Contour Control Research Articles

Sliding mode control with third-order contour error estimation for free-form contour following

To reduce the contour error in contour-following tasks, the most common method is to design a contour controller based on the contour error model. Therefore, how to estimate the contour error in real-time and with high accuracy plays an important role in contour-following control. It is difficult to guarantee real-time performance, high estimation accuracy and strong robustness against arbitrary trajectories at the same time. In this paper, a contour error estimation method based on the third-order osculating helix is proposed. The osculating helix can fully consider the geometric characteristics of the interpolation trajectory and is closer to the desired interpolation trajectory. On this basis, PD-type tracking error sliding mode surface and PD-type contour error sliding mode surface are redesigned to fully take into account the regulating effect of the velocity tracking error and velocity contour error. Experimental results demonstrate the effectiveness of the proposed contour control approach.

Real-time exact contour error calculation of NURBS tool path for contour control

The requirement of high-speed and high-precision contouring with NURBS tool path to the CNC machining process is increasing. The calculation of the contouring error (CE) of the NURBS tool path to real time is necessary for the advanced contour control like the cross-coupled controller (CCC). Based on the complexity of the CE calculation of NURBS, most studies use estimating methods to approximate the real CE in the controller. However, when the cutter is at the large curvature zones in the high-speed machining, the difference between the estimated the CE and the real one becomes large. To solve this problem, an algorithm to calculate the exact CE of NURBS tool path to real time is proposed. The calculation model of the CE of NURBS is derived. Also, the numerical calculation algorithm from Brent’s method is given to solve the CE model. Multiple solutions of CE model is discussed and real-time solution tracking method is developed to determine the intervals of the candidate solutions for numerical calculation. Contour error for control (CCE) is proposed for controller design to improve the stability of contour control, which is different from the definition of conventional control error for measurement (MCE). The proposed algorithm is validated for both the simulation and the experiment on the X–Y table. Experimental results show the effectiveness of the proposed algorithm and the actual CE is reduced significantly compared with other methods.

Reference Trajectory Modification Based on Spatial Iterative Learning for Contour Control of Two-Axis NC Systems

Contour error is a main factor that affects the quality of products in numerical control (NC) machining. This article presents a contour control strategy based on digital curves for high-precision control of computer numerical control (CNC) machines. A contour error estimation algorithm is presented for digital curves based on a geometrical method. The dynamic model of the motion control system is transformed from time domain to space domain because the contour error is dependent on space instead of time. Spatial iterative learning control (sILC) is developed to reduce the contour error, by modifying the reference trajectory in the form of G code. This allows system improvement without interference of low-level controllers so it is applicable to many commercial controllers where interpolators and feed-drive controllers cannot be altered. The effectiveness of this method is verified by experiments on a NC machine, which have shown good performance not only for smooth trajectories but also for large curvature trajectories.

Definition and estimation of joint-space contour error based on generalized curve for five-axis contour following control

Five-axis contour following is one of the main tasks for five-axis CNC machine tools. The contour following accuracy directly determines the final machining precision. Therefore, control of the five-axis contour error is significant. Currently, most existing definitions of five-axis contour error are in the Cartesian task space, and this inevitably requires direct and inverse Jacobian transformations between the task-space contour-error computation and the joint-space contour-error control. Different from them, this paper defines the five-axis contour error in the ℝ5 joint space through adjusting uniform units of five joints, and accordingly proposes a third-order estimation algorithm for the defined joint-space contour error, with the help of the concept of generalized curve. Based on the joint-space contour-error definition and estimation, a joint-space five-axis cross-coupling control scheme is finally provided. Simulation and experimental results demonstrate that the presented third-order joint-space contour-error estimation algorithm has a satisfactory estimation accuracy, and the presented joint-space five-axis contour control method can decrease both of the joint-space and the task-space five-axis contour errors by more than 49%. It is also analyzed and verified that comparing with routine task-space five-axis contour control method, the presented joint-space method not only needs not the direct and inverse Jacobian transformations during error estimation, which saves the computational burden, but also generates minimum axial contour-control commands, which enhances the control stability, thus resulting in better contour-following performances.

Contour Tracking Control Based on Extended State Observer for Multiaxis Motion System

In the contouring process, the trajectory generated by the computer numerical control (CNC) machine tool is a result of the multiaxis coordinated motion. The contour error has a direct impact on the accuracy of the machined product. To obtain higher contouring accuracy of the multiaxis motion control system, this paper presents a cross-coupled control approach based on the extended state observer sliding mode control. First, a single-axis sliding mode controller is designed, and an extended state observer is used to estimate system disturbances and improve the system robustness. Then, the cross-coupled control approach handles the coordinated motion of multiple axes to improve the contour control accuracy. Next, a simulation study is conducted on the three-axis motion platform. Its result shows that the control algorithm is effective in reducing tracking errors and contour errors.

Toward an automatic tool for oligoclonal band detection in cerebrospinal fluid and tears for multiple sclerosis diagnosis: lane segmentation based on a ribbon univariate open active contour.

The latest revision of multiple sclerosis diagnosis guidelines emphasizes the role of oligoclonal band detection in isoelectric focusing images of cerebrospinal fluid. Recent studies suggest tears as a promising noninvasive alternative to cerebrospinal fluid. We are developing the first automatic method for isoelectric focusing image analysis and oligoclonal band detection in cerebrospinal fluid and tear samples. The automatic analysis would provide an accurate, fast analysis and would reduce the expert-dependent variability and errors of the current visual analysis. In this paper, we describe a new effective model for the fully automated segmentation of highly distorted lanes in isoelectric focusing images. This approach is a new formulation of the classic parametric active contour problem, in which an open active contour is constrained to move from the top to the bottom of the image, and the x-axis coordinate is expressed as a function of the y-axis coordinate. The left and right edges of the lane evolved together in a ribbon-like shape so that the full width of the lane was captured reliably. The segmentation algorithm was implemented using a multiresolution approach in which the scale factor and the active contour control points were progressively increased. The lane segmentation algorithm was tested on a database of 51 isoelectric focusing images containing 419 analyzable lanes. The new model gave robust results for highly curved lanes, weak edges, and low-contrast lanes. A total of 98.8% of the lanes were perfectly segmented, and the remaining 1.2% had only minor errors. The computation time (1s per membrane) is negligible. This method precisely defines the region of interest in each lane and thus is a major step toward the first fully automatic tool for oligoclonal band detection in isoelectric focusing images. Graphical abstract.

Design of Contour Error Coupling Controller Based on Neural Network Friction Compensation

In two-axis servo contour motion control, friction and various uncertainties unavoidably exist, reducing the contour control accuracy. This paper proposes a neural network contour error coupling control method based on LuGre friction compensation, which includes a contour error calculation model, single-axis computed torque controller (CTC), and neural network friction compensation controller. The LuGre friction model can describe servo system’s complicated static and dynamic friction characteristics, and the RBF neural network has a universal approximation property to realize compensation control of friction. Simulation results indicate that the proposed contour error control method can effectively compensate for the effect of friction and improve contour control accuracy.

Model Predictive Contouring Control for Collision Avoidance in Unstructured Dynamic Environments

This letter presents a method for local motion planning in unstructured environments with static and moving obstacles, such as humans. Given a reference path and speed, our optimization-based receding-horizon approach computes a local trajectory that minimizes the tracking error while avoiding obstacles. We build on nonlinear model-predictive contouring control (MPCC) and extend it to incorporate a static map by computing, online, a set of convex regions in free space. We model moving obstacles as ellipsoids and provide a correct bound to approximate the collision region, given by the Minkowsky sum of an ellipse and a circle. Our framework is agnostic to the robot model. We present experimental results with a mobile robot navigating in indoor environments populated with humans. Our method is executed fully onboard without the need of external support and can be applied to other robot morphologies such as autonomous cars.

SUV Front View Design Method Selected by Multiple Schemes

Based on the parametric sensibility engineering and computer-aided industrial design basis, the SUV forward-looking contour is used as a target to explore a preferred selection model for multiple design schemes under specific images. Samples of the SUV front view were collected, the design variables were defined using the Bézier curve, and representative samples were selected using multivariate analysis and cluster analysis. Through the questionnaire survey, the sensory image of SUV front view contour was screened to obtain pairs of representative images. Using semantic difference method to conduct perceptual image research and analysis of representative samples. According to the analysis results, the correlation models of perceptual images and related design variables are obtained. The effectiveness of the model is verified by the existing model design of the market. The conclusion proves that there is a correlation between the consumer’s emotional image and the position of the SUV front-view contour feature point. The coordinates of the forward-looking contour control point of the design scheme are brought into the relevant consumer image correlation model, and the optimal image is obtained under the image. The design scheme improves the success rate of the front face design of the SUV.

Nasal Tip Remodeling by Non-Destructive Techniques

AbstractBackground: Nasal tip surgery is regarded as the most challenging aspect of plastic surgery. Control of nasal tip contour has always been a key component of a successful rhinoplasty. Creating a natural-appearing nasal tip contour is a complex task and requires a 3-dimensional approach.Aim of Study: In this study we aimed to study and imple-ment the different non-destructive surgical techniques for the management of the various nasal tip deformities.Patients and Methods: Fifty patients with various tip deformities were operated by an open approach either by sutures, various grafts or both.Results: Decreased need for irreversible techniques, with a concurrent increase in conservative techniques as sutures and grafts techniques that had been done in most of our patients for each.Conclusion: We concluded that management of nasal tip deformities with both suture and grafting provides best results.

Precise Contour Control of Biaxial Motion System Based on MPC

In order to realize accurate and fast contour tracking of biaxial motion system and ensure the smoothness of its path, this paper proposes a model predictive contour control strategy suitable for biaxial system based on the idea of unified modeling. The two permanent magnet synchronous motors driving the biaxial system are considered as a whole to build a unified model. Based on the unified model, a compact model predictive controller is designed, where the contour error, the tracking error, the control increment and the position increment are introduced into the cost function simultaneously, realizing the multivariable collaborative optimization control. In addition, to obtain the better dynamic response and steady-state performance, a method of real-time adaptive adjustment of the position increment weight coefficient and the control increment weight coefficient is proposed. At the same time, considering the constraints, a posteriori constraint limitation network with the current control increment is proposed. Furthermore, the closed-loop stability analysis of the model predictive contour control system is carried out according to the optimal control principle. The experimental results show that the proposed control strategy can not only track the trajectory accurately at steady state, but also improve the transient contour tracking performance.

Generalized Predictive Contour Control of the Biaxial Motion System

In order to overcome the redundancy of the biaxial motion system's traditional control structure and the cumbersome nature of the controller parameter adjustment, this paper simplifies the traditional control structure and proposes a generalized predictive contour control strategy applicable to the biaxial motion system based on the idea of unified modeling. The two permanent magnet synchronous motors that drive the biaxial motion system are considered as a whole to establish a unified model. Through the idea of multistep prediction, rolling optimization, and feedback correction in generalized predictive control, the optimal control input signal is obtained by coordinating the tracking error and contour error. In addition, an actuating value limitation has to be taken into account to design a realizable generalized predictive contour control for the biaxial system. At the same time, the closed-loop stability analysis of the generalized predictive contour control system is carried out according to the optimal control principle and the state equation model. The experimental results show that the proposed control strategy cannot only accurately track the contour trajectory at steady state but also improve the transient contour tracking performance.

HEXAPOD DIGITAL CONTROL USING THE INVERSE DYNAMICS AND IT IMPLEMENTATION ON THE RADIATION-RESISTANT ARM-MICROCONTROLLER

The researches are part of the actual work carried out by BSTU Voenmeh with the financial support of the Ministry of Education and Science of the Russian Federation for the design and creation of a precision mechanism with parallel kinematics of the «hexapod» type. In modern developments of robot control systems, the approach based on the solution of the inverse dynamic model is most popular. In this article, we study the quality of control and the feasibility of this approach in the control system based on the domestic radiation-resistant microcontroller. A mathematical description of the hexapod dynamics model and control algorithm is given. A model of a digital control system for the hexapod of space intended for use in Matlab Simulink is described. Estimates of the quality of hexapode regulation in the contour control regime are obtained. Evaluated the software implementation of the control algorithm in the real-time operating system Keil RTX in the programming language C++. The quantization period necessary for the implementation of the algorithm under investigation is determined.

Numerical and experimental investigation of blasting damage control of a high rock slope in a deep valley

The disturbance of a rock mass due to blasting impact and stress redistribution can significantly affect the overall performance of an excavation. Crack formation during presplit blasting was analyzed with a mathematical model, considering the in situ stress. The results clearly indicate that the in situ stress can inhibit crack formation. The linear density of the explosive and blast hole spacing should be adjusted to improve crack formation. The damage distribution produced by different blasting approaches was reproduced with a numerical simulation based on the secondary development of LS-DYNA. The results demonstrate that the damage control effects of conventional presplit blasting or smooth blasting under in situ stress are not ideal. Owing to the combination of blasting load and stress redistribution, crack formation at the lateral sides was inhibited during presplit blasting, while the middle side could not be sufficiently broken during smooth blasting. An optimized method of presplit-smooth blasting was proposed and verified with numerical simulations. Finally, based on excavation of the Baihetan high rock slope, a comparison of the conventional and optimized approaches was conducted with sonic wave tests and roughness monitoring. The results demonstrate that the presplit-smooth blasting approach inherits the advantages of both presplit and smooth blasting, and could significantly improve contour control effects.

Pneumatic Actuation in Haptic-Enabled Medical Simulators: A Review

Haptic feedback is essential for achieving virtual and augmented reality (VR/AR) systems with high fidelity and realism. Haptic-enabled VR/AR systems offer a proficient environment in which to enhance the skills of medical practitioners. While pneumatic actuation is traditionally used in heavy automation industries, haptics researchers have utilized pneumatic techniques to produce various haptic effects, i.e., stiffness feedback and contour control, and these techniques have shown promising results in the medical domain. In this paper, we focus on the use of pneumatic-actuated haptic systems in VR/AR-based medical simulators. We begin with the taxonomy of the physical-virtual continuum and discuss the role of pneumatics in medical haptic systems. Furthermore, we propose the conceptual design architecture of a pneumatic haptic system. In addition, the systematic state-of-the-art role of pneumatic haptics in medical systems is presented for different categories. In this paper, we provide a systematic review and discuss the study of pneumatics to provide guidelines for the design and development of pneumatic haptic medical systems.

Position domain nonlinear PD control for contour tracking of robotic manipulator

Abstract Contouring control is most important in machining applications to ensure the quality of the final product. In this paper, the contouring control problem for a multi-dof robotic manipulator is studied, and a nonlinear PD (NPD) control law is proposed in position domain and applied to contour tracking control. To develop the position domain control system, the robotic motions are viewed as the combination of a master motion, controlled in time domain, and slave motions controlled in position domain. The master motion is used as a reference for the slave motions, and the slave motions are controlled by the developed NPD and synchronized with the master motion so that a good contour tracking performance can be achieved. Stability analysis is conducted based on the Lyapunov theory for the developed position domain NPD control. Linear and nonlinear contour tracking problems are simulated and compared with existed PD controllers. It is demonstrated that the position domain NPD control can achieve much better contour tracking performance compared with the counterparts in time domain and the linear PD-type position domain control. Furthermore, the proposed NPD controller is much efficient for nonlinear contour tracking problems.

Adaptive estimation and nonlinear variable gain compensation of the contouring error for precise parametric curve following

Contour following is one of the most important issues faced by many computer-numerical-control (CNC) machine tools to achieve high machining precision. This paper presents a new real-time error compensation method aiming at reducing the contouring error caused by facts such as servo lag and dynamics mismatch in parametric curved contour-following tasks. Due to the lack of high-precision contouring-error estimation method for free-form parametric curved toolpath, the error can hardly be compensated effectively. Therefore, an adaptive accurate contouring-error estimation algorithm is proposed first, where a tangential-error backstepping method based on Taylor’s expansion is developed to rapidly find the closest point on the parametric curve to the actual motion position. On this foundation, the contouring error is compensated using a proposed nonlinear variable-gain compensation method, where the compensation gain is obtained according to not only the contouring-error magnitude but also its direction variation. The stability of the system after compensation is analyzed afterwards according to the Jury stability criterion. By design of the compensator in accordance with the presented contouring-error compensation method as well as the stability analyzation result, the balance between the response speed and the contour control stability can be effectively made. Experimental tests demonstrate the feasibility of the presented methods in both contouring-error estimation and contour-accuracy improvement. Contributions of this research are significant for enhancing the contour-following performance of the CNC machine tools.

A fast texture segmentation scheme based on active contours and discrete cosine transform

This paper presents a novel and efficient parametric active contour model based on the texture describing properties derived from coefficients of the two-dimensional Discrete Cosine Transform (2-D DCT) for segmenting texture objects against complex backgrounds. Block based 2-D DCT is applied in the local neighbourhood of all the contour control points and some randomly chosen object points. DCT coefficients in the horizontal, vertical and diagonal directions which represent the dominant textures are used to construct the histograms those exhibit different structures for different texture regions. Heterogeneity of these histograms corresponding to contour and object points is measured by Wasserstein distance metric. Finally, DC coefficient which represents the energy of the corresponding block modulated by the calculated Wasserstein distance is employed as the external energy of the proposed active contour model. Experiments on synthetic and natural texture images show the efficiency of our model in terms of accuracy and speed.

Time Optimal Contouring Control of Industrial Biaxial Gantry: A Highly Efficient Analytical Solution of Trajectory Planning

Contouring control is an important issue in industrial applications. For better product quality and higher productivity, achieving higher contour tracking performance with feed rate as large as possible is essential. However, most existing research has focused on improving contour tracking accuracy only. The potential instability issue due to control input saturation under high feed-rate operations has been largely ignored. In this paper, the minimum time trajectory planning problem is formulated as a step toward solving this practically important problem. A novel back and forward check algorithm is developed to take into account physical constraints of the system when generating the desired trajectory to be followed. Compared with traditional numerical searching methods, the proposed algorithm is very computationally efficient because the optimal solution at each node can be obtained by several analytical equations directly. Moreover, the algorithm can incorporate some velocity-dependent constraints easily. Planning a Lissajous curve is used as the case study to verify the optimality and computational efficiency of the proposed algorithm. Experiments are conducted on an industrial biaxial gantry. Several implementation issues on tracking complicated contours are discussed. Experimental results indicate that the proposed trajectory planning approach enables simultaneous achievement of high contouring tracking accuracy and higher feed rate or shorter operation time.

Cross-Coupled Contouring Control of Multi-DOF Robotic Manipulator

Reduction of contour error is a very important issue for high precise contour tracking applications, and many control systems were proposed to deal with contour tracking problems for two/three axial translational motion systems. However, there is no research on cross-coupled contour tracking control for serial multi-DOF robot manipulators. In this paper, the contouring control of multi-DOF serial manipulators is developed for the first time and a new cross-coupled PD (CC-PD) control law is proposed, based on contour errors of the end-effector and tracking errors of the joints. It is a combination of PD control for trajectory tracking at joint level and PD control for contour tracking at the end-effector level. The contour error of the end-effector is transformed to the equivalent tracking errors of the joints using the Jacobian regulation, and the CC-PD control law is implemented in the joint level. Stability analysis of the proposed CC-PD control system is conducted using the Lyapunov method, followed by some simulation studies for linear and nonlinear contour tracking to verify the effectiveness of the proposed CC-PD control system.