional driving actuators, pneumatic muscle actuators, variable stiffness actuators, and other actuators are compared and the driving compliance and the difficulty in the accurate control are analyzed. Furthermore, other crucial technologies such as motion intention recognition, control strategy and performance evaluation methods of most knee assistive devices are reviewed. Finally, the key technologies of structural design and actuation design in the research of knee exoskeletons are summarized and future research hotspots are proposed.

An explicit integration method with third-order accuracy for linear and nonlinear dynamic systems

Computational efficiency and accuracy are two of the most important properties of integration methods. In this study, an explicit single-step integration method with third-order accuracy is proposed to improve computational efficiency and accuracy. The proposed method can achieve fourth-order accuracy in terms of displacement, velocity, and acceleration responses without physical damping. The algorithmic dissipation property is also improved to filter out high-frequency spurious responses on the premise of sufficient accuracy in the low-frequency response domain. Moreover, since the proposed method can advance the calculation step-by-step via the known displacement and velocity items, the time-consuming factorization of an effective stiffness matrix is not required in the calculation for the structure with a lumped mass matrix. In other words, high computational efficiency is ensured in the proposed method. The properties of the proposed method (i.e., the accuracy, convergence, dissipation, efficiency, and effectiveness of the nonlinearity) are demonstrated by using four representative examples. Specifically, a single-degree-of-freedom (SDOF) dynamic system with a theoretical solution is adopted to comparatively evaluate the accuracy and convergence of the proposed method, a typical nonlinear dynamic system is used to investigate the effectiveness of the nonlinear calculation; a linear Howe truss model is employed to explore the effectiveness and efficiency in the calculation of a multi-DOF structure, and a nonlinear wellbore modelis used to demonstrate the potential to solve the large-scale nonlinear system. Results show that the proposed method can obtain more accurate results in the nonlinear dynamic calculations; and its time consumption is around 65% of that of the Yuan method, 38% of that of the Kim method, and 30% of that of the Zhai method.

Probabilistic Identification of Multi-DOF Structures Subjected to Ground Motion Using Manifold-Constrained Gaussian Processes

Bayesian uncertainty quantification has a pivotal role in structural identification, yet the posterior distribution estimation of unknown parameters and system responses is still a challenging task. This study explores a novel method, named manifold-constrained Gaussian processes (GPs), for the probabilistic identification of multi-DOF structural dynamical systems, taking shear-type frames subjected to ground motion as a demonstrative paradigm. The key idea of the method is to restrict the GPs (priorly defined over system responses) on a manifold that satisfies the equation of motion of the structural system. In contrast to widely used Bayesian probabilistic model updating methods, the manifold-constrained GPs avoid the numerical integration when formulating the joint probability density function of unknown parameters and system responses, hence achieving an accurate and computationally efficient inference for the posterior distributions. An eight-storey shear-type frame is analyzed as a case study to demonstrate the effectiveness of the manifold-constrained GPs. The results indicate the posterior distributions of system responses, and unknown parameters can be successfully identified, and reliable probabilistic model updating can be achieved.

Seismic Responses of Multi-DOF Structures with Shallow Foundation Using Centrifuge Test

Seismic Responses of Multi-DOF Structures with Shallow Foundation Using Centrifuge Test

Spectral Shape in Accordance with the Magnitude and Distance of Earthquakes and Its Effect on Multi-DOF Structures

In this study earthquake records were collected for rock conditions that do not reflect seismic amplification by soil from global earthquake databases such as PEER, USGS, and ESMD. The collected earthquake records were classified and analyzed based on the magnitude and distance of earthquakes. Based on the analyzed earthquakes, the design response spectrum shape, effective ground acceleration, and amplification ratios for each period band are presented. In addition, based on the analyzed data, the story shear force for 5F, 10F, 15F, and 20F were derived through an analysis of the elastic time history for multi-DOF structures. The results from analyzing the rock earthquake record show that the seismic load tends to be amplified greatly in the short period region, which is similar to results observed from the Gyeongju and Pohang earthquakes. In addition, the results of the multi-DOF structure analysis show that existing seismic design criteria can be underestimated and designed in the high-order mode of short- and medium-long cycle structures.

The use of reduced models in the reliability analysis of deformable systems with dynamic vibration dampers

The transformations of the initial design models of complex constructions and structures as the multi-degrees of freedom (DOF) systems is advantageous to use in order to reduce the amount of computational procedures in their dynamic analysis. This becomes particularly relevant in the reliability analysis requiring multiple recalculations for taking into account the stochastic properties of system parameters and impacts. The paper presents a technique based on known approaches of reduction the original multi-DOF system to an equivalent generalized design model with one degree of freedom. Various combinations of the equivalence conditions for the original system and the generalized model, including equalities of their natural frequencies, characteristic displacements or kinetic energies, were used to determine the modelling lumped mass and the corresponding rigidity of the design model. An algorithm for the probabilistic properties evaluation of the design model characteristics has been developed. The verification of the correctness of the proposed model in the area of tuning in to the workload frequency is performed. The quantitative results of solving the model problems in reliability calculations of multi-DOF structures with dynamic vibration dampers (DVD) are presented. The proposed approach allows us to simplify the process of selecting a single-mass DVD taking into account reliability requirements.

A basis for the computer-aided design of the topological structure of planetary gear trains

The design of the optimal topology of transmission systems based on planetary gear trains (PGTs) has become one of the most important problems for the development of many multi-source power systems, such as hybrid electric vehicles (HEVs). However, due to the lack of a method for large-scale scheme design and comparison, the form of manual design often faces heavy workloads and a risk of missing the optimal topology.At present, computer identification and automatic calculation of dynamic parameters for multi-input and multi-DOF structures under different working states remains the key objective of large-scale computing and computer-based optimalization design.To solve these problems, this paper modularizes the topological structures of PGTs and proposes two algorithms based on the connectivity of connected graphs for the first time: the reverse search algorithm and the forward-backtrack algorithm. The results show that the proposed method can not only enable a computer to effectively identify the components of a structure under different working modes but can also automatically obtain the dynamic parameters, transmission efficiency, power flow and recirculating power, thus providing a basis for calculating the optimal topological structure in large-scale design schemes.

Neural Network Based Vibration Control of Seismically Excited Civil Structures

This study proposes a neural network based vibration control system designed to attenuate structural vibrations induced by an earthquake. Classical feedback control algorithms are susceptible to parameter changes. For structures with uncertain parameters they can even cause instability problems. The proposed neural network based control system can identify the structural properties of the system and avoids the above mentioned problems. In the present study it is assumed that a full state of the structure is known, which means the at each floor horizontal displacements and rotations about the vertical axis are measured. Additionally, it is assumed the acceleration signal coming from the earthquake is also available. The proposed neural control strategy is compared with the classical linear quadratic regulator (LQR) not only in terms of displacement responses, but also required control forces. Moreover, the influence of different weighting matrices on performance of the proposed control strategy has been presented.The effectiveness of the neuro-controller has been demonstrated on two numerical examples: a simple single degree of freedom (DOF) structure and a multi-DOF structure representing a twelve story building. Both structures under consideration have been excited with El Centro acceleration signal. The results of numerical simulations on the SDOF system indicate that using neuro-controller it would be possible to obtain smaller amplitudes as compared with the LQ regulator, but it would require higher control effort.

等身大筋骨格ヒューマノイドの高負荷人体模倣足部における分散力覚情報システム

In this paper, we present a distributed haptic system for high-load anthropomimetic feet of the musculoskeletal humanoid “Kengoro”. It features large load-bearing capacity with the multi-DOF structure of the foot. To achieve this, we had three design challenges. First, each GRF sensing unit with biomimetic thick foot rubber can acquire great reaction force via moment. In addition, we developed minimal multi-sensor circuit board that collect signals of 12 loadcell simultaneously. Futhermore, we arranged the units on the foot in a bio-inspired manner. We show high load capacity of the system with experiments including single-unit test and landing by life-sized musculoskeletal leg with the developed haptic system.

The Applied Research on TMD Control in Structures for Seismic Protection

Based on the theoretical analysis of the dynamic parameters of multi-DOF complex structures, it is shown that the optimum TMD parameters under the harmonic base excitation are not the exact optimization for seismic protection, whose main reason is that the optimum damping ratio of TMD for seismic protection is obviously lower than that under the harmonic base excitation. In this paper, an effective TMD design method is developed to control the seismic responses of many-degree-of-freedom complex structures. The EI-Centro seismic wave is introduced as the excitations and the approach to determining the optimum TMD parameters for seismic protection is effectively solved. Then with the case to design the TMD of a series reactor, the optimum TMD parameters for seismic protection are obtained. Its result proves that the designed TMD is able to reduce the seismic responses of the series reactor significantly, and this approach can provide a reference for the TMD design for seismic protection of other multi-DOF structures.

Design of Surface Roughness Measurement Bench Based on Stewart Platform

This paper designed a type of freeform surface roughness measurement bench using parallel-mechanism. The virtual prototype of surface roughness measurement bench has been established. Basic structure parameters and work-space of bench have been calculated according to the program of surface roughness test. An example of bearing outer circle roughness measurement based on Stewart platform has been analysed. From the example of measurement bench it is observed that the designed bench based on Stewart platform can be used as a multi-DOF structure in the freeform surface roughness measurement.

A Switching Command-Based Whole-Body Operation Method for Humanoid Robots

This paper introduces a switching command-based whole-body operation method for humanoid robots. Humanoid robots are biped machines possessing multiple degrees of freedom (DOF). Due to the complexity of their multi-DOF structure, and the difficulty in maintaining postural stability, whole-body operation of humanoid robots is fundamentally different from traditional fixed-base manipulators or stable-base mobile manipulators. By studying the shifts in locus of attention between human body joints during task execution, we developed a switching command-based operation method that allows the operator to select only the necessary points of the humanoid robot's body for manipulation. Whole-body motion satisfying the desired movements of the selected points is generated using an inverse-kinematics motion generation scheme. This switching operation method enables flexible whole-body operation of humanoid robots using simple input devices. The proposed whole-body operation method is implemented as a teleoperation system using two 3-DOF joysticks to operate a 30-DOF humanoid robot (HRP-1S) developed in the Humanoid Robotics Project (HRP) of the Ministry of Economy, Trade, and Industry of Japan. Experiments teleoperating HRP-1S confirmed the effectiveness of our method.