Touch Trigger Probe Research Articles

Milling infiltrated carbon-bonded carbon fiber: Geometric attributes, surface characteristics, and feasibility

This paper describes a manufacturing approach for carbon-bonded carbon fiber where cyanoacrylate and wax infiltration are used to improve the handling and machinability of preforms. Structured light optical coordinate metrology is used to acquire a stock model for computer-aided manufacturing and work coordinate system definition for machining. Non-infiltrated (neat) and infiltrated samples are machined using the same part program to compare results. Geometric attributes are measured with a touch trigger probe coordinate measuring machine and surface characteristics are measured with an optical 3D measuring system. Experimental results show superior geometric accuracy and surface roughness for the infiltrated samples over the neat sample.

Reliability of probes for CNC machine tools

So far, the issue of degradation of touch-trigger probe accuracy during measurements on CNC machines has not been addressed. In the article, for the first time, a procedure for testing and predicting the accuracy and reliability of probes used in machine tools was proposed and experimentally verified. Reliability test procedure covering 30 million triggers was performed under laboratory conditions. Based on the obtained results, a concept of the probe reliability testing procedure was proposed, and an attempt was made to assess the impact of the operational process on the probe's metrological parameters. An important issue of this work is to develop a concept for the analysis and interpretation of the results of such a process by determining which parameters of the probe description provide the most information about the degradation process and how to predict the operating time of such a device.

Thermal Error Measurement and Compensation with Torque Limit Skip in Swiss-type Lathe Manufacturing

This paper presents a new methodology for the measurement of thermal errors of Swiss-type lathes. The basis of the proposed method is the torque limit skip function integrated in the lathe’s control which stops the motion of a linear axis if the torque on the corresponding axis servo is exceeded. The skip signal is triggered via a slow contact between a bar in the lathe’s spindle and an artefact in the lathe’s tool holder. Experimental results indicate that when a sufficiently low torque override limit is applied, the axis positioning repeatability under the repeated application of the torque limit skip is within ±1μm. The relative change in position of the axis after the skip measured over several hours is the thermal error which can be compensated. The proposed measurement technique offers significant advantages over conventional thermal error measurement with a touch-trigger probe or linear displacement sensors: if available on the machine’s control, it does not require any specialized installation, can be used during production, and delivers comparable results without high additional equipment costs.

Influence of rotary axis angular positioning error motions on robotic probing

The accuracy of touch-trigger probing by a six-axis robotic manipulator is determined by the accuracy of the robot forward kinematic model to estimate the stylus sphere position from angular positions of rotary axes. Many conventional studies have employed the Denavit–Hartenberg (DH) model, containing position and orientation errors of the rotary axis average lines as error sources. This paper proposes the application of a new kinematic model, containing the angular positioning deviations of all the rotary axes, to the robotic probing. The probing accuracy is experimentally investigated in profile probing of a straightedge over the robot's workspace.

Touch-trigger probe error compensation for nonvertical on-machine measurement of freeform surface workpieces

Touch-trigger probe error compensation for nonvertical on-machine measurement of freeform surface workpieces

Workshop-suited identification of thermo-elastic errors of three-axis machine tools using on-machine measurement

This paper presents a method for workshop-suited identification of thermo-elastic errors of three-axis machine tools (MTs) using on-machine measurement. For this purpose, a new design for a three dimensional artifact is presented. Using the artifact, it is possible to identify all relevant geometric errors of three-axis portal milling machines in table design. The method presented is therefore suitable for the one-time identification of geometric errors caused by manufacturing inaccuracies, assembly-related deviations and wear, and for the identification of thermally induced geometry errors over a long-term period. Since the artifact is scalable in size, it can be easily adapted to different machine sizes. The presented method thus represents a universal and inexpensive possibility to measure geometric and especially thermo-elastic errors.Within the scope of this paper, an error model was established for the investigated machine type and an artifact design was derived on the basis of this model. The suitability of the artifact for identifying thermo-elastic errors has also been investigated experimentally. For this purpose, an artifact made of thermo-invariant material (Invar) was produced. This artifact was measured cyclically on a MT with three linear axes, which was exposed to a controlled thermal load in a temperature chamber. The positions of the geometric features were collected using a 3D touch trigger probe. In addition, the ambient temperatures were recorded. The results of this measurement are discussed in this paper.

Integrated profile and thickness error compensation for curved part based on on-machine measurement

Curved parts are widely used in aerospace, automotive and energy industries. The profile and thickness accuracy are both critical to some curved parts such as hollow blades. Improving the profile accuracy while ignoring the wall thickness error will reduce the qualified rate of these curved parts, and vice versa. This paper proposes a comprehensive compensation method with constraints of both profile and thickness tolerances for the machining of curved parts. The actual geometry and wall thickness of the parts are obtained by on-machine measurement system after rough machining. Both touch-trigger probe and thickness gage are used to reconstruct the actual outer and inner surface of the workpiece. Then, the comprehensive constraint considering both profile and thickness constraints is established based on the reconstructed workpiece geometry. With the comprehensive constraint, a new target outer surface is constructed. The machining error is calculated from the target surface and compensated via toolpath adjustment. At last, machining experiments are conducted to verify the feasibility of the proposed method.

십자형 교정체를 이용한 5축 공작기계 회전축의 기하학적 오차 추정에 관한 연구

Estimation and compensation of geometric errors for rotary axes are among methods to improve machining accuracy of five-axis machine tools. Studies have been conducted on various methodologies for estimating geometric errors for rotary axes, which are essential for improving machining accuracies of five-axis CNC machine tools. This paper presents a method for estimating geometric errors of a rotating/tilting table using a cross-shaped calibration artifact with a touch trigger probe. The proposed method includes rotary axes error estimation equations for angles of each rotary and tilt axis based on locations of probing points. Computer simulations were performed based on a MATLAB/Simulink and ADAMS cosimulation system using the probing cycle process to verify the proposed method. Computer simulation results confirmed the usefulness of the proposed method in terms of volumetric errors.

A Novel Pretravel Error Compensation Strategy for Five-Axis On-Machine Measurement With a Touch-Trigger Probe

A Novel Pretravel Error Compensation Strategy for Five-Axis On-Machine Measurement With a Touch-Trigger Probe

An electromagnetically actuated ball and socket joint for applications in 3D metrology

The design, development and application of a novel magnetically actuated ball-and-socket joint has been presented here. The joint comprises a current-carrying conductor acting as the socket and a permanent magnet ball. External solenoid coils are employed to orient the ball in any desired direction. A novel strategy, based on providing a small vibratory input, is proposed to eliminate static friction. The joint has been fabricated and experimentally demonstrated to rotate over a large range of about ± with a low cross-axis rotation, of about 8%, and with negligible hysteresis. The developed joint has been employed as a touch-trigger probe in a coordinate measurement machine to access all the three surfaces in a cuboidal corner of a sample.

A self-calibration scheme to monitor long-term changes in linear and rotary axis geometric errors

A calibration scheme of position and orientation errors of rotary axis average lines based on touch-trigger probing is widely available on many commercial five-axis machine tools. Such a measurement is influenced by error motions of both linear and rotary axes. This paper proposes a novel scheme to separately identify linear and rotary axis geometric errors by using a touch-trigger probe and an uncalibrated test piece. Whereas the proposed scheme is based on well-developed self-calibration schemes for the circularity measurement, an original contribution is that it is applied to separate linear and rotary axis geometric errors. Two case studies are presented. First, the proposed tests are performed on the same five-axis machine tool for half a year to observe a long-term change in linear and rotary axis geometric errors. The second case study investigates the influence of room temperature change on linear axis and rotary axis error motions.

Free-form surface form error evaluation based on smaller-scale sampling points in touch-trigger probing

Surface reconstruction is an essential operation in the evaluation of free-form surface form error. As a feasible technology in free-form surface sampling, touch-trigger probing has been widely used in on-machine measurement and coordinate measurement machine. However, surface reconstruction quality is influenced by limited sampling point size. This study proposes a surface reconstruction method based on surface position error and deformation error model. Surface form error is decomposed into surface position error and deformation error. Then, the design surface is taken as a rigid body, and a point-to-surface function-based iterative algorithm is conducted to adjust surface location and orientation to best match the sampling points. The advantage of this algorithm is that it considers the probe dimension, so further compensation of probe radius is not required. The geometry of the adjusted design surface is modified based on thin plate energy minimization and point-to-surface function. Due to the inherent feature of the proposed method, geometric features of the design surface are kept. Experiments are conducted to verify the effectiveness of the proposed method, and results show that the proposed method can achieve lower error compared with existing methods.

Development of a High-Resolution Touch Trigger Probe Based on an Optical Lever for Measuring Micro Components

The characterization of a high-precision component with its dimensions has become a key problem in ensuring the performance of system parts. A touch trigger probe plays an important role in experimentally measuring these properties. In this study, a new high-resolution touch trigger probe based on a modified optical lever method is proposed. Only one optical sensor is adopted. The sensing principle of the developed probe in 3D is investigated through the probe’s sensitivity models. An optimizing design of the elastic suspension is demonstrated. Experiments on probe performance are conducted by measuring a step height and a gauge block. Experimental results indicate that the probe achieves a resolution of up to 1 nm in 3D and a measurement standard deviation of 18.3 nm. The probe has a permissible range of ± <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{m}$ </tex-math></inline-formula> in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}/{y}$ </tex-math></inline-formula> -axis and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu \text{m}$ </tex-math></inline-formula> in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis. The drift of the probe is 5.2 nm within 30 min. The comprehensive uncertainty of the probing system is 18.45 nm. The developed probe can be used in micro/nano coordinate measuring machines.

Workshop-suited geometric errors identification of three-axis machine tools using on-machine measurement for long term precision assurance

In this paper we present a novel methodology for fast geometric errors identification of three-axis machine tools (MTs) using on-machine measurement. For this purpose, a new design of a three-dimensional artifact is proposed. The artifact allows to identify the linear positioning error and the two straightness errors of any linear axis of MTs with cartesian kinematics and the perpendicularity error between the axes. The prerequisite for the measurement is that the roll, pitch and yaw errors of all axes have already been measured and are negligibly small. The presented methodology is especially suitable for regular control of the machine accuracy in order to ensure the precision of the machining in the long term.As part of this work, an artifact was made of thermo-invariant material (Invar) and calibrated with an accurate coordinate measuring machine (CMM). This artifact was used to identify the geometric errors of an MT with three linear axes, with the raw data being collected using a 3D touch trigger probe. The measured errors were compared with results from laser interferometer and ballbar measurements. Moreover, the measurement uncertainty of presented methodology was analysed and compared with those of the laser interferometer and ballbar.

Comparative Performance Evaluation of Multiconfiguration Touch-Trigger Probes for Closed-Loop Machining of Large Jet Engine Cases.

This article presents advances in the methodology of rapid various probe configurations comparison for the five-axis, tilting-head machine tools in conjunction with master artifacts. The research was performed in a direct context of automated machining of large, complex jet engine cases made from 17-4PH and 321 stainless steel materials. The aim of the study was to investigate whether all probe configurations have comparable measurement capability for use in manufacturing environment conditions. Based on the preliminary stage of the study, the T1 main straight probe achieved acceptable results of repeatability and reproducibility, lower than 10%, except for the reference diameter measurement of MT#2, where 15.4% R&R was achieved, conditionally accepted. For the straight probe configuration, error lower than 10 μm was achieved for the true position measurement and error ±10 μm for the reference diameter measurement, in relation to the vertical and horizontal head position, with the exception of the T9 and T5 MT#2 probe configuration, where higher error was noticed. The obtained results of the T5 MT#2 and T9 probes were supplemented with additional tests, which are also included. For the custom styli probes, the T4 and T6 configurations, unacceptable error, higher than 0.30 mm, was observed for the Y axis position. Depending on the shop floor and machine tool condition, variability of the results was also observed. Hence, the collected data and research helped to determine the mutual measurement errors and determine the application limitations of probes for an adaptive process flow.

The share of the probe errors in on-machine measurements

The influence of the errors of touch-trigger probes for machine tools on the result of the basic measuring tasks performed by CNC was examined. The goals of the analysis were, first, to estimate an uncompensated value of the error which occurs during different qualification cycles, and second, to determine the influence of the qualification on the measurement of features such as distance, a circle and the position of corner. The investigation was based on the results of research on a few probes, for which the values of the triggering radius in the form of spatial characteristic in a laboratory were determined. The obtained results show that although the qualification cycle reduces the influence of the probe error on the measurement result and increasing the number of qualification points improves the compensation conditions, this error is not completely eliminated, and its value can reach as much as several tens of micrometres.

Touch Trigger Probe-Based Interference-Free Inspection Path Planning for Free-Form Surfaces by Optimizing the Probe Posture

Free-form surface inspection is a challenging task due to its complex geometry. Coordinate measurement machine (CMM) and on-machine measurement (OMM) equipped with the touch-trigger probe are commonly used for their high accuracy and ease to operate. Path planning plays a pivotal role in measuring free-form surfaces with accuracy and efficiency, which considers accessibility and stability of probe movement, as well as the total inspection time (IT). In this article, an integrated path planning method is proposed for free-form surface inspection by the touch-trigger probe. The accessibility cone is defined to describe the interference-free probe pole directions for gauging an inspection point. A graphic process unit (GPU)-based algorithm that accelerates the computation of accessibility cone is developed. Then, the inspection points are divided into several clusters by a classification algorithm. In each cluster, the inspection points can be detected in the same probe pole direction. Finally, the inspection points in each cluster are sorted according to the spatial location to shorten the total path length, and the global interference-free inspection path is generated. Experimental study is conducted by applying the proposed method and an existing method to an impeller blade, respectively. The variation of probe posture and total IT is estimated and measured. Compared with the existing method, the proposed method prominently reduces motion of rotation axes, resulting in distinct decrease of total measuring time.

Simultaneous calibration of probe parameters and location errors of rotary axes on multi-axis CNC machines by using a sphere

On-machine measurement (OMM) systems with touch-triggered probes are efficacious in productivity improvement. Machine motion errors impose major limitations on their accuracy for any OMM systems, especially when rotary axes motions are involved. This research proposes a precise measurement method to address this problem by simultaneously identifying the probe parameters and the location errors of rotary axes, using a touch-triggered probe to sample a sphere. This method is suitable for both periodic machine checks and OMM system recalibrations. The method formulates a mathematical model based on machine kinematics to represent errors between the theoretical probed data and the actual recorded data, minimizing which can solve for necessary parameters. Two proposed probing patterns simplify the solution to the model. Experiment results demonstrate that the method is effective and accurate. Monte Carlo simulations were carried out to prove the robustness of the method.

A rigid-flexible coupling pretravel error model for a touch-trigger probe in an on-machine inspection system

Touch-trigger probes are widely used in on-machine inspection (OMI) systems, which have become increasingly important in an interprocess inspection. The pretravel errors are often compensated by data-driven calibration. However, its accuracy is significantly affected by its internal mechanical structure and trigger mechanism. In this paper, we propose a rigid-flexible coupling pretravel error model, considering the bending of the stylus and the lifting of the stylus carrier in the triggering process. This paper presents a method to identify the acceleration of machine tool by fitting the measured results at different speeds into quadratic curves and establishes the response error model. The trigger force of 73 direction probes is identified by a three-directional force sensor. The trigger force identified by the experiment is analyzed in the rigid-flexible simulation model, and the trigger resistance threshold of the probe is obtained. The simulation model of trigger error is established. Through the response error model and trigger error simulation model proposed in this paper, the probe pretravel error compensation accuracy can be improved by 39.6%.

Complex Surface Reconstruction Based on Fusion of Surface Normals and Sparse Depth Measurement

Precision measurement and reconstruction of detailed surfaces topography is a challenging task for non-diffuse complex parts. Although coordinate measurement machines (CMM) with the touch-trigger probe are widely used in current industry, the measurement efficiency limits their application in the measurement of complex surfaces. This article proposes a multisensor data fusion strategy by integrating the technical merits of CMM and photometric stereo (PS) to achieve multiscale reconstruction of a complex surface with high efficiency. Considering the complementary measurement characteristics of the two approaches, the sparse points from CMM are used to provide global shape information, and the high-resolution surface normal map from PS is used to provide local detailed structure. A multistage neural network is then proposed to fuse these two kinds of modality information such that the global features from the sparse points and the local features from the surface normal map are fused in a coarse-to-fine multistage process so as to make the training process more stable and the reconstruction more accurate. To enhance the generality of the fusion neural network, a synthetic training data set is also designed to include a large variety of multiscale features enriched surfaces. Experiments are conducted to verify the effectiveness of the proposed multisensor fusion strategy in accurate reconstruction of complex surfaces with high efficiency.