Spray Trajectory Research Articles

Automatic interpolation algorithm for NURBS trajectory of shoe sole spraying based on 7-DOF robot

PurposeThe purpose of this paper is to propose an automatic interpolation algorithm for robot spraying trajectories based on cubic Non-Uniform Rational B-Splines (NURBS) curves, to solve the problem of sparse and incomplete trajectory points of the head and heel of the shoe sole when extracting robot motion trajectories using structured-light 3D cameras and to ensure the robot joints move smoothly, so as to achieve a good effect of automatic spraying of the shoe sole with a 7-degree-of-freedom (DOF) robot.Design/methodology/approachFirstly, the original shoe sole edge trajectory position points acquired by the 3D camera are fitted with NURBS curves. Then, the velocity constraint at the local maximum of the trajectory curvature is used as the reference for curve segmentation and S-shaped acceleration and deceleration planning. Immediately, real-time interpolation is performed in the time domain to obtain the position and orientation of each point of the robot motion trajectory. Finally, the inverse kinematics of the anthropomorphic motion of the 7-DOF robot arm is used to obtain the joint motion trajectory.FindingsThe simulation and experiment prove that the shoe sole spraying trajectory is complete, the spraying effect is good and the robot joint movement is smooth, which show that the algorithm is feasible.Originality/valueThis study is of good practical value for improving the quality of automated shoe sole spraying, and it has wide applicability for different shoe sole shapes.

Depth-camera-based rebar detection and digital reconstruction for robotic concrete spraying

In this paper, we tackle the challenge of detection and accurate digital reconstruction of steel rebar meshes using a set of industrial depth cameras. A construction example under investigation in this paper is robotic concrete spraying, where material is sprayed onto double-curved single layered rebar meshes. Before the spraying process can start, the location and geometry of the rebar mesh needs to be accurately know. We present an automatic image-based processing approach of depth images for grid point extraction at an accuracy of a few mm. Furthermore, we propose a sequence of execution steps in a robotic setup, including the hand–eye calibration, which enables the direct georeferencing of multiple data sets acquired from various poses into a common coordinate system. With the proposed approach we are able to digitally reconstruct a mesh of an unknown geometry in under 10 min with an accuracy better than 5 mm. The digitally reconstructed mesh allows for computation of material needed for its construction, enabling sustainable use of concrete in digital fabrication. The accurately reconstructed digital mesh, generated based on the proposed approach in this paper, is the input for the following spraying step, allowing for generation of accurate spray trajectories.

Theoretical analysis and experimental investigation of flame trajectory of horizontal subsonic jet diesel spray under sub-atmospheric pressure

The safety of a horizontal spray combustion flame and the design of a heating device for a low-pressure area of a plateau have both been widely examined. The shape equation and length of a flame’s trajectory are the two most important indexes. Regardless of the atomization and evaporation process of fuel, the analytical formula of trajectory for a horizontal spray flame supplied by forced swirling air is derived, and the numerical solution is obtained. The variation in flame trajectory and its uplifted characteristics with atmospheric pressure are analyzed theoretically and verified experimentally. The flame trajectory length and its coincidence degree at 0.05 and 0.08 MPa of atmospheric pressure are compared. The results show that the flame trajectories coincide when the rated volume air flow is maintained under different atmospheric pressures. Keeping the same equivalence ratio, the slope of the uplifted trajectory is proportional to the atmospheric pressure. If flame trajectories coincide at any two atmospheric pressures, the ratio of equivalence is the inverse ratio of air density. Finally, based on the air entrainment theory, the flame trajectory length equations for different atmospheric pressures and equivalence ratios are unified. This study is of great theoretical significance to research into low-pressure spray flames and the design of a high-altitude oil burner.

Effect of Cross-Flow Swirl on the Trajectory of Spray in an Annular Passage

Abstract This paper presents the experimental analysis of the impact of swirl number of cross-flowing air stream on liquid jet spray trajectory at a fixed air flow velocity of 42 m/s with the corresponding Mach number of 0.12. The experiments were conducted for 4 different swirl numbers (0, 0.2, 0.42, and 0.73) using swirl vanes at air inlet having angles of 0 deg, 15 deg, 30 deg, and 45 deg, respectively. Liquid to air momentum flux ratio (q) was varied from 5 to 25. High-speed (at 500 fps) images of the spray were captured, and those images were processed using matlab to obtain the path of the spray at various momentum flux ratios. The results show interesting trends for the spray trajectory in swirling air flow. High swirling flows not only lead to spray with lower radial penetration due to sharp bending and disintegration of liquid jet but also result in spray with large spread and spray area. Based on the results, correlations for the spray path have been proposed, which incorporates the effects of the swirl number of the air flow.

Evaporation and mixture formation characteristics of diesel spray under various nozzle hole size and injection pressure condition employing similar injection rate profile

The current work demonstrates investigations of the effects of the nozzle hole size and injection pressure on the diesel spray under evaporating condition. Three single hole injectors with hole diameters of 0.101 mm, 0.122 mm and 0.133 mm were used and their injection rate profiles were shaped in a similar manner. Laser Absorption Scattering technique was implemented in the diesel spray experiments to visualize the vapor phase and measure the mixture concentration. Also, the experimental results were validated with the computational approach. The injection rate profile and initial spray trajectory angle are key inputs for the CFD simulation; thus, careful measurements were taken. The injection rate profiles were measured by Zeuch method and based on the start of injection with the High-speed Video camera frame, the 5 kHz Butterworth low pass filter was applied to the injection rate raw signal. Moreover, the near nozzle field microscopic spray imaging experiments were performed to measure the initial spray trajectory angle. The experimental results show that the 0.101 mm hole diameter injector promotes shorter liquid length, longer vapor length, higher evaporation ratio and higher entrained air mass. The computational results show a reasonable qualitative agreement with the experiments; however, a quantitative discrepancy can be noticed.

Trajectory Planning of Spray Gun With Variable Posture for Irregular Plane Based on Boundary Constraint

In order to solve the problem of low spraying efficiency and excessive paint waste caused by overspray when the robot automatically sprays irregular plane, a method of spray trajectory planning with boundary-constrained considering spray gun changing posture is proposed. The static spraying model of the spray gun with variable posture, and the dynamic spraying model of the spray gun along the arc path are established separately, an optimization method for the symmetry of coating distribution based on the variable spray angle when the gun spraying along the arc path is proposed. Orthogonal experiment method based on numerical simulation is used to clarify the influence of boundary curve shape and spray gun posture on boundary constraint distance, the prediction of the value range of the boundary constraint distance at the boundary of different curvature radius is realized. Within the range of the value of the boundary constraint, combined with the equal division method of the plane intercept line and the distance search method, a boundary constraint spray path generation algorithm is established by setting a uniform boundary constraint distance value. Finally, a multivariable spraying parameter optimization algorithm based on PSO is established, the spraying velocity, spraying height and spraying angle in the dynamic spraying process are solved, and the coating uniformity is optimized. The effectiveness and feasibility of the proposed spray trajectory planning method is verified by robot spraying experiment for any irregular plane.

Influence of spray trajectories on characteristics of cold-sprayed copper deposits

Industrial robots are widely used in cold spray (CS) as well as thermal spray to produce various coatings by precisely controlling kinematic parameters during the process. However, the robot trajectory and its effect on the characteristics of CS deposits are important, but not fully studied. This article introduces four typical spray trajectories, including zigzag path, cross path, parallel path, and spiral path, to elaborate thick CS Cu deposits, and characterizes the corresponding Cu deposits, respectively. The experimental results revealed that the spray trajectories have a major influence on the associated thermal history and the residual stress distribution. However, no significant differences were found by the comparisons of microstructures and mechanical properties. In addition, due to high-velocity impact and extensive deformation of particles during the CS process, the as-sprayed Cu coating presented anisotropic characteristics that influenced the performances in different directions. The post heat treatment (PSH) cannot eliminate this characteristic but improves the mechanical performances to a certain extent. Therefore, reasonable planning of CS trajectory is an indispensable condition for obtaining a desirable coating.

Discharge current of water electrospray with electrical conductivity under high-voltage and high-flow-rate conditions

Recently, several attempts have been made to implement electrospray for electrostatic precipitators (EPs) to reduce water consumption and prevent dust from being rescattered from dry EPs. In particular, the electrospray droplet size in EPs should be sufficiently large to collect dust in the exhaust gas flow, which requires a considerably larger electrospray flow rate than that required for typical applications. In addition, in the case of water electrospray, a high supply voltage is required because of its high surface tension. In this study, the characteristics of water-based electrospray were investigated under a high voltage and high flow rate. Three types of fluids—distilled water, tap water, and saline solution—were used to test for different conductivities under an electric charge with a negative current. The corona discharge and spray trajectories were visualized to determine the spray stability. To verify the influence of the spray current, the waveform of the electrospray was also analyzed under both dry- and wet-spray conditions. From this comparison, a portion of the spray current was estimated out of the total discharge current, which is the sum of the corona discharge and the spray current. The flow rate and voltage of the test were limited at 20 mL/min and −50 kV, respectively. In contrast with previous low flow rate studies, our results showed that the discharge current increased rapidly under flow rates above 6 mL/min, leading to arc discharge. Thus, it is important to adjust the flow and conductivity to guarantee stable and efficient water-based electrosprays.

Research on Spray Trajectory Atomization Based on Mathematical Analysis

The most important part of the spraying process is the paint film thickness uniform and how to plan the spray path. The paper is optimize the trajectory of spray gun by establishing mathematical model. Based on the analysis of the factors affecting the thickness distribution of paint film, establishing the thickness of single-trajectory spraying model, and analysis the relationship and surface geometry invariant to simplified the model, getting the optimal solution by using overlapping thickness model based on the movable surface, useing MATLAB to establish model of the curve surface. Then using projection to establish the thickness distribution model of any curve surface. Then use cloud sectioning to optimize the curve surface and establish the thickness of paint film in double trajectory.

Automatic Spray Trajectory Optimization on Bézier Surface

The trajectory optimization of automatic spraying robot is still a challenging problem, which is very important in the whole spraying work. Spray trajectory optimization consists of two parts: spray space path and end-effector moving speed. A large number of spraying experiments have proved that it is very important to find the best initial trajectory of spraying. This paper presents an automatic spray trajectory optimization that is based on the Bézier surface. Spray the workpiece for Bezier triangular surface modeling and find the best initial trajectory of the spraying robot, establish the appropriate spraying model, plan the appropriate space path, and finally plan the trajectory optimization along the specified painting path. The validity and practicability of the method presented in this paper are proved by an example. This method can also be extended to other applications.

Optimized Combination of Spray Painting Trajectory on 3D Entities

In this research, a novel method of space spraying trajectory optimization is proposed for 3D entity spraying. According to the particularity of the three-dimensional entity, the finite range model is set up, and the 3D entity is patched by the surface modeling method based on FPAG (flat patch adjacency graph). After planning the spray path on each patch, the variance of the paint thickness of the discrete point and the ideal paint thickness is taken as the objective function and the trajectory on each patch is optimized. The improved GA (genetic algorithm), ACO (ant colony optimization), and PSO (particle swarm optimization) are used to solve the TTOI (tool trajectory optimal integration) problem. The practicability of the three algorithms is verified by simulation experiments. Finally, the trajectory optimization algorithm of the 3D entity spraying robot can improve the spraying efficiency.

Droplet Motion Model and Simulation of a Complete Fluidic Sprinkler

Abstract. Simulation and experimental verification of the spray trajectory of a complete fluidic sprinkler was performed. Through further analysis of the forces moving droplets in the air and by exploring the relationship between the air drag coefficient and droplet trajectory, a droplet motion model was established. The velocity of a spray nozzle outlet is a gamma distribution, and the droplet deviation angle is a uniform distribution with a range of 0° to 360° when the sprinkler rotates uniformly for a full circle of spraying. The droplet size distribution in the spray area is approximately log-normal, the wind speed and direction follow a normal distribution, and the initial droplet angle is 27°. Based on a random simulation theory, the droplet trajectories were simulated using MATLAB software. The simulated results show that, compared to the tested value, the error between the simulated and measured values for the average droplet diameter decreased from 53% to 2% with increasing distance. The simulated values for droplet cumulative frequency and droplet speed were nearly the same as the tested value with only a small error. For both droplet distribution and kinetic energy, the relative error was less than 20%. Therefore, the stochastic simulation method can simulate the sprinkler droplet distribution characteristics. Keywords: Complete fluidic sprinkler, Droplet breakup mechanism, Droplet distribution, Droplet motion trajectory.

Liquid jet in crossflow – Effect of liquid entry conditions

The focus of the present article is to study the effect of liquid jet injection entry conditions on the structure of liquid jet in crossflow (JICF). The experiments are conducted over a range of liquid-to-air momentum ratios (Q ∼ 3–100) and aerodynamic Weber numbers (We = 17–89). Control over the exit conditions of the injected liquid is achieved through the usage of different L/D ratios of the nozzle of the plain-orifice atomizer. The geometrical parameter L/D is varied between 10 and 100 in order to obtain fully-developed laminar flow, transition and turbulent flow. High-speed imaging and Shadowgraphy are used to study the trajectory, drop-sizing and transient behaviour of the resultant spray. It is observed that the dependence of trajectory of the spray is not just limited to the momentum ratio, Q, but also requires correction factors with respect to the injection entry conditions, which are in turn related to L/D. The trajectory of the turbulent jet is found to be lower at all times when compared to that of a laminar jet for the corresponding conditions. This behaviour may be attributed to the inherent instabilities present in a turbulent jet as opposed to a perfectly laminar jet. Turbulent jets also observed atomize better, producing smaller droplets when compared to their laminar counterparts. Further, we also investigate the transient phenomena of the liquid jet breakup at different conditions with the aid of Proper Orthogonal Decomposition (POD) analysis. Distinct modes of breakup are captured for the laminar and turbulent cases.

Modeling of Thickness and Profile Uniformity of Thermally Sprayed Coatings Deposited on Cylinders

In thermal spraying processes, kinematic parameters of the robot play a decisive role in the coating thickness and profile. In this regard, some achievements have been made to optimize the spray trajectory on flat surfaces. However, few reports have focused on nonholonomic or variable-curvature cylindrical surfaces. The aim of this study is to investigate the correlation between the coating profile, coating thickness, and scanning step, which is determined by the radius of curvature and scanning angle. A mathematical simulation model was developed to predict the thickness of thermally sprayed coatings. Experiments were performed on cylinders with different radiuses of curvature to evaluate the predictive ability of the model.

A Robot Trajectory Optimization Approach for Thermal Barrier Coatings Used for Free-Form Components

This paper is concerned with a robot trajectory optimization approach for thermal barrier coatings. As the requirements of high reproducibility of complex workpieces increase, an optimal thermal spraying trajectory should not only guarantee an accurate control of spray parameters defined by users (e.g., scanning speed, spray distance, scanning step, etc.) to achieve coating thickness homogeneity but also help to homogenize the heat transfer distribution on the coating surface. A mesh-based trajectory generation approach is introduced in this work to generate path curves on a free-form component. Then, two types of meander trajectories are generated by performing a different connection method. Additionally, this paper presents a research approach for introducing the heat transfer analysis into the trajectory planning process. Combining heat transfer analysis with trajectory planning overcomes the defects of traditional trajectory planning methods (e.g., local over-heating), which helps form the uniform temperature field by optimizing the time sequence of path curves. The influence of two different robot trajectories on the process of heat transfer is estimated by coupled FEM models which demonstrates the effectiveness of the presented optimization approach.

Penetration and breakup of liquid jet in transverse free air jet with application in suspension-solution thermal sprays

The penetration and breakup of water jets in transverse free air jets are experimentally studied at room conditions. After coming out of an orifice and forming a cylindrical jet, water interacts with a free air jet and disintegrates. In the current work, the effects of the instabilities of cylindrical liquid jets, the distance between the liquid orifice and gas nozzle, and the ratio of liquid orifice diameter to the gas nozzle diameter, on the breakup mechanisms and liquid structure are investigated. Moreover, general correlations for spray trajectory and location of the liquid column breakup point are developed. Experimental results indicate that the breakup mechanisms are mainly controlled by the gaseous and liquid Weber numbers. Like other studies, four breakup regimes, namely capillary, bag, multimode, and shear breakup are observed. It is found that, due to the presence of instabilities on the cylindrical liquid jet, large ligaments are formed close to the interaction point of liquid and gas flows. Furthermore, results indicate that the location of liquid column breakup point is mainly dependent on the momentum flux ratio, and perturbations on the liquid jet. This fundamental study is essential to investigate the spray structure of a suspension-solution jet in plasma spray.

Experimental study and implementation of a novel internal foam spraying system for roadheaders

Foam technology utilizes the good coverage of foam to form a closed space around dust sources. The foam then wets the dust particles, causing them to adhere before they spread into the air, resulting in better dust control than with water sprays. In the process of foam dust control at a heading face, the foam spray trajectory is highly influenced by the wind, making it difficult to focus foam on the dust sources, which wastes the foam and reduces dust control efficiency. To resolve this problem, the idea of transporting foam to the cutting head through the roadheader’s inner pipeline is proposed. To adapt to the high resistance of foam delivery in the roadheader’s inner pipeline, according to the water and air supply of the heading face, a table water-jet suction device and porous spiral coupling foaming device were designed, and the working conditions were tested using a self-designed experiment system in the laboratory. The results showed that the foaming agent could be automatically added into the device at a working water flow rate of 1–1.6m3/h at a ratio of 1%. The optimum air flow was 45–50m3/h, in which range the foam expansion ratio reached the maximum and the outlet pressure demand was satisfied. Field application showed that the new foam method had a better dust control efficiencies than traditional foam methods.

LES of spray in crossflow – Effect of droplet distortion

The present investigation is focused on modeling of spray in crossflow using Large Eddy Simulations (LES). The modeling efforts are supported by experiments which are used both to provide accurate boundary and initial conditions and to evaluate droplet shapes in the near nozzle region. The droplets are modeled as Lagrangian parcels in an Eulerian continuum. Droplets in such configuration have been found to be distorted and not in perfect spherical shape from experimental results of our previous study. Droplet distortion is computed by Taylor-Analogy Breakup (TAB) distortion model. Each droplet is modelled as damped spring-mass system, where surface tension acts as a spring on the mass of the droplet and viscous dissipation provides the damping effect. The effort is to examine the effect of drag law used and the effect of this distortion on the droplet sizes produced in the flow field. Spray wind-ward trajectory and droplet sizes obtained from simulations are compared with the experimental results available. Although computational spray trajectory shows a reasonable match with experimental values, droplet sizes using the standard TAB model are found to be larger than that from experimental observation. To account for this distortion and its role in early breakup of droplets, constants of the TAB model are modified and the droplet sizes are found to be in good agreement with the experimental data.

Droplet trajectories of wave-impact sea spray on a marine vessel

Marine icing phenomena are strongly dependent on the rate of water impact to marine vessels. The most important source of this incoming water is wave-impact sea spray. There is limited understanding of droplet size and velocity distributions of wave-impact sea spray. Initial distributions of the size and velocity of droplets are crucial for the calculation of the droplet path and consequently for determining the water impact to every individual place on marine vessels. This paper develops a new model of wave-impact sea spray using a distribution of the size and velocity of droplets at the edge of the vessel. The concepts of water-sheet breakup and droplet breakup lead to an inverse dependence between the size and velocity of droplets after the breakup process. Droplets take different paths and form a spray cloud in front of the vessel. The liquid water content in front of the vessel can be calculated by considering the arrangement, sizes, and velocities of a set of droplets in the spray cloud. The response of the droplet trajectory model to various initial conditions with different sets of droplet sizes and velocities is examined. The numerical results are compared to real data from field observations. Droplet sizes are inversely proportional to droplet velocities, as verified by liquid water content data obtained by the field observations. This paper proposes the use of this inverse relationship based on physics of the breakup process as the initial data for calculating the wave-impact sea spray trajectory in front of a vessel.

Autonomous Fire Suppression System for Use in High and Low Visibility Environments by Visual Servoing

An autonomous fire suppression system was developed for localized fire suppression in high and low visibility environments. The system contains a multispectral sensor suite, including UV sensors and infrared stereovision, to detect and target a fire for suppression. The UV sensor provides an alert to the system to begin fire detection. IR imagery is used to segment fire from the field of view and target the base of the fire and IR stereovision to determine the 3D coordinates of the fire. IR tracking provides continuously updated information on the size and intensity of the fire before and during suppression and alerts the system when to cease suppression activity. Visual servoing is used to correctly position a nozzle based on feedback of changes in the fire location and size. The autonomous system was used to suppress wood crib fires (40 kW to 50 kW) in high and low visibility environments and at varying distances (2.8 m to 5.5 m) and elevations (0.4 m to 1.3 m). The suppression time in clear conditions was 3.72 s ± 1.51 s and 4.49 s ± 1.62 s in low visibility conditions. To simulate wind effects and inaccurate initial target coordinates, forced offsets were input to the system to show effectiveness of the feedback control algorithm when an initial estimate of spray trajectory does not accurately spray the center base of the fire. System performance with a forced offset resulted in suppression times of 4.11 s ± 0.84 s.