Design of a new fast tool positioning system and systematic study on its positioning stability

The challenge of maintaining good surface quality under high operational frequencies in freeform machining invokes the need for a deterministic error analysis approach and a quantitative understanding on how structural design affects the positioning errors. This paper proposes a novel stiff-support positioning system with a systematic error analysis approach which reveals the contributions of disturbances on the tool positioning errors. The new design reduces the structural complexity and enables the detailed modelling of the closed loop system. Stochastic disturbances are analysed in the frequency domain while the non-stochastic disturbances are simulated in the time domain. The predicted following error spectrum agrees with the measured spectrum across the frequency range and this approach is justified. The real tool positioning error, which is free from sensor noise, is revealed for the first time. The influences of moving mass under various bandwidth settings have been studied both theoretically and experimentally. It is found that a larger moving mass helps combating disturbances except the sensor noises. The influences of cutting force are modelled and experimentally verified in the micro lens array cutting experiments. The origins of the form errors of the lenslet are discussed based on the error analysis model

When is the estimated propensity score better? High-dimensional analysis and bias correction

Anecdotally, using an estimated propensity score is superior to the true propensity score in estimating the average treatment effect based on observational data. However, this claim comes with several qualifications: it holds only if propensity score model is correctly specified and the number of covariates $d$ is small relative to the sample size $n$. We revisit this phenomenon by studying the inverse propensity score weighting (IPW) estimator based on a logistic model with a diverging number of covariates. We first show that the IPW estimator based on the estimated propensity score is consistent and asymptotically normal with smaller variance than the oracle IPW estimator (using the true propensity score) if and only if $n \gtrsim d^2$. We then propose a debiased IPW estimator that achieves the same guarantees in the regime $n \gtrsim d^{3/2}$. Our proofs rely on a novel non-asymptotic decomposition of the IPW error along with careful control of the higher order terms.Comment: Fangzhou Su and Wenlong Mou contributed equally to this wor

A real-time interpolator for parametric curves

Driven by the ever increasing need for the high-speed high-accuracy machining of freeform surfaces, the interpolators for parametric curves become highly desirable, as they can eliminate the feedrate and acceleration fluctuation due to the discontinuity in the first derivatives along the linear tool path. The interpolation for parametric curves is essentially an optimization problem, and it is extremely difficult to get the time-optimal solution. This paper presents a novel real-time interpolator for parametric curves (RTIPC), which provides a near time-optimal solution. It limits the machine dynamics (axial velocities, axial accelerations and jerk) and contour error through feedrate lookahead and acceleration lookahead operations, meanwhile, the feedrate is maintained as high as possible with minimum fluctuation. The lookahead length is dynamically adjusted to minimize the computation load. And the numerical integration error is considered during the lookahead calculation. Two typical parametric curves are selected for both numerical simulation and experimental validation, a cubic phase plate freeform surface is also machined. The numerical simulation is performed using the software (open access information is in the Acknowledgment section) that implements the proposed RTIPC, the results demonstrate the effectiveness of the RTIPC. The real-time performance of the RTIPC is tested on the in-house developed controller, which shows satisfactory efficiency. Finally, machining trials are carried out in comparison with the industrial standard linear interpolator and the state-of-the-art Position-Velocity-Time (PVT) interpolator, the results show the significant advantages of the RTIPC in coding, productivity and motion smoothness

Development of a compact ultra-precision six-axis hybrid micro-machine

High precision miniature and micro products which possess 3D complex structures or free-form surfaces are now widely used in industries. These micro products are usually fabricated by several machining processes in order to apply for various materials such as hard-to-machine steel and ceramic etc. The integration of these machining processes onto one machine becomes necessary since this will help reduce realignment errors and also increase the machining efficiency. In this research, an ultra-precision hybrid micro-machine which is capable of micro milling, micro grinding, micro turning, laser machining and laser assisted micro-machining has been designed and commissioned. Control software for on-machine metrology system (contact probe and dispersed reference interferometry (DRI)) and several plug-in modules including camera and handle system are integrated through a customised human-machine interface (HMI)

Construction of microbial consortia for microbial degradation of complex compounds

Increasingly complex synthetic environmental pollutants are prompting further research into bioremediation, which is one of the most economical and safest means of environmental restoration. From the current research, using microbial consortia to degrade complex compounds is more advantageous compared to using isolated bacteria, as the former is more adaptable and stable within the growth environment and can provide a suitable catalytic environment for each enzyme required by the biodegradation pathway. With the development of synthetic biology and gene-editing tools, artificial microbial consortia systems can be designed to be more efficient, stable, and robust, and they can be used to produce high-value-added products with their strong degradation ability. Furthermore, microbial consortia systems are shown to be promising in the degradation of complex compounds. In this review, the strategies for constructing stable and robust microbial consortia are discussed. The current advances in the degradation of complex compounds by microbial consortia are also classified and detailed, including plastics, petroleum, antibiotics, azo dyes, and some pollutants present in sewage. Thus, this paper aims to support some helps to those who focus on the degradation of complex compounds by microbial consortia

Safety-oriented planning of expressway truck service areas based on driver demand

Funding This study was supported by the National Natural Science Foundation of China (51978522).Peer reviewedPublisher PD

Wo, et al, The effect of high frequency stimulation on intracellular Ca 2+ in sympathetic PC12 cells The effect of high frequency stimulation on intracellular Ca 2+ in sympathetic PC12 cells

Abstract Objective. This study were designed to compare the impact of instant high frequency stimulation (HFS) and 3-day continuous HFS on the intracellular Ca 2+ volume in sympathetic PC12 cells and to define the role of Nifedipine(NIF) in this process. Methods. The cells were randomly divided into two groups, namely instant HFS and 3-day continuous HFS. Using a line scanning technique under a Laser Scanning Microscope (LSM) at 1.2 ms -1.25 ms intervals for 60s, we found that the intracellular Ca 2+ fluorescence intensity changes between conduction of HFS and after termination of HFS. Results. The intracellular Ca 2+ fluorescence intensity rapidly declined instantly after HFS on the sympathetic PC12 cells and the range of declination observed through line scanning was 47.7%. HFS was conducted continuously for 3 days, 3 hours per day. After discontinuing HFS, Ca 2+ fluorescence intensity increased sharply with a 60% inclination. This effect was weakened by Ca 2+ channel inhibitor Nifedipine (NIF). Conclusion. These data indicates that the variation of Ca 2+ volume induced through HFS has a significant effect on sympathetic PC12 cells. On commencing instant HFS, Ca 2+ fluorescence intensity increased significantly and decreased sharply after 3-day continuous HFS was terminated. However, NIF can partially counteract the inhibitory effect of HFS on PC12 cells, instead of complete blockage

In situ measurement of spindle radial and tilt error motions by complementary multi-probe method

This paper presents a complementary multi-probe method for measurement of radial and tilt error motions of a spindle. Neither indexing of artefact nor rotating of spindle housing is required and thus make it suitable for in-situ evaluation of spindle performance effectively. In order to minimise the harmonic suppression problems commonly encountered in the multi-probe measurement approach, three sets of probe angle combinations are selected and the smallest harmonics of the three measurements are extracted to compose the true artefact errors in the harmonic domain. The exact probe angles are identified by probe signals after the sensors are mounted onto the fixture and this alleviate the requirement of high precision fixtures. The evaluation of measurement results shows that this method is effective and the erroneous harmonics are greatly reduced. Using this method, the radial error motions of the precision air bearing spindle are measured at seven axial positions and then the synchronised tilts error motions are calculated. This demonstrated an effective approach for measuring 4 degree of freedom error motions in one setup with three displacement sensor probes

Acceleration feedback control for enhancing dynamic stiffness of fast tool servo system considering the sensor imperfections

Lorentz type fast tool servo devices have found wide applications in freeform machining but they face problems of insufficient stiffness with large depth of cut. Acceleration feedback control is an alternative way to enhance the dynamic stiffness without the need for a large inertia, which is strictly limited in fast tool servo devices. However, the current knowledge gap in the understanding of the influences of limited sensor bandwidth and sensor noises on positioning performance has impeded the application of acceleration feedback control approach in fast tool servo devices. This paper established an analytical model to reveal, for the first time, how much positioning errors are caused by the added sensor noises and how the acceleration feedback technique changes the closed loop stiffness. The measured positioning error spectrum agrees with the modelled one with different acceleration gains. The stiffness model is verified through frequency response tests. It is found that the dynamic stiffness is significantly improved by 5.6 folds within the acceleration sensor bandwidth, while the stiffness deteriorates at frequencies beyond the bandwidth due to the low-pass characteristics in the acceleration loop. The stiffness analysis results are further verified in the intermittent facing cut experiments. The measured surface form errors can be mapped to the low frequency and high frequency vibrations caused by the cutting forces. The analysis model provides a theoretical basis for adopting acceleration feedback technique, paving the way for its practical implementations in ultra-precision applications

Adaptive Assignment for Geometry Aware Local Feature Matching

The detector-free feature matching approaches are currently attracting great attention thanks to their excellent performance. However, these methods still struggle at large-scale and viewpoint variations, due to the geometric inconsistency resulting from the application of the mutual nearest neighbour criterion (\ie, one-to-one assignment) in patch-level matching.Accordingly, we introduce AdaMatcher, which first accomplishes the feature correlation and co-visible area estimation through an elaborate feature interaction module, then performs adaptive assignment on patch-level matching while estimating the scales between images, and finally refines the co-visible matches through scale alignment and sub-pixel regression module.Extensive experiments show that AdaMatcher outperforms solid baselines and achieves state-of-the-art results on many downstream tasks. Additionally, the adaptive assignment and sub-pixel refinement module can be used as a refinement network for other matching methods, such as SuperGlue, to boost their performance further. The code will be publicly available at https://github.com/AbyssGaze/AdaMatcher.Comment: Accepted by CVPR202