RESUMO
The single-point diamond-turning operation is a commonly used method for ultra-precision machining of various non-ferrous materials. In this paper, a magnetic field was introduced into a single-point diamond-turning system, and magnetic-field-assisted turning experiments were carried out. The results revealed that the magnetic field affects the metal-cutting process in the form of the cutting force, chip morphology, and surface quality. Compared with traditional turning, magnetic-field assisted turning increases the cutting force by 1.6 times, because of the additional induced Lorentz force, and reduces the cutting-force ratio and friction coefficient on the rake surface by 16%, with the improved tribological property of the tool/chip contact-interface. The chip morphology in the magnetic-field-assisted turning shows the smaller chip-compression ratio and the continuous side-morphology. With the magnetoplasticity effect of the metal material and the friction reduction, magnetic-field-assisted turning is helpful for improving metal machinability and achieving better surface-quality.
RESUMO
The control strategy of multi-stroke repetitive driving is often required in the micro-nano-system. However, the current research only focuses on the modeling algorithm of a single stroke; thus, it is difficult to realize the hysteresis compensation at any stroke of the piezoelectric actuator. This paper proposes a multi-stroke compensation algorithm combined with the inverse model: through the analysis of the hysteresis model, the rising trajectory with better linearity is defined as the target line to find a mathematical expression with fewer parameters to describe the falling trajectory, then to find the relationship between maximum stroke voltage and the above parameters to establish a mathematical model that can describe any stroke, and finally, to verify that the above model applies to any unknown stroke, thereby realizing multi-stroke compensation. The experimental results show that the hysteresis corrected rate after the above algorithm compensation is mostly over 85%, of which the maximum hysteresis corrected rate is 93.81% and the hysteresis error is less than 2.5%. Experiments prove the effectiveness of the above multi-stroke compensation algorithm based on the inverse model and extend the research on piezoelectric hysteresis characteristics to multi-stroke compensation.
RESUMO
OBJECTIVES: The aim of this study was to investigate the prognostic value and preoperative predictors of microvascular invasion (MVI) in solitary hepatocellular carcinoma (HCC) ≤ 5 cm without macrovascular invasion. METHODS: A total of 233 consecutive HCC patients underwent curative hepatectomy were included in our study. Independent risk factors influencing the prognosis were identified, and preoperative predictors for MVI were determined. RESULTS: Multivariate regression analysis identified ICG-R15, BCLC staging and MVI as independent risk factors for the overall survival rate. Type of resection and MVI were independent risk factors for the recurrence-free survival rate. Kaplan-Meier analysis showed the overall survival and recurrence-free survival rates in patients with MVI were significantly poorer than those in patients without MVI (P = 0.002 and P = 0.001). Anatomical resection obviously improved the overall survival and recurrence-free survival rates in patients with MVI compared with non-anatomical resection (P = 0.017 and P = 0.009). A prediction scoring system for MVI was built up according to the three independent predictors (tumor size > 3.5 cm, AFP > 200 ng/mL and GGT > 53 U/L). The prevalence of MVI in HCC patients with predictive score ≥ 2 was 58.3%, which was obviously higher than patients with predictive score < 2 (20.8%). CONCLUSIONS: MVI is associated with a poor prognosis in solitary HCC ≤ 5 cm after hepatectomy. Anatomical resection could improve the prognosis of HCC patients with MVI. The preoperative prediction scoring model has practical value for the prediction of MVI.