Brush Model Research Articles

Dry brush model for robotic painting

Dry brush model for robotic painting

Physically Motivated Model of a Painting Brush for Robotic Painting and Calligraphy

Robot artistic painting and robot calligraphy do require brush models for brushstroke simulation and painting robot control. One of the main features of the brush is its compliance, which describes the relationship between the brush footprint shape and the pressure applied to the brush. In addition, during motion, the brush footprint position lags from the brush handle position in a complicated manner. To date, the question of creating a physically correct model of these effects and choosing the best method for the model parameter calibration has not been presented in the literature. In the current paper, we derive equations of the brush contact patch motion, give their closed-form solutions, and investigate three methods for the brush model calibration: capturing brush footprints on a matte glass with a camera, painting calibration brushstrokes, and capturing a brush shape side projection with a camera. As we show, calibration brushstrokes give us primary information on brush contact patch displacement during painting, and capturing the brush side projection allows the accurate estimation of the gap from the brush tip to the center of the contact patch. Capturing brush footprints is useful for creating a brushstroke executable model. As an example, a model for a round artistic brush was created and verified in three tests, including measuring the coordinates of an angular brushstroke center line, simulating an angular brushstroke, and writing a signature using a robotic setup.

Estimation of Road Adhesion Coefficient Based on Camber Brush Model

Electric vehicles, with their distinct power systems, weight distribution, and power control strategies compared to traditional vehicles, influence the pressure distribution in the tire contact area, thereby affecting the estimation of road adhesion coefficient. In electric vehicle research, tire adhesion coefficient serves as a measure of the frictional force between the vehicle and the road surface, directly impacting the vehicle’s handling performance. The accurate estimation of the adhesion coefficient aids drivers in better understanding the vehicle’s driving state. However, the existing brush models neglect differences in ground pressure distribution along the width direction of tires during tire camber, potentially leading to inaccuracies in adhesion coefficient estimation. This study proposes a camber brush tire model that considers the width-direction pressure distribution characteristics, aiming to enhance the accuracy of adhesion coefficient estimation under camber conditions. Experimental comparisons between the improved and original models reveal a significant enhancement in estimation precision. Consequently, the findings of this study provide valuable insights for deepening our understanding of tire camber dynamics and for designing control systems for electric vehicles, thereby improving vehicle stability and safety.

B-BSMG: Bézier Brush Stroke Model-Based Generator for Robotic Chinese Calligraphy

In robotic Chinese calligraphy, the brush stroke training models for Chinese hairy brushes play a crucial role in stroke generation. The method of combining end-to-end techniques and physical models requires further study, however, it is difficult to obtain large amounts of brush strokes for deep learning and training. To overcome this, we propose using a simulated brush model to train a generator based on the Bézier brush stroke model generator (B-BSMG), which was formed by two symmetric cubic Bézier curves according to the physical characteristics and writing posture of the brush. The B-BSMG can generate images for deep learning and training using a dataset simulated by the Bézier brush stroke model. Our renderer is based on parameterized brush strokes, providing a better foundation for deep learning or robotic writing. The results of several experiments prove that the proposed B-BSMG can generate stroke graphics well and outperforms other advanced stroke models.

A physical tire model for real-time simulations

We present a novel tire brush model with carcass flexibility, primarily designed for real-time applications while preserving the physical significance of its parameters. The tire’s geometry is discretized and represented using a series of ribs, each intersecting the local road surface independently, on the other hand carcass in-plane fore-aft displacement, in-plane deflection, and out-of-plane sidewall torsion are approximated through a second-order polynomial. Forces and torques originating from the tire–road contact area are described using brush mechanics, where bristles’ kinematics is directly linked to carcass deformation. Extensive effort is dedicated to understanding the possible sources of instability, as well as describing and implementing a robust numerical scheme to effectively solve the nonlinear system of equations arising from the modeling. Timing performance results are provided to demonstrate the suitability of the presented model for demanding hard real-time simulations. Finally, validation of the presented tire model is carried out by fitting experimental data and comparing it with the state-of-the-art Magic Formula model, proving its reliability and accuracy in reproducing tire behavior.

Simulation analysis of local temperature field of electric propulsion slip ring

The temperature at which the carbon brushes and the structure of the rings in the electric propulsion slip ring operate has a crucial influence on the safe and reliable operation of the ship. In order to control the temperature of the local structure of the electric propulsion slip ring, this study established a carbon brush and ring piece model through finite element simulation analysis and designed a five-factor, four-level orthogonal test to derive the sensitivity of the final temperature influence factor: initial temperature > current > wind speed > pressure > speed; the optimal combination of parameters is obtained: initial temperature 35 °C, pressure 25 N, speed 5 rpm, wind speed 0.20 m/s, and current 40 A, and the optimal parameters are substituted for the temperature field simulation. The results show that the relatively large area of temperature is distributed on the carbon brushes with a maximum value of 58.3 °C, which is relatively reasonable in size and distribution; the relatively large area of potential is distributed on the carbon brushes, the maximum value of which is 0.3V The entire potential distribution is symmetrical, indicating a reasonable current path; the relatively large area of current density distribution is on the carbon brushes with a value of 64.7 A/cm2, the entire current density distribution is symmetrical and corresponds to the potential distribution, which, together with the frictional rotation, corresponds to the temperature distribution, indicating that the simulation results have a certain degree of reliability.

Coordinated Longitudinal and Lateral Motion Control for Distributed Drive Electric Vehicles With Mechanical Elastic Wheels

The distributed drive electric vehicle (DDEV) with active front wheel steering is an over-actuated system. For such a system, more optimization targets should be considered to make the system better in addition to meeting the driving command of drivers and keeping the vehicle stable. The slip energy generated by excessive tire slipping reduces the utilization of the output energy of the motor, resulting in a reduction of electric vehicle mileage. In order to improve the vehicle performance, a coordinated longitudinal and lateral controller is designed for DDEV with mechanical elastic wheels (MEWs). The motion control layer of the hierarchical controller adopts the integral sliding mode control (ISMC) to determine the desired longitudinal force, lateral force and yaw moment as virtual inputs of the vehicle. Then, a novel tire force distribution strategy is proposed to dynamically assign the virtual inputs among front wheels and four motors with the goal of optimizing the vehicle stability and longitudinal tire slip energy dissipation. To characterize tire slip energy more accurately, the brush model matching MEW is deduced in the combined slip conditions. The proposed controller is evaluated on the hardware-in-the-loop (HIL) test platform under different driving conditions. Simulation results demonstrate that this controller not only ensures the vehicle handling stability performance, but also improves the utilization of motor output energy and reduces tire wear.

Investigation of drivetrain dynamics on low-μ ground using the brush model

Investigation of drivetrain dynamics on low-μ ground using the brush model

Investigation of drivetrain dynamics on low-μ ground using the brush model

Investigation of drivetrain dynamics on low-μ ground using the brush model

Online tire model iterative learning considering tire relaxation behavior

Online tire model learning is of great importance in the application of vehicle dynamics related automated driving functions. Previous research mainly focuses on static tire model identification, for example, based on brush model. However, tire transient behavior, which is difficult to measure directly, plays a critical role on vehicle lateral dynamics, especially on safety-critical handling conditions. In this work, we propose a framework for online tire model iterative learning considering tire relaxation. In each steering scenario, we utilize the learning results of tire model from previous ones as initial condition. Subsequently, we implement singular value decomposition to detect whether there is enough excitation for model learning update with different simplified tire relaxation models. Meanwhile, based on these models, we also recursively calculate and compare the least squares cost function, such that the tire parameters can be robustly estimated and optimized. Furthermore, the estimated tire parameters are then fused with those from previous scenarios based on recursive average for better control application in the next steering maneuver. Experiments demonstrate the proposed online tire model iterative learning framework has similar performance with large-scale data-based offline fitting and can be applied for better predicting tire forces than those with purely recursive least squares methods.

An analytical solution for friction coefficients of grooved pavements considering tire rubber-groove interaction

To reduce the loss of skid resistance of pavement in wet weather, pavement grooving is used to improve aircraft operation safety on runways. This study presents an analytical solution to analyze mechanical interactions between tire tread rubber and pavement surface grooves for calculating friction coefficients of aircraft tires on runway pavements. The energy dissipation theory is utilized to calculate the contribution of rubber-groove interlock and the friction on plane part of pavement surface due to surface texture is accounted using Brush model. The comparison of model results and field measurements proves the capability of the proposed method to predict friction coefficients of aircraft tire on runway pavements with various groove configurations. The evaluation of trapezoidal grooved pavement shows similar friction coefficients compared to the standard square grooved pavement regulated by the Federal Aviation Administration (FAA). The friction coefficients of grooved pavement vary depending on the inclined angles of groove and edge-to-edge spacing that are two important geometry parameters. The findings demonstrate the pronounced influences of rubber deposits and groove deterioration on skid resistance of runway pavements. The analysis results can be further used to design optimized groove configuration and determine maintenance threshold for safe operation of aircraft on runways.

Mechanical Way To Study Molecular Structure of Pericellular Layer.

Atomic force microscopy (AFM) has been used to study the mechanical properties of cells, in particular, malignant cells. Softening of various cancer cells compared to their nonmalignant counterparts has been reported for various cell types. However, in most AFM studies, the pericellular layer was ignored. As was shown, it could substantially change the measured cell rigidity and miss important information on the physical properties of the pericellular layer. Here we take into account the pericellular layer by using the brush model to do the AFM indentation study of bladder epithelial bladder nonmalignant (HCV29) and cancerous (TCCSUP) cells. It allows us to measure not only the quasistatic Young's modulus of the cell body but also the physical properties of the pericellular layer (the equilibrium length and grafting density). We found that the inner pericellular brush was longer for cancer cells, but its grafting density was similar to that found for nonmalignant cells. The outer brush was much shorter and less dense for cancer cells. Furthermore, we demonstrate a method to convert the obtained physical properties of the pericellular layer into biochemical language better known to the cell biology community. It is done by using heparinase I and neuraminidase enzymatic treatments that remove specific molecular parts of the pericellular layer. The presented here approach can also be used to decipher the molecular composition of not only pericellular but also other molecular layers.

Transient tyre models with a flexible carcass

ABSTRACT The accuracy of transient tyre models may be largely improved by considering the flexibility of the tyre carcass. Several formulations, whereby the unsteady behaviour of the tyre is approximated using linear or nonlinear systems of ordinary differential equations (ODEs), are already available in the literature. However, when the tread behaviour is described using a distributed representation, that is, in terms of partial differential equations (PDEs), the inclusion of even the simplest model to represent the deformation of the tyre carcass leads to rather involved PDE or interconnected PDE-ODE systems, with nonlocal and boundary terms. Such descriptions require detailed analyses that have not been attempted so far. Therefore, this paper investigates the salient properties of the classic brush and LuGre-brush models considering the effect of a flexible carcass. For both formulations, the existence and uniqueness of the solution are discussed. For the standard version of the brush models, a closed-form solution is provided under the assumption of vanishing sliding, whereas the case of limited friction is explored only qualitatively. Concerning the LuGre-brush variant, the preliminary intuition gained from the analysis of the distributed representation is effectively used to develop approximated lumped formulations to be used in control-oriented applications.

Study on the Influence of Environmental Conditions on Road Friction Characteristics

This study focuses on changes in the friction characteristics of paved roads under various conditions from the viewpoint of traffic safety. In general, the braking characteristics of road vehicles are examined using the μ–s characteristics of the tires. Therefore, in our research, we used three types of limited datasets and identified them using the Magic Formula proposed by Prof. Pacejka. Based on various experiments, it was shown that changes in the road surface environment, such as dry and wet conditions, significantly affect the μ–s characteristics, and this influence varies significantly depending on the pavement conditions. In this study, as the first stage of the analysis of these influences, it was clarified that the difference in the friction characteristics of wet and dry road surfaces varies significantly depending on the pavement surface, which is based on experimental results obtained using actual roads. As this variation is closely related to the safety of actual road traffic, we used a brush model, which is a dynamic model of the road surface and tires, to clarify the differences in this characteristic.

Effect of carbon black components on rolling mechanical properties of tread rubber material by using improved digital image correlation

AbstractThe rolling and sliding state of the tread rubber material within contact patch was very important to the handling stability and safety of the vehicle. In this paper, first, the absolute coordinate system was introduced into the digital image correlation method, which improved the ability of the traditional digital image correlation method to solve the large deformation of polymer material surface. Second, a new calculation method of rolling friction coefficient based on the brush model was proposed. Third, a non‐contact full‐field rolling dynamics experimental device was developed to study the effects of carbon black components, rotational speed and vertical load on the rolling mechanical characteristics of tread rubber material. On this basis, the rolling mechanical characteristics of tread rubber material with different formulations were obtained by analyzing the distribution properties of global strain rate, full‐field longitudinal speed and full‐field longitudinal acceleration and the variation laws of transverse/longitudinal strain rate, trajectory of marked points, stress‐strain hysteresis curve and rolling friction coefficient. Finally, the influence mechanism of carbon black composition on rolling mechanical properties of tread rubber material was revealed.

Thermomechanical Modeling of Aircraft Tire–Runway Contact for Transient Maneuvers

ABSTRACT The aircraft tire is the link between the aircraft and the runway and transmits forces and moments within the contact area. During ground maneuvers, the tire is exposed to a wide range of operating conditions. The tires support the weight of the aircraft, they ensure safe rolling during taxiing, and they transfer the required forces to the runway during takeoff and landing. Temperature development during these maneuvers is of great importance because temperature can affect both material stiffness and friction behavior as well as wear characteristics. Heat is generated inside the tire due to energy dissipation caused by the cyclic loading of the tire during rolling. In addition, heat is generated due to friction in the tire–runway contact. Experimental measurements of the temperature distribution in the entire tire are not yet possible. The tire temperatures can only be determined at selected critical spots. Simulation models can help to obtain a better understanding of the overall tire temperature distribution during transient maneuvers. In this work, the transient thermomechanical processes of a rolling aircraft tire, e.g., directly following the touchdown process or during taxiing, are modeled based on a simple physical tire model. An extended brush model is used to simulate the contact forces. The tire temperature is determined via the transient heat conduction equation in radial and circumferential directions. The mechanical and thermal models are coupled via the coefficient of friction and the sliding velocities in contact. The free model parameters are parameterized using experimental data, and the overall model is validated by measurements on the whole tire. The validated thermomechanical tire model is used for simulations or the analysis of different driving maneuvers to get a better understanding of the temperature development in the aircraft tire.

Robotic Writing of Arbitrary Unicode Characters Using Paintbrushes

Human handwriting is an everyday task performed regularly by most people. In the domain of robotic painting, multiple calligraphy machines exist which were built to replicate some aspects of human artistic writing; however, most projects are limited to a specific style of handwriting, often Chinese calligraphy. We propose a two-stage pipeline that allows industrial robots to write text in arbitrary typefaces and scripts using paintbrushes. In the first stage, we extract a set of strokes from character glyphs which are similar to how humans choose strokes during writing. In the second stage, we generate corresponding brush trajectories by applying a brush model to the extracted strokes. Our brush model computes the required brush pressure to achieve the given stroke width while also accounting for brush lag. We also present a method to automatically measure the parameters needed to predict brush lag by painting and recording calibration patterns. Our method generates trajectories for text in any given typeface, which, when executed by a robotic arm, results in legible written text. We can render most writing systems, excluding emoji and ligatures, in which arbitrary texts can be specified to write.

An integrated analytical model for friction characteristics of aircraft tire on wet runway pavement

The challenging issues of tire-water-pavement interaction are to determine the deformed tire profile and the effective tire-pavement contact length due to water intrusion. This study aims to develop an integrated analytical model to analyze friction characteristics of an aircraft tire on wet runway pavement. The tire-water-pavement interaction model consists of the Brush model for tire-pavement contact and the flexible ring model for tire deformation with consideration of hydrodynamic force. The feasible contact footprint and the deformed tire profile are solved using an interactive process between two models. The model shows the ability to predict friction coefficients at various tire loading, velocity, slip ratio, and water conditions. The thicker water film depth causes the reduction of tire-pavement contact length and the increases of hydrodynamic force, resulting in poor skid resistance of pavement. The calculated friction coefficients at different velocities are further used to predict hydroplaning speed and calculate braking distance of aircraft tire. The results demonstrate the significant effect of water depth on the risk of aircraft hydroplaning and overrun on runway pavement.

Molecular dynamics simulations of the nickel removal from crude oil by neutral and charged spherical polymer brushes

Nickel in crude oil adversely affects the refining process for rapidly deactivating the hydrogenation and cracking catalysts. Polymer brushes bearing high-density ligands have shown promising nickel removal ability. In this work, submicron polybutadiene (PB) grafted by polyacrylamide (PAM@PB) was prepared and characterized by the transmission electron microscope, dynamic light scattering, and elemental analysis, which was also compared with the PB latex grafted by polyacrylic acid (PAA@PB) synthesized in our previous work. The nickel removal rates by both brushes were evaluated through the electric desalination process. Theresults show that the nickel removal capacity of PAA@PB is higher than that of PAM@PB. By the molecular dynamics simulations, the stretching and competitive chelation of polymer brush models PAA@PB-M and PAM@PB-M were investigated. Charged polyacrylic acid brushes usually have a higher thickness layer and a lower ligand density under the electrostatic repulsion and hydrogen bonding. The electrostatic interaction plays a more important role than the van der Waals interactions on nickel removal. PAA@PB-M is more attractive against Ni2+ ions than PAM@PB-M. The inevitable formation of stable sandwiched π-π stacking structures between Ni2+ ions and multiple porphyrin rings causes great difficulty in nickel removal during the electric desalination process. Adding protons to the oil phase can reduce the formation of the sandwiched structures and further improve nickel removal rates. In this paper, molecular dynamics simulation is innovatively applied to the mechanism of demetallization of polymer brushes, revealing the differences in structure and demetallization between charged and neutral polymer brushes, which provides guidance for the design of core–shell polymer brushes with high demetallization efficiency.

Graphics processing unit‐accelerated high‐quality watercolor painting image generation

AbstractStroke‐based rendering is a rendering method that mimics the actual painting technique by drawing a stroke by stroke on a blank canvas image. In this paper, we propose a watercolor image generation method using stroke‐based rendering. The proposed method generates an image that is a good approximation of the input image as well as having the characteristics of a watercolor painting by repeatedly painting strokes while referring to the input image. To generate a high‐quality image, that is, an image that closely resembles an actual watercolor painting, various techniques are employed: modeling of watercolor paper, detailed physical simulation of the movement of water and pigment, strokes using a brush model, among others. The proposed method generates a large number of strokes and performs computationally intensive watercolor simulations for each stroke. Therefore, this paper also presents its parallel algorithm using a Graphics Processing Unit (GPU). We implemented this parallel algorithm on an NVIDIA A100 GPU. The experimental results show that the CPU implementations with sequential and parallel executions take 34,651 and 867 s to generate a 4K‐watercolor image of size , respectively. In contrast, the GPU implementation with parallel execution succeeded in reducing the time to 44 s.