Axial Error Research Articles

Design of 3D Magnetic Tactile Sensors with High Sensing Accuracy Guided by the Theoretical Model

The past decade has witnessed a surging interest in the study of magnetic tactile sensors that can detect subtle changes in both normal and shear forces. However, due to the lack of guidance by appropriate theoretical models, the development of previous magnetic tactile sensors relies either on a trial‐and‐error manner or tedious point‐by‐point experimental calibrations, which are costly and time‐inefficient. Here, a theoretical model integrating magnetics, artificial neural networks, and nonlinear solid mechanics is proposed for the first time to guide the design of 3D magnetic tactile sensors. Then, a button‐shaped magnetic tactile sensor prototype that can detect subtle triaxial force changes is fabricated, which relates the nonlinear magnetic flux density to the external force, without burdensome calibration procedures. The sensor can achieve an axial measurement error of less than 1% and an in‐plane error of less than 3.7% with excellent durability. This study provides a comprehensive understanding of magnetic tactile sensors and sheds light on their applications in soft robotics, intelligent manipulation, and human–robot interaction (HRI).

Influence of lateral dynamic error on the trajectory error in machine tools

In machine tools, the trajectory error of the tool center point (TCP) is caused due to the dynamic positioning error of feed drive systems according to the relationship in spatial structure and motion. The dynamic positioning error of the feed drive system includes axial dynamic error and lateral dynamic error. To analyze the influence of the lateral dynamic error on the trajectory error of the TCP of multi-axis machine tools, in this study, circular and butterfly trajectories were designed as the set trajectories of a machine tool with three linear axes. In addition, the tracking error models were constructed both considering the lateral dynamic error and without considering the lateral dynamic error, and the difference between the two models was quantified. The Sobol method was then used to analyze the sensitivity of the lateral dynamic error of the feed drive system to the tracking error of the TCP. Finally, experiments were performed on a three-axis machine tool. The results show the maximum lateral dynamic error in the direction perpendicular to the motion direction is 0.026 mm. The lateral dynamic error detrimentally affects the tracking error and contour error of the TCP in multi-axis machine tools.

Meshing performance investigations on a novel end-face roller enveloping cylindrical worm drive with non-backlash

Due to the characteristic of high efficiency and accuracy, roller enveloping hourglass worm drive is widely applied in the robot joints and CNC machine tools, but it's sensitive to the assembly errors. A novel end-face roller enveloping cylindrical worm drive with non-backlash and low error sensitivity is proposed, and an analysis method of corrected angle is presented to improve the analysis accuracy of transmission error. Based on meshing theory, the mathematical model of roller enveloping cylindrical worm drive and it with assembly errors are established, the effects of meshing performance with different design parameters are studied. The error sensitivity is analyzed, and the solution process for the corrected rotation angle is presented. The simulated transmission errors are presented to verify the feasibility of the corrected angle analysis method. Results show that this novel worm drive remains high transmission accuracy with center distance errors, but the worm axial errors and intersection angle errors have great influence on the transmission error.

Simple Technique for Stabilizing Toric Intraocular Lens during Removal of Ophthalmic Viscosurgical Device

Introduction: The aim of this study was to describe a simple technique for the implantation of toric intraocular lenses (IOLs) with increased stability during ophthalmic viscosurgical device (OVD) removal. Methods: The technique was performed on 20 eyes with 20 patients (mean age: 77.9 ± 9.21 years). The patients had cataract surgery with implantation of a single-piece, acrylic IOL (AcrySof Toric IOL, SN6A; Alcon Laboratories, Inc.). The intraoperative IOL rotation during OVD removal, rotational error of toric IOL axis at 30 min and 24 h after surgery, and mean preoperative and postoperative IOP were evaluated. Images were captured before and after removal of OVD from surgical video, and used to evaluate intraoperative IOL rotation. Results: The mean amount of IOL rotation during OVD removal with the current technique was 0.88 ± 0.93°, which was less than the 10.25 ± 5.50° previously reported for the conventional technique. The rotational error of toric IOL axis at 30 min and 24 h were 3.90 ± 3.71 and 3.05 ± 3.22°, respectively. The mean preoperative IOP and postoperative IOP were 13.84 ± 2.39 and 14.15 ± 4.68 mm Hg, respectively. Conclusions: With the current technique, the toric IOL is stable during OVD removal and repositioning of the IOL during surgery is less likely to be required.

Novel kinematic model of articulated arm coordinate measuring machine with angular position measurement errors of rotary axes

The measurement accuracy of an articulated arm coordinate measuring machine (AACMM) is determined by its kinematic model to estimate the end effector position from angular positions of rotary axes. In conventional studies, the Denavit–Hartenberg (DH) model, containing position and orientation errors of the rotary axis average lines as error sources, has been widely employed. This study first proposes a novel kinematic model including angular position measurement errors of rotary axes. To identify the proposed model, a new Single Point Articulation Test (SPAT) setup is presented with the R-Test to measure the stylus sphere's three-dimensional displacement. The prediction accuracy of the proposed model is experimentally evaluated.

Nonlinear dynamics of rotor of an auto-balancing ball device, considering eccentricity and changes in horizontal axes of rotation

This study is devoted to the dynamics of an auto-balancing device (ABD) when the rotor rotates at critical angular speeds. In this article, a model of an auto-balancing device (ABD) is proposed. The rotor is not only eccentric about the symmetry axis but also has a horizontal axis of rotation. A mathematical model is proposed based on the Lagrange equations; it describes the nonlinear motion of a balancing system (BS) with two running lines with a different number of balls, considering eccentricity, angular error, and changes in the horizontal axis of rotation. The nonlinear dynamics of the rotor motion with two running lines and two balls at a constant rotation speed and in the accelerating mode of the rotor motion is studied by a numerical method, taking into account the change in the horizontal axis of rotation.

Analysis of Coupling Efficiency in Optic Gyroscope Transceiver Module With Elliptical Core Fiber

Improving the coupling efficiency of the optical transceiver module in fiber optic gyroscopes (FOGs) benefits both the working efficiency of the module and the signal-to-noise ratio of the FOG system. In this work, a single-mode fiber (SMF) with an elliptical mode field distribution is proposed as the coupling fiber for the FOG transceiver module. The coupling efficiency of the transceiver module using fibers with different mode field distributions at the endface is analyzed. Two structure schemes of the transceiver module are compared: one focuses the beam directly onto the endface of the fiber, and the other collimates the beam and then converge it. The optimal coupling efficiency can reach above 91.5% when the horizontal and vertical mode field radii of the fiber endface are approximately 4.05 μm and 3.37 μm respectively. The influence of the axial and angular alignment errors of the pigtail on the coupling efficiency is also investigated. The maximum tolerance of the axial alignment reaches approximately ±40.10 μm and ±30.08 μm for the two structure schemes. The maximum tolerance of the angular alignment reaches approximately ±4.4° and ±5.2° in the horizontal direction, and approximately ±3.5° and ±3.6° in the vertical direction, respectively. These tolerances are favorable for practical applications.

Residual error correction for reducing the uncertainty of a sample-tracking robotic 3D measurement system

This paper presents a method for post-correction of disturbing relative motion between a robotic 3D measurement system and a sample under test. The active sample-tracking measurement platform carries a high-precision scanning confocal chromatic sensor acts as an end-effector of a robot, targeted for operation in a vibration-prone environment. The proposed method does not require any additional hardware and enables a point-by-point correction of the sequentially acquired 3D point cloud by the measured residual sample-tracking error. For experimental measurements at the maximum frame rate of 1fps in a workshop-like environment, which induces a resonant 47 Hz relative motion, the axial measurement error and uncertainty is reduced by 20% to 0.19µm and 0.25 µm, respectively.

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.

Evaluation of Macular Ganglion Cell-Inner Plexiform Layer in Children with Deprivational Amblyopia Who Underwent Unilateral Cataract Surgery.

Background and Objectives: The aim of the study is to assess macular ganglion cell and inner plexiform layer (mGCIPL) thickness in deprivational amblyopic eyes (AE), fellow non-amblyopic eyes (FE) and normal eyes (NE) using spectral. domain optical coherence tomography (SD-OCT). Materials and Methods: Twenty two children (64% boys) who underwent surgical removal of unilateral congenital or developmental cataracts and exhibited visual impairment despite postoperative visual rehabilitation were included in the study. Cataract surgery was performed in patients aged 55.82 ± 35.85 months (range 6 to 114 months). The mean age of the study group was 9.73 ± 2.85 years (range 5 to 15 years). The comparison group consisted of 22 healthy age- and gender-matched children. The best corrected visual acuity (BCVA) after surgery was: 0.75 ± 0.27 (range 0.3 to 1.3) in AE, 0.1 ± 0.13 (range 0 to 0.5) in FE and 0.04 ± 0.07 (range 0 to 0.2) in NE. OCT scans were performed in all patients and subsequently corrected for axial length related magnification errors. Results: The average thickness of mGCIPL was 70.6 ± 11.28 μm in AE; 77.50 ± 6.72 μm in FE and 81.73 ± 5.18 μm in NE. We found that mGCIPL was statistically significantly thinner in deprivation AE compared to FE (p = 0.038) and NE (p = 0.0005). The minimum thickness of mGCIPL was respectively: 62.68 ± 13.2 μm, 70.3 ± 7.61 μm, and 74.5 ± 5.47, and also differed between AE and FE (p = 0.023) and AE and NE (p = 0.0004). Also, measurements in the inferior, inferotemporal, and superotemporal sectors showed thinning of mGCIPL in AE compared to NE. Conclusions: This analysis may suggest that deprivational amblyopia caused by unilateral congenital or developmental cataract in children may be associated with mGCIPL thinning.

Digital map and probability compensation model for repeated positioning error of feed axis

The randomness of the repeated positioning error of feed shaft is the main reason for the difficulty to address this error. The previous repeated loading and unloading suppression methods will easily do damages to parts. This paper sets out to investigate the probability distribution of all possible error values while feed shaft is at different positions, and determine the maximum value of probability error from the random errors. With feed axis at a certain position, first of all, we count the probability of each error based on a large number of random errors. We also draw the digital map of the repeated positioning error of this error with the error of positive and negative stroke measurement as the x-axis and y-axis coordinates and the probability of each error value as the z-axis coordinates. Secondly, based on the digital map of each position on the feed axis and combined with the dynamic optimization algorithm, we find the highest point on the map and take the coordinate point of this point as the starting point of each position compensation. Then, we set the error probability threshold to control the possibility of compensation errors and output the size and direction of the final compensation value. Finally, we start the compensation command and detect the compensated error. The error data that fail to meet the requirements will enter the probability statistics again, redraw the digital map and update the map. Through real-time detection and feedback, the digital map is dynamically improved to adapt to the changing environment. This probability compensation model of repeated positioning error can end the suppressing repeated positioning errors brought by repeatedly disassembling parts.

Kinematic analysis of forearm rotation using four-dimensional computed tomography.

This study aimed to quantify forearm kinematics with a focus on the forearm rotation axis. Ten healthy volunteers were included in the study. One three-dimensional computed tomographic scan and two four-dimensional computed tomographic scans were done in all the arms to capture forearm joint motion. After image processing, the rotation axis and the movement of the radius with respect to various axes were quantified. The rotation axis was calculated using finite helical axis analysis and a circle fitting approach. The mean error of the rotation axis found through circle fitting was 0.2 mm (SD 0.1) distally and 0.1 mm (SD 0.1) proximally, indicating an improvement in precision over the finite helical axis approach. The translations of the radius along the ulnar axis and the forearm rotation axis were 2.6 (SD 0.8) and 0.6 mm (SD 0.9), respectively. The rotation of the radius around the radial axis was 7.2°. The techniques presented provide a detailed description of forearm kinematics.

Visual measurement method for three-dimensional shape of underwater bridge piers considering multirefraction correction

Underwater structure inspection faces great challenges because of the poor measuring environment. To conduct health monitoring for underwater bridge piers, this paper describes a method mainly composed of multicamera digital image correlation, a multirefraction correction model and an approach of grayscale mapping. Verification tests were carried out to examine the accuracy of the reconstruction results both in air and water, and the effectiveness of the multirefraction correction model was also proven. An underwater measuring system was built and was successfully applied to measure the round surface of a concrete pier underwater. The axial measurement error of the points reconstructed after multirefraction modification under the cylindrical coordinate system was only 1.58% of the diameter of the bridge pier. Furthermore, the gray information was transferred to the three-dimensional point cloud. This paper may promote the detection efficiency and accuracy of underwater bridge pier health monitoring.

Application of the robot-assisted implantation in deep brain stimulation.

This work aims to assess the accuracy of robotic assistance guided by a videometric tracker in deep brain stimulation (DBS). We retrospectively reviewed a total of 30 DBS electrode implantations, assisted by the Remebot robotic system, with a novel frameless videometric registration workflow. Then we selected 30 PD patients who used stereotactic frame surgery to implant electrodes during the same period. For each electrode, accuracy was assessed using radial and axial error. The average radial error of the robot-assisted electrode implantation was 1.28 ± 0.36 mm, and the average axial error was 1.20 ± 0.40 mm. No deaths or associated hemorrhages, infections or poor incision healing occurred. Robot-assisted implantation guided by a videometric tracker is accurate and safe.

An optical method based auto-collimation for measuring five degrees of freedom error motions of rotary axis.

The paper presents an optical method based on auto-collimation to simultaneously measure five degrees of freedom error motions of the rotary axis. The proposed method consists of the collimated lasers, beam splitters, focusing lens, quadrant photodiode detectors, a high-precision steel ball, and a special mirror fixed to the rotary axis. The mathematical model is established byoptical ray tracing, and the corresponding optical path is also simulated by OpticStudio. Meanwhile, an adjusting mechanism for X-Y micro-displacement, based on the elastic deformation of the material, is designed to adjust the installation eccentricity error of the high-precision steel ball. The calibration results of the proposed system demonstrate that the displacement errors are ±0.25 µm within the measuring range of ±10 µm, and the tilt angle errors are ±0.6 arcsec within the measuring range of ±25 arcsec. Taking a direct drive (DD) motor as the test object, the radial error motions of the rotary axis range from -3.2 to 4.1 µm, the axial error motions range from -4.9 to 4.7 µm, and the tilt error motions around the X and Y axes range from -2.8 to 1.8 arcsec and -2.6 to 2.0 arcsec, respectively.

Radial Error Motion Measurement and Its Uncertainty Estimation of Ultra Precision Axes of Rotation with Nanometer Level Precision.

The radial error is the key performance indicator of ultra-precision axis. In order to measure and evaluate the radial error of ultra-precision axis with nanometer accuracy, a measurement system with an accuracy of nanometer based on capacitive displacement probes and standard spheres is developed. The nonlinearity error of capacitive displacement probes, misalignment error of the probes, eccentric error of standard spheres, error caused by environment temperature change, environment vibration and error separation methods are analyzed and the effects of the above factors are obtained; Multiple measurement examples carried out with the measurement system this paaper constructed indicate the repeatability of the measurement system reaches 10.5 nm and the roundness error of artifact separated is less than 4.03 nm. In order to evaluate the measurement dispersion of the ultra-precision axis radial error, the major uncertainty components and the complete process of the comprehensive evaluation of the measurement uncertainty are proposed. The combined uncertainty of radial error motion measurement of the ultra-precision axis with Donaldson reversal is 31.64 nm (k = 2).

Linear Axial Error Signal Measurement and Processing Method of a Machine Tool for Accuracy Compensation Improvement

Linear Axial Error Signal Measurement and Processing Method of a Machine Tool for Accuracy Compensation Improvement

A vision-based error identification method for separating geometric errors of rotating axes in five-axis platforms

In this paper, a programmable identification method for visually measuring and identifying position-independent and position-dependent geometric errors (PIGEs and PDGEs) of rotary axes in compact five-axis platforms is presented. Firstly, the kinematic model of the five-axis platform is established via screw algebraic theory. Then, considering the measurement data diversity, the orientation errors identification mechanism for PIGEs is proposed. The mechanism optimally integrates the coordinate search and the least-squares method. Additionally, a least-squares sample regression model is developed to identify the positional deviation of the rotation axis. After identifying PIGEs, the PDGE sources are identified based on the right multiplication principle. Furthermore, the error estimation accuracy of the proposed method is investigated. Finally, a five-axis dispensing platform is employed to validate the identification accuracy and evaluate its feasibility.

A novel hardware configuration method of contact R-test based on performance-constrained model

R-test is widely used to measure the rotary axis errors of five-axis machine tools due to its accuracy and convenience. There are some deficiencies in the research on the customized design of contact R-test under certain requirements of measuring range and accuracy. A novel hardware configuration method of contact R-test is proposed in this paper to realize customized configuration of hardware parameters of R-test. Firstly, a theoretical measurement model is established according to the structural characteristics of the contact R-test and is used as the evaluation model for measuring accuracy. Secondly, the influence of hardware parameters on the performance indexes is analyzed and the corresponding performance-constrained model is established. Thirdly, the configuration method of hardware parameters based on constraint models is proposed using the exhaustive search method and variable parameter method respectively. Finally, a prototype based on the configuration method is developed and calibrated on the Coordinate Measuring Machine (CMM), then the measuring performance evaluation and on-machine error measuring experiment are performed. The results show that the configuration method satisfies certain measuring requirements without range and precision waste. The proposed methods can guide the customized design of contact R-test.

One-step measurement method of five-axis machine tools using a laser tracer

To improve the motion accuracy of five-axis machine tools, it is important to develop a simple methodology to calibrate all geometric errors. This paper proposes a one-step measurement method to calibrate the five-axis machine tool using a laser tracer. First, a simplified geometric error definition of the five-axis machine tool is presented, which is sufficient and necessary to determine the tool error relative to the workpiece. Subsequently, a one-step measurement method using a laser tracer is proposed, and joint movements of five motion axes are adopted to simultaneously identify all geometric errors. Besides, a measurement path generating method is presented to save the trouble of manually planning the complex measurement path. Compared with the traditional two-step measurement method, the proposed method only needs four laser tracer positions and two reflector offsets, simplifying the measurement procedure and enhancing the measurement accuracy of geometric errors of rotary axes.