Slip Signal Research Articles

Natural sucrose-assisted controllable porous PVDF-HFP films for self-powered tactile sensors with higher sensitivity

Incorporating porous structures into flexible piezoelectric materials has proven to be an effective strategy to enhance the output performance, but the fabrication processes are often intricate or environmentally harmful. In this study, natural sucrose with substantial hydroxyl groups was firstly introduced into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a phase formation inducer, and subsequently removed by the dissolution of water as a pore formation agent, yielding a regular porous structure. Furthermore, porosity of the PVDF-HFP film could be simply modulated by adjusting the mass ratio of sucrose to PVDF-HFP. At low porosity levels, the dielectric constant of PVDF-HFP decreased with the increase of porosity, reaching the minimum at the critical threshold porosity of 38.8%. Owing to the increased β-phase content and the decreased dielectric constant, the sensitivity of the porous PVDF-HFP film based piezoelectric sensor was tripled to 117 mV/N, which held promise for detecting tactile and slip signals in mechanical arms.

CEEMDAN combined wavelet denoising improved the MW cycle slip detection algorithm

In the preprocessing of high-precision navigation and positioning data, the most widely used MW combination cycle slip detection method is greatly affected by pseudorange noise. It has issues such as missing small cycle slips and failing to promptly reset the recursive averaging process after cycle slip detection failure, which leads to subsequent threshold divergence. This paper proposes an improved MW combination cycle slip detection method based on Complete Ensemble Empirical Mode Decomposition (CEEMDAN), permutation entropy, and wavelet denoising, which uses CEEMDAN to decompose the cycle slip signal into a series of intrinsic modal functions (IMFs) and then selects the IMFs that require denoising through the permutation entropy algorithm, and the wavelet denoising technique is combined to eliminate the residual noise further, so that the noise can be removed more accurately. Experimental results show that compared with the original MW algorithm, the proposed improved method can effectively reduce the influence of pseudo-range noise, and reduce the false detection rate of cycle slip from 1.6% and 6–0%. All small period slips can be successfully detected in complex noise environments, avoiding the missed detection of the original MW algorithm and the related threshold divergence problems.

Inversion of fluid-release rates from episodic tremor and slip signals in subduction zones via a coarse-grained reaction diffusion model

Episodic Tremor and Slip (ETS) events showcase dynamic interactions of oscillatory slow slips and tremors deep within subduction zones and offer a window into Earth's internal dynamics. However, the exact mechanisms driving these events remain unresolved. This study proposes a novel approach that goes beyond traditional explanations focused on fluid pressure from mineral dehydration. Existing models often neglect the intricate interplay between fluid and rock pressures across various depths and potential fluid sources. This calls for a more comprehensive understanding of how fluid release from reactions interacts with rock deformation. The present formulation captures the interplay between fluid and solid pressures providing a more rigorous picture of ETS events. It employs a minimalistic and efficient approach based on integrating dehydration reactions. The model thereby develops a generic framework for mineral dehydration, offering an enhanced perspective of the underlying processes without the need to trace down to specific minerals. It allows a refined fit to GPS data by including high-frequency components from linear and nonlinear stability analyses, giving rise to improved correlation coefficients. Through the inclusion of the dynamic interplay between fluid and rock pressure diffusion within subduction zones, we propose a unified model of ETS events.

Serpent-inspired multimodal flexible sensor for multi-signal measurement based on PVDF-TrFE/Fe3O4 nanofibers

Flexible sensors demonstrate enormous potential in remote monitoring, electronic healthcare, human-machine interfaces, and soft robotics. Multi-functional sensing devices with the capability of performing various tasks play an indispensable role in flexible sensors. Herein, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE)/Fe3O4-based nanofibers with a diameter concentrated around 140 nm were prepared using electrospinning technology. Particularly, in the case of adding 5 wt% Fe3O4 nanoparticles (NPs), the β-phase content of these nanofibers exceeds 94 %, exhibiting a sensitivity of 5.02 V/N. Simultaneously, inspired by biomimicry, a serpent-shaped multimodal flexible (SMF) sensor is proposed, consisting of stretchable sinusoidal-shaped silver electrodes, a composite nanofiber membrane, and a PDMS substrate with varying concentration ratios. Subsequently, the SMF sensor is installed on the end effector of the Arm32 robot, capable of recognizing tactile and slip signals, ensuring a success rate of over 92 % in 50 repeated experiments of grasping four different types of objects. Furthermore, thermosensitive tests indicate that the SMF sensor has the ability to perceive different temperatures. Cycling vibration aging experiments have confirmed that the sensor demonstrates excellent robustness and stability. These experimental results highlight the promising application prospects of SMFS in soft robotics and intelligent electronic products.

Experimental evaluation of the purity of medical oxygen obtained by adsorption technology with pressure fluctuations taking into account the variability of the parameters of the incoming air

This study presents the results of the evaluation of the purity of medical oxygen obtained by adsorption technology with pressure fluctuations, taking into account the variability of the parameters of the incoming air, and the results of the correlation analysis of data obtained from the monographs of the European and American Pharmacopoeias. The quality of oxygen obtained from air that meets sanitary standards and under conditions of the “worst case,” while fixing the time of the output of the slip signal of monoxide and carbon dioxide as marker gases, was assessed. The slip time under the experimental conditions was 13 h 22 min. The composition of the gas produced by installation was analyzed. Impurities of nitrogen, argon, and water were recognized as predominant quantitatively. Nitrous gases and sulfur dioxide were not detected. A comparative assessment of the data on medical oxygen (93%) presented in the European EP 8. 0 (No. 2455) and the American USP 38-NF (No. 4180) pharmacopeias showed that no single approach is available to assess the quality of 93% medical oxygen in pharmaceutical practice worldwide. The authors of the above-mentioned pharmacopeias note that installations for obtaining 93% medical oxygen, implementing adsorption technology with pressure fluctuations, must be equipped with gas-analytical devices to quantify the level of at least two impurities: carbon monoxide and dioxide. In general, the data obtained indicate that when obtaining 93% medical oxygen by adsorption technology with pressure fluctuations from air corresponding to sanitary and hygienic indicators (clean), the resulting gas did not contain impurities requiring quantitative assessment and/or identification. If oxygen in its pure form is rarely supplied to the patient, its further dilution to 40%–60% is more often required, and the content of hypothetically possible impurities becomes negligible. However, the technology of air separation on molecular sieves is a complex physicochemical (thermodynamic) process, and its effectiveness depends on the component composition of the incoming air, which may change when working under unfavorable environmental conditions in various locations. In this regard, medical oxygen production plants that implement this technology must employ gas-analytical devices to quantify the level of carbon dioxide and carbon monoxide impurities without fail.

Identification of characteristics of slip signal based on fiber Bragg grating flexible sensor

Identification of characteristics of slip signal based on fiber Bragg grating flexible sensor

Damage Detection of Composite Beams via Variational Mode Decomposition of Shear-Slip Data

Damage of shear connectors in steel-concrete composite (SCC) beams affects the composite action and appears as abnormalities in the shear slip between the composite components. The shear slip at the composite interface causes nonlinearity in the global composite beam response which is an issue beyond the inherent complexity of the composite system. This paper presents a novel approach for damage detection of SCCs by variational mode decomposition (VMD) of shear slip data. Numerical and experimental studies were conducted on steel-concrete composite beams to generate noise-contaminated shear slip data from undamaged and damaged states of the structure. The VMD algorithm is employed to decompose shear slip signals into intrinsic mode functions (IMFs) and then, the center frequency of each mode is captured. The higher center frequency realized in the second mode is taken as a damage sensitive feature. Because IMFs curves are extracted from the signal splines interpolated between the average of the peaks and troughs, the change of energy in the center frequencies of the undamaged and damaged states can be defined as a damage index. Welch power spectral densities of the IMFs are calculated to further investigate changes in the center frequencies of IMFs obtained using the VMD algorithm. The empirical mode decomposition (EMD) technique is also utilized to decompose shear slip signals into IMFs for comparison purposes. The results show that the EMD is not able to detect abnormalities in the shear slip signals affected by damage because of losing information through several mode decompositions and a phenomenon termed mode mixing. However, when the VMD was set to decompose the signal into two IMFs, it was found that it is more efficient in maintaining the frequency content of the shear slip signal. According to the results, the proposed method has been proved successful in detecting damage of composite beams and can be employed as a reliable and robust technique.

Adaptation of Optokinetic Reflex by Training with Different Frequency and Amplitude.

Although the occurrence of optokinetic reflex (OKR) adaptation after OKR training is well established, the dynamic properties of OKR adaptation has not been fully studied. This study aimed to examine the difference in the amount of OKR adaptation according to OKR training protocols which have different frequency or amplitude of drum oscillation. Using C57BL/6N male mice, we induced OKR adaptation by 3 different categories of learning paradigm as follows: (1) Optokinetic drum oscillation for 60 min with same amplitude and different frequency. (2) Optokinetic drum oscillation for 60 min with same frequency and different amplitude. (3) Training with serial combination of different frequency or amplitude. The results show that the amount of OKR adaptation was greater after OKR training with lower frequency or amplitude than that with higher frequency or amplitude. This finding may suggest that the retinal slip signal with lower-velocity OKR stimulation serves as more precise instructive signal for learning, leading to induction of more efficient training effect. Another interesting finding was that the OKR gain increase tended to be greater after training composed of sequential combination of decreasing frequency or amplitude than that composed of sequential combination of increasing frequency or amplitude. Furthermore, the OKR training with high frequency or amplitude eliminated a part of learning effects which have already formed by previous training. We postulate that the stimulation during training with high frequency or amplitude may implement a disturbing instruction for OKR learning when it is conducted in mice with increased OKR gain after previous OKR training.

Fluid-injection-induced earthquakes characterized by hybrid-frequency waveforms manifest the transition from aseismic to seismic slip

Aseismic slip loading has recently been proposed as a complementary mechanism to induce moderate-sized earthquakes located within a few kilometers of the wellbore over the timescales of hydraulic stimulation. However, aseismic slip signals linked to injection-induced earthquakes remain largely undocumented to date. Here we report a new type of earthquake characterized by hybrid-frequency waveforms (EHWs). Distinguishing features from typical induced earthquakes include broader P and S-pulses and relatively lower-frequency coda content. Both features may be causally related to lower corner frequencies, implying longer source durations, thus, either slower rupture speeds, lower stress drop values, or a combination of both. The source characteristics of EHWs are identical to those of low-frequency earthquakes widely documented in plate boundary fault transition zones. The distribution of EHWs further suggests a possible role of aseismic slip in fault loading. EHWs could thus represent the manifestation of slow rupture transitioning from aseismic to seismic slip.

Development of a Nuclear Energy Spectrum Signal Generator

A digital nuclear pulse and digital nuclear energy spectrum signal generator was designed using FPGA and digital frequency synthesizer (DDS). It also includes slip signal, triangle wave, square wave, sine wave output. By randomly sampling the amplitude information and time information of the reference spectrum line, the complex algorithm of nuclear signal reproduction is avoided, and the simulation of the nuclear signal random pulse and nuclear energy spectrum (137Cs gamma spectrum) is realized. The signal amplitude is adjustable from 0.1V to 10V, and the frequency is adjustable from 10Hz to 10kHz.

Differential effects of inferior olive lesion on vestibulo-ocular and optokinetic motor learning.

The combined operation of optokinetic reflex (OKR) and vestibular-ocular reflex (VOR) is essential for image stability during self-motion. Retinal slip signals, which provide neural substrate for OKR and VOR plasticity, are delivered to the inferior olive. Although it has been assumed that the neural circuitry and mechanisms underlying OKR and VOR plasticity are shared, differential role of the inferior olive in the plasticity of OKR and VOR has not been clearly established. To investigate the differential effect of inferior olive lesion on OKR and VOR plasticity, we examined the change of OKR and VOR gains after gain-up and gain-down VOR training. The results demonstrated that inferior olive-lesion differentially affected cerebellum-dependent motor learning. In control mice, OKR gain increased after both gain-up and gain-down VOR training, and VOR gain increased after gain-up VOR training and decreased after gain-down VOR training. In inferior olive-lesioned mice, OKR gain decreased after both gain-up and gain-down VOR training, and while VOR gain did not significantly change after gain-up VOR training, VOR gain decreased after gain-down VOR training. We suggest that multiple mechanisms of plasticity are differentially involved in VOR and OKR adaptation, and gain-up and gain-down VOR learning rely on different plasticity mechanisms.

Separating Sea and Slow Slip Signals on the Seafloor

AbstractSeafloor pressure measurements hold promise for estimating vertical displacements from transient slow slip events on submarine faults. We assess the accuracy of pressure offset estimates that evolve over days to weeks and the confidence with which they may be attributed to tectonic deformation or to the ocean water column. One common approach to resolve this ambiguity assumes water column pressures vary insignificantly over the study region and are represented by stable reference site pressures. Assessing the validity of this assumption requires independent evidence. Correlations between pressures and colocated temperatures collected during the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip experiment suggest temperatures might provide a useful independent proxy for water column pressures. We compared offsets estimated using several methods, with temperature and other proxies. The use of a temperature proxy was unsuccessful, because seafloor temperatures did not track the seasonal signal that contributes significantly to seafloor pressure changes over the slow slip event period. Regardless of the estimation method, offsets varied within a few cm around some uncertain reference level. Commonly used statistical measures are shown not to be reliable indicators of offset accuracy since offsets contribute minimally to the total variance. Offsets estimated using identical methods but with seafloor pressures simulated using a regional ocean model were larger than those derived from the data but had a similar pattern. Since the model simulates only water column processes, this suggests a significant fraction of the estimated pressure offsets are due to seasonal water column signal and are not of tectonic origin.

Slip signal analysis on a Baxter robot

Abstract The Baxter robot by ReThink Robotics is a dual arm collaborative platform, which can perform multiple tasks and is designed for use in an unstructured environment. Such robotic manipulators working in tandem have certain advantages over single arms when manipulating heavy or large, awkwardly shaped objects. With the attachment of two custom 3D-printed end-effectors, the robot gains the ability to push and hold objects of this kind. This paper deals with the preliminary steps in creating a reliable controller feedback signal using the robot’s on-board torque and positioning sensors. Determining the best joint signal and designing a suitable filter are two challenges that are addressed. The paper concludes that the torque values from the centre wrist joint undergo the largest increase in value caused by vibrations during slip. A filtering array technique is also proposed, successfully removing unwanted noise from the torque signal, allowing slip events to be effectively isolated.

An investigation on speed measurement method of hermetic compressor based on current fluctuation

As an important parameter of hermetic compressor, the speed value has direct effects on the cooling capacity, control performance and power consumption of the refrigeration system. Therefore, modern refrigeration industry has put forward higher requirement for measuring the speed of the compressor. Conventional speed measurement methods are based on shell vibration and discharge pressure fluctuation. However, shell vibration-based methods require more elaborate instrumentation, leading to more complex and expensive procedure, as well as unsatisfied accuracy. Discharge pressure fluctuation-based methods can destruct mechanical structure and influence the state of fluid flow. This paper proposed a measurement method based on slip signal and presented a Hilbert transform-based algorithm to improve the extraction accuracy and real-time measurement, and to reduce the complexity of the measurement system. Compared with the standard measurements generated by the compressor with encode, under the 1 s sampling time, it is possible to reach a maximum error smaller than ± 1 rpm, which can prove broad application prospect in the refrigeration industry.

A Novel Approach to Control the Robotic Hand Grasping Process by Using an Artificial Neural Network Algorithm

AbstractThis paper presents an artificial neural network (ANN) trained on the patterns of slip signals; these patterns were generated by using conventional sensors with a novel design of fingertip mechanism for detecting the slippage of a grasped object under different types of dynamic loads. This design is to be used with an underactuated triple finger artificial hand based on the pulleys-tendon mechanism. The grasped object is designed in a prism shape with three direct current motors with unbalance rotating mass to generate excitation in the object. Also, this object is covered with different types of surface materials, namely, spongy rubber, glass, and wood. Three types of external loads are used to disturb the grasping process represented by quasi-static pulling on the object, the dynamic load on the object, and on the artificial arm in separate form. The mathematical modeling has been derived for the proposed design to generate the signal of contact force components ratio through using the conventional sensor signals with the aid of Matlab-Simulink software. The ANN has been trained on the basis of the patterns of force component ratio signals at slippage occurrence, in order to detect slippage and then prevent it without the need for any knowledge about the surface properties of the grasped object. The experimental results are discussed in comparison with the physical aspect of the slippage phenomenon, and they show good agreement with the physical definition of the slippage phenomenon. In addition, the network evaluation results are discussed with different parameters that govern the controller operation, such as network error, classification efficiency, and delay in response time.

A SIMULATION MODEL FOR ROBOT’S SLIP DISPLACEMENT SENSORS

This paper deals with a simulation model of slip displacement sensors for the object slip signals’ registration in the adaptive robot’s gripper. The study presents the analysis of different methods for slip displacement signals detection, as well as authors’ solutions. Special attention is paid to the investigations of the developed sensor with the resistive registration element in rod type structure of sensitive elements, which is able to operate in harsh and corrosive environments. A sensing system for the object slip signals’ registration in the adaptive robot’s gripper with a clamping force correction is developed for proposed slip displacement sensor with multi-component resistive registration elements. The hardware implementation of the sensing system for slip signals’ registration and obtained results are considered in details. The simulation model of the proposed slip displacement sensor based on polytypic conductive rubber is modeled by Proteus software. The intelligent approaches with the use of a field programmable gate array (FPGA) and VHDL-model to the sensing system designing allow to define the slippage direction in slip displacement sensor based on resistive registration elements. Thus, this expands the functionality of the developed sensor.

A Slip Detection and Correction Strategy for Precision Robot Grasping

This paper presents a grasp force regulation strategy for precision grasps. The strategy makes no assumptions about object properties and surface characteristics, and can be used with a wide range of grippers. It has two components, a slip signal detector that computes the magnitude of slip and a grasping force set point generator that acts on the detector's output. The force set point generator is designed to ensure that slip is eliminated without using excessive force. This is particularly important in several situations like grasping fragile objects or in-hand manipulation of thin small objects. Several experiments were conducted to simulate various grasping scenarios with different objects. Results show that the strategy was very successful in dealing with uncertainty in object mass, surface characteristics, or rigidity. The strategy is also insensitive to robot motion.

Development of Polymer Slip Tactile Sensor Using Relative Displacement of Separation Layer

To realize a robot hand interacting like a human hand, there are many tactile sensors sensing normal force, shear force, torque, shape, roughness and temperature. This sensing signal is essential to manipulate object accurately with robot hand. In particular, slip sensors make manipulation more accurate and breakless to object. Up to now several slip sensors were developed and applied to robot hand. Many of them used complicate algorithm and signal processing with vibration data. In this paper, we developed novel principle slip sensor using separation layer. These two layers are moved from each other when slip occur. Developed sensor can sense slip signal by measuring this relative displacement between two layers. Also our principle makes slip signal decoupled from normal force and shear force without other sensors. The sensor was fabricated using the NBR(acrylo-nitrile butadiene rubber) and the Ecoflex as substrate and a paper as dielectric. To verify our sensor, slip experiment and normal force decoupling test were conducted.

Re-gripping mission based on analysis of slip signals for a robotic hand model

Re-gripping mission based on analysis of slip signals for a robotic hand model

Cycle slip detection and repair based on Bayesian compressive sensing

The presence of cycle slips corrupts the carrier phase measurement which is critical for high precision global navigation satellite system static or kinematic positioning. The process of cycle slips is comprised of detecting the slips, estimating its exact integer and making a repair. In this paper, a novel approach to cycle slip detection and repair based on Bayesian compressive sensing is proposed, in order to reduce the noise effects on the performances of cycle slip detection and repair. Unlike traditional cycle slip detection and repair methods, we exploit the sparse property of the cycle slip signal, aiming to obtain the perception matrix and establish the sparse cycle slip detection model. Then in order to estimate and repair the value of cycle slips, the residuals of carrier phase double difference and the interference noise between multiple satellites, when more than one satellite has cycle slips, are taken into consideration, which is used as prior information to obtain the likelihood expression for cycle slip signal. Finally, we use the prior information about signals based on relevance vector machine principle derived from sparse Bayesian learning to predict cycle slip distribution and then estimate the value of cycle slips. The novel approach is tested with the actual collection of satellite data in the experiment. It is shown that the novel approach proposed in this paper can effectively estimate cycle slips and achieve better performance than orthogonal matching pursuit and l1 norm based algorithm when the redundancy of carrier phase is large enough. In the case of single frequency carrier phase observation, when redundancy is not less than 7, the novel approach can completely detect and repair cycle slips; in the case of dual-frequency carrier phase observation, when cycle slips happen in four of the eight satellites, 97.6% probability of accuracy is accomplished by the new approach.