Materials Science Forum Vols. 697-698

Abstract: This paper adopts with a PMAC Programmable Multi-axis Controller to control a linear motor through adjusting PID + velocity and acceleration feedforward parameters of the control card. The motor can reach 50-nm precision at lower speed. The PLC real-time monitoring function of the software is used to monitor the actual pace of registers. The real-time online adjustment of PID parameters of the motor at various speeds is realized, which makes the motor reach high motion accuracy at various velocity and acceleration.

Abstract: A new tool path generation method based on Z-buffer method is proposed for free-form surface machining by using ball-end cutters. Firstly, to avoid ball-end mill cutting the workpiece, we make the cutter shaft which is perpendicular to machining surface tilt angle θ, then determine the examining area and then judge there is or not a interference occurring between ball-end mill and examining area, if there is, then make a adjustment for cutter shaft. The discretized points within the examining area are efficiently read in and stored directly by the computer hardware; no extra searching and iterative methods are needed. Simulation results show that, comparing with the traditional algorithm, the tool-position calculation time is shorter, and the phenomenon of workpiece squeezed and scratched is less in this algorithm. It meets the basic needs of five axis machining accuracy. Finally we make a practical machining experiment for cutter location generated.

Abstract: The paper presents the principle and algorithm of multi-point and time-sharing measurement method to detect the machine geometric accuracy.Its basic principle is based on laser tracker and the multilateral method,moreover,only one laser tracker is used in the measurement.Its cost is lower than multi-point and simultaneous measurement.Then the application of the method is introduced on a glass measuring instrument.The geometric error of the machine is separated in x and y direction.

Abstract: Machine tool joint stiffness has important affects on the dynamic characteristics of the whole machine tool. It is a challenging task to optimize multi-joint stiffness of the overall structure. By discussing the distribution of stiffness of linear guides, ball screws, bolt joints and bearings, a discrete optimization method of multi-joint stiffness of a machining center was presented based on orthogonal experiment and FEA. Mean frequency formulation was adopted to define the index of orthogonal optimization. According to the principle of orthogonal experiment, optimization levels were found out, sequence of the factors on the index of the orthogonal experiment was listed and significant factors were determined. Results of this research proved the validity and feasibility of the discrete optimization method of multi-joint stiffness of the whole machine tool by combining orthogonal experiment and FEA.

Abstract: Sensitivity analysis is to evaluate how sensitive the surface deviation of a workpiece is to a geometric error of locator. With this thinking, the relationship between geometric error of locators and the position error of holes group is presented. The fixture system errors model and evaluation model of position errors are established. Furthermore with both models, a method of optimizing the position errors by adjusting the locators’ position is presented, which can get to accuracy localization. At last, a simulation study is used to verify the method.

Abstract: Geometric errors identification of revolving axle of multi-axis machine tool has encountered a great difficulty in geometric errors compensation. This paper describes a new method to identify geometric errors inherent to revolving axle of multi-axis machine tool based on a ball-bar system. Under RTCP (Rotation Around Tool Center Point) or RPCP (Rotation Around Part Center Point) function, the displacement errors of revolving axle in X, Y and Z direction can be obtained by the ball-bar system respectively at every measurement angle. With the corresponding identification algorithm proposed in this paper, the whole six geometric errors of revolving axle can be identified. This new method is suitable for any type of multi-axis machine tool and without structural constraints. To confirm the validity of the proposed method, an experiment has been conducted on a five-axis machine tool, and the results show that this method is effective and applicable.

Abstract: On-line tool wear sensing was an important subject in the Flexible Manufacturing System. Mathematic method is applied in this paper to analyze the correlation between cutting force and tool wear, and a cutting force model was established based on the tool wear. The predicted value of cutting force was calculated through the cutting test. Predicted value by comparison with the experimental data verifies the accuracy of the cutting force model. On this basis, a new method for monitoring tool wear based on measuring cutting force was proposed.

Abstract: Research on thermal field and thermal errors of NC machine tools were carried on using infrared imaging and laser distance measurement technologies. It mainly focused on the analysis of thermal field distribution of a three-axis horizontal machining center and the relationships between thermal behaviors and their temperatures. It was found experimentally that spindle thermal errors is one of the main errors sources of NC machine tools, and spindle thermal errors has been observed to be closely linked to the temperature distribution of machine tools. There was a significant increase in the axis positioning error related to the spindle temperature increasing. The elongations on Z direction are much larger than the extensions of X and Y directions. Finally, a method by adjusting spindle temperature to control spindle thermal errors was taken.

Abstract: After creating the three-dimensional models of dedicated computer, models can be smoothly put into ANSYS through interface between Pro/E and ANSYS. By selecting the grid cells, setting parameters of material properties, dividing grids, applying load and boundary conditions and post-processing, the temperature contours of the whole case and its key components are got. Compared with the test results, it was verified that the feasibility and rationality of carrying out thermal simulation by ANSYS software, providing a theoretical basis for the designers to optimize dedicated computer case.

Abstract: In order to solve the problems that traditional kinematics model built by the method of D-H parameters can only reflect relative movements between adjacent components and can't express directly the spatial poses of every component relative to static platform, Lie-algebras is used this paper to establish the product of exponential formula of forward direct kinematics of every branch chains. The elimination method and Paden - kahan sub-problems are used to calculate joint variables. Then the quick and intuitive inverse algorithm of cross rods parallel machine tools is acquired. The algorithm provides reliable proofs for the analysis of error compensation, kinematics interference and singularity. Finally we prove our theory with an example of an actual parallel machine tool.