Μm Precision Research Articles

Dimensional accuracy of extrusion- and photopolymerization-based 3D printers: In vitro study comparing printed casts

Statement of problemReliable studies comparing the accuracy of complete-arch casts from 3D printers are scarce. PurposeThe purpose of this in vitro study was to investigate the accuracy of casts printed by using various extrusion- and photopolymerization-based printers. Material and methodsA master file was sent to 5 printer manufacturers and distributors to print 37 identical casts. This file consisted of a standardized data set of a maxillary cast in standard tessellation language (STL) format comprising 5 reference points for the measurement of 3 distances that served as reference for all measurements: intermolar width (IMW), intercanine width (ICW), and dental arch length (AL). The digital measurement of the master file obtained by using a surveying software program (Convince Premium 2012) was used as the control. Two extrusion-based (M2 and Ultimaker 2+) and 3 photopolymerization-based printers (Form 2, Asiga MAX UV, and myrev140) were compared. The casts were measured by using a multisensory coordinate measuring machine (O-Inspect 422). The values were then compared with those of the master file. The Mann-Whitney U test and Levene tests were used to determine significant differences in the trueness and precision (accuracy) of the measured distances. ResultsThe deviations from the master file at all 3 distances for the included printers ranged between 12 μm and 240 μm (trueness), with an interquartile range (IQR) between 17 μm and 388 μm (precision). Asiga MAX UV displayed the highest accuracy, considering all the distances, and Ultimaker 2+ demonstrated comparable accuracy for shorter distances (IMW and ICW). Although myrev140 operated with high precision, it displayed high deviations from the master file. Similarly, although Form 2 exhibited high IQR, it did not deviate significantly from the master file in the longest range (AL). M2 performed consistently. ConclusionsBoth extrusion-based and photopolymerization-based printers were accurate. In general, inexpensive printers were no less accurate than more expensive ones.

Pulsed magnetic field device for laser plasma experiments at Shenguang-II laser facility.

A pulsed intense magnetic field device was developed for the Shanghai Shenguang-II (SG-II) laser facility. The device using a double-turn coil with 12 mm diameter is capable of producing a peak current of 42 kA with 280 ns rising edge and 200 ns flat top width. A peak magnetic field of 8.8 T is achieved at the center of the coil. A two-section transmission line composed by a flexible section and a rigid section is designed to meet the target chamber environment of SG-II laser facility. The flexible section realizes the soft-connection between the capacitor bank and the target chamber, which facilitates the installation of the magnetic field device and the adjustment of the coil. The rigid section is as small as possible so that it can be inserted into the target chamber from any smallest flange, realizing elastic magnetic field configuration. The magnetic coil inside the chamber can be adjusted finely through a mechanical component on the rigid transmission line outside the target chamber. The adjustment range is up to 5 cm in both radial and axial directions with ∼50 µm precision. The device has been successfully operated on SG-II laser facility.

Dual-color near-field imaging by means of thin-film plasmonic waveguide with precise beam control of multiple wavelengths

We describe an improved optical beam control technique combined with a waveguide probe for imaging optical near-field using multiple wavelengths. The beam control technique varies the incident angle of pseudocollimated beams whose spot diameter is ∼10 μm such that it is equal to an arbitrary angle with ∼0.03° precision and the beam position to ∼0.1 μm precision. This helps resonantly excite surface plasmons using visible 660 nm and near-infrared 850 nm on an ∼10 μm width three-dimensional microwaveguide. We demonstrate the operation of this system by imaging the optical near-field and capturing the interference of surface plasmons in a gold microstructure. This system achieved dual-color imaging of the optical near-field of different modulation frequencies with submicrometer lateral spatial resolution.

Compact pulsed intense magnetic field generator for Shenguang-II upgrade laser facility

A compact pulsed intense magnetic field generator is presented for magnetized laser plasma experiments at the Shenguang-II upgrade laser facility (Shanghai). The pulsed magnetic field device can generate a 45 kA peak current with 480 ns rising time at a discharge voltage of 40 kV, time jitter is about 100 ns. The peak magnetic field reaches 9 T using a double-twisted coil of 12 mm diameter. A specially designed tunable transmission line was developed to realize the flexible connection between the capacitor bank and the magnetic field coil. The setup is compatible with the particular target chamber of the laser facility. Thus the coil component can be adjusted separately by the three-dimensional motorized translation stage placed in the target chamber, with 10 cm (transverse) and 1 cm (longitudinal) adjustable scales and 6 μm precision. A high-voltage electric-trigger spark-gap gas switch was used to reduce the operation complexity and the occupied area of the generator. Grounding and shielding structure ensure fine electromagnetic compatibility with the target chamber. The device has been successfully operated in magnetized laser plasma experiments performed on the laser facility.

The DESI Fiber View Camera System

The Dark Energy Spectroscopic Instrument (DESI) is a 5000 fiber multi-object spectrometer now being installed at the prime focus of the 4 m Mayall telescope at Kitt Peak. Using DESI to measure ∼35 million galaxy redshifts and using the Baryon Acoustic Oscillation (BAO) technique to measure distances, the results will probe the nature of the recently discovered mysterious component of our universe called dark energy. Computer controlled robotic positioners move the 120 μm diameter fibers to positions of galaxies whose location on the sky have been obtained in a previous target selection imaging survey. To achieve good throughput the fibers should be centered on the target position to within 3 μm. The robotic positioners however are only capable of a 50 μm precision on their first move. To achieve the desired precision, the Fiber View Camera (FVC) system has been implemented. The FVC, located near the hole in the primary mirror of the Mayall telescope, has been designed to take an exposure of the focal plane, located at the prime focus some 12 m above the FVC, after the robotic positioners have completed their first move. The FVC is intended to measure the fiber locations with a precision of 3 μm and issue a set of fiber coordinate corrections for the second move correcting the fiber positions by the robotic positioners. Tests show that after two iterations better than 99% of the fibers will be in their intended location to within the desired precision. This paper describes the design of the FVC system, the R&D program preceding the final design, and the tests that have been carried out to demonstrate that the FVC can achieve the required precision.

Fundamentals of the Local Anodic Oxidation of Graphene for Scalable Applications

Using a novel instrument previously reported by our group [1], we have been able to perform Local Anodic Oxidation (LAO) over monolayer graphene to create unprecedented large areas (larger than mm2) of single layer Graphene Oxide (GO) with any shape and in a very short time (a few minutes). Our instrument is equipped with three electromechanical steppers with 0.05 µm accuracy and 1 µm precision, and each stepper with a linear piezoactuator. It operates at speeds up to 15 mm/s, and includes a steel/Ni spring probe of typically 6 µm radius to work in tapping or contact mode. The equipment is provided with a humidity control system that allows maintaining a stable Relative Humidity (RH) environment, together with a system of supply and electrical monitoring. Thus, electrical signal coming from the tip-sample interaction is continuously monitored (by means of a high speed oscilloscope). When the tip approaches to graphene on a wet atmosphere (RH higher than 40%), it is commonly accepted that a water bridge is created between them. When a negative bias is applied to the tip respect to the grounded graphene (in our case we operate between 20V - 40 V), the LAO phenomena takes place [2] (Fig. 1a). The process firstly consists on electrical water ionization in H+ and OH- ions. Hydroxyl anions are then conducted to the graphene surface, which is thus oxidized. Within a specific RH range, the oxide patterns created show a good reproducibility and regular shape (Fig. 1b). Controlling the movement of the tip, we can draw the desired patterns over the graphene or any other 2D-substrate (Fig. 1c). We have extensively studied and optimized the influence of the experimental variables affecting the process, like applied bias, contact time or relative humidity. This LAO procedure is so a very powerful tool for the fabrication of electrical devices. Also, the possibility of chemical functionalization of GO allow us to design a large variety of utilities like (bio)chemical sensors, supported catalysts, etc. In addition, we have been able to record the electrochemical trace generated during the oxidation reaction of graphene. To our knowledge, it is the first time these records have been reported. Moreover, based on these data, we have formulated a theoretical model based just on classical first principles that predicts the behavior of the LAO process over graphene. This model shows a very accurate fit for the dependence of the oxide pattern expansion with the applied voltage (Fig. 2a), with the contact time (Fig. 2b), and also for the evolution of the recorded transient electric current (Fig. 2c). This model reveals very relevant information about the processes governing LAO. First, at the beginning (< 20 ms), most of the total current I(t) passing through the tip-substrate junction does not come from the electrochemical reaction but from residual conductance of the non-oxidized graphene. We call this component drift current, IT(t). Second, for longer times (>200 ms), the total current becomes dominated just by the electrochemical reaction, and the drift component almost vanishes. We call this component electrochemical current, IEC(t) (Fig. 2c). Third, the process is mainly driven by the electric field increase at the edge of the pattern. And fourth, the GO generated has a very high oxidation degree. This work opens new promising fields for development of extensive fabrication methods, technical applications and the study of anodic oxidation processes of conducting and any 2d material at large scales.

A nested circle-fitting method for micro-hole centering and its application in electrochemical deburring

To solve these problems (i.e. the accuracy rate and stability of the centering) of enabling secondary machining of micro-holes with a size of 0.1 to 1 mm in high-performance metal alloy parts, a non-standard nested circle-fitting least-square method, with a linear constraint passing through the center (least square method with linear constraint [LSLC]), is proposed in this article. The experimental results show that the center of the circle is fitted with a maximum deviation of ±1.5 µm and good fitting precision, compared to other existing approaches. At the same time, the accuracy rate is increased by at least 20%, delivering a result of more than 99%, so the accuracy of the fitting and the stability of the centering are significantly improved. Finally, the new method is applied in actual micro-hole electrochemical deburring study. With the overall goal of ensuring centering, a rough-and-fine deburring process has been explored. On the premise that the hole is not expanded, the burrs have been quickly and completely removed, and machined surface roughness, Ra, has also reduced from 1.2 to 0.52 µm. The experiment has provided concrete validation of the feasibility of the nested circle-fitting method we have proposed.

Immense random colocalization, revealed by automated high content image cytometry, seriously questions FISH as gold standard for detecting EML4-ALK fusion.

EML4-ALK gene fusion (inv2(p21p23)) of non-small cell lung cancer (NSCLC) predisposes to tyrosine kinase inhibitor treatment. One of the gold standard diagnostics is the dual color (DC) break-apart (BA) FISH technique, however, the unusual closeness of the involved genes has been suggested to raise likelihood of random co-localization (RCL) of signals. Although this is suspected to decrease sensitivity (often to as low as 40-70%), the exact level and effect of RCL has not been revealed thus far. Signal distances were analyzed to the 0.1 µm precision in more than 25,000 nuclei, via automated high content-image cytometry. Negative and positive controls were created using conventional DC BA-, and inv2(p21p23) mimicking probe-sets, respectively. Average distance between red and green signals was 9.72 pixels (px) (±5.14px) and 3.28px (±2.44px), in positives and negatives, respectively; overlap in distribution being 41%. Specificity and sensitivity of correctly determining ALK status was 97% and 29%, respectively. When investigating inv2(p21p23) with DC BA FISH, specificity is high, but seven out of ten aberrant nuclei are inevitably falsely classified as negative, due to the extreme level of RCL. Together with genetic heterogeneity and dilution effect of non-tumor cells in NSCLC, this immense analytical false negativity is the primary cause behind the often described low diagnostic sensitivity. These results convincingly suggest that if FISH is to remain a gold standard for detecting the therapy relevant inv(2), either a modified evaluation protocol, or a more reliable probe-design should be considered than the current DC BA one. © 2018 International Society for Advancement of Cytometry.

A device for high-throughput monitoring of degradation in soft tissue samples

This work describes the design and validation of a novel device, the High-Throughput Degradation Monitoring Device (HDD), for monitoring the degradation of 24 soft tissue samples over incubation periods of several days inside a cell culture incubator. The device quantifies sample degradation by monitoring its deformation induced by a static gravity load. Initial instrument design and experimental protocol development focused on quantifying cartilage degeneration. Characterization of measurement errors, caused mainly by thermal transients and by translating the instrument sensor, demonstrated that HDD can quantify sample degradation with <6 μm precision and <10 μm temperature-induced errors. HDD capabilities were evaluated in a pilot study that monitored the degradation of fresh ex vivo human cartilage samples by collagenase solutions over three days. HDD could robustly resolve the effects of collagenase concentration as small as 0.5 mg/ml. Careful sample preparation resulted in measurements that did not suffer from donor-to-donor variation (coefficient of variance <70%). Due to its unique combination of sample throughput, measurement precision, temporal sampling and experimental versality, HDD provides a novel biomechanics-based experimental platform for quantifying the effects of proteins (cytokines, growth factors, enzymes, antibodies) or small molecules on the degradation of soft tissues or tissue engineering constructs. Thereby, HDD can complement established tools and in vitro models in important applications including drug screening and biomaterial development.

THE METHOD OF GEOMETRIC CALIBRATION OF OPTOELECTRONIC SYSTEMS BASED ON ELECTRONIC TEST OBJECT

Designing remote sensing of the Earth devices is requires a lot of attention to evaluation lens distortion level and providing the required accuracy values of geometric calibration of optoelectronic systems at all. Test- objects known as most common tools for optical systems geometric calibration. The purpose of the research was creating an automatically method of distortion correction coefficients calculating with a 3 μm precision in the measurement process. The method of geometric calibration of the internal orientation elements of the optical system based on the electronic test object is proposed. The calculation of the test string brightness image from its multispectral image and filtered signal extrema position determination are presented. Ratio of magnitude of the distortion and interval center is given. Three variants of electronic test-objects with different step and element size are considered. Оptimal size of calibration element was defined as 3×3 pixels due to shape of the subpixels with the aspect ratio of the radiating areas about 1 : 3. It is advisable to use IPS as an electronic test object template. An experimental test and measurement stand functional diagram based on the collimator and optical bench «OSK-2CL» is showed. It was determined that test objects with a grid spacing of 4 and 8 pixels can’t provide tolerable image because of non-collimated emission of active sites and scattering on optical surfaces – the shape of the elements is substantially disrupted. Test-object with a 12 pixels grid spacing was used to distortion level analyzing as most suitable.Ratio of coordinate increment and element number graphs for two photographic lenses (Canon EF-S 17-85 f/4-5.6 IS USM and EF-S 18-55 f/3.5-5.6 IS II) are presented. A calculation of the distortion values in edge zones was held, which were respectively 43 μm and 51.6 μm. The technique and algorithm of software implementation is described. Possible directions of the method development are mentioned.

Simple measuring rod method for the coaxiality of serial holes.

Aiming at the rapid coaxiality measurement of serial hole part with a small diameter, a coaxiality measuring rod for each layer hole with a single LDS (laser displacement sensor) is proposed. This method does not require the rotation angle information of the rod, and the coaxiality of serial holes can be calculated from the measured values of LDSs after randomly rotating the measuring rod several times. With the mathematical model of the coaxiality measuring rod, each factor affecting the accuracy of coaxiality measurement is analyzed by simulation, and the installation accuracy requirements of the measuring rod and LDSs are presented. In the tolerance of a certain installation error of the measuring rod, the relative center of the hole is calculated by setting the over-determined nonlinear equations of the fitting circles of the multi-layer holes. In experiment, coaxiality measurement accuracy is realized by a 16 μm precision LDS, and the validity of the measurement method is verified. The manufacture and measurement requirements of the coaxiality measuring rod are low, by changing the position of LDSs in the measuring rod, the serial holes with different sizes and numbers can be measured. The rapid coaxiality measurement of parts can be easily implemented in industrial sites.

A reproducible method for μm precision alignment of PDMS microchannels with on-chip electrodes using a mask aligner.

This paper describes a reproducible method for μm precision alignment of polydimethylsiloxane (PDMS) microchannels with coplanar electrodes using a conventional mask aligner for lab-on-a-chip applications. It is based on the use of a silicon mold in combination with a PMMA sarcophagus for precise control of the parallelism between the top and bottom surfaces of molded PDMS. The alignment of the fabricated PDMS slab with electrodes patterned on a glass chip is then performed using a conventional mask aligner with a custom-made steel chuck and magnets. This technique allows to bond and align chips with a resolution of less than 2 μm.

Experimental study on surface characteristics and improvement of microelectrode machined by low speed wire electrical discharge turning

Electrical discharge machining (EDM) as the nontraditional machining process has a unique superiority in fabricating microelectrodes due to its non-contact removal mechanism. Therefore, the method of LS-WEDT (low speed wire electrical discharge turning) is firstly proposed to fabricate microelectrodes in this study. More importantly, the multiple cutting strategy is introduced to divide the machining process into rough cut (RC), trim cut (TC) and finishing trim cut (FTC). Experimental results showed that the ridges will appear after RC, the spherical droplets congregation phenomenon can be observed after TC and the surface will be covered with refined grains in nano level after FTC, which disclosed the unique surface characteristics of LS-WEDT. After FTC, the microelectrode of 90μm in diameter and 1000μm in length is successfully and firstly fabricated by LS-WEDT method, moreover, it has good surface quality with Ra of 0.59μm and high dimensional precision with surface profile accuracy of 3.22μm. Additionally, the comparative analysis was made to investigate the LS-WEDTed and LS-WEDMed surface, the discharge craters distributed in LS-WEDTed surface are longer than LS-WEDM. Finally, the surface quality machined by LS-WEDT after FTC is better than LS-WEDM, which is attributed to the point contact and good flushing conditions.

Accuracy evaluation of intraoral optical impressions: A clinical study using a reference appliance

Statement of problemTrueness and precision are used to evaluate the accuracy of intraoral optical impressions. Although the in vivo precision of intraoral optical impressions has been reported, in vivo trueness has not been evaluated because of limitations in the available protocols. PurposeThe purpose of this clinical study was to compare the accuracy (trueness and precision) of optical and conventional impressions by using a novel study design. Material and methodsFive study participants consented and were enrolled. For each participant, optical and conventional (vinylsiloxanether) impressions of a custom-made intraoral Co-Cr alloy reference appliance fitted to the mandibular arch were obtained by 1 operator. Three-dimensional (3D) digital models were created for stone casts obtained from the conventional impression group and for the reference appliances by using a validated high-accuracy reference scanner. For the optical impression group, 3D digital models were obtained directly from the intraoral scans. The total mean trueness of each impression system was calculated by averaging the mean absolute deviations of the impression replicates from their 3D reference model for each participant, followed by averaging the obtained values across all participants. The total mean precision for each impression system was calculated by averaging the mean absolute deviations between all the impression replicas for each participant (10 pairs), followed by averaging the obtained values across all participants. Data were analyzed using repeated measures ANOVA (α=.05), first to assess whether a systematic difference in trueness or precision of replicate impressions could be found among participants and second to assess whether the mean trueness and precision values differed between the 2 impression systems. ResultsStatistically significant differences were found between the 2 impression systems for both mean trueness (P=.010) and mean precision (P=.007). Conventional impressions had higher accuracy with a mean trueness of 17.0 ±6.6 μm and mean precision of 16.9 ±5.8 μm than optical impressions with a mean trueness of 46.2 ±11.4 μm and mean precision of 61.1 ±4.9 μm. ConclusionsComplete arch (first molar-to-first molar) optical impressions were less accurate than conventional impressions but may be adequate for quadrant impressions.

A lightweight feedback-controlled microdrive for chronic neural recordings

Objective. Chronic neural recordings have provided many insights into the relationship between neural activity and behavior. We set out to develop a miniaturized motorized microdrive that allows precise electrode positioning despite possibly unreliable motors. Approach. We designed a feedback-based motor control mechanism. It contains an integrated position readout from an array of magnets and a Hall sensor. Main results. Our extremely lightweight (<1 g) motorized microdrive allows remote positioning of both metal electrodes and glass pipettes along one motorized axis. Target locations can be defined with a range of 6 mm and they can be reached within 1 µm precision. The incorporated headstage electronics are capable of both extracellular and intracellular recordings. We include a simple mechanism for repositioning electrodes in three dimensions and for replacing them during operation. We present neural data from different premotor areas of adult and juvenile zebra finches. Significance. Our findings show that feedback-based microdrive control requires little extra size and weight, suggesting that such control can be incorporated into more complex multi-electrode designs.

지능형 연성 복합재 구동기 제작을 위한 3D 프린팅-캐스팅 복합 공정

Intricate deflection requires many conventional actuators (motors, pistons etc.), which can be financially and spatially wasteful. Novel smart soft composite (SSC) actuators have been suggested, but fabrication complexity restricts their widespread use as general-purpose actuators. In this study, a hybrid manufacturing process comprising 3-D printing and casting was developed for automated fabrication of SSC actuators with 200 µm precision, using a 3-D printer (3DISON, ROKIT), a simple polymer mixer, and a compressor controller. A method to improve precision is suggested, and the design compensates for deposition and backlash errors (maximum, 170 µm). A suitable flow rate and tool path are suggested for the polymer casting process. The equipment and process costs proposed here are lower than those of existing 3D printers for a multi-material deposition system and the technique has 200 µm precision, which is suitable for fabrication of SSC actuators.

Parabolic single-crystal diamond lenses for coherent x-ray imaging

We demonstrate parabolic single-crystal diamond compound refractive lenses designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic shapes with a ≃1 μm precision and surface roughness. A compound refractive lens comprised of six lenses with a radius of curvature R=200 μm at the vertex of the parabola and a geometrical aperture A=900 μm focuses 10 keV x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of ≃20×90 μm2 with a gain factor of ≃50−100.

High-speed and precision control of a piezoelectric positioner with hysteresis, resonance and disturbance compensation

A novel composite control strategy is developed in this paper to compensate hysteresis, resonance and disturbances in a piezo-actuated nanopositioner. The control objective of the piezoelectric positioner is to achieve high tracking performance in terms of accuracy and speed. For this purpose, a Bouc---Wen model based hysteresis compensator is first applied to mitigate the hysteresis nonlinearity without the complex inverse hysteresis calculation. And then, the linear dynamic of the hysteresis compensated system is identified and inverted to account for the resonance. A model-based inversion feed-forward controller is designed to achieve high speed tracking. Afterwards, a high-gain feedback controller is designed based on a notch filter to handle the modeling inaccuracy and all kinds of disturbances. So, the feed-forward controller can be augmented to the feedback controller to realize high speed and precision tracking. The enhancement of tracking performance is demonstrated through several comparative experiments. The performance of 70 Hz bandwidth and 0.281 μm precision can be achieved, which validated the effectiveness of the proposed composite control scheme.

Dendritic Inhibitory Synapses Punch above Their Weight

Müllner etal. (2015) show that single inhibitory synapses placed in the right location on the dendritic tree can exert a powerful impact on backpropagating action potentials in hippocampal pyramidal neurons by controlling local Ca(2+) influx with μm and ms precision.

CellDyM: A room temperature operating cryogenic cell for the dynamic monitoring of snow metamorphism by time‐lapse X‐ray microtomography

AbstractMonitoring the time evolution of snow microstructure in 3‐D is crucial for a better understanding of snow metamorphism. We, therefore, designed a cryogenic cell that precisely controls the experimental conditions of a sample while it is scanned by X‐ray tomography. Based on a thermoelectrical regulation and a vacuum insulation, the cell operates at room temperature. It is, thus, adaptable to diverse scanners, offering advantages in terms of imaging techniques, resolution, and speed. Three‐dimensional time‐lapse series were obtained under equitemperature and temperature gradient conditions at a 7.8 μm precision. The typical features of each metamorphism and the anisotropic faceting behavior between the basal and prismatic planes, known to occur close to −2°C, were observed in less than 30 h. These results are consistent with the temperature fields expected from heat conduction simulations through the cell. They confirm the cell's accuracy and the interest of relatively short periods to study snow metamorphism.