5-axis Machine Tool Research Articles

New Simplified Inverse Kinematics Method for 5-Axis Machine Tools

New Simplified Inverse Kinematics Method for 5-Axis Machine Tools

Machining Based Geometric Error Estimation Method for 3-Axis CNC Machine

Computer numerical control (CNC) machine tool plays an extremely significant role in any manufacturing industry due to its automation and high accuracy. Keeping the CNC machine tool at its highest performance to meet the demand of high accuracy machining is always significant. To maintain the accuracy of a machine tool over the time, it is important to measure and compensate the geometric error, one of the main error source of machine tool, especially when the machine get old. There are totally 21 geometrical errors in a 3-axis machine tool including three translational errors and three rotational errors for each axis and three perpendicular error (Squareness) within three axes of the machine. This paper presents an economical and simple method for measuring the geometric error of a 3-axis CNC machine tool based on the machining of actual samples. Three samples for each axis will be machined following a design cutting path. The samples will then be measured using a coordinate measuring machine (CMM). The collect data will be used for estimating the geometric errors. The volumetric errors will be then computed and verified through machining of 3D geometries.

Identification and compensation of position-dependent geometric errors of rotary axes on five-axis machine tools by using a touch-trigger probe and three spheres

For the machining accuracy of five-axis machine tools, it must be emphasized that not only the PIGEs but also the PDGEs of rotary axes influence the machining accuracy. However, until now there is no any commercial measurement system available for identifying the PDGEs in the rotary axes of five-axis machine tools. As a result, this study proposes a robust, efficient, and automatic measurement method to identify and compensate the position-dependent geometric errors (PDGEs) of rotary axes on five-axis machine tools. The proposed measurement method has established an on-machine measurement for the PDGEs of rotary axes by using a touch-trigger probe and three spheres installed on the spindle as well as the tilting rotary table, respectively. For each rotary axis, only a single measuring pattern is implemented to measure the PDGEs with a single setup, which delineates the advantages of efficient and automated identifying procedures in each periodical measurement. By implementing the proposed measurement method, 12 PDGEs can be numerically identified based on the measurement algorithm, which is built through a kinematic error model as well as a least square method. Finally, the proposed measurement method is experimentally conducted on a commercial five-axis machine tool. Moreover, after consequently performing the proposed measurement method, the PDGEs of the rotary axes were quantitatively compensated by the commercial controller to validate its feasibility. The experimental results have clearly delineated that the linear errors and angular errors are reduced from at most 37.81 μm and 10.23 mdeg to 0.9 μm and 0.26 mdeg, respectively. Consequently, the experimental results have demonstrated that the proposed measurement method is efficient and precise.

Choice of Noncircular Gears Hobbing Linkage Methods

Background: Various relevant patents and papers which have reported noncircular gears synthesize the advantages of circular gears and cam mechanisms, and are widely used in many types of mechanical instruments. Hobbing is a better method for fabricating noncircular gears. There are 4 linkagemethods to hob noncircular gears. However, which linkage method should be chosen practically has not yet been reported. Objective: The goal of this work is to choose the best linkage method for hobbing noncircular gears. Method: Firstly, the hobbing models of noncircular gears was deduced. Then, based on the model, hobbing linkage methods of noncircular gears were obtained. Thirdly, under different hobbing linkage methods, their aspects (developing regularity of hobbing cutter trace, arc length of program blocks and motion axes of machine tools) were compared. Results: Finally, with the best characteristics of a high density of shaping cutter trace, high uniformity of arc length of program blocks and ease of control, the equal arc-length of gear billet (EALGB) is obtained. It has been proven that EALGB is an excellent linkage method to hob noncircular gears. Conclusion: It has been proven that EALGB is an excellent linkage method to hob noncircular gears.

Five-Axis Machine Tool Coordinate Metrology Evaluation Using the Ball Dome Artefact Before and After Machine Calibration

Now equipped with touch trigger probes machine tools are increasingly used to measure workpieces for various tasks such as rapid setup, compensation of final tool paths to correct part deflections and even verify conformity to finished tolerances. On five-axis machine tools, the use of data acquired for different rotary axes positions angles brings additional errors into play, thus increasing the measurement errors. The estimation of the machine geometric error sources, using such methods as the scale and master ball artefact (SAMBA) method, and their use to calibrate machine tools may enhance five-axis on-machine metrology. The paper presents the use of the ball dome artefact to validate the accuracy improvement when using a calibrated model to process the machine tool axis readings. The inter-axis errors and the scale gain errors were targeted for correction as well the measuring tool length and lateral offsets. Worst case and mean deviations between the reference artefact geometry and the on-machine tool measurement is reduced from 176 and 70 µm down to 31 and 12 µm for the nominal and calibrated machine stylus tip offsets respectively.

Identification of integrated geometric errors of rotary axis and setup position errors for 5-axis machine tools based on machining test

As a fundamental error source, geometric errors of 5-axis machine tools have a negative influence on a machine tool’s motion accuracy. Large numbers of efficient and robust geometric error measurement and compensation methods have been developed by existing researches to improve the performance of the machine tools during the automatic machining of the workpiece. However, influence of the geometric errors on workpiece clamping is hard to measure and evaluate in most of the clamping processes since manual operations are involved. It is important to identify both geometric errors and setup position errors to control the entire machining process, standing from the perspective of a manufacturer. In this study, a position-dependent geometric error and setup position error identification method is investigated based on machining test. A kinematic model for a 5-axis machine tool with tilting rotary table is constructed while considering both geometric errors of the two rotary axes and setup position errors. Machining patterns and calculation algorithm are designed to analytically calibrate these errors. Experimental demonstration is conducted to validate the feasibility of the proposed measurement method.

Method to evaluate speed and accuracy performance of CNC machine tools by speed-error 2-D representation

In this research, we propose a method to evaluate both speed and accuracy performance of CNC machine tools at the same time. An important facet of the contouring performance of machine tools with computer numerical control (CNC) is the machining of workpieces within the desired accuracy and within as short a time as possible. For this reason, a method for evaluating speed and accuracy in the two dimensions of speed and error based on the actual trajectory, which is the actual movement trajectory with respect to the linear axes of CNC machine tools, has been proposed. In this research, we explain the method proposed for linear axes and propose a method to evaluate the speed and accuracy of a rotary axis and a linear axis in the two dimensions of speed and error by introducing a cylindrical surface to the combined movement of the rotary and linear axes. With experiments, we quantitatively evaluated the speed and accuracy of multiple CNC machine tools using two-dimensional representation with graphs of the actual speed and maximum error for the combined movement of a rotary axis and a linear axis.

Virtuelna petoosna mašina alatka integrisana sa sistemom programiranja i upravljanja

Virtuelna petoosna mašina alatka integrisana sa sistemom programiranja i upravljanja

Modelling and characterisation of geometric errors on 5-axis machine-tool

This research work deals with the geometric modelling of 5-axis machine tool based on a standardised parameterisation of geometric errors with the aim to decrease the volumetric error in the workspace. The identification of the model’s parameters is based on the development of a new standard thermo-invariant material namely the Multi-Feature Bar. Thanks to its calibration and a European intercomparison, it now provides a direct metrological traceability to the SI metre for dimensional measurement on machine tool in a hostile environment. The identification of three intrinsic parameters of this standard, coupled with a measurement procedure ensures a complete and traceable identification of motion errors of linear axes. An identification procedure of location and orientation errors of axes is proposed by probing a datum sphere in the workspace and minimising the time drift of the structural loop and the effects of the previously identified motion errors. Finally, the developed model partially identified, allows the characterisation of 95% of the measured volumetric error. Therefore, the mean volumetric error not characterised by the model only amounts to 8 μm.

Hierarchical motion control for real time simulation of industrial robots

Multi axis machine tools implement real time motion control algorithms. Objects including difficult to manufacture and deformable shapes show variable properties when tools apply a pressure on the object surface. Force compliant industrial robots are used to manipulate deformable objects in real time simulation. In this research, a hierarchical method of motion controlling strategy is presented. The proposed approach is described regarding performance characteristics such as accuracy, repeatability, controllability of the motion segmentation and time dynamics. The result shows that a hierarchical control approach can be considered as a potential candidate to manipulate deformable objects where force requirements are critical.

Sustainable selection of optimum toolpath orientation in milling AISI 1018 steel alloy

Toolpath orientations and axes weights have been identified as some of the parameters that could influence the electrical energy consumption and sustainable machining objectives. However, power evaluations of the machine tool axes when carrying different weights and in different toolpath trajectories have not been fully implemented for energy management in machining processes. This work proposes a framework for determining optimum toolpath orientations by conducting a comparative study and individualization analysis of axes weights for electrical power consumption management in slot milling operations of AISI 1018 steel alloy. Results show that performing slot milling at an angle aligned in the direction of the axis with the minimum weights tend to lower the feed axes power consumption.. Therefore, sustainable slot milling operations could be achieved by aligning the toolpaths at an angle oriented in the direction of the lighter axis for minimum feed axes power consumption. This work could further enhance the modeling of power consumption, and hence electrical energy demand in mechanical machining for resource efficiency and green manufacturing.

Identification and compensation of geometric errors of rotary axes in five-axis machine tools through constructing equivalent rotary axis (ERA)

This paper proposes a volumetric accuracy enhancement method of rotary axes in five-axis machine tools through constructing equivalent rotary axis (ERA). The influences of translational axes, setup errors of table ball and tool ball are simultaneously considered. A new concept named ERA, originated from the definition of axis of rotation, is proposed to globally describe the instantaneous position and orientation of rotary axes. Based on this concept, only six parameters are needed to describe the influences of geometric errors rather than ten parameters required by the existing concept of PDGEs and PIGEs. At the same time, the coupled relationship between the compensated motion commands of rotary axes and geometric error components is eliminated, and the geometric error compensation is realized by formulating analytical expressions. The typical characteristics of the proposed method lie in the following three aspects. First, the axis twists in the identification method naturally follow the constraint of rotary axis, and thus the normalization and iteration procedure required by existing literatures are avoided. Second, compact form of geometric error compensation is established and explicit equations are given to generate the compensated motion commands. Specially, the inverse kinematic model of five-axis machine tools can be well integrated into the proposed method. Third, besides machine tools with non-orthogonal rotary axes, the proposed method can also be easily applied to five-axis machine tools with non-orthogonal rotary axes just by modifying the ERA parameters. Simulation results and blade machining tests verify the effectiveness of the proposed method, and more than 70% machining precision improvement is observed.

Semi-Analytical Modelling of Synthetic Static Stiffness for Machining System of Five Axis Machine Tool

A static stiffness model of the machine tool end considering the whole kinematic chain of the machining system is proposed. The whole kinematic chain is divided into the cutter subsystem and the handle-spindle-motion axes subsystem. The two subsystems are equivalent to a variable diameter cantilever and a variable length cantilever. The 3D static stiffness at the end of the machining system could be resulted by both theoretical calculation and experimental measurement. The static stiffness along different directions are analysed based on the force ellipsoid theory.

Pose-dependent tool tip dynamics prediction using transfer learning

Abstract Machining chatter has a great influence on the producing efficiency and surface quality. Frequency response function at the tool tip is a crucial input for constructing accurate milling stability model. However, the tool tip dynamics usually change with the continuously varying postures of the machine tool axes during the whole machining process. How to predict the pose-dependent tool tip dynamics precisely has become one of the most challenging tasks in chatter suppression in both research and industry. Compared to traditional finite element analysis or kinematic modeling based methods, this paper proposes a data-driven method using transfer learning to predict the pose-dependent tool tip dynamics for different tool-holder assemblies. Firstly, a tool-holder assembly is selected as the source tool and its pose-dependent tool tip dynamics are obtained as the source data by sufficient impact tests. For a new tool-holder assembly, namely the target tool, only few impact tests are required to measure the tool tip dynamics as the target data. Then both the target and source data are used to train a regression model for predicting the target pose-dependent tool tip dynamics based on transfer learning by integrating domain adaptation and adaptive weighting. Furthermore, a detailed experimental validation with a five-axis machine tool is carried out to verify the accuracy and efficiency of the proposed method.

The identification method of the relative position relationship between the rotary and linear axis of multi-axis numerical control machine tool by laser tracker

In the multi-axis machining process, the relative position relationship between the linear and rotary axis also has certain influence on the machining accuracy in addition to 6 geometric errors of each axis. How to accurately detect and compensate for this error will have a positive effect on further improving the machining of multi-axis machine tool. The laser tracker is adopted multi-station and time-sharing measurement to identify the relative position relationship between the rotary and linear axis on the basis of global positioning system principle in this paper, which will provide data support for accuracy compensation for multi-axis machine tool. The relative position relationship between the rotary and linear axis is characterized by the homogeneous transformation matrix, and its influence on the motion accuracy of machine tool is also analyzed. Meanwhile, the mathematical model concerning on identifying the relative position relationship between the rotary and linear axis with laser tracker is established, and the corresponding measurement algorithm of machine tool motion and identification algorithm of the relative position relationship are derived respectively. The feasibility and accuracy of the derived algorithms are demonstrated in simulations. Meanwhile, the experiment further validates the feasibility of the proposed method.

Cutter orientation planning in NC machining for surface similar to revolution body with considering kinematic characteristics

In multi-axis numerical control (NC) machining of curved surface with high feed rate, vibration and shock will occur when the velocity and acceleration of the machine tool axis exceed the limit value, which will influence quality of the part surface. Aiming at the NC machining of surface similar to revolution body with high feed speed, a method of cutter orientation planning meeting kinematical constraints that the velocity and acceleration of the machine tool axis cannot over the maximum value is proposed in this paper. First of all, considering the velocity characteristic constraint, the relationship between cutter orientation and the velocity of motional axis is analyzed in machine tool coordinate planes. According to the distribution of the polar radius difference of adjacent cutter location points, the angles between each adjacent cutter orientations are obtained, and these angles are adjusted by an allowable minimum angle. All preliminary cutter orientations are determined by defining the cutter orientation at the first cutter location point. Then, analyzing the acceleration characteristic of motional axis, the acceleration mathematical optimization model is established. Final cutter orientation is determined, and the feed rate machine tool is adjusted by optimization method. Finally, taking shoe last surface as processing example and obtaining cutter orientations by using the proposed and existing methods, respectively, the effectiveness of the method presented in this paper is approved.

Position-dependent geometric errors measurement and identification for rotary axis of multi-axis machine tools based on optimization method using double ball bar

Geometric errors measurement and identification for rotary table are important. However, precisely adjustment for the setup position of a double ball bar in each measurement pattern is inconvenient. This study proposes a novel optimization identification method using a double ball bar to recognize the position-dependent geometric errors (PDGEs) of rotary axis. A mathematical model for ball bar measurement is firstly constructed to map the relationship between measurement direction and position of the double ball bar. And then, the setup positions of the double ball bar for PDGEs identification are analyzed. According to analysis for setup positions of the double ball bar, simplified measurement patterns would be conducted by adjusting only two setup positions for the ball bar and thus reduce the procedure of accurate adjustment for the ball bar. The PDGEs can be fitted as an nth B-spline curve, on the account of its being smooth and continuous. To identify the PDGEs, an optimization method, by computing the suitable value of control points of nth B-spline curve of errors to minimize the optimal value of the target function between the actual measured value and the value derived from a theoretical measurement model, is proposed. Moreover, in order to obtain the accurate value of control points of the error curve, the sensitivity analysis is conducted to acquire the sensitivity matrix with respect to control points of errors. The PDGEs are able to be identified simultaneously after calculating the appropriate values of control points of errors. The proposed identification method is validated by simulation and experiment. The results prove the effectiveness of the proposed method.

Posture adjustment of workpiece based on stepwise matching by self-adaptive differential evolution algorithm

Abstract. The workpiece contour errors from previous process affect current and subsequent process. In order to improve the uniformity of workpiece allowance distribution, a stepwise workpiece matching adjustment method with contact inspection is developed. This method includes two stepwise registration processes. At first, some pairs of measured points on the theoretical and actual surfaces are selected to build the corresponding local coordinate systems, and then the rough matching matrixes are obtained by the coordinate systems alignment. During the fine matching process, the objective function based on the least square method is established by the measured point sets adjusted through the rough matching. The fine matching matrixes can be obtained by self-adaptive differential evolution algorithm. The posture adjustment can be realized by transforming coordinate systems of 5 axis machine tool, of which adjusted values can be calculated by the matching matrixes and the machine tool topology. At last, some experiments were presented to demonstrate the performance of the method.

Development of Novel Tool Center Point Velocity Planning Algorithm for Five Axis Machine Tool

In this paper, a tool center point (TCP) feedrate scheduling algorithm for 5-axis machine tool is developed to generate the axes interpolation commands. The proposed algorithm considers not only the constraints of TCP velocity, acceleration and jerk, but also the velocity differences of each axes at the junction of each block. First, the proposed method determines the maximum speed for each block segment at the TCP coordinate based on the computed length. Then the kinematics of the five axis machine tool is employed to derive the five-axis corner velocity difference (FCVD) formulation. The FCVD utilizes the axis velocity difference at the junction of blocks as the designed variable. As the starting and end velocities of each block are determined, the S-shape acceleration/deceleration (Acc/Dec) method is adopted to generate both smooth TCP and rotary axis profile based on the given interpolation parameters. The servo dynamics of the five axis machine tool are utilized to evaluate the performances of the FCVD. Simulation results demonstrate that the FCVD can achieve better contour accuracy with less machining time as compared to the five-axis feedrate regulation formulation (FFRF) algorithm. Furthermore, the FCVD are compared with Heidenhain CNC controller and the results show that the FCVD has similar behaviors as the Heidenhain controller, but it can achieve less machining time.

A workpiece registration and localization adjustment method with contact inspection under multi-tolerance conditions

The workpiece contour errors from previous process affect current process. In order to improve workpiece allowance distribution, this article presents a workpiece registration and localization adjustment method with contact inspection. According to the analysis of machining deviation, the rotational and translational registration matrixes from multi-tolerance surfaces to workpiece are obtained by surface characteristic and translational vectors. The workpiece localization (position and orientation) adjustment can be realized by transforming coordinate systems of 5-axis machine tool. Through adaptive and iterative registration and adjustment, the optimized workpiece localization for current process is obtained. The experimental results show that the method can improve allowance uniformity effectively.