Xiwen Li

A kinematic calibration method based on the product of exponentials formula for serial robot using position measurements

Based on product of exponentials (POE) formula, three explicit error models are given in this paper for kinematic calibration of serial robot through measuring its end-effector positions. To obtain these error models, the tool frame should be chosen as reference frame at first, and then each position–error-related segment in the error models using pose measurement should be selected. And during kinematic parameter identification, all the errors in joint twists are identifiable, and the initial transformation errors and the joint zero-position errors can be identified conditionally. Namely, the initial transformation errors are identifiable if they do not contain orientation errors. And the joint zero-position errors are identifiable when a robot only consists of prismatic joints and the coordinates of its joint twists are linearly independent. The effectiveness of this calibration method has been validated by simulations and experiments. The results show that: (1) the identification algorithms are robust and practical. (2) The method of position measurement is superior to that of pose measurement.

Inline Measurement of Particle Concentrations in Multicomponent Suspensions using Ultrasonic Sensor and Least Squares Support Vector Machines.

This paper proposes an ultrasonic measurement system based on least squares support vector machines (LS-SVM) for inline measurement of particle concentrations in multicomponent suspensions. Firstly, the ultrasonic signals are analyzed and processed, and the optimal feature subset that contributes to the best model performance is selected based on the importance of features. Secondly, the LS-SVM model is tuned, trained and tested with different feature subsets to obtain the optimal model. In addition, a comparison is made between the partial least square (PLS) model and the LS-SVM model. Finally, the optimal LS-SVM model with the optimal feature subset is applied to inline measurement of particle concentrations in the mixing process. The results show that the proposed method is reliable and accurate for inline measuring the particle concentrations in multicomponent suspensions and the measurement accuracy is sufficiently high for industrial application. Furthermore, the proposed method is applicable to the modeling of the nonlinear system dynamically and provides a feasible way to monitor industrial processes.

Ultrasonic spectrum for particle concentration measurement in multicomponent suspensions

This paper studies the feasibility of applying the ultrasonic spectrum technique to the measurement of particle concentrations in multicomponent suspensions. A combination of the kernel partial least squares (KPLS) model and the interval selection methods is implemented to build the relationship between the ultrasonic spectra of the first reflected pulses and the particle concentrations. First of all, the interval selection methods are used to select optimal spectral interval(s) from full spectra. Then, the KPLS models with optimal spectral interval(s) are tuned, built and evaluated to obtain the optimal model. Finally, the optimal KPLS model is employed to measure the particle concentrations in the mixing process and its online prediction ability is evaluated. In comparison with the linear partial least squares (PLS) models, the optimal KPLS model shows the best performance. The results demonstrate that particle concentrations in multicomponent suspensions can be measured online by the ultrasonic spectrum technique, and the KPLS model with optimal spectral interval(s) shows the superiority in model calibration.

A numerical investigation of the effects of blade’s geometric parameters on the power consumption of the twin-blade planetary mixer:

Blades act as key components for twin-blade planetary mixer; their geometric parameters (blade–blade clearance and helical angle) and two different rotating modes (counter-rotating mode and co-rotating mode) were investigated numerically via commercial software ANSYS Fluent 14.5 to reveal the effects on the power or torque consumption. The results indicate that decreasing the blade–blade clearance or increasing the helical angle increases the power consumption of the twin-blade planetary mixer. The proportionality constant of power curves depends on the geometry of the blades.

Study on double-shaft mixing paddle undergoing planetary motion in the laminar flow mixing system

This article has studied the impact of double-shaft mixing paddle undergoing planetary motion on laminar flow mixing system using flow field visualization experiment and computational fluid dynamics simulation. Digital image processing was conducted to analyze the mixing efficiency of mixing paddle in co-rotating and counter-rotating modes. It was found that the double-shaft mixing paddle undergoing planetary motion would not produce the isolated mixing regions in the laminar flow mixing system, and its mixing efficiency in counter-rotating modes was higher than that in co-rotating modes, especially at low rotating speed. According to the tracer trajectory experiment, it was found that the path line of the tracer in the flow field in co-rotating modes was distributed in the opposite direction to the path line in counter-rotating modes. Planetary motion of mixing paddle had stretching, shearing, and folding effects on the trajectory of the tracer. By means of computational fluid dynamics simulation, it was found that axial flows and tangential flows produced in co-rotating and counter-rotating modes have similar flow velocity but opposite flow directions. It is deduced from the distribution rule of axial flow, radial flow, and tangential flow in the flow field that axial flow is the main reason for causing different mixing efficiencies between co-rotating and counter-rotating modes.

Gas Bubble Effects and Elimination in Ultrasonic Measurement of Particle Concentrations in Solid–Liquid Mixing Processes

In this paper, the online measurement of particle concentrations in suspensions containing gas bubbles is studied using the ultrasonic spectra and the synergy interval partial least squares regression (Si-PLS) model in the solid–liquid mixing processes. At first, a comparison is made among the ultrasonic signals obtained from suspensions and pure water with and without gas bubbles and the gas bubble effects of high agitation speeds on ultrasonic measurement are evaluated. A moving average and standard deviation method is developed to deal with the real-time ultrasonic signals, aiming to decrease the fluctuations and noises of signals and improve the stability of signals. Then, based on the optimal spectral subintervals selected with the Si-PLS model, the prediction model for the particle concentrations is built, which considers the gas bubble effects as an interferent. The optimal model, of which the root-mean-square error of the prediction subset is 0.38 wt%, is successfully applied to measure the concentration of TiO2 suspensions in the range of 0–15.79 wt% when the agitation speed is less than 1200 r/min. The online measurement results suggest that the proposed method has the potential to be a useful tool for eliminating gas bubble effects and measuring particle concentrations in the solid–liquid mixing processes.

Numerical analysis in the effects of blade’s arrangement on the torque load characteristics of the three-blade planetary mixer

The three-blade planetary mixer is one of the important solid propellant mixing equipment, the layout of blades will affect the blades’ torque load and the power consumption. In this paper, the effects of the eccentric distance (Es=0∼16 mm), the solid blade form (two paddles, and four paddlers), and the blade arrangement (linear arrangement, triangle arrangement) on the blades’ torque load are investigated during the mixer stirring the solid propellant process.

In-line mixing states monitoring of suspensions using ultrasonic reflection technique

Based on the measurement of echo signal changes caused by different concentration distributions in the mixing process, a simple ultrasonic reflection technique is proposed for in-line monitoring of the mixing states of suspensions in an agitated tank in this study. The relation between the echo signals and the concentration of suspensions is studied, and the mixing process of suspensions is tracked by in-line measurement of ultrasonic echo signals using two ultrasonic sensors. Through the analysis of echo signals over time, the mixing states of suspensions are obtained, and the homogeneity of suspensions is quantified. With the proposed technique, the effects of impeller diameter and agitation speed on the mixing process are studied, and the optimal agitation speed and the minimum mixing time to achieve the maximum homogeneity are acquired under different operating conditions and design parameters. The proposed technique is stable and feasible and shows great potential for in-line monitoring of mixing states of suspensions.

The vertical kneader stirred blades surface reconstruction based on adaptive implicit T-splines

The vertical kneader is the key equipment of developing solid propellant, and its stirred blades surface shape is more complex. In this paper, the geometric attributes of stirred blades surface point set, such as normal, curvature, are calculated. By selecting point set number threshold and mean curvature threshold in sub-cube, the three-dimensional T-mesh is constructed adaptively based on the octree and subdivision. Through exploiting the surface fitting model, the transform from surface reconstruction problem to optimization problem is done. By solving the linear equations, the implicit T-splines control point coefficients and the stirred blades surface reconstruction are obtained. The experimental results show that the method can effectively realize the complex topological surface reconstruction.