Jesús Velázquez

Articulated Arm Coordinate Measuring Machine Calibration by Laser Tracker Multilateration

A new procedure for the calibration of an articulated arm coordinate measuring machine (AACMM) is presented in this paper. First, a self-calibration algorithm of four laser trackers (LTs) is developed. The spatial localization of a retroreflector target, placed in different positions within the workspace, is determined by means of a geometric multilateration system constructed from the four LTs. Next, a nonlinear optimization algorithm for the identification procedure of the AACMM is explained. An objective function based on Euclidean distances and standard deviations is developed. This function is obtained from the captured nominal data (given by the LTs used as a gauge instrument) and the data obtained by the AACMM and compares the measured and calculated coordinates of the target to obtain the identified model parameters that minimize this difference. Finally, results show that the procedure presented, using the measurements of the LTs as a gauge instrument, is very effective by improving the AACMM precision.

A self-centering active probing technique for kinematic parameter identification and verification of articulated arm coordinate measuring machines

A crucial task in the procedure of identifying the parameters of a kinematic model of an articulated arm coordinate measuring machine (AACMM) or robot arm is the process of capturing data. In this paper a capturing data method is analyzed using a self-centering active probe, which drastically reduces the capture time and the required number of positions of the gauge as compared to the usual standard and manufacturer methods. The mathematical models of the self-centering active probe and AACMM are explained, as well as the mathematical model that links the AACMM global reference system to the probe reference system. We present a self-calibration method that will allow us to determine a homogeneous transformation matrix that relates the probes reference system to the AACMM last reference system from the probing of a single sphere. In addition, a comparison between a self-centering passive probe and self-centering active probe is carried out to show the advantages of the latter in the procedures of kinematic parameter identification and verification of the AACMM.

Development and calibration of self-centring probes for assessing geometrical errors of machines

A new type of probe for calibration, verification or interim checking of machine tools as well as robots or parallel-kinematics machine tools is presented in this paper. This probe is part of a ball-artefact-based method to assess the geometrical errors of linear and angular axes in a quick and reliable way. The discussion about the best design concept for the self-centring probe, the mathematical modelling and design process of one of those concepts and the development of three different prototypes are shown. Different sensors and design options were developed to optimize the size and cost of the probe. The calibration of the probe prototypes by way of a kinematically coupled reference device to allow on-machine tests is shown. The uncertainties obtained were around 1 µm for one of the prototypes and below 5 µm for the other two. Finally, results of a geometrical verification of a machine tool are demonstrated, with values similar to the ones achieved using other methods, such as laser interferometry. Compared to those other methods, the new technique was shown to be less time consuming.

Efficient volumetric error compensation technique for additive manufacturing machines

Purpose – This paper aims to present a methodology for volumetric error compensation. This technique is applied to an Objet Eden350V 3D printer and involves a custom measurement strategy. Design/methodology/approach – The kinematic model of the printer is explained, and its error model is simplified to 18 independent error functions. Each error function is defined by a cubic Legendre polynomial. The coefficients of the polynomials are obtained through a Levenberg–Marquardt optimization process. This optimization process compares, in an iterative algorithm, nominal coordinates with actual values of the cloud of points. The points are built in the faces of a gauge artefact as conical sockets defining one unique point for each socket. These points are measured by a coordinate measuring machine self-centring measurement process. Findings – Most of the errors of the 3D printer are systematic. It is possible to obtain an improvement of 70 per cent in terms of global mean error reduction in single points within ...

Empirical analysis of the efficient use of geometric error identification in a machine tool by tracking measurement techniques

Volumetric verification is becoming increasingly accepted as a suitable technique with which to improve machine tool accuracy. In the same way, the use of laser trackers to obtain machine error information using the new Active Target motorised retro-reflector allows the verification of all types of machine tool throughout their workspaces. Non-linear optimisation methods and machine tool kinematic models are the mainstays of this technique. Whereas the latter provide the relationship between the nominal coordinates, the geometric errors of the machine and laser tracker measurement, the former reduces the combined influence of geometric errors by obtaining their approximation functions. However, within these two procedures, several factors affect the scope of the produced verification results. The present paper focuses on the analysis of the adequacy of commercial measurement techniques using laser trackers and the new motorised retro-reflector in a real milling machine. An examination is also made regarding the influence of the optimisation sequence defined by the identification strategy, as well as the impact of the number of measured points in relation to the employed regression functions.

Procedure for geometrical errors identification in machine tool

This article presents a procedure to determine any of the 21 geometrical errors of a three axes machine tool (MT) taking into account the machine architecture. This verification technique is based on the utilisation of a 1D ball artefact and a self-centring probe, though it could be easily generalised to be used with a laser tracker. Most of the times, users are not interested in evaluating all the errors of their MTs but a subset. In this way, this procedure allows to any potential user the evaluation of any single error by providing a systematic method to obtain the needed equations and the experimental points to measure, as opposed to volumetric error compensation techniques where the work area is globally evaluated and the focus is shifted from the determination of each MT geometrical error to the reduction of the total error in every point. In that case, relevant information related with the physical values of each error is not preserved.

Modelling of Computer-Assisted Machine Tool Volumetric Verification Process

Nowadays, the accuracy of machining parts is essential in order to compete in a global market as demanding as machining. Due to the high cost of these machines continuous operation is required, with a reduction of the downtime owing to production readiness, maintenance or breakdowns. Among all the sources of error that affect the accuracy of machining parts, this paper is focused on improving the positioning accuracy of the machine. This requires periodic inspection of the machine tool, which should be included in maintenance operations. Volumetric verification is a novel technique that is being progressively introduced in machine tool maintenance operations, significantly reducing the time required. Unlike other techniques, this is based on non-linear mathematical models and the optimization process increases the influence factors. This modelling provides a re-creation of the whole verification process for all the influence factors; this allows the determination of the best measurement system distribution and the identification of techniques to use to characterize geometric errors. Thus, the verification time required is reduced, unnecessary tests are eliminated, the conditions under which real tests should be carried out are obtained in advance and machine tool accuracy is improved. (Received in November 2015, accepted in March 2016. This paper was with the authors 1 week for 1 revision.)

Parametric Modeling and Compensation of Layer Manufacturing Machines

Layer manufacturing machines are affected, the same way as traditional manufacturing processes, by systematic errors [.This lack of precision and poor dimensional accuracy can be reduced by software compensation techniques. This paper proposes a parametric error compensation technique based on pattern artifacts. This technique is verified on an Objet 350V 3D printer. To begin, these parametric techniques require the development of the machines kinematic model [. The data acquisition is performed with a CMM and a self-centering technique to measure conical sockets manufactured in the faces of pattern artifacts. After manufacturing various test patterns, with and without compensation, the achieved results are close to 80% reduction in mean error.

Development of a 1D‐displacement low‐cost sensor prototype based on the inverse square law

In this paper the design and development of a new prototype for measuring lineal displacements with micrometric resolution are presented. This device is based on the use of opto‐electronic sensors (photodiodes) with a mechanical displacement system. This generates a more compact and lower cost solution than the commercial ones (LVDT, optical encoders, etc.) usually utilized for measuring in a range of 10 mm with a resolution of tenths of micrometers. The mechanic system for the displacement comes from a relative movement between a linear guide and its slide unit. The final goal of this prototype is the calibration of machine tools with less expensive self‐centering probes than the nowadays available commercial ones. Firstly, the properties and behavior of the photodiodes have been analyzed in order to verify that they are adequate for this appliance. In the following tests carried out the fulfillment of the square law has been verified but the system repeatability has been severely affected by the tempera...