Zhenyu Han

Development of a PC-based Open Architecture Software-CNC System

Abstract As a key technology in the field of advanced manufacturing, an open architecture controller is studied. In order to develop an open architecture software-CNC system on personal computer (PC) according to open modular architecture controllers (OMAC). First, the software and hardware platform is chosen and software realization methodology for the CNC system is determined. Second, static modeling methods of an open architecture controller inclusive of object-oriented (OO) programming technology, dynamic link library (DLL) technology and system modules partition are investigated. Third, the dynamical behavioral modeling and the data flow representation of open architecture controller are discussed, which are both described in hierarchy finite state machine (FSM) model. Fourth, a reusable software module model is established to develop software function module library. Finally, a 3-axis milling machine tool test-bed, named for HIT-CNC, is successfully designed by means of the constructed software function module library and the system configuring method. The experimental results show that, besides increasing the degree of reusability and openness, application of above-mentioned methodology leads to significant decrease of development time as well as maintenance cost.

Integration of a 5-axis Spline Interpolation Controller in an Open CNC System

Abstract A 5-axis controller with curve interpolation function is developed to satisfy high-speed and high-precision computer numerical control (CNC) machining of machine parts with complex shapes in the authors-devised open CNC system. The instruction format of this interpolation method and the generation procedure of the numerical control (NC) files are introduced. The interpolation curves of both position vectors and orientation vectors constructed by the controller are C2 continuous and independent of machine tool kinematics. The controller fits in with any 5-axis machine tools by configuring the related kinematics transformation module. The position curve is to be discretized in realtime using a truncated Taylor series expansion. Coordinated motions of linear axes and rotary axes are achieved by relating the orientation curve parameter to the position curve parameter in the machining process. The performance of the proposed controller is demonstrated by a practical example.

Realization Methodology of a 5-axis Spline Interpolator in an Open CNC System

By making use of the advantages of non-uniform rational B-spline (NURBS) curves to represent spatial curves, an instruction format with double NURBS curves suitable for 5-axis coordinated real-time interpolation is presented to replace the current 5-axis coordinated linear interpolation method defective in low-speed, low-accuracy and enormous numerical control (NC) files in sculptured surface machining. A generation procedure of the NC files with the presented format is introduced and the method to realize the interpolation in an open computer numerical control (CNC) system is developed by ourselves. These illustrated the feasibility of the proposed method and its capability of avoiding all the shortages of 5-axis linear interpolation method.

Design of an industrial Ethernet based embedded open architecture CNC system

In order to promote the high frequency performance of open architecture CNC system, an embedded CNC controller combining FPGA (Field Programmable Gate Array) technology and real-time Ethernet communication bus was designed, which consisted of an embedded ARM (Advanced RISC Machines) processor and an FPGA. An open source CNC software running under Linux operating system was customized to accommodate the ARM processor, in which interpolation and motion control modules were implemented in FPGA for better real-time performance. Meanwhile, the FPGA also acted as the master node communicating with servo drivers via EPL (Ethernet Powerlink) network. The EPL stack was implemented with a Nios II soft processor in the FPGA. Experimental results have shown that the designed system worked properly.

Parametric Study on Heat Transfer for Tow Placement Process of Thermoplastic Composite

Fiber placement process of thermoplastic material is an in situ consolidation process which can significantly reduce consolidation process time and save costs compared with autoclave consolidation. The heat and crystallization behaviours play very critical role in the quality control during the process. In this work, two dimensional model of finite element is presented to perform heat transfer analysis of fiber placement process. The relationship between heat distribution of lamination and process parameters, including roller velocity, main heating temperature, preheating temperature, preheating length and preheating location, is deeply investigated. The numerical results show that for certain heating temperature there is a safe roller velocity which should not be exceeded, and such parameters as main heating length, preheating length and preheating location could be optimized to obtain better quality of product.

Open Architecture CNC Software Package and Key Technology

To meet the need of advanced manufacturing technique, an open computer numerical control (CNC) software package for CNC machining is developed. Module library of the software package was of tree structure with a depth of 5. Terminal nodes of the tree were module units with unambiguous functions. Module units which dealt with real-time tasks were developed adopting real-time dynamical linked library (RTDLL), and non-real-time module units were developed with component object model (COM). CNC controllers for various machine tools could be built with the software package. The controllers’ external interfaces were coincident with the serial real-time communication system (SERCOS) international standards, and the internal interfaces followed the open modular architecture controller (OMAC) agreement. Motion controllers for 3-axis linkage milling machine tools and for 5-axis linkage milling machine tools were built using the software package. It is shown by experiments that controllers built can be used for motion control of CNC machine tools and CNC machine tools with the controllers have good processing performances.

A Heuristic Task Periods Selection Algorithm for Real-Time Control Systems on a Multi-Core Processor

The performance optimization problem is investigated for discrete-time control systems on a multi-core platform. An integrated approach which considers both control performance and real-time scheduling aspects is applied to allocate optimal periods to controller tasks. A real-time control system is modeled as a set of directed acyclic graphs with weighted edges in this paper. The system allows producer/consumer relationship between tasks, and the data dependence relationships between tasks are uncoupled by attaching harmonic constraints to task periods. The period assignment problem is formulated as an optimization problem, which minimizes the system performance loss index under multi-core schedulability constraints. A heuristic search algorithm is proposed to solve this optimization problem and select periods for real-time tasks scheduled by rate-monotonic scheduling algorithm. Experimental results demonstrate that the proposed heuristic algorithm is capable of finding a high quality local optimal solution with fast computing speed. The proposed method is applicable to online failure recovery and reconfiguration in real-time control systems.

Finite difference method–based calculation of gravity deformation curve for the large-span beam of heavy-duty vertical lathe:

To solve the problem that gravity deformation curve of large-span cast-iron beam analyzed by finite element method simulation is inaccurate due to material imperfection, a discretization calculation considering the inhomogeneity of the material based on finite difference method is proposed. Supposing the flexural rigidity of the beam is different along the length, the continuous beam is discretized into segments based on finite difference method, and equivalent flexural rigidity is presented to characterize the inhomogeneity of the material. Correction model of bending deformation is constructed to revise the results of finite element method simulation applying equivalent flexural rigidity that could be obtained by combining the discretization model and deformation data acquired in a simple self-load experiment in which the beam is simply supported without any assembly process. Finally, flowchart of application is presented, and the approach is illustrated through an example from real case. The experimental results show that the computational accuracy is improved from 73.14% to 88.33%, compared with just finite element method simulation.

5-Axis A-Spline Iterpolation Function and Its Realization Strategy

The current 5-axis coordinated linear interpolation method results in low-speed, low-accuracy and enormous numerical control (NC) files in sculptured surface machining. An instruction format with AKIMA spline curves suitable for 5-axis coordinated real-time interpolation is presented by making use of the advantages of AKIMA curves to represent spatial curves. Curve through position vectors in the machining path is constructed using AKIMA spline method. The related orientation vector to each position vector is calculated by angles of the machine tool rotation axis. Then curve through orientation vectors is achieved by AKIMA method too. Real-time interpolation of these curves is accomplished with a method of truncated Taylor series expansion. A controller with this interpolation method is developed in an open computer numerical control (CNC) system developed by ourselves. The performance of the proposed controller is demonstrated using a practical example.