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1.
Five-axis machine tools are designed in a large variety of kinematic configurations and structures. Regardless of the type of the intended analysis, a kinematic model of the machine tool has to be developed in order to determine the translational and rotational joint movements required to achieve a specified position and orientation of the cutting tool relative to the workpiece. A generic and unified model is developed in this study as a viable alternative to the particular solutions that are only applicable to individual machine configurations. This versatile model is then used to verify the feasibility of the two rotational joints within the kinematic chain of three main types of five-axis machine tools: the spindle rotating, rotary table, and hybrid type. A numerical measure of total translational joint movement is proposed to evaluate the kinematic performance of a five-axis machine tool. The corresponding kinematic analyses have confirmed the advantages of the popular machine design that employs intersecting rotational axes and the common industrial practice during setup that minimizes the characteristic rotating arm length of the cutting tool and/or workpiece.  相似文献   

2.
This paper describes in two parts a new method and device for measuring motion accuracy of numerical control (NC) machine tools. In the first part, the measurement principle and the characteristics of the prototype device are proposed. The device consists of a double-bar linkage with two rotary encoders. The working range of the device is disc-shaped with a radius of almost the double the link length, except a small area around the centre of the disc and an outer area both around the change points of the linkage at the centre and the circumference of the disc. Because the method has high resolution for any measuring point within the working range, it can be applied to measure most items of motion accuracy of NC machine tools. The method is particularly suitable to measure the trajectory accuracy of circular motions. The device has a compact structure and its installation on a machine tool to be measured is simple and quick. The experimental results show that the prototype device has very good response to small displacement and good repeatability with high precision to the measurement of circular motion trajectories. The influence of measurement noise is hardly observed in the experimental results.  相似文献   

3.
The complex structures of a multi-axis machine tool may produce inaccuracies at the tool tip caused by dimensional errors in the machine's link parameters. This paper addresses two important issues for precision machining: (1) which link parameters (denoted as active parameters) of a machine tool can affect the machining accuracy of a workpiece and (2) how to measure the active parameters by using a grinding wheel as a measuring probe. To achieve this, a modified Denavit–Hartenberg (D–H) notation is introduced to model a multi-axis machine tool. The NC data equations are then derived in terms of the machine's link parameters. It is found that the link parameters of a machine tool can be divided into two types: active and nonactive parameters. The prerequisite for obtaining an accurately machined workpiece is to have correct values of the active parameters and the workpiece home position. Based on the developed NC data equations of a multi-axis machine tool, this paper also addresses the technique of using a grinding wheel as a measuring probe to determine the active parameters and the workpiece home position. Experimental results are also given with illustrative examples.  相似文献   

4.
A main limitation of parallel kinematics machine tools (PKM) in high-speed machining tasks is their low level of accuracy compared with serial kinematics machine tools, which is largely due to geometrical transformation errors. These errors can be reduced by identifying the geometrical parameters of the inverse kinematics model integrated in the controller by exteroceptive calibration. The aim of this paper is to propose a new external measurement method in order to perform the geometrical calibration of PKM, taking into account machining requirements. This method is implemented in three steps: machining of a dedicated part, measurement, and identification of the geometrical parameter values. In this paper, the method is described with a particular emphasis on the machined surface profiles of the dedicated part and on the numerical calibration approach. Measurement errors on the machined surface enable the identification of the PKM geometrical parameters. Thus, calibration is performed with respect to machined surface defects without taking into account the entire tool pose defect, as is the case in usual calibration methods. The study is illustrated using the Verne PKM, which is located at IRCCyN (Nantes, France).  相似文献   

5.
This paper describes in two parts a new method and device for measuring motion accuracy of NC machine tools. In the first part, the measurement principle and the characteristics of the prototype device have been presented and discussed. In the second part, an efficient and practical approach to identifying the errors of the proposed device after assembly is developed and evaluated. The approach ensures realising the aim of the investigation, i.e. to measure the most items of the motion accuracy, especially, to measure and assess the trajectory accuracy of a general planar motion of NC machine tools. The result of the identification experiment by using the prototype device on a machining centre for the prototype device is presented and it well verifies the validity and practicality of the approach. Some measurement results for the general planar motions of the machining centre are also shown, which sufficiently demonstrate the desirable capability of the proposed method and device.  相似文献   

6.
The current trend within the Tool and Die manufacturing sector is to machine components directly from hardened material using high speed 5-axis machining. This has been driven by the increasing requirements for cost competitiveness and lead-time reduction. Significant research effort has been applied to the optimisation of the process with factors such as tooling and machining strategies being considerably improved. However, the underlying structures of the machine tools used have remained unchanged and still consist of a serial kinematic chain. One of the standard justifications for the development of machines designed around parallel kinematic chains is that they should exhibit inherently greater stiffness, have higher axis accelerations and be capable of generating significantly higher cutting forces than conventional serial machines. This suggests that they should be ideally suited to the direct manufacture of tools and dies from hardened material.The comparison of different machine tool types is a complex and difficult process, particularly when their structures are fundamentally different. This paper describes an approach used to compare the performance of three very different types of machines. The technique uses two parameters; surface finish and geometric accuracy to assess the relative performance of different machine tools when cutting hardened material. The method is used to compare a serial kinematic 5-axis machining centre, a serial kinematic 3-axis machining centre and a parallel kinematic 6-axis machining centre.The results of the comparison are presented in this paper and show that all the machine tools performed to an equal standard for materials with a hardness of 54HRc but for very hard materials, 62HRc, the parallel kinematic machine out performed the serial machine tools.  相似文献   

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