We have demonstrated an imaging-based amplitude laser-beam-shaping technique for material processing by 2D reflectivity tuning of a spatial light modulator. Intensity masks with 256 gray levels were designed to shape the input laser beam in the outline profile and inside intensity distribution. Squared and circular flattop beam shapes were obtained at the diffractive near-field and then reconstructed at an image plane of an f-theta lens (f∼100 mm). The observed intensity distribution inside the beam-shaping geometry was much more even than using binary masks. The ablation footprint well matches the desired beam shape.
The aperture of space telescopes increases with their required resolution, and the transmission optical systems with long focal length and diffractive primary lens are becoming increasingly popular. In space, the changes in the pose of the primary lens relative to the rear lens group have a significant impact on the imaging performance of the telescope system. The measurement of the pose of the primary lens in real-time and with high-precision is one of the important techniques for a space telescope. In this paper, a high-precision real-time pose measurement method for the primary lens of a space telescope in orbit based on laser ranging is proposed, and a verification system is established. The pose change of the telescope's primary lens can be easily calculated through six high-precision laser distance changes. The measurement system can be installed freely, which solves the problems of complex system structure and low measurement accuracy in traditional pose measurement techniques. Analysis and experiments show that this method can accurately obtain the pose of the primary lens in real-time. The rotation error of the measurement system is 2 × 10-5 degrees (0.072 arcsecs), and the translation error is 0.2 μm. This study will provide a scientific basis for high-quality imaging of a space telescope.
Processing of aramid fiber reinforced plastics (AFRP) with traditional cutting or milling methods usually result in low machining accuracy and poor edge quality. In this paper, ultrafast laser ablation of AFRP was systematically implemented to test its applicability for the material processing. The responses of AFRP to ultrafast laser pulse lengths, laser fluence, and repetition rates were carefully studied. It is found that single pulse volume removal rate, material removal efficiency, and the ablated surface roughness are in positive correlation with laser pulse lengths, laser fluence, and repetition rates. Sample surface morphology study revealed that heat accumulation and carbonization are easier to occur for high laser repetition rates due to the low decomposition temperature and thermal conductivity of AFRP components. The findings may give useful guide for ultrafast laser processing of similar composite materials.
Direct numerical simulations (DNS) of knitted textile mechanical behavior are for the first time conducted on high performance computing (HPC) using both the explicit and implicit finite element analysis (FEA) to directly assess effective ways to model the behavior of such complex material systems. Yarn-level models including interyarn interactions are used as a benchmark computational problem to enable direct comparison in terms of computational efficiency between explicit and implicit methods. The need for such comparison stems from both a significant increase in the degrees-of-freedom (DOFs) with increasing size of the computational models considered as well as from memory and numerical stability issues due to the highly complex three-dimensional (3D) mechanical behavior of such 3D architectured materials. Mesh and size dependency, as well as parallelization in an HPC environment are investigated. The results demonstrate a satisfying accuracy combined with higher computational efficiency and much less memory requirements for the explicit method, which could be leveraged in modeling and design of such novel materials.
To explore the effect of laser scanning speed on the microstructure and performance of Cr3C2-NiCr cermet layers fabricated by in-situ laser cladding, Cr3C2-NiCr cermet layers were laser cladded from Ni/Cr/Graphite (25:65:10 wt.%) elemental powder mixtures. The microstructures of the laser cladded cermet layers and the formation mechanism were investigated. In addition, the effect of laser scanning speed on the microstructure, friction and corrosion performance of the Cr3C2-NiCr cermet layers was studied. The results indicated that the in-situ laser cladded Cr3C2-NiCr cermet layers were composed of NiCr binder and Cr3C2. The laser scanning speed had a significant influence on the carbide content, composition and size. Furthermore, it affected the in-situ laser cladded cermet layer’s hardness and wear resistance. The corrosion resistance of the in-situ laser cladded cermet layer was superior to that of laser cladded nickel-based alloy and was improved with decreasing laser scanning speed.
When the citrus harvesting robot harvests citruses, the mechanical properties of citrus stalks have an important influence on the success rate of the citrus harvesting robot. During the harvesting, the maturity of citrus fruits not only determined the harvesting time of citrus fruits but also affected the mechanical properties of citrus fruit stalks. In this study, the changes in the cutting force of citrus fruit stalks were described during the maturity of citrus fruits, and the effect of the maturity on the cutting force of stalks was clarified, so as to determine the harvesting time with the minimum cutting force required for harvesting citrus fruits by the harvesting robot. During the maturity, the relevant parameters of fruit maturity, such as the hardness, pH, and solid solution content of citrus fruits, were monitored. The results showed that there is a significant correlation between the hardness, pH, the solid solution content of citrus fruits, and the cutting force of citrus fruit stalks during maturity. The single-factor mechanical model of hardness, pH, solid solution content of citrus fruits, and the cutting force of citrus fruit stalks were established based on the data of 2019, which were verified through tests in 2020. The test results are as follows: during the ripening period of citrus fruits, the fruit hardness varies in the range of 0.13-0.31 MPa, the hardness changes by 0.02 MPa, and the cutting force changes by about 2.0-6.0 N; the pH of the citrus fruits changes in the range of 2.8-4.0, and the cutting force changes by about 1.5-2.2 N for every 0.1 change in the pH; the variation range of fruit solid solution content is 6.5%-9.0%, and for every 0.2% change in solid solution, the cutting force of citrus fruit stalks changes by about 1.25-2.0 N. The mechanical models can predict the cutting force required to cut off citrus fruit stalks according to the relevant parameters of citrus fruit maturity and can provide a reference for effectively evaluating the required cutting force. Keywords: citrus fruit harvesting, cutting force of citrus fruit stalks, citrus fruit maturity, mechanical regression model DOI: 10.25165/j.ijabe.20221505.7063 Citation: Wang Y, Liu D, Li Y L, Zhao H M, Yang C H, Zhang Y T. Effects of maturity of citrus fruits on their stalks cutting force. Int J Agric & Biol Eng, 2022; 15(5): 23–30.
Presented here are latest advances in ultra short pulse laser based parallel processing using a spatial light modulator (SLM), which has the potential for use in high throughput precision patterning of photovoltaic and other device layers. Ultra short laser pulses allow selective material removal with minimal energy density, while here a computer- generated hologram driven reflective SLM is used to transform a single beam into multiple beamlets for increased process throughput. Based on this technique, the precision patterning of silicon, titanium, thin film ITO and metal on flexible and glass substrates is demonstrated and the benefits and current limitations discussed.
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