Step Motion Research Articles

Vibration monitoring of rotating shafts using DIC and compressed sensing

Monitoring vibrations in rotating shafts is essential for diagnosing and detecting mechanical faults. Digital image correlation (DIC), an optical full-field measurement technique, is increasingly employed in experimental mechanics. This study introduces a novel measurement approach that combines DIC with compressed sensing to monitor high-speed rotating shafts accurately. Traditionally, analyzing rotating shafts requires high-speed sampling devices, which increases experimental costs and reduces spatial resolution. To overcome these limitations, a random exposure sampling method was developed to capture speckle images on the shaft surface with a low frame-rate camera. By leveraging compressed sensing and DIC, the method reconstructs high-speed vibration signals from captured images. Step motion experiments demonstrated that the DIC system achieves a measurement accuracy of 10 µm. Experimental validation was conducted using various setups, including low-speed motors, high-speed rotating shafts, and milling machines, demonstrating the effectiveness of the approach. The measurement results of rotating shafts at 1200 rpm and 6000 rpm, compared with those obtained from laser Doppler vibrometry, demonstrated the effectiveness of the method in vibration measurement. Additionally, experiments on a milling machine showed that vibrations reconstructed using compressed sensing closely matched those measured with a high-speed camera. This measurement system shows significant potential for accurately assessing vibrations in high-speed rotating shafts, offering valuable insights for machinery monitoring and fault diagnosis.

Design and experimental evaluation of a compact inchworm piezoelectric actuator with bridge-type displacement amplification mechanism

Abstract Miniaturization is an important direction in piezoelectric actuator research, with related efforts focusing on reducing structural complexity and simplifying guiding mechanisms. However, some actuators experience backward movement after miniaturization design. There remains significant room for improvement in mechanism configuration and the design of flexible amplification mechanisms to further reduce actuator size. In this paper, a compact inchworm actuator with bridge-type displacement amplification mechanism (BTDAM) is proposed, which does not require an additional guiding mechanism and adopts a three-dimensional packaging approach with high space utilization and a compact amplification mechanism. Because the output capacity of the BTDAM significantly impacts the operating performance of the actuator, mathematical modeling and simulation analysis are conducted. Compared with the experimental results of the amplification ratio of the BTDAM, the error of the theoretical model was 5.05%, and that of the FEM analysis was 9.1%. The dimensions of the prototype are 23 × 23 × 19 mm, and it weighs 23 g. The test results indicate that the proposed actuator can achieve stable stepping motion without backward movement. Under a voltage of 75 V, the proposed actuator achieves a maximum motion speed of 384 μm/s and a maximum output force of 1.7 N. With its compact structure and light weight, the proposed actuator shows promising application prospects in the aerospace and bioengineering fields.

Experimental study on the synchronization mechanism and trigger characteristic density of vertical evacuation in crowds.

Due to simultaneous horizontal and vertical displacement during vertical evacuation, the consequences of stampede congestion accidents can be more severe. Generally, pedestrians trigger a synchronization mechanism at some point during the vertical evacuation process. This synchronization behavior helps prevent stampede congestion and improves evacuation efficiency. This paper designs a well-controlled single-file vertical evacuation experiment. After the experiment, the video footage is imported into the TRACKER system to extract the coordinates of pedestrian step movements, after which the experimental data undergo calculations and visual analysis. The research findings indicate the following: Firstly, when the crowd coordinates trigger the synchronization mechanism, this behavior remains stable as long as pedestrian speed and direction are unchanged; Secondly, the variation in footstep speed over time is not directly related to the footstep synchronization rate of the crowd; Lastly, this study calculated the characteristic density value most likely to trigger the synchronization mechanism during vertical evacuation. This research deepens our understanding of crowd dynamics, reveals the characteristics of pedestrian movement during vertical evacuation, and proposes evacuation guidance strategies based on these features.

Accuracy and Computational Cost Comparison of Numerical Flight Dynamics Reduced-Order Models

This paper compares several approaches to model the unsteady and nonlinear longitudinal aerodynamics of a generic unmanned combat air vehicle configuration based on computational fluid dynamics (CFD). Three different reduced-order models (ROMs) are implemented through unsteady simulations to predict the evolution of forces and moments during prescribed trajectories carried out at M=0.15. The first model investigates a linear quasi-steady model based on a first-order Taylor series expansion of the aerodynamic coefficients. The second one picks up the mathematical formulation of the first model but adds a dynamic coefficient in order to take into account the unsteady effect of rotation rate variations. Finally, the third model is built on indicial functions computed from positive step changes in the angle of attack or pitch rate. The unknown parameters of the first two models and the unknown indicial functions of the third one are obtained, respectively, from the study of forced oscillations and step motions. These prescribed trajectories are performed using unsteady Reynolds-averaged Navier–Stokes simulations coupled with a grid displacement tool. Two different methods are tested and compared to carry out the CFD mesh motions: an overset method and a full moving grid (FMG) method. The indicial functions obtained using the FMG method give results equivalent to those found in the literature in half the time of the overset method. To reduce the computational costs to set up the ROMs, the FMG method is preferred to the overset method. ROMs are then applied, and their predictions are compared with CFD simulations for prescribed trajectories with different angular rates and angles of attack. A study of instantaneous and overall accuracy associated with the implementation cost of the ROMs has allowed to show their strengths and their weaknesses. Similar results are observed at low angles of attack for the ROMs studied, while a major modeling advantage of the indicial method has been identified for higher angles of attack in the nonlinear domain.

A 2-DOF piezoelectric platform for cross-scale semiconductor inspection

To address the challenge of achieving extensive travel and high precision in semiconductor inspection, this study proposes a novel 2-DOF cross-scale piezoelectric positioning platform. In semiconductor inspection, the platform utilizes elliptical, stick-slip, and direct-push drive modes to meet the motion requirements at millimeter, micrometer, and nanometer scales. By applying defined electrical signals to the piezoelectric units, the platform can achieve high-speed continuous mode (HCM) for the millimeter scale, low-speed stepping mode (LSM) for the micrometer scale, and high-precision positioning mode (HPM) for the nanometer scale. Theoretical analysis and simulations were performed to design the flexible stator of the platform, and its dynamic characteristics were analyzed. A prototype was fabricated, assembled, and experimentally tested to investigate the mechanical performance of the proposed platform. The results show that the prototype successfully realizes cross-scale motion in the three modes: achieving a maximum no-load speed of 62.47 mm/s in HCM, a low-speed stepping motion of 14.62 μm/s in LSM, and high-precision positioning with a resolution of 25 nm within a range of ±21 μm in HPM. Through the flexible switching and cooperation of the three drive modes, the platform can quickly approach the target at millimeter speed, further approach with micrometer step motion, and finally achieve nanometer precision positioning. Finally, the positioning platform was successfully applied to inspect semiconductor devices for defect inspection. This study explores a novel cross-scale driving method for piezoelectric positioning platforms, which provides a new approach for precision manipulation research related to semiconductor component inspection.

Beta-frequency sensory stimulation enhances gait rhythmicity through strengthened coupling between striatal networks and stepping movement

Stepping movement is delta (1–4 Hz) rhythmic and depends on sensory inputs. Stepping-related delta-rhythmic neural activity is coupled to beta (10–30 Hz) frequency dynamics that are also prominent in sensorimotor circuits. We explored how beta-frequency sensory stimulation influences stepping and dorsal striatal regulation of stepping. We delivered audiovisual stimulation at 10 or 145 Hz to mice voluntarily locomoting, while recording locomotion, cellular calcium dynamics and local field potentials (LFPs). We found that 10 Hz, but not 145 Hz stimulation prominently entrained striatal LFPs. Even though stimulation at both frequencies promoted locomotion and desynchronized striatal network, only 10 Hz stimulation enhanced the delta rhythmicity of stepping and strengthened the coupling between stepping and striatal LFP delta and beta oscillations. These results demonstrate that higher frequency sensory stimulation can modulate lower frequency striatal neural dynamics and improve stepping rhythmicity, highlighting the translational potential of non-invasive beta-frequency sensory stimulation for improving gait.

A DNA machine-based magnetic resonance imaging nanoprobe for in vivo microRNA detection

In situ monitoring microRNA (miRNA) expression in vivo holds immense potential for directly visualizing the occurrence and progression of tumors. However, the significant barrier to developing a probe that can overcome the low abundance of miRNAs while providing an output signal with unlimited tissue penetration depth remains formidable. In this study, we developed a DNA machine-based magnetic resonance imaging nanoprobe (MRINP) for amplified detection of miR-21 in vivo. The MRINP was constructed with superparamagnetic Fe3O4 nanoparticles (NPs), paramagnetic Gd-DOTA complexes, and miR-21-activated DNA machines; the DNA machine was composed of hairpin DNAzyme (HD) strands serving as the DNAzyme walker and hairpin substrate (HS) strands serving as the track. Once uptake into tumor cells, the intracellular miR-21 specifically recognized and hybridized with the HD strand, restoring the activity of DNAzyme. Subsequently, the DNAzyme walker autonomously traveled on the surface of MRINP, and each step movement of the DNAzyme walker resulted in the cleavage of its substrate strands and the ensued release of the Gd-DOTA complex-labeled oligonucleotides, turning on the T1 signal of Gd-DOTA complexes for in situ imaging of miR-21 in tumor-bearing mice. This strategy would offer a promising approach for mapping tumor-specific biomarkers in vivo with unlimited penetration depth.

A novel linear piezoelectric inchworm actuator based on a ratchet mechanism

Abstract A new working principle of inchworm actuator, which converts vibrations of a single piezo actuator into unidirectional step movement of a mover via a ratchet mechanism, was proposed. The proposed working principle has the following priorities: (1) it requires only one piezoelectric actuator which greatly simplifies its driving signals and driving circuits; (2) it can achieve a large driving speed with little compromise of a large force output while maintaining a high positioning precision of piezoelectric actuator and a theoretically unlimited motion range, although it can only achieve unidirectional movement with unidirectional self-locking capability; (3) it could be open-loop controlled with no accumulated step errors. The proposed actuator was designed with compliant mechanism and an analytical model of the design was developed, validated by finite element simulations carried out in Commercial Software ANSYS and used to guide the selection of design parameters. A prototype was fabricated and tested. Experiments show that the proposed actuator achieved a speed larger than 12 mm s−1, a driving load larger than 60 N in the moving direction, a reliable open-loop controllability with no step accumulated errors even under driving load variations of 60 N, and a working range larger than 1 mm with a high positioning precision around 320 nm under closed-loop control, which validated the superiorities of the proposed actuator.

Beta-frequency sensory stimulation enhances gait rhythmicity through strengthened coupling between striatal networks and stepping movement.

Stepping movement is delta (1-4 Hz) rhythmic and depends on sensory inputs. In addition to delta rhythms, beta (10-30 Hz) frequency dynamics are also prominent in the motor circuits and are coupled to neuronal delta rhythms both at the network and the cellular levels. Since beta rhythms are broadly supported by cortical and subcortical sensorimotor circuits, we explore how beta-frequency sensory stimulation influences delta-rhythmic stepping movement, and dorsal striatal circuit regulation of stepping. We delivered audiovisual stimulation at 10 Hz or 145 Hz to mice voluntarily locomoting, while simultaneously recording stepping movement, striatal cellular calcium dynamics and local field potentials (LFPs). We found that 10 Hz, but not 145 Hz stimulation prominently entrained striatal LFPs. Even though sensory stimulation at both frequencies promoted locomotion and desynchronized striatal network, only 10 Hz stimulation enhanced the delta rhythmicity of stepping movement and strengthened the coupling between stepping and striatal LFP delta and beta oscillations. These results demonstrate that higher frequency sensory stimulation can modulate lower frequency dorsal striatal neural dynamics and improve stepping rhythmicity, highlighting the translational potential of non-invasive beta-frequency sensory stimulation for improving gait.

Collaborative robotics to enable ultra-high-throughput IR-MALDESI

Over the last 5 years, IR-MALDESI-MS (Infrared Matrix-Assisted Laser Desorption Electrospray Ionization Mass Spectrometry) has been demonstrated for use in a range of high-throughput biochemical and cellular assays with remarkable sample acquisition rates up to 22 Hz for a single 384-well assay plate. With such high single plate acquisition rates, the rate limiting step becomes how fast subsequent plates can be presented to the MS for analysis. To make this transfer as fast as possible while maintaining safe operation in a laboratory environment, we developed a collaborative robotic plate transfer system (CRPTS) that combines a 6-axis robot with dual plate grippers, a 7th axis conveyor stage, and a 420-plate capacity sample loading window. As a demonstration of the throughput and flexibility of CRPTS, we performed a biochemical assay that monitored the oxidation of tris(2-carboxyethyl)phosphine (TCEP) to screen for nuisance compounds. Using continuous and step motion scan profiles, we analyzed 158,799 compounds contained in 448 assay plates over the course of 12.5 h (Z-Factor=0.87) and 17.5 h (Z-factor=0.99), respectively. Extrapolating these results enables the screening of a million compounds within 6–7 working days.

Advanced CNC thread milling: a comprehensive canned cycle for efficient cutting of threads with fixed or variable pitch and radius

This paper presents the design, implementation, and experimental validation of a novel canned cycle for CNC milling machines, enabling the precise and efficient cutting of threads with fixed or variable pitch and radius. Conventional canned cycles are limited to fixed pitch threads, restricting the versatility of CNC milling machines in thread machining applications.The development process involves integrating a sophisticated control algorithm into the CNC milling machine's software, giving the operator remarkable control over the thread cutting process. This algorithm allows the operator to choose between external or internal threads, set both initial and final radii, determine initial and final pitches, specify the number of turns, and select the left or right-hand thread type. Such flexibility enables the creation of threads with diverse geometries. Furthermore, the proposed canned cycle provides the capability to switch between roughing and finishing passes by adjusting the step motion along the prescribed helical curve.Simulation tests conducted under various threading cases clearly demonstrate the efficiency of the proposed canned cycle. These results showcase its capability to address a wide range of machining scenarios, offering practical solutions applicable across a spectrum of applications.

Dynamic response of a wind turbine wake subjected to surge and heave step motions under different inflow conditions

The development of floating offshore wind turbines poses new challenges since the floating platform introduces complex dynamics in the wind turbine wake. These wake dynamics are intricately tied to the advection velocity, referring to the velocity of the downstream propagation of the air flow, and used in the context of wind farm modelling. The present article investigates the far-wake dynamic response of a wind turbine model subjected to heave (up-down translation) and surge (fore-aft translation) step motions under two distinct inflow conditions. Wind tunnel experiments were conducted with hot-wires in a realistic turbulent inflow and a low shear and no ground effect inflow, achieved by varying the hub height of the wind turbine model in the atmospheric boundary layer developed in the test section. The results show that the dynamic response of the wake under the low shear and no ground effect inflow conditions aligns with a second-order system with the presence of undershoots and overshoots. In contrast, under realistic conditions, it appears like a first-order system with undershoots and overshoots less evident in most cases. Despite these variations the determined advection velocity remains roughly the same and consistent with the literature for both heave and surge step motions, regardless of the inflow conditions.

Effect of changing the growth mechanism on the synthesis of two-dimensional germanium layers and quantum dots on silicon

Subject of study. The work studied the formation of germanium quantum dots on silicon with (100) crystallographic orientation under different growth regimes. Aim of study. The work is devoted to conducting experimental studies of the influence of growth mechanisms on the formation of germanium layers and quantum dots on a silicon (100) substrate for the production of optical elements based on silicon-germanium nanostructures. Methods. After pre-epitaxial cleaning of the Si substrate, germanium is synthesized on Si(100) through molecular beam epitaxy. The surface morphology is analyzed using reflection high-energy electron diffraction during synthesis and scanning electron microscopy after deposition. Main results. The work determines the temperature ranges at which the Si/Si(100) growth occurs due to the nucleation of islands, due to the movement of steps, and in combination. The effect of changing growth mechanisms on the size and density of Ge quantum dots on Si(100) is shown. Practical significance. The research results provide insight into the influence of growth mechanisms on the sizes of formed germanium quantum dots on silicon, which will make it possible to create nanophotonics and nanoelectronics elements with strictly specified parameters.

Kinematics of Two Special Endurance Trials: A Methodological Contribution to 400-m Performance.

This study aimed to determine changes in the kinematics of sprint steps based on progressive muscular fatigue during high-intensity 350-m and 500-m trials. Twelve elite healthy male 400-m sprinters with a minimum of six years of regular sprint training experience were recruited. They were divided into two groups for the experiment: a 350-m and a 500-m trial group. Time and kinematics of sprinting step motion for specific segments, i.e., starting to final stages of each trial, were obtained using the Opto Jump-Microgate optical measurement system. The starting phase of each sprint was defined as the section without muscular fatigue (noF), and the final phase was the sprint under muscular fatigue (onF). Each last 25 m of the 50-m evaluated section containing ten complete running steps was selected for detailed statistical analysis. Various patterns of temporal and spatial variables of sprinting efforts were observed between 350-m and 500-m trials. Each trial result was influenced by significant individual changes (p < 0.05). All variables indicated that the two distances differed significantly in terms of running kinematics. This was confirmed by significant differences in the mean step frequency (p < 0.001), which presented a difference of 11.75%, and the mean step speed (p < 0.001). As a result of these changes, a hierarchical intermittent endurance training pattern was defined. The research concluded that special endurance (intermittent sprints) based on 350 m differed significantly in kinematics from sprints over 500 m. Therefore, it should be assumed that the distance of 350 m is more similar in its kinematics to the 400-m competition. This should encourage coaches and athletes to apply a 350-m distance in training developing special endurance, especially in the pre-competitive and competitive periods.

Effects of Miscut on Step Instabilities in Homo-Epitaxially Grown GaN.

The rough morphology at the growth surface results in the non-uniform distribution of indium composition, intentionally or unintentionally doped impurity, and thus impacts the performance of GaN-based optoelectronic and vertical power electronic devices. We observed the morphologies of unintentionally doped GaN homo-epitaxially grown via MOCVD and identified the relations between rough surfaces and the miscut angle and direction of the substrate. The growth kinetics under the effect of the Ehrlich-Schwoebel barrier were studied, and it was found that asymmetric step motions in samples with a large miscut angle or those grown at high temperature were the causes of step-bunching. Meandering steps were believed to be caused by surface free energy minimization for steps with wide terraces or deviating from the [11¯00] m-direction.

Sagittal and transverse ankle angle coupling can influence prosthetic socket transverse plane moments.

The intact foot and ankle comprise a complex set of joints that allow rotation in multiple planes of motion. Some of these motions are coupled, meaning rotation in one plane induces motion in another. One such coupling is between the sagittal and transverse planes. For every step, plantar- and dorsi-flexion motion is coupled with external and internal rotation of the shank relative to the foot, respectively. There is no prosthetic foot available for prescription that mimics this natural coupling. The purpose of this study was to determine if a sagittal:transverse ankle angle coupling ratio exists that minimizes the peak transverse plane moment during prosthetic limb stance. A novel, torsionally active prosthesis (TAP) was used to couple sagittal and transverse plane motions using a 60-watt motor. An embedded controller generated transverse plane rotation trajectories proportional to sagittal plane ankle angles corresponding to sagittal:transverse coupling ratios of 1:0 (rigid coupling analogous to the standard-of-care), 6:1, 4:1, 3:1, and 2:1. Individuals with unilateral transtibial amputation were block randomized to walk in a straight line and in both directions around a 2 m circle at their self-selected speed with the TAP set at randomized coupling ratios. The primary outcome was the peak transverse plane moment, normalized to body mass, during prosthetic limb stance. Secondary outcomes included gait biomechanic metrics and a measure of satisfaction. Eleven individuals with unilateral transtibial amputations participated in the study. The 6:1 coupling ratio resulted in reduced peak transverse plane moments in pairwise comparisons with 3:1 and 2:1 coupling ratios while walking in a straight line and with the prosthesis on the outside of the circle (p < .05). Coupling ratio had no effect on gait biomechanic metrics or satisfaction. The general pattern of results suggests a quadratic relationship between the peak transverse plane moment and coupling ratio with a minimum at the 6:1 coupling ratio. The coupling ratio did not appear to adversely affect propulsion or body support. Subjects indicated they found all coupling ratios to be comfortable. While a mechatronic prosthesis like the TAP may have limited commercial potential, our future work includes testing a robust, passive prosthetic foot with a fixed coupling ratio.

Working memory load modulates anticipatory postural adjustments during step initiation.

Working memory (WM) can influence selective attention. However, the effect of WM load on postural standing tasks has been poorly understood, even though these tasks require attentional resources. The purpose of this study was to examine whether WM load would impact anticipatory postural adjustments (APAs) during step initiation. Sixteen healthy young adults performed stepping tasks alone or concurrently with a WM task in a dual-task design. The stepping tasks involved volitional stepping movements in response to visual stimuli and comprised of simple and choice reaction time tasks and the Flanker task which consisted of congruent and incongruent (INC) conditions. In the dual-task condition, subjects were required to memorize either one or six digits before each stepping trial. Incorrect weight transfer prior to foot-lift, termed APA errors, reaction time (RT), and foot-lift time were measured from the vertical force data. The results showed that APA error rate was significantly higher when memorizing six-digit than one-digit numerals in the INC condition. In addition, RT and foot-lift time were significantly longer in the INC condition compared to the other stepping conditions, while there was no significant effect of WM load on RT or foot-lift time. These findings suggest that high WM load reduces the cognitive resources needed for selective attention and decision making during step initiation.

Analysis of Macrostep Interaction via Carbon Diffusion Field in SiC Solution Growth

In the top-seeded solution growth (TSSG) method for SiC, control of macrostep development is crucial for improving the crystal quality. Dislocation conversion phenomena caused by macrosteps with a certain height on the crystal surface can reduce the dislocation density, while over-developed macrosteps bring macroscopic defects such as solvent inclusions. It is experimentally reported that solution flow direction to the step movement has a substantial impact on the macrostep development: parallel solution flow promotes and anti-parallel solution flow suppresses the increase of macrostep height. Our hypothesis is that this macrostep development is governed by the interaction between the macrosteps not by the instability of the density of the atomical steps. In this study, we constructed a computational fluid dynamic model of the boundary layer around macrosteps on the crystal surface, incorporating the solution flow on the boundary layer and consumption of the carbon solute by the macrostep movement quantitatively. The computational simulation reveals that the macrostep with position shift from the center of the adjacent macrosteps moves to the direction of the nearer macrostep under the parallel flow and moves to the farther macrostep under the antiparallel flow. These macrostep movements result in the bunching and debunching of the macrosteps. The mechanisms of macrostep movements demonstrated in this study will be useful for the precise control of macrostep height aiming to the reduction of the dislocation density during SiC solution growth.

Controllable step-flow growth of GaN on patterned freestanding substrate

A new kind of step-flow growth mode is proposed, which adopts sidewall as step source on patterned GaN substrate. The terrace width of steps originated from the sidewall was found to change with the growth temperature and ammonia flux. The growth mechanism is explained and simulated based on step motion model. This work helps better understand the behaviors of step advancement and puts forward a method of precisely modulating atomic steps.

Huge mobility difference between the neutral and charged steps on 180° domain walls of PbTiO3 by first-principles calculations

The microscopic mechanism of ferroelectric switching is the motion of domain walls, which is actually accomplished by the movement of tiny steps on the domain walls. Using first-principles calculations, the detailed polarization structures and the motion barriers of neutral and charged steps on 180° domain walls of prototypical ferroelectrics PbTiO3 are elaborately revealed in this study. While the Bloch components get weakened near all neutral steps, they become weakened/strengthened near the head-to-head/tail-to-tail charged steps. The neutral step possesses a lower formation energy but a higher migration barrier, indicating that the charged step could move faster. Based on these results, the possible motion picture of steps on one 180° domain wall of tetragonal ferroelectrics is proposed, which provides a better understanding of the mechanism of domain wall motion and may shed light on the future development of domain wall–based functional devices.