Nowadays, computer numerical control (CNC) machine tool undertakes more processing tasks than other common machine tools because of its highly automated machining ability and high performance. ...However, due to the lack of intelligence in machining process planning, machining procedure of products mostly depends on process planners rather than CNC machine tools. To make product quality less dependable on process planner’s ability and improve the efficiency of process planning in order to fulfill changeable market, this paper presents an approach to design and develop CNC machining process knowledge base using cloud technology. The general standard STEP-NC is mapped to web ontology language (OWL) to describe machining process-related knowledge in a readable and comprehensible way. This mapping relation also makes knowledge suitable for storage in HBase. Through this ontology model, descriptive and logical knowledge can be collected. Hadoop platform is used in this approach to provide the NoSQL database HBase for large-scale knowledge storage and MapReduce programming model for large-scale knowledge processing. Taking advantage of MapReduce, knowledge query engine and reasoning engine can be developed. Users can submit task and resource descriptive files to the cloud through CNC controller and get machining process solutions from knowledge base. Evaluation mechanism is also adopted to filter low-quality knoweldge.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Non-uniform rational B-spline (NURBS) curve has been widely used in manufacturing systems. A good interpolator can help the system to improve the contour accuracy and get smooth dynamics performance, ...but it is hard to get a balance between the interpolation performance and computational load. As the derivative and curvature of NURBS curves used in manufacturing systems are high-order continuous, it is possible to predict a desired interpolation arc length based on the relationship of historical feed chord length and its corresponding arc length in one interpolation cycle. Therefore, this paper proposes a novel interpolation method, which consists three stages. Firstly, a NURBS curve is split into several high-order continuous segments based on its degrees and control points. Secondly, a prediction model based on Newton’s divided differences interpolation equation is derived from the relationship of interpolated chord length and its corresponding arc length, so that the target arc length of the next interpolation cycle can be predicted. Finally, target parameter
u
of every interpolation cycle is calculated with Taylor’s expansion, whose values are corrected by iteration, and then the position of the target interpolation point can be achieved. Performance of the proposed algorithm is tested and compared with other methods, and the simulation results show the proposed method can achieve smaller velocity fluctuation with low computational load.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Tolerance analysis methods, which are important to achieve a balance between manufacturing costs and functional requirements, have been studied and improved over the last 30 years. This paper ...proposes a new method to improve the precision of assembly simulation for statistical assembly simulation; by investigating the effect of the geometric deviations and mechanical behaviors of assembly contact on the stack-up assembly deviation by combining the recent theories on the tolerance analysis of rigid bodies and local contact deformation. To improve the precision of the tolerance analysis, real parts with form defects were simulated with the help of non-nominal skin model shapes. The SMSs were first considered to be rigid, and a quadratic optimization-based method for the rigid body displacement was used to calculate the initial contact points of all the SMSs. Next, contact deformation, following Hertzian contact theory, occurred at the initial contact points, which changed the relative positions of the SMSs in the subsequent interactions. The iteration process was convergent, and the final simulation for tolerance analysis could be generated after several iterations. Case studies demonstrated the practicality of the proposed method. Their actual assembly deviations were simulated by combining the effects of geometric deviations and local surface deformations. Since the proposed tolerance analysis framework based on statistical assembly simulation, it is expected to control the functional requirements of mechanical assemblies with much rough tolerance design and help optimize the tolerance in the future.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The development of computer, internet and information technology puts forward higher demands for Computer Numerical Control (CNC) machine tools to improve the intelligence in many aspects. Among ...these aspects, intelligent process planning plays an important role in current changeable market and customized product promotion by shortening production cycle and providing more stable process planning ability. To realize intelligent process planning, a CNC controller with cloud knowledge base support is proposed with ability of making process planning autonomously based on workpiece design. Previous work of knowledge model and cloud knowledge base framework design is introduced, and then this paper focuses on the complete process planning method within the intelligent CNC controller. Both interactivity between knowledge base and CNC controller, and query/infer mechanism in knowledge base are illustrated in detail. A case study of two shafts process planning is shown to demonstrate the feasibility of the intelligent process planning method.
When fixed abrasive wire saw is used to cut polysilicon, free SiC abrasives are added into the cutting coolant to form the fixed and free abrasive combined wire sawing process, so as to impact and ...roll the as-sawn wafer surface to remove the ductile amorphous silicon layer. Then, the as-sawn wafer can be textured by acid etching technology. The movement characteristics of free abrasives in sawing area directly affect their lapping behavior and the morphology generation of as-sawn wafer surface. In this paper, the flow field characteristics of cutting coolant and the movement characteristics of free SiC abrasives in the sawing area were studied, when using an abrasive groups interval distribution diamond wire for sawing. A three-dimensional model of cutting coolant in sawing area was established. Based on FLUENT, the influences of wire speed, feed speed, wire pretensioning force, viscosity of cutting coolant and wire surface structure parameters on the concentration peak position of free SiC abrasives in the cutting coolant along the wire axial direction were analyzed. The results show that the concentration peak of free abrasives will gradually shift to both sides along the circumferential direction of the wire in the sawing area. The deflection angle and width angle of free abrasives concentration peak are only related to the length of the bare wire area, and decrease with the increase of its length. Comprehensively considering the hydrodynamic pressure effect in the bare wire area, reducing the wire speed and tension, and increasing the feed speed and cutting coolant viscosity are conducive to enhance the lapping effect of free SiC abrasives on the as-sawn wafer surface. The change of wire structure parameters has no regular effect on the lapping behavior of free SiC abrasives in the bare wire area.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Chatter is the main problem that limits the application of industrial robots in the field of machining process. It is critically important to establish an adaptive chatter detection solution for ...robot machining process and realize the online detection of chatter. However, different from machine tool chatter, the chatter in robotic machining process is more complex to be detected due to the variable stiffness characteristics and weaker stiffness of normal industrial robot, and the existing literature has less research on this problem. This paper presents a comprehensive solution for online chatter detection in robotic machining process. Firstly, in order to detect the chatter in robotic machining process and avoid mode mixing problem in variational mode decomposition (VMD) process, an adaptive variational mode decomposition (AVMD) method based on kurtosis and instantaneous frequency is proposed, which realizes the adaptive selection of the decomposition parameter. Secondly, optimal decomposition parameters are calculated by using genetic algorithm. By optimizing the discrete step length of decomposition parameter, it greatly reduces the optimization time. Last but not least, approximate entropy, energy entropy, and proposed entropy drift coefficient are extracted to distinguish chatter and stable machining state. Simulation and experimental results show that the proposed method can meet the real-time requirements of online detection and detect the occurrence of chatter effectively.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
CNC machine tool plays a vital role in intelligent manufacturing, but up to now, CNC controller, which works as the “brain” of the machine tool, is just a loyal executor of machining command without ...intelligence. This paper is aimed to improve the intelligence of CNC controller from the aspect of machining process planning, which has a great effect on product quality and production efficiency. A STEP-compliant data model is adopted. Compared to previous STEP-NC controller, this paper presents a new paradigm to integrate the ability of autonomous process planning into CNC controller based on cloud knowledge base. A hierarchical and modular architecture is designed to obtain machining process planning from cloud knowledge base timely and to conduct the machining implementation on shop floor. Furthermore, efficient and matching operation mechanism is researched. It offers a proposal to use cloud knowledge to implement intelligent manufacturing. Finally, a case study is demonstrated to verify the feasibility of this intelligent CNC controller.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The round-off error, which is caused by cycle sampling of the interpolation period, affects the interpolation accuracy and motion smoothness of computer numerical control (CNC) machining. To consider ...the round-off error while restricting the motion parameters within their specified ranges, a time-rounding-up-based feedrate scheduling method is proposed. Firstly, the characteristics of S-shaped acceleration/deceleration (ACC/DEC) algorithm are analyzed by setting the jerk of each section as a variable. The expressions of jerk are derived and some important properties are discovered. According to these properties, it is possible to limit all the motion parameters in their given ranges through increasing the interpolation time and adjusting other motion parameters. Secondly, a new time-rounding-up scheme is designed to guarantee that the total interpolation time of each curve segment is an integer multiple of interpolation period. Then, based on the rounded time, the adjustment principles of the displacement and maximum feedrate are proposed to satisfy the various constraints. Its feasibility is also analyzed. Finally, based on the time-rounding-up scheme and the parameter adjustment principles, a series of feedrate scheduling methods are designed for different situations. For most situations, a non-standard S-shaped ACC/DEC profile can be generated with no round-off error and all the motion parameters can be restricted within their given ranges. A series of simulations and practical experiments are conducted to verify the good performance and applicability of the proposed method.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This article considers finite-time trajectory tracking control problem for robotic manipulators with parameter uncertainties and external disturbances. A finite-time controller that achieves high ...precision and strong robustness is proposed without the requirement of the exact dynamic model. First, a novel finite-time model-assisted extended state observer is designed to compensate the system uncertainties with complex and uncertain dynamics. Then, a composite finite-time controller is developed for trajectory tracking control with the help of finite-time model-assisted extended state observer. Compared to the classic extended state observer, it is proved that the estimation error of finite-time model-assisted extended state observer can be stabilized in finite time. Meanwhile, the finite-time convergence of the closed-loop system with the proposed controller can also be proved through Lyapunov’s stability theory. A variable structure term is employed to compensate the estimation errors of finite-time model-assisted extended state observer. The validity of the control scheme is demonstrated by simulations and experiments.
Feedrate scheduling is one of the most important factors of computer numerical control (CNC) machining and has become a crucial research problem. In order to improve the machining accuracy and motion ...smoothness, an optimized feedrate scheduling method considering round-off error compensation based on S-shaped acceleration/deceleration (ACC/DEC) algorithm is proposed in this paper. There are two main stages, namely initial feedrate scheduling and parameters calculation of round-off error compensation. In the stage of initial feedrate scheduling, a novel time rounding principle is introduced to reduce the round-off error. Meanwhile, the motion parameters of each section can be calculated based on the proposed feedrate scheduling method. The constant feedrate section used for round-off error compensation is always guaranteed to exist although the actual maximum feedrate might be smaller than the command feedrate. Then, in the stage of compensation parameters calculation, the round-off error can be obtained based on the proposed time rounding principle and the scheduled parameters should be updated. In order to maintain the continuity of the acceleration profile, the improved trapezoidal ACC/DEC algorithm is introduced to conduct the error compensation and the crucial parameters can be calculated based on its special properties. In addition, the feedrate look-ahead strategy is also tweaked to enhance the reliability of feedrate scheduling. Finally, a series of simulations and practical experiments with two non-uniform rational B-spline (NURBS) curves are conducted to verify the good performance and applicability of the proposed method.
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