Key Engineering Materials Vols. 375-376

Abstract: Thermal errors of CNC machine tools was checked and measured by double-ball bar in this paper. Mathematical model of measuring thermal error of machine tools by DBB on the principle of its basic measurement was derived. Combining it with kinematics model of machine tool, the identification law of error component parameters was established when thermal error was checked and measured by DBB. Thus, all of the thermal error component would be separated from the synthetical error. Finally, the entire analysis was provided to adjust machine tool and actualize error compensation of machine tool through grasping main factors influencing the machining precision of machine tool.

Abstract: An experimental investigation was conducted to reveal the influence of thermocouples on the measurement of grinding temperatures. The temperatures at the wheel-workpiece interface were measured in dry grinding using two types of foil thermocouples. It is shown that the temperatures measured by the different types or geometric parameters of thermocouples were rather different. For a specific thermocouple, the temperatures generally decreased with the reduced end-surface area of the thermocouple, which is possibly related to the reduced number of abrasives at the wheel-thermocouple interface.

Abstract: The tool wear detection system based on the image processing and computer vision has better study value and foreground. The paper brings forward the detection method of the tool wear condition, which solves the two main problems. Firstly, gets the high quality images by fuzzy restoration arithmetic. Because the cutting tool is always at the movement state during the cutting, the real-time collected sequence images by CCD sensor are blurred with noise. Then, obtains the character parameter uniformity Q2 by calculating gray co-occurrence matrix, which can distinguish the cutting tool is weared or not weared. The experimental results indicate that detection of the tool wear condition by computer image processing reach our aim.

Abstract: This paper advances a method to implement the on-machine measurement (OMM) with the touch-trigger probe, also called switching probes. Some of the advantages and disadvantages for touch-trigger probe are discussed. However, the touch-trigger probe errors exist and become one of the major errors for the measurement accuracy. Major factors that influence the probe measurement have been analyzed. The basic technique of probe measurement error modeling with artificial neural network was researched, and also the probe measurement error compensation with 3-layered backpropagation artificial neural network was presented. At last in the experimental system composed of DIXI 50 machining center, Fanuc 16i control system, Blum CNC P82.046 probe and PC, valid the correlated techniques. In addition, the connection and communication between the machining center equipped with probe system and the computer have been introduced. The experiment indicated that, using the touch-trigger probe makes on-machine measurement more automatic and efficient. And by using the back-propagation neural network for error compensation make on-machine measurement more precise.

Abstract: A new dynamics model for multi-degree of freedom high-speed milling system is proposed, which takes account of regenerative effects and the effects of the relative vibration of spindle axis in milling process. Based on the mode synthesis theory and the zeroth-order approximation of the Fourier series, an integrated stability analytical method for multiple frequencies is presented, which involves multiple orders modal characteristics and higher order excitations in high-speed milling process. The chatter stability lobes are predicted in the frequency domain using the proposed stability analytical method, and verified by milling experiments. It is shown that stability regions involving multiple natural modes are reduced contrary to the case of single natural mode.

Abstract: Five-axis NC machining tools can improve the efficiency and accuracy obviously in today’s machining industries, but the machining errors and tool interference are likely to happen due to the complexity of tool motion. So the verification of the tool path is very important and necessary before machining the part. A new algorithm for 5-axis machining verification based on the swept volume has been presented in the paper. Based on the machine tool path and the cutter geometry, the cutter’s instantaneous swept profile is determined. By integrating the intermediate swept volume, the cutter’s swept envelope can be constructed and applied to NC verification. The algorithm has been implemented through Visual C++ and OpenGL language on Windows XP platform; a few examples are to verify the reliability of the proposed algorithms effectively. The experiment results indicate that the proposed method is superior to the traditional methods on the processing time and image quality. This proposed algorithm can be further applied to machining error analysis, collisions interference and NC path optimization, etc.

Abstract: Focusing on the machining complexity of large containers where difficult-to-cut materials are used a lot, a cutting process parameter optimization expert system for difficult-to-cut materials is constructed based on experts’ knowledge and computer soft wares (VC++ 6.0and SQL Server 2000). In this paper, we made construction analysis and module design for the expert system, then constructed the knowledge base according to certain constraint models, and realized the functions of every module of the expert system by using the forward inference. This expert system can play a scientific direction role in the process parameters selection for cutting large containers.

Abstract: In some cases the spatial cam is manufactured with a cutter whose diameter is smaller than that of the roller of cam mechanism, which is defined as nonequivalent manufacture method in the paper. By the analysis for manufacture of contact lines between the cam and the roller, it is indicated that errors caused by the different directions of normal vector are unavoidable for the nonequivalent manufacture method. In order to find the best tool axis vector to minimize the machining error, this paper realized the nonequivalent machining of spatial cam surfaces using the NC flank milling method and proposed a new generation algorithm of the tool path based on NURBS. The NURBS ruled surface of tool axis trajectory is confirmed based on the least square optimization method and the machining error model is given. At last, a numerical calculation and simulation example is described to verify the effectiveness of the algorithm proposed in the paper.

Abstract: Fractal dimension is proposed to evaluate grit protrusion feature concerning grit protrusion area and length. The aim is to investigate crystal integrate of diamond grit protruded from grinding wheel after dressing. First, 3D crystal diamond grits are established in AutoCAD concerning various crystal configurations. Second, fractal dimension for original diamond grit is analyzed theoretically. Then, dressing experiment is carried out to investigate fractal dimension of grit protrusion topography by suing image processing of SEM photos of dressed grinding wheel surface. Finally, grit protrusion feature is investigated by fractal dimension concerning the depth of cut in dressing process. It is confirmed that fractal dimension can display grit protrusion feature and it may be used to evaluate dressing performance.

Abstract: This paper presents a new trajectory tracking control algorithm to uncertain mobile robot with nonholonomic constraints. This algorithm is based on the non-singular terminal sliding mode technique, which can eliminate the singularity problem caused by conventional terminal sliding mode control. The system state vector is designed using backstepping method, this method breaks down nonlinear systems into low dimensional systems and simplifies the controller design. By combining Lyapunov method, it is proved that under this control law, the pose errors converge to zero, the mobile robot can track the desired trajectory when the desired velocity satisfies some assumptions. Simulation results validate the theoretical analysis.