Touch Trigger Probe Research Articles

Identification of geometric errors of rotary axes on 5-axis machine tools by on-machine measurement

Geometric error is among the most important fundamental elements that significantly affect the machining accuracy of multi-axis machine tools. This paper developed an efficient, accurate, and automatic geometric error measurement and identification method for rotary axis of a five-axis machine tool based on on-machine measurement by using a touch-trigger probe with a test piece. Before on-machine measurement, the test piece is installed and pre-machined to a designated geometry. Then, the coordinates of the reference points on the test piece are indirectly measured at different rotary axis positions. The geometric errors of each rotary axis then can be identified individually and the calculation algorithm is easy to establish and solve. Due to the special features of this method, neither the geometric inaccuracy of the test piece nor its installation error on the workbench affects the geometric error measurement and identification results. Geometric errors of a five-axis machine tool with double table rotary axes are measured as an example to validate the efficiency and effectiveness.

Single setup identification of component errors for rotary axes on five-axis machine tools based on pre-layout of target points and shift of measuring reference

This paper proposes a single setup identification method of 12 component errors of rotary axes on five-axis machine tools by using a touch trigger probe and an artefact. At first, a basic idea of pre-layout of target points combined with the shift of measuring reference is proposed. Influence of setup errors of touch trigger probe and artefact on measuring results is identified quantitatively and included in error models. A single setup measuring method is then designed to identify 12 component errors of rotary axes on five-axis machine tools with a tilting head and a rotary table. The expansion of this basic idea on five-axis machine tools with other configurations is also provided. Validation and uncertainty analysis of the identified values are also provided. The measuring accuracy is guaranteed by the complete error model while the measuring efficiency is improved significantly by the single setup measuring method.

Wireless communication influence on CNC machine tool probe metrological parameters

The influence of the wireless communication on CNC machine tools touch-trigger probe inaccuracy of probing is investigated. Factors such as time of processing and wireless transmission of trigger signal from the probe to the CNC machine tool controller including position and orientation of the interface receiver are taken into consideration. A new method allowing to obtain 3D probe error characteristics with several times more accuracy than the procedure used on a CNC machine tools has been applied. The analyses have been performed for several wireless interfaces of two types: an optical and a radio type. The influence of the abovementioned parameters has been analysed theoretically and verified experimentally. Good agreement between the proposed theoretical model and experimental data has been obtained.

Identification of location errors by a touch-trigger probe on five-axis machine tools with a tilting head

Location errors are considered as one class of the fundamental errors of five-axis machine tools. For the improvement of machining accuracy, it is important to propose an efficient and accurate identification method of location errors. This paper uses a touch-trigger probe and a testpiece to identify location errors of a five-axis machine tool with a tilting head. All the measuring procedures are performed based on the single setup of measuring equipment. A model-based decoupling algorithm of squareness errors of linear and rotary axes is proposed. Then, a new probing procedure is proposed based on this algorithm to increase the moving distances of linear axes without additionally auxiliary equipment. This basic idea can also be expanded to other machine configurations, for instances, the one with a tilting-rotary table which is also illustrated. The experimental results demonstrate that this method is efficient and accurate.

Integrated post-processor for 5-axis machine tools with geometric errors compensation

Geometric errors of 5-axis machine tools introduce great deviation in real workpiece manufacture and on-machine measurement like touch-trigger probe measurement. Compensation of those errors by toolpath modification is an effective and distinguished method considering the machine calibration costs and productivity. Development of kinematic transformation model is involved in this paper to clarify the negative influences caused by those errors at first. The deviation of the designed toolpath and the real implemented toolpath in workpiece coordinate system is calculated by this model. An iterative compensation algorithm is then developed through NC code modification. The differential relationship between the NC code and the corresponding real toolpath can be expressed by Jacobi matrix. The optimal linear approximation of the compensated NC code is calculated by utilizing the Newton method. Iteratively applying this approximation progress until the deviation between the nominal and real toolpath satisfies the given tolerance. The variations of the geometric errors at different positions are also taken into account. To this end, the nominal toolpath and the geometric errors of the specific 5-axis machine tool are considered as the input. The new compensated NC code is generated as the output. The methodology can be directly utilized as the post-processor. Experimental results demonstrate the sensibility and effectiveness of the compensation method established in this study.

Formulation of Influence of Machine Geometric Errors on Five-Axis On-Machine Scanning Measurement by Using a Laser Displacement Sensor

For on-machine measurement of workpiece position, orientation, and geometry on machine tools, five-axis continuous (scanning) measurement by using a laser displacement sensor has a strong advantage in its efficiency, compared to conventional discrete measurement using a touch-triggered contact probe. In any on-machine measurement schemes, major contributors to their measurement uncertainty are error motions of the machine tool itself. This paper formulates the influence of geometric errors of rotary axis average lines on the measurement uncertainty of the five-axis on-machine measurement by using a laser displacement sensor. To validate the present simulator, experimental comparison of measured and simulated trajectories is conducted on five-axis on-machine measurement of a precision sphere of the precalibrated geometry. For total 28 paths measured on the spherical surface, an error in the simulated trajectories from measured trajectories (properly low-pass filtered) was at maximum 5 μm. Uncertainty assessment demonstration for more practical application example of a turbine blade measurement is also presented.

A visual non-contact focusing probe for the measurement of micro cavities

The dimensional measurement of micro cavity profile to nanometre resolution is difficult because the edge is not able to be detected accurately with a microscope due to diffraction limit. With a touch-trigger probe on a micro-CMM, the probe cannot enter into the cavity if the tip-ball diameter is larger than the cavity size. In this paper, a vision-assisted non-contact focusing probe is presented to deal with this problem. A blue-ray DVD pickup head is adopted as the focusing sensor which is based on the principle of light reflection. Assisted by a nanopositioning stage, the focusing signal can detect the edge when the spot passes through it. In order to know the measuring point, a CCD is used for viewing the relative position between the focused spot and the edge. Experimental tests of the probe were carried out in association with a micro-coordinate measuring machine. The edge position is obtained up to a resolution of 1 nm with standard deviation of about 26 nm. This performance is beyond the diffraction limit of optical microscopes.

Study on Pre-travel Behaviour of Touch Trigger Probe under Actual Measuring Conditions

In order to increase the accuracy of On-Machine Measurement, it is very necessary to develop a methodology to calibrate and compensate checking errors resulted from the pre-travel behaviour of touch trigger probe under actual measuring conditions accurately. The some factors impacting on the pre-travel behaviour under various measuring situations are investigated in this paper thoroughly. Based on analyzing the probe's triggering mechanism and working procedure, the influencing law of main metrological parameters including measuring speed, the approaching direction, stylus length, material and geometrical characteristics of the detected objects on the pre-travel behaviour has been implemented. A novel measuring-task-oriented calibration method is presented, by which several main factors lessening calibration accuracy such as errors of machine tools and manufacturing errors of artifact are eliminated. By means of this method, the pre-travel behaviours affected by several combinations of the above-mentioned parameters for different measuring task have been obtained. The correctness and efficiency of the theoretical analysis and the calibration method has been verified by a compensation experiment. The experimental results show that the On-Machine Measurement accuracy could be improved obviously.

CNC-CMM Measurement Accuracy and Accompanied Uncertainty at Different Alignment Positions of Long GBs

Coordinate Measuring Machine (CMM) is the most important computer numerical control (CNC) system in dimensional metrology. CNC-CMM is a major metrological tool used for guarantee the quality of engineering products due to its accuracy, precision, speed and general versatility in industry. The alignment position strategy of an object or product on CMM affects the measurement results. In this paper, the verification of CMM working performance with a touch trigger probe is presented. The influence of alignment of long gauge blocks (GBs) artifacts and its positions on CMM measurements have been studied and evaluated in the X-Y plane. This method treats CMM axis length errors of GBs measurements resulted due to their alignment at different angles. Parallelism and GD&T of GBs artifacts are also identified and evaluated. The combined standards uncertainty in measurement is estimated and achieved within the CMM maximum permissible error.

On-Machine Measurement System Implemented Based on Fanuc CNC System Using a Touch Trigger Probe

This paper aims to implement an OMM (on-machine measurement) system using a touch trigger probe installed on the spindle of the milling machine with Fanuc 0i-mc CNC system. The CNC used in the milling machine is Fanuc 0i-mc system. The hardware system configuration for OMM and its software were both presented. The software is composed of several modules, and the most significant one is for generating measurement program based on CAD model of workpiece. This paper mainly presents the specific construction of the measurement macro for Fanuc system.

3-D Model Reconstruction and Mold Flow Simulation for an Existing Shaped Part

This study presents a 3-D model reconstruction method using a multiple coordinate measurement machine that includes a touch-trigger probe and image detection. Control points of the feature curves of an existing shaped part and geometric data of engineering features are first measured, and then the 3-D model is reconstructed in forward design procedure by the common CAD software ‘Pro/E’. This study also develops finite element models based on the 3-D model built to conduct mold flow simulations by the simulating system ‘Moldflow’. A joystick with two cases was adopted as the illustrated case. Final, actual rapid prototyping (RP) models were fabricated for model examination.

In-Situ Measurement and Distributed Computing for Adjustable CNC Machining

ABSTRACTMachining is an established standard for producing the final shape of parts, molds, etc. The nominal CAD representation is used to create sophisticated 3- to 5-axis CNC tool paths. Lack of computational and in-situ measurement resources restricts at machine registration and other adjustments to correct for actual surface geometry. This paper describes progress towards provision of adequate touch trigger probe and laser scanner measurement resources at the machine tool, with supporting computational resources accessed via Ethernet. The emerging MTConnect standard provides executive level monitoring. Illustrative examples include fixture registration using datum spheres, aeroengine assembly weld machining, and associated data fitting and tool path adjustment. The goal is to develop an environment with a higher level of intelligence and decision making ability for machining under variable geometry conditions.

Evaluation of a multi-sensor horizontal dual arm Coordinate Measuring Machine for automotive dimensional inspection

Multi-sensor coordinate measuring machines (CMM) have a potential performance advantage over existing CMM systems by offering the accuracy of a touch trigger probe with the speed of a laser scanner. Before these systems can be used, it is important that both random and systematic errors are evaluated within the context of its intended application. At present, the performance of a multi-sensor CMM, particularly of the laser scanner, has not been evaluated within an automotive environment. This study used a full-scale CNC machined physical representation of a sheet metal vehicle body to evaluate the measurement agreement and repeatability of critical surface points using a multi-sensor horizontal dual arm CMM. It was found that there were errors between CMM arms and with regard to part coordinate frame construction when using the different probing systems. However, the most significant effect upon measurement error was the spatial location of the surface feature. Therefore, for each feature on an automotive assembly, measurement agreement and repeatability has to be individually determined to access its acceptability for measurement with a laser scanner to improve CMM utilisation, or whether the accuracy of a touch trigger probe is required.

5-Axis adaptive flank milling of flexible thin-walled parts based on the on-machine measurement

Deformation of the part and cutter caused by cutting forces immediately affects the dimensional accuracy of manufactured parts. This paper presents an integrated machining deviation compensation strategy based on on-machine measurement (OMM) inspection system. Previous research attempts on this topic deal with deformation compensation in machining of geometries in 3-axis machine tools only. This paper is the first time that concerned with 5-axis flank milling of flexible thin-walled parts. To capture the machined surface precision dimensions, OMM with a touch-trigger probe installed on machine׳s spindle is utilized. Probe path is planned to obtain the coordinate of the sampling points on machined surface. The machined surface can then be reconstructed. Meanwhile, the cutter׳s envelope surface is calculated based on nominal cutter location source file (CLSF). Subsequently, the machining error caused by part and cutter deflection is calibrated by comparing the deviation between the machined surface and the envelope surface. An iteration toolpath compensation algorithm is designed to decrease machining errors and avoid unwanted interference by modifying the toolpath. Experiment of machining the impeller blade is carried out to validate the methodology developed in this paper. The results demonstrate the effectiveness of the proposed method in machining error compensation.

Error Calibration for Five-Axis Machine Tools by On-the-Machine Measurement Using a Touch-Trigger Probe

This paper presents a scheme to calibrate the error map of the rotary axes of a five-axis machine tool. This is done by means of on-the-machine measurement of a test piece using a contact-type touch-trigger probe. The present probing-based approach is more suitable for efficient and automated “self-calibration,” than conventional calibration schemes, such as ball bar tests or R-test. It is thus advantageous in the application to periodic checking of the error map, or periodic updating of its numerical compensation. In the present approach, a test piece of arbitrary geometry, e.g. a raw unmachined workpiece, can be used as the probing target. An experimental demonstration is presented.

Non-contact Type On-machine Measurement System for Turbine Blade

In turbine blade machining from a near net shape (e.g., forged workpiece), it is difficult to use a touch trigger probe for measuring the mounting angle of the workpiece due to its uncertain free-form surface. Therefore, non-contact measurement is required to determine the setup condition of the workpiece. Recently a high-performance laser displacement sensor has been able to measure glossy metal surfaces because of the progress in its sensing device. Using such a high-performance sensor, the non-contact type on-machine measurement system has been developed. It was installed on the multi-functional machine tool to determine validity of the system. This system measured the turbine blade cross-section to compare with CAD data and the measurement data by coordinate measuring machine (CMM). As a result, validity of this system for measuring a turbine blade was proved. We have proposed some application using this measurement system. The application enables optimal machining of a turbine blade from a near net shape at an appropriate phase. This contributes to minimizing the size of expensive material and the machining time.

Fundamental Study of the On-Machine Measurement in the Machining Center with a Touch Trigger Probe

As it contributes to the reduction of processing time and to the raising of accuracy, on-machine measurement is growing in importance in the machining process. On-machine measurement includes the precise positioning of the work piece and the comprehension of its position or shape. However, errors in on-machine measurement could lead to errors in the measured values after the machining process is finished. In this study, measurements taken by the major touch trigger probes available on the market are compared using newly-developed on-machine software that can generate suitable NC programs for automaticmeasurement. As a result, more effective methods of on-machine measurement are defined through the identification of the abovementioned errors.

Technology of NC Machine Error Parameter Identification Based on BP Neural Network

NC machines touch-trigger probes generally have three-dimensional measuring function, its working principle is equivalent to a duplication of contacts with high precision switch, under the control of the measurement software, to achieve high-precision machining center automatically detected. Paper proposed based on BP neural network in NC machines tool probe measurement error parameter identification method. Through theoretical analysis and experimental research to determine the probe installation error parameters and the probe measurement error parameters of the model, but also identify ways to eliminate probe system error term uncertainty of the condition, in order to determine the detection method and planning of testing provides a reliable path basis.

Enhance performance of inspection process on Coordinate Measuring Machine

Coordinate Measuring Machine (CMM) has been an important inspection tool in quality control for several years owing to its high accuracy and precision. Effectiveness of inspection plan generated by CMM greatly depends on measurement cycle time. Lesser the inspection time taken by CMM to measure a given part better will be the performance of inspection process. Therefore, it has been critical to reduce measurement time for efficient performance of inspection process. In this paper, methodologies to generate most suitable measurement path resulting into minimum inspection time has been introduced. These methodologies are based on different algorithms to reduce measurement cycle time for CMM. The different algorithms have successfully been explored and compared to show their effectiveness in minimizing inspection time for stationary CMM equipped with touch trigger probe. The proposed methodologies have also been implemented and tested on real-world mechanical part with certain number of features to demonstrate their applicability.

Measurement Errors of Coordinate Measuring Machine Produced by Touch Trigger Probe System

In this paper, the authors discuss the influence of touch trigger probe system on CMM measurement performance based on measurement experiment results. A ring gage and a plug gage finished in high accuracy are employed as test pieces and the measurements performed under the conditions of combining different extension bar and approaching speed. Two main types of errors, periodic component and high frequency undulation, are verified. Introduction of the extension bar may significantly aggravate the accuracy and reliability, especially, associated with a comparatively large approaching speed. In addition, from the discussions on the generation mechanism of the periodic error and high-frequency undulation, some worthwhile references to engineering applications are also derived.