Machine Tool Motion Research Articles

A simple and robust method for spiral bevel gear generation and tooth contact analysis

A simple and robust method to simulate spiral bevel gears generating and meshing processes is proposed. In a first part, a mathematical model of universal hypoid tooth surfaces generator is formulated. It is based on Fong’s approach. The model takes into account all the kinematic motions of common CNC machine tools dedicated to hypoid gears machining. It is general enough to enable the simulation of various hypoid gears cutting methods such as face-hobbing, face-milling, plunge cutting and bevel-worm-shaped-hobbing processes. In this paper, only developments related to face-milled spiral bevel gear generation are presented. We show that the results obtained are in good agreement with those of certified software. In a second part, a simple and numerically stable algorithm is proposed for unloaded tooth contact analysis. The simulation method is based on a discretization of one of the two tooth flank surfaces in contact and a specific projection of the points on the opposite flank. It gives a good approximation of the contact pattern location. The accuracy of the contact point locations and computing time is directly dependent on the mesh density. However, this approach enables obtaining in a very short time sufficiently accurate results to meet the needs of designers, particularly in the preliminary stages of design. The relative displacements of the gears can be taken into consideration. The robustness of the proposed computing process and the adjustable accuracy of the results are the two main advantages of the presented approaches.

Reduction of geometry-based errors in five-axis machining through enhanced 5D interpolation

Geometry-based errors constitute a special category of CAM-originated machining inaccuracies that significantly influence the precision of five-axis surface machining operations. Geometry-based errors reflect the inability of the cutter to accurately trace a prescribed 3D tool path in five-axis machining. Their magnitude constitutes an overlapped effect of the adopted interpolation scheme, cutter, and surface geometries, as well as kinematics of the five-axis machine tool, assumed free of errors by the CAM software. Although the presence of these errors is inherent in the current configuration of five-axis computer numerically controlled machining systems, little efforts were made so far towards their reduction. In this regard, the present study has investigated the magnitude of geometry-based errors as generated by various 5D interpolation schemes. These enhanced interpolation functions were determined by enforcing better approximations of the ideal machine control coordinate (MCC) trajectory as calculated in five-axis machine tool’s joint space. By comparing the geometry-based errors generated by the enhanced 5D interpolation schemes with linear interpolation baseline, it was found that significant error reductions will be obtained when synchronized 5D quadratic functions are used to approximate the ideal MCC curve in joint space. Moreover, the parametric synchronization between rotational and translational machine tool motions represents an essential requirement for limitation of the amount of geometry-based errors.

Command shaping control for micro-milling operations

Micro milling requires both high speed and high accuracy in order to economically produce parts with features on the scale of 1 μm. Micro mills are smaller and more flexible than traditional large-scale machines. Therefore, vibration of the machine structure is a significant problem. Given that micro milling requires high positioning precision, even small vibrations in the controller dynamics are problematic. The small-scale operation has considerably lower tool/workpiece interaction forces than traditional-scale milling. These low cutting forces have minimal effect on the machine structural response. Therefore, the dominant dynamic factor in exciting vibration can be the machine tool motion, rather than the workpiece/tool interaction. Given this realization, properly shaping the motions of the micro mill is a promising approach to reduce vibration. This paper presents a nonlinear command-shaping technique to reduce the vibrations of a micro mill that can be implemented with a standard CNC controller. The robustness of this technique to modeling errors and disturbances is investigated. Theoretical proofs and experimental demonstrations of the command-shaping technique are presented. The improved performance from the command shaping enables higher throughput and improved accuracy of the micro mill.

Motion and Virtual Cutting Simulation System for a Five-Axis Virtual Machine Tool

Since five-axis machine tools are very costly and their use requires a high level of knowledge and expertise, a virtual machine tool must be used to simulate five-axis machine tool operation. Configuration code or a mechanism topology matrix must be used to describe a machine tool, and can be used as the framework for design of a virtual machine tool system. The first step is to isolate the basic motions of each element of a virtual machine tool and then establish their coordinate systems. The establishment of a node tree allows coordinate transformation matrices for virtual motion components to be derived, which are then used to simulate movements. The simulation of virtual cutting must take into consideration both accuracy and efficiency. While either a GPU or CPU can be used to perform calculations, there are currently restrictions on GPU memory use which results in relatively lower accuracy. In contrast, a CPU can perform calculations using an adaptive octree with voxels and multithreading to yield sufficient accuracy and efficiency. A five-axis virtual machine tool motion and virtual cutting simulation system was written in C/C++ with OpenGL and OpenMP, and can perform real-time cutting simulations.

Vector Calculation for Tool Envelope Surface in Five-Axis NC Machining

A vector calculation method is proposed to compute the tool envelope surface in five-axis machining. By introducing the typical five-axis machine tool motion, the velocity of cutter is obtained with rigid body motion theory. Based on envelope theory and some geometric characteristic of the cutter, the envelope condition is be simplified to find the grazing point with vector calculation method. The results can be applied to NC machining simulation, toolpath verification and optimization.

The Research of Nonlinearity Error Control on Five-Axis Machining Post Processor

Abstract：This paper analyses the causes and effective estimation method of nonlinear error; By machine tool motion solution, established a five-axis machine tool BV100 motion transformation mathematical models, combined with linear interpolation principle established the error compensation and nonlinear motion error model of the machine tool .by VB language, developed nonlinear error compensation function of special post process; and through the impeller cutting experiment validate the processor is correct and practical.

Analysis on the Impact of the Error Mapping for Structural Parameters of Parallel Machine Tool

In order to improve the 6-DOF parallel machine tool motion accuracy and reduce error, the impact of the error mapping for Structural Parameters of Parallel Machine Tool is analyzed. The fixing platform and the moving platform of 6-DOF PMT are linked by six variable-length rod with the kinematic pair (hooke hinge or hooke hinge). By changing the length of the drive rod, causing moving platform position and attitude change, a variety of motion can be simulated and emulated. If the cut tool is installed on the moving platform, the various surface parts can be machined, shown in Figure 1. The above figure shown, in order to obtain the moving platform trajectory, we need measure hooke hinge space position of the fixing platform and the moving platform[1]. There are 6 hooke hinges on the fixing platform and there are 3 parameters (x, y, z) on every hooke hinge. There are 6 hooke hinges on the moving platform and there are 3 parameters (x, y, z) on every hooke hinge. So a total of 12 hooke hinges positions (36 parameters) need be measured. Due to the actual processing, assembly and measurement error, the actual measured values and theoretical values for 36 parameters can not be a complete match and lead to the moving platform errors. This paper will study the 36 parameters on the impact of mapping errors. Firstly, the error mapping formula between drive rod and the moving platform for PMT is established, secondly the performance evaluation index of the error mapping is deducted, and then the relationship between 36 parameters and the error mapping index is established. At last, to the different types of PMT structures and structural parameters, the ideal structural parameters with the aid of the performance evaluation index are optimized.

Development of static friction compensation for feed drive motions of machine tools

Friction exists in feed drive servomechanisms of CNC machine tools, and it usually affects their motion. Although the existing researches have demonstrated good motion results by applying friction compensation, the simplified characteristics of static friction still limit the motion accuracy for feed drives of CNC machine tools. In this study, the breakaway experiment is performed for obtaining the data values used by the identification processes of static friction. Then, an integrated friction model that considers the position-dependent static friction is developed for friction compensation, and a new feedforward friction compensation structure is developed for controlling the motions of the feed drives of CNC milling machines. Several experiments and motion tests were carried out on a three-axis CNC milling machine so as to illustrate the feasibility of the developed identification and compensation methods.

Measurement and Control of Machine Tool Motion

Measurement and Control of Machine Tool Motion

The Lower Control System Development of 3 DOF Parallel Machine Tool CNC System Based on DSP

The 3 DOF parallel machine tool CNC system based on DSP takes 3-HUU configuration of parallel machine tool as the control object, and adopts TMS320F2812 of TI DSP as control core of the CNC system. This paper mainly studies hardware design and software design of the lower control system of the 3 DOF parallel machine tool, and does practical test which shows that the CNC system can well control the parallel machine tool and finish machining movement.

Measurement and Analysis of Static Friction for Feed Drives of CNC Machine Tools

Static friction generally exists in feed drive servomechanisms and usually affects the motions of CNC machine tools. In this study, the breakaway experiment is applied to measure the static friction of a feed drive servomechanism generally used in CNC machine tools, and the spectral analysis using the fast Fourier transformation algorithm is applied to analyze the frequency characteristics of the obtained static friction. Several experiments were carried out on a three-axis CNC milling machine so as to illustrate the feasibility of the developed measurement and analysis methods. The experimental results indicate that the static friction of a feed drive servomechanism is clearly position-dependent and the physical interaction of the mechanical parts in the transmission system used by the feed drive servomechanism significantly affects the characteristics of the static friction.

Micro/nano sculpturing of hardened steel by controlling vibration amplitude in elliptical vibration cutting

A new ultra-precision sculpturing method in micro/nano scale for difficult-to-cut materials is proposed in the present research. Elliptical vibration cutting technology is well-known for its excellent performance in achieving ultra-precision machining of steel materials with single crystal diamond tools. Elliptical vibration locus is generally controlled and held to a constant in practice. On the contrary, the proposed method utilizes the variations of the elliptical vibration locus in a positive manner. Depth of cut can be actively controlled in elliptical vibration cutting by controlling vibration amplitude in the thrust direction. By utilizing this as a fast tool servo function in elliptical vibration cutting, high performance micro/nano sculpturing can be attained without using conventional fast tool servo technology. A high-speed amplitude control system is developed for elliptical vibration, with a bandwidth of more than 300 Hz, where the vibration amplitude can be controlled within 4 μmp–p. The developed control system is applied to sculpturing ultra-precision nano textured grooves on hardened steel with single crystal diamond tools. It is confirmed that the textured grooves have the desired shapes, and their profiles agree well with the vibration amplitude commands input to the control system. Further, a high performance micro/nano sculpturing system for plane surfaces is developed, where the vibration amplitude is controlled in synchronization with the planing motion of an ultra-precision machine tool. Nano sculpturing experiments on hardened steel, carried out by the developed system, are reported, as well as consequent picture images and a variety of dimple patterns that were formed successfully on the hardened steel as nano-scale sculptures.

Study of a High Performance AFM Probe-Based Microscribing Process

In this paper, a mechanical microscribing process is described that combines AFM probe-based microscribing with a five-axis microscale machine tool motion platform in order to achieve high scribing speeds, a large working volume, and the capability of cutting curvilinear patterns of grooves. An experiment is described that demonstrates groove formation, groove shape, and tool wear when long grooves are formed using multiple tool passes. A second more systematic experiment is described in which short-distance single-pass cutting tests were used to explore the effects of cutting speed, nominal tool load, and AFM probe mounting angle on groove geometry, tool wear, effective rake angle, and chip formation. Lastly, an experiment is described in which a long curvilinear groove is cut. It is shown that the most well-formed grooves were cut and acceptable tool wear was achieved, when using a high cutting speed, high nominal tool load, and low probe mounting angle. The capability of cutting grooves as long at 82 mm but with depths of only a few hundred nanometers, using a single tool pass at cutting speeds as high at 25 mm/min is demonstrated.

E15 二次元精密スケールを内蔵した工作機械システムに関する研究 : 第1報 運動精度安定化のための概念設計(OS1 最新工作機械(3))

The paper introduces the concept of the machine tool motion compensation control system when the two dimensional planar motion of the machine is assumed to be detected by high precision two dimensional position sensor system. Also paper describes design study on the machine tool system equipped with two dimensional plane scale sensor system. The study includes the fundamental principle of dynamic identification on the two dimensional motion repeatability when the machine is equipped with two dimensional position sensor, which allows real time two dimensional compensation control for highly accurate machine motion.

Development of universal environment for constructing 5-axis virtual machine tool based on modified D–H notation and OpenGL

For construction of a universal 5-axis virtual machine simulation system, a new methodology is proposed in this paper. The OpenGL library is used to render the virtual environment and to display all motions of the virtual machine tool. In order to achieve the universal construction procedures, the D–H notation is adopted. The user interfaces are developed to help users to select the configuration of machine tool. Once the configuration is decided, the motion directions between adjacent links are known and the kinematic parameters are described by D–H notation. Then the post-processor is derived by D–H notation. Finally, the motion control simulation of the virtual machine tool is executed by D–H transformation matrix. This new methodology can assist developers in constructing the simulation system for the universal 5-axis virtual machine tool efficiently and effectively.

Machine models and tool motions for simulating five-axis machining

This paper presents a method of determining the tool motion of a five-axis machine. The method is motivated by the imprint point method, where points on the machined surface are computed based on the tool position and tool motion. While simple linear motion can be used as a coarse approximation to this motion, this paper looks at more accurate models of tool motion based on machine kinematics that can be generalized and applied to any CNC machine with one tool head. A kinematic chain is created by decomposing the linear motion of a machine's translational and rotational axes into parameterized affine transformations, and a hierarchical model of the machine combines the transformations to provide an accurate model of machine motion.

Five-axis Tool Orientation Optimization Based on Kinematical Method

Quick change in the tool orientation between neighboring contact points can never be made possible in reality due to the physical limit on the velocity and acceleration of the rotary motions of machine tool,a kinematics based method is presented in this research to solve this problem.The presented algorithm will automatically generate an interference-free inclination angle for selected machine tool,and the rotation angle will increase or decrease with the inclination angle increment.After the interference-free region and angular-velocity-feasible-region are generated,optimized tool orientation is chosen from the intersection of the two regions.If the intersection is null,backward-feasible-region will be calculated to ensure the intersection is non-null.Example shows that the method is feasible and the capability of the machine tool can be fully explored.

Improved NC path validation and manipulation with augmented reality methods

Five-axis milling offers many advantages over the conventional three-axis milling process. However, because of the potentially complex motions, it is difficult for the machine tool operator to anticipate the actual movement based on the NC program. In this paper a software system for the NC path validation and manipulation during the milling process is introduced. This system is meant to expand the information given to the machine tool operator by enriching the view with data of a concurrently running milling simulation. The simulation is synchronized with the real-world machine tool movement by detecting the position of a marker that is mounted on the head stock. With this combination of real-world view and computer-generated data, which is called Augmented Reality, the machine tool operator is able to detect critical situations—like collisions between tool holder and workpiece or excessive forces—and may adjust the NC program accordingly.

Straightness Error Compensation for Ultra-Precision Machining Based on a Straightness Gauge

A method of straightness error compensation is presented, which is used in ultra-precision machining with nano-scale accuracy for a large mandrel manufacture. A set of measurement system in situ is developed, in which an ultra-smooth glass-ceramic flatness gauge and a non-contact micro displacement sensor with nano-scale resolution were used as a reference and sensor to get the straightness error of machine tool movement. The real straightness error can be obtained after subtracting the surface profile of the gauge from the original straightness error curve. Based on the real straightness error data, a new NC program was made for compensating the error from the axis movement of machine tool. As a result, after straightness error compensation, the straightness errors of two axes of ultra-precision machine tool are 68nm/400mm and 54nm/300mm respectively.

Kinematics Analysis of Novel 4-DOF Parallel Manipulator

A novel 3-RRUR parallel manipulator is studied.The mechanism having high stiffness and symmetric simple structure can be applied to high precision assembly or used to constitute force sensor or parallel machine tool and micro motion parallel manipulator.It is easy to check and repair when using the 3-RRUR parallel manipulator for there is no moving pair in its limbs. Firstly,the screw system expressing the movements of each limbs is set up by the use of screw theory.The constraining screw system is built up.Then,its degree of freedom and moving characteristics are solved by researching the constraining screw system.The degree of freedom is 4,there are 3-dimensional motions and 1-dimensional rotation around axes vertical to the plane where the axes of kinematic pairs joining every limbs and the fixed platform lie in.In succession,the rationality of the input joints chosen is discussed with the aid of reciprocal screw theory and the method of analyzing the characteristics and the relativity of the constraints to the moving platform after adopting stiffened driving of the moving pairs.Then the constraint equations are obtained considering its moving characteristics and the forward and inverse position kinematics solutions of the mechanism and corresponding numerical examples are given.The research result will play an important role in pushing forward the application of this kind of manipulators.