Input Motion Research Articles

Iterative Learning Control for Robotic Path Following With Trial-Varying Motion Profiles

Iterative learning control (ILC) aims to maximize the performance of systems performing repeated tracking tasks. However, in most existing applications, the motion profile is inherently specified <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> , which has restricted both its application range and scope of performance improvement. For example, the typical repeated path-following task in robotics only requires a spatial path profile rather than a temporal trajectory profile, for which most existing ILC designs are unsuitable. To handle this requirement, this article extends the ILC task description by relaxing this postulate to enable a trial-varying motion profile and formulate an ILC path-following problem with system constraints. Under this extended problem setup, a spatial ILC algorithm is proposed with efficient implementation and robust convergence analysis, which updates the input signal and motion profile at the end of each trial to reduce the tracking error. This algorithm is implemented experimentally on a gantry robot test platform to verify performance, practical feasibility, and reliability. Comparisons with other control methods are also made to clarify its advantages, such as error reduction, control effort reduction, and constraint handling.

Simulation of strong earthquake characteristics of a scenario earthquake (MS7.5) based on the enlightenment of 2022 MS6.9 earthquake in Menyuan

The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan MS6.9 earthquake that occurred on January 8, 2022 had a major impact on the local infrastructure and transportation of this region. Due to the high possibility of similar strong earthquakes occurring in this area in the future, preliminary assessment of the seismic intensity characteristics of destructive earthquakes in this region is essential for effective disaster control. This paper uses the empirical Green′s function (EGF) method as a numerical simulation tool to predict the ground motion intensity of Datong Autonomous County under the action of the scenario earthquake (MS7.5). Seismic records of aftershocks of the 2016 Menyuan MS6.4 earthquake were used as Green’s functions for this simulation. The uncertainties associated with various source parameters were considered, and 36 possible earthquake scenarios were simulated to obtain 72 sets of horizontal ground motions in Datong County. The obtained peak ground acceleration (PGA) vs. time histories of the horizontal ground motion were screened using the attenuation relationships provided by the fifth-edition of China's Seismic Ground Motion Parameter Zoning Map and the NGA-West2 dataset. Ultimately, 32 possible acceleration-time histories were selected for further analysis. The screened PGA values ranged from 78.8 to 153 cm/s2. The uncertainty associated with the initial rupture point was found to greatly affect the results of the earthquake simulation. The average acceleration spectrum of the selected acceleration-time history exceeded the expected spectrum of a intermediate earthquake, which means that buildings in Datong County might sustain some damage should the scenario earthquake occur. This research can provide reliable ground motion input for urban earthquake damage simulation and seismic design in Datong County. Growing the dataset of small earthquakes recorded in this region will facilitate the large-scale simulation of ground motions under different earthquake scenarios.

Online Learning of Minmax Solutions for Distributed Estimation and Tracking Control of Sensor Networks in Graphical Games

In this article, a new target tracking algorithm that is based on a distributed estimation-based control protocol is developed for multiple moving sensors subject to adversarial inputs. An augmented system composed of both the estimation error dynamics and the tracking error dynamics is introduced for the distributed estimation and target tracking control problem. We integrate estimation and control to simultaneously minimize infinite-horizon estimation and tracking errors in sensor networks with disturbances. A Minmax strategy as an alternative goal to Nash equilibrium is proposed to compute the sensor’s optimal motion controls in the presence of worst-case neighbor controls and disturbances. In contrast to Nash, Minmax yields a distributed algebraic Riccati equation that is easily solved locally by each sensor. A method based on reinforcement learning is given to compute sensor motion inputs so that all sensors estimate and track the target states. Value function approximation using neural networks is used to solve the distributed Bellman equations online based on the real-time observed data. Proofs are given to guarantee the performance of the combined distributed estimation and tracking algorithms. Finally, the simulation examples show the effectiveness of the proposed algorithm.

Motion Guided Deep Dynamic 3D Garments

Realistic dynamic garments on animated characters have many AR/VR applications. While authoring such dynamic garment geometry is still a challenging task, data-driven simulation provides an attractive alternative, especially if it can be controlled simply using the motion of the underlying character. In this work, we focus on motion guided dynamic 3D garments, especially for loose garments. In a data-driven setup, we first learn a generative space of plausible garment geometries. Then, we learn a mapping to this space to capture the motion dependent dynamic deformations, conditioned on the previous state of the garment as well as its relative position with respect to the underlying body. Technically, we model garment dynamics, driven using the input character motion, by predicting per-frame local displacements in a canonical state of the garment that is enriched with frame-dependent skinning weights to bring the garment to the global space. We resolve any remaining per-frame collisions by predicting residual local displacements. The resultant garment geometry is used as history to enable iterative roll-out prediction. We demonstrate plausible generalization to unseen body shapes and motion inputs, and show improvements over multiple state-of-the-art alternatives. Code and data is released in https://geometry.cs.ucl.ac.uk/projects/2022/MotionDeepGarment/

Influence of the Duration Compression Ratio of the Input Motion on the Seismic Response of a Soil–Pile–Bridge Structure System in Shaking Table Tests

In the shaking table test of a soil–pile–bridge structure system, it is difficult to keep the similarity relations of the model structure and that of the model soil consistent. Due to the difference of geometry and material similarity ratios for the model structure and model soil, the determination of the duration compression ratio of input motions is a key problem. The spectrum characteristics of input motions will be varied by the duration compression ratio so that the seismic responses of structure and soil system will be affected. There are three commonly used approaches to determine the duration compression ratio of input motions in shaking table tests: the time similarity ratio of model structure; the time similarity ratio of model soil; and uncompressed. To study the influence of the duration compression ratio on the seismic response of a soil–structure system in shaking table tests, the El Centro record and the Wolong record were chosen as the input motions, and the durations were compressed by the three commonly used approaches in this paper. The influence of the duration compression ratios of the input motions on the acceleration response of a soil–pile–bridge structure system was compared and analyzed through a series of shaking table tests. The results showed that the duration compression ratio affected the acceleration response of the model soil and the model structure, and the effect was more obvious when the peak ground acceleration (PGA) was small. If the research is focused on the seismic response of the soil, it is recommended to use the time similarity ratio of the model soil to compress the input motions. If the research is focused on the seismic response of the structure, it is recommended to use the time similarity ratio of the model structure to compress the input motions. This study could provide a reference for the design of the shaking table test of a soil–pile–bridge structure system.

Seismic response characteristics of polymer anti-seepage wall in earth dam based on earthquake wave motion input method

The polymer anti-seepage wall has great application value in the reinforcement of earth dams. At present, the research on polymer anti-seepage walls is limited to the analysis of material properties and mechanical properties under static conditions. The application of polymer anti-seepage walls in earth dams in earthquake area is limited due to lack of research on seismic performance under strong earthquake. Therefore, in this paper, the earthquake wave motion input method is adopted to systematically study the seismic response characteristics of the polymer anti-seepage wall in earth dam. The research shows that the properties of polymer materials and the spectral content of the input ground motion have different effects on the acceleration response of the anti-seepage wall; After the earthquake wave motion input method is adopted, the reduction rates of the horizontal and vertical acceleration of the polymer anti-seepage wall relative to the traditional uniform excitation method range from 10.37% to 34.19% and 12.13% to 36.50%, respectively; For the dam project studied in this paper, the 25° incident angle of the SV wave and the 60° incident angle of the P wave are the most unfavorable incident angles; Compared with concrete anti-seepage walls, polymer anti-seepage walls have better dynamic coordination performance;

An improved time-domain approach for the spectra-compatible seismic motion generation considering intrinsic non-stationary features

The dynamic structural responses are sensitive to the time-frequency content of seismic waves, and seismic input motions in time-history analysis are usually required to be compatible with design response spectra according to nuclear codes. In order to generate spectra-compatible input motions while maintaining the intrinsic non-stationarity of seismic waves, an improved time-domain approach is proposed in this paper. To maintain the nonstationary characteristics of the given seismic waves, a new time-frequency envelope function is constructed using the Hilbert amplitude spectrum. Based on the intrinsic mode functions (IMFs) obtained from given seismic waves through variational mode decomposition, a new corrective time history is constructed to locally modify the given seismic waves. The proposed corrective time history and time-frequency envelope function are unique for each earthquake records as they are extracted from the given seismic waves. In addition, a dimension reduction iterative technique is presented herein to simultaneously superimpose corrective time histories of all the damping ratios at a specific frequency in the time domain according to optimal weights, which are found by the genetic algorithm (GA). Examples are presented to show the capability of the proposed approach in generating spectra-compatible time histories, especially in maintaining the nonstationary characteristics of seismic records. And numerical results reveal that the modified time histories generated by the proposed method can obtain similar dynamic behaviors of AP1000 nuclear power plant with the natural seismic records. Thus, the proposed method can be efficiently used in the design practices.

Influence of facing conditions on the dynamic response of back-to-back MSE walls

This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with full-height rigid facing and modular block facing, respectively, to investigate the influence of facing conditions on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. The threshold acceleration where acceleration amplification factors suddenly increase significantly for the back-to-back MSE walls with modular block facing is smaller than that for the full-height rigid facing walls. The full-height rigid facing walls have smaller facing displacements than those for the modular block facing walls under the same motions and can resist stronger earthquakes in terms of facing displacements. For the back-to-back MSE walls with full-height rigid facing, incremental reinforcement tensile strains increase significantly with increasing input acceleration, while the reinforcement strains of the modular block walls are similar under different input motions for the conditions investigated.

Seismic response and nonlinear characteristics of pile‐soil springs in structures supported by pile group in granular soil on sloping bedrock

AbstractIn places prone to earthquakes, piles need to be designed to resist seismic damage. However, the characteristics of the soil significantly impact the seismic resistance of piles. Accordingly, in this study, shaking table tests and three‐dimensional finite element analyses were conducted to investigate the seismic response and nonlinear characteristics of pile‐soil springs of a structure supported by a pile group in granular soil on a sloping bedrock. The analytical experiments and simulation were conducted on a group of nine piles arranged in the shape of a square. The results showed that the constraint condition at the pile tip influenced the bending moment response of piles during large input motion, such as that observed during earthquakes. Furthermore, the pile location, direction of pile displacement, and depth was found to affect the influence of the sloping bedrock on the pile soil springs.

Dynamic and monotonic response of Monopile Foundations for Offshore wind turbines using centrifuge testing

The seismic response of monopile foundations is a growing area of research as the offshore wind industry expands worldwide, including in earthquake prone regions of the world. This paper presents dynamic centrifuge tests aimed at investigating the dynamic response of monopiles in both dry and saturated sandy soils. The latter case includes soil liquefaction under strong input motions, with measured excess pore pressures indicating liquefaction. The natural frequency of the monopile-soil system is experimentally determined by measuring the response to a sine sweep motion. Strong earthquakes are then applied at this frequency and its harmonics. This paper discusses the response of the monopile in terms of the peak accelerations observed in the dry and saturated tests, as well as using response spectra and amplification ratios. The dynamic bending moments along the pile are also measured to infer the bending moment profile with depth. Finally, two identical monopiles are pushed-over in each of the centrifuge tests to establish the pre and post-earthquake monotonic response, including the lateral stiffness and capacity, which are compared for the dry model tests and the saturated case.

Effect of subterranean levels on the foundation input motions for dynamic response analysis of building structure

Effect of subterranean levels on the foundation input motions for dynamic response analysis of building structure

Cooperative Constrained Control of Autonomous Vehicles With Nonuniform Input Quantization

Responsive and highly controlled autonomous vehicles (AVs) on the road easily form platoons with small inter-vehicle gaps to increase traffic throughput and reduce energy consumption. Unlike human drivers, AVs typically employ discrete quantization signals and only generate finite discrete acceleration. Finite discrete acceleration easily causes unstable inter-vehicle gaps and inter-vehicle collisions, especially when there are inaccurate quantization parameters due to quantizer aging. Based on the backstepping technique, this paper proposes the cooperative constrained control algorithm under unknown quantization parameters for AVs with nonuniform input quantization and motion uncertainties. The control laws of each AV in the platoon only depend on the state information of its consecutive AVs. The position trajectories of consecutive AVs are constructed as inter-vehicle collision-free constraints to avoid emergency braking and inter-vehicle collisions. In addition, the consistent characteristic of two types of nonuniform quantizers (i.e., logarithmic quantizers and hysteresis quantizers) is proposed, and unknown disturbances in vehicle motion are compensated. The Lyapunov based local stability and string stability are proved. Numerical simulation shows that the control algorithm is applicable to AVs with either logarithmic quantizers or hysteresis quantizers. Compared with the previous control algorithms without considering input quantization and inter-vehicle collision avoidance, the control algorithm proposed reduces inter-vehicle spacing errors, avoids high acceleration, and avoids inter-vehicle collisions.

Seismic fragility evaluation of embankments on liquefiable soils and remedial countermeasures

This paper focuses on the evaluation of seismic fragility curves for embankments on liquefiable soils with the aim of improving the reliability of the risk assessment of transport infrastructure systems. Nonlinear dynamic analyses of embankments on liquefiable soils are carried out using the finite difference program FLAC2D with the PM4sand model. Validations of numerical modelling are performed in comparison to the dynamic centrifuge model tests reported in prior investigations. For the establishment of seismic fragility curves, ten input motions are selected and scaled to evaluate the embankment response under increasing shaking intensity levels. The seismic risk of embankments on liquefiable soil is evaluated through fragility curves with the damage states (DSs) described in terms of embankment settlement. The criteria, including correlation, efficiency, practicality, and proficiency, are assessed based on the relationship between the intensity measures (IMs) and the engineering demand parameters (EDPs) for the studied embankments. The embankment responses are compared with the benchmark scenario results to distinguish the relative contribution of the considered liquefaction mitigation strategies (i.e., soil densification, gravel berm, and sheet–pile enclosure). The seismic fragility curve serves as an efficient seismic risk analysis in the selection of liquefaction remedial measures in engineering design.

Generalization of the Den Hartog model and rule-of-thumb formulas for optimal tuned mass dampers

In recent years, the need of improving safety standards for both existing and new buildings against earthquake and wind loads has created a growing interest in the use of the so-called tuned mass dampers, exploited to control, in active or passive way, the dynamic response of structures. To design and optimize tuned mass damper systems, the effective analytical procedure proposed by Den Hartog in his seminal work (Den Hartog, 1985) has been widely adopted over the years, without including damping of the main structure. However, in many cases of engineering interest, the damping of the primary system plays a key role in the overall mechanical response, with the result of an increase in complexity of the related optimization problem, which are in fact solved in the vast majority by means of ad hoc numerical procedures. In the present work, we recover the classical optimization strategy by Den Hartog and generalize it by including the main system’s damping, providing new analytical solutions whose results are consistent with the few ones obtained through alternative mathematical methods by Thompson (1981) and Krenk (2005) and subsequently by Fang et al. (2019). In particular, some closed-form solutions and helpful rule-of-thumb formulas for the optimal setting of the design parameters are derived, by considering two types of incoming excitations, i.e. the force acting on the main mass and the ground motion input, both of interest for engineering applications. Finally, theoretical outcomes are compared with consolidated data from the literature. • Generalization of the Den Hartog model and analytical derivation of optimal tuning frequency ratio and damping of the absorber in Tuned Mass Dampers subjected to force or ground motion inputs. • Definition of rule-of-thumb formulas for design purposes. • Comparison of results from proposed analytical approach and numerical analyses to show advantages and effectiveness of the method, also for design parameters out of classical ranges. • Explicit expressions for optimal Tuned Mass Damper configurations in cases of stochastic ground motion input.

Two-dimensional basin-scale seismic site effects in the Kitimat Valley, British Columbia, Canada: A practical example of using a fast hybrid FE/BE method

The two-dimensional (2-D) basin-scale seismic site response of the Kitimat valley, located in the North Coast region of British Columbia, Canada, was investigated. The valley was subjected to a synthetic ground motion corresponding to a realistic local crustal earthquake of moderate magnitude consistent with the prevailing seismic hazard in the Kitimat region. SiteQUAKE, a fast hybrid finite element (FE)/boundary element (BE) numerical code was used for analyses, in which linear and equivalent-linear soil behavior models were implemented. The near-field (the sedimentary basin infill) and far-field (surrounding bedrock) were modeled by the FE and BE methods, respectively. Responses at different locations along a cross-section were compared with the input motion to illustrate the importance of basin effects. By dissociating the peak ground responses affected by the sub-surface topography (basin emptied of its infill) and by the presence of the sediment infill, it was shown that one-dimensional (1-D) analyses can either underestimate or overestimate 2-D seismic responses, highlighting their inability and insufficiency to correctly address basin effects.

Multi-Institutional Validation of a Smartphone-Based Surface Guided Radiation Therapy (SGRT) Tracking System for Respiratory Monitoring in Radiation Therapy

<h3>Purpose/Objective(s)</h3> Surface guidance radiation therapy (SGRT) systems are becoming standard-of-care for patient setup and motion monitoring. However, commercial systems remain inaccessible to resource-limited clinics around the world. The iOS Surface Audiovisual Biofeedback (iSAVB) system implements ubiquitous mobile technology as a versatile tool for surface imaging in resource-strapped clinics. The purpose of this study is to establish a robust validation platform, commission iSAVB at multiple participating institutions, and validate iSAVB using phantom motion and against commercial systems during patient treatments. <h3>Materials/Methods</h3> Three participating institutions are implementing, validating, and comparing the iSAVB system against current clinical SGRT systems. The iSAVB system consists of depth camera enabled iOS device, to acquire real-time point-cloud data for surface rendering, a 3D printed stand capable of mounting and indexing on a treatment couch, and aa tablet (or external workstation) for audio-visual feedback and signal processing. Validation of the iSAVB system was performed against commercial optical systems at each center using a respiratory motion phantom. Motion traces were analyzed using linear regressions and Bland-Altman analysis. <h3>Results</h3> The iSAVB system was successfully installed at an initial institution and tested on phantoms and healthy volunteers. For free-breathing traces, iSAVB was significantly correlated to phantom input motion (r=0.99, p<0.0001; bias=0.00±0.05cm, 95%CI=−0.1cm,0.1cm) and commercial system motion (r=0.99, p<0.0001; bias=0.00±0.07cm, 95%CI=−0.14cm,0.14cm). Systems are currently being installed at the two additional institutions that will perform similar commissioning and validation. <h3>Conclusion</h3> A multi-center validation shows the iSAVB system can be used for surface motion monitoring and provides SGRT capabilities similar to current high-end clinical systems. The iSAVB system can be used for 3D/IMRT/VMAT treatments, although future validation is required for SBRT treatments. Future work includes establishing reliable commissioning protocols that follow TG-302 guidelines for resource-strapped departments to benefit from affordable and accurate surface imaging guidance. Reference:

PROPOSAL OF SEISMIC LOAD FOR TRADITIONAL HOUSES IN KYOTO

In this paper, first, an approximation formula for the amplification factor of the surface soil is proposed. However, since most of the traditional houses are located on good soil condition, the lower limit of surface soil amplification factor 1.23 may be acceptable in reality. On the other hand, the large amplification sites are hardly related to the large shaking area during the Hanaore-fault-zone earthquake which is deeply related to the safety of traditional houses in Kyoto. We also pointed out that increase in bearing capacity of houses may increase the deformation response in case of pulse-like ground motion input.

Energy response of a passive variable friction damper and numerical simulation on the control effects for high‐rise buildings

In this study, the behavior of a passive displacement-dependent variable friction damper (VFD) was evaluated. The energy response behavior of a VFD specimen was investigated by conducting full-scale dynamic loading tests. Full-scale tests demonstrated that the VFD specimen produced a lower sliding force when the device response exceeded a predetermined displacement, resulting in a decreased dissipated energy ratio as the displacement increased. The VFD specimen exhibited stable energy response behavior as well as a stable friction sliding force and friction coefficient under sinusoidal, seismic response, and 100-cycle loadings. The energy response of the VFD specimen was almost independent of the loading frequency. Moreover, a response simulation was conducted using a two-dimensional 30-story nonlinear mainframe model with brace-type VFDs under various input motions, including observation records and long-period, long-duration waves. From the numerical simulations, the peak story drift in the case with brace-type VFDs was not significantly greater than in the case with conventional friction dampers (FDs). The dissipated energy ratios of the mainframe and dampers in the case with the VFDs were approximately identical to those in the case with the FDs. In comparison with conventional FDs, VFDs can produce a lower peak story shear force and axial compressive force in the lowest-story columns at the device installation span.

Understanding and Creating Spatial Interactions with Distant Displays Enabled by Unmodified Off-The-Shelf Smartphones

Over decades, many researchers developed complex in-lab systems with the overall goal to track multiple body parts of the user for a richer and more powerful 2D/3D interaction with a distant display. In this work, we introduce a novel smartphone-based tracking approach that eliminates the need for complex tracking systems. Relying on simultaneous usage of the front and rear smartphone cameras, our solution enables rich spatial interactions with distant displays by combining touch input with hand-gesture input, body and head motion, as well as eye-gaze input. In this paper, we firstly present a taxonomy for classifying distant display interactions, providing an overview of enabling technologies, input modalities, and interaction techniques, spanning from 2D to 3D interactions. Further, we provide more details about our implementation—using off-the-shelf smartphones. Finally, we validate our system in a user study by a variety of 2D and 3D multimodal interaction techniques, including input refinement.

Fusion classification of stroke patients' biosignals by weighted cross-validation-based feature selection (W-CVFS) method

A multi-source information fusion-based disease class classification of stroke patients was implemented to address the low classification accuracy of pure input motion and electromyographic signals. sEMG sensor MYO arm ring and wearable wireless motion sensor Shimmer were used as data acquisition devices. The Butterworth high-pass filter filtering and envelope thresholding method detected the activity segment. Detection and FIR filtering using the window function method remove interference from the motion signal. A weighted cross-validation-based feature selection (W-CVFS) method is proposed for feature fusion selection. The top 10 features selected by the W-CVFS method and all 18 features are input to the deep neural network for training and testing, and the feature classification result of the W-CVFS method is 79.17%, which is better than the existing mRMR method (66.67%) and ILFS method (62.50%). The classificatip9uon accuracy of multi-source information fusion was 95.385%, which was higher than that of a single input motion signal or sEMG. The experiments showed that the proposed method can retain the features that have more influence on the classification results and can improve the classification accuracy of the rehabilitation model for stroke patients.