High-speed Contouring Research Articles

CEDContours: A high speed contour detector for color images

We propose a high-speed contour detector for color images that produces its contours as set of edge segments, each a chain of pixels. The proposed algorithm performs a multi-scale analysis of the input image by combining the edge segments produced by Color Edge Drawing (CED) at different scales; thus, the name CEDContours. We evaluate the performance of CEDContours both qualitatively by presenting visual experimental results, and quantitatively within the precision-recall framework of the Berkeley Segmentation Dataset and Benchmark (BSDS300 and BSDS500). Experimental results show that CEDContours with the DiZenzo gradient operator, named CEDContours-DiZenzo, surpasses many of the prominent contour detectors found in the literature (0.70 and 0.71 F-score for BSDS300 and BSDS500 respectively), and gives comparable results to the leading contour detectors, i.e., the global Probability of boundary ultrametric contour maps (gPb-ucm: 0.71 and 0.73), and the sparse code gradients (scg: 0.72 and 0.74), but runs up to 100 times faster than these contour detectors (700ms for 481×321 images as opposed to 40s for gPb-ucm and 70s for scg), making it suitable for high-speed image processing and computer vision applications.

Feedrate optimization for smooth minimum-time trajectory generation with higher order constraints

The generation of a time-optimal feedrate trajectory under various machine and process-related constraints has received significant attention in CNC machining and robotics applications. While most of the existing feedrate planning algorithms take velocity and acceleration into the consideration as capability constraints, the introduction of higher order dynamic states, such as jerk and/or jounce, makes the feedrate planning and optimization extremely challenging, as the dimension of the planning problem is increased accordingly. This paper proposes a heuristic trajectory planning algorithm that can provide a near-optimal minimum time trajectory for problems with higher order dynamic states. The algorithm starts with a non-time-optimal but feasible velocity trajectory, which is interpolated from a number of knot points by piecewise spline interpolation with high-order continuity. Then, the trajectory is improved by scanning and increasing the velocity at each knot points while maintaining the feasibility of the resulting trajectory. A near-optimal trajectory is achieved when the improvement in travel time from the last scan iteration is smaller than a given value. The algorithm supports the incorporation of higher order dynamic states (up to the fifth derivative of displacement) in constraints for optimization without sacrificing the computational efficiency. Examples including linear and curved toolpath are presented to illustrate the effectiveness of this algorithm for high-speed contouring.

A Smooth Trajectory Generation Algorithm for Addressing Higher-Order Dynamic Constraints in Nanopositioning Systems

The generation of a time-optimal feedrate trajectory has received significant attention in CNC machining and robotics applications. Most of the existing feedrate planning algorithms take velocity and acceleration into the consideration for capability constraints. The introduction of higher order dynamic states, such as jerk and/or jounce into the feedrate scheduling problem makes generating computationally efficient solutions while simultaneously guaranteeing optimality a challenging problem, as the dimension of the planning problem is increased accordingly. This paper proposes a heuristic trajectory planning algorithm that can provide a near optimal trajectory for problems with higher order dynamic states. The algorithm starts with a non-optimal but feasible velocity trajectory, which is interpolated from a number of knot points by piece-wise spline interpolation with high order continuity. Then the trajectory is improved by scanning the interpolating knot points and increasing the velocity at each knot points while maintaining the feasibility of the resulting trajectory. A near optimal trajectory is achieved when the improvement in travel time is neglectable from the last scan iteration. The algorithm supports the incorporation of high order dynamic states (up to fifth order derivative of position) in constraints for optimization without sacrificing the computational efficiency. Examples including linear and curved toolpaths are presented to illustrate the effectiveness of this algorithm for high-speed contouring.

Cutting Forces Parametric Model for the Dry High Speed Contour Milling of Aerospace Aluminium Alloys

Cutting forces is one of the most important outputs in material removal machining processes. Their values depend on a large number of parameters, such as the cutting tool material and geometry, the workpiece material or the cutting parameters, among others. In this paper, cutting forces behavior have been analyzed as a function of feedrate and cutting speed, for the high-speed peripheral milling of UNS A92024-T3 (Al-Cu) stacks. This alloy is widely used in the manufacturing process of aircraft structural elements. From this analysis, different parametric models have been adjusted to experimental data, establishing Fn=f(fz,V) relationships that allow an approximation to the values of force components for machining conditions dependent on those variables.

Feed-rate optimization with jerk constraints for generating minimum-time trajectories

Competitive pressure requires manufacturers to simultaneously address increasingly stringent constraints on both productivity and quality. From the perspective of numerically controlled (NC) machine tools, this means higher machining performance in terms of speed and accuracy. Conventional approaches to programming NC operations involve selecting a constant feedrate for a given operation to produce acceptable performance (operation time and contouring accuracy). In this paper, we examine the possibility of scheduling or varying the feedrate by taking into consideration the geometry of the contour that the machine is expected to follow and the physical capabilities of the machine (i.e., its maximum velocity, acceleration and jerk constraints). Previous work by the authors has addressed the efficient, off-line computation of time-optimal trajectories with constraints on velocity and acceleration. This paper introduces additional constraints on the permissible jerk (rate of change of acceleration) on the machine's axis. From a practical perspective, excessive jerk leads to excitation of vibrations in components in the machine assembly, accelerated wear in the transmission and bearing elements, noisy operations and large contouring errors at discontinuities (such as corners) in the machining path. The introduction of jerk into the feedrate scheduling problem makes generating computationally efficient solutions while simultaneously guaranteeing optimality a challenging problem. This paper approaches this problem as an extension of our previous bi-directional scan algorithm [23, 29]. A new acceleration-continuation procedure is added to the feedrate optimization algorithm to address jerk constraints and remove discontinuities in the acceleration profile. The algorithm maintains computational efficiency and supports the incorporation of a variety of state-dependent (such as position, velocity, acceleration and jerk) constraints. By carefully organizing the local search and acceleration continuity enforcing steps, a globally optimal solution is achieved. Singularities, or critical points, and critical curves on the trajectory, which are difficult to deal within optimal control approaches, are treated in a natural way in this algorithm. Several application examples and tests are performed to verify the effectiveness of this approach for high-speed contouring.

Seismic and oceanographic evidence of present-day bottom-water dynamics in the Lousy Bank—Hatton Bank area, NE Atlantic

High-resolution multi-channel seismic records from the eastern margin of the Iceland Basin, Northeast Atlantic, are used to infer regional patterns of bottom water dynamics from seafloor morphology and distribution of the most recent geological units deposited along the margin. This information is combined with results from oceanographic and hydrodynamic measurements made in the area. The study area is located between Lousy Bank and Hatton Bank, where deep-water currents are forced around structural highs, leaving a complex pattern of topographically controlled sediment transport pathways. At the top and upper flank of Lousy Bank, George Bligh Bank and Hatton Bank topographic forcing leads to considerable acceleration of the northward flowing North Atlantic Current. At greater water depth, seismic facies indicative of bottom current action are found to be widespread. In addition, seafloor morphology displays moat features extending over large distances. The occurrence of these moats is confined to specific water depths in the range from 700–1400 m and from 1800 to 2200 m depth range. These depth ranges correspond to the basal depth stratum of the North Atlantic Current and the depth range of the Deep Northern Boundary Current, respectively. Geological evidence suggests maximum near-bottom current speed of about 0.5 m/s for these moat areas. Using oceanographic data we suggest that formation of the moats is not likely to be associated with the presence of a persistent high-speed contour current core, but probably originates from the occurrence of solibores and thus may be related to the internal wave field of the Iceland Basin possible linked to atmospheric pressure variation.

Development of a high-speed 3-axis machine tool using a novel parallel-kinematics X-Y table

In this paper we discuss the development and performance evaluation of a high-speed, 3-axis milling machine using a novel parallel kinematics x-y table. The x-y table is based on a an inversion of the Oldham coupling. The advantages of this kinematic configuration include low inertia, uniform kinematic conditioning, and dynamically matched axes. The design of the x-y table makes this system particularly well suited for high-speed contouring in the x-y plane. The kinematics, dynamics, and mechanical design of the system are described. Linear and circular contouring experiments are conducted to evaluate the system capabilities. The stiffness of both the mechanism as well as the direct drive actuation system are measured and reported. The experimental results demonstrate that the proposed mechanism offers an attractive combination of performance characteristics for high-speed contouring and high-speed machining.

Optimal Feed-Rate Scheduling for High-Speed Contouring

The majority of efforts to improve the contouring performance of high-speed CNC systems has focused on advances in feedback control techniques at the single-axis servo level. Regardless of the dynamic characteristics of an individual system, performance will inevitably suffer when that system is called upon to execute a complex trajectory beyond the range of its capabilities. The intent of the present work is to provide a framework for abstracting the capabilities of an individual multiaxis contouring system, and a methodology for using these capabilities to generate a time-optimal feed-rate profile for a particular trajectory on a particular machine. Several constraints are developed to drive the feed-rate optimization algorithm. First, simplified dynamic models of the individual axes are used to generate performance envelopes that couple the velocity versus acceleration capabilities of each axis. Second, bandwidth limitations are introduced to mitigate frequency related problems encountered when traversing sharp geometric features at high velocity. Finally, a dynamic model for the instantaneous following error is used to estimate the contour error as a function of the instantaneous velocity and acceleration state. We present a computationally efficient algorithm for generating a minimum-time feed-rate profile subject to the above constraints, and demonstrate that significant improvements in contouring accuracy can be realized through such an approach. Experimental results are presented on a conventional two-axis X−Y stage executing a complex trajectory.

524 新高速輪郭加工機能「Super-NURBS」

OKUMA heralded in the industry and developed high-speed contour machining technology to control high-accuracy, high-quality and high-speed machining in shape machining as represented by die mold machining. In 1987,the technology was loaded into our company's computer numerical control "OSP". Since then, our company has developed and supplied a series of advanced control functions one after another prior to the needs of a market. OKUMA has developed the new high-speed contour machining technology "super-NURBS" which is based on technologies cultivated for many years. The new control technology "Super-NURBS" always pulls out the highest acceleration and deceleration performance of a machine also in curved surface machining. With this, "Super-NURBS" improves the machined accuracy and quality as well as reducing the machining time sharply (conventional ratio of our company twice). The following describes the abstracts and effects of new numerical control technology "Super-NURBS".

NURBS machining and feed rate adjustment for high-speed cutting of complex sculptured surfaces

Owing to the enormous engineering advancement in modern industry, the competition in the development of advanced manufacturing technologies has been increasingly intense as can be seen in automobile, aerospace and various industries. Not only has product quality improved tremendously, but also the demand over production speed has become higher. Therefore, high-speed and high-accuracy production has become a very important goal of modern manufacturing companies. Thanks to ever increasing computer speed and the open architecture of new controllers in computer-controlled machines, the capability and flexibility of today's CNC machines allow us to machine contoured geometry using non-uniform rational B-spline (NURBS) curves directly from the free-form surfaces of a complex CAD/CAM model. As a result, machining accuracy and product quality can be greatly improved while machining time is also significantly reduced. This paper proposes a post-processing approach to convert G1 NC codes from most CAD/CAM systems to NURBS NC paths for highspeed contour machining. The NURBS interpolation strategy that takes into account the optimized cutting feed rate based on machine dynamic response and curvature of the NURBS curve is also developed. Experiments show that the implemented NURBS cutting can significantly improve machining accuracy and reduce cutting time and therefore satisfies the requirements of today's highspeed and-accuracy machining needs.

Coordinated Position Control of Multi-Axis Mechanical Systems

Position coordination of multi-axis mechanical systems is studied. Under the assumption that the coordination objective can be represented by smooth functions of the positions of the multiple axes control systems, a necessary coupling effect can be introduced to each axis by the proper choice of a Lyapunov-like function. The resulting, control law requires the knowledge of the desired trajectories and their time derivatives as well as actual position and velocity information. Implementation of the proposed control algorithm on a CNC feed drive system shows significant improvement in dimensional accuracy during high speed contouring.

Accurate High Speed Contouring — the Dream to the Reality — Part 3

Summary Part 1 IN Part 1 the problems of achieving the many potential benefits of high speed machining of aluminium alloy were discussed. The greatly increased cutting feedrates, for example, can still be limited by the machine tool design and the limitation of the control and drives capability. The processing speed of the control and its ability to control slideway movement accurately along a contoured path also can create a severe limitation.

Accurate High Speed Contouring — the Dream to the Reality:‐ Part 1

Many papers have been written on the theoretical advantages of high speed machining and its particular attraction for the aircraft industry has fuelled considerable research into its practical development.