A force/stiffness compensation method for precision multi-peg-hole assembly

To realise a high-quality automated and intelligent micro-assembly process, a new method has been propositioned to direct the assembly process. Due to the limitation of visual guidance, a micro-force is used to instruct the contact process: this can not only judge the assembly status but also provide quantitative analysis. These are all realised on the basis of the mapping relationship between assembly force and position, which is established through a combined error back propagation (BP) network and a genetic algorithm (GA). According to the analysis of the mapping relationship and the assembly force, a contact assembly control strategy is designed, which helps achieve high assembly precision and high assembly quality. When two parts make contact in the assembly process, the control system firstly analyses the assembly force information. Once two or three directional force components are of the same order of magnitude, the mutual influence thereof will be decoupled. Then, the direction having the largest force component is chosen and discarded: the relative positions of the matching parts in this direction will be adjusted. Experimental results are included in support of the theoretical work, which demonstrates the assembly precision is less than 2 μm and the minimum to the sub-micron level. The assembly method based on the mapping between assembly force and position is of significance for automated assembly, as it can improve assembly precision and is generally applicable in the area of micro-assembly technology.

To report a rare case of intraocular schwannoma with extrascleral extension in a patient with juvenile idiopathic arthritis and to review the literature for this topic. Case report. A 19-year-old male with a history of juvenile idiopathic arthritis was referred for diagnosis and management of an episcleral mass, initially thought to be focal nodular scleritis. The ocular surface of the right eye revealed an elevated amelanotic episcleral nodule inferonasally, with thin strands of overlying sclera, feeding episcleral vessels, and measuring 11 mm × 11 mm in diameter and 5 mm in thickness. Ophthalmoscopic examination revealed a minimally pigmented ciliochoroidal tumor measuring 13 mm in diameter and 11.4 mm in total thickness and without associated subretinal fluid, orange pigment, or drusen. Ultrasound biomicroscopy and anterior-segment optical coherence tomography confirmed a solid mass with scleral disruption and extraocular extension. Shave biopsy revealed palisading spindle cells and interspersed eosinophilic fibrillary cytoplasmic processes, forming Verocay bodies. The specimen stained positive for S-100 and negative for Melan-A, consistent with benign schwannoma. Observation was recommended. Intraocular schwannoma is a rare, benign uveal tumor that can demonstrate extrascleral extension, mimicking inflammatory and malignant neoplastic processes. Clinical diagnosis is challenging, and tissue biopsy is required for definite diagnosis.

In order to improve the superconducting property and mechanical property of Bi- 2223 sintered bulk, Ni wire meshes were added in the bulk. The mesh concentration was 18 × 18 meshes/cm2 using Ni wires of 0.25 mm in diameter. The Ni meshes were plated with Ag by 0.03 mm in thickness. We prepared the cylindrical sintered bulk, 27 mm in outer diameter 2 mm in thickness and 50 mm in length using a cold isostatic pressing (CIP) method. The samples were sintered at 845 °C for 50 h. Critical current density (Jc) of the samples was estimated at 77 K under self-field. By composing with the Ni meshes the Jc property was improved compared with the samples without the mesh. It is mentioned that the Jc increase of the Bi-2223 bulk by adding with the Ni meshes is attributed from formation of the Bi-2223 plate-like grains in the vicinity of the Ag-plated Ni wires.

Interaction between ring permanent magnets and bulk Dy–Ba–Cu–O superconductors

The utilization of 3D printing technology for the fabrication of intricate transparent ceramics overcomes the limitations associated with conventional molding processes, thereby presenting a highly promising solution. In this study, we employed direct ink writing (DIW) to prepare yttrium oxide transparent ceramics using a ceramic slurry with excellent moldability, solid content of 45 vol%, and shear-thinning behavior. A successfully printed transparent yttrium oxide ring measuring 30 mm in diameter, 10 mm in inner diameter, and 0.9 mm in thickness was obtained from the aforementioned slurry. After de-binding and sintering procedures, the printed ceramic exhibited in-line transmittance of 71% at 850 nm. This work not only produced complex yttria transparent ceramics with intricate shapes, but also achieved in-line transmittance that was comparable to that of the CIP method (79%), which can meet certain optical applications.

Statement of the problem: Dental Ceramics have been widely used in patients seeking ultimate esthetics, however still there is concern about their color stability by time.Aim of the study: To evaluate the color stability of four different CAD/CAM ceramics after immersion in coffee solution.Materials and Methods: A total of twenty ceramic discs with shade A2 (10 mm in diameter and 2mm in thickness) were constructed in standardized manner. Samples were divided into four main equal groups (n=5) each, according to the type of ceramic material used. Group I: IPS e.max CAD. Group V: Vita Suprinity. Group C: Cerec Blocs. Group O: Obsidian. All specimens were fabricated using CNC milling machine and electric isoMet microsaw 4000. A specially constructed cylindrical split teflon mold was fabricated for the construction of twenty composite resin discs shade A3 (10 mm in diameter and 2mm in thickness). Both ceramic and composite discs were constructed according to manufacturer instructions then were adhesively luted using dual cure Rely X U200 Automix self-Adhesive resin cement shade A2 under 2 Kg constant load application. All disc samples were immersed in coffee solution for 3 weeks and were tested twice; before (baseline) and after the immersion. The color of each sample was then assessed using a spectrophotometer. The L* a* b* values of the samples were recorded according to the CIELAB color scale relative to the standard illumination D65. The results were tabulated and statistically analyzed as mean, standard deviation (SD), median, range and with 95% Confidence interval values. For parametric data, one-way ANOVA was used followed by Tukey’s post-hoc test to compare between the four groups. While for non-parametric data, Kruskal-Wallis test was used to compare between the four groups. The significance level was set at P ≤ 0.05. Statistical analysis was performed with IBM® SPSS® Statistics Version 20 for Windows.Results: There was a statistically significant difference between the four ceramic groups after immersion in coffee solution. A decrease in (L*) values was found in all groups. Pair-wise comparisons revealed that IPS e.max CAD showed the highest mean decrease in (ΔL) (-5.19±0.71).

Objective This study evaluated the effect of grape seed extract (GSE) incorporation on the mechanical properties, water sorption, solubility, and GSE release from the experimental adhesive resins.Material and Methods An experimental comonomer mixture, consisting of 40% Bis-GMA, 30% Bis MP, 28% HEMA, 0.26% camphorquinone and 1% EDMAB, was used to prepare four GSE-incorporated adhesive resins at concentrations of 0.5, 1, 1.5, and 2 wt%. The neat resin without GSE was used as the control. Six resin beams (25 mm x 2 mm x 2 mm) per group were prepared for flexural strength and modulus of elasticity evaluations using a universal testing machine at a crosshead speed of 1 mm/min. Five disks (6 mm in diameter and 2 mm in thickness) per group were used for microhardness measurements using a Leitz micro-hardness tester with Leica Qgo software. Five disks (7 mm in diameter and 2 mm in thickness) per group were prepared and stored in deionized water for 28 days. Water sorption, solubility, and GSE release in deionized water were calculated for each GSE-incorporated adhesive at the end of 28th day. Data was evaluated using one-way ANOVA and Tukey multiple comparisons.Results Flexural strength, modulus of elasticity and microhardness of GSE-incorporated adhesive decreased significantly with incorporation of 1.5% of GSE (p<0.05). Addition of GSE had no effect on the water sorption of the adhesive resins (p=0.33). The solubility of the resin also increased significantly with incorporation of 1.5% of GSE (p<0.05). Quantities of GSE release increased with increased concentration of GSE in the adhesive resin.Conclusion Up to 1% of GSE can be incorporated into a dental adhesive resin without interfering with the mechanical properties or solubility of the resins.

Background and objectives. The introduction of zirconia to the dental field created a path for development of new designs and applications, but still, a minimum framework thickness of 0.5 mm with the remaining thickness of the restoration used for building the ceramic veneer was always recommended. This might have possibly affected the final shade of the restoration due to the whitish color of Y-TZP. This in vitro study was designed to assess the color difference of translucent zirconia substructure veneered using a traditional layering technique with two different veneering thicknesses. Methods. A total of twenty translucent Ice zirconia disc samples with standardized dimensions 12 mm in a diameter, 0.5mm in thickness were designed and constructed using zirkonzahn system. The samples were classified into two groups: Group I: (n = 10) veneered by 0.5 mm thickness layering technique using IPS emax Ceram dentin shade A2. Group II (n = 10) veneered by 1 mm thickness layering technique using IPS emax Ceram dentin shade A2. Twenty composite resin discs 12mm in diameter and 5mm in thickness in A3 shade, were fabricated to be bonded to ceramic specimens using Dual-curing translucent rely X Unicem automix Self-Adhesive Resin luting cement. Spectrophotometer was used to measure color parameters L*, a*, b* for all samples. ΔE values were measured to determine color differences between the specimens and the A2 VITA classical shade (target shade). ΔE values were compared with an acceptability threshold (ΔE=3.7). Independent t-test was used to analyze data (P&lt;0.05) in this study and was analyzed using (SPSS) software, version 22. Results. The results showed that veneering thicknesses had a significant effect on the mean (ΔE) Values at P ≤ 0.001. The 0.5 mm veneer thickness showed the higher significant mean color difference (∆E) than the 1.0 mm veneering thickness where the recorded mean (ΔE) Values were (4.15±1.31) (2.65±1.39) respectively at p ≤ 0.001. Conclusions. This study concluded that 1.0 mm veneer thickness was the optimum thickness regarding color matching.

This paper presents a comprehensive methodology to model the assembly process of flip chip on flex interconnections with non-conductive adhesive (NCA). The methodology combines experimental techniques for material characterization, finite element modeling and model validation. The non-conductive adhesive material has been characterized using several techniques. A unique experimental technique has been developed to measure the cure force. A 2-D axisymmetric finite element model is used for analysis of flip chip on flex package with nonconductive adhesive, which takes into account assembly force, cure shrinkage, adhesive modulus buildup, removal of assembly force and cooling down to room temperature. The relationship between the contact pressure obtained from finite element simulation and the measured bump contact resistance has been established through the development of a dedicated experimental setup, which uses a microforce-tester combined with a digital multimeter and nano-voltmeter. The process modeling has been validated by comparing the predicted contact resistance value and the measured contact resistance value after assembly process. The approach developed in this paper can be used to provide guidelines with respect to adhesive material properties, assembly process parameters and good reliability performances.

Positioning error guarantee method with two-stage compensation strategy for aircraft flexible assembly tooling

In this paper, it is shown that traveling length, feed speed, proportional gain and other factors affect the positioning error of CNC machine tools, and that the positioning error can be regarded qualitatively as a multivariant function in high-precision positioning. The positioning error due to these factors is difficult to be solved by traditional compensation methods because the relationship between the positioning error and the machine environment cannot be mathematically expressed. Thus a compensation method using a neural network was proposed in the study. The neural network was used to learn the relationships between the positioning error and the machine environments, and the Back Propagation algorithm was used as the learning algorithm. Through experiments and computer simulation, it is shown that with the aid of a neural network, the nonlinear problems of the positioning error of CNC machine tools can be solved easily and with high-precision.

Traditional manual high-altitude operations have problems of safety risks and low efficiency. However, the combination of unmanned aircraft and mechanical arms can improve efficiency and ensure safety. Flight disturbances will affect the precise control of the mechanical arms. This paper proposes a compensation algorithm based on fuzzy PID control to deal with the motion disturbances of the flight platform. Fuzzy PID control combines the advantages of fuzzy control and classical PID control, and can handle the uncertainty and nonlinearity of the system, and real-time compensate for the disturbances of the flight platform. This innovation can solve the problems of accuracy decline and response delay that traditional PID control may encounter when dealing with disturbances or nonlinear systems. According to the deviation data of the end position of the mechanical arm in the simulation results, it can be concluded that after compensation control, the error of the end position is significantly reduced compared with traditional PID control, and the control accuracy reaches within 0.05mm, and the steady-state error is less than 0.1mm after compensation. This research provides technical support for the application of flight mechanical arms in wind turbine group detection, and provides new ideas for the design of control systems for unmanned aircraft platforms carrying mechanical arms. The simulation results show that this control strategy significantly improves the stability and accuracy of the end position of the mechanical arm, especially under the condition of flight platform disturbances, it can effectively maintain the end position of the mechanical arm at the target position.

80. Estimation of errors in lung tumor size definition for CT based radiotherapy treatment planning

Several self‐assembly structures of anatase TiO2 nanorods were obtained by a two‐step assembly process, and these structures formed different lyotropic liquid crystal in solution. Primary self‐assembly occurred in synthesis process and formed two structures, in the morphology of ribbon and honeycomb, respectively. Secondary‐assembly took place when the products were placed at lower temperature, where unique structures were obtained as the relative amount of ribbon and honeycomb changed with the increase of TiO2 concentration. These structures showed nematic, spherulites, and lamellar phases. The mechanism of the two‐step self‐assembly was clarified. The driving force of primary assembly is deduced to be anisotropic attractive force, for NRs can assemble at any concentrations, while gravity is the driving force of the secondary assembly. It is worth mentioning that this paper is the first report about spherulites composing of anatase TiO2 nanorods. The spherulites obtained were negative or of tangential type, and its structure, growth process, and temperature influences were also investigated. The spherulites may have promising application in temperature microsensor.

Bulk Nd60Fe30Al10−xBx (x=0, 2.5, 5, 7.5 and 10 at%) alloys with hard magnetic properties were prepared by an arc melting method. The bulk alloys have weights of 10 and 100 mg with button shapes of 1 and 6 mm in thickness, respectively. The X-ray diffraction and TEM observation data reveal that the Nd60Fe30Al10 bulk alloy exhibits an amorphous phase while the other alloys consist of partial crystalline and amorphous phases. The bulk Nd60Fe30Al10 amorphous alloy of 1 mm in thickness exhibits crystallization temperature (Tx) of 802 K, eutectic temperature (Te) of 925 K, and reduced crystallization temperature (Tx⁄Te) of 0.87. The alloy exhibits hard magnetic properties at 298 K, i.e., saturation magnetization of 0.13 T, remanance of 0.09 T, and intrinsic coercive filed of 275 kA/m under an applied field of 1242 kA/m. These thermal and magnetic properties are nearly the same as those for the corresponding bulk amorphous cylinders of 1 to 12 mm in diameter prepared by copper mold casting. The replacement of Al with B in Nd–Fe–Al amorphous alloy causes a decrease in amorphous-forming ability (AFA), although their hard magnetic properties remain almost unchanged. The reason for the decrease in AFA was analyzed using mixing enthalpy (ΔHmix) and mismatch entropy (Sσ) corresponding the empirical criteria for the achievement of high AFA. Furthermore, amorphous-forming composition regions (AFCRs) were calculated by giving a limitation for formation of an amorphous phase to ΔHmix and Sσ values, which arises from the statistics for 6500 amorphous alloys listed in a database. The calculated AFCR of the Nd–Fe–Al and Nd–Fe–B alloy systems agrees with the experimental data reported previously. The decrease in AFA by the replacement of Al with B in the Nd60Fe30Al10−xBx alloys is interpreted from the result that Nd60Fe30B10 is located near the edge of the AFCR in Nd–Fe–B system.