Step Displacement Research Articles

A Novel Stick-Slip Nanopositioning Stage Integrated with a Flexure Hinge-Based Friction Force Adjusting Structure.

The piezoelectrically-actuated stick-slip nanopositioning stage (PASSNS) has been applied extensively, and many designs of PASSNSs have been developed. The friction force between the stick-slip surfaces plays a critical role in successful movement of the stage, which influences the load capacity, dynamic performance, and positioning accuracy of the PASSNS. Toward solving the influence problems of friction force, this paper presents a novel stick-slip nanopositioning stage where the flexure hinge-based friction force adjusting unit was employed. Numerical analysis was conducted to estimate the static performance of the stage, a dynamic model was established, and simulation analysis was performed to study the dynamic performance of the stage. Further, a prototype was manufactured and a series of experiments were carried out to test the performance of the stage. The results show that the maximum forward and backward movement speeds of the stage are 1 and 0.7 mm/s, respectively, and the minimum forward and backward step displacements are approximately 11 and 12 nm, respectively. Compared to the step displacement under no working load, the forward and backward step displacements only increase by 6% and 8% with a working load of 20 g, respectively. And the load capacity of the PASSNS in the vertical direction is about 72 g. The experimental results confirm the feasibility of the proposed stage, and high accuracy, high speed, and good robustness to varying loads were achieved. These results demonstrate the great potential of the developed stage in many nanopositioning applications.

Theoretical Study of VX Hydrolysis Mechanism Catalyzed by Phosphotriesterase Mutant H254R

AbstractPhosphotriesterase (PTE) is a bacterial enzyme that can catalyze the hydrolysis of V‐type chemical warfare nerve agents. Herein, the hydrolysis mechanism of VX analogs catalyzed by the H254R PTE mutant, in which the histidine 254 residue is replaced by an arginine, has been investigated using the hybrid density functional theory method B3LYP. The chemical model of the active site of H254R PTE mutant was constructed based on the high resolution X‐ray crystal structure. We have presented the energetics and the characterization of stationary points in the catalytic reaction. The calculations indicate that the catalytic process contain two SN2 displacement steps and the step of hydroxide regeneration is rate‐limiting with an overall barrier of 22.2 kcal/mol. The Arg254 plays an important role as a proton donor/acceptor for protonating leaving group and activating water molecule. Moreover, the H254R PTE mutant with binuclear cobalt center turns out to higher activity towards VX than the binuclear zinc H254R PTE.

Phase detection algorithm using step lengths deviation errors and Hough transform in phase-shifting interferometry

In phase-shifting interferometry (PSI), a set of interferograms with a known phase step displacement is necessary, but incorrect calibration deviation errors can occur in shifter devices. We present a method to recover the phase distribution in the presence of this deviation error through the widely used PSI technique. By applying the radon transform as a profile measurement, our algorithm first estimates the deviations in the phase steps, then these calculations are used to obtain the wrapped phase using the Hough transform as an estimation of coefficients in sinusoidal patterns. Simulation and experimental results have shown good performance. The results reveal that this algorithm is able to detect and decrease the phase error due to miscalibrations.

Designing Ordered Structure with Piezoceramic Actuation Units (OSPAU) for Generating Continual Nanostep Motion.

Continual precision actuations with nanoscale resolution over large ranges have extensive requirements in advanced intelligent manufacturing and precise surgical robots. To produce continual nanostep motion, conventionally, multiple pairs of piezo‐actuators are employed to operate in inchworm principle under complex three‐ or four‐phase timing signal drive. Inspired by the idea of ordered structures with functional units, a much simpler nanostep piezoelectric actuator consisting of (2 × 2) arrayed, cofired multilayer piezoceramic actuation units is developed, which operates in an artificially generated quasi shear mode (AGQSM) that is missing in natural piezoelectric ceramics. Under only one‐phase square‐wave voltage drive, the actuator can produce a stable, continual nanostep motion in two ways at nonresonant frequencies, and the obtained minimum step displacement is as low as 7 nm in open control, indicating its potential application as a precise finger or knife actuator in surgical robots. This work is of great guiding significance for future actuator designs using the methodology of ordered structure with piezoceramic actuation units and AGQSM.

Self-selected Walking Cadence After Light-intensity Physical Activity Intervention For Older Cancer Survivors

PURPOSE: The MY Health randomized controlled trial evaluated the effectiveness of a wrist-worn activity monitor and health coaching to replace sedentary behavior with bouts of light-intensity physical activity among older cancer survivors. Participants were asked to 1) increase average daily steps ≥ 3000 above baseline and 2) disrupt sedentary behavior at least twice per hour. No specific recommendations regarding intensity or minimum bout duration were provided. In this secondary analysis, we hypothesized that participants would self-select to walk faster to meet their daily step goal. METHODS: Average daily steps and free-living walking cadence were measured in 41 participants (age 69±3.1 yr), using an ActivPAL activity monitor for 7 days pre- and post-intervention. Step accumulation patterns associated with intensity of ambulatory behavior were sorted in cadence bands of 20 steps/min from 40-59 (incidental movement) to ≥120 steps/min (fast locomotor movement). Repeated measures ANOVA was used to evaluate intervention induced changes in walking cadence; Wilcoxon rank-sum tests were used to highlight group differences within cadence bands. Medians and interquartile range are reported. RESULTS: Intervention (n=24) and Waitlist Control (n=17) participants exhibited similar characteristics at baseline. The Intervention group increased average daily steps by 976 (IQR: -388 to 3532) from pre- to post-intervention; the control group increased by 354 steps/day (IQR: -658 to 1300); p=.19). There was a significant interaction of the intervention on cadence bands (p<.001). Steps taken in cadence bands denoting moderate intensity physical activity (MPA; 100-119 steps/min) increased by 478 (IQR: -121 to 1844) steps/day in the intervention group, compared to a decrease of 92 (IQR: -510 to 181) steps/day in the control group (p<.01). CONCLUSION: While only 29% of intervention group participants met the daily step goal, there was a displacement of steps taken from cadence bands associated with lower to those of higher intensity of stepping, i.e., participants self-selected to walk faster. These findings may have important clinical implications as both duration and intensity have shown to offer cardioprotective and other health-related benefits.

A walking type piezoelectric actuator with two umbrella-shaped flexure mechanisms

A walking type piezoelectric actuator with two umbrella-shaped flexure mechanisms is proposed to reduce the backward motion. By utilizing two umbrella-shaped flexure mechanisms which could be treated as two ‘legs’, the ‘walking’ motion is accomplished. The structure and motion principle are described; Finite Element Method (FEM) is exploited to explore the static and modal performances of the umbrella-shaped flexure mechanism. Moreover, experiments have been carried out to investigate the working performance of the proposed walking type piezoelectric actuator. Results show that the walking type piezoelectric actuator with umbrella-shaped flexure mechanisms could achieve the ‘walking’ motion and reduce the backward motion. Additionally, the phase difference between two input signals U1 and U2 greatly influences the working performance. In the case of the phase difference Φ= 95°, the backward rate of the slider is able to achieve the minimum 0%; the minimum stepping displacement is 0.3 μm when the frequency f= 1 Hz; the maximum motion speed of the slider is up to 1132 μm s−1 when the input frequency f = 400 Hz and the input voltage U = 120 V; the maximum output force is 700 g while the input voltage U = 120 V and frequency f = 1 Hz.

Experimental investigation on water removal and gas flow during drainage process in tight rocks

High performance water removal plays a significant role in restoring the gas production when water invasion happens to tight gas reservoirs. In this paper, core samples with the air permeability in range of 0.01–1 mD were selected to investigate water removal behavior in tight gas reservoirs. Meanwhile, the gas flow capability during the process of water removal was discussed. The water desaturation curves generally experienced two stages of water removal in a drainage process: a fast water decline stage induced by immiscible displacement, followed by a long period of slow water saturation reduction stage via the gas flow-through drying. It pointed out that the immiscible displacement mainly affects water removal during the drainage process in which period continuous gas flow channel was built. Once the generation of continuous gas flow channel was accomplished during the immiscible displacement stage, a proper increase of displacement pressure difference can efficiently enhance the gas flow-through drying rate. Normally, it was easy for high permeable tight core sample to experience a short immiscible displacement dominant stage and step into gas flow-through drying dominant stage afterwards. Besides, it was found that the enlargement in water invasion depth will weaken gas flow capacity from water removal. These findings help in understanding the physical process of water removal in tight gas reservoirs, as well as designing a better performance of water removal in a tight gas flied.

Numerical study on upheaval buckling for surface laid subsea pipelines with topographic step imperfection

Upheaval buckling may occur for subsea pipelines laid on the seabed with topographic step imperfection under high temperature. In order to predict the post buckling behaviour of upheaval buckling, a finite element model of ABAQUS is proposed to simulate upheaval buckling for surface laid subsea pipelines with step imperfection. Firstly, a new method to introduce a step imperfection from an originally flat seabed is presented. Then, the finite element model of ABAQUS proposed in this paper is verified through the analytical results. The results obtained by FEA and analytical method have a good agreement. The influence of temperature difference, model length and step height on configuration and post buckling behaviour is investigated in detail. Our results show that rigid seabed assumption is reasonable in this study. The model length of the pipeline must be larger than the feed-in length. Otherwise, displacement amplitude, maximum stress and axial thermal expansion will be underestimated. For larger step height, displacement amplitude and maximum stress are larger at lower temperature difference due to the initial deflection induced by step imperfection of seabed, however, they become smaller at high enough temperature difference. The influence of step height and thickness of the pipe on the critical buckling force can be fitted well by a simple formula. The critical buckling force is barely affected by the axial friction coefficient between pipe and seabed.

A two-fixed-end beam piezoelectric inertial actuator using electromagnet controlled magnetorheological fluid (MRF) for friction regulation

Friction is an important parameter to ensure the stable working of inertial actuators. It is usually regulated by adjusting the normal pressure, which will inevitably lead to wear due to the solid-to-solid contact and consequently a degradation of the output performance. This paper proposes to generate friction with magnetorheological fluid (MRF) whose shearing stress could be adjusted by the magnetic induction from an electromagnet. An inertial actuator prototype with a two fixed-end beam asymmetric structure and a MRF friction regulation unit is fabricated to verify the feasibility of electromagnet controlled MRF in friction regulation. COMSOL and MATLAB/Simulink are used for modal analysis and dynamic analysis of the proposed actuator. Experiments are conducted to evaluate the performance of the actuator. Experiment data show that the step displacement of the actuator is dramatically affected by the magnetic induction and reaches a peak value at 8.4 mT. Under the square wave excitation signal of 25 V, 7 Hz, the minimum step displacement is 0.1 μm with a rollback rate of 0.92 at a magnetic field of 19.5 mT, the maximum step displacement is 2.53 μm with a rollback rate of 0 at a magnetic field of 8.4 mT.

An auto-adaptive sub-stepping algorithm for phase-field modeling of brittle fracture

In this work, we propose an auto-adaptive displacement stepping algorithm to auto-adaptively adjust the displacement step size while solving the quasi-static brittle fracture propagation problem with the phase-field method. We employ a step size controller based on an ‘a posteriori’ error estimator to achieve adaptivity in the displacement step size. To capture correct crack propagation behavior near peak load, we propose an energy-based conditional. The conditional is evaluated in a sub-step of the primary displacement step, and it decides whether to accept or reject the step. Based on the step size controller algorithm and the sub-stepping algorithm, we formulate the auto-adaptive sub-stepping algorithm. We investigate the accuracy and computational cost of the proposed algorithm on several benchmark problems from the literature and compare it to the standard alternate minimization (AM) approach. The algorithm auto-adaptively adjusts the size of the displacement step and allows us to use step sizes that may vary by even three orders of magnitude. As compared to the standard AM algorithm, this results in a reduction of 78–90% in the CPU time required to reach peak reaction force, and 56–78% reduction in the CPU time needed to complete analysis, and always maintains the accuracy in crack path prediction.

A Convolutional Deep Self-Organizing Map Feature extraction for machine learning

In this work we propose a new Unsupervised Deep Self-Organizing Map (UDSOM) algorithm for feature extraction, quite similar to the existing multi-layer SOM architectures. The principal underlying idea of using SOMs is that if a neuron is wins n times, these n inputs that activated this neuron are similar. The basic principle consists of an alternation of phases of splitting and abstraction of regions, based on a non-linear projection of high-dimensional data over a small space using Kohonen maps following a deep architecture. The proposed architecture consists of a splitting process, layers of alternating self-organizing, a rectification function RELU and an abstraction layer (convolution-pooling). The self-organizing layer is composed of a few SOMs with each map focusing on modelling a local sub-region. The most winning neurons of each SOM are then organized in a second sampling layer to generate a new 2D map. In parallel to this transmission of the winning neurons, an abstraction of the data space is obtained after the convolution-pooling module. The ReLU is then applied. This treatment is applied more than once, changing the size of the splitting window and the displacement step on the reconstructed input image each time. In this way, local information is gathered to form more global information in the upper layers by applying each time a convolution filter of the level. The architecture of the Unsupervised Deep Self-Organizing Map is unique and retains the same principle of deep learning algorithms. This architecture can be very interesting in a Big Data environment for machine learning tasks. Experiments have been conducted to discuss how the proposed architecture shows this performance.

Opto-locomotor reflexes of mice to reverse-phi stimuli.

In a reverse-phi stimulus, the contrast luminance of moving dots is reversed each displacement step. Under those conditions, the direction of the moving dots is perceived in the direction opposite of the displacement direction of the dots. In this study, we investigate if mice respond oppositely to phi and reverse-phi stimuli. Mice ran head-fixed on a Styrofoam ball floating on pressurized air at the center of a large dome. We projected random dot patterns that were displaced rightward or leftward, using either a phi or a reverse-phi stimulus. For phi stimuli, changes in direction caused the mice to reflexively compensate and adjust their running direction in the direction of the displaced pattern. We show that for reverse-phi stimuli mice compensate in the direction opposite to the displacement direction of the dots, in accordance with the perceived direction of displacement in humans for reverse-phi stimuli.

A parasitic type piezoelectric actuator with the asymmetrical trapezoid flexure mechanism

With the help of the parasitic motion of the asymmetrical trapezoid flexure mechanism, a piezoelectric actuator which could achieve linear motion with large working stroke has been presented and inspected. The structure of the asymmetrical trapezoid flexure mechanism and the motion principle of the proposed piezoelectric actuator are introduced and investigated in details. Finite Element Method (FEM) has been exploited, and an experimental system has been built up to study the working performance of the proposed piezoelectric actuator. Simulation results confirm that the parasitic motion could be achieved by the asymmetrical trapezoid flexure mechanism. Additionally, the dynamic model has been proposed for the investigation. Experimental results show that the presented actuator could obtain continuous linear motion with large working stroke by the parasitic motion of the proposed asymmetrical trapezoid flexure mechanism. The minimum stepping displacement of the proposed actuator is 0.68 μm; the maximum speed is 4676 μm/s; the output force could be as large as 91.3 g. This study shows a meaningful idea of the utilization of the asymmetrical trapezoid flexure mechanism for the design of novel piezoelectric actuators.

19-picometer mechanical step displacement measurement using heterodyne interferometer with phase-locked loop and piezoelectric driving flexure-stage

In this paper, we discuss 20-picometer-order mechanical step displacement measurements using a heterodyne interferometer with a phase-locked loop (PLL) and two piezoelectric (PZT) driving flexure-stages. First, the phase meter for heterodyne interferometry using one simple digital PLL is developed. Two inputs and one output of the single PLL are the reference and measurement signals of the heterodyne interferometer and the phase shift due to the movement of the target mirror, respectively. The PLL includes an active phase shifter, a mixer (multiplier), a low-pass filter combined with an averaging operation, and an integrator. In electronics evaluation of the PLL, the PLL shows a phase resolution of 174 μrad with 4.2 μrad noise (standard deviation) and a phase noise floor of 3 μrad/√Hz above 0.2 Hz with an output sampling rate of 200 Hz. Using the single PLL, a four-pass normal commercial heterodyne interferometer, and high-stiff-parallel spring stage driven by PZT actuator, we demonstrate the actuations and measurements of mechanical step displacements of 19 pm (1.5 mrad) and a displacement noise floor of 1.1 pm/√Hz (90 μrad/√Hz) above 1 Hz in normal air. In the paper, the principle, instrumentation, and experimental results are discussed.

RNA interference supports a role for Nanchung-Inactive in mechanotransduction by the cockroach, Periplaneta americana, tactile spine.

Proteins encoded by nanchung, inactive, nompC and piezo genes have been shown to play crucial roles in the initial detection of mechanical force by various insect auditory neurons, nociceptors and touch receptors. Most of this previous research has been performed on the larval and adult fruit fly, Drosophila melanogaster. We identified and assembled all four homologous genes in transcriptomes from the cockroach, Periplaneta americana. Injection of long double-stranded RNA (dsRNA) into the adult cockroach abdomen successfully reduced the expression of each gene, as measured by quantitative PCR (RT-qPCR). A simple electrophysiological assay was used to record action potential firing in afferent nerves of cockroach femoral tactile spines in response to a standardized mechanical step displacement. Responses of nanchung knockdown animals were significantly reduced compared to matched sham-injected animals at 14 and 21days after injection, and inactive knockdowns similarly at 21days. In contrast, responses of nompC and piezo knockdowns were unchanged. Our results support a model in which Nanchung and Inactive proteins combine to form a part of the mechanotransduction mechanism in the cockroach tactile spine.

A New Inverse Explicit Flow Curve Determination Method for Compression Tests

Flow curves characterize plastic flow in materials and their accurate description is necessary to reproduce any forming process in simulations. For flow curve determination, laboratory uniaxial compression or tensile tests are conducted to record force-displacement during deformation. Flow stress is then calculated as the ratio of force to cross-sectional area. However, this assumption is invalid when the stress state during testing changes to non-uniaxial stress states, e.g. necking in tensile or bulging in compression tests. Alternatively, inverse methods deploy simulation models replicating experiments along with flow curves represented as an analytical equation. The parameters in this equation are then optimized by minimizing the error in simulation and experiments. An a priori guess of the analytical equation is difficult especially when the material behavior is complex e.g. Lüder or DRX flow curves, though. In this paper, a piecewise inverse method without using an analytical equation is therefore introduced and validated with flow curves for aluminum and copper under compression tests. The method determines flow curves points as tabular data at different displacement steps and hence it is easier to represent complex flow curves. Two different methods, a heuristic and an iterative one, are discussed. To minimize the error between simulated and experimental forces, the heuristic method uses an adaptive equation estimating flow stress using predetermined points and experimental force, whereas in the iterative approach the flow curve is adjusted iteratively to minimize the error. The results show that the heuristic method has a limited applicability e.g. for low friction tests, whereas the iterative method can estimate flow curves for generalized deformation conditions. Overall, the flow curves determined with the new method yield an error of less than 2% in the force estimation with simulated compression tests. The presented method hence determines accurate flow curves for forming simulations under multiaxial stress states without the necessity of analytical equations.

A research of sliding mode control method with disturbance observer combining skyhook model for active suspension systems

Based on a nonlinear two-degree-of-freedom model of active suspension systems, an approach of the sliding mode control with disturbance observer combining skyhook model sliding mode control with disturbance observer combining is proposed for improving the performance of active suspension systems, and the effectiveness of the proposed approach is validated by the active suspension system plant. Two problems of active suspension systems are solved by using the proposed approach when the tire is excited by the step displacement. One problem is that the suspension deflection of active suspension systems, i.e. the difference between the sprung mass displacement and the unsprung mass displacement, using conventional sliding mode control with disturbance observer not converges to zero in finite time, and the phenomenon of the impact of suspension against the limit block is produced. This problem is solved by providing a reference value of the sprung mass displacement in an active suspension system, which is obtained from the skyhook model. The other problem is that disturbances exist in active suspension systems, which are caused by the inaccurate parameters of stiffness and damping. This problem is solved by designing a disturbance observer to estimate the summation of the disturbances. Finally, the performance indexes of the active suspension system with the sliding mode control with disturbance observer combining skyhook model are calculated and compared with those of using the conventional sliding mode control with disturbance observer and the linear quadratic regulator approach.

Supercritical drying of vascular endothelial growth factor in mesenchymal stem cells culture fluids

Mesenchymal stem cells (MSCs) culture fluids are frozen and thawed for long-term storage when needed for medical purposes. However, stresses accompanied with freezing and thawing can disrupt the tertiary structures of proteins, which need to be in a certain state to show their therapeutic effect, by affecting their internal interactions. Supercritical drying of MSCs culture fluids using carbon dioxide was conducted to resolve these problems. Various process parameters were controlled to improve process efficiency in the water displacement step which takes place prior to supercritical drying. Among the proteins contained in the MSCs culture fluids, vascular endothelial growth factor (VEGF) was selected as a representative material to optimize the process parameters. Analyzed results show that the tertiary structures of VEGF via supercritical drying are well preserved. In addition, the structural stability and bioactivity of VEGF when re-dissolved in an aqueous environment were better than those obtained from freeze drying.

A linear piezoelectric actuator with the parasitic motion of equilateral triangle flexure mechanism

A parasitic type piezoelectric actuator with an equilateral triangle flexure mechanism is proposed and investigated to achieve large-stroke linear motion. Right-circular flexure hinges with different thicknesses (t1 and t2) are utilized in the design of the equilateral triangle flexure mechanism which is able to generate parasitic motion. The working principle is analyzed and illustrated by the theoretical simulation and finite element method (FEM) simulation. A prototype is manufactured to study the performance of proposed parasitic type actuator, together with an experimental system. Experiments indicate that the maximum stepping displacement is ΔL = 9.00 μm in the case that input voltage Ue = 150 V; the minimum stepping displacement ΔL = 0.24 μm is achieved under Ue = 60 V; the maximum speed is Vs = 180 μm s−1; the largest output force is F = 106.3 g under that input frequency f = 1 Hz and Ue = 100 V. This study demonstrates the feasibility of symmetrical triangle flexure mechanisms in the design of parasitic type piezoelectric actuators with large working stroke.

Design and experimental performance of an inertial giant magnetostrictive linear actuator

In order to meet the requirements of large stroke and high precision linear displacement, an inertial impact type giant magnetostrictive linear actuator was designed according to the principle of the inchworm motion. The stepwise cumulative displacement motion can be realized by applying a sawtooth wave signal to the excitation coil. The superimposed flexible hinge effectively improves the force of the system. The equivalent stiffness is calculated by simplifying the flexible hinge into a cantilever beam, and the strength of the flexible hinge is checked, the modal analysis is carried out. The displacement model of inertial actuator is established according to voltage law, magnetoresistance theory, linear piezomagnetic model and dynamic theory. The experimental platform is built and the prototype is designed for test. The experimental and simulation results show that the operating voltage range of the inertial actuator is 3 V–9 V, the maximum operating frequency is 60 Hz, the minimum and maximum single step displacement are 2.41 μm and 7.49 μm, and the maximum speed is 449.4 μm/s. The displacement output is stable, the maximum relative error of the single step displacement is 3.97 %. In the working voltage range, the maximum error between the simulated and experimental values is 4.84 %. And the maximum error between the simulated and experimental values is 2.96 % in the working frequency range. So the design scheme and the displacement model have certain reference significance for the application of large stroke actuator.