Non-contact Regimes Research Articles

Incipient fault diagnosis for robot manipulators based on evolution of friction characteristics in transmission components

Abstract The tribological behavior can be informative about the incipient faults of robot manipulators. This study explores the evolution of friction characteristics from cold start to thermal equilibrium through a series of steady-state friction experiments. Based on these experimental observations, a friction-based fault diagnosis framework is proposed. The fault diagnosis process primarily involves defining the healthy state, decomposing friction curves and their features, and anomaly detection. Given the dependence of friction characteristics on different sources of faults, the parameters of steady-state experimental friction model are divided into two categories: one associated with contact interactions and the other related to non-contact regimes. Subsequently, confidence regions corresponding to distinguishable friction characteristics are independently constructed. These regions encapsulate the statistical description of the healthy state, characterized by mean values and the covariance of the friction characteristic parameter vectors during the unloaded state. In addition, we conduct experiments that consider the influence of applied loads on friction behavior. These experiments serve as a test set for comparison against nominal statistics. Leveraging the similarity between the effects of wear and load on friction, we introduce equivalent load thresholds to assess the severity of joint degradation. The results demonstrate the feasibility of employing confidence region views based on friction characteristic classification for fault detection and isolation.

Numerical simulation of single bubble motion along inclined walls: A comprehensive map of outcomes

The bubble interactions with a wall affect many industrial application's performance. The single bubble rising in a stagnant fluid is studied next to an inclined wall. The two phases are incompressible, and the interface between phases is captured with the volume of fluid (VoF) method. The influence of various parameters such as wall slope (θ), contact angle (φ), and dimensionless numbers (Morton and Bond) on the bubble-wall regime is investigated. The numerical results (bubble shape and terminal velocity) are validated with experiments.After comprehensive numerical simulation over a wide range of Bond (1≤Bo≤40) and Morton (2.54×10−11≤Mo≤1×100) for inclined walls (0∘<θ<90∘), three bubble-wall interaction regimes: sliding, intermittent and non-contact are proposed and a regime map is plotted. We recognized two sliding regimes based on Bond numbers at small inclined walls (θ≤30∘). In the sticking sliding regime (Bo≤5), bubbles remain attached to the inclined wall. They make the wall dry along their path. But at higher Bond in film sliding, bubbles slip over a thin liquid film. Thus, the wall surface is always wet. The film thickness is linearly proportional to bubble diameter. Non-contact regimes occur at steep walls (θ≥70∘), where the bubble never touches the wall. In moderate wall slopes (30∘<θ<70∘), a bubble repeatedly impacts on and rebounds from the wall. The intermittent regime is an unstable regime, and it alters to a sliding or a non-contact regime based on Bond and Morton numbers.

The Influence of Bout Duration and Rule Modification in Small-Sided Games

PURPOSE: Small-sided games (SSG) are an established training method to develop aerobic capacity in team sports (1). However, there is still a lack of knowledge about the variety of variables that influence the outcomes of SSG (2). Therefore, the present study was designed to investigate the influence of changes in bout durations and rules on physiological and technical parameters in men’s lacrosse. METHODS: Data of 12 elite male Austrian lacrosse athletes were collected. Prior to the intervention athletes maximum heart rate (HR) and aerobic capacity was evaluated. According to results athletes were assigned to 4 even strength teams. Each team participated in 8 SSG training sessions. SSG consisted of 3 vs. 3 self-regulated match-play on a basketball field with small goals at the end lines. Each team performed two sessions of two different bout (3x6 and 6x3-minute) and rule modification (body/non-body contact) regimes. %HRmax for total session time, time spent in 4 different HRzones, rating of perceived exertion (RPE), and technical actions were collected. Statistical significance was set at p ≤0.05 and for an estimate of effects Cohen’s ES was calculated. RESULTS: Physical and technical parameters showed no difference nor effect between different bout regimes (BR). On the other hand, non-contact regimes (NCR) had lower RPE (15.8 ±0.3; p= 0.01; d= 2.04 ±1.56) values, but didn’t show difference in %HRmax for total sessions. NCR spent more time in HRzone 2 (128.0 ±26.5s; p= 0.04; d= 1.37 ±1.32) and 3 (245.4 ±77.0s; p= 0.05; d= 1.41 ±1.56) compared to the contact regime (CR). Similarly, number of total events (761.5 ±56.3; p= 0.00; d= 2.92 ±1.74), passes (254.3 ±26.7; p= 0.00; d= 2.39 ±1.34), and shots (47.3 ±9.0; p= 0.04; d= 1.51 ±1.62) were higher in NCR. CONCLUSION: The findings show no influence on technical and physical parameters between different BR. Further, rule modifications show effects on intensity and technical actions in SSG. Results indicate less intensity (time spent in HRzones and RPE) and more technical actions when no-body contact is allowed. According to the findings, we recommend to implement NCR into sport specific lacrosse training programs to change the outcome of SSG sessions. REFERENCES: 1) Halouani et al. (2014). J Strength Cond Res, 28(12), 3594-3618. 2) Hauer et al. (2018). PLoS ONE 13(10): e0203832

Autodyne effect in a single-mode Er fibre laser and the possibility of its usage for recognising the evaporated biotissue type

The autodyne signal arising in an Er fibre laser in the course of evaporating biological models of different types is studied and the possibility of recognising the biotissue type using the method of autodyne detection of the backscattered Doppler signal is assessed. In the experiments we modelled the process of surgical intervention using the contact (hole perforation with the Er laser fibre) and noncontact (surface evaporation with the focused radiation) regimes of impact on different biological models. The amplitude – frequency characteristic of the autodyne detection for the Er fibre laser is measured and the initial spectra of the backscattered Doppler signal arising under the action of laser radiation on the samples of biological models are obtained. The experiments have shown that the spectra of the backscattered Doppler signal, arising in the course of the contact and noncontact action of the Er fibre laser on different biological models, demonstrate clear-cut distinctions.

Behavior of a water drop impinging on heated porous surfaces

In this work, thermal and hydrodynamic behavior of a water drop impinging on heated porous surfaces was investigated experimentally. Four porous substrates having different permeability and surface roughness were prepared by sintering small glass beads with different sizes and the surface temperature was varied from 60°C to 300°C. The impinging velocity was varied from 0.8m/s to 2.3m/s while the drop diameter was fixed at 2.6mm. Two primary impingement regimes were identified: contact and non-contact regimes, each in the low and the high temperature ranges, respectively. The contact regime, in which the drop evaporated or boiled while maintaining contact with the surface, was further divided into three sub-regimes: internal evaporation, internal boiling, and surface nucleate boiling. In the non-contact (surface film boiling) regime, the drop was levitated but at the lower wall temperature with the larger-bead substrates due to active nucleation on the rougher surfaces. Larger impinging velocity resulted in higher transition temperature from the contact to the non-contact regimes, which is due to the increase of the impact pressure at the liquid–solid interface. Time variation of the surface temperature consisted of three stages: right after the drop impact, the surface temperature sharply decreased and then increased with time to reach a temporal thermal-equilibrium between the permeated liquid and the porous solid (stage I). Then the surface temperature gradually decreased until the evaporation was completed (stage II), and finally increased up to the initial wall temperature (stage III). The total evaporation time decreased with the higher impact velocity because of the larger spreading and wet-diameter ratios. Also, there was an optimum glass-bead size (of the substrate) to minimize the evaporation time. In summary, the spreading and wet-diameter ratios, and the time for complete permeation turned out to be the major indicators of the cooling performance, which were strongly influenced by both the impact condition and the structural characteristics of the porous substrates.

Simultaneous imaging of surface and magnetic forces

We demonstrate quantitative force imaging of long-range magnetic forces simultaneously with near-surface van-der-Waals and contact-mechanics forces using intermodulation atomic force microscopy. Magnetic forces at the 200 pN level are separated from near-surface forces at the 30 nN level. Imaging of these forces is performed in both the contact and non-contact regimes of near-surface interactions.

Interfacial Adhesive Properties between a Rigid-Rod Pyromellitimide Molecular Layer and a Covalent Semiconductor via Atomistic Simulations

We conducted a comprehensive atomistic simulation study of the adhesive properties of aromatic rigid-rod poly-[(4,4'diphenylene) pyromellitimide] on a dimer-reconstructed silicon surface. We describe the structural developments within the adherent's interfacial region at the atomistic scale, and evaluate the energetics of the adhesive interactions between bimaterial constituents. In particular, we observe a transition between noncontact and contact adhesion regimes as a function of the interfacial bonding strength between the polyimide repeat units and the silicon substrate. This transition is manifest by a three- to four-fold increase in adhesive energy, which is entirely attributable to structural relaxation in the organic layer near the interface, revealing the importance of accurately describing structural details at interfaces for reliable interfacial strength predictions. The underlying molecular reconfigurations in the pyromellitimide layer include preferred orientation of the rigid-rod molecules, molecular stacking, ordering, and the local densification. The role of each of these factors in the adhesive behavior is analyzed and conclusively described. Where possible, simulation results are compared with theoretical model predictions or experimental data.

Imaging stability in force-feedback high-speed atomic force microscopy

We studied the stability of force-feedback high-speed atomic force microscopy (HSAFM) by imaging soft, hard, and biological sample surfaces at various applied forces. The HSAFM images showed sudden topographic variations of streaky fringes with a negative applied force when collected on a soft hydrocarbon film grown on a grating sample, whereas they showed stable topographic features with positive applied forces. The instability of HSAFM images with the negative applied force was explained by the transition between contact and noncontact regimes in the force-distance curve. When the grating surface was cleaned, and thus hydrophilic by removing the hydrocarbon film, enhanced imaging stability was observed at both positive and negative applied forces. The higher adhesive interaction between the tip and the surface explains the improved imaging stability. The effects of imaging rate on the imaging stability were tested on an even softer adhesive Escherichia coli biofilm deposited onto the grating structure. The biofilm and planktonic cell structures in HSAFM images were reproducible within the force deviation less than ∼0.5 nN at the imaging rate up to 0.2s per frame, suggesting that the force-feedback HSAFM was stable for various imaging speeds in imaging softer adhesive biological samples.

Sensitivity and resolution in noncontact electrostatic force microscopy in the case of a constant potential

The basic dynamic equations of the electrostatic force microscope are derived, in the case of a constant potential applied to a spherical tip above a conducting plane sample. The microscope tip moves in the electrostatic field, providing a force supposed to be inversely proportional to the distance. The linear and nonlinear approximations are treated to obtain the amplitude and phase of the vibration, at a fixed frequency. Optimal experiment conditions, i.e., distance, frequency, and voltage, which give the best sensitivity and lateral resolution, are discussed. The stability of the oscillations during the scans is dependent on the experiment conditions. In addition to the tapping regime, we show that two stable noncontact regimes may exist in some conditions. Only one stable noncontact oscillation occurs at a working frequency equal or superior to the natural frequency of the system. When a distance equal to the free amplitude is selected, the phase shift due to the potential is linear in function of the applied potential (instead of quadratic as observed at larger distances) and a good sensitivity to the potential of the sample is obtained. The theoretical lateral resolution is derived in the linear and nonlinear approximations, and is shown to depend strongly on the mean tip-sample distance. In the examples shown, the best resolution values are reached at a very close distance, with values much lower than the tip apex radius.

Simulation of the observability of atomic defects by atomic force microscopy in contact and non-contact modes

Atomic force microscopy (AFM) scans of a crystal surface containing an atomic defect were simulated in both contact and non-contact regimes. When scanning in contact mode near a defect, the tip–sample force interaction experiences bifurcation of the lines of constant force. When the load force is small, the bifurcation causes the tip to be “pushed” out of the defect. However, if scan force is higher than some critical value (dependent upon the composition of the tip and sample) the AFM tip becomes “trapped” in the vicinity of defect. The trapped tip remains at the level of the vacancy and consequently crashes into the sample, as the scan continues. This results in either the tip apex being destroyed, or disruption of the crystal lattice around the defect. Both effects result in the “disappearance” of the defect from the scan images. The trap is intrinsic and cannot be avoided. For the case of non-contact mode, the tip position is driven by the scan force gradient rather than the force. Simulations show that for this case the trap does not exist and atomic defects will not be destroyed. This explains why atomic defects are generally not observed when using contact mode AFM, but are observed in non-contact AFM.

Quantitative analysis of dynamic-force-spectroscopy data on graphite(0001) in the contact and noncontact regimes

We present a comparative experimental and theoretical study of the frequency shift in ultrahigh vacuum dynamic force microscopy at 80 K on graphite(0001) measured as a function of the tip-sample distance for different resonance amplitudes A in the repulsive and attractive regime of the tip-sample forces. The resulting frequency shift versus distance curves scale with ${1/A}^{3/2}$ over the full range. We determined the tip-sample force from the frequency shift versus distance curves and found good agreement with specific force laws for long-range (van der Waals), short-range (Lennard-Jones), and contact (Hertz) forces.

Tip-sample interactions in dynamic force microscopy of polyvinyl alcohol films

Dynamic force microscopy (DFM) was performed in air on ultrathin polyvinyl alcohol (PVA) films. Nominal non-contact and intermittent solid contact regimes are identified in measurements of amplitude and phase as a function of the mean distance from the sample. Evidence suggests that the nominal non-contact regime is divided into two subregimes: true non-contact, in which only long- range attractive forces exist, and intermittent fluid contact, involving brief penetration of the tip into a fluidized zone at the tip-polymer interface. Viscous fluid damping differs among three mesoscopic film components, producing variable 'resistance' to intermittent solid contact. As a result, some com- ponents of the film are imaged in intermittent fluid contact and others in intermittent solid contact, within a single image. Approach-withdrawal amplitude hysteresis correlates with amplitude damping, and is consistent with component-specific surface fluidity (meniscus formation). Differences in surface fluidity are interpreted in terms of relative crystallinity. # 2000 Society of Chemical Industry

Mechanisms of dynamic force microscopy on polyvinyl alcohol: region-specific non-contact and intermittent contact regimes

Dynamic force microscopy (DFM) phase signals were studied using heterogeneous films of polyvinyl alcohol (PVA). The phase was measured as a function of distance and drive frequency over regions of the film with different dissipative properties. When driving below the free resonance frequency at moderate amplitudes, the tip–sample interaction jumps between non-contact and intermittent contact regimes, giving rise to large, region-specific changes in phase within a single image. Amplitude damping largely determines the imaging regime. Resistance to intermittent contact can be overcome by selecting larger drive amplitudes at drive frequencies below the free resonance. Phase contrast then is related primarily to differences in viscoelastic loss. Upon nearing quasistatic contact, viscoelastic loss can produce a transition from intermittent contact to non-contact as the amplitude is heavily damped.

Contact control for advanced applications of light weight arms

Many applications of robotic and teleoperated manipulator arms require operation in contact and noncontact regimes. This paper deals with both regimes and the transition between them with special attention given to problems of flexibility in the links and drives. This is referred to as contact control. Inverse dynamics is used to plan the tip motion of the flexible link so that the free motion can stop very near the contact surface without collision due to overshoot. Contact must occur at a very low speed since the high frequency impact forces are too sudden to be affected by any feedback generated torques applied to a joint at the other end of the link. The effects of approach velocity and surface properties are discussed. Force tracking is implemented by commands to the deflection states of the link and the contact force. This enables a natural transition between tip position and tip force control that is not possible when the arm is treated as rigid. The effects of feedback gain, force trajectory, and desired final force level are of particular interest and are studied. Experimental results are presented on a one-link arm and the system performance in the overall contact task is analyzed. Extension to multi-link cases with potential applications are discussed.