Search

Purpose The purpose of this study is to improve the accuracy of a fused deposition modeling three-dimensional (3D) printer by identifying and compensating for position-independent geometric errors using a face-diagonal length test featuring a designed artifact and a Vernier caliper. Design/methodology/approach An artifact that does not require support when printing was designed and printed to allow performance of the face-diagonal length test. A Vernier caliper was used to measure the lengths of diagonals in the XY, YZ and ZX planes of the printed artifact specimen; this completed the face-diagonal length test. The relationships between position-independent geometric errors of the linear axes X, Y and Z and the measured diagonal lengths of the three planes were determined to identify geometric errors. Findings The approach was applied to a commercial fused deposition modeling 3D printer, and three position-independent geometric errors were rapidly identified. The artifact was re-printed after model-based compensation for these errors and the diagonal lengths were re-measured. The results were verified via coordinate measuring machine measurement of a simple test piece without and with model-based compensation for identified geometric errors. Furthermore, the proposed approach was applied to a commercial 3D printer. Research limitations/implications The measured diagonal lengths of the printed artifacts varied greatly. Thus, further studies should investigate the effects of printing materials and parameters on the length discrepancies of 3D printed artifacts. Practical implications A software-based compensation of identified position-independent geometric errors has to be used at commercial 3D printers for accuracy improvements of printed parts. Originality/value Thus, the approach is of practical utility; it can be periodically used to identify position-independent geometric errors and ensure that the 3D printer is consistently accurate.

In this paper, a method is proposed for identification of 11 position-independent geometric errors (PIGEs) of five-axis machine tools with a tilting/rotary table via single-ball measurements and three-dimensional (3D) geometric sensitivity analysis. Eleven PIGEs were identified, including three squareness errors between three linear axes, two offset errors, and two squareness errors for the tilting/rotary axis. The approach uses a set-up of a ball and three circular measurements involving simultaneous control of two linear axes and a tilting/rotary axis. A 3D geometric sensitivity analysis is carried out to investigate the effects of the 11 PIGEs on each of the measurement’s paths and between the measurement paths. The particular measurement paths used allow the radius of the circular path at the first measurement, and the distance between the circular paths of the second and third measurements, to be increased for accurate identification of the 11 PIGEs. The proposed method was also used to derive root-sum-square values of sensitivity coefficients, and then applied to a commercial five-axis machine tool for experimental verification. It calculates the peak-to-valley values of the positional deviations in the x-, y-, and z-directions along the test paths as 152.1, 118.2, and 47.1 μm, respectively, without compensation for the identified PIGEs, and as 17.6, 15.0, and 11.4 μm, respectively, with compensation. The results confirm the validity of our proposed method.

We propose a technique to measure position-independent geometric errors (PIGEs) in the rotary and spindle axes of a hybrid parallel kinematic machine (PKM). The PKM investigated here includes one more rotary axis than an Exechon PKM, which is used to improve the productivity of hybrid processes, such as machining and direct-energy-deposition three-dimensional metal printing. Errors in the measured position and orientation of the rotary axis, and the orientation of the spindle axis produce volumetric errors in the processed workpiece. If accuracy is to be improved, the deviation of each axis must be measured and compensated. In our approach, errors are measured using three methodologies that require only control of the rotary axis: in the first, no offset is applied to account for positional deviation of the rotary axis; in the second, an offset is used to correct the orientation of the rotary axis; and in the third, a tool offset is used to correct the orientation of the spindle axis. We developed an algorithm that uses the three measured datasets to identify PIGEs. The proposed method was applied to a hybrid PKM and the PIGEs were measured and compensated. This technique uses simple measurement paths and sequential measurements to correct rotary and spindle axis errors, and could therefore be widely used in industry.

We introduce a prototype “machine tool analyzer” (MTA), consisting of a nest of five displacement sensors and a dual-ball system with two centering structures, designed to identify 13 position-independent geometric errors (PIGEs) in five-axis machine tools. The 13 PIGEs include three squareness errors in the three linear axes, two squareness errors and two offset errors in the rotary/tilting axis, and two squareness errors in the spindle axis. The MTA completes four circular paths, during which an identification algorithm identifies thirteen possible PIGEs and set-up errors. The MTA was applied to a commercial five-axis machine tool with a swivel head/rotary table and verified experimentally. Cost-effective measurements were achieved using a single set-up of the nest and associated system. In addition, a circular test using a double ball-bar was used to test the volumetric accuracy of the five-axis machine tool and verify the identified PIGEs. The maximum deviation, minimum deviation, and PV values in the circular test were 109, 55, and 55 μm, respectively, without compensation for errors imparted by the PIGEs, and 38, 5, and 33 μm, respectively, with compensation. This demonstrated the validity of the proposed method.

This paper presents a double ballbar method with an extension fixture to identify the position-independent geometric errors of three-axis machine tools with respect to their entire workspace by conducting face- and body-diagonal length tests. To extend the length of the double ballbar to the required nominal length in the face- and body-diagonal directions, an extension fixture is designed and manufactured using a fused-deposition-modeling 3D printer to ensure that it is lightweight. Inherent position-independent geometric errors can be calculated from measured lengths by using homogeneous transformation matrices, which are multiplied under the assumption of small values, to determine the volumetric error produced by a machine tool. The relationships between the position-independent geometric errors, roll-pitch-yaw errors, and measured lengths can be derived according to the definition of the straightness errors, based on the end-point of the reference straight line. Finally, the position-independent geometric errors, with analysis of measurement uncertainties, can be identified by substituting the values of the roll-pitch-yaw errors, measured by a multi-axis calibrator, into the derived relations. The results can then be validated by re-measuring the face- and body-diagonal lengths with error compensation. The main advantage of the proposed approach is that it can be used to identify the inherent position-independent geometric errors of machine tool workspaces. This could contribute to reducing volumetric errors in machine-tool workspaces by allowing compensation for measurement errors, thus making machine tools more effective.

This study proposes an optimal on-machine measurement method to measure position-independent geometric errors of five-axis machines, including machine tools and coordinate measuring machines, with a universal head. This measurement requires only a calibrated three-dimensional (3-D) probe and a precision sphere, which are fundamental components of on-machine measurement systems in general, to minimize measurement costs, including operator effort and operating time. Eight position-independent geometric errors are used to describe the coordinate systems of the two rotary axes through a kinematic analysis. The center of the precision sphere, which is stationary during the measurement, is measured at various angles of the rotary axes. Then, the linearized relationship between the measured positions of the precision sphere and the geometric errors is derived using an error synthesis model under rigid-body and small-value assumptions. The proposed method is tested through a simulation for validation. The geometric errors of a five-axis coordinate measuring machine with a universal head are measured with measurement uncertainty by applying the proposed method. Then, the measurement results are confirmed by comparing the measured positions of the precision sphere and calculated positions using the measured geometric errors at the other (i.e., the arbitrary, or not measured) angles of rotary axes.

Commercially pure titanium (CP Ti) has been actively used in the plate heat exchanger due to its light weight, high specific strength, and excellent corrosion resistance. However, researches for the plastic deformation characteristics and press formability of the CP Ti sheet are not much in comparison with automotive steels and aluminum alloys. The mechanical properties and hardening behavior evaluated in stress–strain relation of the CP Ti sheet are clarified in relation with press formability. The flow curve denoting true stress–true strain relation for CP Ti sheet is fitted well by the Kim–Tuan hardening equation rather than Voce and Swift models. The forming limit curve (FLC) of CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching test and analytically predicted via Hora's modified maximum force criterion. The predicted FLC by adopting Kim–Tuan hardening model and appropriate yield function shows good correlation with the experimental results of punch stretching test.

A compensation mechanism with six degrees of freedom (DOF) was developed to enable precise control of a linear stage. Geometric, thermally induced, and dynamic errors in the linear stage were compensated for in real time by the nanopositioning stage. A stage-based hinge with high structural stiffness and rapid response characteristics was modified for parallel operation. The stage’s full range of motion was measured and kinematics was used to calculate the displacement required by each actuator to compensate for the errors. Except for the displacement error of the linear stage, the contribution of each error source was measured by a reference mirror and five capacitive sensors. A compensation algorithm, based on a recursive method, was used to improve the positioning accuracy of the system. The performance of the stage presented here was investigated by measuring, and compensating for, the five-DOF linear stage errors in real time. In practice, the peak-to-valley errors of the translational and rotational errors were reduced by 89% and 93%, respectively.

This study proposes a method for a quick, simple interim check and practical accuracy improvement of machine tools using just a double ball-bar. The double ball-bar is used to measure sequentially the length of the six sides of a virtual regular tetrahedron within the workspace of the machine tool. Then, the scale and squareness errors of and between the three linear axes are calculated from the length results, and the measured lengths and the calculated errors can be used as criteria for the interim check. The calculated errors can also be compensated for to improve the accuracy of experimented machine tools practically. A sample machine tool was subjected to experimental interim checks applying the proposed method; it showed primarily large length deviations for the six sides due to geometric errors mainly. To improve the geometric accuracy practically, the calculated errors were compensated for and the measurements were repeated, showing significantly improved length deviations for the six sides. The main advantage of the proposed method is that it requires only a double ball-bar and sequential measurements; thus, it is a simple procedure with a measuring time of ∼5 min for a virtual regular tetrahedron. Additionally, the size of the virtual regular tetrahedron can be readily modified by changing the nominal length of the double ball-bar, increasing measurement flexibility. Thus, the proposed method is suitable for quick, simple, cost-effective daily and periodic interim checks, with practical improvement of machine tool accuracy.

Servo mismatch, which affects positioning accuracy in computer numerical control (CNC) machine tools, is an important source of error. Dynamic measurements of simultaneous movements in two axes are essential in determining servo mismatch. A circular test using a double ball-bar (DBB) is used commonly to assess such errors. However, servo-mismatch measurements of some machine tools, such as miniaturized machine tools, remain difficult due to structural restrictions of the measuring devices. In this study, a technique for servo-mismatch measurement via a bi-directional circular test using a laser tracker is described. The laser tracker is easy to set up experimentally and has fewer measuring range restrictions than other measuring devices. In order to ignore the effects of quasi-static errors, a bi-directional circular test is conducted using the laser tracker. Additionally, a compensation procedure, with a proportional equation, is proposed. The validity of the technique described was confirmed by comparison with the DBB result. In a machining test after servo-mismatch compensation, by adjusting the position loop gain, the roundness of a cylinder part was improved by ∼47.9%.

Sheet metal formed of lightweight materials such as aluminum sheeting has received great attention related to the reduction of vehicle emissions. This paper evaluates the anisotropic yield locus using Kuwabara’s biaxial tensile tester and stretches formability using Hecker’s hemispherical punch stretching test for aluminum 6016-T4 sheet material. The anisotropic yield locus of the Al6016-T4 sheet measured is fitted well by the modified Drucker yield function. Moreover the best fitting to the experimental stress-strain curve from the tensile test was obtained by taking an appropriate hardening model. Analytical study to predict the stretch formability by using Hora’s Modified Maximum Force Criterion (MMFC) was performed. The predicted forming limit curves (FLC) based on various yield functions were compared with the experiments and discussed.

In this study, parallelism errors between the spindle axis and the linear axis of machine tools were measured using a double ball-bar. Specifically, two circular tests were performed to measure the parallelism errors using tool balls with different tool lengths and a workpiece ball fixed to a workpiece table. Parallelism errors were calculated by analyzing, simultaneously, the measured double ball-bar (DBB) data from the circular tests. The proposed method provides accurate measurements due to a large offset between the circular tests within the working space of machine tools. Additionally, the approach only requires a DBB and adjustment/extension fixtures; thus, it simplifies measurements and is cost-effective.

Design of polymer composites for tribological applications is a multi-criteria optimization problem. Two-body abrasive wear (2-BAW) behaviour of thermoplastic copolyester elastomer (TCE) reinforced with and without short glass fiber, filled with various fillers (short carbon fiber, polytetrafluoroethylene, silicon carbide and alumina) in different proportions were influenced by the properties of their constituents. 2-BAW behaviour of multi-phased TCE composites was evaluated using pin-on-disc apparatus. This paper presents an approach to establish the model for predicting the specific wear rate (Ks) of TCE composites. Three-factors and three-levels, facecentered central composite design was used for conducting tests. Response surface methodology was applied to derive the second order quadratic model with the selected parameters. The results indicated that the Ks increases with increase in fiber/filler content and decreases with increase in grit size of silicon carbide (SiC) abrasives and abrading distance. The investigation also revealed that the fiber/filler content is the most influencing factor, followed by grit size of SiC abrasives and abrading distance. The predicted results show close agreement with the experimental. Hence the developed model could be used to predict abrasion behaviour of multi-phased TCE composites satisfactorily. The worn surfaces of TCE composites were analyzed with the help of scanning electron microscope.

We report a compensation system for geometric errors of a linear axis to achieve the ultra-precision positioning. The system was miniaturized by integrating the drive and measuring components. A novel joint with three DOFs based on a flexure hinge was developed to obtain the ultra-precision positioning. The drive component, which was adapted to the parallel mechanism, had a high structural stiffness and rapid response characteristics. The rotational stiffness of the joint was calculated and the mode shapes were analyzed to verify the feasibility of three-DOF motion. The measurement component consisted of capacitive sensors and a reference mirror to measure the three geometric errors of the linear axis. In addition, the optimal position between the reference coordinate system and a sensor was determined to minimize the standard uncertainties of the measured errors. The compensation system was fabricated and evaluated experimentally. A compensation algorithm based on a recursive technique was developed to improve the positioning accuracy of the system. The geometric errors of the linear axis were measured and compensated for, and a marked improvement was observed compared to the case with no error compensation. The peak-to-valley error of the translational and rotational errors were reduced by 92% and 98%, respectively.

A hybrid measurement technique using a five-DOF measuring system and laser interferometer is suggested for all geometric errors of a three-axis machine tool. All geometric errors are defined in a single coordinate system, by eliminating the effect of Abbe’s offsets, for accurate measurement. The five-DOF measurement comprises five capacitive sensors and an L-type reference mirror. The system measures three PIGEs (position independent geometric errors) and five PDGEs (position dependent geometric errors) for each axis. The 18 geometric errors of the machine tool are measured using the results from two experiments (XY and YZ-planes), and the homogeneous transform is used to identify the geometric errors in a single coordinate system, eliminating the effects of installation errors such as mirror misalignment. A laser interferometer is used to measure three PDGEs (one linear displacement error and two straightness errors) for each axis. The two straightness errors are used to estimate the optimal Abbe’s offsets (for the X, Y and Zaxes) between the two measuring coordinate systems, and the linear displacement of each axis is calculated, minimizing the effect of Abbe’s offsets. Through this analytical approach, all geometric errors are expressed for a single coordinate system. The suggested measurement technique can therefore be used to investigate all geometric errors of a three-axis machining tool.

The out-of-squareness is one of the error sources that affect the positioning accuracy of machine tools and coordinate measuring machines. Laser interferometer is widely used to measure the position and angular errors, and can measure the squareness using an optical square. However, the squareness measurement using the laser interferometer is difficult, as compared to other errors due to complicated optics setup and Abbe’s error occurrence. The effect of out-of-squareness mainly appears at the face-diagonal of the movable plane. The diagonal displacements are also affected by the position dependent geometric errors. In this study, the squareness estimation techniques via diagonal displacement measurement using the laser interferometer without an optical square were proposed. For accurate estimation and measurement time reduction, the errors selected from proposed discriminant were measured. Discrepancy between the proposed technique with the laser interferometer (with an optical square) result was 0.6 µrad.

We describe a method to separate, measure, and compensate for position-independent and position-dependent geometric errors in the rotary axes of a five-axis machine tool with a tilting rotary table using double ball-bar measurements. The measurement paths require control of a single rotary axis, and they are not affected by the accuracy of the linear axes. The positions of the balls of the double ball-bar are modeled as the nominal positions, with geometric errors considered via a kinematic analysis to represent the measurement configuration. The method is applied to measure both position-independent and position-dependent geometric errors, and the results are verified via measurements with compensation for the geometric errors. Furthermore, the possible range of the measured geometric errors is determined by analyzing the contributors.

In this paper, a measurement system for roll error (angular error of a linear moving stage) is described. The proposed system consists of four capacitance sensors located at four vertices of a tetragon in a fixture. Unnecessary measured data due to global surface roughness on the measuring target is eliminated using a differential method. First, a mathematical model for the proposed system is developed using the error synthesis modeling technique. The zero adjustment difference is a critical parameter for precise measurement. Therefore, an additional measurement procedure is developed to estimate the zero adjustment difference. The x- and y-directional offset errors, which are deviation from the designed position of hole for holding a capacitance sensor, introduce an error in the estimation of roll error. Therefore, a virtual experiment is performed with different values of x- and y-directional offset error to analyze their effect. Then, the roll error is measured using the proposed measurement system. A comparison of the measured data from the proposed method (four capacitance sensors) and the conventional method (two capacitance sensors and a straight-edge) is performed. Finally, the proposed method is verified using a hypothesis test.

The transfer from engine drive vehicles to electric vehicle has been proceeding due to fuel exhaustion, higher fuel costs, and environmental restrictions. This trend has also led to a transition in brake system from the hydraulic brake system to the electric brake system, which uses electric power. This electric brake system has led to an enhancement of safety and eco-friendliness due to a reduction braking distance, a rapid-response property, and the elimination of braking oil. However, one of the big problems to solve for practical usages is the need of a high power motor to enable braking forces as strong as those of hydraulic brake systems. Therefore, it is necessary to develop high efficiency electro mechanical brakes with a proper reinforcement mechanism to solve this problem. In this paper, we describe a wedge structure that has a self-reinforcing effect; we propose a proper actuating direction for a movable wedge to obtain greater clamping efficiency and braking efficiency, which will mean a better relation of the motor force as the input to the braking force as the output. Further, we propose the method to keep the most braking efficiency and clamping efficiency without reference to the variations of frictional coefficient.

This paper describes a new approach for controlling a micro wire electrical discharge machining (μ-WEDM) process. In this approach, the relative feedrate of electrodes was controlled based on the real-time estimation of material removal rate and the identification of the workpiece height. An assisted vibration was applied to the workpiece, eliminating the limitation of a small discharge gap. This allows the electrode to be moved continuously, which cannot be performed in conventional WEDM. To verify the efficiency of the system, two workpieces with different shapes were used. For one workpiece, the height was varied linearly, whereas for the other, the height was varied non-linearly. The discharge current, discharge voltage, and number of discharge pulses were measured using current and voltage probes. The signal was uploaded to a computer through data acquisition devices, and a LabVIEW program was developed to estimate the feedrate and control the stages. The experimental results showed that the developed system worked effectively, with high machining stability and efficiency.

This paper describes the analysis and control method for the kerf of cut slots in dry micro-wire electrical discharge machining (μ-WEDM). First, the influence of the controllable parameters such as the air injection pressure, relative electrode feedrate, open voltage, and input capacitance were investigated based on the Taguchi methodology. The behavior of the kerf with respect to the workpiece height was also considered. Second, to improve the machining accuracy of the dry μ-WEDM, a control method was developed to compensate for the kerf based on real-time estimation of the material removal rate and by controlling the air injection pressure. In this research, all the experiments were performed in a constant-feedrate mode and with various high-pressure air injection. The experimental results show that the kerf in dry μ-WEDM was significantly affected by the air injection pressure, electrode relative feedrate, and cut height of the workpiece. Moreover, by monitoring the material removal rate of the process, the kerf in dry μ-WEDM was efficiently controlled.

Micro-electrical discharge machining (μ-EDM) has recently received increased attentions in high precision machining and micro manufacturing. Since μ-EDM is a very complex process, it is difficult to develop a comprehensive model to analyze and predict its characteristics. This makes μ-EDM more difficult to control and requiring high skilled, experienced operators. Although electro-thermal models have been developed to estimate the material removal rate, tool wear ratio and surface roughness of the μ-EDM process, since they are based on the usage of incorrect value of fraction of energy distributed to electrodes, the estimations deviate significantly from the experimental results. This paper presents an experimental study of the fraction of energy distributed to the electrodes of a μ-EDM process where the material of both electrodes and dielectric are in concern. The fractions of the energy are estimated using an electro-thermal model based on controllable parameters, and were simplified by empirical models for investigation and comparison.

Circular tests to determine the circular/spherical deviation of machine tools based on double ball-bar measurements are proposed and applied to machine tools for accurate performance evaluation. In current circular tests, eccentricity is mathematically removed from the measured data to evaluate performance. However, eccentricity is affected not only by set-up error of the double ball-bar, which is trivial, but also by geometric error, which this test is intended to determine. The relationship between eccentricity and geometric error was investigated during circular deviation measurements using a simple example. The results demonstrated that the measured data must be evaluated as they are, without any mathematical modifications. Additionally, the circular test must be performed while ensuring negligible set-up error. The proposed approach was applied to three machine tools to investigate the effect of eccentricity when circular/spherical deviation appears.

Electro wedge brake (EWB) have been suggested and improved for enhancing the braking efficiency and reducing the weight and power of actuating motor than electro mechanical brake (EMB). This is due to self-reinforcement features of the wedge mechanism. On the other hand, the conventional hydraulic brake system has the passive wear adjustment without any sensors and actuators. This is because of the sealing rubber which is disposed between the hydraulic cylinder and piston, and supply the piston’s same restoring strokes regardless of pad’s wear amounts. This feature leads to the uniform distance between the disc and the pad. In comparison, electronic brake systems such as EMB and EWB don’t have the hydraulic piston and cylinder with the sealing rubber. Therefore the electronic brake systems cannot use the function of this passive wear adjustment. However, if the electronic brake system has gap sensors for detecting distances between the pad and the disc, and actuators for keeping the uniform distances between the pad and the disc, then the brake system can have the function of wear adjustments. One of our research goals is the embodiment of cost-effective and feasible wear adjustment mechanism which is proper to EWB. In this paper, as a chain of EWB’s development, we describe the proposed mechanism for wear adjustment with EWB. Further we describe the feasibility of this mechanism with the simulation study.