Straightness Motion Research Articles

Hybrid optical measurement system for evaluation of precision two-dimensional planar stages

This paper presents an optical measurement system, which is mainly composed of two hybrid sensor modules (HSMs), for evaluation of precision two-dimensional (2D) planar stages. The HSM is designed to integrate two different types of sensors within a single sensor module, so that it can be operated as a profile interferometer or an angle sensor by simply switching the data-processing mode. This enables us to implement efficient on-site evaluation of straightness errors of moving mirrors of a two-axis laser interferometer, and multi-axis parasitic motion errors of a 2D planar stage without reconfiguration of the evaluation setup. To estimate the performance of a prototype measurement system, an exemplary 2D stage was experimentally evaluated, and the straightness and angular motion errors were measured with expanded uncertainty (k = 2) of 40 nm and 0.14″, respectively. Reliability of the measurement system was also verified by comparison with reference instruments.

Self-adaptive and efficient propulsion of Ray sperms at different viscosities enabled by heterogeneous dual helixes

We disclose a peculiar rotational propulsion mechanism of Ray sperms enabled by its unusual heterogeneous dual helixes with a rigid spiral head and a soft tail, named Heterogeneous Dual Helixes (HDH) model for short. Different from the conventional beating propulsion of sperm, the propulsion of Ray sperms is from both the rotational motion of the soft helical tail and the rigid spiral head. Such heterogeneous dual helical propulsion style provides the Ray sperm with high adaptability in viscous solutions along with advantages in linearity, straightness, and bidirectional motion. This HDH model is further corroborated by a miniature swimming robot actuated via a rigid spiral head and a soft tail, which demonstrates similar superiorities over conventional ones in terms of adaptability and efficiency under the same power input. Such findings expand our knowledge on microorganisms' motion, motivate further studies on natural fertilization, and inspire engineering designs.

Analysis of Motion Errors of Linear Guide Pair Based on Parallel Mechanism

This paper systematically summarized the technical state of art and research results on the motion error of a linear guideway, corrected some misconceptions, and further clarified the relationship between the straightness error of the guide rail itself and the motion error of the linear stage. Moreover, a new method based on parallel mechanism is provided to study the motion errors of the linear guide pair. The basic idea is to abstract the structural relationship between the stage and the guide rail into a 4-bar parallel mechanism. Thus, the stage can be considered as a moving platform in the parallel mechanism. Its motion error analysis is also transferred to moving platform position analysis in the parallel mechanism. The straightness motion error and angular motion error of the stage can be analyzed simultaneously by using the theory of parallel mechanism. Some experiments were conducted on the linear guideway of a self-developed parallel coordinate measuring machine. The experimental data and analysis verify the feasibility and correctness of this method.

159 Laparoscopic insemination method in sheep allows the use of an animal protein-free and inexpensive freezing medium

Animal-derived products are widely used in sperm cryopreservation for their cryoprotective properties. These components, however, must be replaced because of sanitary risks. STEMALPHA.CRYO3 (Ref. 5617, Stem Alpha), called CRYO3, is a chemically defined preservation medium currently used for freezing human tissue and adult stem cells. The aim of this study was to evaluate the effects of a CRYO3-based medium and of two cooling rates on invitro parameters and invivo fertility of ram sperm. Six rams (Blanche du Massif Central) were subjected to sperm collection four times using an artificial vagina. Sperm were split and frozen in three media: an egg yolk and milk-based medium (positive control), a CRYO3-based medium (tested medium), and a medium without additives (negative control). The two cooling rates were related to the distance between the straws and the surface of liquid nitrogen during the freezing process (5 and 20cm). Sperm membrane integrity (propidium iodide/SYBR-14), acrosome integrity (fluorescein isothiocyanate-peanut agglutinin/propidium iodide; FITC-PNA/PI), and mitochondrial membrane potential (JC-1) were assessed using flow cytometry, whereas functional membrane integrity was assessed using a hypo-osmotic swelling test and motion characteristics were evaluated using computer-assisted sperm analysis. Pregnancy rate, parturition rate, and prolificacy were evaluated after performing laparoscopic inseminations (n=75 ewes). Moreover, we characterised the freezing media thermodynamically using a differential scanning calorimeter. Statistical analyses were performed using R software. Invitro parameters were assessed using a mixed model including the time and the medium as fixed effects and the ram as a random effect. Pregnancy and parturition rates, following a binomial distribution, and prolificacy, assumed to follow a Poisson distribution, were analysed using generalised linear models, including the medium as a fixed effect and the ram as a random effect. Differences with P<0.05 were considered statistically significant. The cooling rates had no significant effect except on the wobble motion parameter. The positive control medium showed significantly higher results than the CRYO3-based medium and the negative control medium for all invitro parameters except for straightness motion parameter. Conversely, field trials showed no significant difference between the media for pregnancy rate (71, 64, and 74%), parturition rate (68, 61, and 74%) and prolificacy (2.0, 2.1, and 1.7), for the positive control, CRYO3-based medium, and the negative control, respectively. This study showed that the product, CRYO3, cannot replace egg yolk and milk in freezing extenders. Moreover, we showed that laparoscopic inseminations allowed a 74% parturition rate due to an easy and inexpensive medium comprising only a Tris buffer and glycerol. Although it could not be used on a large scale, this medium remains an option for international transport or long-term storage of genetic diversity.

Implementation and verification of a four-probe motion error measurement system for a large-scale roll lathe used in hybrid manufacturing

In this paper, a four-probe measurement system is implemented and verified for the carriage slide motion error measurement of a large-scale roll lathe used in hybrid manufacturing where a laser machining probe and a diamond cutting tool are placed on two sides of a roll workpiece for manufacturing. The motion error of the carriage slide of the roll lathe is composed of two straightness motion error components and two parallelism motion error components in the vertical and horizontal planes. Four displacement measurement probes, which are mounted on the carriage slide with respect to four opposing sides of the roll workpiece, are employed for the measurement. Firstly, based on the reversal technique, the four probes are moved by the carriage slide to scan the roll workpiece before and after a 180-degree rotation of the roll workpiece. Taking into consideration the fact that the machining accuracy of the lathe is influenced by not only the carriage slide motion error but also the gravity deformation of the large-scale roll workpiece due to its heavy weight, the vertical motion error is thus characterized relating to the deformed axis of the roll workpiece. The horizontal straightness motion error can also be synchronously obtained based on the reversal technique. In addition, based on an error separation algorithm, the vertical and horizontal parallelism motion error components are identified by scanning the rotating roll workpiece at the start and the end positions of the carriage slide, respectively. The feasibility and reliability of the proposed motion error measurement system are demonstrated by the experimental results and the measurement uncertainty analysis.

A macro–micro compensation method for straightness motion error and positioning error of an improved linear stage

This research developed a linear stage with improved structures for reducing the error sources and proposed a macro–micro compensation method for both the straightness motion error and positioning error. One improved structure saw flexible steel sheet joints used instead of a rigid plate between the slide and nut to reduce radial error caused by the ball screw nut; the other saw a fine adjustment mechanism used for adjusting the installation angle of the adjustable guideway to reduce parallelism error. A high-precision two-axis (X and Y) micro-stage driven by piezoelectric (PZT) actuator was installed on the improved linear stage (macro-stage), and then compensations for straightness motion error and positioning error were achieved by utilizing the compensation motions of the XY-micro-stage after the coarse motion of the macro-stage. Experiments on the improved linear stage were conducted to verify the effectiveness of the proposed methods. The results have shown that the straightness motion error of the slide was compensated from 1.61 μm/100 mm to 0.55 μm/100 mm, and the forward mean and reverse mean of the positioning error were respectively compensated from 3.05 μm/100 mm and 3.23 μm/100 mm to 0.69 μm/100 mm and 0.79 μm/100 mm.

Online Measurement Experiment and Data Analysis of the Slideway Straightness Motion Error for CMM

The paper introduces the principle of the sequential two points (STP) method, using the error separation technique to isolate slideway straightness error and workpiece straightness error, by means of measurement and data analysis to study the slideway straightness error. Using least square method for fitting to improve the accuracy of three coordinate measuring machine. Last to assess and maintain the accuracy of the measurement machine.

A novel Fourier-Eight-Sensor (F8S) method for separating straightness, yawing and rolling motion errors of a linear slide

A novel method called the Fourier-Eight-Sensor (F8S) method is proposed for the separation of the straightness, yawing and rolling motion errors as well as the profiles of a linear slide. Eight distance sensors are positioned on a vertical stage in two lines parallel to the target profiles with five sensors in the lower row and the other three in the upper row. The outputs of the sensors are fused together at different times to eliminate the dependence of motion errors. The method adopts a two-stage approach. First, the profile faced by the lower row sensors is represented by Fourier series the coefficients of which are obtained by matrix inversion. Then, another Fourier series is used to represent the difference between the two target profiles. By fusing the outputs of the three sensors in the upper row and their corresponding counterparts in the lower row, the coefficients of the Fourier series are determined by the Fourier series based error separation technique. In this way, different error components can be successfully separated from the sensor outputs. The effectiveness of the method is validated by simulation and experiment.

A Novel Method for On-Machine Determination of Slide Motion Errors Considering Thermal Effects

This paper proposes a novel method to on-machine determine the three error components of a precision linear slide: the straightness motion, the yaw and the roll under the effect of thermal distortion caused by friction and drive. The Integrated Sensing System (ISS) is then introduced for implementing this novel method on an illustrative model of a linear slide. The error separation algorithm used in the system is based on the Fourier Eight Sensor (F8S) method. The theory and procedures are presented, and computer results are analyzed. The effectiveness of the novel method is validated through computer simulations.

Profile Estimation of Linear Slide in the Presence of Straightness, Yawing and Rolling Motion Errors

This paper presents a novel measurement system for the on-machine estimation of the profiles of a linear slide in the presence of three motion errors, i.e. straightness, yawing and rolling. The system consists of eight displacement sensors, a mounting stage and a data acquisition system. The Fourier Eight Sensor (F8S) method is employed for the error separation with software programs written in MATLAB codes. A prototype is designed, built and fitted to an axis of the precision slide. Experiments are performed to test the repeatability of the profile results under three different slide speeds. Results confirm that the proposed measurement system is capable of determining the profiles with good repeatability in the presence of straightness, yaw and roll errors of the slide.

Three-face step-diagonal measurement method for the estimation of volumetric positioning errors in a 3D workspace

In this paper, it is demonstrated that volumetric positioning errors can be calculated by measuring the displacements of three face step-diagonals and three additional linear positions. The three-face step-diagonal tests are used in combination with three directly measured linear errors to estimate nine errors in a three-dimensional workspace, including six straightness motion errors and three perpendicular errors. These errors in the workspace were also directly measured to evaluate the estimated errors. The maximum difference between estimated and measured errors was 0.45μm for the straightness errors, 2.8μrad for the perpendicular errors. Moreover, in practice, the three-face step-diagonal method is easier and faster than direct measurement along each axis and more convenient than the conventional step-diagonal technique. Hence, this method is suitable for industrial applications.

Multi-probe scanning system comprising three laser interferometers and one autocollimator for measuring flat bar mirror profile with nanometer accuracy

a b s t r a c t This paper describes a multi-probe scanning system comprising three laser interferometers and one autocollimator to measure a flat bar mirror profile with nanometer accuracy. The laser interferometers probe the surface of the flat bar mirror that is fixed on top of a scanning stage, while the autocollimator simultaneously measures the yaw error of the scanning stage. The flat bar mirror profile and horizon- tal straightness motion error are reconstructed by an application of simultaneous linear equations and least-squares method. Measurement uncertainties of the flat bar mirror profile were numerically eval- uated for different installation distances between the laser interferometers. The average measurement uncertainty was found to be only 10 nm with installation distances of 10 and 21 mm between the first and second, and first and third interferometers, respectively. To validate the simulation results, a prototype system was built using an X-Y linear stage driven by a stepper motor with steps of 1 mm along the X direction. Experiments were conducted with fixed interferometers distances of 10 and 21 mm, as in the simulation, on a flat bar mirror with a profile known to an accuracy of � = 632.8 nm. The average value of two standard deviations (95%) of the profile calculated over ten experiments was approximately 10 nm. Other results from the experiment showed that the system can also measure the yaw and horizontal straightness motion errors successfully at a high horizontal resolution. Comparing with the results mea- sured by ZYGO's interferometer, our measured data excluding some edge points showed agreement to within approximately 10 nm. Therefore, we concluded that our measurement profile has an accuracy in the nanometer range.

Development of high-precision micro-coordinate measuring machine: Multi-probe measurement system for measuring yaw and straightness motion error of XY linear stage

Today, with the development of microsystem technologies, demands for three-dimensional (3D) metrologies for microsystem components have increased. High-accuracy micro-coordinate measuring machines (micro-CMMs) have been developed to satisfy these demands. A high-precision micro-CMM (M-CMM) is currently under development at the National Metrology Institute of Japan in the National Institute of Advanced Industrial Science and Technology (AIST), in collaboration with the University of Tokyo. The moving volume of the M-CMM is 160 mm × 160 mm × 100 mm (XYZ), and our aim is to achieve 50-nm measurement uncertainty with a measuring volume of 30 mm × 30 mm × 10 mm (XYZ). The M-CMM configuration comprises three main parts: a cross XY-axis, a separate Z-axis, and a changeable probe unit. We have designed a multi-probe measurement system to evaluate the motion accuracy of each stage of the M-CMM. In the measurement system, one autocollimator measures the yaw error of the moving stage, while two laser interferometers simultaneously probe the surface of a reference bar mirror that is fixed on top of an XY linear stage. The straightness motion error and the reference bar mirror profile are reconstructed by the application of simultaneous linear equations and least-squares methods. In this paper, we have discussed the simulation results of the uncertainty value of the multi-probe measurement method using different intervals and standard deviations of the laser interferometers. We also conducted preexperiments of the multi-probe measurement method for evaluating the motion errors of the XY linear stage based on a stepper motor system. The results from the pre-experiment verify that the multi-probe measurement method performs the yaw and straightness motion error measurement extremely well. Comparisons with the simulation results demonstrate that the multi-probe measurement method can

An experimental five-sensor system for measuring straightness and yawing motion errors of a linear slide

In this study, a measurement system consisting of five distance sensors is designed and built to on-machine determine the straightness and yawing motion errors of a linear slide. The procedure to implement the proposed error separation method [1] is first discussed. The method can separate the yawing motion error from the straightness motion without knowing the slide profile beforehand. The experimental set-up and the testing procedure are then described. To verify the capability of this measurement system, a series of computer simulation and measurement experiments are undertaken. Comparison of the results with those obtained by a laser interferometer is also made to evaluate the system performance. Two error sources, i.e. sensor gain error and sensor placement error, which cause measurement uncertainty, are also studied by computer simulations. Testing results confirm that the measurement system can be used to determine the straightness motion with accuracy down to 1 µm. Good reproducibility of the profile results is also obtained.

A New Method for Measuring Straightness and Yawing Motion Errors of a Linear Slide

In this paper, an on-machine Fourier five-sensor (F5S) measurement method is developed using Fourier series and sensor integration techniques to determine the straightness and yawing motion errors of a linear slide. The profile of the slide is also determined in this error separation technique. The method is an extension of the previous Fourier three-sensor (F3S) method (Fung, E. H. K., and Yang, S. M., 2000, “An Error Separation Technique for Measuring Straightness Motion Error of a Linear Slide,” Meas. Sci. Technol., 11, pp. 1515–1521; Yang, S. M., Fung, E. H. K., and Chiu, W. M., 2002, “Uncertainty Analysis of On-Machine Motion and Profile Measurement With Sensor Reading Errors,” Meas. Sci. Technol., 13, pp. 1937–1945) by including the effects of yawing error in the straightness motion error and profile measurements. The principles and operation of the F5S measurement method are described. The uncertainty analysis of the method in the presence of a sensor reading error is studied both in the frequency domain and the spatial domain. The spatial domain parameter is first optimized to yield the 12 possible sensor configurations and the final configuration is chosen based on the frequency domain parameter values. The method is evaluated by computer simulation where the simulated sensor outputs are derived from the predefined profile, straightness, and yawing motion errors. By comparing the calculated results with the input data, the F5S method is found to be superior to the F3S method as far as accuracy is concerned. The results reported in this simulation study not only confirm the feasibility of the F5S method but also encourage the author to perform an experimental study in the near future.

Roundness improvement in taper machining based on two-dimensional active error compensation

In this study, an on-line forecasting compensatory control (FCC) strategy is successfully employed to improve the workpiece accuracy in taper machining by compensating the relative two-dimensional motion errors between the workpiece and the cutting tool. The indirect measurement set-up is developed to determine the motion errors, in both radial and longitudinal directions, of the spindle which positions the workpiece via a master taper. Also, the straightness motion errors of the x-y slide are determined to give the actual tool positions. The reference datum in these measurements, i.e. the master form error and the slide profile, can be determined under on-machine conditions and highly accurate precalibrated references are not required. Based on the autoregressive moving average (ARMA) technique, the two-dimensional motion errors are modelled and their future values forecasted and compensated by means of a piezoelectric actuator. The adequate model order and parameters are found by performing off-line simulations. The effectiveness of the FCC strategy is also evaluated by comparing the roundness results with and without compensation. Experimental cutting with FCC reveals that a maximum improvement of 68 per cent and an average improvement of 41 per cent can be achieved for workpiece roundness in this taper machining process.

Roundness improvement in taper machining based on two-dimensional active error compensation

In this study, an on-line forecasting compensatory control (FCC) strategy is successfully employed to improve the workpiece accuracy in taper machining by compensating the relative two-dimensional motion errors between the workpiece and the cutting tool. The indirect measurement set-up is developed to determine the motion errors, in both radial and longitudinal directions, of the spindle which positions the workpiece via a master taper. Also, the straightness motion errors of the x-y slide are determined to give the actual tool positions. The reference datum in these measurements, i.e. the master form error and the slide profile, can be determined under on-machine conditions and highly accurate precalibrated references are not required. Based on the autoregressive moving average (ARMA) technique, the two-dimensional motion errors are modelled and their future values forecasted and compensated by means of a piezoelectric actuator. The adequate model order and parameters are found by performing off-line simulations. The effectiveness of the FCC strategy is also evaluated by comparing the roundness results with and without compensation. Experimental cutting with FCC reveals that a maximum improvement of 68 per cent and an average improvement of 41 per cent can be achieved for workpiece roundness in this taper machining process.

An approach to on-machine motion error measurement of a linear slide

A new system is proposed to measure the straightness motion error of a precision linear slide for the purpose of active error compensation (AEC). In the traditional method, where the slide profile is assumed constant, its motion error can be obtained simply by subtracting the profile data from the output of a displacement sensor. However, under on-machine conditions, such pre-calibrated profiles or references are not reliable, due to deviations from the calibration conditions. To overcome this difficulty, information on multiple displacement sensors is employed to construct an ideal software datum that can be used on-line in AEC. Such a software datum can act as an ideal reference for separating the profile from the motion errors. The characteristics of the proposed method are: (1) the profile is determined under on-machine conditions requiring no pre-calibrations; (2) a novel approach to represent the test section of the profile by one cycle of a periodic function is facilitated by specially arranging three sensors to form a stationary stage. Computer simulations are performed to confirm the feasibility of the method. A measurement system consisting of three non-contact capacitive sensors is built and evaluated experimentally on a laboratory lathe and good repeatability of profile results is obtained.

An error separation technique for measuring straightness motion error ofa linear slide

A novel measurement system for on-machine determination of thestraightness motion error and profile of a precision linear slide for activeerror compensation (AEC) purposes has successfully been developed. Thecharacteristics of the proposed measurement method are: (i) the profile isdetermined under on-machine conditions requiring no pre-calibration; and(ii) a novel approach involving representation of the test section of theprofile by one cycle of a periodic function is facilitated by speciallyarranging three sensors to form a stationary stage. In this paper, theprinciples and operation of the measurement method are presented. The approachof defining a periodic function to deal with the problem of non-periodicity ofa profile is then described. A preliminary analysis of the sensor measurementerrors is also given. Finally, the measurement system consisting of threenon-contact capacitive sensors is built and evaluated experimentally on alaboratory lathe and good reproducibility of profile results is obtained.